APLN and metabolic syndrome: The variety of released adipokines include hormones (e.g. leptin, adiponectin), peptides (e.g. angiotensinogen, apelin, resistin, and plasminogen activator inhibitor 1 (PAI-1), and inflammatory cytokines (IL-6, TNF-α, visfatin, omentin, and chemerin), all of which play a major role in the pathophysiology of insulin resistance and MetS.