Said Hachimi-Idrissi

The dual role of the neuroinflammatory response after ischemic stroke: modulatory effects of hypothermia

Neuroinflammation is a key element in the ischemic cascade after cerebral ischemia that results in cell damage and death in the subacute phase. However, anti-inflammatory drugs do not improve outcome in clinical settings suggesting that the neuroinflammatory response after an ischemic stroke is not entirely detrimental. This review describes the different key players in neuroinflammation and their possible detrimental and protective effects in stroke. Because of its inhibitory influence on several pathways of the ischemic cascade, hypothermia has been introduced as a promising neuroprotective strategy. This review also discusses the influence of hypothermia on the neuroinflammatory response. We conclude that hypothermia exerts both stimulating and inhibiting effects on different aspects of neuroinflammation and hypothesize that these effects are key to neuroprotection.

Postischemic mild hypothermia reduces neurotransmitter release and astroglial cell proliferation during reperfusion after asphyxial cardiac arrest in rats.

The present study investigated whether postischemic mild hypothermia attenuates the ischemia-induced striatal glutamate (GLU) and dopamine (DA) release, as well as astroglial cell proliferation in the brain. Anesthetized rats were exposed to 8 min of asphyxiation, including 5 min of cardiac arrest. The cardiac arrest was reversed to restoration of spontaneous circulation (ROSC), by brief external heart massage and ventilation within a period of 2 min. After the insult and during reperfusion, the extracellular glutamate and dopamine overflow increased to, respectively, 3000% and 5000% compared with the baseline values in the normothermic group and resulted in brain damage, ischemic neurons and gliosis. However, when hypothermia was induced for a period of 60 min after the insult and restoration of spontaneous circulation, the glutamate and dopamine overflows were not significantly different from that in the sham group. Histological analysis of the brain showed that postischemic mild hypothermia reduced brain damage, ischemic neurons, as well as astroglial cell proliferation. Thus, postischemic mild hypothermia reduces the excitotoxic process, brain damage, as well as astroglial cell proliferation during reperfusion. Moreover, these results emphasize the trigger effect of dopamine on the excitotoxic pathway.

Effect of resuscitative mild hypothermia on glutamate and dopamine release, apoptosis and ischaemic brain damage in the endothelin-1 rat model for focal cerebral ischaemia

The relationship between glutamate and dopamine release, apoptosis and ischaemic damage was studied following induction of transient focal cerebral ischaemia under normothermic (37°C) and postischaemic (resuscitative) mild hypothermic (34°C for 2u2003h) conditions in sevoflurane anaesthetized male Wistar rats. Focal ischaemia was induced by infusing endothelin‐1 adjacent to the middle cerebral artery. In vivo microdialysis was used to sample glutamate and dopamine from striatum and parietal cortex of the ipsilateral hemisphere. The volume of ischaemic damage and the degree of apoptosis were determined 24 h after the insult. In both striatum and cortex of the normothermic group an initial increase in extracellular glutamate and dopamine levels following endothelin‐1 infusion was observed. Striatal glutamate levels remained enhanced (250% of baseline) throughout the experiment, while the other neurotransmitter levels returned to baseline values. Hypothermia significantly attenuated the endothelin‐1 induced glutamate release in the striatum. It also reduced apoptosis and infarct volume in the cortex. These results indicate that: (i) postischaemic mild hypothermia exerts its neuroprotective effect by inhibiting apoptosis in the ischaemic penumbral region; and (ii) this effect is not associated with an attenuation of glutamate or dopamine release in the cortex.

Post-ischaemic mild hypothermia inhibits apoptosis in the penumbral region by reducing neuronal nitric oxide synthase activity and thereby preventing endothelin-1-induced hydroxyl radical formation.

Previously, we showed that treatment with resuscitative, post‐ischaemic mild hypothermia (34u2003°C for 2u2003h) reduced apoptosis in the penumbra (cortex), but not in the core (striatum) of an endothelin‐1 (Et‐1)‐induced focal cerebral infarct in the anaesthetized rat. Therefore, the purpose of this study was to investigate by which pathways resuscitative mild hypothermia exerts its neuroprotective effect in this model. The amino acids glutamate, serine, glutamine, alanine, taurine, arginine and the NO‐related compound citrulline were sampled from the striatum and cortex of the ischaemic hemisphere using in vivo microdialysis. The in vivo salicylate trapping method was applied for monitoring hydroxyl radical formation via 2,3 dihydroxybenzoic acid (2,3 DHBA) detection. Caspase‐3, neuronal nitric oxide synthase (nNOS) immunoreactivity and the volume of ischaemic damage were determined 24u2003h after the insult. In both the striatum and the cortex, Et‐1‐induced increases in glutamate, taurine and alanine were refractory to mild hypothermia. However, mild hypothermia significantly attenuated the ischaemia‐induced 2,3 DHBA levels and the nNOS immunoreactivity in the cortex, but not in the striatum. These observations were associated with a decreased caspase‐3 immunoreactivity. These results suggest that mild hypothermia exerts its neuroprotective effect in the penumbra partially by reducing nNOS activity and thereby preventing oxidative stress. Furthermore, we confirm our previous findings that the neuroprotective effect of resuscitative hypothermia is not mediated by changes in ischaemia‐induced amino acid release as they could not be associated with the ischaemia‐induced damage in the Et‐1 rat model.

