Galactosamine prevents ethinylestradiol-induced cholestasis

NADPH oxidase-generated reactive oxygen species are involved in estradiol 17ß-d-glucuronide-induced cholestasis

The endogenous metabolite of estradiol, estradiol 17β-D-glucuronide (E17G), is considered the main responsible of the intrahepatic cholestasis of pregnancy. E17G alters the activity of canalicular transporters through a signaling pathway-dependent cellular internalization, phenomenon that was attributed to oxidative stress in different cholestatic conditions. However, there are no reports involving oxidative stress in E17G-induced cholestasis, representing this the aim of our work. Using polarized hepatocyte cultures, we showed that antioxidant compounds prevented E17G-induced Mrp2 activity alteration, being this alteration equally prevented by the NADPH oxidase (NOX) inhibitor apocynin. The model antioxidant N-acetyl-cysteine prevented, in isolated and perfused rat livers, E17G-induced impairment of bile flow and Mrp2 activity, thus confirming the participation of reactive oxygen species (ROS) in this cholestasis. In primary cultured hepatocytes, pretreatment with specific inhibitors of ERK1/2 and p38MAPK impeded E17G-induced ROS production; contrarily, NOX inhibition did not affect ERK1/2 and p38MAPK phosphorylation. Both, knockdown of p47phox by siRNA and preincubation with apocynin in sandwich-cultured rat hepatocytes significantly prevented E17G-induced internalization of Mrp2, suggesting a crucial role for NOX in this phenomenon. Concluding, E17G-induced cholestasis is partially mediated by NOX-generated ROS through internalization of canalicular transporters like Mrp2, being ERK1/2 and p38MAPK necessary for NOX activation.

Multidrug Resistance-Associated Protein 2 Deficiency Aggravates Estrogen-Induced Impairment of Bile Acid Metabolomics in Rats

Multidrug resistance-associated protein 2 (Mrp2) mediates biliary secretion of anionic endobiotics and xenobiotics. Genetic alteration of Mrp2 leads to conjugated hyperbilirubinemia and predisposes to the development of intrahepatic cholestasis of pregnancy (ICP), characterized by increased plasma bile acids (BAs) due to mechanisms that are incompletely understood. Therefore, this study aimed to characterize BA metabolomics during experimental Mrp2 deficiency and ICP. ICP was modeled by ethinylestradiol (EE) administration to Mrp2-deficient (TR) rats and their wild-type (WT) controls. Spectra of BAs were analyzed in plasma, bile, and stool using an advanced liquid chromatography–mass spectrometry (LC–MS) method. Changes in BA-related genes and proteins were analyzed in the liver and intestine. Vehicle-administered TR rats demonstrated higher plasma BA concentrations consistent with reduced BA biliary secretion and increased BA efflux from hepatocytes to blood via upregulated multidrug resistance-associated protein 3 (Mrp3) and multidrug resistance-associated protein 4 (Mrp4) transporters. TR rats also showed a decrease in intestinal BA reabsorption due to reduced ileal sodium/bile acid cotransporter (Asbt) expression. Analysis of regulatory mechanisms indicated that activation of the hepatic constitutive androstane receptor (CAR)-Nuclear factor erythroid 2-related factor 2 (Nrf2) pathway by accumulating bilirubin may be responsible for changes in BA metabolomics in TR rats. Ethinylestradiol administration to TR rats further increased plasma BA concentrations as a result of reduced BA uptake and increased efflux via reduced Slco1a1 and upregulated Mrp4 transporters. These results demonstrate that Mrp2-deficient organism is more sensitive to estrogen-induced cholestasis. Inherited deficiency in Mrp2 is associated with activation of Mrp3 and Mrp4 proteins, which is further accentuated by increased estrogen. Bile acid monitoring is therefore highly desirable in pregnant women with conjugated hyperbilirubinemia for early detection of intrahepatic cholestasis.

Coenzyme Q 10 supplementation: A potential therapeutic option for the treatment of intrahepatic cholestasis of pregnancy

