Gamma-oryzanol Prevents LPS-induced Brain Inflammation and Cognitive Impairment in Adult Mice

Abstract

Background: Rice (Oryza sativa L.) is the main food source for more than half of humankind. Rice is rich in phytochemicals and antioxidants with several biological activities; among these compounds, the presence of γ-oryzanol is noteworthy. The present study aims to explore the effects of γ-oryzanol on cognitive performance in a mouse model of neuroinflammation and cognitive alterations.

Methods: Mice received 100 mg/kg γ-oryzanol (ORY) or vehicle once daily for 21 consecutive days and were then exposed to an inflammatory stimulus elicited by lipopolysaccharide (LPS). A novel object recognition test and mRNA expression of antioxidant and neuroinflammatory markers in the hippocampus were evaluated.

Results: ORY treatment was able to improve cognitive performance during the neuroinflammatory response. Furthermore, phase II antioxidant enzymes such as heme oxygenase-1 (HO-1) and NADPH-dehydrogenase-quinone-1 (NQO1) were upregulated in the hippocampi of ORY and ORY+LPS mice. Lastly, γ-oryzanol showed a strong anti-inflammatory action by downregulating inflammatory genes after LPS treatment.

Conclusion: These results suggest that chronic consumption of γ-oryzanol can revert the LPS-induced cognitive and memory impairments by promoting hippocampal antioxidant and anti-inflammatory molecular responses.

Keywords: cognitive performance; neuroinflammation; second-generation antioxidant enzymes; γ-oryzanol.

Figure 1

Chemical structures of different organic molecules contained in γ-oryzanol (A). Graphic scheme of γ-oryzanol and lipopolysaccharide (LPS) treatment protocol (B).

Figure 2

Motor performances of mice (A). Graphic scheme of the novel object recognition (NOR) test protocol and data of time spent exploring the familiar and novel objects are reported. For all experimental conditions, the full color bars represent the familiar object, while the patterned bars represent the novel object (B). Data are expressed as the mean ± S.E.M. Two-way ANOVA tests with Sidak’s multiple comparisons test were used to test statistical significance (* p < 0.05 vs. the familiar object). VH: vehicle; ORY: γ-oryzanol; LPS: lipopolysaccharide.

Figure 3

Graphic representation of quantitative RT-PCR data obtained from RNA extracted from the hippocampi of VH, ORY, LPS, and ORY+LPS mice. Data are expressed as the fold change of the target gene (RelA in (A), IL-1β in (B), IL-6 in (C), iNOS in (D) and COX-2 in (E)) normalized to the internal standard control gene (β-Actin). Data are shown as the mean ± S.E.M. One-way ANOVA tests with Newman–Keuls post-test were used to determine statistical significance, * p < 0.05, ** p < 0.005, *** p < 0.0005 and **** p < 0.0001 vs. VH, # p < 0.05, ## p < 0.005 and ### p < 0.0005 vs. LPS. VH: vehicle; ORY: γ-oryzanol; LPS: lipopolysaccharide.

Figure 4

Graphic representation of quantitative RT-PCR data obtained from RNA extracted from VH, ORY, LPS, and ORY+LPS mice hippocampi. Data are expressed as the fold change of target genes (Nrf2 in (A), HO-1 in (B) and NQO1 in (C)) normalized to the internal standard control gene (β-Actin). Data are shown as the mean ± S.E.M. One-way ANOVA tests with the Newman–Keuls post-test were used to determine statistical significance, * p < 0.05 and ** p < 0.005. VH, # p < 0.05, and ## p < 0.005 vs. LPS. VH: vehicle; ORY: γ-oryzanol; LPS: lipopolysaccharide.