Attenuation of neonatal ischemic brain damage using a 20-HETE synthesis inhibitor

Neuroprotection provided by hypothermia initiated with high transnasal flow with ambient air in a model of pediatric cardiac arrest

Clinical trials of hypothermia after pediatric cardiac arrest (CA) have not seen robust improvement in functional outcome, possibly because of the long delay in achieving target temperature. Previous work in infant piglets showed that high nasal airflow, which induces evaporative cooling in the nasal mucosa, reduced regional brain temperature uniformly in half the time needed to reduce body temperature. Here, we evaluated whether initiation of hypothermia with high transnasal airflow provides neuroprotection without adverse effects in the setting of asphyxic CA. Anesthetized piglets underwent sham-operated procedures (n = 7) or asphyxic CA with normothermic recovery (38.5°C; n = 9) or hypothermia initiated by surface cooling at 10 (n = 8) or 120 (n = 7) min or transnasal cooling initiated at 10 (n = 7) or 120 (n = 7) min after resuscitation. Hypothermia was sustained at 34°C with surface cooling until 20 h followed by 6 h of rewarming. At 4 days of recovery, significant neuronal loss occurred in putamen and sensorimotor cortex. Transnasal cooling initiated at 10 min significantly rescued the number of viable neurons in putamen, whereas levels in putamen in other hypothermic groups remained less than sham levels. In sensorimotor cortex, neuronal viability in the four hypothermic groups was not significantly different from the sham group. These results demonstrate that early initiation of high transnasal airflow in a pediatric CA model is effective in protecting vulnerable brain regions. Because of its simplicity, portability, and low cost, transnasal cooling potentially could be deployed in the field or emergency room for early initiation of brain cooling after pediatric CA.NEW & NOTEWORTHY The onset of therapeutic hypothermia after cardiac resuscitation is often delayed, leading to incomplete neuroprotection. In an infant swine model of asphyxic cardiac arrest, initiation of high transnasal airflow to maximize nasal evaporative cooling produced hypothermia sufficient to provide neuroprotection that was not inferior to body surface cooling. Because of its simplicity and portability, this technique may be of use in the field or emergency room for rapid brain cooling in pediatric cardiac arrest victims.

Calpain as a Therapeutic Target for Hypoxic-Ischemic Encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is a complex pathophysiological process with multiple links and factors. It involves the interaction of inflammation, oxidative stress, and glucose metabolism, and results in acute and even long-term brain damage and impairment of brain function. Calpain is a family of Ca2+-dependent cysteine proteases that regulate cellular function. Calpain activation is involved in cerebral ischemic injury, and this involvement is achieved by the interaction among Ca2+, substrates, organelles, and multiple proteases in the neuronal necrosis and apoptosis pathways after cerebral ischemia. Many calpain inhibitors have been developed and tested in the biochemical and biomedical fields. This study reviewed the potential role of calpain in the treatment of HIE and related mechanism, providing new insights for future research on HIE.

Identification of Metabolomic Signatures for Ischemic Hypoxic Encephalopathy Using a Neonatal Rat Model

A study was performed to determine early metabolomic markers of ischemic hypoxic encephalopathy (HIE) using a Rice-Vannucci model for newborn rats. Dried blood spots from 7-day-old male and female rat pups, including 10 HIE-affected animals and 16 control animals, were analyzed by liquid chromatography coupled with mass spectrometry (HPLC-MS) in positive and negative ion recording modes. Multivariate statistical analysis revealed two distinct clusters of metabolites in both HPLC-MS modes. Subsequent univariate statistical analysis identified 120 positive and 54 negative molecular ions that exhibited statistically significant change in concentration, with more than a 1.5-fold difference after HIE. In the HIE group, the concentrations of steroid hormones, saturated mono- and triglycerides, and phosphatidylcholines (PCs) were significantly decreased in positive mode. On the contrary, the concentration of unsaturated PCs was increased in the HIE group. Among negatively charged molecular ions, the greatest variations were found in the categories of phosphatidylcholines, phosphatidylinositols, and triglycerides. The major metabolic pathways associated with changed metabolites were analyzed for both modes. Metabolic pathways such as steroid biosynthesis and metabolism fatty acids were most affected. These results underscored the central role of glycerophospholipid metabolism in triggering systemic responses in HIE. Therefore, lipid biomarkers' evaluation by targeted HPLC-MS research could be a promising approach for the early diagnosis of HIE.

Candidate neuroinflammatory markers of cerebral autoregulation dysfunction in human acute brain injury

The loss of cerebral autoregulation (CA) is a common and detrimental secondary injury mechanism following acute brain injury and has been associated with worse morbidity and mortality. However patient outcomes have not as yet been conclusively proven to have improved as a result of CA-directed therapy. While CA monitoring has been used to modify CPP targets, this approach cannot work if the impairment of CA is not simply related to CPP but involves other underlying mechanisms and triggers, which at present are largely unknown. Neuroinflammation, particularly inflammation affecting the cerebral vasculature, is an important cascade that occurs following acute injury. We hypothesise that disturbances to the cerebral vasculature can affect the regulation of CBF, and hence the vascular inflammatory pathways could be a putative mechanism that causes CA dysfunction. This review provides a brief overview of CA, and its impairment following brain injury. We discuss candidate vascular and endothelial markers and what is known about their link to disturbance of the CBF and autoregulation. We focus on human traumatic brain injury (TBI) and subarachnoid haemorrhage (SAH), with supporting evidence from animal work and applicability to wider neurologic diseases.

Reactive oxygen species-responsive HET0016 prodrug-loaded liposomes attenuate neuroinflammation and improve neurological deficit in a rat model of juvenile traumatic brain injury

The arachidonic acid pathway metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) contributes to ischemia/reperfusion brain injury. Inhibition of 20-HETE formation can protect the developing brain from global ischemia. In previous studies, we have found that treatment with the 20-HETE synthesis inhibitor N-hydroxy-N-4-butyl-2-methylphenylformamidine (HET0016) can protect the immature brain from traumatic brain injury (TBI), but its hydrophobic nature limits its full potential. We designed a reactive oxygen species-responsive HET0016 prodrug, which consists of a thioketal link between HET0016 and stearyl alcohol (HET-TK-SA), and used the nanoprodrug strategy to successfully synthesize liposomes HET0016 prodrug liposomes (HPLs) to facilitate the application of HET0016 in protection from TBI. HPLs demonstrated spherical shape, size of about 127.8 nm, a zeta potential of -28.8 mv, a narrow particle size distribution and good stability. Male rats at postnatal day 16-17 underwent controlled cortical impact (CCI) followed by intravenous injection with vehicle or HET0016 (1 mg/kg, 2 h post-injury, once/day for 3 days). The results of the in vivo demonstrated that HPLs has good biosafety and can pass through the blood-brain barrier. Not only that compared with HET0016, HPLs better-inhibited inflammation and improved neuronal degeneration, which further led to lesion volume reduction, upgraded behavioral task performance, and ameliorated the degree of TBI impairment. Our results demonstrated HPLs could be a new strategy for juvenile TBI therapy.

