L-[1-(13)C] Phenylalanine oxidation as a measure of hepatocyte functional capacity in end-stage liver disease

Serum Metabolomics in Patients with Coexisting NAFLD and T2DM Using Liquid Chromatography-Mass Spectrometry

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM) frequently coexist and can act synergistically to drive adverse outcomes of one another. This study aimed to unravel the metabolomic changes in patients with NAFLD and T2DM, to identify potential noninvasive biomarkers, and to provide insights for understanding the link between NAFLD and T2DM.

METHODS

Three hundred participants aged 35 to 70 years who were diagnosed with NAFLD (n = 100), T2DM (n = 100), or a comorbidity of NAFLD and T2DM (n = 100) were included in this study. Anthropometrics and routine blood chemistry were assessed after overnight fast. The global serum metabolomic analysis was performed by ultra-performance liquid chromatography-Orbitrap mass spectrometry. Multivariate data analysis methods were utilized to identify the potential biomarkers.

RESULTS

A set of serum biomarkers that could effectively separate NAFLD from NAFLD + T2DM and T2DM from NAFLD + T2DM were identified. We found that patients with coexisting NAFLD and T2DM had significantly higher levels of total protein (TP), triglycerides (TG), glucose in urine, and gamma-hydroxybutyric acid than those with NAFLD and had significant increased levels of TP, albumin, alanine aminotransferase, aspartate aminotransferase, total cholesterol, cholinesterase, TG, low-density lipoprotein, and apolipoprotein A when compared to patients with T2DM.

CONCLUSION

The metabolomics results provide evidence that the comorbidity of NAFLD and T2DM considerably altered patients' metabolomics patterns compared to those of patients with only NAFLD or T2DM.

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.

Metabolic analysis of early nonalcoholic fatty liver disease in humans using liquid chromatography-mass spectrometry

Background

Nonalcoholic fatty liver disease (NAFLD) is a common metabolic disease that affects 20–30% of individuals worldwide. Liver puncture remains the gold standard for the diagnosis of liver diseases despite limitations regarding invasive nature and sample variability. It is of great clinical significance to find noninvasive biomarkers to detect and predict NAFLD.

Objective

The aims of this study were to identify potential serum markers in individuals with early-stage NAFLD and to advance the mechanistic understanding of this disease using a high-throughput mass spectrometry-based untargeted metabolomics approach.

Methods

One hundred and twelve patients with early-stage NAFLD aged 18–55 were recruited according to the guidelines. The control group included 112 healthy participants. The demographic, anthropometric, clinical and laboratory data of all participants were systematically collected. Serum samples were obtained after an overnight fast. The comprehensive serum metabolomic analysis was performed by ultra-performance liquid chromatography-Orbitrap mass spectrometry. The resultant data was processed by Compound Discover and SIMCA-P software to validate the potential biomarkers. Significantly altered metabolites were evaluated by variable importance in projection value (VIP > 1) and ANOVA (p < 0.01). Pathway analysis was performed using MetaboAnalyst 4.0.

Results

The liver function test of early NAFLD patients showed no statistical differences to control group (p > 0.05). However, obvious differences in blood lipids were observed between subjects with NAFLD and controls (p < 0.001). In total, 55 metabolites showed significant changes in experimental group were identified. The area under curve (AUC) values deduced by receiver operating curve (ROC) analysis indicated that these newly identified biomarkers have high predictability and reliability. Of these, 15 metabolites with AUC greater than 0.9 were of great diagnostic value in early NAFLD patients.

Conclusion

In this study, a total of 15 serum metabolites were found to strongly associate with early NAFLD. These biomarkers may have great clinical significance in the early diagnosis of NAFLD, as well as to follow response to therapeutic interventions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02820-7.

Induced volatolomics of pathologies

Volatolomics allows us to elucidate cell metabolic processes in real time. In particular, a volatile organic compound (VOC) excreted from our bodies may be specific for a certain disease, such that measuring this VOC may afford a simple, fast, accessible and safe diagnostic approach. Yet, finding the optimal endogenous volatile marker specific to a pathology is non-trivial because of interlaboratory disparities in sample preparation and analysis, as well as high interindividual variability. These limit the sensitivity and specificity of volatolomics and its applications in biological and clinical fields but have motivated the development of induced volatolomics. This approach aims to overcome issues by measuring VOCs that result not from an endogenous metabolite but, rather, from the pathogen-specific or metabolic-specific enzymatic metabolism of an exogenous biological or chemical probe. In this Review, we introduce volatile-compound-based probes and discuss how they can be exploited to detect and discriminate pathogenic infections, to assess organ function and to diagnose and monitor cancers in real time. We focus on cases in which labelled probes have informed us about metabolic processes and consider the potential and drawbacks of the probes for clinical trials. Beyond diagnostics, VOC-based probes may also be effective tools to explore biological processes more generally.

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.

Systems level metabolic phenotype of methotrexate administration in the context of non-alcoholic steatohepatitis in the rat

Adverse drug reactions (ADRs) represent a significant clinical challenge with respect to patient morbidity and mortality. We investigated the hepatotoxicity and systems level metabolic phenotype of methotrexate (MTX) in the context of a prevalent liver disease; non-alcoholic steatohepatitis (NASH). A nuclear magnetic resonance spectroscopic-based metabonomic approach was employed to analyze the metabolic consequences of MTX (0, 10, 40, and 100 mg/kg) in the urine and liver of healthy rats (control diet) and in a model of NASH (methionine-choline deficient diet). Histopathological analysis confirmed baseline (0 mg/kg) liver necrosis, liver inflammation, and lipid accumulation in the NASH model. Administration of MTX (40 and 100 mg/kg) led to liver necrosis in the control cohort, whereas the NASH cohort also displayed biliary hyperplasia and liver fibrosis (100 mg/kg), providing evidence of the synergistic effect of MTX and NASH. The complementary hepatic and urinary metabolic phenotypes of the NASH model, at baseline, revealed perturbation of multiple metabolites associated with oxidative and energetic stress, and folate homeostasis. Administration of MTX in both diet cohorts showed dose-dependent metabolic consequences affecting gut microbial, energy, nucleobase, nucleoside, and folate metabolism. Furthermore, a unique panel of metabolic changes reflective of the synergistic effect of MTX and NASH was identified, including the elevation of hepatic phenylalanine, urocanate, acetate, and both urinary and hepatic formiminoglutamic acid. This systems level metabonomic analysis of the hepatotoxicity of MTX in the context of NASH provided novel mechanistic insight of potential wider clinical relevance for further understanding the role of liver pathology as a risk factor for ADRs.

¹³C-methacetin breath test in the evaluation of disease severity in patients with liver cirrhosis

AIMS

The non-invasive (13)C-methacetin ((13)C-MBT) breath test has been proposed as a measure of metabolic liver function that improves the diagnostic efficacy of serologic and biochemical tests in assessing hepatic functional capacity and liver disease severity, The goal of this study was to establish the clinical utility of this test in quantifying hepatic metabolic function in patients with liver cirrhosis of varying severity and to compare (13)C-MBT measurements with the AST/ALT ratio, APRI score, and other routine liver tests.

