Influence of dietary lipid upon ultraviolet light-carcinogenesis.

Dietary fats are known to influence the rate of formation of certain types of chemically-induced and spontaneous tumors. An earlier report indicated dietary fat also plays an important role in predisposition to ultraviolet light (UV)-carcinogenesis. Thus, an examination of the effects of dietary lipid level, degree of saturation, and antioxidant supplements on UV-carcinogenesis was undertaken. Twelve groups of 42 animals each received a restricted, semipurified, isocaloric diet containing 4%, 12%, or 12% (60% hydrogenated) corn oil with or without antioxidants (2%, w/w). A regimen of escalating UV irradiation was employed until an accumulative dose of 142 J/cm2 had been delivered. Animals were evaluated weekly for actinic lesions and biweekly for body weights, hematocrits, and serum triglyceride levels. A cumulative distribution function of time to tumor formation was estimated for all irradiated groups from which tumor development time in 50% (TDT50) of the population was derived. Although there were no significant differences in TDT50's between animals receiving low and high unsaturated lipid dietary regimens, animals receiving hydrogenated corn oil demonstrated a significantly (P less than 0.01) greater TDT50. Further, animals receiving hydrogenated 12% corn oil demonstrated fewer tumors per animal than those receiving either level of unsaturated corn oil. Antioxidants had no effect on TDT50's within any of the dietary groups. However, in regard to number of tumors per animal, greater tumor multiplicity was observed in groups receiving unsaturated lipid and antioxidants. These data demonstrate that the degree of dietary lipid saturation modifies the carcinogenic response to UV and, in conjunction with an earlier report, suggest that dietary lipid may modify the previously reported inhibitory effect of antioxidants on UV carcinogenesis. It may be concluded that adherence to dietary standards is as important as other experimental parameters when comparisons of UV effects are involved.