EFFECT OF MEMBRANE ENVIRONMENT ON INHIBITION OF ACYL-COA-CHOLESTEROL ACYLTRANSFERASE BY A RANGE OF SYNTHETIC INHIBITORS

The effect of the membrane environment of acyl-CoA:cholesterol acyl tr ansferase (ACAT), an important intracellular enzyme of cholesterol met abolism, on the properties of a range of inhibitors of varying potenci es was studied. ACAT activity from rat liver was solubilised with 3% d eoxycholate (97% solubilised activity). After dilution into cholestero l/phosphatidylcholine liposomes (molar ratio 0.35), the assay of this reconstituted system showed linearity with protein and time. Saturatio n with oleoyl-CoA was achieved at 10 mu M. Comparison of the potency o f the ACAT inhibitors in the reconstituted assay and in a microsomal a ssay revealed a relationship between the lipid content of the assay an d the inhibitory activity for potent inhibitors of ACAT (CI976, CL277, 082, YMI7E and DuP128). This relationship was unrelated to Lipophilici ty of the drugs, Octimibate, lovastatin and progesterone, none of whic h is a potent ACAT inhibitor but which have all been described as ACAT inhibitors in the literature, all had low potencies in both assay sys tems. These results suggest that the lipid concentration must be taken into account when comparing potencies of ACAT inhibitors, The present data also indicate that some compounds which inhibit cholesterol este rification may do so by an indirect mechanism.