Lorenz Hirt

Sniff nasal pressure : A sensitive respiratory test to assess progression of amyotrophic lateral sclerosis

Impairment of pulmonary function is a major prognostic indicator in amyotrophic lateral sclerosis (ALS). Forced vital capacity (FVC) and maximal voluntary ventilation (MVV) decline linearly and are commonly used to assess disease progression. The aim of this study was to evaluate the usefulness of testing respiratory muscle strength in ALS with a novel test, sniff nasal pressure (Pnsn), in parallel with more classic tests such as maximal inspiratory pressure (PImax) and maximal expiratory pressure (PEmax). Sixteen patients with ALS were examined monthly over a period of 18 ± 10 months. At the time of inclusion in the study, values were normal for FVC (107% of predicted value) and MVV (87% of predicted value) but abnormally low for Pnsn (67% of predicted value), PImax (69% of predicted value), and PEmax (54% of predicted value). Late in the course of ALS, all patients could perform Pnsn, whereas 6 could not perform PImax and 7 could not perform PEmax. The rate of deterioration was most often linear and similar for FVC (−4.1% of predicted value per month), MVV (−4.3% of predicted value per month), and Pnsn (−4.2% of predicted value per month). We conclude that Pnsn was the single respiratory test combining linear decline, sensitivity in mild disease, and feasibility in advanced disease. Being easy to perform and inexpensive, Pnsn appears well suited to assess the decline of respiratory muscle strength in ALS.

Protective Role of Early Aquaporin 4 Induction against Postischemic Edema Formation

Aquaporin 4 (AQP4) is a water channel involved in water movements across the cell membrane and is spatially organized on the cell surface in orthogonal array particles (OAPs). Its role in edema formation or resolution after stroke onset has been studied mainly at late time points. We have shown recently that its expression is rapidly induced after ischemia coinciding in time with an early swelling of the ischemic hemisphere. There are two isoforms of AQP4: AQP4-M1 and AQP4-M23. The ratio of these isoforms influences the size of the OAPs but the functional impact is not known. The role of the early induction of AQP4 is not yet known. Thrombin preconditioning in mice provides a useful model to study endogenous protective mechanisms. Using this model, we provide evidence for the first time that the early induction of AQP4 may contribute to limit the formation of edema and that the AQP4-M1 isoform is predominantly induced in the ischemic tissue at this time point. Although it prevents edema formation, the early induction of the AQP4 expression does not prevent the blood—brain barrier disruption, suggesting an effect limited to the prevention of edema formation possibly by removing of water from the tissue.

Early mobilization out of bed after ischaemic stroke reduces severe complications but not cerebral blood flow: a randomized controlled pilot trial

Objective: To evaluate whether early mobilization after acute ischaemic stroke is better than delayed mobilization with regard to medical complications and if it is safe in relation to neurological function and cerebral blood flow. Design: Randomized controlled pilot trial of early versus delayed mobilization out of bed with incidence of severe complications as the primary outcome. Setting: Acute stroke unit in the neurology department of a University Hospital. Participants: Fifty patients after ischaemic stroke with a National Institutes of Health Stroke Scale (NIHSS) score >6 were recruited. Intervention: All patients were treated with physiotherapy immediately after their admission. In the early protocol patients were mobilized out of bed after 52 hours, in the delayed protocol after seven days. Results: Eight out of 50 randomized patients were excluded from the per-protocol analysis because of early transfer to other hospitals. There were 2 (8%) severe complications in the 25 early mobilization patients and 8 (47%) in the 17 delayed mobilization patients (P < 0.006). There were no differences in the total number of complications or in clinical outcome. In the 26 patients (62%) who underwent serial transcranial Doppler ultrasonography, no blood flow differences were found. Conclusion: We found an apparent reduction in severe complications and no increase in total complications with an early mobilization protocol after acute ischaemic stroke. No influence on neurological three-month outcomes or on cerebral blood flow was seen. These results justify larger trials comparing mobilization protocols with possibly even faster mobilization out of bed than explored here.

