Hypoxia-induced neuroinflammatory white-matter injury reduced by minocycline in SHR/SP

Cerebral Small Vessel Disease: a Review of the Pathophysiological Mechanisms

Cerebral small vessel disease (cSVD) refers to the age-dependent pathological processes involving the brain small vessels and leading to vascular cognitive impairment, intracerebral hemorrhage, and acute lacunar ischemic stroke. Despite the significant public health burden of cSVD, disease-specific therapeutics remain unavailable due to the incomplete understanding of the underlying pathophysiological mechanisms. Recent advances in neuroimaging acquisition and processing capabilities as well as findings from cSVD animal models have revealed critical roles of several age-dependent processes in cSVD pathogenesis including arterial stiffness, vascular oxidative stress, low-grade systemic inflammation, gut dysbiosis, and increased salt intake. These factors interact to cause a state of endothelial cell dysfunction impairing cerebral blood flow regulation and breaking the blood brain barrier. Neuroinflammation follows resulting in neuronal injury and cSVD clinical manifestations. Impairment of the cerebral waste clearance through the glymphatic system is another potential process that has been recently highlighted contributing to the cognitive decline. This review details these mechanisms and attempts to explain their complex interactions. In addition, the relevant knowledge gaps in cSVD mechanistic understanding are identified and a systematic approach to future translational and early phase clinical research is proposed in order to reveal new cSVD mechanisms and develop disease-specific therapeutics.

The effects of immunomodulatory drugs on cerebral small vessel disease: A mediation Mendelian randomization analysis

BACKGROUND

There are only a few recognized drug targets for cerebral small vessel disease (CSVD). Though inflammation is increasingly implicated in the development of CSVD, it remains unclear whether immunomodulation could become a therapeutic target. Accordingly, the Mendelian randomization (MR) method was used to assess the genetically proxied impacts of IL6 receptor (IL6R) inhibitor, IL1β inhibitor, Tumor necrosis factor (TNF) inhibitor and β-tubulin inhibitor on CSVD through.

METHODS

Single nucleotide polymorphisms (SNPs) near the IL6R, IL1β, TNFRSF1A and β-tubulin genes were identified as genetic proxies for immunomodulatory drugs. These SNPs exhibited significant associations with serum C-reactive protein (CRP) levels in a large European genome-wide association study. The causal effects of immunomodulatory drugs on CSVD manifestations and the mediation influence of 731 peripheral blood immune phenotypes linking these drugs to CSVD manifestations were examined using a two-sample two-step MR approach.

RESULTS

A total of 9, 18, 4 and 1 SNP were identified to proxy the effects of IL1β inhibitor, IL6R inhibitor, TNF inhibitor and β-tubulin inhibitor, respectively. MR analysis showed a significant causal relationship between IL1β inhibition and reduced volume of periventricular white matter hyperintensity (PWMH). IL6R inhibition was associated with a reduced risk of small vessel stroke, decreased axial diffusivity and mean diffusivity. Genetically proxied TNF inhibition may decrease the occurrence of cerebral microbleeds (CMBs) and severe enlarged perivascular spaces located at white matter (WM-EPVS). It could also protect WM integrity, as evidenced by the reduced volumes of PWMH and deep white matter hyperintensity (DWMH). Various peripheral blood immune phenotypes exhibited significant associations with immunomodulatory drugs. Notably, the median fluorescence intensity (MFI) of CD45 on CD8br cells partially mediated the effects of IL1β inhibitor on PWMH volume. Indirect effects of TNF inhibition on PWMH and DWMH volume through the MFI of CD127 on CD28- CD8br cells were observed. The effects of TNF inhibition on the occurrence of any CMBs were partially mediated by the MFI of CD45 on natural killer T cells, and the effects of TNF inhibition on the occurrence of lobar CMBs were partially mediated by the MFI of HLA DR on CD33- HLA DR+ cells. Furthermore, the MFI of HLA DR on CD33- HLA DR+ cells partially mediated the effects of TNF inhibition on WM-EPVS.

CONCLUSIONS

IL1β inhibitor, IL6R inhibitor and TNF inhibitor were associated with lower burden of CSVD while the activation of certain immune cells such as Tregs and myeloid cells partially mediated their protective effects.

Theta-burst transcranial magnetic stimulation attenuates chronic ischemic demyelination and vascular cognitive impairment in mice

Vascular cognitive impairment and dementia (VCID) is mainly caused by chronic cerebral hypoperfusion and subsequent white matter lesions. Noninvasive transcranial magnetic stimulation has been utilized in treating various neurological disorders. However, the function of theta-burst transcranial magnetic stimulation on VCID remains to be defined. We utilized 4-week bilateral carotid artery stenosis model of male mice to mimic VCID. Intermittent theta-burst stimulation (iTBS) or consecutive theta-burst stimulation (cTBS) was administered for 14 consecutive days. Through luxol fast blue staining, electron microscopy and immunofluorescence, we found that iTBS, not cTBS, significantly improved demyelination, axonal damage and β-amyloid deposition, without affecting cerebral blood flow in VCID mice. At cellular levels, iTBS rescued the loss of mature oligodendrocytes, promoted precursor cell differentiation, and inhibited pro-inflammatory activation of astrocytes and microglia. Notably, iTBS attenuated cognitive deterioration in both short-term retention and long-term spatial memory of VCID mice as indicated by serial neurobehavioral tests. To explore the molecular involvement of iTBS, mRNA sequencing was carried out. By real-time PCR and combined RNA fluorescence in situ hybridization with immunofluorescence, iTBS was confirmed to increase Rxrg expression specifically in mature oligodendrocytes. Collectively, iTBS could ameliorate vascular cognitive dysfunction, probably via mitigating white matter lesions and neuroinflammation in the corpus callosum. Rxrg signaling in mature oligodendrocytes, which was increased by iTBS, might be a potential target for VCID treatment.

Vascular cognitive impairment and dementia: Mechanisms, treatment, and future directions

Worldwide, around 50 million people live with dementia, and this number is projected to triple by 2050. It has been estimated that 20% of all dementia cases have a predominant cerebrovascular pathology, while perhaps another 20% of vascular diseases contribute to a mixed dementia picture. Therefore, the vascular contribution to dementia affects 20 million people currently and will increase markedly in the next few decades, particularly in lower- and middle-income countries.In this review, we discuss the mechanisms of vascular cognitive impairment (VCI) and review management. VCI refers to the spectrum of cerebrovascular pathologies that contribute to any degree of cognitive impairment, ranging from subjective cognitive decline, to mild cognitive impairment, to dementia. While acute cognitive decline occurring soon after a stroke is the most recognized form of VCI, chronic cerebrovascular disease, in particular cerebral small-vessel disease, can cause insidious cognitive decline in the absence of stroke. Moreover, cerebrovascular disease not only commonly co-occurs with Alzheimer's disease (AD) and increases the probability that AD pathology will result in clinical dementia, but may also contribute etiologically to the development of AD pathologies.Despite its enormous health and economic impact, VCI has been a neglected research area, with few adequately powered trials of therapies, resulting in few proven treatments. Current management of VCI emphasizes prevention and treatment of stroke and vascular risk factors, with most evidence for intensive hypertension control. Reperfusion therapies in acute stroke may attenuate the risk of VCI. Associated behavioral symptoms such as apathy and poststroke emotionalism are common. We also highlight novel treatment strategies that will hopefully lead to new disease course-modifying therapies. Finally, we highlight the importance of including cognitive endpoints in large cardiovascular prevention trials and the need for an increased research focus and funding for this important area.

Cognitive impairment in cerebral small vessel disease induced by hypertension

ABSTRACT

Hypertension is a primary risk factor for the progression of cognitive impairment caused by cerebral small vessel disease, the most common cerebrovascular disease. However, the causal relationship between hypertension and cerebral small vessel disease remains unclear. Hypertension has substantial negative impacts on brain health and is recognized as a risk factor for cerebrovascular disease. Chronic hypertension and lifestyle factors are associated with risks for stroke and dementia, and cerebral small vessel disease can cause dementia and stroke. Hypertension is the main driver of cerebral small vessel disease, which changes the structure and function of cerebral vessels via various mechanisms and leads to lacunar infarction, leukoaraiosis, white matter lesions, and intracerebral hemorrhage, ultimately resulting in cognitive decline and demonstrating that the brain is the target organ of hypertension. This review updates our understanding of the pathogenesis of hypertension-induced cerebral small vessel disease and the resulting changes in brain structure and function and declines in cognitive ability. We also discuss drugs to treat cerebral small vessel disease and cognitive impairment.

