Title:
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The effect of dietary-relevant concentrations of flavonoids on neuroprotective pathways in astrocytes
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Neuroinflammation plays an important role in the progression of neurodegenerative
disorders such as Alzheimer's disease (AD) and Parkinson's disease (PO). Sustained
activation of nuclear transcription factor KB (NF-KB) is thought to play an important role
in the pathogenesis of neurodegenerative disorders. Activation of the NF-KB pathway
in astrocytes may elicit a pro-inflammatory response through increased production and
secretion of cytokines such as IL-1, IL-6, TNFa and IFN-y and of nitric oxide. Through
secretion of these molecules, astrocytes may injure surrounding neurons. Glutathione
is the body's predominant defence against oxidative species, and glutathione
dysregulation is linked to numerous neurodegenerative diseases including; AD, PO,
Amyotrophic Lateral Sclerosis (ALS) and Huntington's disease. Flavonoids have been
shown to possess antioxidant and anti-inflammatory properties both in vivo and in vitro,
mainly through their capacity to modulate a number of intracellular signalling pathways.
This study investigated whether different classes of flavonoids were able to modulate
NF-KB signalling and the glutathione system in embryonic mouse cortical astrocytes.
Using luciferase reporter assays and immunocytochemistry, it was found that
astrocytes display functional NF-KB activity which may be induced by TNFa (150
ng/mL), leading to increased NF-KB-mediated transcription and nuclear localisation of
p65. Bacterial Lipopolysaccaride (LPS) treatment did not increase NF-KB activity, but
resulted in nuclear localisation of p65. Astrocytes also display a functional glutathione
system, which was stimulated using tBHQ. To investigate potential flavonoid
modulation of NF-KB activity and intracellular glutathione levels, astrocytes were
treated with flavonoids from different classes; ftavan-a-ols ((-)-epicatechin and (+)-
catechin), flavones (Iuteolin and chrysin), flavonol (kaempferol) or flavanones
(naringenin and hesperetin) at dietary-relevant concentrations (0.1 - 1 I-IM) for 18 h.
None of the flavonoids modulated constitutive or TNFa-induced NF-KB activity.
Kaempferol significantly increased intracellular glutathione levels. Therefore, we
conclude that the astrocyte glutathione system is a target for kaempferol at these
concentrations. However, dietary-relevant concentrations of flavonoids do not
modulate NF-KB activity in astrocytes.
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