Low-level laser therapy for closed-head traumatic brain injury in mice: effect of different wavelengths

Abstract

Background and objectives: Traumatic brain injury (TBI) affects millions worldwide and is without effective treatment. One area that is attracting growing interest is the use of transcranial low-level laser therapy (LLLT) to treat TBI. The fact that near-infrared light can penetrate into the brain would allow non-invasive treatment to be carried out with a low likelihood of treatment-related adverse events. LLLT may treat TBI by increasing respiration in the mitochondria, causing activation of transcription factors, reducing inflammatory mediators and oxidative stress, and inhibiting apoptosis.

Study design/materials and methods: We tested LLLT in a mouse model of closed-head TBI produced by a controlled weight drop onto the skull. Mice received a single treatment with continuous-wave 665, 730, 810, or 980 nm lasers (36 J/cm(2) delivered at 150 mW/cm(2)) 4-hour post-TBI and were followed up by neurological performance testing for 4 weeks.

Results: Mice with moderate-to-severe TBI treated with 665 and 810 nm laser (but not with 730 or 980 nm) had a significant improvement in Neurological Severity Score that increased over the course of the follow-up compared to sham-treated controls. Morphometry of brain sections showed a reduction in small deficits in 665 and 810 nm laser treated mouse brains at 28 days.

Conclusions: The effectiveness of 810 nm agrees with previous publications, and together with the effectiveness of 660 nm and non-effectiveness of 730 and 980 nm can be explained by the absorption spectrum of cytochrome oxidase, the candidate mitochondrial chromophore in transcranial LLLT.

Fig. 1

Graphical illustration of the possible mechanisms of transcranial LLLT for TBI. Red or near-infrared light is absorbed in the mitochondria (possible by cyctochrome c oxidase in the respiratory chain) leading to release of ATP, nitric oxide, and modulation of reactive oxygen species. These second messenger molecules can lead to activation of transcription factors that migrate to the nucleus where they alter expression levels of numerous genes. These new gene products may lead to increased survival of neurons in the damaged brain, to an increase in adult neurogenesis in the hippocampus, for example, to reduced levels of inflammation and to an overall reduced level; of apoptotic and necrotic cell death in the brain.

Fig. 2

Time course of NSS scores of sham and laser-treated mice. A: Sham-treated control versus 665 nm laser. B: Sham-treated control versus 730 nm laser. C: Sham-treated control versus 810 nm laser. D: Sham-treated control versus 980 nm laser. Points are means of 8–12 mice and bars are SD. *P < 0.05; **P < 0.01; ***P < 0.001 (one-way ANOVA).

Fig. 3

Means of AUC values for individual mice in the five groups. Values are means of 8–12 mice per group and bars are SD. P-values shown were determined by one-way ANOVA.

Fig. 4

Morphometry of brain sections removed from mice at day 28. Micrographs of typical H&E stained brain sections showing outline to calculate total brain area and small defects marked with arrows. A: Sham-treated control. B: 665 nm laser-treated mouse. C: 810 nm laser-treated mouse. D: Mean fractional defect area in brains of sham, 665 nm, and 810 nm laser-treated mice. Values are means from 8 to 12 mice per group and bars are SD. *P < 0.05; **P < 0.01 (one-way ANOVA).