Effect of age on the breath methylated alkane contour, a display of apparent new markers of oxidative stress

Human exhaled air analytics: biomarkers of diseases

Over the last few years, breath analysis for the routine monitoring of metabolic disorders has attracted a considerable amount of scientific interest, especially since breath sampling is a non-invasive technique, totally painless and agreeable to patients. The investigation of human breath samples with various analytical methods has shown a correlation between the concentration patterns of volatile organic compounds (VOCs) and the occurrence of certain diseases. It has been demonstrated that modern analytical instruments allow the determination of many compounds found in human breath both in normal and anomalous concentrations. The composition of exhaled breath in patients with, for example, lung cancer, inflammatory lung disease, hepatic or renal dysfunction and diabetes contains valuable information. Furthermore, the detection and quantification of oxidative stress, and its monitoring during surgery based on composition of exhaled breath, have made considerable progress. This paper gives an overview of the analytical techniques used for sample collection, preconcentration and analysis of human breath composition. The diagnostic potential of different disease-marking substances in human breath for a selection of diseases and the clinical applications of breath analysis are discussed.

Volatile biomarkers of pulmonary tuberculosis in the breath

Pulmonary tuberculosis may alter volatile organic compounds (VOCs) in breath because Mycobacteria and oxidative stress resulting from Mycobacterial infection both generate distinctive VOCs. The objective of this study was to determine if breath VOCs contain biomarkers of active pulmonary tuberculosis. Head space VOCs from cultured Mycobacterium tuberculosis were captured on sorbent traps and assayed by gas chromatography/mass spectroscopy (GC/MS). One hundred and thirty different VOCs were consistently detected. The most abundant were naphthalene, 1-methyl-, 3-heptanone, methylcyclododecane, heptane, 2,2,4,6,6-pentamethyl-, benzene, 1-methyl-4-(1-methylethyl)-, and cyclohexane, 1,4-dimethyl-. Breath VOCs were assayed by GC/MS in 42 patients hospitalized for suspicion of pulmonary tuberculosis and in 59 healthy controls. Sputum cultures were positive for Mycobacteria in 23/42 and negative in19/42 patients. Breath markers of oxidative stress were increased in all hospitalized patients (p<0.04). Pattern recognition analysis and fuzzy logic analysis of breath VOCs independently distinguished healthy controls from hospitalized patients with 100% sensitivity and 100% specificity. Fuzzy logic analysis identified patients with positive sputum cultures with 100% sensitivity and 100% specificity (95.7% sensitivity and 78.9% specificity on leave-one-out cross-validation); breath VOC markers were similar to those observed in vitro, including naphthalene, 1-methyl- and cyclohexane, 1,4-dimethyl-. Pattern recognition analysis identified patients with positive sputum cultures with 82.6% sensitivity (19/23) and 100% specificity (18/18), employing 12 principal components from 134 breath VOCs. We conclude that volatile biomarkers in breath were sensitive and specific for pulmonary tuberculosis: the breath test distinguished between "sick versus well" i.e. between normal controls and patients hospitalized for suspicion of pulmonary tuberculosis, and between infected versus non-infected patients i.e. between those whose sputum cultures were positive or negative for Mycobacteria.

Heart allograft rejection: detection with breath alkanes in low levels (the HARDBALL study)

BACKGROUND

We evaluated a new marker of heart transplant rejection, the breath methylated alkane contour (BMAC). Rejection is accompanied by oxidative stress that degrades membrane polyunsaturated fatty acids, evolving alkanes and methylalkanes, which are excreted in the breath as volatile organic compounds (VOCs).

METHODS

Breath VOC samples (n = 1,061) were collected from 539 heart transplant recipients before scheduled endomyocardial biopsy. Breath VOCs were analyzed by gas chromatography and mass spectroscopy, and BMAC was derived from the abundance of C4-C20 alkanes and monomethylalkanes. The "gold standard" of rejection was the concordant set of International Society for Heart and Lung Transplantation (ISHLT) grades in biopsies read by 2 reviewers.

RESULTS

Concordant biopsies were: Grade 0, 645 of 1,061 (60.8%); 1A, 197 (18.6%); 1B, 84 (7.9%); 2, 93 (8.8%); and 3A, 42 (4.0%). A combination of 9 VOCs in the BMAC identified Grade 3 rejection (sensitivity 78.6%, specificity 62.4%, cross-validated sensitivity 59.5%, cross-validated specificity 58.8%, positive predictive value 5.6%, negative predictive value 97.2%). Site pathologists identified the same cases with sensitivity of 42.4%, specificity 97.0%, positive predictive value 45.2% and negative predictive value 96.7%.

