Relationship between the ultrasonographic findings of suspected superficial digital flexor tendon injury and the prevalence of subsequent severe superficial digital flexor tendon injuries in Thoroughbred horses: a retrospective study

The onset of severe injury to the superficial digital flexor tendon (SDFT) is extremely difficult to predict from slight changes in ultrasonographic findings in cases with no apparent clinical signs. This study investigated the relationship between an increased cross-sectional area (CSA) or edema in the subcutaneous tissue around the tendon and the subsequent onset of severe SDFT injury in Thoroughbred racehorses. Horses were classified into three groups based on ultrasound diagnosis (USD) findings: Group A included cases with enlarged tendons; Group B included cases with tendons of normal size but with prominent edema in the peritendinous tissue; and Group C (control group) included cases with no abnormal USD findings. The incidence of subsequent severe tendon injury was significantly higher in the horses in Groups A (25.7%, 28/101) and B (28.3%, 65/212) than in those in Group C (4.9%, 2/41). There were no significant differences in the median period and the median number of races from the first examination to the subsequent tendon injury between Groups A (140 days, 1 race) and B (120 days, 1 race). The results of this study revealed that horses with increased CSA and peritendinous edema are likely to suffer a subsequent severe tendon injury. Also, these two USD findings, i.e., increased CSA and peritendinous edema, indicate the risk of onset of severe SDFT injury.

Detection and longitudinal distribution of GW1516 and its metabolites in equine hair for doping control using liquid chromatography/high-resolution mass spectrometry

RATIONALE

GW1516 is a peroxisome proliferator-activated receptor-δ (PPAR-δ) agonist that is banned in horseracing and equestrian sports. Long-term detection and longitudinal distribution of GW1516 in the mane of a horse are reported for the first time and this hair analysis could prolong the detection window of GW1516 for doping control.

METHODS

Mane hairs were divided into three segments (0-7, 7-15, and >15 cm from the cut end) and completely pulverized and homogenized for analysis. The pulverized hair samples were extracted with methanol followed by further purification and the extracts were analyzed by liquid chromatography/electrospray ionization high-resolution mass spectrometry (LC/ESI-HRMS) using a Q-Exactive instrument. This method was successfully validated and applied to post-administration samples to confirm the presence of GW1516 and its metabolites and estimate the uptake amounts of GW1516.

RESULTS

After administration of 150 mg of GW1516 to a thoroughbred mare, GW1516 was detected in one of two segments of all mane hairs, and four metabolites, namely GW1516 sulfoxide, GW1516 sulfone, 5-(hydroxymethyl)-4-methyl-2-(4-trifluoromethylphenyl)thiazole (HMTT), and 4-methyl-2-[4-(trifluoromethyl)phenyl]-1,3-thiazole-5-carboxylic acid (MTTC), were also identified. The longitudinal distribution analysis results showed that the maximum uptake of GW1516 into hair (approximately 0.05 pg/mg) was observed at around 13 weeks post-administration and GW1516 could be detected and confirmed up to 6 months post-administration.

CONCLUSIONS

The parent drug GW1516 was identified as the most appropriate monitoring target in equine hair for controlling its misuse in horses. The use of hair analysis could extend the detection time of GW1516 to at least 6 months after the administration of 150 mg of GW1516 to a thoroughbred mare.

Metabolic study of GW1516 in equine urine using liquid chromatography/electrospray ionization Q-Exactive high-resolution mass spectrometry for doping control

RATIONALE

The use of GW1516, a peroxisome proliferator-activated receptor δ (PPAR δ) agonist, is strictly prohibited in both horseracing and equestrian competitions. However, little is known about its metabolic fate in horses. To the best of our knowledge, this is the first reported metabolic study of GW1516 in equine urine.

METHODS

Urine samples obtained from a thoroughbred after nasoesophageal administration with GW1516 were protein-precipitated and the supernatants were subsequently analyzed by liquid chromatography/electrospray ionization high-resolution mass spectrometry (LC/ESI-HRMS) with a Q-Exactive mass spectrometer. Monoisotopic ions of GW1516 and its metabolites were monitored from the full-scan mass spectral data of pre- and post-administration samples. A quantification method was developed and validated to establish the excretion profiles of GW1516, its sulfoxide, and its sulfone in equine urine.

RESULTS

GW1516 and its nine metabolites [including GW1516 sulfoxide, GW1516 sulfone, 5-(hydroxymethyl)-4-methyl-2-(4-trifluoromethylphenyl)thiazole (HMTT), methyl 4-methyl-2-[4-(trifluoromethyl)phenyl]-1,3-thiazole-5-carboxylate (MMTC), 4-methyl-2-[4-(trifluoromethyl)phenyl]-1,3-thiazole-5-carboxylic acid (MTTC), and M1 to M4] were detected in post-administration urine samples. GW1516 sulfoxide and GW1516 sulfone showed the longest detection times in post-administration urine samples and were therefore recommended as potential screening targets for doping control purposes. Quantitative analysis was also conducted to establish the excretion profiles of GW1516 sulfoxide and GW1516 sulfone in urine.

CONCLUSIONS

For the purposes of doping control of GW1516, the GW1516 sulfoxide and GW1516 sulfone metabolites are recommended as the target analytes to be monitored in equine urine due to their high specificities, long detection times (1 and 4 weeks, respectively), and the ready availability of their reference materials.

Rational dosage regimens for cephalothin and cefazolin using pharmacokinetics and pharmacodynamics analysis in healthy horses

BACKGROUND

First-generation cephalosporins have good activity against gram-positive bacteria and are extensively used in horses. There are few reports of pharmacokinetics and pharmacodynamics (PK/PD) analysis of cephalosporins in horses.

