Neutrase entrapment in stable multilamellar and large unilamellar vesicles for the acceleration of cheese ripening

Polymer encapsulation within giant lipid vesicles

We report encapsulation of polymers and small molecules within individual giant lipid vesicles (GVs; 3-80 microm), as determined by confocal fluorescence microscopy. Polymer-bound or free dyes were encapsulated within GVs by including these molecules in the aqueous solution during vesicle formation via gentle hydration. Encapsulation efficiencies of individual GVs (EE(ind)) were determined from the fluorescence intensity ratio inside vs outside the vesicle. EE(ind) varied considerably from vesicle to vesicle, with interior solute concentrations for GVs within the same batch ranging from much less than to slightly more than the initial concentration. The majority of GVs had high internal concentrations of polymer or small-molecule encapsulants equal to or slightly greater than the external concentration. EE(ind) decreased for high molecular weight polymers (e.g., dextran 500 000), but was relatively insensitive to the GV diameter, membrane composition, or incubation temperature in our experiments. Knowledge of EE(ind) is important for quantitative evaluation of reactions occurring within GVs (e.g., enzymatic processes) and for optimizing encapsulation conditions.

Biotechnological methods to accelerate cheddar cheese ripening

Cheese is one of the dairy products that can result from the enzymatic coagulation of milk. The basic steps of the transformation of milk into cheese are coagulation, draining, and ripening. Ripening is the complex process required for the development of a cheese's flavor, texture and aroma. Proteolysis, lipolysis and glycolysis are the three main biochemical reactions that are responsible for the basic changes during the maturation period. As ripening is a relatively expensive process for the cheese industry, reducing maturation time without destroying the quality of the ripened cheese has economic and technological benefits. Elevated ripening temperatures, addition of enzymes, addition of cheese slurry, attenuated starters, adjunct cultures, genetically engineered starters and recombinant enzymes and microencapsulation of ripening enzymes are traditional and modern methods used to accelerate cheese ripening. In this context, an up to date review of Cheddar cheese ripening is presented.

Enzymes inside lipid vesicles: preparation, reactivity and applications

There are a number of methods that can be used for the preparation of enzyme-containing lipid vesicles (liposomes) which are lipid dispersions that contain water-soluble enzymes in the trapped aqueous space. This has been shown by many investigations carried out with a variety of enzymes. A review of these studies is given and some of the main results are summarized. With respect to the vesicle-forming amphiphiles used, most preparations are based on phosphatidylcholine, either the natural mixtures obtained from soybean or egg yolk, or chemically defined compounds, such as DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) or POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine). Charged enzyme-containing lipid vesicles are often prepared by adding a certain amount of a negatively charged amphiphile (typically dicetylphosphate) or a positively charged lipid (usually stearylamine). The presence of charges in the vesicle membrane may lead to an adsorption of the enzyme onto the interior or exterior site of the vesicle bilayers. If (i) the high enzyme encapsulation efficiencies; (ii) avoidance of the use of organic solvents during the entrapment procedure; (iii) relatively monodisperse spherical vesicles of about 100 nm diameter; and (iv) a high degree of unilamellarity are required, then the use of the so-called 'dehydration-rehydration method', followed by the 'extrusion technique' has shown to be superior over other procedures. In addition to many investigations in the field of cheese production--there are several studies on the (potential) medical and biomedical applications of enzyme-containing lipid vesicles (e.g. in the enzyme-replacement therapy or for immunoassays)--including a few in vivo studies. In many cases, the enzyme molecules are expected to be released from the vesicles at the target site, and the vesicles in these cases serve as the carrier system. For (potential) medical applications as enzyme carriers in the blood circulation, the preparation of sterically stabilized lipid vesicles has proven to be advantageous. Regarding the use of enzyme-containing vesicles as submicrometer-sized nanoreactors, substrates are added to the bulk phase. Upon permeation across the vesicle bilayer(s), the trapped enzymes inside the vesicles catalyze the conversion of the substrate molecules into products. Using physical (e.g. microwave irradiation) or chemical methods (e.g. addition of micelle-forming amphiphiles at sublytic concentration), the bilayer permeability can be controlled to a certain extent. A detailed molecular understanding of these (usually) submicrometer-sized bioreactor systems is still not there. There are only a few approaches towards a deeper understanding and modeling of the catalytic activity of the entrapped enzyme molecules upon externally added substrates. Using micrometer-sized vesicles (so-called 'giant vesicles') as simple models for the lipidic matrix of biological cells, enzyme molecules can be microinjected inside individual target vesicles, and the corresponding enzymatic reaction can be monitored by fluorescence microscopy using appropriate fluorogenic substrate molecules.

