Intestinal translocation of particulates — implications for drug and antigen delivery

Diatoms pass through the gastrointestinal barrier and lead to false-positive: an animal experiment

The diatom test has been used by forensic pathologist as standard for drowning, but the occurrence of false-positive results (presence of diatoms found in the tissues of subjects who died from causes other than drowning) draws criticism regarding the specificity of the test. Diatoms within food or water can be ingested through the gastrointestinal tract. However, the mechanisms of how the diatoms reach distant organs such as the lung, liver, and kidney have not been studied. In this article, we simulated the process of diatoms entering the gastrointestinal tract using gastric lavage on experimental rabbits. Diatoms are detected in lymph from a lymphatic vessel at the root of the mesentery, portal vein blood, aortic blood, lung, liver, and kidney samples in the gavage group. Of diatoms, 76.24% were the centric diatom, 99.86% of diatoms have a maximum size of less than 50 µm, and most of diatoms concentrate in the lung. Our study provided the evidence supporting the theory that the diatoms could pass through the gastrointestinal barrier and reach the rabbits' other internal organs. The diatoms could reach internal organs through the portal vein and lymphatic vessel at the root of the mesentery. This provides us new insight into our understanding of false-positive diatom test in forensic pathology.

Lipid-Based Nanoparticles as Oral Drug Delivery Systems: Overcoming Poor Gastrointestinal Absorption and Enhancing Bioavailability of Peptide and Protein Therapeutics

Delivery and formulation of oral peptide and protein therapeutics have always been a challenge for the pharmaceutical industry. The oral bioavailability of peptide and protein therapeutics mainly relies on their gastrointestinal solubility and permeability which are affected by their poor membrane penetration, high molecular weight and proteolytic (chemical and enzymatic) degradation resulting in limited delivery and therapeutic efficacy. The present review article highlights the challenges and limitations of oral delivery of peptide and protein therapeutics focusing on the application, potential and importance of solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) as lipid-based drug delivery systems (LBDDSs) and their advantages and drawbacks. LBDDSs, due to their lipid-based matrix can encapsulate both lipophilic and hydrophilic drugs, and by reducing the first-pass effect and avoiding proteolytic degradation offer improved drug stability, dissolution rate, absorption, bioavailability and controlled drug release. Furthermore, their small size, high surface area and surface modification increase their mucosal adhesion, tissue-targeted distribution, physiological function and half-life. Properties such as simple preparation, high-scale manufacturing, biodegradability, biocompatibility, prolonged half-life, lower toxicity, lower adverse effects, lipid-based structure, higher drug encapsulation rate and various drug release profile compared to other similar carrier systems makes LBDDSs a promising drug delivery system (DDS). Nevertheless, undesired physicochemical features of peptide and protein drug development and discovery such as plasma stability, membrane permeability and circulation half-life remain a serious challenge which should be addressed in future.

Oral administration of Escherichia coli in enteric coated microparticles induces serum antibodies against lipopolysaccharide antigens

Heat-killed Escherichia coli O55:B5 were encapsulated in microcapsules coated with a pH-sensitive enteric coating (methacrylic acid copolymer). Oral immunization of C57BI/6 x DBA/2 (BDF1) mice with encapsulated bacteria resulted in a humoral immune response directed against bacterial lipopolysaccharide (LPS). This response was greatly boosted by a second series of immunization and differed both quantitatively and qualitatively from that induced by intraperitoneal immunization with non-encapsulated heat-killed bacteria. The anti-LPS response following oral immunization was comprised almost exclusively of IgG1 subclass antibodies and was highly specific for the LPS of the immunizing bacteria. The anti-LPS response following intraperitoneal immunization consisted mainly of IgM and IgG2a antibodies which were crossreactive with several bacterial strains. Our results demonstrate that whole killed bacteria, encapsulated by an enteric coating and administered orally, effectively induces an antibody response to LPS in mice which shows a typical memory response following secondary challenge.

Development of particulate drug formulation against C. parvum: Formulation, characterization and in vivo efficacy

This research aims towards developing an alternative therapy against Cryptosporidium parvum using bioadhesive paromomycin and diloxanide furoate-loaded microspheres. Microspheres were prepared using chitosan and poly(vinyl alcohol) and two types of cyclodextrins (β-CD and DM-β-CD) for the potential use of treating cryptosporidiosis. This pathogen is associated with gastrointestinal illness in humans and animals. Microparticle formulations were characterized in terms of size, surface charge, drug release and morphology. In vivo bioadhesion properties of CHI/PVA microspheres were also evaluated in mice. Finally, the in vivo efficacy of CHI/PVA microspheres against C. parvum was tested in neonatal mouse model. In this work, microspheres prepared by spray-drying showed spherical shape, diameters between 6.67±0.11 and 18.78±0.07μm and positively surface charged. The bioadhesion studies demonstrated that MS remained attached at +16h (post-infection) to the intestinal cells as detected by fluorescence. This finding was crucial taking use of the fact that the parasite multiplication occurs between 16 and 20h post-infection. The efficacy of treatment was determined by calculating the number of oocysts recovered from the intestinal tract of mice after 7days of post-infection. Mice receiving orally administered microspheres with and without drug exhibited significantly lower parasite loads compared with the control mice. Ultrastructural observations by TEM bring to light the uptake of smallest particles by enterocytes associated with conspicuous changes in enterocytic cells. Completely recovery of cell morphology was detected after 24h of first inoculation with MS. CHI/PVA microspheres appear to be a safe and simple system to be used in an anticryptosporidial treatment. The distinctive features of neonatal mice requires further work to determine the suppressive effect of this particulate delivery system on C. parvum attachment in other animal models.

