Microcirculatory and trophic effects of short chain fatty acids in the human rectum after Hartmann's procedure

Butyrate's role in human health and the current progress towards its clinical application to treat gastrointestinal disease

Butyrate is a key energy source for colonocytes and is produced by the gut microbiota through fermentation of dietary fiber. Butyrate is a histone deacetylase inhibitor and also signals through three G-protein coupled receptors. It is clear that butyrate has an important role in gastrointestinal health and that butyrate levels can impact both host and microbial functions that are intimately coupled with each other. Maintaining optimal butyrate levels improves gastrointestinal health in animal models by supporting colonocyte function, decreasing inflammation, maintaining the gut barrier, and promoting a healthy microbiome. Butyrate has also shown protective actions in the context of intestinal diseases such as inflammatory bowel disease, graft-versus-host disease of the gastrointestinal tract, and colon cancer, whereas lower levels of butyrate and/or the microbes which are responsible for producing this metabolite are associated with disease and poorer health outcomes. However, clinical efforts to increase butyrate levels in humans and reverse these negative outcomes have generated mixed results. This article discusses our current understanding of the molecular mechanisms of butyrate action with a focus on the gastrointestinal system, the links between host and microbial factors, and the efforts that are currently underway to apply the knowledge gained from the bench to bedside.

Gut homeostasis, injury, and healing: New therapeutic targets

The integrity of the gastrointestinal mucosa plays a crucial role in gut homeostasis, which depends upon the balance between mucosal injury by destructive factors and healing via protective factors. The persistence of noxious agents such as acid, pepsin, nonsteroidal anti-inflammatory drugs, or Helicobacter pylori breaks down the mucosal barrier and injury occurs. Depending upon the size and site of the wound, it is healed by complex and overlapping processes involving membrane resealing, cell spreading, purse-string contraction, restitution, differentiation, angiogenesis, and vasculogenesis, each modulated by extracellular regulators. Unfortunately, the gut does not always heal, leading to such pathology as peptic ulcers or inflammatory bowel disease. Currently available therapeutics such as proton pump inhibitors, histamine-2 receptor antagonists, sucralfate, 5-aminosalicylate, antibiotics, corticosteroids, and immunosuppressants all attempt to minimize or reduce injury to the gastrointestinal tract. More recent studies have focused on improving mucosal defense or directly promoting mucosal repair. Many investigations have sought to enhance mucosal defense by stimulating mucus secretion, mucosal blood flow, or tight junction function. Conversely, new attempts to directly promote mucosal repair target proteins that modulate cytoskeleton dynamics such as tubulin, talin, Ehm², filamin-a, gelsolin, and flightless I or that proteins regulate focal adhesions dynamics such as focal adhesion kinase. This article summarizes the pathobiology of gastrointestinal mucosal healing and reviews potential new therapeutic targets.

Role of short-chain fatty acids in colonic inflammation, carcinogenesis, and mucosal protection and healing

Short-chain fatty acids (SCFAs), mainly acetate, propionate, and butyrate, produced by microbial fermentation of undigested food substances are believed to play a beneficial role in human gut health. Short-chain fatty acids influence colonic health through various mechanisms. In vitro and ex vivo studies show that SCFAs have anti-inflammatory and anticarcinogenic effects, play an important role in maintaining metabolic homeostasis in colonocytes, and protect colonocytes from external harm. Animal studies have found substantial positive effects of SCFAs or dietary fiber on colonic disease, but convincing evidence in humans is lacking. Most human intervention trials have been conducted in the context of inflammatory bowel disease. Only a limited number of those trials are of high quality, showing little or no favorable effect of SCFA treatment over placebo. Opportunities for future research include exploring the use of combination therapies with anti-inflammatory drugs, prebiotics, or probiotics; the use of prodrugs in the setting of carcinogenesis; or the direct application of SCFAs to improve mucosal healing after colonic surgery.

Tissue metabolism and host-microbial interactions in the intestinal mucosa

In recent years, studies in the gastrointestinal (GI) mucosa have taught us a number of important lessons related to tissue oxygenation and metabolism in health and disease. The highly vascularized mucosa lies immediately adjacent to an anaerobic lumen containing trillions of metabolically active microbes (i.e. the microbiome) that results in one of the more austere tissue microenvironments in the body. These studies have also implicated a prominent role for oxygen metabolism and hypoxia in inflammation, so called "inflammatory hypoxia", that results from the activation of multiple oxygen consuming enzymes. Inflammation-associated shifts in the composition of the microbiome and microbial-derived metabolites have revealed a prominent role for the transcription factor hypoxia-inducible factor (HIF) in the regulation of key target genes that promote inflammatory resolution. Analyses of these pathways have provided a multitude of opportunities for understanding basic mechanisms of both homeostasis and disease and have defined new targets for intervention. Here, we review recent advances in our understanding of metabolic influences on host-microbe interactions in the GI mucosa.

A Critical Look at Prebiotics Within the Dietary Fiber Concept

This article reviews the current knowledge of the health effects of dietary fiber and prebiotics and establishes the position of prebiotics within the broader context of dietary fiber. Although the positive health effects of specific fibers on defecation, reduction of postprandial glycemic response, and maintenance of normal blood cholesterol levels are generally accepted, other presumed health benefits of dietary fibers are still debated. There is evidence that specific dietary fibers improve the integrity of the epithelial layer of the intestines, increase the resistance against pathogenic colonization, reduce the risk of developing colorectal cancer, increase mineral absorption, and have a positive impact on the immune system, but these effects are neither generally acknowledged nor completely understood. Many of the latter effects are thought to be particularly elicited by prebiotics. Although the prebiotic concept evolved significantly during the past two decades, the line between prebiotics and nonprebiotic dietary fiber remains vague. Nevertheless, scientific evidence demonstrating the health-promoting potential of prebiotics continues to accumulate and suggests that prebiotic fibers have their rightful place in a healthy diet.

Physiologic hypoxia and oxygen homeostasis in the healthy intestine. A Review in the Theme: Cellular Responses to Hypoxia

In recent years, the intestinal mucosa has proven to be an intriguing organ to study tissue oxygenation. The highly vascularized lamina propria juxtaposed to an anaerobic lumen containing trillions of metabolically active microbes results in one of the most austere tissue microenvironments in the body. Studies to date have determined that a healthy mucosa contains a steep oxygen gradient along the length of the intestine and from the lumen to the serosa. Advances in technology have allowed multiple independent measures and indicate that, in the healthy mucosa of the small and large intestine, the lumen-apposed epithelia experience Po2 conditions of <10 mmHg, so-called physiologic hypoxia. This unique physiology results from a combination of factors, including countercurrent exchange blood flow, fluctuating oxygen demands, epithelial metabolism, and oxygen diffusion into the lumen. Such conditions result in the activation of a number of hypoxia-related signaling processes, including stabilization of the transcription factor hypoxia-inducible factor. Here, we review the principles of mucosal oxygen delivery, metabolism, and end-point functional responses that result from this unique oxygenation profile.

