The treatment of hyperlipidemia

A network analysis of the propagation of evidence regarding the effectiveness of fat-controlled diets in the secondary prevention of coronary heart disease (CHD): Selective citation in reviews

OBJECTIVE

To examine how the first randomised controlled trials (RCTs) evaluating the efficacy of cholesterol-lowering diets in the secondary prevention of coronary heart disease were interpreted in reviews of the literature prior to the National Institutes of Health consensus conference in 1984.

DESIGN

Claim-specific citation network analysis was used to study the network of citations between reviews and RCTs over a defined period (1969-1984). RCTs were identified and classified according to whether their conclusions supported or opposed the use of dietary fat modification/restriction in the secondary prevention of coronary heart disease. Each review published in this period that cited any of the RCTs was classified as supportive, neutral, or unsupportive to the use of dietary fat modification based on a quotation analysis of its evaluation of the findings of these RCTs. Citation bias and underutilisation were detected by applying a comparative density measure, in-degree centrality, and out-degree in a series of sub-graph analyses.

RESULTS

In total, 66 unique publications were identified (four RCTs-one supportive, three unsupportive; 62 reviews-28 supportive, 17 neutral, 17 unsupportive). On average, supportive reviews underutilised the available RCTs to a greater degree than other reviews. Amongst the supportive group, citation bias was common-23 (82%) reviews cited only the one RCT that was supportive.

CONCLUSION

Most reviews that disseminated a supportive evaluation of the results of RCTs in the context of secondary prevention cited only data that supported this position.

Is atherosclerosis exclusively a postprandial phenomenon?

1. Atherosclerosis begins with the deposition of cholesterol in arterial tissue that is thought to be derived from circulating lipoproteins. There is considerable evidence implicating low density lipoprotein (LDL) as a primary source of plaque cholesterol and, consequently, there are many articles that deal with various aspects of LDL metabolism. 2. Postprandial lipoproteins (i.e. chylomicrons transporting dietary fats) are also considered pro-atherogenic; however, it is less clear whether their involvement in arterial cholesterol deposition is direct or follows modulation of LDL metabolism. 3. In order to provoke discussion, this article is presented in a manner that suggests atherosclerosis to be exclusively a postprandial phenomenon; that is, we have raised the possibility that LDL is non-atherogenic.

Prolongation of platelet survival in hypercholesterolaemic rabbits by CGS 12970 (3-methyl-2-(3-pyridyl)-1 indoleoctanoic acid) and dazoxiben

In rabbits receiving a normal laboratory diet the platelet half-life was 40.4 +/- 2.5h (mean +/- S.D., n = 35). In animals fed the cholesterol-enriched diet for 12 weeks the platelet half-life was reduced to 31.6 +/- 3.6h (mean +/- S.D., n = 35). Treatment of cholesterol-fed animals with a single daily dose of CGS 12970 (a long acting inhibitor of thromboxane synthase) normalised the platelet half-life. Single daily doses of the relatively shorter acting thromboxane synthase inhibitors (CGS 13080 and dazoxiben) failed to correct the reduced platelet survival. However, twice daily dosing with dazoxiben was effective. The cyclooxygenase inhibitors, aspirin and sulphinpyrazone, failed to correct the reduced platelet survival.

Increased fibrinogen binding to platelets from patients with familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a disease marked by a high incidence of thrombotic episodes and hypersensitivity of the patients' platelets to naturally occurring aggregating agents. Prostaglandin/thromboxane (PG/Tx) formation, adenosine 5'-diphosphate (ADP) secretion, and fibrinogen binding to platelets are all believed to be involved in the mechanisms of platelet aggregation. Therefore, we studied the interrelated roles of these processes in the platelets of nine FH patients and 10 controls. In response to ADP, collagen, or thrombin, FH platelets bound about twice as much 125I-fibrinogen as controls. This ratio did not change after suppression of PG/Tx formation by aspirin. With or without aspirin, FH platelets always aggregated in response to significantly lower concentrations of these agents than did platelets from normal controls. After stimulation with thrombin or collagen, the hyperaggregable platelets from FH patients were shown to bind significantly more fibrinogen than control platelets even when PG/Tx formation was suppressed (aspirin) and secreted ADP was scavenged (apyrase). To determine whether the increased fibrinogen binding observed in FH platelets is due to a qualitative or quantitative abnormality of the platelet receptor, we used a monoclonal antibody (B79.7) that is specific for the receptor. The amount of B79.7 that bound to platelets from control and FH subjects was similar. In addition (as in normal individuals), the antibody inhibited aggregation and fibrinogen binding of FH platelets.

