Topical delivery of artemether, encapsulated in niosome and proniosome carriers

Abstract

Artemisia annua is a Chinese herb discovered by Chinese scientists in 1971. Artemisinin was extracted from this herb and used as a Chinese medicine named Qinghaosu. Artemether (ARM) is a derivative from the artemisinin family and also the active ingredient in the herb Artemisia annua (Ansari et al., 2010:901; Ansari et al., 2015:2; White, 2008:330). Recently a new combination therapy acting as treatment against tuberculosis (TB) has been researched. Artemether and its artemisinin family have certain characteristics which gives these compounds the ability to act as treatment against the M. tuberculosis strain. During this combination therapy, artemether would represent the oxidant drug (Haynes, 2015:3; Miller et al., 201:2076). Infection rates caused by the bacterial species, M. tuberculosis, have increased significantly and cause a lot of deaths each year (Hershkovitz et al., 2008:1). Cutaneous tuberculosis (CTB) is an illness presenting with skin manifestations due to a main infection, generally caused by this bacterium strain, M. tuberculosis, therefore a person must have TB in order to have CTB (Van Zyl et al., 2015:629). The psychological effect of being infected with CTB (Dos Santos et al., 2014:219), along with the severe side effects of TB treatment medication, leads to prolonged treatment periods. The aim for CTB treatments, by means of the topical drug delivery of artemether in conjunction with current TB treatments, is to decrease the overall treatment period. The largest self-renewing organ of the human body is the skin, and the main function of this organ is to protect the body against the intrusion of any harmful external agents. The skin consists of three different layers, i.e. 1) epidermis, 2) dermis and 3) hypodermis, with the main physical barrier lying within the stratum corneum, which is the top layer of the epidermis responsible for the movement of water and electrolytes. The barrier properties of the skin makes the drug delivery of an active pharmaceutical ingredient (API) difficult (Baroni et al., 2012:257; Bolzinger et al., 2012:156; Feingold & Denda, 2012:263; Foldvari, 2000:417). The amount of research conducted on, as well as the execution of topical and transdermal drug delivery methods have increased over the last 50 years. This increased usage is due to the large improvements on the topical and transdermal drug delivery methods over other traditional delivery methods (Moss et al., 2012:166). During topical drug delivery, the drug penetrates the stratum corneum and then permeates into the different skin layers to a targeted site with minimum to no systemic absorption (Rahimpour & Hamishehkar, 2012:141). Successful permeation of an API across the skin is directly proportional to the physicochemical properties of the API (Hadgraft, 2001:291). According to Naik et al. (2000:319), an API should have an aqueous solubility larger than 1 mg/ml to deliver ideal results regarding transdermal drug delivery. The aqueous solubility of artemether is 0.46 mg/ml (Human Metabolome database, 2013:2) and therefore not ideal for topical drug delivery, but might be improved when encapsulated in a vesicle carrier system. Vesicular drug delivery systems function as carrier systems during the topical deliverance of drugs to the targeted sites. Niosomes are non-lipoidal biocarriers consisting of non-ionic surfactants and lipids, therefore these vesicles can encapsulate both lipophilic and hydrophilic drugs. Using niosomes during topical delivery has many advantages, i.e. 1) controlled release of the drug, 2) better drug stability and 3) enhancing the skin permeation of a drug (Jain et al., 2014:1-2; Kamboj et al., 2013:125; Shilakari et al., 2013:77). The aim of this study was to determine if the topical delivery of artemether was possible after being encapsulated in a vesicle. In order to analyse artemether, a high performance liquid chromatography (HPLC) method was developed. Three different niosome dispersions, (1%, 2% and 3%), each encapsulating artemether, were formulated and then characterised to determine the best dispersion for further analysis. The 3% niosome and 3% proniosome vesicle dispersions were chosen, based upon their overall characteristics, i.e. viscosity, pH, entrapment efficiency, zeta-potential, particle size and polydispersity index (PdI). The morphology of the 3% niosome and proniosome placebo dispersions were determined using transmission electron microscopy (TEM). The phosphate buffer solution (PBS; pH 7.4) and water solubility of artemether was determined as 0.09 ± 0.003 mg/ml and 0.11 ± 0.002 mg/ml, respectively. The octanol-water partition coefficient (log P) and the octanol-buffer distribution coefficient (log D) of artemether was 2.26 ± 0.117 and 2.35 ± 0.067, respectively. Hence, it can be said that artemether is more lipophilic in nature and not water-soluble. Membrane and skin diffusion studies were executed with both artemether entrapped vesicle dispersions. During the membrane release studies it was acquired that both vesicles do release the entrapped artemether. The results of the skin diffusion studies revealed low artemether concentrations in some of the epidermis-dermis samples, with no artemether present in the stratum corneum-epidermis and the receptor phase; those concentrations that were present gave an average concentration lower than the limit of quantification (LOQ) of artemether. These results indicated that the stratum corneum-epidermis and epidermis-dermis results were not quantifiable, but the fact that artemether concentrations were acquired in the epidermisdermis indicates that targeted drug delivery occurred (Karim et al., 2010:374). The topical delivery of artemether can be improved by considering a different carrier or by increasing the concentration of artemether added to the formulation (Herkenne et al., 2008). The toxicity determination of artemether, the empty niosomes and the artemether loaded niosomes were determined by means of the lactase dehydrogenase (LDH) assay. During the LDH assay, it was determined that the unloaded vesicle dispersion was not cytotoxic, while the loaded vesicles and the API artemether were strongly cytotoxic to the Cultured Human Keratinocyte (HaCaT) cell cultures from the concentrations 300 μg/ml. Unfortunately in vivo and in vitro toxicity analysis cannot be compared due to other influencing factors present during in vivo exposure (Lόpez-Garcίa et al., 2014:45; Yoon et al., 2012:634). The characteristics of the vesicles indicated they were optimal for topical drug delivery and during this study, it was observed that the vesicles did ensure targeted delivery of artemether into the epidermis-dermis. The cytotoxicity of artemether using the LDH assay indicated artemether and the loaded niosomes were cytotoxic to the cell cultures, while the empty niosomes were not cytotoxic. These cytotoxicity results unfortunately cannot be compared to in vivo circumstances such as topical drug delivery. In conclusion, it can be said that the topical delivery of artemether was reached. Artemether was identified (although unquantifiable) in the target area (epidermis-dermis), but the bioavailability of artemether in the epidermis-dermis can be improved through various methods, such as adding permeation enhancers to the formulation (Herkenne et al., 2008:8; Morrow et al., 2007:39), changing the vesicle system, or by increasing the concentration artemether added to the formulation (Herkenne et al., 2008:87)