Characterization of polyacryl starch microparticles as carriers for proteins and drugs

Recent development of micro-nano carriers for oral antineoplastic drug delivery

Chemotherapy is widely recognized as a highly efficacious modality for cancer treatment, involving the administration of chemotherapeutic agents to target and eradicate tumor cells. Currently, oral administration stands as the prevailing and widely utilized method of delivering chemotherapy drugs. However, the majority of anti-tumor medications exhibit limited solubility and permeability, and poor stability in harsh gastrointestinal environments, thereby impeding their therapeutic efficacy for chemotherapy. Therefore, more and more micro-nano drug delivery carriers have been developed and used to effectively deliver anti-cancer drugs, which can overcome physiological barriers, facilitate oral administration, and ultimately improve drug efficacy. In this paper, we first discuss the effects of various biological barriers on micro-nano drug carriers and oral administration approach. Then, the development of micro-nano drug carriers based on various biomedical components, such as micelles, dendrimers, hydrogels, liposomes, inorganic nanoparticles, etc. were introduced. Finally, the current dilemma and the potential of oral drug delivery for clinical treatment were discussed. The primary objective of this review is to introduce various oral delivery methods and serve as a point of reference for the advancement of novel oral delivery carriers, with the ultimate goal of informing the development of future clinical applications.

Mechanical quantum analysis on the role of transition metals on the delivery of metformin anticancer drug by the boron phosphide nanotube

We scrutinized the impact of doping of X atoms (X = Fe, Co, Ni, Cu, and Zn) on the metformin (MF) drug delivery performance of a BP nanotube (BPNT) using density functional B3LYP calculations. The pristine BPNT was not ideal for the drug delivery of MF because of a weak interaction between the drug and nanotube. Doping of the Zn, Cu, Ni, Co, and Fe into the BPNT surface raised the adsorption energy of MF from -5.3 to -29.1, -28.7, -29.8, -32.1, and -26.9 kcal/mol, respectively, demonstrating that the sensitiveness of the metal-doped BPNT increased after increasing the radius atomic of metals. Ultimately, there was an increase in the adhesion performance and capacity of the MF after X (especially Co atom) doping, making the nanotube suitable for MF drug delivery. The mechanism of MF reaction with the BPNT changed from covalent bonding in the natural environment to hydrogen bonding in the cancerous cells with high acidity.

Hydrogels Classification According to the Physical or Chemical Interactions and as Stimuli-Sensitive Materials

Hydrogels are attractive biomaterials with favorable characteristics due to their water uptake capacity. However, hydrogel properties are determined by the cross-linking degree and nature, the tacticity, and the crystallinity of the polymer. These biomaterials can be sorted out according to the internal structure and by their response to external factors. In this case, the internal interaction can be reversible when the internal chains are led by physicochemical interactions. These physical hydrogels can be synthesized through several techniques such as crystallization, amphiphilic copolymers, charge interactions, hydrogen bonds, stereo-complexing, and protein interactions. In contrast, the internal interaction can be irreversible through covalent cross-linking. Synthesized hydrogels by chemical interactions present a high cross-linking density and are employed using graft copolymerization, reactive functional groups, and enzymatic methods. Moreover, specific smart hydrogels have also been denoted by their external response, pH, temperature, electric, light, and enzyme. This review deeply details the type of hydrogel, either the internal structure or the external response. Furthermore, we detail some of the main applications of these hydrogels in the biomedicine field, such as drug delivery systems, scaffolds for tissue engineering, actuators, biosensors, and many other applications.

A Tribute to Professor Per Artursson - Scientist, Explorer, Mentor, Innovator, and Giant in Pharmaceutical Research

This issue of the Journal of Pharmaceutical Sciences is dedicated to Professor Per Artursson and the groundbreaking contributions he has made and continues to make in the Pharmaceutical Sciences. Per is one of the most cited researchers in his field, with more than 30,000 citations and an h-index of 95 as of September 2020. Importantly, these citations are distributed over the numerous fields he has explored, clearly showing the high impact the research has had on the discipline. We provide a short portrait of Per, with emphasis on his personality, driving forces and the inspirational sources that shaped his career as a world-leading scientist in the field. He is a curious scientist who deftly moves between disciplines and has continued to innovate, expand boundaries, and profoundly impact the pharmaceutical sciences throughout his career. He has developed new tools and provided insights that have significantly contributed to today's molecular and mechanistic approaches to research in the fields of intestinal absorption, cellular disposition, and exposure-efficacy relationships of pharmaceutical drugs. We want to celebrate these important contributions in this special issue of the Journal of Pharmaceutical Sciences in Per's honor.

