First draft prepared by
    Dr R. Walker, Professor of Food Science,
    Department of Biochemistry, University of Surrey, England.


         Erythorbic acid (syn: isoascorbic acid, D-araboascorbic acid)
    is a stereoisomer of ascorbic acid and has similar technological
    applications as a water-soluble antioxidant.  This compound was
    previously evaluated under the name isoascorbic acid by the sixth
    and seventeenth meetings of the Committee (Annex 1, references 6 and
    32); at the last evaluation an ADI of 0-5 mg/kg b.w. was allocated,
    based on a long-term study in rats, and a toxicological monograph
    was prepared (Annex 1, reference 33).  The name was changed to
    erythorbic acid in accordance with the "Guidelines for designating
    titles for specifications monographs" adopted at the thirty-third
    meeting of the Committee (Annex 1, reference 83).

         Since the previous evaluation further data have become
    available and are included in the following monograph.  The
    previously published monograph has been expanded and is reproduced
    in its entirety below.


    2.1  Biochemical aspects

    2.1.1  Absorption, distribution and excretion

         Erythorbic acid is readily absorbed and metabolized.  Following
    an oral dose of 500 mg of erythorbic acid to human subjects the
    blood level curves for ascorbic acid and erythorbic acid showed a
    similar rise.  In five human subjects, an oral dose of 300 mg was
    shown to have no effect on urinary excretion of ascorbic acid (Kadin
    & Osadca, 1959).  Erythorbic acid was found to have no antagonistic
    effect on the action of ascorbic acid (Gould, 1948).

         In hamster, rat and rabbit, for which ascorbate is not an
    essential vitamin, intestinal absorption of L-ascorbic acid is low
    and takes place by passive diffusion; conversely, in guinea pig and
    human, ascorbate absorption is mediated by a saturable, sodium-
    dependent, active transport mechanism.  It follows that the former
    species are not suitable models for human absorption.  Since the
    active transport system is saturable but since passive diffusion
    might also be significant at high dose levels, the absorption of
    ascorbic acid is dose dependent (Kallner  et al., 1977; Kübler &
    Gehler, 1970).  Erythorbic acid appears to be another but much
    poorer substrate for the same transport system and may thus act as a
    weak competitive inhibitor of L-ascorbate uptake (Siliprandi  et
     al., 1979; Mellors  et al., 1977).  In studies using isolated
    brush border vesicles from guinea pig ileum, the K1 has variously
    been estimated at about 11mM (Toggenburger  et al., 1979) and
    around 20mM (Siliprandi  et al., 1979); this compares with an
    apparent Km for ascorbate uptake of about 0.3mM in the same

         In studies using gut sections of humans and guinea pigs, the
    rate of ascorbate uptake was reduced by only 16% when erythorbate
    was added at ten times higher concentrations.  In other species
    (hamster, rat, rabbit) in which absorption is by passive diffusion,
    erythorbate is without effect on ascorbate absorption (Mellors  et
     al., 1977).

         After i.p. or oral administration of [1-14C]-erythorbic acid
    to guinea pigs, most of the labelled material was excreted within
    24h after dosage, only minute amounts being retained in the tissues. 
    After i.p. administration, more than 75% of the dose was excreted in
    urine, about 20% was exhaled as CO2, and about 3% of the label
    appeared in the faeces.  The corresponding figures after oral
    administration were 54% as CO2 (after 12h), 30% in urine and 4% in
    faeces.  The highest activity in tissues was found in liver, lung
    and kidneys but each organ accounted for less than 1% of the dose.

         After simultaneous oral administration of equal amounts of [1-
    14C]-erythorbic and [6-3H]-ascorbic acids there were no
    differences in specific activities of the two in portal blood (ratio
    0.8-1.15) during the first few hours but after 3.5h the ratio in
    adrenals, liver, lung and spleen was approximately 4 in favour of
    ascorbic acid, indicating a preferred uptake of ascorbic acid
    compared to erythorbic acid.  Lower ratios were found in kidney,
    reflecting the large renal excretion rate of erythorbic acid
    relative to ascorbic acid (Hornig, 1975).

         The ascorbic acid transport system in to the brain and
    cerebrospinal fluid is stereospecific with erythorbic acid being
    transported  in vivo less effectively than ascorbic acid (Spector &
    Lorenzo, 1974).

         When guinea pigs on a low ascorbate diet were given a
    supplement of ascorbic acid or erythorbic acid at daily doses of 1.5
    mg/kg b.w., ascorbic acid was deposited in the tissues while
    erythorbic acid was not.  Intramuscularly administered erythorbic
    acid was not retained in the tissues to the same extent as a similar
    dose of ascorbic acid.  The authors concluded that ascorbic acid is
    more readily absorbed from the gastro-intestinal tract and more
    readily abstracted from the blood and/or retained by the tissues
    than is erythorbic acid (Hughes & Hurley, 1969).  When ascorbic acid
    or erythorbic acid were administered in drinking water at doses of
    180 mg/1, tissue levels of ascorbate were higher than erythorbate in
    the tissues examined (spleen, adrenals, brain and eye lens).  The
    ratio of ascorbate: erythorbate concentrations achieved varied from
    8:1 in the spleen to 2.8:1 in the brain.  At higher concentrations
    of 1% in drinking water, higher tissue levels of either ascorbate or
    erythorbate were found and differences in tissue concentrations
    between the two substances was reduced, the ratio varying from 1.7:1
    in spleen to 1.1:1 in brain.  It was concluded that the differences
    arose from the lower absorption efficiency of erythorbic acid and
    that this was partially overcome when higher concentrations were
    given in drinking water rather than as a single supplement (Hughes &
    Jones, 1970).  It appears that in these high concentration
    conditions, the active absorption mechanism for ascorbic acid might
    have been approaching saturation with much of the dose of both
    compounds being absorbed by passive diffusion.

         The erythorbic acid content of the tissues (liver, adrenals,
    kidneys and spleen) of guinea pigs was compared with that of
    ascorbic acid after oral administration of the compounds at doses of
    1, 5, 20 (erythorbic only) and 100 mg/day for 16 days.  Only a small
    amount of erythorbic acid was found in the four organs of animals
    given 20 mg or more of erythorbic acid; conversely, ascorbic acid
    was detected in the tissues of animals from all dose groups.  Even
    at the highest dose, much less erythorbic acid was retained in these
    tissues than ascorbic acid (Suzuki  et al., 1987).

         Guinea-pigs were fed diets containing either 2% erythorbic acid
    or 0.1% ascorbic acid for a period of 9 days followed by a depletion
    period of 4 days during which they received an ascorbic acid-
    deficient diet.  At the end of the 9 day period, tissue levels of
    erythorbic acid were about twice those of ascorbic acid, despite the
    20-fold difference in dose.  After the 4-day depletion period,
    erythorbate levels were much lower than the ascorbate concentrations
    in all the tissues examined except the adrenals.  From the
    calculated turnover rates, the t1/2 was estimated to be 4-5 times
    shorter for erythorbic acid than for ascorbic acid in all the organs
    viz: brain, liver, heart, kidneys, adrenals and spleen. 
    Furthermore, erythorbic acid increased rather than decreased the
    turnover of ascorbic acid (Pelletier, 1969b).

