Impaired triacylglycerol catabolism in hypertriglyceridemia of the diabetic, cholesterol-fed rabbit: a possible mechanism for protection from atherosclerosis

The etiology of the hypertriglyceridemia in alloxan-diabetic rabbits was studied by two independent methods. Production and removal rates of VLDL triacylglycerol were measured in diabetic rabbits by injection of [3H]palmitate-labelled VLDL. Similarly, triacylglycerol total removal rates were determined in non-diabetic rabbits which were infused with Intralipid to mimic the plasma triacylglycerol concentrations of diabetic rabbits. Compared to nondiabetic rabbits, triacylglycerol removal rats were decreased in diabetic rabbits, particularly at higher levels of plasma triacylglycerol. During cholesterol and triacylglycerol supplementation of the diet, post-heparin plasma lipoprotein lipase activity of diabetic rabbits with severe hypertriglyceridemia averaged 36% of that of nondiabetics, suggesting an impaired triacylglycerol removal capacity. Furthermore, plasma triacylglycerol was inversely related to post-heparin plasma lipoprotein lipase activity among diabetic rabbits. VLDL triacylglycerol production increased with increasing plasma triacylglycerol concentration among diabetic cholesterol-fed rabbits with moderately severe hypertriglyceridemia, but reached an apparent plateau among rabbits with plasma triacylglycerol concentrations from approx. 2000-9000 mg/dl. Thus, severe hypertriglyceridemia in this model of insulin deficiency can be attributed only partially to VLDL hypersecretion, whereas a removal defect, resulting in saturation of the triacylglycerol removal mechanism, appears to be largely responsible. The impaired removal of plasma triacylglycerol is also related to the presence of cholesterol predominantly in lipoproteins of increased size. The data support the hypothesis that protection against atherosclerosis in cholesterol-fed diabetic rabbits results from exclusion of very large cholesterol-containing lipoproteins from the arterial wall.     

Turnover of 125I-VLDL and 131I-LDL apolipoprotein B in rabbits fed diets containing casein or soy protein

Rabbits fed low-fat, cholesterol-free, semi-purified diets containing casein developed a marked hypercholesterolemia compared to rabbits fed a similar diet containing soy protein (plasma cholesterol 281 +/- 31 vs. 86 +/- 9 mg/dl; P less than 0.05). Turnover studies (three per dietary group) were carried out in which homologous 125I-labeled VLDL and 131I-labeled LDL were injected simultaneously into casein- (n = 8) or soy protein- (n = 9) fed rabbits. ApoB-specific activities were determined in VLDL, IDL and LDL isolated from the pooled plasma of two or three rabbits per dietary group. The production rate of VLDL apoB (1.20 +/- 0.3 vs. 1.09 +/- 0.1 mg/h per kg) was similar for the two dietary groups. The fractional catabolic rate of VLDL apoB was lower for the casein group (0.15 +/- 0.03 vs. 0.23 +/- 0.01.h-1; 0.05 less than P less than 0.10). Although the pool size of VLDL apoB was higher in the casein group (8 +/- 2 vs. 5 +/- 0.3 mg/kg), this value did not reach statistical significance. For LDL apoB, the increased pool size in casein-fed rabbits (30 +/- 5 vs. 5 +/- 1 mg/kg; P less than 0.01) was associated with a decreased fractional catabolic rate (0.03 +/- 0.005 vs. 0.08 +/- 0.008.h-1; P less than 0.01) and a 2-fold increase in the production rate of LDL apoB (1 +/- 0.3 vs. 0.4 +/- 0.06 mg/kg per h; 0.05 less than P less than 0.10) compared to rabbits fed soy protein. Analysis of precursor-product relationships between the various lipoprotein fractions showed that casein-fed rabbits synthesized a higher proportion of LDL apoB (95% +/- 2 vs. 67% +/- 2; P less than 0.001) independent of VLDL catabolism. These results support the concept that the hypercholesterolemia in casein-fed rabbits is associated with impaired LDL removal consistent with a down-regulation of LDL receptors. These changes do not occur when the casein is replaced by soy protein.     

