The class B scavenger receptor CD36 is expressed on microglia and mediates β-amyloid fibrils-induced production of reactive oxygen species

Alzheimer's disease (AD) is the most common neurodegenerative disorder, yet the cause and progression of this disorder are not completely understood. While the main hallmark of AD is the deposition of amyloid plaques consisting of the β-amyloid (Aβ) peptide, transition metal ions are also known to play a significant role in disease pathology by expediting the formation of neurotoxic soluble β-amyloid (Aβ) oligomers, reactive oxygen species (ROS), and oxidative stress. Thus, bifunctional metal chelators that can control these deleterious properties are highly desirable. Herein, we show that amentoflavone (AMF) – a natural biflavonoid compound, exhibits good metal-chelating properties, especially for chelating Cu2+ with very high affinity (pCu7.4 = 10.44). In addition, AMF binds to Aβ fibrils with a high affinity (Ki = 287 ± 20 nM) – as revealed by a competition thioflavin T (ThT) assay, and specifically labels the amyloid plaques ex vivo in the brain sections of transgenic AD mice – as confirmed via immunostaining with an Ab antibody. The effect of AMF on Aβ42 aggregation and disaggregation of Aβ42 fibrils was also investigated, to reveal that AMF can control the formation of neurotoxic soluble Aβ42 oligomers, both in absence and presence of metal ions, and as confirmed via cell toxicity studies. Furthermore, an ascorbate consumption assay shows that AMF exhibits potent antioxidant properties and can chelate Cu2+ and significantly diminish the Cu2+-ascorbate redox cycling and reactive oxygen species (ROS) formation. Overall, these studies strongly suggest that AMF acts as a bifunctional chelator that can interact with various Aβ aggregates and reduce their neurotoxicity, can also bind Cu2+ and mediate its deleterious redox properties, and thus AMF has the potential to be a lead compound for further therapeutic agent development for AD.

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Effect of reactive oxygen species on NH 4 + permeation in Xenopus laevis oocytes

AJP Cell Physiology ◽

10.1152/ajpcell.00410.2001 ◽

2002 ◽

Vol 282 (6) ◽

pp. C1445-C1453 ◽

Cited By ~ 19

Author(s):

Marc Cougnon ◽

Samia Benammou ◽

Franck Brouillard ◽

Philippe Hulin ◽

Gabrielle Planelles

Keyword(s):

Reactive Oxygen Species ◽

Xenopus Laevis ◽

Reactive Oxygen ◽

Membrane Conductance ◽

Xenopus Laevis Oocytes ◽

Oxygen Species ◽

Cation Conductance ◽

Β Amyloid ◽

Oocyte Membrane ◽

Ros Scavengers

To investigate the effects of reactive oxygen species (ROS) on NH[Formula: see text]permeation in Xenopus laevis oocytes, we used intracellular double-barreled microelectrodes to monitor the changes in membrane potential ( V m) and intracellular pH (pHi) induced by a 20 mM NH4Cl-containing solution. Under control conditions, NH4Cl exposure induced a large membrane depolarization (to V m = 4.0 ± 1.5 mV; n = 21) and intracellular acidification [reaching a change in pHi(ΔpHi) of 0.59 ± 0.06 pH units in 12 min]; the initial rate of cell acidification (dpHi/d t) was 0.06 ± 0.01 pH units/min. Incubation of the oocytes in the presence of H2O2 or β-amyloid protein had no marked effect on the NH4Cl-induced ΔpHi. By contrast, in the presence of photoactivated rose bengal (RB), tert-butyl-hydroxyperoxide ( t-BHP), or xanthine/xanthine oxidase (X/XO), the same experimental maneuver induced significantly greater ΔpHi and dpHi/d t. These increases in ΔpHiand dpHi/d t were prevented by the ROS scavengers histidine and desferrioxamine, suggesting involvement of the reactive species 1ΔgO2 and ·OH. Using the voltage-clamp technique to identify the mechanism underlying the ROS-measured effects, we found that RB induced a large increase in the oocyte membrane conductance ( G m). This RB-induced G m increase was prevented by 1 mM diphenylamine-2-carboxylate (DPC) and by a low Na+concentration in the bath. We conclude that RB, t-BHP, and X/XO enhance NH[Formula: see text] influx into the oocyte via activation of a DPC-sensitive nonselective cation conductance pathway.

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Implication of the small GTPase Rac1 in the generation of reactive oxygen species in response to β-amyloid in C6 astroglioma cells

Biochemical Journal ◽

10.1042/bj20020453 ◽

2002 ◽

Vol 366 (3) ◽

pp. 937-943 ◽

Cited By ~ 26

Author(s):

Mina LEE ◽

Hye-Jin YOU ◽

Sung-Hoon CHO ◽

Chang-Hoon WOO ◽

Min-Hyuk YOO ◽

...

Keyword(s):

