Protective role of probiotics and prebiotics in colon cancer

How host-microbial interactions shape the nutrient environment of the mammalian intestine

Humans and other mammals are colonized by a vast, complex, and dynamic consortium of microorganisms. One evolutionary driving force for maintaining this metabolically active microbial society is to salvage energy from nutrients, particularly carbohydrates, that are otherwise nondigestible by the host. Much of our understanding of the molecular mechanisms by which members of the intestinal microbiota degrade complex polysaccharides comes from studies of Bacteroides thetaiotaomicron, a prominent and genetically manipulatable component of the normal human and mouse gut. Colonization of germ-free mice with B. thetaiotaomicron has shown how this anaerobe modifies many aspects of intestinal cellular differentiation/gene expression to benefit both host and microbe. These and other studies underscore the importance of understanding precisely how nutrient metabolism serves to establish and sustain symbiotic relationships between mammals and their bacterial partners.

Probiotics: on-going research on atopic individuals

The challenge for the modern health care system is to fight against the increasing prevalence of atopic disease. The introduction of scientifically composed probiotic functional foods for prophylactic or therapeutic purposes could be one solution. Probiotics are live microbial food supplements or components of bacteria which have beneficial effects on human health. Specific strains have been demonstrated to exert powerful anti-pathogenic, anti-inflammatory and anti-allergic effects. The hygiene hypothesis suggests that atopic disease may arise from a lack of counterbalancing microbial exposure at an early age. The initial compositional development of the gut microflora is considered a key determinant of the development of both the immune responder phenotype and normal gut barrier functions. The regulatory role of probiotics in human allergic disease was first emphasised in the demonstration of a suppressive effect on lymphocyte proliferation and interleukin-4 generation in vitro. Subsequently, a significant improvement in the clinical course of atopic eczema was reported in infants given a probiotic-supplemented diet. The potential of probiotics to reduce the risk of atopic disease has recently been demonstrated in a double-blind, placebo-controlled study: probiotics administered pre- and postnatally for 6 months to at-risk subjects reduced the prevalence of atopic eczema to half of that observed in infants receiving placebo. Ongoing research is directed towards the development of novel techniques to characterise the gut microflora. Future research will clarify the mechanisms to control specific physiological processes in the evolution of atopic disease in at-risk populations or in the management of allergic diseases.

Gastrointestinal tract and the elderly: functional foods, gut microflora and healthy ageing

Advances in science and medicine as well as improved living standards have led to a steady increase in life expectancy. Yet ageing is associated with increased susceptibility to degenerative or infectious diseases, which may be exacerbated by a poor nutritional status. The intestinal microflora will mediate crucial events towards the protection or degradation of health. It is hence essential and timely that strategies of preventive nutrition aimed at maintaining or improving the quality of life of the ageing population be developed. "CROWNALIFE" is a newly funded EuropeanUnion project, so called because of its emphasis on the preservation of the period of independence of the elderly, recognised as the "crown of life". The project aims at assessing age-related alterations and exploring strategies to restore and maintain a balanced healthy intestinal environment. Current knowledge on the composition and function of the human intestinal microflora is still improving with the use of better methodologies and yet their evolution with ageing has not been investigated in detail. There have been a few reports that putatively protective lactic acid bacteria, in general, and bifidobacteria, in particular, seem less represented in the elderly faecal flora. We have also observed an increase in species diversity of the dominant faecal microflora with ageing. This certainly warrants confirmation and is being addressed by the investigation of age-related changes in the structure and function of the intestinal flora of the elderly in countries across Europe. Ensuing results will constitute a baseline for functional-food based strategies aimed at providing health benefits for the elderly.

Review article: lactose--a potential prebiotic

Lactose maldigestion, which affects a large majority of the world's population, has been mostly linked with uncomfortable symptoms. In addition, dairy consumption is variably blamed or recommended for a number of ill effects. There is, however, emerging evidence that certain lactic acid-producing bacteria, which selectively consume prebiotics, may be beneficial against some lower intestinal diseases. Lactose maldigestion and lactose should perhaps be re-evaluated as a potential provider of such a prebiotic. This historical and observational review discusses lactose and argues the opinion that it has prebiotic potential. Moreover, in maldigesters, natural ingestion or lack thereof may be relevant in the pathogenesis of diseases such as colorectal cancer and inflammatory bowel diseases.

Probiotics and intestinal health effects: a clinical perspective

Probiotics are viable non-pathogenic micro-organisms which, when ingested, exert a positive influence on host health or physiology. We have critically analysed the evidence for the efficacy of specific probiotic strains in human gastrointestinal diseases. The best evidence can be obtained with randomised controlled trials which avoid bias. Good evidence has been obtained with several strains in the prevention or treatment of antibiotic-associated disorders, in the treatment (and to a lesser extent prevention) of gastroenteritis and acute diarrhoea and in the alleviation of lactose intolerance. We also analysed the recent randomised controlled trials performed in patients with Clostridium difficile or Helicobacter pylori, inflammatory bowel disease, irritable bowel syndrome, non-ulcer dyspepsia and colon cancer.

