No abstract

b-amyloid peptide (Ab) is one of the main protein components of senile plaques associated with Alzheimer's disease (AD). Ab readily aggregates to forms fibrils and other aggregated species that have been shown to be toxic in a number of studies. In particular, soluble oligomeric forms are closely related to neurotoxicity. However, the relationship between neurotoxicity and the size of Ab aggregates or oligomers is still under investigation. In this article, we show that different Ab incubation conditions in vitro can affect the rate of Ab fibril formation, the conformation and stability of intermediates in the aggregation pathway, and toxicity of aggregated species formed. When gently agitated, Ab aggregates faster than Ab prepared under quiescent conditions, forming fibrils. The morphology of fibrils formed at the end of aggregation with or without agitation, as observed in electron micrographs, is somewhat different. Interestingly, intermediates or oligomers formed during Ab aggregation differ greatly under agitated and quiescent conditions. Unfolding studies in guanidine hydrochloride indicate that fibrils formed under quiescent conditions are more stable to unfolding in detergent than aggregation associated oligomers or Ab fibrils formed with agitation. In addition, Ab fibrils formed under quiescent conditions were less toxic to differentiated SH-SY5Y cells than the Ab aggregation associated oligomers or fibrils formed with agitation. These results highlight differences between Ab aggregation intermediates formed under different conditions and provide insight into the structure and stability of toxic Ab oligomers.

Growing evidence suggests that on-pathway amyloid-β (Aβ) oligomers are primary neurotoxic species and have a direct correlation with the onset of Alzheimer's disease (AD). One promising therapeutic strategy to block AD progression is to reduce the levels of these neurotoxic Aβ species using small molecules. While several compounds have been shown to modulate Aβ aggregation, compounds with such activity combined with safety and high blood-brain barrier (BBB) permeability have yet to be reported. Brilliant Blue G (BBG) is a close structural analogue of a U.S. Food and Drug Administration (FDA)-approved food dye and has recently garnered prominent attention as a potential drug to treat spinal cord injury due to its neuroprotective effects along with BBB permeability and high degree of safety. In this work, we demonstrate that BBG is an effective Aβ aggregation modulator, which reduces Aβ-associated cytotoxicity in a dose-dependent manner by promoting the formation of off-pathway, nontoxic aggregates. Comparative studies of BBG and three structural analogues, Brilliant Blue R (BBR), Brilliant Blue FCF (BBF), and Fast Green FCF (FGF), revealed that BBG is most effective, BBR is moderately effective, and BBF and FGF are least effective in modulating Aβ aggregation and cytotoxicity. Therefore, the two additional methyl groups of BBG and other structural differences between the congeners are important in the interaction of BBG with Aβ leading to formation of nontoxic Aβ aggregates. Our findings support the hypothesis that generating nontoxic aggregates using small molecule modulators is an effective strategy for reducing Aβ cytotoxicity. Furthermore, key structural features of BBG identified through structure-function studies can open new avenues into therapeutic design for combating AD.

Reduced hydrogen exchange in three CDRs suggests these residues may form strong intermolecular contacts in the antibody aggregates; regions of enhanced HX indicate unfolding. Residue level modeling methods with varying levels of atomistic detail were unable to identify aggregation patterns predictively.

Bacterial chemotaxis has the potential to enhance biodegradation of organic contaminants in polluted groundwater systems. However, studies of bacterial chemotaxis in porous media are scarce. In this study we use magnetic resonance imaging (MRI) for the noninvasive measurement of changes in bacterial-density distributions in a packed column at a spatial resolution of 330 microm as a function of time. We analyze both the diffusive and the chemotactic behavior of Pseudomonas putida F1 in the presence of the chemical stimulus trichloroethylene (TCE). The migration of motile bacteria in experiments without TCE was described using an effective motility coefficient, whereas the presence of TCE required addition of a nonzero chemotactic sensitivity coefficient, indicating a significant response to TCE. The need for a chemotactic sensitivity term was justified by a test for statistical significance. This study represents the first quantification of bacterial chemotactic parameters within a packed column. For conditions under which chemotaxis occurs in porous media, it may potentially be exploited to significantly improve rates of in situ pollutant biodegradation in the subsurface environment, particularlyfor pollutants dissolved in water trapped in low-permeability formations or lenses.