Preventive effect of silymarin against taurolithocholate-induced cholestasis in the rat

Protective impact of lycopene on ethinylestradiol-induced cholestasis in rats

Protection against cholestasis and its consequences are considered an essential issue to improve the quality of a patient's life and reduce the number of death every year from liver diseases. Lycopene, a natural carotenoid, has antioxidant scavenger capacity and inhibits inflammation in many experimental models. The present study aimed to elucidate the potential protective effects of lycopene, in comparison to silymarin, in a rat model of cholestatic liver. Animals were daily injected with 17α-ethinylestradiol (EE; 5 mg/kg) for 18 successive days. Silymarin (100 mg/kg) and lycopene (10 mg/kg) were orally administered once per day through the experimental period. Lycopene significantly decreased the EE-induced rise in the serum levels of total bile acid and total bilirubin as well as the activities of alanine aminotransaminase, aspartate aminotransaminase, alkaline phosphatase, and gamma-glutamyl transaminase. Moreover, lycopene reduced the hepatic levels of thiobarbituric acid reactive substances and tumor necrosis factor-α as well as the hepatic activity of myeloperoxidase that were markedly elevated by EE. Lycopene increased the hepatic levels of total protein and albumin and reduced glutathione. In addition, lycopene improved the hepatic histopathological changes induced by EE. These protective effects of lycopene were comparable to that of silymarin. In conclusion, lycopene was effective in protecting against estrogen-induced cholestatic liver injury through its antioxidant and anti-inflammatory activities. Therefore, lycopene might be a potentially effective drug for protection against cholestasis in susceptible women during pregnancy, administration of oral contraceptives, or postmenopausal replacement therapy.

Natural products for the prevention and treatment of cholestasis: A review

Cholestasis is a common manifestation of decreased bile flow in various liver diseases. It results in fibrosis and even cirrhosis without proper treatment. It is believed that a wide range of factors, including transporter dysfunction, oxidative stress, inflammatory damage, and immune disruption, can cause cholestasis. In recent years, natural products have drawn much attention for specific multiple-target activities in diseases. Many attempts have been made to investigate the anticholestatic effects of natural products with advanced technology. This review summarizes recent studies on the biological activities and mechanisms of recognized compounds for cholestasis treatment. Natural products, including various flavonoids, phenols, acids, quinones, saponins, alkaloids, glycosides, and so on, function as comprehensive regulators via ameliorating oxidative stress, inflammation, and apoptosis, restoring bile acid balance with hepatic transporters, and adjusting immune disruption. Moreover, in this progress, nuclear factor erythroid 2-related factor 2, reactive oxygen species production, heme oxygenase-1, NF-κB, cholesterol 7 alpha-hydroxylase, and farnesoid X receptors are thought as main targets for the activity of natural products. Therefore, this review presents the detailed mechanisms that include multiple targets and diverse signalling pathways. Natural products are the valuable when seeking novel therapeutic agents to treat cholestatic liver diseases.

Influence of Liver Condition and Copper on Selective Parameters of Post-Mortem Dog Tissue Samples

One of the liver functions is copper storage, which can be toxic when in excess. The objective of this retrospective study was to determine the relationship between hepatic copper and pathology conditions in stored samples from 55 post-mortem dogs (37 Beagles, 12 Labrador Retrievers, and 6 Labrador Mixes). The analyses evaluated data from blood chemistry and complete blood count (CBC) that were measured immediately before euthanasia, and liver biopsies which were harvested at necropsy and frozen at -80 °C. Slides for microscopic evaluation were prepared, and liver copper and plasma metabolites were measured. Hepatic copper was correlated (p ≤ 0.001) with monoacylglycerols, 13-HODE + 9-HODE (13-hydroxy-9,11-octadecadienoic acid + 9-hydroxy-10,12-octadecadienoic acid), and stearoyl-arachidonoyl-glycerophosphocholine. This indicates lipid metabolism modification and cell membrane oxidation. However, hepatic copper was not related to liver histopathology severity or altered liver biomarkers. The severity of liver pathology was positively correlated (p ≤ 0.05) with liver enzymes, bile salts, and glycerophosphocholines, suggesting cholestasis and altered lipid and amino acid metabolism. Liver neoplasia had increased (p ≤ 0.05) metabolites derived from nucleotides, along with an increase (p ≤ 0.05) in α-ketoglutarate from the energy and amino acid metabolism (p ≤ 0.05), suggesting rapid cell division. This study offers further insight regarding changes in metabolism due to hepatic tissue damage.

