Protein discoveries point to systemic nature of laminitis

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A horse with laminitis.
A horse with laminitis. © Samantha M Steelman

Texas researchers have identified elevated levels of a protein in horses suffering from chronic laminitis, which may help identify way to reduce the inflammation and pain associated with the devastating hoof disease.

They found that horses that suffer from persistent or recurrent (chronic) laminitis have specific changes in their plasma protein levels which might reflect changes in the immune system that are not confined to the foot.

Laminitis is a painful and debilitating disease. Although its exact cause is unknown, it is often associated with insulin resistance and obesity, and can be preceded by diseases such as colic and diarrhea.

It is known to occur in horses given freedom to eat lots of lush, fresh grass especially after being kept indoors for the winter.

Inflammation can lead to irreversible rotation of the foot bones inside the hoof. In 75 per cent of cases the inflammation becomes chronic “founder”, leaving the horse permanently lame. Euthanasia is often the only humane option.

Professor Bhanu Chowdhary and Dr Samantha Steelman from the College of Veterinary Medicine at Texas A&M University have found that the anti-inflammatory protein apolipoprotein A-IV (APOA-IV) was raised about two-fold in cases of chronic laminitis. This suggested it is linked to a more general inflammation, especially of the digestive system.

In all, they found 16 proteins which have different levels in the blood of horses with and without chronic laminitis.

Horses in both groups were in good health apart from the laminitis.

Eleven of these proteins are involved in response to wounding, coagulation and inflammation, such as coagulation factor X. The remaining proteins included fetuin A and B, both of which are involved in acute immune response, immunoglobin, an indicator of increased antibody levels, and most importantly APOA-IV.

Dr Steelman said APOA-IV was produced by the small intestine.

“One of its functions is to tell the animal when it is full. It also has anti-oxidant and anti-inflammatory properties, which might explain the raised levels of APOA-IV.”

Searching for proteins involved in laminitis
Searching for proteins involved in laminitis. © Samantha M Steelman

Steelman and Chowdhary said that despite intense efforts to understand the root cause of acute laminitis, much less attention had been focused on the changes of normal mechanical, physiological and biochemical functions caused by chronic laminitis.

A handful of studies had investigated changes in laminar morphology, metabolism, and gene expression in foundered horses, they noted, although several recent studies had focused on the effectiveness of different management strategies to ease pain and improve quality of life.

They said the limited information available regarding how chronic laminar inflammation affects the horse as a whole was a major obstacle to understanding why certain horses experience recurrent bouts of laminitis and how these bouts could be prevented.

They said their data described, for the first time, plasma protein changes in chronic equine laminitis.

“Our results suggest that chronic inflammation of the laminae of the hoof might be associated with system-wide changes in immune function and that this hypothesis warrants further investigation.

“Specifically, the altered abundance of complement proteins and acute phase reactants suggests a chronic activation of the innate immune response.

“Our results provide a base upon which to build future studies with the ultimate goal of attenuating inflammation and reducing the pain associated with this devastating disease.”

Their findings have been published in the open-access journal, BMC Veterinary Research.

 

The full study can be read here.

 

 

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