Controlled Stiffness of Direct-Write, Near-Field Electrospun Gelatin Fibers Generates Differences in Tenocyte Morphology and Gene Expression

Tendinopathy is a leading cause of mobility issues. Currently, the cell-matrix interactions involved in the development of tendinopathy are not fully understood. In vitro tendon models provide a unique tool for addressing this knowledge gap as they permit fine control over biochemical, micromechanical, and structural aspects of the local environment to explore cell-matrix interactions. In this study, direct-write, near-field electrospinning of gelatin solution was implemented to fabricate micron-scale fibrous scaffolds that mimic native collagen fiber size and orientation. The stiffness of these fibrous scaffolds was found to be controllable between 1 MPa and 8 MPa using different crosslinking methods (EDC, DHT, DHT+EDC) or through altering the duration of crosslinking with EDC (1 h to 24 h). EDC crosslinking provided the greatest fiber stability, surviving up to 3 weeks in vitro. Differences in stiffness resulted in phenotypic changes for equine tenocytes with low stiffness fibers (∼1 MPa) promoting an elongated nuclear aspect ratio while those on high stiffness fibers (∼8 MPa) were rounded. High stiffness fibers resulted in the upregulation of matrix metalloproteinase (MMPs) and proteoglycans (possible indicators for tendinopathy) relative to low stiffness fibers. These results demonstrate the feasibility of direct-written gelatin scaffolds as tendon in vitro models and provide evidence that matrix mechanical properties may be crucial factors in cell-matrix interactions during tendinopathy formation.

Ultrasoft platelet-like particles stop bleeding in rodent and porcine models of trauma

Uncontrolled bleeding after trauma represents a substantial clinical problem. The current standard of care to treat bleeding after trauma is transfusion of blood products including platelets; however, donated platelets have a short shelf life, are in limited supply, and carry immunogenicity and contamination risks. Consequently, there is a critical need to develop hemostatic platelet alternatives. To this end, we developed synthetic platelet-like particles (PLPs), formulated by functionalizing highly deformable microgel particles composed of ultralow cross-linked poly (N-isopropylacrylamide) with fibrin-binding ligands. The fibrin-binding ligand was designed to target to wound sites, and the cross-linking of fibrin polymers was designed to enhance clot formation. The ultralow cross-linking of the microgels allows the particles to undergo large shape changes that mimic platelet shape change after activation; when coupled to fibrin-binding ligands, this shape change facilitates clot retraction, which in turn can enhance clot stability and contribute to healing. Given these features, we hypothesized that synthetic PLPs could enhance clotting in trauma models and promote healing after clotting. We first assessed PLP activity in vitro and found that PLPs selectively bound fibrin and enhanced clot formation. In murine and porcine models of traumatic injury, PLPs reduced bleeding and facilitated healing of injured tissue in both prophylactic and immediate treatment settings. We determined through biodistribution experiments that PLPs were renally cleared, possibly enabled by ultrasoft particle properties. The performance of synthetic PLPs in the preclinical studies shown here supports future translational investigation of these hemostatic therapeutics in a trauma setting.

No correlation found between palpation and ultrasound for evaluation of effusion in the medial femorotibial and femoropatellar joint compartments of horses

OBJECTIVE

To compare palpation and ultrasound scores of effusion of the medial femorotibial and femoropatellar joints of horses.

ANIMALS

40 horses (80 stifles) were evaluated over a 12-week period.

METHODS

Horses > 1 year of age without history of stifle disease were enrolled from September to December 2022. Palpation of right and left medial femorotibial and femoropatellar joint compartments was performed. Amount of effusion was scored by a board-certified large animal surgeon, a third-year large animal surgery resident, and an equine sports medicine intern. Effusion of right and left medial femorotibial and femoropatellar joints was quantified with ultrasound by a board-certified equine sports medicine and rehabilitation clinician. Amount of effusion on palpation and ultrasound was graded as none-mild (1), moderate (2), or severe (3). A 2-way intraclass correlation coefficient evaluated interrater reliability of palpation scores. The Spearman rank correlation determined association between palpation and ultrasound scores.

RESULTS

Interrater reliability for palpation of effusion was poor between all observers for all joint compartments. No significant correlation was identified between palpation and ultrasound scores for any joint compartment for any observer.

CLINICAL RELEVANCE

Clinicians often rely on palpation of joint effusion as an indication of stifle pathology. We found interrater reliability to be poor for palpation scores, indicating low agreement for palpation of joint effusion between clinicians within our group. No correlation was found between palpation and ultrasound scores for joint effusion, indicating that clinicians should not rely on palpation alone to quantify joint effusion of the medial femorotibial and femoropatellar joints.

IL-1β + TGF-β2 dual-licensed mesenchymal stem cells have reduced major histocompatibility class I expression and positively modulate tenocyte migration, metabolism, and gene expression

OBJECTIVE

The study objectives were to 1) determine the mesenchymal stem cell (MSC) surface expression of major histocompatibility complex (MHC) class I and transcriptome-wide gene expression changes following IL-1β + TGF-β2 dual licensing and 2) evaluate if IL-1β + TGF-β2 dual-licensed MSCs had a greater ability to positively modulate tenocyte function compared to naive MSCs.

SAMPLES

Equine bone marrow-derived MSCs from 6 donors and equine superficial digital flexor tenocytes from 3 donors.

METHODS

Experiments were performed in vitro. Flow cytometry and bulk RNA sequencing were utilized to determine naive and dual-licensed MSC phenotype and transcriptome-wide changes in gene expression. Conditioned media were generated from MSCs and utilized in tenocyte cell culture assays as a method to determine the effect of MSC paracrine factors on tenocyte function.

RESULTS

Dual-licensed MSCs have a reduced expression of MHC class I and exhibit enrichment in functional pathways associated with the extracellular matrix, cell signaling, and tissue development. Additionally, dual-licensed MSC-conditioned media significantly improved in vitro tenocyte migration and metabolism to a greater degree than naive MSC-conditioned media. In tenocytes exposed to IL-1β, dual-licensed conditioned media also positively modulated tenocyte gene expression.

CLINICAL RELEVANCE

Our data indicate that conditioned media containing paracrine factors secreted from dual-licensed MSCs significantly modulates in vitro tenocyte function, which may confer benefits in vivo to healing tendons following injury. Additionally, due to reduced MHC class I expression in dual-licensed MSCs, this technique may also provide an avenue to provide an effective "off-the-shelf" allogenic source of MSCs.

Expanded library of novel 2,3-pyrrolidinedione analogues exhibit anti-biofilm activity

Herein we report a new library of 2,3-pyrrolidinedione analogues that expands on our previous report on the antimicrobial studies of this heterocyclic scaffold. The novel 2,3-pyrrolidinediones reported herein have been evaluated against S. aureus and methicillin-resistant S. aureus (MRSA) biofilms, and this work constitutes our first report on the antibiofilm properties of this class of compounds. The antibiofilm activity of these 2,3-pyrrolidinediones has been assessed through minimum biofilm eradication concentration (MBEC) and minimum biofilm inhibition concentration (MBIC) assays. The compounds displayed antibiofilm properties and represent intriguing scaffolds for further optimization and development.

Surgical procedure of intratympanic injection and inner ear pharmacokinetics simulation in domestic pigs

Introduction: One major obstacle in validating drugs for the treatment or prevention of hearing loss is the limited data available on the distribution and concentration of drugs in the human inner ear. Although small animal models offer some insights into inner ear pharmacokinetics, their smaller organ size and different barrier (round window membrane) permeabilities compared to humans can complicate study interpretation. Therefore, developing a reliable large animal model for inner ear drug delivery is crucial. The inner and middle ear anatomy of domestic pigs closely resembles that of humans, making them promising candidates for studying inner ear pharmacokinetics. However, unlike humans, the anatomical orientation and tortuosity of the porcine external ear canal frustrates local drug delivery to the inner ear. Methods: In this study, we developed a surgical technique to access the tympanic membrane of pigs. To assess hearing pre- and post-surgery, auditory brainstem responses to click and pure tones were measured. Additionally, we performed 3D segmentation of the porcine inner ear images and used this data to simulate the diffusion of dexamethasone within the inner ear through fluid simulation software (FluidSim). Results: We have successfully delivered dexamethasone and dexamethasone sodium phosphate to the porcine inner ear via the intratympanic injection. The recorded auditory brainstem measurements revealed no adverse effects on hearing thresholds attributable to the surgery. We have also simulated the diffusion rates for dexamethasone and dexamethasone sodium phosphate into the porcine inner ear and confirmed the accuracy of the simulations using in-vivo data. Discussion: We have developed and characterized a method for conducting pharmacokinetic studies of the inner ear using pigs. This animal model closely mirrors the size of the human cochlea and the thickness of its barriers. The diffusion time and drug concentrations we reported align closely with the limited data available from human studies. Therefore, we have demonstrated the potential of using pigs as a large animal model for studying inner ear pharmacokinetics.

