Effects of immunosuppressants, calcineurin inhibition, and blockade of endoplasmic reticulum calcium channels on free fatty acid efflux from the ischemic/reperfused rat cerebral cortex

Could dantrolene be explored as a repurposed drug to treat COVID-19 patients by restoring intracellular calcium homeostasis?

Dantrolene, an FDA approved drug to treat malignant hyperthermia and muscle spasm, has been demonstrated to inhibit severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mediated toxicity of host cells. Ryanodine receptor overactivation and associated disruption of intracellular Ca2+ homeostasis play important roles in SARS-CoV-2 infection and replication of host cells. Dantrolene, as an inhibitor of RyRs, is expected to ameliorate these detrimental effects of SARS-CoV-2 in host cells. Additionally, dantrolene has also been shown to inhibit multiple cell or organ damage induced by hypoxia/ischemia, mitochondria damage, oxidative stresses, inflammation, impairment of autophagy and apoptosis, etc., which are often the causes of severity and mortality of COVID-19 patients. We have repurposed that dantrolene has a high potential at treating COVID-19 patients and reducing its morbidity and mortality.

Dissecting Cellular Mechanisms of Long-Chain Acylcarnitines-Driven Cardiotoxicity: Disturbance of Calcium Homeostasis, Activation of Ca2+-Dependent Phospholipases, and Mitochondrial Energetics Collapse

Long-chain acylcarnitines (LCAC) are implicated in ischemia-reperfusion (I/R)-induced myocardial injury and mitochondrial dysfunction. Yet, molecular mechanisms underlying involvement of LCAC in cardiac injury are not sufficiently studied. It is known that in cardiomyocytes, palmitoylcarnitine (PC) can induce cytosolic Ca²⁺ accumulation, implicating L-type calcium channels, Na⁺/Ca²⁺ exchanger, and Ca²⁺-release from sarcoplasmic reticulum (SR). Alternatively, PC can evoke dissipation of mitochondrial potential (ΔΨ_m) and mitochondrial permeability transition pore (mPTP). Here, to dissect the complex nature of PC action on Ca²⁺ homeostasis and oxidative phosphorylation (OXPHOS) in cardiomyocytes and mitochondria, the methods of fluorescent microscopy, perforated path-clamp, and mitochondrial assays were used. We found that LCAC in dose-dependent manner can evoke Ca²⁺-sparks and oscillations, long-living Ca²⁺ enriched microdomains, and, finally, Ca²⁺ overload leading to hypercontracture and cardiomyocyte death. Collectively, PC-driven cardiotoxicity involves: (I) redistribution of Ca²⁺ from SR to mitochondria with minimal contribution of external calcium influx; (II) irreversible inhibition of Krebs cycle and OXPHOS underlying limited mitochondrial Ca²⁺ buffering; (III) induction of mPTP reinforced by PC-calcium interplay; (IV) activation of Ca²⁺-dependent phospholipases cPLA2 and PLC. Based on the inhibitory analysis we may suggest that simultaneous inhibition of both phospholipases could be an effective strategy for protection against PC-mediated toxicity in cardiomyocytes.

Roles of endogenous ether lipids and associated PUFAs in the regulation of ion channels and their relevance for disease

Ether lipids (ELs) are lipids characterized by the presence of either an ether linkage (alkyl lipids) or a vinyl ether linkage [i.e., plasmalogens (Pls)] at the sn1 position of the glycerol backbone, and they are enriched in PUFAs at the sn2 position. In this review, we highlight that ELs have various biological functions, act as a reservoir for second messengers (such as PUFAs) and have roles in many diseases. Some of the biological effects of ELs may be associated with their ability to regulate ion channels that control excitation-contraction/secretion/mobility coupling and therefore cell physiology. These channels are embedded in lipid membranes, and lipids can regulate their activities directly or indirectly as second messengers or by incorporating into membranes. Interestingly, ELs and EL-derived PUFAs have been reported to play a key role in several pathologies, including neurological disorders, cardiovascular diseases, and cancers. Investigations leading to a better understanding of their mechanisms of action in pathologies have opened a new field in cancer research. In summary, newly identified lipid regulators of ion channels, such as ELs and PUFAs, may represent valuable targets to improve disease diagnosis and advance the development of new therapeutic strategies for managing a range of diseases and conditions.