Properties and applications of nanoparticle/microparticle conveyors with adjuvant characteristics suitable for oral vaccination

Vaccination is one of the most effective approaches in the prevention and control of disease worldwide. Oral vaccination could have wide applications if effective protection cannot be achieved through traditional (eg, parenteral) routes of vaccination. However, oral administration is hampered by the difficulties in transferring vaccines in vivo. This has led to the development of materials such as carriers with potential adjuvant effects. Considering the requirements for selecting adjuvants for oral vaccines as well as the advantages of nanoparticle/microparticle materials as immune effectors and antigen conveyors, synthetic materials could improve the efficiency of oral vaccination. In this review, nanoparticles and microparticles with adjuvant characteristics are described with regard to their potential importance for oral immunization, and some promising and successful modification strategies are summarized.

Chemical Synthesis, Versatile Structures and Functions of Tailorable Adjuvants for Optimizing Oral Vaccination

Oral vaccines have become a recent focus because of their potential significance in disease prevention and therapy. In the development of oral vaccine-based therapeutics, synthetic materials with tailorable structures and versatile functions can act as antigen conveyers with adjuvant effects, reduce the time cost for vaccine optimization, and provide high security and enhanced immunity. This review presents an overview of the current status of tailoring synthetic adjuvants for oral vaccination, modification strategies for producing effectors with specific structures and functions, enhancement of immune-associated efficiencies, including the barrier-crossing capability to protect antigens in the gastrointestinal tract, coordination of the antigens penetrating mucosa and cell barriers, targeting of concentrated antigens to immune-associated cells, and direct stimulation of immune cells. Finally, we focus on prospective synthetic adjuvants that facilitate the use of oral vaccines via two approaches, namely, in vivo antigen expression and cancer immunotherapy.

A Mechanistic Assessment of Enzyme-Induced Degradation of Albumin-Crosslinked Hydrogels

Pepsin-induced degradation of albumin-crosslinked hydrogels was studied as a function of the degree of albumin incorporation in the network and the concentration of pepsin. The degree of albumin incorporation, which represents the sum of chemical crosslinks and physical entanglements in the network, was controlled by changing the concentration of initiator in the monomer solution and the degree of vinylic functionality on albumin. Swelling characterization studies showed that the degree of hydrogel swelling decreased as the concentration of chemical initiator for the polymerization increased or as the degree of vinylic functionality on albumin increased. This indicated that the degree of albumin incorporation in the network increased by raising either the concentration of chemical initiator or the degree of albumin functionality. The rate and mechanism of gel degradation was also dependent on the degree of albumin incorporation in the network. A low degree of albumin incorpora tion resulted in a predominance of surface degradation while a high degree of albumin incorporation resulted in a predominance of bulk degradation. The transition from surface degradation to bulk degradation occurred at lower con centrations of chemical initiator when the degree of vinylic functionality on albumin was high. However, when the degree of vinylic functionality on albumin was low, the transition from surface degradation to bulk degradation was observed at higher concentrations of chemical initiator. The rate of gel degradation became slower as the concentration of pepsin was reduced. The results suggest that the rate and mechanism of hydrogel degradation was de pendent on the steric constraints imposed by polymer chains of the network and on the conformational constraints of the albumin crosslinker.

Current understanding of synergistic interplay of chitosan nanoparticles and anticancer drugs: merits and challenges

Recent advances have been made in cancer chemotherapy through the development of conjugates for anticancer drugs. Many drugs have problems of poor stability, water insolubility, low selectivity, high toxicity, and side effects. Most of the chitosan nanoparticles showed to be good drug carriers because of their biocompatibility, biodegradability, and it can be readily modified. The anticancer drug with chitosan nanoparticles displays efficient anticancer effects with a decrease in the adverse effects of the original drug due to the predominant distribution into the tumor site and a gradual release of free drug from the conjugate which enhances drug solubility, stability, and efficiency. In this review, we discuss wider applications of numerous modified chitosan nanoparticles against different tumors and also focusing on the administration of anticancer drugs through various routes. We propose the interaction between nanosized drug carrier and tumor tissue to understand the synergistic interplay. Finally, we elaborate merits of drug delivery system at the tumor site, with emphasizing future challenges in cancer chemotherapy.

Modified biopolymer-dextrin based crosslinked hydrogels: application in controlled drug delivery

This review describes hydrogels and their classifications along with the synthesis and properties of biopolymer-dextrin based crosslinked hydrogels towards potential application in controlled drug delivery.

