绿茶降糖作用机制的研究

给糖尿病大鼠口服蔗糖或淀粉和绿茶提取物后,观察其对糖尿病大鼠糖耐量及血胰岛素的影响,并用比色法测定对α-葡萄糖苷酶(EC 3.2.1.20)和α-淀粉酶(EC 3.2.1.1)的抑制活性,用快速过滤法观察对兔小肠刷状缘囊泡葡萄糖转运活性的影响.结果表明,绿茶提取物明显改善蔗糖或淀粉负荷糖尿病大鼠的血糖水平.绿茶提取物显示较强的α-葡萄糖苷酶抑制活性,其α-葡萄糖苷酶的半抑制浓度(IC50)值为0.13g/L;对α-淀粉酶的抑制活性则较弱,浓度为1g/L时,其对α-淀粉酶的抑制率为21%.绿茶提取物同时明显降低兔小肠刷状缘囊泡葡萄糖转运能力,其半抑制浓度(IC50)值为3.5g/L.提示,绿茶可延缓小肠对糖的消化吸收,经常食用可能有助于延缓餐后血糖的持续升高. C 3.2.1.1)的抑制活性,用快速过滤法观察对兔小肠刷状缘囊泡葡萄糖转运活性的影响.结果表明,绿茶提取物明显改善蔗糖或淀粉负荷糖尿病大鼠的血糖水平.绿茶提取物显示较强的α-葡萄糖苷酶抑制活性,其α-葡萄糖苷酶的半抑制浓度(IC50)值为0.13g/L;对α-淀粉酶的抑制活性则较弱,浓度为1g/L时,其对α-淀粉酶的抑制率为21%.绿茶提取物同时明显降 兔小肠刷状缘囊泡葡萄糖转运能力,其半抑制浓度(IC50)值为3.5g/L.提示,绿茶可延缓小肠对糖的消化吸收,经常食用可能有助于延缓餐后血糖的持续升     

西青果提取物对α-葡萄糖苷酶抑制活性的研究(Ⅲ)

研究西青果提取物对小肠α-葡萄糖苷酶的抑制作用。西青果提取物在体外和小肠模型人类结肠Caco-2细胞中,显示很强的麦芽糖酶抑制活性,而对蔗糖酶的抑制作用不显著。在体内实验中,西青果提取物能降低SD雄性大鼠进食麦芽糖30min后的血糖,而对进食蔗糖后的血糖浓度没有影响。实验结果表明西青果提取物可以预防Ⅱ型糖尿病。     

西青果提取物对a-葡萄糖苷酶抑制活性的研究（III）

研究西青果提取物对小肠α - 葡萄糖苷酶的抑制作用。西青果提取物在体外和小肠模型人类结肠Caco-2 细胞中,显示很强的麦芽糖酶抑制活性,而对蔗糖酶的抑制作用不显著。在体内实验中,西青果提取物能降低SD雄性大鼠进食麦芽糖30min 后的血糖,而对进食蔗糖后的血糖浓度没有影响。实验结果表明西青果提取物可以预防Ⅱ型糖尿病。     

L-阿拉伯糖对α-葡萄糖苷酶抑制活性的体外试验研究

目的探讨L-阿拉伯糖对小肠α-葡萄糖苷酶的抑制作用及与阿卡波糖的联用效应。方法利用体外实验,提取大鼠小肠粘膜上清液为α-葡萄糖苷酶粗酶液,分别以终浓度为60 mg/ml蔗糖、20 mg/ml麦芽糖/α-糊精为底物,建立最佳抑制反应体系,测定L-阿拉伯糖对α-葡萄糖苷酶抑制活性(IC50)及抑制作用类型;采用4×3析因设计,研究L-阿拉伯糖与阿卡波糖联用效果。结果以蔗糖、麦芽糖、α-糊精为底物时,L-阿拉伯糖对小肠α-葡萄糖苷酶活性均有一定抑制作用,但选择性较高地抑制蔗糖酶活性,当L-阿拉伯糖添加量为0.5%蔗糖浓度时酶活性抑制百分率>50%,最高酶活性抑制百分率约93%,且有良好剂量-反应关系,IC50为0.164 mg/ml,抑制类型为反竞争性抑制(Ki,0.558 mg/ml);与阿卡波糖联用二者有交互作用,尤其以蔗糖为底物时联用效果较明显,联合应用可能提高了抑制活性。结论 L-阿拉伯糖有抑制α-葡萄糖苷酶活性作用,尤其对蔗糖酶有良好的选择性抑制;在α-葡萄糖苷酶抑制作用方面,其与阿卡波糖有一定联用效果,L-阿拉伯糖在含糖食品中可能有较良好的实际应用前景。     

