Alteration and clinical potential in gut microbiota in patients with cerebral small vessel disease

Anatomizing causal relationships between gut microbiota, plasma metabolites, and epilepsy: A mendelian randomization study

BACKGROUND

Epilepsy causes a heavy disease burden, and the gut microbiota (GM) influences the progression of epilepsy, while plasma metabolites directly or indirectly associated with GM may play a mediating role. However, the causal relationships between epilepsy, GM, and potential metabolite mediators are lack of investigation.

METHODS

Mendelian randomization (MR) analysis was applied to estimate the effects of GM and plasma metabolites on epilepsy. Genetic instruments were obtained from large-scale genome-wide meta-analysis of GM (n = 5959), plasma metabolites (n = 136,016), and epilepsy (Cases/controls = 12891/312803) of European ancestry. Epilepsy phenotypes included all epilepsy, generalized epilepsy and focal epilepsy from the Finn Gen R10 database. And two-step MR (TSMR) to discover the potential mediating metabolites.

RESULTS

In total, we found 19 gut microbial taxa to be causally associated with the risk of epilepsy, among which Omnitrophota phylum had the strongest association (OR, 2.3; P = 0.009) with promoting effect. We also identified 21 plasma metabolites associated with epilepsy, the strongest ones of which are eastotal fatty acids (OR, 1.12; P = 0.001) that exhibited a facilitating effect. We observed indirect effects of free cholesterol to total lipids ratio in large LDL in associations between Fournierella massiliensis species and epilepsy, with a mediated proportion of -3.64% (95%CI, -7.22%∼-0.06%; P = 0.046).

CONCLUSION

This study supports a causal link between Fournierella massiliensis species, free cholesterol to total lipids ratio in large LDL and epilepsy, as well as a mediating effect of free cholesterol to total lipids ratio in large LDL in epilepsy.

Investigating the role of gut microbiota in hemorrhagic stroke: Evidence from causal analysis

BACKGROUND

Hemorrhagic stroke is potentially fatal and debilitating. Previous studies have indicated a potential correlation between gut microbiota and hemorrhagic stroke.

METHODS

We conducted a two-sample Mendelian randomization (MR) study to assess the potential causal effects of gut microbiota on hemorrhagic stroke, including nontraumatic intracranial hemorrhage (ntICH), intracerebral hemorrhage (ICH), and subarachnoid hemorrhage (SAH). The inverse variance weighted (IVW) method was employed as the primary MR evaluation approach. Complementary methods of MR‒Egger, simple mode, weighted mode, and weighted median were utilized for validation. Heterogeneity and pleiotropy were assessed using Cochran's Q and MR‒Egger intercept tests. MR-PRESSO and leave-one-out analyses were employed to identify instrumental outliers.

RESULTS

The IVW estimates demonstrated significant causal associations between ntICH and taxa from two classes (Clostridia, Methanobacteria), one order (Methanobacteriales), two families (Clostridiales vadin BB60 group, Methanobacteriaceae), and two genera (Catenibacterium, unknown genus id. 1000000073) (P<0.05). Subgroup analyses revealed causal links between ICH and taxa from two classes (Clostridia, Methanobacteria), two orders (Methanobacteriales, Rhodospirillales), two families (Acidaminococcaceae, Methanobacteriaceae), and four genera (Butyricimonas, Catenibacterium, Lachnospiraceae UCG010, unknown genus id.2755) (P<0.05). Furthermore, for the SAH subgroup, we identified causal associations with taxa from one family (Rikenellaceae) and six genera (Alloprevotella, Enterorhabdus, Hungatella, Lachnoclostridium, Parabacteroides, Ruminococcus gauvreauii group) (P<0.05). These findings remained robust across all sensitivity tests.

CONCLUSIONS

Our findings provide support for the causal effects of specific gut microbial taxa on hemorrhagic stroke and identify promising targets for its prevention and therapy. Further research is warranted to validate these associations.

Interaction Between DHCR24 and hsa_circ_0015335 Facilitates Cognitive Impairment in Cerebral Small Vessel Disease Patients

AIMS

The study attempted to determine the underlying role and regulation mechanism of 3β-hydroxysterol-Δ24 reductase (DHCR24) in the pathophysiology of cerebral small vessel disease-associated cognitive impairment (CSVD-CI). An RNA high-throughput sequencing and independent verification were conducted to identify potential circRNAs becoming the upstream regulator.

METHODS

RNA sequencing was performed in whole-blood samples in cohort 1 (10 CSVD-CI and 8 CSVD with cognitively normal [CSVD-CN] patients). The DHCR24 and candidate circRNAs were verified in an independent cohort 2 (45 CSVD-CI participants and 37 CSVD-CN ones). The study also analyzed comprehensive cognitive assessments, plasma molecular index, and brain structure imaging.

