The Methanol Extract of Allium cepa L. Protects Inflammatory Markers in LPS-Induced BV-2 Microglial Cells and Upregulates the Antiapoptotic Gene and Antioxidant Enzymes in N27-A Cells

Abstract

Neuroinflammation, apoptosis, and oxidative stress are connected to the pathogenesis of neurodegenerative diseases (NDDs). Targeting these three factors, the intervention of neuroprotective agents may have great potential in the treatment of NDDs. In the current study, the anti-inflammatory effects of the methanol extract of Allium cepa (MEAC) in lipopolysaccharide (LPS)-induced BV-2 microglial cells were investigated. MEAC has been studied in regard to the regulation of the antiapoptotic gene (Bcl-2) and various antioxidant enzyme (HO-1, NQO-1, and catalase) expressions in N27-A cells. Additionally, the protective action of MEAC has also been studied against MPP⁺-induced death in N27-A cells. The results suggest that MEAC is significantly protected from NO release and increase iNOS expression at the mRNA and protein levels in LPS-stimulated BV-2 microglial cells. MEAC treatment also protects COX-2 expression at the mRNA and protein levels. Furthermore, MEAC treatment prevents LPS-stimulated increases of proinflammatory cytokines, including TNF-α, IL-6, and IL-1β. In N27-A cells, MEAC treatment significantly upregulates antiapoptotic gene (Bcl-2) and antioxidant enzyme (HO-1, NQO1, and catalase) expressions. Moreover, MEAC treatment protects against MPP⁺-induced death in N27-A cells. To conclude, A cepa extract takes protective action against LPS and MPP⁺, and upregulates the antioxidant enzymes that could potentially be used in the therapy of NDDs.

Keywords: Allium cepa; Bcl-2; antioxidant enzymes; inflammatory markers; neurodegenerative diseases; protection.

Figure 1

Effect of methanol extract of A. cepa (MEAC) on nitric oxide (NO) production and cell viability in lipopolysaccharide (LPS)-induced BV-2 microglial cells. (A) The treatment with MEAC on the suppression of LPS-stimulated NO release in BV-2 microglial cells. (B) MEAC treatment-mediated cell viability was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The results present as a percentage of the control samples. Data are presented as the mean ± SEM. ### p < 0.001 versus untreated group; *** p < 0.001 versus LPS group (n = 3).

Figure 2

Effect of MEAC on LPS-induced iNOS expressions at mRNA and protein level in BV-2 microglial cells. (A) MEAC-treated prevention of iNOS expression at mRNA level. (B) The treatment with MEAC protects LPS-stimulated iNOS expression at protein level. Data are presented as the mean ± SEM. ### p < 0.001 versus control group (n = 3); * p < 0.05 and *** p < 0.001 versus LPS group (n = 3).

Figure 3

Effect of MEAC on LPS-induced COX-2 expressions at mRNA and protein levels in BV-2 microglial cells. (A) MEAC-treated prevention of COX-2 expression at mRNA level. (B) The treatment with MEAC protects LPS-stimulated COX-2 expression at protein level. Data are presented as the mean ± SEM. ### p < 0.001 versus control group (n = 3); *** p < 0.001 versus LPS group (n = 3).

Figure 4

MEAC action on LPS-induced cytokine expressions in BV-2 microglial cells. (A) The regulation of TNF-α, IL-1β, and IL-6 mRNA expressions by MEAC treatment (A). The representative densitometry analyses of TNF-α (B), IL-6 (C), and IL-1β (D) compared with GAPDH mRNA. Data are presented as the mean ± SEM. ### p < 0.001 versus control group (n = 3); * p < 0.05 and *** p < 0.001 versus LPS group (n = 3).

Figure 5

MEAC treatment on viability of N27-A cells. (A) Action of different doses of MEAC treatments on the viability of N27-A cells. (B) Action of MEAC treatment against 1-methyl-4-phenylpyridinium (MPP⁺)-induced death in N27-A cells. Data are presented as the mean ± SEM. ### p < 0.001 versus control group; *** p < 0.001 versus MPP⁺-induced group (n = 3).

Figure 6

Effect of MEAC treatment on the expression of Bcl-2, HO-1, NQO1, and catalase at mRNA levels (A). The representative densitometry analyses of Bcl-2 (B), HO-1(C), NQO1 (D), catalase (E) compared with GAPDH mRNA. Data are presented as the mean ± SEM. * p < 0.05, ** p < 0.01 and *** p < 0.001 versus control group (n = 3).