Effects of the PDE5-inhibitor vardenafil in a mouse stroke model

The potential therapeutic effect of phosphodiesterase 5 inhibitors in the acute ischemic stroke (AIS)

Acute ischemic stroke (AIS) is a focal neurological disorder that accounts for 85% of all stroke types, due to occlusion of cerebral arteries by thrombosis and emboli. AIS is also developed due to cerebral hemodynamic abnormality. AIS is associated with the development of neuroinflammation which increases the severity of AIS. Phosphodiesterase enzyme (PDEs) inhibitors have neuro-restorative and neuroprotective effects against the development of AIS through modulation of the cerebral cyclic adenosine monophosphate (cAMP)/cyclic guanosine monophosphate (cGMP)/nitric oxide (NO) pathway. PDE5 inhibitors through mitigation of neuroinflammation may decrease the risk of long-term AIS-induced complications. PDE5 inhibitors may affect the hemodynamic properties and coagulation pathway which are associated with thrombotic complications in AIS. PDE5 inhibitors reduce activation of the pro-coagulant pathway and improve the microcirculatory level in patients with hemodynamic disturbances in AIS. PDE5 inhibitors mainly tadalafil and sildenafil improve clinical outcomes in AIS patients through the regulation of cerebral perfusion and cerebral blood flow (CBF). PDE5 inhibitors reduced thrombomodulin, P-selectin, and tissue plasminogen activator. Herein, PDE5 inhibitors may reduce activation of the pro-coagulant pathway and improve the microcirculatory level in patients with hemodynamic disturbances in AIS. In conclusion, PDE5 inhibitors may have potential roles in the management of AIS through modulation of CBF, cAMP/cGMP/NO pathway, neuroinflammation, and inflammatory signaling pathways. Preclinical and clinical studies are recommended in this regard.

miR-34b-3p Inhibition of eIF4E Causes Post-stroke Depression in Adult Mice

Post-stroke depression (PSD) is a serious and common complication of stroke, which seriously affects the rehabilitation of stroke patients. To date, the pathogenesis of PSD is unclear and effective treatments remain unavailable. Here, we established a mouse model of PSD through photothrombosis-induced focal ischemia. By using a combination of brain imaging, transcriptome sequencing, and bioinformatics analysis, we found that the hippocampus of PSD mice had a significantly lower metabolic level than other brain regions. RNA sequencing revealed a significant reduction of miR34b-3p, which was expressed in hippocampal neurons and inhibited the translation of eukaryotic translation initiation factor 4E (eIF4E). Furthermore, silencing eIF4E inactivated microglia, inhibited neuroinflammation, and abolished the depression-like behaviors in PSD mice. Together, our data demonstrated that insufficient miR34b-3p after stroke cannot inhibit eIF4E translation, which causes PSD by the activation of microglia in the hippocampus. Therefore, miR34b-3p and eIF4E may serve as potential therapeutic targets for the treatment of PSD.

XQ-1H promotes cerebral angiogenesis via activating PI3K/Akt/GSK3β/β-catenin/VEGF signal in mice exposed to cerebral ischemic injury

Stroke still ranks as a most lethal disease worldwide. Angiogenesis during the chronic phase of ischemic stroke can alleviate ischemic injury and attenuate neurological deficit. XQ-1H is a new compound derived from the structure modification of ginkgolide B, which exerts anti-inflammation and neuroprotection against cerebral ischemic injury during the acute or subacute phase. However, whether XQ-1H facilitates angiogenesis and neural functional recovery during the chronic phase remains unclear. This research was designed to explore whether XQ-1H promotes angiogenesis after ischemic stroke and to preliminarily elucidate the mechanism. In vitro, XQ-1H was found to facilitate proliferation, migration and tube formation in bEnd.3 cells. In vivo, XQ-1H raised the CD31 positive microvessel number and increased focal cerebral blood flow in mice exposed to cerebral ischemic injury, and improved the neurological function. Mechanism studies revealed that XQ-1H exerted angiogenesis promoting effect via the PI3K/Akt/GSK3β/β-catenin/VEGF signal pathway, which was reversed by LY294002 (the specific inhibitor of PI3K/Akt). In conclusion, XQ-1H exerts angiogenetic effect both in vivo and in vitro, which is a potential agent against ischemic stroke during chronic phase.

Deficits in motor and cognitive functions in an adult mouse model of hypoxia-ischemia induced stroke

Ischemic strokes cause devastating brain damage and functional deficits with few treatments available. Previous studies have shown that the ischemia-hypoxia rapidly induces clinically similar thrombosis and neuronal loss, but any resulting behavioral changes are largely unknown. The goal of this study was to evaluate motor and cognitive deficits in adult HI mice. Following a previously established procedure, HI mouse models were induced by first ligating the right common carotid artery and followed by hypoxia. Histological data showed significant long-term neuronal losses and reactive glial cells in the ipsilateral striatum and hippocampus of the HI mice. Whereas the open field test and the rotarod test could not reliably distinguish between the sham and HI mice, in the tapered beam and wire-hanging tests, the HI mice showed short-term and long-term deficits, as evidenced by the increased number of foot faults and decreased hanging time respectively. In cognitive tests, the HI mice swam longer distances and needed more time to find the platform in the Morris water maze test and showed shorter freezing time in fear contextual tests after fear training. In conclusion, this study demonstrates that adult HI mice have motor and cognitive deficits and could be useful models for preclinical stroke research.

Behavioral tests in rodent models of stroke

Rodents are the most widely used experimental animals in stroke research due to their similar vascular anatomy, high reproductive rates, and availability of transgenic models. However, the difficulties in assessing higher brain functions, such as cognition and memory, in rodents decrease the translational potential of these studies. In this review, we summarize commonly used motor/sensorimotor and cognition tests in rodent models of stroke. Specifically, we first briefly introduce the objective and procedure of each behavioral test. Next, we summarize the application of each test in both ischemic stroke and hemorrhagic stroke. Last, the advantages and disadvantages of these tests in assessing stroke outcome are discussed. This review summarizes commonly used behavioral tests in stroke studies and compares their applications in different stroke types.

