Valproate competes with palmitate for binding to serum albumin

Use of an immobilised human serum albumin HPLC column as a probe of drug-protein interactions: the reversible binding of valproate

The reversible binding of valproate to human serum albumin determines a decrease of the binding of ligands that selectively bind to site I, site II, and bilirubin binding site. The binding inhibition was followed by displacement chromatography methodology using increasing concentrations of the competitor, i.e. valproate, in the mobile phase. Significant binding inhibition was observed for drugs binding at site I and site II. The greater displacement was observed for the more retained enantiomer of benzodiazepines and profens. A reduction of the affinity was observed also in the case of phenol red, this compound being selected as representative of bilirubin binding site. Difference circular dichroism spectroscopy was also used to characterise the binding of valproate to human serum albumin. This antiepilectic drug was proved to affect the binding at site I, II, and bilirubin binding site. The data have physiological relevance because significant inhibition of the binding resulted at clinic concentrations of valproate.

Valproate and palmitate binding to serum albumin in valproate-treated patients. Relation to obesity

Binding of valproate and palmitate to serum albumin was studied in 29 valproate-treated epileptic patients. The results were compared with similar observations in a reference group of 43 non valproate-treated individuals. The binding affinity for palmitate was decreased (P < 0.0001) resulting in increased availability of long-chain fatty acids (P = 0.008) due to competitive valproate binding in the valproate-treated patients. The findings support a hypothesis on the pathogenesis of obesity as a complication of valproate treatment of epilepsy.

Nonlinear binding of valproic acid (VPA) and E-delta 2-valproic acid to rat plasma proteins

The binding characteristics of valproic acid (VPA) and its pharmacologically active monounsaturated metabolite, E-delta 2-VPA, to rat plasma proteins were compared. The plasma free fraction was determined by a rapid equilibrium procedure, which minimizes the interfering effects of nonesterified fatty acids liberated by in vitro lipolysis. Nonlinear binding behavior was observed with both compounds over their respective pharmacologic concentration range. Multiple binding-site models were invoked to explain the binding isotherm. The 2-unsaturated compound has a much higher affinity for the rat plasma proteins (mainly albumin) than its saturated precursor. The equilibrium association constants for the high- and intermediate-affinity sites were more than an order of magnitude higher with E-delta 2-VPA than with VPA (10(4)-10(6) versus 10(3) M-1). This difference in binding affinity was also reflected by a lower plasma free fraction for E-delta 2-VPA compared with VPA (much less than 10 versus greater than 20% at total concentrations of less than 100 micrograms/ml). A more pronounced dose- and concentration-dependent variation in the distribution and clearance kinetics is predicted for the 2-unsaturated analogue compared to VPA. Also, the structural dependency in plasma protein binding observed with these branched-chain fatty acids may provide insights into the mechanism of interaction between fatty acyl molecules and albumin.