Distinct mechanisms of plasma LDL lowering by dietary fiber in the guinea pig: specific effects of pectin, guar gum, and psyllium

Pectin (PE), guar gum (GG), and psyllium (PSY) lower plasma low density lipoprotein (LDL) cholesterol concentrations in guinea pigs with different orders of magnitude by inducing defined alterations in hepatic cholesterol homeostasis (Fernandez et al. 1994. Am. J. Clin. Nutr. 59: 869-879; 61: 127-134 and 1995. J. Lipid Res. 36: 1128-1138). To further explore specific mechanisms responsible for the differences in plasma and hepatic cholesterol lowering, the effects of these fibers were evaluated on cholesterol absorption, hepatic cholesterol 7 alpha-hydroxylase activity, the rate-limiting enzyme of bile acid synthesis, and in vivo LDL transport to target specific primary and secondary mechanisms accounting for the observed responses. Fibers were fed with physiological (0.04%), low cholesterol (LC), or pharmacological high cholesterol (HC) (0.25%) levels to assess whether cholesterol intake influences plasma LDL lowering mechanisms. Intake of PE, GG, or PSY with LC or HC diets lowered plasma and hepatic cholesterol concentrations (P < 0.001). PE and PSY up-regulated 7 alpha-hydroxylase activity 3-fold with LC and PE by 5-fold with HC diets. In contrast, GG intake had no effect on 7 alpha-hydroxylase activity. Cholesterol absorption was reduced 30% by PE intake while no differences were found between control and PSY groups. GG reduced cholesterol absorption only with HC diets. Intake of PE, GG, or PSY with HC diets resulted in faster plasma LDL fractional catabolic rates (FCR) (P < 0.01) with no effect on LDL apoB flux rates (FR) or pool size, suggesting that fiber reduced LDL cholesterol concentration without decreasing the number of LDL particles. In addition to reducing LDL apoB FR, PE and PSY increased LDL FCR with HC diets while GG effects were limited to lowering LDL apoB FR. These results indicate that the distinctive reductions in hepatic cholesterol induced by PE, GG, and PSY associated with plasma cholesterol lowering result from different mechanisms specific to each fiber and that the levels of dietary cholesterol contribute to the different metabolic responses.     

Inhibition of HMG-CoA reductase by atorvastatin decreases both VLDL and LDL apolipoprotein B production in miniature pigs

In the present studies, the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor atorvastatin was used to test the hypothesis that inhibition of cholesterol biosynthesis in vivo with a consequent reduction in the availability of hepatic cholesterol for lipoprotein synthesis, would (1) reduce very low density lipoprotein (VLDL) apolipoprotein B (apoB) secretion into the plasma, (2) reduce the conversion of VLDL apoB to LDL apoB, and (3) reduce LDL apoB direct synthesis. ApoB kinetic studies were carried out in six control miniature pigs and in six animals after 21 days of administration of atorvastatin (3 mg/kg per day). Pigs were fed a fat- (34% of calories; polyunsaturated to monounsaturated to saturated ratio, 1:1:1) and cholesterol- (400 mg/d cholesterol; 0.1%; 0.2 mg/kcal) containing pig chow-based diet. Atorvastatin treatment significantly reduced plasma total cholesterol, LDL cholesterol, total triglyceride, and VLDL triglyceride concentrations by 16%, 31%, 19%, and 28%, respectively (P < .01). Autologous 131I-VLDL, 125I-LDL, and [3H]leucine were injected simultaneously into each pig, and apoB kinetic data were analyzed using multicompartmental analysis (SAAM II). The VLDL apoB pool size decreased by 29% (0.46 versus 0.65 mg/kg; P = .002), which was entirely due to a 34% reduction in the VLDL apoB production rate (PR) (1.43 versus 2.19 mg/kg per hour; P = .027). The fractional catabolic rate (FCR) was unchanged. The LDL apoB pool size decreased by 30% (4.74 versus 6.75 mg/kg; P = .0004), which was due to a 22% reduction in the LDL apoB PR (0.236 versus 0.301 mg/kg per hour; P = .004), since the FCR was unchanged. The reduction in LDL apoB PR was primarily due to a 34% decrease in conversion of VLDL apoB to LDL apoB; however, this reduction was not statistically significant (P = .114). Hepatic apoB mRNA abundance quantitated by RNase protection assay was decreased by 13% in the atorvastatin-treated animals (P = .003). Hepatic and intestinal LDL receptor mRNA abundances were not affected. We conclude that inhibition of hepatic HMG-CoA reductase by atorvastatin reduces both VLDL and LDL apoB concentrations, primarily by decreasing apoB secretion into the plasma and not by an increase in hepatic LDL receptor expression. This decrease in apoB secretion may, in part, be due to a reduction in apoB mRNA abundance.     

