13C-breath tests: current state of the art and future directions

Exhaled Breath Analysis: From Laboratory Test to Wearable Sensing

Breath analysis and monitoring have emerged as pivotal components in both clinical research and daily health management, particularly in addressing the global health challenges posed by respiratory and metabolic disorders. The advancement of breath analysis strategies necessitates a multidisciplinary approach, seamlessly integrating expertise from medicine, biology, engineering, and materials science. Recent innovations in laboratory methodologies and wearable sensing technologies have ushered in an era of precise, real-time, and in situ breath analysis and monitoring. This comprehensive review elucidates the physical and chemical aspects of breath analysis, encompassing respiratory parameters and both volatile and non-volatile constituents. It emphasizes their physiological and clinical significance, while also exploring cutting-edge laboratory testing techniques and state-of-the-art wearable devices. Furthermore, the review delves into the application of sophisticated data processing technologies in the burgeoning field of breathomics and examines the potential of breath control in human-machine interaction paradigms. Additionally, it provides insights into the challenges of translating innovative laboratory and wearable concepts into mainstream clinical and daily practice. Continued innovation and interdisciplinary collaboration will drive progress in breath analysis, potentially revolutionizing personalized medicine through entirely non-invasive breath methodology.

The 13C Glucose Breath Test Accurately Identifies Insulin Resistance in People With Type 1 Diabetes

OBJECTIVE

This study investigated whether the delta-over-baseline of exhaled 13CO2 (Δ13CO2), generated from a 13C glucose breath test (13C-GBT), measured insulin resistance (IR) in people with type 1 diabetes, using the hyperinsulinemic-euglycemic clamp (HEC) as a reference method. The secondary objective was to compare the 13C-GBT with the estimated glucose disposal rate (eGDR).

METHODS

A 40 mU/m2/min HEC and 2 separate 13C-GBTs (euglycemic with insulin bolus and hyperglycemic without bolus) were consecutively performed in 44 adults with type 1 diabetes with varying body compositions. eGDR was calculated based on hemoglobin A1c (HbA1c), presence of hypertension, and waist circumference.

RESULTS

The mean glucose disposal rate (M-value) was 5.9 ± 3.1 mg/kg/min and mean euglycemic Δ13CO2 was 6.4 ± 2.1 δ‰, while median eGDR was 5.9 [4.3-9.8] mg/kg/min. The hyperglycemic Δ13CO2 did not correlate with the M-value, while the euglycemic Δ13CO2 and the M-value correlated strongly (r = 0.74, P < .001). The correlation between M-value and eGDR was more moderate (Spearman's rho = 0.63, P < .001). Linear regression showed an association between Δ13CO2 and M-value, adjusted for age, sex, and HbA1c ]adjusted R² = 0.52, B = 1.16, 95% confidence interval (CI) .80-1.52, P < .001]. The area under the receiver-operator characteristics curve for Δ13CO2 to identify subjects with IR (M-value < 4.9 mg/kg/min) was 0.81 (95% CI .68-.94, P < .001). The optimal cut-off for Δ13CO2 to identify subjects with IR was ≤ 5.8 δ‰.

CONCLUSION

Under euglycemic conditions, the 13C-GBT accurately identified individuals with type 1 diabetes and concurrent IR, suggesting its potential as a valuable noninvasive index. Clinical Trial Identifier: NCT04623320.

CO2 scrubbing, zero gases, Keeling plots, and a mathematical approach to ameliorate the deleterious effects of ambient CO2 during 13 C breath testing in humans and animals

13 C breath testing is increasingly used in physiology and ecology research because of what it reveals about the different fuels that animals oxidize to meet their energetic demands. Here I review the practice of 13 C breath testing in humans and other animals and describe the impact that contamination by ambient/background CO2 in the air can have on the accuracy of 13 C breath measurements. I briefly discuss physical methods to avoid sample contamination as well as the Keeling plot approach that researchers have been using for the past two decades to estimate δ13 C from breath samples mixed with ambient CO2 . Unfortunately, Keeling plots are not suited for 13 C breath testing in common situations where (1) a subject's VCO2 is dynamic, (2) ambient [CO2 ] may change, (3) a subject is sensitive to hypercapnia, or (4) in any flow-through indirect calorimetry system. As such, I present a mathematical solution that addresses these issues by using information about the instantaneous [CO2 ] and the δ13 CO2 of ambient air as well as the diluted breath sample to back-calculate the δ13 CO2 in the CO2 exhaled by the animal. I validate this approach by titrating a sample of 13 C-enriched gas into an air stream and demonstrate its ability to provide accurate values across a wide range of breath and air mixtures. This approach allows researchers to instantaneously calculate the δ13 C of exhaled gas of humans or other animals in real time without having to scrub ambient CO2 or rely on estimated values.

Amplified Photothermal Phase Modulation for Carbon Dioxide Detection by Operating a Dual-Mode Interferometer at Destructive Interference

Photothermal interferometry is a highly sensitive spectroscopic technique for trace gas detection. However, the performance of the state-of-the-art laser spectroscopic sensors is still insufficient for some high-precision applications. Here, we demonstrate optical phase-modulation amplification by operating a dual-mode optical fiber interferometer at destructive interference for ultrasensitive carbon dioxide detection. With a 50 cm long dual-mode hollow-core fiber, amplification of photothermal phase modulation by a factor of nearly 20 is achieved, which enables carbon dioxide detection down to 1 parts-per-billion with a dynamic range of over 7 orders of magnitude. This technique could be readily used to improve the sensitivity of phase modulation-based sensors with a compact and simple configuration.

The Inhibitory Effects of New Zealand Pine Bark (Enzogenol®) on α-Amylase, α-Glucosidase, and Dipeptidyl Peptidase-4 (DPP-4) Enzymes

The New Zealand pine bark extract (Enzogenol^®) has previously been shown to elicit acute hypoglycaemic effects in humans. The present study investigated the underlying mechanisms of Enzogenol^® in reducing postprandial glucose in humans. The potential inhibitory action of Enzogenol^® against digestive enzymes: α-amylase and α-glucosidase, and dipeptidyl peptidase-4 (DPP-4) enzyme was determined. Enzogenol^® demonstrated the ability to inhibit all three enzymes: α-amylase enzyme activity (IC₅₀ 3.98 ± 0.11 mg/mL), α-glucosidase enzyme activity (IC₅₀ 13.02 ± 0.28 μg/mL), and DPP-4 enzyme activity (IC₅₀ 2.51 ± 0.04 mg/mL). The present findings indicate the potential for Enzogenol^® to improve postprandial glycaemia by delaying carbohydrate digestion via the inhibition of digestive enzymes (α-amylase and α-glucosidase), and enhancing the incretin effect via inhibiting the dipeptidyl-peptidase-4 enzyme. The inhibitory actions of Enzogenol^® on enzymes should therefore be further validated in humans for its potential use in type 2 diabetes mellitus prevention and management.

Non-invasive breath collection in murine models using a newly developed sampling device

Volatile organic compounds (VOCs) in exhaled breath have the potential to be used as biomarkers for screening and diagnosis of diseases. Clinical studies are often complicated by both modifiable and non-modifiable factors influencing the composition of VOCs in exhaled breath. Small laboratory animal studies contribute in obtaining fundamental insight in alterations in VOC composition in exhaled breath and thereby facilitate the design and analysis of clinical research. However, long term animal experiments are often limited by invasive breath collection methods and terminal experiments. To overcome this problem, a novel device was developed for non-invasive breath collection in mice using glass nose-only restrainers thereby omitting the need of anesthetics. C57Bl/6J mice were used to test reproducibility and different air sampling settings for air-flow (ml/min) and time (minutes). Exhaled air was collected on desorption tubes and analysed for VOCs by gas chromatography time-of-flight mass spectrometry (GC-tof-MS). In total 27 compounds were putatively identified and used to assess the variability of the VOC measurements in the breath collections. Best reproducibility is obtained when using an air flow of 185 ml/min and a collection time of 20 minutes. Due to the non-invasive nature of breath collections in murine models, this device has the potential to facilitate VOC research in relation to disturbed metabolism and or disease pathways.