Nanoparticles for oral delivery: targeted nanoparticles with peptidic ligands for oral protein delivery

As the field of biotechnology has advanced, oral protein delivery has also made significant progress. Oral delivery is the most common method of drug administration with high levels of patient acceptance. Despite the preference of oral delivery, administration of therapeutic proteins has been extremely difficult. Increasing the bioavailability of oral protein drugs to the therapeutically acceptable level is still a challenging goal. Poor membrane permeability, high molecular weight, and enzymatic degradation of protein drugs have remained unsolved issues. Among diverse strategies, nanotechnology has provided a glimpse of hope in oral delivery of protein drugs. Nanoparticles have advantages, such as small size, high surface area, and modification using functional groups for high capacity or selectivity. Nanoparticles with peptidic ligands are especially worthy of notice because they can be used for specific targeting in the gastrointestinal (GI) tract. This article reviews the transport mechanism of the GI tract, barriers to protein absorption, current status and limitations of nanotechnology for oral protein delivery system.

Intestinal receptor targeting for peptide delivery: an expert's personal perspective on reasons for failure and new opportunities

The technology has been available more than 25 years that would enable the oral delivery of vaccines, proteins and peptides, thus avoiding the need for injection. To this day, injection is still the mode of delivery, yet not the main mode of choice. This review focuses on several of the potential modes for oral delivery of peptides, proteins and vaccines. Additionally, the review will provide the reader with an insight into the problems and potential solutions for several of these modes of oral delivery of peptides and proteins.

Enhanced mucosal and systemic immune responses obtained by porous silica nanoparticles used as an oral vaccine adjuvant: effect of silica architecture on immunological properties

Three different kinds of silica (S2, S1 and SBA-15) with different particle sizes (130, 430 nm and 1-2 μm) and different pore characteristics (i.e. pore size and shape) were developed as oral vaccine immunological adjuvants and the relationship between the silica architecture and immunological properties was investigated. The silica particles were characterized using SEM, TEM and nitrogen adsorption. Model antigen bovine serum albumin (BSA) was successfully entrapped into the silica pores to produce a sustained release vaccine delivery system. Compared with the responsiveness induced by parenteral administration of BSA emulsified in Freund's complete adjuvant (FCA), oral immunization with the silica/BSA formulation produced a stimulated humoral and mucosal (sIgA) response. The IgG and IgA titers induced by loading BSA was as follows: S1>S2>SBA-15. The highest IgG and IgA titers of S1 were attributed to its large honeycombed pores and the optimal particle diameter of 430 nm. The corresponding IgG1 and IgG2a titers were also investigated to confirm that BSA loaded in nanoparticles by oral immunization can induce both T-helper 1- and T-helper 2- (Th1 or Th2) mediated responses. We believe that the results of our research will open up new avenues for the formulation of oral vaccines.

Synthesis of a novel kind of carbon nanoparticle with large mesopores and macropores and its application as an oral vaccine adjuvant

The purpose of this study is to develop a novel kind of adjuvant for oral vaccine delivery. In order to effectively prevent the degradation of antigens in the gastrointestinal tract and optimize the uptake for M cells, a novel kind of hydrophobic carbon nanoparticle (C1) with the size of 470nm was synthesized by taking silica as a template and sucrose as a carbon source. Notably, there were large mesopores and macropores mainly of 40-60nm, which made it to be excellent candidate as an antigen carrier. C1 was characterized using SEM, TEM and nitrogen adsorption. Following oral immunization with BSA loaded in C1, the IgG titer reached to a level almost equal to that of parenteral administration of antigen emulsified in Freund's complete adjuvant (FCA). Mucosal IgA was also detected in intestinal, salivary and vaginal secretions, suggesting an effective stimulation of mucosal immune response. Besides, both T-helper 1 and T-helper 2 (Th1 or Th2) mediated responses were induced. We believe that the research will help in the design of novel vaccine adjuvant for improvement their potential on modulation of immune response.

Formulation design considerations for oral vaccines

Whilst oral vaccination is a potentially preferred route in terms of patient adherence and mass vaccination, the ability to formulate effective oral vaccines remains a challenge. The primary barrier to oral vaccination is effective delivery of the vaccine through the GI tract owing to the many obstacles it presents, including low pH, enzyme degradation and bile-salt solubilization, which can result in breakdown/deactivation of a vaccine. For effective immune responses after oral administration, particulates need to be taken up by the M cells however, these are few in number. To enhance M-cell uptake, particle characteristics can be optimized with particle size, surface charge, targeting groups and bioadhesive properties all being considerations. Yet improved uptake may not translate into enhanced immune responses and formulating particulates with inherent adjuvant properties can offer advantages. Within this article, we establish the options available for consideration when building effective oral particulate vaccines.

Biopharmaceutical parameters to consider in order to alter the fate of nanocarriers after oral delivery

Oral route is the most common route for the delivery of drugs because it is simple to implement and improves patient compliance and quality of life. However, oral absorption is limited by various physiological barriers and remains a scientific challenge. Nanometric-sized drug delivery systems are being extensively studied and provide promising potential for oral drug delivery. Many different technological solutions have been proposed to enhance the bioavailability or the targeting of drug after oral administration. To reach these goals, it is important to analyze the biopharmaceutical parameters to consider in order to alter the fate of nanocarriers after oral delivery. In the present review, the gastrointestinal barrier and physiological stress factors with regard to nanocarriers' performance or integrity issues are first described. Second, the different characteristics offered by the nanocarriers (size, surface composition and properties mediated by external factors such as ligands) and their effect on the optimal transport of drug into the bloodstream are discussed. Finally, the integrity issue is discussed in function of the expected role of the nanocarriers: bioavailability enhancement or pharmacological targeting.

