Реферат: Humane approches to toxicological evaluations of industrial chemicals
NIZNHNY NOVGOROD UNIVERSITY
DEPARTMENT OF ECOLOGY
Made byLoginov V. V.
d. b. s.,prof. Gelashvili D. B.
NIZHNY NOVGOROD, 1999
Thereare millions of chemical substances recorded in the scientific literature withmany more being added annually through the endeavors of chemists in industryand academia (Tаble 1). Tens of thousands of these substances are used incommerce, as demonstrated by the publication of inventories in the EuropeanEconomic Community under the Sixth Amendment to the Dangerous SubstancesDirective and in the United States through the Toxic Substances Control Act(TSCA).
Theenormous growth of the chemical industry, coupled with the potential forincreased exposure of the population to chemicala, has generated growing publicconcern and an awareness of the need for correct safety aascsfunent. Thetoxicological assessment, therefore, of the potential health hazards posed bychemical substances to which humans and animals may be directly or indirectlyexposed Is a rational requirement of civilized society.
TABLE 1ChemicalSubstances Known
Increase per annum
EINECS (European Inventory of Existing
Commerical Chemical Substances)
ECOIN (European Core Inventory)
Over the last40 years or so, the use of toxicology as a predictive science has developedimmensely. This growth has been stimulated by an increasing amount oflegislation that ensures that relevant toxiclty studies, which includewhole-animal studies, are completed on a variety of chemical substances.The knowledge of whether a chemicalsubstance has the potential to poison a biological system, cause irritation oncontact with the external tissues or cause an allergic response, Is imiwrtantin establishing a safer environment. An awareness of these properties assistssociety in ensuring correct and safe procedures when people or animals areexposed to chemicals.
Trade in chemicals isinternational, and therefore understanding the hazards of chemical substancesand identifying those hazards on the label requires an international languageof hazard warning. Acute toxic effects derived from animal studies have beenthe subject of standardization for classification and labeling for many years.The language of the label-TOXIC, VERY TOXIC, HARMFUL, IRRITANT, CORROSIVE-is understoodby the international community.
Whilesociety demands health and safety as prerequisites for the development,manufacture, and use of chemical substances, society is also concerned with the welfare and humane treatment ofthe laboratory animals used in toxiclty testing. This, of course, poses apotential paradox since the complete assessment of the toxicity of chemical substancesinvolves the use of laboratory animals. Codes of practice have been establishedin many countries to promote humane procedures. The Organisation for EconomicCo-operation and Development (OECD) haa made enormous progress in standardizingtoxicological testa to reduce barriers to trade caused by varying protocolrequirements between nations, and this has had a significant influence inreducing the number of animals used in toxicological studies. The use of liveanimals as experimental models is not in itself inhumane, although this view isnot shared by everyone.
In vitro systems that avoidthe use of live animals have been developed for predicting the mutagenic, andpossibly carcinogenic, potential of chemical substances, one such Is the Salmonella typhimurium reverse mutationassay (Ames test). This has stimulated many toxicologists, biologists,pharmacologists and biochemists to consider whether alternative in vitro/exvivo procedures could minimize the need for whole-animal studies in other areasof toxicology.
Aprimary objective for achieving general acceptance of any in vitro alternativeto an animal model for the assessment of potential risk to humans and theenvironment is to have it accepted by regulatory authorities as a recognizedassessment of a toxic property; nowadays there are very few circumstances inchemical manufacture, marketing, transportation, and use that do not come underthe auspices of a government department somewhere in the world.
Inshort, in vitro alternatives need to satisfy scientific criteria for theiracceptability and need to satisfy the international regulatory community thattheir use will not compromise assessment of risk or pose serious problems tointernational trade in chemicals.
The eye is oneof the most valuable and vulnerable of sense organs (Albino rabbits are used inthe test). Dusturbance of vision, injury to the eye, or even loss of sight dueto chemical or phisical damange must be recognized as a most traumaticexperience. It is the abhorrence of such events that necessitates the testingof chemicals in order to reduce, and hopefully prevent, their occurrence inhumans. This method is the basic for most eye irritation testing today. Newchemicals and mixtures of chemicals pose a potential eye hazards to humans. Thenature of the hazards needs to be assessed because warnings about the potentialharm that a chemical can do to the eye only have credence if they are based onvalid information. Labeling all chemicals as hazardous would substantiallylessen the benefit of the warning label. Convincing workes and customers that ahazards exicts and that there is a need for special care, including the use ofprotective eyeglasses or goggles, has to be related to good extrapolation fromsuitable model systems. The rabbit eye test has its liminations, but in ourview it is still the best practical way of assessing ocular damage and can beconducted using a humane approach.
