Minocycline blocks nitric oxide-induced neurotoxicity by inhibition p38 MAP kinase in rat cerebellar granule neurons

Minocycline Abrogates Individual Differences in Nerve Injury-Evoked Affective Disturbances in Male Rats and Prevents Associated Supraspinal Neuroinflammation

Chronic neuropathic pain precipitates a complex range of affective and behavioural disturbances that differ markedly between individuals. While the reasons for differences in pain-related disability are not well understood, supraspinal neuroimmune interactions are implicated. Minocycline has antidepressant effects in humans and attenuates affective disturbances in rodent models of pain, and acts by reducing neuroinflammation in both the spinal cord and brain. Previous studies, however, tend not to investigate how minocycline modulates individual affective responses to nerve injury, or rely on non-naturalistic behavioural paradigms that fail to capture the complexity of rodent behaviour. We investigated the development and resolution of pain-related affective disturbances in nerve-injured male rats by measuring multiple spontaneous ethological endpoints on a longitudinal naturalistic foraging paradigm, and the effect of chronic oral minocycline administration on these changes. Disrupted foraging behaviours appeared in 22% of nerve-injured rats - termed 'affected' rats - and were present at day 14 but partially resolved by day 21 post-injury. Minocycline completely prevented the emergence of an affected subgroup while only partly attenuating mechanical allodynia, dissociating the relationship between pain and affect. This was associated with a lasting downregulation of ΔFosB expression in ventral hippocampal neurons at day 21 post-injury. Markers of microglia-mediated neuroinflammation were not present by day 21, however proinflammatory microglial polarisation was apparent in the medial prefrontal cortex of affected rats and not in CCI minocycline rats. Individual differences in affective disturbances following nerve injury are therefore temporally related to altered microglial morphology and hippocampal neuronal activation, and are abrogated by minocycline.

Neuro-Inflammation Modulation and Post-Traumatic Brain Injury Lesions: From Bench to Bed-Side

Head trauma is the most common cause of disability in young adults. Known as a silent epidemic, it can cause a mosaic of symptoms, whether neurological (sensory-motor deficits), psychiatric (depressive and anxiety symptoms), or somatic (vertigo, tinnitus, phosphenes). Furthermore, cranial trauma (CT) in children presents several particularities in terms of epidemiology, mechanism, and physiopathology-notably linked to the attack of an immature organ. As in adults, head trauma in children can have lifelong repercussions and can cause social and family isolation, difficulties at school, and, later, socio-professional adversity. Improving management of the pre-hospital and rehabilitation course of these patients reduces secondary morbidity and mortality, but often not without long-term disability. One hypothesized contributor to this process is chronic neuroinflammation, which could accompany primary lesions and facilitate their development into tertiary lesions. Neuroinflammation is a complex process involving different actors such as glial cells (astrocytes, microglia, oligodendrocytes), the permeability of the blood-brain barrier, excitotoxicity, production of oxygen derivatives, cytokine release, tissue damage, and neuronal death. Several studies have investigated the effect of various treatments on the neuroinflammatory response in traumatic brain injury in vitro and in animal and human models. The aim of this review is to examine the various anti-inflammatory therapies that have been implemented.

Revisiting Minocycline in Intracerebral Hemorrhage: Mechanisms and Clinical Translation

Intracerebral hemorrhage (ICH) is an important subtype of stroke with an unsatisfactory prognosis of high mortality and disability. Although many pre-clinical studies and clinical trials have been performed in the past decades, effective therapy that meaningfully improve prognosis and outcomes of ICH patients is still lacking. An active area of research is towards alleviating secondary brain injury after ICH through neuroprotective pharmaceuticals and in which minocycline is a promising candidate. Here, we will first discuss new insights into the protective mechanisms of minocycline for ICH including reducing iron-related toxicity, maintenance of blood-brain barrier, and alleviating different types of cell death from preclinical data, then consider its shortcomings. Finally, we will review clinical trial perspectives for minocycline in ICH. We hope that this summary and discussion about updated information on minocycline as a viable treatment for ICH can facilitate further investigations.

Therapeutic Strategies for Immune Transformation in Parkinson's Disease

Dysregulation of innate and adaptive immunity can lead to alpha-synuclein (α-syn) misfolding, aggregation, and post-translational modifications in Parkinson's disease (PD). This process is driven by neuroinflammation and oxidative stress, which can contribute to the release of neurotoxic oligomers that facilitate dopaminergic neurodegeneration. Strategies that promote vaccines and antibodies target the clearance of misfolded, modified α-syn, while gene therapy approaches propose to deliver intracellular single chain nanobodies to mitigate α-syn misfolding, or to deliver neurotrophic factors that support neuronal viability in an otherwise neurotoxic environment. Additionally, transformative immune responses provide potential targets for PD therapeutics. Anti-inflammatory drugs represent one strategy that principally affects innate immunity. Considerable research efforts have focused on transforming the balance of pro-inflammatory effector T cells (Teffs) to favor regulatory T cell (Treg) activity, which aims to attenuate neuroinflammation and support reparative and neurotrophic homeostasis. This approach serves to control innate microglial neurotoxic activities and may facilitate clearance of α-syn aggregates accordingly. More recently, changes in the intestinal microbiome have been shown to alter the gut-immune-brain axis leading to suppressed leakage of bacterial products that can promote peripheral inflammation and α-syn misfolding. Together, each of the approaches serves to interdict chronic inflammation associated with disordered immunity and neurodegeneration. Herein, we examine research strategies aimed at improving clinical outcomes in PD.

Oral Minocycline Therapy Improves Symptoms of Myalgic Encephalomyelitis, Especially in the Initial Disease Stage

Objective Central nervous system dysfunction associated with myalgic encephalomyelitis (ME) has been suggested to be the main cause of chronic fatigue syndrome. In animal models of chronic fatigue, minocycline was reported to act as a suppressor of neural inflammation. Minocycline may thus exert favorable therapeutic effects in patients with ME. Methods Oral minocycline (100 mg×2 on the first day, followed by 100 mg/day for 41 days) was administered to 100 patients with ME. The performance status score (0-9), orthostatic intolerance during the 10-min standing test, neurologic disequilibrium, and neuropathic pain were compared before and after treatment. Results After therapy completion, favorable effects were observed with a decrease in the performance status score of ≥2 points in 27 patients (27%). Before treatment, 6 of the 27 patients had orthostatic intolerance with an inability to complete the 10-min standing test; after treatment, this symptom resolved in 4 and improved in 2 patients. In addition, after treatment, postural orthostatic tachycardia resolved in five of eight patients, disequilibrium resolved in five of eight patients, and fibromyalgia or neuropathic pain was attenuated in four of five patients. The favorable effects appeared dependent on a shorter disease duration, primarily for a duration of less than three years and most frequently within six months of the disease onset. However, acute adverse effects with nausea and/or dizziness caused 38 patients (38%) to discontinue treatment in the first few days. Conclusion Oral minocycline therapy may be an effective treatment option for patients with ME, especially in the initial stage of the disease.

Mitochondria and Antibiotics: For Good or for Evil?

