In vitro cytotoxicity tests for the prediction of acute toxicity in vivo

Tolfenpyrad Derivatives Exhibit Potent Francisella-Specific Antibacterial Activity without Toxicity to Mammalian Cells In Vitro

Tularemia is a deadly disease caused by Francisella tularensis, an emerging intracellular bacterial pathogen that can be disseminated rapidly through aerosols and vector-borne transmission. Recent surveillance data demonstrate an increasing incidence in several countries. Although clinical isolates of Francisella strains are sensitive to currently used antibiotics, engineered or horizontal acquisition of antibiotic resistance is a constant threat to public health. Therefore, the identification of antibiotics that target previously undrugged pathways is required to safeguard human health. An environmental pesticide that is registered for use in multiple countries, tolfenpyrad, shows promising activity to block Francisella growth; however, it is not a suitable antimicrobial candidate for use in vivo due to potential toxicity in humans and other animals. In this study, we applied a structure-activity relationship approach to tolfenpyrad to generate compounds with improved antibacterial activity and reduced toxicity. Through screening of a library of derivatives, we identified analogs with improved therapeutic windows compared with tolfenpyrad. Although structural diversity exists among these analogs, they inhibit the growth of Francisella species but not other Gram-negative or Gram-positive species. These compounds block intramacrophage growth of F. novicida and pathogenesis in an in vivo arthropod model of infection. Although the biochemical activity of these drugs is unknown, they appear to target the same pathway as the parent molecule because F. novicida mutants that are resistant to tolfenpyrad are also resistant to its analogs. Taken together, these findings suggest that these tolfenpyrad-derived compounds comprise a new class of Francisella-targeted antimicrobials and merit further evaluation and development.

High-Efficiency Effect-Directed Analysis Leveraging Five High Level Advancements: A Critical Review

Organic contaminants are ubiquitous in the environment, with mounting evidence unequivocally connecting them to aquatic toxicity, illness, and increased mortality, underscoring their substantial impacts on ecological security and environmental health. The intricate composition of sample mixtures and uncertain physicochemical features of potential toxic substances pose challenges to identify key toxicants in environmental samples. Effect-directed analysis (EDA), establishing a connection between key toxicants found in environmental samples and associated hazards, enables the identification of toxicants that can streamline research efforts and inform management action. Nevertheless, the advancement of EDA is constrained by the following factors: inadequate extraction and fractionation of environmental samples, limited bioassay endpoints and unknown linkage to higher order impacts, limited coverage of chemical analysis (i.e., high-resolution mass spectrometry, HRMS), and lacking effective linkage between bioassays and chemical analysis. This review proposes five key advancements to enhance the efficiency of EDA in addressing these challenges: (1) multiple adsorbents for comprehensive coverage of chemical extraction, (2) high-resolution microfractionation and multidimensional fractionation for refined fractionation, (3) robust in vivo/vitro bioassays and omics, (4) high-performance configurations for HRMS analysis, and (5) chemical-, data-, and knowledge-driven approaches for streamlined toxicant identification and validation. We envision that future EDA will integrate big data and artificial intelligence based on the development of quantitative omics, cutting-edge multidimensional microfractionation, and ultraperformance MS to identify environmental hazard factors, serving for broader environmental governance.

Liver Extracellular Matrix-Based Nanofiber Scaffolds for the Culture of Primary Hepatocytes and Drug Screening

Immortalized liver cell lines and primary hepatocytes are currently used as in vitro models for hepatotoxic drug screening. However, a decline in the viability and functionality of hepatocytes with time is an important limitation of these culture models. Advancements in tissue engineering techniques have allowed us to overcome this challenge by designing suitable scaffolds for maintaining viable and functional primary hepatocytes for a longer period of time in culture. In the current study, we fabricated liver-specific nanofiber scaffolds with polylactic acid (PLA) along with a decellularized liver extracellular matrix (LEM) by the electrospinning technique. The fabricated hybrid PLA-LEM scaffolds were more hydrophilic and had better swelling properties than the PLA scaffolds. The hybrid scaffolds had a pore size of 38 ± 8 μm and supported primary rat hepatocyte cultures for 10 days. Increased viability (2-fold increase in the number of live cells) and functionality (5-fold increase in albumin secretion) were observed in primary hepatocytes cultured on the PLA-LEM scaffolds as compared to those on conventional collagen-coated plates on day 10 of culture. A significant increase in CYP1A2 enzyme activity was observed in hepatocytes cultured on PLA-LEM hybrid scaffolds in comparison to those on collagen upon induction with phenobarbital. Drugs like acetaminophen and rifampicin showed the highest toxicity in hepatocytes cultured on hybrid scaffolds. Also, the lethal dose of these drugs in rodents was accurately predicted as 1.6 g/kg and 594 mg/kg, respectively, from the corresponding IC50 values obtained from drug-treated hepatocytes on hybrid scaffolds. Thus, the fabricated liver-specific electrospun scaffolds maintained primary hepatocyte viability and functionality for an extended period in culture and served as an effective ex vivo drug screening platform to predict an accurate in vivo drug-induced hepatotoxicity.

Repurposing Disulfiram as an Antimicrobial Agent in Topical Infections

Antimicrobial drugs applied topically offer several advantages. However, the widespread use of antibiotics has led to increasing antimicrobial resistance. One interesting approach in the drug discovery process is drug repurposing. Disulfiram, which was originally approved as an anti-alcoholism drug, offers an attractive alternative to treat topical multidrug resistance bacteria in skin human infections. This study aimed to evaluate the biopharmaceutical characteristics of the drug and the effects arising from its topical application in detail. Microdilution susceptibility testing showed antibacterial activity against Gram-positive bacteria Staphylococcus aureus and Streptococcus pyogenes. Dermal absorption revealed no permeation in pig skin. The quantification of the drug retained in pig skin demonstrated concentrations in the stratum corneum and epidermis, enough to treat skin infections. Moreover, in vitro cytotoxicity and micro-array analyses were performed to better understand the mechanism of action and revealed the importance of the drug as a metal ion chelator. Together, our findings suggest that disulfiram has the potential to be repurposed as an effective antibiotic to treat superficial human skin infections.

The use of Bayesian methodology in the development and validation of a tiered assessment approach towards prediction of rat acute oral toxicity

There exists consensus that the traditional means by which safety of chemicals is assessed-namely through reliance upon apical outcomes obtained following in vivo testing-is increasingly unfit for purpose. Whilst efforts in development of suitable alternatives continue, few have achieved levels of robustness required for regulatory acceptance. An array of "new approach methodologies" (NAM) for determining toxic effect, spanning in vitro and in silico spheres, have by now emerged. It has been suggested, intuitively, that combining data obtained from across these sources might serve to enhance overall confidence in derived judgment. This concept may be formalised in the "tiered assessment" approach, whereby evidence gathered through a sequential NAM testing strategy is exploited so to infer the properties of a compound of interest. Our intention has been to provide an illustration of how such a scheme might be developed and applied within a practical setting-adopting for this purpose the endpoint of rat acute oral lethality. Bayesian statistical inference is drawn upon to enable quantification of degree of confidence that a substance might ultimately belong to one of five LD50-associated toxicity categories. Informing this is evidence acquired both from existing in silico and in vitro resources, alongside a purposely-constructed random forest model and structural alert set. Results indicate that the combination of in silico methodologies provides moderately conservative estimations of hazard, conducive for application in safety assessment, and for which levels of certainty are defined. Accordingly, scope for potential extension of approach to further toxicological endpoints is demonstrated.