The mechanism of lack of hypocholesterolemic effects of pravastatin sodium,a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor,in rats

In order to clarify the reason why pravastatin, a 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitor, did not show hypocholesterolemic effects in rats, the changes of various parameters affecting the serum cholesterol levels by pravastatin were determined in rats and rabbits, as a comparison. In rabbits, pravastatin administration at 50 mg/kg for 14 days decreased serum and liver cholesterol by 40% and 8%, respectively. The hepatic LDL receptor activity was increased 1.7-fold, and VLDL cholesterol secretion was decreased. Cholesterol 7α-hydroxylase activity was not changed. In contrast, in rats, serum cholesterol was increased by 14% at 50 mg/kg and 27% at 250 mg/kg for 7 days, respectively. At 250 mg/kg, liver cholesterol was significantly increased by 11%. Under these conditions, neither the hepatic LDL receptor activity nor cholesterol 7α-hydroxylase was changed, and VLDL cholesterol secretion was increased. At 250 mg/kg, net cholesterol synthesis in rat liver was increased after 7 days of consecutive administration. These results imply that in rats, stimulated net cholesterol synthesis caused the increase of liver cholesterol followed by the increase of VLDL cholesterol secretion, and resulted in the raise of plasma cholesterol. Although hepatic HMG-CoA reductase was induced almost the same fold in both animals at 50 mg/kg, the induced HMG-CoA reductase activity in rats might overcome the inhibitory capability of pravastatin, resulting in an increase of net cholesterol synthesis, but not in rabbits. This overresponse to pravastatin in rats might cause the lack of hypocholesterolemic effects of this drug.     

Abnormalities of low density lipoproteins in normolipidemic type II diabetic and nondiabetic patients with coronary artery disease.

The characteristics of low density lipoproteins (LDL) of ten non-insulin-dependent diabetic (NIDDM) and ten nondiabetic patients with coronary artery disease (CAD) were investigated and compared to LDL of ten NIDDM patients without CAD and ten healthy persons. All subjects had LDL cholesterol below 160 mg/dl and serum triglycerides below 200 mg/dl. The mean LDL particle size and particle distribution profiles were analyzed by using nondenaturing polyacrylamide gradient gel electrophoresis. The LDL composition and hydrated density distribution were investigated by using density gradient ultracentrifugation. Both NIDDM and nondiabetic CAD patients tended to have larger LDL particles than NIDDM patients without CAD and healthy subjects. The increase of LDL particle size of CAD patients was due to marked enrichment of triglycerides (TG) in their LDL. The percentage content of TG in LDL of NIDDM patients with CAD was 14.5% and in LDL of nondiabetic CAD patients 13.4% compared with 7.9% in LDL of NIDDM patients without CAD and 7.2% in normal-LDL (P less than 0.05 or less between either CAD group and NIDDM without CAD or normals). The LDL TG/apolipoprotein (apo) B weight ratio was significantly higher in both CAD groups compared with LDL of the two groups without CAD (0.70 and 0.68 vs. 0.38 and 0.34, respectively, P less than 0.05, P less than 0.05 and P less than 0.01, P less than 0.01). The LDL total lipid to apoB weight ratio was similar in all four groups. Consistent with this, the hydrated density distributions of LDL in the four groups were similar, the average peak densities being 1.0346 g/ml, 1.0331 g/ml, 1.0331 g/ml, and 1.0331 g/ml, respectively. The findings of this study demonstrate that normolipidemic patients with CAD may have marked abnormalities in th eir LDL composition and these anomalies are present in both diabetic and nondiabetic patients.     

Evaluation of the use of serum lathosterol concentration to assess whole-body cholesterol synthesis in rabbits.

