Platelet-Activating Factor and Evidence of Oxidative Stress in the Bronchoalveolar Fluid of Thoroughbred Colts during Race Training

Abstract

Inflammatory airway disease (IAD) is prevalent in young racehorses during training, being the 2nd most commonly diagnosed ailment interrupting training of 2-year-old Thoroughbred racehorses. That stabling and exercise cause oxidative stress, release of platelet-activating factor (PAF) and inflammation in airways of Thoroughbred colts. Colts in breeding farms (NC, n = 45), stabled for 30 days (EC, n = 40), and race trained (EX, n = 34). Cytological profile and parameters of bronchoalveolar lavage fluid (BALF) related to oxidative stress, bioactivity of the proinflammatory mediator PAF, catalase activity, and alveolar macrophage function. Percentages of neutrophils and eosinophils in the BALF of the EX group were higher (5.4 +/- 6.4% versus 0.9 +/- 1.2%) than the upper limits for normal horses (3-5%). BALF from the EX group (45.6 +/- 2.8 cells/microL of BALF) also displayed significantly (P = .017) higher total nucleated cell count. PAF bioactivity and the total protein concentration in the BALF were higher in the EX group (0.0683 +/- 0.076 versus 0.0056 +/- 0.007 340 : 380 nm ratio P = .0039, 0.36 +/- 0.30 versus 0.14 +/- 0.15 mg of proteins/mL of BALF P < .001). Concentration of BALF hydroperoxides was higher in the EC group (104.7 +/- 80.0 versus 35.2 +/- 28.0 nmol/mg of proteins, P = .013) and catalase activity was higher in the EX group (0.24 +/- 0.16 versus 0.06 +/- 0.02 micromol H2O2/min/mg of proteins, P = .0021). Alveolar macrophage phagocytosis (P = .048) as well as production of superoxide anion (P = .0014) and hydrogen peroxide (P = .0011) were significantly lower in EX group. Further studies should be performed to elucidate the role of PAF in the pathophysiology of IAD. Its presence in bronchoalveolar fluid of young athletic horses makes it a potential therapeutic target to be investigated.