Nutritional contribution of volatile fatty acids from the cecum of rats

Fermentation technology as a driver of human brain expansion

Brain tissue is metabolically expensive. Consequently, the evolution of humans' large brains must have occurred via concomitant shifts in energy expenditure and intake. Proposed mechanisms include dietary shifts such as cooking. Importantly, though, any new food source must have been exploitable by hominids with brains a third the size of modern humans'. Here, we propose the initial metabolic trigger of hominid brain expansion was the consumption of externally fermented foods. We define "external fermentation" as occurring outside the body, as opposed to the internal fermentation in the gut. External fermentation could increase the bioavailability of macro- and micronutrients while reducing digestive energy expenditure and is supported by the relative reduction of the human colon. We discuss the explanatory power of our hypothesis and survey external fermentation practices across human cultures to demonstrate its viability across a range of environments and food sources. We close with suggestions for empirical tests.

Creating a low enteric methane emission ruminant: what is the evidence of success to the present and prospects for developing economies?

Enteric methane emissions from livestock constitute a greater part of anthropogenic greenhouse gases (GHGs) in Africa, than in more industrialised economies, providing a strong incentive for the development of low methane phenotype ruminants. Although dietary and husbandry options already exist for lowering methane production, means of changing ‘methane status’ of animals enduringly has a strong appeal. This paper is a critical review the empirical success to date of attempts to alter this status. Introduction of reductive acetogens, defaunation, anti-methanogen vaccines, early life programming and genetic selection at both the rumen and animal level are considered in turn. It is concluded that to date, there is little in vivo evidence to support the practical success of any of these strategies, save selective breeding, and this at a high cost with unknown efficacy. Finally, it is suggested that for developing economies management and nutritional strategies to reduce emissions will have the greatest and most immediate impact, at the lowest cost.

Utilization of cellulose by pigs and its effects on caecal function

1. Six pigs, four with caecal cannulae, were given diets containing 8% or 26% cellulose. Cannulation did not affect the digestibility of dry matter or cellulose.

2. Digestibility of cellulose, though variable, was higher for the 8%-cellulose diet.

3. Pigs on the 26%-cellulose diet had larger amounts of digesta in the caecum, and lower caecal retention times, than pigs on the 8%-cellulose diet.

4. Measurements of production rates of volatile fatty acids in the caecum indicated that only 2·7% and 1·9% of the apparent digestible energy of the 26%- and 8%-cellulose diets respectively came from the acids, and it was concluded that the caecum played only a small role in the breakdown of feed substances.

Acetate Synthesis from H(2) plus CO(2) by Termite Gut Microbes

Gut microbiota from Reticulitermes flavipes termites catalyzed an H(2)-dependent total synthesis of acetate from CO(2). Rates of H(2)-CO(2) acetogenesis in vitro were 1.11 +/- 0.37 mumol of acetate g (fresh weight) h (equivalent to 4.44 +/- 1.47 nmol termite h) and could account for approximately 1/3 of all the acetate produced during the hindgut fermentation. Formate was also produced from H(2) + CO(2), as were small amounts of propionate, butyrate, and lactate-succinate. However, H(2)-CO(2) formicogenesis seemed largely unrelated to acetogenesis and was believed not to be a significant reaction in situ. Little or no CH(4) was formed from H(2) + CO(2) or from acetate. H(2)-CO(2) acetogenesis was inhibited by O(2), KCN, CHCl(3), and iodopropane and could be abolished by prefeeding R. flavipes with antibacterial drugs. By contrast, prefeeding R. flavipes with starch resulted in almost complete defaunation but had little effect on H(2)-CO(2) acetogenesis, suggesting that bacteria were the acetogenic agents in the gut. H(2)-CO(2) acetogenesis was also observed with gut microbiota from Prorhinotermes simplex, Zootermopsis angusticollis, Nasutitermes costalis, and N. nigriceps; from the wood-eating cockroach Cryptocercus punctulatus; and from the American cockroach Periplaneta americana. Pure cultures of H(2)-CO(2)-acetogenic bacteria were isolated from N. nigriceps, and a preliminary account of their morphological and physiological properties is presented. Results indicate that in termites, CO(2) reduction to acetate, rather than to CH(4), represents the main electron sink reaction of the hindgut fermentation and can provide the insects with a significant fraction (ca. 1/3) of their principal oxidizable energy source, acetate.

Probiotic alternatives to reduce gastrointestinal infections: the poultry experience

The intestinal mucosa represents the most active defense barrier against the continuous challenge of food antigens and pathogenic microorganisms present in the intestinal lumen. Protection against harmful agents is conferred by factors such as gastric acid, peristalsis, mucus, intestinal proteolysis, and the intestinal biota. The establishment of beneficial bacterial communities and metabolites from these complex ecosystems has varying consequences for host health. This hypothesis has led to the introduction of novel therapeutic interventions based on the consumption of beneficial bacterial cultures. Mechanisms by which probiotic bacteria affect the microecology of the gastrointestinal tract are not well understood, but at least three mechanisms of action have been proposed: production/presence of antibacterial substances (e.g., bacteriocins or colicins), modulation of immune responses and specific competition for adhesion receptors to intestinal epithelium. The rapid establishment of bacterial communities has been thought to be essential for the prevention of colonization by pathogenic bacteria. Some animal models suggest that the reduction in bacterial translocation in neonatal animals could be associated with an increase in intestinal bacterial communities and bacteriocin-like inhibitory substances produced by these species. This review emphasizes the role of the intestinal microbiota in the reduction of the gastrointestinal infections and draws heavily on studies in poultry.