The Short-Term Effects and Tolerability of Low-Viscosity Soluble Fibre on Gastroparesis Patients: A Pilot Clinical Intervention Study

Gastroparesis is a motility disorder that causes severe gastric symptoms and delayed gastric emptying, where the majority of sufferers are females (80%), with 29% of sufferers also diagnosed with Type-1 or Type-2 diabetes. Current clinical recommendations involve stringent dietary restriction and includes the avoidance and minimization of dietary fibre. Dietary fibre lowers the glycaemic index of food, reduces inflammation and provides laxation. Lack of dietary fibre in the diet can affect long-term gastrointestinal health. Our previously published rheological study demonstrated that "low-viscosity" soluble fibres could be a potentially tolerable source of fibre for the gastroparetic population. A randomised controlled crossover pilot clinical study was designed to compare Partially-hydrolysed guar gum or PHGG (test fibre 1), gum Arabic (test fibre 2), psyllium husk (positive control) and water (negative control) in mild-to-moderate symptomatic gastroparesis patients (requiring no enteral tube feeding). The principal aim of the study was to determine the short-term physiological effects and tolerability of the test fibres. In n = 10 female participants, post-prandial blood glucose, gastroparesis symptoms, and breath test measurements were recorded. Normalized clinical data revealed that test fibres PHGG and gum Arabic were able to regulate blood glucose comparable to psyllium husk, while causing far fewer symptoms, equivalent to negative control. The test fibres did not greatly delay mouth-to-caecum transit, though more data is needed. The study data looks promising, and a longer-term study investigating these test fibres is being planned.

Breath Biomarkers in Diagnostic Applications

The detection of chemical compounds in exhaled human breath presents an opportunity to determine physiological state, diagnose disease or assess environmental exposure. Recent advancements in metabolomics research have led to improved capabilities to explore human metabolic profiles in breath. Despite some notable challenges in sampling and analysis, exhaled breath represents a desirable medium for metabolomics applications, foremost due to its non-invasive, convenient and practically limitless availability. Several breath-based tests that target either endogenous or exogenous gas-phase compounds are currently established and are in practical and/or clinical use. This review outlines the concept of breath analysis in the context of these unique tests and their applications. The respective breath biomarkers targeted in each test are discussed in relation to their physiological production in the human body and the development and implementation of the associated tests. The paper concludes with a brief insight into prospective tests and an outlook of the future direction of breath research.

Isotopic gas analysis by means of mid-infrared photoacoustic spectroscopy targeting human exhaled air

There is a great need for cost-efficient non-invasive medical diagnostic tools for analyzing humanly exhaled air. Compared to present day methods, photoacoustic spectroscopy (PAS) can provide a compact and portable (bedside), sensitive and inexpensive solution. We demonstrate a novel portable photoacoustic spectroscopic platform for isotopic measurements of methane (CH₄). We identify and discriminate the ¹²CH₄- and ¹³CH₄ isotopologues and determine their mixing ratio. An Allan deviation analysis shows that the noise equivalent concentration for CH₄ is 200 ppt (pmol/mol) at 100 s of integration time, corresponding to a normalized noise equivalent absorption coefficient of 5.1×10^-9Wcm^-1Hz^-1/2, potentially making the PAS sensor a truly disruptive instrument for bedside monitoring using isotope tracers by providing real-time metabolism data to clinical personnel.

Overview of Breath Testing in Clinical Practice in North America

Human breath is an easily, noninvasively obtained substance. It offers insight into metabolism and is used to diagnose disaccharide malabsorption, infection, small bowel bacterial over growth, and transit times. Herein, we discuss the readily available clinical breath tests, how they function, how they are administered and interpreted and some pitfalls in their use.

Optimisation, validation and field applicability of a 13C-sucrose breath test to assess intestinal function in environmental enteropathy among children in resource poor settings: study protocol for a prospective study in Bangladesh, India, Kenya, Jamaica, Peru and Zambia

INTRODUCTION

Environmental enteropathy (EE) is suspected to be a cause of growth faltering in children with sustained exposure to enteric pathogens, typically in resource-limited settings. A major hindrance to EE research is the lack of sensitive, non-invasive biomarkers. Current biomarkers measure intestinal permeability and inflammation, but not the functional capacity of the gut. Australian researchers have demonstrated proof of concept for an EE breath test based on using naturally 13C-enriched sucrose, derived from maize, to assay intestinal sucrase activity, a digestive enzyme that is impaired in villus blunting. Here, we describe a coordinated research project to optimise, validate and evaluate the usability of a breath test protocol based on highly enriched 13C-sucrose to quantify physiological dysfunction in EE in relevant target populations.

METHODS AND ANALYSIS

We use the 13C-sucrose breath test (13C-SBT) to evaluate intestinal sucrase activity in two phases. First, an optimisation and validation phase will (1) confirm that a 13C-SBT using highly enriched sucrose tracers reports similar information to the naturally enriched 13C-SBT; (2) examine the dose-response relationship of the test to an intestinal sucrase inhibitor; (3) validate the 13C-SBT in paediatric coeliac disease (4) validate the highly enriched 13C-SBT against EE defined by biopsy in adults and (5) validate the 13C-SBT against EE defined by the urinary lactulose:rhamnose ratio (LR) among children in Peru. Second, a cross-sectional study will be conducted in six resource-limited countries (Bangladesh, India, Jamaica, Kenya, Peru and Zambia) to test the usability of the optimised 13C-SBT to assess EE among 600 children aged 12-15 months old.

ETHICS AND DISSEMINATION

Ethical approval will be obtained from each participating study site. By working as a consortium, the test, if shown to be informative of EE, will demonstrate strong evidence for utility across diverse, low-income and middle-income country paediatric populations.

TRIAL REGISTRATION NUMBER

NCT04109352; Pre-results.

Short Communication: The effects of physical feed properties on gastric emptying in pigs measured with the 13C breath test

The performance of pigs is affected by the rate of nutrient absorption in the gastrointestinal tract, which depends in turn strongly on the rate of stomach emptying. The 13C breath test provides a non-invasive diagnostic tool to measure gastric emptying patterns. Despite the wide acceptance of this method in human intervention studies, it has not found its way to the domain of animal sciences. In this study, we used the breath test to measure gastric emptying in young growing pigs using [1-13C] octanoic acid to trace digesta solids and [1-13C] glycine to study liquids. Pigs were fed a starch-rich diet, varying in starch source (isolated starch from barley, maize or high-amylose maize) or form (isolated barley starch, ground barley or extruded barley), after which 13CO2 enrichment was frequently measured during 11 h. Outliers in 13CO2 enrichment in the response curve of each pig were identified with a Cook's distance outlier test in combination with a leave-one-out analysis. Effects of experimental treatments on breath test parameters were tested using a GLM. In general, pigs were easy to train and the tailor-made mask allowed effortless sampling. Gastric emptying of all pigs followed a biphasic pattern, with a higher 13C recovery during the first peak. The first peak in gastric emptying of solids reached its maximum enrichment within 2 h after feeding in all cases. For digesta liquids, this peak was reached earlier for pigs fed ground barley (2.2 h after feeding), compared to pigs fed diets containing isolated starch (2.8 h after feeding). The second peak in gastric emptying of solids was reached later for pigs fed ground barley (5.9 h after feeding), compared with pigs fed extruded barley (4.5 h after feeding) and pigs fed diets containing isolated barley starch (4.8 h after feeding). In conclusion, the 13C breath test is a convenient, non-invasive tool to gain more insights into the gastric emptying pattern of pigs.

