The Importance of Considering Sex Differences in Translational Stroke Research

Sex differences in risk factors for vascular contributions to cognitive impairment & dementia

Vascular contributions to cognitive impairment and dementia (VCID) is the second most common cause of dementia. While males overall appear to be at a slightly higher risk for VCID throughout most of the lifespan (up to age 85), some risk factors for VCID more adversely affect women. These include female-specific risk factors associated with pregnancy related disorders (e.g. preeclampsia), menopause, and poorly timed hormone replacement. Further, presence of certain co-morbid risk factors, such as diabetes, obesity and hypertension, also may more adversely affect women than men. In contrast, some risk factors more greatly affect men, such as hyperlipidemia, myocardial infarction, and heart disease. Further, stroke, one of the leading risk factors for VCID, has a higher incidence in men than in women throughout much of the lifespan, though this trend is reversed at advanced ages. This review will highlight the need to take biological sex and common co-morbidities for VCID into account in both preclinical and clinical research. Given that there are currently no treatments available for VCID, it is critical that we understand how to mitigate risk factors for this devastating disease in both sexes.

The Role of Sirt1 in Ischemic Stroke: Pathogenesis and Therapeutic Strategies

Silent mating type information regulation 2 homolog 1 (Sirt1), a nicotine adenine dinucleotide (NAD⁺)-dependent enzyme, is well-known in playing a part in longevity. Ischemic stroke is a major neurological disorder and is a leading cause of death and adult disability worldwide. Recently, many studies have focused on the role of Sirt1 in ischemic stroke. Numerous studies consider Sirt1 as a protective factor and investigate the signaling pathways involved in the process under ischemic stress. However, the answer to whether upregulation of Sirt1 improves the outcome of stroke is still a controversy. In this review, we discuss the role and mechanisms of Sirt1 in the setting of ischemic stroke.

Elucidating sex differences in response to cerebral ischemia: immunoregulatory mechanisms and the role of microRNAs

Cerebral ischemia remains a major cause of death and disability worldwide, yet therapeutic options remain limited. Differences in sex and age play an important role in the final outcome in response to cerebral ischemia in both experimental and clinical studies: males have a higher risk and worse outcome than females at younger ages and this trend reverses in older ages. Although the molecular mechanisms underlying sex dimorphism are complex and are still not well understood, studies suggest steroid hormones, sex chromosomes, differential cell death and immune pathways, and sex-specific microRNAs may contribute to the outcome following cerebral ischemia. This review focuses on differential effects between males and females on cell death and immunological pathways in response to cerebral ischemia, the central role of innate sex differences in steroid hormone signaling, and upstreamregulation of sexually dimorphic gene expression by microRNAs.

Emergent Uric Acid Treatment is Synergistic with Mechanical Recanalization in Improving Stroke Outcomes in Male and Female Rats

Preclinical and clinical studies support a promising, albeit not definitive, neuroprotective effect of emergent uric acid (UA) administration in ischemic stroke. We assessed the effects of UA in an ischemic stroke model relevant to the current treatment paradigm of mechanical thrombectomy within the STAIR/RIGOR recommendations. A cohort of male and female Wistar rats was subjected to ischemic stroke with mechanical recanalization under physiological monitoring. The effects of transient middle cerebral artery occlusion (tMCAO) with adjunctive UA (IV, 16 mg/kg) or vehicle treatment were assessed at 24 h and 7 days. Outcomes included neurofunctional impairment, brain infarct (TTC staining, MRI imaging and cresyl violet staining) and edema. At 24 h after tMCAO, neurofunctional scores and brain infarct were significantly reduced in rats subjected to UA treatment compared to vehicle, with a selective effect of UA on cortical infarct. No differential effect of UA between male and female rats was evidenced, as no significant interaction of sex with stroke outcomes was found. Rats achieving higher reperfusion levels after tMCAO showed superior reduction of neurofunctional impairment, cortical infarct and edema by UA. After a 7-day follow-up, male rats subjected to UA treatment still showed reductions in neurofunctional impairment and infarct size, compared to vehicle treatment. In conclusion, UA treatment immediately after transient ischemia results in a sex-independent, maintained reduction of brain damage and neurological impairment, better manifested in hyperperfusion conditions. This synergistic effect of UA with mechanical recanalization supports additional clinical testing of UA as an adjunctive treatment to mechanical thrombectomy.

