Temperature and Cell-Type Dependency of Sulfide Effects on Mitochondrial Respiration

Abstract

Previous studies suggest that sulfide-induced inhibition of cytochrome c oxidase (cCox) and, consequently, the metabolic and toxic effects of sulfide are less pronounced at low body temperature. Because the temperature-dependent effects of sulfide on the inflammatory response are still a matter of debate, we investigated the impact of varying temperature on the cCox excess capacity and the mitochondrial sulfide oxidation by the sulfide-ubiquinone oxidoreductase in macrophage-derived cell lines (AMJ2-C11 and RAW 264.7). Using an oxygraph chamber, the inhibition of mitochondrial respiration was measured by stepwise titrations with sulfide and the nonmetabolizable cCox inhibitor sodium azide at 25°C and 37°C. Using the latter of the two inhibitors, the excess capacity of the cCox was obtained. Furthermore, we quantified the capacity of these cells to withstand sulfide inhibition by measuring the amount required to inhibit respiration by 50% and 90% and the viability of the cells after 24-h exposure to 100 ppm of hydrogen sulfide. At low titration rates, the AMJ2-C11 cells, but not the RAW 264.7 cells, increased their capacity to withstand exogenously added sulfide. This effect was even greater at 25°C than at 37°C. Furthermore, only the AMJ2-C11 cells remained viable after sulfide exposure for 24 h. In contrast, only in the RAW 264.7 cells that an increase in cCox excess capacity was found at low temperatures. In macrophage-derived cell lines, both the excess capacity of cCox and the efficiency of sulfide elimination may increase at low temperatures. These properties may modify the effects of sulfide in immune cells and, potentially, the inflammatory response during sulfide exposure at different body temperatures.

H2S during circulatory shock: Some unresolved questions

“…iii) In liver tissue samples ex vivo , incubation with Na 2 S to achieve concentrations of ~ 1 μM already reduced maximum mitochondrial respiratory activity. Concentrations > 16 μM were associated with a near-complete inhibition of mitochondrial respiration [91,92]. …”

Sulfide-inhibition of mitochondrial respiration at very low oxygen concentrations

“…We used this cell line for our experiments because they provided a reliable model to study the effects of sulfide in our previous investigation [8]. …”

“…Aerobic respiration under Na 2 S exposure was assessed using a similar experimental setup as previously described [8]. Briefly, this technique consists of measuring the J O 2 while continuously injecting a 2 mM Na 2 S solution at a rate of 10 nl/s into the oxygraph chambers containing the cell suspension.…”

“…We hypothesize that in case of decreasing efficiency of the SQR and dioxygenase, the continuous addition of sulfide would lead to a more rapid accumulation and ultimately an earlier inhibition of aerobic respiration. In order to test this assumption, we used a recently established experimental model [8] based on a high-resolution respirometry [9], which had been used to study the relationship between sulfide toxicity and infusion rate. In the present experiment the setup is modified to maintain stable low oxygen conditions throughout the sulfide titration.…”

Is Pharmacological, H2S-induced ‘Suspended Animation’ Feasible in the ICU?

“…It is well-established that H 2 S toxicity is due to inhibition of mitochondrial respiration resulting from blockade of the complex IV of the respiratory chain, i. e., cytochrome c oxidase [44]. When compared to normothermia, hypothermia (27 °C) increased the Na 2 S concentrations necessary to induce inhibition of mitochondrial respiratory activity (from < 1 μM to 2-4 μM), and nearly doubled the Na 2 S con centrations required for a 50 % reduction in mitochondrial respiratory activity [16], [45]. Hypothermia may also infl uence the eff ect of H 2 S on substrate utilization and, thereby, may even improve the yield of the mitochondrial respiration: In anesthetized and ventilated mice, during normothermia, inhaling 100 ppm H 2 S did not aff ect endogenous glucose production (as calculated from the rate of appearance of 1,2,3,4,5,6-13 C 6 -glucose during continuous i.v.…”