Low serum insulin-like growth factor-I (IGF-I) level is associated with increased risk of vascular dementia

Clinical laboratory tests and dementia incidence: A prospective cohort study

BACKGROUND

Dementia is a major public health issue and a heavy economic burden. It is urgently necessary to understand the underlying biological processes and to identify biomarkers predicting risk of dementia in the preclinical stage for prevention and treatment.

METHODS

By using the data of the 367,093 white British individuals from UK Biobank, we investigated the relationship between 56 laboratory measures and 5-year dementia incidence using logistic regression. Adjusted odds ratios for dementia incidence with values below or above the 95 % confidence interval (<2.5th or > 97.5th percentile) on each of clinical laboratory tests were computed.

RESULTS

We observed that markers of endocrine dysregulation: elevated hemoglobin A1C (AOR = 2.01 [1.35, 2.88]) was associated with increased dementia incidence. Indicators of liver dysfunction: elevated gamma glutamyltransferase (AOR = 2.28 [1.49, 3.32]), and albumin (AOR = 2.01 [1.15, 3.25]), indicators of renal impairment: high urea (AOR = 1.69 [1.15, 2.40]), and cystatin C (AOR = 1.89 [1.30, 2.67]), and some immune markers, like elevated neutrophill count, low lymphocyte count, and indicators of anemia were also observed to be associated with increased dementia incidence. Both low and high concentrations of insulin-like growth factor 1 were found to be risk factors for dementia.

LIMITATIONS

This is an observational study.

CONCLUSION

Several systemic biomarkers were associated with dementia incidence. These results implicate a contributory role of diverse biological processes to dementia onset, and enrich our understanding of potential dementia prevention strategy.

The Associations Between Serum Insulin-like Growth Factor-I, Brain White Matter Volumes, and Cognition in Mild Cognitive Impairment and Alzheimer's Disease

Background

Insulin-like growth factor-I (IGF-I) regulates myelin, but little is known whether IGF-I associates with white matter functions in subjective and objective mild cognitive impairment (SCI/MCI) or Alzheimer's disease (AD).

Objective

To explore whether serum IGF-I is associated with magnetic resonance imaging - estimated brain white matter volumes or cognitive functions.

Methods

In a prospective study of SCI/MCI (n = 106) and AD (n = 59), we evaluated the volumes of the total white matter, corpus callosum (CC), and white matter hyperintensities (WMHs) as well as Mini-Mental State Examination (MMSE), Trail Making Test A and B (TMT-A/B), and Stroop tests I-III at baseline, and after 2 years.

Results

IGF-I was comparable in SCI/MCI and AD (113 versus 118 ng/mL, p = 0.44). In SCI/MCI patients, the correlations between higher baseline IGF-I and greater baseline and 2-year volumes of the total white matter and total CC lost statistical significance after adjustment for intracranial volume and other covariates. However, after adjustment for covariates, higher baseline IGF-I correlated with better baseline scores of MMSE and Stroop test II in SCI/MCI and with better baseline results of TMT-B and Stroop test I in AD. IGF-I did not correlate with WMH volumes or changes in any of the variables.

Conclusions

Both in SCI/MCI and AD, higher IGF-I was associated with better attention/executive functions at baseline after adjustment for covariates. Furthermore, the baseline associations between IGF-I and neuropsychological test results in AD may argue against significant IGF-I resistance in the AD brain.

Molecular biomarkers for vascular cognitive impairment and dementia

As disease-specific interventions for dementia are being developed, the ability to identify the underlying pathology and dementia subtypes is increasingly important. Vascular cognitive impairment and dementia (VCID) is the second most common cause of dementia after Alzheimer disease, but progress in identifying molecular biomarkers for accurate diagnosis of VCID has been relatively limited. In this Review, we examine the roles of large and small vessel disease in VCID, considering the underlying pathophysiological processes that lead to vascular brain injury, including atherosclerosis, arteriolosclerosis, ischaemic injury, haemorrhage, hypoperfusion, endothelial dysfunction, blood-brain barrier breakdown, inflammation, oxidative stress, hypoxia, and neuronal and glial degeneration. We consider the key molecules in these processes, including proteins and peptides, metabolites, lipids and circulating RNA, and consider their potential as molecular biomarkers alone and in combination. We also discuss the challenges in translating the promise of these biomarkers into clinical application.

