Structure of cubic phases in ternary systems Glucopone/water/hydrocarbon

Lyotropic liquid crystals for parenteral drug delivery

The necessity for long-term treatments of chronic diseases has encouraged the development of novel long-acting parenteral formulations intending to improve drug pharmacokinetics and therapeutic efficacy. Lately, one of the novel approaches has been developed based on lipid-based liquid crystals. The lyotropic liquid crystal (LLC) systems consist of amphiphilic molecules and are formed in presence of solvents with the most common types being cubic, hexagonal and lamellar mesophases. LC injectables have been recently developed based on polar lipids that spontaneously form liquid crystal nanoparticles in aqueous tissue environments to create the in-situ long-acting sustained-release depot to provide treatment efficacy over extended periods. In this manuscript, we have consolidated and summarized the various type of liquid crystals, recent formulation advancements, analytical evaluation, and therapeutic application of lyotropic liquid crystals in the field of parenteral sustained release drug delivery.

Comparison of lipid liquid crystal formulation and Vivitrol® for sustained release of Naltrexone: In vitro evaluation and pharmacokinetics in rats

Camurus' FluidCrystal® injection depot is a lipid liquid crystal (LLC) phase formation-based method, comprising of glycerol dioleate (GDO) and soy phosphatidylcholine (SPC), together with minute quantities of N-methyl-2-pyrrolidone solvent (NMP). The present study aimed to develop a method for LLC using sorbitan monooleate (LLC-SMO) instead of GDO to prepare a one-month sustained-release formulation of naltrexone (NTX) that is applied for the treatment of autism and treating alcohol dependence. The optical characteristics of the LLC were assessed by polarizing light microscopy (PLM) to reveal the presence of lamellar, hexagonal, and cubic mesophases. Furthermore, in vitro release of NTX and NMP, degradation, pharmacokinetics, and histopathology of LLC-GDO and LLC-SMO in rats were evaluated and compared to those of Vivitrol®. The PLM images revealed that the structure of LLC-SMO is hexagonal, similar to LLC-GDO. The in vitro release of NTX and its pharmacokinetic results in rats indicted that the LLC-SMO system is more uniform than LLC-GDO and Vivitrol® during 35 days. Histopathological results of LLC-GDO and LLC-SMO confirmed the biocompatibility of our LLC delivery systems. Taken together these data demonstrate that the LLC-SMO-based method, was efficient enough to sustain the release of NTX in vitro and in vivo, confirming the biocompatible nature of this delivery system.

Usefulness of liquid-crystal oral formulations to enhance the bioavailability and skin tissue targeting of p-amino benzoic acid as a model compound

Topical formulations are not always suitable to deliver active ingredients to large areas of skin. Thus, in this study, we aimed to develop an oral formulation for skin tissue targeting with a high bioavailability using liquid crystal (LC) dispersions comprising cubosomes of a mal-absorptive model compound, p-amino benzoic acid (PABA), which is an active element in cosmeceuticals, dietary supplements and skin disorder medicines. The bioavailability and skin concentration of PABA were investigated after oral administration in rats. The effect of the remaining amount of the LC formulation in the stomach on the pharmacokinetic profiles of orally administered PABA was evaluated. The skin permeation and concentration of PABA were also investigated using an in vitro permeation experiment. As a result, the bioavailability of PABA was significantly improved by administration of PABA-LC formulations compared with PABA solution alone, although the effect was greatly influenced by the type of LC-forming lipids. The in vitro skin permeation study showed that the PABA concentration in the skin when applied from the dermis side was higher than when applied from the epidermis side. These findings suggested that oral administration advantageously supports skin targeting, and oral LC formulations could be a promising material in cosmeceutical, dietary and clinical fields.

Alkali Metal Cationization of Alkyl Glucosides under Electrospray Ionization Conditions

Alkyl glucosides have been studied by electrospray ionization mass spectrometry. The effect of the hydrophobic and the hydrophilic parts of these compounds on the stability of [M + Na]+ ions has been evaluated by mass spectra at growing cone voltages. The longer the hydrophobic or the hydrophilic part, the higher the stability of these ions. It has been also found that solvent used affects the abundances of [M + Na]+ ions. In order to check if the radii of alkali metal ions influence the stability of their adducts with the compounds studied, the mass spectra have been recorded for solution containing lithium and potassium ions. The cations of smaller radius form more stable adducts, especially with the compounds having longer hydrophobic parts.

Shear-induced topology changes in liquid crystals of the soybean lecithin/DDAB/water system

The viscoelastic behavior of the two different liquid crystalline lamellar phases and the liquid crystalline cubic phase of the mixed soybean lecithin/DDAB system in water was studied through rheology, with mechanical parameters studied as a function of composition. The swollen or diluted lamellar region is formed by vesicles, and its characteristic flow curve presents two-power law regions separated by a region where viscosity passes through a maximum. Yield stress and shear-dependent flow behavior were also observed. The microstructure suffers transformation under shear stress, and rheological response shifts from thixotropic to antithixotropic loops. Similar rheological behavior has been observed for samples in the collapsed or concentrated lamellar region, at the water-rich corner of the phase diagram. Vesicle formation may therefore occur by shearing the initial stacked and open bilayers. However, concentrated lamellar samples in the water-poor part of the phase diagram are less sensitive to shear effects and show plastic behavior and thixotropy. All lamellar samples manifest high elasticity. The dynamic responses of both lamellar topologies, i.e., vesicles and open bilayers, are comparable and exhibit an infinite relation time. The bicontinuous cubic, liquid crystalline phase is highly viscous. Its dynamic response cannot be modeled by a Maxwell model.

Effect of temperature on dynamic rheological behavior of discontinuous cubic liquid crystal

The dynamic rheological properties of discontinuous cubic liquid crystal, formed by nonionic surfactant C(12-14)E(12), were investigated in the discrete and continuous patterns of raising temperature. In the discrete pattern, the discontinuous cubic phase appears in two types of viscoelastic behaviors under the melting points of cubic phase: elastic gel and viscoelastic liquid. When the discontinuous cubic phase begins to melt, it has the weak polymer-like viscoelasticity. Temperature and shear frequency have completely different effects on the ratio of viscous and elastic components of samples in these three states. At low temperature, the samples dominate in elasticity and temperature and shear frequency has hardly any effect on viscoelasticity. At moderate temperature, its ratio of viscous and elastic components increases with increasing temperature and decreasing shear frequency. At the vicinity of the melting point of cubic liquid crystal, the cubic liquid crystal appears to have almost equaled viscous and elastic component; shear has obvious effect on the ratio of viscoelasticity at low frequency. The results from the continuous pattern of raising temperature are consistent with those from the discrete pattern.