MEMBRANES AND TRANSPORT PROCESSES

Lecture #6

permeability

Membrane

drug-bound protein

Protein-Mediated

Transport Types

Transcytosis(Macromolecules)

caveolae

Transport Types

• Paracellular• Transcellular– Diffusion (Small Molecules)– Protein-Mediated (Small Molecules)– Transcytosis (Macromolecules)

Diffusion Transcellular: Passive Diffusion

Factors that Influence Passive Diffusion

Hydrophobicity

Perm

eabi

lity

Factors that Influence Passive Diffusion: pH partition hypothesis

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.

Hydrophobicity

Perm

eabi

lity

Passive Transport Active Transport

Membrane Membrane

Equilibrative Concentrative

Protein-Mediated TranscellularFacilitated Diffusion

(Energy-Independent)

Active Transport(Energy-Dependent)

Equilibrative Transporters Concentrating Transporters

Regulation of Facilitated Diffusion

• Voltage-gated• Ligand-gated• Mechanically-gated• Light-gated

Pore Closed Pore Open

Ligand-gated Transporter• GABAA receptor

Active Transport

• Primary– ATP

• Secondary– Electrochemical Gradient (ion-coupled)

Multidrug Resistance Protein (Primary) Peptide Transporter (Secondary)

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

[Drug], mg/L

Tran

spor

t Rat

eNot Saturable

Saturable

Differences Between Passive and Protein-Mediated Transport

Carriers

Channels and Passive Diffusion

Modes of Transportcotransporter(symporter)

exchanger(antiporter)uniporter

Coupled Transport

A B C

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

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

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

Distribution Rate varies with Tissues

Dru

g Am

ount

, ug

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?

TranscytosisTranscytosis of IgA, an immunoglobin

Transcytosis MechanismsCaveolae-Mediated

(Receptor Independent)Clathrin-mediated

(Receptor-Dependent)

AP2=Adaptor Protein 2

Absorptive TranscytosisReceptor-mediated

Transcytosis

Other ProteinsInvolved

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

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

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)

Distribution is Reversible

Anti-arthritis ProdrugActivated CharcoalKnown since early 1800s

Adverse Drug Reaction (ADR): Severe Skin Reaction

t1/2 = 2 weeks vein

artery