The discovery and application of antibiotics in the common clinical practice has undeniably been one of the major medical advances in our times. Their use meant a drastic drop in infectious diseases-related mortality and contributed to prolonging human life expectancy worldwide. Nevertheless, antibiotics are considered by many a double-edged sword. Their extensive use in the past few years has given rise to a global problem: antibiotic resistance. This factor and the increasing evidence that a wide range of antibiotics can damage mammalian mitochondria, have driven a significant sector of the medical and scientific communities to advise against the use of antibiotics for purposes other to treating severe infections. Notwithstanding, a notorious number of recent studies support the use of these drugs to treat very diverse conditions, ranging from cancer to neurodegenerative or mitochondrial diseases. In this context, there is great controversy on whether the risks associated to antibiotics outweigh their promising beneficial features. The aim of this review is to provide insight in the topic, purpose for which the most relevant findings regarding antibiotic therapies have been discussed.

Stroke and immunotherapy: Potential mechanisms and its implications as immune-therapeutics

Ischemia or brain injuries are mostly associated with emergency admissions and huge mortality rates. Stroke is a fatal cerebrovascular malady and second top root of disability and death in both developing and developed countries with a projected rise of 24.9% (from 2010) by 2030. It's the most frequent cause of morbidities and systemic permanent morbidities due to its multi-organ systemic pathology. Brain edema or active immune response cause disturbed or abnormal systemic affects causing inflammatory damage leading to secondary infection and secondary immune response which leads to activation like pneumonia or urine tract infections. There are a variety of post stroke treatments available which claims their usefulness in reducing or inhibiting post stroke and recurrent stroke damage followed by heavy inflammatory actions. Stroke does change the quality of life and also ensures daily chronic rapid neurodegeneration and cognitive decline. The only approved therapies for stroke are alteplase and thrombectomy which is associated with adverse outcomes and are not a total cure for ischemic stroke. Stroke and immune response are reciprocal to the pathology and time of event and it progresses till untreated. The immune reaction during ischemia opens new doors for advanced targeted therapeutics. Nowadays stem cell therapy has shown better results in stroke-prone individuals. Few monoclonal antibodies like natalizumab have shown great impact on pre-clinical and clinical stroke trial studies. In this current review, we have explored an immunology of stroke, current therapeutic scenario and future potential targets as immunotherapeutic agents in stroke therapeutics.

Tetracyclines, a promise for neuropsychiatric disorders: from adjunctive therapy to the discovery of new targets for rational drug design in psychiatry

Major mental disorders, such as schizophrenia, bipolar disorder, and major depressive disorder, represent the leading cause of disability worldwide. Nevertheless, the current pharmacotherapy has several limitations, and a large portion of patients do not respond appropriately to it or remain with disabling symptoms overtime. Traditionally, pharmacological interventions for psychiatric disorders modulate dysfunctional neurotransmitter systems. In the last decades, compelling evidence has advocated for chronic inflammatory mechanisms underlying these disorders. Therefore, the repurposing of anti-inflammatory agents has emerged as an attractive therapeutic tool for mental disorders. Minocycline (MINO) and doxycycline (DOXY) are semisynthetic second-generation tetracyclines with neuroprotective and anti-inflammatory properties. More recently, the most promising results obtained in clinical trials using tetracyclines for major psychiatric disorders were for schizophrenia. In a reverse translational approach, tetracyclines inhibit microglial reactivity and toxic inflammation by mechanisms related to the inhibition of nuclear factor kappa B signaling, cyclooxygenase 2, and matrix metalloproteinases. However, the molecular mechanism underlying the effects of these tetracyclines is not fully understood. Therefore, the present review sought to summarize the latest findings of MINO and DOXY use for major psychiatric disorders and present the possible targets to their molecular and behavioral effects. In conclusion, tetracyclines hold great promise as (ready-to-use) agents for being used as adjunctive therapy for human neuropsychiatric disorders. Hence, the understanding of their molecular mechanisms may contribute to the discovery of new targets for the rational drug design of novel psychoactive agents.

Potential of Antibiotics for the Treatment and Management of Parkinson Disease: An Overview

Evidences have emerged over the last 2 decades to ascertain the proof of concepts viz. mitochondrial dysfunction, inflammation-derived oxidative damage and cytokine-induced toxicity that play a significant role in Parkinson's disease (PD). The available pharmacotherapies for PD are mainly symptomatic and typically indications of L-DOPA to restrain dopamine deficiency and their consequences. In the 21st century, the role of the antibiotics has emerged at the forefront of medicine in health and human illness. There are several experimental and pre-clinical evidences that supported the potential use of antibiotic as neuroprotective agent. The astonishing effects of antibiotics and their neuroprotective properties against neurodegeneration and neuro-inflammation would be phenomenal for the development of effective therapy against PD. Antibiotics are also testified as useful not only to prevent the formation of alpha-synuclein but also act on mitochondrial dysfunction and neuro-inflammation. Thus, the possible therapy with antibiotics in PD would impact both the pathways leading to neuronal cell death in substantia nigra and pars compacta in midbrain. Moreover, the antibiotic based pharmacotherapy will open a scientific research passageway to add more to the evidence based and rational use of antibiotics for the treatment and management of PD and other neurodegenerative disorders.

Role of CGRP in Neuroimmune Interaction via NF-κB Signaling Genes in Glial Cells of Trigeminal Ganglia

Activation of the trigeminal system causes the release of various neuropeptides, cytokines, and other immune mediators. Calcitonin gene-related peptide (CGRP), which is a potent algogenic mediator, is expressed in the peripheral sensory neurons of trigeminal ganglion (TG). It affects the inflammatory responses and pain sensitivity by modulating the activity of glial cells. The primary aim of this study was to use array analysis to investigate the effect of CGRP on the glial cells of TG in regulating nuclear factor kappa B (NF-κB) signaling genes and to further check if CGRP in the TG can affect neuron-glia activation in the spinal trigeminal nucleus caudalis. The glial cells of TG were stimulated with CGRP or Minocycline (Min) + CGRP. The effect on various genes involved in NF-κB signaling pathway was analyzed compared to no treatment control condition using a PCR array analysis. CGRP, Min + CGRP or saline was directly injected inside the TG and the effect on gene expression of Egr1, Myd88 and Akt1 and protein expression of cleaved Caspase3 (cleav Casp3) in the TG, and c-Fos and glial fibrillary acidic protein (GFAP) in the spinal section containing trigeminal nucleus caudalis was analyzed. Results showed that CGRP stimulation resulted in the modulation of several genes involved in the interleukin 1 signaling pathway and some genes of the tumor necrosis factor pathway. Minocycline pre-treatment resulted in the modulation of several genes in the glial cells, including anti-inflammatory genes, and neuronal activation markers. A mild increase in cleav Casp3 expression in TG and c-Fos and GFAP in the spinal trigeminal nucleus of CGRP injected animals was observed. These data provide evidence that glial cells can participate in neuroimmune interaction due to CGRP in the TG via NF-κB signaling pathway.

