Nucleosides are efficiently absorbed by Na(+)-dependent transport across the intestinal brush border membrane in veal calves

In previous work, a comparatively high capacity for Na(+)-dependent transport of nucleosides across the intestinal brush border membrane (BBM) was observed in dairy cows, which might be related to digestion of the large amount of nucleic acids present in ruminal microorganisms in the ruminant small intestine. If this were the case, the capacity for Na(+)-dependent intestinal nucleoside transport should be much lower in veal calves, in which only small amounts of nucleic acids, nucleotides, and nucleosides reach the small intestine via the milk replacer. To test this hypothesis, we investigated Na(+)-dependent transport of 3H-labeled thymidine and guanosine across the BBM using BBM vesicles (BBMV) isolated from the small intestine of veal calves. In the presence of a transmembrane Na+ gradient both substrates were transported against a concentration gradient. Inhibitory studies showed that thymidine and guanosine are transported by two different transporters with overlapping substrate specificity, one accepting predominantly pyrimidine nucleosides (N2) and one accepting particularly purine nucleosides (N1). Nucleoside transport was inhibited by glucose along the whole small intestine. Maximal transport rates similar to those in dairy cows were obtained for the proximal, mid-, and distal small intestine. These findings suggest that the high absorptive capacity for nucleosides is a genetically fixed property in the bovine small intestine, which is already present in the preruminant state of veal calves. It may contribute to the high digestibility of nucleic acids observed by others in veal calves receiving milk replacer supplemented with RNA. Its main function may be the efficient absorption of nucleosides resulting from the digestion of nucleic acids associated with desquamated enterocytes. Due to the limited de novo synthesis of nucleotides in enterocytes intracellular uptake of nucleosides across the BBM may contribute to nucleic acid synthesis in enterocytes and thus may have a trophic effect on the intestinal epithelium.     

鸡蛋卵转铁蛋白过敏原的体外模拟消化特性

采用体外静态消化模式,分别模拟婴幼儿和成年人的胃液、小肠液以及小肠刷状缘膜酶消化鸡卵转铁蛋白,利用Tricine-SDS-PAGE和MALDI-TOF-MS对消化产物进行分析,研究鸡蛋蛋清过敏原卵转铁蛋白的消化特性.结果表明:婴幼儿和成年人的模拟胃液、小肠液以及小肠刷状缘膜酶都能够消化卵转铁蛋白.在模拟婴幼儿消化体系中...     

Cathepsin B and D activity in the mucous membrane of the small intestine of rats on a high-saccharose diet and added selenium

Selenium added to diets (700-750 micrograms per kg bw) enhanced the activity of cathepsins B and D; in this case, the protein content in the rat small intestine mucosa was found to be considerably reduced. High-sucrose diet did not directly influence the lysosomal proteinase activity, but enhanced selenium action on the proteolysis.     

Characteristics of protein digestion in artificial feeding in an experiment

It has been established that during artificial feeding with milk substitute containing different protein components (casecite, bovine serum albumin, fibrinogen), the proximal-distal gradient of cavitary digestion of proteins is observed, with this gradient being more demonstrable as compared with natural feeding of postnatal animals. It has been shown that during experimental natural feeding, the proximal-distant gradient is observed in the distribution of acid proteinases in the small bowel, whereas during artificial feeding one can see a uniform distribution of acid proteinases in the proximal and distal parts of the small bowel. The activity of acid proteinases in the gastric mucosa of 18-day-old animals kept on natural feeding does not differ from the activity of these proteinases under artificial feeding with a substitute containing casecite as protein component. Artificial feeding with a substitute containing bovine serum albumin and fibrinogen as protein component entails a decrease in the activity of acid proteinases in the gastric mucosa.     

Use of brush border membrane vesicles to simulate the human intestinal digestion

The intestine presides over a series of vital functions in the human body, among which the digestion/absorption of nutrients. Despite their major digestion role, the impact of the enzymes of the luminal intestinal surface on food components has been considered in relatively few experiments of simulated gastrointestinal digestion. In contrast, the identification of proteolitically stable peptides which survived digestion in multiphasal models that also included a step with small intestinal brush border membrane (BBM) peptidases has provided physiologically consistent results. Herein, we critically review the use of BBM enzymes to simulate the intestinal digestion of dietary polypeptides. Addressing the controversial issue of the in vitro–in vivo correspondence of the digestion models, the review emphasizes the need to establish consensus protocols to simulate the intestinal step, for instance using the BBM hydrolases at least in a selected number of cases. The factors that have limited the development of relevant models of intestinal degradation are discussed together with hints to possible alternatives, forthcoming approaches and future perspectives to reproduce the physiopathology of the human small intestine.     