Nectar xylose metabolism in a rodent pollinator (Aethomys namaquensis): defining the role of gastrointestinal microflora using 14C-labeled xylose

The Namaqua rock mouse Aethomys namaquensis, a rodent pollinator of certain geoflorous Protea species, consumes nectar containing xylose. Xylose is not known to be efficiently utilized by mammals. However, it is fermented by certain bacteria, yeasts, and fungi, particularly gastrointestinal bacteria. The end products of microbial fermentation are utilized by the host in oxidative metabolism. Here we investigate the degree to which intestinal bacteria of A. namaquensis contribute to xylose metabolism. Mice were caught during Protea humiflora flowering and nonflowering seasons and given an oral dose of 14C-labeled xylose. Exhaled CO2 and excreted urine and feces were continuously collected for 30 h thereafter, and label recovery was determined. Each mouse was then treated with antibiotics to reduce gut microflora, and the experiment was repeated. With their natural gut flora population intact, mice caught during the flowering season exhaled significantly more 14CO2 than did mice caught during the nonflowering season. Also, during both seasons, mice exhaled significantly more 14CO2 before antibiotic treatment than after. Antibiotic treatment caused a significant increase in the proportion of 14C-labeled xylose that was excreted in the urine. The mouse diet likely influences the composition of the gastrointestinal community. Aethomys namaquensis relies on its gut microflora to ferment xylose, thereby converting it into end products that are used by the mice for metabolism.

Ingestion of resistant starch protects endotoxin influx from the intestinal tract and reduces D-galactosamine-induced liver injury in rats

BACKGROUND AND AIMS

The aim of the present study was to examine the protective effect of a dietary high-amylose cornstarch (HAS) against D-galactosamine (D-GalN)-induced liver injury, focusing specifically on intestinal endotoxin translocation.

METHODS

Male Wistar rats fed a HAS-free basal diet or a 30% HAS-supplemented diet were injected intraperitoneally with D-GalN. Serum transaminase activities, serum concentrations of tumor necrosis factor (TNF)-alpha, and portal venous endotoxin concentrations were determined at various time points. Ileal mucosal proliferation, small intestinal immunoglobulin (Ig)A and mucin, and the size of the cecal short-chain fatty acids (SCFA) pool were also determined.

RESULTS

High-amylose cornstarch ingestion significantly reduced the increase in serum transaminase activities at 22 h after the injection of D-GalN. Rats fed the HAS diet showed a greater cecal SCFA production as measured by pool size than those fed the basal diet. Luminal IgA and mucin content were significantly greater in rats fed the HAS diet. Protein, DNA and RNA contents in the ileal mucosa were also higher in rats fed the 30% HAS diet. In a further experiment, portal venous endotoxin concentrations in rats fed the basal diet reached 72 ng/L at 4 h after D-GalN administration, but endotoxin was not detected in rats fed the HAS diet. At this time, portal endotoxin concentrations were significantly and positively correlated with the serum concentrations of TNF-alpha and serum alanine aminotransferase activities.

CONCLUSION

These data support the view that HAS ingestion may reduce D-GalN-induced liver injury as a result of an inhibitory effect on endotoxin influx from the intestinal tract, at least in part as a result of alterations in the mucosal barrier functions.

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.

Fiber digestion and energy utilization of fat sand rats (Psammomys obesus) consuming the chenopod Anabasis articulata

Most herbivorous rodents consume a variety of plants and, when available, select ones low in fiber content. In contrast, the fat sand rat (Psammomys obesus), a diurnal gerbillid rodent that is wholly herbivorous, is able to survive while consuming only the halophytic chenopod Anabasis articulata. We hypothesized that these gerbils are able to digest chenopods efficiently and that fiber digestion contributes substantially to their energy budget. Digestibility of total fibers (NDF), hemicellulose, and cellulose was 51.6%, 66.4%, and 44.0%, respectively. Energy derived from fiber digestion was 211.7 kJ kg(-0.75) d(-1) and resulted mostly from hemicellulose digestion. Average daily metabolic rate was 658.4 kJ kg(-0.75) d(-1), and basal metabolic rate (BMR) was determined to be close to 192.6 kJ kg(-0.75) d(-1). Therefore, fiber digestion provided 32% of maintenance requirements and 110% of BMR requirements, one of the highest values reported thus far for placental mammals. The efficiency of utilization of the chenopod was 0.29, a low value compared to other dietary items. We concluded that A. articulata fulfills all the energy and nutrient requirements of fat sand rats, even though energy yields and efficiency of utilization of its energy is low.

Fiber digestion and weight gain in guinea pigs fed diets containing different fiber sources

The effects of different fiber sources on feed intake, weight gain and digestibility of fiber were examined in guinea-pigs fed pelleted diets containing alfalfa meal, oaten hay, beet pulp and commercial hay cubes mixed with a basal diet at ratios of 3:1 (75% in the diet), 1:1 (50%) and 1:3 (25%). The basal diet contained 50.0% corn, 4.1% wheat, 22.1% wheat flour and 17.7% corn gluten meal. Food intake increased as the amount of fiber source was increased, but not in the case of beet pulp. The most digestible fiber (ADF and NDF) was that of beet pulp. Apparent digestibility of dry matter decreased with increasing ratios of fiber source to the basal diet for all fiber sources, but fiber and crude protein digestibilities varied and depended not only on the ratio of fiber to the basal diet but also on the source of the fiber.

Short-chain fatty acid-supplemented total parenteral nutrition improves nonspecific immunity after intestinal resection in rats

BACKGROUND

Total parenteral nutrition (TPN) alters both specific and nonspecific immune functions, resulting in immunosuppression. Short-chain fatty acids have been shown to improve the adaptive responses of the gut after surgery. The following study investigates the effects of adding short-chain fatty acids to TPN on the immune system after an 80% small bowel resection.

