Abstract
Thymoquinone (TQ) is a potent phytoconstituent from Nigella sativa and well recognized for its neuroactivity via antioxidant mechanisms, but its higher lipophilicity and plasma protein binding lowers its bioavailability negating any appreciable clinical outcome, thus losing the possibility to form any conventional dosage form. TQ's brain targeted drug delivery can result into an increased efficacy and bioavailability, thus, in a novel attempt, we aim to formulate brain targeted Polysorbate-80 coated thymoquinone PLGA nanoparticles (P-80-TQN) and evaluate their activity towards Alzheimer's disease.
The modified single-emulsion solvent-evaporation technique was employed to formulate the TQN and further coated by Polysorbate-80 to obtain brain targeted P-80-TQN. The effectiveness of TQ released from P-80-TQN was evaluated in Alzheimer's (AD), biochemically by Super-Oxide Dismutase (SOD) enzymatic assay and behaviorally by Despair Test in Streptozotocin-(STZ)-induced Alzheimer's mice models at 5 mg/kg TQ-equivalent dose. AD markers: β-amyloid tangles were validated through histopathology of the brain's hippocampal tissues from euthanized mice.
A Stable and homogenous targeted P-80-TQN (226.2 nm, ζ = −45.6 mV) formulation was prepared and characterized physiochemically and spectrally. It significantly reduced the IT (39.45 ± 3.32 s), and increased SOD functioning (8.33 ± 2.61 units/mg) after treating mice for 28 days at 5 mg/kg equivalent P-80-TQN. An invitro biphasic cumulative release of TQ (59.10 ± 2.10) from P-80-TQN was observed over 24 h, whereas invivo TQ release in brain from P-80-TQN was observed and explained in terms of AUC (0–600mins) and Cmax which were obtained 4.5 and 4.3 times respectively and Tmax was 3 times faster than normal TQ. A reduced and solvated protein aggregates (<30 μm) were observed in the histopathological study proving the effectiveness of P-80-TQN towards AD. Hypotheses was put forth, explaining the proposed mechanism of P-80-TQN entry in brain via endocytosis, STZ mechanism in inducing Alzheimer's Disease, and finally TQ mechanism towards subduing Oxidative stress. TQ in P-80-TQN form rectified the increased SOD levels, improved cognitive and behavioral dysfunctions in AD affected mice.
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