Ascorbic Supplementation Research Articles

In Vivo Reversal of Glutathione Deficiency and Susceptibility to in Vivo Dexamethasone-Induced Apoptosis by N-Acetylcysteine and [formula omitted]-2-Oxothiazolidine- 4-carboxylic Acid, but Not Ascorbic Acid, in Thymocytes from γ-Glutamyltranspeptidase-Deficient Knockout Mice

Cellular glutathione is released during apoptosis and may play a role in the regulation of the mitochondrial permeability transition pore. The question of whether only cytosolic glutathione is important in apoptosis, or whether mitochondrial glutathione also plays a role, was investigated using γ-glutamyltranspeptidase-deficient knockout mice. Thymocytes from these mice were found to have both glutathione pools diminished and they were more susceptible to dexamethasone (DEX)-induced apoptosis. Supplementation with N-acetylcysteine (NAC) and l-2-oxothiazolidine-4-carboxylic acid replenished both glutathione pools and provided protection from apoptosis. Ascorbate supplementation was beneficial to the mitochondrial glutathione pool, but apoptosis was not prevented. NAC supplementation caused an increase in reactive oxygen species formation and cardiolipin oxidation, but had no adverse affect on the amount of apoptotic cells. Our results suggest that the glutathione status is an important factor in apoptosis and indirect evidence indicates that the cytosolic pool of glutathione may be important in DEX-induced apoptosis, with mitochondrial events being secondary, and may reflect the execution phase.

Bioavailability of ascorbyl phosphate calcium in hybrid catfish,Clarias macrocephalus(Gunther) × Clarias gariepinus(Burchell) feed

A 10-week feeding experiment was performed in hybrid catfish (Clarias macrocephalus (Gunther) × C. gariepinus (Burchell, 1822) with initial average weight of 1.17 g, in glass aquaria of 200-L capacity. The experiment comprised seven treatments with three replicates each. Ascorbyl phosphate calcium (APCa) was included at 30, 75, 150, 300 and 1000 mg kg−1 feed and compared with one with ascorbyl polyphosphate (APP) at 36 mg kg−1 feed and one without vitamin C supplementation. Fish fed APCa-supplemented feed showed better growth, feed conversion ratio, survival rate and protein utilization compared with those without such supplementation. Ascorbate concentrations in liver and head kidneys were correlated closely with dietary APCa levels. Vertebral collagen and hydroxyproline contents were significantly lower in the fish group without ascorbate supplementation. Red blood cell and white blood cell counts showed no correlation with vitamin C supplementation. Serum protein level was lowest in the group fed feed without vitamin C supplementation and this was lower than those fed feed with APCa and APP supplementation. The fish fed APCa- and APP-supplemented feed showed no difference in serum protein levels. External scorbutic symptoms and histopathological changes of gill tissue were noted in fish fed feed without APCa supplementation. The study indicates that 12.6 mg kg−1 of ascorbic acid molar equivalent supplied as APCa (30 mg kg−1) provided maximum growth and no gross signs as well as histological changes resulting from vitamin C deficiency.

Iron Supplementation and Oxidative Damage to DNA in Healthy Individuals with High Plasma Ascorbate

Previously, we have investigated the potential for a pro-oxidant interaction of iron and ascorbate in vivo in iron and ascorbate cosupplementation or ascorbate supplementation studies. In this study, for the first time, the effects of iron supplementation on oxidative damage to DNA in healthy individuals with plasma ascorbate levels at the upper end of the normal range were examined. Forty female and male volunteers (mean plasma ascorbate ≈70 μmol/L) were supplemented with a daily dose of syrup (ferrous glycine sulphate equivalent to 12.5 mg iron) for 6 weeks. Serum ferritin, transferrin bound iron, % saturation of transferrin and plasma ascorbate were assessed and the mean dietary intakes of all subjects were estimated through food frequency questionnaires. Oxidative damage to DNA bases from white blood cells was measured by gas chromatography/mass spectrometry with selected-ion monitoring (GC/MS-SIM), using isotope-labelled standards for quantification. Iron supplementation did not affect any of the iron status parameters. There were also no detrimental effects, over the period under investigation, in terms of oxidative damage to DNA. However, the effects of larger doses or of longer supplementation periods should also be investigated.

