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PubMed1989

Bile acid synthesis by cultured rabbit hepatocytes: stimulation by three lipoprotein fractions.

Bile acid and cholesterol synthesis were measured in monolayer cultures of rabbit hepatocytes maintained in a defined culture medium. In the absence of lipoproteins, bile acid synthesis and secretion were correlated with cholesterol synthesis and were increased 245% by mevalonolactone (10 mM) and inhibited 45% by lovastatin (50 micrograms/ml) over 24 h. When included in the culture medium, normal rabbit plasma low-density and high-density lipoproteins increased bile acid synthesis and secretion by up to 140% of values obtained without lipoproteins in hepatocytes from normal or cholestyramine-fed rabbits. Three cholesterol-rich lipoprotein fractions (beta-very low density, low density and high density) also were isolated from rabbits fed 1% cholesterol for 14 days. When added to rabbit hepatocyte cultures, each fraction markedly increased hepatocellular cholesterol content, stimulated bile acid synthesis and secretion in a dose-dependent manner, and inhibited cholesterol synthesis from radioactive acetate. These data indicate that three different lipoprotein fractions can provide cholesterol for uptake and subsequent breakdown to bile acids by cultured rabbit hepatocytes.

Animals↗

PubMed1992

7 alpha-hydroxylation of 27-hydroxycholesterol in human liver microsomes.

Human liver microsomes were found to catalyze 7 alpha-hydroxylation of 27-hydroxycholesterol at a rate of up to about 0.2 nmol/mg protein per min. The product of the reaction, 5-cholestene-3 beta, 7 alpha, 27-triol, was identified by means of combined gas chromatography-mass spectrometry. Liver microsomes from two patients with an upregulated cholesterol 7 alpha-hydroxylase, did not have higher 7 alpha-hydroxylase activity towards 27-hydroxycholesterol than those from untreated patients, suggesting that the 7 alpha-hydroxylase active towards 27-hydroxycholesterol is not the same as that active towards cholesterol. The mitochondrial fraction of liver from untreated patients and patients treated with cholestyramine, had negligible 7 alpha-hydroxylase activity towards 27-hydroxycholesterol less than 0.01 nmol/mg protein per min). The results are in accord with the possibility that there is a pathway to bile acids in human liver in which the first step is a 27-hydroxylation of cholesterol.

Adult↗

PubMed1994

The effect of dietary 7-ketocholesterol, inhibitor of sterol synthesis, on hepatic microsomal cholesterol 7 alpha-hydroxylase activity in rat.

A group of oxygenated sterols has been identified as physiological regulators of hepatic cholesterol biosynthesis. However, the regulatory effects of these oxysterols on cholesterol 7 alpha-hydroxylase, the rate-limiting enzyme in bile acid biosynthesis, is not clearly elucidated. We administered 0.1% 7-ketocholesterol (15 mg/day), a strong inhibitor of sterol synthesis, to rats orally for 6 days. Then, the levels of accumulated oxysterols in liver microsomes and microsomal 7 alpha-hydroxylase activity were determined. The results were compared to those in the groups of rats treated with either control diet or diets containing 0.1 or 1% cholesterol, 0.1% butylated hydroxytoluene, 3% cholestyramine or 1% taurocholate. 7-Ketocholesterol feeding resulted in significant increase of both 7-ketocholesterol and 7 beta-hydroxycholesterol in microsomal fraction (449.4 +/- 36.8 and 438.2 +/- 46.8 ng/mg protein, respectively; mean +/- S.E.). Hepatic microsomal 7 alpha-hydroxylase activity in the rats fed 7-ketocholesterol was significantly elevated as compared with those of control rats; 44.70 +/- 5.97 vs. 16.57 +/- 2.46 pmol/min per mg protein. Addition of BHT to 7-ketocholesterol reduced the accumulation of 7 beta-hydroxycholesterol, and the stimulatory effect of 7-ketocholesterol on 7 alpha-hydroxylase activity was suppressed. Our results demonstrate that oxysterols do not inhibit but rather stimulate hepatic microsomal 7 alpha-hydroxylase.

Animals↗

PubMed1987

Diurnal variation of HMG-CoA reductase activity in rat liver peroxisomes.

The specific activity of hepatic microsomal and peroxisomal 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) was determined at different times during a 24 hour cycle from cholestyramine treated rats. The microsomal HMG-CoA reductase activity displayed a peak at D-6 (6th hour of the dark cycle) as previously reported, whereas, the peroxisomal HMG-CoA reductase activity was the highest at L-2 (2nd hour of the light cycle). Immunoblots of the peroxisomal HMG-CoA reductase suggest that the increase in enzyme activity at L-2 is due to changes in enzyme mass. The different cyclic variations observed in microsomal and peroxisomal HMG-CoA reductase activity may suggest different mechanisms of regulation.