Reactive Oxygen Species ◽

Reactive Oxygen ◽

Leukotriene B4 ◽

Small Gtpase ◽

Cell Surface Receptor ◽

Oxygen Species ◽

Exogenous Application ◽

Essential Components ◽

Β Amyloid ◽

Astroglioma Cells

Exogenous application of β-amyloid (Aβ25—35, a fragment of Aβ1—42) significantly elevated levels of reactive oxygen species (ROS) in C6 astroglioma cells, as measured by confocal microscopic analysis of H2O2-sensitive 2′,7′-dichlorofluorescin fluorescence. Subsequent characterization of the signalling pathway revealed that expression of RacN17, a dominant-negative Rac1 mutant, completely blocked Aβ25—35-induced generation of ROS, which is indicative of the crucial role played by Rac GTPase in this process. To better understand the downstream mediators affected by Rac, we assessed the degree to which inhibition of cytosolic phospholipase A2 (cPLA2) and 5-lipoxygenase (5-LO) contributed to the response and found that inhibition of either enzyme completely blocked Aβ25—35-induced ROS generation, indicating its dependence on arachidonic acid synthesis and metabolism to leukotrienes (e.g. leukotriene B4). Consistent with those findings, Aβ25—35 Rac-dependently stimulated translocation of 5-LO to the nuclear envelope and increased intracellular levels of leukotriene B4, while exogenous application of leukotriene B4 increased intracellular H2O2 via BLT, its cell-surface receptor. In addition to the aforementioned downstream mediators, inhibition of phosphoinositide 3-kinase (PI 3-kinase), an enzyme situated upstream of Rac, also completely blocked Aβ25—35-induced H2O2 generation. Our findings thus demonstrate that PI 3-kinase, Rac, cPLA2 and 5-LO are all essential components of the β-amyloid signaling cascade leading to generation of ROS.

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CD36 Mediates the Innate Host Response to β-Amyloid

Journal of Experimental Medicine ◽

10.1084/jem.20021546 ◽

2003 ◽

Vol 197 (12) ◽

pp. 1657-1666 ◽

Cited By ~ 250

Author(s):

Joseph B. El Khoury ◽

Kathryn J. Moore ◽

Terry K. Means ◽

Josephine Leung ◽

Kinya Terada ◽

...

Keyword(s):

Amyloid Fibrils ◽

Senile Plaques ◽

Scavenger Receptor ◽

Intracerebral Injection ◽

Innate Response ◽

Macrophage Response ◽

Class B ◽

Β Amyloid ◽

Recognition Receptor

Accumulation of inflammatory microglia in Alzheimer's senile plaques is a hallmark of the innate response to β-amyloid fibrils and can initiate and propagate neurodegeneration characteristic of Alzheimer's disease (AD). The molecular mechanism whereby fibrillar β-amyloid activates the inflammatory response has not been elucidated. CD36, a class B scavenger receptor, is expressed on microglia in normal and AD brains and binds to β-amyloid fibrils in vitro. We report here that microglia and macrophages, isolated from CD36 null mice, had marked reductions in fibrillar β-amyloid–induced secretion of cytokines, chemokines, and reactive oxygen species. Intraperitoneal and stereotaxic intracerebral injection of fibrillar β-amyloid in CD36 null mice induced significantly less macrophage and microglial recruitment into the peritoneum and brain, respectively, than in wild-type mice. Our data reveal that CD36, a major pattern recognition receptor, mediates microglial and macrophage response to β-amyloid, and imply that CD36 plays a key role in the proinflammatory events associated with AD.

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Promotion of transition metal-induced reactive oxygen species formation by β-amyloid

Brain Research ◽

10.1016/s0006-8993(98)00461-2 ◽

1998 ◽

Vol 799 (1) ◽

pp. 91-96 ◽

Cited By ~ 85

Author(s):

Stephen C Bondy ◽

Shirley X Guo-Ross ◽

Anh T Truong

Keyword(s):

Reactive Oxygen Species ◽

Transition Metal ◽

Reactive Oxygen ◽

Oxygen Species ◽

Reactive Oxygen Species Formation ◽

Species Formation ◽

Β Amyloid

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Amentoflavone: A Bifunctional Metal Chelator that Controls the Formation of Neurotoxic Soluble Aβ42 Oligomers

10.26434/chemrxiv.12445505.v1 ◽

2020 ◽

Author(s):

Liang Sun ◽

Anuj K. Sharma ◽

Byung-Hee Han ◽

Liviu M. Mirica

Keyword(s):

Reactive Oxygen Species ◽

Metal Ions ◽

Antioxidant Properties ◽

Reactive Oxygen ◽

Amyloid Plaques ◽

Transition Metal Ions ◽

Oxygen Species ◽

High Affinity ◽

Amyloid Aβ ◽

Β Amyloid

Alzheimer's disease (AD) is the most common neurodegenerative disorder, yet the cause and progression of this disorder are not completely understood. While the main hallmark of AD is the deposition of amyloid plaques consisting of the β-amyloid (Aβ) peptide, transition metal ions are also known to play a significant role in disease pathology by expediting the formation of neurotoxic soluble β-amyloid (Aβ) oligomers, reactive oxygen species (ROS), and oxidative stress. Thus, bifunctional metal chelators that can control these deleterious properties are highly desirable. Herein, we show that amentoflavone (AMF) – a natural biflavonoid compound, exhibits good metal-chelating properties, especially for chelating Cu2+ with very high affinity (pCu7.4 = 10.44). In addition, AMF binds to Aβ fibrils with a high affinity (Ki = 287 ± 20 nM) – as revealed by a competition thioflavin T (ThT) assay, and specifically labels the amyloid plaques ex vivo in the brain sections of transgenic AD mice – as confirmed via immunostaining with an Ab antibody. The effect of AMF on Aβ42 aggregation and disaggregation of Aβ42 fibrils was also investigated, to reveal that AMF can control the formation of neurotoxic soluble Aβ42 oligomers, both in absence and presence of metal ions, and as confirmed via cell toxicity studies. Furthermore, an ascorbate consumption assay shows that AMF exhibits potent antioxidant properties and can chelate Cu2+ and significantly diminish the Cu2+-ascorbate redox cycling and reactive oxygen species (ROS) formation. Overall, these studies strongly suggest that AMF acts as a bifunctional chelator that can interact with various Aβ aggregates and reduce their neurotoxicity, can also bind Cu2+ and mediate its deleterious redox properties, and thus AMF has the potential to be a lead compound for further therapeutic agent development for AD.

Download Full-text