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

Prognostic Value of the 13 C-Methacetin Breath Test in Adults with Acute Liver Failure and Non-acetaminophen Acute Liver Injury

BACKGROUND AND AIMS

The 13 C-methacetin breath test (MBT) is a noninvasive, quantitative hepatic metabolic function test. The aim of this prospective, multicenter study was to determine the utility of initial and serial 13 C-MBT in predicting 21-day outcomes in adults with acute liver failure (ALF) and non-acetaminophen acute liver injury (ALI).

APPROACH AND RESULTS

The 13 C-MBT BreathID device (Exalenz Biosciences, Ltd.) provided the percent dose recovery (PDR) for a duration of 60 minutes after administration of 13 C-methacetin solution as the change in exhaled 13 CO2 /12 CO2 compared with pre-ingestion ratio on study days 1, 2, 3, 5, and 7. Results were correlated with 21-day transplant-free survival and other prognostic indices. A total of 280 subjects were screened for enrollment between May 2016 and August 2019. Median age of the 62 enrolled patients with adequate data was 43 years, 79% were Caucasian, 76% had ALF with the remaining 24% having ALI. The mean PDR peak on day 1 or day 2 was significantly lower in nonsurvivors compared with transplant-free survivors (2.3%/hour vs. 9.1%/hour; P < 0.0001). In addition, serial PDR peaks were consistently lower in nonsurvivors versus survivors (P < 0.0001). The area under the receiver operating characteristic curve (AUROC) of the 13 C-MBT in the combined cohort was 0.88 (95% CI: 0.79-0.97) and higher than that provided by King's College (AUROC = 0.70) and Model for End-Stage Liver Disease scores (AUROC = 0.83). The 13 C-MBT was well tolerated with only two gastrointestinal adverse events reported.

CONCLUSIONS

The 13 C-MBT is a promising tool to estimate the likelihood of hepatic recovery in patients with ALF and ALI. Use of the PDR peak data from the 13 C-MBT point-of-care test may assist with medical decision making and help avoid unnecessary transplantation in critically ill patients with ALF and ALI.

Scrutiny of 13C-phenylalanine breath test reproducibility

We evaluated the reproducibility of the ¹³C-phenylalanine breath test (¹³C-PheBT). On three separate days, 21 healthy volunteers (11 F and 10 M) underwent ¹³C-PheBT with 100 mg l-[1-¹³C]phenylalanine taken orally. Short-term reproducibility was evaluated with paired examinations taken 3 days apart; paired examinations separated by 23 days (median) served for the medium-term reproducibility assessment. Expiratory air was sampled at 19 points throughout 3 h. Determined limited reproducibility of the ¹³C-PheBT must be taken into consideration while interpreting the results of this diagnostic tool. The results of this study imply the following conclusions: (i) From among the three parameters examined, the cumulative ¹³C recovery area under the curve (AUC) offers much better reproducibility than the maximum momentary ¹³C recovery in the expiratory air (D_max) or the time to reach the maximum momentary ¹³C recovery (T_max) (ii) Collection of the breath air samples for 2 h results in a much better reproducibility of AUC, than for 1 h only; (iii) Reproducibility of ¹³C-PheBT is affected neither by the duration of the time gap between repeated tests nor by gender; (iv) Comparison with data obtained formerly reveals that reproducibility of the ¹³C-PheBT is worse than either that of of the ¹³C-methacetin (¹³C-MBT) or the ¹³C-alpha-ketoisocaproic acic (¹³C-KICA-BT) breath tests. This finding will have to be taken into consideration while interpreting the results of this diagnostic tool.

Effects of ergot alkaloids on liver function of piglets can be detected by the [(13)C]methacetin breath test irrespective of oral or intramuscular route of tracer administration

Ergot alkaloids (sum=total alkaloids, TA) originate from the phyto-pathogenic fungus Claviceps purpurea and might exert feed intake depressing and hepatotoxic effects on animals. The aim of the study was to evaluate TA effects on performance and liver function of piglets with the [(13)C]methacetin breath test and two routes of tracer administration (orally, p.o.; intramuscularly, i.m.). Two ergot batches were mixed into piglet diets resulting in 21 and 17 mg TA kg(-1) (Ergot-5 and -12, respectively) and compared with an ergot-free control diet. Feed intake was significantly depressed after feeding the ergot containing diets (p=<0.001). The time at maximum (13)CO(2) exhalation (t (max)) and the half-life (t (0.5)) were not influenced by treatments and varied between 25 and 68 min after the p.o., and 28 and 62 min after the i.m. administration of [(13)C]methacetin, respectively. The cumulative (13)C recovery (cPDR(30)) was significantly lower due to feeding the diet Ergot-5 (6.6 %) compared with the Ergot-12 (8.8 %) and the control diet (9.7 %) irrespective of the route of tracer administration (p=0.044). As a discrimination of the diet effects through both tracer administration routes is possible, the i.m. application should be preferred in piglets as this causes less stress than the oral forced administration.

Early diagnosis of primary nonfunction and indication for reoperation after liver transplantation

Initial graft function is a major factor influencing the clinical outcome after liver transplantation (LTX), but a reliable method for assessing and predicting graft dysfunction directly after LTX is not available. Ninety-nine patients undergoing deceased-donor LTX were studied in a prospective pilot study to evaluate the LiMAx test, the indocyanine green test, and conventional biochemical parameters with respect to their sensitivity and prognostic power for the diagnosis of initial graft dysfunction. Patients suffering from initial graft dysfunction (defined as technical complications or primary nonfunction (n = 8)) had significantly decreased LiMAx readouts (43 +/- 18 versus 184 +/- 98 mug/kg/hour, P < 0.001) immediately after LTX. Univariate analysis also showed significant differences for serum bilirubin, ammonia, glutamate dehydrogenase, and the international normalized ratio (P < 0.05), but multivariate analysis revealed LiMAx as the single independent predictor of initial dysfunction (P = 0.008) with an area under the receiver operating characteristic curve (AUROC) of 0.960 (95% confidence interval = 0.921-0.998, P < 0.001). In addition, the diagnosis of primary nonfunction (n = 3) was evaluated with LiMAx and aspartate aminotransferase (AST) activity on the first postoperative day. The calculated AUROC values were 0.992 (0.975-1.0, P = 0.004) for LiMAx and 0.967 (0.929-1.0, P = 0.006) for AST. By a combination of test results obtained directly after LTX and on the first day, LiMAx indicated primary nonfunction with a sensitivity of 1.0 (0.31-1.0) and a positive predictive value of 1.0 (0.31-1.0), whereas AST classification showed a sensitivity of 0.67 (0.13-0.98) and a positive predictive value of 0.29 (0.05-0.70). In conclusion, the assessment of initial graft function using the LiMAx test might be effective for identifying critical complications that could threaten graft survival within 24 hours after LTX.

(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.

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.

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.

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)).