RESULTS

The expression of DHCR24 and has_circ_0015335 in whole-blood samples of CSVD-CI patients was significantly reduced compared to CSVD-CN patients in RNA sequencing and independent verification. Furthermore, the levels of DHCR24 and has_circ_0015335 were significantly related to global cognitive impairment in CSVD-CI patients. Meanwhile, DHCR24 could regulate the correlation between has_circ_0015335 expression and alterations in brain cortex in surface area, thickness, and volume in CSVD-CI patients. Additionally, hsa_circ_0015335 interacted with DHCR24 for plasma 24(S)-hydroxycholesterol levels among CSVD-CI patients.

CONCLUSION

Interaction between DHCR24 and hsa_circ_0015335 cognitively impaired CSVD by affecting brain cholesterol metabolism and brain structural changes.

Atherosclerotic burden and cerebral small vessel disease: exploring the link through microvascular aging and cerebral microhemorrhages

Cerebral microhemorrhages (CMHs, also known as cerebral microbleeds) are a critical but frequently underestimated aspect of cerebral small vessel disease (CSVD), bearing substantial clinical consequences. Detectable through sensitive neuroimaging techniques, CMHs reveal an extensive pathological landscape. They are prevalent in the aging population, with multiple CMHs often being observed in a given individual. CMHs are closely associated with accelerated cognitive decline and are increasingly recognized as key contributors to the pathogenesis of vascular cognitive impairment and dementia (VCID) and Alzheimer's disease (AD). This review paper delves into the hypothesis that atherosclerosis, a prevalent age-related large vessel disease, extends its pathological influence into the cerebral microcirculation, thereby contributing to the development and progression of CSVD, with a specific focus on CMHs. We explore the concept of vascular aging as a continuum, bridging macrovascular pathologies like atherosclerosis with microvascular abnormalities characteristic of CSVD. We posit that the same risk factors precipitating accelerated aging in large vessels (i.e., atherogenesis), primarily through oxidative stress and inflammatory pathways, similarly instigate accelerated microvascular aging. Accelerated microvascular aging leads to increased microvascular fragility, which in turn predisposes to the formation of CMHs. The presence of hypertension and amyloid pathology further intensifies this process. We comprehensively overview the current body of evidence supporting this interconnected vascular hypothesis. Our review includes an examination of epidemiological data, which provides insights into the prevalence and impact of CMHs in the context of atherosclerosis and CSVD. Furthermore, we explore the shared mechanisms between large vessel aging, atherogenesis, microvascular aging, and CSVD, particularly focusing on how these intertwined processes contribute to the genesis of CMHs. By highlighting the role of vascular aging in the pathophysiology of CMHs, this review seeks to enhance the understanding of CSVD and its links to systemic vascular disorders. Our aim is to provide insights that could inform future therapeutic approaches and research directions in the realm of neurovascular health.

A Bidirectional Mendelian Randomization Study of Gut Microbiota and Cerebral Small Vessel Disease

BACKGROUND

The causal nature of gut microbiota and cerebral small vessel disease (CSVD) is still obscure regardless of evidence supporting their observational correlations.

OBJECTIVES

The primary objective of this research is to investigate the potentially pathogenic or protective causal impacts of specific gut microbiota on various neuroimaging subtypes of CSVD.

METHODS

We obtained the latest summary-level genome-wide databases for gut microbiota and 9 CSVD traits. The univariable and multivariable Mendelian randomization (MR) studies were conducted to examine the possible causal link between exposure and outcome. Meanwhile, we conducted sensitivity analyses sequentially, containing the heterogeneity, pleiotropy, and leave-one-out analysis. Additionally, to clarify the potential bidirectional causality, the causality from CSVD traits to the identified gut microbiota was implemented through reverse MR analysis.

RESULTS

The univariable MR analysis identified 22 genetically predicted bacterial abundances that were correlated with CSVD traits. Although conditioning on macronutrient dietary compositions, 2 suggestive relationships were retained using the multivariable MR analysis. Specifically, the class Negativicutes and order Selenomonadales exhibited a negative causal association with strictly lobar cerebral microbleeds, one neuroimaging trait of CSVD. There is insufficient evidence indicating the presence of heterogeneity and horizontal pleiotropy. Furthermore, the identified causal relationship was not driven by any single nucleotide polymorphism. The results of the reverse MR analysis did not reveal any statistically significant causality from CSVD traits to the identified gut microbiota.

CONCLUSIONS

Our study indicated several suggestive causal effects from gut microbiota to different neuroimaging subtypes of CSVD. These findings provided a latent understanding of the pathogenesis of CSVD from the perspective of the gut-brain axis.

