Hepatic lipase deficiency increases plasma cholesterol but reduces susceptibility to atherosclerosis in apolipoprotein E-deficient mice.

The effect of hepatic lipase (HL) deficiency on the susceptibility to atherosclerosis was tested using mice with combined deficiencies in HL and apoE. Mice lacking both HL and apoE (hhee) have a plasma total cholesterol of 917 +/- 252 mg/dl (n = 24), which is 184% that of mice lacking only apoE (HHee; 497 +/- 161 mg/dl, n = 20, p < 0. 001). The increase in cholesterol was mainly in beta-migrating very low density lipoproteins, although high density lipoprotein cholesterol (HDLc) was also increased (53 +/- 37 versus 20 +/- 13 mg/dl, p < 0.01). Despite the increase in plasma cholesterol, we found that HL deficiency significantly decreased aortic plaque sizes in female mice fed normal chow (31 x 10(3) +/- 22 x 10(3) microm2 in hhee versus 115 x 10(3) +/- 69 x 10(3) microm2 in HHee, p < 0.001). Reduction of plaque sizes was also observed in female heterozygous apoE-deficient mice fed an atherogenic diet (2 x 10(3) +/- 2.5 x 10(3) microm2 in hhEe versus 56 x 10(3) +/- 49 x 10(3) microm2 in HHEe, p < 0.01). Changes in aortic lesion size were not apparent in the small number of male mice studied. In HHee females, both HDLc and the capacity of high density lipoprotein (HDL) particles to promote cholesterol efflux from cultured cells were 26% of the wild type. The absence of HL in hhee females partially restored HDLc levels to 57% and cholesterol efflux to 55% of the wild type. Circulating pre-beta1-migrating HDL were present in all mutants, suggesting that there are alternative pathways in the formation of these pre-beta-HDL not involving apoE, HL, or cholesteryl ester transfer protein. The improved capacity to promote cholesterol efflux, together with increased HDL, may explain why these animals can overcome the increase in atherogenic lipoproteins.

Cholesterol efflux, lecithin-cholesterol acyltransferase activity, and pre-beta particle formation by serum from human apolipoprotein A-I and apolipoprotein A-I/apolipoprotein A-II transgenic mice consistent with the latter being less effective for reverse cholesterol transport.

Studies assessing fatty streak formation in mice have revealed that human apolipoprotein A-I (apoAI) transgenic mice (TgAI) have 15-fold less atherosclerosis susceptibility than combined human apolipoprotein A-I/human apolipoprotein A-II (apoAI:AII) transgenics (TgAI:AII) and 40-fold less than nontransgenic control mice. In order to examine the biochemical mechanisms underlying those in vivo observations, we have compared in vitro properties of serum from the different groups of animals for participation in cholesterol efflux, LCAT activation, and pre-beta particle formation. Analysis of cholesterol efflux from both Fu5AH hepatoma and Ob1771 adipose cells revealed serum from the TgAI to be the most efficient in promoting efflux. The two-dimensional electrophoresis of mouse serum shows that control mice have exclusively apoAI in alpha particles. TgAI and TgAI:AII mice have 30 and 38% of total apoAI in particles with pre-beta electrophoretic mobility, respectively. The distribution of cell-derived cholesterol between these apoAI-containing lipoprotein subspecies after 1 and 60 min of incubation with Fu5AH hepatoma cells was examined. This revealed after a 1 min incubation 66 +/- 8 and 83 +/- 9% of the counts in particles with pre-beta mobility for TgAI and TgAI:AII mice, respectively; while after 60 min of incubation, only 6 +/- 2% of counts remained in pre-beta particles from the TgAI and 30 +/- 3% for the TgAI:AII. This suggests faster movement of cholesterol from pre-beta to alpha particles in plasma from the TgAI. Consistent with this is the observation that LCAT activity with both exogenous and endogenous substrate increased in the TgAI versus the TgAI:AII mice. The previously observed decrease in fatty streak formation in the TgAI versus the TgAI:AII and control mice is consistent with the in vitro studies presented here and suggests that HDL containing human apoAI is a more effective participant in the postulated early steps in reverse cholesterol transport than HDL containing both human apoAI and human apoAII, and/or murine HDL.

Cholesterol efflux from Fu5AH hepatoma cells induced by plasma of subjects with or without coronary artery disease and non-insulin-dependent diabetes: importance of LpA-I:A-II particles and phospholipid transfer protein.