Nonselective nerve fibre damage in peripheral nerves after experimental thermocoagulation

BACKGROUND: The insoluble material in supersaturated bile is prerequisite for the formation of gallstones. We therefore studied the biliary precipitable and soluble cholesterol and noncholesterol sterols, including the cholesterol precursor sterols (including lanosterol and lathosterols), and the plant sterols campesterol and sitosterol, and cholestanol, which usually reflect cholesterol synthesis and absorption, respectively, before and after a 6-month treatment with ursodeoxycholic acid (UCDA), 15.4 +/- 4 mg/kg/day (standard error of the mean) or simvastatin (40 mg/day) in 21 patients with cholesterol gallstones, to obtain further information about the factors contributing to the formation of gallstones. METHODS: The sediment and supernatant fractions of duodenal bile samples were separated by ultracentrifugation and analyzed with gas-liquid chromatography. RESULTS: At the base line (n = 21) 50% +/- 3% of biliary cholesterol and a variable amount of the noncholesterol sterols (from 14% of lanosterol to 62% of cholestanol) were in the sediment fraction. The pattern of the noncholesterol sterols in the sediment resembled that of gallstones described previously. At base line body mass index was positively related to the percentage of precipitable cholesterol in bile (r = 0.46, P < 0.05), and the serum sitosterol proportion negatively related to the molar percentage of biliary cholesterol and positively to that of bile acids (r = -0.46 and r = 0.50, P < 0.05 for both). UDCA decreased the precipitable percentage of cholesterol from 46% to 31% (P < 0.03) and simvastatin from 57% to 42% (P = 0.05). Both drugs also decreased the precipitable percentages of lathosterols and cholestanol while increasing that of lanosterol. In relation to cholesterol, the sediment to supernatant ratios of all methylsterols were increased, whereas those of polar lathosterols tended to decrease during UDCA treatment. CONCLUSIONS: Patients with high body mass index have more precipitable cholesterol in their bile. Although both UDCA and simvastatin decreased the precipitable cholesterol, the bile still contained one-third of its cholesterol in the sedimentable form.     

Regulation of classic and alternative bile acid synthesis in hypercholesterolemic rabbits: effects of cholesterol feeding and bile acid depletion

The effect of cholesterol feeding (3 g/day) on bile acid synthesis was examined in 10 New Zealand white rabbits (NZW), 8 Watanabe heterozygous and 10 homozygous rabbits with partial and complete deficiencies of LDL receptors. After 10 days of cholesterol feeding, bile fistulas were constructed and bile acid pool sizes were measured. Cholesterol feeding increased plasma and hepatic cholesterol levels in all rabbit groups. Baseline bile acid pool sizes were smaller (P < 0.01) in heterozygotes (139 +/- 3 mg) and homozygotes (124 +/- 30 mg) than NZW rabbits (254 +/- 44 mg). After feeding cholesterol, bile acid pool sizes doubled with increased cholic acid synthesis in NZW and, to a lesser extent, in Watanabe heterozygous rabbits but not in homozygotes. Baseline cholesterol 7alpha-hydroxylase activity in NZW and heterozygotes declined 69% and 53% (P < 0.001), respectively, after cholesterol feeding. Sterol 27-hydroxylase activity reflecting alternative bile acid synthesis increased 66% (P < 0.01) in NZW and 37% in Watanabe heterozygotes but not in homozygotes after feeding cholesterol. Bile fistula drainage stimulated cholesterol 7alpha-hydroxylase activity but not sterol 27-hydroxylase activity in all three rabbit groups. These results demonstrated that dietary cholesterol increased hepatic sterol 27-hydroxylase activity and alternative bile acid synthesis to expand the bile acid pool and inhibited cholesterol 7alpha-hydroxylase in NZW and in Watanabe heterozygous rabbits but not in homozygotes with absent hepatic LDL receptor function. Thus, in rabbits, sterol 27-hydroxylase is up-regulated by the increased hepatic cholesterol that enters the liver via LDL receptors whereas cholesterol 7alpha-hydroxylase is controlled by the circulating hepatic bile acid flux.     