Small nucleic acids and the path to the clinic for anti-CRISPR

CRISPR-based therapeutics have entered clinical trials but no methods to inhibit Cas enzymes have been demonstrated in a clinical setting. The ability to inhibit CRISPR-based gene editing or gene targeting drugs should be considered a critical step in establishing safety standards for many CRISPR-Cas therapeutics. Inhibitors can act as a failsafe or as an adjuvant to reduce off-target effects in patients. In this review we discuss the need for clinical inhibition of CRISPR-Cas systems and three existing inhibitor technologies: anti-CRISPR (Acr) proteins, small molecule Cas inhibitors, and small nucleic acid-based CRISPR inhibitors, CRISPR SNuBs. Due to their unique properties and the recent successes of other nucleic acid-based therapeutics, CRISPR SNuBs appear poised for clinical application in the near-term.

Macrolides May Prevent Severe Acute Respiratory Syndrome Coronavirus 2 Entry into Cells: A Quantitative Structure Activity Relationship Study and Experimental Validation

The global pandemic caused by the emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is threatening the health and economic systems worldwide. Despite the enormous efforts of scientists and clinicians around the world, there is still no drug or vaccine available worldwide for the treatment and prevention of the infection. A rapid strategy for the identification of new treatments is based on repurposing existing clinically approved drugs that show antiviral activity against SARS-CoV-2 infection. In this study, after developing a quantitative structure activity relationship analysis based on molecular topology, several macrolide antibiotics are identified as promising SARS-CoV-2 spike protein inhibitors. To confirm the in silico results, the best candidates were tested against two human coronaviruses (i.e., 229E-GFP and SARS-CoV-2) in cell culture. Time-of-addition experiments and a surrogate model of viral cell entry were used to identify the steps in the virus life cycle inhibited by the compounds. Infection experiments demonstrated that azithromycin, clarithromycin, and lexithromycin reduce the intracellular accumulation of viral RNA and virus spread as well as prevent virus-induced cell death, by inhibiting the SARS-CoV-2 entry into cells. Even though the three macrolide antibiotics display a narrow antiviral activity window against SARS-CoV-2, it may be of interest to further investigate their effect on the viral spike protein and their potential in combination therapies for the coronavirus disease 19 early stage of infection.

A Review of the Toxicity and Phytochemistry of Medicinal Plant Species Used by Herbalists in Treating People Living With HIV/AIDS in Uganda

Introduction: Despite concerns about toxicity, potentially harmful effects and herb-drug interactions, the use of herbal medicines remains widely practiced by people living with HIV/AIDS (PLHIV) in Uganda. Objective: The objective of the paper was to comprehensively review the literature on the toxicity and chemical composition of commonly used medicinal plant species in treating PLHIV in Uganda. Methods: We reviewed relevant articles and books published over the last sixty years on ethnobotany, antiviral/anti-HIV activity, toxicity, phytochemistry of Vachellia hockii, Albizia coriaria, Bridelia micrantha, Cryptolepis sanguinolenta, Erythrina abyssinica, Gardenia ternifolia, Gymnosporia senegalensis, Psorospermum febrifugium, Securidaca longipendunculata, Warburgia ugandensis and Zanthoxylum chalybeum and their synonyms. We searched PubMed, Web of Science, Scopus, Science Direct and Google Scholar. Discussion: Most of the plant species reviewed apart from P. febrifugium, S. longipedunculata and C. sanguinolenta lacked detailed phytochemical analyses as well as the quantification and characterization of their constituents. Crude plant extracts were the most commonly used. However, purified/single component extracts from different plant parts were also used in some studies. The U87 human glioblastoma was the most commonly used cell line. Water, ethanol, methanol and DMSO were the commonest solvents used. In some instances, isolated purified compounds/extracts such as Cryptolepine and Psorospermin were used. Conclusion: Cytotoxicity varied with cell type, solvent and extract type used making it difficult for direct comparison of the plant species. Five of the eleven plant species namely, A. coriaria, C. sanguinolenta, G. ternifolia, P. febrifugium and Z. chalybeum had no cytotoxicity studies in animal models. For the remaining six plant species, the crude aqueous and ethanol extracts were mainly used in acute oral toxicity studies in mice. Herbalists reported only A. coriaria and W. ugandensis to cause toxic side effects in humans. However, selective cytotoxic plant extracts can potentially be beneficial as anticancer or anti-tumour drugs.

Potential of Human Lung Cells for Predicting Acute Cytotoxicity

— Human fetal lung fibroblasts (HFL1) were studied in culture to evaluate their potential as a screen for cytotoxicity. The cytotoxic concentrations determined in vitro were compared with established human and animal toxicity data. Confluent monolayers were incubated in the absence or presence of increasing concentrations of test chemicals for 24 hours, and the MTT assay was used to assess toxicity. Inhibitory concentrations were extrapolated from concentration-effect curves after linear regression analysis. Comparison of the cytotoxicity data with rodent lethal concentrations and human lethal concentrations obtained from the testing of 50 chemicals in human lung cells, suggests that the experimental IC50 values are as accurate as predictors of human toxicity as the equivalent toxic blood concentrations derived from rodent LD50 tests. In addition, evaluation of the first 15 chemicals reveals no significant differences between results from continuous cell lines of human and rodent origin. Together with a related battery of tests, cell culture procedures have the potential to supplement or replace current animal protocols in screening chemicals for human toxicity.

Effects of Surfactant Retreatment in Vitro: A Method to Evaluate Changes in Cell Junctions and in Cell Viability

Madin-Darby canine kidney (MDCK) cells form cell junctions in vitro, which can be damaged and restored following exposure to a mild cytotoxicant. Both tight junctional integrity and cell viability can be measured by using the fluorescein leakage assay and the Alamar Blue™ assay, respectively, without terminating the cell cultures. By combining these two assay endpoints, it is possible to examine the effects of a repeated cocamidopropylbetaine treatment on a confluent layer of MDCK cells. While the tight junctions could be restored after a single treatment with 2.5mg/ml or 10mg/ml cocamidopropylbetaine, after a second insult, recovery was noted for those treated with 2.5mg/ml, but not for those exposed to 10mg/ml. Following the second insult, the cells did not regain the control level of viability.

Elucidating Compound Mechanism of Action and Predicting Cytotoxicity Using Machine Learning Approaches, Taking Prediction Confidence into Account

The modes of action (MoAs) of drugs frequently are unknown, because many are small molecules initially identified from phenotypic screens, giving rise to the need to elucidate their MoAs. In addition, the high attrition rate for candidate drugs in preclinical studies due to intolerable toxicity has motivated the development of computational approaches to predict drug candidate (cyto)toxicity as early as possible in the drug-discovery process. Here, we provide detailed instructions for capitalizing on bioactivity predictions to elucidate the MoAs of small molecules and infer their underlying phenotypic effects. We illustrate how these predictions can be used to infer the underlying antidepressive effects of marketed drugs. We also provide the necessary functionalities to model cytotoxicity data using single and ensemble machine-learning algorithms. Finally, we give detailed instructions on how to calculate confidence intervals for individual predictions using the conformal prediction framework. © 2019 by John Wiley & Sons, Inc.