METHODS

Routine liver function tests including serum bilirubin, aspartate aminotransferase activity (AST), alanine aminotransferase (ALT), AST/ALT ratio, the APRI score, the percentage of dose rate (PDR) and cumulative percentage of dose rate (CPDR) of the (13)C-MBT were evaluated in 52 cirrhotic patients of alcohol etiology (Child-Pugh A/B/C 10/28/14) and 37 healthy controls.

RESULTS

The (13)C-MBT differed significantly between healthy controls and cirrhotic patients at all time intervals measured. It also proved the ability to differentiate patients with liver cirrhosis based on severity of hepatic impairment corresponding to the Child-Pugh classification A vs. B vs. C. The ROC curve analysis suggested that the best prediction is provided by time intervals between the 10th - 20th or 10th - 40th minute of PDR.

CONCLUSIONS

The (13)C-MBT offers a reliable means for quantification of hepatic metabolic function over the complete range of functional liver impairment. It is non-invasive, easy to perform and completely safe.

Clinical utility of 13C-liver-function breath tests for assessment of hepatic function

13C-Liver-function breath tests have been used in clinical diagnostics and, to a limited extent, to investigate hepatic function. From a practical perspective, tests such as the 13C-aminopyrine and 13C-methacetin breath tests are simple to administer, safe, and relatively inexpensive to perform. Surprisingly, they have not entered the mainstream of clinical practice, because they are perceived to lack the specificity and adequate precision needed to give accurate results in real time. The dynamic nature of 13C-liver-function breath tests, their possible versatility in terms of assessing a range of different liver functions, and the ease with which they can be repeated to follow relative changes in liver function with time, all imply the potential for wider clinical application. Therefore, there is a need for these tests to be critically evaluated and their potential clinical application be tested systematically against defined objectives. We describe refinements in the methodology of the tests and propose several situations in which currently reliable methods for assessment of liver function do not exist and where 13C-liver-function breath tests might be of use. We propose that use has been constrained by practical methodological considerations which could be addressed to offer tests better suited to routine application in the out-patient or community setting.

Clinical research on liver reserve function by 13C-phenylalanine breath test in aged patients with chronic liver diseases

Background

The objective of this study was to investigate whether the ¹³C-phenylalanine breath test could be useful for the evaluation of hepatic function in elderly volunteers and patients with chronic hepatitis B and liver cirrhosis.

Methods

L-[1-¹³C] phenylalanine was administered orally at a dose of 100 mg to 55 elderly patients with liver cirrhosis, 30 patients with chronic hepatitis B and 38 elderly healthy subjects. The breath test was performed at 8 different time points (0, 10, 20, 30, 45, 60, 90, 120 min) to obtain the values of Delta over baseline, percentage ¹³CO₂ exhalation rate and cumulative excretion (Cum). The relationships of the cumulative excretion with the ¹³C-%dose/h and blood biochemical parameters were investigated.

Results

The ¹³C-%dose/h at 20 min and 30 min combined with the cumulative excretion at 60 min and 120 min correlated with hepatic function tests, serum albumin, hemoglobin, platelet and Child-Pugh score. Prothrombin time, total and direct bilirubin were significantly increased, while serum albumin, hemoglobin and platelet, the cumulative excretion at 60 min and 120 min values decreased by degrees of intensity of the disease in Child-Pugh A, B, and C patients (P < 0.01).

Conclusions

The ¹³C-phenylalanine breath test can be used as a non-invasive assay to evaluate hepatic function in elderly patients with liver cirrhosis. The ¹³C-%dose/h at 20 min, at 30 min and cumulative excretion at 60 min may be the key value for determination at a single time-point. ¹³C-phenylalanine breath test is safe and helpful in distinguishing different stages of hepatic dysfunction for elderly cirrhosis patients.

Effect of alcohol consumption on the liver detoxication capacity as measured by [13C2]aminopyrine and L-[1-13C]phenylalanine breath tests

The aim of this study was to investigate the hepatic microsomal and cytosolic functions by using the 13CO2 breath test in healthy subjects either before or after consumption of red wine. Twelve adults received [13C2]aminopyrine and L-[1-13C]phenylalanine together with a standardised dinner. Expired air samples were taken over 6 h. After a wash-out period, the subjects consumed 0.4 ml ethanol per kg per day together with dinner over a 7.5-day period on average. Thereafter, 13C-tracer administration was repeated under identical conditions. The 13CO2 enrichments were measured by isotope ratio mass spectrometry. The mean cumulative percentage 13C-dose recovery after administration of [13C2]aminopyrine and L-[1-13C]phenylalanine either without or with red wine consumption amounted to 17.0+/-4.4 vs. 14.7+/-3.1% (p=0.170) and 14.0+/-2.8 vs. 11.5+/-3.9% (p=0.084), respectively. Moderate alcohol consumption does not induce significant short-term changes of the microsomal and the cytosolic function of the human liver in healthy subjects.

L-[1-13C]phenylalanine breath test in patients with chronic liver disease of different etiologies

The aim of this study was to compare the oxidation of L-[1-(13)C]phenylalanine ((13)C-PheOx) in patients with chronic liver failure due to different etiologies using L-[1-(13)C]phenylalanine breath test. Breath samples were collected before the administration of 100 mg L-[1-(13)C]phenylalanine, and every 10 min thereafter until completion of 1 h. Control subjects (n=9) presented a larger cumulative percentage of (13)C dose recovery (CPDR) than patients (n=124) with chronic liver disease, regardless of the etiology (7.5+/-0.7 vs. 4.2+/-0.2, p=0.001). No differences in CPDR were found considering the Child-Pugh (CP) class or etiology: alcoholic (CP A=7.7+/-0.7, CP B=4.1+/-0.5, CP C=2.0+/-0.3), hepatitis C virus (CP A=5.4+/-0.5, CP B=4.0+/-0.2, CP C=2.2+/-0.3), hepatocellular carcinoma (CP A=5.5+/-1.6, CP B=3.6+/-1.8, CP C=2.2+/-1.0); or cryptogenic cirrhotic patients (CP A=7.4+/-1.5, CP B=4.4+/-0.4, CP C=2.1+/-0.7). Results confirm that (13)C-PheOx decreases in patients with cirrhosis with respect to controls, notwithstanding the etiology.

Effect of alcohol consumption on the liver detoxication capacity as measured by [13C]methacetin- and [methyl-13C]methionine-breath tests

The aim of this study was to investigate the hepatic microsomal and mitochondrial functions by using the 13CO2-breath test in healthy subjects either before or after the consumption of red wine. Fourteen adults received [13C]methacetin and [methyl-13C]methionine together with a standardised dinner. Expired air samples were taken over 6 h. After a wash-out period, the subjects consumed 0.4 ml ethanol/kg/day together with dinner over a 10-day period. Thereafter, 13C-tracer administration was repeated under identical conditions. The 13CO2-enrichments were measured by isotope ratio mass spectrometry. The mean cumulative percentage 13C-dose recovery (CPDR) after administration of [13C]methacetin and [methyl-13C]methionine either without or with red wine consumption amounted to 38.2+/-6.3 vs. 36.3+/-6.7% (p=0.363) and 9.5+/-3.3 vs. 8.8+/-2.5% (p=0.47), respectively. Moderate alcohol consumption does not induce significant short-term changes of the microsomal and the mitochondrial functions of the human liver in healthy subjects.

