4-Methylpyrazole protects against acetaminophen hepatotoxicity in mice and in primary human hepatocytes

Liver injury due to acetaminophen (APAP) overdose is the major cause of acute liver failure in the United States. While treatment with N-acetylcysteine is the current standard of care for APAP overdose, anecdotal evidence suggests that administration of 4-methylpyrazole (4MP) may be beneficial in the clinic. The objective of the current study was to examine the protective effect of 4MP and its mechanism of action. Male C57BL/6J mice were co-treated with 300 mg/kg of APAP and 50 mg/kg of 4MP. The severe liver injury induced by APAP at 6 h as indicated by elevated plasma alanine aminotransferase activities, centrilobular necrosis, and nuclear DNA fragmentation was almost completely eliminated by 4MP. In addition, 4MP largely prevented APAP-induced activation of c-Jun N-terminal kinase (JNK), mitochondrial translocation of phospho-JNK and Bax, and the release of mitochondrial intermembrane proteins. Importantly, 4MP inhibited the generation of APAP protein adducts and formation of APAP-glutathione (GSH) conjugates and attenuated the depletion of the hepatic GSH content. These findings are relevant to humans because 4MP also prevented APAP-induced cell death in primary human hepatocytes. In conclusion, early treatment with 4MP can completely prevent liver injury after APAP overdose by inhibiting cytochrome P450 and preventing generation of the reactive metabolite.

Abundance of Phase 1 and 2 Drug-Metabolizing Enzymes in Alcoholic and Hepatitis C Cirrhotic Livers: A Quantitative Targeted Proteomics Study

To predict the impact of liver cirrhosis on hepatic drug clearance using physiologically based pharmacokinetic (PBPK) modeling, we compared the protein abundance of various phase 1 and phase 2 drug-metabolizing enzymes (DMEs) in S9 fractions of alcoholic (n = 27) or hepatitis C (HCV, n = 30) cirrhotic versus noncirrhotic (control) livers (n = 25). The S9 total protein content was significantly lower in alcoholic or HCV cirrhotic versus control livers (i.e., 38.3 ± 8.3, 32.3 ± 12.8, vs. 51.1 ± 20.7 mg/g liver, respectively). In general, alcoholic cirrhosis was associated with a larger decrease in the DME abundance than HCV cirrhosis; however, only the abundance of UGT1A4, alcohol dehydrogenase (ADH)1A, and ADH1B was significantly lower in alcoholic versus HCV cirrhotic livers. When normalized to per gram of tissue, the abundance of nine DMEs (UGT1A6, UGT1A4, CYP3A4, UGT2B7, CYP1A2, ADH1A, ADH1B, aldehyde oxidase (AOX)1, and carboxylesterase (CES)1) in alcoholic cirrhosis and five DMEs (UGT1A6, UGT1A4, CYP3A4, UGT2B7, and CYP1A2) in HCV cirrhosis was <25% of that in control livers. The abundance of most DMEs in cirrhotic livers was 25% to 50% of control livers. CES2 abundance was not affected by cirrhosis. Integration of UGT2B7 abundance in cirrhotic livers into the liver cirrhosis (Child Pugh C) model of Simcyp improved the prediction of zidovudine and morphine PK in subjects with Child Pugh C liver cirrhosis. These data demonstrate that protein abundance data, combined with PBPK modeling and simulation, can be a powerful tool to predict drug disposition in special populations.

Increased hepatic receptor interacting protein kinase 3 expression due to impaired proteasomal functions contributes to alcohol-induced steatosis and liver injury

Chronic alcohol exposure increased hepatic receptor-interacting protein kinase (RIP) 3 expression and necroptosis in the liver but its mechanisms are unclear. In the present study, we demonstrated that chronic alcohol feeding plus binge (Gao-binge) increased RIP3 but not RIP1 protein levels in mouse livers. RIP3 knockout mice had decreased serum alanine amino transferase activity and hepatic steatosis but had no effect on hepatic neutrophil infiltration compared with wild type mice after Gao-binge alcohol treatment. The hepatic mRNA levels of RIP3 did not change between Gao-binge and control mice, suggesting that alcohol-induced hepatic RIP3 proteins are regulated at the posttranslational level. We found that Gao-binge treatment decreased the levels of proteasome subunit alpha type-2 (PSMA2) and proteasome 26S subunit, ATPase 1 (PSMC1) and impaired hepatic proteasome function. Pharmacological or genetic inhibition of proteasome resulted in the accumulation of RIP3 in mouse livers. More importantly, human alcoholics had decreased expression of PSMA2 and PSMC1 but increased protein levels of RIP3 compared with healthy human livers. Moreover, pharmacological inhibition of RIP1 decreased Gao-binge-induced hepatic inflammation, neutrophil infiltration and NF-κB subunit (p65) nuclear translocation but failed to protect against steatosis and liver injury induced by Gao-binge alcohol. In conclusion, results from this study suggest that impaired hepatic proteasome function by alcohol exposure may contribute to hepatic accumulation of RIP3 resulting in necroptosis and steatosis while RIP1 kinase activity is important for alcohol-induced inflammation.

