New paradigms for organ allocation and distribution in liver transplantation

What is said about #donateliver or #liverdonor? Reflexive thematic analysis of Twitter (X) posts from 2012 to 2022

BACKGROUND

There is sustained interest in understanding the perspectives of liver transplant recipients and living donors, with several qualitative studies shedding light on this emotionally charged subject. However, these studies have relied primarily on traditional semi-structured interviews, which, while valuable, come with inherent limitations. Consequently, there remains a gap in our comprehension of the broader public discourse surrounding living liver donation. This study aims to bridge this gap by delving into public conversations related to living liver donation through a qualitative analysis of Twitter (now X) posts, offering a fresh perspective on this critical issue.

METHODS

To compile a comprehensive dataset, we extracted original tweets containing the hashtags "#donateliver" OR "#liverdonor", all posted in English from January 1, 2012, to December 31, 2022. We then selected tweets from individual users whose Twitter (X) accounts featured authentic human names, ensuring the credibility of our data. Employing Braun and Clarke's reflexive thematic analysis approach, the study investigators read and analysed the included tweets, identifying two main themes and six subthemes. The Health Policy Triangle framework was applied to understand the roles of different stakeholders involved in the discourse and suggest areas for policy improvement.

RESULTS

A total of 361 unique tweets from individual users were analysed. The major theme that emerged was the persistent shortage of liver donors, underscoring the desperation faced by individuals in need of life-saving liver transplants and the urgency of addressing the organ shortage problem. The second theme delved into the experiences of liver donors post-surgery, shedding light on a variety of aspects related to the transplantation process, including the visibility of surgical scars, and the significance of returning to physical activity and exercise post-surgery.

CONCLUSION

The multifaceted experiences of individuals involved in the transplantation process, both recipients and donors, should be further studied in our efforts to improve the critical shortage of liver donors.

Are MELD and MELDNa Still Reliable Tools to Predict Mortality on the Liver Transplant Waiting List?

Liver transplantation is the only curative treatment for end-stage liver disease. Unfortunately, the scarcity of donor organs and the increasing pool of potential recipients limit access to this life-saving procedure. Allocation should account for medical and ethical factors, ensuring equal access to transplantation regardless of recipient's gender, race, religion, or income. Based on their short-term prognosis prediction, model for end-stage liver disease (MELD) and MELD sodium (MELDNa) have been widely used to prioritize patients on the waiting list for liver transplantation resulting in a significant decrease in waiting list mortality/removal. Recent concern has been raised regarding the prognostic accuracy of MELD and MELDNa due, in part, to changes in recipients' profile such as body mass index, comorbidities, and general condition, including nutritional status and cause of liver disease, among others. This review aims to provide a comprehensive view of the current state of MELD and MELDNa advantages and limitations and promising alternatives. Finally, it will explore future options to increase the donor pool and improve donor-recipient matching.

Geographic Variation in Heart Transplant Extended Criteria Donors in the United States

BACKGROUND

Recent research has explored the use of higher risk extended criteria donors (ECDs) as a means of expanding the donor pool for heart transplantation. Here we sought to explore the current geographic distribution and survival outcomes of ECD utilization in various regions across the United States.

METHODS

The United Network for Organ Sharing database was retrospectively queried for adult primary heart transplantation from 2000 to 2019. The EXPAND trial definition of ECD was used: ischemic time ≥ 4 hours, ejection fraction < 50%, age > 55 years, and history of coronary artery disease. Geographic data and 2019 population estimates were obtained from the US Census Bureau.

RESULTS

Of the 42 642 transplants included in our analysis, 11 750 (27.6%) used ECDs. Region utilization of ECDs ranged from 18.4% to 46.5% of transplants. Region 6 had the highest utilization rate at 46.5%; this was primarily driven by the number of transplants with ischemic time ≥ 4 hours. Region 6 encompasses the largest total area (1.08 million square miles) and smallest population density (15.6 people per square mile). Region 8 had the lowest marginal donor utilization rate at 18.4%. Regions with high utilization of low ejection fractions, older donors, and donors with coronary artery disease (ie, regions 1 and 2) were able to maintain an average utilization rate of ECDs by maintaining short ischemic times.

