The effect of dietary mannitol on the caecal microflora and short-chain fatty acids in rats

Wistar rats fed 5%-mannitol diet showed significant decreases of viridans streptococci and bifidobacteria, and a remarkable increase of butyric acid concentration and a decrease of acetic acid in the caecal contents compared with the sucrose and basal diet groups. Stocky fusiform bacteria were increased in concentration in the rats on mannitol compared with the other groups.     

Effects of high dietary cellulose on the large intestinal microflora and short-chain fatty acids in rats

Wistar rats fed diets containing different contents of cellulose or 5% transgalactosylated oligosaccharides (TOS) for 7 weeks were examined for faecal microflora and caecal short-chain fatty acids. High (15%) cellulose diet showed remarkable increases in concentrations of faecal bifidobacteria and caecal butyrate with a reduced concentration of propionate as compared with the other diets. TOS-fed rats showed strikingly increased concentrations of bifidobacteria and acetate. A comparison of pH values between the caecal contents and faeces suggested more fermentation of cellulose in the distal than proximal part of the large bowel of rats.     

乳杆菌胞外多糖对人体粪便菌群及其产生短链脂肪酸的影响

目的在体外利用7名志愿者的新鲜粪便作为来源,选择菊粉作为对照,研究干酪乳杆菌LC2W与鼠李糖乳杆菌Y37胞外多糖对人体肠道菌群的影响。方法利用PCR-DGGE(变性梯度凝胶电泳)方法分析样品中菌群组成,采用高效液相色谱的方法分析短链脂肪酸组成。结果与菊粉相比,粪便菌群在添加乳杆菌胞外多糖培养后,可以促进短链脂肪酸的生成,保持肠道菌群的多样性。结论干酪乳杆菌LC2W与鼠李糖乳杆菌Y37的胞外多糖在体外有调节粪便菌群的作用。     

In vitro production of short-chain fatty acids from resistant starch by pig faecal inoculum

The need to improve the knowledge of fermentation processes within the digestive tract in pigs is growing, particularly for ingredients that may act as potential prebiotic sources, such as resistant starch (RS). A study (based on enzymatic digestion followed by in vitro fermentation) was conducted to investigate whether various sources of RS, obtained from eight native starches characterized by inherent heterogeneous starch chemistry and structure, can influence short-chain fatty acid (SCFA) concentrations and relative production kinetics. Total and individual SCFA productions were evaluated over time and up to 72 h of incubation. The in vitro hydrolysis of native starches allowed a classification from very high [⩾650 g/kg dry matter (DM)] to low (<50 g/kg DM) RS amount. The total SCFA production was similar between ingredients, whereas acetate and butyrate molar ratios in the SCFA profile differed (from 0.48 to 0.56 and from 0.17 to 0.25, respectively; P < 0.05). Differences in fermentation kinetic parameters for total and individual SCFA productions were observed (P < 0.05). Considering the total SCFA production after 72 h of incubation, the time at which half of the maximum production has been reached (T_1/2), the maximum rate of production (R_max) and its time of occurrence (T_max) differed between ingredients (P < 0.05), with values ranging from 6.1 to 11.9 h, from 0.459 to 1.300 mmol/g DM incubated per hour and from 5.1 to 9.8 h, respectively. Overall, a similar trend was observed considering individual SCFA productions. In particular, T_1/2 ranged from 6.4 to 12.5 h, from 5.5 to 12.5 h and from 6.7 to 11.3 h for acetate, propionate and butyrate, respectively (P < 0.05). For R_max, differences were obtained for propionate and butyrate productions (P < 0.05), whereas no difference was recorded for acetate. In summary, our findings indicated that both quantitative and qualitative production of SCFA and related kinetics were influenced by fermentation of RS obtained from native starches characterized by heterogeneous starch characteristics. Current findings are based on an in vitro approach, and thus require further in vivo validations.     

Urea and short-chain fatty acids metabolism in Holstein cows fed a low-nitrogen grass-based diet