A note on the microencapsulation of pancreatic protease for protection against gastric digestion

Zeolite, cellulose acetate phthalate (CAP) and maize starch were used as the coating materials for encapsulating pancreatic protease, which was proposed as an additive to enhance the food efficiency and growth rate of weanling pigs. In this study, microcapsules were formed by the process of coacervation in liquid paraffin media, where the deposition time was in the range of 20 to 60 min, and the concentrations of CAP, zeolite and maize starch were 20, 40 and 120 g/kg respectively. Hardening by n-hexane was achieved with 15 min of stirring. Microcapsules generated by this method were 20 to 30 mesh in diameter. They were stable for at least 3 h in simulated gastric conditions (pH 3·97), but disintegrated rapidly under simulated intestinal conditions (pH 6·82).

Controlled release of theophylline through semi-interpenetrating network microspheres of chitosan-(dextran-g-acrylamide)

Semi-interpenetrating network microspheres of chitosan-(dextran-g-acrylamide) were prepared by emulsion-crosslinking method using glutaraldehyde (GA) as a crosslinking agent. Graft copolymerization of dextran with acrylamide (Dx-g-AAm) was carried out by aqueous free-radical polymerization using ceric ammonium nitrate (CAN) as initiator. The grafting efficiency was found to be 92%. Theophylline (TH), antiasthmatic drug, was successfully encapsulated into semi-INP microspheres by varying the ratio of Dx-g-AAm and amount of GA. The laser light scattering technique shows that the particles size increased with increasing amount of graft copolymer and decrease with increasing amount of GA. The % encapsulation efficiency was found to vary between 50 and 78. MPs were characterized by FTIR spectroscopy and differential scanning calorimetry (DSC) techniques to confirm the graft copolymer, formation of semi-IPN structure of MPs and molecular distribution of the drug molecules in the polymer matrix. In vitro release studies of TH from these matrices have been investigated at Ph 1.2 and 7.4 media and the slow release were extended up to 18 h at 37 degrees C. The release rates were fitted to an empirical equation to estimate the diffusion exponent n, which indicated that the release from the MPs follows non-Fickian type.

Starch Microparticles as Oral Vaccine Adjuvant: Antigen-dependent Uptake in Mouse Intestinal Mucosa

An oral vaccine formulation comprised of starch microparticles with conjugated antigens is being developed. In this report we have examined the uptake of such microparticles by the intestinal mucosa and examined whether the conjugated antigen can influence the uptake. Two model antigens were used: recombinant cholera toxin B subunit (rCTB), which is known to bind to the ubiquitous GM1-receptor, and human serum albumin (HSA) which is not known to have any specific binding properties. The uptake was studied in mouse ligated intestinal loops into which the microparticles were injected. The intestinal loops were excised, fixed in ice-cold 95% ethanol. Entire specimens were mounted, exposed to fluorescence-labeled reagents staining the cytoskeleton, the particles and/or M cells and examined in a confocal laser-scanning microscope. A qualitative difference in the uptake of the rCTB- and HSA-conjugated microparticles was seen. The rCTB-conjugated microparticles were found both in villi and in the follicles of the Peyer's patches. HSA-conjugated microparticles could only be detected in the follicles of the Peyer's patches and not in villi. The rCTB conjugated to the microparticles did not lose its ability to bind the GM1-receptor, as shown with a GM1-ELISA, and the uptake of rCTB-conjugated microparticles in villi is most probably facilitated by the rCTB binding to the GM1-receptor. The qualitative difference in uptake could be of importance for the development of an immune response as the cytokine and chemokine microenvironment during antigen presentation will decide the differentiation of the immune response induced.

Effects of chronic stress on the immune response to oral human serum albumin-conjugated starch microparticles in rats

Uptake of antigens and bacteria over the follicle-associated epithelium (FAE) is increased after chronic psychological stress. We investigated whether stress affects the immune response to particle-conjugated antigens taken up via the FAE. Rats were submitted to two 10-day periods of water avoidance stress and orally immunized during these periods. Stressed immunized rats displayed altered cell populations and a Th1-skewed immune response within the lymphoid follicles, together with enhanced delayed-type hypersensitivity. We conclude that chronic stress affects the cell-mediated immune response after oral immunization, which may have implications for the understanding of allergic and autoimmune diseases and development of oral vaccines.

Starch microparticles as vaccine adjuvant

The demand for new vaccine adjuvants is well documented. New purified antigens from parasites, bacterial or viral pathogens, as well as recombinant subunit antigens and synthetic peptides, are often inherently weak immunogens; therefore, they need some kind of adjuvant to help initiate an immune response. In addition, there are very few adjuvants using the potential of the mucosal immune system, which may play an important role in the defence against air- and food-borne infections. Starch is a natural biocompatible and biodegradable polymer that is suitable for the production of various particulate adjuvant formulations, which can induce mucosal as well as systemic immune responses. This review gives an account of the different starch adjuvants used in immunisation studies. In particular, the properties of polyacryl starch microparticles as an oral vaccine adjuvant that induce protective immune responses in mice challenge experiments are summarised. In addition, a diphtheria booster vaccine has been proposed to be used to proving the concept in man and the possibilities to design an efficient vaccine formulation for human use are discussed.

