Efficacy of progesterone following a moderate unilateral cortical contusion injury

Effects of Progesterone on Preclinical Animal Models of Traumatic Brain Injury: Systematic Review and Meta-analysis

Since the publication of two phase III clinical trials not supporting the use of progesterone in patients with traumatic brain injury (TBI), several possible explanations have been postulated, including limitations in the analysis of results from preclinical evidence. Therefore, to address this question, a systematic review and meta-analysis was performed to evaluate the effects of progesterone as a neuroprotective agent in preclinical animal models of TBI. A total of 48 studies were included for review: 29 evaluated brain edema, 21 evaluated lesion size, and 0 studies reported the survival rate. In the meta-analysis, it was found that progesterone reduced brain edema (effect size - 1.73 [- 2.02, - 1.44], p < 0.0001) and lesion volume (effect size - 0.40 [- 0.65, - 0.14], p = 0.002). Lack of details in the studies hindered the assessment of risk of bias (through the SYRCLE tool). A funnel plot asymmetry was detected, suggesting a possible publication bias. In conclusion, preclinical studies show that progesterone has an anti-edema effect in animal models of TBI, decreasing lesion volume or increasing remaining tissue. However, more studies are needed using assessing methods with lower risk of histological artifacts.

Sodium tanshinone IIA sulfonate ameliorates cerebral ischemic injury through regulation of angiogenesis

Vascular remodeling and neuroprotection are two major adaptable methods for treating ischemic stroke. Edaravone is a protective agent for the treatment of stroke and was used as a positive control in the present study. Sodium tanshinone IIA sulfonate (STS) has demonstrated therapeutic clinical effects in cerebral infarction in China, while its mechanisms of action in ischemic stroke have remained elusive. The angiogenesis and neuroprotective effects of STS were evaluated in a rat model induced by middle cerebral artery occlusion and 3 days of reperfusion. When used at the same dose, the magnitude of the therapeutic effect of STS was similar to that of edaravone in terms of decreased blood-brain barrier damage as indicated by reduced Evans blue leakage, improved neurological deficits, alleviated cerebral edema and inhibition of histopathological changes caused by ischemia/reperfusion. The TUNEL assay demonstrated that the ability of STS to inhibit neuronal apoptosis was equivalent to that of edaravone. Immunofluorescence detection of CD31 and α-smooth muscle actin indicated that the vascular density was significantly reduced in the vehicle group compared with that in the sham operation group, STS increased the microvessel density in the ischemic area. Furthermore, in the vehicle group the protein expression of vascular endothelial growth factor (VEGF) and VEGF receptor 2 (VEGFR) as determined by fluorescence microscopy and immunohistochemistry was significantly reduced compared with that in the sham group. However, STS promoted their expression compared to the vehicle group respectively, and increaed the mRNA expression of VEGF, VEGFR, CD31 and angiopoietin-1 as determined by reverse transcription-quantitative PCR, but these changes were not significant or not present for edaravone apart from Ang-1. In conclusion, STS protected against ischemic brain injury by promoting angiogenesis in ischemic areas and inhibiting neuronal apoptosis. These results provide a potential treatment for stroke recovery.

Neuropharmacology in traumatic brain injury: from preclinical to clinical neuroprotection?

Traumatic brain injury (TBI) constitutes a major health problem worldwide and is a leading cause of death and disability in individuals, contributing to devastating socioeconomic consequences. Despite numerous promising pharmacological strategies reported as neuroprotective in preclinical studies, the translation to clinical trials always failed, albeit the great diversity of therapeutic targets evaluated. In this review, first, we described epidemiologic features, causes, and primary and secondary injuries of TBI. Second, we outlined the current literature on animal models of TBI, and we described their goals, their advantages and disadvantages according to the species used, the type of injury induced, and their clinical relevance. Third, we defined the concept of neuroprotection and discussed its evolution. We also identified the reasons that might explain the failure of clinical translation. Then, we reviewed post‐TBI neuroprotective treatments with a focus on the following pleiotropic drugs, considered “low hanging fruit” with high probability of success: glitazones, glibenclamide, statins, erythropoietin, and progesterone, that were largely tested and demonstrated efficient in preclinical models of TBI. Finally, our review stresses the need to establish a close cooperation between basic researchers and clinicians to ensure the best clinical translation for neuroprotective strategies for TBI.

