Lovastatin increases activated K-ras levels, while Konjac mannan effectively reduces serum cholesterol without altering levels of activated K-ras in lung of C56BL/6 mice.

Proc Amer Assoc Cancer Res, Volume 45, 2004 2021 A published meta-analysis of the human lipid reductions trials of the 1970’s to early ’80’s has found that the treatment subjects had a significant increase in cancer mortality (Kritchevsky & Kritchevsky, Ann Rev Nutr 12:391-416, 1992). Previous studies from our laboratory established that hypocholesterolemic agents could alter K-ras protein quantity and membrane versus cytoplasm distribution. K-ras activity state was examined in the present study to define further the importance of this finding in lung carcinogenesis. K-ras activity state in lung tissue from A/J mice (carcinogen sensitive) was examined in a previously reported abstract (AACR 2003). In the current study, lungs from a carcinogen-resistant strain (C57BL/6) were assayed for K-ras activity state. For three weeks, mice consumed either 2 or 4% cholestyramine (CS), 1% niacin, 5% Konjac mannan (KM), or were injected with 25 mg/kg of lovastatin three or five times weekly (Lov-3X and Lov-5X). At necropsy, serum and lungs were recovered from the mice and frozen in liquid nitrogen. Serum cholesterol was determined by a commercial kit. Activated K-ras protein was isolated by immunoprecipitation with a raf-glutathione-S-transferase fusion protein bound to glutathione-agarose beads. Total K-ras was recovered by immunoprecipitation with a ras antibody bound to agarose beads. After isolation, total and activated K-ras were quantified by polyacrylamide gel electrophoresis and western blotting. Detection was performed with a K-ras specific antibody followed by chemiluminescent visualization. Bands were quantified by densitometry. Only KM significantly reduced total serum cholesterol compared to control, Lov-5X or pair fed. K-ras results are summarized in the table below. Only Lov-3X increased activated K-ras levels significantly higher than control (indicated by the * signifying p = 0.0149, t-test). These results differ markedly from our previous activated K-ras results in male A/J mice. The presently observed lack of increase in activated K-ras with CS feeding contrasts with the dose-dependent increase reported earlier with the A/J mice. The present study showed a large increase in activated K-ras with Lov feeding, in contrast to only a very small effect in the previously studied A/J mice. This may correlate with differences in tumorigenesis between mouse strains. The highly sensitive A/Js would seem perhaps more sensitive to the known tumor promoter CS, while the relatively resistant C57BL/6 mice showed little response to CS.