Clinically used broad-spectrum antibiotics compromise inflammatory monocyte-dependent antibacterial defense in the lung

Hospital-acquired pneumonia (HAP) is associated with high mortality and costs, and frequently caused by multidrug-resistant (MDR) bacteria. Although prior antimicrobial therapy is a major risk factor for HAP, the underlying mechanism remains incompletely understood. Here, we demonstrate that antibiotic therapy in hospitalized patients is associated with decreased diversity of the gut microbiome and depletion of short-chain fatty acid (SCFA) producers. Infection experiments with mice transplanted with patient fecal material reveal that these antibiotic-induced microbiota perturbations impair pulmonary defense against MDR Klebsiella pneumoniae. This is dependent on inflammatory monocytes (IMs), whose fatty acid receptor (FFAR)2/3-controlled and phagolysosome-dependent antibacterial activity is compromized in mice transplanted with antibiotic-associated patient microbiota. Collectively, we characterize how clinically relevant antibiotics affect antimicrobial defense in the context of human microbiota, and reveal a critical impairment of IM´s antimicrobial activity. Our study provides additional arguments for the rational use of antibiotics and offers mechanistic insights for the development of novel prophylactic strategies to protect high-risk patients from HAP.

Gut-immune axis and cardiovascular risk in chronic kidney disease

Patients with chronic kidney disease (CKD) suffer from marked cardiovascular morbidity and mortality, so lowering the cardiovascular risk is paramount to improve quality of life and survival in CKD. Manifold mechanisms are hold accountable for the development of cardiovascular disease (CVD), and recently inflammation arose as novel risk factor significantly contributing to progression of CVD. While the gut microbiome was identified as key regulator of immunity and inflammation in several disease, CKD-related microbiome-immune interaction gains increasing importance. Here, we summarize the latest knowledge on microbiome dysbiosis in CKD, subsequent changes in bacterial and host metabolism and how this drives inflammation and CVD in CKD. Moreover, we outline potential therapeutic targets along the gut-immune-cardiovascular axis that could aid the combat of CVD development and high mortality in CKD.

Sodium perturbs mitochondrial respiration and induces dysfunctional Tregs

FOXP3⁺ regulatory T cells (Tregs) are central for peripheral tolerance, and their deregulation is associated with autoimmunity. Dysfunctional autoimmune Tregs display pro-inflammatory features and altered mitochondrial metabolism, but contributing factors remain elusive. High salt (HS) has been identified to alter immune function and to promote autoimmunity. By investigating longitudinal transcriptional changes of human Tregs, we identified that HS induces metabolic reprogramming, recapitulating features of autoimmune Tregs. Mechanistically, extracellular HS raises intracellular Na⁺, perturbing mitochondrial respiration by interfering with the electron transport chain (ETC). Metabolic disturbance by a temporary HS encounter or complex III blockade rapidly induces a pro-inflammatory signature and FOXP3 downregulation, leading to long-term dysfunction in vitro and in vivo. The HS-induced effect could be reversed by inhibition of mitochondrial Na⁺/Ca²⁺ exchanger (NCLX). Our results indicate that salt could contribute to metabolic reprogramming and that short-term HS encounter perturb metabolic fitness and long-term function of human Tregs with important implications for autoimmunity.

Inflammation in Children with CKD Linked to Gut Dysbiosis and Metabolite Imbalance

BACKGROUND

CKD is characterized by a sustained proinflammatory response of the immune system, promoting hypertension and cardiovascular disease. The underlying mechanisms are incompletely understood but may be linked to gut dysbiosis. Dysbiosis has been described in adults with CKD; however, comorbidities limit CKD-specific conclusions.

METHODS

We analyzed the fecal microbiome, metabolites, and immune phenotypes in 48 children (with normal kidney function, CKD stage G3-G4, G5 treated by hemodialysis [HD], or kidney transplantation) with a mean±SD age of 10.6±3.8 years.

RESULTS

Serum TNF-α and sCD14 were stage-dependently elevated, indicating inflammation, gut barrier dysfunction, and endotoxemia. We observed compositional and functional alterations of the microbiome, including diminished production of short-chain fatty acids. Plasma metabolite analysis revealed a stage-dependent increase of tryptophan metabolites of bacterial origin. Serum from patients on HD activated the aryl hydrocarbon receptor and stimulated TNF-α production in monocytes, corresponding to a proinflammatory shift from classic to nonclassic and intermediate monocytes. Unsupervised analysis of T cells revealed a loss of mucosa-associated invariant T (MAIT) cells and regulatory T cell subtypes in patients on HD.

CONCLUSIONS

Gut barrier dysfunction and microbial metabolite imbalance apparently mediate the proinflammatory immune phenotype, thereby driving the susceptibility to cardiovascular disease. The data highlight the importance of the microbiota-immune axis in CKD, irrespective of confounding comorbidities.

Abstract 013: Microbial Metabolites Induce Pro-inflammatory Mechanisms In Children With Chronic Kidney Disease

Introduction: Chronic inflammation is a major risk factor for cardiovascular disease in chronic kidney disease (CKD). The underlying mechanisms are incompletely understood, but may be linked to gut dysbiosis. We aim to describe the microbiota-immune interaction in a cohort of pediatric CKD, thus independent of confounding comorbidities frequently seen in adult patients.

Methods: We analyzed the fecal microbiome, plasma metabolites and peripheral immune phenotypes in 48 children (normal kidney function (HC, n=10), CKD stage G3-G4 (CKD, n=12), G5 treated by hemodialysis (HD, n=11) or kidney transplantation (KT, n=15)) with a mean age of 10.6 ± 3.8 (mean±SD) years.