Antimicrobial Properties of Equine Stromal Cells and Platelets and Future Directions

Increasing antimicrobial resistance in veterinary practice has driven the investigation of novel therapeutic strategies including regenerative and biologic therapies to treat bacterial infection. Integration of biological approaches such as platelet lysate and mesenchymal stromal cell (MSC) therapy may represent adjunctive treatment strategies for bacterial infections that minimize systemic side effects and local tissue toxicity associated with traditional antibiotics and that are not subject to antibiotic resistance. In this review, we will discuss mechanisms by which biological therapies exert antimicrobial effects, as well as potential applications and challenges in clinical implementation in equine practice.

Preclinical tendon and ligament models: Beyond the 3Rs (replacement, reduction, and refinement) to 5W1H (why, who, what, where, when, how)

Several tendon and ligament animal models were presented at the 2022 Orthopaedic Research Society Tendon Section Conference held at the University of Pennsylvania, May 5 to 7, 2022. A key objective of the breakout sessions at this meeting was to develop guidelines for the field, including for preclinical tendon and ligament animal models. This review summarizes the perspectives of experts for eight surgical small and large animal models of rotator cuff tear, flexor tendon transection, anterior cruciate ligament tear, and Achilles tendon injury using the framework: "Why, Who, What, Where, When, and How" (5W1H). A notable conclusion is that the perfect tendon model does not exist; there is no single gold standard animal model that represents the totality of tendon and ligament disease. Each model has advantages and disadvantages and should be carefully considered in light of the specific research question. There are also circumstances when an animal model is not the best approach. The wide variety of tendon and ligament pathologies necessitates choices between small and large animal models, different anatomic sites, and a range of factors associated with each model during the planning phase. Attendees agreed on some guiding principles including: providing clear justification for the model selected, providing animal model details at publication, encouraging sharing of protocols and expertise, improving training of research personnel, and considering greater collaboration with veterinarians. A clear path for translating from animal models to clinical practice was also considered as a critical next step for accelerating progress in the tendon and ligament field.

Use of mesenchymal stem cells for tendon healing in veterinary and human medicine: getting to the "core" of the problem through a one health approach

The purpose of this manuscript, which is part of the Currents in One Health series, is to take a comparative approach to stem cell treatment for tendon injury and consider how the horse might inform treatment in other veterinary species and humans. There is increasing experimental and clinical evidence for the use of bone marrow-derived mesenchymal stem cells to treat tendon injuries in the horse. The same evidence does not currently exist for other species. This manuscript will review why the equine superficial digital flexor tendon core lesion might be considered optimal for stem cell delivery and stem cell interaction with the injury environment and will also introduce the concept of stem cell licensing for future evaluation. The companion Currents in One Health by Koch and Schnabel, AJVR, October 2023, addresses in detail what is known about stem cell licensing for the treatment of other diseases using rodent models and how this information can potentially be applied to tendon healing.

Mesenchymal stem cell licensing: enhancing MSC function as a translational approach for the treatment of tendon injury

Tendon injuries are common in both veterinary and human clinical patients and result in morbidity, pain, and lost athletic performance. Consequently, utilizing naturally occurring injuries in veterinary patients as a comparative model could inform the development of novel therapies and increase translation for the treatment of human tendon injuries. Mesenchymal stem cells (MSCs) have shown considerable efficacy for the treatment of experimental and clinical superficial digital flexor tendon injury in the horse; however, the reinjury rate following treatment can remain high and MSC efficacy in treating other tendons is less well known. Additionally, the translation of MSC therapy to human tendon injury has remained poor. Recent evidence indicates that naïve MSC function can be enhanced through exogenous stimulation or manipulation of their environment. This stimulation or activation, herein termed MSC licensing, markedly alters MSC functions associated with immunomodulation, extracellular matrix remodeling, vascular development, bioactive factor production, and endogenous stromal/progenitor cell support. Additionally, a variety of licensing strategies has proven to influence MSC-secreted factors that have positively influenced outcome parameters in both in vitro and in vivo disease models separate from musculoskeletal tissues. Therefore, identifying the optimal licensing strategy for MSCs could ultimately provide an avenue for reliable and repeatable treatment of a broad range of tendon injuries of both veterinary and human clinical patients. This article details current evidence on the effects of licensed MSCs in both in vitro and in vivo disease models of different species and provides commentary on how those effector functions identified may be translated to the treatment of tendon injuries.

Effect of gentamicin on CD3+ T-lymphocyte proliferation for treatment of equine recurrent uveitis: An in vitro study

OBJECTIVE

The objective of the study was to determine the effect of gentamicin on CD3+ T-lymphocyte proliferation and cell viability using an in vitro cell culture model as a means of investigating the mechanism of action of low-dose intravitreal gentamicin injection.

ANIMALS STUDIED

Three adult horses with no evidence of ophthalmic or systemic disease.

PROCEDURE

Peripheral blood lymphocytes were treated with gentamicin at concentrations 37.5 μg/mL, 112.5 μg/mL, 187 μg/mL, 375 μg/mL, or 750 μg/mL then stimulated to proliferate with concanavalin A (ConA). 4',6-diamidino-2-phenylindole (DAPI) and carboxyfluoroscein succinimidyl ester (CSFE) were used as markers of cell viability and cell proliferation, respectively. Following 5-day culture, live cell counts and CSFE fluorescent intensity data were collected via automated cell count and flow cytometry. The experimental design was duplicated using preservative-free gentamicin and a proprietary brand formulation. Statistical analysis was performed using two-way ANOVA with Tukey's multiple comparison test.

RESULTS

No statistically significant comparisons in CD3+ T-lymphocyte live cell counts and geometric mean fluorescent intensity of CSFE were identified between gentamicin concentrations or formulations.

CONCLUSIONS

Gentamicin had no effect on equine peripheral blood CD3+ T-lymphocyte cell viability and proliferation in concentrations ranging from "safe" to "retinotoxic" in relation to intravitreal injection volumes. Low-dose intravitreal gentamicin may not suppress the Th1- and Th17-mediated immune response.

Pneumatic compression therapy using the EQ Press accelerates lymphatic flow in healthy equine forelimbs as determined by lymphoscintigraphy

OBJECTIVE

Limb lymphedema in horses can be debilitating and painful. Pneumatic compression therapy has shown significant benefits for people suffering from lymphedema. The objective of this study was to determine the effect of a novel, equine-specific pneumatic compression device on the lymphatic flow of healthy horse forelimbs as determined by Tc-99m sulfur colloid lymphoscintigraphy.

ANIMALS

6 healthy Thoroughbreds.

PROCEDURES

In a randomized crossover design, horses underwent bilateral forelimb lymphoscintigraphy following subcutaneous injection of Tc-99m sulfur colloid at the coronary band as untreated control or with pneumatic compression therapy using the EQ Press. Lateral, static images were obtained of the distal limb (time 0 to 60 minutes) and proximal limb (time 30 to 60 minutes) using a standard gamma camera. Lymphatic flow was determined by assigning a score to the time point at which Tc-99m sulfur colloid was first visualized at the level of the accessory carpal bone (1 to 7) in the distal limb and the cubital lymph node (1 to 4) in the proximal limb.

RESULTS

EQ Press treatment led to a significantly faster lymphatic flow of Tc-99m sulfur colloid to the predetermined anatomic locations of the accessory carpal bone (P = .002) in the distal limb and the cubital lymph node (P = .001) in the proximal limb.

CLINICAL RELEVANCE

Pneumatic compression therapy as provided by an equine-specific device encouraged lymphatic flow in healthy, nonedematous equine forelimbs. These data support further study of the EQ Press for pneumatic compression therapy in horses clinically affected by lymphedema and lymphatic drainage disorders.

