Search

Objective This study aims to explore the associations between diet quality, uraemic toxins, and gastrointestinal microbiota in the chronic kidney disease (CKD) population. Methods This is a baseline cross-sectional study of adults with CKD participating in a randomized controlled trial of prebiotic and probiotic supplementation. Dietary intake was measured using a seven-day diet history method, administered by a specialist dietitian. Diet quality was assessed using plant-based diet index (PDI) (overall PDI, healthy PDI, and unhealthy PDI), food group analysis, protein intake, fiber intake, and dietary protein-to-fiber ratio. Serum uraemic toxins (free and total; indoxyl sulfate and p-cresyl sulfate) were determined by ultraperformance liquid chromatography. Gastrointestinal microbiota richness, diversity, composition, and functional capacity were analyzed via metagenomic sequencing. Results Sixty-eight adults [median age: 70 (interquartile range: 58-75) years, 66% male] with an estimated glomerular filtration rate of 34 ± 11 mL/min/1.73 m2 were included, with 40 participants completing the optional fecal substudy. Dietary fiber intake was associated with lower levels of total indoxyl sulfate, whereas the healthy plant-based diet index was associated with lower levels of free p-cresyl sulfate. A higher protein-to-fiber ratio was associated with an increased relative abundance of unclassified members of order Oscillospirales. Intake of vegetables and whole grains was correlated with Subdoligranulum formicile, whereas an unclassified Prevotella species was correlated with potatoes and food items considered discretionary, including sweet drinks, sweet desserts, and animal fats. Conclusions Diet quality may influence uraemic toxin generation and gut microbiota diversity, composition, and function in adults with CKD. Well-designed dietary intervention studies targeting the production of uraemic toxins and exploring the impact on gut microbiome are warranted in the CKD population. Keywords Kidney disease; diet quality; gut microbiota; p-cresyl sulphate; indoxyl sulfate

IntroductionGut microbiome studies often overlook experimental factors that could influence gut microbiome diversity and could impact findings. Large-scale studies investigating these experimental factors are lacking. Thus, we aimed to determine which experimental factors influence the gut microbiome diversity in pre-clinical animal model studies.MethodsWe extracted DNA and sequenced the V4 region of the 16S rRNA gene of a total of 538 samples from various sections of the gastrointestinal tract of 303 young and aged male and female C57BL/6J mice of three different genotypes on five diets from three animal house facilities. As a proof-of-concept in a disease model, some mice were treated with sham or angiotensin II, a commonly studied agent used as a hypertension model. Some samples were sequenced twice as a matched-comparison group.ResultsUsing over 17 million sequencing reads, we found that experimental factors such as animal house facility, genotype, diet, age, sex, sampling site, and technical factor (i.e., sequencing batch) affected both α- and β-diversity (weighted and unweighted UniFrac), and were associated with compositional changes in the microbiome at varying magnitude, with diet and sampling site having the largest effect. After adjustment by these factors, treatment with angiotensin II had no impact on α-diversity and was only significant in unweighted UniFrac (presence/absence of bacteria) analyses.ConclusionOur data identified several key experimental and technical factors that affect the gut microbiome in laboratory mice. Our findings support that not accounting or adjusting for these factors may lead to false-positive discoveries and non-biologically relevant findings in the gut microbiome field.

biSignificance:/i/bThe metabolic disorder, diabetes mellitus, results in microvascular complications, including diabetic kidney disease (DKD), which is partly believe to involve disrupted energy generation in the kidney, leading to injury that is characterized by inflammation and fibrosis. An increasing body of evidence indicates that the innate immune complement system is involved in the pathogenesis of DKD; however, the precise mechanisms remain unclear.biRecent Advances:/i/bComplement, traditionally thought of as the prime line of defense against microbial intrusion, has recently been recognized to regulate immunometabolism. Studies have shown that the complement activation products, Complement C5a and C3a, which are potent pro-inflammatory mediators, can mediate an array of metabolic responses in the kidney in the diabetic setting, including altered fuel utilization, disrupted mitochondrial respiratory function, and reactive oxygen species generation. In diabetes, the lectin pathway is activated via autoreactivity toward altered self-surfaces known as danger-associated molecular patterns, or via sensing altered carbohydrate and acetylation signatures. In addition, endogenous complement inhibitors can be glycated, whereas diet-derived glycated proteins can themselves promote complement activation, worsening DKD, and lending support for environmental influences as an additional avenue for propagating complement-induced inflammation and kidney injury.biCritical Issues:/i/bRecent evidence indicates that conventional renoprotective agents used in DKD do not target the complement, leaving this web of inflammatory stimuli intact.biFuture Directions:/i/bFuture studies should focus on the development of novel pharmacological agents that target the complement pathway to alleviate inflammation, oxidative stress, and kidney fibrosis, thereby reducing the burden of microvascular diseases in diabetes.iAntioxid. Redox Signal/i. 37, 781-801.