Activation of insulin-like growth factor 1 receptor participates downstream of GPR30 in estradiol-17β-D-glucuronide-induced cholestasis in rats

Estradiol-17β-D-glucuronide (E17G), through the activation of different signaling proteins, induces acute endocytic internalization of canalicular transporters in rat, including multidrug resistance-associated protein 2 (Abcc2) and bile salt export pump (Abcb11), generating cholestasis. Insulin-like growth factor 1 receptor (IGF-1R) is a membrane-bound tyrosine kinase receptor that can potentially interact with proteins activated by E17G. The aim of this study was to analyze the potential role of IGF-1R in the effects of E17G in isolated perfused rat liver (IPRL) and isolated rat hepatocyte couplets. In vitro, IGF-1R inhibition by tyrphostin AG1024 (TYR, 100 nM), or its knock-down with siRNA, strongly prevented E17G-induced impairment of Abcc2 and Abcb11 function and localization. The protection by TYR was not additive to that produced by wortmannin (PI3K inhibitor, 100 nM), and both protections share the same dependency on microtubule integrity, suggesting that IGF-1R shared the signaling pathway of PI3K/Akt. Further analysis of the activation of Akt and IGF-1R induced by E17G indicated a sequence of activation GPR30-IGF-1R-PI3K/Akt. In IPRL, an intraportal injection of E17G triggered endocytosis of Abcc2 and Abcb11, and this was accompanied by a sustained decrease in the bile flow and the biliary excretion of Abcc2 and Abcb11 substrates. TYR did not prevent the initial decay, but it greatly accelerated the recovery to normality of these parameters and the reinsertion of transporters into the canalicular membrane. In conclusion, the activation of IGF-1R is a key factor in the alteration of canalicular transporter function and localization induced by E17G, and its activation follows that of GPR30 and precedes that of PI3K/Akt.

Effect of two esters of N-methylanthranilic acid from Rutaceae species on impaired kidney morphology and function in rats caused by CCl4

AIMS

Herein we investigated the potential protective effects of methyl N-methylanthranilate (MA) and isopropyl N-methylanthranilate (IA), two naturally occurring plant constituents from Rutaceae taxa, in a rat model of acute intoxication with carbon tetrachloride (CCl4) by tracking changes in kidney tissue morphology and function.

MAIN METHODS

The antioxidant capacity of IA and MA was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid radical cation (ABTS(+)) assays and superoxide-scavenging test. Wistar rats were treated daily with MA and IA for seven days in a dose of 200mg/kg. Twenty-four hours after a CCl4 injection, rats were sacrificed and blood samples were used for the evaluation of urea and creatinine. Kidney tissue specimens were stained with hematoxylin and eosin, periodic acid-Schiff and Jones stain and evaluated for morphological changes. Quantification of structural changes determined by histological analysis of kidney tissue was assessed by a morphometric analysis of glomeruli using ImageJ software.

KEY FINDINGS

IA and MA applied in high doses on their own did not cause any significant damage to kidney tissue. A pretreatment with MA prior to the administration of CCl4 significantly prevented the increase of serum levels of decreased kidney function markers, while that of IA did not. Histopathological evaluation of the kidneys also revealed that MA reduced the incidence of kidney lesions.

