Aim: The aim of the project is to understand the role of the intestinal microbiome as determinant of the effect of diet on colorectal cancer risk and to identify specific microbiome/metabolomic profiles associated with cancer risk. We focus our project on red and processed meat based-diets whose consumption is considered a risk factor in colon carcinogenesis. Importantly, although various mechanisms have implicated in such risk, it is still not clear whether intestinal microbiota plays a role in this process. We are comparing in humans (WP1) and experimental animals (WP2-WP3), a high-risk meat-based diet (MBD) with a pesco-vegetarian diet (PVD) associated with a lower CRC risk and a MBD diet supplemented with tocopherol (MBD-T medium risk). Moreover, we will perform a transplant of faeces from rats fed the three diets into germ–free rats (WP4). The intestinal microbiome and metabolomics profiles (WP5) associated with these diets will be correlated with carcinogenesis measuring surrogate biomarkers in the humans and tumorigenesis in rats fed the same diets. 

Results: The results are still preliminary since volunteer’s recruitment (WP1) and colon carcinogenesis in Pirc rats (mutated in Apc gene) just begun. As to the human study (WP1), a total of 98 participants were enrolled and randomly assigned to a MBD (n=32), MBD-T (n=27), or PVD (n=39) so far. Preliminary analyses of changes in body weight, body composition, and biochemical parameters showed no significant changes from pre to post intervention. Changes in fecal water genotoxicity have been analyzed in 38 subjects. Chemically induced carcinogenesis with Azoxymethane in rats (WP2) has been carried out and preneoplastic lesions (ACF & MDF) were counted. Meat based diets increased the number of ACF, but it was significant only of meat-based diet supplemented with tocopherol. The MDF counting showed a trend of increase only with the meat-based diet without tocopherol. In parallel, analyze of urinary and fecal lipid peroxidation biomarkers indicate an increase in luminal lipid peroxidation in the colon of the rats fed the meat-based diets, probably due to the increased concentration in luminal heme iron, when compared to the control or the PVD diet. The addition of antioxidant to the MBD diet induced a slight but not statistically decrease in those parameters. Those results (biomarkers & myeloperoxidase activity (MPO) were overall confirmed in a 2nd experiment with conventional rats. Furthermore, analysis of colon MPO, showed a significant decrease of this parameter with the PVD, when compared to both MBD diets. Regarding colon carcinogenesis in Pirc rats (WP3), the results, although still preliminary, seem to suggest a lower level of colon carcinogenesis in the rats treated with the PVD diet.

Impact: The results will provide fundamental insight into the role of microbiota in determining the effect of the diet, in particular red/processed meat intake, on CRC risk.  

The MeatIC project is the first controlled dietary intervention study to understand the contribution of microbiome in red/processed meat-mediated CRC risk, that we are conducting in parallel in humans and in three relevant models of colon carcinogenesis. The project is focused on the role of microbiome profile and colon metabolites on CRC risk (in human and animals) and will determine whether reduced intake of red and processed meat, will reduce the level of toxic metabolites. We are comparing in human’s volunteers and experimental animals (Chemically-induced carcinogenesis with Azoxymethane (AOM) in rats and colon carcinogenesis in Pirc rats, mutated in Apc gene), a high-risk meat-based diet (MBD) with a pesco-vegetarian diet (PVD) associated with a lower CRC risk. An additional arm is a MBD diet supplemented with tocopherol (MBD-T), possibly reducing risk. Moreover, to better understand the contribution of diet-induced gut microbiome changes on the CRC and to demonstrate causality between dysbiosis and pathology, we will perform a transplant of faeces from rats fed the three diets into germ–free rats. The intestinal microbiome and metabolomics profiles associated with these diets will be correlated with carcinogenesis measuring surrogate biomarkers in the humans and tumorigenesis in rats fed the same diets. The human intervention study has begun and is currently under investigation.

The results are still preliminary since volunteer’s recruitment (WP1) and colon carcinogenesis in Pirc rats (mutated in Apc gene) just begun. Changes in fecal water genotoxicity have been analyzed in 38 subjects. Preliminary results indicate an higher level of DNA strand breaks in subjects with MBD diet.  Instead the integration of this diet with tocopherol appears to exert a protective effect. The chemically induced carcinogenesis with Azoxymethane in rats (WP2) shows that eat based diets increased the number of preneoplastic lesions (Aberrant Crypt Foci), but it was significant only of meat-based diet supplemented with tocopherol. The other preneoplastic lesions as MDF counting (Mucin Depleted Foci) showed a trend of increase only with the meat-based diet without tocopherol. In parallel, analyze of urinary and fecal lipid peroxidation biomarkers indicate an increase in luminal lipid peroxidation in the colon of the rats fed the meat-based diets, probably due to the increased concentration in luminal heme iron, when compared to the control or the PVD diet. The addition of antioxidant to the MBD diet induced a slight but not statistically decrease in those parameters. Those results (biomarkers & myeloperoxidase activity, MPO) were overall confirmed in a second experiment with conventional rats. Furthermore, analysis of colon MPO, showed a significant decrease of this parameter with the PVD, when compared to both MBD diets. Regarding colon carcinogenesis in Pirc rats (WP3), the results, although still preliminary, seem to suggest a lower level of colon carcinogenesis in the rats treated with the PVD diet.