Hydrophobic ion pairing as a method for enhancing structure and activity of lyophilized subtilisin BPN' suspended in isooctane

Development of a stable liquid formulation of live attenuated influenza vaccine

Vaccination is the most effective means of preventing influenza. However, the cost of producing annual seasonal influenza vaccines puts them out of reach for most developing countries. While live attenuated influenza vaccines are among the most efficacious and can be manufactured at low cost, they may require lyophilization to be stable enough for developing-country use, which adds a significant cost burden. The development of a liquid live attenuated seasonal influenza vaccine that is stable for around a year-the duration of an annual influenza season-would significantly improve not only the production output but also the use and accessibility of influenza vaccines in low-resource settings. In this study, potential stabilizing excipients were screened and optimized using the least stable influenza vaccine strain presently known, H1N1 (A/California/07/2009), as a model. The stability-conferring properties of the lead formulations were also tested with a Type B strain of influenza virus (B/Brisbane/60/2008). Stability was also evaluated with higher titers of influenza virus and exposure to agitation and freeze-thaw stresses to further confirm the stability of the lead formulations. Through this process, we identified a liquid formulation consisting of sucrose phosphate glutamate buffer with 1% arginine and 0.5% recombinant human serum albumin that provided storage stability of one year at 2-8°C for the influenza A and B strains tested.

Examining structure-activity correlations of some high activity enzyme preparations for low water media

A first study of the comparison of structures of enzymes (by FT-IR and CD) in different high activity (in low water media) preparations is reported. Using chymotrypsin and subtilisin as models, we have studied various factors that distinguish enzyme precipitated and rinsed with propanol (EPRP), crosslinked enzyme aggregates (CLEA), protein coated microcrystals (PCMC) and crosslinked protein coated microcrystals (CLPCMC). The suspensions in organic media were assayed for catalytic activity, and structures were probed by FT-IR and CD measurements. CD studies of enzyme suspensions were possible by using a rotating cell accessory. There was a generally good correlation between higher catalytic activity and retention of native structures. Activity and retention of native structure was always higher if aqueous enzyme solution was added to propanol rather than vice versa in the precipitation step of these preparations. The work identifies factors which may lead to better biocatalyst designs for low water media.

Evaluation of pharmacological efficacy of 'insulin-surfoplex' encapsulated polymer vesicles

The present study has been designed to study whether formation of ion-pair complex or 'surfoplex' can enhance the pharmacological efficacy of protein-loaded PCL-PEG-based polymerosomes. Insulin was selected as the model protein and was complexed with sodium deoxycholate, a naturally occurring bile salt. The surfoplexes were characterized for extent and site of complexation, stability, mass and partition coefficient. The lipophilicity of insulin was enhanced 5-fold upon complexation resulting in an increase in entrapment efficiency by 10-50% for all formulations compared to free insulin. The release of insulin from the systems was also modulated with reduction in burst release by 30%. The surfoplex was found to be therapeutically active for 8h duration (C(max) serum insulin=64.15+/-13.28 mIU/mL) in diabetic rat model. However, pharmacological efficacy of the complex-loaded nanoparticles (Nps) did not show significant enhancement with respect to insulin-loaded systems. The study therefore suggests that while ion-pair complexes may improve the in vitro kinetics of protein-loaded carriers, their therapeutic potential is dependent on the intensity of interactions between the peptide chains and polymer matrix.

Stable colloidal dispersions of a lipase-perfluoropolyether complex in liquid and supercritical carbon dioxide

The technique of hydrophobic ion pairing was used to solubilize the lipase from Candida rugosa in a fluorinated solvent, perfluoromethylcyclohexane (PFMC), in complex with a perfluoropolyether (PFPE) surfactant, KDP 4606. The enzyme-surfactant complex was determined to have a hydrodynamic diameter of 6.5 nm at atmospheric pressure by dynamic light scattering (DLS), indicating that a single lipase molecule is stabilized by surrounding surfactant molecules. The complex formed a highly stable colloidal dispersion in both liquid and supercritical carbon dioxide at high CO2 densities (>0.92 and 0.847 g/mL, respectively), with 4% by volume PFMC as a cosolvent, yielding a fluid that was orange, optically translucent, and very nearly transparent. DLS demonstrated aggregation of the enzyme-surfactant complexes in CO2 at 25 and 40 degrees C and various pressures (2000-5000 psia) with hydrodynamic diameters ranging from 50 to 200 nm. The mechanism by which the enzyme-surfactant particles aggregate was shown to be via condensation due to very low polydispersities as characterized by the size distribution moments. Interparticle interactions were investigated with respect to density and temperature, and it was shown that on decreasing the CO2 density, the particle size increased, and the stability against settling decreased. Particle size also decreased as the temperature was increased to 40 degrees C, at constant CO2 density. Nanoparticle aggregates of an enzyme-surfactant complex in CO2, which are nearly optically transparent and stable to settling, are a promising new alternative to previous types of dispersions of proteins in CO2 that either required water/CO2 microemulsions or were composed of large particles unstable to settling.