A novel variant of the 13C-methacetin liver function breath test that eliminates the confounding effect of individual differences in systemic CO2 kinetics

The principle of dynamic liver function breath tests is founded on the administration of a ¹³C-labeled drug and subsequent monitoring of ¹³CO₂ in the breath, quantified as time series delta over natural baseline ¹³CO₂ (DOB) liberated from the drug during hepatic CYP-dependent detoxification. One confounding factor limiting the diagnostic value of such tests is that only a fraction of the liberated ¹³CO₂ is immediately exhaled, while another fraction is taken up by body compartments from which it returns with delay to the plasma. The aims of this study were to establish a novel variant of the methacetin-based breath test LiMAx that allows to estimate and to eliminate the confounding effect of systemic ¹³CO₂ distribution on the DOB curve and thus enables a more reliable assessment of the hepatic detoxification capacity compared with the conventional LiMAx test. We designed a new test variant (named "2DOB") consisting of two consecutive phases. Phase 1 is initiated by the intravenous administration of ¹³C-bicarbonate. Phase 2 starts about 30 min later with the intravenous administration of the ¹³C-labelled test drug. Using compartment modelling, the resulting 2-phasic DOB curve yields the rate constants for the irreversible elimination and the reversible exchange of plasma ¹³CO₂ with body compartments (phase 1) and for the detoxification and exchange of the drug with body compartments (phase 2). We carried out the 2DOB test with the test drug ¹³C-methacetin in 16 subjects with chronic liver pathologies and 22 normal subjects, who also underwent the conventional LiMAx test. Individual differences in the systemic CO₂ kinetics can lead to deviations up to a factor of 2 in the maximum of DOB curves (coefficient of variation CV ≈ 0.2) which, in particular, may hamper the discrimination between subjects with normal or mildly impaired detoxification capacities. The novel test revealed that a significant portion of the drug is not immediately metabolized, but transiently taken up into a storage compartment. Intriguingly, not only the hepatic detoxification rate but also the storage capacity of the drug, turned out to be indicative for a normal liver function. We thus used both parameters to define a scoring function which yielded an excellent disease classification (AUC = 0.95) and a high correlation with the MELD score (R_Spearman = 0.92). The novel test variant 2DOB promises a significant improvement in the assessment of impaired hepatic detoxification capacity. The suitability of the test for the reliable characterization of the natural history of chronic liver diseases (fatty liver-fibrosis-cirrhosis) has to be assessed in further studies.

Accuracy of the 13C-glucose breath test to identify insulin resistance in non-diabetic adults

AIMS

To assess the validity of the ¹³C-glucose breath test (¹³C-GBT) to identify insulin resistance (IR) in non-diabetic individuals, using hyperinsulinemic-euglycemic clamps as gold standard. This validity was compared with that of other IR surrogates.

METHODOLOGY

Non-diabetic adults were studied in a cross-sectional design. In a first appointment, oral glucose tolerance tests were conducted simultaneously with ¹³C-GBTs. Oral 75 g glucose dissolved in 150 ml water, followed by 1.5 mg/Kg body weight U-¹³C-glucose dissolved in 50 ml water, was administered. Breath and blood samples were collected at baseline and at 30-min intervals. The percentages of glucose-oxidized dose at given periods were calculated. Clamps were conducted a week later. A clamp-derived M value ≤ 6.0 mg/kg*min was used as cut-off. ROC curves were constructed for ¹³C-GBT, fasting insulin, HOMA, and ISI-composite.

RESULTS

Thirty-eight subjects completed the study protocol. The correlation coefficient between the ¹³C-GBT derived glucose-oxidized dose at 180 min and M values was 0.524 (p = 0.001). The optimal value to identify IR with the ¹³C-GBT was 4.23% (AUC 0.81; ₉₅CI 0.66, 0.96; accuracy 0.82, ₉₅CI 0.66, 0.92). The ¹³C-GBT sensitivity (0.88) was higher than HOMA and fasting insulin sensitivities (0.83 and 0.75 respectively), while their specificities were comparable (0.71, 0.71, and 0.79, respectively). The sensitivity of ISI-C was higher (0.92) than that of the ¹³C-GBT, but its specificity was poor (0.36). The accuracy of the ¹³C-GBT was superior to that of the other studied surrogates.

CONCLUSIONS

The ¹³C-GBT is a valid and accurate method to detect IR in non-diabetic adults. Therefore, it is potentially useful in clinical and community settings.

The safety and sensitivity of a telemetric capsule to monitor gastrointestinal hydrogen production in vivo in healthy subjects: a pilot trial comparison to concurrent breath analysis

BACKGROUND

Intestinal gases are currently used for the diagnosis of disorders including small intestinal bacterial overgrowth and carbohydrate malabsorption.

AIM

To compare the performance of measuring hydrogen production within the gut directly with the telemetric gas-sensing capsule with that of indirect measurement through breath testing.

METHODS

Using standard breath testing protocols, the capsules and breath tests were simultaneously evaluated in a single-blinded trial in 12 healthy subjects. Eight received a single dose of 1.25-40 g inulin and four 20 or 40 g glucose. Safety and reliability of the capsules were also assessed.

RESULTS

There were no reported adverse events. All capsules were retrieved and operated without failure. Capsule measurements were in agreement with breath test measurements in magnitude but not in timing; minimal hydrogen production was observed after glucose ingestion and capsule measurements correlated with breath hydrogen after ingestion of 40 g inulin. A dose-dependent increase in concentration of hydrogen was observed from the capsule following ingestion of inulin as low as 1.25 g compared with >10 g for breath measurements. Specifically, the capsule measured >3000 times higher concentrations of hydrogen compared to breath tests, resulting in a signal-to-noise ratio of 23.4 for the capsule compared to 4.2 for the breath test.

CONCLUSIONS

The capsule showed high sensitivity and signal-to-noise ratio in measuring luminal hydrogen concentrations, provided information on the site of intestinal gas production, and demonstrated safety and reliability. The capsule has potential for improving diagnostic precision for disorders such as small intestinal bacterial overgrowth.

Non-invasive diagnostic tests for Helicobacter pylori infection

BACKGROUND

Helicobacter pylori (H pylori) infection has been implicated in a number of malignancies and non-malignant conditions including peptic ulcers, non-ulcer dyspepsia, recurrent peptic ulcer bleeding, unexplained iron deficiency anaemia, idiopathic thrombocytopaenia purpura, and colorectal adenomas. The confirmatory diagnosis of H pylori is by endoscopic biopsy, followed by histopathological examination using haemotoxylin and eosin (H & E) stain or special stains such as Giemsa stain and Warthin-Starry stain. Special stains are more accurate than H & E stain. There is significant uncertainty about the diagnostic accuracy of non-invasive tests for diagnosis of H pylori.

OBJECTIVES

To compare the diagnostic accuracy of urea breath test, serology, and stool antigen test, used alone or in combination, for diagnosis of H pylori infection in symptomatic and asymptomatic people, so that eradication therapy for H pylori can be started.

SEARCH METHODS

We searched MEDLINE, Embase, the Science Citation Index and the National Institute for Health Research Health Technology Assessment Database on 4 March 2016. We screened references in the included studies to identify additional studies. We also conducted citation searches of relevant studies, most recently on 4 December 2016. We did not restrict studies by language or publication status, or whether data were collected prospectively or retrospectively.

SELECTION CRITERIA

We included diagnostic accuracy studies that evaluated at least one of the index tests (urea breath test using isotopes such as 13C or 14C, serology and stool antigen test) against the reference standard (histopathological examination using H & E stain, special stains or immunohistochemical stain) in people suspected of having H pylori infection.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened the references to identify relevant studies and independently extracted data. We assessed the methodological quality of studies using the QUADAS-2 tool. We performed meta-analysis by using the hierarchical summary receiver operating characteristic (HSROC) model to estimate and compare SROC curves. Where appropriate, we used bivariate or univariate logistic regression models to estimate summary sensitivities and specificities.

