Cannabidiol reduces Aβ-induced neuroinflammation and promotes hippocampal neurogenesis through PPARγ involvement

Abstract

Peroxisome proliferator-activated receptor-γ (PPARγ) has been reported to be involved in the etiology of pathological features of Alzheimer's disease (AD). Cannabidiol (CBD), a Cannabis derivative devoid of psychomimetic effects, has attracted much attention because of its promising neuroprotective properties in rat AD models, even though the mechanism responsible for such actions remains unknown. This study was aimed at exploring whether CBD effects could be subordinate to its activity at PPARγ, which has been recently indicated as its putative binding site. CBD actions on β-amyloid-induced neurotoxicity in rat AD models, either in presence or absence of PPAR antagonists were investigated. Results showed that the blockade of PPARγ was able to significantly blunt CBD effects on reactive gliosis and subsequently on neuronal damage. Moreover, due to its interaction at PPARγ, CBD was observed to stimulate hippocampal neurogenesis. All these findings report the inescapable role of this receptor in mediating CBD actions, here reported.

Figure 1. Effect of CBD on the release of inflammatory mediators by in vitro cultured astrocytes.

Aβ-challenged astrocytes (1 µg/ml) were treated with CBD (10⁻⁹–10⁻⁷ M) in the presence of PPARα (MK886, 3 µM) or PPARγ (GW9662, 9 nM) antagonist. 24 h later, NO production was determined by measuring nitrite (NO₂ ⁻) accumulation in the culture medium (A), whereas IL-1β, TNFα, and S100B release was determined by ELISA experiments (B,C,D). Each bar shows the mean ± S.E.M. of five separate experiments. ***p<0.001 vs. control; °p<0.05, °°p<0.01, and °°°p<0.001 vs. Aβ-challenged cells.

Figure 2. Effects of CBD on Aβ-induced iNOS, GFAP, S100B, and p50/p65 expression in rat astrocytes.

Aβ-challenged cells (1 µg/ml) were treated with CBD (10⁻⁹–10⁻⁷ M) in the presence of PPARα (MK886, 3 µM) or PPARγ (GW9662, 9 nM) antagonist. iNOS, GFAP, and S100B expression was evaluated by Western blot 24 h after treatments. NF-κB activation was evaluated 3 h following treatments by Western blot analysis of its component p50 and p65. Figure shows results of Western blot analysis of proteins (A) and densitometric analysis of corresponding bands (B). Results are the mean ± S.E.M. of four separate experiments. ***p<0.001 vs. control; °p<0.5, °° p<0.01, and °°°p<0.001 vs. Aβ-challenged cells.

Figure 3. Effects of CBD on Aβ-induced iNOS, GFAP, S100B, calbindin, and p50/p65 expression in rat hippocampi.

Results of Western blot analyses of iNOS, GFAP, S100B, calbindin, and p50/p65 performed on rat hippocampus homogenates (A) and densitometric analysis of corresponding bands (B). Results are the mean ± S.E.M. of three separate experiments. *** p<0.001 vs. vehicle inoculated rats; °°p<0.01 and °°° p<0.001 vs. Aβ-inoculated rats.

Figure 4. Effects of CBD on reactive gliosis, neuronal survival, and neurogenesis in rat hippocampi.

A: representative photomicrographs of the CA1 area of rat hippocampus showing the results of immunohistochemical evaluation of GFAP. B: representative photomicrographs showing the results of Nissl staining of the whole rat hippocampus (2X magnification) and the corresponding CA1 region (10X magnification). C: immunofluorescence photomicrographs showing a particular (10X magnification) of DCX-labeled cells in the dentate gyrus (DG) of rat hippocampi.