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.     

Degradation of β-casomorphin-7 through in vitro gastrointestinal and jejunal brush border membrane digestion

This work aimed to study the opioid peptide β-casomorphin-7 (BCM7) degradation or stability during digestion using human gastrointestinal (GI) juices and porcine jejunal brush border membrane (BBM) peptidases. Synthetic BCM7 was subjected to in vitro digestion by GI fluids obtained from human volunteers for 180 min, and to downstream degradation with porcine BBM vesicles. The BCM7 was sampled at 4 time points over 24 h after BBM addition. The digests were profiled by HPLC-electrospray ionization mass spectrometry (ESI/MS) to monitor BCM7 during GI digestion, and intact BCM7 through BBM digestion was quantified by reverse-phase (RP)-HPLC. We found that BCM7 was partly digested with human GI enzymes, as 3 proteolytic fragments in addition to f(60–66) YPFPGPI were detected: f(62–66) FPGPI, f(60–65) YPFPGP and f(61–66) PFPGPI. The RP-HPLC analysis revealed that 42% of the initial peptide was degraded after only 2 h of BBM digestion, and as much as 79% was degraded after 4-h digestion with supplementation of BBM. In conclusion, this study showed that most of BCM7 was degraded during GI and BBM digestion, although a small amount (5%) was still detected after 24-h digestion. It remains to be studied whether the small amount of intact BCM7 detected after in vitro digestion is transported via active transceptors in the human intestinal epithelial cells and enters blood circulation.     

In Vitro Models for Studying Secondary Plant Metabolite Digestion and Bioaccessibility

There is an increased interest in secondary plant metabolites, such as polyphenols and carotenoids, due to their proposed health benefits. Much attention has focused on their bioavailability, a prerequisite for further physiological functions. As human studies are time consuming, costly, and restricted by ethical concerns, in vitro models for investigating the effects of digestion on these compounds have been developed and employed to predict their release from the food matrix, bioaccessibility, and assess changes in their profiles prior to absorption. Most typically, models simulate digestion in the oral cavity, the stomach, the small intestine, and, occasionally, the large intestine. A plethora of models have been reported, the choice mostly driven by the type of phytochemical studied, whether the purpose is screening or studying under close physiological conditions, and the availability of the model systems. Unfortunately, the diversity of model conditions has hampered the ability to compare results across different studies. For example, there is substantial variability in the time of digestion, concentrations of salts, enzymes, and bile acids used, pH, the inclusion of various digestion stages; and whether chosen conditions are static (with fixed concentrations of enzymes, bile salts, digesta, and so on) or dynamic (varying concentrations of these constituents). This review presents an overview of models that have been employed to study the digestion of both lipophilic and hydrophilic phytochemicals, comparing digestive conditions in vitro and in vivo and, finally, suggests a set of parameters for static models that resemble physiological conditions.     

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.     

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.     

Bioaccessibility of carotenoids from plant and animal foods

The frequent consumption of carotenoid-rich foods has been associated with numerous health benefits, such as the supply of provitamin A. To exert these health benefits, carotenoids need to be efficiently liberated from the food matrix, micellized in the small intestine, taken up by the enterocytes and absorbed into the human blood stream. Enormous efforts have been made to better understand these processes. Because human studies are costly, labor-intense and time-consuming, the evaluation of carotenoid liberation and micellization at the laboratory scale using simulated in vitro digestion models has proven to be an important tool for obtaining preliminary results prior to conducting human studies. In particular, the liberation from the food matrix and the intestinal micellization can be mimicked by simulated digestion, yielding an estimate of the so-called bioaccessibility of a carotenoid. In the present review, we provide an overview of the carotenoid digestion process in vivo, the currently used in vitro digestion models and the outcomes of previous bioaccessibility studies, with a special focus on correlations with concomitantly conducted human studies. Furthermore, we advocate for the on-going requirement of better standardized digestion protocols and, in addition, we provide suggestions for the complementation of the acquired knowledge and current nutritional recommendations. © 2018 Society of Chemical Industry     

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。     

Structural breakdown of starch-based foods during gastric digestion and its link to glycemic response: In vivo and in vitro considerations

The digestion of starch-based foods in the small intestine as well as factors affecting their digestibility have been previously investigated and reviewed in detail. Starch digestibility has been studied both in vivo and in vitro, with increasing interest in the use of in vitro models. Although previous in vivo studies have indicated the effect of mastication and gastric digestion on the digestibility of solid starch-based foods, the physical breakdown of starch-based foods prior to small intestinal digestion is often less considered. Moreover, gastric digestion has received little attention in the attempt to understand the digestion of solid starch-based foods in the digestive tract. In this review, the physical breakdown of starch-based foods in the mouth and stomach, the quantification of these breakdown processes, and their links to physiological outcomes, such as gastric emptying and glycemic response, are discussed. In addition, the physical breakdown aspects related to gastric digestion that need to be considered when developing in vitro–in vivo correlation in starch digestion studies are discussed. The discussion demonstrates that physical breakdown prior to small intestinal digestion, especially during gastric digestion, should not be neglected in understanding the digestion of solid starch-based foods.     

