Promoting Effect of (+)-Borneol on Alzheimer's Disease Treatment in APP Transgenic Zebrafish and Its Blood-Brain Barrier Permeation Mechanism.

( +)-Borneol (Bor) has been shown to enhance drug penetration across the blood-brain barrier (BBB); yet its mechanisms of action and adjuvant effects on Alzheimer's disease (AD) drugs remain insufficiently investigated. This study systematically explored the adjuvant effects of Bor and its underlying mechanisms by employing AB wild-type zebrafish and APP transgenic zebrafish models. Results demonstrated that Bor at concentrations of 0.05 mM or lower exhibited no toxicity toward AB wild-type zebrafish, whereas 0.01 and 0.05 mM Bor significantly increased the expression of green fluorescent protein (GFP) in the zebrafish brain. Genetic analyses revealed that Bor downregulated genes encoding tight junction proteins and P-glycoprotein (P-gp). Drug treatment experiments showed that Bor enhanced the efficacy of AD therapeutic agents, including Zhenbaopill (ZBP, a traditional medicinal preparation) and the synthetic drug 8e. Specifically, Bor ameliorated AD-related behavioral impairments, inhibited cerebral apoptosis, restored the expression of AD-associated genes, normalized the activities of acetylcholine (ACh)-related enzymes, and downregulated both the mRNA and protein levels of Claudin 5. In summary, Bor enhances BBB permeability by regulating the expression of genes encoding BBB-related proteins, thereby increasing the brain concentration and bioavailability of AD drugs with anticholinesterase activity. An appropriate dose of Bor may thus contribute to enhancing the therapeutic efficacy of AD drugs.