Modulatory role of neurosteroidogenesis in the spinal cord during peripheral nerve injury-induced chronic pain.

The brain and spinal cord (SC) are both targeted by various hormones, including steroid hormones. However, investigations of the modulatory role of hormones on neurobiological functions usually focus only on the brain. The SC received little attention although this structure pivotally controls motor and sensory functions. Here, we critically reviewed key data showing that the process of neurosteroid biosynthesis or neurosteroidogenesis occurring in the SC plays a pivotal role in the modulation of peripheral nerve injury-induced chronic pain (PNICP) or neuropathic pain. Indeed, several active steroidogenic enzymes expressed in the SC produce endogenous neurosteroids that interact with receptors of neurotransmitters controlling pain. The spinal neurosteroidogenesis is differentially regulated during PNICP condition and its blockade modifies painful sensations. The paper suggests that future investigations aiming to develop effective strategies against PNICP or neuropathic pain must integrate in a gender or sex dependent manner the regulatory effects exerted by spinal neurosteroidogenesis.

Rapid Discrimination of Neuromyelitis Optica Spectrum Disorder and Multiple Sclerosis Using Machine Learning on Infrared Spectra of Sera.

Neuromyelitis optica spectrum disorder (NMOSD) and multiple sclerosis (MS) are both autoimmune inflammatory and demyelinating diseases of the central nervous system. NMOSD is a highly disabling disease and rapid introduction of the appropriate treatment at the acute phase is crucial to prevent sequelae. Specific criteria were established in 2015 and provide keys to distinguish NMOSD and MS. One of the most reliable criteria for NMOSD diagnosis is detection in patient's serum of an antibody that attacks the water channel aquaporin-4 (AQP-4). Another target in NMOSD is myelin oligodendrocyte glycoprotein (MOG), delineating a new spectrum of diseases called MOG-associated diseases. Lastly, patients with NMOSD can be negative for both AQP-4 and MOG antibodies. At disease onset, NMOSD symptoms are very similar to MS symptoms from a clinical and radiological perspective. Thus, at first episode, given the urgency of starting the anti-inflammatory treatment, there is an unmet need to differentiate NMOSD subtypes from MS. Here, we used Fourier transform infrared spectroscopy in combination with a machine learning algorithm with the aim of distinguishing the infrared signatures of sera of a first episode of NMOSD from those of a first episode of relapsing-remitting MS, as well as from those of healthy subjects and patients with chronic inflammatory demyelinating polyneuropathy. Our results showed that NMOSD patients were distinguished from MS patients and healthy subjects with a sensitivity of 100% and a specificity of 100%. We also discuss the distinction between the different NMOSD serostatuses. The coupling of infrared spectroscopy of sera to machine learning is a promising cost-effective, rapid and reliable differential diagnosis tool capable of helping to gain valuable time in patients' treatment.

Neurosteroids and neuropathic pain management: Basic evidence and therapeutic perspectives.

Complex mechanisms involved in neuropathic pain that represents a major health concern make its management complicated. Because neurosteroids are bioactive steroids endogenously synthesized in the nervous system, including in pain pathways, they appear relevant to develop effective treatments against neuropathic pain. Neurosteroids act in paracrine or autocrine manner through genomic mechanisms and/or via membrane receptors of neurotransmitters that pivotally modulate pain sensation. Basic studies which uncovered a direct link between neuropathic pain symptoms and endogenous neurosteroid production/regulation, paved the way for the investigations of neurosteroid therapeutic potential against pathological pain. Concordantly, antinociceptive properties of synthetic neurosteroids were evidenced in humans and animals. Neurosteroids promote peripheral analgesia mediated by T-type calcium and gamma-aminobutyric acid type A channels, counteract chemotherapy-induced neuropathic pain and ameliorate neuropathic symptoms of injured spinal cord animals by stimulating anti-inflammatory, remyelinating and neuroprotective processes. Together, these data open interesting perspectives for neurosteroid-based strategies to manage/alleviate efficiently neuropathic pain.

Allopregnanolone and Progesterone in Experimental Neuropathic Pain: Former and New Insights with a Translational Perspective.