Xanthomas and hyperlipidemias

The ability to recognize diverse clinical forms of xanthomas, such as tuberous, planar, eruptive and tendinous, is important in the detection of underlying systemic disease. A variety of primary genetic disorders, as well as numerous secondary conditions such as diabetes, obstructive liver disease, thyroid disease, renal disease, and pancreatitis, can lead to hyperlipoproteinemia that results in the formation not only of xanthomas but also of life-threatening vascular atherosclerosis. An understanding of the pathogenesis of the underlying lipoprotein alterations provides a rational approach to therapy utilizing dietary manipulations and drugs. Such treatment is capable of correcting most disorders of lipid metabolism, and, if appropriate therapy is initiated at the first sign of xanthoma evolution, it may prevent progression of atherosclerosis, provide resolution of xanthomas, and in some instances prevent serious pancreatitis.

Nutrition and current concepts of obesity

Obesity is and has been one of the foremost health problems in the U.S. and in many other countries. It is so interrelated with different factors that it is very difficult to single out the effect of one particular aspect. However, an effort is made in this review to focus on obesity only from a nutritional point of view. Childhood nutrition and its impact on obesity is particularly emphasised since weight gain during early infancy has been associated with obesity in later stages of life. There is considerable evidence that links obesity with certain diseases of the cardiovascular system and diabetes. A review of this relationship is also outlined based on recent developments. The causes, classification and consequences of obesity are discussed in detail followed by critical evaluation of the possible and prevalent treatment methods.

The effect of oral calcium carbonate administration on serum lipoproteins of children with familial hypercholesterolaemia (type II-A)

The effect of oral calcium carbonate on serum lipoprotein concentrations was tested in 50 children with familial hypercholesterolemia (type II-A) consuming a low cholesterol high polyunsaturated fat diet, using a cross-over design versus a placebo. Cholesterol was measured in serum and in the individual lipoprotein density classes. Serum apolipoprotein B (the protein moiety of low density lipoprotein) and apolipoprotein A-I (the main protein of high density lipoprotein) were measured by specific immunoassays. Calcium carbonate treatment induced only a slight increase in serum apolipoprotein A-I (+ 4%) and a slight decrease in low density lipoprotein cholesterol (-4%), both changes being significant at the P = 0.05 level.

Platelet coagulant activities in arterial occlusive disease of the eye

Ischemic optic neuropathy and retinal arterial occlusion are 2 forms of arterial occlusive disease affecting the eye. Reports in the literature suggest platelet hyperactivity in acute arterial occlusive diseases affecting other organ systems. Therefore, 14 patients with ischemic optic neuropathy and 17 patients with central or branch retinal artery occlusion were studied to determine whether platelets have a role in the pathogenesis of these vascular occlusive disorders. The results of the following investigations were no different in these patients compared with those in 18 control patients with non-vascular eye diseases: prothrombin times, partial thromboplastin times, plasma fibrinogen, factor V, factor VIII, platelet counts and threshold concentrations of ADP, epinephrine and collagen resulting in secondary platelet aggregation and serotonin release. In contrast, platelet coagulant activities concerned with the early stages of intrinsic coagulation were significantly increased in patients with retinal artery occlusion without hypertension or type IV hyperlipoproteinemia, but generally normal in patients with ischemic optic neuropathy and in patients with retinal artery occlusion associated with hypertension, type IV hyperlipoproteinemia, diabetes mellitus and generalized atherosclerosis. These results are consistent with a platelet contribution to retinal arterial occlusive disease in patients without other known contributing factors such as hypertension, serum lipid abnormalities, diabetes mellitus and generalized atherosclerosis and may have implications regarding prophylaxis.

Antihypercholesterolemic studies with sterols: beta-sitosterol and stigmasterol

Stigmasterol, which differs from beta-sitosterol by unsaturation at C22, was tested for antihypercholesterolemic activity under an experimental protocol that gave the results expected with beta-sitosterol and cholestyramine. In terms of serum cholesterol, stigmasterol had a barely significant antihypercholesterolemic effect while exhibiting no obvious effect on the heart or liver. It was concluded that saturation of the side chain, at least at C22, is important in conferring antihypercholesterolemic activity on a sterol.