Transporter Expression in Liver Tissue from Subjects with Alcoholic or Hepatitis C Cirrhosis Quantified by Targeted Quantitative Proteomics

Although data are available on the change of expression/activity of drug-metabolizing enzymes in liver cirrhosis patients, corresponding data on transporter protein expression are not available. Therefore, using quantitative targeted proteomics, we compared our previous data on noncirrhotic control livers (n = 36) with the protein expression of major hepatobiliary transporters, breast cancer resistance protein (BCRP), bile salt export pump (BSEP), multidrug and toxin extrusion protein 1 (MATE1), multidrug resistance-associated protein (MRP)2, MRP3, MRP4, sodium taurocholate-cotransporting polypeptide (NTCP), organic anion-transporting polypeptides (OATP)1B1, 1B3, 2B1, organic cation transporter 1 (OCT1), and P-glycoprotein (P-gp) in alcoholic (n = 27) and hepatitis C cirrhosis (n = 30) livers. Compared with control livers, the yield of membrane protein from alcoholic and hepatitis C cirrhosis livers was significantly reduced by 56 and 67%, respectively. The impact of liver cirrhosis on transporter protein expression was transporter-dependent. Generally, reduced protein expression (per gram of liver) was found in alcoholic cirrhosis livers versus control livers, with the exception that the expression of MRP3 was increased, whereas no change was observed for MATE1, MRP2, OATP2B1, and P-gp. In contrast, the impact of hepatitis C cirrhosis on protein expression of transporters (per gram of liver) was diverse, showing an increase (MATE1), decrease (BSEP, MRP2, NTCP, OATP1B3, OCT1, and P-gp), or no change (BCRP, MRP3, OATP1B1, and 2B1). The expression of hepatobiliary transporter protein differed in different diseases (alcoholic versus hepatitis C cirrhosis). Finally, incorporation of protein expression of OATP1B1 in alcoholic cirrhosis into the Simcyp physiologically based pharmacokinetics cirrhosis module improved prediction of the disposition of repaglinide in liver cirrhosis patients. These transporter expression data will be useful in the future to predict transporter-mediated drug disposition in liver cirrhosis patients.

Lack of direct cytotoxicity of extracellular ATP against hepatocytes: role in the mechanism of acetaminophen hepatotoxicity

BACKGROUND

Acetaminophen (APAP) hepatotoxicity is a major cause of acute liver failure in many countries. Mechanistic studies in mice and humans have implicated formation of a reactive metabolite, mitochondrial dysfunction and oxidant stress as critical events in the pathophysiology of APAP-induced liver cell death. It was recently suggested that ATP released from necrotic cells can directly cause cell death in mouse hepatocytes and in a hepatoma cell line (HepG2).

AIM

To assess if ATP can directly cause cell toxicity in hepatocytes and evaluate their relevance in the human system.

METHODS

Primary mouse hepatocytes, human HepG2 cells, the metabolically competent human HepaRG cell line and freshly isolated primary human hepatocytes were exposed to 10-100 µM ATP or ATγPin the presence or absence of 5-10 mM APAP for 9-24 h.

RESULTS

ATP or ATγP was unable to directly cause cell toxicity in all 4 types of hepatocytes. In addition, ATP did not enhance APAP-induced cell death observed in primary mouse or human hepatocytes, or in HepaRG cells as measured by LDH release and by propidium iodide staining in primary mouse hepatocytes. Furthermore, addition of ATP did not cause mitochondrial dysfunction or enhance APAP-induced mitochondrial dysfunction in primary murine hepatocytes, although ATP did cause cell death in murine RAW macrophages.

CONCLUSIONS

It is unlikely that ATP released from necrotic cells can significantly affect cell death in human or mouse liver during APAP hepatotoxicity.

RELEVANCE FOR PATIENTS

Understanding the mechanisms of APAP-induced cell injury is critical for identifying novel therapeutic targets to prevent liver injury and acute liver failure in APAP overdose patients.

Lack of Direct Cytotoxicity of Extracellular ATP against Hepatocytes: Role in the Mechanism of Acetaminophen Hepatotoxicity

BACKGROUND

Acetaminophen (APAP) hepatotoxicity is a major cause of acute liver failure in many countries. Mechanistic studies in mice and humans have implicated formation of a reactive metabolite, mitochondrial dysfunction and oxidant stress as critical events in the pathophysiology of APAP-induced liver cell death. It was recently suggested that ATP released from necrotic cells can directly cause cell death in mouse hepatocytes and in a hepatoma cell line (HepG2).

AIM

To assess if ATP can directly cause cell toxicity in hepatocytes and evaluate their relevance in the human system.