Effect of PEG modification on subtilisin Carlsberg activity, enantioselectivity, and structural dynamics in 1,4-dioxane

The employment of enzymes as catalysts within organic media has traditionally been hampered by the reduced enzymatic activities when compared to catalysis in aqueous solution. Although several complementary hypotheses have provided mechanistic insights into the causes of diminished activity, further development of biocatalysts would greatly benefit from effective chemical strategies (e.g., PEGylation) to ameliorate this event. Herein we explore the effects of altering the solvent composition from aqueous buffer to 1,4-dioxane on structural, dynamical, and catalytic properties of the model enzyme subtilisin Carlsberg (SBc). Furthermore, we also investigate the effects of dissolving the enzyme in 1,4-dioxane through chemical modification with poly(ethylene)-glycol (PEG, M(W) = 20 kDa) on these enzyme properties. In 1,4-dioxane a 10(4)-fold decrease in the enzyme's catalytic activity was observed for the hydrolysis reaction of vinyl butyrate with D(2)O and a 50% decrease in enzyme structural dynamics as evidenced by reduced amide H/D exchange kinetics occurred. Attaching increasing amounts of PEG to the enzyme reversed some of the activity loss. Evaluation of the structural dynamic behavior of the PEGylated enzyme within the organic solvent revealed an increase in structural dynamics at increased PEGylation. Correlation analysis between the catalytic and structural dynamic parameters revealed that the enzyme's catalytic activity and enantioselectivity depended on the changes in protein structural dynamics within 1,4-dioxane. These results demonstrate the importance of protein structural dynamics towards regulating the catalytic behavior of enzymes within organic media.

Characterization of physiochemical and biological properties of an insulin/lauryl sulfate complex formed by hydrophobic ion pairing

An insulin/lauryl sulfate complex was prepared by hydrophobic ion pairing (HIP). The physiochemical and biological properties of the HIP complex were characterized using octanol/water partition measurement, isothermal titration calorimetry (ITC), ultraviolet-circular dichroism (UV-CD) and Fourier transform infrared spectroscopy (FTIR). Sodium dodecyl sulfate (SDS) bound to the insulin in a stoichiometric manner. The formed complex exhibited lipophilicity, and its insulin retained its native structure integrity. The in vivo bioactivity of the complex insulin was evaluated in rats by monitoring the plasma glucose level after intravenous (i.v.) injection, and the glucose level was compared with that for free insulin. The pharmacodynamic study result in rats showed that the complex insulin had in vivo bioactivity comparable to free insulin.

On the relationship between the activity and structure of PEG-alpha-chymotrypsin conjugates in organic solvents

Enzymes are attractive catalysts for the production of optically active compounds in organic solvents. However, their often low catalytic activity in such applications hampers their practical use. To overcome this, we investigated the effectiveness of the covalent modification of alpha-chymotrypsin with methoxy poly(ethylene glycol) (PEG) with a Mw of 5,000 to enhance its activity. The model transesterification reaction between sec-phenethyl alcohol and vinyl butyrate in various neat dry organic solvents and at a controlled water activity of 0.008 in two solvents was employed to measure the effect of PEGylation on activity and enantioselectivity. Synthesis conditions were varied to obtain various conjugates with average molar ratios of PEG-to-chymotrypsin ranging from ca. 1 to 7. While the enantioselectivity increased only modestly from ca. 4.4 to 6.1 when averaging results in all solvents, PEG was very efficient in increasing the activity of alpha-chymotrypsin up to more than 400-fold compared to that of the powder lyophilized from buffer alone. The activity increase was more pronounced in apolar than in polar organic solvents and also depended on the amount of PEG bound to the enzyme. For example, the activity of the modified enzyme towards the most reactive "S" enantiomer in octane increased 440-fold but increasing the molar ratio of PEG-to-enzyme from 1.1 to 7.1 resulted in a more than twofold decrease in enzyme activity. Controlling the water activity did not prevent the drop in activity. To investigate the possible origin of the activity changes, Fourier transform infrared (FTIR) spectroscopy experiments were conducted. It was found that PEGylation reduced lyophilization-induced structural perturbations, but exposure to the organic solvents caused structural perturbations. These perturbations were more pronounced in polar than in apolar solvents. The pronounced activity drop in polar solvents at increasing PEG-modification levels correlated with an increasing level of solvent-induced structural perturbations. This correlation was less pronounced in apolar solvents where both, activity drop and structural perturbations, were less pronounced at increasing PEGylation levels. In summary, PEG-modified alpha-chymotrypsin might be an interesting system to catalyze reactions, particularly in apolar organic solvents.