The mitochondrial NO-synthase/guanylate cyclase/protein kinase G signaling system underpins the dual effects of nitric oxide on mitochondrial respiration and opening of the permeability transition pore

The available data on the involvement of nitric oxide (NO) and mitochondrial calcium-dependent NO synthase (mtNOS) in the control of mitochondrial respiration and the permeability transition pore (mPTP) are contradictory. We have proposed that the mitochondrial mtNOS/guanylate cyclase/protein kinase G signaling system (mtNOS-SS) is also implicated in the control of respiration and mPTP, providing the interplay between NO and mtNOS-SS, which, in turn, may result in inconsistent effects of NO. Therefore, using rat liver mitochondria, we applied specific inhibitors of the enzymes of this signaling system to evaluate its role in the control of respiration and mPTP opening. Steady-state respiration was supported by pyruvate, glutamate, or succinate in the presence of hexokinase, glucose, and ADP. When applied at low concentrations, l-arginine (to 500 µm) and NO donors (to 50 µm) activated the respiration and increased the threshold concentrations of calcium and d,l-palmitoylcarnitine required for the dissipation of the mitochondrial membrane potential and pore opening. Both effects were eliminated by the inhibitors of NO synthase, guanylate cyclase, and kinase G, which denotes the involvement of mtNOS-SS in the activation of respiration and deceleration of mPTP opening. At high concentrations, l-arginine and NO donors inhibited the respiration and promoted pore opening, indicating that adverse effects induced by an NO excess dominate over the protection provided by mtNOS-SS. Thus, these results demonstrate the opposite impact of NO and mtNOS-SS on the respiration and mPTP control, which can explain the dual effects of NO.

Recent Topics on The Mechanisms of Immunosuppressive Therapy-Related Neurotoxicities

Although transplantation procedures have been developed for patients with end-stage hepatic insufficiency or other diseases, allograft rejection still threatens patient health and lifespan. Over the last few decades, the emergence of immunosuppressive agents such as calcineurin inhibitors (CNIs) and mammalian target of rapamycin (mTOR) inhibitors have strikingly increased graft survival. Unfortunately, immunosuppressive agent-related neurotoxicity commonly occurs in clinical practice, with the majority of neurotoxicity cases caused by CNIs. The possible mechanisms through which CNIs cause neurotoxicity include increasing the permeability or injury of the blood–brain barrier, alterations of mitochondrial function, and alterations in the electrophysiological state. Other immunosuppressants can also induce neuropsychiatric complications. For example, mTOR inhibitors induce seizures, mycophenolate mofetil induces depression and headaches, methotrexate affects the central nervous system, the mouse monoclonal immunoglobulin G2 antibody (used against the cluster of differentiation 3) also induces headaches, and patients using corticosteroids usually experience cognitive alteration. Therapeutic drug monitoring, individual therapy based on pharmacogenetics, and early recognition of symptoms help reduce neurotoxic events considerably. Once neurotoxicity occurs, a reduction in the drug dosage, switching to other immunosuppressants, combination therapy with drugs used to treat the neuropsychiatric manifestation, or blood purification therapy have proven to be effective against neurotoxicity. In this review, we summarize recent topics on the mechanisms of immunosuppressive drug-related neurotoxicity. In addition, information about the neuroprotective effects of several immunosuppressants is also discussed.

Dephosphorylation by calcineurin regulates translocation of dynamin-related protein 1 to mitochondria in hepatic ischemia reperfusion induced hippocampus injury in young mice

