SEPARATION OF IMMUNOMODULATORY AND CHOLESTEROL-LOWERING ACTIVITIES OFHETEROCYCLIC AZASPIRANES

Azaspiranes are novel immunomodulators which are effective in a variet y of autoimmune diseases. One azaspirane analog, SK&F 105685 (N,N-dime thyl-8,8-dipropyl-2-azaspiro [4.5] decane-2-propanamine dihydrochlorid e), caused a decrease in total serum cholesterol in dogs after oral ad ministration. To determine whether an effect on cholesterol was common to this class of compounds, the immunomodulatory activity was compare d with the cholesterol-lowering activity of six azaspirane analogs. Th e compounds were given to beagles at a dose of 1 mg/kg p.o. for 28 day s, and the effect on serum cholesterol was determined. The results fro m this study showed a clear dissociation between the immunomodulatory and hypocholesterolemic activities of these compounds. Studies perform ed to determine the mechanism of the decrease in serum cholesterol cau sed by SK&F 105685 indicated that it was not due to inhibition of 3-hy droxy-3-methylglutaryl coenzyme A reductase or acyl-CoA:cholesterol ac yltransferase activities, or to a potentiation of chotesterol-7 alpha- hydroxylase activity. In addition, analysis by gas chromatography of t he nonsaponifiable sterol fraction in dog plasma after treatment with SK&F 105685 or SK&F 106333 showed a decrease in cholesterol and an acc umulation of lathosterol and an unknown sterol, indicating that the co nversion of these sterols is inhibited and cholesterol synthesis is bl ocked at these steps. SK&F 105685 affected the sterol profile in human hepatoblastoma cells (Hep G2) in a similar way. Characterization of t he unknown sterol by gas chromatography and mass spectrometry indicate d that the unknown sterol is very similar to cholesterol and lathoster ol, but its identity has yet to be established. These results show tha t the hypocholesterolemic effects of azaspiranes are related to inhibi tion of one or more of the final steps in the biosynthetic pathway of cholesterol.