Fasting serum concentration of short-chain fatty acids in subjects with microscopic colitis and celiac disease: no difference compared with controls, but between genders

BACKGROUND

Short-chain fatty acids (SCFAs), particularly propionic and butyric acids, have been shown to have many positive health effects. The amount and type of SCFAs formed from dietary fibre by the colonic microbiota depends on the substrate available and is reflected in blood. The total intake and type of dietary fibre in people with gastrointestinal diseases differs considerably from healthy subjects.

OBJECTIVE

To compare fasting SCFA concentrations in subjects with microscopic colitis (MC), celiac disease and controls without these diseases. SCFAs were also analysed over 6.5 h in young healthy subjects, who had eaten a fibre-rich breakfast, to identify a possible peak concentration of SCFAs after a meal.

METHODS

SCFAs in serum were pre-concentrated using hollow fibre-supported liquid membrane extraction and gas chromatography.

RESULTS

The MC group had a higher concentration of valeric acid than the control group (p < 0.01). No significant differences in other SCFA concentrations were seen between groups, but the control group tended to have higher concentration of acetic acid (p = 0.1). Furthermore, males had higher concentrations of SCFAs (with the exception of valeric acid) than females (p < 0.05), which were independent of groups. The peaks for acetic, propionic and butyric acids came approximately 5 h, 6.5 h and 2-3 h, respectively, after breakfast.

CONCLUSION

The fasting concentrations of SCFAs were quite similar, although the fibre intake had probably been quite different for a long time. The results might have been different if SCFAs had been recorded over a longer period.

Dietary roles of non-starch polysaccharides in human nutrition: a review

Nonstarch polysaccharides (NSPs) occur naturally in many foods. The physiochemical and biological properties of these compounds correspond to dietary fiber. Nonstarch polysaccharides show various physiological effects in the small and large intestine and therefore have important health implications for humans. The remarkable properties of dietary NSPs are water dispersibility, viscosity effect, bulk, and fermentibility into short chain fatty acids (SCFAs). These features may lead to diminished risk of serious diet related diseases which are major problems in Western countries and are emerging in developing countries with greater affluence. These conditions include coronary heart disease, colo-rectal cancer, inflammatory bowel disease, breast cancer, tumor formation, mineral related abnormalities, and disordered laxation. Insoluble NSPs (cellulose and hemicellulose) are effective laxatives whereas soluble NSPs (especially mixed-link β-glucans) lower plasma cholesterol levels and help to normalize blood glucose and insulin levels, making these kinds of polysaccharides a part of dietary plans to treat cardiovascular diseases and Type 2 diabetes. Moreover, a major proportion of dietary NSPs escapes the small intestine nearly intact, and is fermented into SCFAs by commensal microflora present in the colon and cecum and promotes normal laxation. Short chain fatty acids have a number of health promoting effects and are particularly effective in promoting large bowel function. Certain NSPs through their fermented products may promote the growth of specific beneficial colonic bacteria which offer a prebiotic effect. Various modes of action of NSPs as therapeutic agent have been proposed in the present review. In addition, NSPs based films and coatings for packaging and wrapping are of commercial interest because they are compatible with several types of food products. However, much of the physiological and nutritional impact of NSPs and the mechanism involved is not fully understood and even the recommendation on the dose of different dietary NSPs intake among different age groups needs to be studied.

Butyrate esterified to starch is released in the human gastrointestinal tract

BACKGROUND

Short-chain fatty acids (SCFAs) maintain human colonic function and may help prevent colonic disease. A study with ileostomists showed that starches acylated with specific SCFAs largely survive passage through the small intestine, but the percentage released in the colon has not been established.

OBJECTIVE

The objective was to determine the percentage of ingested esterified butyrate released in the human gastrointestinal tract.

DESIGN

The study was a randomized, crossover, controlled trial consisting of baseline and four 2-wk periods during which 16 volunteers consumed diets low in resistant starch plus 20 and 40 g cooked high-amylose maize starch (HAMS: HAMS20 or HAMS40) or butyrylated HAMS (HAMSB20 or HAMSB40) daily. HAMSB20 contained 31.8 mmol esterified butyrate. Complete 48-h fecal collections were made on days 2-3 and 12-13 of each period.

RESULTS

Free fecal butyrate concentrations were higher after HAMSB40 than after HAMSB20 (P < 0.005) and HAMS (P < 0.0001) and higher than baseline data (P < 0.0001). Fecal esterified butyrate concentrations were highest in the HAMSB40 (days 12-13; P < 0.0001) group, and concentrations in the HAMSB40 (days 2-3) and HAMSB20 groups were higher than those in the HAMS groups and those at baseline (P < 0.0001). Ingestion of HAMSB20 and HAMSB40 resulted in the release of 26.8 ± 1.0 and 50.2 ± 2.4 mmol butyrate/d (days 12-13) (84.2 ± 3.0% and 79.0 ± 3.1% of total ingested esterified butyrate), respectively, in the gastrointestinal tract. By calculation, ∼57.2% of ingested esterified butyrate was released in the colon. Microbial analysis showed that this release was probably facilitated mainly by Parabacteroides distasonis, which increased in abundance with HAMSB40 (days 12-13) (P < 0.001).

CONCLUSIONS

This study shows that cooked butyrylated starch delivers esterified butyrate to the human colon effectively and has the potential to improve human bowel health. This trial is registered in the Australian Clinical Trials Registry as ACTRN012606000398505.

Changes in calcium status in aged rats fed Lactobacillus GG and Bifidobacterium lactis and oligofructose-enriched inulin

In this study we hypothesized that an increase in numbers of beneficial bacteria in the large intestine can affect calcium (Ca) status in the elderly. Adult and aged rats were fed a diet with or without synbiotics for 21 days. Synbiotics increased the numbers of lactobacilli and bifidobacteria in large intestine in both adult and aged rats. The plasma Ca concentration was significantly increased while osteocalcin concentration was significantly decreased only in aged rats fed synbiotics.

Suppressive effect of short-chain fatty acids on production of proinflammatory mediators by neutrophils

Short chain fatty acids (SCFAs) are fermentation products of anaerobic bacteria. More than just being an important energy source for intestinal epithelial cells, these compounds are modulators of leukocyte function and potential targets for the development of new drugs. The aim of this study was to evaluate the effects of SCFAs (acetate, propionate and butyrate) on production of nitric oxide (NO) and proinflammatory cytokines [tumor necrosis factor α (TNF-α) and cytokine-induced neutrophil chemoattractant-2 (CINC-2αβ)] by rat neutrophils. The involvement of nuclear factor κB (NF-κB) and histone deacetylase (HDAC) was examined. The effect of butyrate was also investigated in vivo after oral administration of tributyrin (a pro-drug of butyrate). Propionate and butyrate diminished TNF-α, CINC-2αβ and NO production by LPS-stimulated neutrophils. We also observed that these fatty acids inhibit HDAC activity and NF-κB activation, which might be involved in the attenuation of the LPS response. Products of cyclooxygenase and 5-lipoxygenase are not involved in the effects of SCFAs as indicated by the results obtained with the inhibitors of these enzymes. The recruitment of neutrophils to the peritonium after intraperitoneal administration of a glycogen solution (1%) and the ex vivo production of cytokines and NO by neutrophils were attenuated in rats that previously received tributyrin. These results argue that this triglyceride may be effective in the treatment of inflammatory conditions.

