Use of mammalian DNA repair-deficient mutants to assess the effects of toxic metal compounds on DNA

Wild-type and repair-deficient cell lines ( EM9 ) of Chinese Hamster Ovary cells were utilized to assess cytotoxic responses towards metals that produce lesions in DNA. Alkaline elution studies indicated that both CaCrO4 and HgCl2 induced single-strand breaks in the DNA. CaCrO4 and HgCl2 treatments of intact Chinese hamster ovary cells also caused the induction of DNA cross links. The mutant cells, which are thought to have a defect in the repair polymerase enzyme and therefore exhibit greater sensitivity towards a variety of agents that produce lesions in the DNA such as X-rays and ultraviolet-light, also displayed a greater sensitivity, compared to wild-type cells, towards the cytotoxic response of HgCl2 and CaCrO4 . For example, the IC50 (concentration producing a 50% growth inhibition) following exposure for 6-hr to CaCrO4 or 1 hr to HgCl2 was 3.4-fold or 1.8- to 3.9-fold greater in wild-type cells compared to repair-deficient cells respectively. Mutant cells compared to wild-type cells were not more sensitive to growth inhibition by agents whose primary site of action was not at the DNA level (i.e. amphotericin B, trifluoroperazine and cycloheximide). The DNA crosslinks induced by exposure to 10 microM CaCrO4 for 6 hr were almost completely repaired in wild-type cells within 24 hr, whereas in similarly exposed mutant cells this lesion was initially more pronounced and was only partially repaired following a 24-hr recovery period in the absence of CaCrO4 . The repair of single-strand breaks induced by CaCrO4 was more rapid and similar in both wild-type and mutant cells. Since Hg(II) inhibits repair of single-strand breaks, we could not study repair of this lesion induced by this agent; however, at very low concentrations (1 microM) binding of 203Hg(II) to DNA was greater in the mutant cells compared to the wild-type cells. Following removal of 203Hg(II) from the media, mutant cells generally retained more 203Hg bound to DNA relative to the total 203Hg(II) present in the cell. These results demonstrate that an important toxic action of CaCrO4 and HgCl2 involves injury to DNA since the concentrations of these metals causing measurable DNA damage were consistent with their respective cytotoxic concentrations and DNA repair-deficient mutants displayed both enhanced cytotoxicity and decreased repair of metal-induced lesions.     

Use of nontarget organism Chironomus sancticaroli to study the toxic effects of nanoatrazine

Atrazine was banned by the European Union in 2004, but is still used in many countries. Agricultural research employing nanotechnology has been developed in order to reduce the impacts to the environment and nontarget organisms. Nanoatrazine was developed as a carrier system and have been considered efficient in weed control. However, its toxicity must be verified with nontarget organisms. In this context, the aim of the present study was to investigate ecotoxicological effects of solid lipid nanoparticles (empty and loaded with atrazine) and atrazine on Chironomus sancticaroli larvae, evaluating the endpoints: mortality, mentum deformity, development rate and biochemical biomarkers. The contaminant concentrations used were 2, 470, 950, and 1900 μg L⁻¹ in acute (96 h) and 2 μg L⁻¹ in subchronic (10 days) bioassays. An environmentally relevant concentration of atrazine (2 μg L⁻¹) presented toxic and lethal effects towards the larvae. The nanoparticles loaded with atrazine showed toxic effects similar to free atrazine, causing mortality and biochemical alterations on the larvae. The nanoparticle without atrazine caused biochemical alterations and mortality, indicating a possible toxic effect of the formulation on the larvae. In the acute bioassay, most concentrations of nanoparticles loaded with atrazine were not dose dependent for the endpoint mortality. Only the atrazine concentration of 470 μg L⁻¹ was statistically significant to endpoint mentum deformity. The atrazine and nanoparticles (with and without atrazine) did not affect larval development. The results indicate that Chironomus sancticaroli was sensitive to monitor nanoatrazine, presenting potential to be used in studies of toxicity of nanopesticides.

