Evidence Of Biotransformation Research Articles

Identification of environmental chemicals that activate p53 signaling after in vitro metabolic activation

Currently, approximately 80,000 chemicals are used in commerce. Most have little-to-no toxicity information. The U.S. Toxicology in the 21st Century (Tox21) program has conducted a battery of in vitro assays using a quantitative high-throughput screening (qHTS) platform to gain toxicity information on environmental chemicals. Due to technical challenges, standard methods for providing xenobiotic metabolism could not be applied to qHTS assays. To address this limitation, we screened the Tox21 10,000-compound (10K) library, with concentrations ranging from 2.8 nM to 92 µM, using a p53 beta-lactamase reporter gene assay (p53-bla) alone or with rat liver microsomes (RLM) or human liver microsomes (HLM) supplemented with NADPH, to identify compounds that induce p53 signaling after biotransformation. Two hundred and seventy-eight compounds were identified as active under any of these three conditions. Of these 278 compounds, 73 gave more potent responses in the p53-bla assay with RLM, and 2 were more potent in the p53-bla assay with HLM compared with the responses they generated in the p53-bla assay without microsomes. To confirm the role of metabolism in the differential responses, we re-tested these 75 compounds in the absence of NADPH or with heat-attenuated microsomes. Forty-four compounds treated with RLM, but none with HLM, became less potent under these conditions, confirming the role of RLM in metabolic activation. Further evidence of biotransformation was obtained by measuring the half-life of the parent compounds in the presence of microsomes. Together, the data support the use of RLM in qHTS for identifying chemicals requiring biotransformation to induce biological responses.

The Role of FcRn in the Disposition, Metabolism and Pharmacokinetics of Soluble Non‐Crosslinking Immune Complexes

Human interleukin 10 (hIL‐10) is a potent cytokine homodimer that has been investigated in the clinic for inflammatory indications. We have characterized the effects of IL‐10 pegylation and formation of IL‐10/αIL‐10 immune complexes in the pharmacokinetics (PK), biodistribution and biotransformation of IL‐10 in mice. Plasma size exclusion analysis indicated that fluorolabeled native and pegylated murine IL‐10 are stable in the circulation without evidence of biotransformation. Pegylation of IL‐10 resulted in increased exposure, ~2.7‐fold increase in half‐life from 0.098 to 0.26 days and ~20‐fold reduction in clearance. Kidney is the major organ of disposition for both native and pegylated mIL‐10 with renal uptake directly related to systemic clearance. hIL‐10/αIL‐10 complexes were characterized in plasma without evidence of free or degraded hIL‐10 fragments. The hIL‐10 exposure in immune complexes vs. hIL‐10 alone, increased from 0.53 to 11.28 ug*day/ml, with a half‐life of 1.16 days and a ~23‐fold reduction in clearance. In contrast to free interleukin 10, antibody bound hIL‐10 was targeted mainly to the liver with minimal renal distribution. In vitro analysis of FcRn interactions shows a ~10‐fold reduction in binding affinity for the antibody when present as IL‐10/αIL‐10 immune complexes. The changes in FcRn binding and increased liver uptake of IL‐10/αIL‐10 immune complexes may explain in part the unique PK properties of soluble antibody‐bound IL‐10.

Comparisons of Geochemical Signatures of Biotransformation of Fuel Hydrocarbons in Groundwater

Biotransformation processes play an active role in reducing the environmental impact of fuel hydrocarbon releases to groundwater. Because monitoring data at release locations are typically sparse, spatial variations in geochemical indicator parameters are often called upon as indirect evidence of biotransformation. These parameters include concentrations of electron acceptors (O2, NO3-, SO> 4 2- , reduced redox reaction by-products (Fe2+, Mn2+, CH4), as well as bicarbonate alkalinity, pH and Eh. However, background variability in a number of these parameters complicates the task of data interpretation, particularly in the case of small data sets. In this study, correlation analyses are applied to geochemical indicator data at six hydrocarbon groundwater contamination sites in California to identify which parameters are the most reliable indicators. The results of the analyses suggest that the most direct indicators of the local redox environment – Fe2+, Mn2+, CH4, Eh – yield the most consistent evidence of hydrocarbon biotransformation. Indicators which rely largely on mass balance – O2, NO 3 - , SO 4 2- , alkalinity – appear to be less reliable. These findings may provide guidance in both the collection and interpretation of groundwater monitoring data at hydrocarbon contamination sites.

Absence of evidence of biotransformation of morphine to codeine in man.

Nachweis von Codein im Harn von chronisch mit Morphin-Injektionen behandelten Personen. Diese Codein-Spuren konnen jedoch aus Verunreinigungen des benutzten Morphins stammen und bilden daher keinen Beweis dafur, dass Codein beim Menschen durch Biotransformation als Metabolit von Morphin entsteht.

Evaluation of a silicone lubricant injected spinally

Dimethylpolysiloxane fluid, Dow-Corning MF 360, was injected spinally in an appraisal of possible toxic effects which might occur from trace quantities entering the spinal canal. The compound is used as a lubricant in disposable syringes. There was no evidence of neurological effect or tissue inflammation when the compound was injected into the cisterna magna of rats or the spinal canal of rabbits and monkeys. Metabolism studies indicated that most material gaining access to the body was distributed in the fat of the tissues of the gastrointestinal tract and liver. None was excreted and there was no evidence of biotransformation. Most of the material placed in the spinal canal of rats was found there 45 days after injection, and except for the fat only trace quantities were found elsewhere.