RESUMO
Antipsychotic drugs interfere with the antioxidant defense system provoking complex and often toxicological effects. Here we examined differences in plasma albumin reduced free thiol (SH) group content and its reactivity as a consequence of clozapine (CLZ) and ziprasidone (ZIP) binding. Chronic administration of CLZ reduced, whereas treatment with ZIP increased albumin-SH content in rats. Regardless of the ratio of stearic acid (SA) bound to protein, in vitro binding of ZIP to human serum albumin (HSA) increased both the SH group level and reactivity. In contrast, the effect of CLZ on HSA-SH reactivity was dependent on HSA to SA molar ratio. CLZ binding was accompanied by an increase in HSA-SH reactivity in samples with normal, but a reduction of its reactivity level with higher SA/HSA ratio, compared to drug-free samples. We demonstrate by steady-state fluorescence quenching studies that an increase in SA binding to HSA is associated with a significant reduction of binding constant for both antipsychotics. In addition, this is the first report of quantitative characterization of ZIP binding to HSA. Our findings suggest that albumin-SH content and reactivity is modulated by ZIP towards an increased antioxidant defense capacity in circulation, as opposed to CLZ, which can contribute to the safer, more effective treatment of schizophrenia.
Assuntos
Clozapina/química , Ácidos Graxos/química , Piperazinas/química , Albumina Sérica/química , Compostos de Sulfidrila/química , Tiazóis/química , Animais , Clozapina/metabolismo , Ácidos Graxos/metabolismo , Humanos , Masculino , Piperazinas/metabolismo , Ligação Proteica , Ratos , Ratos Wistar , Albumina Sérica/metabolismo , Espectrometria de Fluorescência , Espectrofotometria , Compostos de Sulfidrila/análise , Compostos de Sulfidrila/metabolismo , Tiazóis/metabolismoRESUMO
The interaction of polyphenolic molecules with human serum albumin (HSA) could lead to changes in the reactivity of the HSA Cys34 thiol group (HSA-SH). The influences of enterolactone (EL) and enterodiol (ED) binding on HSA-SH reactivity in fatty acid (FA)-free HSA, and in HSA with bound stearic acid (S) in S/HSA molar ratios of 1:1 and 4:1, were investigated by the determination of the pseudo first order rate constants (k') for the thiol reaction with 5,5'-dithiobis-(2-nitrobenzoic acid). The binding affinities and binding sites of EL and ED were also determined, using fluorescence measurements of the intrinsic fluorescence of Trp214 and diazepam (binding site marker). EL and ED binding to HSA increased the reactivity of HSA-SH in all assayed HSA-enterolignan complexes by 9.1-33.1%. The strongest effects were obtained for FA-free HSA-enterolignan complexes. S modulated/reduced the effect of EL on HSA-SH reactivity, while its influence on the effect of ED was negligible. The binding of enterolignans to HSA was investigated: the binding constants were the highest for FA-free HSA (EL: 11.64 × 10(4) M(-1) and ED: 5.59 × 10(4) M(-1) at 37 °C) and the lowest for S/HSA 4:1-enterolignan complexes (EL: 2.43 × 10(4) M(-1) and ED: 1.92 × 10(4) M(-1)). When the S/HSA ratio was increased, the binding affinities and number of binding sites for EL and ED were decreased. At the same time, a high correlation between binding constants and increased Cys34 reactivity was found (r = 0.974). Competitive experiments using diazepam indicated that the binding of ED and of EL was located in the hydrophobic pocket of site II in HSA. Overall, it is evident that stearic acid could modulate the enterolignan effects on HSA-SH reactivity as well as their binding to HSA. This finding could be important for pharmacokinetics and the expression of enterolignan antioxidant effects in vivo after an intake of lignan rich food.