CONCLUSIONS

A breath test for markers of oxidative stress was more sensitive and less specific for Grade 3 heart transplant rejection than a biopsy reading by a site pathologist, but the negative predictive values of the 2 tests were similar. A screening breath test could potentially identify transplant recipients at low risk of Grade 3 rejection and reduce the number of endomyocardial biopsies.

Pilot study of a breath test for volatile organic compounds associated with oral malodor: evidence for the role of oxidative stress

BACKGROUND

We performed a pilot study of a new method to identify the volatile organic compounds (VOCs) in breath associated with oral malodor, using gas chromatography and mass spectroscopy (GC/MS).

METHODS

Oral cavity breath was collected from seven patients with oral malodor. Breath samples (150 ml) were concentrated onto sorbent traps and analyzed by GC/MS.

RESULTS

Organoleptic scores ranged from 3.0 to 4.0 (mean = 3.3) on a scale of 0-5. Twenty-four of 30 (80.0%) of the most abundant oral malodor volatile organic compounds (OMVOCs) were alkanes and methylated alkanes. These VOCs are products of oxidative stress, generated by lipid peroxidation of polyunsaturated fatty acids in cell membranes.

CONCLUSIONS

Increased oxidative stress in the oral cavity of patients with oral malodor may account for the increased risk of atherosclerosis, coronary heart disease and stroke associated with periodontal disease. The breath test for OMVOCs could potentially provide an objective new test for the assessment of oral malodor.

Prediction of heart transplant rejection with a breath test for markers of oxidative stress

The Heart Allograft Rejection: Detection with Breath Alkanes in Low Levels study evaluated a breath test for oxidative stress in heart transplant recipients, and we report here a mathematical model predicting the probability of grade 3 rejection. The breath test divided the heart transplant recipients into 3 groups: positive for grade 3 rejection, negative for grade 3 rejection, and intermediate. The test was 100% sensitive for grade 3 heart transplant rejection when the p value was >/=0.98, and 100% specific when the p value was </=0.058; in the intermediate group, the breath test determined the probability of grade 3 rejection and the predictive value of the result.

Increased breath biomarkers of oxidative stress in diabetes mellitus

BACKGROUND

Oxidative stress has been implicated in the major complications of diabetes mellitus, including retinopathy, nephropathy, neuropathy and accelerated coronary artery disease. There is a clinical need for a marker of oxidative stress which could potentially identify diabetic patients at increased risk for these complications. We measured oxidative age, a new breath marker of oxidative stress, in diabetic patients.

METHODS

Three groups were studied: type 1 diabetes mellitus (n=9), type 2 diabetes mellitus (n=53) and non-diabetic normals (n=39). Volatile organic compounds (VOCs) in breath were assayed by gas chromatography and mass spectroscopy to construct the breath methylated alkane contour (BMAC), a three-dimensional display of oxidative stress markers, C4-C20 alkanes and monomethylated alkanes. The collective abundance of these VOCs was reduced to a single value, the oxidative age, comprising the volume under the curve of the BMAC corrected for chronological age.

RESULTS

Oxidative age was significantly increased in type 1 diabetes (mean=0.103, S.E.M.=0.119, p<0.01) and type 2 diabetes (mean=0.103, S.E.M.=0.047, p<0.05) compared to age-matched normals (mean=-0.248, S.E.M.=0.079). No significant correlation between oxidative age and blood glucose or hemoglobin A1C was observed in either group.

CONCLUSIONS

Oxidative age, a marker of oxidative stress, was significantly increased in both type 1 and type 2 diabetes mellitus. Oxidative age merits further study as a candidate marker of risk for the complications of diabetes mellitus.

Increased breath markers of oxidative stress in normal pregnancy and in preeclampsia

OBJECTIVES

The purpose of this study was to compare the intensity of oxidative stress in normal pregnancy, preeclampsia, and nonpregnant women using a breath test.