Serum phenylalanine concentration as a marker of liver function in obese patients before and after bariatric surgery

BACKGROUND

Human obesity is associated with increased serum phenylalanine concentration, which is probably caused by liver dysfunction related to liver steatosis. This study examines whether improvements of liver function after bariatric surgery is associated with a decrease of serum phenylalanine concentration caused by an increase of phenylalanine metabolism.

METHOD

Serum phenylalanine and alanine aminotransferase (an independent predictor of liver steatosis) concentrations as well as several parameters related to obesity were measured in 16 obese patients (seven men and nine women) before and 6 months after vertical banded gastroplasty. Ten (six men and four women) lean, healthy subjects served as controls.

RESULTS

Obese patients before surgery had approximately twofold higher serum phenylalanine concentration than control subjects. The serum phenylalanine concentration decreased 6 months after bariatric surgery. Serum alanine aminotransferase (ALT) concentration was higher in obese patients before surgery, and decreased 6 months after bariatric surgery. Changes in serum phenylalanine concentration correlated positively with changes of ALT concentration (r = 0.75; p < 0.001). The body weight, BMI, HOMA-IR, serum triacylglycerol, LDL-cholesterol/HLD-cholesterol ratio, leptin, insulin, and glucose concentrations were higher in obese patients, and decreased 6 months after bariatric surgery. Serum HDL-cholesterol concentration was lower in obese patients before surgery than in control subjects and increased 6 months after surgery.

CONCLUSION

Results obtained indicate that bariatric surgery-induced weight loss had beneficial effects on several laboratory parameters including serum phenylalanine, ALT, lipid concentrations and insulin resistance. A strong positive correlation between serum phenylalanine and serum ALT concentrations suggests that deterioration of liver function in obese patients is contributing to a decrease in phenylalanine metabolism and consequently to the increase of serum phenylalanine concentration. One can suppose that serum phenylalanine concentration could be noninvasive marker of liver dysfunction associated with liver steatosis in obese patients.

(13)C-phenylalanine breath test correlates with liver fibrosis in postoperative biliary atresia

BACKGROUND

Values derived from the (13)C-phenylalanine breath test (PBT) may serve as an index for liver fibrosis and clinically predictive readings for liver diseases in adults. In the present study the PBT was conducted in postoperative biliary atresia (BA) children to evaluate phenylalanine metabolism in the liver, and the results based on biochemical data, especially the index on liver fibrosis, were compared with PBT findings.

METHODS

Hepatofunctional evaluations were conducted in 10 postoperative BA children with moderate (group B; n = 4) and severe (group A; n = 6) liver dysfunction, and the PBT results were compared with those of 13 normal healthy children (group C). Subjects were orally given single-bolus (13)C-phenylalanine at 3.5 mg/kg (maximum dosing: 100 mg) in the morning. Time-related exhaled gas was periodically collected until 120 min after dosing. The (13)CO(2) levels were monitored with gas chromatography-mass spectrometry before and after administration, and the (13)C excretion rate, (13)C cumulative excretion and time of maximum (13)C excretion rate were monitored accordingly.

RESULTS

Total bile acid, hyaluronic acid, type IV collagen 7S, total bilirubin or albumin and the PBT findings were significantly correlated. The PBT findings in group A were significantly lower those of group B, indicating that phenylalanine metabolism was markedly attenuated in the former.

CONCLUSION

The PBT values correlated well with liver fibrosis in postoperative BA children. Because PBT is a non-invasive approach, results from this method may serve as a useful and reliable index for post-surgical monitoring of children operated on for liver fibrosis.

Prognostic value of 13C-phenylalanine breath test on predicting survival in patients with chronic liver failure

AIM: To evaluate the prognostic value of percentage of ¹³C-phenylalanine oxidation (¹³C-PheOx) obtained by ¹³C-phenylalanine breath test (¹³C-PheBT) on the survival of patients with chronic liver failure.

METHODS: The hepatic function was determined by standard liver blood tests and the percentage of ¹³C-PheOx in 118 chronic liver failure patients. The follow-up period was of 64 mo. Survival analysis was performed by the Kaplan-Meier method and variables that were significant (P < 0.10) in univariate analysis and subsequently introduced in a multivariate analysis according to the hazard model proposed by Cox.

RESULTS: Forty-one patients died due to progressive liver failure during the follow-up period. The probability of survival at 12, 24, 36, 48 and 64 mo was 0.88, 0.78, 0.66, 0.57 and 0.19, respectively. Multivariate analysis demonstrated that Child-Pugh classes, age, creatinine and the percentage of ¹³C-PheOx (HR 0.338, 95% CI: 0.150-0.762, P = 0.009) were independent predictors of survival. When Child-Pugh classes were replaced by all the parameters of the score, only albumin, bilirubin, creatinine, age and the percentage of ¹³C-PheOx (HR 0.449, 95% CI: 0.206-0.979, P = 0.034) were found to be independent predictors of survival.

CONCLUSION: Percentage of ¹³C-PheOx obtained by ¹³C-PheBT is a strong predictor of survival in patients with chronic liver disease.

Evaluation of postinjury hepatocyte function by central amino acid clearance

It has been demonstrated by other investigators that central plasma clearance of amino acids accurately predicts hepatocyte function in patients with liver disease and correlates with clinical outcome. This methodology has not heretofore been studied in the trauma patient. It is our hypothesis that central amino acid clearance in trauma patients is more reflective of hepatocyte function than traditional liver function tests. We examined the plasma amino acid clearance rates using L-[1-13C]phenylalanine. Clearance rates were compared to standard liver function tests (LFTs) and the sensitivity and predictability of the technique were determined. The study was conducted on uninjured control subjects and in seriously injured patients, both with and without significant liver injuries. Compared to baseline values in the control group, initial phenylalanine breath scores were reduced in the injured, but exceeded control levels at 7 days postinjury. These changes were statistically significant. There was no difference between those with and without liver trauma. LFTs showed inconsistent and conflicting results. Thus, central amino acid clearance measured by L-[1-13C]phenylalanine oxidation is depressed immediately following injury but reaches supranormal levels at 7 days postinjury. Compared to LFTs, amino acid clearance suggests initial hepatocyte suppression followed by hyperactivity and is a more accurate determinant of hepatocyte function.

