Barbro Leijd

Influence of Age on Secretion of Cholesterol and Synthesis of Bile Acids by the Liver

Supersaturation of bile with cholesterol predisposes to the development of cholesterol gallstones. To identify the factors determining cholesterol saturation of bile, we analyzed the lipid composition of stimulated duodenal bile in 60 healthy subjects of various ages (31 men and 29 women) who were not obese and were free of gallstones. A positive correlation between age and cholesterol saturation of bile was found (P less than 0.001). To analyze the relation between age and cholesterol saturation, we studied the rates of hepatic secretion of biliary lipids and the kinetics of cholic acid and chenodeoxycholic acid in 22 and 18 of the subjects, respectively. Age was positively correlated with the cholesterol secretion rate (r = 0.48) and negatively correlated with bile acid synthesis (r = -0.60) and the size of the cholic acid pool (r = -0.54). We conclude that cholesterol saturation of bile increases with age as a consequence of enhanced hepatic secretion of cholesterol and decreased bile acid synthesis. These findings may explain why age is a risk factor for the development of cholesterol gallstones.

Comparative Effects of Ursodeoxycholic Acid and Chenodeoxycholic Acid on Bile Acid Kinetics and Biliary Lipid Secretion in Humans: Evidence for Different Modes of Action on Bile Acid Synthesis

The effects of ursodeoxycholic acid on biliary lipid secretion and bile acid kinetics were determined in 12 men. For comparison, eight of the subjects were also treated with chenodeoxycholic acid using a crossover study design. The daily dose of each bile acid was 15 mg/kg body wt; each treatment period lasted for 5-6 wk. Kinetics of cholic acid and chenodeoxycholic acid, hepatic secretion rates of biliary lipids, and lipid composition of concentrated fasting duodenal bile were determined before and at the end of each treatment period. The synthesis rates of cholic acid and chenodeoxycholic acid were increased by approximately 80% and 40%, respectively, during treatment with ursodeoxycholic acid. The fractional catabolic rates of the two bile acids were increased by approximately 50%, whereas the pool sizes remained unchanged. Under similar conditions, administration of chenodeoxycholic acid reduced the pool size as well as the synthesis rate of cholic acid by approximately 70%. Ursodeoxycholic acid reduced the hepatic secretion of cholesterol to a higher extent (approximately 50%) than did chenodeoxycholic acid (approximately 30%). The secretion rates of bile acids and phospholipids remained essentially unchanged during the two treatment periods. Fasting duodenal (gallbladder) bile was unsaturated with cholesterol during both regimens. It is concluded that the two bile acids exert different effects on bile acid metabolism. The enhanced conversion of cholesterol to bile acids observed during ursodeoxycholic acid treatment may at least partly explain why ursodeoxycholic acid can reduce the biliary output of cholesterol without suppressing hepatic cholesterol synthesis.

Biliary lipid composition during treatment with different hypolipidaemic drugs

Abstract. In an attempt to clarify the possible lithogenic effects of commonly used hypolipidaemic drugs, gallbladder bile was obtained from patients with primary hyperlipoproteinaemia before and during treatment with nicotinic acid (n= 13), cholestyramine (n= 19), clofibrate (n= 11), and a combination of cholestyramine and clofibrate (n= 11). Each treatment period was minimum 6 weeks, and standardized dietary conditions were obtained.

Prevalence of gallbladder disease in hyperlipoproteinemia

An analysis of the occurrence of gallbladder disease (ie, cholelithiasis, cholecystitis, cholecystectomy) in 210 consecutive patients with primary hyperlipoproteinemia showed that the prevalence of gallbladder disease was 8%, 18%, and 42% in males with type IIa, IIb, and IV hyperlipoproteinemia, and 22%, 48%, and 72% in the corresponding groups of females. The 40–59-year-old patients were compared to three necropsy series from Malmö, Sweden. The occurrence of gallbladder disease was within normal limits in type IIa and abnormally high in type IV hyperlipoproteinemia. There were no differences with regard to age, body weight, glucose intolerance, or ischemic heart disease between type IV patients with and without GBD. It is suggested that certain forms of disturbances of lipoprotein metabolism are associated with an increased risk for development of gallbladder disease.

No Influence of Simvastatin Treatment on Platelet Function In Vivo in Patients With Hypercholesterolemia

Hypercholesterolemia is associated with platelet activation. Reduction of plasma cholesterol levels by the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor simvastatin has been found to improve certain aspects of platelet function in vitro and in vivo, but controlled trials are largely lacking. The present randomized, double-blind, crossover study was performed to evaluate whether 10- to 12-week treatment with simvastatin or placebo affects platelet function in vivo in 23 hypercholesterolemic men. Measurements were performed at rest and during mental stress. Simvastatin treatment reduced plasma total cholesterol levels by 18 +/- 2% and low density lipoprotein cholesterol levels by 26 +/- 2% (P < .001 for both), whereas high density lipoprotein cholesterol levels increased slightly (6 +/- 2%, P < .05). Platelet aggregability as assessed by filtragometry ex vivo was unaffected by simvastatin treatment both at rest and during mental stress. Plasma beta-thromboglobulin levels, which reflect platelet secretion, were also unaltered by simvastatin treatment both at rest (antilog of the mean: 20.2 versus 20.0 ng/mL during placebo) and during mental stress. Moreover, nocturnal excretion of 11-dehydrothromboxane B2 in urine did not differ between placebo and active treatment: 218 versus 216 ng/mmol creatinine, respectively. The corresponding values for urinary excretion of high-molecular-weight beta-thromboglobulin were 1.78 versus 1.92 ng/mmol creatinine. Thus, simvastatin treatment had no clear-cut effect on platelet function, as assessed by four different in vivo related platelet function variables, in hypercholesterolemic men.

