1,720,990 research outputs found
Biokinetics in repeated-dosing in vitro drug toxicity studies
Get PDFThe aim of the EU FP7 Predict-IV project was to improve the predictivity of in vitro assays for unwanted effects of drugs after repeated dosing. The project assessed the added benefit of integrating long-lived in vitro organotypic cell systems with 'omics' technologies and in silico modelling, including systems biology and pharmacokinetic assessments. RPTEC/TERT1 kidney cells, primary rat and human hepatocytes, HepaRG liver cells and 2D and 3D primary brain cultures were dosed daily or every other day for 14days to a selection of drugs varying in their mechanism of pharmacological action. Since concentration-effect relationships not only depend on the activity of the drug or the sensitivity of the target, but also on the distribution of compounds in the in vitro system, the concentration of a selection of drugs in cells, microtitre plate plastic and medium was measured over time. Results, reviewed in this paper, indicate that lipophilic drugs bind significantly to plastic labware. A few drugs, including less lipophilic drugs, bind to cell-attachment matrices. Chemicals that reach high concentrations in cells, including cyclosporin A and amiodarone, significantly accumulate over time after repeated dosing, partly explaining their increased toxicity after repeated dosing, compared to a single dose
Comparison of the acute inhibitory effects of Tetrodotoxin (TTX) in rat and human neuronal networks for risk assessment purposes
No full textTetrodotoxin (TTX) is an extremely toxic marine neurotoxin. TTX inhibits voltage-gated sodium channels, resulting in a potentially lethal inhibition of neurotransmission. Despite numerous intoxications in Asia and Europe, limited (human) toxicological data are available for TTX. Additionally, the degree of interspecies differences for TTX is not well established, hampering the use of available (animal) data for human risk assessment and establishing regulatory limits for TTX concentrations in (shell)fish. We therefore used micro-electrode array (MEA) recordings as an integrated measure of neurotransmission to demonstrate that TTX inhibits neuronal electrical activity in both primary rat cortical cultures and human-induced pluripotent stem cell (hIPSC)-derived iCell® neurons in co-culture with hIPSC-derived iCell® astrocytes, with IC50 values of 7 and 10nM, respectively. From these data combined with LD50 values and IC50 concentrations of voltage-gated sodium channels derived from literature it can be concluded that interspecies differences are limited for TTX. Consequently, we used experimental animal data to derive a human acute reference dose of 1.33μg/kg body weight, which corresponds to maximum concentration of TTX in shellfish of 200μg/kg
Replacing the NIH test for rabies vaccine potency testing: a synopsis of drivers and barriers
No full textApproximately 70% of animal use is utilized to demonstrate quality control of vaccines. Especially rabies vaccine potency testing, using the NIH challenge test, involves objections in terms of scientific relevance, animal welfare concern and costs. Several 3R models have been proposed to refine, reduce or replace this test. Some are formally incorporated into regulatory requirements, but actual regulatory acceptance and use by industry lags behind, raising the question concerning which factors influence this process. This question is answered by a combination of literature review, interviews and a survey among 50 rabies vaccine experts. The findings are analyzed using the multilevel perspective on technology transition, which distinguishes 3 levels of factors influencing innovation acceptance. At the micro level (where 3R models are developed and validated) the dis-advantages of, and fractional experience with, 3R models, scarce data sharing and demanding validation processes exist. The meso level (existing regulatory regime) encloses the barriers of the ‘gold standard’, the lack of harmonization and the driving force of legislation stimulating 3Rs use. The macro level (the societal context) combines risk aversion and increased concern for animal welfare. Regulatory acceptance and use of 3R models requires dedicated stakeholder communication, cooperation and coordination at all three levels
Prediction of in vivo developmental toxicity of all-trans-retinoic acid based on in vitro toxicity data and in silico physiologycally based kinetic modeling
No full textThe use of laboratory animals for toxicity testing in chemical safety assessment meets increasing ethical, economic and legislative constraints. The development, validation and application of reliable alternatives for in vivo toxicity testing are therefore urgently needed. In order to use toxicity data obtained from in vitro assays for risk assessment, in vitro concentration–response data need to be translated into in vivo dose–response data that are needed to obtain points of departure for risk assessment, like a benchmark dose (BMD). In the present study, we translated in vitro concentration–response data of the retinoid all-trans-retinoic acid (ATRA), obtained in the differentiation assay of the embryonic stem cell test, into in vivo dose–response data using a physiologically based kinetic model for rat and human that is mainly based on kinetic model parameter values derived using in vitro techniques. The predicted in vivo dose–response data were used for BMD modeling, and the obtained BMDL10 values [lower limit of the 95 % confidence interval on the BMD at which a benchmark response equivalent to a 10 % effect size (BMR10) is reached (BMD10)] for rat were compared with BMDL10 values derived from in vivo developmental toxicity data in rats reported in the literature. The results show that the BMDL10 values from predicted dose–response data differ about sixfold from the BMDL10 values obtained from in vivo data, pointing at the feasibility of using a combined in vitro–in silico approach for defining a point of departure for toxicological risk assessment
