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Plasma squalene as an index of cholesterol synthesis.

1. Seven subjects were studied before and after the rate of cholesterol synthesis was altered with drugs or dietary cholesterol. 2. The rate at which plasma free cholesterol was formed from squalene during constant infusions of radioactive mevalonate increased with colestipol treatment, decreased with clofibrate treatment and decreased when cholesterol was added to the diet. The plasma squalene concentration showed corresponding changes, confirming that its measurement may qualitatively define changes in cholesterol synthesis. 3. The mean plasma squalene concentration in seven hypertriglyceridaemic, slightly overweight subjects was significantly higher than in six hypercholesterolaemic subjects, which is consistent with other evidence for increased cholesterol synthesis in hypertriglyceridaemia.

Adult↗

Serial quantitative coronary angiography and coronary events.

BACKGROUND: Although assessment of progression of atherosclerosis by quantitative coronary angiography (QCA) is used as a surrogate for coronary events, no validation study has compared the several QCA measures used. METHODS AND RESULTS: The Cholesterol Lowering Atherosclerosis Study was a clinical trial testing the efficacy of colestipol-niacin on the progression of coronary atherosclerosis. Baseline/2-year coronary angiograms were obtained on 156 men with prior coronary artery bypass graft surgery. Changes in percent diameter stenosis and minimum lumen diameter (both measured in coronary lesions and segments) and coronary segment measures of average diameter, percent involvement, and vessel edge roughness were measured by QCA. Coronary events ascertained over 12 years of follow-up included myocardial infarction (MI), coronary death, and coronary artery revascularizations. Proportional hazards models evaluated the relation between QCA change measures and coronary events. Changes in percent diameter stenosis and minimum lumen diameter of coronary artery lesions were significantly related to the risk of MI/coronary death. All QCA measures were significantly related to the risk of any coronary event. Relative risks for each QCA measure were of similar magnitude when estimated separately within each treatment group. Change in minimum lumen diameter of lesions was the only measure independently associated with the risk of coronary events. CONCLUSIONS: All QCA measures of progression of coronary artery disease were related to all coronary events (including revascularizations). Only QCA measures of lesion progression were related to MI/coronary death. QCA measures of lesion change may be better surrogate end points for "hard" coronary events than measures of change in coronary segments.

Adult↗

Regulatory role for hepatic low density lipoprotein receptors in vivo in the dog.

Liver membranes from young beagle dogs were found to possess binding sites that resemble the low density lipoprotein (LDL) receptors originally described in cultured human fibroblasts. Treatment of the dogs with colestipol (a bile acid sequestrant) and mevinolin (a cholesterol synthesis inhibitor) produced a 3-fold increase in LDL binding activity. This increase correlated with a 2-fold increase in the fractional catabolic rate for intravenously administered human or canine 125I-labeled LDL, suggesting that the increased hepatic receptors were responsible for the enhanced clearance of LDL from plasma. The hepatic lipoprotein receptors of control and drug-treated dogs resembled human fibroblast LDL receptors in that they bound apoprotein E-containing lipoproteins, such as very low density lipoproteins and a subfraction of high density lipoproteins (HDL1), with 10-fold higher affinity than the apoprotein B-containing lipoprotein LDL; failed to bind canine HDL2 and human HDL3, which are devoid of apoproteins B and E; failed to bind methylated LDL; required calcium; and were destroyed by Pronase. Treatment of dogs with mevinolin not only increased the fractional catabolic rate for LDL but also reduced the synthetic rate for the lipoprotein. The current data suggest that the liver of dogs contains functional LDL receptors that are susceptible to metabolic regulation and that a drug-induced increase in the activity of these receptors can contribute to a lowering of plasma levels of LDL-cholesterol.

Animals↗

Independent regulation of sterol regulatory element-binding proteins 1 and 2 in hamster liver.