METHODS

Primary mouse hepatocytes, human HepG2 cells, the metabolically competent human HepaRG cell line and freshly isolated primary human hepatocytes were exposed to 10-100 μM ATP or ATγP in the presence or absence of 5-10 mM APAP for 9-24 h.

RESULTS

ATP or ATγP was unable to directly cause cell toxicity in all 4 types of hepatocytes. In addition, ATP did not enhance APAP-induced cell death observed in primary mouse or human hepatocytes, or in HepaRG cells as measured by LDH release and by propidium iodide staining in primary mouse hepatocytes. Furthermore, addition of ATP did not cause mitochondrial dysfunction or enhance APAP-induced mitochondrial dysfunction in primary murine hepatocytes, although ATP did cause cell death in murine RAW macrophages.

CONCLUSIONS

It is unlikely that ATP released from necrotic cells can significantly affect cell death in human or mouse liver during APAP hepatotoxicity.

RELEVANCE FOR PATIENTS

Understanding the mechanisms of APAP-induced cell injury is critical for identifying novel therapeutic targets to prevent liver injury and acute liver failure in APAP overdose patients.

Late-onset renal vein thrombosis: A case report and review of the literature

INTRODUCTION

Renal vein thrombosis, a rare complication of renal transplantation, often causes graft loss. Diagnosis includes ultrasound with Doppler, and it is often treated with anticoagulation or mechanical thrombectomy. Success is improved with early diagnosis and institution of treatment.

PRESENTATION OF CASE

We report here the case of a 29 year-old female with sudden development of very late-onset renal vein thrombosis after simultaneous kidney pancreas transplant. This resolved initially with thrombectomy, stenting and anticoagulation, but thrombosis recurred, necessitating operative intervention. Intraoperatively the renal vein was discovered to be compressed by a large ovarian cyst.

DISCUSSION

Compression of the renal vein by a lymphocele or hematoma is a known cause of thrombosis, but this is the first documented case of compression and thrombosis due to an ovarian cyst.

CONCLUSION

Early detection and treatment of renal vein thrombosis is paramount to restoring renal allograft function. Any woman of childbearing age may have thrombosis due to compression by an ovarian cyst, and screening for this possibility may improve long-term graft function in this population.

Mechanisms of acetaminophen-induced cell death in primary human hepatocytes

Acetaminophen (APAP) overdose is the most prevalent cause of drug-induced liver injury in western countries. Numerous studies have been conducted to investigate the mechanisms of injury after APAP overdose in various animal models; however, the importance of these mechanisms for humans remains unclear. Here we investigated APAP hepatotoxicity using freshly isolated primary human hepatocytes (PHH) from either donor livers or liver resections. PHH were exposed to 5mM, 10mM or 20mM APAP over a period of 48 h and multiple parameters were assessed. APAP dose-dependently induced significant hepatocyte necrosis starting from 24h, which correlated with the clinical onset of human liver injury after APAP overdose. Interestingly, cellular glutathione was depleted rapidly during the first 3h. APAP also resulted in early formation of APAP-protein adducts (measured in whole cell lysate and in mitochondria) and mitochondrial dysfunction, indicated by the loss of mitochondrial membrane potential after 12h. Furthermore, APAP time-dependently triggered c-Jun N-terminal kinase (JNK) activation in the cytosol and translocation of phospho-JNK to the mitochondria. Both co-treatment and post-treatment (3h) with the JNK inhibitor SP600125 reduced JNK activation and significantly attenuated cell death at 24h and 48h after APAP. The clinical antidote N-acetylcysteine offered almost complete protection even if administered 6h after APAP and a partial protection when given at 15 h.

CONCLUSION

These data highlight important mechanistic events in APAP toxicity in PHH and indicate a critical role of JNK in the progression of injury after APAP in humans. The JNK pathway may represent a therapeutic target in the clinic.

Donor risk index predicts graft failure reliably but not post-transplant infections

BACKGROUND

The Donor Risk Index (DRI) is used to predict graft survival following liver transplantation, but has not been used to predict post-operative infections in graft recipients. We hypothesized that lower-quality grafts would result in more frequent infectious complications.

METHODS

Using a prospectively collected infection data set, we matched liver transplant recipients (and the respective allograft DRI scores) with their specific post-transplant infectious complications. All transplant recipients were organized by DRI score and divided into groups with low-DRI and high-DRI scores.

RESULTS

We identified 378 liver transplants, with 189 recipients each in the low-DRI and high-DRI groups. The mean DRI scores for the low- and high-DRI-score groups were 1.14±0.01 and 1.74±0.02, respectively (p<0.0001 for the difference). The mean Model for End-Stage Liver Disease (MELD) scores were 26.25±0.53 and 24.76±0.55, respectively (p=0.052), and the mean number of infectious complications per patient were 1.60±0.19 and 1.94±0.24, respectively (p=0.26). Logistic regression showed only length of hospital stay and a history of vascular disease as being associated independently with infection, with a trend toward significance for MELD score (p=0.13).

