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Breath analysis of ammonia, volatile organic compounds and deuterated water vapor in chronic kidney disease and during dialysis The volatile metabolites present in trace amounts in exhaled breath of healthy individuals and patients, for example those with advanced chronic kidney disease (CKD), can now be detected and quantified by sensitive analytical techniques. In this review, special attention is given to the major retention metabolites resulting from dialysis-dependent CKD stage 5 and especially ammonia, as a potential estimator of the severity of uremia. However, other biomarkers are important, including the hydrocarbons isoprene, ethane and pentane, in that they are likely to indicate tissue injury associated with the dialysis treatment itself. Evaluation of over-hydration, a serious complication of CKD stage5 can be improved by analysis of deuterium in exhaled water vapor after ingestion of a known amount of deuterated water, so providing total body water measurements at the bedside to support clinical management of volume status. The composition of volatile organic compounds (VOCs) in exhaled breath was first investigated using instrumental analytical methods in the 1960s [1,2] and by Pauling and colleagues in the early 1970s [3]. Using the now familiar GC, usually coupled with MS (GC–MS), hundreds of volatile metabolites have been detected in the exhaled breath of healthy people, mostly VOCs but few have been positively identified and fewer quantified even to modest accuracy and precision. Later, Manolis reviewed the diagnostic potential of VOCs in breath analyzed using GC–MS [4]. This work was the stimulus for an increasing interest in breath analysis for clinical diagnosis, a challenge taken up by Phillips and colleagues in the early 1990s [5–7] with a growing number of other research workers attracted to this topic. Thus, in the last two decades, following the development of a variety of sensitive analytical techniques by research scientists and engineers, such as GC–MS coupled with effective capture and preconcentration method for volatile metabolites in exhaled breath, other mass spectrometric methods and spectroscopic methods, the subject has grown rapidly. With involvement of increasing numbers of clinicians and physiologists, the focus has been on the use of breath analysis to noninvasively identify volatile biomarkers of pathophysiological conditions and disease states. This can be seen in the growth of research and review publications in breath analysis and the appearance of the new Journal of Breath Research published by IOP
(London, UK). Useful reports on the scope and application of breath analysis are given in two books, the first published in 2005 [8] and the second recently published in 2013 [9]. While this Review is focused on the potential of breath analysis in probing renal disease and the influence of dialysis treatment, not on experimental developments and protocols, it is pertinent to mention some aspects of breath sampling procedure and analytical methods, since these impinge on the interpretation and the likely quality of the data obtained. This is especially relevant to chronic kidney disease (CKD) where the uremic fetor has long been associated with oral hygiene for reasons which will become apparent. Several techniques have been exploited for the analysis of volatile metabolites in exhaled breath and those utilized in CKD are summarized in Table 1.Thus, it should be noted that GC–MS and most of the analytical procedures that involve the collection of breath samples into some form of vessel or onto some form of (surface) trap followed by offline analysis can compromise the sample, especially when it is realized that the concentrations of the relevant trace compound biomarkers are at low levels ranging from parts-per-million by volume (ppmv) down to parts-per-billion by volume (ppbv). Furthermore, it must be noted that constant calibration of most of the analytical instruments is needed using internal or external standards if sensible accuracy of the VOC concentrations is to be achieved. Thus, it is clearly desirable to
10.4155/BIO.14.26 © 2014 Future Science Ltd
Bioanalysis (2014) 6(6), 843–857
Simon J Davies1,2 , Patrik Španěl1,3 & David Smith*1 Institute for Science & Technology in Medicine, Keele University, Thornburrow Drive, Hartshill, Stoke on Trent, ST4 7QB, UK 2 Department of Nephrology, University Hospital of North Staffordshire, Stoke-on-Trent, ST4 7LN, UK 3 J Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejskova 3, 182 23, Prague 8, Czech Republic *Author for correspondence: Tel.: +44 1782 674988 [email protected] 1
ISSN 1757-6180
843
R eview |
Davies, Španěl & Smith
Table 1. Techniques used for analyses of volatile metabolites in exhaled breath in chronic kidney disease. Techniques
Variants
Notes
GC–MS
Solid-phase microextraction
Hydrocarbons and halocarbons VOC VOC in rats Alkanes and isoprene in hemodialysis Isoprene in peritoneal dialysis Urea Ammonia Trimethylamine Isoprene VOC in rats
Thermal desorption Secondary ESI-MS Selected ion flow tube-MS
Direct breath Bag sampling Direct breath
Proton transfer reaction-MS
Direct breath Quadrupole mass spectrometer Time-of-flight mass spectrometer
Sensors
[89] [90] [64] [74,87] [86] [70] [22,50] [50] [65]
Isoprene C7H14O
[88]
Optoacoustic Cavity ringdown spectroscopy
Ammonia VOC Ammonia Ammonia
[38] [56]
Nanoparticles Carbon nanotubes
Ammonia VOC in rats
Ion mobility spectrometry Infrared laser absorption spectroscopy
Ref.
[57]
[48] [38] [41] [64]
VOC: Volatile organic compound.
Key Terms Volatile metabolites:
Compounds that have a relatively high vapor pressure at room and body temperatures, their molecules can thus be emitted into air and breath. Volatile metabolites enter the breath from alveolar blood or from airways’ surfaces, including the oral and nasal cavities. They can be either products of human metabolism or generated by symbiotic or pathogenic bacteria.
