Honokiol attenuates high glucose-induced peripheral neuropathy via inhibiting ferroptosis and activating AMPK/SIRT1/PGC-1α pathway in Schwann cells.

Schwann cells injury induced by high glucose (HG) contributes to the development of diabetic peripheral neuropathy (DPN). Honokiol has been reported to regulate glucose metabolism, however, its effect on DPN and the precise molecular mechanisms remain unclear. This study aimed to investigate the role of AMPK/SIRT1/PGC-1α axis in the protective effects of honokiol on DPN. The biochemical assay and JC-1 staining results demonstrated that honokiol reduced HG-induced oxidative stress and ferroptosis as well as mitochondrial dysfunction in Schwann cells. RT-qPCR and western blotting were utilized to investigate the mechanism of action of honokiol, and the results showed that HG-induced inhibition of AMPK/SIRT1/PGC-1α axis and changes of downstream gene expression profile were restored by honokiol. Moreover, silencing of Sirt1 by siRNA delivery markedly diminished the changes of gene expression profile induced by honokiol in HG-induced Schwann cells. More importantly, we found that administration of honokiol remarkably attenuated DPN via improving sciatic nerve conduction velocity and increasing thermal and mechanical sensitivity in streptozotocin-induced diabetic rats. Collectively, these results demonstrate that honokiol can attenuate HG-induced Schwann cells injury and peripheral nerve dysfunction, suggesting a novel potential strategy for treatment of DPN.

[Borneol is an inducer of rat hepatic CYP2D activity in vivo].

Borneol is a traditional Chinese medicine. In the past few years, many studies showed that borneol can improve the bioavailability of other drugs, promoting drugs to cross the blood-brain barrier, so the potential drug interactions between borneol and other medicines have attracted great attention, but the influence of borneol to CYP450 and its isoforms are rarely reported. In this research, male Wistar rats were orally administered by borneol for 7 days, then the mRNA and protein expression and the activities of CYP2D were detected, we also compared the pharmacokinetic parameters of CYP2D's specific substrate between control group and borneol group. The results show that borneol (33, 100 and 300 mg x kg(-1) x d(-1)) have no significant effect on CYP2D, while the activites of CYP2D increased 1.71, 1.97 and 2.89 times comparing to the control group. At the same time, borneol (300 mg x kg(-1) x d(-1)) caused the C(max) decreased 10.6% (P > 0.05), AUC(0-∞) decreased 27.5% (P < 0.01), CL/F increased 41.1% (P < 0.01), V(z)/F increased 23.1% (P > 0.05) of dextromethorphan. Our data provided that borneol speed up dextromethorphan's elimination in vivo. Since the activity of CYP2D can be induced by borneol, the metabolic interactions might happen when borneol and the substrate drug CYP2D are used together.