EFFECT OF ACETAMINOPHEN ADMINISTRATION ON HEPATIC GLUTATHIONE COMPARTMENTATION AND MITOCHONDRIAL ENERGY-METABOLISM IN THE RAT

Changes in cell energy metabolism and mitochondrial dysfunction have b een observed after acetaminophen administration. Because consumption o f hepatic glutathione is closely related to acetaminophen toxicity, we investigated the kinetics of: 1. glutathione depletion in liver mitoc hondria and cytosol; 2. State 3 and 4 respiratory rates of succinate-s upplemented mitochondria; 3. rate of ATP synthesis; 4. oligomycin-sens itive ATP hydrolase activity and passive proton conductivity of inside -out vesicles of the inner mitochondrial membrane; and 5. changes in h epatic and mitochondrial malondialdehyde in the rat after in vivo acet aminophen administration. Two hours after acetaminophen injection, hep atic glutathione decreased and malondialdehyde increased. In the same interval, an increase in both State 3 and 4 respiratory rates of succi nate-supplemented mitochondria was observed. This was accompanied by a decrease in the rate of ATP synthesis and the P/O ratio and by an inc rease in the passive proton permeability of the inner mitochondrial me mbrane, which was insensitive to oligomycin. No significant change in oligomycin-sensitive ATP hydrolase activity was observed. Four hours a fter APAP injection, the respiratory rates, as well as the proton cond uctivity, decreased, the rate of ATP synthesis was restored, and the m itochondrial glutathione started to increase; the cytosolic levels of glutathione were still low and the cytosolic and mitochondrial levels of malondialdehyde remained high for 2 more hr. The concentrations of these indices were completely restored 24 hr postdosing. Our findings suggest that acetaminophen administration selectively depletes (within 2 hr) mitochondrial glutathione, and produces local toxicity by alter ing membrane permeability and decreasing the efficiency of oxidative p hosphorylation. This renders mitochondria more susceptible to oxidativ e damage, especially during increased free radical production, as in t he case of enhanced mitochondrial respiration in State 4. The concomit ant restoration of mitochondrial respiration, oxidative phosphorylatio n, membrane permeability, and glutathione levels is consistent with th e importance of the mitochondrial glutathione pool for the protection of the mitochondrial membrane against oxidative damage.