Repositioning of Anti-Diabetic Drugs against Dementia: Insight from Molecular Perspectives to Clinical Trials

Insulin resistance as a hallmark of type 2 DM (T2DM) plays a role in dementia by promoting pathological lesions or enhancing the vulnerability of the brain. Numerous studies related to insulin/insulin-like growth factor 1 (IGF-1) signaling are linked with various types of dementia. Brain insulin resistance in dementia is linked to disturbances in Aβ production and clearance, Tau hyperphosphorylation, microglial activation causing increased neuroinflammation, and the breakdown of tight junctions in the blood-brain barrier (BBB). These mechanisms have been studied primarily in Alzheimer's disease (AD), but research on other forms of dementia like vascular dementia (VaD), Lewy body dementia (LBD), and frontotemporal dementia (FTD) has also explored overlapping mechanisms. Researchers are currently trying to repurpose anti-diabetic drugs to treat dementia, which are dominated by insulin sensitizers and insulin substrates. Although it seems promising and feasible, none of the trials have succeeded in ameliorating cognitive decline in late-onset dementia. We highlight the possibility of repositioning anti-diabetic drugs as a strategy for dementia therapy by reflecting on current and previous clinical trials. We also describe the molecular perspectives of various types of dementia through the insulin/IGF-1 signaling pathway.

Insulin resistance, cognition, and Alzheimer disease

Chronic diseases of aging are increasingly common. Dementia, often due to multiple etiologies including Alzheimer disease (AD), is at the forefront. Previous studies have reported higher rates of dementia among persons with diabetes, yet less is known about how insulin resistance relates to cognition. This article reviews recently published data on the relationship of insulin resistance to cognition and AD, and remaining knowledge gaps in the field are discussed. A structured review of studies was conducted over a 5-year period, investigating insulin and cognitive function in adults with a baseline mean age of ≥65 years. This search yielded 146 articles, of which 26 met the predetermined inclusion and exclusion criteria. Among the nine studies that specifically examined insulin resistance and cognitive dysfunction and/or decline, eight studies suggest an association, but some only in subanalyses. Results are mixed in studies relating insulin to structural and functional changes on brain imaging, and data on intranasal insulin for cognition remain unclear. Future avenues are proposed to elucidate the impact of insulin resistance on brain structure and function, including cognition, in persons with and without AD.

Effects of Resistance Exercise on Neuroprotective Factors in Middle and Late Life: A Systematic Review and Meta-Analysis

Neuroprotective factors are involved in brain functioning. Although physical exercise has been shown to have a positive influence on these factors, the effect of resistance exercise on them is not well known. This systematic review and meta-analysis aimed to 1) estimate the efficacy of resistance exercise on major neuroprotective factors, such as insulin-like growth factor-1 (IGF-1), brain-derived neurotrophic factor (BDNF), and vascular endothelial growth factor (VEGF), in middle and late life and 2) determine whether the effect is dose dependent. A systematic search was conducted in CINAHL, Cochrane CENTRAL, MEDLINE, Scopus, PEDro, SPORTDiscus, and Web of Science up to November 2022. Random effects models were used to estimate standardized mean differences (SMDs) and their respective 95% confidence intervals (CI) for the effect of resistance exercise on peripheral IGF-1, BDNF or VEGF levels in older adults. Thirty randomized clinical trials with 1247 subjects (53.25% women, 45-92 years) were included in the systematic review, and 27 were selected for the meta-analysis. A significant effect of resistance exercise on IGF-1 levels was observed (SMD: 0.48; 95% CI: 0.27, 0.69), being more effective when performing 3 sessions/week (SMD: 0.55; 95% CI: 0.31, 0.79) but not on BDNF (SMD: 0.33; 95% CI: -0.29, 0.94). The effect on VEGF could not be determined due to the scarcity of studies. Our data support the resistance training recommendation in middle and late life, at a frequency of at least 3 sessions/week, to mitigate the neurological and cognitive consequences associated with aging, mainly through IGF-1.

