Effect of membrane fatty acid changes on the radiation sensitivity of human lymphoid cells

An evaluation of the contribution of membrane lipids to protection against ultraviolet radiation

Using dioleoylphosphatidylcholine liposomes incorporating various fatty acids and neutral lipids, we have examined the ability of such lipids to provide protection of Escherichia coli and vesicular stomatitis virus (VSV) against the lethal effect of ultraviolet (254 nm) radiation. While the presence of varying amounts of saturated (palmitic) or polyunsaturated (arachidonic) fatty acids or the lipid antioxidant, alpha-tocopherol, had little effect on killing by ultraviolet radiation, considerable radioprotection was observed with beta-carotene, retinal and vitamin K-1 at final concentrations of 1 mg/ml. In another approach, vesicular stomatitis virus grown under conditions in which its envelope fatty acid composition was substantially modified, showed little change in its sensitivity to inactivation by ultraviolet radiation. The results provide strong evidence for a radioprotective role of certain, relatively rare natural lipid components with conjugated polyene systems, but not of the more ubiquitous and abundant membrane fatty acids.

Lipid composition, lipid fluidity and radioresistance of Deinococcus radiodurans and two mutant strains

The lipid composition of D. radiodurans strain R1 and of two mutant strains has been studied in relation to membrane fluidity and sensitivity to X-ray radiation. No significant difference in the unsaturation degree of fatty acids was found between parental and mutant strains. An important decrease of carbohydrate-containing lipids was observed in the radiosensitive mutant strain. We also observed a higher fluidity in both mutant strains than in the parental one. Modification of membrane lipid fluidity by growing the parental strain at 39 degrees C did not lead to modified radioresistance. These results suggest that a particular chemical composition of the membrane leading to a special lipid phase may be an important parameter in controlling radiosensitivity.

Effect of growth temperature on lipid composition and ultraviolet sensitivity of human cells

Human skin fibroblasts were incubated at either 25 or 37 degrees C before UV irradiation. Cells incubated at 25 degrees C were more resistant to near UV radiation than cells grown at 37 degrees C, but cells grown at the lower temperature were more sensitive to 254 nm radiation. Fatty acid analysis of membranes of cells showed that cells incubated at the lower temperature contained significantly higher amounts of linoleic acid (18:2) and linolenic acid (18:3) than cells incubated at 37 degrees C. To determine if this difference in fatty acid content of the membranes was responsible for the UV survival characteristics of cells incubated at different temperatures, cells were enriched with either linoleate or linolenate during a 37 degrees C incubation period. Gas chromatography revealed that cells incorporated the supplied fatty acid. Fatty acid enriched cells were then irradiated with near UV, and survival characteristics were compared to those obtained with cells grown at the lower incubation temperature. The results suggest that the different proportion of fatty acid content of the cells is not the cause of different UV sensitivities of cells grown at 25 degrees C compared to cells grown at 37 degrees C.

Increasing the thermosensitivity of a mammary tumor (CA755) through dietary modification

Disruption of the integrity of tumor cellular membranes has been proposed as an initiating event in hyperthermic cell death. Thermosensitivity measured by the shift in the harmonic mean of tumor regrowth delay of CA755 mammary adenocarcinomas grown in the hind legs of male BDF1, mice increased 22% when the hosts were fed a diet enriched in polyunsaturated fatty acids. Although the diet elicited the anticipated increase in tumor membrane phospholipid polyunsaturated fatty acids, the proportion of total unsaturated fatty acids decreased and the proportion of membrane-rigidifying saturated fatty acids increased. Concomitantly, the concentrations of cholesterol and phospholipid phosphorus increased and the ratio of phosphatidylethanolamine to phosphatidylcholine decreased, presumably to counter the effect of the change in the fatty acid pattern. In host liver membranes, the diet-mediated increase in proportion of polyunsaturated fatty acids was not accompanied by an increase in the proportion of rigidifying saturated fatty acids. Instead, the homeoviscous adaptation consisted of decreases in monounsaturated fatty acids and cholesterol concentration and an increase in the phosphatidylethanolamine-phosphatidylcholine ratio. Addition of a natural inhibitor of cholesterol biosynthesis to the polyunsaturated fatty acid enriched-diet reversed the diet-mediated increase in the phosphatidylethanolamine-phosphatidylcholine ratio of host liver membranes. Tumor membrane lipids from hosts fed the combined dietary factors were characterized by the formentioned rigidifying increase in saturated fatty acids and compensatory decrease in the phosphatidylethanolamine-phosphatidylcholine ratio. The inhibitor reversed the compensatory increases in cholesterol and phospholipid phosphorus concentrations. As a consequence the thermosensitivity of tumors bearing this perturbed membrane was increased.

Effect of membrane fatty acid composition on radiosensitivity of V79 Chinese hamster cells

Exponentially growing V79-379A Chinese hamster fibroblasts were transferred to low-lipid medium enriched with a single fatty acid of the C18 series. After 24 h at 37 degrees C, the fatty acid composition was determined by gas chromatography of the corresponding methyl esters for the total lipid extracts of the cells and for the nuclear membrane fraction. Radiation survival curves, based upon a clonogenic assay, were obtained by irradiation with low dose-rate 60Co gamma rays at either 4 degrees C or room temperature. We observe no effect of fatty acid upon radiosensitivity of these cells at either temperature, in confirmation of published reports with other mammalian cell lines.