Evaluation by computerized morphometry of histopathological alterations of the colon wall in segments with and without intestinal transit in rats

PURPOSE

To evaluate histopathological alterations of the colon wall in segments with and without intestinal transit, by computer-assisted imaging, and to correlate these with the length of time diversion.

METHODS

Thirty male Wistar rats were subjected to intestinal transit diversion by a proximal colostomy and distal mucosa fistula. The animals were divided into three experimental groups according to how long after the initial surgical procedure they were sacrificed: six, twelve and eighteen weeks. Colon segments with and without transit were subjected to histopathological study. The variables colon crypt length, mucosal ulceration, muscle layer thickness of the muscularis mucosa, submucosa and muscularis propria, vascular congestion, number of caliciform cells, inflammatory grade and degree of inflammation, comparing the two colon segments in the different experimental groups were studied. Intestinal crypt length, muscle layer thickness of the mucosa, submucosa and muscularis propria and caliciform cells were measured by computer-assisted imaging method. Mean equality, variance analysis and correlation tests were used in the statistical analysis, and the significance level was set at 5%.

RESULTS

Comparison between segments with and without transit showed that the latter presented reduced length of colon crypts and increased muscle layer thickness of the muscularis mucosa, submucosa and muscularis propria. There were greater quantities of ulceration of the mucosal and greater degree of inflammation with increasing time without transit. Mucosal ulceration, submucosal vascular congestion, increased thickness of the submucosal and muscularis propria layers, presence of caliciform cells, inflammatory infiltrate and inflammatory grade correlated significantly with the length of time without transit.

CONCLUSIONS

Histological alterations occurred in all layers of the colon wall, in the segments without intestinal transit. Ulcerations in the intestinal mucosa, increased number of caliciform cells, greater vascular congestion of the submucosal layer and inflammatory reaction were related to increasing length of time without transit.

How to treat diversion colitis?--Current state of medical knowledge, own research and experience

The aim of this study was to present current knowledge about a nospecific inflammation of mucosa within segments of colon excluded from normal bowel passage called as a "diversion colitis" (DC) and to try to determine the role of factors which might modify the clinical course of DC. We also unswered the question; how to treat DC: conservatively or surgically? Our own experience with DC concerns 145 patents (which is most numerous and well exactly examined series presented in literature). In the group of patients studied, clinical signs of DC were present in over 70% of patients (early signs were low abdominal pain and tenesmus, while anal oozing appeared later). Predominating endoscopic features of DC in the group of patients studied were: a. blurring of vascular pattern (in app. 90% of patients); b. contact bleeding (in app. 80% of patients); c. mucosal oedema (in app. 60% of patients). Results of own observations and literature data indicate, that morphologic alterations in the segment of bowel excluded from normal passage are probably vasogenic consisting in atrophy and inflammation of the allergic type (this would confirm the theory about vascular etiology of DC). In our material, we have not noticed any trend toward hyperproliferation or dysplasia in the excluded segment of colon, supporting the thesis that these disturbances are largely reversible. Clinical pathology of DC does not depend on age, sex, cause and type of surgical procedure performed, mode of surgery or concomitant diseases. Authors suggested an alternative algorithm of diagnostic work-up in patients suspected of DC, and proposed that patients with a segment of bowel excluded from normal passage be subdivided into three groups: 1. Patients with no clinical, endoscopic nor morphologic signs of DC. 2. Patients with moderate signs of DC. 3. Patients with severe signs of DC. Patients in the group 1 should remain under continuous specialised supervision, because they are at risk of developing DC, while patients in the groups 2 and 3 should undergo surgical restoration of bowel continuity. This applies particularly to group 3, where indications for surgery do not stem from risk of hyperproliferation, dysplasia or malignant transformation, but from that of a massive inflammation, which may constitute a danger for patientis health and even life. Authors also underline that DC can be treated conservatively but the best and most successful and remained method of treatment of DC is the operation of decolostomy, which means restoration continuity of digestive tract.

Sodium butyrate enemas in the treatment of acute radiation-induced proctitis in patients with prostate cancer and the impact on late proctitis. A prospective evaluation

PURPOSE

To evaluate prospectively the effect of sodium butyrate enemas on the treatment of acute and the potential influence on late radiation-induced proctitis.

PATIENTS AND METHODS

31 patients had been treated with sodium butyrate enemas for radiation-induced acute grade II proctitis which had developed after 40 Gy in median. During irradiation the toxicity was evaluated weekly by the Common Toxicity Criteria (CTC) and subsequently yearly by the RTOG (Radiation Therapy Oncology Group) and LENT-SOMA scale.

RESULTS

23 of 31 patients (74%) experienced a decrease of CTC grade within 8 days on median. A statistical significant difference between the incidence and the severity of proctitis before start of treatment with sodium butyrate enemas compared to 14 days later and compared to the end of irradiation treatment course, respectively, was found. The median follow-up was 50 months. Twenty patients were recorded as suffering from no late proctitis symptom. Eleven patients suffered from grade I and 2 of these patients from grade II toxicity, too. No correlation was seen between the efficacy of butyrate enemas on acute proctitis and prevention or development of late toxicity, respectively.

CONCLUSION

Sodium butyrate enemas are effective in the treatment of acute radiation-induced proctitis in patients with prostate cancer but have no impact on the incidence and severity of late proctitis.

Review article: the role of butyrate on colonic function

BACKGROUND

Butyrate, a short-chain fatty acid, is a main end-product of intestinal microbial fermentation of mainly dietary fibre. Butyrate is an important energy source for intestinal epithelial cells and plays a role in the maintenance of colonic homeostasis.

AIM

To provide an overview on the present knowledge of the bioactivity of butyrate, emphasizing effects and possible mechanisms of action in relation to human colonic function.

METHODS

A PubMed search was performed to select relevant publications using the search terms: 'butyrate, short-chain fatty acid, fibre, colon, inflammation, carcinogenesis, barrier, oxidative stress, permeability and satiety'.

RESULTS

Butyrate exerts potent effects on a variety of colonic mucosal functions such as inhibition of inflammation and carcinogenesis, reinforcing various components of the colonic defence barrier and decreasing oxidative stress. In addition, butyrate may promote satiety. Two important mechanisms include the inhibition of nuclear factor kappa B activation and histone deacetylation. However, the observed effects of butyrate largely depend on concentrations and models used and human data are still limited.

CONCLUSION

Although most studies point towards beneficial effects of butyrate, more human in vivo studies are needed to contribute to our current understanding of butyrate-mediated effects on colonic function in health and disease.

Short-chain fatty acid formation in the hindgut of rats fed oligosaccharides varying in monomeric composition, degree of polymerisation and solubility

The contents of short-chain fatty acids were investigated in rats fed lactitol, lactulose and four fructo-oligosaccharides of different degree of polymerisation and solubility. Fructo-oligosaccharides with a low degree of polymerisation (2–8) generated the highest levels of butyric acid all along the hindgut, whereas fructo-oligosaccharides with a high degree of polymerisation (10–60) generated the highest levels of propionic acid. These specific differences were also generally reflected in the caecal pools and molar proportions of short-chain fatty acids. The lower solubility of the fructo-oligosaccharides was related to a lower degree of caecal fermentation. Lactulose and lactitol yielded high proportions of acetic acid and low proportions of butyric acid. It is concluded that both the degree of polymerisation and the solubility may affect short-chain fatty acid formation, whereas the fructose contentper seseem to be of less importance. This may be of interest when designing foods with specific health effects.

