LinShu Liu

Pectin-based systems for colon-specific drug delivery via oral route

Pectin-derived matrices are now being examined and tested for controlled drug delivery. Pectin is intact in the upper gastrointestinal tract and degraded by colonic microflora. The composition of this microflora remains relatively consistent across a diverse human population. Thus, pectin-derived drug carriers provide promising potential for colon-specific drug delivery. This paper reviews recent developments in pectin-derived formulations. Subjects reviewed include gelation of pectin, calcium cross-linked pectinate, composites of pectin and other polymers, technologies to fabricate pectin into useful drug delivery vehicles, and methods to evaluate release kinetics of incorporated drugs. This article discusses advantages, limitations, and possible future developments in pectin-based formulations with particular emphasis on the field of colon-specific drug delivery.

Colon-specific delivery of a probiotic-derived soluble protein ameliorates intestinal inflammation in mice through an EGFR-dependent mechanism

Probiotic bacteria can potentially have beneficial effects on the clinical course of several intestinal disorders, but our understanding of probiotic action is limited. We have identified a probiotic bacteria-derived soluble protein, p40, from Lactobacillus rhamnosus GG (LGG), which prevents cytokine-induced apoptosis in intestinal epithelial cells. In the current study, we analyzed the mechanisms by which p40 regulates cellular responses in intestinal epithelial cells and p40s effects on experimental colitis using mouse models. We show that the recombinant p40 protein activated EGFR, leading to Akt activation. Activation of EGFR by p40 was required for inhibition of cytokine-induced apoptosis in intestinal epithelial cells in vitro and ex vivo. Furthermore, we developed a pectin/zein hydrogel bead system to specifically deliver p40 to the mouse colon, which activated EGFR in colon epithelial cells. Administration of p40-containing beads reduced intestinal epithelial apoptosis and disruption of barrier function in the colon epithelium in an EGFR-dependent manner, thereby preventing and treating DSS-induced intestinal injury and acute colitis. Furthermore, p40 activation of EGFR was required for ameliorating colon epithelial cell apoptosis and chronic inflammation in oxazolone-induced colitis. These data define what we believe to be a previously unrecognized mechanism of probiotic-derived soluble proteins in protecting the intestine from injury and inflammation.

Pectin/Zein Beads for Potential Colon-Specific Drug Delivery: Synthesis and in Vitro Evaluation

Novel complex hydrogel beads were prepared from two edible polymers: pectin, a carbohydrate from citrus fruits, and zein, a protein from corn. The pectin/zein complex hydrogels did not swell in physiological environments, but hydrolyzed in the presence of pectinases. An in vitro study showed the capacity of the hydrogels to endure protease attack and residence time variation. The physical and biological properties of the new hydrogels were attributed to molecular entanglement of the two polymers. The pectin networks were stabilized by the bound zein molecules. In turn, the pectin networks shielded the bound zein from protease digestion.

Preparation of Antimicrobial Membranes: Coextrusion of Poly(lactic acid) and Nisaplin in the Presence of Plasticizers

Nisin is a naturally occurring antimicrobial polypeptide and is popularly used in the food and food-packaging industries. Nisin is deactivated at temperatures higher than 120 degrees C and, therefore, cannot be directly incorporated into poly(L-lactic acid) (PLA), a biomass-derived biodegradable polymer, by coextrusion because PLA melts at temperatures around 160 degrees C or above. However, PLA can remain in a melt state at temperatures below the T(m) in the presence of lactic acid or other plasticizers. In the present study, PLA was coextruded with lactic acid, or lactide, or glycerol triacetate at 160 degrees C. After the PLA was melted, the temperature of the barrels was reduced to 120 degrees C, and then Nisaplin, the commercial formulation of nisin, was added and the extrusion was continued. The resultant extrudates possess the capability to suppress the growth of the pathogenic bacterial Listeria monocytogenes , demonstrating a significant antimicrobial activity. The present study provides a simple method to produce PLA-based antimicrobial membranes. The method can also be used for the coextrusion of other heat-sensitive substances and thermoplastics with high melting temperature.

Radiation sensitization and postirradiation proliferation of Listeria monocytogenes on ready-to-eat deli meat in the presence of pectin-nisin films.

In this study, the ability of pectin-nisin films in combination with ionizing radiation to eliminate Listeria monocytogenes and inhibit its postirradiation proliferation was evaluated. Pectin films containing 0.025% nisin were made by extrusion. The surface of a ready-to-eat turkey meat sample was inoculated with L. monocytogenes at 10(6) CFU/cm2 and covered with a piece of pectin-nisin film. The samples were vacuum packaged and irradiated at 0, 1, and 2 kGy. The treated samples were stored at 10 degrees C and withdrawn at 0, 1, 2, 4, and 8 weeks for microbial analysis. Reductions in L. monocytogenes viability of 1.42, 1.56, 2.85, 3.78, and 5.36 log CFU/cm2 were achieved for the treatments of 1 kGy, pectin-nisin film, 2 kGy, 1 kGy plus pectin-nisin film, and 2 kGy plus pectin-nisin film, respectively. The greatest reduction (5.5 log CFU/cm2) was observed at 1 week for the 2 kGy plus pectin-nisin film treatment, suggesting that nisin was further released from the film to the surface of meat samples. Pectin-nisin films used in this study did not prevent but did significantly slow (P < 0.05) the proliferation of the L. monocytogenes cells that survived irradiation during 8 weeks of storage at 10 degrees C. These data indicate the potential use of pectin-nisin films alone or in combination with ionizing radiation for preventing listeriosis due to postprocessing contamination of ready-to-eat meat products.

