Martin A. Vidal

Equine bone marrow-derived mesenchymal stromal cells (MSCs) and adipose tissue-derived stromal cells (ASCs) were compared for frequency within their respective tissues, cell doubling characteristics and differentiation multipotential in culture based on histochemical staining and compositional analysis. Equine MSCs and ASCs from young adult horses were harvested and isolated from sternal bone marrow and supragluteal subcutaneous adipose tissue, respectively, and grown up to passage 10 (P10) to determine cell doubling characteristics. Limit dilution assays were performed on primary and passaged (P2, P4) MSCs and ASCs to determine the frequency of colony forming units with a fibroblastic phenotype (CFU-F), and the frequency of MSC differentiation into adipocytes (CFU-Ad) and osteoblasts (CFU-Ob). Pellet cultures of MSCs and ASCs at P2 were performed in chondrogenic media with or without transforming growth factor (TGF-â3) and bone morphogenic protein (BMP-6). Collagen type II expression, glycosaminoglycan and DNA content and pellet size were measured. Primary MSCs doubled more slowly than subsequent MSC passages (DT = 4.9 ± 1.6 days compared to 1.4 ± 0.22 days). Doubling time of ASCs (2.1 ± 0.9 days) was significantly slower than that of MSCs. Primary MSC frequency was 1 in 4,224 ± 3,265 nucleated BM cells while the frequency of ASC was 1 in 2.3 ± 0.4 nucleated stromal vascular fraction cells. Primary and subcultured MSCs showed robust adipogenic and osteogenic differentiation potential. MSC pellet cultures developed collagen type II expression by Day 7 and hyaline matrix by Day 14. ASC pellets only exhibited mild matrix or collagen formation under electron microscopic examination but showed no immunohistochemical expression of collagen type II. MSC pellets supplemented with growth factors were larger (p <0.0033) and showed significant increases in GAG concentration by Day 14 compared with all other pellets of both cell types (P<.0001). The frequency, in vitro growth rate, and adipogenic and osteogenic differentiation potential of young adult horses are similar to those documented for MSCs of other species, whereas in vitro growth rate of ASCs differs from human ASCs. MSCs show earlier osteogenesis compared with ASCs and more robust chondrogenesis in the presence or absence of human recombinant TGFâ3 and BMP6.

Summary: Reasons for performing study: Intra‐arterial (i.a.) and intravenous (i.v.) regional limb perfusions ( RLP ) through the median artery and cephalic vein, respectively, have been previously investigated for administration of mesenchymal stem cells ( MSCs ) to the equine distal limb. Limitations due to thrombosis of the arteries after i.a. RLP and poor distribution of MSCs to the foot with i.v. RLP were observed. These techniques need to be modified for clinical use. Objectives: Evaluate the distribution, uptake and persistence of radiolabelled MSCs after i.a. injection through the median artery without a tourniquet and after i.v. RLP through the lateral palmar digital vein. Study design: In vivo experimental study. Methods: ^99m Tc ‐ HMPAO ‐labelled MSCs were injected through the median artery of one limb and the lateral palmar digital vein of the other limb of 6 horses under general anaesthesia. No tourniquet was used for the i.a. injection. A pneumatic tourniquet was placed on the metacarpus for i.v. injection. Scintigraphic images were obtained up to 24 h after injection. Results: Intra‐arterial injection resulted in MSCs retention within the limb despite the absence of a tourniquet and no thrombosis was observed. Both i.a. injection and i.v. RLP led to distribution of MSCs to the foot. The i.a. injection resulted in a more homogeneous distribution. The MSC uptake was higher with i.v. RLP at the initial timepoints, but no significant difference was present at 24 h. Conclusions: Both i.a. injection through the median artery without a tourniquet and i.v. RLP performed through the lateral palmar digital vein under general anaesthesia are safe and reliable methods for administration of MSCs to the equine foot. The i.a. technique is preferred owing to the better distribution, but is technically more challenging. The feasibility of performing these techniques on standing horses remains to be investigated.