MAIN RESULTS

We included 101 studies involving 11,003 participants, of which 5839 participants (53.1%) had H pylori infection. The prevalence of H pylori infection in the studies ranged from 15.2% to 94.7%, with a median prevalence of 53.7% (interquartile range 42.0% to 66.5%). Most of the studies (57%) included participants with dyspepsia and 53 studies excluded participants who recently had proton pump inhibitors or antibiotics.There was at least an unclear risk of bias or unclear applicability concern for each study.Of the 101 studies, 15 compared the accuracy of two index tests and two studies compared the accuracy of three index tests. Thirty-four studies (4242 participants) evaluated serology; 29 studies (2988 participants) evaluated stool antigen test; 34 studies (3139 participants) evaluated urea breath test-13C; 21 studies (1810 participants) evaluated urea breath test-14C; and two studies (127 participants) evaluated urea breath test but did not report the isotope used. The thresholds used to define test positivity and the staining techniques used for histopathological examination (reference standard) varied between studies. Due to sparse data for each threshold reported, it was not possible to identify the best threshold for each test.Using data from 99 studies in an indirect test comparison, there was statistical evidence of a difference in diagnostic accuracy between urea breath test-13C, urea breath test-14C, serology and stool antigen test (P = 0.024). The diagnostic odds ratios for urea breath test-13C, urea breath test-14C, serology, and stool antigen test were 153 (95% confidence interval (CI) 73.7 to 316), 105 (95% CI 74.0 to 150), 47.4 (95% CI 25.5 to 88.1) and 45.1 (95% CI 24.2 to 84.1). The sensitivity (95% CI) estimated at a fixed specificity of 0.90 (median from studies across the four tests), was 0.94 (95% CI 0.89 to 0.97) for urea breath test-13C, 0.92 (95% CI 0.89 to 0.94) for urea breath test-14C, 0.84 (95% CI 0.74 to 0.91) for serology, and 0.83 (95% CI 0.73 to 0.90) for stool antigen test. This implies that on average, given a specificity of 0.90 and prevalence of 53.7% (median specificity and prevalence in the studies), out of 1000 people tested for H pylori infection, there will be 46 false positives (people without H pylori infection who will be diagnosed as having H pylori infection). In this hypothetical cohort, urea breath test-13C, urea breath test-14C, serology, and stool antigen test will give 30 (95% CI 15 to 58), 42 (95% CI 30 to 58), 86 (95% CI 50 to 140), and 89 (95% CI 52 to 146) false negatives respectively (people with H pylori infection for whom the diagnosis of H pylori will be missed).Direct comparisons were based on few head-to-head studies. The ratios of diagnostic odds ratios (DORs) were 0.68 (95% CI 0.12 to 3.70; P = 0.56) for urea breath test-13C versus serology (seven studies), and 0.88 (95% CI 0.14 to 5.56; P = 0.84) for urea breath test-13C versus stool antigen test (seven studies). The 95% CIs of these estimates overlap with those of the ratios of DORs from the indirect comparison. Data were limited or unavailable for meta-analysis of other direct comparisons.

AUTHORS' CONCLUSIONS

In people without a history of gastrectomy and those who have not recently had antibiotics or proton ,pump inhibitors, urea breath tests had high diagnostic accuracy while serology and stool antigen tests were less accurate for diagnosis of Helicobacter pylori infection.This is based on an indirect test comparison (with potential for bias due to confounding), as evidence from direct comparisons was limited or unavailable. The thresholds used for these tests were highly variable and we were unable to identify specific thresholds that might be useful in clinical practice.We need further comparative studies of high methodological quality to obtain more reliable evidence of relative accuracy between the tests. Such studies should be conducted prospectively in a representative spectrum of participants and clearly reported to ensure low risk of bias. Most importantly, studies should prespecify and clearly report thresholds used, and should avoid inappropriate exclusions.

Potato phenolics impact starch digestion and glucose transport in model systems but translation to phenolic rich potato chips results in only modest modification of glycemic response in humans

Beneficial effects of some phenolic compounds in modulation of carbohydrate digestion and glycemic response have been reported, however effects of phenolics from processed potato products on these endpoints are not well known. The aims of this study were to characterize phenolic profiles of fresh potatoes (purple, red, or white fleshed; 2 varieties each) and chips, and to examine the potential for potato phenolic extracts (PPE) to modulate starch digestion and intestinal glucose transport in model systems. Following in vitro assessment, a pilot clinical study (n=11) assessed differences in glycemic response and gastric emptying between chips from pigmented and white potatoes. We hypothesized that phenolics from pigmented potato chips would be recovered through processing and result in a reduced acute glycemic response in humans relative to chips made from white potatoes. PPEs were rich in anthocyanins (~98, 11 and ND mg/100 g dw) and chlorogenic acids (~519, 425 and 157 mg/100 g dw) for purple, red and white varieties respectively. While no significant effects were observed on starch digestion by α-amylase and the α-glucosidases, PPEs significantly (p<0.05) decreased the rate of glucose transport, measured following transport of 1,2,3,4,5,6,6-d7 -glucose (d7-glu) across Caco-2 human intestinal cell monolayers, by 4.5-83.9%. Consistent with in vitro results, consumption of purple potato chips modestly but significantly (p<0.05) decreased blood glucose at 30 and 60 minutes post consumption compared to white chips without impacting gastric emptying. These results suggest that potato phenolics may play a modest role in modulation of glycemic response and these effects may result in subtle differences between consumer products.

Traditional Malian Solid Foods Made from Sorghum and Millet Have Markedly Slower Gastric Emptying than Rice, Potato, or Pasta

From anecdotal evidence that traditional African sorghum and millet foods are filling and provide sustained energy, we hypothesized that gastric emptying rates of sorghum and millet foods are slow, particularly compared to non-traditional starchy foods (white rice, potato, wheat pasta). A human trial to study gastric emptying of staple foods eaten in Bamako, Mali was conducted using a carbon-13 (13C)-labelled octanoic acid breath test for gastric emptying, and subjective pre-test and satiety response questionnaires. Fourteen healthy volunteers in Bamako participated in a crossover design to test eight starchy staples. A second validation study was done one year later in Bamako with six volunteers to correct for endogenous 13C differences in the starches from different sources. In both trials, traditional sorghum and millet foods (thick porridges and millet couscous) had gastric half-emptying times about twice as long as rice, potato, or pasta (p < 0.0001). There were only minor changes due to the 13C correction. Pre-test assessment of millet couscous and rice ranked them as more filling and aligned well with postprandial hunger rankings, suggesting that a preconceived idea of rice being highly satiating may have influenced subjective satiety scoring. Traditional African sorghum and millet foods, whether viscous in the form of a thick porridge or as non-viscous couscous, had distinctly slow gastric emptying, in contrast to the faster emptying of non-traditional starchy foods, which are popular among West African urban consumers.

Deuterium- and Tritium-Labelled Compounds: Applications in the Life Sciences

Hydrogen isotopes are unique tools for identifying and understanding biological and chemical processes. Hydrogen isotope labelling allows for the traceless and direct incorporation of an additional mass or radioactive tag into an organic molecule with almost no changes in its chemical structure, physical properties, or biological activity. Using deuterium-labelled isotopologues to study the unique mass-spectrometric patterns generated from mixtures of biologically relevant molecules drastically simplifies analysis. Such methods are now providing unprecedented levels of insight in a wide and continuously growing range of applications in the life sciences and beyond. Tritium (³ H), in particular, has seen an increase in utilization, especially in pharmaceutical drug discovery. The efforts and costs associated with the synthesis of labelled compounds are more than compensated for by the enhanced molecular sensitivity during analysis and the high reliability of the data obtained. In this Review, advances in the application of hydrogen isotopes in the life sciences are described.

