The aim of this study was to evaluate the vasoprotective effects of HDL isolated from carriers of LCAT deficiency, which are characterized by a selective depletion of LpA-I:A-II particles and predominance of prebeta migrating HDL. HDLs were isolated from LCAT-deficient carriers and tested in vitro for their capacity to promote NO production and to inhibit vascular cell adhesion molecule-1 (VCAM-1) expression in cultured endothelial cells. HDLs from carriers were more effective than control HDLs in promoting eNOS activation with a gene-dose-dependent effect (PTrend = 0.048). As a consequence, NO production induced by HDL from carriers was significantly higher than that promoted by control HDL (1.63 +/- 0.24-fold vs. 1.34 +/- 0.07-fold, P = 0.031). HDLs from carriers were also more effective than control HDLs in inhibiting the expression of VCAM-1 (homozygotes, 65.0 +/- 8.6%; heterozygotes, 53.1 +/- 7.2%; controls, 44.4 +/- 4.1%; PTrend = 0.0003). The increased efficiency of carrier HDL was likely due to the depletion in LpA-I:A-II particles. The in vitro findings might explain why carriers of LCAT deficiency showed flow-mediated vasodilation and plasma-soluble cell adhesion molecule concentrations comparable to controls, despite low HDL-cholesterol levels. These results indicate that selective depletion of apoA-II-containing HDL, as observed in carriers of LCAT deficiency, leads to an increased capacity of HDL to stimulate endothelial NO production, suggesting that changes in HDL apolipoprotein composition may be the target of therapeutic interventions designed to improve HDL functionality.
LCAT (lecithin:cholesterol acyltransferase) catalyzes the transacylation of a fatty acid of lecithin to cholesterol, generating a cholesteryl ester and lysolecithin. The knowledge of LCAT atomic structure and the identification of the amino acids relevant in controlling its structure and function are expected to be very helpful to understand the enzyme catalytic mechanism, as involved in HDL cholesterol metabolism. However - after an early report in the late '90 s - no recent advance has been made about LCAT three-dimensional structure. In this paper, we propose an LCAT atomistic model, built following the most up-to-date molecular modeling approaches, and exploiting newly solved crystallographic structures. LCAT shows the typical folding of the alpha/beta hydrolase superfamily, and its topology is characterized by a combination of alpha-helices covering a central 7-strand beta-sheet. LCAT presents a Ser/Asp/His catalytic triad with a peculiar geometry, which is shared with such other enzyme classes as lipases, proteases and esterases. Our proposed model was validated through different approaches. We evaluated the impact on LCAT structure of some point mutations close to the enzyme active site (Lys218Asn, Thr274Ala, Thr274Ile) and explained, at a molecular level, their phenotypic effects. Furthermore, we devised some LCAT modulators either designed through a de novo strategy or identified through a virtual high-throughput screening pipeline. The tested compounds were proven to be potent inhibitors of the enzyme activity.
Lecithin:cholesterol acyltransferase (LCAT) is the enzyme responsible for cholesterol esterification in plasma. Mutations in the LCAT gene leads to two rare disorders, familial LCAT deficiency and fish-eye disease, both characterized by severe hypoalphalipoproteinemia associated with several lipoprotein abnormalities. No specific treatment is presently available for genetic LCAT deficiency. In the present study, recombinant human LCAT was expressed and tested for its ability to correct the lipoprotein profile in LCAT deficient plasma. The results show that rhLCAT efficiently reduces the amount of unesterified cholesterol (-30%) and promotes the production of plasma cholesteryl esters (+210%) in LCAT deficient plasma. rhLCAT induces a marked increase in HDL-C levels (+89%) and induces the maturation of small prebeta-HDL into alpha-migrating particles. Moreover, the abnormal phospholipid-rich particles migrating in the LDL region were converted in normally sized LDL.
The lecithin:cholesterol acyltransferase (LCAT) enzyme is responsible for the synthesis of cholesteryl esters in human plasma and plays a critical role in high density lipoprotein (HDL) metabolism. Genetic LCAT deficiency is a rare metabolic disorder characterized by low HDL cholesterol levels. This paper reviews the genetic and biochemical features of LCAT deficiency, highlighting the absence of enhanced preclinical atherosclerosis in carriers, despite the remarkably low HDL cholesterol.
BACKGROUND: Lecithin:cholesterol acyltransferase (LCAT) is responsible for cholesterol esterification in plasma. Mutations of LCAT gene cause familial LCAT deficiency, a metabolic disorder characterized by hypoalphalipoproteinemia. Apolipoprotein B (apoB) is the main protein component of very-low-density lipoproteins and low-density lipoprotein (LDL). Mutations of APOB gene cause familial hypobetalipoproteinemia, a codominant disorder characterized by low plasma levels of LDL cholesterol and apoB. OBJECTIVE: This was a genetic and biochemical analysis of an Italian kindred with hypobetalipoproteinemia whose proband presented with hypoalphalipoproteinemia and severe chronic kidney disease. METHODS: Plasma lipids and apolipoproteins, cholesterol esterification, and high-density lipoprotein (HDL) subclass distribution were analyzed. LCAT and APOB genes were sequenced. RESULTS: The proband had severe impairment of plasma cholesterol esterification and high prebeta-HDL content. He was heterozygote for the novel LCAT P406L variant, as were two other family members. The proband's wife and children presented with familial hypobetalipoproteinemia and were heterozygotes for the novel apoB H1401R variant. Cholesterol esterification rate of apoB H1401R carriers was reduced, likely attributable to the low amount of circulating LDL. After renal transplantation, proband's lipid profile, HDL subclass distribution, and plasma cholesterol esterification were almost at normal levels, suggesting a mild contribution of the LCAT P406L variant to his pretransplantation severe hypoalphalipoproteinemia and impairment of plasma cholesterol esterification. CONCLUSION: LCAT P406L variant had a mild effect on lipid profile, HDL subclass distribution, and plasma cholesterol esterification. ApoB H1401R variant was identified as possible cause of familial hypobetalipoproteinemia and resulted in a reduction of cholesterol esterification rate.