Alterations to the synovial invaginations of the navicular bone are associated with pathology of both the navicular apparatus and distal interphalangeal joint when evaluated using high field MRI

Limited information exists regarding associations between distal interphalangeal joint (DIPJ) abnormalities and synovial invagination changes in the distal sesamoid (navicular) bone. This retrospective, analytical study aimed to measure specific characteristics of the synovial invaginations of the navicular bone to determine whether any single characteristic was associated with abnormalities in the DIPJ or navicular apparatus (NA) using high field MRI and a sample of 200 horses' feet. The DIPJ and NA were graded independently by three scorers. The grades were averaged, creating a global pathology score for the DIPJ, NA, and synovial invaginations. Higher global scores represented more severe pathology. The number of invaginations, depth of penetration, invagination shape, and cross-sectional area (CSA) of the largest invagination were recorded. Interobserver agreement was measured using Cohen's Kappa. Associations of global scores of the DIPJ and NA with individual invagination characteristics were assessed using linear mixed modeling. A significant relationship was found between the number of invaginations and global DIPJ score, with higher invagination numbers associated with higher DIPJ scores. For invagination depth and CSA, a significant relationship was noted with global scores of both the DIPJ and NA. Reliable relationships between the shape of synovial invaginations and global scores of DIPJ and NA were not found, likely due to poor interobserver scoring (0.305). These findings suggest that primary DIPJ disease and NA pathology should be considered when noticing alterations to navicular synovial invaginations on MRI. This contrasts traditional views that synovial invagination abnormalities are indicative solely of NA pathology.

TLR-activated mesenchymal stromal cell therapy and antibiotics to treat multi-drug resistant Staphylococcal septic arthritis in an equine model

BACKGROUND

Rapid development of antibiotic resistance necessitates advancement of novel therapeutic strategies to treat infection. Mesenchymal stromal cells (MSC) possess antimicrobial and immunomodulatory properties, mediated through antimicrobial peptide secretion and recruitment of innate immune cells including neutrophils and monocytes. TLR-3 activation of human, canine and equine MSC has been shown to enhance bacterial killing and clearance in vitro, in rodent Staphylococcal biofilm infection models and dogs with spontaneous multi-drug-resistant infections. The objective of this study was to determine if intra-articular (IA) TLR-3-activated MSC with antibiotics improved clinical parameters and reduced bacterial counts and inflammatory cytokine concentrations in synovial fluid (SF) of horses with induced septic arthritis.

METHODS

Eight horses were inoculated in one tarsocrural joint with multidrug-resistant Staphylococcus aureus (S. aureus). Bone marrow-derived MSC from three unrelated donors were activated with TLR-3 agonist polyinosinic, polycytidylic acid (pIC). Recipient horses received MSC plus vancomycin (TLR-MSC-VAN), or vancomycin (VAN) alone, on days 1, 4, 7 post-inoculation and systemic gentamicin. Pain scores, quantitative bacterial counts (SF, synovium), SF analyses, complete blood counts, cytokine concentrations (SF, plasma), imaging changes (MRI, ultrasound, radiographs), macroscopic joint scores and histologic changes were assessed. Results were reported as mean ± SEM.

RESULTS

Pain scores (d7, P=0.01, 15.2±0.2 vs. 17.9±0.5), ultrasound (d7, P=0.03, 9.0±0.6 vs. 11.8±0.5), quantitative bacterial counts (SF d7, P=0.02, 0±0 vs. 3.4±0.4; synovium P=0.003, 0.4±0.4 vs. 162.7±18.4), systemic neutrophil (d4, P=0.03, 4.6±0.6 vs. 7.8±0.6) and serum amyloid A (SAA) (d4, P=0.01, 1,106.0±659.0 vs. 2,858.8±141.3; d7, P=0.02, 761.8±746.2 vs. 2,357.3±304.3), and SF lactate (d7, P<0.0001, 5.4±0.2 vs. 15.0±0.3), SAA (endterm, P=0.01, 0.0 vs. 2,094.0±601.6), IL-6 (P=0.03, 313.0±119.2 vs. 1,328.2±208.9), and IL-18 (P=0.02, 11.1±0.5 vs. 13.3±3.8) were improved in TLR-MSC-VAN vs. VAN horses. Study limitations include the small horse sample size, short study duration, and lack of additional control groups.

CONCLUSIONS

Combined TLR-activated MSC with antibiotic therapy may be a promising approach to manage joint infections with drug resistant bacteria.

TGF-β2 enhances expression of equine bone marrow-derived mesenchymal stem cell paracrine factors with known associations to tendon healing

Background

Mesenchymal stem cells (MSCs) secrete paracrine factors and extracellular matrix proteins that contribute to their ability to support tissue healing and regeneration. Both the transcriptome and the secretome of MSCs can be altered by treating the cells with cytokines, but neither have been thoroughly investigated following treatment with the specific cytokine transforming growth factor (TGF)-β2.

Methods

RNA-sequencing and western blotting were used to compare gene and protein expression between untreated and TGF-β2-treated equine bone marrow-derived MSCs (BM-MSCs). A co-culture system was utilized to compare equine tenocyte migration during co-culture with untreated and TGF-β2-treated BM-MSCs.

Results

TGF-β2 treatment significantly upregulated gene expression of collagens, extracellular matrix molecules, and growth factors. Protein expression of collagen type I and tenascin-C was also confirmed to be upregulated in TGF-β2-treated BM-MSCs compared to untreated BM-MSCs. Both untreated and TGF-β2-treated BM-MSCs increased tenocyte migration in vitro.

Conclusions

Treating equine BM-MSCs with TGF-β2 significantly increases production of paracrine factors and extracellular matrix molecules important for tendon healing and promotes the migration of tenocytes in vitro.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03172-9.

Interleukin-1β in tendon injury enhances reparative gene and protein expression in mesenchymal stem cells

Tendon injury in the horse carries a high morbidity and monetary burden. Despite appropriate therapy, reinjury is estimated to occur in 50–65% of cases. Although intralesional mesenchymal stem cell (MSC) therapy has improved tissue architecture and reinjury rates, the mechanisms by which they promote repair are still being investigated. Additionally, reevaluating our application of MSCs in tendon injury is necessary given recent evidence that suggests MSCs exposed to inflammation (deemed MSC licensing) have an enhanced reparative effect. However, applying MSC therapy in this context is limited by the inadequate quantification of the temporal cytokine profile in tendon injury, which hinders our ability to administer MSCs into an environment that could potentiate their effect. Therefore, the objectives of this study were to define the temporal cytokine microenvironment in a surgically induced model of equine tendon injury using ultrafiltration probes and subsequently evaluate changes in MSC gene and protein expression following in vitro inflammatory licensing with cytokines of similar concentration as identified in vivo. In our in vivo surgically induced tendon injury model, IL-1β and IL-6 were the predominant pro-inflammatory cytokines present in tendon ultrafiltrate where a discrete peak in cytokine concentration occurred within 48 h following injury. Thereafter, MSCs were licensed in vitro with IL-1β and IL-6 at a concentration identified from the in vivo study; however, only IL-1β induced upregulation of multiple genes beneficial to tendon healing as identified by RNA-sequencing. Specifically, vascular development, ECM synthesis and remodeling, chemokine and growth factor function alteration, and immunomodulation and tissue reparative genes were significantly upregulated. A significant increase in the protein expression of IL-6, VEGF, and PGE2 was confirmed in IL-1β-licensed MSCs compared to naïve MSCs. This study improves our knowledge of the temporal tendon cytokine microenvironment following injury, which could be beneficial for the development and determining optimal timing of administration of regenerative therapies. Furthermore, these data support the need to further study the benefit of MSCs administered within the inflamed tendon microenvironment or exogenously licensed with IL-1β in vitro prior to treatment as licensed MSCs could enhance their therapeutic benefit in the healing tendon.

A Platelet-Rich Plasma-Derived Biologic Clears Staphylococcus aureus Biofilms While Mitigating Cartilage Degeneration and Joint Inflammation in a Clinically Relevant Large Animal Infectious Arthritis Model

The leading cause of treatment failure in Staphylococcus aureus infections is the development of biofilms. Biofilms are highly tolerant to conventional antibiotics which were developed against planktonic cells. Consequently, there is a lack of antibiofilm agents in the antibiotic development pipeline. To address this problem, we developed a platelet-rich plasma (PRP)-derived biologic, termed BIO-PLY (for the BIOactive fraction of Platelet-rich plasma LYsate) which has potent in vitro bactericidal activity against S. aureus synovial fluid free-floating biofilm aggregates. Additional in vitro studies using equine synoviocytes and chondrocytes showed that BIO-PLY protected these cells of the joint from inflammation. The goal of this study was to test BIO-PLY for in vivo efficacy using an equine model of infectious arthritis. We found that horses experimentally infected with S. aureus and subsequently treated with BIO-PLY combined with the antibiotic amikacin (AMK) had decreased bacterial concentrations within both synovial fluid and synovial tissue and exhibited lower systemic and local inflammatory scores compared to horses treated with AMK alone. Most importantly, AMK+BIO-PLY treatment reduced the loss of infection-associated cartilage proteoglycan content in articular cartilage and decreased synovial tissue fibrosis and inflammation. Our results demonstrate the in vivo efficacy of AMK+BIO-PLY and represents a new approach to restore and potentiate antimicrobial activity against synovial fluid biofilms.