CONCLUSION

We conclude that although DRI score predicts graft-liver survival, infectious complications depend more heavily on recipient factors.

Self expandable metal stents for anastomotic stricture following liver transplant

BACKGROUND

Endoscopic treatment for biliary strictures with plastic stent placement has been used widely. The use of covered self-expandable metal stents (CSEMS) has been reported in anastomotic strictures post liver transplant. The aim of this study was to evaluate the efficacy of different CSEMS in these subjects.

METHODS

A total of 55 patients with anastomotic stricture received CSEMS, which were removed after 3-4 months. There were 19 patients in group A (partially covered SEMS), 21 patients in group B (fully covered SEMS with fins) and 15 patients in group C (fully covered SEMS with flared ends). Technical success, stricture resolution, follows up, and complications were documented.

RESULTS

CSEMS were successfully deployed in all 55 cases. There was no evidence of significant difference with regards to stricture resolution (14 [74%] vs. 15 [71%] vs. 9 [60%] p=0.6630, df=2) or complications between groups. Stent-related complications were as follows: three in group A (2 migration, 1 occlusion), five in group B (4 occlusions, 1 migration), and one proximal migration in group C (p=0.3894, df=2). Three cases required surgery (hepatico-jejunostomy) due to refractory strictures.

CONCLUSIONS

The observed clinical success rate of CSEMS (70.4%) proved to be below the reported one for multiple plastic stents, while no significant differences between CSEMS types were observed.

Impact of stem cell marker expression on recurrence of TACE-treated hepatocellular carcinoma post liver transplantation

BACKGROUND

Liver transplantation is the most effective therapy for cirrhosis-associated hepatocellular carcinoma (HCC) but its utility is limited by post-transplant tumor recurrence. Use of the Milan, size-based criteria, has reduced recurrence rate to less than 10% but many patients remain ineligible. Reduction of tumor size with local therapies has been used to "downstage" patients to allow them to qualify for transplantation, but the optimal criteria to predict tumor recurrence in these latter patients has not been established. The existence of a progenitor cell population, sometimes called cancer stem cells (CSCs), has been proposed to be one mechanism accounting for the chemotherapy resistance and recurrence of hepatocellular carcinoma. The aim of this study was to determine if transcatheter arterial chemoemolization (TACE) treated tumors have increased CSC marker expression and whether these markers could be used to predict tumor recurrence.

METHODS

Formalin fixed specimens were obtained from 39 HCC liver explants (23 with no treatment and 16 after TACE). Immunohistochemical staining was performed for EpCAM, CD44, CD90, and CD133. Staining for each marker was scored 0-3 by evaluating the number and intensity of positive tumor cells in 5 hpf of tumor in each specimen.

RESULTS

TACE treated tumors displayed greater necrosis and fibrosis than non-TACE treated samples but there were no differences in morphology between the viable tumor cells of both groups. In TACE treated specimens, the staining of both EpCAM and CD133 was greater than in non-TACE specimens but CD44 and CD90 were the same. In the TACE group, the presence of high EpCAM staining was associated with tumor recurrence. Four of ten EpCAM high patients recurred while 0 of 6 EpCAM low patients recurred (P = 0.040). None of the other markers predicted recurrence.

CONCLUSION

High pre-transplant EpCAM staining predicted HCC recurrence. This suggests that the abundance of tumor cells with a CSC phenotype may be a critical factor in the likelihood of tumor recurrence in patients receiving liver transplantation after TACE.

Elderly recipients of hepatitis C positive renal allografts can quickly develop liver disease

Our institution explored using allografts from donors with Hepatitis C virus (HCV) for elderly renal transplantation (RT). Thirteen HCV- elderly recipients were transplanted with HCV+ allografts (eD+/R-) between January 2003 and April 2009. Ninety HCV- elderly recipients of HCV- allografts (eD-/R-), eight HCV+ recipients of HCV+ allografts (D+/R+) and thirteen HCV+ recipients of HCV- allografts (D-/R+) were also transplanted. Median follow-up was 1.5 (range 0.8-5) years. Seven eD+/R- developed a positive HCV viral load and six had elevated liver transaminases with evidence of hepatitis on biopsy. Overall, eD+/R- survival was 46% while the eD-/R- survival was 85% (P = 0.003). Seven eD+/R- died during follow-up. Causes included multi-organ failure and sepsis (n = 4), cancer (n = 1), failure-to-thrive (n = 1) and surgical complications (n = 1). One eD+/R- died from causes directly related to HCV infection. In conclusion, multiple eD+/R- quickly developed HCV-related liver disease and infections were a frequent cause of morbidity and mortality.

Quantifying increased hepatic arterial flow with test balloon occlusion of the splenic artery in liver transplant recipients with suspected splenic steal syndrome: quantitative digitally subtracted angiography correlation with arterial Doppler parameters

PURPOSE

The purpose of this study is to quantify hepatic arterial flow (HAF) in liver transplants with splenic steal syndrome (SSS) pre- and post-test balloon occlusion of the splenic artery utilizing Doppler ultrasound (DUS) and quantitative digitally subtracted angiography (Q-DSA).

