An epidermal equivalent assay for identification and ranking potency of contact sensitizers

The purpose of this study was to explore the possibility of combining the epidermal equivalent (EE) potency assay with the assay which assesses release of interleukin-18 (IL-18) to provide a single test for identification and classification of skin sensitizing chemicals, including chemicals of low water solubility or stability. A protocol was developed using different 3D-epidermal models including in house VUMC model, epiCS® (previously EST1000™), MatTek EpiDerm™ and SkinEthic™ RHE and also the impact of different vehicles (acetone:olive oil 4:1, 1% DMSO, ethanol, water) was investigated. Following topical exposure for 24 h to 17 contact allergens and 13 non-sensitizers a robust increase in IL-18 release was observed only after exposure to contact allergens. A putative prediction model is proposed from data obtained from two laboratories yielding 95% accuracy. Correlating the in vitro EE sensitizer potency data, which assesses the chemical concentration which results in 50% cytotoxicity (EE-EC₅₀) with human and animal data showed a superior correlation with human DSA₀₅ (μg/cm²) data (Spearman r = 0.8500; P value (two-tailed) = 0.0061) compared to LLNA data (Spearman r = 0.5968; P value (two-tailed) = 0.0542). DSA₀₅ = induction dose per skin area that produces a positive response in 5% of the tested population Also a good correlation was observed for release of IL-18 (SI-2) into culture supernatants with human DSA₀₅ data (Spearman r = 0.8333; P value (two-tailed) = 0.0154). This easily transferable human in vitro assay appears to be very promising, but additional testing of a larger chemical set with the different EE models is required to fully evaluate the utility of this assay and to establish a definitive prediction model.     

Polyglutamic acid-based nanocomposites as efficient non-viral gene carriers in vitro and in vivo

A series of polyethylenimine (PEI) and γ-polyglutamic acid (PGA) nanocomposites (PPGA) was prepared and evaluated in terms of their cell viability and transfection efficiency in vitro and in vivo. On complexion with pDNA, the positively charged PPGA/DNA nanocomposites resulted in a higher level of in vitro reporter gene transfection (2.7-7.9-fold) as compared to native PEI, and selected commercial reagents and >95% cell viability in HEK293, HeLa and HepG2 cell lines. Further, PPGA-5 nanocomposite (the best working system in terms of transfection efficiency among the series) was found to efficiently transfect primary mouse keratinocytes up to 22% above the control level. PPGA-5, when tested for in vivo cytotoxicity in Drosophila, did not induce any stress in the exposed larvae in comparison with control. In vivo gene expression using PPGA-5 showed the highest transfection efficiency in spleen of mouse closely followed by heart tissues after intravenous injection through tail vein. Besides, these nanocomposites also delivered siRNA efficiently into mammalian cells, resulting in ∼80% suppression of EGFP expression. These results together demonstrated the potential of the projected nanocomposites for in vivo gene delivery.     

A high-throughput method for assessing chemical toxicity using a Caenorhabditis elegans reproduction assay

The National Research Council has outlined the need for non-mammalian toxicological models to test the potential health effects of a large number of chemicals while also reducing the use of traditional animal models. The nematode Caenorhabditis elegans is an attractive alternative model because of its well-characterized and evolutionarily conserved biology, low cost, and ability to be used in high-throughput screening. A high-throughput method is described for quantifying the reproductive capacity of C. elegans exposed to chemicals for 48 h from the last larval stage (L4) to adulthood using a COPAS Biosort. Initially, the effects of exposure conditions that could influence reproduction were defined. Concentrations of DMSO vehicle ≤ 1% did not affect reproduction. Previous studies indicated that C. elegans may be influenced by exposure to low pH conditions. At pHs greater than 4.5, C. elegans reproduction was not affected; however below this pH there was a significant decrease in the number of offspring. Cadmium chloride was chosen as a model toxicant to verify that automated measurements were comparable to those of traditional observational studies. EC₅₀ values for cadmium for automated measurements (176-192 µM) were comparable to those previously reported for a 72-h exposure using manual counting (151 µM). The toxicity of seven test toxicants on C. elegans reproduction was highly correlative with rodent lethality suggesting that this assay may be useful in predicting the potential toxicity of chemicals in other organisms.     

