more likely to start a race during the 2-year-old racing year versus control
group horses, results for horses in each group were not significantly different
for the 3- and 4-year-old racing years. Therefore, the PRP treatment protocol
evaluated in this study did not seem to improve future racing performance.
There are no published data on the efficacy of PRP in joints although several
reports in the human literature support its efficacy in small case series. A
recent report suggests that the use of PRP in equine joints is safe although
activation with bovine thrombin was considered undesirable because of a
sustained increase in synovial leukcoyte concentrations (Textor and Tablin
2013).
Mesenchymal Stem Cells (MSCs)
Equally, there has been even more interest in the potential therapeutic
benefits of mesenchymal stem cells (MSCs) in regeneration of functional
tendon and ligament tissue. These cells reside in small numbers, within
niches in all mesenchymal tissues, usually closely associated with blood
vessels and are capable of differentiating into a number of different cell types.
As in other species, the ability of MSCs derived from both bone marrow and
fat to differentiate into one or more lineages has also been demonstrated for
equine MSCs. The levels of MSCs in these tissues are, however, very low,
necessitating a culture step to obtain significant numbers of cells.
The mechanisms of action of stem cells remain to be completely elucidated
but they have potentially two important beneficial effects – (1) differentiation
into the target cell (for example, tenocytes or chondrocytes) and thereby
synthesis of new tendon or ligament tissue, or cartilage; and (2) a paracrine
effect via the production of anabolic and anti-inflammatory cytokines which
can induce the resident cells to produce a better quality repair. Of these two
potential roles, there is minimal, if any, evidence for the former, while, in
contrast, there are substantial experimental studies which support the latter
role.
Bone marrow (BM)-derived MSCs have been used in a large number of
experimental laboratory animal models of acute tendon transection and have
demonstrated continued viability and significantly improved outcomes over
controls, supporting the translation of the technology into clinical use. In
horses, Smith et al. (2003) demonstrated the feasibility of in vitro isolation and
expansion of equine BM-derived MSCs, with re-implantation of large numbers
of a utologous MSCs suspended in bone marrow supernatant into damaged
equine SDFTs. The MSCs were combined with bone marrow supernatant so
that the preparation would be completely autologous and also because bone
marrow supernatant had been shown to provide a significant cellular anabolic
stimulus. Since this original publication, the technique has been widely
adopted in many countries for the treatment of tendon (and ligament)
overstrain injuries in horses.
Experimental studies have been conducted, using collagenase tendon injury
models in horses, which have demonstrated significantly improved outcomes
with MSCs compared to saline injected controls (Schnabel et al. 2009;
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February
2016
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London
Convention
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London,
South
Africa
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