Production of Acute Gouty Arthritis by Adrenocorticotropin

Role of proopiomelanocortin-derived peptides and their receptors in the osteoarticular system: from basic to translational research

Proopiomelanocortin (POMC)-derived peptides such as melanocortins and β-endorphin (β-ED) exert their pleiotropic effects via binding to melanocortin receptors (MCR) and opioid receptors (OR). There is now compelling evidence for the existence of a functional POMC system within the osteoarticular system. Accordingly, distinct cell types of the synovial tissue and bone have been identified to generate POMC-derived peptides like β-ED, ACTH, or α-MSH. MCR subtypes, especially MC1R, MC2R (the ACTH receptor), MC3R, and MC4R, but also the μ-OR and δ-OR, have been detected in various cells of the synovium, cartilage, and bone. The respective ligands of these POMC-derived peptide receptors mediate an increasing number of newly recognized biological effects in the osteoarticular system. These include bone mineralization and longitudinal growth, cell proliferation and differentiation, extracellular matrix synthesis, osteoprotection, and immunomodulation. Importantly, bone formation is also regulated by the central melanocortin system via a complex hormonal interplay with other organs and tissues involved in energy metabolism. Among the POMC-derived peptides examined in cell culture systems from osteoarticular tissue and in animal models of experimentally induced arthritis, α-MSH, ACTH, and MC3R-specific agonists appear to have the most promising antiinflammatory actions. The effects of these melanocortin peptides may be exploited in future for the treatment of patients with inflammatory and degenerative joint diseases.

Hyperuricemia and gout

Gout is a clinical syndrome encompassing a group of metabolic diseases that are all characterized by abnormal uric acid metabolism. In its fullest form, gout is defined by: an increase in the serum urate concentration; characteristic, recurrent, acute arthritic attacks, with monosodium urate monohydrate crystals demonstrable in synovial fluid leukocytes; tophi, usually in and around joints of the extremities, composed of monosodium urate monohydrate deposits; renal disease, often accompanied by hypertension with glomerular, tubular, interstitial, and vascular involvement; and uric acid nephrolithiasis. Any combination of these manifestations may occur, although tophi and urate nephropathy rarely antedate gouty arthritis.