DPP4 and metabolic disease: Aiming at the treatment of obesity, according to Zizzari et al. [8], the most sold peptide drug to treat metabolic diseases is liraglutide (Victoza®), an analog of glucagon-like peptide (GLP-1), resistant to degradation by the gastrointestinal tract enzyme dipeptidyl peptidase 4 (DPP-4).