A screen for photoirritants in cultured cells

Adverse photoirritant or photoallergic reactions may be caused by the interaction of certain chemicals with light. The behaviour of 20 chemicals (of which 12 were known UV absorbers and photoirritants, four were known UV absorbers and non-photoirritants and four were known non-UV-absorbers and non-photoirritants) have been screened in an in vitro photoirritation assay using cultured cells [3T3 neutral red uptake (NRU) assay]. Treated cells were exposed to UVA (5 J/cm(2) in 50 min) and visible light in Earle's balanced salt solution and compared with dark controls. The 3T3 NRU assay has shown some promising results for screening photoirritants; however, it is likely that a battery of in vitro assays will be required.

An assessment of the phototoxic hazard of a personal product ingredient using in vitro assays

Where substances are intended for use in personal products applied to the skin an assessment of potential phototoxic hazard is required. This report describes a tiered testing strategy involving in vitro assays used for the phototoxic hazard assessment of a personal product ingredient (Ingredient X). The initial assay was measurement of a UV/visible absorption spectrum to identify absorption at relevant wavelengths. This was followed by in vitro assays for phototoxicity (3T3 cell neutral red uptake phototoxicity test) and photoallergy (photobinding to human serum albumin). These in vitro screens gave equivocal results for Ingredient X which appeared to suggest a weak phototoxic reaction. To further evaluate the phototoxic hazard of Ingredient X to human skin, a phototoxicity assay using a 3-D human skin model was conducted. Ingredient X did not cause phototoxicity in this assay. Overall conclusions from these studies were that although Ingredient X showed slight intrinsic potential for photoactivation, it was unlikely to present a hazard to human skin. This report illustrates the value in a step-wise strategy of the use of human skin models to help interpret the results of other in vitro phototoxicity assays.

Assessment of the potential allergenicity of ice structuring protein type III HPLC 12 using the FAO/WHO 2001 decision tree for novel foods

The introduction of novel proteins into foods carries a risk of eliciting allergic reactions in individuals sensitive to the introduced protein. Therefore, decision trees for evaluation of the risk have been developed, the latest being proposed by WHO/FAO early in 2001. Proteins developed using modern biotechnology and derived from fish are being considered for use in food and other applications, and since allergy to fish is well established, a potential risk from such proteins to susceptible human beings exists. The overall aim of the study was to investigate the potential allergenicity of an Ice Structuring Protein (ISP) originating from an arctic fish (the ocean pout, Macrozoarces americanus) using the newly developed decision tree proposed by FAO/WHO. The methods used were those proposed by FAO/WHO including amino acid sequence analysis for sequence similarity to known allergens, methods for assessing degradability under standardised conditions, assays for detection of specific IgE against the protein (Maxisorb RAST) and histamine release from human basophils. In the present paper we describe the serum screening phase of the study and discuss the overall application of the decision tree to the assessment of the potential allergenicity of ISP Type III. In an accompanying paper [Food Chem. Toxicol. 40 (2002) 965], we detail the specific methodology used for the sequence analysis and assessment of resistance to pepsin-catalysed proteolysis of this protein. The ISP showed no sequence similarity to known allergens nor was it stable to proteolytic degradation using standardised methods. Using sera from 20 patients with a well-documented clinical history of fish allergy, positive in skin prick tests to ocean pout, eel pout and eel were used, positive IgE-binding in vitro to extracts of the same fish was confirmed. The sera also elicited histamine release in vitro in the presence of the same extracts. The ISP was negative in all cases in the same experiments. Using the proposed decision tree, we demonstrated the safety of the ISP to patients already sensitised to fish, as well as to individuals potentially susceptible to producing IgE responses to proteins. Furthermore, the practicability of the new decision tree was confirmed.

Sequence analysis and resistance to pepsin hydrolysis as part of an assessment of the potential allergenicity of ice structuring protein type III HPLC 12

The recently published WHO/FAO guidelines on the assessment of allergenicity of novel food proteins provide a strategy with which to approach the determination of the potential of novel proteins in foods to be allergens. Key to this strategy are the assessment of sequence similarity to known allergens and the assessment of the resistance to pepsin hydrolysis. Ice structuring proteins (also commonly referred to as anti-freeze or thermal hysteresis proteins) are a group of naturally occurring proteins that bind to ice and structure ice crystal formation. The amino acid sequence of the ice structuring protein (ISP) type III HPLC 12 (ISP type III) was compared in silico with the sequences of known allergens. Secondly, the resistance to pepsin hydrolysis of ISP type III and its glycoconjugates (produced in recombinant baker's yeast) was assessed. The results indicate that ISP type III has no sequence similarity with known allergenic proteins. Both ISP type III and ISP type III glycoconjugates contained within the fermentation product were hydrolysed readily by pepsin (50% loss in <10 min at pH 1.5) to give peptide fragments that were too small to be allergenic or to trigger cross-linking to IgE. In an accompanying study, we demonstrated that IgE from fish-allergic individuals did not bind ISP Type III. Therefore, in accordance with the WHO/FAO strategy, the assessment of ISP type III and ISP type III glycoconjugates by sequence analysis together with lack of resistance to pepsin hydrolysis and the absence of IgE binding supports the conclusion that both are unlikely to present a potential sensitisation hazard.

