Re-evaluation of mitochondrial permeability transition as a primary neuroprotective target of minocycline

Systematic Review of the Therapeutic Role of Apoptotic Inhibitors in Neurodegeneration and Their Potential Use in Schizophrenia

Schizophrenia (SZ) is a deleterious brain disorder affecting cognition, emotion and reality perception. The most widely accepted neurochemical-hypothesis is the imbalance of neurotransmitter-systems. Depleted GABAergic-inhibitory function might produce a regionally-located dopaminergic and glutamatergic-storm in the brain. The dopaminergic-release may underlie the positive psychotic-symptoms while the glutamatergic-release could prompt the primary negative symptoms/cognitive deficits. This may occur due to excessive synaptic-pruning during the neurodevelopmental stages of adolescence/early adulthood. Thus, although SZ is not a neurodegenerative disease, it has been suggested that exaggerated dendritic-apoptosis could explain the limited neuroprogression around its onset. This apoptotic nature of SZ highlights the potential therapeutic action of anti-apoptotic drugs, especially at prodromal stages. If dysregulation of apoptotic mechanisms underlies the molecular basis of SZ, then anti-apoptotic molecules could be a prodromal therapeutic option to halt or prevent SZ. In fact, risk alleles related in apoptotic genes have been recently associated to SZ and shared molecular apoptotic changes are common in the main neurodegenerative disorders and SZ. PRISMA-guidelines were considered. Anti-apoptotic drugs are commonly applied in classic neurodegenerative disorders with promising results. Despite both the apoptotic-hallmarks of SZ and the widespread use of anti-apoptotic targets in neurodegeneration, there is a strikingly scarce number of studies investigating anti-apoptotic approaches in SZ. We analyzed the anti-apoptotic approaches conducted in neurodegeneration and the potential applications of such anti-apoptotic therapies as a promising novel therapeutic strategy, especially during early stages.

Minocycline for the management of multiple sclerosis: repositioning potential, opportunities, and challenges

INTRODUCTION

Multiple sclerosis (MS) is a chronic demyelinating inflammatory disorder with variable clinical and pathologic characteristics reflecting multiple underlying pathophysiologic mechanisms. Repositioning of existing drugs for the new indications offers several advantages including significant reduction in the cost and time of drug development and exemption from early phase clinical trials. Minocycline has been reported to exhibit immunomodulation in several pre-clinical and clinical studies through suppression of migratory inflammatory cells, modulation of peripheral immune response, and inhibition of microglial activation within the CNS.

AREAS COVERED

Here, the authors review the repositioning potential of minocycline for the treatment of MS along with appraisal of the evidence obtained from preclinical and clinical research. The authors also discuss the advantages and potential safety concerns related to the use of minocycline for the management of MS.

EXPERT OPINION

Minocycline offers several distinct advantages in terms of well-known safety profile, lower cost of therapy, widespread availability, and being available as an oral formulation. The authors call upon the public and private funders to facilitate well designed and adequately powered randomized clinical trials that can provide conclusive evidence regarding the safety and efficacy of minocycline in patients with MS.

The new role of F1Fo ATP synthase in mitochondria-mediated neurodegeneration and neuroprotection

The mitochondrial F₁F_o ATP synthase is one of the most abundant proteins of the mitochondrial inner membrane, which catalyzes the final step of oxidative phosphorylation to synthesize ATP from ADP and Pi. ATP synthase uses the electrochemical gradient of protons (Δμ_H⁺) across the mitochondrial inner membrane to synthesize ATP. Under certain pathophysiological conditions, ATP synthase can run in reverse to hydrolyze ATP and build the necessary Δμ_H⁺ across the mitochondrial inner membrane. Tight coupling between these two processes, proton translocation and ATP synthesis, is achieved by the unique rotational mechanism of ATP synthase and is necessary for efficient cellular metabolism and cell survival. The uncoupling of these processes, dissipation of mitochondrial inner membrane potential, elevated levels of ROS, low matrix content of ATP in combination with other cellular malfunction trigger the opening of the mitochondrial permeability transition pore in the mitochondrial inner membrane. In this review we will discuss the new role of ATP synthase beyond oxidative phosphorylation. We will highlight its function as a unique regulator of cell life and death and as a key target in mitochondria-mediated neurodegeneration and neuroprotection.

The footprints of mitochondrial impairment and cellular energy crisis in the pathogenesis of xenobiotics-induced nephrotoxicity, serum electrolytes imbalance, and Fanconi's syndrome: A comprehensive review

Fanconi's Syndrome (FS) is a disorder characterized by impaired renal proximal tubule function. FS is associated with a vast defect in the renal reabsorption of several chemicals. Inherited and/or acquired conditions seem to be connected with FS. Several xenobiotics including many pharmaceuticals are capable of inducing FS and nephrotoxicity. Although the pathological state of FS is well described, the exact underlying etiology and cellular mechanism(s) of xenobiotics-induced nephrotoxicity, serum electrolytes imbalance, and FS are not elucidated. Constant and high dependence of the renal reabsorption process to energy (ATP) makes mitochondrial dysfunction as a pivotal mechanism which could be involved in the pathogenesis of FS. The current review focuses on the footprints of mitochondrial impairment in the etiology of xenobiotics-induced FS. Moreover, the importance of mitochondria protecting agents and their preventive/therapeutic capability against FS is highlighted. The information collected in this review may provide significant clues to new therapeutic interventions aimed at minimizing xenobiotics-induced renal injury, serum electrolytes imbalance, and FS.