Probiotics in the third millennium

Probiotics are "living microorganisms which upon ingestion in certain numbers exert health benefits beyond inherent general nutrition". Since 1987, when the first publication on the properties of the Lactobacillus GG was done, overall, there have been over 200 publications in peer-reviewed scientific journals. This paper will report the status and the prospectus of probiotics research at the beginning of the Third Millennium. Probiotics have proven benefits in treatment and prevention of rotavirus diarrhoea in children and reduction of antibiotic-associated intestinal side-effects. Interesting results have recently been published regarding food allergies and atopic eczema in children. Prevention of vaginitis and of travellers' diarrhoea have also been reported. Promising results are being reported in patients with inflammatory bowel disease, cystic fibrosis, dental caries and irritable bowel syndrome. It has also been suggested that probiotics could enhance oral vaccine administration, and that they may help treatment against Helicobacter pylori infection, but further studies are needed. Future areas of research regard probiotics' role in the process of carcinogenesis, given their influence on the gut microflora, and as immune modulators in autoimmune disorders. The possibility of introducing appropriate genes to the probiotics to make them produce various compounds is also under investigation. However, there is still confusion in the minds of the authorities over whether a probiotic is a drug, a food, or a dietary supplement. The challenge is to continue research to define the appropriate uses of probiotics and discover new applications which will bring benefit to humankind.

Meta-analysis: the effect of probiotic administration on antibiotic-associated diarrhoea

BACKGROUND

Antibiotic-associated diarrhoea can be attributed in part to imbalances in intestinal microflora. Therefore, probiotic preparations are used to prevent this diarrhoea. However, although several trials have been conducted, no conclusive evidence has been found of the efficacy of different preparations, e.g. Lactobacillus spp. and Saccharomyces spp.

AIM

To conduct a meta-analysis of the data in the literature on the efficacy of probiotics in the prevention of antibiotic-associated diarrhoea.

METHODS

A literature search was performed of electronic databases, Abstract Books and single paper references. Data were also obtained from the authors. Only placebo-controlled studies were included in the search. The Mantel-Haenszel test was used to estimate the relative risk for single studies and an overall combined relative risk, each study being submitted to the Mantel-Haenszel test for homogeneity.

RESULTS

Twenty-two studies matched the inclusion criteria. Only seven studies (881 patients) were homogeneous. The combined relative risk was 0.3966 (95% confidence interval, 0.27-0.57).

CONCLUSIONS

The results suggest a strong benefit of probiotic administration on antibiotic-associated diarrhoea, but further data are needed. The evidence for beneficial effects is still not definitive. Published studies are flawed by the lack of a placebo design and by peculiar population features.

Probiotics and Functional Foods in Gastrointestinal Disorders

Probiotics are live microbial food supplements that benefit the host animal by improving intestinal microbial balance. When they are fed in yogurts, they can fall into the category of functional foods. Functional foods include these probiotics, prebiotics, and, to a certain extent, dietary fiber. Prebiotics are nondigestible food ingredients or supplements that alter the intestinal flora and stimulate the growth of healthy bacteria. Dietary fibers are part of plant foods that are nonstarch polysaccharides and are poorly digested or not digested by human enzymes. The physiologic process in which probiotics and functional foods affect the intestinal flora is through the balance of the intestinal microecology. This review looks at the four major components of intestinal microecology and describes the probiotics in use today and their clinical relevance. Although probiotics hold great promise and appear to be useful in some settings, more clinical study is needed to firmly establish the relevance of probiotic therapy.

Probiotics in clinical conditions

Probiotics are nonpathogenic microorganisms which, when ingested, exert a positive influence on the health or physiology of the host. Their mechanisms of action and effects are now studied using the same pharmacological approach as for drugs. This article summarizes and comments on evidence for the positive effects of probiotics in various clinical situations. Substantial evidence can be achieved when randomized controlled trials or meta-analyses show positive results. The clinical situations studied include prevention or treatment of antibiotic-associated disorders, gastroenteritis, and diarrhea, lactose intolerance, intestinal infections and colonization by pathogenic bacteria (including Helicobacter pylori and Clostridium difficile), traveler's diarrhea, irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), colonic cancer, urogenital infections and tumors, allergy (especially atopic eczema), vaccination, and cholesterol lowering. Current probiotics have an excellent safety record--another topic discussed in this article.

Two-dimensional electrophoresis study of Lactobacillus delbrueckii subsp. bulgaricus thermotolerance

The response of Lactobacillus delbrueckii subsp. bulgaricus cells to heat stress was studied by use of a chemically defined medium. Two-dimensional electrophoresis (2-DE) analysis was used to correlate the kinetics of heat shock protein (HSP) induction with cell recovery from heat injury. We demonstrated that enhanced viability, observed after 10 min at 65 degrees C, resulted from the overexpression of HSP and from mechanisms not linked to protein synthesis. In order to analyze the thermoadaptation mechanisms involved, thermoresistant variants were selected. These variants showed enhanced constitutive tolerance toward heat shock. However, contrary to the wild-type strain, these variants were poorly protected after osmotic or heat pretreatments. This result suggests that above a certain threshold, cells reach a maximum level of protection that cannot be easily exceeded. A comparison of protein patterns showed that the variants were able to induce more rapidly their adaptive mechanisms than the original strain. In particular, the variants were able to express constitutively more HSP, leading to the higher level of thermoprotection observed. This is the first report of the study by 2-DE of the heat stress response in L. delbrueckii subsp. bulgaricus.