13C Methacetin Breath Test for Assessment of Microsomal Liver Function: Methodology and Clinical Application

Assessment of the liver function, and the need of constant monitoring of the organ's capacity, concerns not only patients with primary liver diseases, but also those at risk of hepatopathies secondary to other chronic diseases. Most commonly, the diagnostics is based on measurements of static biochemical parameters, which allow us to draw conclusions only indirectly about the function and the degree of damage of the organ. On the other hand, liver biopsy is an invasive procedure and therefore it is associated with a considerable risk of complications. Dynamic tests enable us to assess quantitatively the organ's functional reserve by analyzing the kinetics of the metabolization of the substrate by the liver. In practice applied are breath tests using substances such as aminopyrine, caffeine, methacetin, erythromycin (for assessment of the microsomal function); phenylalanine, galactose (for assessment of the cytosolic function); methionine, octanoate, ketoisocaproic acid (for assessment of the mitochondrial function). The test with ¹³C methacetin belongs to the best described and most widely applied methods in noninvasive liver function assessment. Due to the rising availability of this method, knowledge concerning its limitations and controversies regarding the methodology, as well as its usefulness in chosen groups of patients, seems to be vital.

Cut-off optimization for 13C-urea breath test in a community-based trial by mathematic, histology and serology approach

The performance of diagnostic tests in intervention trials of Helicobacter pylori (H.pylori) eradication is crucial, since even minor inaccuracies can have major impact. To determine the cut-off point for ¹³C-urea breath test (¹³C-UBT) and to assess if it can be further optimized by serologic testing, mathematic modeling, histopathology and serologic validation were applied. A finite mixture model (FMM) was developed in 21,857 subjects, and an independent validation by modified Giemsa staining was conducted in 300 selected subjects. H.pylori status was determined using recomLine H.pylori assay in 2,113 subjects with a borderline ¹³C-UBT results. The delta over baseline-value (DOB) of 3.8 was an optimal cut-off point by a FMM in modelling dataset, which was further validated as the most appropriate cut-off point by Giemsa staining (sensitivity = 94.53%, specificity = 92.93%). In the borderline population, 1,468 subjects were determined as H.pylori positive by recomLine (69.5%). A significant correlation between the number of positive H.pylori serum responses and DOB value was found (r_s = 0.217, P < 0.001). A mathematical approach such as FMM might be an alternative measure in optimizing the cut-off point for ¹³C-UBT in community-based studies, and a second method to determine H.pylori status for subjects with borderline value of ¹³C-UBT was necessary and recommended.

Potential use of metabolic breath tests to assess liver disease and prognosis: has the time arrived for routine use in the clinic?

The progression of liver disease may be unique among organ system diseases in that progressive fibrosis compromises not only the sufficiency of hepatocyte mass but also impairs blood flow to the liver, resulting in porto-systemic shunting. Although liver biopsy as an assessment of fibrosis has become the key biomarker of and target for new therapies, it is invasive and subject to sampling error, and cannot quantify metabolic function or porto-systemic shunting. Measurement of the hepatic venous pressure gradient accommodates some of the deficiencies of biopsy but requires expertise not widely available and misses minor changes in hepatocellular mass and thereby information about metabolic function. Thus, an unmet need in clinical hepatology remains unfulfilled: a noninvasive biomarker which quantitates both the hepatocellular insufficiency and porto-systemic shunting inherent in progressive hepatic fibrosis. Ideally, such a biomarker should correlate with clinical endpoints including liver-related survival and cirrhotic complications, be performed at the point-of-care, and be affordable and easy to use. This review, an expert opinion, summarizes background and recent data suggesting that metabolic breath tests may now meet these requirements and have a valid place in clinical hepatology to supplant the time-honoured assessment of hepatic fibrosis.

The 13C-Glucose Breath Test for Insulin Resistance Assessment in Adolescents: Comparison with Fasting and Post-Glucose Stimulus Surrogate Markers of Insulin Resistance

OBJECTIVE

To evaluate the use of the 13C-glucose breath test (13C-GBT) for insulin resistance (IR) detection in adolescents through comparison with fasting and post-glucose stimulus surrogates.

METHODS

One hundred thirty-three adolescents aged between 10 and 16 years received an oral glucose load of 1.75 g per kg of body weight dissolved in 150 mL of water followed by an oral dose of 1.5 mg/kg of U-13C-Glucose, without a specific maximum dose. Blood samples were drawn at baseline and 120 minutes, while breath samples were obtained at baseline and at 30, 60, 90, 120, 150, and 180 minutes. The 13C-GBT was compared to homeostasis model assessment (HOMA) IR (≥p95 adjusted by gender and age), fasting plasma insulin (≥p90 adjusted by gender and Tanner stage), results of 2-h oral glucose tolerance test (OGTT), insulin levels (≥65 μU/mL) in order to determine the optimal cut-off point for IR diagnosis.

RESULTS

13C-GBT data, expressed as adjusted cumulative percentage of oxidized dose (A% OD), correlated inversely with fasting and post-load IR surrogates. Sexual development alters A% OD results, therefore individuals were stratified into pubescent and post-pubescent. The optimal cut-off point for the 13C-GBT in pubescent individuals was 16.3% (sensitivity=82.8% & specificity=60.6%) and 13.0% in post-pubescents (sensitivity=87.5% & specificity=63.6%), when compared to fasting plasma insulin. Similar results were observed against HOMA and 2-h OGTT insulin.

CONCLUSION

The 13C-GBT is a practical and non-invasive method to screen for IR in adolescents with reasonable sensitivity and specificity.

Systemic availability and metabolism of colonic-derived short-chain fatty acids in healthy subjects: a stable isotope study

KEY POINTS

The short-chain fatty acids (SCFAs) are bacterial metabolites produced during the colonic fermentation of undigested carbohydrates, such as dietary fibre and prebiotics, and can mediate the interaction between the diet, the microbiota and the host. We quantified the fraction of colonic administered SCFAs that could be recovered in the systemic circulation, the fraction that was excreted via the breath and urine, and the fraction that was used as a precursor for glucose, cholesterol and fatty acids. This information is essential for understanding the molecular mechanisms by which SCFAs beneficially affect physiological functions such as glucose and lipid metabolism and immune function.

ABSTRACT

The short-chain fatty acids (SCFAs), acetate, propionate and butyrate, are bacterial metabolites that mediate the interaction between the diet, the microbiota and the host. In the present study, the systemic availability of SCFAs and their incorporation into biologically relevant molecules was quantified. Known amounts of ¹³ C-labelled acetate, propionate and butyrate were introduced in the colon of 12 healthy subjects using colon delivery capsules and plasma levels of ¹³ C-SCFAs ¹³ C-glucose, ¹³ C-cholesterol and ¹³ C-fatty acids were measured. The butyrate-producing capacity of the intestinal microbiota was also quantified. Systemic availability of colonic-administered acetate, propionate and butyrate was 36%, 9% and 2%, respectively. Conversion of acetate into butyrate (24%) was the most prevalent interconversion by the colonic microbiota and was not related to the butyrate-producing capacity in the faecal samples. Less than 1% of administered acetate was incorporated into cholesterol and <15% in fatty acids. On average, 6% of colonic propionate was incorporated into glucose. The SCFAs were mainly excreted via the lungs after oxidation to ¹³ CO₂ , whereas less than 0.05% of the SCFAs were excreted into urine. These results will allow future evaluation and quantification of SCFA production from ¹³ C-labelled fibres in the human colon by measurement of ¹³ C-labelled SCFA concentrations in blood.

Estimation of gastric pH in cynomolgus monkeys, rats, and dogs using [(13)C]-calcium carbonate breath test

BACKGROUND

The determination of gastric pH is important for the confirmation of efficacy of anti-secretory drugs. However, current methods for measurement of gastric pH provide significant stress to animals and humans.

AIM

The objective of this study is to establish an easy and reliable gastric pH measurement method by determining (13)CO2 concentration in expired air of monkeys, dogs, and rats after oral administration of Ca(13)CO3.

METHODS

A correlation of (13)CO2 concentration determined by a Ca(13)CO3 breath test with gastric pH just before Ca(13)CO3 administration was analyzed in the 3 animal species. The equations and contribution ratios of regression line were calculated from logarithmic (13)CO2 concentrations at 15min after administration of Ca(13)CO3 using the linear regression analysis.

RESULTS

The (13)CO2 concentration in the Ca(13)CO3 breath test was well correlated with the gastric pH just before Ca(13)CO3 administration in the 3 animal species (r=-0.977 to -0.952). The equations of regression line between the (13)CO2 concentration and the gastric pH in each animal species showed good contribution ratios (R(2)≥0.89).