20-HETE Participates in Intracerebral Hemorrhage-Induced Acute Injury by Promoting Cell Ferroptosis

Intracerebral hemorrhage (ICH) is a highly fatal type of stroke that leads to various types of neuronal death. Recently, ferroptosis, a form of cell death resulting from iron-dependent lipid peroxide accumulation, was observed in a mouse ICH model. N-hydroxy-N'-(4-n-butyl-2-methylphenyl)-formamidine (HET0016), which inhibits synthesis of the arachidonic acid metabolite 20-hydroxyeicosatetraenoic acid (20-HETE), has shown a protective effect after ICH. However, the underlying mechanisms of the neuroprotective effect need further investigation. We explored whether 20-HETE participates in ICH-induced ferroptosis ex vivo by using hemoglobin-treated organotypic hippocampal slice cultures (OHSCs) and in vivo by using a collagenase-induced ICH mouse model. Ex vivo, we found that the 20-HETE synthesis inhibitor HET0016 and antagonist 20-6,15-HEDGE reduced hemoglobin-induced cell death, iron deposition, and lipid reactive oxygen species levels in OHSCs. Furthermore, 20-HETE inhibition in OHSCs increased the expression of glutathione peroxidase (GPX) 4, an antioxidant enzyme that serves as a main regulator of ferroptosis. In contrast, exposure of OHSCs to the 20-HETE stable mimetic 20-5,14-HEDGE induced cell death that was significantly inhibited by the ferroptosis inhibitor ferrostatin-1. In vivo, HET0016 treatment ameliorated focal deficits, reduced lesion volume, and decreased iron accumulation around the lesion at day 3 and 7 after ICH. In addition, lipid peroxidation was decreased and expression of GPX4 was increased in the HET0016-treated ICH group. The mitogen-activated protein kinase pathway also was inhibited by HET0016 in vivo. These results indicate that 20-HETE contributes to ICH-induced acute brain injury in part by activating ferroptosis pathways, thereby providing an upstream target for inhibiting ferroptosis.

Long-term cold storage preservation does not affect fatty livers from rats fed with a methionine and choline deficient diet

BACKGROUND

Waiting lists that continue to grow and the lack of organs available for transplantation necessitate the use of marginal livers, such as fatty livers. Since steatotic livers are more susceptible to damage from ischemia and reperfusion, it was investigated whether fatty livers with different lipidomic profiles show a different outcome when subjected to long-term cold storage preservation.

METHODS

Eight-week-old male Wistar rats fed for 2 weeks by a methionine-choline-deficient (MCD) diet or control diet were employed in this study. Livers were preserved in a University of Wisconsin (UW) solution at 4 °C for 6, 12 or 24 h and, after washout, reperfused for 2 h with a Krebs-Henseleit buffer at 37 °C. Hepatic enzyme release, bile production, O2-uptake, and portal venous pressure (PVP) were evaluated. The liver fatty acid profile was evaluated by a gas chromatography-mass spectrometry (GC/MS).

RESULTS

MCD rats showed higher LDH and AST levels with respect to the control group. When comparing MCD livers preserved for 6, 12 or 24 h, no differences in enzyme release were found during both the washout or the reperfusion period. The same trend occurred for O2-uptake, PVP, and bile flow. A general decrease in SFA and MUFA, except for oleic acid, and a decrease in PUFA, except for arachidonic, eicosadienoic, and docosahexanaeoic acids, were found in MCD rats when compared with control rats. Moreover, the ratio between SFA and the various types of unsaturated fatty acids (UFA) was significantly lower in MCD rats.

CONCLUSIONS

Although prolonged cold ischemia negatively affects the graft outcome, our data suggest that the quality of lipid constituents could influence liver injury during cold storage: the lack of an increased hepatic injury in MCD may be justified by low SFA, which likely reduces the deleterious tendency toward lipid crystallization occurring under cold ischemia.

20-HETE synthesis inhibition attenuates traumatic brain injury-induced mitochondrial dysfunction and neuronal apoptosis via the SIRT1/PGC-1α pathway: A translational study

Objectives

20‐hydroxyeicosatetraenoic acid (20‐HETE) is a metabolite of arachidonic acid catalysed by cytochrome P450 enzymes and plays an important role in cell death and proliferation. We hypothesized that 20‐HETE synthesis inhibition may have protective effects in traumatic brain injury (TBI) and investigated possible underlying molecular mechanisms.

Materials and methods

Neurologic deficits, and lesion volume, reactive oxygen species (ROS) levels and cell death as assessed using immunofluorescence staining, transmission electron microscopy and Western blotting were used to determine post‐TBI effects of HET0016, an inhibitor of 20‐HETE synthesis, and their underlying mechanisms.

Results

The level of 20‐HETE was found to be increased significantly after TBI in mice. 20‐HETE synthesis inhibition reduced neuronal apoptosis, ROS production and damage to mitochondrial structures after TBI. Mechanistically, HET0016 decreased the Drp1 level and increased the expression of Mfn1 and Mfn2 after TBI, indicating a reversal of the abnormal post‐TBI mitochondrial dynamics. HET0016 also promoted the restoration of SIRT1 and PGC‐1α in vivo, and a SIRT1 activator (SRT1720) reversed the downregulation of SIRT1 and PGC‐1α and the abnormal mitochondrial dynamics induced by 20‐HETE in vitro. Furthermore, plasma 20‐HETE levels were found to be higher in TBI patients with unfavourable neurological outcomes and were correlated with the GOS score.

