Published on in CHOP News
Plant Toxin, Bile Duct Injury, Genetics, Targeting T Cells and More
Twenty years ago, a grateful family of a child with biliary atresia had a vision to establish a “center without walls” at Children’s Hospital of Philadelphia (CHOP). Today, under the direction of Kathleen M. Loomes, MD, the Fred and Suzanne Biesecker Pediatric Liver Center supports almost 20 investigators engaged in basic, clinical and translational research in pediatric liver disease at CHOP, the University of Pennsylvania and other centers around the world. Through monthly meetings, these scientists exchange ideas and form new collaborations, leading to sentinel discoveries that continue to advance the field of pediatric liver disease.
Pathophysiology of Biliary Atresia
Through studies to understand the underlying cause of biliary atresia, our goal is to discover new therapies.
Discovery of the plant toxin biliatresone
Investigators in Australia documented several outbreaks of biliary atresia in livestock during times of drought, when pregnant animals were grazing on unusual plants, including Dysphania species. A team of CHOP investigators collaborated to obtain samples of the plant and isolate a novel isoflavenoid toxin, designated biliatresone, that caused biliary injury in zebrafish and mouse cholangiocytes.
Ongoing studies in zebrafish, mouse and cell culture models have identified specific pathways responsible for biliatresonemediated cholangiocyte injury. These studies have not only led to new experimental models for the study of biliary atresia but have elucidated mechanisms of injury that may become novel therapeutic targets.
Recent published research includes:
- Zhao X, Lorent K, Escobar-Zarate D, Rajagopalan R, Loomes KM, Gillespie K, Mesaros C, Estrada MA, Blair IA, Winkler JD, Spinner NB, Devoto M, Pack M. Impaired Redox and Protein Homeostasis as Risk Factors and Therapeutic Targets in Toxin-Induced Biliary Atresia. Gastroenterology. 2020 Sep;159(3):1068-1084. PMID: 32505743; PMCID: PMC7856536.
- Fried S, Gilboa D, Har-Zahav A, Lavrut PM, Du Y, Karjoo S, Russo P, Shamir R, Wells RG, Waisbourd-Zinman O. Extrahepatic cholangiocyte obstruction is mediated by decreased glutathione, Wnt and Notch signaling pathways in a toxic model of biliary atresia. Sci Rep. 2020 May 5;10(1):7599. PMID: 32371929; PMCID: PMC7200694.
- Waisbourd-Zinman O, Koh H, Tsai S, Lavrut PM, Dang C, Zhao X, Pack M, Cave J, Hawes M, Koo KA, Porter JR, Wells RG. The toxin biliatresone causes mouse extrahepatic cholangiocyte damage and fibrosis through decreased glutathione and SOX17. Hepatology. 2016 Sep;64(3):880-93. PMID: 27081925; PMCID: PMC4992464.
- Lorent K, Gong W, Koo KA, Waisbourd-Zinman O, Karjoo S, Zhao X, Sealy I, Kettleborough RN, Stemple DL, Windsor PA, Whittaker SJ, Porter JR, Wells RG, Pack M. Identification of a plant isoflavonoid that causes biliary atresia. Sci Transl Med. 2015 May 6;7(286):286ra67. PMID:25947162; PMCID: PMC4784984.
Mechanisms of neonatal bile duct injury
It is well known that biliary atresia occurs only in young infants, but until recently the factors underlying the unique susceptibility of the neonatal bile duct to injury had not been elucidated. CHOP liver researcher Rebecca G. Wells, MD, and her team conducted detailed studies of neonatal and adult bile ducts to identify specific structural differences. The cholangiocytes of the neonatal extrahepatic bile duct are immature, lacking a well-formed protective glycocalyx layer and mature cell-to-cell junctions. In addition, the submucosal space of the neonatal bile duct lacks the collagen and elastin characteristic of the adult bile duct. Taken together, these differences result in increased permeability of the neonatal bile duct and increased susceptibility to injury from bile acids in cholestasis.
- Khandekar G, Llewellyn J, Kriegermeier A, Waisbourd-Zinman O, Johnson N, Du Y, Giwa R, Liu X, Kisseleva T, Russo PA, Theise ND, Wells RG. Coordinated development of the mouse extrahepatic bile duct: Implications for neonatal susceptibility to biliary injury. J Hepatol. 2020 Jan;72(1):135-145. PMID: 31562906; PMCID: PMC7079197.
Genetic susceptibility to biliary atresia
The etiology of biliary atresia is unknown, but genetic risk factors have been proposed. In collaboration with the Childhood Liver Disease Research Network, Nancy B. Spinner, PhD, FACMG, Chief of the Division of Genomic Diagnostics at CHOP, and her team completed a genomewide association study and an exome sequencing study in biliary atresia. They identified EFEMP1, a gene involved in remodeling of the extracellular matrix, as a new candidate biliary atresia susceptibility gene.
- Rajagopalan R, Tsai EA, Grochowski CM, Kelly SM, Loomes KM, Spinner NB, Devoto M. Exome Sequencing in Individuals with Isolated Biliary Atresia. Sci Rep. 2020 Feb 17;10(1):2709. PMID: 32066793; PMCID: PMC7026070.
- Chen Y, Gilbert MA, Grochowski CM, McEldrew D, Llewellyn J, WaisbourdZinman O, Hakonarson H, Bailey-Wilson JE, Russo P, Wells RG, Loomes KM, Spinner NB, Devoto M. A genome-wide association study identifies a susceptibility locus for biliary atresia on 2p16.1 within the gene EFEMP1. PLoS Genet. 2018 Aug 13;14(8):e1007532. PMID: 30102696; PMCID: PMC6107291.
