Oxidative breakdown of octanoic acid is maintained in patients with cirrhosis despite advanced disease

Abnormal gastrointestinal motility is a major factor in explaining symptoms and a potential therapeutic target in patients with disorders of gut-brain interaction

The objective of this article is to review the evidence of abnormal gastrointestinal (GI) tract motor functions in the context of disorders of gut-brain interaction (DGBI). These include abnormalities of oesophageal motility, gastric emptying, gastric accommodation, colonic transit, colonic motility, colonic volume and rectal evacuation. For each section regarding GI motor dysfunction, the article describes the preferred methods and the documented motor dysfunctions in DGBI based on those methods. The predominantly non-invasive measurements of gut motility as well as therapeutic interventions directed to abnormalities of motility suggest that such measurements are to be considered in patients with DGBI not responding to first-line approaches to behavioural or empirical dietary or pharmacological treatment.

The Role of Noninvasive 13C-Octanoate Breath Test in Assessing the Diagnosis of Nonalcoholic Steatohepatitis

BACKGROUND

The diagnosis of NASH needs a liver biopsy, an invasive procedure that is not frequently accepted by patients. The aim of our study was to evaluate the efficacy of the ¹³C-Octanoate breath test (OBT) as a non-invasive surrogate marker to differentiate patients with NASH from patients with simple steatosis (NAFL).

METHODS

We performed a prospective study on patients with histologically established non-alcoholic steatohepatitis and no other hepatic disease. Each patient underwent a testing protocol, which included a clinical exam, laboratory blood tests, standard abdominal ultrasound, and a ¹³C-Octanoate breath test.

RESULTS

The study group included: 82 patients with steatohepatitis, 64 patients with simple steatosis, and 21 healthy volunteers. The univariate and bivariate analysis identified that significant values were the percent dose recovery (PDR) at 15 min-r = 0.65 (AUROC = 0.902) and cumulative percent dose recovery (cPDR) at 120 min-r = 0.69 (AUROC = 0.899).

DISCUSSION

Our study showed that ¹³C-OBT had good efficacy for identifying patients with NASH from those with NAFL (steatosis alone) but not those with NAFL from healthy subjects. Considering all these pathogenic steps in NASH we considered that OBT could have the clinical utility to identify patients at risk for NASH, especially "fast progressors".

Diagnostic Modalities Used in Diagnosing Gastroparesis: A Clinical Review

Gastroparesis is associated with abnormal gastric motility characterized by delayed gastric emptying without any obvious mechanical gastric outlet obstruction or blockage. Gastroparesis is associated with significant morbidity and mortality. It is pertinent to make a timely diagnosis of gastroparesis so that prompt treatment can be initiated. The purpose of this clinical review article is to help the internist and the primary care providers to get a better idea of various diagnostic modalities used in diagnosing gastroparesis. We have also discussed the advantages and disadvantages of various diagnostic modalities based on the latest evidence.

Mitochondria Matter: Systemic Aspects of Nonalcoholic Fatty Liver Disease (NAFLD) and Diagnostic Assessment of Liver Function by Stable Isotope Dynamic Breath Tests

The liver plays a key role in systemic metabolic processes, which include detoxification, synthesis, storage, and export of carbohydrates, lipids, and proteins. The raising trends of obesity and metabolic disorders worldwide is often associated with the nonalcoholic fatty liver disease (NAFLD), which has become the most frequent type of chronic liver disorder with risk of progression to cirrhosis and hepatocellular carcinoma. Liver mitochondria play a key role in degrading the pathways of carbohydrates, proteins, lipids, and xenobiotics, and to provide energy for the body cells. The morphological and functional integrity of mitochondria guarantee the proper functioning of β-oxidation of free fatty acids and of the tricarboxylic acid cycle. Evaluation of the liver in clinical medicine needs to be accurate in NAFLD patients and includes history, physical exam, imaging, and laboratory assays. Evaluation of mitochondrial function in chronic liver disease and NAFLD is now possible by novel diagnostic tools. "Dynamic" liver function tests include the breath test (BT) based on the use of substrates marked with the non-radioactive, naturally occurring stable isotope 13C. Hepatocellular metabolization of the substrate will generate 13CO2, which is excreted in breath and measured by mass spectrometry or infrared spectroscopy. Breath levels of 13CO2 are biomarkers of specific metabolic processes occurring in the hepatocyte cytosol, microsomes, and mitochondria. 13C-BTs explore distinct chronic liver diseases including simple liver steatosis, non-alcoholic steatohepatitis, liver fibrosis, cirrhosis, hepatocellular carcinoma, drug, and alcohol effects. In NAFLD, 13C-BT use substrates such as α-ketoisocaproic acid, methionine, and octanoic acid to assess mitochondrial oxidation capacity which can be impaired at an early stage of disease. 13C-BTs represent an indirect, cost-effective, and easy method to evaluate dynamic liver function. Further applications are expected in clinical medicine. In this review, we discuss the involvement of liver mitochondria in the progression of NAFLD, together with the role of 13C-BT in assessing mitochondrial function and its potential use in the prevention and management of NAFLD.