A mechanistic model of small intestinal starch digestion and glucose uptake in the cow

The high contribution of postruminal starch digestion (up to 50%) to total-tract starch digestion on energy-dense, starch-rich diets demands that limitations to small intestinal starch digestion be identified. A mechanistic model of the small intestine was described and evaluated with regard to its ability to simulate observations from abomasal carbohydrate infusions in the dairy cow. The 7 state variables represent starch, oligosaccharide, glucose, and pancreatic amylase in the intestinal lumen, oligosaccharide and glucose in the unstirred water layer at the intestinal wall, and intracellular glucose of the enterocyte. Enzymatic hydrolysis of starch was modeled as a 2-stage process involving the activity of pancreatic amylase in the lumen and of oligosaccharidase at the brush border of the enterocyte confined within the unstirred water layer. The Na⁺-dependent glucose transport into the enterocyte was represented along with a facilitative glucose transporter 2 transport system on the basolateral membrane. The small intestine is subdivided into 3 main sections, representing the duodenum, jejunum, and ileum for parameterization. Further subsections are defined between which continual digesta flow is represented. The model predicted nonstructural carbohydrate disappearance in the small intestine for cattle unadapted to duodenal infusion with a coefficient of determination of 0.92 and a root mean square prediction error of 25.4%. Simulation of glucose disappearance for mature Holstein heifers adapted to various levels of duodenal glucose infusion yielded a coefficient of determination of 0.81 and a root mean square prediction error of 38.6%. Analysis of model behavior identified limitations to the efficiency of small intestinal starch digestion with high levels of duodenal starch flow. Limitations to individual processes, particularly starch digestion in the proximal section of the intestine, can create asynchrony between starch hydrolysis and glucose uptake capacity.     

海地瓜岩藻聚糖硫酸酯对环磷酰胺损伤小鼠小肠粘膜的保护作用

目的探讨海地瓜岩藻聚糖硫酸酯,包括原糖及其不同分子量酶解产物(50、100、500kD)对环磷酰胺造成的小鼠小肠粘膜损伤的改善作用,幵对其机制进行探究。方法 60只Balb/c小鼠随机分成6组:空白对照组,环磷酰胺模型组,环磷酰胺损伤小鼠分别干预原糖及50、100、500kD酶解产物组,每组10只。实验周期为14 d,干预组分别ig给予50 mg/(kg·bw)海地瓜岩藻聚糖硫酸酯,第12和13 d给除空白对照组以外小鼠连续ip给予50 mg/(kg·bw)环磷酰胺。测定小鼠体重变化,器官指数变化;采用苏木精-伊红染色法检测小肠组织形态学变化;采用实时荧光定量PCR技术检测溶菌酶、黏蛋白(mucin2,Muc2)、干细胞标志物(leucine-rich repeat-containing G-protein coupled receptor5,Lgr5)mRNA表达水平,幵通过Toll样受体(toll-like receptors, TLRs)和髓样分化因子(myeloid differentiation factor88, MyD88)基因表达的变化探究其作用机制。结果 100 kD和50 kD组枀显著(P0.01)改善环磷酰胺造成的小鼠体重下降; 50 kD组显著(P0.05)提高绒毛长度和隐窝深度比值,改善小鼠小肠形态破坏; 100 kD组和50 kD组小肠溶菌酶、Muc2基因表达量显著高于Cy组,不同分子量的酶解产物均能显著提高Lgr5以及小肠TLRs (TLR-4, TLR-5, TLR-9)和MyD88的基因表达量,且50kD组的改善作用最好。结论酶解片段对化疗型小鼠小肠粘膜损伤的保护效果优于原糖,且50 kD效果最好,作用机制可能与对TLRs/MyD88信号通路的调节有关。     