Mechanisms of drug photobinding to proteins: photobinding of suprofen to human serum albumin

Photobinding of drugs to biomolecules constitutes an important early event in the onset of photoallergy. In the present work, UV irradiation of human serum albumin in the presence of either suprofen (SUP) or its major photoproduct, decarboxylated suprofen (DSUP), has been studied as a model system for drug-photosensitised protein binding. Both dark binding and binding in the presence of light were investigated since this will affect the mode, site and mechanism of drug interaction with the protein. In order to determine the binding features of SUP to albumin, competitive binding experiments were carried out using fluorescent probes specific for site I and II. Suprofen was found to selectively dark bind to site II on HSA. Photobinding of DSUP to HSA was more efficient than SUP. Parallel to this, the intrinsic tryptophan fluorescence of HSA decreased when the protein was previously irradiated in the presence of the photoactive compounds, again being DSUP more efficient compared with SUP. As fluorescence quenching involves electron transfer from the excited Trp to the ground state DSUP, it follows that the photoactive compound binding to HSA must be on (or in close proximity to) site I Trp(214) residue. It appears that photobinding of SUP is largely preceded by its photodecomposition to DSUP which, in turn, associates and photobinds to HSA.

The absorption, distribution and excretion of 1- and 2-

Human breast milk is rich in 2-palmitoyl 1,3 unsaturated triacyglycerols and during the neonatal period, when milk is the sole source of nutrients, their role could be particularly important. Betapol is a novel triacylglycerol mix resembling human breast milk in its high palmitic acid content and positional distribution. The total fat absorption from Betapol has been shown to be higher than fat from conventional infant milk formulas and closer to human breast milk in infants. However, the relative fate of purified palmitic acid esterified to glycerol in the 1-, 3- and 2-positions in neonatal and young animals has not previously been established. Therefore, the fate of orally administered 1-[1-14C]palmitoyl, 2,3 dioleoyl glycerol ([14C]POO) and 1,3 dioleoyl,2-[1-14C]palmitoyl glycerol (O[14C]PO) was investigated in suckling and weanling rats using liquid scintillation counting of tissues and expired air and whole-body autoradiography. The results obtained indicate that orally administered [14C]POO and O[14C]PO are extensively absorbed from the gut, probably either as palmitic acid or as a palmitoyl glyceride in both suckling and weanling rats. Radioactivity initially concentrated in brown fat with apparent migration to the white fat of weanling rats by 96 h. Levels of 14C were low in blood, brain and other tissues. Excretion of 14C was mainly by expiration of CO(2) (approximately 72% in 96 h), indicating beta-oxidation as a major route of metabolism. Urine and faeces accounted for only approximately 6% of the excreted radioactivity. The design and size of the experiment did not allow tests of statistical significance between the absorption and excretion of OPO and POO to be conducted. However, the absorption, distribution, beta-oxidation and excretion appeared to be similar.

Prediction of ocular irritancy of prototype shampoo formulations by the isolated rabbit eye (IRE) test and bovine corneal opacity and permeability (BCOP) assay

The isolated rabbit eye (IRE) test and bovine corneal opacity and permeability (BCOP) assay were evaluated for their ability to predict the eye irritation potential of a range of hair shampoo formulations, some containing a novel non-surfactant ingredient known to be an ocular irritant. The additional endpoints of corneal swelling and histological examination were incorporated into the standard BCOP protocol. Historic Draize data were available for several of the formulations and served as a reference. The standard BCOP assay (without histology) failed to distinguish between shampoos of low and high irritant potential, when exposure times of 10 and 60 min were employed (for undiluted and 10% dilution of the shampoos, respectively) and the in vitro score classified the majority of formulations as mild. The incorporation of the histological endpoint to the BCOP protocol allowed discrimination between formulations of differing irritancy, and should be included to augment the standard BCOP protocol. Corneal swelling values did not, however, correlate with the irritant potential of the shampoos tested. The IRE which includes the endpoints of corneal swelling and histopathological scoring produced classifications of irritancy that were fairly consistent with in vivo data and distinguished between the high and low irritant potential shampoos.