Synthesis and biological assessment of a ruthenium(II) cyclopentadienyl complex in breast cancer cells and on the development of zebrafish embryos

Ruthenium-based complexes currently attract great attention as they hold promise to replace platinum-based drugs as a first line cancer treatment. Whereas ruthenium arene complexes are some of the most studied species for their potential anticancer properties, other types of ruthenium complexes have been overlooked for this purpose. Here, we report the synthesis and characterization of Ru(II) cyclopentadienyl (Cp), Ru(II) cyclooctadienyl (COD) and Ru(III) complexes bearing anastrozole or letrozole ligands, third-generation aromatase inhibitors currently used for the treatment of estrogen receptor positive (ER +) breast cancer. Among these complexes, Ru(II)Cp 2 was the only one that displayed a high stability in DMSO and in cell culture media and consequently, the only complex for which the in vitro and in vivo biological activities were investigated. Unlike anastrozole alone, complex 2 was considerably cytotoxic in vitro (IC50 values < 1 μM) in human ER + breast cancer (T47D and MCF7), triple negative breast cancer (TNBC) (MBA-MB-231), and in adrenocortical carcinoma (H295R) cells. Theoretical (docking simulation) and experimental (aromatase catalytic activity) studies suggested that an interaction between 2 and the aromatase enzyme was not likely to occur and that the bulkiness of the PPh3 ligands could be an important factor preventing the complex to reach the active site of the enzyme. Exposure of zebrafish embryos to complex 2 at concentrations around its in vitro cytotoxicity IC50 value (0.1-1 μM) did not lead to noticeable signs of toxicity over 96 h, making it a suitable candidate for further in vivo investigations. This study confirms the potential of Ru(II)Cp complexes for breast cancer therapy, more specifically against TNBCs that are usually not responsive to currently used chemotherapeutic agents.

In vitro Antibacterial Activity of Isopropoxy Benzene Guanidine Against Multidrug-Resistant Enterococci

Background

Bacterial infections cause a serious public health crisis due to the emergence of resistance towards multiple conventional antibacterial drugs. In particular, multidrug-resistant (MDR) Enterococcus faecium which belongs to "ESKAPE" organisms is causing significant problems worldwide. Hence, there is an urgent need to find alternative therapies. Recently, substituted benzene guanidine compounds have been used as lead structures to discover new promising drugs in both synthetic and medicinal chemistry.

Purpose

Here we investigated the antimicrobial activity of a new substituted benzene guanidine analog, isopropoxy benzene guanidine, against Enterococci.

Material and methods

The isopropoxy benzene guanidine was synthesized by Guangzhou Insighter Biotechnology Co., Ltd and tested on both reference bacterial strain and 32 clinical MDR Enterococci strains. The in vitro antibacterial activity was evaluated by microdilution method and kill kinetic assays. The potential antibacterial mechanism was measured by fluorescence spectrometry using fluorescent membrane potential probe 3, 3-diethyloxacarbocyanine iodide (DiOC₂ (3)).

Results

Isopropoxy benzene guanidine exhibited potent bactericidal activity against both reference strain and MDR Enterococci isolates. The minimum inhibitory concentration (MIC) range for isopropoxy benzene guanidine was 1-4 μg/mL. Minimum bactericidal concentration (MBC) was about 2-8-fold of its MIC values. Time-kill studies showed that isopropoxy benzene guanidine provided superior bactericidal effect against reference and MDR strains within 12 hrs at 2×MIC. Furthermore, isopropoxy benzene guanidine could cause a large reduction in the magnitude of the generated membrane potential compared to that of the untreated cells.

Conclusion

The present study highlights the potent bactericidal activity of isopropoxy benzene guanidine on Enterococci by disrupting the cell membrane potential. These findings demonstrate that isopropoxy benzene guanidine may be a good chemical lead for further medicinal chemistry and pharmaceutical development and could be used as a therapeutic agent for infectious diseases caused by MDR Enterococci.

MXR response in sea anemones: Effect of temperature, salinity and copper

Multixenobiotic resistance (MXR) phenotype is a cellular defense which can eliminate toxic substances from cells. Several studies describe the MXR activity after pollutant exposure, but little is known about the interference of abiotic factors in this mechanism. The present study aimed to evaluate MXR activity in sea anemones Bunodosoma cangicum after in vivo and in vitro exposures to different temperatures (15, 20 and 25C) and salinities (15, 30 and 45‰) associated or not with copper (0, 7.8 and 15.6 μg/L). Results showed that low temperature inhibited the MXR activity in vivo and in vitro, while salinity did not alter this activity. Copper could change the response, mainly at different temperatures (15 and 25 °C) - 7.8 μg/L Cu activated in vivo and in vitro and 15.6 μg/L Cu in vitro inhibited MXR activity in relation to same copper concentrations at 20 °C. Results for MXR activity found between in vivo and in vitro exposures were similar among temperature treatments and salinities; however, under hyperosmotic shock, in vivo exposure showed that animals has different response than isolated cells. The animals exposed to salinity 45‰ produced a mucus layer as a defense mechanism, because of this protection the response was different between in vivo and in vitro exposures. Concluding, temperature affects MXR activity independently of the presence of copper and each model of exposure contributes with different type of knowledge (cellular mechanism/systemic response).

A comparative study on the cellular viability and debridement efficiency of antimicrobial-based wound dressings

A concentrated surfactant gel containing polyhexamethylene biguanide (CSG-PHMB) (CSG: Plurogel) was evaluated for in vitro cell cytotoxicity using the direct contact, extraction, and cell insert assays, along with its ability to breakdown artificial wound eschar and slough, compared with other clinically available wound gels: a wound gel loaded with 0.13% benzalkonium chloride (BXG) and a highly viscous gel loaded with 0.1% polyhexamethylene biguanide (PXG). Following treatment with CSG-PHMB, BXG, and PXG at day 1, the viability of L929 and HDFa cells sharply decreased to lower than 20% of the culture media control in the direct contact assay; however, cell viability of L929 was 128.65 ± 1.41%, 99.90 ± 2.84%*, and 64.08 ± 5.99%* respectively; HDFa was 84.58 ± 10.41%, 19.54 ± 3.06%**, and 96.28 ± 33.67%, respectively, in the extraction assay. In the cell insert model, cell viability of L929 cells were 95.25 ± 0.96%, 47.49 ± 5.37%**, and 48.63 ± 7.00%**, respectively; HDFa cell viability were 92.80 ± 1.29%, 38.86 ± 4.28%**, and 49.90 ± 2.55%** (*: P < .01; **P < .001 compared with CSG-PHMB; cell viability of culture medium without treatment at day 1 was 100%). The cell extraction model on day 1 indicated that CSG-PHMB had higher viability of L929 cells compared with BXG. In addition, the cellular viability results indicated that CSG-PHMB gel exhibited lower cytotoxicity when compared with BXG and PXG in the cell insert model assay. Within the in vitro debridement model, CSG-PHMB exhibited an ability to potentially increase the loosening of the collagen matrix. The reason for this may be because of the concentrated surfactant found within the CSG-PHMB, which has the ability to lower the surface tension, aiding in the movements of fragments and debris in the fluorescent artificial wound eschar model (fAWE).