Mucosal vaccination against diphtheria using starch microparticles as adjuvant for cross-reacting material (CRM197) of diphtheria toxin

Mucosal vaccination has the advantage of eliciting a local mucosal immune response as well as a systemic response. In this investigation, polyacryl starch microparticles were conjugated to diphtheria toxin cross-reacting material (CRM197) as a mucosal adjuvant for oral or intranasal immunisation of mice. Various methods of stabilising CRM197 with formaldehyde were investigated. A good systemic and local mucosal immune response was attained with oral immunisation when CRM197 was treated with a relatively low formaldehyde concentration prior to conjugation to the microparticles. No immune response was seen after intranasal immunisation.

Binding and measuring natural rubber latex proteins on glove powder

Cornstarch used as a donning powder on natural rubber latex (NRL) gloves adsorbs NRL proteins. During glove use, powder-carried proteins can be aerosolized and can cause allergic reactions in NRL sensitized individuals. The amount of NRL proteins bound to glove powder and its relative relationship to the total amount of proteins on the glove has not been studied, due to the difficulty in measuring proteins on powder. Using the ELISA inhibition assay for NRL proteins [Standard test method for the immunological measurement of antigenic protein in natural rubber and its products. In: The Annual Book of ASTM Standards; ASTM: West Conshohocken, PA, 2000; ASTM D 64-0] we have investigated possible protocol modifications in order to include measurement of proteins bound to glove powder, as well as the water-extractable glove proteins. Possible interference of the starch itself was evaluated by adding clean cornstarch to the assay. No significant interference was observed with powder concentrations below 5 mg/mL. We analyzed 19 extracts of powdered surgical and examination gloves before and after removal of the particulate component. Comparison of NRL glove extracts with, and without, the cornstarch powder fraction indicated significant variations in the ratios of powder-bound protein and corresponding water-extractable protein. The ratios did not appear to correlate with either the total protein on the glove, the glove weight, or the total amount of powder on the glove. However, when virgin glove powders were exposed to NRL proteins, binding was proportional to the protein concentration in the suspension. Temperature in the range from 4 degrees C to 37 degrees C, did not affect binding intensity, while a higher pH resulted in a higher level of protein associated with, or bound to, the starch. The major differences in the propensity for NRL protein binding were observed among different glove powders. The data indicate that the amount of protein that binds to glove powder does not depend only on the initial protein levels in the raw NRL. More likely, other physical or chemical factors introduced during the manufacturing process, as well as the properties of the donning powder itself, may influence protein binding. Moreover, we demonstrated that the ELISA inhibition assay could be successfully modified for quantitation of proteins adsorbed on the glove powder, together with water-extractable proteins.

Mucosal immunization with purified flagellin from Salmonella induces systemic and mucosal immune responses in C3H/HeJ mice

This study investigated the immune response elicited in C3H/HeJ mice after oral, parenteral and nasal immunization with purified flagellin from Salmonella enterica serovar Enteritidis alone or conjugated to starch microparticles as adjuvant or together with the uptake-enhancer recombinant cholera toxin B-subunit (rCTB). Systemic (IgM-IgG, IgA, IgG2a, IgG2b, IgG1) and local (s-IgA) humoral immune responses in the mice were analyzed using enzyme-linked immunosorbent assays (ELISA). Primed splenocytes were also stimulated in vitro with flagellin and the supernatants analyzed for cytokine production. Finally, immunized mice were challenged orally with live Salmonella. A high flagellin-specific IgM-IgG response was seen in all groups, especially in mice immunized nasally with flagellin plus rCTB or subcutaneously, but a strong systemic antibody response was also induced when free antigen was given orally. Intranasal or subcutaneous immunization of mice with flagellin plus rCTB or oral immunization with flagellin plus microparticles resulted in a significantly greater mucosal response (higher s-IgA titers in feces) than seen in the control group (P <0.05). The mucosal IgA responses were significantly correlated with the serum IgA titers. The subclass profile in serum revealed a mixed Th1/Th2-type response, with a predominance of Th1-type, as indicated by the subclass ratio (IgG1/IgG2a + IgG2b). The splenocytes stimulated in vitro produced interferon (IFN)-gamma, at levels, which increased with time. The group immunized with flagellin plus rCTB subcutaneously had a relatively higher IFN-gamma response than the other groups. Interleukin (IL)-2 was also produced, especially in mice immunized nasally or subcutaneously with flagellin conjugated to microparticles. However, neither IL-4 nor IL-5 was produced in any of the groups. After oral challenge with live serovar Enteritidis, the groups immunized orally or nasally with free flagellin had significantly lower degree of infection than the control group (P <0.05).