Results: Children exhibit stage-dependently increased cardiovascular risk as seen by the presence of arterial hypertension despite anti-hypertensive medication. Serum TNF-α (2.87±1.10 (HC); 7.54±2.29 (CKD); 9.63±2.73 (HD); 5.70 ± 1.66 (KT) pg/mL) and sCD14 (1.83±0.28 (HC); 2.88±0.47 (CKD); 2.83±0.69 (HD); 2.22±0.34 (KT) μg/mL) were elevated, indicating inflammation, gut barrier dysfunction and endotoxemia. We observed compositional and functional alterations of the microbiome, including a diminished production of short-chain fatty acids (e.g. propionate 10.43±5.49 (HC); 8.95±4.66 (CKD); 2.75±3.84 (HD); 12.49±4.89 (KT) μM). Plasma metabolite analysis revealed a stage-dependent increase of tryptophan metabolites of bacterial origin (e.g. indoxylsulfate). Serum from HD patients activated the aryl hydrocarbon receptor and stimulated TNF production in monocytes (fold change over HC: 1.80±0.61), corresponding to a pro-inflammatory shift from classical to non-classical and intermediate monocytes. Moreover, unsupervised analysis (FlowSOM) of T cells revealed a loss of mucosa-associated invariant T (MAIT) cells and regulatory T cell subtypes (e.g. CCR6+ and CXCR3+ subsets) in HD patients.

Conclusions: In conclusion, gut barrier dysfunction and microbial metabolite imbalance mediate the pro-inflammatory immune phenotype in CKD. These dysbiosis-driven immunological changes are already detectable in children with CKD, in whom comorbidities usually found in adults are absent, highlights the specificity of CKD-related microbiota-immune interaction.

Abstract P087: Metformin Treatment Decreases Blood Pressure But Does Not Ameliorate Hypertensive Cardio-Renal Damage In A Double Transgenic Rat Model

Introduction: Metformin (Met) is used as a first-line treatment in type II diabetes, reduces the cardiovascular (CV) risk in diabetes and may lead to decreased CV mortality independent of diabetes status. Met treatment has been shown to induce gut microbiome changes leading to enhanced production of protective short-chain fatty acids and potentially harmful metabolites (LPS). Our study aims to examine the effects of Met in a model of RAAS-mediated hypertension with cardio-renal damage.

Methods: Four-week-old double transgenic rats (dTGR, transgenic for human renin and angiotensinogen) received oral Metformin (Met) or Vehicle (Veh) for 3 weeks. SD rats served as healthy controls. Flow cytometry (n=10 per group), echocardiography (n=14), radiotelemetric blood pressure (BP) measurements (n=5), clinical chemistry and gene expression analyses (n=14) were used to assess damage to kidney and heart.

Results: Met treatment did not influence survival nor lead to lactate acidosis. Met treatment lowered BP significantly (systolic BP: Met: 218±5 mmHg, Veh: 237±3 mmHg). Interestingly, the decreased BP was accompanied by increased cardiac hypertrophy (heart weight to tibia length, SD: 34±1 g/m, Met: 40±1 g/m, Veh: 37±1 g/m). Echocardiographic systolic and diastolic function was deteriorated (EF: Met: 64±2 %, Veh: 68±4 %; E/A: Met: 0.75±0.1, Veh: 0.93±0.1). Plasma BNP and cardiac ß-to-α MHC ratio were higher in Met-treated dTGR. Intestines, spleens, kidneys and hearts of dTGR showed a strong pro-inflammatory phenotype with increased adaptive (e.g. cardiac T cells % of leucocytes: (SD: 10±0.003 %, Met: 15±0.01 %, Veh: 13±0.01 %) and innate (e.g. cardiac monocytes % of leucocytes: (SD: 2±0.001 %, Met: 3±0.004 %, Veh: 5±0.02 %) immune cell subsets in comparison to SD rats; with almost no differences between Met- and Veh-treated dTGR. Fecal metagenomic shotgun sequencing showed no large-scale taxonomic shifts between Veh- and Met-treated dTGR.

Conclusion: dTGR display a pronounced pro-inflammatory immunophenotype across several organs. Met did not ameliorate hypertensive target organ damage in dTGR despite the BP lowering effect. These findings could help to understand the effects of Met on the microbiome, immunome and organ damage in the context of hypertension.

Quantifying the impact of gut microbiota on inflammation and hypertensive organ damage

AIMS

Hypertension (HTN) can lead to heart and kidney damage. The gut microbiota has been linked to HTN, although it is difficult to estimate its significance due to the variety of other features known to influence HTN. In the present study, we used germ-free (GF) and colonized (COL) littermate mice to quantify the impact of microbial colonization on organ damage in HTN.

METHODS AND RESULTS

Four-week-old male GF C57BL/6J littermates were randomized to remain GF or receive microbial colonization. HTN was induced by subcutaneous infusion with angiotensin (Ang) II (1.44 mg/kg/d) and 1% NaCl in the drinking water; sham-treated mice served as control. Renal damage was exacerbated in GF mice, whereas cardiac damage was more comparable between COL and GF, suggesting that the kidney is more sensitive to microbial influence. Multivariate analysis revealed a larger effect of HTN in GF mice. Serum metabolomics demonstrated that the colonization status influences circulating metabolites relevant to HTN. Importantly, GF mice were deficient in anti-inflammatory fecal short-chain fatty acids (SCFA). Flow cytometry showed that the microbiome has an impact on the induction of anti-hypertensive myeloid-derived suppressor cells and pro-inflammatory Th17 cells in HTN. In vitro inducibility of Th17 cells was significantly higher for cells isolated from GF than conventionally raised mice.