In a stroke cohort with incident hypertension; are more women than men likely to be excluded from recombinant tissue-type Plasminogen Activator (rtPA)?

BACKGROUND

The treatment outcomes in the use of rt-PA have been reported. Some studies reported worse outcome in women than men, while others presented opposing data. Using data from a hospital-based stroke registry, we investigated evidence of gender difference and determined exclusion criteria in a stroke population with incidence of hypertension.

METHOD

In a stroke population of women and men with incident of hypertension from a stroke registry, demographics and clinical factors were compared. Univariate analysis was used to determine gender differences, while multivariable models adjusted for demographic and clinical variables.

RESULTS

Among the 669 stroke patients with incident of hypertension that were excluded from rt-PA treatment, 362 were female and 307 were male. Female patients with increasing age (OR = 0.956-0.984, P < 0.001), diabetes mellitus (OR = 0.095-0.559, P = 0.001), higher NIH stroke scale score (OR = 1.019-1.090, P = 0.002), previous stroke (OR = 0.337-0.850, P = 0.008), diabetes medication (OR = 1.200-7.724, P = 0.019), and INR (OR = 0.033-0.597, P = 0.008) are more likely to be excluded. Male patients with a history of a previous stroke (OR = 0.265-0.704, P = 0.001), risk of mortality (OR = 0.803-0.950, P = 0.002), higher NIH stroke scale score(OR = 1.101-1.276, P < 0.001), cholesterol reducing medication (OR = 1.191-2.910, P = 0.006), weakness at presentation(OR = 1.207-4.421, P = 0.011), and INR (OR = 0.016-0.243, P < 0.001) are more likely to be excluded.

CONCLUSION

Women have a worse outcome than men in an untreated acute ischemic stroke population, but when treated, women have a better treatment outcome compared to men. In a hypertensive stroke population, the clinical variables for the exclusion criteria for women and men are significantly different, even after adjustment for confounding variables.

Is the Efficacy of Endovascular Treatment for Acute Ischemic Stroke Sex-Related

BACKGROUND

Several reports refer to differences in stroke between females and males, namely in incidence and clinical outcome, but also in response to treatments. Driven by a recent analysis of the MR CLEAN trial, which showed a higher benefit from acute stroke endovascular treatment (EVT) in males, we intended to determine if clinical outcomes after EVT differ between sexes, in a real-world setting.

METHODS

We analyzed 145 consecutive patients submitted to EVT for anterior circulation large-vessel occlusion, between January 2015 and September 2016, and compared the outcomes between sexes.

RESULTS

Our population was represented by 81 (55.9%) females, with similar baseline characteristics (pre-stroke disability, baseline NIHSS, and ASPECTS), rate of previous intravenous thrombolysis, time from onset to recanalization, and rate of revascularization; with the exception that women were on average 4 years older and had more hypertension, and men in turn had more tandem occlusions and atherosclerotic etiology (all p < 0.05). Even after adjusting for these statistically significant variables and for intravenous thrombolysis (as some studies advocate a different response to this treatment between sexes), there were no differences in intracranial hemorrhage, functional independence (mRS ≤2 in 60.9% males vs. 66.7% in females, p = 0.48; adjusted p = 0.36), or mortality at 3 months.

CONCLUSION

In a real-world setting, we found no sex differences in clinical and safety outcomes after acute stroke EVT. Our results support the idea that women are equally likely to achieve good outcomes as men after acute stroke EVT.

