Yock Young Dan

New Concepts in Liver Regeneration

The unique ability of the liver to regenerate itself has fascinated biologists for years and has made it the prototype for mammalian organ regeneration. Harnessing this process has great potential benefit in the treatment of liver failure and has been the focus of intense research over the past 50 years. Not only will detailed understanding of cell proliferation in response to injury be applicable to other dysfunction of organs, it may also shed light on how cancer develops in a cirrhotic liver, in which there is intense pressure on cells to regenerate. Advances in molecular techniques over the past few decades have led to the identification of many regulatory intermediates, and pushed us onto the verge of an explosive era in regenerative medicine. To date, more than 10 clinical trials have been reported in which augmented regeneration using progenitor cell therapy has been attempted in human patients. This review traces the path that has been taken over the last few decades in the study of liver regeneration, highlights new concepts in the field, and discusses the challenges that still stand between us and clinical therapy.

Mesenchymal stem cell-derived exosomes promote hepatic regeneration in drug-induced liver injury models

IntroductionMesenchymal stem cell-conditioned medium (MSC-CM) has been shown to have protective effects against various cellular-injury models. This mechanism of protection, however, has yet to be elucidated. Recently, exosomes were identified as the active component in MSC-CM. The aim of this study is to investigate the effect of MSC-derived exosomes in an established carbon tetrachloride (CCl4)-induced liver injury mouse model. This potential effect is then validated by using in vitro xenobiotic-induced liver-injury assays: (1) acetaminophen (APAP)- and (2) hydrogen peroxide (H2O2)-induced liver injury.MethodsThe exosomes were introduced concurrent with CCl4 into a mouse model through different routes of administration. Biochemical analysis was performed based on the blood and liver tissues. Subsequently the exosomes were treated in APAP and H2O2-toxicants with in vitro models. Cell viability was measured, and biomarkers indicative of regenerative and oxidative biochemical responses were determined to probe the mechanism of any hepatoprotective activity observed.ResultsIn contrast to mice treated with phosphate-buffered saline, CCl4 injury in mice was attenuated by concurrent-treatment exosomes, and characterized by an increase in hepatocyte proliferation, as demonstrated with proliferating cell nuclear antigen (PCNA) elevation. Significantly higher cell viability was demonstrated in the exosomes-treated group compared with the non-exosome-treated group in both injury models. The higher survival rate was associated with upregulation of the priming-phase genes during liver regeneration, which subsequently led to higher expression of proliferation proteins (PCNA and cyclin D1) in the exosomes-treated group. Exosomes also inhibited the APAP- and H2O2-induced hepatocytes apoptosis through upregulation of Bcl-xL protein expression. However, exosomes do not mitigate hepatocyte injury via modulation of oxidative stress.ConclusionsIn summary, these results suggest that MSC-derived exosomes can elicit hepatoprotective effects against toxicants-induced injury, mainly through activation of proliferative and regenerative responses.

Oncofetal Gene SALL4 in Aggressive Hepatocellular Carcinoma

BACKGROUND Hepatocellular carcinoma is the third leading cause of cancer-related deaths worldwide. In the heterogeneous group of hepatocellular carcinomas, those with characteristics of embryonic stem-cell and progenitor-cell gene expression are associated with the worst prognosis. The oncofetal gene SALL4, a marker of a subtype of hepatocellular carcinoma with progenitor-like features, is associated with a poor prognosis and is a potential target for treatment. METHODS We screened specimens obtained from patients with primary hepatocellular carcinoma for the expression of SALL4 and carried out a clinicopathological analysis. Loss-of-function studies were then performed to evaluate the role of SALL4 in hepatocarcinogenesis and its potential as a molecular target for therapy. To assess the therapeutic effects of a peptide that targets SALL4, we used in vitro functional and in vivo xenograft assays. RESULTS SALL4 is an oncofetal protein that is expressed in the human fetal liver and silenced in the adult liver, but it is reexpressed in a subgroup of patients who have hepatocellular carcinoma and an unfavorable prognosis. Gene-expression analysis showed the enrichment of progenitor-like gene signatures with overexpression of proliferative and metastatic genes in SALL4-positive hepatocellular carcinomas. Loss-of-function studies confirmed the critical role of SALL4 in cell survival and tumorigenicity. Blocking SALL4-corepressor interactions released suppression of PTEN (the phosphatase and tensin homologue protein) and inhibited tumor formation in xenograft models in vivo. CONCLUSIONS SALL4 is a marker for a progenitor subclass of hepatocellular carcinoma with an aggressive phenotype. The absence of SALL4 expression in the healthy adult liver enhances the potential of SALL4 as a treatment target in hepatocellular carcinoma. (Funded by the Singapore National Medical Research Council and others.).