Inhibition of Microglial Activation in the Amygdala Reverses Stress-Induced Abdominal Pain in the Male Rat

BACKGROUND & AIMS

Psychological stress is a trigger for the development of irritable bowel syndrome and associated symptoms including abdominal pain. Although irritable bowel syndrome patients show increased activation in the limbic brain, including the amygdala, the underlying molecular and cellular mechanisms regulating visceral nociception in the central nervous system are incompletely understood. In a rodent model of chronic stress, we explored the role of microglia in the central nucleus of the amygdala (CeA) in controlling visceral sensitivity. Microglia are activated by environmental challenges such as stress, and are able to modify neuronal activity via synaptic remodeling and inflammatory cytokine release. Inflammatory gene expression and microglial activity are regulated negatively by nuclear glucocorticoid receptors (GR), which are suppressed by the stress-activated pain mediator p38 mitogen-activated protein kinases (MAPK).

METHODS

Fisher-344 male rats were exposed to water avoidance stress (WAS) for 1 hour per day for 7 days. Microglia morphology and the expression of phospho-p38 MAPK and GR were analyzed via immunofluorescence. Microglia-mediated synaptic remodeling was investigated by quantifying the number of postsynaptic density protein 95-positive puncta. Cytokine expression levels in the CeA were assessed via quantitative polymerase chain reaction and a Luminex assay (Bio-Rad, Hercules, CA). Stereotaxic infusion into the CeA of minocycline to inhibit, or fractalkine to activate, microglia was followed by colonic sensitivity measurement via a visceromotor behavioral response to isobaric graded pressures of tonic colorectal distension.

RESULTS

WAS induced microglial deramification in the CeA. Moreover, WAS induced a 3-fold increase in the expression of phospho-p38 and decreased the ratio of nuclear GR in the microglia. The number of microglia-engulfed postsynaptic density protein 95-positive puncta in the CeA was increased 3-fold by WAS, while cytokine levels were unchanged. WAS-induced changes in microglial morphology, microglia-mediated synaptic engulfment in the CeA, and visceral hypersensitivity were reversed by minocycline whereas in stress-naïve rats, fractalkine induced microglial deramification and visceral hypersensitivity.

CONCLUSIONS

Our data show that chronic stress induces visceral hypersensitivity in male rats and is associated with microglial p38 MAPK activation, GR dysfunction, and neuronal remodeling in the CeA.

Minocycline fails to improve neurologic and histologic outcome after ventricular fibrillation cardiac arrest in rats

BACKGROUND

Prolonged cardiac arrest (CA) produces extensive neuronal death and microglial proliferation and activation resulting in neuro-cognitive disabilities. Among other potential mechanisms, microglia have been implicated as triggers of neuronal death after hypoxic-ischemic insults. Minocycline is neuroprotective in some brain ischemia models, either by blunting the microglial response or by a direct effect on neurons.

AIM

To improve survival, attenuate neurologic deficits, neuroinflammation, and histological damage after ventricular fibrillation (VF) CA in rats.

METHODS

Adult male isoflurane-anesthetized rats were subjected to 6 min VF CA followed by 2 min resuscitation including chest compression, epinephrine, bicarbonate, and defibrillation. After return of spontaneous circulation (ROSC), rats were randomized to two groups: (1) Minocycline 90 mg/kg intraperitoneally (i.p.) at 15 min ROSC, followed by 22.5 mg/kg i.p. every 12 h for 72 h; and (2) Controls, receiving the same volume of vehicle (phosphate-buffered saline). The rats were kept normothermic during the postoperative course. Neurologic injury was assessed daily using Overall Performance Category (OPC; 1 = normal, 5 = dead) and Neurologic Deficit Score (NDS; 0% = normal, 100% = dead). Rats were sacrificed at 72 h. Neuronal degeneration (Fluoro-Jade C staining) and microglia proliferation (anti-Iba-1 staining) were quantified in four selectively vulnerable brain regions (hippocampus, striatum, cerebellum, cortex) by three independent reviewers masked to the group assignment.

RESULTS

In the minocycline group, 8 out of 14 rats survived to 72 h compared to 8 out of 19 rats in the control group (P = 0.46). The degree of neurologic deficit at 72 h [median, (interquartile range)] was not different between survivors in minocycline vs controls: OPC 1.5 (1-2.75) vs 2 (1.25-3), P = 0.442; NDS 12 (2-20) vs 17 (7-51), P = 0.328) or between all studied rats. The number of degenerating neurons (minocycline vs controls, mean ± SEM: Hippocampus 58 ± 8 vs 76 ± 8; striatum 121 ± 43 vs 153 ± 32; cerebellum 20 ± 7 vs 22 ± 8; cortex 0 ± 0 vs 0 ± 0) or proliferating microglia (hippocampus 157 ± 15 vs 193 cortex 0 ± 0 vs 0 ± 0; 16; striatum 150 ± 22 vs 161 ± 23; cerebellum 20 ± 7 vs 22 ± 8; cortex 26 ± 6 vs 31 ± 7) was not different between groups in any region (all P > 0.05). Numerically, there were approximately 20% less degenerating neurons and proliferating microglia in the hippocampus and striatum in the minocycline group, with a consistent pattern of histological damage across the individual regions of interest.

CONCLUSION

Minocycline did not improve survival and failed to confer substantial benefits on neurologic function, neuronal loss or microglial proliferation across multiple brain regions in our model of rat VF CA.

The therapeutic role of minocycline in Parkinson's disease

Minocycline, a semisynthetic tetracycline-derived antibiotic, has been shown to exert anti-apoptotic, anti-inflammatory, and antioxidant effects. Furthermore, there is rapidly growing evidence suggesting that minocycline may have some neuroprotective activity in various experimental models such as cerebral ischemia, traumatic brain injury, amyotrophic lateral sclerosis, Parkinson's disease (PD), Huntington's disease, and multiple sclerosis. In this perspective review, we summarize the preclinical and clinical findings suggesting the neuroprotective role of minocycline in PD.

Safety and feasibility of minocycline in treatment of acute traumatic brain injury

BACKGROUND

Minocycline is a pleomorphic neuroprotective agent well studied in animal models of traumatic brain injury (TBI) and brain ischemia.

METHODS

To test the hypothesis that administration of minocycline in moderate to severe TBI (Glasgow Coma Score 3-12). Fifteen patients were enrolled in a two-dose escalation study of minocycline to evaluate the safety of twice the recommended antibiotic dosage; tier 1 n = 7 at a loading dose of 800 mg followed by 200 mg twice a day (BID) for 7 days; tier 2 n = 8 at a loading dose of 800 mg followed by 400 mg BID for 7 days.

RESULTS

The mean initial GCS was 5.6 for Tier 1 patients and 5.4 for Tier 2. The Disability Rating Scale (DRS) had a trend towards improvement with the higher dose 12.5 SD ± 7.7 (N = 5) for Tier 1 at 4 weeks and 8.5 SD ± 9.9 at week 12 (N = 5), whereas for Tier 2 it was 9.7 ± 6.9 (N = 6) for week 4 and 6.0 SD ± 6.1 (N = 7) for week 12 (p = .251 repeated measures ANOVA). Liver function tests increased but resolved after the first week and there were no infections.