Potent Activity of Ertapenem Plus Cefazolin Within Staphylococcal Biofilms: A Contributing Factor in the Treatment of Methicillin-Susceptible Staphylococcus aureus Endocarditis

Background

Besides antistaphylococcal beta-lactams and source control, there are limited validated antimicrobial salvage options in patients with prolonged methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia, including infective endocarditis (IE).

Methods

MSSA IE cases treated with ertapenem (ETP) plus cefazolin (CZ) were compared with matched IE cases treated with standard beta-lactam monotherapy. The bactericidal activity of ETP plus CZ was also compared with nafcillin (NAF), CZ, and ETP alone using an in vitro MSSA biofilm model.

Results

The median duration of bacteremia experienced by patients (n = 12) while on CZ or NAF was 4 days (range 1-16 days) compared with 1 day (range 1-3 days) for patients (n = 5) treated with ETP + CZ (P = .01, Mann-Whitney U test). Cefazolin and NAF alone or in combination did not achieve biofilm eradication at clinically relevant concentrations. However, the addition of ETP to CZ led to bactericidal eradication within biofilms at standard dosing.

Conclusions

Ertapenem reduces CZ concentrations required to eradicate MSSA biofilms to those achievable in vivo by standard dosing, translating into shorter bacteremia duration in patients with MSSA endocarditis. Larger studies are needed to investigate ETP plus CZ therapy in the treatment of biofilm-related MSSA infections such as endocarditis.

Leveraging MRI characterization of longitudinal tears of the deep digital flexor tendon in horses using machine learning

While MRI is the modality of choice for the diagnosis of longitudinal tears (LTs) of the deep digital flexor tendon (DDFT) of horses, differentiating between various grades of tears based on imaging characteristics is challenging due to overlapping imaging features. In this retrospective, exploratory, diagnostic accuracy study, a machine learning (ML) scheme was applied to link quantitative features and qualitative descriptors to leverage MRI characteristics of different grades of tearing of the DDFT of horses. A qualitative MRI characteristic scheme, combining tendon morphologic features, altered signal intensity, and synovial sheath distention, was used for LT classification with an excellent diagnostic accuracy of the high-grade tears but more limited accuracy for the detection of low-grade tears. A quantitative ML approach was followed to measure the contribution of 30 quantitative phenotypic features for characterizing and classifying tendinous tears. Among the 30 imaging features, boundary curvature represented by the standard deviation and maximum had the most significant discriminatory power (P < 0.05) between normal and abnormal tendons and could be used as an aid for classifying the different grades of LTs of DDFTs. Imaging analysis-based 3D interactive surface plot supports qualitative characterization of different grades of LTs of the DDFT through clearer visualization of the tendon in three dimensions and simple integration of two perspectives features (i.e., margin/distribution and intensity/distribution). A systematic approach combining quantitative features with qualitative analyses using ML was diagnostically beneficial in MRI characterization and in discriminating between different grades of LTs of the DDFT of horses.

Non-steroidal anti-inflammatory drugs in equine orthopaedics

Orthopaedic disorders are commonly encountered in equine veterinary medicine, and non-steroidal anti-inflammatory drugs (NSAIDs) play an important role in the management of many equine orthopaedic disorders. There are multiple NSAIDs available for use in horses, including both non-selective and selective NSAIDS, and the body of literature evaluating the efficacy of these medications, their effects on normal and inflamed musculoskeletal tissues, and their side effects is broad. This review aims to summarise the current literature on the use of NSAIDs for equine orthopaedic disorders and examines new and future avenues for the management of inflammation in equine orthopaedics.

Adeno-Associated Virus-Mediated Overexpression of Interleukin-10 Affects the Immunomodulatory Properties of Equine Bone Marrow-Derived Mesenchymal Stem Cells

Joint injury can cause posttraumatic inflammation, which if severe enough can lead to posttraumatic osteoarthritis (PTOA), a progressive and debilitating condition. Posttraumatic inflammation is characterized by an influx of T lymphocytes and upregulation of inflammatory cytokines and degradative enzymes by activated chondrocytes and synoviocytes. Intra-articular bone marrow-derived mesenchymal stem cell (BM-MSC) injection for the treatment of osteoarthritis (OA) has been of interest due to the immunomodulatory properties of these cells. Interleukin (IL)-10, a potent immunomodulatory cytokine, has also been investigated as an OA therapeutic. Therefore, the objective of this study was to evaluate the combinatorial effects of BM-MSCs and IL-10 in OA using a gene therapy approach. We hypothesized that BM-MSCs overexpressing IL-10 would have superior immunomodulatory effects leading to increased suppression of T cell proliferation and decreased production of proinflammatory cytokines, providing protection of the extracellular matrix (ECM) in a stimulated, co-culture OA model. Treatment groups included the following: untransduced BM-MSC, adeno-associated virus (AAV)-IL10-transduced BM-MSC, and AAV-null transduced BM-MSC, which were unstimulated or stimulated with IL-1β/tumor necrosis factor-α (TNF-α). T cell proliferation was significantly decreased by the presence of BM-MSCs, especially when these BM-MSCs were AAV transduced. There was no significant difference in T cell suppression when cells were cultured with AAV-IL10-transduced or AAV-null transduced BM-MSCs. AAV transduction itself was associated with decreased synthesis of IL-1β, IL-6, and TNF-α. Expression of IL-1β and MMP13 was downregulated in AAV-transduced BM-MSCs and MMP13 expression was downregulated in cartilage explants co-cultured with AAV-transduced BM-MSCs. Despite mitigation of some proinflammatory cascades, rescue of ECM loss, as determined by glycosaminoglycan quantification and histological evaluation, did not occur in either AAV-IL10-transduced or AAV-null transduced co-cultures. Although IL-10 overexpression may enhance BM-MSC-mediated T cell suppression, we did not observe significant modulation of inflammation-driven cartilage degradation in cultures containing AAV-IL10-transduced BM-MSCs. AAV transduction itself does appear to affect paracrine signaling by BM-MSCs, which warrants further investigation.

Effects of continuous passage on the immunomodulatory properties of equine bone marrow-derived mesenchymal stem cells in vitro

BACKGROUND

The immunomodulatory properties of mesenchymal stem cells (MSCs) have been studied extensively due to their increasing clinical application for tissue regeneration and repair following culture expansion. We have studied the effect of continuous passage on the immunomodulatory capacity of equine bone marrow-derived MSCs (BM-MSCs). Equine BM-MSCs were isolated and culture expanded to passage three, six, and nine (P3, P6, P9). Immunomodulatory properties of each passage were assessed using a T cell proliferation assay and cytokine synthesis following stimulation with interferon gamma (IFN-γ).

RESULTS

Equine BM-MSCs maintained their primary cell morphology and immunophenotype throughout all passages. T cell proliferation was suppressed by all passages of BM-MSCs, compared to peripheral blood mononuclear cells (PBMCs) alone. There was no significant difference in suppression of T cell proliferation between P3, P6, and P9 BM-MSCs. All passages of BM-MSCs significantly increased cytokine synthesis in response to stimulation with IFN-γ. There were no significant differences in production of interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1) or regulate on activation, normal T cell expressed and secreted (RANTES) following stimulation with IFN-γ between P3, P6, and P9 BM-MSCs. P9 BM-MSCs had significantly increased production of tumor necrosis factor alpha (TNF-α), (IL-1β), and (IL-10) compared to P3 BM-MSCs. Additionally, there was a significant increase in production of (IL-8) in P6 and P9 BM-MSCs in comparison to P3 BM-MSCs.

CONCLUSIONS

Our findings demonstrate that culture expansion affects some of the immunomodulatory properties of BM-MSCs in vitro, which may suggest that MSCs isolated from a single collection of bone marrow may be culture expanded, but only those from lower passage numbers would be ideal for clinical application.