Usefulness of serum lipid determination in diabetic practice

In order to evaluate the importance of measuring serum lipids in the current care of diabetics, blood triglycerides were measured in 155 diabetics and 59 controls. Comparison with a chemical method confirmed the usefulness of the nephelometric method for the diagnosis and control of hyperlipemia in current practice. The importance of measuring serum lipids was confirmed by a close correlation between lipemia and cardiovascular complications such as coronary insufficiency, high blood pressure, and peripheral arterial insufficiency. It appeared also that glycemia and cholesterol are not sufficient to assess the biological pattern and prognosis of diabetes. Thus, lipemia is an essential parameter in the evaluation of any diabetic because of its value regarding prognosis and control therapy.

Bile salt metabolism. II. Bile salts and disease

Alterations of bile salt metabolism have been shown in numerous diseases. Liver damage results in elevated serum bile salt concentrations which may be useful as a sensitive index of hepatocellular disease. Changes in the relative proportions of the individual bile salts in serum occur with cholestasis. Urinary excretion of bile salts, largely in the form of sulphates, increases as a compensatory mechanism. Ileal disease or resection causes bile salt melabsorption. The increase in colonic bile salts produces a watery diarrhoea while the decrease in duodenal levels may cause steatorrhoea. Cholelithiasis may result from alteration in the relative proportions of cholesterol, lecithin and bile salts in bile. The mechanism apparently differs in various conditions predisposing to gallstone formation. A primary alteration of bile salt metabolism has been postulated in several other conditions. Considerable interest centres on the importance of metabolites of bile salts in the pathogenesis of colonic carcinoma. Chenodeoxycholic acid is a successful though costly treatment for selected patients with cholesterol gallstones. Bile salt binding agents, such as cholestyramine, are extremely useful especially in the control of pruritus in patients with cholestasis.

The effect of cholestyramine on serum lipids and platelet aggregation of hypercholesterolemic children (type II A) while on high linoleic acid diet

25 children with familial hypercholesterolemia (type II A) were treated with cholestyramine or placebo in a cross over study during 2 periods of each 10 weeks. The medication was added to a high linoleic acid diet, which had been started at least 1 year earlier. Serum lipids and platelet aggregation were investigated at the end of the 2 periods. On cholestyramine, serum cholesterol levels decreased significantly, whereas the linoleate and oleate content of cholesterylesters and serum triglycerides did not change systematically. Platelet aggregation time, measured with a filtragometer, did not systematically change either.

Effects of propranolol, minoxidil, and clofibrate on cholesterol-induced atherosclerosis in stumptail macaques (Macaca arctoides)

Propanolol, minoxidil, and clofibrate, three different classes of pharmacological agents used clinically in various conditions related to atherosclerosis, were shown not to have any intrinsic potentiating effects on the development of atherosclerosis in stumptail macaques fed an atherogenic diet. We did obtain, however, some results that suggest that clofibrate and propranolol may exert some beneficial actions.

Failure of complete bile diversion and oral bile acid therapy in the treatment of homozygous familial hypercholesterolemia

Two patients with nomozygous familial hypercholesterolemia, refractory to medical therapy, underwent complete bile diversion by common-duct ligation and cholecystostomy, in an attempt to arrest the progression of their xanthomatosis and atherosclerosis by depletion of body cholesterol. Clofibrate was given after operation to one patient, and cholic acid to both, in an effort to enhance further the negative sterol balance. Bile diversion produced an increase of six to eight times in gastrointestinal sterol output, which was not increased further by either clofibrate or cholic acid therapy. Despite a calculated sterol loss of 560 g over 14 months in one patient and 400 g over 10 months in the other, neither plasma cholesterol nor xanthoma size decreased. Continuity of the biliary tree was therefore restored. The data suggest that patients with homozygous familial hypercholesterolemia respond to even massive gastrointestinal sterol depletion with equal increases in sterol synthesis.

Platelet coagulant activities and serum lipids in transient cerebral ischemia

To determine whether platelets play a part in the pathogenesis of transient cerebrovascular ischemia, we studied 22 patients with transient ischemia, 18 control patients and 38 normal subjects. Platelet aggregation and [14C]-serotonin release by ADP, epinephrine and collagen were normal in all patients, as were plasma coagulation assays, except for shortened partial thromboplastin times in the patients with transient ischemia. Platelet coagulant activities concerned with initiation and early stages of intrinsic coagulation were increased two to three times in 12 patients with transient ischemic attacks with normal serum lipids and normal in the 10 others with Type IV hyperlipoproteinemia. These results indicate an association between platelet coagulant hyperactivity and transient ischemic attacks in a group of patients with normal serum lipids.