CONCLUSIONS

Microbial colonization status of mice had potent effects on their phenotypic response to a hypertensive stimulus, and the kidney is a highly microbiota-susceptible target organ in HTN. The magnitude of the pathogenic response in GF mice underscores the role of the microbiome in mediating inflammation in HTN.

TRANSLATION PERSPECTIVE

To assess the potential of microbiota-targeted interventions to prevent organ damage in hypertension, an accurate quantification of microbial influence is necessary. We provide evidence that the development of hypertensive organ damage is dependent on colonization status and suggest that a healthy microbiota provides anti-hypertensive immune and metabolic signals to the host. In the absence of normal symbiotic host-microbiome interactions, hypertensive damage to the kidney in particular is exacerbated. We suggest that hypertensive patients experiencing perturbations to the microbiota, which are common in CVD, may be at a greater risk for target-organ damage than those with a healthy microbiome.

Bacterial metabolites and cardiovascular risk in children with chronic kidney disease

Cardiovascular complications are the major cause of the marked morbidity and mortality associated with chronic kidney disease (CKD). The classical cardiovascular risk factors such as diabetes and hypertension undoubtedly play a role in the development of cardiovascular disease (CVD) in adult CKD patients; however, CVD is just as prominent in children with CKD who do not have these risk factors. Hence, the CKD-specific pathophysiology of CVD remains incompletely understood. In light of this, studying children with CKD presents a unique opportunity to analyze CKD-associated mechanisms of CVD more specifically and could help to unveil novel therapeutic targets.

Here, we comprehensively review the interaction of the human gut microbiome and the microbial metabolism of nutrients with host immunity and cardiovascular end-organ damage. The human gut microbiome is evolutionary conditioned and modified throughout life by endogenous factors as well as environmental factors. Chronic diseases, such as CKD, cause significant disruption to the composition and function of the gut microbiome and lead to disease-associated dysbiosis. This dysbiosis and the accompanying loss of biochemical homeostasis in the epithelial cells of the colon can be the result of poor diet (e.g., low-fiber intake), medications, and underlying disease. As a result of dysbiosis, bacteria promoting proteolytic fermentation increase and those for saccharolytic fermentation decrease and the integrity of the gut barrier is perturbed (leaky gut). These changes disrupt local metabolite homeostasis in the gut and decrease productions of the beneficial short-chain fatty acids (SCFAs). Moreover, the enhanced proteolytic fermentation generates unhealthy levels of microbially derived toxic metabolites, which further accumulate in the systemic circulation as a consequence of impaired kidney function. We describe possible mechanisms involved in the increased systemic inflammation in CKD that is associated with the combined effect of SCFA deficiency and accumulation of uremic toxins. In the future, a more comprehensive and mechanistic understanding of the gut–kidney–heart interaction, mediated largely by immune dysregulation and inflammation, might allow us to target the gut microbiome more specifically in order to attenuate CKD-associated comorbidities.

Abstract MP41: Isolation Of Gastrointestinal Interstitial Fluid As A Novel Method To Capture Host-microbiome Crosstalk

Metabolites produced by the microbiome such as short chain fatty acids (SCFAs) and tryptophan metabolites have been shown to impact the pathogenesis of hypertension. The microenvironment of the host gastrointestinal (GI) tract acts as the site-of-action for many host-microbiome interactions, although this space is not readily accessible. Fecal or serum samples are commonly used as a proxy, relying on the assumption that the obtained information should in some respect represent what is seen at the host epithelial interface. We surmised that it would be feasible to overcome the limitations of such indirect analysis by isolating interstitial fluid (IF) from the gut mucosa. We have established two methodologies to isolate IF from small segments of along GI tract, a centrifugation-based and elution-based approach in rats and mice. For rats and mice, 51 Cr-EDTA tracer experiments were used to demonstrate that fluid obtained was from an extracellular origin and can be reliably considered IF. Using GC-MS, we could identify several SCFAs (acetate, butyrate, propionate, valerate) within eluted IF samples. We were able to empirically measure the enrichment of these metabolites in eluted IF from the colon of rats compared to the duodenum (for propionate; mean difference=59.57 μM, p-value < 0.0001) or the serum (for propionate; mean difference= 60.25 μM, p-value < 0.0001). LC-MS based shotgun proteomics revealed that proteins annotated to the extracellular phase were site-specifically identifiable in IF and were differentially expressed when compared to matched serum samples. Furthermore, we could demonstrate that the use of tissue for IF isolation does not impede the use of other methods such as immunophenotyping or histology. Absolute CD45+ cells from the lamina propria measured using flow cytometry were not influenced by IF methods (p-value = 0.8344) but were unsurprisingly influenced by the gut segment which was analyzed (p-value = 0.0010). The ability to collect IF and directly measure metabolites at the site-of-action overcomes the limitations of indirect analysis of fecal samples or serum from the systemic circulation, and thus offers direct insight into this hitherto underexplored compartment.

Pharmacological inhibition of adipose tissue adipose triglyceride lipase by Atglistatin prevents catecholamine-induced myocardial damage

AIMS

Heart failure (HF) is characterized by an overactivation of β-adrenergic signalling that directly contributes to impairment of myocardial function. Moreover, β-adrenergic overactivation induces adipose tissue lipolysis, which may further worsen the development of HF. Recently, we demonstrated that adipose tissue-specific deletion of adipose triglyceride lipase (ATGL) prevents pressure-mediated HF in mice. In this study, we investigated the cardioprotective effects of a new pharmacological inhibitor of ATGL, Atglistatin, predominantly targeting ATGL in adipose tissue, on catecholamine-induced cardiac damage.

