Quantitative trait locus analysis of circulating adhesion molecules in hyperlipidemic apolipoprotein E-deficient mice

Circulating soluble adhesion molecules have been suggested as useful markers to predict several clinical conditions such as atherosclerosis, type 2 diabetes, obesity, and hypertension. To determine genetic factors influencing plasma levels of soluble vascular cell adhesion molecule-1 (VCAM-1) and P-selectin, quantitative trait locus (QTL) analysis was performed on an intercross between C57BL/6J (B6) and C3H/HeJ (C3H) mouse strains deficient in apolipoprotein E-deficient (apoE^−/−). Female F₂ mice were fed a western diet for 12 weeks. One significant QTL, named sVcam1 (71 cM, LOD 3.9), on chromosome 9 and three suggestive QTLs on chromosomes 5, 13 and 15 were identified to affect soluble VCAM-1 levels. Soluble P-selectin levels were controlled by one significant QTL, named sSelp1 (8.5 cM, LOD 3.4), on chromosome 16 and two suggestive QTLs on chromosomes 10 and 13. Both adhesion molecules showed significant or an apparent trend of correlations with body weight, total cholesterol, and LDL/VLDL cholesterol levels in the F₂ population. These results indicate that plasma VCAM-1 and P-selectin levels are complex traits regulated by multiple genes, and this regulation is conferred, at least partially, by acting on body weight and lipid metabolism in hyperlipidemic apoE^−/− mice. Zuobiao Yuan and Zhiguang Su contributed equally.     

Quantitative trait loci that determine plasma lipids and obesity in C57BL/6J and 129S1/SvImJ inbred mice

The plasma lipid concentrations and obesity of C57BL/6J (B6) and 129S1/SvImJ (129) inbred mouse strains fed a high-fat diet containing 15% dairy fat, 1% cholesterol, and 0.5% cholic acid differ markedly. To identify the loci controlling these traits, we conducted a quantitative trait loci (QTL) analysis of 294 (B6 x 129) F(2) females fed a high-fat diet for 14 weeks. Non-HDL cholesterol concentrations were affected by five significant loci: Nhdlq1 [chromosome 8, peak centimorgan (cM) 38, logarithm of odds [LOD] 4.4); Nhdlq4 (chromosome 10, cM 70, LOD 4.0); Nhdlq5 (chromosome 6, cM 0) interacting with Nhdlq4; Nhdlq6 (chromosome 7, cM 10) interacting with Nhdlq1; and Nhdlq7 (chromosome 15, cM 0) interacting with Nhdlq4. Triglyceride (TG) concentrations were affected by three significant loci: Tgq1 (chromosome 18, cM 42, LOD 3.2) and Tgq2 (chromosome 9, cM 66) interacting with Tgq3 (chromosome 4, cM 58). Obesity measured by percentage of body fat mass and body mass index was affected by two significant loci: Obq16 (chromosome 8, cM 48, LOD 10.0) interacting with Obq18 (chromosome 9, cM 65). Knowing the genes for these QTL will enhance our understanding of obesity and lipid metabolism.     

Loci controlling plasma non-HDL and HDL cholesterol levels in a C57BL /6J x CASA /Rk intercross

Plasma non-HDL and HDL cholesterol levels are predictors of cardiovascular diseases. We carried out a genetic cross between two laboratory inbred mouse strains, C57BL/6J and CASA/Rk, to detect loci that control the plasma levels of non-HDL and HDL cholesterol. With regard to non-HDL cholesterol, chow-fed CASA/Rk males and females had 87% and 25% higher levels, respectively, than did C57BL/6Js. The levels of non-HDL cholesterol in F1s were similar to C57BL/6J. There was no strain difference in HDL cholesterol levels. An intercross between F1s was performed, and plasma non-HDL and HDL cholesterol was measured in 185 male and 184 female mice. In both male and female F2 mice, plasma non-HDL and HDL cholesterol levels were unimodally distributed; however, in both cases the values for females were significantly lower than for males. Therefore, linkage analysis was performed with sex as a covariate. Significant linkage for non-HDL cholesterol was found on chromosome 6 at 49 cM (LOD 5.17), chromosome 4 at 55 cM (LOD 4.22), and chromosome 8 at 7 cM (LOD 3.68). Significant linkage for HDL cholesterol was found on chromosome 9 at 14 cM (LOD 7.52) and chromosome 8 at 76 cM (LOD 4.69). A significant epistatic interaction involving loci on chromosomes 2 and 5 was also observed for non-HDL cholesterol. In summary, linkage analysis in these cross-identified novel loci confirmed previously identified loci in control of plasma non-HDL and HDL cholesterol and disclosed a novel interaction in controlling non-HDL cholesterol levels in the mouse.     