Hepatic ischemia reperfusion (HIR) has been found to induce brain injury and cognitive dysfunction. Dynamin-related protein 1 (Drp1) mediated mitochondrial fission involves oxidative stress, apoptosis and several neurological diseases. In this study, we investigated whether Drp1 translocation to mitochondria was implicated in HIR induced hippocampus injury in young mice, and further detected the role of calcineurin in the regulation of mitochondrial dynamics. 2-week C57BL/6 mice were chosen to make HIR model. Western blot was used to detect mitochondrial dynamics regulating proteins in whole hippocampal tissues and extracted mitochondria. Transmission electron microscopy was used to observe mitochondrial morphology. TUNEL staining and ELISA (serum S100β/NSE concentrations) were used to evaluate neurons apoptosis and brain injury respectively. Drp1 inhibitor Mdivi-1 and calcineurin inhibitor FK506 were utilized to further confirm the role of Drp1 and calcineurin. Results showed that HIR affected mitochondrial dynamics in a fission-dominant manner with translocation of Drp1 to mitochondria in hippocampus of young mice. HIR induced increased expression of calcineurin and dephosphorylation of Drp1 at Ser637 in hippocampus. Treatment with Mdivi-1 and FK506 upregulated the phosphorylation of Drp1, inhibited Drp1 translocation to mitochondria, and alleviated mitochondrial fragmentation after HIR. What's more, Mdivi-1 and FK506 restrained cytochrome c release and cleaved caspase-3 expression, ameliorated hippocampal neurons apoptosis, and decreased serum S100β/NSE concentrations as well. These data suggest that calcineurin mediated Drp1 dephosphorylation and translocation to mitochondria play a crucial role in HIR induced mitochondrial fragmentation and neurons apoptosis in hippocampus.

Calcineurin inhibitors improve memory loss and neuropathological changes in mouse model of dementia

AIM

The present study was designed to investigate the potential of Cyclosporine (CsA) and Tacrolimus, the inhibitors of calcineurin (CaN) in cognitive deficits of mice.

METHODS

Streptozotocin [STZ, 3mg/kg, injected intracerebroventricular (i.c.v.)] was used to induce memory deficits in NIH mice, while aged mice separately taken served as a natural model of dementia. Morris water maze (MWM) test was employed to evaluate learning and memory of the animals. A battery of biochemical and histopathological studies was also performed. Extent of oxidative stress was measured by estimating the levels of brain glutathione (GSH) and thiobarbituric acid reactive species (TBARS). Brain acetylcholinestrase (AChE) activity was estimated to assess cholinergic activity. The brain level of myeloperoxidase (MPO) was measured as a marker of inflammation.

RESULTS

STZ i.c.v. and aging results in marked decline in MWM performance of the animals, reflecting impairment of learning and memory. STZ i.c.v. treated mice and aged mice exhibited a marked accentuation of AChE activity, TBARS and MPO levels along with a fall in GSH level. Further the stained micrographs of STZ treated mice and aged mice indicate pathological changes, severe neutrophilic infiltration and amyloid deposition. Cyclosporine and Tacrolimus treatment significantly attenuated STZ induced and age related memory deficits, biochemical and histopathological alterations.

CONCLUSION

The findings demonstrate the potential of CaN inhibitors Cyclosporine and Tacrolimus in memory dysfunctions which may probably be attributed to anti-cholinesterase, anti-amyloid, anti-oxidative and anti-inflammatory effects. It is concluded that CaN can be explored as a potential therapeutic target in dementia.

Inhibition of Drp1 by Mdivi-1 attenuates cerebral ischemic injury via inhibition of the mitochondria-dependent apoptotic pathway after cardiac arrest

Mitochondrial fission is predominantly controlled by the activity of dynamin-related protein1 (Drp1), which has been reported to be involved in mitochondria apoptosis pathways. However, the role of Drp1 in a rat model of cardiac arrest remains unknown. In this study, we found that activation of Drp1 in the mitochondria was increased after cardiac arrest and inhibition of Drp1 by 1.2 mg/kg of mitochondrial division inhibitor-1 (Mdivi-1) administration after the restoration of spontaneous circulation (ROSC) significantly protected against cerebral ischemic injury, shown by the increased 72-h survival rate and improved neurological function. Moreover, the increase of the vital neuron and the reduction of cytochrome c (CytC) release, apoptosis-inducing factor (AIF) translocation and caspase-3 activation in the brain indicate that this protection might result from the suppression of neuron apoptosis. Altogether, these results indicated that Drp1 is activated after cardiac arrest and the inhibition of Drp1 is protective against cerebral ischemic injury in a rat of cardiac arrest model via inhibition of the mitochondrial apoptosis pathway.