CONCLUSIONS

Large discrepancies in the use of ECDs exist across the different United Network for Organ Sharing regions. This is primarily driven by longer ischemic times, likely guided by variance in population densities between different regions.

Novel NMP split liver model recapitulates human IRI and demonstrates ferroptosis modulators as a new therapeutic strategy

BACKGROUND

Almost 9%of deceased donor livers are discarded as marginal donor livers (MDL) due to concern of severe ischemia reperfusion injury (IRI). Emerging data supports ferroptosis (iron regulated hepatocellular death) as an IRI driver, however lack of robust preclinical model limits therapeutic testing. In this manuscript we describe the development of a novel rigorous internal control system utilizing normothermic perfusion of split livers to test ferroptosis regulators modulating IRI.

METHODS

Upon institutional approval, split human MDLs were placed on our normothermic perfusion machine, Perfusion Regulated Organ Therapeutics with Enhanced Controlled Testing (PROTECT), pumping arterial and portal blood. Experiment 1 compared right (UR) and left (UL) lobes to validate PROTECT. Experiment 2 assessed ferroptosis regulator Deferoxamine in Deferoxamine Agent Treated (DMAT) vs. No Agent Internal Control (NAIC) lobes. Liver serology, histology, and ferroptosis genes were assessed.

RESULTS

Successful MDL perfusion validated PROTECT with no ALT or AST difference between UR and UL (∆ALT UR: 235, ∆ALT UL: 212; ∆AST UR: 576, ∆AST UL: 389). Liver injury markers increased in NAIC vs. DMAT (∆ALT NAIC: 586, ∆ALT DMAT: -405; ∆AST NAIC: 617, ∆AST DMAT: -380). UR and UL had similar expression of ferroptosis regulators RPL8,HO-1 and HIFα. Significantly decreased intrahepatic iron (p = .038), HO-1 and HIFα in DMAT (HO-1 NAIC: 6.93, HO-1 DMAT: 2.74; HIFαNAIC: 8.67, HIFαDMAT: 2.60)and no hepatocellular necrosis or immunohistochemical staining (Ki67/Cytokeratin-7) differences were noted.

CONCLUSION

PROTECT demonstrates the therapeutic utility of a novel normothermic perfusion split liver system for drug discovery and rapid translatability of therapeutics, driving a paradigm change in organ recovery and transplant medicine. Our study using human livers, provides preliminary proof of concept for the novel role of ferroptosis regulators in driving IRI.

Basic principles of liver allocation and development over the years

PURPOSE OF REVIEW

Prior to the enactment of the National Organ Transplant Act in 1984, there was no organized system to allocate donor organs in the United States. The process of liver allocation has come a long way since then, including the development and implementation of the Model for End-stage Liver Disease, which is an objective estimate of risk of mortality among candidates awaiting liver transplantation.

RECENT FINDINGS

The Liver Transplant Community is constantly working to optimize the distribution and allocation of scare organs, which is essential to promote equitable access to a life-saving procedure in the setting of clinical advances in the treatment of liver disease. Over the past 17 years, many changes have been made. Most recently, liver distribution changed such that deceased donor livers will be distributed based on units established by geographic circles around a donor hospital rather than the current policy, which uses donor service areas as the unit of distribution. In addition, a National Liver Review Board was created to standardize the process of determining liver transplant priority for candidates with exceptional medical conditions. The aim of these changes is to allocate and distribute organs in an efficient and equitable fashion.

SUMMARY

The current review provides a historical perspective of liver allocation and the changing landscape in the United States.