Icariside II, a phosphodiesterase 5 inhibitor, attenuates cerebral ischaemia/reperfusion injury by inhibiting glycogen synthase kinase-3β-mediated activation of autophagy

Background and Purpose

Cerebral ischaemia/reperfusion causes exacerbated neuronal damage involving excessive autophagy and neuronal loss. The present study was designed to investigate the effect of icariside II, one of main active ingredients of Herba Epimedii on this loss and whether this is related to its PDE 5 inhibitory action.

Experimental Approach

Focal cerebral ischaemia was induced in the rat by transient middle cerebral artery occlusion over 2 hr, followed by reperfusion with icariside II, 3‐methylamphetamine or rapamycin. The effect of icariside II was determined measuring behaviour changes and the size of the infarction. The expressions of PDE 5, autophagy‐related proteins and the level of phosphorylation of glycogen synthase kinase‐3β (GSK‐3β) were determined. Cultured primary cortical neurons were subjected to oxygen and glucose deprivation followed by reoxygenation in the presence and absence of icariside II. A surface plasmon resonance assay and molecular docking were used to explore the interactions of icariside II with PDE 5 or GSK‐3β.

Key Results

Icariside II not only protected against induced ischaemic reperfusion injury in rats but also attenuated such injury in primary cortical neurons. The neuroprotective effects of icariside II on such injury were attributed to interfering with the PKG/GSK‐3β/autophagy axis by directly bounding to PDE 5 and GSK‐3β.

Conclusions and Implications

These findings indicate that icariside II attenuates cerebral I/R‐induced injury via interfering with PKG/GSK‐3β/autophagy axis. This study raises the possibility that icariside II and other PDE 5 inhibitors maybe effective in the treatment ischaemia stroke.

Behavioral tests that reveal long-term deficits after permanent focal cerebral ischemia in mouse

Efforts are still needed regarding the research of therapeutics for ischemic stroke. While in experimental studies the protective effect of pharmacological agents is often highlighted by a reduction of the lesion size evaluated in the short term (days), in clinical studies a functional recovery of patients suffering from stroke is expected on the long-term (months and years). Long-term functional preclinical studies are highly recommended to evaluate potential neuroprotective agents for stroke, rather than an assessment of the infarction size at a short time point. The present study thus aimed to select among various behavioral tests those able to highlight long-term deficits (3 months) after cerebral ischemia in mice. Permanent focal cerebral ischemia was carried out in male Swiss mice by intraluminal occlusion of the left middle cerebral artery (MCA). Fourteen behavioral tests were assessed from 7 days to 90 days after ischemia (locomotor activity, neurological score, exit circle test, grip and string tests, chimney test, adhesive removal test, pole test, beam-walking tests, elevated plus maze, marble burying test, forced swimming test, novel object recognition test). The present study clearly identified a battery of behavioral tests able to highlight deficits up to 3 months in our mouse model of permanent MCA occlusion (locomotor activity, neurological score, adhesive removal test, pole test, beam-walking tests, elevated plus maze, marble burying test, forced swimming test and novel object recognition test). This battery of behavioral tests highlighting long-term deficits is useful to study future neuroprotective strategies for stroke treatment.

Oral administration of a novel lipophilic PPARδ agonist is not neuroprotective after rodent cerebral ischemia

Peroxisome proliferator-activated receptors are regulators of inflammatory signaling. This has fostered hope that PPAR agonists might have neuroprotective potential. We hypothesized that PPARδ activation by the novel orally administered lipophilic PPARδ agonist SAR145 may improve short- and long-term outcome after focal brain ischemia. We induced ischemia by transient filamentous middle cerebral artery occlusion (MCAo) in 227 C57BL/6 mice and administered SAR145 in varying doses and time windows post-injury. Outcome was assessed by three functional tests and histologically determining ischemic lesion sizes. In a second experiment, we tested SAR145 treatment in 40 PPARδ-knockout mice using the same procedures. Three independent groups treated with 10 mg/kg bodyweight SAR145 directly after filament removal showed a mean reduction in lesion sizes of 18 ± 10% compared to vehicle-treated groups. We did not observe a consistent improvement in the long-term functional outcome by SAR145-treatment. PPARδ-knockout mice showed a significantly higher mortality after MCAo. As expected, we did not find a reduction of lesion size by SAR145-treatment in PPARδ-knockout mice. In summary, we found no evidence of a long-term neuroprotective effect of post-injury SAR145 treatment in cerebral ischemia. However, PPARδ appears to play a pathophysiologic role in acute infarct development and overall mortality after brain ischemia.

Behavioral and monoamine perturbations in adult male mice with chronic inflammation induced by repeated peripheral lipopolysaccharide administration

Considering the limited information on the ability of chronic peripheral inflammation to induce behavioral alterations, including on their persistence after inflammatory stimuli termination and on associated neurochemical perturbations, this study assessed the effects of chronic (0.25 mg/kg; i.p.; twice weekly) lipopolysaccharide (LPS) treatment on selected behavioral, neurochemical and molecular measures at different time points in adult male C57BL/6 mice. Behaviorally, LPS-treated mice were hypoactive after 6 weeks, whereas significant hyperactivity was observed after 12 weeks of LPS and 11 weeks after 13 week LPS treatment termination. Similar biphasic responses, i.e., early decrease followed by a delayed increase were observed in the open field test center time, suggestive of, respectively, increased and decreased anxiety. In a forced swim test, mice exhibited increased immobility (depressive behavior) at all times they were tested. Chronic LPS also produced persistent increase in splenic serotonin (5-HT) and time-dependent, brain region-specific alterations in striatal and prefrontocortical dopamine and 5-HT homeostasis. Microglia, but not astrocytes, were activated by LPS early and late, but their activation did not persist after LPS treatment termination. Above findings demonstrate that chronic peripheral inflammation initially causes hypoactivity and increased anxiety, followed by persistent hyperactivity and decreased anxiety. Notably, chronic LPS-induced depressive behavior appears early, persists long after LPS termination, and is associated with increased splenic 5-HT. Collectively, our data highlight the need for a greater focus on the peripheral/central monoamine alterations and lasting behavioral deficits induced by chronic peripheral inflammation as there are many pathological conditions where inflammation of a chronic nature is a hallmark feature.