Gastroparesis in Parkinson Disease: Pathophysiology, and Clinical Management

Patients with Parkinson disease (PD) experience a range of non-motor symptoms, including gastrointestinal symptoms. These symptoms can be present in the prodromal phase of the disease. Recent advances in pathophysiology reveal that α-synuclein aggregates that form Lewy bodies and neurites, the hallmark of PD, are present in the enteric nervous system and may precede motor symptoms. Gastroparesis is one of the gastrointestinal involvements of PD and is characterized by delayed gastric emptying of solid food in the absence of mechanical obstruction. Gastroparesis has been reported in nearly 45% of PD. The cardinal symptoms include early satiety, postprandial fullness, nausea, and vomiting. The diagnosis requires an appropriate test to confirm delayed gastric emptying, such as gastric scintigraphy, or breath test. Gastroparesis can lead to malnutrition and impairment of quality of life. Moreover, it might interfere with the absorption of antiparkinsonian drugs. The treatment includes dietary modifications, and pharmacologic agents both to accelerate gastric emptying and relieve symptoms. Alternative treatments have been recently developed in the management of gastroparesis, and their use in patients with PD will be reported in this review.

European guideline on indications, performance and clinical impact of 13 C-breath tests in adult and pediatric patients: An EAGEN, ESNM, and ESPGHAN consensus, supported by EPC

Introduction

¹³C‐breath tests are valuable, noninvasive diagnostic tests that can be widely applied for the assessment of gastroenterological symptoms and diseases. Currently, the potential of these tests is compromised by a lack of standardization regarding performance and interpretation among expert centers.

Methods

This consensus‐based clinical practice guideline defines the clinical indications, performance, and interpretation of ¹³C‐breath tests in adult and pediatric patients. A balance between scientific evidence and clinical experience was achieved by a Delphi consensus that involved 43 experts from 18 European countries. Consensus on individual statements and recommendations was established if ≥ 80% of reviewers agreed and <10% disagreed.

Results

The guideline gives an overview over general methodology of ¹³C‐breath testing and provides recommendations for the use of ¹³C‐breath tests to diagnose Helicobacter pylori infection, measure gastric emptying time, and monitor pancreatic exocrine and liver function in adult and pediatric patients. Other potential applications of ¹³C‐breath testing are summarized briefly. The recommendations specifically detail when and how individual ¹³C‐breath tests should be performed including examples for well‐established test protocols, patient preparation, and reporting of test results.

Conclusion

This clinical practice guideline should improve pan‐European harmonization of diagnostic approaches to symptoms and disorders, which are very common in specialist and primary care gastroenterology practice, both in adult and pediatric patients. In addition, this guideline identifies areas of future clinical research involving the use of ¹³C‐breath tests.

13 C-gastric emptying breath tests: Clinical use in adults and children

¹³ C-gastric emptying breath tests (¹³ C-GEBT) are validated, reliable, and non-invasive tools for measurement of gastric emptying (GE) velocity of solids and liquids without radiation exposure or risk of toxicity. They are recommended and routinely used for clinical purposes in adult as well as pediatric patients and can be readily performed onsite or even at the patient's home. However, the underlying methodology is rather complex and test results can be influenced by dietary factors, physical activity, concurrent diseases, and medication. Moreover, epidemiological factors can influence gastric emptying as well as production and exhalation of ¹³ CO₂ , which is the ultimate metabolic product measured for all ¹³ C-breath tests. Accordingly, in this issue of Neurogastroenterology & Motility, Kovacic et al. report performance of the ¹³ C-Spirulina breath test in a large group of healthy children and show significant effects of gender, pubertal status, and body size on test results. The purpose of this mini-review is to evaluate the clinical use of ¹³ C-GEBT in adults and children, exploring available protocols, analytical methods, and essential prerequisites for test performance, as well as the role of GE measurements in the light of the current discussion on relevance of delayed GE for symptom generation.

Exploring Liver Mitochondrial Function by 13C-Stable Isotope Breath Tests: Implications in Clinical Biochemistry

The liver is at the crossroad of key metabolic processes, which include detoxification, glycolipidic storage and export, and protein synthesis. The gut-liver axis, moreover, provides hepatocytes with a series of bacterial products and metabolites, which contribute to maintain liver function in health and disease. Breath tests (BTs) are developed as diagnostic tools for indirect, rapid, noninvasive assessment of several metabolic processes in the liver. BTs monitor the appearance of CO₂ in breath as a marker of a specific substrate metabolized in the liver, typically within microsomes, cytosol, or mitochondria. The noninvasiveness of BTs originates from the use of the, nonradioactive, naturally occurring stable isotope ¹³C marking a specific substrate which is metabolized in the liver, leading to the appearance of ¹³CO₂ in expired air. Some substrates (ketoisocaproic acid, methionine, and octanoic acid) provide information about dynamic liver mitochondrial function in health and disease. In humans, the application of ¹³C-breath tests ranges from nonalcoholic and alcoholic liver diseases to liver cirrhosis, hepatocarcinoma, preoperative and postoperative assessment of liver function, and drug-induced liver damage. ¹³C-BTs are an indirect, cost-effective, and easy method to evaluate dynamic liver function and gastric kinetics in health and disease, with ongoing studies focusing on further applications in clinical medicine.

