Saikosaponin a protects TBI rats after controlled cortical impact and the underlying mechanism

Abstract

The inflammatory response plays a significant role in neuronal cell death and functional deficits after Traumatic brain injury (TBI). Importantly, anti-inflammatory agents have neuroprotective effects. To date, however, no studies have investigated the neuroprotective effects of Saikosaponin a (SSa) after TBI. In the present study, rats with controlled cortical impact (CCI) were used to investigate the neuroprotective effects of SSa. The results showed that SSa reduced body weight loss, improved neurological functions andcognition, and reduced brain edema and blood brain barrier permeability after CCI. Moreover, SSa inhibited aquaporin-4 (AQP-4), matrix metalloprotein-9 (MMP-9), mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (c-JNK), tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). The reduction in the loss of occludin mediated by SSa may partially account for its neuroprotective effects. Together, our results suggest that SSa appears to counteract the inflammatory response and neurological function deficits after TBI and possibly via an anti-inflammatory response and inhibition of the MAPK signaling pathway.

Keywords: Saikosaponin a; controlled cortical impact; inflammation; mitogen-activated protein kinase; neuroprotection.

Figure 1

The Structure of SSa.

Figure 2

Effects of SSa on the body weight loss and NSS after 7 days of CCI. Vehicle or SSa was injected intravenously 15 min after CCI, up to 3 days. Data were presented as mean ± SEM (n=8). NSS: neurological severity scores; CCI: Controlled cortical impact; SSa: Saikosaponin a. (#P<0.01 vs. sham-operated rats; &P<0.05 vs. sham-operated rats, *P<0.05, **P<0.01 vs. vehicle-treated rats).

Figure 3

Effects of SSa on the percent of water content (A) and the contents of EBD (B) in injured hemisphere after CCI. Vehicle or SSa was injected intravenously 15 min after CCI, up to 3 days. (A) water content (n=8); (B) EBD content (n=8). Data were presented as mean ± SEM. CCI: Controlled cortical impact; EBD: Evan’s blue dye. (##P<0.001 vs. sham-operated rats; &P<0.05 vs. sham-operated rats, *P<0.05, **P<0.01 vs. vehicle-treated rats).

Figure 4

Effects of SSa on the levels of IL-6 and TNF-α in injured hemisphere after CCI. Vehicle or SSa was injected intravenously 15 min after CCI, up to 3 days. A. IL-6 level; B. TNF-α level. Data were presented as mean ± SEM (n=10). (##P<0.001 vs. sham-operated rats; &P<0.05 vs. sham-operated rats, *P<0.05, **P<0.01 vs. vehicle-treated rats).

Figure 5

Effects of SSa on the levels AQP-4, MMP-9, occludin, p38 MAPK and c-JNK protein in injured hemisphere after CCI. SSa showed a significant change compared to the vehicle-treated rats. The level was measured by Western blot analysis using actin as a standard control. Data were presented as mean ± SEM (n=10). (##P<0.001 vs. sham-operated rats; &P<0.05 vs. sham-operated rats, **P<0.01 vs. vehicle-treated rats).

Figure 6

Long-term beneficial effects of SSa. Vehicle or SSa was injected intravenously 15 min after CCI, up to 3 days. The Morris water maze test was performed before and after CCI. Results are expressed as a ratio of swimming time at each time point against the pre-injured value. The results are the mean ± SEM of 8 rats. (##P<0.001 vs. sham-operated rats; &P<0.05 vs. sham-operated rats, **P<0.01 vs. vehicle-treated rats).