Use Of Laboratory Animals In Drug Designing And Potency Testing
(Dr.Amrita Behera,Ph.D Scholar, Indian Veterinary Research Institute, Izatnagar, Dr. Deepak Sakhre, Livestock Development Officer, Maharashtra)
Introduction
The use of animals for conducting various scientific investigations can been traced back to ancient history. For example, the reports and writings of Aristotle (384-322 B.C.) and Erasitratus (304-258 B.C.) represent that they had studied the details of anatomy of various animals. Ancient period’s research and investigations such as these were the beginning of study of the basic sciences that it today forms the foundations for a new era of drug development. Till the end of the last century, experiments and research using living animals were carried out on domestic or easily captured wild species. The choice of using only these animals was usually limited and based on availability. But, while approaching towards the end of the 19th century, the abstract and the general idea of the use of laboratory animal has begun to emerge as an deliberately chosen field for its ingrained suitability for the purpose. The animals were especially bred in captivity or they were obtained from its environment not merely on grounds of convenience but rather for its usefulness for the specific investigation at hand.
The observation of humans on animals as objects of study intuitively started in prehistoric times. The first recorded attempt involving the use of live animals for research was by Ersistratis in Alexandria in 300 B.C. The investigations by animals has entirely made this possible to bring the huge advances in drug development in this century. Several mechanisms ofaction and effects on specific organs can be studied by using in vitro techniques. Nevertheless, to identify unexpected exacerbated effects and to estimate the dosages that are pharmacologically active without producing unwanted effects, invitro studies should be conducted.
For many substances, the mechanism of action will be the similar in humans and other mammals. Therefore, quantitative rather than qualitative differences in response are most common. Humans in many cases may be more sensitive to some drugs than certain laboratory animals but usually certain animal species are more sensitive than humans. For example, the mouse and cat are sensitive to atropine, and the dog and rabbit can tolerate atropine at doses 100 times higher than what humans can tolerate. The theory of species differences with respect to sensitivity can be elaborated by differences in metabolism, taking into account both quantitative and qualitative differences in their ability to detoxify drugs and also their differences in the rates of absorption, transport, distribution, and elimination of chemicals. After oral administration, absorption in laboratory animals is generally considered to be similar to that in humans, although there are quantitative differences in respect to some compounds. For example, species differences in the absorption and action of some compounds are related to differences in the bacterial flora of the gastrointestinal tract. The distribution and depository/ storage of drugs are reasonably on a constant trend among mammalian species, although plasma binding tends to be more extensive in humans than in small mammals. Species differences in response to drugs appear to be related mainly to rates of biotransformation, which are generally more rapid in small laboratory animals than in humans.
Animal experimentation and study with regard to drug discovery, development and usage
While the initial screening of new compounds for pharmacologic activity was conducted some thirty years ago using whole animals , tissues and organs being isolated from animals. In today’s time, majority of initial screening and testing for new drugs is being conducted via in vitro including the techniques of biochemistry and molecular biology. Studies are initiated in animals only after a new drug candidate has been identified in vitro. The sole aim of animal studies is to authenticate the pharmacological activity of the new drug and identify any unforseen pharmacologic activity and develop initial data based on the action of the drug in vivo. The most suitable and ideal approach would be to have an invivo screening program developed to allow for the detection of distinct profiles of activity or conglomeration of activities.
(l) Role of animal experimentation in the design and development of drugs
Animal experimentation has been particularly useful and rewarding as well once the cause of a a particular disease has been established and when the disease can be easily reproduced in small animal species. Under such circumstances, the experimental pharmacologists can establish a reliable screening procedure which will permit a team of investigators, trained in several disciplines, to search for agents to either prevent or cure the diseases. Animals are now being used in development of chemotherapy and infectious diseases. In 1935, Domagk’, announced the discovery of prontosil working with experimental streptococcal infections in mice, the first of a number of an outstanding and remarkable sulfonamides and the other synthetic drugs, useful in the cure and prevention of bacterial infections in humans and animals. In today’s time, the use of sulfonamide carry on to be very valuable in the management of certain bacterial and viral infections. There are a plethora of known antibiotics which are useful clinically. Among them, the most broadly used are penicillin and its derivatives, streptomycin. aureomycin, ,tetracycline, erythromycin, achromycin, chloromycin, bacitracin, polymyxin, griseofulvin, nystatin and amphotericin B. All of these antibiotics were discovered and made available by the combined use of in vitro and in vivo screening procedures designed to detect agents which would inhibit the growth or kill the ill microorganisms. Mice those were infected with various gram-positive and gram-negative bacteria were used for the in vivo experiments. The wide expanding list of infectious diseases of animals and humans, which have resulted in the discovery of the sulfonamides, other antibacterial synthetic agents and to the antibiotics, is quite very long. This particularly includes tuberculosis, leprosy and syphillis, these diseases have been the misfortune of mankind for thousands of centuries. But still, much experimental and ground work is there to be done in the area of chemotherapy of viral diseases and the recent animal experiments dealing with interferon.
