Plasma Microbiome in COVID-19 Subjects: An Indicator of Gut Barrier Defects and Dysbiosis

The gut is a well-established route of infection and target for viral damage by SARS-CoV-2. This is supported by the clinical observation that about half of COVID-19 patients exhibit gastrointestinal (GI) complications. We aimed to investigate whether the analysis of plasma could provide insight into gut barrier dysfunction in patients with COVID-19 infection. Plasma samples of COVID-19 patients (n = 146) and healthy individuals (n = 47) were collected during hospitalization and routine visits. Plasma microbiome was analyzed using 16S rRNA sequencing and gut permeability markers including fatty acid binding protein 2 (FABP2), peptidoglycan (PGN), and lipopolysaccharide (LPS) in both patient cohorts. Plasma samples of both cohorts contained predominately Proteobacteria, Firmicutes, Bacteroides, and Actinobacteria. COVID-19 subjects exhibit significant dysbiosis (p = 0.001) of the plasma microbiome with increased abundance of Actinobacteria spp. (p = 0.0332), decreased abundance of Bacteroides spp. (p = 0.0003), and an increased Firmicutes:Bacteroidetes ratio (p = 0.0003) compared to healthy subjects. The concentration of the plasma gut permeability marker FABP2 (p = 0.0013) and the gut microbial antigens PGN (p < 0.0001) and LPS (p = 0.0049) were significantly elevated in COVID-19 patients compared to healthy subjects. These findings support the notion that the intestine may represent a source for bacteremia and contribute to worsening COVID-19 outcomes. Therapies targeting the gut and prevention of gut barrier defects may represent a strategy to improve outcomes in COVID-19 patients.

Circulating Microbial Signatures and Cardiovascular Death in Patients With ESRD

INTRODUCTION

Patients with end-stage renal disease (ESRD) experience disproportionately high cardiovascular morbidity and mortality. Accumulating evidence suggests a role for the circulating microbiome in the pathogenesis of cardiovascular disease; however, little is known about its association with premature cardiovascular mortality in ESRD.

METHODS

In a pilot case-control study of 17 hemodialysis patients who died of a cardiovascular event and 17 matched hemodialysis controls who remained alive during a median follow-up of 2.0 years, we compared the levels and composition of circulating microbiome, including Bacteria, Archaea, and Fungi, in serum samples by quantitative polymerase chain reaction and 16S or Internal Transcribed Spacer (ITS) ribosomal RNA (rRNA) sequencing, respectively. Associations of the circulating cell-free microbial signatures with clinical parameters and cardiovascular death were examined using the Spearman rank correlation and multivariable conditional logistic regression, respectively.

RESULTS

Both 16S and ITS rRNA were detectable in all (except 3 for ITS) examined patients' serum samples. Despite no significant difference in 16S rRNA levels and α diversity between cases and controls, taxonomic analysis demonstrated differential community membership between groups, with significantly greater Actinobacteria and less Proteobacteria observed in cases than in controls at the phylum level. Proportions of Actinobacteria and Proteobacteria phyla were significantly correlated with plasma nuclear factor erythroid 2-related factor 2 (Nrf2) levels (rho = -0.41 and 0.42, P = 0.015 and 0.013, respectively) and marginally associated with risk of cardiovascular death (adjusted odds ratios [95% confidence intervals] = 1.12 [0.98-1.29] and 0.88 [0.76-1.02] for 1% increase, respectively).

CONCLUSION

Alterations of the circulating cell-free microbial signatures may be associated with higher premature cardiovascular mortality in ESRD.

Circulating metabolomics profiling reveals novel pathways associated with cognitive decline in patients with hypertension

Background:

Hypertension is a significant risk factor for cardiovascular disease, and it is associated with dementia, including Alzheimer’s disease (AD). Although it may be correlated with AD in terms of symptoms, the link between hypertension and AD pathological biomarkers, and the potential underlying mechanism of hypertension with cognitive decline, are still not well understood.

Methods:

The Mini-Mental State Examination (MMSE) scores were used to evaluate cognitive function. Enzyme-linked immunosorbent assays were used to examine plasma amyloid-beta (Aβ)₄₀, Aβ₄₂, and tau concentration in hypertensive patients. Metabolomics and metagenomics were performed to identify the significantly changed circulating metabolites and microbiota between healthy individuals and hypertensive patients. Pearson’s correlation was used to examine the association between cognitive indicators and differential metabolites.

Results:

We found significantly decreased MMSE scores, elevated plasma Aβ₄₀, and decreased Aβ₄₂/Aβ₄₀ ratio in hypertensive patients, which are critically associated with AD pathology. Based on metabolomics, we found that significantly altered metabolites in the plasma of hypertensive patients were enriched in the benzoate degradation and phenylpropanoid biosynthesis pathways, and they were also correlated with changes in MMSE scores and Aβ₄₂/Aβ₄₀ ratio. In addition, metabolomics signaling pathway analysis suggested that microbial metabolism was altered in hypertensive patients. We also identified altered blood microbiota in hypertensive patients compared with the controls.

Conclusions:

Our study provides a novel metabolic and microbial mechanism, which may underlie the cognitive impairment in hypertensive patients.

The circulating microbiome signature and inferred functional metagenomics in alcoholic hepatitis

Intestinal dysbiosis is implicated in alcoholic hepatitis (AH). However, changes in the circulating microbiome, its association with the presence and severity of AH, and its functional relevance in AH is unknown. Qualitative and quantitative assessment of changes in the circulating microbiome were performed by sequencing bacterial DNA in subjects with moderate AH (MAH) (n = 18) or severe AH (SAH) (n = 19). These data were compared with heavy drinking controls (HDCs) without obvious liver disease (n = 19) and non-alcohol-consuming controls (NACs, n = 20). The data were related to endotoxin levels and markers of monocyte activation. Linear discriminant analysis effect size (LEfSe) analysis, inferred metagenomics, and predictive functional analysis using PICRUSt were performed. There was a significant increase in 16S copies/ng DNA both in MAH (P < 0.01) and SAH (P < 0.001) subjects. Compared with NACs, the relative abundance of phylum Bacteroidetes was significantly decreased in HDCs, MAH, and SAH (P < 0.001). In contrast, all alcohol-consuming groups had enrichment with Fusobacteria; this was greatest for HDCs and decreased progressively in MAH and SAH. Subjects with SAH had significantly higher endotoxemia (P = 0.01). Compared with alcohol-consuming groups, predictive functional metagenomics indicated an enrichment of bacteria with genes related to methanogenesis and denitrification. Furthermore, both HDCs and SAH showed activation of a type III secretion system that has been linked to gram-negative bacterial virulence. Metagenomics in SAH versus NACs predicted increased isoprenoid synthesis via mevalonate and anthranilate degradation, known modulators of gram-positive bacterial growth and biofilm production, respectively.

CONCLUSION

Heavy alcohol consumption appears to be the primary driver of changes in the circulating microbiome associated with a shift in its inferred metabolic functions. (Hepatology 2018;67:1284-1302).