PROTEIN BINDING

1
PROTEIN BINDING

• Roselyn Aperocho-Naranjo
• Faculty, College of Pharmacy
• USPF

2
Binding of drug to proteins may

• Facilitate the distribution of drugs
• Inactivate the drug by not enabling a sufficient
  concentration of free drug to develop at a
  receptor site
• Retard the excretion of a drug

3
The interaction of drugs to protein may cause

• Displacement of body hormones or coadministered
  agent
• Change the configuration of protein to another
  structure capable of binding a coadministered
  agent
• Inactivates the drug biologically by forming a
  drug-protein complex

4
Structure of Binding Site of Colon-Cancer Drug
and Its Protein Target
Schematic showing how Erbitux takes the place of
the EGFR growth factor, thereby inhibiting
cancerous growth.
5
Two Important Plasma ProteinsALBUMIN

• Is the most important protein that binds to drug
  molecule due to its high concentration compared
  with other proteins
• It binds both acidic and basic
• Constitute 5 of the total plasma

6
Two Important Plasma Protein?1-ACIDGLYCOPROTEIN

• Also known as orosomucoid (?1-globulin)
• Binds to numerous drugs
• Have greater affinity for basic than acidic drugs
  molecules
• Binds only basic and highly lipophilic drugs

7
Things to remember

• Many drugs bind to the same receptor site but
  drugs with higher affinity will replace those
  drugs with lower affinity by competition
• Only free and unbound drugs exert therapeutic
  effect by interacting with receptors

8
Drugs may bind to protein through

• Hydrophobic Interaction
• Proposed by Kauzmann
• tendency to develop of hydrophobic molecules or
  parts of molecules to avoid water because they
  are not readily accommodated in the H-bond
  structure of water

9
Binding of Ca to a target protein
10
Drugs may bind to protein through

• Self-Association
• Some drug may self dissociate to form dimers,
  trimers or aggregates of larger size
• Dimers or trimers - is a reaction product of two
  or three identical molecules
• May affect solubility, diffusion, transport,
  therapeutic action of drugs

11
(No Transcript)
12
Amino Acids A. Basic Group

• Arginine
• Histidine
• Lysine

bind

• Acidic Drugs

Amino Acids B. Acidic Group

• Aspartic Acid
• Glutamic Acid

bind

• Basic Drugs

13
Protein binding is determined by

• Dialysis
• Ultracentrifugation
• Ultrafiltration
• Sephadex-gel filtration
• Molecular filtration
• Electrophoresis
• Agar plate test

14
The Pharmacokinetic Importance of Protein Binding

• Drug-protein binding influences the distribution
  equilibrium of the drug
• Plasma proteins exert a buffer and transport
  function in the distribution process
• Only free and unbound drug acts can leave the
  circulatory system and diffuse into the tissue

15
Disease and Protein Binding

• Protein binding will be affected by the presence
  of diseases

Drugs showing Decrease Extent of Protein Binding in the following diseases Drugs showing Decrease Extent of Protein Binding in the following diseases
LIVER RENAL
Dapsone Diazepam Morphine Phenytoin Prednisolone Quinidine Tolbutamide Triamterene Barbiturates Salicylates Cardiac Glycosides Sulfonamides Chlordiazepoxide Triamterene Clofibrate Diazepam Diazoxide Furosemide Morphine Phenylbutazone Phenytoin
16
Disease and Protein Binding

• When drugs bind to protein, Albumin concentration
  is reduced
• The exchange of proteins between plasma and
  interstitial compartment (normally proceeds at a
  rate of 5 plasma protein per our) will be
  hampered.
• The diffusion of plasma the to interstitial fluid
  is increased by
• Inflammatory process
• Pregnancy
• use of oral contraceptives
• Diabetes
• Septic shock
• Pulmonary Edema

17
Disease and Protein Binding

• The reduced albumin concentration and binding
  capacity is due to
• Change in albumin molecule
• presence of endogenous binding inhibitors such
  as free fatty acids, and metabolic acidosis.

18
Disease and Protein Binding

• Hypoalbuminemia may result in patients with
  cancer, burms, cardiac failure, cystic fibrosis,
  enteropathy, inflammations, liver impairment,
  malabsorption, nephrotic syndrome, renal failure,
  sepsis and trauma.

19
Disease and Protein Binding
Pathological Conditions in which Plasma Concentration of ?1-ACIDGLYCOPROTEIN is increased Pathological Conditions in which Plasma Concentration of ?1-ACIDGLYCOPROTEIN is increased
Cancer Carcinoma, Leukemia, Lymphoma, Malignant melanoma, myeloma
Inflammation Crohns disease, Inflammatory polyarthritis, pneumonia, rheumatoid arthritis, ulcerative colitis, systemic erythematosus
Myocardial Infarction Trauma Burns, extensive tissue damage, surgery, transplantation
20
Binding of Drugs to RBC

• Lipophilic molecules dissolved in the lipid
  material of the RBC membrane
• Anions can be attracted to and enter the
  positively charged pores of RBC
• Lipopilic drugs may be absorbed to rBC membrane
  due to change of
• Change of shape of membrane and membrane proteins
• Membrane extension which may lead to chane of RBC
  shape

21

• Drugs absorbed in the RBC membrane inhibits the
  deformity of RBC thus becoming lodged in the
  capillaries
• Macrophages may remove the RBC, that results in
  increase free drug concentration
• Binding of drugs to RBC may be dependent on age
  (meperidine) and concentration dependent
  (diazepam)

22
The RBC binding sites are

• Intracellular proteins
• Hemoglobin
• Carbonic anhydrase
• Cell membrane
• ATPase

23
Beneficial effects of tissue binding

• Lower tissue uptake
• Lesser retention in critical organ such as
  kidney, etc.

24
Displacement of drugs from Protein Binding is due
to

• Total amount of protein-bound drug in that body
• Extent of tissue binding structure
• Apparent volume of distribution

25
Displacement of Drugs from their Plasma Protein
Binding by Other Drugs given concomitantly
Drug Displaced By Concomitant Drug
Warfarin and other highly bound coumarin-type anticoagulants Clofibrate Phenylbutazone Ethacrynic acid Mefenamic Acid Nalidixic Acid Oxyphebutazone Chloral hydrate
Tolbutamide Phenylbutazone Salicylates Sulfafurazole