SIGNIFICANCE

Our experiments showed that methyl-, and not isopropyl-, N-methylanthranilate possesses a protective potential against CCl4-induced kidney damage in rats. The results are of interest due to the presence of natural or synthetic methyl N-methylanthranilate in the human diet and their potent analgesic properties.

Comparison of the prophylactic effect of silymarin and deferoxamine on iron overload-induced hepatotoxicity in rat

In pathologic conditions or poisoning states, iron overload can affect different tissues including liver. In this study, the prophylactic effect of deferoxamine and silymarin was compared in decreasing experimental iron-overload-induced hepatotoxicity in rats. The study was done in six groups of rats, which received drugs q2 days for 2 weeks. The rats in groups 1 to 6 received drugs, respectively: normal saline, iron dextran, iron dextran + deferoxamine (intraperitoneally), iron dextran + silymarin (orally), iron dextran + silymarin (intraperitoneally), and iron dextran + deferoxamine (intraperitoneally) + silymarin (intraperitoneally). At the end of the study, blood was collected, and serum was separated for laboratory tests. The liver of rats was separated for iron measuring and tissue processing. The serum iron concentration and the serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity were determined. The numbers of necrotic hepatocytes were counted as quantity index tissue injury in light microscopic examination. The mean of serum and liver iron in group 2 was significantly greater than group 1. Liver iron was significantly decreased in other groups except group 4. Also serum iron was decreased in groups 3 to 6 compared to group 2 (nearly 400%). ALT activity in group 3 and AST activity in group 5 were significantly lesser than in other groups. The mean of necrotic hepatocytes in group 2 was significantly increased in comparison to group 1. This elevation was significantly prevented by deferoxamine and silymarin. The result of the present study shows that silymarin has a protective effect similar to deferoxamine on iron overload-induced hepatotoxicity.

Bile acid transporters in health and disease

In recent years the discovery of a number of major transporter proteins expressed in the liver and intestine specifically involved in bile acid transport has led to improved understanding of bile acid homeostasis and the enterohepatic circulation. Sodium (Na(+))-dependent bile acid uptake from portal blood into the liver is mediated primarily by the Na(+) taurocholate co-transporting polypeptide (NTCP), while secretion across the canalicular membrane into the bile is carried out by the bile salt export pump (BSEP). In the ileum, absorption of bile acids from the lumen into epithelial cells is mediated by the apical Na(+) bile salt transporter (ASBT), whereas exit into portal blood across the basolateral membrane is mediated by the organic solute transporter alpha/beta (OSTalpha/beta) heterodimer. Regulation of transporter gene expression and function occurs at several different levels: in the nucleus, members of the nuclear receptor superfamily, regulated by bile acids and other ligands are primarily involved in controlling gene expression, while cell signalling events directly affect transporter function, and subcellular localization. Polymorphisms, dysfunction, and impaired adaptive responses of several of the bile acid transporters, e.g. BSEP and ASBT, results in liver and intestinal disease. Bile acid transporters are now understood to play central roles in driving bile flow, as well as adaptation to various pathological conditions, with complex regulation of activity and function in the nucleus, cytoplasm, and membrane.

