Stereoselective plasma protein binding of amlodipine

Area of Science:

• Pharmacology
• Biochemistry
• Analytical Chemistry

Background:

• Amlodipine is a widely prescribed calcium channel blocker used to treat hypertension and angina.
• The drug exists as a racemic mixture of (R)- and (S)-enantiomers, with the (S)-enantiomer being the pharmacologically active form.
• Understanding the enantioselective binding of amlodipine to plasma proteins is crucial for predicting its pharmacokinetics and pharmacodynamics.

Purpose of the Study:

• To investigate the enantioselective binding of (R)- and (S)-amlodipine to key plasma proteins: bovine serum albumin (BSA), human serum albumin (HSA), and alpha(1)-acid glycoprotein (AGP).
• To determine the binding affinities of amlodipine enantiomers to these proteins using Scatchard analysis.

Main Methods:

• Equilibrium dialysis was employed to study drug-protein interactions over a concentration range of 75-200 microM.
• Enantioselective capillary electrophoresis (CE) with alpha-cyclodextrin as a background electrolyte was used to quantify unbound drug concentrations.
• Scatchard analysis was applied to assess the binding affinities of amlodipine enantiomers.

Main Results:

• Amlodipine enantiomers did not saturate protein binding sites within the tested concentration range.
• (S)-Amlodipine showed higher binding to HSA and human plasma (HP) compared to (R)-amlodipine.
• Conversely, (R)-amlodipine exhibited greater binding to BSA and AGP than (S)-amlodipine.

Conclusions:

• Significant enantioselective binding of amlodipine to plasma proteins was observed, with differential affinities for HSA, AGP, and BSA.
• These findings highlight the importance of considering enantiomer-specific protein binding in the pharmacokinetic profiling of amlodipine.
• The distinct binding patterns suggest potential differences in the distribution and elimination of amlodipine enantiomers in vivo.