Engineering strategies to enhance nanoparticle-mediated oral delivery

Oral delivery is the most preferred route of drug administration due to convenience, patient compliance and cost-effectiveness. Despite these advantages it remains difficult to achieve satisfactory bioavailability levels via oral administration due to the harsh environment of the gastrointestinal (GI) tract, particularly for biomacromolecules. One promising method to increase the bioavailability of macromolecular drugs such as proteins and nucleic acids is to encapsulate them in nanoparticles before oral administration. This review describes innovative strategies for increasing the efficacy of nanoparticle-mediated delivery to the GI tract. Approaches to optimize nanoparticle formulation by exploiting mucoadhesion, environmental responsiveness and external delivery control mechanisms are discussed. The application of recent advances in nanoparticle synthesis using supercritical fluids, microfluidics and imprint lithography to oral delivery are also presented, as well as possible strategies for incorporating nanoparticles into micro- and macroscale oral delivery devices.

The antitumor immune responses induced by nanoemulsion-encapsulated MAGE1-HSP70/SEA complex protein vaccine following peroral administration route

Previous studies have shown that there are profuse lymphatic tissues under the intestinal mucous membrane. Moreover, vaccine administered orally can elicit both mucous membrane and system immune response simultaneously, accordingly induce tumor-specific cytotoxic T lymphocyte. As a result, the oral route is constituted the preferred immune route for vaccine delivery theoretically. However, numerous vaccines especially protein/peptide vaccines remain poorly available when administered by this route. Nanoemulsion has been shown as a useful vehicle can be developed to enhance the antitumor immune response against antigens encapsulated in it and it is good for the different administration routes. Of particular interest is whether the protein vaccine following peroral route using nanoemulsion as delivery carrier can induce the same, so much as stronger antitumor immune response to following conventional ways such as subcutaneous (sc.) or not. Hence, in the present study, we encapsulated the MAGE1-HSP70 and SEA complex protein in nanoemulsion as nanovaccine NE (MHS) using magnetic ultrasound method. We then immuned C57BL/6 mice with NE (MHS), MHS alone or NE (-) via po. or sc. route and detected the cellular immunocompetence by using ELISpot assay and LDH release assay. The therapeutic and tumor challenge assay were examined then. The results showed that compared with vaccination with MHS or NE (-), the cellular immune responses against MAGE-1 could be elicited fiercely by vaccination with NE (MHS) nanoemulsion. Furthermore, encapsulating MHS in nanoemulsion could delay tumor growth and defer tumor occurrence of mice challenged with B16-MAGE-1 tumor cells. Especially, the peroral administration of NE (MHS) could induce approximately similar antitumor immune responses to the sc. administration, but the MHS unencapsulated with nanoemulsion via po. could induce significantly weaker antitumor immune responses than that via sc., suggesting nanoemulsion as a promising carrier can exert potent antitumor immunity against antigen encapsulated in it and make the tumor protein vaccine immunizing via po. route feasible and effective. It may have a broad application in tumor protein vaccine.

Use of Targeting Agents to Increase Uptake and Localization of Drugs to the Intestinal Epithelium

Despite early successes in oral drug delivery of small molecules such as antibiotics, cephalosporins and vitamins, little success has been achieved with more recent pharmaceuticals such as peptides and proteins. This lack of success is primarily due to the impenetrable nature of the gastro-intestinal epithelial cell layers. Despite this, many bacteria, viruses and toxins are readily taken up from the intestine and thereby gain entry into the circulation. This review focuses on the use of various surface molecules from these organisms as well as toxin binding subunits as carriers for oral delivery of other molecules. It also describes the subversion of the natural uptake mechanisms for various vitamins and iron to allow for oral delivery of pharmaceuticals. These mechanisms provide exciting solutions to overcome the problems in oral delivery of peptides and proteins, which has been the nemesis of pharmaceutical scientists for many decades.

Enhanced Oral Bioavailability and Intestinal Lymphatic Transport of a Hydrophilic Drug Using Liposomes

A liposome system was evaluated for oral delivery of a poorly bioavailable hydrophilic drug. The system was prepared from proliposome, which consisted of negatively charged phosphatidylcholine, whereas cefotaxime was chosen as the model drug. An in vivo study was carried out on nine rats according to a three-way crossover design to compare the oral bioavailability of cefotaxime from the liposomal formulation with that of an aqueous drug solution and a physical mixture of cefotaxime with blank liposomes. The results indicated that the extent of bioavailability of cefotaxime was increased approximately 2.7 and 2.3 times compared with that of the aqueous solution and the physical mixture, respectively. In a separate study, simultaneous determination of cefotaxime in intestinal lymph (collected from the mesenteric lymph duct) and in plasma (collected from the tail vein) revealed that its concentration was consistently higher in the lymph than in the plasma when administered via the liposomal formulation, whereas the reverse was observed with the aqueous solution. Thus, the results indicated that the liposomes system has the potential of increasing the oral bioavailability of poorly bioavailable hydrophilic drugs and also promote their lymphatic transport in the intestinal lymph.