Intrahepatic cholestasis of pregnancy (ICP) is a pregnancy specific liver disease characterized by pruritus, elevated serum bile acids and abnormal liver function that may be associated with severe adverse pregnancy outcomes. We previously reported that plasma coenzyme Q10 (CoQ10) is decreased in women with ICP as it is its analogue coenzyme Q9 (CoQ9) in rats with ethinyl estradiol (EE)-induced cholestasis. The aim of the present study was to evaluate the possible therapeutic role of CoQ10 in experimental hepatocellular cholestasis and to compare it with ursodeoxycholic acid (UDCA) supplementation. Bile acids, CoQ9, CoQ10, transaminases, alkaline phosphatase, retinol, α-tocopherol, ascorbic acid, thiobarbituric acid reactive substances, carbonyls, glutathione, superoxide dismutase and catalase were assessed in plasma, liver and/or hepatic mitochondria in control and cholestatic rats supplemented with CoQ10 (250 mg/kg) administered alone or combined with UDCA (25 mg/kg). CoQ10 supplementation prevented bile flow decline (P < 0.05) and the increase in serum alkaline phosphatase and bile acids, particularly lithocholic acid (P < 0.05) in cholestatic rats. Furthermore, it also improved oxidative stress parameters in the liver, increased both CoQ10 and CoQ9 plasma levels and partially prevented the fall in α-tocopherol (P < 0.05). UDCA also prevented cholestasis, but it was less efficient than CoQ10 to improve the liver redox environment. Combined administration of CoQ10 and UDCA resulted in additive effects. In conclusion, present findings show that CoQ10 supplementation attenuated EE-induced cholestasis by promoting a favorable redox environment in the liver, and further suggest that it may represent an alternative therapeutic option for ICP.

Pharmacokinetic Characteristics of Baicalin in Rats with 17α-ethynyl-estradiol-induced Intrahepatic Cholestasis

Baicalin is one of the main active ingredients of choleretic traditional Chinese medicine drug Radix Scutellariae. The aim of this study was to explore the pharmacokinetic characteristics of baicalin in rats with 17α-ethynylestradiol (EE)-induced intrahepatic cholestasis (IC) based on its choleretic effects. Firstly, rats were subcutaneously injected with EE solution (5 mg/kg, 0.25 mL/100 g) for 5 consecutive days to construct an IC model. Then the bile excretion rate, serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and total bile acid (TBA) and pathological changes of the liver were detected. Secondly, after successfully modeling, the rats were intragastrically given baicalin solution (200 mg/kg) (n=6). Blood samples were collected from the tail vein at different time points after intragastric administration. The protective effects of low- (50 mg/kg), medium- (100 mg/kg) and high-dose (200 mg/kg) baicalin on the liver in IC rats were evaluated. The content of baicalin in plasma was detected by liquid chromatography-mass spectrometry/mass spectrometry and pharmacokinetics parameters were calculated. Pharmacodynamic results showed that low-, medium- and high-dose baicalin all significantly increased the average excretion rate of bile (P<0.05), and significantly decreased serum levels of ALT, AST and ALP and TBA (P<0.05). Meanwhile, HE staining showed that baicalin significantly relieved EE-induced hepatocyte edema and necrosis. Pharmacokinetic results exhibited that the absorption of baicalin in both IC and normal control rats showed bimodal phenomenon. C_max, AU_(0-t) and AUC_(0-∞) of baicalin in IC rats were significantly higher than those of the normal control group (P<0.01). T_1/2 of plasma baicalin in the model group was significantly extended to (11.09±1.84) h, with clearance dropping to 61.78% of that of the normal control group (P<0.01). The above results suggested that baicalin had protective effects on the liver of IC rats, accompanied by significantly increased in vivo exposure, delayed in vivo clearance and markedly alterative pharmacokinetic characteristics. This study provides a theoretical basis for further development of baicalin as a feasible drug for treating IC.

Mouse models of liver fibrosis mimic human liver fibrosis of different etiologies

The liver has the amazing capacity to repair itself after injury; however, the same processes that are involved in liver regeneration after acute injury can cause serious consequences during chronic liver injury. In an effort to repair damage, activated hepatic stellate cells trigger a cascade of events that lead to deposition and accumulation of extracellular matrix components causing the progressive replacement of the liver parenchyma by scar tissue, thus resulting in fibrosis. Although fibrosis occurs as a result of many chronic liver diseases, the molecular mechanisms involved depend on the underlying etiology. Since studying liver fibrosis in human subjects is complicated by many factors, mouse models of liver fibrosis that mimic the human conditions fill this void. This review summarizes the general mouse models of liver fibrosis and mouse models that mimic specific human disease conditions that result in liver fibrosis. Additionally, recent progress that has been made in understanding the molecular mechanisms involved in the fibrogenic processes of each of the human disease conditions is highlighted.

Coenzyme Q in pregnant women and rats with intrahepatic cholestasis

BACKGROUND & AIMS

Intrahepatic cholestasis of pregnancy is a high-risk liver disease given the eventual deleterious consequences that may occur in the foetus. It is accepted that the abnormal accumulation of hydrophobic bile acids in maternal serum are responsible for the disease development. Hydrophobic bile acids induce oxidative stress and apoptosis leading to the damage of the hepatic parenchyma and eventually extrahepatic tissues. As coenzyme Q (CoQ) is considered an early marker of oxidative stress in this study, we sought to assess CoQ levels, bile acid profile and oxidative stress status in intrahepatic cholestasis.