Two sterol regulatory element-binding proteins (SREBPs, designated SREBP-1 and SREBP-2), each approximately 1150 amino acids in length, are attached to membranes of the endoplasmic reticulum and nuclear envelope in human and hamster tissue culture cells. In the absence of sterols, soluble fragments of approximately 470 amino acids are released from both proteins by proteolytic cleavage. The soluble fragments enter the nucleus, where they bind to sterol regulatory elements in the promoters of genes encoding the low density lipoprotein receptor and 3-hydroxy-3-methylglutaryl CoA synthase, thereby activating transcription. Proteolytic processing of both SREBPs is blocked coordinately by sterol overloading and enhanced coordinately when sterols are depleted by treatment with an inhibitor of cholesterol synthesis. In contrast to these findings in cultured cells, the current data show that SREBP-1 and -2 are not coordinately regulated in hamster liver. In untreated animals the soluble fragment of SREBP-1, but not of SREBP-2, was detected by immunoblotting of a liver nuclear extract. Depletion of sterols by treatment with a bile acid-binding resin (colestipol) and a cholesterol synthesis inhibitor (mevinolin) led to a marked increase in the nuclear form of SREBP-2 and a reciprocal decline in the nuclear form of SREBP-1. These findings suggest that SREBP-1 is responsible for basal transcription of the low density lipoprotein receptor and 3-hydroxy-3-methylglutaryl CoA synthase genes in hamster liver and that SREBP-2 is responsible for the increased transcription that follows sterol depletion with a bile acid-binding resin and a cholesterol synthesis inhibitor.

Animals↗

Regression of tendon xanthomas in patients with familial hypercholesterolemia treated with lovastatin.

Plasma concentrations of total and low-density lipoprotein cholesterol are increased twofold to threefold in patients with heterozygous familial hypercholesterolemia. This sustained increase leads to accelerated rates of cholesterol deposition in the coronary arteries and to the development of tendon xanthomas. To assess whether hypolipidemic therapy with lovastatin, alone and in combination therapy with colestipol hydrochloride or nicotinic acid, results in regression of lipid deposits in the tendons of these patients, we have measured Achilles tendon diameters by xeroradiography before and after treatment. In 20 patients treated for a mean of 43 months (during which time plasma cholesterol concentrations decreased from 430 to 247 mg/dL), the diameter of both the left and right Achilles tendons measured at three different locations decreased by 0.55 to 1.5 mm. Larger reductions were seen in the tendons of seven of these patients who were treated for a mean of 64 months and whose mean concentrations of cholesterol fell from 488 to 279 mg/dL. We conclude that effective long-term hypolipidemic therapy leads to diminution in the size of Achilles tendon xanthomas in patients with heterozygous familial hypercholesterolemia and that such therapy is associated with mobilization of tissue stores of cholesterol in these patients.

Achilles Tendon↗

Clinical utility of bile acid sequestrants in the treatment of dyslipidemia: a scientific review.

Bile acid sequestrants (BAS) continue to command a position in the treatment of dyslipidemias 25 years after their introduction. Partial diversion of the enterohepatic circulation using BAS depletes the endogenous bile acid pool by approximately 40%, thus stimulating an increase in bile acid synthesis from cholesterol, which lowers low-density lipoprotein cholesterol (LDL-C) by 15 to 26%. Three BAS are currently used for treating hypercholesterolemia in the United States: the conventional sequestrants, cholestyramine and colestipol, and the specifically engineered BAS, colesevelam hydrochloride (HCl). Compared with conventional BAS, colesevelam HCl has enhanced specificity, greater affinity, and higher capacity for binding bile acids, due to its polymer structure engineered for bile acid sequestration. BAS are not absorbed by the intestine and thus have no systemic drug-drug interactions, but may interfere with the absorption of some drugs. Although BAS monotherapy effectively lowers LDL-C, combination therapy, especially with BAS and statins, is becoming increasingly common due to complementary mechanisms of action. Low-dose statin plus BAS combinations lead to greater or similar LDL-C reductions compared with high-dose statin monotherapy and may have a better safety profile. Combinations of BAS with nonstatin lipid-lowering agents, including niacin, fibrates, and cholesterol absorption inhibitors, may be useful in those patients who require intensive lipid-lowering, but are statin intolerant. BAS treatment can significantly reduce coronary artery disease (CAD) progression and the risk of CAD-associated outcomes. It is also becoming clear that BAS and other therapies that manipulate the bile acid synthetic pathway may have clinically useful therapeutic effects on other metabolic disorders including type 2 diabetes.