L-[1-13C] phenylalanine breath test results reflect the activity of phenylalanine hydroxylase in carbon tetrachloride acute injured rat liver

L-[1-13C] phenylalanine breath tests (PheBTs) have been used to determine the hepatocyte functional capacity of patients. This study investigated the relationship between the PheBT parameter 13C excretion rate constant (PheBT-k) and activity of the phenylalanine metabolic rate-limiting enzyme phenylalanine hydroxylase (PAH) in rat liver. We noted that the time-course curves of 13C excretion presented as a single peak, which appeared 2 min after administration of L-[1-13C] phenylalanine (13C-Phe). 13C excretion during exhalation can be divided into a slow phase and a rapid phase. The PheBT-k in rats with carbon tetrachloride acute liver injury was.significantly lower than that of control rats. The rapid phase 13C disposition constants of the acute liver injured rats did not differ from that of the controls. The peak value of 13C abundance in the breath of the acute liver injured rats was markedly higher than that of the control group. Total liver PAH activity in the acute liver injured rats was significantly lower than that in the control group. PheBT-k was highly correlated with the total activity of liver PAH (r = 0.92, P < 0.001). The present findings indicate that PheBT results reflect PAH activity levels. The PheBT-k parameter is a sensitive index that can be used to evaluate PAH function in the liver. In addition we demonstrated that the rodent model used in this study is a valuable tool for basic research studies of the breath test.

Results of L-[1-13C]phenylalanine breath test with air isotope ratio mass spectrometry can reflect the activity of phenylalanine hydroxylase in cirrhotic rat liver

The L-[1-13C]phenylalanine breath test (PheBT) could potentially advance the evaluation of hepatocyte function and liver functional reserve. However, because the factors influencing PheBT results have not been clarified, the clinical application of the test has been limited. This study investigated the relationship between the parameters of PheBT, performed with air isotope ratio mass spectrometry, and the activity of phenylalanine hydroxylase (PAH), the phenylalanine metabolism rate-limiting enzyme, in rat liver, and proposes valid parameters for the assessment of liver function. Chronic injury to the liver was induced by the administration of CCl4 to male Sprague-Dawley rats for either 8 or 12 weeks. Livers from rats in the two cirrhotic groups were discolored, enlarged and roughly textured, with cells filled with fat granules of various sizes, pseudolobuli formations, and regenerated tubercles. Of the 12 parameters tested, only the unit liver weight (LW) breath test parameters, including the maximum abundance of 13C in breath (13Cmax/LW), 13C abundance in breaths 2 and 7 min after administration of L-[1-(13)C]phenylalanine (13C-phe) (13C2/LW and 13C7/LW), cumulative 13C excretion 10 and 30 min after 13C-phe administration (AUC10/LW and AUC30/LW), and the 13C excretion rate constant (PheBT-k/LW) were significantly affected in the chronic liver injury groups. There was no significant difference in the total PAH activity in liver among the three groups, but there was significant difference in unit LW PAH activity. Total PAH activity in the liver was significantly correlated with 13Cmax, 13C2, 13C7, AUC10, AUC30 and PheBT-k, while the unit LW PAH activity was significantly correlated with 13Cmax/LW, 13C2/LW, 13C7/LW, AUC10/LW, AUC30/LW and PheBT-k/LW. PheBT-k/LW was also correlated with biochemical indices that are used to assess liver function. The present findings indicate that the PheBT results based on air isotope ratio mass spectrometry can quantitatively reflect the change in total PAH activity in the livers of chronically injured rats. PheBT-k and PheBT-k/LW are the most sensitive among the test parameters, and can be used to assess liver functional reserve and hepatocyte damage at the molecular level.

Branched-chain amino acid needs in children with mild-to-moderate chronic cholestatic liver disease

Protein-energy malnutrition is prevalent in children with chronic cholestatic liver disease. Supplementation of branched-chain amino acids (BCAA) in infants and children with chronic liver disease has been associated with significant improvement in growth and nitrogen balance, suggesting that BCAA requirements are increased in chronic liver disease. The goal of the present study was to determine the total BCAA requirement in children with mild-to-moderate chronic cholestatic (MCC) liver disease using indicator amino acid oxidation (IAAO). Total BCAA requirements were determined in 6 children (6.3 +/- 3.7 y, mean +/- SD) with MCC liver disease. Children were randomly assigned to receive 7 graded intakes of total BCAA. Individual BCAA in the test diet were provided in the same proportions as those present in egg protein to minimize the potential interactive effects of individual BCAA on assessment of requirement. The total BCAA requirement was determined by measuring the oxidation of l-[1-13C] Phe to 13CO2 [F13CO2 in micromol/(kg x h)], after a primed, continuous oral administration of the tracer and using a 2-phase linear regression crossover regression analysis. The estimated mean requirement and the upper limit of the 95% CI for total BCAA establishing using the IAAO in children with MCC liver disease were 209 and 272 mg/(kg x d), respectively. Total BCAA estimated average requirements using the IAAO were significantly higher than mean requirements established previously for healthy children (P < 0.05).

Phenylalanine breath test as a method to evaluate hepatic dysfunction in obstructive jaundice

BACKGROUND

The purpose of this study was to investigate whether the hepatic dysfunction associated with obstructive jaundice can be measured from changes in expiratory 13CO2 levels after intravenous administration of l-[1-(13)C]phenylalanine, using a rat model of obstructive jaundice.

MATERIALS AND METHODS

Under pentobarbital anesthesia, bile duct ligation (BDL) was performed (n=12). In the control group, simple laparotomy was performed (n=12). On postoperative day 7, 20 mg/kg l-[1-(13)C]phenylalanine was administered via the femoral vein. Phenylalanine breath test (PBT) was performed for 30 min. We compared single point of 13CO2 level (SPT: T: min) and sum of 13CO2 output (ST) values between BDL and control rats. We examined the correlation of SPT or ST with phenylalanine hydroxylase activity (PHA) and blood chemical parameters.

RESULTS

Both SPT and ST values decreased in BDL compared to control 3 min after the start of PBT (SP10; 103+/-12 (per thousand) versus 84+/-16 (per thousand) P=0.025). PHA/g liver in BDL was significantly decreased compared to control (40.81+/-4.80 (U) versus 28.93+/-9.60 (U) P=0.008). PHA/g liver was correlated with SPT with correlation coefficient of more than 0.715, 10 min after the start of PBT, and the maximum correlation was at SP20 (r=0.801). Blood chemical parameters were correlated with S15 (total bilirubin, r=-0.717; alkaline phosphatase, r=-0.841; gamma-glutamyl transpeptidase, r=-0.759; alanine aminotransferase, r=-0.776; albumin, r=0.819).

CONCLUSIONS

In the breath test with intravenously l-[1-(13)C]phenylalanine, hepatic dysfunction associated with obstructive jaundice could be measured in a short period.

[13C] phenylalanine breath test and hepatic phenylalanine metabolism enzymes in cirrhotic rats

BACKGROUND

Stable isotope 13C-labelled phenylalanine breath test has been applied to enable the quantitative evaluation of hepatic functional reserve, but the mechanism underlying the changes in function has not been resolved. This study evaluated the correlation between expression of the mRNA of key enzymes mediating phenylalanine metabolism and the metabolism of L-[1-13C] phenylalanine (13C-phe) assessed by the excretion of 13C-CO2 in the breath of rats with, and without, chronic hepatic injury induced by administration of carbon tetrachloride (CCl4).

