Synthesis, Optimization, and Structure-Activity Relationships of Nicotinamide Phosphoribosyltransferase (NAMPT) Positive Allosteric Modulators (N-PAMs)

Mechanisms of the NAD+ salvage pathway in enhancing skeletal muscle function

Nicotinamide adenine dinucleotide (NAD+) is crucial for cellular energy production, serving as a coenzyme in oxidation-reduction reactions. It also supports enzymes involved in processes such as DNA repair, aging, and immune responses. Lower NAD+ levels have been associated with various diseases, highlighting the importance of replenishing NAD+. Nicotinamide phosphoribosyltransferase (NAMPT) plays a critical role in the NAD+ salvage pathway, which helps sustain NAD+ levels, particularly in high-energy tissues like skeletal muscle.This review explores how the NAMPT-driven NAD+ salvage pathway influences skeletal muscle health and functionality in aging, type 2 diabetes mellitus (T2DM), and skeletal muscle injury. The review offers insights into enhancing the salvage pathway through exercise and NAD+ boosters as strategies to improve muscle performance. The findings suggest significant potential for using this pathway in the diagnosis, monitoring, and treatment of skeletal muscle conditions.

Design of NAMPTs with Superior Activity by Dual-Channel Protein Engineering Strategy

The nicotinamide phosphoribosyltransferase (NAMPT)-catalyzed substitution reaction plays a pivotal role in the biosynthesis of nucleotide compounds. However, industrial applications are hindered by the low activity of NAMPTs. In this study, a novel dual-channel protein engineering strategy was developed to increase NAMPT activity by enhancing substrate accessibility. The best mutant (CpNAMPTY13G+Y15S+F76P) with a remarkable 5-fold increase in enzyme activity was obtained. By utilizing CpNAMPTY13G+Y15S+F76P as a biocatalyst, the accumulation of β-nicotinamide mononucleotide reached as high as 19.94 g L-1 within 3 h with an impressive substrate conversion rate of 99.8%. Further analysis revealed that the newly generated substrate channel, formed through crack propagation, facilitated substrate binding and enhanced byproduct tolerance. In addition, three NAMPTs from different sources were designed based on the dual-channel protein engineering strategy, and the corresponding dual-channel mutants with improved enzyme activity were obtained, which proved the effectiveness and practicability of the approach.

Channeling Nicotinamide Phosphoribosyltransferase (NAMPT) to Address Life and Death

Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the rate-limiting step in NAD+ biosynthesis via salvage of NAM formed from catabolism of NAD+ by proteins with NADase activity (e.g., PARPs, SIRTs, CD38). Depletion of NAD+ in aging, neurodegeneration, and metabolic disorders is addressed by NAD+ supplementation. Conversely, NAMPT inhibitors have been developed for cancer therapy: many discovered by phenotypic screening for cancer cell death have low nanomolar potency in cellular models. No NAMPT inhibitor is yet FDA-approved. The ability of inhibitors to act as NAMPT substrates may be associated with efficacy and toxicity. Some 3-pyridyl inhibitors become 4-pyridyl activators or "NAD+ boosters". NAMPT positive allosteric modulators (N-PAMs) and boosters may increase enzyme activity by relieving substrate/product inhibition. Binding to a "rear channel" extending from the NAMPT active site is key for inhibitors, boosters, and N-PAMs. A deeper understanding may fulfill the potential of NAMPT ligands to regulate cellular life and death.

Nicotinamide Phosphoribosyltransferase Positive Allosteric Modulators Attenuate Neuronal Oxidative Stress

Evidence supports boosting nicotinamide adenine dinucleotide (NAD+) to counteract oxidative stress in aging and neurodegenerative disease. One approach is to enhance the activity of nicotinamide phosphoribosyltransferase (NAMPT). Novel NAMPT positive allosteric modulators (N-PAMs) were identified. A cocrystal structure confirmed N-PAM binding to the NAMPT rear channel. Early hit-to-lead efforts led to a 1.88-fold maximum increase in the level of NAD+ in human THP-1 cells. Select N-PAMs were assessed for mitigation of reactive oxygen species (ROS) in HT-22 neuronal cells subject to inflammatory stress using tumor necrosis factor alpha (TNFα). N-PAMs that increased NAD+ more effectively in THP-1 cells attenuated TNFα-induced ROS more effectively in HT-22 cells. The most efficacious N-PAM completely attenuated ROS elevation in glutamate-stressed HT-22 cells, a model of neuronal excitotoxicity. This work demonstrates for the first time that N-PAMs are capable of mitigating elevated ROS in neurons stressed with TNFα and glutamate and provides support for further N-PAM optimization for treatment of neurodegenerative diseases.