Elsevier

Nitric Oxide

Volume 27, Issue 3, 15 October 2012, Pages 169-175
Nitric Oxide

Plasma and exhaled breath condensate nitrite–nitrate level in relation to environmental exposures in adults in the EGEA study

https://doi.org/10.1016/j.niox.2012.06.007Get rights and content

Abstract

This study evaluated the associations between biological markers in the nitrate–nitrite–NO pathway and four environmental exposures among subjects examined in the second survey (2003–2007) of the French Epidemiological study on Genetics and Environment of Asthma (EGEA). Total nitrite and nitrate (NO2- /NO3-) levels were measured both in plasma and in exhaled breath condensate (EBC) in 949 adults. Smoking, diet and exposure to chlorine products were assessed using standardized questionnaires. Exposure to air pollutants was estimated by using geostatistical models. All estimates were obtained with generalized estimating equations for linear regression models. Median levels of NO2-/NO3- were 36.3 μM (1st–3rd quartile: 25.7, 51.1) in plasma and 2.0 μmol/mg proteins (1st–3rd quartile 0.9, 3.9) in EBC. After adjustment for asthma, age, sex and menopausal status, plasma NO2-/NO3- level increased with leafy vegetable consumption (above versus below median = 0.04 (95%CI: 0.001, 0.07)) and decreased in smokers (versus non/ex-smokers = −0.08 (95%CI: −0.11, −0.04). EBC NO2-/NO3- level decreased in smokers (−0.08 (95%CI: −0.16, −0.001)) and with exposure to ambient O3 concentration (above versus below median = −0.10 (95%CI: −0.17, −0.03)). Cured meat, chlorine products, PM10 and NO2 concentrations were not associated with NO2-/NO3- levels. Results suggest that potential modifiable environmental and behavioral risk factors may modify NO2-/NO3- levels in plasma and EBC according to the route of exposure.

Highlights

► We studied associations of nitrite/nitrate level and four environmental exposures. ► In plasma nitrite/nitrate level increased with consumption of leafy vegetables. ► In EBC nitrite/nitrate level decreased with exposure to ambient ozone. ► Tobacco smoke was associated with lower plasma and EBC nitrite/nitrate level. ► Environmental exposures may modify plasma and EBC nitrite/nitrate levels.

Introduction

Known biological markers involved in the nitrosative pathway, also called the “nitrate–nitrite–nitric oxide” pathway, are nitric oxide (NO), nitrites (NO2-) and nitrates (NO3-), which are indirect stable indicators of NO synthesis. These biological markers play a key role in several physiological functions ranging from neuromodulation to regulation of vascular tone [1], and are involved in local host defense, gut mucosal integrity and also in cardiovascular [2] and airway diseases [3]. Pharmacological and dietary interventions on prevention and treatment of diseases are now under study [4]. Until now, epidemiological studies have been mainly conducted on the fraction of exhaled NO (FeNO). Diet is the most important source of both NO2- (mostly from cured meats) and NO3- (mostly from leafy vegetables) [5]. Formation of NO2- and NO3- can also take place after inhalation of exogenous compounds like oxidants from cigarette smoke [6], [7], nitrogen dioxide (NO2) and ozone (O3) from air pollution [8], and chlorine from cleaning agents [9].

The negative association between exposure to tobacco smoke and FeNO is well known [10], while the association between FeNO with other environmental exposures has been explored more in children [11], [12] than in adults [13]. However, few epidemiological and clinical studies have focused on the associations between environmental exposures and NO2-/NO3-. In the occupational setting, Gube et al. [14] reported that welders had high NO3- concentrations, and Ghasemi et al. [15] found increasing serum NO2-/NO3- levels in smokers compared to non- and ex-smokers.

In biological fluids, the half-life of nitric oxide (NO) is extremely short owing to its rapid oxidation to nitrites (NO2-) and nitrates (NO3-) [16]. Total NO2-/NO3- levels are usually measured in blood (plasma or serum) but can also be measured in exhaled breath condensate (EBC). Interest in the analysis of EBC constituents has increased in the last 10 years, because EBC is viewed as a promising tool for non-invasive evaluation of lung diseases [17]. As plasma and EBC are two distinct body constituents, we hypothesized that direct or indirect environmental sources of NO2- and NO3- might have differential effects on NO2-/NO3- levels in plasma and EBC. Production of NO2-/NO3- in plasma is more complex than in EBC. In the latter, ionized NO3- and NO2- (not volatile) may be produced from NO after reaction with oxygen [18] or from activated immune cells present in the lining of the lungs [19]. In plasma, NO2-/NO3- production derives from several sources, such as bacteria, enzymatic production and dietary sources [16]. To clarify the role of environmental exposures on levels of biological markers in the nitrosative pathway, associations between smoking, dietary habits, ambient air pollution, and chlorine products with total NO2-/NO3- level both in plasma and EBC were evaluated in adults from the Epidemiological study on the Genetics and Environment of Asthma (EGEA).

Section snippets

Study population

Data used for the analyses were collected in the framework of the 12-year follow-up of the EGEA study (http://cesp.vjf.inserm.fr/egeanet/). The EGEA study has been described elsewhere [20], [21]. Briefly, it combines a case-control study with a family study of asthma cases (children or adults) conducted between 1991 and 1995 in 2047 subjects from five French cities. A follow-up of the initial cohort was conducted between 2003 and 2007 [22]. Among the alive cohort (n = 2002), 92% (n = 1845)

Results

Characteristics of the 949 adults according to their asthma status and sex are summarized in Table 1. EBC NO2-/NO3- levels did not vary with storage time and plasma NO2-/NO3- slightly decreased with storage time (Beta for linear regression model = −0.03, P = 0.03).

Analysis of variations according to sex and 10-year age classes was first performed (see Supplementary Fig. A.1). It showed that women older than 45 years had higher total plasma NO2-/NO3- levels (P-value for interaction between age and

Discussion

The present study focused for the first time on the associations between four environmental exposures and total NO2-/NO3- levels measured both in plasma and in EBC among nearly 1000 adults. Total plasma NO2-/NO3- levels were higher in menopausal women, increased with leafy vegetable consumption, and decreased in current smokers. A similar association with smoking was observed in EBC. Lower levels of total EBC NO2-/NO3- were found in association with increasing annual ambient concentration

Conclusion

In conclusion, we report for the first time that environmental and behavioral risk factors may modify NO2-/NO3- levels. Our results suggest specificities of NO metabolism in EBC and in plasma and highlight the importance of studying the same biological marker in different compartments. These findings could have implications for several diseases for which oxidative and nitrosative stresses are involved in their physiopathological pathways. Further studies are needed especially in the general

Acknowledgments

The authors thank all those who participated in the study and in the various aspects of the examinations and all those who supervised the study in all centers. The authors are grateful to the three CIC-Inserm units of Necker, Grenoble and Marseille which supported the study and where subjects were examined. They are also grateful to the three biobanks in Lille (CIC-Inserm), Evry (Centre National de Genotypage) and Annemasse (Etablissement francais du sang) where biological samples are stored.

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