Dane O. Kildsig

Pulmonary Delivery of Free and Liposomal Insulin

The effects of oligomerization and liposomal entrapment on pulmonary insulin absorption were investigated in rats using an intratracheal instillation method. The results indicated that both dimeric and hexameric insulins can be rapidly absorbed into the systemic circulation, producing a significant hypoglycemic response. Intratracheal instillation of insulin in two different oligomerized states has not resulted in any significant difference in the duration of hypoglycemic effect. However, the initial hypoglycemic response (first 10 min) obtained from intratracheal administration of 25 IU/kg hexameric insulin appears to be slower than that from the 25 IU/kg dimeric insulin, thereby suggesting that hexameric insulin may have a lower permeability coefficient across alveolar epithelium than the dimeric insulin. Intratracheal administration of insulin liposomes (dipalmitoylphosphatidyl choline:cholesterol, 7:2) led to facilitated pulmonary uptake of insulin and enhanced the hypoglycemic effect. Nevertheless, similar insulin uptake and pharmacodynamic response were obtained from both the physical mixture of insulin and blank liposomes and liposomally entrapped insulin.

Hydrotropic solubilization--mechanistic studies.

AbstractPurpose. This study examines the mechanism of hydrotropic solubilization using the riboflavin-nicotinamide system. The most commonly proposed mechanism for hydrotropic solubilization is complexation, and therefore, is investigated. Additionally, since nicotinamide and several other hydrotropic agents self-associate in aqueous solution, the possibility that self-association of the hydrotropic agent is important mechanistically is examined by studying the effect of temperature on hydrotropic ability. Researchers have shown that the degree of self-association decreases with increasing temperature. Therefore, if temperature affects the solubilizing capacity of nicotinamide, self-association must be mechanistically significant. Methods. The complexation hypothesis is tested by looking at nicotinamides ability to quench riboflavin fluorescence and by examining changes in the UV/Vis spectrum of riboflavin upon addition of nicotinamide. The solubility of riboflavin in nicotinamide solutions as a function of temperature is determined to assess the impact of self-association on hydrotropicity. Results. Nicotinamide does not alter the intrinsic fluorescence of riboflavin nor are changes indicative of complexation observed in the UV/Vis spectrum. Temperature does have an effect on the hydrotropic ability of nicotinamide. Specifically, as temperature increases, the solubilizing capacity of nicotinamide decreases. Conclusions. Because nicotinamide is unable to quench riboflavin fluorescence, and does not produce significant spectral changes, complexation of nicotinamide and riboflavin does not occur. However, since increasing temperature causes a decrease in the hydrotropic ability of nicotinamide and in its degree of self-association, it is proposed here that the self-association of nicotinamide impacts the hydrotropic mechanism.

Beta-Cyclodextrin/Steroid Complexation: Effect of Steroid Structure on Association Equilibria

Molecular associations of beta-cyclodextrin (beta-CyD) with four steroids (cortisone, hydrocortisone, progesterone, and testosterone) have been studied using phase-solubility and spectroscopic techniques. Phase solubility diagrams could be categorized as B type. The complexes are formed at the stoichiometric ratios of 1:2 (drug:beta-CyD). A mathematical model has been proposed to calculate the apparent stability constants. The results suggest that the inclusion of a steroid molecule into the first beta-CyD cavity is thermodynamically more favorable over the association of 1:1 complex with the second beta-CyD molecule except for cortisone, which exhibits anomalous behavior. A mechanism of complexation has been proposed based on the apparent stability constants and chemical structures of the steroids and beta-CyD. It suggests that complexation is first brought about by inclusion of the five-member cyclopentane ring of the steroid molecule into the first beta-CyD cavity. The 1:1 complex subsequently binds with the second beta-CyD to form the 1:2 complex. The association constants of steroid/beta-CyD complexes are of the following order: progesterone > cortisone > testosterone > hydrocortisone. The order of aqueous solubilities of the complexes is hydrocortisone > cortisone > testosterone > progesterone.

