Roles of short-chain fatty acids in kidney diseases

Multi-omics investigation of Porphyromonas gingivalis exacerbating acute kidney injury through the gut-kidney axis

Periodontitis is closely related to renal health, but the specific influence of Porphyromonas gingivalis (P. gingivalis), a key pathogen in periodontitis, on the development of acute kidney injury (AKI) in mice has not been fully elucidated. In our study, AKI was induced in mice through ischemia-reperfusion injury while administering oral infection with P. gingivalis. Comprehensive analyses were conducted, including 16S rRNA sequencing, liquid chromatography-mass spectrometry (LC-MS) metabolomics, and transcriptome sequencing. In vitro, the identified metabolite was used to stimulate mouse neutrophils. Subsequently, these modified neutrophils were co-cultured with mouse renal tubular epithelial cells. The results showed that oral infection with P. gingivalis significantly exacerbated AKI in mice. 16S rRNA sequencing revealed notable shifts in gut microbiota composition. LC-MS metabolomics analysis identified significant metabolic alterations, particularly the upregulation of 3-indoleacrylic acid in the serum. Transcriptome sequencing showed an increased expression of neutrophilic granule protein (Ngp), which was closely associated with 3-indoleacrylic acid, and the presence of Porphyromonas. Cellular experiments demonstrated that 3-indoleacrylic acid could activate neutrophils, leading to an elevation in NGP protein levels, a response that was associated with renal epithelial cell injury. Oral infection with P. gingivalis exacerbated AKI through the gut-kidney axis, involving gut microbiota dysbiosis, metabolic disturbances, and increased renal expression of Ngp.

IMPORTANCE

This study provides novel insights into the relationship between periodontal health and renal function. Porphyromonas gingivalis oral infection disrupted the balance of gut microbiota and was an important modifier determining the severity of acute kidney injury. Under the "gut-kidney axis," P. gingivalis might cause an increase in the level of the gut microbial metabolite 3-indoleacrylic acid, interfering with kidney immunity and disrupting the maintenance of kidney epithelium.

Gut microbiota and kidney function in autosomal dominant polycystic kidney disease participants in Cameroon: a cross-sectional study

BACKGROUND AND HYPOTHESIS

Gut dysbiosis characterized by an imbalance in pathobionts (Enterobacter, Escherichia and Salmonella) and symbionts (Bifidobacterium, Lactobacillus and Prevotella) can occur during chronic kidney disease (CKD) progression. We evaluated the associations between representative symbionts (Bifidobacterium and Lactobacillus) and pathobionts (Enterobacteriaceae) with kidney function in persons with autosomal dominant polycystic kidney disease (ADPKD).

METHODS

In this cross-sectional study, 29 ADPKD patients were matched to 15 controls at a 2:1 ratio. Clinical data and biological samples were collected. The estimated glomerular filtration rate (eGFR) was calculated from the serum creatinine concentration using the 2009 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. Microbial DNA extracted from stool specimens and amplified by qPCR was used to quantify Enterobacteriaceae, Bifidobacterium and Lactobacillus abundance. Differences between ADPKD subgroups and controls were assessed using nonparametric tests.

RESULTS

The mean age (SD) of the 44 participants was 40.65 (± 11.9) years. Among the participants with ADPKD, 62.1% experienced flank pain, and 48.3% had hypertension. Their median eGFR [IQR] was 74.4 [51.2-94.6] ml/min/1.73m2. All stool samples had Enterobacteriaceae. Lactobacillus abundance was lower in ADPKD participants with more pronounced kidney function decline (CKD G3-5: 0.58 ng/μL) than in those with milder damage and controls (G1-2: 0.64 ng/μL, p = 0.047; controls: 0.71 ng/μL, p = 0.043), while Enterobacteriaceae abundance was greater in ADPKD patients with lower kidney function (CKD G3-5: 78.6 ng/μL) than in those in the other two groups (G1-2: 71.6 ng/μL, p = 0.048; controls: 70.5 ng/μL, p = 0.045).

CONCLUSION

Decreased kidney function was associated with decreased symbiont and increased pathobiont abundance in ADPKD patients, suggesting a potential role for the microbiota in disease progression and possible targets for further research.

