The feasibility of measuring volatile organic compounds (VOCs) on breath in response to a lactulose challenge

Introduction

Fermentation by the microbiome produces many metabolic by products including short chain fatty acids (SCFA), gases and VOCs. Collecting these by products on breath allows for non-invasive biomarker detection. A high abundance of VOCs come from the gastrointestinal tract and they allow us to see what is happening in real time rather than afterward via stool sample collection. VOCs can be endogenously or exogenously produced allowing differentiation between human and microbial functions using baseline collections and subsequent breath collections following the ingestion of a carbohydrate probe.

Methods

25 healthy volunteers completed a 3hr lactulose breath test providing breath samples at 0-, 45-, 90- and 180-minutes post lactulose ingestion. Samples were collected using 500ml polyvinylidene fluoride bags and analysed using SIFT-MS.

Results

We identified 20 VOCs on breath using SIFT-MS. These included the SCFA’s and other significant compounds of interest including, but not limited to hydrogen sulphide, isoprene, and methane. These compounds were all detected in the parts per billion (ppb) range, except for methane which was found in the parts per million (ppm) range. Significant trends in response to lactulose challenge was noticed for three VOCs; isoprene, propanoic acid and acetic acid. All three compounds saw an increase in production over time post lactulose ingestion.

Conclusions

We have developed a simple method for breath VOCs collection which can easily be performed in a non-invasive clinical setting and alongside a hydrogen and methane breath test. Exogenously produced VOCs, namely isoprene, propanoic acid and acetic acid, respond to a lactulose challenge via increase in levels over the time course of a breath test. Most VOCs were found in the ppb range, with the exception of methane in the ppm range, which is as expected due to the concentrations commonly found in hydrogen and methane breath tests and other studies. Further insight into each VOC, its metabolic pathway and clinical relevance could allow for VOCs to become the next generation of breath testing for digestive health and as an alternative to stool testing.