         Comparative studies on the transport of ascorbic and erythorbic
    acids across various tissue membranes have been carried out  in vivo
    using the  guinea pig eye (Linner & Nordstrom, 1969) and  in vitro
    using guinea pig and rabbit ocular ciliary body-iris preparations
    (Becker, 1967; Chu & Candia, 1988), cat retinal pigment cells
    (Khatami  et al., 1986), rabbit choroid plexus membranes (Spector &
    Lorenzo, 1974) and human placental microvillus membranes (Iioka  et
     al., 1987).  In all cases, a carrier-mediated ascorbate transport
    system was identified which was inhibited competitively by
    erythorbic acid.  However, the affinity of erythorbate for the
    carrier was weak and the Km for ascorbate was in all cases several
    times lower than the K1 of erythorbate.

         There are significant differences between ascorbic and
    erythorbic acids in renal excretion in humans.  Studies in vitamin
    C-depleted humans indicated that the rate and extent of urinary
    excretion of erythorbic acid are much greater than those of ascorbic
    acid.  At oral doses of 50-300 mg per person about 50-70% of the
    dose of erythorbic acid was excreted in 24 hour urine (mainly in the
    first 6 hours) but only 15% of a 100 mg dose of ascorbic acid
    appeared in urine; the rate of urinary excretion of erythorbic acid
    was 10-15 times that of ascorbic acid.  (Ikeuchi 1955).  Similar
    results have been obtained in later studies in humans (Wang  et al.,
    1962; Rivers  et al., 1963).

         In guinea pigs receiving daily doses of ascorbic acid (2 mg/d)
    or erythorbic acid (40 mg/d) the 12h urinary excretion of these two
    compounds was found to be 0.13% and 1.9% of the daily dose
    respectively at the end of the experiment.  No further metabolites
    of erythorbic acid were identified although the authors pointed out
    that as so little was incorporated into organs it would be of
    interest to determine how it is metabolized (Pelletier & Godin,

         In trout and rats which received 14C-labelled ascorbic or
    erythorbic acid (dose not specified) the rate of excretion of label

    was about 10 times faster for erythorbic than ascorbic acid.  The
    primary urinary metabolite of ascorbate was ascorbate-2-sulfate but
    the corresponding erythorbate-2-sulfate could not be detected in the
    urine of rats receiving erythorbic acid (Baker  et al., 1973).

         At very high levels of intake (5% in the diet) in the rat, the
    urinary concentration of erythorbate was about twice as high as that
    of ascorbate (Fukushima  et al., 1984).

         In dogs, less marked differences in excretion between ascorbic
    acid erythorbic acids have been reported.  From equivalent doses on
    a molar basis of 5 g of sodium erythorbate or 4.1 g of ascorbic
    acid, about 19% and 12% of the dose respectively was excreted within
    24 hours (Robinson & Umbreit, 1956).  After a single i.v. dose of 1
    g ascorbic acid or 1.23 g sodium erythorbate the plasma half-lives
    were similar, indicating a similar rate of elimination (Robinson  et
     al., 1956).

         Ascorbic acid is believed to be recovered from the glomerular
    filtrate by active renal reabsorption involving a sterospecific,
    energy-requiring transport process (Ahlborg, 1946).  On the basis of
    studies conducted in brush border membrane vesicles from kidney
    cortex  in vitro, erythorbate appears to be another, but poorer
    substrate, of the same transport system.  In view of the more than
    fifty-fold difference between the Km for ascorbate and the
    competitive K1 for erythorbate (approximately 16mM) (Toggenburger
     et al., 1981) it appears unlikely that erythorbate would reduce
    the reabsorption of ascorbate from the glomerular filtrate under
    conditions likely to be encountered  in vivo.

         Since erythorbic acid is less readily resorbed than ascorbic
    acid in the kidney, this affords a rational explanation for the
    observation that whereas a daily intake of 600 mg erythorbic acid by
    non-pregnant women resulted in a steady state plasma concentration
    of about 16 µmol/1, a similar plasma level of ascorbic acid required
    an intake only 60 mg/d (Sauberlich  et al., 1989).

    2.1.2  Biotransformation

         The metabolism of erythorbate has not been examined in detail. 
    The occurrence of dehydro-erythorbate in the urine of erythorbate-
    fed rats (Fukushima  et al., 1984) indicates that ascorbate oxidase
    may accept both stereoisomers as substrates.  However, although
    ascorbate-2-sulfate is quantitatively an important metabolite of
    ascorbate in trout and rat, erythorbate-2-sulfate could not be
    detected in these species (Baker  et al., 1973).

         There are indications that oxalate is a minor metabolite of
    ascorbic acid and high doses are associated with an increase in
    urinary oxalate.  The urinary excretion of oxalate was examined in

    women receiving increasing increments of 30, 60 or 90 mg ascorbic
    acid per day for 10 days in the presence or absence of 600 mg/d of
    erythorbic acid.  Increasing the ascorbic acid intake from 30 mg/d
    to 90 mg/d increased daily oxalate excretion by 67 µmol but an
    intake of 600 mg/d of erythorbic acid increased daily oxalate
    excretion by 67-133 µmol.  This indicates that little if any of the
    erythorbic acid was metabolized to oxalate (Sauberlich  et al.,

    2.2  Toxicological studies

    2.2.1  Acute toxicity

    Species   Sex      Route       LD50      Reference
                               (mg/kg b.w.)

    Mouse     Male     oral        8,300     Orahovats, 1957

    Rat       Male     oral       18,000     Orahovats, 1957


    2.2.2  Short-term studies  Mice

         Six groups of 10 male and 10 female eight week-old B6C3F1 mice
    were given sodium erythorbate in drinking water at concentrations of
    0, 0.625, 1.25, 2.5, 5 or 10% for 10 weeks.  At termination, all
    survivors were sacrificed, autopsied and the major visceral organs
    examined histologically.

         The mean body-weight gain of male mice given 5% sodium
    erythorbate was less than 90% of that of controls but the females in
    this dose group had a higher weight gain than controls and it was
    concluded that the MTD for males and females was 2.5% and 5%
    respectively.  Histological examination of organs from mice which
    had received above the MTD of erythorbate showed marked atrophy of
    liver cells, marked atrophy of splenic lymphoid follicles and
    hydropic degeneration of renal tubular epithelium.  No significant
    changes were observed in the visceral organs of control mice nor of
    mice which had received erythorbic acid at or below the MTD (Inai
     et al., 1989).  It is noted that this experiment was not
    controlled for sodium ion concentration in the drinking water of
    treated animals.  Rat

         Groups of 10 male rats were fed for 36 weeks on diets
    containing 0 or 1% of erythorbic acid.  There was no difference
    between treated rats and controls with respect to growth rate and
    mortality.  Gross post-mortem examination and microscopic studies of
    various organs revealed no lesions attributable to erythorbic acid
    (Fitzhugh & Nelson, 1946).