MATERIALS AND METHODS

Male Sprague-Dawley (SD) rats (n = 29) were given subcutaneous injections of CCl4 to induce chronic hepatic injury. L-[1-13C] phenylalanine breath tests (PheBT) were then applied to the rats to assess hepatic function. Expression of phenylalanine hydroxylase (PHH) and tyrosine transaminase (TYT) mRNA in liver was detected by real-time fluorescence quantification RT-PCR, using TaqMan as the probe. It was then determined whether the PheBT results correlated with PHH and/or TYT mRNA expression. In addition, immunohistochemical labelling was used to visualize PHH protein expression in the control and injured liver tissue.

RESULTS

There were significant decreases in PheBT and PHH mRNA expression in the cirrhotic rats relative to the uninjured controls and these two measures of liver function were correlated. However, TYT mRNA expression was not changed by CCl4-induced liver injury. The immunohistochemical analysis revealed that PHH protein was expressed predominantly in the cytoplasm of liver cells.

CONCLUSIONS

The results of the PheBT were consistent with the changes in PHH gene expression following liver injury. The present findings indicate that decreased expression of the rate-limiting enzyme PHH, but not of TYT, might underlie the functional deficits detected as decreased PheBT. The 13C excretion rate constant per mass liver (PheBT-k/LW) was the most sensitive index that could be used to evaluate the PHH mRNA expression in the liver.

Validity of 13C-phenylalanine breath test to evaluate functional capacity of hepatocyte in patients with liver cirrhosis and acute hepatitis

BACKGROUND

No definitive method for quantitative evaluation of hepatic function has as yet been established.

AIM

To investigate whether the (13)C-phenylalanine breath test would be useful for the evaluation of hepatic function in patients with liver cirrhosis and acute hepatitis.

METHODS

L-[1-(13)C]-phenylalanine was administered orally in a dose of 100 mg to 25 patients with liver cirrhosis, 22 patients with acute hepatitis and 10 healthy subjects. The relationships of the cumulative excretion with the (13)C-%dose/h, blood biochemical parameters and asialoscintigraphy were investigated.

RESULTS

In liver cirrhosis patients, the cumulative excretion showed correlations with hepatic function tests, asialoscintigraphy, clinical stage and portal hypertension. In acute hepatitis patients, the cumulative excretion showed correlations with hepatic function tests. There were positive correlations between the cumulative excretion and the (13)C-%dose/h at 20 min (Phe20) and (13)C-%dose/h at 30 min (Phe30) in liver cirrhosis and acute hepatitis patients. Multiple regression analysis demonstrated that total bilirubin, total cholesterol and absence of varices were independent determinants of cumulative excretion in liver cirrhosis patients and prothrombin time in acute hepatitis patients.

CONCLUSION

The (13)C-phenylalanine breath test may allow hepatic function to be evaluated non-invasively in liver cirrhosis and acute hepatitis patients, and the Phe20 and Phe30 may be useful for determination of function at a single time-point.

Ornithine breath test as a method to evaluate functional liver volume1

BACKGROUND

The purpose of this study was to investigate whether the functional liver volume can be measured from changes in expiratory 13CO2 levels after intravenous administration of L-[1, 2-13C] ornithine, using a rat model of hepatectomy.

MATERIALS AND METHODS

Under pentobarbital anesthesia, 30%, 70%, or 90% hepatectomy was performed. In the control group, simple laparotomy was performed. Then, 20 mg/kg L-[1, 2-13C] ornithine was administered to rats via the femoral vein. A breath test was conducted 20 min after laparotomy. We examined the correlation of the sum of 13CO2 output (S) or a single point of 13CO2 level (SP) with liver weight/body weight (LW/BW) (%) every 15 min.

RESULTS

In all of the groups, the ornithine breath test (OBT) graph reached a plateau level at about 6 min. The correlation coefficient between S15 and LW/BW was highest 0.952 (P <0.0001). The correlation coefficient between SP14 and LW/BW was highest, 0.944 (P <0.0001). The severity of hepatic injury could be evaluated, with significant differences in S5-15 and SP5-15 in all comparisons between groups.

CONCLUSION

In the breath test with intravenously administered L-[1, 2-13C] ornithine, functional liver volume could be evaluated accurately in a short period.

Correlation between L-[1-13C] phenlalanine breath test and activity of phenylalanine hydroxylase

AIM: To investigate the correlation between the result of L-[1-¹³C]phenylalanine breath test (PheBT) and the phenylalanine hydroxylase(PAH)activity of the liver in rats.

METHODS: PheBT was performed in Prague-Dawley (SD) rats with acute tetrachloride (CCl₄) hepatitis (n = 10) and control SD rats (n = 10). 20mg/kg body weight L-[1-¹³C]phenylalanine (¹³C-phe) was administered via tail vein, and breath samples were taken before administration and at different time within 60 minutes after administration. ¹³CO₂ abundance was measured with isotope ratio mass spectrometer, and ¹³C excretion rate constant (PheBT-k) was calculated. The PAH activity in the liver tissues was determined by enzyme-coupled assay.

RESULTS: After the intravenous administration of ¹³C-phe, ¹³C excretion reached the peak in two minutes in most acute hepatitis rats (8/10) and control rats (9/10). The time-course of ¹³C excretion had two phases: fast phase and slow phase. PheBT-k of CCl₄ hepatitis rats was significantly less than that of normal control rats [(2.45±0.25)×10^-2 /min vs (2.98±0.19)×10^-2 /min, P<0.01]. There was no significant difference for ¹³C fast phase disposition constant between the two groups [(9.463.27)×10^-2 /min vs (10.17±2.10)×10^-2 /min, P>0.05]. However, the peak value of ¹³C excretion of acute hepatitis rats was significantly higher than that of controls [(204.33±35.80) vs (170.65±22.85) (P<0.05 )]. The PAH activity of whole liver of hepatitis rats was significantly lower than that of control rats (P<0.01). PheBT-k was highly correlated to the PAH activity of the whole liver (r = 0.92, P<0.01) in all rats.

CONCLUSION: It is strongly indicated that decreased activity of PAH of the whole liver is the most direct reason for decreased¹³C excretion rate in acute CCl₄ hepatitis rats, and the PheBT-k can be used to quantify the degree of liver injure.

Measurement of hepatic functional mass by means of 13C-methacetin and 13C-phenylalanine breath tests in chronic liver disease: Comparison with Child-Pugh score and serum bile acid levels

AIM: To evaluate and compare the clinical usefulness of ¹³C-phenylalanine and ¹³C-methacetin breath tests in quantitating functional hepatic mass in patients with chronic liver disease and to further compare these results with those of conventional tests, Child-Pugh score and serum bile acid levels.

METHODS: One hundred and forty patients (50 HCV- related chronic hepatitis, 90 liver cirrhosis patients) and 40 matched healthy controls were studied. Both breath test and routine liver test, serum levels of cholic and chenodeoxycholic acid conjugates were evaluated.

