LCN2 and obesity due to melanocortin 4 receptor deficiency: Among the recently identified regulatory peptides secreted by both adipose tissue and peripheral organs, which play an important role in the pathogenesis of metabolic changes in the course of obesity associated with type 2 diabetes, omentin-1, neutrophil gelatinase-associated lipocalin and complement C1q tumor necrosis factor-related protein-3 (also known as cartonectin or cartducin), are an essential part [4,7,8].