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Green vegetables, red meat and colon cancer: chlorophyll prevents the cytotoxic and hyperproliferative effects of haem in rat colon.
Authors: de Vogel J, Jonker-Termont DS, van Lieshout EM, Katan MB, van der Meer R.
Source: Carcinogenesis. 2004 Nov 18
Diets high in red meat and low in green vegetables are associated with increased colon cancer risk. This association might be partly due to the haem content of red meat. In rats, dietary haem is metabolized in the gut to a cytotoxic factor that increases colonic cytotoxicity and epithelial proliferation. Green vegetables contain chlorophyll, a magnesium-porphyrin structurally analogous to haem. We studied whether green vegetables inhibit the unfavourable colonic effects of haem. First, rats were fed a purified control diet or purified diets supplemented with 0.5 mmol haem/kg, spinach (chlorophyll concentration of 1.2 mmol/kg) or haem plus spinach (n=8/group) for 14 days. In the second experiment, we also studied a group that received haem plus purified chlorophyll (1.2 mmol/kg). Cytotoxicity of faecal water was determined with a bioassay and colonic epithelial cell proliferation was quantified in vivo by [methyl-(3)H]thymidine incorporation into newly synthesized DNA. Exfoliation of colonocytes was measured as the amount of rat DNA in faeces. In both studies haem increased cytotoxicity of the colonic contents about eight-fold and proliferation of the colonocytes almost two-fold. Spinach or an equimolar amount of chlorophyll supplemented to the haem diet inhibited these haem effects completely. Haem clearly inhibited exfoliation of colonocytes, an effect counteracted by spinach and chlorophyll. Finally, size-exclusion chromatography showed that chlorophyll prevented the formation of the cytotoxic haem metabolite. We conclude that green vegetables may decrease colon cancer risk because chlorophyll prevents the detrimental, cytotoxic and hyperproliferative, colonic effects of dietary haem.