Blocking stroke-induced immunodeficiency increases CNS antigen-specific autoreactivity but does not worsen functional outcome after experimental stroke

Stroke-induced immunodepression (SIDS) is an essential cause of poststroke infections. Pharmacological inhibition of SIDS appears promising in preventing life-threatening infections in stroke patients. However, SIDS might represent an adaptive mechanism preventing autoreactive immune responses after stroke. To address this, we used myelin oligodendrocyte glycoprotein (MOG) T-cell receptor transgenic (2D2) mice where >80% of peripheral CD4(+) T cells express a functional receptor for MOG. We investigated in a murine model of middle cerebral artery occlusion the effect of blocking SIDS by inhibiting body's main stress axes, the sympathetic nervous system (SNS) with propranolol and the hypothalamic-pituitary-adrenal axis (HPA) with mifepristone. Blockade of both stress axes robustly reduced infarct volumes, decreased infection rate, and increased long-term survival of 2D2 and C57BL/6J wild-type mice. Despite these protective effects, blockade of SIDS increased CNS antigen-specific Type1 T helper cell (Th1) responses in the brains of 2D2 mice 14 d after middle cerebral artery occlusion. One month after experimental stroke, 2D2 mice developed signs of polyradiculitis, which were diminished by SIDS blockade. Adoptive transfer of CD4(+) T cells, isolated from 2D2 mice, into lymphocyte-deficient Rag-1KO mice did not reveal differences between SIDS blockade and vehicle treatment in functional long-term outcome after stroke. In conclusion, inhibiting SIDS by pharmacological blockade of body's stress axes increases autoreactive CNS antigen-specific T-cell responses in the brain but does not worsen functional long-term outcome after experimental stroke, even in a mouse model where CNS antigen-specific autoreactive T-cell responses are boosted.

Regional cerebral blood flow following single-dose and continuous-dose tadalafil after stroke

PURPOSE

Tadalafil is a potent and selective phosphodiesterase type 5 inhibitor that provides effective treatment for erectile dysfunction (ED). The purpose of this study was to explore the effect of a single on-demand dose of tadalafil compared to low-dose continuous administration on regional cerebral blood flow (rCBF), in patients after stroke.

METHODS

Thirty consecutive male patients (mean age 58.3 ± 7.9 years) with ED and a history of stroke were included in the study. The baseline single-photon emission computed tomography (SPECT) study was performed 15 min after iv injection of 740 MBq Tc-99m-HMPAO (Ceretec; GE Healthcare Ltd. Chalfont St. Giles, UK). Fifteen randomized patients received a single dose of 20 mg tadalafil in the morning, and a second SPECT study was performed 6 h later. Fifteen other patients received 5 mg of tadalafil each morning for seven consecutive days, and the second SPECT study was performed 6 h after the last dose. The imaging data were evaluated using SPM software (Wellcome Department of Cognitive Neurology, University College, London).

RESULTS

Associations between any of the risk factors/comorbidities and the perfusion changes were not detected. All patients showed areas of reduced relative rCBF in the affected hemisphere after tadalafil administration compared to baseline (P < 0.001). No significant difference was found between patients on 5 mg tadalafil and 20 mg dose.

CONCLUSION

Tadalafil administration after cerebral stroke may be associated with diminished blood flow to areas adjacent to the stroke. The alterations in perfusion suggest a need for caution in prescribing tadalafil to patients with a history of stroke, especially with continuous administration that may impose constant stress on the cerebral circulation.

Noggin improves ischemic brain tissue repair and promotes alternative activation of microglia in mice

We previously reported that bone morphogenetic proteins (BMPs) and their endogenous antagonist noggin are expressed in the brain weeks after an ischemic insult. Here, to define their roles in ischemic brain tissue repair and remodeling, we infused recombinant BMP7 or noggin into the ipsilateral ventricle of mice for 2weeks starting 2weeks after transient middle cerebral artery occlusion (MCAO). Four weeks after MCAO, we measured ischemic brain volume, functional recovery, and molecules related to neurogenesis and angiogenesis such as synaptophysin, GAP-43, and VEGF. Noggin-treated mice but not BMP7-treated mice showed preserved ipsilateral brain volume and reduced neurological deficits compared with artificial cerebrospinal fluids (aCSF)-treated mice. Noggin treatment also decreased glial scar thickness, increased levels of GAP-43 and VEGF protein, and increased the number of Iba1-positive activated microglia in the ipsilateral brain. Furthermore, noggin treatment decreased M1 markers (IL-1β, TNF-α, IL-12, CCL2 and CD86) and increased M2 markers (IL-1ra, IL-10, arginase 1, CD206 and Ym1) of activated microglia, suggesting a shift from M1 to M2 phenotypes. These results suggest that noggin improves functional recovery from ischemic stroke and enhances alternatively activated microglia, thereby promoting tissue repair and remodeling.

Yonkenafil: a novel phosphodiesterase type 5 inhibitor induces neuronal network potentiation by a cGMP-dependent Nogo-R axis in acute experimental stroke

Yonkenafil is a novel phosphodiesterase type 5 (PDE5) inhibitor. Here we evaluated the effect of yonkenafil on ischemic injury and its possible mechanism of action. Male Sprague-Dawley rats underwent middle cerebral artery occlusion, followed by intraperitoneal or intravenous treatment with yonkenafil starting 2h later. Behavioral tests were carried out on day 1 or day 7 after reperfusion. Nissl staining, Fluoro-Jade B staining and electron microscopy studies were carried out 24h post-stroke, together with an analysis of infarct volume and severity of edema. Levels of cGMP-dependent Nogo-66 receptor (Nogo-R) pathway components, hsp70, apaf-1, caspase-3, caspase-9, synaptophysin, PSD-95/neuronal nitric oxide synthases (nNOS), brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (TrkB) and nerve growth factor (NGF)/tropomyosin-related kinase A (TrkA) were also measured after 24h. Yonkenafil markedly inhibited infarction and edema, even when administration was delayed until 4h after stroke onset. This protection was associated with an improvement in neurological function and was sustained for 7d. Yonkenafil enlarged the range of penumbra, reduced ischemic cell apoptosis and the loss of neurons, and modulated the expression of proteins in the Nogo-R pathway. Moreover, yonkenafil protected the structure of synapses and increased the expression of synaptophysin, BDNF/TrkB and NGF/TrkA. In conclusion, yonkenafil protects neuronal networks from injury after stroke.

