Effect of membrane surface potential on the uptake of anionic compounds by liposomes

Experimental design by response surface methodology for efficient cefixime uptake from hospital effluents using anion exchange membrane

The excessive use of antibiotics and their ultimate routes to the environment have prompted the drug resistance, which is becoming a major ecological issue. In this work, we have evaluated the performance of quaternary ammonium poly (2, 6-dimethyl-1,4-phenylene oxide) and polyvinyl alcohol (QPPO/PVA) based anion exchange membrane against cefixime (a third generation cephalosporin antibiotic) present in hospital effluents. The membrane's surface morphology was studied through scanning electron microscopy. The optimization of experimental parameters through Response Surface Methodology helped to evaluate the inter parameter dependence and predict maximum uptake capacity (qe). The speculated value of qe (6.72 mg g-1) obtained through central composite design was close to the experimental value of 7.01 mg g-1 with percent relative error of 4.31%. Further, the evaluation of experimental data using isotherms (Langmuir and Freundlich) and kinetic models (pseudo-first-order and second-order) proposed that the interactions between cefixime and the membrane were physisorptive in nature. The intra-day and inter-day assays exhibited lower %RSD values of 0.4% (n = 5) and 0.3% (n = 5). Furthermore, a percentage recovery of 98.2% (n = 9) and limit of detection 1 × 10-5 μg mL-1 was observed. The chromatogram of the treated water samples presented only negligible amount of cefixime indicating a great potential of QPPO/PVA membrane for the removal of cefixime from real water samples. The membrane could be regenerated for three consecutive cycles without any prominent loss in efficiency.

Co-hybridized composite nanovesicles for enhanced transdermal eugenol and cinnamaldehyde delivery and their potential efficacy in ulcerative colitis

Percutaneous absorption of drugs can be enhanced by ethosomes, which are nanocarriers with excellent deformability and drug-loading properties. However, the ethanol within ethosomes increases phospholipid membrane fluidity and permeability, leading to drug leakage during storage. Here, we developed and characterized a new phospholipid nanovesicles that is co-hybridized with hyaluronic acid (HA), ethanol and the encapsulated volatile oil medicines (eugenol and cinnamaldehyde [EUG/CAH]) for transdermal administration. In comparison with EUG/CAH-loaded ethosomes (ES), the formulation stability and percutaneous drug absorption of EUG/CAH-loaded HA-immobilized ethosomes (HA-ES) were significantly improved. After transdermal administration of HA-ES, the interstitial cells of Cajal in the colon of rats with trinitrobenzene sulfonate-induced ulcerative colitis (UC) were significantly increased, and the stem cell factor/c-kit signaling pathway was partly repaired. Overall, HA-ES possesses excellent deformability and showed improved efficacy against UC compared with ES, which is demonstrated as a promising transdermal delivery vehicle for volatile oil medicines.

Interactions of oritavancin, a new semi-synthetic lipoglycopeptide, with lipids extracted from Staphylococcus aureus

Oritavancin, a lipoglycopeptide with marked bactericidal activity against vancomycin-resistant Staphylococcus aureus and enterococci, induces calcein release from CL:POPE and POPG:POPE liposomes, an effect enhanced by an increase in POPG:POPE ratio, and decreased when replacing POPG by DPPG (Domenech et al., Biochim Biophys Acta 2009; 1788:1832-40). Using vesicles prepared from lipids extracted from S. aureus, we showed that oritavancin induces holes, erosion of the edges, and decrease of the thickness of the supported lipid bilayers (atomic force microscopy; AFM). Oritavancin also induced an increase of membrane permeability (calcein release) on a time- and dose-dependent manner. These effects were probably related to the ability of the drug to bind to lipid bilayers as shown by 8-anilino-1- naphthalene sulfonic acid (ANS) assay. Interaction of oritavancin with phospholipids at the level of their glycerol backbone and hydrophobic domain was studied by monitoring changes of Laurdan excitation generalized polarization (GP(ex)) and 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence anisotropy upon temperature increase. Oritavancin increased GP(ex) values and the transition temperature, indicating a more ordered structure at the level of the glycerol backbone. Oritavancin slightly decreased DPH fluorescence depolarization intensities, suggesting an increase in fluidity at the level of acyl chains. Together, our data confirm the interaction of oritavancin with lipids and the potential role of a rigidifying effect at the level of glycerol backbone for membrane permeabilization. This work shows how AFM and biophysical methods may help in characterizing drug-membrane interactions, and sheds further light on the mode of action of oritavancin.