METHODS

A total of 193 liver transplants were evaluated retrospectively. Hepatic arterial velocity (HAV) and HAF were calculated utilizing DUS and Q-DSA (i-flow prototype, Siemens) pre- and post-splenic artery balloon occlusion. The rate of HAF increase, total HAF, and peak contrast density (PKD) by Q-DSA were compared with HAF by DUS.

RESULTS

Of all, 4 suspected SSS cases underwent test-balloon occlusion with DUS and Q-DSA. Using DUS, HAV and HAF increased by 1.6- to 1.8-fold and 1.7- to 2.6-fold, respectively. Using Q-DSA, the HAF rate, total HAF, and PKD increased by 1.1 to 12.8, 1.5 to 7.6, and 1.3 to 5.3, respectively.

CONCLUSION

Occlusion of the splenic artery in liver transplants with SSS doubles the HAF (+1.7- to 2.6-fold). The Q-DSA parameters correlate qualitatively but overestimate the resultant increased HAF.

Regional variability in symptom-based MELD exceptions: a response to organ shortage?

MELD (model for end-stage liver disease) exception awards affect the liver allocation process. Award rates of specific nonhepatocellular carcinoma exceptions, termed symptom-based exceptions (SBE), differ across UNOS regions. We aimed to characterize the regional variability in SBE awards and examine predictive factors for receiving a SBE in the MELD era. The OPTN liver transplant and waiting list dataset was analyzed for waiting list registrants during the MELD allocation on February 27, 2002, until November 22, 2006. Competing risks proportional hazards regression analysis was used to examine predictors for receiving a SBE in 39 169 registrants. The hazard ratios for receiving a SBE differed significantly across regions when adjusted for multiple variables including age, gender, ethnicity, physiologic MELD score, blood group, functional status, etiology of liver disease, insurer and education level. Utilization of SBE is highly significantly variable across UNOS regions, and does not correlate with organ availability as estimated by the regional mean physiologic MELD score at transplantation. Patients with Medicaid as their primary payer have a lower likelihood of receiving a SBE award, while patients with cryptogenic/NASH cirrhosis or cholestatic liver disease have a higher likelihood of receiving a SBE. Reasons for these regional and demographic disparities deserve further investigation.

Endovascular therapy for hepatic artery stenosis and thrombosis following liver transplantation

PURPOSE

To evaluate the effectiveness of endovascular management of steno-oclusive disease in liver transplants.

METHODS

Retrospective review of liver transplant recipients with hepatic artery stenosis (HAS) or thrombosis (HAT) was performed. The HAS group was treated with balloon angioplasty with selective stent placement. The HAT group was treated with catheter-directed thrombolysis. Primary, unassisted, and assisted patency and graft survival rates were calculated.

RESULTS

In all, 31 patients were identified (21 males; mean age, 51 years). A total of 25 of 31 (81%) patients had HAS and 6 of 31 (19%) had HAT. Collectively, a total of 35 endovascular procedures were performed to treat HAS in 25 patients. Overall technical success rate was 91%, with 11% major complication rate. Primary-assisted patency rate and graft survival at 6 and 12 months were 87% and 81%, and 76% and 72%, respectively. Only 1 successful thrombolysis of HAT was achieved.

CONCLUSION

Endovascular management is effective for HAS but not for HAT.

Evolution of β-Cell Replacement Therapy in Diabetes Mellitus: Pancreas Transplantation

Diabetes mellitus remains one of the leading causes of morbidity and mortality worldwide. According to the Centers for Disease Control and Prevention, approximately 23.6 million people in the United States are affected. Of these individuals, 5-10% have been diagnosed with type 1 diabetes mellitus (TIDM), an autoimmune disease. Although it often appears in childhood, T1DM may manifest at any age. The effects of T1DM can be devastating, as the disease often leads to significant secondary complications, morbidity, and decreased quality of life. Since the late 1960s, surgical treatment for diabetes mellitus has continued to evolve and has become a viable alternative to chronic insulin administration. In this review, the historical evolution, current status, graft efficacy, benefits, and complications of pancreas transplantation are explored.

Liver allografts from hepatitis C positive donors can offer good outcomes in hepatitis C positive recipients: a US National Transplant Registry analysis

Organ donors are screened for the hepatitis C antibody (anti-HCV) and those with positive tests can be used under extended criteria donation. However, there is still a question of long-term organ viability. The aim of this study was to assess the long-term outcomes of anti-HCV positive (HCV+) liver grafts. The US Organ Procurement and Transplantation Network Scientific Registry was reviewed for the period from April 1994 to February 6, 2008 and 56,275 liver transplantations were analyzed. In total, there were 19,496 HCV+ recipients and 934 HCV+ donors. Patient and graft survival were assessed accounting for both donor and recipient anti-HCV status. Multivariable proportional hazards survival models were developed to adjust for factors known to affect post-transplant survival. With anti-HCV negative (HCV-) recipient/HCV- donor as the reference, the adjusted hazard ratio for death was similar for HCV+ recipient/HCV- donor compared with HCV+ recipient/HCV+ donor (1.176 vs. 1.165, P = 0.91). Our results suggest that HCV+ liver donors do not subject the HCV+ recipient to an increased risk for death over the HCV- donor, keeping in mind that careful donor and recipient selection is critical for the proper use of these extended criteria donors.