Milk whey culture with Propionibacterium freudenreichii ET-3 is effective on the colitis induced by 2,4,6-trinitrobenzene sulfonic acid in rats

This study aimed to evaluate whether milk whey culture with Propinibacterium freudenreichii ET-3 (milk whey culture), which has been reported to have Bifidogenic activity, is effective on the colitis induced by 2,4,6-trinitrobenzene sulfonic acid (TNBS) in rats. For the induction of colitis, the colon was clamped and 0.1 M TNBS in 35% ethanol was injected into the luminal side of the clamped portion under pentobarbital anesthesia. From the next day of colitis induction, milk whey culture was administered orally at doses of 1 and 3 g/kg, twice a day for 9 days. On the 10th day, rats were sacrificed and ulcer size was measured. Milk whey culture significantly accelerated the healing of the colitis in a dose-dependent manner, but culture medium did not. To clarify the active substance, the effects of propionic acid and acetic acid contained in milk whey culture was tested. Sodium propionate significantly accelerated the healing of TNBS-induced colitis, but sodium acetate did not. The above results show that milk whey culture may become a useful prebiotic for the therapy of inflammatory bowel disease and that propionic acid may be one of the active substances contained in milk whey culture.

A novel bifunctionality: PAT1 and PAT2 mediate electrogenic proton/amino acid and electroneutral proton/fatty acid symport

Recently, the PAT family of proton-dependent amino acid transporters has been identified as a novel class of mammalian amino acid symporters. PAT1 and PAT2 members mediate electrogenic uptake of small, neutral amino acids and derivatives by cotransport of protons. Analysis of the structural requirements for substrate recognition by PAT1 identified that a free amino group in a substrate is not essential for recognition. We therefore hypothesized that PAT1 and its ortholog PAT2 may also be able to recognize and transport the homologous short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate. We examined in Xenopus laevis oocytes whether the SCFAs interact with the transporter by employing flux studies, electrophysiology and intracellular pH recordings. SCFAs did not induce positive inward currents but inhibited glycine-induced transport currents. PAT-mediated uptake of radiolabeled proline was also dose-dependently reduced by SCFA and could be described by first order competition kinetics with apparent Ki-values for butyrate of 6.0 +/- 0.7 and 7.6 +/- 1.3 mM for PAT1 and PAT2, respectively. Acetate as well as propionate uptake was significantly enhanced in oocytes expressing PAT1 or PAT2. An electroneutral H+/SCFA symport mode was demonstrated by recording intracellular pH changes under voltage clamp conditions with rate constants for the initial intracellular acidification in the presence of SCFAs significantly increased in PAT-expressing oocytes. In conclusion, our data demonstrate that the PAT1 and PAT2 proteins are capable to transport selected SCFAs in an electroneutral and the homologous amino acids in an electrogenic mode and are therefore a paradigm for bifunctional solute carriers.

New approaches to the role of diet in the prevention of cancers of the alimentary tract

Cancers of the alimentary tract are, collectively, amongst the major causes of morbidity and deaths from cancer across the world today. Of the 10 million new cases of cancer diagnosed in 2000, about 2.3 million were cancers of the pharynx, oesophagus, stomach or colorectum. Nevertheless, epidemiological studies indicate that cancers of the digestive organs are also amongst the most susceptible to modification by dietary factors. International variations in incidence suggest that round three quarters of all sporadic colorectal cancers are attributable to diet. Even within the relatively uniform environment of the European Union, there are variations in the incidence of colorectal and oesophageal cancers of about two- and six-fold, respectively. Carcinomas of the alimentary tract arise from epithelial cells via distinct sequences of neoplastic change, which require a large fraction of an individual's lifespan. The best characterised of these is the adenoma-carcinoma sequence of colorectal carcinogenesis, in which progressive loss of differentiation and normal morphology in a growing lesion is associated with the acquisition of somatic mutations, and of aberrant methylation of CpG-islands, leading to gene silencing. These molecular events are accompanied by functional changes, including increased mitosis and evasion of apoptosis. There is little evidence that diet exerts its effects primarily through food-borne carcinogens that can be identified and eliminated from the food-chain. It is far more probable that the adverse effects of diet are caused largely by over-consumption of energy, coupled with inadequate intakes of protective substances, including micronutrients, dietary fibre and a variety of phytochemicals. The latter are biologically active secondary plant metabolites, many of which modify cell proliferation and induce apoptosis in vitro. There is growing evidence that such effects also occur in vivo, and that they can suppress the progress of neoplasia. Carcinomas of the oesophagus, stomach and colon all appear to be partially preventable by diets rich in fruits and vegetables. Plant foods contain a variety of components including micronutrients, polyunsaturated fatty acids, and secondary metabolites such as glucosinolates and flavonoids, many of which can inhibit cell proliferation and induce apoptosis, and which may well act synergistically when combined in the human diet. The future challenge is to fully characterise and evaluate these effects at the cellular and molecular level, so at to exploit their full potential as protective mechanisms for the population as a whole.

Os ácidos graxos de cadeia curta na cicatrização de anastomoses colônicas: estudo experimental em ratos

OBJETIVO: Avaliar a ação dos ácidos graxos de cadeia curta (AGCC) na cicatrização de anastomoses colônicas em ratos. MÉTODO: Utilizaram-se 50 ratos divididos em 4 grupos. Dois desses grupos, vinte e seis animais, foram submetidos à operação de Hartmann; metade destes (grupo HF) recebeu infusões retais diárias, no pós-operatório, de solução fisiológica a 0,9% ; a outra metade (grupo HA) recebeu solução de butirato de sódio à 80mmol/l (AGCC) (HA). Os dois grupos restantes, vinte e quatro animais foram submetidos à anastomose colônica término-terminal a 4 cm da borda anal. Destes, 12 animais (grupo AF) receberam infusões retais de soro fisiológico a 0,9% e 12 animais (grupo AA) receberam a solução com AGCC. Os animais foram avaliados no 7º e 14º dia do pós-operatório. Foi realizada análise histológica da densitometria do colágeno pela coloração do sirius red, utilizando-se a microscopia de polarização com método computadorizado. RESULTADOS: Comparando-se os grupos submetidos à cirurgia de Hartmann, portanto na ausência do trânsito intestinal, observou-se concentração significativamente maior de colágeno I e total no grupo que recebeu AGCC (p=0,001). Comparando-se os grupos submetidos à anastomose término-terminal, com interferência do trânsito intestinal, não se encontrou diferença significante da concentração de colágeno I e total (p=0,056 e p=0,397, respectivamente). A ação isolada do trânsito intestinal promoveu também aumento da produção de colágeno, quando comparado ao grupo sem atuação do trânsito intestinal. CONCLUSÃO: A administração via retal de AGCC, na ausência do trânsito intestinal mostrou-se de grande valia, promovendo aumento da síntese do colágeno. Independentemente da interferência do trânsito intestinal, o principal efeito do AGCC esteve relacionado com o aumento da maturação do colágeno.