The new drugs such as thiobendazole, which is a highly effective, broad spectrum anthelmintic has been developed which is now used in wide scale to treat and cure the infections. As, it is not possible to culture these organisms in vitro, the use of infected experimental animal has been the sole choice available to search for the drugs which can control this disease. Few similar examples can be traced with animal screening and experimental programs which give way to drugs now currently used in the treatment of trypanosomiasis amebiasis, schistosomiasis leishmaniasis, filariasis and tapeworms.
The use of animal experimental models which have been developed, have allowed scientists to search and find drugs highly useful for the symptomatic treatment of diseases of allergic origin. Compounds were found which protected guinea pigs against several lethal doses of histamine. Moreover, these compounds lessened the symptoms of anaphylactic shock by inducing spasms of various smooth muscles. Therefore, a group of drugs known as antihistamines were developed as a result of such animal experimentation. and tend to have significantvalue in the symptomatic treatment of various allergic diseases.
(2).Role of animal experiinentatinn in the development of drugs useful in diseases of unknown efficacy.
Animal experimentation played an important role in developing drugs for the systematic treatment of diabetes, rheumatic fever, hypertension, addisons disease etc. Animal investigations concerned with the chemothernpy of cancer; certain diseases of central nervous system, such as multiple sclerosis and psychoses and others, continue to receive huge and enormous attention.
(3). Animal experimentation useful in regulating organ function
In recent times, animal investigations have occupied an imperative position in the design and development or drugs which stimulate or depress specific physiologic activities of normal humans and animals. The most important and striking example of this wide area of pharmacological research are the animal investigations leading to the development of drugs which regulates and controls ovulation.
(4). Animal experimentation useful in drug safety testing.
Before any new drug being given to people for its use for the very first time, it must be tested in animals to determine the concerned side effects and the dose at which these side effects will appear. This testing has to be done in vivo because of the effects of the processes of absorption, distribution, metabolism, excretion etc. The various interactions among these processes and the subsequent interactions among the various organs and neuroendocrine systems within the entire animal cannot be duplicated in vitro. It is therefore very necessary to give much higher dosages than the usual doses that would be given clinically and sometimes given for its use over prolonged periods of time to characterize the nature of the side effects of the newly developed drug. This is because the dosages of drugs needed to elicit pharmacologic or toxicologic effects are often higher in laboratory animals than in humans and because the side effects of drugs suitable for clinical use are usually provoked only by exacerbated dosages.
It is routine practice to test new drugs for safety in at least two species to ensure that the safety of a new drug has not been over predicted and that any potential side effects have not been overlooked. In most cases these will be a rodent and a non rodent species. The variety of animal tests and the length of the studies required for a new drug depends on the nature of the drug (pharmacologic or chemical class), the intended clinical use of the drug (for example, length of the usual course of treatment) and to some extent, on the requirements of the countries in which the new drug will be registered for marketing. The following are various types of toxicity studies used for drug safety testing.
(i) Acute toxicology (ii)Subchronic and chronic toxicology (iii) Reproductive toxicology (iv) Muta- genicity (v) Carcinogenicity (vi) Primary irritation testing (vii) Antigeniciiy testing
Legislation on Animal Experimentation
To assure the validity and reproductibility of little results obtained, the proper care of laboratory animals used in research is a basic requirement. Animals used in dmg research are subject to stringent standards of care beginning with the animal supplier. For the most commonly used laboratory animals, these standards of care often apply for the entire life of the animal.