CONCLUSIONS

Minocycline was safe for moderate to severe TBI at a dose twice that as recommended for treatment of infection. The higher dose did trend towards an improved outcome.

Combination therapy of human bone marrow-derived mesenchymal stem cells and minocycline improves neuronal function in a rat middle cerebral artery occlusion model

BACKGROUND

The positive effects of human bone marrow-derived mesenchymal stem cells (hBM-MSCs) and minocycline on ischemic stroke models have been well described through numerous studies. The aim of this study was to evaluate the effectiveness of combination therapy of hBM-MSCs with minocycline in a middle cerebral artery occlusion rat model.

METHODS

Forty male Sprague-Dawley rats were enrolled in this study. After right middle cerebral artery occlusion, rats were randomly assigned to one of four groups: control, minocycline, hBM-MSCs, or hBM-MSCs with minocycline. Rotarod test, adhesive-removal test, and modified neurological severity score grading were performed before and 1, 7, 14, 21, and 28 days after right middle cerebral artery occlusion. All rats were sacrificed at day 28. The volume of the infarcted area was measured with triphenyl tetrazolium chloride staining. Neuronal nuclear antigen (NeuN)- and vascular endothelial growth factor (VEGF)-positive cells in the ischemic boundary zone were assessed by immunofluorescence.

RESULTS

Neurological outcome in the adhesive-removal test and rotarod test and modified neurological severity score were better in the combination therapy group than in the monotherapy and control groups. The volume of the infarcted area was smaller in the combination group compared with the others. The proportions of NeuN- and VEGF-positive cells in the ischemic boundary were highest in the combination therapy group.

CONCLUSIONS

Early combination therapy of hBM-MSCs with minocycline in an ischemic stroke model may enhance neurological recovery, reduce the volume of the infarcted area, and promote the expression of NeuN and VEGF in ischemic boundary cells.

Stress-Activated Protein Kinases in Spinal Cord Injury: Focus on Roles of p38

Spinal cord injury (SCI) consists of three phases-acute, secondary, and chronic damages-and limiting the development of secondary damage possibly improves functional recovery after SCI. A major component of the secondary phase of SCI is regarded as inflammation-triggered events: induction of cytokines, edema, microglial activation, apoptosis of cells including oligodendrocytes and neurons, demyelination, formation of the astrocytic scar, and so on. Two major stress-activated protein kinases (SAPKs)-c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK)-are activated in various types of cells in response to cellular stresses such as apoptotic stimuli and inflammatory waves. In animal models of SCI, inhibition of either JNK or p38 has been shown to promote neuroprotection-associated functional recovery. Here, we provide an overview on the roles of SAPKs in SCI and, in particular, the pathological role of p38 will be discussed as a promising target for therapeutic intervention in SCI.

Protective Effect of Minocycline Against Ketamine-Induced Injury in Neural Stem Cell: Involvement of PI3K/Akt and Gsk-3 Beta Pathway

It has been suggested that ketamine cause injury during developing brain. Minocycline (MC) could prevent neuronal cell death through the activation of cell survival signals and the inhibition of apoptotic signals in models of neurodegenerative diseases. Here we investigated the protective effect of MC against ketamine-induced injury in neural stem cells (NSCs) from neonatal rat. Ketamine (100 μM/L) significantly inhibited NSC proliferation, promoted their differentiation into astrocytes and suppressed neuronal differentiation of NSCs. Moreover, the apoptotic level was increased following ketamine exposure. MC pretreatment greatly enhanced cell viability, decreased caspase-3-like activity, even reversed the differentiation changes caused by ketamine. To elucidate a possible mechanism of MC' neuroprotective effect, we investigated the phosphatidylinositol 3-kinase (PI3K) pathway using LY294002, a specific PI3K inhibitor. Immunoblotting revealed that MC enhanced the phosphorylation/activation of Akt and phosphorylation/inactivation of glycogen synthase kinase-3beta (Gsk-3β). Our results suggest that PI3K/Akt and Gsk-3β pathway are involved in the neuroprotective effect of MC.

Minocycline as a Neuroprotective Agent

Several studies have shown that minocycline, a semisynthetic, second-generation tetracycline derivative, is neuroprotective in animal models of central nervous system trauma and several neurodegenerative diseases. Common to all these reports are the beneficial effects of minocycline in reducing neural inflammation and preventing cell death. Here, the authors review the proposed mechanisms of action of minocycline and suggest that minocycline may inhibit several aspects of the inflammatory response and prevent cell death through the inhibition of the p38 mitogen-activated protein kinase pathway, an important regulator of immune cell function and cell death.

Microglia and inflammation: conspiracy, controversy or control?

Microglial cells contribute to normal function of the central nervous system (CNS). Besides playing a role in the innate immunity, they are also involved in neuronal plasticity and homeostasis of the CNS. While microglial cells get activated and undergo phenotypic changes in different disease contexts, they are far from being the "villains" in the CNS. Mounting evidence indicates that microglial dysfunction can exacerbate the pathogenesis of several diseases in the CNS. Several molecular mechanisms tightly regulate the production of inflammatory and toxic factors released by microglia. These mechanisms involve the interaction with other glial cells and neurons and the fine regulation of signaling and transcription activation pathways. The purpose of this review is to discuss microglia activation and to highlight the molecular pathways that can counteract the detrimental role of microglia in several neurologic diseases. Recent work presented in this review support that the understanding of microglial responses can pave the way to design new therapies for inflammatory diseases of the CNS.

Inhibition of neuronal p38α, but not p38β MAPK, provides neuroprotection against three different neurotoxic insults

The p38 mitogen-activated protein kinase (MAPK) pathway plays a key role in pathological glial activation and neuroinflammatory responses. Our previous studies demonstrated that microglial p38α and not the p38β isoform is an important contributor to stressor-induced proinflammatory cytokine upregulation and glia-dependent neurotoxicity. However, the contribution of neuronal p38α and p38β isoforms in responses to neurotoxic agents is less well understood. In the current study, we used cortical neurons from wild-type or p38β knockout mice, and wild-type neurons treated with two highly selective inhibitors of p38α MAPK. Neurons were treated with one of three neurotoxic insults (L-glutamate, sodium nitroprusside, and oxygen-glucose deprivation), and neurotoxicity was assessed. All three stimuli led to neuronal death and neurite degeneration, and the degree of neurotoxicity induced in wild-type and p38β knockout neurons was not significantly different. In contrast, selective inhibition of neuronal p38α was neuroprotective. Our results show that neuronal p38β is not required for neurotoxicity induced by multiple toxic insults, but that p38α in the neuron contributes quantitatively to the neuronal dysfunction responses. These data are consistent with our previous findings of the critical importance of microglia p38α compared to p38β, and continue to support selective targeting of the p38α isoform as a potential therapeutic strategy.

