Oil-encapsulating PEO-PPO-PEO/PEG shell cross-linked nanocapsules for target-specific delivery of paclitaxel

PEO-PPO-PEO/PEG shell cross-linked nanocapsules encapsulating an oil phase in their nanoreservoir structure was developed as a target-specific carrier for a water-insoluble drug, paclitaxel. Oil-encapsulating PEO-PPO-PEO/PEG composite nanocapsules were synthesized by dissolving an oil (Lipiodol) and an amine-reactive PEO-PPO-PEO derivative in dichloromethane and subsequently dispersing in an aqueous solution containing amine-functionalized six-arm-branched poly(ethylene glycol) by ultrasonication. The resultant shell cross-linked nanocapsules had a unique core/shell architecture with an average size of 110.7 +/- 9.9 nm at 37 degrees C, as determined by dynamic light scattering and transmission electron microscopy. Paclitaxel could be effectively solubilized in the inner Lipiodol phase surrounded by a cross-linked PEO-PPO-PEO/PEG shell layer. The paclitaxel-loaded nanocapsules were further conjugated with folic acid to achieve folate receptor targeted delivery. Confocal microscopy and flow cytometric analysis revealed that folate-mediated targeting significantly enhanced the cellular uptake and apoptotic effect against folate receptor overexpressing cancer cells. The present study suggested that these novel nanomaterials encapsulating an oil reservoir could be potentially applied for cancer cell targeted delivery of various water-insoluble therapeutic and diagnostic agents.     

Oral bioavailability and drug/carrier particulate systems

The oral route remains the preferred route of administration to ensure patient satisfaction and compliance. However, new chemical entities may exhibit low bioavailability after oral administration because of poor stability within the gastrointestinal tract, poor solubility in gastrointestinal fluids, low mucosal permeability, and/or extensive first-pass metabolism. Consequently, these new drug substances cannot be further developed using conventional oral formulations. This issue is addressed by an innovative approach based on the entrapment of drug molecules in drug/carrier assembling systems. The carrier materials are lipids, naturally occurring polymers or synthetic polymers, which are considered as nontoxic and biocompatible materials. Drug entrapment is intended to protect drug substances against degradation by gastrointestinal fluids. Fine drug/carrier particle size ensures increased drug dissolution rates. Carriers and particle supramolecular organization can be designed to enhance drug absorption through the intestinal epithelium and lymphatic transport. Promising preclinical results have been obtained with model drugs like paclitaxel, insulin, calcitonin, or cyclosporin. Attention has focused on mucoadhesive carriers like chitosan that favor an intimate and extended contact between drugs and intestinal cells, thus enhancing absorption. Addition of ligands such as lectins improves intestinal drug absorption through specific binding of the carrier to intestinal cell carbohydrates. In conclusion, drug/carrier particulate systems are an attractive and exciting drug delivery strategy for highly potent drug substances unsuitable for oral use. Further evidence will determine whether this approach has marked therapeutic benefits over conventional drug formulations and is compatible with large-scale industrial production and stringent registration requirements. Producing highly effective particulate systems requiring low-complexity manufacturing processes is therefore an ongoing challenge.     

