Lecture 13 Flashcards
What is Thalidomide/Contergan?
It was a drug marked in the 1950s to alleviate morning sickness in pregnant woman
What was the issue with Thalidomide/Contergan?
It ended up causing thousands of infants to be born with phocomelia which is the severe malformation of limbs
When Thalidomide/Contergan withdrawn and what is it now used for?
-Withdrawn in 1961
-now used to treat leprosy and multiple myeloma as an orphan drug
What is potential drug teratogenicity?
It is the ability of a substance to cause birth defect
Why are animals used in toxicity testing
Because they are the most reliable testing source in the absence of human data
Toxixty tests depend on?
-The type of substance
-Regulations of the country
-The use of the test agent
How does tissue-specific toxicity occur?
Usually occurs from specific interactions between the test substance and a particular biological system
Considerations for toxicity testing:
-Biological considerations
-Physio-chemical properties of test substance
Biological considerations for toxicity testing includes:
-Species, strain, and sex of test animal
-Metabolic and physiological similarity to humans
-Duration of toxicity testing
-Number and diet of test animals
Physico-chemical properties of test substance includes:
-Structure
-Vapour pressure
-pKa (acid dissociation constant)
-Solubility (water vs fat)
-Melting point
-Purity
Compounds which undergo toxicity testing are divided into?
- Intended for administration to humans
- Non intended for administration to humans
Examples of substances intended for administration to humans:
-Pharmaceuticals
-Food additives
-Drug additives
Examples of substances non-intended for administration to humans:
-Biocides(pesticides)
-Environmental contaminants
-Industrial chemical
-Household chemical
-Natural toxins
Preclinical testing can be done on what?
-Animals
-Animal models of human disease
-Isolated organs
-Cell cultures
How does toxicity ratings work?
It goes from 1 to 6
1 being super toxic and 6 being practically non toxic
Reasons tests may vary between laboratories:
-Differing genotype or phenotype of sample population
-Difference in tested range of animal species
-Influence of environmental factors
-Mode of drug administration
What a slightly toxic agent?
-Ethanol
-Has a high LD50 value
Chronic exposure of ethanol results in what?
It triggers severe side effects in various tissues based on drastic metabolic disturbances
Example of a super toxic agent?
-Botulinum toxin
-Has an extremely low LD50 value
What bacteria is botulinum toxin produced by?
Clostridium botulinum
What can exposure to botulinum toxin cause?
Sever food poisoning called Botulism
How does Botulinum toxin work?
It is a protein that binds to cholinergic nerve terminals which inhibits the release or Achieve by degrading key proteins for the vesicular docking process
What is a dose-response curve?
Can determine the concentration of an agent that causes the median lethal dose
What alternative approach can be used for reduce the number of animals in toxicity testing?
Fixed Dose procedure
Traditional whole animal toxicity tests:
-Acute
-Sub chronic
-Chronic
-Reproductive
-Behavioural
Pathological and histological examination:
Involves weight and histology of organs
Analytical and functional tests employed in chronic toxicity tests:
-Hematology
-Blood chemistry
-Urine analysis
Advantages of non-animal alternative in vitro toxicity testing
-Improved screening purposes
-For regulatory purposes
Advantages of increased screening purposes:
-Good correlation with in vivo toxicity data
-Low incidence of false negatives
-Low incidence of false positives
-Cheap and fast
Advantages of improved regulatory purposes:
-High interpretability
-Mechanistically based assay
-High predictive power
-Rapid and reliable tests
Advantages of proper in vitro test systems?
-Drastic reduction of animal usage
-Smaller quantities of test chemicals needed
-Reduced variability between analytical experiments
-see slide 19 for more info
Examples of in vitro test system:
-Cell culture based cytotoxicity assay
-Chicken egg CAM test
-Genotoxicity AMES test (used for Salmonella)
-Organ/Tissue-derived cell testing
Examples of cell culture based cytotoxicity assays:
-Kenacid Blue total protein assay
-MTT metabolism assay
-Neutral red dye uptake assay
-Crystal violet dye assay
-ATP content assay
-LDH leakage assay
What are AMES tests (Salmonella) used for?
-Initial screening of potential genotoxins
-Determins mutagenic of test chemical prior to measuring mutagenic potential in animals
Types of salmonella strains:
- Histidine positive
- Histidine negative
Chicken egg Het-CAM test is used to?
To asses membrane irritation