Liver allografts from hepatitis C positive donors can offer good outcomes in hepatitis C positive recipients: a US National Transplant Registry analysis

Organ donors are screened for the hepatitis C antibody (anti-HCV) and those with positive tests can be used under extended criteria donation. However, there is still a question of long-term organ viability. The aim of this study was to assess the long-term outcomes of anti-HCV positive (HCV+) liver grafts. The US Organ Procurement and Transplantation Network Scientific Registry was reviewed for the period from April 1994 to February 6, 2008 and 56,275 liver transplantations were analyzed. In total, there were 19,496 HCV+ recipients and 934 HCV+ donors. Patient and graft survival were assessed accounting for both donor and recipient anti-HCV status. Multivariable proportional hazards survival models were developed to adjust for factors known to affect post-transplant survival. With anti-HCV negative (HCV-) recipient/HCV- donor as the reference, the adjusted hazard ratio for death was similar for HCV+ recipient/HCV- donor compared with HCV+ recipient/HCV+ donor (1.176 vs. 1.165, P = 0.91). Our results suggest that HCV+ liver donors do not subject the HCV+ recipient to an increased risk for death over the HCV- donor, keeping in mind that careful donor and recipient selection is critical for the proper use of these extended criteria donors.

Liver transplantation for T3 lesions has higher waiting list mortality but similar survival compared to T1 and T2 lesions

BACKGROUND

Restrictive staging criteria for liver transplant (LT) patients with HCC in the U.S. have resulted in favorable long-term recurrence-free survival, but these criteria exclude a subgroup of patients who, despite tumor size beyond T2 stage, demonstrate an acceptable outcome. The aim of this study was to assess the waiting list and post-transplant mortality of patients with HCC tumors greater than Milan T2 stage.

METHODS

The U.S. OPTN standard transplant dataset was analyzed for patients with a diagnosis of HCC who were listed for liver transplantation between February 2002 and 2008. Those patients with Milan T3 stage tumors were compared to patients with T1 and T2 lesions. Multivariate survival models were developed to investigate independent predictors of death or tumor recurrence post-transplant.

RESULTS

7,391 patients with HCC were identified. 351 (4.75%) had T3 lesions. Compared to non-T3 patients, total tumor burden was greater and total alpha-fetoprotein (AFP) was higher in the T3 patients. T3 patients also were more likely to receive pretransplant locoregional therapy. There were no significant differences between T3 patients and non-T3 patients in demographic variables or physiologic MELD score at the time of transplant, waiting time, or donor risk index. Waiting list mortality was increased for T3 patients compared to non-T3 and tumor progression while waiting was higher. Independent predictors of waiting list mortality included physiologic MELD score at the time of listing, total tumor burden, and serum AFP. There was significant regional variation in the utilization of exceptions for T3 patients and UNOS regions 4, 9, and 10 performed a higher percentage of their transplants in T3 patients compared to other regions. There was no difference in post transplant survival between T3 and non-T3 patients. Independent predictors of post-transplant mortality included physiologic MELD score at the time of transplant, recipient age, and donor risk index. In patients with T3 tumors, total tumor burden was not an independent predictor of post transplant survival.

CONCLUSIONS

Patients who are listed for liver transplantation with Milan stage T3 HCC have higher waiting list mortality but have similar post-transplant survival compared to patients with T1 and T2 HCC.

Advanced recipient age (>60 years) alone should not be a contraindication to liver retransplantation

Advanced age has been shown to be a risk factor for survival in primary liver transplantation. We sought to determine the independent influence of recipient age on retransplantation survival. The UNOS dataset was analyzed for adult, nonstatus 1, liver retransplantations since February 27, 2002. The univariate effect of age on 90-day and 1-year survival was analyzed. Multivariate survival models were used to determine 90-day, 1-year, and overall survival. Recipient age, donor age, model for end-stage liver disease (MELD) score, and hepatitis C status were used to construct multivariable survival models. Some 2141 liver retransplantations were analyzed. Overall, increasing recipient age was independently predictive of increasing mortality after liver retransplantation. In recipients between 18 and 60, there remained a direct relationship between age and mortality. However, in recipients aged over 60, increasing age was not independently associated with 90-day mortality (P = 0.88) and 1-year mortality (P = 0.74), despite adjusting for donor age, MELD score, and viral hepatitis status, suggesting that their original liver condition, their co-morbidities or perioperative condition plays an important role in retransplantation survival. Increasing recipient age up to 60, adversely affects liver retransplantation survival. After 60, there are no additional risks. Advanced age alone should not be an exclusionary factor when considering liver retransplantation; only the overall ability of the patient to tolerate a major surgery should be the determining factor.

