5000/壳聚糖水凝胶微球模板的载肝素层层自组装微胶囊

静电层层自组装是微胶囊载药简单有效的方法。本文采用硫酸钠沉淀的方法制备了具有正电荷的壳聚糖微球模板,通过层层自组装的方法装载抗凝血药物肝素。壳聚糖（CS）作为聚阳离子和肝素作为聚阴离子,在壳聚糖微球的模板上层层自组装形成{CS/Hep}3。{CS/Hep}3包被壳聚糖微球模板的微胶囊通过荧光倒置显微镜、激光共聚焦显微镜和激光粒度分析进行了表征。壳聚糖和肝素的层层自组装过程通过Zeta电位分析进行了监测。结果表明{CS/Hep}3包被壳聚糖微球模板的微胶囊平均直径1μm,包封率和载肝素量分别为83.8%和3.05%。     

壳聚糖微球/纳米羟基磷灰石/聚乳酸-羟基乙酸复合支架制备及其蛋白缓释效果：与单纯纳米羟基磷灰石/聚乳酸-羟基乙酸支架、壳聚糖微球的比较

背景：骨组织工程骨构建中如何使生长因子持续高效发挥作用是影响成骨速度和质量的关键,现多以各种材料的微球或支架作为缓释载体,但缓释作用有待提高。 目的：实验拟制备壳聚糖微球,然后复合到纳米羟基磷灰石/聚乳酸-羟基乙酸支架上,形成双重缓释作用,并测量对牛血清白蛋白的释放效果。 方法：以牛血清白蛋白为模型药物,采用乳化交联法制备壳聚糖微球。将微球与纳米羟基磷灰石、聚乳酸-羟基乙酸按一定比例混合,以冰粒子为致孔剂,采用冷冻干燥法制备壳聚糖微球/纳米羟基磷灰石/聚乳酸-羟基乙酸复合支架。利用扫描电镜、激光粒度分析仪、压泵仪和力学性能测试仪检测复合支架的形态性能,考察药物在缓释支架上的体外释放规律。 结果与结论：所制备的壳聚糖微球形态良好,呈规则圆球形,粒径集中分布在20~40 μm,微球药物包封率为86.5%,载药量为0.8%,随牛血清白蛋白初始用量的增加,载药量可升高至2.6%,但包封率下降至74.1%。壳聚糖微球能均匀分布在聚乳酸-羟基乙酸支架上,形成壳聚糖微球/纳米羟基磷灰石/聚乳酸-羟基乙酸复合支架,孔径为100~400 μm,孔隙率> 80%,压缩强度为1.1~2.3 MPa,10周降解率为26.5%。单纯纳米羟基磷灰石/聚乳酸-羟基乙酸支架其牛血清白蛋白在36 h累积释放量达85%以上,壳聚糖微球其牛血清白蛋白10 d累积释放量为33.6%,复合支架其牛血清白蛋白40 d累积释放量为81.5%。结果证实包埋壳聚糖微球的纳米羟基磷灰石/聚乳酸-羟基乙酸支架其压缩强度和降解速率合适,对蛋白类药物具有良好的缓释作用,有望作为组织工程的支架材料和生长因子的缓释载体。 关键词：聚乳酸-羟基乙酸;支架;壳聚糖;缓释载体;骨修复材料,组织工程;生物材料 doi:10.3969/j.issn.1673-8225.2010.03.017     

Centrally mediated hypoglycemic effect of insulin: apparent involvement of specific insulin receptors

We have studied the involvement of central nervous system (CNS) insulin receptors in mediating the central hypoglycemic effect of insulin by using insulin derivatives modified at regions of the hormone necessary for receptor reactivity and peripheral bioactivity. Acetylation or succinylation of the 3 free amino groups of insulin at positions A1, B1 and B29 resulted in a corresponding decrease in lipogenic activity in isolated rat adipocytes, with concentrations of hormone required to produce half the maximal effect (ED₅₀) being 0.15 ng/ml, 3 ng/ml and 50 ng/ml for native insulin, acetyl₃ insulin and succinyl₃ insulin, respectively. Moreover, the modified insulins exhibited diminished hypoglycemic effect following central administration in mice, with the doses needed for suppresion of plasma glucose to 50% of basal levels being 1 μg, 10 μg and 25 μg for native insulin, acetyl₃ insulin and succinyl₃ insulin, respectively. Because binding of insulin derivatives to CNS receptors can be predicted from their peripheral bioactivity, the present finding of parallel decrements in lipogenic activity in vitro and central hypoglycemic effect in vivo, following modification of insulin at regions implicated in receptor activation, is consistent with the view that insulin exerts its central effect on plasma glucose by interacting with specific CNS receptor sites which are closely related to the peripheral insulin receptors.     

