Local Shifts in Inflammatory and Resolving Lipid Mediators in Response to Tendon Overuse

Abstract

Tendon inflammation has been implicated in both adaptive connective tissue remodeling and overuse-induced tendinopathy. Lipid mediators control the initiation and resolution of inflammation, but their roles within tendon are largely unknown. Here we profiled local shifts in intratendinous lipid mediators via liquid chromatography-tandem mass spectrometry in response to synergist ablation-induced plantaris tendon overuse. Sixty-four individual lipid mediators were detected in homogenates of habitually loaded plantaris tendons from healthy ambulatory rats. This included many bioactive metabolites of the cyclooxygenase (COX), lipoxygenase (LOX), and epoxygenase (CYP) pathways. Synergist ablation induced a robust inflammatory response at day 3 post-surgery characterized by epitenon infiltration of polymorphonuclear leukocytes (PMNs) and macrophages (MΦ), heightened expression of inflammation-related genes, and increased intratendinous concentrations of the pro-inflammatory eicosanoids thromboxane B2 (TXB2) and prostaglandin E2 (PGE2). By day 7, MΦ became the predominant myeloid cell type in tendon and there were further delayed increases in other COX metabolites including PGD2, PGF2α and PGI2. Specialized pro-resolving mediators (SPMs) including protectin D1 (PD1) and resolvin D6 (RvD6), as well as related pathway markers of D-resolvins (17-HDoHE), E-resolvins (18-HEPE) and lipoxins (15-HETE) were also increased locally in response to tendon overuse, as were many anti-inflammatory fatty acid epoxides of the CYP pathway (e.g. EpETrEs). Nevertheless, intratendinous prostaglandins remained markedly increased even following 28 days of tendon overuse together with a lingering MΦ presence. These data reveal a delayed and prolonged local inflammatory response to tendon overuse characterized by an overwhelming predominance of pro-inflammatory eicosanoids and a relative lack of pro-resolving lipid mediators.

E-series resolvin metabolome, biosynthesis and critical role of stereochemistry of specialized pro-resolving mediators (SPMs) in inflammation-resolution: Preparing SPMs for long COVID-19, human clinical trials, and targeted precision nutrition

“…It is appropriate to emphasize that these early fundamental studies are vital to understanding the pathogenesis of COVID-19 infections and the potential role of lipid mediators that could give useful new directions for treatments of COVID-19, long COVID and in lasting immunity. These new findings ( Table 1 ) and many other human studies for SPMs from international experts [ [35] , [36] , [37] , [38] , [39] , [40] , [41] , [42] , [43] , [44] , [45] , [46] , [47] , [48] , [49] , [50] , [51] , [52] , [53] , [54] , [55] ] would not have been possible without the i) complete stereochemical assignments of each of the potent bioactive SPMs produced by human and mouse leukocytes, ii) their biosynthesis from n-3 essential fatty acids (EPA and DHA) and iii) total organic synthesis with rigorous matching studies with endogenous SPMs along with our dedicated and talented organic chemistry collaborators summarized herein. In this relatively new SPM field, the Serhan lab has collaborated for many years with Professor Nicos Petasis and colleagues as part of the total synthesis core of our NIH-supported Program Project grant P01GM095467, Professor Trond Hansen and team in Oslo, Norway [ 56 ], Professor Bernd Spur and Anna Rodriguez [ [57] , [58] , [59] ], and the organic synthesis group at Cayman Chemical; for examples, see the custom synthesis of benzo-RvD1 analog mimetic [ 60 ] and the new RvE4 [ 61 ].…”

“…Importantly, the many other elegant human studies on SPMs would not have been possible without reliance on the complete stereochemically defined synthetic SPMs and their internal standards for LC-MS-MS-based analyses with adult tissues [ [35] , [36] , [37] , [38] , [39] , [40] , [41] , [42] , [43] , [44] , [45] , [46] , [47] , [48] , [49] , [50] , [51] , [52] , [53] , [54] , [55] ] and adolescent human peripheral blood samples [ 38 ] as well as their scale-up for commercial availability [ 62 ]. A recent clinical trial reported that local topical treatment of gingival inflammation with a proresolving lipoxin/resolvin stable analog is safe and effective as well as activated endogenous production of SPMs present in peripheral blood [ 63 ].…”

“…These novel and unique structures were determined using both LC-MS-MS and GC-MS fragmentation and bioassays. Resolvin D6 has a role in reducing muscle inflammation associated with injury and aging [ 48 ] and in tendon overuse [ 49 ]. Recently, a Resolvin D6 isomer and Elovanoid-N32 were discovered to reduce ACE2 and binding of the virus spike protein to human corneal epithelial cells of the eye following injury or exposure to IFNγ [ 158 , 159 ] and to stimulate nerve regeneration, wound healing and pain [ 160 ].…”

Innate and adaptive immune system cells implicated in tendon healing and disease

“…Innate immune system cells have a rapid, nonspecific response to microbes and injured cells. In fact, most innate immune system cells have PRR, which bind and recognise both PAMP present on microbes as well as DAMP (Kumar et al, 2011;Marshall et al, 2018). DAMPs, also known as alarmins, are nuclear, mitochondrial or cytosolic proteins released by cells upon infection, necrosis or injury (Roh and Sohn, 2018).…”

“…DAMPs, also known as alarmins, are nuclear, mitochondrial or cytosolic proteins released by cells upon infection, necrosis or injury (Roh and Sohn, 2018). Once innate immune system cells bind proteins that trigger an immune response, they release a large number of cytokines, which in turn stimulate the blood flow to recruit more immune system cells to the site, thereby increasing inflammation (D'Addona et al, 2017;Marshall et al, 2018). Interestingly, tenocytes release pro-inflammatory cytokines upon injury, contributing to oedema and hyperaemia (D'Addona et al, 2017;Millar et al, 2017).…”