Pathophysiology, Aetiology and Treatment of Gastroparesis

Gastroparesis is characterized by delayed gastric emptying, with symptoms such as nausea, vomiting and abdominal pain, in the absence of mechanical obstruction. In most cases, it is idiopathic although diabetes mellitus is another leading cause. The physiology of gastric emptying is a complex process which is influenced by various inputs including the central nervous system, enteric nervous system and gut hormones. Developments in our understanding of gastroparesis have now demonstrated dysfunction in these systems, thus disrupting normal gastric emptying. Once mechanical obstruction is excluded, gastric scintigraphy remains the gold standard for diagnosis although wireless motility capsule and breath testing are alternative methods for diagnosis. Treatment for gastroparesis is challenging, and widely available therapies are often limited either by their poor evidence for efficacy or concerns over their long-term safety profile. Novel prokinetic agents have shown initial promise in clinical trials, and new endoscopic techniques such as gastric per-oral endoscopic myotomy are emerging. These new treatment modalities may provide an option in refractory gastroparesis with the adage of reduced morbidity compared to surgical treatments.

Gastroparesis

Gastroparesis is a disorder characterized by delayed gastric emptying of solid food in the absence of a mechanical obstruction of the stomach, resulting in the cardinal symptoms of early satiety, postprandial fullness, nausea, vomiting, belching and bloating. Gastroparesis is now recognized as part of a broader spectrum of gastric neuromuscular dysfunction that includes impaired gastric accommodation. The overlap between upper gastrointestinal symptoms makes the distinction between gastroparesis and other disorders, such as functional dyspepsia, challenging. Thus, a confirmed diagnosis of gastroparesis requires measurement of delayed gastric emptying via an appropriate test, such as gastric scintigraphy or breath testing. Gastroparesis can have idiopathic, diabetic, iatrogenic, post-surgical or post-viral aetiologies. The management of gastroparesis involves: correcting fluid, electrolyte and nutritional deficiencies; identifying and treating the cause of delayed gastric emptying (for example, diabetes mellitus); and suppressing or eliminating symptoms with pharmacological agents as first-line therapies. Several novel pharmacologic agents and interventions are currently in the pipeline and show promise to help tailor individualized therapy for patients with gastroparesis.

The safety evaluation of food flavouring substances: the role of metabolic studies

The safety assessment of a flavour substance examines several factors, including metabolic and physiological disposition data. The present article provides an overview of the metabolism and disposition of flavour substances by identifying general applicable principles of metabolism to illustrate how information on metabolic fate is taken into account in their safety evaluation. The metabolism of the majority of flavour substances involves a series both of enzymatic and non-enzymatic biotransformation that often results in products that are more hydrophilic and more readily excretable than their precursors. Flavours can undergo metabolic reactions, such as oxidation, reduction, or hydrolysis that alter a functional group relative to the parent compound. The altered functional group may serve as a reaction site for a subsequent metabolic transformation. Metabolic intermediates undergo conjugation with an endogenous agent such as glucuronic acid, sulphate, glutathione, amino acids, or acetate. Such conjugates are typically readily excreted through the kidneys and liver. This paper summarizes the types of metabolic reactions that have been documented for flavour substances that are added to the human food chain, the methodologies available for metabolic studies, and the factors that affect the metabolic fate of a flavour substance.

Expert consensus document: Advances in the diagnosis and classification of gastric and intestinal motility disorders

Disturbances of gastric, intestinal and colonic motor and sensory functions affect a large proportion of the population worldwide, impair quality of life and cause considerable health-care costs. Assessment of gastrointestinal motility in these patients can serve to establish diagnosis and to guide therapy. Major advances in diagnostic techniques during the past 5-10 years have led to this update about indications for and selection and performance of currently available tests. As symptoms have poor concordance with gastrointestinal motor dysfunction, clinical motility testing is indicated in patients in whom there is no evidence of causative mucosal or structural diseases such as inflammatory or malignant disease. Transit tests using radiopaque markers, scintigraphy, breath tests and wireless motility capsules are noninvasive. Other tests of gastrointestinal contractility or sensation usually require intubation, typically represent second-line investigations limited to patients with severe symptoms and are performed at only specialized centres. This Consensus Statement details recommended tests as well as useful clinical alternatives for investigation of gastric, small bowel and colonic motility. The article provides recommendations on how to classify gastrointestinal motor disorders on the basis of test results and describes how test results guide treatment decisions.

