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Adaptations in the liver and kidney to obstructive cholestasis
in activated i m m u n e and inflammatory cells, particularly leukocytes, macrophages, and endothelial cells. In this study, the role of COX-2 and production of prostaglandins in the d e v e l o p m e n t of postoperative ileus was e x p l o r e d in normal and COX-2 / knockout mice. Intestinal manipulation significantly up-regulated the expression of COX-2 within resident muscularis macrophages, discrete subpopulations of myenteric neurons, and recruited monocytes, effects that were accompanied by increased prostaglandin synthesis (see Figure). Selective pharmacologic inhibition or absence (COX-2 knockouts) of COX-2 resulted in amelioration of the postoperative inhibition of circular muscle contractility and gastrointestinal transit. The implications of these studies to the clinical area are obvious, particularly for development of therapeutic strategies for preventing postoperative ileus. See page 1354
Blocking Interleukin 18, an Important Proinflammatory Cytokine That May Have a Role in the Pathogenesis of IBD Interleukin (IL)-18 is a proinflammatory cytokine that has many effects, including a major role in initiating a T-helper type I response and activation of macrophages that produce tumor necrosis factor (TNF)-a and IL-l~3 in response. In addition, IL-18 is elevated in colonic specimens of patients with Crohn's disease and in some forms of experimentally induced colitis such as the TNBS (2,4,5-trinitrobenzene sulfonic acid) model. In this study, the potential role of IL-18 in the pathogenesis of TNBS-induced colitis was studied by treating mice with a recombinant human IL-18 binding protein isoform (rhIL-18BPa). As s h o w n in the H&Estained histologic sections of colon (see Figure), rhIL-18BPa treatment attenuates colonic inflammation. In panel A, active colitis develops in saline-treated TNBS mice, characterized by edema, ulceration, influx of inflammatory cells, and crypt loss. In panel B, these effects are mitigated by treatment with rhIL-18BPa. Cytokine production was also reduced substantially by this agent. Thus, it appears that rhlL-18BPa, and agents like it, have bioactivity conducive to inhibiting proinflammatory processes and may be useful in treating patients with inflammatory bowel diseases. See page 1372
Adaptations in the Liver and Kidney to Obstructive Cholestasis Although the liver adapts to cholestasis by altering the expression of bile salt, other organs such as the kidney may play a significant role as well. The kidney expresses both the ileal Na-dependent bile salt transporter (Isbt) and the multidrug resistance-associated protein 2, which is also capable of transporting sulfated bile acids. In this study, the role of these bile salt transporters in the adaptation process after obstructive cholestasis was studied in rats 14 days after bile duct ligation. Within the first 3 days of bile duct ligation, serum bile salts rose but then declined to levels that w e r e still significantly higher than sham-operated controls, an effect temporally related to increased urinary bile salt excretion. An increase in cholangiocyte Isbt expression was observed, w h i c h was related to the extent of bile duct proliferation. This response likely represents an adaptive response to reabsorb bile salts from the obstructed lumen of the biliary tree. Concurrently, renal Isbt messenger RNA and protein expression decreased along with diminished Na-dependent uptake of taurocholate in brush border membranes. In contrast, the expression of the multi-drug resistance-associated protein 2 was significantly increased even 1 day after bile duct ligation. This change could explain the adaptive role of the kidney in providing an alternative route for elimination of potentially toxic bile salts in cholestatic liver disease. The adjacent figure provided by the authors depicts adaptive changes in several organs that occur in response to bile duct obstruction.
See page 1473
1270
Hepatocyte
Model depicting adaptive changes in bile acid transporters of various organs in response to obstructive cholestasis. Ntcp, sodium taurocholate cotransporting polypeptide; Bsep, bile salt export pump; Mrp, multidrug resistanceassociated protein; t-ASBT, truncated apical Nadependent bile salt transporter; Isbt, ileal Nadependent bile salt transporter; BS, bile salts; A , organic anions.
