Nudix hydrolases constitute a large family of proteins distributed in all living organisms and hydrolyze a wide variety of substrates, including coenzymes of niacin, pantothenic acid, and flavin, that contain a nucleoside diphosphate linked to some other moiety, X. There is increasing evidence of the regulatory roles for plant Nudix hydrolases in various physiological processes such as stress responses and the metabolism of various molecules. Arabidopsis thaliana has 28 Nudix hydrolases (AtNUDX1-27, and AtDCP2) located in the cytosol, mitochondria, and chloroplasts. Among them, AtNUDX2, 6, and 7 play regulatory roles in biotic and abiotic stress responses through the precise modulation of the intracellular levels of ADP-ribose and/or NAD(P)H. On the other hand, AtNUDX11 and 15 affect CoA biosynthesis and various CoA-related pathways in the cytosol and mitochondria. Flavin homeostasis is achieved by the regulation of the balance of FAD and FMN by AtNUDX23 in chloroplasts. These findings suggest that plants develop degradation pathways for vitamin coenzymes by Nudix hydrolases essential for their growth and survival.

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Although often used for such purposes, dietary assessments cannot adequately evaluate nutritional status. Alternatively, a biomarker can be an indicator of nutritional status with respect to intake or metabolism of dietary constituents. Recent validation studies have developed the use of urinary compounds as nutritional biomarkers to estimate nutrient intakes, and levels of urinary nitrogen and sodium have been well established as nutritional biomarkers. We have worked to establish levels of urinary water-soluble vitamins as nutritional biomarkers to assess intake, and report the following findings to contribute to the establishment and effectiveness of levels of urinary water-soluble vitamins as potential nutritional biomarkers. Eight of nine water-soluble vitamin levels in 24-hr urine samples increased in a dose-dependent-manner, and were strongly correlated with vitamin intakes under strictly controlled conditions. In contrast, urinary vitamin B_<12> content reflects urine volume but not vitamin B12 intake. The cross-sectional studies show that levels of each urinary water-soluble vitamin, with the exception of vitamin B_<12>, are positively correlated with mean intake over a recent 2-4 day period in free-living children, young and the elderly. These findings suggest that levels of urinary water-soluble vitamins can be used as nutritional biomarkers to assess mean vitamin intakes in these groups.

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Biotin serves as a covalently bound coenzyme for various carboxylases in mammals. Deficiency of this vitamin leads to a variety of clinical abnormalities that include neurological disorders and dermatological abnormalities. It has been thought that human biotin deficiency is extremely rare since biotin is present in various foods. However, it has been reported that marginal biotin deficiency develops during normal human gestation and that biotin deficiency is teratogenic in several animal species. It has also been reported that the possibility of biotin deficiency is increased in infants who were fed a special formula for the treatment of allergies. These findings indicate that it is still needed to evaluate the biotin status of human subjects. This review provides the recent advances in methods for the assessment of the biotin status.

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Homocysteine is a non-protein-constituting amino acid. It is, however, one of the well-known amino acids as a biomarker. Hyperhomocysteinemia is a condition characterized by an elevated level of homocysteine in blood. Since hyperhomocysteinemia is reported as an independent risk factor for cardiovascular disease, a number of researches related to homocysteine metabolism have been reported. Many water-soluble vitamins act as a cofactor for homocysteine metabolism. Homocysteine is a metabolite of methionine, and it is involved in highly regulated folate and methionine metabolism. In this metabolism, homocysteine is one of the key metabolites. In this review,the function of vitamins in this important metabolism is described; especially focused on two enzymes, methionine synthase and methylenetetrahydrofolate reductase.

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Hepatic stellate cells (HSCs), which are also known as vitamin A-storing cells, reside in a space between hepatocytes and liver sinusoids. Two proteins, cellular retinol-binding protein (CRBP) and lecithin:retinol acyltransferase (LRAT), are known to play an important role in vitamin A storage in HSCs, because retinol bound to CRBP is a good substrate for LRAT. After the discovery that HSCs are responsible for the development of liver fibrosis and subsequent liver cirrhosis, functions of HSCs in pathological conditions have been extensively studied. However, the roles of HSCs in physiological conditions remain to be elucidated. Here we present a hypothesis that an increased retinoid signaling in activated HSCs makes a feedback loop toward vitamin A restoration. The hypothesis is based on our previous finding that HSCs acquire retinoid responsiveness after activation in vitro by post-transcriptional up regulation of retinoic acid receptor alpha gene expression

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A major disadvantage of a systemic VDR-null mouse model is that the expected 1,25 dihydroxy vitamin D [1,25(OH)_2D] -mediated skeletal and renal adaptations to reduced intestinal calcium absorption do not occur, due to the lack of VDR activity in these tissues. Systemic VDR-null mice, therefore, are not an appropriate model to unravel the physiological repercussions of negative calcium balance (or lack of intestinal 1,25(OH)_2D activity) on calcium and bone homeostasis. Accordingly, we have generated tissue specific VDR-ablation to manipulate local 1,25(OH)_2D activity. Furthermore, calcium movement from bone after osteoclastic bone resorption is a large calcium supply to maintain calcium homeostasis, the system supporting calcium homeostasis in osteoclast has not yet been identified. Transient receptor potential vanilloid (TRPV) 4, mediates Ca^<2+>influx in the late stage of osteoclast differentiation and, thereby regulates Ca^<2+> signaling. However, the system-modifying effect of TRPV4 activity remains to be determined. To elucidate the consequences of insufficient intestinal calcium absorption on calcium and bone homeostasis, and how cellular calcium homeostasis has been regulated during bone remodeling, whether 1,25(OH)_2D or calcium homeostasis influences osteoclastogenesis should be solved as an important question

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