Continuous Infusion of Phenelzine, Cyclosporine A, or Their Combination: Evaluation of Mitochondrial Bioenergetics, Oxidative Damage, and Cytoskeletal Degradation following Severe Controlled Cortical Impact Traumatic Brain Injury in Rats

Abstract

To date, all monotherapy clinical traumatic brain injury (TBI) trials have failed, and there are currently no Food and Drug Administration (FDA)-approved pharmacotherapies for the acute treatment of severe TBI. Due to the complex secondary injury cascade following injury, there is a need to develop multi-mechanistic combinational neuroprotective approaches for the treatment of acute TBI. As central mediators of the TBI secondary injury cascade, both mitochondria and lipid peroxidation-derived aldehydes make promising therapeutic targets. Cyclosporine A (CsA), an FDA-approved immunosuppressant capable of inhibiting the mitochondrial permeability transition pore, and phenelzine (PZ), an FDA-approved monoamine oxidase inhibitor capable of scavenging neurotoxic lipid peroxidation-derived aldehydes, have both been shown to be partially neuroprotective following experimental TBI. Therefore, it follows that the combination of PZ and CsA may enhance neuroprotection over either agent alone through the combining of distinct but complementary mechanisms of action. Additionally, as the first 72 h represents a critical time period following injury, it follows that continuous drug infusion over the first 72 h following injury may also lead to optimal neuroprotective effects. This is the first study to examine the effects of a 72 h subcutaneous continuous infusion of PZ, CsA, and the combination of these two agents on mitochondrial respiration, mitochondrial bound 4-hydroxynonenal (4-HNE), and acrolein, and α-spectrin degradation 72 h following a severe controlled cortical impact injury in rats. Our results indicate that individually, both CsA and PZ are able to attenuate mitochondrial 4-HNE and acrolein, PZ is able to maintain mitochondrial respiratory control ratio and cytoskeletal integrity but together, PZ and CsA are unable to maintain neuroprotective effects.

Effects of Phenelzine Administration on Mitochondrial Function, Calcium Handling, and Cytoskeletal Degradation after Experimental Traumatic Brain Injury

“…Although it has been previously demonstrated that administration of PZ can reduce the levels of 4-HNE and acrolein following TBI, 47,66 there was not correlative preservation of mitochondrial bioenergetics in any comprehensive manner (i.e., across all states of respiration) as seen in the current study, thus suggesting suboptimal PZ dosing. The current series of studies demonstrates a positive correlation between functional mitochondrial protection with a corresponding decrease in 4-HNE and acrolein accumulation following TBI.…”

“…The results showed only minimal improvement in mitochondrial respiratory rates and modest reductions in mitochondrial aldehyde accumulation. 66 In the current study, by comparison, a more limited dosing paradigm of PZ produced significantly higher mitochondrial respiration rates compared with the rates from animals that received the continuous infusion out to 72 hpi: 39.7 -7.6% higher rates, on average, across all five individual states of respiration (as shown in Fig. 3; t test/state: p £ 0.01).…”

“…Similar deleterious, high dose-dependent effects presumably related to excessive inhibition of MAO activity were also observed in recent studies in our lab with PZ. 47,66 In agreement with these data, an in vitro study performed in our lab looked at the protective effects of pargyline, which has MAO inhibitory activity but lacks the hydrazine functional group, compared with PZ, and demonstrated that MAO-B inhibition alone was not able to protect isolated cortical mitochondria from aldehydeinduced loss of bioenergetics. 47 It's possible that PZ's neuroprotective strength comes from its ability to both scavenge reactive aldehydes and inhibit the activity of both isoforms MAO-A and MAO-B.…”

“…As previously suggested, 46 PZ acts to scavenge 4-HNE at a 1:1 equimolar ratio, whereas acrolein requires a 10-fold higher level of PZ to be effective. 47 This suggests that a higher dosage of PZ could potentially do a better job of scavenging acrolein because of its greater toxicity; however, this does not appear to be the case in vivo, as we were able to more sufficiently protect mitochondrial function with this lower dosing paradigm compared with less mitochondrial protection with more PZ (e.g., continuous infusion with osmotic pumps) 66 and higher doses. 47 Because PZ has multiple molecules with which it can react, and because these reactions are irreversible, it would be pharmacologically and clinically beneficial to more clearly understand its binding preferences with regards to its hydrazine aldehyde binding and its capacity for MAO inhibition.…”

“…In recent years, the use of PZ as a neuroprotectant has proven effective in a number of animal models including TBI, 46,47,66 SCI, 48 ischemic-reperfusion, 55 and experimental autoimmune encephalomyelitis (EAE). 67,68 PZ, a well-known MAO inhibitor, has also been shown to exert its neuroprotective effect through the covalent binding of its hydrazine moiety (-NH-NH 2 ) to the carbonyl functional group (R-CHO) of reactive LP-derived aldehydes 4-HNE and acrolein in a dose-dependent manner 46 as well as 3-AP (refer to section on polyamine metabolism).…”