In the recently published article we reported on decreased activity of PON1 paraoxonase and/or PON1 arylesterase activities in patients with COPD (Citation1). There are certain diseases such as psoriasis, chronic renal failure, inflammatory bowel diseases, hypertension, Parkinson's disease, Alzheimer disease, vascular dementia, chronic liver disease, systemic lupus erythematosus, hyperlipidemia and acute phase response status that might influence PON1 activity, and confounding effects might be seen in other syndromes and diseases.
We absolutely agree to the point raised by Agilli et al. in the Letter to the Editor that proper characterisation of patients and selection of correct controls is of utmost importance for making the right conclusions. To select the appropriate study groups we set exclusion and inclusion criteria in a very precise way. Inclusion criteria for COPD group were clinical diagnosis of COPD according to GOLD report. COPD was diagnosed by a pulmonary specialist based on clinical examination (chronic and progressive dyspnoea, cough and sputum production) and spirometry results, measured on the first admission to the Hospital.
Exclusion criteria, for both COPD patients and healthy subjects, included the presence of pulmonary diseases other than COPD, infective and inflammatory diseases, neoplastic pathologies, renal, gastrointestinal, endocrine and hepatic diseases, and excessive alcohol consumption (≥40 g/day). Those conditions and diseases were excluded by inspecting anamnesis data. To additionally confirm the exclusion of infective and other inflammatory diseases we determined complete blood count and concentration of CRP. Detailed analysis on the sensitivity and specificity of CRP as the biomarker for inflammation in COPD was described in our previously published paper with the same group of patients (Citation2). Erythrocyte sedimentation rate was not determined because there is a general consensus for clinical and laboratory medicine practice that this measurement is considered redundant if CRP concentration is measured.
One of the exclusion criteria, for both COPD patients and healthy subjects, was the presence of endocrine diseases so we find the comment to include thyroid function tests unnecessary.
We do agree that medication might influence PON1 activity and that COPD patients often use some additional drugs, e.g. lipid-lowering drugs, aspirin, dexametazon, phenofibrate, phenobarbital, and hormone replacement therapy, as well as dietary supplements such as vitamin E, vitamin C, zinc, iron, and flavonoids, to deal with various COPD co-morbidities. However, during clinical examination, the data on medication and vitamins/minerals supplements usage were taken. None of the above mentioned list of drugs was used by our study subjects.
The question was raised on possible gender and age influence on PON1 activity and concentration. The influence of gender and age was thoroughly explored in this and our previous paper. In the Results section we clearly pointed out that gender did not influence PON1 values, neither for COPD nor for control subjects, however the details were not shown in the article. Results of linear regression analysis showed no significant association between PON1 activities and gender in COPD patients, what could be seen from the p values obtained for the respective enzyme activities (POX: p = 0.245; POX1: p = 0.138; ARE: p = 0.832), or in controls (POX: p = 0.091; POX1: p = 0.085; ARE: p = 0.609). In addition to linear regression analysis we have subdivided study subjects according to gender and performed basic statistical analysis (t-test). No statistical differences in PON1 paraoxonase and/or PON1 arylesterase activities according to gender were found.
In the previous publication, cited in this paper, we reported that gender does not affect PON1 activity in healthy Croatian population (Citation3). Similar findings were reported by Yunaki et al. (Citation4) and they demonstrated no gender differences in PON1 concentration and arylesterase activity, but paraoxonase activity was different according to gender. However, Costa et al. (Citation5) suggested that genetic heterogeneity in humans might obscure gender effect on PON1 activity. We believe that the influence of gender must be tested for certain population, and inconsistency of results most probably reflects different genetic and non-genetic factors that might affect PON1 serum concentration and activity.
As to the question of influence of age on PON1 activity and concentration, we have tested the possible influence of age on PON1 paraoxonase and arylesterase activities in linear regression analysis model, and no significant association between PON1 activities and age was found, as it was emphasized in the Results section. Results of linear regression analysis showed no significant association between PON1 activities and age in COPD patients and p values for the respective enzymes were as follows (POX: p = 0.225; POX1: p = 0.197; ARE: p = 0.753), or in controls (POX: p = 0.644; POX1: p = 0.738; ARE: p = 0.337). To investigate influence of age on PON1 paraoxonase and/or PON1 arylesterase activities we have searched the literature on association of PON1 and age, and have read completely and carefully all relevant articles.
In the article by Mehdi and Rizvi (Citation6) only PON1 arylesterase, and not PON1 paraoxonase, activity was determined. In addition, Indian population was examined, which could differ from our population group. The study comprised 90 healthy subjects of both gender between the ages of 20 and 81 years, but subjects were not subdivided into young, middle-aged and elderly groups. This subdivision seems to be of the utmost importance, as shown in a few relevant articles. Seres et al. (Citation7) examined PON1 paraoxonase activity, PON1 arylesterase activity and PON1 plasma concentration in 129 healthy subjects, all Caucasian, originating from Europe (Hungary), aged 22–89 years. The subjects were subdivided into young (22–45 years; n = 27), middle-aged (46–65 years; n = 62) and elderly (66–89 years; n = 40) groups.
No differences between those age subgroups were found for PON1 arylesterase activity and PON1 concentration; only PON1 paraoxonase activity differed between middle-aged and elderly subjects when compared to young subjects, but not when compared middle-aged to elderly subjects. The age distribution in the middle-aged group of this article was similar to our control group (52 (46–56)), age distribution in the elderly group of this research was similar to our COPD group (71 (65–76)), and population used was similar to ours. Thus, it appears that our results are in agreement with published papers, meaning that PON1 activities differ for young population, but no significant differences were observed between middle-aged and elderly individuals, what was confirmed by linear regression analysis performed in our study.
Finally, we would like to thank Agilli et al. for their meaningful comments regarding our manuscript.
Declaration of Interest Statement
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
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