Protective effects of three kinds of borneol on different brain regions in acute cerebral ischemia/reperfusion model rats

Abstract

This study compared the ameliorating effects of L-borneol, natural borneol, and synthetic borneol on the injury of different brain regions in the rat model of acute phase of cerebral ischemia/reperfusion(I/R) for the first time, which provides a reference for guiding the rational application of borneol in the early treatment of ischemic stroke and has important academic and application values. Healthy specific pathogen-free(SPF)-grade SD male rats were randomly assigned into 13 groups: a sham-operation group, a model group, a Tween model group, a positive drug(nimodipine) group, and high-, medium-, and low-dose(0.2, 0.1, and 0.05 g·kg~(-1), respectively) groups of L-borneol, natural borneol, and synthetic borneol according to body weight. After 3 days of pre-administration, the rat model of I/R was established by suture-occluded method and confirmed by laser speckle imaging. The corresponding agents in different groups were then administered for 1 day. The body temperature was monitored regularly before pre-administration, days 1, 2, and 3 of pre-administration, 2 h after model awakening, and 1 d after model establishment. Neurological function was evaluated based on Zea-Longa score and modified neurological severity score(mNSS) 2 h and next day after awakening. The rats were anesthetized 30 min after the last administration, and blood was collected from the abdominal aorta. Enzyme-linked immunoassay assay(ELISA) was employed to determine the serum levels of tumor necrosis factor-alpha(TNF-α), interleukin-6(IL-6), IL-4, and transforming growth factor-beta1(TGF-β1). The brain tissues were stained with triphenyltetrazolium chloride(TTC) for the calculation of cerebral infarction rate, and hematoxylin-eosin(HE) staining was used for observing and semi-quantitatively evaluating the pathological damage in different brain regions. Immunohistochemistry was employed to detect the expression of ionized calcium binding adapter molecule 1(IBA1) in microglia. q-PCR was carried out to determine the mRNA levels of iNOS and arginase 1(Arg1), markers of polarization phenotype M1 and M2 in microglia. Compared with the sham-operation group, the model group and the Tween model group showed significantly elevated body temperature, Zea-Longa score, mNSS, and cerebral infarction rate, severely damaged cortex, hippocampus, and striatum, increased serum levels of IL-6 and TNF-α, and decreased serum levels of IL-4 and TGF-β1. The three borneol products had a tendency to reduce the body temperature of rats 1 day after modeling. Synthetic borneol at the doses of 0.2 and 0.05 g·kg~(-1), as well as L-borneol of 0.1 g·kg~(-1), significantly reduced Zea-Longa score and mNSS. The three borneol products at the dose of 0.2 g·kg~(-1) significantly reduced the cerebral infarction rate. L-borneol at the doses of 0.2 and 0.1 g·kg~(-1) and natural borneol at the dose of 0.1 g·kg~(-1) significantly reduced the pathological damage of the cortex. L-borneol and natural borneol at the dose of 0.1 g·kg~(-1) attenuated the pathological damage of hippocampus, and 0.2 g·kg~(-1) L-borneol attenuated the damage of striatum. The 0.2 g·kg~(-1) L-borneol and the three doses of natural borneol and synthetic borneol significantly reduced the serum level of TNF-α, and the 0.1 g·kg~(-1) synthetic borneol reduced the level of IL-6. L-borneol and synthetic borneol at the dose of 0.2 g·kg~(-1) significantly inhibited the activation of cortical microglia, and 0.2 g·kg~(-1) L-borneol up-regulated the expression of Arg1 and down-regulated the expression level of iNOS. In conclusion, the three borneol products may alleviate inflammation to ameliorate the pathological damage of brain regions of rats in the acute phase of I/R by inhibiting the activation of microglia and promoting the polarization of microglia from M1 type to M2 type. The protective effect on brain followed a trend of L-borneol > synthetic borneol > natural borneol. We suggest L-borneol the first choice for the treatment of I/R in the acute phase.