Delirium induced by tigecycline treatment for Acinetobacter baumannii infection: A case report

RATIONALE

Tigecycline is a broad-spectrum antimicrobial agent structurally belong to tetracyclines and covers against many multidrug-resistant organisms. Arising clinical cases reporting its adverse drug reactions have emerged alongside with the increasing off label use globally. By literature review, delirium caused by tigecycline has not been reported yet. We present what we believe to be the first case of tigecycline-induced delirium.

PATIENT CONCERNS

A 77-year-old male patient with end-stage renal disease was hospitalized due to acute exacerbation of chronic obstructive pulmonary disease.

DIAGNOSIS

The patient developed delirium after infused with a loading dose of tigecycline for pulmonary infection.

INTERVENTIONS

All potential causes inducing delirium were evaluated and the symptoms improved soon after discontinuation of tigecycline. He experienced delirium once again after reusing tigecycline for the exacerbation of the pulmonary infection even without a loading dose. Tigecycline was discontinued and the symptoms quickly relieved.

OUTCOMES

According to the Naranjo adverse drug reaction probability scale, tigecycline was the probable cause of his delirium.

LESSONS

Clinicians should be aware of this potential adverse effect of tigecycline. We recommend that clinicians monitor patients for signs and symptoms of delirium during treatment with tigecycline.

Human VDAC isoforms differ in their capability to interact with minocycline and to contribute to its cytoprotective activity

It has been previously demonstrated that cytoprotective activity displayed by minocycline in the case of the yeast Saccharomyces cerevisiae cells pretreated with H2O2 requires the presence of functional VDAC (YVDAC1). Thus, we decided to transform YVDAC1-depleted yeast cells (Δpor1 cells) with plasmids expressing human VDAC isoforms (HVDAC1, HVDAC2, HVDAC3) to estimate their involvement in the minocycline cytoprotective effect. We observed that only expression of HVDAC3 in Δpor1 cells provided minocycline-mediated cytoprotection against H2O2 although all human isoforms are functional in Δpor1 cells. The observation appears to be important for on-going discussion concerning VDAC isoform roles in mitochondria and cell functioning.

Strategies for Pharmacological Organoprotection during Extracorporeal Circulation Targeting Ischemia-Reperfusion Injury

Surgical correction of congenital cardiac malformations or aortocoronary bypass surgery in many cases implies the use of cardiopulmonary-bypass (CPB). However, a possible negative impact of CPB on internal organs such as brain, kidney, lung and liver cannot be neglected. In general, CPB initiates a systemic inflammatory response (SIRS) which is presumably caused by contact of blood components with the surface of CPB tubing. Moreover, during CPB the heart typically undergoes a period of cold ischemia, and the other peripheral organs a global low flow hypoperfusion. As a result, a plethora of pro-inflammatory mediators and cytokines is released activating different biochemical pathways, which finally may result in the occurrence of microthrombosis, microemboli, in depletion of coagulation factors and haemorrhagic diathesis besides typical ischemia-reperfusion injuries. In our review we will focus on possible pharmacological interventions in patients to decrease negative effects of CPB and to improve post-operative outcome with regard to heart and other organs like brain, kidney, or lung.

Minocycline ameliorates prenatal valproic acid induced autistic behaviour, biochemistry and blood brain barrier impairments in rats

Autism is a neurodevelopment disorder. One percent worldwide population suffers with autism and males suffer more than females. Microglia plays an important role in neurodevelopment, neuropsychiatric and neurodegenerative disorders. The present study has been designed to investigate the role of minocycline in prenatal valproic acid induced autism in rats. Animals with prenatal valproic acid have reduced social interaction (three chamber social behaviour apparatus), spontaneous alteration (Y-Maze), exploratory activity (Hole board test), intestinal motility, serotonin levels (both in prefrontal cortex and ileum) and prefrontal cortex mitochondrial complex activity (complexes I, II, IV). Furthermore, prenatal valproic acid treated animals have shown an increase in locomotion (actophotometer), anxiety (elevated plus maze), brain oxidative stress (thiobarbituric acid reactive species, glutathione, catalase), nitrosative stress (nitrite/nitrate), inflammation (both in brain and ileum myeloperoxidase activity), calcium and blood brain barrier permeability. Treatment with minocycline significantly attenuated prenatal valproic acid induced reduction in social interaction, spontaneous alteration, exploratory activity intestinal motility, serotonin levels and prefrontal cortex mitochondrial complex activity. Furthermore, minocycline has also attenuated prenatal valproic acid induced increase in locomotion, anxiety, brain oxidative and nitrosative stress, inflammation, calcium and blood brain barrier permeability. Thus, it may be concluded that prenatal valproic acid has induced autistic behaviour, biochemistry and blood brain barrier impairment in animals, which were significantly attenuated by minocycline. Minocycline should be explored further for its therapeutic benefits in autism.

