Oral administration of monogalactosyl diacylglycerol from spinach inhibits colon tumor growth in mice

Abstract

Previously, we observed that purified monogalactosyl diacylglycerol (MGDG), a major glycoglycerolipid from spinach, selectively inhibits the activities of mammalian replicative DNA polymerases (α, δ and ε). However, the function of MGDG following ingestion is not well-known. In the present study, spinach MGDG suppressed the proliferation of Colon26 mouse colon cancer cells with an LD(50) of 24 μg/ml in vitro. γ-cyclodextrin (CD)-MGDG complex was prepared and administered orally following Colon26 mouse tumor adhesion for 26 days. It was observed that 20 mg/kg equivalent (eq.) of the CD-MGDG complex reduced tumor volume by ∼60% compared with that of the vehicle-treated controls. In immunohistochemical analysis, the CD-MGDG complex group showed a decreased number of proliferating cell nuclear antigen (PCNA)-positive cells and reduction of mitosis in the tumor cells compared with the control group. In addition, the CD-MGDG complex increased the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive apoptotic cells and inhibited CD31-positive tumor blood vessel growth significantly. These results suggest that MGDG has the potential for cancer prevention and health promotion.

Figure 1

Chemical structure of monogalactosyl diacylglycerol (MGDG). R₁ and R₂ are acyloxy groups (derived from fatty acids).

Figure 2

Dose-response curve of purified MGDG from spinach on the cell growth inhibition of the cultured mouse colon cancer cell line, Colon26. Colon26 cells were cultured for 24 h in media containing the indicated concentrations of MGDG. Cell proliferation was determined using the MTT assay (19). All values are expressed as the mean ± SE of five independent experiments. MGDG, monogalactosyl diacylglycerol; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide.

Figure 3

Effect of CD-MGDG complex on tumor growth in mice. (A) Mice with Colon26 solid tumors were orally administered CD (200 mg/kg) as a control group (vehicle control, n=6), CD (40 mg/kg)-MGDG (4 mg/kg) complex (n=5) or CD (200 mg/kg)-MGDG (20 mg/kg) complex (n=6). (B) Body weight curves of mice. All data are expressed as the mean ± SE. ^*Significantly different from the control, P<0.05. CD, γ-cyclodextrin; MGDG, monogalactosyl diacylglycerol.

Figure 4

Immunofluorescence staining for CD31 in Colon26 solid tumor tissue. Groups of mice were treated with (A) CD (200 mg/kg) as a control group (vehicle control, n=6), (B) CD (40 mg/kg)-MGDG (4 mg/kg) complex (n=6) or (C) CD (200 mg/kg)-MGDG (20 mg/kg) complex (n=5). (D) Mean fluorescence intensity values of CD31. ^*Significantly different from the control, P<0.05. CD, γ-cyclodextrin; MGDG, monogalactosyl diacylglycerol.