Of mice and men: modelling post-stroke depression experimentally

At least one-third of stroke survivors suffer from depression. The development of comorbid depression after stroke is clinically highly significant because post-stroke depression is associated with increased mortality, slows recovery and leads to worse functional outcomes. Here, we review the evidence that post-stroke depression can be effectively modelled in experimental rodents via a variety of approaches. This opens an exciting new window onto the neurobiology of depression and permits probing potential underlying mechanisms such as disturbed cellular plasticity, neuroendocrine dysregulation, neuroinflammation, and neurodegeneration in a novel context. From the point of view of translational stroke research, extending the scope of experimental investigations beyond the study of short-term end points and, in particular, acute lesion size, may help improve the relevance of preclinical results to human disease. Furthermore, accumulating evidence from both clinical and experimental studies offers the tantalizing prospect of 5-hydroxytryptaminergic antidepressants as the first pharmacological therapy for stroke that would be available during the subacute and chronic phases of recovery. Interdisciplinary neuropsychiatric research will be called on to dissect the mechanisms underpinning the beneficial effects of antidepressants on stroke recovery.

A method for generating a mouse model of stroke: evaluation of parameters for blood flow, behavior, and survival [corrected]

Stroke is one of the common causes of death and disability. Despite extensive efforts in stroke research, therapeutic options for improving the functional recovery remain limited in clinical practice. Experimental stroke models using genetically modified mice could aid in unraveling the complex pathophysiology triggered by ischemic brain injury. Here, we optimized the procedure for generating mouse stroke model using an intraluminal suture in the middle cerebral artery and verified the blockage of blood flow using indocyanine green coupled with near infra-red radiation. The first week after the ischemic injury was critical for survivability. The survival rate of 11% in mice without any treatment but increased to 60% on administering prophylactic antibiotics. During this period, mice showed severe functional impairment but recovered spontaneously starting from the second week onward. Among the various behavioral tests, the pole tests and neurological severity score tests remained reliable up to 4 weeks after ischemia, whereas the rotarod and corner tests became less sensitive for assessing the severity of ischemic injury with time. Further, loss of body weight was also observed for up 4 weeks after ischemia induction. In conclusion, we have developed an improved approach which allows us to investigate the role of the cell death-related genes in the disease progression using genetically modified mice and to evaluate the modes of action of candidate drugs.

Effects of tadalafil on ischemia/reperfusion injury in rat brain

Cerebral ischemia-reperfusion (I/R) injury is caused by lack of blood supply to the brain. The accumulation of toxic products such as reactive oxygen species (ROS) occurs on reperfusion, when the occlusion is removed. The resulting oxidative stress results in the initiation of pathways leading to necrotic and apoptotic cell death. Tadalafil (TAD) prevents the accumulation of ROS and increases antioxidant cellular protective mechanisms. The aim of this study was to investigate the effect of TAD treatment against short-term global brain I/R injury in rats. The study was carried out on 30 Wistar-albino rats, which were divided into three groups including a control group (n = 10), an I/R group (n = 10) and an I/R + TAD group (n = 10) (2 mg/kg/day for 4 days before ischemia). At the end of the experiment, tissue samples were collected for both biochemical and histopathological analyses. Malondialdehyde was significantly lower in the TAD-administered group (9.06 ± 0.15) than in the I/R group (p < 0.05). However, no significant difference was observed in nitric oxide levels in the TAD-administered group compared to the I/R group. The mean superoxide dismutase level was significantly higher in the I/R-TAD group than the I/R group. There was no statistically significant difference in glutathione peroxidase levels in I/R + TAD group compared to I/R group. Histopathologically, TAD-administered group provided significant morphological improvement compared to the I/R group. We concluded that TAD prevented I/R-induced neurotoxicity as shown by obtained biochemical and histopathological findings.

Assessment of behavioral flexibility after middle cerebral artery occlusion in mice

Middle cerebral artery occlusion (MCAO) is the most common animal model of cerebral ischemia and induces various functional impairments. Long-lasting deficits resulting from MCAO however, remain insufficiently characterized, especially regarding cognition. Yet, behavioral flexibility, a prominent cognitive process is found impaired after stroke in humans. We thus used an operant-based task to assess behavioral flexibility in mice after MCAO. Three weeks after 30 min MCAO surgery, mice were subjected to a battery of sensorimotor tests (rotarod, vertical pole test, spontaneous locomotion and grip-strength test). Behavioral flexibility was then assessed in an operant task, in which mice, rewarded according to a FR5 schedule of reinforcement, had to alternate their operant responses between two levers from trial to trial. Regarding sensory and motor functioning, only the pole test yielded a significant difference between MCAO and sham mice. In the operant flexibility task, results showed a behavioral flexibility deficit in MCAO mice; neither the operant response acquisition nor the appeal for food rewards was altered. In conclusion, our operant-based task revealed a long-lasting behavioral flexibility deficit after MCAO in mice.

Neuroprotection by sildenafil: neuronal networks potentiation in acute experimental stroke

AIMS

Sildenafil, a phosphodiesterase type 5 inhibitor, has been found to produce functional recovery in ischemic rats by increasing the cGMP level and triggering neurogenesis. The aim of this study was to investigate further sildenafil mechanisms.

METHODS

Male Sprague-Dawley rats underwent middle cerebral artery occlusion and reperfusion, followed by intraperitoneal or intravenous treatment of sildenafil starting 2 h later. Behavioral tests were performed on day 1 or day 7 after reperfusion, while cerebral infarction, edema, Nissl staining, Fluoro-Jade B staining, and electron microscopy studies were carried out 24 h poststroke. The cGMP-dependent Nogo-66 receptor (Nogo-R) pathway, synaptophysin, PSD-95/neuronal nitric oxide synthases (nNOS), brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (TrkB), and nerve growth factor (NGF)/tropomyosin-related kinase A (TrkA) were measured.

