Jacalin Has Chemopreventive Effects on Colon Cancer Development

Abstract

Colorectal cancer, which is one of the most common causes of cancer-related deaths worldwide, has a slow natural history that provides a great opportunity for prevention strategies. Plant-derived natural products have received considerable attention because of their inherent colorectal cancer chemopreventive effects. The plant lectin jacalin specifically recognizes the tumor-associated Thomsen-Friedenreich antigen and has antiproliferative effects on human colon cancer cells, highlighting its potential antitumor activity. To evaluate jacalin's potential application in colorectal cancer chemoprevention, we studied its effects on the early stages of carcinogenesis. Balb/c mice were given 4 intrarectal deposits of 0.1 ml solution of Methyl-N'-Nitro-N-Nitroso-Guanidine (5 mg/ml) twice a week (with a 3-day interval) for 2 weeks. Starting 2 weeks before carcinogen administration, animals were treated orally with jacalin (0.5 and 25 μg) three times a week (on alternate weekdays) for 10 weeks. We show that jacalin treatment reduced the number of preneoplastic lesions in carcinogen-exposed mice. This anticarcinogenic activity was associated with decreased colonic epithelial cell proliferation and stromal COX-2 expression and with increased intestinal production of TNF-α. Our results demonstrate that jacalin is able to modulate the early stages of colon carcinogenesis and emphasize its promising chemopreventive activity in colorectal cancer.

Figure 1

Treatment protocol. Mice received 4 successive intrarectal deposits of 0.1 ml of PBS or MNNG solution (5 mg/ml) twice a week for 2 weeks. Starting 2 weeks before carcinogen administration, animals were treated orally (0.1 ml/mouse) with PBS (→) or jacalin (0.5 and 25 μg) (→) three times a week for 10 weeks. After 10 weeks of treatment, mice were euthanized, and the colons were removed, fixed, and processed for histological and immunohistochemical analysis.

Figure 2

Jacalin treatment reduces the number of aberrant crypt foci in mice colon. (a) Quantification of aberrant crypt foci. The aberrant crypt foci index (ACF-i) shows the number of lesions per mm². (b) Representative histological image of a characteristic ACF with compressed cryptal luminal opening (400x magnification, scale bars represent 20 μm). Statistical analysis: one-way analysis of variance. ^#Compared to PBS group. ^#P < 0.05.

Figure 3

Jacalin treatment affects colonic epithelial cell proliferation but not apoptosis. (a) Proliferative activity in the colon was assessed by using proliferating cell nuclear antigen (PCNA) antibody. The index of colonic crypt cells expressing proliferating cell nuclear antigen (PCNA-i) was calculated from the ratio of positively stained nuclei to a total number of nuclei counted. (b) Apoptotic cells were detected by caspase-3 immunoreactivity in colonic stromal cells. Apoptosis index shows the number of stained cells in the intercrypt spaces. (c) Representative immunohistochemistry images of proliferating cells of the control group; (d) MNNG-exposed group; (e) MNNG-exposed group treated with jacalin 0.5 μg; and (f) MNNG-exposed group treated with jacalin 25 μg. Results are expressed as mean ± SEM for each group. Statistical analysis: (a) one-way analysis of variance and (b) one-way ANOVA (Kruskal-Wallis) and Dunn's multiple comparison post hoc tests. ^∗Compared to control group. ^#Compared to PBS group. ^#P < 0.05; ^∗∗∗  or ^###P < 0.001.

Figure 4

Downregulation of COX-2 expression in colonic tissue of jacalin-treated mice. (a) Cyclooxygenase-2 expression was evaluated using anti-COX-2 antibody. Morphometric analysis showed decreased COX-2 expression in both MNNG-exposed and unexposed animals treated with the higher dose of jacalin. (b) Representative immunohistochemistry images of COX-2 positive cells in the intercrypt spaces of the control group; (c) MNNG-exposed group; (d) MNNG-unexposed group treated with jacalin 25 μg; and (e) MNNG-exposed group treated with jacalin 25 μg. COX-2 index was calculated as the number of stained cells in the intercrypt spaces and is expressed as mean ± SEM for each group. Statistical analysis: one-way ANOVA (Kruskal-Wallis) and Dunn's multiple comparison post hoc tests. ^∗Compared to control group. ^#Compared to PBS group. ^#P < 0.05; ^∗∗P < 0.01. Arrows show COX-2-positive cells.

Figure 5

Jacalin treatment affects intestinal cytokine production. MNNG-exposed mice were treated with jacalin (0.5 and 25 μg) and proinflammatory and anti-inflammatory cytokine levels in colon homogenates were determined by ELISA. Jacalin treatment led to a significant increase in TNF and TGF-β1 levels in colonic tissue. Results are expressed as mean ± SEM for each group. Statistical analysis: one-way analysis of variance. ^∗Compared to control group; ^#compared to PBS group. ^∗  or ^#P < 0.05; ^∗∗P < 0.01 and ^∗∗∗P < 0.001.