Outcome from treatment for spinal arteriovenous malformation

BACKGROUND: prospective studies have demonstrated that a predominance of small, dense LDL particles (pattern B) precedes the clinical onset of coronary heart disease. Prevalence and characteristics of subjects with this LDL size abnormality were studied in young, nonobese, Japanese normolipidemic men. METHODS AND RESULTS: LDL peak particle diameter (PPD) was measured by continuous disc polyacrylamide gel electrophoresis in 223 nonobese normolipidemic men aged 18-20 years (mean+/-S.D. body mass index: 21.9+/-3.7 kg/m2, total cholesterol: 180+/-29 mg/dl, triglyceride: 62+/-34 mg/dl, HDL cholesterol: 58+/-12 mg/dl). Men with small LDL (PPD < 25.8 nm) were found in only 5.4% (n=12) whereas 197 men (88.3%) had a preponderance of large LDL (PPD 26.3 nm). As compared with men in a top tertile (PPD 27.5 nm) those in a low tertile (PPD < 26.9 nm) had higher serum levels of LDL cholesterol (120+/-31 vs 104+/-24 mg/dl), triglyceride (72+/-39 vs 49+/-16 mg/dl) and apolipoprotein (apo) B (84+/-21 vs 68+/-14 mg/dl), and lower HDL cholesterol (54+/-10 vs 60+/-12 mg/dl). They also had greater body mass index (23.2+/-4.6 vs 20.9+/-3.1 kg/m2) and percent body fat (21.5+/-7.7 vs 17.5+/-4.9%). LDL-PPD was positively correlated with HDL cholesterol (R=0.20, P=0.002) and was negatively correlated with apoB (R=0.34, P < 0.001), triglyceride (R=0.32, P < 0.001). percent body fat (R=0.26, P < 0.001), body mass index (R=0.24, P < 0.001), fat mass (R=0.23, P=0.001), total cholesterol (R=0.20, P=0.002). In multiple regression analysis, apoB, triglyceride, HDL cholesterol, apoAI and percent body fat explained 18% of LDLPPD variability. CONCLUSION: even in young, nonobese, normolipidemic men, LDL size appears to be associated with triglyceride-rich lipoprotein metabolism and body fat.     

Effects of apoE gene polymorphism on Lp(a) concentrations depend on the size of apo(a): a study of 466 white men

Polymorphisms in the genes for the low-density lipoprotein (LDL) receptor ligands, apolipoprotein E (apoE), and apolipoprotein B (apoB) are associated with variation in plasma levels of LDL cholesterol. Lp(a) lipoprotein(a) [Lp(a)] is LDL in which apoB is attached to a glycoprotein called apolipoprotein(a) [apo(a)]. Apo(a) has several genetically determined isoforms differing in molecular weight, which are inversely correlated with Lp(a) concentrations in blood. The interaction of apo(a) with triglyceride-rich lipoproteins differs with the size of apo(a), and therefore the effects of apoE gene polymorphism on Lp(a) levels could also depend on apo(a) size. We have investigated the possible effect of genetic variation in the apoE and apoB genes on plasma Lp(a) concentrations in 466 white men with different apo(a) phenotypes. Overall there was no significant association between the common apoE polymorphism and Lp(a), but in the subgroup with apo(a)-S4, concentrations of Lp(a) differed significantly among the apoE genotypes (P = 0.05). Lp(a) was highest in the apoE genotypes epsilon 2 epsilon 3 and epsilon 3 epsilon 3 and lowest in genotype epsilon 3 epsilon 4, and the apoE polymorphism was estimated to account for about 2.4% of the variation in Lp(a). In contrast, in the subgroup with apo(a)-S2 Lp(a) was significantly lower (P = 0.04) in apoE genotype epsilon 2 epsilon 3 than in genotype epsilon 3 epsilon 3. Lp(a) concentrations did not differ among the XbaI (P = 0.65) or SP 24/27 (P = 0.26) polymorphisms of the apoB gene. The expected effects of both apoE and apoB polymorphism on LDL levels were significant in the whole population sample and in subjects with large-sized apo(a) isoforms (P < 0.01), whereas no effect was seen in those with low molecular weight apo(a) isoforms. We conclude that the influence of apoE genotypes on Lp(a) concentrations depends on the size of the apo(a) molecule in Lp(a), possibly because both apo(a)-S4 and apoE4 have high affinity for triglyceride-rich lipoproteins and may be taken up and degraded rapidly by remnant receptors.     

Altered apolipoprotein B metabolism in very low density lipoprotein from lovastatin-treated guinea pigs

Previous studies have shown that treatment of guinea pigs with lovastatin alters the composition and the metabolic properties of circulating low density lipoprotein (LDL). Specifically, LDL isolated from lovastatin-treated animals is cleared from plasma more slowly than LDL isolated from control animals, when injected into the guinea pig. In the present study, we examine whether lovastatin also affects the metabolic properties of very low density lipoprotein (VLDL), the metabolic precursor of LDL. VLDL isolated from lovastatin-treated guinea pigs (L-VLDL) and VLDL isolated from untreated (control) guinea pigs (C-VLDL) were radioiodinated and simultaneously injected into eight untreated guinea pigs. Radioactivity associated with apolipoprotein B-100 (apoB) was measured in four plasma density fractions and analyzed using a compartmental model consisting of fast and slow pools for VLDL, fast and slow pools for intermediate density lipoprotein (IDL), and a single slow pool for LDL. The fractional catabolic rate (FCR) for C-VLDL apoB was 2.8 +/- 1.0 h-1 and for L-VLDL apoB was 5.1 +/- 2.0 h-1 (P < 0.002, paired t test). The fractions of control and lovastatin VLDL apoB converted to LDL averaged 0.15 +/- 0.15 and 0.02 +/- 0.02, respectively (P < 0.05, paired t test). Finally, the FCRs of LDL apoB derived from control and lovastatin VLDL were similar (0.059 +/- 0.007 h-1 and 0.083 +/- 0.038 h-1, respectively; paired t test not significant). These data indicate that L-VLDL was irreversibly removed from the plasma of an untreated guinea pig more rapidly than was C-VLDL. Thus, the metabolic behavior of VLDL apoB is affected by lovastatin. Therefore, changes in lipoprotein particles themselves must be considered in assessing the overall impact of treatment with lovastatin.     