Probiotic interventions in peritoneal dialysis: A review of underlying mechanisms and therapeutic potentials

Peritoneal dialysis (PD) is a commonly used modality for kidney replacement therapy for patients with end-stage kidney disease (ESKD). PD offers many benefits, including home-based care, greater flexibility, and preservation of residual kidney function compared to in-center hemodialysis. Nonetheless, patients undergoing PD often face significant challenges, including systemic inflammation, PD-related peritonitis, metabolic disorders, and cardiovascular issues that can negatively affect their quality of life and treatment outcomes. Recent studies have demonstrated the crucial role of the gut microbiome in overall health and treatment results, supporting the hypothesis that probiotics may bring potential benefits to the general population of ESKD patients. However, specific data on probiotic use in PD patients are limited. This opinion review aims to summarize the current knowledge on the relationship between PD and the gut microbiome and offers a novel perspective by specifically exploring how probiotic interventions could improve the outcomes of PD treatment. The review also outlines some clinical data supporting the effectiveness of probiotics in patients undergoing PD and considers the difficulties and restrictions in their application. Based on the current knowledge gaps, this study seeks to explore future research directions and their implications for clinical practice.

Influence of gut flora on diabetes management after kidney transplantation

Post-transplant diabetes mellitus (PTDM) is a common complication following renal transplantation, and its incidence has been gradually increasing in recent years, posing a significant public health challenge. Managing PTDM is complex, as studies suggest that it involves changes in the microbial flora across multiple organs. Recent research highlights the critical role of gut flora metabolism in the development of diabetes among post-renal transplant patients. This paper reviews the alterations in gut flora observed in PTDM patients and explores how gut flora influences PTDM. These findings may offer new perspectives on targeting gut flora metabolites for the prevention and treatment of PTDM.

Gut microbiota regulates oxidative stress and inflammation: a double-edged sword in renal fibrosis

Gut microbiota is a complex and dynamic system that plays critical roles in human health and various disease. Progressive chronic kidney disease (CKD) suggests that patients irreversibly progress to end-stage kidney disease and need renal replacement treatments, including dialysis and transplantation. Ample evidence indicates that local oxidative stress and inflammation play pivotal roles in the pathogenesis and progression of CKD and dysbiosis of gut microbiota. CKD is always accompanied by intestinal inflammation and oxidative stress, which lead to rapid systemic translocation of bacterial-derived uraemic toxins, including indoxyl sulphate, phenyl sulphate and indole-3-acetic acid, and the consequent development and aggravation of renal fibrosis. Although inflammation and oxidative stress have been extensively discussed, there is a paucity of reports on the effects of gut microbiota on renal fibrosis and gut microbiota mediation of oxidative stress and inflammation. This review provides an overview of gut microbiota on inflammation and oxidative stress in renal fibrosis, briefly discusses regulation of the gut flora using microecological preparations and natural products, such as resveratrol, curcumin and emodin as treatments for CKD, and provides a clear pathophysiological rationale for the design of promising therapeutic strategies.

Oral Astragalus polysaccharide alleviates adenine-induced kidney injury by regulating gut microbiota-short-chain fatty acids-kidney G protein-coupled receptors axis

Chronic kidney disease (CKD) can cause gut microbiota dysbiosis and decreasing production of short-chain fatty acids (SCFAs), which aggravate the injury of kidney. It has been found that a variety of Chinese medicine polysaccharides can regulate gut microbiota, especially probiotics, and have beneficial effects on human health. Astragalus polysaccharide (APS) is a major component of Astragalus aceus. The aim of this study was to investigate whether APS can regulate gut microbiota-SCFAs to slow the progression of CKD. Adenine-induced CKD mice (Ade) were established and APS was treated. The renal protection of APS on CKD mice was evaluated by renal function and pathological staining of renal tissues. Feces samples were collected for 16SrRNA sequence and LC-MS/MS analysis. Kidney G protein-coupled receptor (GPR) levels were also detected in renal tissue. APS supplementation can reduce serum creatinine and urea nitrogen levels in mice model (Ade) and attenuate renal tubular interstitial injury and renal fibrosis. Further application of 16SrRNA sequencing showed that the abundance of SCFA producing bacteria, such as Kineothrix, Faecalibaculum, Akkermansia, Lactobacillus, and Roseburia, was upregulated after APS treatment. Fecal LC-MS/MS detection showed that the levels of acetate, propionate and butyrate in Ade mice increased after APS supplementation. The detection of renal GPRs showed that APS supplementing could significantly increase the levels of renal GPR41 and GPR43, and also partially increase the levels of GPR109a in Ade mice. Our research confirms that APS supplementation can upregulate the abundance of SCFA producing bacteria and increase SCFA levels to attenuate renal tubular interstitial injury and fibrosis via GPRs.