Characterization and in-vivo ocular absorption of liposome-encapsulated acyclovir

The potential of liposomes as an in-vivo ophthalmic drug delivery system for acyclovir was investigated. The drug-membrane interaction was evaluated by means of differential scanning calorimetry analysis. These experiments showed that acyclovir is able to interact with both positively and negatively charged membranes via electrostatic or hydrogen bonds. No interaction was observed with neutral membranes made up of dipalmitoylphosphatidylcholine. Different liposome preparation procedures were carried out to encapsulate acyclovir. The drug encapsulation mainly depends on the amount of water which the liposome system is able to entrap. In the case of multilamellar vesicles, charged systems showed the highest encapsulation efficiency. No particular difference in the encapsulation efficiency was observed for oligolamellar vesicles prepared with the reverse-phase evaporation technique. Oligolamellar liposomes showed the highest acyclovir encapsulation parameters and had release profiles similar to those of multilamellar liposomes. In-vivo experiments using male New Zealand albino rabbits were carried out to evaluate the aqueous humour concentration of acyclovir bioavailability. The most suitable ophthalmic drug delivery system was oligolamellar systems made up of dipalmitoylphosphatidylcholine-cholesterol-dimethyldioctadecyl glycerole bromide (7:4:1 molar ratio), which presented the highest encapsulation capacity and were able to deliver greater amounts of the drug into the aqueous humour than a saline acyclovir solution or a physical liposome/drug blend.

Release of enzymes from liposomes during cheese ripening

Changes in proteolysis and in residual enzymatic activity as a function of time were compared in model cheeses, made with either free enzymes or liposomes containing enzymes and in control model cheeses. Cheeses were ripened under different conditions of pH, fat content and temperature. The release of enzymes from liposomes was significantly stimulated by increasing the fat content from 0 to 20% and the pH from 4.9 to 5.5. Ripening temperature (6 degrees C or 13 degrees C) did not affect 2 months of ripening, proteolysis was 30% lower in liposome-than in free enzyme-treated cheeses, indicating a possible inhibition of released enzymes.

Liposomal delivery of a 30-mer antisense oligodeoxynucleotide to inhibit proopiomelanocortin expression

An oligodeoxynucleic sequence of 30 bases (30-mer ODN), complementary to a region of beta-endorphin mRNA, was synthesized to have an antisense effect with regard to the expression of this oligopeptide. Following the solid-phase synthesis of the oligodeoxynucleotide, the 30-mer ODN was encapsulated within liposomes to provide a higher resistance against DNases and an improved entrance into cells. The most suitable liposome formulation as a 30-mer ODN carrier consisted of small unilamellar vesicles (50 nm) with an encapsulation capacity of 4.76 microL/micromol. The liposomal formulations containing dipalmitoyl-DL-alpha-phosphatidyl-L-serine presented fusogenic properties, which are of great importance for the delivery of antisense compounds. The antisense activity of 30-mer ODN-loaded liposomes was evaluated by the determination of beta-endorphin levels in AtT-20 cells. The free 30-mer ODN did not provide any lowering of the beta-endorphin production, whereas the liposomally entrapped compound elicited a concentration-dependent inhibition. The inhibition was determined by a sequence-specific binding of the 30-mer ODN with the target mRNA.

Survival rate improvement in a rat ischemia model by long circulating liposomes containing cytidine-5I-diphosphate choline

Unilamellar liposomes made up of DPPC-DPPS-Chol (7:4:7 molar ratio) and ganglioside GM1 8% mol were used to deliver cytidine-5I-diphosphate choline (CDP-choline) to the brain. The liposomal suspension consisted of unilamellar vesicles with a mean size of 50 nm and a very narrow size distribution. The therapeutic effectiveness of CDP-choline-loaded liposomes was investigated by an in vivo model of cerebral ischemia on Wistar rats (320-350 g). The animals were made ischemic to different extents (5, 15 and 30 min) by bilateral clamping of the common carotid arteries. The effect of free and liposomally encapsulated CDP-choline on the survival rate of post-ischemic reperfused rats was evaluated. The liposome formulation was much more active against ischemic injury than the free CDP-choline, ensuring a noticeable improvement of the survival rate with regards to the free drug ranging from 45% to 100% as a function of the duration of the ischemic event.