Potential Problems of Ascorbate and Iron Supplementation: Pro-Oxidant Effect in Vivo?

The comparison was undertaken between the effects of ascorbate versus ascorbate plus iron supplementation on DNA damage. Twenty healthy subjects with initial levels of plasma ascorbate of 67.2 ± 23.3 μmol/l were randomly assigned to and cycled through one of three supplementation regimes: placebo, 260 mg/d ascorbate, 260 mg/d ascorbate plus 14 mg/d iron for 6 weeks separated by 8-week washout periods. Supplementation did not cause a rise in total oxidative DNA damage measured by GC-MS. However, a significant decrease occurred in levels of 8-oxo-7,8-dihydroguanine by ascorbate supplementation and 5-hydroxymethyl uracil by both ascorbate and ascorbate plus iron supplementation, relative to the pre-supplemental levels but not to the placebo group. In addition, levels of 5-hydroxymethyl hydantoin and 5-hydroxy cytosine increased significantly, only relative to pre-supplementation, by ascorbate plus iron treatment. No compelling evidence for a pro-oxidant effect of ascorbate supplementation, in the presence or absence of iron, on DNA base damage was observed.

Ascorbic acid supplementation to primary culture of chicken hepatocytes with non-serum medium

Chicken liver is lack of ascorbic acid biosynthesis system, different from mammals and highly evoluted birds. Chicken hepatocytes cultured without ascorbate was expected to have lower ascorbate amounts than physiological levels. Intracellular was decreased as compared with intact liver by cell preparation performed with in situ collagenase perfusion. We added ascorbate to a primary culture of chicken hepatocytes in order to restore the amount of ascorbate. Serum-free Leivobitz's L-15 medium which do not contain ascorbate was used for control medium. Cells were cultured with several concentrations of ascorbate for 24 or 48 h. After ascorbate supplementation for 24 to 48 h, cellular ascorbate concentration increased depending on the dose of medium ascorbate. Medium lactate dehydrogenase activity derived from hepatocytes, an index of cell injury, decreased upon 5–100 mg/l of ascorbate supplementation for 48 h. Tyrosine aminotransferase activity, an index of liver function, increased following culture with 50 and 100 mg/l ascorbate for 48 h. The activities, however, decreased by supplementation with 1000 mg/l of ascorbate. In conclusion hepatocytes lost intracellular ascorbate during preparation by in situ collagenase perfusion. Supplementation of ascorbate restored cellular ascorbate concentration, lowered cell injury and raised tyrosine aminotransferase activitv in primary cultured chicken hepatocytes. Ascorbate treatment for 48 h at 50 mg/l was the best combination in this study for primary culture of chicken hepatpcyte with non-serum L-15 medium

Effect of Ascorbate Supplements on Urinary Oxalate and Risk of Kidney Stones

Effect of Ascorbate Supplements on Urinary Oxalate and Risk of Kidney Stones

Age-Associated Plasma Lipids, Lipid Peroxidation, and Antioxidant Systems in Relation to Vitamin C Supplementation in Humans

It is hypothesized that a reduction in the level of ascorbic acid with age leads to an impairment in the quenching of free radicals by antioxidants, which in turn increases the risk of succumbing to age-associated disorders. Healthy volunteers of both sexes at different age group were selected from the geriatric community. They were subjected to vitamin C supplementation. Lipids, lipid peroxidation, enzymatic, and nonenzymatic antioxidant status were gauged at the end of 30, 60, and 90 days. The activities/levels of enzymatic and nonenzymatic antioxidants were found to be low in the aged humans, whereas the lipid peroxidation status was found to be high. Supplementation of vitamin C lowered the levels of lipid peroxides, cholesterol, triacylglycerol, and phospholipids and increased the activities of enzymatic antioxidants such as superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and glutathione-S-transferase in the geriatric population. A substantial rise in the levels of nonenzymatic antioxidants such as vitamins C, E, and A were also observed but no significant alterations were noticed in the levels of bilirubin and uric acid. From our observations, we conclude that ascorbic acid normalizes lipid peroxidation and partially restores the antioxidant status. Thus ascorbate supplementation could be beneficial in minimizing age-associated disorders where free radicals are the major cause.