GASTROENTEROLOGY2001;121:1473-1484
Adaptive Regulation of Bile Salt Transporters in Kidney and Liver in Obstructive Cholestasis in the Rat JOHN LEE,* FRANCESCO AZZAROLI,* LIN WANG,* CAROL J. SOROKA,* ALESSANDRO GIGLIOZZI,* KENNETH D. R. SETCHELL,* WERNER KRAMER,§ and JAMES L. BOYER* *Liver Center and Department of Medicine, Yale UniversitySchool of Medicine, New Haven, Connecticut; *Clinical Mass Spectrometry, Childrens Hospital Medical Center, Cincinnati, Ohio; and §Aventis Pharma Deutschland, Frankfurt, Germany
Background & Aims: Cholestasis results in adaptive regulation of bile salt transport proteins in hepatocytes that may limit liver injury. However, it is not known if changes also occur in the expression of bile salt transporters that reside in extrahepatic tissues, particularly the kidney, which might facilitate bile salt excretion during obstructive cholestasis. Methods: RNA and protein were isolated from liver and kidney 14 days after common bile duct ligation in rats and assessed by RNA protection assays, Western analysis, and tissue immunofluorescence. Sodium-dependent bile salt transport was also measured in brush border membrane vesicles from the kidney. Results: After common bile duct ligation, serum bile salts initially rose and then declined to lower levels after 3 days. In contrast, urinary bile salt excretion rose progressively over the 2-week period. By that time, the ileal sodium-dependent bile salt transporter messenger RNA and protein expression in total liver had increased to 300% and 200% of controls, respectively, while falling to 46% and 37% of controls, respectively, in the kidney. Sodium-dependent uptake of aH-taurocholate in renal brush border membrane vesicles was decreased. In contrast, the multidrug resistance-associated protein 2 expression in the kidney was increased 2-fold, even 1 day after ligation. Immunofluorescent studies confirmed the changes in the expression of these transporters in liver and kidney. Conclusions: These studies show that the molecular expression of bile salt transporters in the kidney and cholangiocytes undergo adaptive regulation after common bile duct obstruction in the rat. These responses may facilitate extrahepatic pathways for bile salt excretion during cholestasis.
ecent studies in experimental models and clinical cholestatic disorders indicate that cholestatic liver injury is associated with alterations in the molecular expression of bile salt transporters in the liver. 1,2 These adaptive responses serve to diminish the hepatic uptake of bile salts while at the same time minimizing the impairment in the liver's ability to extrude bile salts. 3,4 Thus, in several models of cholestasis in the rat, both the molecular and functional expression of the Na+-tauro -
R
cholate cotransporting peptide, Ntcp (Slcl0al), and several members of the Oatp (Slc21) family, which mediate bile salt uptake at the hepatocyte basolateral membrane, are reduced. 3,5 lo Mrp3 (Abcc3), which is up-regulated at the sinusoidal membrane of the hepatocyte after bile duct obstruction, may also function to return bile salts from the hepatocyte to the systemic circulation, t1,~2 In contrast, the molecular expression of several selected transporters at the hepatocyte canalicular membrane, including Bsep (Abcbil), are relatively well maintained. 4,13,14 These molecular events are supported by functional studies in the rat that demonstrate continued bile salt secretion into the biliary tree after common bile duct ligation (CBDL). 4,15 Because the biliary outflow tract is completely obstructed in this model of cholestasis, these observations suggest that there should be mechanisms for the reabsorption of bile salts from the obstructed lumen of the biliary tree. Indeed, recent studies provide convincing molecular and functional evidence for the expression of the ileal Na+-dependent bile salt transporter, Isbt (Slcl0a2), on the apical membrane of cholangiocytes, where it has been shown to be capable of bile salt uptake from the biliary tree. 16,1v Although less is known about bile salt transport in the kidney, bile salts that escape first-pass clearance by the