Progesterone treatment following traumatic brain injury in the 11-day-old rat attenuates cognitive deficits and neuronal hyperexcitability in adolescence

Traumatic brain injury (TBI) in children younger than 4 years old results in cognitive and psychosocial deficits in adolescence and adulthood. At 4 weeks following closed head injury on postnatal day 11, male and female rats exhibited impairment in novel object recognition memory (NOR) along with an increase in open arm time in the elevated plus maze (EPM), suggestive of risk-taking behaviors. This was accompanied by an increase in intrinsic excitability and frequency of spontaneous excitatory post-synaptic currents (EPSCs), and a decrease in the frequency of spontaneous inhibitory post-synaptic currents in layer 2/3 neurons within the medial prefrontal cortex (PFC), a region that is implicated in both object recognition and risk-taking behaviors. Treatment with progesterone for the first week after brain injury improved NOR memory at the 4-week time point in both sham and brain-injured rats and additionally attenuated the injury-induced increase in the excitability of neurons and the frequency of spontaneous EPSCs. The effect of progesterone on cellular excitability changes after injury may be related to its ability to decrease the mRNA expression of the β3 subunit of the voltage-gated sodium channel and increase the expression of the neuronal excitatory amino acid transporter 3 in the medial PFC in sham- and brain-injured animals and also increase glutamic acid decarboxylase mRNA expression in sham- but not brain-injured animals. Progesterone treatment did not affect injury-induced changes in the EPM test. These results demonstrate that administration of progesterone immediately after TBI in 11-day-old rats reduces cognitive deficits in adolescence, which may be mediated by progesterone-mediated regulation of excitatory signaling mechanisms within the medial PFC.

Neuroprotective effect of salvianolate on cerebral ischaemia-reperfusion injury in rats by inhibiting the Caspase-3 signal pathway

Salvianolate has been widely used for the treatment of cerebrovascular diseases. However, the detailed molecular mechanism of how it alleviates cerebral ischaemia-reperfusion injury is not well understood. In the present study, we investigated the neuroprotective effects of salvianolate in acute cerebral infarction using the PC12 cell oxygen-glucose deprivation (OGD) model in vitro and the rat transient middle cerebral artery occlusion (MCAO) model in vivo. The results showed that the salvianolate significantly reduced the level of reactive oxygen species and inhibited the Caspase-3 signalling pathway in vitro; at the same time, in vivo experiments showed that salvianolate obviously reduced the infarct area (12.9%) and repaired cognitive function compared with the model group (28.28%). In conclusion, our data demonstrated that the salvianolate effectively alleviated cerebral ischaemia-reperfusion injury via suppressing the Caspase-3 signalling pathway.

Sex-related responses after traumatic brain injury: Considerations for preclinical modeling

Traumatic brain injury (TBI) has historically been viewed as a primarily male problem, since men are more likely to experience a TBI because of more frequent participation in activities that increase risk of head injuries. This male bias is also reflected in preclinical research where mostly male animals have been used in basic and translational science. However, with an aging population in which TBI incidence is increasingly sex-independent due to falls, and increasing female participation in high-risk activities, the attention to potential sex differences in TBI responses and outcomes will become more important. These considerations are especially relevant in designing preclinical animal models of TBI that are more predictive of human responses and outcomes. This review characterizes sex differences following TBI with a special emphasis on the contribution of the female sex hormones, progesterone and estrogen, to these differences. This information is potentially important in developing and customizing TBI treatments.

Effects of Female Sex Steroids Administration on Pathophysiologic Mechanisms in Traumatic Brain Injury

Secondary brain damage following initial brain damage in traumatic brain injury (TBI) is a major cause of adverse outcomes. There are many gaps in TBI research and a lack of therapy to limit debilitating outcomes in TBI or enhance the neurogenesis, despite pre-clinical and clinical research performed in TBI. Females show harmful outcomes against brain damage including TBI less than males, independent of different TBI occurrence. A significant reduction in secondary brain damage and improvement in neurologic outcome post-TBI has been reported following the use of progesterone and estrogen in many experimental studies. Although useful features of sex steroids including progesterone have been identified in TBI clinical trials I and II, clinical trials III have been unsuccessful. This review article focuses on evidence of secondary injury mechanisms and neuroprotective effects of estrogen and progesterone in TBI. Understanding these mechanisms may enable researchers to achieve greater success in TBI clinical studies. It seems that the design of clinical studies should be revised due to translation loss of animal studies to clinical studies. The heterogeneous and complex nature of TBI, the endogenous levels of sex hormones at the time of taking these hormones, the therapeutic window of the drug, the dosage of the drug, the selection of appropriate targets in evaluation, the determination of responsive population, gender and age based on animal studies should be considered in the design of TBI human studies in future.