In the last decades, an active and stimulating area of research has been devoted to explore the role of neuroactive steroids in pain modulation. Despite challenges, these studies have clearly contributed to unravel the multiple and complex actions and potential mechanisms underlying steroid effects in several experimental conditions that mimic human chronic pain states. Based on the available data, this review focuses mainly on progesterone and its reduced derivative allopregnanolone (also called 3α,5α-tetrahydroprogesterone) which have been shown to prevent or even reverse the complex maladaptive changes and pain behaviors that arise in the nervous system after injury or disease. Because the characterization of new related molecules with improved specificity and enhanced pharmacological profiles may represent a crucial step to develop more efficient steroid-based therapies, we have also discussed the potential of novel synthetic analogs of allopregnanolone as valuable molecules for the treatment of neuropathic pain.

Serum-based differentiation between multiple sclerosis and amyotrophic lateral sclerosis by Random Forest classification of FTIR spectra.

The challenging diagnosis and differentiation between multiple sclerosis and amyotrophic lateral sclerosis relies on the clinical assessment of the symptoms along with magnetic resonance imaging and sampling cerebrospinal fluid for the search of biomarkers for either disease. Despite the progress made in imaging techniques and biomarker identification, misdiagnosis still occurs. Here we used 2.5 µL of serum samples to obtain the infrared spectroscopic signatures of sera of multiple sclerosis and amyotrophic lateral sclerosis patients and compared them to those of healthy controls. The spectra are then classified with the help of a two-fold Random Forest cross-validation algorithm. This approach shows that infrared spectroscopy is powerful in discriminating between the two diseases and healthy controls by offering high specificity for multiple sclerosis (100%) and amyotrophic lateral sclerosis (98%). In addition, data after six and twelve months of treatment of the multiple sclerosis patients with biotin are discussed.

Beneficial effects of Gelsemium-based treatment against paclitaxel-induced painful symptoms.

Chemotherapeutic drugs induce various side effects including painful peripheral neuropathy that represents a major concern. The widely used anticancer drug paclitaxel causes neurological side effects such as burning pain, allodynia, and hyperalgesia. Neuroprotective substances that may effectively counteract paclitaxel-induced neuropathic symptoms are needed. Here, we investigated the potential of Gelsemium sempervirens (GS) to counteract paclitaxel-evoked painful neuropathy in rats. Using the von Frey hair and acetone behavioral tests, we investigated the potential of GS centesimal (C) dilutions 3, 5, and 9C to prevent or to correct paclitaxel-induced cold allodynia and mechanical allodynia/hyperalgesia involved in neuropathic pain. We found that a prophylactic or corrective treatment with GS dilutions prevented or suppressed PAC-evoked cold allodynia and mechanical allodynia/hyperalgesia, by reversing to normal, decreased cold thermal and mechanical pain thresholds of PAC-treated rats. In particular, preventive or corrective treatments with GS dilution 3C counteracted PAC-evoked allodynic and hyperalgesic responses. Also, GS dilution 5C (in a lesser extent than 3C) significantly reduced PAC-induced mechanical allodynia/hyperalgesia while GS dilution 9C was ineffective. PAC-evoked neuropathic symptoms were efficiently reduced after 1 week treatment with GS dilutions 3 or 5C and the beneficial action increased after 2 weeks. GS dilutions, particularly 3C, also counteracted or prevented PAC-induced sciatic nerve axon alterations and decreased the density of intraepidermal nerve fibers. Altogether, these results obtained in the rat preclinical model suggest that GS dilution-based treatment may constitute an interesting option to explore for the long-term management of pain without undesirable effects.

The translocator protein ligand XBD173 improves clinical symptoms and neuropathological markers in the SJL/J mouse model of multiple sclerosis.

