Original Article

Correction of hypoalphalipoproteinemia in LDL receptor-deficient rabbits by lecithin:cholesterol acyltransferase

Correspondence to: Jeffrey M. Hoeg.

Familial hypercholesterolemia (FH), a disease caused by a variety of mutations in the low density lipoprotein receptor (LDLr) gene, leads not only to elevated LDL-cholesterol (C) concentrations but to reduced high density lipoprotein (HDL)-C and apolipoprotein (apo) A-I concentrations as well. The reductions in HDL-C and apoA-I are the consequence of the combined metabolic defects of increased apoA-I catabolism and decreased apoA-I synthesis. The present studies were designed to test the hypothesis that overexpression of human lecithin:cholesterol acyltransferase (hLCAT), a pivotal enzyme involved in HDL metabolism, in LDLr defective rabbits would increase HDL-C and apoA-I concentrations. Two groups of hLCAT transgenic rabbits were established: 1) hLCAT+/LDLr heterozygotes (LDLr+/-) and 2) hLCAT+/LDLr homozygotes (LDLr-/-). Data for hLCAT+ rabbits were compared to those of nontransgenic (hLCAT-) rabbits of the same LDLr status. In LDLr+/- rabbits, HDL-C and apoA-I concentrations (mg/dl), respectively, were significantly greater in hLCAT+ (62 ± 8, 59 ± 4) relative to hLCAT- rabbits (21 ± 1, 26 ± 2). This was, likewise, the case when hLCAT+/LDLr-/- (27 ± 2, 19 ± 6) and hLCAT-/LDLr-/- (5 ± 1, 6 ± 2) rabbits were compared. Kinetic experiments demonstrated that the fractional catabolic rate (FCR, d^-1) of apoA-I was substantially delayed in hLCAT+ (0.376 ± 0.025) versus hLCAT- (0.588) LDLr+/- rabbits, as well as in hLCAT+ (0.666 ± 0.033) versus hLCAT- (1.194 ± 0.138) LDLr-/- rabbits. ApoA-I production rate (PR, mg· kg· d^-1) was greater in both hLCAT+/LDLr+/- (10 ± 2 vs. 6) and hLCAT+/ LDLr-/- (9 ± 1 vs. 4 ± 1) rabbits. Significant correlations (P < 0.02) were observed between plasma LCAT activity and HDL-C (r = 0.857), apoA-I FCR (r = -0.774), and apoA-I PR (r = 0.771), while HDL-C correlated with both apoA-I FCR (-0.812) and PR (0.751).

In summary, these data indicate that hLCAT overexpression in LDLr defective rabbits increases HDL-C and apoA-I concentrations by both decreasing apoA-I catabolism and increasing apoA-I synthesis, thus correcting the metabolic defects responsible for the hypoalphalipoproteinemia observed in LDLr deficiency.—Brousseau, M. E., J. Wang, S. J. Demosky, Jr., B. L. Vaisman, G. D. Talley, S. Santamarina-Fojo, H. B. Brewer, Jr., and J. M. Hoeg. Correction of hypoalphalipoproteinemia in LDL receptor-deficient rabbits by lecithin:cholesterol acyltransferase. J. Lipid. Res. 39: 1558–1567.

Supplementary key words: familial hypercholesterolemia, high density lipoproteins, apolipoprotein A-I, metabolism, lecithin:cholesterol acyltransferase, WHHL rabbit

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