The chorioallantoic membrane in irritation testing

The HET-CAM Test: A Study of the Irritation Potential of Chemicals and Formulations

The HET-CAM (hen's egg test-chorio-allantoic membrane), described by Luepke in 1985, permits the study of immediate effects following the administration of test substances to the chorioallantoic membrane of 10-day-incubated White Leghorn chicken eggs. The results of a study of 60 chemicals and 41 cosmetic formulations are presented here.

Intralaboratory reproducibility was established with a double-blind study of 20 surfactants at two concentrations. The results show a high rank correlation between the scores given by both experimenters: the Spearman's rho is greater than 0.9 (p < 10-8).

The 60 chemicals were studied at a concentration equivalent to 10% of the concentration tested in vivo. They were classified according to the three EEC categories of ocular irritancy, and when a correlation between the HET-CAM scores and historical Draize in vivo data was determined, the corresponding Spearman's rho value was 0.72 (p < 10-4).

The 41 formulations (make-up removers, shower gels, shampoos, creams and body milks) were tested by two protocols: rinsed and non-rinsed. The correlation between the HET-CAM scores and the historical Draize in vivo maximum average scores was studied, and the rhos obtained were 0.77 and 0.76 (p < 10 -8), respectively.

The advantages of the HET-CAM method lie in its sensitivity, rapidity and moderate cost. Both chemicals and cosmetics formulations can be tested, and specific families can be assessed using modified and more-appropriate protocols. However, to ensure that a good reproducibility and sensitivity is provided, the use of reference materials is strongly recommended.

The satisfactory performances of the HET-CAM test in many previous evaluation studies (e.g. those of the BGA, CTFA, EEC and OPAL) show that it can be a useful assay as part of a battery of in vitro tests for the screening of new ingredients and formulations.

Chick chorioallantoic membrane as an in situ biological membrane for pharmaceutical formulation development: a review

The use of animals in research has always been a debatable issue. Over the past few decades, efforts have been made to reduce, replace, and refine experiments for ethical use of experimental animals. The use of chick chorioallantoic membrane (CAM) was one of the proposed alternatives to the Draize rabbit ocular irritation test with several advantages including simplicity, rapidity, sensitivity, ease of performance, and cost-effectiveness. The recent use of CAM in the development of pharmaceuticals and testing models to mimic human tissue, including drug transport across CAM, will be discussed in this review.

Lysinoalanine in food and in antimicrobial proteins

Heat and alkali treatment of food proteins widely used in food processing results in the formation of crosslinked amino acids such as lysinoalanine, ornithinoalanine, lanthionine, and methyl-lanthionine and concurrent racemization of L-amino acid isomers to D-analogues. The mechanism of lysinoalanine formation is a two-step process: first, hydroxide ion-catalyzed elimination of cysteine and serine residues to a dehydroalanine intermediate; second, reaction of the double bond of dehydroalanine with the epsilon-NH2 group of lysine to form a lysinoalanine crosslink. The corresponding elimination-addition reaction of threonine produces methyl-dehydroalanine, which then reacts with the NH2 and SH groups to form methyl-lysinoalanine and methyl-lanthionine, respectively. The crosslinked amino acids lanthionine and methyl-lanthionine are formed by analogous nucleophilic addition reactions of the SH group of cysteine to dehydroalanine and methyl-dehydroalanine, respectively. Processing conditions that favor these transformations include high pH, temperature and exposure time. Factors which minimize lysinoalanine formation include the presence of SH-containing amino acids such as cysteine, N-acetyl-cysteine, and glutathione, dephosphorylation of O-phosphoryl esters, and acylation of epsilon-NH2 groups of lysine side chains. The presence of lysinoalanine residues along a protein chain decreases digestibility and nutritional quality in rodents but enhances nutritional quality in ruminants. Protein-bound and free lysinoalanines are reported to induce enlargement of nuclei of rat kidney cells. All of the mentioned dehydro and crosslinked amino acids also occur naturally in certain peptide and protein antibiotics. These include duramycin, cinnamycin, epidermin, subtilin and the widely used food preservative nisin. Mechanistic rationalizations are offered for the observed antimicrobial activities of these compounds in relation to their structures. The cited findings and new research to better define the chemistry and dietary and antimicrobial roles of lysinoalanine and related compounds should lead to better and safer foods.

The Galileo Data Bank on Toxicity Testing with In Vitro Alternative Methods. II. Toxicology Profiles of 20 Chemicals

The identification of the hazard of chemicals to man has relied on the use of several animal models. However, the availability of various cell toxicity models as alternatives to the use of animals has stimulated attempts to evaluate in vitro data for use in the prediction of human toxicity.

The cell toxicity models developed previously are capable of indicating a variety of endpoints susceptible to the activity of various chemical substances.

The in vitro data derived so far from testing a variety of types of chemicals, have been used to develop toxicology profiles for twenty chemicals, which are presented in this paper. Data have been selected from among those already entered in the Galileo Data Bank, a computerised data system containing all the available existing data derived using in vitro methods.

Evaluation of in vitro predictive tests for irritation and allergic sensitization

Investigations of in vitro procedures to predict the potential of substances as skin irritants and as allergens inducing delayed hypersensitivity (contact dermatitis) are described, with indications of possible advances and known limitations. The examination of keratome slices of skin for release of enzymes, for changed histochemistry and for utilization of radioisotope-labelled amino acids will detect weak irritants but is of doubtful value for moderate irritants and will detect corrosive substances only through their inhibition of all cell activities. Fibroblast cultures, tested with Clostridium perfringens toxin and chemicals, show similar limitations in detecting moderate or severe irritants. Fibroblast cultures can be made more relevant to epidermal exposure by an overlying layer of agar containing keratin. In vitro tests to detect induction of sensitizing potential for delayed hypersensitivity have made little progress. The most promising approach is to treat antigen-presenting Langerhans cells with antigen and co-culture with lymphocytes. The lymphocytes may be examined for changes in receptor expression, for synthesis of interleukin 2, and possibly for responses to allergen if sufficient cells become specifically sensitized. There are several in vitro techniques to detect responses of in vivo- or in vitro-sensitized lymphocytes treated with antigen.