STUDY DESIGN

We studied primiparous women in third trimester pregnancy (38 uncomplicated, 26 with preeclampsia) and 60 nonpregnant control subjects. Volatile organic compounds (VOCs) in alveolar breath were analyzed by gas chromatography/mass spectroscopy to construct the breath methylated alkane contour (BMAC), a 3-dimensional display of abundance of C4-C20 alkanes and monomethylated alkanes.

RESULTS

The mean volume under curve (VUC) of the BMAC was significantly higher in preeclampsia patients than in normal pregnant women (P < .003) and nonpregnant control subjects (P < .005). A predictive model employing 5 VOCs distinguished preeclampsia from uncomplicated pregnancy (sensitivity = 92.3%, specificity = 89.7%; cross-validated sensitivity = 88.5%, specificity = 79.3%).

CONCLUSION

A breath test significantly demonstrated greater oxidative stress in women with preeclampsia than in uncomplicated pregnancy and nonpregnant control subjects. The breath test accurately identified women with established preeclampsia, but further studies are required to determine if this test can predict the onset of disease.

Detection of lung cancer with volatile markers in the breath

STUDY OBJECTIVES

To evaluate volatile organic compounds (VOCs) in the breath as tumor markers in lung cancer. Alkanes and monomethylated alkanes are oxidative stress products that are excreted in the breath, the catabolism of which may be accelerated by polymorphic cytochrome p450-mixed oxidase enzymes that are induced in patients with lung cancer.

DESIGN

Combined case-control and cross-sectional study.

SETTING

Five academic pulmonary medicine services in the United States and the United Kingdom.

PATIENTS AND PARTICIPANTS

One hundred seventy-eight bronchoscopy patients and 41 healthy volunteers.

INTERVENTION

Breath samples were analyzed by gas chromatography and mass spectroscopy to determine alveolar gradients (ie, the abundance in breath minus the abundance in room air) of C4-C20 alkanes and monomethylated alkanes.

MEASUREMENTS

Patients with primary lung cancer (PLC) were compared to healthy volunteers, and a predictive model was constructed using forward stepwise discriminant analysis of the alveolar gradients. This model was cross-validated with a leave-one-out jackknife technique and was tested in two additional groups of patients who had not been used to develop the model (ie, bronchoscopy patients in whom cancer was not detected, and patients with metastatic lung cancer [MLC]).

RESULTS

Eighty-seven of 178 patients had lung cancer (PLC, 67 patients; MLC, 15 patients; undetermined, 5 patients). A predictive model employing nine VOCs identified PLC with a sensitivity of 89.6% (60 of 67 patients) and a specificity of 82.9% (34 of 41 patients). On cross-validation, the sensitivity was 85.1% (57 of 67 patients) and the specificity was 80.5% (33 of 41 patients). The stratification of patients by tobacco smoking status, histologic type of cancer, and TNM stage of cancer revealed no marked effects. In the two additional tests, the model predicted MLC with a sensitivity of 66.7% (10 of 15 patients), and it classified the cancer-negative bronchoscopy patients with a specificity of 37.4% (34 of 91 patients).

CONCLUSIONS

Compared to healthy volunteers, patients with PLC had abnormal breath test findings that were consistent with the accelerated catabolism of alkanes and monomethylated alkanes. A predictive model employing nine of these VOCs exhibited sufficient sensitivity and specificity to be considered as a screen for lung cancer in a high-risk population such as adult smokers.

Volatile markers of breast cancer in the breath

Breast cancer is accompanied by increased oxidative stress and induction of polymorphic cytochrome P-450 mixed oxidase enzymes (CYP). Both processes affect the abundance of volatile organic compounds (VOCs) in the breath because oxidative stress causes lipid peroxidation of polyunsaturated fatty acids in membranes, producing alkanes and methylalkanes which are catabolized by CYP. We performed a pilot study of breath VOCs, a potential new marker of disease in women with breast cancer. This was a combined case-control and cross-sectional study of women with abnormal mammograms scheduled for a breast biopsy. Breath samples were analyzed by gas chromatography and mass spectroscopy in order to determine the breath methylated alkane contour (BMAC), a three-dimensional display of the alveolar gradients (abundance in breath minus abundance in room air) of C4-C20 alkanes and monomethylated alkanes. BMACs in women with and without breast cancer were compared using forward stepwise discriminant analysis. Two hundred one breath samples were obtained from women with abnormal mammograms and biopsies read by two pathologists. There were 51 cases of breast cancer in 198 concordant biopsies. The breath test distinguished between women with breast cancer and healthy volunteers with a sensitivity of 94.1% (48/51) and a specificity of 73.8% (31/42) (cross-validated sensitivity 88.2% (45/51), specificity 73.8% (31/42)). Compared to women with abnormal mammograms and no cancer on biopsy, the breath test identified breast cancer with a sensitivity of 62.7% (32/51) and a specificity of 84.0% (42/50) (cross-validated sensitivity of 60.8% (31/51), specificity of 82.0% (41/50)). The negative predictive value (NPV) of a screening breath test for breast cancer was superior to a screening mammogram (99.93% versus 99.89%); the positive predictive value (PPV) of a screening mammogram was superior to a screening breath test (4.63% versus 1.29%). A breath test for markers of oxidative stress accurately identified women with breast cancer, with an NPV superior to a screening mammogram. This breath test could potentially be employed as a primary screen for breast cancer. Confirmatory studies in larger groups are required.

