alpha-Tocopherol transfer protein expression in rat liver exposed to hyperoxia.

alpha-Tochopherol transfer protein (alpha TTP), a 32 kDa protein exclusively expressed in liver cytosol, has a high binding affinity for alpha-tochopherol. The factors that regulate the expression of hepatic alpha TTP are not clearly understood. In this study, we investigated whether or not exposure to hyperoxia (> 95% O2 for 48 h) could alter the expression of hepatic alpha TTP. We also examined the association between the expression of antioxidant enzymes (hepatic glutathione peroxidase (GPX) and Mn-superoxide dismutase (Mn-SOD)) and the expression of hepatic alpha TTP. The levels of thiobarbituric acid-reactive substances (TBARS) in both plasma and liver were significantly higher after rats were exposed to hyperoxia for 48 h when compared with the levels in control rats. Northern blotting showed a decrease in the expression of alpha TTP messenger RNA (mRNA) after hyperoxia, although the alpha TTP protein level remained constant. Expression of Mn-SOD mRNA and protein, as well as the expression of GPX mRNA, were stable after hyperoxia. These findings indicate that mRNA for hepatic alpha TTP, rather than Mn-SOD or GPX, may be highly responsive to oxidative stress.