Squalene epoxidase, oxido-squalene cyclase and cholesterol biosynthesis in normal and tumoral mucosa of the human gastro-intestinal tract: Evidence of post-HMG CoA regulation

Abstract

Cholesterol biosynthesis was evaluated in different parts of the human gastro-intestinal tract by incorporation of labelled acetic or mevalonic acid into non-saponifiable metabolites and also by measuring squalene epoxidase activity, oxido-squalene cyclase activity and dihydrolanosterol demethylation rate. With respect to rat liver, whole cholesterol biosynthesis was generally low and we found an anatomic localization of activity towards the end of the gastro-intestinal tract. The results of analysis of mevalonic acid metabolites implied the existence of post-HMG CoA regulation. A comparison with the corresponding data obtained from homologous cancerous tissues (in the case of high cholesterogenic activity) did not show a greater activity in the tumor, in spite of higher levels of epoxidase concentration.