     

Comparison of two in vitro systems to assess cellular effects of nanoparticles-containing aerosols

Inhalation treatment with nanoparticle containing aerosols appears a promising new therapeutic option but new formulations have to be assessed for efficacy and toxicity. We evaluated the utility of a VITROCELL®6 PT-CF + PARI LC SPRINT® Baby Nebulizer (PARI BOY) system compared with a conventional MicroSprayer. A549 cells were cultured in the air–liquid interface, exposed to nanoparticle aerosols and characterized by measurement of transepithelial electrical resistance and staining for tight junction proteins. Deposition and distribution rates of polystyrene particles and of carbon nanotubes on the cells were assessed. In addition, cytotoxicity of aerosols containing polystyrene particles was compared with cytotoxicity of polystyrene particles in suspension tested in submersed cultures. Exposure by itself in both exposure systems did not damage the cells. Deposition rates of aerosolized polystyrene particles were about 700 times and that of carbon nanotubes about 4 times higher in the MicroSprayer than in the VITROCELL®6 PT-CF system. Cytotoxicity of amine-functionalized polystyrene nanoparticles was significantly higher when applied as an aerosol on cell cultured in air–liquid interface culture compared with nanoparticle suspensions tested in submersed culture. The higher cytotoxicity of aerosolized nanoparticles underscores the importance of relevant exposure systems.     

A regulatory approach to assess the potency of substances toxic to the reproduction

In order to develop a method for setting specific concentration limits (SCLs) for substances toxic to the reproduction within the European classification and labelling system, this study investigated possible parameters for reproductive toxicity potency and the quantitative distribution of those parameters. For that purpose, two databases were created comprising substances classified in the European Union for developmental toxicity or for effects on sexual function and fertility. For these substances six parameters including NOAEL, LOAEL and ED₁₀ were determined for effects on reproduction based on existing data summaries. The potency was defined independent of the type of reproductive effect as generally severe effects on reproduction warranting classification were already observed at the lowest dose showing reproductive effects. The reproductive toxicity potency range of substances in the databases was a factor of approximately one million. This shows that SCL setting is needed to adjust the classification of mixtures. The average potency distribution of substances classified according to the hazard classification as required by the European CLP regulation in category 1 versus category 2 was similar. The ED₁₀ for effects warranting classification is proposed as the best parameter for the potency based on its independence of administered dose levels.     

Use of the SPA in assessing toxic effects on male fertilizing potential

The sperm penetration assay (SPA), which involves the use of zona-free hamster eggs to assess fertilizing potential of human spermatozoa, has the capability of evaluating the functional capacity of sperm. If men are exposed to a toxic insult that could result in impaired fertility, this has been monitored historically by determining the routine semen parameters of concentration, motility, and morphology. The lack of availability of the SPA for evaluating toxic exposure in field studies has hampered its utilization. The purpose of this article is to illustrate the use of the SPA in a specific field study and to describe to recent innovations in the SPA that make its use more accessible for field studies. These two innovations are shipping semen samples in TEST-yolk buffer by overnight express to a central laboratory for testing and using frozen hamster eggs in the test. The report is divided into the following three major sections: I. Kunia study; II. TEST-yolk buffer modifications of SPA; and III. Use of frozen eggs in SPA.     

Use of computer-assisted prediction of toxic effects of chemical substances

The current revision of the European policy for the evaluation of chemicals (REACH) has lead to a controversy with regard to the need of additional animal safety testing. To avoid increases in animal testing but also to save time and resources, alternative in silico or in vitro tests for the assessment of toxic effects of chemicals are advocated. The draft of the original document issued in 29th October 2003 by the European Commission foresees the use of alternative methods but does not give further specification on which methods should be used. Computer-assisted prediction models, so-called predictive tools, besides in vitro models, will likely play an essential role in the proposed repertoire of "alternative methods". The current discussion has urged the Advisory Committee of the German Toxicology Society to present its position on the use of predictive tools in toxicology. Acceptable prediction models already exist for those toxicological endpoints which are based on well-understood mechanism, such as mutagenicity and skin sensitization, whereas mechanistically more complex endpoints such as acute, chronic or organ toxicities currently cannot be satisfactorily predicted. A potential strategy to assess such complex toxicities will lie in their dissection into models for the different steps or pathways leading to the final endpoint. Integration of these models should result in a higher predictivity. Despite these limitations, computer-assisted prediction tools already today play a complementary role for the assessment of chemicals for which no data is available or for which toxicological testing is impractical due to the lack of availability of sufficient compounds for testing. Furthermore, predictive tools offer support in the screening and the subsequent prioritization of compound for further toxicological testing, as expected within the scope of the European REACH program. This program will also lead to the collection of high-quality data which will broaden the database for further (Q)SAR approaches and will in turn increase the predictivity of predictive tools.     