liver after reabsorption from the intestine are filtered at the glomerulus, where they are thought to be reabsorbed by a sodium-dependent bile salt transport mechanism in the proximal convoluted tubule. ~8-e° Thus, under normal conditions, bile salt losses in urine are minimal. Sodium-dependent uptake of bile salts from the glomerular filtrate is believed to be mediated by Isbt, which is localized to the brush border membrane of the rat proxAbbreviationsused in this paper: BBMV, brush border membrane vesicle; CBDL, common bile duct ligation; FAB-MS, fast atom bombardment ionization-mass spectrometry; RPA, ribonuclease protection assay. © 2001 by the American GastroenterologicalAssociation 0016-5085/01/$35.00 doi:10.1053/gast.2001.29608
Blocking Interleukin 18, an Important Proinflammatory Cytokine That May Have a Role in the Pathogenesis of IBD Interleukin (IL)-18 is a proinflammatory cytokine that has many effects, including a major role in initiating a T-helper type I response and activation of macrophages that produce tumor necrosis factor (TNF)-a and IL-l~3 in response. In addition, IL-18 is elevated in colonic specimens of patients with Crohn's disease and in some forms of experimentally induced colitis such as the TNBS (2,4,5-trinitrobenzene sulfonic acid) model. In this study, the potential role of IL-18 in the pathogenesis of TNBS-induced colitis was studied by treating mice with a recombinant human IL-18 binding protein isoform (rhIL-18BPa). As s h o w n in the H&Estained histologic sections of colon (see Figure), rhIL-18BPa treatment attenuates colonic inflammation. In panel A, active colitis develops in saline-treated TNBS mice, characterized by edema, ulceration, influx of inflammatory cells, and crypt loss. In panel B, these effects are mitigated by treatment with rhIL-18BPa. Cytokine production was also reduced substantially by this agent. Thus, it appears that rhlL-18BPa, and agents like it, have bioactivity conducive to inhibiting proinflammatory processes and may be useful in treating patients with inflammatory bowel diseases. See page 1372
Adaptations in the Liver and Kidney to Obstructive Cholestasis Although the liver adapts to cholestasis by altering the expression of bile salt, other organs such as the kidney may play a significant role as well. The kidney expresses both the ileal Na-dependent bile salt transporter (Isbt) and the multidrug resistance-associated protein 2, which is also capable of transporting sulfated bile acids. In this study, the role of these bile salt transporters in the adaptation process after obstructive cholestasis was studied in rats 14 days after bile duct ligation. Within the first 3 days of bile duct ligation, serum bile salts rose but then declined to levels that w e r e still significantly higher than sham-operated controls, an effect temporally related to increased urinary bile salt excretion. An increase in cholangiocyte Isbt expression was observed, w h i c h was related to the extent of bile duct proliferation. This response likely represents an adaptive response to reabsorb bile salts from the obstructed lumen of the biliary tree. Concurrently, renal Isbt messenger RNA and protein expression decreased along with diminished Na-dependent uptake of taurocholate in brush border membranes. In contrast, the expression of the multi-drug resistance-associated protein 2 was significantly increased even 1 day after bile duct ligation. This change could explain the adaptive role of the kidney in providing an alternative route for elimination of potentially toxic bile salts in cholestatic liver disease. The adjacent figure provided by the authors depicts adaptive changes in several organs that occur in response to bile duct obstruction.
See page 1473
1270
Hepatocyte
Model depicting adaptive changes in bile acid transporters of various organs in response to obstructive cholestasis. Ntcp, sodium taurocholate cotransporting polypeptide; Bsep, bile salt export pump; Mrp, multidrug resistanceassociated protein; t-ASBT, truncated apical Nadependent bile salt transporter; Isbt, ileal Nadependent bile salt transporter; BS, bile salts; A , organic anions.
