Disulfide cytotoxicity under hypoxia

The cytotoxicity of the disulfide n-butyl 2-imidazolyl disulfide (III-2) was determined to be the result of a disruption in the cellular redox state and inhibition of critical membrane enzymes. These events cause perturbations in Ca2+ homeostasis, which may affect the cell signalling machinery and cause the activation of catabolic enzymes. Exposure of EMT6 cells to III-2 resulted in depletion of nonprotein and protein thiols. Under hypoxic conditions, the depletion of reduced glutathione was less than that measured when cells were treated in air, whereas following an exposure to 500 microM III-2 for 2 h the enzymes glutathione S-transferase and glutathione reductase were inhibited to a greater extent under hypoxia. Ca2+ homeostasis was disrupted with an initial shift from the mitochondrial to the cytoplasmic pool. The inhibition of plasma membrane Ca(2+)-ATPase resulted in accumulation of Ca2+ in the cytoplasm. At higher concentrations, further disruption was seen as a net loss of Ca2+ of the cytoplasmic excess with no change in the mitochondrial levels, resulting in lower total cellular Ca2+. Neither the inhibition of Ca(2+)-ATPase nor the disruption of Ca2+ homeostasis were different under hypoxic vs. oxic conditions. Due to these observations, HL60 cells were used to measure whether III-2 stimulated apoptosis. Morphologic changes and DNA laddering were observed following exposure to the disulfide, with lower concentrations required to stimulate the cellular changes under hypoxia. These events may be the result of the disruption in Ca2+ homeostasis due to thiolation or alteration in redox status of the cells.(ABSTRACT TRUNCATED AT 250 WORDS)