There is increasing evidence of the influence of the gut microbiota on hypertension and its complications, such as chronic kidney disease, stroke, heart failure, and myocardial infarction. This is not surprising considering that the most common risk factors for hypertension, such as age, sex, medication, and diet, can also impact the gut microbiota. For example, sodium and fermentable fiber have been studied in relation to both hypertension and the gut microbiota. By combining second- and, now, third-generation sequencing with metabolomics approaches, metabolites, such as short-chain fatty acids and trimethylamine N-oxide, and their producers, have been identified and are now known to affect host physiology and the cardiovascular system. The receptors that bind these metabolites have also been explored with positive findings—examples include known short-chain fatty acid receptors, such as G-protein coupled receptors GPR41, GPR43, GPR109a, and OLF78 in mice. GPR41 and OLF78 have been shown to have inverse roles in blood pressure regulation, whereas GPR43 and GPR109A have to date been demonstrated to impact cardiac function. New treatment options in the form of prebiotics (eg, dietary fiber), probiotics (eg, Lactobacillus spp.), and postbiotics (eg, the short-chain fatty acids acetate, propionate, and butyrate) have all been demonstrated to be beneficial in lowering blood pressure in animal models, but the underlying mechanisms remain poorly understood and translation to hypertensive patients is still lacking. Here, we review the evidence for the role of the gut microbiota in hypertension, its risk factors, and cardiorenal complications and identify future directions for this exciting and fast-evolving field.

It is increasingly recognized that the gut microbiota plays a role in the progression of chronic diseases and that diet may confer health benefits by altering the gut microbiota composition. This is of particular relevance for chronic kidney disease (CKD), as the gut is a source of uremic retention solutes, which accumulate as a result of impaired kidney function and can exert nephrotoxic and other harmful effects. Kidney dysfunction is also associated with changes in the composition of the gut microbiota and the gastrointestinal tract. Diet modulates the gut microbiota, and there is much interest in the use of prebiotics, probiotics, and synbiotics as dietary therapies in CKD, as well as dietary patterns that beneficially alter the microbiota. This review provides an overview of the gut microbiota and its measurement, its relevance in the context of CKD, and the current state of knowledge regarding dietary manipulation of the microbiota.

Background: High blood pressure (BP) continues to be a major, poorly controlled but modifiable risk factor for cardiovascular death. Among key Western lifestyle factors, a diet poor in fiber is associated with prevalence of high BP. The impact of lack of prebiotic fiber and the associated mechanisms that lead to higher BP are unknown. Here we show that lack of prebiotic dietary fiber leads to the development of a hypertensinogenic gut microbiota, hypertension and its complications, and demonstrate a role for G-protein coupled-receptors (GPCRs) that sense gut metabolites. Methods: One hundred seventy-nine mice including C57BL/6J, gnotobiotic C57BL/6J, and knockout strains for GPR41, GPR43, GPR109A, and GPR43/109A were included. C57BL/6J mice were implanted with minipumps containing saline or a slow-pressor dose of angiotensin II (0.25 mg·kg -1 ·d -1 ). Mice were fed diets lacking prebiotic fiber with or without addition of gut metabolites called short-chain fatty acids ([SCFA)] produced during fermentation of prebiotic fiber in the large intestine), or high prebiotic fiber diets. Cardiac histology and function, BP, sodium and potassium excretion, gut microbiome, flow cytometry, catecholamines and methylation-wide changes were determined. Results: Lack of prebiotic fiber predisposed mice to hypertension in the presence of a mild hypertensive stimulus, with resultant pathological cardiac remodeling. Transfer of a hypertensinogenic microbiota to gnotobiotic mice recapitulated the prebiotic-deprived hypertensive phenotype, including cardiac manifestations. Reintroduction of SCFAs to fiber-depleted mice had protective effects on the development of hypertension, cardiac hypertrophy, and fibrosis. The cardioprotective effect of SCFAs were mediated via the cognate SCFA receptors GPR43/GPR109A, and modulated L-3,4-dihydroxyphenylalanine levels and the abundance of T regulatory cells regulated by DNA methylation. Conclusions: The detrimental effects of low fiber Westernized diets may underlie hypertension, through deficient SCFA production and GPR43/109A signaling. Maintaining a healthy, SCFA-producing microbiota is important for cardiovascular health.

