Somatostatin replacement: a new strategy for treating diabetic retinopathy

Diabetic retinopathy (DR) has been classically considered to be a microcirculatory disease of the retina. However, there is growing evidence to suggest that retinal neurodegeneration is an early event in the pathogenesis of DR which participates in the microcirculatory abnormalities that occur in DR. Among the neuroprotective factors synthesized by the retina, somatostatin (SST) is one of the most relevant. In DR there is a downregulation of retinal expression of SST that is associated with retinal neurodegeneration. There is growing evidence suggesting that SST could play a key role in the main pathogenic mechanisms involved in the development of DR (neurodegeneration, neovascularization and vascular leackage). Recently, first evidence that the topical administration of SST prevents retinal neurodegeneration in streptozotozin- induced diabetic rats has been reported. Indeed, SST eye drops prevented b-wave abnormalities in the ERG which are considered sensitive indicators of DR. In addition, SST eye drops prevented, glial activation, apoptosis and the misbalance between proapoptotic and survival signalling caused by diabetes. Furthermore, SST eye drops reduce glutamate- induced excitotoxicity. Therefore, topical administration of SST could be contemplated as an appropriate therapeutic approach for DR. However, clinical trials will be needed to establish its exact position in the treatment of this devastating complication of diabetes. Diabetic retinopathy (DR) has been classically considered to be a microcirculatory disease of the retina. However, there is growing evidence to suggest that retinal neurodegeneration is an early event in the pathogenesis of DR which participates in the microcirculatory abnormalities that occur in DR [1]. The retina synthesizes neuroprotective factors which counteract the deleterious effects of neurotoxic factors involved in neurodegeneration. The loss of these neuroprotective factors or the reduction of their effectiveness is essential for the development of retinal neurodegeneration. Among the neuroprotective and neurotrophic factors somatostatin (SST) is one of the most relevant. The main aim of the present review is to provide experimental evidence supporting the promising therapeutical use of SST to prevent or arrest DR.