Oral administration of peptides and proteins: nanoparticles and cyclodextrins as biocompatible delivery systems

This review discusses drawbacks to peptide and protein oral formulations related to these drugs’ chemical and physical instability. Means used to overcome such limitations are mentioned and discussed in parallel with manufacturing considerations, metabolism, absorption mechanisms and the efflux systems that peptides and proteins experience as they travel through the gastrointestinal tract. Special focus is given to the use of delivery systems based on nanoparticles and cyclodextrins. Advantages of these systems relate to the protection from degradation, enhancement of absorption, targeting and controlling the release of the drug. Biodistribution and safety issues are discussed once material from the delivery system is expected to be absorbed by the body and thus interact with biological components. Operating parameters regarding nanoparticle manufacture and composition are also overviewed since nanoparticle physicochemical characteristics influence the ability to successfully entrap the intended drug as well as interaction with body.

Nanoparticles as potential oral delivery systems of proteins and vaccines: a mechanistic approach

Peptides and proteins remain poorly bioavailable upon oral administration. One of the most promising strategies to improve their oral delivery relies on their association with colloidal carriers, e.g. polymeric nanoparticles, stable in gastrointestinal tract, protective for encapsulated substances and able to modulate physicochemical characteristics, drug release and biological behavior. The mechanisms of transport of these nanoparticles across intestinal mucosa are reviewed. In particular, the influence of size and surface properties on their non-specific uptake or their targeted uptake by enterocytes and/or M cells is discussed. Enhancement of their uptake by appropriate cells, i.e. M cells by (i) modeling surface properties to optimize access to and transport by M cells (ii) identifying surface markers specific to human M cell allowing targeting to M cells and nanoparticles transcytosis is illustrated. Encouraging results upon in vivo testing are reported but low bioavailability and lack of control on absorbed dose slow down products development. Vaccines are certainly the most promising applications for orally delivered nanoparticles.

Systemic trafficking of plant virus nanoparticles in mice via the oral route

The plant virus, cowpea mosaic virus (CPMV), is increasingly being used as a nanoparticle platform for multivalent display of peptides. A growing variety of applications have employed the CPMV display technology including vaccines, antiviral therapeutics, nanoblock chemistry, and materials science. CPMV chimeras can be inexpensively produced from experimentally infected cowpea plants and are completely stable at 37 degrees C and low pH, suggesting that they could be used as edible or mucosally-delivered vaccines or therapeutics. However, the fate of CPMV particles in vivo, or following delivery via the oral route, is unknown. To address this question, we examined CPMV in vitro and in vivo. CPMV was shown to be stable under simulated gastric conditions in vitro. The pattern of localization of CPMV particles to mouse tissues following oral or intravenous dosing was then determined. For several days following oral or intravenous inoculation, CPMV was found in a wide variety of tissues throughout the body, including the spleen, kidney, liver, lung, stomach, small intestine, lymph nodes, brain, and bone marrow. CPMV particles were detected after cardiac perfusion, suggesting that the particles entered the tissues. This pattern was confirmed using methods to specifically detect the viral capsid proteins and the internal viral RNA. The stability of CPMV virions in the gastrointestinal tract followed by their systemic dissemination supports their use as orally bioavailable nanoparticles.

Enhanced mucosal and systemic immune response with intranasal immunization of mice with HIV peptides entrapped in PLG microparticles in combination with Ulex Europaeus-I lectin as M cell target

The predominant route of HIV infection is through the sexual transmission via M cells. Most of the peptide and protein vaccines show poor transport across the epithelial barrier and are commonly administered by parenteral route. In the present study four HIV peptides from envelope (gp 41-LZ (leucine zipper), gp 41-FD (fusion domain) and gp120-C2) and regulatory (Nef) region in poly lactic-co-glycolide (PLG) micro-particle delivery were evaluated in mice of outbred and with different genetic background to compare immune response versus MHC restriction. Out of the combinational and single routes of immunization attempted, the single route maintained the IgG, IgA and sIgA in sera and washes for longer duration as compared to combinational routes in which the response was declined. The study demonstrated that single intranasal immunization offered significantly higher immune response (p<0.05) over oral and rectal mucosal routes in terms of inducing systemic as well as mucosal response. Also, the specific activity measurement of IgA and IgG in sera and sIgA in washes were correlating to the antibody titers. However, the intramuscular route of immunization generated systemic response only. The entrapment of plant lectin UEA-1 a ligand specific for M cells in micro-particle further enhanced the immune response in all the mucosal routes. The IgG isotypes generated were of IgG1 and IgG2a/2b in sera for all the peptides. The T cell proliferation response study with and without UEA-1 lectin in micro-particles showed significantly high (p<0.05) stimulation index (SI) with intranasal immunization for all the peptides from cells collected from spleen (SP), peyer's patches (PP) and lamina propria (LP) with SI in the order LP cells>PP>or=SP. The cytokine measurement profile of IL-2, IFN-gamma and IL-6 and low levels of IL-4 in the cultural supernatants of SP, PP and LP showed mixed CD4(+) Th1 and Th2 immune response. The p24 assay showed high percent inhibition of HIV-IIIB virus with sera and washes obtained from intranasal route. Thus, overall the study highlighted the combination of UEA-1 lectin with HIV peptides in micro-particles through intranasal immunization generated systemic as well as mucosal immune response.