Breath markers of oxidative stress in patients with unstable angina

Cardiac chest pain is accompanied by oxidative stress, which generates alkanes and other volatile organic compounds (VOCs). These VOCs are excreted in the breath and could potentially provide a rational diagnostic marker of disease. The breath methylated alkane contour (BMAC), a 3-dimensional surface plot of C4-C20 alkanes and monomethylated alkanes, provides a comprehensive set of markers of oxidative stress. In this pilot study, we compared BMACs in patients with unstable angina pectoris and in healthy volunteers. Breath VOCs were analyzed in 30 patients with unstable angina confirmed by coronary angiography and in 38 age-matched healthy volunteers with no known history of heart disease (mean age +/- SD, 62.7 +/- 12.3 years and 62.5 +/- 10.0, not significant). BMACs in both groups were compared to identify the combination of VOCs that provided the best discrimination between the 2 groups. Forward stepwise entry discriminant analysis selected 8 VOCs to construct a predictive model that correctly classified unstable angina patients with sensitivity of 90% (27 of 30) and specificity of 73.7% (28 of 38). On cross-validation, sensitivity was 83.3% (25 of 30) and specificity was 71.1% (27 of 38). We conclude that the breath test distinguished between patients with unstable angina and healthy control subjects.

Increased oxidative stress in younger as well as in older humans

BACKGROUND

The free radical theory of aging is based upon the adverse effects of oxidative stress (OS), and indices of OS generally increase with advancing age. However, since OS may also be a normal physiological response in youth, when reactive oxygen species (ROS) act as signal transducers during normal growth and development, we compared markers of OS in normal humans over a wide spectrum of different ages.

METHODS

Fasting breath samples were collected from 102 healthy volunteers (age 9 to 89 years) and volatile organic compounds (VOCs) were assayed by gas chromatography and mass spectroscopy. The intensity of OS in each volunteer was estimated by the breath methylated alkane contour (BMAC), a three-dimensional display of the abundance of C4-C20 alkanes and monomethylated alkanes. The collective abundance of these VOCs in a breath sample was reduced to a single value, the volume under curve (VUC), and correlated with chronological age.

RESULTS

Compared to subjects aged 20-40 years, the mean BMAC VUC was significantly increased in subjects aged < 20 (p < 0.0001) and >40 years (p < 0.001). A cubic function correlated BMAC VUC (x) with chronological age (y): y = 33.7 - 3.29x + 0.072x(2) - 0.0004x(3) (r = 0.48).

CONCLUSIONS

Breath markers of OS were significantly increased both in younger and in older subjects, compared to those aged 20-40 years. Increased OS in older subjects was consistent with previous reports, but increased OS in younger subjects aged < 20 years is a new observation; this may be a normal physiological response in youth.

Oxidative Stress in Critically Ill Patients

Oxygen-derived free radicals play an important role in the development of disease in critically ill patients. Normally, oxygen free radicals are neutralized by antioxidants such as vitamin E or enzymes such as superoxide dismutase. However, in patients who require intensive care, oxygen free radicals become a problem when either a decrease in the removal or an overproduction of the radicals occurs. This oxidative stress and the damage due to it have been implicated in many diseases in critically ill patients. Many drugs and treatments now being investigated are directed toward preventing the damage from oxidative stress. The formation of reactive oxygen species, the damage caused by them, and the body’s defense system against them are reviewed. New interventions are described that may be used in critically ill patients to prevent or treat oxidative damage.