Assessing LSAMs ability to account for changes in organ donation and transplant center behavior

BACKGROUND

The Liver Simulated Allocation Model (LSAM) is used to evaluate proposed organ allocation policies. Although LSAM has been shown to predict the directionality of changes in transplants and non-used organs, the magnitude is often overestimated. One reason is that policymakers and researchers using LSAM assume static levels of organ donation and center behavior because of challenges with predicting future behavior.

METHODS

We sought to assess the ability of LSAM to account for changes in organ donation and organ acceptance behavior using LSAM 2019. We ran 1-year simulations with the default model, and then ran simulations changing donor arrival rates (i.e., organ donation) and center acceptance behavior.

RESULTS

Changing the donor arrival rate was associated with a progressive simulated increase in transplants, with corresponding simulated decreases in waitlist deaths. Changing parameters related to organ acceptance was associated with important changes in transplants, non-used organs, and waitlist deaths in the expected direction in data simulations, although to a much lesser degree than changing the donor arrival rate. Increasing the donor arrival rate was associated with a marked decrease in the travel distance of donor livers in simulations.

CONCLUSION

We demonstrate that LSAM can account for changes in organ donation and organ acceptance in a manner aligned with historical precedent that can inform future policy analyses. As SRTR develops new simulation programs, the importance of considering changes in donation and center practice is critical to accurately estimate the impact of new allocation policies.

Variability in Organ Procurement Organization Performance by Individual Hospital in the United States

Importance

Availability of organs inadequately addresses the need of patients waiting for a transplant.

Objective

To estimate the true number of donor patients in the United States and identify inefficiencies in the donation process as a way to guide system improvement.

Design, Setting, and Participants

A retrospective cross-sectional analysis was performed of organ donation across 13 different hospitals in 2 donor service areas covered by 2 organ procurement organizations (OPOs) in 2017 and 2018 to compare donor potential to actual donors. More than 2000 complete medical records for decedents were reviewed as a sample of nearly 9000 deaths. Data were analyzed from January 1, 2017, to December 31, 2018.

Exposure

Deaths of causes consistent with donation according to medical record review, ventilated patient referrals, center acceptance practices, and actual deceased donors.

Main Outcomes and Measures

Potential donors by medical record review vs actual donors and OPO performance at specific hospitals.

Results

Compared with 242 actual donors, 931 potential donors were identified at these hospitals. This suggests a deceased donor potential of 3.85 times (95% CI, 4.23-5.32) the actual number of donors recovered. There was a surprisingly wide variability in conversion of potential donor patients into actual donors among the hospitals studied, from 0% to 51.0%. One OPO recovered 18.8% of the potential donors, whereas the second recovered 48.2%. The performance of the OPOs was moderately related to referrals of ventilated patients and not related to center acceptance practices.

Conclusions and Relevance

In this cross-sectional study of hospitals served by 2 OPOs, wide variation was found in the performance of the OPOs, especially at individual hospitals. Addressing this opportunity could greatly increase the organ supply, affirming the importance of recent efforts from the federal government to increase OPO accountability and transparency.

Associations between social determinants of health and abdominal solid organ transplant wait-lists in the United States

BACKGROUND

Societal factors that influence wait-listing for transplantation are complex and poorly understood. Social determinants of health (SDOH) affect rates of and outcomes after transplantation.

METHODS

This cross-sectional study investigated the impact of SDOH on additions to state-level, 2017-2018 kidney and liver wait-lists. Principal components analysis, starting with 127 variables among 3142 counties, was used to derive novel, comprehensive state-level composites, designated (1) health/economics and (2) community capital/urbanicity. Stepwise multivariate linear regression with backwards elimination (n = 51; 50 states and DC) tested the effects of these composites, Medicaid expansion, and center density on adult disease burden-adjusted wait-list additions.

RESULTS

SDOH related to increased community capital/urbanicity were independently associated with wait-listing (starting models: B = .40, P = .010 Kidney; B = .36, P = .038 Liver) (final models: B = .31, P = .027 Kidney, B = .34, P = .015 Liver). In contrast and surprisingly, no other covariates were associated with wait-listing (P ≥ .122).

CONCLUSIONS

These results suggest that deficits in community resources are important contributors to disparities in wait-list access. Our composite SDOH metrics may help identify at-risk communities, which can be the focus of local and national policy initiatives to improve access to organ transplantation.

Suppressors of Cytokine Signaling and Hepatocellular Carcinoma

Simple Summary

Hepatocellular carcinoma (HCC) is a common malignancy worldwide. The HCC generally develops in the liver of patients already suffering from chronic liver disease. There have been significant advances in both the curative and palliative treatment of HCC. Although liver resection is a curative treatment for HCC, its indication is often limited due to an impaired liver function reservoir. There is still a need to understand how to control liver regeneration after resection and find better cancer immunotherapy and anticancer drugs for advanced HCC. Suppressors of cytokine signaling (SOCS) negatively regulate cytokine signaling related to cell proliferation, differentiation, and immune response; therefore, SOCS are thought to play an important role in HCC development and liver regeneration.

