Validation study of alternatives to the Draize eye irritation test in Germany: Cytotoxicity testing and HET-CAM test with 136 industrial chemicals

Biological aspects of modern dental composites

Biological evaluation of resin-based dental composites has traditionally been based on in vitro endpoint tests with different methods to determine loss of cell viability and cell morphology changes after exposure to the material or monomer constituents. The data reveals a potential for biological effects, but clinical relevance of such data is limited. Positive allergy tests and allergic clinical reactions to dental monomers are observed in dental personnel and patients. The aim of this review is to address newer research on molecular events caused by exposure to resin-based composites to have a better understanding of the potential for clinical adverse effects. A more accurate understanding of the biological aspects of dental composite materials has been found after studying parameters like glutathione depletion, oxidative stress, genotoxicity, and immunomodulatory key effects in various cell culture models. Using omics-based approaches allow for a broader and non-specified search of changes caused by methacrylate exposure. Defense mechanisms and adaption are observed in cells exposed to monomer concentrations relevant to clinical exposure. The above-mentioned methods are the foundations for modified testing strategies. The clinical relevance of most available in vitro endpoint tests is of limited relevance for the patient. Research focusing on molecular mechanisms has given new insight into methacrylate toxicity in exposed cells. Using this knowledge from mechanistic studies to develop standardized in vitro biocompatibility tests will likely improve their clinical relevance.

Effects of Non-Conventional Sterilisation Methods on PBO-Reinforced PVA Hydrogels for Cartilage Replacement

Articular cartilage (AC) degradation is a recurrent pathology that affects millions of people worldwide. Polyvinyl alcohol (PVA) hydrogels have been widely explored for AC replacement. However, their mechanical performance is generally inadequate, and these materials need to be reinforced. Moreover, to be used in a clinical setting, such materials must undergo effective sterilisation. In this work, a PVA hydrogel reinforced with poly(p-phenylene-2,6-benzobisoxazole) (PBO) nanofibres was submitted to three non-conventional sterilisation methods: microwave (MW), high hydrostatic pressure (HHP), and plasma (PM), in order to evaluate their impact on the properties of the material. Sterilisation was achieved in all cases. Properties such as water content and hydrophilicity were not affected. FTIR analysis indicated some changes in crystallinity and/or crosslinking in all cases. MW was revealed to be the most suitable method, since, unlike to PM and HHP, it led to a general improvement of the materials’ properties: increasing the hardness, stiffness (both in tensile and compression), and shear modulus, and also leading to a decrease in the coefficient of friction against porcine cartilage. Furthermore, the samples remained non-irritant and non-cytotoxic. Moreover, this method allows terminal sterilisation in a short time (3 min) and using accessible equipment.

Preparation and Characterisation of a Cyclodextrin-Complexed Mānuka Honey Microemulsion for Eyelid Application

Honey has been widely purported as a natural remedy due to its antimicrobial and anti-inflammatory effects. In recent years, several studies have suggested that the considerably high methylglyoxal (MGO) concentration in Mānuka honey (MH) makes it particularly effective to manage bacterial overload, such as that observed in blepharitis. However, the poor solubility, high viscosity, and osmolarity of aqueous honey solutions, especially at the high MGO concentrations studied in the literature, render the formulation of an acceptable dosage form for topical application to the eyelids challenging. Here, the antibacterial properties of raw MH and alpha-cyclodextrin (α-CD)-complexed MH were evaluated at relatively low MGO concentrations, and a liquid crystalline-forming microemulsion containing α-CD-complexed MH was formulated. After determining pH and osmolarity, ocular tolerability was assessed using human primary corneal epithelial cells and chorioallantoic membranes, while the antibacterial efficacy was further evaluated in vitro. The α-CD–MH complex had significantly greater antibacterial activity against Staphylococcus aureus than either constituent alone, which was evident even when formulated as a microemulsion. Moreover, the final formulation had a physiologically acceptable pH and osmolarity for eyelid application and was well-tolerated when diluted 1:10 with artificial tear fluid, as expected to be the case after accidental exposure to the ocular surface in the clinical setting. Thus, a safe and efficient MH dosage form was developed for topical application to the eyelids, which can potentially be used to support optimal eyelid health in the management of blepharitis.

Design, optimization, and in vitro characterization of idebenone-loaded PLGA microspheres for LHON treatment

Biodegradable poly(lactic-co-glycolic acid) microspheres (PLGA MSs) are attractive delivery systems for site-specific maintained release of therapeutic active substances into the intravitreal chamber. The design, development, and characterization of idebenone-loaded PLGA microspheres by means of an oil-in-water emulsion/solvent evaporation method enabled the obtention of appropriate production yield, encapsulation efficiency and loading values. MSs revealed spherical shape, with a size range of 10-25 μm and a smooth and non-porous surface. Fourier-transform infrared spectroscopy (FTIR) spectra demonstrated no chemical interactions between idebenone and polymers. Solid-state nuclear magnetic resonance (NMR), X-ray diffractometry, differential scanning calorimetry (DSC) and thermogravimetry (TGA) analyses indicated that microencapsulation led to drug amorphization. In vitro release profiles were fitted to a biexponential kinetic profile. Idebenone-loaded PLGA MSs showed no cytotoxic effects in an organotypic tissue model. Results suggest that PLGA MSs could be an alternative intraocular system for long-term idebenone administration, showing potential therapeutic advantages as a new therapeutic approach to the Leber's Hereditary Optic Neuropathy (LHON) treatment by intravitreal administration.

Comparison of the different protocols of the Hen's Egg Test-Chorioallantoic Membrane (HET-CAM) by evaluating the eye irritation potential of surfactants

The Hen's Egg Test - Chorioallantoic Membrane (HET-CAM) is a valid alternative method used to assess the potential for eye irritation from chemicals. This method is the only one that mimics the conjunctivae of the eye and aims to semi-quantitatively evaluate the irritant potential of a chemical on the chorioallantoic membrane surrounding the chicken embryo in egg by observing the irritation effects on the membrane immediately after the pure or diluted chemical is applied. The purpose of this study was to compare the different protocols of the HET-CAM, the French and German protocols, by evaluating the eye irritation potential of surfactants. The comparison led to the optimization of the French protocol, generating an adapted one, to reduce subjectivity in the test evaluation, ensuring more accurate results and greater quality control. The comparison showed that there are no significant differences between the results obtained in the French and German protocols. HET-CAM is known to overestimate the results and to be able to accurately identify non-irritant products and it is a great candidate to be part of a Bottom-up test strategy. It also can be used in a battery of tests to completely replace rabbits.

