Crocin nano-chitosan-coated compound mitigates hippocampal blood-brain barrier disruption, anxiety, and cognitive deficits in chronic immobilization stress-induced rats

Stressful conditions can disrupt the central nervous system's normal homeostasis and physiological functions, resulting in blood-brain barrier malfunction, memory and learning impairment, anxiety, etc. Crocin is a long-investigated natural compound that has been documented to have anti-inflammation and neuroprotective effects, albeit it comes with some limitations such as low stability and bioavailability. Therefore, we aimed to overcome crocin's limitations by coating crocin with a nano-carrier (chitosan) in the chronic immobilization stress-induced rat model. Crocin was encapsulated into chitosan nanoparticles by a modified method. A total of 35 male Wistar rats were selected as our study subjects (220-250 g) which were randomly divided into 5 groups (control, stress, nanoparticle, crocin, and chitosan). Chronic immobilization stress was induced by placing rats for 2 h into a plastic bottle with specific measurements (for 14 consecutive days) to prevent animals from moving. To evaluate the memory and learning changes, we used the Barnes maze test and the Passive avoidance test followed by the evaluation of the N-methyl-D-aspartate |(NMDA) receptor subunits genes (GRIN1 and GRIN2A) expression. Anxiety levels were evaluated by elevated plus maze test. Furthermore, the changes in the expression of genes responsible for encoding the tight junction proteins of BBB including ZO1, CLDN5, and OCLN were assessed by RT-PCR. Compared to intact crocin, the administration of crocin nano-chitosan-coated compound resulted in significant improvement of specific memory and learning indicators as well as a significant reduction of anxiety levels in chronic immobilization stress-induced rats. Finally, we observed that treatment with the crocin nano-chitosan-coated compound can elevate the expression levels of the genes responsible for encoding NMDA receptor subunits, and the genes responsible for encoding the tight junction proteins of blood-brain barriers in the hippocampus.