Diane O. Thompson

The effect of a modified β-cyclodextrin, SBE4-β-CD, on the aqueous stability and ocular absorption of pilocarpine

In the present study, the effects of a novel, modified beta-cyclodextrin derivative (SBE4-beta-CD; a variably substituted sulfobutyl ether of beta-cyclodextrin with an average degree of substitution of four) on the aqueous stability of pilocarpine and on its ocular absorption in albino rabbits were studied. For stability reasons, commercial pilocarpine eyedrops are formulated at pH 4-5, a pH range where pilocarpine (pKa approximately 7) is almost completely ionized. As shown in the present and past studies, increasing the pH of the pilocarpine solution from 4.5 to 7.0 increases the ocular absorption of pilocarpine. SBE4-beta-CD increased the aqueous stability of pilocarpine (0.36 mM) at pH 7.0 (4 degrees C, projected values from Arrhenius data at 25 degrees C, 37 degrees C and 50 degrees C); in the absence of SBE4-beta CD, t90% was 236 days. In the presence of 1 mM and 25 mM of SBE4-beta-CD, t90% was 382 days and 2054 days, respectively suggesting that indeed, pilocarpine does interact with SBE4-beta-CD. SBE4-beta-CD did not damage the corneal epithelium in vitro and was well-tolerated by the rabbit eye in vivo. Coadministered SBE4-beta-CD did not significantly affect the miotic response of pilocarpine solutions at pH values of 4.5 or 7.0 when the molar ratio of SBE4-beta-CD to pilocarpine was between 0.2:1-7:1. The effect of the coadministered SBE4-beta-CD on the miotic response of pilocarpine solutions was also compared to that of 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) which has recently been suggested to increase ocular bioavailability of pilocarpine in rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential Effects of Sulfate and Sulfobutyl Ether of β-Cyclodextrin on Erythrocyte Membranes in Vitro

The hemolytic activity of β-cyclodextrin (β-CyD) on rabbit erythrocytes was reduced by the introduction of negatively-charged groups onto the hydroxyls of β-CyD; the membrane disrupting abilities decreased in the order of β-CyD > 2-hydroxypropyl-β-CyD (HP-β-CyD) > sulfobutyl-β-CyD (SB-β-CyD) >> β-CyD sulfate (S-β-CyD). Under pre-hemolytic concentrations, both β-CyD and SB-β-CyD induced shape changes of membrane invagination on the erythrocytes. In sharp contrast, S-β-CyD showed biphasic effect on the shape of the erythrocytes; i.e. the crenation at relatively low concentrations and the invagination at higher concentrations. The S-β-CyD-induced membrane crenation arose from a direct action on the membranes rather than cell metabolism-mediated effects. Unlike β-CyD, S-β-CyD was found to bind to the erythrocytes and may be confined to the outer surface of the membrane bilayer, which may expand the exterior layer relative to the cytoplasmic half, thereby inducing the cells to crenate. On the other hand, the membrane invagination mediated by the three β- CyDs was initiated by extracting specific membrane lipids from the cells, depending upon their inclusion abilities, subsequently leading to the lysis of the cells. These results indicate that SB-β-CyD and S-β-CyD interact with the erythrocyte membranes in a differential manner and possess lower membrane disrupting abilities than the parent β-CyD and HP-β-CyD.

Fractionation and characterization of 4-sulfobutyl ether derivatives of cyclomaltoheptaose (β-cyclodextrin)

Abstract 4-Sulfobutyl ether derivatives of cyclomaltoheptaose (β-cyclodextrin) (SBE-β-CD) are being developed as parenterally safe solubilizing and stabilizing agents. SBE-β-CDs are a mixture of positional and regional isomers containing from one to as many as twelve sulfobutyl ether (SBE) groups per cyclodextrin. Capillary electrophoretic (CE) analysis of these mixtures resolves these isomers based on the molar degree of SBE substitution (ds), and the electropherogram shows an almost symmetrical distribution of SBE incorporation centered around the band which represents the apparent average degree of substitution for the mixture. The objectives of this study were to isolate the different substitution bands for their characterization and to evaluate their mass contribution to the mixture. Mixtures of SBE-β-CDs containing from mono- up to deca-SBE substitutions were fractionated by preparative anion-exchange chromatography with salt concentration gradient elution. The bands for each ds were well resolved as characterized by CE analysis with indirect UV detection. The isolated materials were desalted and lyophilized to obtain white solids, which were then characterized by nuclear magnetic resonance ( 1 H NMR) spectroscopy, capillary electrophoresis (CE), and fast-atom-bombardment mass spectrometry (FABMS). The CE molar response factor of each ds was then determined, and the actual percent mass composition of a SBE-β-CD mixture was calculated. 4-Sulfobutyl ether derivatives of cyclomaltoheptaose (β-cyclodextrin) of ds 1–10 were prepared, separated by anion-exchange chromatography, analyzed by capillary electrophoresis, and characterized by 1 H NMR spectroscopy and FAB mass spectrometry.

Isolation and characterization by NMR spectroscopy of three monosubstituted 4-sulfobutyl ether derivatives of cyclomaltoheptaose (β-cyclodextrin)

Abstract The substitution profile of 4-sulfobutyl ether derivatives of cyclomaltoheptaose (β-cyclodextrin) (SBE-β-CD) prepared in our laboratories has been previously described. However, in those studies, no attempt was made to characterize the positional or regional isomers of this material. SBE-β-CD derivatives with degrees of substitution of two or higher represent a large number of possible isomers dependent on this positional and regional substitution. The monosubstituted SBE derivative, however, cannot have regional isomers and, therefore, has only three possible substitution products related to the 2-, 3-, and 6-hydroxyl groups of a glucose unit. In this study the isomers were fractionated by preparative anion-exchange chromatography with the progress of the elution being followed by a capillary electrophoretic (CE) method that resolved these isomers. The eluent containing the isomers was processed, and the pure materials were characterized by nuclear magnetic resonance spectroscopy ( 1 H NMR, DEPT, HETCOR, HOHAHA). Through this analysis the assignment of the positional isomers was made. Three isomeric monosubstituted 4-sulfobutyl ether derivatives of cyclomaltoheptaose (β-cyclodextrin) were separated by anion-exchange chromatography and characterized by 2D NMR spectroscopy.