Crystallization of human nicotinamide phosphoribosyltransferase

Crystal structure-based comparison of two NAMPT inhibitors

Inhibition of nicotinamide phosphoribosyltransferase (NAMPT) is a novel strategy for cancer therapy, but only two inhibitors of NAMPT (FK866 and CHS828) have progressed into clinical trials. This study seeks to compare a novel potent NAMPT inhibitor, MS0, with a classical inhibitor FK866 in their biological activity and molecular binding mode, thereby contributing to future chemical optimization and a further understanding of the action mode of NAMPT inhibitors. The IC₅₀ values of MS0 and FK866 in inhibition of recombinant human NAMPT activity were 9.08±0.90 and 1.60±0.32 nmol/L, respectively. Consistently, FK866 exerted better antiproliferation in 6 human cancer cell lines (HepG2, A2780, 95-D, A549, U2OS and U266) than MS0 with IC50 values nearly 12-fold to 225-fold lower than those of MS0. Co-crystal structures of wild-type human NAMPT complexed with MS0 or FK866 were elucidated, which revealed that MS0 did not interact with Ser241. The hydrogen bond mediated by crystallographic water between MS0 and His191 or Val350 of NAMPT did not exist in FK866. Instead, FK866 exhibited hydrophobic interactions with Arg349. Based on the activity assays and crystal structure analyses, we elaborate the reason why the antiproliferation activity of MS0 was not as good as that of FK866, which would contributes to the current understanding of the mode of action of NAMPT inhibitors and will also contribute to further development of anticancer drugs in the future.

Chicken Is a Useful Model to Investigate the Role of Adipokines in Metabolic and Reproductive Diseases

Reproduction is a complex and essential physiological process required by all species to produce a new generation. This process involves strict hormonal regulation, depending on a connection between the hypothalamus-pituitary-gonadal axis and peripheral organs. Metabolic homeostasis influences the reproductive functions, and its alteration leads to disturbances in the reproductive functions of humans as well as animals. For a long time, adipose tissue has been recognised as an endocrine organ but its ability to secrete and release hormones called adipokines is now emerging. Adipokines have been found to play a major role in the regulation of metabolic and reproductive processes at both central and peripheral levels. Leptin was initially the first adipokine that has been described to be the most involved in the metabolism/reproduction interrelation in mammals. In avian species, the role of leptin is still under debate. Recently, three novel adipokines have been discovered: adiponectin (ADIPOQ, ACRP30), visfatin (NAMPT, PBEF), and chemerin (RARRES2, TIG2). However, their mode of action between mammalian and nonmammalian species is different due to the different reproductive and metabolic systems. Herein, we will provide an overview of the structure and function related to metabolic and reproductive mechanisms of the latter three adipokines with emphasis on avian species.

Physiological and pathophysiological roles of NAMPT and NAD metabolism

Nicotinamide phosphoribosyltransferase (NAMPT) is a regulator of the intracellular nicotinamide adenine dinucleotide (NAD) pool. NAD is an essential coenzyme involved in cellular redox reactions and is a substrate for NAD-dependent enzymes. In various metabolic disorders and during ageing, levels of NAD are decreased. Through its NAD-biosynthetic activity, NAMPT influences the activity of NAD-dependent enzymes, thereby regulating cellular metabolism. In addition to its enzymatic function, extracellular NAMPT (eNAMPT) has cytokine-like activity. Abnormal levels of eNAMPT are associated with various metabolic disorders. NAMPT is able to modulate processes involved in the pathogenesis of obesity and related disorders such as nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM) by influencing the oxidative stress response, apoptosis, lipid and glucose metabolism, inflammation and insulin resistance. NAMPT also has a crucial role in cancer cell metabolism, is often overexpressed in tumour tissues and is an experimental target for antitumour therapies. In this Review, we discuss current understanding of the functions of NAMPT and highlight progress made in identifying the physiological role of NAMPT and its relevance in various human diseases and conditions, such as obesity, NAFLD, T2DM, cancer and ageing.