An in vivo hamster bioassay to assess the toxicity of particulates for the lungs

We have developed a short-term bioassay to predict the toxicity of particulates for the lungs using hamsters exposed by intratracheal instillation. After exposure the animals were killed, their lungs were lavaged, and the pulmonary damage was characterized by cellular and biochemical assays of lavage fluid: (a) changes in in situ phagocytic ability of macrophages; (b) damage to the air-blood barrier shown by increases in albumin and red blood cells; (c) inflammation shown by increases in polymorphonuclear neutrophils (PMNs) and macrophages; and (d) cellular damage, measured by the levels of lactate dehydrogenase (LDH), β-N-acetylglucosaminidase, peroxidase, and elastase in the extracellular supernatant fraction of the lavage fluid. The system was calibrated using toxic α-quartz and two nontoxic dusts, aluminum oxide and iron oxide. Increases in albumin and red blood cells one day after exposure were greater following quartz than aluminum oxide and iron oxide; in contrast, a large part of the LDH increase was a nonspecific response to increased dust within the lungs. Most of the indicators, including red blood cell numbers, glucosaminidase, and peroxidase, either approached or were at control levels 4 days after exposure to iron oxide or α-quartz. In α-quartz-exposed animals, macrophage and PMN numbers were more elevated at 4 days that at 1 day and remained elevated for at least 14 days. In contrast, in iron oxide-exposed hamsters, macrophage numbers did not differ from control levels and PMN numbers approached control levels with time. The ability to cause a prolonged infiltration of macrophages and PMNs may be an important determinant of the toxicity of mineral dusts.     

Use of a treatment algorithm to achieve NCEP ATP III goals with atorvastatin

This multicenter, 8-week, single-step titration, open-label study sought to assess the percentage of subjects who achieved their National Cholesterol Education Program Adult Treatment Panel (NCEP ATP) III low-density lipoprotein (LDL)-cholesterol target when assigned a starting dose of atorvastatin (10 mg, 20 mg, 40 mg, or 80 mg) selected using an algorithm based on their 10-year CHD risk and the magnitude of LDL-cholesterol lowering necessary to reach goal. Following an 8-week washout period, 1298 subjects, categorized as low, medium, or high risk, were assigned to 4 weeks of treatment with a starting dose of atorvastatin selected by the algorithm. At week 4, subjects who did not achieve goal (15.8%) were titrated to the next-higher dose. The primary endpoint was the percentage of subjects in each risk group who achieved LDL-cholesterol goal at week 8. At 8 weeks, 84.8% of subjects (low risk 92.9%; moderate risk 84.0%; high risk 81.1%) achieved LDL-cholesterol target. The majority of patients (84.2%) achieved their lipid target through the use of the algorithm-based starting dose (10-80 mg) without the need for titration. No patient had elevations in creatine phosphokinase >10 times the upper limit of normal. Elevations in alanine aminotransaminase or aspartate aminotransaminase were observed in <1% of study subjects and were unrelated to dose. Selecting the starting dose of atorvastatin using a treatment algorithm achieves NCEP ATP III LDL-cholesterol goals in the majority of patients and minimizes the need for dose titration.     

Randomized 5-treatment crossover study to assess the effects of external heat on serum fentanyl concentrations during treatment with transdermal fentanyl systems

This randomized, open-label, 5-treatment, 5-sequence crossover study was designed to evaluate the effects of a heating pad on serum fentanyl concentrations with reservoir and matrix transdermal fentanyl systems. Subjects were randomized to 1 of 5 treatment sequences, receiving 5 fentanyl treatments (1 per period) for 36 hours: 25 μg/h reservoir without heat, 25 μg/h reservoir with heat, 25 μg/h matrix without heat, 25 μg/h matrix with heat, and a 50 μg/h reservoir without heat. The 25 μg/h systems with heat had a heating pad applied from 0 to 10 and 26 to 36 hours post application. Washout periods between treatments were 5 to 14 days. Naltrexone was given to block the opioid effects of fentanyl. Study results indicate that external heat had a similar effect on both matrix and reservoir systems, with heat applied during the first 10 hours of treatment increasing fentanyl exposure by approximately 61% to 81% at 10 hours (observed serum concentration at 10 hours) and overall exposure (area under the curve from 0 to 10 hours) by approximately 120% to 184%, but had minimal effect from 26 to 36 hours. The increased exposure observed with heat in both 25 μg/h systems, between 0 and 10 hours, was higher than that obtained with the 50 μg/h reservoir system applied without heat.     