Abstract

Cytokines are secreted soluble glycoproteins that regulate cellular growth, proliferation, and differentiation. Suppressors of cytokine signaling (SOCS) proteins negatively regulate cytokine signaling and form a classical negative feedback loop in the signaling pathways. There are eight members of the SOCS family. The SOCS proteins are all comprised of a loosely conserved N-terminal domain, a central Src homology 2 (SH2) domain, and a highly conserved SOCS box at the C-terminus. The role of SOCS proteins has been implicated in the regulation of cytokines and growth factors in liver diseases. The SOCS1 and SOCS3 proteins are involved in immune response and inhibit protective interferon signaling in viral hepatitis. A decreased expression of SOCS3 is associated with advanced stage and poor prognosis of patients with hepatocellular carcinoma (HCC). DNA methylations of SOCS1 and SOCS3 are found in HCC. Precise regulation of liver regeneration is influenced by stimulatory and inhibitory factors after partial hepatectomy (PH), in particular, SOCS2 and SOCS3 are induced at an early time point after PH. Evidence supporting the important role of SOCS signaling during liver regeneration also supports a role of SOCS signaling in HCC. Immuno-oncology drugs are now the first-line therapy for advanced HCC. The SOCS can be potential targets for HCC in terms of cell proliferation, cell differentiation, and immune response. In this literature review, we summarize recent findings of the SOCS family proteins related to HCC and liver diseases.

Procurement characteristics of high- and low-performing OPOs as seen in OPTN/SRTR data

To meet new Centers for Medicare and Medicaid Services (CMS) metrics, organ procurement organizations (OPOs) will benefit from understanding performance across decedent and hospital types. We sought to determine the utility of existing data-reporting structures for this purpose by reviewing Scientific Registry of Transplant Recipient (SRTR) OPO-Specific Reports (OSRs) from 2013 to 2019. OSRs contain both the Standardized donation rate ratio (SDRR) metric and OPO-reported numbers of "eligible deaths" and donors by hospital. Donor hospitals were characterized using information from Homeland Infrastructure Foundation-Level Data, Dartmouth Atlas Hospital Service Area data, and the US Census Bureau. Hospital data reported by OPOs showed 51% higher eligible death donors and 140% higher noneligible death donors per 100 inpatient beds in CMS ranked top versus bottom-quartile OPOs. Top-quartile OPOs by the CMS metric recovered 78% more donors than those in the bottom quartile, but were indistinguishable by SDRR rankings. These differences persisted across hospital sizes, trauma case mix, and area demographics. OPOs with divergent performance were indistinguishable over time by SDRR, but showed changes to hospital-level recovery patterns in SRTR data. Contemporaneous recognition of underperformance across hospitals may provide important and actionable data for regulators and OPOs for focused quality improvement projects.

Opportunity to increase deceased donation for United States veterans

Recent changes to organ procurement organization (OPO) performance metrics have highlighted the need to identify opportunities to increase organ donation in the United States. Using data from the Organ Procurement and Transplantation Network (OPTN), Scientific Registry of Transplant Recipients (SRTR), and Veteran Health Administration Informatics and Computing Infrastructure Clinical Data Warehouse (VINCI CDW), we sought to describe historical donation performance at Veteran Administration Medical Centers (VAMCs). We found that over the period 2010-2019, there were only 33 donors recovered from the 115 VAMCs with donor potential nationwide. VA donors had similar age-matched organ transplant yields to non-VA donors. Review of VAMC records showed a total of 8474 decedents with causes of death compatible with donation, of whom 5281 had no infectious or neoplastic comorbidities preclusive to donation. Relative to a single state comparison of adult non-VA inpatient deaths, VAMC deaths were 20 times less likely to be characterized as an eligible death by SRTR. The rate of conversion of inpatient donation-consistent deaths without preclusive comorbidities to actual donors at VAMCs was 5.9% that of adult inpatients at non-VA hospitals. Overall, these findings suggest significant opportunities for growth in donation at VAMCs.

Regional ethics of surgeon resuscitation for organ transplantation after lethal injury

BACKGROUND

Trauma patients may present with nonsurvivable injuries, which could be resuscitated for future organ transplantation. Trauma surgeons face an ethical dilemma of deciding whether, when, and how to resuscitate a patient who will not directly benefit from it. As there are no established guidelines to follow, we aimed to describe resuscitation practices for organ transplantation; we hypothesized that resuscitation practices vary regionally.

METHOD

Over a 3-month period, we surveyed trauma surgeons practicing in Levels I and II trauma centers within a single state using an instrument to measure resuscitation attitudes and practices for organ preservation. Descriptive statistics were calculated for practice patterns.

RESULTS

The survey response rate was 51% (31/60). Many (81%) had experience with resuscitations where the primary goal was to preserve potential for organ transplantation. Many (90%) said they encountered this dilemma at least monthly. All respondents were willing to intubate; most were willing to start vasopressors (94%) and to transfuse blood (84%) (range, 1 unit to >10 units). Of respondents, 29% would resuscitate for ≥24 hours, and 6% would perform a resuscitative thoracotomy. Respect for patients' dying process and future organ quality were the factors most frequently considered very important or important when deciding to stop or forgo resuscitation, followed closely by concerns about excessive resource use.

CONCLUSION

Trauma surgeons' regional resuscitation practices vary widely for this patient population. This variation implies a lack of professional consensus regarding initiation and extent of resuscitations in this setting. These data suggest this is a common clinical challenge, which would benefit from further study to determine national variability, areas of equipoise, and features amenable to practice guidelines.

Effect of Donor Transaminase Levels on Graft Survival Following Liver Transplant: An Analysis of the Organ Procurement and Transplantation Network Database

OBJECTIVES

Despite data showing equivalent outcomes between grafts from marginal versus standard criteria deceased liver donors, elevated donor transaminases constitute a frequent reason to decline potential livers. We assessed the effect of donor transaminase levels and other characteristics on graft survival.

MATERIALS AND METHODS

We performed a retrospective cohort analysis of adult first deceased donor liver transplant recipients with available transaminase levels registered in the Organ Procurement and Transplantation Network database (2008-2018). We used Cox proportional hazards regression to determine the effects of donor characteristics on graft survival.