Inhibition of the Rho/ROCK pathway prevents neuronal degeneration in vitro and in vivo following methylmercury exposure

Methylmercury (MeHg) is an environmental neurotoxicant which induces neuropathological changes in both the central nervous and peripheral sensory nervous systems. Our recent study demonstrated that down-regulation of Ras-related C3 botulinum toxin substrate 1 (Rac1), which is known to promote neuritic extension, preceded MeHg-induced damage in cultured cortical neurons, suggesting that MeHg-mediated axonal degeneration is due to the disturbance of neuritic extension. Therefore we hypothesized that MeHg-induced axonal degeneration might be caused by neuritic extension/retraction incoordination. This idea brought our attention to the Ras homolog gene (Rho)/Rho-associated coiled coil-forming protein kinase (ROCK) pathway because it has been known to be associated with the development of axon and apoptotic neuronal cell death. Here we show that inhibition of the Rho/ROCK pathway prevents MeHg-intoxication both in vitro and in vivo. A Rho inhibitor, C3 toxin, and 2 ROCK inhibitors, Fasudil and Y-27632, significantly protected against MeHg-induced axonal degeneration and apoptotic neuronal cell death in cultured cortical neuronal cells exposed to 100 nM MeHg for 3 days. Furthermore, Fasudil partially prevented the loss of large pale neurons in dorsal root ganglia, axonal degeneration in dorsal spinal root nerves, and vacuolar degeneration in the dorsal columns of the spinal cord in MeHg-intoxicated model rats (20 ppm MeHg in drinking water for 28 days). Hind limb crossing sign, a characteristic MeHg-intoxicated sign, was significantly suppressed in this model. The results suggest that inhibition of the Rho/ROCK pathway rescues MeHg-mediated neuritic extension/retraction incoordination and is effective for the prevention of MeHg-induced axonal degeneration and apoptotic neuronal cell death.     

Genotoxic activities of the food contaminant 5-hydroxymethylfurfural using different in vitro bioassays

5-Hydroxymethylfurfural (5-HMF) is known as an indicator of quality deterioration in a wide range of foods. 5-HMF is formed as an intermediate in the Maillard reaction and has been identified in a wide variety of heat-processed foods. In recent years, the presence of 5-HMF in foods has raised toxicological concerns: data have shown cytotoxic, genotoxic and tumoral effects but further studies suggest that 5-HMF does not pose a serious health risk. However the subject is still a matter of debate. We investigated the genotoxicity of the food-borne contaminant 5-HMF using the Ames test, the micronucleus (MN) and the single-cell gel electrophoresis (SCGE) assays in the human metabolically active HepG2 cell line. Cytotoxic effect of 5-HMF was first assessed using Alamar Blue™ as a sensitive sub-lethal assay. 5-HMF did not induce any genic mutation in bacteria whatever the concentration in the Ames test. Furthermore, it does not induce clastogenic or aneugenic effects in the HepG2 cells. In contrast, 5-HMF induced HepG2 DNA damage at concentrations from 7.87 to 25 mM in the comet assay suggesting a weak genotoxic effect of 5-HMF in the HepG2 cells probably repaired.     

Effect of green tea on pharmacokinetics of 5-fluorouracil in rats and pharmacodynamics in human cell lines in vitro

Tea drinking is widely practiced in the world and has recently increased among cancer patients. However, the effects of concurrent consumption of tea on the bioavailability and the net therapeutic potential of co-administered chemical drugs are not clear. In this study, the effects of green tea on the pharmacokinetics of 5-fluorouracil (5-FU) in rats and the pharmacodynamics in human cell lines in vitro were studied. The pharmacokinetic experiment indicated that there was an approximately 151% increase in the maximum plasma concentration (C_max) and an approximately 425% increase in the area under the plasma concentration curve (AUC) of 5-FU in the green tea-treated group compared with the control group. Green tea consumption increased the plasma concentration of 5-FU. In addition, the pharmacodynamics experiment showed that at the moderate dose level (equivalent to <6 cups daily in human), neither fresh green tea extract nor (−)-epigallocatechin-3-gallate (EGCG) showed significant additive effects on the cytotoxicity of 5-FU in human cell lines. The results showed that it is crucial to perform therapeutic drug monitoring (TDM) when the cancer patients have a habit of drinking green tea.     