Stable isotope-based flux studies in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease and is associated with the worldwide epidemics of obesity, diabetes and cardiovascular diseases. NAFLD ranges from benign fat accumulation in the liver (steatosis) to non-alcoholic steatohepatitis (NASH), and cirrhosis which can progress to hepatocellular carcinoma and liver failure. Mass spectrometry and magnetic resonance spectroscopy-coupled stable isotope-based flux studies provide new insights into the understanding of NAFLD pathogenesis and the disease progression. This review focuses mainly on the utilization of mass spectrometry-based methods for the understanding of metabolic abnormalities in the different stages of NAFLD. For example, stable isotope-based flux studies demonstrated multi-organ insulin resistance, dysregulated glucose, lipids and lipoprotein metabolism in patients with NAFLD. We also review recent developments in the stable isotope-based technologies for the study of mitochondrial dysfunction, oxidative stress and fibrogenesis in NAFLD. We highlight the limitations of current methodologies, discuss the emerging areas of research in this field, and future directions for the applications of stable isotopes to study NAFLD and its complications.

Gastrointestinal Motility Disorders and Their Clinical Implications in Cirrhosis

Gastrointestinal motility is impaired in a substantial proportion of patients with cirrhosis. Cirrhosis-related autonomic neuropathy, increased nitric oxide production, and gut hormonal changes have been implicated. Oesophageal dysmotility has been associated with increased frequency of abnormal gastro-oesophageal reflux. Impaired gastric emptying and accommodation may result in early satiety and may have an impact on the nutritional status of these patients. Small intestinal dysmotility might be implicated in small intestinal bacterial overgrowth and increased bacterial translocation. The latter has been implicated in the pathophysiology of hepatic encephalopathy and spontaneous bacterial peritonitis. Enhanced colonic motility is usually associated with the use of lactulose. Pharmacological interventions aiming to alter gastrointestinal motility in cirrhosis could potentially have a beneficial effect reducing the risk of hepatic decompensation and improving prognosis.

Influence of habitual physical activity on gastric emptying in healthy males and relationships with body composition and energy expenditure

Although a number of studies have examined the role of gastric emptying (GE) in obesity, the influences of habitual physical activity level, body composition and energy expenditure (EE) on GE have received very little consideration. In the present study, we compared GE in active and inactive males, and characterised relationships with body composition (fat mass and fat-free mass) and EE. A total of forty-four males (active n 22, inactive n 22; BMI 21-36 kg/m2; percentage of fat mass 9-42%) were studied, with GE of a standardised (1676 kJ) pancake meal being assessed by the [13C]octanoic acid breath test, body composition by air displacement plethysmography, RMR by indirect calorimetry, and activity EE (AEE) by accelerometry. The results showed that GE was faster in active compared with inactive males (mean half-time (t 1/2): active 157 (sd 18) and inactive 179 (sd 21) min, P< 0.001). When data from both groups were pooled, GE t 1/2 was associated with percentage of fat mass (r 0.39, P< 0.01) and AEE (r - 0.46, P< 0.01). After controlling for habitual physical activity status, the association between AEE and GE remained, but not that for percentage of fat mass and GE. BMI and RMR were not associated with GE. In summary, faster GE is considered to be a marker of a habitually active lifestyle in males, and is associated with a higher AEE level and a lower percentage of fat mass. The possibility that GE contributes to a gross physiological regulation (or dysregulation) of food intake with physical activity level deserves further investigation.

Exploring liver mitochondrial function by ¹³C-stable isotope breath tests: implications in clinical biochemistry

The liver plays a pivotal role in a myriad of metabolic processes, including detoxification, glycolipidic storage and export, and protein synthesis. Breath tests employing (13)C as stable isotope have been introduced to explore such energy-dependent pathways involving mitochondrial function in the liver. Specific substrates are ketoisocaproic acid, methionine, and octanoic acid. In humans, the application of (13)C-breath tests ranges from nonalcoholic and alcoholic liver diseases to liver cirrhosis, hepatocarcinoma, preoperative and postoperative assessment of liver function, and drug-induced liver damage. Studying liver mitochondrial function by (13)C-breath tests represents a complementary tool to monitor complex metabolic processes in health and disease.

Dynamic carbon 13 breath tests for the study of liver function and gastric emptying

In gastroenterological practice, breath tests (BTs) are diagnostic tools used for indirect, non-invasive assessment of several pathophysiological metabolic processes, by monitoring the appearance in breath of a metabolite of a specific substrate. Labelled substrates originally employed radioactive carbon 14 (¹⁴C) and, more recently, the stable carbon 13 isotope (¹³C) has been introduced to label specific substrates. The ingested ¹³C-substrate is metabolized, and exhaled ¹³CO₂ is measured by mass spectrometry or infrared spectroscopy. Some ¹³C-BTs evaluate specific (microsomal, cytosolic, and mitochondrial) hepatic metabolic pathways and can be employed in liver diseases (i.e. simple liver steatosis, non-alcoholic steato-hepatitis, liver fibrosis, cirrhosis, hepatocellular carcinoma, drug and alcohol effects).