Absorption, metabolism, and serum concentrations of cholesterol in vegetarians: effects of cholesterol feeding

Serum concentrations and metabolism of cholesterol were studied in vegetarians basally and during a dietary cholesterol load. Cholesterol absorption efficiency was normal and synthesis was slightly enhanced, even though serum cholesterol precursors were not increased. The serum concentrations of total and low-density-lipoprotein cholesterol were decreased proportionally to the reduced intake and absolute absorption of cholesterol. Fecal plant sterols were negatively correlated with the absorption efficiency of cholesterol and positively with fecal sterols and cholesterol synthesis, suggesting interference of high plant sterol intakes with cholesterol absorption. Cholesterol saturation and bile acid composition of the bile were not changed. The increased serum plant sterol-cholesterol ratios were positively related to the intake and negatively to the biliary secretion of plant sterols. Cholesterol feeding increased absolute cholesterol absorption and serum concentrations of total and low-density-lipoprotein cholesterol, did not change absorption efficiency or synthesis of cholesterol, but increased fecal cholestanol excretion.     

Genetic factors precipitating type III hyperlipoproteinemia in hypolipidemic transgenic mice expressing human apolipoprotein E2

Several factors are hypothesized to precipitate or exacerbate type III hyperlipoproteinemia (HLP) in humans. Among such factors are those that directly overload remnant lipoprotein production or disrupt removal pathways, including an increased ratio of apolipoprotein (apo) E2 to normal apoE, overproduction of apoB-containing lipoproteins, and decreased LDL receptor activity. Hypolipidemic apoE2-transgenic mice bred onto an apoE-null background had dramatically higher plasma total cholesterol (192 +/- 26 mg/dL for males, 203 +/- 40 mg/dL for females) and triglyceride (295 +/- 51 mg/dL for males, 277 +/- 58 mg/dL for females) levels than apoE2 mice with endogenous mouse apoE. Thus, eliminating normal apoE in the presence of apoE2 (thereby increasing the relative abundance of the defective ligand) can convert a hypolipidemic to a hyperlipidemic phenotype. Hypolipidemic apoE2 transgenic mice overexpressing human apoB had moderate remnant accumulation compared with apoE2-only or apoB-only transgenic mice, indicating that overproduction of apoB-containing lipoproteins in the presence of apoE2 can augment remnant production. Hypolipidemic apoE2 transgenic mice bred-onto an LDL receptor-null background had markedly higher plasma total cholesterol (288 +/- 51 mg/dL for males, 298 +/- 73 mg/dL for females) and triglyceride (356 +/- 72 mg/dL for males, 317 +/- 88 mg/dL for females) levels than apoE2-only mice, and remnant accumulation increased even in apoE2 mice with a heterozygous LDL receptor-knockout background (compared with apoE2-only mice), suggesting that reducing or eliminating a major receptor-mediated remnant-removal pathway in the presence of apoE2 can also precipitate a hyperlipidemic phenotype. In all cases where either lipoprotein remnant production or removal pathways were severely stressed, increased remnant accumulation was apparent. As judged by the chemical characteristics of the remnant lipoproteins, the lipoprotein phenotype was quite similar to that of human type III HLP, especially in the apoE2-expressing mice with no endogenous apoE or LDL receptors, and thus these mice represent improved models of the disorder.     

Differences in receptor binding of LDL subfractions

Differences in low density lipoprotein (LDL) receptor-binding affinity among LDL particles of different size were examined in competitive binding assays in human skin fibroblasts and LDL (d = 1.020 to 1.050 g/mL) from subjects with a predominance of large (> or = 272 A), medium (259 to 271 A), and small (< or = 257 A) LDL. Among 57 normolipidemic subjects with LDL cholesterol (-C) levels < 160 mg/dL, binding affinity was reduced by 16% in those with predominantly large LDL and by 14% in those with small LDL compared with most subjects who had a predominance of medium-size LDL and in all LDL size subgroups in 66 subjects with LDL-C > or = 160 mg/dL. Differences in LDL receptor-binding affinity were further investigated by using LDL density subfractions (I, d = 1.026 to 1.032 g/mL; II, d = 1.032 to 1.038 g/mL; and III, d = 1.038 to 1.050 g/mL) from three subjects with predominantly large (pattern A) and small (pattern B) LDL particles. The binding affinity (Kd) of LDL-II was similar for patterns A and B (9.2 +/- 1.4 and 9.4 +/- 0.7, respectively) and 30% lower in LDL-III from both groups (P < .05). The binding affinity of LDL-I in pattern A (12.6 +/- 1.5 micrograms/mg) was lower (P < .05) than that in LDL-II and LDL-I from pattern B (8.0 +/- 2.4 micrograms/mg). After incubation with a monoclonal antibody that specifically blocked the LDL receptor-binding domain of apoE, LDL-I from two pattern B subjects showed substantially lower binding affinity (Kd = 20.0 and 19.2 micrograms/mg) than in pattern A (Kd = 13.2 and 14.2 micrograms/mg), a result consistent with our finding of a higher apoE content in pattern B LDL-I (P < .001). Thus, factors associated with variations in particle size and apoE content in LDL subclasses in normolipidemic subjects contribute to the differences in LDL receptor binding that may result in differing metabolic behavior in vivo.     

