Influence of antibiotics on microbial intestinal transformation of cholesterol to coprostanol in man

Cholesterol-to-Coprostanol Conversion by the Gut Microbiota: What We Know, Suspect, and Ignore

Every day, up to 1 g of cholesterol, composed of the unabsorbed dietary cholesterol, the biliary cholesterol secretion, and cholesterol of cells sloughed from the intestinal epithelium, enters the colon. All cholesterol arriving in the large intestine can be metabolized by the colonic bacteria. Cholesterol is mainly converted into coprostanol, a non-absorbable sterol that is excreted in the feces. Interestingly, cholesterol-to-coprostanol conversion in human populations is variable, with a majority of high converters and a minority of low or inefficient converters. Two major pathways have been proposed, one involving the direct stereospecific reduction of the Δ5 double bond direct while the indirect pathway involves the intermediate formation of 4-cholelesten-3-one and coprostanone. Despite the fact that intestinal cholesterol conversion was discovered more than a century ago, only a few cholesterol-to-coprostanol-converting bacterial strains have been isolated and characterized. Moreover, the responsible genes were mainly unknown until recently. Interestingly, cholesterol-to-coprostanol conversion is highly regulated by the diet. Finally, this gut bacterial metabolism has been linked to health and disease, and recent evidence suggests it could contribute to lower blood cholesterol and cardiovascular risks.

Conceptualizing the Vertebrate Sterolbiome

Vertebrates synthesize a diverse set of steroids and bile acids that undergo bacterial biotransformations. The endocrine literature has principally focused on the biochemistry and molecular biology of host synthesis and tissue-specific metabolism of steroids. Host-associated microbiota possess a coevolved set of steroid and bile acid modifying enzymes that match the majority of host peripheral biotransformations in addition to unique capabilities. The set of host-associated microbial genes encoding enzymes involved in steroid transformations is known as the sterolbiome. This review focuses on the current knowledge of the sterolbiome as well as its importance in medicine and agriculture.

Absence of intestinal microbiota increases ß-cyclodextrin stimulated reverse cholesterol transport

SCOPE

Non-digestible oligosaccharides are used as prebiotics for perceived health benefits, among these modulating lipid metabolism. However, the mechanisms of action are incompletely understood. The present study characterized the impact of dietary ß-cyclodextrin (ßCD, 10%, w/w), a cyclic oligosaccharide, on sterol metabolism and reverse cholesterol transport (RCT) in conventional and also germ-free mice to establish dependency on metabolism by intestinal bacteria.

METHODS AND RESULTS

In conventional ßCD-fed C57BL/6J wild-type mice plasma cholesterol decreased significantly (-40%, p < 0.05), largely within HDL, while fecal neutral sterol excretion increased (3-fold, p < 0.01) and fecal bile acid excretion was unchanged. Hepatic cholesterol levels and biliary cholesterol secretion were unaltered. Changes in cholesterol metabolism translated into increased macrophage-to-feces RCT in ßCD-administered mice (1.5-fold, p < 0.05). In germ-free C57BL/6J mice ßCD similarly lowered plasma cholesterol (-40%, p < 0.05). However, ßCD increased fecal neutral sterol excretion (7.5-fold, p < 0.01), bile acid excretion (2-fold, p < 0.05) and RCT (2.5-fold, p < 0.01) even more substantially in germ-free mice compared with the effect in conventional mice.

CONCLUSION

In summary, this study demonstrates that ßCD lowers plasma cholesterol levels and increases fecal cholesterol excretion from a RCT-relevant pool. Intestinal bacteria decrease the impact of ßCD on RCT. These data suggest that dietary ßCD might have cardiovascular health benefits.

Real-time estimation of small-area populations with human biomarkers in sewage

A new approach is conceptualized for measuring small-area human populations by using biomarkers in sewage. The basis for the concept (SCIM: Sewage Chemical-Information Mining) is supported by a comprehensive examination and synthesis of data published across several disciplines, including medicine, microbiology, clinical chemistry, and environmental science. Accurate measures of human populations are fundamental to numerous disciplines, including economics, marketing, politics, sociology, public health and safety (e.g., disease management; assessment of natural hazards; disaster prevention and response), quality of life, and the environment. Knowing the size, distribution, and flow of a small-area (local) population facilitates understanding the numerous and complex linkages and interactions between humans and the environment. Examples include material-flow (substance-flow) analysis, determining the magnitude of per capita contribution of pollutant loadings to watersheds, or forecasting future impacts of local populations on the environment or a population's demands on resources. While no definitive approach exists for measuring small-area populations, census-taking is a long-established convention. No approach exists, however, for gauging small-area populations in real-time, as none is able to capture population dynamics, which involve transient changes (e.g., daily influx and efflux) and lasting changes (e.g., births, deaths, change in residence). Accurate measurement of small-area populations in real time has never been possible but is essential for facilitating the design of more sustainable communities. Real-time measurement would provide communities the capability of testing what-if scenarios in design and policy decisions. After evaluation of a range of biomarkers (including the nitrogenous waste product creatinine, which has been long used in clinical chemistry as a parameter to normalize the concentrations of other urinary excretion products to account for urine dilution), the biomarker with the most potential for the SCIM concept for real-time measurement of population was determined to be coprostanol - the major sterol produced by microbial reduction of cholesterol in the colon.