Conclusions

The inhibition of 20‐HETE synthesis represents a novel strategy to mitigate TBI‐induced mitochondrial dysfunction and neuronal apoptosis by regulating the SIRT1/PGC‐1α pathway.

Sulforaphane Protects Piglet Brains from Neonatal Hypoxic-Ischemic Injury

The striatal, primary sensorimotor cortical, and thalamic neurons are highly vulnerable to hypoxia-ischemia (HI) in term newborns. In a piglet model of HI that exhibits similar selective regional vulnerability, we tested the hypothesis that early treatment with sulforaphane, an activator of the Nrf2 transcription factor, protects vulnerable neurons from HI injury. Anesthetized piglets (aged 3-7 days) were subjected to 45 min of hypoxia and 7 min of airway occlusion. At 15 min after resuscitation, the piglets received intravenous vehicle or sulforaphane. At 4 days of recovery, the density of viable neurons in the putamen of vehicle-treated piglets was 31 ± 34% (±SD) that of sham-operated controls. Treatment with sulforaphane significantly increased viability to 77 ± 31%. In the sensorimotor cortex, neuronal viability was also increased; it was 59 ± 35% in the vehicle-treated and 89 ± 15% in the sulforaphane-treated animals. Treatment with sulforaphane increased the nuclear Nrf2 and γ-glu-tamylcysteine synthetase expression at 6 h of recovery in these regions. We conclude that systemic administration of sulforaphane 15 min after HI can induce the translocation of Nrf2 to the nucleus, increase expression of an enzyme involved in glutathione synthesis, and salvage neurons in the highly vulnerable putamen and sensorimotor cortex in a large-animal model of HI. Therefore, targeting Nrf2 activation soon after recovery from HI is a feasible approach for neuroprotection in the newborn brain.

Potential Drug Candidates to Treat TRPC6 Channel Deficiencies in the Pathophysiology of Alzheimer's Disease and Brain Ischemia

Alzheimer’s disease and cerebral ischemia are among the many causative neurodegenerative diseases that lead to disabilities in the middle-aged and elderly population. There are no effective disease-preventing therapies for these pathologies. Recent in vitro and in vivo studies have revealed the TRPC6 channel to be a promising molecular target for the development of neuroprotective agents. TRPC6 channel is a non-selective cation plasma membrane channel that is permeable to Ca²⁺. Its Ca²⁺-dependent pharmacological effect is associated with the stabilization and protection of excitatory synapses. Downregulation as well as upregulation of TRPC6 channel functions have been observed in Alzheimer’s disease and brain ischemia models. Thus, in order to protect neurons from Alzheimer’s disease and cerebral ischemia, proper TRPC6 channels modulators have to be used. TRPC6 channels modulators are an emerging research field. New chemical structures modulating the activity of TRPC6 channels are being currently discovered. The recent publication of the cryo-EM structure of TRPC6 channels should speed up the discovery process even more. This review summarizes the currently available information about potential drug candidates that may be used as basic structures to develop selective, highly potent TRPC6 channel modulators to treat neurodegenerative disorders, such as Alzheimer’s disease and cerebral ischemia.

Administration of a 20-Hydroxyeicosatetraenoic Acid Synthesis Inhibitor Improves Outcome in a Rat Model of Pediatric Traumatic Brain Injury

The arachidonic acid pathway metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) contributes to ischemia/reperfusion brain injury. Inhibition of 20-HETE formation can protect the developing brain from global ischemia. Here, we examined whether treatment with the 20-HETE synthesis inhibitor N-hydroxy-N-4-butyl-2-methylphenylformamidine (HET0016) can protect the immature brain from traumatic brain injury (TBI). Male rats at postnatal day 9-10 underwent controlled cortical impact followed by intraperitoneal injection with vehicle or HET0016 (1 mg/kg, 5 min and 3 h post-injury). HET0016 decreased the lesion volume by over 50% at 3 days of recovery, and this effect persisted at 30 days as the brain matured. HET0016 decreased peri-lesion gene expression of proinflammatory cytokines (tumor necrosis factor-α [TNF-α], interleukin-1β [IL-1β]) at 1 day and increased reparative cytokine (IL-4, IL-10) expression at 3 days. It also partially preserved microglial ramified processes, consistent with less activation. HET0016 decreased contralateral hindlimb foot faults and improved outcome on the novel object recognition memory task 30 days after TBI. In cultured BV2 microglia, HET0016 attenuated the lipopolysaccharide-evoked increase in release of TNF-α. Our data show that HET0016 improves acute and long-term histologic and functional outcomes, in association with an attenuated neuroinflammatory response after contusion of an immature rat brain.

The Role of Mitochondrial and Endoplasmic Reticulum Reactive Oxygen Species Production in Models of Perinatal Brain Injury

Significance: Perinatal brain injury is caused by hypoxia-ischemia (HI) in term neonates, perinatal arterial stroke, and infection/inflammation leading to devastating long-term neurodevelopmental deficits. Therapeutic hypothermia is the only currently available treatment but is not successful in more than 50% of term neonates suffering from hypoxic-ischemic encephalopathy. Thus, there is an urgent unmet need for alternative or adjunct therapies. Reactive oxygen species (ROS) are important for physiological signaling, however, their overproduction/accumulation from mitochondria and endoplasmic reticulum (ER) during HI aggravate cell death. Recent Advances and Critical Issues: Mechanisms underlying ER stress-associated ROS production have been primarily elucidated using either non-neuronal cells or adult neurodegenerative experimental models. Findings from mature brain cannot be simply transferred to the immature brain. Therefore, age-specific studies investigating ER stress modulators may help investigate ER stress-associated ROS pathways in the immature brain. New therapeutics such as mitochondrial site-specific ROS inhibitors that selectively inhibit superoxide (O2•-)/hydrogen peroxide (H2O2) production are currently being developed. Future Directions: Because ER stress and oxidative stress accentuate each other, a combinatorial therapy utilizing both antioxidants and ER stress inhibitors may prove to be more protective against perinatal brain injury. Moreover, multiple relevant targets need to be identified for targeting ROS before they are formed. The role of organelle-specific ROS in brain repair needs investigation. Antioxid. Redox Signal. 31, 643-663.

