早产儿喂养不耐受与肠道菌群关系的研究进展

喂养不耐受是指无法实现肠内营养的目标摄入量的同时出现了胃肠道功能障碍的症状,如大量胃潴留、腹胀、腹泻及呕吐等.菌群与宿主之间的动态平衡是维持机体健康的重要保证,对消化道营养吸收、内脏感知及运动、黏膜免疫以及量代谢调节等起关键作用.随着新一代测序技术的发展,关于早产儿喂养不耐受与肠道菌群的关系有了更深刻的认识,最新研究发...     

草鱼肠道酸碱度的研究

胃肠道是一个复杂的消化系统, 每一部分都具有独特的生理特征。酸碱度(pH)是消化道重要的生理指标之一, 其对营养物质的消化、吸收和肠道微生物的生长等具有重要影响。为了研究草鱼在食物消化过程中, 肠道的酸碱度变化, 测定了草鱼肠道食物糜、肠液和黏膜的pH。结果显示, 随着食物的消化, 它们的pH都有下降的趋势。肠道食物糜pH在6.86±0.24到8.43±0.10之间, 肠液pH在7.14±0.22到8.63±0.02之间, 相同时间点相同肠段两者之间的pH差异很小, 并且在实验期间两者的pH变化趋势相同。黏膜pH在6.23±0.04到6.7±0.13之间, 为弱酸性。除了时间点12h外, 相同时间点和相同肠道部位黏膜的pH与食物糜、肠液的pH相比均有显著性差异(P<0.05)。分析发现草鱼摄食食物的pH与上述三相的pH之间均有显著性差异(P<0.05), 研究结果为草鱼消化生理及营养学研究提供了基础资料。     

Influence of Xylella fastidiosa infection of citrus on host selection by leafhopper vectors

Infection of plants by pathogens can influence their attractiveness and suitability to insect vectors and other herbivores. Here we examined the effects of Citrus sinensis (L.) Osbeck (Rutaceae) infection by the bacterium Xylella fastidiosa, which causes citrus variegated chlorosis (CVC), on the feeding preferences of two sharpshooter vectors, Dilobopterus costalimai Young and Oncometopia facialis (Signoret) (Homoptera: Cicadellidae). Experiments were performed inside observation chambers, in which a healthy plant and an infected one (with or without CVC symptoms) were supplied to a group of 40 sharpshooters. The number of insects that selected each treatment was recorded at several time intervals in 48 h. In another experiment, the ingestion rate on healthy and infected (symptomatic or not) plants was evaluated by measuring the liquid excretion of sharpshooters that were confined on branches of each plant for 72 h. Both sharpshooter species preferred healthy plants to those with CVC symptoms. However, O. facialis did not discriminate between healthy citrus and symptomless infected plants. Feeding by D. costalimai was markedly reduced when confined on CVC‐symptomatic plants, but not on asymptomatic infected ones. The ingestion rate by O. facialis was not affected by the presence of CVC symptoms. The results suggest that citrus trees with early (asymptomatic) infections by X. fastidiosa may be more effective as inoculum sources for CVC spread by insect vectors than those with advanced symptoms.     

The inhibitory effects of berry polyphenols on digestive enzymes

The evidence for the effect of polyphenol components of berries on digestive enzymes is reviewed. Anthocyanins inhibit alpha-glucosidase activity and can reduce blood glucose levels after starch-rich meals, a proven clinical therapy for controlling type II diabetes. Ellagitannins inhibit alpha-amylase activity and there is potential for synergistic effects on starch degradation after ingestion of berries such as raspberries and strawberries, which contain substantial amounts of ellagitannins and anthocyanins. A range of berry polyphenols (e.g. flavonols, anthocyanidins, ellagitannins and proanthocyanidins) can inhibit protease activities at levels which could affect protein digestion in the gastrointestinal tract. In contrast, potential for the inhibition of gastrointestinal lipase activity, a proven therapeutic target for the control of obesity through reduced fat digestion, may be limited to proanthocyanidins. Taking into account the manifold possible synergies for inhibition of starch, protein and/or lipid digestion by the spectrum of polyphenol components present within berry species, the inhibition of digestive enzymes by dietary polyphenols may represent an under-reported mechanism for delivering some of the health benefits attributed to a diet rich in fruit and vegetables.     