Starch microparticles as an adjuvant in immunisation: effect of route of administration on the immune response in mice

This paper describes the effects on the development of an immune response by changing the route of administration of a new vaccine adjuvant, starch microparticles with human serum albumin (HSA) as a model antigen. The model vaccine was administered to mice by oral, subcutaneous and intramuscular routes in various combinations and both the local secretory immunoglobulin antibody (s-IgA) and systemic humoral and cellular (delayed-type hypersensitivity assay (DTH)) responses were followed. The only immunisation regimens inducing a significant s-IgA response were those incorporating oral booster doses. Oral and subcutaneous immunisations had similar effects on the Th1/Th2 balance, as indicated by the IgG subclass ratios and cytokine analyses. However, significant differences between oral and intramuscular immunisations were seen in the IgG subclass ratios. The Th2 influence was stronger after oral primary immunisation than after intramuscular primary immunisation, while oral boosters elicited a comparatively stronger Th1 response than intramuscular boosters. This result was also supported by the DTH analyses. Subcutaneous immunisation induced a stronger Th2 response than intramuscular immunisation, as indicated by subclass ratio and the IgE response. In conclusion, our results show that the profile of an immune response depends on the route of administration, which should be considered when developing new vaccines or new routes of administration.

Immunogenic properties of the Salmonella atypical fimbriae in BALB/c mice

Components of the Salmonella atypical fimbriae (Saf) were investigated for potential inclusion in a Salmonella vaccine. Recombinant histidine-tagged SafB chaperone complexed with SafD adhesin was expressed in Escherichia coli and purified. Starch microparticles were used, as an adjuvant and recombinant cholera toxin B subunit (rCTB) was included as a mucosal antigen-uptake enhancer. BALB/c mice were immunized orally or subcutaneously with SafB/D- and rCTB-conjugated microparticles and nasally or subcutaneously with SafB/D mixed with rCTB. The systemic and mucosal immune responses were studied, and an oral challenge with Salmonella enteritidis was performed. All immunized groups except that receiving oral immunization responded with high IgM-IgG titers to SafB/D. Analysis of the subclass ratio (IgG1/IgG2a+IgG2b) indicated a mixed Th1 and Th2 response, with Th1 predominating. The mucosal response, measured as specific IgA/total IgA (from fecal samples), was significantly greater than that in the untreated control group only in the group receiving intranasal immunization (P<0.05). Spleens were removed 6 days after oral challenge and Salmonella colony-forming units (CFU) were counted. The group immunized subcutaneously with SafB/D- and rCTB-conjugated microparticles had significantly lower CFU counts than the untreated control group (P<0.05).

Oral vaccination against diphtheria using polyacryl starch microparticles as adjuvant

Oral vaccination offers the advantage of eliciting both a mucosal and a systemic immune response. This study investigated the use of polyacryl starch microparticles as adjuvant for oral vaccination against diphtheria. Diphtheria toxin or cross-reacting material (CRM197) were covalently conjugated to the microparticles and fed to mice by oral gavage. Investigation of formaldehyde treatment as a means of either detoxifying (diphtheria toxin) or stabilising (CRM197) these formulations were also made. We show that all our formulations given orally or parenterally to mice induced a strong systemic immune response. Only formulations given orally induced a mucosal IgA-response. Furthermore, our formulations given parenterally or orally induced a strong diphtheria toxin-neutralising antibody response.