Allylamine↗

Treatment of the arthropathy of familial hypercholesterolaemia.

A 29-year-old woman suffering from the arthropathy of familial hypercholesterolaemia was treated with a fat-modified low-cholesterol diet and colestipol. Symptomatic improvement occurred in association with a moderate reduction in the plasma cholesterol concentration. The pathogenesis of the musculoskeletal features of this disease is reviewed, and the implications of this patient's therapeutic response are explored.

Adult↗

Role of bile acids and bile acid binding agents in patients with collagenous colitis.

BACKGROUND: In a retrospective study bile acid malabsorption was observed in patients with collagenous colitis. AIMS: To study the occurrence of bile acid malabsorption and the effect of bile acid binders prospectively in patients with chronic diarrhoea and collagenous colitis. METHODS: Over 36 months all patients referred because of chronic diarrhoea completed a diagnostic programme, including gastroscopy with duodenal biopsy, colonoscopy with biopsies, and the (75)Se-homocholic acid taurine ((75)SeHCAT) test for bile acid malabsorption. Treatment with a bile acid binder (cholestyramine in 24, colestipol in three) was given, irrespective of the results of the (75)SeHCAT test. RESULTS: Collagenous colitis was found in 28 patients (six men, 22 women), 27 of whom had persistent symptoms and completed the programme. Four patients had had a previous cholecystectomy or a distal gastric resection. The (75)SeHCAT test was abnormal in 12/27 (44%) of the collagenous colitis patients with (75)SeHCAT values 0.5-9.7%, and normal in 15 patients (56%). Bile acid binding treatment was followed by a rapid, marked, or complete improvement in 21/27 (78%) of the collagenous colitis patients. Rapid improvement occurred in 11/12 (92%) of the patients with bile acid malabsorption compared with 10/15 (67%) of the patients with normal (75)SeHCAT tests. CONCLUSION: Bile acid malabsorption is common in patients with collagenous colitis and is probably an important pathophysiological factor. Because of a high response rate without serious side effects, bile acid binding treatment should be considered for collagenous colitis, particularly patients with bile acid malabsorption.

Adult↗

Localization of cholesterol synthesis in the small intestine of diabetic rats.

Previous studies have demonstrated that cholesterol synthesis is increased twofold in the small intestine of diabetic animals. The present study demonstrates that the stimulation of small intestinal cholesterol synthesis by diabetes is a generalized phenomenon occurring in all segments of the small intestine. Quantitatively, in control animals the proximal two segments of the small intestine account for the majority of the total small intestinal cholesterol synthesis, whereas in the diabetic animals, because of the generalized stimulation in cholesterogenesis, the contribution of the terminal segments to total small intestinal cholesterol synthesis is of increased importance. The various manipulations that regulate cholesterol synthesis in the small intestine of diabetic animals also affect cholesterol synthesis in all portions of the small intestine. In diabetic animals cholesterol feeding and the limitation of food intake decrease cholesterol synthesis in the total small intestine and in all segments of the small intestine. Conversely, colestipol feeding increases cholesterol synthesis in all segments of the small intestine. These results demonstrate that, despite the obvious structural, functional, and environmental differences among the various segments of the small intestine, the stimulation of cholesterol synthesis that occurs secondary to diabetes mellitus is a generalized phenomenon. Similarly, the factors that regulate small intestinal cholesterol synthesis do so in a generalized manner.

Animals↗

Review of clinical studies of bile acid sequestrants for lowering plasma lipid levels.