Design, development, and characterization of an idebenone-loaded poly-ε-caprolactone intravitreal implant as a new therapeutic approach for LHON treatment

Leber's Hereditary Optic Neuropathy (LHON) is a hereditary mitochondrial neurodegenerative disease of unclear etiology and lack of available therapeutic alternatives. The main goal of the current pilot study was based on the evaluation of the feasibility and characteristics of prolonged and controlled idebenone release from a PCL intravitreal implant. The design, development, and characterization of idebenone-loaded PCL implants prepared by an homogenization/extrusion/solvent evaporation method allowed the obtention of high PY, EE and LC values. In vitro characterization was completed by the assessment of mechanical and instrumental properties. The in vitro release of idebenone from the PCL implants was assessed and the implant erosion was monitored by the mass loss and surface morphology changes. DSC was used to estimate stability and interaction among implant's components. The present work demonstrated the controlled and prolonged idebenone delivery from the PCL implants in an in vitro model. A consistent preclinical base was established, supporting the idea of idebenone-loaded PCL implants as a new strategy of long-term sustained intraocular delivery for the LHON treatment.

The chick embryo chorioallantoic membrane model: a research approach for ex vivo and in vivo experiments

BACKGROUND

The chick chorioallantoic membrane (CAM) model has attracted a great deal of interest in pharmaceutical and biological research as an alternative or complementary in vivo assay to animal models. Traditionally, CAM assay has been widely used to perform some toxicological studies, specifically to evaluate the skin, ocular and embryo toxicity of new drugs and formulations, and perform angiogenesis studies. Due to the possibility to generate the tumors onto the CAM, this model has also become an excellent strategy to evaluate the metastatic potential of different tumours and test the efficacy of novel anticancer therapies in vivo. Moreover, in the recent years, its use has considerably grown in other research areas, including the evaluation of new anti-infective agents, the development of biodistribution studies and tissue engineering research.

OBJECTIVES

This manuscript provides a critical overview of the use of CAM model in pharmaceutical and biological research, especially to test the toxicity of new drugs and formulations and the biodistribution and the efficacy of novel anticancer and anti-infective therapies, analyzing its advantages and disadvantages compared to animal models.

CONCLUSION

The chick chorioallantoic membrane model shows great utility in several research areas, such as cancer, toxicology, biodistribution studies and anti-infective therapies. In fact, it has become an intermediate stage between in vitro experiments and animal studies, and, in the case of toxicological studies (skin and ocular toxicity), has even replaced the animal models.

[Development of an ivermectin-containing syrup as an extemporaneous preparation for treatment of scabies in children]

BACKGROUND

Oral ivermectin can be used to treat scabies. Evidence for safe and effective use in young children in individual treatment situations has been developed and published. In order to also ensure a body weight-adapted dosage for children, an ivermectin-containing syrup was developed as an extemporaneous preparation.

MATERIALS AND METHODS

Since ivermectin is not available as a pure substance for the formulation, tablets containing active ingredient were used as a basic material for development. The formulation was designed according to pharmaceutical, regulatory and use-oriented criteria. An HPLC (high-pressure liquid chromatography) method was developed and validated to demonstrate chemical stability. In order to facilitate the practical implementation, information on suitable packaging material and application aids was also developed and the formulation was evaluated.

RESULTS

It has been demonstrated that the final formulation produced in the pharmacy was stable and can be stored for 3 weeks. No concerns were raised regarding the tolerability of the syrup formulation. The physicochemical properties and the taste of the formulation allow the intended use as a well-dosed syrup for children.

CONCLUSION

The developed formulation meets the requirements of the Apothekenbetriebsordnung (Pharmacy Work Rules; Section 7 ApBetrO) and enables an exact, body weight-adapted dosage of oral ivermectin in young children. Studies on human pharmacokinetics or clinical studies to demonstrate tolerability and/or efficacy are not available for the formulation.

Comparative evaluation of HET-CAM and ICE methods for objective assessment of ocular irritation caused by selected pesticide products

Eye irritation potency of pesticides (fungicides, herbicides, insecticides) was comparatively tested by HET-CAM and ICE method. Based on the results of the tests the statistical analysis of agreement between classification using individual methods was done by Goodman-Kruskal's rank correlation and determination (calculation) of Cohen's kappa coefficient. Statistical analysis of agreement between classification revealed significant correlation between results of in vivo and in HET-CAM assays (76%). There was no significant correlation between result of in vivo and in ICE methods (64%). Weakest correlation was found between the data from in vitro HET-CAM and ICE tests. The percentage of agreement between two in vitro data was 48%. They may be recommended as a part of a battery of tests to reduce experimentation on mammals and to limit or eliminate pain and injury inflicted on experimental animals. The HET-CAM test is a useful tool for studying in vivo the potential conjunctival irritation, while the ICE test can be used to study corneal irritant effects in detail.

Design, Optimization, and Characterization of Lactoferrin-Loaded Chitosan/TPP and Chitosan/Sulfobutylether-β-cyclodextrin Nanoparticles as a Pharmacological Alternative for Keratoconus Treatment

This research study describes the design, optimization, and characterization of two different types of chitosan-based nanoparticles as novel drug delivery systems of a protein drug, lactoferrin. A preclinical consistent base was obtained for both nanosystems, being considered as the first pharmacological treatment for keratoconus as an alternative to current invasive clinical methods. Both types of nanoparticles were obtained via the ionotropic gelation technique. The size and morphology of the nanoparticles were studied as a function of the preparation conditions. A mean size of 180.73 ± 40.67 nm, a size distribution [polydispersity index (PDI)] of 0.170 ± 0.067, and positive ζ-potential values, ranging from 17.13 to 19.89 mV, were achieved. Lactoferrin was successfully incorporated into both types of nanocarriers. In vitro release profiles showed a lactoferrin enhanced, prolonged, and controlled delivery from the polymeric matrix. These formulations also demonstrated no stability or cytotoxicity problems, as well as appropriate mucoadhesive properties, with a high permanence time in the ocular surface. Thus, both types of nanoparticles may be considered as nanocarriers for the controlled release of lactoferrin as novel topical ophthalmic drug delivery systems.

