Jules S. Jacob

Nanosphere based oral insulin delivery

Zinc insulin is successfully encapsulated in various polyester and polyanhydride nanosphere formulations using Phase Inversion Nanoencapsulation (PIN). The encapsulated insulin maintains its biological activity and is released from the nanospheres over a span of approximately 6 h. A specific formulation, 1.6% zinc insulin in poly(lactide-co-glycolide) (PLGA) with fumaric anhydride oligimer and iron oxide additives has been shown to be active orally. This formulation is shown to have 11.4% of the efficacy of intraperitoneally delivered zinc insulin and is able to control plasma glucose levels when faced with a simultaneously administered glucose challenge. A number of properties of this formulation, including size, release kinetics, bioadhesiveness and ability to traverse the gastrointestinal epithelium, are likely to contribute to its oral efficacy.

Correlation of two bioadhesion assays: the everted sac technique and the CAHN microbalance

This contribution correlates two in vitro methods utilized to determine bioadhesion. One method, the everted intestinal sac technique, is a passive test for bioadhesion involving several polymer microspheres and a section of everted intestinal tissue. The other method, the CAHN microbalance, employs a CAHN dynamic contact angle analyzer with modified software to record the tensile forces measured as a single polymer microsphere is pulled from intestinal tissue. This study demonstrates that CAHN and everted sac experiments yield similar results when used to quantify the bioadhesive nature of polymer microsphere systems. A polymer showing high adhesion in one method also demonstrates high bioadhesion in the other method; polymers that exhibit high fracture strength and tensile work measurements with the CAHN microbalance also yield high binding percentages with the everted sac method. The polymers tested and reported here are poly(caprolactone) and different copolymer ratios of poly(fumaric-co-sebacic anhydride). The results of this correlation demonstrate that each method alone is a valuable indicator of bioadhesion.

Bioadhesive microspheres : III. An in vivo transit and bioavailability study of drug-loaded alginate and poly(fumaric-co-sebacic anhydride) microspheres

Bioadhesive drug delivery systems (BDDSs) could improve bioavailability by protecting bioactive molecules from physical and chemical degradation, enhancing absorption rates by minimizing diffusion barriers, and increasing the period for absorption by prolonging residence time. The in vivo bioadhesive performance of calcium alginate microspheres and poly(fumaric-co-sebacic anhydride) 20:80 microspheres were evaluated in two ways. Firstly, effect on GI transit was measured in rats. P(FA:SA) 20:80 microspheres showed significantly prolonged retention in the gut when compared to alginate microspheres. Secondly, the ability of these polymers to improve relative bioavailability of a model drug, dicumarol, in rats was assayed. A significant increase was measured in the area under the plasma concentration-time curve for dicumarol encapsulated in P(FA:SA) 20:80 when compared to its controls. The results of this study suggest that polymers which have been shown to produce strong bioadhesive forces in vitro and delayed GI transit in vivo may be used to improve oral bioavailability of certain drugs.

Cytokine immunotherapy of cancer with controlled release biodegradable microspheres in a human tumor xenograft/SCID mouse model.

Abstract A novel biodegradable poly(lactic acid) microsphere formulation was evaluated for in vivo cytokine immunotherapy of cancer in a human tumor xenograft/severe combined immunodeficiency (SCID) mouse model. Co-injection of interleukin-2 (IL-2)-loaded microspheres with tumor cells into a subcutaneous site resulted in the complete suppression of tumor engraftment in 80% of animals. In contrast, bovine-serum-albumin(BSA)-loaded particles or bolus injections of poly(ethylene glycol)/IL-2 were ineffective in preventing tumor growth. The antitumor effect of IL-2 released by the microspheres was shown to be mediated by the mouse natural killer cells. This is the first evidence that the rejection of human tumor xenografts can be provoked by the sustained in vivo delivery of IL-2 from biodegradable microspheres. The use of poly(lactic acid) microspheres to deliver cytokines to the tumor environment could provide a safer and simpler alternative to gene therapy protocols in the treatment of cancer.

Poly(fumaric-co-sebacic) microspheres as oral drug delivery systems.

The current study focuses on the development of bioadhesive oral delivery systems based on bioerodible polyanhydrides. The polymers were studied and characterized using a novel tensiometer based on a very sensitive electrobalance. The system was designed to mimic in vivo interactions, thus all experiments were conducted with freshly excised tissue immersed in physiological saline at 37 degrees C. Poly(fumaric-co-sebacic) [P(FA:SA)] was found to be the most bioadhesive polymer from a series of different thermoplastic materials evaluated. Correlation with in vivo performance was investigated by determining gastrointestinal (GI) residence time of barium-loaded microspheres. Residence times of 24 to 36 h provided a strong indication that these microspheres were good candidates for bioadhesive drug delivery systems. To evaluate the effect of these materials on bioavailability, the anticoagulant drug, dicumarol, was encapsulated. Systemic blood levels demonstrated increased bioavailability for the encapsulated dicumarol formulation as compared with unencapsulated drug. (c) 1996 John Wiley & Sons, Inc.