The National Institute of Health (NIH) requires that contractors who are using live vertebrate animals in projects supported by NIH follow the guidelines prescribed in the “Guide”. The Public Health Service further requires the grant-seeking institutions either be accredited by the American Association for Accreditation of Laboratory Animal Care (AAALAC) or have an institutional committee that reviews its animal facilities and practices for compliance with the “Guide”.
The overall objective of these legislations and guidelines is to restrict the use of animals in the scientific experiments. However, experiments whose aim is the extension of new discovery of biological knowledge or knowledge useful for saving and increasing the longevity of life or reducing suffering will be considered. During the experiments, where survival of the animals is expected, the procedure is governed by the pain condition which at most prohibits severe pain which is likely to endure.
Use of Vaccines in Veterinary Medicine
The clinical development of vaccines may require further safety tests in animals, which are broadly similar to those required for human medicines. The exact nature of these tests depends on the results of clinical trials.
Conclusion
There is a long history for the use of live animals as the subjects of research in science and medicine. And so is the history of those who have protested against this practice. As many theories and practices may have developed extensively, but the ethical and social questions raised by experiments on animals remain unchanged. Animal experimentation has contributed greatly to the welfare and development of man and all other animal species. Animal experimentation has played a major and important role in making drugs available to alleviate pain and other depressing signs and symptoms of disease. The control of parasitic diseases have been attributed to use of animals experimentally. Some of the same drugs have reduced the load on chronic disease hospitals as well, while still others greatly decreased the population of our mental institutions. Animalexperimentationhas therefore provided ways and means to regulate the population size of the world and contributed to enhance our food supply and make available nutrients to maintain good health. India’s Prevention and Cruelty to Animals Act of 1960 is an act of faith on the part of civil society and at the same time it tacitly recognises the principle that animals may have to be used in experiments. It is therefore very necessary to have well-defined rules and guidelines which will safe guard the interest of the scientists, the animals and the society without hampering useful biomedical research. The CPCSEA can invite reports from the institutional committees ftom time to time and conduct occasional inspections to the centers to ensure that animal welfare conditions are properly observed.
References
1 Cohen B 1 & Loew F M, in Laboratory Animal Medicine, edited by I G Fox, B J Cohen and fi M Loex, (Academic Press. Orlando), 1984, 1.
Domagk G, Ein beitrag zur chemotherapie der bacteriellen
Feingold D S, Aniimicrobial chemotherapeutic agents: the naiure of their action and selective toxicity, New England I Med, 269 (1963) 900,957.
Robinson H J & Gracssle O E, fn vitro and in rivo studies of gramicidin, tyroihricin and tyrocidine. I Pharmacol Exy Ther. 76 (1942) 3I6.
Isaacs 1, Interferon as a factor in recovery from vinis infection, Proc boy Soc Med 55 (1962) 725.
Stoll N R, The wormy world. I Parasi(ol, 33 (1947) 1.
Cuckler A C & Mezey K C, The therapeutic efficacy of thiabendazole for helminthic infections in man, Arzncimiirr/- Forsch, 16 (1966) 411.
Cockier A C, Ott W H, Cobb W R, Polin D & Stoerk H C. Biological studies in poultry, World’s Poultry
Congress Section Payers, 293 (1962).
Hooijmans, C. R., Rovers, M. M., de Vries, R. B. M., Leenaars, M., RitskesHoitinga, M., and Langendam, M. W. (2014).
SYRCLE’s risk of bias tool for animal studies. BMC Med Res Method 14, 43. doi:10.1186/1471-2288- 14-
43.
Howells, D. W., and Macleod, M. R. (2013). Evidence-based translational medicine. Stroke 44, 1466–71.
Institute for Laboratory Animal Research, National Research Council. 2011. Guidance for the
Description of Animal Research in Scientific Publications.
The National Academies Press, Washington, DC. Kilkenny, C., Browne, W. J., Cuthill, I. C., Emerson, M., and Altman, D. G. (2010).
Improving bioscience research reporting: The ARRIVE guidelines for reporting animal research. PloS Biol 8, e1000412. Kilkenny, C., Parsons, N., Kadyszewski, E., Festing, M. F., Cuthill, I. C., Fry, D., Hutton, J., and Altman, D. G. (2009).
Survey of the quality of experimental design, statistical analysis and reporting of research using animals.
PLoS One 4, e7824.