Sex differences in neuroinflammation and neuroprotection in ischemic stroke

Stroke is not only a leading cause of mortality and morbidity worldwide it also disproportionally affects women. There are currently over 500,000 more women stroke survivors in the US than men, and elderly women bear the brunt of stroke-related disability. Stroke has dropped to the fifth leading cause of death in men, but remains the third in women. This review discusses sex differences in common stroke risk factors, the efficacy of stroke prevention therapies, acute treatment responses, and post-stroke recovery in clinical populations. Women have an increased lifetime risk of stroke compared to men, largely due to a steep increase in stroke incidence in older postmenopausal women, yet most basic science studies continue to only evaluate young male animals. Women also have an increased lifetime prevalence of many common stroke risk factors, including hypertension and atrial fibrillation, as well as abdominal obesity and metabolic syndrome. None of these age-related risk factors have been well modeled in the laboratory. Evidence from the bench has implicated genetic and epigenetic factors, differential activation of cell-death programs, cell-cell signaling pathways, and systemic immune responses as contributors to sex differences in ischemic stroke. The most recent basic scientific findings have been summarized in this review, with an emphasis on factors that differ between males and females that are pertinent to stroke outcomes. Identification and understanding of the underlying biological factors that contribute to sex differences will be critical to the development of translational targets to improve the treatment of women after stroke. © 2016 Wiley Periodicals, Inc.

Sex as a Biological Variable in Emergency Medicine Research and Clinical Practice: A Brief Narrative Review

The National Institutes of Health recently highlighted the significant role of sex as a biological variable (SABV) in research design, outcome and reproducibility, mandating that this variable be accounted for in all its funded research studies. This move has resulted in a rapidly increasing body of literature on SABV with important implications for changing the clinical practice of emergency medicine (EM). Translation of this new knowledge to the bedside requires an understanding of how sex-based research will ultimately impact patient care. We use three case-based scenarios in acute myocardial infarction, acute ischemic stroke and important considerations in pharmacologic therapy administration to highlight available data on SABV in evidence-based research to provide the EM community with an important foundation for future integration of patient sex in the delivery of emergency care as gaps in research are filled.

Blood-brain barrier dysfunction and recovery after ischemic stroke

The blood-brain barrier (BBB) plays a vital role in regulating the trafficking of fluid, solutes and cells at the blood-brain interface and maintaining the homeostatic microenvironment of the CNS. Under pathological conditions, such as ischemic stroke, the BBB can be disrupted, followed by the extravasation of blood components into the brain and compromise of normal neuronal function. This article reviews recent advances in our knowledge of the mechanisms underlying BBB dysfunction and recovery after ischemic stroke. CNS cells in the neurovascular unit, as well as blood-borne peripheral cells constantly modulate the BBB and influence its breakdown and repair after ischemic stroke. The involvement of stroke risk factors and comorbid conditions further complicate the pathogenesis of neurovascular injury by predisposing the BBB to anatomical and functional changes that can exacerbate BBB dysfunction. Emphasis is also given to the process of long-term structural and functional restoration of the BBB after ischemic injury. With the development of novel research tools, future research on the BBB is likely to reveal promising potential therapeutic targets for protecting the BBB and improving patient outcome after ischemic stroke.

Precision Stroke Animal Models: the Permanent MCAO Model Should Be the Primary Model, Not Transient MCAO

An argument for preclinical stroke research to make more use of the permanent middle cerebral artery occlusion (MCAO) model, rather than transient MCAO, is presented. Despite STAIR recommending permanent MCAO as the primary model, preclinical stroke research has not been listened. In 2012, Hossmann reported that 64% of the treatment studies for MCAO used prompt transient MCAO models and only 36% of the studies used permanent MCAO or gradual transient MCAO (i.e., embolic stroke model). Then, in 2014 and 2015, 88% of published basic science studies on large vessel occlusion used the transient MCAO model. However, this model only represents 2.5-11.3% of large vessel stroke patients. Therefore, the transient MCAO model, which mimics stroke with reperfusion, does not accurately reflect the majority of clinical stroke cases. Thus, once again, the argument for studying permanent MCAO as a primary model is made and supported.

