[Nuclear receptor PPAR and hepatology: pathophysiological and therapeutical aspects]

An insight into the role of telmisartan as PPAR-γ/α dual activator in the management of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common hepatic disease. It is rapidly emerging as the frequent cause for liver transplantation with the risk of disease recurrence, even after transplantation. Clinical evidence showed an abnormally altered expression of different peroxisome proliferator-activated receptor (PPAR) isotypes (PPAR-α/γ/δ) in NAFLD with an involvement in the induction of insulin resistance, hepatic steatosis, reactive oxygen species (ROS) formation, and hepatic inflammation. Recently, several dual PPAR-γ/α agonists were developed to simultaneously achieve the insulin-sensitizing effect of PPAR-γ as well as lipid catabolizing effect of PPAR-α. PPAR-α activation could counterbalance the steatogenic and adipogenic effects of PPAR-γ. But most of the drugs were ended in the initial level itself due to harmful adverse effects. In the present review, we discuss the possible mechanism of telmisartan, a typical angiotensin receptor blocker with excellent safety and pharmacokinetic profile, as a PPAR-γ/α dual agonist in the treatment of NAFLD.

Microtargeting cancer metabolism: opening new therapeutic windows based on lipid metabolism

Metabolic reprogramming has emerged as a hallmark of cancer. MicroRNAs are noncoding RNAs that posttranscriptionally repress the expression of target mRNAs implicated in multiple physiological processes, including apoptosis, differentiation, and cancer. MicroRNAs can affect entire biological pathways, making them good candidates for therapeutic intervention compared with classical single target approaches. Moreover, microRNAs may become more relevant in the fine-tuning adaptation to stress situations, such as oncogenic events, hypoxia, nutrient deprivation, and oxidative stress. Furthermore, artificial microRNAs can be designed to modulate the expression of multiple targets of a specific pathway. In this review, we describe the metabolic reprogramming associated to cancer, with a special interest in the altered lipid metabolism. Next, we describe specific features of microRNAs that make them relevant to target cancer cell metabolism. Finally, in an attempt to open new therapeutic windows, we emphasize two exciting scenarios for microRNA-mediated intervention that need to be further explored: 1) the cooperation between FA biosynthesis (lipogenesis) and FA oxidation as complementary partners for the survival of cancer cells; and 2) the regulation of the intracellular lipid content modulating both lipid storage into lipid droplets, and lipid mobilization through lipolysis and/or lipophagy.

PPARs in Liver Diseases and Cancer: Epigenetic Regulation by MicroRNAs

Peroxisome-proliferator-activated receptors (PPARs) are ligand-activated nuclear receptors that exert in the liver a transcriptional activity regulating a whole spectrum of physiological functions, including cholesterol and bile acid homeostasis, lipid/glucose metabolism, inflammatory responses, regenerative mechanisms, and cell differentiation/proliferation. Dysregulations of the expression, or activity, of specific PPAR isoforms in the liver are therefore believed to represent critical mechanisms contributing to the development of hepatic metabolic diseases, disorders induced by hepatic viral infections, and hepatocellular adenoma and carcinoma. In this regard, specific PPAR agonists have proven to be useful to treat these metabolic diseases, but for cancer therapies, the use of PPAR agonists is still debated. Interestingly, in addition to previously described mechanisms regulating PPARs expression and activity, microRNAs are emerging as new important regulators of PPAR expression and activity in pathophysiological conditions and therefore may represent future therapeutic targets to treat hepatic metabolic disorders and cancers. Here, we reviewed the current knowledge about the general roles of the different PPAR isoforms in common chronic metabolic and infectious liver diseases, as well as in the development of hepatic cancers. Recent works highlighting the regulation of PPARs by microRNAs in both physiological and pathological situations with a focus on the liver are also discussed.