Evaluation of in vitro cytotoxicity of 6-benzylaminopurine carboplatin derivatives against human cancer cell lines and primary human hepatocytes

A series of seven platinum(II) cyclobutane-1,1-dicarboxylato (cbdc) complexes {[Pt(cbdc)(L_n)₂], 1-7}, derived from carboplatin by a substitution of two NH₃ molecules for two 2,6,9-trisubstituted 6-benzylaminopurine-based N-donor ligands (L_n), was studied by the MTT assay for their in vitro cytotoxic activity against seven human cancer cell lines, i.e. lung carcinoma (A549), cervix epithelioid carcinoma (HeLa), osteosarcoma (HOS), malignant melanoma (G361), breast adenocarcinoma (MCF7), ovarian carcinoma (A2780) and its cisplatin-resistant analogue (A2780cis), and against two primary cultures of human hepatocytes (LH31 and LH32). The prepared complexes were cytotoxic against several cancer cells, in some cases even more than cisplatin. The best results were achieved for complexes 1 (IC₅₀ = 17.4 ± 2.0 μM) and 2 (IC₅₀ = 14.8 ± 2.1 μΜ) against HOS cells, 1 (IC₅₀ = 15.1 ± 6.8 μM), 2 (IC₅₀ = 13.6 ± 5.2 μM) and 6 (IC₅₀ = 19.0 ± 6.6 μM) against MCF7, 6 (IC₅₀ = 6.4 ± 0.1 μM) against A2780, and 1-6 (IC₅₀ = 15.6 ± 4.0, 12.9 ± 3.7, 15.8 ± 3.8, 16.6 ± 5.5, 22.1 ± 2.5, and 5.6 ± 1.7 μM, respectively) against A2780cis. Viability of human hepatocytes was not declined by the tested complexes up to the concentration of 50 μM (for 1, 3-7) and 20 μM (for 2; caused by lower solubility of this complex).     

Evaluation of the cytotoxicity of 10 chemicals in human and rat hepatocytes and in cell lines: Correlation between in vitro data and human lethal concentration

The cytotoxicity of 10 chemicals from the Multicentre Evaluation of In vitro Cytotoxicity (MEIC) list (nos 21–30) was evaluated in human and rat cultured hepatocytes and in two established cell lines (HepG2 and 3T3) according to the MEIC programme organized by the Scandinavian Society of Cell Toxicology. The MTT test was used as the endpoint of cytotoxicity after 24hr of exposure to the chemicals. Theophylline, phenobarbital and paraquat were the least cytotoxic compounds in the cellular systems (IC₅₀ = 450-17,000 μm) except for the 3T3 cells. The seven remaining chemicals (dextropropoxyphene, propranolol, arsenic trioxide, cupric sulfate, mercuric chloride, thioridazine and thallium sulfate) showed a similar relative cytotoxic ranking in the four in vitro systems in the lower range of concentrations (IC₅₀ = 2–350 μm). The data suggest that these 10 chemicals have a basal cytotoxic effect common to the four in vitro systems, and probably none of these compounds could be considered either hepatotoxic or species specific. The correlation between in vitro data and human lethal blood concentrations showed that the predictability of the in vitro systems was similar to that of in vivo rodent tests (LD₅₀) only when low cytotoxic concentrations (IC₁₀) were used for correlation.     

