Different role of Schisandrin B on mercury-induced renal damage in vivo and in vitro.

Mercuric chloride (HgCl2) causes acute oxidant renal failure that affects mainly proximal tubules. Schisandrin B (Sch B), an active lignan from the fruit of Schisandra chinensis, has been successfully used to treat gentamicin nephrotoxicity, but its role against mercury damage is still largely unknown. Here we analysed in vivo and in vitro the efficacy of Sch B supplementation against HgCl2 nephrotoxicity, focusing on histopathology, stress proteins, oxidative (cytochrome c oxidase) and nitrosactive markers (eNOS, nNOS). Wistar rats were treated with Sch B (10 mg/kg/day p.o.) or vehicle (olive oil) for 9 days, then coadministered with a single HgCl2 nephrotoxic dose (3.5 mg/kg i.p.) and killed after 24 h. The tubular and mitochondrial damage induced by mercury was limited by Sch B coadministration in vivo. Remarkably, after Sch B and mercury challenge, HSP25, HSP72, GRP75 were reduced in the renal cortex, cytochrome c oxidase increased and eNOS and nNOS were restored in glomeruli. In contrast, NRK-52E proximal tubular cells treated with Sch B 6.25 µM plus HgCl2 20 µM did not show any amelioration on viability and oxidative stress in respect to HgCl2 20 µM alone. Moreover, after Sch B plus mercury in vitro treatment, HSP72 staining persisted while HSP25 further increased. Thus, in our experimental conditions, Sch B cotreatment afforded better protection against mercury poisoning in vivo than in vitro. This discrepancy might be partly attributable to Sch B influence on glomerular perfusion as corroborated by the recovery of vasoactive markers like macular and endothelial nitric oxide isoforms.

Stress proteins and oxidative damage in a renal derived cell line exposed to inorganic mercury and lead.

A close link between stress protein up-regulation and oxidative damage may provide a novel therapeutic tool to counteract nephrotoxicity induced by toxic metals in the human population, mainly in children, of industrialized countries. Here we analysed the time course of the expression of several heat shock proteins, glucose-regulated proteins and metallothioneins in a rat proximal tubular cell line (NRK-52E) exposed to subcytotoxic doses of inorganic mercury and lead. Concomitantly, we used morphological and biochemical methods to evaluate metal-induced cytotoxicity and oxidative damage. In particular, as biochemical indicators of oxidative stress we detected reactive oxygen species (ROS) and nitrogen species (RNS), total glutathione (GSH) and glutathione-S-transferase (GST) activity. Our results clearly demonstrated that mercury increases ROS and RNS levels and the expressions of Hsp25 and inducible Hsp72. These findings are corroborated by evident mitochondrial damage, apoptosis or necrosis. By contrast, lead is unable to up-regulate Hsp72 but enhances Grp78 and activates nuclear Hsp25 translocation. Furthermore, lead causes endoplasmic reticulum (ER) stress, vacuolation and nucleolar segregation. Lastly, both metals stimulate the over-expression of MTs, but with a different time course. In conclusion, in NRK-52E cell line the stress response is an early and metal-induced event that correlates well with the direct oxidative damage induced by mercury. Indeed, different chaperones are involved in the specific nephrotoxic mechanism of these environmental pollutants and work together for cell survival.