Comparative analyses of response surface methodology and artificial neural networks on incorporating tetracaine into liposomes

This study evaluated the incorporation of tetracaine into liposomes by RSM (Response Surface Methodology) and ANN (Artificial Neural Networks) based models. RCCD (rotational central composite design) and ANN were performed to optimize the sonication conditions of particles containing 100 % lipid. Laser light scattering was used to perform measure hydrodynamic radius and size distribution of vesicles. The liposomal formulations were analyzed by incorporating the drug into the hydrophilic phase or the lipophilic phase. RCCD and ANN were conducted, having the lipid/cholesterol ratio and concentration of tetracaine as variables investigated and, the encapsulation efficiency and mean diameter of the vesicles as response variables. The optimum sonication condition set at a power of 16 kHz and 3 minutes, resulting in sizes smaller than 800 nm. Maximum encapsulation efficiency (39.7 %) was obtained in the hydrophilic phase to a tetracaine concentration of 8.37 mg/mL and 79.5:20.5% lipid/cholesterol ratio. Liposomes were stable for about 30 days (at 4 ºC), and the drug encapsulation efficiency was higher in the hydrophilic phase. The experimental results of RCCD-RSM and ANN techniques show ANN obtained more refined prediction errors that RCCD-RSM technique, therefore, ANN can be considered as an efficient mathematical method to characterize the incorporation of tetracaine into liposomes.

Lung specific stealth liposomes as antitubercular drug carriers in guinea pigs.

The problem of patient non-compliance in the management of tuberculosis (TB) can be overcome by reducing the dosing frequency of antitubercular drugs (ATD) employing drug carriers. This study reports on the intravenous (iv) administration of lung specific stealth liposomes encapsulating ATD (rifampicin and isoniazid in combination) to guinea pigs and the detailed pharmacokinetic/chemotherapeutic studies. Following a single iv administration of liposomal drugs, the latter were found to exhibit sustained therapeutic levels in plasma for 96-168 hr with half-lives of 24-70 hr, mean residence time (MRT) of 35-81 hr and organ drug levels up to day 7. The relative bioavailability (as compared to oral free drugs) was increased by 5.4-8.9 folds, whereas the absolute bioavailability (as compared to iv free drugs) was increased by 2.9-4.2 folds. Weekly therapy with liposomal ATD for 6 weeks produced equivalent clearance of Mycobacterium tuberculosis from organs as did daily therapy with oral free drugs. Hence, intravenous liposomal ATD offer the therapeutic advantage of reducing the dosing frequency and improving the patient compliance in the management of TB.

Zinc in the prevention of Fe2+-initiated lipid and protein oxidation

In the present study we characterized the capacity of zinc to protect lipids and proteins from Fe2+-initiated oxidative damage. The effects of zinc on lipid oxidation were investigated in liposomes composed of brain phosphatidylcholine (PC) and phosphatidylserine (PS) at a molar relationship of 60:40 (PC:PS, 60:40). Lipid oxidation was evaluated as the oxidation of cis-parinaric acid or as the formation of 2-thiobarbituric acid-reactive substances (TBARS). Zinc protected liposomes from Fe2+ (2.5-50 microM)-supported lipid oxidation. However, zinc (50 microM) did not prevent the oxidative inactivation of glutamine synthetase and glucose 6-phosphate dehydrogenase when rat brain supernatants were oxidized in the presence of 5 microM Fe2+ and 0.5 mM H2O2. We also studied the interactions of zinc with epicatechin in the prevention of lipid oxidation in liposomes. The simultaneous addition of 0.5 microM epicatechin (EC) and 50 microM zinc increased the protection of liposomes from oxidation compared to that observed in the presence of zinc or EC separately. Zinc (50 microM) also protected liposomes from the stimulatory effect of aluminum on Fe2+-initiated lipid oxidation. Zinc could play an important role as an antioxidant in biological systems, replacing iron and other metals with pro-oxidant activity from binding sites and interacting with other components of the oxidant defense system.

El método ELISA para determinar proteína unida a liposomas / The ELISA method for the determination of protein bounded to liposomes

Se aplicó el método ELISA para tratar de determinar anticuerpos unidos covalentemente a liposomas, demostrando que sí es posible aplicar este método para dicha determinación, ya que los liposomas fueron resistentes a todo el procedimiento del ELISA y por sí mismos no desarrollaron color. Solamente hubo desarrollo de color cuando la inmunoplaca fue sensibilizada con los liposomas que llevan anticuerpo en su superficie. El ELISA se aplicó en su forma más simple, porque los anticuerpos, tanto libres como unidos a los liposomas se determinaron directamente por su antigenicidad empleando el conjugado anti-anticuerpo-peroxidasa. La aplicación del método ELISA para determinar anticuerpo unido a liposomas tiene la ventaja sobre otros que se han descrito en la literatura, de que es un método rápido y sencillo, que además solo permite determinar anticuerpos que conservan su actividad biológica después de unirlo a liposomas. Como los liposomas fueron resistentes a todo el proceso que se aplica en ELISA, proponemos que podrían usarse por si mismos como soportes que sustituyan a la inmunoplaca que se usa en ELISA; con la ventaja de que a los liposomas podrían fijarse antígenos no solo de naturaleza proteica si no también lipídica, en este último caso por inserción en la bicapa lipídica del liposoma. Esta posibilidad es interesante porque en la actualidad es difícil determinar antígenos lipídicos