Pravastatin modulates liver bile acid and cholesterol homeostasis in rats with chronic cholestasis

BACKGROUND AND AIM

The administration of pravastatin to patients with cholestatic liver disease has suggested the potential of the drug with regard to reducing raised plasma cholesterol and bile acid levels. Information about the mechanisms associated with this effect is lacking. Thus, the aim of the present study is to evaluate pravastatin effects on the liver bile acid and cholesterol homeostasis in healthy and cholestatic rats.

METHODS

Control sham-operated and reversibly bile duct-obstructed (BDO) rats were treated with pravastatin (1 or 5 mg/kg) or the vehicle alone for 7 days after surgery.

RESULTS

Lower doses of pravastatin reduced bile acid plasma concentrations in cholestatic animals. The effect was associated with reduced liver mRNA expression of Cyp7a1, Cyp8b1, Mrp2, Ugt1a1 and the increased expression of Bsep. In addition, BDO-induced increase in the liver content of cholesterol was normalized by pravastatin. The change was accompanied by the reduced liver expression of Hmg-CoA reductase, LDL receptor, and Acat2, and induced the expression of Abca1 and Mdr2. These changes corresponded with the upregulation of nuclear receptors LXRα and PPARα, and the downregulation of FXR, CAR, SREBP-2 and HNF1α. High doses of pravastatin lacked any positive effects on bile acids and cholesterol homeostasis, and blocked bile formation through the reduction of the biliary excretion of bile acids.

CONCLUSIONS

Pravastatin rendered a positive reduction in BDO-induced increases in plasma bile acid concentrations and cholesterol liver content, mainly through the transcriptionally-mediated downregulation of genes involved in the synthesis of these compounds in the liver.

Alteration of methotrexate biliary and renal elimination during extrahepatic and intrahepatic cholestasis in rats

Methotrexate (MTX), an important anticancer and immunosuppressive agent, has been suggested for the treatment of primary biliary cirrhosis. However, the drug's pharmacodynamics and toxicity is dependent on its concentrations in plasma which in turn are directly related to MTX's elimination in the liver and kidney. Therefore, the aim of this study was to evaluate changes in MTX biliary and renal excretion during either intrahepatic or obstructive cholestasis in rats. The steady state pharmacokinetic parameters of MTX were evaluated in rats one (BDO1) or seven (BDO7) days after bile duct obstruction (BDO) or 18 h after administration of lipopolysaccharide (LPS). In comparison to the respective control groups, biliary and total clearances of MTX were decreased to 12% and 49% in the BDO1 group, to 5% and 56% in the BDO7 animals, and to 42% and 43% in the LPS group, respectively. Renal clearance of MTX was unchanged in BDO groups, but decreased to 23% of controls in the LPS animals. The serum biochemistry and expression of main hepatic MTX transporters (Mrp2, Mrp3, Mrp4, Bcrp, Oatp1a1, Oatp1a4 and Oatp1b2) confirmed the pathological cholestatic changes in the liver and partly elucidated the cause of changes in MTX pharmacokinetic parameters. In conclusion, this study is the first describing marked alteration of MTX hepatic and renal elimination induced by cholestasis in rats. Moreover, the reported changes in MTX pharmacokinetics and respective transporter expression suggest important mechanistic differences between the two widely used cholestatic models.

Endoglin co-expression with eNOS, SMAD2 and phosphorylated SMAD2/3 in normocholesterolemic and hypercholesterolemic mice: an immunohistochemical study

Endoglin, a homodimeric transmembrane glycoprotein, is a part of the transforming growth factor-beta (TGF-beta) receptor cascade. It has been demonstrated that endoglin can affect TGF-beta signaling and eNOS expression by affecting SMAD proteins in vitro. We planned to go one step forward and evaluate whether endoglin is co-expressed with SMAD2, phosphorylated SMAD2/3 protein and eNOS in endothelium of normocholesterolemic C57BL/6J mice, and in advanced atherosclerotic lesions in hypercholesterolemic apoE/LDLr-deficient mice by means of fluorescence immunohistochemistry. Female C57BL/6J mice were fed with a chow diet (standard laboratory diet) for 12 weeks after weaning (at the age of 4 weeks). Two-month-old female apoE/LDLr-deficient mice were fed the western type diet (atherogenic diet) containing 21% fat (11% saturated fat) and 0.15% cholesterol for 2 months. Immunohistochemical analysis of endoglin, SMAD2, phosphorylated SMAD2/3 and eNOS expression was performed in mice aortic sinus. Immunohistochemical analysis showed the expression of endoglin in intact endothelium in both C57BL/6J and apoE/LDLr-deficient mice and in endothelium covering the atherosclerotic lesion in apoE/LDLr-deficient mice. Fluorescence immunohistochemistry revealed co-expression of endoglin with SMAD2, phosphorylated SMAD2/3 and eNOS in intact aortic endothelium in C57BL/6J mice. Moreover, strong co-localization of endoglin, SMAD2, phosphorylated SMAD2/3 and eNOS was also detected in endothelium covering atherosclerotic lesions in apoE/LDLr-deficient mice. In conclusion, we suggest that endoglin, SMAD2, phosphorylated SMAD2/3 and eNOS may be important in vessel endothelium homeostasis underlying their role in atherogenesis.

