MPO and obesity due to melanocortin 4 receptor deficiency: Given that inflammatory stimuli suppress the production of APN,41 and that APN exhibits anti-inflammatory effects by reducing MPO release from PMN in vitro, this suggests a potential vicious cycle: inflammation in obesity reduces APN expression, leading to higher MPO release by PMN in PVAT, which in turn further reduces APN secretion and exacerbates endothelial dysfunction.