First Pass Miss Exam 1 Flashcards
What is the mechanism by which a Jak kinase carries signal downstream and give one receptor example?
Jak kinases will bind and phosphorylate STAT receptors, which dimerize and regulate transcription of target genes
I.e. growth hormone
What are the molecular mechanisms underlying desensitization and resensitization?
Desensitization - phosphorylation of GPCR via GPCR kinases when activated allows binding of Beta-arrestin, which diminishes the receptor’s ability to interact with Gs subunit, terminating the response.
Resensitization - GPCR activation is terminated, disallowing further GPCR kinase activation, and phosphatases will subsequently cause removal of Beta-arrestin
What are the functions of Beta-arrestin?
- Blocks Gs binding
- Accelerated endocytosis of receptors, which allows quicker resensitization via phosphatases. However, endocytosis also means that cells may be degraded by the lysosome more readily.
What is the certain safety factor vs therapeutic index?
Therapeutic index = LD50/ED50 (based on animal studies)
Certain safety factor = TD1/ED99
What is tachyphylaxis?
When responsiveness diminishes rapidly after administration of a drug -> rapid tolerization
What relays in electrons to CYP in microsomal CYPs?
the NADPH-cytochrome P450 oxidoreductase (utilizes a flavin group to do single electron transfers) - also known as P450 reductase
What is the mechanism of action of CYP450s?
- RH drug binds to CYP with its heme iron in Fe+3 state.
- First electron is provided by P450 reductase, reducing the iron to +2.
- Molecular oxygen binds, and second electron is donated to oxygen by P450 reductase or cytochrome b5 (giving it a -1 charge).
- One oxygen gains the second electron from Fe+2 as well as two protons, forming water (the reduction). The other oxygen is incorporated into the substrate as ROH (oxygen is reduced here as well, but the substrate is oxidized).
Two electrons come from NADPH to form water, two electrons come from the substrate to oxidize molecular oxygen into the organic compound
List two major groups of enzymes that carry out hydrolysis reactions?
- Carboxylesterases -> as in the hydrolysis of novocaine
2. Epoxide hydrolases -> including microsomal and soluble
How do epoxide hydrolases function and why are they important?
Trans-addition of water to epoxides to form alcohols
Important for detoxifying electrophilic epoxides which can bind proteins and nucleic acids and cause toxicity. They will break up epoxides formed by CYP450s so they are expressed in the same cells to detoxify them
What co-factor is required for sulfonation reaction, and what is one substrate which cannot be used?
PAPS - 3-PhosphoAdenosine-5’PhosphoSulfate
Sulfate cannot be attached to a carboxylic acid
Usually attaches to alcohols, phenols, and nitrogens via sulfotransferases (SULTS)
What are the two types of reactions which occur for amino acid conjugation?
- Conjugation of carboxylic acid to glycine, glutamate, or taurine via intermediate activation with CoA
- Conjugation of aromatic hydroxylamine via aminoacyl tRNA synthetase. Literally add via carboxylic acid and it looks like a peptide bond of a protein.
What is the debrisoquine polymorphism example?
Dr. Robert Smith was developing an anti-hypertensive drug. Took a dose of it, and had orthostatic hypertension for several days. Was found to have a CYP2D6 mutation which made him metabolically deficient in drug processing -> drug product found in his urine even days later.
What two sites for SNPs show the largest association with human variants in disease?
- Intronic - due to splice site changes
2. Intergenic - due to altered interaction with chromatin, topoisomerases, or DNA replication
What is the acetylation polymorphism and what is the major gene affected?
NAT2 is primarily affected
“Fast” acetylation is dominant, individual must have two “slow” alleles to see an affect. Large ethnic variability, with altered response to many chemicals including caffeine and 4-aminobiphenyl (bladder carcinogen) and sulfa drugs (hemolytic anemia)
What is enterohepatic cycling? What drug can inhibit this?
Excretion of drugs in the bile, and reabsorption from the intestine into the body
Drug: cholestyramine, a nonspecific adsorbent
Also ezetimibe, lowers LDL cholesterol by reducing enterohepatic cycling
What is the steady state equation?
input = output
f(D/T) = (C_ss)(CL) concentration/time = (concentration/volume)(volume/time)
Where C_ss = Concentration at steady state
Why is clearance useful?
The clearance multipled by the plasma concentration of the drug will predict the rate of elimination (the output)
This is why Css*CL = steady state elimination,
Because CL = Rate of elimination / C (concentration of drug in plasma)
Furthermore, CL = Vd * Ke
CL has units volume / time
If a drug has a very high distribution, will the required dose be high or low?
High distribution = high dose (lower effective concentrations at any place, due to large Vd)
What is the formula for a loading dose?
Loading dose = Css * Vd
Css = desired plasma concentration at steady state Vd = Volume of distribution, a property of the drug
How is Pb poisoning diagnosed?