CONCLUSIONS

The Ca(13)CO3 breath test is an informative tool to estimate gastric pH in animals and will be applicable as a new noninvasive tool for patients with GERD/PPI-resistant symptoms.

Use of the Biphasic (13)C-Sucrose/Glucose Breath Test to Assess Sucrose Maldigestion in Adults with Functional Bowel Disorders

Sucrase insufficiency has been observed in children with of functional bowel disorders (FBD) and symptoms of dietary carbohydrate intolerance may be indistinguishable from those of FBD. A two-phase (13)C-sucrose/(13)C-glucose breath test ((13)C-S/GBT) was used to assess sucrase activity because disaccharidase assays are seldom performed in adults. When (13)C-sucrose is hydrolyzed to liberate monosaccharides, oxidation to (13)CO2 is a proportional indicator of sucrase activity. Subsequently, (13)C-glucose oxidation rate was determined after a secondary substrate ingestion (superdose) to adjust for individual habitus effects (Phase II). (13)CO2 enrichment recovery ratio from (13)C-sucrose and secondary (13)C-glucose loads reflect the individualized sucrase activity [Coefficient of Glucose Oxidation for Sucrose (CGO-S)]. To determine if sucrase insufficiency could be a factor in FBD, (13)C-S/GBT was validated using subjects with known sucrase gene mutation status by comparing (13)CO2-breath enrichment with plasma (13)C-glucose enrichment. (13)C-S/GBT was used to assess sucrose digestion in FBD patients and asymptomatic controls. (13)CO2-breath enrichment correlated with the appearance of (13)C-sucrose-derived glucose in plasma (r (2) = 0.80). Mean, control group CGO-S-enrichment outcomes were 1.01 at 60', 0.92 at 75', and 0.96 at mean 60'-75' with normal CGO-S defined as >0.85 (95% C.I.). In contrast, FBD patients demonstrated lower CGO-S values of 0.77 at 60', 0.77 at 75', and 0.76 at mean 60'-75' (Chi Square: 6.55; p < 0.01), which points to sucrose maldigestion as a cause of FBD.

Supplementation of ursodeoxycholic acid improves fat digestion and absorption in cystic fibrosis patients with mild liver involvement

BACKGROUND

Ursodeoxycholic acid (UDCA) supplementation is recommended for cystic fibrosis (CF) patients with associated liver disease. However, its effect on fat digestion and absorption is not known.

MATERIALS AND METHODS

In 23 patients with mild liver involvement, a C-mixed triglyceride breath test was performed on UDCA supplementation (with and without pancreatic enzymes - standard and increased dose) and after 1 month of UDCA withdrawal. Cumulative percentage dose recovery [CPDR; median (interquartile range)] has been considered to reflect lipid digestion and absorption.

RESULTS

The enzyme supplementation resulted in a significant CPDR improvement [0% (0-0) vs. 4.6% (0.4-6.0); P<0.00046]. With the increased dose of enzymes in 16 patients with abnormal C-mixed triglyceride breath test results and lipase dose less than 3000 U/g of fat, higher CPDR values [8.6% (5.6-12.7); P<0.000027] were observed. However, a 1-month UDCA withdrawal resulted in a significant reduction in (P<0.000031) fat digestion and absorption [2.9% (0.7-5.8)].

CONCLUSION

UDCA supplementation seems to enhance lipid digestion and absorption in pancreatic insufficient CF patients with mild liver involvement. This finding points toward the potential impact of UDCA supplementation on nutritional status in CF patients with liver disease and underscores the often overlooked role of factors other than pancreatic enzymes on digestion and absorption of fats in CF.

Molecular changes in hepatic metabolism and transport in cirrhosis and their functional importance

Liver cirrhosis is the common endpoint of many hepatic diseases and represents a relevant risk for liver failure and hepatocellular carcinoma. The progress of liver fibrosis and cirrhosis is accompanied by deteriorating liver function. This review summarizes the regulatory and functional changes in phase I and phase II metabolic enzymes as well as transport proteins and provides an overview regarding lipid and glucose metabolism in cirrhotic patients. Interestingly, phase I enzymes are generally downregulated transcriptionally, while phase II enzymes are mostly preserved transcriptionally but are reduced in their function. Transport proteins are regulated in a specific way that resembles the molecular changes observed in obstructive cholestasis. Lipid and glucose metabolism are characterized by insulin resistance and catabolism, leading to the disturbance of energy expenditure and wasting. Possible non-invasive tests, especially breath tests, for components of liver metabolism are discussed. The heterogeneity and complexity of changes in hepatic metabolism complicate the assessment of liver function in individual patients. Additionally, studies in humans are rare, and species differences preclude the transferability of data from rodents to humans. In clinical practice, some established global scores or criteria form the basis for the functional evaluation of patients with liver cirrhosis, but difficult treatment decisions such as selection for transplantation or resection require further research regarding the application of existing non-invasive tests and the development of more specific tests.

Effect of posture on 13C-urea breath test in partial gastrectomy patients

AIM: To investigate whether posture affects the accuracy of ¹³C-urea breath test (¹³C-UBT) for Helicobacter pylori (H. pylori) detection in partial gastrectomy patients.

METHODS: We studied 156 consecutive residual stomach patients, including 76 with H. pylori infection (infection group) and 80 without H. pylori infection (control group). H. pylori infection was confirmed if both the rapid urease test and histology were positive during gastroscopy. The two groups were divided into four subgroups according to patients’ posture during the ¹³C-UBT: subgroup A, sitting position; subgroup B, supine position; subgroup C, right lateral recumbent position; and subgroup D, left lateral recumbent position. Each subject underwent the following modified ¹³C-UBT: 75 mg of ¹³C-urea (powder) in 100 mL of citric acid solution was administered, and a mouth wash was performed immediately; breath samples were then collected at baseline and at 5-min intervals up to 30 min while the position was maintained. Seven breath samples were collected for each subject. The cutoff value was 2.0‰.

RESULTS: The mean delta over baseline (DOB) values in the subgroups of the infection group were similar at 5 min (P > 0.05) and significantly higher than those in the corresponding control subgroups at all time points (P < 0.01). In the infection group, the mean DOB values in subgroup A were higher than those in other subgroups within 10 min and peaked at the 10-min point (12.4‰± 2.4‰). The values in subgroups B and C both reached their peaks at 15 min (B, 13.9‰± 1.5‰; C, 12.2‰± 1.7‰) and then decreased gradually until the 30-min point. In subgroup D, the value peaked at 20 min (14.7‰± 1.7‰). Significant differences were found between the values in subgroups D and B at both 25 min (t = 2.093, P = 0.043) and 30 min (t = 2.141, P = 0.039). At 30 min, the value in subgroup D was also significantly different from those in subgroups A and C (D vs C: t = 6.325, P = 0.000; D vs A: t = 5.912, P = 0.000). The mean DOB values of subjects with Billroth I anastomosis were higher than those of subjects with Billroth II anastomosis irrespectively of the detection time and posture (P > 0.05).

CONCLUSION: Utilization of the left lateral recumbent position during the procedure and when collecting the last breath sample may improve the diagnostic accuracy of the ¹³C-UBT in partial gastrectomy patients.

Carbon stable-isotope tracking in breath for comparative studies of fuel use

Almost half a century ago, researchers demonstrated that the ratio of stable carbon isotopes in exhaled breath of rats and humans could reveal the oxidation of labeled substrates in vivo, opening a new chapter in the study of fuel use, the fate of ingested substrates, and aerobic metabolism. Until recently, the combined use of respirometry and stable-isotope tracer techniques had not been broadly employed to study fuel use in other animal groups. In this review, we summarize the history of this approach in human and animal research and define best practices that maximize its utility. We also summarize several case studies that use stable-isotope measurements of breath to explore the limits of aerobic metabolism and substrate turnover among several species and various physiological states. We highlight the importance of a comparative approach in revealing the profound effects that phylogeny, ecology, and behavior can have in shaping aerobic metabolism and energetics as well as the fundamental biological principles that underlie fuel use and metabolic function across taxa. New analytical equipment and refinement of methodology make the combined use of respirometry and stable-isotope tracer techniques simpler to perform, less costly, and more field ready than ever before.