Another field of clinical application for ¹³C-BTs is the assessment of gastric emptying kinetics in response to liquids (¹³C-acetate) or solids (¹³C-octanoic acid in egg yolk or in a pre-packed muffin or the ¹³C-Spirulina platensis given with a meal or a biscuit). Studies have shown that ¹³C-BTs, used for gastric emptying studies, yield results that are comparable to scintigraphy and can be useful in detecting either delayed- (gastroparesis) or accelerated gastric emptying or changes of gastric kinetics due to pharmacological effects. Thus, ¹³C-BTs represent an indirect, cost-effective and easy method of evaluating dynamic liver function and gastric kinetics in health and disease, and several other potential applications are being studied.

Rapid alternative absorption of dietary long-chain fatty acids with upregulation of intestinal glycosylated CD36 in liver cirrhosis

BACKGROUND

Dietary long-chain fatty acid (LCFA) intake is an important risk factor for hepatic inflammation and hepatocarcinogenesis. An alternate route of dietary LCFA absorption has been suggested in patients with liver cirrhosis (LC).

OBJECTIVE

We aimed to determine this alternate route and to identify its mechanism.

DESIGN

Twenty healthy control subjects and 47 patients with LC-n = 23 with portal hypertension [PH(+)LC] and 24 without portal hypertension [PH(-)LC)]-were enrolled. [¹³C]Palmitate (an LCFA) and octanoate (a medium-chain fatty acid [MCFA]) were administered by using gastrointestinal endoscopy. Breath ¹³CO₂ was measured to quantify metabolized fatty acids. We also examined intestinal specimens of patients in these groups.

RESULTS

A more rapid increase in metabolized palmitate, which showed a pattern similar to that of octanoate metabolism, was observed in patients with LC than in healthy control subjects. The increase in the PH(-)LC group was higher than that in the PH(+)LC group. However, the concentration of metabolized palmitate increased with treatment of the PH(+)LC group with a portal-systemic shunt. Morphologic changes such as expanded lymph and blood vessels were present, and glycosylated CD36 increased in the jejunum of the PH(+)LC group. This group had high serum concentrations of glucagon-like peptide-2. These data suggest that dietary LCFAs, similar to MCFAs, are absorbed via blood vessels in patients with LC.

CONCLUSIONS

Rapid absorption of LCFAs by an alternative method occurred in patients with LC. This altered LCFA processing is likely related to upregulation of intestinal glycosylated CD36 and could contribute to pathogenesis in patients with LC.

Evaluation of gastrointestinal transit in clinical practice: position paper of the American and European Neurogastroenterology and Motility Societies

BACKGROUND

Disorders of gastrointestinal (GI) transit and motility are common, and cause either delayed or accelerated transit through the stomach, small intestine or colon, and affect one or more regions. Assessment of regional and/or whole gut transit times can provide direct measurements and diagnostic information to explain the cause of symptoms, and plan therapy.

PURPOSE

Recently, several newer diagnostic tools have become available. The American and European Neurogastroenterology and Motility Societies undertook this review to provide guidelines on the indications and optimal methods for the use of transit measurements in clinical practice. This was based on evidence of validation including performance characteristics, clinical significance, and strengths of various techniques. The tests include measurements of: gastric emptying with scintigraphy, wireless motility capsule, and (13)C breath tests; small bowel transit with breath tests, scintigraphy, and wireless motility capsule; and colonic transit with radioopaque markers, wireless motility capsule, and scintigraphy. Based on the evidence, consensus recommendations are provided for each technique and for the evaluations of regional and whole gut transit. In summary, tests of gastrointestinal transit are available and useful in the evaluation of patients with symptoms suggestive of gastrointestinal dysmotility, since they can provide objective diagnosis and a rational approach to patient management.

Intrasubject variability of gastric emptying in the critically ill using a stable isotope breath test

BACKGROUND AND AIMS

Isotope breath tests are increasingly used to evaluate the effects of prokinetic drugs on gastric emptying. The aim was to assess intrasubject variability in gastric emptying, when using an isotope breath test in the critically ill.

METHODS

A retrospective analysis of data was undertaken in 12 patients who had gastric emptying measurements on consecutive days using a (13)C-octanoic acid breath test. The gastric emptying coefficient--GEC (a global index for the gastric emptying rate), and the t(50) (calculated time for 50% of meal to empty) were calculated, together with the coefficient of variability for these parameters. Data are mean (SD).