抗性淀粉体外消化模拟的研究

采用体外消化模拟方法,研究了抗性淀粉在人工胃肠液和大肠液中的消化吸收情况,并用原淀粉作为对照组。结果表明,抗性淀粉和原淀粉在生理盐水中均没有被分解,生理盐水对抗性淀粉的消化毫无影响。与对照组原淀粉相比,抗性淀粉在人工胃液(pH3、pH4、pH5)和人工肠液(pH6.8)中变化很小,人工胃液和人工肠液对抗性淀粉不起消化作用。抗性淀粉在大肠液中有明显的失重,说明大肠液对抗性淀粉有影响,抗性淀粉能够被大肠中的微生物发酵或部分发酵。从而说明抗性淀粉不能在胃和小肠中消化吸收。     

肠类器官应用于营养素吸收的研究进展

肠道不仅是营养物质消化吸收的主要部位,也是重要的免疫器官和内分泌器官。营养物质在肠道内的消化吸收状况是决定其高效利用的重要因素。构建适宜的体外肠道模型对明确营养物质的有效吸收部位、吸收效率及机制具有重要意义。类器官由于可高度模拟目标组织或器官的遗传特性和表观特征被广泛应用于各个领域。本文综述了近年来肠类器官在营养物质消化吸收方面的研究进展,以期为肠类器官在营养物质的消化吸收中的广泛应用提供参考。     

大豆胚轴提取物体外对小肠黏膜蔗糖酶、麦芽糖酶及葡萄糖转运活性的影响

在体外比色法观察大豆胚轴提取物对大鼠小肠黏膜蔗糖酶和麦芽糖酶活性的影响,并用快速过滤法观察其对兔小肠刷状缘囊泡葡萄糖转运活性的影响。结果表明,大豆胚轴提取物明显降低大鼠小肠蔗糖酶、麦芽糖酶活性和兔小肠刷状缘囊泡葡萄糖转运能力。提示,大豆胚轴提取物可延缓小肠对糖的消化和吸收,经常食用可能有助于延缓餐后血糖的持续升高。     

Lactose--a potential dietary fiber. The regulation of its microecological effect in the intestinal tract. 1. Problems, state of knowledge and methods]

Food components of different chemical structure which attain the colon without being attacked by digestion and absorption during their transit through the small intestine are defined as dietary fibre. In the colon they serve as energy or nutrient source for the intestinal microflora or are excreted without change. Not only chemical structure is decisive when a food component has to be assigned to either nutrients or dietary fibre: Substances resisting small intestine digestion due to the lack of corresponding catabolizing enzymes in man are supposed to be "obligate" dietary fibre. "Potential" dietary fibre are nutrients which are only partially digested in the small intestine. Lactose--the main carbohydrate of milk--represents a typical potential dietary fibre. The present paper investigates the factors being responsible for both the degree of lactose utilization in the small intestine and its efficiency in the colon.     

掺入外源淀粉的魔芋豆腐体外消化和发酵性能研究

通过体外模拟口腔、胃、小肠消化,探讨掺入淀粉的魔芋豆腐体外消化性能,并将消化后的剩余部分作为小鼠盲肠内容物体外发酵底物,研究其在盲肠中的发酵性能。结果表明,纯魔芋豆腐在口腔、胃、小肠中均不被消化,掺入魔芋豆腐中的淀粉从口腔开始被水解,在胃部不被水解,进入小肠后20 min内即可完成大部分水解,但与纯淀粉相比,掺入魔芋豆腐中的淀粉的快消化淀粉含量减少,总水解率无显著变化,说明脱乙酰基魔芋葡甘聚糖可延缓淀粉消化,但不能阻止淀粉消化。体外模拟盲肠发酵过程中,掺入淀粉的魔芋豆腐降低pH值的能力高于纯魔芋豆腐,但前者生成的短链脂肪酸及发酵24 h后乳酸菌含量少于后者。综上表明,食用掺入淀粉的魔芋豆腐相较纯魔芋豆腐会快速升高血糖和降低魔芋豆腐的肠道益生作用。     