Mild hypothermia causes differential, time- dependent changes in cytokine expression and gliosis following endothelin-1-induced transient focal cerebral ischemia

BackgroundStroke is an important cause of morbidity and mortality and few therapies exist thus far. Mild hypothermia (33°C) is a promising neuroprotective strategy to improve outcome after ischemic stroke. However, its complete mechanism of action has not yet been fully elaborated. This study is the first to investigate whether this neuroprotection occurs through modulation of the neuroinflammatory response after stroke in a time-dependent manner.MethodsThe Endothelin-1 (Et-1) model was used to elicit a transient focal cerebral ischemia in male Wistar rats. In this model, the core and penumbra of the insult are represented by the striatum and the cortex respectively. We assessed the effects of 2 hours of hypothermia, started 20 minutes after Et-1 injection on neurological outcome and infarct volume. Furthermore, pro- and anti-inflammatory cytokine expression was determined using ELISA. Microgliosis and astrogliosis were investigated using CD-68 and GFAP staining respectively. All parameters were determined 8, 24, 72 hours and 1 week after the administration of Et-1.ResultsEt-1 infusion caused neurological deficit and a reproducible infarct size which increased up to 3 days after the insult. Both parameters were significantly reduced by hypothermia. The strongest reduction in infarct volume with hypothermia, at 3 days, corresponded with increased microglial activation. Reducing the brain temperature affected the stroke induced increase in interleukin-1β and tumor necrosis factor α in the striatum, 8 hours after its induction, but not at later time points. Transforming growth factor β increased as a function of time after the Et-1-induced insult and was not influenced by cooling. Hypothermia reduced astrogliosis at 1 and 3 days after stroke onset.ConclusionsThe beneficial effects of hypothermia after stroke on infarct volume and functional outcome coincide with a time-dependent modulation of the cytokine expression and gliosis.

Long-term functioning following whiplash injury: the role of social support and personality traits

Transition from acute whiplash injury to either recovery or chronicity and the development of chronic whiplash-associated disorders (WAD) remains a challenging issue for researchers and clinicians. The roles of social support and personality traits in long-term functioning following whiplash have not been studied concomitantly. The present study aimed to examine whether social support and personality traits are related to long-term functioning following whiplash. One hundred forty-three subjects, who had experienced a whiplash injury in a traffic accident 10–26xa0months before the study took place, participated. The initial diagnoses were a ‘sprain of the neck’ (ICD-9 code 847.0); only the outcome of grades I–III acute WAD was studied. Long-term functioning was considered within the biopsychosocial model: it was expressed in terms of disability, functional status, quality of life and psychological well-being. Participants filled out a set of questionnaires to measure the long-term functioning parameters (i.e. the Neck Disability Index, Medical Outcome Study Short-Form General Health Survey, Anamnestic Comparative Self-Assessment measure of overall well-being and the Symptom Checklist-90) and potential determinants of long-term functioning (the Dutch Personality Questionnaire and the Social Support List). The results suggest that social support (especially the discrepancies dimension of social support) and personality traits (i.e. inadequacy, self-satisfaction and resentment) are related to long-term functioning following whiplash injury (Spearman rho varied between 0.32 and 0.57; pu2009<u20090.01). Within the discrepancy dimension, everyday emotional support, emotional support during problems, appreciative support and informative support were identified as important correlates of long-term functioning. Future prospective studies are required to confirm the role of social support and personality traits in relation to long-term functioning following whiplash. For such studies, a broad view of long-term functioning within the biopsychological model should be applied.

Mild hypothermia reduces activated caspase-3 up to 1 week after a focal cerebral ischemia induced by endothelin-1 in rats.

Hypothermia is a promising neuroprotective therapy that has been shown to reduce apoptosis after an ischemic insult. This study evaluated the effect of mild hypothermia on activated caspase-3 up to 1 week after the induction of a stroke. Endothelin-1 (Et-1) was used to elicit transient focal cerebral ischemia in rats. Twenty minutes after the ischemic insult, a state of mild hypothermia (33°C) was imposed for a duration of 2h. The functional outcome, infarct volume and activated caspase-3 immunoreactivity (IR) were assessed at 8, 24 and 72h, and one week after the insult. During the experiment the cerebral blood flow (CBF) was measured via Laser Doppler Flowmetry. Hypothermia improved the neurological outcome at all of the time points studied compared to the normothermic group, and was associated with a reduction in infarct volume. In both groups, activated caspase-3 IR peaked 24h after the Et-1 induced insult and hypothermia significantly reduced the number of apoptotic cells at 8h, 24h and 1 week after ischemia. Furthermore, the hypothermic treatment did not affect the CBF in the Et-1 model. These findings indicate that in the Et-1 model, hypothermia exerts a long lasting effect on stroke-induced apoptosis.