Cognitive performance of male and female C57BL/6J mice after repetitive concussive brain injuries

In contact sports, repetitive concussive brain injury (rCBI) is the prevalent form of head injury seen in athletes. The need for effective treatment is urgent as rCBI has been associated with a host of cognitive, behavioral and neurological complaints. There has been a growing trend in the use of female animals in pre-clinical research, but few studies have investigated possible sex differences following rCBI. The goal of the current study was to determine any differences between male and female C57BL/6J mice on assessments of learning and memory after repetitive concussive injury. Following rCBI by impact to the scalp, male mice exhibited longer righting reflexes during acute recovery. In both sexes, there were no evident histopathological changes observed in the underlying cerebral cortex or hippocampus. Reactive astrogliosis was elevated in the corpus callosum and optic tract, and astrogliosis was slightly less in the optic tract of female mice. rCBI mice exhibited impairment during the learning phase of the Morris water maze (MWM), but female mice, in comparison to male mice, were observed to have superior spatial memory during standard MWM probe trials. Female mice were overall more active, evidenced by greater distances traveled in the y-maze and greater swim speeds in the MWM. The results of this study demonstrate sex differences in cognitive performance following rCBI and support previous research suggesting the neuroprotective role of sex in brain injury.

Progesterone neuroprotection: The background of clinical trial failure

Since the first pioneering studies in the 1990s, a large number of experimental animal studies have demonstrated the neuroprotective efficacy of progesterone for brain disorders, including traumatic brain injury (TBI). In addition, this steroid has major assets: it easily crosses the blood-brain-barrier, rapidly diffuses throughout the brain and exerts multiple beneficial effects by acting on many molecular and cellular targets. Moreover, progesterone therapies are well tolerated. Notably, increased brain levels of progesterone are part of endogenous neuroprotective responses to injury. The hormone thus emerged as a particularly promising protective candidate for TBI and stroke patients. The positive outcomes of small Phase 2 trials aimed at testing the safety and potential protective efficacy of progesterone in TBI patients then provided support and guidance for two large, multicenter, randomized and placebo-controlled Phase 3 trials, with more than 2000 TBI patients enrolled. The negative outcomes of both trials, named ProTECT III and SyNAPSE, came as a big disappointment. If these trials were successful, progesterone would have become the first efficient neuroprotective drug for brain-injured patients. Thus, progesterone has joined the numerous neuroprotective candidates that have failed in clinical trials. The aim of this review is a reappraisal of the preclinical animal studies, which provided the proof of concept for the clinical trials, and we critically examine the design of the clinical studies. We made efforts to present a balanced view of the strengths and limitations of the translational studies and of some serious issues with the clinical trials. We place particular emphasis on the translational value of animal studies and the relevance of TBI biomarkers. The probability of failure of ProTECT III and SyNAPSE was very high, and we present them within the broader context of other unsuccessful trials.

Imatinib treatment reduces brain injury in a murine model of traumatic brain injury

Current therapies for Traumatic brain injury (TBI) focus on stabilizing individuals and on preventing further damage from the secondary consequences of TBI. A major complication of TBI is cerebral edema, which can be caused by the loss of blood brain barrier (BBB) integrity. Recent studies in several CNS pathologies have shown that activation of latent platelet derived growth factor-CC (PDGF-CC) within the brain can promote BBB permeability through PDGF receptor α (PDGFRα) signaling, and that blocking this pathway improves outcomes. In this study we examine the efficacy for the treatment of TBI of an FDA approved antagonist of the PDGFRα, Imatinib. Using a murine model we show that Imatinib treatment, begun 45 min after TBI and given twice daily for 5 days, significantly reduces BBB dysfunction. This is associated with significantly reduced lesion size 24 h, 7 days, and 21 days after TBI, reduced cerebral edema, determined from apparent diffusion co-efficient (ADC) measurements, and with the preservation of cognitive function. Finally, analysis of cerebrospinal fluid (CSF) from human TBI patients suggests a possible correlation between high PDGF-CC levels and increased injury severity. Thus, our data suggests a novel strategy for the treatment of TBI with an existing FDA approved antagonist of the PDGFRα.