Colonic epithelial atrophy induced by a fibre-free diet in rats is reversed by minimal amounts of luminal butyrate, but only in the short term

BACKGROUND

Luminal butyrate may be trophic to the colonic epithelium, but this effect is poorly characterized. The aim of the present study was to define the dose-response, time-course, site-specificity and the dependence on background diet of the effects of butyrate on epithelial proliferation in normal distal colon, using an in vivo rat model of colonic substrate delivery.

METHODS

Male Sprague-Dawley rats, maintained on a fibre-free diet, had butyrate infused twice daily into the colonic lumen via polyethylene tubes placed at laparotomy. Varying dose levels (0-80 micro mol/d; 4 d), site (caecal vs distal colonic), duration of infusions (1-5 weeks; 80 micro mol/d), or dietary fibre intake were investigated. Epithelial proliferative indices were assessed stathmokinetically.

RESULTS

Four-day infusions of butyrate led to a progressive trophic effect (cells/crypt column increased from 37.9 +/- 1.6 at 0 micro mol/d to 44.7 +/- 1.2 at 80 micro mol/d) on fibre-deprived colonic mucosa, related linearly to the daily butyrate dose (P < 0.001, linear regression). This effect was mediated by increases in the number and proportion of mitoses, related to the square of the butyrate dose (P < 0.001 in each case, polynomial regression). Butyrate (80 micro mol/d) was associated with significantly higher cellularity (59.9 +/- 1.4) and mitotic activity (4.9 +/- 0.6) per crypt column compared to vehicle controls (50.3 +/- 1.6 and 0.9 +/- 0.2, respectively; P < 0.05, t-tests), at 1 and 3 weeks, but not at 5 weeks. Butyrate had similar effects on distal colonic crypt cellularity (62.0 +/- 1.5) when delivered caecally, but in rats fed a fibre-containing diet, colonic crypt cellularity (55.3 +/- 3.2) was similar to baseline (59.6 +/- 1.9).

CONCLUSIONS

Trophic effects of butyrate are concentration-dependent and occur at low doses in the short term, but are not sustained over longer periods. They are seen only in a fibre-deprived state and appear to be independent of the site of administration.

Anticarcinogenic effects of diet-related apoptosis in the colorectal mucosa

The crypt is the fundamental unit of epithelial proliferation in the intestinal mucosa. The progeny of the pluripotent stem cells located near the base of the crypt migrate towards the crypt orifice, divide once or twice more, and then undergo differentiation, senescence and exfoliation. Programmed cell death (apoptosis) also occurs deep in the proliferative zone. Various lines of evidence suggest that apoptosis provides a protective mechanism against neoplasia by removing genetically damaged stem cells from the epithelium before they can undergo clonal expansion. Several different classes of food constituents, including certain polyunsaturated fatty acids, the short-chain fatty acid butyrate, and some phytochemicals including flavonoids and glucosinolates breakdown products, can modulate both cellular proliferation and programmed death. Each of these food components has also been shown to suppress the emergence of aberrant crypt foci in animal models of carcinogenesis. Further mechanistic and clinical studies are required to establish whether such dietary effects can be exploited to achieve preventive or therapeutic effects in humans.

Mechanism of n-butyrate uptake in the human proximal colonic basolateral membranes

Current studies were undertaken to characterize the mechanism of short-chain fatty acid (SCFA) transport in isolated human proximal colonic basolateral membrane vesicles (BLMV) utilizing a rapid-filtration n-[(14)C]butyrate uptake technique. Human colonic tissues were obtained from mucosal scrapings from organ donor proximal colons. Our results, consistent with the existence of a HCO(3)(-)/SCFA exchanger in these membranes, are summarized as follows: 1) n-[(14)C]butyrate influx was significantly stimulated into the vesicles in the presence of an outwardly directed HCO(3)(-) and an inwardly directed pH gradient; 2) n-[(14)C]butyrate uptake was markedly inhibited (approximately 40%) by anion exchange inhibitor niflumic acid (1 mM), but SITS and DIDS (5 mM) had no effect; 3) structural analogs e.g., acetate and propionate, significantly inhibited uptake of HCO(3)(-) and pH-gradient-driven n-[(14)C]butyrate; 4) n-[(14)C]butyrate uptake was saturable with a K(m) for butyrate of 17.5 +/- 4.5 mM and a V(max) of 20.9 +/- 1.2 nmol x mg protein(-1) x 5 s(-1); 5) n-[(14)C]butyrate influx into the vesicles demonstrated a transstimulation phenomenon; and 6) intravesicular or extravesicular Cl(-) did not alter the anion-stimulated n-[(14)C]butyrate uptake. Our results indicate the presence of a carrier-mediated HCO(3)(-)/SCFA exchanger on the human colonic basolateral membrane, which appears to be distinct from the previously described anion exchangers in the membranes of colonic epithelia.

Key nutrients and growth factors for the neonatal gastrointestinal tract

The nutritional support of gastrointestinal growth and function is an important consideration in the clinical care of neonatal infants. In most health infants, the provision of either breast milk or formula seems to support normal intestinal mucosal growth, but the most significant advantages of breast milk may be for host defense or gut barrier-related functions that are involved in reducing infection. The specific effects of various milk-borne growth factors on key mucosal immune and barrier functions are likely to provide valuable new clues to the advantages of human milk. A substantial number of preterm, low-birth weight babies or those suffering from compromised intestinal function, however, often cannot tolerate oral feedings and instead receive TPN. The consequences of TPN on gastrointestinal function and how this contributes to morbidity of these infants warrants further study, with respect to both clinical and basic research questions. Although enteral nutrition seems to be a critical stimulus for intestinal function, the minimal amounts and composition of nutrients necessary to maintain specific intestinal functions remain to be established. The experimental tools exist to start defining the specific nutrient requirements for the infant gut and some of these nutrients are known (e.g., glutamate, glutamine, and threonine). Peptide growth factors and gut hormones clearly play a role in gut growth and in several ways mediate the trophic actions of enteral nutrition. Although a number of these growth factors are good candidates for therapeutic use, their clinical application in the management of gastrointestinal insufficiency and disease has been slow. The emergence of GLP-2 as a trophic peptide that seems to target the gut is a promising candidate on the horizon.

Complications after colorectal surgery without mechanical bowel preparation

BACKGROUND

The current practice of mechanical bowel preparation (MBP) before colorectal surgery is questionable. Mechanical bowel preparation is unpleasant for the patient, often distressful, and potentially harmful. The results are often less than desired, increasing the risk of contamination. Cleansing the colon and rectum before surgery has never been shown in clinical trials to benefit patients. In animal experiments MBP has a detrimental effect on colonic healing.