Development and Characterization of a Tacrolimus/Hydroxypropyl-β-Cyclodextrin Eye Drop

Uveitis is a vision inflammatory disorder with a high prevalence in developing countries. Currently, marketed treatments remain limited and reformulation is usually performed to obtain a tacrolimus eye drop as a therapeutic alternative in corticosteroid-refractory eye disease. The aim of this work was to develop a mucoadhesive, non-toxic and stable topical ophthalmic formulation that can be safely prepared in hospital pharmacy departments. Four different ophthalmic formulations were prepared based on the tacrolimus/hydroxypropyl-β-cyclodextrin (HPβCD) inclusion complexes’ formation. Phase solubility diagrams, Nuclear Magnetic Resonance (NMR) and molecular modeling studies showed the formation of 1:1 and 1:2 tacrolimus/HPβCD inclusion complexes, being possible to obtain a 0.02% (w/v) tacrolimus concentration by using 40% (w/v) HPβCD aqueous solutions. Formulations also showed good ophthalmic properties in terms of pH, osmolality and safety. Stability studies proved these formulations to be stable for at least 3 months in refrigeration. Ex vivo bioadhesion and in vivo ocular permanence showed good mucoadhesive properties with higher ocular permanence compared to the reference pharmacy compounding used in clinical settings (t_1/2 of 86.2 min for the eyedrop elaborated with 40% (w/v) HPβCD and Liquifilm^® versus 46.3 min for the reference formulation). Thus, these novel eye drops present high potential as a safe alternative for uveitis treatment, as well as a versatile composition to include new drugs intended for topical ophthalmic administration.

Results of a Validation Study in Germany on Two in Vitro Alternatives to the Draize Eye Irritation Test, the HET-CAM Test and the 3T3 NRU Cytotoxicity Test

During 1988–1992, a validation study was carried out in Germany on the capacity of two in vitro tests to replace the Draize eye test for severely eye irritating chemicals, namely, the hen's egg chorio-allantoic membrane (HET-CAM) test and the 3T3 cell neutral red uptake (NRU) cytotoxicity test, which had shown promising results in an earlier test development project. The formal validation study, which was coordinated by Centre for Documentation and Evaluation of Alternative Methods to Animal Experiments (ZEBET) and funded by the German Department of Research and Technology (BMBF), was conducted in two phases: Phase I consisted of a prevalidation study and a blind trial (1988–1990); and Phase II was the database development phase (1991/1992). During prevalidation, the two in vitro tests were established in 13 laboratories, standard protocols were developed, including PC-based software programs for data recording, and 34 chemicals backed by high quality literature data were selected for the ring trial. In the 1-year ring trial, the two in vitro tests were validated with 34 coded chemicals under blind conditions in 13 laboratories, to evaluate the reproducibility of the two tests within and among laboratories. In the blind trial, the 3T3 NRU cytotoxicity test showed a better reproducibility than the HET-CAM test, but compared to the cytotoxicity test, the HET-CAM test permitted a significantly better classification of severely eye irritating chemicals, which are labelled R41 according to EU regulations.

Since it was recommended in 1990 by the first Amden validation workshop that a database of around 200 chemicals is required for the assessment of test performance to reach regulatory acceptance at the international level, a 2-year database development was conducted as Phase II, during which 166 coded chemicals were tested in the two in vitro tests, each of them in two laboratories. Test chemicals backed by high-quality Draize eye test data were provided by industry and selected to represent a wide spectrum of chemical classes and eye irritation properties. Independent quality control of in vitro and in vivo data and biostatistical evaluation were performed during an additional BMBF project on biostatistics. In the quality assurance step, which is an essential prerequisite for biostatistics, the number of chemicals was reduced to 143, and these data were entered into an MS-EXCEL database to facilitate determination of in vitro/in vivo correlations.

Unexpectedly, the evaluation of the study had to take into account a change of criteria within the EU for classifying severely eye irritating chemicals as R41, since irreversible damage within a 21-day observation period was introduced as a new criterion for R41 chemicals. The results of the 3T3 NRU cytotoxicity test showed an insufficient in vitro/in vivo correlation for classifying R41 chemicals. Classification of HET-CAM data was also insufficient in the Bundesgesundhütsamt (BGA) scoring system, which uses an empirically developed weighted scoring of the three endpoints, namely, haemorrhage, lysis and coagulation. Discriminant analysis of ten endpoints routinely determined in the HET-CAM test and in the 3T3 NRU cytotoxicity test revealed that the detection time of coagulation, the most severe reaction on the CAM, was significantly better suited to identifying severely eye irritating properties than any other endpoint, and better than the BGA score for the HET-CAM test. For water-soluble chemicals (mean time for detection of coagulation [mtc]10), the detection time for coagulation of a 10% solution had the highest discriminant power, and for less water-soluble chemicals (mtc100), the detection time of coagulation of the undiluted chemical was more appropriate.

Discriminant analysis of the combination of mtc10 and mtc100 with other endpoints of the two in vitro tests revealed that classification of water-soluble chemicals is significantly improved by combining mtc10 and lgfg50m (logarithm of IC50 value calculated with the Fit-Graph program), the endpoint of the 3T3 NRU cytotoxicity test. Further analysis of data from Phase I and Phase II of the study demonstrated that chemicals characterised by an mtc10 of < 50 seconds can be labelled R41 without any false positive classifications. By using this cut-off point, around 25% of R41 chemicals can be classified without further testing in vitro or in vivo.

Classification was further improved when solubility in water and oil was taken into account. The best classification of water-soluble R41 chemicals (> 10%) was obtained when the mtc10 of the HET-CAM test and the lgfg50m of the 3T3 NRU cytotoxicity test were combined. For chemicals soluble in oil (> 10%) and for insoluble chemicals, the mtc100 provided the best classification. The in vitro classification results were confirmed by cross-validation.

These promising results allowed a sequential approach to be developed for classifying severely eye irritating chemicals as R41 according to EU regulations by combining the HET-CAM test and the 3T3 NRU cytotoxicity test results. The present study suggests that severely eye irritating chemicals can be classified as R41 with a sufficiently high level of confidence with the two in vitro tests, since the percentage of false positive and false negative results are kept within an acceptably low range. Thus, the combined use of the HET-CAM test and the 3T3 NRU cytotoxicity test meets the requirements for “well-validated” tests, as defined in the escape clause of OECD Guideline 405 for eye irritation testing.

Application of Statistical Classification Methods to the Evaluation of In Vitro Tests

The first Amden Report defines validation as “The process by which the reliability and relevance of a test are established”. The recommendations of the Amden conference mention the need for biometric methods, but, unfortunately, most publications on alternatives to animal testing procedures do not pay much attention to statistical problems in the validation process. The biometric repertoire consists mainly of scatterplots, correlation coefficients and linear regression.

