Cell-mediated cytotoxicity and humoral immune response in ascorbic acid-deficient guinea pigs.

Guinea pigs were divided into three dietary groups: ascorbic-acid deficient, pair-fed, and ad libitum control. Two weeks later guinea pigs were immunized intradermally with 5 x 10(8) chicken erythrocytes in Freund's complete adjuvant. Hemagglutinating antibody titers to chicken erythrocytes 2 weeks after immunization were comparable in all three dietary groups. In vitro 51Cr release from labeled chicken erythrocyte target cells incubated with lymphoid cells from spleens of ascorbic acid-deficient guinea pigs was significantly less than with spleen cells from pair-fed and ad libitum control guinea pigs. The percentage of splenic lymphoid cells that formed rosettes with rabbit erythrocytes, a T cell marker, was the same in all three dietary groups. The defect of ascorbic acid deficiency may reflect an impairment of T lymphocytes function in cell-mediated cytotoxicity or a change in number or function of another cell type.     

Phagocytosis and leukocyte enzymes in ascorbic acid deficient guinea pigs.

Enzymes related to bactericidal activities of leukocytes were studied in ascorbic acid deficient guinea pig leukocytes. The activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were not affected either under resting or phagocytizing conditions in ascorbic acid deficiency. Granule bound NADPH-oxidase activity of resting leukocytes also was not altered in ascorbic acid deficiency. However, the extent of stimulation in NADPH-oxidase activity under phagocytizing condition was found to be significantly lower in ascorbic acid deficient leukocytes than that in control leukocytes. Similary, the extent of release of acid phosphatase from lysosomes during phagocytosis was also low in ascorbic acid deficient leukocytes. Ascorbic acid deficiency did not influence the activities of glutathione reductase and myeloperoxidase of leukocytes. The significance of these enzyme changes is discussed in relation to the decreased phagocytic and bactericidal activities of leukocytes in ascorbic acid deficiency.     

Urinary ascorbic acid levels following the withdrawal of large doses of ascorbic acid in guinea pigs

Male guinea pigs received sodium ascorbate solution [equivalent to 1 g ascorbic acid/(kg body weight.d)] by intraperitoneal injection for 4 wk. During the ascorbic acid treatment period, plasma and urinary ascorbic acid levels rose markedly. Three weeks after the ascorbic acid treatment was withdrawn, mean urinary ascorbic acid levels were significantly lower than their corresponding basal levels. At both 2 and 5 wk after withdrawal of ascorbic acid treatment, mean plasma ascorbic acid levels were below normal. The results indicate that these animals had experienced a transient withdrawal effect after administration of large doses of ascorbic acid that lasted about 1 wk. This, in turn, indicates that the rate of ascorbic acid turnover was probably increased during treatment, and this effect persisted even after the ascorbic acid was withdrawn. Examination of data from each individual experimental animal revealed that the pattern of urinary ascorbic acid excretion after the withdrawal of large doses of ascorbic acid varied from animal to animal. Among the twelve experimental guinea pigs, seven had abnormally low urinary ascorbic acid levels 2-4 wk after the withdrawal of the large doses of ascorbic acid.     

High-dose ascorbic acid decreases cholesterolemic factors of an atherogenic diet in guinea pigs

BACKGROUND: The study evaluates the effect of a high supplemental dose of ascorbic acid (AA) on plasma concentrations of total cholesterol (TC), triglycerides (TG), total lipids (TL), and lipoprotein fractions high-density, very-low-density-, and low-density lipoprotein (HDL, VLDL, LDL) in guinea pigs fed with atherogenic diet. METHODS: Group I consisted of 5 normally fed guinea pigs plus a low dose of AA (1 mg/100 g/day), group II consisted of 7 guinea pigs fed with food enriched with 2% cholesterol plus a low dose of AA (1 mg/100 g/day), and group III consisted of 7 guinea pigs fed with food enriched with 2% cholesterol plus a high dose of AA (30 mg/100 g/day). Cholesterolemic factors concentrations were determined after nine weeks. RESULTS: Concentrations of TC, TG, TL, LDL, and VLDL were increased in group II compared to group I (p < 0.01 for all differences). Supplementation with a high dose of AA resulted in decreased concentrations of TC (p < 0.01), TG (p < 0.01), TL (p < 0.01), and LDL (p < 0.01) in group III compared to group II. Additionally, concentration of HDL was increased in group III compared to group II (p < 0.01). CONCLUSION: High-dose AA supplementation to an atherogenic diet decreases concentrations of TC, TG, TL, and LDL and increases concentration of HDL compared to low-dose AA.     

