Progesterone in the clinical treatment of acute traumatic brain injury

Temporal changes of cytochrome P450 (Cyp) and eicosanoid-related gene expression in the rat brain after traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) induces arachidonic acid (ArA) release from cell membranes. ArA metabolites form a class of over 50 bioactive eicosanoids that can induce both adaptive and/or maladaptive brain responses. The dynamic metabolism of ArA to eicosanoids, and how they affect the injured brain, is poorly understood due to their diverse activities, trace levels, and short half-lives. The eicosanoids produced in the brain postinjury depend upon the enzymes present locally at any given time. Eicosanoids are synthesized by heme-containing enzymes, including cyclooxygenases, lipoxygenases, and arachidonate monoxygenases. The latter comprise a subset of the cytochrome P450 "Cyp" gene family that metabolize fatty acids, steroids, as well as endogenous and exogenous toxicants. However, for many of these genes neither baseline neuroanatomical nor injury-related temporal expression have been studied in the brain.In a rat model of parietal cortex TBI, Cyp and eicosanoid-related mRNA levels were determined at 6 h, 24 h, 3d, and 7d postinjury in parietal cortex and hippocampus, where dynamic changes in eicosanoids have been observed. Quantitative real-time polymerase chain reaction with low density arrays were used to assay 62 rat Cyps, 37 of which metabolize ArA or other unsaturated fatty acids; 16 eicosanoid-related enzymes that metabolize ArA or its metabolites; 8 eicosanoid receptors; 5 other inflammatory- and recovery-related genes, plus 2 mouse Cyps as negative controls and 3 highly expressed "housekeeping" genes.

RESULTS

Sixteen arachidonate monoxygenases, 17 eicosanoid-related genes, and 12 other Cyps were regulated in the brain postinjury (p < 0.05, Tukey HSD). Discrete tissue levels and distinct postinjury temporal patterns of gene expression were observed in hippocampus and parietal cortex.

CONCLUSIONS

The results suggest complex regulation of ArA and other lipid metabolism after TBI. Due to the temporal nature of brain injury-induced Cyp gene induction, manipulation of each gene (or its products) at a given time after TBI will be required to assess their contributions to secondary injury and/or recovery. Moreover, a better understanding of brain region localization and cell type-specific expression may be necessary to deduce the role of these eicosanoid-related genes in the healthy and injured brain.

Progestogens used in postmenopausal hormone therapy: differences in their pharmacological properties, intracellular actions, and clinical effects

The safety of progestogens as a class has come under increased scrutiny after the publication of data from the Women's Health Initiative trial, particularly with respect to breast cancer and cardiovascular disease risk, despite the fact that only one progestogen, medroxyprogesterone acetate, was used in this study. Inconsistency in nomenclature has also caused confusion between synthetic progestogens, defined here by the term progestin, and natural progesterone. Although all progestogens by definition have progestational activity, they also have a divergent range of other properties that can translate to very different clinical effects. Endometrial protection is the primary reason for prescribing a progestogen concomitantly with postmenopausal estrogen therapy in women with a uterus, but several progestogens are known to have a range of other potentially beneficial effects, for example on the nervous and cardiovascular systems. Because women remain suspicious of the progestogen component of postmenopausal hormone therapy in the light of the Women's Health Initiative trial, practitioners should not ignore the potential benefits to their patients of some progestogens by considering them to be a single pharmacological class. There is a lack of understanding of the differences between progestins and progesterone and between individual progestins differing in their effects on the cardiovascular and nervous systems, the breast, and bone. This review elucidates the differences between the substantial number of individual progestogens employed in postmenopausal hormone therapy, including both progestins and progesterone. We conclude that these differences in chemical structure, metabolism, pharmacokinetics, affinity, potency, and efficacy via steroid receptors, intracellular action, and biological and clinical effects confirm the absence of a class effect of progestogens.

The effect of nicotinamide on gene expression in a traumatic brain injury model

Microarray-based transcriptional profiling was used to determine the effect of nicotinamide on gene expression in an experimental traumatic brain injury (TBI) model. Ingenuity Pathway Analysis (IPA) was used to evaluate the effect on relevant functional categories and canonical pathways. At 24 h, 72 h, and 7 days, respectively, 70, 58, and 76%, of the differentially expressed genes were up-regulated in the vehicle treated compared to the sham animals. At 24 h post-TBI, there were 150 differentially expressed genes in the nicotinamide treated animals compared to vehicle; the majority (82%) down-regulated. IPA analysis identified a significant effect of nicotinamide on the functional categories of cellular movement, cell-to-cell-signaling, antigen presentation and cellular compromise, function, and maintenance and cell death. The canonical pathways identified were signaling pathways primarily involved with the inflammatory process. At 72 h post-cortical contusion injury, there were 119 differentially expressed genes in the nicotinamide treated animals compared to vehicle; the majority (90%) was up-regulated. IPA analysis identified a significant effect of nicotinamide on cell signaling pathways involving neurotransmitters, neuropeptides, growth factors, and ion channels with little to no effect on inflammatory pathways. At 7 days post-TBI, there were only five differentially expressed genes with nicotinamide treatment compared to vehicle. Overall, the effect of nicotinamide on counteracting the effect of TBI resulted in significantly decreased number of genes differentially expressed by TBI. In conclusion, the mechanism of the effect of nicotinamide on secondary injury pathways involves effects on inflammatory response, signaling pathways, and cell death.

