The structure, stability, and complex behavior of recombinant human gelatins

Gelatin prepared from animal sources is widely used as a stabilizer in vaccine formulations. The disadvantages associated with their use such as heterogeneity and allerginicity, have led to the development of recombinant human gelatins (rhGs) as a substitute. This study focuses on characterizing the structure and monitoring the physical stability of four molecular weights ( approximately 8.5, 25, 50, and 100 kDa) of rhGs as a function of temperature and pH. The information supplied should be useful in predicting the behavior of rhGs under formulation conditions. A number of spectroscopic techniques were employed in this study. Experimental results indicated that the solution properties of all four rhGs were unpredictable with micro-aggregation observed at various pH values. The 8.5 kDa rhG was found to be in a micro-aggregated state at pH 5 while the 25 kDa rhG was found to be more aggregated at pHs 5, 7, and 8. The properties of these aggregates have been analyzed as a function of temperature. The rhGs were also found to complex with the polyanion heparin through electrostatic and nonelectrostatic interactions. The stability of these complexes has been studied as a function of temperature and pH.

Stabilization of proteins by recombinant human gelatins

Porcine gelatins have been widely used as stabilizers of macromolecular based pharmaceuticals but the mechanism by which they stabilize has not been precisely established. Their variability and immunogenicity, however, make them less than ideal excipients. In this work, we take advantage of the availability of recombinant human gelatins (rhGs) to explore the mechanism by which they may stabilize proteins. Three model recombinant proteins, human serum albumin (HSA), bovine granulocyte colony stimulating factor (bGCSF), and human fibroblast growth factor-20 (FGF-20) that display a range of isoionic points have been selected for this study. The interaction of these model proteins with four different molecular weight rhGs and porcine gelatin was studied using a variety of biophysical techniques including fluorescence, CD and second derivative UV spectroscopy to monitor tertiary and secondary structure as a function of temperature. The 8.5, 25, and 100 kDa rhGs had the greatest effect on conformational and colloidal stability of HSA. The 8.5, 25, and 50 kDa rhGs also increased the T(0) of aggregation of bGCSF and FGF-20. Experiments to probe the mechanism of interaction of model proteins with rhGs suggest that the rhGs might interact with the partially unfolded states of target proteins through a combination of electrostatic and other intermolecular mechanisms to inhibit aggregation.

Probing protein structure and dynamics by second-derivative ultraviolet absorption analysis of cation-{pi} interactions

We describe an alternate approach for studying protein structure using the detection of ultraviolet (UV) absorbance peak shifts of aromatic amino acid side chains induced by the presence of salts. The method is based on the hypothesis that salt cations (Li+, Na+, and Cs+) of varying sizes can differentially diffuse through protein matrices and interact with benzyl, phenyl, and indole groups through cation-pi interactions. We have investigated the potential of this method to probe protein dynamics by measuring high resolution second-derivative UV spectra as a function of salt concentration for eight proteins of varying physical and chemical properties and the N-acetylated C-ethyl esterified amino acids to represent totally exposed side chains. We show that small shifts in the wavelength maxima for Phe, Tyr, and Trp in the presence of high salt concentrations can be reliably measured and that the magnitude and direction of the peak shifts are influenced by several factors, including protein size, charge, and the local environment and solvent accessibility of the aromatic groups. Evaluating the empirical UV spectral data in light of known protein structural information shows that probing cation-pi interactions in proteins reveals unique information about the influence of structure on aromatic side chain spectroscopic behavior.

Formulation and accelerated stability studies for an extemporaneous suspension of amiodarone hydrochloride

Amiodarone is commercially available as both a tablet and an injectable formulation. It is widely dispensed as an extemporaneously compounded suspension for pediatric and geriatric patients. Extensive stability data at numerous temperatures and a calculated shelf life based on kinetics for such a formulation have not been reported. Refrigeration and room temperature data for finite times have been reported in the literature. In this study, a stable extemporaneous formulation of amiodarone hydrochloride was formulated using Paceron tablets. The formulation consisted of 0.75% carboxymethylcellulose and 0.75% Veegum as suspending agents; 25% sucrose, provided as simple syrup; and aqueous strawberry concentrate as flavor. A total of 2.5L of the formulation was compounded and stored in quanitites of 150 mL in 8-oz glass containers. The initial drug content was determined by reverse-phase high-performance liquid chromatography, with a method that was developed in our laboratory. The stability study was carried out by storing three containers at five different temperatures, namely 4, 30, 40, 50, and 60 deg C. The suspension was analyzed at the end of 2, 6, 12, 24, and 48 hours at 7 days, and, therafter, at the end of every week for 13 weeks. The percentage of drug remaining was plotted against time for each temperature. The slope of the regression line was obtained for each temperature and the zero-order degradation rate constant obtained. The logarithm of the zero-order degradation rate constants was plotted against the inverse of the temperature in degrees Kelvin to obtain the Arrhenius plot. From the regression line for the Arrhenius plot, the zero-order degradation constant at 25 deg C was calculated to be 0.0517 day -1. The shelf life for the formulation at 25 deg C was calculated to be 193.4 days; the shelf life under refrigeration (4 deg C) was found to be 677.3 days. The degradation products were characterized using high-performance liquid chromatographic-mass spectrometry. Data obtained from the analysis suggested that amiodarone cleaved at its ketone and ether linkages to yield corresponding degradation products.