A Proposed Hypothesis on Dementia: Inflammation, Small Vessel Disease, and Hypoperfusion Is the Sequence That Links All Harmful Lifestyles to Cognitive Impairment.

There is growing consensus that certain lifestyles can contribute to cognitive impairment and dementia, but the physiological steps that link a harmful lifestyle to its negative impact are not always evident. It is also unclear whether all lifestyles that contribute to dementia do so through the same intermediary steps. This article will focus on three lifestyles known to be risk factors for dementia, namely obesity, sedentary behavior, and insufficient sleep, and offer a unifying hypothesis proposing that lifestyles that negatively impact cognition do so through the same sequence of events: inflammation, small vessel disease, decline in cerebral perfusion, and brain atrophy. The hypothesis will then be tested in a recently identified risk factor for dementia, namely hearing deficit. If further studies confirm this sequence of events leading to dementia, a significant change in our approach to this debilitating and costly condition may be necessary, possible, and beneficial.

Depression, dementia and immune dysregulation.

Major depression is a prevalent illness that increases the risk of several neurological conditions. These include stroke, cardiovascular disease, and dementia including Alzheimer's disease. In this review we ask whether certain types of depression and associated loneliness may be a harbinger of cognitive decline and possibly even dementia. We propose that chronic stress and inflammation combine to compromise vascular and brain function. The resulting increases in proinflammatory cytokines and microglial activation drive brain pathology leading to depression and mild cognitive impairment, which may progress to dementia. We present evidence that by treating the inflammatory changes, depression can be reversed in many cases. Importantly, there is evidence that anti-inflammatory and antidepressant treatments may reduce or prevent dementia in people with depression. Thus, we propose a model in which chronic stress and inflammation combine to increase brain permeability and cytokine production. This leads to microglial activation, white matter damage, neuronal and glial cell loss. This is first manifest as depression and mild cognitive impairment, but can eventually evolve into dementia. Further research may identify clinical subgroups with inflammatory depression at risk for dementia. It would then be possible to address in clinical trials whether effective treatment of the depression can delay the onset of dementia.

Small Vessel Disease.

Small vessel disease (SVD) refers to conditions where damage to arterioles and capillaries is predominant, leading to reduced, or interrupted perfusion of the affected organ. Data suggest that when this condition is evident in any organ, it is already systemic in its occurrence and consequences. SVD affects primarily organs that receive significant portions of cardiac output such as the brain, the kidney, and the retina. Thus, SVD is a major etiologic cause in debilitating conditions such as renal failure, blindness, lacunar infarcts, and dementia. The factors that lead to this devastating condition include all the known vascular risk factors when they are not strictly controlled, but lifestyles that include sedentary existence, obesity, and poor sleep patterns are also recognized drivers of SVD. In addition, depression is now recognized as a vascular risk factor. Inflammation is a mediator of SVD, but it is not known which factor(s) predominate in its etiology. This article emphasizes the need for more investigations to define this link further and suggests clinical and societal responses that might reduce the major impacts of this condition on populations.

Cilostazol reduces blood brain barrier dysfunction, white matter lesion formation and motor deficits following chronic cerebral hypoperfusion.

Cerebral small vessel disease (CSVD) is a pathological process leading to lacunar infarcts, leukoaraiosis and cerebral microbleeds. Dysfunction of the blood brain barrier (BBB) has been proposed as a mechanism in the progression cerebral small vessel disease. A rodent model commonly used to study some aspects of CSVD is bilateral common carotid artery occlusion (BCCAO) in the rat. In the present study it was determined that gait impairment, as determined by a tapered beam test, and BBB permeability increased following BCCAO. Cilostazol, a type III phosphodiesterase inhibitor, has been shown to have anti-apoptotic effects and prevent white matter vacuolation and rarefaction induced by BCCAO in rats. In this study the protective effect of cilostazol administration on the increase BBB permeability following BCCAO was determined as well as the effect on plasma levels of circulating microparticles (MPs), cerebral white matter rarefaction, glial activation and gait disturbance. The effect of cilostazol on in vitro endothelial barriers was also evaluated. Cilostazol treatment improved BBB permeability and reduced gait disturbance, visual impairment and microglial activation in optic tract following BCCAO in vivo. It also reduced the degree of cell death and the reduction in trans-endothelial electrical resistance (TEER) in artificial endothelial barriers in vitro induced by MP treatment of in vitro barriers.

Integrated systems of stroke care and reduction in 30-day mortality: A retrospective analysis.

