Comparative analysis of the neurovascular injury and functional outcomes in experimental stroke models in diabetic Goto-Kakizaki rats

Neuroprotective Effects of Metformin in Stroke Patients: A Systematic Review and Meta-analysis of Cohort Studies

OBJECTIVES

People with diabetes are 1.5 times more likely to experience stroke than those without diabetes, underlining the urgent need to address this issue. Metformin is often the initial medication chosen to manage diabetes mellitus (DM). The purpose of our systematic review and meta-analysis is to explore the potential neuroprotective effects of metformin in individuals who have received it prior to stroke.

METHOD

Our study encompassed cohort studies that drew a comparison between the severity and diverse outcomes of stroke among individuals with DM who were administered metformin prior to the stroke event and those with DM who did not receive the treatment.

RESULTS

Ten studies met the eligibility criteria. Prestroke metformin use was associated with a significantly lower National Institutes of Health Stroke Scale score (mean difference = -1.29, 95% confidence interval: -2.11 to -0.47) in ischemic stroke. Metformin pretreatment in ischemic stroke was associated with increased odds of favorable outcome (mRS < 2) at 90 days (odds ratio [OR] = 1.45, 95% confidence interval [CI]: 1.06 to 1.99), but it was not significant at discharge. Metformin was found to be associated with reduced mortality (OR = 0.52, 95% CI: 0.42 to 0.64) in ischemic stroke. In hemorrhagic stroke, the results showed a significantly lower intracranial hemorrhage volume in prestroke metformin use (mean difference = -4.77, 95% CI: -6.56 to -2.98).

CONCLUSIONS

We found that prestroke metformin use in diabetic patients yielded neuroprotective effects. In ischemic strokes, metformin reduces stroke severity and 90-day mortality; it also improves 90-day functional outcomes. In hemorrhagic strokes, prestroke metformin use can also cause less intracranial hemorrhage volume. Further clinical trials are needed to confirm its efficacy and verify its benefits in stroke management.

Repurposing metformin: A potential off-label indication for ischaemic stroke?

The term 'clinical cemetery' is frequently used to characterize ischaemic stroke, one of the leading causes of mortality and long-term morbidity globally. Over the past two decades, a number of novel therapies have been investigated for ischaemic stroke. However, aside from mechanical thrombectomy, the only FDA-approved prescription for treating ischaemic stroke is tissue plasminogen activator, which has a limited therapeutic period. Although post-stroke rehabilitation therapies are helpful in improving functional recovery, their benefits cannot be yielded promptly. Nowadays, drug repurposing might be an appealing approach to expanding therapeutic options for ischaemic stroke. During the last decade, metformin has been extensively researched as a potential repurposing medicine for ischaemic stroke, with a focus on both preventive and therapeutic approaches. With regard to the idea of repurposing metformin in ischaemic stroke, this review aims to compile the available data from pre-clinical and clinical trials, address and clarify any discrepancies, and offer solutions.

The Role and Mechanism of Metformin in the Treatment of Nervous System Diseases

Nervous system diseases represent a significant global burden, affecting approximately 16% of the world's population and leading to disability and mortality. These conditions, encompassing both central nervous system (CNS) and peripheral nervous system (PNS) disorders, have substantial social and economic impacts. Metformin, a guanidine derivative derived from a plant source, exhibits therapeutic properties in various health conditions such as cancer, aging, immune-related disorders, polycystic ovary syndrome, cardiovascular ailments, and more. Recent studies highlight metformin's ability to cross the blood-brain barrier, stimulate neurogenesis, and provide beneficial effects in specific neurological disorders through diverse mechanisms. This review discusses the advancements in research on metformin's role and mechanisms in treating neurological disorders within both the central and peripheral nervous systems, aiming to facilitate further investigation, utilization, and clinical application of metformin in neurology.

Role of HbA1c in Mortality Among Patients With a Medical History of Ischemic Stroke and Paroxysmal Atrial Fibrillation: A Systematic Review

Elevated HbA1c, a marker of poor glycemic control, is associated with adverse cardiovascular outcomes and mortality. HbA1c influences outcomes through distinct mechanisms of vascular dysfunction and atherosclerosis in ischemic stroke, during atrial remodeling and thrombus formation in paroxysmal atrial fibrillation (PAF). Optimal HbA1c thresholds are generally below optimal levels, with levels above this being linked to higher mortality in both populations. At extremes of glycemic control in ischemic stroke, patients face recurrence and poor recovery, while PAF patients experience amplified thromboembolic risks. In patients with both conditions, poor HbA1c control synergistically raises mortality. This systematic review explores how HbA1c levels directly contribute to mortality in patients with ischemic stroke and PAF, aiming to establish a causal link between elevated HbA1c and increased mortality risk. This review includes a comprehensive analysis of four cross-sectional studies, five randomized controlled trials (RCTs), and 17 cohort studies, providing a diverse range of evidence on the topic. The inclusion of these study designs offers a well-rounded understanding of the impact and outcomes observed in the research. Mortality metrics include short-term mortality, such as 30-day or 90-day, and long-term mortality over one, three, or five years. Specific metrics, like cardiovascular mortality, focus on deaths from stroke; some studies link mortality to functional decline post-stroke, where complications from immobility or recurrent vascular events contribute to outcomes. Secondary outcomes include survival metrics, functional recovery metrics, and complications. Studies use narrative synthesis due to its ability to accommodate heterogeneity in study designs, populations, and outcome measures, enabling a nuanced interpretation of complex, context-dependent data. HbA1c levels' impact on stroke outcomes, considering age, gender, and severity, is also examined. Confounding factors, functional recovery, and complications are also considered. A narrative synthesis was chosen. The study emphasizes the importance of strict glycemic control in patients with ischemic stroke or PAF, especially those with elevated HbA1c levels. It supports clinical guidelines for individualized HbA1c targets, with most stroke patients having a target of <7%. Clinicians should prioritize close monitoring and tailor treatment plans to avoid extreme HbA1c levels, which could inform more personalized and effective treatment strategies. Tight control of HbA1c levels entails individualized targets based on patient characteristics, with an emphasis on personalized treatment strategies that may include lifestyle modifications, oral hypoglycemics, or insulin therapy to optimize glycemic control.

Chlorogenic acid ameliorates memory dysfunction via attenuating frontal lobe oxidative stress and apoptosis in diabetic rat model

Background/aim

Diabetes mellitus, characterized by hyperglycemia, causes various complications, one of which is memory dysfunction. The frontal lobe is known to be responsible for impaired memory function due to hyperglycemia and is associated with oxidative stress-mediated neuronal cell apoptosis. Chlorogenic acid (CGA) is reported to have neuroprotective effects. However, its effect on the frontal lobe in diabetes mellitus (DM) rats is not widely known. This research aimed to elucidate the effect of CGA on the mRNA expressions of SOD1, SOD2, p53, and Bcl-2 in the frontal lobe of DM rats.

Materials and methods

Thirty male Wistar rats (2-month-old, 150-200 gBW) were randomly divided into six groups: C (control), DM1.5 (1.5-month DM), DM2 (2-month DM), CGA12.5, CGA25 and CGA50 (DM+CGA 12.5, 25, and 50 mg/kgBW, respectively). A single dose of streptozotocin (60 mg/kgBW) was intraperitoneally injected. Intraperitoneal CGA injection was administered daily for DM1.5 rats for 14 days. Path length was measured in the Morris water maze (MWM) probe test. After termination, the frontal lobes were carefully harvested for RNA extraction. Reverse transcriptase PCR was performed to examine the mRNA expression of SOD1, SOD2, p53, and Bcl-2.

Results

The DM2 group demonstrated significant shorter path length on the MWM probe test and significantly lower mRNA expression of SOD1 and Bcl-2, compared to the C group. After CGA administration, the CGA25 group showed a significantly shorter path length than the C group. The CGA12.5 and CGA25 groups had significantly higher mRNA expression of SOD1 than the DM1.5 group. Compared to the DM1.5 and DM2 groups, SOD2 mRNA expression of the administration of all three CGA doses increased markedly. Furthermore, Bcl-2 mRNA expression was significantly increased in the CGA12.5 and CGA50 groups, compared with the DM2 group.

Conclusion

Chlorogenic acid might improve memory function through upregulation of frontal lobes' SOD1, SOD2, and Bcl-2 mRNA expression in DM rats.