OBJECTIVE

To optimise the dosages of the two first-generation cephalosporins cephalothin (CET) and cefazolin (CEZ) in horses using PK/PD concepts.

STUDY DESIGN

Experimental study with single administration.

METHODS

Drug plasma concentrations following a single intravenous (i.v.) administration of 22 mg/kg bodyweight (bwt) CET in 12 horses and of 10 mg/kg bwt CEZ in six horses were measured using LC-MS/MS. Data were modelled using a nonlinear mixed effect modelling followed by Monte Carlo simulations. Minimum inhibitory concentrations (MICs) against Streptococcus zooepidemicus and Staphylococcus aureus isolated from horses were determined by the microbroth dilution method.

RESULTS

The percentages of CET and CEZ binding to serum proteins were 19.9% ± 8.4% and 15.2% ± 8.5% respectively. For both CET and CEZ, the MIC₉₀ against S. zooepidemicus was 0.12 mg/L and against S. aureus was 0.5 mg/L. For CET, to achieve a probability of target attainment (PTA) of 90% for a PK/PD target of a free serum plasma concentration exceeding the MIC₉₀ for 40% of the dosing interval, an empirical CET dosage regimen of 22 mg/kg bwt q8h and 22 mg/kg bwt q4h i.v. administration were required for S. zooepidemicus and S. aureus respectively. For CEZ, the corresponding dosage regimens were 10 mg/kg bwt q12h and 10 mg/kg bwt q8h.

MAIN LIMITATIONS

Small sample size only in healthy horses.

CONCLUSIONS

For CET, more frequent administration than that currently recommended (22 mg/kg bwt q6-12h) is required to empirically control S. aureus infection in horses. For CEZ, less frequent administration compared to the dosage regimen currently proposed (10-22 mg/kg bwt q6h) could control S. zooepidemicus and S. aureus infections in horses.

Optimal double-spin method for maximizing the concentration of platelets in equine platelet-rich plasma

This study optimized the double-spin conditions for preparing equine platelet-rich plasma (PRP): leukocyte-rich PRP (L-PRP) and leukocyte-poor PRP (P-PRP). Whole blood samples were centrifuged at various double-spin conditions. Both L-PRP and P-PRP were prepared at each stage, and complete blood counts and growth factor concentrations were compared. Samples centrifuged at 160 × 900 g, 160 × 2,000 g, and 400 × 2,000 g exhibited the highest platelet counts. P-PRP had significantly lower leukocyte and erythrocyte contents than L-PRP, especially at 400 × 2,000 g. No significant differences were observed in growth factor concentrations. Our data suggest that optimum L-PRP preparation should include centrifugation under the aforementioned conditions, whereas centrifugation at 400 × 2,000 g is optimal for P-PRP.

Doping control analysis of GW1516 in equine plasma using liquid chromatography/electrospray ionization Q-Exactive high-resolution mass spectrometry

RATIONALE

GW1516 is a peroxisome proliferator-activated receptor-δ agonist in the class of hormones and metabolic modulators. The use of GW1516 is banned in both horseracing and equestrian competitions. To the best of our knowledge, this is the first metabolic study of GW1516 in horses.

METHODS

After protein precipitation of pre- and post-administration plasma GW1516 samples, the supernatants were analyzed using liquid chromatography/electrospray ionization Q-Exactive high-resolution mass spectrometry to detect GW1516 and its metabolites. Monoisotopic ions of GW1516 and its metabolites were monitored from the full-scan mass spectral data of pre- and post-administration samples. Quantification methods were developed and validated to establish the elimination profiles of GW1516, its sulfoxide, and its sulfone in equine plasma.

RESULTS

GW1516 and its four metabolites GW1516 sulfoxide, GW1516 sulfone, 5-(hydroxymethyl)-4-methyl-2-(4-trifluoromethylphenyl)thiazole (HMTT), and M1 were detected in post-administration plasma samples. GW1516 sulfoxide, GW1516 sulfone, and HMTT were identified by comparison with their respective reference standards whereas M1 was tentatively identified as 4-methyl-2-[4-(trifluoromethyl)phenyl]-1,3-thiazole-5-carboxylic acid by mass spectral interpretation. GW1516 had the longest detection time in post-administration plasma. The elimination profiles of GW1516, its sulfoxide, and its sulfone in plasma were established.

CONCLUSIONS

For the purpose of doping control, GW1516 is recommended as the target analyte to be monitored in equine plasma due to its long detection time (around 1 week) and the ready availability of its reference material.

Pharmacokinetics and pharmacodynamics of olopatadine following administration via nasogastric tube to healthy horses

OBJECTIVE

To investigate the pharmacokinetics and antihistaminic effects (pharmacodynamics) of olopatadine in a small population of healthy horses after administration via nasogastric tube.

ANIMALS

4 healthy adult Thoroughbreds.

PROCEDURES

Olopatadine (0.1 mg/kg, once) was administered via nasogastric tube. Blood samples were collected at predetermined time points for pharmacokinetic analyses of the drug in plasma. Olopatadine effects were investigated by measurement of cutaneous wheals induced by ID histamine injection (0.1 mL [10 μg]/injection) at predetermined time points. Inhibition effect ratios were calculated on the basis of measured wheal size (area) after versus before olopatadine administration.

RESULTS

Mean ± SD maximum plasma olopatadine concentration was 48.8 ± 11.0 ng/mL approximately 1.5 hours after administration. Median terminal half-life was 6.11 hours. Mean ± SD maximal effect was 88.2 ± 4.9% inhibition approximately 3.5 hours after drug delivery, and the inhibition effect remained > 80% for 12.5 hours after treatment. No signs of adverse clinical effects were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested olopatadine may have a strong, long-term inhibitory effect against histamine-induced wheals in the skin of horses. Clinical research with a larger number of horses is warranted.