TGF-β2 Reduces the Cell-Mediated Immunogenicity of Equine MHC-Mismatched Bone Marrow-Derived Mesenchymal Stem Cells Without Altering Immunomodulatory Properties

Allogeneic mesenchymal stem cells (MSCs) are a promising cell therapy for treating numerous diseases, but major histocompatibility complex (MHC)-mismatched MSCs can be rejected by the recipient’s immune system. Pre-treating MSCs with transforming growth factor-β2 (TGF-β2) to downregulate surface expression of MHC molecules may enhance the ability of allogeneic MSCs to evade immune responses. We used lymphocyte proliferation assays and ELISAs to analyze the immunomodulatory potential of TGF-β2-treated equine bone marrow-derived MSCs. T cell activation and cytotoxicity assays were then used to measure the in vitro cell-mediated immunogenicity. Similar to untreated MSCs, TGF-β2-treated MSCs inhibited T cell proliferation and did not stimulate MHC-mismatched T cells to proliferate. Additionally, similar quantities of prostaglandin E2 and TGF-β1 were detected in assays with untreated and TGF-β2-treated MSCs supporting that TGF-β2-treated MSCs retain their strong immunomodulatory properties in vitro. Compared to untreated MSCs, TGF-β2-treated MSCs induced less T cell activation and had reduced cell-mediated cytotoxicity in vitro. These results indicate that treating MSCs with TGF-β2 is a promising strategy to reduce the cell-mediated immunogenicity of MHC-mismatched MSCs and facilitate allogeneic MSC therapy.

Cross-matching of allogeneic mesenchymal stromal cells eliminates recipient immune targeting

Allogeneic mesenchymal stromal cells (MSCs) have been used clinically for decades, without cross-matching, on the assumption that they are immune-privileged. In the equine model, we demonstrate innate and adaptive immune responses after repeated intra-articular injection with major histocompatibility complex (MHC) mismatched allogeneic MSCs, but not MHC matched allogeneic or autologous MSCs. We document increased peri-articular edema and synovial effusion, increased synovial cytokine and chemokine concentrations, and development of donor-specific antibodies in mismatched recipients compared with recipients receiving matched allogeneic or autologous MSCs. Importantly, in matched allogeneic and autologous recipients, but not mismatched allogeneic recipients, there was increased stromal derived factor-1 along with increased MSC concentrations in synovial fluid. Until immune recognition of MSCs can be avoided, repeated clinical use of MSCs should be limited to autologous or cross-matched allogeneic MSCs. When non-cross-matched allogeneic MSCs are used in single MSC dose applications, presensitization against donor MHC should be assessed.

The AVMA's definitions of antimicrobial uses for prevention, control, and treatment of disease

Recent state and federal legislative actions and current recommendations from the World Health Organization seem to suggest that, when it comes to antimicrobial stewardship, use of antimicrobials for prevention, control, or treatment of disease can be ranked in order of appropriateness, which in turn has led, in some instances, to attempts to limit or specifically oppose the routine use of medically important antimicrobials for prevention of disease. In contrast, the AVMA Committee on Antimicrobials believes that attempts to evaluate the degree of antimicrobial stewardship on the basis of therapeutic intent are misguided and that use of antimicrobials for prevention, control, or treatment of disease may comply with the principles of antimicrobial stewardship. It is important that veterinarians and animal caretakers are clear about the reason they may be administering antimicrobials to animals in their care. Concise definitions of prevention, control, and treatment of individuals and populations are necessary to avoid confusion and to help veterinarians clearly communicate their intentions when prescribing or recommending antimicrobial use.

Platelet-rich plasma lysate displays antibiofilm properties and restores antimicrobial activity against synovial fluid biofilms in vitro

Infectious arthritis is difficult to treat in both human and veterinary clinical practice. Recent literature reports Staphylococcus aureus as well as other gram-positive and gram-negative isolates forming free-floating biofilms in both human and equine synovial fluid that are tolerant to traditional antimicrobial therapy. Using an in vitro equine model, we investigated the ability of platelet-rich plasma (PRP) formulations to combat synovial fluid biofilm aggregates. Synovial fluid was infected, and biofilm aggregates allowed to form over a 2-hour period. PRP was collected and processed into different formulations by platelet concentration, leukocyte presence, and activation or lysis. Infected synovial fluid was treated with different PRP formulations with or without aminoglycoside cotreatment. Bacterial load (colony-forming unit/mL) was determined by serial dilutions and plate counting at 8 hours posttreatment. All PRP formulations displayed antimicrobial properties; however, formulations containing higher concentrations of platelets without leukocytes had increased antimicrobial activity. Lysis of PRP and pooling of the PRP lysate (PRP-L) from multiple horses as compared to individual horses further increased antimicrobial activity. This activity was lost with the removal of the plasma component or inhibition of the proteolytic activity within the plasma. Fractionation of pooled PRP-L identified the bioactive components to be cationic and low-molecular weight (<10 kDa). Overall, PRP-L exhibited synergism with amikacin against aminoglycoside tolerant biofilm aggregates with greater activity against gram-positive bacteria. In conclusion, the use of PRP-L has the potential to augment current antimicrobial treatment regimens which could lead to a decrease in morbidity and mortality associated with infectious arthritis.

TGF-β downregulates MHC I surface expression through a Smad3-dependent mechanism

Major histocompatibility complex (MHC) expression is tightly regulated in nucleated cells to prevent unnecessary and damaging immune responses. Transforming growth factor-β (TGF-β) has previously been shown to downregulate MHC I surface expression, although this mechanism is unknown. We hypothesized that TGF-β downregulates MHC I gene expression thereby inhibiting MHC I surface expression. TGF-β1, TGF-β2, and TGF-β3 were all similarly effective at downregulating constitutive MHC I expression. Inhibition of TGF-βRII (ALK5) or Smad3 prevented downregulation of MHC I surface expression by TGF-β indicating this mechanism is through canonical TGF-β signaling. RNA-sequencing revealed that TGF-β significantly downregulated gene expression of accessory proteins necessary for stable MHC I protein expression including β2-microglobulin (B2M). qPCR confirmed that B2M expression was significantly lower in TGF-β-treated MSCs compared to untreated, while MHC I gene expression was not significantly different. However, downregulation of B2M gene expression did not occur until at least 24 hours after TGF-β treatment suggesting an intermediate step may be involved between Smad3 activation and downregulation of B2M. These results support that TGF-β regulates MHC I surface expression by downregulating gene expression of proteins associated with antigen processing and presentation through a Smad3-dependent pathway. Further investigation is needed to analyze which antigen processing and presentation genes regulated by TGF-β are the limiting factor for MHC I surface expression and how Smad3 influences expression of these genes.

5-Benzylidene-4-Oxazolidinones Are Synergistic with Antibiotics for the Treatment of Staphylococcus aureus Biofilms

The failure of frontline antibiotics in the clinic is one of the most serious threats to human health and requires a multitude of novel therapeutics and innovative approaches to treatment so as to curtail the growing crisis. In addition to traditional resistance mechanisms resulting in the lack of efficacy of many antibiotics, most chronic and recurring infections are further made tolerant to antibiotic action by the presence of biofilms. Herein, we report an expanded set of 5-benzylidene-4-oxazolidinones that are able to inhibit the formation of Staphylococcus aureus biofilms, disperse preformed biofilms, and, in combination with common antibiotics, are able to significantly reduce the bacterial load in a robust collagen-matrix model of biofilm infection.

Equine or porcine synovial fluid as a novel ex vivo model for the study of bacterial free-floating biofilms that form in human joint infections

Bacterial invasion of synovial joints, as in infectious or septic arthritis, can be difficult to treat in both veterinary and human clinical practice. Biofilms, in the form of free-floating clumps or aggregates, are involved with the pathogenesis of infectious arthritis and periprosthetic joint infection (PJI). Infection of a joint containing an orthopedic implant can additionally complicate these infections due to the presence of adherent biofilms. Because of these biofilm phenotypes, bacteria within these infected joints show increased antimicrobial tolerance even at high antibiotic concentrations. To date, animal models of PJI or infectious arthritis have been limited to small animals such as rodents or rabbits. Small animal models, however, yield limited quantities of synovial fluid making them impractical for in vitro research. Herein, we describe the use of ex vivo equine and porcine models for the study of synovial fluid induced biofilm aggregate formation and antimicrobial tolerance. We observed Staphylococcus aureus and other bacterial pathogens adapt the same biofilm aggregate phenotype with significant antimicrobial tolerance in both equine and porcine synovial fluid, analogous to human synovial fluid. We also demonstrate that enzymatic dispersal of synovial fluid aggregates restores the activity of antimicrobials. Future studies investigating the interaction of bacterial cell surface proteins with host synovial fluid proteins can be readily carried out in equine or porcine ex vivo models to identify novel drug targets for treatment of prevention of these difficult to treat infectious diseases.

Effects of acellular equine amniotic allografts on the healing of experimentally induced full-thickness distal limb wounds in horses

OBJECTIVE

To characterize the growth factors contained in equine amniotic membrane allograft (eAM; StemWrap scaffold and StemWrap+ injection) and to evaluate the effect of eAM on equine distal limb wound healing.