Effects of ascorbic acid and inflammation on ceruloplasmin activity levels in guinea pigs

The possibility that ascorbic acid exerts a postabsorptive effect on copper metabolism in guinea pigs was examined. A pair of ascorbic acid injections (20 mg/kg, ip, 18 h apart) caused a small but statistically significant increase in oxidase activity levels of ceruloplasmin, a serum copper protein. In contrast, dietary ascorbic acid deprivation for 14 days did not prevent increases in ceruloplasmin activity levels caused by turpentine-induced inflammation. The ascorbic acid deprivation did reduce weight gain and adrenal ascorbic acid contents but serum ascorbic acid concentrations were not significantly lowered. In summary, ascorbic acid can produce postabsorptive changes in copper metabolism but adequate intake of the vitamin is not necessary for inflammation-induced elevations of ceruloplasmin activity levels.     

Prolonged marginal ascorbic acid deficiency induces oxidative stress in retina of guinea pigs

We examined whether prolonged marginal ascorbic acid deficiency induces oxidative stress in the retina of guinea pigs. Male guinea pigs aged four weeks were given a scorbutic diet (20 g/animal per day) with either marginally deficient ascorbic acid (0.5 mg/animal per day) or adequate ascorbic acid (1 g/animal per day) in drinking water for three and six months. The retinal contents of the reduced form of ascorbic acid in the deficient group at three and six months were 68.1 and 43.5%, respectively, of that in the corresponding adequate group. The retinal contents of the oxidized form of ascorbic acid in the deficient group at three and six months were 1.9- and 2.7-fold, respectively, higher than that in the corresponding adequate group. The content of retinal thiobarbituric acid reactive substances (TBARS), an index of lipid peroxidation, in the deficient group was 2.5-fold higher than that in the adequate group at six months. The retinal contents of reduced glutathione (GSH) in the deficient group at three and six months were 84.8 and 66.7%, respectively, of that in the corresponding adequate group. The deficient group had 37.5% of retinal vitamin E content of the adequate group at six months. The deficient group had higher serum vitamin E concentration than the adequate group in both experimental periods. There were no differences in serum TBARS and GSH concentrations between the groups at both periods. These results indicate that prolonged marginal ascorbic acid deficiency induces oxidative stress in the retina of guinea pigs without systemic oxidative stress.     

Modulation of the flavin-containing monooxygenase in guinea pigs by ascorbic acid and food restriction

Modulation of the flavin-containing monooxygenase (FMO) by varying the ascorbic acid and food intake was investigated. Hepatic activity of the FMO in ascorbic acid-deficient guinea pigs fed a restricted amount of diet which resulted in a 10-15% body weight loss, was 17% of that in animals fed restricted amounts of the adequate diet. FMO hepatic activity in ascorbic acid-supplemented guinea pigs on a food-restricted regimen was 176% of that found in animals fed the adequate diet ad libitum. This increase in activity was not related to stress. Alteration in the activity of this important drug-metabolizing enzyme system by a combination of ascorbic acid deficiency and reduced food intake could potentially alter the rate of metabolism of a great variety of pharmaceutical drugs and environmental chemicals.     

Effect of ascorbic acid nutriture on blood histamine and neutrophil chemotaxis in guinea pigs

Histamine suppresses certain immune responses, including neutrophil chemotaxis. The present study examined whether the histamine-lowering effect of ascorbate was accompanied by enhanced chemotaxis in guinea pigs. Animals were fed low ascorbate, adequate or high ascorbate diets (0.5, 2.0 or 50 mg ascorbate.100 g body wt-1.d-1) for 4 wk. Mean liver ascorbate paralleled dietary intake, and these values differed significantly. Blood histamine was significantly depressed in the high ascorbate group compared to the adequate and low ascorbate groups, and liver ascorbate was inversely correlated to blood histamine levels (r = -0.64, P less than 0.001). The random migration of neutrophils was not significantly affected by vitamin dosage. Leukocyte chemotaxis was significantly impaired in low ascorbate animals compared to that of animals with adequate ascorbate nutriture. Leukocyte chemotaxis in high ascorbate animals did not differ significantly from that in the adequate or low ascorbate groups. Furthermore, chemotaxis was significantly lower when cells extracted from animals with adequate ascorbate nutriture were incubated in low ascorbate or high ascorbate serum rather than in autologous serum. These data suggest that the histamine-lowering effect of supplemental ascorbate does not appear to enhance leukocyte chemotaxis and that serum from guinea pigs fed low or high levels of ascorbate appears to contain factors that depress chemotaxis.     