Use of cultured cells of kidney origin to assess specific cytotoxic effects of nephrotoxins.

During drug discovery, assessment of renal safety for a compound is important for further development of a candidate drug. In this study, we describe an in vitro cell-based assay capable of discerning nephrotoxicity. Three cell types, two of kidney origin and one of liver origin, were used to examine the effects of nephrotoxins. The cell types were the porcine normal kidney tubular epithelial cell line (LLC-PK1), the primary human renal proximal tubular epithelial cells (hRPTEC) and the human liver cell line (HepG2). Cytotoxicity was measured using a luciferin/luciferase assay that measures cellular ATP levels. Four known nephrotoxins, 4-aminophenol, cisplatin, cyclosporin A and paraquat, were tested in this cell-based assay to evaluate cytotoxicity on drug exposure. Kidney-derived LLC-PK1 cells and hRPTECs were found to be sensitive to selected nephrotoxins while liver-derived HepG2 cells were insensitive. Human RPTEC cells obtained from three individual donors demonstrated highly reproducible effects on drug exposure. With respect to drug discovery efforts, integration of the cell models described here are valuable for evaluation of nephrotoxic potentials during lead selection and optimization processes.     

Use of polar organic chemical integrative samplers to assess the effects of chronic pesticide exposure on biofilms

The responses of aquatic organisms to chronic exposure to environmental concentrations of toxicants, often found in mixtures, are poorly documented. Here passive sampler extracts were used in experimental contamination of laboratory channels, to investigate their effects on natural biofilm communities. A realistic mixture of pesticides extracted from Polar Organic Chemical Integrative Samplers was used to expose biofilms in laboratory channels to total pesticide concentrations averaging 0.5 ± 0.1 μg l^?1. The level of exposure was representative of field conditions in terms of relative proportions of the substances but the exposure concentration was not maintained (decreasing concentrations between contamination occasions). The impact on the structural as well as the functional characteristics of the autotrophic and heterotrophic components was determined, using biofilm grown in uncontaminated conditions (reference site) and in sites exposed to pesticides (contaminated site). The exposure imposed did not significantly modify the structure or functions of reference biofilms, nor did it modify tolerance as measured by mixture EC₅₀ (EC₅₀ mix). In contrast, the communities from the more contaminated downstream section lost tolerance following decreased dose exposure, but community composition remained fairly stable. Overall, these results indicate that low levels of contamination did not lead to strong changes in community structure, and 14-day changes in tolerance seemed to depend mainly on physiological adaptation, suggesting that other environmental factors or longer-lasting processes prevailed. This study reports the first attempt to use passive sampler extracts as a realistic composite contaminant for experimental exposure of biofilms, with promising perspectives in further ecotoxicology studies.     

Potential ecotoxic effects probe (PEEP): A novel index to assess and compare the toxic potential of industrial effluents

An index allowing the assessment and comparison of the toxic potential of industrial effluents is described. Integrating the results of practical small-scale screening bioassays (Photobacterium phosphoreum Microtox® test. Selenastrum capricornutum growth inhibition microtest, Ceriodaphnia dubia lethality and reproduction inhibition tests, Escherichia coli genotoxicity SOS Chromotest), this index takes into account persistence of toxicity, (multi) specificity of toxic impact, as well as effluent flow. The resulting Potential Ecotoxic Effects Probe (PEEP) index number is reflected by a log₁₀ value that varies from 0 to infinity but normally will not surpass a value of 10. The structure of the mathematical formula generating PEEP values is simple and “user friendly” in that it can accommodate numbers and types of bioassays to fit particular needs. Thirty-seven effluents from 8 industrial sectors (pulp and paper, petroleum refining, inorganic/organic chemical production, mining, metallurgy, metal plating, textile production) were appraised and compared with the proposed PEEP scale. The pulp and paper sector effluents (n = 15) markedly stood out from the others owing to their greater toxicity and higher discharge volume, with reported PEEP values lying between 4.4 and 7.5. For most of these effluents, toxicity was found to be persistent, multitrophic (i.e., affecting our bacterial, algal, and crustacean bioindicators), and it expressed itself at all levels of assessment (i.e., lethal, acute sublethal, chronic sublethal, and genotoxic levels). The usefulness of the PEEP index in the environmental management of industrial effluent toxicity is discussed herein. © 1993 John Wiley & Sons, Inc.     