Glial TLR4 signaling does not contribute to opioid-induced depression of respiration

Opioids activate glia in the central nervous system in part by activating the toll-like receptor 4 (TLR4)/myeloid differentiation 2 (MD2) complex. TLR4/MD2-mediated activation of glia by opioids compromises their analgesic actions. Glial activation is also hypothesized as pivotal in opioid-mediated reward and tolerance and as a contributor to opioid-mediated respiratory depression. We tested the contribution of TLR4 to opioid-induced respiratory depression using rhythmically active medullary slices that contain the pre-Bötzinger Complex (preBötC, an important site of respiratory rhythm generation) and adult rats in vivo. Injection with DAMGO (μ-opioid receptor agonist; 50 μM) or bath application of DAMGO (500 nM) or fentanyl (1 μM) slowed frequency recorded from XII nerves to 40%, 40%, or 50% of control, respectively. This DAMGO-mediated frequency inhibition was unaffected by preapplication of lipopolysaccharides from Rhodobacter sphaeroides (a TLR4 antagonist, 2,000 ng/ml) or (+)naloxone (1-10 μM, a TLR4-antagonist). Bath application of (-)naloxone (500 nM; a TLR4 and μ-opioid antagonist), however, rapidly reversed the opioid-mediated frequency decrease. We also compared the opioid-induced respiratory depression in slices in vitro in the absence and presence of bath-applied minocycline (an inhibitor of microglial activation) and in slices prepared from mice injected (ip) 18 h earlier with minocycline or saline. Minocycline had no effect on respiratory depression in vitro. Finally, the respiratory depression evoked in anesthetized rats by tail vein infusion of fentanyl was unaffected by subsequent injection of (+)naloxone, but completely reversed by (-)naloxone. These data indicate that neither activation of microglia in preBötC nor TLR4/MD2-activation contribute to opioid-induced respiratory depression.

Complex I function and supercomplex formation are preserved in liver mitochondria despite progressive complex III deficiency

Functional oxidative phosphorylation requires appropriately assembled mitochondrial respiratory complexes and their supercomplexes formed mainly of complexes I, III and IV. BCS1L is the chaperone needed to incorporate the catalytic subunit, Rieske iron-sulfur protein, into complex III at the final stage of its assembly. In cell culture studies, this subunit has been considered necessary for supercomplex formation and for maintaining the stability of complex I. Our aim was to assess the importance of fully assembled complex III for supercomplex formation in intact liver tissue. We used our transgenic mouse model with a homozygous c.232A>G mutation in Bcs1l leading to decreased expression of BCS1L and progressive decrease of Rieske iron-sulfur protein in complex III, resulting in hepatopathy. We studied supercomplex formation at different ages using blue native gel electrophoresis and complex activity using high-resolution respirometry. In isolated liver mitochondria of young and healthy homozygous mutant mice, we found similar supercomplexes as in wild type. In homozygotes aged 27–29 days with liver disorder, complex III was predominantly a pre-complex lacking Rieske iron-sulfur protein. However, the main supercomplex was clearly detected and contained complex III mainly in the pre-complex form. Oxygen consumption of complex IV was similar and that of complex I was twofold compared with controls. These complexes in free form were more abundant in homozygotes than in controls, and the mRNA of complex I subunits were upregulated. In conclusion, when complex III assembly is deficient, the pre-complex without Rieske iron-sulfur protein can participate with available fully assembled complex III in supercomplex formation, complex I function is preserved, and respiratory chain stability is maintained.

Functional and pharmacological characteristics of permeability transition in isolated human heart mitochondria

The objective of the present study was to validate the presence and explore the characteristics of mitochondrial permeability transition (mPT) in isolated mitochondria from human heart tissue in order to investigate if previous findings in animal models of cardiac disorders are translatable to human disease. Mitochondria were rapidly isolated from fresh atrial tissue samples obtained from 14 patients undergoing Maze surgery due to atrial fibrillation. Human heart mitochondria exhibited typical mPT characteristics upon calcium overload such as swelling, evaluated by changes in light scattering, inhibition of respiration and loss of respiratory coupling. Swelling was a morphologically reversible event following transient calcium challenge. Calcium retention capacity (CRC), a quantitative measure of mPT sensitivity assayed by following extramitochondrial [Ca(2+)] and changes in respiration during a continuous calcium infusion, was significantly increased by cyclophilin D (CypD) inhibitors. The thiol-reactive oxidant phenylarsine oxide sensitized mitochondria to calcium-induced mPT. Release of the pro-apoptotic intermembrane protein cytochrome c was increased after, but not before, calcium discharge and respiratory inhibition in the CRC assay. From the present study, we conclude that adult viable heart mitochondria have a CypD- and oxidant-regulated mPT. The findings support that inhibition of mPT may be a relevant pharmacological target in human cardiac disease and may underlie the beneficial effect of cyclosporin A in reperfusion injury.