Gonadal hormones and the control of reactive gliosis

Astrocytes and microglia respond to central nervous system (CNS) injury with changes in morphology, proliferation, migration and expression of inflammatory regulators. This phenomenon is known as reactive gliosis. Activation of astrocytes and microglia after acute neural insults, such as stroke or traumatic CNS injury, is considered to be an adaptive response that contributes to minimize neuronal damage. However, reactive gliosis may amplify CNS damage under chronic neurodegenerative conditions. Progesterone, estradiol and testosterone have been shown to control reactive gliosis in different models of CNS injury, modifying the number of reactive astrocytes and reactive microglia and the expression of anti-inflammatory and proinflammatory mediators. The actions of gonadal hormones on reactive gliosis involve different mechanisms, including the modulation of the activity of steroid receptors, such as estrogen receptors α and β, the regulation of nuclear factor-κB mediated transcription of inflammatory molecules and the recruitment of the transcriptional corepressor c-terminal binding protein to proinflammatory promoters. In addition, the Parkinson's disease related gene parkin and the endocannabinoid system also participate in the regulation of reactive gliosis by estradiol. The control exerted by gonadal hormones on reactive gliosis may affect the response of neural tissue to trauma and neurodegeneration and may contribute to sex differences in the manifestation of neurodegenerative diseases. However, the precise functional consequences of the regulation of reactive gliosis by gonadal hormones under acute and chronic neurodegenerative conditions are still not fully clarified.

Animal models of traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of mortality and morbidity both in civilian life and on the battlefield worldwide. Survivors of TBI frequently experience long-term disabling changes in cognition, sensorimotor function and personality. Over the past three decades, animal models have been developed to replicate the various aspects of human TBI, to better understand the underlying pathophysiology and to explore potential treatments. Nevertheless, promising neuroprotective drugs that were identified as being effective in animal TBI models have all failed in Phase II or Phase III clinical trials. This failure in clinical translation of preclinical studies highlights a compelling need to revisit the current status of animal models of TBI and therapeutic strategies.

Sex, stroke, and inflammation: the potential for estrogen-mediated immunoprotection in stroke

Stroke is the third leading cause of death and the primary cause of disability in the developed world. Experimental and clinical data indicate that stroke is a sexually dimorphic disease, with males demonstrating an enhanced intrinsic sensitivity to ischemic damage throughout most of their lifespan. The neuroprotective role of estrogen in the female brain is well established, however, estrogen exposure can also be deleterious, especially in older women. The mechanisms for this remain unclear. Our current understanding is based on studies examining estrogen as it relates to neuronal injury, yet cerebral ischemia also induces a robust sterile inflammatory response involving local and systemic immune cells. Despite the potent anti-inflammatory effects of estrogen, few studies have investigated the contribution of estrogen to sex differences in the inflammatory response to stroke. This review examines the potential role for estrogen-mediated immunoprotection in ischemic injury.

Are there cognitive and neurobehavioural correlates of hormonal neuroprotection for women after TBI?

This study examined possible cognitive correlates of hormonal neuroprotection following traumatic brain injury (TBI) using archival neuropsychological findings for 1563 individuals undergoing acute TBI rehabilitation between 1989 and 2002. Presumed age of menopause was based on the STRAW (Stages of Reproductive Aging) staging system (Soules, 2005; Soules et al., 2001) and general linear model (GLM) analysis of performance on neuropsychological testing by participants across gender and age groups (25-34, 35-44, 45-54, and 55-64) was performed. Hypotheses were (1) women with TBI in the oldest age group would have lower scores on neuropsychological tests and functional outcome measures than women in the younger groups, and (2) men in the oldest age group would have higher scores than women of the same age group. Analyses revealed that oldest females had significantly worse Trails B and SDMT written and oral scores than the youngest females. In addition, oldest females had significantly better Trails B, Rey AVLT and SDMT written scores than the oldest males. Possible cohort exposure to hormone replacement therapy, unknown hormonal status at time of testing, and sample-specific injury characteristics may have contributed to these findings.

Neuroprotective and neurorestorative effects of thymosin β4 treatment following experimental traumatic brain injury

Traumatic brain injury (TBI) remains a leading cause of mortality and morbidity worldwide. No effective pharmacological treatments are available for TBI because all phase II/III TBI clinical trials have failed. This highlights a compelling need to develop effective treatments for TBI. Endogenous neurorestoration occurs in the brain after TBI, including angiogenesis, neurogenesis, synaptogenesis, oligodendrogenesis, and axonal remodeling, which may be associated with spontaneous functional recovery after TBI. However, the endogenous neurorestoration following TBI is limited. Treatments amplifying these neurorestorative processes may promote functional recovery after TBI. Thymosin beta 4 (Tβ4) is the major G-actin-sequestering molecule in eukaryotic cells. In addition, Tβ4 has other properties including antiapoptosis and anti-inflammation, promotion of angiogenesis, wound healing, stem/progenitor cell differentiation, and cell migration and survival, which provide the scientific foundation for the corneal, dermal, and cardiac wound repair multicenter clinical trials. Here, we describe Tβ4 as a neuroprotective and neurorestorative candidate for treatment of TBI.