大豆蛋白纤维聚集体的体外消化特性研究

本研究以大豆分离蛋白为材料,通过在pH 2.0条件下调控大豆蛋白形成大豆蛋白纤维聚集体。采用标准的静态体外消化模型INFOGEST 2.0对大豆蛋白纤维聚集体进行体外模拟消化实验,并对不同消化时间的胃肠消化产物通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）、动态激光散射仪（DLS）及液相色谱-质谱联用（LC-MS）对其分子质量、粒径及肽段组成进行鉴定。结果表明,大豆蛋白纤维聚集体通过消化后被水解为小分子的肽,并LC-MS证实消化过程中肽段数量随着消化时间的增加呈阶梯式水解。本实验探究了大豆蛋白在体外模拟消化过程中的消化特性,这将有助于更好地了解植物蛋白在人体中的消化方式及其对健康的影响。     

Stability of milk fat globule membrane proteins toward human enzymatic gastrointestinal digestion

The milk fat globule membrane (MFGM) fraction refers to the thin film of polar lipids and membrane proteins that surrounds fat globules in milk. It is its unique biochemical composition that renders MFGM with some beneficial biological activities, such as anti-adhesive effects toward pathogens. However, a prerequisite for the putative bioactivity of MFGM is its stability during gastrointestinal digestion. We, therefore, subjected MFGM material, isolated from raw milk, to an in vitro enzymatic gastrointestinal digestion. Sodium dodecyl sulfate PAGE, in combination with 2 staining methods, Coomassie Blue and periodic acid Schiff staining, was used to evaluate polypeptide patterns of the digest, whereas mass spectrometry was used to confirm the presence of specific MFGM proteins. Generally, it was observed that glycoproteins showed higher resistance to endogenous proteases compared with non-glycosylated proteins. Mucin 1 displayed the highest resistance to digestion and a considerable part of this protein was still detected at its original molecular weight after gastric and small intestine digestion. Cluster of differentiation 36 was also quite resistant to pepsin. A significant part of periodic acid Schiff 6/7 survived the gastric digestion, provided that the lipid moiety was not removed from the MFGM material. Overall, MFGM glycoproteins are generally more resistant to gastrointestinal digestion than serum milk proteins and the presence of lipids, besides glycosylation, may protect MFGM glycoproteins from gastrointestinal digestion. This gastrointestinal stability makes MFGM glycoproteins amenable to further studies in which their putative health-promoting effects can be explored.     

Metabolism of Maillard reaction products by the human gut microbiota--implications for health

The human colonic microbiota imparts metabolic versatility on the colon, interacts at many levels in healthy intestinal and systemic metabolism, and plays protective roles in chronic disease and acute infection. Colonic bacterial metabolism is largely dependant on dietary residues from the upper gut. Carbohydrates, resistant to digestion, drive colonic bacterial fermentation and the resulting end products are considered beneficial. Many colonic species ferment proteins but the end products are not always beneficial and include toxic compounds, such as amines and phenols. Most components of a typical Western diet are heat processed. The Maillard reaction, involving food protein and sugar, is a complex network of reactions occurring during thermal processing. The resultant modified protein resists digestion in the small intestine but is available for colonic bacterial fermentation. Little is known about the fate of the modified protein but some Maillard reaction products (MRP) are biologically active by, e. g. altering bacterial population levels within the colon or, upon absorption, interacting with human disease mechanisms by induction of inflammatory responses. This review presents current understanding of the interactions between MRP and intestinal bacteria. Recent scientific advances offering the possibility of elucidating the consequences of microbe-MRP interactions within the gut are discussed.     

破壁灵芝孢子的体外模拟消化特性研究

为探究破壁灵芝孢子在口腔和胃肠道中的消化吸收情况以及对肠道环境的影响。以机械碾压法、微波法和超声法破壁的灵芝孢子（Ganoderma lucidum spore,GLS）为研究对象,经体外模拟人体口腔、胃、小肠消化系统及透析模型,随后将消化后的底物进行体外发酵。测定消化各个阶段的灵芝孢子失质量率、多糖和三萜化合物释放量、生物可接受率和透析率以及小肠消化底物在0、6、12、24、48 h体外发酵过程中pH变化。结果显示,胃和小肠是灵芝孢子的主要消化场所,破壁组平均失质量率达到23.84%,其中机械碾压组更易被消化,其失质量率为29.46%。97%的多糖在胃肠液中溶出,机械碾压组多糖的生物可接受率具有最高水平,为87.33%。三萜只在破壁组小肠模拟消化中有微量溶出,平均约1.50±0.04 mg/g,95.2%的三萜随沉淀进入结肠。体外发酵结果显示,发酵液pH在0~12 h持续下降,并在12 h基本到达发酵终点。对比三种破壁灵芝孢子的消化特性,机械碾压法破壁的品质可观,不失为企业规模化破壁生产的优选。综上所述,破壁有利于提高灵芝孢子的有效成分在人体消化环境内释放量和生物可接受率,促进结肠发酵产酸,有助于调节人体肠道环境。     