METHODS AND RESULTS

Male 129/Sv mice received repeated injections of isoproterenol (ISO, 25 mg/kg BW) to induce cardiac damage. Five days prior to ISO application, oral Atglistatin (2 mmol/kg diet) or control treatment was started. Two and twelve days after the last ISO injection cardiac function was analysed by echocardiography. The myocardial deformation was evaluated using speckle-tracking-technique. Twelve days after the last ISO injection, echocardiographic analysis revealed a markedly impaired global longitudinal strain, which was significantly improved by the application of Atglistatin. No changes in ejection fraction were observed. Further studies included histological-, WB-, and RT-qPCR-based analysis of cardiac tissue, followed by cell culture experiments and mass spectrometry-based lipidome analysis. ISO application induced subendocardial fibrosis and a profound pro-apoptotic cardiac response, as demonstrated using an apoptosis-specific gene expression-array. Atglistatin treatment led to a dramatic reduction of these pro-fibrotic and pro-apoptotic processes. We then identified a specific set of fatty acids (FAs) liberated from adipocytes under ISO stimulation (palmitic acid, palmitoleic acid, and oleic acid), which induced pro-apoptotic effects in cardiomyocytes. Atglistatin significantly blocked this adipocytic FA secretion.

CONCLUSION

This study demonstrates cardioprotective effects of Atglistatin in a mouse model of catecholamine-induced cardiac damage/dysfunction, involving anti-apoptotic and anti-fibrotic actions. Notably, beneficial cardioprotective effects of Atglistatin are likely mediated by non-cardiac actions, supporting the concept that pharmacological targeting of adipose tissue may provide an effective way to treat cardiac dysfunction.

Salt Transiently Inhibits Mitochondrial Energetics in Mononuclear Phagocytes

Supplemental Digital Content is available in the text.

Background:

Dietary high salt (HS) is a leading risk factor for mortality and morbidity. Serum sodium transiently increases postprandially but can also accumulate at sites of inflammation affecting differentiation and function of innate and adaptive immune cells. Here, we focus on how changes in extracellular sodium, mimicking alterations in the circulation and tissues, affect the early metabolic, transcriptional, and functional adaption of human and murine mononuclear phagocytes.

Methods:

Using Seahorse technology, pulsed stable isotope-resolved metabolomics, and enzyme activity assays, we characterize the central carbon metabolism and mitochondrial function of human and murine mononuclear phagocytes under HS in vitro. HS as well as pharmacological uncoupling of the electron transport chain under normal salt is used to analyze mitochondrial function on immune cell activation and function (as determined by Escherichiacoli killing and CD4⁺ T cell migration capacity). In 2 independent clinical studies, we analyze the effect of a HS diet during 2 weeks (URL: http://www.clinicaltrials.gov. Unique identifier: NCT02509962) and short-term salt challenge by a single meal (URL: http://www.clinicaltrials.gov. Unique identifier: NCT04175249) on mitochondrial function of human monocytes in vivo.

Results:

Extracellular sodium was taken up into the intracellular compartment, followed by the inhibition of mitochondrial respiration in murine and human macrophages. Mechanistically, HS reduces mitochondrial membrane potential, electron transport chain complex II activity, oxygen consumption, and ATP production independently of the polarization status of macrophages. Subsequently, cell activation is altered with improved bactericidal function in HS-treated M1-like macrophages and diminished CD4⁺ T cell migration in HS-treated M2-like macrophages. Pharmacological uncoupling of the electron transport chain under normal salt phenocopies HS-induced transcriptional changes and bactericidal function of human and murine mononuclear phagocytes. Clinically, also in vivo, rise in plasma sodium concentration within the physiological range reversibly reduces mitochondrial function in human monocytes. In both a 14-day and single meal HS challenge, healthy volunteers displayed a plasma sodium increase of and respectively, that correlated with decreased monocytic mitochondrial oxygen consumption.

Conclusions:

Our data identify the disturbance of mitochondrial respiration as the initial step by which HS mechanistically influences immune cell function. Although these functional changes might help to resolve bacterial infections, a shift toward proinflammation could accelerate inflammatory cardiovascular disease.

The Gut Microbiome in Hypertension: Recent Advances and Future Perspectives

The pathogenesis of hypertension is known to involve a diverse range of contributing factors including genetic, environmental, hormonal, hemodynamic and inflammatory forces, to name a few. There is mounting evidence to suggest that the gut microbiome plays an important role in the development and pathogenesis of hypertension. The gastrointestinal tract, which houses the largest compartment of immune cells in the body, represents the intersection of the environment and the host. Accordingly, lifestyle factors shape and are modulated by the microbiome, modifying the risk for hypertensive disease. One well-studied example is the consumption of dietary fibers, which leads to the production of short-chain fatty acids and can contribute to the expansion of anti-inflammatory immune cells, consequently protecting against the progression of hypertension. Dietary interventions such as fasting have also been shown to impact hypertension via the microbiome. Studying the microbiome in hypertensive disease presents a variety of unique challenges to the use of traditional model systems. Integrating microbiome considerations into preclinical research is crucial, and novel strategies to account for reciprocal host-microbiome interactions, such as the wildling mouse model, may provide new opportunities for translation. The intricacies of the role of the microbiome in hypertensive disease is a matter of ongoing research, and there are several technical considerations which should be accounted for moving forward. In this review we provide insights into the host-microbiome interaction and summarize the evidence of its importance in the regulation of blood pressure. Additionally, we provide recommendations for ongoing and future research, such that important insights from the microbiome field at large can be readily integrated in the context of hypertension.

