Heme oxygenase-1 induction by hemin prevents oxidative stress-induced acute cholestasis in the rat.

We previously demonstrated in in vitro and ex vivo models that physiological concentrations of unconjugated bilirubin (BR) prevent oxidative stress (OS)-induced hepatocanalicular dysfunction and cholestasis. Here, we aimed to ascertain, in the whole rat, whether a similar cholestatic OS injury can be counteracted by heme oxygenase-1 (HO-1) induction that consequently elevates endogenous BR levels. This was achieved through the administration of hemin, an inducer of HO-1, the rate-limiting step in BR generation. We found that BR peaked between 6 and 8 h after hemin administration. During this time period, HO-1 induction fully prevented the pro-oxidant tert-butylhydroperoxide (tBuOOH)-induced drop in bile flow, and in the biliary excretion of bile salts and glutathione, the two main driving forces of bile flow; this was associated with preservation of the membrane localization of their respective canalicular transporters, bile salt export pump (Bsep) and multidrug resistance-associated protein 2 (Mrp2), which are otherwise endocytosed by OS. HO-1 induction counteracted the oxidation of intracellular proteins and membrane lipids induced by tBuOOH, and fully prevented the increase in the oxidized-to-total glutathione (GSHt) ratio, a sensitive parameter of hepatocellular OS. Compensatory elevations of the activity of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) were also prevented. We conclude that in vivo HO-1 induction protects the liver from acute oxidative injury, thus preventing consequent cholestasis. This reveals an important role for the induction of HO-1 and the consequently elevated levels of BR in preserving biliary secretory function under OS conditions, thus representing a novel therapeutic tool to limit the cholestatic injury that bears an oxidative background.

Morphological alterations of central nervous system (CNS) myelin in vanadium (V)-exposed adult rats.

In the present work we show morphological data of the in vivo susceptibility of CNS myelin to sodium metavanadate [V(+5)] in adult rats. The possible role of vanadium in behavioral alterations and in brain lipid peroxidation was also investigated. Animals were injected intraperitoneally (i.p.) with 3 mg/kg body weight (bw) of sodium metavanadate [1.25 V/kg bw/day] for 5 consecutive days. Open field and rotarod tests were performed the day after the last dose had been administered and then animals were sacrificed by different methods for histological and lipid peroxidation studies. The present results show that intraperitoneal administration of V(+5) to adult rats resulted in changes in locomotor activity, specific myelin stainings and lipid peroxidation in some brain areas. They support the notion that CNS myelin could be a preferential target of V(+5)-mediated lipid peroxidation in adult rats. The mechanisms underlying this action could affect the myelin sheath leading to behavioral perturbations.