Chronic Infection With Camelid Hepatitis E Virus in a Liver-transplant Recipient Who Regularly Consumes Camel Meat and Milk.

There have been increasing reports of food-borne zoonotic transmission of hepatitis E virus (HEV) genotype 3, which causes chronic infections in immunosuppressed patients. We performed phylogenetic analyses of the HEV sequence (partial and full-length) from 1 patient from the Middle East who underwent liver transplantation, and compared it with other orthohepevirus A sequences. We found the patient to be infected by camelid HEV. This patient regularly consumed camel meat and milk, therefore camelid HEV, which is genotype 7, might infect human beings. Our finding links consumption of camel-derived food products to post-transplantation hepatitis E, which, if detected at early stages, can be cured with antiviral therapy and reduced administration of immunosuppressive agents.

Non‐invasive models for predicting histology in patients with chronic hepatitis B

Abstract: Background and aim: In contrast to chronic hepatitis C (CHC), few studies had been performed in assessing non‐invasive models for predicting significant fibrosis or cirrhosis in chronic hepatitis B (CHB) patients. We aimed to evaluate non‐invasive markers for diagnosing significant fibrosis/cirrhosis in patients with CHB, and to evaluate accuracy of models from CHC in CHB patients.

Liver stem cells: A scientific and clinical perspective

The promise of liver stem cells lie in their potential to provide a continual and readily available source of liver cells that can be used for gene therapy, cellular transplant, bioartificial liver‐assisted devices, drug toxicology testing and use as an in vitro model to understand the developmental biology of the liver. Both the rodent and human embryonic stem cell, bone marrow hematopoietic stem cell, mesenchymal stem cell, umbilical cord blood cell, fetal liver progenitor cell, adult liver progenitor cell as well as the mature hepatocyte have been reported to be capable of self‐renewal, giving rise to daughter hepatocytes both in vivo and in vitro. These cells can repopulate livers in animal models of liver injury and seemingly improve liver function. However, significant challenges still exist before these cells can be used in humans. These include lack of consensus in immunophenotype of liver progenitor cells, uncertainty of the physiological role of reported candidate stem/progenitor cell, practicality in obtaining sufficient quantity of cells for clinical use and concerns over ethics, long‐term efficacy and safety. Current molecular techniques of stem cell identification are confounded by cell fusion, horizontal gene transfer, incomplete differentiation and fetal microchimerism. Reports of stem cell transplantation and phase 1 trials of bone marrow transplantation in humans for liver diseases are exciting but require more robust verification. We review the evidence for various candidate stem cells, human clinical trials reported to date and highlight the challenges facing clinicians in their quest to use liver stem cells to save lives.

Prophylactic strategies for hepatitis B patients undergoing liver transplant: A cost‐effectiveness analysis

Hepatitis B immunoglobulin with lamivudine prophylaxis (LAM/HBIG) is effective in preventing Hepatitis B (HBV) recurrence posttransplant but is expensive and inconvenient. Lamivudine‐resistant HBV, which has limited the usefulness of lamivudine monoprophylaxis in transplant, can now be effectively controlled with adefovir dipivoxil. We performed a cost‐effectiveness analysis on the strategies of lamivudine prophylaxis with adefovir rescue(LAM/ADV) compared to combination LAM/intravenous fixed high‐dose HBIG prophylaxis(LAM/ivHBIG) or LAM/intramuscular HBIG prophylaxis(LAM/imHBIG). Markov modeling was performed with analysis from societal perspective. Probability rates were derived from systematic review of the literature and cost taken from MEDICARE database. Outcome measures were incremental cost‐effectiveness ratio(ICER) and cost to prevent each HBV recurrence and death. Analysis was performed at 5 years posttransplant as well as at end of life expectancy (15 years). Combination LAM/ivHBIG cost an additional USD562,000 at 15 years, while LAM/imHBIG cost an additional USD139,000 per patient compared to LAM/ADV. Although there is an estimated increase in recurrence of 53% with LAM/ADV and 7.6% increased mortality at the end of life expectancy (15 years), the ICER of LAM/ivHBIG over LAM/ADV treatment is USD760,000 per quality‐adjusted life‐years and for LAM/imHBIG, USD188,000. Cost‐effectiveness is most sensitive to cost of HBIG. Lamivudine prophylaxis with adefovir dipivoxil salvage offers the more cost‐effective option for HBV patients undergoing liver transplant but with higher recurrence and death rate using a model that favors LAM/HBIG. Lowering the cost of HBIG maintenance will improve cost‐effectiveness of LAM/HBIG strategy. In conclusion, a tailored approach based on individual risks will optimize the cost‐benefit of HBV transplant prophylaxis. Liver Transpl 12:736–746, 2006.