Serum lathosterol concentration in rabbits was assessed as a possible indicator of whole-body cholesterol synthesis. In random-bred New Zealand White (NZW) rabbits fed a control diet or a diet containing either cholesterol, simvastatin, or cholestyramine, neither serum lathosterol concentration nor the serum lathosterol:total cholesterol ratio systematically corresponded with the anticipated rate of cholesterol synthesis. In control rabbits and those fed simvastatin or cholestyramine, whole-body cholesterol synthesis, which was calculated from the sterol balance, was correlated with serum lathosterol concentration when expressed relative to cholesterol in very low, intermediate, and low density lipoproteins (VLDL + IDL + LDL) (r = 0.61; n = 23; P = 0.002). The low correlation coefficient indicates that the predictive value of the lathosterol: (VLDL + IDL + LDL) cholesterol ratio is limited when applied to individual rabbits. Cholesterol and simvastatin feeding reduced the group mean serum lathosterol:(VLDL + IDL + LDL) cholesterol ratio, whereas cholestyramine in the diet raised the group mean ratio in the NZW rabbits. We conclude that the serum lathosterol:(VLDL + IDL + LDL) cholesterol ratio may be an indicator of group mean rates of whole-body cholesterol synthesis in rabbits but may not yield reliable information on individual rabbits. The lathosterol:(VLDL + IDL + LDL) cholesterol ratio predicted that in hyperresponsive inbred rabbits, showing an excessive hypercholesterolemia after cholesterol feeding, baseline whole-body cholesterol synthesis is lower than in hyporesponsive rabbits. Addition of cholesterol to the diet caused a reduction of predicted cholesterol synthesis in hypo- but not in hyper-responsive rabbits.     

Comparative effects of simvastatin (MK-733) and pravastatin (CS-514) on hypercholesterolemia induced by cholesterol feeding in rabbits

The preventive effects of simvastatin (MK-733) and pravastatin (CS-514), 3-hydroxy-3-methylglutarylcoenzyme A (HMG-CoA) reductase inhibitors, on hypercholesterolemia induced by 0.25% cholesterol feeding were compared in rabbits. MK-733 (6, 2 and 0.7 mg/kg) was found to prevent the increase in serum total cholesterol levels dose-dependently. High dose CS-514 (18 mg/kg) also limited the increase in the cholesterol levels, but medium (6 mg/kg) and low doses (2 mg/kg) of CS-514 were ineffective in preventing it. MK-733 inhibited the increase in VLDL and LDL cholesterol levels dose-dependently. MK-733 suppressed the increase in serum phospholipid levels. MK-733 inhibited the accumulation of cholesterol in the liver. The high dose of CS-514 also limited it. High dose MK-733 (6 mg/kg) reduced the cholesterol concentration in gallbladder bile. Neither MK-733 nor CS-514 affected bile acid excretion in the gallbladder bile. High dose MK-733 decreased the lithogenic index. MK-733 increased the number of LDL receptors, and high dose CS-514 also increased it. The suppressive effect of CS-514 on serum cholesterol levels at 18 mg/kg was found to be less than that of MK-733 at 0.7 mg/kg.     

Measurment of rhesus monkey (Macaca mulatta) apolipoprotein B in serum by radioimmunoassay: comparison of immunoreactivities of rhesus and human low density lipoproteins.

A sensitive and specific double antibody radio-immunoassay for the major apolipoprotein (apoB) of rhesus (Macaca mulatta) serum very low density lipoprotein (VLDL) and low density lipoprotein (LDL) is described. The anti-serum was raised to LDL (d 1.030-1.040 g/ml) and the LDL(2) (d 1.020-1.050 g/ml) was labeled with (125)I by the chloramine-T or iodine monochloride method. The assay, which was sensitive to 0.02-0.5 micro g of LDL(2), had an inter-assay coefficient of variation of 4.5%. This assay was successfully used to measure apoB in the whole serum and low density lipoproteins of control monkeys maintained on a standard Purina monkey chow (PMC) diet and of three groups of monkeys fed atherogenic diets: an "average American diet," a 25% peanut oil and 2% cholesterol-supplemented PMC diet, and a 25% coconut oil and 2% cholesterol-supplemented PMC diet. The control monkeys (n = 13) had a serum cholesterol of 146 +/- 28 mg/dl and an apoB of 50 +/- 18 mg/dl. In the monkeys maintained on the atherogenic diets the serum apoB was elevated: 103 +/- 28 mg/dl (American), 102 +/- 35 mg/dl (peanut oil), and 312 +/- 88 mg/dl (coconut oil). The values for serum total cholesterol were 333 +/- 65 mg/dl (American), 606 +/- 212 mg/dl (peanut oil), and 864 +/- 233 mg/dl (coconut oil) and were elevated relative to controls (P < 0.001). For each of the diets, total serum cholesterol correlated with serum apoB (P < 0.001). The slopes of the regression lines of serum apoB vs. cholesterol for the monkeys on the PMC, American, and coconut oil diets were similar (m = 0.531, 0.401, and 0.359, respectively), but differed from that of monkeys on the peanut oil diet (m = 0.121). The immunoreactivities of rhesus and human LDL were compared using specific antisera raised against these antigens. In homologous assay systems, monkey and human LDL exhibited unique immunological determinants. The same results were obtained with the delipidated preparations of the two LDLs using antisera raised against either monkey or human apoB. Crossover studies using a heterologous tracer with each anti-serum resulted in the selection of a specific population of antibodies directed against antigenic sites shared by these two LDL species.     