Controlled Contrast Transcranial Doppler and Arterial Blood Gas Analysis to Quantify Shunt Through Patent Foramen Ovale

Background and Purpose— A right-to-left shunt can be identified by contrast transcranial Doppler ultrasonography (c-TCD) at rest and/or after a Valsalva maneuver (VM) or by arterial blood gas (ABG) measurement. We assessed the influence of controlled strain pressures and durations during VM on the right-to-left passage of microbubbles, on which depends the shunt classification by c-TCD, and correlated it with the right-to-left shunt evaluation by ABG measurements in stroke patients with patent foramen ovale (PFO). Methods— We evaluated 40 stroke patients with transesophageal echocardiography–documented PFO. The microbubbles were recorded with TCD at rest and after 4 different VM conditions with controlled duration and target strain pressures (duration in seconds and pressure in cm H2O, respectively): V5-20, V10-20, V5-40, and V10-40. The ABG analysis was performed after pure oxygen breathing in 34 patients, and the shunt was calculated as percentage of cardiac output. Results— Among all VM conditions, V5-40 and V10-40 yielded the greatest median number of microbubbles (84 and 95, respectively; P <0.01). A significantly larger number of microbubbles were detected in V5-40 than in V5-20 (P <0.001) and in V10-40 than in V10-20 (P <0.01). ABG was not sensitive enough to detect a shunt in 31 patients. Conclusions— The increase of VM expiratory pressure magnifies the number of microbubbles irrespective of the strain duration. Because the right-to-left shunt classification in PFO is based on the number of microbubbles, a controlled VM pressure is advised for a reproducible shunt assessment. The ABG measurement is not sensitive enough for shunt assessment in stroke patients with PFO.

Coagulation factor Xa activates thrombin in ischemic neural tissue

Thrombin is involved in mediating neuronal death in cerebral ischemia. We investigated its so far unknown mode of activation in ischemic neural tissue. We used an in vitro approach to distinguish the role of circulating coagulation factors from endogenous cerebral mechanisms. We modeled ischemic stroke by subjecting rat organotypic hippocampal slice cultures to 30‐min oxygen (5%) and glucose (1 mmol/L) deprivation (OGD). Perinuclear activated factor X (FXa) immunoreactivity was observed in CA1 neurons after OGD. Selective FXa inhibition by fondaparinux during and after OGD significantly reduced neuronal death in the CA1 after 48 h. Thrombin enzyme activity was increased in the medium 24 h after OGD and this increase was prevented by fondaparinux suggesting that FXa catalyzes the conversion of prothrombin to thrombin in neural tissue after ischemia in vitro. Treatment with SCH79797, a selective antagonist of the thrombin receptor protease‐activated receptor‐1 (PAR‐1), significantly decreased neuronal cell death indicating that thrombin signals ischemic damage via PAR‐1. The c‐Jun N‐terminal kinase (JNK) pathway plays an important role in excitotoxicity and cerebral ischemia and we observed activation of the JNK substrate, c‐Jun in our model. Both the FXa inhibitor, fondaparinux and the PAR‐1 antagonist SCH79797, decreased the level of phospho‐c‐Jun Ser73. These results indicate that FXa activates thrombin in cerebral ischemia, which leads via PAR‐1 to the activation of the JNK pathway resulting in neuronal death.

c-Jun N-Terminal Kinase Pathway Inhibition in Intracerebral Hemorrhage

Background: Inhibition of the c-Jun N-terminal kinase (JNK) pathway by the TAT-coupled peptide XG-102 (formerly D- JNKI1) induces strong neuroprotection in ischemic stroke in rodents. We investigated the effect of JNK inhibition in intracerebral hemorrhage (ICH). Methods: Three hours after induction of ICH by intrastriatal collagenase injection in mice, the animals received an intravenous injection of 100 µg/kg of XG-102. The neurological outcome was assessed daily and the mice were sacrificed at 6 h, 1, 2 or 5 days after ICH. Results: XG-102 administration significantly improved the neurological outcome at 1 day (p < 0.01). The lesion volume was significantly decreased after 2 days (29 ± 11 vs. 39 ± 5 mm3 in vehicle-treated animals, p < 0.05). There was also a decreased hemispheric swelling (14 ± 13 vs. 26 ± 9% in vehicle-treated animals, p < 0.05) correlating with increased aquaporin 4 expression. Conclusions: XG-102 attenuates cerebral edema in ICH and functional impairment at early time points. The beneficial effects observed with XG-102 in ICH, as well as in ischemic stroke, open the possibility to rapidly treat stroke patients before imaging, thereby saving precious time.

Improved long-term outcome after transient cerebral ischemia in aquaporin-4 knockout mice:

A hallmark of stroke is water accumulation (edema) resulting from dysregulation of osmotic homeostasis. Brain edema contributes to tissue demise and may lead to increased intracranial pressure and lethal herniation. Currently, there are only limited treatments to prevent edema formation following stroke. Aquaporin 4 (AQP4), a brain water channel, has become a focus of interest for therapeutic approaches targeting edema. At present, there are no pharmacological tools to block AQP4. The role of AQP4 in edema after brain injury remains unclear with conflicting results from studies using AQP4−/− mice and of AQP4 expression following stroke. Here, we studied AQP4 and its role in edema formation by testing AQP4−/− mice in a model of middle cerebral artery occlusion using novel quantitative MRI water content measurements, histology and behavioral changes as outcome measures. Absence of AQP4 was associated with decreased mortality and increased motor recovery 3 to 14 days after stroke. Behavioral improvement was associated with decreased lesion volume, neuronal cell death and neuroinflammation in AQP4−/− compared to wild type mice. Our data suggest that the lack of AQP4 confers an overall beneficial role at long term with improved neuronal survival and reduced neuroinflammation, but without a direct effect on edema formation.