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,卵转铁蛋白胃消化产物分子质量范围为5~15 ku和30~50 ku,进一步经小肠消化后的产物分布在0.4~10 ku,最后经小肠刷状缘膜酶消化生成0.5~0.7 ku的肽段及部分5~13 ku的蛋白。卵转铁蛋白经模拟成年人胃消化的产物分子质量范围与模拟婴幼儿的一致,胃-小肠消化主要生成0.5~0.8 ku的肽段,再经小肠刷状缘膜酶消化后仍可生成0.5~0.7 ku的肽段。研究初步揭示卵转铁蛋白体外胃肠消化的规律,为卵转铁蛋白导致婴幼儿过敏提供部分试验依据。     

不同碳源对黑曲霉产糖化酶活力的影响

碳源对黑曲霉产糖化酶活力有很大影响。研究可溶性淀粉、葡萄糖、蔗糖、麦芽糖、乳糖和β-环糊精为碳源时,分别对黑曲霉产糖化酶活力的影响。结果表明,可溶性淀粉为碳源时酶活力最高,最高可达350．34±14．06U／ml;其次是葡萄糖;蔗糖和麦芽糖为碳源时酶活力没有显著性差异;乳糖为碳源时酶活力低于蔗糖和麦芽糖;β-环糊精的酶活力最低。不同碳源发酵培养基中生物量研究表明,黑曲霉能充分利用可溶性淀粉、葡萄糖、蔗糖和麦芽糖,对乳糖的利用较差,几乎不能利用β-环糊精。     

大豆肽对断奶小鼠肠道生长和粘膜二糖酶活性的影响

大豆蛋白经木瓜蛋白酶酶解并过层析柱后得到大豆肽,茚三酮法测定其平均肽链长度,观察了灌喂0.25ml/d生理盐水(对照组)、4、12、20mg/ml大豆肽对小鼠肠道生长和粘膜二糖酶活性的影响。结果表明:与对照组相比,灌喂0.25ml浓度为12mg/ml的大豆肽可显著提高小鼠的体增重和小肠粘膜蛋白质含量(p<0.05),但对小肠长度和重量没有显著影响。灌喂0.25ml浓度为12和20mg/ml的大豆肽都极显著降低小鼠小肠粘膜麦芽糖酶和蔗糖酶的活性(p<0.01)。     

脱脂米糠可溶性膳食纤维对小肠葡萄糖吸收和转运的影响及其作用机制

目的:探讨绿色木霉发酵法制备的脱脂米糠可溶性膳食纤维(soluble dietary fiber from defatted rice bran,DRB-SDF)对小肠葡萄糖吸收和转运的影响及其作用机制。方法:以Caco-2细胞为研究对象,分别建立葡萄糖吸收和转运模型,设置正常组、阳性阿卡波糖对照组(25μg/mL)以及DRB-SDF低、中、高(2、4、8 mg/mL)剂量组。在DRB-SDF作用一定时间后,采用CCK-8法检测Caco-2细胞活力、氧化酶-偶联比色法检测葡萄糖质量浓度、酶活力检测试剂盒测定α-葡萄糖苷酶活力、逆转录实时荧光定量聚合酶链式反应测定α-葡萄糖苷酶以及SGLT-1、GLUT-2和Na~+-K~+-ATP酶mRNA的表达水平。结果:DRB-SDF质量浓度小于8 mg/mL时对Caco-2细胞增殖未产生显著影响。相比于正常组,DRB-SDF低、中、高剂量组葡萄糖吸收和转运水平均被抑制,并呈浓度依赖性。DRB-SDF作用后,Caco-2细胞α-葡萄糖苷酶活力明显被抑制,同时α-葡萄糖苷酶、SGLT-1、GLUT-2和Na~+-K~+-ATP酶mRNA的表达水平均显著下降(P0.05)。结论:DRB-SDF可能通过抑制α-葡萄糖苷酶活性,降低小肠上皮细胞葡萄糖转运载体蛋白SGLT-1、GLUT-2和Na~+-K~+-ATP酶mRNA的表达,抑制碳水化合物水解,占据葡萄糖的吸收位点等途径,延缓小肠葡萄糖的吸收和转运,最终降低餐后高血糖。     