Neutrophil Phagocytic Function and Humoral Immune Response with Reference to Ascorbate Supplementation in Aging Humans

Age-associated deficiency of vitamin C contributes to the impaired humoral immune response, which in turn plays a role in the increased risk of illness in old age. Healthy volunteers were given vitamin C supplementation. Neutrophil phagocytic function, complement C3 concentration, and immunoglobulin status were measured at 30, 60, and 90 days. Neutrophil phagocytic function and levels of serum IgG and IgM and leukocytic ascorbate were considerably lower in the aged humans, but these decreases were attenuated by vitamin C supplementation. The level of IgA was not affected by aging. Improved neutrophil phagocytic function and humoral immune response were associated with increased vitamin C status in the aged population and might well contribute to the decreased risk of disease in the aged.

Effect of antioxidant supplementation on the adaptive response of human skin fibroblasts to UV-induced oxidative stress

The effect of supplementation with substances having antioxidant properties on the adaptive responses of human skin fibroblasts to UV-induced oxidative stress was studied in vitro. UVR was found to induce a substantial oxidative stress in fibroblasts, resulting in an increased release of superoxide anions and an increase in lipid peroxidation (shown by an elevated malonaldehyde content). Sub-lethal doses of UVR were also found to induce adaptive responses in the fibroblast antioxidant defences, with a transient rise in catalase and superoxide dismutase activities followed by a slower, large increase in cellular glutathione content. Supplementation of the fibroblasts with the antioxidants, Trolox (a water soluble analogue of α-tocopherol), ascorbic acid or β-carotene, had differential effects on these responses. Trolox supplementation reduced the UVR-induced cellular oxidative stress and adaptive response in a predictable concentration-dependant manner. This was in contrast to ascorbic acid which increased superoxide release from fibroblasts. At low doses, ascorbate supplements also reduced the magnitude of the adaptive increases in catalase and superoxide dismutase activities and increase in glutathione content. β-Carotene had a similar effect to ascorbic acid, reducing the extent of the adaptations to UVR at lower doses while simultaneously increasing superoxide release and malonaldehyde content. These in vitro data indicate that only the vitamin E analogue suppressed UVR-induced oxidative stress in a predictable manner and suggest that common dietary antioxidants may not be equally effective in reducing the potential deleterious effects of UVR-induced oxidative stress in skin.

Ascorbic acid metabolism in rats and guinea pigs after the administration of ethanol

Ascorbic acid metabolism was studied in guinea pigs and rats after the administration of ethanol and a high dose of ascorbic acid (AA). Male guinea pigs were maintained for 30 days as follows: (1) controls (1 mg AA/100 g body wt.); (2) ethanol (1 mg AA/100 g body wt.+900 mg ethanol/100 g body wt); (3) ascorbic acid (25 mg AA/100 g body wt.); (4) ascorbic acid+ethanol (25 mg AA/100 g body wt.+900 mg ethanol/100 g body wt.). Rats were also grouped into four groups as in the case of guinea pigs, but the dose of AA was 200 mg/100 g body weight. Rats adjusted to ethanol intoxication by enhancing the biosynthesis of ascorbate as evidenced by elevated activity of l-gulono lactone oxidase (GLO). Hence ascorbate levels were not lowered in rats after administration of alcohol. However, alcohol administration lowered tissue levels of ascorbate in guinea pigs. But the supplementation of ascorbate along with alcohol raised the tissue level of this vitamin. Guinea pigs responded to the ascorbate deficiency during alcohol administration by lowering the degradation of ascorbate, as seen by the lower activity of the degrading enzyme gulono lactone hydrolase. It is concluded that on the administration of alcohol, guinea pigs are dependent upon additional exogenous supplies of ascorbic acid, whereas rats are not.

