Significant changes occur in the salivary proteins of horses with acute abdominal disease when compared with healthy animals, researchers report.
The study team said their work is the first to identify changes in the composition of the salivary proteome between horses with colic and their healthy counterparts.
Alberto Muñoz-Prieto and his colleagues, reporting in the journal Animals, noted a growing interest in saliva as a biological sample since it can reflect physiological changes and be a possible source of biomarkers for diagnosing and monitoring diseases.
“Compared to blood or urine, the main advantage of saliva is its easy and noninvasive collection,” they said.
In horses, cortisol is probably the most commonly measured analyte in saliva, being used as a biomarker of stress.
However, other biomarkers of stress (such as alpha-amylase), the immune system (such as adenosine deaminase), or tissue damage (such as creatine kinase) can also be analyzed in saliva.
For their study, the researchers took saliva samples from eight horses with colic and six that were healthy, identifying a total of 118 proteins.
Seventeen of the proteins showed significant changes between the two groups.
Eleven were produced in smaller quantities (downregulated) in the sick horses, and six tended to be produced in greater quantities (upregulated).
The researchers said the changes observed in the proteins were closely related to an impaired primary immune defense and antimicrobial capacity in the mucosa.
Such protein changes included the downregulation of gamma-enteric smooth muscle actin (ACTA2), latherin isoform X1, and lactoferrin.
There was an upregulation of mucin 19 (MUC19) and the serine protease inhibitor Kazal-type 5 (SPINK5), all of which are proteins associated with a protective effect during inflammation.
“The proteins identified in our study could have the potential to be novel biomarkers for diagnosis or monitoring the physiopathology of the disease,” they said.
“These results may increase the background and knowledge of saliva composition in horses with acute abdominal disease and further understanding of the physiopathological changes occurring in the organism in this disease.”
Lactoferrin showed particular promise, they said. It decreased in the saliva of horses with acute abdominal disease and was successfully measured using a commercially available test.
The researchers said, to the best of their knowledge, lactoferrin has not been previously measured in the saliva of horses.
It is a glycoprotein contained in most mammalian exocrine secretions, including milk, tears, and saliva. It is involved in the primary innate immune defense system of mammals due to its antimicrobial and antiviral activity, and it has immunomodulatory properties.
Lactoferrin is also related to the gastrointestinal tract, playing a key role in maintaining gut balance.
“In this line, lactoferrin serum concentration has been used as an indicator of severity in gastrointestinal tract inflammation in various species,” they said.
It was important to point out that stress could also influence this protein since its decrease has been reported in the saliva of sheep, they said.
The study team comprised Muñoz-Prieto, Damián Escribano, María Dolores Contreras-Aguilar, Anita Horvatić, Nicolas Guillemin, Stine Jacobsen, José Joaquín Cerón and Vladimir Mrljak, variously affiliated with the University of Zagreb in Croatia, the University of Murcia in Spain, and the University of Copenhagen in Denmark.
Muñoz-Prieto, A.; Escribano, D.; Contreras-Aguilar, M.D.; Horvatić, A.; Guillemin, N.; Jacobsen, S.; Cerón, J.J.; Mrljak, V. Tandem Mass Tag (TMT) Proteomic Analysis of Saliva in Horses with Acute Abdominal Disease. Animals 2021, 11, 1304. https://doi.org/10.3390/ani11051304