RESPIRATORY

Equine Immunosuppression Linked to Dexamethasone Treatment for Asthma

By Landon Gray

There is no evidence that inhaled ciclesonide suppresses the immune systems of horses with equine asthma. However, dexamethasone treatment does have immune-suppressive effects, according to research presented at the 69th AAEP Annual Convention, held in San Diego.

Common Condition

“I think we all recognize that equine asthma is a common condition that's treated in equine practice—most often being with dexamethasone as the first-line treatment,” said study researcher Allen Page, DVM, PhD, a scientist and veterinarian at the Gluck Equine Research Center, in Lexington, Ky. “Although, we certainly recognize also, at the same time, that dexamethasone does have some potential side effects.”

To identify the potential effects of inhaled ciclesonide compared with dexamethasone on systemic markers of immune function in horses, researchers evaluated 18 light, mixed breed horses (age range, 3-8 years). The horses were randomly assigned to either nontreated controls, ciclesonide treatment or dexamethasone treatment. For steady-state messenger RNA (mRNA) analysis, the researchers collected blood daily. In addition, they also collected blood at days 0, 5, 10 and 15 of treatment for Concanavalin A (ConA) in vitro stimulation. To determine the mRNA relative quantities, the researchers used real time quantitative polymerase chain reaction (RTqPCR) to look for genetic mutations (P<0.05).

Although dexamethasone is used frequently to treat equine asthma, it does have potential concerning side effects.

In the dexamethasone arm, when compared with controls, the researchers found significant decreases in the steady-state, whole-blood expression of granzyme B and interferon-gamma. They also reported that this suppressive effect remained within ConA-stimulated samples.

Granzyme B cells are key in the response to viral intracellular infections. Likewise, interferon-gamma is critical for innate and adaptive immune responses, Dr. Page noted.

“While in this project, we're talking about messenger RNA expression, a decreased production of those proteins would in fact be considered to be immunosuppressive,” he said.

The researchers reported there were no similar effects in the horses treated with ciclesonide, and there were no significant effects on immune function markers linked to treatment with ciclesonide found in this study. This suggests a low risk for immunosuppression associated with ciclesonide.

Dr. Page noted the study was limited by the fact that mRNA expressions do not always correlate with protein concentrations, a limited panel of mRNA targets and that only younger horses were evaluated.

“While short-term treatment with dexamethasone—so 10 days, as is kind of typical with equine asthma—it's not thought to be immunosuppressive, this study suggests that caution is warranted due to the suppression of granzyme B and interferon-gamma mRNA expression,” Dr. Page concluded. “Based on mRNA expression, there was no evidence of an immunosuppressive effect of inhaled ciclesonide in horses.”

Ciclesonide (Boehringer Ingelheim) is indicated for equine asthma in the Aservo EquiHaler formulation. MeV

For more information:

Page AE, Mackenzie J, Parker JL, et al. The effect of inhaled ciclesonide treatment on systemic markers of immune function in horses. J Equine Vet Sci. 2023;130:104925) https://www.sciencedirect.com/science/article/abs/pii/S0737080623007414