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Traumatic brain injury (TBI) results in the production of peroxynitrite (PN), leading to oxidative damage of lipids and protein. PN-mediated lipid peroxidation (LP) results in production of reactive aldehydes 4-hydroxynonenal (4-HNE) and acrolein. The goal of these studies was to explore the hypothesis that interrupting secondary oxidative damage following a TBI via phenelzine (PZ), analdehyde scavenger, would protect against LP-mediated mitochondrial and neuronal damage. Male Sprague-Dawley rats received a severe (2.2 mm) controlled cortical impact (CCI)-TBI. PZ was administered subcutaneously (s.c.) at 15 min (10 mg/kg) and 12 h (5 mg/kg) post-injury and for the therapeutic window/delay study, PZ was administered at 1 h (10 mg/kg) and 24 h (5 mg/kg). Mitochondrial and cellular protein samples were obtained at 24 and 72 h post-injury (hpi). Administration of PZ significantly improved mitochondrial respiration at 24 and 72 h compared with vehicle-treated animals. These results demonstrate that PZ administration preserves mitochondrial bioenergetics at 24 h and that this protection is maintained out to 72 hpi. Additionally, delaying the administration still elicited significant protective effects. PZ administration also improved mitochondrial Ca(2+) buffering (CB) capacity and mitochondrial membrane potential parameters compared with vehicle-treated animals at 24 h. Although PZ treatment attenuated aldehyde accumulation post-injury, the effects were insignificant. The amount of α-spectrin breakdown in cortical tissue was reduced by PZ administration at 24 h, but not at 72 hpi compared with vehicle-treated animals. In conclusion, these results indicate that acute PZ treatment successfully attenuates LP-mediated oxidative damage eliciting multiple neuroprotective effects following TBI.

Lipid peroxidation (LP) is a key contributor to the pathophysiology of traumatic brain injury (TBI). Traditional antioxidant therapies are intended to scavenge the free radicals responsible for either initiation or propagation of LP. A more recently explored approach involves scavenging the terminal LP breakdown products that are highly reactive and neurotoxic carbonyl compounds, 4-hydroxynonenal (4-HNE) and acrolein (ACR), to prevent their covalent modification and rendering of cellular proteins nonfunctional leading to loss of ionic homeostasis, mitochondrial failure, and subsequent neuronal death. Phenelzine (PZ) is a U.S. Food and Drug Administration–approved monoamine oxidase (MAO) inhibitor (MAO-I) used for treatment of refractory depression that possesses a hydrazine functional group recently discovered by other investigators to scavenge reactive carbonyls. We hypothesized that PZ will protect mitochondrial function and reduce markers of oxidative damage by scavenging LP-derived aldehydes. In a first set of in vitro studies, we found that exogenous application of 4-HNE or ACR significantly reduced respiratory function and increased markers of oxidative damage (p

Traumatic brain injury (TBI) results in mitochondrial dysfunction and induction of lipid peroxidation (LP). Lipid peroxidation-derived neurotoxic aldehydes such as 4-HNE and acrolein bind to mitochondrial proteins, inducing additional oxidative damage and further exacerbating mitochondrial dysfunction and LP. Mitochondria are heterogeneous, consisting of both synaptic and non-synaptic populations, with synaptic mitochondria being more vulnerable to injury-dependent consequences. The goal of these studies was to explore the hypothesis that interrupting secondary oxidative damage following TBI using phenelzine (PZ), an aldehyde scavenger, would preferentially protect synaptic mitochondria against LP-mediated damage in a dose- and time-dependent manner. Male Sprague-Dawley rats received a severe (2.2 mm) controlled cortical impact (CCI)-TBI. PZ (3–30 mg/kg) was administered subcutaneously (subQ) at different times post-injury. We found PZ treatment preserves both synaptic and non-synaptic mitochondrial bioenergetics at 24 h and that this protection is partially maintained out to 72 h post-injury using various dosing regimens. The results from these studies indicate that the therapeutic window for the first dose of PZ is likely within the first hour after injury, and the window for administration of the second dose seems to fall between 12 and 24 h. Administration of PZ was able to significantly improve mitochondrial respiration compared to vehicle-treated animals across various states of respiration for both the non-synaptic and synaptic mitochondria. The synaptic mitochondria appear to respond more robustly to PZ treatment than the non-synaptic, and further experimentation will need to be done to further understand these effects in the context of TBI.