In the evaluation of an interlaboratory study, we applied multivariate statistical methods to analyse the ability of two in vitro tests to identify severely irritating substances. In this study, conducted by the German Bundesgesundheitsamt, two alternatives to the well-known Draize eye irritancy test — the neutral red uptake test and the HET-CAM test — were investigated. The statistical methods applied were discriminant analysis and the Classification and Regression Trees (CART) method.

The results presented here show that the combination of the endpoints of the in vitro tests, analysed by using the CART method, can give a sensitivity of about 67% with 76% specificity. Discriminant analysis models only achieve a sensitivity of 55%. The results obtained with the data presented here show that these statistical methods are very suitable and useful for this type of problem. This was confirmed by further analyses with discriminant analysis models, which gave a sensitivity of about 80%.

The Use of Artificial Gel Forming Bolalipids as Novel Formulations in Antimicrobial and Antifungal Therapy

The alarming growth of multi-drug resistant bacteria has led to a quest for alternative antibacterial therapeutics. One strategy to circumvent the already existing resistance is the use of photodynamic therapy. Antimicrobial photodynamic therapy (aPDT) involves the use of non-toxic photosensitizers in combination with light and in situ oxygen to generate toxic radical species within the microbial environment which circumvents the resistance building mechanism of the bacteria. Hydrogels are used ubiquitously in the biological and pharmaceutical fields, e.g., for wound dressing material or as drug delivery systems. Hydrogels formed by water-insoluble low-molecular weight gelators may potentially provide the much-needed benefits for these applications. Bolalipids are a superior example of such gelators. In the present work, two artificial bolalipids were used, namely PC-C32-PC and Me2PE-C32-Me2PE, which self-assemble in water into long and flexible nanofibers leading to a gelation of the surrounding solvent. The aim of the study was to create stable hydrogel formulations of both bolalipids and to investigate their applicability as a novel material for drug delivery systems. Furthermore, methylene blue-a well-known photosensitizer-was incorporated into the hydrogels in order to investigate the aPDT for the treatment of skin and mucosal infections using a custom designed LED device.

Assessment of the Eye Irritating Properties of Chemicals by Applying Alternatives to the Draize Rabbit Eye Test: The Use of QSARs and In Vitro Tests for the Classification of Eye Irritation

Huggins has reported on the current situation relating to the development of alternatives to the Draize eye irritation test with rabbits, and an ECVAM Working Group have reviewed the efforts needed in order to replace this animal test within the next 10 years by using the results of non-animal assessment methods. Our report reviews regulatory experience gained over the last 20 years with the EU chemicals notification procedure with respect to the assessment of eye lesions observed in Draize tests. The nature of eye lesions and their importance for classification and labelling of possible hazards to human eyes are evaluated and discussed, with a view to promoting the development of specific in vitro assays which are able to discriminate between eye damage, moderate eye irritation, and minor irritation effects which are completely reversible within a few days. Structural alerts for the prediction of eye irritation/corrosion hazards to be classified and labelled according to international classification criteria, are presented, which should be validated in accordance with internationally agreed (OECD) principles for (Q)SAR system validation. Physicochemical limit values for prediction of the absence of any eye irritation potential relevant for human health can make available a definition of the applicability domains of alternative methods developed for the replacement of the Draize eye irritation test.

Irritative potency of selected wound antiseptics in the hen's egg test on chorioallantoic membrane to predict their compatibility to wounds

Antiseptics are being used for prevention of infections in acute wounds and for treatment of infections in acute and chronic wounds. However, some antiseptics' high tissue toxicity might delay the healing process. The aim of this study was to investigate the tissue toxicity of preferentially used wound antiseptics and the influence of antiphlogistic additives via the hen's egg test on the chorioallantoic membrane (HET-CAM). The HET-CAM is a semi-in-vivo method testing the tissue tolerability of wound antiseptics by evaluating the blood vessel reaction of the chorioallantoic membrane in terms of hemorrhage, vessel lysis, and coagulation. For each test day, selected test substances were applied on the membranes of two to three eggs according to the test protocol. The overall irritation was then evaluated by referring to a calculated score. Normal distribution of the resulting scores was confirmed by D'Agostino-Pearson omnibus K2 test. Significant differences between the antiseptics were calculated by Tukey's multiple comparisons test. Severe CAM reactions were observed after short-term application of octenidine based wound gel (0.05%) and chlorhexidine digluconate (0.5% solution), moderate reactions for octenidine (0.05%) in aqueous solution combined with dexpanthenol (1.34%) and allantoin (0.2%) or for hydrogen peroxide (1.5% and 0.5%) in aqueous solution, slight reactions were observed for hydrogen peroxide (1.5%) in aqueous solution in combination with sodium thiocyanate (0.698%) and for the combination of NaOCl/HOCl (each 0.004%). Polyhexanide (0.04%) in Ringer solution and polyhexanide (0.05%) in Lipofundin, the hemoglobin spray (10%), dexpanthenol, and allantoin showed no irritation. The HET-CAM qualifies as a primary screening test for tissue tolerance of wound antiseptics. Regarding local tolerability, polyhexanide and hypochlorite are superior to other antiseptics.

Alternatives to In Vivo Draize Rabbit Eye and Skin Irritation Tests with a Focus on 3D Reconstructed Human Cornea-Like Epithelium and Epidermis Models

Human eyes and skin are frequently exposed to chemicals accidentally or on purpose due to their external location. Therefore, chemicals are required to undergo the evaluation of the ocular and dermal irritancy for their safe handling and use before release into the market. Draize rabbit eye and skin irritation test developed in 1944, has been a gold standard test which was enlisted as OECD TG 404 and OECD TG 405 but it has been criticized with respect to animal welfare due to invasive and cruel procedure. To replace it, diverse alternatives have been developed: (i) For Draize eye irritation test, organotypic assay, in vitro cytotoxicity-based method, in chemico tests, in silico prediction model, and 3D reconstructed human cornea-like epithelium (RhCE); (ii) For Draize skin irritation test, in vitro cytotoxicity-based cell model, and 3D reconstructed human epidermis models (RhE). Of these, RhCE and RhE models are getting spotlight as a promising alternative with a wide applicability domain covering cosmetics and personal care products. In this review, we overviewed the current alternatives to Draize test with a focus on 3D human epithelium models to provide an insight into advancing and widening their utility.

