IN-VITRO AND IN-VIVO TEMPERATURE MODULATION OF HEPATIC-METABOLISM ANDDNA ADDUCTION OF AFLATOXIN-B1 IN RAINBOW-TROUT

Alterations in membrane lipid composition during temperature acclimati on of poikilotherms is hypothesized to compensate for direct effects o f temperature on membrane fluidity. Temperature also influences dispos ition and actions of some xenobiotics. This suggests the potential for complex interactions between temperature and metabolism of chemical c arcinogens. Whole livers and hepatic microsomes from rainbow trout acc limated at 18 degrees C have more saturated fatty acids and less mono- and polyunsaturated fatty acids than those from fish acclimated at 10 degrees C. Such changes are consistent with a role for membrane lipid fluidity in temperature compensation. When 10 and 18 degrees C acclim ated fish are ip injected with 0.4 mg/kg [H-3]aflatoxin BI (AFB1) at t heir respective acclimation temperatures, hepatic disposition of AFB1, DNA adduction, and biliary metabolites are similar. An acute shift of 18 degrees C acclimated trout to 14 degrees C reduces [H-3]AFB-DNA ad duct formation, while [H-3]AFB1 adduction after acute shift of 10 degr ees C acclimated fish to 14 degrees C is no different than in nonshift ed fish. Hepatic microsomes isolated from 10 or 18 degrees C acclimate d trout, incubated with 10 mu M [H-3]AFB1 and calf thymus DNA between 6 and 22 degrees C exhibit no differences in the ''break points'' of A rrhenius plots (16 degrees C in both groups). There is, however, more in vitro DNA adduction of [H-3]AFB1 by microsomes from 18 degrees C ac climated fish, a difference abolished by 0.5 mM cu-naphthoflavone (ANF ). These results suggest that temperature acclimation of trout differe ntially modifies activities of cytochrome P-450 isozymes. When assayed at respective acclimation temperatures, hepatic cytosol from 18 degre es C fish produces more aflatoxicol, a detoxication product of AFB1, t han cytosol from 10 degrees C fish. Therefore, this soluble enzyme doe s not exhibit ideal temperature compensation. Such temperature-induced differences in microsomal cytochrome P-450 isozymes and cytosolic deh ydrogenase partially explain temperature-modulated AFB1 genotoxicity.