RESULTS

Of 53 913 liver transplants, 52 158 were allografts from donors with low transaminases (≤ 500 U/L; group A) and 1755 were from donors with elevated transaminases (> 500 U/L; group B). Group A recipients were more likely to be hospitalized (P = .01) or in intensive care (P < .001) or to have mechanical assistance (P < .001), portal vein thrombosis (P = .01), diabetes mellitus (P = .003), or dialysis the week before liver transplant (P = .004). Multivariable analysis (controlling for recipient characteristics) showed donor risk factors of graft failure included diabetes mellitus (P < .001), donation after cardiac death (P < .001), total bilirubin > 3.5 mg/dL (P < .001), serum creatinine > 1.5 mg/dL (P = .01), and cold ischemia time > 6 hours (P < .001). Regional organ sharing showed lower risk of graft failure (P = .02). Donor transaminases > 500 U/L were not associated with graft failure (relative risk, 1.02; 95% CI, 0.91-1.14; P = .74).

CONCLUSIONS

Donor transaminases > 500 U/L should not preclude the use of liver grafts. Instead, donor total bilirubin > 3.5 mg/dL and serum creatinine > 1.5 mg/dL appear to be associated with higher likelihood of graft failure after liver transplant.

A retrospective approach to evaluating potential adverse outcomes associated with delay of procedures for cardiovascular and cancer-related diagnoses in the context of COVID-19

OBJECTIVE

During the COVID-19 pandemic, health systems postponed non-essential medical procedures to accommodate surge of critically-ill patients. The long-term consequences of delaying procedures in response to COVID-19 remains unknown. We developed a high-throughput approach to understand the impact of delaying procedures on patient health outcomes using electronic health record (EHR) data.

MATERIALS AND METHODS

We used EHR data from Vanderbilt University Medical Center's (VUMC) Research and Synthetic Derivatives. Elective procedures and non-urgent visits were suspended at VUMC between March 18, 2020 and April 24, 2020. Surgical procedure data from this period were compared to a similar timeframe in 2019. Potential adverse impact of delay in cardiovascular and cancer-related procedures was evaluated using EHR data collected from January 1, 1993 to March 17, 2020. For surgical procedure delay, outcomes included length of hospitalization (days), mortality during hospitalization, and readmission within six months. For screening procedure delay, outcomes included 5-year survival and cancer stage at diagnosis.

RESULTS

We identified 416 surgical procedures that were negatively impacted during the COVID-19 pandemic compared to the same timeframe in 2019. Using retrospective data, we found 27 significant associations between procedure delay and adverse patient outcomes. Clinician review indicated that 88.9% of the significant associations were plausible and potentially clinically significant. Analytic pipelines for this study are available online.

CONCLUSION

Our approach enables health systems to identify medical procedures affected by the COVID-19 pandemic and evaluate the effect of delay, enabling them to communicate effectively with patients and prioritize rescheduling to minimize adverse patient outcomes.

Integrin β1 Establishes Liver Microstructure and Modulates Transforming Growth Factor β during Liver Development and Regeneration

A unique and complex microstructure underlies the diverse functions of the liver. Breakdown of this organization, as occurs in fibrosis and cirrhosis, impairs liver function and leads to disease. The role of integrin β1 was examined both in establishing liver microstructure and recreating it after injury. Embryonic deletion of integrin β1 in the liver disrupts the normal development of hepatocyte polarity, specification of cell-cell junctions, and canalicular formation. This in turn leads to the expression of transforming growth factor β (TGF-β) and widespread fibrosis. Targeted deletion of integrin β1 in adult hepatocytes prevents recreation of normal hepatocyte architecture after liver injury, with resultant fibrosis. In vitro, integrin β1 is essential for canalicular formation and is needed to prevent stellate cell activation by modulating TGF-β. Taken together, these findings identify integrin β1 as a key determinant of liver architecture with a critical role as a regulator of TGF-β secretion. These results suggest that disrupting the hepatocyte-extracellular matrix interaction is sufficient to drive fibrosis.

Immunosuppression in Donation After Circulatory Death Liver Transplantation: Can Induction Modify Graft Survival?

Recipients of donation after circulatory death (DCD) LTs historically have an increased risk of graft failure. Antibody induction (AI) with antithymocyte globulin (ATG) or anti-interleukin 2 receptor (anti-IL2R) immunotherapy may decrease the incidence of graft failure by mitigating ischemia/reperfusion injury. A retrospective review of the United Network for Organ Sharing (UNOS) database for LTs between 2002 and 2015 was conducted to determine whether ATG or anti-IL2R AI was associated with graft survival in DCD. A secondary endpoint was postoperative renal function as measured by estimated glomerular filtration rate at 6 and 12 months. Among DCD recipients, ATG (hazard ratio [HR] = 0.71; P = 0.03), but not anti-IL2R (HR = 0.82; P = 0.10), was associated with a decrease in graft failure at 3 years when compared with recipients without AI. ATG (HR = 0.90; P = 0.02) and anti-IL2R (HR = 0.94; P = 0.03) were associated with a decreased risk of graft failure in donation after brain death (DBD) liver recipients at 3 years compared with no AI. When induction regimens were compared between DCD and DBD, only ATG (HR = 1.19; P = 0.19), and not anti-IL2R (HR = 1.49; P < 0.01) or no AI (HR = 1.77; P < 0.01), was associated with similar survival between DCD and DBD. In conclusion, AI therapy with ATG was associated with improved longterm liver allograft survival in DCD compared with no AI. ATG was associated with equivalent graft survival between DCD and DBD, suggesting a beneficial role of immune cell depletion in DCD outcomes.