A monoclonal antibody to tryptophan hydroxylase: applications and identification of the epitope

Recombinant rabbit tryptophan hydroxylase (TPH) was expressed in Escherichia coli and purified from inclusion bodies by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A mouse monoclonal antibody and rabbit and sheep polyclonal antibodies were generated. In immunohistochemical studies of formaldehyde-fixed primate brain, the monoclonal strongly labeled not only cell bodies in the raphe nuclei but also fibers in the cerebral cortex. Truncation mutants and peptide pre-competition were used to localize the epitope to E103SVPWFP109. Although the primary sequences of TPH encoded by mRNAs from brain and pineal gland are identical, differences in the immunoreactivity of TPH protein from these two sources were observed in blot immunolabeling studies. TPH immunoreactivity migrated as an M(r) approximately equal 56000 band in each of the tissues except human pineal glands, in which the TPH reactivity was approximately 3 kDa lower. In addition, the relative intensities of TPH immunolabeling across the four tissues differed among these antibodies and a previously described monoclonal antibody against phenylalanine hydroxylase (PH8), which cross-reacts with TPH. Whereas PH8 exhibited roughly equivalent TPH reactivity per protein in both tissues from both species, TPH from human and rat raphe nuclei was preferentially recognized by the present monoclonal. By contrast, the affinity-purified sheep polyclonal antibody reacted preferentially with TPH from human and rat pineal gland, and the affinity-purified rabbit polyclonal antibody appeared to selectively recognize TPH from human pineal gland.

Carboxyl terminal deletion analysis of tryptophan hydroxylase

Tryptophan hydroxylase (TPH) catalyzes the rate-limiting step in the synthesis of serotonin and participates (in a non-rate-limiting fashion) in melatonin biosynthesis. In rabbit, TPH exists as a tetramer of four identical 51007 dalton (444 amino acids) protein subunits. An intersubunit binding domain responsible for tetramer formation of TPH was identified by assessing the role of a carboxyl terminal leucine heptad and 4-3 hydrophobic repeat. These repeats are conserved in all of the aromatic amino acid hydroxylases and have been shown to be required for the assembly of tyrosine hydroxylase tetramers. Polymerase chain reaction was utilized to create three TPH carboxyl terminal deletions (C delta8, C delta12 and C delta17) that sequentially remove members of the leucine heptad and 4-3 hydrophobic repeat. Each deletion and full-length recombinant TPH was expressed in bacteria to obtain soluble enzyme extracts for subsequent activity and structural analysis. It was found that removal of 8, 12 or 17 amino acids from the carboxyl terminus of TPH did not significantly alter enzymatic activity when compared to full-length recombinant TPH. However, the macromolecular structure of the deletions was dramatically affected as determined by dimeric and monomeric profiles on size exclusion chromatography. It can be concluded that amino acids 428-444 (the C-terminal 17 amino acids) comprise an intersubunit binding domain that is required for tetramer formation of TPH, but that tetramer assembly is not essential for full enzymatic activity.

Amino-terminal analysis of tryptophan hydroxylase: protein kinase phosphorylation occurs at serine-58

Tryptophan hydroxylase (TPH) catalyzes the rate-limiting and committed step in serotonin biosynthesis. Within this enzyme, two distinct domains have been hypothesized to exist, an amino-terminal regulatory domain and a carboxyl-terminal catalytic domain. In the present experiments, the functional boundary between the putative domains was defined using deletion mutagenesis. A full-length cDNA clone for rabbit TPH was engineered for expression in bacteria. Five amino-terminal deletions were constructed using PCR, i.e., Ndelta50, Ndelta60, Ndelta90, Ndelta106, and Ndelta116 (referring to the number of amino acids deleted from the amino terminus). Enzymatic activity was determined for each mutant after expression in bacteria. Whereas deletion of 116 amino acids (Ndelta116) abolished enzyme activity, all of the other amino-terminal deletions exhibited increased specific activity relative to the recombinant wild-type TPH. The ability of the cyclic AMP-dependent protein kinase (PKA) to phosphorylate members of the deletion series was also examined. Deletion of the first 60 amino-terminal residues abolished the ability of the enzyme to serve as a substrate for PKA, yet the native and Ndelta50 enzymes were phosphorylated. Moreover, a serine-58 point mutant (S58A) was not phosphorylated by PKA. In conclusion, the first 106 amino acids comprise a regulatory domain that is phosphorylated by PKA at serine-58. In addition, the boundary between regulatory and catalytic domains is analogous to the domain structure observed for the related enzyme tyrosine hydroxylase.

