Summary
We treated mice with SPM's and reduced the onset and severity of PTOA
Abstract
Introduction
It is well established at this time, that chronicity of inflammation following the ACL injury is associated with gradual chondral breakdown and development of progressive osteoarthritis phenotypical changes resulting in pain and structural damage.
Inflammation after ACL injury is a physiologic response. The required inflammation resolution after injury is an active process modulated by pro-resolving molecules that ultimately influence immune cells such as macrophages to become pro-regenerative. The resolution of a normal initial inflammatory response and why it is insufficient after ACL injury has been the focus of our work regarding specialized pro-resolving mediators.
This experimental work builds on previously presented work describing the normal course of inflammation after ACL injury and takes it one step further into the treatment of chronic inflammation post ACL injury using specialized pro-resolving mediators as a therapeutic strategy after ACL injury.
We specifically use Mar1 and RvD1 , two specialized pro-resolving mediators, to boost the natural resolution of inflammation after ACL injury. We aim to show that the progression to established PTOA can be delayed or halted using this strategy.
Methods
36 C57BL6/J mice underwent ACLT and injection of 100ng of either MaR1 or RvD1 intraarticularly at the time of surgery. Animals were followed for 1, 14, 28 and 56 days post-injury and analyzed. Knee tissues were harvested and gene expression of pro-inflammatory cytokines (IL-1ß and TNF-a) as well as expression of SPM biosynthetic enzyme (12/15-lipoxygenase [12/15Alox]) and SPM receptors (LGR6 and FPR2) was assessed by rt-PCR. Synovial fluid was used for measurement of MaR1 and RvD1 levels (ELISA). Micro CT and histological analysis will be done to show structural changes after ACL injury and compare severity of OA.
One-way ANOVA and Tukey’s post hoc tests were used for statistical analysis. Statistical significance was set at p < 0.05.
Results
ACLT induced an acute inflammatory response characterized by increased synovium tissue expression of TNF-a and IL-1ß that peaked at day 1 to day 7 post-injury as previously shown. This established the consistency of our model between experimental cohorts, the addition of Mar1 and RvD1 at the time of surgery leads to a marked reduction of inflammatory cells and chondral breakdown markers (CTX-II) at day 7 after ACL injury
We will be presenting additional data at 14 and 28 days as well as 56 days after the treatment and compare structural endpoints as well as biomarker endpoints. (these experiments are currently ongoing)
Discussion
SPM’s are involved in the initial inflammation resolution after ACL injury. Exogenous administration of SPM’s may be able to overcome the failure to resolve chronic inflammation and can reduce the progression to PTOA in ACL injured mice. This work starts paving the way for a potentially easily translatable therapeutic approach after ACL injury.