Protection against thermal cell death in Chinese hamster ovary cells by glucose, galactose, or mannose.

The addition of D-glucose, D-galactose, or D-mannose to culture medium increased survival of heated Chinese hamster ovary cells in a concentration- and time-dependent manner. Heat protection by sugars was not immediate but required prior incubation in the sugar medium before hyperthermia. The degree of heat protection conferred by each sugar and its time dependence differed characteristically: galactose protection appeared rapidly (within 1 hr) and was proportional to the galactose concentration in the medium up to 0.3 M. Glucose and mannose were less effective heat protectors at 0.3 M concentrations when compared with galactose, but cell survival after 40 min, 45 degrees, at concentrations below 0.1 M was similar in the three hyperosmotic sugar media. Heat protection by 0.3 M glucose under hyperosmotic conditions (600 mOSM) became apparent only after a preincubation period of at least 5 hr, 37 degrees. Under isoosmotic conditions (300 mOSM, 10% medium-10 mM morpholinopropanesulfonic acid-250 mM glucose), heat protection by glucose appeared more rapidly (3 hr), but the time dependence of heat protection was not eliminated. Under the same isoosmotic conditions in galactose medium, the survival of heated cells was not measurable. The 45 degrees survival curve in hyperosmotic galactose medium (6 hr, 37 degrees prior to heating, 0.3 M) was characterized by a DO of 10 min (controls, 3 min) and a quasithreshold dose of 17 min (controls, 17.5 min). When galactose-loaded cells were returned to fresh medium, heat protection decayed rapidly; cell survival measured 1 or 6 hr later showed a small degree of residual heat protection. A 5-hr incubation period at 37 degrees in galactose-supplemented medium resulted in a major intracellular accumulation of free galactose with smaller accumulations of glucose, sorbitol, and dulcitol. A similar incubation in glucose medium showed only minor intracellular elevations of polyols or sugars. A flow-cytometric analysis of the age distribution showed that incubation in the sugar-supplemented media slightly reduced the fractional cell population in G1 with concomitant gains in both the S- and G2-phase populations. Thus, heat protection by galactose or glucose is probably neither the result of a redistribution of cells in the cycle, nor does it always require the intracellular accumulation of free sugars and polyols. The greater degree of heat protection by galactose and its rapid manifestation under hyperosmotic conditions may be related to the intracellular accumulation of free galactose and/or its metabolites.