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.