METHODS

CoQ, vitamin E and malondialdehyde were measured in plasma and/or tissues by HPLC-UV method whereas serum bile acids by capillary electrophoresis in rats with ethinyl estradiol-induced cholestasis and women with pregnancy cholestasis.

RESULTS

CoQ and vitamin E plasma levels were diminished in both rats and women with intrahepatic cholestasis. Furthermore, reduced CoQ was also found in muscle and brain of cholestatic rats but no changes were observed in heart or liver. In addition, a positive correlation between CoQ and ursodeoxycholic/lithocholic acid ratio was found in intrahepatic cholestasis suggesting that increased plasma lithocholic acid may be intimately related to CoQ depletion in blood and tissues.

CONCLUSION

Significant CoQ and vitamin E depletion occur in both animals and humans with intrahepatic cholestasis likely as the result of increased hydrophobic bile acids known to produce significant oxidative stress. Present findings further suggest that antioxidant supplementation complementary to traditional treatment may improve cholestasis outcome.

Ursodeoxycholic acid in cholestasis: linking action mechanisms to therapeutic applications

UDCA (ursodeoxycholic acid) is the therapeutic agent most widely used for the treatment of cholestatic hepatopathies. Its use has expanded to other kinds of hepatic diseases, and even to extrahepatic ones. Such versatility is the result of its multiple mechanisms of action. UDCA stabilizes plasma membranes against cytolysis by tensioactive bile acids accumulated in cholestasis. UDCA also halts apoptosis by preventing the formation of mitochondrial pores, membrane recruitment of death receptors and endoplasmic-reticulum stress. In addition, UDCA induces changes in the expression of metabolizing enzymes and transporters that reduce bile acid cytotoxicity and improve renal excretion. Its capability to positively modulate ductular bile flow helps to preserve the integrity of bile ducts. UDCA also prevents the endocytic internalization of canalicular transporters, a common feature in cholestasis. Finally, UDCA has immunomodulatory properties that limit the exacerbated immunological response occurring in autoimmune cholestatic diseases by counteracting the overexpression of MHC antigens and perhaps by limiting the production of cytokines by immunocompetent cells. Owing to this multi-functionality, it is difficult to envisage a substitute for UDCA that combines as many hepatoprotective effects with such efficacy. We predict a long-lasting use of UDCA as the therapeutic agent of choice in cholestasis.

Nrf2 the rescue: effects of the antioxidative/electrophilic response on the liver

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that positively regulates the basal and inducible expression of a large battery of cytoprotective genes. These gene products include proteins that catalyze reduction reactions (NAD(P)H:quinone oxidoreductase 1, Nqo1), conjugation reactions (glutathione-S-transferases, Gsts and UDP-glucuronosyltransferases, Ugts), as well as the efflux of potentially toxic xenobiotics and xenobiotic conjugates (multidrug resistance-associated proteins, Mrps). The significance of Nrf2 in the liver has been established, as livers of Nrf2-null mice are more susceptible to various oxidative/electrophilic stress-induced pathologies than wild-type mice. In contrast, both pharmacological and genetic models of hepatic Nrf2 activation are protective against oxidative/electrophilic stress. Furthermore, because certain Nrf2-target genes in the liver could affect the distribution, metabolism, and excretion of xenobiotics, the effects of Nrf2 on the kinetics of drugs and other xenobiotics should also be considered, with a special emphasis on metabolism and excretion. Therefore, this review highlights the research that has contributed to the understanding of the importance of Nrf2 in toxicodynamics and toxicokinetics, especially that which pertains to the liver.

The elderly as a sensitive population in environmental exposures: making the case

