Potential protective effects of the water-soluble Chinese propolis on experimental ulcerative colitis

Abstract

Objective: To investigate the outcome of Chinese water-soluble propolis (WSP) on the inflammatory response and oxidative stress (OS) of colonic mucosa in rats with ulcerative colitis.

Methods: Dextran sulfate sodium (DSS) was employed to establish the ucerative colitis (UC) rat model. Forty-eight male rats were arbitrarily separated into six groups, namely control, UC, low-dose water-soluble propolis (L-WSP), medium-dose water-soluble propolis (M-WSP), high-dose water-soluble propolis (H-WSP), and sulfasalazine (Sulfa). In this study, we adopted a method of pre-administration and reconstruction of the model that assessed the water-soluble propolis mediated protection against DSS-induced UC rats. Moreover, we examined the body weight (BW), disease activity index (DAI), bloody stool, colon length, and intestinal mucosal injury index of rats. In addition, using enzyme linked immunosorbent assays, we assessed indicators, such as, colonic myeloperoxidase (MPO), interleukin-6 (IL-6), interleukin-9 (IL-9), tumor necrosis factor-ɑ (TNF-ɑ), superoxide dismutase (SOD), malondialdehyde, and glutathione peroxidase (GSH-Px) levels.

Results: The pro-inflammatory cytokine expression, as well as OS, was increased in the model rats. However, upon WSP intervention, both pro-inflammatory cytokine levels and OS reduced dramatically, and the therapeutic effect was dose-dependent.

Conclusion: WSP downregulates OS by enhancing the function of endogenous antioxidant enzymes like SOD and GSH-Px, that inhibit neutrophil activity, as well as diminish pro-inflammatory cytokines like TNF-ɑ, IL-6, and IL-9, along with mechanisms that attenuate intestinal inflammation in UC rat model.

Keywords: natural products; oxidative stress; pro-inflammatory cytokine; ulcerative colitis; water-soluble propolis.

Figure 1. Effects of WSP on weight loss, DAI score, colon length, CMDI socre and colon W/L ratio over the whole experimental period

A: weight loss; B: DAI score; C-D: colon length; E: CMDI socre; F: colon W/L ratio. CON: control group; UC: ulcerative colitis group; L-WSP: low-dose water-soluble propolis group (50 mg·kg^-1·d^-1); M-WSP: medium-dose water-soluble propolis group (100 mg·kg^-1·d^-1); H-WSP: high-dose water-soluble propolis group (200 mg·kg^-1·d^-1); Sulfa: sulfasalazine group (100 mg·kg^-1·d^-1). The drug was administered by gavage once a day for 16 d. DAI: disease activity index; CMDI: colonic mucosal damage index; colon W/L: colon weigh (g) / colon length (cm). Data are expressed as mean ± standard deviation (n = 8). Compared to CON group, ^aP < 0.01, ^cP < 0.05; compared to UC group, ^bP < 0.01, ^dP < 0.05.

Figure 2. Effects of WSP on microscopic changes in colon tissue of rats in each group

A: representative images of microscopic appearance colon slices with HE staining of all groups, magnification × 40; A1: CON; A2: UC; A3: L-WSP; A4: M-WSP; A5: H-WSP; A6: Sulfa; B: Score of histological changes. CON: control group; UC: ulcerative coloits group; L-WSP: low-dose water-soluble propolis group (50 mg·kg^-1·d^-1); M-WSP: medium-dose water-soluble propolis group (100 mg·kg^-1·d^-1); H-WSP: high-dose water-soluble propolis group (200 mg·kg^-1·d^-1); Sulfa: sulfasalazine group (100 mg·kg^-1·d^-1). The drug was administered by gavage once a day for 16 d. HS: histological score. Data are expressed as mean ± standard deviation (n = 8). Compared to CON group, ^aP < 0.01; compared to UC group, ^bP < 0.05, ^cP < 0.01.

Figure 3. Effects of WSP on the colonic inflammatory response in UC rats

A: MPO levels in colon tissue homogenate; B: TNF-α levels in colon tissue homogenate; C: IL-6 levels in colon tissue homogenate; D: IL-9 levels in colon tissue homogenate. CON: control group; UC: ulcerative colitis group; L-WSP: low-dose water-soluble propolis group (50 mg·kg^-1·d^-1); M-WSP: medium-dose water-soluble propolis group (100 mg·kg^-1·d^-1); H-WSP: high-dose water-soluble propolis group (200 mg·kg^-1·d^-1); Sulfa: sulfasalazine group (100 mg·kg^-1·d^-1). The drug was administered by gavage once a day for 16 d. MPO: myeloperoxidase; TNF-α: tumor necrosis factor-α; IL-6: interleukin-6; IL-9: interleukin-9. Data are expressed as mean ± standard deviation (n = 8). Compared to CON group, ^aP < 0.01; compared to UC group, ^bP < 0.01.

Figure 4. Effects of WSP on the SOD, GHS-Px, MDA and ROS contents in the colon tissue of rats in each group

A: SOD contents in colon tissue homogenate; B: GSH-Px contents in colon tissue homogenate; C: MDA contents in colon tissue homogenate; D: ROS contents in colon tissue homogenate. CON: control group; UC: ulcerative colitis group; L-WSP: low-dose water-soluble propolis group (50 mg·kg^-1·d^-1); M-WSP: medium-dose water-soluble propolis group (100 mg·kg^-1·d^-1); H-WSP: high-dose water-soluble propolis group (200 mg·kg^-1·d^-1); Sulfa: sulfasalazine group (100 mg·kg^-1·d^-1). The drug was administered by gavage once a day for 16 d. SOD: superoxide dismutase; GSH-Px: glutathione peroxidase; MDA: malondialdehyde; ROS: reactive oxygen species. Data are expressed as mean ± standard deviation (n = 8). Compared to CON group, ^aP < 0.01; compared to UC group, ^bP < 0.05, ^cP < 0.01.