Hyperglycemia-induced ascorbic acid deficiency promotes endothelial dysfunction and the development of atherosclerosis

Dehydroascorbic acid, the oxidized form of vitamin C, is transported into mammalian cells via facilitative glucose transporters and hyperglycemia inhibits this process by competitive inhibition. This inhibited transport may promote oxidative stress and contribute to the increase in atherosclerotic cardiovascular disease observed in patients with diabetes mellitus. This review explores the importance of this proposed mechanism in light of current research. For example, recent reports suggest that administration of antioxidants, such as vitamin C, may slow atherogenesis by improving endothelium-dependent vasodilation in individuals with abnormal glucose and lipid metabolism, perhaps by preventing the oxidation of nitric oxide, an important regulator of vasomotor tone. Endothelial dysfunction plays a key role in the development of atherosclerosis and endothelial cells may be particularly affected by hyperglycemia-induced ascorbic acid deficiency as they line the interior of blood vessels. In addition, we discuss evidence of several other mechanisms by which vitamin C status may affect the development of atherosclerotic cardiovascular disease, particularly its inverse relationship to multiple cardiovascular disease risk factors and indicators. Given these factors, vitamin C administration is recommended during periods of both acute and chronic hyperglycemia to help preserve endothelial function.

Effect of vitamin supplementation on cytokine response and on muscle damage after strenuous exercise

The present double-blinded, placebo-controlled study investigated whether antioxidant vitamin supplementation was able to modulate the cytokine and lymphocyte responses after strenuous eccentric exercise. Furthermore, muscle enzyme release was examined to see whether antioxidant treatment could reduce muscle damage. Twenty male recreational runners randomly received either antioxidants (500 mg of vitamin C and 400 mg of vitamin E) or placebo for 14 days before and 7 days after a 5% downhill 90-min treadmill run at 75% V˙o 2 max. Although the supplemented group differed significantly with regard to plasma vitamin concentration before and after exercise when compared with the placebo group, the two groups showed identical exercise-induced changes in cytokine, muscle enzyme, and lymphocyte subpopulations. The plasma level of interleukin (IL)-6 and IL-1 receptor antagonist increased 20- and 3-fold after exercise. The plasma level of creatine kinase was increased sixfold the day after exercise. The concentrations of CD4+ memory T cells, CD8+ memory and naı̈ve T cells, and natural killer cells increased at the end of exercise. The total lymphocyte concentration was below prevalues in the postexercise period. In conclusion, the present study does not support the idea that exercise-induced inflammatory responses are induced by free oxygen radicals.

Antioxidant nutrients: current dietary recommendations and research update

OBJECTIVE

To review the importance of antioxidant nutrients in the maintenance of health and the prevention and treatment of disease, with a focus on data pertaining to vitamin C, vitamin E, selenium, and carotenoids. A secondary objective was to discuss the new Dietary Reference Intakes released by the Institute of Medicine (IOM) for these nutrients.

DATA SOURCES

IOM reports on the use of antioxidant vitamins were reviewed for nutrient recommendations. In addition, a MEDLINE search was performed to identify recent research and review articles on the topic, which were analyzed to identify key research findings in the area.

DATA SYNTHESIS

The review discusses the biologic processes of oxidation reactions and antioxidants in biologic systems, provides an overview of information on selected antioxidant nutrients, and explores their role in the prevention and treatment of cancer, cardiovascular disease, ocular disorders, and respiratory disorders.

CONCLUSION

There appear to be significant health benefits from dietary antioxidants, as can be found in fruits and vegetables. Some prospective assessment of the effect of supplemental antioxidants also suggests benefit, especially for vitamin E; however, there are conflicting results in this area. Overall, it appears that antioxidant nutrients, especially those from food sources, have important roles in preventing pathogenic processes related to cancer, cardiovascular disease, macular degeneration, cataracts, and asthma, and may enhance immune function.

Vitamin E and immunity

Vitamin E is a potent antioxidant and has an ability to modulate host immune functions. This chapter consists of five parts: (1) vitamin E deficiency and immunity, (2) vitamin E supplementation and immunity, (3) vitamin E and the decreased cellular immunity with aging, (4) vitamin E and T-cell differentiation in the thymus, and (5) vitamin E and acquired immune deficiency syndrome (AIDS). In vitamin E deficiency most of the immune parameters show a downward trend, which is associated with increased infectious diseases and the incidence of tumors. In contrast, vitamin E supplementation has various beneficial effects on the host immune system. The decreased cellular immunity with aging or during the development of AIDS is markedly improved by the intake of a high vitamin E diet. In addition, vitamin E plays an important role in the differentiation of immature T cells in thymus. Vitamin E deficiency induces the decreased differentiation of immature T cells, which results in the early decrease of cellular immunity with aging in spontaneously hypertensive rats. Conversely, vitamin E supplementation induces a higher differentiation of immature T cells via increased positive selection by thymic epithelial cells, which results in the improvement of decreased cellular immunity in the aged. Furthermore, vitamin E supplementation induces the early recovery of thymic atrophy following X-ray irradiation. Taken together, these results suggest that vitamin E is an important nutrient for maintaining the immune system, especially in the aged.

