Opinion Paper: Nanotechnology: A Successful Approach to Improve Oral Bioavailability of Phytochemicals.

Abstract

Abstract Phytochemicals have gained significant recognition for their potential therapeutic uses against a variety of human diseases. However, the poor water solubility, limited intestinal absorption and low water stability of phytochemicals generally prevent from achieving a high oral bioavailability and even detectable plasma levels of the parent compound. Dose escalation is not always a solution to address limited oral bioavailability, and may increase the risk of adverse events, most frequently in the gastrointestinal system [1]. Low water solubility is a common reason for the limited bioavailability of drug candidates because passing through the unstirred aqueous layer on the surface of the intestinal epithelium is a pre-requisite for the intestinal absorption of compounds. It has been estimated that over 40 % of the drugs being identified through combinatorial screening programs are poorly soluble in water [2]. Therefore, formulation improvement into highly stable, water-soluble and orally bioavailable forms is regarded as a prerequisite for the clinical application of phytochemicals. Nanotechnology has emerged as an efficient tool to address the problems regarding solubility, stability and oral bioavailability of phytochemicals [3]. Several nano-sized delivery systems have been utilized to enhance the physicochemical properties of phytochemicals. Characteristics of the most common biocompatible and biodegradable nanoparticulate systems used for the delivery of natural products are summarized in Table 1. Nanoparticulate delivery systems confer a number of advantages, including facilitated transport of incorporated phytochemicals across the biological barriers, enhanced bioavailability of poorly water-soluble phytochemicals, targeted delivery of phytochemicals, protection of sensitive compounds from biological and environmental degradation, and controlled release [4]. Some famous examples of nanoformulated phytochemicals are shown in Table 2 [5-7]. Furthermore, many nanomaterials are being studied in clinical trials or have been approved by the Food and Drug Administration to be used in humans. Liposomal daunorubicin (Daunoxome®; described in patents EP0004467 and US20070286897) and albumin-bound paclitaxel (Abraxane®, described in patents WO2014105644 and WO2008057562) are two breakthrough examples of successful formulation of natural products using nanotechnology-based approaches. Table 2 summarizes some pharmacologically important phytochemicals with optimized nanoformulations [8, 9]. Curcumin is another important anti-cancer and cardioprotective phytopharmaceutical [10-12] for which various nanoformulations have been developed [12], as described in patents WO2013108270 and EP2349237. While nanotechnology offers promising solutions for the formulation of phytochemicals, some challenges still remain to be overcome before developing any nanoparticulate system to be used in clinical practice. These considerations include potential long-term toxicity of nanoparticles, non-specific uptake into cells, off-target biodistribution and tissue accumulation, and costly and complicated manufacturing process of some nanocomposites particularly in the targeted forms [8]. In spite of these challenges, biocompatible and biodegradable nanocarriers are increasingly finding applications in pharmaceutical and nutraceutical industries. Future investigations should address long-term safety issues of nanomaterials particularly when used repeatedly for chronic diseases.