Isoprene in breath

Isoprene (CsHg) is an abundant endogenous hydrocarbon contained in exhaled breath (typically at a level of hundreds of ppbv) and is considered to be linked to a number of metabolic processes in the human body, and in particular as a biomarker for cholesterol 

A comprehensive study involving 21 healthy volunteers by Schubert et al. assessed correlations between exhaled concentrations of isoprene (in addition to ammonia and acetone) with metabolism and physiological parameters [58]. Isoprene concentrations showed a close correlation with cardiac output, in agreement with previous studies, and minute ventilation (the total volume of gas in Utres exhaled from the lungs per minute). 

An investigation of offline isoprene levels in the breath of patients suffering from end-stage renal disease following haemodialysis (HD) found that statistically significant increases in isoprene concentrations occurred after HD compared to those levels found 

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Isoprene is known to be derived from the cholesterol synthesis pathway [29]. Nonetheless, a fraction of isoprene in breath may be of bacterial origin and may be indicative of oxidative damage of the fluid lining of the lung [30] and in more complex diseases such as cystic fibrosis [31]. 

Mendis, S., P. A. Sobotka, and D. E. Euler, Pentane and Isoprene in Expired Air from Humans Gas-Chromatographic Analysis of Single Breath, Clin. Chem., 40, 1485-1488 (1994). 

This evidently accounts for the presence of isoprene in the breath.34 Isoprene is also formed by many plants and is released into the atmosphere in large amounts, which contribute to photochemical formation of haze. A Mg2+-dependent enzyme catalyzes the elimination of pyrophosphate.35 Isoprene emissions rise with increasing temperature, and it has been suggested that the isoprene may dissolve in chloroplast membranes and in some way confer increased heat resistance.36 37 Hydrolytic dephosphorylation can lead to dimethylallyl alcohol, which is oxidized in the liver to dimethy-lacrylyl-CoA (Eq. 22-1). 

Diskin A.M., P. Spanel and D. Smith Time variation of ammonia, acetone, isoprene and ethanol in breath a quantitative SIFT-MS study over 30 days. Physiol. Meas. 24 (2003) I07-II9. 

Figure 20. A decline in serum cholesterol and low density lipoprotein (LDL) levels induced by the cholesterol-lowering drug, Lipitor, is paralleled by a decline in breath isoprene concentrations. Breath isoprene was measured by PTR-MS under carefully controlled conditions as described in the text. Replotted from data presented in Ref. [89], where two atypical samples ( ) are discussed.

So far PTR-MS has been successful in measuring the concentration of selected VOCs in exhaled breath. Examples include several main compounds in breath, tentatively identified as acetaldehyde (m/z 45), ethanol (tn/z 47), isoprene (m/z 69), acetone (m/z 59), and methanol (m/z 33). In addition, other compounds such as acetonitrile (m/z 42) and benzene (m/z 79) were found related to smoking behavior [32]. 

Figure 9 Concentration time profiles of the trace gases acetone and isoprene in single exhalations of breath obtained with the SIFT using HsO, NO and 0+ precursor ions. Concentrations are given in parts per million (ppm) of the breath.

King, J., Kupferthaler, A., Frauscher, B. et al. (2012) Measurement of endogenous acetone and isoprene in exhaled breath during sleep. Physiol. Meas. 33,413. 

Fuchs, D., Jamnig, H., Heininger, P. et al. (2012) Decline of exhaled isoprene in lung cancer patients correlates with immune activation. J. Breath Res. 6,027101. 

The non-aqueous system of spherical micelles of poly(styrene)(PS)-poly-(isoprene)(PI) in decane has been investigated by Farago et al. and Kanaya et al. [298,299]. The data were interpreted in terms of corona brush fluctuations that are described by a differential equation formulated by de Gennes for the breathing mode of tethered polymer chains on a surface [300]. A fair description of S(Q,t) with a minimum number of parameters could be achieved. Kanaya et al. [299] extended the investigation to a concentrated (30%, PI volume fraction) PS-PI micelle system and found a significant slowing down of the relaxation. The latter is explained by a reduction of osmotic compressibihty in the corona due to chain overlap. 

Foster, W. M L. Jiang, P. T. Stetkiewicz, and T. H. Risby, Breath Isoprene Temporal Changes in Respiratory Output after Exposure to Ozone, J. Appl Physiol., 80, 706-710 (1996). 

Kushch 1, Arendacka B, Stoic S et al (2008) Breath isoprene - aspects of normal physiology related to age, gender and cholesterol profile as determined in a proton transfer reaction mass spectrometry study. Clin Chem Lab Med 46(7) 1011-1018... 

Ueta, I., Mizuguchi, A., Okamoto, M., Sakamaki, H., Hosoe, M., Ishigurod, M., Saito, Y. Determination of breath isoprene and acetone concentration with a needle-type extraction device in gas chromatography-mass spectrometry. Clin. Chim. Acta 430, 156-159 (2014)... 

In the literature, the major VOCs found in the breath of healthy persons are isoprene (10-600 pph ), acetone (1-2000 ppbv), ethanol (10-1000 ppbv) and methanol (150-200 ppbv). All are products of the standard metabolic processes in the human body [7]. 

Figure 19, Isoprene concentrations in human breath during exercise on a stationary bicycle. Breath isoprene was measured by PTR-MS, and the heart beat rate was varied by changing the exercise rate in steps breathing frequency was also monitored. The exercise started at 2.5 min and ended at 60 min. A curve (solid line) derived from a two-compartment isoprene model (see the text) shows an excellent fit to the measured breath isoprene data. Replotted from data presented in Ref. [89].

If you walk into a garden in bloom and breathe deeply, you are likely to encounter great smells. In many cases, the molecules that bring those scents to your nose are terpenes. Terpenes are a class of molecules that typically contain either ten or fifteen carbon atoms built from a five-carbon building block called isoprene. It is important to note these molecules are volatile—they tend to evaporate relatively easily— which allows them to reach one s nose and trigger the olfactory senses. Figure 1 shows the structure of several molecules in this category and identifies the plant from which they are derived. 

About 67 possible indicators were found in the breath of patients. Among them only 22 were determinant for the correct identification of the disease. In particular, the differences with normal breath were not related to novel compounds but rather to a different concentration of some compounds that are present also in the normal breath. Among these compounds isoprene, benzene, and four derivates of benzene (o-toluidine and aniline among the others) were found. It is worth to note that the presence of benzene in human breath is still not explained. 

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