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Introduction to Toxicology

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Introduction to Toxicology Introduction to Toxicology Presented by: Dr. Marjan Shariatpanahi Department of Toxicology and Pharmacology, School of Pharmacy, International Campus,, Iran Department of Toxicology and Pharmacology, School of Pharmacy, International Campus, Iran University of Medical Sciences, Tehran, Iran IUMS Nanosafety Summer School Toxins - are naturally produced by plants, animals, or bacteria. Xenobiotic - man-made substance and/or produced by but not normally found in the body. Terminology of Definitions • The literal meaning of the word ‘toxicology’ is the study of toxins. • The root of the word is from the Latin word Toxicus (meaning poison), which came into English around 1655 and is derived from the word Toxikon. • Toxikon is an ancient Greek word, and at that time it was called the poisons that impregnated the spears. • Exposure: • Any toxic compound for causing an adverse effect, must first contact the live being. It means that the live being is Exposed to chemicals through a particular path (Air, soil, food). • Toxicant: Any substance that causes harmful effects on a living organism at a specified concentration is called a toxicant. • Hazard: The qualitative nature of adverse effects arising from exposure to a physical agent or a particular toxicant. For example, suffocation is a danger caused by severe exposure to carbon monoxide. • Safety: The extent or likelihood that a material with a specified dose and specific exposure conditions will not produce any toxic effect. • Risk: The extent or likelihood that a substance with a certain dose and specific exposure conditions will cause a toxic effect. • Risk Assessment: The process by which the potential for causing adverse effects on health is recognized after exposure to toxins . • Toxicology fields • Mechanistic toxicology: • Analytical Toxicology • Forensic Toxicology • Environmental Toxicology: Investigates the toxic effects of chemical compounds in the environment on living organisms, especially non-human beings. • Ecosystem Toxicology • Industrial Toxicology • Military Toxicology • Food Toxicology • Evolutionary Toxicology - Teratology • Epidemiological Toxicology • Regulatory Toxicology • Pharmaceutical Toxicology • Toxicovegillance • Clinical Toxicology • Oncologic toxicity or Carcinogenicity • Immunotoxicology • Toxic compound: Any agent that causes harmful effects on a biological system. Depending on the concentration, these harmful effects can range from a simple, reversible disorder to the death. • The severity of toxic effects varies depending on the duration of exposure, dose, and type of exposure. • The classification of toxic compounds can vary depending on the field of toxicology. Classification of toxic compounds by toxicity severity The experimental animals: Rat Exposure Features Mice Hindi pigs • Routs of administration Rabbit • Oral Dog • Cutaneous Monkey • Inhale Squirrel • Intravenous Chinese hamster • Intramuscular Syrian hamster • Subcutaneous Mini pig • Inside the brain ventricle Micro pig Factors affecting the toxicity of a chemical compound • Dose of chemical compound • Duration of Administration • Species, subspecies, age, sex, nutritional status, health status, individual allergy, presence of other chemicals • Physicochemical properties of toxin such as solubility, melting rate, boiling point, vapor pressure, purity. If the chemical is a volatile solution and has high vapor pressure, it must be tested for toxicity by inhalation and skin absorption Criteria for choosing the suitable Species for toxicological studies • Best species to study • Animal sex used • How to keep the animal • Animal diet • Animal health • Metabolic similarity of animal to human • The way of taking poison • Duration of study • Number of animals needed Toxicology Definitions • Tolerance: Decrease in response to the toxic effect of a chemical compound resulting from previous exposure to that chemical or structure-dependent chemical compound. • Reversible and irreversible complications • Idiosyncratic Reactions Example: Succinylcholine, a genetic polymorphism in plasma butyrylcholinesterase • Other than dose, factor that influence the body response to drugs: idiosyncratic (occurring for no known reason) • Allergic complications Interaction of chemicals with one another • The interaction of toxic agents can be studied at both kinetic and dynamic levels. • The effect of two chemicals administered concurrently may manifest as one of the followings: • Additive effects: The effect obtained from the administration of two compounds at the same time is equal to the sum of the effects of each compound alone. • Synergistic effects: The effect of the two compounds being administered simultaneously more than the sum of the