Identification of distinct and shared biomarker panels in different manifestations of cerebral small vessel disease through proteomic profiling

The pathophysiology underlying various manifestations of cerebral small vessel disease (cSVD) remains obscure. Using cerebrospinal fluid proximity extension assays and co-expression network analysis of 2,943 proteins, we found common and distinct proteomic signatures between white matter lesions (WML), microbleeds and infarcts measured in 856 living patients, and validated WML-associated proteins in three additional datasets. Proteins indicative of extracellular matrix dysregulation and vascular remodeling, including ELN, POSTN, CCN2 and MMP12 were elevated across all cSVD manifestations, with MMP12 emerging as an early cSVD indicator. cSVD-associated proteins formed a co-abundance network linked to metabolism and enriched in endothelial and arterial smooth muscle cells, showing elevated levels at early disease manifestations. Later disease stages involved changes in microglial proteins, associated with longitudinal WML progression, and changes in neuronal proteins mediating WML-associated cognitive decline. These findings provide an atlas of novel cSVD biomarkers and a promising roadmap for the next generation of cSVD therapeutics.

Activation of NLRP3 inflammasome in a rat model of cerebral small vessel disease

Cerebral small vessel disease (CSVD) is increasingly being recognized as a leading contributor to cognitive impairment in the elderly. However, there is a lack of effective preventative or therapeutic options for CSVD. In this exploratory study, we investigated the interplay between neuroinflammation and CSVD pathogenesis as well as the cognitive performance, focusing on NLRP3 signaling as a new therapeutic target. Spontaneously hypertensive stroke-prone (SHRSP) rats served as a CSVD model. We found that SHRSP rats showed decline in learning and memory abilities using morris water maze test. Activated NLRP3 signaling and an increased expression of the downstream pro-inflammatory factors, including IL (interleukin)-6 and tumor necrosis factor α were determined. We also observed a remarkable increase in the production of pyroptosis executive protein gasdermin D, and elevated astrocytic and microglial activation. In addition, we identify several neuropathological hallmarks of CSVD, including blood-brain barrier breakdown, white matter damage, and endothelial dysfunction. These results were in correlation with the activation of NLRP3 inflammasome. Thus, our findings reveal that the NLRP3-mediated inflammatory pathway could play a central role in the pathogenesis of CSVD, presenting a novel target for potential CSVD treatment.

Matrix metalloproteinase 9 (MMP-9) activity, hippocampal extracellular free water, and cognitive deficits are associated with each other in early phase psychosis

Increasing evidence points toward the role of the extracellular matrix, specifically matrix metalloproteinase 9 (MMP-9), in the pathophysiology of psychosis. MMP-9 is a critical regulator of the crosstalk between peripheral and central inflammation, extracellular matrix remodeling, hippocampal development, synaptic pruning, and neuroplasticity. Here, we aim to characterize the relationship between plasma MMP-9 activity, hippocampal microstructure, and cognition in healthy individuals and individuals with early phase psychosis. We collected clinical, blood, and structural and diffusion-weighted magnetic resonance imaging data from 39 individuals with early phase psychosis and 44 age and sex-matched healthy individuals. We measured MMP-9 plasma activity, hippocampal extracellular free water (FW) levels, and hippocampal volumes. We used regression analyses to compare MMP-9 activity, hippocampal FW, and volumes between groups. We then examined associations between MMP-9 activity, FW levels, hippocampal volumes, and cognitive performance assessed with the MATRICS battery. All analyses were controlled for age, sex, body mass index, cigarette smoking, and years of education. Individuals with early phase psychosis demonstrated higher MMP-9 activity (p < 0.0002), higher left (p < 0.05) and right (p < 0.05) hippocampal FW levels, and lower left (p < 0.05) and right (p < 0.05) hippocampal volume than healthy individuals. MMP-9 activity correlated positively with hippocampal FW levels (all participants and individuals with early phase psychosis) and negatively with hippocampal volumes (all participants and healthy individuals). Higher MMP-9 activity and higher hippocampal FW levels were associated with slower processing speed and worse working memory performance in all participants. Our findings show an association between MMP-9 activity and hippocampal microstructural alterations in psychosis and an association between MMP-9 activity and cognitive performance. Further, more extensive longitudinal studies should examine the therapeutic potential of MMP-9 modulators in psychosis.

MINocyclinE to Reduce inflammation and blood-brain barrier leakage in small Vessel diseAse (MINERVA): A phase II, randomized, double-blind, placebo-controlled experimental medicine trial

INTRODUCTION

Cerebral small vessel disease (SVD) is a common cause of stroke/vascular dementia with few effective treatments. Neuroinflammation and increased blood-brain barrier (BBB) permeability may influence pathogenesis. In rodent models, minocycline reduced inflammation/BBB permeability. We determined whether minocycline had a similar effect in patients with SVD.

METHODS

MINERVA was a single-center, phase II, randomized, double-blind, placebo-controlled trial. Forty-four participants with moderate-to-severe SVD took minocycline or placebo for 3 months. Co-primary outcomes were microglial signal (determined using 11C-PK11195 positron emission tomography) and BBB permeability (using dynamic contrast-enhanced MRI).

RESULTS

Forty-four participants were recruited between September 2019 and June 2022. Minocycline had no effect on 11C-PK11195 binding (relative risk [RR] 1.01, 95% confidence interval [CI] 0.98-1.04), or BBB permeability (RR 0.97, 95% CI 0.91-1.03). Serum inflammatory markers were not affected.

DISCUSSION

11C-PK11195 binding and increased BBB permeability are present in SVD; minocycline did not reduce either process. Whether these pathophysiological mechanisms are disease-causing remains unclear.

INTERNATIONAL CLINICAL TRIALS REGISTRY PORTAL IDENTIFIER

ISRCTN15483452 HIGHLIGHTS: We found focal areas of increased microglial signal and increased blood-brain barrier permeability in patients with small vessel disease. Minocycline treatment was not associated with a change in these processes measured using advanced neuroimaging. Blood-brain barrier permeability was dynamic but MRI-derived measurements correlated well with CSF/serum albumin ratio. Advanced neuroimaging is a feasible outcome measure for mechanistic clinical trials.

Targeting inflammation to reduce recurrent stroke

BACKGROUND

Approximately one in four stroke patients suffer from recurrent vascular events, underlying the necessity to improve secondary stroke prevention strategies. Immune mechanisms are causally associated with coronary atherosclerosis. However, stroke is a heterogeneous disease and the relative contribution of inflammation across stroke mechanisms is not well understood. The optimal design of future randomized control trials (RCTs) of anti-inflammatory therapies to prevent recurrence after stroke must be informed by a clear understanding of the prognostic role of inflammation according to stroke subtype and individual patient factors.

AIM

In this narrative review, we discuss (1) inflammatory pathways in the etiology of ischemic stroke subtypes; (2) the evidence on inflammatory markers and vascular recurrence after stroke; and (3) review RCT evidence of anti-inflammatory agents for vascular prevention.

SUMMARY OF REVIEW

Experimental work, genetic epidemiological data, and plaque-imaging studies all implicate inflammation in atherosclerotic stroke. However, emerging evidence also suggests that inflammatory mechanisms are also important in other stroke mechanisms. Advanced neuroimaging techniques support the role of neuroinflammation in blood-brain barrier dysfunction in cerebral small vessel disease (cSVD). Systemic inflammatory processes also promote atrial cardiopathy, incident and recurrent atrial fibrillation (AF). Although several inflammatory markers have been associated with recurrence after stroke, interleukin-6 (IL-6) and high-sensitivity C-reactive protein (hsCRP) are presently the most promising markers to identify patients at increased vascular risk. Several RCTs have shown that anti-inflammatory therapies reduce vascular risk, including stroke, in coronary artery disease (CAD). Some, but not all of these trials, selected patients on the basis of elevated hsCRP. Although unproven after stroke, targeting inflammation to reduce recurrence is a compelling strategy and several RCTs are ongoing.

CONCLUSION

Evidence points toward the importance of inflammation across multiple stroke etiologies and potential benefit of anti-inflammatory targets in secondary stroke prevention. Taking the heterogeneous stroke etiologies into account, the use of serum biomarkers could be useful to identify patients with residual inflammatory risk and perform biomarker-led patient selection for future RCTs.

