Flavonoids,
Flavonoid Metabolites, and Phenolic Acids
Inhibit Oxidative Stress in
the Neuronal Cell Line HT-22 Monitored by ECIS and MTT Assay: A Comparative
Study
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Abstract
A real-time and label-free in vitro
assay based on electric cell-substrate
impedance sensing (ECIS) was established, validated, and compared
to an end-point MTT assay within an experimental trial addressing
the cytoprotective effects of 19 different flavonoids, flavonoid metabolites,
and phenolic acids and their methyl esters on the HT-22 neuronal cell
line, after induction of oxidative stress with <i>tert</i>-butyl hydroperoxide. Among the flavonoids under study, only those
with a catechol unit and an additional 4-keto group provided cytoprotection.
The presence of a 2,3-double bond was not a structural prerequisite
for a neuroprotective effect. In the case of the phenolics, catechol
substitution was the only structural requirement for activity. The
flavonoids and other phenolics with a ferulic acid substitution or
a single hydroxy group showed no activity. Electrochemical characterization
of all compounds via square-wave voltammetry provided a rather specific
correlation between cytoprotective activity and redox potential for
the active flavonoids, but not for the active phenolics with a low
molecular weight. Moreover this study was used to compare label-free
ECIS recordings with results of the established MTT assay. Whereas
the former provides time-resolved and thus entirely unbiased information
on changes of cell morphology that are unequivocally associated with
cell death, the latter requires predefined exposure times and a strict
causality between metabolic activity and cell death. However, MTT
assays are based on standard lab equipment and provide a more economic
way to higher throughput