Reactive oxygen species-induced oxidative damage remains an extensively validated secondary injury mechanism in traumatic brain injury (TBI) as demonstrated by the efficacy of various pharmacological antioxidants agents in decreasing post-traumatic free radical-induced lipid peroxidation (LP) and protein oxidative damage in preclinical TBI models. Based upon strong preclinical efficacy results, two antioxidant agents, the superoxide radical scavenger polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) and the 21-aminosteroid LP inhibitor tirilazad, which inhibits lipid peroxidation, (LP) were evaluated in large phase III trials in moderately- and severely-injured TBI patients. Both failed to improve 6 month survival and neurological recovery. However, in the case of tirilazad, a post hoc analysis revealed that the drug significantly improved survival of male TBI patients who exhibited traumatic subarachnoid hemorrhage (tSAH) that occurs in half of severe TBIs. In addition to reviewing the clinical trial results with PEG-SOD and tirilazad, newer antioxidant approaches which appear to improve neuroprotective efficacy and provide a longer therapeutic window in rodent TBI models will be presented. The first approach involves pharmacological enhancement of the multi-mechanistic Nrf2-antioxidant response element (ARE) pathway. The second involves scavenging of the neurotoxic LP-derived carbonyl compounds 4-hydroxynonenal (4-HNE) and acrolein which are highly damaging to neural protein and stimulate additional free radical generation. A third approach combines mechanistically complimentary antioxidants to interrupt post-TBI oxidative neurodegeneration at multiple points in the secondary injury cascade. These newer strategies appear to decrease variability in the neuroprotective effect which should improve the feasibility of achieving successful translation of antioxidant therapy to TBI patients.

Traumatic brain injury (TBI) results in mitochondrial dysfunction and induction of lipid peroxidation (LP). Lipid peroxidation-derived neurotoxic aldehydes such as 4-HNE and acrolein bind to mitochondrial proteins, inducing additional oxidative damage and further exacerbating mitochondrial dysfunction and LP. Mitochondria are heterogeneous, consisting of both synaptic and non-synaptic populations. Synaptic mitochondria are reported to be more vulnerable to injury; however, this is the first study to characterize the temporal profile of synaptic and non-synaptic mitochondria following TBI, including investigation of respiratory dysfunction and oxidative damage to mitochondrial proteins between 3 and 120 h following injury. These results indicate that synaptic mitochondria are indeed the more vulnerable population, showing both more rapid and severe impairments than non-synaptic mitochondria. By 24 h, synaptic respiration is significantly impaired compared to synaptic sham, whereas non-synaptic respiration does not decline significantly until 48 h. Decreases in respiration are associated with increases in oxidative damage to synaptic and non-synaptic mitochondrial proteins at 48 h and 72 h, respectively. These results indicate that the therapeutic window for mitochondria-targeted pharmacological neuroprotectants to prevent respiratory dysfunction is shorter for the more vulnerable synaptic mitochondria than for the non-synaptic population.

Currently, there are no Food and Drug Administration (FDA)-approved pharmacotherapies for the treatment of those with traumatic brain injury (TBI). As central mediators of the secondary injury cascade, mitochondria are promising therapeutic targets for prevention of cellular death and dysfunction after TBI. One of the most promising and extensively studied mitochondrial targeted TBI therapies is inhibition of the mitochondrial permeability transition pore (mPTP) by the FDA-approved drug, cyclosporine A (CsA). A number of studies have evaluated the effects of CsA on total brain mitochondria after TBI; however, no study has investigated the effects of CsA on isolated synaptic and non-synaptic mitochondria. Synaptic mitochondria are considered essential for proper neurotransmission and synaptic plasticity, and their dysfunction has been implicated in neurodegeneration. Synaptic and non-synaptic mitochondria have heterogeneous characteristics, but their heterogeneity can be masked in total mitochondrial (synaptic and non-synaptic) preparations. Therefore, it is essential that mitochondria targeted pharmacotherapies, such as CsA, be evaluated in both populations. This is the first study to examine the effects of CsA on isolated synaptic and non-synaptic mitochondria after experimental TBI. We conclude that synaptic mitochondria sustain more damage than non-synaptic mitochondria 24 h after severe controlled cortical impact injury (CCI), and that intraperitoneal administration of CsA (20 mg/kg) 15 min after injury improves synaptic and non-synaptic respiration, with a significant improvement being seen in the more severely impaired synaptic population. As such, CsA remains a promising neuroprotective candidate for the treatment of those with TBI.