The effect of ascorbate and alpha-tocopherol supplementation in vitro on DNA integrity and hydrogen peroxide-induced DNA damage in human spermatozoa.

The aim of this study was to determine the effects of supplementation with ascorbate and alpha-tocopherol, both singly and in combination, during sperm preparation on subsequent sperm DNA integrity, induced DNA damage and reactive oxygen species (ROS) generation. Semen samples with normozoospermic and asthenozoospermic profiles (n = 15 for each control and antioxidant group) were prepared by Percoll density centrifugation (95.0-47.5%) where the medium had been supplemented with these antioxidants to a number of different concentrations, all within physiological levels. Controls were included which had no ascorbate or alpha-tocopherol added. DNA damage was induced using hydrogen peroxide (H(2)O(2)) and DNA integrity was determined using a modified alkaline single cell gel electrophoresis (Comet) assay, while ROS generation was measured using chemiluminescence. Addition of ascorbate to sperm preparation medium did not affect baseline DNA integrity but did provide sperm with complete protection against H(2)O(2)-induced DNA damage. Generation of H(2)O(2)-induced ROS was also significantly reduced after treatment with ascorbate, although baseline levels were unaffected by this antioxidant. Supplementation of sperm preparation medium with alpha-tocopherol did not influence baseline DNA integrity but provided sperm with dose-dependent protection against H(2)O(2)-induced DNA damage. Generation of H(2)O(2)-induced ROS was significantly reduced after treatment with alpha-tocopherol, although baseline ROS levels were unaffected by this antioxidant. Addition of both ascorbate and alpha-tocopherol in combination to sperm preparation medium actually induced DNA damage and intensified the damage induced by H(2)O(2), however, H(2)O(2)-induced ROS production was significantly reduced in a dose-dependent manner by supplementation with both vitamins.

Influence of dietary ascorbate derivatives on tissue copper, iron and zinc concentrations in grass shrimp, Penaeus monodon

Effects of three ascorbate derivatives namely, l-ascorbyl-2-sulfate (C2S), l-ascorbyl-2-monophosphate–Mg (C2MP–Mg) and l-ascorbyl-2-polyphosphate (C2PP) on tissue (hepatopancreas and muscle) copper, iron and zinc concentration in juvenile grass shrimp, Penaeus monodon, were studied. The control diet contained 12 mg/kg copper, 318.1 mg/kg iron, 125.8 mg/kg zinc and 0 mg/kg ascorbate supplemented with either adequate or high (5× adequate) dietary levels of C2S, C2MP–Mg and C2PP. Each diet was fed to triplicate groups of shrimp (mean initial weight: 0.67±0.05 g) for 8 weeks. Significantly ( P<0.05) higher tissue iron and lower copper concentrations were observed in shrimp fed diets containing ascorbate and high ascorbate, respectively, than shrimp fed the control diet regardless of the ascorbate source. Shrimp fed C2MP–Mg- and C2PP-containing diets had higher tissue iron concentrations than shrimp fed C2S-containing diets regardless of ascorbate supplementation level. Lower hepatopancreas copper concentrations were observed in shrimp fed C2MP–Mg- and C2PP-containing diets than in shrimp fed C2S-containing diets at the high ascorbate supplementation level. Tissue zinc concentrations in shrimp were not affected by either ascorbate source or ascorbate supplementation level.

