Ginkgo biloba extract EGb 761® ameliorates cognitive impairment and alleviates TNFα response in 5xFAD Alzheimer's disease model mice

Abstract

Background: Ginkgo biloba leaf extract EGb 761® has shown clinical efficacy in patients with mild cognitive impairment and dementia. However, the pharmacological action of EGb 761® in Alzheimer's disease (AD) remains unclear and molecular mechanisms targeted in the brain are not completely understood.

Hypothesis/purpose: We aimed to investigate 1) the potential sex-dependent effects of oral administration of EGb 761® in 5xFAD mice, an AD mouse model, and 2) the underlying microglial subtype responsible for the observed anti-inflammatory effects in the brain.

Methods: Eight-week old 5xFAD and wild type mice received EGb 761®-supplemented diet or control diet for eight weeks. The study investigated changes in cognitive function as well as amyloid plaque load, expression of AD-related genes, and anti-inflammatory effects. Moreover, we used organotypic brain slices for confirmation and assessment of concentration-dependency of the observed EGb 761® effects and performed single cell RNA sequencing on the prefrontal cortex of male mice with focus on microglia.

Results: We demonstrate that EGb 761® treatment improves cognitive function in 5xFAD mice in several behavioral tests. Analysis of the brain tissue from these animals indicated a reduction in amyloid plaque load in the prefrontal cortex (PFC). This brain area was further investigated to assess the molecular changes that occurred following EGb 761® intake. Alterations in the expression of genes related to AD were highly sex-specific with effects on the cholinergic system, the γ-secretase complex, and neuroinflammation. Anti-inflammatory effects of EGb 761® with a particularly pronounced reduction of the TNFα-response could be shown for the PFC but also peripherally in the serum of 5xFAD mice of both sexes. Single-cell RNA sequencing revealed that EGb761® mainly affected disease-associated microglia stage 2 (DAM2), which are thought to have a detrimental role in AD.

Conclusions: EGb 761® shows efficacy in the treatment of cognitive deficits in the 5xFAD mouse model via multimodal activity, including sex-specific and sex-unrelated mechanisms including the normalization of neuroinflammatory parameters.

Keywords: Alzheimer's disease; Cognitive deficits; EGb 761®; Ginkgo biloba extract; Microglia; Single-cell RNA sequencing; TNFα.