生物响应酸性磷酸酶浓度的载药聚电解质的体外控释分析

研制一种可响应酸性磷酸酶浓度变化的聚电解质胶囊,(PAH/PSS-β-甘油磷酸酯)胶囊,在分析胶囊的理化性质的基础上对其阿霉素药物包封和体外控释行为进行研究.通过层层组装的方法,制备囊壁含有酸性磷酸酶底物β-甘油磷酸酯的空壳胶囊和囊壁不含酸性磷酸酶底物的对照空壳胶囊;用电镜测定胶囊的大小和形态:用MTT方法分析胶囊的生物相容性.通过药物浓度梯度法进行胶囊的阿霉素药物包封并测定其包封率.将酸性磷酸酶标准品、分泌酸性磷酸酶的HepG2细胞株分别与载药阿霉素胶囊和载药阿霉素对照胶囊作用,观察阿霉素胶囊的药物控释情况和对肿瘤细胞生长的影响.空壳(PAH/PSS-β-甘油磷酸酯)胶囊粒径多在200-300 nm之间,胶囊浓度≤250μtg/mL时生物相容性良好,对阿霉素的包封率迭68.12%;载药胶囊组和对照组分别与酸性磷酸酶标准品作用,至48 h时分别释放出载药量的38%和15%,两者差异具有显著的统计学意义(P<0.05);载药胶囊组较载药对照组对HepG2细胞株的生长抑制作用明显增加,24 h HepG2细胞凋亡相差7.59%(13.73 Vs 6.14),有明显统计学意义(P<0.05).囊壁含有酸性磷酸酶底物的载药聚电解质胶囊,可在体外响应酸性磷酸酶浓度变化,具有药物控释性状,为临床上有酸性磷酸酶升高的良、恶性疾病的药物控释治疗提供了一种新的方法,其应用前景值得进一步探讨.     

The effects of mefenamic acid on postprandial intestinal carbohydrate metabolism

The effects of mefenamic acid on the food-induced changes in intestinal carbohydrate metabolism were determined in an attempt to elucidate the mechanism(s) by which inhibition of prostaglandin synthesis enhances the postprandial increases in intestinal blood flow and oxygen consumption. The data show that when the luminal perfusate was was changed from saline to a nutrient/bile solution, there was an increase in carbohydrate utilization, which was offset by absorption of glucose from the lumen. Intravenous administration of mefenamic acid significantly increased both carbohydrate absorption and metabolism when food was placed in the lumen. Changes in carbohydrate absorption and metabolism have been shown to play an important role in determining the magnitude of glucose induced changes in intestinal blood flow and oxygen consumption. Therefore, it is possible that the ability of mefenamic acid to enhance significantly the food-induced increases in blood flow and oxygen consumption may be due in part to its effects on intestinal carbohydrate absorption and utilization.     

Characterisation of Mixing in the Proximal Duodenum of the Rat during Longitudinal Contractions and Comparison with a Fluid Mechanical Model Based on Spatiotemporal Motility Data

The understanding of mixing and mass transfers of nutrients and drugs in the small intestine is of prime importance in creating formulations that manipulate absorption and digestibility. We characterised mixing using a dye tracer methodology during spontaneous longitudinal contractions, i.e. pendular activity, in 10 cm segments of living proximal duodenum of the rat maintained ex-vivo. The residence time distribution (RTD) of the tracer was equivalent to that generated by a small number (8) of continuous stirred tank reactors in series. Fluid mechanical modelling, that was based on real sequences of longitudinal contractions, predicted that dispersion should occur mainly in the periphery of the lumen. Comparison with the experimental RTD showed that centriluminal dispersion was accurately simulated whilst peripheral dispersion was underestimated. The results therefore highlighted the potential importance of micro-phenomena such as microfolding of the intestinal mucosa in peripheral mixing. We conclude that macro-scale modeling of intestinal flow is useful in simulating centriluminal mixing, whereas multi-scales strategies must be developed to accurately model mixing and mass transfers at the periphery of the lumen.     

Topography of the rat blood-testis barrier after intratubular administration of intercellular tracers

Intratubular injection of electron-opaque tracers (lanthanum hydroxide, peroxidase) by micromanipulation showed that the intercellular spaces of the adluminal compartment are in continuity with the lumen of the rat seminiferous tubule at all stages of the spermatogenic cycle. This continuity involves the intercellular spaces which surround zygotene spermatocytes and late leptotene spermatocytes in stages X-XI. The present observations would seem to cast doubt on the real existence of a third compartment, or intermediate compartment, in the seminiferous epithelium. In the material which, in addition to intratubular administration, had been treated with intravascular tracer perfusion, we found the presence of a parabasal region of interSertoli junctions where the tracer stopped whatever its direction. Freeze-fracture replicas exhibit interSertoli tight junctions arranged, from basal lamina to lumen, in three well-defined patterns: in the most basal area, which is the zone of free penetration of tracers from the peritubular environment, junctions are very sparse or absent; a belt of closely apposed continuous and parallel junctions, also parallel to the basal lamina, is the exclusion zone which prevents tracer penetration from either direction; the most apical membrane areas display irregularly arranged, loosely spaced and frequently interrupted rows of particles, most tending to be perpendicular to the basal lamina. This area corresponds to the territory where the intraluminally injected tracer permeates the interSertoli space.     

