Preparation, physicochemical characterization and antioxidant activity of diphenyl diselenide-loaded poly(lactic acid) nanoparticles

Abstract

In this study, we developed, characterized and evaluated the antioxidant activity of poly (lactic acid) nanoparticles containing diphenyl diselenide (PhSe)₂. Nanoparticles were characterized in terms of mean particle size, polydispersity index, zeta potential, encapsulation efficiency, in vitro release profile, physical stability, polymer-drug interactions and thermal properties. Also, the antioxidant activity of nanoparticles on hypochlorous acid (HOCl) was assessed. Nanoparticles presented a mean size of 210 nm, had low polydispersity, zeta potential of −24 mV, and an encapsulation efficiency over 90%. Differential scanning calorimetry and X-ray diffraction results showed (PhSe)₂ is dispersed in PLA matrix in an amorphous state. Lyophilized nanoparticles maintained physical stability over three months, while nanoparticles dispersed in water did not present stability over 7 days. In vitro release assay was characterized by a biphasic release pattern with burst effect in 8 h followed by a sustained release diffusion governed over 192 h. Nanoencapsulation did not alter the antioxidant activity of (PhSe)₂ on HOCl. The study concludes these properties of (PhSe)₂-loaded nanoparticles can be useful to extend the biological effects of (PhSe)₂.

Introduction

Oxygen is essential for the oxidation of organic compounds, and energy production for cellular metabolism [1]. However, a small amount of oxygen consumed (2–5%) is reduced to produce a variety of highly reactive chemicals, called reactive oxygen species (ROS). Excess of ROS such as superoxide anion, hydroxyl radical and hydrogen peroxide can cause deleterious effects on cells, causing or aggravating cellular aging and/or mutagenic events, promoting growth of malignant tumors or the surging of cardiovascular and neurological diseases, as Alzheimer and Parkinson [2], [3], [4]. Strategies using antioxidant compounds as a way to reduce or significantly inhibit oxidation, thus providing decreased production of free radicals have been explored in biology and medicine [5].

Molecules containing selenium may be great antioxidants [6]. Diphenyl diselenide (PhSe)₂ is a selenium organocompound and it has an important protective role in a variety of experimental models associated with exacerbated free radicals production [7], [8], [9], [10], [11]. Its antioxidant activity is due to its ability to mimic glutathione peroxidase enzyme [12], [13]. Despite (PhSe)₂ pharmacological effects, high doses of it have demonstrated injury to the central nervous system of mice, causing decrease in glutamatergic transmission, as well as hepatic and renal toxicity [14], [15]. Another limitation is the low aqueous solubility of (PhSe)₂ [16]_, resulting in a slow rate of dissolution in biological fluids, and consequently, in poor oral absorption. This effect associated with extensive metabolism and rapid elimination of (PhSe)₂ results in low bioavailability by oral route.

The use of nanotechnology is an excellent tool for increasing the oral bioavailability of molecules and as well reduce their toxicity. Polymeric nanoparticles emerged in the last three decades as drug carriers mainly due to its stability in biological fluids and during storage; they also protect drugs against premature degradation and have greater ability to improve pharmacokinetics and pharmacodynamics properties of the drug loaded [17], [18], [19]. Also, polymeric nanoparticles promote sustained drug release profile, depending on polymer composition, thereby, leading to constant drug concentration in plasma and tissues [17], [20], [21]. Polymeric nanoparticles can be composed of natural [22], [23] or synthetic polymers [24], [25]. Among the synthetic ones, poly (lactic acid) (PLA) is the polyester approved by the FDA for human use [26]. It is biodegradable in nontoxic byproducts, and thus elected the polymer of choice for application in the medical and pharmaceutical field [27]. Polymeric nanoparticles present diameter lower than 1000 nm and are carriers for oral [28], parenteral [29], nasal [30], ocular [31] and topical drug delivery [32]. Nanoparticles could be interesting tools to improve (PhSe)₂ oral bioavailability and consequently its biological effects. In this sense, particle size is an important characteristic for efficient internalization into epithelia of the gastrointestinal tract, and as consensus, sizes smaller than 500 nm are required [33], [34].

Although, several studies have reported the use of selenium in biogenic nanoparticles with reduced toxicity [35], [36], [37], [38], the application of polymeric nanoparticles as carriers of (PhSe)₂ is rarely discussed [39], [40]. In this study, PLA nanoparticles containing (PhSe)₂ were obtained and characterized considering the mean particle size, polydispersity index, zeta potential, encapsulation efficiency, in vitro drug release profile, thermal properties and solid physical state. Moreover, storage stability and in vitro scavenging assay over HOCl were evaluated.