Helium-oxygen improves Clinical Asthma Scores in children with acute bronchiolitis

Sprague-Dawley rats (n = 32) were fed diets without fiber (control) or containing 1 or 5% chicory extract or 5% inulin for 4 wk; 0.2% cholesterol was added to all diets. Rats fed chicory extract and inulin diets had significantly higher serum high density lipoprotein (HDL) cholesterol and generally lower low density lipoprotein (LDL) cholesterol concentrations, thus significantly greater ratios of HDL/LDL cholesterol compared with the controls (P < 0.05). The serum apolipoprotein B/apolipoprotein A-1 ratio was significantly lower in rats fed diets containing chicory extract or inulin than that in rats fed fiber-free diets, due to significant reductions in apolipoprotein B concentration (P < 0.05). Greater liver lipid and triglyceride concentrations were observed in rats fed chicory extract or inulin diets compared with the controls (P < 0.05). However, liver phospholipid and cholesterol concentrations were not significantly different among groups (P > 0.05). Addition of 5% inulin to the diet resulted in greater cecal weight, whereas both 5% chicory extract and 5% inulin resulted in greater cecal propionic acid concentration compared with the controls (P < 0.05). Rats fed chicory extract and inulin had significantly greater fecal lipid, cholesterol and bile acid excretions than those fed fiber-free diets (P < 0.05). The results of this study suggest that the improved lipid metabolism observed in rats fed chicory extract (mainly inulin component) may be caused by an alteration in the absorption and/or synthesis of cholesterol, which might result from the changes in cecal fermentation, and by an increase in the fecal excretion of lipid, cholesterol and bile acid.     

Familial hypercholesterolemia in the Finnish north Karelia. A molecular, clinical, and genealogical study

A specific mutation termed FH-North Karelia [FH-NK] accounts for almost 90% of familial hypercholesterolemia [FH] cases in the Finnish North Karelia, with a population of about 180,000. Extensive search for its presence in the entire North Karelia province revealed 340 carriers of this mutation. Other mutations of the LDL receptor [LDLR] gene accounted for 67 cases of heterozygous FH. This gives a minimum FH prevalence of 1 in 441 inhabitants in North Karelia, with the highest density of patients in the Polvij?rvi commune (1 in 143 inhabitants). Old parish records, confirmation records, and tax records were used to track a common ancestor for most of the present-day North Karelian FH-NK patients in the village of Puso, located within an area where the FH prevalence today is the highest. DNA analysis indicated that 2% of the subjects aged 1 to 25 years would have been diagnosed as false-negative and 7% as false-positive FH patients on the basis of LDL cholesterol [LDL-C] determinations alone. Common genetic variations of apolipoprotein E [apoE], XbaI, polymorphism of apolipoprotein B [apoB], and PvuII polymorphism of the intact LDLR allele contributed little to serum lipid variation in established carriers of the FH-NK allele, although apoE2/4 genotype and the presence of the PvuII restriction site tended to be associated with relatively low LDL-C levels. Coronary heart disease (CHD) was present in 65 (30%) out of the 179 FH gene carriers aged > or = 25 years, and 19 individuals had a previous history of acute myocardial infarction (AMI). The average age (mean +/- SD) at onset of CHD was 42 +/- 7 years for males and 48 +/- 11 years for females (P < .05). In stepwise logistic regression analysis carried out in carriers of the FH-NK allele, age, gender, smoking, and apoE allele E2 all emerged as independent determinants of risk of CHD or AMI. It may be concluded that the relatively high prevalence of FH patients in North Karelia province provides a unique founder population in which genetic and nongenetic factors modifying the course of FH can be effectively investigated.     