Alterations in gut homeostasis may contribute to the progression of diabetic nephropathy. There has been recent attention on the renoprotective effects of metabolite-sensing receptors in chronic renal injury, including the G-protein-coupled-receptor (GPR)109a, which ligates the short chain fatty acid butyrate. However, the role of GPR109a in the development of diabetic nephropathy, a milieu of diminished microbiome-derived metabolites, has not yet been determined. This study aimed to assess the effects of insufficient GPR109a signalling via genetic deletion of GPR109a on the development of renal injury in diabetic nephropathy. Gpr109a−/− mice or their wildtype littermates (Gpr109a+/+) were rendered diabetic with streptozotocin (STZ). Mice received a control diet or an isocaloric high fiber diet (12.5% resistant starch) for 24 weeks and gastrointestinal permeability and renal injury were determined. Diabetes was associated with increased albuminuria, glomerulosclerosis and inflammation. In comparison, Gpr109a−/− mice with diabetes did not show an altered renal phenotype. Resistant starch supplementation did not afford protection from renal injury in diabetic nephropathy. Whilst diabetes was associated with alterations in intestinal morphology, intestinal permeability assessed in vivo using the FITC-dextran test was unaltered. GPR109a deletion did not worsen gastrointestinal permeability. Further, 12.5% resistant starch supplementation, at physiological concentrations, had no effect on intestinal permeability or morphology. These studies indicate that GPR109a does not play a critical role in intestinal homeostasis in a model of type 1 diabetes or in the development of diabetic nephropathy.

Mitochondrial stress has been widely observed in diabetic kidney disease (DKD). Cyclophilin D (CypD) is a functional component of the mitochondrial permeability transition pore (mPTP) which allows the exchange of ions and solutes between the mitochondrial matrix to induce mitochondrial swelling and activation of cell death pathways. CypD has been successfully targeted in other disease contexts to improve mitochondrial function and reduced pathology. Two approaches were used to elucidate the role of CypD and the mPTP in DKD. Firstly, mice with a deletion of the gene encoding CypD (Ppif−/−) were rendered diabetic with streptozotocin (STZ) and followed for 24 weeks. Secondly, Alisporivir, a CypD inhibitor was administered to the db/db mouse model (5 mg/kg/day oral gavage for 16 weeks). Ppif−/− mice were not protected against diabetes-induced albuminuria and had greater glomerulosclerosis than their WT diabetic littermates. Renal hyperfiltration was lower in diabetic Ppif−/− as compared with WT mice. Similarly, Alisporivir did not improve renal function nor pathology in db/db mice as assessed by no change in albuminuria, KIM-1 excretion and glomerulosclerosis. Db/db mice exhibited changes in mitochondrial function, including elevated respiratory control ratio (RCR), reduced mitochondrial H2O2 generation and increased proximal tubular mitochondrial volume, but these were unaffected by Alisporivir treatment. Taken together, these studies indicate that CypD has a complex role in DKD and direct targeting of this component of the mPTP will likely not improve renal outcomes.

There is increasing evidence for the role of intestinal permeability as a contributing factor in the pathogenesis of diabetes; however, the molecular mechanisms are poorly understood. Advanced glycation endproducts, of both exogenous and endogenous origin, have been shown to play a role in diabetes pathophysiology, in part by their ligation to the receptor for advanced glycation endproducts (RAGE), leading to a proinflammatory signalling cascade. RAGE signalling has been demonstrated to play a role in the development of intestinal inflammation and permeability in Crohn’s disease and ulcerative colitis. In this review, we explore the role of AGE-RAGE signalling and intestinal permeability and explore whether activation of RAGE on the intestinal epithelium may be a downstream event contributing to the pathogenesis of diabetes complications.