Methotrexate released in vitro from bone cement inhibits human stem cell proliferation in S/G2 phase

Methotrexate (MTX) released from bone cement showed a useful local effect in animal models of bone tumours. However, local toxic reactions such as impaired wound healing were observed in areas surrounding the MTX-loaded implant. Therefore, we hypothesised that MTX released from bone cement would have harmful effects on human mesenchymal stem cells (MSC)-one of the basic components of bone marrow and tissue reparatory processes. Moreover, elution of MTX was calculated from implants prepared either with liquid or powdered MTX. During the 28-day incubation, the cement compounded with liquid MTX showed the highest elution rate of the drug. MTX released from pellets produced a significant decrease in proliferation of MSC as a consequence of a blockade of their cell cycle in the S/G2 phase. These findings indicate impairment of stem cell function in marginal areas surrounding the MTX-loaded cement and may help to explain problems with regeneration of tissues in these locations.

The influence of simvastatin, atorvastatin and high-cholesterol diet on acetylcholinesterase activity, amyloid beta and cholesterol synthesis in rat brain

OBJECTIVE

There is evidence to suppose that cholesterol-lowering medicine might confer protection against dementia, probably via modulation of cholesterol synthesis in the brain. The aim of the present study was to investigate the potential influence of statins and cholesterol diet on selected parameters relevant to Alzheimer's disease pathophysiology.

METHODS

For 15 days, rats were orally administered simvastatin (10 or 20mg/kg b.wt.), atorvastatin (10 or 20mg/kg b.wt.), or aqua (control group); and one group was fed high-cholesterol (2%) diet. At the end of experiments brain (and plasma) cholesterol, lathosterol, hydroxymethylglutaryl-coenzyme A reductase protein, acetylcholinesterase activity, amyloid beta (40 and 42) and cholesterol synthesis rate (using the incorporation of deuterium from deuterated water) were determined and statistically compared to those of aqua.

RESULTS

Both statins were able to lower cholesterol in the plasma, but none elicited an effect on total brain cholesterol. Significant reductions of brain lathosterol and cholesterol synthesis rate were observed after simvastatin and atorvastatin treatment. Acetylcholinesterase activity, amyloid beta and hydroxymethylglutaryl-coenzyme A reductase levels remained unaffected by the two drugs.

CONCLUSIONS

This study brings additional evidence of a role for statins in cholesterol synthesis in the brain. Our data question the relationship between amyloid beta, acetylcholinesterase activity and cholesterol synthesis in the rat brain as well as the assumption about no exchange between peripheral and brain cholesterol pools.

Increased melibiose/rhamnose ratio in bile of rats with acute cholestasis

BACKGROUND AND AIM

Melibiose/rhamnose permeability test is used for noninvasive intestinal mucosa barrier testing. However, the possible escape route of the absorbed saccharides through either intact or impaired blood-biliary barriers has not so far been explored. The objective of the present study was therefore two-fold: First, to describe in detail the biliary pharmacokinetics of melibiose and rhamnose in rats; second, to evaluate the changes of both sugars' pharmacokinetics upon impairment of the blood-biliary barrier by acute extrahepatic cholestasis in rats.

METHODS

Bile duct obstructed (BDO), sham-operated and intact (unoperated) male Wistar rats were administered, 24 h after the appropriate intervention, with a single intravenous dose of melibiose and rhamnose, and a 4-h pharmacokinetic study was performed.

RESULTS

In intact animals, the biliary excretion of melibiose and rhamnose was only 0.06% and 0.4% of the administered dose, respectively, while the urinary excretion accounted for 70.6% and 61.7%, respectively. In BDO animals, the biliary excretion rate of both saccharides, especially that of melibiose, was increased with a consequent 4.4-fold rise of the biliary melibiose/rhamnose ratio, the accepted paracellular permeability indicator. Both, the renal clearance of melibiose and the urinary melibiose/rhamnose ratio remained uninfluenced by cholestasis.

CONCLUSION

The present study is the first to describe in detail pharmacokinetic parameters and the biliary excretion of melibiose and rhamnose in healthy and cholestatic rats. The altered melibiose/rhamnose biliary excretion ratio in BDO rats indicates that the test is able to detect the impairment of the blood-biliary barrier in acute extrahepatic cholestasis.

