toxicology ………… Is the study of the harmful effects of chemicals and physical agents on living organisms Examines adverse effects ranging from acute to long-term `
toxicology ………… Is used to assess the probability of hazards caused by adverse effects Is used to predict effects on individuals, populations and ecosystems `
These adverse effects may occur in many forms, ranging from immediate death to subtle changes not realized until months or years later. They may occur at various levels within the body, such as an organ, a type of cell, or a specific biochemical.
Sources of toxic compounds Synthetic organic compound 1. Air, water, and food pollutants Air- CO, oxides of nitrogen, oxides of sulfur, hydrocarbons and particulates Water-agricultural chemicals including pesticides, herbicides, fugicides, nematocides, rodenticides, fertilizer Halogenated hydrocarbons- chloroform, dichloroethane, tetrachloride Clorinated aromatics-PCB, TCDD Detergents-alkyl benzene sulfonates
2. Chemical additives in food As preservatives-antibacterial, antifungal, or antioxidant To change physical characteristics, taste, color, odor
. 3.Chemicals in work place Inorganics-metals and flurides, CO, etc. Organic compounds-aliphatic hydrocarbons (hexene) aromatic hydrocarbons (eg. benzene, toluene) halogenated hydrocarbons alcohols esters organometallics amino compounds
5.Therapeutic drugs The danger to the individual depends on : the nature of the toxic response the dose necessary to produce the toxic response the relationship between the therapeutic dose and the toxic dose eg, anticancer drugs are carcinogens Diethylstilbestrol (DES) Thalidomide Chloroquinol-SMON-subacute myelo-optic neuropathy Methyldopa, chloropromazine, methotrexate In general, toxic side effects are not common and may occur only in susceptible individuals or populations.
6. Pesticides 7. Solvents 8. Polycyclic aromatic hydrocarbons (PAH) Incomplete combustion of organic materials, in smoke from wood, coal, oil, tobacco, in tar and broiled foods Carcinogens
9. Cosmetics Allergic reactions and contact dermatitis Bromate, cold-wave neutralizer Thioglycolates and tioglycerol-cold-wave lotion and depilatories Sodium hydroxide-hair straighteners
Naturally occurring toxins 1. Mycotoxins 2. Microbial toxins 3. Plant toxins 4. Animal toxins "Toxin"=refers to toxic substances that are produced naturally "Toxicant"=substance that is produced by anthropogenic origin
Descriptive Toxicology: The science of toxicity testing to provide information for safetyevaluation and regulatory requirements.
The study of poisons or the adverse effects of chemical and physical agents on living organisms. Toxicology Definitions
“The sensitivity of the individual differentiates a poison from a remedy. The fundamental principle of toxicology is the individual’s response to a dose.” S. G. Gilbert (1997) An Individual View
Mechanistic Toxicology: Identification and understanding cellular, biochemical and molecular basis by which chemicals exert toxic effects.
Regulatory Toxicology: Determination of risk based on descriptive and mechanistic studies, and developing safety regulations.
Clinical Toxicology: Diagnosis and treatment of poisoning; evaluation of methods of detection and intoxication, mechanism of action in humans (human tox, pharmaceutical tox) and animals (veterinary tox). Integrates toxicology, clinical medicine, clinical biochemistry/pharmacology..
Occupational Toxicology : Combines occupational medicine and occupational hygeine. Environmental Toxicology: Integrates toxicology with sub-disciplines such as ecology, wildlife and aquatic biology, environmental chemistry.
The scope of toxicity A.Mechanisms of Toxic Action 1. Biochemical toxicology 2. Behavioral toxicology-behavior is the final integrated expression of nervous function 3. Nutritional toxicology-the effects of diet 4. Carcinogenesis-cell growth 5. Teratogenesis-developmental process 6. Mutagenesis-genetic material 7. Organ toxicity-organ function
B. Measurement of toxicants and toxicity 1. Analytic toxicology 2. Toxicity testing 3. Toxicologic pathology 4. Structure-activity study 5. Biomathematics and statistics 6. Epidemiology C. Applied Toxicology 1. Clinical toxicology 2. Veterinary toxicology 3. Forensic toxicology 4. Environmental toxicology 5. Industrial toxicology
D. Chemical use classes 1. Agricuture chemicals 2. Clinical drugs 3. Drugs of abuse 4. Food additives 5. Industrial chemicals 6. Naturally occurring substances- phytotoxin, mycotoxin, inorganic minerals 7. Combustion products
E. Regulatory Toxicology 1. Legal aspects-formulation of laws and regulations and their enforcement 2. Risk assessment- the definition of risks, potential risks and risk-benefit equations F. Development of antidotes
Toxic Effects 1.Immediate effect and delayed effect CO, cyanide 2. Local effect and systemic effect target organ 3. Reversible and irreversible effect 4. Anaphylactic reaction (allergic reaction) 5. Idiosyncratic reaction
Dose Dose by definition is the amount of a substance administered at one time. However, other parameters are needed to characterize the exposure to xenobiotics. The most important are the number of doses, frequency, and total time period of the treatment. For example: 650 mg Tylenol as a single dose 500 mg Penicillin every 8 hours for 10 days 10 mg DDT per day for 90 days
A common dose measurement is mg/kg body weight. The commonly used time unit is one day and thus, the usual dosage unit is mg/kg/day. Environmental exposure units are expressed as the amount of a xenobiotic in a unit of the media. mg/liter (mg/l) for liquids mg/gram (mg/g) for solids mg/cubic meter (mg/m 3 ) for air Other commonly used dose units for substances in media are parts per million (ppm), parts per billion (ppb) and parts per trillion (ppt).
