The natural compound Cyclo Histidine-Proline (CHP) was initially discovered in the brain, but thereafter evaluated in the context of diabetes because of its hypoglycemic action. The pharmacokinetics and the toxicological profile of CHP showed it can be dosed orally and is safe for human administration; however, its biological role, mechanism of action and overall pharmacodynamics are poorly understood. My thesis aimed to better characterize the therapeutic effects of CHP and to evaluate its potential for drug repurposing. With these aims, two major studies were performed:
Evaluation of CHP for the prevention and treatment of steatohepatitis. Non-alcoholic fatty liver disease (NAFLD) is a common disease in which liver function is disrupted by progressive steatosis. The term NAFLD covers a spectrum of liver diseases, as simple steatosis can further aggravate to steatohepatitis (NASH) and eventually progress towards cirrhosis and hepatocellular carcinoma. NAFLD currently affects 25% of the worldwide adult population, nonetheless, there is no approved treatment yet. The work presented in this thesis proved that CHP was effective in preventing the onset of NASH, but also in partially reverting liver damage when given in a therapeutic setting. Using two different mouse models of NAFLD-a model of the metabolic syndrome achieved by thermoneutral housing (TN) in combination with feeding a western diet (WD), and a model of liver fibrosis caused by repeated injections with carbon tetrachloride (CCl4)-we showed that CHP reduced hepatosteatosis and overall liver lipid accumulation, together with a remarkable attenuation of liver inflammation and fibrosis.
Evaluation of CHP for muscle degeneration and cardiomyopathy in Duchenne muscular dystrophy. Duchenne muscular dystrophy (DMD) is a devastating X-linked muscle disorder occurring in 1:3500 male newborns, caused by mutations in dystrophin. The lack of a functional dystrophin causes extensive damage to muscle fibers, prompting cycles of fiber degeneration and regeneration that eventually exhaust the repair capacity of muscle tissue, resulting in the development of fibrosis and the disruption of muscle biomechanics. DMD progresses rapidly, with children needing a wheelchair by 10, a ventilator by 20 and a mean life expectancy of roughly 28 years. Despite the recent progress in gene therapy, no treatment has been approved yet and the current standard of care protocols come with several severe side effects. There is hence still a pressing demand for new supportive therapies that can reduce inflammation, prevent fibrosis and help manage symptoms. In this study, we used the mdx mouse model of DMD to show that CHP preserved muscle strength and supported the generation of contraction, decreased skeletal muscle inflammation and prevented fibrosis. Additionally, CHP was effective in preventing the systolic dysfunction and cardiac hypertrophy that eventually lead to cardiomyopathy and heart failure, the prime cause of death for DMD patients.
In combination, our two studies defined CHP as a broad anti-inflammatory and anti-fibrotic agent that enhances mitochondrial activity. We provided a further characterization of its pharmacological profile and set the basis for future translation to clinics.