Insights on in vitro models for safety and toxicity assessment of cosmetic ingredients

According to the current European legislation, the safety assessment of each individual cosmetic ingredient of any formulation is the basis for the safety evaluation of a cosmetic product. Also, animal testing in the European Union is prohibited for cosmetic ingredients and products since 2004 and 2009, respectively. Additionally, the commercialization of any cosmetic products containing ingredients tested on animal models was forbidden in 2009. In consequence of these boundaries, the European Centre for the Validation of Alternative Methods (ECVAM) proposes a list of validated cell-based in vitro models for predicting the safety and toxicity of cosmetic ingredients. These models have been demonstrated as valuable and effective tools to overcome the limitations of animal in vivo studies. Although the use of in vitro cell-based models for the evaluation of absorption and permeability of cosmetic ingredients is widespread, a detailed study on the properties of these platforms and the in vitro-in vivo correlation compared with human data are required. Moreover, additional efforts must be taken to develop in vitro models to predict carcinogenicity, repeat dose toxicity and reproductive toxicity, for which no alternative in vitro methods are currently available. This review paper summarizes and characterizes the most relevant in vitro models validated by ECVAM employed to predict the safety and toxicology of cosmetic ingredients.

Magnetic Surfactants and Polymers with Gadolinium Counterions for Protein Separations

New magnetic surfactants, (cationic hexadecyltrimethlyammonium bromotrichlorogadolinate (CTAG), decyltrimethylammonium bromotrichlorogadolinate (DTAG), and a magnetic polymer (poly(3-acrylamidopropyl)trimethylammonium tetrachlorogadolinate (APTAG)) have been synthesized by the simple mixing of the corresponding surfactants and polymer with gadolinium metal ions. A magnetic anionic surfactant, gadolinium tri(1,4-bis(2-ethylhexoxy)-1,4-dioxobutane-2-sulfonate) (Gd(AOT)3), was synthesized via metathesis. Both routes enable facile preparation of magnetically responsive magnetic polymers and surfactants without the need to rely on nanocomposites or organic frameworks with polyradicals. Electrical conductivity, surface tensiometry, SQUID magnetometry, and small-angle neutron scattering (SANS) demonstrate surface activity and self-aggregation behavior of the magnetic surfactants similar to their magnetically inert parent analogues but with added magnetic properties. The binding of the magnetic surfactants to proteins enables efficient separations under low-strength (0.33 T) magnetic fields in a new, nanoparticle-free approach to magnetophoretic protein separations and extractions. Importantly, the toxicity of the magnetic surfactants and polymers is, in some cases, lower than that of their halide analogues.

Evaluation of Eye Irritation Potential of Solid Substance with New 3D Reconstructed Human Cornea Model, MCTT HCE(TM)

The eye irritation potential of drug candidates or pharmaceutical ingredients should be evaluated if there is a possibility of ocular exposure. Traditionally, the ocular irritation has been evaluated by the rabbit Draize test. However, rabbit eyes are more sensitive to irritants than human eyes, therefore substantial level of false positives are unavoidable. To resolve this species difference, several three-dimensional human corneal epithelial (HCE) models have been developed as alternative eye irritation test methods. Recently, we introduced a new HCE model, MCTT HCE^TM which is reconstructed with non-transformed human corneal cells from limbal tissues. Here, we examined if MCTT HCE^TM can be employed to evaluate eye irritation potential of solid substances. Through optimization of washing method and exposure time, treatment time was established as 10 min and washing procedure was set up as 4 times of washing with 10 mL of PBS and shaking in 30 mL of PBS in a beaker. With the established eye irritation test protocol, 11 solid substances (5 non-irritants, 6 irritants) were evaluated which demonstrated an excellent predictive capacity (100% accuracy, 100% specificity and 100% sensitivity). We also compared the performance of our test method with rabbit Draize test results and in vitro cytotoxicity test with 2D human corneal epithelial cell lines.

Flexible modelling of simultaneously interval censored and truncated time-to-event data

This paper deals with the analysis of data from a HET-CAM(VT) experiment. From a statistical perspective, such data yield many challenges. First of all, the data are typically time-to-event like data, which are at the same time interval censored and right truncated. In addition, one has to cope with overdispersion as well as clustering. Traditional analysis approaches ignore overdispersion and clustering and summarize the data into a continuous score that can be analysed using simple linear models. In this paper, a novel combined frailty model is developed that simultaneously captures all of the aforementioned statistical challenges posed by the data.

Assessing the systemic toxicity in rabbits after sub acute exposure to ocular irritant chemicals

Eye is a highly vascularised organ. There are chances that a foreign substance can enter the systemic circulation through the eye and cause oxidative stress and evoke immune response. Here the eyes of rabbits were exposed, for a period of 7 days, to 5 known ocular irritants: Cetyl pyridinium chloride (CPC), sodium salicylate (SS), imidazole (IMI), acetaminophen (ACT) and nicotinamide (NIC). The eyes were scored according to the draize scoring. Blood collected from the treated rabbit were analyzed for haematological and biochemical parameters. After sacrifice, histological analysis of the eye and analysis of pro-inflammatory biomarkers (IL-1α, IL-1β, IL-8 and TNF-α) in the cornea using ELISA was carried out. Spleen was collected and the proliferation capacities of spleenocytes were analyzed. Liver and brain were collected and assessed for oxidative stress. The eye irritation potential of the chemicals was evident from the redness and swelling of the conjunctiva and cornea. Histopathological analysis and ELISA assay showed signs of inflammation in the eye. However, the haematological and biochemical parameters showed no change. Spleenocyte proliferations showed only slight alterations which were not significant. Also oxidative stress in the brain and liver were negligible. In conclusion, chemicals which cause ocular irritation and inflammation did not show any systemic side-effects in the present scenario.

Retrospective analysis of the Draize test for serious eye damage/eye irritation: importance of understanding the in vivo endpoints under UN GHS/EU CLP for the development and evaluation of in vitro test methods

For more than two decades, scientists have been trying to replace the regulatory in vivo Draize eye test by in vitro methods, but so far only partial replacement has been achieved. In order to better understand the reasons for this, historical in vivo rabbit data were analysed in detail and resampled with the purpose of (1) revealing which of the in vivo endpoints are most important in driving United Nations Globally Harmonized System/European Union Regulation on Classification, Labelling and Packaging (UN GHS/EU CLP) classification for serious eye damage/eye irritation and (2) evaluating the method’s within-test variability for proposing acceptable and justifiable target values of sensitivity and specificity for alternative methods and their combinations in testing strategies. Among the Cat 1 chemicals evaluated, 36–65 % (depending on the database) were classified based only on persistence of effects, with the remaining being classified mostly based on severe corneal effects. Iritis was found to rarely drive the classification (<4 % of both Cat 1 and Cat 2 chemicals). The two most important endpoints driving Cat 2 classification are conjunctiva redness (75–81 %) and corneal opacity (54–75 %). The resampling analyses demonstrated an overall probability of at least 11 % that chemicals classified as Cat 1 by the Draize eye test could be equally identified as Cat 2 and of about 12 % for Cat 2 chemicals to be equally identified as No Cat. On the other hand, the over-classification error for No Cat and Cat 2 was negligible (<1 %), which strongly suggests a high over-predictive power of the Draize eye test. Moreover, our analyses of the classification drivers suggest a critical revision of the UN GHS/EU CLP decision criteria for the classification of chemicals based on Draize eye test data, in particular Cat 1 based only on persistence of conjunctiva effects or corneal opacity scores of 4. In order to successfully replace the regulatory in vivo Draize eye test, it will be important to recognise these uncertainties and to have in vitro tools to address the most important in vivo endpoints identified in this paper.

