In vitro permeability of PBCA nanoparticles through porcine small intestine

The complex task of measuring intestinal permeability in basic and clinical science

Intestinal permeability is a key feature of intestinal barrier function. Altered intestinal permeability is described in many chronic diseases and may be a risk factor for disease development and a target for emerging therapeutics. Thus, reliable and sensitive methods to measure intestinal permeability in both the clinical and preclinical setting are needed. There is currently a large array of tests to choose from, each with advantages and disadvantages. When possible, a combination of methods should be used. The choice of tests should be based on a deep understanding of intestinal barrier physiology and the recognition of their limitations. This mini-review will highlight the advantages and limitations associated with intestinal permeability tests and will identify current problems in the field and how they can be addressed in the future.

Oral delivery of proteins by biodegradable nanoparticles

Successful administration of therapeutic proteins via the oral route has long eluded the drug delivery community; a variety of factors, both physical and physiological, have hindered the myriad approaches to increasing the bioavailability of orally administered therapeutic proteins, including: 1) pre-systemic degradation by enzymes and 2) poor penetration of the intestinal mucosa and epithelium. Even when bypassing the harsh, acidic environment of the stomach, the intestines pose significant obstacles to systemic uptake. For example, the lining of the gastrointestinal tract comprises a thick wall of epithelial cells covered by a layer of polysaccharides and mucus. In this review, we will discuss the biology underlying intestinal uptake of protein-containing, biodegradable nanoparticles, review insulin delivery as the most accepted model for oral delivery of proteins, and present a variety of new material systems enabling novel approaches to oral protein delivery which we believe will bring to bear the next therapeutic advances in our field.

Effect of crystal size on the in vitro dissolution and oral absorption of nitrendipine in rats

PURPOSE

To investigate the effect of crystal size on the dissolution and oral absorption of nitrendipine, a poorly soluble drug, in rats.

METHODS

Five types of nitrendipine crystal suspensions with different particle sizes (200 nm, 620 nm, 2.7 microm, 4.1 microm, 20.2 microm) were prepared either by the precipitation-ultrasonication or the anti-solvent precipitation method. The simulated intestinal fluid in the fasted state (FaSSIF) was selected as the dissolution medium, and the dissolution behaviors of different nitrendipine crystals were simulated based on a Noyes-Whitney type equation. The in vivo absorption and the absolute bioavailability of the different nitrendipine crystals were evaluated in Wistar rats.

RESULTS

The dissolution rate of nitrendipine was significantly increased by a reduction in particle size. The dissolution test in FaSSIF could discriminate between the differences in the dissolution rates of the different particle sizes, and the simulated results were in agreement with the observed dissolution curves. From the simulated T(50%) values (50% dissolution time), the dissolution rates of crystals with particle sizes of 200 nm, 620 nm, 2.7 microm, 4.1 microm and 20.2 microm were calculated to be 5.1 x 10(4), 1.0 x 10(4), 237, 64 and 11-fold greater than that of the raw crystals and resulted in absolute bioavailability of 61.4% 51.5%, 29.4%, 26.7%, 24.7%, respectively. The reduction in the drug particle size correlated well with incremental improvements in oral absorption. A good linear relationship was observed between the Log (T(50%)) and the absolute bioavailability of nitrendipine.

CONCLUSIONS

The dissolution rate and the oral bioavailability of nitrendipine were significantly affected by the crystal size, and the oral bioavailability could be improved significantly by preparing it as nanocrystals. FaSSIF can be used to predict differences in oral absorption of crystals with different particle sizes.