Two metabolites isolated from endophytic fungus Coniochaeta sp. F-8 in Ageratina adenophora exhibit antioxidative activity and cytotoxicity

Ageratina adenophora is an invasive plant of global importance and has a broad distribution in the Western Himalayas. Endophtytic fungus Coniochaeta sp.F-8 was found in Ageratina adenophora. In this paper, we aim to investigate the antioxidative activity and cytotoxicity of the metabolites from Coniochaeta sp.F-8. Consequently, two compounds Phomoxanthone A and Penialidin A were isolated from the endophytic fungus of Ageratina adenophora for the first time. The structures of compounds were identified by IR, NMR and ESI-MS methods. Moreover, both of those compounds showed considerable antioxidative activity in vitro and resulted cytotoxicity in mouse embryo fibroblasts cell line Balb/c3T3. The present study provides a theoretical foundation for the development and utilization of endophytic fungi in Ageratina adenophora as a medicinal substance.

Nonanimal Models for Acute Toxicity Evaluations: Applying Data-Driven Profiling and Read-Across

BACKGROUND

Low-cost, high-throughput in vitro bioassays have potential as alternatives to animal models for toxicity testing. However, incorporating in vitro bioassays into chemical toxicity evaluations such as read-across requires significant data curation and analysis based on knowledge of relevant toxicity mechanisms, lowering the enthusiasm of using the massive amount of unstructured public data.

OBJECTIVE

We aimed to develop a computational method to automatically extract useful bioassay data from a public repository (i.e., PubChem) and assess its ability to predict animal toxicity using a novel bioprofile-based read-across approach.

METHODS

A training database containing 7,385 compounds with diverse rat acute oral toxicity data was searched against PubChem to establish in vitro bioprofiles. Using a novel subspace clustering algorithm, bioassay groups that may inform on relevant toxicity mechanisms underlying acute oral toxicity were identified. These bioassays groups were used to predict animal acute oral toxicity using read-across through a cross-validation process. Finally, an external test set of over 600 new compounds was used to validate the resulting model predictivity.

RESULTS

Several bioassay clusters showed high predictivity for acute oral toxicity (positive prediction rates range from 62-100%) through cross-validation. After incorporating individual clusters into an ensemble model, chemical toxicants in the external test set were evaluated for putative acute toxicity (positive prediction rate equal to 76%). Additionally, chemical fragment -in vitro-in vivo relationships were identified to illustrate new animal toxicity mechanisms.

CONCLUSIONS

The in vitro bioassay data-driven profiling strategy developed in this study meets the urgent needs of computational toxicology in the current big data era and can be extended to develop predictive models for other complex toxicity end points. https://doi.org/10.1289/EHP3614.

Engineering fast dissolving sodium acetate mediated crystalline solid dispersion of docetaxel

It is hypothesized that a novel crystalline solid dispersion (CSD) of docetaxel (C-DXT) can be engineered by dispersing native docetaxel (DXT, a BCS class II drug) in sodium acetate crystal (SA). DXT is dissolved in glacial acetic/SA solution and freeze-dried. The resulting C-DXT is characterized by differential scanning calorimetry (DSC), powder X-ray analysis (PXRD), LC-MS/MS, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Quartz crystal microbalance with dissipation monitoring (QCM-D) and dynamic light scattering (DLS). Its cytotoxicity on model cancerous (MCF-7, MDA-MB-468) and normal breast cells (MCF-10A) is assessed by MTS assay. SEM/TEM data and the absence of the characteristics peaks of DXT on the DSC curve (at 193.4 °C) and the XRD scan (at 2θ = 15.31 °C and 23.04 °C) confirm the presence of C-DXT in SA. The LC-MS/MS data indicates the chemical stability of DXT. The yield and C-DXT loading are 95.2% and 6.52% w/w, respectively. The C-DXT rapidly forms an aqueous non-rigid nanosuspension with a faster drug dissolution rate compared to native DXT. Unlike, control Tween 80/ethanol, SA is noncytotoxic to normal cells. However, C-DXT's cytotoxicity is time and dose dependent for all diseased cells. This unique CSD process might be applicable to other hydrophobic bioactive agents to enhance their safety and efficacy.

Evaluation of robenidine analog NCL195 as a novel broad-spectrum antibacterial agent

The spread of multidrug resistance among bacterial pathogens poses a serious threat to public health worldwide. Recent approaches towards combating antimicrobial resistance include repurposing old compounds with known safety and development pathways as new antibacterial classes with novel mechanisms of action. Here we show that an analog of the anticoccidial drug robenidine (4,6-bis(2-((E)-4-methylbenzylidene)hydrazinyl)pyrimidin-2-amine; NCL195) displays potent bactericidal activity against Streptococcus pneumoniae and Staphylococcus aureus by disrupting the cell membrane potential. NCL195 was less cytotoxic to mammalian cell lines than the parent compound, showed low metabolic degradation rates by human and mouse liver microsomes, and exhibited high plasma concentration and low plasma clearance rates in mice. NCL195 was bactericidal against Acinetobacter spp and Neisseria meningitidis and also demonstrated potent activity against A. baumannii, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae and Enterobacter spp. in the presence of sub-inhibitory concentrations of ethylenediaminetetraacetic acid (EDTA) and polymyxin B. These findings demonstrate that NCL195 represents a new chemical lead for further medicinal chemistry and pharmaceutical development to enhance potency, solubility and selectivity against serious bacterial pathogens.

Early Genotoxic and Cytotoxic Effects of the Toxic Dinoflagellate Prorocentrum lima in the Mussel Mytilus galloprovincialis

Okadaic acid (OA) and dinophysistoxins (DTXs) are the main toxins responsible for diarrhetic shellfish poisoning (DSP) intoxications during harmful algal blooms (HABs). Although the genotoxic and cytotoxic responses to OA have been evaluated in vitro, the in vivo effects of these toxins have not yet been fully explored. The present work fills this gap by evaluating the in vivo effects of the exposure to the DSP-toxin-producing dinoflagellate Prorocentrum lima during the simulation of an early HAB episode in the mussel Mytilus galloprovincialis. The obtained results revealed that in vivo exposure to this toxic microalgae induced early genotoxicity in hemocytes, as a consequence of oxidative DNA damage. In addition, the DNA damage observed in gill cells seems to be mainly influenced by exposure time and P. lima concentration, similarly to the case of the oxidative damage found in hemocytes exposed in vitro to OA. In both cell types, the absence of DNA damage at low toxin concentrations is consistent with the notion suggesting that this level of toxicity does not disturb the antioxidant balance. Lastly, in vivo exposure to growing P. lima cell densities increased apoptosis but not necrosis, probably due to the presence of a high number of protein apoptosis inhibitors in molluscs. Overall, this work sheds light into the in vivo genotoxic and cytotoxic effects of P. lima. In doing so, it also demonstrates for the first time the potential of the modified (OGG1) comet assay for assessing oxidative DNA damage caused by marine toxins in marine invertebrates.

Self-healing of thermally-induced, biocompatible and biodegradable protein hydrogel

Almost 100% self-healing extent recovery performance was observed in thermal-induced bovine serum albumin hydrogel with external heating. Good biocompatibility and biodegradability of this materials were also demonstrated.