Cholesterol synthesis is increased in mixed hyperlipidaemia

We showed previously that hypertriglyceridaemia, but not hypercholesterolaemia, is correlated with increases in cholesterol synthesis and apolipoprotein B secretion in patients with secondary hypertriglyceridaemia. The aim of the present study was to compare the rate of cholesterol synthesis, using fasting plasma mevalonic acid (MVA) as an index, in patients with primary mixed hyperlipidaemia (type IIb phenotype, n=45) and primary hypercholesterolaemia (type IIa phenotype, n=92). LDL cholesterol was significantly higher in types IIa (6.38+/-0.18 mmol/l) and IIb (5.89+/-0.25 mmol/l) compared to 40 normolipidaemic controls (2. 99+/-0.1 mmol/l, P<0.0001), whereas serum triglyceride was higher in type IIb (2.62 (range 2.2-3.0) mmol/l) than type IIa (1.22 (range 0. 85-1.60) mmol/l, P<0.001) and controls (0.90 (range 0.68-1.24) mmol/l, P<0.001). Similarly, MVA was higher in type IIb (7.0+/-0.46 ng/ml) than IIa (5.6+/-0.23 ng/ml, P<0.0) and controls (5.6+/-0.36 ng/ml, P<0.05). Plasma MVA correlated positively with serum triglyceride (r=0.22, P=0.004) and negatively with LDL cholesterol (r=-0.21, P=0.014). These results are in accordance with previous observations that VLDL-apolipoprotein B secretion and cholesterol synthesis are linked and demonstrate that the latter is increased in mixed hyperlipidaemia.     

Effects of age, gender, and menopausal status on plasma low density lipoprotein cholesterol and apolipoprotein B levels in the Framingham Offspring Study

Plasma low density lipoprotein (LDL) cholesterol, non-high density lipoprotein (HDL) cholesterol, and apolipoprotein (apo) B, the major protein constituent of LDL, were measured in 1,533 men (mean age 49 +/- 10 years) and 1,597 women (mean age 49 +/- 10 years) participating in the 3rd examination cycle of the Framingham Offspring Study. Mean plasma levels of LDL cholesterol and apoB were higher in men than in women (136 versus 132 mg/dl, P < 0.0001; and 109 versus 95 mg/dl, P < 0.0001, respectively). Increased age was associated with higher plasma LDL cholesterol and apoB levels, especially in women. After adjustment for age and body mass index, LDL cholesterol and apoB levels were still significantly higher in postmenopausal than in premenopausal women, indicating a hormonal effect on LDL metabolism. The associations between coronary heart disease (CHD) and LDL cholesterol, non-HDL cholesterol, apoB, and other plasma lipid and lipoprotein parameters were examined by dividing participants in four groups, based on approximate quartiles for these parameters. Elevated LDL cholesterol levels were not significantly associated with CHD in men, but were in women. This result, at variance with that of several longitudinal studies, is likely due to the cross-sectional design of our analysis. Elevated non-HDL cholesterol and apoB levels were significantly associated with the presence of CHD, in both males and females. A plasma apoB value > or = 125 mg/dl may be associated with an increased risk for CHD. Low plasma levels of HDL cholesterol were also significantly associated with CHD. Plasma triglyceride levels, age and body mass index were strong determinants of LDL cholesterol, non-HDL cholesterol, and apoB levels in men and women. In women, postmenopausal status and elevated blood pressure were also significantly associated with elevated levels of these parameters.     

Selective uptake of low density lipoprotein-cholesteryl ester is enhanced by inducible apolipoprotein E expression in cultured mouse adrenocortical cells

Apolipoprotein (apo) E is expressed at high levels by steroidogenic cells of the adrenal gland, ovary, and testis. The cell surface location of apoE in adrenocortical cells suggests that apoE may facilitate the uptake of lipoprotein cholesterol by either the endocytic or the selective uptake pathways, or both. To examine these possibilities, the human apoE gene was expressed in murine Y1 adrenocortical cells under control of an inducible tetracycline-regulated promoter. The results show that induction of apoE yielded a 2-2.5-fold increase in the uptake of low density lipoprotein-cholesteryl ester (LDL-CE) but had little effect on high density lipoprotein-CE uptake. Analysis of lipoprotein uptake pathways showed that apoE increased LDL-CE uptake by both endocytic and selective uptake pathways. In terms of cholesterol delivery to the adrenal cell, the apoE-mediated enhancement of LDL-CE selective uptake was quantitatively more important. Furthermore, the predominant effect of apoE expression was on the low affinity component of LDL-CE selective uptake. LDL particles incubated with apoE-expressing cells contained 0.92 +/- 0.11 apoE molecules/apoB after gel filtration chromatography, indicating stable complex formation between apoE and LDL. ApoE expression by Y1 cells was necessary for enhanced LDL-CE selective uptake. This result may indicate an interaction between apoE-containing LDL and cell surface apoE. These data suggest that apoE produced locally by steroidogenic cells facilitates cholesterol acquisition by the LDL selective uptake pathway.     

