Role of Immune and Inflammatory Mechanisms in Stroke: A Review of Current Advances

Extreme Temperatures and Stroke Mortality: Evidence From a Multi-Country Analysis

BACKGROUND

Extreme temperatures contribute significantly to global mortality. While previous studies on temperature and stroke-specific outcomes presented conflicting results, these studies were predominantly limited to single-city or single-country analyses. Their findings are difficult to synthesize due to variations in methodologies and exposure definitions.

METHODS

Within the Multi-Country Multi-City Network, we built a new mortality database for ischemic and hemorrhagic stroke. Applying a unified analysis protocol, we conducted a multinational case-crossover study on the relationship between extreme temperatures and stroke. In the first stage, we fitted a conditional quasi-Poisson regression for daily mortality counts with distributed lag nonlinear models for temperature exposure separately for each city. In the second stage, the cumulative risk from each city was pooled using mixed-effect meta-analyses, accounting for clustering of cities with similar features. We compared temperature-stroke associations across country-level gross domestic product per capita. We computed excess deaths in each city that are attributable to the 2.5% hottest and coldest of days based on each city's temperature distribution.

RESULTS

We collected data for a total of 3 443 969 ischemic strokes and 2 454 267 hemorrhagic stroke deaths from 522 cities in 25 countries. For every 1000 ischemic stroke deaths, we found that extreme cold and hot days contributed 9.1 (95% empirical CI, 8.6-9.4) and 2.2 (95% empirical CI, 1.9-2.4) excess deaths, respectively. For every 1000 hemorrhagic stroke deaths, extreme cold and hot days contributed 11.2 (95% empirical CI, 10.9-11.4) and 0.7 (95% empirical CI, 0.5-0.8) excess deaths, respectively. We found that countries with low gross domestic product per capita were at higher risk of heat-related hemorrhagic stroke mortality than countries with high gross domestic product per capita (P=0.02).

CONCLUSIONS

Both extreme cold and hot temperatures are associated with an increased risk of dying from ischemic and hemorrhagic strokes. As climate change continues to exacerbate these extreme temperatures, interventional strategies are needed to mitigate impacts on stroke mortality, particularly in low-income countries.

Role of microglia in stroke

Microglia play key roles in the post-ischemic inflammatory response and damaged tissue removal reacting rapidly to the disturbances caused by ischemia and working to restore the lost homeostasis. However, the modified environment, encompassing ionic imbalances, disruption of crucial neuron-microglia interactions, spreading depolarization, and generation of danger signals from necrotic neurons, induce morphological and phenotypic shifts in microglia. This leads them to adopt a proinflammatory profile and heighten their phagocytic activity. From day three post-ischemia, macrophages infiltrate the necrotic core while microglia amass at the periphery. Further, inflammation prompts a metabolic shift favoring glycolysis, the pentose-phosphate shunt, and lipid synthesis. These shifts, combined with phagocytic lipid intake, drive lipid droplet biogenesis, fuel anabolism, and enable microglia proliferation. Proliferating microglia release trophic factors contributing to protection and repair. However, some microglia accumulate lipids persistently and transform into dysfunctional and potentially harmful foam cells. Studies also showed microglia that either display impaired apoptotic cell clearance, or eliminate synapses, viable neurons, or endothelial cells. Yet, it will be essential to elucidate the viability of engulfed cells, the features of the local environment, the extent of tissue damage, and the temporal sequence. Ischemia provides a rich variety of region- and injury-dependent stimuli for microglia, evolving with time and generating distinct microglia phenotypes including those exhibiting proinflammatory or dysfunctional traits and others showing pro-repair features. Accurate profiling of microglia phenotypes, alongside with a more precise understanding of the associated post-ischemic tissue conditions, is a necessary step to serve as the potential foundation for focused interventions in human stroke.

Long-term Risk of Stroke in Patients With Inflammatory Bowel Disease: A Population-Based, Sibling-Controlled Cohort Study, 1969-2019

BACKGROUND AND OBJECTIVES

Patients with inflammatory bowel disease (IBD) are at an increased risk of thromboembolic events, but evidence on the long-term risk of stroke remains scarce. We aimed to explore whether patients with a biopsy-confirmed IBD had an increased long-term risk of stroke.

METHODS

This cohort included all patients with biopsy-confirmed IBD in Sweden between 1969 and 2019 and up to 5 matched reference individuals per patient who were randomly selected from the general population and IBD-free full siblings. The primary outcome was incident overall stroke; secondary outcomes were ischemic and hemorrhagic strokes. Stroke was identified from the Swedish National Patient Register by using both primary and secondary diagnoses. Adjusted hazard ratios (aHRs) for stroke were estimated by flexible parametric survival models.

RESULTS

A total of 85,006 patients with IBD (including Crohn disease [CD, n = 25,257], ulcerative colitis [UC, n = 47,354], and IBD-unclassified [IBD-U, n = 12,395]), 406,987 matched reference individuals, and 101,082 IBD-free full siblings were included in the analysis. We observed 3,720 incident strokes in patients with IBD (incidence rate [IR] 32.6 per 10,000 person-years) and 15,599 in reference individuals (IR 27.7; aHR 1.13, 95% CI 1.08-1.17). The elevated aHR remained increased even 25 years after diagnosis, corresponding to 1 additional stroke case per 93 patients with IBD until then. The excess aHR was mainly driven by ischemic stroke (aHR 1.14; 1.09-1.18) rather than hemorrhagic stroke (aHR 1.06; 0.97-1.15). The risk of ischemic stroke was significantly increased across IBD subtypes (CD [IR 23.3 vs 19.2; aHR 1.19; 1.10-1.29], UC [IR 25.7 vs 22.6; aHR 1.09; 1.04-1.16], and IBD-U [IR 30.5 vs 22.8; aHR 1.22; 1.08-1.37]). Similar results were found when patients with IBD were compared with their siblings.

DISCUSSION

Patients with IBD were at an increased risk of stroke, especially of ischemic events, irrespective of the IBD subtype. The excess risk persisted even 25 years after diagnosis. These findings highlight the need for clinical vigilance about the long-term excess risk of cerebrovascular events in patients with IBD.

Leukocyte indicators and variations predict worse outcomes after intravenous thrombolysis in patients with acute ischemic stroke

Leukocytes are systematic inflammation indicators related to stroke prognosis and can exhibit large dynamic waves before and after recombinant tissue plasminogen activator (r-tPA) therapy. However, additional evidence is needed to determine the prognostic significance of various leukocytes including both static and dynamic data among patients who underwent r-tPA therapy. A total of 251 patients treated with r-tPA were included; their leukocyte data were collected at two time points, and patients were followed up for three months. Analysis revealed the following findings. (i) Patients with hemorrhagic transformation (HT) and unfavorable outcomes had a higher level of leukocytes after r-tPA therapy (leukocyte count (adjusted OR (aOR) 1.191 for HT and 1.184 for unfavorable outcomes), neutrophil count (aOR 1.215 and 1.214), neutrophil-to-lymphocyte ratio (NLR; aOR 1.084 and 1.091)) and larger dynamic leukocyte changes. (ii)Among all leukocytes, the NLR after r-tPA administration demonstrated the strongest correlation with HT and unfavorable outcomes. (iii) Patients with an NLR ≥ 3.322 had a 3.492-fold increased risk for HT, and those with an NLR ≥ 5.511 had a 3.024-fold increased risk for functional outcomes. Overall, this study shows that leukocytes, especially leukocyte count, neutrophil count and the NLR, are independently associated with HT and functional outcomes in stroke patients.