The principle of 13C breath-testing
The performance of stable isotope (13C) breath-testing is based on the detection of 13C-labeled carbon dioxide (13CO2) in the exhaled air after administering 13C labe-led substrate. The substrate is chosen depending on which enzyme activity is going to be measured, and is expected to be metabolized by the target enzyme. Based on the measurements of 13CO2 in the exhaled air, it is possible to have indirect judgment on the activity of the target enzyme.
A number of different substrates have been used to measure the functional ac-tivity of the liver; these could be classified in three major groups depending on the liver function the tests are targeting, i.e., microsomal, cytosolic, or mitochondial.
Mārcis Leja, Žanete Zvirbule, Agnese Sudraba, Ilva Nakurte, Ilze Plinte, Pēteris Mekšs, 153 Ivars Tolmanis,Viesturs Boka, Uldis Vikmanis. Liver Function as Determined By..
Breath-testing applications in oncology
Until recent time, breath test applications have been limited in oncology, in par-ticular in the field of testing the liver functions. A few years ago, Paul Watkins’
group in the USA published their results on the erythromycin breath test and doxe-taxel (another drug of the taxane family) clearance. Erythromycin (14 C-N-methyleryt-hromycin) is a substrate metabolized via CYP 450 (CYP3A4 subtype), similarly to doxetaxel. The authors have demonstrated good correlation between the results of the erythromycin test and clearance of doxetaxel9.
More recent studies in oncology have also used erythromycin breath test for CYP 450 3A phenotyping to seek the correlation to CYP3A4 genomic DNA variants in cancer patients10.
Description of the method
75mg 13C-methacetine (99% 13C enrichment) was administered in a gelatinous capsule after an overnight fast; the measurements of 13C/ 12C ratio in the exhaled air were performed by isotope-selective non-dispersive infrared spectrometry (IRIS, Wagner Analyzen Technik, GmbH, Germany) at baseline as well as at 10, 20, 30, 40, 50, 60, 80, 100, and 120 min. intervals after the admission of the substrate. Cumu-lative 13C dose recovered over 120 min period and expressed as percentage of the total 13C dose administered (CUM 120) was used for comparison between the MBT results.
Patients
Altogether seven female patients (aged 45–66 years) scheduled for paclitaxel based chemotherapy treatment due to ovarian cancer were involved before starting the 1st cycle of chemotherapy. They were tested by MBT before the admission of the therapy as well as on the 1st, 2nd, and 28th day after the administration of the initial therapy, i.e., prior to the 2nd chemotherapy cycle. The administered chemotherapy regimen consisted of paclitaxel (75 mg/m2) and carboplatin (300 mg/m2)
Results
Considerable variations of baseline MBT results were observed in the tested patients (range of CUM 120: 11.8 – 35.8), although only one patient could be diag-nosed with pathologically decreased liver function, following the criteria suggested by the manufacturer (CUM 120 – 11.8).
There was no liver disease history reported in the previous disease histories, nor abdominal ultrasound and liver clinical chemistry tests were indicating liver disease in any of the patients referred to therapy and diagnostic work-up (neither in the pa-tient with decreased MBT results at the inclusion).
The mean value (CUM 120) of the MBT results prior to the therapy was 24.6%
recovered with SD 8.82; Day 1 after the treatment – 22.54% recovered with SD 8.51; Day 2 – 23.07% recovered with SD 8.46; and Day 28 – 25.07% recovered with SD 5.46.
There was no common trend observed in MBT results according to CUM 120 following the drug administration for the studied patients. Only two patients demonstrated decreased MBT results on the first day after the treatment.
15 17 19 21 23 25 27 29
Before therapy Day1 Day2 Day28
CUM 120 (% recovered)
Figure 1. Distribution of 13C methacetine breath test results (CUM 120) before and after the admission of chemotherapy treatment (mean values, standard deviation)
13C metacetīna elptestu rezultāti (CUM 120) pirms un pēc ķīmijterapijas preparātu ievadīšanas (vidējās vērtības, standarta novirze)
Statistical Analysis
The statistical analysis by ANOVA did not demonstrate significant differences between the MBT results obtained at different times, i.e., before the therapy and 1, 2, and 28 days after the admission of paclitaxel-containing therapy (p-value 0.921;
F critical value 3.009).
To evaluate whether paclitaxel-containing therapy has influenced the results of the MBT, the breath test results prior to the therapy and on the first day after the therapy were compared by t-test for equality of means, and no statistical significance between the two test results was confirmed (t Stat = 1.01; p = 0.35).