Immunology and probiotic impact of the newborn and young children intestinal microflora

Human body has developed a holistic defence system, which mission is either to recognize and destroy the aggressive invaders or to evolve mechanisms permitting to minimize or restore the consequences of harmful actions. The host immune system keeps the capital role to preserve the microbial intestinal balance via the barrier effect. Specifically, pathogenic invaders such as, bacteria, parasites, viruses and other xenobiotic invaders are rejected out of the body via barriers formed by the skin, mucosa and intestinal flora. In case physical barriers are breached, the immune system with its many components comes into action in order to fence infection. The intestine itself is considered as an "active organ" due to its abundant bacterial flora and to its large metabolic activity. The variation among different species or even among different strains within a species reflects the complexity of the genetic polymorphism which regulates the immune system functions. Additionally factors such as, gender, particular habits, smoking, alcohol consumption, diet, religion, age, gender, precedent infections and vaccinations must be involved. Hormonal profile and stress seems to be associated to the integrity microbiota and inducing immune system alterations. Which bacterial species are needed for inducing a proper barrier effect is not known, but it is generally accepted that this barrier function can be strongly supported by providing benefic alimentary supplements called functional foods. In this vein it is stressed the fact that early intestinal colonization with organisms such as Lactobacilli and Bifidobacteria and possibly subsequent protection from many different types of diseases. Moreover, this benefic microflora dominated but Bifidobacteria and Lactobacilli support the concept of their ability to modify the gut microbiota by reducing the risk of cancer following their capacity to decrease β-glucoronidase and carcinogen levels. Because of their beneficial roles in the human gastrointestinal tract, LAB are referred to as "probiotics", and efforts are underway to employ them in modern nutrition habits with so-called functional foods. Members of Lactobacillus and Bifidobacterium genera are normal residents of the microbiota in the human gastrointestinal tract, in which they developed soon after birth. But, whether such probiotic strains derived from the human gut should be commercially employed in the so-called functional foods is a matter of debate between scientists and the industrial world. Within a few hours from birth the newborn develops its normal bacterial flora. Indeed human milk frequently contains low amounts of non-pathogenic bacteria like Streptococcus, Micrococcus, Lactobacillus, Staphylococcus, Corynebacterium and Bifidobacterium. In general, bacteria start to appear in feces within a few hours after birth. Colonization by Bifidobacterium occurs generally within 4 days of life. Claims have been made for positive effects of Bifidobacterium on infant growth and health. The effect of certain bacteria having a benefic action on the intestinal ecosystem is largely discussed during the last years by many authors. Bifidobacterium is reported to be a probiotic bacterium, exercising a beneficial effect on the intestinal flora. An antagonism has been reported between B. bifidum and C. perfringens in the intestine of newborns delivered by cesarean section. The aim of the probiotic approach is to repair the deficiencies in the gut flora and restore the protective effect. However, the possible ways in which the gut microbiota is being influenced by probiotics is yet unknown.

Influence of antibiotics on some intestinal microflora associated characteristics

Intestinal functions related to the presence of microbes in host organisms are normally heavily influenced by administration of antimicrobial drugs. We have investigated the effect of several antibiotics in man and rat, on some MACs (Microflora Associated Characteristics). A MAC is defined as the recording of any anatomical structure, biochemical or physiological function in the host organism which is influenced by microflora. When functional, active microbes are absent as in germfree animals, healthy newborns, or in relation to antimicrobial therapies, a MAC defined as a GAC (Germfree Animal Characteristic). Faecal samples have been collected prior to, during and up to several weeks after the antimicrobial administration in order to investigate different MAC/GAC patterns. Microbial conversion of cholesterol to coprostanol, bilirubin to urobilinogen and 7-alpha-dehydroxylation of cholic acid have been investigated to evaluate hepatic/intestinal co-functions, and degradation of intestinal mucin in order to evaluate the integrity in the intestinal mucosa. Furthermore, degradation of the dietary derived beta-aspartylglycine, the level of faecal trypsin and production of short chain fatty acids were investigated to evaluate dietary/intestinal co-functions. It is concluded that each antimicrobial drug creates its own profile, both with regard to duration and function.