Cellular, histological, and behavioral pathological alterations associated with the mouse model of photothrombotic ischemic stroke

BACKGROUND

Photothrombotic (PT) stroke model is a reliable method to induce ischemic stroke in the target site using the excitation of photosensitive agents such as Rose Bengal (RB) dye after light illumination. Here, we performed a PT-induced brain ischemic model using a green laser and photosensitive agent RB and confirmed its efficiency through cellular, histological, and neurobehavioral approaches.

METHODS

Mice were randomly allocated into RB; Laser irradiation; and RB + Laser irradiation groups. Mice were exposed to a green laser at a wavelength of 532 nm and intensity of 150 mW in a mouse model after injection of RB under stereotactic surgery. The pattern of Hemorrhagic and ischemic changes were evaluated throughout the study. The volume of the lesion site was calculated using unbiased stereological methods. For investigation of neurogenesis, we performed double - (BrdU/NeuN) immunofluorescence (IF) staining on day 28 following the last- BrdU injection. To assess the effect and quality of ischemic stroke on neurological behavior, the Modified neurological severity score (mNSS) test was done on days 1, 7, 14, and 28 days after stroke induction.

RESULTS

Laser irradiation plus RB induced hemorrhagic tissue and pale ischemic changes over the 5 days. In the next few days, microscopic staining revealed neural tissue degeneration, demarcated necrotic site, and neuronal injury. BrdU staining showed a significant number of proliferating cells in the periphery of the lesion site in the Laser irradiation plus RB group compared to the group (p < 0.05) while the percent of NeuN+ cells per BrdU- positive cells was reduced. Also, prominent astrogliosis was observed in the periphery of irradiated sites on day 28. Neurological deficits were detected in mice from Laser irradiation plus the RB group. No histological or functional deficits were detected in RB and Laser irradiation groups.

CONCLUSIONS

Taken together, our study showed cellular and histologic pathological changes which are associated with the PT induction model. Our findings indicated that the undesirable microenvironment and inflammatory conditions could affect neurogenesis concomitantly with functional deficits. Moreover, this research showed that this model is a focal, reproducible, noninvasive and accessible stroke model with a distinctive demarcation similar to human stroke conditions.

Intermittent fasting alleviates type 1 diabetes-induced cognitive dysfunction by improving the frontal cortical metabolic disorder

Intermittent fasting (IF) is an ecological strategy to control various metabolic disorder symptoms, but its protective effect on type 1 diabetes (T1D)-induced cognitive dysfunction and the underlying mechanisms remain poorly defined. Herein, we examined the efficacy of IF in altering the behaviors and brain metabolome in T1D mice and investigated the potential molecular mechanisms. We demonstrated that IF remarkably improved frontal cortical-dependent memory in T1D mice and reduced the loss of neuronal cells. Metabolomics and targeted mass spectrometry assay showed that IF reprogrammed the frontal cortical metabolome composition, including activated the aspartate and glutamate pathway and reversed glycerophospholipid and sphingolipid depositions in T1D mice. Mechanistically, IF attenuated the levels of oxidative stress proteins, such as NOX2, NOX4, 8-OHdG, 4-HNE, and inhibited the levels of pro-apoptotic factors Bax and cleaved Caspase-3, finally improved the memory ability of T1D mice. In vitro studies confirmed the protective effect of the supplemented N-acetylaspartate, a pivotal metabolite involved in IF-regulated T1D-induced cognitive dysfunction, in high glucose-stimulated SH-SY5Y cells by eliminating toxic lipids accumulation, oxidative stress and apoptosis. To conclude, the frontal cortical metabolites mediated the protective effects of IF against T1D-induced cognitive dysfunction by attenuating oxidative stress and apoptotic signaling. Thus, IF can be a potential therapeutic strategy for T1D-induced cognitive dysfunction.

Anti-apoptosis effect of traditional Chinese medicine in the treatment of cerebral ischemia-reperfusion injury

Cerebral ischemia, one of the leading causes of neurological dysfunction of brain cells, muscle dysfunction, and death, brings great harm and challenges to individual health, families, and society. Blood flow disruption causes decreased glucose and oxygen, insufficient to maintain normal brain tissue metabolism, resulting in intracellular calcium overload, oxidative stress, neurotoxicity of excitatory amino acids, and inflammation, ultimately leading to neuronal cell necrosis, apoptosis, or neurological abnormalities. This paper summarizes the specific mechanism of cell injury that apoptosis triggered by reperfusion after cerebral ischemia, the related proteins involved in apoptosis, and the experimental progress of herbal medicine treatment through searching, analyzing, and summarizing the PubMed and Web Of Science databases, which includes active ingredients of herbal medicine, prescriptions, Chinese patent medicines, and herbal extracts, providing a new target or new strategy for drug treatment, and providing a reference for future experimental directions and using them to develop suitable small molecule drugs for clinical application. With the research of anti-apoptosis as the core, it is important to find highly effective, low toxicity, safe and cheap compounds from natural plants and animals with abundant resources to prevent and treat Cerebral ischemia/reperfusion (I/R) injury (CIR) and solve human suffering. In addition, understanding and summarizing the apoptotic mechanism of cerebral ischemia-reperfusion injury, the microscopic mechanism of CIR treatment, and the cellular pathways involved will help to develop new drugs.

Metformin treatment and acute ischemic stroke outcomes in patients with type 2 diabetes: a retrospective cohort study

BACKGROUND AND PURPOSE

Preclinical studies have shown that metformin has neuroprotective actions in stroke. However, the optimal treatment timing and duration remain unknown. Herein, we examined the efficacy of metformin treatment on prognosis in acute ischemic stroke (AIS) patients, and assessed the optimal treatment timing and duration.

METHODS

AIS patients with type 2 diabetes mellitus were retrospectively enrolled. Patients were grouped into those who never received metformin (MET - group), those who received metformin continuously before stroke and after admission (pre-stroke + /post-stroke + group), those who only received metformin before stroke onset (pre-stroke + /post-stroke - group), and those who only received metformin after admission (pre-stroke - /post-stroke + group). The all MET + group represents the sum of the three metformin treatment groups. The efficacy outcome was the 90-day modified Rankin Scale (mRS) score.

RESULTS

In total, 309 eligible patients were included (MET - [N = 130], pre-stroke + /post-stroke + [N = 94], pre-stroke + /post-stroke - [N = 30], pre-stroke - /post-stroke + [N = 55]; all MET + [N = 179]). The all MET + group had a trend toward a lower 90-day mRS score compared with that in the MET - group (1 [0-2] vs 1 [0-3], unadjusted odds ratio [OR] = 0.652, P = 0.041; adjusted OR = 0.752, P = 0.218). In the three metformin treatment groups, only the pre-stroke + /post-stroke + group had a significantly lower 90-day mRS score (1 [0-1] vs 1 [0-3], adjusted OR = 0.497, 95%CI = 0.289-0.854; P = 0.011) and higher proportion of mRS score 0-1 (78.7% vs. 61.5%, adjusted OR = 2.278, 95%CI = 1.108-4.680; P = 0.025) than the MET - group.

CONCLUSION

AIS patients with type 2 diabetes mellitus who receive continuous metformin treatment before stroke onset and after admission have improved functional outcome at 90 days.

Apelin-13 prevents the effects of oxygen-glucose deprivation/reperfusion on bEnd.3 cells by inhibiting AKT-mTOR signaling

Autophagy plays works by degrading misfolded proteins and dysfunctional organelles and maintains intracellular homeostasis. Apelin-13 has been investigated as an agent that might protect the blood-brain barrier (BBB) from cerebral ischemia/reperfusion (I/R) injury. In this study, we examined whether apelin-13 protects cerebral microvascular endothelial cells, important components of the BBB, from I/R injury by regulating autophagy. To mimic I/R injury, the mouse cerebral microvascular endothelia l cell line bEnd 3 undergoes the process of oxygen and glucose deprivation and re feeding in the process of culture. Cell viability was detected using a commercial kit, and cell migration was monitored by in vitro scratch assay. The tight junction (TJ) proteins ZO-1 and occludin; the autophagy markers LC3 II, beclin 1, and p62; and components of the AKT-mTOR signaling pathway were detected by Western blotting and immunofluorescence. To confirm the role of autophagy in OGD/R and the protective effect of apelin-13, we treated the cells with 3-methyladenine (3-MA), a pharmacological inhibitor of autophagy. Our results demonstrated that OGD/R increased autophagic activity but decreased viability, abundance of TJs, and migration. Viability and TJ abundance were further reduced when the OGD/R group was treated with 3-MA. These results indicated that bEnd.3 upregulates autophagy to ameliorate the effects of OGD/R injury on viability and TJs, but that the autophagy induced by OGD/R alone is not sufficient to protect against the effect on cell migration. Treatment of OGD/R samples with apelin-13 markedly increased viability, TJ abundance, and migration, as well as autophagic activity, whereas 3-MA inhibited this increase, suggesting that apelin-13 exerted its protective effects by upregulating autophagy.

