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ABSTRACT: probiotics and prebiotics can exert several beneficial effects in the gastrointestinal tract, such as antitumor activity; many studies have been conducted to analyze this activity and its mechanisms. However, their mode of action is not yet well understood. Recent data show the relationship between colon cancer and intestinal bacterial flora. We reviewed the evidence from different studies in order to prove these beneficial effects on the host.
KEYWORDS: Probiotics, Prebiotics, Microbiota, Colorectal Cancer, Chemotherapy
INTRODUCTION
According to the currently adopted definition by FAO/ WHO, probiotics are "live microorganisms which, when administered in adequate amounts, confer a health benefit on the host" (FAO/WHO, 2001). Prebiotics are defined as "nonabsorbable food components that beneficially stimulate one or more of the gut-beneficial microbe groups and thus have a positive effect on human health"; they can be defined as the cofactors of probiotics activity. The most commonly used prebiotics are carbohydrate substrates (e.g. dietary fiber) that show the ability to promote the survival of the intestinal microflora with health benefit to the host (Gibson et al., 1995; Harish et al., 2006). The combination of specific prebiotics with probiotics to provide health benefits by synergistic action are defined "synbiotic effect".
At least 500 different microbial species exist in the gastrointestinal tract with the predomination of about 20 genera; bacterial strains with beneficial properties include mainly bifidobacteria and lactobacilli. This microflora is an important constituent of the intestine's defense barrier and probiotics enhance their function by introducing new microbes to the gastrointestinal tract; most prebiotic components have been shown to enhance particularly the growth of Bifidobacterium biota (Harish et al., 2006).
Several epidemiological evidences support the protective role of probiotics against cancer. The probioactive cellular substances of lactic acid bacteria may exert several beneficial effects in the gastrointestinal tract, namely anti-tumor effects. This capability is attributed to the inhibition of mutagenic activity, for example with a role in decreasing several enzymes implicated in the generation of carcinogens, mutagens, or tumor-promoting agents and suppression of tumors. The anti- cancer activity may be due to the modulation of cell-mediated immune responses, the activation of the reticulo-endothelial system, the disregulation of cytokine pathways and the inhibition of interleukins and tumor necrosis factors through specific cellular components that seem to induce these...