Probiotics: potential pharmaceutical applications

Realisation of the importance of human gut microbiota in health restoration and maintenance has kindled an interest in probiotics. Probiotics are defined as the microbial food supplements, which beneficially affect the host by improving its intestinal microbial balance. Probiotics are the health enhancing functional food ingredients used therapeutically to prevent diarrhea, improve lactose tolerance and modulate immunity. They may also have potential to prevent cancer and lower serum cholesterol levels. Lactobacillus, Bifidobacterium and several other microbial species are perceived to exert such effects by changing the composition of the gut microbiota. However, it is important that exogenously administered bacteria reach and establish themselves in the large intestine in an intact form. The use of non-digestible oligosaccharides ('prebiotics') can fortify intestinal microflora and stimulate their growth. The present review encompasses information regarding the probiotics and their proposed uses. It addresses the concepts of prebiotics and synbiotics, the application of genetic engineering to produce newer probiotics. Finally, the list of commercially available products are reviewed with discussion of questions regarding the reliability, utility and the safety of these products.

Probiotics and functional foods in gastrointestinal disorders

Probiotics are live microbial food supplements that benefit the host animal by improving intestinal microbial balance. When they are fed in yogurts, they can fall into the category of functional foods. Functional foods include these probiotics, prebiotics, and, to a certain extent, dietary fiber. Prebiotics are nondigestible food ingredients or supplements that alter the intestinal flora and stimulate the growth of healthy bacteria. Dietary fibers are part of plant foods that are nonstarch polysaccharides and are poorly digested or not digested by human enzymes. The physiologic process in which probiotics and functional foods affect the intestinal flora is through the balance of the intestinal microecology. This review looks at the four major components of intestinal microecology and describes the probiotics in use today and their clinical relevance. Although probiotics hold great promise and appear to be useful in some settings, more clinical study is needed to firmly establish the relevance of probiotic therapy.

Prebiotics: preferential substrates for specific germs?

A prebiotic is "a non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or the activity of one or a limited number of bacteria in the colon." The premise is based on the hypothesis that the large gut in humans contains bacteria that are beneficial or detrimental to health. Although this generalization probably gives too simplistic a view of gut microbiology, it is a feasible working concept. Currently, food components that seem to exert the best prebiotic effects are inulin-type fructans. In pure culture, most species of bifidobacteria are adapted to the utilization of these nondigestible oligosaccharides but many other bacteria are also capable of metabolizing them. Clearly, these studies of pure bacteria are of limited use unless their results are supported by the results of studies using mixed cultures. Indeed, as many components of the gut microbiota as possible should be measured to indicate a true prebiotic effect. Simple stimulation of bifidobacteria is insufficient to demonstrate an effect; the effects on other gut microorganisms in vivo with human volunteers is necessary. Adjustment of the composition and activities of the colonic microflora so that health-promoting activities are optimized remains key in functional food development. New methods are being applied extensively to human gut microbiology and promise the degree of reliability required to detect subtle changes in colonic microflora composition and to correlate such changes with health benefits. This is a review of the present state of knowledge concerning prebiotics, with emphasis on the criteria used for classification, mechanisms of selective growth stimulation, and physiologic effects.

Protection from gastrointestinal diseases with the use of probiotics

Probiotics are nonpathogenic microorganisms that, when ingested, exert a positive influence on the health or physiology of the host. They can influence intestinal physiology either directly or indirectly through modulation of the endogenous ecosystem or immune system. The results that have been shown with a sufficient level of proof to enable probiotics to be used as treatments for gastrointestinal disturbances are 1) the good tolerance of yogurt compared with milk in subjects with primary or secondary lactose maldigestion, 2) the use of Saccharomyces boulardii and Enterococcus faecium SF 68 to prevent or shorten the duration of antibiotic-associated diarrhea, 3) the use of S. boulardii to prevent further recurrence of Clostridium difficile-associated diarrhea, and 4) the use of fermented milks containing Lactobacillus rhamnosus GG to shorten the duration of diarrhea in infants with rotavirus enteritis (and probably also in gastroenteritis of other causes). Effects that are otherwise suggested for diverse probiotics include alleviation of diarrhea of miscellaneous causes; prophylaxis of gastrointestinal infections, which includes traveler's diarrhea; and immunomodulation. Trials of gastrointestinal diseases that involve the ecosystem are currently being performed, eg, Helicobacter pylori infections, inflammatory bowel disease, and colon cancer.