Living vs deceased donor liver transplantation in cholestatic liver disease: An analysis of the OPTN database

BACKGROUND

Living donor liver transplantation (LDLT) and donation after circulatory death (DCD) can expand the donor pool for cholestatic liver disease (CLD) patients. We sought to compare the outcomes of deceased donor liver transplant (DDLT) vs LDLT in CLD patients.

METHODS

Retrospective cohort analysis of adult CLD recipients registered in the OPTN database who received primary LT between 2002 and 2018. Cox proportional hazards regression models with mixed effects were used to determine the impact of graft type on patient and graft survival.

RESULTS

Five thousand, nine hundred ninety-nine DDLT (5730 donation after brain death [DBD], 269 DCD) and 912 LDLT recipients were identified. Ten-year patient/graft survival rates were DBD: 73.8%/67.9%, DCD: 74.7%/60.7%, and LDLT: 82.5%/73.9%. Higher rates of biliary complications as a cause of graft failure were seen in DCD (56.8%) than LDLT (30.5%) or DBD (18.7%) recipients. On multivariable analysis, graft type was not associated with patient mortality, while DCD was independently associated with graft failure (P = .046).

CONCLUSION

DBD, DCD, and LDLT were associated with comparable overall patient survival. No difference in the risk of graft failure could be observed between LDLT and DBD. DCD can be an acceptable alternative to DBD with equivalent patient survival, but inferior graft survival likely related to the high rate of biliary complications.

Noninvasive Assessment of Liver Fibrosis: Current and Future Clinical and Molecular Perspectives

Liver fibrosis is one of the risk factors for hepatocellular carcinoma (HCC) development. The staging of liver fibrosis can be evaluated only via a liver biopsy, which is an invasive procedure. Noninvasive methods for the diagnosis of liver fibrosis can be divided into morphological tests such as elastography and serum biochemical tests. Transient elastography is reported to have excellent performance in the diagnosis of liver fibrosis and has been accepted as a useful tool for the prediction of HCC development and other clinical outcomes. Two-dimensional shear wave elastography is a new technique and provides a real-time stiffness image. Serum fibrosis markers have been studied based on the mechanism of fibrogenesis and fibrolysis. In the healthy liver, homeostasis of the extracellular matrix is maintained directly by enzymes called matrix metalloproteinases (MMPs) and their specific inhibitors, tissue inhibitors of metalloproteinases (TIMPs). MMPs and TIMPs could be useful serum biomarkers for liver fibrosis and promising candidates for the treatment of liver fibrosis. Further studies are required to establish liver fibrosis-specific markers based on further clinical and molecular research. In this review, we summarize noninvasive fibrosis tests and molecular mechanism of liver fibrosis in current daily clinical practice.

Intensive Care Unit Enhanced Recovery Pathway for Patients Undergoing Orthotopic Liver Transplants Recipients: A Prospective, Observational Study

BACKGROUND

Liver transplant recipients continue to have high perioperative resource utilization and prolonged length of stay despite improvements in perioperative care. Enhanced recovery pathways have been shown in other surgical populations to produce reductions in hospital resource utilization.

METHODS

A prospective, observational study was performed to examine the effect of an enhanced recovery pathway for postoperative care after liver transplantation. Outcomes from patients undergoing liver transplantation from November 1, 2013, to October 31, 2014, managed by the pathway were compared to transplant recipients from the year before pathway implementation. Multivariable regression analysis was used to assess the association of the clinical pathway on clinical outcomes.

RESULTS

The intervention and control groups included 141 and 106 patients, respectively. There were no demographic differences between the control and intervention group including no differences between the length of surgery and cold ischemic time. Median intensive care unit length of stay was reduced from 4.4 to 2.6 days (P < .001). The intervention group had a higher likelihood of earlier discharge (hazard ratio [95% CI], 2.01 [1.55-2.62]; P < .001), and a 69% and 65% lower odds of receiving a plasma (P < .001) or packed red blood cell (P < .001) transfusion. There was no significant effect on hospital mortality (P = .40), intensive care unit readmission rates (P = .75), or postoperative infections (urinary traction infections: P = .09; pneumonia: P = .27).

CONCLUSIONS

An enhanced recovery pathway focused on milestone-based elements of intensive care unit management and predetermined management triggers including hemodynamic goals, fluid therapy, perioperative antibiotics, glycemic control, and standardized transfusion triggers led to reductions in intensive care unit length of stay without an increase in perioperative complications.

Moving past "think local, act global": A perspective on geographic disparity

The transplant community has debated the necessity and merits of broader organ distribution for several years, but the debate has been fundamentally shaped by inaccurate assessments of donor supply and demand. The possible legal requirements of distribution must be balanced with (a) the moral and statutory imperatives to reduce inequities resulting from socioeconomic disparity, and (b) the shortcomings of MELD in predicting mortality risk in rural areas. In this viewpoint, we use the example of liver transplantation to discuss the drivers of geographic disparity as a direct consequence of donation rates, local organ use, wealth, and poverty. Seen in this light, strategies seeking to equalize MELD at transplant across the United States risk severely exacerbating existing inequalities in access to health care.

