NNMT and obesity due to melanocortin 4 receptor deficiency: Nicotinamide N-methyltransferase (NNMT) is an intracellular enzyme over expressed in many diseases such as obesity, diabetes, and alcohol related liver diseases.51–55 Identified using mRNA display, 24 (macrocyclic peptide) exhibited good inhibitory activity for NNMT with an IC50 = 0.1 μM but lacked cellular potency.