Amiodarone modulates pharmacokinetics of low-dose methotrexate in rats

Clinical studies of low-dose methotrexate (LDMTX) pharmacokinetics document increased plasma concentrations of MTX after co-administration of the drug with amiodarone or macrolide antibiotics. As drug-drug interactions may increase the toxicity of LDMTX, a rat model was used to follow renal and biliary elimination of MTX during its constant-rate i.v. infusion and concomitant single bolus i.v. injections of amiodarone or azithromycin. The mean steady-state plasma concentration of 1.7+/-0.1 micromol/l was reached and the total clearance achieved 17.7+/-1.0 ml/min/kg. Administration of amiodarone decreased the biliary clearance of MTX to 73% of the control values (p<0.05). Correspondingly, the total clearance decreased to 72% and plasma MTX concentrations were augmented to 2.5+/-0.4 micromol/l (p<0.05). Amiodarone-treated rats exhibited a 3.3-fold decrease in the renal clearance (p<0.05) of conjugated bilirubin, which was associated with its increased plasma concentration. In contrast, azithromycin did not alter any of the MTX pharmacokinetic parameters. In conclusion, this is the first report describing the impairment of MTX hepatic elimination during co-administration with amiodarone. This study also provides new insight into acute amiodarone-induced hyperbilirubinaemia, where increased bilirubin production and decreased renal clearance may contribute to this effect. Importantly, azithromycin seems to be a safe co-medication during LDMTX therapy.

Zonation of multidrug resistance-associated protein 2 in rat liver after induction with dexamethasone

BACKGROUND AND AIM

The present study was aimed to evaluate the hepatic zonation of multidrug resistance-associated protein 2 (mrp2), an important drug transporter, and its potential changes during the induction of its expression by known inducer, dexamethasone (DEX).

METHODS

The hepatic expression of mrp2 was studied by immunohistochemistry with consequent quantification by measurement of integral optical densities of mrp2 staining in the periportal and perivenous areas of the liver acinus in control and DEX-pretreated rats (1 mg/kg daily per os for 4 days). Overall changes in mrp2 expression and function produced by DEX were monitored using Western blotting and an in vivo clearance study of endogenous-conjugated bilirubin, a mrp2 substrate.

RESULTS

In the control animals, a quantitative image analysis revealed the primary periportal localization of mrp2 within the liver acinus with the expression of mrp2 being 16.7-fold of that in the perivenous area. After DEX pretreatment, the expression of mrp2 increased, especially in the perivenous hepatocytes. The overall expression of mrp2 increased 3.2-fold in comparison with the control group. This observation was confirmed by Western blotting, which showed a 1.3-fold increase in the mrp2 protein after DEX pretreatment. The functional consequences of the induced mrp2 protein in the livers of the DEX-pretreated rats were demonstrated by the increased biliary excretion of conjugated bilirubin.

CONCLUSION

In conclusion, these results indicate the zonation of mrp2 protein expression primarily to periportal hepatocytes. The induction by DEX produced spatially disproportional changes with an increase in the mrp2 protein being most prominent in the perivenous hepatocytes.

Morphological and functional changes in p-glycoprotein during dexamethasone-induced hepatomegaly

1. The effect of dexamethasone on hepatic and renal P-glycoprotein (P-gp) expression, localization and activity was investigated in rats after 4 days oral administration of two dose regimens (1 or 25 mg/kg per day). Simultaneous increases in liver weight were evaluated by quantitative histological examination. 2. In the liver, dexamethasone pretreatment produced hepatomegaly as a consequence of extensive periportal fat accumulation, which was quantified by densitometry of oil red O-stained liver sections. Quantitative immunohistochemical analysis revealed preferential periportal zonation of P-gp in control animals. Dexamethasone pretreatment resulted in spatially disproportional induction of P-gp protein expression within the liver acinus characterized by preferential increase in pericentral areas, with consequent uniform panlobular distribution. Western blot analysis confirmed these results, showing increases in P-gp protein. Quantitative reverse transcription-polymerase chain reaction analysis revealed no statistically significant change in liver mdr1b mRNA expression after either dexamethasone treatment regimen. The expression of mdr1a mRNA was significantly decreased by 85-87%. 3. In the kidney, dexamethasone reduced mdr1a mRNA expression by 69-89%, whereas mdr1b mRNA expression was increased in a dose-dependent manner. However, despite tendencies, no significant increases in P-gp expression were observed at the protein level. 4. The in vivo function of P-gp was evaluated by measuring renal and biliary secretion of rhodamine-123 (Rho123) under a steady state plasma concentration. The biliary, renal and tubular secretory clearance of Rho123 was significantly increased only after high-dose dexamethasone. 5. In conclusion, the present study suggests that drug interactions observed during corticosteroid therapy may be mediated, at least in part, through increased biliary, and also renal, excretion of P-gp substrates. Expression of P-gp in the liver showed primary periportal zonation with differential changes during induction. Accompanying hepatomegaly may be explained by severe microvesicular steatosis selectively localized to the periportal areas.