The Use of VOCs in Biomarker Research
The journey towards non-invasive breath tests that can be used for the early detection of diseases such as cancer, gastrointestinal diseases, liver disease, and more is a promising, and ever-advancing field. As with any relatively new area of research, there are several challenges that need to be overcome before implementation as a diagnostic and monitoring test is possible. Accordingly, the number of breath-based biomarkers that have been successfully translated from bench to bedside to diagnostic tests used routinely in the clinic today are limited. An untargeted approach is traditionally used to identify potential breath biomarkers, an approach whereby a broad spectrum of the VOCs on patients’ breath is analyzed and compared to a control population, and potential biomarkers are searched for in the differences between the data. Further to this, there have been a lack of standardized controls for both background air and healthy participant comparisons.
There are over 1000 different volatile organic compounds (VOCs) found on the breath, so the combination of an untargeted approach without adequate controls can lead to a high amount of false positive hits, especially as the variability of VOCs in a natural human population is not well described. Establishing the composition of normal breath is an essential foundational step toward improving breath biomarker research. To address this crucial need for improved biomarker discovery we have developed the Breath Biopsy VOC Atlas, the largest available dataset of validated VOCs on the breath, identified in a group of diverse, healthy volunteers.
What is the VOC Atlas?
The VOC Atlas is a database of VOCs that we have developed through extensive study, containing compounds that were commonly found on the breath, alongside their concentrations in a group of healthy volunteers. The compounds within the VOC Atlas have been carefully validated for their presence on the breath, as opposed to originating from environmental contaminants. This is an important step for breath analysis, recently exemplified in an article in Drug Discovery News, where a promising VOC lead in fact turned out to be an environmental contaminant from the handwash at the hospital location where the disease cohort was based. This demonstrates why establishing a baseline of statistically supported validated breath VOCs is so important.
As well as providing precise information about the baseline levels of VOCs, the VOC Atlas also includes scientific context for a growing number of these molecules, including the biochemical pathways that produce them, and which metabolic processes in the body they are linked to. We previously explored why understanding the origins of VOCs in the body is particularly important. It is of utmost importance to ensure that diagnostic technology is based on strong scientific evidence, and so it is essential to ensure that we know exactly where VOCs originate mechanistically within the body. This will allow for a more confident, and targeted selection of candidate VOCs when developing study designs for identifying disease biomarkers in the breath.
Further to understanding where VOCs originate from in the body, it is also important to know how differences in individuals can affect concentrations of VOCs in exhaled breath. People naturally show variation in their bodily metabolic pathways due to a combination of genetics, dietary, and other environmental factors. To set a baseline for understanding how this can affect compounds on the breath, the VOC Atlas contains breath samples from a heterogenous population over broad demographic criteria to map out the normal variation that is expected in a healthy population. The VOC Atlas can therefore act as a robust comparison group when measuring potential VOC disease biomarkers on the breath.
Validated VOCs can provide ‘Metabolic Snapshots’ of the Body
There are over 150 VOCs in the VOC Atlas at present, spanning over a range of chemical classes and originate from both endogenous sources such as organ-specific metabolism to exogenous sources such as bacterial metabolism. Up until this point, only a relatively limited number of VOCs have been specifically linked to metabolic processes in the body and disease. One such example is “fetor hepaticus” identified more than 2500 years ago by Hippocrates, who linked a specific breath odor to liver failure. We now know dimethyl sulfide is one of the major VOCs responsible for this odor, and is easily detectable in the breath (1,2).
For example, one of the most abundant VOCs in the breath is acetaldehyde. Acetaldehyde is an aldehyde produced in different ways in the body, both through immune cells such as eosinophils and neutrophils, as well as through bacterial metabolism (3). Another key compound in the VOC Atlas is the ketone, acetone. Both acetone and acetaldehyde can be produced in the body through fatty acid beta-oxidation, which involves a cyclical process whereby a large acyl-CoA molecule is broken down into smaller acetyl CoA molecules. This process is an important energy source, and its relative abundance in the body changes depending on circadian rhythms and ongoing energy demands. Therefore, detecting the volatile metabolites of fatty acid beta-oxidation in the breath samples of volunteers can give a direct insight into this metabolic pathway, particularly if this pathway is thought to have a specific role in the disease process of interest.
As our research knowledge expands, we will be adding further validated breath VOCs and their links to specific organs and pathways, and ultimately to specific diseases in the VOC Atlas.
The VOC Atlas is a growing resource
We are on a very ambitious mission to save 100,000 lives and $1.5 billion in healthcare costs. Here at Owlstone Medical, we have an innovative and talented team that is dedicated to achieving our goal of non-invasive breath tests for disease diagnosis and monitoring being used in the clinic. One of the biggest challenges to breath biomarker research currently is the lack of validated VOCs on the breath, and a lack of understanding of how VOC concentrations in the breath differ in individuals, as well as across different dietary, and lifestyle factors. The VOC Atlas is our answer to these challenges.
We hope that the VOC Atlas will serve as an important reference resource for the entire breath research community, providing a comparison database from which known chemical VOC baselines can be established. We believe that the VOC Atlas is an incredible resource, and we hope that it will bring substantial benefit to the community of breath biomarker researchers that work alongside us. The VOC Atlas is intended as an ever-expanding resource that will be added to as more research is conducted on healthy participants. We look forward to seeing the benefits to the community that the VOC Atlas will provide.
We are the world leader in Breath Biopsy for early detection and precision medicine, and we are always glad to offer support on how to include breath analysis in your research. If you are considering working with us and would like to utilize our Breath Biopsy OMNI platform in your research our team of scientists will now be able to cross-check customer data against our VOC Atlas to better understand how individual VOCs behave in a healthy population and eventually across different disease states. Researchers performing their own breath studies using Owlstone’s Breath Biopsy Collection Station will also be able to submit identified VOCs for reference against the VOC Atlas to provide contextual information, including whether the compound of interest is truly on-breath. We also have our in vitro headspace sampling pipeline supported by our Breath Biopsy Services, which can help you to identify VOCs produced by your laboratory samples that have the potential to be effective biomarkers for non-invasive clinical breath testing. If you have any questions or would like more information, please do not hesitate to contact us to discuss investigating VOC biomarkers for your disease of interest.
- Tangerman A, Meuwese-Arends M, Jansen JMJ. Cause and composition of foetor hepaticus. The Lancet. 1994 Feb 19;343(8895):483. DOI: 10.1016/s0140-6736(94)92729-4
- Ajibola OA, Smith D, Španěl P, Ferns GAA. Effects of dietary nutrients on volatile breath metabolites. J Nutr Sci. 2013 ed;2:e34. DOI: 10.1017/jns.2013.26
- Belizário JE, Faintuch J, Malpartida MG. Breath biopsy and discovery of exclusive volatile organic compounds for diagnosis of infectious diseases. Frontiers in cellular and infection microbiology. 2021 Jan 7;10:564194. DOI: 10.3389/fcimb.2020.564194