Differential permeation of propranolol enantiomers across human skin in vitro from formulations containing an enantioselective excipient

Development of a reversed-phase high-performance liquid chromatographic method for the determination of propranolol in different skin layers

The aim of this work was to develop and validate an analytical method using HPLC for the determination of propranolol in the different layers of the skin to be used in kinetic studies of skin permeation. The development of the method was based on the suitability of the chromatogram, and the validation followed the international health regulation for bioanalytical methods. In addition, the method was tested in an in vitro permeation assay using porcine skin. The drug was determined using an RP-C18 column at 30°C, a mobile phase comprising acidic aqueous phase:acetonitrile (75:25 v/v), at a flow rate of 1.0 mL min^-1 , and UV detection at 290 nm. The method was demonstrated to be selective against skin contaminants, linear in a wide range of concentrations (3-20 μg mL^-1 ), sensitive enough to quantify less than 0.1% of the drug dosage in skin matrices, and precise regardless of analysis variations such as day of analysis, analyst, or equipment. In addition, the method presented a high drug extraction capacity greater than 90% for all skin layers (stratum corneum, hair follicle, and remaining skin). Finally, the method was successfully tested in skin permeation assays, proving its value in the development of topical formulations containing propranolol.

An electrochemical study of microporous track-etched membrane permeability and the effect of surface protein layers

Microporous track-etched membranes serve as important permeable growth surfaces for cell culture where diffusive solute transport is needed across two growth compartments. This study has established effective solute diffusion coefficients for four probe micro-solutes: hydrogen peroxide, pyrocatechol, acetaminophen and ascorbic acid across three track-etched membranes formulated, respectively, from polycarbonate and polyethylene terephthalate. Chronoamperometry and cyclic voltammetry were used for the diffusion measurements. These showed substantially reduced intra-pore diffusion in relation to available pore area. Diffusion coefficients ranging from 1.43×10^-10 to 3.17×10^-7cm²s^-1 were demonstrated. This strongly suggests that water organisation in micro-pores is not equivalent to that of bulk water. Superimposed protein layers of Type I and IV collagen, Type I collagen-fibronectin, Type I collagen-heparin, and Type I collagen-chondroitin sulphate increased diffusional resistance, but with disproportional retardation of ascorbate diffusion due to charge repulsion at collagen-heparin and collagen-chondroitin sulphate combinations. Diffusive resistance at natural tendon and cartilage was considerably smaller; diffusion coefficients ranged from 8.33×10^-6 to 1.09×10^-8cm²s^-1.

Enantioselective penetration enhancing effect of carvone on the in vitro transdermal permeation of nicorandil

The objective was to investigate the difference in penetration enhancing effect of R-carvone, S-carvone and RS-carvone on the in vitro transdermal drug permeation. In vitro permeation studies were carried out across neonatal rat epidermis from 2%w/v HPMC (hydroxypropyl methylcellulose) gel containing 4%w/v of nicorandil (a model drug) and a selected concentration (12%w/v) of either R-carvone, S-carvone or RS-carvone against a control. The stratum corneum (SC) of rats was treated with vehicle (70%v/v ethanol-water) or ethanolic solutions of 12%w/v R-carvone, S-carvone or RS-carvone. The enhancement ratio (ER) of R-carvone, S-carvone and RS-carvone when compared to control was about 37.1, 31.2 and 29.9, respectively indicating enantioselective penetration enhancing effect of carvone enantiomers. Furthermore, there was a significant decrease in the lag time required to produce a steady-state flux of nicorandil with S-carvone when compared to R-carvone and RS-carvone. DSC and FT-IR studies indicate that the investigated enantiomers of carvone exhibit a difference in their ability to affect the cellular organization of SC lipids and proteins thereby showing enantioselective transdermal drug permeation. It was concluded that R-carvone exhibited a higher penetration enhancing activity on transdermal permeation of nicorandil when compared to its S-isomer or racemic mixture.

Percutaneous absorption of the montoterpene carvone: implication of stereoselective metabolism on blood levels

The purpose of this study was to determine whether an enantioselective difference in the metabolism of topically applied R-(—)- and S-(+)-carvone could be observed in man. In a previous investigation we found that R-(—)- and S-(+)-carvone are stereoselectively biotransformed by human liver microsomes to 4R,6S-(—)- and 4S,6S-(+)-carveol, respectively, and 4R,6S-(—)-carveol is further glucuronidated. We therefore investigated the metabolism and pharmacokinetics of R-(—)- and S-(+)-carvone in four healthy subjects using chiral gas chromatography as the analytical method. Following separate topical applications at a dose of 300 mg, R-(—)- and S-(+)-carvone were rapidly absorbed, resulting in significantly higher Cmax levels for S-(+)-carvone (88.0 vs 23.9 ng mL−1) and longer distribution half-lives (t2α1) (19.4 vs 7.8 min), resulting in 3.4-fold higher areas under the blood concentration-time curves (5420 vs 1611 ng min mL−1). The biotransformation products for both enantiomers in plasma were below detection limit. Analysis of control- and β-glucuronidase pretreated urine samples, however, revealed a stereoselective metabolism of R-(—)-carvone to 4R,6S-(—)-carveol and 4R,6S-(—)-carveol glucuronide. No metabolites could be found in urine samples after S-(+)-carvone application. These data indicate that stereoselectivity in phase-I and phase-II metabolism has significant effects on R-(—)- and S-(+)-carvone pharmacokinetics. This might serve to explain the increased blood levels of S-(+)-carvone.

Effects of Enantiomer and Isomer Permeation Enhancers on Transdermal Delivery of Ligustrazine Hydrochloride

Enantiomers and isomers, such as D-limonene, L-limonene, and alpha-terpinene, were selected as enhancers. The effects and mechanisms of penetration enhancers on in vitro transdermal delivery of ligustrazine hydrochloride (LH) across hairless porcine dorsal skin were investigated. Transdermal fluxes of LH through porcine skin were determined in vitro by Franz-type diffusion cells. D-limonene, L-limonene, and alpha-terpinene could significantly promote the transdermal fluxes of LH, but no statistical difference (p > 0.05) between them was found. The lag time of L-limonene and alpha-terpinene were 2.55 and 2.20 times compared with that of D-limonene. Fourier transform-infrared (FTIR) was carried out to analyze the effects of enhancers on the biophysical natures of the stratum corneum (SC) and the permeation enhancement mechanism. FTIR spectra revealed that the changes of peak shift and peak area due to C-H stretching vibrations in the SC lipids were associated with the selected enhancers. All of them could perturb and extract the SC lipids to different extent and L-limonene showed obvious changes. Morphological changes of the skin treated with enhancers were monitored by a scanning electron microscope (SEM). The extraction of the SC lipids by the enhancers led to the disruption of SC and the desquamated SC flake. Apparent density (AD) was newly proposed to estimate the desquamated extent of SC flake. The results showed that the enantiomers and isomers enhanced the permeation of LH by pleiotropic mechanisms.

Stereoselective chromatography of cardiovascular drugs: an update

This review reports the latest achievements in chromatographic enantioseparations of various classes of cardiovascular drugs and selected applications of these methods in pharmaceutical and clinical analysis. The use of these drugs as test compounds for new chiral stationary phases and different parameters of chromatographic processes is also presented.

Recent applications of stereoselective chromatography

Some recent applications of stereoselective chromatography in the fields of clinical pharmacy, drug analysis, food, and natural products are reviewed. The review is documented with up-to-date literature, which will assist further expansion of research in these areas.