Minocycline increases the activity of superoxide dismutase and reduces the concentration of nitric oxide, hydrogen peroxide and mitochondrial malondialdehyde in manganese treated Drosophila melanogaster

The toxicity caused by high concentrations of manganese (Mn) could be due to a production of free radicals. Minocycline is an effective antioxidant with a high potential to capture free radicals. We investigated the effect of minocycline in the activities of superoxide dismutase (SOD) and catalase, and in the concentrations of nitric oxide (NO), hydrogen peroxide (H2O2) and mitochondrial malondialdehyde (MDA) in manganese-treated Drosophila melanogaster. Five groups of flies were used: (1) control: not treated; (2) continuously treated with minocycline (0.05 mM); (3) treated with 30 mM Mn for 6 days and then no additional treatment; (4) continuously treated with Mn; (5) treated only with Mn for 6 days and then treated with minocycline; (6) simultaneously treated with Mn and minocycline. On the 6th day, Mn treatment caused 50% mortality; in the surviving flies increased levels of MDA (67.93%), NO (11.04%), H2O2 (14.62%) and SOD and catalase activity (165.34 and 71.43%, respectively) were detected. All the flies continuously treated with Mn died by the 21st day. On day 40, MDA levels were decreased in groups two, three and five (43.04, 29.67, and 34.72% respectively), as well as NO in group two (29.21%) and H2O2 in groups two and five (53.94% and 78.69%, respectively), while in group three the concentration of H2O2 was increased (408.25%). In conclusion, Mn exerted a pro-oxidant effect on the 6th day as shown by the increased levels of oxidative markers. Minocycline extended the lifespan, increased the activity of SOD and reduced the levels of NO, H2O2 and mitochondrial MDA.

Minocycline development for acute ischemic stroke

Minocycline, a tetracycline antibiotic, has shown anti-inflammatory, anti-apoptotic, and neuroprotective effects in many models of cerebral ischemia and neurodegenerative disease. Its high penetration of the blood-brain barrier, good safety profile, and delayed therapeutic window make it an ideal candidate for use in stroke. In animal models, minocycline reduced infarct size and improved neurologic outcome when administered acutely, with similar neuroprotective benefits seen following delayed administration. To date, two early phase clinical trials have shown minocycline to be safe and potentially effective in acute ischemic stroke, alone or in combination with tissue plasminogen activator. A large efficacy clinical trial is now needed to confirm previous studies, allow for subgroup analysis, and pinpoint the potential place for minocycline in acute stroke therapy.

Minocycline influences the anti-inflammatory interleukins and enhances the effectiveness of morphine under mice diabetic neuropathy

A single streptozotocin (STZ) injection in mice can induce significant neuropathic pain along with an increase in plasma glucose levels and a decrease in body weight. Seven days after the administration of STZ, an upregulation of C1q-positive cells was observed. Additionally, interleukins (IL-1beta, IL-3, IL-4, IL-6, IL-9, IL12p70, IL-17); proteins of the tumor necrosis factor (TNF) family, e.g., IFNgamma and sTNF RII, were upregulated. Chronic administration of minocycline increases antinociceptive factors (IL-1alpha, IL-2, IL-10, sTNFRII) in diabetic mice. Minocycline also reduces the occurrence of neuropathic pain and significantly potentiates the antiallodynic and antihyperalgesic effects of morphine.

The endogenous regenerative capacity of the damaged newborn brain: boosting neurogenesis with mesenchymal stem cell treatment

Neurogenesis continues throughout adulthood. The neurogenic capacity of the brain increases after injury by, e.g., hypoxia-ischemia. However, it is well known that in many cases brain damage does not resolve spontaneously, indicating that the endogenous regenerative capacity of the brain is insufficient. Neonatal encephalopathy leads to high mortality rates and long-term neurologic deficits in babies worldwide. Therefore, there is an urgent need to develop more efficient therapeutic strategies. The latest findings indicate that stem cells represent a novel therapeutic possibility to improve outcome in models of neonatal encephalopathy. Transplanted stem cells secrete factors that stimulate and maintain neurogenesis, thereby increasing cell proliferation, neuronal differentiation, and functional integration. Understanding the molecular and cellular mechanisms underlying neurogenesis after an insult is crucial for developing tools to enhance the neurogenic capacity of the brain. The aim of this review is to discuss the endogenous capacity of the neonatal brain to regenerate after a cerebral ischemic insult. We present an overview of the molecular and cellular mechanisms underlying endogenous regenerative processes during development as well as after a cerebral ischemic insult. Furthermore, we will consider the potential to use stem cell transplantation as a means to boost endogenous neurogenesis and restore brain function.

COL-3, a chemically modified tetracycline, inhibits lipopolysaccharide-induced microglia activation and cytokine expression in the brain

Microglia activation results in release of proinflammatory molecules including cytokines, which contribute to neuronal damage in the central nervous system (CNS) if not controlled. Tetracycline antibiotics such as minocycline inhibit microglial activation and cytokine expression during CNS inflammation. In the present study we found that administration of chemically modified tetracycline-3 (COL-3), inhibits lipopolysaccharide (LPS)-induced microglial and p38 MAPK activation, as well as the increase in TNF-α, but not IL-1β expression, in the brains of BALB/c mice. COL-3 has been described to have no antibacterial activity. We observed that COL-3 had no activity against a Gram-negative bacteria, Escherichia coli; however surprisingly, COL-3 had antibacterial activity against a Gram-positive bacteria Staphylococcus aureus, with a minimum inhibitory concentration of 1 mg/ml. Our data show that COL-3 has some antibacterial activity against S. aureus, inhibits LPS-induced neuroinflammation, and displays potential as a therapeutic agent for treatment of conditions involving CNS inflammation.

Randomized trial of minocycline in the treatment of HIV-associated cognitive impairment

OBJECTIVE

To evaluate the efficacy and safety of minocycline in the management of HIV-associated cognitive impairment.

METHODS

We enrolled HIV-positive participants with a CD4 count of 250 to 500 cells/μL in a randomized, double-blind, placebo-controlled study. They received 100 mg of minocycline or matching placebo orally every 12 hours for 24 weeks. Cognitive function was measured using the Uganda neuropsychological test battery summary measure (U NP Sum) and the Memorial Sloan-Kettering (MSK) scale. The primary efficacy measure was the 24-week change in an average of 9 standardized U NP Sum z scores.

RESULTS

Seventy-three participants were enrolled. Of these, 90% were female, 49% were between the ages 30 and 39 years, and 74% had 6 or more years of education. One participant had MSK score of stage 1 (i.e., mild HIV dementia), and 72 participants had MSK stage 0.5 (i.e., equivocal or subclinical dementia) at the baseline evaluation. The minocycline effect on the 24-week change of the U NP Sum compared with placebo was 0.03 (95% confidence interval -0.51, 0.46; p = 0.37).

CONCLUSION

Minocycline was safe and well tolerated in HIV-positive individuals. However, it did not improve HIV-associated cognitive impairment.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that 100 mg of minocycline given orally every 12 hours for 24 weeks had no significant effect compared with placebo in the improvement of cognitive function in antiretroviral therapy-naive, HIV-positive patients.