RESULTS: Methacetin breath test, expressed as 60 min cumulative percent of oxidation, discriminated the hepatic functional capacity not only between controls and liver disease patients, but also between different categories of chronic liver disease patients. Methacetin breath test was correlated with liver function tests and serum bile acids. Furthermore, methacetin breath test, as well as serum bile acids, were highly predictive of Child-Pugh scores. The diagnostic power of phenylalanine breath test was always less than that of methacetin breath test.

CONCLUSION: Methacetin breath test represents a safe and accurate diagnostic tool in the evaluation of hepatic functional mass in chronic liver disease patients.

Measurement of hepatic phenylalanine metabolism in children using the [13C]-phenylalanine breath test and gas chromatography–mass spectrometry

The essential amino acid, phenylalanine (PA), is known to be metabolized mainly in the liver of human adults. Because the liver is still in the developmental phase, the PA-related metabolic events in infants remain unsolved. In this study, evaluations of development in hepatic PA metabolism in 37 children and 16 adults were attempted using the (13)C -PA breath test (PBT). The subjects were categorized into four groups according to their ages in years and months: 2 years and 0 month to 3 years and 5 months (group I; n = 12); 3 years and 6 months to 4 years and 11 months (group II, n = 12); 5 years and 0 month to 6 years and 11 months (group III, n = 13); and healthy adults (group IV; n = 16). Changes in CO(2) level of exhaled gas at various time intervals after oral administration of (13)C -PA were monitored using gas chromatography-mass spectrometry to derive the (13)C excretion rate, cumulative excretion curve and time maximum [(13)C excretion rate (T(MAX)). In the present investigation involving children, significant increases of maximum(13)C excretion rate and cumulative excretion at 120 min after administration were established in group III. Furthermore, differences in PBT were not established between groups III and IV. The index for first-pass effect, T(MAX), did not change with time. From the above findings, the (13)C excretion rate increased with time although hepatic PA metabolism in infants remained underdeveloped, and children at the age of 5-7 years manifested PA metabolism similar to that of adults.

L-[1-13C] phenylalanine breath test reflects histological changes in the liver

OBJECTIVE

Compared with healthy individuals, patients with chronic liver disease reportedly have lower L-[1-13C] phenylalanine breath test (PBT) values. However, there is no report detailing the relationship between the results of PBT and pathological data in liver disease patients. This study was designed to investigate the degree of histological changes in the liver that induce PBT changes and the time of measurement that reflects the histological change.

MATERIALS AND METHODS

PBT was performed in 47 patients (10 with a normal liver, and 37 with chronic hepatitis C). After administering 10 mg/kg L-[1-13C] phenylalanine, 300 mL of expired air was collected over 90 min at 15-min intervals. The rate of hepatic phenylalanine oxidation (%13C dose h(-1)) at each time point was calculated from the amount of 13CO(2) in the exhaled air, assuming a CO(2) production rate of 300 mmol m(-2) body surface area per hour. Subsequently, we examined the relationship between the results of PBT and METAVIR pathological scoring.

RESULTS

The highest correlation coefficients between the fibrosis score and %13C dose h(-1) and between the fibrosis score and %13C cumulative excretion were obtained at 45 min (r = -0.779, R(2) = 0.607; P < 0.0001) and 75 min (r = -0.768, R(2) = 0.590; P < 0.0001), respectively.

CONCLUSION

PBT is a useful adjunct for detecting histological changes in the liver. The %13C dose h(-1) value at 45 min and the %13C cumulative excretion value at 75 min of PBT are useful for detecting hepatic histological change.

13C-methacetin breath test for monitoring hepatic function in cirrhotic patients before and after liver transplantation

BACKGROUND

In patients with chronic liver disease, the measurement of liver function is critical for monitoring disease progression, predicting the prognosis and choosing therapeutic strategies. The 13C-methacetin breath test is a simple, non-invasive diagnostic tool based on an inexpensive, non-toxic substance, which allows the accurate measurement of liver functional reserve.

AIM

To investigate the 13C-methacetin breath test as a tool to monitor hepatic function in liver transplant candidates and recipients.

METHODS

Twenty-eight cirrhotic patients listed for orthotopic liver transplantation and 10 healthy controls were studied. The 13C-methacetin breath test (75 mg per os) was performed at baseline and at 12-week intervals. Intra-operative measurements were obtained during the liver transplantation procedure in nine patients. Results were expressed as the 13C-methacetin cumulative oxidation percentage 45 min after substrate ingestion.

RESULTS

The mean 13C-methacetin cumulative oxidation at 45 min was 16.4 +/- 3.5% in healthy controls and 5.4 +/- 4.2% in cirrhotic patients at the time of listing. In 11 patients who underwent successful liver transplantation, mean oxidation increased from 3.3 +/- 1.6% before transplantation to 17.0 +/- 5.2% at 6 months of follow-up. Variations in methacetine oxidation were closely related to the recovery of liver function. The mean intra-operative 13C-methacetin cumulative oxidation increased from 0.1% during the anhepatic phase to 3.7 +/- 2.0% 2 h after reperfusion.

CONCLUSIONS

The 13C-methacetin breath test is a simple and potentially useful tool for monitoring hepatic function in cirrhotic patients listed for liver transplantation, and during the intra-operative and post-operative phases.

L-[1-13C] phenylalanine breath test reflects phenylalanine hydroxylase activity of the whole liver

OBJECT

The purpose of this study was to perform L-[1-13C] phenylalanine breath test (PBT), measure phenylalanine hydroxylase (PAH) activity in liver tissue biopsies from patients, analyze the relationship between PBT results and PAH activity, and determine the time point at which measurements best reflect PAH activity in liver tissue.

METHODS

PBT was performed in 25 patients (10 with normal liver and 15 with liver cirrhosis). After administering 10 mg/kg L-[1-13C] phenylalanine, 300 ml of expired air was collected over 90 min at 15-min intervals. The rate of hepatic phenylalanine oxidation (%13C dose h(-1)) at each time point was calculated from the amount of 13CO(2) in the breath, assuming a CO(2) production rate of 300 mmol m(-2) body surface area per hour. Subsequently, we examined the relationship between the results of PBT and PAH activity.

RESULTS

PAH activity of the whole liver was significantly decreased in hepatic cirrhosis patients (P < 0.05). The results of PBT %13C dose h(-1) correlated with the PAH activity/liver, with correlation coefficients at 30, 45, and 60 min of more than 0.7, and the maximum correlation was at 30 min (r = 0.821, P < 0.0001). %13C cumulative excretion correlated with the PAH activity/liver with correlation coefficients of more than 0.7 after 45 min. The maximum correlation was at 90 min (r = 0.770, P = 0.001).

CONCLUSION

PBT values reflect PAH activity in the whole liver and, in particular, the % dose h(-1) at 30 min after oral administration highly correlates with PAH activity, providing an important indicator for monitoring changes in whole liver PAH activity.