Effects of carvacrol on defects of ischemia-reperfusion in the rat liver

Many plants found in nature have been used to treat various illnesses. One such plant is oregano (Kekik in Turkish). Health beneficial effects of carvacrol obtained from oregano oil have been shown scientifically. We have investigated the comparative effects of carvacrol in the liver of rats subjected to ischemia-reperfusion defect, with silymarin. To test the effects we formed four groups using male Wistar albino rats. Group I was control. The other three groups of animals were administered 60min prior to surgical operation single doses of physiological serum, carvacrol and silymarin, respectively. Group II, III and IV animal were subjected to 45min long liver ischemia and 60min reperfusion. Blood and tissue samples were collected for biochemical and histological analysis following the test. AST and ALT values obtained after biochemical analysis of the serums showed statistically significant difference in group II than the other three groups. A statistical evaluation of the serum AST levels among the groups II, III and IV showed that both groups III and IV which had no difference in between were significantly different in a positive way from group II (p<0.001). As to the serum ALT levels, difference between group II and group III (p<0.001) and group II and group IV (p<0.01) was found significant. No statistical difference was observed in groups I, III and IV for GSH, MDA and CAT levels of the liver. A statistical evaluation of the GSH level in group III and group IV was found to be significantly different from group II (p<0.001) without any difference between them. A similar evaluation for MDA and CAT levels among the revealed no difference between group III and group IV, however, group II showed difference with group II and group IV (p<0.05). Histological findings were in harmony with the biochemical results. We conclude that carvacrol protects the liver against defects caused by ischemia and reperfusion, and carvacrol is not hepatotoxic at the applied dosage.

Bile acid transporters: structure, function, regulation and pathophysiological implications

Specific transporters expressed in the liver and the intestine, play a critical role in driving the enterohepatic circulation of bile acids. By preserving a circulating pool of bile acids, an important factor influencing bile flow, these transporters are involved in maintaining bile acid and cholesterol homeostasis. Enterohepatic circulation of bile acids is fundamentally composed of two major processes: secretion from the liver and absorption from the intestine. In the hepatocytes, the vectorial transport of bile acids from blood to bile is ensured by Na+ taurocholate co-transporting peptide (NTCP) and organic anion transport polypeptides (OATPs). After binding to a cytosolic bile acid binding protein, bile acids are secreted into the canaliculus via ATP-dependent bile salt excretory pump (BSEP) and multi drug resistant proteins (MRPs). Bile acids are then delivered to the intestinal lumen through bile ducts where they emulsify dietary lipids and cholesterol to facilitate their absorption. Intestinal epithelial cells reabsorb the majority of the secreted bile acids through the apical sodium dependent bile acid transporter (ASBT) and sodium independent organic anion transporting peptide (OATPs). Cytosolic ileal bile acid binding protein (IBABP) mediates the transcellular movement of bile acids to the basolateral membrane across which they exit the cells via organic solute transporters (OST). An essential role of bile acid transporters is evident from the pathology associated with their genetic disruption or dysregulation of their function. Malfunctioning of hepatic and intestinal bile acid transporters is implicated in the pathophysiology of cholestatic liver disease and the depletion of circulating pool of bile acids, respectively. Extensive efforts have been recently made to enhance our understanding of the structure, function and regulation of the bile acid transporters and exploring new potential therapeutics to treat bile acid or cholesterol related diseases. This review will highlight current knowledge about structure, function and molecular characterization of bile acid transporters and discuss the implications of their defects in various hepatic and intestinal disorders.

Silymarin modulates Cisplatin-induced oxidative stress and hepatotoxicity in rats

Cisplatin (CDDP) is a widely used anticancer drug, but at high dose, it can produce undesirable side effects such as hepatotoxicity. Because silymrin has been used to treat liver disorders, the protective effect of silymarin on CDDP-induced hepatotoxicity was evaluated in rats. Hepatotoxicity was determined by changes in serum alanine aminotransferase [ALT] and aspartate aminotransferase [AST], nitric oxide [NO] levels, albumin and calcium levels, and superoxide dismutase [SOD], glutathione peroxidase [GSHPx] activities, glutathione content, malondialdehyde [MDA] and nitric oxide [NO] levels in liver tissue of rats. Male albino rats were divided into four groups, 10 rats in each. In the control group, rats were injected i.p. with 0.2 ml of propylene glycol in saline 75/25 (v/v) for 5 consecutive days [Silymarin was dissolved in 0.2 ml of propylene glycol in saline 75/25 v/v]. The second group were injected with CDDP (7.5 mg /kg, I.P.), whereas animals in the third group were i.p. injected with silymarin at a dose of 100 mg/kg/day for 5 consecutive days. The Fourth group received a daily i.p. injection of silymarin (100 mg/kg/day for 5 days) 1 hr before a single i.p. injection of CDDP (7.5 mg/kg). CDDP hepatotoxicity was manifested biochemically by an increase in serum ALT and AST, elevation of MDA and NO in liver tissues as well as a decrease in GSH and the activities of antioxidant enzymes, including SOD, GSHPx in liver tissues. In addition, marked decrease in serum NO, albumin and calcium levels were observed. Serum ALT, AST, liver NO level, MDA was found to decreased in the combination group in comparison with the CDDP group. The activities of SOD, GSHPx, GSH and serum NO were lower in CDDP group than both the control and CDDP pretreated with silymarin groups. The results obtained suggested that silymarin significantly attenuated the hepatotoxicity as an indirect target of CDDP in an animal model of CDDP-induced nephrotoxicity.