Acute Ischemic Stroke by Middle Cerebral Artery Occlusion in Rat Models of Diabetes: Importance of Pre-op and Post-op Care, Severity of Hyperglycemia, and Sex

Diabetes mellitus (DM) is associated with poor stroke outcomes, including high mortality and disability rates. Ischemic injury modeling large artery stroke in diabetic animals also results in high mortality and poor acute and long-term outcomes. In this chapter, we describe middle cerebral artery occlusion (MCAO) in a high-fat diet/low-dose streptozotocin (STZ) model of diabetes including details on pre-op and post-op care that improve survival rate for successful completion of the studies.

Cerebral microvascular matrix metalloproteinase-3 (MMP3) contributes to vascular injury after stroke in female diabetic rats

Diabetes exacerbates hemorrhagic transformation (HT) after stroke and worsens clinical outcomes. Female patients with diabetes are at a greater risk of stroke and worsened recovery. We have shown that activation of matrix metalloprotease 3 (MMP3) in hyperglycemic settings mediates HT in male rats. In light of our recent findings that diabetic female rats develop greater HT, the current study was designed to test the hypotheses that: 1) cerebral microvascular MMP3 activation contributes to poor functional outcomes and increased hemorrhagic transformations (HT) after ischemic stroke, and 2) MMP3 inhibition can improve functional outcomes in female diabetic rats. Female control and diabetic Wistar rats were subjected to 60 min of middle cerebral artery occlusion (MCAO). One cohort of diabetic animals received a single dose of MMP3 inhibitor (UK356618; 15 mg/kg; iv) or vehicle after reperfusion. Neurobehavioral outcomes, brain infarct size, edema, HT, and MMPs were measured in brain tissue. Diabetic rats had significant neurological deficits on Day 3 after stroke. MMP3 expression and enzyme activity were significantly increased in both micro and macro vessels of diabetic animals. MMP3 inhibition improved functional outcomes and reduced brain edema and HT scores. In conclusion, cerebral endothelial MMP3 activation to vascular injury in female diabetic rats. Our findings identify MMP3 as a potential therapeutic target in diabetic stroke.

Vascular contributions to cognitive impairment/dementia in diabetes: role of endothelial cells and pericytes

Vascular contributions to cognitive impairment/dementia (VCID) are a leading cause of dementia, a known neurodegenerative disorder characterized by progressive cognitive decline. Although diabetes increases the risks of stroke and the development of cerebrovascular disease, the cellular and vascular mechanisms that lead to VCID in diabetes are yet to be determined. A growing body of research has identified that cerebrovascular cells within the neurovascular complex display an array of cellular responses that impact their survival and reparative properties, which plays a significant role in VCID development. Specifically, endothelial cells and pericytes are the primary cell types that have gained much attention in dementia-related studies due to their molecular and phenotypic heterogeneity. In this review, we will discuss the various morphological subclasses of endothelial cells and pericytes as well as their relative distribution throughout the cerebrovasculature. Furthermore, the use of diabetic and stroke animal models in preclinical studies has provided more insight into the impact of sex differences on cerebral vascularization in progressive VCID. Understanding how cellular responses and sex differences contribute to endothelial cell and pericyte survival and function will set the stage for the development of potential preventive therapies for dementia-related disorders in diabetes.

Optimized integration of metabolomics and lipidomics reveals brain region-specific changes of oxidative stress and neuroinflammation in type 1 diabetic mice with cognitive decline

INTRODUCTION

Type 1 diabetes (T1D) causes cognitive decline and has been associated with brain metabolic disorders, but its potential molecular mechanisms remain unclear.

OBJECTIVES

The purpose of this study was to explore the molecular mechanisms underlying T1D-induced cognitive impairment using metabolomics and lipidomics.

METHODS

We developed an optimized integration approach of metabolomics and lipidomics for brain tissue based on UPLC-Q-TOF-MS and analyzed a comprehensive characterization of metabolite and lipid profiles in the hippocampus and frontal cortex of T1D male mice with cognitive decline (T1DCD) and age-matched control (CONT) mice.

RESULTS

The results show that T1DCD mice had brain metabolic disorders in a region-specific manner relative to CONT mice, and the frontal cortex exhibited a higher lipid peroxidation than the hippocampus in T1DCD mice. Based on metabolic changes, we found that microglia was activated under diabetic condition and thereby promoted oxidative stress and neuroinflammation, leading to neuronal injury, and this event was more pronounced in the frontal cortex than the hippocampus.

CONCLUSION

Our results suggest that brain region-specific shifts in oxidative stress and neuroinflammation may contribute to diabetic cognitive decline, and the frontal cortex could be the more vulnerable brain region than the hippocampus.

Relationships Among Gut Microbiota, Ischemic Stroke and Its Risk Factors: Based on Research Evidence

Stroke is a highly lethal disease and disabling illness while ischemic stroke accounts for the majority of stroke. It has been found that inflammation plays a key role in the initiation and progression of stroke, and atherosclerotic plaque rupture is considered to be the leading cause of ischemic stroke. Furthermore, chronic inflammatory diseases, such as obesity, type 2 diabetes mellitus (T2DM) and hypertension, are also considered as the high-risk factors for stroke. Recently, the topic on how gut microbiota affects human health has aroused great concern. The initiation and progression of ischemic stroke has been found to have close relation with gut microbiota dysbiosis. Hence, this manuscript briefly summarizes the roles of gut microbiota in ischemic stroke and its related risk factors, and the practicability of preventing and alleviating ischemic stroke by reconstructing gut microbiota.

Novel Targets and Interventions for Cognitive Complications of Diabetes

Diabetes and cognitive dysfunction, ranging from mild cognitive impairment to dementia, often coexist in individuals over 65 years of age. Vascular contributions to cognitive impairment/dementia (VCID) are the second leading cause of dementias under the umbrella of Alzheimer's disease and related dementias (ADRD). Over half of dementia patients have VCID either as a single pathology or a mixed dementia with AD. While the prevalence of type 2 diabetes in individuals with dementia can be as high as 39% and diabetes increases the risk of cerebrovascular disease and stroke, VCID remains to be one of the less understood and less studied complications of diabetes. We have identified cerebrovascular dysfunction and compromised endothelial integrity leading to decreased cerebral blood flow and iron deposition into the brain, respectively, as targets for intervention for the prevention of VCID in diabetes. This review will focus on targeted therapies that improve endothelial function or remove iron without systemic effects, such as agents delivered intranasally, that may result in actionable and disease-modifying novel treatments in the high-risk diabetic population.

Deferoxamine Treatment Prevents Post-Stroke Vasoregression and Neurovascular Unit Remodeling Leading to Improved Functional Outcomes in Type 2 Male Diabetic Rats: Role of Endothelial Ferroptosis

It is a clinically well-established fact that patients with diabetes have very poor stroke outcomes. Yet, the underlying mechanisms remain largely unknown. Our previous studies showed that male diabetic animals show greater hemorrhagic transformation (HT), profound loss of cerebral vasculature in the recovery period, and poor sensorimotor and cognitive outcomes after ischemic stroke. This study aimed to determine the impact of iron chelation with deferoxamine (DFX) on (1) cerebral vascularization patterns and (2) functional outcomes after stroke in control and diabetic rats. After 8 weeks of type 2 diabetes induced by a combination of high-fat diet and low-dose streptozotocin, male control and diabetic animals were subjected to thromboembolic middle cerebral artery occlusion (MCAO) and randomized to vehicle, DFX, or tPA/DFX and followed for 14 days with behavioral tests. Vascular indices (vascular volume and surface area), neurovascular remodeling (AQP4 polarity), and microglia activation were measured. Brain microvascular endothelial cells (BMVEC) from control and diabetic animals were evaluated for the impact of DFX on ferroptotic cell death. DFX treatment prevented vasoregression and microglia activation while improving AQP4 polarity as well as blood-brain barrier permeability by day 14 in diabetic rats. These pathological changes were associated with improvement of functional outcomes. In control rats, DFX did not have an effect. Iron increased markers of ferroptosis and lipid reactive oxygen species (ROS) to a greater extent in BMVECs from diabetic animals, and this was prevented by DFX. These results strongly suggest that (1) HT impacts post-stroke vascularization patterns and recovery responses in diabetes, (2) treatment of bleeding with iron chelation has differential effects on outcomes in comorbid disease conditions, and (3) iron chelation and possibly inhibition of ferroptosis may provide a novel disease-modifying therapeutic strategy in the prevention of post-stroke cognitive impairment in diabetes.