The US population is aging. CDC has estimated that 20% of all Americans will be 65 or older by the year 2030. As a part of the aging process, the body gradually deteriorates and physiologic and metabolic limitations arise. Changes that occur in organ anatomy and function present challenges for dealing with environmental stressors of all kinds, ranging from temperature regulation to drug metabolism and excretion. The elderly are not just older adults, but rather are individuals with unique challenges and different medical needs than younger adults. The ability of the body to respond to physiological challenge presented by environmental chemicals is dependent upon the health of the organ systems that eliminate those substances from the body. Any compromise in the function of those organ systems may result in a decrease in the body's ability to protect itself from the adverse effects of xenobiotics. To investigate this issue, we performed an organ system-by-organ system review of the effects of human aging and the implications for such aging on susceptibility to drugs and xenobiotics. Birnbaum (1991) reported almost 20 years ago that it was clear that the pharmacokinetic behavior of environmental chemicals is, in many cases, altered during aging. Yet, to date, there is a paucity of data regarding recorded effects of environmental chemicals on elderly individuals. As a result, we have to rely on what is known about the effects of aging and the existing data regarding the metabolism, excretion, and adverse effects of prescription medications in that population to determine whether the elderly might be at greater risk when exposed to environmental substances. With increasing life expectancy, more and more people will confront the problems associated with advancing years. Moreover, although proper diet and exercise may lessen the immediate severity of some aspects of aging, the process will continue to gradually degrade the ability to cope with a variety of injuries and diseases. Thus, the adverse effects of long-term, low-level exposure to environmental substances will have a longer time to be manifested in a physiologically weakened elderly population. When such exposures are coupled with concurrent exposure to prescription medications, the effects could be devastating. Public health officials must be knowledgeable about the sensitivity of the growing elderly population, and ensure that the use of health guidance values (HGVs) for environmental contaminants and other substances give consideration to this physiologically compromised segment of the population.

Regulation of expression and activity of rat intestinal multidrug resistance-associated protein 2 by cholestatic estrogens

The effect of the cholestatic estrogens ethynylestradiol (EE) and estradiol 17beta-D-glucuronide (E2-17G) on expression and activity of intestinal multidrug resistant-associated protein 2 (Mrp2, Abcc2) was studied in rats. Expression and localization of Mrp2 were evaluated by Western blotting, real-time polymerase chain reaction, and confocal immunofluorescence microscopy. Mrp2 transport activity toward dinitrophenyl-S-glutathione (DNP-SG) was assessed in vitro in intestinal sacs. EE, administered subcutaneously at a 5 mg/kg b.wt. dose, for 5 consecutive days, produced a marked decrease in Mrp2 expression at post-transcriptional level, without affecting its normal localization at the apical membrane of the enterocyte. This effect was selective because expression of other ATP-binding cassette proteins such as breast cancer resistance protein and Mrp3 were not affected and that of multidrug resistance protein 1 was only minimally impaired. Consistent with down-regulation of expression of Mrp2, a significant impairment in serosal to mucosal transport of DNP-SG and in protection against absorption of this same compound were registered. Simultaneous administration of EE with spironolactone (200 micromol/kg b.wt./day for 3 days), an Mrp2 inducer, prevented these alterations, confirming down-regulation of expression of Mrp2 by EE as a major component of functional changes. Incorporation of E2-17G (30 microM) in the serosal medium of intestinal sacs decreased serosal to mucosal transport of DNP-SG, probably because of competitive inhibition, without affecting normal Mrp2 expression or localization. Our data indicate impairment of function of intestinal Mrp2 by both cholestatic estrogens, although through a different mechanism. This finding represents an aggravation of deteriorated hepatic Mrp2 function that could further increase bioavailability of specific xenobiotics after oral exposure.

Disruption of function and localization of tight junctional structures and Mrp2 in sustained estradiol-17beta-D-glucuronide-induced cholestasis

Estradiol-17beta-D-glucuronide (E(2)17G) induces immediate and profound but transient cholestasis in rats when administered as a single bolus dose. Here, we examined the consequence of sustained E(2)17G cholestasis and assessed the function and localization of the tight junctional proteins zonula occludens-1 (ZO-1) and occludin and of the canalicular transporter multidrug resistance-associated protein-2 (Mrp2). An initial dose of E(2)17G (15 mumol/kg iv) followed by five subsequent doses of 7.5 mumol/kg from 60 to 240 min induced a sustained 40-70% decrease in bile flow. Following their biliary retrograde administration, cholera toxin B subunit-FITC or horseradish peroxidase were detected at the sinusoidal domain, indicating opening of the paracellular route; this occurred as early as 15 min after the first dose as well as 15 min after the last dose of E(2)17G, but not following the administration of vehicle in controls. Localization of ZO-1 and occludin was only slightly affected under acute cholestatic conditions but was severely disrupted under sustained cholestasis, with their appearance suggesting a fragmented structure. Endocytic internalization of Mrp2 to the pericanalicular region was apparent 20 min after a single E(2)17G administration; however, Mrp2 was found more deeply internalized and partially redistributed to the basolateral membrane under sustained cholestasis. In conclusion, acute E(2)17G-induced cholestasis increased permeability of the tight junction, while sustained cholestasis provoked a significant redistribution of ZO-1, occludin, and Mrp2 in addition to increased permeability of the tight junction. Altered tight junction integrity likely contributes to impaired bile secretion and may be causally related to changes in Mrp2 localization.