Discussion
The obtained results do not confirm our hypothesis that admission of paclitaxel-containing chemotherapy may alter the results of MBT. We did not find any common pattern of MBT results following the admission of paclitaxel-based chemotherapy.
There might be a possibility of subgroup differences, but the small experiment group size does not allow distinguishing between subgroups.
Further studies involving a larger group size and adding information on the sub-stance elimination speed to the MBT results would be needed to address the poten-tial role of MBT in paclitaxel chemotherapy.
Mārcis Leja, Žanete Zvirbule, Agnese Sudraba, Ilva Nakurte, Ilze Plinte, Pēteris Mekšs, 155 Ivars Tolmanis,Viesturs Boka, Uldis Vikmanis. Liver Function as Determined By..
Conclusions
The administration of paclitaxel in combined cancer patient chemotherapy does not significantly alter the results of 13C-methacetine breath test in the majority of patients.
Acknowledgements
The work was supported by the research grant of the University of Latvia (2007/
ZP-83), State Research Program on Health No. 8 (project No. 3), as well as by an EU Social Fund project.
The authors thank Prof. Uldis Teibe for his valuable support to statistical analy-sis of the data.
References
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2. Dees EC, Watkins PB. Role of cytochrome P450 phenotyping in cancer treatment. J Clin Oncol 2005; 23: 1053–5.
3. Lexi-Comp., Inc. Paclitaxel (Protein-bound): Drug information. Accessed September, 2007. Copyright 1978−2008 Lexi-Comp, Inc. http://www.uptodate.com/online/content/
topic.do?topicKey=drug_l_z/53931
4. Zipprich A, Meiss F, Steudel N, Sziegoleit U, Fleig WE, Kleber G. 13C-Methacetin metabolism in patients with cirrhosis: relation to disease severity, haemoglobin content and oxygen supply. Aliment Pharmacol Ther 2003;17: 1559–62.
5. Modak AS. Stable isotope breath tests in clinical medicine: a review. J Breath Res 2007; 1.
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7. Ciccocioppo R, Candelli M, Di Francesco D, et al. Study of liver function in healthy elderly subjects using the 13C-methacetin breath test. Aliment Pharmacol Ther 2003; 17: 271–7.
8. Armuzzi A, Candelli M, Zocco MA, et al. Review article: breath testing for human liver function assessment. Aliment Pharmacol Ther 2002; 16: 1977–96.
9. Hirth j, Watkins PB, Strawderman M, Schott A, Bruno R, Baker LH. The effect of an individual’s cytochrome CYP3A4 activity on docetaxel clearance. Clin Cancer Res 2000;
6: 1255–8.
10. Baker SD, van Schaik RH, Rivory LP, et al. Factors affecting cytochrome P-450 3A activity in cancer patients. Clin Cancer Res 2004; 10: 8341–50.
Kopsavilkums
Ķīmijterapijā lietojamie medikamenti, t. sk. taksānu grupa (pie tās pieder arī plaši lietotais paklitaksels), kuri tiek metabolizēti aknu citohroma P450 sistēmā (CYP450), nereti izraisa nopietnas blaknes. Pašlaik nav pieejama neviena metode, ar kuras palīdzību būtu iespējams prognozēt iespējamo ķīmijpreparātu toksicitāti. Metacetīnu, kura metabolisms arī notiek caur CYP450, iespējams izmantot diagnostiskā stabilo izotopu (13C) elptestā (MBT) ar mērķi noteikt
aknu funkcionālo spēju. Autori izvirzīja hipotēzi, ka MBT rezultāts varētu būtiski izmainīties pēc paklitakselu saturošas ķīmijterapijas ievades.
Septiņām sievietēm (vecumā 45–66 gadi), kurām bija ordinēta paklitakselu saturoša ķīmijterapija olnīcu vēža ārstēšanai pirms terapijas un 1., 2. un 28. dienā pēc ķīmijterapijas medikamentu ievades, tika veikts MBT. Iegūtie rezultāti neapstiprināja statistiski ticamas atšķirības starp izmeklējumu rezultātiem, kas bija veikti minētajos laika intervālos. Netika konstatēta arī pārliecinoša MBT rezultāta izmaiņa pirmajā dienā pēc preparāta ievades.
Ir iespējams plānot turpmākus pētījumus, meklējot iespējamo MBT rezultātu korelāciju ar paklitaksela eliminācijas ātrumu, kā arī palielinot izmeklējamo pacienšu skaitu apakšgrupu analīzes veikšanai.
LATVIjAS UNIVERSITāTES RAKSTI. 2008, 735. sēj.:
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