A comparison of the effects of nicotinamide and progesterone on functional recovery of cognitive behavior following cortical contusion injury in the rat

The primary goal of this study was to compare clinically relevant doses of progesterone and nicotinamide within the same injury model. Progesterone has been shown to reduce edema and inflammation and improve functional outcomes following brain injury. Nicotinamide has also been shown to be an effective neuroprotective agent in a variety of neurological injury models. In the current study, nicotinamide was administered beginning 4 h post-cortical contusion injury (CCI) with a loading dose (75 mg/kg, i.p.) combined with continuous infusion (12 mg/h/kg, s.c.) for 72 h post-injury. Progesterone was administered beginning 4 h post-CCI at a dose of 10 or 20 mg/kg, i.p. every 12 h for 72 h. This resulted in the following groups: Injured-nicotinamide treated, Injured-progesterone-10 treated, Injured-progesterone-20 treated, Injured-vehicle treated, and Sham. Functional recovery was assessed with two spatial memory tasks in the Morris water maze (MWM) the acquisition of a reference memory task and a reversal learning task. Neuropathological assessments were conducted in the cortex and hippocampus. It was found that both progesterone (10 mg/kg) and nicotinamide improved reference memory acquisition and reversal learning in the MWM compared with vehicle treatment. The lower dose of progesterone and nicotinamide also reduced tissue loss in the injured cortex and ipsilateral hippocampus compared with vehicle. The beneficial effects of progesterone appear to be dose dependent with the lower 10 mg/kg dose producing significant effects that were not observed at the higher dose. Direct comparison between nicotinamide and low dose progesterone appears to suggest that both are equally effective. The general findings of this study suggest that both nicotinamide and progesterone produce significant improvements in recovery of function following CCI.

Distribution of membrane progesterone receptor alpha in the male mouse and rat brain and its regulation after traumatic brain injury

Progesterone has been shown to exert pleiotropic actions in the brain of both male and females. In particular, after traumatic brain injury (TBI), progesterone has important neuroprotective effects. In addition to intracellular progesterone receptors, membrane receptors of the hormone such as membrane progesterone receptor (mPR) may also be involved in neuroprotection. Three mPR subtypes (mPRα, mPRβ, and mPRγ) have been described and mPRα is best characterized pharmacologically. In the present study we investigated the distribution, cellular localization and the regulation of mPRα in male mouse and rat brain. We showed by reverse transcription-PCR that mPRα is expressed at similar levels in the male and female mouse brain suggesting that its expression may not be influenced by steroid levels. Treatment of males by estradiol or progesterone did not modify the level of expression of mPRα as shown by Western blot analysis. In situ hybridization and immunohistochemistry analysis showed a wide expression of mPRα in particular in the olfactory bulb, striatum, cortex, thalamus, hypothalamus, septum, hippocampus and cerebellum. Double immunofluorescence and confocal microscopy analysis showed that mPRα is expressed by neurons but not by oligodendrocytes and astrocytes. In the rat brain, the distribution of mPRα was similar to that observed in mouse brain; and after TBI, mPRα expression was induced in oligodendrocytes, astrocytes and reactive microglia. The wide neuroanatomical distribution of mPRα suggests that this receptor may play a role beyond neuroendocrine and reproductive functions. However, in the absence of injury its role might be restricted to neurons. The induction of mPRα after TBI in microglia, astrocytes and oligodendrocytes, points to a potential role in mediating the modulatory effects of progesterone in inflammation, ion and water homeostasis and myelin repair in the injured brain.

Neuroinflammation after traumatic brain injury: opportunities for therapeutic intervention

Traumatic brain injury (TBI) remains one of the leading causes of mortality and morbidity worldwide, yet despite extensive efforts to develop neuroprotective therapies for this devastating disorder there have been no successful outcomes in human clinical trials to date. Following the primary mechanical insult TBI results in delayed secondary injury events due to neurochemical, metabolic and cellular changes that account for many of the neurological deficits observed after TBI. The development of secondary injury represents a window of opportunity for therapeutic intervention to prevent progressive tissue damage and loss of function after injury. To establish effective neuroprotective treatments for TBI it is essential to fully understand the complex cellular and molecular events that contribute to secondary injury. Neuroinflammation is well established as a key secondary injury mechanism after TBI, and it has been long considered to contribute to the damage sustained following brain injury. However, experimental and clinical research indicates that neuroinflammation after TBI can have both detrimental and beneficial effects, and these likely differ in the acute and delayed phases after injury. The key to developing future anti-inflammatory based neuroprotective treatments for TBI is to minimize the detrimental and neurotoxic effects of neuroinflammation while promoting the beneficial and neurotrophic effects, thereby creating optimal conditions for regeneration and repair after injury. This review outlines how post-traumatic neuroinflammation contributes to secondary injury after TBI, and discusses the complex and varied responses of the primary innate immune cells of the brain, microglia, to injury. In addition, emerging experimental anti-inflammatory and multipotential drug treatment strategies for TBI are discussed, as well as some of the challenges faced by the research community to translate promising neuroprotective drug treatments to the clinic.

