Effect of NPY5R Antagonist MK-0557 on Weight Regain after Very-low-calorie Diet-induced Weight Loss*

Objective: To evaluate whether MK-0557, a highly selective, orally administered neuropeptide Y Y5 receptor antagonist, could limit weight regain after very-low-calorie diet (VLCD)-induced weight loss. Research Methods and Procedures: We enrolled 502 patients 18 to 65 years of age with a BMI of 30 to 43 kg/m2. Patients were placed on a VLCD (800 kcal/d liquid diet) for 6 weeks. Patients who lost ≥6% of initial body weight (n = 359) were randomized to 52 weeks of 1 mg/d MK-0557 or placebo and maintained on a hypocaloric diet (300 kcal below weight maintenance requirements). Results: In randomized patients, the VLCD was associated with an average weight loss of 9.1 kg. After 12 weeks of double-blind treatment, weight began to gradually increase for both placebo- and MK-0557-treated patients. The mean weight change (95% confidence interval) from baseline at the end of the VLCD to Week 52 was +3.1 (2.1, 4.0) and +1.5 (0.5, 2.4) kg for patients treated with placebo and MK-0557, respectively. The difference of 1.6 kg between the two groups was significant (p = 0.014). Secondary endpoints, such as blood pressure, lipid profile, insulin, and leptin, as well as waist circumference and quality-of-life measurements, did not show significant differences between MK-0557 and placebo treatments. Discussion: Although the difference in weight regain between placebo- and MK-0557-treated patients was statistically significant, the magnitude of the effect was small and not clinically meaningful. Antagonism of the neuropeptide Y Y5 receptor is not an efficacious treatment strategy for reducing weight regain after VLCD.