Review article: breath testing for human liver function assessment

Carbon-labelled breath tests were proposed as tools for the evaluation of human liver function 30 years ago, but have never become part of clinical routine. One reason for this is the complex role of the liver in metabolic regulation, making it difficult to provide essential information for the management of patients with liver disease with a single test and to satisfy the hepatology community. As a result, a battery of breath tests have been developed. Depending on the test compound administered, different metabolic pathways (microsomal, cytosolic, mitochondrial) can be examined. Most available data come from microsomal function tests, whilst information about cytosolic and mitochondrial liver function is more limited. However, breath tests have shown promise in some studies, in particular to predict the outcome of patients with chronic liver disease or to monitor hepatic function after treatment. Whilst we await new substrates that can be used to measure liver function in a more valid manner, and large prospective studies to assess the usefulness of available test compounds, the aim of this review is to describe how far we have come in this controversial and unresolved issue.

Phenylalanine kinetics in healthy volunteers and liver cirrhotics: implications for the phenylalanine breath test

Expired 13CO2 recovery from an oral l-[1-13C]phenylalanine ([13C]Phe) dose has been used to quantify liver function. This parameter, however, does not depend solely on liver function but also on total CO2 production, Phe turnover, and initial tracer distribution. Therefore, we evaluated the impact of these factors on breath test values. Nine ethyl-toxic cirrhotic patients and nine control subjects received intravenously 2 mg/kg of [13C]Phe, and breath and blood samples were collected over 4 h. CO2 production was measured by indirect calorimetry. The exhaled 13CO2 enrichments were analyzed by isotope ratio mass spectrometry and the [13C]Phe and l-[1-13C]tyrosine enrichments by gas chromatography-mass spectrometry. The cumulative 13CO2 recovery was significantly lower in cirrhotic patients (7 vs. 12%; P < 0.01), in part due to lower total CO2 production rates. Phe turnover in cirrhotic patients was significantly lower (33 vs. 44 micro mol. kg(-1). h(-1); P < 0.05). When these extrahepatic factors were considered in the calculation of the Phe oxidation rate, the intergroup differences were even more pronounced (3 vs. 7 micro mol. kg(-1). h(-1)) than those for 13CO2 recovery data. Also, the Phe-to-Tyr conversion rate, another indicator of Phe oxidation, was significantly reduced (0.7 vs. 3.0 micro mol. kg(-1). h(-1)).

Recovery of liver function in two-third partial hepatectomized rats evaluated by L-[1-13C]phenylalanine breath test

BACKGROUND

We have previously reported that by means of a breath test with intravenously administered L-[1-13C] phenylalanine (13Cphe), hepatopathy could be quantitatively evaluated by measuring expiratory 13CO2 levels in a short period. It is known that phenylalanine hydroxylase activity (PAHA) plays an important role in phenylalanine metabolism. We examined the relationship between changes in PAHA and the results of the 13Cphe breath test during hepatic regeneration in a rat model of 70% hepatectomy, to assess their usefulness for evaluating hepatic regeneration.

METHODS

Male Wistar rats (Shizvoka Laboratory Animal Center, Hamamatsu, Japan) weighing 230 to 290 g were subjected to 70% hepatectomy under anesthesia with sodium pentobarbital. One, 2, 3, 5, 7, and 14 days postoperatively, 30 mg/kg 13Cphe was intravenously injected into the femoral vein, and the increase in exhaled 13CO2 (Delta 13CO2) was measured for 15 minutes. Simple laparotomy was performed in control rats. After the breath test, the regenerated liver was removed and weighed. The amount of DNA, amount of hepatic tissue total protein (TP), and PAHA were determined.

RESULTS

The r between liver weight/body weight and PAHA, between DNA and PAHA, and between TP and PAHA were 0.832, 0.720, and 0.758, respectively. Breath test graphs revealed that liver weight/body weight, DNA, and TP showed the best correlations with the peak value of Delta 13CO2 (liver weight/body weight percentage, r = 0.801; DNA, r = 0.660; TP, r = 0.706), and r between PAHA and peak value was 0.638.

CONCLUSIONS

These results suggest that measurement of PAHA in regenerated liver is an effective method for following up liver function after hepatic resection. Moreover, the 13Cphe breath test may also be useful to evaluate liver function after partial hepatectomy.

[Evaluation of liver function with 13C-labelled amino acid using hepatectomized rat model]

Using a rat model of hepatectomy, we investigated whether the severity of hepatopathy could be quantitatively measured from changes in expiratory 13CO2 levels after intravenous administration of L-[1-(13)C]phenylalanine, L-[1-(13)C]methionine or L-[1-(13)C]alanine.

MATERIALS AND METHODS

Under nembutal anesthesia, 30 mg/kg L-[1-(13)C]phenylalanine, 40 mg/kg L-[1-(13)C]methionine or 20 mg/kg L-[1-(13)C]alanine was administered to rats through the femoral vein, and expiratory 13CO2 levels were measured for 15 min. Thirty percent, 70% or 90% hepatectomy was performed. In the control group, simple laparotomy was performed.

RESULTS

The correlation coefficient between total 13CO2 output over 15 min after L-[1-(13)C]phenylalanine administration and liver weight/body weight was 0.883 (P < 0.001). The correlation coefficient between total 13CO2 output over 15 min after L-[1-(13)C]methionine administration and liver weight/body weight was 0.922 (P < 0.001). The correlation coefficient between total 13CO2 output over 15 min after L-[1-(13)C]alanine administration and liver weight/body weight was 0.902 (P < 0.0001).

CONCLUSION

In the breath test with intravenously administered L-[1-(13)C]phenylalanine, L-[1-(13)C]methionine, or L-[1-(13)C]alanine, hepatopathy could be quantitatively evaluated by measuring expiratory 13CO2 levels over 15 min.

Evaluation of 13C-phenylalanine and 13C-tyrosine breath tests for the measurement of hepatocyte functional capacity in patients with liver cirrhosis

Liver disease is associated with an abnormal elevation of the plasma concentrations of the aromatic amino acids phenylalanine and tyrosine. The liver is the main site of aromatic amino acid metabolism, particularly the hydroxylation of phenylalanine to tyrosine and further tyrosine degradation. In the present study, we have examined the usefulness of the L-[1-13C]phenylalanine breath test (13C-PheBT) and L-[13C]tyrosine breath test (13C-TyrBT) for the detection of hepatic damage in patients with liver cirrhosis. First, the time courses of 13CO2 excretion after the administration of L-[1-13C]phenylalanine and L-[1-13C]tyrosine were compared. The peak times (the time expressed in minutes at which 13CO2 excretion was maximal) were 20 min in both breath tests, but 13C-TyrBT gave a higher peak than 13C-PheBT. Next, the parameters of 13C-PheBT and 13C-TyrBT were compared with biochemical liver function test values. These parameters were well correlated with several liver blood test values conventionally regarded as measures of hepatocyte functional reserve. Therefore, 13C-PheBT and 13C-TyrBT may be useful to assess the degree and progression of hepatic dysfunction.

Hepatic phenylalanine metabolism measured by the [13C]phenylalanine breath test

BACKGROUND

The amino acid clearance test including phenylalanine is known to reflect liver functional reserve, which correlates with surgical outcome; however, the procedure is not clinically useful because of its laborious and time-consuming nature. This study evaluates whether phenylalanine oxidation capacity measured by a breath test could reflect liver functional reserve.