We measured the capacity of human plasma to induce cholesterol efflux from Fu5AH rat hepatoma cells in four groups of men with or without non-insulin-dependent diabetes mellitus (NIDDM) and coronary artery disease (CAD). Plasma from men with both NIDDM and CAD (n = 47) had the lowest efflux capacity (17.3 +/- 3.6%) whereas healthy control subjects with neither diabetes nor CAD (n = 25) had the highest capacity (19.8 +/- 3.4%). The groups with CAD but no diabetes (n = 44) and with NIDDM but no CAD (n = 35) had intermediate efflux values (18.5 +/- 3.8 and 18.5 +/- 3.9%, respectively). In a 2 x 2 factorial ANOVA, the differences were significant with respect to the presence of CAD (P = 0.038) and NIDDM (P = 0.041), with no interaction between the factors. The concentration of HDL particles containing apolipoprotein (apo) A-I but no apo A-II (LpA-I) was not related to efflux capacity in univariate or multivariate analyses. A multivariate regression analysis showed that when controlled for the presence of NIDDM and CAD, the concentration of particles containing both apo A-I and apo A-II (LpA-I:A-II) and plasma phospholipid transfer protein activity were both positively, independently, and significantly (P < 0.001) related to cholesterol efflux capacity.

Occurrence of a cytosolic neutral chitobiase activity involved in oligomannoside degradation: a study with Madin-Darby bovine kidney (MDBK) cells.

Neutral oligomannosides possessing one GlcNAc (OS-Gn1) and two GlcNAc (Os-Gn2) at the reducing end have been reported to be released during the N-glycosylation process in various biological models. To investigate which enzyme is responsible for OS-Gn1 formation, we used the Madin-Darby bovine kidney (MDBK) cell line which exhibits neither lysosomal chitobiase nor endoglucosaminidase activities. However, these cells produced OS-Gn1 and we showed that a neutral chitobiase is responsible for the transformation of OS-Gn2 into OS-Gn1. Using streptolysin O-permeabilized MDBK cells, we demonstrated that this neutral chitobiase activity is located in the cytosolic compartment and is active on oligomannoside species released during the N-glycosylation process.

Modulation of cholesterol efflux from Fu5AH hepatoma cells by the apolipoprotein content of high density lipoprotein particles. Particles containing various proportions of apolipoproteins A-I and A-II.

The influence of apolipoproteins (apo) A-I and A-II on the ability of high density lipoproteins (HDL) to remove cholesterol from cultured Fu5AH rat hepatoma cells was studied independently on alterations in the overall structure and lipid composition of the lipoprotein particles. To this end, apoA-I was progressively replaced by apoA-II in ultracentrifugally isolated HDL3 without inducing changes in other remaining lipoprotein components. As apoA-II was progressively substituted for apoA-I in HDL3 (A-II:A-I+A-II percentage mass: 29.5, 47.6, 71.5, 97.4, and 98.9%), the rate of cholesterol efflux from Fu5AH hepatoma gradually and significantly decreased after 2 or 4 h of incubation at 37 degrees C (cholesterol efflux: 30.4 +/- 0.8, 24.1 +/- 1.0, 19.8 +/- 1.2, 15.7 +/- 1.4, and 13.4 +/- 1.3%/2h, respectively; 38.4 +/- 1.5, 29.2 +/- 0.9, 27.0 +/- 0.2, 20.4 +/- 0.4, and 17.5 +/- 1.0%/4h, respectively) (p < 0.01 with all A-II-enriched HDL3 fractions as compared with non-enriched homologues). In agreement with data obtained with total HDL3, increasing the A-II:A-I+A-II percentage mass in HDL3 particles containing initially only apoA-I (HDL3-A-I) progressively reduced cellular cholesterol efflux. After 2 h of incubation, cholesterol efflux correlated negatively with A-II:A-I+A-II percentage mass (r = -0.86; p < 0.0001; n = 20), but not with either free cholesterol:phospholipid ratio, A-I+A-II:total lipid ratio or mean size of HDL3. As determined by using Spearman rank correlation analysis, the A-II:A-I+A-II% mass ratio correlated negatively with the apparent maximal efflux (Vmax(efflux)) (rho = -0.68; p < 0.05, n = 10), but not with the HDL3 concentration required to obtain 50% of maximal efflux (Km(efflux)) (rho = -0.08; not significant, n = 10). It was concluded that the apoA-I and apoA-II content of HDL3 is one determinant of its ability to promote cholesterol efflux from Fu5AH rat hepatoma cells.