During primate evolution, a major factor in lengthening life-span and decreasing age-specific cancer rates may have been improved protective mechanisms against oxygen radicals. We propose that one of these protective systems is plasma uric acid, the level of which increased markedly during primate evolution as a consequence of a series of mutations. Uric acid is a powerful antioxidant and is a scavenger of singlet oxygen and radicals. We show that, at physiological concentrations, urate reduces the oxo-heme oxidant formed by peroxide reaction with hemoglobin, protects erythrocyte ghosts against lipid peroxidation, and protects erythrocytes from peroxidative damage leading to lysis. Urate is about as effective an antioxidant as ascorbate in these experiments. Urate is much more easily oxidized than deoxynucleosides by singlet oxygen and is destroyed by hydroxyl radicals at a comparable rate. The plasma urate levels in humans (about 300 microM) is considerably higher than the ascorbate level, making it one of the major antioxidants in humans. Previous work on urate reported in the literature supports our experiments and interpretations, although the findings were not discussed in a physiological context.

https://www.pnas.org/content/pnas/78/11/6858.full.pdf

Uric acid provides an antioxidant defense in humans against oxidant- and radical-caused aging and cancer: a hypothesis.

Publisher Summary This chapter reviews the histopathologic, serologic, lymphocytic, virological, hormonal, and genetic characteristics of murine models of systemic lupus erythematosus (SLE). The pathogenetic mechanisms underlying murine SLE are highly complex, apparently well-programmed genetically, but still diverse and their bases not as yet well defined. Significant serologic and cellular experimental data support the statement that the final immunopathologic perturbation in murine (and human) SLE is a B lymphocyte hyperactivity with corresponding enhancement of serum antibodies and autoantibodies, particularly IgG, and consequent formation of pathogenic antigen–antibody ICs. On the basis of the available data, it appears that this B cell hyperactivity is polyclonal but not necessarily panclonal in nature, because not only antibodies against a wide array of autoantigens but also antibodies against incidental antigens, such as haptens, can be detected. The presence of autoantibodies and of their idiotypes in some recombinant lupus x normal murine lines expressing the normal partner's V genes, normal mice in which an exogenous or endogenous (Ipr gene) immunostimulator has been introduced, and unmanipulated normal mice indicate that lupus mice are not unique in their structural genetic Ig elements, whose presence determines the development of their autoimmune disease. The cause of B cell hyperactivity in lupus has not yet been fully elucidated. Autonomous B cell maturation does not appear likely, because B cell proliferation and differentiation in lupus mice was found to be dependent on the same number of accessory signals as in normal mice.

Murine models of systemic lupus erythematosus.

Endometriosis

The temporal disappearance in human blood plasma of endogenous antioxidants in relation to the appearance of various classes of lipid hydroperoxides measured by HPLC postcolumn chemiluminescence detection has been investigated under two types of oxidizing conditions. Exposure of plasma to aqueous peroxyl radicals generated at a constant rate leads immediately to oxidation of endogenous ascorbate and sulfhydryl groups, followed by sequential depletion of bilirubin, urate, and alpha-tocopherol. Stimulating polymorphonuclear leukocytes in plasma initiates very rapid oxidation of ascorbate, followed by partial depletion of urate. Once ascorbate is consumed completely, micromolar concentrations of hydroperoxides of plasma phospholipids, triglycerides, and cholesterol esters appear simultaneously, even though sulfhydryl groups, bilirubin, urate, and alpha-tocopherol are still present at high concentrations. Nonesterified fatty acids, the only lipid class in plasma not transported in lipoproteins but bound to albumin, are preserved from peroxidative damage even after complete oxidation of ascorbate, most likely due to site-specific antioxidant protection by albumin-bound bilirubin and possibly by albumin itself. Thus, in plasma ascorbate and, in a site-specific manner, bilirubin appear to be much more effective in protecting lipids from peroxidative damage by aqueous oxidants than all the other endogenous antioxidants. Hydroperoxides of linoleic acid, phosphatidylcholine, and cholesterol added to plasma in the absence of added reducing substrates are degraded, in contrast to hydroperoxides of trilinolein and cholesterol linoleate. These findings indicate the presence of a selective peroxidase activity operative under physiological conditions. Our data suggest that in states of leukocyte activation and other types of acute or chronic oxidative stress such a simple regimen as controlled ascorbate supplementation could prove helpful in preventing formation of lipid hydroperoxides, some of which cannot be detoxified by endogenous plasma activities and thus might cause damage to critical targets.

https://www.pnas.org/content/pnas/85/24/9748.full.pdf

Antioxidant defenses and lipid peroxidation in human blood plasma.