Mucus-penetrating nanoparticles for drug and gene delivery to mucosal tissues

Mucus is a viscoelastic and adhesive gel that protects the lung airways, gastrointestinal (GI) tract, vagina, eye and other mucosal surfaces. Most foreign particulates, including conventional particle-based drug delivery systems, are efficiently trapped in human mucus layers by steric obstruction and/or adhesion. Trapped particles are typically removed from the mucosal tissue within seconds to a few hours depending on anatomical location, thereby strongly limiting the duration of sustained drug delivery locally. A number of debilitating diseases could be treated more effectively and with fewer side effects if drugs and genes could be more efficiently delivered to the underlying mucosal tissues in a controlled manner. This review first describes the tenacious mucus barrier properties that have precluded the efficient penetration of therapeutic particles. It then reviews the design and development of new mucus-penetrating particles that may avoid rapid mucus clearance mechanisms, and thereby provide targeted or sustained drug delivery for localized therapies in mucosal tissues.

Preparation and evaluation of poly-butylcyanoacrylate nanoparticles for oral delivery of thymopentin

Thymopentin (Tp5) was loaded in poly-butylcyanoacrylate (PBCA) nanoparticles (NP) in order to enhance the oral bioavailability of Tp5. PBCA-Tp5-NP was prepared by nanoprecipitation methods. Dialyzing membrane method was employed to examine the in vitro release of PBCA-Tp5-NP in PBS, and Tp5 samples in the release medium were detected by HPLC. The cell proliferation test (³H-thymidine) was conducted to verify the PBCA-Tp5-NP bioactivity in vitro. The pharmacodynamical studies were performed on preimmunoinhibited rats and in flow cytometer. The size and the entrapment efficiency of PBCA-Tp5-NP were 178 ± 39 nm and 92.21 ± 1.08%, respectively. In vitro release data show that less than 60% Tp5 was released from lyophilized PBCA-Tp5-NP while 80% Tp5 was released from the colloidal PBCA-Tp5-NPs in 48 h. The proliferation test showed that PBCA-Tp5-NP had the similar effect as Tp5. The in vivo data showed that oral PBCA-Tp5-NPs had similar function as what intravenous Tp5 did. The oral bioavailability of Tp5 could be enhanced by PBCA nanoparticles. PBCA-Tp5-NP had the property of sustained-release and the efficacy of Tp5 was not changed after formulation.

Bioadhesive properties of Gantrez nanoparticles

Bioadhesive nanoparticles have been proposed as carriers for the oral delivery of poorly available drugs and facilitate the use of this route. This work summarises some experiments describing the bioadhesive potential of Gantrez nanoparticles fluorescently labeled with rhodamine B isothiocyanate. The adhesive potential of Gantrez was found to be stronger when folded as nanoparticles than in the solubilised form. Conventional nanoparticles displayed a tropism for the upper areas of the gastrointestinal tract, with a maximum of adhesion 30 min post-administration and a decrease in the adhered fraction along the time depending on the given dose. The cross-linkage of nanoparticles with increasing amounts of 1,3-diaminopropane stabilised the resulting carriers and prolonged their half-life in an aqueous environment; although, the adhesive capacity of nanoparticles, the intensity and the relative duration of the adhesive interactions within the gut as a function of the cross-linking degree. Finally, nanoparticles were coated with either gelatin or albumin. In the first case, the presence of gelatin dramatically decreased the initial capacity of these carriers to interact with the gut mucosa and the intensity of these phenomenons. In the latter, bovine serum albumin coated nanoparticles (BSA-NP) showed an important tropism for the stomach mucosa without further significant distribution to other parts of the gut mucosa.

Waiting to inhale: noninjectable insulin, are we there yet?

Subcutaneous injection has been the only route of insulin administration for patients with type 1 or type 2 diabetes for the past 80 years. Although research and development in this time has improved the insulin treatments themselves, it is only now that alternative routes of insulin administration are becoming viable. Many avenues of insulin administration have been explored, including oral, buccal, and pulmonary routes. However, these methods of noninvasive insulin delivery are not free from difficulties and only preliminary data are available for oral insulin pills and buccal insulin sprays. The most promising alternative route of delivery appears to be inhaled insulin and two devices are already in phase III testing. Nevertheless, inhaled insulin devices will still have to overcome some problems and recent studies show that these challenges are currently being confronted. It appears that years of research into noninvasive methods of insulin administration are close to fruition and this review outlines the most recent findings in this area.