What is behind the non-antibiotic properties of minocycline?

Minocycline is a second-generation, semi-synthetic tetracycline that has been in use in therapy for over 30 years for its antibiotic properties against both Gram-positive and Gram-negative bacteria. It displays antibiotic activity due to its ability to bind to the 30S ribosomal subunit of bacteria and thus inhibit protein synthesis. More recently, it has been described to exert a variety of biological actions beyond its antimicrobial activity, including anti-inflammatory and anti-apoptotic activities, inhibition of proteolysis, as well as suppression of angiogenesis and tumor metastasis, which have been confirmed in different experimental models of non-infectious diseases. There are also many studies that have focused on the mechanisms involved in these non-antibiotic properties of minocycline, including anti-oxidant activity, inhibition of several enzyme activities, inhibition of apoptosis and regulation of immune cell activation and proliferation. This review summarizes the current findings in this topic, mainly focusing on the mechanisms underlying the immunomodulatory and anti-inflammatory activities of minocycline.

Limiting spinal cord injury by pharmacological intervention

The direct primary mechanical trauma to neurons, glia and blood vessels that occurs with spinal cord injury (SCI) is followed by a complex cascade of biochemical and cellular changes which serve to increase the size of the injury site and the extent of cellular and axonal loss. The aim of neuroprotective strategies in SCI is to limit the extent of this secondary cell loss by inhibiting key components of the evolving injury cascade. In this review we will briefly outline the pathophysiological events that occur in SCI, and then review the wide range of neuroprotective agents that have been evaluated in preclinical SCI models. Agents will be considered under the following categories: antioxidants, erythropoietin and derivatives, lipids, riluzole, opioid antagonists, hormones, anti-inflammatory agents, statins, calpain inhibitors, hypothermia, and emerging strategies. Several clinical trials of neuroprotective agents have already taken place and have generally had disappointing results. In attempting to identify promising new treatments, we will therefore highlight agents with (1) low known risks or established clinical use, (2) behavioral data gained in clinically relevant animal models, (3) efficacy when administered after the injury, and (4) robust effects seen in more than one laboratory and/or more than one model of SCI.

Minocycline protects SH-SY5Y cells from 6-hydroxydopamine by inhibiting both caspase-dependent and -independent programmed cell death

Minocycline, a tetracyclic antibiotic, exerts both antiinflammation by acting on microglia and a direct protection on neurons by inhibiting the apoptotic machinery at various levels. However, we are not aware of any study investigating the effects of minocycline on caspase-independent programmed cell death (PCD) pathways. This study investigated these alternative pathways in SH-SY5Y cells, a human dopaminergic cell line, challenged with 6-hydroxydopamine (6-OHDA). Minocycline exhibited neuroprotection and inhibition of the toxin-induced caspase-3-like activity, DNA fragmentation, and chromatin condensation, hallmarks of apoptosis. Moreover, we revealed that 6-OHDA also activated caspase-independent PCDs (such as paraptosis), which required de novo protein synthesis. Additionally, by separately monitoring caspase-dependent and caspase-independent pathways, we showed that inhibition of apoptosis only partially explained the protective effect of minocycline. Moreover, we observed that minocycline reduced the protein content of cells but, unexpectedly, increased the protein synthesis. These findings suggest that minocycline may actually increase protein degradation, so it may also accelerate the clearance of aberrant proteins. In conclusion, we report for the first time evidence indicating that minocycline may inhibit PCD pathways that are additional to conventional apoptosis.

Minocycline exerts uncoupling and inhibiting effects on mitochondrial respiration through adenine nucleotide translocase inhibition

The present study was aimed to provide a better understanding of the mitochondria-targeted actions of minocycline (MC), a second-generation tetracycline which has cytoprotective effects. Although the specific mechanisms underlying its activity remained elusive, considerable amounts of data indicated mitochondria as the primary pharmacological target of MC. Previous reports have shown that MC affects the oxygen-uptake rate by isolated mitochondria in different respiratory states. Here, we report on the effect of MC, in the range 50-200μM, on mitochondrial respiration. State 3 respiration titration with carboxyatractyloside revealed that MC inhibits the adenine nucleotide translocase. Furthermore, we analyze MC channel-forming capacity in the lipid membrane bilayer. Our results confirmed the crucial role of Δψ and showed a dependence on Ca(2+) for MC to have an effect on mitochondria. Our data also indicated that outer and inner mitochondrial membranes contribute differently to this effect, involving the presence of Δψ (the inner membrane) and VDAC (the outer membrane). Data from three isosmotic media indicate that MC does not increase the permeability of the inner membrane to protons or potassium. In addition, by using mitoplasts and ruthenium red, we showed that Ca(2+) uptake is not involved in the MC effect, suggesting involvement of VDAC in the MC interaction with the outer membrane. Our data contribute to unravel the mechanisms behind the mitochondria-targeted activity of the cytoprotective drug MC.