Novel perfluorocarbon-based oxygenation therapy alleviates Post-SAH hypoxic brain injury by inhibiting HIF-1α

In comparison to other stroke types, subarachnoid hemorrhage (SAH) is characterized by an early age of onset and often results in poor prognosis. The inadequate blood flow at the site of the lesion leads to localized oxygen deprivation, increased level of hypoxia-inducible factor-1α (HIF-1α), and triggers inflammatory responses and oxidative stress, ultimately causing hypoxic brain damage. Despite the potential benefits of oxygen (O2) administration, there is currently a lack of efficient focal site O2 delivery following SAH. Conventional clinical O2 supply methods, such as transnasal oxygenation and hyperbaric oxygen therapy, do not show the ideal therapeutic effect in severe SAH patients. The perfluorocarbon oxygen carrier (PFOC) demonstrates efficacy in transporting O2 and responding to elevated levels of CO2 at the lesion site. Through cellular experiments, we determined that PFOC oxygenation serves as an effective therapeutic approach in inhibiting hypoxia. Furthermore, our animal experiments showed that PFOC oxygenation outperforms O2 breathing, leading to microglia phenotypic switching and the suppression of inflammatory response via the inhibition of HIF-1α. Therefore, as a new type of O2 therapy after SAH, PFOC oxygenation can effectively reduce hypoxic brain injury and improve neurological function.

Immune regulation and blood-brain barrier permeability in cerebral small vessel disease: study protocol of the INflammation and Small Vessel Disease (INSVD) study - a multicentre prospective cohort study

INTRODUCTION

The INflammation and Small Vessel Disease (INSVD) study aims to investigate whether peripheral inflammation, immune (dys)regulation and blood-brain barrier (BBB) permeability relate to disease progression in cerebral small vessel disease (SVD). This research aims to pinpoint specific components of the immune response in SVD relating to disease progression. This could identify biomarkers of SVD progression, as well as potential therapeutic targets to inform the development and repurposing of drugs to reduce or prevent SVD, cognitive decline and vascular dementia.

METHODS AND ANALYSIS

INSVD is a prospective observational multicentre cohort study in individuals with symptomatic SVD. This longitudinal study combines comprehensive immunophenotyping of the peripheral blood immune compartment with advanced neuroimaging markers of SVD and BBB permeability. The main SVD marker of interest is white matter microstructure as determined by diffusion tensor imaging, a valuable marker of disease progression owing to its sensitivity to early alterations to white matter integrity. The research is being conducted in two sites-in the UK (Cambridge) and the Netherlands (Nijmegen)-with each site recruiting 100 participants (total n=200). Participants undergo clinical and cognitive assessments, blood draws, and brain MRI at baseline and 2-year follow-up.

ETHICS AND DISSEMINATION

This study received ethical approval from the local ethics boards (UK: East of England-Cambridge Central Research Ethics Committee (REC) ref: 22/EE/00141, Integrated Research Application System (IRAS) ID: 312 747. Netherlands: Medical Research Ethics Committee (MREC) Oost-Nederland, ref: 2022-13623, NL-number: NL80258.091.22). Written informed consent was obtained from all subjects before the study. Any participant-derived benefits resulting from this research, such as new insights into disease mechanisms or possible novel therapies, will be disseminated to study participants, patient groups and members of the public.

TRIAL REGISTRATION NUMBER

NCT05746221.

Genotypes of Stim1 and the proximal region on chromosome 1 exert opposite effects on stroke susceptibility in stroke-prone spontaneously hypertensive rat

BACKGROUND

The stroke-prone spontaneously hypertensive rat (SHRSP) is a genetic model for cerebral stroke. Although a recent study on a congenic SHRSP suggested that a nonsense mutation in stromal interaction molecule 1 ( Stim1 ) encoding a major component of store-operated Ca 2+ entry was a causal variant for stroke in SHRSP, this was not conclusive because the congenic region including Stim1 in that rat was too wide. On the other hand, we demonstrated that the Wistar-Kyoto (WKY)-derived congenic fragment adjacent to Stim1 exacerbated stroke susceptibility in a congenic SHRSP called SPwch1.71. In the present study, we directly examined the effects of the Stim1 genotype on stroke susceptibility using SHRSP in which wild-type Stim1 was knocked in (called Stim1 -KI SHRSP). The combined effects of Stim1 and the congenic fragment of SPwch1.71 were also investigated.

METHODS

Stroke susceptibility was assessed by the stroke symptom-free and survival periods based on observations of behavioral symptoms and reductions in body weight.

RESULTS

Stim1 -KI SHRSP was more resistant to, while SPwch1.71 was more susceptible to stroke than the original SHRSP. Introgression of the wild-type Stim1 of Stim1 -KI SHRSP into SPwch1.71 by the generation of F1 rats ameliorated stroke susceptibility in SPwch1.71. Gene expression, whole-genome sequencing, and biochemical analyses identified Art2b , Folr1 , and Pde2a as possible candidate genes accelerating stroke in SPwch1.71.

CONCLUSION

The substitution of SHRSP-type Stim1 to wild-type Stim1 ameliorated stroke susceptibility in both SHRSP and SPwch1.71, indicating that the nonsense mutation in Stim1 is causally related to stroke susceptibility in SHRSP.

[Cerebral Small Vessel Disease: Advances in Understanding its Pathophysiology]

Sporadic cerebral small vessel disease determines age- and vascular-risk-factor-related processes of the small brain vasculature. The underlying pathology develops in a stage-dependent manner - probably over decades - often already starting in midlife. Endothelial and pericyte activation precedes blood-brain barrier leaks, extracellular matrix remodeling and neuroinflammation, which ultimately result in bleeds, synaptic and neural dysfunction. Hemodynamic compromise of the small vessel walls promotes perivascular drainage failure and accumulation of neurotoxic waste products in the brain. Clinical diagnosis is mainly based on magnetic resonance imaging according to the Standards for Reporting Vascular Changes on Neuroimaging 2. Cerebral amyloid angiopathy is particularly stratified according to the Boston v2.0 criteria. Small vessel disease of the brain could be clinically silent, or manifested through a heterogeneous spectrum of diseases, where cognitive decline and stroke-related symptoms are the most common ones. Prevention and therapy are centered around vascular risk factor control, physically and cognitively enriched life style and, presumably, maintenance of a good sleep quality, which promotes sufficient perivascular drainage. Prevention of ischemic stroke through anticoagulation that carries at the same time an increased risk for large brain hemorrhages - particularly in the presence of disseminated cortical superficial siderosis - remains one of the main challenges. The cerebral small vessel disease field is rapidly evolving, focusing on the establishment of early disease stage imaging and biofluid biomarkers of neurovascular unit remodeling and the compromise of perivascular drainage. New prevention and therapy strategies will correspondingly center around the dedicated targeting of, e. g., cellular small vessel wall and perivascular tissue structures. Growing knowledge about brain microvasculature bridging neuroimmunological, neurovascular and neurodegenerative fields might lead to a rethink about apparently separate disease entities and the development of overarching concepts for a common line of prevention and treatment for several diseases.

A cluster of blood-based protein biomarkers associated with decreased cerebral blood flow relates to future cardiovascular events in patients with cardiovascular disease

Biological processes underlying decreased cerebral blood flow (CBF) in patients with cardiovascular disease (CVD) are largely unknown. We hypothesized that identification of protein clusters associated with lower CBF in patients with CVD may explain underlying processes. In 428 participants (74% cardiovascular diseases; 26% reference participants) from the Heart-Brain Connection Study, we assessed the relationship between 92 plasma proteins from the Olink® cardiovascular III panel and normal-appearing grey matter CBF, using affinity propagation and hierarchical clustering algorithms, and generated a Biomarker Compound Score (BCS). The BCS was related to cardiovascular risk and observed cardiovascular events within 2-year follow-up using Spearman correlation and logistic regression. Thirteen proteins were associated with CBF (ρSpearman range: -0.10 to -0.19, pFDR-corrected <0.05), and formed one cluster. The cluster primarily reflected extracellular matrix organization processes. The BCS was higher in patients with CVD compared to reference participants (pFDR-corrected <0.05) and was associated with cardiovascular risk (ρSpearman 0.42, p < 0.001) and cardiovascular events (OR 2.05, p < 0.01). In conclusion, we identified a cluster of plasma proteins related to CBF, reflecting extracellular matrix organization processes, that is also related to future cardiovascular events in patients with CVD, representing potential targets to preserve CBF and mitigate cardiovascular risk in patients with CVD.

