Etanercept Reduces Matrix Metalloproteinase-9 Level in Children with Polyarticular Juvenile Idiopathic Arthritis and TNF-alpha-308GG Genotype

Genetic contribution of tumor necrosis factor polymorphism (TNF-alpha-308G/A) in patients with juvenile idiopathic arthritis (JIA) on response to TNF blocking agents, as well as matrix metalloproteinase-9 (MMP-9) production, is not yet well established. We have investigated whether the TNF-alpha-308G/A polymorphism can influence MMP-9 level and clinical response to etanercept (TNF receptor II-Fc fusion protein) in JIA patients, after 1 year of treatment. A total of 66 patients with polyarticular JIA and 65 healthy children were screened for the polymorphism using the polymerase chain reaction-restriction fragment length polymorphism method. JIA patients donated paired blood samples prior to and 12 months after etanercept therapy. Plasma MMP-9 level was determined using an enzyme-linked immunosorbent assay kit. Clinical assessment was performed according to ACR Pedi 50 improvement criteria. The frequency of the A allele was significantly higher in JIA patients compared to controls (39% vs. 26%, P = 0.026). Patients with the -308GG genotype achieved an ACR Pedi 50 response significantly more frequently than those with the -308AA genotype (P = 0.035). MMP-9 level in patients with the genotype -308GG was significantly decreased after 1 year of treatment with etanercept compared to the value from before (P = 0.036). On the other hand, there was a decrease of MMP-9 levels after treatment, but not statistically significant in patients with the genotypes -308GA/AA. We conclude that etanercept reduces MMP-9 level in children with polyarticular JIA and TNF-alpha-308GG genotype. Our results correlate with findings that the -308A allele is associated with a lower response to etanercept treatment.