Decreasing Ascorbate Intake Does Not Affect the Levels of Glutathione, Tocopherol or Retinol in the Ascorbate-Requiring Osteogenic Disorder Shionogi Rats

Levels of glutathione in liver and kidney, and other nutrients in plasma were evaluated in male and female ascorbate-requiring osteogenic disorder Shionogi (ODS) rats fed semipurified diets in which the concentrations of ascorbate were gradually decreased from 1965 to 180 mg/kg. Plasma ascorbate levels in ODS rats were unaffected when ascorbate levels in the diet were decreased from 1965 to 768 mg/kg. However, plasma ascorbate levels decreased progressively when levels of ascorbate in the diet were decreased from 527 to 180 mg/kg. Plasma ascorbate levels decreased up to 77% when the dietary ascorbate concentration decreased from 1965 to 180 mg/kg. Ascorbate levels in liver and kidney fell as much as 60–70% when the dietary ascorbate levels were reduced from 1965 to 180 mg/kg. However, the glutathione levels in these tissues were not affected. Plasma retinol and vitamin E levels were not affected by decreasing dietary ascorbate intake. Total cholesterol levels increased significantly in female rats as dietary ascorbate intake declined. Levels of glycated hemoglobin decreased significantly when dietary ascorbate levels decreased from 1965 to 527 mg/kg. This study suggests that levels of vitamin E, retinol and glutathione are not affected by decreased dietary intake of ascorbate under nonscorbutic conditions, whereas elevated ascorbate intake is associated with a decrease in levels of plasma cholesterol in female ODS rats. However, excessive intake of ascorbate may be associated with elevated glycation of hemoglobin. To achieve the maximal health benefit of ascorbate supplementation, further studies are necessary to define optimal ascorbate intakes.

Erythropoietin hyporesponsiveness: From iron deficiency to iron overload

Iron deficiency is the most frequently encountered cause of suboptimal response to recombinant human erythropoietin (rHuEPO). Carefully assessing iron status is of paramount importance in chronic renal failure patients prior to or during rHuEPO therapy. Because there is great need for iron in the EPO-stimulated erythroid progenitors, it is essential that serum ferritin and transferrin saturation levels should be maintained over 300 microg/liter and 30%, respectively. Investigators have shown that oral iron is unlikely to keep pace with the iron demand for an optimal rHuEPO response in uremics. Therefore, patients with iron deficiency will always require intravenous iron therapy. The early and prompt iron supplementation can lead to reductions in rHuEPO dose and hence cost. After the iron deficiency has been corrected or excluded, we must remember all of the possible causes of hyporesponsiveness in every rHuEPO-treated patient. As dose requirements vary, it is not clear which dose of rHuEPO causes this hyporesponsiveness. However, if the patient with iron repletion does not respond well after the induction period, the major causes blunting the response to rHuEPO should be investigated. Most factors are reversible and remediable, except resistant anemia associated with hemoglobinopathy or bone marrow fibrosis, which requires a further increase in the rHuEPO dose. By means of early detection and correction of the possible causes, the goal of increasing therapeutic efficacy can be achieved. Iron overload may lead to an enhanced risk for infection, cardiovascular complication, and cancer. Over-treatment with iron should be avoided in dialysis patients, despite the fact that the safe upper limit of serum ferritin to avoid iron overload is not clearly defined. On the other hand, functional iron deficiency may develop even when serum ferritin levels are increased. Controversy remains as to whether intravenous iron therapy can overcome this form of hyporesponsiveness in iron-overloaded patients. Moreover, a treatment option of iron supplementation is not warranted in these patients, as the potential hazards of iron overload will be worsened. We demonstrated that the mean hematocrit significantly increased from 25.1+/-0.9% to 31+/-1.2% after eight weeks of intravenous ascorbate therapy (300 mg three times a week) in 12 hemodialysis patients with serum ferritin levels of more than 500 microg/liter. The enhanced erythropoiesis paralleled with a rise in transferrin saturation (27.8+/-2.5% vs. 44.8+/-9.5%, P < 0.05) and reductions in erythrocyte zinc protoporphyrin (130+/-32 vs. 72+/-19 micromol/mol heme, P < 0.05) and monthly rHuEPO dose (24.2+/-4.5 vs. 16.8+/-3.4 x 10(3) units, P < 0.05) at the end of study. It is speculated that ascorbate supplementation not only facilitates the iron release from storage sites and its delivery to hematopoietic tissues, but also increases iron utilization in erythroid cells. Our study provides a more complete understanding of the pathogenesis of iron overload-related anemia and the development of an adjuvant therapy, intravenous ascorbic acid, to the existing treatments.