In testing foracute systemic toxicity, it is our opinion that in vitro test systems areunlikely to replace in vivo studies. The principle of the test method andprocedures generally recommended have been reviewed by many, recently byOrganisation for Economic Co-operation and Development. The rat and mouse are the species of choice becausethey are able to display a full range of clinical signs of toxicity. The testsubstance is administered by the most appropriate route (either oral, dermal,or inhalation) to small groups of animals at a range of draduated doses. Theformulations of substance and volume administered are standardized as far aspossible to avoid the confounding effects of minor protocol variation. Acutesystemic toxicity studies assess the relationship between the dose of asubstance and adverse effects, its toxicity relative to other substances ofknow toxicity, the specific clinicalsings of toxicity, the physiological systems affected, and often an indicationof the mode and potential mechanism of toxic action. Such information may helpthe clinical to diagnose and treat adverse effects when they occur in humansusing specific antidotes. The humane approach employed in most industriallaboratories is he use of the minimum number of experimental animals and theuse of euthanasia when toxic effects are detected. In our own laboratory, withexperience of a number of different types of industrial chemicals, many substances are defined adequately by alimit dose or rangefinding study. Indeed, following acute exposure, arelatively small number of substances produce observable adverse systemiceffects (Table 2).
Toxic Categories Following Acute Oral and Dermal Dosing Studies in the Rat
The use offewer laboratory animals, coupled with a less rigid adherence to the need for statisticalprecision, is a rational approach that will allow assessment of toxicity hazardand heme prevent human suffering.
Skin contactis probably the most common form of exposure to industrial chemicals.The mostcommon in vivo approach to determine such potential is based on the method ofDraize et al. In the Draize skin test the animal of choice is the albinorabbit. The skin, like many other organs, is complex is born structure andfunction. Substances that interact with this tissue can produce different toxiceffects. The skin represents tissue that will allow more readly the developmentof a variety of in vitro and ex vivo systems to assessirritancy andcorrosivity. However, the complexity of the immunological system means thatcontact allergy may not be as readily stadied using in vitro tecniques.
The preceding section ofthis chapter have deal with the areas of ocular toxicity, acute sustemictoxicity,and cutaneous toxicity, and a common theme has emerged. There is, in ouropinion, no immediate likelihood of in vitro alternatives replacing laboratoryanimals in the assessment of acute effects caused by chemical substances.
Society demands of thetoxicologist a high degree of certainty in determining health hazards, with aminimal tolerance of error. Toxicologists, therefore, need to be cautious that,in their search for alternatives to laboratory animals, they do not reduce thepredictive quality of toxicological assessment to the point where people willbe put at risk.
Selection of a hazard labelis particularly dependent on knowing the relative systemictoxicity through the estimation of the median lethal dose (LP50) and theirritant class. The vast majority of chemicals have been classified by dataderived from toxicity studies in laboratory animals and, in our experience,with only a small number of chemicals producing adverse acute effects in theacute toxicity tests (Fig. 1). Thus, if there is to be an in vitro alternativeto studies in laboratory animals that will have a role in internationallabeling and classification, it must be very well validated against the animalmodel. This difficulty should not, however, preclude the use of in vitro testsper se, although it will certainly have a modifying influence on the rate atwhich they gain acceptance by regulatory authorities.
SYSTEMIC — oral (10%)
— dermal (8%)
IRRITATION — skin (20%)
— eye (21%)
SENSITISATION — skin (31%)
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FIGURE 1Acute toxicity studies (outcome of ICI experiments, 1976-1983). (a)Proportion of studies, (b) Proportion of studies with effects, (c) Proportionof all studies.
Thechemical industry is most concerned for the health and safety of people who maybe affected by its products and activities. The toxicologist is pivotal inproducing the data that can help reduce risks by improving the knowledge andunderstanding of the hazardous properties of chemical substances. The use oflaboratory animals to investigate these hazards is unavoidable until such timeas in vitro alternatives have proven ability to predict the dangers to humans.
1. Jackson S.J., Rhodes C.,Oliver G.J.A. Humane approaches to Acute Toxicity Assessment of IndustrialChemicals. // Toxic Substances Journal. 1989. pp.279-299.
2. O Flanerty E.J. DoseDependens Toxicity. // Commenis Toxicology. 1986. Vol.1. pp. 23-34.
3. ToxicologicalEvaluations. Potential health hazards of existing chemicals. BG Chemie. Berlin.1990. 341 p.