Cell non-autonomous regulation of cerebrovascular aging processes by the somatotropic axis

Age-related cerebrovascular pathologies, ranging from cerebromicrovascular functional and structural alterations to large vessel atherosclerosis, promote the genesis of vascular cognitive impairment and dementia (VCID) and exacerbate Alzheimer's disease. Recent advances in geroscience, including results from studies on heterochronic parabiosis models, reinforce the hypothesis that cell non-autonomous mechanisms play a key role in regulating cerebrovascular aging processes. Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) exert multifaceted vasoprotective effects and production of both hormones is significantly reduced in aging. This brief overview focuses on the role of age-related GH/IGF-1 deficiency in the development of cerebrovascular pathologies and VCID. It explores the mechanistic links among alterations in the somatotropic axis, specific macrovascular and microvascular pathologies (including capillary rarefaction, microhemorrhages, impaired endothelial regulation of cerebral blood flow, disruption of the blood brain barrier, decreased neurovascular coupling, and atherogenesis) and cognitive impairment. Improved understanding of cell non-autonomous mechanisms of vascular aging is crucial to identify targets for intervention to promote cerebrovascular and brain health in older adults.

Identification of the molecular mechanism of insulin-like growth factor-1 (IGF-1): a promising therapeutic target for neurodegenerative diseases associated with metabolic syndrome

Neurodegenerative disorders are accompanied by neuronal degeneration and glial dysfunction, resulting in cognitive, psychomotor, and behavioral impairment. Multiple factors including genetic, environmental, metabolic, and oxidant overload contribute to disease progression. Recent evidences suggest that metabolic syndrome is linked to various neurodegenerative diseases. Metabolic syndrome (MetS) is known to be accompanied by symptoms such as hyperglycemia, abdominal obesity, hypertriglyceridemia, and hypertension. Despite advances in knowledge about the pathogenesis of neurodegenerative disorders, effective treatments to combat neurodegenerative disorders caused by MetS have not been developed to date. Insulin growth factor-1 (IGF-1) deficiency has been associated with MetS-related pathologies both in-vivo and in-vitro. IGF-1 is essential for embryonic and adult neurogenesis, neuronal plasticity, neurotropism, angiogenesis, metabolic function, and protein clearance in the brain. Here, we review the evidence for the potential therapeutic effects of IGF-1 in the neurodegeneration related to metabolic syndrome. We elucidate how IGF-1 may be involved in molecular signaling defects that occurs in MetS-related neurodegenerative disorders and highlight the importance of IGF-1 as a potential therapeutic target in MetS-related neurological diseases.

Patients with Alzheimer's Disease Have Increased Levels of Insulin-like Growth Factor-I in Serum but not in Cerebrospinal Fluid

BACKGROUND

Insulin-like growth factor-I (IGF-I) is important for amyloid-β (Aβ) metabolism, and also interacts with the brain vasculature. In previous IGF-I studies, it has not been evaluated whether Alzheimer's disease (AD) patients had vascular comorbidities.

OBJECTIVE AND METHODS

A cross-sectional study of 40 consecutive non-diabetic AD patients and 36 healthy controls. We measured IGF-I in serum and cerebrospinal fluid (CSF) and also serum insulin. Mixed forms of AD and vascular dementia were excluded.

RESULTS

After adjustment for covariates including age, serum IGF-I level was higher in the AD group than in the controls, whereas CSF IGF-I and serum insulin were unchanged. Binary logistic regression confirmed that high serum IGF-I was associated with increased prevalence of AD [adjusted Odds Ratio (OR) = 1.83, 95% confidence interval (CI): 1.005-3.32 per standard deviation (SD) increase in serum IGF-I]. This association was more robust after exclusion of patients receiving treatment with acetylcholinesterase inhibitors or N-methyl D-aspartate (NMDA) receptor antagonists (OR = 2.23, 95 % CI: 1.10-4.48). In the total study population (n = 76) as well in the AD group (n = 40), serum IGF-I correlated negatively with CSF Aβ1-42, and CSF IGF-I correlated positively with CSF/serum albumin ratio, CSF total tau, and CSF phosphorylated tau.

CONCLUSION

In AD patients without major brain vascular comorbidities, serum but not CSF levels of IGF-I were increased after correction for covariates. This association was strengthened by exclusion of patients receiving medical treatment. Overall, the results support the notion of IGF-I resistance in mild AD dementia.

