Efficacy of mild hypothermia (35°C) and moderate hypothermia (33°C) with and without magnesium when administered 30min post-reperfusion after 90min of middle cerebral artery occlusion in Spontaneously Hypertensive rats

A Systematic Review and Meta-Analysis of Therapeutic Hypothermia and Pharmacological Cotherapies in Animal Models of Ischemic Stroke

Therapeutic hypothermia (TH) lessens ischemic brain injury. Cytoprotective agents can augment protection, although it is unclear which combinations are most effective. The objective of this study is to identify which cytoprotective drug works best with delayed TH. Following PRISMA guidelines, a systematic review (PubMed, Web of Science, MEDLINE, Scopus) identified controlled experiments that used an in vivo focal ischemic stroke model and evaluated the efficacy of TH (delay of ≥1 hour) coupled with cytoprotective agents. This combination was our main intervention compared with single treatments with TH, drug, or no treatment. Endpoints were brain injury and neurological impairment. The CAMARADES checklist for study quality and the SYRCLE's risk of bias tool gauged study quality. Twenty-five studies were included. Most used young, healthy male rats, with only one using spontaneously hypertensive rats. Two studies used mice models, and six used adult animals. Study quality was moderate (median score = 6), and risk of bias was high. Pharmacological agents provided an additive effect on TH for all outcomes measured. Magnesium coupled with TH had the greatest impact compared with other agent-TH combinations on all outcomes. Longer TH durations improved both behavioral and histological outcomes and had greater cytoprotective efficacy than shorter durations. Anti-inflammatories were the most effective in reducing infarction (standardized mean difference [SMD]: -1.64, confidence interval [CI]: [-2.13, -1.15]), sulfonylureas reduced edema the most (SMD: -2.32, CI: [-3.09, -1.54]), and antiapoptotic agents improved behavioral outcomes the most (normalized mean difference: 52.38, CI: [45.29, 59.46]). Statistically significant heterogeneity was observed (I2 = 82 - 98%, all p < 0.001), indicating that studies wildly differ in their effect size estimates. Our results support the superiority of adding cytoprotective therapies with TH (vs. individual or no therapy). Additional exploratory and confirmatory studies are required to identify and thoroughly assess combination therapies owing to limited work and inconsistent translational quality.

Efficacy analysis of mechanical thrombectomy combined with prolonged mild hypothermia in the treatment of acute middle cerebral artery occlusion: a single-center retrospective cohort study

Objective

To determine the efficacy of mechanical thrombectomy combined with prolonged mild hypothermia compared with conventional treatment in managing acute middle cerebral artery occlusion, and to explore whether extending the duration of hypothermia can improve neurological function.

Method

From 2018 to June 2023, a retrospective analysis was conducted on 45 patients with acute middle cerebral artery occlusion treated at the NICU of Suzhou Kowloon Hospital, affiliated with Shanghai Jiao Tong University School of Medicine. After thrombectomy, patients were admitted to the neurological intensive care unit (NICU) for targeted temperature management. Patients were divided into two groups: the mild hypothermia group (34.5-35.9°C) receiving 5-7 days of treatment, and the normothermia group (control group) whose body temperature was kept between 36 and 37.5°C using pharmacological and physical cooling methods. Baseline characteristics and temperature changes were compared between the two groups of patients. The primary outcome was the modified Rankin Scale (mRS) score at 3 month after surgery, and the secondary outcomes were related complications and mortality rate. Prognostic risk factors were investigated using both univariate and multivariate logistic regression analyses.

Results

Among 45 patients, 21 underwent prolonged mild hypothermia, and 24 received normothermia, with no significant differences in baseline characteristics between the two groups. The duration of mild hypothermia ranged from 5 to 7 days. The incidence of chills (33.3% vs. 8.3%, p = 0.031) and constipation (57.1% vs. 20.8%, p = 0.028) was significantly higher in the mild hypothermia group compared with the control group. There was no significant difference in mortality rates between the mild hypothermia and the control group (4.76% vs. 8.33%, p = 1.000, OR = 1.75, 95% CI, 0.171-17.949). At 3 month, there was no significant difference in the modified mRS (0-3) score between the mild hypothermia and control groups (52.4% vs. 25%, p = 0.114, OR = 0.477, 95% CI, 0.214-1.066). Infarct core volume was an independent risk factor for adverse neurological outcomes.