Traditional Chinese medicine improved diabetic kidney disease through targeting gut microbiota

CONTEXT

Diabetic kidney disease (DKD) affects nearly 40% of diabetic patients, often leading to end-stage renal disease that requires renal replacement therapies, such as dialysis and transplantation. The gut microbiota, an integral aspect of human evolution, plays a crucial role in this condition. Traditional Chinese medicine (TCM) has shown promising outcomes in ameliorating DKD by addressing the gut microbiota.

OBJECTIVE

This review elucidates the modifications in gut microbiota observed in DKD and explores the impact of TCM interventions on correcting microbial dysregulation.

METHODS

We searched relevant articles from databases including Web of Science, PubMed, ScienceDirect, Wiley, and Springer Nature. The following keywords were used: diabetic kidney disease, diabetic nephropathy, gut microbiota, natural product, TCM, Chinese herbal medicine, and Chinese medicinal herbs. Rigorous criteria were applied to identify high-quality studies on TCM interventions against DKD.

RESULTS

Dysregulation of the gut microbiota, including Lactobacillus, Streptococcus, and Clostridium, has been observed in individuals with DKD. Key indicators of microbial dysregulation include increased uremic solutes and decreased short-chain fatty acids. Various TCM therapies, such as formulas, tablets, granules, capsules, and decoctions, exhibit unique advantages in regulating the disordered microbiota to treat DKD.

CONCLUSION

This review highlights the importance of targeting the gut-kidney axis to regulate microbial disorders, their metabolites, and associated signaling pathways in DKD. The Qing-Re-Xiao-Zheng formula, the Shenyan Kangfu tablet, the Huangkui capsule, and the Bekhogainsam decoction are potential candidates to address the gut-kidney axis. TCM interventions offer a significant therapeutic approach by targeting microbial dysregulation in patients with DKD.

Engineered microorganisms: A new direction in kidney stone prevention and treatment

Numerous studies have shown that intestinal and urinary tract flora are closely related to the formation of kidney stones. The removal of probiotics represented by lactic acid bacteria and the colonization of pathogenic bacteria can directly or indirectly promote the occurrence of kidney stones. However, currently existing natural probiotics have limitations. Synthetic biology is an emerging discipline in which cells or living organisms are genetically designed and modified to have biological functions that meet human needs, or even create new biological systems, and has now become a research hotspot in various fields. Using synthetic biology approaches of microbial engineering and biological redesign to enable probiotic bacteria to acquire new phenotypes or heterologous protein expression capabilities is an important part of synthetic biology research. Synthetic biology modification of microorganisms in the gut and urinary tract can effectively inhibit the development of kidney stones by a range of means, including direct degradation of metabolites that promote stone production or indirect regulation of flora homeostasis. This article reviews the research status of engineered microorganisms in the prevention and treatment of kidney stones, to provide a new and effective idea for the prevention and treatment of kidney stones.

Quantifying Gut Microbial Short-Chain Fatty Acids and Their Isotopomers in Mechanistic Studies Using a Rapid, Readily Expandable LC-MS Platform

Short-chain fatty acids (SCFAs) comprise the largest group of gut microbial fermentation products. While absorption of most nutrients occurs in the small intestine, indigestible dietary components, such as fiber, reach the colon and are processed by the gut microbiome to produce a wide array of metabolites that influence host physiology. Numerous studies have implicated SCFAs as key modulators of host health, such as in regulating irritable bowel syndrome (IBS). However, robust methods are still required for their detection and quantitation to meet the demands of biological studies probing the complex interplay of the gut-host-health paradigm. In this study, a sensitive, rapid-throughput, and readily expandible UHPLC-QqQ-MS platform using 2-PA derivatization was developed for the quantitation of gut-microbially derived SCFAs, related metabolites, and isotopically labeled homologues. The utility of this platform was then demonstrated by investigating the production of SCFAs in cecal contents from mice feeding studies, human fecal bioreactors, and fecal/bacterial fermentations of isotopically labeled dietary carbohydrates. Overall, the workflow proposed in this study serves as an invaluable tool for the rapidly expanding gut-microbiome and precision nutrition research field.