METHODS

Rats (237 +/- 3 g) were infused with either TPN (n = 25) or TPN supplemented with short-chain fatty acids (n = 26) for 3 or 7 days. Hematologic analysis was performed on peripheral blood and splenocytes were isolated to characterize cell phenotypes, natural killer cell cytotoxicity and to estimate proliferative response.

RESULTS

The relative percent of T (CD3+) cells increased (p < .05) and the relative percent of macrophages decreased (p < .001, n = 13) in the spleens of the 3-day TPN-fed rats. By day 7, these differences disappeared. The natural killer cells from rats that were supplemented with short-chain fatty acids had higher (p < .0001) cytotoxic activity than the TPN groups at day 3. Mitogenic response did not differ between groups but were depressed compared with sham-treated rats. By day 7, rats on standard TPN had larger (p < .0001) spleens than all other groups. This group also had a higher total white blood cell count because of increased numbers of macrophages and neutrophils (p < .02).

CONCLUSION

Short-chain fatty acids improve components of nonspecific immune responses and may be beneficial in reducing certain aspects of TPN-associated immunosuppression after major surgery.

Evaluation of fermentability of acid-treated maize husk by rat caecal bacteria in vivo and in vitro

Fermentable energy in insoluble dietary fibre (DF) sources was evaluated by in vivo and in vitro methods using rats. Test diets contained 50 and 100 g maize husk or organic-acid-treated maize husk/kg diet. Soluble fractions were removed from both the DF sources by washing. The acid treatment increased digestibility by a microbial hemicellulase from 12.7% to 32.6%. The fermentability of DF was evaluated by measurement of the production rate of short-chain fatty acids (SCFA) in a short-term in vitro incubation of the caecal contents of rats fed on test diets for 22 d. The production rates of the major SCFA, acetic, propionic and butyric acids, were increased by feeding both DF sources, and these production rates in the acid-treated DF group were significantly higher than those in the untreated DF group. The production rate of a minor SCFA, isovaleric acid, was decreased by feeding both diets. The production rate of total SCFA in rats given the acid-treated maize husk was 32.6% higher than that in rats given the untreated maize husk. The fermentable energy in DF was estimated in vivo by subtracting the faecal excretion of DF energy from ingested DF energy. The fermentable energy in DF was increased by the acid treatment (32.5% in maize husk and 63.4% in acid-treated maize husk), which agreed with the SCFA production rate predicted in the caecum. These results indicate that a short-term incubation of caecal contents is a useful method for evaluation of the fermentability of DF sources, and that acid treatment can increase the fermentability of an insoluble DF source.

Short-chain fatty acids, lactate, and ammonia in ileorectal and ileal pouch contents: a model of cecal fermentation

Fecal concentrations of total short-chain fatty acids were normal in 16 patients with ileorectal anastomoses (mean +/- SEM, 99.7 +/- 10.3 mmol/L) and 28 patients with ileal pouch-anal anastomoses (138.8 +/- 8.5 mmol/L) and did not differ from those in 14 healthy noncolectomized controls (130.7 +/- 12.6 mmol/L). Acetate:propionate:butyrate:isobutyrate+valerate+isovalerate ratios were similar in the ileorectum (71:12:12:5%) and in the colorectum (66:14:13:7%) of healthy noncolectomized controls, whereas the concentration of acetate was increased at the expense of the polypeptide-derived isobutyrate, valerate, and isovalerate in the ileal pouch (77:12:11:1%). Ammonia was accordingly significantly diminished in ileal pouch contents (28.8 +/- 3.2 mmol/L vs 45.2 +/- 4.1 mmol/L in controls) in contrast to concentrations in ileorectal contents (36.2 +/- 5.3 mmol/L). Concentrations of lactate were normal and low. Twenty-four-hour productions of total short-chain fatty acids in 16.6% fecal homogenates from both groups of patients were normal. Addition of saccharides (eg, glucose, starch, pectin, ispaghula husk) increased the production of acetate, propionate, and butyrate and decreased the production of ammonia and isobutyrate, valerate, and isovalerate, which was increased in homogenates with albumin added. This pattern of substrate fermentation was similar in homogenates from ileal pouch, ileorectum, and control colorectum. In conclusion, the concentrations of short-chain fatty acids, lactate, and ammonia indicate that ileorectal fermentation resembles normal colorectal fermentation in noncolectomized healthy individuals, whereas the fermentation in ileal pouch contents seems to be more carbohydrate predominated.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the lipid and fatty acid composition of rat caecal mucosa: effect of intestinal resection

The lipid composition and the fatty acid profile of the lipid fraction (phospholipid, triacylglycerol, diacylglycerol and cholesterol ester) of the caecum were studies 6 weeks after both 50% and 75% distal small bowel resection (DSBR). Triacylglycerol (TG) and cholesterol ester (CE) levels were decreased after resection but the total phospholipid (PL), free cholesterol (FC), and diacylglycerol (DG) contents were not significantly modified after the operation. Different fatty acid changes in the caecum lipid fractions were found after the surgical operation, with the greatest differences after 75% DSBR. Saturated fatty acids were increased in PL, TG and CE fractions as a consequence of DSBR. Similarly, these fractions presented the lowest amounts of n-6 and polyunsaturated fatty acids after resection. On the contrary, the levels of saturated fatty acids was decreased and both n-6 and polyunsaturated fatty acid levels increased in the DG fraction of resected animals. These results are discussed in terms of adaptation to intestinal resection.

