Low-level light therapy for zymosan-induced arthritis in rats
2007
It has been known for many years that low level laser (or light) therapy (LLLT) can ameliorate the pain, swelling
and inflammation associated with various forms of arthritis. Light is absorbed by mitochondrial chromophores
leading to an increase in ATP, reactive oxygen species and/or cyclic AMP production and consequent gene
transcription via activation of transcription factors. However, despite many reports about the positive effects of
LLLT in medicine, its use remains controversial. Our laboratory has developed animal models designed to
objectively quantify response to LLLT and compare different light delivery regimens. In the arthritis model we
inject zymosan into rat knee joints to induce inflammatory arthritis. We have compared illumination regimens
consisting of a high and low fluence (3 J/cm 2 and 30 J/cm 2 ), delivered at a high and low irradiance (5 mW/cm2 and 50 mW/cm 2 ) using 810-nm laser light daily for 5 days, with the effect of conventional corticosteroid
(dexamethasone) therapy. Results indicated that illumination with 810-nm laser is highly effective (almost as good
as dexamethasone) at reducing swelling and that longer illumination time was more important in determining
effectiveness than either total fluence delivered or irradiance. Experiments carried out using 810-nm LLLT on
excisional wound healing in mice also confirmed the importance of longer illumination times. These data will be of
value in designing clinical trials of LLLT.
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