Expanding analytic possibilities in pediatric solid organ transplantation through linkage of administrative and clinical registry databases

Database linkage is a common strategy to expand analytic possibilities. Our group recently completed a linkage between the SRTR and PHIS databases for pediatric heart transplant recipients. The aim of this project was to expand the linkage between SRTR and PHIS to include liver, kidney, lung, heart-lung, and small bowel transplants. All patients (<21 years) who underwent liver, kidney, lung, heart-lung, or small bowel transplant were identified from the PHIS database using APR-DRG codes (2002-2018). Linkage was performed in a stepwise approach using indirect identifiers. Hospital costs were estimated based on hospital charges and cost-to-charge ratios, inflated to 2018 dollars and described by transplant type. A total of 14 061 patients overlapped between databases. Of these, 13 388 (95.2%) were uniquely linked. Linkage success ranged from 92.6% to 97.8% by organ system. A total of 12 940 (92%) patients had complete cost data. Hospitalization costs were greatest for patients undergoing small bowel transplantation with a median cost of $734 454 (IQR $336 174 - $1 504 167), followed by heart $565 386 (IQR $352 813 - $999 216), heart-lung $471 573 (IQR $328 523 - 992 438), lung $303 536 (IQR $215 383 - $612 749), liver $200 448 (IQR $130 880 - $357 897), and kidney transplant $94 796 (IQR $73 157 -$131 040). We report a robust linkage between the SRTR and PHIS databases, providing an invaluable tool to assess resource utilization in solid organ transplant recipients. Our analysis provides contemporary cost data for pediatric solid organ transplantation from the largest US sample reported to date. It also provides a platform for expanded analyses in the pediatric transplant population.

Public attitudes toward contemporary issues in liver allocation

Allocation of scarce livers for transplantation seeks to balance competing ethical principles of autonomy, utility, and justice. Given the history and ongoing dependence of transplantation on public support for funding and organs, understanding and incorporating public attitudes into allocation decisions seems appropriate. In the context of the current controversy around liver allocation, we sought to determine public preferences about issues relevant to the debate. We performed multiple surveys of attitudes around donation and evaluated these using conjoint analysis and clarifying follow-up questions. We found little public support that allocation decisions should be based solely on risk of waiting-list mortality. Strong public sentiment supported maximizing outcomes after transplantation, prioritizing US citizens or residents, keeping organs local, and considering cost in allocation decisions. We then present a methodology for incorporating these preferences into the Model for End-Stage Liver Disease (or MELD) priority score. Taken together, these findings suggest that current allocation schemes do not accurately reflect public preferences and suggest a framework to better align allocation with the values of the public.

State-Based Liver Distribution: Broad Sharing With Less Harm to Vulnerable and Underserved Communities Compared With Concentric Circles

Allocation of livers for transplantation faces regulatory pressure to move toward broader sharing. A current proposal supported by the United Network for Organ Sharing Board of Directors relies on concentric circles, but its effect on socioeconomic inequities in access to transplant services is poorly understood. In this article, we offer a proposal that uses the state of donation as a unit of distribution, given that the state is a recognized unit of legal jurisdiction and socioeconomic health in many contexts. The Scientific Registry of Transplant Recipients liver simulated allocation model algorithm was used to generate comparative estimates of regional transplant volume and the impact of these considered changes with regard to vulnerable and high-risk patients on the waiting list and to disparities in wait-list access. State-based liver distribution outperforms the concentric circle models in overall system efficiency, reduced discards, and minimized flights for organs. Furthermore, the efflux of organs from areas of greater sociodemographic vulnerability and lesser wait-list access is more than 2-fold lower in a state-based model than in concentric circle alternatives. In summary, we propose that a state-based system offers a legally defensible, practical, and ethically sound alternative to geometric zones of organ distribution.

Directed solutions to address differences in access to liver transplantation

The United Network for Organ Sharing recently altered current liver allocation with the goal of decreasing Model for End-Stage Liver Disease (MELD) variance at transplant. Concerns over these and further planned revisions to policy include predicted decrease in total transplants, increased flying and logistical complexity, adverse impact on areas with poor quality health care, and minimal effect on high MELD donor service areas. To address these issues, we describe general approaches to equalize critical transplant metrics among regions and determine how they alter MELD variance at transplant and organ supply to underserved communities. We show an allocation system that increases minimum MELD for local allocation or preferentially directs organs into areas of need decreases MELD variance. Both models have minimal adverse effects on flying and total transplants, and do not disproportionately disadvantage already underserved communities. When combined together, these approaches decrease MELD variance by 28%, more than the recently adopted proposal. These models can be adapted for any measure of variance, can be combined with other proposals, and can be configured to automatically adjust to changes in disease incidence as is occurring with hepatitis C and nonalcoholic fatty liver disease.

Dicer-dependent production of microRNA221 in hepatocytes inhibits p27 and is required for liver regeneration in mice

Dicer processes microRNAs (miRs) into active forms in a wide variety of tissues, including the liver. To determine the role of Dicer in liver regeneration, we performed a series of in vivo and in vitro studies in a murine 2/3 hepatectomy model. Dicer was downregulated after 2/3 hepatectomy, and loss of Dicer inhibited liver regeneration associated with decreased cyclin A2 and miR-221, as well as increased levels of the cell cycle inhibitor p27. In vitro, miR-221 inhibited p27 production in primary hepatocytes and increased hepatocyte proliferation. Specific reconstitution of miR-221 in hepatocyte-specific Dicer-null mice inhibited p27 and restored liver regeneration. In wild type mice, targeted inhibition of miR-221 using a cholesterol-conjugated miR-221 inhibited hepatocyte proliferation after 2/3 hepatectomy. These results identify Dicer production of miR-221 as an essential component of a miRNA-dependent mechanism for suppression of p27 that controls the rate of hepatocyte proliferation after partial hepatectomy.NEW & NOTEWORTHY Our findings demonstrate a direct role for microRNAs in controlling the rate of liver regeneration after injury. By deleting Dicer, an enzyme responsible for processing microRNAs into mature forms, we determined miR-221 is a critical microRNA in the physiological process of restoration of liver mass after injury. miR-221 suppresses p27, releasing its inhibitory effects on hepatocyte proliferation. Pharmaceuticals based on miR-221 may be useful to modulate hepatocyte proliferation in the setting of liver injury.