Does the injection of platelet-rich plasma induce changes in the gene expression and morphology of intact Thoroughbred skeletal muscle?

Platelet-rich plasma (PRP) therapy is promising for treating skeletal muscle injuries in human athletes by promoting muscle regeneration. It might also be useful for treating muscle injuries in equine athletes. In the present study, muscle regeneration induced by injection of PRP into intact muscle of Thoroughbred was investigated. Autologous PRP and saline were injected twice into intact left and right gluteus medius muscles of seven clinically healthy Thoroughbreds. Muscle samples were collected from the injection sites by needle biopsy at 2 and 7 days after PRP injection. Immunohistochemical staining to identify the types of myosin heavy chains (MHCs) and satellite cells was performed to compare morphological changes among intact (pre-injection), saline-, and PRP-injected muscles. The expression of marker genes related to muscle regeneration (MHC-I, MHC-II, and embryonic MHC [MHC-e]), satellite cell activity (CK, Pax7, MyoD, and myogenin), and proinflammatory and promyogenic cytokines (IL-6, IGF-1, and HGF) was analyzed and compared between saline- and PRP-injected muscles. There were no obvious morphological differences among the three treatments. There were no significant differences in gene expression associated with satellite cell activity between saline and PRP injection at 7 days after injection. MHC genes showed significantly higher expression levels with PRP than with saline, including MHC-e at 2 days and MHC-I at 7 days after injection. It is suggested that injection of PRP into intact skeletal muscle does not induce specific morphological changes, but upregulate the expression of genes related to muscle regeneration.

The use of sonoelastography to assess the recovery of stiffness after equine superficial digital flexor tendon injuries: A preliminary prospective longitudinal study of the healing process

BACKGROUND

The objective assessment of the mechanical properties of the superficial digital flexor tendon (SDFT) could provide useful information for the rehabilitation of horses with SDFT injuries. Assessment of strain ratio (the strain of a standard reference divided by that of lesions) is a quantitative method in sonoelastography for evaluating tissue stiffness in vivo. As yet, no longitudinal studies have used strain ratio to evaluate the progression of stiffness in SDFT injuries.

OBJECTIVES

To test the hypothesis that strain ratio can evaluate the recovery of stiffness during the healing of SDFT injuries.

STUDY DESIGN

Prospective and longitudinal study with observer-blinded evaluation.

METHODS

Ultrasonography, including sonoelastography, was performed in seven Thoroughbred horses with naturally occurring SDFT injuries at five time points: within 20 days of the injury, and at 2, 3, 6 and 9 months after the injury. Blinded sonoelastographic images were independently evaluated by two veterinarians to assess interobserver agreement. The recovery of stiffness and echogenicity in lesions were evaluated using the strain ratio and grey-scale ratio (echogenicity of lesions divided by that of the surrounding area), respectively.

RESULTS

Interobserver agreement was assessed as 'almost perfect'. Strain ratios were significantly higher at 9 months after injury than at the other time points (all P<0.05). Strain ratios at 6 months after injury were significantly higher than those at earlier time points (P<0.05). Grey-scale ratios within 20 days of injury were significantly lower than those at the other time points (all P<0.05).

MAIN LIMITATIONS

Validations of SDFT status were evaluated only by recovery of the echogenicity in lesions and not by histopathological examination.

CONCLUSIONS

Although further studies are needed to validate the relationships between injured SDFT status and sonoelastographic findings, this preliminary study shows that strain ratio may provide a means to monitor the recovery of stiffness in lesions during rehabilitation, even when the grey-scale ratio remains unchanged from a few months after SDFT injury. The Summary is available in Chinese - see Supporting Information.

Application of sonoelastography for evaluating the stiffness of equine superficial digital flexor tendon during healing

Sonoelastography can assess the inner stiffness of tissues. Sonoelastographic evaluation of injured equine superficial digital flexor tendons (SDFTs) is considered to be useful for assessing the stiffness of a lesion even during late-stage rehabilitation. The purpose of this study was to investigate and compare the sonoelastographic appearance of injured SDFTs over time from the onset of the injury. Eighteen horses were classified into three groups according to the length of time from injury onset: group A, within two weeks after injury; group B, approximately five months after injury; and group C, approximately nine months after injury. Longitudinal and transverse images of all injured SDFTs were obtained using grey-scale ultrasonography and sonoelastography. Grey-scale and sonoelastographic images were evaluated by two observers using echogenicity-grading and colour-grading systems, respectively. The authors evaluated the interobserver agreement and compared the grades among the three groups. The results indicated almost perfect interobserver agreement. Significant differences were found in the sonoelastography among the three groups, whereas no significant difference was found in the grey-scale ultrasonography between groups B and C. Sonoelastography is a feasible and useful modality to evaluate the equine injured SDFTs in vivo and to distinguish between them among the different phases even during the chronic phase.

Feasibility study of monitoring of plasma etching chamber conditions using superimposed high-frequency signals on rf power transmission line

An in situ monitoring system that can detect changes in the conditions of a plasma etching chamber has been developed. In the system, low-intensity high-frequency signals are superimposed on the rf power transmission line used for generating plasma. The system measures reflected high-frequency signals and detects the change in their frequency characteristics. The results indicate that the system detects the changes in the conditions in etching chambers caused by the changes in the electrode gap and the inner wall condition and demonstrate the effectiveness of the system. The system can easily be retrofitted to mass-production equipment and it can be used with or without plasma discharge. Therefore, our system is suitable for in situ monitoring of mass-production plasma etching chambers. The system is expected to contribute to development of predictive maintenance, which monitors films deposited on the inner wall of the chamber and prevents equipment faults caused by misalignment of chamber parts in mass-production equipment.

