Physiologic study of bile salt and lipid secretion in rats after liver transplantation

Quality assessment by bile composition in normothermic machine perfusion of rat livers

BACKGROUND

The persistent challenge of organ scarcity in liver transplantation leads to an escalating dependence on organs obtained from extended criteria donors (ECD). Normothermic machine perfusion (NMP) is used for improved preservation. Due to the mimicked in vivo conditions during normothermic machine perfusion, the liver is metabolic active, which allows quality assessment during perfusion. Bile seems to be of rising interest in clinical studies since it is easily collectible for analysis. As there is currently no data on biliary bile acids during NMP, the primary objective of this study was to use our experimental rodent NMP model to assess changes in bile composition through organ damage during perfusion to inform clinical evaluation of donor organs during NMP.

METHODS

30 livers from male Sprague Dawley rats in five groups and underwent 6 hours of NMP using either erythrocyte-supplemented DMEM or Steen solution, with or without 30min of warm ischemia time (WIT). We conducted regular measurements of AST, ALT, LDH, and urea levels in the perfusate at three-hour intervals. Bile samples were analyzed for biliary pH, LDH and GGT as well as biliary bile acids via mass spectrometry and UHPLC.

RESULTS

Compared to regular livers, liver injury parameters were significantly higher in our donation after circulatory death (DCD) model. Bile production was significantly reduced in livers exposed to WIT, and the bile showed a significantly more alkaline pH. This correlated with the concentration of total bile acids, which was significantly higher in livers experiencing WIT. However, regular livers produced a higher total amount of biliary bile acids during perfusion. Taurocholic acid and its metabolites were most prominent. Secondary bile acids were significantly reduced during perfusion due to the missing enterohepatic circulation.

CONCLUSIONS

WIT-induced liver injury affects bile composition within our small animal NMP model. We hypothesize this phenomenon to be attributed to the energy-driven nature of bile secretion, potentially explaining why DCD livers produce less, yet more concentrated, bile. Our results may inform clinical studies, in which biliary bile acids might have a potential as a quantifiable viability marker in human NMP liver transplantation studies.

Serum bile acid levels assist the prediction of biliary stricture and survival after liver transplantation in children

Biliary stricture is an important biliary complication after liver transplant in children. We aimed to investigate the utility of serum bile acid levels for prediction of biliary stricture in children after liver transplant. This study enrolled 60 children who underwent liver transplantation at a mean age of 2.04±0.30 years; serum bile acid levels were surveyed in a cross-sectional design. These patients were followed regularly at our institute, and the clinical data were collected prospectively. The major indication of liver transplant in this pediatric cohort was biliary atresia (78.33%). During the follow-up period (3.08±0.30 years), nine patients (15%) developed biliary stricture after the check of serum bile acid. A receiver operating characteristic curve analysis yielded a serum bile acid cutoff of >40 μM for the prediction of biliary stricture (P = 0.002). A serum bile acid level >40 is the most important predictor of a biliary stricture after liver transplant (odds ratio=65.65, P = 0.003) after adjusting for gender and GGT levels. The phenomenon remained on Cox's proportional hazard survival analysis (hazard ratio =15.42, P = 0.001). The mortality risk after liver transplant was significantly higher in subjects with serum bile acid levels >40 μM than in those with levels ≤40 μM (log-rank test, P = 0.004).Conclusion: Serum bile acid levels can be used for non-invasive screening and prediction of biliary stricture and mortality in children after liver transplantation. What is Known: • Biliary stricture is a major biliary complication after pediatric liver transplantation, and we showed the serum bile acid level significantly associates with biliary stricture. What is New: • In this study, we demonstrated the serum bile acid level may assist in the early detection of biliary stricture and mortality non-invasively.