Hematological abnormalities typically:
Blood lead concentration >0.5 mg/mL
Elevated free erythrocyte protoporphyrin test (FEP)
What causes Severe gingivitis, discolored gums, and metallic taste in mouth. (stomatitis)?
Mercury poisoning
Why are these compounds elevated in lead poisoning?
Lead inhibits several SH-containing enzymes of heme biosynthesis, causing anemia by inhibiting hemoglobin synthesis (microcytic anemia).
Major enzyme blocked: Ferrochelatase -> build up of protoporphyrin 9
Secondary: delta-ALA dehydratase, and co-PPR oxidase
What is trivalent vs pentavalent arsenic?
Trivalent - inhibits pyruvate dehydrogenase via lipoamide
pentavalent - uncoupler of oxidative phosphorylation
More water soluble derivatives have been made which have less adverse effects: DMSA (succinate) and DMPS (propane sulfonate)
How have the toxicities of dimercaprol been overcome?
these include tachycardia, hypertension, and nausea/vom
More water soluble derivatives have been made which have less adverse effects: DMSA (succinate) and DMPS (propane sulfonate)
How have the toxicities of dimercaprol been overcome?
these include tachycardia, hypertension, and nausea/vom
What is the primary side effect of all chelators except maybe dimercaprol?
nephrotoxicity
How is HCN poisoning diagnosed?
- By abruptness of onset of symptoms (within seconds of inhalation)
- Almond odor on breath
- Ataxia, convulsions, coma, nausea, vomiting
Can be from insecticides, inhalation of fumes from burning nitrogen-containing compounds, or fruit seeds
What does Rhodanese do?
Detoxifies CN- in vivo to SCN- (thiocyanate)
It is a thiosulfate sulfurtransferase
What is responsible for methanol toxicity? What do they cause?
The biproducts of oxidation are:
Formaldehyde - blindness -> damage retinal cells
Formic acid - Acidosis, cardiotoxic (cardiac depression)
How is ethylene glycol toxic? What is the treatment?
Metabolized by alcohol dehydrogenase (like methanol).
Forms:
- Oxalate - produces crystals which cause kidney damage
- Formic acid - causes acidosis like methanol
Treatment is same as methanol poisoning, with option for hemodialysis
What are some examples of chlorinated hydrocarbon insecticides and what is their mechanism of action of toxicity?
DDT, chlordane, lindane
Interfere with the inactivation of sodium channel, thus causing repetitive firing in response to a single stimulus -> CNS stimulation and effects
-> these bioaccumulate in adipose tissue due to their high lipid solubility, unlike organophosphates
What is the mechanism of action of carbamate insecticides and how do they differ from organophosphorous compounds?
They inhibit acetylcholinesterase via carbamoylation of esteric site of enzyme. However, this is more reversible than organophosphorous (which phosphorylate the active site irreversibly)
Carbamates thus have a shorter duration of action and are less toxic.
What is the major drug interaction of concern with tobacco use?
Induces some drug-metabolizing enzymes, thus decreasing the effectiveness of some drugs like TCA, acetaminophen, benzodiazepines, cimetidine, oral contraceptives, estrogens, insulin, propanolol, and theophylline
- > caffeine tends to block
- > alcohol tends to induce
How does fluoroacetate toxicity work?
Lethal synthesis - similar structure to acetate and is made into fluoracetyl-CoA in the mitochondria, then forms fluorocitrate which will block aconitase -> citrate accumulates and mitochondrial energy is destroyed
What are the biogenic amines and their functional groups?
- Dopamine
- Norepinephrine
- Epinephrine
(all three made from tyrosine, have catechol group) - histamine - imidazole - from histidine
- serotonin - indole - from tryptophan
What produces the slow EPSP via acetylcholine and what is the mechanism?
Muscarinic Ach receptor activation -> stimulates PLC to hydrolyze PIP2 to IP3 and DAG
Decrease in PIP2 causes the closure of M-type delayed rectifier K+ channel -> depolarizes the neuron
IPSP is due to G-protein-gated K+ channel activation in heart via M2 receptor
How does the acetylcholinesterase enzyme work? How does this relate to ACh inhibitors?
Enzyme is negatively charged to attract ACh, then uses a serine to do an Acyl transfer reaction. The intermediate is an acetyl group covalently attached to serine. The structure is ultimately resolved via hydrolysis (this step is blocked via acetylcholinesterase inhibitors which remain covalently bound)
What are the presynaptic receptors of skeletal muscle?
Nicotinic -> increasing tetanus
What are the reversible anticholinesterases which act by slow removal from the enzyme?
Physostigmine (tertiary), neostigmine (quaternary), rivastigmine (tertiary), pyridostigmine (quaternary)