Endothelin-converting enzyme activity in serum lipoprotein and total cholesterol level

Dietary L-arginine normalizes endothelin-induced vascular contractions in cholesterol-fed rabbits

The endothelium regulates vascular function by releasing the vasodilator autacoid nitric oxide (NO) and the vasoconstrictor peptide endothelin-1 (ET-1). Impaired activity of NO as well as excessive activity of ET-1 have been demonstrated in hypercholesterolemia and atherosclerosis. Because dietary L-arginine can restore NO function and improve abnormal endothelium-dependent relaxation in hypercholesterolemic rabbits, we examined the effects of dietary supplementation with L-arginine in cholesterol-fed rabbits on endothelium-dependent vascular relaxation and ET-1-induced vascular contraction, as well as the systemic synthesis of ET-1. Rabbits were initially fed a diet enriched with 1% cholesterol for 4 weeks, followed by 0.5% cholesterol alone or supplemented with 2% L-arginine in drinking water during the next 12 weeks. Cholesterol feeding impaired endothelium-dependent relaxation of rabbit aortic rings ex vivo and increased urinary immunoreactive ET-1 excretion, along with decreased urinary nitrate excretion, an index of NO production. L-Arginine partially restored endothelium-dependent relaxation in parallel to increased urinary nitrate excretion and decreased urinary immunoreactive ET-1 excretion. Selective inhibition of ET-A receptors with BQ123 partially restored endothelium-dependent relaxation in hypercholesterolemic rabbits but had no effect on arterial rings from rabbits supplemented with L-arginine or from control animals. The contractile vascular response of aortic rings to exogenous ET-1 was increased in rabbits fed a high-cholesterol diet; this enhanced contractility to ET-1 was completely reversed by L-arginine. These data suggest that L-arginine restores endothelial function and normalizes the synthesis and vasoconstrictor response to ET-1 in hypercholesterolemia.

Partial characterization of endothelin-converting enzyme activity in human serum lipoproteins

Endothelin (ET)-1 is an endothelium-derived vasoconstrictor and mitogen peptide generated from an intermediate form (big ET-1) by endothelin-converting enzyme(s) (ECE). In this study, we partially characterized ECE activity in human serum lipoprotein fraction. By gel filtration chromatography, lipoprotein ECE activities consisted of three major components: the first and the second peak eluted in the positions of very low density lipoprotein (VLDL) and low density lipoprotein (LDL), respectively, while the third peak eluted earlier than that of high density lipoprotein (HDL), whose apparent molecular weight (550 kDa) was similar to that of apolipoprotein B (apo B). Both VLDL/LDL-associated and free ECE fractions were similarly inhibited by metalloproteinase and serine proteinase inhibitors. Free ECE fraction was precipitable with dextran sulphate and manganese ion in the same manner as lipoprotein ECE. Apo B purified by high performance liquid chromatography had the same ECE activity as lipoprotein ECE, whose activity was removed after immunoprecipitation with polyclonal anti-apo B antibody. Our data suggest that ECE activity in human serum lipoproteins may be associated with an apo B-like component, although it needs to be characterized completely.