Raman and surface-enhanced Raman spectroscopy investigation of vasopressin analogues containing 1-aminocyclohexane-1-carboxylic acid residue

In this work, Raman spectroscopy (RS) was employed to characterize molecular structures of [Arg8]vasopressin (AVP) and its [Acc2,D-Arg8]AVP, [Acc3]AVP, and [Cpa1, Acc3]AVP analogues. The RS band assignments have been proposed. To determine the mechanism of adsorption of the above-mentioned compounds adsorbed on a colloidal silver surface, surface-enhanced Raman spectra (SERS) were measured. The SERS spectra were used to determine relative proximity of the adsorbed functional groups of [corrected] investigated peptides and their orientation on the silver surface. The AVP and [Acc3]AVP SERS spectra (Acc: 1-aminocyclohexane-1-carboxylic acid) show that the L-tyrosine (Tyr) lies far from the metal surface, whereas the [Cpa1,Acc3]AVP spectrum (Cpa: 1-mercaptocyclohexaneacetic acid) provides evidence that Tyr interacts with the silver surface. These results suggest that [corrected] the binding of the Tyr-ionized phenolic group might be responsible for the selectivity of the analogues. We show that the aromatic ring of L-phenylalanine (Phe) of AVP and [Acc2,D-Arg8]AVP interacts with the silver surface. The strength of this interaction is considerably weaker for [Acc2,D-Arg8]AVP than for AVP. This might be due either to a longer distance between the Phe ring and the silver surface, or to the almost perpendicular orientation of the Phe ring towards the surface. The carbonyl group of the L-glutamine [corrected] (Gln) or L-asparagine [corrected](Asn) of AVP, [Acc2,D-Arg8]AVP, and [Acc3]AVP is strongly bound to the silver surface. We have also found that all peptides adsorb on the silver surface via sulfur atoms of the disulfide bridge, adopting a "GGG" conformation, except [Cpa1,Acc3]AVP, which accepts a "TGG" geometry.

Preparation and catalytic performance of surfactant-manganese peroxidase-Mn(II) ternary complex in organic media

A novel preparation method for surfactant-MnP-Mn(II) ternary complex utilizing water-in-oil emulsions has been developed. The surfactant-MnP complex was spectroscopically characterized, strongly suggesting that the heme environment of the surfactant-MnP complex in benzene is identical to that of native MnP in the aqueous buffer. o-Phenylenediamine oxidation catalyzed by the surfactant-MnP-Mn(II) ternary complex was performed in benzene. The ternary complex efficiently catalyzed the oxidation, and the complex was catalytically stable. Kinetic experiments revealed that the reaction mechanism was as follows: MnP is oxidized by H(2)O(2) and the oxidized intermediate catalyzes the oxidation of Mn(II) to Mn(III) and the latter, after complexed with malonate, readily oxidizes o-PDA inside the complex. Thus, the organic substrate o-PDA, but not Mn(III), shuttled between the surfactant-MnP-Mn(II) ternary complex and organic solvent.

Protein-fatty acid complex for enhanced loading and stability within biodegradable nanoparticles

Lysozyme was hydrophobically modified with a fatty acid, sodium oleate, via an ion-pairing mechanism. Ionic binding between an anionic carboxylic group of sodium oleate and basic amino groups in lysozyme was primarily utilized to form lysozyme-oleate complex. The complex formation was pH dependent. The lysozyme-oleate complex dissolved in an organic solvent exhibited much higher conformational stability at elevated temperature compared with free lysozyme in the same solvent. The complex was formulated into biodegradable nanoparticles by a spontaneous emulsion and solvent diffusion method. The resultant formulation showed near 100% encapsulation efficiency of lysozyme within nanoparticles with < 100 nm in diameter with a narrow size distribution. Lysozyme could be loaded into the nanoparticles up to 18.6% (w/w) with concomitantly increased particle sizes. This study demonstrates a new formulation method of biodegradable nanoparticles with highly efficient encapsulation of proteins, which are potentially useful for oral protein delivery including mucosal vaccination.

