Human irritation tests

K. P. Wilheilm. M, Sambtehe, C. P. Siegers. Quantitative in vitro asses.snteni of N-alkyl sulphate-Induced cytotoxicity in human keraiinocytes. Comparison with in vivo human irritation tests. Br. J. Demiatoi. 130(1) 18-23, 1994. 

Sensitization results are based on a human maximization test (103) usiag a petrolatum vehicle. The effect is expressed as the number of paneHsts responding over the total number of paneHsts tested and was 0/25 except for spearmint (0/32). That is, at the dose iadicated, the oils werenot irritating when tested ia a 48-h closed patch test ia humans. 

Van Paassen [57,67] reported a synergistic decrease of the skin and eye irritation level of sodium lauryl ether sulfate by combination with lauryl ether carboxylates. The investigations have been carried out using the Draize eye irritation test and human patch test (Tables 13 and 14). Furthermore, measurements by in vitro methods, the Zein test, and the red blood cell test show low to no irritancy [251-253]. 

FIG. 7 Skin irritation according to the human patch test of alkyl ether carboxylic acids compared to other mild cosurfactants. CFTA-names 1, cocamidopropylbetaine 2, sodium PEG-6 cocamide carboxylate 3, sodium laureth-11 carboxylate 4, cocoamphocarboxypropionate 5, protein hydrolyzate 6, disodium laureth-3 sulfo-succinate SLES, sodium laureth sulfate. (From Ref. 68.)... 

Generally speaking, up to now the importance of a-sulfo fatty acid esters in cosmetic products has been low [1 p. 367], In the future they may become more interesting because of their mildness. a-Sulfomethyl laurate and most other ester sulfonates are mild to the skin also, they are not human skin sensitizers or primary skin irritants. Tests have shown that a-sulfomethyl laurate is mild enough to be in bath products, such as bubble bath [62]. Three patents for different applications are given to show how ester sulfonates can be used in cosmetics. 

Dermal Effects. There have been no reports of adverse dermal effects associated with exposure to endosulfan in humans. When tested in farmers, endosulfan did not cause contact dermatitis (Schuman and Dobson 1985). Studies in experimental animals have shown that dermal exposure to endosulfan is only slightly to moderately irritating at relatively high doses (Hoechst 1983b, 1985c, 1985d, 1989b Industria Prodotti Chimici 1975). 

The design of vaginal, rectal, and nasal irritation studies is less formalized, but follows the same basic pattern as the primary dermal irritation test. The rabbit is the preferred species for vaginal and rectal irritation studies, but the monkey and dog have also been used for these (Eckstein et al., 1969). Both the rabbit and rat have commonly seen use for nasal irritation evaluations. Defined quantities (typically 1.0 ml) of test solutions or suspensions are instilled into the orifice in question. For the vagina or rectum inert bungs are usually installed immediately thereafter to continue exposure for a defined period of time (usually the same period of hours as future human exposure). The orifice is then flushed clean, and 24 h after exposure it is examined and evaluated (graded) for irritation using the scale in Table 11.1. 

F. Both the age of the test animal and the application site (saddle of the back versus flank) can markedly alter test outcome. Both of these factors are also operative in humans, of course (Mathias, 1983), but in dermal irritation tests, the objective is to remove all such sources of variability. In general, as an animal ages, sensitivity to irritation decreases. For the dermal test, the skin middle of the back (other than directly over the spine) tends to be thicker (and therefore less sensitive to irritations) than that on the flanks. 

In three cases of acute human exposure from industrial accidents, symptoms included light-headedness, drowsiness, anxiety and apprehension, and nausea slurred speech and vomiting also occurred in one case. In human patch tests, a 23% solution caused severe irritation and possible sensitization. However, guinea pig sensitization tests did not confirm a potential for sensitization. ... 

In hirman keratinocyte cultures, triethanolamine was categorized as a weak inducer of a delayed (> 4 h) stimulation of the release of key mediators (arachidonic acid, eicosanoids, interleukin-la) that are known to be indicative of hyperproliferative and inflammatory events in human skin (Miiller-Decker et al., 1994). In line with the in-vitro irritancy tests, triethanolamine was found to be a non-irritant in a clinical patch testing study of human skin in 20 male volunteers (Miiller-Decker et al., 1998). 