Bile Composition as a Diagnostic and Prognostic Tool in Liver Transplantation

Bile secretion and composition reflects the functional status of hepatocytes and cholangiocytes. Bile composition can have a role in the assessment of donor grafts before implantation in the recipient. In addition, changes in bile composition after liver transplantation can serve as a diagnostic and prognostic tool to predict posttransplant complications, such as primary nonfunction, acute cellular rejection, or nonanastomotic biliary strictures. With the popularization of liver machine perfusion preservation in the clinical setting, there is a revisited interest in biliary biomarkers to assess graft viability before implantation. This review discusses current literature on biliary biomarkers that could predict or assess liver graft and bile duct viability. Bile composition offers an exciting and novel perspective in the search for reliable hepatocyte and cholangiocyte viability biomarkers.

Bile Duct Ligation Induces ATZ Globule Clearance in a Mouse Model of α-1 Antitrypsin Deficiency

α-1 Antitrypsin deficiency (A1ATD) can progress to cirrhosis and hepatocellular carcinoma; however, not all patients are susceptible to severe liver disease. In A1ATD, a toxic gain-of-function mutation generates insoluble ATZ "globules" in hepatocytes, overwhelming protein clearance mechanisms. The relationship between bile acids and hepatocytic autophagy is less clear but may involve altered gene expression pathways. Based on previous findings that bile duct ligation (BDL) induces autophagy, we hypothesized that retained bile acids may have hepatoprotective effects in PiZZ transgenic mice, which model A1ATD. We performed BDL and partial BDL (pBDL) in PiZZ mice, followed by analysis of liver tissues. PiZZ liver subjected to BDL showed up to 50% clearance of ATZ globules, with increased expression of autophagy proteins. Analysis of transcription factors revealed significant changes. Surprisingly nuclear TFEB, a master regulator of autophagy, remained unchanged. pBDL confirmed that ATZ globule clearance was induced by localized stimuli rather than diet or systemic effects. Several genes involved in bile metabolism were overexpressed in globule-devoid hepatocytes, compared to globule-containing cells. Retained bile acids led to a dramatic reduction of ATZ globules, with enhanced hepatocyte regeneration and autophagy. These findings support investigation of synthetic bile acids as potential autophagy-enhancing agents.

Risk factors and outcomes in post-liver transplantation bile duct stones and casts: A case-control study

Bile duct stones and casts (BDS) after liver transplantation are associated with significant morbidity. Risk factors for BDS formation and the efficacy of treatment in liver transplant recipients have not been systematically studied. The aim of this study was to evaluate potential risk factors for the formation of BDS in patients post-liver transplant. A case-control study of consecutive liver transplant recipients at a university hospital from 1989 to 2007 was performed to identify risk factors for BDS formation. Cases included all liver transplant recipients with BDS, excluding those with concurrent t-tubes or biliary stents. Controls were chosen randomly from the total liver transplant population matched for year of transplantation. Pre- and post-OLT risk factors were analyzed with univariate and multivariate analyses. There were 49 cases and 101 controls over an 18-year-period (1289 liver transplants performed) with an incidence of 3.8% for BDS. In the cases, the median time to BDS diagnosis was 613 days from time of transplant. The controls had a median follow-up of 1530 days. Use of ursodeoxycholic acid was protective (P = 0.005), whereas bile duct pathology (P = 0.003), total cholesterol >/= 200 mg/dL (P = 0.008), and triglyceride >/= 150 mg/dL (P = 0.008) were significant risk factors for BDS formation. Endoscopic retrograde cholangiopancreatography (ERCP) was technically successful in all cases with resolution or improvement of liver chemistries in 59% (29) of patients. In conclusion, significant risk factors for forming BDS included bile duct pathology and elevated total cholesterol and triglyceride levels. Ursodeoxycholic acid had a significant effect in preventing the development of posttransplant BDS and should be used in those that are at increased risk. ERCP is a safe and effective diagnostic and therapeutic modality for these patients.

