Artificial liver support at present and in the future

The development of artificial livers

PURPOSE OF REVIEW

While liver transplantation is an established treatment for liver failure, the number of patients with liver failure amenable to such intervention far outnumbers the donor supply of livers. Technologies serving to bridge this gap are required. Artificial livers may serve as an alternative. In this review, we discuss the development of artificial liver technologies.

RECENT FINDINGS

The accrued clinical data suggest that current liver assist devices may serve a role in specific liver diseases, but for the most part no survival benefit has been demonstrated. More clinical trials are expected to elucidate their utilization. Simultaneously, recent advances in materials and tissue engineering are allowing for exciting developments for novel artificial livers.

SUMMARY

As there continues to be more clinical data regarding the use of current liver devices, new intricate artificial liver technologies, with the use of sophisticated three-dimensional materials, are being developed that may help improve outcomes of liver failure patients.

A systematic review of prediction models for post-hepatectomy liver failure in patients undergoing liver surgery

BACKGROUND

The aim of this systematic review is to evaluate the current evidence in the context of clinical prediction model for post-hepatectomy liver failure (PHLF).

METHODS

A systematic search of the English literature for a period from December 2005 to September 2020 was conducted. Primary outcome was defined using the three common PHLF criteria (50-50 criteria, peak bilirubin>7 mg/dl criteria, and ≥ grade B PHLF criteria by the International Study Group of Liver Surgery). Studies that reported the value of area under receiver operative characteristic curve (AUC) for the occurrence of PHLF were included.

RESULTS

Twenty eight of 1327 screened articles were eligible for inclusion. Eighteen studies developed the prediction models. The median AUC was found to be 0.79 (0.65-0.933). The parameters related to the amount of future liver remnant volume were most commonly identified as significant predictors for PHLF in statistical analysis (24 studies) and were most frequently incorporated in the prediction models (18 studies). The parameters associated with portal hypertension were significant for predicting PHLF in 16 studies and were adopted in the prediction models in 14 studies.

CONCLUSION

Parameters related to future liver remnant volume and portal hypertension seem to be facilitating in predicting PHLF.

Bilirubin adsorption versus plasma exchange for hyperbilirubinemia in patients after cardiac surgery: a retrospective study

Objective

Hyperbilirubinemia after cardiac surgery increases in-hospital mortality and is associated with poor prognosis. Our present study aimed to compare the efficacy of bilirubin adsorption (BA) and plasma exchange (PEX) in patients with hyperbilirubinemia after cardiac surgery.

Methods

We retrospectively included patients who underwent BA treatment or PEX treatment due to severe hyperbilirubinemia after cardiac surgery at our center from 2015 to 2020. We collected results from urine and liver function tests before and after treatment and compared the in-hospital mortality and morbidity between the two treatment groups.

Results

A total of 56 patients were enrolled in this study: 14 patients received BA treatment, and 42 patients received PEX treatment. Compared to the PEX group, the BA group exhibited a statistically significant reduction in total bilirubin (p = 0.016) and direct bilirubin (p = 0.036) levels. The in-hospital mortality was 85.7% (48/56) in the whole group, and the BA group had a lower mortality than the PEX group (71.4% vs. 90.5%, p = 0.078). The BA group showed better circulatory support, including lower risks of IABP (21.4% vs. 52.4%, p = 0.044), ECMO (21.4% vs. 50.0%, p = 0.061), reintubation (64.3% vs. 40.5%, p = 0.122) and ventricular arrhythmias (64.3% vs. 45.2%, p = 0.217). The in-hospital mortality was still lower in the BA treatment group than in the PEX treatment group (71.4% vs. 100%, p = 0.049) in the matched cohort.

Conclusions

Compared to PEX treatment, BA treatment had a higher bilirubin removal ability in patients with hyperbilirubinemia and could reduce the mortality and risks of poor clinical outcomes. BA treatment should be considered an effective treatment method for patients with higher total bilirubin or direct bilirubin levels.

Artificial liver research output and citations from 2004 to 2017: a bibliometric analysis

Background

Researches on artificial livers greatly contribute to the clinical treatments for liver failure. This study aimed to evaluate the research output of artificial livers and citations from 2004 to 2017 through a bibliometric analysis.

Methods

A list of included articles on artificial livers were generated after a comprehensive search of the Web of Science Core Collection (from 2004 to 2017) with the following basic information: number of publications, citations, publication year, country of origin, authors and authorship, funding source, journals, institutions, keywords, and research area.