Progesterone increases the release of brain-derived neurotrophic factor from glia via progesterone receptor membrane component 1 (Pgrmc1)-dependent ERK5 signaling

Progesterone (P4) is cytoprotective in various experimental models, but our understanding of the mechanisms involved is still incomplete. Our laboratory has implicated brain-derived neurotrophic factor (BDNF) signaling as an important mediator of P4's protective actions. We have shown that P4 increases the expression of BDNF, an effect mediated by the classical P4 receptor (PR), and that the protective effects of P4 were abolished using inhibitors of Trk receptor signaling. In an effort to extend our understanding of the interrelationship between P4 and BDNF signaling, we determined whether P4 influenced BDNF release and examined the role of the classical PR and a putative membrane PR, progesterone receptor membrane component-1 (Pgrmc1), as mediators of this response. Given recent data from our laboratory that supported the role of ERK5 in BDNF release, we also tested whether P4-induced BDNF release was mediated by ERK5. In this study, we found that P4 and the membrane-impermeable P4 (P4-BSA) both induced BDNF release from cultured C6 glial cells and primary astrocytes. Both these cells lack the classical nuclear/intracellular PR but express high levels of membrane-associated PR, including Pgrmc1. Using RNA interference-mediated knockdown of Pgrmc1 expression, we determined that P4-induced BDNF release was dependent on the expression of Pgrmc1, although pharmacological inhibition of the PR failed to alter the effects of P4. Furthermore, the BDNF release elicited by P4 was mediated by ERK5, and not ERK1/2. Collectively, our data describe that P4 elicits an increase in BDNF release from glia via a Pgrmc1-induced ERK5 signaling mechanism and identify Pgrmc1 as a potential therapeutic target for future hormone-based drug development for the treatment of such degenerative diseases as Alzheimer's disease as well as other diseases wherein neurotrophin dysregulation is noted.

Water-soluble progesterone analogues are effective, injectable treatments in animal models of traumatic brain injury

After more than 30 years of research and 30 failed clinical trials with as many different treatments, progesterone is the first agent to demonstrate robust clinical efficacy as a treatment for traumatic brain injuries. It is currently being investigated in two, independent phase III clinical trials in hospital settings; however, it presents a formidable solubility challenge that has so far prevented the identification of a formulation that would be suitable for emergency field response use or battlefield situations. Accordingly, we have designed and tested a novel series of water-soluble analogues that address this critical need. We report here the synthesis of C-20 oxime conjugates of progesterone as therapeutic agents for traumatic brain injuries with comparable efficacy in animal models of traumatic brain injury and improved solubility and pharmacokinetic profiles. Pharmacodynamic analysis reveals that a nonprogesterone steroidal analogue may be primarily responsible for the observed activity.

Targeting mTOR as a novel therapeutic strategy for traumatic CNS injuries

The adult central nervous system (CNS) has a remarkable ability to repair itself. However, severe brain and spinal cord injuries (SCIs) cause lasting disability and there are only a few therapies that can prevent or restore function in such cases. In this review, we provide an overview of traumatic CNS injuries and discuss several emerging pharmacological options that have shown promise in preclinical and early clinical studies. We highlight therapies that modulate mammalian target of rapamycin (mTOR) signaling, a pathway that is well known for its roles in cell growth, metabolism and cancer. Interestingly, this pathway is also gaining newfound attention for its role in CNS repair and regeneration.

Is TNF a link between aging-related reproductive endocrine dyscrasia and Alzheimer's disease?

This commentary addresses a novel mechanism by which aging-related changes in reproductive hormones could mediate their action in the brain. It presents the evidence that dyotic endocrine signals modulate the expression of tumor necrosis factor (TNF) and related cytokines, and that these cytokines are a functionally important downstream link mediating neurodegeneration and dysfunction. This convergence of dyotic signaling on TNF-mediated degeneration and dysfunction has important implications for understanding the pathophysiology of AD, stroke, and traumatic brain disease, and also for the treatment of these diseases.

Progesterone and low-dose vitamin D hormone treatment enhances sparing of memory following traumatic brain injury

Progesterone (PROG) has been shown to protect the brain from traumatic injury and is now in Phase III clinical trials. Our work shows that PROG's beneficial effects can be reduced in vitamin D hormone (VDH)-deficient subjects. VDH can modulate neuronal apoptosis, trophic factors, inflammation, oxidative stress, excitotoxicity, and myelin and axon repair. We investigated whether VDH combined with PROG could improve behavioral outcomes more than PROG alone in VDH-sufficient rats given bilateral contusions of the medial frontal cortex. PROG and different doses of VDH (1 μg/kg, VDH1; 2.5 μg/kg, VDH2; 5 μg/kg, VDH3) were injected intraperitoneally 1 h post-injury. Eight additional doses of PROG were given subcutaneously over 8 days with tapering over the last 2 days. Neurobehavioral tests, necrotic cavity, neuronal death and activation of astrocytes were evaluated 21 days post-injury. We found that PROG and PROG + VDH preserve spatial memory processing. VDH1 + PROG improved performance in acquisition more effectively than PROG alone, indicating that the low VDH dose is optimal for combination therapy. There were no significant differences in necrotic cavity size among the groups. The density of positive staining for reactive astrocytes (glial fibrillary acidic protein (GFAP)) increased and the cell bodies and processes of GFAP-positive cells were enlarged in the PROG + VDH1 group. Our data indicate that the combination of PROG and VDH is more effective than PROG alone in preserving spatial and reference memory, and that PROG plus low-dose VDH can activateGFAP reactions up to 21 days after injury. This effect may be one of the mechanisms underlying PROG's neuroprotective effects in combination with VDH.