         Six groups of 10 male and 10 female F344/DuCrj rats were given
    sodium erythorbate in drinking water at concentrations of 0, 0.625,
    1.25, 2.5, 5.0 or 10.0% for 13 weeks.  All rats given the 10%
    solution refused to drink and died within 2 to 5 weeks.  Three males
    and one female  out of the group receiving 5% erythorbate died
    during the first 4 days.  All the rats receiving erythorbate at
    concentrations of 2.5% or less survived to the end of the study. 
    The 2.5% solution depressed body weight gains by 12% in males and 6%
    in females compared to untreated controls.  This study was a pilot
    for a long-term carcinogenicity study and no further details were
    reported (Abe  et al., 1984).  Guinea pig

         In an experiment on the influence of protein-induced
    differences in growth rate on tissue concentrations of erythorbic
    acid, two groups of 10 male guinea pigs were fed an ascorbic acid-
    free diet with either dried skimmed milk or gluten as protein
    source.  After a vitamin C depletion period of 10 days, the animals
    were given daily doses of sodium erythorbate of 800 mg/kg b.w.
    intraperitoneally.  No adverse effects to the treatment with
    erythorbate were noted and body weight gains were similar to those
    of guinea pigs receiving ascorbic acid orally at a dose of 5 mg/kg
    b.w.  The highest tissue levels of ascorbic acid were found in the
    adrenals and dietary protein source had no influence on organ
    distribution (Williams & Hughes, 1972).  Note that in this study,
    erythorbic acid i.p. showed antiscorbutic activity (see also 2.2.12
    Special studies of vitamin C activity of erythorbic acid).  Dog

         Groups of 2 male and 2 female beagles received  per os daily
    doses of either 1 g erythorbic acid for 240 days or 5 g ascorbic
    acid for 50 days then 7.5 g for a further 190 days; a third group
    served as control.  No signs of toxicity were observed. 
    Biochemical, haematological and urine analysis showed no treatment
    related changes in haemoglobin, haematocrit, RBC and WBC counts,
    differential counts, sedimentation rate, urea N, fibrinogen,
    glucose, total and free cholesterol, total protein, albumin,
    globulin, inorganic phosphorus, alkaline phosphatase nor in urinary
    S.G., pH, urine blood, sugar or protein.  At termination all the 

    animals were autopsied and no gross or histological changes were
    found (Orahovats, 1957).  Note that this report was available in
    summary only.

    2.2.3  Long-term/carcinogenicity studies  Mice

         Sodium erythorbate was administered to groups of 50 male
    B6C3F1 mice in drinking water at concentrations of 0, 1.25 or 2.5%
    (MTD); groups of 50 females received concentrations of 0, 2.5 or 5%
    (MTD).  Treatment commenced at eight weeks of age and continued for
    96 weeks; the test substance was then withdrawn for a further 14
    weeks when the study was terminated.  The animals were weighed at
    regular intervals throughout and any mouse found dead or moribund in
    the course of the experiment was autopsied.  At termination all
    surviving animals were sacrificed and autopsied.  All visceral
    organs and any tumours were weighed and examined grossly and

         The mean body weights of the treated mice were generally
    similar to those of controls throughout but, at the end of the
    study, there was a dose-related increase in body weight and an
    associated decrease in relative organ weights of heart, lungs,
    kidney and brain.  Survival rates were higher in treated mice. 
    Histological examination did not show any significant differences
    between the treated and control groups.

         Tumours were observed at various sites including liver,
    haematopoietic system, lung and integumentary tissue but the tumour
    incidence, time to death with tumours or histological distribution
    of tumours differed significantly from untreated controls at none of
    the sites.  The authors concluded that the study did not demonstrate
    any tumorigenic effect of sodium erythorbate on oral administration
    to B6C3F1 mice (Inai  et al., 1989).  Rat

         Groups of 10 rats (sex not specified) were fed diets containing
    0 or 1% erythorbic acid for two years.  The growth rate, mortality
    and histopathology were not affected by the treatment (Lehman  et
     al., 1951).

         Groups of 52 male and 50 female F344/DuCrj rats were given
    sodium erythorbate in drinking water at concentrations of 0
    (control), 1.25 or 2.5% from 8 weeks of age for 104 weeks.  The
    sodium erythorbate was then removed and the animals received plain
    tap water for a further 8 weeks when the experiment was terminated. 
    Autopsies were performed on all rats; major organs and lesions
    (details not given) were prepared for histological examination.

         At the 2.5% level, sodium erythorbate significantly inhibited
    weight gain in both sexes from weeks 40 to 90, the deficit being
    maximally 8.5% in males at week 88 and 15.5% at week 85 in females,
    relative to controls.  No suppression of weight gain was observed at
    the 1.25% dose level.  The total intakes achieved in the treated
    groups were estimated to be 217 g/rat and 430 g/rat for males in the
    1.25% and 2.5% dose groups respectively; the corresponding intakes
    for females were 206 and 583 g/rat.  Between 60% and 82% of animals
    in the various groups survived the treatment period and the mean
    lifespan of tumour bearing rats was similar in the three groups,
    viz:  117, 114 and 111 weeks for control, 1.25% and 2.5% males,  and
    114, 113 and 113 for the corresponding females.

         All males except two in the higher dose group showed testicular
    interstitial-cell tumours (typical of the strain of rat used).  The
    incidence of other tumours was 80%, 69% and 78% in control, 1.25%
    and 2.5% males respectively, the more common tumours encountered
    being leukaemia, phaeochromocytoma, mammary fibroadenoma and
    mesothelioma with incidences of 6 - 18%.  Aggregate tumour
    incidences in females were 94%, 88% and 78% in control, 1.25% and
    2.5% groups respectively, the latter group incidence being
    significantly lower than controls, and the pattern of occurrence of
    various tumour types was similar in the three groups.  There was no
    treatment-related acceleration in tumour development nor in
    malignant transformation of benign tumours and the authors concluded
    that sodium erythorbate was not carcinogenic to F344 rats (Abe  et
     al., 1984).

    2.2.4  Special studies on bone mineralization

         Male guinea pigs, 14 days old, were given 8.7% ascorbic acid in
    the diet for up to 8 weeks.  Two comparison groups were fed
    corresponding amounts of ascorbate or erythorbate as a mixture of
    the respective sodium, potassium and calcium salts and a control
    group received 0.2% ascorbic acid.  In a later 6-week experiment
    using a similar protocol, guinea pigs were given 8.7% free
    erythorbate acid in the diet.  The results of bone and urinary
    analysis demonstrated that the animals given 8.7% ascorbic acid had
    decreased bone density and lower urinary hydroxyproline compared to
    controls.  No significant bone changes were observed in any of the
    other groups, including those animals given free erythorbic acid. 
    It appears that the observed bone demineralization was a combination
    of an effect of an acid diet together with a more specific effect of
    ascorbate, not shared by erythorbate (Bray & Briggs, 1984).