RESULTS

Sildenafil enhanced neurological recovery and inhibited infarction, even following delayed administration 4 h after stroke onset. Furthermore, sildenafil reduced the loss of neurons and modulated the expressions of the cGMP-dependent Nogo-R pathway. Moreover, sildenafil protected the structure of synapses and mediated the expressions of synaptophysin, PSD-95/nNOS, BDNF/TrkB, and NGF/TrkA.

CONCLUSIONS

Sildenafil produces significant neuroprotective effects on injured neurons in acute stroke, and these are mediated by the cGMP-dependent Nogo-R pathway, NGF/TrkA, and BDNF/TrkB.

Protective effect of sildenafil on liver injury induced by intestinal ischemia/reperfusion

BACKGROUND

This study evaluated the protective effect of sildenafil on liver injury induced by intestinal ischemia-reperfusion.

METHODS

Forty female Sprague Dawley rats were divided into 4 groups: sham-control (SC), ischemia (I), ischemia-reperfusion (IR), and ischemia-reperfusion+sildenafil (SIL; sildenafil gavaged at 50mg/kg before operating). A 2-h ischemia-reperfusion was performed by clamping the superior mesenteric artery. Liver function, plasma alanine (ALT) and aspartate (AST) aminotransferase, and intestinal and liver malondialdehyde (MDA) were measured at the end of the experiment. Intestinal and liver tissue damage was examined by histology. Liver samples were immunologically stained for endothelial nitric oxide synthase (eNOS) and proliferating cell nuclear antigen (PCNA).

RESULTS

The ALT and AST levels were highest in the IR group and were lower in the SIL group (p<0.05). Intestinal MDA levels were statistically higher in the IR group than in the SC, I and SIL groups. Liver MDA levels were significantly higher in the IR group than in the I and SC groups (p<0.05) and higher than in the SIL group (p>0.05). Intestinal damage based on Chiu scoring was more severe in the IR than in the SIL group (p<0.05). Sildenafil reduced damage and also increased eNOS and PCNA immunoreactivity in liver tissue.

CONCLUSIONS

Sildenafil shows a protective effect on intestinal ischemia-reperfusion-induced liver injury, possibly by decreasing vascular resistance through increased nitric oxide levels.

Brain deposition and neurotoxicity of manganese in adult mice exposed via the drinking water

Natural leaching processes and/or anthropogenic contamination can result in ground water concentrations of the essential metal manganese (Mn) that far exceed the current regulatory standards. Neurological consequences of Mn drinking water (DW) overexposure to experimental animals, i.e., mice, including its brain deposition/distribution and behavioral effects are understudied. Adult male C57BL/6 mice were exposed to Mn via the DW for 8 weeks. After 5 weeks of Mn exposure, magnetic resonance imaging revealed significant Mn deposition in all examined brain regions; the degree of Mn deposition did not increase further a week later. Behaviorally, early hyperactivity and more time spent in the center of the arenas in an open field test, decreased forelimb grip strength and less time swimming in a forced swim test were observed after 6 weeks of Mn DW exposure. Eight-week Mn DW exposure did not alter striatal dopamine, its metabolites, or the expression of key dopamine homeostatic proteins, but it significantly increased striatal 5-hydroxyindoleacetic acid (a serotonin metabolite) levels, without affecting the levels of serotonin itself. Increased expression (mRNA) of glial fibrillary acidic protein (GFAP, an astrocyte activation marker), heme oxygenase-1 and inducible nitric oxide synthase (oxidative and nitrosative stress markers, respectively) were observed 8 weeks post-Mn DW exposure in the substantia nigra. Besides mRNA increases, GFAP protein expression was increased in the substantia nigra pars reticulata. In summary, the neurobehavioral deficits, characterized by locomotor and emotional perturbations, and nigral glial activation associated with significant brain Mn deposition are among the early signs of Mn neurotoxicity caused by DW overexposure.

Neuroprotective role of PDE4 and PDE5 inhibitors in 3-nitropropionic acid induced behavioral and biochemical toxicities in rats

Phosphodiesterase inhibitors have been reported to be beneficial in cognitive and motor disorders. In the present study, we have investigated the effects of RO 20-1724 (PDE4 inhibitor) and sildenafil (PDE5 inhibitor) in 3-nitropropionic acid (3-NP) induced experimental Huntington's disease in rats. 3-Nitropropionic acid was administered for 14 days (10 mg/kg i.p.) 1h following 3-NP administration, the rats were treated with either vehicle, RO 20-1724 (0.25 and 0.5 mg/kg i.p.) or sildenafil (2 and 4 mg/kg i.p.) for 14 days. Cognitive functions were assessed by using Morris water maze whereas, motor functions were assessed by spontaneous locomotor activity, limb withdrawal and suspended wire test at different time points. Biochemically, markers of oxidative stress and cell damage, such as reduced glutathione, malondialdehyde, nitrite and lactate dehydrogenase levels were assessed terminally in the brain homogenate. Chronic administration of 3-NP produced significant decrease in body weight, showed marked abnormalities in cognitive and motor functions. Further, significant oxidative-nitrosative stress and cell damage was also observed. Chronic administration of RO 20-1724 and sildenafil in 3-NP treated rats significantly and dose dependently attenuated 3-NP induced behavioral and biochemical abnormalities in rats. Both these drugs were equally effective in attenuating 3-NP induced neurotoxicity. These results suggesting that the inhibition of PDE4 and PDE5 would be therapeutic in neurodegenerative disorders associated with cognitive and motor dysfunction.