High-heat processed foods contain proteins that are partially resistant to enzymatic digestion and pass through to the colon. The fermentation of resistant proteins by gut microbes produces products that may contribute to chronic disease risk. This pilot study examined the effects of a resistant protein diet on growth, fecal microbiome, protein fermentation metabolites, and the biomarkers of health status in pigs as a model of human digestion and metabolism. Weanling pigs were fed with standard or resistant protein diets for 4 weeks. The resistant protein, approximately half as digestible as the standard protein, was designed to enter the colon for microbial fermentation. Fecal and blood samples were collected to assess the microbiome and circulating metabolites and biomarkers. The resistant protein diet group consumed less feed and grew to ~50% of the body mass of the standard diet group. The diets had unique effects on the fecal microbiome, as demonstrated by clustering in the principal coordinate analysis. There were 121 taxa that were significantly different between groups (adjusted-p < 0.05). Compared with control, plasma tri-methylamine-N-oxide, homocysteine, neopterin, and tyrosine were increased and plasma acetic acid was lowered following the resistant protein diet (all p < 0.05). Compared with control, estimated glomerular filtration rate (p < 0.01) and liver function marker aspartate aminotransferase (p < 0.05) were also lower following the resistant protein diet. A resistant protein diet shifted the composition of the fecal microbiome. The microbial fermentation of resistant protein affected the levels of circulating metabolites and the biomarkers of health status toward a profile indicative of increased inflammation and the risk of chronic kidney disease.

Diabetic kidney disease (DKD) remains the number one cause of end-stage renal disease in the western world. In experimental diabetes, mitochondrial dysfunction in the kidney precedes the development of DKD. Reactive 1,2-dicarbonyl compounds, such as methylglyoxal, are generated from sugars both endogenously during diabetes and exogenously during food processing. Methylglyoxal is thought to impair the mitochondrial function and may contribute to the pathogenesis of DKD. Here, we sought to target methylglyoxal within the mitochondria using MitoGamide, a mitochondria-targeted dicarbonyl scavenger, in an experimental model of diabetes. Male 6-week-old heterozygous Akita mice (C57BL/6-Ins2-Akita/J) or wildtype littermates were randomized to receive MitoGamide (10 mg/kg/day) or a vehicle by oral gavage for 16 weeks. MitoGamide did not alter the blood glucose control or body composition. Akita mice exhibited hallmarks of DKD including albuminuria, hyperfiltration, glomerulosclerosis, and renal fibrosis, however, after 16 weeks of treatment, MitoGamide did not substantially improve the renal phenotype. Complex-I-linked mitochondrial respiration was increased in the kidney of Akita mice which was unaffected by MitoGamide. Exploratory studies using transcriptomics identified that MitoGamide induced changes to olfactory signaling, immune system, respiratory electron transport, and post-translational protein modification pathways. These findings indicate that targeting methylglyoxal within the mitochondria using MitoGamide is not a valid therapeutic approach for DKD and that other mitochondrial targets or processes upstream should be the focus of therapy.

Background/Objectives: Faecal microbiota transplant (FMT) is a powerful tool used to connect changes in gut microbial composition with a variety of disease states and pathologies. While FMT enables potential causal relationships to be identified, the experimental details reported in preclinical FMT protocols are highly inconsistent and/or incomplete. This limitation reflects a current lack of authoritative guidance on reporting standards which would facilitate replication efforts and ultimately reproducible science. We therefore systematically reviewed all FMT protocols used in mouse models with the goal of formulating recommendations on the reporting of preclinical FMT protocols. Methods: Search strategies were applied across three databases (PubMed, EMBASE and Ovid Medline) until June 30, 2020. Data related to donor attributes, stool collection, processing/storage, recipient preparation, administration and quality control were extracted.Results: A total of 1753 papers were identified, with 241 identified for data extraction and analysis. Of the papers included, 92.5% reported a positive outcome with FMT intervention. However, the vast majority of studies failed to address core methodological aspects including the use of anaerobic conditions (91.7% of papers lacked information), storage (49.4%), homogenisation (33.6%), concentration (31.5%), volume (19.9%) and administration route (5.3%). To address these reporting limitations, we developed the Guidelines for Reporting Animal Faecal Transplant (GRAFT) that guide reporting standards for preclinical FMT. Conclusion: The GRAFT recommendations will enable robust reporting of preclinical FMT design, and facilitate high quality peer review, improving the rigour and translation of knowledge gained through preclinical FMT studies.

