CYP27A1 participates in the degradation of cholesterol to bile acids in both the classic and acidic pathways.[1] It is the initiating enzyme in the acidic pathway to bile acids, yielding oxysterols by introducing a hydroxyl group to the carbon at the 27 position in cholesterol. In the acidic pathway, it produces 27-hydroxycholesterol from cholesterol whereas in the classic or neutral pathway, it produces 3beta-hydroxy-5-cholestenoic acid.It is also involved in the metabolism of vitamin D3. While CYP27A1 is present in many different tissues, its function in these tissues is largely uncharacterized. In macrophages, 27-hydroxycholesterol generated by this enzyme may be helpful against the production of inflammatory factors associated with cardiovascular disease.