H₂S toxicity via oxidative damage in erythrocytes of a sulfide‐tolerant marine invertebrate

Abstract

Marine organisms adapted to H2S exposure utilize a variety of mechanisms, including H2S oxidation, to minimize its toxicity. However, this may lead to increased free radical production. We tested whether H2S exerts at least some of its toxicity via free radical damage in erythrocytes from the sulfide‐tolerant marine polychaete Glycera dibranchiata. We exposed erythrocytes to H2S in vitro and assessed oxidative stress, oxidative damage and cell death, and whether exogenous antioxidants reduced H2S toxicity. Exposure to 0.1–3% H2S for 0.5–2 h significantly increased oxidative stress (carboxy‐H2DCFDA labeling; p<0.0001), mitochondrial superoxide production (dihydroethidium labeling; p=0.0003), and oxidative damage to RNA and DNA (via HPLC‐EC‐UV; p<0.05), consistent with increased free radical production. Exposure to H2S caused a dose‐dependent increase in cell death (via propidium iodide and calcein green AM labeling, p<0.0001), but the antioxidants glutathione ethyl ester, dithiothreitol and N‐acetylcysteine reduced this cell death by up to 70% (p<0.0001), 78% (p=0.041), and 85% (p=0.0006), respectively. Therefore, in erythrocytes of a sulfide‐tolerant marine invertebrate, oxidative damage was increased by H2S, and H2S‐induced cell death was reduced by antioxidants, both of which are consistent with free radical damage as an important mechanism of H2S toxicity.

Were the First Trace Fossils Really Burrows or Could They Have Been Made by Sediment-Displacive Chemosymbiotic Organisms?

“…One of the most distinctive aspects of the earliest Ediacaran soft-bodied macrobiotas is that-with few rare exceptions-they were immotile, and in many cases grew to very large sizes on matgrounds [29,47,48] (Figure 1B). Being immotile on a porous organic-rich seafloor potentially results in serious biogeochemical challenges in the form of hydrogen sulfide buildup below the body tissues [49][50][51]. If hydrogen sulfide accumulates unchecked next to the epithelium of an immotile recliner it would likely cause cell-death, meaning that soft-bodied Ediacaran organisms must have been able to modify the organism-substrate interface in a manner that detoxified, or otherwise mitigated, sulfide toxicity [52].…”

Were the First Trace Fossils Really Burrows or Could They Have Been Made by Sediment-Displacive Chemosymbiotic Organisms?

“…1b). Being immotile on a porous organic-rich seafloor potentially results in serious biogeochemical challenges in the form of hydrogen sulfide buildup below the body tissues (Ortega et al 2008;Dufour & McIlroy 2017a, b). If hydrogen sulfide accumulates unchecked next to the epithelium of an immotile recliner it would likely cause cell-death, meaning that soft-bodied Ediacaran organisms must have been able to modify the organism-substrate interface in a manner that detoxified, or otherwise mitigated, sulfide toxicity (McIlroy et al 2021).…”