Procalcitonin as a biomarker in equine chronic pneumopathies

Barton et al. BMC Veterinary Research (2016) 12:281 DOI 10.1186/s12917-016-0912-4 RESEARCH ARTICLE Open Access Procalcitonin as a biomarker in equine chronic pneumopathies Ann Kristin Barton1* , Anna Pelli1, Martin Rieger2 and Heidrun Gehlen1 Abstract Background: Procalcitonin (PCT), a precursor protein of the hormone calcitonin, is a sensitive inflammatory marker in human medicine, which is primarily used for diagnosis of bacterial sepsis, but is also useful in diagnosis of exacerbation of asthma and COPD. In this study, PCT was evaluated as a potential biomarker for different chronic pneumopathies in the horse using an equine specific ELISA in comparison to established clinical markers and different interleukins. Sixty-four horses were classified as free of respiratory disease, recurrent airway obstruction (RAO), inflammatory airway disease (IAD) or chronic interstitial pneumopathy (CIP) using a scoring system. PCT concentrations were measured in plasma (n = 17) and in the cell-free supernatant of bronchoalveolar lavage (n = 64). PCT concentrations were correlated to interleukins IL-1ß and IL-6 in BALF, clinical findings and BALF cytology. Results: The median PCT concentrations in plasma were increased in respiratory disease (174.46 ng/ml, n = 7) compared to controls (13.94 ng/ml, n = 10, P = 0.05) and correlated to PCT in BALF supernatant (rs = 0.48). Compared to controls (5.49 ng/ml, n = 15), median PCT concentrations in BALF supernatant correlated to the overall clinical score (rs = 0.32, P = 0.007) and were significantly increased in RAO (13.40 ng/ml, n = 21) and IAD (16.89 ng/ml, n = 16), while no differences were found for CIP (12.02 ng/ml, n = 12). No significant increases were found for IL-1 and IL-6 between controls and respiratory disease in general as well as different disease groups. Conclusions: Although some correlations were found between PCT in plasma, BALF supernatant and clinical scores, PCT in BALF does not seem to be a superior marker compared to established clinical markers. PCT in plasma seems to be more promising and a greater number of samples should be evaluated in further studies. Keywords: Horse, Recurrent airway obstruction, Inflammatory airway disease, Chronic interstitial pneumopathy, Procalcitonin, Biomarker Background Since the 1970s, hypocalcemia and its correlation to sepsis have been in the focus of research [1]. Procalcitonin (PCT) is a precursor protein of the hormone calcitonin, which regulates the calcium homeostasis by inhibition of osteoclastic activity. In health, preprocalcitonin (prePCT) is exclusively produced in the thyroid c-cells. Low concentrations of <0.1 ng/ml are found in human serum [2]. During sepsis, PCT is found in high concentrations in blood and almost all tissues [3], but PCT is not only a precursor of calcitonin leading to hypocalcemia. It seems to have another pathophysiologic role as an inflammatory * Correspondence: 1 Equine Clinic, Freie Universitaet Berlin, Oertzenweg 19b, 10163 Berlin, Germany Full list of author information is available at the end of the article mediator and is found in almost all inflammatory processes independent from hypocalcemia. Its synthesis can be triggered by TNF-α and several interleukins [4, 5]. Despite lower PCT concentrations in plasma compared to endotoxemia and sepsis, differentiation between different forms of pneumonia is possible [6–8] and chronic respiratory diseases like asthma or COPD (chronic obstructive pulmonary disease) are also characterized by increases in PCT concentrations. As acute exacerbation of asthma is often caused by bacterial infections of the lower airways, PCT can be used for the decision pro or contra the initiation and duration of antibiotic therapy [9] and can help in the interpretation of indifferent thoracic radiographs [10]. Similar results have been found for COPD, where PCT measurement can support the decision for individual © The Author(s). 2016 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Barton et al. BMC Veterinary Research (2016) 12:281 therapy involving antibiotics or glucocorticoids and is considered to be helpful in long-term management [11, 12]. Equine RAO (recurrent airway obstruction) is known for parallels to human asthma (respiratory hypersensitivity, good response to bronchodilators and glucocorticoids) as well as COPD (airway neutrophilia, epithelial metaplasia and hypersecretion into the lower airways), resembling what is called “wheezy bronchitis” in men [13]. During disease exacerbation, increased inflammatory markers may be found in plasma as described for haptoglobin and serumamyloid A [14], but local neutrophila in bronchoalveolar lavage fluid (BALF) is considered the most reliable feature [15]. Inflammatory airway disease (IAD), a possible precursor of RAO [16], shows a lower grade of inflammation including airway neutrophilia and/or increases in mast cell and eosinophil counts [17], while interstitial pneumopathies are characterized by increases in macrophage percentages in BALF cytology [18, 19]. As systemic markers were only increased in RAO exacerbation, measurement of biomarkers may be more rewarding out of BALF in chronic respiratory disease. High disease prevalence and economic impact have been described for equine chronic respiratory disease, therefore new biomarkers may help to differentiate these pneumopathies and to identify cases of subclinical disease. A species specific ELISA for equine PCT (ePCT) was established [20], which allows quantitative measurements instead of gene expression with a high specificity and sensitivity. High ePCT concentrations were found in plasma of endotoxemic horses suffering from colic [21, 22]. In this study, we aimed to compare ePCT concentrations in BALF with clinicals findings, BALF cytology and other biomarkers, namely interleukins 1ß and 6, which have been shown to stimulate hyperprocalcitonemia in other species [4, 23]. Additionally, ePCT concentrations were measured in plasma. We hypothesized that ePCT correlates with clinical scores, BALF cytology and interleukins in RAO, IAD and CIP and may be a superior marker in cases of low-grade inflammation. Methods Preparticipation examination A total of 71 horses were examined, of which 15 had no clinical signs or history of respiratory disease and 56 were presented to the clinic with a history of chronic lower airway disease. The pre-participation examination included anamnesis docu (...truncated)