Drug release from starch-acetate films

The aim of the present work was to compare the drug release rates from the native and acetylated starches. The average degree of acetyl substitution per glucose residue of potato starch was either 1.9 (SA DS 1.9) or 2.6 (SA DS 2.6). Bovine serum albumin (BSA) (mol. wt. 68,000), FITC-dextran (mol. wt. 4400), timolol (mol. wt. 332, log P=1.91) and sotalol-HCl (mol. wt. 308, log P=-0.62) were used as model drugs. All of the model drugs were released rapidly from the potato starch film in PBS pH 7.4 with and without alpha-amylase in the dissolution medium (t50% varied from 0.17 to 3.37 h). When compared to the potato starch film, all of the studied drugs were released at a substantially slower rate from the SA films in the corresponding mediums. The release of the smaller drugs (sotalol, timolol) from the SA films was faster than that of the macromolecules (FITC-dextran, BSA). Furthermore, sotalol was released faster than the more lipohilic timolol from the SA films. Release of macromolecules from the SA films was biphasic with and without alpha-amylase in the dissolution medium: an initial fast release phase was followed by a slower release phase (SA DS 1.9) or no release occurred after the initial phase (SA DS 2.6). All of the drugs were released faster from the SA DS 1.9 film than the weight loss of the film itself. When compared to the SA DS 1.9 film, the model drugs (except sotalol) were released slower from the SA DS 2.6 film. The macromolecule release from the SA DS 2.6 film was erosion-controlled. The weight loss of the SA DS 2.6 film was slow with and without alpha-amylase in the incubation medium. The present results show that acetylation of potato starch can substantially retard drug release. The drug release profiles may be controlled by the degree of substitution, since drug release from the SA DS 1.9 film was faster than the corresponding release from the SA DS 2.6 film.

Uptake of ovalbumin-conjugated starch microparticles by pig respiratory nasal mucosa in vitro

The uptake of ovalbumin-conjugated starch microparticles (OVA-MP) was studied after application to porcine respiratory nasal mucosa in vitro. Nasal mucosa from freshly slaughtered pigs was mounted in horizontal Ussing chambers, which permit monitoring of the viability of the tissue exposed to microparticles and ensure that the microparticles are deposited on the mucosa. The antigen-conjugated starch microparticles have previously been shown to produce strong mucosal, cellular and systemic immune responses to conjugated model antigens following oral administration. Intranasal administration of vaccines for mucosal immunisation is an interesting alternative to oral administration, since nasal delivery systems generally require lower doses of antigen and the site of application is better suited for protection against air-borne antigens. Most of a nasally administered dose is deposited on the surface of the respiratory area of the nasal mucosa. It is therefore important to examine whether the microparticles are taken up in this area and, if so, by which cell type. Confocal laser scanning microscopy and transmission electron microscopy (TEM) of the nasal tissue both showed intracellular OVA-MP in non-ciliated epithelial cells after 45 min' incubation. The morphology of the cells in the TEM preparations did not support the presence of either M cells (specialised antigen sampling cells) or adjacent lymphocytes. Anticytokeratin-18 (Ac18) was used as a potential M cell marker. However, there was no indication of Ac18 binding to M cells, but it did bind to mucus-producing cells in the respiratory nasal mucosa. In conclusion, OVA-MP were taken up intracellularly by non-ciliated epithelial cells in the nasal respiratory mucosa of pigs, in vitro.

Extracellular antigens from Salmonella enteritidis induce effective immune response in mice after oral vaccination

We have studied polyacryl starch microparticles as an adjuvant in oral vaccination in mice. Secreted antigens from Salmonella enterica serovar Enteritidis were administered covalently conjugated to microparticles, or as free antigens, orally or intramuscularly and evaluated for their immunogenicity and ability to elicit protective immune response against an oral challenge with live serovar Enteritidis. The highest immunoglobulin M (IgM)-plus-IgG titers were obtained in the groups immunized with antigen-conjugated microparticles. The subclass profile switched to a stronger Th1 influence in the oral groups after booster, while the intramuscular group showed a constant Th1/Th2 profile. A strong specific IgA response was seen in feces in the oral groups, which was further confirmed in an enzyme-linked immunospot assay. The delayed-type hypersensitivity test, as a measure of the cellular response, showed a significant increase in ear thickness in all the immunized groups, except for the group that received free antigen orally, compared to the nonimmunized group. The cytokines released from in vitro-stimulated spleens showed a strong gamma interferon response in all immunized groups. A significant reduction in CFU in liver and spleen was seen in the orally immunized groups compared to the nonimmunized group after oral challenge with serovar Enteritidis. Western blotting analysis with both sera and feces revealed that antibodies against three bands, 53, 56, and 60 kDa, dominated the oral groups, and an electrospray-mass spectroscopy analysis of these bands showed amino acid sequences coinciding with those of phase-1 flagellin and hook-associated protein 2.

Novel crosslinking methods to design hydrogels

Hydrogels are presently under investigation as matrices for the controlled release of bioactive molecules, in particular pharmaceutical proteins, and for the encapsulation of living cells. For these applications, it is often required that the gels degrade under physiological conditions. This means that the originally three-dimensional structure has to disintegrate preferably in harmless products to ensure a good biocompatibility of the hydrogel. In this overview, different chemical and physical crosslinking methods used for the design of biodegradable hydrogels are summarized and discussed. Chemical crosslinking is a highly versatile method to create hydrogels with good mechanical stability. However, the crosslinking agents used are often toxic compounds, which have been extracted from the gels before they can be applied. Moreover, crosslinking agents can give unwanted reactions with the bioactive substances present in the hydrogel matrix. Such adverse effects are avoided with the use of physically crosslinked gels.