Castor oil and mineral oil nanoemulsion: development and compatibility with a soft contact lens

CONTEXT

The non-invasive ophthalmic therapy has a drawback: low residence time in the eye socket. Nanoparticles and contact lenses have been studied as promising ocular drug delivery systems.

OBJECTIVE

To develop a nanoemulsion and evaluate its compatibility with a soft contact lens as a potential strategy for ocular delivery.

MATERIALS AND METHODS

The formulations were developed by spontaneous emulsification and fully characterized. Two drops of nanoemulsion were instilled on the surface of a commercial contact lens and its transparency was measured using a UV-Vis spectrophotometer. Before and after the instillation of the drops, the morphology (scanning electron microscopy - SEM) and ion permeability of the lenses were analyzed.

RESULTS

The formulations had a mean particle size of 234 nm, polydispersity below 0.16, zeta potential of -8.56 ± 3.49 mV, slightly acid pH, viscosity ≈1.2 mPa s(-1) and spherical-shaped particles. Nanoemulsion was non-irritant (hen's egg test-chorioallantoic membrane), which was confirmed by the cytotoxicity studies in the SIRC cell cultures. After instillation, SEM analysis showed nanodroplets inside and on the surface of the lenses, although their transparency remained near 100%. No significant differences were found between lens ion permeability coefficients before and after instillation.

CONCLUSIONS

Formulations presented appropriate physicochemical characteristics and suitability for ocular application. The contact lens remained transparent and ion-permeable after association with the formulation.

Survey of ocular irritation predictive capacity using Chorioallantoic Membrane Vascular Assay (CAMVA) and Bovine Corneal Opacity and Permeability (BCOP) test historical data for 319 personal care products over fourteen years

The Chorioallantoic Membrane Vascular Assay (CAMVA) and Bovine Corneal Opacity and Permeability (BCOP) test are widely used to predict ocular irritation potential for consumer-use products. These in vitro assays do not require live animals, produce reliable predictive data for defined applicability domains compared to the Draize rabbit eye test, and are rapid and inexpensive. Data from 304 CAMVA and/or BCOP studies (319 formulations) were surveyed to determine the feasibility of predicting ocular irritation potential for various formulations. Hair shampoos, skin cleansers, and ethanol-based hair styling sprays were repeatedly predicted to be ocular irritants (accuracy rate=0.90-1.00), with skin cleanser and hair shampoo irritation largely dependent on surfactant species and concentration. Conversely, skin lotions/moisturizers and hair styling gels/lotions were repeatedly predicted to be non-irritants (accuracy rate=0.92 and 0.82, respectively). For hair shampoos, ethanol-based hair stylers, skin cleansers, and skin lotions/moisturizers, future ocular irritation testing (i.e., CAMVA/BCOP) can be nearly eliminated if new formulations are systematically compared to those previously tested using a defined decision tree. For other tested product categories, new formulations should continue to be evaluated in CAMVA/BCOP for ocular irritation potential because either the historical data exhibit significant variability (hair conditioners and mousses) or the historical sample size is too small to permit definitive conclusions (deodorants, make-up removers, massage oils, facial masks, body sprays, and other hair styling products). All decision tree conclusions should be made within a conservative weight-of-evidence context, considering the reported limitations of the BCOP test for alcohols, ketones, and solids.

In vitro assessment of eye irritancy using the Reconstructed Human Corneal Epithelial SkinEthic HCE model: application to 435 substances from consumer products industry

The 7th amendment of the EU Cosmetics Directive led to the ban of eye irritation testing for cosmetic ingredients in animals, effective from March 11th 2009. Over the last 20years, many efforts have been made to find reliable and relevant alternative methods. The SkinEthic HCE model was used to evaluate the in vitro eye irritancy potential of substances from a cosmetic industry portfolio. An optimized protocol based on a specific 1-h treatment and a 16-h post-treatment incubation period was first assessed on a set of 102 substances. The prediction model (PM) based on a 50% viability cut-off, allowed to draw up two classes (Irritants and Non-Irritants), with good associated sensitivity (86.2%) and specificity (83.5%). To check the robustness of the method, the evaluated set was expanded up to 435 substances. Final performances maintained a high level and were characterized by an overall accuracy value > 82% when using EU or GHS classification rules. Results showed that the SkinEthic HCE test method is a promising in vitro tool for the prediction of eye irritancy. Optimization datasets were shared with the COLIPA Eye Irritation Project Team and ECVAM experts, and reviewed as part of an ongoing progression to enter an ECVAM prospective validation study for eye irritation.

Hen Egg Chorioallantoic Membrane Bioassay: An In Vitro Alternative to Draize Eye Irritation Test for Pesticide Screening

As an alternative to the standard Draize eye irritation test, the potential irritancy of compounds was evaluated by observing adverse changes that occur in chorioallantoic membrane CAM) of the hen egg (HECAM) after exposure to a test chemical placed directly on the CAM. The occurrence of hemorrhage, coagulation, and lysis in response to a test compound is the basis for employing this technique to evaluate its potential for in vivo damage to mucous membrane, in particular the eye. Irritancy is scored according to the severity and speed at which damage occurs. In the present study, five different classes of pesticides were screened for irritation potential. There was good correlation between the HECAM assay and the in vivo Draize eye irritation test. The proposed HECAM assay, which reduces the requirement for laboratory animals, could be a painless alternative to the Draize test.

