Exercise-induced effects on inflammatory biomarkers and BDNF in osteoarthritis: a systematic review with meta-analysis

Aim: To summarize the literature regarding the acute and/or basal exercise-induced effects on inflammatory biomarkers and BDNF in patients with knee osteoarthritis (KOA).
Methods: PubMed, Web Of Science and PEDro were systematically searched for appropriate studies. A meta-analysis was performed or effect sizes (ES) were estimated, where possible.
Results: Twenty-one studies were included: 15 investigated basal exercise-induced effects, 4 acute effects, and 2 both. Biomarkers were intra-articular (n=4) or serologically (n=17) determined. Meta-analyses showed that basal CRP was reduced in KOA patients after exercise therapy, although, IL-6 and TNF-α levels did not significantly change. Also, sTNFR1/2 did not significantly change after exercise therapy. The exercise-effect on different other biomarkers was less clear and, there were insufficient data available to perform a meta-analysis. However, a low degree of evidence was present for a decrease in IL-6 after swimming or cycling for 6 weeks, increase in sTNFR1 (ES: 2.325), decrease in sTNFR2 (ES: -0.997) and increase in BDNF (ES: 1.412) after 12 weeks of walking. Locally, intra-articular IL-10 (ES: 9.163) increased, and IL-1β (ES: -6.199) and TNF-α decreased (ES: -2.322) after strength exercises. An acute training session elicited a myokine response (ES IL-6: 0.314), and an increase in BDNF. No inflammatory effect (ES CRP: 0.052; ES TNF-α: -0.019; 0.081) following an acute bout of training was found. However, a single bout of exercise elicited an increase in intra-articular IL-10.
Conclusion: The anti-inflammatory properties of exercise therapy have important implications for informing KOA patients and clinicians about this underlying effect.