Assessing post-stroke behavior in mouse models of focal ischemia

Experimental treatment strategies and neuroprotective drugs that showed therapeutic promise in animal models of stroke have failed to produce beneficial effects in human stroke patients. The difficulty in translating preclinical findings to humans represents a major challenge in cerebrovascular research. The reasons behind this translational road block might be explained by a number of factors, including poor quality control in various stages of the research process, the validity of experimental stroke models, and differences in drug administration and pharmacokinetics. Another major difference between animal studies and clinical trials is the choice of end point or outcome measures. Here, we discuss the necessity of poststroke behavioral testing to bridge the gap between clinical and experimental end points. We review established sensory-motor tests for outcome determination after focal ischemia based on the published literature as well as our own personal experience. Selected tests are described in more detail and good laboratory practice standards for behavioral testing are discussed. This review is intended for stroke researchers planning to use behavioral testing in mice.

Regulatory T cells accumulate and proliferate in the ischemic hemisphere for up to 30 days after MCAO

Local and peripheral immune responses are activated after ischemic stroke. In our present study, we investigated the temporal distribution, location, induction, and function of regulatory T cells (Tregs) and the possible involvement of microglia, macrophages, and dendritic cells after middle cerebral artery occlusion (MCAO). C57BL/6J and Foxp3(EGFP) transgenic mice were subjected to 30 minutes MCAO. On days 7, 14, and 30 after MCAO, Tregs and antigen presenting cells were analyzed using fluorescence activated cell sorting multicolor staining and immunohistochemistry. A strong accumulation of Tregs was observed on days 14 and 30 in the ischemic hemisphere accompanied by the elevated presence and activation of microglia. Dendritic cells and macrophages were found on each analyzed day. About 60% of Foxp3(+) Tregs in ischemic hemispheres were positive for the proliferation marker Ki-67 on days 7 and 14 after MCAO. The transfer of naive CD4(+) cells depleted of Foxp3(+) Tregs into RAG1(-/-) mice 1 day before MCAO did not lead to a de novo generation of Tregs 14 days after surgery. After depletion of CD25(+) Tregs, no changes regarding neurologic outcome were detected. The sustained presence of Tregs in the brain after MCAO indicates a long-lasting immunological alteration and involvement of brain cells in immunoregulatory mechanisms.

Oral tadalafil reduces intra-abdominal adhesion reformation in rats

BACKGROUND

Currently, there is no ideal agent to prevent adhesion formation. We have shown that sildenafil, a phosphodiesterase-5 (PDE-5) inhibitor, reduces post-operative adhesion formation by vasodilatation and increases fibrinolytic activity. Here, we evaluated whether tadalafil, a long-acting PDE-5 inhibitor, decreases post-operative adhesion reformation in rats.

MATERIALS AND METHODS

Standardized lesions were created in Wistar albino rats by cauterization of uterine horns and abrasion of adjacent peritonium. The extent and severity of adhesions were scored on the 14th post-operative day and adhesiolysis was performed at the second laparotomy. Animals were then assigned randomly into two groups. The study group (n = 11) received 10 mg/kg oral tadalafil by gavage 60 min before the second laparotomy and daily for 14 days afterwards. Controls (n = 11) received the same volume of tap water for 14 days by gavage. Animals were killed 15 days after adhesiolysis and adhesions were scored blind during the third laparotomy. RESULTS Basal adhesion scores at the time of the second laparotomy were comparable in the study and control groups. Scores for the extent of adhesion reformation in the study and control groups did not differ [median 1 (range 0-3) versus median 2 (range 1-3); P: 0.81] but tadalafil reduced the respective severity scores [median 0.5 (range 0-1) versus median 1 (range 0.5-1); P: 0.02] and total scores [median 2 (range 0-4) versus median 2.5 (range 1.5-4); P: 0.042].

CONCLUSIONS

Oral administration of tadalafil during the perioperative period reduces intra-abdominal adhesion reformation in rats.

Effect of a phosphodiesterase 5 inhibitor on pulmonary and cerebral arteries of newborn piglets with chronic hypoxia-induced pulmonary hypertension

BACKGROUND

The use of phosphodiesterase 5 (PDE5) inhibitors to treat newborns with pulmonary hypertension is increasing. The effect of PDE5 inhibitors on the neonatal cerebral circulation remains unknown. The neonatal piglet model of chronic hypoxia-induced pulmonary hypertension allows the study of the effects of PDE5 inhibitors on both the pulmonary and cerebral circulations.

OBJECTIVES

To determine whether the PDE5 inhibitor, zaprinast, causes dilation in pulmonary and middle cerebral arteries (MCA) of normoxic newborn piglets and those with chronic hypoxia-induced pulmonary hypertension, and to evaluate whether zaprinast alters responses to increased pressure (autoregulatory ability) of the MCA.

METHODS

Two-day-old piglets were raised in normoxia or hypoxia for 3 or 10 days. Pulmonary arteries and MCA were isolated and pressurized, after which changes in diameter to zaprinast were measured. MCA pressure-diameter relationships were determined.

RESULTS

Dilation to zaprinast was similar in pulmonary arteries from normoxic and hypoxic piglets. Zaprinast dilated MCA from all groups but the response was diminished in MCA from piglets raised in hypoxia for 10 days. MCA pressure-diameter relationships (autoregulation) did not differ between the groups.

CONCLUSIONS

Pulmonary artery dilation to zaprinast supports the use of PDE5 inhibitors to treat pulmonary hypertension in neonates. PDE5 inhibitors function as MCA dilators but do not impair the pressure-diameter behavior of the cerebral circulation of either normoxic newborn piglets or those with chronic hypoxia-induced pulmonary hypertension. These findings suggest that cerebral autoregulation is likely to be intact with acute PDE5 inhibitor treatment in infants with pulmonary hypertension in conditions associated with chronic hypoxia.