Both alone and in combination with other lipid-lowering drugs, the bile acid sequestrants cholestyramine and colestipol, are excellent agents for lowering circulating low-density lipoprotein (LDL) cholesterol levels. They have been shown to lower the incidence of new coronary events and to retard the progression of coronary atherosclerosis. They also induce qualitative changes in lipoproteins whose significance requires further investigation but may be of significance in coronary disease prevention. While side effects may be bothersome for some patients, they can generally be managed effectively. In particular, modest lowering of dosage may preserve considerable LDL cholesterol lowering and virtually eliminate side effects. Sequestrants appear to be among the safest and most effective drugs in the cholesterol-lowering armamentarium.

Cholestyramine Resin↗

Prediction of angiographic change in native human coronary arteries and aortocoronary bypass grafts. Lipid and nonlipid factors.

A within-group risk factor analysis was conducted to predict angiographic change in the Cholesterol Lowering Atherosclerosis Study, a randomized, placebo-controlled trial of colestipol plus niacin therapy in men with previous coronary bypass surgery. Global angiographic change, including both native coronary arteries and bypass grafts after 2 treatment years, was the end point. Risk factors included on-trial clinical measures, plasma lipids, lipoproteins, and apolipoproteins. Univariate analysis indicated that risk factors previously observed by others in epidemiologic investigation of ischemic heart disease--total cholesterol, LDL cholesterol, non-HDL cholesterol, triglycerides, apolipoprotein B, and diastolic blood pressure--had significant effects in the placebo-treated group. Univariate analysis indicated significant effects of apolipoprotein C-III in drug- and placebo-treated groups. Multivariate analysis indicated the predominant risk factor predicting the probability of global coronary progression was non-HDL cholesterol in placebo-treated subjects and the content of apolipoprotein C-III in high density lipoproteins of drug-treated subjects. Both drug- and placebo-treated group findings point to an important role for triglyceride-rich lipoproteins in progression and regression of human atherosclerosis.

Apolipoprotein C-III↗

Levels of soluble cell adhesion molecules in patients with dyslipidemia.

BACKGROUND: Increased expression of cell adhesion molecules (CAMs) on the vascular endothelium has been postulated to play an important role in atherogenesis. Both in vitro and in vivo studies have suggested that dyslipidemia may increase expression of CAMs. METHODS AND RESULTS: To determine whether dyslipidemia is associated with increased expression of CAMs, we examined the levels of soluble intercellular adhesion molecule 1 (sICAM-1), soluble vascular cell adhesion molecule 1 (sVCAM-1), and soluble E-selectin (sE-selectin) in individuals with either hypercholesterolemia or hypertriglyceridemia and in control subjects matched for age and sex. Patients with hypertriglyceridemia had significantly higher levels of sVCAM-1 (739 +/- 69 ng/mL) compared with patients with hypercholesterolemia (552 +/- 63 ng/mL) and control subjects (480 +/- 56 ng/mL). Levels of sICAM-1 were significantly increased in both the hypercholesterolemic and hypertriglyceridemic groups (298 +/- 29 and 342 +/- 31 ng/mL, respectively) compared with the control group (198 +/- 14 ng/mL). Levels of sE-selectin were significantly increased in hypercholesterolemic patients (74 +/- 9 ng/mL) compared with control subjects (48 +/- 5 ng/mL). Ten hypercholesterolemic patients were treated aggressively with atorvastatin alone or a combination of colestipol and either atorvastatin or simvastatin for a mean of 42 weeks and had an average LDL cholesterol reduction of 51%. Comparison of soluble CAMs before and after treatment showed a significant reduction only in sE-selectin (77 +/- 11 versus 56 +/- 6 ng/mL, P < or = .03) but not for sVCAM-1 or sICAM-1. CONCLUSIONS: Although severe hyperlipidemia is associated with increased levels of soluble CAMs, aggressive lipid-lowering treatment had only limited effects on the levels. Increased levels of soluble CAMs in patients with hyperlipidemia may be a marker for atherosclerosis.

Anticholesteremic Agents↗

Lack of effect of lovastatin therapy on the parameters of whole-body cholesterol metabolism.