Multiple sclerosis (MS) is a severe autoimmune disease characterized by inflammatory, demyelinating and neurodegenerative components causing motor, sensory, visual and/or cognitive symptoms. The relapsing-remitting MS affecting 85% of patients is reliably mimicked by the proteolipid-protein (PLP)-induced experimental autoimmune encephalomyelitis (EAE) SJL/J-mouse model. Significant progress was made for MS treatment but the development of effective therapies devoid of severe side-effects remains a great challenge. Here, we combine clinical, behavioral, histopathological, biochemical and molecular approaches to demonstrate that low and well tolerated doses (10-20mg/kg) of TSPO ligand XBD173 (Emapunil) efficiently ameliorate clinical signs and neuropathology of PLP-EAE mice. In addition to the conventional clinical scoring of symptoms, we applied the robust behavioral Catwalk-method to confirm that XBD173 (10mg/kg) increases the maximum contact area parameter at EAE-disease peak, indicating an improvement/recovery of motor functions. Consistently, histopathological studies coupled with microscope-cellSens quantification and RT-qPCR analyzes showed that XBD173 prevented demyelination by restoring normal protein and mRNA levels of myelin basic protein that was significantly repressed in PLP-EAE mice spinal cord and brain. Interestingly, ELISA-based measurement revealed that XBD173 increased allopregnanolone concentrations in PLP-EAE mice spinal and brain tissues. Furthermore, flow cytometry assessment demonstrated that XBD173 therapy decreased serum level of pro-inflammatory cytokines, including interleukin-17A, Interleukin-6 and tumor-necrosis-factor alpha in PLP-EAE mice. As the optimal XBD173 dosing exerting the maximal beneficial action in EAE mice is the lower 10mg/kg dose, the paper opens interesting perspectives for the development of efficient and safe therapies against MS with slight or no side-effects.

Monomeric Amyloid Peptide-induced Toxicity in Human Oligodendrocyte Cell Line and Mouse Brain Primary Mixed-glial Cell Cultures: Evidence for a Neuroprotective Effect of Neurosteroid 3α-O-allyl-allopregnanolone.

Amyloid-peptide (Aß) monomeric forms (ABM) occurring in presymptomatic Alzheimer's disease (AD) brain are thought to be devoid of neurotoxicity while the transition/aggregation of ABM into oligomers is determinant for Aß-induced toxicity since Aß is predominantly monomeric up to 3 µM and aggregates over this concentration. However, recent imaging and/or histopathological investigations revealed alterations of myelin in prodromal AD brain in absence of aggregated Aß oligomers, suggesting that ABM may induce toxicity in myelin-producing cells in early AD-stages. To check this hypothesis, here we studied ABM effects on the viability of the Human oligodendrocyte cell line (HOG), a reliable oligodendrocyte model producing myelin proteins. Furthermore, to mimic closely interactions between oligodendrocytes and other glial cells regulating myelination, we investigated also ABM effects on mouse brain primary mixed-glial cell cultures. Various methods were combined to show that ABM concentrations (600 nM-1 µM), extremely lower than 3 µM, significantly decreased HOG cell and mouse brain primary mixed-glial cell survival. Interestingly, flow-cytometry studies using specific cell-type markers demonstrated that oligodendrocytes represent the most vulnerable glial cell population affected by ABM toxicity. Our work also shows that the neurosteroid 3α-O-allyl-allopregnanolone BR351 (250 and 500 nM) efficiently prevented ABM-induced HOG and brain primary glial cell toxicity. Bicuculline (50-100 nM), the GABA-A-receptor antagonist, was unable to block/reduce BR351 effect against ABM-induced HOG and primary glial cell toxicity, suggesting that BR351-evoked neuroprotection of these cells may not depend on GABA-A-receptor allosterically modulated by neurosteroids. Altogether, our results suggest that further exploration of BR351 therapeutic potential may offer interesting perspectives to develop effective neuroprotective strategies.

Myelin in Alzheimer's disease: culprit or bystander?

Alzheimer's disease (AD) is a neurodegenerative disorder with neuronal and synaptic losses due to the accumulation of toxic amyloid ß (Αß) peptide oligomers, plaques, and tangles containing tau (tubulin-associated unit) protein. While familial AD is caused by specific mutations, the sporadic disease is more common and appears to result from a complex chronic brain neuroinflammation with mitochondriopathies, inducing free radicals' accumulation. In aged brain, mutations in DNA and several unfolded proteins participate in a chronic amyloidosis response with a toxic effect on myelin sheath and axons, leading to cognitive deficits and dementia. Αß peptides are the most frequent form of toxic amyloid oligomers. Accumulations of misfolded proteins during several years alters different metabolic mechanisms, induce chronic inflammatory and immune responses with toxic consequences on neuronal cells. Myelin composition and architecture may appear to be an early target for the toxic activity of Aß peptides and others hydrophobic misfolded proteins. In this work, we describe the possible role of early myelin alterations in the genesis of neuronal alterations and the onset of symptomatology. We propose that some pathophysiological and clinical forms of the disease may arise from structural and metabolic disorders in the processes of myelination/demyelination of brain regions where the accumulation of non-functional toxic proteins is important. In these forms, the primacy of the deleterious role of amyloid peptides would be a matter of questioning and the initiating role of neuropathology would be primarily the fact of dysmyelination.