Animals↗

PubMed1988

The effect of methimazole on bile flow and bile acid secretion in the rat.

The effect of methimazole on bile flow and composition was studied in male Wistar rats. Administration of methimazole as a single bolus (175-700 mumol/kg body wt) or infusion over three hours (1 mumol/100 g body wt/min) significantly increased bile flow and the biliary output of bile acids and inorganic electrolytes. Choleresis was a transient phenomenon and at the end of the experiments bile flow had returned to control values, although bile acid output was significantly lowered. When the amounts of bile acids arriving into the liver were increased by taurocholate infusion or decreased by cholestyramine pretreatment, a transitory enhancement was also found in bile flow and bile acid output, but the amounts of bile acid secreted and the choleretic effect induced were different according to the bile acid secretory rate found before methimazole administration. The bile acid content in the liver of taurocholate-infused rats was reduced during methimazole-induced choleresis. Our data indicate that the higher bile flow in methimazole-treated rats is related to an enhanced biliary secretion of bile acids probably due to a transitory stimulating effect on the transport into bile of the intrahepatocytary bile acid pool. The choleretic effect is not apparently shared by other thiocarbamide compounds.

Animals↗

PubMed1990

Effects of novel bile salts on cholesterol metabolism in rats and guinea-pigs.

Novel bile salts (quaternary ammonium conjugates) inhibited cholic acid binding and transport in everted ileal sacs in vitro. The cationic piperazine conjugate of lithocholic acid (di-iodide salt, compound 8, BRL 39924A) appeared most active, inhibiting binding by 29% and transport by 59% in guinea-pig ileum (200 microM). BRL 39924A also inhibited taurocholate uptake into guinea-pig ileal sacs and cholate uptake into rat ileal sacs and was selected for further study in vivo. In hyperlipidaemic rats, BRL 39924A significantly raised cholesterol 7 alpha-hydroxylase activity and decreased hepatic accumulation of exogenous cholic acid. HDL cholesterol concentration in the serum increased and the level of VLDL plus LDL cholesterol decreased. In hyperlipidaemic guinea-pigs. BRL 39924A lowered serum total cholesterol and triglyceride levels. Although metabolic changes were less than those achieved with the bile acid sequestrant, cholestyramine, the doses of BRL 39924A used were much lower (100-500 mg/kg body wt). Selective inhibition of receptor mediated bile acid uptake may be associated with local side-effects but these novel bile salts are useful pharmacological tools to examine the effects of receptor blockade on lipoprotein metabolism.

Animals↗

PubMed1991

A novel rat hepatic clofibrate-inducible cytochrome P450 that is not a lauric acid hydroxylase.

2-Methoxy-6-[1-methylethyl]naphthalene (MMEN) was hydroxylated in an NADPH-dependent manner to the (omega-1)-alcohol and the (R)-omega- and (S)-omega-alcohols by rat hepatic microsomes. (S)-omega-Hydroxylation was selectively induced 7-fold by clofibrate treatment. Phenobarbital, 3-methyl-cholanthrene, dexamethasone, cholestyramine, and MMEN did not induce this activity to the same extent. Incubation of the racemic omega-alcohols with microsomes isolated from rats resulted in a greater rate of degradation of the (S)- than the (R)-omega-alcohol confirming (S)-omega-hydroxylation to be an initial catalytic event. MMEN and lauric acid were not competitive inhibitors of each other in microsomes from clofibrate-treated rats, indicating the (S)-omega-MMEN hydroxylase to be a different enzyme from the characterized clofibrate-inducible lauric acid hydroxylases, CYP4A1 and CYP4A3. This was confirmed by the observations that (1) lauric acid hydroxylation was inhibited by 0.02% Tween 20 or Tween 80 and 25 microM capric or myristic acids, whereas omega-MMEN hydroxylation was not, (2) omega-MMEN hydroxylation was inhibited by ketoconazole, cholesterol and acetone, whereas lauric acid hydroxylation was not, and (3) CYP4A1 and CYP4A3 expressed in Hep G2 cells did not catalyze MMEN hydroxylation. Microsomes from the lungs of rabbits treated with progesterone and kidney of untreated rats did not support selective (S)-omega-MMEN hydroxylation, indicating that this activity is not associated with CYP4A4 or CYP4A2, respectively. Leukotriene B4 (LTB4) hepatic microsomal hydroxylation was not inhibited by MMEN and microsomes from human neutrophils did not support the reaction. These data identify a hitherto uncharacterized cytochrome P450 which is selectively induced by clofibrate and does not catalyze the omega-hydroxylation of the fatty acids or prostaglandins investigated. It is proposed that the enzyme catalyzing the selective (S)-omega-hydroxylation of MMEN is a novel rat P450 and that it is either a new member of the CYP4 family or a clofibrate-inducible P450 from another gene family.

