Journal
ARCHIVES OF TOXICOLOGY
Volume 94, Issue 2, Pages 401-415Publisher
SPRINGER HEIDELBERG
DOI: 10.1007/s00204-020-02654-0
Keywords
C-13-methacetin; Liver function; Breath test; Compartment model; (CO2)-C-13 kinetics
Categories
Funding
- German Systems Biology Programs LiSyM [31L0057, 031L0058]
- German Federal Ministry of Education and Research (BMBF)
- Max Planck Society
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The principle of dynamic liver function breath tests is founded on the administration of a C-13-labeled drug and subsequent monitoring of (CO2)-C-13 in the breath, quantified as time series delta over natural baseline (CO2)-C-13 (DOB) liberated from the drug during hepatic CYP-dependent detoxification. One confounding factor limiting the diagnostic value of such tests is that only a fraction of the liberated (CO2)-C-13 is immediately exhaled, while another fraction is taken up by body compartments from which it returns with delay to the plasma. The aims of this study were to establish a novel variant of the methacetin-based breath test LiMAx that allows to estimate and to eliminate the confounding effect of systemic (CO2)-C-13 distribution on the DOB curve and thus enables a more reliable assessment of the hepatic detoxification capacity compared with the conventional LiMAx test. We designed a new test variant (named 2DOB) consisting of two consecutive phases. Phase 1 is initiated by the intravenous administration of C-13-bicarbonate. Phase 2 starts about 30 min later with the intravenous administration of the C-13-labelled test drug. Using compartment modelling, the resulting 2-phasic DOB curve yields the rate constants for the irreversible elimination and the reversible exchange of plasma (CO2)-C-13 with body compartments (phase 1) and for the detoxification and exchange of the drug with body compartments (phase 2). We carried out the 2DOB test with the test drug C-13-methacetin in 16 subjects with chronic liver pathologies and 22 normal subjects, who also underwent the conventional LiMAx test. Individual differences in the systemic CO2 kinetics can lead to deviations up to a factor of 2 in the maximum of DOB curves (coefficient of variation CV approximate to 0.2) which, in particular, may hamper the discrimination between subjects with normal or mildly impaired detoxification capacities. The novel test revealed that a significant portion of the drug is not immediately metabolized, but transiently taken up into a storage compartment. Intriguingly, not only the hepatic detoxification rate but also the storage capacity of the drug, turned out to be indicative for a normal liver function. We thus used both parameters to define a scoring function which yielded an excellent disease classification (AUC = 0.95) and a high correlation with the MELD score (R-Spearman = 0.92). The novel test variant 2DOB promises a significant improvement in the assessment of impaired hepatic detoxification capacity. The suitability of the test for the reliable characterization of the natural history of chronic liver diseases (fatty liver-fibrosis-cirrhosis) has to be assessed in further studies.
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