Effect of estrogen and progesterone on the expression of hepatic and extrahepatic sterol 27-hydroxylase in baboons (Papio sp)

Sterol 27-hydroxylase plays an important role in cholesterol metabolism in hepatic and extrahepatic tissues. To determine whether female sex steroid hormones influence its expression, we measured plasma and hepatic 27-hydroxycholesterol, hepatic mRNA levels, activity of sterol 27-hydroxylase, and adrenal mRNA levels of this enzyme in baboons (n = 6 per group) treated with placebo, estrogen, estrogen + progesterone, and progesterone. We also measured hepatic cholesterol concentration and hepatic acyl coenzyme A:cholesterol acyltransferase (ACAT) activity to determine their relationship with hepatic sterol 27-hydroxylase activity. Plasma 27-hydroxycholesterol concentration was increased by estrogen and estrogen + progesterone and was negatively correlated with plasma (P = .090) and LDL (P = .026) cholesterol concentrations. Similarly, hepatic sterol 27-hydroxylase activity was increased by estrogen and estrogen + progesterone and was negatively correlated with plasma (P = .056) and LDL (P = .052) cholesterol concentrations but was positively correlated with hepatic and plasma 27-hydroxycholesterol concentrations (P < .001). Hepatic ACAT activity was increased by progesterone (P < .004) and was positively correlated with plasma (P = .002) and LDL (P = .009) cholesterol concentrations but was negatively correlated with hepatic sterol 27-hydroxylase activity (P = .035). Hepatic and adrenal gland mRNA levels for sterol 27-hydroxylase were increased by estrogen alone or in combination with progesterone (P < .05). Hepatic sterol 27-hydroxylase activity was positively correlated with hepatic mRNA levels (P < .001), an observation suggesting that estrogen increases the activity of sterol 27-hydroxylase by increasing its synthesis. Hepatic cholesterol concentration was not influenced by the hormone treatment. These observations suggest that estrogen alone or in combination with progesterone increases the synthesis of sterol 27-hydroxylase in hepatic and extrahepatic tissues, and the increased activity of hepatic sterol 27-hydroxylase resulting from the increased synthesis is associated with a hypolipidemic effect on plasma LDL levels. Furthermore, progesterone alone increases the hepatic ACAT activity, but given in combination with estrogen progesterone does not have the same effect on hepatic ACAT activity. The effect of estrogen on hepatic ACAT activity may be mediated by sterol 27-hydroxylase and its effect on cholesterol metabolism (decreased cholesterol synthesis and increased output of cholesterol in the bile) in liver.     

Atherosclerosis, vascular remodeling, and impairment of endothelium-dependent relaxation in genetically altered hyperlipidemic mice

We examined the vascular structure and endothelium-dependent relaxation in two genetic models of hypercholesterolemia: apolipoprotein E (apoE)-knockout mice and combined apoE/LDL receptor-double-knockout mice. Intimal area was increased markedly in proximal segments of thoracic aortas from apoE/LDL receptor-knockout mice [0.13 +/- 0.03 (mean +/- SE) mm2] compared with normal (C57BL/6J) mice (0.002 +/- 0.002 mm2, P < .05). Despite intimal thickening, the vascular lumen was not smaller in the aortas of apoE/LDL receptor-knockout mice (0.52 +/- 0.03 mm2) than in normal mice (0.50 +/- 0.03 mm2). In apoE-deficient mice, intimal thickening was minimal or absent, even though the concentration of plasma cholesterol was only modestly less than that in the double-knockout mouse (14.9 +/- 1.1 vs 18.0 +/- 1.2 mmol/L, respectively, P < .05). Relaxation of the aorta was examined in vitro in vascular rings precontracted with U46619. In normal mice, acetylcholine produced relaxation, which was markedly attenuated by the nitric oxide synthase inhibitor NG-nitro-L-arginine (100 microM). Relaxation to acetylcholine and the calcium ionophore A23187 was normal in apoE-deficient mice (in which lesions were minimal) but greatly impaired in the proximal segments of thoracic aortas of apoE/LDL receptor-deficient mice, which contained atherosclerotic lesions. Vasorelaxation to nitroprusside was similar in normal and apoE-knockout mice, with modest but statistically significant impairment in atherosclerotic segments of apoE/LDL receptor-knockout mice. In distal segments of the thoracic aorta of apoE/LDL receptor-deficient mice, atherosclerotic lesions were minimal or absent, and the endothelium-dependent relaxation to acetylcholine and calcium ionophore was normal. Thus, in apoE/LDL receptor-knockout mice (a genetic model of hyperlipidemia), there is vascular remodeling with preservation of the aortic lumen despite marked intimal thickening, with impairment of endothelium-dependent relaxation to receptor- and nonreceptor-mediated agonists. Atherosclerosis may be accelerated in the apoE/LDL receptor-double-knockout mouse compared with the apoE-knockout strain alone. We speculate that other factors, such as the absence of LDL receptors, may contribute to the differences in the extent of atherosclerosis in these two models of hyperlipidemia.     

