Therapeutic Potential of Remote Ischemic Conditioning in Vascular Cognitive Impairment

The role of the neurovascular unit in vascular cognitive impairment: Current evidence and future perspectives

Vascular cognitive impairment (VCI) is a progressive cognitive impairment caused by cerebrovascular disease or vascular risk factors. It is the second most common type of cognitive impairment after Alzheimer's disease. The pathogenesis of VCI is complex, and neurovascular unit destruction is one of its important mechanisms. The neurovascular unit (NVU) is responsible for combining blood flow with brain activity and includes endothelial cells, pericytes, astrocytes and many regulatory nerve terminals. The concept of an NVU emphasizes that interactions between different types of cells are essential for maintaining brain homeostasis. A stable NVU is the basis of normal brain function. Therefore, understanding the structure and function of the neurovascular unit and its role in VCI development is crucial for gaining insights into its pathogenesis. This article reviews the structure and function of the neurovascular unit and its contribution to VCI, providing valuable information for early diagnosis and prevention.

Mechanisms of cognitive impairment associated with cerebral infarction

Cerebral infarction is a common type of stroke with high incidence and disability rates, and most patients experience varying degrees of cognitive impairment. The manifestations and severity of post-infarction cognitive impairment are influenced by multiple interacting factors, and its pathophysiological mechanisms are highly complex, involving pericyte degeneration, excessive generation of reactive oxygen species (ROS), overproduction of glutamate, and overactivation of autophagy. After cerebral infarction, abnormal pericyte function activates neuroinflammation and facilitates the entry of inflammatory mediators into the brain; detachment of pericytes from blood vessels disrupts the integrity of the blood-brain barrier. Although angiogenesis and glial scar formation may alleviate injury, excessive scarring can inhibit neuronal regeneration. Excessive ROS trigger oxidative stress, leading to mitochondrial dysfunction, ferroptosis, and suppression of endothelial nitric oxide synthase/nitric oxide signaling, thereby damaging neurons. An excessive surge in glutamate release, coupled with insufficient clearance, results in its accumulation in the intercellular space, leading to excitotoxicity; the influx of calcium ions subsequently activates proteases and apoptotic pathways, causing neuronal death. Overactivation of autophagy alters lysosomal membrane permeability and results in leakage of lysosomal enzymes; oligodendrocyte necrosis then leads to severe demyelination, further exacerbating brain injury, although promoting the autophagic clearance of damaged mitochondria can ameliorate cognitive deficits arising from mitochondrial dysfunction.

Effect of Remote Ischemic Conditioning in Ischemic Stroke Subtypes: A Post Hoc Subgroup Analysis From the RESIST Trial

BACKGROUND

Remote ischemic conditioning (RIC) is a simple and noninvasive procedure that has proved to be safe and feasible in numerous smaller clinical trials. Mixed results have been found in recent large randomized controlled trials. This is a post hoc subgroup analysis of the RESIST trial (Remote Ischemic Conditioning in Patients With Acute Stroke), investigating the effect of RIC in different acute ischemic stroke etiologies, and whether an effect was modified by treatment adherence.

METHODS

Eligible patients were adults (aged ≥18 years), independent in activities of daily living, who had prehospital stroke symptoms with a duration of less than 4 hours. They were randomized to RIC or sham. The RIC treatment protocol consisted of 5 cycles with 5 minutes of cuff inflation alternating with 5 minutes with a deflated cuff. Acceptable treatment adherence was defined as when at least 80% of planned RIC cycles were received. The analysis was performed using the entire range (shift analysis) of the modified Rankin Scale (ordinal logistic regression).

RESULTS

A total of 698 had acute ischemic stroke, 253 (36%) were women, and the median (interquartile range) age was 73 (63-80) years. Median (interquartile range) overall adherence to RIC/sham was 91% (68%-100%). In patients with a stroke due to cerebral small vessel disease, who were adherent to treatment, RIC was associated with improved functional outcome, and the odds ratio for a shift to a lower score on the modified Rankin Scale was 2.54 (1.03-6.25); P=0.042. The association remained significant after adjusting for potential confounders. No significant associations were found with other stroke etiologies, and the overall test for interaction was not statistically significant (χ2, 4.33, P=0.23).

CONCLUSIONS

In patients with acute ischemic stroke due to cerebral small vessel disease, who maintained good treatment adherence, RIC was associated with improved functional outcomes at 90 days. These results should only serve as a hypothesis-generating for future trials.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT03481777.

