Decreased synovial fluid ghrelin levels are linked with disease severity in primary knee osteoarthritis patients and are increased following laser therapy.

BACKGROUND: Ghrelin has been proved to inhibit inflammation and promote cartilage growth. So far, its role in patients with primary knee osteoarthritis has not been investigated.

OBJECTIVE: The current study was performed to explore the serum and synovial ghrelin levels as well as the relationship between ghrelin levels and disease severity in primary knee OA patients.

METHODS: 52 primary knee OA patients were recruited in the study. 52 sex and age-matched patients visiting our hospital for regular body check were selected as controls. The serum and synovial fluid ghrelin levels were examined by enzyme linked immunosorbent assay (ELISA) before treatment, one week and four weeks after laser therapy, respectively. The inflammation markers IL-6 and TNF-α were also investigated. The radiographic progression was assessed by Kellgren-Lawrence (K-L) grade scale and the symptomatic severity was evaluated by visual analog scale (VAS), Lequesne index and Lysholm scores. The Receiver Operating Characteristic (ROC) analysis curve was conducted to test the diagnostic value of ghrelin, IL-6 and TNF-α for radiographic progression.

RESULTS: No significant difference of serum ghrelin levels was found between knee OA patients and healthy controls. Synovial fluid ghrelin concentrations were significantly negatively correlated with K-L grading (r=-0.591, P<0.001).Attenuated synovial fluid ghrelin levels were also related to clinical severity determined by Lequesne index (r=-0.308, P=0.025),VAS scores (r=-0.591, P<0.001) and Lysholm scores (r=0.381, P=0.005).In addition, ghrelin levels were also negatively associated with TNF-α (r=-0.424, P=0.002) and IL-6 concentrations (r=-0.428, P=0.002). ROC curve analysis demonstrated that ghrelin exhibited more diagnostic value than IL-6 and TNF-α for assessing radiographic progression in medium-late stage.

CONCLUSIONS: Decreased synovial fluid ghrelin levels are related to disease severity in patients with primary osteoarthritis and are increased following laser therapy. Local application of ghrelin may serve as an adjunctive therapy for knee OA.