Bioencapsulation within synthetic polymers (Part 2): non-sol-gel protein-polymer biocomposites

Since the introduction of sol-gel bioencapsulation and the demonstration that biological function can be incorporated into, and preserved within, polymer matrices, a number of alternative polymers have been used to immobilize proteins. Various enzymes have been trapped in such diverse polymers as epoxy-amine resins, polyvinyl plastics, polyurethane foams and silicone elastomers. Together with sol-gel encapsulates, these biocomposites represent a powerful approach for immobilizing biological materials for applications as biosensors and biocatalysts, and hold promise as bioactive, fouling-resistant polymers for environmental, food and medical uses. Although still at the developmental stage, these biocomposites promise to revolutionize the whole arena of high-performance bioimmobilization.

Hydrophobic ion pair formation between leuprolide and sodium oleate for sustained release from biodegradable polymeric microspheres

Leuprolide acetate, an analogue of luteinizing hormone-releasing hormone (LH-RH), was hydrophobically ion paired with a long chain fatty acid, sodium oleate, in an aqueous solution. Solution behaviors of the complex formed between leuprolide and sodium oleate were investigated in terms of aqueous solubility, turbidity, particle size, and zeta potential as a function of molar ratio between the two species. It was found that with increasing the stoichiometric molar amounts of sodium oleate to leuprolide approached up to 2.5-3, the solution became gradually turbid with increasing particle sizes, indicating leuprolide precipitation as a result of hydrophobic ion pairing. On the other hand, beyond that critical molar ratio range, the solution turned into clear with much reduced particle size, indicative of micelle formation. The hydrophobically modified leuprolide-oleate complex was lyophilized and directly encapsulated within biodegradable poly(D, L-lactic-co-glycolic acid) (PLGA) microspheres via a single oil-in-water (O/W) emulsion method. Microsphere morphology, leuprolide release behavior, and polymer mass erosion profiles were examined in comparison to the PLGA microspheres prepared with free leuprolide.

Catalytic activity and conformation of chemically modified subtilisin Carlsberg in organic media

Subtilisin Carlsberg, an alkaline protease from Bacillus licheniformis, was modified with polyoxyethylene (PEG) or aerosol-OT (AOT), and the solubility, conformation, and catalytic activity of the modified subtilisins in some organic media were compared under the same conditions. The solubility of modified subtilisins depended on the solubility of the modifier. On the other hand, the conformational changes depended on the solubility, rather than the property, of the modifier. When the modified subtilisin was dissolved in water-miscible polar solvents such as dimethylsulfoxide, acetonitrile, and tetrahydrofuran, significant conformational changes occurred. When modified subtilisin was dissolved in water-immiscible organic solvents, such as isooctane and benzene, the solvent did not induce significant conformational changes. The catalytic activity in the transesterification reaction of the N-acetyl-L-phenylalanine ethylester of the modified subtilisin in organic solvents was higher than that of native subtilisin. The high activity of modified subtilisin was thought to be due to a homogeneous reaction by the dissolved enzymes.

Effects of additives on the stability of Humicola lanuginosa lipase during freeze-drying and storage in the dried solid

The effects of various classes of additives on the stability of a protein with a relatively hydrophobic surface, Humicola lanuginosa lipase (HLL), during lyophilization and storage in the dried solid, were investigated. Prior to lyophilization, it was found that 1 M trehalose or 1% (wt/vol) Tween 20 caused the protein to precipitate. Infrared spectroscopy indicated that trehalose "salted-out" native HLL, whereas Tween 20 induced non-native aggregates. Optimal recovery of native protein in the initial dried solid was obtained in the presence of additives which formed an amorphous phase and which had the capacity to hydrogen bond to the dried protein (e.g., trehalose and sucrose). Additives which crystallized during lyophilization (e.g., mannitol) or which remained amorphous, but were unable to hydrogen bond to the dried protein (e.g., dextran), afforded less stabilization relative to that seen in the absence of additives. Optimal storage stability in the dried solid required that both protein unfolding during lyophilization was minimized and that the formulation was stored at a temperature below its Tg value. Crystallization of sucrose during storage greatly reduced the storage stability of HLL. This was attributed to the increased moisture content and the reduced Tg value in the remaining amorphous phase containing the protein. Sucrose crystallization and the resulting damage to the protein were inhibited by decreasing the mass ratio of sucrose:protein.