Nuclear scintigraphic assessment of radiation-induced intestinal dysfunction

Radiation-induced damage to the intestine can be measured by abnormalities in the absorption of various nutrients. Changes in intestinal absorption occur after irradiation because of loss of the intestinal absorptive surface and a consequent decrease in active transport. In our study, the jejunal absorption of (99m)Tc-pertechnetate, an actively transported gamma-ray emitter, was assessed in C3H/Kam mice given total-body irradiation with doses of 4, 6, 8 and 12.5 Gy and correlated with morphological changes in the intestinal epithelium. The absorption of (99m)Tc-pertechnetate from the intestinal lumen into the circulation was studied with a dynamic gamma-ray-scintigraphy assay combined with a multichannel analyzer to record the radiometry data automatically in a time-dependent regimen. The resulting radioactivity-time curves obtained for irradiated animals were compared to those for control animals. A dose-dependent decrease in absorptive function was observed 3.5 days after irradiation. The mean absorption rate was reduced to 78.8 +/- 9.3% of control levels in response to 4 Gy total-body irradiation (mean +/- SEM tracer absorption lifetime was 237 +/- 23 s compared to 187 +/- 12 s in nonirradiated controls) and to 28.3 +/- 3.7% in response to 12.5 Gy (660 +/- 76 s). The decrease in absorption of (99m)Tc-pertechnetate at 3.5 days after irradiation correlated strongly (P < 0.001) with TBI dose, with the number of cells per villus, and with the percentage of cells in the crypt compartment that were apoptotic or mitotic. A jejunal microcolony assay showed no loss of crypts and hence no measured dose-response effects after 4, 6 or 8 Gy TBI. These results show that dynamic enteroscintigraphy with sodium (99m)Tc-pertechnetate is a sensitive functional assay for rapid evaluation of radiation-induced intestinal damage in the clinically relevant dose range and has a cellular basis.     

Internalization and transcytosis of pancreatic enzymes by the intestinal mucosa.

As early as the beginning of the twentieth century some data indicated that macromolecules are able to cross the intestinal mucosa to reach the blood. Further evidence was added over the years; however, pathways for this transport still remain to be established. We report here the transfer of two pancreatic enzymes, amylase and lipase, from the intestinal lumen to the blood. Both are present in higher concentrations in the intestinal mucosa and in blood of fed rats. Upon cholinergic stimulation of pancreatic secretion, there was not only an increase in blood enzyme concentrations, but evidence for internalization by duodenal enterocytes was obtained. Following insertion of fluorochrome-tagged amylase and lipase into the duodenal lumen of fasting rats, blood and intestinal tissues were sampled at different time points. Serum activities for both enzymes clearly increased with time. Light microscopy established internalization of both proteins by duodenal enterocytes, and immunogold outlined the pathway taken by both proteins across the enterocytes. From the intestinal lumen, enzymes are channeled through the endosomal compartment to the Golgi apparatus and to the basolateral membrane reaching the interstitial space and blood circulation. Transcytosis through the intestinal mucosa thereby represents an access route for pancreatic enzymes to reach blood circulation.     

Ferritin intestinal absorption.

Ferritin as a source of iron was consiered. A good iron absorption rate appears in normal rats with an in vivo absorption technique. The same absorption appears in iron-deficient animals. The iron stored in intestinal wall is lower in anemic rats than in normal ones, suggesting a higher draw of iron from lumen to blood.     