RESULTS

Neither GEC (day 1: 3.3 (0.8) vs. day 2: 3.1 (0.6); P = 0.31) nor t(50) (day 1: 127 (43) min vs. day 2: 141 (48) min; P = 0.46) were significantly different between the two days. Intrasubject variability was less for GEC (15.6%) than for t(50) (31.8%).

CONCLUSION

There is only modest intrasubject variability in GEC measurements using the (13)C-octanoic acid breath test in critically ill patients. As such, it may be an acceptable measurement tool to assess the effects of prokinetic drugs in this group.

13C-breath tests for clinical investigation of liver mitochondrial function

BACKGROUND

Mitochondria play a major role in cell energetic metabolism; therefore, mitochondrial dysfunction inevitably participates in or even determines the onset and progression of chronic liver diseases. The assessment of mitochondrial function in vivo, by providing more insight into the pathogenesis of liver diseases, would be a helpful tool to study specific hepatic functions and to develop rational diagnostic, prognostic and therapeutic strategies.

DESIGN

This review focuses on the utility of breath tests to assess mitochondrial function in humans and experimental animals.

RESULTS

The introduction in the clinical setting of specific breath tests may allow elegantly and noninvasively overcoming the difficulties caused by previous complex techniques and might provide clinically relevant information, i.e the effects of drugs on mitochondria. Substrates meeting this requirement are alpha-keto-isocaproic acid and methionine that are both decarboxylated by mitochondria. Long-and medium-chain fatty acids that are metabolized through the Krebs cycle, and benzoic acid which undergoes glycine conjugation, may also reflect the function of mitochondria.

CONCLUSIONS

Breath tests to assess in vivo mitochondrial function in humans represent a potentially useful diagnostic and prognostic tool in clinical investigation.

Evaluation of the 13C-octanoate breath test as a surrogate marker of liver damage in animal models

BACKGROUND

Octanoate (also known as sodium octanoate), a medium-chain fatty acid metabolized in the liver, is a potential substrate for non-invasive breath testing of hepatic mitochondrial beta-oxidation.

METHODS

We evaluated the 13C-octanoate breath test (OBT) for assessing injury in acute hepatitis and two rat models of liver cirrhosis, first testing octanoate absorption (per os or intraperitoneally (i.p.)) in normal rats. We then induced acute hepatitis with thioacetamide (300 mg/kg/i.p., 24-h intervals). Liver injury end points were serum aminotransferase levels and 13C-OBT (24 and 48 h following initial injection). Thioacetamide (200 mg/kg/i.p., twice per week, 12 weeks) was used to induce liver cirrhosis. OBT and liver histological assessment were performed every 4 weeks. Bile duct ligation (BDL) was used to induce cholestatic liver injury. We completed breath tests with 13C-OBT and 13C-methacetin (MBID), liver biochemistry, and liver histology in BDL and sham-operated rats (baseline, 6, 14, 20 days post-BDL).

RESULTS

Octanoate absorbs well by either route. Peak amplitudes and cumulative percentage dose recovered at 30 and 60 min (CPDR30/60), but not peak time, correlated with acute hepatitis. Fibrosis stage 3 at week 8 significantly correlated with each OBT parameter. Cholestatic liver injury (serum bilirubin, ALP, gamma-GT, liver histology) was associated with significant suppression of the maximal peak values and CPDR30/60, respectively (P<0.05),using MBID but not 13C-octanoate.

CONCLUSIONS

OBT is sensitive for potentially evaluating liver function in rat models of acute hepatitis and thioacetamide-induced liver cirrhosis but not in cholestatic liver injury. The MBID test may be better for evaluation of cholestatic liver disease in this model.

Stomach dysfunction in diabetes mellitus: emerging technology and pharmacology

Gastroparesis and other types of gastric dysfunction result in substantial morbidity in diabetes patients. The pathophysiology of these disorders is incompletely understood. This article reviews techniques applicable to the assessment of gastric function in diabetes patients, including the measurement of emptying, accommodation, and contractility. Available treatment options are also reviewed, including novel yet unapproved serotonin 5-HT(4) agonist pharmacological treatments, as well as the role of endoscopic, surgical, and device treatments of gastroparesis.