Sildenafil improves epicenter vascular perfusion but not hindlimb functional recovery after contusive spinal cord injury in mice

Nitric oxide (NO) is an important regulator of vasodilation and angiogenesis in the central nervous system (CNS). Signaling initiated by the membrane receptor CD47 antagonizes vasodilation and angiogenesis by inhibiting synthesis of cyclic guanosine monophosphate (cGMP). We recently found that deletion of CD47 led to significant functional locomotor improvements, enhanced angiogenesis, and increased epicenter microvascular perfusion in mice after moderate contusive spinal cord injury (SCI). We tested the hypothesis that improving NO/cGMP signaling within the spinal cord immediately after injury would increase microvascular perfusion, angiogenesis, and functional recovery, with an acute, 7-day administration of the cGMP phosphodiesterase 5 (PDE5) inhibitor sildenafil. PDE5 expression is localized within spinal cord microvascular endothelial cells and smooth muscle cells. While PDE5 antagonism has been shown to increase angiogenesis in a rat embolic stroke model, sildenafil had no significant effect on angiogenesis at 7 days post-injury after murine contusive SCI. Sildenafil treatment increased cGMP concentrations within the spinal cord and improved epicenter microvascular perfusion. Basso Mouse Scale (BMS) and Treadscan analyses revealed that sildenafil treatment had no functional consequence on hindlimb locomotor recovery. These data support the hypothesis that acutely improving microvascular perfusion within the injury epicenter by itself is an insufficient strategy for improving functional deficits following contusive SCI.

Effect of vardenafil on nitric oxide synthase expression in the paraventricular nucleus of rats without sexual stimulation

Vardenafil hydrochloride (HCl) is a potent and selective phosphodiesterase type-5 (PDE-5) inhibitor that enhances nitric oxide (NO)-mediated relaxation of human corpus cavernosum and NO-induced rabbit penile erection, and enhances erectile function in patients. In the present study, the effect of vardenafil on nitric oxide synthase (NOS) and neuronal NOS expressions in the paraventricular nucleus (PVN) of rats without sexual stimulation was investigated using nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry and neuronal NOS (nNOS) immunohistochemistry and western blot analysis. The present results showed that NOS and nNOS expression in the PVN was increased by vardenafil treatment as the dose- and duration-dependently without sexual stimulation. The phosphodiesterase type-5 inhibitor, vardenafil, augmented NOS expression in the brain without sexual stimulation. The present study suggests that sexual behaviour can be directly modulated by neurotransmitters such as nitric oxide.

Vardenafil Enhances Oxytocin Expression in the Paraventricular Nucleus without Sexual Stimulation

Purpose

Oxytocin is associated with the ability to form normal social attachments. c-Fos is an immediate early gene whose expression is used as a marker for stimulus-induced changes in neurons. The effect of phosphodiesterase-5 (PDE-5) inhibitors on oxytocin activation in the brain without sexual stimuli has not yet been reported. In the present study, we investigated the effects of vardenafil on oxytocin and c-Fos expression in the paraventricular nucleus (PVN) of conscious rats.

Methods

Male Sprague-Dawley rats weighing 300±10 g were divided into 6 groups (n=5 in each group): the control group, the 1-day-0.5 mg/kg, the 1-day-1 mg/kg, the 1-day-2 mg/kg, the 3-day-1 mg/kg, and the 7-day-1 mg/kg vardenafil administration group. The experiment was conducted without sexual stimulation. Vardenafil was orally administered. The animals in the control group received an equivalent amount of distilled water orally. The expression of oxytocin and c-Fos in the PVN was detected by immunohistochemistry.

Results

Oxytocin expression in the PVN was increased by 1 day administration of 2 mg/kg vardenafil, and this effect of vardenafil appeared in a duration-dependent manner. c-Fos in the oxytocin neurons of the PVN was increased by 1 day administration of 2 mg/kg vardenafil, and this effect of vardenafil also appeared in a duration-dependent manner. These results showed that vardenafil augments the expression of oxytocin with activation of oxytocin neurons in the PVN.

Conclusions

In this study, we showed that the PDE-5 inhibitor, vardenafil directly enhances oxytocin expression and also activates oxytocin neurons in the PVN, which indicates that vardenafil may exert positive effects on affiliation behavior and social interaction.

Determination of the brain-blood partition coefficient for water in mice using MRI

Cerebral blood flow (CBF) quantification is a valuable tool in stroke research. Mice are of special interest because of the potential of genetic engineering. Magnetic resonance imaging (MRI) provides repetitive, noninvasive CBF quantification. Many MRI techniques require the knowledge of the brain-blood partition coefficient (BBPC) for water. Adopting an MRI protocol described by Roberts et al (1996) in humans, we determined the BBPC for water in 129S6/SvEv mice from proton density measurements of brain and blood, calibrated with deuterium oxide/water phantoms. The average BBPC for water was 0.89 ± 0.03 mL/g, with little regional variation within the mouse brain.

Effect of vardenafil on cerebral vasospasm following experimental subarachnoid hemorrhage in rats

We examined the effects of the phosphodiesterase 5 (PDE-5) inhibitor vardenafil on cerebral vasospasm in an experimental rat subarachnoid hemorrhage (SAH) model. Thirty-two albino Wistar rats were divided into five groups: G1, no experimental intervention; G2, administered subarachnoid physiological saline after sham surgery; G3, subjected to SAH; G4, subjected to SAH and administered low-dose (0.5 mg/kg) vardenafil treatment; and G5, subjected to SAH and administered high-dose (5 mg/kg) vardenafil treatment. For animals in G3, G4 and G5, SAH was induced by an injection of autologous non-heparinized blood into the cisterna magna. Immediately after SAH, for animals in G4 and G5, vardenafil was administered by gavage at intervals of 8 hours for 2 days. The rats were then decapitated, and basilar arteries and blood samples were taken for biochemical and histopathological examination. Malonyldialdehyde values in G2 (p = 0.004) and G3 (p = 0.002) were significantly higher than those in G1. G4 and G5 had significantly lower values than G2 and G3 (p = 0.014, G4 v. G2; p = 0.005, G4 v. G3; p = 0.005, G5 v. G2; p = 0.002, G5 v. G3). Total antioxidant capacity (TAC) values in G3 were significantly lower than those in G1 (p = 0.041). TAC values in G4 and G5 were significantly higher than those in G3 (p = 0.043). Mean luminal diameter in G3 was significantly smaller compared with G1 and G2 (p = 0.002), but larger in G4 (p = 0.002) and G5 (p = 0.001) compared with G3. Mean luminal diameter was also significantly larger in G5 than in G2 (p = 0.008) and G4 (p = 0.038). Mean wall thickness in G2 (p = 0.015) and G3 (p = 0.002) was significantly thicker compared with G1. Wall thickness was significantly thinner in G4 and G5 compared with G2 and G3 (p = 0.008, G4 v. G2; p = 0.001, G4 v. G3; p = 0.005, G5 v. G2; p = 0.001, G5 v. G3). Our results confirm that vardenafil may induce vasodilatation and provide potential benefits in SAH therapy by preventing vasospasm.

