A meroterpene and four flavonoids were isolated from the seeds of Psoralea corylifolia as antioxidative components. Their structures were elucidated by spectral data and identified as bakuchiol (1), bavachinin (2), bavachin (3), isobavachin (4) and isobavachalcone (5). In particular, meroterpene 1 and flavonoids 4 and 5 showed broad antioxidative activities in rat liver microsomes and mitochondria. They inhibited NADPH-, ascorbate-, t-BuOOH- and CCl(4)-induced lipid peroxidation in microsomes. They also prevented NADH-dependent and ascorbate-induced mitochondrial lipid peroxidation. Bakuchiol (1) was the most potent antioxidant in microsomes and the inhibition of oxygen consumption induced by lipid peroxidation was time-dependent. Furthermore, bakuchiol (1) protected human red blood cells against oxidative haemolysis. These phenolic compounds in P. corylifolia were shown to be effective in protecting biological membranes against various oxidative stresses.

This study was performed to examine the effect of dietary polyphenols on fecal secondary bile acids, such as deoxycholic acid and lithocholic acid, the risk factors of colon cancer, in rats fed a high-fat diet. In experiment 1, rats were fed a 30% beef tallow diet containing 0.5% polyphenols for 3 weeks. Dietary curcumin and caffeic acid significantly reduced the fecal concentration of deoxycholic acid. Dietary caffeic acid, catechin, rutin, and ellagic acid significantly reduced fecal lithocholic acid. Fecal hyodeoxycholic acid, a metabolite of lithocholic acid, was markedly lowered by dietary curcumin, caffeic acid, catechin, and rutin. In experiment 2, rats were fed a 30 or 5% beef tallow diet with or without the addition of 0.5% curcumin. In the rats without receiving curcumin, the fecal level of deoxycholic acid was significantly higher in the high-fat diet group than in the low-fat diet group. Fecal deoxycholic acid was significantly reduced by dietary curcumin in the high-fat diets but not in the low-fat diets. The results suggest novel effects of some polyphenols favorable for colon health by reducing secondary bile acids in animals fed a high-fat diet.

Bakuchiol, a meroterpene isolated from Psoralea corylifolia, prevented mitochondrial lipid peroxidation. Inhibition of oxygen consumption originating in lipid peroxidation was time-dependent. Bakuchiol protected mitochondrial respiratory enzyme activities against both NADPH-dependent and dihydroxyfumarate-induced peroxidation injury. Bakuchiol was shown to be effective to protect mitochondrial functions against oxidative stress.

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