Concentration and distribution of apolipoproteins A-I and E in normolipidemic, WHHL and diet-induced hyperlipidemic rabbit sera.

Two sandwich-type enzyme immunoassays have been developed to measure apolipoproteins A-I and E in rabbit serum. Specific goat antibodies were purified by affinity chromatography and used both for coating and for preparing antibody-peroxydase conjugates. The sensitivity of these assays is sufficient to allow studies of apo A-I and E distribution in lipoproteins fractionated by gel filtration from 50 microliters of serum. In WHHL rabbits, apo A-I is 5-fold lower (5.2 +/- 2.5 mg/dl) and apo E is 8-fold higher (9.9 +/- 3.5 mg/dl) than in normolipidemic rabbits (29 +/- 4.3 mg/dl and 1.3 +/- 0.5 mg/dl, respectively). In hyperlipidemic rabbits, fed 2 months on a 0.5% cholesterol diet, the apo A-I level was similar (32 +/- 12 mg/dl) to that of normolipidemic rabbits, but the apo E level is 12-fold higher (15.1 +/- 5.5 mg/dl). In addition, HDL particles were enriched with cholesterol and apo E. The bulk of apo E and cholesterol is located in large beta-VLDL in diet-induced hyperlipidemia, whereas they are mainly located in smaller size beta-VLDL in WHHL rabbits. In normolipidemic rabbits apo E occurs mainly in HDL, and cholesterol is distributed in the main three lipoprotein fractions VLDL, LDL and HDL. Interestingly, HDL of WHHL rabbit are deficient in apo A-I. These results are compatible with profound perturbations of lipoprotein composition and metabolism in atherogenic hyperlipidemia.     

Cholesterol homeostasis in guinea pigs fed saturated and polyunsaturated fat diets

Whole body sterol balance, hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity, hepatic low-density lipoprotein (LDL) receptor levels and net tissue cholesterol concentrations were determined in guinea pigs fed either a corn oil- or lard-based purified diet for 6-7 weeks. In comparison to the saturated lard diet, the polyunsaturated corn oil diet resulted in a 34% reduction in plasma total cholesterol levels (P less than 0.02) and a 40% lower triacylglycerol level (P less than 0.02). Feeding the corn oil diet altered very-low-density lipoprotein (VLDL) and LDL composition; the percent cholesterol ester in both particles was decreased and the relative percentages of VLDL triacylglycerol and LDL phospholipid increased. The ratio of surface to core components of LDL from corn oil-fed guinea pigs was significantly higher compared to LDL from animals fed lard. Dietary fat quality had no effect on fecal neutral or acidic steroid excretion, net tissue accumulation of cholesterol, whole body cholesterol synthesis or gallbladder bile composition. Consistent with these results was the finding that fat quality did not alter either expressed (non-phosphorylated) or total hepatic HMG-CoA reductase activities. The hepatic concentrations of free and esterified cholesterol were significantly increased in corn oil-fed animals, as were cholesterol concentrations in intestine, adipose tissue, muscle and total carcass. Analysis of receptor-mediated LDL binding to isolated hepatic membranes demonstrated that the polyunsaturated corn-oil based diet caused a 1.9-fold increase in receptor levels (P less than 0.02). The data indicate that the hypocholesterolemic effects of dietary polyunsaturated fat in the guinea pig are not attributable to changes in endogenous cholesterol synthesis or catabolism but rather may result from a redistribution of plasma cholesterol to body tissue due to an increase in tissue LDL receptors.     

