Thymoquinone Lipid Nanoparticles Cut the Gordian Knots of Depression via Neuroprotective BDNF and Downregulation of Neuro-inflammatory NF-ΚB, IL-6, and TNF-α in LPS Treated Rats

Background: In over 300 million clinical cases, antidepressant drugs seem to provide only symptomatic relief and limited protection in life-threatening depressive events. Objectives: To compare neuronal-signaling mechanism and neuroprotective roles of Thymoquinone (TQ) suspension and its SLN (TQSLN) against standard antidepressant drug fluoxetine. Methods: This research investigated in-silico docking at NF-KB p50 active site, CLSM based gut permeation, screening of antidepressant activities and neurosignaling pathways involved. Results: As compared to fluoxetine, TQ reporteda significantly better docking score (-6.83 v/s -6.22) and a better lower free binding energy of (-34.715 Kcal/mol v/s -28.537 Kcal/mol). While poorly oral bioavailable and P-gp substrate TQ reported approximately 250% higher gut permeation if delivered as TQSLN formulation. In locomotor studies, as compared to TQS, TQSLN favored more prominent (p< 0.010) elevation in average time, horizontalactivity, average-velocity, and total-movement with reduced rest time LPS treated groups. However, in the tail suspension test, TQSLN significantly reduced immobility time (p<0.010). Similarly, In the modified force swimming test, TQSLN also significantly reduced immobility time (p<0.010), but swimming time (p<0.010) and climbing time (p<0.050) were significantly elevated. Subsequently, TQSLN reported significantly elevated neuroprotective BDNF (p<0.010) as well as hippocampal 5HT/TRP; accompanied with reduced levels of hippocampal inflammatory markers TNF-α (p<0.001) and IL-6 (p<0.010) as well as lower kynurenine and tryptophan ratio (KYN/TRP). Similarly, the hippocampal CA1 region further revealed TQSL more predominantly attenuated NF-kB nuclear translocation in the brain. Conclusion: Despite the poor bioavailability of TQ, TQSLN potentially attenuates neuroinflammatory transmitters and favors BDNF to modulate depressive neurobehavioral states.