A Narrative Review on Axonal Neuroprotection in Multiple Sclerosis.

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) resulting in demyelination and neurodegeneration. The therapeutic strategy is now largely based on reducing inflammation with immunosuppressive drugs. Unfortunately, when disease progression is observed, no drug offers neuroprotection apart from its anti-inflammatory effect. In this review, we explore current knowledge on the assessment of neurodegeneration in MS and look at putative targets that might prove useful in protecting the axon from degeneration. Among them, Bruton's tyrosine kinase inhibitors, anti-apoptotic and antioxidant agents, sex hormones, statins, channel blockers, growth factors, and molecules preventing glutamate excitotoxicity have already been studied. Some of them have reached phase III clinical trials and carry a great message of hope for our patients with MS.

Translocator Protein Ligand PIGA1138 Reduces Disease Symptoms and Severity in Experimental Autoimmune Encephalomyelitis Model of Primary Progressive Multiple Sclerosis.

Multiple sclerosis (MS) is an autoimmune and demyelinating disease of the central nervous system (CNS) caused by CNS infiltration of peripheral immune cells, immune-mediated attack of the myelin sheath, neuroinflammation, and/or axonal/neuronal dysfunctions. Some drugs are available to cope with relapsing-remitting MS (RRMS) but there is no therapy for the primary progressive MS (PPMS). Because growing evidence supports a regulatory role of the translocator protein (TSPO) in neuroinflammatory, demyelinating, and neurodegenerative processes, we investigated the therapeutic potential of phenylindolyilglyoxylamydes (PIGAs) TSPO ligands in myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) mice mimicking the human PPMS. MOG-EAE C57Bl/6-mice were treated by TSPO ligands PIGA839, PIGA1138, or the vehicle. Several methods were combined to evaluate PIGAs-TSPO ligand effects on MOG-EAE symptoms, CNS infiltration by immune cells, demyelination, and axonal damages. PIGA1138 (15 mg/kg) drastically reduced MOG-EAE mice clinical scores, ameliorated motor dysfunctions assessed with the Catwalk device, and counteracted MOG-EAE-induced demyelination by preserving Myelin basic protein (MBP) expression in the CNS. Furthermore, PIGA1138-treatment prevented EAE-evoked decreased neurofilament-200 expression in spinal and cerebellar axons. Moreover, PIGA1138 inhibited peripheral immune-CD45 + cell infiltration in the CNS, suggesting that it may control inflammatory mechanisms involved in PPMS. Concordantly, PIGA1138 enhanced anti-inflammatory interleukin-10 serum level in MOG-EAE mice. PIGA1138-treatment, which increased neurosteroid allopregnanolone production, ameliorated all pathological biomarkers, while PIGA839, unable to activate neurosteroidogenesis in vivo, exerted only moderate/partial effects in MOG-EAE mice. Altogether, our results suggest that PIGA1138-based treatment may represent an interesting possibility to be explored for the innovation of effective therapies against PPMS.

Cellular and functional evidence for a protective action of neurosteroids against vincristine chemotherapy-induced painful neuropathy.

