Quiz #1 Material Flashcards
Pharmacodynamics vs. Pharmacokinetics
- Pharmacodynamics: Effects of drug on body
- Receptor binding, signaling, agonism/antagonism, dose-response curve, physiological effect
- Pharmacokinetics: Effects of body on drug
- ADME
Drug Size
- Majority with MW 100-1000
- Too small: insufficient selectivity at target site
- Too large: poor absorption and distribution in the body
Receptors
- Interact with drugs to cause change in biological system
- Only care about those with drug specificity
- Conformational change
- Cascade of events
Example of Receptor: Ach receptors
- 5 subunits (two alpha, beta, delta, gamma)
- Ach bind to the two alpha subunits
- Conformational change to allow for Na+ to flow through
- Small molecule (Ach) binds to a large macromolecule (Ach receptor)
- Cause conformational change in the large receptor
- Results in physiological effect (muscle contraction)
Effectors:
- Translate drug binding into change in cellular activity
- Often enzymes (kinase, phosphodiesterase, etc.)
- _Can be part of recepto_r:
- Insulin receptor: Tyrosine kinase is part of receptor
- Nicotinic acetylcholine receptor: Ion channel that functions as the effector
Receptor Types:
- Proteins: bind hormones/neurotransmitters, channels, enzymes
- Nucleic acids
- Membrane lipids
Protein Receptor Signaling Mechanisms:
- Nuclear receptors (intracellular): steroid hormones, estrogen, vitamin D
- Kinase linked receptors: growth factors, cytokines (phosphorylate proteins)
- Ion channels: acetylcholine, glutamate
- GPCRs: histamines, opioids, serotonin
Properties of Drug-Receptor Interactions:
- Multiple sites where drug-receptor interact
- Short range interactions
- Specific interactions between chemical groups on drug and receptor
Relative strengths of Drug-Receptor Interactions
Strongest: Covalent, Ionic, Hydrogen, Hydrophobic, Van de Waals: Weakest
At least how many points of contact between a drug and receptor are required to see a difference in isomer activity?
Three. With 2 you can flip bonds.
Enkephalin and Morphine have similar regions that can interact with opiate receptors. More interactions means that there will be a more potent drug. How chemical groups are presented to a receptor determines how a drug will work.
- N-methyl piperidine is an essential feature
- Oxygen at C3 is essential
- Oriented cleft in piperidine ring
Extracellular Messengers
Circulating hormones, neurotransmitter, cytokines, etc.
Animal Cells Communicate via Circulating Hormones
- Hormones are synthesized, stored for secretion, secreted, and induced biophysical/physiological change at target cells
- Secretion and degradation are regulated
- Feedback inhibition at synthesis, storage and secretion steps
- Drug can interfere with signaling sometime within these steps.
General Receptor Coupling Mechanisms (4)
-
Two Messenger System:
- Receptor coupled to an effector system that changed intracellular concentration of 2nd messenger
- Usually an enzyme
- Usually; 1st messenger→effector→2nd messenger→protein kinase cascade
-
Ion Channel Coupled Receptors:
- Receptor directly coupled to/is an ion channel
- Response time fast because no intervening messenger (milliseconds)
-
Steroid Hormone Receptors
- Hormone crosses to a membrane and binds intracellular with receptor
- Hormone:Receptor complex goes to nucleus to regulate gene transcription
- Response elements in gene promoters
-
Receptor Kinases/Phosphotases or other enzymatic activity
- Receptor is a kinase
- When activated, initiated protein kinase cascade
- No intermediate, diffusible messengers
Two Messenger Systems:
- Extracellular message (hormone or neurotransmitter) never enters the cell
- The second messenger concentrations are changed within the cell after receptor activation
- 2nd messenger can increase or decrease from a signal
Regulatory Advantages of Second Messenger Systems (5):
- Without entering cell
- Fast reponse/termination
- Amplification
- Multiple inputs onto one 2nd messanger
- Cross-talk between different signal transduction systems
Common Second Messengers:
- cAMP: First one described; autonomic, CNS and endocrine; all types of physiology
- cGMP: vision, smooth muscle contraction,
- Ca2+: universal (prokaryotes as well); autonomic and CNS
- Phosphoinositide breakdown products; IP3
- Arachidonic acid derived from lipids
- NO, nitric oxide: diffuse across cell membranes from one cell to another
What is the pharmacological significance of the two-messenger system?