Homer1 Scaffold Proteins Govern Ca2+ Dynamics in Normal and Reactive Astrocytes

Abstract In astrocytes, the intracellular calcium (Ca2+) signaling mediated by activation of metabotropic glutamate receptor 5 (mGlu5) is crucially involved in the modulation of many aspects of brain physiology, including gliotransmission. Here, we find that the mGlu5‐mediated Ca2+ signaling leading to release of glutamate is governed by mGlu5 interaction with Homer1 scaffolding proteins. We show that the long splice variants Homer1b/c are expressed in astrocytic processes, where they cluster with mGlu5 at sites displaying intense local Ca2+ activity. We show that the structural and functional significance of the Homer1b/c‐mGlu5 interaction is to relocate endoplasmic reticulum (ER) to the proximity of the plasma membrane and to optimize Ca2+ signaling and glutamate release. We also show that in reactive astrocytes the short dominant‐negative splice variant Homer1a is upregulated. Homer1a, by precluding the mGlu5‐ER interaction decreases the intensity of Ca2+ signaling thus limiting the intensity and the duration of glutamate release by astrocytes. Hindering upregulation of Homer1a with a local injection of short interfering RNA in vivo restores mGlu5‐mediated Ca2+ signaling and glutamate release and sensitizes astrocytes to apoptosis. We propose that Homer1a may represent one of the cellular mechanisms by which inflammatory astrocytic reactions are beneficial for limiting brain injury.

Risk factor impact on blood flow velocities and clinical outcomes of stented cervical and intracranial stenoses: preliminary observations

OBJECTIVES The role of angioplasty/stenting procedures, neurointerventionist experience, vascular risk factors, medical treatment and blood flow velocities were analysed to identify possible causes of intra-stent restenosis (ISR) following stenting of cervical and/or intracranial arteries, assuming progressive atherosclerosis to be the shared mechanism in both territories. Patients. 26 cerebrovascular patients subjected to stenting of severe (≥85%) symptomatic or asymptomatic carotid stenoses or moderate-to-severe (≥50%) intracranial or vertebral stenoses were included. METHODS Clinical, radiological and ultrasonographic follow-up data were analysed retrospectively. RESULTS Overall, stenting of the internal carotid artery (ICA) induced significant reductions in peak systolic velocities at 2 years (96±31 cm/s vs. 358.2±24.9 cm/s at baseline). The procedure-related ischemic complications rate was 7.4% (one hemispheric stroke and one TIA). The rate of ISR≤50% was 8% in the ICA at 2 years; was 50% in the common carotid artery (CCA) at 1 year, with concomitant distal ICA stenosis in 75% of CCA stenting, but all ISR were asymptomatic. Patients with ISR of the ICA were significantly younger (56.8±4.5 vs. 71.3±3.6 years, P=0.042) and had significantly more risk factors (5.5±0.9 vs. 3±0.3, P=0.012). No ISR≥70% was detected. CONCLUSIONS ISR is relatively infrequent and, when present, it is mild and asymptomatic. Restenosis is more frequent in younger patients and those with several risk factors, and it may also be related to stenting of previous carotid endarterectomy.

Increase of aquaporin 9 expression in astrocytes participates in astrogliosis

Here we assess the potential functional role of increased aquaporin 9 (APQ9) in astrocytes. Increased AQP9 expression was achieved in primary astrocyte cultures by transfection of a plasmid‐containing green fluorescent protein fused to either wild‐type or mutated human AQP9. Increased AQP9 expression and phosphorylation at Ser222 were associated with a significant change in astrocyte morphology, mainly with a higher number of processes. Similar phenotypic changes are observed in astrogliosis processes after injury. In parallel, we observed that in vivo, thrombin preconditioning before ischemic stroke induced an early increase in AQP9 expression in the male mouse brain. This increased AQP9 expression was also associated with astrocyte morphological changes, especially in the white matter tract. Astrocyte reactivity is debated as being either beneficial or deleterious. As thrombin preconditioning leads to a decrease in lesion size after stroke, our data suggest that the early increase in AQP9 concomitant with astrocyte reactivity leads to a beneficial effect.