Flow cytometric analysis of ca-induced membrane permeability transition of isolated rat liver mitochondria

The membrane permeability transition (MPT) of mitochondria plays an important role in the mechanism of apoptotic cell death in various cells. Classic type MPT is induced by Ca²⁺ in the presence of inorganic phosphate and respiratory substrate, and is characterized by various events including generation of reactive oxygen species (ROS), membrane depolarization, swelling, release of Ca²⁺ and high sensitivity to cyclosporine A. However, the sequence of these events and the effect of antioxidants on their events remain obscure. Flow cytometry is a convenient method to investigate the order of events among various functions occurring in MPT using a limited amount of mitochondria (200 µl of 0.02 mg protein/ml) without contamination by other organelles. Flow cytometric analysis revealed that Ca²⁺ sequentially induced ROS generation, depolarization, swelling and Ca²⁺ release in mitochondria by a cyclosporine A-inhibitable mechanism. These results were supported by the finding that Ca²⁺-induced MPT was inhibited by antioxidants, such as glutathione and N-acetylcysteine. It was also revealed that various inhibitors of Ca²⁺-induced phospholipase A₂ suppressed all of the events associated with Ca²⁺-induced MPT. These results suggested that ROS generation and phospholipase A₂ activation by Ca²⁺ underlie the mechanism of the initiation of MPT.

Effects of Dantrolene on Ischemia-Reperfusion Injury in Animal Models: A Review of Outcomes in Heart, Brain, Liver, and Kidney

Background/Objectives

Ischemia-reperfusion (IR) is the restoration of blood flow to a tissue that was formerly deficient of blood flow. Tissue damage after IR is considered an IR injury (IRI). During IR, there is an increased level of cytosolic calcium ([Ca2+]i) due to the release of calcium from mitochondrial, sarcoendoplasmic reticulum, and nuclear organelles. Dantrolene sodium (dantrolene) is a 1-[[[5-(4-nitrophenol)-2-furanyl]methylene]amino]-2, 4-imidazolidinedione sodium salt with a nonspecific mechanism, inhibiting organelle release of Ca2+ into the cytosol. This work reviews the outcomes of administering dantrolene in brain, heart, liver, and kidney animal models of IRI.

Methods

An extensive PubMed, MEDLINE, and MEDLAR literature review during the last 30 years on the effect of dantrolene in IRI in animal models was analyzed to determine the clinical implications of this important study. Particular attention was given to dantrolene in heart, brain, liver, and kidney IRI.

Results

Heart: Nine studies of heart IRI were reviewed and include an in vivo dog model (n = 1), in vivo rabbit model (n = 1), isolated dog myocardial fibers (n = 1), and isolated rat hearts (n = 6). Four studies showed decreased infarct size and increased cardiac function after IRI. One in vivo rabbit study found no difference in infarct size or cardiac function after IRI versus controls. Dantrolene may be protective or inductive of post-IRI arrhythmias depending on preestablished myocyte cycling times. Brain: Nine studies of brain IRI were reviewed and include an in vivo dog model (n = 1), in vivo gerbil model (n = 2), and in vivo rat models (n = 6). Dantrolene shows protective decreases in apoptotic markers in 6 studies, but it shows no effect on the necrotic core and mixed effects on reduction of infarct volume. One study found increased mortality in the dantrolene group. Liver: One study of in vivo rat liver IRI found that dantrolene decreased liver function tests, tissue necrosis factor α, tissue necrosis, and increased interleukin 10. Kidney: One study of in vivo rat kidney IRI showed that dantrolene had no effect.

Conclusions

Dantrolene shows protective effects in animal models of heart, brain, and potentially liver IRI, reinforcing the importance of calcium homeostasis during IRI. Variations of dose, timing of administration, route of administration, and outcomes between studies make definitive conclusions difficult. The nonspecific mechanism of action of dantrolene may also account for the variation among studies. Lack of studies in the liver and kidney makes any consensus in these organs premature, and thus, emphasis for this review was put on studies of the heart and brain.

Calcineurin-mediated GABA(A) receptor dephosphorylation in rats after kainic acid-induced status epilepticus

