Formulation of water-in-oil nanoemulsion containing roselle extract for controlled delivery

Abstract

The anthocyanin-rich roselle extract has the potential to inhibit lung cancer. However, the compounds demonstrate poor bioavailability and low stability in a biological application. Therefore, the present study proposed the formulation of a roselle extract containing W/O nanoemulsion (NE) as a nanocarrier for pulmonary delivery. This study utilized an integrated low and high energy methods of ultrasonication, Ultra-homogenizer, and hot temperature inversion methods to prepare the w/o roselle extract. Composition of the stable w/o formulation comprised roselle extract (0.04 w/w%), sodium chloride solution (3.0 w/w%), medium-chain triglyceride (81.93 w/w%), a ratio of surfactants Tween 80:Span 80 (15 w/w%) at 22.5:77.5, which gave a HLB of 6.7. Next, the corresponding physicochemical and morphological characterizations showed the NE has a mean droplet size of 298 ± 9 nm, a zeta potential of -49± 0.05 mV, and a polydispersity index (PDI) of 0.61 ± 0.009. Most importantly, the produced droplets were spherically shaped without any aggregation. The NE’s pH was found to be in the range of 6.1-5.8 after 30 days of observation, agreeing well with the recommended range for safe delivery into the human lung. The low conductivity (0.009 mS/cm) of the roselle extract w/o NE verified its W/O characteristic, while the rheological test proved its shear-thinning (pseudoplastic) behaviour. The W/O NE remained stable without phase separation in the accelerated stability tests (centrifugation test, freeze-thaw cycle) and the long-term storage stability test at 4°C, 25°C, and 35°C, done at 60 days. The in vitro release of the entrapped roselle extract at different pH buffer solutions showed that their release at pH 6.5 was 45.19%. The percentage release seen here was higher than at pH 7.4 (40.2%). Pertinently, the two release kinetics behaviour adhered to the Korsmeyer-Peppas kinetic mechanism (R2 = 0.9702 for pH 7.4 and R2 = 0.9722 for pH 6.5). The Korsmeyer–Peppas Model of the roselle extract w/o NE gave a release exponent (n) of 0.77 at pH 6.5 and 0.49 at pH 7.4. The study results verified that the release pattern of the extracts at both pH conditions followed non-Fickian diffusion mechanism. This meant that more than one type of release phenomenon might be involved in the case of the roselle extract, in which diffusion along with erosion through the simulated lung fluid could be the mechanism of release. In conclusion, the present study collectively showed the successful development of the W/O nanoemulsion containing the roselle extract. Thus, the results support its potential as a nanocarrier for pulmonary delivery application for lung cancer treatment.