Introduction of various transporters. Their various types and locations in different systems. Pharmacological role of these transporters.

1. Membrane Transporters
& Drug Response
Dr Bhagyashree Mohod
MD Pharmacology

2. Overview
 Introduction
 Mechanism of transport
 Role of transporters
 ABC Superfamily
 SLC transporters
 Intestinal transporters
 Hepatic transporters
 Renal transporters
 Transporters in brain

3. transport
Movement of drug across
biological membranes or
barriers is called drug transport

4. Biological Membranes
Bilayer (100 A° thick)
Made up of phospholipid & cholesterol
Polar groups are oriented at two surfaces
Non polar hydrocarbon chains are
embedded in matrix to form continuous
sheet

6. Transport Mechanisms
Passive
Diffusion
Carrier
Mediated
Transport

8. Passive Diffusion
Transfer process from higher to lower
concentration
Along concentration gradient
Without requiring energy

9. Carrier mediated transport

 Protein + drug substrate →complex
 Types :
Facilitated diffusion
Active transport
Pinocytosis
Filtration
Carrier molecules - proteins

10. Facilitated diffusion
 Down hill transport
 Carrier moves drug along its concentration
gradient
 No energy required
 Drugs →Anti cancer drugs, antiviral drugs,
certain vitamins: riboflavin, thiamine, vit
B12

12. Active transport
 Up hill transport
 Against electrochemical gradient
 Energy dependent - Generated by membrane
ATPase
 Drugs : 5-fluorouracil, Methyldopa & levodopa,
Enalapril

13. Primary active transport :
Direct energy is required
Carried by ATP binding cassette group of
transporters
Carried one ion -unidirectional flow
E.g. Absortion of glucose

14. Secondary active transport :
One ion /solute (x) supplies driving force for
transport of other solute (y)
Symporters : Na+ glucose symporters
Antiporters : Na+/H+ gradient in kidney

16. A patient comes with chief
complaint of diarrhoea. He is
a known case of arrhythmias
on quinidine. You advice him
to take loperamide.
After taking the drug , he
goes into respiratory
depression. Why???

17. Transporters
Membrane proteins
Control Influx of essential nutrients &
ions.
Efflux of cellular waste, environmental
toxins, drugs and other xenobiotics

18. ABC SLC
ATP binding
cassette
Unidirectional
Widely recognised
are P-glycoprotein
(encoded by ABCB1
known as MDR1) &
cystic fibrosis
transmembrane
regulator (CFTR)
Solute carrier
Bidirectional
widely recognised
are serotonin (5HT) &
dopamine transporter
SERT→SLC6A4
DAT → SLC6A3

19. Membrane transporters in
therapeutic drug response
Pharmacokinetics :
Transporters located in intestinal, renal &
hepatic epithelia
Functions:
1. Selective absorption of endogenous substance
e.g. Glucose by sodium-glucose transporters (SLT1
& SLG2)

20. Transporters eliminate drugs & their
metabolites
Act as protective barriers to particular
organ cell type
e.g. P -glycoprotein in blood brain barrier
protects CNS from a variety of drugs through
its efflux mechanism
Response in pharmacokinetics (cont)……

21. Pharmacodynamics :
Transporters act as drug target :
e.g. Transporters of neurotransmitter→
target for drug used in neuropsychiatric disorder
e.g. SERT target for major class of
antidepressant drug & serotonin reuptake
inhibitor

22. ABC transporters :
Primary active transporters
Energy- from ATP hydrolysis
49 known genes for ABC protein
→ 7 subclasses(ABCB1 TO ABCG)

23. Best recognized transporter :
 P glycoprotein (encoded by
ABCB1 also called (MDR1)
 cystic fibrosis transmembrane
regulators (encoded by ABCC7 )
ABC transporter (cont)…

24. SLC transporters :
Facilitate transporters & ion coupled
secondary active transporters
48 SLC families with ~315 transporters
present in human genome
E.g. serotonin(5HT) & dopamine transporters
First SLC family transporter cloned in 1987

27. Intestinal transporter

28. Influx transporters improve absorption
 eg. PEPT-1 ( peptide like transporters),
OATB1 (organic anionic transporting
polypeptide)
PEPT1 mediates transport of drugs :
B-lactam, ACE Inhibitors

29. Intestinal transporter (cont)….
Efflux transporters limit absorption of
drugs
E.g. P-gp,
BCRP9 ( breast cancer resistance protein)
MRP2 (ABCC1)

30. Intestinal transporter (cont)…
E.g. P-gp → substrate – Digoxin
inhibitor - Quinidine
BCRP → substrate- Methotraxate
inhibitor - Omeprazole
Clinical applied aspect

31. Hepatic Transporters

32. SLC transporters:
Basolateral membrane of hepatocyte
Uptake of organic anions ( drugs, billirubin),
cations & bile salts
OATPs → anions
OCTs (organic cation transport protein) &
NTCP → cation & bile salt

33. ABC transporters :
Present in bile canalicular membrane of
hepatocyte
MRP2, MDR1, BCRP, BSEP & MDR2
Mediate efflux of drugs & their metabolites,
bile salts & phospholipids
→ Against concentration gradient from liver to
bile

34. Vectorial transport
Asymmetrical transport across monolayer of
polarised cells
Important in transfer of solute across the
epithelial & endothelial barriers
ABC transporters → unidirectional efflux
SLC transporters → either drug uptake or
efflux

35.  Kidney→ tubular secretion
 Brain capillaries → barrier functions
Vectorial transport (cont)….
 Intestine →absorption of nutrients & bile acids
 Liver → hepatobiliary transport

