On the Importance of the Level of Glutathione and the Activity of the Pentose Phosphate Pathway in Heat Sensitivity and Thermotolerance

Summary

Heating of Ehrlich ascites tumour (EAT) cells and mouse fibroblast LM cells to 43 or 44°C respectively, results in an increased level of reduced gluthathione (GSH). The maximum elevation in GSH was to 140 per cent for LM cells and to 120 per cent for EAT cells. No increase of GSH in EAT cells was observed after heating at 44°C. LM cells were treated with diethylmaleate (DEM) and the EAT cells with buthionine-sulphoximine (BSO) at non-toxic doses to deplete the levels of GSH. No effect on thermosensitivity or on the development of thermotolerance was observed when the DEM and BSO treatments were chosen such that the lowering of GSH was just down to the level of detection (about 5 per cent of control). When higher concentrations of DEM were used, thermal sensitization was observed. The activity of the pentose phosphate pathway (PPP) was also investigated because of its importance in supplying NADPH for the regeneration of GSH from GSSG and for the endogenous production of polyols. Hyperthermia was found to enhance markedly the flux of glucose through the PPP. While the DEM treatment inhibited glucose oxidation through the PPP, BSO addition to the cells resulted in a slightly increased activity of the PPP. The PPP activity of thermotolerant cells was lower (fibroblasts) or hardly affected (EAT cells) compared to control cells. The extent of PPP activation by hyperthermia was comparable for thermotolerant and control cells. For the two cell lines studied neither a high level of GSH nor an active PPP is a prerequisite for the development of thermotolerance.