Effects of alpha-D-glucosylglycerol on the in vitro digestion of disaccharides by rat intestinal enzymes

Alpha-D-glucosylglycerol (GG) is a mixture of 2-O-alpha-D-glucosylglycerol (GG-II), (2R)-1-O-alpha-D-glucosylglycerol (R-GG-I) and (2S)-1-O-alpha-D-glucosylglycerol (S-GG-I). GG has been found to be slightly hydrolyzed in vitro only by rat intestinal enzymes, but hardly at all by other digestive juices. GG suppressed the hydrolysis of maltose, sucrose and isomaltose by rat intestinal enzymes because the amount of glucose in the digestion of a mixture of GG and disaccharide was less than the sum of that in each individual digestion. The consumption of GG was suppressed by isomaltose, but promoted by maltose, with the hydrolysis of GG being suppressed. Sucrose appeared to suppress only the consumption of S-GG-I, suggesting that S-GG-I was hydrolyzed by the active site of sucrase in a sucrase-isomaltase complex. Transglucosylation seems to have occurred more frequently in the individual digestion of maltose and isomaltose than in that of GG and sucrose. GG seemed to promote transglucosylation in the presence of maltose, to suppress it with sucrose, and to delay it with isomaltose.     

Designing Food Structure to Control Stability, Digestion, Release and Absorption of Lipophilic Food Components

The bioavailability of dietary lipophilic components may be either increased or decreased by manipulating the microstructure and/or physicochemical properties of the foods that contain them. This article stresses how knowledge of the molecular, physicochemical, and physiological processes that occur during lipid ingestion, digestion, and absorption can be used to rationally design food structures to control these processes and therefore impact the rate or extent of lipid digestion and/or absorption. These approaches include controlling the molecular characteristics of the lipid molecules, altering lipid droplet size or interfacial properties, and manipulating food matrix structure and composition. Improved knowledge of the molecular, physicochemical, and physiological processes that occur during lipid ingestion, digestion, and absorption will facilitate the rational design and fabrication of functional foods for improved health and wellness.     

The tidal rhythm of feeding and digestion in the pacific oyster, Crassostrea gigas (Thunberg)

A study has been made of the processes of extra- and intracellular digestion in the Pacific oyster, Crassostrea gigas (Thunberg) over two 24-h cycles in winter and summer.The results show that the digestive processes are discontinuous and related to the tidal cycle. Variations in tidal height resulting from a diurnal inequality of the tide affect both the relative dissolution of the crystalline style and the relative lengths of the constituent phases of the intracellular digestive process in the digestive diverticula. On a seasonal basis the style is present for a greater length of time in winter and, conversely, remains dissolved longer in summer. A seasonal variation in the structure of the digestive tubules has also been found.The results confirm conclusions reached earlier that the processes of extracellular digestion in the stomach and intracellular digestion in the digestive diverticula of intertidal bivalves are both discontinuous, alternate, and irrevocably interrelated since breakdown of the digestive cells of the digestive diverticula following intracellular digestion results in the dissolution of the crystalline style. The arrival of food in the stomach has a minimal effect upon the style. Moreover, the cytological structure of the digestive diverticula of C. gigas undergoes a series of synchronized changes related to the tidal cycle.     

Citrate binding of Al3+ and Fe3+

Citrate occurs at about 0.1 mM in blood plasma and is the most likely small molecule plasma binder of both Al3+ and Fe3+. This paper assesses published stability constants for citrate binding to each metal ion. From pH 2 to 5 Al3+ forms a neutral complex with citrate that may be absorbed into the body in the upper regions of the gastrointestinal tract. It is especially dangerous to ingest aluminum-containing antacids with citrus fruit or juices. Ignoring the likely occurrence of a competing 2:1 citrate-Fe3+ complex necessitates adjustments in reported stability constants for Fe3+ binding to transferrin. In the blood, plasma transferrin steals both Fe3+ and Al3+ from citrate.     

The role of bile and digestive juices in cadmium effect on the absorption processes in rat small intestine

The effects of bile and digestive juices was studied on the intestinal absorption of water, sodium and glucose in the small intestine of rats after their intoxication with one dose of cadmium 1.33 mg/kg of body weight injected intravenously. The investigations were carried out on 60 rats by the method of intestinal perfusion. The obtained results showed that cadmium inhibited the intestinal absorption of these substances. Bile and digestive juices abolished partially this effect during their physiological secretion. After administration of cholagogues no protective role of bile and digestive juices was observed alleviating the toxic effects of cadmium, and the intestinal absorption was even more reduced.     

