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MMP Enzymes and Laminitis
Eleanor M. Kellon, VMD

MMPs are matrix metalloproteinases – enzymes that break down connective tissue protein/collagen in the body. If you follow news releases and articles about equine laminitis, you have surely seen mention of MMP enzymes since the late 1990s. Turns out they are not the major players as was originally thought.

The basement membrane (BM) in the hoof is a thin layer of connective tissue lining the junction between the dead laminae of the hoof wall, and the live laminae of the inner hoof. This system locks the hoof wall to the tissues inside like Velcro.

In laminitis caused by things like colic/gut infections, black walnut shavings, grain, or experimental fructan overload, it was noted the basement membrane is damaged or destroyed and that the level of MMP enzymes is increased. This led to the theory that the activation of MMP is what causes laminitis.

These various causes of laminitis are also associated with inflammation. White blood cells invade the hoof and the body, in general, is in an inflammatory state. It didn’t take long for research to start showing inflammation was not a feature of endocrinopathic laminitis, which is caused by high insulin.

Basement membrane damage and high MMP levels are also not a feature of endocrinopathic laminitis. In fact Visser and Pollitt (2012), have also shown that most of the MMP present in fructan-induced laminitis is inactive, bringing into question what, if any, role it plays.

These differences are summarized in an article by Patterson-Kane, et al. (2017), which you can download for free here

Since it is estimated that 90% of all laminitis cases are caused by high insulin, these findings have important indications. They explain why anti-inflammatories like phenylbutazone or fibrocoxib have limited effect in laminitis pain. They also mean you need to involve your veterinarian in a diagnostic plan that determines what type of hormonal disorder your horse has, and how to most effectively get insulin down, because that is the only thing that will relieve the pain.

Ancillary supplements to balance the diet and improve blood flow to the hoof also play an important role.