Interaction between cytokines and ammonia in the mitochondrial permeability transition in cultured astrocytes

Hepatic encephalopathy (HE) is the major neurological complication occurring in patients with acute and chronic liver failure. Elevated levels of blood and brain ammonia are characteristic of HE, and astrocytes are the primary target of ammonia toxicity. In addition to ammonia, recent studies suggest that inflammation and associated cytokines (CKs) also contribute to the pathogenesis of HE. It was previously established that ammonia induces the mitochondrial permeability transition (mPT) in cultured astrocytes. As CKs have been shown to cause mitochondrial dysfunction in other conditions, we examined whether CKs induce the mPT in cultured astrocytes. Cultures treated with tumor necrosis factor-α, interleukin-1β, interleukin-6, and interferon-γ, individually or in a mixture, resulted in the induction of the mPT in a time-dependent manner. Simultaneous treatment of cultures with a mixture of CKs and ammonia showed a marked additive effect on the mPT. As oxidative stress (OS) is known to induce the mPT, so we examined the effect of CKs and ammonia on hemeoxygenase-1 (HO-1) protein expression, a marker of OS. Such treatment displayed a synergistic effect in the upregulation of HO-1. Antioxidants significantly blocked the additive effects on the mPT by CKs and ammonia, suggesting that OS represents a major mechanism in the induction of the mPT. Treatment of cultures with minocycline, an antiinflammatory agent, which is known to inhibit OS, also diminished the additive effects on the mPT caused by CKs and ammonia. Induction of the mPT in astrocytes appears to represent a major pathogenetic factor in HE, in which CKs and ammonia are critically involved.

The prospects of minocycline in multiple sclerosis

Multiple sclerosis (MS) is the most common inflammatory demyelinating disease of the central nervous system (CNS). Although there are several approved drugs for MS, not all patients respond optimally to these drugs. More effective, well-tolerated therapeutic strategies for MS are necessary, either through the development of new medication or combination of existing ones. Minocycline is a traditional antibiotic with profound anti-inflammatory and neuroprotective effects and good tolerance for long-term use. The encouraging results from the animal model and clinical experiments on minocycline make it a promising candidate for MS treatment whether used alone or combined with other drugs. In this review, we summarized the pharmacological actions of minocycline and focused on its therapeutic effects and safety in experimental autoimmune encephalomyelitis (EAE) and MS. The data obtained here showed that minocycline would be an effective and safe therapy for MS.

Minocycline chelates Ca2+, binds to membranes, and depolarizes mitochondria by formation of Ca2+-dependent ion channels

Minocycline (an anti-inflammatory drug approved by the FDA) has been reported to be effective in mouse models of amyotrophic lateral sclerosis and Huntington disease. It has been suggested that the beneficial effects of minocycline are related to its ability to influence mitochondrial functioning. We tested the hypothesis that minocycline directly inhibits the Ca(2+)-induced permeability transition in rat liver mitochondria. Our data show that minocycline does not directly inhibit the mitochondrial permeability transition. However, minocycline has multiple effects on mitochondrial functioning. First, this drug chelates Ca(2+) ions. Secondly, minocycline, in a Ca(2+)-dependent manner, binds to mitochondrial membranes. Thirdly, minocycline decreases the proton-motive force by forming ion channels in the inner mitochondrial membrane. Channel formation was confirmed with two bilayer lipid membrane models. We show that minocycline, in the presence of Ca(2+), induces selective permeability for small ions. We suggest that the beneficial action of minocycline is related to the Ca(2+)-dependent partial uncoupling of mitochondria, which indirectly prevents induction of the mitochondrial permeability transition.

Evaluation of putative inhibitors of mitochondrial permeability transition for brain disorders--specificity vs. toxicity

