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The activity of rhodanese, 3-mercaptopyruvate sulfurtransferase (MPST) and cystathionase in mouse liver, kidney, and four brain regions: tele-, meso-, di- and rhombencephalon was studied 30 min and 2 h following a sublethal dose of cyanide (4 mg/ kg body weight) intraperitoneal injection. Simultaneously, sulfane sulfur levels and total sulfur content, a direct or indirect source of sulfur for CN(-) conversion to SCN(-), were also investigated in these tissues. In the liver this dose of cyanide seemed to impair the process of cyanide detoxification by MPST, as well as rhodanese inhibition. The effects of cyanide administration to mice proved to be totally different in the liver and kidney. In the kidney, a significant increase in the rhodanese activity was observed as early as 30 min following cyanide intoxication, and an elevated cystathionase activity after 2 h was detected. This suggests the involvement of cystathionase in cyanide detoxification in the kidney. The activity of MPST remained at the same level as in the control group. In the rhombencephalon, similarly as in the kidney, L-cysteine desulfuration pathways, which generate sulfane sulfur and sulfurtransferases that transfer sulfane sulfur atoms to CN(-), seemed to play an important role as a defense system against cyanide. The stable level of sulfane sulfur and total sulfur content was accompanied in the rhombencephalon by an increased activity of MPST, cystathionase and rhodanese. In other brain regions the role of these three sulfurtransferases was not so clear and it seemed that in the telencephalon, where the total sulfur content, but not the sulfane sulfur level, was significantly increased, some sulfur-containing compounds, such as GSH and/or cysteine, appeared in response to cyanide.

The expression and activity of cystathionine γ-lyase (CST) and 3-mercaptopyruvate sulfurtransferase (MPST) were investigated in the human neoplastic cells lines: astrocytoma U373, neuroblastoma SH-SY5Y, melanoma A375, and melanoma WM35. Gene expression analysis demonstrated that the investigated neoplastic cells showed the expression of MPST and what is particularly interesting, the expression of CST. The presence of CST in these cells was confirmed using RT-PCR and western blot analysis. However, in U373 cells, a very low activity of CST was detected. In all the investigated cell lines, the activity of MPST was higher than that of CST, which suggests that in these cells, the main pathway of sulfane sulfur formation is the MPST-catalyzed reaction. RP-HPLC analysis showed a large disparity between the level of cystathionine and GSH in the investigated neoplastic cells. In SH-SY5Y cells, the low level of GSH and low GSH/GSSG ratio corresponded with the highest CST activity. Further investigations could aim at verifying whether the stimulation of CST, at the level of protein or gene expression, could change the proliferation of neoplastic cells.

Abstract:We characterized γ-cystathionase, rhodanese and 3-mercaptopyruvate sulfurtransferase activities in various regions of human brain (the cortex, thalamus, hypothalamus, hippocampus, cerebellum and subcortical nuclei) and human gliomas with II to IV grade of malignancy (according to the WHO classification). The human brain regions, as compared to human liver, showed low γ-cystathionase activity. The activity of rhodanese was also much lower and it did not vary significantly between the investigated brain regions. The activity of 3-mercaptopyruvate sulfurtransferase was the highest in the thalamus, hypothalamus and subcortical nuclei and essentially the same level of sulfane sulfur was found in all the investigated brain regions. The investigations demonstrated that the level of sulfane sulfur in gliomas with the highest grades was high in comparison to various human brain regions, and was correlated with a decreased activity of γ-cystathionase, 3-mercaptopyruvate sulfurtransferase and rhodanese. This can suggest sulfane sulfur accumulation and points to its importance for malignant cell proliferation and tumor growth. In gliomas with the highest grades of malignancy, despite decreased levels of total free cysteine and total free glutathione, a high ratio of GSH/GSSG was maintained, which is important for the process of malignant cells proliferation. A high level of sulfane sulfur and high GSH/GSSG ratio could result in the elevated hydrogen sulfide levels. Because of the OPEN ACCESSMolecules 2014, 19 21351 disappearance of γ-cystathionase activity in high-grade gliomas, it seems to be possible that 3-mercaptopyruvate sulfurtransferase could participate in hydrogen sulfide production. The results confirm sulfur dependence of malignant brain tumors.

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