INSR and obesity due to melanocortin 4 receptor deficiency: From animal and in vitro studies, it may be that the best way to measure the effect of MMPI on MMP activity is not through blood samples but in tissues such as adipose tissue, where MMP activity is increased in obesity and tissue inhibitors of MMPs (TIMPs) are decreased.[2] Studies are ongoing to test whether MMPI can affect MMP and TIMP levels, and insulin receptor integrity in humans.