Bezafibrate therapy and biliary lipids: effects of short-term and long-term treatment in patients with various forms of hyperlipoproteinaemia

Gallstone disease: Free radical reactions and the ambivalent role of bilirubin in the pathomechanism of gallstone formation

Az epekőbetegségek kialakulásában számos gén működését teszik felelőssé, melyek kapcsolatba hozhatók elsődlegesen a máj betegségeivel, az epeelfolyási és -képződési rendellenességekkel, a lipidmetabolizmus módosulásával, diabetes mellitussal, obesitassal, glutensensitiv enteropathiával, Crohn-betegséggel, Down-szindrómával, Gaucher-kórral, cysticus fibrosissal, valamint haematológiai kórképekkel és ileumresectiot követő állapottal. Kialakulásában szerepet játszanak gyógyszermellékhatások, bakteriális fertőzések, gyulladások, fémionterhelés és szabadgyökös reakciók. A zsírmájból az epébe telítetlen zsírsavak, lipidoxidok, diénkonjugátumok, és egyéb lipidperoxidációs termékek kerülnek, melyek az epevezetékben és a hólyagban primer és szekunder szabadgyökös folyamatokat indítanak el. Az epehólyagfalban lejátszódó gyulladásos folyamatok szabadgyöktermeléssel járnak. Az epe szabad bilirubin-tartalma koncentrációfüggően pro-, illetve antioxidánsként viselkedik. Az ambivalens tulajdonságú szabad bilirubin, amely a mikroszómák szivárgása révén, illetve a bél felől a baktériumok deglükorinidáló hatása következtében kimutatható mennyiségben van jelen az epehólyagban, a szabadgyökös reakciókat felerősíti. A szabad bilirubin kőalkotó reakciója az epében jelen lévő fémionokkal, elsődlegesen a Ca++-ionokal kalcium-(hidrogén)-bilirubinátot eredményez. A Ca++a zsírsavakkal is reakcióba lép, és ezzel megváltoztatja az epe viszkozitását. A lipidek, a szabad bilirubin és a fémionok együttesen kőalkotó komponensek. Az antioxidánsok, illetve azok derivátumai vagy hatásukban antioxidáns tulajdonságot fokozó vegyületek, készítmények több szinten is kedvezően befolyásolhatják az epe összetételét, illetve az epekőképződés gátlását.

Influence of bezafibrate on hepatic cholesterol metabolism in gallstone patients: reduced activity of cholesterol 7 alpha-hydroxylase

Bezafibrate is a hypolipidemic fibric acid derivative known to induce cholesterol supersaturation of bile. To characterize its effects on hepatic cholesterol metabolism, 31 normolipidemic, normal-weight patients with gallstones undergoing cholecystectomy were studied. Eleven patients (5 men) were randomized to treatment with bezafibrate, 200 mg three times daily for 4 weeks before operation; the remaining 20 patients (5 men) served as nontreatment controls. At operation, a liver biopsy specimen was obtained under standardized conditions and several important parameters of cholesterol metabolism were assayed. Bezafibrate treatment lowered total plasma cholesterol and triglycerides 30% and 37%, respectively. The hepatic cholesterol 7 alpha-hydroxylase activity was reduced by approximately 60% in the bezafibrate treated patients compared with the controls, whereas the acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity was similar in the two groups. The total 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase activity was increased twofold in the treated patients, whereas the active enzyme remained about the same as in the controls. The low-density lipoprotein (LDL) receptor binding activity was unaffected by the treatment. Bezafibrate treatment significantly reduces cholesterol 7 alpha-hydroxylase activity, and it is suggested that this may play an important role for the development of supersaturated bile during such therapy.

The effects of probucol and clofibrate alone and in combination on hepatic cholesterol metabolism in the male rat

Male rats were fed for 10 days on a diet supplemented with either probucol or clofibrate, alone or in combination, and the effects of the drugs on hepatic cholesterol metabolism studied. Plasma triacylglycerols were significantly lowered (15.6%, P < 0.05) by the drugs in combination but not individually whereas plasma cholesterol levels were reduced by probucol alone (22.4%, P < 0.05) and the combined treatment effected a further decrease leading to a total reduction of 50.6% (P < 0.001). Probucol reduced hepatic cellular triacylglycerols (20.0%, P < 0.05) and cholesterol (15.3%, P < 0.05) but cholesteryl esters were unaffected. In combination with clofibrate, probucol accentuated the reductions in both cellular cholesterol and cholesteryl esters produced by clofibrate alone and lowered their levels by 22.8%, P < 0.01 and 38.5%, P < 0.001, respectively. Although probucol, on its own, did not affect the activity of acyl-coenzyme A:cholesterol acyltransferase (ACAT), its combination with clofibrate caused less inhibition (43.5%, P < 0.01) of this enzyme activity than clofibrate alone (65.7%, P < 0.001). Probucol had a similarly moderating effect on the clofibrate-induced reductions in microsomal cholesterol and cholesteryl esters. Neither the microsomal nor the cytosolic neutral cholesteryl ester hydrolase was affected by probucol alone although both enzymes were dramatically increased (between 350% and 550%) by clofibrate and the combined treatment. The activity of the hepatic cytosolic inhibitor of cholesteryl ester hydrolase was unaffected by clofibrate or probucol individually but the two drugs in combination increased the total activity of the inhibitor by 52.1%, P < 0.01. When allowance was made for this increased inhibitor activity, it was clear that probucol accentuated the stimulatory effect of clofibrate on the cytosolic nCEH.