Pathophysiology and probable etiology of cerebral small vessel disease in vascular dementia and Alzheimer's disease

Vascular cognitive impairment and dementia (VCID) is commonly caused by vascular injuries in cerebral large and small vessels and is a key driver of age-related cognitive decline. Severe VCID includes post-stroke dementia, subcortical ischemic vascular dementia, multi-infarct dementia, and mixed dementia. While VCID is acknowledged as the second most common form of dementia after Alzheimer's disease (AD) accounting for 20% of dementia cases, VCID and AD frequently coexist. In VCID, cerebral small vessel disease (cSVD) often affects arterioles, capillaries, and venules, where arteriolosclerosis and cerebral amyloid angiopathy (CAA) are major pathologies. White matter hyperintensities, recent small subcortical infarcts, lacunes of presumed vascular origin, enlarged perivascular space, microbleeds, and brain atrophy are neuroimaging hallmarks of cSVD. The current primary approach to cSVD treatment is to control vascular risk factors such as hypertension, dyslipidemia, diabetes, and smoking. However, causal therapeutic strategies have not been established partly due to the heterogeneous pathogenesis of cSVD. In this review, we summarize the pathophysiology of cSVD and discuss the probable etiological pathways by focusing on hypoperfusion/hypoxia, blood-brain barriers (BBB) dysregulation, brain fluid drainage disturbances, and vascular inflammation to define potential diagnostic and therapeutic targets for cSVD.

Acupuncture with twirling reinforcing and reducing manipulation shows a control of hypertension and regulation of blood pressure-related target brain regions in spontaneously hypertensive rat: a preliminary resting-state functional MRI study

Aim

To observe the effects of acupuncture manipulations on blood pressure and brain function in spontaneously hypertensive rats and elucidate the anti-hypertensive effect of the manipulations' central mechanism.

Methods

This study used acupuncture twirling reinforcing, acupuncture twirling reducing, and acupuncture twirling uniform reinforcing-reducing manipulations to act on the bilateral TaiChong point of rats. The depth of acupuncture was 1.5-2 mm, and twisting was performed at a frequency of 60 times/min within ±360° for 3 min, followed by the needle being retained for 17 min. Functional magnetic resonance imaging was performed at the end of the intervention. Regional homogeneity and amplitude of low-frequency fluctuations were used to assess the differences in brain regions in each group of rats, and the core brain region (left hypothalamus) among the differential brain regions was selected as the seed for functional connectivity analysis.

Results

(1) The anti-hypertensive effect was achieved by acupuncture manipulations, and the anti-hypertensive effect of twirling reducing manipulation on spontaneously hypertensive rats was better than that of twirling uniform reinforcing-reducing and twirling reinforcing manipulations. (2) After regional homogeneity and amplitude of low-frequency fluctuations analyses, the hypothalamus, the brain region related to blood pressure, was activated in the twirling uniform reinforcing-reducing manipulation group; the corpus callosum and cerebellum were activated in the twirling reinforcing manipulation group; and the hypothalamus, olfactory bulb, corpus callosum, brainstem, globus pallidum, and striatum were activated in the twirling reducing manipulation group. (3) According to the functional connectivity analysis, different acupuncture manipulations increased the functional connections between seed points and the brainstem, olfactory bulb, and cerebellum, etc.

Conclusion

These results suggest that acupuncture manipulations achieved the hypotensive effect and the twirling reducing manipulation had a better hypotensive effect on spontaneously hypertensive rats than twirling uniform reinforcing-reducing and twirling reinforcing manipulations; the central mechanism of the anti-hypertensive effect of twirling reinforcing and reducing manipulation may be related to the activation of brain regions associated with blood pressure regulation and the functional connections between them. Furthermore, brain regions involved in motor control, cognition, and hearing were also activated. We hypothesize that activation of these brain regions may help prevent or mitigate the onset and progression of hypertensive brain damage.

Low vitamin D status is associated with inflammatory response in older patients with cerebral small vessel disease

OBJECTIVES

This study aimed to determine the association of the NF-κB inflammatory signaling pathway with vitamin D status in older cerebral small vessel disease (SVD) patients.

METHODS

We measured serum 25(OH)D, pro-and anti-inflammatory cytokines, and mRNA levels of the vitamin D-activating enzyme, CYP27B1, as well as NF-kB, COX-2, the chemokine-CCL2, IL-1β, IL-6, TNF-α, TGF-β, and IL-10, in cerebral SVD patients aged ≥60 years presenting with vascular dementia and age and gender-matched healthy controls.

RESULTS

Low vitamin D status (insufficiency: serum 25(OH)D 12-20 ng/ml; deficiency: ≤12 ng/ml) was more prevalent among patients compared to controls. The mRNA levels of NF-kB, COX-2, CCL2, IL-1β, and IL-6, and serum levels of pro-inflammatory cytokines (IL-1α, IL-1β, IL-6, and TNF-α) were significantly higher in cases compared to controls. There was a significant correlation between CYP27B1 and NF-kB, COX-2, CCL2, and IL-1β gene expression. Serum IL-1α, IL-1β, and IL-6 concentrations and the expression of CCL-2, NF-kB2, and NF-kB3 genes were higher in vitamin D-deficient subjects compared to vitamin D-sufficient subjects. There was a significant negative correlation between serum 25(OH)D and IL-1α, IL-6, and TNF-α, and a positive correlation between 25(OH)D and IL-10.

CONCLUSION

Low vitamin D is associated with an inflammatory response via NF-kB signaling, which could play a role in the etio-pathogenesis of SVD. Further large-scale studies are required to validate our findings.

Do Regions of Increased Inflammation Progress to New White Matter Hyperintensities?: A Longitudinal Positron Emission Tomography-Magnetic Resonance Imaging Study

BACKGROUND

Recent studies have demonstrated increased microglial activation using 11C-PK11195 positron emission tomography imaging, indicating central nervous system inflammation, in cerebral small vessel disease. However, whether such areas of neuroinflammation progress to tissue damage is uncertain. We determined whether white matter destined to become white matter hyperintensities (WMH) at 1 year had evidence of altered inflammation at baseline.

METHODS

Forty subjects with small vessel disease (20 sporadic and 20 cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy) and 20 controls were recruited to this case-control observational study from in- and out-patient clinics at Addenbrooke's Hospital, Cambridge, UK and imaged at baseline with both 11C-PK11195 positron emission tomography and magnetic resonance imaging; and magnetic resonance imaging including diffusion tensor imaging was repeated at 1 year. WMH were segmented at baseline and 1 year, and areas of new lesion identified. Baseline 11C-PK11195 binding potential and diffusion tensor imaging parameters in these voxels, and normal appearing white matter, was measured.

RESULTS

Complete positron emission tomography-magnetic resonance imaging data was available for 17 controls, 16 sporadic small vessel disease, and 14 cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy participants. 11C-PK11195 binding in voxels destined to become new WMH was lower than in normal appearing white matter, which did not progress to WMH (-0.133[±0.081] versus -0.045 [±0.044]; P<0.001). Mean diffusivity was higher and mean fractional anisotropy lower in new WMH voxels than in normal appearing white matter (900 [±80]×10-6 versus 1045 [±149]×10-6 mm2/s and 0.37±0.05 versus 0.29±0.06, both P<0.001) consistent with new WMH showing tissue damage on diffusion tensor imaging a year prior to developing into new WMH; similar results were seen across the 3 groups.

CONCLUSIONS

White matter tissue destined to develop into new WMH over the subsequent year is associated with both lower neuroinflammation, and white matter ultrastructural damage at baseline. Our results suggest that this tissue is already damaged 1 year prior to lesion formation. This may reflect that the role of neuroinflammation in the lesion development process occurs at an early stage, although more studies over a longer period would be needed to investigate this further.