Growth Hormone Receptor Regulation in Cancer and Chronic Diseases

The GHR signaling pathway plays important roles in growth, metabolism, cell cycle control, immunity, homeostatic processes, and chemoresistance via both the JAK/STAT and the SRC pathways. Dysregulation of GHR signaling is associated with various diseases and chronic conditions such as acromegaly, cancer, aging, metabolic disease, fibroses, inflammation and autoimmunity. Numerous studies entailing the GHR signaling pathway have been conducted for various cancers. Diverse factors mediate the up- or down-regulation of GHR signaling through post-translational modifications. Of the numerous modifications, ubiquitination and deubiquitination are prominent events. Ubiquitination by E3 ligase attaches ubiquitins to target proteins and induces proteasomal degradation or starts the sequence of events that leads to endocytosis and lysosomal degradation. In this review, we discuss the role of first line effectors that act directly on the GHR at the cell surface including ADAM17, JAK2, SRC family member Lyn, Ubc13/CHIP, proteasome, βTrCP, CK2, STAT5b, and SOCS2. Activity of all, except JAK2, Lyn and STAT5b, counteract GHR signaling. Loss of their function increases the GH-induced signaling in favor of aging and certain chronic diseases, exemplified by increased lung cancer risk in case of a mutation in the SOCS2-GHR interaction site. Insight in their roles in GHR signaling can be applied for cancer and other therapeutic strategies.

Blood-based biomarkers in hypothalamic-pituitary axes for the risk of dementia or cognitive decline: a systematic review and meta-analysis

Blood-based biomarkers are ideal candidates for dementia prediction. This systematic review and meta-analysis aimed to evaluate longitudinal relationships of blood hormones and hormone-binding proteins in hypothalamic-pituitary (HP) axes with dementia or cognitive decline. PubMed, MEDLINE, EMBASE, PsycINFO, and BIOSIS were systematically searched from 1919 to June 2020. Fifteen types of hormones and four types of hormone-binding proteins were measured in 48 prospective studies. Increased risk of dementia or cognitive decline could be predicted by elevated blood concentrations of free-thyroxine (free-T4, RR = 1.06, p = 0.001) and sex hormone-binding globulin (SHBG, RR = 1.10, p = 0.025). Lower thyroid-stimulating hormone (TSH) levels within (RR = 1.28, p < 0.001) and below (RR = 1.27, p = 0.004) the normal range were both risky. Current evidence suggests the alterations of multiple blood molecules in HP axes, especially TSH, free-T4, and SHBG precede the incidence of dementia or cognitive decline. The underpinning etiology remains to be elucidated in the future.

Cerebrolysin in the therapy of mild cognitive impairment and dementia due to Alzheimer's disease: 30 years of clinical use

Alzheimer's disease (AD) is the most common neurocognitive disorder and a global health problem. The prevalence of AD is growing dramatically, especially in low- and middle-income countries, and will reach 131.5 million cases worldwide by 2050. Therefore, developing a disease-modifying therapy capable of delaying or even preventing the onset and progression of AD has become a world priority, and is an unmet need. The pathogenesis of AD, considered as the result of an imbalance between resilience and risk factors, begins many years before the typical clinical picture develops and involves multiple pathophysiological mechanisms. Since the pathophysiology of AD is multifactorial, it is not surprising that all attempts done to modify the disease course with drugs directed towards a single therapeutic target have been unsuccessful. Thus, combined modality therapy, using multiple drugs with a single mechanism of action or multi-target drugs, appears as the most promising strategy for both effective AD therapy and prevention. Cerebrolysin, acting as a multitarget peptidergic drug with a neurotrophic mode of action, exerts long-lasting therapeutic effects on AD that could reflect its potential utility for disease modification. Clinical trials demonstrated that Cerebrolysin is safe and efficacious in the treatment of AD, and may enhance and prolong the efficacy of cholinergic drugs, particularly in moderate to advanced AD patients. In this review, we summarize advances of therapeutic relevance in the pathogenesis and the biomarkers of AD, paying special attention to neurotrophic factors, and present results of preclinical and clinical investigations with Cerebrolysin in AD.

Latent Cognitive Profiles Differ Between Incipient Alzheimer's Disease and Dementia with Subcortical Vascular Lesions in a Memory Clinic Population

BACKGROUND

It is unclear if latent cognitive profiles can distinguish between dementia with subcortical vascular lesions and Alzheimer's disease (AD) at the incipient stage, and if they differ in performance from the Petersen subtypes.