Intestinal absorption and metabolism of chlorpheniramine enantiomers in rat

Chlorpheniramine (CPAM) is a chiral antihistaminic drug commercialized as a racemic mixture. The intestinal absorption and metabolism of CPAM have been investigated in rat using in vivo (oral and IV administration), in situ (intestinal loop model), and in vitro (everted sac model) experiments. Oral and IV administrations of 20 mg/kg of the racemic mixture show that the pharmacokinetics of CPAM are stereoselective, with higher AUCs for the (+)-S-enantiomer compared to its antipode. The monodesmethyl metabolite (DCPM) was quantifiable in blood and its pharmacokinetics are stereoselective after oral but not after IV administration. Experiments using intestinal loops and everted sacs showed that the absorption is not stereoselective and that in vivo stereoselective formation of DCPM is presumably due to stereoselective hepatic metabolism. Moreover, the in vitro and in situ absorption of CPAM are not modified by modulators of P-glycoprotein and cytochromes P450 (cyclosporin A, ketoconazole).     

Absorption, migration and kinetics in peripheral blood of orally administered ovalbumin in a mouse model

Intestinal absorption of food proteins is well known, whereas its physiological significance remains to be investigated. Various amounts (1, 10 and 50 mg) of ovalbumin were orally administered to mice and the blood kinetics were subsequently analyzed by two-site ELISA. The blood ovalbumin concentration consistently reached its maximum (7-90 ng/ml) about 20 min after the oral administration and then gradually decreased in a dose-dependent manner. Only intact (45 kDa) and truncated (40 kDa) ovalbumins were always detected in the blood independently of the administration site, intra-stomach or intra-intestine, while various fragments of the protein were observed in the gastrointestinal lumen after the oral administration. Recognition by a specific monoclonal antibody and an acidic shift of its pI value suggested that the 40-kDa truncated ovalbumin was produced by intracellular limited proteolysis at its C-terminus. Such stable absorption and blood kinetics of undigested ovalbumin in normal mice suggest some sort of physiological significance for the intestinal uptake of intact food proteins.     

Evaluation of intestinal absorption of calcium by means of double-isotope methods and oral administration of the tracer

The percent intestinal absorption of calcium was measured in normal volunteers and in patients with idiopathic hypercalciuria employing the deconvolution method, the ratio of the two administered isotopes at equilibrium and the percent of dose present in plasma 2 hr after oral administration of the tracer. Comparison of results obtained showed that the technique based on the ratio between the two radioisotopes overestimates intestinal absorption by about 9% with respect to values calculated with the deconvolution method, but gives results comparable to those determined by oral administration of the isotope. The percent dose of the tracer 2 h after i.v. administration is closely correlated with the size of the miscible calcium pool. A less significant correlation exists between the size of the pool and percent of the dose 2 h after oral administration.     

Intestinal handling of an oral oleoyl-estrone gavage by the rat

Adult Zucker lean (Fa/?) female rats received a single 250 nmol oral gavage of 3H-labelled oleoylestrone in 0.2 ml of sunflower oil. After one hour, samples of arterial, portal and suprahepatic blood, and lymph were obtained and fractioned to determine the amount of radioactivity present in the form of free estrone, acyl-estrone and hydrophilic estrone esters in the blood of each vessel. Lipoprotein fractions (chylomicra + VLDL, LDL, HDL and lipoprotein-depleted plasma) were also analysed as well as the distribution of absorbed 3H-estrone in the intestine, specific organs and carcass. About one third of the oleoyl-estrone dose recovered was found in the tissues, mainly in the blood, the rest remaining relatively untouched in the intestinal content. High hypothalamic estrone uptake (compared with the rest of the brain) was observed. Data from non-radioactive estrone measurements showed a similar pattern of absorption and tissue distribution to that obtained by 3H-estrone tracking alone. In both cases, most of the estrone present in the intestinal lumen was absorbed as intact oleoyl-estrone, but a significant part was absorbed as free estrone. There is a net transfer of 3H-estrone into portal blood HDL, and part of the 3H-estrone is also loaded into lymph-carried chylomicra. A large share of free estrone is filtered by the liver, but most of the acyl-estrone absorbed passes unaltered. The oral administration of oleoyl-estrone results in significant absorption of the unaltered molecule, which is transferred to lymph-carried chylomicra and also directly to plasma HDLs. It may be inferred that the HDL fraction contains the physiological carrier of oleoyl-estrone in its role of ponderostat signal.     