Increase of octanoate concentrations during extracorporeal albumin dialysis treatments

Extracorporeal liver support procedures based on albumin dialysis require the use of pharmaceutical-grade human serum albumin (HSA). Those preparations contain octanoate, which is added as stabilizer during the production process. For octanoate, a direct involvement in the pathogenesis of liver failure complications as well as an indirect influence by competitive displacement effects at the albumin molecule have been described. During five Single Pass Albumin Dialysis (SPAD) and three Molecular Adsorbent Recirculating System (MARS) treatments the changes of octanoate concentrations in blood and dialysate were investigated. An octanoate increase in patient blood was observed during passage of the filter for both SPAD (585 micromol/L [338-1022 micromol/L]) (median [range]) and MARS (182 micromol/L [71-437 micromol/L]) during the first three hours of treatment. The molar ratio of octanoate/albumin at the blood outflow was significantly higher during SPAD treatments (1.73 [0.86-2.64] vs. 0.54 [0.31-1.1]; P = 0.001) during MARS. Changes of octanoate blood levels during SPAD were significantly higher than during MARS (P < 0.001). The shift of octanoate from the dialysate to the patient was persistent during SPAD (median 67.6 micromol/min), whereas during MARS a decrease over time was observed (from 25.5 to 7.5 micromol/min). During albumin dialysis procedures a transfer of octanoate into patient blood occurs. The time-course and extent are different between both albumin dialysis procedures. Given the positive clinical effects reported mainly for MARS, the clinical impact of albumin dialysis-associated transfer of octanoate during extracorporeal liver support needs to be evaluated further.

Influence of clinical parameters on the results of 13C-octanoic acid breath tests: examination of different mathematical models in a large patient cohort

It is assumed, although not proven, that 13CO2-excretion following ingestion of 13C-octanoic acid (13C-OA) does not only depend on gastric emptying (GE) but also on absorption and metabolism of 13C-OA and endogenous CO2-production. Our aims were (i) to test the effects of patient characteristics and of diseases that may impair 13C-OA-metabolism on GE parameters. (ii) To compare different GE endpoints. Therefore, we investigated effects of age, gender, BMI and diseases with potential impact on 13C-OA-metabolism (including pancreatic, liver and lung disease, diabetes, IBD) on cumulative 4h-13CO2-excretion (4h-CUM) and T1/2 calculated by non-linear regression model (NL, determined by shape of breath test curve) and generalized linear regression model (GLR, reflects absolute 13CO2-excretion) in 1279 patients and 19 healthy controls who underwent a standardized 13C-OA-breath test. Digestive and metabolic disturbances hardly influenced 4h-CUM or T1/2 calculated by NL or GLR models. In the multivariate linear regression models, 4h-CUM was significantly predicted by diabetes adjusted for age, gender and IBD but influence of these parameters was small (R2 = 0.028, P < 0.0001). T1/2(NL) and 4h-CUM were weakly correlated, even after exclusion of tests with unrealistically high estimates for T1/2(NL) (n = 1095, R(2) = 0.029, P < 0.0001). Conversely, 4h-CUM was closely associated with T(1/2)(GLR) (exponential correlation, R(2) = 0.774, P < 0.00001, n = 1279). We conclude that influences of digestive and metabolic disturbances on 13CO2-excretion following 13C-OA-application are generally low. Thus, our findings resolve an important criticism of methods using absolute 13CO2-excretion for evaluation of 13C-OA-breath tests and suggest that such models may correctly identify T1/2 in a mixed patient population.

Will the 13C-octanoic acid breath test ever replace scintigraphy as the gold standard to assess gastric emptying?

The applicability of the 13C-octanoic acid breath test for the assessment of gastric emptying is discussed. In the current issue of this journal, Keller and her colleagues described the application of different mathematical models for analysis of the 13C-octanoic acid test in a very large patient population.

Methods for measurement of gastric motility

There is an array of tests available to measure gastric motility. Some tests measure end points, such as gastric emptying, that result from several different functions, whereas other tests are more specific and test only a single parameter, such as contractility. This article reviews the tests most commonly available in practice and research to evaluate in vivo the gastric functions of emptying, accommodation, contractility, and myoelectrical activity. The rationale for testing, the relative strengths and weaknesses of each test, and technical details are summarized. We also briefly indicate the applications and validations of the tests for use in experimental animal studies.

Validity of 13C octanoic acid breath test for measurement of solid meal gastric emptying time in children

BACKGROUND/PURPOSE

It is important to establish a physiologic range of gastric emptying (GE) in children. Gastric emptying time measured with (99)Tc-labeled solid meal (GE(Tc)) is the gold standard. Large-scale studies with GE(Tc) are ideal but not feasible because of radiation exposure. The (13)C-labeled octanoic acid breath test (GE(13C)) does not involve radiation and is suitable for large studies. The aim of this study was to validate GE(13C) with GE(Tc) and to explore whether GE(13C) could be used to establish a physiologic range of GE in children.

METHOD

Twenty-five healthy children underwent simultaneous GE(Tc) and GE(13C) using a standardized solid test meal. The time taken for the stomach to empty half its content (T(1/2)(13C)) and solid lag phase (lag(13C)) for GE(13C) were computed from the fractional excretion of (13)C in expired air. T(1/2)(13C) and lag(13C) were compared with corresponding values obtained by GE(Tc).

RESULT

Correlation coefficient between T(1/2)(13C) and T(1/2)(Tc) was 0.69 (P < .01; r = 0.92 if 3 outliers were omitted). Correlation coefficient between lag(13C) and lag(Tc) was 0.39 (P < .05). There was good agreement between the methods by the Bland Altman method.