Role of nitric oxide in cerebellar development and function: focus on granule neurons

More than 20 years of research have firmly established important roles of the diffusible messenger molecule, nitric oxide (NO), in cerebellar development and function. Granule neurons are main players in every NO-related mechanism involving cerebellar function and dysfunction. Granule neurons are endowed with remarkable amounts of the Ca(2+)-dependent neuronal isoform of nitric oxide synthase and can directly respond to endogenously produced NO or induce responses in neighboring cells taking advantage of the high diffusibility of the molecule. Nitric oxide acts as a negative regulator of granule cell precursor proliferation and promotes survival and differentiation of these neurons. Nitric oxide is neuroprotective towards granule neurons challenged with toxic insults. Nitric oxide is a main regulator of bidirectional plasticity at parallel fiber-Purkinje neuron synapses, inducing long-term depression (LTD) or long-term potentiation (LTP) depending on postsynaptic Ca(2+) levels, thus playing a central role in cerebellar learning related to motor control. Granule neurons cooperate with glial cells, in particular with microglia, in the regulation of NO production through the respective forms of NOS present in the two cellular types. Aim of the present paper is to review the state of the art and the improvement of our understanding of NO functions in cerebellar granule neurons obtained during the last two decades and to outline possible future development of the research.

Challenging New Targets for CNS-HIV Infection

The central nervous system (CNS) represents an important target for HIV infection during multiple stages of the disease: early, after invasion of the host, acting as a viral reservoir; lately, subverting its function and causing peripheral neuropathies and neurocognitive disorders; and lastly, during the final stage of NeuroAIDS, triggering opportunistic infections, cancers, and dementia. Highly active antiretroviral therapy, a combination of drugs that inhibits enzymes essential for HIV replication, can reduce the viremia and the onset of opportunistic infections in most patients, and prolong the survival. Among the limits of the current treatments the most noticeable is the inability to eradicate HIV-infected cells, both, limiting the time frame in which antiretroviral therapies initiated after exposure to HIV can prevent infection, and allowing replication-competent virus that persists in infected cells to emerge rapidly after the cessation of treatments. Many strategies are currently under evaluation to improve HIV treatment, unfortunately more than 98% of drug candidates for CNS disorders never make it to the clinic; here in we report how nanoformulated strategies might be adapted and applied to the field of CNS–HIV infection.

Minocycline attenuates microglia activation and blocks the long-term epileptogenic effects of early-life seizures

Innate immunity mediated by microglia appears to play a crucial role in initiating and propagating seizure-induced inflammatory responses. To address the role of activated microglia in the pathogenesis of childhood epilepsy, we first examined the time course of microglia activation following kainic acid-induced status epilepticus (KA-SE) in Cx3cr1(GFP/+) transgenic mice whose microglia are fluorescently labeled. We then determined whether this seizure-induced microglia activation primes the central immune response to overreact and to increase the susceptibility to a second seizure later in life. We used an inhibitor of microglia activation, minocycline, to block the seizure-induced inflammation to determine whether innate immunity plays a causal role in mediating the long-term epileptogenic effects of early-life seizure. First status epilepticus was induced at postnatal day (P) 25 and a second status at P39. KA-SE at P25 caused nearly a two-fold increase in microglia activation within 24h. Significant seizure-induced activation persisted for 7 days and returned to baseline by 14 days. P39 animals with prior exposure to KA-SE not only responded with greater microglial activation in response to "second hit" of KA, but shorter latency to express seizures. Inhibition of seizure-induced inflammation by 7 day minocycline post-treatment abrogated both the exaggerated microglia activation and the increased susceptibility to the second seizure later in life. The priming effect of early-life seizures is accompanied by modified and rapidly reactivated microglia. Our results suggest that anti-inflammatory therapy after SE may be useful to block the epileptogenic process and mitigate the long-term damaging effects of early-life seizures.

Minocycline increases the life span and motor activity and decreases lipid peroxidation in manganese treated Drosophila melanogaster

The objective of this study was to investigate the effect of Minocycline in the life span, motor activity, and lipid peroxidation of Drosophila melanogaster treated with manganese. Two days after emerging from the pupa male wild-type D. melanogaster were fed for 13 days with corn media containing 15 mM manganese. Then, they were divided in six groups of 300 flies each: group (a) remained treated with manganese (Mn group); group (b) began treatment with Minocycline (0.05 mM) (Mn-Minocycline group); group (c) received no additional treatment (Mn-no treatment group); group (d) simultaneously fed with manganese and Minocycline (Mn+Minocycline group). Additionally, a control (group e) with no treatment and another group (f) fed only with Minocycline after emerging from the pupa were added. All the manganese treated flies (group a) were dead on the 25th day. The life span in group f (101.66±1.33 days, mean S.E.M.) and of group b (97.00±3.46 days) were similar, but in both cases it was significantly higher than in group e (68.33±1.76 days), group c (67.05±2.30 days) and in those of group d (37.33±0.88). Manganese (groups a and d) decreased motor activity in D. melanogaster. In the Minocycline fed flies (groups b and f) a higher motor activity was detected. In Mn-Minocycline and Mn+Minocycline treated flies a significant decrease of MDA levels was detected when compared to the Minocycline group indicating that Minocycline and Mn appear to have a synergistic effect. In conclusion, Minocycline increased the life span and motor activity and decreased MDA formation of manganese treated D. melanogaster, probably by an inhibition of the production of reactive oxygen species. Manganese also exerted an antioxidant effect as shown by the significant decrease of MDA levels when compared to control flies.

Minocycline and magnesium in combination may be a good therapeutic intervention for cerebral ischemia

A neuroprotective strategy through a combination therapy is always being superior to any other singular therapeutic interventions, as these acts through a multifauceted approach within the brain during cerebral ischemia. Therefore, the development of a potential new combination of drug is necessitated which can bring about desirable improved neuroprotection targeting different pathways against ischemic stroke. Numerous past studies have enumerated the neuroprotective roles of minocycline and magnesium administered in single against cerebral ischemia in animal model hence we hypothesized that by using magnesium with minocycline in combination would provide additive neuroprotection than either of the agents used alone. In this article, we discuss our hypothesis regarding the possibility of minocycline and magnesium as a potent combination which may have a positive therapeutic role in treatment of cerebral ischemia through its anti-inflammatory, anti-apoptotic and anti-oxidative characteristics with magnesium contributing as a regulator of increased calcium influx.

Minocycline fails to modulate cerebrospinal fluid HIV infection or immune activation in chronic untreated HIV-1 infection: results of a pilot study

BACKGROUND

Minocycline is a tetracycline antibiotic that has been shown to attenuate central nervous system (CNS) lentivirus infection, immune activation, and brain injury in model systems. To initiate assessment of minocycline as an adjuvant therapy in human CNS HIV infection, we conducted an open-labelled pilot study of its effects on cerebrospinal fluid (CSF) and blood biomarkers of infection and immune responses in 7 viremic subjects not taking antiretroviral therapy.

RESULTS

There were no discernable effects of minocycline on CSF or blood HIV-1 RNA, or biomarkers of immune activation and inflammation including: CSF and blood neopterin, CSF CCL2, CSF white blood cell count, and expression of cell-surface activation markers on CSF and blood T lymphocytes and monocytes.

CONCLUSIONS

This pilot study of biological responses to minocycline suggests little potential for its use as adjunctive antiviral or immunomodulating therapy in chronic untreated HIV infection.