Low-density lipoprotein catabolism in WHHL rabbits after partial ileal bypass surgery

The effect of partial ileal bypass surgery (PIB) on lipoprotein concentrations and compositions and on the catabolism of low-density lipoproteins (LDL) was studied in Watanabe heritable hyperlipidemic (WHHL) rabbits. After PIB, total serum cholesterol was 65% lower (6.22 +/- 1.58 vs. 17.24 +/- 3.22 mmol/l) and LDL cholesterol 81% lower (2.02 +/- 0.95 vs. 10.90 +/- 3.60 mmol/l) than in control WHHL rabbits; cholesteryl esters, expressed as percentage of mass, were 55% lower in the very-low and intermediate-density lipoprotein (VLDL + IDL) fractions, and 45% lower in LDL, whereas triacylglycerols were 89% higher in VLDL + IDL and 121% higher in LDL. The fractional catabolic rate (FCR) of LDL protein (apoLDL) from operated animals was 10% higher than that from controls in all animals (0.55 +/- 0.10 vs. 0.50 +/- 0.10 pools/day; P less than 0.01). The FCR of autologous apoLDL in PIB rabbits was 50% higher than that of autologous apoLDL in control rabbits (0.63 +/- 0.05 vs. 0.42 +/- 0.06 pools/day); this was not caused by induction of receptor-mediated clearance of LDL. The production rate of apoLDL after PIB in PIB rabbits was 50% lower compared to control apoLDL in controls (26.0 +/- 6.7 vs. 51.7 +/- 16.4 mg/kg per day). We conclude that PIB lowers LDL cholesterol in WHHL rabbits by a decreased production of LDL, by an increased non-specific clearance of LDL and by compositional changes, which lead to LDL particles containing less cholesterol.     

Increase in hepatic low-density lipoprotein receptor activity during pregnancy in Watanabe heritable hyperlipidemic rabbits; an animal model for familial hypercholesterolemia

In homozygous Watanabe heritable hyperlipidemic (WHHL) rabbits, the serum cholesterol level and serum low-density lipoprotein (LDL) level decreased from 562 +/- 76 (mean +/- S.E.) to 144 +/- 34 mg/dl and 410 +/- 56 to 90 +/- 25 mg/dl, respectively, during pregnancy, although the LDL receptor in this rabbit is genetically deficient. When Tyroxapol, which inhibits the degradation of very-low-density lipoprotein (VLDL), as well as Triton WR-1339, was injected into WHHL rabbits, the rate of the increase in serum cholesterol level in pregnant rabbits was not statistically different from that in non-pregnant rabbits. This result implied that the secretion rate of VLDL-cholesterol, the precursor of LDL-cholesterol, did not decrease during pregnancy. The amount of 125I-labeled LDL bound to LDL receptor was increased 1.8-fold in normal rabbits (from 29.3 +/- 4.3 to 52.3 +/- 4.6 ng/mg protein) and 12-fold in WHHL rabbits (from 0.5 +/- 0.2 to 6.0 +/- 0.7 ng/mg protein) during pregnancy. These results suggest that the decrease in serum cholesterol level in WHHL rabbits during pregnancy was associated with an increase in hepatic LDL receptor activity, which plays an important role in the regulation of serum cholesterol level.     

Effect of atorvastatin on plasma apoE metabolism in patients with combined hyperlipidemia