Effect of reproductive status on uptake of latex microparticles in rat small intestine

This study investigates whether pregnancy or lactation affects microparticle uptake across the small intestinal mucosal barrier, since aspects of gastrointestinal physiology such as motility may be altered in these conditions. It also reports on validation of the model by several methods and discusses the findings in relation to possible mechanisms. Anaesthetised, pregnant, lactating, virgin female or male adult rats were gavaged with fluorescent latex microparticles. The small intestine was removed and fixed either 5 or 30 min later and successive segments of equal length were examined with fluorescence microscopy. Minor adjustments were made to experimental methods to explore details of the uptake mechanism. Control sections contained no particles. All experimental samples showed luminal and surface particles and also contained particles within the tissue, most associated with villous absorptive enterocytes. Particle uptake was greatest at the 30-min time-point, when maximum uptake was usually in the proximal jejunum; although in the early lactating group, this was shifted distally. Total tissue uptake was increased in pregnant and early lactating groups, mainly at villous absorptive and mucus-secreting cells. Accumulation and progression of particles was reflected in increased numbers in the lamina propria. These data were validated by several methods, including particle detection in the blood and mesenteric lymph nodes in some groups. At both time-points, uptake profiles for pregnancy and early lactation differed from those of other groups, implying possible links between particle uptake and hormone levels, surface mucus and tight junction patency.

Microencapsulated subunit vaccine approach to enterotoxigenic Escherichia coli and other mucosal pathogens

Infections of the intestinal, urogenital, and respiratory tracts are serious health problems worldwide from both a morbidity and mortality perspective. Mucosal pathogens attach to surfaces of mucosa as a prerequisite for colonization and subsequent pathogenesis. By expressing various surface adhesins (colonization factors, CF) they are able to bind to specific mucosal receptors. Enterotoxigenic Escherichia coli (ETEC) can express numerous CF that allow them to attach to a variety of hosts. Mucosal immunity directed against pathogenic microorganisms is critical in host protection with secretory IgA being particularly important in preventing microoganisms from colonizing host cells. M cells likewise have an important immunological function in the small intestines by binding and transporting antigens to lymphocytes and macrophages thus enhancing the immune response. The use of subunit vaccines, such as antigen encapsulated microspheres, can act to effectively deliver specific antigens so as to optimize their immunological response. With the threat of bioterrorism becoming a reality in recent years, the miroencapsulation of antigens from potential bioterrorist agents may be an effective method of delivery so as to induce a level of protection in at risk individuals. The encapsulation of ETEC colonization factors in microspheres and their subsequent administration in small animals and humans has been conducted for many years. Evidence suggests that this type of delivery system for ETEC antigens may enhance their immunogenicity and provide protection against this microorganism.

Drug delivery system using microspheres that contain tacrolimus in porcine small bowel transplantation

Rejection remains a major barrier to successful bowel transplantation, in spite of improved immunosuppressive techniques. Therefore, new, more effective, immunosuppressants, with fewer side effects, are needed. Biodegradable microspheres containing tacrolimus (FK506) were used in an experimental porcine small bowel transplantation. Twenty pigs underwent transplantation and were divided into four groups according to the immunosuppressive regimen. Group A (n = 5): no immunosuppression; group B (n = 6): 0.2 mg/kg per day of FK506; group C (n = 3): 1.0 mg/kg per day of FK506; group D (n = 6): 0.04 mg/kg per day of FK506 contained in biodegradable microspheres. Rejection was diagnosed macroscopically by endoscopic examination and histologically by biopsy specimen analysis. The mean survival time and standard deviation (SD) were 8.8+/-3.5, 11.0+/-1.4, 9.7+/-2.5 and 28.6+/-22.5 days for groups A, B, C, and D, respectively, with a statistically significant difference found between group D, on the one hand, and groups A, B and C, on the other. The mean trough blood concentration of FK506 was 10.5+/-2.2, 27.9+/-6.0 and 10.5+/-3.5 ng/ml in groups B, C and D, respectively. In groups A and B, all pigs died of rejection, without infection. In group C, all died of infection, without rejection. In contrast, none of the pigs in group D developed rejection or infection. Our results clearly show that the drug delivery system using biodegradable microspheres that contain FK506 is effective for controlling rejection with fewer side effects in the porcine small bowel transplantation.

Microparticles for the delivery of DNA vaccines

DNA vaccines have demonstrated a lack of adequate potency in humans, which has necessitated the exploration of various adjunct technologies. Inefficient delivery of DNA vaccines, particularly to antigen-presenting cells, may be contributing to this lack of potency. One effective means of facilitating delivery of DNA vaccines to APCs is through the use of microparticles. In this article, we review the background and rationale for microparticles as a vaccine delivery system, data demonstrating their utility and mode of action for DNA delivery, and the prospects for their development.

Sonication parameters for the preparation of biodegradable nanocapsules of controlled size by the double emulsion method

The main goal of the present work was to study the influence of the sonication process on the characteristics of poly(lactide-co-glycolide) nanocapsules prepared by the water-in-oil-in-water solvent evaporation method. The duration and intensity of sonication were investigated with respect to their ability to modify the size and distribution of the nanocapsule population. It has been demonstrated that the duration of the second mixing step (leading to the w/o/w emulsion) is of greater influence than that of the first step (water-in-oil emulsion) on the final mean particle size. A three-dimensional response surface was drawn up to show that when the second emulsification time increased, the mean size decreased until reaching a plateau. A threshold in sonication intensity also exists, allowing optimization of both parameters and the formation of nanocapsules of controlled size with a rather narrow distribution. The use of a vortex mixer instead of a sonicator during the first mixing step led to nanocapsules with a similar response surface, supporting the idea that the second step is the decisive one. Finally, nanocapsules loaded with methylene blue, a hydrophilic model compound with a positive charge, were characterized and the encapsulation efficiency calculated. Their size and distribution were similar to that of the blank nanocapsules. Entrapment efficiency was independent of duration, intensity, and type of mixing. From these results, it was concluded that nanocapsules of controlled size could be obtained upon optimizing certain process parameters.