Preclinical models in the study of sex differences

The biology of sex differences deals with the study of the disparities between females and males and the related biological mechanisms. Gender medicine focuses on the impact of gender and sex on human physiology, pathophysiology and clinical features of diseases that are common to women and men. The term gender refers to a complex interrelation and integration of sex-as a biological and functional determinant-and psychological and cultural behaviours (due to ethnical, social or religious background). The attention to the impact of gender differences on the pathophysiology and, therefore, on the clinical management of the most common diseases, such as cardiovascular diseases (CVD), neurodegenerative disorders, immune and autoimmune diseases as well as several tumours, is in fact often neglected. Hence, studies covering different fields of investigation and including sex differences in the pathogenesis, in diagnostic and prognostic criteria as well as in response to therapy appear mandatory. However, prerequisites for this development are preclinical studies, including in vitro and in vivo approaches. They represent the first step in the development of a drug or in the comprehension of the pathogenetic mechanisms of diseases, in turn a necessary step for the development of new or more appropriate therapeutic strategies. However, sex differences are still poorly considered and the great majority of preclinical studies do not take into account the relevance of such disparities. In this review, we describe the state of the art of these studies and provide some paradigmatic examples of key fields of investigation, such as oncology, neurology and CVD, where preclinical models should be improved.

Cytoprotective Drug-Tissue Plasminogen Activator Protease Interaction Assays: Screening of Two Novel Cytoprotective Chromones

Tissue plasminogen activator (tPA) is currently used in combination with endovascular procedures to enhance recanalization and cerebral reperfusion and is also currently administered as standard-of-care thrombolytic therapy to patients within 3-4.5 h of an ischemic stroke. Since tPA is not neuroprotective or cytoprotective, adjuvant therapy with a neuroprotective or an optimized cytoprotective compound is required to provide the best care to stroke victims to maximally promote clinical recovery. In this article, we describe the use of a sensitive standardized protease assay with CH3SO2-D-hexahydrotyrosine-Gly-Arg-p-nitroanilide•AcOH, a chromogenic protease substrate that is cleaved to 4-nitroaniline (p-nitroaniline) and measured spectrophotometrically at 405 nm (OD405 nm), and how the assay can be used as an effective screening assay to study drug-tPA interactions. While we focus on two compounds of interest in our drug development pipeline, the assay is broadly applicable to all small molecule neuroprotective or cytoprotective compounds currently being discovered and developed worldwide. In this present study, we found that the specific tPA inhibitor, plasminogen activator inhibitor-1 (PAI-1; 0.25 μM), significantly (p < 0.0001) inhibited 4-nitroaniline release, by 97.74% during the 10-min duration of the assay, which is indicative of tPA protease inhibition. In addition, two lead chromone cytoprotective candidates, 2-(3',4',5'-trihydroxyphenyl)chromen-4-one (3',4',5'-trihydroxyflavone) (CSMC-19) and 3-hydroxy-2-[3-hydroxy-4-(pyrrolidin-1-yl)phenyl]benzo[h]chromen-4-one (CSMC-140), also significantly (p < 0.05) reduced 4-nitroaniline accumulation, but to a lesser extent. The reduction was 68 and 45%, respectively, at 10 μM, and extrapolated IC50 values were 4.37 and >10 μM for CSMC-19 and CSMC-140, respectively. Using bonafide 4-nitroaniline, we then demonstrated that the reduction of 4-nitroaniline detection was not due to drug-4-nitroaniline quenching of signal detection at OD405 nm. In conclusion, the results suggest that high concentrations of both cytoprotectives reduced 4-nitroaniline production in vitro, but the inhibition only occurs with concentrations 104-1025-fold that of EC50 values in an efficacy assay. Thus, CSMC-19 and CSMC-140 should be further developed and evaluated in embolic stroke models in the absence or presence of a thrombolytic. If necessary, they could be administered once effective tPA thrombolysis has been confirmed to avoid the possibility that the chromone will reduce the efficacy of tPA in patients. Stroke investigator developing new cytoprotective small molecules should consider adding this sensitive assay to their development and screening repertoire to assess possible drug-tPA interactions in vitro as a de-risking step.