Selenium attenuates ischemia/reperfusion injury‑induced damage to the blood‑brain barrier in hyperglycemia through PI3K/AKT/mTOR pathway‑mediated autophagy inhibition

Ischemic stroke is a leading cause of mortality and disability. Diabetes mellitus, characterized by hyperglycemia, is a common concomitant disease of ischemic stroke, which is associated with autophagy dysfunction and blood‑brain barrier (BBB) damage following cerebral ischemia/reperfusion (I/R) injury. At present, there is no effective treatment strategy for the disease. The purpose of the present study was to explore the molecular mechanisms underlying the protective effects of selenium on the BBB following I/R injury in hyperglycemic rats. Middle cerebral artery occlusion was performed in diabetic Sprague‑Dawley rats. Treatment with selenium and the autophagy inhibitor 3‑methyladenine significantly reduced cerebral infarct volume, brain water content and Evans blue leakage, while increasing the expression of tight junction (TJ) proteins and decreasing that of autophagy‑related proteins (P<0.05). In addition, selenium increased the phosphorylation levels of PI3K, AKT and mTOR (P<0.05). A mouse bEnd.3 brain microvascular endothelial cell line was co‑cultured in vitro with an MA‑h mouse astrocyte‑hippocampal cell line to simulate the BBB. The cells were then subjected to hyperglycemia, followed by oxygen‑glucose deprivation for 1 h and reoxygenation for 24 h. It was revealed that selenium increased TJ protein levels, reduced BBB permeability, decreased autophagy levels and enhanced the expression of phosphorylated (p)‑AKT/AKT and p‑mTOR/mTOR proteins (P<0.05). Treatment with wortmannin (an inhibitor of PI3K) significantly prevented the beneficial effects of selenium on the BBB, whereas insulin‑like growth factor 1 (a PI3K activator) mimicked the effects of selenium. In conclusion, the present findings indicated that selenium can inhibit autophagy by regulating the PI3K/AKT/mTOR signaling pathway, significantly preventing BBB damage following cerebral I/R injury in hyperglycemic conditions.

Damage to the blood‑brain barrier and activation of neuroinflammation by focal cerebral ischemia under hyperglycemic condition

Hyperglycemia aggravates brain damage caused by cerebral ischemia/reperfusion (I/R) and increases the permeability of the blood‑brain barrier (BBB). However, there are relatively few studies on morphological changes of the BBB. The present study aimed to investigate the effect of hyperglycemia on BBB morphological changes following cerebral I/R injury. Streptozotocin‑induced hyperglycemic and citrate‑buffered saline‑injected normoglycemic rats were subjected to 30 min middle cerebral artery occlusion. Neurological deficits were evaluated. Brain infarct volume was assessed by 2,3,5‑triphenyltetrazolium chloride staining and BBB integrity was evaluated by Evans blue and IgG extravasation following 24 h reperfusion. Changes in tight junctions (TJ) and basement membrane (BM) proteins (claudin, occludin and zonula occludens‑1) were examined using immunohistochemistry and western blotting. Astrocytes, microglial cells and neutrophils were labeled with specific antibodies for immunohistochemistry after 1, 3 and 7 days of reperfusion. Hyperglycemia increased extravasations of Evan's blue and IgG and aggravated damage to TJ and BM proteins following I/R injury. Furthermore, hyperglycemia suppressed astrocyte activation and damaged astrocytic endfeet surrounding cerebral blood vessels following I/R. Hyperglycemia inhibited microglia activation and proliferation and increased neutrophil infiltration in the brain. It was concluded that hyperglycemia‑induced BBB leakage following I/R might be caused by damage to TJ and BM proteins and astrocytic endfeet. Furthermore, suppression of microglial cells and increased neutrophil infiltration to the brain may contribute to the detrimental effects of pre‑ischemic hyperglycemia on the outcome of cerebral ischemic stroke.

The treament of hyperglycemia in acute ischemic stroke with incretin-based drugs

Stroke is a major cause of mortality and morbidity worldwide. Considerable experimental and clinical evidence suggests that both diabetes mellitus (DM) and post-stroke hyperglycemia are associated with increased mortality rate and worsened clinical conditions in acute ischemic stroke (AIS) patients. Insulin treatment does not seem to provide convincing benefits for these patients, therefore prompting a change of strategy. The selective agonists of Glucagon-Like Peptide-1 Receptors (GLP-1Ras) and the Inhibitors of Dipeptidyl Peptidase-IV (DPP-IVIs, gliptins) are two newer classes of glucose-lowering drugs used for the treatment of DM. This review examines in detail the rationale for their development and the physicochemical, pharmacokinetic and pharmacodynamic properties and clinical activities. Emphasis will be placed on their neuroprotective effects at cellular and molecular levels in experimental models of acute cerebral ischemia. In perspective, an adequate basis does exist for a novel therapeutic approach to hyperglycemia in AIS patients through the additive treatment with GLP-1Ras plus DPP-IVIs.

The beneficial roles of metformin on the brain with cerebral ischaemia/reperfusion injury

Cerebral ischaemia/reperfusion (I/R) injury is the transient loss, followed by rapid return, of blood flow to the brain. This condition is often caused by strokes and heart attacks. The underlying mechanisms resulting in brain damage during cerebral I/R injury include mitochondrial dysregulation, increased oxidative stress/reactive oxygen species, blood-brain-barrier breakdown, inflammation of the brain, and increased neuronal apoptosis. Metformin is the first-line antidiabetic drug which has recently been shown to be capable of acting through the aforementioned pathways to improve recovery following cerebral I/R injury. However, some studies have suggested that metformin therapy may have no effect or even worsen recovery following cerebral I/R injury. The present review will compile and examine the available in vivo, in vitro, and clinical data concerning the neuroprotective effects of metformin following cerebral I/R injury. Any contradictory evidence will also be assessed and presented to determine the actual effectiveness of metformin treatment in stroke recovery.

Glomerular Filtration Rate is Associated with Hemorrhagic Transformation in Acute Ischemic Stroke Patients without Thrombolytic Therapy

Background:

Whether there is a relationship between glomerular filtration rate (GFR) and hemorrhagic transformation (HT) after acute ischemic stroke (AIS) is still under debate. The aim of our study was to determine whether the GFR level is a predictor of HT in AIS patients without thrombolytic therapy (TT).

Methods:

Consecutive AIS patients without TT were included in this prospective study from January 2014 to December 2016 in the First Affiliated Hospital of Chongqing Medical University. We divided them into two groups (HT and non-HT group) and meticulously collected baseline characteristics and laboratory and imaging data of interested individuals. Multivariate regression analysis was performed to assess the correlation between GFR and HT in stroke patients without TT.

Results:

Among 426 consecutive patients, 74 (17.3%) presented HT (mean age: 65 ± 12 years, number of male patients: 47) on the follow-up scans. In multivariate regression analysis, HT was significantly associated with low GFR (odds ratio [OR] = 3.708, confidence interval [CI] = 1.326–10.693, P = 0.013), atrial fibrillation (AF; OR = 2.444, CI = 1.087–5.356, P = 0.027), large cerebral infarction (OR = 2.583, CI = 1.236–5.262, P = 0.010), and hypoalbuminemia (HA; OR = 4.814, CI = 1.054–22.153, P = 0.037) for AIS patients without TT.

Conclusions:

The present study strongly showed that lower GFR is an independently predictor of HT; in addition, large infarct volume, AF, and HA are also important risks of HT for AIS patients without TT, which offered a practical information that risk factors should be paid attention or eliminated to prevent HT for stroke patients though the level of evidence seems to be unstable.