Validation of the hepatocyte-like HPCT-1E3 cell line as an in vitro model for the prediction of acute in vivo toxicity

In a pilot study, we tested 20 randomly-selected chemicals for their cytotoxicity toward the HPCT-1E3 cell model, in order to prove the ability of this in vitro model to predict human acute in vivo toxicity. The study revealed that, in contrast to most other in vitro models, results from the HPCT-1E3 cell-based system show better correlation with the more-relevant human acute lethal doses, whereas results from most other systems have a high predictivity for human lethal serum concentrations. For the prevalidation of the HPCT-1E3 model as a surrogate for regulatory acute in vivo toxicity tests, we have now expanded the list of tested chemicals to 57 substances, and have compared the results with data from the HepG2 cell assay. Again, a better correlation of HPCT-1E3 IC50 values with human oral lethal doses, as compared to correlation with human lethal serum concentrations, was observed after the pooling of all the tested substances (r(2) = 0.53 [P < 0.001] and r(2) = 0.41 [P = 0.009], respectively). Therefore, the HPCT-1E3 in vitro model may be a valuable tool for prediction of human oral toxicity, and may help to further reduce the number of animals used for in vivo toxicity tests.

Toxicity monitoring with primary cultured hepatocytes underestimates the acetaminophen-induced inflammatory responses of the mouse liver

In vitro gene expression profiling with isolated hepatocytes has been used to assess the hepatotoxicity of certain chemicals because of animal welfare issues. However, whether an in vitro system can completely replace the in vivo system has yet to be elucidated in detail. Using a focused microarray established in our laboratory, we examined gene expression profiles in the mouse liver and primary cultured hepatocytes after treatment with different doses of acetaminophen, a widely used analgesic that frequently causes liver injury. The acute hepatotoxicity of acetaminophen was confirmed by showing the induction of an oxidative stress marker, heme oxygenase-1, elevated levels of serum transaminase, and histopathological findings. In vivo microarray and network analysis showed that acetaminophen treatment provoked alterations in relation to the inflammatory response, and that tumor necrosis factor-α plays a central role in related pathway alterations. By contrast, pathway analyses in in vitro isolated hepatocytes did not find such prominent changes in the inflammation-related networks compared with the in vivo situation. Thus, although in vitro gene expression profiles are useful for evaluating the direct toxicity of chemicals, indirect toxicities including inflammatory responses mediated by cell-cell interactions or secondary toxicity due to pathophysiological changes in the whole body may be overlooked. Our results indicate that the in vitro hepatotoxicity prediction system using isolated hepatocytes does not fully reflect the in vivo cellular response. An in vitro system may be appropriate, therefore, for high throughput screening to detect the direct hepatotoxicity of a test compound.

Estimation of reliability of predictions and model applicability domain evaluation in the analysis of acute toxicity (LD50)

This study presents a new type of acute toxicity (LD(50)) prediction that enables automated assessment of the reliability of predictions (which is synonymous with the assessment of the Model Applicability Domain as defined by the Organization for Economic Cooperation and Development). Analysis involved nearly 75,000 compounds from six animal systems (acute rat toxicity after oral and intraperitoneal administration; acute mouse toxicity after oral, intraperitoneal, intravenous, and subcutaneous administration). Fragmental Partial Least Squares (PLS) with 100 bootstraps yielded baseline predictions that were automatically corrected for non-linear effects in local chemical spaces--a combination called Global, Adjusted Locally According to Similarity (GALAS) modelling methodology. Each prediction obtained in this manner is provided with a reliability index value that depends on both compound's similarity to the training set (that accounts for similar trends in LD(50) variations within multiple bootstraps) and consistency of experimental results with regard to the baseline model in the local chemical environment. The actual performance of the Reliability Index (RI) was proven by its good (and uniform) correlations with Root Mean Square Error (RMSE) in all validation sets, thus providing quantitative assessment of the Model Applicability Domain. The obtained models can be used for compound screening in the early stages of drug development and prioritization for experimental in vitro testing or later in vivo animal acute toxicity studies.

Screening of herbal medicines for the recovery of cisplatin-induced nephrotoxicity

The goal of this study was to quantitatively determine the recovery effects of herbal medicines (HM) on the cisplatin-induced nephrotoxicity. In the present study, the recovery effects of 239 HM on HEK 293 cells that had been damaged by cisplatin were evaluated by a mitochondrial activity MTS assay. After the first round of screening, candidate HM were selected based on a recovery rate of greater than 20%. The efficacy of the selected herbs was then determined by dose response kinetic analysis. Of the extracts evaluated, 7 HM (Paeonia suffruticosa (PS), Curcuma longa (CL), Centipeda minima (CM), Loranthus parasiticus (LP), Pulsatilla dahurica (PD), Sinapis alba (SA), and Scutellaria barbata (SB)) had a strong recovery effect on cisplatin-induced damage in HEK 293 cells. An LDH assay showed that LP, CM, SB, CL, SA, and PS had the best recovery effect, whereas a comet assay indicated that PS, SB, SA, PD, and CL had the best recovery effect. Taken together, these results suggest that SB, CL, PS, and SA are the best candidate HM for the recovery of cisplatin-induced nephrotoxicity. Therefore, additional studies should be conducted to determine if these HM possess novel therapeutic agents that can be used for the prevention or treatment of renal disorders.

Screening of herbal medicines for recovery of acetaminophen-induced nephrotoxicity

This study was conducted to quantitatively evaluate the recovery effects of herbal medicines on acetaminophen-induced nephrotoxicity. In the present study, the recovery effects of 251 herb medicines on HEK 293 cells that had been damaged by acetaminophen were evaluated using an MTS assay. HEK 293 cells were cultured in 96-well plates and then pretreated with or without 20μM acetaminophen (IC(50) value: 17.5±1.9) for 1h. Next, different herbal medicines were added to the wells, after which the cells were reincubated at 37°C for 24h. After the first round of screening, the candidate herbal medicines were selected based on a recovery rate of greater than 20% and their efficacy were then determined by dose response kinetic analysis. Among these extracts, 8 herbal medicines (Ledebouriella divaricata, Sparganium simplex, Panax ginseng, Aster tataricus, Citrus aurantium, Sanguisorba officianlis, Arisaema consanguineum, and Polygonum aviculare) had a strong recovery effect on acetaminophen-induced damage in HEK 293 cells. Dose response non-linear regression analysis demonstrated that P. aviculare showed the best recovery rate (98%), and that its EC(50) (0.1ng/mL) was the smallest among the screened candidate herbal medicines. Additional studies of these herbal medicines should be conducted to determine if they possess novel therapeutic agents for the prevention or treatment of renal disorders.

Lipophilicity parameters for ionic liquid cations and their correlation to in vitro cytotoxicity

Regarding the great structural variability of the currently expanding group of ionic liquids, it is highly desirable to understand the basic factors affecting their toxicity in different biological systems. The present study of a set of 74 ionic liquids with imidazolium, pyrrolidinium, pyridinium, quinolinium, quaternary phosphonium and quaternary ammonium cations and the comparatively small anions Cl(-), Br(-), BF(4)(-), or PF(6)(-) demonstrates the influence of the cation lipophilicity on the cytotoxicity in IPC-81 leukemia cells from rats. The scope of this correlation is limited to ionic liquids with these or similarly small anions that are sufficiently nonreactive under physiological and chromatographic conditions and whose cation lipophilicity does not exceed a certain threshold.