Reactive oxygen-induced lipid peroxidation (LP) has been documented to play a critical role in pathophysiology, neurodegeneration, and neurological disability that follows acute traumatic brain injury (TBI) and spinal cord injury (SCI). Consistent with that fact, a number of antioxidant compounds that either scavenges reactive oxygen species or directly inhibit LP have been shown to be protective in preclinical models of TBI and SCI. Although LP is able to damage neural cellular and intracellular membranes, much of the damage is caused by the generation of neurotoxic aldehydic end products derived from peroxidized polyunsaturated fatty acids such as arachidonic acid. Most notably, these reactive compounds, 4-hydroxynonenal (4-HNE) and 2-propenal (acrolein), induce further reactive oxygen species formation and LP. This chapter reviews a relatively new antioxidant strategy involving the pharmacological scavenging of 4-HNE and acrolein referred to as “carbonyl scavenging” that is neuroprotective in SCI and TBI animal models. The prototypes of this class are hydralazine and phenelzine (PZ) that contain hydrazine moieties that can covalently react with the carbonyl function groups of 4-HNE or acrolein thus intercepting them and thus preventing their ability of exacerbate posttraumatic oxidative neurodegeneration.

This study investigated whether neuronal inhibitor of DNA binding 2 (Id2), a regulator of basic helix-loop-helix (bHLH) transcription factors, can activate the intrinsic neuritogenetic mode of dorsal root ganglion (DRG) neurons in adult mice following spinal cord injury (SCI). First, the Id2 developmental expression profile of DRG neurons, along with the correlated activity of Cdh1-anaphase promoting complex (Cdh1-APC), was characterized. Next, a D-box mutant Id2 (Id2DBM) adenoviral vector, resistant to Cdh1-APC degradation, was developed to enhance neuronal Id2 expression. After the vector was introduced into DRG neurons, the effect of Id2 on neurite outgrowth of cultured DRG neurons and sensory axonal regeneration following spinal cord dorsal hemisection was evaluated. The expression of Id2 in DRG neurons was high in the embryonic stage, downregulated after birth, and significantly reduced in the adult. Expression of Cdh1-APC was opposite to Id2, which may be responsible for Id2 degradation during DRG maturation. Overexpression of Id2DBM in DRG neurons enhanced neuritogenesis on both permissive and inhibitory substrates. Following spinal cord dorsal hemisection, overexpression of Id2DBM reduced axon dieback and increased the number and length of regenerative fibers into the lesion gap. Reprogramming the intrinsic growth status of quiescent adult DRG neurons by enhancing Id2 expression results in active neuritogenesis following SCI. Id2 may be a novel target for enhancing sensory axonal regeneration following injuries to the adult spinal cord.

To study the pathophysiology of spinal cord injury (SCI), we used the LISA-Vibraknife to generate a precise and reproducible dorsal laceration SCI in the mouse. The surgical procedure involved a T9 laminectomy, dural resection, and a spinal cord laceration to a precisely controlled depth. Four dorsal hemisection injuries with lesion depths of 0.5, 0.8, 1.1, and 1.4 mm, as well as normal, sham (laminectomy and dural removal only), and transection controls were examined. Assessments including the Basso Mouse Scale (BMS), footprint analysis, beam walk, toe spread reflex, Hargreaves' test, and transcranial magnetic motor-evoked potential (tcMMEP) analysis were performed to assess motor, sensorimotor, and sensory function. These outcome measures demonstrated significant increases in functional deficits as the depth of the lesion increased, and significant behavioral recovery was observed in the groups over time. Quantitative histological examination showed significant differences between the injury groups and insignificant lesion depth variance within each of the groups. Statistically significant differences were additionally found in the amount of ventral spared tissue at the lesion site between the injury groups. This novel, graded, reproducible laceration SCI model can be used in future studies to look more closely at underlying mechanisms that lead to functional deficits following SCI, as well as to determine the efficacy of therapeutic intervention strategies in the injury and recovery processes following SCI.