The intra- and inter-laboratory reproducibility and predictivity of the KeratinoSens assay to predict skin sensitizers in vitro: Results of a ring-study in five laboratories

Due to regulatory constraints and ethical considerations, research on alternatives to animal testing to predict the skin sensitization potential of novel chemicals has gained a high priority. Accordingly, different in vitro, in silico and in chemico approaches have been described in the scientific literature to achieve this goal. To replace regulatory approved animal tests, these alternatives need to be transferable to other labs, their within and between laboratory reproducibility must be assured, and their predictivity should be high. The KeratinoSens assay is a cell-based reporter gene assay to screen substances with a full dose-response assessment. It is based on a stable transgenic keratinocyte cell line. The induction of a luciferase gene under the control of the antioxidant response element (ARE) derived from the human AKR1C2 gene is determined. Here we report on the results of a ring-study with five laboratories performing the KeratinoSens assay on a set of 28 test substances. The assay was found to be easily transferable to all laboratories. Overall both the qualitative (sensitizer/non-sensitizer categorization) and the quantitative (concentration for significant gene induction) results were reproducible between laboratories. A detailed analysis of the transferability, the within- and between laboratory reproducibility and the predictivity is presented.     

Chlorpyrifos and its metabolites alter gene expression at non-cytotoxic concentrations in D3 mouse embryonic stem cells under in vitro differentiation: Considerations for embryotoxic risk assessment

The effects of organophosphate insecticide chlorpyrifos (CPF) on development are currently under discussion. CPF and its metabolites, chlorpyrifos-oxon (CPO) and 3,5,6-trichloro-2-pyridinol (TClP), were more cytotoxic for D3 mouse embryonic stem cells than for differentiated fibroblasts 3T3 cells. Exposure to 10 μM CPF and TClP and 100 μM CPO for 12 h significantly altered the in vitro expression of biomarkers of differentiation in D3 cells. Similarly, exposure to 20 μM CPF and 25 μM CPO and TClP for 3 days also altered the expression of the biomarkers in the same model. These exposures caused no significant reduction in D3 viability with mild inhibition of acetylcholinesterase and neuropathy target esterase by CPF and severe inhibition by CPO. We conclude that certain in vivo exposure scenarios are possible, which cause inhibition of acetylcholinesterase but without clinical symptoms that reach high enough systemic CPF concentrations able to alter the expression of genes involved in cellular differentiation with potentially hazard effects on development. Conversely, the risk for embryotoxicity by CPO and TClP was very low because the required exposure would induce severe cholinergic syndrome.     

Synergistic drug-cytokine induction of hepatocellular death as an in vitro approach for the study of inflammation-associated idiosyncratic drug hepatotoxicity

Idiosyncratic drug hepatotoxicity represents a major problem in drug development due to inadequacy of current preclinical screening assays, but recently established rodent models utilizing bacterial LPS co-administration to induce an inflammatory background have successfully reproduced idiosyncratic hepatotoxicity signatures for certain drugs. However, the low-throughput nature of these models renders them problematic for employment as preclinical screening assays. Here, we present an analogous, but high-throughput, in vitro approach in which drugs are administered to a variety of cell types (primary human and rat hepatocytes and the human HepG2 cell line) across a landscape of inflammatory contexts containing LPS and cytokines TNF, IFNγ, IL-1α, and IL-6. Using this assay, we observed drug-cytokine hepatotoxicity synergies for multiple idiosyncratic hepatotoxicants (ranitidine, trovafloxacin, nefazodone, nimesulide, clarithromycin, and telithromycin) but not for their corresponding non-toxic control compounds (famotidine, levofloxacin, buspirone, and aspirin). A larger compendium of drug-cytokine mix hepatotoxicity data demonstrated that hepatotoxicity synergies were largely potentiated by TNF, IL-1α, and LPS within the context of multi-cytokine mixes. Then, we screened 90 drugs for cytokine synergy in human hepatocytes and found that a significantly larger fraction of the idiosyncratic hepatotoxicants (19%) synergized with a single cytokine mix than did the non-hepatotoxic drugs (3%). Finally, we used an information theoretic approach to ascertain especially informative subsets of cytokine treatments for most highly effective construction of regression models for drug- and cytokine mix-induced hepatotoxicities across these cell systems. Our results suggest that this drug-cytokine co-treatment approach could provide a useful preclinical tool for investigating inflammation-associated idiosyncratic drug hepatotoxicity.     