Fractionating a total dose usually decreases the probability that the total dose will cause toxicity. The reason for this is that the body often can repair the effect of each subtoxic dose if sufficient time passes before receiving the next dose. In such a case, the total dose, harmful if received all at once, is non-toxic when administered over a period of time. For example, 30 mg of strychnine swallowed at one time could be fatal to an adult whereas 3 mg of strychnine swallowed each day for ten days would not be fatal.
vinyl chloride, high dose-hepatotoxicant long latent period at lower doses-carcinogen very low dose-no effect aspirin chronic use-deleterious effects on the gastric mucosa, fatal dose 0.2-0.5 g/kg metals dietary essentials eg. Iron, copper, magnesium, cobalt, manganese, and zinc toxic at higher dose
"All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy.“ Paracelsus (1493-1541)
Knowledge of the dose-response relationship: establishes causality that the chemical has in fact induced the observed effects establishes the lowest dose where an induced effect occurs - the threshold effect determines the rate at which injury builds up - the slope for the dose response.
Dose Response Individual, or graded, dose-response relationship results from an alteration of a specific biochemical process Quantal dose-response relationship in a population-”all or none” determination of the LD50 LD (lethal dose)50-the dose required to kill 50% of a population of an organism under stated conditions
Normal equivalent deviations(NEDs) NED for 50% response is 0 NED for 84.1% response is 1 Probit (probability unit)=NED+5
LD50 is used to: A) classify substances or products for regulatory purposes including safe transportation and labeling, B) provide information for treatment of acute intoxications C) standardize certain biological products, D) set dose levels for subsequent toxicity studies E) provide comparative information on the chemical's dose response curve F) provide data for evaluation and validation of alternative test methods.
Classical LD50 The Classical LD50 test is used to determine the lethal dose (LD50) of a substance that will kill 50% of test animals. Typically, this method can use 100 or more animals. The test material is administered in increasing doses, usually 5 or more, to groups of 10 male and 10 female animals. Mortalities are recorded within a given period, and the LD50 is determined with the aid of statistical calculations.
2. Limit Test Acute toxicity test in which, if no ill-effects occur at a pre-selected maximum dose, no further testing at greater exposure levels is required. Five to ten animals of each sex or 10 animals of the susceptible sex are administered a dose specified by regulations. Toxic responses occurring within a given period are recorded. Based on the results, a regulatory action or additional testing may be required.
The LD50 tests have become controversial among toxicologists, animal welfare organizations, legislators and the public primarily due to the ethics of using a large number of animals and evaluating only mortality.
CURRENT POLICIES Food and Drug Administration: Does not require the use of the Classical LD50 test. Accepts alternatives. Refers to the Limit test.
Organization for Economic Cooperation and Development: Discourages the use of Classical LD50 test. Recommends the Limit test (2 g/kg dose). When compound related mortality occurs in the limit test, then 5 animals per dose, at least 3 dose levels are used to produce a range of toxic effects and mortality rates; clinical observations and pathological investigations are conducted. A fixed dose procedure, which uses morbidity instead of mortality as the end point, is also recommended.
British Toxicology Society: The LD50 should only be determined with any accuracy where scientifically and ethically justified. Such cases are relatively rare. Examination of few animals in detail rather than many for statistical purposes. Limit tests could be used, provided animals in distress are killed humanely, if this would not interfere with the objectives. For classification of substances and preparations, a fixed-dose procedure targeted to acute signs could replace the current practice of LD50 determination.
Descriptive animal toxicity tests Two main principle 1.The effects produced by a compound in laboratory animals, when properly qualified, are applicable to humans. 2. The exposure of experimental animals to toxic agents in high dose is necessary and valid method of discovering possible hazards in human.
Descriptive animal toxicity tests Acute Single dose with effects occurring for a short period of time (usually up to 96 hr) Acute lethality (die in a 14-day period) LD50 (Median Lethal Concentration) Skin & eye irritation sensitization Subacute Multiple doses administered for up to 14 days
Subchronic Continuous dosing for up to 90 days NOAEL-no observed adverse effect level Chronic Continuous dosing for up to 6 months to 2 years carcinogenic potential Acute effects do not predict chronic effects Doses causing chronic effects may not cause acute or sub-acute effects Chronic effects of a chemical exposure may manifest themselves as a common disease and go unnoticed
Course Objectives Understand……. mechanisms by which chemicals cause cell injury and cell death the mode of action of specific organic and inorganic chemicals how to interpret results of in vitro tests for the evaluation of in vivo toxicity How multiple chemical exposures and other stressors can alter toxicity
What factors influence individual susceptibility the importance of dose in determining adverse effects of chemicals what factors influence the target organ dose of a chemical mechanisms by which chemicals affect specific organ system functions
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