Background and Aims Individuals with chronic kidney disease (CKD) have significantly increased risk of cardiovascular mortality which is only partially explained by Framingham risk factors. There is a growing body of evidence linking the gut-derived uraemic toxins indoxyl sulphate (IS) and p-cresyl sulphate (PCS) with accelerated kidney disease progression and cardiovascular burden in CKD. Whilst the effect of specific nutrients on uraemic toxin generation has been explored, few studies have characterised the impact of diet quality on the gastrointestinal microbiome in the CKD population. This study aims to explore the associations between dietary quality, protein-bound uraemic toxins and gastrointestinal microbiome in adults with CKD. Method This was a baseline cross-sectional study of adults with stage 3 to 4 CKD who were enrolled in a randomised controlled trial of prebiotic and probiotic supplementation. Habitual dietary intake was measured using a 7-day diet history method by a specialist Dietitian. Diet quality was assessed using food group analysis; protein intake, fibre intake, dietary protein:fibre ratio and adherence to plant-based diet index (PDI) (overall PDI, healthy PDI, unhealthy PDI). Serum uraemic toxins (free and total; IS and PCS) were determined by ultra-performance liquid chromatography. Metagenomic sequencing was used to determine gastrointestinal microbiota richness, diversity, composition and functional capacity. Results There were 68 CKD patients [66% male, median age 70 (IQR 58-75) years] with a mean estimated glomerular filtration rate of 34 ± 11 mL/min/1.73m2. Greater adherence to a hPDI was associated with lower levels of free PCS [-0.021 µmol/L (95% CI -0.042 to -0.001)], while a higher intake of dietary fibre intake was associated with lower levels of free IS [-0.022 µmol/L (95% CI -0.043 to -0.001)]. Compositionally, the gastrointestinal microbiota of this cohort was dominated by members of the phyla Firmicutes and Bacteroidetes. Supervised analysis at the species level demonstrated that 21% of variance in gastrointestinal microbial composition could be attributed to protein:fibre ratio (F=1.27, p=0.04). Further, a higher protein:fibre ratio was associated with an increased relative abundance of unclassified members of order Oscillospirales. Subdoligranulum formicile was correlated with dietary intake of vegetables and wholegrains while an unclassified Prevotella species was correlated with food items considered discretionary including sweet drinks, sweet desserts, animal fats and potatoes. Conclusion The study suggests that habitual diets that are higher in fibre and plant-based foods may positively influence uraemic toxin levels and gut microbiota diversity and composition in adults with CKD. These findings provide rationale for well-designed dietary intervention studies targeting the production of uraemic toxins and exploring the impact on gut microbiome in the CKD population.

Background and Aims Synbiotics, co-administered prebiotics and probiotics, have emerged over the last decade as an innocuous intervention targeting the microbial generation of the uraemic toxins, indoxyl sulphate (IS) and p-cresyl sulphate (PCS). However, most trials to date are of short duration (2-24 weeks). In order to inform translation into clinical practice, it is imperative to consider the efficacy of synbiotic supplementation as a long-term intervention. The aims of this study were to evaluate the feasibility and acceptability (including symptoms and adherence) of long-term synbiotic supplementation in adults with chronic kidney disease (CKD), as well as explore the perspectives of these patients on nutrition supplementation for gut health, including strategies to optimise adherence in practice. Method SYNERGY II was a double-blind randomised controlled trial in adults (>18years) with stage 3-4 CKD over 12 months. The intervention comprised of daily prebiotic powder (2 x 10g/day resistant starch) and probiotic supplementation (single sachet of 6g/day multi strain 4.5x1011CFU) or placebo control (waxy maize powder and a sachet of maltodextrin). Adherence to nutrition supplementation was defined as participants consuming >80% of the prescribed sachets/powder. Symptoms were monitored via Gastrointestinal Symptom Rating Scale (GSRS) and Bristol Stool Score (BSS). Semi-structured interviews were conducted in person or by telephone with a sample of 30 participants at the completion of the intervention. The interviews explored experiences and perspectives regarding frequencies, timing and difficulties experienced with each aspect of the intervention and overall perceptions of the intervention as a strategy to improve gut health. Results Sixty-eight participants [66% male, median age 70 (IQR 58-75) years] were consented and randomised to either intervention or control groups, with a mean estimated glomerular filtration rate of 34 ± 11 mL/min/1.73m2. A total of 56 participants (82%) completed the 12-month intervention with no differences in withdrawals between groups (p=0.6). One participant from each group withdrew at week 2, citing palatability of the study product as the reason for withdrawal. Overall adherence to study supplementation was excellent in both intervention and placebo groups [median intake 92.1% (85.9-95.2%) placebo versus 89.5% (84.4-94.5%) synbiotic; P=0.4)]. Overall, there was no significant change from baseline to end of study visit for mean BSS (3.6 ± 1.4 to 3.6 ± 1.4 placebo versus 3.6 ± 1.1 to 4.1 ± 1.2 synbiotic, P=0.13), mean bowel movements (1.3 ± 0.6 to 1.6 ± 0.9 placebo versus 1.3 ± 0.6 to 1.8 ± 1.0 synbiotic, P=0.70) or GSRS [1.3 (1.1 - 1.9) to 1.3 (1.1 - 1.5) placebo versus 1.1 (1.1 - 1.5) to 1.3 (1.1 - 1.5) synbiotic, P=0.83]. Acceptability components described by participants were appreciating convenience and improving health and well-being. Participants discussed the following feasibility components: integrating easily into lifestyle and social accountability. Tablets or capsules were the preferred supplement formulation with a probiotic drink made from a SCOBY (synbiotic culture of bacteria and yeast) the least preferred. Conclusion Among adults with stage 3-4 CKD, synbiotic supplementation is a well-tolerated and acceptable form of nutrition supplementation. People with CKD would prefer nutrition supplements to be formulated as a tablet or capsule, which is an important consideration when translating into clinical practice.