Evaluation of the Hen's Egg Test–Chorioallantonic Membrane (CAM) Method in Prediction of the Eye Irritation Potential Formulated Personal Wash Products

A large database has demonstrated a robust relationship between the chorioallantonic membrane (CAM) and the Draize rabbit eye tests. The precision, sensitivity, and direct correlation of the CAM with human eye evaluations were critically appraised in this work. A total of 24 studies, including 12 CAM assays and 12 human clinical studies were conducted. Both the CAM assay and the human tests demonstrated good interassay precision and a robust correlation between the CAM scores and the inflammatory responses of human eye bulbar conjunctiva, palpebral conjunctiva and scleral vessels. This provided sound evidence that the CAM assay could be a predictive screen for eye irritation assessment for personal wash products and a key element of the tiered scientific approach in supporting labeling claims such as "tear free".

An Integrated Decision-tree Testing Strategy for Eye Irritation with Respect to the Requirements of the EU REACH Legislation

This paper presents some results of a joint research project, sponsored by Defra and conducted by FRAME and Liverpool John Moores University, on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for the safety testing and risk assessment of chemicals. The project covered all the main toxicity endpoints associated with REACH. This paper focuses on the use of alternative (non-animal) methods (both in vitro and in silico) for eye irritation testing. The manuscript reviews numerous in vitro tests and their possible collation into test batteries, in silico models and a refined in vivo method (the low volume eye test), before combining the use of all these methods into an integrated testing strategy. The aim of this strategy is a reduction in the number of animal tests which would need to be performed in the process of fulfilling the REACH system criteria; this would also lead to a lowering of the number of animals required in compliance with the REACH system requirements.

Final Report on the Safety Assessment of Pentasodium Pentetate and Pentetic Acid as Used in Cosmetics

Pentasodium Pentetate and Pentetic Acid function as chelating agents in cosmetics. Pentasodium Pentetate is readily soluble in water, but the corresponding free acid is not. Pentasodium Pentetate is used in almost 400 cosmetic products over a wide range of product categories, although it is mostly used in hair dyes and colors at use concentrations of 0.1% to 1.0%. Pentetic Acid is used in 150 cosmetic products, mostly in hair dyes and colors. Chelating agents are used in cosmetics to remove calcium and magnesium cations, which impede foaming and cleansing performance and which can cause a haze in clear liquids. The acute oral LD50 of Pentasodium Pentetate in rats was >5 g/kg. The acute dermal LD50 of Pentapotassium Pentetate using rats was reported to be >2 g/kg. The intraperitonal LD50 of Pentetic Acid was reported to be 585 mg/kg. Short-term studies of the calcium and sodium salts of Pentetic Acid in male mice demonstrated no dose-related toxicity over the dose range of 10, 100, and 250 mg/kg. In a 4-week dermal toxicity study, daily topical application of 0.05% Pentasodium Pentetate to shaved and abraded rabbit skin produced moderate erythema after the first week and throughout the study, but no systemic tox-icity. Pentasodium Pentetate or Pentapotassium Pentetate applied to intact albino rabbit skin were not irritating. A 40% solution of Pentapotassium Pentetate was not sensitizing in a guinea pig maximization test. The no observed adverse effect level (NOAEL) for rats given 40% Pentapotassium Pentetate by oral gavage was reported to be 83 mg/kg day-1. Subchronic inhalation evaluation of a bath freshener containing 0.05% or 0.09% Pentasodium Pentetate using albino rats determined that there was no cumulative systemic toxicity attributable to the ingredient at either concentration. The no observed effect level (NOEL) for maternal toxicity in pregnant rats was 400 mg/kg body weight and for fetal toxicity was 100 mg/kg body weight. Another reproductive toxicity study evaluated Pentetic Acid–Zn with and without sodium chloride in pregnant C57/B1 Dougherty mice. No toxicity was found without added sodium chloride. Pentapotassium Pentetate was not muta-genic in an Ames test, with or without metabolic activation. The same material tested in Chinese hamster ovary cells was not clas-togenic. Calcium Pentetate at 1.351 µg/ml produced a statistically significant increase in the number of sister-chromatid exchanges. Pentasodium Pentetate is nonirritating to moderately irritating, but not a sensitizer in clinical tests. A human comedogenicity (acne promotion) test using Pentasodium Pentetate found no effect. Although data are lacking on the dermal penetration of these two ingredients, other chelating agents such as EDTA do not penetrate the skin, so it is likely that Pentasodium Pentetate and Pentetic Acid also would not penetrate. The high water solubility of Pentasodium Pentetate and the low water solubility of Pentetic Acid also support that their dermal penetration will be low. Other chelating agents, including EDTA and its salts, have been determined to be safe in the current practices of use in cosmetics. Meta-, Tri-, and Hexam-etaphosphate salts are chelating agents determined to be safe in the current practices of use in cosmetics. Metasilicate salts were found to be safe as chelating agents in cosmetics when formulated to avoid irritation. Overall, these data were considered sufficient to support the safety of Pentesodium Pentetate and Pentetic Acid as used in cosmetics.

An integrated decision-tree testing strategy for eye irritation with respect to the requirements of the EU REACH legislation

This paper presents some results of a joint research project, sponsored by Defra and conducted by FRAME and Liverpool John Moores University, on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for the safety testing and risk assessment of chemicals. The project covered all the main toxicity endpoints associated with REACH. This paper focuses on the use of alternative (non-animal) methods (both in vitro and in silico) for eye irritation testing. The manuscript reviews numerous in vitro tests and their possible collation into test batteries, in silico models and a refined in vivo method (the low volume eye test), before combining the use of all these methods into an integrated testing strategy. The aim of this strategy is a reduction in the number animal tests which would need to be performed in the process of fulfilling the REACH system criteria; this would also lead to a lowering of the number of animals required in compliance with the REACH system requirements.

The chorioallantoic membrane test as a model to predict the potential human eye irritation induced by commonly used laboratory solvents

The purpose of this study was to investigate the potential eye irritation of a range of solvents, extensively used in industry and laboratory and the capacity of the chorioallantoic membrane test to predict this eye irritation. The irritation has been evaluated by an in vitro method using the chorioallantoic membrane as an alternative to in vivo Draize rabbit test. All the solvents studied are potentially strongly irritants, even though diluted, except dimethyl sulfoxide which was moderately irritant at a concentration of 10% v/v. In some cases there is a correlation between the concentration of the solvent and the potential eye irritation induced. The method allows prediction of the potential eye irritation of the solvents studied.

Irritation and cytotoxic potential of denture adhesives

OBJECTIVE

The present study aimed to examine the in vitro biocompatibility of denture adhesives.

