Hypotaurine and sulfhydryl-containing antioxidants reduce H2S toxicity in erythrocytes from a marine invertebrate

Abstract

SUMMARY Hypotaurine (HT) has been proposed to reduce sulfide toxicity in some deep-sea invertebrates by scavenging free radicals produced from sulfide oxidation or by scavenging sulfide via the reaction of HT with sulfide, forming thiotaurine (ThT). We tested whether HT or several antioxidants could reduce the total dissolved sulfide concentration in buffered seawater exposed to H2S, and whether HT, ThT or antioxidants could increase the viability of Glycera dibranchiataerythrocytes exposed to H2S in vitro. We found that 5 and 50 mmol l–1 HT reduced the dissolved sulfide in cell-free buffer exposed to H2S by up to 80% whereas the antioxidants glutathione ethyl ester (GEE), N-acetylcysteine (NAC), l-ascorbic acid (ASC), Tempol and Trolox had no consistent effect. Exposure of erythrocytes to 0.10%–3.2% H2S (producing 0.18–4.8 mmol l–1 sulfide) decreased the fraction of viable cells, as evidenced by loss of plasma membrane integrity, with virtually no cells remaining viable at 1.0% or more H2S. Addition of HT (0.5–50 mmol l–1) significantly increased the fraction of viable cells (e.g. from 0.01 to 0.84 at 0.32% H2S) whereas ThT (0.5 and 5 mmol l–1) decreased cell viability. GEE (0.03–3 mmol l–1) and NAC (0.001–1 mmol l–1), which contain sulfhydryl groups, increased cell viability during H2S exposure but to a lesser extent than HT whereas ASC, Tempol and Trolox, which do not contain sulfhydryl groups, decreased viability or had no effect. These data show that HT can protect cells from sulfide in vitro and suggest that sulfide scavenging, rather than free radical scavenging, is the most important mechanism of protection.