STUDY DESIGN

Prospective experimental controlled study.

SAMPLE POPULATION

Eight adult horses.

METHODS

Transforming growth factor (TGF)-β1, vascular endothelial growth factor (VEGF), epidermal growth factor, platelet-derived growth factor-BB, and prostaglandin E₂ (PGE₂ ) concentrations in StemWrap+ were assessed with enzyme-linked immunosorbent assay. Two full-thickness 6.25-cm² skin wounds were created on each metacarpus. On one forelimb, one wound was treated with eAM, and the other was left untreated (eAM control). On the contralateral limb, one wound was treated with a silicone dressing, and the other served as negative control. Three-dimensional images were obtained to determine wound circumference and surface area analyses at each bandage change until healed. Excessive granulation tissue was debrided once weekly for 4 weeks. Biopsy samples were taken to evaluate quality of wound healing via histologic and immunohistochemistry assays.

RESULTS

StemWrap+ contained moderate concentrations of TGF-β1 (494.10 pg/mL), VEGF (212.52 pg/mL), and PGE₂ (1811.61 pg/mL). Treatment of wounds with eAM did not affect time to healing or histologic quality of the healing compared with other groups but was associated with increased granulation tissue production early in the study, particularly on day 7.

CONCLUSION

Application of eAM resulted in increased granulation tissue production while maintaining appropriate healing of experimental wounds.

CLINICAL SIGNIFICANCE

Use of eAM is likely most beneficial for substantial wounds in which expedient production of large amounts of granulation tissue is desirable.

Subconjunctival bone marrow-derived mesenchymal stem cell therapy as a novel treatment alternative for equine immune-mediated keratitis: A case series

Equine immune-mediated keratitis (IMMK) leads to increased corneal opacity and inflammation secondary to an alteration of the local immune system. Bone marrow-derived mesenchymal stem cells (BM-MSC) have been shown to modulate the immune system by downregulating inflammation. Four horses with unilateral IMMK poorly responsive to traditional medical treatments underwent novel, autologous subconjunctival BM-MSC therapy. Bone marrow was harvested and processed as previously described for equine orthopedic disease. Horses received autologous subconjunctival BM-MSC injections approximately every 3-4 weeks for 1-5 treatments total. Horses were maintained on their current medical treatment regimen throughout the BM-MSC treatment period. Three horses had a positive response to therapy as demonstrated by an increase in corneal clarity, a decrease in neovascularization and a reduction in surface irregularity. One horse was nonresponsive to therapy. These experimental results demonstrate the safety and potential efficacy of an innovative solution for IMMK.

Oral reserpine administration in horses results in low plasma concentrations that alter platelet biology

BACKGROUND

Reserpine is a popular drug in the equine industry for long-term tranquilisation. Clinical observations revealed that blood from horses receiving oral reserpine was hypercoagulable. No studies have documented the pharmacokinetics of orally administered reserpine nor the effects of reserpine on platelets in horses.

OBJECTIVES

To evaluate the pharmacokinetics of oral reserpine in horses and the effects of clinically relevant concentrations of reserpine on platelet functionality in vitro.

STUDY DESIGN

Experimental controlled study.

METHODS

The pharmacokinetics of oral reserpine (2.5 mg/horse, once) were determined in six healthy adult horses. Plasma samples were collected and concentrations of reserpine were determined by UPLC-MS/MS. Using this data, the in vitro effects of reserpine on platelets were examined. Aggregation, adhesion and releasate assays for serotonin and thromboxane B₂ were performed on platelets exposed to varying concentrations of reserpine (0.01-10 ng/mL), aspirin (negative control) and saline (unexposed control).

RESULTS

Oral reserpine administration demonstrated low plasma concentrations with a C_max of 0.2 ± 0.06 ng/mL and a prolonged half-life of 23.6 ± 6.24 h. Simulations over a dose range of 2-8 μg/kg predicted C_max at steady state between 0.06-0.9 ng/mL. Platelets exposed to these reserpine concentrations in vitro displayed increased aggregation and adhesion compared to unexposed or aspirin-exposed platelets as well as compared to higher concentrations of reserpine. These functional changes correlated with lower concentrations of serotonin and higher concentrations of thromboxane B₂ in the platelet suspension supernatant.

MAIN LIMITATIONS

This study used a small number of horses and only in vitro platelet experiments.

CONCLUSIONS

Oral reserpine demonstrates low plasma concentrations and a prolonged half-life in horses. At these concentrations, reserpine causes significant changes in platelet function, most likely due to serotonin release and re-uptake which primes platelets for activation and thromboxane B₂ release. These findings suggest that clinicians should harvest blood for biological processing prior to the onset of reserpine administration.

Gram-negative multi-drug resistant bacteria influence survival to discharge for horses with septic synovial structures: 206 Cases (2010-2015)

Bacterial colonization of synovial structures can cause infections that are difficult to treat. Systemic and local antimicrobials and repeated joint lavages are the mainstays of therapy. However, despite aggressive treatments, infection may persist, leading to significant tissue damage or death of the patient. In order to investigate the impact of bacterial culture and antimicrobial resistance on survival to discharge, we reviewed medical records of horses admitted to the University of Pennsylvania's large animal teaching hospital from 2010-2015. Two-hundred and six cases with a definitive diagnosis of septic synovitis and a synovial fluid sample submitted for microbiological culture were included in the study. Of these horses, 48% were culture negative and 52% were positive for any bacterial growth, of which 66% were gram-positive and 28% were gram-negative aerobic organisms with 4% anaerobic and 2% fungal organisms. Overall survival to discharge from hospital was 86%. Horses that had negative growth on culture were more likely to survive until discharge (p < 0.02). Multivariable analyses revealed that the likelihood of euthanasia was significantly associated with identification of coagulase positive Staphylococcus spp. (OR 7.66, 5.46-10.74, p < 0.0001), β-hemolytic Streptococcus spp. (OR 5.18, 3.56-7.55, p < 0.0001), Enterococcus spp. (OR 18.38, 11.45-29.52, p = 0.002), Enterobacteriaceae (OR 31.37, 22.28-44.17, p < 0.0001), Pseudomonas aeruginosa (OR 9.31, 5.30-16.34, p = 0.0004) or other gram-negative species (OR 3.51, 2.07-5.94, p = 0.001). Multi-drug resistance and gram-negative bacteria species were associated with significantly decreased survival rates (OR 119.24, 70.57-201.46, p < 0.0001). In conclusion, prognosis for survival to discharge was poor for horses that were infected with gram-negative organisms, particularly those with MDR phenotypes.

Pooled Platelet-Rich Plasma Lysate Therapy Increases Synoviocyte Proliferation and Hyaluronic Acid Production While Protecting Chondrocytes From Synoviocyte-Derived Inflammatory Mediators

Platelet-rich plasma (PRP) preparations are being used with moderate success to treat osteoarthritis (OA) in humans and in veterinary species. Such preparations are hindered, however, by being autologous in nature and subject to tremendous patient and processing variability. For this reason, there has been increasing interest in the use of platelet lysate preparations instead of traditional PRP. Platelet lysate preparations are acellular, thereby reducing concerns over immunogenicity, and contain high concentrations of growth factors and cytokines. In addition, platelet lysate preparations can be stored frozen for readily available use. The purpose of this study was to evaluate the effects of a pooled allogeneic platelet-rich plasma lysate (PRP-L) preparation on equine synoviocytes and chondrocytes challenged with inflammatory mediators in-vitro to mimic the OA joint environment. Our hypothesis was that PRP-L treatment of inflamed synoviocytes would protect chondrocytes challenged with synoviocyte conditioned media by reducing synoviocyte pro-inflammatory cytokine production while increasing synoviocyte anti-inflammatory cytokine production. Synoviocytes were stimulated with either interleukin-1β (IL-1β) or lipopolysaccharide (LPS) for 24 h followed by no treatment or treatment with platelet-poor plasma lysate (PPP-L) or PRP-L for 48 h. Synoviocyte growth was evaluated at the end of the treatment period and synoviocyte conditioned media was assessed for concentrations of hyaluronic acid (HA), IL-1β, tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6). Chondrocytes were then challenged for 48 h with synoviocyte conditioned media from each stimulation and treatment group and examined for gene expression of collagen types I (COL1A1), II (COL2A1), and III (COL3A1), aggrecan (ACAN), lubricin (PRG4), and matrix metallopeptidase 3 (MMP-3) and 13 (MMP-13). Treatment of inflamed synoviocytes with PRP-L resulted in increased synoviocyte growth and increased synoviocyte HA and IL-6 production. Challenge of chondrocytes with conditioned media from PRP-L treated synoviocytes resulted in increased collagen type II and aggrecan gene expression as well as decreased MMP-13 gene expression. The results of this study support continued investigation into the use of pooled PRP-L for the treatment of osteoarthritis and warrant further in-vitro studies to discern the mechanisms of action of PRP-L.

