Induction of Metallothionein-I Protects Glomeruli from Superoxide-Mediated Increase in Albumin Permeability

Abstract

Metallothioneins (MT) are low-molecular-weight, heat-stable, cysteine-rich proteins with four isoforms. MT-I and MT-II are ubiquitous and are induced by oxidative, physical, and chemical stress. MT-I is an efficient scavenger of superoxide (O2) and hydroxyl ion (OH–). We have demonstrated that O2 and hypohalous acid can cause an increase in glomerular albumin permeability (Palb) in vitro. The purpose of this study was to document the protective effect of MT gene product on the O2-mediated increase in Palb. Glomeruli from Sprague-Dawley rats in 4% BSA medium were incubated for 4 hr at 37°C in duplicate tubes. Each set contained glomeruli alone or with 5 μM Cd++, 0.3 mM Spermine-NONOate (NO donor), 0.3 mM Sulfo-NONOate (nitrous oxide donor), 0.6 mM SNP (nonspecific NO donor) and SNP + carboxy-PTIO (10 mg/ml). After incubation, one set of tubes was used to isolate total RNA for the measurement of the mRNA levels of MT-I by reverse transcriptase polymerase chain reaction (RT-PCR). Duplicate tubes were incubated for an additional 10 min with 10 nM of O2, and Palb was measured using video microscopy. RT-PCR of total RNA from Cd++ and Spermine-NONOate treated glomeruli revealed a 2-fold induction of MT-I expression at the mRNA level. O2 caused a significant increase in Palb (0.8 ± 0.06 vs. control 0.0 ± 0.12, P < 0.05) and induction of MT-I in glomeruli by Cd++ or by Spermine-NONOate blocked this effect (0.21 ± 0.12 and 0.24 ± 0.19, respectively, P < 0.05 vs. O2). In contrast, Sulfo-NONOate and SNP did not induce mRNA for MT-I in glomeruli and did not provide protection against O2-mediated increase in Palb We conclude that MT-I gene products may play an important role in protecting the glomerular filtration barrier from the injury induced by reactive oxygen species in immune and/or nonimmune renal diseases