VITAMINS

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Oxidative stress receives much attention in relation to ageing, cancer, atherosclerosis, diabetes, and so on. However a reliable biomarker to evaluate oxidative stress in the tissue is not available. Based on chemical analysis of radical reactions in the cell, lipid hydroperoxide (LOOH), a mediator of oxidative stress and antioxidants such as vitamins C (C) and E can be biomarkers of oxidative stress. We developed a specific and sensitive method to determine tissue concentration of LOOH and C. We compared the efficiency of these markers using a drug-induced hepatitis as a model system. The liver C concentration was decreased firstly by administration of drugs such as CCl_4, thioacetamide, and D-galactosamine, showing that C concentration was the most sensitive biomarker in animal tissues. Oxidation of low-density lipoprotein (LDL), which was assumed to be the initial reaction in atherogenesis, caused fragmentation and cross-link of apolipoprotein B-100 (apoB). Fragmented and conjugated apoB proteins were calibrated using Western blot analysis of human plasma samples and named as B-OX. B-OX significantly correlated positively with conventional clinical parameters of atherosclerosis such as LDL cholesterol, triglyceride, IMT (intima-media thickness of the carotid artery), and age. A significant negative relationship was also found between B-OX and plasma C concentration, suggesting that plasma C and B-OX are reliable biomarkers of oxidative stress in humans. When oxidative stress was enhanced in the liver by hepatitis or during atherogenesis, the level of plasma ceramide was increased. Further studies are necessary to elucidate the underlying mechanism between ceramide metabolism and oxidative stress.

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Vitamin D plays an important role in regulation of calcium homeostasis and bone metabolism. Among vitamin D metabolites, serum 25-hydroxyvitamin D (25-D) concentration is a best indicator to assess the vitamin D status. It is known that a mild decrease of serum 25-D concentration (vitamin D insufficiency) leads to secondary hyperparathyroidism, which has a negative effect on bone metabolism in the elderly. Therefore, vitamin D insufficiency is thought to be one of the risk factors of osteoporosis. Vitamin D insufficiency is commonly observed in the world. In Japan, we have also confirmed that around half of elderly women were in vitamin D insufficient. Recently, several meta-analysis about vitamin D supplementation to prevent fracture and bone loss in elderly people have been reported. In the present review, current epidemiological studies about vitamin D status and prevention of osteoporosis, and requirement of vitamin D to prevent osteoporosis would be discussed.

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