Inhibitory effect of low-level laser irradiation on LPS-stimulated prostaglandin E-2 production and cyclooxygenase-2 in human gingival fibroblasts

It has been reported that lipopolysaccharide (LPS) from periodontal pathoge ns can penetrate gingival tissues and stimulate the production of prostagla ndin E-2 (PGE(2)), which is known as a potent stimulator of inflammation an d bone resorption. Although biostimulatory effects of low-level laser irrad iation such as anti-inflammatory results have been reported, the physiologi cal mechanism is not yet clarified. The purpose of the present study was to determine the effect of laser irradiation on PGE(2) production and cycloox ygenase (COX)-1 and COX-2 gene expression in LPS-challenged human gingival fibroblast (hGF) cells in vitro. hGF cells were prepared from healthy gingi val tissues and challenged with LPS, and Ga-Al-As diode laser was irradiate d to the hGF cells. The amount of PGE(2) released in the culture medium was measured by radioimmunoassay, and mRNA levels were analyzed by reverse tra nscriptase-polymerase chain reaction (RT-PCR). Irradiation with Ga-Al-As di ode low-level laser significantly inhibited PGE2 production in a dose-depen dent manner, which led to a reduction of COX-2 mRNA levels. In conclusion, low-level laser irradiation inhibited PGE2 by LPS in hGF cells through a re duction of COX-2 mRNA level. The findings suggest that low-level laser irra diation may be of therapeutic benefit against the aggravation of gingivitis and periodontitis by bacterial infection.