Econutrition and health maintenance — A new concept to prevent GI inflammation, ulceration and sepsis

The nutritional needs of the gastrointestinal mucosa per se has until today been largely neglected. It is a rather novel finding, that the lower part of the digestive tract is most dependent on luminal nutrition for maintaining its integrity, structure and function. Even the most complete parenteral nutrition (PN) regimen cannot, in the absence of adequate enteral nutrition (EN), fully prevent the development of mucosal atrophy in the lower part of the digestive tract, especially the colon. Nor can PN prevent the downregulation of the colon's many important functions. Increased microbial translocation and a predisposition to sepsis are consequences of inadequate luminal nutrition. Such developments can only be prevented by oral feeding and the local 'manufacturing' of essential nutrients in the colon. Probiotic bacteria are also important, especially with respect to the function of the colonic mucosa, which is the focus of this review.

Intestinal microbial conversion of cholesterol to coprostanol in man. Influence of antibiotics

The intestinal microbial conversion of cholesterol to coprostanol has been measured in groups of healthy subjects before, during and after they received the antibiotics ampicillin, bacitracin, clindamycin, co-trimoxazole, doxycycline, erythromycin, metronidazole, nalidixic acid, ofloxacin or vancomycin orally for 6 days. Before they received antibiotics, the subjects demonstrated two distinct patterns of cholesterol conversion. One pattern was characterised by extensive conversion of cholesterol, the other by little or no conversion. Intake of bacitracin, clindamycin, erythromycin, metronidazole and vancomycin significantly reduced the conversion to coprostanol. In the groups receiving ampicillin or doxycycline, marked reductions were found in most of the subjects. No alterations were found in the groups receiving co-trimoxazole, nalidixic acid or ofloxacin. In 6 subjects no conversion of cholesterol to coprostanol was found up to 5 weeks after the end of the antibiotic intake. We conclude that orally given antibiotics may cause alterations in the intestinal conversion of cholesterol, reflecting changes in the anaerobic, Gram-positive component of the gut flora.

Super-efficient starch absorption. A risk factor for colonic neoplasia?

We tested the hypothesis that super-efficient starch absorption, by reducing the supply of carbohydrate to the colon, may be associated with and possibly promote colonic neoplasia. By means of breath hydrogen measurements following a potato meal and comparison with the hydrogen response to lactulose, the amount of starch escaping small bowel absorption was measured in 10 patients who had a colonic adenoma removed endoscopically and in 10 controls. The subjects' consumption of starch and fiber was assessed. Percentage unabsorbed starch was approximately half as much in the patients (5.3%) compared with the controls (10.9%, P less than 0.05). Consumption of starch and dietary fiber, and mouth-to-cecum transit times were not significantly different. Unabsorbed starch was calculated to contribute to 6.0 g/day colonic carbohydrate in the patients and 10.9 g/day in the controls (P less than 0.05). This study confirms that unabsorbed starch provides an important quantity of colonic carbohydrate and suggests that super-efficient starch absorption, by reducing this provision, may promote colonic neoplasia.

Influence of peroral antibiotics upon the biotransformatory activity of the intestinal microflora in healthy subjects

The effects of ampicillin, clindamycin or metronidazole, given perorally for 6 days to eighteen healthy volunteers, upon the following intestinal microflora-associated characteristics (MACs) were evaluated: breakdown of mucin, formation of coprostanol, hydrolysis of bilirubin conjugates, formation of urobilinogen, and of some short chain fatty acids (SCFAs), presence of beta-aspartylglycine and inactivation of trypsin. Clindamycin markedly influenced the expression of all characteristics, but trypsin and beta-aspartylglycine, resulting in a pattern very much alike what has been found in germ-free animals. Ampicillin caused a significant reduction in total amount of SCFAs (P less than 0.05) and urobilinogen (P less than 0.05) present in the faecal samples. Metronidazole caused a significant reduction in the formation of coprostanol and the deconjugation of bilirubin (P less than 0.05). We conclude that orally given antibiotics may cause major alterations in several parameters reflecting the normal biotransformatory activity of the intestinal microflora, probably caused by severe disturbances in the intestinal ecosystem.

Clindamycin-induced alterations in intestinal microflora-associated characteristics in rats

Conventional Sprague-Dawley rats were treated with clindamycin, 40 mg/kg/day and 0.04 mg/kg/day, for 5 days. At a dose of 40 mg/kg/day, microflora-associated characteristics (MACs), such as shape, color, and consistency of feces, proteolytic activity, electrophoretic pattern, and cholesterol and bilirubin metabolism were transformed into values like those found in germfree rats: germfree animal characteristics (GACs). The effect on the proteolytic activity lasted longest. It did not disappear until one or two enemas with cecal contents from intact conventional rats were administered. At a dose of 0.04 mg/kg/day, effects on the proteolytic activity and cholesterol metabolism were seen. With the exception of one rat, the effect on proteolytic activity did not disappear until one or two enemas were given. The results indicate that clindamycin, even in very small daily doses, has a profound and long-lasting influence on many intestinal MACs in rats.