Effect of ciprofibrate treatment on biliary lipids in patients with hyperlipoproteinaemia

Abstract. Treatment with hypolipidaemic drugs such as clofibrate increases secretion of biliary cholesterol and induces supersaturation of bile, leading to an increased risk of gallstone formation. Ciprofibrate is a phenoxyisobutyrate derivative with lipid‐lowering effects in hyperlipoproteinaemia. We analysed serum lipid levels and biliary lipid composition and cholesterol saturation of gallbladder bile in nineteen hyperli‐poproteinaemic patients before and after 6 weeks treatment with ciprofibrate, 100 mg daily. In addition, hepatic secretion rates of biliary lipids were determined in eight of the patients. Ten of the patients were also studied after 1 year of treatment.

Increased turnover of very low density lipoprotein triglyceride during treatment with cholestyramine in familial hypercholesterolaemia.

Abstract. Kinetics of very low density lipoprotein (VLDL) triglyceride were determined in seven patients with heterozygous familial hypercholesterolaemia, using a 3H‐glycerol technique. The study was repeated after 5–7 weeks of therapy with the bile acid‐binding resin, cholestyramine. The rate of synthesis of VLDL triglyceride was increased by 85% (P < 0.05) during resin therapy. Simultaneously, the fractional catabolic rate of VLDL was increased by 40% (P < 0.02), so that only a moderate increase in plasma concentration was observed.

Clofibrate treatment and bile cholesterol saturation: short-term and long-term effects and influence of combination with chenodeoxycholic acid

Abstract. In order to determine whether the clofibrate‐induced increase in bile cholesterol saturation is transitory, duodenal bile samples were analysed from sixteen hyperlipoproteinaemic patients before and after 6 months to 2 years treatment with clofibrate, 2 g daily. Standardized dietary and weight conditions were obtained. In all but two subjects cholesterol saturation remained elevated (150 ± 7%, mean ± SEM) compared to pretreatment values (112 ± 6%, P < 0.01).

Bile acid metabolism in hypothyroid subjects: response to substitution therapy

Abstract. Bile acid kinetics and biliary lipid composition were determined in ten hypothyroid patients before and after treatment with L‐thyroxine. Hypothyroid patients had normal synthesis rates of cholic acid and chenodeoxycholic acid. Hormone treatment, which lowered plasma cholesterol by about 35%, stimulated the formation of chenodeoxycholic acid by about 40% but did not significantly change the synthesis of cholic acid or total primary bile acids. The mean relative biliary concentration of deoxycholic acid was decreased from 30% to 19% and that of chenodeoxycholic acid was concomitantly increased. Cholesterol saturation of bile was decreased by treatment in six of the patients, but the mean value before treatment (135 ± 13%) was not significantly different from that obtained after treatment (108 ± 9%). It is suggested that the hypocholesterolaemic effect of thyroid hormones is not primarily due to an increased degradation of cholesterol to bile acids. Similar to what is observed in heterozygous familial hypercholesterolaemia, the defective receptor mediated degradation of plasma low density lipoproteins in hypothyroidism is thus apparently associated with a quantitatively normal catabolic rate of cholesterol to bile acids.

Interindividual variability in biliary excretion of ceftriaxone: effects on biliary lipid metabolism and on intestinal microflora

Abstract. Ceftriaxone is a broad spectrum parenteral cephalosporin that is eliminated through renal as well as biliary excretion. In order to characterize factors influencing the biliary excretion of ceftriaxone, and possible effects of this organic anion on biliary lipid transport, we studied six healthy volunteers before and during ceftriaxone infusion. The biliary secretion rates of cholesterol, bile acids, phospholipids and ceftriaxone were determined using a duodenal perfusion technique, and the biliary lipid composition and cholesterol saturation of stimulated hepatic bile were determined. Changes in the intestinal microflora induced by ceftriaxone treatment were also analysed. There was a three‐fold interindividual variation in biliary excretion of ceftriaxone, and this was correlated with the secretion rate of bile acids (rs=0·83, P=0·05). During ceftriaxone infusion, the secretion rate of cholesterol was reduced by 32% (P<0·05), which resulted in a reduction of cholesterol saturation of bile, from 107±11 to 75±12% (SEM, P<0·05). The suppression of intestinal Escherichia coli and Bacteroides, and the proliferation of enterococci and lactobacilli were related to the biliary excretion of ceftriaxone. We conclude (i) that biliary excretion of ceftriaxone is of major importance for its effects on intestinal microflora, (ii) that secretion of this organic anion into bile is largely dependent on bile acid secretion, and (iii) that ceftriaxone inhibits the biliary secretion of cholesterol.