Renal elimination of organic anions in cholestasis

The disposition of most drugs is highly dependent on specialized transporters. OAT1 and OAT3 are two organic anion transporters expressed in the basolateral membrane of renal proximal tubule cells, identified as contributors to xenobiotic and endogenous organic anion secretion. It is well known that cholestasis may cause renal damage. Impairment of kidney function produces modifications in the renal elimination of drugs. Recent studies have demonstrated that the renal abundance of OAT1 and OAT3 plays an important role in the renal elimination of organic anions in the presence of extrahepatic cholestasis. Time elapsed after obstructive cholestasis has an important impact on the regulation of both types of organic anion transporters. The renal expression of OAT1 and OAT3 should be taken into account in order to improve pharmacotherapeutic efficacy and to prevent drug toxicity during the onset of this hepatic disease.     

Novel liver-specific organic anion transporter OAT7 that operates the exchange of sulfate conjugates for short chain fatty acid butyrate

The liver plays an important role in the elimination of endogenous and exogenous lipophilic organic compounds from the body, which is mediated by various carrier proteins that differ in substrate specificity and kinetic properties. Here, we have characterized a novel member of the organic anion transporter family (SLC22) isolated from human liver. The transporter named organic anion transporter 7 (OAT7/ SLC22A9) showed 35% to 46% identities to those of other organic anion transporters of SLC22 family. When expressed in Xenopus oocytes, OAT7 mediated Na(+)-independent, high-affinity transport of sulfate-conjugated steroids, estrone sulfate (ES; K(m) = 8.7 microM), and dehydroepiandrosterone sulfate (K(m) = 2.2 microM). In addition, OAT7 interacted with negatively charged sulfobromophthalein, indocyanine green, and several sulfate-conjugated xenobiotics. In contrast, glucuronide and glutathione conjugates exhibited no inhibitory effects on OAT7-mediated [(3)H]ES transport. OAT7-mediated [(3)H]ES transport was trans-stimulated by three-carbon to five-carbon (C3 to C5) short-chain fatty acids. The efflux of [(14)C]butyrate (C4) via OAT7 was significantly trans-stimulated by extracellular ES. Furthermore, OAT7 mediated [(14)C]butyrate uptake and [(3)H]ES efflux in exchange for extracellular butyrate both in Xenopus oocytes and OAT7-stably expressing cells. OAT7 protein was localized in the sinusoidal membrane of hepatocytes by immunohistochemical analysis. CONCLUSION: OAT7 is the first liver-specific transporter among members of the organic anion transporters of SLC22 family. Our findings suggest a new class of substrates for organic anion transporters and provide evidence for the transport of anionic substances such as sulfate-conjugates in exchange for butyrate in hepatocytes.     

Expression and function of renal and hepatic organic anion transporters in extrahepatic cholestasis

Obstructive jaundice occurs in patients suffering from cholelithiasis and from neoplasms affecting the pancreas and the common bile duct. The absorption, distribution and elimination of drugs are impaired during this pathology. Prolonged cholestasis may alter both liver and kidney function. Lactam antibiotics, diuretics, non-steroidal anti-inflammatory drugs, several antiviral drugs as well as endogenous compounds are classified as organic anions. The hepatic and renal organic anion transport pathways play a key role in the pharmacokinetics of these compounds. It has been demonstrated that acute extrahepatic cholestasis is associated with increased renal elimination of organic anions. The present work describes the molecular mechanisms involved in the regulation of the expression and function of the renal and hepatic organic anion transporters in extrahepatic cholestasis, such as multidrug resistance-associated protein 2, organic anion transporting polypeptide 1, organic anion transporter 3, bilitranslocase, bromosulfophthalein/bilirubin binding protein, organic anion transporter 1 and sodium dependent bile salt transporter. The modulation in the expression of renal organic anion transporters constitutes a compensatory mechanism to overcome the hepatic dysfunction in the elimination of organic anions.     