    2.2.5  Special studies on collagen and elastin synthesis  in vivo

         Based on observations in cultured smooth muscle and fibroblast
    cells, it was hypothesized that elevated ascorbic acid levels should
    increase collagen and decrease elastin deposition in neonatal rat

    lung and a comparative study was conducted with erythorbic acid. 
    Rat pups, 2 days post partum, were given ascorbic or erythorbic
    acids by daily oral gavage at a level of 2% of the total consumed
    milk solids for 19 or 23 days; controls received saline.  No
    treatment-related differences were observed in lung, liver or body
    weights, or collagen accumulation in the lung.  The relative rates
    of lung protein and elastin synthesis were lowered by both ascorbic
    or erythorbic acid but mechanical lung function (pressure-volume
    curves) was not influenced by treatment (Critchfield  et al., 

    2.2.6  Special studies on effects on bioavailability and
           toxicity of metals

         The concentration of metallothioneins, a group of low molecular
    weight proteins which form complexes with various heavy metals, in
    mouse liver was increased from 26 to 341 µg/g tissue after i.p.
    administration of ascorbic acid at a dose of 1 g/kg b.w.  The same
    dose of erythorbic acid caused a similar increase in metallothionein
    levels to 378 µg/g liver (Onasaka  et al., 1987).  The elevated
    metallothionein level caused by ascorbic acid was associated with a
    reduced mortality after administration of a lethal dose of cadmium
    but erythorbic acid was not included in this test.

         Ascorbic acid is known to increase the bioavailability of iron
    and the activity of erythorbic acid in this respect was examined in
    a haem-repletion assay in iron deficient male weanling rats.  The
    bioavailability of iron from bologna-type sausages cured with 550
    mg/kg erythorbate and 156 mg/kg nitrite was assayed.  Groups of 6
    rats were limit-fed for 2 weeks diets that contained as their sole
    protein sources uncured meat, meat cured with nitrite alone or with
    erythorbic acid.  Curing with nitrite and/or erythorbate had no
    significant effect on iron absorption or iron incorporation into
    tissues (Lee  et al., 1984; Lee & Greger, 1985).  In a critique of
    the above study, similar results were confirmed in an analogous
    experiment (Mahoney & Hendricks, 1985).

         Adult male volunteers received a constant mixed diet which
    contained  200g processed meat for 51 days.  The processed meats
    used were uncured sausage, sausage cured with nitrite (156 mg/kg
    meat) and sausage cured with a mixture of nitrite (156 mg/kg meat)
    and erythorbic acid (550 mg/kg meat).  The dietary treatments had no
    significant effects on apparent absorption of iron, zinc or copper,
    nor on serum zinc or copper levels, plasma ferritin, transferrin or
    ceruloplasmin levels.  The authors concluded that commercial curing
    processes do not adversely affect the bioavailability of zinc or
    copper in meat (Greger  et al., 1984; 1985).

    2.2.7  Special studies on embryotoxicity and teratogenicity  Mouse

         Groups of pregnant CD-1 mice were given erythorbic acid at
    doses of 0, 10.3, 47.6, 221.9 or 1030 mg/kg by gavage on days 6-15
    of gestation.  On day 17 the pups were removed by Caesarian section
    and the number of implantation sites and urogenital abnormalities
    determined in the dams.  The number of live foetuses and body
    weights were determined and the foetuses were given a gross
    examination for abnormalities.  Foetuses were then prepared and
    examined for skeletal or soft tissue anomalies.  None of the
    treatment groups showed any significant differences from controls in
    these parameters (Food and Drug Research Laboratories, 1974).  Rat

         Pregnant Wistar rats were fed a diet containing 0 (control),
    0.05, 0.5 or 5% sodium erythorbate from day 7 through day 14 of
    pregnancy.  On day 20 of pregnancy, 5-7 dams from each group were
    killed and the foetuses removed for teratological examination.  All
    gross anomalies were recorded and half of the foetuses from each
    litter were examined for skeletal anomalies (Alizarin red).  The
    remaining foetuses were fixed in Bouin's solution and examined for
    soft tissue defects using Wilson's technique.

         Another 5 dams from each group were allowed to proceed to
    parturition and the number of live and dead offspring delivered was
    recorded.  The litter size was standardized to 4 males and 4 females
    per litter and development of the offspring monitored to weaning for
    a further 10 weeks.  The dams were killed at weaning and the number
    of implantation remnants recorded.

         No adverse effect on body weight gain nor any clinical sign of
    toxicity was observed in any of the dams during pregnancy. There
    were no significant differences between treated and control groups
    in the incidence of intrauterine fetal death, number of live
    foetuses per dam, sex ratio of fetuses, fetal body weight or
    placental weight.  External, skeletal and soft tissue examinations
    did not reveal any evidence of teratogenicity and the post-natal
    development of the offspring of treated dams was uneventful (Ema  et
     al., 1985).

         A teratogenicity study was conducted in pregnant Wistar rats
    given sodium erythorbate from day 6 of gestation for 10 consecutive
    days at doses of 0, 9.0, 41.8, 194 or 900 mg/kg b.w.  per os.  No
    differences were observed in implantation rates, live births or
    gross, skeletal or soft tissue morphological abnormalities (Food and
    Drug Research Laboratories, 1974).  Chick

         Erythorbic acid was tested for embryotoxic and teratogenic
    effects to the developing chick embryo under four sets of
    conditions.  The test compound was administered in aqueous solution
    via the air cell or via the yolk at 0 or 96 hours of incubation and
    at doses of 0, 0.5, 1, 5, 10 or 20 mg/egg.  All the eggs were
    candled daily and non-viable embryos removed; survivors were allowed
    to hatch.  Non-viable embryos and hatched chicks were examined for
    gross anomalies (externally and by dissection) and for toxic
    responses such as oedema and haemorrhage.  Histological examination
    was carried out on liver, heart, kidney, lung, brain, intestine,
    gonads and some endocrine organs from a representative number of
    animals from each group.

         Erythorbic acid was quite embryotoxic under all test
    conditions, except at the lowest dose level via the air sac at 0
    hours.  The LD50 was estimated as 3.7 mg/egg and 4.5 mg/egg via the
    air cell at 0 and 96 hours respectively.  Yolk treatment at 0 and 96
    hours resulted in LC50s of 4.6 and 5.4 respectively.  The incidence
    of structural abnormalities of head, limbs, skeleton or viscera was
    not significantly different from sham-treated controls (Hwang &
    Conors, 1974).  The data do not provide evidence of any teratogenic
    effect but the significance of the embryotoxicity is difficult to
    ascertain since the experiment was not controlled for sodium ion.

         In a comparative study on embryotoxicity in the chick in which
    both sodium ascorbate and sodium erythorbate were tested via
    administration into the air sac at 96 hours incubation, the LC50
    was found to be 100 and 84 mg/kg egg respectively (approximately 6
    mg and 5 mg/egg respectively) (Naber, 1975).