Bile secretory function after warm hepatic ischemia-reperfusion injury in the rat

Hepatic ischemia-reperfusion (I-R) injury frequently is associated with cholestasis. However, the underlying mechanisms are not fully understood. The aim of the study is to assess bile secretory function in vivo in rats subjected to warm lobar hepatic ischemia at different times during reperfusion. A model of lobar 70% warm hepatic ischemia for 30 minutes was used with studies conducted at 1 and 6 hours and 1, 3, and 7 days after reperfusion. Bile secretory function was assessed after selective cannulation of bile ducts of ischemic (ILs) and nonischemic lobes (NILs). Serum activity of hepatic alanine and aspartate aminotransferase was slightly increased in rats subjected to I-R, whereas serum bile salt levels increased early during reperfusion, returning to control values after 7 days. ILs showed mild reversible leukocyte infiltration and no significant necrosis. Bile flow and bile salt excretion were significantly decreased in ILs during the first 24-hour reperfusion period compared with sham-operated rats and NILs. A marked reduction in glutathione (GSH) excretion occurred at 1 and 6 hours and 1 and 3 days, which returned to control values after 7 days. Total GSH and both reduced and oxidized GSH levels in liver homogenate and arterial blood GSH levels were unchanged at all times. Protein mass of multidrug resistance protein 2 and its function, assessed by the hepatic maximum secretory rate of ceftriaxone, did not show significant changes in ILs or NILs compared with sham-operated rats. Liver tissue gamma-glutamyl transpeptidase (GGT) and gamma-glutamylcysteine synthetase activities remained unchanged, whereas biliary GGT and cysteine secretory rates were significantly increased in ILs and NILs. Administration of acivicin, a GGT inhibitor, resulted in decreased secretion of this enzyme into bile and a parallel marked increase in biliary GSH secretion compared with untreated ischemic rats. In conclusion, warm hepatic I-R induces reversible cholestatic changes in ILs. GSH secretory rates from both ILs and NILs were markedly decreased during reperfusion. The reversibility of this effect after GGT inhibition, as well as increased release of active GGT into bile and cysteine biliary secretory rates, suggest increased GSH degradation in bile. These findings might be relevant for the I-R-induced clinical cholestasis, as well as cholangiocyte injury, seen after hepatic ischemia.

Biliary inorganic phosphate as a tool for assessing cold preservation-reperfusion injury: a study in the isolated perfused rat liver model

Ischemia-reperfusion injury is a major cause of early graft dysfunction after liver transplantation. The bile flow has been suggested as an index of ischemic damage, and severely impaired bile flow seems to be predictive of poor survival in experimental studies. Looking for injury markers, biliary inorganic phosphate has the potential of being a useful endogenous marker of diminished hepatobiliary function because this anion is excreted in the bile by a paracellular pathway and it can detect changes in permeability. The goal of this study was to evaluate the effects of cold preservation-reperfusion of the liver on bile flow and bile inorganic phosphate and their relationship with storage-related graft failure. The isolated and perfused rat liver was used to evaluate the injury for ischemia-reperfusion. The intrahepatic resistance, lactate dehydrogenase release, and potassium and biliary inorganic phosphate concentration were used to estimate viability and function of freshly isolated or cold-preserved livers. The intrahepatic resistance and the bile flow were consistent and significantly decreased throughout the perfusion time in relation to the increment in storage. Inorganic phosphate is more concentrated in bile from preserved livers, showing an alteration in paracellular pathway, confirmed by the biliary excretion of horseradish peroxidase. After preservation, concentration and excretion of the paracellular marker were increased during the first peak. The second peak appears earlier in preserved livers (10 minutes) with a different shape but without changes in concentration. In conclusion, inorganic phosphate in bile shows changes in paracellular permeability as occurs in livers after 48 hours of cold preservation.