Lipid composition, phospholipid profile and fatty acid of rat caecal mucosa

In this study, we examined the lipid composition of rat caecal mucosa, including the fatty acid composition of major phospholipid classes. Phospholipids accounted for 90% of the total lipid, with cholesterol, triacylglycerols, diacylglycerols, fatty acids and cholesterol ester making up the remainder. Therefore, a phospholipid to neutral lipid ration of 9:1 was found. Phosphatidylethanolamine was the predominant phospholipid, with phosphatidylcholine as the second most abundant phospholipid. Cardiolipin, phosphatidylserine, phosphatidylinositol and lysophosphatidylcholine were present in lesser amounts. Sphingomyelin and lysophosphatidylethanolamine were only detected in trace amounts. The major fatty acids present in both the lipid and all phospholipid fractions were palmitate, stearate, oleate, linoleate and arachidonate. Other fatty acids of chain length greater than C20 were only detected in phospholipid fraction and accounted for < 5% of the total fatty acids in this fraction. However, 11.10% of 22:6 (n-3) and 7.17% of 24:0 were detected in phosphatidylserine and lysophosphatidylcholine, respectively. The results are discussed in terms of their possible physiological significance.

Short-chain fatty acids in pouch contents from patients with and without pouchitis after ileal pouch-anal anastomosis

Fecal concentrations of short-chain fatty acids were markedly reduced in 6 patients with pouchitis (mean +/- SE, 56.2 +/- 13.3 mmol/L) compared with 28 patients without pouchitis (139.0 +/- 8.5 mmol/L; P less than 10(-3)). The ratios of acetate to propionate to butyrate were not changed (pouchitis, 75:12:11%; normal pouches, 76:12:11%), i.e., all acids were equally reduced. The 24-hour production of total short-chain fatty acids in 16.6% fecal homogenates from patients with pouchitis was decreased (17.5 +/- 5.3 mmol/L) compared with patients without pouchitis (33.3 +/- 3.4 mmol/L; P less than 0.05), which could be overcome by the addition of saccharides to the homogenates. Pouch excretions of saccharides were similar in the two groups, but dilution occurred during pouchitis because of the increased outputs. Concentrations and productions of short-chain fatty acids correlated with pouch concentrations and excretions of sodium and saccharides. L-Lactate was elevated in pouchitis outputs, but differences in stool culture counts, mucosal histology, fecal concentration, assimilation or production of ammonia, nitrogen excretion, pH, and osmolality were not found. Pouchitis is characterized by decreased fecal concentrations and productions of short-chain fatty acids possibly caused by low pouch concentrations of fermentable saccharides.

Selection of optimal lipid sources in enteral and parenteral nutrition

The manipulation of dietary fat intake can affect the response to disease, injury, and infection. These effects include enhancement or inhibition of immune function, altered susceptibility to cardiovascular disease, promotion or maintenance of gut integrity, and prevention of total parenteral nutrition-induced hepatic dysfunction. These effects may occur as a result of changes in the fatty acid composition of biomembranes or changes in concentrations of lipid moieties such as prostaglandins or leukotrienes. Those fats that have been shown to affect physiologic function include long-chain, medium-chain, and short-chain fatty acids and omega-3 and omega-6 fatty acids. Currently available enteral and parenteral products used for nutrition support contain widely varied amounts of these different fatty acids. Therefore, the selection of the most appropriate product or nutrition support regimen for an individual patient requires an understanding of the metabolism of these different fat substrates, their therapeutic indications, and the contraindications and controversies that surround their use. This article reviews these issues and also focuses on several alternate lipid sources such as short-chain fatty acids, medium-chain fatty acids, omega-3 fatty acids, and blended and structured lipids.

Determination of phospholipid fatty acid and triacylglycerol composition of rat caecal mucosa

The lipid composition of rat caecal mucosa, including the fatty acid composition of phospholipids and triacylglycerols, has been examined by capillary gas chromatography. Thirty-seven peaks were resolved, ranging in chain length from 12 to 24 carbon atoms. Preliminary identification of fatty acids by comparison with authentic standards was confirmed by gas chromatography-mass spectrometry using electron-impact ionization. The neutral and polar components were examined. Fatty acid methyl esters were quantified in absolute amounts with respect to the percentage of total phospholipid and triacylglycerols. The results show significantly higher levels of 16:0, 18:0, 18:1(n-9), 18:1(n-7), 18:2(n-6) and 20:4(n-6) in phospholipids, and higher levels of 16:0, 18:1(n-9) and 18:2(n-6) in triacylglycerols. On the other hand, analysis of caecal triacylglycerols revealed sn-glycerol-palmitate-oleate-palmitate, sn-glycerol-palmitate-linoleate-palmitate and sn-glycerol-palmitate-linoleate-oleate as major components.

Fermentable fibers and vitamin B12 dependency

Addition of the fermentable fiber pectin to a B12-deficient diet accelerates development of deficiency symptoms. This appears to be the result of changes in the intestinal bacteria that bind vitamin B12, interfere with enterohepatic circulation, and accelerate depletion of this vitamin.

Microbial H2/CO2 acetogenesis in animal guts: nature and nutritional significance

The intestinal tract of invertebrate and vertebrate animals, including man, is an anoxic habitat wherein microbial formation of acetate from H2 + CO2 is often a major H2-consuming reaction. This paper will discuss the magnitude and microbiology of H2/CO2 acetogenesis in animal guts, its impact on host animal nutrition, competition for H2 between anaerobic microbes, and the global significance of intestinal H2/CO2 acetogenesis.

Metabolic and intestinal effects of short-chain fatty acids

Current research has identified the metabolic and intestinal effects of SCFA in experimental models and humans. Ample physiologic rationale has come forth to justify controlled studies of the administration of SCFA in selected patients with intestinal dysfunction.