Results

A total of 968 included articles ranged from 47 citations to 394 citations with a fluctuation. The publications were distributed in 12 countries, led by China (n = 212) and the US (n = 207). There were strong correlations of the number of citations with authors (r ² = 0.133, p < 0.001), and countries (r ² = 0.275, p < 0.001), while no correlations of the number of citations with the years since publication (r ² = 0.016, p = 0.216), and funding (r ² < 0.001, p = 0.770) were identified. Keyword analysis demonstrated that with the specific change of "acute liver failure," decrease in "bioartificial livers" and "hepatocyte," and increase in "tissue engineering" were identified. The top 53 cited keyword and keyword plus (including some duplicates counts) were identified, led by bioartificial liver (405 citations) and hepatocyte (248 citations). The top 50 cited keywords bursts were mainly "Blood" (2004-2008), "hepatocyte like cell" (2008-2015), and "tissue engineering" (2014-2017). All keywords could be classified into four categories: bioartificial livers (57.40%), blood purification (25.00%), clinical (14.81%), and other artificial organs (2.78%).

Discussion

This study shows the process and tendency of artificial liver research with a comprehensive analysis on artificial livers. However, although it seems that the future of artificial livers seems brighter for hepatocyte transplantation, the systems of artificial livers now are inclined on focusing on blood purification, plasma exchange, etc.

Postoperative Liver Failure

Technical innovations in surgical techniques, anaesthesia, critical care and a spatial understanding of the intra-hepatic anatomy of the liver, have led to an increasing number of liver resections being performed all over the world. However, the number of complications directly attributed to the procedure and leading to inadequate or poor hepatic functional status in the postoperative period remains a matter of concern. There has always been a problem of arriving at a consensus in the definition of the term: postoperative liver failure (PLF). The burgeoning rate of living donor liver transplants, with lives of perfectly healthy donors involved, has mandated a consensual definition, uniform diagnosis and protocol for management of PLF. The absence of a uniform definition has led to poor comparison among various trials. PLF remains a dreaded complication in resection of the liver, with a reported incidence of up to 8 % [1], and mortality rates of up to 30–70 % have been quoted [2]. Several studies have quoted a lower incidence of PLF in eastern countries, but when it occurs the mortality is as high as in the West [3].

Perioperative management in liver transplantation for acute liver failure

Acute liver failure occurs abruptly with rapid progression. Traditional medical treatment and simple non-bioartificial liver support system cannot reverse the prognosis of acute liver failure (ALF), and liver transplantation is the only effective treatment. However, donor liver shortage, the need of a life-long immunosuppressive therapy as well as complex postoperative complications make ALF patients facing a variety of challenges in the perioperative period of liver transplantation, which are directly related to the success rate of surgery and the mortality. This article aims to discuss perioperative difficulties and preventive measures in liver transplantation for ALF by exploring how to extend the lives of patients before liver transplantation and how to deal with postoperative complications.

Comparative study of efficacy of different types of artificial liver treatments in management of hepatitis B-associated liver failure

AIM: To investigate the clinical efficacy of plasma exchange (PE), plasma bilirubin adsorption (PBA), and PE combined with PBA in the treatment of hepatitis B-associated liver failure.

METHODS: The clinical data for 150 patients with hepatitis B-associated liver failure were retrospectively analyzed. These patients were randomly divided into a PE group, a PBA group, and a PE + PBA group. The volume of plasma consumed once, the effective rate, liver function, alanine aminotransferase (ALT), total bilirubin (TBIL), albumin (ALB), prothrombin time (PT), prothrombin time activity (PTA), creatinine (Cr) and plasma ammonia were recorded both before and after treatment and compared among the three groups. The incidence of adverse reactions was also observed.