A Rehabilomics focused perspective on molecular mechanisms underlying neurological injury, complications, and recovery after severe TBI

The molecular mechanisms underlying TBI pathophysiology and recovery are both complex and varied. Further, the pathology underlying many of the clinical sequelae observed in this population evolve over the acute injury period and encompass the subacute and chronic phases of recovery, supporting the contemporary concept that TBI is a chronic disease rather than a static insult from which limited recovery occurs. TBI related complications can also span from acute care to the very chronic stages of recovery that occur years after the initial trauma. Despite ongoing neurodegeneration, the TBI recovery period is also characterized by a propensity for neuroplasticity and rewiring through multiple mechanisms. This review summarizes key elements of acute pathophysiology, how they link to structural damage and ongoing degeneration, and how this process coincides with a permissive neuroplastic environment. The pathophysiology of selected TBI related complications is also discussed. Each of these concepts is studied through the lens of Rehabilomics, wherein an emphasis is placed on biomarker studies characterizing these pathophysiological mechanisms, and biomarker profiles are assessed in relation to multi-modal outcomes and susceptibility to rehabilitation relevant complications. In reviewing these concepts, implications for future research and theranostic principles for patient care are presented.

Novel actions of progesterone: what we know today and what will be the scenario in the future?

Objectives

This article is aimed to review the novel actions of progesterone, which otherwise is considered as a female reproductive hormone. The article focuses on its important physiological actions in males too and gives an overview of its novel perspectives in disorders of central and peripheral nervous system.

Key findings

Progesterone may have a potential benefit in treatment of traumatic brain injury, various neurological disorders and male related diseases like benign prostatic hypertrophy (BPH), prostate cancer and osteoporosis. Norethisterone (NETA), a progesterone derivative, decreases bone mineral loss in male castrated mice suggesting its role in osteoporosis. In the future, progesterone may find use as a male contraceptive too, but still needs confirmatory trials for safety, tolerability and acceptability. Megestrol acetate, a progesterone derivative is preferred in prostatic cancer. Further, it may find utility in nicotine addiction, traumatic brain injury (recently entered Phase III trial) and Alzheimer's disease, diabetic neuropathy and crush injuries. Studies also suggest role of progesterone in stroke, for which further clinical trials are needed. The non genomic actions of progesterone may be in part responsible for these novel actions.

Summary

Although progesterone has shown promising role in various non-hormonal benefits, further clinical studies are needed to prove its usefulness in conditions like stroke, traumatic brain injury, neuropathy and crush injury. In male related illnesses like BPH and prostatic Ca, it may prove a boon in near future. New era of hormonal male contraception may be initiated by use of progesterone along with testosterone.

Progesterone synthesis in the nervous system: implications for myelination and myelin repair

Progesterone is well known as a female reproductive hormone and in particular for its role in uterine receptivity, implantation, and the maintenance of pregnancy. However, neuroendocrine research over the past decades has established that progesterone has multiple functions beyond reproduction. Within the nervous system, its neuromodulatory and neuroprotective effects are much studied. Although progesterone has been shown to also promote myelin repair, its influence and that of other steroids on myelination and remyelination is relatively neglected. Reasons for this are that hormonal influences are still not considered as a central problem by most myelin biologists, and that neuroendocrinologists are not sufficiently concerned with the importance of myelin in neuron functions and viability. The effects of progesterone in the nervous system involve a variety of signaling mechanisms. The identification of the classical intracellular progesterone receptors as therapeutic targets for myelin repair suggests new health benefits for synthetic progestins, specifically designed for contraceptive use and hormone replacement therapies. There are also major advantages to use natural progesterone in neuroprotective and myelin repair strategies, because progesterone is converted to biologically active metabolites in nervous tissues and interacts with multiple target proteins. The delivery of progesterone however represents a challenge because of its first-pass metabolism in digestive tract and liver. Recently, the intranasal route of progesterone administration has received attention for easy and efficient targeting of the brain. Progesterone in the brain is derived from the steroidogenic endocrine glands or from local synthesis by neural cells. Stimulating the formation of endogenous progesterone is currently explored as an alternative strategy for neuroprotection, axonal regeneration, and myelin repair.

The neurosteroids, allopregnanolone and progesterone, induce autophagy in cultured astrocytes

Recent studies have suggested that neurosteroids such as pregnenolone, progesterone (PG) and their derivatives, have a role in activating autophagy in addition to diverse other functions. In our previous studies, we demonstrated that cellular free Zn(2+) is involved in oxidative stress-induced autophagy and autophagic cell death in astrocytes. In the present study, we examined the possibility that neurosteroids, allopregnanolone (Allo) and PG, also activate autophagy in cultured mouse astrocytes through modulation of intracellular Zn(2+). Exposure of astrocytes to 250 nM Allo or 500 nM PG caused cytosolic vacuoles to appear within a few hours of treatment onset. Live-cell confocal microscopy of astrocytes transfected with red fluorescent protein-conjugated LC3 (RFP-LC3), a marker for autophagic vacuoles (AVs), as well as transmission electron microscopy, revealed that these vacuoles were AVs. In addition, Western blots showed increases in LC3-II levels. Interestingly, mTOR and Akt were concurrently activated, and their blockade further increased LC3-II levels and caused some cell death. These results indicate that co-activation of mTOR and Akt may act to limit neurosteroid-induced autophagy and thus inhibit autophagic cell death. As in other cases of autophagy, cellular Zn(2+) levels increased after treatment with neurosteroids. The neurosteroid-induced increase in LC3-II levels was inhibited by addition of the Zn(2+) chelator TPEN. Both the increase in LC3-II levels and activation of Akt and mTOR by neurosteroids were all mediated by PG receptors, as the effects were blocked by the addition of RU-486, a PG receptor antagonist. Moreover, mutant huntingtin (mHtt) aggregates in GFP-mHttQ74-transfected astrocytes were substantially reduced by neurosteroid treatment, indicating that neurosteroid-induced autophagy may be functional. Present results demonstrate that Allo and PG activate autophagy in astrocytes. Notably, unlike several other autophagy inducers that, in excess, may cause autophagic cell death, Allo and PG are relatively non-toxic, possibly because of concurrent Akt and mTOR activation. Thus, as natural endogenous brain substances, Allo and PG may have a potential as therapeutic agents in neurodegenerative conditions in which abnormal protein aggregates are involved.

