More Research from 'Down Under'

We have again been blessed by some great research from the Southern Hemisphere, Melinda Fitzgerald of Experimental and Regenerative Neurosciences, School of Animal Biology, The University of Western Australia, Crawley, 6009, WA, Australia, has been kind enough to share her recent publication. I have just shared the abstract and the discussion, if you'd like to see more, let me know your opinion of the article!

Near Infra-red Light Reduces Oxidative Stress and Preserves Function in CNS
Tissue Vulnerable to Secondary Degeneration Following Partial Transection of the Optic Nerve, Journal of Neurotrauma, (doi: 10,1089/neu.2010.1426) Melinda Fitzgerald: Assistant Professor, PhD, Carole A. Bartlett: MSc, Sophie C. Payne: BSc (Hons), Nathan S. Hart: Associate Professor, PhD, Jenny Rodger: Assistant Professor, PhD, Alan R. Harvey: Winthrop Professor, PhD, Sarah A. Dunlop: Professor, PhD

Abstract

Traumatic injury to the central nervous system 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, where axons of retinal ganglion cells in 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 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, centre wavelength 670nm, irradiance 252 Wm-2, 30 minute exposure), as opposed to perception of light at this wavelength, reduced oxidative stress in areas of ON vulnerable to secondary degeneration, following partial injury. The WARP 10 NIR light treatment also prevented increases in NG2 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 Ymaze pattern discrimination task. To our knowledge, this is the first demonstration that 670nm NIR light can reduce oxidative stress and improve function in the CNS following traumatic injury in vivo.

Discussion
In this partial injury study, we have demonstrated that treatment with NIR light (WARP 10 LED array, 670nm) reduced oxidative stress in areas of ON vulnerable to secondary degeneration. NIR light treatment also prevented the secondary increases in NG2 immunopositive OPCs that occurred as a result of partial ON transection. Importantly, visual function was restored to normal by NIR light treatment using 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 670nm NIR light can reduce oxidative stress and improve function in the CNS after traumatic injury in vivo.

Improvements in visual function following partial ON transection were achieved with daily 30 minute exposures to the WARP 10 array, for the six days immediately following injury. It is possible that the improvements in performance in the Y-maze pattern discrimination task were partially due to non-specific improvements in working memory with NIR light treatment (Michalikova et al., 2008). Similarly, improvements in optokinetic nystagmus may be influenced by neuroprotective mechanisms not directly related to protection of the injured ON, perhaps involving transfer of visual responses to motor commands (Delgado-Garcia, 2000; Haustead et al., 2008). However, electroretinogram responses in completely normal rats were not altered with exposure to 670nm NIR light LED arrays (Eells et al., 2003), indicating that our observed improvements in visual function following traumatic injury are likely to be a result of direct effects on the partially injured ON. Furthermore, our demonstration that 670nm NIR light penetrates to the injured ON as well as through the retina to the back of the eye supports the premise of a direct effect of NIR light on ON. Beneficial outcomes may also be due to direct effects of 670nm NIR light on RGC somata in the retina, although we did not observe improvements in RGC axonal profiles.

Traumatic injury to the CNS results in glutamate excitotoxicity and altered Ca2+ flux, which leads to oxidative stress and reduced function of neurons and glia (Park et al., 2004; Tezel, 2006). We have recently demonstrated that oxidative stress spreads rapidly through ON vulnerable to secondary degeneration, through the linked astrocytic network (Fitzgerald et al., 2010). In this study, we demonstrate that NIR light treatment using the WARP 10 array reduced this early oxidative stress in hypertrophic astrocytes of ventral ON vulnerable to secondary degeneration in vivo, as well as reducing the later accumulation of MnSOD immunoreactive aggregates within cellular debris (Fitzgerald et al., 2009a), 10 days after injury. Our observed effects of NIR light treatment in reducing secondary oxidative stress after traumatic injury are likely to be due to increases in cytochrome c oxidase activity, reduced reactive oxygen species and improvements in mitochondrial function that have been described in a number of in vitro and in vivo studies (Wong-Riley et al., 2005; Liang et al., 2006; Rojas et al., 2008).

Reductions in oxidative stress in astrocytes may also protect oligodendrocytes in ventral ON vulnerable to secondary degeneration, with resultant beneficial effects on the integrity of myelin and visual function (Park et al., 2004; Williams et al., 2007;Fitzgerald et al., 2009a; Nave, 2010). However, due to the short term nature of the current study, myelin was not yet sufficiently disrupted to enable detection of improvements in myelination following treatment with NIR light. Nevertheless, the increases in NG2 immunopositive OPCs that occur in ON vulnerable to secondary degeneration were prevented with NIR light treatment using the WARP 10 LED array. Disruption to myelin causes increases in NG2 immunopositive cells (Franklin and Ffrench-Constant, 2008). We hypothesize therefore, that NIR light treatment may reduce oxidative stress in astrocytes leading to protection of oligodendrocytes and myelin, thereby preventing increased numbers of NG2 immunopositive OPCs in nerve vulnerable to secondary degeneration. Improvements in visual function would result from the preservation of myelin sheaths surrounding axons in areas of the ON vulnerable to secondary degeneration. NIR light treatment did not prevent reductions in β-III tubulin immunopositive axonal profiles or increases in resident or activated microglia / macrophages in ventral ON vulnerable to secondary degeneration.

However, visual function can be maintained with a small percentage of intact retinal ganglion cells (Sabel, 1999) and it may be that preservation of the myelin sheath is more important for preservation of function than large numbers of axons. Nevertheless it is likely that combinatorial treatment strategies that protect axons as well as reduce oxidative stress in glia, for example NIR light combined with the CNS specific neuroprotective calcium channel blocker lomerizine, will be required for even more effective prevention of secondary degeneration (Fitzgerald et al., 2009a; Fitzgerald et al., 2009b).

The relatively long duration for each treatment using the WARP 10 array necessitated repeated anaesthesia of experimental animals, which can be problematic. Therefore, assessing longer term outcomes using this successful treatment regime was beyond the scope of the current study. Treatment using a commercially available LED array delivering greater irradiance (VET 75 array), which provided a larger treatment area and potentially more thorough exposure to NIR light in a shorter time period, resulted in minimal improvements that were not sustained. It is possible that use of LED arrays with higher energy densities may enable reductions in treatment times.

Light in the red to NIR region of the spectrum has positive effects on a range of neural cells both in vitro and in vivo, when delivered by low energy laser or LED (Rochkind et al., 1990; Eells et al., 2004; Wong-Riley et al., 2005; Liang et al., 2008; Rochkind, 2009; Rochkind et al., 2009). LED delivery of NIR light avoids some of the potential pitfalls of low energy laser delivery, with flat arrays providing wider treatment areas and minimal heat production (Eells et al., 2004). It has been calculated that light emitted by LED arrays can penetrate tissue to a depth of 23cm (Beauvoit et al., 1994; Whelan et al., 2001) and we have demonstrated penetration of 670nm light over the distance of a few cm through skull, brain and associated tissue around the ON. Use of the arrays has been deemed a non-significant risk for use in humans by the FDA (Desmet et al., 2006). Our study indicates that 670nm NIR light offers a potential treatment for prevention of secondary degeneration following partial traumatic injury to the CNS, which may be particularly useful in combination with other neuroprotective agents. Use of NIR light LED arrays therefore represents a feasible alternative for treatment of secondary degeneration following traumatic injury to the CNS.