MicroRNA regulation of drug metabolism in stem cell - derived hepatocytes

Abstract

The liver is a multi-functional and highly regenerative organ. While resilient, the liver is susceptible to organ damage and failure. In both the acute and chronic settings liver disease has dire consequences for health. A common cause of liver damage is adverse reactions to drugs which can lead to drug induced liver injury (DILI). This creates major problems for patients, clinicians, the pharmaceutical industry and regulatory authorities. In the context of drug overdose or serious adverse reactions, liver failure can be acute and life threatening, and in some cases require orthotopic liver transplantation. While transplantation is highly successful, such an approach has limitations and justifies basic science attempts to develop better human models to study liver injury and to develop scalable intervention strategies. With this in mind, we have studied the importance of microRNAs (miRs) in regulating human drug metabolism in pluripotent stem cell – derived hepatocytes and their potential to reduce liver toxicity in response to toxic levels of paracetamol. miRs are small non-coding RNAs that are approximately 20 - 24 nucleotides long and their major function is to fine tune gene expression of their target genes. Recently, it has been demonstrated that microRNAs play a role in regulating the first phase of drug metabolism however the second phase of drug metabolism, drug conjugation, has not been studied in detail. Drug conjugation is a crucial stage in human drug metabolism, and any alterations in this process can lead to changes in compound pharmacology, including therapeutic dose and clearance from the body. To test the importance of miRs in regulating phase II drug metabolism we opted to study the metabolism of a common used analgesic, paracetamol. When taken in the appropriate amounts paracetamol is modified by sulfotransferases (SULTs) and UDP - glucuronosyltransferases (UGTs) and removed from the body without organ damage. However, when paracetamol is taken above the recommended dose it is metabolised by phase I enzymes to generate a toxic intermediate N-acetyl-p-benzoquinone imine (NAPQI), which if untreated can lead to massive hepatocyte cell death and liver failure, placing the patient in a life threatening situation. In order to promote non-toxic drug metabolism, in the context of drug overdose, we employed candidate miRs to regulate different parts of the paracetamol metabolism pathway. In summary, we have focused on studying human drug metabolism in the major metabolic cell type of the liver, the hepatocyte. We have identified a novel microRNA (called miR-324-5p) which regulates phase II drug metabolism and reduces cell cytotoxicity. Additionally, a supportive role of anti-microRNA- 324 in response to fulminant plasma collected from paracetamol overdose patients is also observed. The findings of this project are novel, provide proof of concept and exemplify the power of stem cell based models to identify new approaches to treating human liver damage.