Cecectomized rat. A model of experimental secretory diarrhea in conscious animals

Evaluation of antisecretory antidiarrheal agents in animal models is limited primarily to extrapolations of efficacy from enteropooling studies in vivo, isolated intestinal loops in situ, and Ussing flux chamber preparations in vitro. While these standard techniques are useful, they do not mimic secretory diarrhea. Our studies indicate that in rats, the cecum may serve a "reservoir" function in response to secretagogue administration. Thus, diarrhea is not observed consistently and reliably in this species to allow valid evaluation of potential antidiarrheal agents. Therefore, we have developed a reproducible model of secretory diarrhea utilizing conscious cecectomized rats by surgical resection of the cecum, without compromising ileocecal patency, and by the use of potent intestinal secretagogues. Animals quickly recover and maintain normal growth and other physiologic parameters for as long as 60 days. After 48 hr on standard chow, secretory diarrhea can be induced by oral administration of standard intestinal secretagogues (dimethyl prostaglandin E2, cholera toxin, or carbachol). Dimethyl prostaglandin E2 (300 micrograms/kg, p.o.) induces diarrhea within 1 hr that continues for approximately 3.5 hr. Oral administration of known antidiarrheal agents chlorpromazine (10 mg/kg), clonidine (1 mg/kg), or morphine (10 mg/kg) all significantly reduce fecal output within 30-60 min following administration. These studies indicate that in the rat, the cecum may serve as a fluid reservoir during periods of small intestinal hypersecretion and that the cecectomized rat serves as a useful, accurate, and reliable tool for evaluating new compounds with proposed antidiarrheal activity.

Stimulation of intestinal mucosal growth with intracolonic infusion of short-chain fatty acids

Dietary fiber, which stimulates intestinal mucosal growth, is fermented by anaerobic bacteria in the rat hindgut to the short-chain fatty acids (SCFA) acetate, propionate, and butyrate. Butyrate is the preferred oxidative fuel of the colonocyte in vitro, and the provision of preferred intestinal fuels has been shown to stimulate mucosal proliferation in vivo. This study determined whether chronic colonic infusion of butyrate or a combination of SCFA would stimulate intestinal mucosal growth in an animal deprived of its normal source of SCFA, fiber fermentation in the cecum. Adult male Sprague-Dawley rats were fed a fat- and fiber-free elemental liquid diet and underwent cecectomy, ileocolic anastomosis, and insertion of a proximal colonic infusion catheter. Rats were then assigned to receive either a continuous infusion of butyrate (20 mM, 40 mM, or 150 mM), SCFA (70 mM acetate + 35 mM propionate + 20 mM butyrate), or saline, or to receive no infusion. A seventh group underwent proximal colonic transection and reanastomosis. After 7 days, jejunal, ileal, and proximal colonic segments were analyzed for mucosal weight, protein, RNA, and DNA. In the colon, the 40-mM butyrate infusion resulted in significant elevations in all mucosal parameters relative to all three control groups, saline infusion, no infusion, and transection. Both the 20-mM butyrate and the SCFA groups showed increased colonic mucosal DNA compared to controls. In the jejunum and ileum, mucosal DNA content was significantly greater in the SCFA group than in the control groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidative metabolism of rabbit and rat intestine with short chain fatty acids and glucose: an evaluation of data analysis

1. Glucose sustained VO2 of rabbit ileum, caecum, and distal colon better than SCFAs. 2. In rabbit proximal colon, while VO2 was stimulated in the presence of butyrate it was not sustained. 3. Rat caecum utilized glucose but it was not necessarily the best substrate for either the ileum or colon of this species and SCFAs appeared to stimulate VO2 of rat ileum and inhibit VO2 in rat caecum and colon. 4. It was concluded from the comparison of the two methods of data analyses that curve-fitting the data by a negative exponential equation provides for a more clear and in depth interpretation of such studies.

Effect of parenteral nutrition supplemented with short-chain fatty acids on adaptation to massive small bowel resection

After massive small bowel resection, total parenteral nutrition (TPN) is prescribed to maintain nutritional status. However, TPN reduces the mass of the remaining intestinal mucosa, whereas adaptation to small bowel resection is associated with increased mucosal mass. Short-chain fatty acids (SCFAs) have been shown to stimulate mucosal cell mitotic activity. This study determined whether the addition of SCFAs to TPN following small bowel resection would prevent intestinal mucosal atrophy produced by TPN. Adult rats underwent an 80% small bowel resection and then received either standard TPN or TPN supplemented with SCFAs (sodium acetate, propionate, and butyrate). After 1 wk, jejunal and ileal mucosal weights, deoxyribonucleic acid, ribonucleic acid, and protein contents were measured and compared with the parameters obtained at the time of resection. Animals receiving TPN showed significant loss of jejunal mucosal weight, deoxyribonucleic acid, ribonucleic acid, and protein and ileal mucosal weight and deoxyribonucleic acid after small bowel resection, whereas animals receiving SCFA-supplemented TPN showed no significant change in the jejunal mucosal parameters and a significant increase in ileal mucosal protein. These data demonstrate that SCFA-supplemented TPN reduces the mucosal atrophy associated with TPN after massive bowel resection and thys may facilitate adaptation to small bowel resection.