The role of hepatic Surf4 in lipoprotein metabolism and the development of atherosclerosis in apoE−/− mice

Elevated plasma levels of low-density lipoprotein-C (LDL-C) increase the risk of atherosclerotic cardiovascular disease. Circulating LDL is derived from very low-density lipoprotein (VLDL) metabolism and cleared by LDL receptor (LDLR). We have previously demonstrated that cargo receptor Surfeit 4 (Surf4) mediates VLDL secretion. Inhibition of hepatic Surf4 impairs VLDL secretion, significantly reduces plasma LDL-C levels, and markedly mitigates the development of atherosclerosis in LDLR knockout (Ldlr^?/?) mice. Here, we investigated the role of Surf4 in lipoprotein metabolism and the development of atherosclerosis in another commonly used mouse model of atherosclerosis, apolipoprotein E knockout (apoE^?/?) mice. Adeno-associated viral shRNA was used to silence Surf4 expression mainly in the liver of apoE^?/? mice. In apoE^?/? mice fed a regular chow diet, knockdown of Surf4 expression significantly reduced triglyceride secretion and plasma levels of non-HDL cholesterol and triglycerides without causing hepatic lipid accumulation or liver damage. When Surf4 was knocked down in apoE^?/? mice fed the Western-type diet, we observed a significant reduction in plasma levels of non-HDL cholesterol, but not triglycerides. Knockdown of Surf4 did not increase hepatic cholesterol and triglyceride levels or cause liver damage, but significantly diminished atherosclerosis lesions. Therefore, our findings indicate the potential of hepatic Surf4 inhibition as a novel therapeutic strategy to reduce the risk of atherosclerotic cardiovascular disease.     

Quantitative trait loci analysis for the differences in susceptibility to atherosclerosis and diabetes between inbred mouse strains C57BL/6J and C57BLKS/J.

Mice from the inbred strain C57BLKS/J (BKS) exhibit increased susceptibility to both diabetes and atherosclerosis compared to C57BL/6J (B6) mice. To determine whether the differences in diabetes and atherosclerosis are related, we carried out a cross between B6-db/db and BKS. We selected 99 female F2-db/db progeny, tested the progeny for plasma lipids, plasma glucose, and fatty-streak lesions, and used quantitative trait loci (QTL) analysis to identify the chromosomal regions associated with these phenotypes. No major QTL were found for total cholesterol, VLDL-cholesterol, or triglycerides. Two suggestive QTL were found for HDL-cholesterol (LOD scores of 2. 7 and 2.8), and two suggestive loci were found for plasma glucose (LOD scores of 2.3 and 2.0). Lesion size was not correlated with plasma lipid levels or glucose. Lesion size was determined by a locus at D12Mit49 with a LOD score of 2.5 and a significant likelihood ratio statistic. The gene for apolipoprotein apoB lies within the region, but apoB levels were similar in strains B6 and BKS. The QTL on Chr 12 was confirmed by constructing a congenic strain with BKS alleles in the QTL region on a B6 genetic background. We conclude that susceptibilities to diabetes and atherosclerosis are not conferred by the same genes in these strains and that a major gene on Chr 12, which we name Ath6, determines the difference in atherosclerosis susceptibility.     