The potential mechanism of gut microbiota-microbial metabolites-mitochondrial axis in progression of diabetic kidney disease

Diabetic kidney disease (DKD), has become the main cause of end-stage renal disease (ESRD) worldwide. Lately, it has been shown that the onset and advancement of DKD are linked to imbalances of gut microbiota and the abnormal generation of microbial metabolites. Similarly, a body of recent evidence revealed that biological alterations of mitochondria ranging from mitochondrial dysfunction and morphology can also exert significant effects on the occurrence of DKD. Based on the prevailing theory of endosymbiosis, it is believed that human mitochondria originated from microorganisms and share comparable biological characteristics with the microbiota found in the gut. Recent research has shown a strong correlation between the gut microbiome and mitochondrial function in the occurrence and development of metabolic disorders. The gut microbiome's metabolites may play a vital role in this communication. However, the relationship between the gut microbiome and mitochondrial function in the development of DKD is not yet fully understood, and the role of microbial metabolites is still unclear. Recent studies are highlighted in this review to examine the possible mechanism of the gut microbiota-microbial metabolites-mitochondrial axis in the progression of DKD and the new therapeutic approaches for preventing or reducing DKD based on this biological axis in the future.

Combined Intake of Fish Oil and D-Fagomine Prevents High-Fat High-Sucrose Diet-Induced Prediabetes by Modulating Lipotoxicity and Protein Carbonylation in the Kidney

Obesity has been recognized as a major risk factor for chronic kidney disease, insulin resistance being an early common metabolic feature in patients suffering from this syndrome. This study aims to investigate the mechanism underlying the induction of kidney dysfunction and the concomitant onset of insulin resistance by long-term high-fat and sucrose diet feeding in Sprague Dawley rats. To achieve this goal, our study analyzed renal carbonylated protein patterns, ectopic lipid accumulation and fatty acid profiles and correlated them with biometrical and biochemical measurements and other body redox status parameters. Rats fed the obesogenic diet developed a prediabetic state and incipient kidney dysfunction manifested in increased plasma urea concentration and superior levels of renal fat deposition and protein carbonylation. An obesogenic diet increased renal fat by preferentially promoting the accumulation of saturated fat, arachidonic, and docosahexaenoic fatty acids while decreasing oleic acid. Renal lipotoxicity was accompanied by selectively higher carbonylation of proteins involved in the blood pH regulation, i.e., bicarbonate reclamation and synthesis, amino acid, and glucose metabolisms, directly related to the onset of insulin resistance. This study also tested the combination of antioxidant properties of fish oil with the anti-diabetic properties of buckwheat D-Fagomine to counteract diet-induced renal alterations. Results demonstrated that bioactive compounds combined attenuated lipotoxicity, induced more favorable lipid profiles and counteracted the excessive carbonylation of proteins associated with pH regulation in the kidneys, resulting in an inhibition of the progression of the prediabetes state and kidney disease.

Sodium Butyrate Attenuates AGEs-Induced Oxidative Stress and Inflammation by Inhibiting Autophagy and Affecting Cellular Metabolism in THP-1 Cells

In recent years, sodium butyrate has gained increased attention for its numerous beneficial properties. However, whether sodium butyrate could alleviate inflammatory damage by macrophage activation and its underlying mechanism remains unclear. The present study used an advanced glycosylation products- (AGEs-) induced inflammatory damage model to study whether sodium butyrate could alleviate oxidative stress, inflammation, and metabolic dysfunction of human monocyte-macrophage originated THP-1 cells in a PI3K-dependent autophagy pathway. The results indicated that sodium butyrate alleviated the AGEs-induced oxidative stress, decreased the level of reactive oxygen species (ROS), increased malondialdehyde (MDA) and mRNA expression of pro-inflammatory cytokines of interleukin (IL)-1β and tumor necrosis factor (TNF)-α, and increased the content of superoxide dismutase (SOD). Sodium butyrate reduced the protein expression of the NLR family, pyrin domain-containing protein 3 (NLRP3) and Caspase-1, and decreased the nucleus expression of nuclear factor-kappaB (NF-κB). Sodium butyrate decreased the expression of light-chain-associated protein B (LC3B) and Beclin-1, and inhibited autophagy. Moreover, sodium butyrate inhibited the activation of the PI3K/Akt pathway in AGEs-induced THP-1 cells. In addition, the metabolomics analysis showed that sodium butyrate could affect the production of phosphatidylcholine, L-glutamic acid, UDP-N-acetylmuraminate, biotinyl-5'-AMP, and other metabolites. In summary, these results revealed that sodium butyrate inhibited autophagy and NLRP3 inflammasome activation by blocking the PI3K/Akt/NF-κB pathway, thereby alleviating oxidative stress, inflammation, and metabolic disorder induced by AGEs.