Embracing failure: What the Phase III progesterone studies can teach about TBI clinical trials

Background: Despite positive preclinical studies and two positive Phase II clinical trials, two large Phase III clinical trials of progesterone treatment of acute traumatic brain injury (TBI) recently ended with negative results, so a 100% failure rate continues to plague the field of TBI trials.

Methods: This paper reviews and analyses the trial structures and outcomes and discusses the implications of these failures for future drug and clinical trial development. Persistently negative trial outcomes have led to disinvestment in new drug research by companies and policy-makers and disappointment for patients and their families, failures which represent a major public health concern. The problem is not limited to TBI. Failure rates are high for trials in stroke, sepsis, cardiology, cancer and orthopaedics, among others.

Results: This paper discusses some of the reasons why the Phase III trials have failed. These reasons may include faulty extrapolation from pre-clinical data in designing clinical trials and the use of subjective outcome measures that accurately reflect neither the nature of the deficits nor long-term quantitative recovery.

Conclusions: Better definitions of injury and healing and better outcome measures are essential to change the embrace of failure that has dominated the field for over 30 years. This review offers suggestions to improve the situation.

Progesterone and vitamin D combination therapy modulates inflammatory response after traumatic brain injury

OBJECTIVE

Inflammation is an important component of the response to traumatic brain injury (TBI). Progesterone has been shown to inhibit neuroinflammation following (TBI) and may do so through Toll-like receptor (TLR)-mediated pathways. In vitro studies indicate that 1,25-dihydroxyvitamin D(3) (VDH) may also modulate the inflammatory response through the TLR4 pathway. This study tested the hypothesis that PROG and VDH would exert additive and synergistic neuroprotective effects compared with individual treatment by modulating TLR4/NF-κB-mediated inflammation pathways after TBI in rats.

RESEARCH DESIGN AND METHODS

Bilateral medial frontal cortical impact injury was induced in young adult Sprague-Dawley rats. Progesterone (i.p., 16 mg kg^-1 body weight) and VDH (1 µg kg^-1 body weight) were injected separately or combined at 1 and 6 hours after surgery. Rats were killed 24 hours post-surgery and peri-contusional brain tissue harvested for immunostaining and protein measurement.

RESULTS

TLR4, phosphorylation of NF-κB, neuronal loss and astrocyte activation were significantly reduced with combination treatment after TBI compared to each agent given individually.

CONCLUSIONS

At 24 hours after TBI, combination therapy shows greater efficacy in reducing neuroinflammation compared to progesterone and VDH given separately, and does so by modulating the TLR4/NF-κB signalling pathway.

Investigational agents for treatment of traumatic brain injury

INTRODUCTION

Traumatic brain injury (TBI) is a major cause of death and disability worldwide. To date, there are no pharmacologic agents proven to improve outcomes from TBI because all the Phase III clinical trials in TBI have failed. Thus, there is a compelling need to develop treatments for TBI.

AREAS COVERED

The following article provides an overview of select cell-based and pharmacological therapies under early development for the treatment of TBI. These therapies seek to enhance cognitive and neurological functional recovery through neuroprotective and neurorestorative strategies.

EXPERT OPINION

TBI elicits both complex degenerative and regenerative tissue responses in the brain. TBI can lead to cognitive, behavioral, and motor deficits. Although numerous promising neuroprotective treatment options have emerged from preclinical studies that mainly target the lesion, translation of preclinical effective neuroprotective drugs to clinical trials has proven challenging. Accumulating evidence indicates that the mammalian brain has a significant, albeit limited, capacity for both structural and functional plasticity, as well as regeneration essential for spontaneous functional recovery after injury. A new therapeutic approach is to stimulate neurovascular remodeling by enhancing angiogenesis, neurogenesis, oligodendrogenesis, and axonal sprouting, which in concert, may improve neurological functional recovery after TBI.

