Gastrointestinal tract: intestinal fatty acid metabolism and implications for health

Short-chain fatty acids (SCFA) are formed from the fermentation of sugars by intestinal bacteria. Acetate is the most abundant SCFA, with lower amounts of propionate and butyrate formed. Propionate and butyrate are also formed from the products of carbohydrate fermentation by other bacteria, for example from lactate and acetate. SCFA play a role in regulating transit of digesta through the intestine, and butyrate formation is thought to be beneficial to health because butyrate decreases the risk of colon cancer. Major butyrate-producing species are among the most abundant present in the colon, including Roseburia and Faecalibacterium spp. Metabolism of longer-chain fatty acids occurs mainly by hydration or hydrogenation of unsaturated fatty acids. Hydroxystearic acids are formed in the intestine, particularly under disease conditions. Metabolism of linoleic acid results in the formation of conjugated linoleic acids (CLA) by several species, including Roseburia hominis and Roseburia inulinovorans. Enhancement of intestinal CLA formation, possibly using probiotics, may be useful in preventing or treating inflammatory bowel disease.

What do we mean when we refer to Bacteroidetes populations in the human gastrointestinal microbiota?

Recent large-scale cloning studies have shown that the ratio of Bacteroidetes to Firmicutes may be important in the obesity-associated gut microbiota, but the species these phyla represent in this ecosystem has not been examined. The Bacteroidetes data from the recent Turnbaugh study were examined to determine those members of the phylum detected in human faecal samples. In addition, FISH analysis was performed on faecal samples from 17 healthy, nonobese donors using probe Bac303, routinely used by gut microbiologists to enumerate BacteroidesPrevotella populations in faecal samples, and another probe (CFB286) whose target range has some overlap with that of Bac303. Sequence analysis of the Turnbaugh data showed that 23/519 clones were chimeras or erroneous sequences; all good sequences were related to species of the order Bacteroidales, but no one species was present in all donors. FISH analysis demonstrated that approximately one-quarter of the healthy, nonobese donors harboured high numbers of Bacteroidales not detected by probe Bac303. It is clear that Bacteroidales populations in human faecal samples have been underestimated in FISH-based studies. New probes and complementary primer sets should be designed to examine numerical and compositional changes in the Bacteroidales during dietary interventions and in studies of the obesity-associated microbiota in humans and animal model systems.

Casein and whey exert different effects on plasma amino acid profiles, gastrointestinal hormone secretion and appetite

Protein, generally agreed to be the most satiating macronutrient, may differ in its effects on appetite depending on the protein source and variation in digestion and absorption. We investigated the effects of two milk protein types, casein and whey, on food intake and subjective ratings of hunger and fullness, and on postprandial metabolite and gastrointestinal hormone responses. Two studies were undertaken. The first study showed that energy intake from a buffet meal ad libitum was significantly less 90 min after a 1700 kJ liquid preload containing 48 g whey, compared with an equivalent casein preload (P<0.05). In the second study, the same whey preload led to a 28 % increase in postprandial plasma amino acid concentrations over 3 h compared with casein (incremental area under the curve (iAUC), P<0.05). Plasma cholecystokinin (CCK) was increased by 60 % (iAUC, P<0.005), glucagon-like peptide (GLP)-1 by 65 % (iAUC, P<0.05) and glucose-dependent insulinotropic polypeptide by 36 % (iAUC, P<0.01) following the whey preload compared with the casein. Gastric emptying was influenced by protein type as evidenced by differing plasma paracetamol profiles with the two preloads. Greater subjective satiety followed the whey test meal (P<0.05). These results implicate post-absorptive increases in plasma amino acids together with both CCK and GLP-1 as potential mediators of the increased satiety response to whey and emphasise the importance of considering the impact of protein type on the appetite response to a mixed meal.

Adverse gastrointestinal effects of arginine and related amino acids

Oral supplements of arginine and citrulline increase local nitric oxide (NO production in the small intestine and this may be harmful under certain circumstances. Gastrointestinal toxicity was therefore reviewed with respect to the intestinal physiology of arginine, citrulline, ornithine, and cystine (which shares the same transporter) and the many clinical trials of supplements of the dibasic amino acids or N-acetylcysteine (NAC. The human intestinal dibasic amino acid transport system has high affinity and low capacity. L-Arginine (but not lysine, ornithine, or D-arginine) induces water and electrolyte secretion that is mediated by NO, which acts as an absorbagogue at low levels and as a secretagogue at high levels. The action of many laxatives is NO mediated and there are reports of diarrhea following oral administration of arginine or ornithine ihine. The clinical data cover a wide span of arginine intakes f rom 3 g/d to > 100 g/d, but the standard of reporting adverse effects (e.g. nausea, vomiting, and diarrhea) was variable. Single doses of 3-6 g rarely provoked side effects and healthy athletes appeared to be more susceptible than diabetic patients to gastrointestinal symptoms at individual doses >9 g. This may relate to an effect of disease on gastrointestinal motility and pharmacokinetics. Most side effects of arginine and NAC occurred at single doses of >9 g in adults >140 mg/kg) often when part of a daily regime of similar to>30 g/d (>174 mmol/d). In the case of arginine, this compares with the laxative threshold of the nonabsorbed disaccharide alcohol, lactitol (74 g or 194 mmol). Adverse effects seemed dependent on the dosage regime and disappeared if divided doses were ingested (unlike lactitol). Large single doses of poorly absorbed amino acids seem to provoke diarrhea. More research is needed to refine dosage strategies that reduce this phenomenon. It is suggested that dipeptide forms of arginine may meet this criterion.