The effects of clofibrate and bezafibrate on cholesterol metabolism in the liver of the male rat

Fibric acid derivatives are used to treat hyperlipidemia and have wide ranging effects on lipid metabolism. The action of these compounds on cholesterol esterification, catalyzed by acyl-coenzyme A:cholesterol acyltransferase (ACAT), has been quite widely studied, but their effect on cholesteryl ester hydrolysis and the enzyme neutral cholesteryl ester hydrolase (nCEH) has been largely ignored. Male rats were therefore fed for 10 d on a standard chow diet supplemented with either clofibrate or bezafibrate, to study their effects on plasma lipid levels and hepatic cholesterol metabolism. Plasma triacylglycerols were not significantly altered by these diets, but bezafibrate significantly lowered plasma cholesterol levels (29.7%, P < 0.01). When expressed per unit weight of DNA, both fibrates reduced the hepatic content of triacylglycerol, cholesterol and cholesteryl esters (40, 18.7, 16.5 and 66.7, 28.6, 34.2% for clofibrate and bezafibrate, respectively). ACAT activity was significantly reduced by both drugs, but clofibrate (65% inhibition) was more effective than bezafibrate (35% inhibition). The most dramatic effect of the diets was a marked increase in the activity of both the microsomal and the cytosolic nCEH. When expressed on a whole liver basis, the effect of bezafibrate on the cytosolic enzyme (13.6-fold increase in activity) was much greater than that of clofibrate (4.8-fold increase). Increases in the activity of a cytosolic protein that inhibits the activity of nCEH were also noted, but these changes were relatively small. The results suggest that the activation of nCEH, in combination with the inhibition in ACAT activity, contributes to a decrease in the cholesteryl ester content of the liver which may influence the secretion of very low density lipoprotein.

Tolerability of fibric acids. Comparative data and biochemical bases

Fibric acids are an established class of drugs for the treatment of hyperlipoproteinaemias. Although they have been in use for 30 years or longer, some doubts remain as to their relative tolerability, both as a class and as single agents. Some side effects, e.g. lithogenicity, may be related to their mode of action, while others, e.g. the acute muscular syndrome, may be linked to the spatial conformation of the molecule. These disadvantages should, however, be weighed against the additional, potentially therapeutic properties shown by these compounds. In particular, effects on maturity onset diabetes and hyperuricaemia, as well as a very interesting fibrinolytic potential, have been described for some of them. A painstaking comparative analysis of the major literature data pertaining to the clinical toxicological profile of these agents allow to conclude that, while belonging to a chemical class, fibric acids show dramatic differences from one another, in terms of side effects and of additional pharmacodynamic activities. Moreover, in the case of lithogenicity for example, considerable differences exist between normo- and hyperlipidaemic subjects. Overall, newer molecules of more sophisticated design have a significantly improved tolerability profile vs the old clofibrate.

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.

Effects of bezafibrate on hepatic cholesterol metabolism

The influence of bezafibrate treatment on hepatic cholesterol metabolism was studied in rats and in humans. The activities of the three key enzymes involved in cholesterol metabolism [3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, cholesterol 7 alpha-hydroxylase, and acyl-coenzyme A: cholesterol acyltransferase (ACAT)] were suppressed by bezafibrate treatment in rats, but only the ACAT activity was significantly decreased when the activity was related to total liver weight. In humans, HMG-CoA reductase activity was increased about twice in the treated normolipidemic gallstone patients. In contrast, the concentration of lathosterol in serum decreased, indicating depression of the cholesterol synthesis. The increase in HMG-CoA reductase activity may be a compensatory effect of an inhibition of some other enzymes in the synthesis of cholesterol, as in vitro study on liver microsomes excluded a direct inhibitory effect of bezafibrate on HMG-CoA reductase. The ACAT activity was not significantly changed, and the cholesterol 7 alpha-hydroxylase activity was decreased by 55-60% compared with controls. The LDL-receptor-binding activity was unaffected by bezafibrate treatment.

Biliary lipids in familial combined hyperlipidaemia: effects of acipimox therapy

Biliary lipid composition and plasma lipoprotein levels were determined in nine gallstone-free male patients with familial combined hyperlipidaemia (FCHL). In the basal situation, stimulated fasting duodenal bile from the patients contained a higher relative concentration of cholesterol than bile obtained from age- and sex-matched normal controls (n = 22), 6.5 +/- 0.3 (SEM) vs. 4.7 +/- 0.2 mol % (P less than 0.01). This resulted in a higher cholesterol saturation of bile from FCHL patients, 85 +/- 6 vs. 70 +/- 2% (P less than 0.05). After 6 weeks of treatment with acipimox, 750 mg day-1, total plasma triglycerides were lowered from 7.5 +/- 1.5 to 4.6 +/- 0.7 mmol l-1 (P less than 0.05) and plasma cholesterol decreased from 8.0 +/- 0.1 to 7.1 +/- 0.3 mmol l-1 (P less than 0.05) in the FCHL patients. These changes were mainly due to a decrease in very low density lipoprotein concentrations while low density lipoprotein levels remained unaltered. The relative proportion of cholesterol in stimulated fasting duodenal bile was reduced from 6.5 +/- 0.3 to 4.3 +/- 0.5 mol % (P less than 0.01), resulting in 'normalization' of biliary cholesterol saturation, from 85 +/- 6 to 58 +/- 6% (P less than 0.005). No correlations between the changes in biliary lipid composition and those in plasma lipoprotein levels were observed. The results indicate that treatment with acipimox in patients with FCHL, a disorder commonly associated with supersaturated bile, does not increase biliary cholesterol, and presumably not the risk for gallstone formation.