Short-term ascorbic acid deficiency does not impair antioxidant status in lens of guinea pigs

We examined whether short-term ascorbic acid deficiency impairs antioxidant status in the lens of guinea pigs. Male guinea pigs aged 4 wk were given a scorbutic diet (20 g/animal per day) with and without ascorbic acid (400 mg/animal per day) in drinking water for 3 wk. The ascorbic acid-deficient group showed no lens opacity. The ascorbic acid-deficient group had 14% of serum ascorbic acid concentration, 6% of aqueous humor ascorbic acid concentration, and 18% of lens ascorbic acid content in the ascorbic acid-adequate group. There were no differences in the contents of lens reduced glutathione and thiobarbituric acid reactive substances, an index of lipid peroxidation, between the ascorbic acid-deficient and adequate groups, while the deficient group had higher lens vitamin E content than the adequate group. The ascorbic acid-deficient group had higher serum vitamin E concentration than the ascorbic acid adequate group, while there were no differences in the concentrations of serum reduced glutathione and tiobarbituric acid reactive substances between the deficient and adequate groups. These results indicate that short-term ascorbic acid deficiency does not impair antioxidant status in the lens of guinea pigs despite induction of severe ascorbic acid depletion in the tissue, which may result in no cataract formation.     

Effect of dietary ascorbic acid on levels of serum mineral nutrients in guinea pigs

The effect of dietary ascorbic acid on the serum mineral nutrients, Ca, Cu, Fe, K, Mg, Mn, Na and Zn in guinea pigs has been studied. Large amounts of ascorbic acid were administered to experimental animals in their drinking water. The daily ascorbic acid intake from the diet for the control animals was 10 mg/kg body weight. The mean ascorbic acid intakes for the two groups of experimental animals were 366 (37 times control) and 722 (72 times control) mg/kg body weight/day. In the ascorbic acid-treated animals, there was a significant increase in serum ascorbic acid levels in comparison with the controls. No substantial differences were observed in the body weights. The large quantities of dietary ascorbic acid did not influence serum levels of all eight minerals studied when the experimental and control values were compared using the two-tailed Student's t-test. However, serum level of copper in the guinea pigs ingesting a daily dose of 722 mg of ascorbic acid per kg body weight was slightly below control value when one-tailed Student's t-test was used.     

Glycolytic, hexose monophosphate shunt and bactericidal activities of leukocytes in ascorbic acid deficient guinea pigs.

It is well known that glycolytic and hexose monophosphate shunt activities of leukocytes increase during phagocytosis. The relevance of these metabolic changes to particle uptake and particle destruction is also well established. In the present study, these metabolic activities were studied to assess the phagocytic function of leukocytes isolated from ascorbic acid deficient guinea pigs. Glycolytic activity which provides the necessary energy for particle uptake was found to be decreased in both resting and phagocytizing leukocytes for ascorbic acid deficient guinea pigs. The direct oxidation of glucose through the hexose monophosphate shunt (HMS) was stimulated to a significantly lesser extent during phagocytosis in ascorbic acid deficient leukocytes. There was a progressive decline in phagocytosis induced shunt activity of leukocytes as the deficiency of ascorbic acid progressed. These findings show that particle uptake (as indicated by glycolytic activity) as well as particle destruction (as indicated by HMS activity) by leukocytes are impaired in ascorbic acid deficiency. Bactericidal capacity of leukocytes against Escherichia coli was also found to be low in ascorbic acid deficient guinea pigs as compared to those in the pair-fed control group.     

Effect of increasing storage iron on ascorbic acid metabolism in the guinea pig

Ascorbic acid (AA) metabolism was studied in control and iron-loaded guinea pigs. All animals were fed an AA-deficient diet and given a daily intraperitoneal (ip) dose of 10 mg sodium ascorbate. The control-diet formula contained 0.10 g Fe/kg diet; the experimental diet contained an additional 3.33 g Fe/kg diet as FeSO4. After 14 wk animals were injected (ip) with 9.25 x 10(3) Bq [1-14C]L-ascorbic acid. Blood was collected for 10 d and plasma specific activity of AA was determined. All animals were subsequently killed and selected tissues were analyzed for AA and iron concentrations. In spite of marked elevation of iron concentrations in plasma, spleen, and liver in experimental animals compared with controls, no differences in AA metabolism as determined by tissue AA concentrations and AA half-life, turnover rate, and body-pool size were evident. These results demonstrate that iron loading has no effect on the rate of AA catabolism in guinea pigs.     

Decrease in bone density in young male guinea pigs fed high levels of ascorbic acid

These experiments were conducted to investigate the effects of high oral intakes of ascorbic acid on bone metabolism in young guinea pigs and to inquire into the mechanism mediating these effects. Male guinea pigs 14 days old fed 8.7% of ascorbic acid for 6 weeks had decreased bone density and decreased urinary hydroxyproline compared to control animals fed 0.2% of ascorbic acid. To assess whether these changes were due to the acidity of the diet or to vitamin activity, salts of ascorbic acid, salts of erythorbic acid and free erythorbic acid were fed. There were no significant bone changes in any of these groups. The results strongly indicate that the acidity of ascorbic acid plays a part in the decrease in bone density but do not rule out that some other metabolic property specific to ascorbic acid may also be implicated.