The sequelae of diabetes include microvascular complications such as diabetic kidney disease (DKD), which involves glucose-mediated renal injury associated with a disruption in mitochondrial metabolic agility, inflammation, and fibrosis. We explored the role of the innate immune complement component C5a, a potent mediator of inflammation, in the pathogenesis of DKD in clinical and experimental diabetes. Marked systemic elevation in C5a activity was demonstrated in patients with diabetes; conventional renoprotective agents did not therapeutically target this elevation. C5a and its receptor (C5aR1) were upregulated early in the disease process and prior to manifest kidney injury in several diverse rodent models of diabetes. Genetic deletion of C5aR1 in mice conferred protection against diabetes-induced renal injury. Transcriptomic profiling of kidney revealed diabetes-induced downregulation of pathways involved in mitochondrial fatty acid metabolism. Interrogation of the lipidomics signature revealed abnormal cardiolipin remodeling in diabetic kidneys, a cardinal sign of disrupted mitochondrial architecture and bioenergetics. In vivo delivery of an orally active inhibitor of C5aR1 (PMX53) reversed the phenotypic changes and normalized the renal mitochondrial fatty acid profile, cardiolipin remodeling, and citric acid cycle intermediates. In vitro exposure of human renal proximal tubular epithelial cells to C5a led to altered mitochondrial respiratory function and reactive oxygen species generation. These experiments provide evidence for a pivotal role of the C5a/C5aR1 axis in propagating renal injury in the development of DKD by disrupting mitochondrial agility, thereby establishing a new immunometabolic signaling pathway in DKD.

This study shows how highly processed foods can cause innate immune inflammation that promotes chronic microvascular disease., Intake of processed foods has increased markedly over the past decades, coinciding with increased microvascular diseases such as chronic kidney disease (CKD) and diabetes. Here, we show in rodent models that long-term consumption of a processed diet drives intestinal barrier permeability and an increased risk of CKD. Inhibition of the advanced glycation pathway, which generates Maillard reaction products within foods upon thermal processing, reversed kidney injury. Consequently, a processed diet leads to innate immune complement activation and local kidney inflammation and injury via the potent proinflammatory effector molecule complement 5a (C5a). In a mouse model of diabetes, a high resistant starch fiber diet maintained gut barrier integrity and decreased severity of kidney injury via suppression of complement. These results demonstrate mechanisms by which processed foods cause inflammation that leads to chronic disease.

Fecal microbiota transplant (FMT) is a powerful tool used to connect changes in gut microbial composition with a variety of disease states and pathologies. While FMT enables potential causal relationships to be identified, the experimental details reported in preclinical FMT protocols are highly inconsistent and/or incomplete. This limitation reflects a current lack of authoritative guidance on reporting standards that would facilitate replication efforts and ultimately reproducible science. We therefore systematically reviewed all FMT protocols used in mouse models with the goal of formulating recommendations on the reporting of preclinical FMT protocols. Search strategies were applied across three databases (PubMed, EMBASE, and Ovid Medline) until June 30, 2020. Data related to donor attributes, stool collection, processing/storage, recipient preparation, administration, and quality control were extracted. A total of 1753 papers were identified, with 241 identified for data extraction and analysis. Of the papers included, 92.5% reported a positive outcome with FMT intervention. However, the vast majority of studies failed to address core methodological aspects including the use of anaerobic conditions (91.7% of papers lacked information), storage (49.4%), homogenization (33.6%), concentration (31.5%), volume (19.9%) and administration route (5.3%). To address these reporting limitations, we developed theGuidelines for Reporting Animal Fecal Transplant (GRAFT) that guide reporting standards for preclinical FMT. The GRAFT recommendations will enable robust reporting of preclinical FMT design, and facilitate high-quality peer review, improving the rigor and translation of knowledge gained through preclinical FMT studies., Graphical abstract

