Tolerance to cadmium hepatotoxicity by metallothionein and zinc: in vivo and in vitro studies with MT-null mice

The protective role of metallothionein (MT) in Cd-mediated hepatotoxicity w as investigated in vivo and in vitro. Following injection of Cd (2 mg/kg, i ntraperitoneal or subcutaneous) hepatoxicity was significantly greater at 2 0 h in metallothionein-null (MT -/-) mice, compared with controls (MT +/+). The decrease in the blood and liver glucose concentrations correlated with the extent of hepatotoxicity, with blood glucose 43% lower in MT -/- mice. Zinc (50 mu M) and/or Dex (1 mu M) were used in hepatocyte cultures to rai se MT 2-5-fold. When Cd at 10 mu M was co-treated with Zn and/or Dex, lacta te dehydrogenase (LD) leakage in the MT +/+ and MT -/- hepatocytes was redu ced only when Zn was present. Cellular glutathione (GSH) was the same in co ntrol MT +/+ and MT -/- cultures and was uninfluenced by Zn and Dex. After treatment with 5 and 10 mu M Cd, GSH levels were lower in MT -/- than MT +/ + hepatocytes in the control and Dex groups. Higher GSH concentrations were maintained in Zn co-treated cultures from both genotypes, indicating that the superior protective effect of Zn may in part derive from its influence on cellular GSH. Pre-treatment with Zn and/or Dex provided no further prote ction than co-treatment. Tolerance to brief (15 min) Cd exposure was also i nvestigated in the presence of MT inducers including progesterone (100 mu M ). Zn, Dex and progesterone treated hepatocytes had less LD leakage than co ntrols with Zn giving the greatest protection (LD leakage 18% of controls a t 100 mu M Cd). Zn pre-treated cells had higher cytosolic/particulate ratio s of Cd. These findings demonstrate that MT protects primary cultures of mo use hepatocytes from short-term exposure to Cd. Zn enhances the protection through MT and non-MT mechanisms. (C) 2000 Elsevier Science Ireland Ltd. Al l rights reserved.