Silymarin and epithelial cancer chemoprevention: how close we are to bedside?

Failure and high systemic toxicity of conventional cancer therapies have accelerated the focus on the search for newer agents, which could prevent and/or slow-down cancer growth and have more human acceptability by being less or non-toxic. Silymarin is one such agent, which has been extensively used since ages for the treatment of liver conditions, and thus has possibly the greatest patient acceptability. In recent years, increasing body of evidence has underscored the cancer preventive efficacy of silymarin in both in vitro and in vivo animal models of various epithelial cancers. Apart from chemopreventive effects, other noteworthy aspects of silymarin and its active constituent silibinin in cancer treatment include their capability to potentiate the efficacy of known chemotherapeutic drugs, as an inhibitor of multidrug resistance-associated proteins and as an adjunct to the cancer therapeutic drugs due to their organ-protective efficacy specifically liver, and immunostimulatory effects. Widespread use of silymarin for liver health in humans and commercial availability of its formulations with increased bioavailability, further underscore the necessity of carrying out controlled clinical trials with these agents in cancer patients. In this review, we will briefly discuss the outcomes of clinical trials being conducted by us and others in cancer patients to provide insight into the clinical relevance of the observed chemopreventive effects of these agents in various epithelial cancer models.

In vitro and in vivo assessment of herb drug interactions

Herbal products contain several chemicals that are metabolized by phase 1 and phase 2 pathways and also serve as substrates for certain transporters. Due to their interaction with these enzymes and transporters there is a potential for alteration in the activity of drug metabolizing enzymes and transporters in presence of herbal components. Induction and inhibition of drug metabolizing enzymes and transporters by herbal component has been documented in several in vitro studies. While these studies offer a system to determine the potential for a herbal component to alter the pharmacokinetics of a drug, they cannot always be used to predict the magnitude of any potential effect in vivo. In vivo studies are the ultimate way to determine the clinical importance of herb drug interactions. However, lack of content uniformity and lack of documentation of the bioavailability of herbal components makes even in vivo human studies difficult to interpret as the effect may be product specific. It appears that St. John's wort extract is probably one of the most important herbal product that increases the metabolism and decreases the efficacy of several drugs. Milk thistle on the other hand appears to have minimal effect on phase 1 pathways and limited data exists for phase 2 pathways and transporter activity in vivo. Further systematic studies are necessary to assess the significance of herb drug interactions.

