Dietary (+)-catechin and BHT markedly increase α-tocopherol concentrations in rats by a tocopherol-ω-hydroxylase-independent mechanism

Abstract

The effects of dietary (+)-catechin (CAT) and BHT on plasma and tissue concentrations of α-tocopherol (α-T), γ-tocopherol (γ-T) and cholesterol (C) were studied in male Sprague-Dawley rats. The rats were fed the compounds during a 4-wk period at concentrations of 2 g/kg in standardized diets, low but adequate in vitamin E, with 2 g/kg cholesterol. The CAT-regimen did not affect weight gain, feed intake or organ weights. BHT did not affect feed intake but lowered the body weight and the amount of liver lipids and increased the weights of livers and lungs relative to the body weight. Rats consuming CAT had 2.5-3.5-fold increased plasma, liver and lung α-T concentrations, but C concentrations remained unchanged. BHT-feeding resulted in 2.4- and 1.7-fold elevation in α-T but ∼50% decrease in γ-T concentrations in blood plasma and liver, respectively. BHT also lowered total C in the liver without affecting the concentration of C in the liver lipids. To investigate whether the α-T-sparing action of the studied compounds was due to the inhibition of tocopherol-ω-hydroxylase, HepG2 cells were incubated with CAT or BHT in the presence of δ-tocopherol (δ-T) and the 3′- and 5′-δ -carboxychromanol metabolites in the media were analyzed by GC/MS. Neither CAT nor BHT inhibited tocopherol-ω-hydroxylase activity in hepatocyte cultures; CAT was also inactive in a rat microsomal assay. In conclusion, both dietary CAT and BHT markedly increased α-T concentrations in plasma and organs of Sprague-Dawley rats by a mechanism that apparently does not involve inhibition of tocopherol-ω-hydroxylase, a key enzyme in tocopherol catabolism.