Hydrogen-rich saline alleviates early brain injury through inhibition of necroptosis and neuroinflammation via the ROS/HO-1 signaling pathway after traumatic brain injury

Abstract

Traumatic brain injury (TBI) has been recognized as a serious public health issue and a key contributor to disability and death, with a huge economic burden worldwide. Hydrogen, which is a slight and specific cytotoxic oxygen radical scavenger, has been demonstrated to ameliorate early brain injury (EBI) through reactive oxygen species (ROS), oxidative stress injury, apoptosis and necroptosis. Necroptosis refers to a type of programmed cell death process that has a vital function in neuronal cell death following TBI. The specific function of necroptosis in hydrogen-mediated neuroprotection after TBI, however, has yet to be determined. The present study aimed to examine the neuroprotective effects and possible molecular basis that underly hydrogen-rich saline in TBI-stimulated EBI by examining neural necroptosis in the C57BL/6 mouse model. The brain water content, neurological score, neuroinflammatory cytokines (NF-κΒ, TNF-α, IL-6 and IL-1β) and ROS were evaluated using flow cytometry. Malondialdehyde, superoxide dismutase (SOD) and glutathione (GSH) levels were evaluated using a biochemical kit. Receptor-interacting protein kinase (RIP)1, RIP3, Nrf2 and Heme oxygenase-1 (HO-1) were evaluated using western blotting. mRNA of Nrf2 and HO-1 were evaluated using quantitative PCR. Neuronal death was evaluated by TUNEL staining. The outcomes illustrated that hydrogen-rich saline treatment considerably enhanced the neurological score, increased neuronal survival, decreased the levels of serum MDA and brain ROS, increased the levels of serum GSH and SOD. In addition the protein expression levels of RIP1 and RIP3 and the cytokines NF-κB, TNF-α, IL-1β and IL-6 were downregulated compared with the TBI group, which demonstrated that hydrogen-rich saline-induced inhibition of necroptosis and neuroinflammation ameliorated neuronal death following TBI. The neuroprotective capacity of hydrogen-rich saline was demonstrated to be partly dependent on the ROS/heme oxygenase-1 signaling pathway. Taken together, the findings of the present study indicated that hydrogen-rich saline enhanced neurological outcomes in mice and minimized neuronal death by inducing protective effects against neural necroptosis as well as neuroinflammation.

Keywords: early brain injury; hydrogen-rich saline; necroptosis; neuroinflammation; traumatic brain injury.

Figure 1

HS alleviates neurological impairment and brain edema after TBI. (A) Neurological scores of mice in the sham, TBI and TBI + HS cohorts 72 h after TBI (median and interquartile range; n=10). (B) Brain water content in the three cohorts. Brain water content decreased significantly after HS treatment (mean ± SEM; n=5). TBI, traumatic brain injury; HS, hydrogen-rich saline.

Figure 2

HS alleviates neuronal necroptosis after TBI. (A) TUNEL assay demonstrated that HS alleviated neuronal necroptosis. (B) Expression of RIP1 and RIP3 in the brain cortex of mice following TBI was evaluated via western blotting. Quantification of (C) RIP1 and (D) RIP3 protein levels in the brain cortex relative to β-actin loading control, indicating that HS suppressed RIP1 and RIP3 expression after TBI in mice (mean ± SEM; n=6). TBI, traumatic brain injury; HS, hydrogen-rich saline; RIP, receptor-interacting protein kinase.

Figure 3

HS alleviates neuroinflammation after TBI. HS significantly decreased the levels of hippocampal (A) TNF-α, (B) IL-1β, (C) IL-6 and (D) NF-κB at 72 h after TBI (mean ± SEM; n=6). TBI, traumatic brain injury; HS, hydrogen-rich saline.

Figure 4

HS inhibits TBI-induced oxidative stress and decreases ROS levels. HS significantly (A) decreased the expression levels of serum MDA, increased the expression levels of (B) serum SOD and (C) serum GSH, and (D) decreased the levels of brain tissue ROS after TBI (mean ± SEM; n=6). TBI, traumatic brain injury; HS, hydrogen-rich saline; MDA, malondialdehyde; SOD, superoxide dismutase; GSH, glutathione; ROS, reactive oxygen species.

Figure 5

HS regulates necroptosis via the ROS/HO-1 signaling pathway after TBI. (A) HO-1 and (B) Nrf2 mRNA levels in the brain of TBI mice were quantified via reverse transcription-quantitative PCR. (C) Expression of HO-1 and Nrf2 in the brain cortex of mice following TBI was assessed via western blotting. Quantification of (D) HO-1 and (E) Nrf2 protein levels in the brain cortex relative to β-actin loading control. HS increased HO-1 and Nrf2 expression following TBI in mice. (mean ± SEM; n=6). TBI, traumatic brain injury; HS, hydrogen-rich saline; HO-1, heme oxygenase-1; Nrf2, nuclear factor erythroid 2-related factor 2.