Painful neuropathy is a major side-effect limiting cancer chemotherapy. Therefore, novel strategies are required to suppress the neuropathic effects of anticancer drugs without altering their chemotherapeutic effectiveness. By combining biochemical, neuroanatomical/neurochemical, electrophysiological and behavioral methods, we demonstrated that progesterone-derived neurosteroids including 5alpha-dihydroprogesterone and 3alpha,5alpha-tetrahydroprogesterone suppressed neuropathic symptoms evoked in naive rats by vincristine. Neurosteroids counteracted vincristine-induced alterations in peripheral nerves including 2',3'-cyclic nucleotide 3'-phosphodiesterase, neurofilament-200 kDa and intraepidermal nerve fiber repression, nerve conduction velocity, and pain transmission abnormalities (allodynia/hyperalgesia). In skin-tumor rats generated with carcinosarcoma-cells, vincristine, which suppressed the skin tumor and restored normal blood concentration of vascular endothelial growth factor (VEGF), reproduced neuropathic side-effects. Administered alone, neurosteroids did not affect the tumor and VEGF level. Combined with vincristine, neurosteroids preserved vincristine anti-tumor action but counteracted vincristine-induced neural side-effects. Together, these results provide valuable insight into the cellular and functional mechanisms underlying anticancer drug-induced neuropathy and suggest a neurosteroid-based strategy to eradicate painful neuropathy.

Comparative Analysis of Gelsemine and Gelsemium sempervirens Activity on Neurosteroid Allopregnanolone Formation in the Spinal Cord and Limbic System.

Centesimal dilutions (5, 9 and 15 cH) of Gelsemium sempervirens are claimed to be capable of exerting anxiolytic and analgesic effects. However, basic results supporting this assertion are rare, and the mechanism of action of G. sempervirens is completely unknown. To clarify the point, we performed a comparative analysis of the effects of dilutions 5, 9 and 15 cH of G. sempervirens or gelsemine (the major active principle of G. sempervirens) on allopregnanolone (3α,5α-THP) production in the rat limbic system (hippocampus and amygdala or H-A) and spinal cord (SC). Indeed, H-A and SC are two pivotal structures controlling, respectively, anxiety and pain that are also modulated by the neurosteroid 3α,5α-THP. At the dilution 5 cH, both G. sempervirens and gelsemine stimulated [(3)H]progesterone conversion into [(3)H]3α,5α-THP by H-A and SC slices, and the stimulatory effect was fully (100%) reproducible in all assays. The dilution 9 cH of G. sempervirens or gelsemine also stimulated 3α,5α-THP formation in H-A and SC but the reproducibility rate decreased to 75%. At 15 cH of G. sempervirens or gelsemine, no effect was observed on 3α,5α-THP neosynthesis in H-A and SC slices. The stimulatory action of G. sempervirens and gelsemine (5 cH) on 3α,5α-THP production was blocked by strychnine, the selective antagonist of glycine receptors. Altogether, these results, which constitute the first basic demonstration of cellular effects of G. sempervirens, also offer interesting possibilities for the improvement of G. sempervirens-based therapeutic strategies.

Microglial Cell Morphology and Phagocytic Activity Are Critically Regulated by the Neurosteroid Allopregnanolone: A Possible Role in Neuroprotection.

Microglial cells are key players in neural pathogenesis and microglial function regulation appears to be pivotal in controlling neuroinflammatory/neurological diseases. Here, we investigated the effects and mechanism of action of neurosteroid allopregnanolone (ALLO) on murine microglial BV-2 cells and primary microglia in order to determine ALLO-induced immunomodulatory potential and to provide new insights for the development of both natural and safe neuroprotective strategies targeting microglia. Indeed, ALLO-treatment is increasingly suggested as beneficial in various models of neurological disorders but the underlying mechanisms have not been elucidated. Therefore, the microglial cells were cultured with various serum concentrations to mimic the blood-brain-barrier rupture and to induce their activation. Proliferation, viability, RT-qPCR, phagocytosis, and morphology analyzes, as well as migration with time-lapse imaging and quantitative morphodynamic methods, were combined to investigate ALLO actions on microglia. BV-2 cells express subunits of GABA-A receptor that mediates ALLO activity. ALLO (10µM) induced microglial cell process extension and decreased migratory capacity. Interestingly, ALLO modulated the phagocytic activity of BV-2 cells and primary microglia. Our results, which show a direct effect of ALLO on microglial morphology and phagocytic function, suggest that the natural neurosteroid-based approach may contribute to developing effective strategies against neurological disorders that are evoked by microglia-related abnormalities.

Raman Imaging Reveals Accumulation of Hemoproteins in Plaques from Alzheimer's Diseased Tissues.