Progesterone for neuroprotection in pediatric traumatic brain injury

OBJECTIVE

To provide an overview of the preclinical literature on progesterone for neuroprotection after traumatic brain injury and to describe unique features of developmental brain injury that should be considered when evaluating the therapeutic potential for progesterone treatment after pediatric traumatic brain injury.

DATA SOURCES

National Library of Medicine PubMed literature review.

STUDY SELECTION

The mechanisms of neuroprotection by progesterone are reviewed, and the preclinical literature using progesterone treatment in adult animal models of traumatic brain injury is summarized. Unique features of the developing brain that could either enhance or limit the efficacy of neuroprotection by progesterone are discussed, and the limited preclinical literature using progesterone after acute injury to the developing brain is described. Finally, the current status of clinical trials of progesterone for adult traumatic brain injury is reviewed.

DATA EXTRACTION AND DATA SYNTHESIS

Progesterone is a pleiotropic agent with beneficial effects on secondary injury cascades that occur after traumatic brain injury, including cerebral edema, neuroinflammation, oxidative stress, and excitotoxicity. More than 40 studies have used progesterone for treatment after traumatic brain injury in adult animal models, with results summarized in tabular form. However, very few studies have evaluated progesterone in pediatric animal models of brain injury. To date, two human phase II trials of progesterone for adult traumatic brain injury have been published, and two multicenter phase III trials are underway.

CONCLUSIONS

The unique features of the developing brain from that of a mature adult brain make it necessary to independently study progesterone in clinically relevant, immature animal models of traumatic brain injury. Additional preclinical studies could lead to the development of a novel neuroprotective therapy that could reduce the long-term disability in head-injured children and could potentially provide benefit in other forms of pediatric brain injury (global ischemia, stroke, and statue epilepticus).

Neuroprotection for traumatic brain injury

Traumatic brain injury (TBI) is a major cause of mortality and morbidity worldwide. Despite extensive preclinical research supporting the effectiveness of neuroprotective therapies for brain trauma, there have been no successful randomized controlled clinical trials to date. TBI results in delayed secondary tissue injury due to neurochemical, metabolic and cellular changes; modulating such effects has provided the basis for neuroprotective interventions. To establish more effective neuroprotective treatments for TBI it is essential to better understand the complex cellular and molecular events that contribute to secondary injury. Here we critically review relevant research related to causes and modulation of delayed tissue damage, with particular emphasis on cell death mechanisms and post-traumatic neuroinflammation. We discuss the concept of utilizing multipotential drugs that target multiple secondary injury pathways, rather than more specific "laser"-targeted strategies that have uniformly failed in clinical trials. Moreover, we assess data supporting use of neuroprotective drugs that are currently being evaluated in human clinical trials for TBI, as well as promising emerging experimental multipotential drug treatment strategies. Finally, we describe key challenges and provide suggestions to improve the likelihood of successful clinical translation.

Pharmacotherapy of traumatic brain injury: state of the science and the road forward: report of the Department of Defense Neurotrauma Pharmacology Workgroup

Despite substantial investments by government, philanthropic, and commercial sources over the past several decades, traumatic brain injury (TBI) remains an unmet medical need and a major source of disability and mortality in both developed and developing societies. The U.S. Department of Defense neurotrauma research portfolio contains more than 500 research projects funded at more than $700 million and is aimed at developing interventions that mitigate the effects of trauma to the nervous system and lead to improved quality of life outcomes. A key area of this portfolio focuses on the need for effective pharmacological approaches for treating patients with TBI and its associated symptoms. The Neurotrauma Pharmacology Workgroup was established by the U.S. Army Medical Research and Materiel Command (USAMRMC) with the overarching goal of providing a strategic research plan for developing pharmacological treatments that improve clinical outcomes after TBI. To inform this plan, the Workgroup (a) assessed the current state of the science and ongoing research and (b) identified research gaps to inform future development of research priorities for the neurotrauma research portfolio. The Workgroup identified the six most critical research priority areas in the field of pharmacological treatment for persons with TBI. The priority areas represent parallel efforts needed to advance clinical care; each requires independent effort and sufficient investment. These priority areas will help the USAMRMC and other funding agencies strategically guide their research portfolios to ensure the development of effective pharmacological approaches for treating patients with TBI.

