Glutathione depletion alters hepatocellular high-energy phosphate metabolism

Oxygen free radicals have recently been implicated as a major cause of tissue injury in critically ill patients. Glutathione (GSH) is a potent endogenous antioxidant that may be important in minimizing oxidant-induced organ damage. However, this tripeptide is depleted during severe illness. In order to determine the effect of GSH depletion on hepatic high-energy phosphate metabolism, in vivo³¹P magnetic resonance spectroscopy was used to measure phosphate ratios in male Wistar rats given 1 ml/kg of diethylmaleate (DEM), an agent that binds and thus depletes tissue GSH, or corn oil vehicle intraperitoneally. Spectra of the liver were obtained in noninjected animals (baseline, n = 15) and in rats 2 and 24 hr after the intraperitoneal injection of DEM (n = 20) or corn oil (control, n = 20). These spectra were used to measure hepatocellular pH, phosphomonoester to ATP (PME/ATP), and phosphodiester to ATP ratios, measures of hepatocellu]ar damage; and the inorganic phosphate (P_i)/ATP ratio, a measure of energy status. In addition, tissue GSH, phosphofructokinase, citrate synthase, and β-OH-acyl-Co-A dehydrogenase activities as well as hepatocellular ATP were measured in vitro in representative liver samples. Hepatic GSH levels were maximally depressed by 85% 2 hr after the injection of DEM (6.94 ± 0.34 vs 0.94 ± 0.22 μM/g wet wt, baseline vs 2° DEM). This was associated with a marked increase in the PME/ATP and P_i/ ATP ratios by 25 and 33%, respectively, and both ratios were significantly correlated with the severity of hepatic GSH depletion (r = 0.63, P < 0.001 and r = 0.42, P < 0.01, respectively). In addition, the intracellular pH decreased from 7.41 ± 0.02 to 7.33 ± 0.02 (P < 0.05) 2 hr after the injection of DEM. At this time citrate synthase and β-OH-acyl-Co-A dehydrogenase activities were significantly elevated in the GSH-depieted animals. In contrast, ATP levels did not change significantly (2.92 ± 0.07 vs 3.20 ± 0.28 μM/g wet wt, baseline vs 2° DEM) and PFK activity was similar in both groups. We conclude that (1) GSH depletion in rats alters the hepatocellular energy status primarily due to increased ATP turnover; (2) under these conditions, hepatic ATP synthesis via the oxidation of fatty acids accelerates to meet an increased energy demand; and (3) these changes in hepatocellular energetics and PME/ATP ratios may indicate early hepatocyte injury and are likely due to increased oxidative stress unveiled by GSH depletion. The GSH depletion associated with critical illness may contribute to the development of liver dysfunction in severely injured patients.