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.

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

Depletion of nicotinamide adenine dinucleotide (NAD+) is associated with aging and disease, spurring the study of dietary supplements to replenish NAD+. The catabolism of NAD+ to nicotinamide (NAM) requires the salvage of NAM to replenish cellular NAD+, which relies on the rate-limiting enzyme nicotinamide phosphoribosyltransferase (NAMPT). Pharmacological activation of NAMPT provides an alternative to dietary supplements. Screening for activators of NAMPT identified small molecule NAMPT positive allosteric modulators (N-PAMs). N-PAMs bind to the rear channel of NAMPT increasing enzyme activity and alleviating feedback inhibition by NAM and NAD+. Synthesis of over 70 N-PAMs provided an excellent correlation between rear channel binding affinity and potency for enzyme activation, confirming the mechanism of allosteric activation via binding to the rear channel. The mechanism accounts for higher binding affinity leading to loss of efficacy. Enzyme activation translated directly to elevation of NAD+ measured in cells. Optimization led to an orally bioavailable N-PAM.

Orthodontic bracket removal using conventional and ultrasonic debonding techniques, enamel loss, and time requirements

The purpose of this study was to examine the effects of ultrasonic orthodontic bracket removal and cleanup and compare them with conventional debonding and cleaning of the enamel surfaces with burs and polishing disks. The amount of enamel loss and time for bracket removal and clean-up were also addressed. Thirty extracted human premolars were collected. The teeth were randomly placed in one of the three debonding groups: debonding with orthodontic pliers and enamel clean-up with finishing burs and polishing disks (group 1), debonding with orthodontic pliers and ultrasonic clean-up of the enamel surface (group 2), and ultrasonic debonding enamel clean-up (group 3). The teeth were stored for 48 hours in 100% humidity before bracket removal. All brackets were then removed. Polyvinyl siloxane impressions were made before and after bracket removal. Direct measurements of the teeth in micrometers were made at all steps. An additional 30 teeth were similarly prepared, and the brackets were debonded and cleaned-up as in the three groups previously described. The total time for bracket removal and enamel clean-up for each group was recorded in seconds.(ABSTRACT TRUNCATED AT 250 WORDS)