Vieira WF1, Fernandes de Magalhães S1, Franco Malange K1, Gonçalves dos Santos G1, Borges Paes Lemes J1, de Thomaz AA2, Parada CA1
1State University of Campinas (UNICAMP), Department of Structural and Functional Biology, Institute of Biology, Campinas, Brazil, 2State University of Campinas (UNICAMP), Department of Quantum Electronics, Institute of Physics Gleb Wataghin, Campinas, Brazil
Background: Approximately 60% of diabetic patients develop peripheral neuropathy. Besides pain, peripheral diabetic neuropathy (PDN) could be associated with declines in motor compound action potential and abnormalities in plantar pressure during gait. PDN was also related to the activation of mitogen-activated protein kinases (MAPK) in the dorsal root ganglia (DRG), in response to extracellular stimulus, such as TNF-α and IL-1β pro-inflammatory interleukins. Due to be a high complexity syndrome, PDN still untreated. Pharmacological treatment has little effectiveness. Efficacy of photobiomodulation therapy (PBMT) in painful clinical conditions has been established by several recent studies, but there is few information about the effects of PBMT in PDN treatment.
Purpose: The aim of this study was to verify the pain relief potential and possible mechanisms of PBMT through low-level laser irradiation (904 nm) in streptozotocin (STZ)-induced diabetic neuropathic rats.
Methods: Experiments were approved by the UNICAMP Ethic's Committee (CEUA #3902-1). Male Lewis rats (200-250 g; 6-8-weeks-old) received 5x streptozotocin (STZ)-low doses (25 mg/kg). Diabetic animals (≥250 mg/dL blood glucose) were submitted to electronic von Frey and CatWalk gait analysis tests at 0, 7, 14, 21, 24, and 28 days after injections. Once neuropathic, rats were submitted to daily PBMT through low-level laser irradiation (GaAs 904 nm; 2.03 Joule; 70 mW; 29 seconds; continuous mode; direct contact) at the region between L4/L5 dorsal root ganglia (DRG). At the 28th day, irradiated DRG were collected and used to ELISA, real-time RT-qPCR, immunofluorescence, and Raman spectroscopy assays.
Results: PBMT was able to reduce the intensity of hyperalgesia (Δ withdrawal threshold, g) of PDN rats. We detected alterations in CatWalk spatial gait parameters of PDN animals [Max. Contact Area (cm²); Print Area (cm²); Stride length (cm)], which were strongly correlated with withdrawal thresholds. Such spatial parameters were counteracted by PBMT at 28 days after STZ injections. PBMT decreased TNF-α and IL-1β levels, and p38-MAPK mRNA expression in DRG. PDN induced the activation of phosphorylated p38-MAPK and this activation was partially prevented by PBMT. Three characteristic peaks of DRG tissue were identified: 2850 cm-1, 2885 cm-1, and 2940 cm-1, whose assignments are CH2/CH3 symmetric stretch of lipids, CH2/CH3 asymmetric stretch of lipids and proteins, and C-H vibrations in lipids and proteins, respectively. DRG from PDN rats showed an increase in the normalized intensity of 2850 cm-1 and 2885 cm-1 peaks. These same peaks had their altered intensity reduced by PBMT.
Conclusion(s): PBMT was able to reduce hyperalgesia in STZ-induced diabetic neuropathic rats and ameliorate spatial gait parameters. In addition, PBMT reduced the p38-MAPK expression linked to the presence of pro-inflammatory interleukins. Raman spectroscopy was able to diagnose spectral alterations in DRG of STZ-induced diabetic neuropathic animals and the positive influence of PBMT over such alterations.
Implications: Innovative topical therapeutic approaches to be used with anti-hyperalgesic purposes are of interest. A better understanding of PBMT effects in STZ-induced diabetic neuropathy is therefore of particular interest since the physical therapists may help to minimize the severity of painful states with a typical and accessible therapeutic resource.
Keywords: PBMT, laser irradiation, diabetic neuropathy
Funding acknowledgements: FAPESP (Sao Paulo Research Foundation, Process 2015/12673-5; 2018/05108-8; and 2014/25153-7) and CAPES (Coordination of Improvement of Higher Education Personnel).
Purpose: The aim of this study was to verify the pain relief potential and possible mechanisms of PBMT through low-level laser irradiation (904 nm) in streptozotocin (STZ)-induced diabetic neuropathic rats.
Methods: Experiments were approved by the UNICAMP Ethic's Committee (CEUA #3902-1). Male Lewis rats (200-250 g; 6-8-weeks-old) received 5x streptozotocin (STZ)-low doses (25 mg/kg). Diabetic animals (≥250 mg/dL blood glucose) were submitted to electronic von Frey and CatWalk gait analysis tests at 0, 7, 14, 21, 24, and 28 days after injections. Once neuropathic, rats were submitted to daily PBMT through low-level laser irradiation (GaAs 904 nm; 2.03 Joule; 70 mW; 29 seconds; continuous mode; direct contact) at the region between L4/L5 dorsal root ganglia (DRG). At the 28th day, irradiated DRG were collected and used to ELISA, real-time RT-qPCR, immunofluorescence, and Raman spectroscopy assays.
Results: PBMT was able to reduce the intensity of hyperalgesia (Δ withdrawal threshold, g) of PDN rats. We detected alterations in CatWalk spatial gait parameters of PDN animals [Max. Contact Area (cm²); Print Area (cm²); Stride length (cm)], which were strongly correlated with withdrawal thresholds. Such spatial parameters were counteracted by PBMT at 28 days after STZ injections. PBMT decreased TNF-α and IL-1β levels, and p38-MAPK mRNA expression in DRG. PDN induced the activation of phosphorylated p38-MAPK and this activation was partially prevented by PBMT. Three characteristic peaks of DRG tissue were identified: 2850 cm-1, 2885 cm-1, and 2940 cm-1, whose assignments are CH2/CH3 symmetric stretch of lipids, CH2/CH3 asymmetric stretch of lipids and proteins, and C-H vibrations in lipids and proteins, respectively. DRG from PDN rats showed an increase in the normalized intensity of 2850 cm-1 and 2885 cm-1 peaks. These same peaks had their altered intensity reduced by PBMT.
Conclusion(s): PBMT was able to reduce hyperalgesia in STZ-induced diabetic neuropathic rats and ameliorate spatial gait parameters. In addition, PBMT reduced the p38-MAPK expression linked to the presence of pro-inflammatory interleukins. Raman spectroscopy was able to diagnose spectral alterations in DRG of STZ-induced diabetic neuropathic animals and the positive influence of PBMT over such alterations.
Implications: Innovative topical therapeutic approaches to be used with anti-hyperalgesic purposes are of interest. A better understanding of PBMT effects in STZ-induced diabetic neuropathy is therefore of particular interest since the physical therapists may help to minimize the severity of painful states with a typical and accessible therapeutic resource.
Keywords: PBMT, laser irradiation, diabetic neuropathy
Funding acknowledgements: FAPESP (Sao Paulo Research Foundation, Process 2015/12673-5; 2018/05108-8; and 2014/25153-7) and CAPES (Coordination of Improvement of Higher Education Personnel).
Topic: Electrophysical & isothermal agents; Pain & pain management
Ethics approval required: Yes
Institution: State University of Campinas (UNICAMP)
Ethics committee: CEUA/UNICAMP
Ethics number: 3902-1
All authors, affiliations and abstracts have been published as submitted.
