The potential role of octreotide in the treatment of diabetic retinopathy.
Proliferative diabetic retinopathy is the main cause of vision loss in young and middle-aged adults. There is no accepted pharmaceutical therapy for this disease, although analogs of the naturally occurring growth hormone inhibitor, somatostatin, have been considered leading candidates for developing such therapies. This review examines the history of somatostatin analogs, especially octreotide, in the treatment of ocular complications of diabetes mellitus. The historical observations that indicated a role for somatostatin in retinopathy are discussed from an endocrinology perspective. The molecular mechanisms by which somatostatin may exert its anti-angiogenic effects, both indirect (through antagonism of the growth hormone axis) and direct (through direct antiproliferative and apoptotic effects on endothelial cells mediated by specific receptor subtypes) are described. Animal models that were used to demonstrate an anti-angiogenic effect of octreotide are detailed, as are the results of numerous clinical trials that used octreotide and other somatostatin analogs to treat diabetic retinopathy. The mixed results of these clinical results are examined along with possible explanations as to why these analogs both have and have not shown efficacy in limited clinical settings. Even with these mixed results, somatostatin analogs remain the only therapeutic alternative to patients with proliferative diabetic retinopathy who have failed to respond to panretinal photocoagulation.