OBJECTIVE: To evaluate the association between the presence of integrated systems of stroke care and stroke case-fatality across Canada. METHODS: We used the Canadian Institute of Health Information's Discharge Abstract Database to retrospectively identify a cohort of stroke/TIA patients admitted to all acute care hospitals, excluding the province of Quebec, in 11 fiscal years from 2003/2004 to 2013/2014. We used a modified Poisson regression model to compute the adjusted incidence rate ratio (aIRR) of 30-day in-hospital mortality across time for provinces with stroke systems compared to those without, controlling for age, sex, stroke type, comorbidities, and discharge year. We conducted surveys of stroke care resources in Canadian hospitals in 2009 and 2013, and compared resources in provinces with integrated systems to those without. RESULTS: A total of 319,972 patients were hospitalized for stroke/TIA. The crude 30-day mortality rate decreased from 15.8% in 2003/2004 to 12.7% in 2012/2013 in provinces with stroke systems, while remaining 14.5% in provinces without such systems. Starting with the fiscal year 2009/2010, there was a clear reduction in relative mortality in provinces with stroke systems vs those without, sustained at aIRR of 0.85 (95% confidence interval 0.79-0.92) in the 2011/2012, 2012/2013, and 2013/2014 fiscal years. The surveys indicated that facilities in provinces with such systems were more likely to care for patients on a stroke unit, and have timely access to a stroke prevention clinic and telestroke services. CONCLUSION: In this retrospective study, the implementation of integrated systems of stroke care was associated with a population-wide reduction in mortality after stroke.

Microparticles generated during chronic cerebral ischemia increase the permeability of microvascular endothelial barriers in vitro.

Numbers of circulating microparticles (MPs) are elevated in a variety of cardiovascular disorders, and recent studies indicate that they are involved in inflammatory intercellular signaling. In the present study the signaling properties of MPs were assessed in an in vitro model of the blood brain barrier. MPs isolated from the plasma of rats exposed to chronic cerebral ischemia caused a significant reduction in the transendothelial electrical resistance (TEER) when applied to in vitro endothelial barriers, while MPs isolated from an equal volume of plasma from unoperated or sham operated rats did not. The reduction in TEER was attenuated by treating endothelial barriers prior to exposure to MPs with the caspase 3 inhibitor AC-DEVD-CHO, the TNF-α inhibitor SPD304, the tumor necrosis factor alpha-converting enzyme (TACE, ADAM 17) inhibitor TAPI-0-1 and the Rho kinase (ROCK) inhibitor Y-27632, and by treating the MPs themselves with these inhibitors prior to applying them to cultured cells. This observation indicates that MPs generated during cerebral ischemia contain pro-TNF-α, active TACE and active ROCK. ROCK and Ras homolog gene family member A (RhoA) were detected in MPs by western blot. The growth factor VEGF stimulated transcellular transport in endothelial barriers while exposure to MPs did not. We conclude that the increase in permeability of artificial barriers induced by MPs is primarily due to enhanced apoptosis induced by activation of the TNF-α pathway and activated caspase 3 and Rho kinases delivered to endothelial cells by MPs.

Heart disease as a risk factor for dementia.

As life expectancy lengthens, dementia is becoming a significant human condition in terms of its prevalence and cost to society worldwide. It is important in that context to understand the preventable and treatable causes of dementia. This article exposes the link between dementia and heart disease in all its forms, including coronary artery disease, myocardial infarction, atrial fibrillation, valvular disease, and heart failure. This article also explores the cardiovascular risk factors and emphasizes that several of them are preventable and treatable. In addition to medical therapies, the lifestyle changes that may be useful in retarding the onset of dementia are also summarized.

Preeclampsia is a biomarker for vascular disease in both mother and child: the need for a medical alert system.

This paper reviews the literature pertaining to the impact of preeclampsia not only on the mother but particularly on the children. The review points to the higher blood pressure in children born to preeclamptic mothers compared to controls, their increased tendency to suffer strokes, the reduction in their cognitive ability, and their vulnerability to depression. Mechanisms that may induce these changes are emphasized, particularly the placental vascular insufficiency and the resulting hypoxic and proinflammatory environments in which the fetus develops. The hypothesis proposed is that these changes in the fetal-placental environment result in epigenetic programming of the child towards a higher propensity for vascular disease. The review's main recommendation is that, within ethical boundaries, the medical records of individuals born to preeclamptic mothers should clearly indicate this event and should be made available to the affected individuals so that preventive measures against vascular complications and lifestyle changes that may mitigate the latter can be instituted.

Stroke prevention and cognitive reserve: emerging approaches to modifying risk and delaying onset of dementia.

Demographic changes and improvements in health care are projected to result in dramatic increases in the prevalence of dementia. Alzheimer's disease is widely considered to be the primary cause of dementia - a disease for which there is currently no cure nor effective treatment, and for which it is thought that little can be done to mitigate risk. However, an increasing understanding of the role and extent of vascular contributions to the development of dementia, and appreciation of the interactions between stroke and Alzheimer's disease, suggest that targeting vascular risk factors may be very beneficial in reducing the impact of dementia. We also describe how active stimulation of the brain throughout the life course builds cognitive reserve that can offset or compensate for cognitive decline in later life. Finally, we discuss the implications of these emerging approaches for dementia prevention and advocate for the urgent implementation of more extensive public health strategies to improve vascular health.