Proton transfer reaction-mass spectrometry: online and rapid determination of volatile organic compounds of microbial origin

Analytical tools for the identification and quantification of volatile organic compounds (VOCs) produced by microbial cultures have countless applications in an industrial and research context which are still not fully exploited. The various techniques for VOC analysis generally arise from the application of different scientific and technological philosophies, favoring either sample throughput or chemical information. Proton transfer reaction-mass spectrometry (PTR-MS) represents a valid compromise between the two aforementioned approaches, providing rapid and direct measurements along with highly informative analytical output. The present paper reviews the main applications of PTR-MS in the microbiological field, comprising food, environmental, and medical applications.

Longer oral exposure with modified sham feeding does not slow down gastric emptying of low- and high-energy-dense gastric loads in healthy young men

BACKGROUND

A long oral exposure to food and a high-energy density of food have been shown to increase satiety feelings. The effect of energy density is predominantly caused by an inhibition of gastric emptying. It is hypothesized that prolonging oral exposure may have an additional effect on this inhibition of gastric emptying. However, little human data are available to support this hypothesis.

OBJECTIVE

The objective was to assess the effect of the duration of oral exposure to food on gastric emptying rate of gastric loads (GLs) low and high in energy density and on satiety feelings.

METHODS

Twenty-six healthy men [mean ± SD age: 22 ± 3 y; BMI (in kg/m(2)): 23 ± 1] participated in a randomized crossover trial with 4 treatments and a control. Treatments consisted of either 1- or 8-min modified sham feeding (MSF) of cake, and a GL of either 100 or 700 kcal infused in the stomach via a nasogastric tube (500 mL, 62.5 mL/min). The control consisted of no MSF and a GL of 500 mL of water. Gastric emptying rate was assessed with a (13)C breath test. Breath samples and satiety feelings were collected at fixed time points until 90 min after start of the treatment.

RESULTS

Gastric emptying rate and satiety feelings were not affected by duration of MSF (P ≥ 0.27). However, the 700-kcal GL treatments slowed gastric emptying [41% lower area under the curve (AUC)] and increased satiety feelings (22-31% higher AUC) compared with the 100-kcal GL treatments (P < 0.001). No interaction between MSF duration and energy density of GL was found (P ≥ 0.44).

CONCLUSIONS

Higher gastric energy density inhibited gastric emptying and increased satiety feelings in healthy young men. However, prolonging oral exposure to food did not have an additional effect. This study provides more insight in satiety regulation. This trial was registered at trialregister.nl as NTR3601.

Non-(13)CO2 targeted breath tests: a feasibility study

Breath tests allow a non-invasive and fast diagnostic of different specific enzymes' phenotypic functionality. Over the last decade several 13C-breath tests were successfully tested, with the (13)C-urea breath test being approved by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA). The use of other targets than labeled (13)CO2 in exhaled breath offers additional possibilities. High sensitivity analytical technologies, such as proton-transfer reaction time-of-flight mass spectrometry, enable the detection of different volatile targets in the low ppb (parts per billion) range in real-time.In the current study volunteers received 0.8 mg deuterated 2-propanol, which was converted to d3-acetone (m/z 62.08) by alcohol dehydrogenase. D3-acetone (m/z 62.08) appeared in exhaled breath concentrations up to 30 ppb (at maximum). Parallel consumption of ethanol seems to reduce the activity of the enzyme, resulting in approximately 15-30% reduction of the produced d3-acetone. Phenotypic determination of enzyme activities is important, since the functionality of enzymes is influenced by factors such as age, sex, life-style, diet, organ function, metabolism, etc, which cannot be entirely accounted for by genetic factors.

The [(13)c]glucose breath test is a reliable method to identify insulin resistance in Mexican adults without diabetes: comparison with other insulin resistance surrogates

BACKGROUND

Insulin resistance (IR) precedes type 2 diabetes, but tests used to detect it in clinical settings reported poor reproducibility. We assessed the reliability of the [(13)C]glucose breath test ((13)C-GBT) in a sample of subjects without diabetes. Repeatability of the test was compared with that of other IR surrogates derived from the fasting or oral glucose tolerance test (OGTT).

SUBJECTS AND METHODS

Eighty-six healthy volunteers received an oral load of 75 g of glucose in 150 mL of water followed by 1.5 mg/kg of [U-(13)C]glucose in 50 mL of water. Breath and blood samples were collected at baseline and at 10, 20, 30, 60, 90, 120, 150, and 180 min following the glucose load; the same procedure was repeated within 1 week. The enrichment of breath (13)CO2 was measured by ratio mass spectrometry and expressed as percentage oxidized dose at a given time period. Intrasubject variability was assessed with Bland-Altman plots and coefficients of variation (CVs).

RESULTS

The overall CV of the (13)C-GBT was 12.99±11.61%, compared with 18.42% of fasting insulin, 19.44% for homeostasis model assessment, 17.06% of the composite insulin sensitivity index, and 29.99% for insulin in the 2-h oral glucose tolerance test. The variability of the (13)C-GBT tended to be higher in lean (17.40%) than in overweight (10.17%) and obese (12.61%) individuals.

CONCLUSIONS

The variability of the (13)C-GBT is lower than that of other IR surrogates, making it a reproducible method to estimate insulin sensitivity in overweight and obese adults without diabetes. Because the individuals did not have diabetes but were within a high range of insulin sensitivity, the test should have application in clinical and population-based studies, given the evidence for the utility and limitations of this surrogate.

Total cholesterol level for assessing pancreatic insufficiency due to chronic pancreatitis

Background/Aims

To determine the nutritional markers important for assessing the degree of pancreatic insufficiency due to chronic pancreatitis in routine clinical practice.

Methods

A total of 137 patients with chronic pancreatitis were followed up for more than 1 year. They were divided into two groups: a pancreatic diabetes mellitus (DM) group, consisting of 47 patients undergoing medical treatment for DM of pancreatic origin, and a nonpancreatic DM group, consisting of 90 other patients (including 86 patients without DM). Serum albumin, prealbumin, total cholesterol, cholinesterase, magnesium, and hemoglobin were compared between the two groups.

Results

The total cholesterol was significantly lower in the pancreatic than the nonpancreatic DM group (164 mg/dL vs 183 mg/dL, respectively; p=0.0028). Cholinesterase was significantly lower in the former group (263 U/L vs 291 U/L, respectively; p=0.016). Among the 37 patients with nonalcoholic pancreatitis, there was no difference in the cholinesterase levels between the pancreatic and nonpancreatic (296 U/L vs 304 U/L, respectively; p=0.752) DM groups, although cholesterol levels remained lower in the former (165 mg/dL vs 187 mg/dL, respectively; p=0.052).

Conclusions

Cholinesterase levels are possibly affected by concomitant alcoholic liver injury. The total cholesterol level should be considered when assessing pancreatic insufficiency due to chronic pancreatitis.

An efficient laboratory-scale preparative method for [1-(13)C]glycocholic acid

A breath test using [1-(13)C]glycocholic acid as a substrate is a potential diagnostic method for small intestinal bacterial overgrowth syndrome. [1-(13)C]Glycocholic acid has been thus synthesized in an excellent yield from ethyl [1-(13)C]glycinate hydrochloride in a one-pot reaction. This method is suitable for the preparation of the labeled compound on a laboratory scale, which helps to perform extensive clinical studies of the breath test.

