Infrared (810-nm) low-level laser therapy on rat experimental knee inflammation

Abstract

Arthritis of the knee is the most common type of joint inflammatory disorder and it is associated with pain and inflammation of the joint capsule. Few studies address the effects of the 810-nm laser in such conditions. Here we investigated the effects of low-level laser therapy (LLLT; infrared, 810-nm) in experimentally induced rat knee inflammation. Thirty male Wistar rats (230-250 g) were anesthetized and injected with carrageenan by an intra-articular route. After 6 and 12 h, all animals were killed by CO(2) inhalation and the articular cavity was washed for cellular and biochemical analysis. Articular tissue was carefully removed for real-time PCR analysis in order to evaluate COX-1 and COX-2 expression. LLLT was able to significantly inhibit the total number of leukocytes, as well as the myeloperoxidase activity with 1, 3, and 6 J (Joules) of energy. This result was corroborated by cell counting showing the reduction of polymorphonuclear cells at the inflammatory site. Vascular extravasation was significantly inhibited at the higher dose of energy of 10 J. Both COX-1 and 2 gene expression were significantly enhanced by laser irradiation while PGE(2) production was inhibited. Low-level laser therapy operating at 810 nm markedly reduced inflammatory signs of inflammation but increased COX-1 and 2 gene expression. Further studies are necessary to investigate the possible production of antiinflammatory mediators by COX enzymes induced by laser irradiation in knee inflammation.

Fig. 1

Analysis of articular wash 3 and 6 h after induced inflammation. a Total number of leukocytes in articular lavage fluid after 3 h in the control group and after LLLT (n = 6 animals per group (*p < 0.05) (**p < 0.001). b Total number of leukocytes in articular lavage fluid after 6 h in the control group and after LLLT (n = 6 animals per group arthritis group (AT); the arthritis group treated with diclofenac (Diclof); the arthritis group treated with 1 J LLLT (AT + 1 J); the arthritis group treated with 3 J LLLT (AT + 3 J); the arthritis group treated with 6 J LLLT (AT + 6 J); the arthritis group treated with 10 J LLLT (AT + 10 J). Results are expressed as mean ( ± SEM)

Fig. 2

a The number of neutrophils in the articular wash fluid 6 h after induced inflammation in the control group and after LLLT. b The number of mononuclear cells in the articular wash fluid 6 h after induced inflammation in the control group and after LLLT (n = 6 animals per group). Arthritis group (AT); arthritis group treated with diclofenac (Diclof); arthritis group treated with 1 J LLLT (AT + 1 J); arthritis group treated with 3 J LLLT (AT + 3 J); arthritis group treated with 6 J LLLT (AT + 6 J); arthritis group treated with 10 J LLLT (AT + 10 J). Results are expressed as mean ± SEM (**p < 0.001)

Fig. 3

a The protein extravasation as an indicator of vascular permeability 6 h after induced inflammation. b The activity of myeloperoxidase 3 h after induced inflammation in the control and treated groups. c The activity of myeloperoxidase 6 h after induced inflammation in control and treated groups (* p < 0.05) (***p < 0.001). Arthritis group (AT); arthritis group treated with diclofenac (Diclof); arthritis group treated with 1 J LLLT (AT + 1 J); arthritis group treated with 3 J LLLT (AT + 3 J); arthritis group treated with 6 J LLLT (AT + 6 J); arthritis group treated with 10 J LLLT (AT + 10 J). Results are expressed as mean ± SEM

Fig. 4

a The RNA expression of COX-1 enzyme measured by real-time PCR in joint cartilage. b The RNA expression of COX-2 enzyme measured by real-time PCR in joint cartilage (n = 6 animals per group (*p < 0.01). Arthritis group (AT); arthritis group treated with diclofenac (Diclof); arthritis group treated with 1 J LLLT (AT + 1 J); arthritis group treated with 3 J LLLT (AT + 3 J); arthritis group treated with 6 J LLLT (AT + 6 J); arthritis group treated with 10 J LLLT (AT + 10 J). Results are expressed as mean ± SEM

Fig. 5

a The COX-1 RNA expression measured by real-time PCR at articular wash fluid. b The COX-2 RNA expression measured by real-time PCR at articular wash fluid (*p < 0.01) (n = 6 animals per group. Arthritis group (AT); arthritis group treated with diclofenac (Diclof); arthritis group treated with 1 J LLLT (AT + 1 J); arthritis group treated with 3 J LLLT (AT + 3 J); arthritis group treated with 6 J LLLT (AT + 6 J); arthritis group treated with 10 J LLLT (AT + 10 J). Results are expressed as mean ± SEM

Fig. 6

a IL-1 levels at articular wash fluid measured by ELISA. b IL-6 levels at articular wash fluid measured by ELISA. c PGE₂ levels at articular wash fluid measured by ELISA (*p < 0.05) (**p < 0.01) (***p < 0.001) (n = 6 animals per group). Arthritis group (AT); arthritis group treated with diclofenac (Diclof); arthritis group treated with 1 J LLLT (AT + 1 J); arthritis group treated with 3 J LLLT (AT + 3 J); arthritis group treated with 6 J LLLT (AT + 6 J); arthritis group treated with 10 J LLLT (AT + 10 J). Results are expressed as mean ± SEM