Flavanones and rotenoids from the roots of Amorpha fruticosa L. that inhibit bacterial neuraminidase

Neuraminidase is a proven target in anti-viral drug development. It also appears to be important for infection by certain pathogenic bacteria and has been implicated in biofilm formation. Based on activity-guided fractionation, the acetone extract of Amorpha fruticosa roots gave four flavanones 1-4 and three rotenoids 5-7 which were identified as amoradicin (1), amorisin (2), isoamoritin (3), amoricin (4), amorphigeni (5), dalbinol (6), and 6-ketodehydroamorphigenin (7), respectively. All isolated inhibitors showed strong neuraminidase inhibition with IC₅₀s between 0.12 and 22.03 μM. In particular, amorisin 2 exhibited 120 nM IC₅₀, which is 30-fold more potent than the positive control, quercetin. In addition, this is the first report detailing rotenoids (IC₅₀ = 8.34-16.74 μM) exhibiting neuraminidase inhibition. Kinetic analysis revealed that all inhibitors were noncompetitive. The most active neuraminidase inhibitors (2, 3, 5, 6) were proven to be present in the native root in high quantities by HPLC. Finally, at concentrations where no toxicity was observed, 3 and 6 inhibited Pseudomonas aeruginosa biofilm production. 29.7% and 21.0% inhibition respectively was observed at 25 μΜ.     

Mechanistic insights into antitumor effects of new dinuclear cis Pt complexes containing aromatic linkers

The primary objective was to understand more deeply the molecular mechanism underlying different antitumor effects of dinuclear Pt^II complexes containing aromatic linkers of different length, {[cis-Pt(NH₃)₂Cl]₂(4,4′-methylenedianiline)}²⁺ (1) and {[cis-Pt(NH₃)₂Cl]₂(α,α′-diamino-p-xylene)}²⁺ (2). These complexes belong to a new generation of promising polynuclear platinum drugs resistant to decomposition by sulfur nucleophiles which hampers clinical use of bifunctional polynuclear trans Pt^II complexes hitherto tested. Results obtained with the aid of methods of molecular biophysics and pharmacology reveal differences and new details of DNA modifications by 1 and 2 and recognition of these modifications by cellular components. The results indicate that the unique properties of DNA interstrand cross-links of this class of polynuclear platinum complexes and recognition of these cross-links may play a prevalent role in antitumor effects of these metallodrugs. Moreover, the results show for the first time a strong specific recognition and binding of high-mobility-group-domain proteins, which are known to modulate antitumor effects of clinically used platinum drugs, to DNA modified by a polynuclear platinum complex.     

A critical review of the data related to the safety of quercetin and lack of evidence of in vivo toxicity, including lack of genotoxic/carcinogenic properties.

Quercetin is a naturally-occurring flavonol (a member of the flavonoid family of compounds) that has a long history of consumption as part of the normal human diet. Because a number of biological properties of quercetin may be beneficial to human health, interest in the addition of this flavonol to various traditional food products has been increasing. Prior to the use of quercetin in food applications that would increase intake beyond that from naturally-occurring levels of the flavonol in the typical Western diet, its safety needs to be established or confirmed. This review provides a critical examination of the scientific literature associated with the safety of quercetin. Results of numerous genotoxicity and mutagenicity, short- and long-term animal, and human studies are reviewed in the context of quercetin exposure in vivo. To reconcile results of in vitro studies, which consistently demonstrated quercetin-related mutagenicity to the absence of carcinogenicity in vivo, the mechanisms that lead to the apparent in vitro mutagenicity, and those that ensure absence of quercetin toxicity in vivo are discussed. The weight of the available evidence supports the safety of quercetin for addition to food.