Fermentation of polysaccharides and absorption of short chain fatty acids in the mammalian hindgut

1. Hindgut volume varies considerably between carnivores, omnivores and herbivores. But a common feature in all mammals is an extensive microbial fermentation of polysaccharides in the hindgut. Large amounts of short chain fatty acids (SCFA) are produced. Total concentrations of SCFA are generally ca 100 mmol/l. SCFA metabolism contributes considerably to the energy metabolism of the animal. 2. In hindgut fermenting herbivores ileal outflow provides fluid and the buffering capacity essential for microbial metabolism. 3. SCFA are rapidly absorbed. Absorption is passive and, unexpectedly, nearly independent from luminal pH. This is attributed to the presence of a constant pH-microclimate at the epithelial surface. 4. The permeability of the proximal compared to the distal colon of guinea pig is higher for acetate, equal for propionate and lower for butyrate. This difference is due to partial absorption of SCFA in the dissociated form in the proximal segment. 5. Protons required for SCFA transport in the undissociated form may be partially explained by HCO3 accumulation or by Na-H exchange. Findings are controversial.

Effect of dietary fiber on colonic cell proliferation and its relationship to colon carcinogenesis

The addition of specific fiber supplements to semipurified diets has been shown to stimulate large bowel cell proliferation in laboratory rodents. Relatively insoluble fibers such as cellulose, which is poorly fermented, the more-soluble oat bran, and inert bulking agents such as kaolin produce little or no effect on cell growth. On the other hand, wheat bran, pectin, guar gum, and degraded carageenan all stimulate large bowel cell proliferation, the greatest growth response tending to occur in the cecum or proximal colon. The proximal large bowel is also the major site for the intestinal fermentation of dietary fiber and any other nonabsorbed carbohydrates. The fermentation of fiber by colonic microorganisms results in the production of short-chain fatty acids and a lower pH of large bowel contents, metabolic events known to be associated with increased epithelial cell growth. In general, factors that stimulate cell growth also enhance tumor development, a concept that holds true in the colon even for dietary fibers such as pectin and guar gum. Wheat bran can also stimulate colon carcinogenesis when fed only during carcinogen exposure. Oat bran and corn bran may stimulate colon carcinogenesis by increasing fecal bile acid excretion, a feature of many soluble fibers, while the acidification of large bowel contents is associated with an increased frequency of chemically induced colonic cancers. A greater understanding of colonic metabolism and cell physiology is needed to define fully the mechanisms by which dietary fibers modify colon cancer development.

Stimulatory effect of short-chain fatty acids on epithelial cell proliferation in the rat intestine: a possible explanation for trophic effects of fermentable fibre, gut microbes and luminal trophic factors

1. Effects of short-chain fatty acids (SCFA) on epithelial proliferation of the intestine were studied in ileally fistulated rats fed on an elemental diet. 2. The stimulatory effect of daily doses of acetic, propionic and n-butyric acids (100, 20 and 60 mM respectively; pH 6.1) per fistula (3 ml, twice daily) on crypt cell production rate (CCPR) appeared within 2 d and lasted for at least 5 d. 3. The daily doses of SCFA for 14 d increased daily CCPR three to four fold. This effect was independent of the presence of gut bacteria. 4. Effects of SCFA were dose-dependent and varied among acids (butyrate greater than propionate greater than acetate). The effect was independent of low lumen pH. 5. In contrast, SCFA inhibited epithelial proliferation of isolated rat caecal tissue in vitro. 6. These results suggest that SCFA are physiological lumen trophic factors mediated by a systemic mechanism in vivo. 7. It is concluded that SCFA are involved in the trophic effects of gut microbes, ingestion of fermentable fibre, and lumen contents.

Occurrence, absorption and metabolism of short chain fatty acids in the digestive tract of mammals

Short chain fatty acids (SCFA) also named volatile fatty acids, mainly acetate, propionate and butyrate, are the major end-products of the microbial digestion of carbohydrates in the alimentary canal. The highest concentrations are observed in the forestomach of the ruminants and in the large intestine (caecum and colon) of all the mammals. Butyrate and caproate released by action of gastric lipase on bovine milk triacylglycerols ingested by preruminants or infants are of nutritional importance too. Both squamous stratified mucosa of rumen and columnar simple epithelium of intestine absorb readily SCFA. The mechanisms of SCFA absorption are incompletely known. Passive diffusion of the unionized form across the cell membrane is currently admitted. In the lumen, the necessary protonation of SCFA anions could come first from the hydration of CO2. The ubiquitous cell membrane process of Na+-H+ exchange can also supply luminal protons. Evidence for an acid microclimate (pH = 5.8-6.8) suitable for SCFA-protonation on the surface of the intestinal lining has been provided recently. This microclimate would be generated by an epithelial secretion of H+ ions and would be protected by the mucus coating from the variable pH of luminal contents. Part of the absorbed SCFA does not reach plasma because it is metabolized in the gastrointestinal wall. Acetate incorporation in mucosal higher lipids is well-known. However, the preponderant metabolic pathway for all the SCFA is catabolism to CO2 except in the rumen wall where about 80% of butyrate is converted to ketone bodies which afterwards flow into bloodstream. Thus, SCFA are an important energy source for the gut mucosa itself.

Caecal size and function in the rock elephant shrew Elephantulus myurus (Insectivora, Macroscelididae) and the Namaqua rock mouse Aethomys namaquensis (Rodentia, Muridae)

1. The relative size of the digestive organs and the function of the caeca of an insectivorous elephant shrew Elephantulus myurus (Macroscelididae) and of a herbivorous rodent Aethomys namaquensis (Muridae) were compared. 2. Both species had similar body mass but A. namaquensis had a significantly heavier total digestive tract, full stomach, and caecum and a longer large intestine and caecum than E. myurus. 3. Both species had similar total volatile fatty acid (VFA) concentration and VFA % composition although A. namaquensis had a significantly higher % of n-butyric acid. Both had a similar caecal NH3-N concentration. 4. The presence of a functional caecum in E. myurus supports the view that Macroscelididae have evolved from ancestral herbivores and not from insectivores.

