1H and 19F-nmr spectroscopic studies on the metabolism and urinary excretion of mono- and disubstituted phenols in the rat

Relative embryotoxic potency of p-substituted phenols in the embryonic stem cell test (EST) and comparison to their toxic potency in vivo and in the whole embryo culture (WEC) assay

The applicability of the embryonic stem cell test (EST) as an alternative for in vivo embryotoxicity testing was evaluated for a series of five p-substituted phenols. To this purpose, the potency ranking for this class of compounds derived from the inhibition of cardiomyocyte differentiation in the EST was compared to in vivo embryotoxic potency data obtained from literature and to the potency ranking defined in the in vitro whole embryo culture (WEC) assay. From the results obtained it appears that the EST was able to identify the embryotoxic potential for p-substituted phenols, providing an identical potency ranking compared to the WEC assay. However, the EST was not able to predict an accurate ranking for the phenols compared to their potency observed in vivo. Only phenol, the least potent compound within this series, was correctly ranked. Furthermore, p-mercaptophenol was correctly identified as a relative potent congener of the phenols tested, but its ranking was distorted by p-heptyloxyphenol, of which the toxicity was overestimated in the EST. It is concluded that when attempting to explain the observed disparity in potency rankings between in vitro and in vivo embryotoxicity, the in vitro models should be combined with a kinetic model describing in vivo absorption, distribution, metabolism and excretion processes of the compounds.

New advances in MR-compatible bioartificial liver

MR-compatible bioartificial liver (BAL) studies have been performed for 30 years and are reviewed. There are two types of study: (i) metabolism and drug studies using multinuclear MRS; primarily short-term (< 8 h) studies; (ii) the use of multinuclear MRS and MRI to noninvasively define the features and functions of BAL systems for long-term liver tissue engineering. In the latter, these systems often undergo not only modification of the perfusion system, but also the construction of MR radiofrequency probes around the bioreactor. We present novel MR-compatible BALs and the use of multinuclear MRS ((13)C, (19)F, (31)P) for the noninvasive monitoring of their growth, metabolism and viability, as well as (1)H MRI methods for the determination of flow profiles, diffusion, cell distribution, quality assurance and bioreactor integrity. Finally, a simple flexible coil design and circuit, and life support system, are described that can make almost any BAL MR-compatible.

Mild hydrolysis of 2-trifluoromethylphenol: kinetics, mechanism and environmental relevance

2-Trifluoromethylphenol was hydrolysed in a phosphate buffer at neutral pH. At mild temperatures ranging from 34 degrees C to 69 degrees C this compound liberates consecutively fluorine anions to form salicylic acid. This process is energetically driven by the hydration of the fluorine anions. No intermediates have been detected by HPLC and (19)F-NMR and this was confirmed by computer calculations which favor the first step in the whole reaction sequence being rate-limiting. Accordingly, the reaction energy of the first dehalogenation of the trifluoromethyl anion is 28.4 kcal mol(-1) higher than for the second dehalogenation. The pseudo-first-order kinetic was determined and from an Arrhenius diagram an activation energy of E(a)=25.1 kcal mol(-1) has been estimated. At 37 degrees C and a pH of 7.4 the half-life was 6.9 h. The rate of hydrolysis was favored at higher pH and it was not influenced by oxygen, sunlight or trace elements found in natural water. The latter was shown by incubations with lake water instead of distilled water.

QUANTITATIVE STRUCTURE-METABOLISM RELATIONSHIP MODELING OF METABOLICN-DEALKYLATION REACTION RATES

It is widely recognized that preclinical drug discovery can be improved via the parallel assessment of bioactivity, absorption, distribution, metabolism, excretion, and toxicity properties of molecules. High-throughput computational methods may enable such assessment at the earliest, least expensive discovery stages, such as during screening compound libraries and the hit-to-lead process. As an attempt to predict drug metabolism and toxicity, we have developed an approach for evaluation of the rate of N-dealkylation mediated by two of the most important human cytochrome P450s (P450), namely CYP3A4 and CYP2D6. We have taken a novel approach by using descriptors generated for the whole molecule, the reaction centroid, and the leaving group, and then applying neural network computations and sensitivity analysis to generate quantitative structure-metabolism relationship models. The quality of these models was assessed by using the cross-validated correlation coefficients of 0.82 for CYP3A4 and 0.79 for CYP2D6 as well as external test molecules for each enzyme. The relative performance of different neural networks was also compared, and modular neural networks with two hidden layers provided the best predictive ability. Functional dependencies between the neural network input and output variables, generalization ability, and limitations of the described approach are also discussed. These models represent an initial approach to predicting the rate of P450-mediated metabolism and may be applied and integrated with other models for P450 binding to produce a systems-based approach for predicting drug metabolism.