Electrospinning of agar/PVA aqueous solutions and its relation with rheological properties

In this work, we report the successful fabrication of agar-based nanofibers by electrospinning technique, using water as solvent media. A tubeless spinneret was attached inside the electrospinning chamber, operating at 50°C, to avoid agar gelation. Agar pure solution (1 wt%) showed inadequate spinnability regardless of the used electrospinning conditions. The addition of a co-blending polymer such as PVA (10 wt% starting solution) improved the solutions viscoelasticity and hence, the solutions spinnability. Agar/PVA solutions were prepared with different mass ratios (100/0, 50/50, 40/60, 30/70, 20/80 and 0/100) and electrospun at various sets of electrospinning conditions. Best nanofibers were obtained with 30/70 and 20/80 agar/PVA blends while samples with higher agar contents (50/50 and 40/60 agar/PVA) were harder to process and led to discontinuous fibrous mats. This first set of encouraging results can open a new window of opportunities for agar-based biomaterials in the form of nanofibers.

Pectin Gel Vehicles for Controlled Fragrance Delivery

Using citronellal as a model compound, pectin gels formulations were evaluated for the controlled fragrance release by kinetic and static methods. The pectins with higher degrees of esterification induced a stronger molecular association with the nonpolar fragrance. This resulted in a prolonged duration of fragrance release and the limitation of fragrance adsorption to the receptor skin layers. The increase in pectin concentrations suppressed the fragrance release by a diffusion mechanism. Blocking the carboxyl groups of pectin with calcium ions reduces the hydrophilicity of pectin and provides physical barriers for citronellal diffusion. The pectin/calcium microparticles are promising materials for controlled fragrance release.

Choline chloride based ionic liquid analogues as tool for the fabrication of agar films with improved mechanical properties.

In the present paper, we test the suitability of ChCl/urea (DES-U) and ChCl/glycerol (DES-G) eutectic mixtures, each one prepared at 1:2 molar ratio, for the production of agar films. A three-step process is proposed: pre-solubilization of polymer in DES followed by compression-molding and subsequent drying. The mechanical properties, water resistance and microstructure of the films were evaluated at different polymer concentrations (i.e. 2-6%, w/w). DES-U showed by far, the best film forming ability. Agreeing with the diffusion and SEM data, films with the best mechanical properties were found at the lowest and highest agar concentrations (tensile strengths of 24.2-42 MPa and elongations of 15.4-38.9%). The water sorption and contact angle studies suggested increased hydrophilicity for the film containing the lowest concentration of agar. The use of choline chloride based ionic liquid analogues as solvent and plasticizer might be a promising tool for the development of new non-aqueous materials based on seaweed polysaccharides.

Preserving viability of Lactobacillus rhamnosus GG in vitro and in vivo by a new encapsulation system

Probiotics have shown beneficial effects on health and prevention of diseases in humans. However, a concern for application of probiotics is the loss of viability during storage and gastrointestinal transit. The aim of this study was to develop an encapsulation system to preserve viability of probiotics when they are administrated orally and apply Lactobacillus rhamnosus GG (LGG) as a probiotic model to evaluate the effectiveness of this approach using in vitro and in vivo experiments. LGG was encapsulated in hydrogel beads prepared using pectin, a food grade polysaccharide, glucose, and calcium chloride, and lyophilized by freeze-drying. Encapsulated LGG was cultured in vitro under the condition that mimicked the physiological environment of the human gastrointestinal tract. Compared to non-encapsulated LGG, encapsulation increased tolerance of LGG in the acid condition, protected LGG from protease digestion, and improved shelf time when stored at the ambient condition, in regard of survivability and production of p40, a known LGG-derived protein involved in LGGs beneficial effects on intestinal homeostasis. To evaluate the effects of encapsulation on p40 production in vivo and prevention of intestinal inflammation by LGG, mice were gavaged with LGG containing beads and treated with dextran sulphate sodium (DSS) to induce intestinal injury and colitis. Compared to non-encapsulated LGG, encapsulated LGG enhanced more p40 production in mice, and exerted higher levels of effects on prevention of DSS-induced colonic injury and colitis and suppression of pro-inflammatory cytokine production. These data indicated that the encapsulation system developed in this study preserves viability of LGG in vitro and in vivo, leading to longer shelf time and enhancing the functions of LGG in the gastrointestinal tract. Thus, this encapsulation approach may have the potential application for improving efficacy of probiotics.

Antimicrobial Effects of Allyl Isothiocyanate and Modified Atmosphere on Pseduomonas Aeruginosa in Fresh Catfish Fillet under Abuse Temperatures

The effects of allyl isothiocyanate (AIT; 18 and 36 μg/L) in vapor phase, modified atmosphere (MA; 49% CO2 , 0.5% O2 , and 50.5% N2 ), and their combinations on the growth behavior of Pseduomonas aeruginosa in fresh catfish fillet at different abuse temperatures (8, 15, and 20 °C) were evaluated in this study. Lag phase, maximum growth rate, and shelf life were used as parameters to analyze the antimicrobial effects. Both gaseous AIT and MA alone inhibited the growth potential of P. aeruginosa effectively, prolonging the shelf life by 1.5 to 3.4 times compared to the control at abuse temperatures between 8 and 20 °C. The synergistic effect was observed at 8 °C, extending the shelf life of fresh catfish by more than 6.5 times (≥ 550 h). In addition, the maximum growth rate decreased with decreasing storage temperature, but it was not significantly influenced by the addition of AIT or MA. Hence, the combination of AIT and MA may be used as an effective antimicrobial system to reduce the microbial risks due to temperature abuse and to improve the shelf life of fresh catfish fillet. The proper combination of AIT and MA may be further optimized for industrial applications.