The use of triamcinolone acetonide (TA) in performance horses necessitates establishing appropriate withdrawal times prior to performance. To describe the plasma pharmacokinetics of TA and time-related urine and synovial fluid concentrations following i.m. and intra-articular administration to exercised Thoroughbred horses. Block design. Twelve racing fit adult Thoroughbred horses received a single i.m. administration of TA (0.1 mg/kg bwt). After an appropriate washout period, the same horses then received a single intra-articular TA administration (9 mg) into the right antebrachiocarpal joint. Blood, urine and synovial fluid samples were collected prior to, and at various times, up to 60 days post drug administration and analysed using liquid chromatography-mass spectrometry. Plasma data were analysed using noncompartmental analysis. Maximum measured plasma TA concentrations were 0.996 ± 0.391 at 13.2 h and 1.27 ± 0.278 ng/ml at 6.5 h for i.m. and intra-articular administration, respectively. The plasma terminal elimination half-life was 11.4 ± 6.53 and 0.78 ± 1.00 days for i.m. and intra-articular administration, respectively. Following i.m. administration, TA was below the limit of detection (LOD) by Days 52 and 60 in plasma and urine, respectively. Following intra-articular administration TA was undetectable by Day 7 in plasma and Day 8 in urine. Triamcinolone acetonide was also undetectable in any of the joints sampled following i.m. administration and remained above the limit of quantitation (LOQ) for 21 days following intra-articular administration. This study extends previous studies describing the pharmacokinetics of TA following i.m. and intra-articular administration to the horse and suggests that plasma and urine concentrations are not a good indicator of synovial fluid concentrations. Furthermore, results of this study supports an extended withdrawal time for TA given i.m.

Summary: Reasons for performing study: Intralesional (i.l.) injection is currently the most commonly used technique for stem cell therapy in equine tendon injury. A comparison of different techniques of injection of mesenchymal stem cells for the treatment of tendon lesions is required. Objectives: We hypothesised that vascular perfusion of the equine distal limb with mesenchymal stem cells ( MSC s) would result in preferential distribution of MSC s to acute tendon injuries. Study design: In vivo experimental study. Methods: Lesions were surgically induced in forelimb superficial digital flexor tendons of 8 horses. Three or 10 days after lesion induction, technetium‐99 hexamethyl propylene amine oxime‐labelled MSC s were injected via i.v. or intra‐arterial (i.a.) regional limb perfusion ( RLP ) at the level of the distal antebrachium and compared to i.l. injection. Mesenchymal stem cell persistence and distribution within the forelimb and tendon lesions was assessed with scintigraphy for 24 h. Results: Lesion uptake was higher with i.l. injection than with RLP , but MSC persistence decreased similarly over time in all 3 techniques. Intra‐arterial RLP resulted in a better distribution of MSC s and a higher uptake at the lesion site than i.v. RLP . Limbs perfused i.a. on Day 10 showed greater accumulation of MSC s in the lesion than limbs perfused on Day 3. Arterial thrombosis occurred in 50% of the i.v. RLP limbs and in 100% of the i.a. RLP limbs, which led to clinical complications in one horse. Conclusions and potential relevance: Compared with i.l. injection, RLP results in lower uptake but similar persistence of MSC s at the site of tendon lesions. A time dependent accumulation of MSC s was identified with i.a. RLP . The i.a. RLP appears more advantageous than the i.v. RLP in terms of distribution and uptake. However, the described i.a. technique produced arterial thrombosis and thus cannot currently be recommended for clinical use. The S ummary is available in C hinese – see S upporting information.

