Quality by design-assisted development of an intranasal Shikonin-loaded Mucoadhesive microemulsion for enhanced brain delivery: optimization, characterization, and Pharmacodynamic evaluation in a schizophrenia model.

Abstract

The present study aimed to develop and optimize a shikonin-loaded mucoadhesive microemulsion for intranasal delivery with the objective of improving nasal residence and facilitating central drug delivery. Shikonin is a naturally occurring naphthoquinone derivative with reported anti-inflammatory and neuroprotective properties. A Quality by Design (QbD)-based strategy was employed to establish a robust formulation with defined critical quality attributes and improved nasal delivery characteristics. Solubility screening identified castor oil, Tween 80, and propylene glycol as the most suitable oil, surfactant, and co-surfactant, respectively. Pseudoternary phase diagram studies facilitated the selection of an optimal microemulsion region, and formulation optimization was performed using a Box-Behnken design by evaluating the effects of oil concentration, Smix concentration, and sonication time on critical quality attributes. The optimized formulation consisted of 10% oil, 30% Smix, and 10 min sonication time, producing nanosized droplets with a particle size below 100 nm, a polydispersity index below 0.30, a positive zeta potential of approximately +30 mV, and entrapment efficiency exceeding 85%. Chitosan was incorporated as a mucoadhesive polymer to increase formulation viscosity and interaction with the nasal mucosa, thereby promoting prolonged nasal residence and potentially facilitating drug absorption. The resulting formulation exhibited markedly increased viscosity and mucoadhesive strength, confirming improved nasal retention. Transmission electron microscopy confirmed the formation of uniformly distributed spherical nanodroplets. The optimized shikonin-loaded mucoadhesive microemulsion exhibited significantly improved in vitro drug release (87.3 ± 1.25% at 8 h) compared with the plain shikonin solution (69.2 ± 1.63%). Ex vivo permeation studies across sheep nasal mucosa demonstrated superior permeation from shikonin-loaded mucoadhesive microemulsion (91.2 ± 0.41%) relative to the drug solution (73.27 ± 0.14%), accompanied by higher steady-state flux and apparent permeability coefficient values. In ketamine-induced schizophrenia-like behavioral model rats, intranasal shikonin-loaded mucoadhesive microemulsion significantly reduced hyperlocomotion, improved motor coordination, and attenuated cataleptic behavior relative to the disease control group. Orally administered chlorpromazine was included as a pharmacological reference treatment; however, the findings were not interpreted as evidence of route-equivalent or therapeutic equivalence between the two treatments. Histopathological analyses of cortical and hippocampal tissues revealed preservation of neuronal architecture and attenuation of ketamine-associated tissue alterations. Collectively, these findings provide preliminary evidence supporting the potential of the optimized intranasal shikonin-loaded mucoadhesive microemulsion for central delivery and modulation of schizophrenia-like behavioral abnormalities. However, the formulation was evaluated at laboratory scale, and pilot-scale/large-scale manufacturing feasibility and scale-up validation remain to be established before further translational development.