Conclusion

Prolonged mild hypothermia following mechanical thrombectomy had no severe complications and shows a trend to improve the prognosis of neurological function. The Infarct core volume on CTP was an independent risk factor for predicting neurological function.

Research hotpots and frontier trends of neuroprotective effects of magnesium from 1999 to 2023: A bibliometric analysis

BACKGROUND

The neuroprotective effect of magnesium has been widely discussed, and its effectiveness has been confirmed by animal and clinical trials. However, there are still difficulties in clinical translation in diseases such as cerebral ischemia and subarachnoid hemorrhage. Therefore, it is necessary to analyze the literatures about neuroprotection of magnesium to reveal a more comprehensive knowledge framework, research hotspots and trends in the future.

METHODS

Original articles and reviews related to neuroprotective effects of magnesium from 1999 to 2022 were retrieved from the Web of Science Core Collection (WoSCC). The bibliometrics CiteSpace 6.2.R4 software was used to conduct co-occurrence/co-citation network analysis and plot knowledge visualization maps.

RESULTS

A total of 762 articles from 216 institutions in 64 countries were included in this study. The United States had the largest number of publications, followed by China and Canada. The University of California, UDICE-French Research Universities, and the University of Adelaide were the top three institutions in publication volume. Crowther Caroline A was the most published and cited author. Among the top 10 cited articles, there were seven articles on neuroprotection in preterm infants and three on acute stroke. Keyword cluster analysis obtained 11 clusters, showing that current research hotspots focused on magnesium therapy in neurovascular diseases such as cerebral ischemia, spinal cord injury, subarachnoid hemorrhage, and emerging treatment strategies.

CONCLUSION

The neuroprotective effects of magnesium in preterm infants have been extensively studied and adequately confirmed. The therapeutic effects of magnesium on cerebral ischemia and subarachnoid hemorrhage have been demonstrated in animal models. However, the results of clinical studies were not satisfactory, and exploring new therapeutic strategies may be the solution. Recently, the combination of magnesium and hypothermia had great potential in neuroprotective therapy and may become a development trend and hotspot in the future.

The Association of Serum Magnesium Levels and QT Interval with Neurological Outcomes After Targeted Temperature Management

Targeted temperature management (TTM) is associated with corrected QT (QTc) prolongation and decrease in serum magnesium (Mg) levels that may lead to recurrent ventricular arrhythmia and poor neurological outcomes. We aimed to evaluate the association between QTc interval and Mg levels during TTM with neurological outcomes. We reviewed the electrocardiograms of 366 patients who underwent TTM during the induction, maintenance, and rewarming phase after cardiac arrest. We reviewed the association of change in QTc interval, and Mg levels with neurological outcomes. In total, 71.3% of the patients had a significant increase in QTc interval defined as >60 ms or any QTc >500 ms during TTM. Poor neurological outcome was associated with persistent prolongation of QTc after rewarming (507 vs. 483 ms, p = 0.046) and higher Mg levels at presentation (2.08 ± 0.41 mg/dL, p = 0.014). Supplemental Mg did not have any significant change in their QTc. Patients with prolonged QTc during TTM should be promptly evaluated for QTc-prolonging factors given its association with worse neurological outcomes. The inverse correlation between Mg levels and poor neurological outcomes deserves further investigation.

Neuroprotective effect of epidermal growth factor plus growth hormone-releasing peptide-6 resembles hypothermia in experimental stroke

BACKGROUND

Combined therapy with epidermal growth factor (EGF) and growth hormone-releasing peptide 6 (GHRP-6) in stroke models has accumulated evidence of neuroprotective effects from several studies, but needs further support before clinical translation. Comparing EGF + GHRP-6 to hypothermia, a gold neuroprotection standard, may contribute to this purpose.

