Novel approach to improve permeation of ondansetron across shed snake skin as a model membrane

An investigation of the chick chorioallantoic membrane as an alternative model to various biological tissues for permeation studies

OBJECTIVES

The chick chorioallantoic membrane (CAM) was explored as a biological membrane for use in the study of drug permeation with a Franz diffusion cell.

METHODS

The CAM was removed from fertilized chicken eggs of embryo age 9-18 days. The permeation profiles of nicotine through the fresh CAM were first obtained with a Franz diffusion cell. The permeation profiles of nicotine through frozen CAM, snake skin, pig skin, pig retina and pig buccal mucosa were also determined and compared with those of the fresh CAM.

KEY FINDINGS

The permeability coefficient of the CAM varied with its age. The CAM at embryo age 13 was the most robust, showing the lowest standard error in permeability. It was thus chosen for comparative studies with snake skin, pig skin, retina and buccal mucosa. The CAM was found to be most similar to the buccal mucosa in terms of permeation profile and permeability coefficient values. Frozen CAM was also found to have a higher permeability coefficient than fresh CAM. The enhanced permeability was attributed to freezing, which affected the integrity of the CAM structure.

CONCLUSIONS

From the findings, CAM shows potential as an alternative to the pig buccal mucosa as an in-vitro buccal model. The robustness of the CAM for drug permeation studies is affected by its age.

Different stimulatory effects of methylisogermabullone on the spontaneous contractility of rat gastrointestinal segments

Using rat gastrointestinal (GI) strips, this study investigated the stimulatory effects of methylisogermabullone (MIGB) purified from radish on the spontaneous contractility of GI smooth muscles and pharmacological mechanisms involved in the MIGB-induced GI contraction. MIGB at 30 microM differently regulated the tone and amplitude of spontaneous GI contractility according to the region (fundus through distal colon) and orientation (longitudinal and circular) of smooth muscles: a significant increase in both tone and amplitude of spontaneous contraction in the ileum longitudinal and distal colon circular muscles and in amplitude only in the fundus, jejunum and distal colon longitudinal muscles. Pretreatment of ileum longitudinal muscles with atropine (0.5 microM) or 4-DAMP (0.5 microM) significantly inhibited the acetylcholine (ACh, 1 microM)- and MIGB (30 microM)-stimulated contraction, and methoctramine (0.5 microM) also obviously reduced the tone and amplitude increased by ACh and MIGB, respectively. In the presence of methysergide (1 microM), pretreatment of ileum longitudinal muscles with both ondansetron (0.1 microM) and GR113808 (0.1 microM) significantly inhibited the contraction stimulated by 5-HT (10 microM), but not by MIGB. Taken together, it is concluded that MIGB differently regulates the spontaneous contractility (tone and/or amplitude) of GI segments according to the region of gut and orientation of smooth muscles, and these contractile responses of GI tracts to MIGB are likely mediated, at least, by activation of acetylcholinergic M2 and M3 receptors.

Ion-pairs of ibuprofen: increased membrane diffusion

The purpose of the present study was to determine the influence of pH and ion-pairing on the permeation of ibuprofen across polydimethylsiloxane (PDMS) membrane. The solubility of ibuprofen sodium was determined at a range of pH values. Saturated solutions were then used to determine the influence of pH on diffusion across PDMS as a model membrane. The apparent partition coefficient of ibuprofen sodium between n-octanol and phosphate buffer at various pH values was also investigated. Organic salts of ibuprofen using ethylamine, diethylamine, triethylamine and ethylene diamine as counter-ions were synthesized and the influence of these counter-ions on the permeation of ibuprofen was studied. The presence of ion-pairing was confirmed using 1H NMR and 13C NMR. Diffusion studies at different pH values (4.0, 5.0, 6.0, 7.0 and 8.0) indicated that ibuprofen sodium flux increased significantly with increasing pH from 4.0 to 7.0. Above pH 7.0 a decrease in diffusion was observed. The permeability coefficient increased with an increase in the amount of unionized acid. The apparent partition coefficient was directly related to the steady-state flux. The steady-state flux of ibuprofen increased up to 16-fold using different counter-ions. The highest flux was measured from ibuprofen triethylamine. The flux of ibuprofen salts across a lipophilic membrane can be increased by formation of ion-pairs. The extent of enhancement is associated with the lipophilicity, extent of ion-pairing and reduction in charge over the drug molecule.

Ion Pair Formation as a Possible Mechanism for the Enhancement Effect of Lauric Acid on the Transdermal Permeation of Ondansetron

Transdermal application can be an alternative drug delivery route for ondansetron, an antiemetic drug. Previous studies found that fatty acids, namely oleic and lauric, were the most effective penetration enhancers. The aim of this study was to investigate the formation of an ion pair between ondansetron and lauric acid as a possible mechanism of its enhancing action. Several techniques were used to reveal the formation of an ion pair complex. Partitioning experiments, where the n-octanol/water coefficient was measured, showed an increase in the distribution coefficient in the presence of the acid, possibly as a result of the formation of more lipophilic ion pairs between the charged molecules of ondansetron and lauric acid. Further evidence of complex formation between ondansetron and lauric acid, was gained from the 13C-nuclear magnetic resonance (13C-NMR) spectra of ondansetron, lauric acid, and their mixture (molar ratio 1:1). The NMR spectra revealed alterations to the magnetic environment of the carbon atoms adjacent to the ionized group, which are the carbonyl group of the acid and the nitrogen of the imidazole ring of ondansetron. This evidence substantiates the theory of ion pair formation. Finally, thermal analysis of the binary mixtures of ondansetron and lauric acid revealed the formation of an additional compound, with different melting point from pure ondansetron and lauric acid, which is thermodynamically favored.