Population doubling level-dependent change of secreted glycosaminoglycan in equine bone marrow-derived mesenchymal stem cells

In regenerative medicine using transplantation of mesenchymal stem cells (MSCs), the importance of regulating the quality of MSCs has been well recognized; however, there is little information concerning the relationship between the population doubling level (PDL) and the stemness of MSCs in equine medicine. In this study, we showed that the amount of glycosaminoglycan (GAG) secreted by bone marrow-derived MSCs (BMSCs) decreases with increase of PDL. Enzymatic digestion and two-dimensional electrophoresis revealed that a main component of GAG produced by BMSCs was hyaluronan with a small amount of chondroitin sulfate. Increase of PDL downregulated the expression of MSC CD markers, including CD44, CD73, CD90, CD105, and CD146, along with loss of differentiation capacity. Thus, the effect of hyaluronan supplement to the growth medium on both expression of CD markers and the tri-lineage potential of BMSCs was evaluated. Expression of CD73 and CD90 was preserved by continuous addition of hyaluronan to the growth medium, whereas mRNA levels corresponding to CD44, CD105 and CD146 were not preserved by supplementation of hyaluronan. BMSCs subcultured with hyaluronan-supplemented growth medium to PDL-12 showed osteogenic capacity, however adipogenic and chondrogenic activities at PDL-12 were not preserved by exogenous hyaluronan. These results suggest that downregulation of CD44, CD105 and CD146 might not affect the osteogenic capacity. Taken together, the results suggested that supplementation of hyaluronan to the growth medium might be effective at maintaining the osteogenic capacity of equine BMSCs.

Regulation of Tenomodulin Expression Via Wnt/β-catenin Signaling in Equine Bone Marrow-derived Mesenchymal Stem Cells

Tenomodulin has been recognized as a biomarker for tendon differentiation, and its gene expression is regulated by several transcription factors including Scleraxis and Mohawk. In this study, we found a novel regulatory mechanism of tenomodulin expression. Equine bone marrow-derived mesenchymal stem cells (BMSCs) in monolayer culture showed a low mRNA level of tenomodulin in comparison with the level in the tendon. When cultured in collagen gel containing a glycogen synthase kinase-3 (GSK-3) inhibitor (BIO), expression of tenomodulin in BMSCs increased up to the level in the tendon. Participation of GSK-3 in its gene expression was further demonstrated by a gene silencing experiment with small interference RNA corresponding to GSK-3, suggesting that Wnt/β-catenin signaling mediated expression of tenomodulin. These results were confirmed by nuclear translocation of β-catenin in BIO-treated BMSCs cultured in collagen gel. Under this culture condition, expression of tenomodulin-related transcription factors including Scleraxis and Mohawk was not affected, suggesting that Wnt/β-catenin signaling was independent from these transcription factors. Additionally, BIO strongly enhanced expression of type XIV collagen in collagen-embedded BMSCs up to the level in the tendon, and other tendon-related extracellular matrix components such as decorin and fibromodulin were also upregulated. Taken together, these results indicated that activation of Wnt/β-catenin signaling could induce differentiation of BMSCs into tenomodulin-expressing tendon cells in collagen gel.

Note: practical monitoring system using characteristic impedance measurement during plasma processing

A method for characteristic impedance monitoring (CIM) is developed for anomaly detection during plasma processing. Advantages of the method include high-sensitivity and real-time monitoring, as well as structural simplicity to install the measurement system in the mass production equipment. To obtain real-time monitoring without time delay, our CIM system consists of a directional coupler and a newly developed vector processing system instead of the conventional high voltage and current probes. The system can measure the time variations of characteristic and load impedances even while the plasma is generated.

Injury induces a change in the functional characteristics of cells recovered from equine tendon

Injury initiates a repair process characterized by influx of fibroblasts and the rapid formation of fibrous scar tissue and subsequent tissue contraction. The response to injury and behavior of the different tendon fibroblast populations, however, has been poorly characterized. We hypothesized that the fibroblasts recovered from tendon with acute injury would exhibit different cell properties relating to adhesion, migration and tensegrity. To test this hypothesis we evaluated the ability of fibroblasts recovered from normal and injured equine superficial digital flexor tendons (SDFTs). The injured tendon-derived cells showed greater contraction of the collagen gel but poorer adhesion to pepsin-digested collagen, and migration over extracellular matrix proteins compared to normal SDFT-derived fibroblasts. Thus, the cells present within the tendon after injury display different behavior related to wound healing.

Optimisation of bone marrow aspiration from the equine sternum for the safe recovery of mesenchymal stem cells

REASONS FOR PERFORMING STUDY

Mesenchymal stem cell (MSC) therapy for orthopaedic disease is being used with increasing frequency; there is a need to define a safe, reliable and effective technique for the recovery of MSCs from the sternum of the horse.

OBJECTIVES

To describe an optimised safe technique for obtaining bone marrow-derived MSCs from the sternum of the Thoroughbred horse.

METHODS

The anatomical relationship of the sternum with the heart and internal anatomy was demonstrated in cadavers. Sternal anatomy was evaluated ultrasonographically and after midline sectioning. Sternebrae were examined histologically after aspiration to determine the effect of needle insertion. The quality of the aspirate was evaluated as the number of colony-forming units from sequential and separately aspirated 5 ml aliquots and assessed for their multipotency using trilineage differentiation.