Dermal. Dermal administration is required for estimation of toxicity of chemicals that may be absorbed through the skin, as well as for estimation of skin irritation and photosensitization. Compounds are applied, either directly or in a suitable solvent, to the skin of experimental animals after hair has been removed by clipping. Often dry materials are mixed with water to make a thick paste that can be applied in a manner that ensures adequate contact with the skin. Frequently the animals must be restrained to prevent licking and hence oral uptake of the material. Solvent and restraint controls should be considered when stress is involved. Skin irritancy tests may be conducted on either animals or humans, using volunteer test panels for human tests. 

The eye irritation test is probably the most criticized by advocates of animal rights and animal welfare, primarily because it is inhumane. It has also been criticized on narrower scientific grounds in that both concentration and volumes used are unrealistically high, and that the results, because of high variability and the greater sensitivity of the rabbit eye, may not be applicable to humans. It is clear, however, that because of great significance of visual impairment, tests for ocular toxicity will continue. 

Attempts to solve the dilemma have taken two forms to find substitute in vitro tests and to modify the Draize test so that it becomes not only more humane but also more predictive for humans. Substitute tests consist of attempts to use cultured cells or eyes from slaughtered food animals, but neither method is yet acceptable as a routine test. Modifications consist primarily of using fewer animals. Usually one animal is tested first and, if the material is severely irritating no further eye testing is conducted. EPA has reduced the required number of animals from 6 to 3. In addition eye irritation should never be carried out on materials with a pH of less than 2 or more than 10 as these materials can be assumed to be potential eye irritants. 

Frosch, P.J., Kurte, A., and Pilz, B., Efficacy of skin barrier creams (III). The repetitive irritation test (RIT) in humans, Contact Dermatitis, 29, 113, 1993. 

York, M., Griffiths, H.A., Whittle, E., and Basketter, D.A. Evaluation of a human patch test for the identification and classification of skin irritation potential. Contact Dermatitis 1996 34 204—212. 

Basketter, D.A., Griffiths, H.A., Wang, X.M., Wilhelm, K.-P., and McFadden, J. Individual, ethnic and seasonal variability in irritant susceptibility of skin the implications for a predictive human patch test. Contact Dermatitis 1996 35 208-213. 

The Draize eye irritancy test, in which unanesthetized rabbits have irritant substances applied to their eyes, yields results that are inherently unreliable in predicting human toxicity. Humans and rabbits differ in the structure of their eyelids and corneas as well as in their abilities to produce tears. When comparing rabbit to human data on the duration of inflammation after exposure to 14 household products, they differed by a factor of 18 to 250. 

The Human Maximization Test was designed and later modified by Kligman et al. (1959, 1966). This test uses irritancy as an adjuvant. Irritating compounds... 

Brown VKH (1971) A comparison of predictive irritation tests with surfactants on human and animal skin. J Soc Cosmet Chem 22 411M20... 

Opdyke DL, Burnett CM (1965) Practical problems in the evaluation of the safety of cosmetics. Proceedings of the Scientific Section of the Toilet Goods Association 44 3 1 Opdyke D (1971) The guinea pig immersion test A 20 year appraisal. CFTA Cosmetic J 3 46—47 Phillips L, Steinberg M, Maibach HI, Akers WA (1972) A comparison of rabbit and human skin response to certain irritants. Toxicol Appl Pharmacol 21(3) 369-382 Uttley M, Van Abbe NJ (1973) Primary irritation of the skin Mouse ear test and human patch test procedures. J Soc Cosmet Chem 24 217-227... 

Smiles KA, Pollack ME (1977) A quantitative human patch testing procedure for low level skin irritants. J Soc Cosmet Chem 26 755-764... 

Various tissue constructs have been reassembled from isolated constituents, including resident cell types whose numbers have been amplified or modified in culture. A three-dimensional co-culture system for human skin keratinocytes layered upon a synthetic mesh infiltrated with dermal fibroblasts, when floated to allow contact of the uppermost keratinocytes with air, exhibits stratification and cornification remarkably similar to in vivo squamous epithelia. This reconstructed epithelial model has been recommended as an in vitro replacement for dermal corrosivity testing. It has been anticipated that this and a similar noncomified model will have application in dermal and ocular irritation testing, but thus far validation studies have yielded mixed results. Reconstructed tissues can also provide context for basic toxicological research on aberrant cellular interactions with cellular and acellular constituents, as illustrated by invasion of cancerous epithelial cells into underlying dermis of a skin equivalent model. 

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