Clofibrate, caloric restriction, supersaturation of bile, and cholesterol crystals

Effects of gemfibrozil and other fibric acid derivatives on blood lipids and lipoproteins

Fibric acid derivatives (FADs) are a class of drugs that have been shown to reduce the production of very low-density lipoprotein (VLDL) while enhancing VLDL clearance due to the stimulation of lipoprotein lipase activity. The drugs can reduce plasma triglyceride levels while raising high-density lipoprotein (HDL) cholesterol levels. Their effects on low-density lipoprotein (LDL) cholesterol levels are less marked and more variable. There is evidence that oral gemfibrozil (Lopid, Parke-Davis, Morris Plains, NJ) can reduce the risk of serious coronary events, specifically in those patients who had elevations of both LDL cholesterol levels and total plasma triglyceride levels with lower HDL cholesterol levels. Newer FADs (bezafibrate, ciprofibrate, fenofibrate) have been shown to have greater efficacy in reducing LDL cholesterol than gemfibrozil but, in general, these drugs are not as effective as the other primary drugs used to lower LDL levels. The FADs are also used to treat adult patients with very high levels of triglycerides who have pancreatitis and whose disease cannot be managed with dietary therapy. The FADs are well tolerated, with dyspepsia and abdominal pain the most common adverse effects. A small risk of cholelithiasis exists with these drugs, and caution should be used when combining these drugs with HMG-CoA reductase inhibitors because the combination increases the incidence of hyperlipidemic myositis and rhabdomyolysis.

Biliary lipid composition in monozygotic and dizygotic pairs of twins

The relative contribution of genetic factors to biliary and serum lipid composition was studied in 17 monozygotic and 18 dizygotic middle aged male pairs of twins. Cholesterol precursors, squalene and Methylated sterols which reflect the activity of cholesterol synthesis were also measured. Pairwise intraclass correlations were determined for monozygotic and dizygotic twin pairs and heritability estimates were calculated. Molar % of biliary cholesterol and percentage distribution of biliary cholic acid and particularly deoxycholic acid showed significant pairwise correlations within the monozygotic but not the dizygotic pairs. Similar correlations were found for total biliary methylsterols and of the methylsterol subfractions for the two methostenols but not for squalene, lanosterol and dimethylsterols. In serum, the precursor sterols, but not squalene, showed even higher pairwise correlations in the monozygotic twins than the corresponding precursors in bile. Molar per cent of bile acids and phospholipids and cholesterol saturation index were not correlated significantly in either twin pairs, but the pairwise correlations tended to be higher in the monozygotic than in the dizygotic pairs. Gall stones were found in seven monozygotic and three dizygotic subjects. Two monozygotic twin pairs were concordant for gall stones; all the dizygotic pairs were discordant. Overall, these data suggest that molar percentage of biliary cholesterol, bile acid composition, cholesterol synthesis, bile cholesterol saturation, and gall stone formation may be under a significant genetic control.

Nutritional management of plasma lipid disorders

Prevention of vascular disease and acute pancreatitis is the goal of hyperlipidemia treatment. The risk of coronary heart disease (CHD) increases with increasing plasma cholesterol levels because low-density lipoprotein (LDL), the major carrier of cholesterol in the plasma, is atherogenic. High-density lipoprotein (HDL), especially the HDL2 subfraction, protects against CHD. Hypertriglyceridemia, although not an independent risk factor for CHD, is generally accompanied by low HDL cholesterol (HDLch), which may predispose to CHD. Reducing plasma LDL and raising HDL levels are thus goals in preventing CHD. Serum LDL levels may be lowered by reducing saturated fat and cholesterol intake; weight loss may decrease LDL but is more effective in lowering plasma triglycerides and raising HDLch. The percent of total calories from polyunsaturated, monounsaturated, and saturated fats should be less than 10%, up to 10-15%, and less than 10%, respectively. High cholesterol intake increases the flux of cholesterol, which may be harmful to arterial walls, but beyond a certain point does not increase plasma cholesterol levels. Some diets change the composition rather than the level of LDL and apoproteins. Weight reduction and maintenance are the most effective dietary measures to lower plasma triglycerides; omega-3 fatty acids (fish oils) have shown promise in reducing triglyceride but not cholesterol levels. Substitution of starch for sugar lowered triglyceride levels toward normal in hypertriglyceridemia patients. Fasting triglyceride levels rise in all individuals fed high-carbohydrate diets, but the high levels persist in hypertriglyceridemia patients. Weight loss, cessation of cigarette smoking, increased physical activity, good control of diabetes, and moderate alcohol use all raise HDLch levels. Vitamin E deficiency causes neurological sequelae in children with severe malabsorption problems due to abetalipoproteinemia or cholestatic liver disease.