Oral insulin delivery using P(MAA-g-EG) hydrogels: effects of network morphology on insulin delivery characteristics

Hydrogels of poly(methacrylic acid-g-ethylene glycol) were prepared using different reaction water contents in order to vary the network mesh size, swelling behavior and insulin loading/release kinetics. Gels prepared with greater reaction solvent contents swelled to a greater degree and had a larger network mesh size. All of the hydrogels were able to incorporate insulin and protected it from release in acidic media. At higher pH (7.4), the release rates increased with reaction solvent content. Using a closed loop animal model, all of the insulin loaded formulations produced significant insulin absorption in the upper small intestine combined with hypoglycemic effects. In these studies, bioavailabilities ranged from 4.6% to 7.2% and were dependent on reaction solvent content.

Formulation and characterization of spray-dried powders containing nanoparticles for aerosol delivery to the lung

Spray-drying is a common practice of powder preparation for a wide range of drugs. Spray-dried powders can be used to deliver particles to the lungs via a dry powder inhaler (DPI). The present study investigated the feasibility of developing a platform for aerosol delivery of nanoparticles. Lactose was used as the excipient and spray-dried with two different types of nanoparticles: gelatin and polybutylcyanoacrylate nanoparticles. Results showed that some carrier particles were hollow while others had a continuous matrix. Gelatin nanoparticles were incorporated throughout the matrix and sometimes accumulated at one end of the lactose. Polycyanoacrylate nanoparticles mostly clustered in different spots within the lactose carriers. The mean sizes of both nanoparticle types were characterized at two different times: before they were spray-dried and after they were redissolved from the spray-dried powders. Both nanoparticle types remained in the nano-range size after spray-drying. The mean nanoparticle sizes were increased by approximately 30% after spray-drying, though this increase was statistically significant only for the gelatin nanoparticles. Dispersion of the powder with an in-house passive dry powder inhaler and subsequent cascade impaction measurements showed that incorporation of the nanoparticles did not affect the fine particle fraction (FPF) or mass median aerodynamic diameter (MMAD) of the powders. FPF was approximately 40% while MMAD was 3.0+/-0.2 microm, indicating the present formulations yield aerosols of a suitable particle size for efficient lung delivery of nanoparticles. The present work demonstrates that nanoparticles can be delivered to the lungs via carrier particles that dissolve after coming in contact with the aqueous environment of the lung epithelium. This opens the way for new drug-targeting strategies using nanoparticles for pulmonary delivery of drugs and diagnostics.

Regional intestinal absorption of FITC-dextran 4,400 with nanoparticles based on beta-sitosterol beta-D-glucoside in rats

Nanoparticles (NP) are potential carriers for drug delivery to the targeted intestine. NP based on beta-sitosterol beta-D-glucoside (Sit-G) enhanced the colon-specific absorption of FITC-dextran 4,400 (FD-4), because the concentration-dependent increase of bioavailability appeared in only the colon. In a permeation study, the absorption enhancement in the colon was suppressed in the following conditions: (1) the addition of Sit-G NP to serosa; (2) a permeation study at 4 degrees C; (3) the addition of endocytosis inhibitor, cytochalasin B. NP based on sitosterol, the aglycon of Sit-G, did not increase the FD-4 colonic permeation. The addition of Sit-G NP to the mucosal side induced a decrease of transepithelial resistance (TEER), but this phenomenon was suppressed by an inhibitor of Na(+)-dependent specific glucose transporter, phrolidzin, which did not affect FD-4 permeation. These findings suggested that absorption enhancement by Sit-G NP may not be due to opening of a tight junction, but might be related to endocytosis via glucose residue of Sit-G.

