Dissecting the steroid metabolome in the pathogenesis and treatment of metabolic liver disease

We are currently in the midst of a global epidemic of metabolic disease that includes obesity and type 2 diabetes. These conditions are frequently associated with fat deposition in the liver, so-called non-alcoholic fatty liver disease (NAFLD). NAFLD is a spectrum of disease that extends from simple fat accumulation through to inflammation (non-alcoholic steatohepatitis, NASH) which can progress to fibrosis and scarring and eventually lead to cirrhosis of the liver which may require a liver transplant. In addition, it significantly increases your risk of developing primary liver cancer (hepatocellular cancer, HCC). Within 5 years, this will become the commonest cause of liver transplantation. The condition is also associated with an increased risk of heart attacks and strokes as well as problems directly related to the liver. There are currently no specific treatments that are licenced for the treatment of NAFLD and the gold-standard test to diagnose the stage and severity of the condition (liver biopsy) is associated with significant complications.

As part of this proposal, we will measure natural steroid hormone metabolites in urine samples from patients with NAFLD (as identified on liver biopsy) as well as HCC to see if this can provide an alternative way to diagnose and stage the severity of the disease without the need for a liver biopsy. This approach will be compared against standard blood tests as well as scans including magnetic resonance imaging. The data that we have generated leading up to this proposal have suggested that we can very effectively diagnose the most extreme ends of the NAFLD spectrum and this has helped to identify one specific steroid metabolizing enzyme (AKR1D1) that we believe to be crucial in the progression and development of NAFLD. We have already generated a mouse model with deletion of AKR1D1 and the female mice do not put on weight with a high fat diet and are protected from diabetes. Within this proposal we will further characterize the metabolism of these animals looking at food consumption, energy expenditure as well as using different dietary regimens to replicate all the stages of NAFLD to see if they are protected from the development of NAFLD and HCC. Finally, we will also begin to develop drugs that are specific inhibitors of AKR1D1 to see if these may represent potential treatments for NAFLD and metabolic liver disease in the future.

The global burden of metabolic disease, including its hepatic manifestation, non-alcoholic fatty liver disease (NAFLD), continues to escalate and contribute significantly to morbidity and mortality. NAFLD is a spectrum of disease ranging from simple steatosis through to inflammation (non-alcoholic steatohepatitis, NASH), scarring, fibrosis and cirrhosis with a risk of development of hepatocellular carcinoma (HCC). Within 5 years, NAFLD will become the leading indication for liver transplantation.
Steroid hormones are potent regulators of metabolic phenotype and have been implicated in the pathogenesis of obesity, diabetes and NAFLD. Using computational analysis of the urinary steroid metabolome, we have identified unique profiles that distinguish patients with cirrhosis from healthy controls. We will define the changes in these profiles that occur across the spectrum of NAFLD correlated with biopsy-proven stage of disease. This approach offers potential as a sensitive and specific non-invasive marker of disease stage, and has allowed us to identify a specific molecular target (AKR1D1, 5beta-reductase) that may drive the pathogenesis of NAFLD and metabolic disease.
AKR1D1 is highly expressed in the liver generating all 5beta-reduced dihydro-steroid metabolites as well as having a crucial role in bile acid synthesis. We have generated a rodent model with global deletion of AKR1D1 that has a sexually dimorphic phenotype; female mice resist diet-induced obesity and glucose intolerance. We will define the metabolic and hepatic phenotype of this model using state-of-the-art imaging and molecular biology techniques, generating conditional models with liver-specific deletion and transgenic over-expression. In addition, in vitro experiments will examine the role of AKR1D1 in human hepatocyte models. AKR1D1 may represent a therapeutic target and we have begun to develop a high throughput assay to screen >350,000 compounds to identify specific and potent AKR1D1 inhibitors.

Obesity, type 2 diabetes and non-alcoholic fatty liver disease (NAFLD) are associated with significant morbidity and premature mortality and present a significant economic burden to the UK economy, not only through health care costs, but through loss of earnings due to ill-health and decreased life expectancy. Faced with the magnitude of the clinical problem, research that helps understand the processes that drive these conditions, identifies novel methodologies for assessing disease severity and stage and identifies new treatment targets has the potential to deliver significant impact for patients, academics, clinicians and industrial partners.

The investigators on this proposal have an established track record and have been instrumental in identifying the fundamental contribution of steroid hormone and bile acid biology to the regulation of metabolic phenotype and have published many of the seminal pieces of work in the highest quality journals with high impact factors (Lancet, JCI, PNAS, BMJ, Nature Genetics).

The impact for academic community, both clinical and basic, is clear. The proposal will begin the evaluation of novel non-invasive testing approaches for NAFLD, which if validated, have the potential to be incorporated into clinical practice in the relatively short term. In addition, the proposal will determine the specific role of a novel target using state-of-the-art methodology. Perhaps most importantly, this proposal has the potential to impact significantly on patients with NAFLD and metabolic disease. The availability of a non-invasive urine test that can significantly reduce the number of liver biopsies that are performed (current gold-standard test, but associated with significant morbidity and cost) will have a dramatic impact on patient care. In the longer term, there is the potential for the development of new treatments derived from the high throughput selective inhibitor screen that will be performed as part of the proposal.

The translational steroid metabolome approach as well as the identification of a specific target and development of a potent selective inhibitor may lead to the generation of significant intellectual property. Preliminary discussions with the technology transfer and commercial exploitation arm of the University of Oxford subsidiary company, Isis innovations ltd (http://isis-innovation.com) have already taken place. Regular consultation throughout the research programme will ensure that all potential IP is protected and no unwanted disclosures occur.

In conclusion, this proposal offers novel approaches and targets that will significantly advance our current and future approach to the management of patients with NAFLD. It has the potential to achieve significant impact for both academics and most importantly for patients and for the health service.