RESULTS

The optimal safe location for the needle was the 5th sternebra because it had a safe dorsoventral thickness and was cranial to the apex of the heart. This sternebra could be reliably identified ultrasonographically. Aspirates could also be obtained from the 4th and 6th sternebrae, although the former is between the front limbs and the latter closer to the heart. Minimal disruption of the internal bony architecture was seen after needle insertion through the thin outer cortex and the first 5 ml aliquot contained the greatest number of colony-forming units of mesenchymal stem cells with trilineage capabilities.

CONCLUSIONS

Accurate placement of a Jamshidi needle into the medullary cavity of the 4th-6th individual sternebrae is facilitated by the use of ultrasonography and enables aspiration of bone marrow reliably with minimal damage to the sternum and risk to the horse.

POTENTIAL CLINICAL RELEVANCE

Sternal marrow aspiration as described is a safe and reliable technique to obtain MSCs for orthopaedic cell-based therapies.

Effect of uphill exercise on equine superficial digital flexor tendon forces at trot and canter

REASONS FOR PERFORMING STUDY

One cause of overstrain injury to the superficial digital flexor tendon (SDFT) in horses is the force loaded on the SDFT during repeated running. Therefore, decreasing this force may reduce SDFT injury. It has been reported that strain on the SDFT decreases with a toe-wedge shoe. Uphill courses are used for training of racehorses, and the angle of hoof-sole to the horizon during uphill running is similar to that of the toe-wedge shoe.

OBJECTIVES

To determine the effects of uphill exercise on the force on the SDFT during trotting and cantering.

METHODS

Arthroscopically implantable force probes (AIFP) were implanted into the SDFT of the left or right forelimb of 7 Thoroughbred horses and AIFP output recorded during trotting and cantering on a treadmill inclined at slopes of 0, 3 or 8%, and then 0% again. Superficial digital flexor tendon force was calculated as a relative value, with the amplitude of AIFP output voltage at initial 0% slope equal to 100.

RESULTS

Out of 14 sets of experiments, AIFP data were analysed successfully in 9 at the trot, in 3 at the canter in the trailing forelimb on a slope of 3 and 8%, and in 2 at the canter in the leading forelimb on a slope of 3%. Increasing the incline from 0-8% tended to decrease peak force in the SDFT at the trot, and in the trailing forelimb at the canter. However, force in the SDFT was unchanged in the leading forelimb at the canter on the 3% incline.

CONCLUSIONS

The force in the SDFT trotting or cantering uphill is unchanged or lower than that loaded at the same speed on a flat surface. Because at similar speeds the workload for uphill exercise is greater than on the flat, uphill running increases exercise intensity without increasing force in the SDFT.

POTENTIAL RELEVANCE

Uphill exercise may reduce the risk of SDFT injury as both running speed and SDFT force are decreased on an incline as compared to the flat, even when exercise intensity is the same. Further study is needed to confirm these findings at canter in a larger population of horses.

Effect of controlled exercise on middle gluteal muscle fibre composition in Thoroughbred foals

REASONS FOR PERFORMING STUDY

Most racehorses are trained regularly from about age 18 months; therefore, little information is available on the effect of training in Thoroughbred foals.

HYPOTHESIS

Well-controlled exercise could improve muscle potential ability for endurance running.

METHODS

Thoroughbred foals at age 2 months were separated into control and training (treadmill exercise) groups and samples obtained from the middle gluteal muscle at 2 and 12 months post partum. Muscle fibre compositions were determined by histochemical and electrophoretical techniques and succinic dehydrogenase (SDH) activity was analysed in each fibre type.

RESULTS

All fibre types were hypertrophied with growth and type I and IIA fibres were significantly larger in the training than the control group at age 12 months. A significant increase of SDH activity was found in type IIX muscle fibres in the training group.

CONCLUSIONS

Training in young Thoroughbred horses can facilitate muscle fibre hypertrophy and increase the oxidative capacity of type IIX fibres, which could potentially enhance stamina at high speeds.

POTENTIAL RELEVANCE

To apply this result to practical training, further studies are needed to determine more effective and safe intensities of controlled exercise.

Can exercise modulate the maturation of functionally different immature tendons in the horse?

Tendons can be considered in two functional groups, those contributing to energetics of locomotion and those acting solely to position the limb. The energy-storing tendons in both human and equine athletes have a high frequency of injury with similar pathophysiology. In previous studies, high-intensity exercise appears to induce a disruption of the matrix rather than functional adaptation in adults. Here we explore the hypothesis that the introduction of controlled exercise during growth would result in an adaptive response without deleterious effects. Young horses were given a controlled exercise program similar to that previously shown to induce matrix changes in energy-storing tendons of skeletally mature animals. The tendons were assessed in relation to mechanical properties, molecular composition, and morphology. Results showed a significant increase in cartilage oligomeric matrix protein (COMP) in the positional tendon but not in the energy-storing tendon. Other matrix properties and mechanical properties were not significantly changed. While the imposition of high-strain-rate exercise in immature horses failed to augment the development of the energy-storing tendon over and above that induced by normal pasture exercise, it did not induce deleterious changes, supporting an earlier introduction of athletic training in horses.

Active Expression of Matrix Metalloproteinase-13 mRNA in the Granulation Tissue of Equine Superficial Digital Flexor Tendinitis

The DNA microarray analysis for matrix metalloproteinase (MMP)-related mRNA expression in equine superficial digital flexor tendinitis indicated that mRNA level of MMP-13 was apparently up-regulated in the tendinitis as compared to normal tendon. In situ hybridization also revealed that fibroblastic cells proliferated in the granulation tissue generated in the tendinitis actively expressed MMP-13 mRNA. On the other hand, in normal tendon, a few fibroblastic cells and vascular components lied in the endotenon barely expressed its mRNA, but other cellular components in the tendon bundle were not positively hybridized. As mentioned above, MMP-13 but not other collagenases or gelatinases, may play an important role in tendon injuries in the racehorses.