OBJECTIVE

To identify latent cognitive profiles in a naturalistic population of patients from a memory clinic sample, and investigate the derived classes not only in terms of conversion to AD, but also in terms of conversion to dementia with subcortical vascular lesions. Another objective was to compare the derived classes to the Petersen subtypes.

METHODS

We performed a latent profile analysis (LPA) on standardized neuropsychological test scores from 476 memory clinic patients (age 64±8) without dementia, and analyzed progression to dementia after 2 years.

RESULTS

The LPA resulted in two classes with impaired cognition (Amnestic and Slow/Dysexecutive) and two classes with normal cognition (Normal-Low and Normal-High cognition). Belonging to the Amnestic class predicted progression to all-cause dementia and to AD; belonging to the Slow/Dysexecutive class predicted progression to all-cause dementia, AD, and dementia with subcortical vascular lesions. Of the Petersen MCI subtypes, only amnestic multi-domain MCI predicted progression to all-cause dementia, AD, and dementia with subcortical vascular lesions.

CONCLUSION

Latent cognitive profiles separated between AD and dementia with subcortical vascular lesions, while the Petersen subtypes did not. However, similar to the Petersen subtypes, LPA classes work better for ruling out progression to dementia than for case finding.

The role of exercise in the reversal of IGF-1 deficiencies in microvascular rarefaction and hypertension

Hypertension has been linked with peripheral and central reductions in vascular density, and with devastating effects on brain function. However, the underlying mechanisms in the relationship between blood pressure and cognitive impairment have yet to be fully elucidated. Here, we review compelling evidence from two lines of inquiry: one that links microvascular rarefaction with insulin-like growth factor 1 (IGF-1) deficiencies, and another which posits that vascular dysfunction precedes hypertension. Based on the findings from experimental and clinical studies, we propose that these lines of evidence converge, and suggest that age-related declines in IGF-1 concentrations precede microvascular rarefaction, initiate an increase in vascular resistance, and therefore are causally linked to onset of hypertension. Physical exercise provides a relevant model for supporting our premise, given the well-established effects of exercise in attenuating vascular dysfunction, hypertension, IGF-1 deficiency, and cognitive decline. We highlight here the role of exercise-induced increases in blood flow in improving vascular integrity and enhancing angiogenesis via the actions of IGF-1, resulting in reversal of rarefaction and hypertension, and enhancement of cerebral blood flow and cognition.

The enigmatic role of growth hormone in age-related diseases, cognition, and longevity

Growth hormone (GH) is secreted by the anterior pituitary gland and regulates various metabolic processes throughout the body. GH and IGF-1 levels are markedly reduced in older humans, leading some to hypothesize GH supplementation could be a viable "anti-aging" therapy. However, there is still much debate over the benefits and risks of GH administration. While an early study of GH administration reported reduced adiposity and lipid levels and increased bone mineral density, subsequent studies failed to show significant benefits. Conversely, other studies found positive effects of GH deficiency including extended life span, improved cognitive function, resistance to diseases such as cancer and diabetes, and improved insulin sensitivity despite a higher fat percentage. Thus, the roles of GH in aging and cognition remain unclear, and there is currently not enough evidence to support use of GH as an anti-aging or cognitive impairment therapy. Additional robust and longer-duration studies of efficacy and safety of GH administration are needed to determine if modulating GH levels could be a successful strategy for treating aging and age-related diseases.

G protein-coupled estrogen receptor is involved in the neuroprotective effect of IGF-1 against MPTP/MPP+-induced dopaminergic neuronal injury