Cholelithiasis in pediatric organ transplantation: detection and management

The real incidence and the underlying causes of cholelithiasis in pediatric solid organ recipients is probably not exactly known. In addition to well-established risk factors for cholelithiasis, children after heart, kidney, or liver transplantation may develop gallstones due to drug therapy, sepsis, parenteral nutrition, or surgical complications. For pediatric patients, data are very limited and heterogeneous. However, the incidence in pediatric heart recipients seems to be substantially higher compared with kidney or liver graft recipients. In this review article the present data are discussed focusing on incidence, detection, and management of cholelithiasis in pediatric organ transplantation. In general, surgery is the therapy of choice in symptomatic patients; however, the pharmacological profile of ursodeoxycholic acid and the first results on its clinical impact are promising. The value of prophylactic therapy with ursodeoxycholic acid must be determined in further studies.

Biliary lipid composition after liver transplantation: effect of allograft function and cyclosporine

Biliary lipid composition and bile flow are altered after orthotopic liver transplantation. Cyclosporine may have additional effects on biliary lipid composition and secretion. We studied the effects of liver transplantation, allograft function, and cyclosporine on biliary lipids in humans. Changes in lipid composition and secretion were correlated with serum cyclosporine levels, clinical events, and allograft function. Bile samples were withdrawn via a T-tube at interval time points in 17 patients during the first 3 months posttransplantation. Total and individual bile acid, cholesterol, and phospholipid were determined using high-performance liquid chromatography. Biliary lipid profiles were then correlated with clinical events, serum cyclosporine levels, and other clinical laboratory values. Biliary lipid concentrations decreased in 3 patients during periods of graft dysfunction (acute cellular rejection, drug-induced hepatitis, and inferior vena caval thrombosis) and increased with resolution of the graft injury. Serum cyclosporine levels were positively correlated with total bile acid, cholesterol, and phospholipid concentrations in bile. There was no relationship between the composition of secreted bile acids and serum cyclosporine levels. Bile acid, cholesterol, and phospholipid secretion were not uncoupled in the presence of cyclosporine. We concluded that (1) a decrease in biliary lipid concentrations may be an indicator of worsened graft function in some allografts; (2) biliary lipid concentrations are correlated with increasing cyclosporine levels; and (3) bile acid composition is unchanged, and uncoupling of secretion of other biliary lipids is not observed in the presence of cyclosporine.

Role of glutathione in hepatic bile formation during reperfusion after cold ischemia of the rat liver

BACKGROUND/AIMS

Liver reperfusion following cold ischemia is frequently associated with diminished bile flow in patients undergoing liver transplantation. Glutathione is a major determinant of bile-acid independent bile flow, and the effects of cold ischemia on biliary glutathione excretion are unknown.

METHODS

We examined the effects of cold ischemia (University of Wisconsin solution (4 degrees C), 24 h) with subsequent reperfusion (100 min) on biliary glutathione excretion in a recirculating system. Since glutathione might represent an important antioxidant within the biliary tract and oxidative stress in the biliary tract during reperfusion could contribute to the pathogenesis of bile duct injury after liver transplantation, we also assessed bile duct morphology in reperfused livers of mutant TR- -rats, in whom biliary excretion of glutathione is already impaired.

RESULTS

Hepatic bile formation was diminished in reperfused Wistar rat livers after cold ischemia. Biliary glutathione concentrations and output were significantly decreased and correlated with postischemic changes in bile secretion. An increased biliary oxidized glutathione/glutathione ratio, indicating oxidative stress, was detected only immediately after the onset of reperfusion. Basal bile flow rates in TR- -rat livers which were already markedly reduced in control-perfused livers, decreased further during the early but not the later reperfusion period. Reperfusion of both Wistar and TR- -rat livers was not associated with electron microscopic evidence of bile duct damage.

CONCLUSIONS

We conclude that impaired biliary excretion of glutathione contributes to decreased bile flow after cold ischemia. The absence of biliary glutathione does not appear to promote ultrastructural evidence of bile duct injury during reperfusion in the isolated perfused rat liver.