Mitogen-activated protein kinase p38 in HIV infection and associated brain injury

Infection with human immunodeficiency virus-1 (HIV-1) often leads to HIV-associated neurocognitive disorders (HAND) prior to the progression to acquired immunodeficiency syndrome (AIDS). At the cellular level, mitogen-activated protein kinases (MAPK) provide a family of signal transducers that regulate many processes in response to extracellular stimuli and environmental stress, such as viral infection. Recently, evidence has accumulated suggesting that p38 MAPK plays crucial roles in various pathological processes associated with HIV infection, ranging from macrophage activation to neurotoxicity and impairment of neurogenesis to lymphocyte apoptosis. Thus, p38 MAPK, which has generally been linked to stress-related signal transduction, may be an important mediator in the development of AIDS and HAND.

Neuroinflammation is associated with changes in glial mGluR5 expression and the development of neonatal excitotoxic lesions

It has been hypothesized that neuroinflammation triggered during brain development can alter brain functions later in life. We investigated the contribution of inflammation to the alteration of normal brain circuitries in the context of neuroexcitotoxicity following neonatal ventral hippocampal lesions in rats with ibotenic acid, an NMDA glutamate receptor agonist. Excitotoxic ibotenic acid lesions led to a significant and persistent astrogliosis and microglial activation, associated with the production of inflammatory mediators. This response was accompanied by a significant increase in metabotropic glutamate receptor type 5 (mGluR5) expression within two distinct neuroinflammatory cell types; astrocytes and microglia. The participation of inflammation to the neurotoxin-induced lesion was further supported by the prevention of hippocampal neuronal loss, glial mGluR5 expression and some of the behavioral perturbations associated to the excitotoxic lesion by concurrent anti-inflammatory treatment with minocycline. These results indicate that neuroinflammation significantly contributes to long-lasting excitotoxic effects of the neurotoxin and to some behavioral phenotypes associated with this model. Thus, the control of the inflammatory response may prevent the deleterious effects of excitotoxic processes that are triggered during brain development, limiting the risk to develop some of the behavioral manifestations related to these processes in adulthood.

Neuroprotection by minocycline caused by direct and specific scavenging of peroxynitrite

Minocycline prevents oxidative protein modifications and damage in disease models associated with inflammatory glial activation and oxidative stress. Although the drug has been assumed to act by preventing the up-regulation of proinflammatory enzymes, we probed here its direct chemical interaction with reactive oxygen species. The antibiotic did not react with superoxide or (•)NO radicals, but peroxynitrite (PON) was scavenged in the range of ∼1 μm minocycline and below. The interaction of pharmacologically relevant minocycline concentrations with PON was corroborated in several assay systems and significantly exceeded the efficacy of other antibiotics. Minocycline was degraded during the reaction with PON, and the resultant products lacked antioxidant properties. The antioxidant activity of minocycline extended to cellular systems, because it prevented neuronal mitochondrial DNA damage and glutathione depletion. Maintenance of neuronal viability under PON stress was shown to be solely dependent on direct chemical scavenging by minocycline. We chose α-synuclein (ASYN), known from Parkinsonian pathology as a biologically relevant target in chemical and cellular nitration reactions. Submicromolar concentrations of minocycline prevented tyrosine nitration of ASYN by PON. Mass spectrometric analysis revealed that minocycline impeded nitrations more effectively than methionine oxidations and dimerizations of ASYN, which are secondary reactions under PON stress. Thus, PON scavenging at low concentrations is a novel feature of minocycline and may help to explain its pharmacological activity.

Mesenchymal stem cell-secreted superoxide dismutase promotes cerebellar neuronal survival

It has been postulated that bone marrow-derived mesenchymal stem cells (MSCs) might be effective treatments for neurodegenerative disorders either by replacement of lost cells by differentiation into functional neural tissue; modulation of the immune system to prevent further neurodegeneration; and/or provision of trophic support for the diseased nervous system. Here we have performed a series of experiments showing that human bone marrow-derived MSCs are able to protect cultured rodent cerebellar neurons, and specifically cells expressing Purkinje cell markers, against either nitric oxide exposure or withdrawal of trophic support via cell-cell contact and/or secretion of soluble factors, or through secretion of soluble factors alone. We have demonstrated that MSCs protect cerebellar neurons against toxic insults via modulation of both the phosphatidylinositol 3-kinase/Akt and MAPK pathways and defined superoxide dismutase 3 as a secreted active antioxidant biomolecule by which MSCs modulate, at least in part, their neuroprotective effect on cerebellar cells in vitro. Together, the results demonstrate new and specific mechanisms by which MSCs promote cerebellar neuronal survival and add further evidence to the concept that MSCs may be potential therapeutic agents for neurological disorders involving the cerebellum.

Proton magnetic resonance spectroscopy reveals neuroprotection by oral minocycline in a nonhuman primate model of accelerated NeuroAIDS

BACKGROUND

Despite the advent of highly active anti-retroviral therapy (HAART), HIV-associated neurocognitive disorders continue to be a significant problem. In efforts to understand and alleviate neurocognitive deficits associated with HIV, we used an accelerated simian immunodeficiency virus (SIV) macaque model of NeuroAIDS to test whether minocycline is neuroprotective against lentiviral-induced neuronal injury.

METHODOLOGY/PRINCIPAL FINDINGS

Eleven rhesus macaques were infected with SIV, depleted of CD8+ lymphocytes, and studied until eight weeks post inoculation (wpi). Seven animals received daily minocycline orally beginning at 4 wpi. Neuronal integrity was monitored in vivo by proton magnetic resonance spectroscopy and post-mortem by immunohistochemistry for synaptophysin (SYN), microtubule-associated protein 2 (MAP2), and neuronal counts. Astrogliosis and microglial activation were quantified by measuring glial fibrillary acidic protein (GFAP) and ionized calcium binding adaptor molecule 1 (IBA-1), respectively. SIV infection followed by CD8+ cell depletion induced a progressive decline in neuronal integrity evidenced by declining N-acetylaspartate/creatine (NAA/Cr), which was arrested with minocycline treatment. The recovery of this ratio was due to increases in NAA, indicating neuronal recovery, and decreases in Cr, likely reflecting downregulation of glial cell activation. SYN, MAP2, and neuronal counts were found to be higher in minocycline-treated animals compared to untreated animals while GFAP and IBA-1 expression were decreased compared to controls. CSF and plasma viral loads were lower in MN-treated animals.

CONCLUSIONS/SIGNIFICANCE

In conclusion, oral minocycline alleviates neuronal damage induced by the AIDS virus.

Therapeutic targets and limits of minocycline neuroprotection in experimental ischemic stroke

BACKGROUND

Minocycline, a second-generation tetracycline with anti-inflammatory and anti-apoptotic properties, has been shown to promote therapeutic benefits in experimental stroke. However, equally compelling evidence demonstrates that the drug exerts variable and even detrimental effects in many neurological disease models. Assessment of the mechanism underlying minocycline neuroprotection should clarify the drug's clinical value in acute stroke setting.