Identifying gut microbiota with high specificity for ischemic stroke with large vessel occlusion

Gut microbiota can regulate the metabolic and immunological aspects of ischemic stroke and modulate the treatment effects. The present study aimed to identify specific changes in gut microbiota in patients with large vessel occlusion (LVO) ischemic stroke and assess the potential association between gut microbiota and clinical features of ischemic stroke. A total of 63 CSVD patients, 64 cerebral small vessel disease (CSVD) patients, and 36 matching normal controls (NCs) were included in this study. The fecal samples were collected for all participants and analyzed for gut microbiota using 16S rRNA gene sequencing technology. The abundances of five gut microbiota, including genera Bifidobacterium, Butyricimonas, Blautia, and Dorea and species Bifidobacterium_longum, showed significant changes with high specificity in the LVO patients as compared to the NCs and CSVD patients. In LVO patients, the genera Bifidobacterium and Blautia and species Bifidobacterium_longum were significantly correlated with the National Institutes of Health Stroke Scale (NIHSS) scores at the admission and discharge of the patients. Serum triglyceride levels could significantly affect the association of the abundance of genus Bifidobacterium and species Bifidobacterium_longum with the NIHSS scores at admission and modified Rankin Scale (mRS) at discharge in LVO patients. The identification of five gut microbiota with high specificity were identified in the early stage of LVO stroke, which contributed to performed an effective clinical management for LVO ischemic stroke.

Lipopolysaccharide-induced intestinal inflammation on AIM2-mediated pyroptosis in the brain of rats with cerebral small vessel disease

Cerebral small vessel disease (CSVD) is a cerebral vascular disease with insidious onset and poor clinical treatment effect, which is related to neuroinflammation. This study investigated whether lipopolysaccharide-induced intestinal inflammation enhanced the level of pyroptosis in the brain of rats with CSVD. The bilateral carotid artery occlusion (BCAO) model was selected as the object of study. Firstly, behavioral tests and Hematoxylin-eosin staining (HE staining) were performed to determine whether the model was successful, and then the AIM2 inflammasome and pyroptosis indexes (AIM2, ASC, Caspase-1, IL-1β, GSDMD, N-GSDMD) in the brain were detected by Western blotting and Immunohistochemistry (IHC). Finally, a single intraperitoneal injection of lipopolysaccharide (LPS) was used to induce intestinal inflammation in rats, the expression of GSDMD and N-GSDMD in the brain was analyzed by Western blotting and to see if pyroptosis caused by intestinal inflammation can be inhibited by Disulfiram, an inhibitor of pyroptosis. The results showed that the inflammatory response and pyroptosis mediated by the AIM2 inflammasome in BCAO rats were present in both brain and intestine. The expression of N-GSDMD, a key marker of pyroptosis, in the brain was significantly increased and inhibited by Disulfiram after LPS-induced enhancement of intestinal inflammation. This study shows that AIM2-mediated inflammasome activation and pyroptosis exist in both brain and intestine in the rat model of CSVD. The enhancement of intestinal inflammation will increase the level of pyroptosis in the brain. In the future, targeted regulation of the AIM2 inflammasome may become a new strategy for the clinical treatment of CSVD.

Macrophage Migration Inhibitory Factor as a Potential Plasma Biomarker of Cognitive Impairment in Cerebral Small Vessel Disease

As the pathogenesis of cerebral small vessel disease with cognitive impairment (CSVD-CI) remains unclear, identifying effective biomarkers can contribute to the clinical management of CSVD-CI. This study recruited 54 healthy controls (HCs), 60 CSVD-CI patients, and 57 CSVD cognitively normal (CSVD-CN) patients. All participants underwent neuropsychological assessments and multimodal magnetic resonance imaging. Macrophage migration inhibitory factors (MIFs) were assessed in plasma. The least absolute shrinkage and selection operator model was used to determine a composite marker. Compared with HCs or CSVD-CN patients, CSVD-CI patients had significantly increased plasma MIF levels. In CSVD-CI patients, plasma MIF levels were significantly correlated with multiple cognitive assessment scores, plasma levels of blood-brain barrier (BBB)-related indices, white matter hyperintensity Fazekas scores, and the mean amplitude of low-frequency fluctuation in the right superior temporal gyrus. Higher plasma MIF levels were significantly associated with worse global cognition and information processing speed in CSVD-CI patients. The composite marker (including plasma MIF) distinguished CSVD-CI patients from CSVD-CN and HCs with >80% accuracy. Meta-analysis indicated that blood MIF levels were significantly increased in CSVD-CI patients. In conclusion, plasma MIF is a potential biomarker for early identification of CSVD-CI. Plasma MIF may play a role in cognitive decline in CSVD through BBB dysfunction and changes in white matter hyperintensity and brain activity.