Greige-Gerges H, Abou Khalil R, Chahine R, Haddad C, Harb W, Ouaini N
Biochemistry Department, Holy Spirit University of Kaslik, B.P. 446 Jounieh, Lebanon.
Life Sci. 2007 Jan 16;80(6):579-85. doi: 10.1016/j.lfs.2006.10.005. Epub 2006 Oct 14.
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.
本研究旨在探讨三种葫芦素（Cuc）E、D和I对人血清白蛋白（HSA）及血浆中胆红素-白蛋白结合的影响。制备了不含葫芦素的胆红素-HSA溶液和血浆，以及含有系列浓度葫芦素的溶液。采用Jendrassik和Grof法测定胆红素-HSA溶液中未结合胆红素的浓度，并测定血浆（胆红素血症正常或升高）中的直接胆红素和总胆红素浓度。在我们采用的条件下，Cuc E和D（程度较轻）以剂量依赖的方式降低了胆红素-HSA溶液中未结合胆红素的水平，并降低了血浆中的直接胆红素浓度和总胆红素浓度，而Cuc I没有影响。Cuc的作用与天然HSA的存在有关。因此，当不存在白蛋白或白蛋白因加热或尿素而变性时，Cuc E不会改变胆红素水平，这表明白蛋白的天然结构对于这种活性至关重要。通过荧光光谱法研究了HSA与Cuc E的相互作用。Cuc E增加了蛋白质的固有荧光以及胆红素-白蛋白复合物的荧光强度大小。我们得出结论，Cuc E和D导致白蛋白结构发生重排，特别是在结构域II，导致胆红素与白蛋白的结合增加，无论其是否与葡萄糖醛酸结合或未结合。