Evaluation of developmental changes in the coexpression of myosin heavy chains and metabolic properties of equine skeletal muscle fibers

OBJECTIVE

To determine the growth-related changes in metabolic and anatomic properties in equine muscle fiber type, including hybrid fibers identified with immunohistochemical analysis.

ANIMALS

24 2-, 6-, 12-, and 24-month-old female Thoroughbreds.

PROCEDURE

Samples were obtained from the gluteus medius muscle of all horses. Expression of myosin heavy chain (MHC) isoforms MHC-I, -IIa, -IIb, and -IIx in each muscle fiber was detected by use of 4 primary monoclonal antibodies: BA-D5, SC-71, BF-F3, and BF-35, respectively. Five muscle fiber types (types I, I/IIA, IIA, IIA/IIX, and IIX) were immunohistochemically identified. The area and activity of succinic dehydrogenase (SDH) in each fiber type were determined by use of quantitative histochemical staining and image analysis.

RESULTS

Although the proportion of type I and IIX fibers did not change with age, the proportion of type IIA and IIA/IIX fibers significantly increased and decreased, respectively, from 2 months to 24 months of age. The increase in proportion of type IIA fibers with growth may have been attributable to muscle fiber-type transition from type IIA/IIX fibers but not from type IIX fibers. Values for SDH activity and fiber area in hybrid fiber types were intermediate to those for their respective pure phenotypes.

CONCLUSIONS AND CLINICAL RELEVANCE

Hybrid fibers have an important role for determining the proportion of muscle fiber type in horses < 24 months old, and the metabolic and anatomic properties of the hybrid fibers are well coordinated, as in mature horses.

Prevalence of superficial digital flexor tendonitis and suspensory desmitis in Japanese Thoroughbred flat racehorses in 1999

REASONS FOR PERFORMING STUDY

Overstrain injuries to the superficial digital flexor tendon (SDFT) and suspensory ligament (SI) are among the most common musculoskeletal injuries which contribute to the considerable wastage of racing Thoroughbreds. Many epidemiological studies have demonstrated the prevalence of and risk factors for tendon injury when racing but have not included those injuries sustained during training. However, since tendon injury during training is seen commonly in clinical practice, it is appropriate to determine the overall prevalence of tendon injury sustained during both training and racing.

OBJECTIVE

To determine the prevalence of overstrain injury to the SDFT and SL during training and racing among Thoroughbred flat racehorses in Japan in 1999.

METHODS

A retrospective study was performed using a sample population of 10,262 Thoroughbred racehorses. The medical information database of Thoroughbred racehorses registered by the Japan Racing Association (JRA) in 1999 was analysed for SDFT and SL overstrain injury diagnosed by a veterinarian employed by JRA during training and racing. Jump racehorses were excluded from this study.

RESULTS

The prevalence of forelimb SDFT tendonitis and SL desmitis was 11.1% (1130 cases) and 3.61% (370 cases) of the population, respectively. In the hindlimb, there were 0.06% (6 cases) and 0.14% (14 cases), respectively. Risks of SDF tendonitis in the forelimb in 3-year-olds or older horses were significantly higher than in 2-year-olds. In contrast, the risk of SL desmitis in the forelimb at age 3 and 4 years was 2.23 and 2.11 times higher, respectively, than in 2-year-olds, but this increased to 5.07 times in those age > or = 5 years. Entire males were at greater risk in comparison to females and geldings.

CONCLUSIONS

The results suggest that the prevalence of SDF tendonitis and SL desmitis in the forelimb was associated with the horse's age and sex. The prevalence of SL desmitis increased further with age compared with SDF tendonitis, possibly reflecting a more rapid accumulation of degeneration in this structure.

POTENTIAL RELEVANCE

The age-related risk demonstrated in this study provides further support that overstrain injuries are associated with accumulated degeneration. These data provide a valuable resource for further research into the aetiology of tendon injury in the racehorse.

Association between race history and risk of superficial digital flexor tendon injury in Thoroughbred racehorses

OBJECTIVE

To determine whether race history, including the number of races and total race distance, was associated with risk of superficial digital flexor tendon (SDFT) injury in Thoroughbred racehorses in Japan.

DESIGN

Matched case-control study.

ANIMALS

515 Thoroughbred racehorses (case horses) that sustained an SDFT injury during training or racing in Japan during 2002 and 951 horses (control horses) without SDFT injury that were matched with case horses on the basis of age and month of the latest race.

PROCEDURE

Variables related to race history were compared between case and control horses by means of conditional logistic regression.

RESULTS

The odds of SDFT injury increased as mean race distance and mean body weight at race time increased. Compared with females that had never competed in steeplechase races, males regardless of steeplechase race history and females that had competed in steeplechase races had higher odds of SDFT injury.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that longer mean distance per race, heavier mean body weight at race time, steeplechase experience, and sex (male) increased the risk of SDFT injury in Thoroughbred racehorses.

Bronchoalveolar Lavage Fluid Findings in the Atelectatic Regions of Anesthetized Horses

To evaluate the effects of compression atelectasis on the composition of pulmonary secretions in anesthetized horses, cytological and biochemical examinations were performed on bronchoalveolar lavage (BAL) fluids obtained from both dependent and independent lung regions. Six horses were anesthetized with isoflurane and oxygen for 120 min, and were positioned in right lateral recumbency. Percentage of neutrophils and total protein concentration in BAL fluids significantly increased at the end of anesthesia, and total phosphorous concentration significantly decreased at 72 hr after anesthesia in dependent lung. Such changes were not observed within 168 hr after anesthesia. These findings suggest that the effects of compression atelectasis on the composition of pulmonary secretions may be eliminated within 168 hr after anesthesia.