SOCS2 Balances Metabolic and Restorative Requirements during Liver Regeneration

After significant injury, the liver must maintain homeostasis during the regenerative process. We hypothesized the existence of mechanisms to limit hepatocyte proliferation after injury to maintain metabolic and synthetic function. A screen for candidates revealed suppressor of cytokine signaling 2 (SOCS2), an inhibitor of growth hormone (GH) signaling, was strongly induced after partial hepatectomy. Using genetic deletion and administration of various factors we investigated the role of SOCS2 during liver regeneration. SOCS2 preserves liver function by restraining the first round of hepatocyte proliferation after partial hepatectomy by preventing increases in growth hormone receptor (GHR) via ubiquitination, suppressing GH pathway activity. At later times, SOCS2 enhances hepatocyte proliferation by modulating a decrease in serum insulin-like growth factor 1 (IGF-1) that allows GH release from the pituitary. SOCS2, therefore, plays a dual role in modulating the rate of hepatocyte proliferation. In particular, this is the first demonstration of an endogenous mechanism to limit hepatocyte proliferation after injury.

Cytometry-based single-cell analysis of intact epithelial signaling reveals MAPK activation divergent from TNF-α-induced apoptosis in vivo

Understanding heterogeneous cellular behaviors in a complex tissue requires the evaluation of signaling networks at single-cell resolution. However, probing signaling in epithelial tissues using cytometry-based single-cell analysis has been confounded by the necessity of single-cell dissociation, where disrupting cell-to-cell connections inherently perturbs native cell signaling states. Here, we demonstrate a novel strategy (Disaggregation for Intracellular Signaling in Single Epithelial Cells from Tissue-DISSECT) that preserves native signaling for Cytometry Time-of-Flight (CyTOF) and fluorescent flow cytometry applications. A 21-plex CyTOF analysis encompassing core signaling and cell-identity markers was performed on the small intestinal epithelium after systemic tumor necrosis factor-alpha (TNF-α) stimulation. Unsupervised and supervised analyses robustly selected signaling features that identify a unique subset of epithelial cells that are sensitized to TNF-α-induced apoptosis in the seemingly homogeneous enterocyte population. Specifically, p-ERK and apoptosis are divergently regulated in neighboring enterocytes within the epithelium, suggesting a mechanism of contact-dependent survival. Our novel single-cell approach can broadly be applied, using both CyTOF and multi-parameter flow cytometry, for investigating normal and diseased cell states in a wide range of epithelial tissues.

Specific activin receptor-like kinase 3 inhibitors enhance liver regeneration

Pharmacologic agents to enhance liver regeneration after injury would have wide therapeutic application. Based on previous work suggesting inhibition of bone morphogenetic protein (BMP) signaling stimulates liver regeneration, we tested known and novel BMP inhibitors for their ability to accelerate regeneration in a partial hepatectomy (PH) model. Compounds were produced based on the 3,6-disubstituted pyrazolo[1,5-a] pyrimidine core of the BMP antagonist dorsomorphin and evaluated for their ability to inhibit BMP signaling and enhance liver regeneration. Antagonists of the BMP receptor activin receptor-like kinase 3 (ALK3), including LDN-193189 (LDN; 4-[6-[4-(1-piperazinyl)phenyl]pyrazolo[1,5-a]pyrimidin-3-yl]-quinoline), DMH2 (4-(2-(4-(3-(quinolin-4-yl)pyrazolo[1,5-a]pyrimidin-6-yl)phenoxy)ethyl)morpholine; VU0364849), and the novel compound VU0465350 (7-(4-isopropoxyphenyl)-3-(1H-pyrazol-4-yl)imidazo[1,2-a]pyridine; VU5350), blocked SMAD phosphorylation in vitro and in vivo, and enhanced liver regeneration after PH. In contrast, an antagonist of the BMP receptor ALK2, VU0469381 (5-(6-(4-methoxyphenyl)pyrazolo[1,5-a]pyrimidin-3-yl)quinolone; 1LWY), did not affect liver regeneration. LDN did not affect liver synthetic or metabolic function. Mechanistically, LDN increased serum interleukin-6 levels and signal transducer and activator of transcription 3 phosphorylation in the liver, and modulated other factors known to be important for liver regeneration, including suppressor of cytokine signaling 3 and p53. These findings suggest that inhibition of ALK3 may be part of a therapeutic strategy for treating human liver disease.

CD39 modulates hematopoietic stem cell recruitment and promotes liver regeneration in mice and humans after partial hepatectomy

OBJECTIVE

To study molecular mechanisms involved in hematopoietic stem cell (HSC) mobilization after liver resection and determine impacts on liver regeneration.

BACKGROUND

Extracellular nucleotide-mediated cell signaling has been shown to boost liver regeneration. Ectonucleotidases of the CD39 family are expressed by bone marrow-derived cells, and purinergic mechanisms might also impact mobilization and functions of HSC after liver injury.

