Effect of Particulate Matter on Achilles Tendon Healing: An Experimental Study in Rats

Abstract

Category: Basic Sciences/Biologics; Ankle; Sports; Trauma Introduction/Purpose: Exposure of particulate matter (PM) has been linked to several diseases including pulmonary, cardiovascular, oncology, neurology system, and etc. Even though tendon injury has become increasingly common recently, there has been no study of relationship between tendon healing and PM. Hence, we performed experimental study in rats to evaluate whether PM has significant effect on tendon healing. We hypothesized that PM exposure may substantially influence Achilles tendon healing. Here, we evaluated whether PM exposure led to deleterious effect on tendon healing in a rat model of Achilles tendon rupture (ATR). Methods: All experiments with rats were approved by the Institutional Animal Care and Use Committee. The Achilles tendons of 20 Sprague-Dawley rats were transected by open tenotomy. The animals were divided into two groups according to exposure of PM 2.5 (particulate matter less than 2.5µm): control group (Non-PM group) or PM exposure group (PM group). 30 minutes of PM inhalational exposure was performed 3 days a week for 6 weeks in closed chamber systems. After 6 weeks, histologic study of lung, laboratory test and enzyme-linked immunosorbent assay (ELISA) of blood samples, histologic study, transmission electron microscopy (TEM) analysis, biomechanical study, RNA sequencing, and western blot analysis of Achilles tendon was performed. Results: Hematoxylin and eosin (H&E) stain of lung tissue in PM group showed inflammation of alveolar wall and increased macrophage. Laboratory test and ELISA of blood samples from PM group showed significantly higher expression of white blood cell count and tissue necrosis factor alpha (TNF-α) than those from non-PM group, respectively. Histologic study of Achilles tendon in PM group exhibited increased lymphocyte and ossification findings with inflammatory change of cell morphology. TEM analysis showed decreased collagen fibril in PM group than non-PM group. Load to failure was decreased in the PM group than non-PM group. RNA sequencing and ingenuity pathway analysis showed increased cAMP-PKA-CREB signal pathway in PM group and the results were consistent with western blot outcomes. Conclusion: Achilles tendon healing was substantially affected by the PM exposure. Based on the present data, PM exposure induces detrimental histological and biomechanical results on Achilles tendon healing through cAMP-PKA-CREB pathway. Further in-vitro study and larger in-vivo study with longer time period are needed to support the present data.