B-cell lymphoma/leukaemia 10 and angiotensin II-induced kidney injury

AIMS

B-cell lymphoma/leukaemia 10 (Bcl10) is a member of the CARMA-Bcl10-MALT1 signalosome, linking angiotensin (Ang) II, and antigen-dependent immune-cell activation to nuclear factor kappa-B signalling. We showed earlier that Bcl10 plays a role in Ang II-induced cardiac fibrosis and remodelling, independent of blood pressure. We now investigated the role of Bcl10 in Ang II-induced renal damage.

METHODS AND RESULTS

Bcl10 knockout mice (Bcl10 KO) and wild-type (WT) controls were given 1% NaCl in the drinking water and Ang II (1.44 mg/kg/day) for 14 days. Additionally, Bcl10 KO or WT kidneys were transplanted onto WT mice that were challenged by the same protocol for 7 days. Kidneys of Ang II-treated Bcl10 KO mice developed less fibrosis and showed fewer infiltrating cells. Nevertheless, neutrophil gelatinase-associated lipocalin (Ngal) and kidney injury molecule (Kim)1 expression was higher in the kidneys of Ang II-treated Bcl10 KO mice, indicating exacerbated tubular damage. Furthermore, albuminuria was significantly higher in Ang II-treated Bcl10 KO mice accompanied by reduced glomerular nephrin expression and podocyte number. Ang II-treated WT mice transplanted with Bcl10 KO kidney showed more albuminuria and renal Ngal, compared to WT- > WT kidney-transplanted mice, as well as lower podocyte number but similar fibrosis and cell infiltration. Interestingly, mice lacking Bcl10 in the kidney exhibited less Ang II-induced cardiac hypertrophy than controls.

CONCLUSION

Bcl10 has multi-faceted actions in Ang II-induced renal damage. On the one hand, global Bcl10 deficiency ameliorates renal fibrosis and cell infiltration; on the other hand, lack of renal Bcl10 aggravates albuminuria and podocyte damage. These data suggest that Bcl10 maintains podocyte integrity and renal function.

Microscopy with undetected photons in the mid-infrared

Owing to its capacity for unique (bio)-chemical specificity, microscopy with mid-infrared (IR) illumination holds tremendous promise for a wide range of biomedical and industrial applications. The primary limitation, however, remains detection, with current mid-IR detection technology often marrying inferior technical capabilities with prohibitive costs. Here, we experimentally show how nonlinear interferometry with entangled light can provide a powerful tool for mid-IR microscopy while only requiring near-IR detection with a silicon-based camera. In this proof-of-principle implementation, we demonstrate widefield imaging over a broad wavelength range covering 3.4 to 4.3 μm and demonstrate a spatial resolution of 35 μm for images containing 650 resolved elements. Moreover, we demonstrate that our technique is suitable for acquiring microscopic images of biological tissue samples in the mid-IR. These results form a fresh perspective for potential relevance of quantum imaging techniques in the life sciences.

Abstract P027: Hypertensive Cardiorenal Damage Is Aggravated In Axenic Mice

Introduction: The gut microbiota is suspected to play a role in hypertension and hypertensive end organ damage. In the present study, we used germ-free mice to demonstrate that microbial colonization modulates the response to a hypertensive stimulus.

Methods: Four-week-old male germ-free C57BL6/J littermates were randomized to remain germ-free (GF) or to receive microbiota transfer from SPF donor mice to achieve full colonization status (COL). At 12 weeks, Angiotensin (Ang) II was infused s.c. for 14 days (1.44mg/kg/d, osmotic minipumps) and 1% NaCl added to the drinking water; sham-treated mice served as control. After 14 days of AngII we assessed inflammation and organ damage.

Results: Fecal bacterial load in COL mice was similar to SPF donor mice (qPCR). Shotgun metagenomic sequencing of fecal samples revealed hypertension-induced alterations in microbiome composition confirming previous reports. Serum metabolome analysis ( Biocrates MxP Quant 500) confirmed the absence of microbiota-dependent metabolites in GF. Interestingly, microbiota-dependent metabolites relevant for cardiovascular risk (TMAO, indoxyl sulfate) were elevated in hypertensive COL mice compared to sham-treated. Hypertensive kidney damage was aggravated in GF mice. However, marker genes for tubular damage ( Lcn2 ), inflammation ( Ccl2 ), and fibrosis ( Col1a3 ) showed a stronger increase in GF mice (fold changes [fc] COL vs. GF: 7.5 vs 11.0, 1.2 vs 3.3, 1.3 vs 2.2, respectively). Albuminuria (fc 2 vs 25) and histology for kidney fibrosis (fc 1.1 vs 1.4) confirmed the aggravated kidney damage in GF mice. Similarly, we observed an aggravated cardiac damage in GF mice. Flow cytometry of splenic lymphocytes showed that the adaptive immune response to AngII + 1% NaCl, as evidenced by Th17 (fc 1.4 vs 2) and CD8+ central memory cells, was intensified in GF mice. In vitro , naïve T cells isolated from GF mice more readily polarized into Th17 (26 ± 5%) compared to T cells from SPF mice (19 ± 1%).

Conclusion: The bacterial colonization status has potent effects on the phenotypic response to a hypertensive stimulus, evident to varying degrees in hearts and kidneys. The inflammatory response and the end organ damage in GF compared to COL mice demonstrates the importance of the gut microbiota in hypertension.