19F NMR spectroscopic investigation into the absorption and metabolism of 3-trifluoromethylaniline in Eisenia veneta

19F nuclear magnetic resonance (NMR) spectroscopy was used as a specific tool to investigate the metabolism of 3-trifluoromethylaniline (3-TFMA) in the earthworm species Eisenia veneta. Exposure was via a filter-paper contact toxicity test using five exposure levels (1000, 100, 10, 1, and 0.1 microg/cm(2)). Instant lethality was observed at the two highest levels. Worms exposed at the lower levels appeared to tolerate the compound. The 19F label of 3-TFMA allowed the uptake and metabolism of the earthworms to be monitored by 19F NMR spectroscopy. Metabolism of 3-TFMA was observed at 10 microg/cm(2) and, to a lesser extent, at 1 microg/cm(2). The possibility of 3-TFMA accumulation in specific organs was also investigated. As a simplified model, worms were cut into distinct anatomical regions (head, testes, crop, clitellum, and gut). At the two highest exposure levels, "uniform distribution" was observed. However, accumulation appeared to be proportional to the "size" of the extracted segments at the lower levels.

Metabolism of 4-fluoroaniline and 4-fluorobiphenyl in the earthworm Eisenia veneta characterized by high-resolution NMR spectroscopy with directly coupled HPLC-NMR and HPLC-MS

1. Little is known about metabolism of xenobiotics by earthworms, despite their importance in soil ecotoxicity testing. Normal earthworms and earthworms treated with antibiotics to ensure inhibition of gut microflora were exposed to two model xenobiotic compounds, 4-fluoroaniline and 4-fluorobiphenyl, to determine which metabolites were produced, and whether the pattern of metabolism was affected by the presence of microbial transformation ability. 2. (19)F-NMR spectroscopy detected the number and relative proportions of metabolites and directly coupled HPLC-(1)H-NMR spectroscopy and HPLC-MS then identified the metabolites. 3. Despite uptake, no metabolism of 4-fluorobiphenyl was observed at any stage, which appears to be a consequence of the lack of oxidative Phase I metabolic activity of the earthworms towards this substrate. In contrast, 4-fluoroaniline exhibited dose-dependent metabolism. At high doses (leading to mortality within 24 h) one predominant metabolite was observed, which was identified as the N-beta-glucoside conjugate. At lower dose levels, the predominant metabolite was the gamma-glutamyl conjugate, although the glucoside and another as yet unidentified metabolite were also detected. 4. The inhibition of gut microflora did not have any influence on metabolism. The study represents the first evidence for glucoside and glutamyl conjugation as a pathway for xenobiotic metabolism in earthworms.

Degradation of 4-fluorobiphenyl by mycorrhizal fungi as determined by (19)F nuclear magnetic resonance spectroscopy and (14)C radiolabelling analysis

The pathways of biotransformation of 4-fluorobiphenyl (4FBP) by the ectomycorrhizal fungus Tylospora fibrilosa and several other mycorrhizal fungi were investigated by using (19)F nuclear magnetic resonance (NMR) spectroscopy in combination with (14)C radioisotope-detected high-performance liquid chromatography ((14)C-HPLC). Under the conditions used in this study T. fibrillosa and some other species degraded 4FBP. (14)C-HPLC profiles indicated that there were four major biotransformation products, whereas (19)F NMR showed that there were six major fluorine-containing products. We confirmed that 4-fluorobiphen-4'-ol and 4-fluorobiphen-3'-ol were two of the major products formed, but no other products were conclusively identified. There was no evidence for the expected biotransformation pathway (namely, meta cleavage of the less halogenated ring), as none of the expected products of this route were found. To the best of our knowledge, this is the first report describing intermediates formed during mycorrhizal degradation of halogenated biphenyls.