Sitagliptin, a dipeptidyl peptidase-IV inhibitor, improves psoriasis

A patient with a 17-year history of plaque psoriasis accompanied by type 2 diabetes mellitus discontinued cyclosporine and steroid ointment given for treatment of psoriasis because she was dissatisfied with the effects of the drugs. After sitagliptin, a dipeptidyl peptidase-IV (DPP-IV) inhibitor, was administered for control of blood glucose, psoriatic skin lesions were gradually diminished, although HbA1c did not improve. Three months after the administration of sitagliptin, infiltration, scales and erythema on all psoriatic plaques disappeared, leaving pigmentation on flat skin. DPP-IV in serum degrades the incretin hormones which stimulate β-cell insulin secretion. DPP-IV inhibitors, as incretin enhancers, cause an increase in glucose-dependent insulin secretion, and are applied for the treatment of diabetes mellitus. DPP-IV is also expressed on T cells as CD26, a surface antigen which plays an important role in activating T cells. As helper T cells are involved in the pathogenesis of psoriasis, it is possible that DPP-IV inhibitors improve psoriatic skin lesions by inhibiting T cell activation, independently of glycemic control. DPP-IV inhibitors could be an alternative for the treatment of psoriasis.