Soluble TREM2, Alzheimer's Disease Pathology, and Risk for Progression of Cerebral Small Vessel Disease: A Longitudinal Study

BackgroundUntil recently, studies on associations between neuroinflammation in vivo and cerebral small vessel disease (CSVD) are scarce. Cerebrospinal fluid (CSF) levels of soluble triggering receptor expressed on myeloid cells 2 (sTREM2), a candidate biomarker of microglial activation and neuroinflammation, were found elevated in Alzheimer's disease (AD), but they have not been fully explored in CSVD.ObjectiveTo determine whether CSF sTREM2 levels are associated with the increased risk of CSVD progression.MethodsA total of 426 individuals from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database were included in this study. All participants underwent measurements of CSF sTREM2 and AD pathology (Aβ1-42, P-tau181P). The progression of CSVD burden and imaging markers, including cerebral microbleeds (CMBs), white matter hyperintensities and lacunes, were estimated based on neuroimaging changes. Logistic regression and moderation effect models were applied to explore associations of sTREM2 with CSVD progression and AD pathology.Results Higher CSF sTREM2 levels at baseline were associated with increased CSVD burden (OR = 1.28 [95% CI, 1.01-1.62]) and CMBs counts (OR = 1.32 [95% CI, 1.03-1.68]). Similarly, increased change rates of CSF sTREM2 might predict elevated CMBs counts (OR = 1.44 [95% CI, 1.05-1.98]). Participants with AD pathology (Aβ1-42 and P-tau181P) showed a stronger association between CSF sTREM2 and CSVD progression.ConclusionThis longitudinal study found a positive association between CSF sTREM2 and CSVD progression, suggesting that neuroinflammation might promote CSVD. Furthermore, neuroinflammation could be a shared pathogenesis of CSVD and AD at the early stage. Targeting neuroinflammation to intervene the progression of CSVD and AD warrants further investigation.

Cerebral small vessel disease: Recent advances and future directions

Cerebral small vessel disease (SVD) causes lacunar stroke and intracerebral hemorrhage, and is the most common pathology underlying vascular cognitive impairment. Increasingly, the importance of other clinical features of SVD is being recognized including motor impairment, (vascular) parkinsonism, impaired balance, falls, and behavioral symptoms, such as depression, apathy, and personality change. Epidemiological data show a high prevalence of the characteristic magnetic resonance imaging (MRI) features of white matter hyperintensities and lacunar infarcts in community studies, and recent data suggest that it is also a major health burden in low- and middle-income countries. In this review, we cover advances in diagnosis, imaging, clinical presentations, pathogenesis, and treatment.The two most common pathologies underlying SVD are arteriolosclerosis caused by aging, hypertension, and other conventional vascular risk factors, and cerebral amyloid angiopathy (CAA) caused by vascular deposition of β-amyloid. We discuss the revised Boston criteria of CAA based on MRI features, which have been recently validated. Imaging is providing important insights into pathogenesis, including improved detection of tissue damage using diffusion tensor imaging (DTI) leading to its use to monitor progression and surrogate endpoints in clinical trials. Advanced MRI techniques can demonstrate functional or dynamic abnormalities of the blood vessels, while the high spatial resolution provided by ultrahigh field MRI at 7 T allows imaging of individual perforating arteries for the first time, and the measurement of flow velocity and pulsatility within these arteries. DTI and structural network analysis have highlighted the importance of network disruption in mediating the effect of different SVD pathologies in causing a number of symptoms, including cognitive impairment, apathy, and gait disturbance.Despite the public health importance of SVD, there are few proven treatments. We review the evidence for primary prevention, and recent data showing how intensive blood pressure lowering reduces white matter hyperintensities (WMH) progression and delays the onset of cognitive impairment. There are few treatments for secondary prevention, but a number of trials are currently evaluating novel treatment approaches. Recent advances have implicated molecular processes related to endothelial dysfunction, nitric oxide synthesis, blood-brain barrier integrity, maintenance and repair of the extracellular matrix, and inflammation. Novel treatment approaches are being developed to a number of these targets. Finally, we highlight the importance of large International collaborative initiatives in SVD to address important research questions and cover a number which have recently been established.

Plasma inflammatory biomarkers in cerebral small vessel disease: A review

Cerebral small vessel disease (CSVD) is a group of pathological processes affecting small arteries, arterioles, capillaries, and small veins of the brain. It is one of the most common subtypes of cerebrovascular diseases, especially highly prevalent in elderly populations, and is associated with stroke occurrence and recurrence, cognitive impairment, gait disorders, psychological disturbance, and dysuria. Its diagnosis mainly depends on MRI, characterized by recent small subcortical infarcts, lacunes, white matter hyperintensities (WMHs), enlarged perivascular spaces (EPVS), cerebral microbleeds (CMBs), and brain atrophy. While the pathophysiological processes of CSVD are not fully understood at present, inflammation is noticed as playing an important role. Herein, we aimed to review the relationship between plasma inflammatory biomarkers and the MRI features of CSVD, to provide background for further research.

Willis Lecture: Biomarkers for Inflammatory White Matter Injury in Binswanger Disease Provide Pathways to Precision Medicine

Binswanger disease is the small vessel form of vascular cognitive impairment and dementia. Deposition of Alzheimer disease proteins can begin in midlife and progress slowly, whereas aging of the vasculature also can begin in midlife, continuing to progress into old age, making mixed dementia the most common type of dementia. Biomarkers facilitate the early diagnosis of dementias. It is possible to diagnose mixed dementia before autopsy with biomarkers for vascular disease derived from diffusor tensor images on magnetic resonance imaging and Alzheimer disease proteins, Aβ (amyloid β), and phosphorylated tau, in cerebrospinal fluid or in brain with positron emission tomography. The presence of vascular disease accelerates cognitive decline. Both misfolded proteins and vascular disease promote inflammation, which can be detected in cerebrospinal fluid by the presence of MMPs (matrix metalloproteinases), angiogenic growth factors, and cytokines. MMPs disrupt the blood-brain barrier and break down myelin, producing Binswanger disease's 2 main pathological features. Advances in detecting biomarkers in plasma will provide early detection of dementia and aided by machine learning and artificial intelligence, will enhance diagnosis and form the basis for early treatments.

Cerebral small vessel disease: Pathological mechanisms and potential therapeutic targets

Cerebral small vessel disease (CSVD) represents a diverse cluster of cerebrovascular diseases primarily affecting small arteries, capillaries, arterioles and venules. The diagnosis of CSVD relies on the identification of small subcortical infarcts, lacunes, white matter hyperintensities, perivascular spaces, and microbleeds using neuroimaging. CSVD is observed in 25% of strokes worldwide and is the most common pathology of cognitive decline and dementia in the elderly. Still, due to the poor understanding of pathophysiology in CSVD, there is not an effective preventative or therapeutic approach for CSVD. The most widely accepted approach to CSVD treatment is to mitigate vascular risk factors and adopt a healthier lifestyle. Thus, a deeper understanding of pathogenesis may foster more specific therapies. Here, we review the underlying mechanisms of pathological characteristics in CSVD development, with a focus on endothelial dysfunction, blood-brain barrier impairment and white matter change. We also describe inflammation in CSVD, whose role in contributing to CSVD pathology is gaining interest. Finally, we update the current treatments and preventative measures of CSVD, as well as discuss potential targets and novel strategies for CSVD treatment.

Cognitive decline in heart failure: Biomolecular mechanisms and benefits of exercise

By definition, heart failure (HF) is a human pathological condition affecting the structure and function of all organs in the body, and the brain is not an exception to that. Failure of the heart to pump enough blood centrally and peripherally is at the foundation of HF patients' inability to attend even the most ordinary daily activities and progressive deterioration of their cognitive capacity. What is more, between heart and brain exists a bidirectional relationship that goes well beyond hemodynamics and concerns bioelectric and endocrine signaling. This increasingly consolidated evidence makes the scenario even more complex. Studies have mainly chased how HF impairs cognition without focusing much on preventive measures, notably cardio-cerebral health proxies. Here, we aim to provide a brief account of known and hypothetical factors that may explain how exercise can help obviate cognitive dysfunction associated with HF in its different forms. As we shall see, there is a stringent need for a deeper grasp of such mechanisms. Indeed, gaining this new knowledge will automatically shed new light on the inner workings of HF itself, thus resulting in more effective prevention and treatment of this escalating syndrome.

