Equine suspensory ligament and tendon explants cultured with platelet-rich gel supernatants release different anti-inflammatory and anabolic mediators

The aim of this study was to evaluate the release of pro- and anti-inflammatory as well as anabolic mediators stimulated by a leukocyte-reduced platelet-rich gel supernatant (Lr-PRGS) and a leukocyte-reduced plasma supernatant (Lr-PL) at two concentrations (25 and 50%) on normal equine suspensory ligament explants (SLEs) and tendon explants (TEs). SLEs and TEs from six horses were independently incubated for 48 h with Lr-PRGS and Lr-PL at concentrations of 25 and 50%, respectively. Samples were collected from the incubated tissues at 1 h and 48 h, which were employed for ELISA determination of interleukin 1 beta (IL-1β), tumor necrosis factor alpha (TNF-α),  IL-4, IL-1 receptor antagonist (IL-1ra), platelet-derived growth factor isoform BB (PDGF-BB), transforming growth factor beta-1 (TGF-β1, and hyaluronic acid (HA). Overall, 50% Lr-PRGS induced significantly less IL-1β release than the other hemoderivatives in both tissues. At 48 h, both Lr-PRGS and 25% Lr-PL induced significantly higher TNF-α concentrations in SLEs when compared to TEs, whereas both Lr-PRGS concentrations induced significantly higher IL-4 concentrations in SLEs in comparison to TEs. IL-1ra release was not different between tissues. However, this cytokine was significantly higher in tissue explants cultured with both Lr-PRGS concentrations. HA concentration was lower in tissue explants cultured with all hemoderivatives at two concentrations when compared to the control group. The positive effects observed for ligaments and tendons treated with Lr-PRGS may be mediated by the inhibition of IL-1β release of and increased release of IL-4 and IL-1ra. Furthermore, PDGF-BB could be a polypeptide responsible for mediating the release of anti-inflammatory cytokines in SLEs and TEs incubated with Lr-PRGS.