Treatment with sildenafil prevents impairment of learning in rats born to pre-eclamptic mothers

Pre-eclampsia is an important hypertensive pregnancy disorder and a main cause of maternal and fetal morbidity and mortality. Children born from mothers with pre-eclampsia may present cognitive deficits. The mechanisms leading to this cognitive impairment remain unclear and no treatments to improve it have been tested. Pre-eclampsia is associated with impaired regulation of the nitric oxide-3'-5'guanosine monophosphate cyclic (cGMP) pathway, which modulates some cognitive functions. We hypothesized that alterations in the NO-cGMP pathway would be involved in the mechanisms leading to cognitive impairment in rats born to pre-eclamptic mothers and that treatment with sildenafil, an inhibitor of the phosphodiesterase that degrades cGMP, could restore their cognitive function. To test these hypotheses, we used an animal model of pre-eclampsia in rats: pregnant rats treated with l-nitro-arginine methyl ester, an inhibitor of nitric oxide synthase. Using this model, we assessed: (1) whether rats born to pre-eclamptic mothers show reduced learning ability and/or altered motor activity or coordination when they are 2 months-old; (2) whether cognitive impairment is associated with reduced function of the glutamate-NO-cGMP pathway in brain in vivo; and (3) whether treatment of the mothers with sildenafil prevents this cognitive and motor alterations. The results reported show that the ability to learn a conditional discrimination task in a Y maze is reduced in rats born to pre-eclamptic mothers. This impairment was associated with reduced function of the glutamate-NO-cGMP pathway in brain in vivo, as assessed by microdialysis in freely moving rats. Treatment with sildenafil restores the function of this pathway and learning ability.

Statistics in experimental cerebrovascular research: comparison of more than two groups with a continuous outcome variable

A common setting in experimental cerebrovascular research is the comparison of more than two experimental groups. Often, continuous measures such as infarct volume, cerebral blood flow, or vessel diameter are the primary variables of interest. This article presents the principles of the statistical analysis of comparing more than two groups using analysis of variance (ANOVA). We will also explain post hoc comparisons, which are required to show which groups significantly differ once ANOVA has rejected the null hypothesis. Although statistical packages perform ANOVA and post hoc contrast at a key stroke, in this study, we use examples from experimental stroke research to reveal the simple math behind the calculations and the basic principles. This will enable the reader to understand and correctly interpret the readout of statistical packages and to help prevent common errors in the comparison of multiple means.

Phosphodiesterase 5A inhibitors improve functional recovery after stroke in rats: optimized dosing regimen with implications for mechanism

Phosphodiesterase 5A (PDE5A) inhibitors improve functional recovery after middle cerebral artery occlusion (MCA-o) in rats. We used the PDE5A inhibitor 3-(4-(2-hydroxyethyl)piperazin-1-yl)-7-(6-methoxypyridin-3-yl)-1-(2-propoxyethyl)pyrido[3,4-b]pyrazin-2(1H)-one hydrochloride (PF-5) to determine the timing, duration, and degree of inhibition that yields maximum efficacy. We also investigated the localization of PDE5A to determine the tissues and cells that would be targets for PDE5 inhibition and that may mediate efficacy. Nearly complete inhibition of PDE5A, starting 24 h after MCA-o and continued for 7 days, resulted in nearly complete recovery of sensorimotor function that was sustained for 3 months. Delaying administration until 72 h after MCA-o resulted in equivalent efficacy, whereas delaying treatment for 14 days was ineffective. Treatment for 7 days was equivalently efficacious to 28 or 84 days of treatment, whereas treatment for 1 day was less effective. In the normal forebrain, PDE5A immunoreactivity was prominent in smooth muscle of meningeal arteries and a few smaller blood vessels, with weak staining in a few widely scattered cortical neurons and glia. At 24 and 48 h after MCA-o, the number and intensity of blood vessel staining increased in the infarcted cortex and striatum. PDE5A immunoreactivity also was increased at 48 h in putative microglia in penumbra, whereas there was no change in staining of the scattered cortical neurons. Given the window for efficacy and the PDE5A distribution, we hypothesize that efficacy results from an effect on vasculature, and perhaps modulation of microglial function, both of which may facilitate recovery of neuronal function.

Effects of gemfibrozil on outcome after permanent middle cerebral artery occlusion in mice

Fibrates are lipid lowering drugs and found as ligands for peroxisome proliferator-activated receptors (PPARs). A clinical study has shown that one type of fibrate gemfibrozil reduces stroke incidence in men. However, it remains unknown whether gemfibrozil improves outcome after stroke. We hypothesized that prophylactic administration of gemfibrozil improves outcome after ischemic stroke. In this study, we measured the impact of gemfibrozil in two permanent middle cerebral artery occlusion (MCAO) models in young adult male mice on normal diet. First, we tested gemfibrozil in a filamentous MCAO model. Pretreatment with gemfibrozil (30 mg/kg) for 7 days moderately but significantly reduced infarct size at 24 h after MCAO. A higher dose (120 mg/kg) did not attenuate infarct size. Rather, it tended to increase brain swelling. Second, we tested in a distal MCAO model. Gemfibrozil (30 mg/kg) for 7 days before and after stroke significantly attenuated cortical lesion size at 7 days after MCAO. Cortical blood flow measured by laser speckle imaging was improved by gemfibrozil in the ischemic hemisphere. In non-stroke animals gemfibrozil also altered gene expression levels of PPARs in both the aorta and brain in organ specific manners; however, endothelial nitric oxide synthase (eNOS) was not significantly affected. These findings suggested the possibility that the observed infarct reductions and cortical blood flow improvements in ischemic brains were not through eNOS-mediated mechanisms. Further investigations may be meritorious to examine whether prophylactic usage of gemfibrozil against stroke is beneficial.