Eye Irritation Testing: The Way Forward. The Report and Recommendations of ECVAM Workshop 34

This is the report of the thirty-fourth of a series of workshops organised by the European Centre for the Validation of Alternative Methods (ECVAM). ECVAM's main goal, as defined in 1993 by its Scientific Advisory Committee, is to promote the scientific and regulatory acceptance of alternative methods which are of importance to the biosciences and which reduce, refine or replace the use of laboratory animals. One of the first priorities set by ECVAM was the implementation of procedures which would enable it to become well-informed about the state-of-the-art of non-animal test development and validation, and the potential for the possible incorporation of alternative tests into regulatory procedures. It was decided that this would be best achieved by the organisation of ECVAM workshops on specific topics, at which small groups of invited experts would review the current status of various types of in vitro tests and their potential uses, and make recommendations about the best ways forward (1). The workshop on Eye Irritation Testing: The Way Forward was held in Egham, UK, on 15-17 June 1998, under the chairmanship of Michael Balls (ECVAM, Italy). The workshop had two aims, the first of which was to review some of the previous multi-laboratory validation studies on alternatives to the Draize eye test and assess why many promising alternative methods were not successful in these studies. The second aim was to discuss strategies for making progress toward the short-term reduction, refinement, and eventual replacement, of the Draize test, including: a new approach to the validation of in vitro tests for eye irritancy, based on the use of reference standards, which promises to overcome some of the problems encountered in previous studies; the use of stepwise testing strategies which reduce and refine the use of animals in eye irritation testing; the use of multivariate and other statistical techniques for the further analysis of data generated in previous validation studies; and a programme of research aimed at understanding the underlying mechanisms of eye irritation.

Report on the COLIPA Workshop on Mechanisms of Eye Irritation

This report summarises the discussions of a workshop sponsored by the European Cosmetics, Toiletries and Perfumery Association (COLIPA). The workshop discussed the state-of-the-art of eye irritancy testing, and made recommendations as to the best ways in which to validate alternatives to the Draize eye irritation test. The importance of understanding the mechanisms of eye irritation, particularly when attempting to improve in vitro prediction of in vivo eye irritancy, was also emphasised.

An evaluation of the proposed OECD testing strategy for skin corrosion

The use of testing strategies which incorporate a range of alternative methods and which use animals only as a last resort is widely considered to provide a reliable way of predicting chemical toxicity while minimising animal testing. The widespread concern over the severity of the Draize rabbit test for assessing skin irritation and corrosion led to the proposal of a stepwise testing strategy at an OECD workshop in January 1996. Subsequently, the proposed testing strategy was adopted, with minor modifications, by the OECD Advisory Group on Harmonization of Classification and Labelling. This article reports an evaluation of the proposed OECD testing strategy as it relates to the classification of skin corrosives. By using a set of 60 chemicals, an assessment was made of the effect of applying three steps in the strategy, taken both individually and in sequence. The results indicate that chemicals can be classified as corrosive (C) or non-corrosive (NC) with sufficient reliability by the sequential application of three alternative methods, i.e., structure-activity relationships (where available), pH measurements, and a single in vitro method (either the rat skin transcutaneous electrical resistance (TER) assay or the EPISKIN™ assay). It is concluded that the proposed OECD strategy for skin corrosion can be simplified without compromising its predictivity. For example, it does not appear necessary to measure acid/alkali reserve (buffering capacity) in addition to pH for the classification of pure chemicals.

The CTFA Evaluation of Alternatives Program: an evaluation of in vitro alternatives to the Draize primary eye irritation test. (Phase III) surfactant-based formulations

The CTFA Evaluation of Alternatives Program is an evaluation of the relationship between data from the Draize primary eye irritation test and comparable data from a selection of promising in vitro eye irritation tests. In Phase III, data from the Draize test and 41 in vitro endpoints on 25 representative surfactant-based personal care formulations were compared. As in Phase I and Phase II, regression modelling of the relationship between maximum average Draize score (MAS) and in vitro endpoint was the primary approach adopted for evaluating in vitro assay performance. The degree of confidence in prediction of MAS for a given in vitro endpoint is quantified in terms of the relative widths of prediction intervals constructed about the fitted regression curve. Prediction intervals reflect not only the error attributed to the model but also the material-specific components of variation in both the Draize and the in vitro assays. Among the in vitro assays selected for regression modeling in Phase III, the relationship between MAS and in vitro score was relatively well defined. The prediction bounds on MAS were most narrow for materials at the lower or upper end of the effective irritation range (MAS = 0-45), where variability in MAS was smallest. This, the confidence with which the MAS of surfactant-based formulations is predicted is greatest when MAS approaches zero or when MAS approaches 45 (no comment is made on prediction of MAS > 45 since extrapolation beyond the range of observed data is not possible). No single in vitro endpoint was found to exhibit relative superiority with regard to prediction of MAS. Variability associated with Draize test outcome (e.g. in MAS values) must be considered in any future comparisons of in vivo and in vitro test results if the purpose is to predict in vivo response using in vitro data.