The specific aim of the study was to test the safety and tolerance of systemically applied and nebulized pyrrolidine dithiocarbamate (PDTC). PDTC has antioxidant activity and inhibits NF[kappa]B, which could be of potential use for therapy of recurrent airway obstruction (RAO) and equine influenza virus (EIV) infection.
A 100 mM solution with 0.9 % saline was prepared for intravenous use.
For nebulation 25mM and 2.5 mM solutions were prepared. Eight mature Haflinger were used. The i.v. dose was 1.5 mg/kg body weight, the nebulized volume was 5 ml. Treatment was done twice daily for 5 consecutive days. Before and after the intravenous treatment blood samples were taken and lungfunction was measured by means of forced oscillatory mechanics (FOM). Total and differential cell counts were performed and clinical chemistry includes liver -, kidney and muscle profiles. Hydrogen peroxide concentration was measured by Free Radical Analytical System (FRAS). Total antioxidant status with a test kit (Randox) was also measured. A calculation with a formula of the plasma redox status by using albumin, bilirubin and uric acid concentrations was also performed. Before and after the two intranasal treatment periods blood samples, FOM, endoscopic examination and bronchoalveolar lavage was done. Not normally distributed data were analysed using Friedman and Wilcoxon test, for normally distributed data ANOVA were used.
During nebulation, the main clinical sign was a dyspnoea, lasting for 3 hours. This observation was the reason that lungfunction testing was performed during nebulisation. The systemic treatment did not result in clinically noticeable changes. Some horses showed increased muscle enzyme activities, but those were not directly related to PDTC application. Selenium or vitamin E deficiency was the cause for these changes. TAS was not significantly increased (p = 0.214), therefore, there was no indication for an antioxidant effect of PDTC. No correlation with TAS and FRAS could be found. The endoscopic abnormalities were attributed to PDTC. BALF cytology did not show inflammatory activity, but a trend in decrease of neutrophile leukocytes was noticed. The increase of resistance, observed with both methods of lungfunction testing, is produced by PDTC and was possibly dose related.
We concluded that nebulisation of PDTC in the present concentrations and formulation could result in a mild degree of bronchoconstriction.