Calcineurin (CaN) is a neuronally enriched, calcium-dependent phosphatase, which plays an important role in a number of neuronal processes including development of learning and memory, and modulation of receptor's function and neuronal excitability as well as induction of apoptosis. It has been established in kindling model that the status epilepticus (SE)-induced increase in CaN activity is involved in the development of seizures through down-regulation of gamma-aminobutyric acid A receptor (GABA(A)R) activation. However, the mechanism by which CaN mediates GABA(A) receptor dephosphorylation in SE is not fully understood. Here, using a model of kainic acid (KA)-induced SE and CaN inhibitor FK506, we observed the behaviors induced by KA and levels of CaN activity and CaN expression in hippocampus by immunobloting. The results showed that the SE-induced CaN activity was time-dependent, with a peak at 2h and a return to basal level at 24h, whereas a significant increase in CaN expression was seen at 24h after SE. It is proposed that the rapid elevation in CaN activity after KA-induced SE is not likely due to an increase in CaN expression but rather an increase in CaN activation state or kinetics. In addition, we also demonstrated that pre-treatment with FK506 remarkably suppressed the SE-induced CaN activity and its expression, and reversed the SE-induced dephosphorylation of GABA(A)R 2/3 subunits. Taken together, our data suggest that down-regulation in inhibition of GABA(A)R 2/3 by CaN activity contributes to an elevation in neuronal excitability of hippocampus, which may be involved in development of chronic processes of seizures.

Dantrolene: mechanisms of neuroprotection and possible clinical applications in the neurointensive care unit

Calcium plays a central role in neuronal function and injury. Dantrolene, an inhibitor of the ryanodine receptor, inhibits intracellular calcium release from the sarco-endoplasmic reticulum. We review the available data of dantrolene as a potential neuroprotective agent and briefly summarize its other pharmacologic effects that may have potential applications for patients in the neurointensive care unit (NICU). Areas with the need for continued research are identified.

Trifluoperazine protects brain plasma membrane Ca(2+)-ATPase from oxidative damaging

In the central nervous system (CNS), a number of different pathological processes such as necrosis, Parkinson's and Alzheimer's diseases are related to disturbance in calcium homeostasis associated with oxidative stress. Here we compare the susceptibility of rat brain plasma membrane Ca(2+)-ATPase (PMCA) and sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA) isoforms to in vitro oxidative stress, and investigate a putative role of trifluoperazine (TFP), an antipsychotic drug that is also a powerful inhibitor of Ca(2+)-transporter proteins, in protecting these enzymes. It is shown that, in rat brain, PMCA is very sensitive to the damage induced by preincubation with Fe(2+)-ascorbate, or Fe(2+)-ascorbate plus H2O2, while SERCA is resistant. Inhibition of PMCA activity promoted by Fe(2+)/ascorbate medium is fully prevented by the presence of microM concentrations of either butylated hydroxytoluene (BHT) or TFP, but only partially protected, or reversed, by dithiothreitol (DTT), pointing to some protein cysteine(s) as one of the main targets for a lipid peroxidation-dependent damaging mechanism. However, when 0.5-1 mM H2O2 is added together with Fe(2+)/ascorbate, both BHT and TFP only partially prevent ATPase activity inhibition, and DTT does not confer any protection, suggesting two possible additional mechanisms involving both lipid peroxidation and direct damage to PMCA at amino acid residues other than cysteines. A possible use of micromolar concentrations of TFP as a direct antioxidant protector for PMCA under oxidative stress conditions is discussed.

Gossypol inhibits calcineurin phosphatase activity at multiple sites

Calcineurin, the Ca2+/calmodulin-dependant serine/threonine phosphatase is the target for the immunosuppressant drugs FK506 and cyclosporine-A. These established calcineurin inhibitors each require an immunophilin protein cofactor. Gossypol, a polyphenol produced by the cotton plant, inhibits calcineurin (IC50=15 microM), in a noncompetitive, reversible manner, and is independent of any cofactor. We found that gossypol acts by at least two mechanisms to inhibit calcineurin phosphatase activity. A calmodulin-independent form of calcineurin was less sensitive to inhibition by gossypol than native calcineurin (IC50=41 and 18 microM, respectively) indicating that gossypol may interfere with calmodulin binding. A fluorescence polarization based assay demonstrated that 100 microM gossypol reduced the affinity of calmodulin for calcineurin (from K(d)=2.4 to 250 nM). Inhibition of calcineurin phosphatase activity by gossypol could not be overcome by adding excess calmodulin or by testing the inhibition toward a calmodulin-independent calcineurin indicating that gossypol acts at a site different from the calmodulin-binding site. Gossypol decreased the affinity of calcineurin for immunosuppressant/immunophilin complexes only in the presence of calmodulin, indicating that gossypol blocks the effects of calmodulin binding to calcineurin. In addition, gossypol had a stimulatory effect on native calcineurin in the absence of calmodulin, possibly indicating a calmodulin mimetic effect. Gossypol exists in two enantiomeric forms which are reported to have different potency for cell toxicity. (+) and (-) gossypol had equivalent potency for inhibition of native and calmodulin-independent calcineurin phosphatase activity, and for inhibition of calmodulin binding. The inhibition of calcineurin by gossypol via multiple binding sites without stereo-specificity indicates that gossypol is not a specific calcineurin inhibitor.

