PPT- Paul Flashcards
What does conventional toxicity studies provide indications of?
Appropriate dose range
Probable adverse effect
Target organ or system
Special toxicity
What is an issue with toxicity studies?
Involved the use of animal models
How is knowledge of toxicity primarily obtained?
Study and observation of people during normal use of a substance or from accidental exposure
Experimental studies using animals or plants under controlled conditions (in vivo)
Using cells, sub cellular fractions or single-celled organisms to the chemical (in vitro)
How is knowledge of xenobiotics to humans derived?
Clinical investigations
Epidemiological studies
Adverse reactions
What are examples of testing performed during short and long term studies?
Haematological
Biochemical
Urine analysis
Neurological and physical changed
Post morgen examination
What is acute toxicity?
Investigation of the harmful effect which will bring mortality over a short term exposure of organisms (up to 96 hours) to relatively high doses of a substance
What is chronic toxicity?
The harmful effect that will bring mortality over a long term exposure of organisms to toxicants at relatively low concentrations
What is lethal dose (LD50)?
The dose of the pollutant which will result in mortality of half the subject population
Why do we perform testing on animals?
Animal testing generates histopathological, clinical and biochemical data
What do the most common gene mutation tests involve?
Microorganisms-culture systems
Mammalian cells-
Fruit flies-sex linked recessive lethal mutations
Mice
What is the Ames test?
A biological assay to assess the mutagenic potential of chemical compounds.
What is the exposure phase?
The moment at which the toxic substance comes into contact with the body
What is the toxicokinetic phase?
The description of what rate a chemical will enter the body and what happens to it once it is the body
What is the toxicodynamic phase?
Forms the interactions of toxic ants with the organisms causing harmful effects
What does ADME stand for?
Absorption, distribution, metabolism and elimination
Dose meaning?
Concentration or amount of toxin that enters the living organism at a given time
Exposure dose?
Dose present in environment
Absorbed dose?
Proportion of exposure dose that enters the living organisms
3 main routes of absorption
Gastrointestinal tracts
Lungs
Skin
Main site of absorption through lungs?
Alveoli
Bio transformation phase 1 metabolic enzymes
Oxidative process- cytochrome P-540 and NADPH cytochrome P 450
Reduction process- reverse reaction of alcohol dehydrogenase
Hydrolysis
Bio transformation phase 2 conjugation reactions
Glucuronide formation – catalysed by uridine diphosphate glucuronyl transferase in endoplasmic reticulum.
Sulphate conjugation – catalysed by sulphotransferases found in the cytoplasmic fraction of the liver, kidney and intestine.
Methylation – catalysed by methyl transferases located in the mitochondria & cytosolic fractions, not a major source of biotransformation since methylated products are not always more water soluble, therefore difficult to excrete.
Acetylation – catalysed by N-acetyl transferase.
Amino Acid Conjugation – catalysed by amino acid conjugates and co-enzyme A.
Glutathione Conjugation – Affected by glutathione transferases and the co-factor glutathione. Glutathione conjugates subsequently undergo enzymatic cleavage and acetylation forming N-acetylcysteine derivatives of the toxicant which are readily excreted.
Types of storage
Adipose tissue- lipophilic compounds
Bones- chemicals similar to calcium, fluorine, lead and strontium
Blood- plasma proteins
Liver and kidneys- higher capacity for binding chemicals
Excretion
Kidney- water soluble compounds in the urine
Lungs- volatile compounds, gaseous metabolites
Liver- bile, fat soluble compounds
Other routes- hair, nails, skin, sweat and milk
Dose amount
A measure of the magnitude of the dose
Dose frequency
How often exposure occurs
Dose duration
Over what period of time the dose occurs
Toxic effect calculation
Dose x exposure
Monotonic curve
May be linear or non linear but the slope never reversed from positive to negative or vice versa
Non monotonic curve
Changes sign, from positive to negative or vice versa
Biologically relevant nonmonotonic curve
U-shaped or inverted U-shaped dose-response relationship
What is paracetamol?
A synthetic non-opioid analgesic and antipyretic
Bioavailability of paracetamol
60% after 500mg and 90% after 1000mg ingested
Plasma half life of paracetamol
1.25- 3 hours
What is ATP?
Carrier required; against gradient; requires ATP
How does the binding of chemicals to plasma proteins effect its availability?
The less bound a drug is, the more efficiently it can diffuse across cell membranes.
Reduces biologically effective dose delivered to the target organ
Blood proteins that drugs bind are albumin, lipoprotein, glycoprotein
What is cytochrome P-540?
