Probiotics are live microorganisms that, when ingested in adequate amounts, provide health benefits to the host. The strains most frequently used as probiotics include lactic acid bacteria and bifidobacteria, which are isolated from traditional fermented products and the gut, faeces and breast milk of human subjects. The identification of microorganisms is the first step in the selection of potential probiotics. The present techniques, including genetic fingerprinting, gene sequencing, oligonucleotide probes and specific primer selection, discriminate closely related bacteria with varying degrees of success. Additional molecular methods, such as denaturing gradient gel electrophoresis/temperature gradient gel electrophoresis and fluorescence in situ hybridisation, are employed to identify and characterise probiotics. The ability to examine fully sequenced genomes has accelerated the application of genetic approaches to elucidate the functional roles of probiotics. One of the best-demonstrated clinical benefits of probiotics is the prevention and treatment of acute and antibioticassociated diarrhoea; however, there is mounting evidence for a potential role for probiotics in the treatment of allergies and intestinal, liver and metabolic diseases. These positive effects are generally attributed to the ability of probiotics to regulate intestinal permeability, normalise host intestinal microbiota, improve gut immune barrier function and equilibrate the balance between pro-inflammatory and antiinflammatory cytokines. However, the positive effects of probiotics are not always substantiated by findings from properly conducted clinical trials. Notably, even when the results from randomised, placebo-controlled trials support the beneficial effects of a particular probiotic for a specific indication, the benefits are generally not translatable to other probiotic formulations.

The microorganisms that live symbiotically in human beings are increasingly recognized as important players in health and disease. The largest collection of these microorganisms is found in the gastrointestinal tract. Microbial composition reflects both genetic and lifestyle variables of the host. This microbiota is in a dynamic balance with the host, exerting local and distant effects. Microbial perturbation (dysbiosis) could contribute to the risk of developing health problems. Various bacterial genes capable of producing estrogen-metabolizing enzymes have been identified. Accordingly, gut microbiota is capable of modulating estrogen serum levels. Conversely, estrogen-like compounds may promote the proliferation of certain species of bacteria. Therefore, a crosstalk between microbiota and both endogenous hormones and estrogen-like compounds might synergize to provide protection from disease but also to increase the risk of developing hormone-related diseases. Recent research suggests that the microbiota of women with breast cancer differs from that of healthy women, indicating that certain bacteria may be associated with cancer development and with different responses to therapy. In this review, we discuss recent knowledge about the microbiome and breast cancer, identifying specific characteristics of the human microbiome that may serve to develop novel approaches for risk assessment, prevention and treatment for this disease.

Oxidative stress plays a key role in liver fibrosis. Both inflammatory cells and activated Kupffer cells produce H2O2, an oxidant involved in the activation of hepatic stellate cells (HSC). Increased production of reactive oxygen intermediates (ROIs) in fibrotic livers is associated in part with the up-regulation of transforming growth factor beta (TGF-beta), and this cytokine enhances collagen production by cultured HSC. However, the possible link between oxidative stress and the molecular mechanisms by which TGF-beta induces collagen gene expression in HSC remains to be elucidated. To address this question, we investigated whether H2O2 is a mediator of TGF-beta-elicited alpha1(I) collagen gene (col1a1) up-regulation. We demonstrated that TGF-beta induces the accumulation of H2O2, and that this oxidant is, in turn, directly involved in up-regulating the expression of the col1a1 gene. While the addition of H2O2 to HSC induced the expression of alpha1(I) procollagen mRNA, catalase, an H2O2 enzyme scavenger, abrogated TGF-beta-mediated col1a1 gene up-regulation. We transfected HSC with chimeric plasmids driven by different segments of the mouse col1a1 promoter and mapped a cis-acting element (-370 to -344) essential for TGF-beta responsiveness. We further showed that TGF-beta induced the activation and binding of a C/EBPbeta-containing transcriptional complex to this sequence, an effect that was also mimicked by the addition of H2O2. Taken together, these data demonstrate a direct connection between TGF-beta-mediated accumulation of H2O2 and the up-regulation of col1a1 gene in HSC.