Comparison of poly(acryl starch) and poly(lactide-co-glycolide) microspheres as drug delivery system for a rotavirus vaccine

Drug delivery systems allowing controlled release of antigen are of particular interest in the development of vaccines. We have compared poly(acrylic starch) microspheres (PAS) and poly(lactide-co-glycolide) microspheres (PLG) as drug delivery systems for a rotavirus vaccine. The polymers are both biodegradable but have different degradation mechanisms and antigen release profiles. PAS are enzymatically degraded and have a continuous fast antigen release rate compared to the hydrolytically degraded PLG which release the incorporated antigen in a pulsatile manner. In this study mice were immunised intramuscularly and orally on three occasions with formalin-inactivated rotavirus (FRRV) incorporated in PAS and PLG and with FFRV alone. Serum and faeces samples were collected and analysed by ELISA for rotavirus specific IgG and IgA antibodies. A neutralising assay was also conducted on both serum and faeces antibodies. The two different polymer drug delivery systems induced different immune responses depending on administration route. PAS elicited significant antibody levels and neutralising effect after oral administration while PLG showed high antibody levels after intramuscular administration. The immune response appears to be dependent on the differences in antigen release and degradation mechanism for the two polymer systems.

Enzymatic degradation of epichlorohydrin crosslinked starch microspheres by alpha-amylase

PURPOSE

The influence of chemical parameters on the sensitivity to enzymatic degradation by alpha-amylase of starch microspheres cross-linked by epichlorohydrin was studied.

METHODS

Starch microspheres were prepared using epichlorohydrin as a crosslinking agent. Their swelling degree, reflecting the number of glycerol diether bridges in the polymeric network, and the number of non-crosslinking monoglycerol ether groups corresponding to a side-reaction of epichlorohydrin with starch were determined. Degradation rates of the microspheres in presence of porcine alpha-amylase were determined by a microvolumetric method.

RESULTS

Degradation by alpha-amylase was surface-controlled and could be modulated by the introduction in the polymeric network of: (i) non-hydrolysable alpha-1,6 bonds related to the presence of amylopectin in the raw starch, (ii) glycerol diether and, (iii) monoether groups, all of these being likely to block the activity of alpha-amylase. In the case of highly cross-linked microspheres, the number of glycerol monoether pendent chains had a predominant effect on the degradation rate which ranged between 10(-2) and 10(-5) min(-1).

CONCLUSIONS

It was possible to modulate simultaneously the swelling degree and the enzymatic degradability of starch microspheres by adjusting the chemical parameters during the crosslinking reaction.

An original method for studying in vitro the enzymatic degradation of cross-linked starch microspheres

A reproducible technique based on microvolume measurements has been described which can be used for the assessment of the enzymatic degradation of small samples of microspheres (typically 104 to 105 micrometer3). As a model, the degradation pattern of epichlorohydrin cross-linked starch microspheres by alpha-amylase has been studied in the range of 5 to 100 IU/l by this technique. On the one hand, analysis of the decrease in volume of the microspheres by a cubic root law suggested that the degradation profiles were dependent on the initial size distribution of the microspheres. On the other hand, no internal rupture of the microspheres was detected from size distribution data, suggesting that enzymatic degradation of starch microspheres is surface-controlled.

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.

Development of a statistical model for the formation of poly [acryloyl hydroxyethyl starch] microspheres

PURPOSE

To develop a mathematical model for predicting the molecular weight between crosslinks, Mc, of poly[Acryloyl Hydroxyethyl Starch] (Ac-HES) microspheres system and to identify and evaluate the key microsphere preparation parameters which affect the Mc of the formed microsphere structure based on the developed model.

METHODS

Link probability generating functions (LPGFs) based on the classical branching theory were used to derive a model for the calculation of Mc for the Ac-HES system. Based on the developed model, simulation was made to study the effects of the microsphere preparation variables on Mc of the formed microspheres. The process variables were the degree of derivatization (DD) of the Ac-HES, the molar ratio (MR) of the Ac-HES to acrylamide monomer, the fractional conversion of the unsaturation (alpha), the initiator efficiency (f), the molar concentration of initiator (I), the fraction of intramolecular cyclization (c), and the total weight of the reactable monomer and polymer (s).

RESULTS

A model to describe the crosslinking reaction of Ac-HES system and predict Mc was developed. Simulation based on the model showed that Mc decreased as alpha increased and reached a limiting value before total conversion. At constant alpha, Mc initially decreased with MR to a minimum and then increased with MR; while Mc decreased monotonically with DD. I and c affected Mc only at very low alpha and changes in s and f had no effect on Mc.