Surgical techniques of orthotopic rat liver transplantation

Liver transplantation in rats is frequently used as a transplantation model. Although liver transplantation in larger laboratory animals such as dogs and pigs is technically easier, the rat has become the most important subject for experimental liver transplantation because of the availability of genetically defined animals. Numerous surgical techniques have been developed that permit the investigator to carry out studies with high clinical relevance. In this article the principal models of orthotopic rat liver transplantation and their technical modifications of vessel anastomoses, rearterialization, and bile duct reconstruction techniques are reviewed. More than 20 transplantation models are described in detail and demonstrated with clear illustrations. Finally, the advantages and uses of all the surgical procedures (e.g., suture and cuff anastomoses, bile duct anastomoses, and rearterialization techniques), specific problems, and survival criteria are discussed and the experiences of investigators who applied these techniques are analyzed. In conclusion, an overview and critical evaluation of all surgical techniques of orthotopic rat liver transplantation are given, together with instructions for learning these techniques.

The effects of liver transplantation and cyclosporine on bile formation and lipid composition: an experimental study in the rat

BACKGROUND/AIMS

Hepatic graft dysfunction is a major management problem in the early post-liver transplantation period. Our aims were to study how liver transplantation per se affects bile formation, and to investigate the role of cyclosporine in the pathogenesis of early graft dysfunction.

METHODS

Syngeneic liver transplantation used male Lewis rats. Two weeks after transplantation, the rats were randomly assigned to receive either daily subcutaneous injections of cyclosporine 10 mg/kg for 1 week (n=8), or daily saline injections (Placebo, n=8). 24-h bile collections were performed 18 h after the last injection. Eight non-transplanted rats served as controls.

RESULTS

Liver transplantation per se (Placebo) significantly increased basal bile flow (51%), particularly that portion which was bile salt-independent flow (81%), but did not impair bile salt kinetics or biliary lipid composition. Cyclosporine reduced basal bile flow and bile salt-independent flow by 41% and 30%, respectively. Bile salt synthesis was 52% suppressed, leading to a 22% decrease in the bile salt pool size. The recycling frequency of the bile salt pool was unaffected. The drug inhibited bile salt (37%) and phospholipid (23%) outputs; cholesterol secretion remained unaltered. This significantly elevated the cholesterol saturation of bile (25%).

CONCLUSIONS

Liver transplantation per se is choleretic and does not impair bile formation or lipid composition in this inbred rat model. Parenteral administration of high-dose cyclosporine induces cholestasis by inhibiting bile salt secretion and BSIF. Bile salt synthesis is down-regulated and the bile salt pool size decreased. The drug adversely affects biliary lipid composition by differential inhibition of bile salt and phospholipid outputs relative to an unchanged cholesterol secretion.

Endoscopic diagnosis and management of biliary complications following orthotopic liver transplantation

Nonoperative management of biliary complications (BC) with endoscopic retrograde cholangiopancreatography (ERCP) is a natural sequel to the emergence of choledochocholedochostomy as the preferred biliary reconstruction for orthotopic liver transplantation (OLT). Overall, therapeutic ERCP's efficacy for posttransplant BC is difficult to assess because most published data are retrospective, anecdotal, or in abstract form, and there are no prospective, randomized studies. Thus, endoscopic management of posttransplant BC must be individualized. While T-tube-related late bile leaks and ductal calculi are amenable to endoscopic therapy, its efficacy for strictures is more difficult to define. Refined surgical technique has prevented many unifocal anastomotic lesions, while multifocal strictures (for which endoscopic therapeutic experience is minimal) are increasingly prevalent. Whether endoscopic sphincterotomy is appropriate for posttransplant sphincter of Oddi dysfunction is controversial, because the disorder may be transient and the risk significant. Multicenter, prospective studies are needed to determine more accurately the optimal role of endoscopic therapy after OLT.