OBJECTIVES: The primary objective of this study was to ascertain whether thermally processed diets influence albuminuria and intestinal permeability via alterations in the complement cascade. A secondary objective was to see whether these pathological alterations could be ameliorated by a gut-targeted dietary intervention, resistant starch. METHODS: Six-week-old Sprague Dawley rats were randomised to receive a control (CON; AIN93G), thermally processed diet (TPD) (AIN93G baked at 160°C for 1h) or TPD with daily gavage of either 10 mg/kg/d alagebrium chloride (ALA), an inhibitor of advanced glycation end products or daily gavage of 2mg/kg/d PMX-53, a C5a receptor inhibitor for 24 weeks. Six-week-old diabetic mice (db/db) received the CON diet or TPD with or without 12.5% resistant starch (RS) for 10 weeks. Albumin, MCP-1 and C5a were measured by ELISA. Endotoxin was measured using a limulus amoebocyte lysate kit. Intestinal permeability was assessed in vivo by the clearance of FITC-labelled dextran. Transcriptomic profiling of renal cortex was determined by RNA-Sequencing. RESULTS: The TPD increased albuminuria, plasma endotoxin and MCP-1 which were ameliorated with ALA or PMX-53. TPD increased urinary C5a, which was decreased with ALA. In db/db mice, RS supplementation of the TPD reduced albuminuria and intestinal permeability. Gene set enrichment analysis showed an upregulation in the complement cascade in TPD db/db mice, which was normalized by RS. Similarly, RS supplementation reduced urinary C5a in TPD-fed db/db mice. CONCLUSIONS: These results demonstrate that thermally processed diets lead to worsening albuminuria via activation of the complement cascade. These results also indicate that resistant starch supplementation may ameliorate some of the negative effects observed with excessive intake of thermally processed. FUNDING SOURCES: This study was funded by the National Health and Medical Research Council of Australia (NHMRC) and the Australian and New Zealand Society of Nephrology (ANZSN).

Diabetes is a metabolic condition. The composition of the gut microbiota is altered in diabetes with reduced levels of short chain fatty acids (SCFA) producers, notably butyrate. Butyrate is associated with a number of beneficial effects including promoting the integrity of the gastrointestinal barrier. Diabetes may lead to an increase in the permeability of the gut barrier, which is thought to contribute to systemic inflammation and worsen the microvascular complications of diabetes. Prebiotics, non-digestible carbohydrates, are fermented by the colonic microbiota leading to the production of a range of metabolites including SCFAs. Thus, prebiotics represent a dietary approach to increase levels of microbially produced SCFAs and improve intestinal permeability in diabetes. Whether prebiotics can lead to a reduction in the risk of developing diabetes complications in individuals with type 2 diabetes needs to be explored.

Background: High fibre intake is associated with lower blood pressure (BP) in epidemiological and clinical studies. Prebiotic fibre resists digestion in the upper gastrointestinal tract and is fermented by gut microbiota in the intestine. The impact of lack of prebiotic dietary fibre in BP remains unknown. Objectives: To determine the consequences of lack of prebiotic dietary fibre to the development of hypertension through changes in the gut microbiome, associated receptors and immune-based mechanisms using a slow pressor angiotensin II (Ang II) model. Methods: C57BL/6 mice were fed a ‘no fibre’ or ‘high fibre’ diets for 3-weeks prior to sham or Ang II minipump implantation (n=4-21/group), and were followed for 4-weeks post-surgery. Gnotobiotic mice received faecal transplant from ‘no fibre’ sham or Ang II mice (n=5-6/group). Cardiac function, BP and gut microbiome (by 16S sequencing) were determined. Results: Ang II mice that received a ‘no fibre’ diet had significantly higher BP than sham (SBP mean±SEM: 143.7±3.5 vs 91.2±1.8, P Conclusions: Lack of prebiotic dietary fibre leads to the development of a hypertensinogenic gut microbiome, hypertension and its complications. SCFA might represent new therapeutic opportunities through modulation of G-coupled protein receptors and Treg cells.

This thesis examines the detrimental effects of heat-processed foods on the kidneys. It then examines whether using a prebiotic fibre can be beneficial in limiting the negative impacts from heat-processed foods.