effects of each combination alone. • Potentiation: When a substance does not have a known toxicity effect, but if co-administered with another compound, it can exacerbate the toxicity effects of that compound. • Antagonism: If two different substances counteract the effects of each other. Additive Effects A + B Response A B Time The effect of two chemicals is equal to sum of the effect of two chemicals taken separately. Synergistic Effects A + B Response A B Time The effect of two chemicals taken together is greater than the sum of their separate effect at the same doses, e.g., alcohol and other drugs Antagonistic Effects A + B Response A B Time The effect of two chemicals taken together is less than the sum of their separate effect at the same doses Important principles in toxicology tests • If the dose is calculated on the basis of body weight, the human dose is equal to one tenth of the animal dose to observe a toxic effect that had previously occurred in the animal. • All carcinogenic compounds in animals are assumed to be carcinogenic in humans. • Exposure of experimental animals to high doses of a toxic compound is a prerequisite and valid method of detecting possible hazards in humans. Toxicology experiments in animal studies (Acute toxicity test) • (Subacute toxicity test) • (Subchronic toxicity test) • (Chronic toxicity test) • Acute toxicity test • Duration of study 24 hours after administration of the specified dose of the substance • The purpose of acute toxicity tests : • Calculating LD50 • Identification of target organs and other clinical signs of acute toxicity • Reversibility of Toxic Responses • Determination of dose range for other toxicological studies • Evaluating the ability of a toxin to irritate skin or eyes What is LD50? • LD50 is equal to the amount of toxic compound that causes 50% death in the animals. • LD50 is an indicator to compare the toxicity of a substance with other substances in a specified condition. In order to evaluate the therapeutic effects of a substance (known as an antidote) on the toxicity of a toxicant, an LD50 calculation of that toxin is necessary. • It requires the use of two different administration routs and in two different animal species (mice and rats). • At least 3 different doses are required to calculate this index. • The mortality rate is assessed 24 hours after drug administration, and the remaining animals will be monitored for up to 14 days. Draize test • Draize Test: The ability of a chemical to induce skin and eye irritation after an acute exposure is usually determined in rabbits. • In order to evaluate the potential of a chemical compound to cause skin sensitization, the effect of other accompanying compounds should also be studied in addition to the desired compound. Subacute toxicity test • Purpose: To obtain information on the toxicity of a chemical compound after repeated doses. • The results of this study can be used to determine the doses required in subchronic studies. • The maximum duration of the study is one month. • A typical protocol is to give three to four different dosages of the chemicals to the animals by mixing it in their feed. For rats, 10 animals per sex per dose are often used; for dogs, three dosages and 3 to 4 animals per sex are used. Clinical chemistry and histopathology are performed after 14 days of exposure. Subchronic toxicity test • The duration of contact in this study is usually between 1 - 3 months. • Usually two animal species (rat and dog) and three different doses are used. • The rout of administration depends on the method of use or contact with the studied chemical compound. • The purpose of subchronic studies: Determination of NOAEL (No observed adverse effect level) Determination of LOAEL (Lowest observed adverse effect level) Identifying the tissues that are specifically affected by the toxic compound. The possibility of predicting appropriate doses for chronic studies Chronic toxicity test • The purpose of the chronic toxicity test is to evaluate the cumulative toxicity of the substance, along with its potential for cancer. • Study duration is 3 months to 2 years. • The animal species is determined by subchronic studies. • The study should be carried out in at least 3 animal species. • The route of administration depends on how the toxic compound is used or contacted. • Investigating the effects of the toxic compounds on the fetus, genetic toxicity, and mutagenesis are among other things that are being evaluated for completing the test. Chronic toxicity is in 2 category: 1. Chronic toxicity requiring prolonged or repeated exposure to a compound. Example: Long exposure to low concentrations of metals such as arsenic, mercury, and cadmium, which can cause a variety of cancers. 2. Chronic toxicity that occurs after a prolonged period following exposure to only
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