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

Abstract

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.

Original article Effects of hypothermia on ex vivo microglial production of pro- and anti-inflammatory cytokines and nitric oxide in hypoxic-ischemic brain-injured mice

“…In addition, an ex vivo culture of microglia isolated from CNS preserves the in vivo phenotype of microglia [18,51]. Importantly, as mentioned above, in terms of the temporal changes of neuroinflammatory responses, our present ex vivo findings, as well as our previous in vitro findings [33][34][35][36], appear to be similar to the in vivo findings for brain injury [9,11], as well as to those regarding IL-10 in vivo, which indicate that the levels in the brain show a peak during the first days (24-48 h) after brain injury [6,14,25]. Temporal similarity between the ex vivo and in vivo expressions of a signalling molecule in microglia has also been reported [12,51].…”

“…Interestingly, the concept that we proposed here and in our previous study [36] of the temporal modulation of cytokine production and/or inflammation (neuroinflammatory response) by hypothermia is associated with its neuroprotective effect is supported by the findings of two recent studies: one in animals and one in humans. In an animal model of CNS injury that was induced by cerebral ischaemia, reducing the brain temperature attenuated the early-phase (8 h) production of interleukin-1 beta (IL-1β) in the brain, and this coincided with a reduced infarct size and improved functional outcome [11]. In patients with ischemic and hemorrhagic stroke, the beneficial effects of low temperature on functional outcomes occurred within the first 24 h after the stroke onset, whereas the harmful effects of high temperatures that are associated with inflammation occurred later (in the first 48 h) [9].…”

Effect of mild hypothermia on breast cancer cells adhesion and migration

“…However, a significant reduction in IL-8 and IL-1β mRNA expression was seen in human cerebral endothelial cells exposed to IL-1β at 32ºC. In contrast to IL-1β, TNF-α is increased after application of hypothermia (32ºC) 8 h after the insult in an endothelin-1-induced transient focal cerebral ischemia model (19). Therefore, it is likely that the inhibition of ICAM-1 overexpression by mild hypothermia in injury models is a cumulative outcome due to different effects of mild hypothermia on individual inflammatory factors (such as TNF-α and IL-1β), transcription factors involved in inflammation (such as NF-κB and signal transducer and activator of transcription-3 (STAT3)).…”

“…One of the important mechanisms is that mild hypothermia inhibits the inflammation response which contributes significantly to secondary injury after ischemia (19,20). Mild hypothermia suppresses ICAM-1 overexpression and neutrophil accumulation following acid-induced lung injury (21) and experimental stroke (20,22).…”

Molecular Mechanisms Underlying the Neuroprotective Effect of Hypothermia in Cerebral Ischemia

“…Recently, more direct and dynamic inflammatory changes have been speculated to be induced by hypothermia www.intechopen.com during ischemia. And now it has become clear that the neuroinflammatory response could be detrimental and that even peripheral immune responses can be regulated by the brain (Ceulemans et al, 2011).…”