Histopathological examination and transcriptome analyses to assess the acute toxic effects of arsenite exposure on rare minnows (Gobiocypris rarus)

Ecotoxicology - Arsenic is ubiquitously present in the aquatic environment. We investigated the acute toxic effects of arsenite [As(III)] exposure on rare minnows (Gobiocypris rarus) in vivo. The...     

Use of a bioassay in healthy men to evaluate diuretic-spironolactone combinations.

The plasma potassium responses to 1 week's treatment with metolazone 0.625 mg, 1.25 mg and 2.5 mg in combination with spironolactone 50 mg, and metolazone 2.5 alone were examined in a double-blind, crossover study in twelve healthy subjects. Spironolactone attenuated the hypokalaemia induced by metolazone--addition of spironolactone 50 mg to metolazone 2.5 mg raised plasma potassium by 0.18 mmol/l (P less than 0.025). In the presence of spironolactone, a linear log metolazone dose-plasma potassium response relationship (P less than 0.01) was demonstrated. Spironolactone was unable to compensate fully for metolazone's hypokalaemic effect although in combination with metolazone 0.625 mg and 1.25 mg, plasma potassium concentration was maintained close to pretreatment levels. The human bioassay employed provided conveniently quantitative information which allows the rational development of a fixed dose diuretic-spironolactone combination tablet.     

Use of the cassette-dosing approach to assess brain penetration in drug discovery

The objective of the present study was to examine the cassette dosing method in determination of brain-to-plasma concentration ratio (area under the concentration-time profiles for plasma/area under the concentration-time profiles for brain, K(p)). Eleven model compounds, amprenavir, citalopram, digoxin, elacridar, imatinib, (3S,6S,12aS)-1,2,3,4,6,7,12,12a-octahydro-9-methoxy-6-(2-methylpropyl)-1,4-dioxopyrazino[1',2':1,6]pyrido[3,4-b]indole-3-propanoic acid 1,1-dimethylethyl ester (Ko143), loperamide, prazosin, quinidine, sulfasalazine, and verapamil, were selected to compare their K(p) determined from discrete dosing in wild-type mice and their K(p) from cassette dosing in wild-type, Mdr1a/1b(-/-), Bcrp1(-/-), and Mdr1a/1b(-/-)/Bcrp1(-/-) mice at 1 to 3 mg/kg. The mice brain and plasma were collected at 0.25, 1, and 3 h and were analyzed using high-performance liquid chromatography-tandem mass spectrometry methods. The K(p) determined from discrete dosing versus cassette dosing in the wild-type mice were within 2-fold for all the compounds except sulfasalazine and Ko143. The brain concentrations of sulfasalazine and Ko143 and the plasma concentrations of Ko143 were below the lower limit of quantitation. In addition, the K(p) values estimated by mass spectrometry responses, namely the ratio of compound peak area to internal standard peak area, were within 2-fold of the K(p) observed from the actual concentrations. Furthermore, the ratios of K(p) in Mdr1a/1b(-/-), Bcrp1(-/-), and Mdr1a/1b(-/-)/Bcrp1(-/-) mice versus the K(p) in the wild-type mice from cassette dosing were consistent with the ones reported in the literature where the compounds were dosed discretely. These results demonstrate that drug-drug interactions at the blood-brain barrier are unlikely at a subcutaneous dose of 1 to 3 mg/kg and support the use of the cassette dosing approach to assess brain penetration in drug discovery.     

