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 ofthese 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 level in humans (about 300 ILM) 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.Toxicity by oxygen radicals has been suggested as a major cause of cancer, heart disease, and aging (1-13). Oxygen radicals and other oxidants appear to be toxic in large part because they initiate the chain reaction of lipid peroxidation (rancidity). Lipid peroxidation generates various reactive species-such as radicals, hydroperoxides, aldehydes, and epoxides-with the capability of causing damage to DNA, RNA, proteins, cellular membranes, and cellular organization. Aerobic organisms have an array of protective mechanisms both for preventing the formation of oxidants and lipid peroxidation and for repairing oxidative damage. The protective systems include enzymes, such as superoxide dismutase (12) and the selenium-containing glutathione peroxidase (9, 10), and antioxidants and radical scavengers, such as a-tocopherol (vitamin E) and a-carotene in the lipid portion ofthe cell and glutathione and ascorbic acid in the aqueous phase (9, 10). These protective mechanisms are now being recognized as anticarcinogenic and, in some cases, even as life-span extending (5-7).A marked increase in life-span has occurred in human evolution during the descent from prosimians over the past 60 million years (4). At the same time an enormous decrease in the age-specific cancer rate has occurred in humans compared to short-lived mammals (14, 15). It seems likely that a major factor in lengthening life-span and decreasing age-specific cancer rates may have been the evolution ofeffective protective mechanisms against oxygen radicals (2-7, 10). We propose that one such mechanism is high plasma uric acid. MATERIALS AND METHODS'y-Ray Irradiation. Solutions of substrate (0.3 mM) in potassium phosphate buffer (20 mM, pH 7.4) were purged with 2, N2, or N20, sealed, and irradiated at room temperature with a 60Co y-ray source [12.7 krads/mi...

No abstract

Thymine glycol is a DNA damage product of ionizing radiation and other oxidative mutagens. In an attempt to find a noninvasive assay for oxidative DNA damage in individuals, we have developed an HPLC assay for free thymine glycol and thymidine glycol in urine. Our results indicate that humans excrete about 32 nmol of the two glycols per day. Rats, which have a higher specific metabolic rate and a shorter life span, excrete about 15 times more thymine glycol plus thymidine glycol per kg of body weight than' do humans.' We present evidence that thymine glycol and thymidine glycol are likely to be derived from repair of oxidized DNA, rather than from alternative sources such as the diet or bacterial flora. This noninvasive assay of DNA oxidation products may allow the direct testing of current theories which relate oxidative metabolism to the processes of aging and cancer in man.Oxygen radicals and other reactive oxygen species are generated in vivo as a consequence of normal metabolism (1-4). The oxidation of certain cellular components by these oxygen species could contribute to aging and age-dependent diseases such as cancer. Oxygen radicals have been shown to produce base damage and strand breaks in DNA (1, 3), as well as to initiate the process of lipid peroxidation (1, 3). The latter results in the formation of lipid hydroperoxides, which, in the presence of cellular iron-containing compounds, can also break down to yield oxygen radicals (1).Numerous defense mechanisms within the cell have evolved to limit the levels of reactive oxygen species and the damage they induce (1-5). Among the cellular defenses are the enzymes superoxide dismutase, catalase, and glutathione peroxidase (1-4), as well as antioxidants such as (3-carotene (1-4), the tocopherols (6), and uric acid (7). However, low levels of reactive oxygen species can escape these cellular defenses (8) and produce damage to DNA, protein, and unsaturated fats. One product that is formed in DNA in vitro as a consequence of chemical oxidation or ionizing radiation (an oxidative mutagen) is thymine glycol (5,6-dihydroxydihydrothymine) (9,10). Mammalian DNA repair systems are known to excise this lesion from DNA in vitro (5,(11)(12)(13)(14)(15)(16)(17). We report here the identification, in both human and rat urine, of the cis isomer of thymine glycol (5,6-dihydroxydihydrothymine) and its deoxyribonucleoside thymidine glycol (5,6-dihydroxydihydrothymidine) and we propose that these bases are derived from repair of oxidized DNA.MATERIALS AND METHODS GBq), were oxidized to the cis-glycols by potassium permanganate (9). After removal of the unreacted permanganate with Na2S205, the supernatant was adjusted to 1 M NH4OAc (pH 8.8) and loaded onto a 0.5 x 2 cm boronate affinity column (Affi-Gel 601, Bio-Rad), equilibrated with the same buffer. The column was washed with 1 M NH4OAc (pH 8.8) (buffer A), the cis-glycol fraction was removed by elution with 0.1 M HOAc, and the eluate was concentrated by lyophilization.[3H]Thymine glycol and [3H]thymidine glycol ...

No abstract

No abstract

No abstract

The effects of acute digitalization upon the dynamics of the circulation were observed in patients with chronic cor pulmonale, using the technic of cardiac catheterization. The state of the circulation was further investigated in the same patients following recovery from failure. The mode of action of intravenous digoxin is discussed, and a tentative concept of the pathogenesis of chronic cor pulmonale is presented.

Hemodynamic studies were made in 42 patients with rheumatic heart disease with various valvular lesions and in different stages of cardiac function. These studies include observations not only at rest, but also during exercise, following the acute administration of Digoxin, and after recovery from failure. The relationship between symptomatology and hemodynamic findings were considered and the importance of differentiating between mechanical block and left ventricular myocardial failure as causes for pulmonary artery hypertension is stressed.