Metformin, Rapamycin, or Nicotinamide Mononucleotide Pretreatment Attenuate Cognitive Impairment After Cerebral Hypoperfusion by Inhibiting Microglial Phagocytosis

Vascular cognitive impairment (VCI) is the second leading form of dementia after Alzheimer's disease (AD) plaguing the elder population. Despite the enormous prevalence of VCI, the biological basis of this disease has been much less well-studied than that of AD, with no specific therapy currently existing to prevent or treat VCI. As VCI mainly occurs in the elderly, the role of anti-aging drugs including metformin, rapamycin, and nicotinamide mono nucleotide (NMN), and the underlying mechanism remain uncertain. Here, we examined the role of metformin, rapamycin, and NMN in cognitive function, white matter integrity, microglial response, and phagocytosis in a rat model of VCI by bilateral common carotid artery occlusion (BCCAO). BCCAO-induced chronic cerebral hypoperfusion could cause spatial working memory deficits and white matter lesions (WMLs), along with increasing microglial activation and phagocytosis compared to sham-operated rats. We found the cognitive impairment was significantly improved in BCCAO rats pretreated with these three drugs for 14 days before BCCAO compared with the vehicle group by the analysis of the Morris water maze and new object recognition tests. Pretreatment of metformin, rapamycin, or NMN also increased myelin basic protein (MBP, a marker for myelin) expression and reduced SMI32 (a marker for demyelinated axons) intensity and SMI32/MBP ratio compared with the vehicle group, suggesting that these drugs could ameliorate BCCAO-induced WMLs. The findings were confirmed by Luxol fast blue (LFB) stain, which is designed for staining myelin/myelinated axons. We further found that pretreatment of metformin, rapamycin, or NMN reduced microglial activation and the number of M1 microglia, but increased the number of M2 microglia compared to the vehicle group. Importantly, the number of MBP⁺/Iba1⁺/CD68⁺ microglia was significantly reduced in the BCCAO rats pretreated with these three drugs compared with the vehicle group, suggesting that these drugs suppress microglial phagocytosis. No significant difference was found between the groups pretreated with metformin, rapamycin, or NMN. Our data suggest that metformin, rapamycin, or NMN could protect or attenuate cognitive impairment and WMLs by modifying microglial polarization and inhibiting phagocytosis. The findings may open a new avenue for VCI treatment.

Neuroinflammation in Vascular Cognitive Impairment and Dementia: Current Evidence, Advances, and Prospects

Vascular cognitive impairment and dementia (VCID) is a major heterogeneous brain disease caused by multiple factors, and it is the second most common type of dementia in the world. It is caused by long-term chronic low perfusion in the whole brain or local brain area, and it eventually develops into severe cognitive dysfunction syndrome. Because of the disease’s ambiguous classification and diagnostic criteria, there is no clear treatment strategy for VCID, and the association between cerebrovascular pathology and cognitive impairment is controversial. Neuroinflammation is an immunological cascade reaction mediated by glial cells in the central nervous system where innate immunity resides. Inflammatory reactions could be triggered by various damaging events, including hypoxia, ischemia, and infection. Long-term chronic hypoperfusion-induced ischemia and hypoxia can overactivate neuroinflammation, causing apoptosis, blood–brain barrier damage and other pathological changes, triggering or aggravating the occurrence and development of VCID. In this review, we will explore the mechanisms of neuroinflammation induced by ischemia and hypoxia caused by chronic hypoperfusion and emphasize the important role of neuroinflammation in the development of VCID from the perspective of immune cells, immune mediators and immune signaling pathways, so as to provide valuable ideas for the prevention and treatment of the disease.

MINocyclinE to Reduce inflammation and blood brain barrier leakage in small Vessel diseAse (MINERVA) trial study protocol

Background:

Cerebral small vessel disease (SVD) is a common cause of stroke and cognitive impairment. Recent data has implicated neuroinflammation and increased blood-brain barrier (BBB) permeability in its pathogenesis, but whether such processes are causal and can be therapeutically modified is uncertain. In a rodent model of SVD, minocycline was associated with reduced white matter lesions, inflammation and BBB permeability.

Aims:

To determine whether blood-brain barrier permeability (measured using dynamic contrast-enhanced MRI) and microglial activation (measured by positron emission tomography using the radioligand 11C-PK11195) can be modified in SVD.

Design:

Phase II randomised double blind, placebo-controlled trial of minocycline 100 mg twice daily for 3 months in 44 participants with moderate to severe SVD defined as a clinical lacunar stroke and confluent white matter hyperintensities.

Outcomes:

Primary outcome measures are volume and intensity of focal increases of blood-brain barrier permeability and microglial activation determined using PET-MRI imaging. Secondary outcome measures include inflammatory biomarkers in serum, and change in conventional MRI markers and cognitive performance over 1 year follow up.

Discussion:

The MINERVA trial aims to test whether minocycline can influence novel pathological processes thought to be involved in SVD progression, and will provide insights into whether central nervous system inflammation in SVD can be therapeutically modulated.

Vascular cognitive impairment and dementia: An early career researcher perspective

The field of vascular contributions to cognitive impairment and dementia (VCID) is evolving rapidly. Research in VCID encompasses topics aiming to understand, prevent, and treat the detrimental effects of vascular disease burden in the human brain. In this perspective piece, early career researchers (ECRs) in the field provide an overview of VCID, discuss past and present efforts, and highlight priorities for future research. We emphasize the following critical points as the field progresses: (a) consolidate existing neuroimaging and fluid biomarkers, and establish their utility for pharmacological and non-pharmacological interventions; (b) develop new biomarkers, and new non-clinical models that better recapitulate vascular pathologies; (c) amplify access to emerging biomarker and imaging techniques; (d) validate findings from previous investigations in diverse populations, including those at higher risk of cognitive impairment (e.g., Black, Hispanic, and Indigenous populations); and (e) conduct randomized controlled trials within diverse populations with well-characterized vascular pathologies emphasizing clinically meaningful outcomes.

Stroke Genetics: Discovery, Insight Into Mechanisms, and Clinical Perspectives

Stroke is the second leading cause of death worldwide and a complex, heterogeneous condition. In this review, we provide an overview of the current knowledge on monogenic and multifactorial forms of stroke, highlighting recent insight into the continuum between these. We describe how, in recent years, large-scale genome-wide association studies have enabled major progress in deciphering the genetic basis for stroke and its subtypes, although more research is needed to interpret these findings. We cover the potential of stroke genetics to reveal novel pathophysiological processes underlying stroke, to accelerate the discovery of new therapeutic approaches, and to identify individuals in the population who are at high risk of stroke and could be targeted for tailored preventative interventions.

Cardiovascular co-morbidities, inflammation and cerebral small vessel disease

Cerebral small vessel disease (cSVD) is the most common cause of vascular cognitive impairment and affects all levels of the brain's vasculature. Features include diverse structural and functional changes affecting small arteries and capillaries that lead to a decline in cerebral perfusion. Due to an aging population, incidence of cerebral small vessel disease (cSVD) is continually rising. Despite its prevalence and its ability to cause multiple debilitating illnesses, such as stroke and dementia, there are currently no therapeutic strategies for the treatment of cSVD. In the healthy brain, interactions between neuronal, vascular and inflammatory cells are required for normal functioning. When these interactions are disturbed, chronic pathological inflammation can ensue. The interplay between cSVD and inflammation has attracted much recent interest and this review discusses chronic cardiovascular diseases, particularly hypertension, and explores how the associated inflammation may impact on the structure and function of the small arteries of the brain in cSVD. Molecular approaches in animal studies are linked to clinical outcomes in patients and novel hypotheses regarding inflammation and cSVD are proposed that will hopefully stimulate further discussion and study in this important area.

Neuroprotective effect of minocycline on rat retinal ischemia-reperfusion injury

Purpose

To examine the neuroprotective effect of minocycline on retinal ischemia-reperfusion (IR) injury in rats and investigate its possible mechanism of action.

Methods

Retinal IR injury was established by increasing the intraocular pressure in rats up to 110 mmHg for 60 min. The animals with retinal IR injury were intraperitoneally injected with 22.5 mg/kg minocycline twice a day for 14 days. The control group received the same amount of saline. Subsequently, funduscopic examination, retinal thickness measurement, retinal microvascular morphology, full-field electroretinography (ERG), retinal apoptotic cell count, and remaining retinal ganglion cell (RGC) count were performed. The expression of iNOS, Bax, Bcl2, IL-1α, IL-6, TNF-α, caspase-3, GFAP, Iba-1, Hif-1α, and Nrf2 was examined with real-time PCR and western blotting.

Results

Minocycline treatment prevented IR-induced rat retinal edema and retinal cells apoptosis at the early stage and alleviated retina atrophy, blood vessel tortuosity, functional photoreceptor damage, and RGC degeneration at the late stage of the IR injury. At the molecular level, minocycline affected retinal gene and protein expression induced by IR.

Conclusions

The results suggested that minocycline has a neuroprotective effect on rat retinal IR injury, possibly through anti-inflammation, antiapoptosis, antioxidation, and inhibition of microglial activation.

