Apigenin inhibits colonic inflammation and tumorigenesis by suppressing STAT3-NF-κB signaling

Abstract

Apigenin is a naturally occurring compound with anti-inflammatory, antioxidant, and anticancer properties. Here, we investigated the effects of apigeninin inflammatory bowel disease (IBD) and colitis-associated cancer (CAC). Apigenin effectively inhibited ulcerative colitis, a type of IBD, and CAC. Apigenin decreased myeloperoxidase (MPO), inflammatory cytokine and COX-2 levels, and it attenuated inflammatory cell infiltration in treated colon tissues as compared to untreated model colon tissues. Apigenin also reduced NF-κB and STAT3 activity in vitro and in vivo, thereby inhibiting inflammation and inflammation-induced carcinogenesis. Thus apigenin appears to inhibit inflammation and inflammation-induced carcinogenesisin IBD and CAC by suppressing STAT3-NF-κB signaling.

Keywords: CAC; IBD; NF-κB; STAT3; apigenin.

Figure 1. Apigenin protects against chronic UC in mice

(A) Model of chronic DSS-induced UC in mice. (B) Body weights (g) of chronic UC group mice. (C) DAI values of chronic UC groupmice. (D) Average colon lengths for each group. Data are presented as means of three experiments; error bars represent standard deviation (^*P < 0.05, ^**P <0.01).

Figure 2. Apigenin inhibits colon damage and inflammatory cytokine production in UC mice

(A and B) Photographs of colons from chronic UC mice and associated macroscopic damage scores, respectively. (C and D) Photographs of pathological sections of H&E-stained colon from chronic UC mice and associated microscopic damage scores, respectively. (E) MPO levels for each group. (F) Levels of the inflammatory cytokines TNF-α, IL-1β, IL-6, MCP-1, and CSF-1 and of COX-2. Data are presented as means of three experiments; error bars represent standard deviation (^*P < 0.05, ^**P <0.01).

Figure 3. Apigenin protects against CAC in mice

(A) Mouse model of AOM/DSS-induced CAC. (B) Body weights (g) of CAC mice. (C) DAI values of CAC mice. (D) Survival curves for each group. (E) Colon morphology of each group. (F–H) Tumor count, tumor load, and tumor sizesfor each group, respectively. (I and J) Photographs of pathologic colon sections from each group and associated colon histological scores, respectively. Data are presented as means of three experiments; error bars represent standard deviation (^*P < 0.05, ^**P <0.01).

Figure 4. Apigenin reduces levels of inflammatory cytokines and colon cancer markers

(A) Colon levels of the inflammatory cytokines TNF-α, IL-1β, IL-6, MCP-1, and CSF-1 and of COX-2foreach group. (B) MPO levels for each group. (C) Representative photos of IHC staining of the cancer markers CEA, CK8, CK18, and p53. (D) Staining scores for the cancer markers and cytokines listed above. Data are presented as means of three experiments; error bars represent standard deviation (^*P < 0.05, ^**P <0.01).

Figure 5. Apigenin suppresses the NF-κB/STAT3 pathway in colon carcinoma cells

(A) Dual-luciferase assay results for NF-κB transcription in HCT-116 cells. (B) Levels of p-NF-κB p65 and T-NF-κB p65 after LPS administration in HCT-116 cells treated with apigenin or vehicle. (C) Dual-luciferase assay results for STAT3 in HCT-116 cells. (D) Levels of p-STAT3 and T-STAT3 after LPS administration in HCT-116 cells treated with apigenin or vehicle. (E) Levels of secreted IL-6 and IL-10 after LPS administration in HCT-116 cells treated with apigenin or vehicle. (F) Expression of p-STAT3 and T-STAT3 in HCT-116 cells pretreated with HO-3867.

Figure 6. Apigenin inhibits NF-κB/STAT3 pathway protein expression in tumor tissues in colitis-associated colon cancer (CAC) tumor tissues

(A) Results of Western blot analysis of NF-κB p65 and STAT3 expression in CAC tumor tissues. (B) Model showing the role of apigenin as a negative regulator of STAT3-NF-κB pathway.