γ-Glutamyltranspeptidase–Deficient Knockout Mice as a Model to Study the Relationship Between Glutathione Status, Mitochondrial Function, and Cellular Function

Abstract

γ-Glutamyltranspeptidase (GGT)-deficient mice (GGT−/−) display chronic glutathione (GSH) deficiency, growth retardation, and die at a young age (<20 weeks). Using livers from these mice, we investigated the relationship between GSH content, especially mitochondrial, and mitochondrial and cellular function. We found that the GSH content of isolated liver mitochondria was diminished by ≥50% in GGT−/− mice when compared with wild-type mice. Respiratory control ratios (RCRs) of GGT−/− mice liver mitochondria were ≤60% those of wild-type mice primarily as a result of impaired state 3 respiration. Mitochondrial adenine nucleotide content was decreased by ≥40% in mitochondria obtained from GGT−/− mice. We observed a strong correlation between mitochondrial GSH content and RCRs. Even moderate decreases (<50%) correlated with adverse effects with respect to respiration. Electron microscopy revealed that livers from GGT−/− knockout mice were deprived of fat and glycogen, and swollen mitochondria were observed in animals that were severely deprived of GSH. Thus, GGT−/− mice exhibit a loss of GSH homeostasis and impaired oxidative phosphorylation, which may be related to the rate of adenosine triphosphate (ATP) formation and subsequently leads to progressive liver injury, which characterizes the diseased state. We also found that supplementation of GGT−/− mice with N-acetylcysteine (NAC) partially restored liver GSH, but fully restored mitochondrial GSH and respiratory function. Electron microscopy revealed that the livers of NAC-supplemented GGT−/− mice contained fat and glycogen; however, slightly enlarged mitochondria were found in some livers. NAC supplementation did not have any beneficial effect on the parameters examined in wild-type mice.(Hepatology 2000;32:740-749.)