α-Tocopherol transfer protein expression in rat liver exposed to hyperoxia

alpha-Tochopherol transfer protein (alphaTTP), 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 alphaTTP are not clearly understood. In this study, we investigated whether or not exposure to hyperoxia (>95% O-2 for 48 h) could alter the expression of hepatic alphaTTP. 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 alphaTTP. 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 alphaTTP messenger RNA (mRNA) after hyperoxia, although the alphaTTP 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 alphaTTP, rather than Mn-SOD or GPX, may be highly responsive to oxidative stress.