        2.2.8  Special studies on genotoxicity
    Test system         Test object         Substance and       Results        Reference

    Ames test1          S. typhimurium      erythorbic          weakly         Ishidate et al., 
                        TA100,              acid 5-50           positive       1984
                        TA92, TA1535,       mg/plate            negative
                        TA1537, TA94,

                        TA100, TA92         sodium              negative       Ishidate et al., 
                                            erythorbate                        1984
                                            5-50 mg/plate

    Ames test1          S. typhimurium      erythorbic          negative       Litton Bionetics, 
                                            acid 0.25-0.5%                     1976

    Mitotic rec.        Saccharomyces       erythorbic          negative       Litton Bionetics, 
    assay               cerevisiae D3       acid 2.0-4.0%                      1976

    Ames test1          S. typhimurium      sodium              negative       Newell et al., 
                        TA1530, TA1535      erythorbate                        1974
                        TA1536, TA1537      100 mg/plate

    Mitotic rec.        S. cerevisiae D3    sodium              negative       Newell et al., 
    assay                                   erythorbate 5%                     1974

    Ames test           S. typhimurium      sodium              equivocal      Kawachi et al., 
                        TA100               erythorbate         negative       1980
                        TA98                ?concn. not 
                                            ?concn. not 


    Test system         Test object         Substance and       Results        Reference

    Rec assay 1         B. subtilis         ? concn. not        negative       Kawachi et al., 
                                            given                              1980

    Chromosome          Chinese hamster     erythorbic          negative       Ishidate et al., 
    aberration          fibroblast cell     acid, sodium        negative       1984
                        line (CHL)          erythorbate 
                                            0-0.25 mg/ml

    Chromosome          CHL                 sodium              negative       Matsuoka et al., 
    aberration1                             erythorbate                        1979
                                            2.0 mg/ml

    Chromosome          Human fibroblast    sodium              negative       Sasaki et al., 
    aberration          cell line           erythorbate                        1980
                        (HE2144)            0.0099-0.0198 

    Rat                 bone marrow         sodium              positive2      Kawachi et al., 
    micronucleus                            erythorbate                        1980

    Rat                 bone marrow         erythorbic                         Hayashi et al., 
    micronucleus                            acid                negative       1988
                                            mg/kg b.w. 
                                            i.p.; 4x705         negative
                                            mg/kg b.w. 


    Test system         Test object         Substance and       Results        Reference

    Rat dominant        rat sperm/off-      sodium              negative       Newell et al., 
    lethal assay        spring              erythorbate                        1974
                                            1x0.2-5.0 g/kg 
                                            b.w. orally; 
                                            5x0.2-5.0 g/kg      negative
                                            b.w. orally

    Mouse in vivo       mouse sperm/off-    sodium              negative       Newell et al., 
    heritable           spring              erythorbate                        1974
    trans-location                          1% & 5% in 
                                            diet for 7 


    1.  With and without rat liver S9 fraction
    2.  Insufficient detail to evaluate this study

    2.2.9  Special studies on interactions between erythorbic acid and
           ascorbic acid (see also Biochemical Aspects)

         In view of the observations that ascorbic acid is absorbed from
    the gut and selectively concentrated in various tissues by active
    transport systems, and that their affinity for erythorbate is only
    about one-fifth of that for ascorbic acid (see Biochemical Aspects
    above), a number of studies have investigated the possibility that
    erythorbic acid might antagonize the absorption/tissue uptake of
    ascorbic acid and exert an anti-vitamin effect.  Mouse

         In a study of the scorbutigenic activity of glucoascorbic acid
    due to antagonism of ascorbic acid, an additional group of mice was
    given 5% erythorbic acid in the diet for two weeks.  Glucoascorbic
    acid caused severe symptoms of scurvy in this species, which is not
    dependent on dietary vitamin C (i.e. antagonized the synthesis or
    effects of ascorbic acid in the tissues).  Conversely, erythorbic
    acid was without effect and the general health and weight gain of
    treated mice was normal (Woolley & Krampitz, 1943).

         Erythorbic acid or ascorbic acid was fed to female Swiss
    Webster mice in the diet at a concentration of 5% for 2 months and
    then at 10% of the diet for a further 5 months; a control group
    received an ascorbic acid-free diet throughout.  Urinary ascorbic
    and erythorbic acids were determined two weeks prior to termination. 
    At the end of the study tissue levels were measured in plasma, liver
    and brain.  In the  ascorbic acid treated animals there was a marked
    elevation of urinary and plasma ascorbate and a 38% increase in the
    ascorbate level in the liver but there was no substantial increase
    in the four brain regions studied viz: cerebrum, cerebellum, medulla
    and brain stem.  In the erythorbic acid-treated animals, the
    erythorbate was well absorbed and rapidly excreted in the urine.  It
    was found that these extremely high dietary levels of erythorbic
    acid caused a reduction of tissue ascorbic acid of 45% in the liver
    and 28-39% in the brain, interpreted by the authors as "replacing"
    ascorbic acid in these organs.  Although erythorbic acid was found
    in high levels in the plasma, it did not cause a reduction in plasma
    ascorbic acid concentration.  The body weight gain in both the
    erythorbic acid and ascorbic acid groups was reduced by 40% relative
    to mice receiving control diet (Tsao & Salimi, 1983).  Guinea pig

         The effect of co-administration of ascorbic and erythorbic
    acids compared with ascorbic acid alone was investigated in two
    groups of guinea pigs receiving a semi-purified diet containing 0.1%
    ascorbic acid with or without 2% erythorbic acid.  It was found that
    the organs of the guinea pigs retained a significant quantity of

    erythorbic acid which replaced a corresponding quantity (about half)
    of the ascorbic acid.  The erythorbic acid incorporated was lost
    rapidly and replaced by ascorbic acid when treatment with erythorbic
    acid was discontinued and ascorbic acid only was given (Pelletier,

         Erythorbic acid was fed to groups of 7 male guinea pigs, body
    weight 220-250g, at daily dose levels of 0, 20, 50, 100 or 400 mg
    together with ascorbic acid (20 mg/d).  After three days on these
    regimes, a single oral dose of 14C-ascorbic acid was given orally. 
    There was a dose related reduction in the amount of 14C taken up by
    the tissues which was significant at the 50 mg erythorbic acid dose
    level when there was a 17-26% reduction in activity in the lungs,
    kidneys, testes, eyes and pancreas and a 55% reduction in the
    adrenals.  Higher dose levels of erythorbic acid did not further
    decrease the retention of 14C-label in the adrenals and the
    reduction in other organs never exceeded 50% (Hornig  et al., 

         In a study in guinea pigs of the absorption, transport through
    cell membranes at the tissue level, and catabolism of ascorbic acid,
    and of the effects of erythorbic acid, it was found that after oral
    administration there was no difference in the absorption of these
    compounds, whereas uptake by the tissues was approx. 4 to 1 in
    favour of ascorbate.  Feeding studies with daily co-administration
    of erythorbic and ascorbic acids indicated that the availability of
    ascorbic acid was diminished by 40-60% (Hornig, 1977).