Prebiotics and resistance to gastrointestinal infections

Acute gut disorder is a cause for significant medicinal and economic concern. Certain individual pathogens of the gut, often transmitted in food or water, have the ability to cause severe discomfort. There is a need to manage such conditions more effectively. The route of reducing the risk of intestinal infections through diet remains largely unexplored. Antibiotics are effective at inhibiting pathogens; however, these should not be prescribed in the absence of disease and therefore cannot be used prophylactically. Moreover, their indiscriminate use has reduced effectiveness. Evidence has accumulated to suggest that some of the health-promoting bacteria in the gut (probiotics) can elicit a multiplicity of inhibitory effects against pathogens. Hence, an increase in their numbers should prove effective at repressing pathogen colonisation if/when infectious agents enter the gut. As such, fortification of indigenous bifidobacteria/lactobacilli by using prebiotics should improve protection. There are a number of potential mechanisms for lactic acid bacteria to reduce intestinal infections. Firstly, metabolic endproducts such as acids excreted by these micro-organisms may lower the gut pH to levels below those at which pathogens are able to effectively compete. Also, many lactobacilli and bifidobacteria species are able to excrete natural antibiotics, which can have a broad spectrum of activity. Other mechanisms include an improved immune stimulation, competition for nutrients and blocking of pathogen adhesion sites in the gut. Many intestinal pathogens like type 1 fimbriated Escherichia coli, salmonellae and campylobacters utilise oligosaccharide receptor sites in the gut. Once established, they can then cause gastroenteritis through invasive and/or toxin forming properties. One extrapolation of the prebiotic concept is to simulate such receptor sites in the gut lumen. Hence, the pathogen is 'decoyed' into not binding at the host mucosal interface. The combined effects of prebiotics upon the lactic acid flora and anti-adhesive strategies may lead towards new dietary interventions against food safety agents.

The fate of olive oil polyphenols in the gastrointestinal tract: implications of gastric and colonic microflora-dependent biotransformation

We have conducted a detailed investigation into the absorption, metabolism and microflora-dependent transformation of hydroxytyrosol ( HT), tyrosol (TYR) and their conjugated forms, such as oleuropein (OL). Conjugated forms underwent rapid hydrolysis under gastric conditions, resulting in significant increases in the amount of free HT and TYR entering the small intestine. Both HT and TYR transferred across human Caco-2 cell monolayers and rat segments of jejunum and ileum and were subject to classic phase I/II biotransformation. The major metabolites identified were an O-methylated derivative of HT, glucuronides of HT and TYR and a novel glutathionylated conjugate of HT. In contrast, there was no absorption of OL in either model. However, OL was rapidly degraded by the colonic microflora resulting in the formation of HT. Our study provides additional information regarding the breakdown of complex olive oil polyphenols in the GI tract, in particular the stomach and the large intestine.

Evaluating a realistic agent in an advice-giving task

The aim of this study was to empirically evaluate an embodied conversational agent called GRETA in an effort to answer two main questions: (1) What are the benefits (and costs) of presenting information via an animated agent, with certain characteristics, in a 'persuasion' task, compared to other forms of display? (2) How important is it that emotional expressions are added in a way that is consistent with the content of the message, in animated agents? To address these questions, a positively framed healthy eating message was created which was variously presented via GRETA, a matched human actor, GRETA's voice only (no face) or as text only. Furthermore, versions of GRETA were created which displayed additional emotional facial expressions in a way that was either consistent or inconsistent with the content of the message. Overall, it was found that although GRETA received significantly higher ratings for helpfulness and likability, presenting the message via GRETA led to the poorest memory performance among users. Importantly, however, when GRETA's additional emotional expressions were consistent with the content of the verbal message, the negative effect on memory performance disappeared. Overall, the findings point to the importance of achieving consistency in animated agents. (c) 2005 Elsevier Ltd. All rights reserved.

Multi-agent building control in shared environment

Multi-agent systems have been adopted to build intelligent environment in recent years. It was claimed that energy efficiency and occupants' comfort were the most important factors for evaluating the performance of modem work environment, and multi-agent systems presented a viable solution to handling the complexity of dynamic building environment. While previous research has made significant advance in some aspects, the proposed systems or models were often not applicable in a "shared environment". This paper introduces an ongoing project on multi-agent for building control, which aims to achieve both energy efficiency and occupants' comfort in a shared environment.

Landscape of intelligent cores: An autonomic multi-agent approach for space application

Space applications are challenged by the reliability of parallel computing systems (FPGAs) employed in space crafts due to Single-Event Upsets. The work reported in this paper aims to achieve self-managing systems which are reliable for space applications by applying autonomic computing constructs to parallel computing systems. A novel technique, 'Swarm-Array Computing' inspired by swarm robotics, and built on the foundations of autonomic and parallel computing is proposed as a path to achieve autonomy. The constitution of swarm-array computing comprising for constituents, namely the computing system, the problem / task, the swarm and the landscape is considered. Three approaches that bind these constituents together are proposed. The feasibility of one among the three proposed approaches is validated on the SeSAm multi-agent simulator and landscapes representing the computing space and problem are generated using the MATLAB.