Deficiency and absence of endogenous isoprene in adults, disqualified its putative origin

Abstract

Background: Isoprene (C 5 H 8 ) is a clinically important breath metabolite. Although, hundreds of studies have reported differential expressions in isoprene exhalation as breath biomarker for diverse diseases, the substance couldn't enter to clinical practice as diagnostic marker. Moreover, many experimental/basic observations upon breath isoprene remained unrelated to the corresponding pathophysiological effects on its putative metabolic origin (i.e. mevalonate pathway). Here, we investigated the fundamental reason that hindered the rational interpretation and translation of this marker from basic to clinical science. Methods: Via high-resolution mass-spectrometry based breathomics in 1026 human subjects, we discovered adults with significant deficiency (order of magnitude lower than the normal) and complete absence of breath isoprene. We prospectively applied real-time breathomics, quantitative gene expression analysis of the mevalonate pathway enzymes, lipid-profiling and hemodynamic monitoring on those isoprene deficient subjects and controls. Additionally, the subject with absence of isoprene was followed up throughout different phases of her womanhood. Results: In contrast to convention, we witnessed that adults can live healthy without exhaling isoprene or with significant deficiency. This rare phenotype represents a recessive inheritance. Despite physio-metabolic changes during menstrual cycle (that is known to profoundly affect isoprene exhalation) and profoundly increased plasma cholesterol during pregnancy and after childbirth, isoprene remained absent. All genes of mevalonate pathway enzymes were normally expressed in all participants, without any down-regulation or compensatory upregulation. Conclusions: Absence/deficiency of isoprene despite normal lipid profiles and no mevalonate pathway malfunction disqualifies the long-believed metabolic origin of isoprene from cholesterol biosynthesis. Thus, clinical translation of breath isoprene expressions should not be generally attributed to corresponding pathophysiological effects onto mevalonate/cholesterol pathway. Our finding has refined and optimized the clinical interpretation of isoprene as biomarker in volatile metabolomics and breathomics. Future studies will address the correct metabolic origin of isoprene to imply this important marker to routine practice.

Physiological and metabolic effects of healthy female aging on exhaled breath biomarkers

“…Here, we observed effects of female aging and endocrine steady state (under contraception) on exhaled isoprene. Although C 5 H 8 was believed to be a product of the mevalonate pathway (cholesterol biosynthesis) ( Stone et al., 1993 ), our latest breathomic findings on >1000 subjects in association with lipid profiling and genetic analysis has disregarded the putative in vivo source ( Sukul et al., 2021 ). Here, the overall C 5 H 8 expressions in premenopausal (i.e., gradual increase from preteen to adulthood) and postmenopausal (i.e., maximum increase just after the menopause and then gradual decrease with further aging) women cohorts indicate its relation to sex hormone regulation i.e., estrogen-progesterone interplay.…”

“…High-resolution and real time mass spectrometry based noninvasive, rapid, and repeated evaluation of exhaled volatile metabolites offers immediate overview of various physio-metabolic ( Spacek et al., 2018 ; Sukul et al., 2014 , 2015 , 2017a ), biochemical ( Refat et al., 1991 ; Sukul et al., 2021 ; Weber et al., n.d. ) and pathological/therapeutic processes ( Löser et al., 2020 ; Paardekooper et al., 2017 ; Trefz et al., 2019 ) via breathomics. Previously we have demonstrated the effects of natural menstrual cycle and oral contraception on the exhaled volatile organic compounds (VOCs) profile from healthy adults ( Sukul et al., 2018 ).…”

Liver Impairment—The Potential Application of Volatile Organic Compounds in Hepatology

“…Increased isoprene levels were found in AFLD and advanced fibrosis stage patients [ 35 , 49 , 55 ], and it is suggested that they are the result of impairment in the cholesterol biosynthesis pathway or that they might be the result of disturbed colon flora. However, other literature suggests that subjects should be at rest before testing because isoprene absence/deficiency maybe the result of exercise and that generally, it should not be attributed to pathophysiological effects onto mevalonate/cholesterol pathways [ 73 , 74 ]. Increased acetone levels were found in stage 1 or 2 fibrosis patients, as well as NAFLD and AH patients [ 5 , 21 , 55 ]; acetone is believed to be associated with lipolysis and carbohydrate metabolism, where increased expression of the CYP450 enzyme would result in fatty acid beta-oxidation, which then would lead to excess of acetyl-CoA.…”

Putative markers for the detection of early-stage bladder cancer selected by urine metabolomics

“…Even if these putative markers exhibit discriminating power from the computational point of view, we need carefully examine their true endogenous origins of substances to see whether they are qualified markers. An important example is the disqualification of the putative in vivo origin of isoprene, which is repeatedly reported as a metabolic marker of cancer, cardio-pulmonary diseases, and rare genetic disorders in human [37].…”