Inflammatory licensed equine MSCs are chondroprotective and exhibit enhanced immunomodulation in an inflammatory environment

Background

Inflammatory licensed mesenchymal stem cells (MSCs) have the ability to promote functional tissue repair. This study specifically sought to understand how the recipient tissue environment reciprocally affects MSC function. Inflammatory polarized macrophages, modeling an injured tissue environment, were exposed to licensed MSCs, and the resultant effects of MSC immunomodulation and functionality of the MSC secretome on chondrocyte homeostasis were studied.

Methods

Inflammatory licensed MSCs were generated through priming with either IFN-γ or polyinosinic:polycytidylic acid (poly I:C). Macrophages were polarized to an inflammatory phenotype using IFN-γ. Licensed MSCs were co-cultured with inflammatory macrophages and immunomodulation of MSCs was assessed in a T-cell proliferation assay. MSC gene expression was analyzed for changes in immunogenicity (MHC-I, MHC-II), immunomodulation (IDO, PTGS2, NOS2, TGF-β1), cytokine (IL-6, IL-8), and chemokine (CCL2, CXCL10) expression. Macrophages were assessed for changes in cytokine (IL-6, IL-10, TNF-α, IFN-γ) and chemokine (CCL2, CXCL10) expression. Conditioned medium representing the secretome from IFN-γ or poly I:C-primed MSCs was applied to IL-1β-stimulated chondrocytes, which were analyzed for catabolic (IL-6, TNF-α, CCL2, CXCL10, MMP-13, PTGS2) and matrix synthesis (ACAN, COL2A1) genes.

Results

IFN-γ-primed MSCs had a superior ability to suppress T-cell proliferation compared to naïve MSCs, and this ability was maintained following exposure to proinflammatory macrophages. In naïve and licensed MSCs exposed to inflammatory macrophages, MHC-I and MHC-II gene expression was upregulated. The secretome from licensed MSCs was chondroprotective and downregulated inflammatory gene expression in IL-1β-stimulated chondrocytes.

Conclusions

In-vitro inflammatory licensing agents enhanced the immunomodulatory ability of MSCs exposed to inflammatory macrophages, and the resultant secretome was biologically active, protecting chondrocytes from catabolic stimulation. Use of licensing agents produced a more consistent immunomodulatory MSC population compared to exposure to inflammatory macrophages. The clinical implications of this study are that in-vitro licensing prior to therapeutic application could result in a more predictable immunomodulatory and reparative response to MSC therapy compared to in-vivo inflammatory licensing by the recipient environment.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0840-2) contains supplementary material, which is available to authorized users.

Immunoprivileged no more: measuring the immunogenicity of allogeneic adult mesenchymal stem cells

Background

Autologous and allogeneic adult mesenchymal stem/stromal cells (MSCs) are increasingly being investigated for treating a wide range of clinical diseases. Allogeneic MSCs are especially attractive due to their potential to provide immediate care at the time of tissue injury or disease diagnosis. The prevailing dogma has been that allogeneic MSCs are immune privileged, but there have been very few studies that control for matched or mismatched major histocompatibility complex (MHC) molecule expression and that examine immunogenicity in vivo. Studies that control for MHC expression have reported both cell-mediated and humoral immune responses to MHC-mismatched MSCs. The clinical implications of immune responses to MHC-mismatched MSCs are still unknown. Pre-clinical and clinical studies that document the MHC haplotype of donors and recipients and measure immune responses following MSC treatment are necessary to answer this critical question.

Conclusions

This review details what is currently known about the immunogenicity of allogeneic MSCs and suggests contemporary assays that could be utilized in future studies to appropriately identify and measure immune responses to MHC-mismatched MSCs.

The immunomodulatory function of equine MSCs is enhanced by priming through an inflammatory microenvironment or TLR3 ligand

Mesenchymal stem cells (MSCs) have the therapeutic potential to treat a variety of inflammatory and degenerative disease processes, however the effects of the tissue environment on MSCs have been overlooked. Our hypothesis was that the immunomodulatory function of MSCs would be impaired by TLR4 stimulation or exposure to inflammatory macrophages, whereas their immunosuppressive properties would be enhanced by TLR3 stimulation. MSCs were exposed to polyinosinic:polycytidylic acid (poly I:C) to stimulate TLR3 receptors or lipopolysaccharide (LPS) to stimulate TLR4 receptors. MSC1 proinflammatory phenotype in human MSCs was associated with increased IL-6 and IL-8 and MSC2 regenerative phenotype was associated with increased CCL2 and CXCL10. MSC immunomodulatory function was assessed by measuring the ability of primed MSCs to suppress mitogen-stimulated T cell proliferation. Peripheral blood monocytes were isolated using CD14 MACs positive selection, differentiated into macrophages, and polarized using interferon-gamma (IFN-γ). Polarization was confirmed by increased gene expression of TNFα, CCL2, and CXCL10. Inflammatory macrophages were co-cultured with MSCs for 6h, and the resultant MSC phenotype was analyzed as described above. Both TLR3 and TLR4 priming and co-culture of MSCs with inflammatory macrophages resulted in increased expression of IL-6, CCL2, and CXCL10 in MSCs. Both TLR3 and TLR4 priming or exposure of MSCs to inflammatory macrophages significantly (p<0.05) enhanced their immunomodulatory function, demonstrated by a decrease in T cell proliferation in the presence of poly I:C primed MSCs (11%), LPS primed MSCs (7%), or MSCs exposed to inflammatory macrophages (12%), compared to unstimulated MSCs. Additionally, MHC class II positive MSCs tended to have a greater magnitude of response to priming compared to MHC class II negative MSCs. These results suggest that MSCs can be activated by a variety of inflammatory stimuli, but the recipient injured tissue bed in chronic injuries may not contain sufficient inflammatory signals to activate MSC immunomodulatory function. Enhancement of MSCs immunomodulatory function through inflammatory priming prior to clinical application might improve the therapeutic effect of MSC treatments.

Transforming Growth Factor-β2 Downregulates Major Histocompatibility Complex (MHC) I and MHC II Surface Expression on Equine Bone Marrow-Derived Mesenchymal Stem Cells Without Altering Other Phenotypic Cell Surface Markers

Allogeneic mesenchymal stem cells (MSCs) are a promising cell source for treating musculoskeletal injuries in horses. Effective and safe allogeneic therapy may be hindered, however, by recipient immune recognition and rejection of major histocompatibility complex (MHC)-mismatched MSCs. Development of strategies to prevent immune rejection of MHC-mismatched MSCs in vivo is necessary to enhance cell survival and potentially increase the efficacy and safety of allogeneic MSC therapy. The purposes of this study were to evaluate if transforming growth factor-β2 (TGF-β2) downregulated MHC expression on equine MSCs and to determine if TGF-β2 treatment altered the phenotype of MSCs. Equine bone marrow-derived MSCs from 12 horses were treated with 1, 5, or 10 ng/ml TGF-β2 from initial isolation until MHC expression analysis. TGF-β2-treated MSCs had reduced MHC I and MHC II surface expression compared to untreated controls. TGF-β2 treatment also partially blocked IFN-γ-induced upregulation of MHC I and MHC II. Constitutive and IFN-γ-induced MHC I and MHC II expression on equine MSCs was dynamic and highly variable, and the effect of TGF-β2 was significantly dependent on the donor animal and baseline MHC expression. TGF-β2 treatment did not appear to change morphology, surface marker expression, MSC viability, or secretion of TGF-β1, but did significantly increase the number of cells obtained from culture. These results indicate that TGF-β2 treatment has promise for regulating MHC expression on MSCs to facilitate allogeneic therapy, but further work is needed to maintain MHC stability when exposed to an inflammatory stimulus.

Effect of needle diameter on the viability of equine bone marrow derived mesenchymal stem cells

OBJECTIVES

Mesenchymal stem cells (MSCs) are frequently delivered via needle injection for treatment of musculoskeletal injuries. The purpose of this study was to evaluate the effect of needle diameter on the viability of MSCs.