Animals↗

PubMed1984

Capillary gas chromatographic determination of cholestanol/cholesterol ratio in biological fluids. Its potential usefulness for the follow-up of some liver diseases and its lack of specificity in diagnosing CTX (cerebrotendinous xanthomatosis).

The concentration ratios of cholestanol/cholesterol in biological materials (serum, cerebrospinal fluid and tendon biopsy) were determined using a capillary gas chromatographic method. The method was validated by gas chromatography-mass spectrometry. The ratio was determined in several groups of patients: (a) patients with cerebrotendinous xanthomatosis (in serum, cerebrospinal fluid and tendon biopsy), before and during chenodeoxycholic acid therapy, (b) patients receiving cholestyramine therapy (in serum), (c) patients suffering from various liver diseases (in serum) and (d) one patient before and after liver transplantation (in serum). It can be concluded that the cholestanol/cholesterol concentration ratio is a potentially useful parameter for monitoring liver diseases but is not specific for establishing the diagnosis of cerebrotendinous xanthomatosis.

Brain Diseases, Metabolic↗

PubMed1985

The effect of a rat plasma high-density lipoprotein subfraction on the synthesis of bile salts by rat hepatocyte monolayers.

The effect of a rat high-density lipoprotein subfraction (HDL2) on the synthesis of bile salts by rat hepatocyte monolayers prepared from rats fed a diet containing cholestyramine, was investigated. The synthesis of bile salts as measured by radioimmunoassay of conjugated cholic, chenodeoxycholic and beta-muricholic acids was significantly increased when hepatocytes were incubated with a physiological concentration (500 micrograms HDL2 protein X ml-1) of HDL2.

Animals↗

PubMed1986

Use of 23-selena-25-homocholyltaurine to detect bile acid malabsorption in patients with illeal dysfunction or diarrhea.

Abdominal gamma-counting after oral administration of 23-selena-25-homocholyltaurine (75SeHCAT) was carried out on 23 healthy volunteers and 66 patients: 33 with distal ileum resections, 3 with Crohn's disease of the ileum, 17 suffering from various intestinal diseases but with normal ileum, and 13 with chronic diarrhea syndrome but without evident intestinal or extraintestinal pathology. The percentage value of 75SeHCAT abdominal retention was assessed by analysis of the activity versus time curve, obtained by single exponential least-squares fit in five consecutive measurements (time zero and 1, 3, 5, and 7 days after 75SeHCAT administration) and directly by the gamma-camera countings on days 3, 5, and 7. The percentage values obtained from the curve on the third day were found to be the most suitable for differentiating between the groups, giving the 75SeHCAT test a 94% sensitivity and a 100% specificity. Our data show that this test is a valid indicator of bile acid loss: actually, it gave evidence of idiopathic malabsorption of bile salts in 6 patients with diarrhea of unknown origin who responded to cholestyramine and showed a correlation (correlation index = 0.585) with the residual ileum of the last meter in resected patients. Moreover, the 75SeHCAT test is easy to perform in any hospital with gamma-counting facilities and has negligible radiation risk.

Adolescent↗

PubMed1990

Rifampin relieves pruritus in children with cholestatic liver disease.

Chronic cholestatic liver disease in children frequently results in severe intractable pruritus. Current forms of therapy, including cholestyramine, are usually ineffective. Therefore, a 6-wk, double-blind, crossover study was designed to test the ability of rifampin to relieve pruritus in children with chronic cholestasis. Rifampin proved effective in alleviating pruritus in all five children tested compared with a placebo-treated group. After the 6-wk study period, rifampin was continued for 6 mo, and its effectiveness was maintained. No complications resulted from rifampin use. This study and a similar study in older patients with primary biliary cirrhosis suggest that a highly effective form of therapy is available for treatment of severe pruritus in patients with chronic cholestasis. These patients must be carefully selected and frequently monitored.

Adolescent↗

PubMed1991

Treatment of primary biliary cirrhosis with low-dose weekly methotrexate.