Anti-oxidants as modulators of immune function

In order to confirm the hypothesis of the immunomodulating action of anti-oxidants (bringing back altered immune function to more optimum values), the possibility that anti-oxidants may be useful in two experimental models of altered immune function has been studied. The first is a pathological model, that is, lethal murine endotoxic shock caused by an LPS injection of 100 mg/kg, in which the lymphocytes show increased adherence and depressed chemotaxis. The injection of N-acetylcysteine (150 mg/kg), which increased both functions in control animals, decreased adherence and increased chemotaxis in mice with endotoxic shock. The second is a physiological model; aged human subjects (70 +/- 5-year-old men) who, in their largest segment of population ('standard' group) showed an increased lymphocyte adherence and decreased lymphoproliferative response to mitogens compared with younger adults. The ingestion of vitamin E (200 mg daily for 3 months in this standard group) lowered adherence and stimulated lymphoproliferation. However, a smaller segment of the human population tested showed 'non-standard' values in these lymphocyte functions, that is, very low adherence and very high proliferation. In those subjects, vitamin E showed the opposite effects, namely adherence increase and depressed lymphoproliferation. In both age groups of men, these functions reached adult levels after vitamin E ingestion. These data suggest that anti-oxidants preserve adequate function of immune cells against homeostatic disturbances such as those caused by endotoxic shock and ageing.

Ascorbic acid modulates in vitro the function of macrophages from mice with endotoxic shock

The toxic effects of oxygen radicals produced by immune cells can be controlled to certain degree by endogenous antioxidants because of their scavenger action. This control is specially important in a type of immune cell, i.e., the phagocyte, which produces oxygen-free radicals and uses antioxidants in order to support its functions. Antioxidants, such as ascorbic acid (AA), are free radical scavengers and improve the immune response. In the pathogenesis of endotoxic shock, a disease with high mortality caused by gram-negative bacterial endotoxin, the reactive oxygen species (ROS) produced by phagocytes have been implicated. In a previous study, we observed in peritoneal macrophages from BALB/c mice suffering lethal endotoxic shock caused by intraperitoneal (i.p.) injection of Escherichia coli lipopolysaccharide (LPS; 100 mg/kg) a high production of superoxide anion. Therefore, in the present work, we have studied the in vitro effect of AA, at different concentrations (0.001, 0.01, 0.1, 1 and 2.5 mM), on the various steps of the phagocytic process, i.e., adherence to substrate, chemotaxis, ingestion of particles and superoxide anion production of murine peritoneal macrophages obtained from BALB/c mice with that of endotoxic shock, at 2, 4, 12 and 24 h after LPS injection. The increased adherence, ingestion and superoxide anion production by macrophages from animals with endotoxic shock were lower in the presence of AA, reaching similar values to those of the control animals. The most effective AA concentration in cells from mice with endotoxic shock was 0.01 mM. These data suggest that AA can regulate the phagocytic process in endotoxic shock, principally decreasing free radical production and thus it could reduce endotoxic shock severity.

Improvement of murine immune functions in vitro by thioproline

Previous studies have shown that several immune functions were improved in mice after the ingestion of a thioproline (thiazolidine-4-carboxylic acid) enriched diet. In the present work, we have studied the in vitro effects of several concentrations of this thiol compound (0.1, 0.5, 1, 2.5 and 5 mM) on the most relevant functions of three pivotal immune cells, namely, macrophages, lymphocytes, and natural killer (NK) cells from BALB/c mice. The results show that thioproline stimulates the phagocytic process of macrophages, increasing the mobility directed to the inflammatory focus (chemotaxis) and the phagocytosis of inert particles. It increases the adherence and the chemotaxis capacities of lymphocytes, their proliferative activity and favours the natural cytotoxic activity that could improve the capacity to destroy malignant cells. Thioproline concentrations of 0.5 and 1 mM were the most effective regarding the different functions analysed. These results suggest that the improvement of immune functions, observed in previous work, after thioproline-enriched diet ingestion is due to a direct action of this thiol compound on immune cells.

Effects in vitro of several antioxidants on the natural killer function of aging mice

The aim of the present work is to study the change with aging in the effect in vitro of several antioxidants: thiazolidine-4-carboxylic acid or thioproline, N-acetylcysteine (NAC), ascorbic acid (AA), and alpha-tocopherol (vitamin E, VE) on the natural killer (NK) activity in mononuclear cells from axillary nodes, spleen, thymus and peritoneal leukocytes from BALB/c male mice. Young (8+/-2 weeks), adult (24+/-2 weeks). mature (48+/-2 weeks), and old (72+/-2 weeks) animals were studied. A nonradioactive cytotoxic assay with cells from the murine lymphoma YAC-1 as target cells and a relation effector cells/target cells of 10/1 were used. The concentrations of the different antioxidants were: 1 mM for thioproline and N-acetylcysteine and 5 microM for ascorbic acid and alpha-tocopherol, which induced a maximum effect in our previous dose-response experiments. The results show that, in general, the above antioxidants cause an enhancement of the NK activity at all ages studied, this stimulation being higher with thioproline and N-acetylcysteine than with ascorbic acid and alpha-tocopherol. The effects were similar for the three lymphoid organs and the peritoneum. This stimulation of the NK activity by antioxidants is an important favorable response, especially in old mice, in which age results in a decrease in NK function and, therefore, in a higher incidence of neoplasia.