TLR4 and obesity due to melanocortin 4 receptor deficiency: The levels of free fatty acid (FFA), and lipopolysaccharide (LPS) released by gut bacteria increase during obesity which triggers activation of the (i) Toll-like receptor 4 (TLR4) pathway, (ii) adipose tissue macrophages (30) as well as (iii) nuclear factor-kappa β (NF-κβ) pathway (31).