Atorvastatin, a synthetic HMG-CoA reductase inhibitor used for the treatment of hyperlipidemia and the prevention of coronary artery disease, significantly lowers plasma cholesterol and low-density lipoprotein cholesterol (LDL-C) levels. It also reduces total plasma triglyceride and apoE concentrations. In view of the direct involvement of apoE in the pathogenesis of atherosclerosis, we have investigated the effect of atorvastatin treatment (40 mg/day) on in vivo rates of plasma apoE production and catabolism in six patients with combined hyperlipidemia using a primed constant infusion of deuterated leucine. Atorvastatin treatment resulted in a significant decrease (i.e., 30-37%) in levels of total triglyceride, cholesterol, LDL-C, and apoB in all six patients. Total plasma apoE concentration was reduced from 7.4 +/- 0.9 to 4.3 +/- 0.2 mg/dl (-38 +/- 8%, P < 0.05), predominantly due to a decrease in VLDL apoE (3.4 +/- 0.8 vs. 1.7 +/- 0.2 mg/dl; -42 +/- 11%) and IDL/LDL apoE (1.9 +/- 0.3 vs. 0.8 +/- 0.1 mg/dl; -57 +/- 6%). Total plasma lipoprotein apoE transport (i.e., production) was significantly reduced from 4.67 +/- 0.39 to 3.04 +/- 0.51 mg/kg/day (-34 +/- 10%, P < 0.05) and VLDL apoE transport was reduced from 3.82 +/- 0.67 to 2.26 +/- 0.42 mg/kg/day (-36 +/- 10%, P = 0.057). Plasma and VLDL apoE residence times and HDL apoE kinetic parameters were not significantly affected by drug treatment. Percentage decreases in VLDL apoE concentration and VLDL apoE production were significantly correlated with drug-induced reductions in VLDL triglyceride concentration (r = 0.99, P < 0.001; r = 0.88, P < 0.05, respectively, n = 6). Our results demonstrate that atorvastatin causes a pronounced decrease in total plasma and VLDL apoE concentrations and a significant decrease in plasma and VLDL apoE rates of production in patients with combined hyperlipidemia.     

Compensatory mechanisms governing the concentration of plasma low density lipoprotein

To evaluate factors regulating the concentrations of plasma low density lipoproteins (LDL), apolipoprotein B metabolism was studied in nine Pima Indians (25 +/- 2 yr, 191 +/- 20% ideal wt) with low LDL cholesterol (77 +/- 7 mg/dl) and apoB (60 +/- 4 mg/dl) and in eight age- and weight-matched Caucasians with similar very low density lipoprotein (VLDL) concentrations, but higher LDL (cholesterol = 104 +/- 18; apoB = 82 +/- 10; P less than 0.05). Subjects received autologous 131I-labeled VLDL and 125I-labeled LDL, and specific activities of VLDL-apoB, intermediate density lipoprotein (IDL)-apoB, and LDL-apoB were analyzed using a multicompartmental model. Synthesis of LDL-apoB was similar (1224 +/- 87 mg/d in Pimas vs 1218 +/- 118 mg/d in Caucasians) but in Pimas the fractional catabolic rate (FCR) for LDL-apoB was higher (0.48 +/- 0.02 vs 0.39 +/- 0.04 d-1, P less than 0.05). In the Pimas, a much higher proportion of VLDL-apoB was catabolized without conversion to LDL (47 +/- 3 vs 30 +/- 5%, P less than 0.01). When all subjects were considered together, LDL-apoB concentrations were negatively correlated with both FCR for LDL-apoB (r = -0.79, P less than 0.0001) and the non-LDL pathway (r = -0.43, P less than 0.05). Also, the direct removal (non-LDL) path was correlated with VLDL-apoB production (r = 0.49, P = 0.03), and the direct removal pathway and FCR for LDL-apoB were correlated (r = 0.49, P = 0.03). In conclusion, plasma LDL appear to be regulated by both the catabolism of LDL and the extent of metabolism of VLDL without conversion to LDL; both of these processes may be mediated by the apoB/E receptor, and appear to increase in response to increasing VLDL production.     

Effects of pravastatin and cholestyramine on products of the mevalonate pathway in familial hypercholesterolemia

Patients with heterozygous familial hypercholesterolemia (n = 12) were treated either with pravastatin, a specific inhibitor of HMG-CoA reductase, or cholestyramine, followed by a period of combined treatment with both drugs. Initially, these patients had increased serum levels of low density lipoprotein (LDL) cholesterol (8.77 +/- 0.48 mmol/l; SEM), lathosterol (5.32 +/- 0.60 mg/l), and ubiquinone (0.76 +/- 0.09 mg/l), while the serum dolichol concentration was in the normal range. Cholestyramine treatment (n = 6) decreased the levels of LDL cholesterol (-32%) and increased lathosterol (+125%), but did not change dolichol or ubiquinone levels in a significant manner. Pravastatin treatment (n = 6) decreased LDL cholesterol (-27%), lathosterol (-46%), and ubiquinone (-29%). In this case, the amount of dolichol in serum also showed a small but statistically insignificant decrease (-16%) after 12 weeks of treatment. Combined treatment with cholestyramine and pravastatin (n = 6) resulted in changes that were similar to, but less pronounced than, those observed during pravastatin treatment alone. In no case was the ratio between ubiquinone and LDL cholesterol reduced. Possible effects on hepatic cholesterol, ubiquinone, and dolichol concentrations were studied in untreated (n = 2), cholestyramine-treated (n = 2), and pravastatin-treated (n = 4) gallstone patients and no consistent changes could be observed. The results indicate that treatment with pravastatin in familial hypercholesterolemia decreases serum ubiquinone levels in proportion to the reduction in LDL cholesterol.     