METHODS

Partial hepatectomy was performed in C57BL/6 wild-type, Cd39 ectonucleotidase-null mice and in chimeric mice after transplantation of wild-type or Cd39-null bone marrow. Bone marrow-derived HSCs were purified by fluorescence-activated cell sorting and administered after hepatectomy. Chemotactic studies were performed to examine effects of purinergic receptor agonists and antagonists in vitro. Mobilization of human HSCs and expression of CD39 were examined and linked to the extent of resection and liver tests.

RESULTS

Subsets of HSCs expressing Cd39 are preferentially mobilized after partial hepatectomy. Chemotactic responses of HSCs are increased by CD39-dependent adenosine triphosphate hydrolysis and adenosine signaling via A2A receptors in vitro. Mobilized Cd39 HSCs boost liver regeneration, potentially limiting interleukin 1β signaling. In clinical studies, mobilized human HSCs also express CD39 at high levels. Mobilization of HSCs correlates directly with the restoration of liver volume and function after partial hepatectomy.

CONCLUSIONS

We demonstrate CD39 to be a novel HSC marker that defines a functionally distinct stem cell subset in mice and humans. HSCs are mobilized after liver resection, limit inflammation, and boost regeneration in a CD39-dependent manner. These observations have implications for monitoring and indicate future therapeutic avenues.

Renal transplantation in the setting of early steroid withdrawal: a comparison of rabbit antithymocyte globulin induction dosing in two eras

BACKGROUND

Modern immunosuppression and rabbit antithymocyte globulin (rATG) have facilitated the success of early steroid withdrawal (ESW) protocols. Little data exist on optimal rATG dosing in ESW protocols.

METHODS

Rejection at 12 months in era 1 (four doses of rATG, 1.25 mg/kg) vs. era 2 (three doses of rATG, 1.25 mg/kg) was the primary endpoint. Secondary endpoints included patient and graft survival, renal function and infectious complications. Factors associated with rejection at 1 year were identified.

RESULTS

199 patients received rATG induction and ESW: 102 in era 1 and 97 in era 2. Compared to era 1, era 2 was not associated with worse outcomes, including rejection, renal function, infection or graft survival. Rejection at 1 year and uncensored graft survival differed between the dosing groups. Rejection rates were significantly higher in the <4 mg/kg group compared to the 4-5.9-mg/kg and the ≥6-mg/kg groups, whereas uncensored graft survival was the lowest in the ≥6-mg/kg group. Factors associated with rejection at 12 months included: rATG dose received of 4-5.9 versus <4 mg/kg (OR 0.20, 95% CI 0.036-0.85, p = 0.026); recipient age (per year, OR 0.94, 95% CI 0.89-1.0, p = 0.038); panel reactive antibody 10-79.9 versus <10% (OR 5.4, 95% CI 1.2-25, p = 0.030) and rATG dose held (OR 4.0, 95% CI 1.0-15, p = 0.049).

CONCLUSIONS

A comparison of rATG dosing based on era did not result in a significant difference in rejection, renal function, infection or graft survival. However, when evaluating the study population based on actual dose received there were notable differences in both rejection rates and uncensored graft survival.

Scar formation and lack of regeneration in adult and neonatal liver after stromal injury

Known as a uniquely regenerative tissue, the liver shows a remarkable capacity to heal without scarring after many types of acute injury. In contrast, during chronic liver disease, the liver responds with fibrosis, which can progress to cirrhosis and ultimately liver failure. The cause of this shift from a nonfibrotic to a fibrotic response is unknown. We hypothesized that stromal injury is a key event that prevents restoration of normal liver architecture. To test this, we developed a model of stromal injury using a surgical incision through the normal liver in adult and neonatal mice. This injury produces minimal cell death but locally complete stromal (extracellular matrix) disruption. The adult liver responds with inflammation and stellate cell activation, culminating in fibrosis characterized by collagen deposition. This sequence of events is remarkably similar to the fibrotic response leading to cirrhosis. Studies in neonates reveal a similar fibrotic response to a stromal injury. These findings suggest that extracellular matrix disruption leads not to regeneration but rather to scar, similar to other mammalian organs. These findings may shed light on the pathogenesis of chronic liver disease, and suggest therapeutic strategies.

BMP4 is a novel paracrine inhibitor of liver regeneration

Transforming growth factor (TGF)-β family members exert strong effects on restoration of liver mass after injury. Bone morphogenetic proteins (BMPs) are members of the TGF-β family and are found in the liver, suggesting that these proteins may play a role in liver regeneration. We examined BMP signaling in the liver during hepatectomy. We found that BMP4 is constitutively expressed in the peribiliary stroma and endothelial cells of the liver and that expression is decreased after hepatectomy. Mice driven to maintain BMP4 expression in the liver display inhibited hepatocyte proliferation and restoration of liver mass after hepatectomy, suggesting that reduced BMP4 is necessary for normal regeneration. Consistent with this finding, hepatocyte-specific deletion of the BMP receptor activin receptor-like kinase 3 (Alk3) enhances regeneration and reduces phosphorylation of SMAD1/5/8, a transducer of BMP signaling. In contrast to experiments in wild-type mice, maintaining BMP4 levels has no effect on liver regeneration in hepatocyte-specific Alk3 null mice, providing evidence that BMP4 signals through Alk3 to inhibit liver regeneration. Consistent with these findings, the BMP4 antagonist Noggin enhances regeneration. Furthermore, high-dose BMP4 inhibits proliferation of primary hepatocytes and HepG2 cells in culture. These findings elucidate a new, potentially clinically relevant paradigm in which a constitutively expressed paracrine inhibitory factor plays a critical role in liver regeneration.

