Effects of deslorelin on the feline immune system: concentration of cytokines in plasma and mononuclear cells of tomcats treated with 9.4 mg deslorelin implant.

Deslorelin is a GnRH agonist recently approved for contraception in male cats at the dosage of 4.7 mg. Side effects due to chronic use (requiring reimplantations) of the 9.4 mg formula have not been fully investigated. The aim of this ongoing four-year study is to evaluate the effect of consecutive reimplantations of 9.4 mg deslorelin on the immune system of tomcats by measuring levels of cytokines in the blood, as they can provide valuable information about the immune status. Preliminary results are presented. Nine post puberal intact male cats were selected based on health criteria and received a 9.4 mg deslorelin implant (SuprelorinTM, Virbac), undergoing clinical re-evaluations every six-months. Blood samples for hematology, biochemistry, cytokine assay and serum testosterone were obtained pre-implantation and at each follow-up visit. A multiplex feline-specific cytokine immunoassay kit (Milliplex® MAP Feline Cytokine/Chemokine Magnetic Bead Panel, Millipore-Sigma, Billerica, MA) was used to assay 19 cytokines in plasma and peripheral blood mononuclear cells (PBMC’s). Pre and post-implantation values were statistically analyzed with an ANOVA test for covariance analysis. Treatment with deslorelin was effective in all the subjects, with no side effects. The average duration of efficacy was 462.5±85.6 days considering the two subjects in which the effect came to an end: one cat re-implanted after one year and one month and one surgically neutered after one year and five months of treatment. One cat died due to unrelated causes with ongoing effect for one year and three months. All other subjects are still under treatment and deslorelin has been effective for at least one year, with the longest duration of one year and nine months. Results of the 19 cytokines’ assay at T0 (pre-implantation), T1 (6 months post-implantation) and T2 (12 months post-implantation) revealed no significant statistical difference in the plasma. Whereas in the PBMC’s, Interleukin-2 (IL-2) was significantly increased at T2 versus T0 (p=0,033). This is the first study addressing the immune system of deslorelin-implanted cats. Amongst 19 cytokines assayed in 2 different substrates, only 1 was significantly elevated (in PBMCs) in cats implanted for over 1 year, suggesting a contained effect of the drug on the tomcats’ immune system. The motive and clinical significance of the increased IL-2 in the PMCs of T2 cats is yet unknown. Further research is needed with an increased number of samples.