A physiological approach for preparing and conducting intestinal bioavailability studies using experimental systems

Various in vitro models, such as digestion procedures, element dialysis across membranes and also the Caco-2 cellular absorptive system, are currently used to study intestinal nutrient bioavailability. These systems were established as an alternative to human and animal studies. The principle requirement for successfully performing such kinds of experimental studies is to achieve conditions, which are similar to in vivo conditions. Therefore, it is absolutely necessary to consider the natural environment in the human gut. Consequently, in vitro studies should be prepared and conducted according to evidence-based gastrointestinal physiology. This concise review summarizes important processes in the human intestine, like peptic and pancreatic digestion, adjustment of pH, peristaltic frequency, osmolality, composition of the serosal (= acceptor) solution, and permeability characteristics of the enterocyte monolayer, which are relevant for bioavailability studies using in vitro models.     

Degradation of pectic substances by two pectate lyases from a human intestinal bacterium, Clostridium butyricum-beijerinckii group

Clostridium butyricum-beijerinckii group, an anaerobic human intestinal bacterium, produced exo-pectate lyase, endo-pectate lyase, and pectin methylesterase, but not polygalacturonase. The production of the two pectate lyases was strongly influenced by the composition of the carbon sources added to the medium. The enzymes secreted by the bacterium into the human large intestine cooperatively digested pectic substances, producing mainly 4,5-unsaturated digalacturonic acid with the participation of the pectin methylesterase. The findings suggest that in the human intestine the bacterium contributes to the digestion of ingested pectic substances.     

In vitro human digestion models for food applications

In vitro digestion models are widely used to study the structural changes, digestibility, and release of food components under simulated gastrointestinal conditions. However, the results of in vitro digestion models are often different to those found using in vivo models because of the difficulties in accurately simulating the highly complex physicochemical and physiological events occurring in animal and human digestive tracts. This paper provides an overview of current trends in the development and utilisation of in vitro digestion models for foods, as well as information that can be used to develop improved digestion models. Our survey of in vitro digestion models found that the most predominant food samples tested were plants, meats, fish, dairy, and emulsion-based foods. The most frequently used biological molecules included in the digestion models were digestive enzymes (pancreatin, pepsin, trypsin, chymotrypsin, peptidase, α-amylase, and lipase), bile salts, and mucin. In all the in vitro digestion models surveyed, the digestion temperature was 37 °C although varying types and concentrations of enzymes were utilised. With regard to digestion times, 2 h (the stomach, small intestine, and large intestine each) was predominantly employed. This survey enhances the understanding of in vitro digestion models and provides indications for the development of improved in vitro digestion models for foods or pharmaceuticals.     

基于AGDS和静态消化模型的全麦面条体外消化特性研究

采用动态(人工胃模拟系统，AGDS)和静态(振荡水浴)2种体外消化模型，分别对全麦面条的消化特性进行考察，探究不同消化模型在全麦面条消化特性研究中的差异，对消化过程中pH、胃排空情况、粒径变化、淀粉水解和蛋白质胃内降解进行表征。结果表明：全麦面条在AGDS模型胃消化阶段的颗粒降解程度高于静态模型，这可能是由于AGDS模型对胃内机械力的模拟有利于促进全麦面条食糜的物理破碎。全麦面条淀粉组分在2种模型的胃消化阶段均发生少量水解，当小肠消化结束时，静态和AGDS模型的淀粉水解率分别为66.51%和53.49%。同时，全麦面条蛋白质组分在静态消化模型胃消化阶段的水解速度快于AGDS。     

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...     

Protein assimilation and acid proteinases in the postnatal gastrointestinal tract in experimental studies

Proximal-distant gradient of the lysosomal proteinase activity distribution is observed in the mammals at the postnatal period of development. In various species of mammals the proximal-distal gradient of the lysosomal proteinase distribution is attended by the shift of the final stages of the intestinal digestion to the distal part of the small intestine. These features are typical of the protein digestion in the mammals at the postnatal period of development. The protein digestion in adult mammals is characterized by a uniform distribution of lysosomal proteinases between the small intestine parts and by the completion of the protein intestinal digestion in the proximal part of the small intestine.     