Comparative antilipidemic effects of various ethyl 5-substituted benzofuran-, 2,3-dihydrobenzofuran-, and 3(2H)-benzofuranone-2-carboxylate analogs of clofibrate in a triton hyperlipidemic rat model

The antilipidemic properties of certain benzofuran-, 2,3-dihydrobenzofuran-, and 3(2H)-benzofuranone-2-carboxylate analogs of clofibrate in a hyperlipidemic rat model are described. The hyperlipidemia was induced by intraperitoneal injection of Triton WR-1339. The results were analyzed in light of structural modifications as well as the lipid solubility of substituted compounds as assessed by a consideration of calculated log P values. Comparisons are made between the activity of these compounds and the activity of related cyclic analogs previously reported. Among the various compounds tested, only the 5-C1 and phenylsybstituted dihydrobenzofurans were selective against elevated serum cholesterol levels in this animal model. The data presented support the hypothesis that the cholesterol and triglyceride lowering activity of clofibrate related analogs in this animal model may be separated through a consideration of log P, conformational, and electronic changes. The proposal is advanced that relatively minor structural modification of clofibrate related analogs may lead to compounds which are not only selective in the Triton model but also to compounds which are likely to exert their effects by differing modes of action.

Drug treatment of hyperlipidemia

The most frequent indication for treatment of hyperlipidemia is for prevention of arteriosclerosis, a suspected but unproved benefit. The cornerstone of treatment of primary hyperlipidemia is diet; drugs may be added to, but do not replace, diet. When a drug is used with any patient, its potential benefits and hazards must be carefully weighed for the given subject. The subjects should be carefully followed and observed for side effects. Plasma lipids should be monitored during the course of treatment. Five drugs have been approved by the U.S. Food and Drug Administration for the treatment of hyperlipidemia: cholestyramine, clofibrate, nicotinic acid, sodium dextrothyroxine and beta-sitosterol. The use, the actions and the side effects of each and of several nonapproved agents are discussed.

Combined para-aminosalicylic acid and dietary therapy in long-term control of hypercholesterolemia and hypertriglyceridemia (Types IIa and IIb hyperlipoproteinemia)

The hypolipidemic effect of PAS-C-diet treatment was studied in 63 patients with Types IIa and IIb hyperlipoproteinemia for 6-36 months. Serum lipids and body weights of all patients were stabilized by a low cholesterol-saturated fat-refined carbohydrate diet before the initiation of an eight-week placebo-drug single-blind crossover study. During the placebo period the plasma lipids levels, mean +/- SD: cholesterol 355 +/- 63.5 mg%, triglyceride 141 +/- 68.7 mg%, and LDL-cholesterol 279 +/- 56.8 mg% were lowered to 274 +/- 53.1 mg+, 98 +/- 40.6 mg%, and 209 +/- 52.9 mg%, respectively (P less than 0.001 in each instance), with 7.5-11.0 grams of PAS-C/day given in one to three divided doses. In ten patients who have completed three years of treatment similar results were obtained. They showed no tendency to develop drug tolerance. Eight had watery diarrhea during the initial period which promptly subsided with interruption of drug therapy. Reintroduction of PAS-C in smaller dose (4.5 g/day) with gradual increment to effective dosage level was tolerated by all. No hematologic, hepatic, and ophthalmologic abnormalities were demonstrated by periodic monitoring. The hypoplipidemic effect of the drug was found to be diminished by alcohol and caloric excess.

Milk and its role in the American diet

A decline in milk consumption is postulated as a possible factor contributing to poor nutritional status. Certain common prejudices against milk may, rightly or wrongly, act as barriers to its consumption and, therefore, to its nutritional contributions. Beliefs such as "adults don't need milk;" "raw milk is better than pasteurized milk;" "nonwhite people shouldn't drink milk;" "saturated fat and cholesterol 'cause' heart disease;" "cows are ecologically unsound;" and "nutrition doesn't sell milk" can be counteracted in light of current scientific knowledge and information. It is reaffirmed that milk, in moderation, is a desirable inclusion in most people's diets.

Effects of intravenous hyperalimentation of plasma-lipoproteins in severe familial hypercholesterolaemia

The plasma-lipoprotein response to intravenous hyperalimentation was studied in three patients with severe familial hypercholesterolaemia. Hyperalimentation substantially lowered plasma concentrations of cholesterol, low-density lipoproteins (L.D.L.P.), and high-density lipoproteins. The chemical composition of L.D.L.P. did not change. Triglyceride levels increased slightly in two patients and decreased in the third. Turnover of radiolabelled L.D.L.P. was disturbed as L.D.L.P. concentration fell but then returned to normal. The mechanism by which intravenous hyperalimentation rapidly lowers plasma-cholesterol in severe hypercholesterolaemia is unknown.