Traumatic brain injury using mouse models

The use of mouse models in traumatic brain injury (TBI) has several advantages compared to other animal models including low cost of breeding, easy maintenance, and innovative technology to create genetically modified strains. Studies using knockout and transgenic mice demonstrating functional gain or loss of molecules provide insight into basic mechanisms of TBI. Mouse models provide powerful tools to screen for putative therapeutic targets in TBI. This article reviews currently available mouse models that replicate several clinical features of TBI such as closed head injuries (CHI), penetrating head injuries, and a combination of both. CHI may be caused by direct trauma creating cerebral concussion or contusion. Sudden acceleration-deceleration injuries of the head without direct trauma may also cause intracranial injury by the transmission of shock waves to the brain. Recapitulation of temporary cavities that are induced by high-velocity penetrating objects in the mouse brain are difficult to produce, but slow brain penetration injuries in mice are reviewed. Synergistic damaging effects on the brain following systemic complications are also described. Advantages and disadvantages of CHI mouse models induced by weight drop, fluid percussion, and controlled cortical impact injuries are compared. Differences in the anatomy, biomechanics, and behavioral evaluations between mice and humans are discussed. Although the use of mouse models for TBI research is promising, further development of these techniques is warranted.

Neuroprotective strategies for traumatic brain injury: improving clinical translation

Traumatic brain injury (TBI) induces secondary biochemical changes that contribute to delayed neuroinflammation, neuronal cell death, and neurological dysfunction. Attenuating such secondary injury has provided the conceptual basis for neuroprotective treatments. Despite strong experimental data, more than 30 clinical trials of neuroprotection in TBI patients have failed. In part, these failures likely reflect methodological differences between the clinical and animal studies, as well as inadequate pre-clinical evaluation and/or trial design problems. However, recent changes in experimental approach and advances in clinical trial methodology have raised the potential for successful clinical translation. Here we critically analyze the current limitations and translational opportunities for developing successful neuroprotective therapies for TBI.

The neuroprotective effects of progesterone on traumatic brain injury: current status and future prospects

Traumatic brain injury is the leading cause of morbidity and mortality in young adults. The secondary injury in traumatic brain injury consists of a complex cascade of processes that simultaneously react to the primary injury to the brain. This cascade has been the target of numerous therapeutic agents investigated over the last 30 years, but no neuroprotective treatment option is currently available that improve neurological outcome after traumatic brain injury. Progesterone has long been considered merely a female reproductive hormone. Numerous studies, however, show that progesterone has substantial pleiotropic properties as a neuroprotective agent in both animal models and humans. Here, we review the increasing evidence that progesterone can act as a neuroprotective agent to treat traumatic brain injury and the mechanisms underlying these effects. Additionally, we discuss the current progress of clinical studies on the application of progesterone in the treatment of traumatic brain injuries.

Progesterone's role in neuroprotection, a review of the evidence

The sex hormone progesterone has been shown to improve outcomes in animal models of a number of neurologic diseases, including traumatic brain injury, ischemia, spinal cord injury, peripheral nerve injury, demyelinating disease, neuromuscular disorders, and seizures. Evidence suggests it exerts its neuroprotective effects through several pathways, including reducing edema, improving neuronal survival, and modulating inflammation and apoptosis. In this review, we summarize the functional outcomes and pathophysiologic mechanisms attributed to progesterone treatment in neurologic disease. We then comment on the breadth of evidence for the use of progesterone in each neurologic disease family. Finally, we provide support for further human studies using progesterone to treat several neurologic diseases.

A clinical/translational perspective: can a developmental hormone play a role in the treatment of traumatic brain injury?

Despite decades of laboratory research and clinical trials, a safe and effective treatment for traumatic brain injury (TBI) has yet to be put into successful clinical use. I suggest that much of the problem can be attributed to a reductionist perspective and attendant research strategy directed to finding or designing drugs that target a single receptor mechanism, gene, or brain locus. This approach fails to address the complexity of TBI, which leads to a cascade of systemic toxic events in the brain and throughout the body that may persist over long periods of time. Attention is now turning to pleiotropic drugs: drugs that act on multiple genomic, proteomic and metabolic pathways to enhance morphological and functional outcomes after brain injury. Of the various agents now in clinical trials, the neurosteroid progesterone (PROG) is gaining attention despite the widespread assumption that it is "just a female hormone" with limited, if any, neuroprotective properties. This perspective should change. PROG is also a powerful developmental hormone that plays a critical role in protecting the fetus during gestation. I argue here that development, neuroprotection and cellular repair have a number of properties in common. I discuss evidence that PROG is pleiotropically neuroprotective and may be a useful therapeutic and neuroprotective agent for central nervous system injury and some neurodegenerative diseases.