OBJECTIVES

The aims of this study were to compare the neuroprotective effects of a combined therapy based on EGF + GHRP-6 with hypothermia in animal models of (a) global ischemia representing myocardial infarction and (b) focal brain ischemia representing ischemic stroke.

METHODS

(a) Global ischemia was induced in Mongolian gerbils by a 15-min occlusion of both carotid arteries, followed by reperfusion. (b) Focal brain ischemia was achieved by intracerebral injection of endothelin 1 in Wistar rats. In each experiment, three ischemic treatment groups - vehicle, EGF + GHRP-6, and hypothermia - were compared to each other and to a sham-operated control group. End points were survival, neurological scores, and infarct volume.

RESULTS

(a) In global ischemia, neurological score at 48-72 h, infarct volume, and neuronal density of hippocampal CA1 zone in gerbils treated with EGF + GHRP-6 were similar to the hypothermia-treated group. (b) In focal ischemia, the neurologic score and infarct volume of rats receiving EGF + GHRP-6 were also similar to animals in the hypothermia group.

DISCUSSION

With hypothermia being a good standard neuroprotectant reference, these results provide additional proof of principle for EGF and GHRP-6 co-administration as a potentially neuroprotective stroke therapy.

Novel method for inducing rapid, controllable therapeutic hypothermia in rats using a perivascular implanted closed-loop cooling circuit

BACKGROUND

Hypothermia is the most potent protective therapy available for cerebral ischemia. In experimental models, cooling the brain even a single degree Celsius alters outcome after global and focal ischemia. Difficulties translating therapeutic hypothermia to patients with stroke or after cardiac arrest include: uncertainty as to the optimal treatment duration; best target-depth temperature; and longest time delay after which therapeutic hypothermia won't benefit. Recent results from human clinical trials suggest that cooling with surface methods provides insufficient cooling speed or control over target temperature.

COMPARISON WITH EXISTING METHODS

Available animal models incorporate surface cooling methods that are slow, and do not allow for precise control of the target temperature.

NEW METHOD

To address this need, we developed a rapid, simple, inexpensive model for inducing hypothermia using a perivascular implanted closed-loop cooling circuit. The method allows precise control of the target temperature.

RESULTS

Using this method, target temperature for therapeutic hypothermia was reached within 13±1.07min (Mean±SE). Once at target, the temperature was maintained within 0.09°C for 4h.

CONCLUSIONS

This method will allow future experiments to determine under what conditions therapeutic hypothermia is effective, determine the optimal relationship among delay, duration, and depth, and provide the research community with a new model for conducting further research into mechanistic questions underlying the efficacy of therapeutic hypothermia.

Very Mild Hypothermia (35°C) Postischemia Reduces Infarct Volume and Blood/Brain Barrier Breakdown Following tPA Treatment in the Mouse

Reperfusion therapies for stroke diminish in effectiveness and safety as time to treatment increases. Hypothermia neuroprotection for stroke is established, but its clinical translation has been hampered by uncertainties regarding optimal temperature and complications associated with moderate hypothermia. Also, hypothermia targeting temperatures of 32-33°C is associated with clinical and logistical problems related to induction and adverse side effects. We hypothesized that ischemic damage and tPA-exacerbated blood/brain barrier (BBB) breakdown produced following 30 minutes of middle cerebral artery occlusion and either 1 hour of saline or tPA infusion would be reduced by treatment with very mild cooling of 1.5°C for 48 hours followed by 24 hours of gradual rewarming. Infarct volume was reduced by 29.6% (p<0.001) and 41.9% (p<0.001) in hypothermic-tPA (Hypo_tPA)-treated and hypothermic-saline (Hypo_Sal)-treated animals compared to normothermic-tPA (Norm_tPA) and saline (Norm_Sal)-treated animals, respectively. Hypothermia also reduced IgG extravasation in tPA-treated, but not saline-treated groups compared to their normothermic controls (p<0.001). The ipsilateral-contralateral changes in optical density for IgG extravasation were 18.4% greater in the Norm_tPA than Norm_Sal (p<0.001) group. The ipsilateral-contralateral changes in optical density for IgG extravasation were reduced by 17.8% (p<0.001) in the Hypo_tPA compared to Norm_tPA group. No significant mean difference in IgG extravasation was seen between Hypo_tPA and Hypo_Sal groups (p>0.05). Very modest hypothermia to reduce the BBB breakdown could improve the availability and safety of reperfusion treatments for stroke.