A model for Acartia tonsa: effect of turbulence and consequences for the related physiological processes

A mathematical model of the energy budget of the coped Acartiatonsa is proposed. It takes into account the processes of ingestion(encounter, capture, ingestion sensu stricto), digestion (assimilation,gut transit and egestion), catabolic expenses and biomass production.In order to represent the potential effects of small-scale turbulenceon the whole physiological processes of a copepod, some processsubmodels already published are combined. A major assumptionof the model is a satiety effect resulting from midgut filling,which leads to a decrease in the feeding activity. The modelpermits the simulation of the short-term dynamics of ingestionunder different food and turbulence conditions, as well as anintegrated physiological balance over 24 h. The model is validatedthrough comparison with data at both scales Simulations showthat turbulence increases ingestion rates and gut contents,and causes a decrease in gut passage time and assimilation efficiency.As a consequence, the dependent physiological processes areaffected differently by turbulence, which preferentially increasesegestion and egg-production rates Simulated daily ingestionrates of A.tonsa, for suspension feeding on. Thalassiosira weissflogiiand for ambush predation on Strombidium sulcatum, are in goodagreement wth the available experimental observations. The concurrentdirect effect of turbulence on the copepod's metabolism, dueto increased escape reactions, is also simulated. Results ofthe model show that a switch from suspension feeding on diatomsin calm condition to ambush predation on ciliates in turbulentconditions, might allow A.tonsa to maintain its gross growthefficiency at the same level. It is suggested that a dynamicrepresentation of processes occurring over a time scale of afew seconds is necessary to obtain, once integrated over 24h, the correct simulation of the effect of microscale turbulenceon ingestion and the related physiological processes.     

Decreasing unpalatable flavonoid components in Citrus: the effect of transformation construct

Citrus species accumulate large quantities of flavanone glycosides in their leaves and fruit. The physiological role(s) of these compounds in citrus plants are unknown, but they have been documented to benefit human health upon consumption. Flavanone rutinosides are tasteless, whereas flavanone neohesperidosides, such as naringin, give a bitter taste to fruit and fruit juice products, reducing their palatability. In an effort to alter the types and levels of flavanone neohesperidosides in citrus, an Agrobacterium -mediated genetic transformation approach was employed. Citrus paradisi Macf. (grapefruit) epicotyl stem segments were transformed with sense (S) and antisense (AS) constructs of the target genes chalcone synthase (CHS) and chalcone isomerase (CHI), whose products catalyze the first two steps in the flavonoid biosynthetic pathway. Transformation with each of the individual constructs led to a different and unpredictable combination of viability, phenotypic change, transgene steady-state expression and alteration in flavonoid content in the resulting transgenic plants. These qualities were consistent within the transgenic plants obtained using any particular construct. Transgenic plants with decreased leaf naringin levels were obtained, particularly when the CHS-AS constructs were employed.     

The use of biomarkers in Daphnia magna toxicity testing

We investigated the effect of short-term exposure to cadmium and 2,4-dichlorophenoxy acetic acid on the digestive physiology of Daphnia magna and the consequences for the bioenergetics of the organism. In both cases, ingestion was more drastically reduced compared to digestive enzyme activity. Furthermore a differential shift in catabolism was noted: in general polysaccharidases were less affected than the enzymes responsible for protein and lipid digestion. Comparison of the ‘1 h in vivo fluorescence’ criterion (Janssen & Persoone, 1993) with the ingestion and digestive enzyme activity revealed that this rapid screening assay should be considered as a quantification of ingestion inhibition rather than a methodology assessing digestive enzyme inhibition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Isomerization of feruloylputrescine in orange juice by light exposure

Exposure to light may adversely affect the quality of foods. This investigation of how light exposure affects citrus (orange and mandarin blend) juice in polyethylene terephthalate (PET) bottles demonstrated that the isomeric form of a compound in the juice changed during storage. This compound was identified as feruloylputrescine (FP; CAS: 501-13-3; C₁₄H₂₀N₂O₃) using LC/MS (Q-TOF). LC/MS and NMR measurements showed that the content of the original form, trans-FP, decreased as it isomerized to cis-FP during storage. This phenomenon could be observed in citrus fruit juices containing FP, such orange and grapefruit juices. Therefore, determining the content of these two isomers of FP could be used to indicate the level of light exposure experienced by citrus fruit products.     

Acidic digestion in a teleost: postprandial and circadian pattern of gastric pH, pepsin activity, and pepsinogen and proton pump mRNAs expression

Two different modes for regulation of stomach acid secretion have been described in vertebrates. Some species exhibit a continuous acid secretion maintaining a low gastric pH during fasting. Others, as some teleosts, maintain a neutral gastric pH during fasting while the hydrochloric acid is released only after the ingestion of a meal. Those different patterns seem to be closely related to specific feeding habits. However, our recent observations suggest that this acidification pattern could be modified by changes in daily feeding frequency and time schedule. The aim of this study was to advance in understanding the regulation mechanisms of stomach digestion and pattern of acid secretion in teleost fish. We have examined the postprandial pattern of gastric pH, pepsin activity, and mRNA expression for pepsinogen and proton pump in white seabream juveniles maintained under a light/dark 12/12 hours cycle and receiving only one morning meal. The pepsin activity was analyzed according to the standard protocol buffering at pH 2 and using the actual pH measured in the stomach. The results show how the enzyme precursor is permanently available while the hydrochloric acid, which activates the zymogen fraction, is secreted just after the ingestion of food. Results also reveal that analytical protocol at pH 2 notably overestimates true pepsin activity in fish stomach. The expression of the mRNA encoding pepsinogen and proton pump exhibited almost parallel patterns, with notable increases during the darkness period and sharp decreases just before the morning meal. These results indicate that white seabream uses the resting hours for recovering the mRNA stock that will be quickly used during the feeding process. Our data clearly shows that both daily illumination pattern and feeding time are involved at different level in the regulation of the secretion of digestive juices.     