In vitro cytotoxicity assay with selected chemicals using human cells to predict target-organ toxicity of liver and kidney

In order to elucidate the feasibility of predicting liver and kidney target-organ toxicity using in vitro cytotoxicity assay, cytotoxicity of selected chemicals, acetaminophen (AAP), mitomycin (MMC), cupric chloride (CuCl2), phenacetin, cadmium chloride (CdCl2) and aristolochic acid (AA), was studied using human hepatoma (Bel-7402) cells and human renal tubular epithelial (HK-2) cells. Cell viability and mitochondrial permeability transition (MPT) were assessed by the neutral red (NR) assay and laser scanning confocal microscope, respectively. The results of the NR assay indicated that cytotoxicity of hepatoxicants, AAP, MMC and CuCl2 in liver cells was higher than that in kidney cells. Cytotoxicitiy of nephrotoxicant, CdCl2 was lower in liver cells than that in kidney cells, but nephrotoxicant phenacetin and AA was higher cytotoxicity in liver cells than that in kidney cells. The cytotoxicity of AAP and phenacetin was strengthened in the presence of S9 mixture, indicating that they are metabolism-mediated cytotoxicants. All selected chemicals disrupted MPT in dose-dependent manner. Linear regression analysis revealed a good correlation between the IC50 values of cytotoxicity and the EC50 values of MPT in Bel-7402 cells and HK-2 cells (R2 = 0.987 and 0.823, respectively). Cytotoxicity assay in vitro using specific cells show good compatibility with target-organ toxicity in vivo. However, limitations of in vitro cytotoxicity assay are due to its incomplete process of ADME and the defect of predicting chronic toxicity effect after long-term exposure to a chemical.

Primary culture of rat hepatocytes in 96-well plates: Effects of extracellular matrix configuration on cytochrome P450 enzyme activity and inducibility, and its application in in vitro cytotoxicity screening

Basal level enzyme activities and enzyme inducibility were compared for rat hepatocytes that were cultured in 96-well plates with three different extracellular matrix configurations: single layer (SL) collagen type I, SL Matrigel, and collagen/Matrigel (C/M) sandwich. Overall, C/M sandwich and SL Matrigel plates were both superior to SL collagen type I plates in maintaining enzyme activities and inducibility and C/M sandwich plates had higher induced activity for CYP3A enzymes than SL Matrigel plates did. Cytotoxicity of nine reference compounds to rat hepatocytes (C/M sandwich configuration), rat hepatoma H4IIE and mouse fibroblast Balb/c 3T3 (3T3) cells was evaluated in 96-well plates using neutral red uptake (for 3T3) and tetrazolium salt MTS assays (for H4IIE and rat hepatocytes). For compounds chlorpromazine, quinidine, trichlorfon, thiopental, and antipyrine, the absolute differences in cytotoxicity LogIC(50) values obtained from different cell types were relatively small and without an obvious trend. The DeltaLogIC(50) values between cultured hepatocytes and the cell lines were much larger for acetaminophen and cyclophosphamide (1.35 < or =/DeltaLogIC(50)/ < or = 3.40), and for clofibrate and thioacetamide (not cytotoxic in hepatocytes at their highest dose levels). These large differences were likely the result of metabolism of these compounds in rat hepatocytes. The relationship between in vitro cytotoxicity LogIC(50) values and in vivo mouse or rat oral acute LogLD(50) values showed that compared to the cell lines, cultured rat hepatocytes improved correlation for acetaminophen and cyclophosphamide. The potential benefit of conducting in vitro cytotoxicity screening using a combination of permanent cell lines and cultured hepatocytes would allow us to obtain mechanistic insight on bioactivation, as well as improve the predictability of metabolism-mediated toxicity.

An evaluation of the in vitro cytotoxicities of 50 chemicals by using an electrical current exclusion method versus the neutral red uptake and MTT assays

According to the 2001 National Institutes of Health guidance document on using in vitro data to estimate in vivo starting doses for acute toxicity, the performance of the electrical current exclusion method (ECE) was studied for its suitability as an in vitro cytotoxicity test. In a comparative study, two established in vitro assays based on the quantification of metabolic processes necessary for cell proliferation or organelle integrity (the MTT/WST-8 [WST-8] assay and the neutral red uptake [NRU] assay), and two cytoplasm membrane integrity assays (the trypan blue exclusion [TB] and ECE methods), were performed. IC50 values were evaluated for 50 chemicals ranging from low to high toxicity, 46 of which are listed in Halles Registry of Cytotoxicity (RC). A high correlation was found between the IC50 values obtained in this study and the IC50 data published in the RC. The assay sensitivity was highest for the ECE method, and decreased from the WST-8 assay to the NRU assay to the TB assay. The consistent results of the ECE method are based on technical standardisation, high counting rate, and the ability to combine cell viability and cell volume analysis for detection of the first signs of cell necrosis and damage of the cytoplasmic membrane caused by cytotoxic agents.

IN VIVO HEPATOTOXICITY STUDY OF RATS IN COMPARISON WITH IN VITRO HEPATOTOXICITY SCREENING SYSTEM

For the establishment of a high throughput screening system using primary cell cultures, investigation of elucidated toxicities to assess the correlation between in vitro and in vivo hepatotoxicity is necessary in the safety evaluation of the compound. In the previous study, we reported the usability of rat primary cultured hepatocytes for establishment of high throughput screening system. To confirm the reliability of rat primary hepatocytes culture screening system, we conducted a single-dose in vivo study with relatively high dose of hepatotoxicant in rats using 4 reference compounds (acetaminophen, amiodarone, tetracycline, carbon tetrachloride), and investigated histopathological changes and expression of oxidative stress-related proteins by immunohistochemistry. We also carried out a proteomics analysis for estimating the reliable and sensitive biomarkers. Histopathologically, compound-specific hepatotoxicity was detected at 24 hr after administration in all compounds except amiodarone, which is known to induce phospholipidosis. Immunohistochemically, oxidative stress-related proteins were increased within 6 hr after administration in all treated groups. Proteomics analysis revealed several protein biomarkers related to oxidative stress and mitochondrial metabolism-regulation, which had been previously detected by proteomics analysis in in vitro screening system. Oxidative stress-related proteins were considered as useful biomarkers of hepatotoxicity; since they were detected by immunohistochemistry and proteomics analysis prior to appearance of compound-specific histopathological changes detected by light microscopy. Considering the relevance of in vitro system to in vivo system from the aspect of new biomarkers related to the toxicogenomics/toxicoproteomics, in vitro primary cell culture system would be sufficient to detect hepatotoxicity in the early stage of drug discovery.