UNLABELLED: The effects of lovastatin therapy on the parameters of body cholesterol metabolism were explored in nine hypercholesterolemic patients. Long-term cholesterol turnover studies were performed before therapy, and were repeated after 15 mo of lovastatin therapy (40 mg/d) while continuing on therapy. The major question addressed was whether a reduction in plasma cholesterol level with lovastatin would be associated with a reduction in the whole-body production rate of cholesterol or with the sizes of exchangeable body cholesterol pools as determined by the three-pool model of cholesterol turnover. The mean plasma cholesterol level decreased 19.4% (from 294 to 237 mg/dl), and low-density lipoprotein cholesterol decreased 23.8% (from 210 to 159 mg/dl) with lovastatin therapy. Changes in high-density lipoprotein cholesterol level were not significant. The cholesterol production rate did not change significantly with therapy (1.09 +/- 0.10 [mean +/- S.D.] vs. 1.17 +/- 0.09 g/d). By comparison, colestipol and niacin treatment in three other subjects more than doubled the cholesterol production rate (1.14 +/- 0.28 vs. 2.42 +/- 0.34 g/d). Thus, hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase inhibition by lovastatin at the therapeutic dose used here did not change the steady-state rate of whole-body cholesterol synthesis. Despite the changes in plasma cholesterol levels, no significant changes were seen in the values of M1, of M3 or of Mtot, the sizes of the pools of rapidly, of slowly, and of total body exchangeable cholesterol. CONCLUSION: lovastatin therapy to lower plasma cholesterol does not lead to corresponding reductions in body cholesterol pools or to a reduction in the rate of whole-body cholesterol synthesis. In the new steady state that exists during long-term lovastatin therapy, along with increased expression of the genes for HMG-CoA reductase and the LDL receptor, the body compensates for the effects of the drug so that cholesterol production rate and tissue pool sizes are not changed from pretreatment values.

Adult↗

Blind comparison of patient preference for Flavored Colestid Granules and Questran Light.

OBJECTIVE: To compare the sensory and mixability characteristics of Flavored Colestid Granules (a new colestipol formulation) with Questran Light (the most recent cholestyramine formulation). METHODOLOGY: Seventy-two nonsmoking adults between the ages of 25 and 64 years were enrolled in the study. Subjects assessed the sensory and mixability characteristics of each product in chilled bottled water and orange juice after at least a one-hour fast. Products were administered in a double-blind, randomized fashion. The sensory characteristics that were rated included overall rating, aftertaste, appearance, aroma, color, consistency, flavor, sweetness, mouthfeel, and thickness. Each characteristic was rated with a nine-point hedonic scale. Mixability of the products was assessed on a five-point scale. Subjects also were asked to choose which product they preferred as to sensory and mixability characteristics in each vehicle. RESULTS: Fifty-three of the 72 subjects preferred the sensory characteristics of Flavored Colestid Granules in water (p < 0.001). Questran Light was preferred by 61 subjects when mixed in orange juice (p < 0.001). The sensory characteristic rating scores also supported subject preferences for Flavored Colestid Granules in water and Questran Light in orange juice. Mixability of Flavored Colestid Granules was rated significantly better (p < 0.001) than Questran Light in water. There was no significant difference for mixability between the products in orange juice. CONCLUSIONS: Questran Light was significantly preferred on a sensory basis when mixed in orange juice. Flavored Colestid Granules was significantly preferred over Questran Light for both sensory and mixability characteristics with water as the vehicle.

Adult↗

Impact of pharmacy counseling on compliance and effectiveness of combination lipid-lowering therapy in patients undergoing coronary artery revascularization: a randomized, controlled trial.