Calcineurin and Erk1/2-signaling pathways are involved in the antiapoptotic effect of cyclosporin A on astrocytes exposed to simulated ischemia in vitro

The present study focused on mechanisms involved in the anti-apoptotic effect of cyclosporin A (CsA) towards ischemic injured astrocytes in vitro [under combined oxygen glucose deprivation (OGD)]. We investigated whether this action might be mediated through activation of extracellular signal regulated kinases 1 and 2 (Erk1/2) or attenuation of calcineurin (CaN) by immunosuppressant in ischemic astrocytes. Additionally, the influence of CsA on phosphorylation of Akt kinase was determined. After 21 days of in vitro culture, astrocytes were subjected to OGD (for 8 h) and CsA (0.25-10 microM); 0.25 microM CsA distinctly stimulated the Erk1/2 pathway in astrocytes exposed to OGD. This protective effect of CsA was strongly associated with CaN inhibition, increased expression of anti-apoptotic factors such as Bcl-X(L) and NF-kappaB, as well as suppression of caspase-3 activity. Maximum p-Akt kinase expression was observed following treatment with 1 microM CsA. Finally, we also demonstrated that the beneficial effect of CsA at a concentration of 10 microM is related mainly to strong CaN inhibition. The results obtained suggest that, depending on the concentration used, CsA might act as a protective agent towards ischemia-injured astroglial cells through alternative intracellular pathways associated with increased p-Erk1/2 and p-Akt expression or CaN inactivation.

Role of T lymphocytes and interferon-gamma in ischemic stroke

BACKGROUND

Although lymphocyte recruitment and activation are associated with cerebral ischemia-reperfusion (I/R) injury, the contributions of specific lymphocyte subpopulations and lymphocyte-derived interferon-gamma (IFN-gamma) to stroke remain unknown. The objectives of this study were to define the contribution of specific populations of lymphocytes to the inflammatory and prothrombogenic responses elicited in the cerebral microvasculature by I/R and to investigate the role of T-cell-associated IFN-gamma in the pathogenesis of ischemic stroke.

METHODS AND RESULTS

Middle cerebral artery occlusion was induced for 1 hour (followed by 4 or 24 hours of reperfusion) in wild-type mice and mice deficient in lymphocytes (Rag1(-/-)), CD4+ T cells, CD8+ T cells, B cells, or IFN-gamma. Platelet and leukocyte adhesion was assessed in cortical venules with intravital video microscopy. Neurological deficit and infarct volume were determined 24 hours after reperfusion. Rag1(-/-), CD4+ T-cell(-/-), CD8+ T-cell(-/-), and IFN-gamma(-/-) mice exhibited comparable significant reductions in I/R-induced leukocyte and platelet adhesion compared with wild-type mice exposed to I/R. Infarct volume was reduced and I/R-induced neurological deficit was improved in immunodeficient Rag1(-/-) mice. These protective responses were reversed in Rag1(-/-) mice reconstituted with either wild-type or, to a lesser extent, IFN-gamma(-/-) splenocytes. B-cell-deficient mice failed to show improvement against ischemic stroke injury.

CONCLUSIONS

These findings indicate that CD4+ and CD8+ T lymphocytes, but not B lymphocytes, contribute to the inflammatory and thrombogenic responses, brain injury, and neurological deficit associated with experimental stroke. Although IFN-gamma plays a pivotal role in stroke-induced inflammatory responses, T lymphocytes appear to be a minor source of this cytokine.

