Heme oxygenase (HO)-1, the rate-limiting enzyme in heme catabolism, can be induced in response to various oxidative stimuli, and its induction is thought to be critical in the cellular defense against oxidative tissue injuries. Carbon tetrachloride (CCl4) treatment of rats causes lipid peroxidation of cell membranes and produces massive hepatic injury. We previously demonstrated that HO-1 induction following CCl4 treatment is an essential part of the cellular defense against the CCl4-inducible toxic changes. As recombinant human interleukin-11 (rhIL-11) has been shown to induce HO-1 in cultured hepatoma cells, we examined the effect of rhIL-11 in vivo in rats on the CCl4-induced tissue injury. rhIL-11 treatment of animals by itself markedly induced HO-1 mRNA and its functional protein principally in the liver. rhIL-11 treatment (150 µg/kg) of the CCl4-administered (1 ml/kg) animals led to a further increase in HO-1 mRNA, while it markedly suppressed CCl4-induced serum alanine transaminase, hepatic malondialdehyde formation, tumor necrosis factor-α mRNA, nitric oxide synthase mRNA, nuclear factor-κB DNA-binding activity, as well as inflammatory changes of hepatocytes. In contrast, inhibition of HO activity by tin-mesoporphyrin, a competitive specific inhibitor of HO, entirely abolished the cytoprotective effect of rhIL-11. These findings thus demonstrate that rhIL-11 confers significant protection against CCl4-induced hepatic injury by virtue of its liver-specific HO-1 induction.

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