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.
In children and adolescents with ALL after therapy antibody levels of D and T are dependent on treatment intensity. Revaccination leads to an adequate immunological answer against T in most patients , which is not the case for the diphtheria vaccination. Prospective multicenter trials starting together with the ALL-treatment should be able to gain more information about the behavior of antibody levels and the risk of infection from vaccine-preventable disease in immunocompromised patients and thus lead to standardized vaccination guidelines such as immunization with conjugate vaccines already during maintenance treatment.
Our aim was to study the capacity of an immortalized cell line (AMJ2-C11) to sustain aerobic cell respiration at decreasing oxygen concentrations under continuous sulfide exposure. We assumed that the capacity of the pathway metabolizing and eliminating sulfide, which is linked to the mitochondrial respiratory chain and therefore operates under aerobic conditions, should decrease with limiting oxygen concentrations. Thus, sulfide’s inhibition of cellular respiration would be dependent of the oxygen concentration in the very low range. The experiments were performed with an O2K-oxygraph (Oroboros Instruments) by suspending 0.5 – 1 × 106 cells in 2 ml of continuously stirred respiration medium at 37°C and calculating the oxygen flux (JO2) as the negative derivative of the oxygen concentration in the medium. The cells were studied in two different metabolic states, namely under normal physiologic respiration (1) and after uncoupling of mitochondrial respiration (2). Oxygen concentration was controlled by means of a titration-injection pump, resulting in average concentration values of 0.73 ± 0.05 μM, 3.1 ± 0.2 μM, and 6.2 ± 0.2 μM. Simultaneously we injected a 2 mM Na2S solution at a continuous rate of 10 μl/s in order to quantify the titration-time required to reduce the JO2 to 50% of the initial respiratory activity. Under the lowest oxygen concentration this effect was achieved after 3.5 [0.3; 3.5] and 11.7 [6.2;21.2] min in the uncoupled and coupled state, respectively. This time was statistically significantly shorter when compared to the intermediate and the highest O2 concentrations tested, which yielded values of 24.6[15.5;28.1] min (coupled) and 35.9[27.4;59.2] min (uncoupled), as well as 42.4 [27.5;42.4] min (coupled) and 51.5 [46.4;51.7] min (uncoupled). All data are medians [25%, and 75% percentiles]. Our results suggest that elimination of sulfide in these cells is limited by oxygen availability when approaching the anoxic condition. This property may contribute to the physiological role of sulfide as an oxygen sensor.
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