Abstract
Thymoquinone (TQ) is the main constituent of Nigella sativa L. essential oil. In vitro studies have shown its protective effect against H2O2-induced oxidative stress in human retinal pigment epithelium cells, and in vivo experiments have demonstrated its effect in decreasing corneal neovascularization and reducing the inflammation in an experimental dry eye model in mice. Its therapeutic use is limited by poor bioavailability, low solubility, and scarce permeability. In this study, two liposomal formulations have been developed, both of which consist of phosphatidylcholine and Plurol Oleique, a liquid lipid, and one of which is coated with 0.1% w/v hyaluronic acid (HA) to increase both TQ solubility and its ocular therapeutic potential. Each formulation has a size <200 nm and an EE% around 70%, determined by scattering techniques and the HPLC-DAD analytical method, respectively, and they result in a 2-fold increase in TQ solubility. HA-coated liposomes are stable over 2 months at +4 °C, and coated and uncoated liposomes present a gradual and prolonged release of TQ. Two cell lines, human corneal epithelial cells (HCEC-2) and human conjunctival epithelial cells (HConEC) were used to investigate the safety of the liposomal formulations. Uptake studies were also performed using fluorescent liposomes. Both liposomes and, in particular, HA-coated liposomes reduce the TQ toxicity observed at high doses in both HCEC-2 and HConEC cells, and both formulations increase the absorption at the cellular level and especially at the nucleus level, with a more pronounced effect for HA-coated liposomes.
Highlights
Thymoquinone (TQ), the main constituent of Nigella sativa L. seed essential oil, has various pharmacological properties useful for the treatment of a wide range of diseases including chronic non-infectious diseases and infectious diseases [1,2,3,4,5].In particular, the protective effect of TQ against H2 O2 -induced oxidative stress in human retinal pigment epithelium cells has been reported [6]
TQ acts on the immune system, modulating the levels of pro- and anti-inflammatory mediators that are involved in corneal neovascularization, and it is as effective as topical triamcinolone when topically applied to the eye at 0.4% [8]
The purpose of this study is to develop liposomal formulations of TQ, to improve its biopharmaceutical performance, and to enhance the delivery and the activity at the eye level
Summary
Thymoquinone (TQ), the main constituent of Nigella sativa L. seed (black seed) essential oil, has various pharmacological properties useful for the treatment of a wide range of diseases including chronic non-infectious diseases (neurological disorders, diabetes mellitus, hypertension, dyslipidemia, inflammatory disorders, cancer, etc.) and infectious diseases [1,2,3,4,5].In particular, the protective effect of TQ against H2 O2 -induced oxidative stress in human retinal pigment epithelium cells has been reported [6]. TQ has shown anti-inflammatory properties in an experimental dry eye model, and it has decreased corneal neovascularization in a dose-dependent manner after topical administration in a rat model [7]. The purpose of this study is to develop liposomal formulations of TQ, to improve its biopharmaceutical performance, and to enhance the delivery and the activity at the eye level. Liposomes, due to their unique structure, are extremely beneficial drug carriers as they can entrap both the hydrophilic and hydrophobic drugs [13]. Phospholipids are the major components of most liposomes Extensive testing of these naturally occurring compounds has revealed them to be remarkably safe for pharmaceutical use. Liposomes enhance corneal permeability due to their ability to come in close contact with cornea and conjunctiva, increasing the extent of corneal uptake and prolonging corneal contact time [13]
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