Suppressing Interferon-γ Stimulates Microglial Responses and Repair of Microbleeds in the Diabetic Brain

Microcirculatory damage is a common complication for those with vascular risk factors, such as diabetes. To resolve vascular insults, the brain's immune cells (microglia) must rapidly envelop the site of injury. Currently, it is unknown whether Type 1 diabetes, a condition associated with chronic immune system dysfunction, alters microglial responses to damage and what mechanisms are responsible. Using in vivo two-photon microscopy in adult male mice, we show that microglial envelopment of laser-induced cerebral microbleeds is diminished in a hyperglycemic mouse model of Type 1 diabetes, which could not be fully rescued with chronic insulin treatment. Microglia were important for vessel repair because reduced microglial accumulation in diabetic mice or near-complete depletion in healthy controls was associated with greater secondary leakage of the damaged vessel. Broadly suppressing inflammation with dexamethasone in diabetic mice but not healthy controls, significantly enhanced microglial responses to microbleeds and attenuated secondary vessel leakage. These enhancements were associated with changes in IFN-γ signaling because dexamethasone suppressed abnormally high levels of IFN-γ protein levels in brain and blood serum of diabetic mice. Further, blocking IFN-γ in diabetic mice with neutralizing antibodies restored normal microglial chemotaxic responses and purinoceptor P2ry12 gene expression, as well as mitigated secondary leakage. These results suggest that abnormal IFN-γ signaling disrupts microglial function in the diabetic brain, and that immunotherapies targeting IFN-γ can stimulate microglial repair of damaged vessels.SIGNIFICANCE STATEMENT Although Type 1 diabetes is an established risk factor for vascular complications, such as microbleeds, and is known to hinder wound healing in the body, no study has examined how diabetes impacts the brain's innate immune reparative response (involving cells called microglia) to vascular injury. Here we show that microglial responses to brain microbleeds were diminished in diabetic animals, which also exacerbated secondary leakage from damaged vessels. These impairments were related to abnormally high levels of the proinflammatory cytokine IFN-γ because reducing IFN-γ with immunosuppressant drugs or blocking antibodies helped restore normal microglial responses and repair of damaged vessels. These data highlight the use of IFN-γ modulating therapeutics to enhance vascular repair in at-risk populations.

Post-stroke neovascularization and functional outcomes differ in diabetes depending on severity of injury and sex: Potential link to hemorrhagic transformation

Diabetes is associated with increased risk and worsened outcome of stroke. Previous studies showed that male diabetic animals had greater hemorrhagic transformation (HT), profound loss of cerebral vasculature, and poor behavioral outcomes after ischemic stroke induced by suture or embolic middle cerebral artery occlusion (MCAO). Females are protected from stroke until reaching the menopause age, but young females with diabetes have a higher risk of stroke and women account for the majority of stroke mortality. The current study postulated that diabetes is associated with greater vascular injury and exacerbated sensorimotor and cognitive outcome after stroke even in young female animals. Male and female control and diabetic animals were subjected to transient MCAO and followed for 3 or 14 days to assess the neurovascular injury and repair. The vascularization indices after stroke were lower in male diabetic animals with 90-min but not 60-min ischemia/reperfusion injury, while there was no change in female groups. Cognitive deficits were exacerbated in both male and female groups regardless of the injury period, while the sensorimotor dysfunction was worsened in male diabetic animals with longer ischemia time. These results suggest that diabetes negates the protection afforded by sex in young female animals, and post-stroke vascularization pattern is influenced by the degree of injury and correlates with functional outcome in both sexes. Vasculoprotection after acute ischemic stroke may provide a novel therapeutic strategy in diabetes.

Pinocembrin Protects Blood-Brain Barrier Function and Expands the Therapeutic Time Window for Tissue-Type Plasminogen Activator Treatment in a Rat Thromboembolic Stroke Model

Tissue-type plasminogen activator (t-PA) remains the only approved therapy for acute ischemic stroke but has a restrictive treatment time window of 4.5 hr. Prolonged ischemia causes blood-brain barrier (BBB) damage and increases the incidence of hemorrhagic transformation (HT) secondary to reperfusion. In this study, we sought to determine the effect of pinocembrin (PCB; a pleiotropic neuroprotective agent) on t-PA administration-induced BBB damage in a novel rat thromboembolic stroke model. By assessing the leakage of Evans blue into the ischemic hemisphere, we demonstrated that PCB pretreatment 5 min before t-PA administration significantly reduced BBB damage following 2 hr, 4 hr, 6 hr, and even 8 hr ischemia. Consistently, PCB pretreatment significantly decreased t-PA infusion-resulting brain edema and infarction volume and improved the behavioral outcomes following 6 hr ischemia. Mechanistically, PCB pretreatment inhibited the activation of MMP-2 and MMP-9 and degradation of tight junction proteins (TJPs) occludin and claudin-5 in the ischemic hemisphere. Moreover, PCB pretreatment significantly reduced phosphorylation of platelet-derived growth factor receptor α (PDGFRα) as compared with t-PA alone. In an in vitro BBB model, PCB decreased transendothelial permeability upon hypoxia/aglycemia through inhibiting PDGF-CC secretion. In conclusion, we demonstrated that PCB pretreatment shortly before t-PA infusion significantly protects BBB function and improves neurological outcomes following prolonged ischemia beyond the regular 4.5 hr t-PA time window. PCB pretreatment may represent a novel means of increasing the safety and the therapeutic time window of t-PA following ischemic stroke.

MAPK pathway mediates the anti-oxidative effect of chicoric acid against cerebral ischemia-reperfusion injury in vivo

The aim of the present study was to investigate the protective effect of chicoric acid on oxidative stress and inflammation in rats with cerebral ischemia-reperfusion injury. A cerebral ischemia-reperfusion injury rat model was created via transient middle cerebral artery occlusion (MCAO) and rats were treated with various doses of chicoric acid (0, 1, 10 and 100 mg/kg). Neurological deficits and infarct volume were used to estimate the protective effects of chicoric acid treatment. Levels of reactive oxygen species (ROS), tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, nitric oxide (NO) and prostaglandin E2 (PGE2) were assessed. Western blot analysis was also used to measure the expression of cyclooxygenase (COX)-2, p38-mitogen activated protein kinase (MAPK), c-Jun, phosphorylated protein kinase B (p-AKT) and AKT. Chicoric acid exposure was observed to reduce neurological deficits and infarct volume in rats with cerebral ischemia-reperfusion injury. In addition, ROS production and inflammation were significantly suppressed following treatment with chicoric acid. Chicoric acid was demonstrated to significantly inhibit the upregulation of NO and PGE2 levels in rats following MCAO. Furthermore, chicoric acid significantly suppressed the MCAO-induced promotion of COX-2, p38-MAPK and c-Jun protein expression and enhanced the inhibition of p-AKT/AKT. These results suggest that chicoric acid has a protective effect, preventing oxidative stress and inflammation in rats with cerebral ischemia-reperfusion injury via the p38-MAPK, c-Jun and AKT signaling pathways.

Effect of TTC Treatment on Immunohistochemical Quantification of Collagen IV in Rat Brains after Stroke

Although used extensively in stroke research, there is limited knowledge of how 2, 3, 5-triphenyltetrazolium chloride (TTC)-treated rat brain sections are altered and if they can be used for immunohistochemical quantification after staining with TTC. In the present study, we hypothesized that TTC treatment (TTC+) would not interfere with collagen IV immunohistochemical staining compared with non-TTC-treated (TTC-) brain slices. We further hypothesized that there would be no difference in autofluorescence or nonspecific secondary antibody fluorescence between TTC+ and TTC- brain slices. Coronal brain sections of male Wistar rats (n = 5/group) were either treated with TTC or not after middle cerebral artery occlusion or sham surgery, and processed for immunohistochemical staining with mouse anti-collagen IV as the primary antibody, and goat anti-IgM as the secondary antibody. Four images were taken in the cerebral cortex of the contralateral side of infarction in each brain slice using an Olympus BX50 fluorescence microscope, and average intensity of the entire image was quantified using the Metamorph software. Compared with TTC- brain slices, TTC+ brain slices showed a significantly lower autofluorescence (P < 0.05), but was unchanged for nonspecific secondary antibody fluorescence. In addition, TTC+ brain slices had similar collagen IV staining intensity compared with TTC- brain slices. These results demonstrate that TTC+ brain slices are usable for immunohistochemical quantification.

