The Transcriptional Effects of Photobiomodulation in an In Vitro Model of Diabetic Retinopathy

Abstract

Diabetic retinopathy (DR) is the most common complication of diabetes mellitus and a leading cause of blindness. The pathophysiology of DR is complicated, involving inflammation, oxidative stress, retinal vascular proliferation, and vascular degeneration. Symptomatically, the growth and subsequent rupture of vessels within the frame of view leads to the development of vision loss and eventual blindness. Prior to the development of symptoms, oxidative stress involved in DR leads to the activation of the transcription factor, nuclear factor-kB (NF-kB), resulting in the excess production of vascular endothelial growth factor (VEGF) and intracellular adhesion molecule-1 (ICAM-1), proteins involved in vascular development and immune dysregulation, respectively. The most common therapeutic approach for DR utilizes anti-VEGF agents to reduce vascular proliferation. These treatments are expensive, invasive, frequently ineffective, and have numerous adverse effects, such as retinal detachment, infection, and inflammation inside the eye. A non-invasive alternative therapy is clearly needed. Photobiomodulation (PBM) using far-red to near infrared (NIR) light has been shown to reduce oxidative stress and inflammation in vitro and in vivo and is an ideal candidate for an alternative therapy. Indeed, PBM slows the progression of DR in animal models via attenuation of oxidative stress and by reducing the relative level of ICAM-1. We hypothesize that PBM will reduce the activity of NF-kB and reduce the production of VEGF and ICAM-1 in an in vitro model of DR. To test this hypothesis, we used an in vitro model system of cultured retinal Müller glial cells grown in normal (5 mM) or high (25 mM) glucose conditions for either 3 or 6 days to simulate normoglycemia and hyperglycemia. Cultures were treated with 670 nm light emitting diode (LED) (180 seconds at 25 mW/cm2; 4.5 J/cm2) or no light (sham) for 3 or 5 days. NF-kB activity and ICAM-1 concentrations were significantly increased under high glucose conditions, as measured by a dual luciferase assay or western blot, respectively. Treatment with 670 nm LED significantly reduced NF-kB activity of high glucose culture cells to values comparable to transcriptional activity measured under normoglycemic condition and decreased the level of ICAM-1. VEGF concentrations were not affected by high glucose or PBM. These data are in partial support of our central hypothesis that in an in vitro model of DR, 670 nm light will reduce activation of NF-kB, and reduce the synthesis of ICAM-1 and VEGF. The lack of an observable effect of hyperglycemia or PBM on VEGF concentrations indicates that the stimulation of VEGF secretion requires the activation of additional signaling pathways not induced by high glucose alone.