CONCLUSIONS

Simulation based on the model suggested that the most important microsphere preparation parameters influencing Mc of the Ac-HES system are the number of functional groups on the Ac-HES (DD) and the stoichiometry (MR) of the crosslinking reaction.

Protein delivery from biodegradable microspheres

The key components to the successful development of a biodegradable microsphere formulation for the delivery of proteins are polymer chemistry, engineering, and protein stability. These areas are intricately related and require a thorough investigation prior to embarking on the encapsulation of proteins. While each of these components is important for the development of a biodegradable microsphere formulation for protein delivery, other critical issues should also be considered. In particular, preclinical studies in the appropriate animal model are usually necessary to assess the potential feasibility of a continuous-release dosage form. These studies should be performed at the earliest possible stage of development to validate the feasibility of a controlled release formulation. After the utility of a controlled release formulation has been demonstrated, the polymer matrix should be chosen and bench-scale production of microspheres initiated. The only polymers presently approved for human use for controlled delivery are the polylactides [poly(lactic acid), poly(glycolic acid), and poly(lactic-coglycolic) acid]. These polymers require multiphase processes involving several steps to produce microspheres containing the desired protein. A thorough review of previous work on encapsulation with these polymers should provide some insight into conditions to be assessed in developing a process. Once a process is chosen, it must be optimized to provide the highest possible yield of microspheres with the desired characteristics (e.g., loading, release, size, etc.). Finally, the final aseptic process should be validated and methods generated to assess the final product. The clinical studies should then start upon approval of the IND application. In the future, the biotechnology industry, and the pharmaceutical industry in general, will be seeking new methods to improve the delivery of therapeutic agents such as proteins and peptides. Formulations like biodegradable microspheres significantly reduce health-care costs since fewer administrations are needed, and they provide a competitive advantage in markets with several competing products (e.g., LHRH agonist market). Further, many new indications such as neurological diseases may require a long-term delivery system. The future success of biodegradable microsphere formulations will primarily depend on the commitment of the pharmaceutical and biotechnology industries to the development of this technology.

Novel polymer-grafted starch microparticles for mucosal delivery of vaccines

Recent studies have demonstrated that systemic and mucosal administration of soluble antigens in biodegradable microparticles can potentiate antigen-specific humoral and cellular immune responses. However, current microparticle formulations are not adequate for all vaccine antigens, necessitating the further development of microparticle carrier systems. In this study, we developed a novel microparticle fabrication technique in which human serum albumin (HSA) was entrapped in starch microparticles grafted with 3-(triethoxysilyl)-propyl-terminated polydimethylsiloxane (TS-PDMS), a biocompatible silicone polymer. The immunogenicity of HSA was preserved during the microparticle fabrication process. Following intraperitoneal immunization of mice, TS-PDMS-grafted microparticles (MP) dramatically enhanced serum IgG responses compared with ungrafted MP and soluble HSA alone (P < 0.001). When delivered orally, both TS-PDMS-grafted and ungrafted microparticles elicited HSA-specific IgA responses in gut secretions, in contrast to orally administered soluble antigen. Indeed, TS-PDMS-grafted microparticles stimulated significantly stronger serum IgG (P < 0.005) and IgA (P < 0.001) responses compared with those elicited by ungrafted microparticles. These findings indicate that TS-PDMS-grafted starch microparticles have potential as systemic and mucosal vaccine delivery vehicles.

Effect of controlled release of platelet-derived growth factor from a porous hydroxyapatite implant on bone ingrowth

Platelet-derived growth factor (PDGF) is one of several osteogenic factors which affect bone growth and fracture healing. This study examined the potential of hydroxyapatite (HA) rods with interconnected pores of mean diameter 200 microns to be used as a matrix for the release of PDGF to enhance bone ingrowth into the implant. In the initial phase of the study the sustained release of PDGF from the HA rods was characterized in vitro for two different PDGF loadings, 10 and 100 micrograms per implant. The second phase of the study examined bone ingrowth in HA implants placed into the medullary canals of rabbit femora. The specimens were dumb-bell shaped, with a reduced central diameter so that bone growth across a gap could also be determined. Bone ingrowth into HA implants was compared with growth into HA implants loaded with 100 micrograms of PDGF. Pushout measurements were made of average shear strength across the bone-implant interface and backscatter scanning electron microscopy of thick sections was used to quantify the amount of bone ingrowth into the implant. Although greater interfacial shear strength and area of ingrowth were observed, especially across gap sites, in specimens loaded with PDGF, no difference was statistically significant.