STUDY DESIGN

To investigate the outcomes of colorectal surgery without MBP, we prospectively evaluated a consecutive series of patients who underwent resection and primary anastomosis of the colon and upper rectum, including emergency operations. One surgeon performed all operations. Endpoints were wound infection, anastomotic failure, and death. Late signs and symptoms that might be secondary to leakage of the anastomosis were considered as an anastomotic failure as well, during a followup of 1 year.

RESULTS

Two hundred fifty operations were performed, of which 199 (79.6%) were elective. Colectomies were left-sided in 65.6%. Anastomoses were ileocolic in 32%, colocolic in 20.8%, colorectal intraperitoneal in 34.4%, and extraperitoneal in 12.8%. No patient suffered from fecal impaction. Followup was complete in 97.2%. Eight patients (3.3%; 95% confidence interval [CI]: 1.4-6.4) developed superficial wound infections. In three patients there was leakage from an extraperitoneal colorectal anastomosis, in two of them after hospital discharge. The overall anastomotic failure rate was 1.2% (95% CI: 0.3-3.6). The in-hospital mortality rate was 0.8% (95% CI: 0.1-2.9) and was not related to abdominal or septic complications.

CONCLUSION

Mechanical bowel preparation is not a sine qua non for safe colorectal surgery.

New food components and gastrointestinal health

Apart from its main functions of digestion, absorption and faecal processing, the human gastrointestinal tract has a complex pattern of muscular activity regulated by a largely autonomous nervous system, and its various organs contain large concentrations of immune and endocrine tissues. Any failure of these closely-integrated systems can lead to diseases ranging from the mildly irritating to the life threatening. Food contains a huge variety of chemical species, many of which are biologically active, and the distal regions of the gut are colonised by a rich and metabolically-active commensal flora that depend on nutrients derived ultimately from the host's dietary residues. The present paper explores the evidence for significant effects of food ingredients on functional bowel disorders, intestinal infections, and aspects of epithelial cell physiology involved in the development of colo-rectal neoplasia. Various strategies, including the manipulation of the colo-rectal microflora with pre- and probiotics, and the development of new products and plant varieties containing biologically-active constituents, have the potential to underpin the development of novel functional food products. However, these products will need to be based on proven biological principles, and fully tested for efficacy and safety. The rapidly-developing fields of functional genomics and cell biology will open up new experimental strategies to explore these possibilities, and emerging processing technologies seem likely to provide novel methods for their exploitation.

Short-chain fatty acids and human colonic function: roles of resistant starch and nonstarch polysaccharides

Resistant starch (RS) is starch and products of its small intestinal digestion that enter the large bowel. It occurs for various reasons including chemical structure, cooking of food, chemical modification, and food mastication. Human colonic bacteria ferment RS and nonstarch polysaccharides (NSP; major components of dietary fiber) to short-chain fatty acids (SCFA), mainly acetate, propionate, and butyrate. SCFA stimulate colonic blood flow and fluid and electrolyte uptake. Butyrate is a preferred substrate for colonocytes and appears to promote a normal phenotype in these cells. Fermentation of some RS types favors butyrate production. Measurement of colonic fermentation in humans is difficult, and indirect measures (e.g., fecal samples) or animal models have been used. Of the latter, rodents appear to be of limited value, and pigs or dogs are preferable. RS is less effective than NSP in stool bulking, but epidemiological data suggest that it is more protective against colorectal cancer, possibly via butyrate. RS is a prebiotic, but knowledge of its other interactions with the microflora is limited. The contribution of RS to fermentation and colonic physiology seems to be greater than that of NSP. However, the lack of a generally accepted analytical procedure that accommodates the major influences on RS means this is yet to be established.

Short-chain fatty acid enemas stimulate plasminogen activator inhibitor-1 after abdominal aortic graft surgery: a double-blinded, placebo-controlled study

Colonic ischaemia may complicate aortic graft surgery with high mortality from associated colonic necrosis. Loss of the mucosal barrier function due to ischaemia may promote translocation of endotoxins with secondary systemic disseminated coagulation leading to multiple organ failure. Short-chain fatty acids (SCFAs) stimulate the microcirculation in the human rectum. The aim of this study was to investigate whether SCFA enemas influence systemic endotoxinaemia and fibrinolytic activity during and after elective aortic graft surgery for arteriosclerosis. Thirty-two patients were randomized to SCFA or placebo enemas twice daily from the day before surgery to 7 days after. Blood samples for endotoxin, plasminogen activator inhibitor-1 (PAI-1) activity, tissue-type plasminogen activator (t-PA) antigen, and cross-linked fibrin degradation products (XL-FDP) were drawn before, during, and 7 days after surgery. Four patients, two in each treatment group, developed postoperative endotoxinaemia. PAI-1 was significantly higher on days 2 and 4 in SCFA-treated patients, whereas t-PA was comparable Petween the groups. During the postoperative course, a progressive and near-identical XL-FDP increase was found in the two groups. In elective aortic graft surgery for arteriosclerosis, SCFA enemas likely stimulate systemic PAI-1 activity by promoting colonic tissue reperfusion following aortic unclamping. Endotoxinaemia and fibrinolytic shutdown are uncommon findings.

A ação dos ácidos graxos de cadeia curta na cicatrização de anastomoses colônicas: estudo experimental em ratos

Os ácidos graxos de cadeia curta (AGCC) derivam da fermentação das fibras ingeridas na dieta e atuam como substrato das células da mucosa colônica. O presente estudo tem como objetivo avaliar a ação dos AGCC na cicatrização do cólon. Utilizaram-se 16 ratos fêmea divididos em 2 grupos de 8 animais. No grupo controle (HC) os animais foram submetidos à cirurgia de Hartmann e infusão pós-operatória de solução salina isotônica via retal por 7 dias. No grupo experimento (HA) a solução salina foi substituída por solução isosmolar contendo AGCC. Nos animais do grupo controle, a pressão média de ruptura do segmento distal do cólon foi de 128,37 mmHg, sendo este valor de 137,25 mmHg no grupo experimento (p=0,5693). A avaliação histológica em hematoxilina-eosina foi semelhante nos dois grupos estudados. A densitometria do colágeno demonstrou concentração significativamente maior de colágeno maduro (tipo I) no grupo experimento, quando comparado com o grupo controle (p=0,0094). O colágeno total também foi mais encontrado no grupo experimento, comparado-se com o grupo controle (p=0,0371). Conclui-se que os ratos submetidos à infusão intraluminal de AGCC têm maior concentração de colágeno maduro e total na linha de sutura do coto retal, quando comparados com o grupo controle.

Experimental study of neorectal physiology after formation of a transverse coloplasty pouch

BACKGROUND

A novel transverse coloplasty pouch (TCP) with a larger neorectal volume than a straight coloanal anastomosis (CAA) but a smaller volume than a short colonic J pouch (CJP) may improve short-term function after rectal excision.

METHODS

Twelve pigs were investigated 6 weeks after complete rectal excision followed by reconstruction with a CAA, CJP or TCP. The results were compared with findings in the normal pig rectum.