20-HETE synthesis inhibition promotes cerebral protection after intracerebral hemorrhage without inhibiting angiogenesis

20-HETE, an arachidonic acid metabolite synthesized by cytochrome P450 4A, plays an important role in acute brain damage from ischemic stroke or subarachnoid hemorrhage. We tested the hypothesis that 20-HETE inhibition has a protective effect after intracerebral hemorrhage (ICH) and then investigated its effect on angiogenesis. We exposed hippocampal slice cultures to hemoglobin and induced ICH in mouse brains by intrastriatal collagenase injection to investigate the protective effect of 20-HETE synthesis inhibitor N-hydroxy-N'-(4-n-butyl-2-methylphenyl)-formamidine (HET0016). Hemoglobin-induced neuronal death was assessed by propidium iodide after 18 h in vitro. Lesion volume, neurologic deficits, cell death, reactive oxygen species (ROS), neuroinflammation, and angiogenesis were evaluated at different time points after ICH. In cultured mouse hippocampal slices, HET0016 attenuated hemoglobin-induced neuronal death and decreased levels of proinflammatory cytokines and ROS. In vivo, HET0016 reduced brain lesion volume and neurologic deficits, and decreased neuronal death, ROS production, gelatinolytic activity, and the inflammatory response at three days after ICH. However, HET0016 did not inhibit angiogenesis, as levels of CD31, VEGF, and VEGFR2 were unchanged on day 28. We conclude that 20-HETE is involved in ICH-induced brain damage. Inhibition of 20-HETE synthesis may provide a viable means to mitigate ICH injury without inhibition of angiogenesis.

Perinatal hypoxic-ischemic brain injury in large animal models: Relevance to human neonatal encephalopathy

Perinatal hypoxia-ischemia resulting in death or lifelong disabilities remains a major clinical disorder. Neonatal models of hypoxia-ischemia in rodents have enhanced our understanding of cellular mechanisms of neural injury in developing brain, but have limitations in simulating the range, accuracy, and physiology of clinical hypoxia-ischemia and the relevant systems neuropathology that contribute to the human brain injury pattern. Large animal models of perinatal hypoxia-ischemia, such as partial or complete asphyxia at the time of delivery of fetal monkeys, umbilical cord occlusion and cerebral hypoperfusion at different stages of gestation in fetal sheep, and severe hypoxia and hypoperfusion in newborn piglets, have largely overcome these limitations. In monkey, complete asphyxia produces preferential injury to cerebellum and primary sensory nuclei in brainstem and thalamus, whereas partial asphyxia produces preferential injury to somatosensory and motor cortex, basal ganglia, and thalamus. Mid-gestational fetal sheep provide a valuable model for studying vulnerability of progenitor oligodendrocytes. Hypoxia followed by asphyxia in newborn piglets replicates the systems injury seen in term newborns. Efficacy of post-insult hypothermia in animal models led to the success of clinical trials in term human neonates. Large animal models are now being used to explore adjunct therapy to augment hypothermic neuroprotection.

20-HETE Inhibition by HET0016 Decreases the Blood-Brain Barrier Permeability and Brain Edema After Traumatic Brain Injury

Recent studies have implicated 20-HETE as a vasoconstrictive mediator in trauma, the purpose of this study was to determine whether administration of HET0016, the 20-HETE inhibitor, could protect neurons from trauma and the effect of HET0016 on the blood–brain barrier (BBB) and brain edema in experimental traumatic brain injury (TBI). Rat models with TBI were established. Brain edema was measured according to the wet and dry weight method at 3, 24, and 72 h after injury. The BBB permeability was quantified by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Superoxide production, the activity of superoxide dismutase (SOD) and total antioxidative capability (T-AOC) in traumatic brain tissues were also measured. Western blot analysis was used to analyze the expression of the occludin, ZO-1, Matrix metalloproteinase-9 (MMP-9), and c-Jun N-terminal protein kinase (JNK) pathways. At 24 and 72 h after administration of HET0016 following TBI, the BBB permeability and brain edema decreased. The decrease in superoxide production and the increase in the activity of SOD and T-AOC were measured in this study. Western blot analysis showed that the expression of MMP-9 and JNK pathways was suppressed, but the expression of ZO-1 and occludin was increased. These results suggest that the administration of HET0016 could protect the BBB function and decrease brain edema after experimental traumatic injury by suppressing the expression of MMP-9 and activating the expression of tight junction proteins via suppressing the JNK pathway and oxidative stress.

The contribution of TRPV1 channel to 20-HETE-Aggravated ischemic neuronal injury

20-Hydroxyeicosatetraenoic acid (20-HETE), a cytochrome P450 (CYP) 4A/4F-derived metabolite of arachidonic acid, directly contributes to ischemic neuronal injury. However, little is known about mediators of 20-HETE neurotoxicity after ischemia. Here, we focus on the role of transient receptor potential cation channel subfamily V member 1 (TRPV1) in 20-HETE-induced neurotoxicity. Our results showed that TRPV1 and CYP4A immunoreactivity were colocalized in neurons. TRPV1 inhibition attenuated 20-HETE mimetic 20-5,14-HEDGE-induced reactive oxygen species (ROS) production and neuronal injury in cultured neurons and protected ischemic neurons in vitro and in vivo. TRPV1 inhibition in combination with 20-HETE synthesis inhibitor HET0016 did not produce additional protective effects. Furthermore, TRPV1 genetic inhibition and NADPH oxidase inhibitor gp91ds-dat each attenuated ROS production to a similar extent. However, combined treatment did not achieve additional reduction. Therefore, we conclude that TRPV1 channels are involved in 20-HETE's ROS generation and neurotoxicity after ischemia.

P450 Eicosanoids and Reactive Oxygen Species Interplay in Brain Injury and Neuroprotection

Significance: Eicosanoids are endogenous lipid mediators that play important roles in brain function and disease. Acute brain injury such as that which occurs in stroke and traumatic brain injury increases the formation of eicosanoids, which, in turn, exacerbate or diminish injury. In chronic neurodegenerative diseases such as Alzheimer's disease and vascular dementia (VD), eicosanoid synthetic and metabolizing enzymes are altered, disrupting the balance between neuroprotective and neurotoxic eicosanoids. Recent Advances: Human and experimental studies have established the opposing roles of hydroxy- and epoxyeicosanoids and their potential utility as diagnostic biomarkers and therapeutic targets in neural injury. Critical Issues: A gap in knowledge remains in understanding the cellular and molecular mechanisms underlying the neurovascular actions of specific eicosanoids, such as specific isomers of epoxyeicosatrienoic (EETs) and hydroxyeicosatetraenoic acids (HETEs). Future Directions: EETs and HETEs exert their actions on brain cells by targeting multiple mechanisms, which include surface G-protein coupled receptors. The identification of high-affinity receptors for EETs and HETEs and their cellular localization in the brain will be a breakthrough in our understanding of these eicosanoids as mediators of cell-cell communications and contributors to brain development, function, and disease. Antioxid. Redox Signal. 28, 987-1007.