Transport of nanoparticles across the rat nasal mucosa

The transport of 125I-radiolabelled latex nanoparticles across the nasal mucosa of rats was studied using a range of particle sizes and surface coatings. Translocation of the particles into the blood stream was examined by means of monitoring the radiolabel associated with the particles. Particles were detected in the blood after 5 minutes. The number of particles in the blood peaked at 60 minutes, and then remained constant for a further 2 hours. The smallest particles (20 nm) showed greater uptake than the largest particles investigated (1000 nm). The total maximum uptake seen for the smallest particles was in the order of 3.25% of administered dose. 100 nm particles coated with chitosan showed an increase in both the extent and rate of uptake, with the concentration in the blood peaking at 15 minutes rather than at 60 minutes. It is suggested that transport of the particles across the nasal membrane is due mainly to a transcellular transport mechanisms by the nasal associated lymphoid tissue (NALT), especially the M-cell like cells. However, some paracellular transport cannot totally be ruled out for the smallest particles, especially if coated with chitosan.

Induction of systemic and mucosal immune response in cattle by intranasal administration of pig serum albumin in alginate microparticles

Biodegradable microparticles are an efficient mucosal delivery system that protect antigens from the harsh mucosal environment and facilitate their uptake by M cells at the epithelium of mucosal-associated lymphoid tissue. In this study, we determined the systemic and mucosal immune response in calves following intranasal and oral immunization with pig serum albumin (PSA) encapsulated in alginate microparticles. The size of the particles ranged from 1 to 50 microm in diameter, with 95% of the particles being smaller than 5 microm. High levels of anti-PSA IgG1 antibodies were found in the serum, nasal secretions, and to a less extent in saliva of calves vaccinated intranasally, but not orally, with PSA-microparticles. There was no significant increase of PSA-specific IgA. A weak lymphocyte proliferative immune response was observed in peripheral blood mononuclear cells (PBMCs), and few anti-PSA antibody-secreting cells (ASC) were detected in the blood of calves immunized intranasally. The combined systemic and mucosal response observed in intranasally immunized animals may be attributed to the wide variation in the size of the alginate microparticles, with smaller particles translocating to regional lymph nodes and inducing a systemic immune response, and larger particles being retained in the NALT and inducing a mucosal immune response. The procedure presented here may be useful as an intranasal vaccine against respiratory diseases in cattle.

The efficacy of oral vaccination of mice with alginate encapsulated outer membrane proteins of Pasteurella haemolytica and One-Shot

The goal of this study was to examine the efficacy of oral delivery of alginate encapsulated outer membrane proteins (OMP) of Pasteurella haemolytica and a commercial One-Shot vaccine in inducing protection in mice against lethal challenge with virulent P. haemolytica. We examined two alginate microsphere formulations and compared them with oral unencapsulated and subcutaneously administered vaccines. Alginate microspheres were made by the emulsion-cross-linking technique. They were examined for size, hydrophobicity, and antigen loading efficiency before they were used in the study. Mice were vaccinated by administering 200 microg of antigens in 200 microl of microspheres suspension orally or subcutaneously. One group of mice received blank microspheres and a second group was given unencapsulated antigen orally. A third and a fourth group received different formulations of alginate encapsulated antigens by oral administration. Three groups received subcutaneous inoculations (alginate encapsulated, non-adjuvanted and unencapsulated antigens, and adjuvanted One-Shot), and one group received water (naïve group). Mice were vaccinated orally for four consecutive days and challenged with P. haemolytica 5 weeks after the first vaccination. Weekly serum and feces samples were assayed for antigen specific antibodies. The number of dead mice in each group 4 days post challenge was used to compare the efficacy of the various vaccination groups. The mean volume sizes of blank alginate microsphere formulations A, and AA were 15.9, 16 and 9.2 microm, respectively. Hydrophobicity of the microspheres was evaluated by measuring contact angle on a glass slide coated with the microspheres. The contact angles on A and AA were 37.8 and 74.3 degrees, respectively. Antigen concentration in a 1:1 w/w suspension of microspheres in water was 0.9 mg/ml. Rate of death for the blank group was 42.8% whereas for groups vaccinated with antigens encapsulated in A and AA the death rates were 40 and 33.33%, respectively. The death rate in mice vaccinated with unencapsulated antigens was 55.6%. Groups vaccinated by subcutaneous inoculation showed the lowest death rate. These results show that encapsulating OMP and One-Shot in alginate microspheres improves their performance as an oral vaccine.

Protection against Bordetella pertussis infection following parenteral or oral immunization with antigens entrapped in biodegradable particles: effect of formulation and route of immunization on induction of Th1 and Th2 cells

The immunogenicity and protective efficacy of systemically and orally delivered pertussis antigens entrapped in either microparticle poly-lactide-co-glycolide (PLG) or nanoparticle PLG formulations were evaluated in a murine respiratory challenge model for infection with Bordetella pertussis. The results demonstrate that immunization with two parenteral doses of 1 microg or three oral doses of 100 microg of pertussis toxoid (PTd) and filamentous haemagglutinin (FHA) encapsulated in PLG conferred a high level of protection against B. pertussis challenge. Furthermore protection could be generated with a single parenteral immunization with a combined microparticle and nanoparticle formulation. However, the route of immunization and the size of the particles affected the type of T cell response induced. Parenteral immunization with PTd and FHA entrapped in PLG microparticles elicits a potent type 1 T cell response and potent antibody response when given by the intraperitoneal (i.p.) or intramuscular (i.m.) route. In contrast, nanoparticle formulations favoured the induction of Th2 cells.

