The study of the adverse effects of a toxicant on living organisms. Principles of Toxicology: The Study of Poisons. Axioms of Toxicology

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1 Principles of Toxicology: The Study of Poisons The study of the adverse effects of a toxicant on living organisms Adverse effects any change from an organism s normal state dependent upon the concentration of active compound at the target site for a sufficient time. Toxicant (Poison) any agent capable of producing a deleterious response in a biological system 1 2 Axioms of Toxicology Axioms of Toxicology There is a dosage or exposure level that has no effect on the health of animals as measured by methods which have a finite sensitivity to measure dysfunction or injury. (NOAEL) Does this mean it is safe? Any substance can provoke a dysfunction or injury at some degree of exposure the dose makes the poison. Attenuation of injury can often be achieved by dilution. Complications can occur when there is exposure to more than one agent even at non-toxic doses. In general, laboratory studies do not look at these complicated cases. What does this say about the state of our knowledge? There is essential uniformity in the biochemistry in similar species among biological mechanisms in mammals. This allows for extrapolation from animal data for predictions in humans. What are advantages/disadvantages of animal testing? Toxicological data from animal experiments can be used to assess the degree of exposure or dosage that will NOT adversely affect human health. However, potential or real differences between animals and humans require that judgmental factors be applied when extrapolating animal threshold doses in order to insure an adequate margin of safety for humans. Animal testing must be extrapolated carefully We should error on the side of caution 3 4 Dose Dose: The amount of chemical entering the body This is usually given as mg of chemical/kg of body weight = mg/kg The dose is dependent upon: * The environmental concentration * The properties of the toxicant *The frequency of exposure *The length of exposure * The exposure pathway (route) What is a Response? The degree and spectra of responses depend upon the dose and the organism Change from normal state could be on the molecular, cellular, organ, or organism level--the symptoms Local vs. Systemic Reversible vs. Irreversible Immediate vs. Delayed Graded or Quantal degrees of the same damage vs. all or none 5 6

2 Ranges: 4 Maximum Response 2-3 Linear Range 0-1 NOAEL Dose-Response Relationship: As the dose of a toxicant increases, so does the response Limitations Often derived from acute exposure data. Species variation RESPONSE DOSE Dose determines the biological response If Mortality is the response, the dose that is lethal to 50% of the population LD 50 can be generated from this curve Not everybody reacts in the same way to a toxic exposure LD % 50% LD 50 Dose fold variation w/in a population! 8 LD50 Comparison Chemical LD 50 (mg/kg) Ethyl Alcohol 10,000 Sodium Chloride 4,000 Ferrous Sulfate 1,500 Morphine Sulfate 900 Strychnine Sulfate 150 Nicotine 1 (1 mg) Black Widow 0.55 Curare 0.50 Rattle Snake 0.24 Dioxin (TCDD) Botulinum toxin Different toxicants can be compared--lowest dose is most potent Sources of Caffeine Source Amount mg / 12 oz Dose if 150lbs ie. 68 kg Coffee - brew /16oz or 3.6 mg/kg Coffee - decaf 5 Iced tea 70 Nestea 25 Coke /36oz or 1.5 mg/kg Mt. Dew 55 Monster, RedBull /24oz or 3.5 mg/kg Source: Read Carefully! The actual caffeine content for many energy drinks is not easily identified on product packaging or via the Internet. The total amount of caffeine contained in some cans or bottles of energy drinks can exceed 500 mg (equivalent to 14 cans of common caffeinated soft drinks) and is clearly high enough to result in caffeine toxicity. 23 A lethal dose of caffeine is considered to be 200 to 400 mg/kg. 24 Clinical Report Sports Drinks and Energy Drinks for Children and Adolescents: Are They Appropriate? Guidance for the Clinician in Rendering Pediatric Care: WARNING: distinguish amount from dose Toxicity vs. Health Impacts MY COUSIN IS 16 YEARS OLD AND HE WOULD DRINK UP TO FIVE MONSTERS A DAY. FOR THE PAST MONTH HES BEEN ACTING REALLY WEIRD. HE TALKS TO HIMSELF, HES REALLY SHAKY, HE CANT SIT NOT EVEN FOR A MINUTE. HE HAS TO BE MOVING AND HE SLEEPS ALOT THE FAMILY IS SO WORRIED. ITS SCARY TO SEE WHAT A ENERGY DRINK IS DOING TO MY TEENAGE COUSIN. Anonymous

3 Exposure Routes & Doses Chemical Animal Route LD 50 Dose Caffeine Mouse Rat Rat Mouse IV IV 620 mg/kg 192 mg/kg 105 mg/kg 68 mg/kg Amt: 200 g rat 38 mg; 70 kg person 13,440 mg = 54 cups HgCl (II) Rat Mouse 37 mg/kg 10 mg/kg Dimethylarsenic (cotton defoilant) Rat 700 mg/kg Factors Influencing Toxicity Related to the: chemical person exposure environment The Human Factors Gender Age Duration Route of exposure Genetics Species variation Individual Susceptibility There can be fold difference in response to a toxicant in a population Genetics-species, strain variation, interindividual variations (yet still can extrapolate between mammals--similar biological mechanisms) Gender (gasoline nephrotox in male mice only) Age--young (old too) underdeveloped excretory mechanisms underdeveloped biotransformation enzymes underdeveloped blood-brain barrier Individual Susceptibility Age--old changes in excretion and metabolism rates, body fat Nutritional status Health conditions Previous or Concurrent Exposures additive --antagonistic Synergistic The disadvantaged are often more susceptible Exposure: Duration Acute < 24hr usually 1 exposure Subacute 1 month repeated doses Subchronic 1-3mo repeated doses Chronic > 3mo repeated doses Over time, the amount of chemical in the body can build up, it can redistribute, or it can overwhelm repair and removal mechanisms 17 18

