Serum levels of hydroxylated metabolites of arachidonic acid cross-sectionally and longitudinally predict knee pain progression: an observational cohort study.

Objective To examine associations between serum oxylipins, which regulate tissue repair and pain signalling, and knee pain/radiographic osteoarthritis (OA) at baseline and knee pain at 3 year follow-up. Method Baseline, and 3 year follow-up, knee pain phenotypes were assessed from 154 participants in the Knee Pain in the Community Cohort (KPIC) study. Serum and radiographic Kellgren and Lawrence (KL) and Nottingham line drawing atlas (NLDA) OA scores were collected at baseline. Oxylipin levels were quantified using liquid chromatography coupled with mass spectrometry (LC-MS/MS). Associations were measured by linear regression and Receiver Operator Characteristics (ROC). Results Serum levels of 8,9-epoxyeicosatrienoic acid (EET) (β(95%CI)=1.809(-0.71-2.91)), 14,15-dihydroxyeicosatrienoic acid (DHET) (β(95%CI)=0.827(0.34-1.31)), and 12-hydroxyeicosatetraenoic acid (β(95%CI)=4.090(1.92-6.26)) and anandamide (β(95%CI)=3.060(1.35-4.77)) were cross-sectionally associated with current self-reported knee pain scores (NRS item 3, average pain). Serum levels of 9- (β(95%CI)=0.467(0.18-0.75)) & 15-hydroxyeicosatetraenoic acid (β(95%CI)=0.759(0.29-1.22)), 14-hydroxydocosahexaenoic acid (β(95%CI)=0.483(0.24-0.73)), and the ratio of 8,9-EET:DHET (β(95%CI)=0.510(0.19-0.82)) were cross-sectionally associated with K/L scores. Baseline serum concentrations of 8,9-EET (β(95%CI)=2.166(0.89-3.44)), 5,6-DHET (β(95%CI)=152.179(69.39-234.97)), and 5-HETE (β(95%CI)=1.724(0.677-2.77) showed positive longitudinal associations with follow-up knee pain scores (NRS item 3, average pain). Combined serum 8,9-EET and 5-HETE concentration showed the strongest longitudinal association (β(95%CI)=1.156(0.54-1.77) with pain scores at 3 years, and ROC curves distinguished between participants with no pain and high pain scores at follow-up (AUC(95%CI)=0.71(0.61-0.82)). Conclusions Serum levels of a combination of hydroxylated metabolites of arachidonic acid may have prognostic utility for knee pain, providing a potential novel approach to identify people who are more likely to have debilitating pain in the future.