Paradoxical effects of acute cigarette smoking on plasma antioxidant status in humans

We set out to study the effects of acute cigarette smoking on plasma antioxidants and lipid oxidation and whether these effects could be ameliorated by prior supplementation with ascorbate. Blood samples were taken from 9 apparently healthy male smokers before and after a 1 h smoking test (3 cigarettes/h). The men were then randomly allocated to two groups in a double-blind cross-over design; either taking ascorbate (100 mg/d) or placebo. After 2 wk of supplementation, the men were given a fat meal to consume and after 3 h the smoking test was repeated. Blood samples were taken before the fat tolerance test and at 3 and 4 h postprandially. In response to ascorbate supplementation, total plasma ascorbate increased relative to the placebo period (mean ± SEM: 70 ± 5 vs 46 ± 9 μmol/L, P = 0.01), with significantly less ( P = 0.025) ascorbate in the oxidized form (dehydroascorbate). Contrary to the depletion of antioxidants reported by others when plasma is exposed to cigarette smoke in vitro, no change was observed in plasma antioxidants in response to acute smoking, apart from a paradoxical decrease in the plasma concentration of dehydroascorbate after acute smoking (6.8 ± 1.1 vs 5.0 ± 1.1 μmol/L, P < 0.01). Plasma lipid peroxides (measured as thiobarbituric acid reactive substances) and copper-induced oxidizability of low-density lipoprotein showed no change after acute smoking. In response to a fat meal, plasma triglyceride concentrations peaked on average between 3 and 4h postprandially and LDL's content of lipid-soluble antioxidants (mostly α-tocopherol) decreased (8.1 ± 0.4 vs 7.4 ± 0.4 molecules/LDL particle, P = 0.023). This may render postprandial LDL more vulnerable to oxidation. The lack of effect of acute cigarette smoking on plasma antioxidant vitamins, apart from an apparent decrease in dehydroascorbate, suggests that compensatory mechanisms are at work in vivo with plasma ascorbate concentrations possibly replenished from other metabolic pools.

The prooxidant and antioxidant effects of ascorbate supplementation on skin keratinocytes

The prooxidant and antioxidant effects of ascorbate supplementation on skin keratinocytes

Enrichment of live food with essential fatty acids and vitamin C: effects on milkfish ( Chanos chanos) larval performance

The effects of essential fatty acids (EFA) and vitamin C-enriched live food on growth, survival, resistance to salinity stress and incidence of deformity in milkfish larvae reared in tanks were investigated. Larvae were either fed rotifers cultured on Chlorella sp. and newly hatched Artemia nauplii (control), highly unsaturated fatty acid (HUFA)-enriched rotifers and Artemia nauplii or HUFA+vitamin C-enriched rotifers and Artemia nauplii. Milkfish growth in outdoor nursery ponds was also assessed to compare with growth in indoor tanks. Milkfish fed rotifers/ Artemia enriched with HUFA (32–48 mg dry weight, DW) or HUFA+vitamin C (33–45 mg DW) exhibited significantly ( P<0.05) higher growth than those given unenriched live food (24–27 mg DW) after 40 days of culture. Growth of milkfish in nursery ponds (albeit lower in stocking density) showed similar trends as those reared in tanks. When subjected to salinity stress (Day 25), mortality of the HUFA+vitamin C-treated fish and HUFA-treated fish were significantly lower ( P<0.05) than the control fish. Survival of 26-day old milkfish, however, did not differ significantly ( P>0.05) among the treatment groups. Forty-day-old milkfish fed HUFA+vitamin C-enriched live food had significantly lower ( P<0.05) incidence of opercular deformity (mainly cleft branchiostegal membrane) (8.4–14.7%) compared with those given HUFA-enriched (15.8–23.5%) or unenriched (27.3–33.5%) live food. Results demonstrated the effect of HUFA enrichment in enhancing milkfish larval growth and resistance to salinity stress but not overall survival. Moreover, HUFA and ascorbate supplementation decreased but did not totally eliminate incidence of opercular deformity in milkfish larvae.