Effects of fibric acid derivatives on biliary lipid composition

Fenofibrate, a potent analogue of clofibrate, causes changes in biliary lipid composition similar to those seen with clofibrate and other derivatives of fibric acid, although there is a suggestion that the increase in cholesterol content may be accompanied by an increase in phospholipid content as well as a decrease in bile acid content. This may favor liquid crystal formation, and fenofibrate may have less propensity to cause gallstones than would other derivatives. Many other factors are also important in determining whether supersaturated bile will result in gallstone formation, and the use of this compound should be monitored in the future to determine the clinical importance of these findings.

Cholesterol precursor sterols, plant sterols, and cholestanol in human bile and gallstones

Biliary and gallstone sterol compositions were analyzed in 20 consecutive cholecystectomized patients. The main intention was to identify and quantitate noncholesterol sterols and to compare the sterol patterns of the two sources. Cholesterol comprised approximately 97% of the stone and gallbladder bile sterols; the remainder were from plant sterols, cholestanol, and cholesterol precursors, mainly lathosterol and methylsterols (two methostenols, lanosterol, and two dimethylsterols). Desmosterol and delta 8-lathosterol were also identified in both the bile and the gallstones. The sterol patterns of the bile and gallstones differed markedly. Thus, the contents of the two lathosterols and the two methostenols were clearly higher in the gallstones, whereas lanosterol stayed almost totally, and other minor sterols were preferentially, in the bile. In fact, the gallstone methylsterols consisted mainly of the two methostenols, a pattern usually seen in esterified methylsterols in serum. The core and matrix of the stone, and large and small stones as well, had only a small variation in their sterol composition within each individual, suggesting that the pattern of the noncholesterol sterol precipitation remains the same during the growth of the stone. Centrifugation of the bile revealed sedimentation of methylsterols with the stonelike sterol pattern. It can be speculated that the soluble and poorly soluble bile sterols have different hepatic origins and that the similarity between (a) methylsterols in the stone and sediment and (b) esterified methylsterols in serum points to a common hepatic site of origin.

Effects of fenofibrate on bile lipid composition

In humans, clofibrate increases the degree of bile cholesterol saturation and predisposes patients to cholesterol gallstone formation. To determine if this activity extends to the related hypolipidemic agent fenofibrate, duodenal bile lipid composition was studied in 15 subjects before they participated in a double-blind study of that drug. Eight subjects were studied again on fenofibrate and six on placebo; five placebo patients were also studied later on open-label fenofibrate. The results were similar in the double-blind and open-label studies, and changes in bile lipid composition were comparable to those seen in studies of clofibrate. Fenofibrate caused a significant decrease in the molar percentage of bile acids and increases in the molar percentage of phospholipids and cholesterol. The changes in bile acids and phospholipids had opposing effects on the cholesterol-holding capacity of bile. A statistically significant increase in the cholesterol saturation index was only apparent when all fenofibrate bile analyses were compared with all untreated bile analyses. The results demonstrated that fenofibrate has clear effects on bile lipid composition that may be associated with an increased propensity for gallstone formation, and when fenofibrate is used, patients should be monitored for this possibility.