Effect of preparation temperature on the characteristics and release profiles of PLGA microspheres containing protein fabricated by double-emulsion solvent extraction/evaporation method

This study describes the influence of preparation temperature on the various characteristics and release profiles of poly(DL-lactide-co-glycolide) (PLGA) microspheres. The bovine serum albumin (BSA)-loaded microspheres were prepared using the water-in-oil-in-water (w/o/w) technique with poly(vinyl alcohol) as surfactant in the external aqueous phase. We have varied the preparation temperature to observe its effect on microsphere characteristics such as the microsphere shrinking rate during formation, particle size, density, surface and internal morphology, BSA encapsulation efficiency, BSA initial release, microsphere degradation and BSA in vitro release behaviour. During fabrication, a low preparation temperature of 5 degrees C gives the fastest initial but the slowest overall shrinking rate. Microspheres formed at high temperatures of 38 degrees C and 42 degrees C on the other hand have the lowest initial yet the highest overall shrinking rate. Subsequently, microsphere mean size increases and the particle size distribution widens with increase in the preparation temperature. Although all the microspheres have a porous surface as well as internal structure, microspheres fabricated at high temperatures have a uniform internal pore distribution and a very thin dense skin layer, while microspheres fabricated at lower temperatures have a thicker but porous skin layer and bigger pores in the middle of the sphere. Microspheres formed at 33 degrees C are found to give the highest initial burst release. In terms of in vitro release, microspheres fabricated at low temperatures (5 degrees C, 15 degrees C and 22 degrees C) exhibit similar, steady rates. Microspheres formed at higher temperatures however give very low release rates after their initial release. The results obtained suggest that preparation temperature significantly affects microsphere formation, resulting in their structural and protein release profile differences. These differences ultimately work together to affect the initial release and overall release patterns of the microspheres.

Oral tolerance elicited in mice by beta-lactoglobulin entrapped in biodegradable microspheres

Oral administration of antigen is known to be appropriate for some vaccine purposes as well as oral tolerance induction. In the present study, oral administration of beta-lactoglobulin (BLG) loaded poly(D,L-lactide-co-glycolide) (D,L-PLG) microspheres induced tolerance was evaluated. A single feeding of 5 micrograms of encapsulated BLG tolerized BALB/c mice to subsequent BLG parenteral challenge, suppressing the specific humoral, intestinal and cellular responses. The tolerogenic efficient dose was then reduced 10,000 times, compared to oral administration of soluble BLG. This suggests that loading food proteins into D,L-PLG microspheres might be a potential tool for inducing oral tolerance with allergens.

Lectin-mediated transport of nanoparticles across Caco-2 and OK cells

Recent experiments by a number of workers have suggested that it may be possible to use various targeting molecules, which bind to the intestinal epithelium, to promote the uptake and transport of nanoparticles from the intestine to the circulation. We have used commercial nanoparticles to examine the effect of size, density and inhibitors on uptake of lectin-coated nanoparticles by epithelial cells. The degree of uptake was most influenced by the density of lectin on the particle, with size and type of lectin being less important. Uptake could be inhibited by the presence of specific sugars or free lectin. These studies should provide a good basis for the design of targetable biodegradable drug-loadable particles suitable for oral delivery.

Controlled release opportunities for oral peptide delivery in aquaculture

Over the last decade, fish supplies for human consumption have reached over 100 million tons. Due to overfishing, future increases in demand can only be met from the aquaculture industry. This will require increased research in areas such as the control and manipulation of fish reproduction. There is increasing interest in the oral delivery of peptides that control gamete reproduction. However, compared to mammalian species, little is known about the barriers to peptide delivery and methods to improve such delivery. The three major barriers to peptide delivery are the enzymatic barriers sourced from the host luminal and membrane bound peptidases, the immunological cells present within both the enterocytes and underlying connective tissue and the physical barrier of the epithelial cells. Furthermore, the anatomy and physiology of the gastrointestinal tract of these species are markedly different when compared to higher vertebrates and therefore must be considered when designing appropriate delivery systems. Research to date has focused on the oral delivery and subsequent pharmacodynamic responses to the peptides associated with growth and reproduction. However, minimal work has been undertaken to overcome the identified barriers and therefore any future investigations need to attend to these obstacles before the oral delivery of bioactive peptides can become a commercial reality.

Biodegradable microparticles of influenza viral vaccine: comparison of the effects of routes of administration on the in vivo immune response in mice

The objective of this study was to investigate the comparative immune response following administration of biodegradable microparticles loaded with influenza viral vaccine using subcutaneous and oral routes. Influenza viral vaccine was entrapped in poly(d,l-lactide-co-glycolide) (PLG) and poly(isobutylcyanoacrylate) (PIBCA) microparticles. Stability and immunogenicity of entrapped antigen were retained, as evaluated by SDS-PAGE and immunoblot. Microparticles in the size range of <11 microm were evaluated for protein loading and in vitro antigen release. The mice were immunized with microparticle loaded antigen and IgG levels in blood and IgA levels in saliva and gastric secretions were monitored by ELISA method. When the mice were immunized with microparticle suspensions, IgG levels were higher if administered by subcutaneous primed by oral route compared to oral primed by subcutaneous route or subcutaneous or oral route. The IgA level in saliva and gastric secretions were also found to be higher when subcutaneous immunization was given followed by oral booster than oral priming followed by subcutaneous booster. The polymer types of the microparticles had effects on both IgG and IgA levels. This study provided insights into the design of microparticles of influenza vaccine for subcutaneous administration followed by an unlimited oral boosting, which will have high cost-effectiveness and patient compliance.