Peroxynitrite-Induced Tyrosine Nitration Contributes to Matrix Metalloprotease-3 Activation: Relevance to Hyperglycemic Ischemic Brain Injury and Tissue Plasminogen Activator

Matrix metalloprotease-3 (MMP3) activation mediates the tissue plasminogen activator (tPA)-induced hemorrhagic transformation after stroke. Hyperglycemia (HG) further exacerbates this outcome. We have recently shown that HG increases MMP3 activity in the brain after stroke. However, the combined HG-tPA effect on MMP3 activation, and the mechanisms through which MMP3 is activated were not previously reported. Accordingly, this study tested the hypothesis that tPA and HG increases MMP3 activity in the brain after stroke through peroxynitrite induced tyrosine nitration. Normoglycemic and mildly hyperglycemic male Wistar rats were subjected to middle cerebral artery suture occlusion for 90 min or thromboembolic occlusion, and up to 24 h reperfusion, with and without tPA. MMP3 activity and tyrosine nitration were evaluated in brain homogenates at 24 h. Brain microvascular endothelial cells (BMVEC) were subjected to either 3 h hypoxia or 6 h OGD under either normal or high glucose conditions with or without tPA, with or without peroxynitrite scavenger, FeTPPs. MMP3 activity and MMP3 tyrosine nitration were assessed at 24 h. HG and tPA significantly increased activity and tyrosine nitration of MMP3 in the brain. In BMVECs, tPA but not HG increased MMP3 activity. Treating BMVEC with FeTPPs significantly reduced the tPA-induced increase in MMP3 activity and nitration. Augmented oxidative and nitrative stress may be potential mechanisms contributing to MMP3 activation in hyperglycemic stroke, especially with tPA administration. Peroxynitrite may be playing a critical role in mediating MMP3 activation through tyrosine nitration in hyperglycemic stroke.

Lycium Barbarum Polysaccharides Decrease Hyperglycemia-Aggravated Ischemic Brain Injury through Maintaining Mitochondrial Fission and Fusion Balance

Although it has been reported that polysaccharides found in Lycium barbarum possess neuroprotective effects, little is known of their ability to ameliorate hyperglycemia-aggravated ischemia/reperfusion brain injury. In this study, normoglycemic (NG) and hyperglycemic (HG) rats were compared after 30 minutes of middle cerebral artery occlusion (MCAO), followed by 24 or 27 hours of reperfusion, with HG rats pretreated with lyceum barbarum polysaccharides (LBP) or insulin. In each group, the neurological deficit, infarct volume, pathohistology, and expression of proteins, Opa1 and Drp1, were assessed to determine the efficacy of LBP in alleviating hyperglycemia-aggravated ischemia/reperfusion brain injury. Our results show that, compared to the NG group, the HG group had increases in neurological deficits, infarct volume, and evidence of neuronal pyknosis at 24- and/or 72-h of reperfusion (P<0.05) and that pre-treatment with LBP decreased these effects (P<0.05). In addition, immunohistochemistry revealed an increase of Drp1 and a decrease of Opa1 positive neurons in the HG group after 24 and 72 hours of reperfusion when compared to the NG group. LBP treatment prevented the HG-induced alterations in Drp-1 and Opa1 expression. Western blots further confirmed these findings showing that HG caused an increase in phospho-Drp1 and a decrease in Opa1 which were subsequently reversed by LBP addition. These results suggest that hyperglycemia-aggravated ischemic brain damage is associated with an alteration of mitochondrial dynamics and that pre-treatment with LBP ameliorates the hyperglycemia-enhanced ischemic brain damage through maintaining mitochondrial dynamic balance.

Diabetic aggravation of stroke and animal models

Cerebral ischemia in diabetics results in severe brain damage. Different animal models of cerebral ischemia have been used to study the aggravation of ischemic brain damage in the diabetic condition. Since different disease conditions such as diabetes differently affect outcome following cerebral ischemia, the Stroke Therapy Academic Industry Roundtable (STAIR) guidelines recommends use of diseased animals for evaluating neuroprotective therapies targeted to reduce cerebral ischemic damage. The goal of this review is to discuss the technicalities and pros/cons of various animal models of cerebral ischemia currently being employed to study diabetes-related ischemic brain damage. The rational use of such animal systems in studying the disease condition may better help evaluate novel therapeutic approaches for diabetes related exacerbation of ischemic brain damage.

Brain injury with diabetes mellitus: evidence, mechanisms and treatment implications

Diabetes mellitus is a risk for brain injury. Brain injury is associated with acute and chronic hyperglycaemia, insulin resistance, hyperinsulinemia, diabetic ketoacidosis (DKA) and hypoglycaemic events in diabetic patients. Hyperglycemia is a cause of cognitive deterioration, low intelligent quotient, neurodegeneration, brain aging, brain atrophy and dementia. Areas covered: The current review highlights the experimental, clinical, neuroimaging and neuropathological evidence of brain injury induced by diabetes and its associated metabolic derangements. It also highlights the mechanisms of diabetes-induced brain injury. It seems that the pathogenesis of hyperglycemia-induced brain injury is complex and includes combination of vascular disease, oxidative stress, neuroinflammation, mitochondrial dysfunction, apoptosis, reduction of neurotrophic factors, acetylcholinesterase (AChE) activation, neurotransmitters' changes, impairment of brain repair processes, impairment of brain glymphatic system, accumulation of amyloid β and tau phosphorylation and neurodegeneration. The potentials for prevention and treatment are also discussed. Expert commentary: We summarize the risks and the possible mechanisms of DM-induced brain injury and recommend strategies for neuroprotection and neurorestoration. Recently, a number of drugs and substances [in addition to insulin and its mimics] have shown promising potentials against diabetes-induced brain injury. These include: antioxidants, neuroinflammation inhibitors, anti-apoptotics, neurotrophic factors, AChE inhibitors, mitochondrial function modifiers and cell based therapies.

Diabetes Worsens Functional Outcomes in Young Female Rats: Comparison of Stroke Models, Tissue Plasminogen Activator Effects, and Sexes

Diabetes worsens stroke outcome and increases the risk of hemorrhagic transformation (HT) after ischemic stroke, especially with tissue plasminogen activator (tPA) treatment. The widespread use of tPA is still limited by the fear of hemorrhagic transformation (HT), and underlying mechanisms are actively being pursued in preclinical studies. However, experimental models use a 10 times higher dose of tPA than the clinical dose (10 mg/kg) and mostly employ only male animals. In this translational study, we hypothesized that low-dose tPA will improve the functional recovery after the embolic stroke in both control and diabetic male and female animals. Diabetes was induced in age-matched male and female Wistar rats with high fat diet and low-dose streptozotocin (30 mg/kg, i.p.). Embolic stroke was induced with clot occlusion of the middle cerebral artery (MCA). The animals were treated with or without tPA (1 mg/kg, i.v.) at 90 min after surgery. An additional set of animals were subjected to 90 min MCAO with suture. Neurological deficits (composite score and adhesive removal test-ART), infarct size, edema ratio, and HT index were assessed 3 days after surgery. In the control groups, female rats had smaller infarcts and better functional outcomes. tPA decreased infarct size in both sexes with a greater effect in males. While there was no difference in HT between males and females without tPA, HT was less in the female + tPA group. In the diabetic groups, neuronal injury increased in females reaching that of the infarct sizes seen in male rats. tPA decreased infarct size in females but not males. HT was greater in female rats than in males and was not further increased with tPA. Diabetes worsened neurological deficits in both sexes. Male animals showed improved sensorimotor skills, especially with tPA treatment, but there was no improvement in females. These data suggest that diabetes amplifies neurovascular injury and neurological deficits in both sexes. Human dose tPA offers some degree of protection in male but not female rats. Given that control female animals experience less injury compared to male rats, the diabetes effect is more profound in females.

White matter changes after stroke in type 2 diabetic rats measured by diffusion magnetic resonance imaging

Diffusion-related magnetic resonance imaging parametric maps may be employed to characterize white matter of brain. We hypothesize that entropy of diffusion anisotropy may be most effective for detecting therapeutic effects of bone marrow stromal cell treatment of ischemia in type 2 diabetes mellitus rats. Type 2 diabetes mellitus was induced in adult male Wistar rats. These rats were then subjected to 2 h of middle cerebral artery occlusion, and received bone marrow stromal cell (5 × 10⁶, n = 8) or an equal volume of saline (n = 8) via tail vein injection at three days after middle cerebral artery occlusion. Magnetic resonance imaging was performed on day one and then weekly for five weeks post middle cerebral artery occlusion. The diffusion metrics complementarily permitted characterization of axons and axonal myelination. All six magnetic resonance imaging diffusion metrics, confirmed by histological measures, demonstrated that bone marrow stromal cell treatment significantly (p < 0.05) improved magnetic resonance imaging diffusion indices of white matter in type 2 diabetes mellitus rats after middle cerebral artery occlusion compared with the saline-treated rats. Superior to the fractional anisotropy metric that provided measures related to organization of neuronal fiber bundles, the entropy metric can also identify microstructures and low-density axonal fibers of cerebral tissue after stroke in type 2 diabetes mellitus rats.