         After a vitamin C depletion period of 12 days, groups of 7-9
    male guinea pigs were given daily supplements of ascorbic acid,
    erythorbic acid or a mixture of both isomers at dose levels of 5, 50
    or 5+50 mg/kg b.w. for 16 days.  The animals were then given an oral
    dose of 1-14C-ascorbic acid and respiratory CO2, urine and faeces
    were collected for 96 hours.  In comparison with animals treated
    with 5 mg/kg ascorbic acid alone, body weight gains were depressed
    by 49g and 22g in animals given erythorbic acid alone or with
    ascorbic acid, respectively.  No differences were observed in faecal
    or urinary excretion of radioactivity between the three groups but
    the exhalation of 14CO2 was increased in both groups receiving
    erythorbic acid.  Kinetic analysis of the data showed that the
    disappearance of ascorbic acid from the organism was accelerated
    during the initial phase by erythorbic acid at a dose of 50 mg/kg
    b.w./day and the half-life was shortened from 97h in animals
    receiving ascorbic acid alone to 50h or 59h in the groups given
    erythorbate alone or with ascorbic acid, respectively.  However,
    during the later, linear phase of disappearance the half-lives were
    not significantly different between the groups receiving ascorbic
    acid with or without erythorbic acid (Hornig & Weiser, 1976; Hornig,
    1977).  The increased catabolism of ascorbic acid was accompanied by

    a lower ascorbic acid body pool, which was reduced by 30% in animals
    receiving ascorbic acid plus erythorbic acid compared with animals
    receiving ascorbic acid alone.

         In a more recent study, groups of male guinea pigs, initial
    b.w. 220 g were given a scorbutigenic diet together with 5 mg
    ascorbic acid/day, 100 mg erythorbic acid/day, a combination of
    both, or no supplement.  On days 1, 4, 10, 16 and 30 of the
    treatment period, tissue concentrations of ascorbic and erythorbic
    acids in the liver, adrenals, spleen and kidneys were determined
    following a 24 hour fasting period by a HPLC method.  The ascorbic
    acid content in the tissues of animals given ascorbic plus
    erythorbic acids was lower than that of animals given only ascorbic
    acid.  However, the rate of disappearance of ascorbic plus
    erythorbic acids was lower than that of animals given only ascorbic
    acid.  However, the rate of disappearance of ascorbic acid from the
    tissues of ascorbic acid-deficient animals was similar to that of
    animals given erythorbic acid alone.  The authors concluded that
    erythorbic acid does not accelerate the catabolism of ascorbic acid
    but interferes with its uptake into or its storage in the tissues
    when given at twenty-fold higher amounts (Arakawa  et al., 1986). 
    The reviewer concluded that the results are also consistent with
    accelerated catabolism limited to freshly absorbed ascorbic acid
    before it has entered the tissues.

         Groups of male guinea pigs, initial body weight about 220 g,
    were given daily doses of 5 mg ascorbic acid and 1, 5, 20 or 100 mg
    erythorbic acid; or 1 mg ascorbic acid and 1 or 10 mg erythorbic
    acid; or 20 mg ascorbic acid and 20 mg erythorbic acid for 16 days. 
    The animals were then sacrificed and the ascorbic and erythorbic
    acid content of the liver, adrenals, spleen and kidneys determined
    by HPLC.  The tissue content of ascorbic acid of animals given less
    than 5 mg erythorbic acid with 5 mg ascorbic acid was not
    significantly different from that of animals given 5 mg ascorbic
    acid alone.  The co-administration of 100 mg erythorbic acid caused
    a decrease in the amount of ascorbic acid in the tissues of animals
    given 5 mg ascorbic acid.  The tissue content of animals given
    erythorbic acid together with 1 mg ascorbic acid was not
    significantly different from that of animals given 1 mg ascorbic
    acid alone.  In the case of animals given equal amounts of ascorbic
    and erythorbic acids, the tissue levels of the former were
    consistently much higher than the latter.  The results were taken to
    indicate that relatively small amounts of erythorbic acid do not
    appear to reduce the availability of ascorbic acid (Suzuki  et al.,

         The activities of some ascorbic acid-dependent enzymes, liver
    aniline hydroxylase and acid phosphatase, and serum alkaline
    phosphatase, as well as liver cytochrome P450 content, were assayed
    to investigate the effect of erythorbic acid administration on

    ascorbic acid availability in male guinea pigs.  The animals were
    given 5 mg ascorbic acid and 1, 5, 20 or 100 mg erythorbic acid; or
    1 mg ascorbic acid and 1 or 20 mg erythorbic acid daily for 16 days. 
    The body weight gains were similar in all groups.  The liver
    ascorbic acid content of animals receiving 5 mg ascorbic acid and
    100 mg erythorbic acid was about 50% lower than that of animals
    receiving 5 mg ascorbic acid alone, however neither liver cytochrome
    P450 levels nor any of the enzyme activities of animals receiving 5
    mg ascorbic acid were affected regardless of erythorbic acid
    supplement.  In animals given 1 mg ascorbic acid, liver aniline
    hydroxylase and acid phosphatase activities were significantly
    different from those in animals receiving 5 mg ascorbic acid;
    however, the enzyme activities in animals given 20 mg erythorbic
    acid together with 1 mg ascorbic acid were similar to those of
    animals given 5 mg ascorbic acid alone.  These results were taken to
    indicate that erythorbic acid had no effect on these parameters in
    animals receiving adequate (5 mg daily) amounts of ascorbic acid but
    that administration of 20 mg erythorbic acid was effective in
    maintaining normal levels of hepatic aniline hydroxylase and acid
    phosphatase in animals receiving marginal amounts (1 mg daily) of
    ascorbic acid (Suzuki  et al., 1988).

         In follow-up experiments, four groups of male guinea pigs, body
    weight 220 g, received ascorbic acid (5 mg/d), erythorbic acid (100
    mg/d) a combination of both isomers (5 mg + 100 mg/d) or no
    supplement for a period of up to 30 days (16 days in the
    unsupplemented group).  Liver aniline hydroxylase, cytochrome P450
    and acid phosphatase, and serum alkaline phosphatase showed
    significant differences between the ascorbic acid deficient
    (unsupplemented) group and the group receiving 5 mg/d.  No
    significant differences were seen between the other three groups. 
    In a further experiment, guinea pigs depleted of ascorbic acid for
    16 days were divided into three groups which subsequently received
    ascorbic acid (5 mg/d), erythorbic acid (100 mg/kd) or a combination
    of the two (5 mg + 100 mg/d) for up to 20 days.  During the
    repletion period a similar pattern of recovery was observed and
    there were no significant differences in enzyme activities or
    cytochrome P450 content among the animals given ascorbic acid and/or
    erythorbic acid.  The results demonstrate that, using these
    criteria, erythorbic acid in adequate amounts has a vitamin C-like
    activity.  The authors suggested that erythorbic acid administration
    may not affect ascorbic acid availability in guinea pigs but, as the
    ascorbic acid was given at above minimal requirement levels and the
    high dose of erythorbic acid has a significant antiscorbutic effect,
    the position with respect to effects on ascorbic acid availability
    was not clearly demonstrated (Suzuki  et al., 1989).  Monkey

         Two groups of 4 male Cynomolgus monkeys were depleted of
    ascorbic acid by feeding an ascorbic acid-free total liquid diet for
    eight weeks; by this time plasma ascorbic acid levels had fallen
    from 1.1 mg/dl to 0.04 mg/dl but the animals showed no signs of
    scurvy.  The animals were given a daily oral dose of ascorbic acid
    of 10 mg/kg b.w. with or without 200 mg/kg b.w. erythorbic acid.  In
    all animals repletion was accomplished in two to three weeks using
    return to initial plasma levels as the criterion.  After treatment
    for 4 weeks, the total amount of "apparent ascorbic acid" (ascorbic
    plus erythorbic acid) was determined in whole blood 21 hours after
    the last administration of the supplements.  No difference was found
    between the two treatment groups.  Based on the assumption that most
    of the erythorbic acid would have been excreted in the 21 hours
    before blood samples were taken and therefore did not significantly
    inflate the apparent blood ascorbic acid levels, the authors
    concluded that erythorbic acid at the dose used did not antagonize
    ascorbic acid (Turnbull  et al., 1979).