Enhanced immune response after subcutaneous and oral immunization with biodegradable PLGA microspheres

PLGA microspheres containing bovine serum albumin (BSA) as a model antigen, were prepared by a double emulsion/solvent extraction method and their in vitro characterization was performed. The same microspheres were used in a series of in vivo studies to evaluate the immune response induced after subcutaneous or oral inoculation following different immunization protocols. The in vivo data confirm that the immunogenicity of the albumin is not affected by the encapsulation procedure. The subcutaneous administration of microspheres showed an immune response (serum IgG levels by ELISA) statistically above BSA solution, even when the dose administered was 10 times lower. The adjuvanticity of the microspheres was found to be comparable to that of Freund's complete adjuvant (FCA), but in contrast to FCA they are biocompatible and did not induce any adverse reaction at the site of injection. A single oral administration of the microspheres was not a successful strategy for the induction of a reproducible response. Therefore, microspheres of 1 and 5 micrometer were orally administered on 3 consecutive days and the response obtained showed that the use of a boosting dose was not necessary for the 1 micrometer particles. These results suggest the possibility of simplifying the immunization schedule to a primary immunization if 1 micrometer particles are administered.

Effect of polytyrosine on the hydrophobicity of hydroxyethyl starch microspheres

The polypeptide, poly-l-tyrosine (PTYR) was incorporated into hydroxyethyl starch (HES) microspheres to modify the surface hydrophobicity in order to allow subsequent radioiodination and assessment of uptake into the intestinal mucosa following oral administration. The HES microspheres were prepared by a crosslinking polymerization process and characterized for particle size, peptide content and surface morphology. The hydrophobicity of the characterized microspheres was assessed by two techniques-water uptake (swelling) of the microspheres and contact angle measurement using the sessile drop method. Spherical microspheres containing PTYR were prepared with a greater than 80% loading efficiency in the 1-10 microns size range. The surface morphology suggested localization of the PTYR at the surface proportionate to the loading. The percent water uptake of the blank HES microspheres was 87%, whereas that of the 5, 10 and 20% PTYR/HES microspheres was 84%, 61% and 55%, respectively. HES/PTYR was polymerized as films to facilitate contact angle measurement. A monotonical increase in the contact angle was observed as the concentration of the PTYR was increased to 20%. Contact angle of pure HES (0% PTYR) films was 16 degrees and for the PTYR-containing films was 29 degrees for 5% PTYR, 39 degrees for 10% and 57 degrees for 20%. The hydrophobicity of the HES microsphere system could be increased by the incorporation of polytyrosine thereby paving the way to radioiodinate the microspheres and perform uptake studies in an animal model.

Intestinal uptake of particulate material by dexamethasone-treated rats: use of a novel technique to avoid intestinal mucosal contamination

The aim of this study was to investigate the effect of immune suppression on the uptake of particles across the wall of the intestine and the dissemination of the particles to systemic organs. Normal and dexamethasone-immunosuppressed rats were dosed orally with 0.5 mL distilled water or fluorescent polystyrene latex particle suspension containing 2.33 x 10(9) 2-microm diameter particles. One hour after particle dosing, the animals were killed by CO2 asphyxiation. The intestinal tissues and systemic organs were sampled for particle quantitation. To avoid contamination by particles adherent to intestinal mucosa the epithelium of intestinal tissue samples was removed before quantification. The number of fluorescent particles in tissues was determined by fluorescence microscopy of digests of selected samples. The uptake of particulate material across the intestinal wall was significantly (P < 0.05) increased in rats treated with dexamethasone but the number of particles transferred to systemic organs did not differ from values found for control animals. The results suggest that although dexamethasone increased intestinal permeability the apparatus or mechanisms involved in particle transport to distal sites were not affected during immune suppression.

Mucosal immunogenicity elicited in mice by oral vaccination with phosphorylcholine encapsulated in poly (D,L-lactide-co-glycolide) microspheres

Poly(D,L-lactide-co-glycolide) microspheres loaded with phosphorylcholine linked to thyroglobulin (PC-Thyr) as protein carrier were prepared. The entrapment efficiency reached 80% when the initial protein:polymer ratio was 1:8. Ninety-four percent of the loaded microspheres had a diameter < or = 10 microns. The encapsulation process did not alter PC-Thyr absorbance nor PC antigenic reactivity. Oral administration of these microspheres induced a specific IgA response in intestinal, pulmonary and vaginal secretions, as well as a strong specific systemic immune response in female Balb/c mice. This suggests the need to explore further the potential ability of PC-Thyr loaded microspheres to protect against infections caused by PC-bearing microorganisms which invade or colonize different mucosal sites.

Novel liposaccharide conjugates for drug and peptide delivery

Sugar-lipid conjugates with general structure 1-4 were prepared by coupling amino sugars with N-Boc-protected lipoamino acids and oligomers. Conjugates with general structure 5 were also prepared from glucuronic acid and methyl 2-aminohexadecanoate. The physicochemical properties of the conjugates were modified by varying the nature and number of sugars or the number of lipoamino acids or their alkyl chain length. The ability of the liposaccharides to aggregate was examined. These preliminary experiments have demonstrated the ability of the liposaccharides to form particulate systems per se and also their ability to be incorporated into conventional liposomal systems. The structure of the respective liposaccharides and the molar ratio of liposaccharide to dimyristoyl lecithin and cholesterol were found to have a profound effect on the type of colloidal systems produced.