Institute of Biosensor Technology, University of the West of England, Coldharbour Lane, Frenchay, Bristol BS16 1QY, United Kingdom.
J Breath Res. 2020 May 27;14(3):034001. doi: 10.1088/1752-7163/ab7f9d.
The assessment of volatile compounds (VOCs) for disease diagnosis is a growing area of research. There is a need to provide hard evidence i.e. biochemical routes, to justify putative VOC biomarkers, as in many cases this remains uncertain, which weakens their authenticity. Recently reports of volatile hydrocarbons and or aldehydes in bodily fluids and breath have been attributed to oxidative stress, although as discussed here, fewer compounds have been reported than expected from a mechanistic examination. Oxidative stress can result from many disease states which produce inflammation, and a better understanding of the interconnection between oxidative stress and the release of VOCs from target diseased and healthy organs could greatly help diagnoses. It is generally considered that oxidation of unsaturated fatty acids are a major source of these VOCs. An investigation listing the many possible volatile oxidation products has not been undertaken. This is described here using a mechanistic analysis (based on the literature) of the compounds derived from molecular cleavage and the results compared with a recent review of all the VOCs emanating from the human body, which satisfactorily explains the presence of at least 100 VOCs. Six important unsaturated fatty acids, oleic, palmitoleic, linoleic, linolenic, arachidonic, and cervonic acids have been shown to be capable of producing up to 18 n+6 unique breakdown products (where n = the number of alkene double bonds in the fatty acid hydrocarbon chain), in total 299 compounds. In many cases these have not been reported. We suggest several reasons for this: these VOCs have not been expected, so researchers are not looking for them and importantly some are not present in the mass spectral libraries, or they are too low a concentration to have been detected, or are not present. Furthermore a theoretical explanation for the origins of branched aldehydes and other compounds arising from bacterial oxidative metabolism of unsaturated fatty acids are described.
用于疾病诊断的挥发性化合物 (VOCs) 的评估是一个不断发展的研究领域。需要提供确凿的证据，即生化途径，以证明假定的 VOC 生物标志物的合理性，因为在许多情况下，这仍然不确定，这削弱了它们的真实性。最近，有人在体液和呼吸中报告了挥发性碳氢化合物和/或醛类，这些被归因于氧化应激，尽管如这里所讨论的，从机械检查中预期的化合物要少。氧化应激可能由产生炎症的许多疾病状态引起，如果能更好地理解氧化应激与目标患病和健康器官释放 VOC 之间的相互关系，这将极大地有助于诊断。一般认为，不饱和脂肪酸的氧化是这些 VOC 的主要来源。尚未进行列出许多可能的挥发性氧化产物的调查。这里使用基于文献的化合物的分子裂解的机理分析（mechanistic analysis）对此进行了描述，并将结果与最近对源自人体的所有 VOC 的综述进行了比较，这令人满意地解释了至少 100 种 VOC 的存在。已经证明，六种重要的不饱和脂肪酸，油酸、棕榈油酸、亚油酸、亚麻酸、花生四烯酸和二十碳五烯酸能够产生多达 18 种 n+6 独特的分解产物（其中 n = 脂肪酸碳氢链中烯烃双键的数量），总共有 299 种化合物。在许多情况下，这些尚未被报道。我们为此提出了几个原因：这些 VOC 没有被预料到，因此研究人员没有寻找它们，而且重要的是，有些不在质谱文库中，或者它们的浓度太低而无法检测到，或者不存在。此外，还描述了细菌氧化代谢不饱和脂肪酸产生支链醛和其他化合物的起源的理论解释。