[Gut-heart axis : How gut bacteria influence cardiovascular diseases]

The view of humans as holobionts consisting of eukaryotic host cells and associated prokaryotic organisms, has opened up a new perspective on cardiovascular pathophysiology. In particular, intestinal bacteria influence the cell and organ functions of the host. Intestinal bacteria represent a metabolically active community whose composition and function can influence cardiovascular health and disease. The interaction between the intestinal microbiota and the heart occurs via metabolites of bacterial origin, which are resorbed in the intestine and distributed via the circulation. Bacterial metabolites are produced from food components, which in turn emphasizes the importance of nutrition. Some of these metabolites, such as trimethylamine N‑oxide (TMAO), can exacerbate cardiovascular pathologies. Short-chain fatty acids (SCFA) in turn are considered to be protective metabolites. The host's immune system is an important target for these metabolites and explains much of their effects. In the future, the targeted manipulation of intestinal bacteria could help to prevent the development and progression of cardiovascular diseases.

Quantifying technical confounders in microbiome studies

AIMS

Recent technical developments have allowed the study of the human microbiome to accelerate at an unprecedented pace. Methodological differences may have considerable impact on the results obtained. Thus, we investigated how different storage, isolation, and DNA extraction methods can influence the characterization of the intestinal microbiome, compared to the impact of true biological signals such as intraindividual variability, nutrition, health, and demographics.

METHODS AND RESULTS

An observative cohort study in 27 healthy subjects was performed. Participants were instructed to collect stool samples twice spaced by a week, using six different methods (naive and Zymo DNA/RNA Shield on dry ice, OMNIgene GUT, RNALater, 95% ethanol, Zymo DNA/RNA Shield at room temperature). DNA extraction from all samples was performed comparatively using QIAamp Power Fecal and ZymoBIOMICS DNA Kits. 16S rRNA sequencing of the gut microbiota as well as qPCRs were performed on the isolated DNA. Metrics included alpha diversity as well as multivariate and univariate comparisons of samples, controlling for covariate patterns computationally. Interindividual differences explained 7.4% of overall microbiome variability, whereas the choice of DNA extraction method explained a further 5.7%. At phylum level, the tested kits differed in their recovery of Gram-positive bacteria, which is reflected in a significantly skewed enterotype distribution.

CONCLUSION

DNA extraction methods had the highest impact on observed microbiome variability, and were comparable to interindividual differences, thus may spuriously mimic the microbiome signatures of various health and nutrition factors. Conversely, collection methods had a relatively small influence on microbiome composition. The present study provides necessary insight into the technical variables which can lead to divergent results from seemingly similar study designs. We anticipate that these results will contribute to future efforts towards standardization of microbiome quantification procedures in clinical research.

Short-Chain Fatty Acid Propionate Protects From Hypertensive Cardiovascular Damage

Supplemental Digital Content is available in the text.

Background:

Arterial hypertension and its organ sequelae show characteristics of T cell–mediated inflammatory diseases. Experimental anti-inflammatory therapies have been shown to ameliorate hypertensive end-organ damage. Recently, the CANTOS study (Canakinumab Antiinflammatory Thrombosis Outcome Study) targeting interleukin-1β demonstrated that anti-inflammatory therapy reduces cardiovascular risk. The gut microbiome plays a pivotal role in immune homeostasis and cardiovascular health. Short-chain fatty acids (SCFAs) are produced from dietary fiber by gut bacteria and affect host immune homeostasis. Here, we investigated effects of the SCFA propionate in 2 different mouse models of hypertensive cardiovascular damage.

Methods:

To investigate the effect of SCFAs on hypertensive cardiac damage and atherosclerosis, wild-type NMRI or apolipoprotein E knockout–deficient mice received propionate (200 mmol/L) or control in the drinking water. To induce hypertension, wild-type NMRI mice were infused with angiotensin II (1.44 mg·kg^–1·d^–1 subcutaneous) for 14 days. To accelerate the development of atherosclerosis, apolipoprotein E knockout mice were infused with angiotensin II (0.72 mg·kg^–1·d^–1 subcutaneous) for 28 days. Cardiac damage and atherosclerosis were assessed using histology, echocardiography, in vivo electrophysiology, immunofluorescence, and flow cytometry. Blood pressure was measured by radiotelemetry. Regulatory T cell depletion using PC61 antibody was used to examine the mode of action of propionate.

Results:

Propionate significantly attenuated cardiac hypertrophy, fibrosis, vascular dysfunction, and hypertension in both models. Susceptibility to cardiac ventricular arrhythmias was significantly reduced in propionate-treated angiotensin II–infused wild-type NMRI mice. Aortic atherosclerotic lesion area was significantly decreased in propionate-treated apolipoprotein E knockout–deficient mice. Systemic inflammation was mitigated by propionate treatment, quantified as a reduction in splenic effector memory T cell frequencies and splenic T helper 17 cells in both models, and a decrease in local cardiac immune cell infiltration in wild-type NMRI mice. Cardioprotective effects of propionate were abrogated in regulatory T cell–depleted angiotensin II–infused mice, suggesting the effect is regulatory T cell–dependent.

Conclusions:

Our data emphasize an immune-modulatory role of SCFAs and their importance for cardiovascular health. The data suggest that lifestyle modifications leading to augmented SCFA production could be a beneficial nonpharmacological preventive strategy for patients with hypertensive cardiovascular disease.

