ApoE and apoC-III-defined HDL subtypes: A descriptive study of their LCAT and CETP content and activity

Background High-density lipoproteins (HDL) functionality predicts cardiovascular risk better than HDL concentrations. The apolipoprotein composition of HDL may be a determinant of their function. Lecithin-cholesterol acyl transferase (LCAT) and cholesterol-ester transfer protein (CETP) are key enzymes for HDL-mediated reverse cholesterol transport. We assessed the distribution and activity of LCAT and CETP in HDL subspecies defined by their content of apolipoproteins E (apoE) and C-III (apoC-III) in humans. Methods We isolated in 18 adult humans of both sexes (mean age 55.6, BMI 26.9 Kg/m2, HbA1c 5.4%), four subspecies of HDL containing respectively: No apoE and no apoC-III (E-C-), apoE but not apoC-III (E+C-), apoC-III but no apoE (E-C+) and both apoE and apoC-III (E+C+). In each HDL subspecies, we measured LCAT and CETP concentration and activity using immunoenzymatic and fluorometric methods. Additionally, we determined the size distribution of HDL in each apolipoprotein-defined fraction using non-denaturing electrophoresis and anti-ApoA-I western blot. Results Similar to previous studies, HDL in the E-C- fraction was the predominant subtype. The size distribution of HDL was very similar across all four apolipoprotein-defined fractions. LCAT was most abundant in E-C- HDL (3.58 mg/mL, 59.6 % of plasma LCAT mass), while HDL with apoE or apoC-III had much less LCAT (19.8%, 12.2% and 8.37% of plasma LCAT respectively for E+C-, E-C+ and E+C+). LCAT mass was lower in E+C- HDL relative to E-C- HDL, but LCAT activity was similar in both fractions, signaling a greater activity-to-mass ratio associated with the presence of apoE. Both CETP mass and CETP activity showed only slight variations across HDL subspecies. There was an inverse correlation between plasma LCAT activity and both E-C+ pre-beta HDL (r=-0.55, p=0.017) and E-C- alpha 1 HDL (r=-0.49, p=0.041). Conversely, there was a direct correlation between E-C+ alpha 1 HDL and CETP activity in plasma (r=0.52, p=0.025). Conclusions Our results suggest that LCAT activity in humans is influenced by the presence of small interchangeable apolipoproteins. The presence of apoE in small HDL is correlated with increased LCAT activity and esterification of plasma cholesterol.

ApoE and apoC-III-defined HDL subtypes: A descriptive study of their LCAT and CETP content and activity

Background High-density lipoproteins (HDL) in plasma are strongly and negatively associated with cardiovascular risk, yet interventions to raise HDL have not improved cardiovascular outcomes. HDL functionality and heterogeneity may hold the clue to this paradox. The apolipoprotein composition of HDL may be an important determinant of their functionality. Lecithin-cholesterol acyl transferase (LCAT) and cholesterol-ester transfer protein (CETP) are key enzymes for HDL-mediated reverse cholesterol transport. We assessed the distribution and activity of LCAT and CETP in HDL subspecies defined by their content of apolipoproteins E (apoE) and C-III (apoC-III) in humans. Methods We isolated in adult humans of both sexes (mean age 55.6, BMI 26.9 Kg/m2, HbA1c 5.4%), four subspecies of HDL containing respectively: No apoE and no apoC-III (E-C-), apoE but not apoC-III (E+C-), apoC-III but no apoE (E-C+) and both apoE and apoC-III (E+C+). In each HDL subspecies, we measured LCAT and CETP concentration and activity using immunoenzymatic and fluorometric methods. Additionally, we determined the size distribution of HDL in each apolipoprotein-defined fraction using non-denaturing electrophoresis and anti-ApoA-I western blot. Results Similar to previous studies, HDL in the E-C- fraction was the predominant subtype. The size distribution of HDL was very similar across all four apolipoprotein-defined fractions. LCAT was most abundant in E-C- HDL (3.58 mg/mL, 59.6 % of plasma LCAT mass), while HDL with apoE or apoC-III had much less LCAT (19.8%, 12.2% and 8.37% of plasma LCAT respectively for E+C-, E-C+ and E+C+). Despite a much lower LCAT mass, LCAT activity in E+C- HDL was comparable to that in E-C- HDL. Both CETP mass and CETP activity showed only slight variations across HDL subspecies. There was an inverse correlation between plasma LCAT activity and both E-C+ pre-beta HDL (r=-0.55, p=0.017) and E-C- alpha 1 HDL (r=-0.49, p=0.041). Conversely, there was a direct correlation between E-C+ alpha 1 HDL and CETP activity in plasma (r=0.52, p=0.025). Conclusions Our results suggest that LCAT activity in humans is influenced by the presence of small interchangeable apolipoproteins. The presence of apoE in small HDL is correlated with increased LCAT activity and esterification of plasma cholesterol.

Pleiotropy of ABO gene: correlation of rs644234 with E-selectin and lipid levels

Background:TheABOgene has been widely studied and associated with many different diseases such as myocardial infarction and diabetes. Pleiotropic effects of theABOlocus have been demonstrated. Indeed it affects different phenotypes such as E- and P-selectins, triglycerides and total cholesterol. The goal of this work was to study the SNP rs644234 located in theABOgene with different phenotypes related with diseases where theABOgene has been involved.Methods:We analyzed the SNP rs644234 located in theABOgene, by performing association studies with different lipid phenotypes as well as with the soluble E-selectin levels in 348 adults from the STANISLAS Family Study.Results:The major rs644234*T allele was associated with increased levels of soluble E-selectin (p=8.7×10−12). According to the lipid phenotypes, the major rs644234*T allele was associated with decreased levels of apolipoproteins E (ApoE) (p=0.001) and low-density lipoprotein cholesterol (LDL-C) (p=0.032) but was associated with increased levels of high-density lipoprotein cholesterol (HDL-C) (p=0.013). The association of the HDL-C was especially significant in the male individuals (p=0.001).Conclusions:We confirmed thatABOis a major locus for serum soluble E-selectin levels variability, and we also correlated this gene with different lipid phenotypes. Furthermore, we demonstrated that this pleiotropic effect is independent. This is the first time that a correlation has been made between the ABOgene and the ApoE levels. According to these results, the major allele of this polymorphism may have a protective effect when it comes to cardiovascular related diseases, and more specifically when it comes to the lipid phenotypes.