Vitamin C is an essential micronutrient for humans, with pleiotropic functions related to its ability to donate electrons. It is a potent antioxidant and a cofactor for a family of biosynthetic and gene regulatory enzymes. Vitamin C contributes to immune defense by supporting various cellular functions of both the innate and adaptive immune system. Vitamin C supports epithelial barrier function against pathogens and promotes the oxidant scavenging activity of the skin, thereby potentially protecting against environmental oxidative stress. Vitamin C accumulates in phagocytic cells, such as neutrophils, and can enhance chemotaxis, phagocytosis, generation of reactive oxygen species, and ultimately microbial killing. It is also needed for apoptosis and clearance of the spent neutrophils from sites of infection by macrophages, thereby decreasing necrosis/NETosis and potential tissue damage. The role of vitamin C in lymphocytes is less clear, but it has been shown to enhance differentiation and proliferation of B- and T-cells, likely due to its gene regulating effects. Vitamin C deficiency results in impaired immunity and higher susceptibility to infections. In turn, infections significantly impact on vitamin C levels due to enhanced inflammation and metabolic requirements. Furthermore, supplementation with vitamin C appears to be able to both prevent and treat respiratory and systemic infections. Prophylactic prevention of infection requires dietary vitamin C intakes that provide at least adequate, if not saturating plasma levels (i.e., 100–200 mg/day), which optimize cell and tissue levels. In contrast, treatment of established infections requires significantly higher (gram) doses of the vitamin to compensate for the increased inflammatory response and metabolic demand.

Vitamin C and Immune Function

The role of free radicals and lipid peroxidation is reviewed with regard to the aging process. Free radicals are produced during mitochondrial respiration, during the autooxidation of a variety of biological molecules and chemicals, during irradiation damage, and are found as environmental pollutants. Free radicals induce lipid peroxidation which results in membrane damage, increased disulfide/sulfhydryl ratios, and accumulation of aging pigments. Superoxide dismutase, glutathione peroxidase, vitamin E, vitamin C, and selenium are of importance with respect to free radical and lipid peroxide quenching. During aging, the levels of vitamin C appear to decline in the human, guinea pig, and the mouse. Synthetic antioxidants, added to the diets of mice, have been noted to extend the lifespan and mean half-survivale times.

Aspects of Free Radical Reactions in Biological Systems: Aging

Antinuclear autoantibodies (ANA) appeared in the plasma of lethally irradiated H-2d histocompatible DBA/2 and BALB/c mice several weeks after intravenous transplantation of 2 to 4 × 106 bone marrow cells from 3-week-old animals of the autoimmune New Zealand Black (NZB) strain. Little or no ANA development was observed in DBA/2 or BALB/c strains when syngeneic or nonautoimmune allogeneic marrow was grafted, or when NZB marrow was injected into untreated DBA mice or mice receiving 200 rads of x-irradiation. Transfer of 5 × 106 spleen cells from 8-day-old NZB mice into lethally irradiated BALB/c mice effected substantial ANA formation by the ninth day after transfer, compared to a 20-day latency following transfer of the same number of bone marrow cells. This earlier conversion with splenocytes may have been due to the presence of immunocompetent T and B cells, since stem cell numbers of the two tissues were similar. Transplantation of NZB marrow to lethally irradiated H-2 incompatible SJL/J (H-2s) and C57B1/6 (H-2b) strains brought about less ANA conversion than the transfer of compatible (SJL × NZB)F1 and (C57B1 × NZB)F1 marrow cells to the respective nonautoimmune SJL or C57B1 parental strain. Graft-versus-host reactions thus did not appear to play a requisite or determining role in the autoimmune development observed following grafting of NZB hemopoietic tissues. Reconstitution of lethally irradiated NZB mice with BALB/c or SJL/J bone marrow depressed the recurrence of ANA for 30 days, compared to rapid ANA recovery following NZB marrow injection. The characteristics that ultimately provoke or permit spontaneous auto-reactivity are inherent in the hemopoietic stem cell population of the NZB strain.

Transplantation of autoimmune potential. I. Development of antinuclear antibodies in H-2 histocompatible recipients of bone marrow from New Zealand Black mice.

Electron microscopic studies on the subcellular origin and ultrastructure of melanin granules in mammalian melanomas.

WE have reported1 an increased response to interferon induction in mice fed a diet containing vitamin C, and have now found a similar phenomenon in vitro. Addition of L-ascorbate to cultures of mouse cells (transformed L cells and normal embryonic fibroblasts) stimulated with polyinosinic acid · polycytidylic acid (poly(rI)·poly(rC)) resulted in increased synthesis of interferon.

Enhancement of interferon production by poly(rI)-poly(rC) in mouse cell cultures by ascorbic acid.

The inclusion of vitamin C in the drinking water of BALB/c mice was without effect on the humoral antibody response to sheep red blood cells and bacterial lipopolysaccharide. However, there was a significantly increased cell-mediated immune response as determined by increased T-lymphocyte responses to concanavalin A. This might suggest a mechanism, along with interferon enhancement, for the possible protection by vitamin C against some viral infections.

Benjamin V. Siegel

Papers

Aspects of Free Radical Reactions in Biological Systems: Aging

Transplantation of autoimmune potential. I. Development of antinuclear antibodies in H-2 histocompatible recipients of bone marrow from New Zealand Black mice.

Electron microscopic studies on the subcellular origin and ultrastructure of melanin granules in mammalian melanomas.

Enhancement of interferon production by poly(rI)-poly(rC) in mouse cell cultures by ascorbic acid.

Vitamin C and the immune response.