Ammonia absorption from different parts of chicken intestine and its quantitative evaluation in situ

Ammonia was more rapidly absorbed from the ileum than the jejunum, and the lower the small intestine was, the more rapid was the absorption of lumen fluid. About 95% of ammonia-15N introduced into the intestinal sac having Meckel's diverticulum in the middle part disappeared in 30 min, of which 90% was recovered as non-protein-N in the blood of the mesenteric vein draining the sac and in the mucosa of the tested portion in 30 min. About 57% of ammonia which disappeared from the intestinal lumen was found as ammonia-N and 26% as other non-protein-N in the mesenteric blood. Maximal rates of appearance of total non-protein-15N and ammonia-15N in the mesenteric blood were found within 10 min and returned to the levels at 0-5 min in 30 min.     

Iodized oil as a complement to iodized salt in schoolchildren in endemic goiter in Romania

OBJECTIVE: To evaluate the long-term efficacy and possible side effects of low doses of iodized oil on iodine nutrition and thyroid function in endemic goiter in Romania. METHODS: Random selection of 214 schoolchildren aged 6-14 years. Serial measurements of urinary iodine, thyroid volume with ultrasound, serum concentrations of thyrotropin, free thyroxine, thyroglobulin and thyroid autoantibodies before and up to 2 years after the oral administration of 200 mg iodine in iodized oil. RESULTS: Urinary iodine concentrations indicated a moderate iodine deficiency before therapy, sharply increased soon after therapy and slowly decreased thereafter but remained within the normal range up to more than 1 year after therapy. The prevalence of goiter was 29% before the administration of iodized oil and 9% 1 year later. Thyroid function tests and autoantibodies were normal before and up to 2 years after therapy. CONCLUSION: A single dose of 200 mg iodine from oral Lipiodol appears adequate and safe for correcting moderate iodine deficiency in children.     

Intestinal single-pass in situ perfusion technique in rat: the influence of L-carnitine on absorption of 7-methoxytacrine

7-Methoxytacrine (7-MEOTA) is an acetylcholine-esterase inhibitor that is potentially useful in the therapy of some neurodegenerative disorders. L-carnitine (CRT) is a naturally occuring compound that is known to increase penetration of some compounds through biological barriers. Aim of this study was how CRT influenced transintestinal absorption transport 7-MEOTA in rat using single-pass intestinal in situ perfusion method. The rate of absorption of 7-MEOTA during luminal perfusion with single 7-MEOTA was compared with rate of absorption during simultaneous perfusion with 7-MEOTA and CRT and with absorption rate after the premedication with CRT for period of three days before beginning of perfusion. The methodical system was the perfusion of mesenterial bed (from arteria mesenterica superior to vena portae) and intestinal luminal perfusion (from duodenum to ileum). The lower transintestinal absorption in the course of simultaneously administration of CRT than just in case of perfusion with single 7-MEOTA has been found. On the contrary a significantly higher absorption of 7-MEOTA has been noted in group of rats premedicated with CRT for three consecutive days. The interpretation suggested that molecules of CRT incorporated into the metabolism of intestinal cells facilitated transport of 7-MEOTA (as a representative substance which is at least partly transferred by carrier mechanism). In case of simultaneous luminal perfusion with CRT and 7-MEOTA competitive over-saturation of carrier systems is probably.     

Absorption and metabolism of the mycotoxins alternariol and alternariol-9-methyl ether in Caco-2 cells in vitro

