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Pulmonary epithelial lining fluid and plasma ascorbic acid concentrations in horses affected by recurrent airway obstruction

Christopher M. DeatonCentre for Equine Studies, Animal Health Trust, Lanwades Park, Kentford, Suffolk, CB8 7UU, UK.

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David J. MarlinCentre for Equine Studies, Animal Health Trust, Lanwades Park, Kentford, Suffolk, CB8 7UU, UK.

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Nicola C. SmithCentre for Equine Studies, Animal Health Trust, Lanwades Park, Kentford, Suffolk, CB8 7UU, UK.

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Pat A. HarrisEquine Studies Group, WALTHAM Centre for Pet Nutrition, Waltham-on-the-Wolds, Leicestershire, UK.

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Colin A. RobertsDepartment of Clinical Veterinary Medicine, University of Cambridge, Cambridge, CB3 0ES, UK.

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Robert C. SchroterDepartment of Bioengineering, Imperial College of Science, Technology and Medicine, London, SW7 2BX, UK.

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Frank J. KellySchool of Health & Life Sciences, Franklin-Wilkins Building, King's College London, London, SE1 9NN, UK.

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Abstract

Objective—To determine the pulmonary epithelial lining fluid (ELF) concentrations and degree of oxidation of ascorbic acid in horses affected by recurrent airway obstruction (RAO) in the presence and absence of neutrophilic airway inflammation.

Animals—6 RAO-affected horses and 8 healthy control horses.

Procedure—Nonenzymatic antioxidant concentrations were determined in RBC, plasma, and ELF samples of control horses and RAO-affected horses in the presence and absence of airway inflammation.

Results—ELF ascorbic acid concentration was decreased in RAO-affected horses with airway inflammation (median, 0.06 mmol/L; 25th and 75th percentiles, 0.0 and 0.4 mmol/L), compared with RAOaffected horses without airway inflammation (1.0 mmol/L; 0.7 and 1.5 mmol/L) and control horses (2.2 mmol/L; 1.4 and 2.2 mmol/L). Epithelial lining fluid ascorbic acid remained significantly lower in RAOaffected horses without airway inflammation than in control horses. Moreover, the ELF ascorbic acid redox ratio (ie, ratio of the concentrations of dehydroascorbate to total ascorbic acid) was higher in RAO-affected horses with airway inflammation (median, 0.85; 25th and 75th percentiles, 0.25 and 1.00), compared with RAOaffected horses without airway inflammation (0.04; 0.02 and 0.22). The number of neutrophils in bronchoalveolar lavage fluid was inversely related to the ELF ascorbic acid concentration ( r = –0.81) and positively correlated with the ascorbic acid redox ratio ( r= 0.65).

Conclusions and Clinical Relevance—Neutrophilic inflammation in horses affected by RAO is associated with a reduction in the ELF ascorbic acid pool. Nutritional supplementation with ascorbic acid derivatives in horses affected by RAO is an area for further investigation. ( Am J Vet Res2004;65:80–87)

Abstract

Objective—To determine the pulmonary epithelial lining fluid (ELF) concentrations and degree of oxidation of ascorbic acid in horses affected by recurrent airway obstruction (RAO) in the presence and absence of neutrophilic airway inflammation.

Animals—6 RAO-affected horses and 8 healthy control horses.

Procedure—Nonenzymatic antioxidant concentrations were determined in RBC, plasma, and ELF samples of control horses and RAO-affected horses in the presence and absence of airway inflammation.

Results—ELF ascorbic acid concentration was decreased in RAO-affected horses with airway inflammation (median, 0.06 mmol/L; 25th and 75th percentiles, 0.0 and 0.4 mmol/L), compared with RAOaffected horses without airway inflammation (1.0 mmol/L; 0.7 and 1.5 mmol/L) and control horses (2.2 mmol/L; 1.4 and 2.2 mmol/L). Epithelial lining fluid ascorbic acid remained significantly lower in RAOaffected horses without airway inflammation than in control horses. Moreover, the ELF ascorbic acid redox ratio (ie, ratio of the concentrations of dehydroascorbate to total ascorbic acid) was higher in RAO-affected horses with airway inflammation (median, 0.85; 25th and 75th percentiles, 0.25 and 1.00), compared with RAOaffected horses without airway inflammation (0.04; 0.02 and 0.22). The number of neutrophils in bronchoalveolar lavage fluid was inversely related to the ELF ascorbic acid concentration ( r = –0.81) and positively correlated with the ascorbic acid redox ratio ( r= 0.65).

Conclusions and Clinical Relevance—Neutrophilic inflammation in horses affected by RAO is associated with a reduction in the ELF ascorbic acid pool. Nutritional supplementation with ascorbic acid derivatives in horses affected by RAO is an area for further investigation. ( Am J Vet Res2004;65:80–87)