medsci 204 (copy)

4 primary drug targets

receptors, enzymes, carrier molecules, ion channels

4 steps of neurotransmission

neurotransmitter synthesis

neurotransmitter release

action on receptors

inactivation

two main sites of neurotransmitter synthesis action

choline transporter

- critical for uptake of choline; rate limiting

choline acetyl transferase (chAT)

-enzyme involved in choline synthesis

4 main families of receptors

tyrosine kinase receptor (RTKs)

g-coupled protein receptors (GPCRs)

ligand gated ion channels (ionotropic receptors)

nuclear/steroid hormone receptors

define receptor

proteins which specifically recognise a particular neurotransmitter/hormone and upon binding undergo a conformational change leading to the activation/inhibition of cell signalling

3 important properties for ligand-gated ion channels

-they are activated in response to specific ligands ie highly specific

-they conduct ions through the otherwise impermeable cell membrane

-they select among ions ie ion specificity

nicotinic acetylcholine receptor structure

-5 subunits around central receptor channel

-each subunit has 4 transmembrane domains

-Ach binding site is a dimer

-binding to both sites needed for channel opening

3 ionotropic receptors

-GABAa

-glutamate

-nicotinic

activation of presynaptic receptors leads to...

inhibition of voltage sensitive Ca2+ channels

examples of receptors that are GPCRS:

-B-adrenoceptor

-adenosine receptor

-dopamine receptor

-serotonin receptor

-opioid receptor

-muscarinic receptors

-cannabinoid receptors

what does an RTK do?

transfers phosphate groups from ATP to tyrosine residues on intracellular target proteins. can lead to phosphorylation cascade

How do drugs bind to receptors?

-VdW forces

-hydrophobic binding

-ionic interactions

-covalent binding

affinity constant equation

FO = [L]/Kd+[L]

[L] = drug conc

FO = fractional occupancy

EC50 is used to measure...

the potency of an agonist that produces 50% of the maximal response

higher potency = lower EC50

define efficacy

the ability of a drug to bind to a receptor and cause a change in the receptors action. measured by Emax.

define full agonist

drugs that elicit the max response

define partial agonist

drugs that produce less than the max response. cannot reach 100% response even at 100% receptor occupancy

define antagonist

a compound that binds to but does not activate (or inactivate) a receptor

an allosteric interaction occurs between...

the orthosteric site and an additional conformationally linked site when both sites are occupied by ligands

define allosteric modulator

a ligand that binds to an allosteric site (not the orthosteric site) on the GPCR to modulate the binding and/or signalling properties of the orthosteric site

2 key mechanisms of neurotransmitter inactivation

- transport back into the presynaptic receptor

-enzymic degradation

Serotonin (5HT) transporter is involved in...

sleep, appetite, memory, sexual behaviour, neuroendocrine function and mood

all radioligand binding assays require:

-a radioactively labelled, high affinity, highly selective, high specific activity compound

-require you to incubate radiolabelled compounds with tissue of interest

competition and saturation binding assays must be carried out under __________ conditions

equilibrium

in a binding assay, after the incubation of the tissue and ligand:

the bound compound must be separated from free (washing, filtration, centrifugion etc)

saturation binding assays can be used to:

-compare Bmax values in different tissues

-investigate if receptor mutations alter ligand affinity or expression

-compare ligand affinity (Kd) across different species of receptor

define non-specific binding

binding to something other than the receptor

competition assays allow the investigation of:

unlabeled drugs which compete for the binding site with a labelled ligand (cheaper than saturation assays)

in a competition binding assay, the unlabeled drug will act as an ________ of the binding site of the labeled drug

inhibitor

what is IC50?

The concentration of a drug or inhibitor needed to inhibit a biological process or response by 50%

what does RAAS stand for?

renin angiotensin aldosterone system

main role of RAAS

critical for controlling blood pressure

2 main processes by RAAS to control blood pressure

-alteration of vascular tone

-controlling natriuresis (excretion of sodium in the urine)

what is the enzyme that converts angiotensinogen to angiotensin I?

renin

enzyme that converts angiotensin I to angiotensin II?

ACE (angiotensin converting enzyme)

angiotensin II is very _______ and is a potent ____________ via AT-1 receptors

active, vasocontrictor

can ang II be further cleaved?

yes, into ang III and IV

what molecule is the main effector of RAAS?

ang II

drugs targeting the RAAS (renin-angiotensin-aldosterone system)

-ACE inhibitors (ACE-I)

-angiotensis receptor antagonists (ARBS)

-aldosterone antagonists

-calcium channel blockers

-diuretics

-beta-blockers

how do ACE-Is work?

mimic section of ang I that binds to ACE. leads to decreased ang II levels

THC is a _________ __________ agonist at ______

weak, partial, CB1

are there any cannabis based medicines?

sativex, marinol, nabilone

what is the purpose of the psychoactive substances act 2013?

to regulate the availability of psychoactive substances in NZ to protect health and minimise harm of individuals

what does ADME stand for

absorption, distribution, metabolism and excretion

what type of drug/molecule will most easily pass though a typical cell membrane?