Hemes have been suggested to play a central role in Alzheimer's disease since they show high peroxidase reactivity when bound to amyloid ß peptides, leading to the production of reactive oxygen species. Here we used Fourier transform infrared and Raman imaging on Alzheimer's diseased mice and human brain tissue. Our finding suggests the accumulation of hemes in the senile plaques of both murine and human samples. We compared the Raman signature of the plaques to the ones of various hemeoproteins and to the hemin-Aß-42 complex. The detected Raman signature of the plaques does not allow identifying the type of heme accumulating in the plaques.

Sciatic nerve injury induces apoptosis of dorsal root ganglion satellite glial cells and selectively modifies neurosteroidogenesis in sensory neurons.

Neurosteroids are synthesized either by glial cells, by neurons, or within the context of neuron-glia cross-talk. Various studies suggested neurosteroid involvement in the control of neurodegeneration but there is no evidence showing that the natural protection of nerve cells against apoptosis directly depends on their own capacity to produce neuroprotective neurosteroids. Here, we investigated the interactions between neurosteroidogenesis and apoptosis occurring in sensory structures of rats subjected to neuropathic pain generated by sciatic nerve chronic constriction injury (CCI). Using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), we observed no apoptotic cells in the spinal cord up to 30 days after CCI although pain symptoms such as mechano-allodynia, thermal and mechanical hyperalgesia were evidenced with the Hargreaves's behavioral and von Frey filament tests. In contrast, double-labeling experiments combining TUNEL and immunostaining with antibodies against glutamine synthetase or neuronal nuclei protein revealed apoptosis occurrence in satellite glial cells (SGC) (not in neurons) of CCI rat ipsilateral dorsal root ganglia (DRG) at day 30 after injury. Pulse-chase experiments coupled with high performance liquid chromatography and flow scintillation detection showed that, among numerous biosynthetic pathways converting [(3)H]pregnenolone into various [(3)H]neurosteroids, only [(3)H]estradiol formation was selectively modified and upregulated in DRG of CCI rats. Consistently, immunohistochemical investigations localized aromatase (estradiol-synthesizing enzyme) in DRG neurons but not in SGC. Pharmacological inhibition of aromatase caused apoptosis of CCI rat DRG neurons. Altogether, our results suggest that endogenously produced neurosteroids such as estradiol may be pivotal for the protection of DRG sensory neurons against sciatic nerve CCI-induced apoptosis.

Tryptophan metabolites modify brain Aß peptide degradation: A role in Alzheimer's disease?

Among several processes, a decrease in amyloid-beta (Aß) peptide elimination is thought to be one of the major pathophysiological factors in Alzheimer's disease (AD). Neprilysin (NEP) is a key metalloproteinase controlling the degradation and clearance of Aß peptides in the brain. NEP is induced by several pharmacological substances, amyloid deposits and somatostatin, but the physiological regulation of its expression remains unclear. This situation hampers the exploitation of NEP regulatory factors/mechanisms to develop effective strategies against Aß peptide accumulation-induced brain toxicity. Based on recent data aimed at elucidating this major question, the present paper addresses and critically discusses the role of 5-hydroxyindole-acetic acid (5-HIAA) and kynurenic acid (KYNA) in the regulation of NEP activity/expression in the brain. Both 5-HIAA and KYNA are endogenous metabolites of tryptophan, an essential amino-acid obtained through diet and gut microbiome. By interacting with the aryl hydrocarbon receptor, various tryptophan metabolites modulate several metalloproteinases regulating brain Aß peptide levels under normal and pathological conditions such as AD. In particular, interesting data reviewed here show that 5-HIAA and KYNA stimulate NEP activity/expression to prevent Aß peptide-induced neurotoxicity. These data open promising perspectives for the development of tryptophan metabolite-based therapies against AD.

Biochemical and functional evidence for the control of pain mechanisms by dehydroepiandrosterone endogenously synthesized in the spinal cord.