- Drugs can affect the concentration of intracellular 2nd messengers
- Beta-adrenergic receptors coupled to adenylyl cyclase, action mediated through cAMP. Beta agonist/antagonist modify cAMP
- Understanding mechanism of 2-messenger system is crucial for understanding how drugs work
The Structure of cAMP:
- Synthesized from ATP
- 3’, 5’ cyclic adenosine monophosphate
- Sutherland in 1957 studying glycogen breakdown in liver and muscle
- Adrenaline→^cAMP→glycogen breakdown
- Adenylyl cyclase catalyzes formation of cAMP
Physiological Processes Controlled by cAMP: (in all cells except for erythrocytes)
- Glycogenolysis: stimulates breakdown of glycogen (use stored energy)
- Gluconeogenesis: inhibits synthesis of glycogen
- Lipolysis: stimulates breakdown of triglycerides
- Secretion of neurotransmitters: generally stimulates secretion
- Ion channel activity: activates ion channels
- Either directly or through cAMP-dependent protein kinases (ex: glutamate AMPA receptors)
- Muscle contractility: stimulates cardiac muscle stimulant: adrenaline→^cAMP→heart rate
- Growth: antiproliferative
- Differentiation: stop proliferating so they can differentiate
- Gene transcription: CRE (cAMP response element) in promoters, long term memory
- Memory formation
- Melatonin synthesis from serotonin regulated by cAMP
cAMP is Synthesized from ATP:
- Catalyzed by adenylyl cyclases
- In cytoplasmic membranes
- Regulated by receptors and intracellular protein kinases
- ATP→cAMP+ PPi (uses Mg2+) cofactor
Synthesis and Degradation of cAMP
- Degradation: cyclic nucleotide phosphodiesterases
- cAMP to 5’-AMP
- PDE with different tissue distributions and regulatory properties
- Common drug target site
- Inhibit PDE, Increase [cAMP]
Synthesis and Degradation of cGMP:
- Similar to cAMP
- Guanylyl cyclases to form cGMP from GTP
- PDE to degrage cGMP
Structure of Xanthenes and Methylxanthines:
- Two mechanisms to increase cAMP
- Inhibit PDE and elevate cAMP levels
- Stimualate adenosine receptors that are coupled to stimulation of AC
- No methylation→3 methyl
- xanthine, theobromine, theophylline, caffiene
Viagra Increases Penile Erection by Increasing cGMP:
- Viagra: potent and selective PDE5 inhibitor
- cGMP promotes smooth-muscle relaxation, blood flow, erection enhancement
- Inhibiting PDE5 increases cGMP concentrations
- Originally for BP due to vasodilator properties
Different Types of cAMP Transients Used for Signaling:
- High cAMP levels are toxic
- Want transient cAMP levels
- Shape and duration encode specific information
- (Example: signaling to nucleus for transcription require more robust or prolonged cAMP increases)
- Shape and duration encode specific information
- Olfactory: oscillating cAMP
- Mechanisms to rapidly produce in a local area and then degrade
The cAMP Signal Transduction System:
- Agnosists (peptide hormones, catacholamines, muscarinic agonists and neurotransmitters) to receptors to influence AC (adenylyl cyclases)
- cAMP activates protein kinases to phosphorylate proteins and modulate their activity
- Exception: Olfactory epithelium
- CNG-cyclic nucleotide gated ion channels
- Opens ion channels without protein kinases
- Exception: Olfactory epithelium
- Specificity is dictated by receptors on cells.
- Cells will have multiple types of receptors coupled to the stimulation or inhibition of adenylyl cyclases
- 1st messenger doesn’t need to enter the cell to cause physiological effects
PKA Reaction:
- Discovered by Krebs and Fischer at UW
- Regulatory (R) and catalytic (C) subunits
- R is inhibitory
- cAMP:R→R:cAMP complex dissociates from PKA→C is activated
- Need R to dissociate for PKA to work
- cAMP causes R to dissociate