RESULTS

The colonic transit times assessed by radio-opaque marker transit were 24 h for CAA, 60 h for CJP and 32 h for TCP. Non-operated control pigs had a mean transit time of 46 h. Pigs that had a CJP developed colonic dilatation and substantial faecal impaction. Colonic electrostimulation induced an adaptive relaxation in the normal rectum but a pressure increase in all neorecta, particularly after CAA. The neorectal longitudinal smooth muscle layer in pigs with a TCP was significantly thicker than that in pigs with a CAA or CJP; its thickness was closest to that of the normal pig rectum. Colonic smooth muscle layers 10 cm proximal to the coloanal anastomosis, above the neorecta, were significantly thicker after CJP than after CAA or TCP formation. No significant difference in microcirculation was observed between the three restorative procedures.

CONCLUSION

Accelerated colonic transit and a lack of adequate relaxation upon endoluminal pressure increase was associated with urgency and incontinence after CAA. Delayed colonic transit, faecal impaction and ineffective muscular hypertrophy due to pouch dilatation and constipation indicated evacuation problems after CJP construction. Functional and morphometric data for TCPs suggested almost normal defaecation. Of the three restorative procedures, the data for TCPs were most similar to those obtained in the normal pig rectum at short-term follow-up.

L-glutamine enemas attenuate mucosal injury in experimental colitis

PURPOSE

The aim of this study was to investigate the role of 1-glutamine, short chain fatty acid, prednisolone, and mesalazine (5-aminosalicylic acid) enemas on mucosal damage and inflammation in experimental colitis.

METHODS

Colitis was induced in rats with trinitrobenzene sulfonic acid in ethanol. Saline (n = 14), prednisolone (n = 13), 5-aminosalicylic acid (n = 14), 1-glutamine (n = 14), and short chain fatty acid (n = 13) enemas were applied twice daily to the rats for seven days after the induction of colitis. The sham group (n = 9) received only saline enemas. Rats were killed at the seventh day and their colonic macroscopic inflammatory scores were determined. Colonic mucosal gamma glutamyl transpeptidase activity and colonic mucosal malondialdehyde levels were measured. The same measurements but no enemas were done in the control group (n = 7).

RESULTS

There were significant differences in macroscopic inflammatory scores between sham and colitis groups (P < 0.001). The macroscopic inflammatory scores of the colitis group were higher than the short chain fatty acid and glutamine groups (P < 0.05). Whereas the mucosal gamma glutamyl transpeptidase activity was diminished in prednisolone, 5-aminosalicylic acid, and short chain fatty acid groups when compared with the control group; in the colitis, sham, and glutamine groups the activity of this enzyme did not change. The mucosal malondialdehyde levels were significantly lower in the prednisolone and glutamine groups than in the colitis group.

CONCLUSION

Only one of four agents tested, namely, 1-glutamine enemas, could decrease the severity of colitis both morphologically and biochemically. Moreover, L-glutamine prevented the colitis-induced oxidant injury in the colonic mucosa. On the other hand, prednisolone and short chain fatty acids seemed to improve only the physiologic changes of colitis.

Short chain fatty acids are effective in short-term treatment of chronic radiation proctitis: randomized, double-blind, controlled trial

PURPOSE

Short chain fatty acids are the main energy source of colonocytes and their use may be impaired in chronic radiation proctitis. The aim of the present study was to evaluate the therapeutic effect of short chain fatty acid enemas in patients with chronic radiation proctitis.

METHODS

A prospective, randomized, double-blind trial comparing short chain fatty acid enemas with placebo was conducted in 19 patients with chronic radiation proctitis. Short chain fatty acid enemas contained 60 mM sodium acetate, 30 mM sodium propionate, and 40 mM sodium butyrate. The treatment period lasted five weeks and patients were followed up for six months.

RESULTS

On admission, both groups were similar regarding all parameters evaluated. After five weeks short chain fatty acid-treated patients showed a significant decrease in the number of days with rectal bleeding from the previous week (4.4+/-1.8 to 1.4+/-2.2; P = 0.001) and an improvement of endoscopic score (4.8+/-1.4 to 2.2+/-1.2; P = 0.001). Hemoglobin values were also significantly higher in short chain fatty acid-treated patients (13.1+/-0.9 g/dl vs. 10.7+/-2.1 g/dl; P = 0.02). Mucosal DNA and protein concentrations decreased in both groups but significantly so only in placebo-treated patients (P = 0.05). Changes in histologic parameters were not significant in either group. Although short chain fatty acid-treated patients did not get worse in the next six months, placebo-treated ones gradually improved, and at the end of six months, differences between the two groups were no longer observed.

CONCLUSIONS

Short chain fatty acid enemas can accelerate the process of healing in chronic radiation proctitis, but treatment has to be continuous if a complete and sustained clinical, endoscopic, and histologic response is to be obtained.

Effects of short-chain fatty acids on the inflamed colonic mucosa

Selected inflammatory conditions of the distal alimentary tract may respond to topical SCFA treatment. The rationale for using SCFA enemas is based on Roediger's (1980) observation that butyrate is the preferred fuel of colonocytes and that SCFA deficiency could lead, in the short term, to mucosal hypoplasia and, in the long term, to colitis. The absence of luminal nutrients is especially evident in the excluded rectum after complete diversion of the faecal stream. Harig et al. (1989) were the first to treat successfully diversion colitis with SCFA irrigation (acetate 60 mM, propionate 30 mM, n-butyrate 40 mM). However, subsequent studies could not reproduce the initial positive data. In distal ulcerative colitis an impaired mucosal oxidation of SCFAs has been described despite their luminal abundance. Pilot studies using either the SCFA mixture or butyrate monotherapy have yielded promising results. However, extended confirmatory studies with a larger sample size have not yet been performed. Preliminary data are also available for the use of SCFA in pouchitis and radiation proctitis. In summary, SCFA topical therapy seems to be a promising option in distinct forms of inflammatory bowel disease; however, the routine use of SCFAs cannot be recommended until their efficacy has been confirmed in larger trials.

Short-chain fatty acids in the human colon: relation to gastrointestinal health and disease

Fermentation, the process whereby anaerobic bacteria break down carbohydrates to short-chain (C2-C6) fatty acids (SCFAs), is an important function of the large bowel. SCFAs constitute approximately two-thirds of the colonic anion concentration (70-130 mmol/l), mainly as acetate, propionate, and butyrate. Gastroenterologists have, in spite of these facts, addressed this scientific field surprisingly late, in contrast to veterinarians, for whom the fermentative production of SCFAs has been acknowledged as a principal mechanism of intestinal digestion in plant-eating animals for decades. Interest in the effects of SCFA production on the human organism has been growing rapidly in the last 10 years, because gastrointestinal functions and beneficial effects are associated with these acids. SCFAs are of major importance in the understanding of the physiological function of dietary fibre and their possible role for colonic neoplasia. SCFA production and absorption are closely related to the nourishment of the colonic mucosa and sodium and water absorption, and mechanisms of diarrhoea. Patients with severe malabsorption compensate by the fermentation of otherwise osmotic active saccharides to SCFAs, which are readily absorbed and used as energy fuels in the organism. SCFA production from dietary carbohydrates is a mechanism whereby considerable amounts of calories can be salvaged in short-bowel patients with remaining colonic function if dietary treatment is adjusted. SCFA enemas are a new and promising treatment modality for patients with ulcerative colitis. The effect has been attributed to the oxidation of SCFAs in the colonocytes. An impressive number of papers have described the effects of butyrate on various cell functions, the significance of which is still unknown. Up until now, attention has been related especially to cancer prophylaxis and treatment. Diminished production of SCFAs appears to be involved in antibiotic-associated diarrhoea, diversion colitis, and possibly in pouchitis. The interaction between bacterial fermentation, ammonia metabolism, and bacterial growth and protein synthesis appears to be the main mechanism of action of lactulose treatment in hepatic coma. Pathological and extremely high rates of saccharide fermentation explain the severe deterioration in patients with D-lactate acidosis. Hence, this scientific field has come late to clinical working gastroenterologists, but as work is progressing the production of SCFAs in the large bowel becomes involved in several well-known intestinal disorders.