    2.2.10  Special studies on nitrosation  in vivo

         Co-administration of aminopyrine (0.4 mmol/kg b.w.) and sodium
    nitrite (1.0 mmol/kg b.w.) caused alterations in serum GOT and GPT
    activities and in hepatic G-6-PDH, microsomal drug metabolizing
    enzymes, and lysosomal enzymes attributed to the formation of N-
    nitrosodimethylamine  in vivo.  Sodium erythorbate (1.0 mmol/kg)
    had no effect on these parameters  per se but repressed the changes
    induced by aminopyrine + nitrite (Kawanashi  et al., 1981).

    2.2.11  Special studies on tumour promotion

         In a series of studies on the promoting effect of a series of
    antioxidants in rats, mice, or hamsters, sodium erythorbate was
    found to have no effect on the induction of tumours by methyl-N-
    nitroso guanidine (MNNG)in the stomach, by DMH in the colon, by N-
    ethyl-N-hydroxyethyl nitrosamine in the liver or by DMBA in the ear
    duct.  However, sodium erythorbate (and to a greater extent sodium
    ascorbate) enhanced the induction of bladder tumours by N-butyl-N-
    (4-hydroxybutyl) nitrosamine (BBN) when administered at 5% of the
    diet for 32 weeks after treatment with the carcinogen (Ito  et al.,
    1986a,b; 1987).

         In similar studies, the lack of effect of sodium erythorbate on
    MNNG-induced stomach tumorigenesis was confirmed when the compound
    was administered in drinking water at a concentration of 2.5% (Abe
     et al., 1983) while a level of 5% in the diet was reported to
    cause a decreased incidence of dysplasia of the pylorus and, more
    marginally, papilloma of the forestomach (Shirai  et al., 1985). 
    In the latter study, sodium ascorbate (1% or 5%) or ascorbic acid
    (5%) in the diet had no effect.

         With regard to the reported potentiation of BBN-induced bladder
    carcinogenesis by sodium erythorbate, this was supported by the
    observation that this compound at a dietary level of 5% caused a
    significant increase in bladder tumours (Fukushima  et al., 1984)
    or premalignant papillary or nodular hyperplasias (Miyata  et al.,
    1985) in BBN-pretreated rats.  However, using a similar protocol,
    free erythorbate acid had no such promoting effect but actually
    reduced the incidence of preneoplastic changes and tumours
    (Fukushima  et al., 1987) while high dietary levels (0.375 - 3.0%)
    of sodium bicarbonate increased the incidence of urinary bladder
    carcinomas in the BBN-treated rat (Fukushima  et al., 1988). 
    Further, while free ascorbic acid was without effect, high dietary
    concentrations of the sodium salt (5% but not 1%) had a promoting
    effect on the BBN-treated rat (Fukushima  et al., 1983).

    2.2.12  Special studies on vitamin C activity of erythorbic acid

         (a)   in vivo studies

         In studies on the anti-scorbutic effect of erythorbic acid in
    guinea pigs, as much as 250 mg per day did not support animals fed a
    vitamin C-deficient diet although administration of erythorbic acid
    tended to slow down the development of acute vitamin C deficiency. 
    In vitamin C-depleted guinea pigs, erythorbic acid had no
    therapeutic effect whereas the animals responded to vitamin C;
    however, animals maintained on a suboptimal intake of ascorbic acid
    showed some response to erythorbic acid.  The authors concluded that
    erythorbic acid has a protective effect on ascorbic acid in the body
    but no significant antiscorbutic activity  per se (Reiff & Free,

         Groups of seven young adult male guinea pigs were fed a
    scorbutigenic diet and supplemented with daily oral doses of 1, 2,
    10, 50, 100 or 200 mg erythorbic acid for 38 days (3 animals from
    the 10 mg/d group were treated for 115 days).  Comparison groups
    which received 10 mg erythorbic acid/d survived, including those
    maintained for 115 days, although they had a slightly reduced weight
    gain.  For ascorbic acid, a dose of 1-2 mg/d was sufficient to
    sustain appropriate growth.  In contrast to the preceding study, the
    authors concluded that daily oral doses of 10 to 200 mg erythorbic
    acid replaced the anti-scorbutic activity of L-ascorbic acid and
    this prevented them from developing any sign of scurvy discernible
    at autopsy (Fabianek & Herp, 1967).

         After 6 days on a scorbutigenic diet, female guinea pigs were
    given daily supplements of 10 mg ascorbic acid, 100 mg erythorbic
    acid or combinations of 100 mg erythorbic acid with 0.5 or 5 mg
    ascorbic acid for 7 weeks.  Their responses were judged by body
    weight gain, serum alkaline phosphatase (SAP) levels, wound healing
    and tooth structure.  The supplement of 100 mg erythorbic acid

    resulted in normal growth, SAP levels, tooth structure development
    and collagen formation after wounding and the addition of 0.5 or 5
    mg ascorbic acid did not further improve growth nor collagen
    deposition after wounding.  It was concluded that erythorbic acid
    has about 1/20th the antiscorbutic potency of ascorbic acid and its
    additive effect to sub-minimal levels of ascorbic acid implied that
    there was no competitive inhibition in the utilization of the two
    compounds.  The authors further concluded that the weakly
    antiscorbutic effect of erythorbic acid relative to ascorbic acid is
    due to its poor absorption and tissue retention, and that to the
    degree that it is taken up and retained by the tissues, it may be
    equal in potency to ascorbic acid (Goldman  et al., 1981).

         Groups of seven male guinea pigs were depleted of vitamin C for
    17 days then the scorbutic animals were treated daily with 40 mg
    erythorbic acid or 2 mg ascorbic acid for 2 months.  Both isomers
    restored the growth of the animals and caused the disappearance of
    scorbutic symptoms.  Animals given erythorbic acid ate less and had
    lower weight gains than those given ascorbic acid but this was
    overcome by pair feeding.  At autopsy, none of the animals had the
    enlarged kidneys or adrenals characteristic of chronic
    hypovitaminosis C and scurvy.  Only a small proportion of the
    erythorbic acid administered was recovered in organs or urine.  The
    total "ascorbic acid" (erythorbate plus ascorbate) content of the
    erythorbic acid treated animals was less than that of the ascorbic
    acid treated and the low content of ascorbic acid in the organs of
    erythorbic acid-treated animals indicated that erythorbic acid had
    "no significant sparing action on ascorbic acid".  From the relative
    tissue concentrations it may be concluded that the activity of
    erythorbic acid in the organs is similar to that of ascorbic acid
    but, as a result of less efficient uptake after dietary exposure and
    more rapid excretion the apparent physiological activity is about
    1/20th of that of ascorbic acid (Pelletier & Godin, 1969).