CONCLUSION

There is good agreement between GE(13C) and GE(Tc). GE(13C) can be safely used to establish the reference range of GE in healthy children.

Impact of gastric emptying on levodopa pharmacokinetics in Parkinson disease patients

Adjunction of the catechol-O-methyltransferase (COMT) inhibitor entacapone (EN) to levodopa/carbidopa (LD/CD) improves motor symptoms in patients with Parkinson disease (PD) by a prolonged elimination of LD. But it is not known whether EN addition influences gastric emptying and thus LD pharmacokinetics and pharmacodynamics. Objectives were to simultaneously determine plasma LD elimination, gastric emptying, and clinical response after a single intake of the same LD dosage as LD/CD--or as (LD/CD/EN) formulation on 2 consecutive days. In both groups, PD patients with delayed gastric emptying had significant lower LD plasma concentrations. Addition of EN did not influence gastric emptying but significantly improved motor response, which was not different for patients with delayed gastric emptying. However, with and without EN adjunction gastric emptying distinctly contributes to the variability of plasma LD bioavailability. This may impact LD delivery to the brain and thus motor response in PD patients. Therefore, fine tuning of LD application, which considers gastric emptying, becomes more and more essential in advanced PD stages with a reduced striatal neuronal dopamine capacity, which is responsible for maintenance of motor response in early PD patients.

Total body metabolism of 13C-octanoic acid is preserved in patients with non-alcoholic steatohepatitis, but differs between women and men

OBJECTIVES

Among numerous factors which account for the pathogenesis of non-alcoholic steatohepatitis (NASH), hepatic mitochondrial beta-oxidation is considered to play a pivotal role. We performed a (13)C-based breath test with a medium-chain fatty acid to non-invasively assess total body beta-oxidation in patients with NASH and in healthy controls.

METHODS

We performed a simplified (13)CO(2)-based breath test in 16 patients with histologically proven NASH and 24 healthy controls. One hundred milligrams of sodium (13)C-octanoate dissolved in 200 ml of water were orally administered and breath samples were collected before and during 3 h following administration. The samples were analysed for the cumulative (13)CO(2) recovery (%-cum-dose) by non-dispersive infrared spectrometry. Additionally, data of 69 patients who had undergone a C-octanoate breath test for the assessment of gastric emptying were retrospectively evaluated for the %-cum-dose.

RESULTS

The cumulative (13)CO(2) recovery 3 h after the administration of the substrate did not differ among patients with NASH and controls (34.6 +/- 7.0% vs. 34.6 +/- 6.5%, P = 0.90). Compared with men, women yielded a significantly higher cumulative (13)CO(2) excretion in both controls (30.1 +/- 5.7% vs. 38.5 +/- 4.4%, P = 0.0008) and NASH patients (30.2 +/- 5.4% vs. 39.0 +/- 6.5%, P = 0.031). Forty-two of 69 patients (61%) of the gastric emptying group showed a normal gastric emptying rate. Among these patients, women also demonstrated a tendency for a higher (13)CO(2) recovery compared with men (P = 0.055). This was not the case in 27 patients with delayed gastric emptying (P = 0.47).

CONCLUSIONS

Though hepatic mitochondrial function might be impaired in patients with NASH, total beta-oxidation of octanoic acid remains normal. Gender-specific metabolic modifications seem to account for significant differences of the cumulative (13)CO(2) recovery in women and men. This may have further consequences for the appraisal of (13)C breath tests which involve octanoic acid. Further trials focusing on the assessment of body composition and energy expenditure could contribute essential further information.

Measurement of gastric emptying by octanoate metabolism

PURPOSE OF REVIEW

Since its introduction just over 10 years ago, there have been a number of studies that have used the octanoate breath test to assess gastric emptying. Although use of the method is on the increase (the number of gastric emptying studies published on PubMed using the octanoate breath test has doubled between the periods 1997-2000 and 2001-2004 compared with a drop of approximately 20% in the use of scintigraphy over the same periods), the methodology has not achieved universal acceptance, primarily because it can provide results comparable to established techniques only indirectly.

RECENT FINDINGS

Recent methods for overcoming this difficulty are reviewed, including modified methods for breath test interpretation and the application of the related saliva test. The latter promises to be useful as a non-invasive proxy for established techniques, such as scintigraphy, for further validation of the breath test. Recent applications of octanoate-based methods are briefly considered.

SUMMARY

A novel approach detailed in this review for breath test interpretation, where the bicarbonate pool is modelled as a single compartment, could prove useful for obtaining breath test gastric emptying parameters that are directly comparable with those obtained from the gold standard, gamma scintigraphy. In combination with the saliva test, this could add credence to use of the octanoate breath test as a clinically accepted diagnostic tool, in addition to its potential in research.