Inhibition of mitochondrial permeability transition (mPT) has emerged as a promising approach for neuroprotection and development of well-tolerated mPT inhibitors with favorable blood-brain barrier penetration is highly warranted. In a recent study, 28 clinically available drugs with a common heterocyclic structure were identified as mPT inhibitors e.g. trifluoperazine, promethazine and nortriptyline. In addition, neuroprotection by structurally unrelated drugs e.g. neurosteroids, 4-hydroxy-tamoxifen and trimetazidine has been attributed to direct inhibition of mPT. The regulation of mPT is complex and highly dependent on the prevailing experimental conditions. Several features of mPT, such as swelling, depolarization or NADH oxidation, can also occur independently of the mPT phenomenon. Here, in isolated rodent brain-derived and human liver mitochondria, we re-evaluate drugs promoted as potent mPT inhibitors. We address the definition of an mPT inhibitor and present strategies to reliably detect mPT inhibition in vitro. Surprisingly, none of the 12 compounds tested displayed convincing mPT inhibition or effects comparable to cyclophilin D inhibition by the non-immunosuppressive cyclophilin inhibitor D-MeAla(3)-EtVal(4)-Cyclosporin (Debio 025). Propofol and 2-aminoethoxydiphenyl borate (2-APB) inhibited swelling in de-energized mitochondria but did not increase calcium retention capacity (CRC). Progesterone, trifluoperazine, allopregnanolone and 4-hydroxy-tamoxifen dose-dependently reduced CRC and respiratory control and were thus toxic rather than beneficial to mitochondrial function. Interestingly, topiramate increased CRC at high concentrations likely by a mechanism separate from direct mPT inhibition. We conclude that a clinically relevant mPT inhibitor should have a mitochondrial target and increase mitochondrial calcium retention at concentrations which can be translated to human use.

Biapigenin modulates the activity of the adenine nucleotide translocator in isolated rat brain mitochondria

In this study, we investigated the effects of biapigenin, a biflavone present in the extracts of Hypericum perforatum, in rat brain mitochondrial bioenergetics and calcium homeostasis. We found that biapigenin significantly decreased adenosine diphosphate (ADP)-induced membrane depolarization and increased repolarization (by 68 and 37%, respectively). These effects were blocked by atractyloside and bongkrekic acid, but not oligomycin. In the presence of biapigenin, an ADP-stimulated state 3 respiration was still noticeable, which did not happen in the presence of adenine nucleotide translocator (ANT) inhibitors. Taking in consideration the relevance of the ANT in the modulation of the mitochondrial permeability transition pore (mPTP), mitochondrial calcium homeostasis was evaluated alone or in the presence of biapigenin. We found that biapigenin reduces mitochondrial calcium retention by increasing calcium efflux, an effect that was blocked by ADP plus oligomycin, an efficient blocker of the mPTP in brain mitochondria. Taken together, the results in this article suggest that biapigenin modulates mPTP opening, possibly by modulating ANT function, contributing for enhanced mitochondrial calcium efflux, thereby reducing calcium burden and contributing for neuroprotection against excitotoxicity.

Minocycline: a neuroprotective agent for hypoxic-ischemic brain injury in the neonate?

Minocycline is a second-generation tetracycline and a potential neuroprotective intervention following brain injury. However, despite the recognized beneficial effects of minocycline in a multitude of adult disease states, the clinical application of minocycline in neonates is contentious. Tetracyclines, as a class, are not usually administered to neonates, but there is compelling evidence that minocycline reduces brain injury after neonatal hypoxic-ischemic brain injury. This Review focuses on the evidence for minocycline use in neonates by considering aspects of pharmacology, drug regimens, functional outcomes, and mechanisms of action.

Impairment of mitochondrial function by minocycline

There is an ongoing debate on the presence of beneficial effects of minocycline (MC), a tetracycline-like antibiotic, on the preservation of mitochondrial functions under conditions promoting mitochondria-mediated apoptosis. Here, we present a multiparameter study on the effects of MC on isolated rat liver mitochondria (RLM) suspended either in a KCl-based or in a sucrose-based medium. We found that the incubation medium used strongly affects the response of RLM to MC. In KCl-based medium, but not in sucrose-based medium, MC triggered mitochondrial swelling and cytochrome c release. MC-dependent swelling was associated with mitochondrial depolarization and a decrease in state 3 as well as uncoupled respiration. Swelling of RLM in KCl-based medium indicates that MC permeabilizes the inner mitochondrial membrane (IMM) to K(+) and Cl(-). This view is supported by our findings that MC-induced swelling in the KCl-based medium was partly suppressed by N,N'-dicyclohexylcarbodiimide (an inhibitor of IMM-linked K(+)-transport) and tributyltin (an inhibitor of the inner membrane anion channel) and that swelling was less pronounced when RLM were suspended in choline chloride-based medium. In addition, we observed a rapid MC-induced depletion of endogenous Mg(2+) from RLM, an event that is known to activate ion-conducting pathways within the IMM. Moreover, MC abolished the Ca(2+) retention capacity of RLM irrespective of the incubation medium used, most likely by triggering permeability transition. In summary, we found that MC at low micromolar concentrations impairs several energy-dependent functions of mitochondria in vitro.

Influence of HFE variants and cellular iron on monocyte chemoattractant protein-1

Background

Polymorphisms in the MHC class 1-like gene known as HFE have been proposed as genetic modifiers of neurodegenerative diseases that include neuroinflammation as part of the disease process. Variants of HFE are relatively common in the general population and are most commonly associated with iron overload, but can promote subclinical cellular iron loading even in the absence of clinically identified disease. The effects of the variants as well as the resulting cellular iron dyshomeostasis potentially impact a number of disease-associated pathways. We tested the hypothesis that the two most common HFE variants, H63D and C282Y, would affect cellular secretion of cytokines and trophic factors.