Chronic kidney disease:
Also called kidney failure or renal insufficiency. A condition in which the kidneys fail to adequately filter and remove waste products (uremic toxins) from the blood. Chronic kidney disease stage 5 refers to advanced kidney disease where the filtration rate is
Breath analysis of ammonia, volatile organic compounds and deuterated water vapor in chronic kidney disease and during dialysis The volatile metabolites present in trace amounts in exhaled breath of healthy individuals and patients, for example those with advanced chronic kidney disease (CKD), can now be detected and quantified by sensitive analytical techniques. In this review, special attention is given to the major retention metabolites resulting from dialysis-dependent CKD stage 5 and especially ammonia, as a potential estimator of the severity of uremia. However, other biomarkers are important, including the hydrocarbons isoprene, ethane and pentane, in that they are likely to indicate tissue injury associated with the dialysis treatment itself. Evaluation of over-hydration, a serious complication of CKD stage5 can be improved by analysis of deuterium in exhaled water vapor after ingestion of a known amount of deuterated water, so providing total body water measurements at the bedside to support clinical management of volume status. The composition of volatile organic compounds (VOCs) in exhaled breath was first investigated using instrumental analytical methods in the 1960s [1,2] and by Pauling and colleagues in the early 1970s [3]. Using the now familiar GC, usually coupled with MS (GC–MS), hundreds of volatile metabolites have been detected in the exhaled breath of healthy people, mostly VOCs but few have been positively identified and fewer quantified even to modest accuracy and precision. Later, Manolis reviewed the diagnostic potential of VOCs in breath analyzed using GC–MS [4]. This work was the stimulus for an increasing interest in breath analysis for clinical diagnosis, a challenge taken up by Phillips and colleagues in the early 1990s [5–7] with a growing number of other research workers attracted to this topic. Thus, in the last two decades, following the development of a variety of sensitive analytical techniques by research scientists and engineers, such as GC–MS coupled with effective capture and preconcentration method for volatile metabolites in exhaled breath, other mass spectrometric methods and spectroscopic methods, the subject has grown rapidly. With involvement of increasing numbers of clinicians and physiologists, the focus has been on the use of breath analysis to noninvasively identify volatile biomarkers of pathophysiological conditions and disease states. This can be seen in the growth of research and review publications in breath analysis and the appearance of the new Journal of Breath Research published by IOP
(London, UK). Useful reports on the scope and application of breath analysis are given in two books, the first published in 2005 [8] and the second recently published in 2013 [9]. While this Review is focused on the potential of breath analysis in probing renal disease and the influence of dialysis treatment, not on experimental developments and protocols, it is pertinent to mention some aspects of breath sampling procedure and analytical methods, since these impinge on the interpretation and the likely quality of the data obtained. This is especially relevant to chronic kidney disease (CKD) where the uremic fetor has long been associated with oral hygiene for reasons which will become apparent. Several techniques have been exploited for the analysis of volatile metabolites in exhaled breath and those utilized in CKD are summarized in Table 1.Thus, it should be noted that GC–MS and most of the analytical procedures that involve the collection of breath samples into some form of vessel or onto some form of (surface) trap followed by offline analysis can compromise the sample, especially when it is realized that the concentrations of the relevant trace compound biomarkers are at low levels ranging from parts-per-million by volume (ppmv) down to parts-per-billion by volume (ppbv). Furthermore, it must be noted that constant calibration of most of the analytical instruments is needed using internal or external standards if sensible accuracy of the VOC concentrations is to be achieved. Thus, it is clearly desirable to
10.4155/BIO.14.26 © 2014 Future Science Ltd
Bioanalysis (2014) 6(6), 843–857
Simon J Davies1,2 , Patrik Španěl1,3 & David Smith*1 Institute for Science & Technology in Medicine, Keele University, Thornburrow Drive, Hartshill, Stoke on Trent, ST4 7QB, UK 2 Department of Nephrology, University Hospital of North Staffordshire, Stoke-on-Trent, ST4 7LN, UK 3 J Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejskova 3, 182 23, Prague 8, Czech Republic *Author for correspondence: Tel.: +44 1782 674988 [email protected] 1
ISSN 1757-6180
843
R eview |
Davies, Španěl & Smith
Table 1. Techniques used for analyses of volatile metabolites in exhaled breath in chronic kidney disease. Techniques
Variants
Notes
GC–MS
Solid-phase microextraction
Hydrocarbons and halocarbons VOC VOC in rats Alkanes and isoprene in hemodialysis Isoprene in peritoneal dialysis Urea Ammonia Trimethylamine Isoprene VOC in rats
Thermal desorption Secondary ESI-MS Selected ion flow tube-MS
Direct breath Bag sampling Direct breath
Proton transfer reaction-MS
Direct breath Quadrupole mass spectrometer Time-of-flight mass spectrometer
Sensors
[89] [90] [64] [74,87] [86] [70] [22,50] [50] [65]
Isoprene C7H14O
[88]
Optoacoustic Cavity ringdown spectroscopy
Ammonia VOC Ammonia Ammonia
[38] [56]
Nanoparticles Carbon nanotubes
Ammonia VOC in rats
Ion mobility spectrometry Infrared laser absorption spectroscopy
Ref.
[57]
[48] [38] [41] [64]
VOC: Volatile organic compound.
Key Terms Volatile metabolites:
Compounds that have a relatively high vapor pressure at room and body temperatures, their molecules can thus be emitted into air and breath. Volatile metabolites enter the breath from alveolar blood or from airways’ surfaces, including the oral and nasal cavities. They can be either products of human metabolism or generated by symbiotic or pathogenic bacteria.
Chronic kidney disease:
Also called kidney failure or renal insufficiency. A condition in which the kidneys fail to adequately filter and remove waste products (uremic toxins) from the blood. Chronic kidney disease stage 5 refers to advanced kidney disease where the filtration rate is
