Effect of Ga‐Al‐As laser irradiation on COX‐2 and cPLA 2 ‐α expression in compressed human periodontal ligament cells

Background and Objective Prostaglandin E 2 (PGE 2 ), which has bone‐resorptive activity, is produced by human periodontal ligament (PDL) cells in response to mechanical stress. We previously reported that low level laser (LLL) irradiation inhibited PGE 2 production in PDL cells in response to mechanical stress; however, the mechanism underlying this inhibitory effect was unclear. Thus, we sought to determine the mechanism underlying the inhibitory effect of LLL on PGE 2 production in compressed PDL cells. Study Design/Materials and Methods A compressive force of 2.0 g/cm 2 was applied for 24 hours to human PDL cells obtained from premolars extracted for orthodontic treatment. LLL irradiation (Ga‐Al‐As laser, 830 nm, 3.82 J/cm 2 ) was applied 6 hours before, 1 hour before, and immediately after the application of compressive force. The mRNA expression of COX‐2 and cPLA 2 ‐α was then examined by real‐time PCR. Results LLL irradiation significantly inhibited COX‐2 and cPLA 2 ‐α mRNA expression, which was increased in response to the application of a compressive force. Moreover, LLL irradiation immediately after compression had the strongest inhibitory effect on the expression of these genes. Conclusions The inhibition of PGE 2 production by LLL irradiation in compressed PDL cells may be due to the inhibition of COX‐2 and cPLA 2 ‐α expression and is most pronounced immediately after the application of a compressive force. Lasers Surg. Med. 42:489–493, 2010. © 2010 Wiley–Liss, Inc.