Influence of experimental diets on cholesterol and triglyceride levels of rabbit blood serum lipoproteins

Groups of rabbits were fed for six weeks various diets: standard died + ethanol, high-cholesterol diet and a high-cholesterol + ethanol one. During the next six weeks every diet was supplemented with a fresh vegetable (carrot). Cholesterol and triglycerides were determined in the whole serum and in lipoprotein fractions. In rabbits fed standard diet ethanol caused a moderate elevation of VLDL cholesterol and triglyceride and LDL cholesterol levels. In animals on high-cholesterol diet cholesterol and triglyceride concentrations in these fractions were very high. Simultaneous consumption of large amounts of cholesterol and of ethanol resulted in a greater rise of cholesterol concentration in the whole serum and in VLDL and LDL fraction than did high-cholesterol diet alone. Addition of carrot caused a pronounced reduction of serum cholesterol concentration in animals fed all kinds of diets. The reduction concerned mainly VLDL.     

CD45: a leukocyte-specific member of the protein tyrosine phosphatase family.

In a recent study from this laboratory, rhesus monkeys fed a 90% palm oil/10% soybean oil-containing diet (PS), rich in 16:0 and 18:1 fatty acids, had decreased total and LDL cholesterol concentrations compared to monkeys fed a 90% coconut oil/10% soybean oil-containing diet (CS), rich in 12:0 and 14:0 fatty acids. To investigate the metabolic basis of these changes, homologous 125I-VLDL and 131I-LDL were injected simultaneously into eight monkeys (four per dietary group). Analysis of apo B specific activity curves revealed that PS monkeys had an increased pool size of VLDL apo B (P less than 0.02), a 3-fold increase in the total VLDL apo B transport rate (P less than 0.001), a decreased pool size of LDL apo B (P less than 0.01) and a 2-fold decrease in the total transport rate of LDL apo B (P less than 0.001), while the irreversible FCR for VLDL apo B and LDL apo B was similar between dietary groups. PS monkeys derived a greater percentage of LDL apo B from VLDL catabolism resulting in a greater transport rate of LDL apo B from VLDL catabolism (P less than 0.055), in comparison to CS monkeys. For CS monkeys the proportion as well as the amount of LDL apo B derived from VLDL-independent catabolism (i.e., LDL apo B derived from sources other than VLDL catabolism) was higher (P less than 0.001) than the values obtained in PS monkeys. In both dietary groups the proportion of VLDL apo B converted to LDL apo B was similar, although the absolute amount was higher for the PS monkeys (P less than 0.06). The proportion of VLDL apo B directly removed from the circulation was similar for both dietary groups, with the absolute amount being higher for the PS monkeys (P less than 0.001). Consistent with the lower pool size of LDL apo B and the higher pool size of VLDL apo B observed in PS monkeys, plasma and LDL cholesterol concentrations tended to be lower, whereas plasma triacylglycerol and VLDL cholesterol concentrations tended to be higher, but these changes were not statistically significant. Although total apo B and VLDL apo B transport rates were increased 2-3-fold in PS monkeys, LDL apo B concentration was reduced by 40% (P less than 0.02) attributed to a significant reduction in the mass and proportion of LDL apo B derived independent of VLDL catabolism.(ABSTRACT TRUNCATED AT 400 WORDS)     

Lovastatin therapy reduces low density lipoprotein apoB levels in subjects with combined hyperlipidemia by reducing the production of apoB-containing lipoproteins: implications for the pathophysiology of apoB production