Three ruminally cannulated and multicatheterised lactating dairy cows were used to investigate the effect of different supplement strategies to fresh clover grass on urea and short-chain fatty acid (SCFA) metabolism in a zero-grazing experiment with 24-h blood and ruminal samplings. Fresh clover grass was cut every morning and offered from 0800 to 1500 h. Maize silage was fed at 1530 h. The three treatments, arranged in a Latin square, differed by timing of feeding rolled barley and soya-bean hulls relative to fresh clover grass. All diets had the same overall composition. Treatments were soya-bean hulls fed at 0700 h and barley fed at 1530 h (SAM), barley fed at 0700 h and soya-bean hulls fed at 1530 h (BAM), and both soya-bean hulls and barley fed at 1530 h (SBPM). The grass had an unexpectedly low content of crude protein (12.7%) and the cows were severely undersupplied with rumen degradable protein. The treatment effects were numerically small; greater arterial ammonia concentration, net portal flux of ammonia and net hepatic flux of urea during part of the day were observed when no supplementary carbohydrate was fed before grass feeding. A marked diurnal variation in ruminal fermentation was observed and grass feeding increased ruminal concentrations of propionate and butyrate. The net portal fluxes of propionate, butyrate, isovalerate and valerate as well as the net hepatic uptake of propionate, butyrate, valerate and caproate increased after feeding at 0700 h. The hepatic extraction of butyrate showed a relatively large depression with grass feeding with nadir at 1200 to 1330 h. The increased net portal absorption and the decreased hepatic extraction resulted in an approximately six-fold increase in the arterial blood concentration of butyrate. The gut entry rate of urea accounted for 70 ± 10% of the net hepatic production of urea. Saliva contributed to 14% of the total amount of urea recycled to the gut. Urea recycling to the gut was equivalent to 58% of the dietary nitrogen intake. Despite the severe undersupply of rumen degradable protein, the portal-drained viscera did not extract more than 4.3% of the urea supplied with arterial blood. This value is in line with the literature values for cows fed diets only moderately deficient in rumen degradable protein and indicates that cows maximise urea transfer across gut epithelia even when the diet is moderately deficient in rumen degradable protein.     

Headspace solid-phase microextraction with 1-pyrenyldiazomethane in-fibre derivatisation for analysis of faecal short-chain fatty acids

Short chain fatty acids (SFCAs) are nutritionally important products of colonic bacteria. Their analysis in faeces is problematic. We report a headspace solid-phase microextraction procedure in which faecal SCFAs are derivatised on the fibre in-situ with 1-pyrenyldiazomethane. With this method sharp, well-resolved chromatographic peaks were obtained with no interferences. Inclusion of deuterated analogues enabled accurate quantification. Good linearity, recoveries and precision were achieved. Differences observed between the SCFA profiles of normal subjects and patients with cystic fibrosis indicate the potential of this new technique for clinical studies. 2-Methylbutyric acid was found in all faecal samples. Few have reported this before.     

Growth of Rhodocyclus purpureus on short-chain fatty acids

Abstract The ability of Rhodocyclus purpureus to grow on a range of short-chain fatty acids in the light was investigated. Growth on n -valerate, n -hexanoate and n -heptanoate was proportional to concentration. Growth on n -octanoate was proportional to concentration up to 0.04% (w/v), but no growth occurred on 0.05% octanoate. Propionate, n -nonanoate and n -decanoate did not support growth at any concentration tested. None of these fatty acids appeared to be inhibitory, apart from possibly n -nonanoate at 0.05% concentration. However, R. purpureus did not produce propionate as an end product when grown on n -valerate and n -heptanoate, indicating that propionate is utilized when produced intracellularly but not when supplied exogenously.     

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.     

The role of short-chain fatty acids in the interplay between diet,gut microbiota,and host energy metabolism

Short-chain fatty acids (SCFAs), the end products of fermentation of dietary fibers by the anaerobic intestinal microbiota, have been shown to exert multiple beneficial effects on mammalian energy metabolism. The mechanisms underlying these effects are the subject of intensive research and encompass the complex interplay between diet, gut microbiota, and host energy metabolism. This review summarizes the role of SCFAs in host energy metabolism, starting from the production by the gut microbiota to the uptake by the host and ending with the effects on host metabolism. There are interesting leads on the underlying molecular mechanisms, but there are also many apparently contradictory results. A coherent understanding of the multilevel network in which SCFAs exert their effects is hampered by the lack of quantitative data on actual fluxes of SCFAs and metabolic processes regulated by SCFAs. In this review we address questions that, when answered, will bring us a great step forward in elucidating the role of SCFAs in mammalian energy metabolism.     

Changes with time in the oral microflora and dental caries induction in hyposalivated rats fed on sucrose diet.

