fA Beta Research Articles

Optimized Turmeric Extracts have Potent Anti-Amyloidogenic Effects

Inhibition of beta-amyloid (A beta) accumulation and A beta fibril (fA beta) formation from A beta are attractive therapeutic targets for the treatment of Alzheimer's disease (AD). While previous studies have shown anti-amyloidogenic effects of curcumin in vitro and in vivo, no studies have examined optimized turmeric extracts enriched in curcuminoids or turmerones. Three standardized turmeric extracts, HSS-838, HSS-848, and HSS-888, were prepared with different chemical profiles to investigate their potential therapeutic benefits for AD. These extracts were fingerprinted by DART TOF-MS to reveal the significant chemical complexity. In addition four curcuminoids (curcumin, tetrahydrocurcumin, demethoxycurcumin and bisdemethoxycurcumin) were also examined. We measured the effects of the extracts and curcuminoids, on the aggregation of A beta by using a thioflavin T cell-free assay and the secretion of A beta from human neuronal cells (SweAPP N2A cells) in vitro. All three extracts and the curcuminoids showed dose-dependent inhibition of fA beta aggregation from A beta(1-42) in the cell-free assay, with IC(50) values of <or= 5 microg/mL. However, only HSS-888, curcumin and demethoxycurcumin significantly decreased A beta secretion (approximately 20%) in SweAPP N2A cells. Interaction matrices were used to examine possible synergistic interactions between HS-888 and the other extracts and the individual curcuminoids on A beta aggregation. Only simple additive effects were observed for the A beta aggregation inhibition, supporting the notion that the known curcuminoids are not strong inhibitors of this activity. However, HSS-888 showed strong inhibition of A beta aggregation and secretion, thus indicating that there are novel bioactive molecules in this extract that might be important leads for future AD drug discovery efforts.

Proton pump inhibitors: predisposers to Alzheimer disease?

The abnormal processing of amyloid-beta peptide (A beta) and resultant formation of fibrillar A beta (fA beta) are major events in the pathogenesis of Alzheimer disease (AD). Microglia as the phagocytic cells of the brain can engulf and digest fA beta within their acidic lysosomes. The lysosomes of AD patients are less acidic and therefore less capable of clearance of fA beta. Vacuolar proton pumps (V-ATPases) which are found abundantly in microglia and macrophages, acidify lysosomes by pumping protons into these structures. Proton pump inhibitors (PPIs) can inhibit V-ATPases of the lysosomes. These drugs are shown to penetrate the blood-brain barrier in animals. PPIs are consumed for long periods in conditions such as gastroesophageal reflux disease, with the resultant exposure of the human brain to the substantial amounts of PPIs. We hypothesize that by blocking the V-ATPases on microglial lysosomes, PPIs may basify lysosomes and hamper degradation of fA beta. Chronic consumption of PPIs may thus be a risk factor for AD.

The Glucagon Receptor Is Required for the Adaptive Metabolic Response to Fasting

Glucagon receptor (Gcgr) signaling maintains hepatic glucose production during the fasting state; however, the importance of the Gcgr for lipid metabolism is unclear. We show here that fasted Gcgr-/- mice exhibit a significant increase in hepatic triglyceride secretion and fasting increases fatty acid oxidation (FAO) in wild-type (WT) but not in Gcgr-/- mice. Moreover fasting upregulated the expression of FAO-related hepatic mRNA transcripts in Gcgr+/+ but not in Gcgr-/- mice. Exogenous glucagon administration reduced plasma triglycerides in WT mice, inhibited TG synthesis and secretion, and stimulated FA beta oxidation in Gcgr+/+ hepatocytes. The actions of glucagon on TG synthesis and FAO were abolished in PPARalpha-/- hepatocytes. These findings demonstrate that the Gcgr receptor is required for control of lipid metabolism during the adaptive metabolic response to fasting.

Macrophage colony stimulatory factor and interferon-gamma trigger distinct mechanisms for augmentation of beta-amyloid-induced microglia-mediated neurotoxicity.

Dysregulated stimulation of microglia, the resident macrophages in the brain, can lead to excessive induction of inflammatory agents and subsequently damage to neurons. Fibrillar beta-amyloid peptide (fA beta), a major component of senile plaques in Alzheimer's disease (AD) brain, is known to induce microglial-mediated neurotoxicity under certain conditions. Microglial 'priming' by macrophage colony stimulatory factor (MCSF) or interferon-gamma (IFN gamma) appears to be required for this fA beta-induced microglia mediated neurotoxicity in vitro. We report here that while both MCSF and IFN gamma induce microglial-mediated fA beta neurotoxicity, their mechanisms of toxicity differ. The enhancement of neurotoxicity by IFN gamma or MCSF is not due to enhanced A beta ingestion by microglia or to the direct effect of proinflammatory cytokine production. The neurotoxicity resulting from IFN gamma/fA beta treatment was blocked by pretreatment with nitric oxide synthase inhibitor L-N-5-(1-iminoethyl) ornithine hydrochloride (L-NIO), consistent with a role for nitric oxide in the IFN gamma-mediated toxicity mechanism. In contrast, no induction of nitric oxide production was detected for microglia treated with MCSF/fA beta. Furthermore, inhibiting the generation of reactive oxygen species (ROS) using the specific NADPH oxidase inhibitor apocynin reversed fA beta/MCSF-induced neurotoxicity while L-NIO had little effect. As MCSF is endogenously expressed within the brain, and both its level and that of the MCSF receptor are dramatically increased in the AD brain, the neurotoxicity resulting from ROS release by fA beta/MCSF coactivated microglia may be a more appropriate model for assessing fA beta-induced microglial-mediated neuropathology in AD.

