Induction of metallothionein-I protects glomeruli from superoxide-mediated increase in albumin permeability

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 (O-.(2)) and hydroxyl ion (OH-). We have demonstrated that O-.(2) and hypohalous acid can cause an increase in glomerular albumin permeability (P-alb) in vitro. The purpose of this study was to document the protective effect of MT gene product on the O-.(2) mediated increase in P-alb. Glomeruli from Sprague-Dawley rats in 4% BSA medium were incubated for 4 hr at 37 degreesC in duplicate tubes. Each set contained glomeruli alone or with 5 muM 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 O-.(2), and P-alb 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. O-.(2) caused a significant increase in P-alb (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. O-.(2)). In contrast, Sulfo-NONOate and SNP did not induce mRNA for MT-I in glomeruli and did not provide protection against O-.(2) mediated increase in P-alb. 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.