Microglial activation and blood-brain barrier leakage: chicken and egg?

This scientific commentary refers to ‘Microglial activation and blood–brain barrier permeability in cerebral small vessel disease’ by Walsh et al. (doi:10.1093/brain/awab003).

Microglial activation and blood-brain barrier permeability in cerebral small vessel disease

Cerebral small vessel disease (SVD) is a major cause of stroke and dementia. The underlying pathogenesis is poorly understood, but both neuroinflammation and increased blood-brain barrier permeability have been hypothesized to play a role, and preclinical studies suggest the two processes may be linked. We used PET magnetic resonance to simultaneously measure microglial activation using the translocator protein radioligand 11C-PK11195, and blood-brain barrier permeability using dynamic contrast enhanced MRI. A case control design was used with two disease groups with sporadic SVD (n = 20), monogenic SVD (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, CADASIL), and normal controls (n = 20) were studied. Hotspots of increased glial activation and blood-brain barrier permeability were identified as values greater than the 95th percentile of the distribution in controls. In sporadic SVD there was an increase in the volume of hotspots of both 11C-PK11195 binding (P = 0.003) and blood-brain barrier permeability (P = 0.007) in the normal appearing white matter, in addition to increased mean blood-brain barrier permeability (P < 0.001). In CADASIL no increase in blood-brain barrier permeability was detected; there was a non-significant trend to increased 11C-PK11195 binding (P = 0.073). Hotspots of 11C-PK11195 binding and blood-brain barrier permeability were not spatially related. A panel of 93 blood biomarkers relating to cardiovascular disease, inflammation and endothelial activation were measured in each participant; principal component analysis was performed and the first component related to blood-brain barrier permeability and microglial activation. Within the sporadic SVD group both hotspot and mean volume blood-brain barrier permeability values in the normal appearing white matter were associated with dimension 1 (β  =  0.829, P = 0.017, and β  =  0.976, P = 0.003, respectively). There was no association with 11C-PK11195 binding. No associations with blood markers were found in the CADASIL group. In conclusion, in sporadic SVD both microglial activation and increased blood-brain barrier permeability occur, but these are spatially distinct processes. No evidence of increased blood-brain barrier permeability was found in CADASIL.

Improving Age-Related Cognitive Decline through Dietary Interventions Targeting Mitochondrial Dysfunction

Aging is inevitable and it is one of the major contributors to cognitive decline. However, the mechanisms underlying age-related cognitive decline are still the object of extensive research. At the biological level, it is unknown how the aging brain is subjected to progressive oxidative stress and neuroinflammation which determine, among others, mitochondrial dysfunction. The link between mitochondrial dysfunction and cognitive impairment is becoming ever more clear by the presence of significant neurological disturbances in human mitochondrial diseases. Possibly, the most important lifestyle factor determining mitochondrial functioning is nutrition. Therefore, with the present work, we review the latest findings disclosing a link between nutrition, mitochondrial functioning and cognition, and pave new ways to counteract cognitive decline in late adulthood through diet.

The gut microbiome contributes to blood-brain barrier disruption in spontaneously hypertensive stroke prone rats

In recent years, it has become apparent that the gut microbiome can influence the functioning and pathological states of organs and systems throughout the body. In this study, we tested the hypothesis that the gut microbiome has a major role in the disruption of the blood-brain barrier (BBB) in the spontaneously hypertensive stroke prone rats (SHRSP), an animal model for hypertensive cerebral small vessel disease (CSVD). Loss of BBB is thought to be an early and initiating component to the full expression of CSVD in animal models and humans. To test this hypothesis, newly born SHRSP pups were placed with foster dams of the SHRSP strain or dams of the WKY strain, the control strain that does not demonstrate BBB dysfunction or develop hypertensive CSVD. Similarly, WKY pups were placed with foster dams of the same or opposite strain. The rationale for cross fostering is that the gut microbiomes are shaped by environmental bacteria of the foster dam and the nesting surroundings. Analysis of the bacterial genera in feces, using 16S rRNA analysis, demonstrated that the gut microbiome in the rat pups was influenced by the foster dam. SHRSP offspring fostered on WKY dams had systolic blood pressures (SBPs) that were significantly decreased by 26 mmHg (P < .001) from 16-20 weeks, compared to SHRSP offspring fostered on SHRSP dams. Similarly WKY offspring fostered on SHRSP dams had significantly increased SBP compared to WKY offspring fostered on WKY dams, although the magnitude of SBP change was not as robust. At ~20 weeks of age, rats fostered on SHRSP dams showed enhanced inflammation in distal ileum regardless of the strain of the offspring. Disruption of BBB integrity, an early marker of CSVD onset, was improved in SHRSPs that were fostered on WKY dams when compared to the SHRSP rats fostered on SHRSP dams. Although SHRSP is a genetic model for CSVD, environmental factors such as the gut microbiota of the foster dam have a major influence in the loss of BBB integrity.

Modeling subcortical ischemic white matter injury in rodents: unmet need for a breakthrough in translational research

Subcortical ischemic white matter injury (SIWMI), pathological correlate of white matter hyperintensities or leukoaraiosis on magnetic resonance imaging, is a common cause of cognitive decline in elderly. Despite its high prevalence, it remains unknown how various components of the white matter degenerate in response to chronic ischemia.This incomplete knowledge is in part due to a lack of adequate animal model. The current review introduces various SIWMI animal models and aims to scrutinize their advantages and disadvantages primarily in regard to the pathological manifestations of white matter components. The SIWMI animal models are categorized into 1) chemically induced SIWMI models, 2) vascular occlusive SIWMI models, and 3) SIWMI models with comorbid vascular risk factors. Chemically induced models display consistent lesions in predetermined areas of the white matter, but the abrupt evolution of lesions does not appropriately reflect the progressive pathological processes in human white matter hyperintensities. Vascular occlusive SIWMI models often do not exhibit white matter lesions that are sufficiently unequivocal to be quantified. When combined with comorbid vascular risk factors (specifically hypertension), however, they can produce progressive and definitive white matter lesions including diffuse rarefaction, demyelination, loss of oligodendrocytes, and glial activation, which are by far the closest to those found in human white matter hyperintensities lesions. However, considerable surgical mortality and unpredictable natural deaths during a follow-up period would necessitate further refinements in these models. In the meantime, in vitro SIWMI models that recapitulate myelinated white matter track may be utilized to study molecular mechanisms of the ischemic white matter injury. Appropriate in vivo and in vitro SIWMI models will contribute in a complementary manner to making a breakthrough in developing effective treatment to prevent progression of white matter hyperintensities.

In vivo neuroinflammation and cerebral small vessel disease in mild cognitive impairment and Alzheimer's disease

INTRODUCTION

Associations between cerebral small vessel disease (SVD) and inflammation have been largely examined using peripheral blood markers of inflammation, with few studies measuring inflammation within the brain. We investigated the cross-sectional relationship between SVD and in vivo neuroinflammation using [11C]PK11195 positron emission tomography (PET) imaging.

METHODS

Forty-two participants were recruited (according to NIA-AA guidelines, 14 healthy controls, 14 mild Alzheimer's disease, 14 amyloid-positive mild cognitive impairment). Neuroinflammation was assessed using [11C]PK11195 PET imaging, a marker of microglial activation. To quantify SVD, we assessed white matter hyperintensities (WMH), enlarged perivascular spaces, cerebral microbleeds and lacunes. Composite scores were calculated for global SVD burden, and SVD subtypes of hypertensive arteriopathy and cerebral amyloid angiopathy (CAA). General linear models examined associations between SVD and [11C]PK11195, adjusting for sex, age, education, cognition, scan interval, and corrected for multiple comparisons via false discovery rate (FDR). Dominance analysis directly compared the relative importance of hypertensive arteriopathy and CAA scores as predictors of [11C]PK11195.

RESULTS

Global [11C]PK11195 binding was associated with SVD markers, particularly in regions typical of hypertensive arteriopathy: deep microbleeds (β=0.63, F(1,35)=35.24, p<0.001), deep WMH (β=0.59, t=4.91, p<0.001). In dominance analysis, hypertensive arteriopathy score outperformed CAA in predicting [11C]PK11195 binding globally and in 28 out of 37 regions of interest, especially the medial temporal lobe (β=0.66-0.76, t=3.90-5.58, FDR-corrected p (pFDR)=<0.001-0.002) and orbitofrontal cortex (β=0.51-0.57, t=3.53-4.30, pFDR=0.001-0.004).