The effects of hyposalivation on the induction of dental caries and the change in oral microflora were examined at weekly intervals in Sprague-Dawley rats fed on diet 2000 containing 56% sucrose. In hyposalivated rats, significant dental caries was induced within one week and its severity increased with the experimental period. Bacteriological examinations demonstrated that the number of total cultivable microorganisms, lactobacilli and Staphylococcus aureus increased significantly shortly after surgical induction of hyposalivation, while the number of streptococci and yeasts did not increase significantly until the 7th week, beyond which time remarkable gross caries developed. A positive correlation was found between the caries score and the recovery of lactobacilli from mandibles of hyposalivated rats, while there was no statistically significant correlation between the caries score and the recoveries of S. aureus. On the other hand, dental caries was not induced in control rats fed on sucrose diet with no surgically-induced hyposalivation. It was also found that the number of lactobacilli increased significantly shortly after diet 2000 was given to control rats, but S. aureus was rarely recovered from the mandibles of control rats throughout the experiments. The roles of lactobacilli and S. aureus in the induction of dental caries under the hyposalivated condition were discussed and it was suggested that lactobacilli may play some significant role in the induction of dental caries in hyposalivated rats.     

短链脂肪酸对肠黏膜屏障的影响

肠黏膜屏障具有将致病性抗原等肠内物质与内环境隔离的功能,以维持内环境的相对稳定和机体的正常生命活动。其功能的维持依赖于人肠黏膜上皮细胞、肠道内正常菌群、肠道内分泌物和肠相关免疫细胞之间的功能协调,而其功能的发挥又受体内许多信号分子的影响。短链脂肪酸（short-chain fatty acids,SCFAs）就是其中一种重要的信号分子。SCFAs是肠道菌群的主要代谢产物之一,是肠道菌群与宿主代谢相互作用的媒介。宿主体内的SCFAs主要来自肠道菌群对膳食纤维的酵解,越来越多的研究证实,SCFAs不仅可以被肠道菌群利用,还可调节肠黏膜屏障及多种组织器官的代谢。本文主要就SCFAs对肠黏膜屏障的影响进行综述。

     

Effect of dietary short-chain fructooligosaccharides on the cecal microflora in gastrectomized rats

Total gastric resection is known to lead to changes in the microflora in the whole gastrointestinal tract. Dietary short-chain fructooligosaccharides (Sc-FOS) have been shown to also induce a change in the microflora in the large bowel by promoting an increase in the numbers of Bifidobacterium and Lactobacillus which have beneficial effects on the host. In the present study, 4-week-old male Sprague-Dawley rats received total gastrectomy or laparotomy, and each of these surgically treated groups was randomly divided into two experimental diet groups and given a 7.5% Sc-FOS diet or control diet. Enumeration and identification of the cecal bacteria was performed by using selective and non-selective media. In the gastrectomized rats, the total bacterial count, and the counts of Bacteroidaceae and Enterobacteriaceae were higher than those in the sham-operated rats. Sc-FOS promoted an increase in the numbers of Bifidobacterium and Lactobacillus, In the rats fed on the Sc-FOS diet, the predominant type of bacteria was Lactobacillus and in the rats fed on the control diet, it was Bacteroidaceae irrespective of gastrectomy. We confirmed that both gastrectomy and dietary Sc-FOS changed the composition of cecal microflora in the rats. Dietary Sc-FOS in the gastrectomized rats increased the proportions of Lactobacillus relative to other types of bacteria to levels similar to those seen in healthy normal rats, and decreased the proportion of Bacteroidaceae.     

On the mechanism of the so-called uncoupling effect of medium- and short-chain fatty acids

Octanoate applied to rat liver mitochondria respiring with glutamate plus malate or succinate (plus rotenone) under resting-state (State 4) conditions stimulates oxygen uptake and decreases the membrane potential, both effects being sensitive to oligomycin but not to carboxyatractyloside. Octanoate also decreases the rate of pyruvate carboxylation under the same conditions, this effect being correlated with the decrease of intramitochondrial content of ATP and increase of AMP. The decrease of pyruvate carboxylation and the change of mitochondrial adenine nucleotides are both reversed by 2-oxoglutarate. Fatty acids of shorter chain length have similar effects, though at higher concentrations. Addition of octanoate in the presence of fluoride (inhibitor of pyrophosphatase) produces intramitochondrial accumulation of pyrophosphate, even under conditions when oxidation of octanoate is prevented by rotenone. In isolated hepatocytes incubated with lactate plus pyruvate, octanoate also increases oxygen uptake and produces a shift in the profile of adenine nucleotides similar to that observed in isolated mitochondria. It decreases the ‘efficiency’ of gluconeogenesis, as expressed by the ratio between an increase of glucose production and an increase of oxygen uptake upon addition of gluconeogenic substrates (lactate plus pyruvate), and increases the reduction state of mitochondrial NAD. These effects taken together are not compatible with uncoupling, but point to intramitochondrial hydrolysis of octanoyl-CoA and probably also shorter chain-length acyl-CoAs. This mechanism probably functions as a ‘safety valve’ preventing a drastic decrease of intramitochondrial free CoA under a large supply of medium- and short-chain fatty acids.