RESULTS

Here, we demonstrate that minocycline attenuates both in vitro (oxygen glucose deprivation) and in vivo (middle cerebral artery occlusion) experimentally induced ischemic deficits by direct inhibition of apoptotic-like neuronal cell death involving the anti-apoptotic Bcl-2/cytochrome c pathway. Such anti-apoptotic effect of minocycline is seen in neurons, but not apparent in astrocytes. Our data further indicate that the neuroprotection is dose-dependent, in that only low dose minocycline inhibits neuronal cell death cascades at the acute stroke phase, whereas the high dose exacerbates the ischemic injury.

CONCLUSION

The present study advises our community to proceed with caution to use the minimally invasive intravenous delivery of low dose minocycline in order to afford neuroprotection that is safe for stroke.

Deleterious effects of minocycline after in vivo target deprivation of thalamocortical neurons in the immature, metallothionein-deficient mouse brain

Compared with adults, immature metallothionein I and II knockout (MT(-/-)) mice incur greater neuronal loss and a more rapid rate of microglia accumulation after target deprivation-induced injury. Because minocycline has been proposed to inhibit microglial activation and associated production of neuroinflammatory factors, we investigated its ability to promote neuronal survival in the immature, metallothionein-deficient brain. After ablation of the visual cortex, 10-day-old MT(-/-) mice were treated with minocycline or saline and killed 24 or 48 hr after injury. By means of stereological methods, the number of microglia and neurons were estimated in the ipsilateral dorsal lateral geniculate nucleus (dLGN) by an investigator blinded to the treatment. No effect on neuronal survival was observed at 24 hr, but 48 hr after injury, an unanticipated but significant minocycline-mediated increase in neuronal loss was detected. Further, while failing to inhibit microglial accumulation, minocycline treatment increased the proportion of amoeboid microglia in the ipsilateral dLGN. To understand the molecular mechanisms underlying this neurotoxic response, we identified minocycline-mediated changes in the expression of three potentially proapoptotic/inflammatory genes: growth arrest- and DNA damage-inducible gene 45gamma (GADD45gamma); interferon-inducible protein 1 (IFI1), and cytokine-induced growth factor. We also observed increased mitogen-activated protein kinase p38 phosphorylation with minocycline treatment. Although minocycline inhibited calpain activity at 12 hr after injury, this effect was not sustained at 24 hr. Together, these results help to explain how minocycline has a deleterious effect on neuronal survival in this injury model.

Minocycline attenuates cognitive impairment and restrains oxidative stress in the hippocampus of rats with chronic cerebral hypoperfusion

OBJECTIVE

Nitric oxide (NO) was speculated to play an important role in the pathophysiology of cerebral ischemia. Minocycline, a tetracycline derivative, reduced inflammation and protected against cerebral ischemia. To study the neuroprotection mechanism of minocycline for vascular dementia, the influences of minocycline on expressions of inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) were observed in the brains of Wistar rats.

METHODS

The vascular dementia rat model was established by permanent bilateral common carotid arteries occlusion (BCCAO). Wistar rats were divideded into 3 groups randomly: sham-operation group (S group), vascular dementia model group (M group), and minocycline treatment group (MT group). The behaviour was tested with Morris water maze and open-field task. Expressions of iNOS and eNOS were measured by immunohistochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR). The optical density value was measured by imaging analysis. Percentage of positive cells with iNOS and eNOS expression was analyzed with optical microscope.

RESULTS

Minocycline attenuated cognitive impairment. Inducible NOS was significantly down-regulated in MT group, compared with that in M group (P < 0.01), while eNOS was significantly up-regulated, compared with that in M group (P < 0.01). The expressions of iNOS and eNOS in M and MT groups were higher than those in S group (P < 0.01).

CONCLUSION

Minocycline can down-regulate the expression of iNOS and up-regulate the expression of eNOS in vascular dementia, which restrains apoptosis and oxidative stress to protect neural function.

Minocycline suppresses morphine-induced respiratory depression, suppresses morphine-induced reward, and enhances systemic morphine-induced analgesia

Recent data suggest that opioids can activate immune-like cells of the central nervous system (glia). This opioid-induced glial activation is associated with decreased analgesia, owing to the release of proinflammatory mediators. Here, we examine in rats whether the putative microglial inhibitor, minocycline, may affect morphine-induced respiratory depression and/or morphine-induced reward (conditioned place preference). Systemic co-administration of minocycline significantly attenuated morphine-induced reductions in tidal volume, minute volume, inspiratory force, and expiratory force, but did not affect morphine-induced reductions in respiratory rate. Minocycline attenuation of respiratory depression was also paralleled with significant attenuation by minocycline of morphine-induced reductions in blood oxygen saturation. Minocycline also attenuated morphine conditioned place preference. Minocycline did not simply reduce all actions of morphine, as morphine analgesia was significantly potentiated by minocycline co-administration. Lastly, morphine dose-dependently increased cyclooxygenase-1 gene expression in a rat microglial cell line, an effect that was dose-dependently blocked by minocycline. Together, these data support that morphine can directly activate microglia in a minocycline-suppressible manner and suggest a pivotal role for minocycline-sensitive processes in the mechanisms of morphine-induced respiration depression, reward, and pain modulation.

Minocycline and neurodegenerative diseases

Minocycline is a semi-synthetic, second-generation tetracycline analog which is effectively crossing the blood-brain barrier, effective against gram-positive and -negative infections. In addition to its own antimicrobacterial properties, minocycline has been reported to exert neuroprotective effects over various experimental models such as cerebral ischemia, traumatic brain injury, amyotrophic lateral sclerosis, Parkinson's disease, kainic acid treatment, Huntington' disease and multiple sclerosis. Minocycline has been focused as a neuroprotective agent over neurodegenerative disease since it has been first reported that minocycline has neuroprotective effects in animal models of ischemic injury [Yrjanheikki J, Keinanen R, Pellikka M, Hokfelt T, Koisinaho J. Tetracyclines inhibit microglial activation and are neuroprotective in global brain ischemia. Proc Natl Acad Sci USA 1998;95:15769-74; Yrjanheikki J, Tikka T, Keinanen R, Goldsteins G, Chan PH, Koistinaho J. A tetracycline derivative, minocycline, reduces inflammation and protects against focal cerebral ischemia with a wide therapeutic window. Proc Natl Acad Sci USA 1999;96:13496-500]. Recently, the effect of minocycline on Alzheimer's disease has been also reported. Although its precise primary target is not clear, the action mechanisms of minocycline for neuroprotection reported so far are; via; the inhibition of mitochondrial permeability-transition mediated cytochrome c release from mitochondria, the inhibition of caspase-1 and -3 expressions, and the suppression of microglial activation, involvement in some signaling pathways, metalloprotease activity inhibition. Because of the high tolerance and the excellent penetration into the brain, minocycline has been clinically tried for some neurodegenerative diseases such as stroke, multiple sclerosis, spinal cord injury, amyotropic lateral sclerosis, Hungtington's disease and Parkinson's disease. This review will briefly summarize the effects and action mechanisms of minocycline on neurodegenerative diseases.