Stroke and T-cells

The microvasculature of the brain region affected by a stroke assumes an inflammatory phenotype that is characterized by endothelial cell activation and barrier dysfunction and the recruitment of adherent leukocytes. Although most attention has been devoted to the possible role of neutrophils in the tissue responses to ischemic stroke there is evidence that T-lymphocytes also accumulate in the postischemic brain. Although comparable detailed analyses of lymphocyte involvement in ischemic brain injury have not been performed, emerging findings suggest a role for T-cells in the pathogenesis of ischemic stroke. The recruitment of T-cells to the site of brain injury is critically dependent on the coordinated expression of adhesion molecules on the activated capillary endothelium. Whether the recruited lymphocytes are acting directly on brain tissue or indirectly through activation of other circulating blood cells and/or extravascular cells remain unclear. Cytotoxic CD8+ T-cells may induce brain injury through molecules released from their cytotoxic granules. CD4+ T-helper 1 (TH1) cells, which secrete proinflammatory cytokines, including interleukin-2 (IL-2), IL-12, interferon-gamma, and tumor necrosis factor-alpha, may play a key role in the pathogenesis of stroke, whereas CD4+TH2 cells may play a protective role through anti-inflammatory cytokines such as IL-4, IL-5, IL-10, and IL-13. T-cells should be considered as therapeutic targets for ischemic stroke. However, because infection is a leading cause of mortality in the postacute phase of ischemic stroke, and considering anti-inflammatory role of CD4+TH2, treatment targeting T-cells should be carefully designed to reduce deleterious and enhance protective actions of T-cells.

AMPA/kainate receptor-mediated downregulation of GABAergic synaptic transmission by calcineurin after seizures in the developing rat brain

Hypoxia is the most common cause of perinatal seizures and can be refractory to conventional anticonvulsant drugs, suggesting an age-specific form of epileptogenesis. A model of hypoxia-induced seizures in immature rats reveals that seizures result in immediate activation of the phosphatase calcineurin (CaN) in area CA1 of hippocampus. After seizures, CA1 pyramidal neurons exhibit a downregulation of GABA(A) receptor (GABA(A)R)-mediated inhibition that was reversed by CaN inhibitors. CaN activation appears to be dependent on seizure-induced activation of Ca2+-permeable AMPA receptors (AMPARs), because the upregulation of CaN activation and GABA(A)R inhibition were attenuated by GYKI 52466 [1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine hydrochloride] or Joro spider toxin. GABA(A)R beta2/3 subunit protein was dephosphorylated at 1 h after seizures, suggesting this subunit as a possible substrate of CaN in this model. Finally, in vivo administration of the CaN inhibitor FK-506 significantly suppressed hypoxic seizures, and posttreatment with NBQX (2,3-dihydroxy-6-nitro-7-sulfonyl-benzo[f]quinoxaline) or FK-506 blocked the hypoxic seizure-induced increase in CaN expression. These data suggest that Ca2+-permeable AMPARs and CaN regulate inhibitory synaptic transmission in a novel plasticity pathway that may play a role in epileptogenesis in the immature brain.

Cyclosporine modulates the response to hypoxia-reoxygenation in pulmonary artery endothelial cells

BACKGROUND

Depletion of macrophages, neutrophils, or lymphocytes confers only partial protection against experimental lung reperfusion injury, suggesting that inflammatory responses in other cell types contribute to tissue injury. Endothelial cell activation has previously been shown to be critical to the development of ischemia-reperfusion injury in other vascular beds. Furthermore, cyclosporine (CSA) reduces in vivo lung reperfusion injury through attenuated secretion of proinflammatory mediators. These studies determined whether pulmonary artery endothelial cells (PAEC), subjected to hypoxia and reoxygenation, promote inflammation and whether CSA afforded any modulation of that response.

METHODS

Isolated rat PAEC were subjected in vitro to 2 hours hypoxia followed by up to 4 hours reoxygenation. Cells were pretreated with CSA or a cremaphor vehicle. Differences in activation of signaling kinases and transcription factors were assessed, as was cytokine-chemokine protein secretion.

RESULTS

There was significant signaling kinase (extracellular signal regulated kinase [ERK 1/2]) activation by 15 minutes reoxygenation, which was temporally associated with marked activation of the transcription factors nuclear factor kappa B (NFkappaB) and early growth response one (EGR-1). At 4 hours reoxygenation there were significant increases in chemokine protein secretion. The CSA decreased ERK 1/2 phosphorylation and significantly attenuated transcription factor transactivation at 15 minutes reoxygenation. The CSA was found to be selective in reducing cytokine-chemokine elaboration at 4 hours reoxygenation.