Nine women with symptomatic precirrhotic primary biliary cirrhosis have been treated with oral pulse methotrexate, 15 mg/wk, for 12-34 months. Three women had pruritus, two fatigue, and four pruritus and fatigue. Itching disappeared and fatigue lessened or disappeared in all within 4-11 months after starting methotrexate. All who itched were able to discontinue cholestyramine (five) or antihistamines (two). Biochemical tests of liver function improved in all patients and then worsened in three when methotrexate was discontinued or the dose lowered. Mean serum alkaline phosphatase decreased from 471 to 171 U/L (P less than 0.01), serum bilirubin from 0.99 to 0.59 mg/dL (P less than 0.05), and serum alanine aminotransferase from 132 to 61 U/L (P = 0.02), and serum cholesterol fell from 265 to 213 mg/dL (NS). The decrease in serum cholesterol was significant, P = 0.05, if data were used just from the six women whose baseline serum cholesterol levels were elevated. Serum albumin remained normal in all. The serum bilirubin levels became normal in three of four patients with elevated levels. The serum alkaline phosphatase levels became normal in four patients and the alanine aminotransferase levels in three. Liver histology improved in five patients and was stable in the remaining four based on a quantitative evaluation of coded liver biopsy specimens. The improvement in histology was primarily due to decreased portal inflammation and bile duct injury. The titer of antimitochondrial antibody decreased in seven patients. The data suggest that methotrexate may be effective treatment for precirrhotic primary biliary cirrhosis. Controlled trials are needed to evaluate long-term efficacy and toxicity.

Adult↗

PubMed1993

Prolonged postpartum course of intrahepatic cholestasis of pregnancy.

Cholestatic jaundice of pregnancy is generally a self-limiting condition that occurs in the last trimester and disappears within 1-2 weeks after delivery. The cases of two women who developed severe intrahepatic cholestasis of pregnancy are presented. After delivery, pruritus and jaundice increased and the maximal level of bilirubin reached 500 and 433 mumol/L, respectively (normal, < 20 mumol/L). A familial aggregation was present in one case. Extensive laboratory, radiological, and histopathological investigation showed no other cause of jaundice. Cholestyramine, ursodeoxycholic acid, S-adenosylmethionine, evening primrose oil, and ultraviolet light were used without evidence of efficacy. On the other hand, after corticosteroids were given pruritus ceased and biochemical alterations became normal 35 and 43 weeks, respectively, after delivery. During follow-up 2 years after delivery in one patient, symptoms have not recurred and liver function tests have remained normal. A therapy-resistant dry cough in the other patient is described as a new clinical symptom of severe cholestasis.

Adult↗

PubMed1994

A double-blind controlled trial of oral-pulse methotrexate therapy in the treatment of primary sclerosing cholangitis.

BACKGROUND/AIMS: Primary sclerosing cholangitis (PSC) is a progressive disease with no accepted effective treatment. Because methotrexate was associated with clinical and histological improvement in two men with PSC, we conducted a prospective trial of methotrexate in PSC. METHODS: A prospective placebo-controlled, double-blind trial of methotrexate in PSC was performed. Twenty-four patients with PSC were randomized to receive methotrexate or placebo for a 2-year period. Seven of 12 taking methotrexate and five taking placebo had cirrhosis. Serial liver biopsies, endoscopic retrograde cholangiopancreatography (ERCP), and biochemical tests of liver function were followed. RESULTS: There were no significant changes in liver histological results, ERCP findings, tests of liver function (other than alkaline phosphatase), or outcome between the two groups. Mean alkaline phosphatase levels decreased by 152 IU in the methotrexate group and increased by 30 IU in the placebo group (P = 0.032). Patients taking methotrexate were more likely to reduce or discontinue cholestyramine than patients taking placebo. CONCLUSIONS: This study does not support efficacy for methotrexate in the treatment of PSC. On the basis of this study, the empiric use of methotrexate in patients with PSC is not recommended. However, methotrexate is being further evaluated in patients with precirrhotic PSC.

Adolescent↗

PubMed1977

Regression of arteriosclerotic lesions in rhesus monkey aortas after regression diet. Scanning and transmission electron microscope observations of the endothelium.

Scanning and transmission microscopy were used to study aortic intima atherosclerotic lesions in Rhesus monkeys during both progression and regression phases. Scanning micrographs of severely atherosclerotic lesions showed areas of disjunctive endothelium and discontinuous basement membranes, frequently accompanied by red blood cells and other circulating elements adhering to the surface. Transmission micrographs also showed occasional areas of endothelial cell damage and loss with lipid-laden smooth muscle cells and foam cells beneath. Regressed lesions (affected by low-fat, low-cholesterol diet with or without cholestyramine) showed endothelial changes suggestive of reparative processes. Scanning micrographs showed flattened residual lesions with continous endothelial lining, while transmission microscopy disclosed interdigitated intercellular tight junctions and frequently reduplicated basement membranes.