small, uncharged and lipid soluble drugs

4 mechanisms of transport across the membrane

-transcellular passive diffusion

-facilitated diffusion

-active transport

-endocytosis

what is the most important mechanism of transport across the membrane?

passive diffusion (applies to non polar drugs)

what type of membrane transport appears to depends on an oscillating carrier protein?

facilitated diffusion

does facilitated diffusion depend on concentration gradient?

yes

what are the usual substrates for facilitated diffusion?

sugars and amino acids

what type of membrane transport can proceed against a concentration gradient?

active transport

what is endocytosis?

internalisation of large molecules and nonparticles by the cell. mainly for drugs with MW > 1000

3 steps involved in endocytosis

-substrate binds to the receptor

-invagination of receptor-substrate complex

-budding off and delivery of vesicle into cell

drug absorption refers to:

the passage of the drug from the site of administeration into general circulation

can a drug that is administered orally be 100% bioavailable?

no

define absorption rate

how rapidly does the drug get from its site of administration to the general circulation?

define absorption extent?

how much of the administered dose enters the general circulation (% bioavailability = F)

enteral routes of administration:

oral, sublingual, rectal

parental routes of administration:

intravenous (iv), subcutaneous, intradermal, intramuscular, lungs

iv advantages

very rapid, 100% bioavailable, good for drugs that are too irritating to be taken by mouth or soft tissue injection

iv disadvantages

skill advantages, careful prep of injected material (sterile, non-particulate), most hazardous (no recall)

oral advantages

safest, economic, convenient, no skill required

oral disadvantages

slow, unpredictable with regard to rate, extent and reproducibility

patient factors influencing absorption

-stomach emptying rate

-intestinal motility

-interactions with food

what kind of capillary has no pores?

brain capillaries (brain capillaries + extra layer of glial cells = blood brain barrier)

the tissue that receives more ______________ receives more ___________

bloodflow, drug

possible sites of drug metabolism

liver (most important), GI tract, intestinal wall, plasma

drug metabolism results in:

more water soluble metabolite (favours increased excretion in urine and bile)

how many phases of drug metabolism are there?

2

what is the purpose of phase 1 drug metabolism

the addition or uncovering of a reactive group

what is the purpose of phase 2 drug metabolism

conjugation of endogenous molecule with drug

what is the most important reaction for phase 1 drug metabolism?

oxidation

which family of enzymes are most important in drug oxidation?

CYPs eg cytochrome P450

Drug + ________ + ________ +__________ --> Oxidised drug + H20 + ____________

O2, H+, NADPH, NADP+

define excretion

the process whereby compounds are removed from the body to the external environment

sites of drug excretion

kidney (most important), biliary excretion, lungs

factors influencing renal drug excretion

gender, age, pregnancy, disease

define pharmacokinetics (PK)

the study of ADME on a quantitative bases ie study drug concentrations in blood (plasma).

define bioavailability

the fraction of dose reaching the sustemic circulation

F = AUCpo/AUCiv x doseiv/dosepo

pharmacokinetic parameters:

volume of distribution (V), plasma clearance (CL), plasma half life (T1/2)

define distribution

the processes involved in delivery of the drug to the tissues via the arterial blood. defined by the volume of distribution (V)

V = (equation)

amount of drug in the body/plasma drug concentration

define loading dose (LD)

first dose of drug treatment, and is required to achieve a target concentration rapidly. LD = V(L) x target concentration (mg/L)

define drug elimination

the irreversible removal of a drug from the body. defined by clearance (CL)

2 process drug elimination occurs by:

drug metabolism, drug excretion

define clearance

volume of plasma cleared of drug per unit time (L/h). constant for a particular drug in a particular patient. CL = dose/AUC

define maintenance dose rate

dose rate to achieve and maintain a target concentration

MD(mg/h) = CL(L/h) x target concentration (mg/L)

define half life

time required for the drug concentration to fall by half. constant irrespective of drug concentration.

T1/2 = 0.7V/CL

drug is said to be eliminated after ____ half lifes

4. >90% of drug has been eliminated

CYP _____________ 1000s of endogenous and exogenous compounds

metabolise

the major drug metabolising CYP are:

CYP1, CYP2, CYP3 families

define heredity

the passing of traits from parents to their offspring

define polymorphism

when two or more clearly different phenotypes exist in the same population

define genetic polymorphism

gene mutations with results in an altered protein and altered phenotype

define poor metaboliser trait

inherited loss of function in a drug metabolism enzyme. null enzyme activity = PM of drugs. inherited in an autosomal recessive mendelian manner ie. PM homozymgous for deleterious allele

define intermediate metaboliser (IM)

heterozygote carrier of deleterious allele

define extensive metaboliser (EM)

normal function. homozygous for wildtype gene

function of omeprazole

protein pump inhibitor

define metabolic ratio (MR)

drug/metabolite plasma concentration. high ratio = PM. low ration = EM

what does a * "star" allele denote?

polymorphic forms of each CYP gene