Following liver transplantation, patients receive immunosuppression to prevent rejection of the graft. Currently, immunosuppression is “one size fits all,” but it would be ideal to personalize immunosuppression according to the individual patient’s state of immune activation or tolerance, thereby reducing long-term side effects and risk of infection or malignancy.
Targeting regulatory T cell function
Increased activity of regulatory T cells (Tregs) is associated with tolerance to an allograft. The research of Wayne W. Hancock, MBBS, PhD, FRCPA, Chief of the Division of Transplantation Immunology, is focused on novel techniques for measuring Treg activity and therapeutic interventions to augment Treg function in transplant models. These types of studies may lead to new, tailored immunosuppressive therapies for transplant recipients.
- Di Giorgio E, Wang L, Xiong Y, Christensen LM, Akimova T, Han R, Samanta A, Trevisanut M, Brancolini C, Beier UH, Hancock WW. A Biological Circuit Involving Mef2c, Mef2d, and Hdac9 Controls the Immunosuppressive Functions of CD4+Foxp3+ T-Regulatory Cells. Front Immunol. 2021 Jul 5;12:703632. PMID: 34290714; PMCID: PMC8287581.
- Wang L, Beier UH, Akimova T, Dahiya S, Han R, Samanta A, Levine MH, Hancock WW. Histone/protein deacetylase inhibitor therapy for enhancement of Foxp3+ T-regulatory cell function post-transplantation.Am J Transplant. 2018 Jul;18(7):1596-1603. PMID: 29603600;PMCID: PMC6035084.
- Huang J, Wang L, Dahiya S, Beier UH, Han R, Samanta A, Bergman J, Sotomayor EM, Seto E, Kozikowski AP, Hancock WW. Histone/protein deacetylase 11 targeting promotes Foxp3+ Treg function. Sci Rep. 2017 Aug 17;7(1):8626. PMID: 28819166; PMCID: PMC5561267.
Non-invasive biomarkers of rejection
Currently acute cellular rejection of a liver allograft can only be diagnosed by liver biopsy. Brendan J. Keating, PhD, and Abraham Shaked, MD, PhD, are working to identify serum microRNA signatures as a non-invasive biomarker of rejection. The ability to diagnose rejection by a blood test would significantly advance patient care and the ability to tailor immunosuppression to each patient’s immune activation state.
- Zhu A, Leto A, Shaked A, Keating B. Immunologic Monitoring to Personalize Immunosuppression After Liver Transplant. Gastroenterol Clin North Am. 2018 Jun;47(2):281-296. PMID: 29735024.
- Shaked A, Chang BL, Barnes MR, Sayre P, Li YR, Asare S, DesMarais M, Holmes MV, Guettouche T, Keating BJ. An ectopically expressed serum miRNA signature is prognostic, diagnostic, and biologically related to liver allograft rejection. Hepatology. 2017 Jan;65(1):269-280. PMID: 27533743.
Wearable devices for early detection of infection in transplant recipients
Studies are ongoing to determine if wearable devices can detect early, subtle changes in heart rate and other biological parameters that can allow early detection of COVID-19 and other infections in transplant patients.
Collaborative liver studies and trials
Liver disease in children is rare; that’s why collaboration is so important to new discoveries, Dr. Loomes says. CHOP is an active participant in several landmark, ongoing national studies and clinical trials to learn more about liver disease, ways to improve management of the disease in children, and identify trends that may offer new clues for future therapies.
A few of these established studies include:
- Childhood Liver Disease Research Network (ChiLDReN): This NIH-funded collaborative of 13 clinical sites in North America is conducting observational studies of participants with pediatric liver diseases including biliary atresia, Alagille syndrome, progressive familial intrahepatic cholestasis (PFIC), primary sclerosing cholangitis and others. Through collaborative, longitudinal studies of these rare diseases, we can learn more about natural history and underlying pathophysiology.
- Pediatric Acute Liver Failure Immune Response Network (PALFIRN): This NIH-funded consortium will be conducting a clinical trial in PALF – TRIUMPH (Treatment for Immune-Mediated Pathophysiology).
- Studies in Pediatric Liver Transplant (SPLIT), a multicenter, observational study to collect prospective data on the success of pediatric liver transplantation, identify trends in patient and graft survival, rejection incidence and more.
- Improving Medication Adherence in Liver Transplant (iMALT): This NIH-funded multi-center study is testing a telemetric intervention to improve adherence and thereby reduce rejection in adolescent liver transplant recipients.
- Industry-sponsored clinical trials: studies of ileal bile acid transport inhibitors in biliary atresia and PFIC; studies of directacting antiviral agents in children with viral hepatitis; study of a new oral chelation agent for children with Wilson disease.
Clinicians and researchers at CHOP are also actively participating in dozens more site-specific and regional studies to investigate new or adjunct treatments for patients with liver disease, improve patients’ quality of life and prevent long-term liver damage.
Renewed hope for expanded liver treatments
“Not many FDA-approved treatments exist for pediatric liver diseases,” says Dr. Loomes. For more than 50 years, the Kasai procedure – and later liver transplant – were the only proven treatments for biliary atresia, for example.
“New drugs are being studied,” she adds, “And we’re hopeful these medications – as well as other interventions – can help patients remain healthy long term, to keep their own livers longer and, in some cases, avoid the need for a transplant entirely.”