[The transport mechanism of polycationic compounds across intestinal and renal cell membrane]

This article reviewed the transport mechanism of polycationic compounds across rat intestinal and renal cell membranes. The inside-negative diffusion potential stimulated the initial uptake of dicationic compounds into intestinal brush-border membrane vesicles, and a good correlation was observed between lipophilicity and the amount of diffusion potential-dependent transport of the dications. On the other hand, tri- and tetracationic compounds were not affected by the diffusion potential because of their much lower lipophilicity. The membrane surface potential affected to the transport of polycationic compounds, similar to monocationic compounds. Therefore it appears that the membrane surface potential plays a common role in the transport of mono- and polycationic compounds across cell membranes. On the intestinal basolateral membrane, it was found that there was a Na+/putrescine symporter. This recognized dicationic compounds and transported them from the blood into intestinal cells. This transporter did not recognize spermine and spermidine. Furthermore, we found a novel transport system, a Na+/spermine antiporter, on the rat renal brush-border membrane. This transporter recognized aliphatic polycation, which has more than four amino groups, and actively secreted spermine and trientine into the renal proximal tubules in vitro and in vivo. However, this transporter did not recognize trientine-copper complex. These results are useful for the prediction of the intestinal absorption and renal excretion of polyamine derivatives.

Ionic strength has a greater effect than does transmembrane electric potential difference on permeation of tryptamine and indoleacetic acid across Caco-2 cells

The effects of transmembrane electric potential difference and ionic strength on the permeation of tryptamine and indoleacetic acid across a Caco-2 cell monolayer were examined. A decrease in the transmembrane electric potential difference caused by the addition of potassium ion to the transport buffer had no effect on the permeation rate of either compound. On the other hand, an increase in ionic strength resulted in a decrease in the permeation rate of tryptamine and an increase in the permeation rate of indoleacetic acid. The changes in the permeation rate with changes in the ionic strength were correlated with the membrane surface potential monitored by 1-anilino-8-naphthalenesulfonic acid (ANS), a fluorescent probe. We tested these effects using several other cationic and anionic compounds. These effects of ionic strength were found to be common to all drugs tested. The compound that showed a relatively lower permeation rate was given relatively stronger effect. The possibility of overestimation or underestimation caused by these effects should be considered when the permeation of an ionic compound is evaluated using a cell monolayer system.

A general approach for the prediction of the intestinal absorption of drugs: regression analysis using the physicochemical properties and drug-membrane electrostatic interaction

A general method for predicting the intestinal absorption of a wide range of drugs using multiple regression analysis of their physicochemical properties and the drug-membrane electrostatic interaction was developed. The absorption rates of tested drugs from rat jejunum were measured by the in situ single-pass perfusion technique. The drugs used in this study were divided into three groups for regression analysis, and a smaller "test" set of compounds was used to assess the predictive capacity of the regression equation. When the analysis was applied to each respective group of drugs (i.e., anionic, cationic, and nonionized compounds), obtained regression coefficients were 0.569, 0.821, 0.728 by using the organic solvent (n-octanol)/buffer partition coefficient, 0.730, 0.734, 0.914 using the permeation rate across a silicon membrane, and 0.790, 0.915, 0.941 using an EVA membrane, respectively. However, smaller regression coefficients of 0.377, 0. 468, and 0.718 were obtained when these three groups of drugs were put together for prediction. Meanwhile, correlation was improved remarkably when drug-membrane electrostatic interactions, namely, hydrogen-bonding donor (Halpha) and acceptor (Hbeta) activity or index of electricity (Ec), were added to the other parameters of lipophilicity and permeation rate across the EVA membrane (r = 0.880 and 0.883, respectively). Moreover, the equation obtained from these regression analyses was applicable even to the prediction of the absorption of the zwitterionic drugs. These results suggest that including the electrostatic interaction parameters in addition to lipophilicity and permeability across artificial membranes would afford a better prediction for the intestinal absorption of the vast majority of drugs.

Effect of membrane surface potential on the uptake and the inhibition of cationic compounds in rat intestinal brush-border membrane vesicles and liposomes

The effect of membrane surface potential on the uptake of tryptamine, an organic cation, by rat intestinal brush-border membrane vesicles was investigated. In the presence of an inside-negative K(+)-diffusion potential, the manner of initial uptake of tryptamine appeared to be pH-dependent and the uptake in the acidic medium was lower than that in the neutral medium. Changes in surface potential of brush-border membrane vesicles were monitored using 8-anilino-1-naphthalenesulfonic acid (ANS) and the results suggested that the membrane surface potential (negative charge on the membrane surface) decreased in the acidic medium. A good correlation was observed between the K(+)-diffusion potential-dependent uptake of tryptamine and membrane surface potential monitored by ANS at various pH levels. The uptake of tryptamine by liposomes (large unilamellar vesicles), which contained various amounts of dipalmitoylphosphatidylserine (DPPS), was also examined. The uptake of tryptamine decreased with a decrease of DPPS content in the liposomes, and was correlated with the membrane surface potential monitored by ANS. Moreover, the effect of organic cations on the uptake of tryptamine by intestinal brush-border membrane vesicles was examined. The uptake of tryptamine was inhibited by tetracaine and imipramine. The inhibitory effect of these cations was well correlated with changes in the membrane surface potential in the presence of tetracaine or imipramine. These results suggest that the K(+)-diffusion potential-dependent uptake of tryptamine by intestinal brush-border membrane vesicles is affected by membrane surface potential, and the inhibition of tryptamine uptake originates in changes in the membrane surface potential caused by the organic cations.