Title: Harnessing the potential of 17-HDHA a novel biomarker of OA pain status
Funder: Versus Arthritis

Abstract: Chronic pain is a major cause of disability and suffering in many, but not all, osteoarthritis (OA) patients. Specialised endogenous pro-resolving molecules curtail inflammatory responses, one of the intermediate lipid mediators (17-HDHA) is significantly associated with pain. Lower blood levels of 17-HDHA are associated with higher OA pain scores and lower pain pressure thresholds in healthy volunteers. Exogenous 17-HDHA attenuated established pain behaviour in rodent models of OA pain. Aim: to test the hypothesis that levels of 17-HDHA predict OA pain progression, to identify the mechanisms underlying differences in blood levels of 17-HDHA and the analgesic effects of this molecule. Experimental Plan: We have stored blood from 358 OA participants with temporal summation and pain pressure thresholds measured at baseline, and are close to completing a 3 year follow up blood collection and pain testing (Q2 2018), as part of other ongoing ARUK Pain Centre studies. To test our hypothesis, sera levels of 17-HDHA, RvD3 and 4, protectin D1, 17-oxoDHA will be measured using liquid chromatography tandem mass spectrometry (716 samples). Blood levels of IL-6, IL-1 and TNF-alpha will be measured by ELISA. Standard parametric analyses using linear and logistic regression models adjusting for the standard confounders (age, sex, BMI) will be performed. The longitudinal predictive effect of 17-HDHA levels on pain trajectories and joint pathology in OA patients will be calculated. The basis for differences in sera levels of 17-HDHA will be investigated. Using a 2x2 factorial design with a subset of the participants we will determine whether levels of 17-HDHA and OA pain are associated with a specific subpopulation of monocytes (Flow Cytometric Cell Sorting). Differential expression analysis (RNAseq) of the monocyte populations will then provide new evidence for whether differences in gene expression, or enrichment of functional polymorphisms in genes, of key enzyme pathways provide an explanation for the variance in levels of 17-HDHA and OA pain. Mathematical models will be developed that test the biological hypothesis that enzymatic pathways which generate / metabolise 17-HDHA and related bioactive products are associated with the varying levels of OA pain. A clinically relevant rodent model of OA pain will be used to investigate the mechanisms underlying the analgesic effects of 17-HDHA. Sera and synovial fluid levels of the same bioactive lipids measured in the clinical study will be quantified at the peak of the inhibitory effects of 17-HDHA in the rodent OA pain model, and compared to the profile of these molecules in the human OA serum samples. We will confirm whether the principle molecules associated with the analgesic effect of 17-HDHA in the OA model also have associations with clinical OA pain scores. Prediction of future OA pain status would provide an invaluable tool for personalised pain treatment. This research will provide the foundations for follow-on funding to develop a test which predicts future OA pain outcomes, which could be used to stratify patients for analgesic treatment and clinical trials. Understanding why 17-HDHA is analgesic will provide a platform for new analgesic strategies.


Research activity codes: 4.1 DISCOVERY AND PRECLINICAL TESTING OF MARKERS AND TECHNOLOGIES
Health categories: MUSCULOSKELETAL