Effect of cucurbitacins on bilirubin-albumin binding in human plasma.
The aim of this study is to investigate the effect of three cucurbitacins (Cuc) E, D and I on the bilirubin-albumin binding, both in human serum albumin (HSA) and in plasma. Bilirubin-HSA solution and plasma free of cucurbitacins were prepared as well as others containing serial concentrations of cucurbitacins. The concentration of unbound bilirubin was determined in bilirubin-HSA solution and the direct and total bilirubin concentrations were measured in plasma (with normal or elevated bilirubinemia) by Jendrassik and Grof method. In the conditions we adopted Cuc E and D (to a lesser extent), decreased the levels of unbound bilirubin in bilirubin-HSA solution and decreased direct bilirubin concentration and total bilirubin concentration in plasma in a dose-dependent manner while Cuc I had no effect. The effect of Cuc is related to the presence of native HSA. Thus, when albumin was absent or has been denatured by heating or by urea, Cuc E did not modify bilirubin levels, suggesting that the native structure of albumin is essential for such activity. The interaction of HSA with Cuc E was investigated by fluorescence spectroscopy. Cuc E increased the intrinsic fluorescence of the protein and the magnitude of fluorescence intensity of bilirubin-albumin complex. We concluded that Cuc E and D produced a rearrangement in the structure of albumin, particularly in the domain-II, resulting in an increase in the binding of bilirubin to albumin regardless to whether it's conjugated to glucuronic acid or unconjugated.
Greige-Gerges
H
H
Biochemistry Department, Holy Spirit University of Kaslik, B.P. 446 Jounieh, Lebanon. helenegreige@usek.edu.lb
Abou Khalil
R
R
Chahine
R
R
Haddad
C
C
Harb
W
W
Ouaini
N
N
D001663:Bilirubin / Q000097:blood* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006932:Hyperbilirubinemia / Q000097:blood / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D012709:Serum Albumin / Q000378:metabolism*; D014315:Triterpenes / Q000494:pharmacology*
D012709:Serum Albumin; D014315:Triterpenes; C038105:cucurbitacin D; D001663:Bilirubin; C038106:cucurbitacin I; C102326:cucurbitacin E