Plasma levels of vitamin C components in normal and diabetic subjects

Vitamin C Status in People with Types 1 and 2 Diabetes Mellitus and Varying Degrees of Renal Dysfunction: Relationship to Body Weight

Diabetes mellitus is a chronic metabolic disorder and is associated with depleted vitamin C status. The underlying aetiologies and pathogeneses responsible for this association are poorly understood. This retrospective study explored the vitamin C status of 136 adult outpatients with types 1 and 2 diabetes mellitus (T1DM/T2DM), with a focus on indices of renal function and metabolic health, including body weight. In the T1DM group (n = 73), the median plasma vitamin C concentration was 33 (18, 48) µmol/L, with 37% hypovitaminosis C and 12% deficiency. In the T2DM group (n = 63), the median plasma concentration was 15 (7, 29) µmol/L, with 68% hypovitaminosis C and 38% deficiency. Lower vitamin C was associated with macroalbuminuria (p = 0.03), renal dysfunction (p = 0.08), and hypertension (p = 0.0005). Inverse associations were also observed between plasma vitamin C and various other metabolic health parameters (p < 0.05), especially body weight (p < 0.0001), which was higher in those with hypovitaminosis C (<23 µmol/L; p = 0.0001). The association with bodyweight remained, even after multivariable analysis. In summary, body weight was a significant predictor of low vitamin C status in people with diabetes. This suggests that people with both diabetes and a high body weight may have greater than average vitamin C requirements.

Relationship of Helicobacter pylori CagA(+) status to gastric juice vitamin C levels

BACKGROUND

To date it is not known whether gastric juice vitamin C levels are influenced by Helicobacter pylori CagA(+) strains. The aim of the present study, therefore, was to study the impact of H. pylori CagA status on gastric juice vitamin C levels.

MATERIALS AND METHODS

We studied 30 H. pylori(+) patients, and the results were compared with 10 endoscopically and histologically normal H. pylori(-) subjects (control group) who were similar to the H. pylori(+) group in terms of age and sex. In all patients, gastric juice vitamin C levels were determined and the severity of gastritis was graded on a scale of 0 (absent) to 3 (severe). CagA was determined by immunoblotting the sera from patients against H. pylori antigens.

RESULTS

Among 30 H. pylori(+) patients, 20 were CagA(+) and 10 CagA(-). In the entire group of H. pylori(+) patients, the median gastric juice vitamin C levels (mg L-1) were 16.35 (range 3.5-33.6) and were significantly lower (P < 0.001) than in the control group of H. pylori(-) patients [35.5 (23.1-50.2)]. In addition, in the entire group of H. pylori(+) patients there was a highly significant (P < 0.0001) inverse correlation between the gastritis activity score and the gastric juice vitamin C levels. In the group of H. pylori CagA(+) patients, the median levels of gastric juice vitamin C were 13.8 (3.5-31.2) and were significantly lower than the corresponding levels in both the H. pylori CagA(-) group [24.8 (22-33.6), P < 0.01] and the H. pylori(-) control group [35.5 (23.1-50.2), P < 0.001], the last groups being similar. Furthermore, the gastritis activity median score in the H. pylori CagA(+) group [2 (1-3)] was significantly higher (P < 0.05) than in the H. pylori CagA(-) group [1 (1-2)].

CONCLUSION

These data indicate that infection with CagA(+) H. pylori strains significantly lowers the gastric juice vitamin C levels in comparison with CagA(-) H. pylori strains, which might have a significant impact on gastric carcinogenesis.