Liver Graft Susceptibility during Static Cold Storage and Dynamic Machine Perfusion: DCD versus Fatty Livers

We compared static preservation (cold storage, CS, 4 °C) with dynamic preservation (machine perfusion, MP, 20 °C) followed by reperfusion using marginal livers: a model of donation after cardiac death (DCD) livers and two models of fatty livers, the methionine-choline deficient (MCD) diet model, and obese Zucker (fa/fa) rats. CS injury in DCD livers was reversed by an oxygenated washout (OW): hepatic damage, bile flow, and the ATP/ADP ratio in the OW + CS group was comparable with the ratio obtained with MP. Using fatty livers, CS preservation induced a marked release in hepatic and biliary enzymes in obese Zucker rats when compared with the MCD group. The same trend occurred for bile flow. No difference was found when comparing MP in MCD and obese Zucker rats. Fatty acid analysis demonstrated that the total saturated (SFA)/polyunsaturated fatty acid (PUFA) ratio was, respectively, 1.5 and 0.71 in obese Zucker and MCD rats. While preservation damage in DCD livers is associated with the ATP/ADP recovered with OW, injury in fatty livers is linked to fatty acid constituents: livers from obese. Zucker rats, with greater content in saturated FA, might be more prone to CS injury. On the contrary, MCD livers with elevated PUFA content might be less susceptible to hypothermia.

Cytochrome P450 eicosanoids in cerebrovascular function and disease

Cytochrome P450 eicosanoids play important roles in brain function and disease through their complementary actions on cell-cell communications within the neurovascular unit (NVU) and mechanisms of brain injury. Epoxy- and hydroxyeicosanoids, respectively formed by cytochrome P450 epoxygenases and ω-hydroxylases, play opposing roles in cerebrovascular function and in pathological processes underlying neural injury, including ischemia, neuroinflammation and oxidative injury. P450 eicosanoids also contribute to cerebrovascular disease risk factors, including hypertension and diabetes. We summarize studies investigating the roles P450 eicosanoids in cerebrovascular physiology and disease to highlight the existing balance between these important lipid signaling molecules, as well as their roles in maintaining neurovascular homeostasis and in acute and chronic neurovascular and neurodegenerative disorders.

Effects of Panax notoginseng ginsenoside Rb1 on abnormal hippocampal microenvironment in rats

Cerebral ischemia damages central neurons, and abnormal microenvironment in ischemic condition is the key factor to the damages. The increase of local concentration of glutamic acid, the overload of Ca²⁺, and the mitochondrial stress caused by release of cytochrome C are important factors of abnormal microenvironment in cerebral ischemia. In this study ginsenoside Rb1, a compound from Panax Notoginseng, was used to intervene abnormal environment of neurons in the hippocampal CA1 region in two animal models (microperfusion model and photothrombosis model).

RESULTS

Compared with the vehicle in the sham group, ginsenoside had following effects. a) ginsenoside Rb1 increased the regional cerebral blood flow (rCBF) and the stability of neuronal ultrastructure in in the hippocampal CA1 region and improved the adaptability of neurons in two models. b) ginsenoside Rb1 improved the expression level of glial glutamate transporter1 (GLT-1) and reversed the uptake of glutamate (Glu) after ischemia, and as a result thereby decreased the excitability of Glu and the expression level of GLT-1 was proportional to the dose of ginsenoside Rb1 and similar to that of Nimodipine. c) ginsenoside Rb1 inhibited the expression level of NMDAR and the overload of Ca²⁺, thereby reducing neuronal damages. Meanwhile, the expression level of NMDAR was inversely proportional to the dose of ginsenoside Rb1, which was similar to that of Nimodipine. d) ginsenoside Rb1 decreased the release of cytochrome C (Cyt-C) and reduced the damages caused by neuronal mitochondrial stress. Meanwhile, the release of Cyt-C was inversely proportional to the dose of ginsenoside Rb1, which was similar to that of Nimodipine. Ginsenoside Rb1 may be as an effective drug for neuroprotection and improve cerebral blood flow after acute ischemia and prevent the secondary brain damage induced by stroke.

Clinical Implications of 20-Hydroxyeicosatetraenoic Acid in the Kidney, Liver, Lung and Brain: An Emerging Therapeutic Target

Cytochrome P450-mediated metabolism of arachidonic acid (AA) is an important pathway for the formation of eicosanoids. The ω-hydroxylation of AA generates significant levels of 20-hydroxyeicosatetraenoic acid (20-HETE) in various tissues. In the current review, we discussed the role of 20-HETE in the kidney, liver, lung, and brain during physiological and pathophysiological states. Moreover, we discussed the role of 20-HETE in tumor formation, metabolic syndrome and diabetes. In the kidney, 20-HETE is involved in modulation of preglomerular vascular tone and tubular ion transport. Furthermore, 20-HETE is involved in renal ischemia/reperfusion (I/R) injury and polycystic kidney diseases. The role of 20-HETE in the liver is not clearly understood although it represents 50%-75% of liver CYP-dependent AA metabolism, and it is associated with liver cirrhotic ascites. In the respiratory system, 20-HETE plays a role in pulmonary cell survival, pulmonary vascular tone and tone of the airways. As for the brain, 20-HETE is involved in cerebral I/R injury. Moreover, 20-HETE has angiogenic and mitogenic properties and thus helps in tumor promotion. Several inhibitors and inducers of the synthesis of 20-HETE as well as 20-HETE analogues and antagonists are recently available and could be promising therapeutic options for the treatment of many disease states in the future.