Objective—To evaluate use of a diode laser to induce tendinopathy in the superficial digital flexor tendon (SDFT) of horses. Animals—4 equine cadavers and 5 adult horses. Procedures—Cadaveric SDFT samples were exposed to a diode laser at various energy settings to determine an appropriate energy for use in in vivo experiments; lesion size was assessed histologically. In vivo experiments involved laser energy induction of lesions in the SDFT (2 preliminary horses [0, 25, 75, and 87.5 J] and 3 study horses [0 and 125 J]) and assessment of lesions. Study duration was 21 days, and lesions were assessed clinically and via ultrasonography, MRI, and histologic evaluation. Results—Lesion induction in cadaveric tissues resulted in a spherical cavitated core with surrounding tissue coagulation. Lesion size had a linear relationship (R² = 0.9) with the energy administered. Size of in vivo lesions in preliminary horses indicated that larger lesions were required. In study horses, lesions induced with 125 J were ultrasonographically and histologically larger than were control lesions. At proximal and distal locations, pooled (preliminary and study horses) ultrasonographically assessed lesions were discrete and variable in size (mean ± SEM lesion percentage for control lesions, 8.5 ± 3%; for laser lesions, 12.2 ± 1.7%). Ultrasonography and MRI measurements were associated (R² > 0.84) with cross-sectional area measurements. Conclusions and Clinical Relevance—In vivo diode laser–induced lesions did not reflect cadaveric lesions in repeatable size. Further research is required before diode lasers can reliably be used for inducing tendinopathy.

Magic angle magnetic resonance (MR) imaging consists of imaging tendons at 55° to the magnetic field. In people, magic angle MR imaging is valuable for detection of chronic tendon lesions and allows calculation of tendon T1 values. Increased T1 values occur in people with chronic tendinopathy. The T1 values of normal equine tendons have been reported but there are no available data for abnormal equine tendons. Twelve limbs were studied. Two limbs had diode laser tendon lesions induced postmortem, four limbs had diode laser tendon lesions induced in vivo and six limbs had naturally occurring tendon lesions. The limbs were imaged at 1.5 T using both conventional MR imaging and magic angle MR imaging. The post‐mortem laser induced lesions were identified only with magic angle MR imaging. The in vivo induced lesions and naturally occurring lesions were identified with both techniques but had a different appearance with the two imaging techniques. Magic angle imaging was helpful at identifying lesions that were hypointense on conventional imaging. Increased T1 values were observed in all abnormal tendons and in several tendons with a subjectively normal MR appearance. The increased T1 value may reflect diffuse changes in the biochemical composition of tendons. Magic angle imaging has potential as a useful noninvasive tool to assess the changes of the extracellular tendon matrix using T1 values.

Reasons for performing study: Mesenchymal stem cells (MSCs) are commonly injected intralesionally for treatment of soft tissue injuries in the horse. Alternative routes of administration would be beneficial for treatment of lesions that cannot be accessed directly or to limit needle-induced iatrogenic damage to the surrounding tissue. Objectives: The purpose of our study was to evaluate MSC distribution after intra-arterial (IA) and intravenous (IV) regional limb perfusions (RLP) using scintigraphy. We hypothesised that MSCs would persist in the distal limb after tourniquet removal and that both techniques would lead to diffuse MSC distribution. Methods: Six horses were used in the study. MSCs were labelled with hexamethyl propylene amine oxime (HMPAO) and technetium-99m. RLP was performed through the median artery of one forelimb and the cephalic vein of the opposite limb under general anaesthesia. The tourniquet was left in place for 45 min. Scintigraphic images were obtained at 0, 45, 75 min, 6 h and 24 h post injection. Results: Distribution of labelled MSCs through the entire distal limb was achieved with all 6 IA RLP, but 3 out of 6 IV RLP showed poor or absent uptake distal to the metacarpus. Mesenchymal stem cell persistence was 39% (30–60%) and 28% (14–50%) (median [minimum–maximum]) at 6 h for IA and IV RLP, respectively. Severe arterial thrombosis occurred in one horse after IA RLP. Conclusions: Both IA and IV RLP of the distal limb result in MSC persistence in perfused tissues. The IA perfusion resulted in more reliable cell distribution to the pastern and foot area. Potential relevance: Regional limb perfusion of MSCs might be used in cases where intralesional injection is not possible or in order to avoid iatrogenic needle damage. Further work is needed to assess the safety of IA RLP before its clinical use.