Study on Metabolism-regulating Trace Food Factors

(JSNFS Award for Excellence in Research (2020))

Abstract

Minerals, vitamins, and phytochemicals, present in trace amounts in the diet, play important roles in regulating multiple metabolic systems as well as bone metabolism. For clinical screening of phytoestrogen levels in large populations, time-resolved fluoroimmunoassay (TR-FIA) has been developed, and later applied for animal studies as well. Since the intestinal environment affects phytoestrogen metabolism, we investigated how a combination of prebiotics and isoflavone intake would affect isoflavone metabolism in models of osteoporosis. Equol, an isoflavone metabolite, contains enantiomers, and the (S) form is considered to exhibit higher bioavail­ability than the (R) form, associated with a stronger inhibitory effect on bone loss in osteoporotic rodents. However, hesperidin, a citrus bioflavonoid, is thought to suppress bone loss via a cholesterol synthesis pathway different from isoflavone-related mechanisms. Sulforaphane, an anti-inflammatory sulfur-containing compound, has been considered to regulate osteoclast differentiation through suppression of osteoclast fusion molecules in addition to conventional suppression of osteoclast differentiation factors. Finally, with regard to minerals, it has been reported that lipid peroxidation is unlikely to occur in an iron-deficient state. However, in contrast to the conventional theory, we demonstrated that the in vivo oxidation mechanism was caused by iron deficiency. Furthermore, we suggested that metabolism of β-carotene and α-tocopherol was changed during iron deficiency, since it may require an iron-containing enzyme.