Linagliptin treatment improves cerebrovascular function and remodeling and restores reduced cerebral perfusion in Type 2 diabetes

The antihyperglycemic agent linagliptin, a dipeptidyl peptidase-4 (DPP-IV) inhibitor, has been shown to reduce inflammation and improve endothelial cell function. In this study, we hypothesized that DPP-IV inhibition with linagliptin would improve impaired cerebral perfusion in diabetic rats, as well as improve insulin-induced cerebrovascular relaxation and reverse pathological cerebrovascular remodeling. We further postulated that these changes would lead to a subsequent improvement of cognitive function. Male Type-2 diabetic and nondiabetic Goto-Kakizaki rats were treated with linagliptin for 4 wk, and blood glucose and DPP-IV plasma levels were assessed. Cerebral perfusion was assessed after treatment using laser-Doppler imaging, and dose response to insulin (10(-13) M-10(-6) M) in middle cerebral arteries was tested on a pressurized arteriograph. The impact of DPP-IV inhibition on diabetic cerebrovascular remodeling was assessed over a physiologically relevant pressure range, and changes in short-term hippocampus-dependent learning were observed using a novel object recognition test. Linagliptin lowered DPP-IV activity but did not change blood glucose or insulin levels in diabetes. Insulin-mediated vascular relaxation and cerebral perfusion were improved in the diabetic rats with linagliptin treatment. Indices of diabetic vascular remodeling, such as increased cross-sectional area, media thickness, and wall-to-lumen ratio, were also ameliorated; however, improvements in short-term hippocampal-dependent learning were not observed. The present study provides evidence that linagliptin treatment improves cerebrovascular dysfunction and remodeling in a Type 2 model of diabetes independent of glycemic control. This has important implications in diabetic patients who are predisposed to the development of cerebrovascular complications, such as stroke and cognitive impairment.

Pre-stroke Metformin Treatment is Neuroprotective Involving AMPK Reduction

Long-term metformin treatment reduces the risk of stroke. However, the effective administration pattern and indications of metformin on acute cerebral ischemia are unclear. To investigate the neuroprotective treatment duration and dosage of metformin on focal ischemia mice and the association of neuroprotection with 5'-adenosine monophosphate-activated protein kinase (AMPK) regulations, male C57BL/6 mice were subjected to permanent or transient middle cerebral artery occlusion (MCAO) and metformin of 3, 10 and 30 mg/kg was intraperitoneally injected 1, 3 or 7 days prior to MCAO, or at the onset, or 1, 3 or 6 h after reperfusion, respectively. Infarct volumes, neurological deficit score, cell apoptosis, both total and phosphorylated AMPK expressions were assessed. Results showed that prolonged pretreatment to 7 days of metformin (10 mg/kg) significantly ameliorated brain infarct, neurological scores and cell apoptosis in permanent MCAO mice. Shorter (3 days or 1 day) or without pretreatment of metformin was not effective, suggesting a pretreatment time window. In transient MCAO mice, metformin showed no neuroprotection even with pretreatment. The expressions of total and phosphorylated AMPK were sharply decreased with effective metformin pretreatments in ischemic brains. Our data provided the first evidence that in acute ischemic injury, a 7-days pretreatment duration of 10 mg/kg metformin is necessary for its neuroprotection, and metformin may not be beneficial in the cases of blood reperfusion.

Impact of Comorbidities on Acute Injury and Recovery in Preclinical Stroke Research: Focus on Hypertension and Diabetes

Human ischemic stroke is very complex, and no single preclinical model can comprise all the variables known to contribute to stroke injury and recovery. Hypertension, diabetes, and hyperlipidemia are leading comorbidities in stroke patients. The use of predominantly young adult and healthy animals in experimental stroke research has created a barrier for translation of findings to patients. As such, more and more disease models are being incorporated into the research design. This review highlights the major strengths and weaknesses of the most commonly used animal models of these conditions in preclinical stroke research. The goal is to provide guidance in choosing, reporting, and executing appropriate disease models that will be subjected to different models of stroke injury.

Cell Treatment for Stroke in Type Two Diabetic Rats Improves Vascular Permeability Measured by MRI

Treatment of stroke with bone marrow stromal cells (BMSC) significantly enhances brain remodeling and improves neurological function in non-diabetic stroke rats. Diabetes is a major risk factor for stroke and induces neurovascular changes which may impact stroke therapy. Thus, it is necessary to test our hypothesis that the treatment of stroke with BMSC has therapeutic efficacy in the most common form of diabetes, type 2 diabetes mellitus (T2DM). T2DM was induced in adult male Wistar rats by administration of a high fat diet in combination with a single intraperitoneal injection (35mg/kg) of streptozotocin. These rats were then subjected to 2h of middle cerebral artery occlusion (MCAo). T2DM rats received BMSC (5x10⁶, n = 8) or an equal volume of phosphate-buffered saline (PBS) (n = 8) via tail-vein injection at 3 days after MCAo. MRI was performed one day and then weekly for 5 weeks post MCAo for all rats. Compared with vehicle treated control T2DM rats, BMSC treatment of stroke in T2DM rats significantly (p<0.05) decreased blood-brain barrier disruption starting at 1 week post stroke measured using contrast enhanced T₁-weighted imaging with gadopentetate, and reduced cerebral hemorrhagic spots starting at 3 weeks post stroke measured using susceptibility weighted imaging, although BMSC treatment did not reduce the ischemic lesion volumes as demarcated by T₂ maps. These MRI measurements were consistent with histological data. Thus, BMSC treatment of stroke in T2DM rats initiated at 3 days after stroke significantly reduced ischemic vascular damage, although BMSC treatment did not change infarction volume in T2DM rats, measured by MRI.

Cellular connections, microenvironment and brain angiogenesis in diabetes: Lost communication signals in the post-stroke period

Diabetes not only increases the risk but also worsens the motor and cognitive recovery after stroke, which is the leading cause of disability worldwide. Repair after stroke requires coordinated communication among various cell types in the central nervous system as well as circulating cells. Vascular restoration is critical for the enhancement of neurogenesis and neuroplasticity. Given that vascular disease is a major component of all complications associated with diabetes including stroke, this review will focus on cellular communications that are important for vascular restoration in the context of diabetes. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Autophagy protects human brain microvascular endothelial cells against methylglyoxal-induced injuries, reproducible in a cerebral ischemic model in diabetic rats

Cerebral microvascular endothelial cells (ECs) are crucial for brain vascular repair and maintenance, but their physiological function may be impaired during ischemic stroke and diabetes. Methylglyoxal (MGO), a reactive dicarbonyl produced during glucose metabolism, could exacerbate ischemia-induced EC injury and dysfunction. We investigated the protective effect of autophagy on cultured human brain microvascular endothelial cells (HBMEC) that underwent MGO treatment. A further study was conducted to explore the underlying mechanisms of the protective effect. Autophagic activity was assessed by evaluating protein levels, using western blot. 3-methyladenine (3-MA), bafilomycin A1, ammonium chloride (AC), Beclin 1 siRNA, and chloroquine (CQ) were used to cause autophagy inhibition. Alarmar blue assay and lactate dehydrogenase release assay were used to evaluate cell viability. Streptozotocin was administered to induce type I diabetes in rats and post-permanent middle cerebral artery occlusion was performed to elicit cerebral ischemia. Blood-brain barrier permeability was also assessed. Our study found that MGO reduced HBMEC cell viability in a concentration- and time-dependent manner, and triggered the responsive autophagy activation. Autophagy inhibitors bafilomycin A1, AC, 3-MA, and BECN1 siRNA exacerbated MGO-induced HBMEC injury. FAK phosphorylation inhibitor PF573228 inhibited MGO-triggered autophagy and enhanced lactate dehydrogenase release. Meanwhile, similar autophagy activation in brain vascular ECs was observed during permanent middle cerebral artery occlusion-induced cerebral ischemia in diabetic rats, while chloroquine-induced autophagy inhibition enhanced blood-brain barrier permeability. Taken together, our study indicates that autophagy triggered by MGO defends HBMEC against injuries.