A gross and histopathological study of an ectopic white line development in equine laminitis

In horses with chronic laminitis, an abnormal horny structure called lamellar wedge, is generated between the hoof wall and the laminar epidermis. To be able to manage horses with chronic laminitis correctly, more information about the pathological state of this abnormal horn is required. The aim of this study was to collect and analyze objective morphological data about the abnormal horn in order to understand its morphology and development. In the study, the abnormal horn was grossly visible on the sagittal hoof section from approximately 20 days after the onset of disease. In the histological observations, the structural characteristics of this abnormal horn were similar to the white line tissue, suggesting it is an ectopic white line. Mean value of the cross-sectional area of the abnormal horn against the distal phalanx section area (A/D) was 0.29 cm(2) SD +/- 0.14 and it finally showed an eight-fold increase over the mean value of normal white line section area against the distal phalanx section area. In conclusion, a large amount of the ectopic white line is thought to be finally able to inhibit normal hoof wall growth, so that it should be resected at the optimum time when would be after one month from the onset of the disease.

Exercise-induced tendon hypertrophy: cross-sectional area changes during growth are influenced by exercise

Most skeletal tissues are thought to adapt to the mechanical environment they experience. While this has been demonstrated for muscle and bone, previous studies in the mature horse have failed to demonstrate adaptation in the superficial digital flexor tendon (SDFT), which suffers a high frequency of injury. This study tested the hypothesis that imposed exercise during growth would result in an increase in SDFT cross-sectional area (CSA). Fourteen Thoroughbred foals were divided into 2 sex-matched groups. A control group received 4 h pasture exercise and an exercise group had the same amount of pasture exercise with an additional short period of treadmill exercise daily from age 2-15 months. Activity at pasture was assessed objectively using a visual system. There was no significant difference in pasture activity between groups, although males were more active than females. The exercise programme resulted in a significantly larger tendon CSA in the exercise group at several, but not all, timepoints, which may be attributed to levels of variance. However, there was a significantly greater rate of increase in tendon CSA as a function of time in the exercised compared to the control group. This is the first evidence to suggest that tendon development can be modulated by exercise during growth in the horse, potentially increasing the ability of tendon to withstand the rigours of later athletic activity.

Magnetic resonance imaging application to live horse for diagnosis of tendinitis

Six live horses with various stages of acute to chronic superficial digital flexor (SDF) tendinitis were examined using magnetic resonance imaging (MRI). In each case, MRI findings were compared to the corresponding ultrasonographic (USD) and histologic findings, to establish the usefulness of MRI. In the acute cases, lesions characterized by hemorrhage were well defined as high signal intensity on MRI and hypoechoic regions on USD. Chronic tendon fibrosis was slightly hyperechoic and difficult to distinguish from the normal tendon tissue around the original injury by using USD. In contrast, MRI visualized the chronic lesion as a low intensity signal, which could be distinguished from the black background of the normal SDF tendon tissue. This study clearly demonstrated MRI was the better imaging modality for the objective detection of chronic scar tissue in live horses. These findings, from living horses, suggest an advantage of MRI in the clinical application to diagnose tendinitis in cases where there is chronic scar tissue that is difficult to discern on USD.

Horse lumbrical muscle: possible structural and functional reorganization in regressive muscle

An anatomical study of horse lumbrical muscle (Lm) was carried out by light and electron microscopy in combination with immunochemical and cytochemical methods. Paraffin sections were subjected to haematoxylin and eosin (H & E) and Masson's trichrome staining for morphometric analysis. Paraffin sections were also used for immunostaining by anti-PGP 9.5 for reaction with nerve-protein associated-structures, anti-heat-shock protein 70 (hsp 70) for detection of gene expression changes, anti-fast myosin for the determination of muscle fibre types, and for detection of apoptotic gene expression of muscle fibres by the TUNEL method. The distribution of muscle fibre types on frozen sections was also examined by assaying ATPase (pH 4.2). We found that the proximal end of the tendon of the unipennate-shaped Lm binds to the deep digital flexor tendon, and the distal end of the Lm tendon connects to the medial surface of the palmar annular ligament. The Lm was not always present, but when found it varied in length greatly, up to 8 cm (muscle part alone), and weighed less than 1 g. The Lm was white, pale, or reddish in colour depending on the ratio of muscle fibre and connective tissue contents. The semi-tendinized regressive Lm was composed of rich vasculature, peripheral nerves, and nerve-like organs similar to the neuromuscular spindle (NMS). The extrafusal muscle fibres (e-lm) that surround the NMS were replaced with a thick outer capsule of connective tissues (CT) in the Lm nerve-like organ, which we named the neurotendinous capsule (NTC) organ. NTC organs exist alone or as multiple structures (up to eight) surrounded by a common outer capsule at the outermost CT ring. The NTC possesses several intrafusal muscle fibres (ifm) just as the NMS does. That the ifm was associated with nerve endings was confirmed by anti-PGP 9.5 and electron microscopic observation. Some muscle fibres in ifm and e-lm reacted with anti-fast twitch myosin and with anti-hsp 70. The e-lm exhibited at least two fibre types, determined by ATPase (pH 4.2) assay. The ifm exhibited mainly type I (slow twitch) fibres. No apoptotic gene expression was detected in either ifm or e-lm, suggesting the Lm is a vital organ. The degenerating fibres observed in ifm and e-lm indicate that the turnover rate of cytoplasmic components is accelerated. We attribute this phenomenon to the necessity for adaptation to new environmental demands. The surprising finding of tubular aggregates (TAs) in ifm of the NTC organ suggests that the Lm is continuously adapting. Some results related to variation in diameter of the collagen fibrils, isolation of the NTC organ and the myofibrillar protein constituents are also discussed. In conclusion, the so-called regressive Lm has rich vasculature, many peripheral nerves, and newly described NTC organs. The induction of heat-shock protein, lack of apoptotic gene expression in ifm and e-lm fibres, and TA formation in ifm suggest that horse Lm responds to environmental stress through reorganization and/or remodelling of cell constituents. We hypothesize that the horse Lm has lost its original role as a contractile element and changed to another function, likely as a vital nerve organ.