Neuroprotective actions of estradiol revisited

Results from animal experiments showing that estradiol is neuroprotective were challenged 10 years ago by findings indicating an increased risk of dementia and stroke in women over 65 years of age taking conjugated equine estrogens. Our understanding of the complex signaling of estradiol in neural cells has recently clarified the causes of this discrepancy. New data indicate that estradiol may lose its neuroprotective activity or even increase neural damage, a situation that depends on the duration of ovarian hormone deprivation and on age-associated modifications in the levels of other molecules that modulate estradiol action. These studies highlight the complex neuroprotective mechanisms of estradiol and suggest a window of opportunity during which effective hormonal therapy could promote brain function and cognition.

Is progesterone a worthy candidate as a novel therapy for traumatic brain injury?

Although progesterone is critical to a healthy pregnancy, it is now known to have other important functions as well. Recent research demonstrates that this hormone is also a potent neurosteroid that can protect damaged cells in the central and peripheral nervous systems and has rapid actions that go well beyond its effects on the classical intranuclear progesterone receptor. Based on years of preclinical research demonstrating its safety and effectiveness in animal models of central nervous system injury the hormone was recently tested in two Phase II clinical trials for traumatic brain injury (TBI). A US National Institutes of Health-sponsored, nationwide Phase III clinical trial is now evaluating progesterone for moderate-to-severe TBI in 1200 patients. An industry-sponsored Phase III international trial is also under way, and planning for a trial using progesterone to treat pediatric brain injury has begun. Preclinical data suggest that progesterone may also be effective in stroke and some neurodegenerative disorders.

Progesterone and Nestorone facilitate axon remyelination: a role for progesterone receptors

Enhancing the endogenous capacity of myelin repair is a major therapeutic challenge in demyelinating diseases such as multiple sclerosis. We found that progesterone and the synthetic 19-norprogesterone derivative 16-methylene-17α-acetoxy-19-norpregn-4-ene-3,20-dione (Nestorone) promote the remyelination of axons by oligodendrocytes after lysolecithin-induced demyelination in organotypic cultures of cerebellar slices taken from postnatal rats or mice. The intracellular progesterone receptors (PR) mediate the proremyelinating actions of Nestorone, because they are not observed in slices from PR knockout mice. Notably, Nestorone was less efficient in heterozygous mice, expressing reduced levels of PR, suggesting PR haploinsufficiency in myelin repair. Using mice expressing the enhanced green fluorescent protein (EGFP) under the control of the proteolipid gene promoter, we showed that both progesterone and Nestorone strongly increased the reappearance of cells of the oligodendroglial lineage in the demyelinated slices. In contrast to Nestorone, the pregnane derivative medroxyprogesterone acetate had no effect. The increase in oligodendroglial cells by Nestorone resulted from enhanced NG2(+) and Olig2(+) oligodendrocyte progenitor cell (OPC) recruitment. In cocultures of lysolecithin-demyelinated cerebellar slices from wild-type mice apposed to brain stem slices of proteolipid gene promoter-EGFP mice, Nestorone stimulated the migration of OPC towards demyelinated axons. In this coculture paradigm, Nestorone indeed markedly increased the number of EGFP(+) cells migrating into the demyelinated cerebellar slices. Our results show that Nestorone stimulates the recruitment and maturation of OPC, two steps which are limiting for efficient myelin repair. They may thus open new perspectives for the use of progestins, which selectively target PR, to promote the endogenous regeneration of myelin.

The effect of progesterone dose on gene expression after traumatic brain injury

Microarray-based transcriptional profiling was used to determine the effect of progesterone in the cortical contusion (CCI) model. Gene ontology (GO) analysis then evaluated the effect of dose on relevant biological pathways. Treatment (vehicle, progesterone 10 mg/kg or 20 mg/kg given i.p.) was started 4 h post-injury and administered every 12 h post-injury for up to 72 h, with the last injection 12 hr prior to death for the 24 h and 72 h groups. In the CCI-injured vehicle group compared to non-injured animals, expression of 1,114, 4,229, and 291 distinct genes changed >1.5-fold (p<0.05) at 24 h, 72 h, and 7 days, respectively. At 24 h, the effect of low-dose progesterone on differentially expressed genes was <20% the effect of higher dose compared to vehicle. GO analysis identified a significant effect of low- and high-dose progesterone treatment compared to vehicle on DNA damage response. At 72 h, high-dose progesterone treatment compared to vehicle affected expression of almost twice as many genes as did low-dose progesterone. Both low- and high-dose progesterone resulted in expression of genes regulating inflammatory response and apoptosis. At 7 days, there was only a modest difference in high-dose progesterone compared to vehicle, with only 14 differentially expressed genes. In contrast, low-dose progesterone resulted in 551 differentially expressed genes compared to vehicle. GO analysis identified genes for the low-dose treatment involved in positive regulation of cell proliferation, innate immune response, positive regulation of anti-apoptosis, and blood vessel remodeling.

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.