Alternative approaches for identifying acute systemic toxicity: Moving from research to regulatory testing
Get PDFAcute systemic toxicity testing provides the basis for hazard labeling and risk management of chemicals. A number of international efforts have been directed at identifying non-animal alternatives for in vivo acute systemic toxicity tests. A September 2015 workshop, Alternative Approaches for Identifying Acute Systemic Toxicity: Moving from Research to Regulatory Testing, reviewed the state-of-the-science of non-animal alternatives for this testing and explored ways to facilitate implementation of alternatives. Workshop attendees included representatives from international regulatory agencies, academia, nongovernmental organizations, and industry. Resources identified as necessary for meaningful progress in implementing alternatives included compiling and making available high-quality reference data, training on use and interpretation of in vitro and in silico approaches, and global harmonization of testing requirements. Attendees particularly noted the need to characterize variability in reference data to evaluate new approaches. They also noted the importance of understanding the mechanisms of acute toxicity, which could be facilitated by the development of adverse outcome pathways. Workshop breakout groups explored different approaches to reducing or replacing animal use for acute toxicity testing, with each group crafting a roadmap and strategy to accomplish near-term progress. The workshop steering committee has organized efforts to implement the recommendations of the workshop participants
The in vitro biokinetics of chlorpromazine and diazepam in aggregating rat brain cell cultures after repeated exposure
Get PDFNeurotoxic effects of compounds can be tested in vitro using cell systems. One example is aggregating rat brain cell cultures. For the extrapolation of in vitro data to the in vivo situation, it is important to take the biokinetics of the test compound into account. In addition, the exposure in vivo is often for a longer period of time; therefore, it is crucial to incorporate this into in vitro assays as well. In this study, aggregating rat brain cell cultures were exposed to chlorpromazine (CPZ) and diazepam (DZP) for 12-days with repeated exposure. Samples were taken from the stocks, test media, cell culture media and cells at specific time points on the first and last exposure day. These samples were analysed by HPLC-UV. The amount of CPZ in the medium decreased over time, whereas the amount in the cells showed an increase. Accumulation of CPZ in the cells was seen over the 12-day repeated exposure. The amount of DZP in the medium remained stable over time and only up to 2% of DZP added was found in the cells. Different biokinetic behaviour was found for CPZ and DZP. Possible explanations are differences in uptake into the cells or efflux out of the cells. The decrease of CPZ in the medium versus the stable amount of DZP results in differences in exposure concentrations over time, which should be taken into account when interpreting in vitro effect data
Dose metric considerations in in vitro assays to improve quantitative in vitro–in vivo dose extrapolations
No full textChallenges to improve toxicological risk assessment to meet the demands of the EU chemical’s legisla- tion, REACH, and the EU 7th Amendment of the Cosmetics Directive have accelerated the development of non-animal based methods. Unfortunately, uncertainties remain surrounding the power of alterna- tive methods such as in vitro assays to predict in vivo dose–response relationships, which impedes their use in regulatory toxicology. One issue reviewed here, is the lack of a well-defined dose metric for use in concentration-effect relationships obtained from in vitro cell assays. Traditionally, the nominal con- centration has been used to define in vitro concentration–effect relationships. However, chemicals may differentially and non-specifically bind to medium constituents, well plate plastic and cells. They may also evaporate, degrade or be metabolized over the exposure period at different rates. Studies have shown that these processes may reduce the bioavailable and biologically effective dose of test chemicals in in vitro assays to levels far below their nominal concentration. This subsequently hampers the interpretation of in vitro data to predict and compare the true toxic potency of test chemicals. Therefore, this review discusses a number of dose metrics and their dependency on in vitro assay setup. Recommendations are given on when to consider alternative dose metrics instead of nominal concentrations, in order to reduce effect concentration variability between in vitro assays and between in vitro and in vivo assays in toxicology
- …