Delayed inhibition of VEGF signaling after stroke attenuates blood-brain barrier breakdown and improves functional recovery in a comorbidity-dependent manner

Diabetes is a common comorbidity in stroke patients and a strong predictor of poor functional outcome. To provide a more mechanistic understanding of this clinically relevant problem, we focused on how diabetes affects blood-brain barrier (BBB) function after stroke. Because the BBB can be compromised for days after stroke and thus further exacerbate ischemic injury, manipulating its function presents a unique opportunity for enhancing stroke recovery long after the window for thrombolytics has passed. Using a mouse model of Type 1 diabetes, we discovered that ischemic stroke leads to an abnormal and persistent increase in vascular endothelial growth factor receptor 2 (VEGF-R2) expression in peri-infarct vascular networks. Correlating with this, BBB permeability was markedly increased in diabetic mice, which could not be prevented with insulin treatment after stroke. Imaging of capillary ultrastructure revealed that BBB permeability was associated with an increase in endothelial transcytosis rather than a loss of tight junctions. Pharmacological inhibition (initiated 2.5 d after stroke) or vascular-specific knockdown of VEGF-R2 after stroke attenuated BBB permeability, loss of synaptic structure in peri-infarct regions, and improved recovery of forepaw function. However, the beneficial effects of VEGF-R2 inhibition on stroke recovery were restricted to diabetic mice and appeared to worsen BBB permeability in nondiabetic mice. Collectively, these results suggest that aberrant VEGF signaling and BBB dysfunction after stroke plays a crucial role in limiting functional recovery in an experimental model of diabetes. Furthermore, our data highlight the need to develop more personalized stroke treatments for a heterogeneous clinical population.

Comparative Analysis of Different Methods of Ischemia/Reperfusion in Hyperglycemic Stroke Outcomes: Interaction with tPA

Acute hyperglycemia (HG) exacerbates reperfusion injury and aggravates tissue plasminogen activator (tPA)-induced hemorrhagic transformation (HT). Previous experimental hyperglycemic stroke studies employed very high blood glucose levels and exclusively used suture occlusion model to induce ischemia. Only few studies evaluated HG in embolic stroke and mostly involving the use of 10-fold higher dose of tPA than that is used in patients. However, the interaction between acute HG and low (human) dose tPA in different experimental models of stroke has never been reported. We first tested the impact of the severity of acute HG on stroke outcome. Building upon our findings, we then compared the impact of mild acute HG on neurovascular injury in rats subjected to suture or thromboembolic occlusion with and without low dose tPA. We assessed cerebral blood flow, neurobehavioral outcomes, infarction, hemorrhage, and edema. tPA did not change the infarct size in either control or hyperglycemic animals when compared to no tPA groups. HG increased HT and worsened functional outcomes in both suture and embolic occlusion models. The combination of HG and tPA exacerbated the vascular injury and worsened the neurological deficits more than each individual treatment in both models. Our findings show that the interaction between HG and even low dose tPA has detrimental effects on the cerebrovasculature and functional outcomes independent of the method of reperfusion.

Interleukin-1 and acute brain injury

Inflammation is the key host-defense response to infection and injury, yet also a major contributor to a diverse range of diseases, both peripheral and central in origin. Brain injury as a result of stroke or trauma is a leading cause of death and disability worldwide, yet there are no effective treatments, resulting in enormous social and economic costs. Increasing evidence, both preclinical and clinical, highlights inflammation as an important factor in stroke, both in determining outcome and as a contributor to risk. A number of inflammatory mediators have been proposed as key targets for intervention to reduce the burden of stroke, several reaching clinical trial, but as yet yielding no success. Many factors could explain these failures, including the lack of robust preclinical evidence and poorly designed clinical trials, in addition to the complex nature of the clinical condition. Lack of consideration in preclinical studies of associated co-morbidities prevalent in the clinical stroke population is now seen as an important omission in previous work. These co-morbidities (atherosclerosis, hypertension, diabetes, infection) have a strong inflammatory component, supporting the need for greater understanding of how inflammation contributes to acute brain injury. Interleukin (IL)-1 is the prototypical pro-inflammatory cytokine, first identified many years ago as the endogenous pyrogen. Research over the last 20 years or so reveals that IL-1 is an important mediator of neuronal injury and blocking the actions of IL-1 is beneficial in a number of experimental models of brain damage. Mechanisms underlying the actions of IL-1 in brain injury remain unclear, though increasing evidence indicates the cerebrovasculature as a key target. Recent literature supporting this and other aspects of how IL-1 and systemic inflammation in general contribute to acute brain injury are discussed in this review.

Persistent cerebrovascular damage after stroke in type two diabetic rats measured by magnetic resonance imaging

BACKGROUND AND PURPOSE

Diabetes mellitus is a disease with vascular components. Consequently, the blood-brain barrier disruption after stroke may differ between diabetic and nondiabetic animals. However, few studies have documented the longitudinal blood-brain barrier disruption afte stroke in diabetic animals. In this study, using MRI, we noninvasively evaluated the blood-brain barrier damage after middle cerebral artery occlusion in diabetic and nondiabetic rats.

METHODS

Type 2 diabetes mellitus (T2DM) was induced in adult male Wistar rats by administration of a high-fat diet in combination with a single intraperitoneal injection (35 mg/kg) of streptozotocin. T2DM rats (n=9) and nondiabetic wild-type (WT) rats (n=9) were subjected to middle cerebral artery occlusion for 2 hours using the filament model. MRI was performed 1 day and then weekly for 5 weeks after middle cerebral artery occlusion for all rats.

RESULTS

The ischemic lesion volumes after stroke as measured using T2 maps were not significantly different between the T2DM and WT rats. Compared with the WT rats, the volumes of blood-brain barrier disruption evaluated using contrast-enhanced T1-weighted imaging with gadolinium-diethylenetriamine penta-acetic acid and the cerebral hemorrhagic volumes measured with susceptibility-weighted imaging were significantly (P<0.05) larger in the T2DM rats from 1 to 5 weeks after stroke; values of diffusion fractional anisotropy were significantly lower in T2DM rats (P<0.03) than in WT rats after stroke. These MRI measurements were consistent with histological data.

CONCLUSIONS

Using MRI, T2-weighted imaging did not detect significant differences of the ischemic lesion volumes between T2DM and WT rats. In contrast to the WT rats, however, contrast-enhanced T1-weighted imaging and susceptibility-weighted imaging identified much more severe ischemic vascular damage, whereas fractional anisotropy demonstrated lower axonal density in the T2DM rats after stroke.

Metformin attenuates blood-brain barrier disruption in mice following middle cerebral artery occlusion

BACKGROUND

Metformin, a widely used hypoglycemic drug, reduces stroke incidence and alleviates chronic inflammation in clinical trials. However, the effect of metformin in ischemic stroke is unclear. Here, we investigated the effect of metformin on ischemic stroke in mice and further explored the possible underlying mechanisms.

METHODS

Ninety-eight adult male CD-1 mice underwent 90-minute transient middle cerebral artery occlusion (tMCAO). Metformin (200 mg/kg) was administrated for up to 14 days. Neurobehavioral outcomes, brain infarct volume, inflammatory factors, blood-brain barrier (BBB) permeability and AMPK signaling pathways were evaluated following tMCAO. Oxygen glucose deprivation was performed on bEND.3 cells to explore the mechanisms of metformin in inhibiting inflammatory signaling pathways.

RESULTS

Infarct volume was reduced in metformin-treated mice compared to the control group following tMCAO (P < 0.05). Neurobehavioral outcomes were greatly improved in metformin-treated mice (P < 0.05). MPO+ cells, Gr1+ cells, MPO activity and BBB permeability were decreased after metformin administration (P < 0.05). In addition, metformin activated AMPK phosphorylation, inhibited NF-κB activation, down-regulated cytokine (IL-1β, IL-6, TNF-α) and ICAM-1 expression following tMCAO (P < 0.05). Furthermore, metformin activated AMPK signaling pathway and alleviated oxygen-glucose deprivation-induced ICAM-1 expression in bEND.3 cells (P < 0.05). Compound C, a selective AMPK inhibitor, eliminated this promotional effect.

CONCLUSIONS

Metformin down-regulated ICAM-1 in an AMPK-dependent manner, which could effectively prevent ischemia-induced brain injury by alleviating neutrophil infiltration, suggesting that metformin is a promising therapeutic agent in stroke therapy.

Insulin action in brain regulates systemic metabolism and brain function

Insulin receptors, as well as IGF-1 receptors and their postreceptor signaling partners, are distributed throughout the brain. Insulin acts on these receptors to modulate peripheral metabolism, including regulation of appetite, reproductive function, body temperature, white fat mass, hepatic glucose output, and response to hypoglycemia. Insulin signaling also modulates neurotransmitter channel activity, brain cholesterol synthesis, and mitochondrial function. Disruption of insulin action in the brain leads to impairment of neuronal function and synaptogenesis. In addition, insulin signaling modulates phosphorylation of tau protein, an early component in the development of Alzheimer disease. Thus, alterations in insulin action in the brain can contribute to metabolic syndrome, and the development of mood disorders and neurodegenerative diseases.