Traumatic brain injury (TBI) is a major health concern worldwide and is classified based on severity into mild, moderate, and severe. The mechanical injury in TBI leads to a metabolic and ionic imbalance, which eventually leads to excessive production of reactive oxygen species (ROS) and a state of oxidative stress. To date, no drug has been approved by the food and drug administration (FDA) for the treatment of TBI. Nevertheless, it is thought that targeting the pathology mechanisms would alleviate the consequences of TBI. For that purpose, antioxidants have been considered as treatment options in TBI and were shown to have a neuroprotective effect. In this review, we will discuss oxidative stress in TBI, the history of antioxidant utilization in the treatment of TBI, and we will focus on two novel antioxidants, mitoquinone (MitoQ) and edaravone. MitoQ can cross the blood brain barrier and cellular membranes to accumulate in the mitochondria and is thought to activate the Nrf2/ARE pathway leading to an increase in the expression of antioxidant enzymes. Edaravone is a free radical scavenger that leads to the mitigation of damage resulting from oxidative stress with a possible association to the activation of the Nrf2/ARE pathway as well.

Traumatic brain injury (TBI) is a heterogeneous disease in its origin, neuropathology, and prognosis, with no FDA-approved treatments. The pathology of TBI is complicated and not sufficiently understood, which is the reason why more than 30 clinical trials in the past three decades turned out unsuccessful in phase III. The multifaceted pathophysiology of TBI involves a cascade of metabolic and molecular events including inflammation, oxidative stress, excitotoxicity, and mitochondrial dysfunction. In this study, an open head TBI mouse model, induced by controlled cortical impact (CCI), was used to investigate the chronic protective effects of mitoquinone (MitoQ) administration 30 days post-injury. Neurological functions were assessed with the Garcia neuroscore, pole climbing, grip strength, and adhesive removal tests, whereas cognitive and behavioral functions were assessed using the object recognition, Morris water maze, and forced swim tests. As for molecular effects, immunofluorescence staining was conducted to investigate microgliosis, astrocytosis, neuronal cell count, and axonal integrity. The results show that MitoQ enhanced neurological and cognitive functions 30 days post-injury. MitoQ also decreased the activation of astrocytes and microglia, which was accompanied by improved axonal integrity and neuronal cell count in the cortex. Therefore, we conclude that MitoQ has neuroprotective effects in a moderate open head CCI mouse model by decreasing oxidative stress, neuroinflammation, and axonal injury.

Mild traumatic brain injury (mTBI) or concussion accounts for the bulk of all head injuries and represents a major health concern. Although an mTBI event may not manifest in neurobehavioral impairment, repeated injuries, known as repeated mTBI (rmTBI), can result in a cumulative effect that may progress to long-term cognitive and functional deficits. To date, there is no FDA-approved drug for TBI in general and rmTBI in particular. In previous studies, we have demonstrated the neuroprotective role of mitoquinone (MitoQ), a mitochondrial antioxidant, in an open head injury model and a model of repeated mild TBI (rmTBI) at a chronic time point (30 days). In this work, we set out to assess the neuroprotective potential of MitoQ at acute (3 days) and subacute time points (7 days) post-injury in a controlled cortical impact model of rmTBI. C57BL/6 male mice were injected intraperitoneally with MitoQ (5 mg/kg) one hour after the first mTBI, and three days after the first injury in both the 3-day and 7-day MitoQ + rmTBI subgroups, with an additional injection four days after the second injection in the 7-day group. Cognitive function was evaluated using the Morris water maze (MWM) while gross and fine motor functions were evaluated by the pole climbing, grip strength, and ladder rung tests. Dihydroethidium (DHE) staining was performed to evaluate oxidative stress while qRT-PCR was used to measure the gene expression of different antioxidant enzymes. Also, immunofluorescence staining was performed on brain tissue to assess the degree of microgliosis and astrocytosis. Our results showed that MitoQ conferred significant protection on days 3 and 7 post-injury against fine motor function impairment induced by rmTBI. Moreover, MitoQ enhanced cognitive function and reduced astrogliosis, microgliosis, and levels of oxidative stress on day 7 post-injury. However, antioxidant gene expression generally remained unaffected. In light of our results, MitoQ administration may be considered a preventive approach that helps to alleviate the neurological manifestations associated with rmTBI early before symptoms progress to long-term deficits.