In vitro digestion and characterisation of 2S albumin and digestion‐resistant peptides in pecan

The 2S albumins are one of the major protein families involved in severe food allergic reactions to nuts, seeds and legumes, thus potentially making these proteins clinically relevant for allergic sensitisation and potential diagnostic markers. In this study, we sought to purify native 2S albumin protein from pecan to further characterise this putative allergen. The purified 2S albumin, Car i 1, from pecan was found to be resistant to digestion by pepsin in simulated gastric fluid (SGF) and comparatively stable to proteolysis by trypsin and pancreatin in simulated intestinal fluid (SIF). Digestion of purified Car i 1 in SGF and SIF resulted in formation of different digestion‐resistant peptides that were capable of binding IgE antibodies from allergic individuals. Digestion stability of Car i 1 and formation of digestion‐resistant antigenic peptides may explain why it is a potent sensitising protein in pecan for susceptible individuals. The observation that digestion‐resistant peptides are able to bind IgE implies that pecan can trigger systemic allergic reactions even after digestion in the stomach and small intestine.     

Role tunica mucosa small intestinal in exchange processes

The review of the experimental and clinical data confirming active participation small intestinal in exchange processes at a pathology of bodies of digestion and malnutrition. The features of assimilation and turnover protein of a diet in small intestinal.     

软枣猕猴桃在体外模拟消化过程中酚类物质及抗氧化活性的变化规律

本研究以4 种软枣猕猴桃为原料，探讨了其整果、游离型酚类提取物和果渣样品在体外模拟消化过程中酚类物质的含量及抗氧化活性的变化规律，采用福林-酚法测定样品每个消化阶段总酚含量，采用超高效液相色谱-四极杆飞行时间质谱联用和高效液相色谱-光电二极管阵列质谱联用对软枣猕猴桃中酚类单体化合物进行定性定量分析。通过过氧自由基清除能力来探究胃肠消化处理对软枣猕猴桃抗氧化活性的影响，并通过细胞抗氧化活性进一步探究体外模拟消化后样品的抗氧化水平。结果表明：在体外模拟消化过程中，软枣猕猴桃整果和游离型酚类提取物中总酚含量的变化趋势相同：未消化＞口腔＞胃＞肠；果渣中总酚含量表现出不同的变化趋势：肠＞胃＞未消化＞口腔。不同的消化阶段环境条件不同，胃（低pH值环境）和肠（高pH值环境）对酚类化合物稳定性影响不同，使酚类物质发生降解或转化；同时，酚类化合物结构也影响其自身的降解和转化。由于酚类是软枣猕猴桃中最主要的抗氧化活性物质，在体外消化过程中，过氧自由基清除能力与其对应的酚类含量变化趋势一致。本研究结果为软枣猕猴桃天然产品的开发及应用提供科学依据。     

牡蛎肽肠内营养制剂对小鼠肠道功能作用的研究

本文主要探讨牡蛎肽肠内营养制剂对小鼠肠道功能的作用。将动物随机分为阴性对照组、阳性对照组和低、中、高剂量组5组,灌胃给予不同剂量牡蛎肽肠内营养制剂,每天测定各组体重和进食量,最后测定食物利用系数、小肠推进率、小肠吸收等评价指标。结果显示,与阴性对照组相比,低、中剂量组食物利用系数和小肠推进率均有明显增加,低剂量组木糖浓度明显增高。可见,牡蛎肽肠内营养制剂能促进小肠推进和消化吸收,可以作为肠内营养制剂应用于临床营养支持。