Design of nanoparticles composed of graft copolymers for oral peptide delivery

The development of a dosage form that improves the absorption of peptide and protein drugs via the gastrointestinal tract is one of the greatest challenges in the pharmaceutical field. Many researchers have taken up the challenge, using approaches including mucoadhesive drug delivery, colon delivery, particulate drug delivery such as nanoparticles, microcapsules, liposomes, emulsions, micelles, and so on. The objective of this article is to provide the reader with outlines of novel nanoparticle technologies for oral peptide delivery based on polymer chemistry. The physicochemical properties of nanoparticles and their behavior on exposure to physiological media are greatly dominated by their chemical structures and surface characteristics. We will especially focus on the design of nanoparticles composed of novel graft copolymers having a hydrophobic backbone and hydrophilic branches as drug carriers.

Ileal uptake of polyalkylcyanoacrylate nanocapsules in the rat

The ileal uptake of polyalkylcyanoacrylate nanocapsules (less than 300 nm in diameter) has been investigated in the rat. Iodised oil (Lipiodol) was used as the tracer for X-ray microprobe analysis in scanning electron microscopy. Lipiodol nanocapsules, or an emulsion of Lipiodol, were administered in the lumen of an isolated ileal loop of rat. Lipiodol nanocapsules improved the absorption of the tracer as indicated by increased concentrations of iodine in the mesenteric blood (+27%, P < 0-01, compared with Lipiodol emulsion). Intestinal biopsies were taken at different time points and the samples underwent cryofixation and freeze-drying. The nanocapsules were characterized by their strong iodine emission, and electron microscopy of the biopsy samples revealed nanocapsules in the intraluminal mucus of the non-follicular epithelium, then in the intercellular spaces between enterocytes, and finally the nanocapsules were found within intravillus capillaries. However, nanocapsules were most abundant in the Peyer's patches, where the intestinal epithelium had been crossed by way of the specialized epithelial cells, designated membranous cells, or M cells, and their adjacent absorptive cells. These observations were confirmed quantitatively by measuring iodine concentrations in the various tissue compartments. Ten minutes after the intraluminal administration of Lipiodol nanocapsules, the emission of iodine peaked in the mucus (+77%, P < 0.01), in M cells (+366%, P <0.001), in enterocytes adjacent to M cells (+70%, P < 0.05) and in lymph vessels (+59%, P < 0.05). Polyalkylcyanoacrylate nanocapsules were able to pass through the ileal mucosa of the rat via a paracellular pathway in the non-follicular epithelium, and most predominantly, via M cells and adjacent enterocytes in Peyer's patches.

Ex vivo and in situ PLGA microspheres uptake by pig ileal Peyer's patch segment

We investigated the ability of pig ileal Peyer's patch segments to transport intestinal poly (D,L-lactide-co-glycolide) microspheres (PLGA MS) from intestinal lumen across the mucosae using in situ and ex vivo segments with confocal laser scanning microscopy (CLSM) and transmission electronic microscopy (TEM). From a global aspect, CLSM suggested that PLGA MS were translocated by M cells labelled with a FITC-conjugated anti-cytokeratin peptide 18, and transported through the follicle-associated epithelium (FAE) in the dome area in both types of experiments. At the ultrastructural level, TEM showed the traffic of PLGA MS throughout M cells, their transport into the basolateral invaginations of the M cells and their subsequent migration into the dome area and the follicular area in contact with macrophages and lymphatic vessels. Although in situ experiments allowed following the migration of PLGA MS until mesenteric lymph nodes, an ex vivo model could be used as a useful tool to study the targeting ability of PLGA MS formulations to the gut-associated lymphoid tissue (GALT).