SIRC-CVS CYTOTOXICITY TEST: AN ALTERNATIVE FOR PREDICTING RODENT ACUTE SYSTEMIC TOXICITY

An in vitro crystal violet staining method using the rabbit cornea-derived cell line (SIRC-CVS) has been developed as an alternative to predict acute systemic toxicity in rodents. Seventy-nine chemicals, the in vitro cytotoxicity of which was already reported by the Multicenter Evaluation of In vitro Toxicity (MEIC) and ICCVAM/ECVAM, were selected as test compounds. The cells were incubated with the chemicals for 72 hrs and the IC(50) and IC(35) values (microg/mL) were obtained. The results were compared to the in vivo (rat or mouse) "most toxic" oral, intraperitoneal, subcutaneous and intravenous LD(50) values (mg/kg) taken from the RTECS database for each of the chemicals by using Pearson's correlation statistics. The following parameters were calculated: accuracy, sensitivity, specificity, prevalence, positive predictability, and negative predictability. Good linear correlations (Pearson's coefficient; r>0.6) were observed between either the IC(50) or the IC(35) values and all the LD(50) values. Among them, a statistically significant high correlation (r=0.8102, p<0.001) required for acute systemic toxicity prediction was obtained between the IC(50) values and the oral LD(50) values. By using the cut-off concentrations of 2,000 mg/kg (LD(50)) and 4,225 microg/mL (IC(50)), no false negatives were observed, and the accuracy was 84.8%. From this, it is concluded that this method could be used to predict the acute systemic toxicity potential of chemicals in rodents.

Comparison of basal cytotoxicity data between mammalian and fish cell lines: A literature survey

During the last 20 years, in vitro assays with fish cells have been used in ecotoxicology for testing chemicals, effluents and in toxicity identification evaluations (TIE) studies. Due to the good correlation found between the in vitro data and the in vivo fish data in ranking chemical toxicity, they have been proposed as an alternative to acute fish bioassays for toxicity screening of chemicals. Nevertheless, they are recognized to be less sensitive when compared with in vivo fish bioassays. Fish cells have slower cell cycles than mammalian cells, so it was suggested that mammalian cells could be more sensitive than fish cells for testing chemicals. However, as fish cells offer some advantages over mammalian cells, mainly related to their ease of handling, some authors found them preferable to use for routine testing. The present study was undertaken to analyze whether mammalian cell lines are more, less, or equally sensitive, compared to fish cells lines. To this end, basal cytotoxicity data from a literature survey of mammalian and fish cell lines have been compared. There was a good linear correlation of IC50 values (r = 0.915) between fish and mammalian cells for a set of 51 chemicals after 24-h of treatment. The correlation coefficient of IC50 values (r = 0.888) decreased when 24-h treated mammalian cells were correlated against 48-h treated fish cell lines. For the dataset selected for this study, fish and mammalian cells showed a similar sensitivity for most of the chemicals after being treated for 24 h. We conclude that fish and mammalian cells can equally well predict the basal toxicity of the set of chemicals used in this study, and that increased exposure periods did not increase the correlation between midpoint toxicities nor sensitivities for any of the cell lines used. The more practical handling of fish cells favors their recommendation as a better alternative for replacing fish bioassay than mammalian cells.

Experimental survey of non-clonogenic viability assays for adherent cells in vitro

Results of rapid cell viability assays were experimentally compared in order to reveal the most suitable test for in vitro investigations of the combination of photodynamic therapy (PDT) with chemotherapeutic drugs. meso-Tetra(3-hydroxyphenyl)-chlorin (m-THPC) accumulating in cell membranes and meso-tetra(4-sulfonatophenyl)-porphin (TPPS4) accumulating in lysosomes were used as photosensitisers. Doxorubicin that localises, mainly, to nucleus and vincristine that binds to microtubules were used as cytostatic drugs. Two adherent rodent cell lines, baby hamster kidney (BHK-21) and murine hepatoma (MH-22A), were used to examine the contribution of a cell. We tested cytotoxicity assays of the main groups of fast (non-clonogenic) methods of cell viability measuring. Plasma membrane integrity was estimated by trypan blue exclusion and LDH leakage, metabolic activity was tested by [3H]-thymidine incorporation and MTT assay, loss of monolayer adherence was measured by staining with crystal violet and CyQUANT. The most sensitive test in each case was the assay related to the site of the direct damage, and measurement of the loss of monolayer adherence proved to be as sensitive assay as the damage-specific one. All the assays applied, except for the LDH release, revealed a higher effect of combination of m-THPC-mediated phototreatment and doxorubicin compared to either of the single treatments.

INVESTIGATION OF A HEPATOTOXICITY SCREENING SYSTEM IN PRIMARY CELL CULTURES-"WHAT BIOMARKERS WOULD NEED TO BE ADDRESSED TO ESTIMATE TOXICITY IN CONVENTIONAL AND NEW APPROACHES?"-

High throughput toxicological estimation is required for safety evaluation in the early stage of drug discovery. In this context, establishment of an in vitro screening system reflecting in vivo toxicity is demanded for earlier safety assessment. We investigated LDH release and mitochondrial respiration (WST-1 reduction assay; WST-1) to detect cytotoxicity, morphological evaluation, and proteomics for estimating the reliable and sensitive biomarkers by using rat primary hepatocytes exposed to the compounds (acetaminophen, amiodarone, tetracycline and carbon tetrachloride) that are known to induce hepatotoxicity. In LDH release, no significant difference was detected between the control and compound exposed cells after exposure for 3 or 6 hr, but a dose-dependent increase was observed after exposure for 24 hr. Regarding the WST-1 assay, a dose-dependent reduction was detected after exposure for 6 and 24 hr to all of the compounds evaluated. In the proteomics analysis, 31 candidate proteins were identified from among the 103 demonstrating altered expression spots after exposure to acetaminophen. It was concluded that the cytotoxicity was detected earlier by measuring WST-1 than by measuring LDH release because the reduction of mitochondrial respiration is an expressions of earlier toxicity for cellular function, while the measured increase in the LDH release occurs after the failure of the cell membrane. Mitochondrial respiration ability was a useful parameter for cytotoxicity in in vitro hepato-toxicity screening, as cytotoxicity can be detected during the early stage of exposure. In addition to the conventional biomarkers, several protein biomarkers which relate to oxidative stress and metabolism-regulation were detected. Further comprehensive analysis of defined proteins would be necessary to estimate the more sensitive toxicology biomarker.

A physiological perspective on the swelling properties of the mammalian corneal stroma

PURPOSE

The present studies were designed to assess whether measurement of corneal stroma swelling in the laboratory, especially in non-physiological solutions, was associated with a measurable effect on the keratocytes.

METHODS

Complete corneal stroma preparations were made from quality- and age-selected recent post-mortem cattle eyes. These were either assessed immediately or incubated in three different solutions, namely a balanced salts solution with glucose (BSSG), isotonic phosphate buffered saline (PBS) or pure water. Incubations were carried out at 37 degrees C for 9h, and repeated measures of wet mass made so that the rates and extent of swelling could be determined. After incubation, an aqueous extract was made of the stroma for measurements of the levels the enzymes lactate dehydrogenase (LDH), aldehyde dehydrogenase (ALDH) and N-acetyl-beta-glucosaminidase.

RESULTS

The initial rates of swelling were lowest in BSSG, marginally faster in PBS and much faster in water. The secondary rates of swelling showed the same sequence being 10.0%/h in BSSG, 14.8%/h in PBS and 34.2%/h in water. Compared to non-incubated preparations, reductions in all three enzyme activities occurred. For LDH, these were 15% with BSSG, 40% in PBS and 80% with water. Similar results were seen with ALDH activity when comparing the three incubation solutions, while incubation in BSSG also resulted in a substantial (40%) reduction in N-acetyl-glucosaminidase activity.