4 Exposure: Pathways Routes and Sites of Exposure Injection intravenous Inhalation (Lungs) Injection Intraperitoneal, intramuscular Ingestion (Gastrointestinal Tract) Dermal/Topical (Skin) Typical Effectiveness of Route of Exposure iv > inhale > ip > im > ingest > topical Response to Toxic Substances Skin/eyes Central Nervous system Respiratory tract Circulation system Liver / Kidneys Digestive system Reproductive system Bones and joints Cancer and others Target Organs: adverse effect is dependent upon the concentration of active compound at the target site for enough time Not all organs are affected equally greater susceptibility of the target organ higher concentration of active compound Liver--high blood flow, oxidative reactions Kidney--high blood flow, concentrates chemicals Lung--high blood flow, site of exposure Neurons--oxygen dependent, irreversible damage Myocardium--oxygen dependent Bone marrow, intestinal mucosa--rapid divide ADME: Absorption, Distribution, Metabolism, and Excretion Once a living organism has been exposed to a toxicant, the compound must get into the body and to its target site in an active form in order to cause an adverse effect. The body has defenses: Membrane barriers passive and facilitated diffusion, active transport Biotransformation enzymes, antioxidants Elimination mechanisms Absorption: ability of a chemical to enter the blood Inhalation--readily absorb gases into the blood stream via the alveoli. (Large alveolar surface, high blood flow, and proximity of blood to alveolar air) Ingestion--absorption through GI tract stomach (acids), small intestine (long contact time, large surface area--villi; bases and transporters for others) Dermal--absorption through epidermis (stratum corneum), then dermis; site and condition of skin Distribution: the process in which a chemical agent translocates throughout the body Blood carries the agent to and from its site of action, storage depots, organs of transformation, and organs of elimination Rate of distribution (rapid) dependent upon blood flow characteristics of toxicant (affinity for the tissue, and the partition coefficient) Distribution may change over time 23 24

5 Distribution: Storage and Binding Storage in Adipose tissue--very lipophylic compounds (DDT) will store in fat. Rapid mobilization of the fat (starvation) can rapidly increase blood concentration Storage in Bone--Chemicals analogous to Calcium--Fluoride, Lead, Strontium Binding to Plasma proteins--can displace endogenous compounds. Only free is available for adverse effects or excretion 25 Complex Mixtures Cigarette smoke Breakdown products of PCE Gasoline Potential Health Effects: May be similar to dominant chemical potential interactions VERY uncertain Exposure guidelines are just now being written 26 Complex Example Concentration (mg/l) / Ref Dose (mg/kg*d) = Non carcinogenic Risk factor (R n ) Concentration (mg/l) * Slope Factor (kg*d/mg) = Carcinogenic Risk factor (R c ) R n + R c = R total (compound specific) Volume Weighted Average Concentrations from Both Wells Chemical Water Concentration (mg/l) Water Quality Standard (mg/l) RfD (mg/kg*d) SF (kg*d/mg) R oral, noncarcinogenic (chemical score) R oral, carcinogenic (chemical score) Rtotal Percent Rtotal Rank Cumulative Percent Risk Arsenic E Fluoride 7.7 4/ Nitrate Barium Target Sites: Mechanisms of Action Adverse effects can occur at the level of the molecule, cell, organ, or organism Molecularly, chemical can interact with Proteins Lipids DNA Cellularly, chemical can interfere with receptor-ligand binding interfere with membrane function interfere with cellular energy production bind to biomolecules perturb homeostasis (Ca) 28 Excretion: Toxicants are eliminated from the body by several routes Urinary excretion water soluble products are filtered out of the blood by the kidney and excreted into the urine Exhalation Volatile compounds are exhaled by breathing Biliary Excretion via Fecal Excretion Compounds can be extracted by the liver and excreted into the bile. The bile drains into the small intestine and is eliminated in the feces. Milk Sweat Saliva Metabolism: adverse effect depends on the concentration of active compound at the target site over time The process by which the administered chemical (parent compounds) are modified by the organism by enzymatic reactions. 1 o objective--make chemical agents more water soluble and easier to excrete decr. lipid solubility --> decr. amount at target increase excretion rate --> decrease toxicity Bioactivation--Biotransformation can result in the formation of reactive metabolites 29 30

6 Biotransformation (Metabolism) Biotransformation Can drastically effect the rate of clearance of compounds Can occur at any point during the compound s journey from absorption to excretion Compound Without With Metabolism Metabolism Ethanol 4 weeks 10mL/hr Phenobarbital 5 months 8hrs DDT infinity Days to weeks Key organs in biotransformation LIVER (high) Lung, Kidney, Intestine (medium) Others (low) Biotransformation Pathways * Phase I--make the toxicant more water soluble * Phase II--Links with a soluble endogenous agent (conjugation) Toxicology Exposure + Hazard = Risk All substances can be a poison Dose determines the response Pathway, Duration of Frequency of Exposure and Chemical determine Dose Absorption, Distribution, Metabolism & Excretion The extent of the effect is dependent upon the concentration of the active compound at its site of action over time Bioactivation: compounds to reactive metabolites Individual variation of the organism will affect ADME Chemical EPA Risk Paradigm Health Effect Emission Transport Receptor Conclusions What is a Poison? Due to the variability of humans, it is extremely difficult to establish causation with any degree of certainty Prevention is the most effective method to minimize the impact of exposure to environmental chemicals Human exposures are most often associated with complex mixtures. All populations include sensitive and resistant individuals, thus it is difficult to predict effects based on an average. Uncertainty is a fact of life All substances are poisons; there is none that is not a poison. The right dose differentiates a poison and a remedy. Paracelsus ( ) 35 36