Carnitine esters: novel inhibitors of plasma lecithin: cholesterol acyltransferase in experimental animals but not in man (Homo sapiens)

1. Long-chain fatty acid esters of carnitine were observed to inhibit lecithin: cholesterol Acyltransferase (LCAT, EC 2.3.1.43) in plasma from the rat (Rattus sativa) and rabbit (Oryctolagus cuniculus) but not in man (Homo sapiens). At a level of 500 nmol/ml of plasma, L-palmitoylcarnitine, L-stearoylcarnitine, and L-oleoylcarnitine inhibit the formation of cholesteryl esters by LCAT by 25-30%. 2. The inhibition is concentration-dependent and is observed only with acylcarnitine esters with acyl chains of 12C or greater. 3. Equipotent activity is obtained using either the DL-acylcarnitine esters or the L-acylcarnitine esters. 4. Inhibition of LCAT by carnitine esters is greater than that achievable with sodium dodecylsulfate on a mol:mol basis and is not reversible with albumin. 5. The failure of the carnitine esters to inhibit plasma LCAT from man suggests the possibility of subtle differences in the structure of human LCAT compared with that in Other species.