Upregulation of 20-HETE Synthetic Cytochrome P450 Isoforms by Oxygen-Glucose Deprivation in Cortical Neurons

20-Hydroxyeicosatetraenoic acid (20-HETE), a potent vasoconstrictor, is a cytochrome P450 (CYP) 4A/4F-derived metabolite of arachidonic acid. Inhibition of 20-HETE synthesis protects brain from ischemic injury. However, that protection is not associated with changes in cerebral blood flow. The present study examined whether CYP4A isoforms are expressed in neurons, whether they produce 20-HETE in neurons, and whether neuronally derived 20-HETE exerts direct neurotoxicity after oxygen-glucose deprivation (OGD). The expression of Cyp4a10 and Cyp4a12a mRNA in cultured mouse cortical neurons increased significantly at 1 and 3 h after exposure to 1 h of OGD. Reoxygenation also markedly augmented the expression of CYP4A protein in neurons and increased 20-HETE levels in the culture medium. Cell viability after OGD increased after treatment with a 20-HETE synthesis inhibitor or an antagonist. That effect was reversed by co-administration of a 20-HETE agonist. These results indicate that neurons express Cyp4a10 and 4a12a, that expression of these isoforms is upregulated by OGD stress, and that neuronally derived 20-HETE directly contributes to neuronal death after reoxygenation.

Ischemia/Reperfusion

Ischemic disorders, such as myocardial infarction, stroke, and peripheral vascular disease, are the most common causes of debilitating disease and death in westernized cultures. The extent of tissue injury relates directly to the extent of blood flow reduction and to the length of the ischemic period, which influence the levels to which cellular ATP and intracellular pH are reduced. By impairing ATPase-dependent ion transport, ischemia causes intracellular and mitochondrial calcium levels to increase (calcium overload). Cell volume regulatory mechanisms are also disrupted by the lack of ATP, which can induce lysis of organelle and plasma membranes. Reperfusion, although required to salvage oxygen-starved tissues, produces paradoxical tissue responses that fuel the production of reactive oxygen species (oxygen paradox), sequestration of proinflammatory immunocytes in ischemic tissues, endoplasmic reticulum stress, and development of postischemic capillary no-reflow, which amplify tissue injury. These pathologic events culminate in opening of mitochondrial permeability transition pores as a common end-effector of ischemia/reperfusion (I/R)-induced cell lysis and death. Emerging concepts include the influence of the intestinal microbiome, fetal programming, epigenetic changes, and microparticles in the pathogenesis of I/R. The overall goal of this review is to describe these and other mechanisms that contribute to I/R injury. Because so many different deleterious events participate in I/R, it is clear that therapeutic approaches will be effective only when multiple pathologic processes are targeted. In addition, the translational significance of I/R research will be enhanced by much wider use of animal models that incorporate the complicating effects of risk factors for cardiovascular disease. © 2017 American Physiological Society. Compr Physiol 7:113-170, 2017.

Fatty Acid Regulation of Voltage- and Ligand-Gated Ion Channel Function

Free fatty acids (FFA) are essential components of the cell, where they play a key role in lipid and carbohydrate metabolism, and most particularly in cell membranes, where they are central actors in shaping the physicochemical properties of the lipid bilayer and the cellular adaptation to the environment. FFA are continuously being produced and degraded, and a feedback regulatory function has been attributed to their turnover. The massive increase observed under some pathological conditions, especially in brain, has been interpreted as a protective mechanism possibly operative on ion channels, which in some cases is of stimulatory nature and in other cases inhibitory. Here we discuss the correlation between the structure of FFA and their ability to modulate protein function, evaluating the influence of saturation/unsaturation, number of double bonds, and cis vs. trans isomerism. We further focus on the mechanisms of FFA modulation operating on voltage-gated and ligand-gated ion channel function, contrasting the still conflicting evidence on direct vs. indirect mechanisms of action.

Expression of CYP 4A ω-hydroxylase and formation of 20-hydroxyeicosatetreanoic acid (20-HETE) in cultured rat brain astrocytes

Astrocytes secrete vasodilator and vasoconstrictor factors via end feet processes, altering blood flow to meet neuronal metabolic demand. Compared to what is known about the ability of astrocytes to release factors that dilate local cerebral vasculature, very little is known regarding the source and identity of astrocyte derived constricting factors. The present study investigated if astrocytes express CYP 4A ω-hydroxylase and metabolize arachidonic acid (AA) to 20-hydroxyeicotetraenoic acid (20-HETE) that regulates KCa channel activity in astrocytes and cerebral arterial myocyte contractility. Here we report that cultured astrocytes express CYP 4A2/3 ω-hydroxylase mRNA and CYP 4A protein and produce 20-HETE and the CYP epoxygenase metabolites epoxyeicosatrienoic acids (EETs) when incubated with AA. The production of 20-HETE and EETs was enhanced following stimulation of metabotropic glutamate receptors (mGluR) on the astrocytes. Exogenous application of 20-HETE attenuated, whereas inhibition of 20-HETE production with HET-0016 increased the open state probabilities (NPo) of 71pS and 161pS KCa single-channel currents recorded from astrocytes. Exposure of isolated cerebral arterial myocytes to conditioned media from cultured astrocytes caused shortening of the length of freshly isolated cerebral arterial myocytes that was not evident following inhibition of astrocyte 20-HETE synthesis and action. These findings suggest that astrocytes not only release vasodilator EETs in response to mGluR stimulation but also synthetize and release the cerebral arterial myocyte constrictor 20-HETE that also functions as an endogenous inhibitor of the activity of two types of KCa channel currents found in astrocytes.

Progesterone exerts neuroprotective effects and improves long-term neurologic outcome after intracerebral hemorrhage in middle-aged mice

In this study, we examined the effect of progesterone on histopathologic and functional outcomes of intracerebral hemorrhage (ICH) in 10- to 12-month-old mice. Progesterone or vehicle was administered by intraperitoneal injection 1 hour after collagenase-induced ICH and then by subcutaneous injections at 6, 24, and 48 hours. Oxidative and nitrosative stress were assayed at 12 hours post-ICH. Injury markers were examined on day 1, and lesion was examined on day 3. Neurologic deficits were examined for 28 days. Progesterone posttreatment reduced lesion volume, brain swelling, edema, and cell degeneration and improved long-term neurologic function. These protective effects were associated with reductions in protein carbonyl formation, protein nitrosylation, and matrix metalloproteinase-9 activity and attenuated cellular and molecular inflammatory responses. Progesterone also reduced vascular endothelial growth factor expression, increased neuronal-specific Na(+)/K(+) ATPase ɑ3 subunit expression, and reduced protein kinase C-dependent Na(+)/K(+) ATPase phosphorylation. Furthermore, progesterone reduced glial scar thickness, myelin loss, brain atrophy, and residual injury volume on day 28 after ICH. With multiple brain targets, progesterone warrants further investigation for its potential use in ICH therapy.

