Experimental approaches and clinical opportunities in metabolic liver diseases

Abstract

Metabolic liver diseases are uncommon individually, however, collectively they represent significant cause of morbidity and mortality globally. The liver has many diverse functions, such as; detoxification from hazardous compounds, either ingested or produced by the body, and production of vital proteins, e.g. coagulation factors and acute phase proteins. Liver disease manifestations are therefore immensely diverse and may present both in a strictly hepatic or extra-hepatic manner. Metabolic liver diseases are usually monogenic, meaning a single point mutation is causing the propagation of the disease. Orthotopic liver transplantation has been employed for the treatment of a broad range of metabolic liver diseases and is indeed a curative method in most instances.

In this thesis, we focused on alpha 1-antitrypsin deficiency–one of the monogenetic liver diseases with both hepatic and pulmonary manifestations. In Study I, we examined and showed that alpha 1-antitrypsin replacement therapy may also have an impact on hepatocytes and the propagation of liver disease. Replacement therapy is currently only reserved for pulmonary manifestation of alpha 1-antitrypsin deficiency. Addition of exogenous alpha 1- antitrypsin protein reduced alpha 1-antitrypsin (SERPINA1) mRNA expression in primary human hepatocytes from both deficient and proficient patients. Furthermore, similar results were seen in lung tissue samples from deficient patients. Altogether, the results may indicate a feedback mechanism where adequate circulating alpha 1-antitrypsin causes a reduction in its own production and replacement therapy may be beneficial for the reduction of hepatic damage caused by mutant alpha 1-antitrypsin.

Study II focused on investigating the novel promising mRNA-based therapies for protein replacement in alpha 1-antitrypsin deficiency. Modified mRNA encoding alpha 1-antitrypsin protein was delivered in vitro to primary human hepatocytes from both deficient and proficient patients. Subsequently in vivo delivery of modified mRNA was conducted in wild type mice and the NSG-PiZ AATd mouse model. Translated and functional AAT protein was detected both in vitro and in vivo. At time of liver transplantation, explanted livers from metabolic liver disease patients may be recovered and used as a graft for another patient with chronic liver disease in a procedure called domino liver transplantation. In Study III, we evaluated the domino liver transplant program at Karolinska University Hospital, Huddinge from 2007–2017. Patients undergoing domino liver transplant had similar survival rate and time spent on waiting list as age and diagnosis matched patients undergoing deceased donor liver transplantation.

To conclude, we have shown hepatic benefits of replacement therapy in alpha 1-antitrypsin deficiency and explored mRNA therapy as a novel way to replace the missing protein. We have further evaluated the domino liver transplant program, in which livers from metabolic liver disease patients are used as donor grafts and concluded that the program has enabled additional transplantations without affecting patients’ waiting time or survival.