Combination therapy of human umbilical cord blood cells and granulocyte colony stimulating factor reduces histopathological and motor impairments in an experimental model of chronic traumatic brain injury

Traumatic brain injury (TBI) is associated with neuro-inflammation, debilitating sensory-motor deficits, and learning and memory impairments. Cell-based therapies are currently being investigated in treating neurotrauma due to their ability to secrete neurotrophic factors and anti-inflammatory cytokines that can regulate the hostile milieu associated with chronic neuroinflammation found in TBI. In tandem, the stimulation and mobilization of endogenous stem/progenitor cells from the bone marrow through granulocyte colony stimulating factor (G-CSF) poses as an attractive therapeutic intervention for chronic TBI. Here, we tested the potential of a combined therapy of human umbilical cord blood cells (hUCB) and G-CSF at the acute stage of TBI to counteract the progressive secondary effects of chronic TBI using the controlled cortical impact model. Four different groups of adult Sprague Dawley rats were treated with saline alone, G-CSF+saline, hUCB+saline or hUCB+G-CSF, 7-days post CCI moderate TBI. Eight weeks after TBI, brains were harvested to analyze hippocampal cell loss, neuroinflammatory response, and neurogenesis by using immunohistochemical techniques. Results revealed that the rats exposed to TBI treated with saline exhibited widespread neuroinflammation, impaired endogenous neurogenesis in DG and SVZ, and severe hippocampal cell loss. hUCB monotherapy suppressed neuroinflammation, nearly normalized the neurogenesis, and reduced hippocampal cell loss compared to saline alone. G-CSF monotherapy produced partial and short-lived benefits characterized by low levels of neuroinflammation in striatum, DG, SVZ, and corpus callosum and fornix, a modest neurogenesis, and a moderate reduction of hippocampal cells loss. On the other hand, combined therapy of hUCB+G-CSF displayed synergistic effects that robustly dampened neuroinflammation, while enhancing endogenous neurogenesis and reducing hippocampal cell loss. Vigorous and long-lasting recovery of motor function accompanied the combined therapy, which was either moderately or short-lived in the monotherapy conditions. These results suggest that combined treatment rather than monotherapy appears optimal for abrogating histophalogical and motor impairments in chronic TBI.

Evidence for the therapeutic efficacy of either mild hypothermia or oxygen radical scavengers after repetitive mild traumatic brain injury

Repetitive brain injury, particularly that occurring with sporting-related injuries, has recently garnered increased attention in both the clinical and public settings. In the laboratory, we have demonstrated the adverse axonal and vascular consequences of repetitive brain injury and have demonstrated that moderate hypothermia and/or FK506 exerted protective effects after repetitive mild traumatic brain injury (mTBI) when administered within a specific time frame, suggesting a range of therapeutic modalities to prevent a dramatic exacerbation. In this communication, we revisit the utility of targeted therapeutic intervention to seek the minimal level of hypothermia needed to achieve protection while probing the role of oxygen radicals and their therapeutic targeting. Male Sprague-Dawley rats were subjected to repetitive mTBI by impact acceleration injury. Mild hypothermia (35 °C, group 2), superoxide dismutase (group 3), and Tempol (group 4) were employed as therapeutic interventions administered 1  h after the repetitive mTBI. To assess vascular function, cerebral vascular reactivity to acetylcholine was evaluated 3 and 4 h after the repetitive mTBI, whereas to detect the burden of axonal damage, amyloid precursor protein (APP) density in the medullospinal junction was measured. Whereas complete impairment of vascular reactivity was observed in group 1 (without intervention), significant preservation of vascular reactivity was found in the other groups. Similarly, whereas remarkable increase in the APP-positive axon was observed in group 1, there were no significant increases in the other groups. Collectively, these findings indicate that even mild hypothermia or the blunting free radical damage, even when performed in a delayed period, is protective in repetitive mTBI.