Microparticles: biomarkers and beyond.

Membrane microparticles are submicron fragments of membrane shed into extracellular space from cells under conditions of stress/injury. They may be distinguished from other classes of extracellular vesicles (i.e. exosomes) on the basis of size, content and mechanism of formation. Microparticles are found in plasma and other biological fluids from healthy individuals and their levels are altered in various diseases, including diabetes, chronic kidney disease, pre-eclampsia and hypertension among others. Accordingly, they have been considered biomarkers of vascular injury and pro-thrombotic or pro-inflammatory conditions. In addition to this, emerging evidence suggests that microparticles are not simply a consequence of disease, but that they themselves may contribute to pathological processes. Thus microparticles appear to serve as both markers and mediators of pathology. The present review examines the evidence for microparticles as both biomarkers of, and contributors to, the progression of disease. Approaches for the detection of microparticles are summarized and novel concepts relating to the formation of microparticles and their biological effects are examined.

The future of stroke thrombolysis.

Studies with tissue plasminogen activator (t-PA) published in 1995 showed significant improvement in stroke outcome if the drug was administered within 3 hours from stroke onset. Several recent reports, however, show that less than 5% of stroke patients may be receiving t-PA in many parts of North America. This paper explores how this may be improved by examining some of the steps taken in Canada, where a recent audit showed that 8.2% of ischemic stroke patients received t-PA, and in those arriving within 2.5 hours to regional stroke centers in Ontario, 42.2% received t-PA. The paper also reviews the potential for t-PA to be given by more physicians, in remote regions using Telestroke, the possibility for using imaging characteristics rather than the onset of stroke as a determinant of eligibility for t-PA, the status of contraindications for thrombolysis, and the possibility of combining t-PA with immune modulation for improved stroke outcomes.

C-reactive protein expression in a rodent model of chronic cerebral hypoperfusion.

White matter lesions (WML) are a clinically significant, common feature of the aging brain and have been associated with cognitive decline and depression. They are a manifestation of cerebral small vessel disease, which is associated with the progression of vascular dementia. Recent research has been focused on identifying biomarkers which may have a correlation with WML. Previous population based studies have indicated a relation between the serum level of the acute phase protein, C-reactive protein (CRP), and WML. However no previous studies have demonstrated its expression and relation to WML in brain tissue itself. Here we use the rodent model of permanent bilateral common carotid artery ligation (BCCAL) to assess CRP expression during chronic cerebral hypoperfusion (CCH). Our results show that CRP is up-regulated at the mRNA and protein levels in brain tissue from BCCAL animals. The expression of CRP mRNA was upregulated on day 3 following surgery. Because previous studies, as well as the present study, have shown that microglial activity is prominent after the third day of CCH, we sought to determine the role of microglia in CRP expression. Results indicate that cultured microglia express mRNA and protein for CRP and this expression is increased when cells are treated with interleukin-1ß (IL-1ß), interleukin-6 (IL-6) or a combination of the two.. This finding could indicate a possible role for CRP in the progression of small vessel disease in the brain and provide a therapeutic target.

The management of hypertension for primary stroke prevention: a proposed approach.

The prevalence of hypertension in society is high and increasing. Untreated hypertension results in stroke, dementia, and damage to major organs. This article reviews the risks that hypertension causes and the issues now generally accepted as playing a role in the low level of hypertension control. These include lack of public awareness of the significance of elevated blood pressure, lack of impetus to measure blood pressure, lack of sites to perform the measurements, occasional therapeutic inertia on the part of the medical community, and poor compliance with treatment on the part of affected individuals. Innovative measures that may result in improved management of this risk factor are discussed. These include ubiquitous blood pressure measurement sites, expanding therapeutic potential by involving allied health professionals, and offering rewards for treatment and for compliance. The article also emphasises that the ideal blood pressure target for the primary prevention of stroke remains unclear.

Primary prevention of stroke: blood pressure, lipids, and heart failure.

