35 Address all correspondence to Reza Mahjub, r.mahjoub@umsha.ac.ir Does Encapsulation of Propolis Flavonoids into Poly-Lactide-Co-Glycolide Nanoparticles Enhance Sun Protection Factor of Propolis-Based Sunscreen Formulations? ASA CHAVOSHI, MEYSAM SOLEIMANI, MOJDEH MOHAMMADI, M.R. MOZAFARI AND REZA MAHJUB Department of Pharmaceutics, School of Pharmacy, Hamadan University of Medical Sciences, Hamadan, Iran (A.C., R.M.) Department of Pharmaceutical Biotechnology, School of Pharmacy, Hamadan University of Medical Sciences, Hamadan, Iran (M.S.) Department of Pharmacology and Toxicology, School of Pharmacy, Hamadan University of Medical Sciences, Hamadan, Iran (M.M.) Australasian Nanoscience and Nanotechnology Initiative (ANNI), Monash University LPO, Clayton, Australia (M.R.M.) Accepted for publication December 26, 2021. Synopsis Propolis is a natural substance and exerts the potency for absorption of ultraviolet radiation in a wide range of wavelengths. The aim of this study was to prepare a sunscreen formulation incorporating poly-lactide-co- glycolide nanoparticles encapsulating propolis flavonoids (PFs). The nanoparticles were prepared using oil- in-water emulsification and solvent evaporation technique. Their morphology was examined using scanning electron microscopy and the release profile of PF was determined in vitro. Finally, the prepared nanoparticles were incorporated into a sunscreen formulation and the appropriate sun protection factor (SPF) was calculated using in vitro method. The value was compared with the SPF values of the formulations containing either free PF or plain nanoparticles. The size, polydispersity index, zeta potential, entrapment efficiency percentage, and loading efficiency percentage of propolis-containing nanoparticles were 299 ± 14 nm, 0.381 ± 0.025, −15.4 ± 0.2 mV, 72 ± 2.3%, and 5.15 ± 0.41, respectively. Finally, it was observed from in vitro studies that sunscreen formulations incorporating nanoparticles exhibited higher SPF values compared to either free PFs or plain nanoparticles. INTRODUCTION Propolis, a dark-brown, viscous resin material produced by honeybees, is naturally used to cover the inside of the hive. Although the constituents of propolis are varied based on J. Cosmet. Sci., 73, 35–48 (January/February 2022)

36 JOURNAL OF COSMETIC SCIENCE the origin, it usually contains resin and balsam (55%), honey (30%), aromatic oils (10%), and pollen (5%) (1). Flavonoids, as the major ingredients of propolis, exhibit antimicrobial, antiulcer, and wound healing effects. Propolis flavonoids (PFs) have also demonstrated antitumor, antibacterial, antifungal, antiparasitic, antioxidant, anti-inflammatory, and anticaries properties (2). Based on the wavelengths, ultraviolet (UV) rays, which are radiated by the sun, are divided into three categories of UVA (320–400 nm), UVB (290–320 nm), and UVC (290–320 nm). In contrast to UVC, which is absorbed by the ozone layer of the atmosphere, UVA and UVB can reach to the surface of earth and, therefore, have the potential for development of a wide range of skin diseases, from mild sunburn and light skin inflammations to severe malignancies (3). UVB radiations can penetrate the skin to a depth of 160–180 μm and cause wrinkles, scaling, dryness, dilation of blood vessels, and collagen loss as well as increase the risk of skin cancer and melanoma (4,5). UVA radiation can penetrate deeper into the epidermis and dermis and produce reactive oxygen species that can pose damaging effects on proteins, lipids, and DNA structures (6). Therefore, in recent decades, researches for development of a sun protection formulation have been intensified (7). Either two mechanisms of chemical (i.e., absorption of the radiation) or physical (i.e., blocking of the radiation) are involved in sun protection effects of sunscreens (8). Their ability to protect the skin is explained by sun protection factor (SPF) unit (9). This term indicates the degree of skin protection against scorching rays of the sun. However, the skin permeation of the common synthetic sunscreen components such as oxybenzone, avobenzone ecamsule, and octocrylene may pose serious side effects, including allergic reactions, DNA damages, antiandrogenic effects, and development of cancer and other health issues (10–12). Therefore, many researches are focused to find a natural sunscreen that is expected to have fewer side effects (13). Due to protective effects of propolis on the skin, it can be considered as a good candidate for incorporation in skin-care cosmeceuticals (e.g., sunscreen) (14). Moreover, propolis exhibits potent anti-inflammatory effects, and therefore it is suitable for treatment of sunburns and other radiation-dependent skin problems (15). Simultaneously, by preserving the collagen contents of the skin, it can act as an anti-aging product (16). Furthermore, since propolis contains various flavonoids and antioxidants, it can protect the skin from UV rays (17). The sun protection effects of the propolis are mainly attributed to the presence of PFs that can demonstrate the potential for direct absorption of UV radiations (4). In addition, due to exertion of antioxidant properties, these flavonoids can eliminate UV-induced ROS and exhibit skin protection effects against sunlight. However, due to poor skin penetration, application of propolis for skin protection is limited (18). It is suggested that the issue can be resolved by development of an efficient nanoparticulate drug delivery system incorporating PFs (19–21). Poly-lactide-co-glycolide (PLGA), due to its biocompatibility, biodegradability, and low toxicity, is one of the widely studied polymers in fabrication of drug delivery systems (22). Moreover, by controlling the particle size and surface charge, their cargo can be released slowly over the period of several days (23). The aim of this study was to develop a sunscreen formulation containing PF-encapsulated PLGA nanoparticles. For this purpose, an optimized formulation of nanoparticles that exhibited proper physicochemical characteristics including particle size, polydispersity index (PdI), zeta potential, entrapment efficiency (EE%), and drug release behavior was achieved. The nanoparticles were incorporated to a sunscreen formulation and their sun protection effect was determined using in vitro method.