A chimeric tyrosine/tryptophan hydroxylase. The tyrosine hydroxylase regulatory domain serves to stabilize enzyme activity

The neurotransmitter biosynthetic enzymes, tyrosine hydroxylase (TH), and tryptophan hydroxylase (TPH) are each composed of an amino-terminal regulatory domain and a carboxyl-terminal catalytic domain. A chimeric hydroxylase was generated by coupling the regulatory domain of TH (TH-R) to the catalytic domain of TPH (TPH-C) and expressing the recombinant enzyme in bacteria. The chimeric junction was created at proline 165 in TH and proline 106 in TPH because this residue is within a conserved five amino-acid span (ValProTrpPhePro) that defines the beginning of the highly homologous catalytic domains of TH and TPH. Radioenzymatic activity assays demonstrated that the TH-R/TPH-C chimera hydroxylates tryptophan, but not tyrosine. Therefore, the regulatory domain does not confer substrate specificity. Although the TH-R/TPH-C enzyme did serve as a substrate for protein kinase (PKA), activation was not observed following phosphorylation. Phosphorylation studies in combination with kinetic data provided evidence that TH-R does not exert a dominant influence on TPH-C. Stability assays revealed that, whereas TH exhibited a t1/2 of 84 min at 37 degrees C, TPH was much less stable (t1/2 = 28.3 min). The stability profile of TH-R/TPH-C, however, was superimposable on that of TH. Removal of the regulatory domain (a deletion of 165 amino acids from the N-terminus) of TH rendered the catalytic domain highly unstable, as demonstrated by a t1/2 of 14 min. The authors conclude that the regulatory domain of TH functions as a stabilizer of enzyme activity. As a corollary, the well-characterized instability of TPH may be attributed to the inability of its regulatory domain to stabilize the catalytic domain.

Tyrosinase mRNA is expressed in human substantia nigra

Dopamine acts, under appropriate conditions, as a selective neurotoxin. This toxicity is attributed to the autoxidation of the neurotransmitter into a reactive quinone that covalently modifies cellular macromolecules (i.e. proteins and nucleic acids). The oxidation of the catecholamine to a quinone is greatly accelerated by the enzyme tyrosinase. There is controversy, however, as to whether or not tyrosinase is expressed in human brain. In the present study, RT-PCR was utilized to demonstrate the presence of tyrosinase mRNA in post-mortem human brain tissues. Using gene-specific amplification primers, specific tyrosinase amplicons were detected following analysis of RNA from substantia nigra of four individuals. Analysis of cerebellar RNA from the same individuals produced no amplification products. Control reactions performed in the absence of reverse transcriptase failed to generate PCR products for any tissue tested. Three amplicons were subjected to direct DNA sequencing and all proved to be identical with tyrosinase sequences, thus obviating the possibility of amplification of a related gene. It is clear, therefore, that the tyrosinase gene is expressed in the human substantia nigra, lending support to previous studies describing tyrosinase-like activity and immunoreactive protein in the brain. This enzyme could be central to dopamine neurotoxicity as well as contribute to the neurodegeneration associated with Parkinson's disease.

Intricate regulation of tyrosine hydroxylase activity and gene expression

Tyrosine hydroxylase catalyzes the rate-limiting step in the biosynthesis of the catecholamines dopamine, norepinephrine, and epinephrine. Therefore, the regulation of tyrosine hydroxylase enzyme number and intrinsic enzyme activity represents the central means for controlling the synthesis of these important biogenic amines. An intricate scheme has evolved whereby tyrosine hydroxylase activity is modulated by nearly every documented form of regulation. Beginning with the genomic DNA, evidence exists for the transcriptional regulation of tyrosine hydroxylase mRNA levels, alternative RNA processing, and the regulation of RNA stability. There is also experimental support for the role of both translational control and enzyme stability in establishing steady-state levels of active tyrosine hydroxylase protein. Finally, mechanisms have been proposed for feedback inhibition of the enzyme by catecholamine products, allosteric modulation of enzyme activity, and phosphorylation-dependent activation of the enzyme by various different kinase systems. Given the growing literature suggesting that different tissues regulate tyrosine hydroxylase mRNA levels and activity in different ways, regulatory mechanisms provide not only redundancy but also diversity in the control of catecholamine biosynthesis.

Recombinant rabbit tryptophan hydroxylase is a substrate for cAMP-dependent protein kinase

A full-length cDNA clone for rabbit tryptophan hydroxylase (TPH) was modified and subcloned into a bacterial expression vector. Expression of this gene in the protease-deficient strain of bacteria, BL21[DE3], produced TPH immunoreactive protein which exhibited enzyme activity. Treatment of the recombinant enzyme (in bacterial extracts) with the purified catalytic subunit of the cAMP-dependent protein kinase and [gamma-32P]-ATP resulted in specific phosphorylation of TPH. This expression system provides a means of generating and purifying large amounts of this important enzyme. Moreover, these experiments establish that TPH will serve as an in vitro substrate for cAMP-dependent protein kinase.