Quantitative trait loci for electrical seizure threshold mapped in C57BLKS/J and C57BL/10SnJ mice

We mapped the quantitative trait loci (QTL) that contribute to the robust difference in maximal electroshock seizure threshold (MEST) between C57BLKS/J (BKS) and C57BL10S/J (B10S) mice. BKS, B10S, BKS × B10S F1 and BKS × B10S F2 intercross mice were tested for MEST at 8-9 weeks of age. Results of F2 testing showed that, in this cross, MEST is a continuously distributed trait determined by polygenic inheritance. Mice from the extremes of the trait distribution were genotyped using microarray technology. MEST correlated significantly with body weight and sex; however, because of the high correlation between these factors, the QTL mapping was conditioned on sex alone. A sequential series of statistical analyses was used to map QTLs including single-point, multipoint and multilocus methods. Two QTLs reached genome-wide levels of significance based upon an empirically determined permutation threshold: chromosome 6 (LOD = 6.0 at ～69 cM) and chromosome 8 (LOD = 5.7 at ～27 cM). Two additional QTLs were retained in a multilocus regression model: chromosome 3 (LOD = 2.1 at ～68 cM) and chromosome 5 (LOD = 2.7 at ～73 cM). Together the four QTLs explain one third of the total phenotypic variance in the mapping population. Lack of overlap between the major MEST QTLs mapped here in BKS and B10S mice and those mapped previously in C57BL/6J and DBA/2J mice (strains that are closely related to BKS and B10S) suggest that BKS and B10S represent a new polygenic mouse model for investigating susceptibility to seizures.     

Genome-wide scan for quantitative trait loci influencing LDL size and plasma triglyceride in familial hypertriglyceridemia

Small, dense LDLs and hypertriglyceridemia, two highly correlated and genetically influenced risk factors, are known to predict for risk of coronary heart disease. The objective of this study was to perform a whole-genome scan for linkage to LDL size and triglyceride (TG) levels in 26 kindreds with familial hypertriglyceridemia (FHTG). LDL size was estimated using gradient gel electrophoresis, and genotyping was performed for 355 autosomal markers with an average heterozygosity of 76% and an average spacing of 10.2 centimorgans (cMs). Using variance components linkage analysis, one possible linkage was found for LDL size [logarithm of odds (LOD) = 2.1] on chromosome 6, peak at 140 cM distal to marker F13A1 (closest marker D6S2436). With adjustment for TG and/or HDL cholesterol, the LOD scores were reduced, but remained in exactly the same location. For TG, LOD scores of 2.56 and 2.44 were observed at two locations on chromosome 15, with peaks at 29 and 61 cM distal to marker D15S822 (closest markers D15S643 and D15S211, respectively). These peaks were retained with adjustment for LDL size and/or HDL cholesterol. These findings, if confirmed, suggest that LDL particle size and plasma TG levels could be caused by two different genetic loci in FHTG.     

Localization of genes for V+LDL plasma cholesterol levels on two diets in the opossum Monodelphis domestica

Plasma cholesterol levels among individuals vary considerably in response to diet. However, the genes that influence this response are largely unknown. Non-HDL (V+LDL) cholesterol levels vary dramatically among gray, short-tailed opossums fed an atherogenic diet, and we previously reported that two quantitative trait loci (QTLs) influenced V+LDL cholesterol on two diets. We used hypothesis-free, genome-wide linkage analyses on data from 325 pedigreed opossums and located one QTL for V+LDL cholesterol on the basal diet on opossum chromosome 1q [logarithm of the odds (LOD) = 3.11, genomic P = 0.019] and another QTL for V+LDL on the atherogenic diet (i.e., high levels of cholesterol and fat) on chromosome 8 (LOD = 9.88, genomic P = 5 × 10⁻⁹). We then employed a novel strategy involving combined analyses of genomic resources, expression analysis, sequencing, and genotyping to identify candidate genes for the chromosome 8 QTL. A polymorphism in ABCB4 was strongly associated (P = 9 × 10⁻¹⁴) with the plasma V+LDL cholesterol concentrations on the high-cholesterol, high-fat diet. The results of this study indicate that genetic variation in ABCB4, or closely linked genes, is responsible for the dramatic differences among opossums in their V+LDL cholesterol response to an atherogenic diet.     

Interaction of cholesterol ester and triglyceride in human plasma very low density lipoprotein.