RESULTS: The total effective rate was higher in the combination group than in the PE group and PBA group (65.45% vs 62.5%, 59.58%), but the difference was not statistically significant (both P > 0.05). TBIL was significantly decreased 4 hours after treatment compared to pre-treatment values in the PE, PBA and combination groups (410.3 µmol/L ± 208.6 µmol/L vs 292.5 µmol/L ± 175.4 µmol/L, 432.7 µmol/L ± 242.5 µmol/L vs 298.8 µmol/L ± 201.7 µmol/L, 468.2 µmol/L ± 241.6 µmol/L vs 288.5 µmol/L ± 184.5 µmol/L, all P < 0.05), but the decline showed no significantly statistical difference among the three groups. After treatment, PT was significantly shortened and PTA was increased in the combination group and PE group (both P < 0.05), but the changes showed no significant difference between the two groups (both P > 0.05). In the PBA group, PT was increased and PTA was decreased after treatment, but the differences were not significant (P > 0.05). Blood ammonia and Cr were significantly decreased in the three groups of patients after treatment (all P < 0.05), although there was no significantly statistical difference among the three groups. No serious adverse reactions occurred. The volume of plasma consumed once was significantly less in the combination group than in the PE group (1107.1 mL ± 212.3 mL vs 2911.5 mL ± 352.3 mL, P < 0.05).

CONCLUSION: PE combined with PBA can effectively reduce the amount of plasma consumed and the incidence of adverse reactions, improve survival and therefore represent a safe and effective treatment for hepatitis B-associated liver failure.

Use of perfluorocarbons to enhance the performance of perfused three-dimensional hepatic cultures

Bioartificial liver devices (BALs) are extracorporeal systems designed to temporarily bridge patients until a suitable donated liver is available for transplantation and also have value for pharmaceutical testing applications. Yet critical issues exist that limit the functional performance of their current designs. One of these concerns scale up issues connected to oxygen (O2 ) delivery to the cells housed within their three-dimensional (3D) configurations, and its consequences to device performance. As primary blood substitute candidates with extraordinarily high O2 capacity, perfluorocarbons (PFCs) offer hope as one strategy for addressing the O2 delivery issue encountered when scaling up the tissue space of current BAL designs. This study utilizes a PFC-based second-generation O2 carrier OXYCYTE®, as an additive to regular nutrient medium, for augmenting O2 delivery in a customized 3D tissue assembly system. The results demonstrate that the addition of PFCs significantly increases the O2 capacity of regular medium and that net cytochrome P450 activity levels are considerably increased under flow in PFC-treated systems, as compared to controls. This work thus clarifies the benefits of using PFCs to enhance the functional performance of 3D liver systems.

Artificial liver support system combined with liver transplantation in the treatment of patients with acute-on-chronic liver failure

Background

The search for a strategy to provide temporary liver support and salvage the patients with acute-on-chronic liver failure (ACLF) remains an important issue. This study was designed to evaluate the experience in artificial liver support system (ALSS) combined with liver transplantation (LT) in the treatment of ACLF.

Methodology/Principal Findings

One hundred and seventy one patients with HBV related ACLF undergoing LT between January 2001 and December 2009 were included. Of the 171 patients, 115 received 247 sessions of plasma exchange-centered ALSS treatment prior to LT (ALSS-LT group) and the other 56 received emergency LT (LT group). The MELD score were 31±6 and 30±7 in ALSS-LT group and LT group. ALSS treatment resulted in improvement of liver function and better tolerance to LT. The average level of serum total bilirubin before LT was lower than that before the first time of ALSS treatment. The median waiting time for a donor liver was 12 days (2–226 days) from the first run of ALSS treatment to LT. Compared to LT group, the beneficial influences of ALSS on intraoperative blood loss and endotracheal intubation time were also observed in ALSS-LT group. The 1-year and 5-year survival rates in the ALSS-LT group and LT group were 79.2% and 83%, 69.7% and 78.6%.

Conclusions/Significance

Plasma exchange-centered ALSS is beneficial in salvaging patients with ACLF when a donor liver is not available. The consequential LT is the fundamental treatment modality to rescue these patients and lead to a similar survival rate as those patients receiving emergency transplantation.

Use of hepatocyte and stem cells for treatment of post-resectional liver failure: are we there yet?

Post-operative liver failure following extensive resections for liver tumours is a rare but significant complication. The only effective treatment is liver transplantation (LT); however, there is a debate about its use given the high mortality compared with the outcomes of LT for chronic liver diseases. Cell therapy has emerged as a possible alternative to LT especially as endogenous hepatocyte proliferation is likely inhibited in the setting of prior chemo/radiotherapy. Both hepatocyte and stem cell transplantations have shown promising results in the experimental setting; however, there are few reports on their clinical application. This review identifies the potential stem cell sources in the body, and highlights the triggering factors that lead to their mobilization and integration in liver regeneration following major liver resections.