Sex differences in the inflammatory response of primary astrocytes to lipopolysaccharide

Background

Numerous neurological and psychiatric disorders show sex differences in incidence, age of onset, symptomatology or outcome. Astrocytes, one of the glial cell types of the brain, show sex differences in number, differentiation and function. Since astrocytes are involved in the response of neural tissue to injury and inflammation, these cells may participate in the generation of sex differences in the response of the brain to pathological insults. To explore this hypothesis, we have examined whether male and female astrocytes show a different response to an inflammatory challenge and whether perinatal testosterone influences this response.

Methods

Cortical astrocyte cultures were prepared from postnatal day 1 (one day after birth) male or female CD1 mice pups. In addition, cortical astrocyte cultures were also prepared from female pups that were injected at birth with 100 μg of testosterone propionate or vehicle. Cultures were treated for 5 hours with medium containing lipopolysaccharide (LPS) or with control medium. The mRNA levels of IL6, interferon-inducible protein 10 (IP10), TNFα, IL1β, Toll-like receptor 4 (TLR4), steroidogenic acute regulatory protein and translocator protein were assessed by quantitative real-time polymerase chain reaction. Statistical significance was assessed by unpaired t-test or by one-way analysis of variance followed by the Tukey post hoc test.

Results

The mRNA levels of IL6, TNFα and IL1β after LPS treatment were significantly higher in astrocytes derived from male or androgenized females compared to astrocytes derived from control or vehicle-injected females. In contrast, IP10 mRNA levels after LPS treatment were higher in astrocytes derived from control or vehicle-injected females than in those obtained from males or androgenized females. The different response of male and female astrocytes to LPS was due neither to differences in the basal expression of the inflammatory molecules nor to differences in the expression of the LPS receptor TLR4. In contrast, the different inflammatory response was associated with increased mRNA levels of translocator protein, a key steroidogenic regulator, in female astrocytes that were treated with LPS.

Conclusions

Male and female cortical astrocytes respond differentially to an inflammatory challenge and this may be predetermined by perinatal testosterone exposure.

Progesterone treatment normalizes the levels of cell proliferation and cell death in the dentate gyrus of the hippocampus after traumatic brain injury

Traumatic brain injury (TBI) increases cell death in the hippocampus and impairs hippocampus-dependent cognition. The hippocampus is also the site of ongoing neurogenesis throughout the lifespan. Progesterone treatment improves behavioral recovery and reduces inflammation, apoptosis, lesion volume, and edema, when given after TBI. The aim of the present study was to determine whether progesterone altered cell proliferation and short-term survival in the dentate gyrus after TBI. Male Sprague-Dawley rats with bilateral contusions of the frontal cortex or sham operations received progesterone or vehicle at 1 and 6 h post-surgery and daily through post-surgery Day 7, and a single injection of bromodeoxyuridine (BrdU) 48 h after injury. Brains were then processed for Ki67 (endogenous marker of cell proliferation), BrdU (short-term cell survival), doublecortin (endogenous marker of immature neurons), and Fluoro-Jade B (marker of degenerating neurons). TBI increased cell proliferation compared to shams and progesterone normalized cell proliferation in injured rats. Progesterone alone increased cell proliferation in intact rats. Interestingly, injury and/or progesterone treatment did not influence short-term cell survival of BrdU-ir cells. All treatments increased the percentage of BrdU-ir cells that were co-labeled with doublecortin (an immature neuronal marker in this case labeling new neurons that survived 5 days), indicating that cell fate is influenced independently by TBI and progesterone treatment. The number of immature neurons that survived 5 days was increased following TBI, but progesterone treatment reduced this effect. Furthermore, TBI increased cell death and progesterone treatment reduced cell death to levels seen in intact rats. Together these findings suggest that progesterone treatment after TBI normalizes the levels of cell proliferation and cell death in the dentate gyrus of the hippocampus.

Genomic profile of Toll-like receptor pathways in traumatically brain-injured mice: effect of exogenous progesterone

Background

Traumatic brain injury (TBI) causes acute inflammatory responses that result in an enduring cascade of secondary neuronal loss and behavioral impairments. It has been reported that progesterone (PROG) can inhibit the increase of some inflammatory cytokines and inflammation-related factors induced by TBI. Toll-like receptors (TLRs) play a critical role in the induction and regulation of immune/inflammatory responses. Therefore, in the present study, we examined the genomic profiles of TLR-mediated pathways in traumatically injured brain and PROG's effects on these genes.

Methods

Bilateral cortical impact injury to the medial frontal cortex was induced in C57BL/6J mice. PROG was injected (i.p., 16 mg/kg body weight) at 1 and 6 h after surgery. Twenty-four hours post-surgery, mice were killed and peri-contusional brain tissue was harvested for genomic detection and protein measurement. RT-PCR arrays were used to measure the mRNA of 84 genes in TLR-mediated pathways. Western blot, ELISA and immunohistochemistry were used to confirm the protein expression of genes of interest.

Results

We found that 2 TLRs (TLR1 and 2), 5 adaptor/interacting proteins (CD14, MD-1, HSPA1a, PGRP and Ticam2) and 13 target genes (Ccl2, Csf3, IL1a, IL1b, IL1r1, IL6, IL-10, TNFa, Tnfrsf1a, Cebpb, Clec4e, Ptgs2 and Cxcl10) were significantly up-regulated after injury. Administration of PROG significantly down-regulated three of the 13 increased target genes after TBI (Ccl-2, IL-1b and Cxcl-10), but did not inhibit the expression of any of the detected TLRs and adaptor/interacting proteins. Rather, PROG up-regulated the expression of one TLR (TLR9), 5 adaptor/interacting proteins, 5 effectors and 10 downstream target genes. We confirmed that Ccl-2, Cxcl-10, TLR2 and TLR9 proteins were expressed in brain tissue, a finding consistent with our observations of mRNA expression.