New serum markers of hepatocellular carcinoma

Hepatocellular carcinoma (HCC), one of the most common cancers worldwide, usually develops in a liver already suffering from chronic damages, often cirrhosis. There has been marked progress in the treatment of HCC. However, effective treatments are limited to patients with less advanced HCC. The detection of HCC at an early stage is still a prerequisite for improved prognosis. To address this problem, a variety of screening modalities are used, including measurement of alpha-fetoprotein (AFP) and ultrasonography (US) at regular intervals in high-risk populations. Unfortunately, poor sensitivity and specificity of AFP and the operator-dependency of US limit the value of either test to diagnose early-stage lesions. Other tests, including Lens culinaris agglutinin-reactive AFP and des-gamma carboxyprothrombin (DCP), are currently being evaluated and may be superior to current tests. Recent developments in gene-expressing microarrays and proteomics promise even more potential diagnostic options. The strict application of the Early Detection Research Network methodology will aid in the assessment of their diagnostic utility, and provide an objective basis for the assessment of their clinical utility.

Transcriptional ontogeny of the developing liver

Background

During embryogenesis the liver is derived from endodermal cells lining the digestive tract. These endodermal progenitor cells contribute to forming the parenchyma of a number of organs including the liver and pancreas. Early in organogenesis the fetal liver is populated by hematopoietic stem cells, the source for a number of blood cells including nucleated erythrocytes. A comprehensive analysis of the transcriptional changes that occur during the early stages of development to adulthood in the liver was carried out.

Results

We characterized gene expression changes in the developing mouse liver at gestational days (GD) 11.5, 12.5, 13.5, 14.5, 16.5, and 19 and in the neonate (postnatal day (PND) 7 and 32) compared to that in the adult liver (PND67) using full-genome microarrays. The fetal liver, and to a lesser extent the neonatal liver, exhibited dramatic differences in gene expression compared to adults. Canonical pathway analysis of the fetal liver signature demonstrated increases in functions important in cell replication and DNA fidelity whereas most metabolic pathways of intermediary metabolism were under expressed. Comparison of the dataset to a number of previously published microarray datasets revealed 1) a striking similarity between the fetal liver and that of the pancreas in both mice and humans, 2) a nucleated erythrocyte signature in the fetus and 3) under expression of most xenobiotic metabolism genes throughout development, with the exception of a number of transporters associated with either hematopoietic cells or cell proliferation in hepatocytes.

Conclusions

Overall, these findings reveal the complexity of gene expression changes during liver development and maturation, and provide a foundation to predict responses to chemical and drug exposure as a function of early life-stages.

What's New, What's Hot in Solid Organ Transplantation? Summary of the American Transplant Congress 2011

Breakthroughs in basic and clinical science in solid organ transplantation were presented at the American Transplant Congress 2011. Key areas of presentation included the pathogenesis of late allograft failure, immune regulation and tolerance, pathways in allograft injury, electing appropriate patients for transplantation, determining the best allocation schemes to maximize effective utilization, organ preservation, monitoring the alloimmune response and immunosuppressive management. In this review, we present highlights of the meeting. These presentations demonstrate the exciting promise in translating from the bench to affect patient care.

Minimising cold ischaemic time is essential in cardiac death donor-associated liver transplantation

BACKGROUND

An important issue in the transplantation of livers procured from cardiac death donors (CDDs) concerns why some centres report equivalent outcomes and others report inferior outcomes in transplantations using CDD organs compared with standard criteria donor (SCD) organs. Resolving this discrepancy may increase the number of usable organs.

OBJECTIVES

This study aimed to test whether differences in cold ischaemic time (CIT) are critical during CDD organ transplantation and whether such differences might explain the disparate outcomes.

METHODS

Results of CDD liver transplants in our own centre were compared retrospectively with results in a matched cohort of SCD liver recipients. Endpoints of primary non-function (PNF) and ischaemic cholangiopathy (IC) were used because these outcomes are clearly associated with CDD organ use.

RESULTS

In 22 CDD organ transplants, CIT was a strong predictor of PNF or IC (P = 0.021). Minimising CIT in CDD organ transplants produced outcomes similar to those in a matched SCD organ transplant cohort at our centre and in SCD organ transplant results nationally (1- and 3-year graft and patient survival rates: 90.9% and 73.3% vs. 77.6% and 69.2% in CDD and SCD grafts, respectively. A review of the published literature demonstrated that centres with higher CITs tend to have higher rates of PNF or IC (correlation coefficient: 0.41).

CONCLUSIONS

These findings suggest that a targeted effort to minimise CIT might improve outcomes and allow the safer use of CDD organs.

Tob1 is a constitutively expressed repressor of liver regeneration

How proliferative and inhibitory signals integrate to control liver regeneration remains poorly understood. A screen for antiproliferative factors repressed after liver injury identified transducer of ErbB2.1 (Tob1), a member of the PC3/BTG1 family of mito-inhibitory molecules as a target for further evaluation. Tob1 protein decreases after 2/3 hepatectomy in mice secondary to posttranscriptional mechanisms. Deletion of Tob1 increases hepatocyte proliferation and accelerates restoration of liver mass after hepatectomy. Down-regulation of Tob1 is required for normal liver regeneration, and Tob1 controls hepatocyte proliferation in a dose-dependent fashion. Tob1 associates directly with both Caf1 and cyclin-dependent kinase (Cdk) 1 and modulates Cdk1 kinase activity. In addition, Tob1 has significant effects on the transcription of critical cell cycle components, including E2F target genes and genes involved in p53 signaling. We provide direct evidence that levels of an inhibitory factor control the rate of liver regeneration, and we identify Tob1 as a crucial check point molecule that modulates the expression and activity of cell cycle proteins.