The properties of human plasma very low density lipoproteins (VLDL), low density lipoproteins (LDL), and their extracted lipids were compared using calorimetric, X-ray scattering, and polarizing microscopy techniques. Intact LDL, and cholesterol esters isolated from LDL and VLDL each undergo reversible changes in their physical state around body temperature. These transitions are associated with ordered liquid crystalline to liquid phase changes of the cholesterol esters. In contrast to LDL, VLDL has no reversible transitions and shows no evidence of ordered liquid crystalline structures between 10 and 45 degrees C. Therefore, unlike LDL, VLDL does not contain a separate cholesterol ester region capable of undergoing cooperative melting. Solubility studies at 37 degrees C of cholesterol esters and triglyceride isolated from VLDL show that even at a weight ratio of 1:1, which greatly exceeds the relative amount of cholesterol esters in VLDL, cholesterol ester is completely soluble in triglyceride. Thus, the cholesterol ester in VLDL is not sequestered in a separate domain within VLDL, but is dissolved in the liquid core of the particle.     

Reduction of VLDL Secretion Decreases Cholesterol Excretion in Niemann-Pick C1-Like 1 Hepatic Transgenic Mice

An effective way to reduce LDL cholesterol, the primary risk factor of atherosclerotic cardiovascular disease, is to increase cholesterol excretion from the body. Our group and others have recently found that cholesterol excretion can be facilitated by both hepatobiliary and transintestinal pathways. However, the lipoprotein that moves cholesterol through the plasma to the small intestine for transintestinal cholesterol efflux (TICE) is unknown. To test the hypothesis that hepatic very low-density lipoproteins (VLDL) support TICE, antisense oligonucleotides (ASO) were used to knockdown hepatic expression of microsomal triglyceride transfer protein (MTP), which is necessary for VLDL assembly. While maintained on a high cholesterol diet, Niemann-Pick C1-like 1 hepatic transgenic (L1Tg) mice, which predominantly excrete cholesterol via TICE, and wild type (WT) littermates were treated with control ASO or MTP ASO. In both WT and L1Tg mice, MTP ASO decreased VLDL triglyceride (TG) and cholesterol secretion. Regardless of treatment, L1Tg mice had reduced biliary cholesterol compared to WT mice. However, only L1Tg mice treated with MTP ASO had reduced fecal cholesterol excretion. Based upon these findings, we conclude that VLDL or a byproduct such as LDL can move cholesterol from the liver to the small intestine for TICE.     

Genetic determinants of obesity-related lipid traits

In our ongoing effort to identify genes influencing the biological pathways that underlie the metabolic disturbances associated with obesity, we performed genome-wide scanning in 2,209 individuals distributed over 507 Caucasian families to localize quantitative trait loci (QTLs), which affect variation of plasma lipids. Pedigree-based analysis using a quantitative trait variance component linkage method that localized a QTL on chromosome 7q35-q36, which linked to variation in levels of plasma triglyceride [TG, logarithm of odds (LOD) score = 3.7] and was suggestive of linkage to LDL-cholesterol (LDL-C, LOD = 2.2). Covariates of the TG linkage included waist circumference, fasting insulin, and insulin:glucose, but not body mass index or hip circumference. Plasma HDL-cholesterol (HDL-C) levels were suggestively linked to a second QTL on chromosome 12p12.3 (LOD = 2.6). Five other QTLs with lower LOD scores were identified for plasma levels of LDL-C, HDL-C, and total cholesterol. These newly identified loci likely harbor genetic elements that influence traits underlying lipid adversities associated with obesity.     

Hypolipidemic effect of young persimmon fruit in C57BL/6.KOR-ApoEshl mice

We investigated the hypolipidemic effects of young persimmon fruit (YP) on apolipoprotein E-deficient C57BL/6.KOR-ApoEshl mice. These mice exhibited higher plasma cholesterols, except for high-density lipoprotein (HDL), and lower plasma HDL cholesterol than C57BL/6.Cr mice that had the same genetic background as the C57BL/6.KOR-ApoEshl mice. Male C57BL/6.KOR-ApoEshl mice (n=5) were fed a diet supplemented with dry YP, Hachiya-kaki, at a concentration of 5% (w/w) for 10 weeks. YP treatment significantly lowered plasma chylomicron, very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) cholesterols, and triglyceride, and this response was accompanied by an elevation of fecal bile acid excretion. In the liver, sterol regulatory element binding protein-2 gene expression was significantly higher in mice fed YP, while the mRNA and protein levels of the LDL receptor did not change. These results indicate that acceleration of fecal bile acid excretion is a major mechanism of the hypolipidemic effect induced by YP in C57BL/6.KOR-ApoEshl mice.     