[Use of sugar beet in porcine nutrition. 1. Effect of various methods of treatment on the gastrointestinal tract]

The influence of the size of particles, of steaming and preserving (formic acid) of the sugar beet 'Rosamona' was studied with respect to apparent digestibility and tract parameters. Digestibility measuring only resulted in an improvement for crude protein due to the cutting up into small pieces. Tract measures and fillings, microbial activity and an estimate of the absorption rates of nutrients indicate that the bigger part of fresh and silaged coarse particles is digested in the colon but that the nutrients of steamed (and partly mashed) beets are predominantly pre-caecally digested.

An experimental design to study colonic fibre fermentation in the rat: the duration of feeding

1. The time-course of metabolic adaptation by rats to diets containing either wheat bran or gum arabic was studied during a 12-week period. 2. Stool weight was increased with wheat bran but not with gum arabic, and had stabilized after 4 weeks. 3. Bacterial mass as measured by diaminopimelic acid content had stabilized by week 4. Bacterial mass increased on feeding gum arabic but was unchanged with wheat bran. 4. There was increased caecal short-chain fatty acid, hydrogen and methane production with gum arabic but not with wheat bran. The change in caecal metabolic activity was slow to stabilize (8-12 weeks at least). 5. The faecal excretion of bile acids increased twofold with the wheat-bran-supplemented diet compared with the gum-arabic-supplemented and unsupplemented diets. Relatively greater amounts of muricholic acids were present in the caeca and faeces of gum-arabic-fed rats compared with the other groups.

[Effect of bran diet on organic acids in the gastrointestinal tract and apparent digestibility in weanling piglets]

Over a period of four weeks 88 piglets of an average weaning weight of 9.5 kg received rations with 2.1, 3.1 and 5.5% crude fibre in the original substance in the form of wheat bran. Between the 42nd and 49th day of life a digestibility investigation was carried out by means of Cr2O3, and on the 42nd and the 63rd day of life the organic acids in the complete gastro-intestinal tract could be ascertained, the causes of which are to be found in the lack of easily soluble carbohydrates (increased passage rate, bran quota). Due to crude fibre, the apparent digestibility of all nutrients decreased, which resulted in a lower live weight on the 63rd day of life. The effect of a bran diet in the alimentary prophylaxis of coli enterotoxaemia is thus furthermore substantiated.

Role of volatile fatty acids in colonization resistance to Clostridium difficile

The in vitro inhibition of Clostridium difficile by volatile fatty acids was correlated with the pH and concentrations of volatile fatty acids in the ceca of hamsters of different ages. The concentrations of cecal volatile fatty acids increased with the age of the animals. Maximum concentrations of individual volatile fatty acids were attained when the animals were ca. 19 days old, with acetic, propionic, and butyric acids occurring in the highest concentrations (72, 16, and 32 microequivalents/g of cecum, respectively). The cecal pH was approximately the same in hamsters of all ages (pH 6.6 to 7.0). Only butyric acid reached a concentration in the ceca of hamsters which was inhibitory to the in vitro multiplication of C. difficile. This inhibitory concentration was attained when the animals were ca. 19 days of age. When mixtures of volatile fatty acids were prepared at concentrations equal to those present in the ceca of hamsters, there was a direct correlation between the in vitro inhibitory activity of the volatile fatty acids and the susceptibility of hamsters 4 days of age or older to C. difficile intestinal colonization. The resistance of hamsters less than 4 days of age to C. difficile intestinal colonization appears to be due to factors other than volatile fatty acids.

Effects of increasing the fibre content of a layer diet

The fibre content of a basal diet fed to laying hens was increased from 149.2 g to between 218.6 and 292.3 g/kg by the inclusion of various fibrous farm wastes and by-products at 200 g/kg diet. The fibrous ingredients lowered the metabolisable energy (ME) of the basal diet from 11.82 to between 9.31 and 11.21 MJ/kg. Utilisation (g food/kg egg) of the basal diet was not significantly different from values for diets containing maize cob, cassava or maize starch residues. The diet containing maize cob supported a performance similar to that of the basal diet, despite a lower energy content (10.08 MJ/kg). Diets containing cowpea shell, cassava peel or sawdust, with lower energy contents, and those containing maize starch residue, palm kernel meal or dried brewers grains, with higher energy contents, were not as good. The diet containing cassava starch residue supported similar egg production to the basal but egg size was less. Inclusion of some of the fibre sources caused slight decreases in yolk cholesterol, although this could not be correlated with dietary fibre content. Additional dietary fibre caused slight increases in gizzard weight but this was also not simply related to dietary fibre content.

Factors in the control of feed intake of horses and ponies

Ponies are large nonruminant herbivores which are capable of utilizing the products of both enzymatic digestion in the small intestine and bacterial fermentation (volatile fatty acids, VFAs) in the cecum and large colon as sources of metabolizable energy. Recent studies have demonstrated that ponies utilize nutrient stimuli from both carbohydrate and fat digestion in the small intestine and VFAs in the cecum and large colon in the control of meal frequency. These animals, however, rely primarily upon oropharyngeal and external stimuli to control the size and duration of meals. This is perhaps an adaptation to a feeding pattern of small frequent meals and food sources which provide significant amounts of nutrients to the animal system only after microbial fermentation in the hind gut. Nutrient cues which are operant in controlling feed intake in omnivores, carnivores, and ruminants appear to be important primarily in the regulation of meal frequency and long-term energy balance in the equine animal. The emphasis on oropharyngeal stimuli in the immediate control of feed intake of ponies reflects the unusual digestive physiology of these animals relative to other species studied to date.