TGF-beta alters collagen XII and XIV mRNA levels in cultured equine tenocytes

The effects of TGF-beta 1, beta 2 and beta 3 (TGF-beta) on levels of mRNA corresponding to the alpha chains of type XII and type XIV collagens in equine tenocyte cultures were assessed using the ribonuclease protection assay (RPA). The level of alpha1(XII) mRNA in untreated monolayer cultures was approximately 50- to 100-fold greater than alpha1(XIV) mRNA level. Addition of TGF-beta resulted in an increase in the amount of alpha1(XII) present and a decrease of alpha1(XIV) mRNA in a dose-dependent manner. Specifically, the level of alpha1(XII) mRNA was doubled, but alpha1(XIV) was decreased to 30% of control by the addition of 2 ng/ml of TGF-beta 1 to the cultures. These effects were completely abrogated by neutralizing antibody specific for TGF-beta. In addition, electron microscopy demonstrated that bundled collagen fibers were formed in the intercellular spaces of multilayered tenocytes which had been cultured for 2 weeks in the presence of exogenous TGF-beta 1 together with ascorbic acid phosphate. These results suggest that type XII and/or type XIV collagens modulate the structure of ECM formed by tenocytes in culture.

A semi-immobilization of a partial auricle induces hypertrophy and ultrastructural alteration of cardiomyocytes

Semi-immobilization of a partial area of the ventral edge, lateral epicardium of the left auricle (ventrolateral of left auricle), by using quick adhesion glue induces moderate hypertrophy of myocytes with an average increase of 34% in cross-sectional area. Intercellular connective tissues increased, and cellular sizes varied markedly. The ultrastructure of immobilized (semi-immobilized) myocytes commonly exhibited degenerating features in myofibrils, various cytoplasmic organelles including mitochondrial cristae and sarcoplasmic reticulum (SR) were disrupted, and T-tubules disappeared. Z-line streaming and widening (hypertrophic Z-line, rod bodies) and increase of metabolic particle deposition are typical phenomena in addition to intercalated disc (Id) disorganization. The results suggest that semi-immobilization of the auricle induces hypertrophy of myocytes in association with degeneration and disruption of myofibrils and other cytoplasmic organelles, and an increase of intercellular connective tissues, rather than increase of myofibril mass. This is the first study to immobilize only a part of the heart rather than the whole animal. Our results using artificial immobilization of cardiac myocytes were extremely significant since the structural alterations obtained were similar to that observed in cardiomyopathies. This suggests that myocytes progressing to heart failure are also subjected to inhibition of movement. Therefore, this experiment may prove very useful as a model for studying the functional effect of heart failure observed in cardiomyopathy.

Tubular aggregates observed in spindle muscle fiber of horse lumbrical muscle

Tubular aggregates (TAs) originate from the sarcoplasmic reticulum (SR) and form polymorphic double (or single) -walled structures in cross section. TAs are involved in various human skeletal muscle disorders including periodic paralysis, congenital myasthenic syndromes, inflammatory myopathies, and malignant hyperthermias. Horse lumbrical muscle (LM) is a slender fusiform muscle that shows varying degrees of regression due to its limited activity in the limb. Double-walled TAs were found in degenerating spindle fibers and with a range of 80-116 nm (average 92 nm, n=135) for outer layer and 50-78 nm (average 59 nm, n=135) for the inner layer. TAs exhibit degradation of myofibrillar proteins, disruption of mitochondria with cristae lost, glycogen accumulation, electron-dense metabolic products, blebbing appearance of sarcolemma, and presence of various vacuoles. LM fibers also show a similarly degenerative state. The disassembly of the SR structure probably produces a large accumulation of SR proteins which remain as molecules without being further degraded and which could aggregate to form the orderly structure of TAs. We believe that TA formation may be an adaptation to store unbalanced extra proteins by forming ordered aggregates in degeneration caused by stress in cells.

Effects of tri-, di- and monobutyltin on synaptic parameters of the cholinergic system in the cerebral cortex of mice

Triorganotin compounds like tributyltin have been reported to be biodegraded to diorganotin, monoorganotin and then inorganic tin in animals after they have been ingested. Effects of tributyltin, dibutyltin and monobutyltin on various cholinergic parameters that are involved in synaptic transmission in the mouse cerebral cortex were investigated in vitro. Tributyltin and dibutyltin, but not monobutyltin, inhibited the activity of choline acetyltransferase, both the high-affinity and low-affinity uptakes of choline into synaptosomes, and the binding of [3H]quinuclidinyl benzilate to muscarinic acetylcholine receptors. Tributyltin and dibutyltin, but not monobutyltin, had a slightly suppressive effect on the K(+)-induced release and synthesis of acetylcholine in slices of the cortex. All three butyltins at concentrations from 10(-6) to 10(-4) M had no effect on the activity of acetylcholinesterase. The extent of the inhibitory effects on the cholinergic parameters, apart from the activity of acetylcholinesterase, was slightly greater in the case of tributyltin than dibutyltin, in particularly at the highest concentration (10(-4) M) tested. Therefore, it is concluded that tributyltin metabolites inhibit various parameters of cholinergic activity with a potency ranking of tributyltin > dibutyltin > monobutyltin.