Differential effects of 670 and 830 nm red near infrared irradiation therapy: a comparative study of optic nerve injury, retinal degeneration, traumatic brain and spinal cord injury.

Red/near-infrared irradiation therapy (R/NIR-IT) delivered by laser or light-emitting diode (LED) has improved functional outcomes in a range of CNS injuries. However, translation of R/NIR-IT to the clinic for treatment of neurotrauma has been hampered by lack of comparative information regarding the degree of penetration of the delivered irradiation to the injury site and the optimal treatment parameters for different CNS injuries. We compared the treatment efficacy of R/NIR-IT at 670 nm and 830 nm, provided by narrow-band LED arrays adjusted to produce equal irradiance, in four in vivo rat models of CNS injury: partial optic nerve transection, light-induced retinal degeneration, traumatic brain injury (TBI) and spinal cord injury (SCI). The number of photons of 670 nm or 830 nm light reaching the SCI injury site was 6.6% and 11.3% of emitted light respectively. Treatment of rats with 670 nm R/NIR-IT following partial optic nerve transection significantly increased the number of visual responses at 7 days after injury (P ≤ 0.05); 830 nm R/NIR-IT was partially effective. 670 nm R/NIR-IT also significantly reduced reactive species and both 670 nm and 830 nm R/NIR-IT reduced hydroxynonenal immunoreactivity (P ≤ 0.05) in this model. Pre-treatment of light-induced retinal degeneration with 670 nm R/NIR-IT significantly reduced the number of Tunel+ cells and 8-hydroxyguanosine immunoreactivity (P ≤ 0.05); outcomes in 830 nm R/NIR-IT treated animals were not significantly different to controls. Treatment of fluid-percussion TBI with 670 nm or 830 nm R/NIR-IT did not result in improvements in motor or sensory function or lesion size at 7 days (P>0.05). Similarly, treatment of contusive SCI with 670 nm or 830 nm R/NIR-IT did not result in significant improvements in functional recovery or reduced cyst size at 28 days (P>0.05). Outcomes from this comparative study indicate that it will be necessary to optimise delivery devices, wavelength, intensity and duration of R/NIR-IT individually for different CNS injury types.

Near infrared light reduces oxidative stress and preserves function in CNS tissue vulnerable to secondary degeneration following partial transection of the optic nerve.

Traumatic injury to the central nervous system (CNS) is accompanied by the spreading damage of secondary degeneration, resulting in further loss of neurons and function. Partial transection of the optic nerve (ON) has been used as a model of secondary degeneration, in which axons of retinal ganglion cells in the ventral ON are spared from initial dorsal injury, but are vulnerable to secondary degeneration. We have recently demonstrated that early after partial ON injury, oxidative stress spreads through the ventral ON vulnerable to secondary degeneration via astrocytes, and persists in the nerve in aggregates of cellular debris. In this study, we show that diffuse transcranial irradiation of the injury site with far red to near infrared (NIR) light (WARP 10 LED array, center wavelength 670 nm, irradiance 252 W/m(-2), 30 min exposure), as opposed to perception of light at this wavelength, reduced oxidative stress in areas of the ON vulnerable to secondary degeneration following partial injury. The WARP 10 NIR light treatment also prevented increases in NG-2-immunopositive oligodendrocyte precursor cells (OPCs) that occurred in ventral ON as a result of partial ON transection. Importantly, normal visual function was restored by NIR light treatment with the WARP 10 LED array, as assessed using optokinetic nystagmus and the Y-maze pattern discrimination task. To our knowledge, this is the first demonstration that 670-nm NIR light can reduce oxidative stress and improve function in the CNS following traumatic injury in vivo.

Neuroprotective effect on retinal ganglion cells by transpupillary laser irradiation of the optic nerve head.

This study demonstrates that subthreshold transpupillary thermotherapy (TTT) laser irradiation on optic nerve head protects retinal ganglion cells (RGCs) in an optic nerve crush (ONC) model. TTT was performed in right eyes with an 810-nm diode laser aimed at the center of the optic nerve head, using the following protocol: power 60mW, duration 60s, spot size 500mum. Fluoro-Gold was injected into bilateral superior colliculi 5 days before sacrifice and fluorescent gold labeled RGCs were counted under fluorescence microscopy. In the ONC group, a progressive loss of RGCs was observed; however, in comparison with the ONC group, RGCs density was significantly higher (P=0.001, independent samples t-test) at day 7 postoperative and only borderline significances were obtained at days 14 and 28 postoperative (P=0.044 and P=0.045, respectively, independent samples t-test) in ONC+TTT group, which implies the potential neuroprotective role of TTT. This protective effect seems to be heat shock proteins (HSPs) related, because intraperitoneal Quercetin (an inhibitor of HSPs, 4mg/kg/day for 7 days) could completely abolish this protective effect at days 7, 14 and 28 postoperative (P=0.012, P=0.002, and P=0.000, respectively, independent samples t-test). Minimal collateral damage of TTT on optic nerve head tissue, peripapillary RGCs and the myelin sheath of the optic nerve were observed under transmission electron microscopy. These findings suggested that subthreshold TTT might be a safe and practical approach to protect RGCs. The underlying mechanisms may involve TTT-induced HSPs in RGCs.