Effect of gender on recovery after spinal cord injury

Spinal cord injury (SCI) is a debilitating condition that affects thousands of new individuals each year, the majority of which are males. Males with SCI tend to be injured at an earlier age, mostly during sports or motor vehicle accidents, whereas females tend be injured later in life, particularly in the age group 65 and older. In both experimental and clinical studies, the question as to whether gender affects outcome has been addressed in a variety of patient groups and animal models. Results from experimental paradigms have suggested that a gender bias in outcome exists that favors females and appears to involve the advantageous or disadvantageous effects of the gonadal sex hormones estrogen and progesterone or testosterone, respectively. However, other studies have shown an absence of gender differences in outcome in specific SCI models and work has also questioned the involvement of female sex hormones in the observed outcome improvements in females. Similar controversy exists clinically, in studies that have examined gender disparities in outcome after SCI. The current review examines the experimental and clinical evidence for a gender bias in outcome following SCI and discusses issues that have made it difficult to conclusively answer this question.

Progesterone and vitamin d hormone as a biologic treatment of traumatic brain injury in the aged

There is growing recognition that traumatic brain injury is a highly variable and complex systemic disorder that is refractory to therapies that target individual mechanisms. It is even more complex in elderly persons, in whom frailty, previous comorbidities, altered metabolism, and a long history of medication use are likely to complicate the secondary effects of brain trauma. Progesterone, one of the few neuroprotective agents that has shown promise for the treatment of acute brain injury, is now in national and international phase 3 multicenter trials. New findings show that vitamin D hormone (VDH) and VDH deficiency in the aging process (and across the developmental spectrum) may interact with progesterone and treatment for traumatic brain injury. In this article we review the use of progesterone and VDH as biologics-based therapies along with recent studies demonstrating that the combination of progesterone and VDH may promote better functional outcomes than either treatment independently.

Modulation of traumatic brain injury using progesterone and the role of glial cells on its neuroprotective actions

TBI is a complex disease process caused by a cascade of systemic events. Attention is now turning to drugs that act on multiple pathways to enhance survival and functional outcomes. Progesterone has been found to be beneficial in several animal species, different models of brain injury, and in two preliminary human clinical trials. It holds promise as a treatment for TBI. Progesterone's multiple mechanisms of action may work synergistically to prevent the death of neurons and glia, leading to reduced morbidity and mortality. This review highlights the importance of glial cells as mediators of progesterone's actions on the CNS and describes progesterone's pleiotrophic effects on immune enhancement and neuroprotection in TBI.

Progesterone in the treatment of acute traumatic brain injury: a clinical perspective and update

Despite decades of laboratory research and clinical trials, a safe and effective treatment for traumatic brain injury has yet to reach clinical practice. The failure is due in part to the prevalence of a reductionist philosophy and research praxis that targets a single receptor mechanism, gene, or brain locus. This approach fails to account for the fact that traumatic brain injury is a very complex disease caused by a cascade of systemic toxic events in the brain and throughout the body. Attention is now turning to pleiotropic drugs that act on multiple genomic, proteomic, and metabolic pathways to enhance morphological and functional outcomes after brain injury. Of the agents now in clinical trial, the neurosteroid progesterone appears to hold considerable promise. Many still assume that progesterone is "just a female hormone" with limited, if any, neuroprotective properties, but this view is outdated. This review will survey the evidence that progesterone has salient pleiotropic properties as a neuroprotective agent in a variety of central nervous system injury models. This article is part of a Special Issue entitled: Neuroactive Steroids: Focus on Human Brain.