Bone marrow mononuclear cell transplantation improves survival and induces hepatocyte proliferation in rats after CCl(4) acute liver damage

AIM

The aim of this research was to evaluate the effects of bone marrow mononuclear cell (BMC) transplantation in rats with toxic acute liver damage induced by carbon tetrachloride (CCl(4)).

METHODS

Cells from male Wistar rats were obtained using Ficoll density gradient and 0.2 ml (1 × 10(6) cells) were injected into the portal vein of female rats (n = 15) 24 h after damage. Sham group (n = 15) was performed injecting only vehicle in CCl(4)-treated animals. Survival, liver histology, number of mitosis and apoptosis, and identification of stained donor cells were observed 72 h after damage. ALT levels were measured at 0 h, 24 h, 48 h, and 72 h after injury.

RESULTS

Donor cells could be detected in recipient rats' livers by fluorescence staining and Sry PCR. The treated group revealed a significant improvement in survival rate after 72 h (p = 0.003). There was also a significant increase in the number of mitotic events in treated livers (p = 0.029). This result was confirmed using an in vitro cell proliferation assay in isolated hepatocytes treated with conditioned medium from BMC. ALT was reduced in the treated group after 72 h (p = 0.034).

CONCLUSIONS

Results indicate that BMC transplantation has potential as a new therapeutic option for acute liver disease and suggest that these cells may contribute to hepatic recovery through release of mitotic cytokines.

Eleven cases of postoperative hepatic infarction following pancreato-biliary surgery

BACKGROUND

Postoperative hepatic infarction is rare; therefore, clinical characteristics and outcomes of postoperative hepatic infarction after pancreatobiliary surgery have not been obvious.

METHODS

Eleven patients encountered hepatic infarction after pancreato-biliary surgery. Management, clinical course, and outcome of these 11 patients were retrospectively analyzed.

RESULTS

Possible causes of the hepatic infarction were inadvertent injury of the hepatic artery during lymph node dissection in five patients, right hepatic artery ligation in two patients, long-term clamp of the hepatic artery during hepatic arterial reconstruction in two patients, suturing for bleeding from the right hepatic artery in one patient, and celiac axis compression syndrome in one patient. Five of the 17 infarcts extended for one whole section of the liver, and distribution of the other 12 was less than one section. Ten patients discharged from hospital; however, one patient died of sepsis of unknown origin.

CONCLUSIONS

Attention should be paid to inadvertent injury of hepatic artery to prevent hepatic infarction. Hepatic infarctions after pancreato-biliary surgery seldom extend to the entire liver and most of them are able to be treated without intervention.

In vitro evaluation of a multi-layer radial-flow bioreactor based on galactosylated chitosan nanofiber scaffolds

Clinical use of bioartificial livers (BAL) strongly relies on the development of bioreactors. In this study, we developed a multi-layer radial-flow bioreactor based on galactosylated chitosan nanofiber scaffolds and evaluated its efficacy in vitro. The bioreactor contains 65 layers of stacked flat plates, on which the nanofiber scaffolds were electrospinned for hepatocyte immobilization and aggregation. Culture medium containing pig red blood cells (RBCs) was perfused from the center to periphery, so that exchange materials are sufficient to afford enough oxygen. We determined the parameters for hepatocyte-specific function and general metabolism and also measured the oxygen consumption rate (OCR). Microscope and scanned electron microscopy observation showed a tight adhesion between cells and scaffolds. Compared with the control (bioreactors without nanofiber scaffolds), the number of adhered cells in our bioreactor was 1.59-fold; the protein-synthesis capacity of hepatocytes was 1.73-fold and urea was 2.86-fold. Moreover, the OCR of bioreactors with RBCs was about 1.91-fold that of bioreactors without RBCs. The galactosylated chitosan nanofiber scaffolds introduced into our new bioreactor greatly enhanced cell adhesion and function, and the RBCs added into the culture medium were able to afford enough oxygen for hepatocytes. Importantly, our new bioreactor showed an exciting efficiency, and it may afford the short-term support of patients with hepatic failure.

What clinical alternatives to whole liver transplantation? Current status of artificial devices and hepatocyte transplantation

Shortage of organ donors limits the number of possible liver transplantations. Alternative therapies for treatment of liver failure are currently being developed: (i) extracorporeal artificial liver devices; (ii) bioartificial liver devices using hepatocytes; and (iii) hepatocyte transplantation. The objective of these strategies is to bridge patients with liver failure until a suitable liver allograft is obtained for transplantation or the patient's own liver regenerates sufficiently to resume normal function. In this review, we discuss these strategies and summarize the current status of clinical experience.