Use of an 8132Asymmetrical Factorial Design for the In Vitro Evaluation of Ondansetron Permeation Through Human Epidermis

The in vitro permeation of ondansetron through human cadaver epidermis, as a preliminary step toward the development of a transdermal therapeutic system, was investigated. In vitro release studies were carried out using modified Franz diffusion cells and human epidermis, taken from cadaver skin by heat separation technique. To estimate the effect of the type and concentration of the penetration enhancers and the skin from different donors, an 8(1)3(2) asymmetrical factorial design was used. Formulations containing lauric acid and oleic acid as penetration enhancers, showed the largest Q values [amounts of ondansetron permeated per unit area of epidermal membrane (microg/cm2)] at 24, 48, and 72 hr, as well as steady-state flux values, among all formulations tested. The other enhancers increased the flux in the following order: lauryl alcohol>glycerol monooleate>Azone >cineole>oleyl alcohol>1-methyl-2-pyrrolidinone. Moreover, the concentration of the penetration enhancer and the type of the skin were proved to significantly affect the permeation rate of ondansetron through human epidermis. From the results obtained, it was shown that the formulations containing lauric acid or oleic acid at 5% or 10% could increase sufficiently the permeation of ondansetron. Therefore, the transdermal administration of ondansetron seems feasible.

Influence of lipophilic counter-ions in combination with phloretin and 6-ketocholestanol on the skin permeation of 5-aminolevulinic acid

In this study, the effect of lipophilic counter-ions on the permeation of 5-aminolevulinic acid (ALA) in combination with skin impregnation by phloretin and 6-ketocholestanol was evaluated. Standard in vitro permeation experiments with porcine skin were performed analysing the ALA content by HPLC and fluorescent detection after ALA derivatisation. The shake flask method in combination with a trinitrobenzensulfonic acid test for ALA analysis was performed to calculate the apparent partition coefficient (logP(Oct)). The permeation of ALA was enhanced by cetylpyridinium chloride and benzalkonium chloride at pH 7.0 and by sodium-1-octanesulfonic acid, sodium-1-heptanesulfonic acid and sodium-1-pentanesulfonic acid monohydrate at pH 4.0. Corresponding effects of these additives were observed on the partitioning of ALA. Pre-impregnation of porcine skin with phloretin and 6-ketocholestanol increased the ALA diffusion about 1.7-fold at pH 7.0. Moreover, this transport enhancement by 6-ketocholestanol was 3.5-fold higher when a combination of ALA and cetylpyridinium chloride was used as donor.

Nail morphology studies as assessments for onychomycosis treatment modalities

The purpose of this investigation was to study the morphology of the human nail treated with chemical penetration enhancers (CPE), bioadhesives and surface modifiers for assessment of topical treatment modalities for onychomycosis. CPEs, including dimethyl sulfoxide (DMSO) and urea were applied to human nail samples. Additional samples were treated with surface modifiers, tartaric acid (TTA) and phosphoric acid gel (PA). Other nail specimens were subjected to the bioadhesive polymers Carbopol 971P and Klucel MF. Atomic force microscopy (AFM), scanning electron microscopy (SEM) and polarized light microscopy (PLM) were utilized to visualize nail morphology and topographical changes of the human nail samples subjected to the various chemical agents. AFM, SEM and PLM micrographs revealed changes in topography to the dorsal layer when CPEs and surface modifiers were applied. Roughness scores as determined by NANOSCOPE IIIA software indicated a 2-fold increase when the dorsal nail layer was subjected to PA versus the control (147.8 vs. 85.0 nm, respectively). In contrast, when carbomer 971P was applied to the dorsal surface, roughness scores decreased significantly (44.6 vs. 85.0 nm, respectively). AFM, SEM and PLM studies of the human nail subjected to various chemical agents may be useful in the design and formulation of novel drug delivery systems for the topical treatment of onychomycosis. The AFM studies offer both a qualitative and quantitative assessment for nail treatment opportunities.

Shed king cobra and cobra skins as model membranes for in-vitro nicotine permeation studies

Shed king cobra skin (SKCS) and shed cobra skin (SCS) were investigated for use as barrier membranes, including some pre-hydration factors, for in-vitro nicotine permeation. Inter-specimen variations in nicotine fluxes using shed snake skin were compared with those using human epidermis. Nicotine in the form of 1% w/v aqueous buffer solution at pH 5 and transdermal patches (dose 14 mg day(-1)) were used. The nicotine fluxes across the shed snake skin were not significantly affected (P > 0.05) by temperature and duration of hydration pre-treatment. Scanning electron micrographs of SKCS and SCS revealed a remarkable difference in surface morphology, but the nicotine fluxes using both shed skins were not significantly different (P > 0.05). When compared with the results obtained using human epidermis, there were similarities in fluxes and permeation profiles of nicotine. Using nicotine solution, the nicotine permeation profiles of all membranes followed zero order kinetics. The amount of nicotine permeated provided good linearity with the square root of time over 24 h (R(2) > 0.98) when using nicotine patches. The nicotine fluxes using SKCS and SCS had less inter-specimen variation than those using human epidermis. The results suggest a potential use for SKCS or SCS as barrier membranes for in-vitro nicotine permeation studies.