Abstract P2072: Integrative Network Analysis Of Microbiome-Immune Axis In Metabolic Syndrome Patients During A Fasting Intervention

Fasting can prolong survival and reduce disease burden in rodent models, and possibly in humans. The relationship between diet, gut microbiota, immune system and host (patho)physiology has only recently been explored, and information is lacking on how periodic fasting affects the gut microbiome in patients with metabolic syndrome (MetS). We show a 5-day fast (FAST) in humans, followed by a modified DASH diet is more effective than DASH alone (DASH) at reducing systolic blood pressure (SBP change measured by ABPM, 95% CI; FAST: [-7.053,-1.142], DASH: [-5.880,1.477]), need for antihypertensive medication (FAST: n=15 of n=35, DASH: n=6 of n=36 patients), and body-mass index at three months post intervention. Fasting altered the gut microbiome, impacting bacterial taxa and functional gene modules associated with the production of short-chain fatty acids (e.g. Faecalibacterium prausnitzii , Eubacterium rectale, Coprococcus comes ), previously linked to vascular health and immunity. Immunophenotyping and cross-system analyses revealed that SBP changes correlated with circulating Il-2 + TNFα + mucosa-associated invariant T (MAIT) cells (FDR-corr P(q) =0.044, Spearman’s rho=0.44), Il-17 - IFNγ + MAITs (FDR-corr P(q) =0.022, Spearman’s rho=0.49), and effector CD4 + T cells (FDR-corr P(q)=0.047, Spearman’s rho=0.43). By stratifying the fasting group into BP responders and non-responders, we identified a set of 76 microbial and 99 immune responder-specific features. Machine learning algorithms could predict long-term SBP responsiveness from baseline immunome data, identifying changes in effector CD8 + T cells, Th17 cells and Tregs as discriminators (Single-subject prediction: 71%). This is the first high-resolution multi-omics characterization of fasting in MetS. Fasting induced long-term reduction in body weight and SBP, accompanied by changes in microbiome and immune homeostasis. Our data implicate fasting as a promising non-pharmacological intervention in MetS.

Abstract P2032: Differential Response To Angiotensin II Depends On Microbial Colonization

The gut microbiome is suspected to play a role in hypertension and target organ damage. In the present study, we used the germ-free mice (GF), which are devoid of bacteria, to investigate if bacterial colonization modulates the response to a hypertensive stimulus.

GF C57BL/6 littermates were separated at 4 weeks and randomized to remain GF or receive bacterial colonization (COL). Angiotensin (Ang) II minipumps were implanted at 12 weeks (+AngII) to induce hypertension, sham-infused mice served as non-hypertensive controls. At 14 weeks, all mice were sacrificed, and inflammation and target organ damage were assessed.

AngII induced a comparable cardiac hypertrophic response in both groups, as measured by left ventricular mass/tibia length. However, accounting for the low basal heart weight in non-hypertensive GF, the hypertrophic response was greater in GF than COL (in mg/cm; GF: 47.2, GF+AngII: 70.17, fold change: 1.5 and COL: 57.9, COL+AngII: 76.09, fold change: 1.3). Similarly, the increase in cardiac perivascular fibrosis in response to AngII was greater in GF than COL (fibrotic/medial area; GF: 3.8, GF+AngII: 5.8 and COL: 3.9, COL+AngII: 5). Inflammation of the cardiac tissue, as evidenced by relative mRNA expression of MCP-1 and TNFa, increased significantly in GF and not in COL. Using flow cytometry, we found that innate anti-inflammatory immune subsets (myeloid derived suppressor cells) are notably missing in GF, and the adaptive immune response to AngII (e.g. Th17 (in % of CD4+: GF: 0.26; GF+AngII: 0.5 and COL: 0.28; COL+AngII: 0.39)) was exacerbated. Kidney damage was also evident in AngII-infused GF and COL. However, genes indicative of tubular damage (KIM-1: GF: 0.3, GF+AngII: 3.3, fold change: 11.0 and COL: 0.2, COL+AngII: 1.5, fold change: 7.5 ), inflammation (TNFa, MCP-1, ICAM), and fibrosis (Col3a1, Col1a2) increased significantly in GF and were only mildly implicated in COL.

Bacterial colonization sizably impacts the response to AngII and hypertensive target organ damage. The magnitude of the pathogenic response to AngII in GF compared to COL mice demonstrates the importance of the gut microbiota in modulating target-organ damage.

Abstract 131: Microbiota-Derived Metabolite Propionate Protects From Hypertensive Cardiovascular Damage

Objective: Inflammation drives cardiovascular disease, anti-inflammatory approaches may be beneficial. Short-chain fatty acids (SCFA) are bacterial metabolites with anti-inflammatory properties affecting host immune homeostasis including regulatory T cells (Treg). We investigated effects of the SCFA propionate (administered in drinking water, NaCl as control) in two mouse models, namely hypertensive heart disease (wild-type NMRI (WT), angiotensin (Ang)II infusion 1.44 mg/kg/d s.c. for 14 days) and atherosclerosis (Apolipoprotein E knockout (ApoE), AngII infusion 0.72 mg/kg/d s.c. for 28 days), respectively.

