amyloid-beta-peptides and 6-carboxyfluorescein

Calcium dysregulation, membrane leakage and Aβ amyloid growth are hallmarks of Alzheimer's disease. Here we show that Ca2+ ions inhibit membrane damage due to amyloid channels but enhance membrane disruption associated with fibers growing on the lipid surface. The similarities with IAPP suggest that this may represent a mechanism common to all proteinopathies.

Topics: Amyloid; Amyloid beta-Peptides; Animals; Calcium; Cell Membrane; Fluoresceins; Fluorescent Dyes; Fura-2; Kinetics; Mice; Peptide Fragments; Porosity; Protein Multimerization

The protein transport inside a cell is a complex phenomenon that goes through several difficult steps. The facilitated transport requires sophisticated machineries involving protein assemblies. In this work, we developed a diffusion-reaction model to simulate co-transport kinetics of proteins and lipids. We assume the following: (a) there is always a small lipid concentration of order of the Critical Micellar Concentration (CMC) in equilibrium with the membrane; (b) the binding of lipids to proteins modulates the hydrophobicity of the complexes and, therefore, their ability to interact and merge with the bilayer; and (c) some lipids leave the bilayer to replenish those bound to proteins. The model leads to a pair of integral equations for the time-evolution of the adsorbed proteins in the lipid bilayer. Relationships between transport kinetics, CMC, and lipid-protein binding constants were found. Under particular conditions, a perturbation analysis suggests the onset of kinks in the protein adsorption kinetics. To validate our model, we performed leakage measurements of vesicles composed by either high or low CMC lipids interacting with Islet Amyloid PolyPeptide (IAPP) and Aβ (1-40) used as sample proteins. Since the lipid-protein complex stoichiometry is not easily accessible, molecular dynamics simulations were performed using monomeric IAPP interacting with an increasing number of phospholipids. Main results are the following: (a) 1:1 lipid-protein complexes generally show a faster insertion rate proportional to the complex hydrophobicity and inversely related to lipid CMC; (b) on increasing the number of bound lipids, the protein insertion rate decreases; and

Topics: Adsorption; Amyloid beta-Peptides; Dimyristoylphosphatidylcholine; Facilitated Diffusion; Fluoresceins; Hydrophobic and Hydrophilic Interactions; Islet Amyloid Polypeptide; Kinetics; Lipid Bilayers; Models, Chemical; Molecular Dynamics Simulation; Peptide Fragments; Phosphatidylcholines; Protein Binding; Protein Transport

A disrupted blood-brain barrier (BBB) might have major effects on the progression of Alzheimer's disease (AD). This supports the theory of blood as a chronic source of exogenous amyloid-beta (Abeta) peptide as well as other neurotoxic substances in the brain, which would normally be excluded by an intact BBB. In addition to Abeta, neuroinflammation is suggested to contribute to the pathological conditions in AD and is a known disruptor of BBB integrity. Consequently, new therapeutic approaches to stabilize the BBB should be developed. Serum derived immunoglobulins, also called intravenous immunoglobulins (IVIG), are gained from plasma of healthy individuals and were found to induce positive effects in some patients with AD, but mechanisms of action are unclear by now. Moreover, there are no data on how IVIG affects the BBB itself. Therefore, we examined the potency of Abeta peptides as well as neuroinflammatory mediators (TNF-alpha and LPS) either alone or after simultaneous application of IVIG to disintegrate the BBB by evaluating the transport rate of carboxyfluorescein, a marker of paracellular leakage. Our results showed beneficial effects of IVIG on a disrupted BBB, which could positively influence diseases outcome in AD. With a stabilized BBB the brain is prevented from systemic Abeta entry, as well as from entry of other toxic substances from the blood.

Topics: Amyloid beta-Peptides; Animals; Biological Transport; Blood-Brain Barrier; Cell Line, Tumor; Culture Media, Serum-Free; Dose-Response Relationship, Drug; Drug Interactions; Fluoresceins; Fluorometry; Glioma; Immunoglobulins, Intravenous; Lipopolysaccharides; Peptide Fragments; Rats; Time Factors; Tumor Necrosis Factor-alpha