ABSTRACT
Keywords: biocompatible and biodegradable nanocarriers, phytochemicals, green tea catechins, (-)-epigallocatechin gallate, quercetin, resveratrol, curcumin, bioavailability, bioactivities, cancer, atherosclerosis, stability, sustained release, nanoliposomes, emulsions, micelles, lipid nanoparticles, PLGA nanoparticles
health. There is a critical need for using nanoparticles to enhance their stability, solubility, absorption, bioavailability, target specificity and bioactivities, protect them from premature degradation in the liver and other tissues, and lower their toxicity to normal tissues. 39.2 Nanoparticles
Although no official universally accepted definition for nanoparticles has been established, most experts consider them to be particles that are in the range of 10-1000 nm. Nanoliposomes, emulsions, micelles, lipid nanocarriers, and poly(lactic-co-glycolic acid) (PLGA) nanoparticles are commonly used biocompatible and biodegrad-able nanoparticles [1]. 39.2.1 NanoliposomesPhospholipids and cholesterol are commonly used to synthesize nanoliposomes. The extruder and sonicator are common equipment to make nanoliposomes. After dissolving and drying phosphatidylcholine and cholesterol, saline or aqueous solutions can be added into the dry lipids. After vortexing, the suspension can either pass through the extruder with different sizes of filters or be sonicated to form nanoliposomes. Nanoliposomes are spherical and have lipid bilayered membrane structures. Multilamellar vesicles (MLVs), small unilamellar vesicles (SUVs) and large unilamellar vesicle (LUVs) are major types of nanoliposomes. Hydrophilic phytochemicals can be encapsulated into the central aqueous compartment of nanoliposomes, and the hydrophobic phytochemicals can be embedded into their lipid bilayers [2].Since all components of nanoliposomes are biocompatible and biodegradable, nanoliposomes have been widely used as delivery carriers in pharmaceuticals and nutraceuticals [2-5]. 39.2.2 EmulsionsEmulsions consist of two immiscible liquids. Oil-in-water (O/W) emulsions are made by adding oil into an aqueous phase, and water-in-oil (W/O) emulsions are made by adding an aqueous solution into an oil phase. In order to reduce the interfacial tension, surfactants or co-surfactants are needed. More surfactants or co-
surfactants are required to make the smaller size of emulsions. Since our physiological environment is aqueous, O/W emulsions are the common emulsion type. The first FDA approved intravenous fat emulsion was Intralipid®, which was composed of soybean oil, egg phospholipids, and glycerin. Intralipid® can deliver essential fatty acids via intravenous injection to the patients who cannot absorb those nutrients through diet [6]. Many phytochemicals, especially resveratrol, quercetin, and curcumin, are hydrophobic. O/W emulsions can increase their aqueous solubility, stability, bioavailability, and bioactivities. 39.2.3 MicellesMicelles are composed of many amphiphilic monomers, such as phospholipids and some synthetic polymers. When reaction temperatures reach the critical micellization temperature and amphiphilic monomers concentrations reach the critical micelle concentration (CMC), micelles are formed [7, 8]. Micelles found in human intestines are made by phospholipids and bile acids. Hydrophilic (polar) phospholipid heads form the outer surface of micelles, while hydrophobic (nonpolar) phospholipid fatty acid tails form a hydrophobic core, which can accommodate dietary lipids, lipid-soluble vitamins, phytochemicals, and other hydrophobic compounds. Polymeric micelles are composed of block-copolymers that are made of hydrophobic (nonpolar) and hydrophilic (polar) monomer units in different arrangements [9]. The commonly used core-forming blocks are poly(caprolactone), poly(propylene oxide), poly(D,L-lactic acid) and poly(L-aspartic acid), and polyethylene glycol (PEG) is the widely used hydrophilic monomer [9, 10]. Many hydrophobic compounds can be encapsulated or incorporated into micelles and be used for oral, parenteral, nasal, ocular, and topical administration [9]. Micelles are excellent carriers for phytochemicals. 39.2.4 PLGA Nanoparticles
PLGA is a FDA approved and widely used biocompatible and biod-egradable polymer [11]. PLGA is composed of lactic acid and glycolic acid. PLGA can have different numbers of lactic acid and glycolic acid that give PLGA different molecular weights and properties.