         Guinea pigs maintained on a scorbutigenic diet could be
    maintained in good health if erythorbic acid was included in
    drinking water at a concentration of 0.1%.  However, animals
    pretreated with erythorbic acid were depleted of vitamin C twice as
    fast as those which received ascorbic acid prior to the depletion
    phase (Hughes  et al., 1971).

         Scorbutic (low collagen) granulomas were induced by s.c.
    injection of carrageenan to vitamin C-deficient male guinea pigs. 
    Isoascorbic acid and ascorbic acid (6 doses of 100 mg i.p. at 12 h
    intervals) were similarly effective in restoring collagen synthesis
    in the granuloma although the concentration of erythorbic acid 12 h
    after injection was lower than that of ascorbic acid 24 h after
    injection (Robertson, 1963).

         (b)   in vitro studies

         Ascorbic acid and erythorbic acid demonstrated similar activity
    in promoting the hydroxylation of peptidyl proline in a cell-free
    system (Hutton  et al., 1967; Kutnink  et al., 1969) and these
    observations have been confirmed using a purified prolyl 4-
    dihydroxylase preparation (Kurata  et al., 1987).

         Erythorbic acid had a similar effect to ascorbic acid in
    protecting hepatic microsomal UDP-glucuronyltransferase activity
    towards p-aminophenol against excess substrate but no protection was
    afforded by ascorbate-2-sulfate or alpha-tocopherol (Neumann &
    Zannoni, 1988).

         The effects of ascorbate and erythorbate on collagen synthesis
    were studied in cultured human skin fibroblasts.  At concentrations
    of 0.25 mM in the culture medium both ascorbate and erythorbate
    increased collagen synthesis about eightfold with no significant
    change in synthesis of non-collagen protein.  Lysyl hydroxylase
    activity increased 3-fold in response to ascorbate or erythorbate
    administration.  After prolonged exposure of cells to ascorbate or
    erythorbate, prolyl hydroxylase activity was decreased to a similar
    extent.  The results were taken to indicate that collagen
    polypeptide synthesis, posttranslational hydroxylations and
    activities of the two hydroxylases are independently regulated by
    ascorbate, with erythorbate having similar effects at the high
    concentrations used (Murad  et al., 1981).

         In further studies using human skin fibroblasts, ascorbate
    stimulated the rate of incorporation of labelled proline into total
    collagenase-sensitive protein without changing the specific activity
    of intracellular free proline.  The effect of ascorbate was maximal
    at a concentration of 30 µM and resulted in a four-fold increase of
    incorporation.  Erythorbate also stimulated collagen synthesis but
    at considerably higher concentrations of 250-300 µM.  The
    stimulation of collagen synthesis by ascorbate and erythorbate was
    accompanied by a decline in prolyl hydroxylase activity and a rise
    in lysyl hydroxylase activity; again ascorbate was the more
    effective (Murad  et al., 1983).

         The protective effects of ascorbic and erythorbic acid against
    carbon tetrachloride-induced lipid peroxidation were investigated in
    guinea pigs using exhalation of pentane and ethane as an index of
     in vivo lipid peroxidation.  It was observed that equal doses (750
    mg/kg b.w., i.p.) of ascorbic acid or isoascorbic acid provided the
    same degree of protection for a period of at least 4 hours (Kunert &
    Tappel, 1983).  The authors concluded that the antioxidant function
    of ascorbic acid is relatively non-specific and that the two
    stereoisomers do not differ with regard to their antioxidant
    properties  in vivo.

    2.3  Observations in humans

         In order to determine whether erythorbic acid could displace
    ascorbic acid from the tissue, urinary levels of ascorbic acid were
    measured after ingestion of 300 mg erythorbic acid by 5 healthy
    human volunteers who had been previously repleted by administration
    of 500 mg ascorbic acid for 7 days.  Urinary analyses indicated that
    ascorbic acid excretion was not affected by treatment with
    erythorbic acid and that there was no significant displacement of
    ascorbic acid from tissues (Kadin & Osadca, 1959).

         The influence of erythorbic acid on ascorbic acid metabolism
    and status was investigated in 11 healthy, non-pregnant women
    volunteers.  The volunteers were maintained in a metabolic unit and
    fed a formula diet devoid of vitamin C for 54 days.  After depletion
    of 24 days, the subjects received increasing supplements of ascorbic
    acid (30 mg/d, 60 mg/d and 90 mg/d for successive periods of 10
    days) in the presence or absence of  600 mg/d of erythorbic acid. 
    The depletion resulted in a marked decrease in ascorbic acid in all
    blood indices and during the study some subjects developed signs of
    scurvy.  Ascorbic acid supplements of 30 mg/d for 10 days failed to
    increase plasma ascorbate concentrations; 60 mg for 10 days caused a
    small increase and 90 mg/d resulted in a mean ascorbic acid
    concentration of 29 mmol/l.  Erythorbic acid did not cause any
    adverse effects but rather had a small ascorbic acid-sparing effect
    (Sauberlich  et al., 1989).


         At the last evaluation an ADI of 0-5 mg/kg b.w. was allocated
    based on a long-term study in the rat.  The present Committee
    reviewed new toxicological studies on isoascorbic acid and its
    sodium salt, and metabolic and nutritional studies of the
    interactions with ascorbic acid.

         In rodent tests for embryotoxicity and teratogenicity,
    erythorbic acid was without effect at dose levels up to 1 g/kg b.w.
    and the Committee did not consider that chick embryo tests were
    indicative of potential teratogenicity or fetotoxicity for man.

         New long-term toxicity and carcinogenicity studies in rats and
    mice did not show any specific toxic or carcinogenic effects up to
    the maximum tolerated dose and most genotoxicity studies were
    negative.  Studies on tumour promotion were also negative with
    exception of those on bladder tumours initiated by N-butyl-N-(4-
    hydroxybutyl) nitrosamine in which high doses of sodium erythorbate
    (but not free erythorbic acid) showed effects.  Similar effects were
    seen with sodium ascorbate (but not ascorbic acid) and various
    sodium salts and the Committee concluded that this was not a
    specific effect of erythorbate.

         Erythorbic acid is much more poorly absorbed and retained in
    the tissues than ascorbic acid, is poorly reabsorbed in the kidney
    and rapidly excreted.  As a result it has low anti-scorbutic
    activity and only interferes significantly with ascorbic acid uptake
    and retention in the tissues when concentrations are at least an
    order of magnitude higher than ascorbic acid.  Human studies showed
    that daily doses of 600 mg  per capita had no adverse effects on
    ascorbic acid repletion in depleted volunteers.


         A new ADI "not specified" was allocated to erythorbic acid and
    its sodium salt.


    ABE, I., SAITO, S., HORI, K., SUZUKI, M., & SATO, H. (1983).  Effect
    of erythorbate on N-methyl-N'-nitro-N-nitrosoguanidine-induced
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    See Also:
       Toxicological Abbreviations