GASTROENTEROLOGY2001;121:1473-1484
Adaptive Regulation of Bile Salt Transporters in Kidney and Liver in Obstructive Cholestasis in the Rat JOHN LEE,* FRANCESCO AZZAROLI,* LIN WANG,* CAROL J. SOROKA,* ALESSANDRO GIGLIOZZI,* KENNETH D. R. SETCHELL,* WERNER KRAMER,§ and JAMES L. BOYER* *Liver Center and Department of Medicine, Yale UniversitySchool of Medicine, New Haven, Connecticut; *Clinical Mass Spectrometry, Childrens Hospital Medical Center, Cincinnati, Ohio; and §Aventis Pharma Deutschland, Frankfurt, Germany
Background & Aims: Cholestasis results in adaptive regulation of bile salt transport proteins in hepatocytes that may limit liver injury. However, it is not known if changes also occur in the expression of bile salt transporters that reside in extrahepatic tissues, particularly the kidney, which might facilitate bile salt excretion during obstructive cholestasis. Methods: RNA and protein were isolated from liver and kidney 14 days after common bile duct ligation in rats and assessed by RNA protection assays, Western analysis, and tissue immunofluorescence. Sodium-dependent bile salt transport was also measured in brush border membrane vesicles from the kidney. Results: After common bile duct ligation, serum bile salts initially rose and then declined to lower levels after 3 days. In contrast, urinary bile salt excretion rose progressively over the 2-week period. By that time, the ileal sodium-dependent bile salt transporter messenger RNA and protein expression in total liver had increased to 300% and 200% of controls, respectively, while falling to 46% and 37% of controls, respectively, in the kidney. Sodium-dependent uptake of aH-taurocholate in renal brush border membrane vesicles was decreased. In contrast, the multidrug resistance-associated protein 2 expression in the kidney was increased 2-fold, even 1 day after ligation. Immunofluorescent studies confirmed the changes in the expression of these transporters in liver and kidney. Conclusions: These studies show that the molecular expression of bile salt transporters in the kidney and cholangiocytes undergo adaptive regulation after common bile duct obstruction in the rat. These responses may facilitate extrahepatic pathways for bile salt excretion during cholestasis.
ecent studies in experimental models and clinical cholestatic disorders indicate that cholestatic liver injury is associated with alterations in the molecular expression of bile salt transporters in the liver. 1,2 These adaptive responses serve to diminish the hepatic uptake of bile salts while at the same time minimizing the impairment in the liver's ability to extrude bile salts. 3,4 Thus, in several models of cholestasis in the rat, both the molecular and functional expression of the Na+-tauro -
R
cholate cotransporting peptide, Ntcp (Slcl0al), and several members of the Oatp (Slc21) family, which mediate bile salt uptake at the hepatocyte basolateral membrane, are reduced. 3,5 lo Mrp3 (Abcc3), which is up-regulated at the sinusoidal membrane of the hepatocyte after bile duct obstruction, may also function to return bile salts from the hepatocyte to the systemic circulation, t1,~2 In contrast, the molecular expression of several selected transporters at the hepatocyte canalicular membrane, including Bsep (Abcbil), are relatively well maintained. 4,13,14 These molecular events are supported by functional studies in the rat that demonstrate continued bile salt secretion into the biliary tree after common bile duct ligation (CBDL). 4,15 Because the biliary outflow tract is completely obstructed in this model of cholestasis, these observations suggest that there should be mechanisms for the reabsorption of bile salts from the obstructed lumen of the biliary tree. Indeed, recent studies provide convincing molecular and functional evidence for the expression of the ileal Na+-dependent bile salt transporter, Isbt (Slcl0a2), on the apical membrane of cholangiocytes, where it has been shown to be capable of bile salt uptake from the biliary tree. 16,1v Although less is known about bile salt transport in the kidney, bile salts that escape first-pass clearance by the liver after reabsorption from the intestine are filtered at the glomerulus, where they are thought to be reabsorbed by a sodium-dependent bile salt transport mechanism in the proximal convoluted tubule. ~8-e° Thus, under normal conditions, bile salt losses in urine are minimal. Sodium-dependent uptake of bile salts from the glomerular filtrate is believed to be mediated by Isbt, which is localized to the brush border membrane of the rat proxAbbreviationsused in this paper: BBMV, brush border membrane vesicle; CBDL, common bile duct ligation; FAB-MS, fast atom bombardment ionization-mass spectrometry; RPA, ribonuclease protection assay. © 2001 by the American GastroenterologicalAssociation 0016-5085/01/$35.00 doi:10.1053/gast.2001.29608