Multifunctionality of Acidulated Serum Albumin on Inhibiting Zn²⁺-Mediated Amyloid β-Protein Fibrillogenesis and Cytotoxicity

Abstract

Fibrillogenesis of amyloid β-proteins (Aβ) mediated by transition-metal ions such as Zn(2+) in neuronal cells plays a causative role in Alzheimer's disease. Hence, it is highly desired to design multifunctional agents capable of inhibiting Aβ aggregation and modulating metal-Aβ species. In this study, we fabricated acidulated human serum albumin (A-HSA) as a multifunctional agent for binding Zn(2+) and modulating Zn(2+)-mediated Aβ fibrillogenesis and cytotoxicity. On average, 19.5 diglycolic anhydrides were modified onto the surface of human serum albumin (HSA). It was confirmed that A-HSA kept the stability and biocompatibility of native HSA. Moreover, it could inhibit Aβ42 fibrillogenesis and change the pathway of Zn(2+)-mediated Aβ42 aggregation, as demonstrated by extensive biophysical assays. In addition, upon incubation with A-HSA, the cytotoxicity presented by Zn(2+)-Aβ42 aggregates was significantly mitigated in living cells. The results showed that A-HSA had much stronger inhibitory effect on Zn(2+)-mediated Aβ42 fibrillogenesis and cytotoxicity than equimolar HSA. Isothermal titration calorimetry and stopped-flow fluorescence measurements were then performed to investigate the working mechanism of A-HSA. The studies showed that the A-HSA surface, with more negative charges, not only had stronger affinity for Zn(2+) but also might decrease the binding affinity of Aβ42 for Zn(2+). Moreover, hydrophobic binding and electrostatic repulsion could work simultaneously on the bound Aβ42 on the A-HSA surface. As a result, Aβ42 conformations could be stretched, which avoided the formation of toxic Zn(2+)-Aβ42 aggregates. The research thus revealed that A-HSA is a multifunctional agent capable of altering the pathway of Zn(2+)-mediated Aβ42 aggregation and greatly mitigating the amyloid cytotoxicity.

Metabolic relationship between diabetes and Alzheimer's Disease affected by Cyclo(His-Pro) plus zinc treatment

“…These proteins contain a variable number of histidine, similar to Cyclo(His-Pro). Human serum albumin has a stronger inhibitory effect on zinc medicated Aβ-42 fibrillogenesis and cytotoxicity [75]. Evidence from these studies for inhibiting zinc mediated amyloid β-protein fibrillogenesis and cytotoxicity by serum albumin support the hypothesis that Cyclo-Z, which contains dipeptides similar to serum albumin may be helpful in preventing and treating AD, based on the fact that Cyclo-Z contains high amounts of histidine to chelate zinc and thus stimulate intestinal zinc absorption.…”

Iminodiacetic Acid-Modified Human Serum Albumin: A Multifunctional Agent against Metal-Associated Amyloid β-Protein Aggregation and Cytotoxicity

“…Remarkably, the potency of I-HSA under physiological conditions was much stronger than that of both native HSA and A-HSA designed in our previous work (Figure 2a, Lanes 3−5). 27,28 The favorable result suggests that the carboxyl groups on the I-HSA surface contributed to the prominent inhibition activity by the hydrophobic binding-electrostatic repulsion (HyBER) mechanism proposed previously. 27,28 In addition, Zn 2+ obviously reduced the ThT intensity of Aβ 42 fibrils to 17.9% (Figure 2a, Lane 6) due to the formation of spherical aggregates with a small β-sheet structure, 27,30 which was also confirmed by transmission electron microscopy (TEM) to be discussed below.…”

“…27,28 The favorable result suggests that the carboxyl groups on the I-HSA surface contributed to the prominent inhibition activity by the hydrophobic binding-electrostatic repulsion (HyBER) mechanism proposed previously. 27,28 In addition, Zn 2+ obviously reduced the ThT intensity of Aβ 42 fibrils to 17.9% (Figure 2a, Lane 6) due to the formation of spherical aggregates with a small β-sheet structure, 27,30 which was also confirmed by transmission electron microscopy (TEM) to be discussed below. It is seen from Lane 7 (Figure 2a) that IDA increased the ThT fluorescent signal to 88.1% by chelating Zn 2+ and diminishing the effect of Zn 2+ on Aβ 42 aggregation.…”

“…29 As reported previously, Aβ 42 aggregation reached a steady state by 24 h of incubation. 27,28 Hence, the fluorescence signals of Aβ 42 aggregates at 24 h of incubation are presented for comparison (Figure 2a). It can be seen that the ThT fluorescence intensity with IDA was almost the same as that of the sample of Aβ 42 alone, indicating that IDA has an inappreciable effect on Aβ 42 aggregation.…”

“…24−26 However, the metal-chelate capacity of HSA is very limited, making it unable to deal with the high-concentration metal ions in the brain tissues of AD patients. 27 Hence, we have focused on the use of HSA to develop potent inhibitors of Aβ aggregation. Previously, we have proven that the extra negative charges on an acidulated HSA (A-HSA) surface aided the inhibitory effects of Aβ aggregation more than native HSA.…”