Ginkgo biloba extract (Egb761) attenuates zinc-induced tau phosphorylation at Ser262 by regulating GSK3β activity in rat primary cortical neurons

Food Funct. 2015 Jun;6(6):2058-67. doi: 10.1039/c5fo00219b.

Abstract

In the brain, an excessive amount of zinc promotes the deposition of β-amyloid proteins and the intraneuronal accumulation of neurofibrillary tangles composed of hyperphosphorylated tau proteins. These consequences are key neuropathological traits that reflect Alzheimer's disease. Egb761, a standardized Ginkgo biloba extract, is a powerful antioxidant known to exhibit neuroprotective actions. In this study, we investigated whether Egb761 can counteract the zinc-induced tau phosphorylation in rat primary cortical neurons. To determine the modification of tau phosphorylation by Egb761 treatment, we conducted Western blot analyses, MTT assay, ROS measurements and immunocytochemistry. We found that zinc-induced tau phosphorylation occurred at Ser262 in a time- and dose-dependent manner while other tau sites were not phosphorylated. Tau phosphorylation at Ser262 was increased 30 min after zinc treatment and peaked 3 h after zinc treatment (control: 100 ± 1.2%, 30 min: 253 ± 2.24%, 3 h: 373 ± 1.3%). Interestingly, Egb761 treatment attenuated the zinc-induced tau hyperphosphorylation at Ser262 in a concentration-dependent manner while the antioxidant N-acetylcysteine showed a similar effect. Furthermore, Egb761 prevented the zinc-induced activation of p38 MAPK and GSK3β, as well as the zinc-induced increase in ROS production and neuronal cell death. Lithium chloride also inhibited the zinc-induced tau phosphorylation but did not affect ROS levels. These results suggest the potential of Egb761 for inhibiting the zinc-induced tau phosphorylation at Ser262 through its anti-oxidative actions involving the regulation of GSK3β. Therefore, Egb761 may be a candidate for the treatment of tauopathy present in neurological disorders such as Alzheimer's disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antioxidants / pharmacology
  • Cell Survival / drug effects
  • Cells, Cultured
  • Cerebral Cortex / cytology
  • Cerebral Cortex / drug effects*
  • Cerebral Cortex / metabolism
  • Chlorides / antagonists & inhibitors
  • Chlorides / toxicity
  • Embryo, Mammalian / cytology
  • Ginkgo biloba
  • Glycogen Synthase Kinase 3 / antagonists & inhibitors*
  • Glycogen Synthase Kinase 3 / chemistry
  • Glycogen Synthase Kinase 3 / metabolism
  • Glycogen Synthase Kinase 3 beta
  • Kinetics
  • Nerve Tissue Proteins / agonists
  • Nerve Tissue Proteins / antagonists & inhibitors
  • Nerve Tissue Proteins / metabolism
  • Neurons / cytology
  • Neurons / drug effects*
  • Neurons / metabolism
  • Neuroprotective Agents / pharmacology*
  • Oxidants / antagonists & inhibitors
  • Oxidants / toxicity
  • Phosphorylation / drug effects
  • Plant Extracts / pharmacology*
  • Protein Processing, Post-Translational / drug effects*
  • Rats, Sprague-Dawley
  • Reactive Oxygen Species / agonists
  • Reactive Oxygen Species / antagonists & inhibitors
  • Reactive Oxygen Species / metabolism
  • Serine / metabolism
  • Zinc Compounds / antagonists & inhibitors
  • Zinc Compounds / toxicity
  • tau Proteins / metabolism*

Substances

  • Antioxidants
  • Chlorides
  • Mapt protein, rat
  • Nerve Tissue Proteins
  • Neuroprotective Agents
  • Oxidants
  • Plant Extracts
  • Reactive Oxygen Species
  • Zinc Compounds
  • tau Proteins
  • Ginkgo biloba extract
  • Serine
  • zinc chloride
  • Glycogen Synthase Kinase 3 beta
  • Gsk3b protein, rat
  • Glycogen Synthase Kinase 3