CONCLUSIONS

When immersed in an isotonic BSSG with added glucose at 37 degrees C, the swelling of a complete bovine corneal stroma is much less than smaller pieces of stroma, and also slightly less than if isotonic PBS was used. With the use of BSSG, little or no change in cytoplasmic enzyme activities occurred, but measurable decreases were noted with PBS and very substantial decreases when water was used, indicating a toxic effect on the keratocytes. The observation that substantial decreases in a lysosomal enzyme activity could occur even with the use of BSSG indicate substantial stress is imposed on the stroma during these types of experiments. Notwithstanding, the data collectively indicate that the keratocyte cells within the collagen matrix of the stroma can be substantially damaged and this needs to be taken into account in future experiments on the true physiology of the corneal stroma.

In vitro-in vivo extrapolation: estimation of human serum concentrations of chemicals equivalent to cytotoxic concentrations in vitro

In the present study an extrapolation model for estimating serum concentrations of chemicals equivalent to in vitro effective concentrations is developed and applied to median cytotoxic concentrations (EC(50)) determined in vitro. Nominal concentrations of a chemical in serum and in vitro are regarded as equivalent, if they result in the same aqueous concentration of the unbound form. The algorithm used is based on equilibrium distribution and requires albumin binding data, the octanol-water partition coefficient (K(ow)), and the albumin concentrations and lipid volume fractions in vitro and in serum. The chemicals studied cover wide ranges of cytotoxic potency (EC(50): 2.5-530,000 microM) and lipophilicity (logK(ow): -5 to 7). Their albumin binding characteristics have been determined by means of an in vitro cytotoxicity test as described previously. The equivalent serum concentrations of 19 of the 33 compounds investigated, having high protein binding and/or lipophilicity, were substantially higher than the EC(50)-values, by factors of 2.5-58. Prominent deviations between the equivalent nominal concentrations in serum and in vitro were largely restricted to chemicals with higher cytotoxic potency (EC(50)< or =1000 microM). The results suggest that estimates of equivalent serum concentrations based on in vitro data are robust for chemicals with low lipophilicity (logK(ow)< or =2) and low potency (EC(50)>1000 microM). With more potent chemicals or those with higher lipophilicity partitioning into lipids and/or binding to serum proteins have to be taken into account when estimating in vivo serum concentrations equivalent to in vitro effective concentrations.

Serum albumin binding at cytotoxic concentrations of chemicals as determined with a cell proliferation assay

The aim of the present study was to measure the influence of albumin binding on cytotoxic concentrations of chemicals and to determine binding parameters which can be used for quantitative in vitro-in vivo extrapolations. Protein binding parameters were determined from cytotoxic potencies measured with Balb/c 3T3 cells cultured in the presence of 18 and 600 microM bovine serum albumin (BSA). A subset of 27 chemicals from the Multicenter Evaluation of In Vitro Cytotoxicity (MEIC) project was investigated. At 18 microM BSA the EC(50)-values ranged from 2.54 microM (As(III)) to 527 mM (ethylene glycol). Increasing the BSA concentration either decreased the cytotoxic potency (12 compounds) by factors up to 34 (pentachlorophenol), had no effect (14 compounds), or increased the cytotoxicity (paraquat). Calculated molar ratios of binding ranged from 0.05 (Hg(2+)) to 4.8 moles per mole albumin (acetylic salicylic acid). At 18 microM BSA fractional binding of most of these compounds was low (<25%) but increased up to > or =90% (hexachlorophene, mercuric chloride, thioridazine, pentachlorophenol) at 600 microM BSA. The results obtained in general were compatible with available protein binding data and can be used to calculate equipotent concentrations of chemicals in biological systems containing different albumin concentrations.

Advantages of in vitro cytotoxicity testing by using primary rat hepatocytes in comparison with established cell lines

We investigated and compared the cytotoxicity of 16 reference compounds in four in vitro systems: primary cultured rat hepatocytes, hepatoma HepG2 cell line, non-hepatic HeLa and Balb/c 3T3 cell lines. After 24 hr of exposure to the test compounds, the water-soluble tetrazolium salts WST-1 assay was used as an endpoint to evaluate cytotoxicity. Acetaminophen, diclofenac sodium cyclophosphamide and disulfiram displayed from 2 to more than 10 times higher IC50 values in three cell lines than in rat primary cultured hepatocytes. The cytotoxic effects of aspirin, amiodarone, clorfibiric acid, chlorpromazine, erythomycin, lithocholic acid, cisplatin and quinidine in rat hepatocytes were similar or 2 times stronger than those observed in cell lines. Ketoconazole resulted in the lowest IC50 value in the HeLa cell line. The data suggested that the compounds which are known to be metabolism-mediated liver toxicants have a differential hepatotoxicity in vitro and that primary cultured rat hepatocytes could represent a valuable tool for both screening and study of the effects of bio-transformation on the cytotoxicity of new chemical entities and xenobiotics in vitro.

Lactate dehydrogenase activity as an effect criterion in toxicity tests with Daphnia magna straus

Activity of lactate dehydrogenase (LDH) was used as an effect criterion in toxicity tests with Daphnia magna. In the first part of the work, the conditions for the use of LDH activity in toxicity tests with juveniles and adults of D. magna, were optimized. The influence of parameters such as the number of animals per sample, nutritional status, age and the presence of eggs in the brood chamber were investigated. In the second part of the study, both in vivo and in vitro tests based on the alteration of LDH activity of D. magna were developed and tested using zinc chloride as test substance. The results obtained indicate that LDH activity of D. magna may be used as an indicative parameter in aquatic toxicity tests.

Development of a high throughput in vitro toxicity screen predictive of high acute in vivo toxic potential

At an early stage of drug discovery high throughput screens are an invaluable tool to de-select compounds with undesirable properties. A high throughout in vitro toxicity screen has been developed and validated to identify compounds that have a high potential to be acutely toxic in vivo. This screen is based on treating Chinese hamster ovary (CHO) cells with test compounds for 24 h and then determining the degree of cytotoxicity by the reduction of Resazurin. Twenty-six structurally unrelated compounds were chosen that spanned a range of acute LD(50) values and mechanisms of toxicity. The acute LD(50) values (intraperitoneal and intravenous routes) from rat and mouse were taken from the RTECS database. Experimentally derived in vitro IC(35) results were compared to the 'most toxic' (lowest) LD(50) values for each compound. The resulting correlation was statistically significant (r=0.8475). However, due to the scatter of the data points, it was considered not appropriate to rank compounds according to their degree of in vivo toxicity on the basis of the in vitro result. However, by defining cut-off concentrations for both the in vivo (LD(50)) and the in vitro (IC(35)) values it was possible, using the in vitro result (IC(35) <10 microM), to identify compounds that had a high potential to be acutely toxic in vivo ('most toxic' LD(50) <25 micromol/kg). Further development led to a high throughput screen capable of giving a 'Yes', 'No' or 'Borderline' classification as to whether a compound has a high acute in vivo toxic potential. This screen is highly specific (no false positive classifications) and has a sensitivity of approximately 80%. This is deemed acceptable for a first tier toxicity screen at an early stage in the drug discovery process. Transfer of this screen from GlaxoSmithKline UK to sites in Italy, Spain and the USA resulted in very similar findings indicating the inter-laboratory robustness of this screen and therefore the ability to compare results across the GlaxoSmithKline sites.