The influence of dietary fibre on caecal metabolism in the rat

The influence of three diets ((1) high-fibre - low-fat, (2) low-fibre - high-fat, (3) commercial breeding diet) on the concentration of short chain fatty acids (SCFA) has been investigated in male and female rats up to 14 weeks of age. Hydrogen was detected in respired gas in all rats with no significant differences between diets or sex. Methane was detected only in control-fed rats at 12 weeks of age and thereafter. Caecal contents contained higher concentrations of SCFA than were found in faeces. There were no significant differences in the total faecal SCFA excreted by rats on the three diets. The proportions of SCFA in the caecum and faeces were influenced by diet. The production and excretion of hydrogen, methane and SCFA in the rat appeared to reflect different aspects of bacterial metabolism. Comparison of caecal and faecal SCFA may indicate differential absorption from the colon or differential metabolism by bacteria or colonic mucosa which may be influenced by diet.

Influence of diet and microbial activity in the digestive tract on digestibility, and nitrogen and energy metabolism in rats and pigs

1. Balance trials with respiration measurements were performed with twelve rats and twelve pigs given either low- or high-crude-fibre diets. There were six collection periods with the rats over a live-weight range of 86-264 g and three collection periods with the pigs over a live-weight range of 30-55 kg. Measurements were made on the influence of microbial activity in the digestive tract on digestibility and nitrogen and energy metabolism. Dietary inclusion of the antibiotic Nebacitin was the method used to reduce the microbial population. 2. The microbial activity in the hind-gut (mumol ATP/g air-dry contents) of antibiotic-treated rats was reduced to approximately one-tenth of that of untreated rats. 3. Live-weight gain was not significantly affected in either species by a reduction in the microbial activity, in spite of a reduction in dry matter digestibility in animals with reduced microflora. 4. For rats on low-crude-fibre diets, a reduction in microflora reduced digestibility of all nutrients and energy and metabolizability of digestible energy by approximately 5.4%. All differences were highly significant. On high-crude-fibre diets the decrease was approximately 5.9%. In pigs on both crude fibre levels, the digestibility was also influenced by the level of microflora, but the pattern was somewhat different from that obtained with rats, with the Nebacitin treatment increasing the digestibility of N slightly, and the digestibility of fat markedly. 5. Retained N in rats reached a maximum when the rats were approximately 60 d old and thereafter decreased with increasing age. However, for pigs daily N retention increased with age. The retained N: digested N value decreased linearly with age in the rats, but varied little with age over the range (104-146 d) studied in the pigs. 6. The metabolizability of gross energy (metabolizable energy (ME): gross energy) was significantly reduced with an increase in crude fibre level and by the addition of Nebacitin. 7. Retained energy (RE) in relation to ME (RE:ME), was not significantly affected either by level of microbial activity or by crude fibre. 8. The ratio, RE as fat (RF): RE as protein (RP) increased as the animals grew. In the rat experiment there was a tendency for RP to be higher for animals with normal microflora than for animals with reduced microflora for both crude fibre levels. 9. With rats, the regression analyses indicated that the energy requirement for maintenance could be influenced by both the level of microbial activity in the digestive tract and by the level of fibre in the diet. The net availability of ME for maintenance and growth by rats averaged 0.72 for all treatments. 10. The net availability of ME for growth in the pigs averaged 0.65 for all treatments.

Methylmalonic acid metabolism of germfree and conventional vitamin B-12 deprived rats fed precursors of methylmalonate

Experiments using germfree (GF), ex-germfree (XGF) and conventional (CONV) rats were conducted to study the relationship of intestinal microorganisms to vitamin B-12 (B-12) status and to methylmalonic acid (MMA) excretion of the host animal, since B-12 depleted GF rats have been found to excrete less than expected level of urinary MMA. The possibility that the GF rat lacks sufficient precursor of MMA was tested by feeding GF, XGF and CONY rats diets low or high in MMA precursors and examining urinary excretion of MMA and formiminoglutamic acid at intervals. The possibility that the GF rat may metabolize propionate and MMA differently from the CONV rat was examined by a MMA loading-recovery study and a CO2 collection study after [14C]propionate injection. Plasma and tissue B-12 levels were determined at the beginning and the end of the study. Results indicate that 1) lack of sufficient precursor of MMA is partly responsible for the failure of GF, B-12 deficient rat to excrete MMA, 2) GF and CONV rats metabolize propionate and MMA by the same pathways and 3) the presence of intestinal microorganism depletes the body B-12 store of the rat.

[Influence of date seed flour and cellulose on growth, food utilization and parameters of fat metabolism of growing and adult rats]

In experiments with growing and adult Wistar-rats, the influence of date-seed flour on growth, food intake/utilization and lipid metabolism was studied. Cellulose powder was used as control substance. Unlike cellulose the date-seed flour increased the food intake and the gained body weights of the animals. The food utilization impaired after supplying both date-seed flour and cellulose. Date-seed flour as source of crude fibers in the diet caused a higher increase of weight and volume of the faeces than equivalent amounts of cellulose. Cellulose fed animals showed a higher crude fiber content of the faeces. The crude fiber of date seeds is supposed to consist of compounds more easily digested than cellulose such as hemicelluloses. Date-seed flour led to a significant increase of serum total lipids and serum cholesterol of growing rats. In the liver of adult rats the neutral fats and total lipids were increased too. A clear fatty infiltration in the liver of growing rats was detected. Cellulose did not significantly influence the lipid metabolism of both growing and adult rats. There must be a certain compound in the date seeds causing this lipid anabolic effect, which is not compensated by their relatively high crude fiber-content.