Use of in vitro assays to assess the potential cytotoxic,genotoxic and antigenotoxic effects of vanillic and cinnamic acid

Vanillic acid (VA) found in vanilla and cinnamic acid (CA) the precursor of flavonoids and found in cinnamon oil, are natural plant phenolic acids which are secondary aromatic plant products suggested to possess many physiological and pharmacological functions. In vitro and in vivo experiments have shown that phenolic acids exhibit powerful effects on biological responses by scavenging free radicals and eliciting antioxidant capacity. In the present study, we investigated the antioxidant capacity of VA and CA by the trolox equivalent antioxidant capacity (TEAC) assay, cytotoxicity by neutral red uptake (NRU) assay in Chinese Hamster Ovary (CHO) cells and also the genotoxic and antigenotoxic effects of these phenolic acids using the cytokinesis-blocked micronucleus (CBMN) and the alkaline comet assays in human peripheral blood lymphocytes. At all tested concentrations, VA (0.17–67.2?μg/ml) showed antioxidant activity but CA (0.15–59.2?μg/ml) did not show antioxidant activity against 2,2-azino-bis (3-ethylbenz-thiazoline-6-sulphonic acid) (ABTS). VA (0.84, 4.2, 8.4, 16.8, 84 and 168?μg/ml) and CA (0.74, 3.7, 7.4, 14.8, 74, 148?μg/ml) did not have cytotoxic and genotoxic effects alone at the studied concentrations as compared with the controls. Both VA and CA seem to decrease DNA damage induced by H₂O₂ in human lymphocytes.     

Use of in vitro assays to assess the potential antigenotoxic and cytotoxic effects of saffron (Crocus sativus L.).

Saffron is harvested from the dried, dark red stigmas of Crocus sativus L. flowers. It is used as a spice for flavoring and coloring food and as a perfume. It is often used for treating several diseases. We assessed the antimutagenic, comutagenic and cytotoxic effects of saffron and its main ingredients using the Ames/Salmonella test system, two well known mutagens (BP, 2AA), the in vitro colony formation assay and four different cultured human normal (CCD-18Lu) and malignant (HeLa, A-204 and HepG2) cells. When only using the TA98 strain in the Ames/Salmonella test system, saffron showed non-mutagenic, as well as non-antimutagenic activity against BP-induced mutagenicity, and demonstrated a dose-dependent co-mutagenic effect on 2-AA-induced mutagenicity. The saffron component responsible for this unusual comutagenic effect was safranal. In the in vitro colony formation test system, saffron displayed a dose-dependent inhibitory effect only against human malignant cells. All isolated carotenoid ingredients of saffron demonstrated cytotoxic activity against in vitro tumor cells. Saffron crocin derivatives possessed a stronger inhibitory effect on tumor cell colony formation. Overall, these results suggest that saffron itself, as well as its carotenoid components might be used as potential cancer chemopreventive agents.     

Use of hepatocytes to assess the contribution of hepatic uptake to clearance in vivo.

The wealth of information that has emerged in recent years detailing the substrate specificity of hepatic transporters necessitates an investigation into their potential role in drug elimination. Therefore, an assay in which the loss of parent compound from the incubation medium into hepatocytes ("media loss" assay) was developed to assess the impact of hepatic uptake on unbound drug intrinsic clearance in vivo (CL(int ub in vivo)). Studies using conventional hepatocyte incubations for a subset of 36 AstraZeneca new chemical entities (NCEs) resulted in a poor projection of CL(int ub in vivo) (r2 = 0.25, p = 0.002, average fold error = 57). This significant underestimation of CL(int ub in vivo) suggested that metabolism was not the dominant clearance mechanism for the majority of compounds examined. However, CL(int ub in vivo) was described well for this dataset using an initial compound "disappearance" CL(int) obtained from media loss assays (r2 = 0.72, p = 6.3 x 10(-11), average fold error = 3). Subsequent studies, using this method for the same 36 NCEs, suggested that the active uptake into human hepatocytes was generally slower (3-fold on average) than that observed with rat hepatocytes. The accurate prediction of human CL(int ub in vivo) (within 4-fold) for the marketed drug transporter substrates montelukast, bosentan, atorvastatin, and pravastatin confirmed further the utility of this assay. This work has described a simple method, amenable for use within a drug discovery setting, for predicting the in vivo clearance of drugs with significant hepatic uptake.