Therapeutic targets for neuroprotection and/or enhancement of functional recovery following traumatic brain injury

Traumatic brain injury (TBI) is a significant public health concern. The number of injuries that occur each year, the cost of care, and the disabilities that can lower the victim's quality of life are all driving factors for the development of therapy. However, in spite of a wealth of promising preclinical results, clinicians are still lacking a therapy. The use of preclinical models of the primary mechanical trauma have greatly advanced our knowledge of the complex biochemical sequela that follow. This cascade of molecular, cellular, and systemwide changes involves plasticity in many different neurochemical systems, which represent putative targets for remediation or attenuation of neuronal injury. The purpose of this chapter is to highlight some of the promising molecular and cellular targets that have been identified and to provide an up-to-date summary of the development of therapeutic compounds for those targets.

Neuroprotective actions of neurosteroids

Neurosteroids were initially defined as steroid hormones locally synthesized within the nervous tissue. Subsequently, they were described as steroid hormone derivatives that devoid hormonal action but still affect neuronal excitability through modulation of ionotropic receptors. Neurosteroids are further subdivided into natural (produced in the brain) and synthetic. Some authors distinguish between hormonal and regular neurosteroids in the group of natural ones. The latter group, including hormone metabolites like allopregnanolone or tetrahydrodeoxycorticosterone, is devoid of hormonal activity. Both hormones and their derivatives share, however, most of the physiological functions. It is usually very difficult to distinguish the effects of hormones and their metabolites. All these substances may influence seizure phenomena and exhibit neuroprotective effects. Neuroprotection offered by steroid hormones may be realized in both genomic and non-genomic mechanisms and involve regulation of the pro- and anti-apoptotic factors expression, intracellular signaling pathways, neurotransmission, oxidative, and inflammatory processes. Since regular neurosteroids show no affinity for steroid receptors, they may act only in a non-genomic mode. Multiple studies have been conducted so far to show efficacy of neurosteroids in the treatment of the central and peripheral nervous system injury, ischemia, neurodegenerative diseases, or seizures. In this review we focused primarily on neurosteroid mechanisms of action and their role in the process of neurodegeneration. Most of the data refers to results obtained in experimental studies. However, it should be realized that knowledge about neuroactive steroids remains still incomplete and requires confirmation in clinical conditions.

Neuroprotection for traumatic brain injury: translational challenges and emerging therapeutic strategies

Traumatic brain injury (TBI) causes secondary biochemical changes that contribute to subsequent tissue damage and associated neuronal cell death. Neuroprotective treatments that limit secondary tissue loss and/or improve behavioral outcome have been well established in multiple animal models of TBI. However, translation of such neuroprotective strategies to human injury have been disappointing, with the failure of more than thirty controlled clinical trials. Both conceptual issues and methodological differences between preclinical and clinical injury have undoubtedly contributed to these translational difficulties. More recently, changes in experimental approach, as well as altered clinical trial methodologies, have raised cautious optimism regarding the outcomes of future clinical trials. Here we critically review developing experimental neuroprotective strategies that show promise, and we propose criteria for improving the probability of successful clinical translation.

Effects of progesterone administration on infarct volume and functional deficits following permanent focal cerebral ischemia in rats

Recent experimental evidence indicates that progesterone (PROG) protects against various models of brain injury, including ischemic stroke. Most human studies of pharmacologic treatments for acute cerebral stroke have failed despite initial success in animal models. To simulate better the typical human stroke without reperfusion, the present study was conducted to examine the efficacy of PROG on infarct volume and functional outcome in a permanent model of stroke, using direct cauterization of the middle cerebral artery (MCA). Twenty-four male adult Sprague-Dawley rats underwent pMCAO by electro-coagulation and sham operation. After induction of permanent MCA occlusion (pMCAO), the rats received an initial intraperitoneal injection of PROG (8 mg/kg) or vehicle at 1 h post-occlusion followed by subcutaneous injections at 6, 24 and 48 h. Functional deficits were tested on the rotarod and grip-strength meter at 24, 48 and 72 h after pMCAO. The rats were killed 72 h after surgery and isolated brain was sectioned into coronal slices and stained with 2, 3, 5-triphenyltetrazolium chloride (TTC). PROG-treated rats showed a substantial reduction (54.05%) in the volume of the infarct (% contralateral hemisphere) compared to vehicle controls. In addition there was a significant improvement in ability to remain on an accelerating rotarod and increased grip strength observed in the pMCAO rats treated with PROG compared to vehicle. Taken together, these data indicate that PROG is beneficial in one of the best-characterized models of stroke, and may warrant further testing in future clinical trials for human stroke.