Epidemiological studies have suggested that frequent olive oil consumption may be a protective factor against lung cancer formation. Squalene, a characteristic compound in olive oil, is an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and has been proposed to inhibit the farnesylation of ras oncoproteins. The present study investigated the effect of dietary olive oil and squalene in a mouse lung tumorigenesis model. Female A/J mice were fed AIN-76A diets containing 5%

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... n oil (control), 19.6% olive oil, or 2% squalene starting at 3 weeks before a single dose of 4-(methylnitrosamino)-1-(3-pyridyl)-1butanone (NNK) (103 mg/kg, i.p.). Animals were maintained on their respective diets throughout the study. At 16 weeks after NNK administration, 100% of the mice in the control group had lung tumors with a tumor multiplicity of 16 tumors per mouse. The olive oil and squalene diets significantly (P Ͻ 0.05) decreased the lung tumor multiplicity by 46 and 58%, respectively. The squalene diet significantly (P Ͻ 0.05) decreased lung hyperplasia by 70%. In mice fed a diet containing 2% squalene for 3 weeks, the activation of NNK was increased by 1.4-and 2.0-fold in lung and liver microsomes, respectively, but its relationship to the inhibition of carcinogenesis is not clear. These results demonstrate that dietary olive oil and squalene can effectively inhibit NNK-induced lung tumorigenesis.