Controlled release of plasmid DNA

Abstract Very large molecular weight reporter plasmids (pCMV- β gal, pSV- β gal) and lower molecular weight (herring sperm) DNA were encapsulated in polyethylene vinyl co-acetate (EVAc). In vitro release studies were performed to determine release rates and duration of delivery. The swelling behavior and morphological changes of these formulations were studied to elucidate the potential mechanism of DNA release. The bioactivity of the released plasmid DNA was assessed through analysis of conformation using agarose gel electrophoresis and in vitro transfection of C 2 C 12 myoblasts using liposome (Lipofectin™) complexation. Extraction of plasmid DNA from the delivery systems indicated that the fabrication conditions did not degrade the DNA. Depending on initial DNA loading, detectable levels were released for 1–6 months. Pore formation was accompanied by swelling which varied according to DNA loading as well as the type of DNA (herring sperm, plasmid). Conformational analysis of released plasmid DNA showed DNA was released without degradation and retained the ability to transfect cells in vitro. The results demonstrate that controlled release systems can be fabricated for the release of very large molecular weight plasmid DNA which may provide an alternative approach to plasmid-based gene transfer.

Bioadhesive microspheres, II. Characterization and evaluation of bioadhesion involving hard, bioerodible polymers and soft tissue

Abstract Several bioerodible polymers and one hydrogel were studied as potential bioadhesive materials. A microbalance-based method was used to measure bioadhesive interactions between individual polymer microspheres and rat intestinal tissue. In addition, surface and bulk properties of these microspheres were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and contact angle measurements. Polyanhydride microspheres composed of copolymers of fumaric and sebacic acid, produced bioadhesive fracture strengths greater than 50 mN/cm2 with rat small intestinal mucosa in vitro. We suggest that bioadhesion in these bioerodible materials is not attributable to chain entanglement, but instead to hydrogen bonding between hydrophilic functional groups (COOH) and mucus glycoproteins. We also believe that continuous degradation of these materials may enhance their bioadhesive properties by changing surface energy, and increasing both carboxylic acid concentration and surface roughness.

Unique insights into the intestinal absorption, transit, and subsequent biodistribution of polymer-derived microspheres

Polymeric microspheres (MSs) have received attention for their potential to improve the delivery of drugs with poor oral bioavailability. Although MSs can be absorbed into the absorptive epithelium of the small intestine, little is known about the physiologic mechanisms that are responsible for their cellular trafficking. In these experiments, nonbiodegradable polystyrene MSs (diameter range: 500 nm to 5 µm) were delivered locally to the jejunum or ileum or by oral administration to young male rats. Following administration, MSs were taken up rapidly (≤5 min) by the small intestine and were detected by transmission electron microscopy and confocal laser scanning microscopy. Gel permeation chromatography confirmed that polymer was present in all tissue samples, including the brain. These results confirm that MSs (diameter range: 500 nm to 5 µm) were absorbed by the small intestine and distributed throughout the rat. After delivering MSs to the jejunum or ileum, high concentrations of polystyrene were detected in the liver, kidneys, and lungs. The pharmacologic inhibitors chlorpromazine, phorbol 12-myristate 13-acetate, and cytochalasin D caused a reduction in the total number of MSs absorbed in the jejunum and ileum, demonstrating that nonphagocytic processes (including endocytosis) direct the uptake of MSs in the small intestine. These results challenge the convention that phagocytic cells such as the microfold cells solely facilitate MS absorption in the small intestine.

Novel desiccants based on designed polymeric blends

We describe a novel concept for the preparation of desiccants based on polymeric blends. A hydrophilic channeling agent (e.g., PEG) is blended with a hydrophobic polymer (e.g., polypropylene) to produce interconnecting hydrophilic channels within the hydrophobic polymer. To make the system desiccating, a water-absorbing material is blended into the polymeric matrix to become distributed within the hydrophilic portion. The resultant blend may be molded and cast into plug-type inserts and liners for closed containers, or formed into films, sheets, beads, or pellets; its uses include pharmaceutical and industrial applications.

Heliobacterium chlorum: cell organization and structure.

The basic cellular organization of Heliobacterium chlorum is described using the freeze-etching technique. Internal cell membranes have not been observed in most cells, leading to the conclusion that the photosynthetic apparatus of these organisms must be localized in the cell membrane of the bacterium. The two fracture faces of the cell membrane are markedly different. The cytoplasmic (PF) face is covered with densely packed particles averaging 8 nm in diameter, while the exoplasmic (EF) face contains far fewer particles, averaging approximately 10 nm in diameter. Although a few differentiated regions were noted within these fracture faces, the overall appearance of the cell membrane was remarkably uniform. The Heliobacterium chlorum cell wall is a strikingly regular structure, composed of repeating subunits arranged in a rectangular pattern at a spacing of 11 nm in either direction. We have isolated cell wall fragments by brief sonication in distilled water, and visualized the cell wall structure by negative staining as well as deep-etching.