We investigated the role and mechanism of action of dehydroepiandrosterone (DHEA) produced by the spinal cord (SC) in pain modulation in sciatic-neuropathic and control rats. Real-time polymerase chain reaction (PCR) after reverse transcription revealed cytochrome P450c17 (DHEA-synthesizing enzyme) gene repression in neuropathic rat SC. A combination of pulse-chase experiments, high performance liquid chromatography (HPLC), and flow-scintillation detection showed decreased DHEA biosynthesis from pregnenolone in neuropathic SC slices. Radioimmunoassays demonstrated endogenous DHEA level drop in neuropathic SC. Behavioral analysis showed a rapid pronociceptive and a delayed antinociceptive action of acute DHEA treatment. Inhibition of DHEA biosynthesis in the SC by intrathecally administered ketoconazole (P450c17 inhibitor) induced analgesia in neuropathic rats. BD1047 (sigma-1 receptor antagonist) blocked the transient pronociceptive effect evoked by acute DHEA administration. Chronic DHEA treatment increased and maintained elevated the basal nociceptive thresholds in neuropathic and control rats, suggesting that androgenic metabolites generated from daily administered DHEA exerted analgesic effects while DHEA itself (before being metabolized) induced a rapid pronociceptive action. Indeed, intrathecal administration of testosterone, an androgen deriving from DHEA, caused analgesia in neuropathic rats. Together, these molecular, biochemical, and functional results demonstrate that DHEA synthesized in the SC controls pain mechanisms. Possibilities are opened for pain modulation by drugs regulating P450c17 in nerve cells.

Peripheral neuropathy and neurosteroid formation in the central nervous system.

Neurons and glial cells are capable of synthesizing bioactive steroids also called neurosteroids which modulate the nervous system activity. Neurosteroids act via autocrine or paracrine mechanisms. Therefore, before neurosteroids can be considered as endogenous modulators of a specific neurophysiologic function, it is compulsory that the process of neurosteroidogenesis occurs in neural pathways controlling this function. Based on pharmacological observations, various studies suggested the involvement of endogenous neurosteroids in the modulation of a variety of neurobiological processes. However, the direct link between these processes and endogenous production of neurosteroids in the nervous system remains unknown. The present review recapitulates a series of results showing the existence of interactions between peripheral nerve injury and neurosteroid biosynthesis in the central nervous system (CNS). In particular, the paper discusses the impact of sciatic nerve ligature on genomic and biochemical components of neurosteroidogenesis in the spinal cord and brainstem areas including the parabrachial, raphe magnus and dorsal raphe nuclei which control nociception. It appears that peripheral nerve injuries evoke changes in the gene expression and biological activity of cytochrome P450side-chain-cleavage, the key enzyme catalyzing the onset of neurosteroidogenesis in the CNS. Owing to neurosteroid involvement in the control of various neurobiological functions, these data suggest that neurosteroidogenesis is an endogenous mechanism activated in the CNS for adaptation of the body to chronic peripheral neuropathies. Therefore, strategies based on selective targeting of neurosteroidogenic pathways may constitute interesting approaches to develop novel therapy against disorders provoked by central and peripheral neuropathies.

The biological activity of 3alpha-hydroxysteroid oxido-reductase in the spinal cord regulates thermal and mechanical pain thresholds after sciatic nerve injury.

Identification of cellular targets pertinent for the development of effective therapies against pathological pain constitutes a difficult challenge. We combined several approaches to show that 3alpha-hydroxysteroid oxido-reductase (3alpha-HSOR), abundantly expressed in the spinal cord (SC), is a key target, the modulation of which markedly affects nociception. 3alpha-HSOR catalyzes the biosynthesis and oxidation of 3alpha,5alpha-reduced neurosteroids as allopregnanolone (3alpha,5alpha-THP), which stimulates GABA(A) receptors. Intrathecal injection of Provera (pharmacological inhibitor of 3alpha-HSOR activity) in naive rat SC decreased thermal and mechanical nociceptive thresholds assessed with behavioral methods. In contrast, pain thresholds were dose-dependently increased by 3alpha,5alpha-THP. In animals subjected to sciatic nerve injury-evoked neuropathic pain, molecular and biochemical experiments revealed an up-regulation of 3alpha-HSOR reductive activity in the SC. Enhancement of 3alpha,5alpha-THP concentration in the SC induced analgesia in neuropathic rats while Provera exacerbated their pathological state. Possibilities are opened for chronic pain control with drugs modulating 3alpha-HSOR activity in nerve cells.