Animals↗

PubMed1977

Hypocholesterolemic action of a novel delta8-dihydroabietamide derivative, THD-341, in rats.

The hypocholesterolemic properties of THD-341, N-(2,6-dimethylphenyl)-delta8-dihydroabietamide, were studied in rats. THD-341 reduced serum cholesterol levels in cholesterol-cholate-fed rats at a concentration of less than 0.001% in the diet or an oral dose of less than 3 mg/kg, once a day. When compared in terms of the 50% inhibitory dose for serum cholesterol elevation (ID 50%, % in diet), THD-341 (0.0008%) was comparable to D-thyroxine (0.0005%), more potent than estradiol (0.003%), and far more potent than clofibrate (0.2%), beta-sitosterol (0.8%), cholestyramine (2%), or nicotinic acid (3%). A daily intravenous injection of THD-341 was also effective (ID 50%: 7 mg/kg). THD-341 reduced serum and liver cholesterol in rats made hypercholesterolemic by 0.3% dietary thiouracil or 0.25% dietary cholate. Liver cholesteriol was more profoundly affected than the serum cholesterol. In normal rats, cholesterol was reduced in liver but not in serum. Its mechanism of action is unknown but the results suggest that THD-341 inhibits cholesterol absorption or re-absorption.

Abietanes↗

PubMed1987

Evaluation of the hypolipidemic activity of xenalipin in experimental animals.

Xenalipin (4'-trifluoromethyl-2-biphenylcarboxylic acid) is a chemically novel compound which has been found to be an effective hypolipidemic agent in two animal species. Significant reductions in serum cholesterol and triglycerides were observed in cholesterol-cholic acid-fed rats following oral doses of 10-30 mg/kg/day. Xenalipin was considerably more potent than clofibrate, nicotinic acid, and cholestyramine in the same model. Lipoprotein analysis showed that xenalipin reduced cholesterol and protein content in very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL), and low density lipoprotein (LDL). Triglycerides were reduced in VLDL and IDL. Xenalipin was also effective in reducing serum cholesterol and triglyceride concentrations in normocholesterolemic rats. In diet-induced hypercholesterolemic African green monkeys, xenalipin at oral doses of 15-60 mg/kg b.i.d. reduced serum LDL-cholesterol concentrations. These results suggest that xenalipin has a profile of activity which would be beneficial in therapy for hyperlipidemia.

Animals↗

PubMed1987

Multicentric reticulohistiocytosis, another lipid disorder with normolipidemic xanthomatosis?

This report describes a 72-year-old female patient with 2 types of severely disfiguring xanthomas, particularly on the facial area and the upper arms. Biopsy revealed xanthoma-type cells, histiocytes, and multiple giant cells. The soft yellowish facial xanthomata were rich in esterified cholesterol, whereas the cholesterol content of the colorless, firm, fibrous xanthoma of the arms was relatively low. The clinical course of insidiously starting polyarthritis, the formation of skin and tendon xanthomas (at the age of 63) and, finally, the histological findings verified the diagnosis of multicentric reticulohistiocytosis. The family history and findings were noncontributory. The patient had symptoms of moderate coronary heart disease and died from an acute myocardial infarction. Her total cholesterol and triglyceride levels were 182 and 89 mg/dl, and the HDL cholesterol value was 43 mg/dl. Plasma levels of apolipoprotein A-I, A-II and B were normal, and her apoprotein E pattern was E3/E3. The triglyceride/cholesterol ratio of VLDL, the concentration of apo-LDL (LDL protein) and the LDL-protein/cholesterol ratio were normal. The apo-LDL production, the total clearance rate of apo-LDL, and the receptor-mediated and receptor-independent catabolism of LDL were also normal. Fecal output of neutral sterols and bile acids and the total body cholesterol synthesis were normal, but cholesterol absorption tended to be increased. The response to cholestyramine treatment showed a 44% decrease in the serum cholesterol level and a normal 5-fold increase in cholesterol synthesis. The patient's xanthoma formation could not be associated with any of the causes known to promote the development of normolipidemic xanthomatosis. It is suggested that multicentric reticulohistiocytosis should be considered in the differential diagnosis of patients with normolipidemic xanthomatosis.

Aged↗