INS and obesity due to melanocortin 4 receptor deficiency: As a newly discovered adipokine, visceral adipose tissue-derived serine protease inhibitor (vaspin) was identified as a member of the serine protease inhibitor (serpin) family, which is highly expressed in visceral adipose tissue when obesity and insulin levels peak in Otsuka Long-Evans Tokushima Fatty (OLETF) rats [15].