Computer simulation of molecular diffusion in amorphous polymers

Abstract Diffusion of small molecules in amorphous polymers has been examined by computer simulation. Diffusion coefficients of small molecules with molecular weights ranging from 16.04 (methane) to 452.50 (fluocinolone acetonide) Da in four amorphous polymers were calculated using the QUANTA, CHARMM and Cerius 2 programs. The four amorphous polymers used in our calculation were polyethylene (PE), poly(dimethyl siloxane) (PDMS), poly(methyl methacrylate-co-hydroxyethyl methacrylate) (P(MMA-co-HEMA)), and ethyl and benzyl esters of hyaluronic acid (HA-E, HA-B). The calculated diffusion coefficients ( D c ) were compared with the experimentally obtained values ( D e ) found in the literature. The ratio of D c / D e varied from 0.04 to 24 000. In general, the close values of D c to D e were obtained when the system dealt with hydrophobic molecules diffusing through hydrophobic polymers. The D c / D e ratio became either very high or very low when the experimental system included hydrophilic diffusants and/or a hydrophilic polymer. The simulation time and the size of molecular models also played key roles in determining the consistency of calculations and the correlation with experimental values. Our study suggests that the current computer simulation of molecular diffusion may be useful in obtaining relative values rather than absolute diffusion coefficient values.

Pulmonary biotransformation of insulin in rat and rabbit

In vitro biodegradation of insulin in rabbit and rat lung homogenates was investigated. Insulin can be sequentially metabolized into two primary fragments in rabbit lung homogenate by an aminopeptidase. The amino acid sequences of the fragments were found to be the des-Phe-InsulinB1 (Metabolite I) and des-Phe-Val-InsulinB1-2 (Metabolite II). However, only the former metabolite (Metabolite I) was identified in the rat lung homogenate. The km and Vm values associated with rabbit lung homogenate were 0.29 +/- 0.14 mM and 16.4 +/- 6.9 microM/hr/mg protein, respectively, whereas those for a rabbit lung preparation containing both microsomes and cytosol were 0.22 +/- 0.07 mM and 17.9 +/- 5.4 microM/hr/mg protein, respectively. The km and Vm associated with the cytosolic fraction of rabbit lung were 0.32 +/- 0.16 and 20.6 +/- 6.1 microM/hr/mg protein, respectively. The results indicate that the lung aminopeptidase may be a cytosolic enzyme. The degradation of dimeric insulin in the lung homogenate was faster than that of hexameric insulin due to the difference in collision frequency between the enzyme and insulin aggregates. The major metabolites in the lungs reportedly retain almost the same bioactivity of insulin, suggesting that the pulmonary route of insulin delivery will not adversely affect its hypoglycemic activity.

An examination of the moisture sorption characteristics of commercial magnesium stearate

The objective of this study was to characterize the moisture sorption of magnesium stearate and the morphological changes, if any, resulting from moisture sorption. Six samples of commercial magnesium stearate USP were examined. Moisture sorption isotherms were obtained at 25°C and 5% to 98% relative humidity (RH) using a moisture balance. Changes in crystal form resulting from moisture sorption were determined by x-ray diffraction. There were differences in the shape of the isotherm, reversibility of moisture uptake, and shape of the hysteresis loop in the isotherms of crystalline and amorphous magnesium stearates. The isotherm of crystalline magnesium stearate was almost parallel to the pressure axis until and RH of ∼80%. The isotherm of the amorphous sample was characterized by continuous uptake of water over the entire range of RH. Exposure of amorphous magnesium stearate to RH greater than 70% resulted in the formation of the trihydrate. The trihydrate was converted into the anhydrous form when heated to a temperature of 100°C to 105°C. The trihydrate could be generated by exposing the anhydrate to RH higher than 70%.

