Thomas R. Tice

Controlled vaccine release in the gut-associated lymphoid tissues. I. Orally administered biodegradable microspheres target the peyer's patches

Abstract Microspheres prepared from various polymers were evaluated for their usefulness as carriers for the targeted delivery of vaccine antigens to the gut-associated lymphoid tissues. Following oral administration to mice, microspheres consisting of polystyrene, poly(methyl methacrylate), poly(hydroxybutyrate), poly( dl -lactide), poly( l -lactide), and of poly( dl -lactide-co-glycolide) with various ratios of lactide to glycolide were absorbed into the Peyers patches of the small intestine. In contrast, no or very little uptake was observed with microspheres consisting of ethyl cellulose, cellulose acetate hydrogen phthalate or cellulose triacetate. Tissue penetration was specific to the Peyers patches and was restricted to microspheres ⩽ 10 μm in diameter. Time-course studies on the fate of the poly( dl -lactide-co-glycolide) microspheres within the gut-associated lymphoid tissue showed that the majority of the microspheres dl -lactide-co-glycolide) microspheres containing a toxoid vaccine of staphylococcal enterotoxin B were prepared and characterized for their size distribution, surface morphology and toxoid release kinetics in an aqueous environment. Oral immunization with these microspheres effectively delivered and released the vaccine in the gutassociated lymphoid tissue as determined by their ability to induce a disseminated mucosal IgA anti-toxin antibody response.

Biodegradable microspheres as a vaccine delivery system

The utility of biodegradable and biocompatible microspheres as a vaccine delivery system for the induction of systemic and disseminated mucosal antibody responses was investigated. Intraperitoneal (ip) injection into mice of 1-10 microns microspheres, constructed of the copolymer poly(DL-lactide-coglycolide) (DL-PLG) which contained approximately 1% by weight a formalinized toxoid vaccine of staphylococcal enterotoxin B (SEB), dramatically potentiated the circulating IgG anti-toxin antibody response as compared to the free toxoid. The initiation of vaccine release was delayed in larger microspheres, and a mixture of 1-10 and 20-50 microns microspheres stimulated both a primary and an anamnestic secondary anti-toxin response following a single injection. However, neither free nor microencapsulated SEB toxoid induced a detectable mucosal IgA anti-toxin response following systemic injection. In contrast, three peroral immunizations with toxoid-microspheres stimulated circulating IgM, IgG and IgA anti-toxin antibodies and a concurrent mucosal IgA response in saliva, gut washings and lung washings. Systemic immunization with microencapsulated toxoid primed for the induction of disseminated mucosal IgA responses by subsequent oral or intratracheal (it) boosting in microspheres, while soluble toxoid was ineffective at boosting. These results indicate that biodegradable and biocompatible microspheres represent an adjuvant system with potentially widespread application in the induction of both circulating and mucosal immunity.

Release of Human Serum Albumin from Poly(lactide-co-glycolide) Microspheres

Human serum albumin (HSA) was encapsulated in a 50:50 copolymer of DL-lactide/glycolide in the form of microspheres. These microspheres were used as a model formulation to study the feasibility of controlling the release of large proteins over a 20- to 30-day period. We show that HSA can be successfully incorporated into microspheres and released intact from these microspheres into various buffer systems at 37°C. A continuous release of the protein could be achieved in physiological buffers at 37°C over a 20- to 30-day period from microspheres with high protein loadings (11.6%). These results demonstrate the potential of poly(DL-lactide-co-glycolide) microspheres for continuous delivery of large proteins.

Biodegradable Microspheres: Vaccine Delivery System for Oral Immunization

The potential of biocompatible and biodegradable microspheres as a controlled release oral vaccine delivery system has been examined. Orally-administered 1-10 micron microspheres composed of poly (DL-lactide-co-glycolide) were specifically taken up into the Peyers patch lymphoid tissue of the gut, where those greater than or equal to 5 micron remained for up to 35 days. Microspheres less than 5 micron disseminated within macrophages to the mesenteric lymph nodes and spleen. In contrast to soluble staphylococcal enterotoxin B toxoid, oral immunization with enterotoxoid in microspheres induced circulating toxin-specific antibodies and a concurrent secretory IgA anti-toxin response in saliva and gut fluid.

Preparation of injectable controlled-release microcapsules by a solvent-evaporation process☆

Abstract The solvent-evaporation microencapsulation process can be used to prepare high-quality, injectable, controlled-release microcapsules containing as little as 1 wt.% drug to as much as 90 wt.% drug. This process is useful for the microencapsulation of water-soluble and water-insoluble drugs. When the process conditions are optimized, the process affords good yields of a free-flowing powder comprising smooth spherical particles. Using this process, a batch of microcapsules can be made to have a wide or narrow size distribution. The micro-capsules can have diameters from less than 1 μm to as large as 250 μm. During the early stages of a microcapsule development project, problems can often arise, and high-quality microcapsules are difficult to fabricate. Some of these problems and how to remedy them with respect to the solvent-evaporation process are discussed.