Impaired absorption of cholesterol and bile acids in patients with an ileoanal anastomosis

BACKGROUND: No data exist on cholesterol absorption in patients with an ileoanal anastomosis (IAA). AIMS: To study cholesterol absorption and its effects on cholesterol and bile acid metabolism in patients with an IAA. PATIENTS AND METHODS: Cholesterol absorption, and serum, biliary, and faecal lipids were studied in 24 patients with an IAA and 20 controls. RESULTS: Fractional cholesterol absorption was significantly lower in the patients (36% versus 47% in controls). Surprisingly, the calculated intestinal influx of endogenous cholesterol was reduced so that the absolute absorption of cholesterol was decreased; elimination of cholesterol as faecal neutral steroids remained normal. Thus, the slightly increased cholesterol synthesis was mainly due to increased faecal bile acid excretion, which, in turn, was associated with reduced absorption and biliary secretion of bile acids. Serum total and low density lipoprotein (LDL) cholesterol and LDL triglycerides were lower in the patients. Molar percentage and saturation index of biliary cholesterol were slightly higher in patients with an IAA. Proportions of secondary bile acids in bile and faeces were diminished, and faecal unidentified bile acids were higher in patients. CONCLUSIONS: Cholesterol absorption is significantly impaired in patients with an IAA, and is closely related to changes in serum and biliary lipids observed in these patients.     

Increased bile acid pool inhibits cholesterol 7 alpha-hydroxylase in cholesterol-fed rabbits

BACKGROUND & AIMS: Cholesterol feeding unexpectedly inhibits cholesterol 7 alpha-hydroxylase in rabbits. The aim of this study was to explore the mechanism. METHODS: Twenty male New Zealand white rabbits were fed regular chow with and without 2% cholesterol for 10 days followed by 7 days of bile drainage. The activities of hepatic cholesterol 7 alpha-hydroxylase and sterol 27-hydroxylase that control bile acid synthesis in classic and alternative pathways were related to the size and composition of bile acid pool. RESULTS: After feeding cholesterol, plasma and hepatic cholesterol concentrations increased, the bile acid pool doubled (from 254 +/- 44 to 533 +/- 51 mg; P < 0.001), cholesterol 7 alpha-hydroxylase activity decreased 68% (P < 0.01), but sterol 27-hydroxylase activity increased 66% (P < 0.05) with increased cholic acid synthesis (P < 0.01). Bile drainage in the cholesterol-fed rabbits depleted the bile acid pool and stimulated down-regulated cholesterol 7 alpha-hydroxylase activity 11.4-fold (P < 0.001), although hepatic cholesterol remained elevated. Hepatic sterol 27-hydroxylase activity was unaffected. CONCLUSIONS: Feeding cholesterol increased hepatic cholesterol and stimulated sterol 27-hydroxylase and alternative bile acid synthesis, which expanded the bile acid pool and inhibited cholesterol 7 alpha-hydroxylase in rabbits. In distinction, hepatic sterol 27-hydroxylase was insensitive to changes in the bile acid pool.     

Plasma lipoprotein and apolipoprotein levels in Taipei and Framingham

We compared the plasma lipoprotein cholesterol, triglyceride, apolipoprotein (apo) A-I, apoB, and lipoprotein(a) [Lp(a)] concentrations in a low coronary heart disease (CHD) risk population (n = 440) in Taipei with a high CHD risk population (n = 428) in Framingham matched for age, sex, and menopausal status. Taipei men had significantly lower low-density lipoprotein cholesterol (LDL-C) (-20 mg/dL, -14%, P < .01) and apoB (-7 mg/dL, -6%, P < .05) levels and significantly higher high-density lipoprotein cholesterol (HDL-C) levels (6 mg/dL, 13%, P < .01) than Framingham men. Taipei women had significantly lower LDL-C (-18 mg/dL, -15%, P < .01) and higher HDL-C (4 mg/dL, 7%, P < .01) levels than Framingham women. Median concentrations and distributions of Lp(a) by sex were similar in Taipei and Framingham. After adjusting for body mass index and smoking status, only differences in total cholesterol and LDL-C levels remained significantly different for both sexes between the two populations (P < .01). Gender differences for lipids within populations were similar. After adjusting for age, body mass index, and smoking status, women in both Taipei and Framingham had significantly lower mean triglyceride, LDL-C, and apoB levels and significantly higher HDL-C and apoA-I levels than men. Postmenopausal women in Taipei had significantly higher mean total cholesterol, LDL-C, HDL-C, apoA-I, apoB, and Lp(a) levels than premenopausal women (P < .05), whereas in Framingham postmenopausal women had significantly higher total cholesterol, triglyceride, LDL-C, and apoB levels than premenopausal women (P < .05). Our data are consistent with the concept that plasma lipoprotein cholesterol levels (especially LDL-C) but not apolipoprotein values explain some of the twofold difference in age-adjusted CHD mortality between these two populations.