有机阴离子转运蛋白在药物肾脏转运中的作用

近端肾小管上皮细胞有机阴离子转运蛋白家族（OATs）介导多种内源性和外源性有机阴离子包括多种药物的肾脏分泌和重吸收。其中OAT1和OAT3主要表达在近端肾小管上皮细胞基底侧膜,在介导有机阴离子进入肾小管上皮细胞中发挥重要作用。本文综述。TOAT1和OAT3对药物肾脏转运以及药物相互作用的影响。     

Increased expression of multidrug resistance-associated protein 1 (mrp1) in hepatocyte basolateral membrane and renal tubular epithelia after bile duct ligation in rats

Components of the multidrug resistance-associated protein (mrp) family mediate the adenosine triphosphate (ATP)-dependent transport of conjugated organic anions in the liver. Of these, mrp1 and mrp2 have been shown to have similar substrate specificity and nucleotide sequence. The intracellular localization and distribution of mrp1 under normal condition and cholestasis have not been as yet completely elucidated. To clarify this point, in the present study we evaluated the intracellular localization of mrp1 in rat liver and kidney after bile duct ligation (BDL). Bile duct was ligated in Wistar rats. Sequential staining of mrp1 by immunofluorescence was carried out in rat liver and kidneys 1, 3, and 5 days after bile duct ligation using confocal laser scanning microscopy. Weak granular staining of mrp1 was observed in cytoplasm of control rat hepatocytes. In addition to increased cytoplasm staining of mrp1, belt-and granule-like staining of mrp1 in basolateral membrane of hepatocytes was also shown after BDL. Furthermore, mrp1 immunofluorescence increased over time after BDL. No specific immunoflurescence of mrp1 was detected in control rat kidney. However, mrp1-positive staining was observed in epithelia of some renal tubules after BDL. This study showed that mrp1 immunofluorescence increased in hepatocyte basolateral membrane and cytoplasm and epithelia of some renal tubules after BDL. This increased mrp1 expression may be an adaptive response to impairment of hepato-biliary organic anion transport during obstructive cholestasis.     

Renal tubular transporters and antiviral drugs: an update

Systemic disposition of antiviral drugs partly depends on renal handling of these compounds. There are some known, functionally characterized anionic and cationic transporters with varying substrate specificities for those drugs: human organic anion transporter (OAT) family (hOAT1-3) and human organic cation transporter (OCT) family (hOCT1-3), which mediate the intracellular flux, and adenosine 5'-triphosphate (ATP) binding cassette transporter family (P-glycoprotein, MRP2-5), which mediate the cellular efflux of antiviral drugs. The peptide transporter (PEPT1-2) mediate bi-directional facilitated diffusion of valacyclovir. All these transporters are expressed in the kidney. Organic anion and cation transporters primarily localize to the basolateral membrane of renal epithelial cells while ATP-binding cassette transporters primarily localize to the apical membrane. These transporters work in concert to mediate renal intracellular concentration of occurring antiviral drugs. Along with drug-metabolizing enzymes, these transporters are important determinants of drug effectiveness and toxicity. This review examines the role that these transporters play in renal disposition of antiviral drugs.     

Propolis reduces bacterial translocation and intestinal villus atrophy in experimental obstructive jaundice

AIM: To investigate the effects of propolis on bacterial translocation and ultrastructure of intestinal morphology in experimental obstructive jaundice. METHODS: Thirty Wistar-Albino male rats were randomly divided into three groups, each including 10 animals: group—effect on ileal mucosa and reduced bacterial translocation in the experimental obstructive jaundice model. Further studies should be carried out to explain the mechanisms of these effects.     

Effect of honey on bacterial translocation and intestinal morphology in obstructive jaundice