METHODS

Equine bone marrow-derived MSCs from 5 horses were suspended in PBS, and held at room temperature for 7 hours to mimic shipping conditions. Two replicate samples for each needle size (20, 22, 23, or 25-gauge [ga]) were aspirated into a 3 mL syringe and re-injected into the holding vial 3 times, to reproduce the resuspension of cells prior to injection in clinical cases. Cells were stained with fluorescein diacetate and propidium iodide to measure viability. Flow cytometry (FC) was performed to compare cell debris and intact cells between groups.

RESULTS

MSC viability was higher when cells were passed through a 20-ga rather than a 25-ga needle. Cell suspensions passed through a 20-ga needle contained a larger percentage of intact cells, compared to 25-ga samples. The percentage of debris present in cell suspensions tended to increase with decreasing needle diameter. Neither horse nor passage had a significant effect on viability.

CONCLUSIONS

Cell damage is more likely when MSCs are passed through 25-ga rather than 20-ga needles.

CLINICAL RELEVANCE

Use of needles larger than 25-ga is recommended to maintain the viability of MSCs injected in horses.

Allogeneic major histocompatibility complex-mismatched equine bone marrow-derived mesenchymal stem cells are targeted for death by cytotoxic anti-major histocompatibility complex antibodies

Background

Allogeneic mesenchymal stem cells (MSCs) are a promising cell source for treating musculoskeletal injuries in horses. Controversy exists, however, over whether major histocompatibility complex (MHC)‐mismatched MSCs are recognised by the recipient immune system and targeted for death by a cytotoxic antibody response.

Objectives

To determine if cytotoxic anti‐MHC antibodies generated in vivo following MHC‐mismatched MSC injections are capable of initiating complement‐dependent cytotoxicity of MSCs.

Study design

Experimental controlled study.

Methods

Antisera previously collected at Days 0, 7, 14 and 21 post‐injection from 4 horses injected with donor MHC‐mismatched equine leucocyte antigen (ELA)‐A2 haplotype MSCs and one control horse injected with donor MHC‐matched ELA‐A2 MSCs were utilised in this study. Antisera were incubated with ELA‐A2 MSCs before adding complement in microcytotoxicity assays and cell death was analysed via eosin dye exclusion. ELA‐A2 peripheral blood leucocytes (PBLs) were used in the assays as a positive control.

Results

Antisera from all 4 horses injected with MHC‐mismatched MSCs contained antibodies that caused the death of ELA‐A2 haplotype MSCs in the microcytotoxicity assays. In 2 of the 4 horses, antibodies were present as early as Day 7 post‐injection. MSC death was consistently equivalent to that of ELA‐A2 haplotype PBL death at all time points and antisera dilutions. Antisera from the control horse that was injected with MHC‐matched MSCs did not contain cytotoxic ELA‐A2 antibodies at any of the time points examined.

Main limitations

This study examined MSC death in vitro only and utilized antisera from a small number of horses.

Conclusions

The cytotoxic antibody response induced in recipient horses following injection with donor MHC‐mismatched MSCs is capable of killing donor MSCs in vitro. These results suggest that the use of allogeneic MHC‐mismatched MSCs must be cautioned against, not only for potential adverse events, but also for reduced therapeutic efficacy due to targeted MSC death.

TGF-β2 decreases surface expression of MHC I and MHC II on equine bone marrow-derived mesenchymal stromal cells

Allogeneic bone marrow-derived mesenchymal stromal cells (MSCs) are a promising cell source for treatment of inflammatory diseases, but elicit immune responses in vivo due to recipient recognition of mismatched Major Histocompatibility Complex (MHC) molecules. The purposes of this study were to evaluate the effectiveness of TGF-β2 in decreasing and stabilizing MHC expression on equine bone marrow-derived MSCs before and after IFN-γ stimulation. FACS analysis showed that MSCs treated with 1, 5, or 10 ng/ml of TGF-β2 had significantly reduced MHC I expression. MHC I expression levels on TGF-β2-treated MSCs were also quantified and determined to be similar to fetal fibroblasts. MHC II expression in two positive animals was greatly reduced compared to untreated MSCs. MSCs pre-treated and continuously treated with 1 ng/ml TGF-β2 had significantly lower MHC I expression following stimulation with IFN-γ for 72 hours compared with untreated. Continuously treated MSCs that were baseline positive for MHC II had significantly lower MHC II expression following IFN-γ stimulation, but there was no significant difference in MHC II expression between TGF-β2-treated and untreated MHC II-negative MSCs after IFN-γ stimulation. These results indicate TGF-β2 treatment has significant promise for reducing recipient immune recognition of MHC-mismatched molecules on allogeneic MSCs, but further work is needed to maintain MHC expression stability.

Equine allogeneic bone marrow-derived mesenchymal stromal cells elicit antibody responses in vivo

Introduction

This study tested the hypothesis that Major Histocompatibility Complex (MHC) incompatible equine mesenchymal stromal cells (MSCs) would induce cytotoxic antibodies to donor MHC antigens in recipient horses after intradermal injection. No studies to date have explored recipient antibody responses to allogeneic donor MSC transplantation in the horse. This information is critical because the horse is a valuable species for assessing the safety and efficacy of MSC treatment prior to human clinical application.

Methods

Six MHC heterozygote horses were identified as non-ELA-A2 haplotype by microsatellite typing and used as allogeneic MHC-mismatched MSC recipients. MHC homozygote horses of known ELA-A2 haplotype were used as MSC and peripheral blood leukocyte (PBL) donors. One MHC homozygote horse of the ELA-A2 haplotype was the recipient of ELA-A2 donor MSCs as an MHC-matched control. Donor MSCs, which were previously isolated and immunophenotyped, were thawed and culture expanded to achieve between 30x10⁶ and 50x10⁶ cells for intradermal injection into the recipient’s neck. Recipient serum was collected and tested for the presence of anti-donor antibodies prior to MSC injection and every 7 days after MSC injection for the duration of the 8-week study using the standard two-stage lymphocyte microcytotoxicity dye-exclusion test. In addition to anti-ELA-A2 antibodies, recipient serum was examined for the presence of cross-reactive antibodies including anti-ELA-A3 and anti-RBC antibodies.

Results

All MHC-mismatched recipient horses produced anti-ELA-A2 antibodies following injection of ELA-A2 MSCs and developed a wheal at the injection site that persisted for the duration of the experiment. Anti-ELA-A2 antibody responses were varied both in terms of strength and timing. Four recipient horses had high-titered anti-ELA-A2 antibody responses resulting in greater than 80% donor PBL death in the microcytotoxicity assays and one of these horses also developed antibodies that cross-reacted when tested on lymphocyte targets from a horse with an unrelated MHC type.

Conclusions

Allogeneic MSCs are capable of eliciting antibody responses in vivo that can be strong and also cross-reactive with MHC types other than that of the donor. Such responses could limit the effectiveness of repeated allogeneic MSC use in a single horse, and could also result in untoward inflammatory responses in recipients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0053-x) contains supplementary material, which is available to authorized users.

Navigational ultrasound imaging: A novel imaging tool for aiding interventional therapies of equine musculoskeletal injuries

REASONS FOR PERFORMING STUDY

Navigational ultrasound imaging, also known as fusion imaging, is a novel technology that allows real-time ultrasound imaging to be correlated with a previously acquired computed tomography (CT) or magnetic resonance imaging (MRI) study. It has been used in man to aid interventional therapies and has been shown to be valuable for sampling and assessing lesions diagnosed with MRI or CT that are equivocal on ultrasonography. To date, there are no reports of the use of this modality in veterinary medicine.

OBJECTIVES

To assess whether navigational ultrasound imaging can be used to assist commonly performed interventional therapies for the treatment of equine musculoskeletal injuries diagnosed with MRI and determine the appropriateness of regional anatomical landmarks as registration sites.

STUDY DESIGN

Retrospective, descriptive clinical study.

METHODS

Horses with musculoskeletal injuries of the distal limb diagnosed with MRI scheduled for ultrasound-guided interventional therapies were evaluated (n = 17 horses with a total of 29 lesions). Anatomical landmarks used for image registration for the navigational procedure were documented. Accuracy of lesion location and success of the procedure were assessed subjectively and described using a grading scale.

RESULTS

All procedures were accurately registered using regional anatomical landmarks and considered successful based on our criteria. Anatomical landmarks were described for each lesion type. The addition of navigational imaging was considered to greatly aid the procedures in 59% of cases and added information to the remainder of the procedures. The technique was considered to improve the precision of these interventional procedures.

CONCLUSIONS

Navigational ultrasound imaging is a complementary imaging modality that can be used for the treatment of equine soft tissue musculoskeletal injuries diagnosed with MRI.