Glucose transporter isoforms GLUT1 and GLUT3 transport dehydroascorbic acid

Dehydroascorbic acid (DHA) is rapidly taken up by cells and reduced to ascorbic acid (AA). Using the Xenopus laevis oocyte expression system we examined transport of DHA and AA via glucose transporter isoforms GLUT1-5 and SGLT1. The apparent Km of DHA transport via GLUT1 and GLUT3 was 1.1 +/- 0.2 and 1.7 +/- 0.3 mM, respectively. High performance liquid chromatography analysis confirmed 100% reduction of DHA to AA within oocytes. GLUT4 transport of DHA was only 2-4-fold above control and transport kinetics could not be calculated. GLUT2, GLUT5, and SGLT1 did not transport DHA and none of the isoforms transported AA. Radiolabeled sugar transport confirmed transporter function and identity of all cDNA clones was confirmed by restriction fragment mapping. GLUT1 and GLUT3 cDNA were further verified by polymerase chain reaction. DHA transport activity in both GLUT1 and GLUT3 was inhibited by 2-deoxyglucose, D-glucose, and 3-O-methylglucose among other hexoses while fructose and L-glucose showed no inhibition. Inhibition by the endofacial inhibitor, cytochalasin B, was non-competitive and inhibition by the exofacial inhibitor, 4,6-O-ethylidene-alpha-glucose, was competitive. Expressed mutant constructs of GLUT1 and GLUT3 did not transport DHA. DHA and 2-deoxyglucose uptake by Chinese hamster ovary cells overexpressing either GLUT1 or GLUT3 was increased 2-8-fold over control cells. These studies suggest GLUT1 and GLUT3 isoforms are the specific glucose transporter isoforms which mediate DHA transport and subsequent accumulation of AA.

Does diabetes mellitus increase the requirement for vitamin C?

This paper reviews the scientific evidence regarding the vitamin C status of people with diabetes mellitus and whether they might have increased dietary vitamin C requirements. English language articles published from 1935 to the present that either compare ascorbic acid concentrations of persons with and without diabetes mellitus or assess the impact of vitamin C supplementation on various health outcomes among persons with diabetes mellitus were examined. Most studies have found people with diabetes mellitus to have at least 30% lower circulating ascorbic acid concentrations than people without diabetes mellitus. Vitamin C supplementation had little impact on blood glucose concentrations, but was found to lower cellular sorbitol concentrations and to reduce capillary fragility. Much of the past research in this area has been methodologically weak. To further understand the relation of ascorbic acid and diabetes mellitus, randomized clinical trials of ascorbic acid supplementation should be a high priority for research.

Alteration of antioxidant status in diabetic rats by chronic exposure to psychological stressors

Antioxidant status was measured in heart, liver, kidney, lung, and erythrocytes of 2-week streptozotocin-diabetic male Wistar rats exposed to chronic intermittent psychological stress consisting of 1 h of restraint twice daily for 14 days. Diabetes reduced erythrocyte and heart and liver susceptibility to hydrogen peroxide-induced glutathione depletion. Susceptibility to peroxide-induced thiobarbituric acid reactive substance (TBARS) formation increased in erythrocytes, liver, kidney, and lung but decreased in heart. Significant changes also occurred in glutathione levels (increased in heart and decreased in liver) and in the activities of catalase (reduced in liver and kidney), glutathione reductase (elevated in heart and liver), and glutathione peroxidase (decreased in liver and lung), but not Cu,Zn-superoxide dismutase. Stress potentiated diabetes-associated hyperglycemia and attenuated diabetes-induced hyperlipidemia. In addition, the reduction in peroxide-induced glutathione depletion in heart and liver and the increased TBARS formation in kidney and lung were reversed. Similarly, the diabetes-induced induced increase in liver glutathione reductase and decreases in liver and lung glutathione peroxidase activities were abolished by stress. Thus, the relative resistance of antioxidant systems to stress can be modified under pathologic conditions in which antioxidant alterations are present.

