The interplay between dietary fatty acids and gut microbiota influences host metabolism and hepatic steatosis

Dietary lipids can affect metabolic health through gut microbiota-mediated mechanisms, but the influence of lipid-microbiota interaction on liver steatosis is largely unknown. We investigate the impact of dietary lipids on human gut microbiota composition and the effects of microbiota-lipid interactions on steatosis in male mice. In humans, low intake of saturated fatty acids (SFA) is associated with increased microbial diversity independent of fiber intake. In mice, poorly absorbed dietary long-chain SFA, particularly stearic acid, induce a shift in bile acid profile and improved metabolism and steatosis. These benefits are dependent on the gut microbiota, as they are transmitted by microbial transfer. Diets enriched in polyunsaturated fatty acids are protective against steatosis but have minor influence on the microbiota. In summary, we find that diets enriched in poorly absorbed long-chain SFA modulate gut microbiota profiles independent of fiber intake, and this interaction is relevant to improve metabolism and decrease liver steatosis.

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.