A spectroscopic study of phenylbutazone and aspirin bound to serum albumin in rheumatoid diseases

Interaction of phenylbutazone (PBZ) and aspirin (ASA), two drugs recommended in rheumatoid diseases (RDs), when binding to human (HSA) and bovine (BSA) serum albumins, has been studied by quenching of fluorescence and proton nuclear magnetic resonance (1HNMR) techniques.On the basis of spectrofluorescence measurements high affinity binding sites of PBZ and ASA on albumin as well as their interaction within the binding sites were described. A low affinity binding site has been studied by proton nuclear magnetic resonance spectroscopy.Using fluorescence spectroscopy the location of binding site in serum albumin (SA) for PBZ and ASA was found. Association constants Ka were determined for binary (i.e. PBZ–SA and ASA–SA) and ternary complexes (i.e. PBZ–[ASA]–SA and ASA–[PBZ]–SA).PBZ and ASA change the affinity of each other to the binding site in serum albumin (SA). The presence of ASA causes the increase of association constants KaI of PBZ–SA complex. Similarly, PBZ influences KaI of ASA–SA complex. This phenomenon shows that the strength of binding and the stability of the complexes increase in the presence of the second drug. The decrease of KaII values suggests that the competition between PBZ and ASA in binding to serum albumin in the second class of binding sites occurs. The analysis of 1HNMR spectral parameters i.e. changes of chemical shifts and relaxation times of the drug indicate that the presence of ASA weakens the interaction of PBZ with albumin. Similarly PBZ weakens the interaction of ASA with albumin. This conclusion points to the necessity of using a monitoring therapy owning to the possible increase of uncontrolled toxic effects.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► We studied interaction of PBZ and ASA with SA. ► We used 1HNMR and fluorescence techniques. ► We concluded that PBZ and ASA change affinity of each other to binding site in SA. ► We showed that stability of the complexes increase in the presence of second drug. ► We confirmed the necessity of using a monitoring therapy.