Prevention of preneoplastic lesions by dietary vitamin D in a mouse model of colorectal carcinogenesis

Colorectal cancer (CRC) is one of the leading causes of cancer morbidity and mortality in Western countries. One of the risk factors for colorectal tumorigenesis is vitamin D insufficiency. The aim of this study was to establish whether increasing dietary vitamin D intake can prevent or delay development of chemically induced preneoplastic lesions in the colon of mice. We fed six weeks old female C57BL/6 J mice (n = 28) with increasing vitamin D(3) concentrations (100, 400, 1000, 2500, 5000 IU/kg diet). To induce dysplasia, a preneoplastic lesion, we injected mice with the carcinogen azoxymethane (10 mg/kg) intraperitoneally, followed by three cycles of 2% dextran sodium sulfate salt, a tumor promoter, in the drinking water. To test our hypothesis that high vitamin D intake prevents formation of preneoplastic lesions, we have investigated the effect of increasing dietary vitamin D on development of premalignant colorectal lesions, serum 25-hydroxyvitamin D(3) (25-D(3)) levels, and expression of renal vitamin D system genes. Dietary vitamin D concentration correlated inversely with dysplasia score (Spearman's correlation coefficient, ρ: −0.579, p = 0.002) and positively with serum 25-D(3) levels (ρ: 0.752, p = 0.001). Increasing dietary vitamin D concentration beyond 1000 IU/kg led to no further increase in circulating 25-D(3) levels, while the dysplasia score leveled out at ≥2500 IU/kg vitamin D. High dietary vitamin D intake led to increased renal mRNA expression of the vitamin D catabolizing enzyme cyp24a1 (ρ: 0.518, p = 0.005) and decreased expression of the vitamin D activating enzyme cyp27b1 (ρ: −0.452, p = 0.016), protecting the body from toxic serum levels of the active vitamin D metabolite 1,25-dihydroxyvitamin D(3) (1,25-D(3)). Our data showed that increasing dietary vitamin D intake is able to prevent chemically induced preneoplastic lesions. The maximum impact was achieved when the mice consumed more than 2500 IU vitamin D/kg diet. This article is part of a Special Issue entitled ‘Vitamin D Workshop’.