36. Vectorial transport (cont)…
Different examples illustrate the importance
of vectorial transport in determining the drug
exposure in circulating blood & liver
1. HMG COA reductase inhibitors
2. ACE inhibitors
3. Irinotecan

37. HMG COA reductase inhibitors
 Inhibit cholesterol
biosynthesis
 Statins :- Parvastatin
Fluvastatin
Atorvastatin
 OATP1B1 →uptake
 MRP2 → efflux

38. Irinotecan Irinotecan
↓
Active metabolite SN 38
↓
excreted in bile by MRP2
↓
Diarrhea
↓
+ Probenecid → inhibit
MRP2
↓
↓ diarrhoea
Anticancer drug
GI effect →diarrhoea

39. Temocapril
 Temocaprilate excreted in bile & urine
 Other ACE inhibitors mainly by kidney
 Temocaprilate is bisubstrate of OATP family &
MRP2
 Other ACE inhibitors are not good substrate
of MRP2

40. Renal failure → plasma
concentration of temocaprilate
unchanged & other ACE inhibitor plasma
concentration ↑
Temocapril (cont)…..

41. Renal transporters
 Renal transporters play an important role in
drug elimination ,toxicity and response
 Transporters may have dual specificity for
organic anions and cations

42. Organic cation transport
Cations secreted in proximal tubules
Cations →endogenous compounds e.g. choline &
dopamine
Primary function for secretion →eliminate body
xenobiotics, positively charged drugs & their
metabolites
E.g. Cimetidine
Ranitidine
Metformin
Procainamide

43. SLC family

44. Organic anion transport
 Primary function → removal of body
xenobiotics including weakly acidic drug e.g.
parvastatin, captopril, & penicillins
 Two primary transporters on basolateral
membrane → OAT1 & OAT3 →Flux organic
anions from intestinal fluid to tubular cells
 OAT4 luminal membrane transporter

45. Renal transporters (cont)….
E.g.
1. Uric acid reabsorbed by active transport
by transporter of OTP family
Probenecid blocks transport→
uric acid excretion ↑

46. Transporters in Brain

47. Involved in neuronal reuptake of
neurotransmiters → SLC1 & SLC6
transporters
SLC6 responsible for reuptake of
1. Norepinephrine transporters
(NET/SLC6A2)
2. Dopamine transporters (DAT/SLC6A4)
3. Serotonin transporters (SERT/SLC6A4)
4. GABA transporters (GAT)

48. Transporters in brain (cont)…
 Act as pharmacological targets for
neuropsychiatric drug
 SLC6 regulate concentration
neurotransmitter in synaptic cells
→ Function in reversible direction
→ Depend on NA+ gradient to transport
their substrate

49. GAT
GAT1 → GABA transporter present on
presynaptic neuron
GAT3 → on glial cells
GAT2 → Absent on presynaptic neuron
present on choroid plexus
primary role to maintain homeostasis
of GABA in CSF
Drug target

50. SLC6A2/ NET
 On CNS, PNS
& adrenal
chromaffin
 Limit synaptic
dwell time of
noradrenaline &
limits its action
 Regulation of
memory & mood
SLC6A3 /DAT
 Mainly on
presynaptic
neurons
 Reuptake of
dopamine &
terminate
dopamine action
 Regulation of
behavior, mood,
reward,cognition
SLC6A/ SERT
 On CNS, PNS
& axonal
membrane
 Reuptake &
clearance of
serotonin in
brain

51. Drug targeted on transporters
SLC6A1 /GAT1 → Tiagabine
SLC6A2/NET → Desipramine
SLC6A3/DAT → Cocaine & Amphetamine
SLC6A4/SERT → Fluoxetine & Paroxetine

52. P- glycoprotein
 Primary active transporter
 Encoded by MDR gene
 Expressed → intestinal mucosa, renal tubule,
bile canaliculi, blood brain barrier, testicular &
placental blood vessels.
 Pumps out many drugs / metabolites → Limits
absorption as well as promote their elimination

53. Blood brain barrier (BBB)
 Drugs acting on CNS have to cross BBB
 In this efflux transporters play role
 P-glycoprotein extrudes its substrate drugs on
luminal membrane of brain capillary endothelial
cells into blood
 Limiting brain penetration

54. Drug resistance
Play role in development of resistance to:
Anticancer drugs
Antiviral drugs
Anticonvulsant
Mechanism of resistance :-
- ↓ drug uptake
- ↑ efflux of drug

55. ↓ drug uptake –
→ by reduced expression of influx
transport
→ E.g. Folate antagonist
Nucleoside analogue
↑ efflux
→ by overexpression of P-gp in tumor cells
→ Pumps out anticancer drugs
→ Other transporter BCRP, MRP

56. Membrane transport & Adverse drug
responses
Play important role in cellular toxicity
Transporters control exposure of cells to
chemical carcinogens, environmental toxins &
drugs
Transporters expressed in liver & kidney→
main determinants of drug exposure in
circulating blood.

57. Kinetics of transport
Rate of transport across biological membrane
→ saturability
Relationship between rate of transport (flux)
& substrate concentration is given by :
Michaelis Menten equation :
v = Vmax C / Km +C

58. Summary
 Transporters control the influx
of essential nutrients and ions and
the efflux of cellular waste,
environmental toxins, and other
xenobiotics.
 The functions of membrane
transporters may be facilitated or
active

59.  Play critical role in the
development of resistance to
drugs
 Drug-transporting proteins operate
in pharmacokinetic and
pharmacodynamic pathways
 ABC & SLC two major families