Alternariol (AOH) and alternariol-9-methyl ether (AME) are major toxins produced by fungi of the genus Alternaria. In order to simulate their in vivo intestinal absorption and metabolism, AOH and AME have been studied in differentiated Caco-2 cells and in the Caco-2 Millicell® system in vitro. AOH was found to be readily conjugated to two glucuronides and one sulfate, whereas AME gave rise to one major glucuronide and one sulfate. Whereas the glucuronides of AOH and AME were sequestered about equally well into the basolateral and the apical compartment, the sulfates of both toxins were preferentially released to the apical side. Unconjugated AOH but not AME aglycone reached the basolateral chamber. The apparent permeability coefficients (P_app values) were calculated for the aglycones as well as total mycotoxin-associated compounds using an initial apical concentration of 20 µmol/l AOH or AME. Based on these P_app values, AOH must be expected to be extensively and rapidly absorbed from the intestinal lumen in vivo and reach the portal blood both as aglycone and as glucuronide and sulfate. In contrast, intestinal absorption of AME appears to be poor and sluggish, with no AME agylcone and only AME conjugates reaching the portal blood.     

The effects of mefenamic acid on postprandial intestinal carbohydrate metabolism

The effects of mefenamic acid on the food-induced changes in intestinal carbohydrate metabolism were determined in an attempt to elucidate the mechanism(s) by which inhibition of prostaglandin synthesis enhances the postprandial increases in intestinal blood flow and oxygen consumption. The data show that when the luminal perfusate was changed from saline to a nutrient/bile solution, there was an increase in carbohydrate utilization, which was offset by absorption of glucose from the lumen. Intravenous administration of mefenamic acid significantly increased both carbohydrate absorption and metabolism when food was placed in the lumen. Changes in carbohydrate absorption and metabolism have been shown to play and important role in determining the magnitude of glucose induced changes in intestinal blood flow and oxygen consumption. Therefore, it is possible that the ability of mefenamic acid to enhance significantly the food-induced increases in blood flow and oxygen consumption may be due in part to its effects on intestinal carbohydrate absorption and utilization.     

A simplified method for determination of radioactive iron in whole-blood samples

For studies on iron absorption in man radioisotopes represent an easy and simple tool However, measurement of the orbital electron emitting radioiron, 55Fe, in blood is difficult and insufficiently described in the literature. The present study describes a relatively simple method for simultaneous determination of 55Fe and 59Fe in blood, using a dry-ashing procedure and recrystallization of the remaining iron. The detection limit of the method permits measurements of 0.1 Bq/ml blood thus allowing detection of less than 1% absorption from a 40 kBq dose, which is ethically acceptable in humans. The overall recovery of radioiron from blood is more than 90%, and the coefficient of variation, as judged by the variation in the ratio 55Fe/59Fe is in the order of 4%. Combined with whole-body counting of 59Fe and direct gamma-counting of 59Fe on blood samples, this method represents a sensitive method for studying the intestinal absorption of 55Fe and 59Fe in man and at the same time allows estimation of the amount of radioiron located in the vascular compartment.     

Intestinal transit of a glucose bolus and incretin kinetics: a mathematical model with application to the oral glucose tolerance test

The rate of appearance (R(a)) of exogenous glucose in plasma after glucose ingestion is presently measured by tracer techniques that cannot be used in standard clinical testing such as the oral glucose tolerance test (OGTT). We propose a mathematical model that represents in a simple way the gastric emptying, the transport of glucose along the intestinal tract, and its absorption from gut lumen into portal blood. The model gives the R(a) time course in terms of parameters with a physiological counterpart and provides an expression for the release of incretin hormones as related to glucose transit into gut lumen. Glucose absorption was represented by assuming two components related to a proximal and a distal transporter. Model performance was evaluated by numerical simulations. The model was then validated by fitting OGTT glucose and GLP-1 data in healthy controls and type 2 diabetic patients, and useful information was obtained for the rate of gastric emptying, the rate of glucose absorption, the R(a) profile, the insulin sensitivity, and the glucose effectiveness. Model-derived estimates of insulin sensitivity were well correlated (r = 0.929 in controls and 0.886 in diabetic patients) to data obtained from the euglycemic hyperinsulinemic clamp. Although the proposed OGTT analysis requires the measurement of an additional hormone concentration (GLP-1), it appears to be a reasonable choice since it avoids complex and expensive techniques, such as isotopes for glucose R(a) measurement and direct assessment of gastric emptying and intestinal transit, and gives additional correlated information, thus largely compensating for the extra expense.