Ion mobility spectrometry for pharmacokinetic studies--exemplary application

Breath analysis is an attractive non-invasive method for diagnosis and therapeutic monitoring. It uses endogenously produced compounds and metabolites of isotopically labeled precursors. In order to make such tests clinically useful, it is important to have relatively small portable instruments detecting volatile compounds within short time. A particularly promising analytical technique is ion mobility spectrometry (IMS) coupled to a multi capillary column (MCC). This paper focuses on demonstrating the suitability of breath analysis for pharmacokinetic applications using MCC-IMS with respect to practicability and reproducibility testing the model substrate eucalyptol. Validation of the MCC-IMS measurements were performed using proton transfer reaction mass spectrometry (PTR-MS) and resulted in an excellent correspondence of the time-dependent concentrations presented by the two different analytical techniques. Moreover, the good accordance in variance of kinetic parameters with repeated measures, and the determined inter-subject differences indicate the eligibility of the analysis method.

Effects of dietary nutrients on volatile breath metabolites

Breath analysis is becoming increasingly established as a means of assessing metabolic, biochemical and physiological function in health and disease. The methods available for these analyses exploit a variety of complex physicochemical principles, but are becoming more easily utilised in the clinical setting. Whilst some of the factors accounting for the biological variation in breath metabolite concentrations have been clarified, there has been relatively little work on the dietary factors that may influence them. In applying breath analysis to the clinical setting, it will be important to consider how these factors may affect the interpretation of endogenous breath composition. Diet may have complex effects on the generation of breath compounds. These effects may either be due to a direct impact on metabolism, or because they alter the gastrointestinal flora. Bacteria are a major source of compounds in breath, and their generation of H₂, hydrogen cyanide, aldehydes and alkanes may be an indicator of the health of their host.

Assessment of hepatic detoxification activity: proposal of an improved variant of the (13)c-methacetin breath test

Breath tests based on the administration of a (13)C-labeled drug and subsequent monitoring of (13)CO2 in the breath (quantified as DOB - delta over baseline) liberated from the drug during hepatic CPY-dependent detoxification are important tools in liver function diagnostics. The capability of such breath tests to reliably indicate hepatic CYP performance is limited by the fact that (13)CO2 is not exclusively exhaled but also exchanged with other compartments of the body. In order to assess this bias caused by variations of individual systemic CO2 kinetics we administered intravenously the test drug (13)C-methacetin to 25 clinically liver-healthy individuals and monitored progress curves of DOB and the plasma concentration of (13)C-methacetin. Applying compartment modelling we estimated for each individual a set of kinetic parameters characterizing the time-dependent exchange of the drug and of CO2 with the liver and non-hepatic body compartments. This analysis revealed that individual variations in the kinetics of CO2 may account for up to 30% deviation of DOB curve parameters from their mean at otherwise identical (13)C-methacetin metabolization rates. In order to correct for this bias we introduced a novel detoxification score which ideally should be assessed from the DOB curve of a 2-step test ("2DOB") which is initialized with the injection of a standard dose of (13)C-labeled bicarbonate (in order to provide information on the actual CO2 status of the individual) followed by injection of the (13)C-labeled test drug (the common procedure). Computer simulations suggest that the predictive power of the proposed 2DOB breath test to reliably quantity the CYP-specific hepatic detoxification activity should be significantly higher compared to the conventional breath test.

Combined oral contraceptives affect liver mitochondrial activity

OBJECTIVES

To examine liver mitochondrial function in women using combined oral contraceptives (COCs) containing ethinylestradiol.

METHODS

A breath test after oral administration of 1 mg/kg (13)C-alpha-ketoisocaproic acid ((13)C-KICA) and 20 mg/kg L-leucine was performed twice: (i) in 15 women on day 14, 15, 16, 17 or 18 of COC intake, and between day 1 and 5 of the withdrawal bleeding; and (ii) in 15 regularly menstruating females not taking hormonal contraceptives: during the luteal phase, between the 18th and the 22nd day of the cycle, and again between day 1 and 5 of the menstruation.

RESULTS

In women on COCs the maximum (13)C elimination in breath air (Dmax) was higher (26.8 ± 1.6%/h) than during withdrawal bleeding (23.5 ± 1.2%/h; p = 0.012). The time to reach the Dmax was similar on the two study days: 33.3 ± 2.4 min during the phase of pill intake vs. 37.0 ± 2.5 min during the pill-free interval. The one-hour cumulative breath (13)C elimination was greater after two weeks of COC intake than during the withdrawal bleeding: 17.49 ± 1.03% vs. 15.32 ± 0.85% (p = 0.024). In the control group no menstrual cycle phase-dependent fluctuations in the results of the (13)C-KICA breath test were observed.

CONCLUSION

The metabolism of (13)C-alpha-ketoisocaproic acid augments during the intake of COCs containing ethinylestradiol, reflecting enhanced liver mitochondrial metabolic activity.

Effect of Casilan(®) on (13)C-caffeine metabolism in overnight-fasted healthy Nigerian children

Objective:

To determine the effect of Casilan^® on ¹³C-caffeine metabolism in healthy Nigerian children.

Materials and Methods:

Twelve healthy Nigerian children (male: six, female: six) aged 3–8 years were studied on three occasions. After an overnight fast, the children were studied after ingesting Casilan^® only (Week 1). They were restudied after ingesting 3 mg/kg of labeled caffeine only (Week 2), and further re-studied after ingesting both Casilan^® and labeled caffeine (Week 3). Breath samples were collected by blowing via a straw into an exentainer bottle. The cumulative percentage of ¹³C-caffeine exhaled as ¹³CO₂ was measured over 2 h.

Results:

The time courses of ¹³C-enrichments in exhaled CO₂ for all the children, after they had ingested labeled caffeine only and after they had ingested both Casilan^® and labeled caffeine, were identical. There was a gradual rise and peak of the enrichments at about 60–75 min, followed by a gradual fall (II) or a plateau (III). Contrarily, the time course of ¹³C-enrichments for all the children was consistently low and stable after they had ingested Casilan^® only (I). The mean values of cumulative percent ¹³C-doses recovered in the CO₂ exhaled over a 2-h period, after ingesting labeled caffeine only (8.59 ± 1.10 δ%/mg) and after ingesting both Casilan^® and labeled caffeine (8.58 ± 1.33 δ%/mg), were identical, with no statistically significant difference (P = 0.972). This suggests that Casilan^® did not affect the CYP1A2 metabolic pathway.

Conclusions:

Casilan^® is a safe, reliable and quantitative food supplement for overnight-fasted children undergoing caffeine breath test.

Supplementing monosodium glutamate to partial enteral nutrition slows gastric emptying in preterm pigs(1-3)

Emerging evidence suggests that free glutamate may play a functional role in modulating gastroduodenal motor function. We hypothesized that supplementing monosodium glutamate (MSG) to partial enteral nutrition stimulates gastric emptying in preterm pigs. Ten-day-old preterm, parenterally fed pigs received partial enteral nutrition (25%) as milk-based formula supplemented with MSG at 0, 1.7, 3.0, and 4.3 times the basal protein-bound glutamate intake (468 mg·kg(-1)·d(-1)) from d 4 to 8 of life (n = 5-8). Whole-body respiratory calorimetry and (13)C-octanoic acid breath tests were performed on d 4, 6, and 8. Body weight gain, stomach and intestinal weights, and arterial plasma glutamate and glutamine concentrations were not different among the MSG groups. Arterial plasma glutamate concentrations were significantly higher at birth than after 8 d of partial enteral nutrition. Also at d 8, the significant portal-arterial concentration difference in plasma glutamate was substantial (∼500 μmol/L) among all treatment groups, suggesting that there was substantial net intestinal glutamate absorption in preterm pigs. MSG supplementation dose-dependently increased gastric emptying time and decreased breath (13)CO2 enrichments, (13)CO2 production, percentage of (13)CO2 recovery/h, and cumulative percentage recovery of (13)C-octanoic acid. Circulating glucagon-like peptide-2 (GLP-2) concentration was significantly increased by MSG but was not associated with an increase in intestinal mucosal growth. In contrast to our hypothesis, our results suggest that adding MSG to partial enteral nutrition slows the gastric emptying rate, which may be associated with an inhibitory effect of increased circulating GLP-2.