Stroke contributes significantly to morbidity, mortality, and disability worldwide. Despite the successes accomplished in the acute treatment and rehabilitation of stroke, the global burden of this disease can only be tackled with co-ordinated approaches for primary prevention. Stroke is a heterogeneous disease and the contribution of individual risk factors to its occurrence estimated by population attributable risk differs from coronary heart disease. Here, we review evidence to demonstrate the prominent role of elevated blood pressure (BP) and heart disease on risk of stroke, while the influence of lipids on stroke is less clear; we also demonstrate that stroke is an important complication of heart failure. Current approaches to primary preventive action emphasize the need to target the absolute risk of cardiovascular diseases rather than individual risk factors. Lifestyle interventions serve as a basis for primary prevention of cardiovascular diseases. It is estimated that 70% of strokes are potentially preventable by lifestyle modification but prospective evidence is needed to support these hypotheses derived from epidemiological studies. Different strategies for drug interventions in primary prevention are discussed, including the polypill strategy. Additional measures are needed for the primary prevention of stroke which focus on BP, chronic heart failure, and possibly lipids.

Depression, strokes and dementia: new biological insights into an unfortunate pathway.

The literature emphasizes the risk of depression after a stroke. Less well known is the fact that depression may be as big a risk factor for strokes as hypertension, particularly in the older age group. This article reviews the risk for stroke and cognitive impairment consequent to depression, and describes the cardiovascular and immunological mechanisms that would appear to link depression to its cerebrovascular consequences. As well, the article refers to the brain imaging signatures that may allow prediction of impending brain injury. Finally, some questions that might be explored by future research are suggested, and some practical means to identify and help those at risk for the development of depression-associated vascular disease of the brain are suggested.

Living beyond our physiological means: small vessel disease of the brain is an expression of a systemic failure in arteriolar function: a unifying hypothesis.

BACKGROUND AND PURPOSE: It is our premise that the pathophysiology of small vessel disease in the brain is similar to small vessel disease in other heavily perfused tissues and that the presence of small vessel disease elsewhere in the body foretells its presence in the brain as well as its consequences on cognitive function. The hypothesis presented in this article is that small vessel disease is a systemic condition of aging that is exacerbated by vascular risk factors, which results from dysfunction of arteriolar perfusion. This condition, which we term systemic arteriolar dysfunction, affects the brain as well as a number of extracranial systems. SUMMARY OF REVIEW: Recent literature is synthesized to suggest a possible etiology of this condition, highlighting the multiple pathways that may conspire to produce the endothelial and other vascular changes seen in systemic arteriolar dysfunction. CONCLUSIONS: Regardless of the etiology, we emphasize that small vessel disease is a systemic condition with major healthcare consequences, requiring a new paradigm in the way we practice medicine. Because this condition can be decelerated by control of vascular risk factors, doing so may significantly reduce morbidity, mortality, and healthcare costs.

Protection conferred by Corticotropin-releasing hormone in rat primary cortical neurons against chemical ischemia involves opioid receptor activation.

Different studies have supported neuroprotective effects of Corticotropin-releasing hormone (CRH) against various excitotoxic and oxidative insults in vitro. However, the physiological mechanisms involved in this protection remain largely unknown. The present study was undertaken to determine the impact of CRH administration (at concentrations ranging from 200 fmol to 2 nmol) before and at delayed time intervals following potassium cyanide (KCN)-induced insult in rat primary cortical neurons. A second objective aimed to determine whether kappa and delta opioid receptor (KOR and DOR) blockade, using nor-binaltorphimine and naltrindole respectively (10 microM), could alter CRH-induced cellular protection. Our findings revealed that CRH treatments before or 3 and 8 h following KCN insult conferred significant protection against cortical injury, an effect blocked in cultures treated with alpha-helical CRH (9-41) prior to KCN administration. In addition, KOR and DOR blockade significantly reduced CRH-induced neuronal protection observed 3 but not 8 h post-KCN insult. Using western blotting, we demonstrated increased dynorphin, enkephalin, DOR and KOR protein expression in CRH-treated primary cortical neurons, and immunocytochemistry revealed the presence of opioid peptides and receptors in cortical neurons. These findings suggest protective effects of CRH against KCN-induced neuronal damage, and the contribution of the opioid system in modulating CRH actions.

ATP release by way of connexin 36 hemichannels mediates ischemic tolerance in vitro.

Spreading depression (SD) is a self-propagating wave of neuronal and glial depolarization that may occur in virtually any gray matter region in the brain. One consequence of SD is an increased tolerance to ischemia. It has been shown that during cortical SD ATP is released into the extracellular space and activation of purinergic receptors leads to the induction of ischemic tolerance. In the present study we show that depolarization of cultured neurons induces ischemic tolerance which is mediated by purinergic receptor activation. Depolarization causes the release of ATP into the extracellular medium, which may be prevented by treatment with the connexin hemichannel blockers flufenamic acid and quinine, but not the pannexin hemichannel blocker carbenoxolone. Knockdown of connexin 36 expression by siRNA greatly reduces the amount of ATP released during depolarization and the subsequent degree of ischemic tolerance. We conclude that during depolarization neurons release ATP by way of connexin 36 hemichannels.