PROTEIN BINDING

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Tissue distribution of a compound is affected by its protein binding properties. Extensive plasma protein binding slows the metabolism and elimination and also limits the amount of free compound available to the site of action. Extensive protein binding can also have dramatic effect on both drug metabolism and efficacy by limiting the free unbound drug concentration available to the tissues.

Plasma Protein binding:

Physicochemical properties such as charge and lipophilicity are the main factors which influence the Plasma Protein binding. Most drugs are, at least to some extent, bound to plasma proteins, especially albumin and α1-acid glycoprotein. 

Whole Blood Protein Binding:

Whole blood binding in comparison to plasma protein binding is important in identifying if differential binding to a specific component in the blood occurs and in interpreting pharmacokinetic data.

Tissue Binding:

Binding of the compounds to the tissue proteins can significantly reduce the fraction of drug available for target binding or elimination. 

Equilibrium dialysis is the preferred method for assessing plasma, whole blood and tissue protein binding.

Protein Binding Assay Protocol:

Method: Equilibrium dialysis

Test article concentration: 5  µM (other upon request) 

Incubation time: Overnight incubation 

Incubation temperature: 37 C 

Number of Replicates: n = 2  

Assay condition: 100% Plasma, whole blood or 50% tissue homogenate (as per request); Phosphate-buffered saline (PBS) pH 7.4  

Species: Human; rat; dog; cynomolgus monkey; guinea pig; mouse (other upon request) 

Positive control: Propranolol (other upon request) 

Analysis Method: LC/MS/MS 

Data Delivery: % free (% unbound)