The decreasing predictive power of MELD in an era of changing etiology of liver disease

The field of liver transplantation has shifted considerably in the MELD era, including changing allocation, immunosuppression, and liver failure etiologies, as well as better supportive therapies. Our aim was to evaluate the predictive accuracy of the MELD score over time. The United Network for Organ Sharing provided de-identified data on 120 156 patients listed for liver transplant from 2002-2016. The ability of the MELD score to predict 90-day mortality was evaluated by a concordance (C-) statistic and corroborated with competing risk analysis. The MELD score's concordance with 90-day mortality has downtrended from 0.80 in 2003 to 0.70 in 2015. While lab MELD scores at listing and transplant climbed in that interval, score at waitlist death remained steady near 35. Listing age increased from 50 to 54 years. HCV-positive status at listing dropped from 33 to 17%. The concordance of MELD and mortality does not differ with age (>60 = 0.73, <60 = 0.74), but is lower in diseases that are increasing most rapidly-alcoholic liver disease and non-alcoholic fatty liver disease-and higher in those that are declining, particularly in HCV-positive patients (HCV positive = 0.77; negative = 0.73). While MELD still predicts mortality, its accuracy has decreased; changing etiology of disease may contribute.

Geographic disparities in liver supply/demand ratio within fixed-distance and fixed-population circles

Recent OPTN proposals to address geographic disparity in liver allocation have involved circular boundaries: the policy selected 12/17 allocated to 150-mile circles in addition to DSAs/regions, and the policy selected 12/18 allocated to 150-mile circles eliminating DSA/region boundaries. However, methods to reduce geographic disparity remain controversial, within the OPTN and the transplant community. To inform ongoing discussions, we studied center-level supply/demand ratios using SRTR data (07/2013-06/2017) for 27 334 transplanted deceased donor livers and 44 652 incident waitlist candidates. Supply was the number of donors from an allocation unit (DSA or circle), allocated proportionally (by waitlist size) to the centers drawing on these donors. We measured geographic disparity as variance in log-transformed supply/demand ratio, comparing allocation based on DSAs, fixed-distance circles (150- or 400-mile radius), and fixed-population (12- or 50-million) circles. The recently proposed 150-mile radius circles (variance = 0.11, P = .9) or 12-million-population circles (variance = 0.08, P = .1) did not reduce the geographic disparity compared to DSA-based allocation (variance = 0.11). However, geographic disparity decreased substantially to 0.02 in both larger fixed-distance (400-mile, P < .001) and larger fixed-population (50-million, P < .001) circles (P = .9 comparing fixed distance and fixed population). For allocation circles to reduce geographic disparities, they must be larger than a 150-mile radius; additionally, fixed-population circles are not superior to fixed-distance circles.

Liver Allocation Policies in the USA: Past, Present, and the Future

Identifying the optimal allocation policy with regard to hepatocellular carcinoma has been a persistent and evolving challenge. The current criteria for LT for HCC endorsed by the United Network of Organ Sharing (UNOS) are based on the Milan Criteria: a solitary tumor < 5 cm, or maximum of three tumors ≤ 3 cm each, without vascular invasion or evidence of extrahepatic spread. Contraindications to HCC exception points include: stage 1 HCC, ruptured HCC, extrahepatic HCC, and main portal or hepatic vein HCC invasion. Based upon projected waitlist dropout rates due to tumor growth, patients with HCC are assigned MELD standardized exception points. In addition to tumor size and number, AFP levels are an important predictor of recurrence of HCC following liver transplantation. Standardized exception points for HCC patients are not awarded to patients with AFP levels > 1000 ng/mL that do not decrease to < 500 ng/mL with treatment. Appeals for MELD exception points for patients with HCC vary widely between UNOS regions, with success of nonstandardized exception point appeals varying from 3.1 to 21% between regions. In an effort to make prioritization for HCC more consistent, a national liver review board (NLRB)is being convened that will focus on developing a national guidance for assessing common requests and addressing exception points, including for HCC.