Methods

We screened a panel of cytokines and trophic factors using a multiplexed immunoassay in human neuroblastoma SH-SY5Y cells expressing different variants of HFE. The influence of cellular iron secretion on the potent chemokine monocyte chemoattractant protein-1 (MCP-1) was assessed using ferric ammonium citrate and the iron chelator, desferroxamine. Additionally, an antioxidant, Trolox, and an anti-inflammatory, minocycline, were tested for their effects on MCP-1 secretion in the presence of HFE variants.

Results

Expression of the HFE variants altered the labile iron pool in SH-SY5Y cells. Of the panel of cytokines and trophic factors analyzed, only the release of MCP-1 was affected by the HFE variants. We further examined the relationship between iron and MCP-1 and found MCP-1 secretion tightly associated with intracellular iron status. A potential direct effect of HFE is considered because, despite having similar levels of intracellular iron, the association between HFE genotype and MCP-1 expression was different for the H63D and C282Y HFE variants. Moreover, HFE genotype was a factor in the effect of minocycline, a multifaceted antibiotic used in treating a number of neurologic conditions associated with inflammation, on MCP-1 secretion.

Conclusion

Our results demonstrate that HFE polymorphisms influence the synthesis and release of MCP-1. The mechanism of action involves cellular iron status but it appears there could be additional influences such as ER stress. Finally, these data demonstrate a pharmacogenetic effect of HFE polymorphisms on the ability of minocycline to inhibit MCP-1 secretion.

The mitochondrial death pathway: a promising therapeutic target in diseases

The mitochondrial pathway to apoptosis is a major pathway of physiological cell death in vertebrates. The mitochondrial cell death pathway commences when apoptogenic molecules present between the outer and inner mitochondrial membranes are released into the cytosol by mitochondrial outer membrane permeabilization (MOMP). BCL-2 family members are the sentinels of MOMP in the mitochondrial apoptotic pathway; the pro-apoptotic B cell lymphoma (BCL)-2 proteins, BCL-2 associated x protein and BCL-2 antagonist killer 1 induce MOMP whereas the anti-apoptotic BCL-2 proteins, BCL-2, BCL-x_l and myeloid cell leukaemia 1 prevent MOMP from occurring. The release of pro-apoptotic factors such as cytochrome c from mitochondria leads to formation of a multimeric complex known as the apoptosome and initiates caspase activation cascades. These pathways are important for normal cellular homeostasis and play key roles in the pathogenesis of many diseases. In this review, we will provide a brief overview of the mitochondrial death pathway and focus on a selection of diseases whose pathogenesis involves the mitochondrial death pathway and we will examine the various pharmacological approaches that target this pathway.

Inhibitory modulation of the mitochondrial permeability transition by minocycline

The semi-synthetic tetracycline derivative minocycline exerts neuroprotective properties in various animal models of neurodegenerative disorders. Although anti-inflammatory and anti-apoptotic effects are reported to contribute to the neuroprotective action, the exact molecular mechanisms underlying the beneficial properties of minocycline remain to be clarified. We analyzed the effects of minocycline in a cell culture model of neuronal damage and in single-channel measurements on isolated mitoplasts. Treatment of neuron-enriched cortical cultures with rotenone, a high affinity inhibitor of the mitochondrial complex I, resulted in a deregulation of the intracellular Ca2+-dynamics, as recorded by live cell imaging. Minocycline (100 microM) and cyclosporin A (2 microM), a known inhibitor of the mitochondrial permeability transition pore, decreased the rotenone-induced Ca2+-deregulation by 60.9% and 37.6%, respectively. Investigations of the mitochondrial permeability transition pore by patch-clamp techniques revealed for the first time a dose-dependent reduction of the open probability by minocycline (IC(50)=190 nM). Additionally, we provide evidence for the high antioxidant potential of MC in our model. In conclusion, the present data substantiate the beneficial properties of minocycline as promising neuroprotectant by its inhibitory activity on the mitochondrial permeability transition pore.

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.

Genetic findings in Parkinson's disease and translation into treatment: a leading role for mitochondria?

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder and in most patients its aetiology remains unknown. Molecular genetic studies in familial forms of the disease identified key proteins involved in PD pathogenesis, and support a major role for mitochondrial dysfunction, which is also of significant importance to the common sporadic forms of PD. While current treatments temporarily alleviate symptoms, they do not halt disease progression. Drugs that target the underlying pathways to PD pathogenesis, including mitochondrial dysfunction, therefore hold great promise for neuroprotection in PD. Here we summarize how the proteins identified through genetic research (alpha-synuclein, parkin, PINK1, DJ-1, LRRK2 and HTRA2) fit into and add to our current understanding of the role of mitochondrial dysfunction in PD. We highlight how these genetic findings provided us with suitable animal models and critically review how the gained insights will contribute to better therapies for PD.