碳源对白桦茸菌丝体生长及多糖活性的影响

以白桦茸为研究对象,采用平板培养及液体摇瓶培养的方式,观察、比较不同碳源（麦芽糖、葡萄糖、蔗糖、玉米淀粉、乳糖、玉米面粉、果糖、甘露醇、红薯淀粉、可溶性淀粉）对菌丝部分生物学特性及液体发酵产物活性的影响。固体培养结果表明：果糖、麦芽糖、蔗糖对菌丝生长速度影响较大,麦芽糖为碳源时,菌丝生长速度最快,达到0.302 cm/d,果糖和蔗糖可以延缓菌丝老化,而玉米面粉和葡萄糖的菌丝最为粗壮,麦芽糖和红薯淀粉的菌丝生长密度最高（密集处呈羊毛毡状）;同时,液体发酵结果表明：玉米面粉总生物量最大,葡萄糖次之。对于活性物质来说,随着培养时间的延长,大部分碳源均可促进活性物质的积累,以葡萄糖为碳源,11 d菌丝体多糖含量最高,其次为乳糖。红薯淀粉、玉米淀粉、麦芽糖、乳糖为碳源时,其菌丝水提液1,1-二苯基-2-三硝基苯肼（1,1-diphenyl-2-picrylhydrazyl radical,DPPH）自由基清除率可达到70%以上。     

大豆异黄酮植物雌激素在大鼠离体小肠中吸收的研究

目的：研究大豆黄酮和染料木素在雄性大鼠离体小肠中的吸收情况。方法：利用翻转的离体小肠囊，通过RP-HPLC检测囊腔内液、囊腔外液、粘膜中大豆黄酮和染料木素的含量，粘膜中总ATP酶活性对异黄酮的吸收进行研究。结果：在外翻的小肠囊腔内大豆黄酮(Da)和染料木素(Gen)吸收达到峰值所需的时间分别为2～3h、3～4h，且最大吸收率随着浓度的增加而呈逐渐降低的趋势；小肠粘膜中Da、Gen的含量呈现出明显的剂量依赖性，在同一浓度下小肠粘膜中Da、Gen的含量也呈现出明显的时间依赖性；Da和Gen对小肠粘膜中总ATP酶活性均有显著的促进作用。结论：上述结果提示，大豆异黄酮在离体小肠中的吸收主要是主动吸收。     

Effects of 50% Ethanol Extract from Rosemary (Rosmarinus officinalis) on α-Glucosidase Inhibitory Activity and the Elevation of Plasma Glucose Level in Rats, and Its Active Compound

ABSTRACT:  Rosemary ( Rosmarinus officinalis ) extract with 50% ethanol remarkably inhibited rat intestinal α-glucosidase (sucrase) activity when compared with 31 different herbs and spices (aqueous and 50% ethanol aqueous extracts). Rosemary-distilled extract obtained from 50% ethanol extract by evaporation inhibited α-glucosidase activity in the reaction with both maltose and sucrose. Maltose or sucrose was orally administered, with or without rosemary-distilled extract, to mice at a dose of 20 mg/mouse. A postprandial elevation in plasma glucose levels 30 min after administration of maltose or sucrose plus the distilled extract was significantly suppressed compared with glucose levels in mice that did not receive the distilled extract. A 0.01% aqueous solution of rosemary-distilled extract supplied as drinking water to streptozotocin (STZ)-induced diabetic mice significantly suppressed an increase in plasma glucose levels 4 d after injection of STZ. It was also shown that a 0.01% aqueous solution of the distilled extract inhibited α-glucosidase (maltase and sucrase) in the small intestine of STZ-induced diabetic mice. An active compound with IC₅₀ values of 290 μg/mL (maltase inhibitory activity) and 150 μg/mL (sucrase inhibitory activity) was isolated and identified to be 5,7,3',4'-tetrahydroxy flavone (luteolin). These results suggested that rosemary extract might be a beneficial food material in the prevention of diabetes and obesity.     

Bitter gourd (Momordica charantia) modulates activities of intestinal and renal disaccharidases in streptozotocin-induced diabetic rats

During diabetes, structural and functional changes in the alimentary tract are known to take place resulting in increased absorption of intestinal glucose and alterations in the activities of brush border disaccharidases. Similar observations are also reported in the renal cortex. In the present investigation, we examined the effect of feeding bitter gourd fruit devoid of seeds on activities of intestinal and renal disaccharidases, viz., maltase, sucrase, and lactase in streptozotocin-induced diabetic rats. Normal and diabetic rats were fed either with basal diet or a diet containing 10% bitter gourd powder. Specific activities of intestinal disaccharidases were significantly increased during diabetes, and supplementing bitter gourd in the diet clearly indicated amelioration in the activities of maltase and lactase during diabetes. However, a significant change was not observed with sucrase activity by feeding of bitter gourd. During diabetes, renal disaccharidase activities were significantly lower than those in the control rats. Bitter gourd supplementation was beneficial in alleviating the reduction in maltase activity during diabetes. However, not much change in the activities of sucrase and lactase was observed upon feeding. This positive influence of feeding bitter gourd on intestinal and renal disaccharidases clearly indicates their beneficial role in the management of diabetes, thus making diabetic animals more tolerant to hyperglycemia.     