Conclusion

The results demonstrate that TBI can increase gene expression in TLR-mediated pathways. PROG does not down-regulate the increased TLRs or their adaptor proteins in traumatically injured brain. Reduction of the observed inflammatory cytokines by PROG does not appear to be the result of inhibiting TLRs or their adaptors in the acute stage of TBI.

Progesterone, administered before kainic acid, prevents decrements in cognitive performance in the Morris Water Maze

The nature of progesterone (P₄)'s neuroprotective effects is of interest. We investigated effects of P₄ when administered before, or after, kainic acid, which produces ictal activity and damage to the hippocampus, to mediate effects on spatial performance. The hypothesis was that P₄, compared with vehicle, would reduce decrements in Morris Water Maze performance induced by kainic acid. Experiment 1: We examined the effects of kainic acid on plasma stress hormone, corticosterone, and progestogen (P₄ and its metabolites) levels in plasma and the hippocampus after subcutaneous (s.c.) P₄ administration to ovariectomized rats. Rats administered kainic acid had the highest corticosterone levels immediately following injection. P₄ is 5α-reduced to dihydroprogesterone (DHP) and subsequently metabolized to 5α-pregnan-3α-ol-20-one (3α,5α-THP) by 3α-hydroxysteroid dehydrogenase. The regimen of P₄ used produced circulating and hippocampal levels of P₄, DHP, and 3α,5α-THP within a physiological range, which declined at 14 hours postinjection and were not altered by kainic acid. Experiment 2: The physiological P₄ regimen was administered to rats before, or after, kainic acid-induced seizures, and later effects on water maze performance were compared with that of rats administered vehicle. Rats administered kainic acid had significantly poorer performance in the water maze (i.e., increased latencies and distances to the hidden platform) than did rats administered vehicle. Administration of P₄ before, but not after, kainic acid prevented these performance deficits. Thus, these data suggest that a physiological regimen of P₄ can prevent some of the deficits in water maze performance produced by kainic acid.

Progesterone prevents development of neuropathic pain in a rat model: Timing and duration of treatment are critical

BACKGROUND

Progesterone is emerging as an important protective agent against various injuries to the nervous system. Neuroprotective and remyelinating effects have been documented for this neurosteroid, which is synthesized by, and acts on, the central and peripheral nervous systems. Neuropathic pain is a severe, persistent condition that is generally resistant to treatment, and poses major personal, social, and economic burdens. The purpose of this study was to determine if single-dose or repeated progesterone administration would alleviate tactile hypersensitivity in a rat model of neuropathic pain, and to determine if early versus late initiation of treatment has an effect on the outcome.

METHODS

Rats were unilaterally implanted with a polyethylene cuff around the sciatic nerve, and sensitivity to von Frey filament stimulation was measured over approximately 12 weeks.

RESULTS

Rats given progesterone starting one hour after cuff implantation, and daily until day 4, exhibited tactile hypersensitivity similar to that of vehicle-treated rats for the duration of the study. When progesterone was started one hour after cuff implantation and given daily until day 10, rats exhibited no tactile hypersensitivity in the later part of the study, after treatment had stopped. When progesterone treatment was initiated at 20 days, once the model had been fully established, and given daily for 4 or even 11 days, no differences in withdrawal thresholds were observed compared with controls. Progesterone did not have any effect on withdrawal thresholds when given as a single dose, as measured at 30, 60 and 90 minutes after administration.

CONCLUSION

These results indicate that progesterone, when administered immediately after nerve injury, and for a sufficient period of time, can prevent the development of neuropathic pain, and may offer new strategies for the treatment of this highly debilitating condition.

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.

Progesterone and allopregnanolone attenuate blood-brain barrier dysfunction following permanent focal ischemia by regulating the expression of matrix metalloproteinases

Blood-brain barrier (BBB) breakdown after stroke is linked to the up-regulation of metalloproteinases (MMPs) and inflammation. This study examines the effects of progesterone (PROG) and its neuroactive metabolite allopregnanolone (ALLO) on BBB integrity following permanent middle cerebral artery occlusion (pMCAO). Rats underwent pMCAO by electro-coagulation and received intraperitoneal injections of PROG (8 mg/kg), ALLO (8 mg/kg) or vehicle at 1 h post-occlusion and then subcutaneous injections (8 mg/kg) at 6, 24, and 48 h. MMP activation and expression were analyzed by Western blot, immunohistochemistry and gelatin zymography 72 h post-pMCAO. Occludin1, claudin5, tumor necrosis factor-alpha (TNF-α) and Interleukin-6 (IL-6) were analyzed at 72 h post-pMCAO with Western blots. BBB permeability was measured by Evans blue extravasation and infarct size was evaluated by cresyl violet at 72 h after pMCAO. Ischemic injury significantly (p<0.05) increased the expression of MMP-9, MMP-2, TNF-α and IL-6, and reduced the levels of occludin1 and claudin5. These changes were followed by increased infarct size (% contralateral hemisphere) and Evans blue extravasation into the brain indicating compromise of the BBB. PROG and ALLO attenuated BBB disruption and infarct size following pMCAO by reducing MMPs and the inflammatory response and by preventing the degradation of occludin1 and claudin5. We conclude that PROG and ALLO can help to protect BBB disruption following pMCAO.