CONCLUSION

Microglial activation is associated with SVD, particularly with the hypertensive arteriopathy subtype of SVD. Although further research is needed to determine causality, our study suggests that targeting neuroinflammation might represent a novel therapeutic strategy for SVD.

Cerebrovascular disease promotes tau pathology in Alzheimer's disease

Small vessel cerebrovascular disease, visualized as white matter hyperintensities on T2-weighted magnetic resonance imaging, contributes to the clinical presentation of Alzheimer's disease. However, the extent to which cerebrovascular disease represents an independent pathognomonic feature of Alzheimer's disease or directly promotes Alzheimer's pathology is unclear. The purpose of this study was to examine the association between white matter hyperintensities and plasma levels of tau and to determine if white matter hyperintensities and tau levels interact to predict Alzheimer's disease diagnosis. To confirm that cerebrovascular disease promotes tau pathology, we examined tau fluid biomarker concentrations and pathology in a mouse model of ischaemic injury. Three hundred ninety-one participants from the Alzheimer's Disease Neuroimaging Initiative (74.5 ± 7.1 years of age) were included in this cross-sectional analysis. Participants had measurements of plasma total-tau, cerebrospinal fluid beta-amyloid, and white matter hyperintensities, and were diagnosed clinically as Alzheimer's disease (n = 97), mild cognitive impairment (n = 186) or cognitively normal control (n = 108). We tested the relationship between plasma tau concentration and white matter hyperintensity volume across diagnostic groups. We also examined the extent to which white matter hyperintensity volume, plasma tau, amyloid positivity status and the interaction between white matter hyperintensities and plasma tau correctly classifies diagnostic category. Increased white matter hyperintensity volume was associated with higher plasma tau concentration, particularly among those diagnosed clinically with Alzheimer's disease. Presence of brain amyloid and the interaction between plasma tau and white matter hyperintensity volume distinguished Alzheimer's disease and mild cognitive impairment participants from controls with 77.6% and 63.3% accuracy, respectively. In 63 Alzheimer's Disease Neuroimaging Initiative participants who came to autopsy (82.33 ± 7.18 age at death), we found that higher degrees of arteriosclerosis were associated with higher Braak staging, indicating a positive relationship between cerebrovascular disease and neurofibrillary pathology. In a transient middle cerebral artery occlusion mouse model, aged mice that received transient middle cerebral artery occlusion, but not sham surgery, had increased plasma and cerebrospinal fluid tau concentrations, induced myelin loss, and hyperphosphorylated tau pathology in the ipsilateral hippocampus and cerebral hemisphere. These findings demonstrate a relationship between cerebrovascular disease, operationalized as white matter hyperintensities, and tau levels, indexed in the plasma, suggesting that hypoperfusive injury promotes tau pathology. This potential causal association is supported by the demonstration that transient cerebral artery occlusion induces white matter damage, increases biofluidic markers of tau, and promotes cerebral tau hyperphosphorylation in older-adult mice.

Longshengzhi Capsules Improve Ischemic Stroke Outcomes and Reperfusion Injury via the Promotion of Anti-Inflammatory and Neuroprotective Effects in MCAO/R Rats

Stroke is the leading cause of death in the elderly. Traditional Chinese medicine provides an exciting strategy for treating stroke. Previous reports indicated that Longshengzhi capsules (LSZ), a modified Chinese formula, reduced formed thrombi and oxidative stress and were promising in the clinical treatment of ischemic stroke. However, the specific therapeutic effect and mechanism of LSZ are still ambiguous. This study aimed to define the effects of LSZ on proinflammatory mediators and neuroprotective effects on middle cerebral artery occlusion and refusion (MCAO/R) rats. Rats were treated with different doses of LSZ (0.54, 1.62, and 4.32 g/(kg·d)) in a week after model building. LSZ could improve the survival rate, ischemic stroke outcome, and infarct volume. In addition, significant decrease was observed in reactive oxygen species (ROS) levels and inflammatory factor levels in LSZ-treated groups, concomitant with increase in activities of superoxide dismutase (SOD), neurosynaptic remodeling, and decrease in brain edema. It is proposed that LSZ has anti-inflammatory and neuroprotective effects resulting in downregulating matrix metalloproteinase 2/9 (MMP-2/9) and vascular endothelial growth factor (VEGF) and nuclear factor kappa-B (NF-κB) and upregulating microtubule-associated protein-2 (Map-2) and growth-associated protein-43 (GAP-43) via p38 MAPK and HIF-1α signaling pathways in MCAO/R rats. This study provides potential evidences that p38 MAPK and HIF-1α/VEGF signaling pathways play significant roles in the anti-inflammatory and neuroprotective effects of LSZ.

Small Vessel Disease-Related Dementia: An Invalid Neurovascular Coupling?

The arteriosclerosis-dependent alteration of brain perfusion is one of the major determinants in small vessel disease, since small vessels have a pivotal role in the brain's autoregulation. Nevertheless, as far as we know, endothelium distress can potentiate the flow dysregulation and lead to subcortical vascular dementia that is related to small vessel disease (SVD), also being defined as subcortical vascular dementia (sVAD), as well as microglia activation, chronic hypoxia and hypoperfusion, vessel-tone dysregulation, altered astrocytes, and pericytes functioning blood-brain barrier disruption. The molecular basis of this pathology remains controversial. The apparent consequence (or a first event, too) is the macroscopic alteration of the neurovascular coupling. Here, we examined the possible mechanisms that lead a healthy aging process towards subcortical dementia. We remarked that SVD and white matter abnormalities related to age could be accelerated and potentiated by different vascular risk factors. Vascular function changes can be heavily influenced by genetic and epigenetic factors, which are, to the best of our knowledge, mostly unknown. Metabolic demands, active neurovascular coupling, correct glymphatic process, and adequate oxidative and inflammatory responses could be bulwarks in defense of the correct aging process; their impairments lead to a potentially catastrophic and non-reversible condition.

Proceedings from the Albert Charitable Trust Inaugural Workshop on white matter and cognition in aging

This third in a series of vascular cognitive impairment (VCI) workshops, supported by "The Leo and Anne Albert Charitable Trust," was held from February 8 to 12 at the Omni Resort in Carlsbad, CA. This workshop followed the information gathered from the earlier two workshops suggesting that we focus more specifically on brain white matter in age-related cognitive impairment. The Scientific Program Committee (Frank Barone, Shawn Whitehead, Eric Smith, and Rod Corriveau) assembled translational, clinical, and basic scientists with unique expertise in acute and chronic white matter injury at the intersection of cerebrovascular and neurodegenerative etiologies. As in previous Albert Trust workshops, invited participants addressed key topics related to mechanisms of white matter injury, biomarkers of white matter injury, and interventions to prevent white matter injury and age-related cognitive decline. This report provides a synopsis of the presentations and discussions by the participants, including the existing knowledge gaps and the delineation of the next steps towards advancing our understanding of white matter injury and age-related cognitive decline. Workshop discussions and consensus resulted in action by The Albert Trust to (1) increase support from biannual to annual "White Matter and Cognition" workshops; (2) provide funding for two collaborative, novel research grants annually submitted by meeting participants; and (3) coordinate the formation of the "Albert Research Institute for White Matter and Cognition." This institute will fill a gap in white matter science, providing white matter and cognition communications, including annual updates from workshops and the literature and interconnecting with other Albert Trust scientific endeavors in cognition and dementia, and providing support for newly established collaborations between seasoned investigators and to the development of talented young investigators in the VCI-dementia (VCID) and white matter cognition arena.

Opportunities and Limitations of Vascular Risk Factor Models in Studying Plasticity-Promoting and Restorative Ischemic Stroke Therapies

Major efforts are currently made promoting neuronal plasticity and brain remodeling in the postacute stroke phase. Experimental studies evaluating new stroke therapies are mostly performed in rodents, which compared to humans exhibit a short lifespan. These studies widely employ young, otherwise healthy, rodents that lack the vascular risk factors and comorbidities of stroke patients. These risk factors compromise postischemic neurological recovery and brain plasticity and in several contexts reduce the brain responsiveness to recovery-inducing plasticity-promoting treatments. By examining risk factor models, which have hitherto been used for studying experimentally induced ischemic stroke, this review outlines the possibilities and limitations of risk factor models in the evaluation of plasticity-promoting and restorative stroke treatments.