Beta-Galactosidases with a lectin-like domain are expressed in strawberry

Strawberry fruits (Fragaria x ananassa Duch.) undergo a marked softening during their ripening, and the process is accompanied by a release of free sugars with galactose among them. In this work total beta-galactosidase activity was measured in cell wall proteins from strawberry fruits at different developmental stages. Three full-length cDNAs (Fa beta gal1, Fa beta gal2 and Fa beta gal3, respectively) encoding different beta-galactosidases (EC 3.2.1.23) were isolated from a library representing red fruit transcripts. All of them could be detected both in fruits and in vegetative tissues. However, only Fa beta gal1 showed an increasing expression during the ripening stages up to a maximum in the red fruits, while the other two (Fa beta gal2 and Fa beta gal3) were mostly found in green fruits and became barely detectable during ripening proper. The three beta-galactosidase-encoding cDNAs were expressed in the yeast Pichia pastoris, and it was thus possible to demonstrate that each of them encode a beta-galactosidase. The expression of the three beta-galactosidase genes appears to be down-regulated by auxin, as already observed for other ripening-related genes of the non-climacteric strawberry. An unusual characteristic of two strawberry beta-galactosidases (Fa beta gal1 and Fa beta gal2) is that at the C-terminus of the enzymes a domain is found which is structurally related to known animal peptides with a sugar-binding ability.

Uptake of fibrillar beta-amyloid by microglia isolated from MSR-A (type I and type II) knockout mice.

To characterize the receptors involved in binding fibrillar amyloid A-beta (fA beta), we compared the uptake of fA beta in microglia from wildtype (MSR-A+/+) and MSR-A knockout (MSR-A-/-) mice. On average, there was a 60% reduction in the uptake of Cy3-fA beta in microglia from the MSR-A-/- mice. Cy3-fA beta uptake in the MSR-A-/- mice was still competable by scavenger receptor ligands, including acetylated low-density lipoprotein (Ac-LDL) and fucoidan. This indicates that uptake by MSR-B and/or other MSRs is also involved in the uptake of fA beta by microglia. However, the significant reduction in the uptake of fA beta in the MSR-A-/- microglia suggests that fA beta gets internalized mostly by MSR-As in microglia. Uptake of modified fA beta (ClqA beta) was similar in the MSR-A-/- microglia as in the wildtype indicating that the uptake of the opsonized fA beta is independent of MSR-A.

Interaction between A beta(1-42) and A beta(1-40) in Alzheimer's beta-amyloid fibril formation in vitro.

We analyzed the interaction of two kinds of amyloid beta-peptides (A beta), i.e., A beta(1-42) and A beta(1-40), in the kinetics of beta-amyloid fibril (fA beta) formation in vitro, based on a nucleation-dependent polymerization model using fluorescence spectroscopy with thioflavin T. When 25 microM A beta(1-42) was incubated with increasing concentrations of amyloidogenic A beta(1-40), the time to proceed to equilibrium was extended dose-dependently. A similar inhibitory effect was observed when 45 microM A beta(1-40) was incubated with increasing concentrations of A beta(1-42). On the other hand, when 50 microM of nonamyloidogenic A beta(1-40) was incubated with A beta(1-42) at a molar ratio of 10:1 or 5:1, A beta(1-42) initiated fA beta formation from A beta(1-40). The lag time of the reaction shortened in a concentration-dependent manner, with A beta(1-42). We next examined the seeding effect of fA beta formed from A beta(1-42) (fA beta(1-42)) on nonamyloidogenic A beta(1-40). When 50 microM of nonamyloidogenic A beta(1-40) was incubated with 10 or 20 microg/mL (2.2 or 4.4 microM) of fA beta(1-42), the fluorescence showed a sigmoidal increase. The lag time of the reaction was shortened by fA beta(1-42) in a concentration-dependent manner. However, the time to proceed to equilibrium was much longer than when an equal concentration of fA beta formed from A beta(1-40) (fA beta(1-40)) was added to A beta(1-40). The fluorescence increased hyperbolically without a lag phase when 25 microM A beta(1-42) was incubated with 10 or 20 microg/mL (2.3 or 4.6 microM) of fA beta(1-40), and proceeded to equilibrium more rapidly than without fA beta(1-40). An electron microscopic study indicated that the morphology of fA beta formed is governed by the major component of fresh A beta peptides in the reaction mixture, not by the morphology of preexisting fibrils. These results may indicate the central role of A beta(1-42) for fA beta deposition in vivo, among the different coexisting A beta species.