Intestinal disaccharidase and dipeptidase activities in growing rats fed on a raw field bean diet

The effect of a faba bean diet on disaccharidase and dipeptidase activities in rat small intestine has been studied. Both maltase and sucrase activities significantly decreased in rats fed on the faba bean diet as compared with the controls. The inhibition seems to follow a non-competitive or mixed non-competitive pattern. On the other hand, legume-fed rats showed a slightly higher activity for intestinal glycyl-l-valine hydrolase. It has been suggested that the low nutritional value of diets containing Vicia faba, as a source of protein, was due to a reduction in both nutrient utilisation and intestinal enzymic activity, where polyphenolic compounds are possibly involved.     

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.     

Antihyperglycemic activity of polyphenolic components of black/bitter cumin <Emphasis Type="Italic">Centratherum anthelminticum</Emphasis> (L.) Kuntze seeds

The effect of black/bitter cumin seeds Centratherum anthelminticum (L.) Kuntze extract (CA) containing mixture of polyphenolic compounds was tested on rat intestinal α-glucosidases, human salivary α-amylase activity and postprandial hyperglycemia in rats. Polyphenolic components of C. anthelminticum seeds (CA) dose dependently inhibited rat intestinal disaccharidases. IC₅₀ values were found to be 34.1 ± 3.8, 62.2 ± 4.5 and 500.5 ± 11.9 μg of CA for rat intestinal sucrase, maltase and p-nitrophenyl α-d-glucopyranoside (PNP-glycoside), respectively. CA also inhibited human salivary α-amylase activity with IC₅₀ value of 185.5 ± 4.9 μg. The inhibitory effect of CA was found to be 8–32 fold more potent than dl-catechin but less effective than acarbose on rat intestinal disaccharidases and salivary α-amylase. The enzyme kinetic studies showed a non-competitive type of inhibition with a low K _i value of 30.24 μg, 76.67 μg and 341.60 μg of CA for maltase, sucrase and PNP-glycoside hydrolysis activities, respectively. The in vitro inhibition of glucosidases was further confirmed by in vivo maltose tolerance test in rats. Feeding of CA at 50–200 mg/kg body weight (b.wt) to maltose (2.0 g/kg b.wt), loaded rats significantly reduced the postprandial plasma glucose levels compared with acarbose. The inhibitory components of CA were identified as a mixture of polyphenolic compounds viz., gallic acid, protocatechuic acid, caffeic acid, ellagic acid, ferulic acid, quercetin and kaempferol. This study demonstrated that CA exerts antihyperglycemic effect by decreasing postprandial glucose in rats by modulating α- amylase and glucosidases (sucrase and maltase) activity and thus may be useful for the management of diabetes mellitus.     

Preparation of brush border membrane vesicles from fresh and frozen bovine intestine for nutrient uptake studies

Purified brush border membranes were obtained from homogenized jejunal epithelial cells of cattle by divalent cation aggregation of nonbrush border membranes and differential centrifugation. Membrane marker enzyme assays determined effectiveness of the fractionation procedure. Compared with cellular homogenate, maltase and sodium+-potassium+-adenosine triphosphatase specific activities in the membrane fraction isolated from the interface of discontinuous (35 and 45% wt/wt) sucrose gradients increased 14.5- and 1.9-fold whereas enzyme recoveries averaged 20.2 and 2.4%. These data indicate significant enrichment in brush border membranes with minimal basolateral membrane contamination. Vesicles formed from this membrane fraction had a predominately (93%) luminal side out orientation. After incubating vesicles with radiolabeled substrates, vesicles and accumulated substrates were separated from the incubation buffer by filtration and substrate uptake quantified by liquid scintillation counting. Observed uptake was the result of substrate accumulation within an osmotically active intravesicular space and was not due to nonspecific binding of the substrate to vesicular membranes. Vesicles exhibited sodium-dependent and independent substrate uptake pathways and were able to discriminate between substrate stereoisomers for uptake. Major differences were not detected between results obtained with vesicles prepared from fresh or frozen intestines. These vesicles can be utilized to investigate nutrient uptake by the bovine small intestine.     

Quercetin alleviates activities of intestinal and renal disaccharidases in streptozotocin-induced diabetic rats

Specific activities of both intestinal and renal dissacharidases, such as sucrase, maltase, and lactase, were altered in diabetic rats. Our study was focused to evaluate the effect of feeding quercetin - a bioflavanoid on intestinal and renal dissacharidases in streptozotocin-induced diabetic rats. The rats were fed with 0.1% quercetin in diet. A reduction in intestinal maltase and sucrase, activities in quercetin-fed diabetic rats was observed in contrast to the increased activities in the starch-fed diabetic rats. A significant amelioration in renal dissacharidase activities in quercetin-fed diabetic rats was observed when compared to decreased activity in starch-fed diabetic rats.