Effect of high concentration of ascorbate on catalase activity in cultured cells and tissues of guinea pigs.

This study showed that the inhibition of cell growth in 3T6, induced by the supplementation of ascorbate at 0.5 mM in cultured medium, was prevented by the addition of catalase in the range of 25-750 units/mL regardless of the degree of activity. However, cytotoxicity induced by concentrations of more than 2 mM ascorbate could not be prevented even when a high level of catalase (5,000 units/mL) was added to the medium. Catalase activity in medium supplemented with ascorbate decreased with incubation time; the higher the concentration of ascorbate, the greater the decrease in catalase activity. These results indicate that even though catalase is present at a high concentration in the medium, it cannot prevent cytotoxicity by a high concentration of ascorbate because the oxygen radical derived from ascorbate inhibits its activity. We therefore investigated whether the inhibition of catalase activity by ascorbate could be observed in animal tissues. The catalase activity in the tissues of guinea pigs 6h after the administration of ascorbate was lower than that in non-administered animals. When guinea pigs were fed diets containing 5 mg or 100 mg ascorbate/animal over a 90 weeks period, a clear affect on catalase activity in the high-dose ascorbate group as compared to that in the low-dose ascorbate group was not observed.

Ascorbate Differentially Regulates Elastin and Collagen Biosynthesis in Vascular Smooth Muscle Cells and Skin Fibroblasts by Pretranslational Mechanisms

Ascorbate contributes to several metabolic processes including efficient hydroxylation of hydroxyproline in elastin, collagen, and proteins with collagenous domains, yet hydroxyproline in elastin has no known function. Prolyl hydroxylation is essential for efficient collagen production; in contrast, ascorbate has been shown to decrease elastin accumulation in vitro and to alter morphology of elastic tissues in vivo. Ascorbate doses that maximally stimulated collagen production (10-200 microM) antagonized elastin biosynthesis in vascular smooth muscle cells and skin fibroblasts, depending on a combination of dose and exposure time. Diminished elastin production paralleled reduced elastin mRNA levels, while collagen I and III mRNAs levels increased. We compared the stability of mRNAs for elastin and collagen I with a constitutive gene after ascorbate supplementation or withdrawal. Ascorbate decreased elastin mRNA stability, while collagen I mRNA was stabilized to a much greater extent. Ascorbate withdrawal decreased collagen I mRNA stability markedly (4.9-fold), while elastin mRNA became more stable. Transcription of elastin was reduced 72% by ascorbate exposure. Differential effects of ascorbic acid on collagen I and elastin mRNA abundance result from the combined, marked stabilization of collagen mRNA, the lesser stability of elastin mRNA, and the significant repression of elastin gene transcription.

A positive correlation between catalase activity and ascorbate uptake in the tissues of guinea pigs and cultured cells of mammals.

We recently reported that the concentration of supplemental ascorbate which inhibits cell growth is positively related to intracellular catalase activity. It is assumed that the cells with high catalase activity are resistant to high concentrations of ascorbate since catalase can decompose hydrogen peroxide (H2O2) induced by the auto-oxidation of ascorbate in cultured medium. In this study, we investigated whether intracellular catalase activity affects the uptake of ascorbate into animal tissue and cultured cells. Ascorbate concentrations in the tissues of guinea pigs and various cultured cells, with and without supplementation of ascorbate, were determined to evaluate the efficiency of ascorbate uptake. We found a positive correlation between the efficiency of ascorbate uptake and catalase activity in various tissues of guinea pigs (r = 0.767, p < 0.05). Furthermore, a positive correlation between the two was also found in various species of cultured cells. This study indicates that tissues and cells with higher efficiency of ascorbate uptake are required for higher catalase activity, presumably for the decomposition of H2O2 from ascorbate.