Poly(alkyl cyanoacrylate) nanospheres for oral administration of insulin

Poly(alkyl cyanoacrylate) nanocapsules have been successfully used for oral administration of insulin in diabetic rats. This work reports a suitable formulation for insulin-loaded nanospheres composed of full polymeric structures formed by polymerization of isobutyl cyanoacrylate (IBCA) in an acidic medium, insulin (15 U/mL) being added to the polymerization medium 60 min after the onset of polymerization. These nanospheres (MW 364) displayed a mean size of 145 nm and an association rate of 1 U of insulin/mg of polymer. They protected insulin from the degradation by proteolytic enzymes in vitro, especially when they were dispersed in an oily medium (Miglyol 812) containing surfactive agents (Poloxamer 188 and deoxycholic acid). When dispersed in the same medium, insulin-loaded nanospheres (100 U/kg of body weight), administered perorally in streptozotocin-induced diabetic rats, provoked a 50% decrease of fasted glycemia from the second hour up to 10-13 days. This effect was shorter (2 days) or absent when nanospheres were dispersed in water with surfactive agents or not. Using 14C-labeled nanospheres loaded with [125I]insulin, it was found that nanospheres increased the uptake of [125I]insulin or its metabolites in the gastrointestinal tract, blood, and liver while the excretion was delayed when compared to [125I]insulin nonassociated to nanospheres; in addition, 14C- and 125I-radioactivities disappeared progressively as a function of time, parallel to the biological effect. Thus insulin-loaded nanospheres can be considered as a convenient delivery system for oral insulin at the prerequisite that they were dispersed in an oily phase containing surfactants.

Passage of peptides through the blood-brain barrier with colloidal polymer particles (nanoparticles)

Transport of the hexapeptide dalargin across the blood-brain barrier was accomplished using a nanoparticle formulation. The formulation consisted of dalargin bound to poly(butyl cyanoacrylate) nanoparticles by sorption, coated with polysorbate 80. Intravenous injection of this formulation to mice resulted in an analgesic effect. All controls, including a simple mixture of the three components (drugs, nanoparticles, and surfactant) mixed directly before i.v. injection, exhibited no effect. Analgesia was also prevented by pretreatment with naloxone. Fluorescent and electron microscopic studies indicated that the passage of the particle-bound drug occurred by phagocytic uptake of the polysorbate 80-coated nanoparticles by the brain blood vessel endothelial cells.

A distinctive electrophysiological signature from the Peyer's patches of rabbit intestine

1. Rabbit small intestinal segments containing Peyer's patches (PP) were examined in Ussing chambers using short-circuit current (Isc) recording. By comparison with control small intestinal mucosal segments, rabbit PP-containing epithelia exhibited decreased basal Isc, increased transepithelial resistance (TER) and unchanged potential difference (PD). 2. Carbachol caused a decrease in Isc in rabbit PP epithelia. Forskolin, dibutyryl cyclic GMP, histamine and the calcium ionophore, A23187, were without effect. In contrast, control epithelial segments of rabbit intestine responded to carbachol and forskolin with an increased Isc, indicative of electrogenic chloride secretion. The EC50 for carbachol was approximately 2 microM in both types of epithelia. Methacholine also caused an outward current in rabbit PP epithelia which had similar properties to that of carbachol. The effect of the cholinomimetics on rabbit PP was basolateral-sided, reversible, and sensitive to low concentrations of the general muscarinic cholinoceptor blockers, atropine, scopolamine and also to the M1 cholinoceptor blocker, pirenzepine. 3. The Isc response to cholinomimetics in rabbit PP was insensitive to bumetanide, amiloride, TEA, barium, acetazolamide, piroxicam and omeprazole, but was attenuated in the presence of ouabain. Using bilaterally-substituted solutions, the carbachol effect on rabbit PP Isc was abolished in chloride/bicarbonate-free, but not in chloride-free solutions, suggestive of stimulation of electrogenic bicarbonate absorption by the agent. Substitution for sodium abolished both the basal current and the Isc response to carbachol. Part of the effect of carbachol on PP Isc appeared to be mediated by submucosal neurones because addition of tetrodotoxin reduced the effect by 60%. 4 As microfold (M) epithelial cells predominate in the PP of the rabbit, the unusual phenotype of cholinomimetic-induced outward current may be used as an electrophysiological marker for these potential sites of oral vaccine delivery, and in particular it may also be of use as a marker for rabbit M cells.