AIM：To evaluate the effects of honey on bacterial translocation and intestinal villus histopathology in experimental obstructive jaundice.
METHODS：Thirty Wistar-Albino rats were randomly divided into three groups each including 10 animals：group Ⅰ,sham-operated;group Ⅱ,ligation and section of the common bile duct（BDL）;group Ⅲ,bile duct ligation followed by oral supplementation of honey（BDL＋honey） 10 g/kg per day.Liver,blood,spleen,mesenteric lymph nodes,and ileal samples were taken for microbiological,light and transmission electrone microscopic examination.
RESULTS：Although the number of villi per centimeter and the height of the mucosa were higher in sham group,there was no statistically significant difference between sham and BDL ＋ honey groups（P〉0.05）.On the other hand,there was a statistically significant difference between BDL group and other groups（P〈0.05）.The electron microscopic changes werealso different between these groups.Sham and honey groups had similar incidence of bacterial translocation（P〉0.05）.BDL group had significantly higher rates of bacterial translocation as compared with sham and honey groups.Bacterial translocation was predominantly detected in mesenteric lymph nodes.
CONCLUSION：Supplementation of honey in presence of obstructive jaundice ameliorates bacterial translocation and improves ileal morphology.     

Organ-specific alterations in RAR alpha:RXR alpha abundance regulate rat Mrp2 (Abcc2) expression in obstructive cholestasis

BACKGROUND & AIMS: Obstructive cholestasis is associated with adaptive changes in expression of hepatocyte transport proteins. These include a significant reduction in hepatic expression of Mrp2 (Abcc2), the principal canalicular multispecific organic anion transporter. Renal Mrp2 expression is preserved under these conditions. We have recently reported that the rat Mrp2 promoter is activated by RAR alpha:RXR alpha, and that interleukin 1 beta (IL-1 beta) repressed promoter activity via this element. We hypothesized that cytokines, which are up-regulated in obstructive cholestasis, would reduce nuclear RAR alpha:RXR alpha levels, and that this would be associated with suppression of hepatic Mrp2 expression. METHODS: Male Sprague-Dawley rats were subjected to bile duct ligation (BDL) or sham surgery, and liver and kidney RNA and protein were isolated. Primary rat hepatocytes were treated with bile acids, retinoids, or cytokines, and RNA and protein were isolated. Mrp2 and RAR alpha:RXR alpha protein abundance and activity were assessed by using electrophoretic mobility shift assays (EMSA) and immunoblots. IL-1 beta abundance was determined by enzyme-linked immunosorbent assay. RAR alpha, RXR alpha, and Mrp2 RNA levels were determined by using ribonuclease protection assays (RPA). RESULTS: Mrp2 down-regulation and IL-1 beta up-regulation were observed in liver after BDL. This was temporally associated with down-regulation of liver RAR alpha:RXR alpha nuclear protein levels and binding to the Mrp2 promoter cis element. Renal RAR alpha:RXR alpha and Mrp2 expression were preserved under these conditions. IL-1 beta treatment of primary hepatocytes reduced Mrp2 and RXR alpha expression. CONCLUSIONS: Organ-specific regulation of Mrp2 expression in obstructive cholestasis is associated with cytokine-dependent alterations in RAR alpha:RXR alpha nuclear receptors. Preservation of renal Mrp2 expression may permit urinary excretion of toxic organic anions and xenobiotics under conditions in which biliary excretion is impaired.     

Obstructive jaundice increases sensitivity to lipopolysaccharide via TLR4 upregulation: possible involvement in gut-derived hepatocyte growth factor-protection of hepatocytes

BACKGROUND: Patients with obstructive jaundice are prone to sepsis after biliary tract surgery. The present study was designed to determine the effect of biliary obstruction on cytokine responses to lipopolysaccharide (LPS). METHODS: Wister rats were allocated into two groups; the BDL group underwent bile duct ligation, followed 2 weeks later by administration of LPS into the duodenum. The control group underwent sham operation, and similarly received enteral LPS. Specimens were collected serially, and applied for the assays. RESULTS: Serum aspartate aminotransferase and alanine aminotransferase levels were significantly increased in BDL rats. High tumor necrosis factor alpha (TNF-alpha) and interleukin (IL)-6 levels in peripheral blood were observed 2 h after LPS administration in BDL rats. In contrast, no increases in both cytokines were noted in peripheral and portal blood in control rats. Baseline HGF levels in portal and peripheral blood in BDL rats were significantly higher than in control rats. LPS significantly increased hepatocyte growth factor (HGF) levels in portal blood and decreased in peripheral blood in BDL rats, but not in control rats. Immunohistochemical analysis revealed that BDL increased expressions of Toll-like receptor (TLR)4, CD14 and CD68 both in the small intestine and liver. Both TLR4 and CD14 mRNAs were upregulated in the small intestine and liver after LPS administration in BDL rats. CONCLUSION: Obstructive jaundice and LPS stimulation induced TLR4 upregulation both in the liver and small intestine, which led to increased TNF-alpha and IL-6 production in liver and HGF production in the small intestine. The upregulation of TLR4 may lead to pathological and host defense reactions in obstructive jaundice complicated with Gram-negative bacterial infection.     