Inhibition of rat liver UDP-glucuronosyltransferase by silymarin and the metabolite silibinin-glucuronide

The inhibitory effects of silymarin, its main constituent silibinin and the metabolite silibinin-glucuronide on UDP-glucuronosiltransferase (UGT) were evaluated in rat hepatic microsomes. Three substrates were chosen to cover both UGT1A and UGT2B family isozymes: bilirubin (substrate of UGT1A1), p-nitrophenol (UGT1A6) and ethinylestradiol (UGT2B1 and 2B3 for position C17 and UGT1A1 for position C3). The study of p-nitrophenol and bilirubin glucuronidation indicated that silymarin (SM) and silibinin glucuronide (SB-G) were enzyme inhibitors. The kinetic analysis showed that the type of inhibition was competitive in all cases and the Ki obtained were: for p-nitrophenol glucuronidation, KiSB-Gapp: 14+/-1 microg/ml and KiSMapp: 51+/-10 microg/ml and for bilirubin glucuronidation, KiSB-Gapp: 16+/-3 microg/ml. In turn, ethinylestradiol glucuronidation was not affected by any of the compounds studied suggesting that the inhibitory effect was restricted to UGT1A isozymes. Similar studies performed using human hepatic microsomes showed that SM and SB-G were also inhibitors of human UGT1A isozymes. In conclusion, administration of silymarin or its main constituent silibinin could lead to the decrease in the glucuronidation of substrates whose conjugation depends on UGT1A isozymes in a process mediated by silibinin-glucuronide, though their effect in humans needs further investigation.

Silibinin prevents cholestasis-associated retrieval of the bile salt export pump, Bsep, in isolated rat hepatocyte couplets: possible involvement of cAMP

Estradiol-17beta-d-glucuronide (E(2)17G) and taurolithocholate (TLC) induce acute cholestasis-associated with retrieval of the bile salt export pump (Bsep), which parallels with alteration in transport activity. cAMP stimulates the apically directed vesicular trafficking of transporters, partially preventing these alterations. The hepatoprotector, silymarin, which inhibits cAMP-phosphodiesterase, prevents the cholestasis induced in vivo by both estrogens and TLC. We aimed to assess the ability of silibinin (Sil), the silymarin active component, to prevent the retrieval of Bsep induced by TLC and E(2)17G, and the associated alteration in its transport function. The possible involvement of cAMP as a second messenger and the intracellular signalling pathways implicated were also evaluated. Functional studies were performed analysing the proportion of isolated rat hepatocyte couplets (IRHC) accumulating the fluorescent bile salt analogue, cholyl-lysylfluorescein (CLF), into their sealed canalicular vacuoles. Cellular localisation of Bsep was assessed by immunofluorescent staining. Intracellular levels of cAMP were measured by ELISA. Sil (2.5microM) elevated by 40+/-3% intracellular cAMP, and mimicked the ability of dibutyryl-cAMP (10microM) to prevent internalisation of Bsep and the TLC (2.5microM)- and E(2)17G (50microM)-induced impairment in the capacity of IRHC to accumulate CLF apically. Preventive effects of Sil and dibutyryl-cAMP were not abolished by the specific protein kinase A inhibitors, KT5720 and H89. Contrarily, the intracellular Ca(2+) chelator, BAPTA/AM, significantly blocked the protective effect of both compounds. We conclude that Sil prevented TLC- and E(2)17G-induced bile salt secretory failure, at least in part, by avoiding redistribution of Bsep, by a mechanism probably involving cAMP-induced cytosolic Ca(2+) elevations.

Cholestatic syndromes

PURPOSE OF REVIEW

This review highlights recent developments in the molecular pathogenesis of cholestasis as well new aspects of pathogenesis and management of clinical cholestatic disorders.

RECENT FINDINGS

Highlights include the role of nuclear receptors including FXR ligands as potential therapeutic agents, new genetic defects for pediatric cholestasis and sclerosing cholangitis, and novel infections and environmental agents as etiologies for primary biliary cirrhosis. Important clinical studies have been published in the area of pediatric cholestatic syndromes, intrahepatic cholestasis of pregnancy, primary biliary cirrhosis, primary and secondary sclerosing cholangitis, cholestasis of sepsis, viral cholestatic syndromes, and drug-induced cholestasis.

SUMMARY

These advances continue to improve understanding of the pathophysiology, diagnosis, and management of cholestatic liver disease.