Background and aims: Diabetic neuropathy is a complex syndrome, which affects peripheral nerves and culminates in mechanical hyperalgesia. Hyperglycemia-induced oxidative stress leads to neuronal damage through the formation of free radicals, reactive oxygen species, and mitochondrial failure. Efficacy of photobiomodulation therapy (PBMT) on painful clinical conditions has been established by several studies. We verified the pain relief potential of PBMT on diabetic neuropathic rats and investigated in vitro potential mechanisms. Methods: Experiments were approved by UNICAMP's Ethics Committee (#3902-1). Male Lewis rats received five streptozotocin (STZ) low-doses (Sigma-Aldrich®, 25 mg/kg) and were submitted to electronic von Frey test at 0, 7, 14, 21, 24 and 28 days after STZ injections. After the 21st day, rats were submitted to daily PBMT (GaAs 904 nm; 2.03 Joule; 70 mW; 29”) at the region between L4/L5 dorsal root ganglia (DRG). In addition, primary cell cultures of DRG were kept at low (5.5 mM) or high glucose (55 mM) for 24 h and exposed to PBMT. To measure the calcium influx, neurons were loaded with FLUO 4-AM (InvitrogenTM, USA); Tetramethylrhodamine ethyl ester (TMRE) (InvitrogenTM, USA) was used for measure the mitochondrial membrane potential (MMP). Results: PBMT was able to reduce the hyperalgesia at the 24th and 28th days. After stimulus with 15 mM KCl, DRG neurons previously exposed to PBMT showed a reduced fluorescence related to calcium influx. PBMT also showed influence over altered-MMP on hyperglycemia-stressed DRG neurons. Conclusions: PBMT could be used as a coadjutant tool for the treatment of diabetic neuropathic pain.

PHOTOBIOMODULATION THERAPY (904 NM) AS AN ALTERNATIVE TREATMENT TO PERIPHERAL DIABETIC NEUROPATHY: IN VIVO AND IN VITRO ASSESSMENTS