Results: Propionate attenuated cardiac hypertrophy and fibrosis in both models significantly. Susceptibility to cardiac ventricular arrhythmias was significantly reduced in propionate-treated WT mice. Aortic atherosclerotic lesion area was significantly reduced in propionate-treated ApoE (27.6±8 vs. 7.9±2.4%). Treatment reduced splenic effector memory (CD4+ CD44+ CD62L-) T cell frequencies (WT: 30.5±4.6 vs. 19.1±1.6; ApoE: 41.1±3.1 vs. 32.7±1.4%) and splenic Th17 cells (WT: 1.0±0.2 vs. 0.6±0.1; ApoE: 1.3±0.1 vs. 0.9±0.1%) in both models, indicating beneficial effects on systemic inflammation. Similarly, propionate reduced cardiac immune cell infiltration (CD4+, CD8+, F4/80+) in WT mice. Propionate improved vascular dysfunction and moderately reduced blood pressure in both models. Organ-protective actions of propionate (cardiac inflammation and fibrosis) were abrogated in Treg-depleted (antiCD25-treated) AngII-infused WT mice, suggesting a central role for Treg. To verify our findings in a human cohort, we re-analyzed clinical and metagenomic data from a recent randomized controlled trial investigating the effect of a 90-day synbiotic intervention in 84 subjects with metabolic syndrome including healthy controls. Interestingly, in synbiotic-treated subjects an increased capacity for SFCA production was significantly correlated to blood pressure reduction.

Conclusion: Data underscore the importance of SCFA for cardiovascular health and suggest that lifestyle modifications leading to augmented SCFA production could be a beneficial non-pharmacological add-on strategy for cardiovascular disease.

Nitric oxide-sensitive guanylyl cyclase stimulation improves experimental heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) can arise from cardiac and vascular remodeling processes following long-lasting hypertension. Efficacy of common HF therapeutics is unsatisfactory in HFpEF. Evidence suggests that stimulators of the nitric oxide-sensitive soluble guanylyl cyclase (NOsGC) could be of use here. We aimed to characterize the complex cardiovascular effects of NOsGC stimulation using NO-independent stimulator BAY 41-8543 in a double-transgenic rat (dTGR) model of HFpEF. We show a drastically improved survival rate of treated dTGR. We observed less cardiac fibrosis, macrophage infiltration, and gap junction remodeling in treated dTGR. Microarray analysis revealed that treatment of dTGR corrected the dysregulateion of cardiac genes associated with fibrosis, inflammation, apoptosis, oxidative stress, and ion channel function toward an expression profile similar to healthy controls. Treatment reduced systemic blood pressure levels and improved endothelium-dependent vasorelaxation of resistance vessels. Further comprehensive in vivo phenotyping showed an improved diastolic cardiac function, improved hemodynamics, and less susceptibility to ventricular arrhythmias. Short-term BAY 41-8543 application in isolated untreated transgenic hearts with structural remodeling significantly reduced the occurrence of ventricular arrhythmias, suggesting a direct nongenomic role of NOsGC stimulation on excitation. Thus, NOsGC stimulation was highly effective in improving several HFpEF facets in this animal model, underscoring its potential value for patients.

Salt-responsive gut commensal modulates TH17 axis and disease

A Western lifestyle with high salt consumption can lead to hypertension and cardiovascular disease. High salt may additionally drive autoimmunity by inducing T helper 17 (TH17) cells, which can also contribute to hypertension. Induction of TH17 cells depends on gut microbiota; however, the effect of salt on the gut microbiome is unknown. Here we show that high salt intake affects the gut microbiome in mice, particularly by depleting Lactobacillus murinus. Consequently, treatment of mice with L. murinus prevented salt-induced aggravation of actively induced experimental autoimmune encephalomyelitis and salt-sensitive hypertension by modulating TH17 cells. In line with these findings, a moderate high-salt challenge in a pilot study in humans reduced intestinal survival of Lactobacillus spp., increased TH17 cells and increased blood pressure. Our results connect high salt intake to the gut-immune axis and highlight the gut microbiome as a potential therapeutic target to counteract salt-sensitive conditions.

Abstract 026: Gut Bacteria Metabolite Attenuates Ang II-induced Cardiac Damage

Increasing evidence suggests that the gut microbiota critically influence host health and immune homeostasis. Microbiome-host communication occurs via gut bacterial metabolites which are resorbed by the host and target various organs. Short-chain fatty acids (SCFA) are produced from bacterial fermentation, are highly abundant in the gut but can also be detected in the blood. Recently, the SCFA propionate has been shown to regulate T cell differentiation into effector and regulatory T cells in peripheral tissues. Since activation of the immune system is known to substantially contribute to hypertensive target organ damage and anti-inflammatory strategies have been shown to be beneficial in animal models, we hypothesized that treatment with propionate would be beneficial in angiotensin (AngII)-induced target organ damage. Male NMRI mice received AngII infusions for two weeks and propionate (P) or vehicle (C) in drinking water. To deplete endogenous SCFA production mice were fed a low-fibre diet. Body weight was similar among all groups. Propionate treatment significantly reduced albuminuria (C 1143 ± 193; P 302 ± 69 μg/d). Propionate significantly reduced cardiac hypertrophy as measured by heart-to-tibia ratio (C 10.1 ± 0.4; P 8.9 ± 0.4 mg/mm) and was confirmed by echocardiography. Propionate treatment significantly reduced interstitial (C 16.5 ± 0.8%; P 6.6 ± 0.2%) and perivascular cardiac fibrosis (C 1.5 ± 0.06; P 1.1 ± 0.03 μm/μm) as measured by fibronectin and collagen I immunofluorescence, respectively. In vivo cardiac electrophysiology studies showed a significantly reduced susceptibility to ventricular arrhythmias in propionate-treated mice (C 71 ± 14%; P 24 ± 16%), indicating the functional relevance of the improved cardiac morphology. Propionate reduced the expression of IL-17 in CD4+ T cells in spleen and lymph nodes as measured by flow cytometry. Our data indicate that propionate attenuates AngII-induced cardiac remodeling and reduces susceptibility to arrhythmias. The gut microbiome is a promising target for treatment of hypertensive heart disease.