Introduction

Non-invasive biomarkers that enable accurate diagnosis, patient stratification, and therapy monitoring in irritable bowel syndrome (IBS) are still lacking in clinical practice. Volatile organic compounds (VOCs) produced by the host metabolism, inflammatory processes, and the gut microbiota are present in exhaled breath and have recently gained attention as promising biomarker candidates. Prior research (Van Malderen et al. (2020)) demonstrated that breath VOC profiling could accurately distinguish IBS patients from healthy controls using multicapillary column/ion‑mobility spectrometry (MCC/IMS).

Aims & Methods

The present study aimed to assess the potential of high-resolution gas chromatography-quadrupole time‑of‑flight mass spectrometry (GC-QTOF-MS) profiling of breath VOCs to define distinct compound classes that enhance the mechanistic understanding of breath-based biomarkers in IBS. To this end, breath samples from 12 IBS patients and 11 healthy controls were collected, together with matched ambient air samples and were analyzed using GC-QTOF-MS. Breath samples were corrected by background subtraction and least‑absolute‑shrinkage‑and‑selection‑operator (LASSO) regression was applied with leave‑one‑out cross‑validation (LOOCV) to identify discriminative VOC signatures. The feature set was subsequently filtered to exclude sporadically detected VOCs and compounds of exogenous (non-host) origin. Finally, the remaining VOCs were mapped to putative pathways.

Results

IBS patients had a mean ± SD age of 36 ± 15.3 years, compared with 56 ± 15.4 for the healthy controls. The male-to-female ratio was 3:9 in the IBS cohort and 5:6 among the healthy controls. Within the IBS group, 7 patients had diarrhea-predominant IBS, 4 had constipation-predominant IBS, and 1 had mixed-type IBS. The LASSO regression model, validated with LOOCV, demonstrated high discriminative performance in differentiating IBS patients from healthy controls, with the corresponding model metrics in Table 1. Furthermore, the feature selection identified a panel of discriminative VOCs - predominantly alkanes, aldehydes, and ketones - that were up-regulated in the IBS breath profiles. These elevated compound classes could putatively be linked to mechanisms relevant to IBS pathophysiology, including altered microbial metabolism, increased oxidative stress, and low-grade inflammation.

Table 1: Model metrics

Conclusion

Volatomic breath profiling in IBS, shows great potential for discriminating IBS from healthy controls and for defining clinically relevant biomarkers composed of specific VOCs. Nonetheless, the limited sample size might risk model overfitting and introduces uncertainty in the estimates. Further research including larger, confounder-controlled cohorts is necessary, along with the targeted validation of the identified VOCs to further confirm their mechanistic role in IBS.

References

Van Malderen K, Hanning N, Lambrechts H, Haverhals T, Van Marcke S, Ceuleers H, De Man JG, De Winter BY, Lamote K, De Schepper HU. Volatile organic compound profiling as a potential biomarker in irritable bowel syndrome: A feasibility study. Front Med (Lausanne). 2022 Aug 4;9:960000. doi: 10.3389/fmed.2022.960000. PMID: 35991639; PMCID: PMC9388331.

Clinical Case Summary

A 57 years-old patient with a history of active smoking, moderate body overweight (BMI 29 Kg/mq) and mild systolic hypertension in treatment with Olmesartan complained history of chronic diarrea and abdominal pain since 2006, rarely associated with hematochezia. After replacement of antihypertensive therapy to eliminate a potential confouding factor, he underwent multiple colonoscopies through the years with nonspecific findings until 2017, when moderated discontinuos inflammation with multiple erosions was seen in the transverse colon and in the rectum. Histologic examination described presence of chronic inflammation with cryptic microabscesses and cryptitis suggetive for Crohn's disease, while intestinal ultrasound revealed no small bowel localizations. He was treated with 2.4 daily grams of oral mesalamine with benefit until the end of 2023, when he came up to our clinic complaining resumption of bloody diarrhoea and abdominal pain, with 3-4 liquid stools per day. Addition of topic mesalamine was not of benefit. The patient underwent another colonoscopy which confirmed presence of hyperemic mucosa with diffuse erosions in the rectum, with histology confirming active Inflammatory Bowel Disease. In march 2024, after neurological investigations for recurrent paresthesias and strength deficits, the patient was diagnosed with relapsing-remitting Multiple Sclerosis. After multidisciplinary consultation, negative cardiologic evaluation, chest X-ray and blood screening exams, in October 2024 the patient started the anti sphingosine-1 phosphate Ozanimod, which was well-tolerated at maintenance dose of 0.92 milligrams per day. Three months after, he came back for scheduled follow-up reporting 1 or 2 daily evacuations in absence of abdominal pain and rectal bleeding. Calprotectin levels droped up to 17 ug/g. He also described complete neurological remission and complete absence of drug side effects.

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