CONCLUSIONS

Hypoxia-reoxygenation induces ERK 1/2 phosphorylation, as well as transactivation of the transcription factors NFkappaB and EGR-1 in PAEC. Cyclosporine selectively reduces proinflammatory mediator secretion, likely by transcriptional regulation through NFkappaB and EGR-1. This is the first demonstration of ERK 1/2 inhibition afforded by CSA.

Investigations on gossypol: past and present developments

Gossypol has received significant attention as a result of its potential therapeutic application as a male antifertility agent. Furthermore, recent research examining the biological activity of gossypol has revealed a number of other promising lines of enquiry. These have focused on the antitumour, antiviral and antioxidant actions of the compound in various disease states. This article provides an overview of the studies on the biological activity of gossypol, with particular attention paid to the mechanisms of its activity and its prospect as a medicinal product.

Physiology and Pathophysiology of the Calcium Store in the Endoplasmic Reticulum of Neurons

The endoplasmic reticulum (ER) is the largest single intracellular organelle, which is present in all types of nerve cells. The ER is an interconnected, internally continuous system of tubules and cisterns, which extends from the nuclear envelope to axons and presynaptic terminals, as well as to dendrites and dendritic spines. Ca2+release channels and Ca2+pumps residing in the ER membrane provide for its excitability. Regulated ER Ca2+release controls many neuronal functions, from plasmalemmal excitability to synaptic plasticity. Enzymatic cascades dependent on the Ca2+concentration in the ER lumen integrate rapid Ca2+signaling with long-lasting adaptive responses through modifications in protein synthesis and processing. Disruptions of ER Ca2+homeostasis are critically involved in various forms of neuropathology.

Hydrophobic dipeptide Leu-Ile protects against neuronal death by inducing brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor synthesis

We investigated whether certain hydrophobic dipeptides, Leu-Ile, Leu-Pro, and Pro-Ile, which partially resemble the site on FK506 that binds to immunophilin, could stimulate glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) synthesis in cultured neurons and found only Leu-Ile to be an active dipeptide. Leu-Ile protected against the death of mesencephalic neurons from wild-type mice but not from mice lacking the BDNF or GDNF gene. Next, we examined the effects of i.p. or i.c.v. administration of Leu-Ile on BDNF and GDNF contents. Both types of administration increased the contents of BDNF and GDNF in the striatum of mice. Also, peripheral administration of Leu-Ile inhibited dopaminergic (DA) denervation caused by unilateral injection of 6-hydroxydopamine (6-OHDA) into the striatum of mice. The number of rotations following a methamphetamine challenge was lower in the Leu-Ile-treated group than in the nontreated group. Next, we compared the calcineurin activity and immunosuppressant activity of Leu-Ile with those of FK506. Leu-Ile was not inhibitory toward calcineurin cellular activity in cultured neuronal cells. Furthermore, Leu-Ile did not suppress concanavalin A (ConA)-induced synthesis/secretion of interleukin-2 by cultured spleen cells, suggesting that the immunosuppressant activity of Leu-Ile may be negligible when used as a therapeutic tool for neurodegenerative diseases.

A potentially critical role of phospholipases in central nervous system ischemic, traumatic, and neurodegenerative disorders

Phospholipases are a diverse group of enzymes whose activation may be responsible for the development of injury following insult to the brain. Amongst the numerous isoforms of phospholipase proteins expressed in mammals are 19 different phospholipase A2's (PLA2s), classified functionally as either secretory, calcium dependent, or calcium independent, 11 isozymes belonging to three structural groups of PLC, and 3 PLD gene products. Many of these phospholipases have been identified in selected brain regions. Under normal conditions, these enzymes regulate the turnover of free fatty acids (FFAs) in membrane phospholipids affecting membrane stability, fluidity, and transport processes. The measurement of free fatty acids thus provides a convenient method to follow phospholipase activity and their regulation. Phospholipase activity is also responsible for the generation of an extensive list of intracellular messengers including arachidonic acid metabolites. Phospholipases are regulated by many factors including selective phosphorylation, intracellular calcium and pH. However, under abnormal conditions, excessive phospholipase activation, along with a decreased ability to resynthesize membrane phospholipids, can lead to the generation of free radicals, excitotoxicity, mitochondrial dysfunction, and apoptosis/necrosis. This review evaluates the critical contribution of the various phospholipases to brain injury following ischemia and trauma and in neurodegenerative diseases.