Metabolic effects of dietary carbohydrates: The importance of food digestion

High blood glucose and insulin concentrations, even if within the normal range, are associated with an increased risk to develop type 2 diabetes and cardiovascular diseases. Dietary carbohydrates are the main determinants of blood glucose levels in the postprandial period; therefore, the effects of dietary carbohydrates on human health are strongly related to their rate of digestion in the small intestine. This has raised much interest on food properties able to retard carbohydrate digestion and absorption. This review is focused to examine food properties which influence carbohydrate digestion in order to predict their potential influence on health markers. Among them, it is worth to underline the role of viscosity, the physical form of the food, cooking methods and processing, the type of starch (amylose or amylopectin), the presence of anti-nutrients and the amount of fiber, fat, and proteins. In this respect particularly relevant is the type of starch present in the food, since amylose is slowly digested by intestinal α-amylases while the digestion of amylopectin is faster. However, the food component that has the strongest impact on digestion and absorption of dietary carbohydrates is dietary fiber that modulates the postprandial glucose rise by multiple mechanisms. In fact, dietary fibers may increase ingesta viscosity, thus delaying the gastric emptying time and slowing both carbohydrate digestion and the rate of glucose transport to enterocytes. In addition, they can influence the composition of the gut microbiota and induce the production of short-chain fatty acids that beneficially affect glucose and lipid metabolism. In short, the knowledge of food characteristics able to retard carbohydrate digestion and absorption in the intestine can help modify food properties with the aim of improving their functionality.     

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。     

人工模拟胃肠道模型在食源性致病菌异质性研究中的应用进展

探究食源性致病菌在人体胃肠道环境中的异质性以及与肠道菌群间的相互作用对食源性致病菌的控制和预防具有十分重要的意义。人工模拟胃肠道模型基于人体胃肠道的生理过程,在体外条件下模拟体内的消化吸收情况,可以部分或完全替代活体实验,是研究食源性致病菌异质性以及致病机理的一种重要工具。本文系统综述应用人工模拟胃肠道模型研究食源性致病菌在胃肠道中的耐受、耐药异质性,为研究食源性致病菌在人体胃肠道中的异质性提供理论参考,同时将其与食源性致病菌动物感染模型（体内胃肠道模型）进行比较,综合评价人工模拟胃肠道模型在食源性致病菌异质性研究中的应用,以期为构建更加全面、科学的食品安全风险评估体系提供一定指导。     

大米主食制品中污染物镉的体外消化释放研究

对含污染物镉的大米主食样品米饭和米线进行体外模拟消化,采用石墨炉原子吸收分光光度法(GF-AAS)对样品中镉进行定量检测。口腔阶段镉释放率:生大米原料粉(34.85%)米线(5.69%)米饭(0%);胃阶段释放率:米饭(74.51%)米线(71.62%)生大米原料粉(0%);小肠阶段中的最大释放率为:4 h时生大米原料粉(60.19%)7 h时米线(45.35%)5 h时米饭(37.06%)。结果表明:不同大米主食样品在不同消化阶段中污染物镉的消化释放有显著差异,已消化释放出的镉在不同时间和消化部位还会被重新吸附结合,使镉释放率增加又降低;在小肠1~3 h消化时间下,米饭中镉消化释放率显著大于米线样品,而小肠消化3h后,则相反。该研究结果可作为大米及制品中污染物镉生物可给性的研究基础,为进一步合理食用和风险暴露评估提供参考。     

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。     

Invited review: Dairy proteins and bioactive peptides: Modeling digestion and the intestinal barrier

Dairy products are one of the most important sources of biologically active proteins and peptides. The health-promoting functions of these peptides are related to their primary structure, which depends on the parent protein composition. A crucial issue in this field is the demonstration of a cause-effect relationship from the ingested protein form to the bioactive form in vivo. Intervention studies represent the gold standard in nutritional research; however, attention has increasingly been focused on the development of sophisticated in vitro models of digestion to elucidate the mechanism of action of dairy nutrients in a mechanistic way and significantly reduce the number of in vivo trials. On the other hand, the epithelial intestinal barrier is the first gate that actively interacts with digestion metabolites, making the intestinal cells the first target tissue of dairy nutrients and respective metabolites. An evolution of the in vitro digestion approach in the study of dairy proteins and derived bioactive compounds is the setup of combined in vitro digestion and cell culture models taking into consideration the endpoint to measure the target organism (e.g., animal, human) and the key concepts of bioaccessibility, bioavailability, and bioactivity. This review discusses the relevance and challenges of modeling digestion and the intestinal barrier, focusing on the implications for the modeling of dairy protein digestion for bioactivity evaluation.