Transmural trophic effect of short chain fatty acid infusions on atrophic, defunctioned rat colon

PURPOSE

This study was designed to investigate and quantify trophic alterations in the defunctioned, atrophic rat colon after short chain fatty acid (SCFA) treatment was administered in a clinically relevant way.

METHODS

Diverting colostomy with exclusion of distal colon was performed on adult female rats (58), and treatment was started four weeks later. Enemas of either a SCFA solution of sodium-acetate, sodium-propionate and sodium-butyrate (concentration, 780 mM), or isotonic saline (placebo) were instilled through the anus into the defunctioned colon. This was done twice daily for 7 or 14 days before death.

RESULTS

After SCFA instillation for 14 days, the colonic wet weight was 18 percent higher compared with placebo (P < 0.01), and there was a similarly significant difference in dry weight (P < 0.05). Using stereologic assessment to determine the histologic composition of defunctioned colon, we found significant increases among SCFA-treated rats in the weight of the mucose (P < 0.05), the submucosa (P < 0.05), and the muscularis propria (P < 0.05) and a 30 percent increase in the mucosal surface area compared with placebo-treated in the mucosal surface area compared with placebo-treated rats (P < 0.05). Measurements of breaking strength and hydroxyproline content showed no differences between treatment groups.

CONCLUSIONS

SCFA enemas have a transmural trophic effect and preserve mucosal surface area of defunctioned and atrophic colon in rats.

Short chain fatty acids relax isolated resistance arteries from the human ileum by a mechanism dependent on anion-exchange

Ileal resistance arteries (internal diameter 184-337 microns) were discussed out under microscope and mounted in a microvascular myograph for isometric tension recording. Experiments were designed to test compounds trophic to the small intestine, namely, epidermal growth factor, glutamine and the three short chain fatty acids, acetic, propionic and butyric acid, for effects on vascular tone. Glutamine in concentrations up to 30 mM and epidermal growth factor in concentrations up to 1 microM had no contractile or relaxant effects on the resistance arteries. The three short chain fatty acids alone and in combination, however, caused a concentration-dependent (range 0.1-30 mM) relaxation of resistance arteries precontracted with 50 mM KCl. This relaxant effect was significantly inhibited by the presence of the anion-exchange inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid whereas it was unaffected by removal of the endothelium, presence of indomethacin, propranolol or phentolamine. These data suggest that the trophic effects of glutamine and epidermal growth factor on the small intestinal mucosa cannot be explained through actions on the resistance vasculature. In contrast, the relaxant effect of short chain fatty acid on resistance arteries in vitro suggests that these compounds may be able to improve the microcirculation in vivo. An improved microcirculation will, all things considered, facilitate the growth of the small intestinal mucosa.

Effects of the short-chain triglyceride triacetin on intestinal mucosa and metabolic substrates in rats

Diets containing either triacetin (the water-soluble triglyceride of acetate) or long-chain triglycerides (LCTs) were fed to rats to determine the effects on intestinal mucosa cells and plasma substrates. Male Sprague-Dawley rats were fed one of three diets, a control diet containing 5% of energy as LCTs or one of two experimental diets that contained 30% of energy as lipid. The lipid component of the two experimental diets was either 100% LCTs or 95% triacetin/5% LCTs. Plasma lactate, glucose, and total ketone body concentrations were not significantly different among dietary treatment groups. Compared with animals fed LCTs and control diet, plasma pyruvate and free fatty acid concentrations were decreased in animals fed triacetin. In contrast, plasma triglyceride concentrations were elevated in animals fed triacetin compared with other groups. Intestinal biochemical measures included total DNA, RNA, protein, and the protein:DNA ratio. Histologic indices measured were villus height in the jejunum and crypt depth in the colon. No significant difference in mucosal protein concentration was observed in the jejunum and colon. Jejunal RNA was significantly decreased in animals fed triacetin compared with other diets. Triacetin feeding significantly increased the DNA content in the jejunum and colon (thereby lowering the protein:DNA ratio), indicating smaller, more numerous cells. Jejunal villus height and colonic crypt depth were not significantly different among dietary treatment groups. Provision of a balanced diet containing 28.5% of the total calories as triacetin had no adverse effects on metabolic substrates and resulted in smaller and more numerous mucosal cells in the jejunum and colon.(ABSTRACT TRUNCATED AT 250 WORDS)

Mediation of the trophic effects of short-chain fatty acids on the rat jejunum and colon

BACKGROUND/AIMS

Short-chain fatty acids (SCFAs) are trophic to small intestinal and colonic mucosa. This study determined whether SCFAs infused into the cecum out of continuity stimulated jejunal and colonic cellularity and whether these effects were mediated by the autonomic nervous system and/or enterotrophic hormones.

METHODS

To eliminate direct trophic effects of SCFAs in contact with mucosa, 60 rats underwent cecal isolation with placement of an infusion catheter into the proximal cecum, formation of distal cecocutaneous stoma, and restoration of intestinal continuity with ileocolonic anastomosis. Rats underwent cecal denervation or remained normally innervated and received 1 of 3 infusions for 10 days: SCFAs, saline, or no infusion. Twenty-four additional rats were assigned to the same groups but underwent infusion into the proximal colon (in circuit).

RESULTS

Cecal infusion of SCFAs into innervated rats increased (P < 0.05) jejunal DNA, villous height, surface area, crypt depth, and gastrin without increasing colonic variables. In denervated rats, SCFAs did not significantly affect these variables. However, direct intracolonic infusions of SCFAs increased (P < 0.05) colonic mucosal DNA and crypt depth.

CONCLUSIONS

Jejunotrophic effects of cecally infused SCFAs are mediated afferently by the autonomic nervous system and are associated with increased jejunal gastrin. SCFAs have local trophic effects on the colon.

Trophic effects of different enteral diets in the rat intestine

The trophic effect of 4 commercial diets compared to chow was studied in 50 rats. The 4 commercial diets were: a free amino acid diet, a diet based on soy protein hydrolysate and two diets based on intact protein with and without extra fibre added. Bowel weight, mucosa weight and DNA content were measured after 7 days of treatment. The enteral formula based on a soy protein hydrolysate had a significant growth stimulating effect on the proximal small bowel compared to rat chow. In the ileum and in the colon all diets without fibre supplementation caused significantly lower bowel weights than rat chow.