Cyclooxygenase- and cytochrome P450-derived eicosanoids in stroke

Arachidonic acid (AA) is metabolized by cyclooxygenase (COX) and cytochrome P450 (CYP) enzymes into eicosanoids, which are involved in cardiovascular diseases and stroke. Evidence has demonstrated the important functions of these eicosanoids in regulating cerebral vascular tone, cerebral blood flow, and autoregulation of cerebral circulation. Although COX-2 inhibitors have been suggested as potential treatments for stroke, adverse events, including an increased risk of stroke, occur following long-term use of coxibs. It is important to note that prolonged treatment with rofecoxib increased circulating levels of 20-hydroxyeicosatetraenoic acid (20-HETE), and 20-HETE blockade is a possible strategy to prevent coxib-induced stroke events. It appears that 20-HETE has detrimental effects in the brain, and that its blockade exerts cerebroprotection against ischemic stroke and subarachnoid hemorrhage (SAH). There is clear evidence that activation of EP2 and EP4 receptors exerts cerebroprotection against ischemic stroke. Several elegant studies have contributed to defining the importance of stabilizing the levels of epoxyeicosatrienoic acids (EETs), by inhibiting or deleting soluble epoxide hydrolase (sEH), in stroke research. These reports support the notion that sEH blockade is cerebroprotective against ischemic stroke and SAH. Here, we summarize recent findings implicating these eicosanoid pathways in cerebral vascular function and stroke. We also discuss the development of animal models with targeted gene deletion and specific enzymatic inhibitors in each pathway to identify potential targets for the treatment of ischemic stroke and SAH.

20-Hydroxyeicosatetraenoic Acid Inhibition by HET0016 Offers Neuroprotection, Decreases Edema, and Increases Cortical Cerebral Blood Flow in a Pediatric Asphyxial Cardiac Arrest Model in Rats

Vasoconstrictive and vasodilatory eicosanoids generated after cardiac arrest (CA) may contribute to cerebral vasomotor disturbances and neurodegeneration. We evaluated the balance of vasodilator/vasoconstrictor eicosanoids produced by cytochrome P450 (CYP) metabolism, and determined their role on cortical perfusion, functional outcome, and neurodegeneration after pediatric asphyxial CA. Cardiac arrest of 9 and 12 minutes was induced in 16- to 18-day-old rats. At 5 and 120 minutes after CA, we quantified the concentration of CYP eicosanoids in the cortex and subcortical areas. In separate rats, we inhibited 20-hydroxyeicosatetraenoic acid (20-HETE) synthesis after CA and assessed cortical cerebral blood flow (CBF), neurologic deficit score, neurodegeneration, and edema. After 9 minutes of CA, vasodilator eicosanoids markedly increased versus sham. Conversely, after 12 minutes of CA, vasoconstrictor eicosanoid 20-HETE increased versus sham, without compensatory increases in vasodilator eicosanoids. Inhibition of 20-HETE synthesis after 12 minutes of CA decreased cortical 20-HETE levels, increased CBF, reduced neurologic deficits at 3 hours, and reduced neurodegeneration and edema at 48 hours versus vehicle-treated rats. In conclusion, cerebral vasoconstrictor eicosanoids increased after a pediatric CA of 12 minutes. Inhibition of 20-HETE synthesis improved cortical perfusion and short-term neurologic outcome. These results suggest that alterations in CYP eicosanoids have a role in cerebral hypoperfusion and neurodegeneration after CA and may represent important therapeutic targets.

Additive Neuroprotection of a 20-HETE Inhibitor with Delayed Therapeutic Hypothermia after Hypoxia-Ischemia in Neonatal Piglets

The severity of perinatal hypoxia-ischemia and the delay in initiating therapeutic hypothermia limit the efficacy of hypothermia. After hypoxia-ischemia in neonatal piglets, the arachidonic acid metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) has been found to contribute to oxidative stress at 3 h of reoxygenation and to eventual neurodegeneration. We tested whether early administration of a 20-HETE synthesis inhibitor after reoxygenation augments neuroprotection with 3-hour delayed hypothermia. In two hypothermic groups, whole body cooling from 38.5 to 34°C was initiated 3 h after hypoxia-ischemia. Rewarming occurred from 20 to 24 h; then anesthesia was discontinued. One hypothermic group received a 20-HETE inhibitor at 5 min after reoxygenation. A sham-operated group and another hypoxia-ischemia group remained normothermic. At 10 days of recovery, resuscitated piglets with delayed hypothermia alone had significantly greater viable neuronal density in the putamen, caudate nucleus, sensorimotor cortex, CA3 hippocampus, and thalamus than did piglets with normothermic recovery, but the values remained less than those in the sham-operated group. In piglets administered the 20-HETE inhibitor before hypothermia, the density of viable neurons in the putamen, cortex and thalamus was significantly greater than in the group with hypothermia alone. Cytochrome P450 4A, which can synthesize 20-HETE, was expressed in piglet neurons in these regions. We conclude that early treatment with a 20-HETE inhibitor enhances the therapeutic benefit of delayed hypothermia in protecting neurons in brain regions known to be particularly vulnerable to hypoxia-ischemia in term newborns.