Oral nicotine induces an atherogenic lipoprotein profile

Male squirrel monkeys were used to evaluate the effect of chronic oral nicotine intake on lipoprotein composition and metabolism. Eighteen yearling monkeys were divided into two groups: 1) Controls fed isocaloric liquid diet; and 2) Nicotine primates given liquid diet supplemented with nicotine at 6 mg/kg body wt/day. Animals were weighed biweekly, plasma lipid, glucose, and lipoprotein parameters were measured monthly, and detailed lipoprotein composition, along with postheparin plasma lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) activity, was assessed after 24 months of treatment. Although nicotine had no effect on plasma triglyceride or high density lipoproteins (HDL), the alkaloid caused a significant increase in plasma glucose, cholesterol, and low density lipoprotein (LDL) cholesterol plus protein while simultaneously reducing the HDL cholesterol/plasma cholesterol ratio and animal body weight. Levels of LDL precursors, very low density (VLDL) and intermediate density (IDL) lipoproteins, were also lower in nicotine-treated primates while total postheparin lipase (LPL + HTGL) activity was significantly elevated. Our data indicate that long-term consumption of oral nicotine induces an atherogenic lipoprotein profile (increases LDL, decreases HDL/total cholesterol ratio) by enhancing lipolytic conversion of VLDL to LDL. These results have important health implications for humans who use smokeless tobacco products or chew nicotine gum for prolonged periods.     

Lecithin:cholesterol acyltransferase deficiency increases atherosclerosis in the low density lipoprotein receptor and apolipoprotein E knockout mice.

The purpose of the present study was to test the hypothesis that lecithin:cholesterol acyltransferase (LCAT) deficiency would accelerate atherosclerosis development in low density lipoprotein (LDL) receptor (LDLr-/-) and apoE (apoE-/-) knockout mice. After 16 weeks of atherogenic diet (0.1% cholesterol, 10% calories from palm oil) consumption, LDLr-/- LCAT-/- double knockout mice, compared with LDLr-/- mice, had similar plasma concentrations of free (FC), esterified (EC), and apoB lipoprotein cholesterol, increased plasma concentrations of phospholipid and triglyceride, decreased HDL cholesterol, and 2-fold more aortic FC (142 +/- 28 versus 61 +/- 20 mg/g protein) and EC (102 +/- 27 versus 61+/- 27 mg/g). ApoE-/- LCAT-/- mice fed the atherogenic diet, compared with apoE-/- mice, had higher concentrations of plasma FC, EC, apoB lipoprotein cholesterol, and phospholipid, and significantly more aortic FC (149 +/- 62 versus 109 +/- 33 mg/g) and EC (101 +/- 23 versus 69 +/- 20 mg/g) than did the apoE-/- mice. LCAT deficiency resulted in a 12-fold increase in the ratio of saturated + monounsaturated to polyunsaturated cholesteryl esters in apoB lipoproteins in LDLr-/- mice and a 3-fold increase in the apoE-/- mice compared with their counterparts with active LCAT. We conclude that LCAT deficiency in LDLr-/- and apoE-/- mice fed an atherogenic diet resulted in increased aortic cholesterol deposition, likely due to a reduction in plasma HDL, an increased saturation of cholesteryl esters in apoB lipoproteins and, in the apoE-/- background, an increased plasma concentration of apoB lipoproteins.     

Inhibition by a coantioxidant of aortic lipoprotein lipid peroxidation and atherosclerosis in apolipoprotein E and low density lipoprotein receptor gene double knockout mice.