Insulin Aggregation in Aqueous Media and Its Effect on Alpha-Chymotrypsin-Mediated Proteolytic Degradation

Self-association of zinc–insulin monomers into dimers and hexamers may lead to enhanced protection of the peptide from proteolytic degradation. The present study has been undertaken to investigate the relationship, if any, between the rate of enzymatic degradation of insulin by a protease, alpha-chymotrypsin, and the extent of insulin aggregation in aqueous solutions. Insulin solutions (0.6 mg/ml) containing varying proportions of dimer and hexamer were obtained by adding ethylene diamine tetraacetic acid (EDTA) within a concentration range of 0.005 to 0.040 mM. As the EDTA concentration was increased above 0.040 mM, a complete dissociation of hexamers to dimers occurred and the rate of enzymatic degradation reached its maximum. The overall first-order rate constants appeared to be linearly related to the square of EDTA concentrations. The apparent first-order rate constants for dimer and hexamer degradation obtained from a linear plot of rate constant versus EDTA squared concentration were found to be 0.02800 ± 0.00065 and 0.00798 ± 0.00075 min−1, respectively. Two major insulin degradation products were also detected and the kinetics of product appearance agreed well with the disappearance kinetics of insulin. The results indicated that the degradation of insulin dimers by alpha-chymotrypsin is about 3.5 times faster than the degradation of the hexamer. The second-order dependency of degradation rate on EDTA concentration might be due to the fact that insulin hexamers contain two zinc ions which are sequestered by two EDTA molecules. Chelation of zinc ions by EDTA lead to hexamer deaggregation to dimers as was evidenced from a circular dichroism study. Formation of three dimer species from one hexamer aggregate should theoretically enhance the rate of degradation threefold, a value consistent with the experimentally determined ratio of 3.5.

The Effect of Particle Morphology on the Physical Stability of Pharmaceutical Powder Mixtures: The Effect of Surface Roughness of the Carrier on the Stability of Ordered Mixtures

The effect of particle morphology of the components on the physical stability of ordered mixtures was determined for a model system comprised of a mixture of micronized aspirin and a monodisperse carrier. Spray-dried lactose, crystallized lactose, microcrystalline cellulose, and dextrate were used as carriers. The surface texture of the carriers was quantified in terms of the ratio of the perimeter of the particles to that of an idealized shape at a constant magnification. Mixtures containing highly textured carriers segregated to a lesser extent than those containing smoother textured carriers. This was postulated to be due to the presence of a higher concentration of surface asperities on the coarse carriers that can constitute potentially strong adhesion sites for the fine component because of their higher energy relative to adjacent areas on the surface. The effect of the addition of a ternary component, magnesium stearate, on the stability of the above mixtures was studied. The observed differences in the segregation response were attributed to electrostatic charge effects.

Complexation of 6-ACYL-O-β-Cyclodextrin derivatives with steroids - effects of chain length and substitution degree

AbstractThis study was designed to test a hypothesis that the esterification of the primary 6-hydroxyl groups on β-cyclodextrin (β-CD) may disrupt its crystallinity, thereby enhancing its aqueous solubility and increasing its ability to solubilize water-insoluble compounds. 6-acyl-o-β-CD derivatives with different chain length and substitution degree were synthesized by esterifying the primary hydroxyl groups at 6-position of β-CD with various acyl chlorides. X-ray diffraction patterns confirmed the existence of 6-acyl-o-β-CD derivatives as amorphous solid. Effects of chain length and substitution degree of the acyl groups on 6-acyl-o-β-CD/steroid complexation and solubilization were investigated with the phase solubility method. The results indicated that the solubilities of 6-acyl-o-β-CD derivatives were significantly higher than that of β-CD itself, which resulted in an increase in their ability to solubilize poorly water-soluble drugs such as steroids. The addition of side chains to β-CD did not chang...

Aspartame-Direct Compression Excipients: Preformulation Stability Screening Using Differential Scanning Calorimetry

AbstractDifferential scanning calorimetry was used as a screening technique for assessing the compatibility of Aspartame with some of the currently available direct compression excipients. AsDartame was found to be compatible with Avicel PH 101, Avicel PH 105, Elcema F 150, Elcema G 250, Sta-Rx 1500, Cab-O-Sil, Sorbitol, Di-Pac and Brownex Sugar, while incompatible with dicalcium phosphate dihydrate. It appears that stearic acid can be used as a lubricant in formulations containing Aspartame while magnesium stearate cannot.