Heat protection by sugars and sugar analogues

Abstract

We have examined the relative ability of 16 sugars and sugar analogues to reduce cell killing by hyperthermia of 40 min, 45°C. In general, sugars were added to the culture medium 6 h prior to heating at a concentration of 100 mM (400 mosmol). The results show that D-hexoses, L-hexoses, methylated or thiolated sugars and disaccharides significantly protected cells against thermal damage, increasing survival by factors of 10 to 100. The degree of protection varied for specific sugars and could not be predicted on the basis of sugar conformation or the number of hydroxyl groups. Relative heat protection was partially dependent on the survival assay technique (pre-and post-plating); consistently lower cell survival was measured when cells were subcultured after hyperthermia, both in medium-control and sugar-protected cells. However, the time dependence of heat protection appeared independent of pre-and post-plating.

Cell survival after heating was not increased by two sugars: (a) D-idose, and (b) 2-deoxy-D-galactose. The latter sugar, curiously, was also a heat protector but only when cells were trypsinized after hyperthermia. Both of these sugars were relatively more toxic at 37°C under identical treatment conditions. The lack of protection by these two sugars is not understood. Another reported non-sugar heat protector, sodium butyrate, was included as an additional control. Heat protection by butyrate was not observed in CHO cells.

The accumulation of intracellular free sugar was measured by gas chromatography after incubating cells for 6 h, 37°C with talose, idose, L-galactose or 1-O-methyl-D-glucose. All of these sugars were found in high concentrations inside of cells. The data are consistent with the hypothesis that polyhydroxy compounds must accumulate intracellularly for cellular heat protection.

Key Words:

• hyperthermia
• heat protection
• sugars
• thermotolerance