Data Standardization and Quality Management

Important questions regarding the conduct of scientific research and data transparency have been raised in various scientific forums over the last 10 years. It is becoming clear, that in spite of published RIGOR guidelines, that improvement in the transparency of scientific research is required to focus on the discovery and drug development process so that a treatment can be provided to stroke patients. We have the unique privilege of conducting research using animal models of a disease so that we can address the development of a new therapy, and we should do this with great care and vigilance. This document identifies valuable resources for researchers to become Good Laboratory Practices compliant and increase and improve data transparency and provides guidelines for accurate data management to continue to propel the translational stroke research field forward while recognizing that there is a shortage of research funds worldwide. While data audits are being considered worldwide by funding agencies and they are used extensively by industry, they are still quite controversial for basic researchers. Due to the special exploratory nature of basic and translational science research, the current challenging funding environment, and independent and individualized laboratory activities, it is debatable if current individualized non-standardized data management and monitoring represents the best approach. Thus, herein, we propose steps to prepare research study data in an acceptable form for archival purposes so that standards for translational research data can be comparable to those that are accepted and adhered to by the clinical community. If all translational research laboratories follow and institute the guidelines while conducting translational research, data from all sources may be more comparable and reliable.

SIRT1-dependent AMPK pathway in the protection of estrogen against ischemic brain injury

AIMS

Stroke is a major cause of mortality and disability, especially for postmenopausal women. In view of the protective action of estrogen, hormone therapy remains the only effective way to limit this risk. The objective of this study was to investigate the efficiency and underlying mechanisms of estrogen neuroprotection.

METHODS

Subcutaneous injection of 17β-estradiol in rats after ovariectomy (OVX) was used to manipulate estrogen level and explore the effects of estrogen in cerebral ischemic damage both in vivo and in vitro. Silent mating type information regulation 2 homolog 1 (SIRT1) knockout mice and adenosine monophosphate (AMP)-activated kinase (AMPK) inhibitor Compound C were also used to investigate the underlying pathway of estrogen.

RESULTS

Estrogen deficiency induced by OVX aggravated brain infarction in experimentally induced cerebral ischemia rats, whereas estrogen pretreatment reduced ischemia-induced cerebral injuries. Neurons of estrogen deficiency models were susceptible to apoptosis under oxygen-glucose deprivation (OGD). In contrast, neurons with estrogen-supplemented serum exhibited restored resistance to cell apoptosis. In OGD neurons, estrogen promoted AMPK activation through estrogen receptor α, and neuroprotection of estrogen was prevented by AMPK inhibition. Estrogen increased SIRT1 expression and activation, and estrogen-induced AMPK activation disappeared in SIRT1 knockout neurons. Moreover, estrogen-induced neuroprotection was abolished in SIRT1 knockout mice and AMPK-inhibited rats.

CONCLUSION

Our data support that estrogen protects against ischemic stroke through preventing neuron death via the SIRT1-dependent AMPK pathway.

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.

The High Cost of Stroke and Stroke Cytoprotection Research

Acute ischemic stroke is inadequately treated in the USA and worldwide due to a lengthy history of neuroprotective drug failures in clinical trials. The majority of victims must endure life-long disabilities that not only affect their livelihood, but also have an enormous societal economic impact. The rapid development of a neuroprotective or cytoprotective compound would allow future stroke victims to receive a treatment to reduce disabilities and further promote recovery of function. This opinion article reviews in detail the enormous costs associated with developing a small molecule to treat stroke, as well as providing a timely overview of the cell-death time-course and relationship to the ischemic cascade. Distinct temporal patterns of cell-death of neurovascular unit components provide opportunities to intervene and optimize new cytoprotective strategies. However, adequate research funding is mandatory to allow stroke researchers to develop and test their novel therapeutic approach to treat stroke victims.