Remote ischemic preconditioning and cognitive dysfunction following coronary artery bypass grafting: A systematic review and meta-analysis of randomized controlled trials

INTRODUCTION

Postoperative cognitive dysfunction (POCD) is a common neurological issue following cardiopulmonary bypass (CPB)-assisted heart surgery. Remote ischemic preconditioning (RIPC) increases the tolerance of vital organs to ischemia/reperfusion injury, leading to reduced brain injury biomarkers and improved cognitive control. However, the exact mechanisms underlying RIPC's neuroprotective effects remain unclear. This systematic review aimed to explore the hypothesis that RIPC lowers neurocognitive dysfunction in patients undergoing CPB surgery.

METHOD

All relevant studies were searched in PubMed, ScienceDirect, EBSCOhost, Google Scholar, Semantic Scholar, Scopus, and Cochrane Library database. Assessment of study quality was carried out by two independent reviewers individually using the Cochrane Risk of Bias (RoB-2) tool. Meta-analysis was performed using a fixed-effect model due to low heterogeneity among studies, except for those with substantial heterogeneity.

RESULTS

A total of five studies with 1,843 participants were included in the meta-analysis. RIPC was not associated with reduced incidence of postoperative cognitive dysfunction (five RCTs, odds ratio [OR:] 0.79, 95% confidence interval [CI]: 0.56-1.11) nor its improvement (three RCTs, OR: 0.80, 95% CI: 0.50-1.27). In addition, the analysis of the effect of RIPC on specific cognitive function tests found that pooled SMD for RAVLT 1-3 and RAVLT LT were -0.07 (95% CI: -0.25,012) and -0.04 (95% CI: -0.25-0.12), respectively, and for VFT semantic and phonetic were -0.15 (95% CI: -0.33-0.04) and 0.11 (95% CI: -0.40-0.62), respectively.

CONCLUSION

The effect of RIPC on cognitive performance in CABG patients remained insignificant. Results from previous studies were unable to justify the use of RIPC as a neuroprotective agent in CABG patients.

Neuroadaptive Biochemical Mechanisms of Remote Ischemic Conditioning

This review summarizes the currently known biochemical neuroadaptive mechanisms of remote ischemic conditioning. In particular, it focuses on the significance of the pro-adaptive effects of remote ischemic conditioning which allow for the prevention of the neurological and cognitive impairments associated with hippocampal dysregulation after brain damage. The neuroimmunohumoral pathway transmitting a conditioning stimulus, as well as the molecular basis of the early and delayed phases of neuroprotection, including anti-apoptotic, anti-oxidant, and anti-inflammatory components, are also outlined. Based on the close interplay between the effects of ischemia, especially those mediated by interaction of hypoxia-inducible factors (HIFs) and steroid hormones, the involvement of the hypothalamic-pituitary-adrenocortical system in remote ischemic conditioning is also discussed.

Effects of remote ischemic conditioning on cognitive performance: A systematic review

The aging process leads to subtle decline in cognitive function, and in some overt dementia. Like physical activity Remote Ischemic Conditioning (RIC) may ameliorate these changes on cognitive impairment in humans. The purpose of this study was to compared the effects of single, repeated short-term and long-term treatment RIC, and analyze its effect registered as immediate vs. long-term on cognitive performance in humans. This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement and was registered with PROSPERO, number (CRD42021285668). A systematic review was conducted to identify relevant studies through six healthcare science databases (Cochrane, PubMed, EMBASE, EBSCO, Scopus, and Web of Science) up to December 2021. Eligibility criteria included (1) a study sample of participants aged ≥18 years, (2) post-intervention changes on cognitive performance in humans, and (3) this systematic review included only randomized controlled trials of RIC in humans. The quality of the included studies was assessed by GRADEpro tool. A total of 118 articles were initially identified, 35 of which met the inclusion criteria. Based on title/abstract, age and RIC protocol, 14 articles were included in this review: 5 studies investigated the immediate and long-term effect of a single RIC (n = 370 patients), 4 studies examined intermittent short-term RIC (n = 174 patients) and 5 studies evaluated repeated long-term RIC (n = 228 patients). A single pre-operative RIC treatment had an immediate effect that disappeared at one week. Short-term RIC showed either a positive or no effects on cognitive function. The majority of studies examining long-term RIC treatment showed improvements in cognitive performance, particularly in very old adults and older patients with cognitive impairments. Single RIC treatment did not show any persisting effect on cognition. However, repeated short term RIC showed some improvement and long-term RIC may improve cognitive performance after stroke or enhance neuropsychological tests in patients diagnosed with vascular dementia. The mixed results might be explained by different RIC treatment protocols and populations investigated.