Chitosan nanofiber scaffold enhances hepatocyte adhesion and function

To enhance cell attachment and promote liver functions of hepatocytes cultured in bioreactors, a chitosan nanofiber scaffold was designed and prepared via electrospinning. Effects of the scaffold on hepatocyte adhesion, viability and function were then investigated. Data showed that hepatocytes on chitosan nanofiber scaffold exhibited better viability and tighter cell-substrate contact than cells on regular chitosan film. In addition, urea synthesis, albumin secretion and cytochrome P450 activity of hepatocytes on chitosan nanofiber scaffold were all 1.5 to 2 folds higher than the controls. Glycogen synthesis was also increased as compared with the controls. These results suggested the potential application of this chitosan nanofiber scaffold as a suitable substratum for hepatocyte culturing in bioreactors.

Research progress and prospects of bioartificial liver system

Liver transplantation is the only established treatment for acute liver failure (ALF), one of the most challenging clinical syndromes; however, donor shortages remain problematic. Artificial livers as a bridge to liver transplantation are being considered worldwide. Non-bioarticifical liver (NBAL) have limitations in improving the survival rates. Therefore, a biological artificial liver (BAL) that has metabolic, detoxic,and synthetic function of hepatocytes is anticipated. Biological artificial livers are classified by cell source, types of culture system for hepatocytes, and types of bioreactor. This paper reviews the bioartificial liver devices that have been clinically tested to support ALF patients. Finally, we identify several improvements critical to bioartificial liver replacement therapy in the future.

Liver failure after partial hepatic resection: definition, pathophysiology, risk factors and treatment

Liver failure is a dreaded and often fatal complication that sometimes follows a partial hepatic resection. This article reviews the definition, incidence, pathogenesis, risk factors, risk assessment, prevention, clinical features and treatment of post-resectional liver failure (PLF). A systematic, computerized search was performed using key words related to 'partial hepatic resection' and 'liver failure' to review most relevant literature about PLF published in the last 20 years. The reported incidence of PLF ranges between 0.7 and 9.1%. An inadequate quantity or quality of residual liver mass are key events in its pathogenesis. Major risk factors are the presence of comorbid conditions, pre-existent liver disease and small remnant liver volume (RLV). It is essential to identify these risk factors during the pre-operative assessment that includes evaluation of liver volume, anatomy and function. Preventive measures should be applied whenever possible as curative treatment options for PLF are limited. These preventive measures intend to increase RLV and protect remnant liver function. Management principles focus on support of end-organ and liver function. Further research is needed to elucidate the exact pathogenesis of PLF and to develop and validate adequate treatment options.

Cells for bioartificial liver devices: the human hepatoma-derived cell line C3A produces urea but does not detoxify ammonia

Extrahepatic bioartificial liver devices should provide an intact urea cycle to detoxify ammonia. The C3A cell line, a subclone of the hepatoma-derived HepG2 cell line, is currently used in this context as it produces urea, and this has been assumed to be reflective of ammonia detoxification via a functional urea cycle. However, based on our previous findings of perturbed urea-cycle function in the non-urea producing HepG2 cell line, we hypothesized that the urea produced by C3A cells was via a urea cycle-independent mechanism, namely, due to arginase II activity, and therefore would not detoxify ammonia. Urea was quantified using (15)N-ammonium chloride metabolic labelling with gas chromatography-mass spectrometry. Gene expression was determined by real-time reverse transcriptase-PCR, protein expression by western blotting, and functional activities with radiolabelling enzyme assays. Arginase inhibition studies used N(omega)-hydroxy-nor-L-arginine. Urea was detected in C3A conditioned medium; however, (15)N-ammonium chloride-labelling indicated that (15)N-ammonia was not incorporated into (15)N-labelled urea. Further, gene expression of two urea cycle genes, ornithine transcarbamylase and arginase I, were completely absent. In contrast, arginase II mRNA and protein was expressed at high levels in C3A cells and was inhibited by N(omega)-hydroxy-nor-L-arginine, which prevented urea production, thereby indicating a urea cycle-independent pathway. The urea cycle is non-functional in C3A cells, and their urea production is solely due to the presence of arginase II, which therefore cannot provide ammonia detoxification in a bioartificial liver system. This emphasizes the continued requirement for developing a component capable of a full repertoire of liver function.