Thermogenic and hormonal responses to palatable protein and carbohydrate rich food.

Simultaneous variations of oxygen consumption, and plasma insulin and norepinephrine were measured during the postprandial cephalic and gastrointestinal phases of feeding in six human subjects following the ingestion of various nutrients. On alternative days the subjects were given foods (1280 kjoules) either rich in carbohydrates (sugar pie) or in proteins (fish). Both nutrients produced an initial (0-40 min) enhanced thermogenesis and an early (2 min) cephalic insulin release. During that period, elevations of plasma norepinephrine were also observed with pie feeding at 10 and 30 min and at 10 min with fish. Palatability ratings indicated that both food items were equally tasting. During the gastrointestinal phase (40 to 120 min) the variations of these same parameters including glucagon seem to be explained by the content in carbohydrates and proteins in the food rather than by its palatability. Indeed during that period the protein meal was more thermogenic and the carbohydrate meal induced the expected insulin secretion. These results suggest that the palatability of the food is responsible for the early cephalic increase in postprandial thermogenesis, and for the insulin and norepinephrine release. During the subsequent gastrointestinal phase the increased thermogenesis is related to the composition of the food which exerts its action by the biochemical processes involved in the disposal of the absorbed nutrients.     

Immunoglobulins anti-Anisakis simplex in patients with gastrointestinal diseases

The nematode Anisakis simplex causes anisakidiasis, a disease that often mimics other gastrointestinal diseases. Patients with digestive haemorrhaging, Crohn's disease, digestive cancer and appendicitis were analysed for antibodies to A. simplex. Antibody detection was carried out by enzyme-linked immunosorbent assay (ELISA) and immunoblotting using crude extract (CE) antigen and excretory-secretory (ES) products. Total immunoglobulin (Igs), IgG, IgM, IgA and IgE were studied. The highest percentage was obtained when Igs were tested against CE antigen. A higher percentage of positivity was observed with the appendicitis group. The Crohn's disease group showed the highest levels of IgG against the ES antigen. Using immunoblotting, 24% and 48% of sera from patients with symptoms of Crohn's disease and digestive haemorrhaging, respectively, showed a positive immunorecognition pattern of CE antigen. The prevalence of detectable antibodies against A. simplex is higher in patients with digestive disorders than in the healthy population. A linear correlation was observed between prothrombin activity and Igs-CE, IgA-CE and IgA-ES but not between IgE-CE and the other immunoglobulin levels. Specific IgA is associated with a higher activity index of Crohn's disease. Specific antibodies were observed against A. simplex in patients with appendicitis and gastrointestinal cancer, indicating a higher rate of positivity for IgA.     

<Emphasis Type="SmallCaps">d</Emphasis>-Galacturonic acid catabolism in microorganisms and its biotechnological relevance

d-Galacturonic acid is the main constituent of pectin, a naturally abundant compound. Pectin-rich residues accumulate when sugar is extracted from sugar beet or juices are produced from citrus fruits. It is a cheap raw material but currently mainly used as animal feed. Pectin has the potential to be an important raw material for biotechnological conversions to fuels or chemicals. In this paper, we review the microbial pathways for the catabolism of d-galacturonic acid that would be relevant for the microbial conversion to useful products.     

Alteration and release of aliphatic compounds by the polychaete Nereis virens (Sars) experimentally fed with hydrocarbons

In the laboratory, marine worms were fed with a mixture of algae and several aliphatic hydrocarbons for 15 days. After ingestion by the worms, 34.9% of hydrocarbons are found in the faeces and only 3.1% accumulated in the gut. The comparison between the initial mixture and the faeces shows that the worm's digestive process lead to changes in the distribution of the n-alkane mixture. These changes are different from those only due to physical processes in the experimental conditions. In our experiment, no variation in the distribution of hydrocarbons in faeces with time and no microbial hydrocarbon biodegradation were evidenced. Our results suggest that marine worm feeding can substantially affect the fate of hydrocarbons in the sedimentary marine ecosystem by predominantly stimulating dissolution processes.