Minocycline and N-methyl-4-isoleucine cyclosporin (NIM811) mitigate storage/reperfusion injury after rat liver transplantation through suppression of the mitochondrial permeability transition

Graft failure after liver transplantation may involve mitochondrial dysfunction. We examined whether prevention of mitochondrial injury would improve graft function. Orthotopic rat liver transplantation was performed after 18 hours' cold storage in University of Wisconsin solution and treatment with vehicle, minocycline, tetracycline, or N-methyl-4-isoleucine cyclosporin (NIM811) of explants and recipients. Serum alanine aminotransferase (ALT), necrosis, and apoptosis were assessed 6 hours after implantation. Mitochondrial polarization and cell viability were assessed by intravital microscopy. Respiration and the mitochondrial permeability transition (MPT) were assessed in isolated rat liver mitochondria. After transplantation with vehicle or tetracycline, ALT increased to 5242 U/L and 4373 U/L, respectively. Minocycline and NIM811 treatment decreased ALT to 2374 U/L and 2159 U/L, respectively (P < 0.01). Necrosis and terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL) also decreased from 21.4% and 21 cells/field, respectively, after vehicle to 10.1% and 6 cells/field after minocycline and to 8.7% and 5.2 cells/field after NIM811 (P < 0.05). Additionally, minocycline decreased caspase-3 activity in graft homogenates (P < 0.05). Long-term graft survival was 27% and 33%, respectively, after vehicle and tetracycline treatment, which increased to 60% and 70% after minocycline and NIM811 (P < 0.05). In isolated mitochondria, minocycline and NIM811 but not tetracycline blocked the MPT. Minocycline blocked the MPT by decreasing mitochondrial Ca(2+) uptake, whereas NIM811 blocks by interaction with cyclophilin D. Intravital microscopy showed that minocycline and NIM811 preserved mitochondrial polarization and cell viability after transplantation (P < 0.05).

CONCLUSION

Minocycline and NIM811 attenuated graft injury after rat liver transplantation and improved graft survival. Minocycline and/or NIM811 might be useful clinically in hepatic surgery and transplantation.

Minocycline, a possible neuroprotective agent in Leber’s hereditary optic neuropathy (LHON): Studies of cybrid cells bearing 11778 mutation

Leber's hereditary optic neuropathy (LHON) is a retinal neurodegenerative disorder caused by mitochondrial DNA point mutations. Complex I of the respiratory chain affected by the mutation results in a decrease in ATP and an increase of reactive oxygen species production. Evaluating the efficacy of minocycline in LHON, the drug increased the survival of cybrid cells in contrast to the parental cells after thapsigargin-induced calcium overload. Similar protection was observed by treatment with cyclosporine A, a blocker of the mitochondrial permeability transition pore (mPTP). Ratiometric Ca(2+) imaging reveals that acetylcholine/thapsigargin triggered elevation of the cytosolic calcium concentration is alleviated by minocycline and cyclosporine A. The mitochondrial membrane potential of LHON cybrids was significantly conserved and the active-caspase-3/procaspase-3 ratio was decreased in both treatments. Our observations show that minocycline inhibits permeability transition induced by thapsigargin in addition to its antioxidant effects. In relation with its high safety profile, these results would suggest minocycline as a promising neuroprotective agent in LHON.

Lithium desensitizes brain mitochondria to calcium, antagonizes permeability transition, and diminishes cytochrome C release

Among the numerous effects of lithium on intracellular targets, its possible action on mitochondria remains poorly explored. In the experiments with suspension of isolated brain mitochondria, replacement of KCl by LiCl suppressed mitochondrial swelling, depolarization, and a release of cytochrome c induced by a single Ca2+ bolus. Li+ robustly protected individual brain mitochondria loaded with rhodamine 123 against Ca2+-induced depolarization. In the experiments with slow calcium infusion, replacement of KCl by LiCl in the incubation medium increased resilience of synaptic and nonsynaptic brain mitochondria as well as resilience of liver and heart mitochondria to the deleterious effect of Ca2+. In LiCl medium, mitochondria accumulated larger amounts of Ca2+ before they lost the ability to sequester Ca2+. However, lithium appeared to be ineffective if mitochondria were challenged by Sr2+ instead of Ca2+. Cyclosporin A, sanglifehrin A, and Mg2+, inhibitors of the mitochondrial permeability transition (mPT), increased mitochondrial Ca2+ capacity in KCl medium but failed to do so in LiCl medium. This suggests that the mPT might be a common target for Li+ and mPT inhibitors. In addition, lithium protected mitochondria against high Ca2+ in the presence of ATP, where cyclosporin A was reported to be ineffective. SB216763 and SB415286, inhibitors of glycogen synthase kinase-3beta, which is implicated in regulating reactive oxygen species-induced mPT in cardiac mitochondria, did not increase Ca2+ capacity of brain mitochondria. Altogether, these findings suggest that Li+ desensitizes mitochondria to elevated Ca2+ and diminishes cytochrome c release from brain mitochondria by antagonizing the Ca2+-induced mPT.