Antioxidants can inhibit atherosclerosis in animals, though it is not clear whether this is due to the inhibition of aortic lipoprotein lipid (per)oxidation. Coantioxidants inhibit radical-induced, tocopherol-mediated peroxidation of lipids in lipoproteins through elimination of tocopheroxyl radical. Here we tested the effect of the bisphenolic probucol metabolite and coantioxidant H 212/43 on atherogenesis in apolipoprotein E and low density lipoprotein (LDL) receptor gene double knockout (apoE-/-;LDLr-/-) mice, and how this related to aortic lipid (per)oxidation measured by specific HPLC analyses. Dietary supplementation with H 212/43 resulted in circulating drug levels of approximately 200 microM, increased plasma total cholesterol slightly and decreased plasma and aortic alpha-tocopherol significantly relative to age-matched control mice. Treatment with H 212/43 increased the antioxidant capacity of plasma, as indicated by prolonged inhibition of peroxyl radical-induced, ex vivo lipid peroxidation. Aortic tissue from control apoE-/-;LDLr-/- mice contained lipid hydro(pero)xides and substantial atherosclerotic lesions, both of which were decreased strongly by supplementation of the animals with H 212/43. The results show that a coantioxidant effectively inhibits in vivo lipid peroxidation and atherosclerosis in apoE-/-;LDLr-/- mice, consistent with though not proving a causal relationship between aortic lipoprotein lipid oxidation and atherosclerosis in this model of the disease.     

Pleiotropic QTL on chromosome 12q23-q24 influences triglyceride and high-density lipoprotein cholesterol levels: the HERITAGE family study

To determine whether a common quantitative trait locus (QTL) influences the variation of fasting triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) levels, we used a bivariate multipoint linkage analysis with 654 polymorphic markers in 99 white and 101 black families. The phenotypes were investigated under two conditions: at baseline and after a 20-week exercise training intervention. A maximum genome-wide bivariate LOD score of 3.0 (p = 0.00010) was found on chromosome 12q23-q24, located within the IGF1 gene (insulin-like growth factor 1, at 107 cM) for TG and HDL-C at baseline in whites. This bivariate linkage peak is considerably higher than the univariate linkage results at the same chromosome location for either trait (for TG, LOD = 2.07, p = 0.00108; for HDL-C, LOD = 2.04, p = 0.00101). The genetic correlations between baseline TG and HDL-C levels were -0.14 for the residual and -0.33 for the QTL components. Moreover, association analysis showed that TG, HDL-C, and IGF1 are significantly associated (p = 0.04). In conclusion, these results suggest that a QTL on chromosome 12q23-q24 influences the variation of plasma TG and HDL-C levels. Further investigation should confirm whether IGF1 or another nearby gene is responsible for the concomitant variation in TG and HDL-C levels.     

Quantitative trait loci influencing low density lipoprotein particle size in African Americans

Genomic regions that influence LDL particle size in African Americans are not known. We performed family-based linkage analyses to identify genomic regions that influence LDL particle size and also exert pleiotropic effects on two closely related lipid traits, high density lipoprotein cholesterol (HDL-C) and triglycerides, in African Americans. Subjects (n = 1,318, 63.0 +/- 9.5 years, 70% women, 79% hypertensive) were ascertained through sibships with two or more individuals diagnosed with essential hypertension before age 60. LDL particle size was measured by polyacrylamide gel electrophoresis, and triglyceride levels were log-transformed to reduce skewness. Genotypes were measured at 366 microsatellite marker loci distributed across the 22 autosomes. Univariate and bivariate linkage analyses were performed using a variance components approach. LDL particle size was highly heritable (h(2) = 0.78) and significantly (P < 0.0001) genetically correlated with HDL-C (rho(G) = 0.32) and log triglycerides (rho(G) = -0.43). Significant evidence of linkage for LDL particle size was present on chromosome 19 [85.3 centimorgan (cM), log of the odds (LOD) = 3.07, P = 0.0001], and suggestive evidence of linkage was present on chromosome 12 (90.8 cM, LOD = 2.02, P = 0.0011). Bivariate linkage analyses revealed tentative evidence for a region with pleiotropic effects on LDL particle size and HDL-C on chromosome 4 (52.9 cM, LOD = 2.06, P = 0.0069). These genomic regions may contain genes that influence interindividual variation in LDL particle size and potentially coronary heart disease susceptibility in African Americans.     