DESIGN

We determined phenylalanine oxidation capacity in 42 subjects using the L-[1-13C]phenylalanine breath test (PBT). The 13CO2 breath enrichment was measured at 10-min intervals for 120 min after oral administration of 100 mg of L-[1-13C]phenylalanine. Subjects were divided into the following three groups according to their plasma retention rate of indocyanine green at 15 min (ICG R15): Group I (ICG R15 < 10%), Group II (ICG R15 10--20%), and Group III (ICG R15 > 20%). First, we determined the parameters of the phenylalanine oxidation capacity that differentiated these groups and then, using these parameters, we compared the PBT with the ICG clearance test, Child-Pugh classification score and standard liver blood tests.

RESULTS

The %13C dose h(-1) at 30 min and cumulative excretion at 80 min were significantly different among the three groups (P < 0.05). These two parameters significantly correlated with the ICG R15, Child-Pugh classification score (P < 0.0001) and results of standard liver blood tests (P < 0.05).

CONCLUSIONS

Phenylalanine oxidation capacity measured by the PBT was reduced according to the severity of liver injury assessed by the ICG clearance test, Child-Pugh classification, and standard liver blood tests. These results indicate that the PBT can be used as a noninvasive method to determine liver functional reserve.

13C-phenylalanine and 13C-methacetin breath test to evaluate functional capacity of hepatocyte in chronic liver disease

BACKGROUND

To grade liver damage, Child-Pugh classification is used but these tests do not reflect the quantitative functional hepatic reserve.

AIMS

13C-Phenylalanine Breath Test and 13C-Methacetin Breath Test are evaluated as possible tools, being both safe and easy to perform, to quantify functional hepatic reserve in chronic liver disease patients.

PATIENTS

Both tests were performed in 48 healthy volunteers and 48 chronic liver disease patients.

METHODS

Breath samples were collected after taking 13C-Phenylalanine (100 mg) and 13C-Methacetin (75 mg). 13CO2 enrichment was measured using mass spectrometry

RESULTS

Both tests discriminated the hepatic function, decreasing results of the 13CO2 enrichment agreeing with the increasing severity of the hepatic patient (13C-Phenylalanine Breath Test multiple correlation coefficient: 0.72, global p<0.001; Methacetin Breath Test: 0.73, p<0.001). Correlation between 13C-Phenylalanine Breath Test and Methacetin Breath Test was 0.63, p<0.001. If both tests were pathological, the sensitivity for the diagnosis of hepatic dysfunction was high (98%), although the specificity decreased to 60%. Best results were obtained at 30 minutes with 13C-Phenylalanine Breath Test and at 10 minutes with Methacetin Breath Test.

CONCLUSIONS

Both 13C-Phenylalanine Breath Test and Methacetin Breath Test are safe and easy tests to perform and both are able to discriminate the hepatic functional capacity between the different groups studied.

Comparison between the oral and intravenous L-[1-13C]phenylalanine breath test for the assessment of liver function

To simplify the L-[1-13C]phenylalanine breath test which is used to assess liver function the tracer is usually given orally, and CO2 production rate is estimated. In 12 healthy volunteers and 10 liver cirrhotics we compared the oral approach with i.v. tracer administration combined with measurement of individual CO2 production rate. The 13CO2/12CO2 enrichment was assessed by isotope-ratio mass spectrometry. After i.v. [1-13C]phenylalanine application exhaled 13C recovery per minute peaked within 10 minutes (controls: 0.17 +/- 0.06%; cirrhotics: 0.05 +/- 0.02%, p < 0.01). The oral approach yielded comparable separation between 30-60 minutes, with average peak values being 0.18 +/- 0.03% and 0.06 +/- 0.03% (p < 0.01), respectively. Variable gastrointestinal resorption kinetics after oral application probably causes this difference.

13CO(2) peak value of L-[1-(13)C]phenylalanine breath test reflects hepatopathy

BACKGROUND

Using a rat model of hepatectomy, we investigated whether the severity of hepatopathy could be quantitatively measured from changes in expiratory (13)CO(2) levels after intravenous administration of L-[1-(13)C]methionine or L-[1-(13)C]phenylalanine.

MATERIALS AND METHODS

Under nembutal anesthesia, 30 mg/kg L-[1-(13)C]phenylalanine or 40 mg/kg L-[1-(13)C]methionine was administered to rats through the femoral vein, and expiratory (13)CO(2) levels were measured for 15 min. A 30, 70, or 90% hepatectomy was performed. In the control group, simple laparotomy was performed. Breath test was conducted 20 min after laparotomy. We examined the correlation of the total (13)CO(2) output over 15 min or peak (13)CO(2) level with liver weight/body weight (%).

RESULTS

In breath test graphs, L-[1-(13)C]methionine did not show any peak level during measurement. L-[1-(13)C]phenylalanine showed a specific peak level 6 +/- 1 min after administration. The correlation coefficient between total (13)CO(2) output over 15 min after L-[1-(13)C]methionine administration and liver weight/body weight was 0.922 (P < 0.001). The correlation coefficient between total (13)CO(2) output over 15 min after L-[1-(13)C]phenylalanine administration and liver weight/body weight was 0.883 (P < 0.001). The correlation coefficient between peak L-[1-(13)C]phenylalanine level and liver weight/body weight was highest, 0.927 (P < 0.001).

CONCLUSION

In a breath test with intravenously administered L-[1-(13)C]methionine or L-[1-(13)C]phenylalanine, hepatopathy could be quantitatively evaluated by measuring expiratory (13)CO(2) levels over 15 min. After administration of L-[1-(13)C]phenylalanine, hepatopathy could be quantitatively evaluated in a short period by measuring the peak expiratory (13)CO(2) level.

Amino acid metabolism in liver disease

The impairment of transsulphuration during methionine degradation in hepatic failure can be counteracted by treatment with S-adenosylmethionine. Regarding the pathogenesis of hepatic encephalopathy, no convincing evidence exists for tryptophan, glutamine or glutamate being involved. Portal-systemic shunting-induced hyperammonaemia may reduce plasma branched-chain amino acids. The glucose effect on urea synthesis does not exist in cirrhosis.

Simultaneous determination of plasma enrichments of 1-13C- and 15N-labelled phenylalanine and tyrosine

A methylchloroformate derivative was used for the simultaneous determination of plasma enrichments of 1-13C-phenylalanine, 1-13C-tyrosine, 15N-phenylalanine and 15N-tyrosine by gas chromatography/mass spectrometry. All four tracer enrichments could be measured in a single GC run. A specific ion fragment was obtained for each tracer. This approach allowed an easy determination of the "tracer to tracee ratios". Each ion fragment could be measured with an appropriate single-to-noise ratio and precision in samples obtained from 100 microliters plasma. The derivatization consists of a fast one-step reaction. Therefore it is well suited for studies involving a large number of samples, such as non-steady state bolus studies.