This randomized, controlled trial evaluated the impact of personalized follow-up on compliance rates in high-risk patients receiving combination lipid-lowering therapy over 2 years. A random sample of 30 patients 7-30 days after cardiac surgery had baseline fasting low-density lipoprotein levels higher than 130 mg/dl. All patients received lovastatin 20 mg/day and colestipol 5 g twice/day. Weekly telephone contact was made with each patient for 12 weeks. Short- and long-term compliance was assessed by pill and packet counts and refill records. Compliance and lipid profile results were significantly better in the intervention group (p<0.05) up to 2 years after the start of therapy than in the control group for all parameters except high-density lipoprotein. However, this effect was not apparent during the first 12 weeks of therapy. Short-term telephone follow-up favorably affected compliance and lipid profile results up to 2 years after start of therapy.

Aged↗

Cost-effectiveness of drug therapy for hypercholesterolaemia: a review of the literature.

In this article we review published studies of the cost-effectiveness of drug therapy for hypercholesterolaemia to take stock of the principal findings that have been reported to date. We identified 9 studies that met all criteria for inclusion in our review, including 3 of bile-acid sequestrants (cholestyramine, colestipol), 2 of HMG-CoA reductase inhibitor (lovastatin), and 4 that considered both an HMG-CoA reductase inhibitor (simvastatin) and a bile-acid sequestrant (cholestyramine). While these studies were largely consistent in methodological approach, some differences were noted in the costs attributed to drug therapy. The cost-effectiveness of therapy with bile-acid sequestrants was found to range from $100 000 to $209 000 per year of life saved (1991 $US) for middle-aged men (42 to 55 years of age) with moderately high cholesterol levels (280 to 290 mg/dl) and otherwise average coronary risk characteristics. Corresponding cost-effectiveness ratios that have been reported for lovastatin range from $64 000 to $82 000, while those for simvastatin range from $45 000 to $65 000. Studies to date therefore suggest that therapy with HMG-CoA reductase inhibitors (i.e. lovastatin and simvastatin) is substantially more cost-effective than treatment with bile-acid sequestrants.

Age Factors↗

Binding of bile acids to anion-exchanging drugs in vitro.

Equal amounts of anion exchanger of the drugs, Secholex, Colestipol, Cuemid, and Questran, were incubated at 37 degrees C with human duodenal fluid containing about 7 mM total bile acid. Binding of bile acid to Qestran, which contains about 45% cholestyramine, was fastest: concentration of unbound bile acid after 2 hours was less than 3 mM compared to about 5 mM in the solutions incubated with the other drugs, including Cuemid, which contains about 83% cholestyramine. After 24 hours, differences were less marked, but binding to Qestran was still greatest. Glycocholic acid was least efficiently bound, especially to Secholex and Cuemid. The differences in rates of binding were unaffected by preincubation of the drugs with 1 N HCl to simulate stomach conditions. Although differences between the cholestyramine components of Cuemid and Questran are not ruled out, it is possible that one or more of the other components of Questran significantly affect the in vitro binding of bile acids. Cholestryramine in the form of Questran may be the drug of choice in the treatment of hypercholesterolemia, in which reduction of the bile acid pool is desirable. In cholegenic diarrhoea, however, one of the drugs with lower affinity for glycocholic acid may be preferable.

Acacia↗

Influence of combined therapy with mevinolin and interruption of bile-acid reabsorption on low density lipoproteins in heterozygous familial hypercholesterolemia.

Patients with heterozygous familial hypercholesterolemia have a 50% deficiency of receptors for plasma low density lipoproteins (LDL) that induces a marked increase in plasma LDL levels. Two therapeutic measures that seem to increase the synthesis of LDL receptors are interruption of the enterohepatic circulation of bile acids with either bile-acid sequestrants or the ileal-exclusion operation, and competitive inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase with mevinolin or compactin. To determine the effectiveness of this combination and the mechanisms of lowering LDL levels, we measured turnover rates of LDL apoprotein (apo-LDL) before and during treatment with mevinolin and colestipol in eight patients with heterozygous familial hypercholesterolemia. Drug therapy reduced LDL cholesterol levels by an average of 52%; this response was due to a 40% increase in fractional catabolic rate of apo-LDL and a 26% decrease in its production rate. A similar response was obtained in two patients who had previously had an ileal-exclusion operation for severe hypercholesterolemia and who were treated with mevinolin.

Adult↗