Lipoprotein lipase deficiency and CETP in streptozotocin-treated apoB-expressing mice

Both hyperglycemia and hyperlipidemia have been postulated to increase atherosclerosis in patients with diabetes mellitus. To study the effects of diabetes on lipoprotein profiles and atherosclerosis in a rodent model, we crossed mice that express human apolipoprotein B (HuB), mice that have a heterozygous deletion of lipoprotein lipase (LPL1), and transgenic mice expressing human cholesteryl ester transfer protein (CETP). Lipoprotein profiles due to each genetic modification were assessed while mice were consuming a Western type diet. Fast-protein liquid chromatography analysis of plasma samples showed that HuB/LPL1 mice had increased VLDL triglyceride, and HuB/LPL1/CETP mice had decreased HDL and increased VLDL and IDL/LDL. All strains of mice were made diabetic using streptozotocin (STZ); diabetes did not alter lipid profiles or atherosclerosis in HuB or HuB/LPL1/CETP mice. In contrast, STZ-treated HuB/LPL1 mice were more diabetic, severely hyperlipidemic due to increased cholesterol and triglyceride in VLDL and IDL/LDL, and had more atherosclerosis.     

Folic acid supplementation delays atherosclerotic lesion development in apoE-deficient mice

Folic acid is a vitamin that when used as a dietary supplementation can improve endothelial function. To assess the effect of folic acid on the development of atherosclerosis, male apolipoprotein E-deficient mice fed a standard chow diet received either water (control group) or an aqueous solution of folic acid that provided a dose of 75 microg/kg/day, for ten weeks. At the time of sacrifice, blood was drawn and the heart removed. The study measured plasma homocysteine, lipids, lipoproteins, low-density lipoprotein (LDL) oxidation, isoprostane, paraoxonase, and apolipoproteins, and aortic atherosclerotic areas. In folic acid-treated animals, total cholesterol, mainly carried in very low-density and low-density lipoproteins, increased significantly, and homocysteine, HDL cholesterol, paraoxonase, and triglyceride levels did not change significantly. Plasma isoprostane and apolipoprotein (apo) B levels decreased. The resistance of LDL to oxidization and plasma apoA-I and apoA-IV levels increased with a concomitant decrease in the area of atherosclerotic lesions. The administration of folic acid decreased atherosclerotic lesions independently of plasma homocysteine and cholesterol levels, but was associated with plasma levels of apolipoproteins A-I, A-IV and B, and decreased oxidative stress.     

Oral nicotine impairs clearance of plasma low density lipoproteins

The effect of chronic oral nicotine intake on plasma low density lipoprotein (LDL) clearance, lipid transfer protein, and lecithin:cholesterol acyltransferase (LCAT) was examined in male atherosclerosis susceptible squirrel monkeys. Eighteen yearling primates were divided into two groups: 1) Controls fed isocaloric liquid diet; and 2) Nicotine monkeys given liquid diet supplemented with nicotine at 6 mg/kg body wt/day for a two-year period. Averaged over 24 months of treatment, animals in the Nicotine group had significantly higher levels of plasma and LDL cholesterol compared to Controls while plasma LCAT activity was similar for both groups. Following simultaneous injection of 3H LDL and 14C high density lipoprotein (HDL) cholesteryl ester (CE), removal of the latter was not altered by oral nicotine while plasma clearance of 3H LDL was dramatically delayed in Nicotine monkeys. Transfer of 14C HDL CE to very low density lipoprotein (VLDL)-LDL particles was greatly accelerated in the Nicotine group vs Controls while the reciprocal movement of 3H LDL CE to HDL was only higher in experimental animals at two time points following injection of the isotopes. Results from this study provide evidence that one major detrimental effect of long-term oral nicotine use is an increase in the circulating pool of atherogenic LDL which is due to: 1) accelerated transfer of lipid from HDL; and 2) impaired clearance of LDL from the plasma compartment. Diminished removal of LDL is of particular importance because an extended residence time of these particles in circulation would increase the likelihood of their deposition in the arterial wall.