We investigated the metabolism of very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL), and low density lipoprotein (LDL) apolipoprotein B (apoB) in seven patients with combined hyperlipidemia (CHL), using 125I-labeled VLDL and 131I-labeled LDL and compartmental modeling, before and during lovastatin treatment. Lovastatin therapy significantly reduced plasma levels of LDL cholesterol (142 vs 93 mg/dl, P less than 0.0005) and apoB (1328 vs 797 micrograms/ml, P less than 0.001). Before treatment, CHL patients had high production rates (PR) of LDL apoB. Three-fourths of this LDL apoB flux was derived from sources other than circulating VLDL and was, therefore, defined as "cold" LDL apoB flux. Compared to baseline, treatment with lovastatin was associated with a significant reduction in the total rate of entry of apoB-containing lipoproteins into plasma in all seven CHL subjects (40.7 vs. 25.7 mg/kg.day, P less than 0.003). This reduction was associated with a fall in total LDL apoB PR and in "cold" LDL apoB PR in six out of seven CHL subjects. VLDL apoB PR fell in five out of seven CHL subjects. Treatment with lovastatin did not significantly alter VLDL apoB conversion to LDL apoB or LDL apoB fractional catabolic rate (FCR) in CHL patients. In three patients with familial hypercholesterolemia who were studied for comparison, lovastatin treatment increased LDL apoB FCR but did not consistently alter LDL apoB PR. We conclude that lovastatin lowers LDL cholesterol and apoB concentrations in CHL patients by reducing the rate of entry of apoB-containing lipoproteins into plasma, either as VLDL or as directly secreted LDL.     

Oxidative modification of lipoproteins in hypertriglyceridemic patients and hypercholesterolemic rabbits in vivo

Many lines of evidence suggest that LDL is oxidized in vivo and that Ox-LDL is present in the artery wall. But the oxidation of VLDL and HDL in vivo has not yet been reported. In this study, the oxidative modification of serum LDL, VLDL, and HDL in patients with endogenous hypertriglyceridemia (HTG) and in serum of rabbits fed on high cholesterol diet were made. The serum LDL, VLDL and HDL were isolated by the density gradient ultracentrifugation. The oxidative modification of LDL, VLDL and HDL were identified by agarose eletrophoresis, absorbance at 234 nm and fluorescence of TBARS. The results showed that serum TC, TG and TBARS in the HTG group (n= 25) and in rabbits fed with a high fat diet (for 12 weeks, n = 8) were significantly higher than those of the corresponding control groups (normal subjects, n = 25; rabbits fed with a normal diet, n = 8; p < 0.01). The electrophoretic mobilities of LDL, VLDL and HDL were increased when compared with the controls, and absorbance at 234 nm and TBARS of LDL, VLDL and HDL in the HTG group and in the high fat diet rabbits were significantly higher than those of the controls (p < 0.01). These results suggest that not only LDL but also VLDL and HDL were oxidatively modified in vivo in the patients with HTG and in the rabbits fed with a high cholesterol diet.     

Preventive effect of pravastatin sodium, a potent inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, on coronary atherosclerosis and xanthoma in WHHL rabbits

In this paper, we examined whether the development of atherosclerosis in the Watanabe heritable hyperlipidemic (WHHL) rabbit, an animal model of familial hypercholesterolemia in man, could be prevented by the reduction of serum cholesterol levels. Pravastatin sodium (the generic name of CS-514), a potent inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, was used as a cholesterol-lowering drug. The drug was administered orally to 12 WHHL rabbits (2-3 months old) at a dose of 50 mg/kg per day for 24 weeks, and 13 animals were given water as control. In the treated group, serum cholesterol, phospholipid and triacylglycerol levels were significantly reduced by 28%, 32% and 16%, respectively, as compared with those of the control group. Although the prevention of development of the aortic atherosclerosis was not significant, the progression of coronary atherosclerosis was significantly prevented. The incidence of atherosclerosis in four main coronary arteries was reduced from 42% (control group) to 19% (treated group, P less than 0.01), and the development of lesion of coronary arteries evaluated by area of lesion was reduced from 19.7% (control group) to 9.1% (treated group, P less than 0.05). Histopathological findings supported the above observations. In addition, development of xanthoma in digital joints was also reduced from 90.4% (control group) to 58.3% (treated group, P less than 0.005). These results suggest that the development of coronary atherosclerosis and xanthoma in WHHL rabbit was reduced by continuous reduction of serum cholesterol levels treated with pravastatin sodium.