Plasma levels of the hormone resistin in horses show promise as a biomarker for inflammatory conditions, researchers report.
Obesity and its associated complications, such as metabolic syndrome, are an increasing problem in both humans and horses.
Equine metabolic syndrome is characterized by increased body fat, insulin regulation problems, and a predisposition to laminitis.
Fat tissue is a way to store energy, but it also has an endocrine action regulated by cell-signaling molecules called adipokines.
Elevated levels of one of these adipokines, resistin, originally discovered in mice in 2001, have been linked to metabolic changes and inflammation.
Recent evidence suggests that circulating resistin concentrations do not reflect obesity levels in humans, but it is related to some inflammatory diseases such as chronic kidney disorders, rheumatoid arthritis, heart disease, diabetes and sepsis.
Researchers in Spain, writing in the journal Animals, noted that the relationship between plasma resistin levels and insulin resistance is not clearly established in humans.
Beatriz Fuentes-Romero and her fellow researchers set out to investigate the usefulness of resistin as a biomarker, exploring its relationship with insulin dysregulation and selected indicators of inflammation in horses.
Seventy-two horses enrolled in the study were divided into four groups. One group comprised 14 healthy controls, 21 had inflammatory conditions, 18 had mild insulin dysregulation, and 19 had severe insulin dysregulation.
Plasma resistin concentrations were found to be significantly different between the groups, the researchers reported.
Higher values were recorded in the groups with inflammatory conditions and severe insulin dysregulation. Plasma resistin concentrations were not altered in horses with only moderate insulin dysregulation.
The study team found that plasma resistin levels were not correlated with basal insulin concentrations, but they did find a significant correlation between higher resistin levels and the inflammatory marker serum amyloid A.
The lack of correlation of resistin with base insulin level and its significant correlation with serum amyloid A suggest that, as in humans, plasma resistin concentrations in horses are mostly related to inflammatory conditions and not insulin dysregulation, they said.
The higher resistin levels seen in horses with insulin dysregulation may well be secondary to the inflammatory status associated with equine metabolic syndrome, they said.
Discussing their findings, the researchers said the diagnostic value of resistin has been reported to differ between species.
“While in some species, like rodents, plasma resistin concentrations increase with obesity and metabolic syndrome, in other species, like humans, plasma resistin concentrations increase preferentially when associated with inflammatory problems.
“These differences are probably related to the cellular origin of resistin. In mice, resistin is produced mainly by adipocytes, whereas in humans, it is generated predominantly in peripheral blood mononuclear cells, macrophages, and bone marrow cells.
“As far as we know, there is still no report on the origin of resistin in horses.”
The mechanisms that influence the elevation of resistin associated with inflammation are not well known, they said.
In conclusion, the researchers said resistin can be reliably measured in equine plasma and that its concentrations increase preferentially in horses with inflammatory conditions as opposed to those with insulin dysregulation.
“From a diagnostic point of view, the usefulness of resistin seems to be related preferentially with inflammatory conditions and has little value for the diagnosis of insulin dysregulation.”
Further studies will be needed to better understand the diagnostic value of resistin within a spectrum of inflammatory conditions and to determine if resistin measurements may have diagnostic value to evaluate the inflammatory status in horses with insulin dysregulation.
The study team comprised Fuentes-Romero, María Martín-Cuervo and Manuel Iglesias-García, with the University of Extremadura; Alberto Muñoz-Prieto and José Cerón, with the University of Murcia; and Escolástico Aguilera-Tejero and Elisa Díez-Castro, with the University of Córdoba.
Fuentes-Romero, B.; Muñoz-Prieto, A.; Cerón, J.J.; Martín-Cuervo, M.; Iglesias-García, M.; Aguilera-Tejero, E.; Díez-Castro, E. Measurement of Plasma Resistin Concentrations in Horses with Metabolic and Inflammatory Disorders. Animals 2022, 12, 77. https://doi.org/10.3390/ani12010077