Endogenous opioids modulate the effect of cholecystokinin on insulin release in dogs

Recently we have demonstrated in dogs and man that endogenous opioids participate in the regulation of pancreatic endocrine function following the ingestion of a meal. Since intestinal hormones such as cholecystokinin (CCK) are also released by the presence of nutrients in the gastrointestinal tract and participate in the postprandial stimulation of pancreatic endocrine function, an interaction between CCK and endogenous opioids seems possible. The present study was designed to examine this further. In a group of 8 conscious dogs the octapeptide of CCK was infused intravenously in its sulfated (CCK-8S) or nonsulfated (CCK-8NS) form and in addition the tetrapeptide of CCK (CCK-4) was given at increasing infusion rates of 50, 200 and 500 pmol/kg . h, respectively. The experiments were performed during a background infusion of saline to assess the effect on basal insulin and during a background infusion of glucose (0.2 g/min) to determine the effects on stimulated insulin release. The effect of endogenous opioids was examined by addition of the opiate-receptor antagonist naloxone. The studies demonstrate that in the basal state CCK-8S has no stimulatory effect on insulin secretion unless naloxone is added indicating that endogenous opioids help to prevent insulin secretion in the absence of elevated glucose levels. During i.v. glucose naloxone reduced the stimulatory effect of CCK-8S at 50 and 200 pmol/kg . h and that of CCK-4 at 50 pmol/kg . h. Infusion of CCK-8S and CCK-4 at 500 pmol/kg . h had no effect on glucose-stimulated insulin levels, however, the addition of naloxone elicited a significant stimulatory effect. These data demonstrate stimulatory as well as inhibitory effects of endogenous opioids depending on the dose of CCK-8 and -4. CCK-8NS reduced glucose-stimulated insulin release already at the lowest dose of 50 pmol/kg . h. This was reversed to a stimulatory effect with the addition of naloxone. These data demonstrate that the interaction between CCK-8 and -4 and endogenous opioids on prestimulated insulin secretion is much more dependent on the dose of CCK - low doses induce stimulatory and high doses inhibitory mechanisms via endogenous opioids. In view of previous in vitro and in vivo studies with exogenously infused opiate-active compounds it might be speculated that increasing doses of CCK elicit a parellel increase in the release of endogenous opioids which might be responsible for some but certainly not all of the effects observed recently for the action of naloxone in the post-prandial state.     

Nervous regulation of insulin release by the intestinal vagal glucoreceptors

In anesthetized cats and rats, it is demonstrated that glucose perfusion of the small intestine produces a rapid increase of insulin secretion (IRI) which precedes glycemia variation. This mechanism involves the autonomic nervous system and originates from intestinal glucoreceptors, the existence of which was recently reported. The nervous pathways are described in this study:(1) the afferent pathway is represented by vagal fibers coming from the intestinal glucoreceptors; (2) the efferent pathway involves both sympathetic fibers (splanchnic nerves) and chiefly parasympathetic fibers (vagal nerves). These results are established after surgical suppression of afferent and efferent vagal fibers, and pharmacological exclusion of parasympathetic or sympathetic fibers. The role of this nervous regulation of insulin secretion is discussed with special reference to other already known mechanisms.     

Neurogenic and non-neurogenic mechanisms in response of rat distal colon muscle to dextran sulphate sodium treatment

We studied, by organ bath methodology, how experimental colitis in rat, induced by the administration of dextran sulphate sodium (DSS) in the drinking water (3% for 3 or 7 days, or 5% for 7 days; Controls received ordinary tap water), may influence spontaneous, contractile activity of the longitudinal muscle layer. DSS treatment caused a dose-dependent increase in phasic contractile activity of the colon muscle. This effect needed an optimal preload of the tissues to be evident, and was non-neurogenic (i.e. myogenic and/or paracrine) in nature. Moreover, the DSS treatment appeared to impair a neurogenic, nitric oxide (NO)-dependent, relaxant response to the stretch (i.e. preload) applied to the tissues. Inducible NO synthase was localized by immunohistochemistry to infiltrating mononuclear cells in the colon wall. We propose that NO, via the inducible pathway, exerts marked effects on the neuromuscular apparatus in the DSS model of experimental colitis.     

海藻酸钠-多聚赖氨酸-海藻酸钠微囊内细胞浓度与胰岛素和C肽的释放**

摘要 背景：微囊化已经普遍应用于各种实验研究,微囊包裹的干细胞治疗糖尿病问题也成为当今的热点,但是囊内包裹的细胞浓度与胰岛素释放量的关系成为目前需要解决的问题之一。 目的：运用海藻酸钠-多聚赖氨酸-海藻酸钠微囊包裹胰岛素产生细胞,观察细胞浓度对胰岛素和C肽释放情况的影响。 方法：制备大鼠胰腺损伤提取物,将小鼠骨髓间充质干细胞诱导分化为胰岛素产生细胞。免疫荧光和双硫腙染色鉴定诱导后细胞内胰岛素的表达。然后将胰岛素产生细胞制成浓度分别为1×107 L-1,5×107 L-1,1×108 L-1,5×108 L-1,1×109 L-1,5× 109 L-1的细胞悬液,气体吹喷法制成微囊,用6-羧基乙二酸荧光素检测囊内细胞活力,用葡萄糖刺激微囊内细胞检查其胰岛素和C肽的分泌情况。 结果与结论：胰腺损伤提取物诱导后双硫腙染色和细胞免疫荧光鉴定出胰岛素产生细胞内有胰岛素的表达;胰岛素产生细胞制成的微囊直径约为400 µm,大小均一,6-羧基乙二酸荧光素检测到囊内细胞的活力很好。用葡萄糖刺激不同细胞浓度的微囊,发现细胞浓度为1×108 L-1时,胰岛素和C肽的分泌达到最高。 关键词：微囊化;骨髓间充质干细胞;胰岛素产生细胞;胰岛素;C肽 doi:10.3969/j.issn.1673-8225.2011.03.046