Helicobacter pylori infection and gastric juice vitamin C levels. Impact of eradication

H. pylori has recently been recognized as a novel risk factor of gastric cancer, but its precise role in gastric carcinogenesis is as yet unknown. The aim of the present study was to assess the relationship between H. pylori infection and vitamin C levels in gastric juice and also to examine whether eradication of H. pylori could have any impact on these levels. Gastric juice and plasma vitamin C levels were measured in 88 dyspeptic patients who had an upper gastrointestinal endoscopy. In the subgroup of H. pylori-positive patients, eradication was attempted with triple therapy. This subgroup was studied on two occasions, ie, before and after treatment. There were 58 H. pylori-positive and 30 -negative patients. Gastric juice vitamin C levels in H. pylori-positive patients were statistically lower (P < 0.001) than the levels in the H. pylori-negative patients. Triple therapy achieved eradication in 45 patients (77.6%) of the 58 H. pylori-positive patients. Before H. pylori was eradicated in these 45 patients gastric juice vitamin C levels were significantly (P < 0.001) lower than those after eradication, the latter being no different than the group of 30 H. pylori-negative patients. There was a significant (P < 0.001) improvement of gastritis after eradication, which paralleled the elevation of gastric juice vitamin C levels. No difference was noted in plasma vitamin C levels between H. pylori-negative and -positive patients or in the latter before and after H. pylori treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Disturbed handling of ascorbic acid in diabetic patients with and without microangiopathy during high dose ascorbate supplementation

Abnormalities of ascorbic acid metabolism have been reported in experimentally-induced diabetes and in diabetic patients. Ascorbate is a powerful antioxidant, a cofactor in collagen biosynthesis, and affects platelet activation, prostaglandin synthesis and the polyol pathway. This suggests a possible close interrelationship between ascorbic acid metabolism and pathways known to be influenced by diabetes. We determined serum ascorbic acid and its metabolite, dehydroascorbic acid, as indices of antioxidant status, and the ratio, dehydroascorbate/ascorbate, as an index of oxidative stress, in 20 matched diabetic patients with and 20 without microangiopathy and in 22 age-matched control subjects. Each study subject then took ascorbic acid, 1 g daily orally, for six weeks with repeat measurements taken at three and six weeks. At baseline, patients with microangiopathy had lower ascorbic acid concentrations than those without microangiopathy and control subjects (42.1 +/- 19.3 vs 55.6 +/- 20.0, p less than 0.01, vs 82.9 +/- 30.9 mumol/l, p less than 0.001) and elevated dehydroascorbate/ascorbate ratios (0.87 +/- 0.46 vs 0.61 +/- 0.26, p less than 0.01, vs 0.38 +/- 0.14, p less than 0.001). At three weeks, ascorbate concentrations rose in all groups (p less than 0.0001) and was maintained in control subjects (151.5 +/- 56.3 mumol/l), but fell in both diabetic groups by six weeks (p less than 0.01). Dehydroascorbate/ascorbate ratios fell in all groups at three weeks (p less than 0.0001) but rose again in the diabetic groups by six weeks (p less than 0.001) and was unchanged in the control subjects. Dehydroascorbate concentrations rose significantly from baseline in all groups by six weeks of ascorbic acid supplementation (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin C in the human stomach: relation to gastric pH, gastroduodenal disease, and possible sources

Fasting gastric juice pH and concentrations of vitamin C in gastric aspirate and plasma were measured in 73 patients undergoing endoscopy. Vitamin C concentrations were significantly lower in those with hypochlorhydria (pH greater than 4; n = 23) compared with those with pH less than or equal to 4 (p less than 0.005) and there was a significant correlation between gastric juice and plasma concentrations (p = 0.002). Patients with normal endoscopic findings had significantly higher intragastric concentrations of vitamin C than those with gastric cancer (p less than 0.001), pernicious anaemia (p less than 0.005), gastric ulcer (p less than 0.01), duodenal ulcer (p less than 0.05), or after gastric surgery (p less than 0.01). There was a strong trend (0.05 less than p less than 0.1) towards lower intragastric concentrations of vitamin C in patients with chronic atrophic gastritis. In vitro, vitamin C concentrations remained stable in acidic but fell significantly over 24 hours in alkaline gastric aspirate. Gastric secretory studies in five volunteers showed that vitamin C concentrations increased significantly after intramuscular pentagastrin. These findings suggest that the low fasting levels of vitamin C in hypochlorhydric gastric juice may be caused by chemical instability and that vitamin C may be secreted by the human stomach.