非诺贝特对梗阻性黄疸大鼠肝细胞凋亡、肝糖原含量的影响

目的探讨非诺贝特对胆管结扎大鼠血清肝脏生化指标、肝细胞凋亡、肝糖原含量的影响。方法采用胆总管结扎手术制备胆汁淤积大鼠模型。48只雄性W istar大鼠随机分为4组（每组均为12只）：A组为对照组,B组为胆管结扎组,C组为胆管结扎＋非诺贝特组（30 mg.kg-1.d-1）,D组为胆管结扎＋非诺贝特（60 mg.kg-1.d-1）。术后7 d留取血标本及肝组织后处死,分别用全自动生化分析仪测定血清ALT、AST、ALP、GGT、TBA,TUNEL法检测肝细胞凋亡数目以及过碘酸希夫（PAS）染色法检测肝糖原含量。结果 B、C、D组大鼠血清ALT、AST、ALP、GGT、TBA显著高于A组（P〈0.001）,B组与C组大鼠血清ALT、AST、ALP、GGT、TBA差异无统计学意义,D组血清AST、ALP、GGT、TBA显著低于B、C组（P〈0.01）,而ALT在D与C组之间差异无统计学意义（P=0.021〉0.01）。所有胆管结扎组大鼠肝细胞凋亡显著高于对照组（P〈0.001）,C组肝细胞凋亡显著低于B组（P=0.007〈0.01）,D组肝细胞凋亡显著低于B组（P=0.000〈0.001）,D组肝细胞凋亡显著低于C组（P=0.000〈0.001）。PAS反应显示,非诺贝特可增加梗阻性黄疸大鼠肝糖原合成。结论非诺贝特可显著改善梗阻性黄疸大鼠血清肝脏生化指标、肝细胞凋亡以及增加肝细胞糖原合成。     

Effect of cisplatin on organic ion transport in membrane vesicles from rat kidney cortex

Purified renal membrane vesicles were utilized to gain indirect information regarding the renal handling of cisplatin. The effects of cisplatin on prototypical organic anion (p-amino-hippurate, PAH) and cation (N1-methylnicotinamide; tetraethylammonium, TEA) transport in brush border and basolateral membrane vesicles prepared from rat kidney cortex were observed. While cisplatin inhibited organic cation transport (N1-methylnicotinamide; TEA) in brush border and basolateral membranes, no interaction with the organic anion (p-amino-hippurate) system was observed. Kinetic analyses revealed that cisplatin is a competitive inhibitor of TEA transport in brush border membranes with a ki of 0.12 mM. While the relationship between organic cation transport inhibition and cisplatin nephrotoxicity is unknown, it may suggest that the cisplatin complex itself is transported into the kidney by the organic cation system. The reported effect of the organic anion, probenecid, on the renal handling of cisplatin is discussed in light of these results.     

The sodium-dependent di- and tricarboxylate transporter, NaCT, is not responsible for the uptake of D-, L-2-hydroxyglutarate and 3-hydroxyglutarate into neurons