The neuroprotective effect of post ischemic brief mild hypothermic treatment correlates with apoptosis, but not with gliosis in endothelin-1 treated rats

BackgroundStroke remains one of the most common diseases with a serious impact on quality of life but few effective treatments exist. Mild hypothermia (33°C) is a promising neuroprotective therapy in stroke management. This study investigated whether a delayed short mild hypothermic treatment is still beneficial as neuroprotective strategy in the endothelin-1 (Et-1) rat model for a transient focal cerebral ischemia. Two hours of mild hypothermia (33°C) was induced 20, 60 or 120u2009minutes after Et-1 infusion. During the experiment the cerebral blood flow (CBF) was measured via Laser Doppler Flowmetry in the striatum, which represents the core of the infarct. Functional outcome and infarct volume were assessed 24u2009hours after the insult. In this sub-acute phase following stroke induction, the effects of the hypothermic treatment on apoptosis, phagocytosis and astrogliosis were assessed as well. Apoptosis was determined using caspase-3 immunohistochemistry, phagocytic cells were visualized by CD-68 expression and astrogliosis was studied by glial fibrillary acidic protein (GFAP) staining.ResultsCooling could be postponed up to 1u2009hour after the onset of the insult without losing its positive effects on neurological deficit and infarct volume. These results correlated with the caspase-3 staining. In contrast, the increased CD-68 expression post-stroke was reduced in the core of the insult with all treatment protocols. Hypothermia also reduced the increased levels of GFAP staining, even when it was delayed up to 2u2009hours after the insult. The study confirmed that the induction of the hypothermia treatment in the Et-1 model does not affect the CBF.ConclusionsThese data indicate that in the Et-1 rat model, a short mild hypothermic treatment delayed for 1u2009hour is still neuroprotective and correlates with apoptosis. At the same time, hypothermia also establishes a lasting inhibitory effect on the activation of astrogliosis.

Recruitment bias in chronic pain research: whiplash as a model

In science findings which cannot be extrapolated to other settings are of little value. Recruitment methods vary widely across chronic whiplash studies, but it remains unclear whether this generates recruitment bias. The present study aimed to examine whether the recruitment method accounts for differences in health status, social support, and personality traits in patients with chronic whiplash-associated disorders (WAD). Two different recruitment methods were compared: recruiting patients through a local whiplash patient support group (group 1) and local hospital emergency department (group 2). The participants (nu2009=u2009118) filled in a set of questionnaires: the Neck Disability Index, Medical Outcome Study Short-Form General Health Survey, Anamnestic Comparative Self-Assessment measure of overall well-being, Symptom Checklist-90, Dutch Personality Questionnaire, and the Social Support List. The recruitment method (either through the local emergency department or patient support group) accounted for the differences in insufficiency, somatization, disability, quality of life, self-satisfaction, and dominance (all p values <.01). The recruitment methods generated chronic WAD patients comparable for psychoneurotism, social support, self-sufficiency, (social) inadequacy, rigidity, and resentment (pu2009>u2009.01). The recruitment of chronic WAD patients solely through patient support groups generates bias with respect to the various aspects of health status and personality, but not social support. In order to enhance the external validity of study findings, chronic WAD studies should combine a variety of recruitment procedures.

Neuroprotective effect of N‐acetyl‐aspartyl‐glutamate in combination with mild hypothermia in the endothelin‐1 rat model of focal cerebral ischaemia

Previously we showed that treatment with mild hypothermia (34°C for 2u2003h) after a focal cerebral infarct was neuroprotective by reducing apoptosis in the penumbra (cortex), but not in the core (striatum) of the infarct. In this study we examined whether administration of N‐acetyl‐aspartyl‐glutamate (NAAG) in combination with mild hypothermia could improve striatal neuroprotection in the endothelin‐1 rat model. NAAG (10u2003mg/kg i.p.) was injected under normothermic (37°C) or mild hypothermic conditions, either 40u2003min before or 20u2003min after the insult. NAAG reduced caspase 3 immunoreactivity in the striatum, irrespective of the time of administration and brain temperature. This neuroprotective effect could be explained, at least partially, by decreased nitric oxide synthase activity in the striatum and was blocked by the group II metabotropic glutamate receptor antagonist, LY341495. Hypothermia applied together with NAAG reduced both cortical and striatal caspase 3 immunoreactivity, as well as the overall ischaemic damage in these areas. However, no pronounced improvement was seen in total damaged brain volume. Extracellular glutamate levels did not correlate with the observed protection, whatever treatment protocol was applied. We conclude that treatment with NAAG causes the same degree of neuroprotection as treatment with hypothermia. Combination of the two treatments, although reducing apoptosis, does not considerably improve ischaemic damage.