Untitled

Abstract

Fibrillar amyloid beta-protein (Abeta) is the major protein of amyloid plaques in the brains of patients with Alzheimer's disease (AD). The mechanism by which normally produced soluble Abeta gets fibrillized in AD is not clear. We studied the effect of neutral, zwitterionic, and anionic lipids on the fibrillization of Abeta 1-40. We report here that acidic phospholipids such as phosphatidic acid, phosphatidylserine, phosphatidylinositol (PI), PI 4-phosphate, PI 4,5-P2 and cardiolipin can increase the fibrillization of Abeta, while the neutral lipids (diacylglycerol, cholesterol, cerebrosides), zwitterionic lipids (phosphatidylcholine, phosphatidylethanolamine, sphingomyelin) and anionic lipids lacking phosphate groups (sulfatides, gangliosides) do not affect Abeta fibrillization. Abeta was found to increase the fluorescence of 1-acyl-2-[12-[(7-nitro-2-1, 3-benzoxadiazol-4-yl) amino] dodecanoyl]-sn-glycero-3-phosphate (NBD-PA) in a concentration-dependent manner, while no change was observed with 1-acyl-2- [12-[(7-nitro-2-1, 3-benzoxadiazol-4-yl) amino] dodecanoyl]-sn-glycero-3-phosphoethanolamine (NBD-PE). Under similar conditions, other proteins such as apolipoprotein E, gelsolin and polyglutamic acid did not interact with NBD-PA. The order of interaction of amyloid beta-peptides with NBD-PA was Abeta 1-43 = Abeta 1-42 = Abeta 17-42 > Abeta 1-40 = Abeta 17-40. Other Abeta peptides such as Abeta 1-11, Abeta 1-16, Abeta 1-28, Abeta 1-38, Abeta 12-28, Abeta 22-35, Abeta 25-35, and Abeta 31-35 did not increase the NBD-PA fluorescence. These results suggest that phosphate groups, fatty acids, and aliphatic amino acids at the C-terminus end of Abeta 1-40/Abeta 1-42 are essential for the interaction of Abeta with anionic phospholipids, while hydrophilic Abeta segment from 1-16 amino acids does not participate in this interaction. Since positively charged amino acids in Abeta are necessary for the interaction with negatively charged phosphate groups of phospholipids, it is suggested that Lys28 of Abeta may provide anchor for the phosphate groups of lipids, while aliphatic amino acids (Val-Val-Ile-Ala) at the C-terminus of Abeta interact with fatty acids of phospholipids.

Effect of copper (II) ion against elongation behavior of amyloid β fibrils on liposome membranes

“…It is therefore considered that the Aβ fibrils can be regarded as a crystal-like aggregate. Fibril growth behavior of Aβ in the presence of copper (II) ion and liposomes It has been reported that the fibril growth of Aβ was affected by the copper (II) ion [22][23][24][25] and the liposomes [10,17,18]. It seems that those factors could affect both the nucleation and elongation steps.…”

“…The excess copper (II) ion (Aβ:Cu II = 1:20) considerably inhibited the increase in ThT fluorescence intensity. Alternatively, the liposome could affect the fibril growth [10,17,18]. In order to investigate whether the liposome was effective in the elongation step, a growth behavior of seeds of Aβ fibrils was studied in the presence of the copper (II) ion.…”

“…However, Aβ fibrils are considered to be formed on biomembranes, not in a bulk aqueous solution, considering the realistic environment in which the Aβ fibrils were formed in a biological system. Indeed, the model biomembrane, liposome (a closed-phospholipid bilayer membrane system), could affect the fibril growth behavior of Aβ [5,8,[13][14][15][16][17][18]. Especially, the liposome composed of oxidized lipids [15] or negatively charged liposomes [17,18] gave an impact on the fibril growth behavior.…”

“…Indeed, the model biomembrane, liposome (a closed-phospholipid bilayer membrane system), could affect the fibril growth behavior of Aβ [5,8,[13][14][15][16][17][18]. Especially, the liposome composed of oxidized lipids [15] or negatively charged liposomes [17,18] gave an impact on the fibril growth behavior. Considering the phospholipid contents of neural cell membrane of AD patient, it is therefore expected that the (model) biomembrane might affect the inhibitory effect of the chemical compounds against the fibril growth.…”

Amphotericin B-induced ion flux is markedly attenuated in phosphatidylglycerol membrane as evidenced by a newly devised fluorometric method

“…In the case of antibacterial antibiotics, polar head groups often play an important role for their selective toxicity. [20][21][22][23][24] The membrane-permeabilizing antibiotics have been studied using artificial liposomes with various methods. 19,[23][24][25][26][27][28][29] Among them, a fluorometric method using dye-encapsulated liposomes is effective for the real-time monitoring of ion flux, which enable the detection of minute difference in the activity.…”