Serum Levels of Oxylipins in Achilles Tendinopathy: An Exploratory Study

BACKGROUND Linoleic acid-derived oxidation products are found in experimental pain models. However, little is known about the levels of such oxylipins in human pain. In consequence, in the present study, we have undertaken a lipidomic profiling of oxylipins in blood serum from patients with Achilles tendinopathy and controls. METHODOLOGY/PRINCIPAL FINDINGS A total of 34 oxylipins were analysed in the serum samples. At a significance level of P<0.00147 (<0.05/34), two linoleic acid-derived oxylipins, 13-hydroxy-10E,12Z-octadecadienoic (13-HODE) and 12(13)-dihydroxy-9Z-octadecenoic acid (12,13-DiHOME) were present at significantly higher levels in the Achilles tendinopathy samples. This difference remained significant when the dataset was controlled for age, gender and body-mass index. In contrast, 0/21 of the arachidonic acid- and 0/4 of the dihomo-γ-linolenic acid, eicosapentaenoic acid or docosahenaenoic acid-derived oxylipins were higher in the patient samples at this level of significance. The area under the Receiver-Operator Characteristic (ROC) curve for 12,13-DiHOME was 0.91 (P<0.0001). Levels of four N-acylethanolamines were also analysed and found not to be significantly different between the controls and the patients at the level of P<0.0125 (<0.05/4). CONCLUSIONS/SIGNIFICANCE It is concluded from this exploratory study that abnormal levels of linoleic acid-derived oxylipins are seen in blood serum from patients with Achilles tendinopathy. Given the ability of two of these, 9- and 13-HODE to activate transient receptor potential vanilloid 1, it is possible that these changes may contribute to the symptoms seen in Achilles tendinopathy.