LEP and obesity due to melanocortin 4 receptor deficiency: To test efficacy of leptin produced by [3T3Lep] adipocytes in vivo, we injected two groups of old WT mice with a high-fat diet-obesity and insulin resistance with encapsulated acellular capsules (WT[Emp]), and encapsulated 3T3Lep (WT[Lep]) in both visceral fat pads (Fig 5F).