BACKGROUND

Denture adhesives absorb water to become viscous and sticky, and by this process, other constituents like colouring, flavouring, wetting and preserving agents may be released. Some of these constituents may induce adverse reactions among users of denture adhesives.

MATERIALS AND METHODS

Five commercially available denture adhesives; three different creams, a powder, and a cushion were included in the study. The irritation and cytotoxic potential was evaluated using the Hen's Egg Test Chorioallantoic Membrane (HET-CAM) method and three cell culture methods; filter diffusion, dimethylthiazol diphenyltetrazolium bromide (MTT) assay and agar diffusion.

RESULTS

None of the tested denture adhesives showed a noteworthy acute irritation as evaluated by the HET-CAM method. None of the tested denture adhesives induced cytotoxicity in the filter diffusion test. One of the denture adhesives induced a severe cytotoxic reaction in both the MTT and agar diffusion assays. These tests employ longer exposure times than in both the filter diffusion and the HET-CAM test.

CONCLUSION

Denture adhesives are commonly used throughout the day, and our results raise the concern that denture adhesives may contribute to mucosal inflammation in denture wearers.

Animal testing and alternative approaches for the human health risk assessment under the proposed new European chemicals regulation

During the past 20 years the EU legislation for the notification of chemicals has focussed on new chemicals and at the same time failed to cover the evaluation of existing chemicals in Europe. Therefore, in a new EU chemicals policy (REACH, Registration, Evaluation and Authorization of Chemicals) the European Commission proposes to evaluate 30,000 chemicals within a period of 15 years. We are providing estimates of the testing requirements based on our personal experiences during the past 20 years. A realistic scenario based on an in-depth discussion of potential toxicological developments and an optimised "tailor-made" testing strategy shows that to meet the goals of the REACH policy, animal numbers may be significantly reduced below 10 million if industry would use in-house data from toxicity testing, which are confidential, if non-animal tests would be used, and if information from quantitative structure activity relationships (QSARs) would be applied in substance-tailored testing schemes. The procedures for evaluating the reproductive toxicity of chemicals have the strongest impact on the total number of animals bred for testing under REACH. We are assuming both an active collaboration with our colleagues in industry and substantial funding of the development and validation of advanced non-animal methods by the EU Commission, specifically in reproductive and developmental toxicity.

An evaluation of the cytotoxic effects of orthodontic bonding adhesives upon a primary human oral gingival fibroblast culture and a permanent, human oral cancer-cell line

The purpose of this investigation was to determine the cytotoxic effects of three different kinds of orthodontic adhesive on a human primary gingival fibroblast culture (GF) and a human oral cancer-cell line (OC2). The adhesives comprised a self-cure bonding resin, a light-cure bonding resin, and a hybrid glass ionomer. Any differences between the cytotoxic potencies of eluates of the orthodontic materials on GF and OC2 cells were quantified colorimetrically (MTT test). The results are as follows: For the hybrid glass ionomer, the survival rate of GF cells exposed to the liquid component revealed a significant dose-dependent decrease (p < 0.05). The liquid component and the mixed hybrid glass-ionomer material reflected a significant dose-dependent decrease (p < 0.05) in exposed OC2 cell survival. Associated with an increase in the cell exposure concentration of Resin A, Resin B, Paste A, Paste B, Resin A + B, Paste A + B and the set material of the self-cure resin adhesive, was a significant decrease in survival rate for cultured GF and OC2 cells (p < 0.05). Associated with an increase in the concentration of the primer, paste, and mixed material of the light-cure resin adhesive to which test cells were exposed, the survival rate reflected a decrease for GF cells (p < 0.05). The survival rate of cells exposed to light-cure resin paste reflected no difference for OC2 cells. It is concluded that the liquid of the hybrid glass-ionomer cement, Resin A and Resin B and Resin A + B of the self-cure resin and the primer of the light-cure resin are toxic agents to the GF and OC2 cell lines. Primary human gingival fibroblasts were found to be more sensitive than the tested human oral carcinoma cell line from most of the substances.

ECVAM's research and validation activities in the fields of topical toxicity and human studies

This paper outlines the research, prevalidation and validation activities that ECVAM has undertaken in collaboration with its partners in the field of topical toxicity testing and human volunteer studies, from its creation until now (1994-2002).

Evaluation of eight in vitro assays for assessing the cytotoxicity of cigarette smoke condensate

The accurate assessment of cytotoxicity is important for evaluating the potential of a test agent to induce pathologies that result from cell killing and to determine appropriate doses for other endpoints, such as genetic toxicology studies. The objective of this work was to determine the most sensitive assays for assessing cytotoxicity in Chinese hamster ovary (CHO) cells following short-term (1 h) and long-term (24 h) exposure to cigarette smoke condensate (CSC). Eight in vitro cytotoxicity assays with different endpoints were used to evaluate the cytotoxicity of Kentucky reference 1R4F (K1R4F) CSC in CHO cells. The assays used for this study were neutral red uptake, LDH release, kenacid blue binding, MTT formation, XTT formation, acid phosphatase activity, sulforhodamine B binding and resazurin binding. Four of the more widely used cytotoxicity assays (neutral red, MTT, kenacid blue and LDH) were also evaluated at 3-, 6-, 12- and 18-h time points. At the 1-h exposure time, LDH was the most sensitive with toxicity observed beginning at 100 microg/ml. None of the other assays demonstrated a concentration-dependent increase in toxicity after 1-h exposures even at the maximum concentration of 150 microg/ml of CSC. Following 24 h of exposure, neutral red and kenacid blue were the most sensitive. The results of our study indicate the assay that measured membrane integrity was the most sensitive for short exposure times, whereas the neutral red and kenacid blue assays that measured total cell number were more sensitive for longer exposure times.

An investigation of new toxicity test method performance in validation studies: 2. Comparison of three measures of toxicity test performance

An area that requires further research is how best to measure test method performance in validation studies and how to set criteria that should be used to judge the adequacy of this performance. The studies reported here were designed to begin an investigation of these questions. Computer simulations were used to generate data sets similar to those that might be obtained from a large validation study. These data were then analysed using three procedures including determination of the 95% prediction interval (PI), calculation of Pearson's correlation coefficient and calculation of the contingent probability statistics (CPS), sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). The results of this work suggest that of the three approaches examined, quantitative measurements with calculation of the 95% PI provide the most information to allow discrimination between the performance of several different NTMs. The results also suggest that dividing data sets into positive and negative toxicity classifications followed by the calculation of CPS leads to considerable information loss. This loss of information may be so significant that it is not possible in certain circumstances to distinguish between NTMs that are adequate and those that are not.