Aim: We did a prospective study to investigate the binding of stilbene glucoside (2,3,5,4'-tetrahydroxystilbene-2-O-beta-D-glucoside, TSG) to plasma, albumin, and alpha1-AGP (2.0, 10.0, or 50 microg/mL) by three different methods: ultrafiltration, equilibrium dialysis and cloud-point extraction (CPE).
Method: Drug stability in plasma was assessed at different temperatures (4, 25, and 37 degrees C) and on the condition of thawing and freezing. A previously validated high-performance liquid chromatography (HPLC) method was used to analyze the total concentration of drug and free fraction in the samples.
Results: The binding of TSG to plasma increased with adding drug concentration. The binding to albumin was constant (about 60%) within concentration range studied while the binding to alpha1-AGP decreased with increasing drug concentration indicating that albumin is more important in clinical settings.
Conclusions: alpha1-AGP might be important when plasma proteins change with disease. The results to plasma obtained by CPE were in good agreement to those observed by ultrafiltration and equilibrium dialysis, indicating that CPE was a highly sensitive and selective method for the measurement to plasma protein binding of TSG. The results obtained in our studies are important before clinical trials and to perform pharmacokinetic studies.