[8] Poly(lactide-co-glycolide) microcapsules for controlled release of steroids

Publisher Summary This chapter addresses long-acting, drug-delivery systems comprising steroidal drugs microencapsulated in aliphatic polyester resins. Because the aliphatic polyesters slowly degrade, owing to hydrolysis of ester linkages, when they are exposed to water they disappear from the tissues soon after (or during) drug release. Many drug and biologic substances, other than the steroids, can be microencapsulated in the biodegradable polyesters to produce injectable controlled-release doses. The specific copolymer resins and the appropriate microencapsulation processes must be chosen carefully, however, to achieve the rates and durations of drug release desired. When steroid hormones are microencapsulated in the biodegradable copolyesters in which the drug is homogeneously dispersed within the resin matrix to form a monolithic microcapsule and the microcapsules are injected either intramuscularly or subcutaneously, the drugs are slowly released into the tissues principally by a diffusion mechanism. The microcapsules are designed to release norethisterone at a nearly constant rate for 3 months. The 85:15 poly(DL-lactide-co-glycolide) resin is selected as the biodegradable excipient because the onset of resin fragmentation occurs at about 50 days postinjection. Total resorption of the resin by the tissues is complete in about 180 days.

Vaccine-Containing Biodegradable Microspheres Specifically Enter the Gut-Associated Lymphoid Tissue Following Oral Administration and Induce a Disseminated Mucosal Immune Response

Biodegradable and biocompatible microspheres have been investigated for their usefulness as a vaccine delivery system for both parenteral and enteral immunization. Microspheres composed of poly(DL-lactide-co-glycolide) which contained a toxoid vaccine of Staphylococcal enterotoxin B were found to strongly potentiate the circulating anti-toxin antibody response following intraperitoneal injection. Following oral administration, microspheres less than 10 microns in diameter were specifically taken up into the Peyers patches of the gut-associated lymphoid tissue, where those greater than or equal to 5 microns remained fixed for an extended period. Microspheres less than 5 microns were disseminated within macrophages to the mesenteric lymph nodes, blood circulation and spleen. Oral immunization with enterotoxoid-containing microspheres induced circulating toxin-specific antibodies and a concurrent secretory IgA anti-toxin response in saliva, gut wash fluids and bronchial-alveolar wash (BAW) fluids. In contrast, soluble enterotoxoid was completely ineffective as an oral immunogen.

Biodegradable microcapsules: Acceleration of polymeric excipient hydrolytic rate by incorporation of a basic medicament

The degradation rate of the polymer, poly(d,l-lactide), was accelerated in the presence of the tertiary amino compound, thioridazine. The poly(d,l-lactide) component of micro-capsules containing up to 50% thioridazine free base showed a decrease in molecular weight during microcapsule fabrication and in the course of dissolution-rate studies. This effect was evidenced on dissolution by an unexpectedly rapid release of thioridazine as a function of time. Polymer hydrolysis was neither appreciable in microcapsules containing no drug nor when the amino group of thioridazine was protonated in the form of the pamoate salt. This enhancement of degradation rate may be attributed to amine-influenced hydrolysis of poly(d,l-lactide). Thioridazine blood levels obtained from the microcapsules in dogs paralleled the in vitro results. There was an initial lag time followed by a rapid release of the drug producing blood levels over about a six-day span. Polymeric decomposition was also determined in vitro, pH 7.4, by gel-permeation chromatography. The results indicate a rapid molecular-weight decrease of the polymer, corroborating the in vivo and in vitro results.

The effect of hydrocortisone acetate loaded poly(DL-lactide) films on the inflammatory response☆

Abstract Poly ( DL -lactide) (DL-PL) films loaded with hydrocortisone acetate (HCA) were prepared and the effects of this drug releasing system on the inflammatory and healing responses were investigated in vivo using a cage implant technique. Cytochemical staining procedures and extracellular enzyme activity assays were performed in order to characterize the cellular events in the inflammatory exudate over a 21-day implantation period. The results showed that the HCA/DL-PL sustained drug releasing system dramatically inhibited all aspects of inflammation. The white cell concentration in the HCA/DL-PL exudates was markedly lower than the white cell concentrations of both the empty cage and DL-PL controls throughout the implantation period. The drug inhibited the accumulation of all types of leukocytes at the site of inflammation including polymorphonuclear leukocytes, macrophages and lymphocytes. Additionally, examination of the retrieved cages 21 days after implantation revealed minimal connective tissue development around the HCA/DL-PL implants compared to the two sets of controls. This indicated that the healing phase of inflammation was being repressed.

Development of Encapsulated Antibiotics for Topical Administration to Wounds

The most difficult wound to treat is one characterized by the presence of infection, devitalized tissue, and foreign-body contaminants. In efforts to improve methods of treating these wounds and to prevent infection, antibiotics microencapsulated in poly(DL-lactide-co-glycolide) (DL-PLG) have been formulated to release drug at a controlled rate over an extended period. The microcapsules are applied topically to open contaminated wounds so that the antibiotics are released from multiple sites within the tissue where they are concentrated in the area of need.