Combined therapy with COX-2 inhibitor and 20-HETE inhibitor reduces colon tumor growth and the adverse effects of ischemic stroke associated with COX-2 inhibition

20-Hydroxyeicosatetraenoic acid (20-HETE), Cyp4a-derived eicosanoid, is a lipid mediator that promotes tumor growth, as well as causing detrimental effects in cerebral circulation. We determined whether concurrent inhibition of cyclooxygenase-2 (COX-2) and 20-HETE affects colon tumor growth and ischemic stroke outcomes. The expression of Cyp4a and COXs and production of 20-HETE and PGE2 were determined in murine colon carcinoma (MC38) cells. We then examined the effects of combined treatment with rofecoxib, a potent COX-2 inhibitor, and HET0016, a potent Cyp4a inhibitor, on the growth and proliferation of MC38 cells. Subsequently, we tested the effects of HET0016 plus rofecoxib in MC38 tumor and ischemic stroke models. Cyp4a and COXs are highly expressed in MC38 cells. Respectively, HET0016 and rofecoxib inhibited 20-HETE and PGE2 formation in MC38 cells. Moreover, rofecoxib combined with HET0016 had greater inhibitory effects on the growth and proliferation of MC38 cells than did rofecoxib alone. Importantly, rofecoxib combined with HET0016 provided greater inhibition on tumor growth than did rofecoxib alone in MC38 tumor-bearing mice. Prolonged treatment with rofecoxib selectively induced circulating 20-HETE levels and caused cerebrovascular damage after ischemic stroke, whereas therapy with rofecoxib and HET0016 attenuated 20-HETE levels and reduced rofecoxib-induced cerebrovascular damage and stroke outcomes during anti-tumor therapy. Thus these results demonstrate that combination therapy with rofecoxib and HET0016 provides a new treatment of colon tumor, which can not only enhance the anti-tumor efficacy of rofecoxib, but also reduce rofecoxib-induced cerebrovascular damage and stroke outcomes.

Minocycline attenuates brain tissue levels of TNF-α produced by neurons after prolonged hypothermic cardiac arrest in rats

Neuro-cognitive disabilities are a well-recognized complication of hypothermic circulatory arrest. We and others have reported that prolonged cardiac arrest (CA) produces neuronal death and microglial proliferation and activation that are only partially mitigated by hypothermia. Microglia, and possibly other cells, are suggested to elaborate tumor necrosis factor alpha (TNF-α), which can trigger neuronal death cascades and exacerbate edema after CNS insults. Minocycline is neuroprotective in some brain ischemia models in part by blunting the microglial response. We tested the hypothesis that minocycline would attenuate neuroinflammation as reflected by brain tissue levels of TNF-α after hypothermic CA in rats. Rats were subjected to rapid exsanguination, followed by a 6 min normothermic CA. Hypothermia (30 °C) was then induced by an aortic saline flush. After a total of 20 min CA, resuscitation was achieved via cardiopulmonary bypass (CPB). After 5 min reperfusion, minocycline (90 mg kg−1; n = 6) or vehicle (PBS; n = 6) was given. Hypothermia (34 °C) was maintained for 6 h. Rats were sacrificed at 6 or 24 h. TNF-α was quantified (ELISA) in four brain regions (cerebellum, CEREB; cortex, CTX; hippocampus, HIP; striatum, STRI). Naïve rats (n = 6) and rats subjected to the same anesthesia and CPB but no CA served as controls (n = 6). Immunocytochemistry was used to localize TNF-α. Naïve rats and CPB controls had no detectable TNF-α in any brain region. CA markedly increased brain TNF-α. Regional differences were seen, with the highest TNF-α levels in striatum in CA groups (10-fold higher, P < 0.05 vs. all other brain regions). TNF-α was undetectable at 24 h. Minocycline attenuated TNF-α levels in CTX, HIP and STRI (P < 0.05). TNF-α showed unique co-localization with neurons. In conclusion, we report region-dependent early increases in brain TNF-α levels after prolonged hypothermic CA, with maximal increases in striatum. Surprisingly, TNF-α co-localized in neurons and not microglia. Minocycline attenuated TNF-α by approximately 50% but did not totally ablate its production. That minocycline decreased brain TNF-α levels suggests that it may represent a therapeutic adjunct to hypothermia in CA neuroprotection. University of Pittsburgh IACUC 0809278B-3.

Increase of 20-HETE synthase after brain ischemia in rats revealed by PET study with 11C-labeled 20-HETE synthase-specific inhibitor

20-Hydroxyeicosatetraenoic acid (20-HETE), an arachidonic acid metabolite known to be produced after cerebral ischemia, has been implicated in ischemic and reperfusion injury by mediating vasoconstriction. To develop a positron emission tomography (PET) probe for 20-HETE synthase imaging, which might be useful for monitoring vasoconstrictive processes in patients with brain ischemia, we synthesized a (11)C-labeled specific 20-HETE synthase inhibitor, N'(4-dimethylaminohexyloxy)phenyl imidazole ([(11)C]TROA). Autoradiographic study showed that [(11)C]TROA has high-specific binding in the kidney and liver consistent with the previously reported distribution of 20-HETE synthase. Using transient middle cerebral artery occlusion in rats, PET study showed significant increases in the binding of [(11)C]TROA in the ipsilateral hemisphere of rat brains after 7 and 10 days, which was blocked by co-injection of excess amounts of TROA (10 mg/kg). The increased [(11)C]TROA binding on the ipsilateral side returned to basal levels within 14 days. In addition, quantitative real-time PCR revealed that increased expression of 20-HETE synthase was only shown on the ipsilateral side on day 7. These results indicate that [(11)C]TROA might be a useful PET probe for imaging of 20-HETE synthase in patients with cerebral ischemia.

Cell biology of ischemia/reperfusion injury

Disorders characterized by ischemia/reperfusion (I/R), such as myocardial infarction, stroke, and peripheral vascular disease, continue to be among the most frequent causes of debilitating disease and death. Tissue injury and/or death occur as a result of the initial ischemic insult, which is determined primarily by the magnitude and duration of the interruption in the blood supply, and then subsequent damage induced by reperfusion. During prolonged ischemia, ATP levels and intracellular pH decrease as a result of anaerobic metabolism and lactate accumulation. As a consequence, ATPase-dependent ion transport mechanisms become dysfunctional, contributing to increased intracellular and mitochondrial calcium levels (calcium overload), cell swelling and rupture, and cell death by necrotic, necroptotic, apoptotic, and autophagic mechanisms. Although oxygen levels are restored upon reperfusion, a surge in the generation of reactive oxygen species occurs and proinflammatory neutrophils infiltrate ischemic tissues to exacerbate ischemic injury. The pathologic events induced by I/R orchestrate the opening of the mitochondrial permeability transition pore, which appears to represent a common end-effector of the pathologic events initiated by I/R. The aim of this treatise is to provide a comprehensive review of the mechanisms underlying the development of I/R injury, from which it should be apparent that a combination of molecular and cellular approaches targeting multiple pathologic processes to limit the extent of I/R injury must be adopted to enhance resistance to cell death and increase regenerative capacity in order to effect long-lasting repair of ischemic tissues.