membranes and transport processes lecture #6. permeability membrane
TRANSCRIPT
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MEMBRANES AND TRANSPORT PROCESSES
Lecture #6
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permeability
Membrane
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drug-bound protein
Protein-Mediated
Transport Types
Transcytosis(Macromolecules)
caveolae
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Transport Types
• Paracellular• Transcellular– Diffusion (Small Molecules)– Protein-Mediated (Small Molecules)– Transcytosis (Macromolecules)
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Diffusion Transcellular: Passive Diffusion
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Factors that Influence Passive Diffusion
Hydrophobicity
Perm
eabi
lity
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Factors that Influence Passive Diffusion: pH partition hypothesis
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Permeability PropertiesMembrane hydrophobicity ionization molecular weight
Blood Capillaries* independent independent < 5 kD
Renal glomerulus dependent
Nasal mucosa dependent dependent dependent
Buccal mucosa dependent dependent dependent
GI Tract dependent dependent dependent
Lung dependent dependent dependent
Hepatocyte highly dependent highly dependent highly dependent
Renal Tubule highly dependent highly dependent highly dependent
Blood Brain Barrier highly dependent highly dependent highly dependent
* Except testes, placenta and CNS.
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Hydrophobicity
Perm
eabi
lity
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Passive Transport Active Transport
Membrane Membrane
Equilibrative Concentrative
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Protein-Mediated TranscellularFacilitated Diffusion
(Energy-Independent)
Active Transport(Energy-Dependent)
Equilibrative Transporters Concentrating Transporters
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Regulation of Facilitated Diffusion
• Voltage-gated• Ligand-gated• Mechanically-gated• Light-gated
Pore Closed Pore Open
Ligand-gated Transporter• GABAA receptor
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Active Transport
• Primary– ATP
• Secondary– Electrochemical Gradient (ion-coupled)
Multidrug Resistance Protein (Primary) Peptide Transporter (Secondary)
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Classes of Protein Transporters
• Carriers – active (energy-dependent) or
passive (energy-independent)– bind solute on one site and
release it on the other• Channels– passive (energy-independent)– solutes diffuse through the protein
Channel Carrier
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[Drug], mg/L
Tran
spor
t Rat
eNot Saturable
Saturable
Differences Between Passive and Protein-Mediated Transport
Carriers
Channels and Passive Diffusion
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Modes of Transportcotransporter(symporter)
exchanger(antiporter)uniporter
Coupled Transport
A B C
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BCRP = Breast Cancer Resistance ProteinLAT = Large Neutral Amino Acids TransporterOAT = Organic Anionic TransporterOATP = Organic Anionic Transporting PolypeptideOCT = Organic Cationic TransporterMDR = Multidrug Resistance Protein MRP = Multidrug Resistance ProteinSVCT = Sodium-Dependent Vitamin C Transporter
Most Important Transporters in PK
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Transporters
ASBT = Ileal Apical Sodium/Bile Acid Co-TransporterBCRP = Breast Cancer Resistance ProteinOAT = Organic Anionic TransporterOATP = Organic Anionic Transporting PolypeptideOCT = Organic Cationic TransporterMATE = Multidrug and Toxin Extrusion ProteinMCT = Monocarboxylic Acid TransporterMDR (P-gp) = Multidrug Resistance Protein MRP = Multidrug Resistance ProteinPEPT = Peptide Transporter URAT = Urate Transporter
http://www.ncbi.nlm.nih.gov/pubmed/20190787
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Brain
Blood PlasmaBlood Plasma
Brain[Dru
g], n
M
[Dru
g], n
M
[Drug] varies with Tissue
HIV Protease Inhibitor
Volume Distribution (V) = 122 L
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Distribution Rate varies with Tissues
Dru
g Am
ount
, ug
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Drugs: Biologics• Not typically produced by chemical synthesis and macromolecules originating from
a biological organism• Extracted from living systems
– Antibodies– Pig insulin– Heparin (Sugar)
• Protein from Recombinant DNA (modified/unmodified)– Erythropoietin– Human growth hormone– Blood clotting factors
• Engineered Viruses– Gene Therapy– Oncolytic Virus
• DNA/RNA– Vaccines– Control Gene Expression
Are engineered viruses drugs?
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TranscytosisTranscytosis of IgA, an immunoglobin
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Transcytosis MechanismsCaveolae-Mediated
(Receptor Independent)Clathrin-mediated
(Receptor-Dependent)
AP2=Adaptor Protein 2
Absorptive TranscytosisReceptor-mediated
Transcytosis
Other ProteinsInvolved
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Methods: Drug Delivery and Transcytosis
• Chemical Linkage to Targeting Vector
• Non-covalent streptavidin/biotin linkage– Biotin streptavidin (1-10 fM)– Biotinylated drug Streptavidin-
Targeting Vector• Liposome with Targeting Vector
– Drug inside liposome• Nanoparticles (polymers)
– Coated for drug delivery
Drug
TargetingVector
Streptavidin
Biotin
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Targets: Drug Delivery and Transcytosis
• Transferrin Receptor– Transferrin-Drug
• Insulin Receptor and Insulin-like Growth Factor Receptor– Insulin-Drug
• Low Density Lipoprotein Receptor Related Proteins 1 and 2– LDL (Drug Inside)
• Diphtheria toxin receptor/Heparin binding epidermal growth factor– Non-toxic diphtheria toxin mutant-Drug– Heparin-Drug
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Examples: Directed-Drug Delivery and Transcytosis
• Melanotransferrin (Protein) (p97)– Covalently linked with anti-cancer
drugs– GPI-anchor– Transferrin Receptor
• Angiopeps (Peptide)– small/large molecule delivery– alpha-2-macroglobulin receptor
• Leptin (Peptide)– Leptin receptor
Glycosylphosphatidylinositol(GPI anchor)
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Distribution is Reversible
Anti-arthritis ProdrugActivated CharcoalKnown since early 1800s
Adverse Drug Reaction (ADR): Severe Skin Reaction
t1/2 = 2 weeks vein
artery