Khan Alya, Staimer Norbert, Tjoa Thomas, Galassetti Pietro, Blake Donald R, Delfino Ralph J
Division of Occupational and Environmental Medicine, Department of Medicine, University of California, Irvine, CA, USA.
J Breath Res. 2013 Sep;7(3):036007. doi: 10.1088/1752-7155/7/3/036007. Epub 2013 Sep 3.
The role of endogenous isoprene in the human body, if any, is unclear because previous research is inconsistent and mechanistic evidence for the biologic function of isoprene is lacking. Given previous evidence that exhaled isoprene is elevated in systemic inflammatory states, we hypothesized that exhaled isoprene would be positively associated with a breath biomarker of airway inflammation, the fractional concentration of exhaled nitric oxide (FENO). We examined relationships of exhaled breath isoprene with FENO and with outdoor ozone given that ozone chemically reacts with isoprene and has been positively associated with FENO in past studies. Sixteen elderly subjects were followed with ≤12 weekly exhaled hydrocarbon and FENO collections at the subjects' retirement community. Outdoor ozone concentrations were measured continuously on site. Mixed-effects regression analyses tested relations of FENO with isoprene, and FENO and isoprene with ozone, adjusted for temperature. We found FENO was inversely associated with isoprene, and this was not confounded by ozone. Isoprene was inversely related to ozone. FENO was positively related to ozone and this relation was not confounded by isoprene. In contrast to hypothesized relations, we conclude that exhaled isoprene is inversely associated with FENO as well as outdoor ozone, which suggests possible protective ozone-scavenging functions of endogenous isoprene. Findings may indicate chemical reactions of isoprene oxidation by ozone and by hydroxyl radicals in the presence of O2 that is dependent on NO concentration. These preliminary results need to be confirmed in additional studies of human subjects, particularly as they apply to FENO monitoring in asthma.
内源性异戊二烯在人体中的作用（如果存在的话）尚不清楚，因为先前的研究结果并不一致，且缺乏关于异戊二烯生物学功能的机制证据。鉴于先前有证据表明，在全身性炎症状态下呼出的异戊二烯会升高，我们推测呼出的异戊二烯会与气道炎症的一种呼吸生物标志物——呼出一氧化氮分数浓度（FENO）呈正相关。鉴于臭氧与异戊二烯会发生化学反应，且在过去的研究中臭氧与FENO呈正相关，我们研究了呼出的异戊二烯与FENO以及与室外臭氧之间的关系。在16名老年受试者的退休社区对其进行随访，每周收集≤12次呼出的碳氢化合物和FENO样本。现场连续测量室外臭氧浓度。采用混合效应回归分析来测试FENO与异戊二烯的关系，以及FENO和异戊二烯与臭氧的关系，并对温度进行了校正。我们发现FENO与异戊二烯呈负相关，且这一关系不受臭氧的干扰。异戊二烯与臭氧呈负相关。FENO与臭氧呈正相关，且这一关系不受异戊二烯的干扰。与我们所假设的关系相反，我们得出结论，呼出的异戊二烯与FENO以及室外臭氧呈负相关，这表明内源性异戊二烯可能具有保护作用的臭氧清除功能。研究结果可能表明，在氧气存在的情况下，异戊二烯会被臭氧和羟基自由基氧化，这种化学反应取决于一氧化氮的浓度。这些初步结果需要在更多人体研究中得到证实，特别是在哮喘患者的FENO监测方面。