Scope: This study evaluates the effects of a chronic high protein diet (HPD) on kidney injury, intestinal permeability and gut microbiota perturbations in a mouse model. Method and results: Mice are fed a diet containing either 20% or 52% energy from protein for 24 weeks; protein displaced an equivalent amount of wheat starch. The HPD does not alter glycemic control or body weight. The HPD induces kidney injury as evidenced by increase in albuminuria, urinary kidney injury molecule-1, blood urea nitrogen, urinary isoprostanes and renal cortical NF-κB p65 gene expression. HPD decreases intestinal occludin gene expression, increases plasma endotoxin and plasma monocyte chemoattractant protein-1, indicating intestinal leakiness and systemic inflammation. Cecal microbial analysis reveals that HPD feeding does not alter alpha diversity; however, it does alter beta diversity, indicating an altered microbial community structure with HPD feeding. Predicted metagenome pathway analysis demonstrates a reduction in branched-chain amino acid synthesis and an increase of the urea cycle with consumption of a HPD. Conclusion: These results demonstrate that long term HPD consumption in mice causes albuminuria, systemic inflammation, increase in gastrointestinal permeability and is associated with gut microbiome remodeling with an increase in the urea cycle pathway, which may contribute to renal injury.

Chronic kidney disease (CKD) has been associated with changes in gut microbial ecology, or "dysbiosis," which may contribute to disease progression. Recent studies have focused on dietary approaches to favorably alter the composition of the gut microbial communities as a treatment method in CKD. Resistant starch (RS), a prebiotic that promotes proliferation of gut bacteria such as Bifidobacteria and Lactobacilli, increases the production of metabolites including short-chain fatty acids, which confer a number of health-promoting benefits. However, there is a lack of mechanistic insight into how these metabolites can positively influence renal health. Emerging evidence shows that microbiota-derived metabolites can regulate the incretin axis and mitigate inflammation via expansion of regulatory T cells. Studies from animal models and patients with CKD show that RS supplementation attenuates the concentrations of uremic retention solutes, including indoxyl sulfate and p-cresyl sulfate. Here, we present the current state of knowledge linking the microbiome to CKD, we explore the efficacy of RS in animal models of CKD and in humans with the condition, and we discuss how RS supplementation could be a promising dietary approach for slowing CKD progression.

Diet is one of the largest modifiable risk factors for chronic kidney disease (CKD)-related death and disability. CKD is largely a progressive disease; however, it is increasingly appreciated that hallmarks of chronic kidney disease such as albuminuria can regress over time. The factors driving albuminuria resolution remain elusive. Since albuminuria is a strong risk factor for GFR loss, modifiable lifestyle factors that lead to an improvement in albuminuria would likely reduce the burden of CKD in high-risk individuals, such as patients with diabetes. Dietary therapy such as protein and sodium restriction has historically been used in the management of CKD. Evidence is emerging to indicate that other nutrients may influence kidney health, either through metabolic or haemodynamic pathways or via the modification of gut homeostasis. This review focuses on the role of diet in the pathogenesis and progression of CKD and discusses the latest findings related to the mechanisms of diet-induced kidney disease. It is possible that optimizing diet quality or restricting dietary intake could be harnessed as an adjunct therapy for CKD prevention or progression in susceptible individuals, thereby reducing the burden of CKD.

Published evidence exploring the effects of dietary resistant starch (RS) on human cardiometabolic health is inconsistent. This review aimed to investigate the effect of dietary RS type 2 (RS2) supplementation on body weight, satiety ratings, fasting plasma glucose, glycated hemoglobin (HbA1c), insulin resistance and lipid levels in healthy individuals and those with overweight/obesity, the metabolic syndrome (MetS), prediabetes or type 2 diabetes mellitus (T2DM). Five electronic databases were searched for randomized controlled trials (RCTs) published in English between 1982 and 2018, with trials eligible for inclusion if they reported RCTs involving humans where at least one group consumed ≥ 8 g of RS2 per day and measured body weight, satiety, glucose and/or lipid metabolic outcomes. Twenty-two RCTs involving 670 participants were included. Meta-analyses indicated that RS2 supplementation significantly reduced serum triacylglycerol concentrations (mean difference (MD) = −0.10 mmol/L; 95% CI −0.19, −0.01, P = 0.03) in healthy individuals (n = 269) and reduced body weight (MD = −1.29 kg; 95% CI −2.40, −0.17, P = 0.02) in people with T2DM (n = 90). However, these outcomes were heavily influenced by positive results from a small number of individual studies which contradicted the conclusions of the majority of trials. RS2 had no effects on any other metabolic outcomes. All studies ranged from 1−12 weeks in duration and contained small sample sizes (10−60 participants), and most had an unclear risk of bias. Short-term RS2 supplementation in humans is of limited cardiometabolic benefit.