Enzymes that predominantly catalyse oxidation reactions in association with NADPH
Found in the endoplasmic reticulum
Molecular weight of 40-60kDa
From which site would you expect a weak acid toxic ant to be absorbed?
The smooch- in the stomach the pH is around 2 and at this pH weak acids will be non-ionised.
Examples of phase 2 metabolic transformations?
Biosynthetic union/coupling of foreign compounds or Phase I metabolites of foreign compounds with endogenous intermediates (co-factors)
Glucuronidation – catalysed by uridine diphosphate glucuronyl transferase
Acetylation catalysed by acetyl transferases/acetylases.
Methylation – catalysed by methyl transferases
Glutathione conjugation – catalysed by glutathione transferases.
Amino acid – catalysed by amino acid conjugation enzymes
What is glutathione?
Tripeptide composed of three amine acids:which are glutamic acid cysteine and lysine. It is involved in detoxification by conjugation with reactive metabolites by reducing reactive metabolites, and by reacting with and donating a hydrogen atom to free radicals.
How are dose response curve is used to evaluate toxicity
Slope indications how much the response changes as the dose changes
4 mechanisms for the transport of toxicant through biological membranes
Passive diffusion
Active transport
Facilitated diffusion
Endocytosis
Factors that affect the absorption of toxic substances across the cell membrane
Concentration gradient across membrane
Lipid solubility of xenobiotic
Electrical change of xenobiotic
How does the size of particles influence their absorption from the lungs?
> 10um do not enter respiratory tract
<0.01um are likely to be exhaled
0.01-10um are deposited in various parts of the respiratory tract
How does phagocytosis enable xenobiotics to enter cells?
Involves the encirclement of particles by the plasma membrane and subsequent engulfment
Particles such as asbestos, silica dust or uranium dioxide are engulfed by white blood cells found in the respiratory tract
What role does pinocytosis play in toxicokinetics?
Water soluble chemicals are transported via pinocytosis in the lining of lumen in the small intestine
Lipid droplets/solutes in extracellular fluid
What attribute of the skin limits the rate of absorption?
Keratin- cohesive protein filaments found in the outer layer of the skin which forms a chemically resistant barrier
What characteristics of the small intestine account for toxicant absorption?
Large surface area for xenobiotics to passively diffuse
Intestine supported by extensive vascular system close to the villi/microvilli to facilitate absorption.
Long transit time and therefore increased opportunity for absorption
Higher pH facilitates the absorption of weak bases.
Bile acids emulsify fats in order to increase absorption of lipid soluble toxicants.
What is a dose-response curve?
Defines potency of a chemical
Describes how a chemical’s effects changes as exposure increases
What is chemical distribution?
Toxicity is reduced by concentrating the chemical in an organ other than the target organ.
Blood flow through an organ
Ease of chemical transfer across the capillary wall and cell membrane
Affinity of the components of the organ for the chemical
Lipid solubility (Blood brain barrier)
How does Adipose tissue affect availability of toxicants?
It is served as storage, holding toxicants
Losing weight fast can mobilize toxicant and release to the blood stream and site of action
Increase toxicity as a result of bioaccumulation.
Why are newborn and infants more susceptible to some toxicants?
Newborn, infants and toddlers are more susceptible to the toxicity of an agent (at same dose equivalent) than an adult due to inefficiency of enzymes pathways responsible for biotransformation.
Reduced blood brain barrier
Increased uptake of some toxicants e.g. in the lungs
How does bone increase half life of toxicants?
Serves as storage for toxicants, as such performs a detoxicification role until toxicant released into the system, usually happens slowly e.g. fluoride, lead and strontium.
e.g. T½ of lead for 20 years
List 3 factors that affect the toxicology of a substance
Route of exposure
Duration of exposure
Frequency of exposure
What is a xenobiotic?
Xenobiotic is a foreign chemical substance found within an organism that is not normally naturally produced by or expected to be present within that organism. It can also cover substances which are present in much higher concentrations than are usual.
How is necrosis differentiated from apoptosis?
A form of cell death that is distinguishable from apoptosis in that it is not controlled and orderly
What is the NOAEL?
No Observe Adverse Effect Level
Highest dose at which a significant adverse effect could not be found
What is bioactivation?
The process by which a xenobiotic may be converted to more reactive or toxic forms
In toxicity testing name 3 tests that are routinely performed and give the rationale for inclusion of these tests.
Haematology e.g. rbc, wbc, plts, retics.
Biochemistry – Liver function tests, renal function tests.
Neurological tests – cognitive behaviour, spatial recognition