Insulin-like growth factor-1 (IGF-1), an endogenous peptide, exerts important role in brain development, neurogenesis and neuroprotection. There are accumulating evidence for the interaction of IGF-1 and 17β-estradiol systems. IGF-1/IGF-1 receptor (IGF-1R) signaling has been reported to regulate G-protein estrogen receptor (GPER) expression in cancer cells. Whether GPER is involved in the neuroprotective effect of IGF-1 against MPTP/MPP⁺-induced dopaminergic neuronal injury remains unclear. We showed that IGF-1 could improve MPTP-induced motor deficits and ameliorate the decreased contents of DA and its metabolites in striatum as well as the loss of TH-IR neurons in the substantia nigra (SN). IGF-1 pretreatment also reversed the changes of Bcl-2 and Bax protein expressions in SN in MPTP mice. These effects were abolished by IGF-1 receptor (IGF-1R) antagonist JB-1 or GPER antagonist G15 except the inhibitory effect of G15 on Bax protein expression. Moreover, IGF-1 pretreatment enhanced cell survival against MPP⁺-induced neurotoxicity in SH-SY5Y cells. IGF-1 exerted anti-apoptotic effects by restoring MPP⁺-induced changes of Bcl-2 and Bax protein expressions as well as mitochondria membrane potential. Co-treatment with JB-1 or G15 could block these effects. Furthermore, IGF-1 regulated the protein expression of GPER through activation of phosphatidylinositol 3-kinase (PI3-K) and mitogen-activated protein kinase (MAPK) signaling pathways. Overall, we show for the first time that GPER may contribute to the neuroprotective effects of IGF-1 against MPTP/MPP⁺-induced dopaminergic neuronal injury.

Early Secure Attachment as a Protective Factor Against Later Cognitive Decline and Dementia

The etiology of neurodegenerative disorders such as dementia is complex and incompletely understood. Interest in a developmental perspective to these pathologies is gaining momentum. An early supportive social environment seems to have important implications for social, affective and cognitive abilities across the lifespan. Attachment theory may help to explain the link between these early experiences and later outcomes. This theory considers early interactions between an infant and its caregiver to be crucial to shaping social behavior and emotion regulation strategies throughout adult life. Furthermore, research has demonstrated that such early attachment experiences can, potentially through epigenetic mechanisms, have profound neurobiological and cognitive consequences. Here we discuss how early attachment might influence the development of affective, cognitive, and neurobiological resources that could protect against cognitive decline and dementia. We argue that social relations, both early and late in life, are vital to ensuring cognitive and neurobiological health. The concepts of brain and cognitive reserve are crucial to understanding how environmental factors may impact cognitive decline. We examine the role that attachment might play in fostering brain and cognitive reserve in old age. Finally, we put forward the concept of affective reserve, to more directly frame the socio-affective consequences of early attachment as protectors against cognitive decline. We thereby aim to highlight that, in the study of aging, cognitive decline and dementia, it is crucial to consider the role of affective and social factors such as attachment.

Emerging Biomarkers in Vascular Cognitive Impairment and Dementia: From Pathophysiological Pathways to Clinical Application

Vascular pathology is the second most common neuropathology of dementia after Alzheimer’s disease (AD), with small vessels disease (SVD) being considered the major cause of vascular cognitive impairment and dementia (VCID). This review aims to evaluate pathophysiological pathways underlying a diagnosis of VCID. Firstly, we will discuss the role of endothelial dysfunction, blood-brain barrier disruption and neuroinflammation in its pathogenesis. Then, we will analyse different biomarkers including the ones of inflammatory responses to central nervous system tissue injuries, of coagulation and thrombosis and of circulating microRNA. Evidences on peripheral biomarkers for VCID are still poor and large-scale, prospectively designed studies are needed to translate these findings into clinical practice, in order to set different combinations of biomarkers to use for differential diagnosis among types of dementia.

Vascular Cognitive Impairment: Information from Animal Models on the Pathogenic Mechanisms of Cognitive Deficits

Vascular cognitive impairment (VCI) is the second most common cause of cognitive deficit after Alzheimer's disease. Since VCI patients represent an important target population for prevention, an ongoing effort has been made to elucidate the pathogenesis of this disorder. In this review, we summarize the information from animal models on the molecular changes that occur in the brain during a cerebral vascular insult and ultimately lead to cognitive deficits in VCI. Animal models cannot effectively represent the complex clinical picture of VCI in humans. Nonetheless, they allow some understanding of the important molecular mechanisms leading to cognitive deficits. VCI may be caused by various mechanisms and metabolic pathways. The pathological mechanisms, in terms of cognitive deficits, may span from oxidative stress to vascular clearance of toxic waste products (such as amyloid beta) and from neuroinflammation to impaired function of microglia, astrocytes, pericytes, and endothelial cells. Impaired production of elements of the immune response, such as cytokines, and vascular factors, such as insulin-like growth factor 1 (IGF-1), may also affect cognitive functions. No single event could be seen as being the unique cause of cognitive deficits in VCI. These events are interconnected, and may produce cascade effects resulting in cognitive impairment.