Concentrations of glutarate (GA) and its derivatives such as 3-hydroxyglutarate (3OHGA), D- (D-2OHGA) and L-2-hydroxyglutarate (L-2OHGA) are increased in plasma, cerebrospinal fluid (CSF) and urine of patients suffering from different forms of organic acidurias. It has been proposed that these derivatives cause neuronal damage in these patients, leading to dystonic and dyskinetic movement disorders. We have recently shown that these compounds are eliminated by the kidneys via the human organic anion transporters, OAT1 and OAT4, and the sodium-dependent dicarboxylate transporter 3, NaDC3. In neurons, where most of the damage occurs, a sodium-dependent citrate transporter, NaCT, has been identified. Therefore, we investigated the impact of GA derivatives on hNaCT by two-electrode voltage clamp and tracer uptake studies. None of these compounds induced substrate-associated currents in hNaCT-expressing Xenopus laevis oocytes nor did GA derivatives inhibit the uptake of citrate, the prototypical substrate of hNaCT. In contrast, D- and L-2OHGA, but not 3OHGA, showed affinities to NaDC3, indicating that D- and L-2OHGA impair the uptake of dicarboxylates into astrocytes thereby possibly interfering with their feeding of tricarboxylic acid cycle intermediates to neurons.     

Bile duct ligation in rats： A reliable model of hepatorenal syndrome？

The two most widely used experimental models of advanced liver disease are the administration of carbon tetrachloride, and common bile duct ligation （BDL）, however, neither has been systematically evaluated as a model of hepatorenal syndrome （HRS）. The BDL model in rats, studied at diverse time points, induced a progressive renal dysfunction without structural changes in the kidney. The authors concluded that BDL is a good model for further studies of HRS and its treatment. However, the renal impairment observed at the acute phase of the BDL model is based on a different pathophysiology than that of HRS. Specifically, in acute obstructive jaundice, cholemia predominates over parenchymal liver disease （reversible at this stage without portal hypertension or cirrhosis） and independently induces negative inotropic and chronotropic effects on the heart, impaired sympathetic vasoconstriction response and profound natriuresis and diuresis that might lead to volume depletion. In addition, systemic endotoxemia contributes to the prerenal etiology of renal impairment and promotes direct nephrotoxicity and acute tubular necrosis. On the other hand, the renal failure observed in the chronic BDL model （with development of biliary cirrhosis, portal hypertension and ascites） shares pathophysiological similarities with HRS, but the accordance of the chronic BDL model to the diagnostic criteria of HRS （e.g. absence of spontaneous bacterial peritonitis, no renal function improvement after plasma volume expansion） should have been confirmed. In conclusion, we think that the BDL model is not suitable for the study of the natural history of HRS, but the chronic BDL model might be valid for the study of established HRS and its potential therapies.     

Administration of protegrin peptide IB-367 to prevent endotoxin induced mortality in bile duct ligated rats

BACKGROUND: Postoperative morbidity in patients with obstructive jaundice remains high because of increased susceptibility to endotoxin and the inflammatory cascade. AIMS: An experimental study was designed to investigate the efficacy of protegrin peptide IB-367, an antimicrobial positively charged peptide, in neutralising Escherichia coli 0111:B4 lipopolysaccharide (LPS) in bile duct ligated rats. METHODS: Adult male Wistar rats were injected intraperitoneally with 2 mg/kg E coli 0111:B4 LPS one week after sham operation or bile duct ligation (BDL). Six groups were studied: sham with placebo, sham with 120 mg/kg tazobactam-piperacillin (TZP), sham with 1 mg/kg IB-367, BDL with placebo, BDL with 120 mg/kg TZP, and BDL with 1 mg/kg IB-367. RESULTS: Main outcome measures were: endotoxin and tumour necrosis factor alpha (TNF-alpha) concentrations in plasma, evidence of bacterial translocation in blood and peritoneum, and lethality. After LPS, TNF-alpha plasma levels were significantly higher in BDL rats compared with sham operated animals. IB-367 caused a significant reduction in plasma endotoxin and TNF-alpha concentrations compared with placebo and TZP treated groups. In contrast, both TZP and IB-367 significantly reduced bacterial growth compared with saline treatment. Finally, LPS induced 60% and 55% lethality in BDL placebo and TZP treated rats and no lethality in sham operated rats, while only IB-367 significantly reduced lethality to 10%. CONCLUSIONS: By virtue of its dual antimicrobial and antiendotoxin properties, IB-367 could be an interesting compound to inhibit bacterial translocation and endotoxin release in obstructive jaundice.