Defective DNA strand break repair causes chromosomal instability and accelerates liver carcinogenesis in mice

Chromosomal instability is a characteristic feature of hepatocellular carcinoma (HCC) but its origin and role in liver carcinogenesis are undefined. We tested whether a defect in the nonhomologous end‐joining (NHEJ) DNA repair gene Ku70 was associated with chromosomal abnormalities and enhanced liver carcinogenesis. Male Ku70 NHEJ‐deficient (Ku70−/−), heterozygote (Ku70 +/−), and wild‐type (WT) mice were injected with diethylnitrosamine (DEN), a liver carcinogen, at age 15 days. Animals were killed at 3, 6, and 9 months for assessment of tumorigenesis and hepatocellular proliferation. For karyotype analysis, primary liver tumor cell cultures were prepared from HCCs arising in Ku70 mice of all genotypes. Compared to WT littermates, Ku70−/− mice injected with DEN displayed accelerated HCC development. Ku70−/− HCCs harbored clonal increases in numerical and structural aberrations of chromosomes 4, 5, 7, 8, 10, 14, and 19, many of which recapitulated the spectrum of equivalent chromosomal abnormalities observed in human HCC. Ku70−/− HCCs showed high proliferative activity with increased cyclin D1 and proliferating cell nuclear antigen expression, Aurora A kinase activity, enhanced ataxia telangiectasia mutated kinase and ubiquitination, and loss of p53 via proteasomal degradation, features which closely resemble those of human HCC. Conclusion: These findings demonstrate that defects in the NHEJ DNA repair pathway may participate in the disruption of cell cycle checkpoints leading to chromosomal instability and accelerated development of HCC. (HEPATOLOGY 2008;47:2078–2088.)

Intragastric balloon significantly improves nonalcoholic fatty liver disease activity score in obese patients with nonalcoholic steatohepatitis: a pilot study

BACKGROUND There is no satisfactory treatment for nonalcoholic steatohepatitis (NASH). The Bioenterics intragastric balloon (BIB) can be an effective treatment for weight reduction in obese patients. OBJECTIVE We evaluated the efficacy of the BIB in improving the histology of NASH in obese patients. DESIGN Randomized, controlled study. SETTING University hospital. PATIENTS Obese patients with body mass indexes (BMI) ≥27 kg/m(2) and who had histologic evidence of NASH were recruited. INTERVENTION Patients were randomly assigned to a step 1 American Heart Association (AHA) diet plus exercise and BIB placement or step 1 AHA diet plus exercise and sham BIB placement for a period of 6 months. MAIN OUTCOME MEASUREMENTS Liver histology was the primary outcome measure recorded before and after treatment. RESULTS A total of 18 patients completed the study. Baseline characteristics of the BIB and sham groups were similar. At 6 months, a significant reduction in the mean BMI was seen in the BIB group (1.52 vs 0.8; P = .0008). The median nonalcoholic fatty liver disease activity scores at the end of treatment were significantly lower in the BIB-treated compared with the sham-treated groups (2 [0.75] vs 4 [2.25]; P = .03). There was a trend toward improvement in the median steatosis scores (1 [0.75] vs 1 [1]; P = .075). There was no change in the median loblular inflammation, hepatocellular ballooning, or fibrosis scores in both groups after treatment. LIMITATIONS Pilot study with small numbers and short duration. CONCLUSION Results from this pilot study demonstrated that addition of BIB for 6 months provided a greater loss of BMI and improvement in 2 of 5 histologic parameters of nonalcoholic fatty liver disease. A longer study with larger numbers will be required to prove whether or not the therapy is meaningful in the treatment of NASH.

MARS®: a futile tool in centres without active liver transplant support

Background and aim: Studies on Molecular Adsorbent Recycling Systems (MARS®) showed inconclusive survival benefits.