Mechanisms of the intestinal and urinary microbiome in kidney stone disease

Kidney stone disease affects ~10% of the global population and the incidence continues to rise owing to the associated global increase in the incidence of medical conditions associated with kidney stone disease including, for example, those comprising the metabolic syndrome. Considering that the intestinal microbiome has a substantial influence on host metabolism, that evidence has suggested that the intestinal microbiome might have a role in maintaining oxalate homeostasis and kidney stone disease is unsurprising. In addition, the discovery that urine is not sterile but, like other sites of the human body, harbours commensal bacterial species that collectively form a urinary microbiome, is an additional factor that might influence the induction of crystal formation and stone growth directly in the kidney. Collectively, the microbiomes of the host could influence kidney stone disease at multiple levels, including intestinal oxalate absorption and direct crystal formation in the kidneys.

Berberine ameliorates chronic kidney disease through inhibiting the production of gut-derived uremic toxins in the gut microbiota

At present, clinical interventions for chronic kidney disease are very limited, and most patients rely on dialysis to sustain their lives for a long time. However, studies on the gut-kidney axis have shown that the gut microbiota is a potentially effective target for correcting or controlling chronic kidney disease. This study showed that berberine, a natural drug with low oral availability, significantly ameliorated chronic kidney disease by altering the composition of the gut microbiota and inhibiting the production of gut-derived uremic toxins, including p-cresol. Furthermore, berberine reduced the content of p-cresol sulfate in plasma mainly by lowering the abundance of g_Clostridium_sensu_stricto_1 and inhibiting the tyrosine-p-cresol pathway of the intestinal flora. Meanwhile, berberine increased the butyric acid producing bacteria and the butyric acid content in feces, while decreased the renal toxic trimethylamine N-oxide. These findings suggest that berberine may be a therapeutic drug with significant potential to ameliorate chronic kidney disease through the gut-kidney axis.

Insoluble Fiber in Barley Leaf Attenuates Hyperuricemic Nephropathy by Modulating Gut Microbiota and Short-Chain Fatty Acids

Hyperuricemia (HUA), characterized by abnormal serum uric acid (UA) levels, is recognized as an important risk factor for hyperuricemic nephropathy (HN), which is strongly linked to gut microbiota. This study investigated the protective effects and regulatory mechanisms of insoluble fiber from barley leaves (BL) against HN, induced by adenine (Ad) and potassium oxonate (PO). The results showed that BL dramatically reduced the levels of serum UA and creatinine (CR) and alleviated renal injury and fibrosis. Moreover, BL modulated oxidative stress and downregulated the expression of urate transporter 1 (URAT1) and glucose transporter 9 (GLUT9) in the kidneys of mice with HN. In addition, the 16S rRNA sequence data showed that BL also increased the relative abundance of short-chain fatty acids (SCFAs)-producing bacteria, including Bacteroides, Alloprevotella, and Eisenbergiella. Besides, BL treatment also increased SCFAs levels. Of interest, the application of SCFAs in hyperuricemic mice effectively reduced their serum UA. Furthermore, SCFAs dose-dependently inhibited URAT1 and GLUT9 in vitro and potently interacted with URAT1 and GLUT9 in the docking analysis. When taken together, our results indicate that BL and its metabolite SCFAs may be potential candidates for relieving HUA or HN.

Stewed Rhubarb Decoction Ameliorates Adenine-Induced Chronic Renal Failure in Mice by Regulating Gut Microbiota Dysbiosis

This study aimed to investigate the protective effect of Stewed Rhubarb (SR) decoction on chronic renal failure (CRF) through the regulation of gut microbiota. Using a CRF mouse model induced by a 0.2% adenine diet, we proved that SR decoction (2.0 g crude SR/kg) significantly reduced the levels of urea and creatinine in plasma of CRF mice, accompanied by the improvement of renal fibrosis and tubular atrophy, amelioration of inflammation, and inhibition of aquaporins damage. Also, SR decoction alleviated gut barrier damage, indicative of the elevated mRNA expression of intestinal mucins and tight junctions. By 16S rDNA sequencing, SR decoction reshaped the imbalanced gut microbiota in CRF mice by statistically reversing the abundance changes of a wide range of intestinal bacteria at family and genus levels, which further led to balance in the production of intestinal metabolites, including short-chain fatty acids (acetic acid, propionic acid, and valeric acid), indole, and bile acids (TUDCA and CDCA). Inversely, SR decoction failed to repress the occurrence of CRF in mice with gut microbiota depletion, confirming the essential role of gut microbiota in SR decoction-initiated protection against CRF. In summary, SR decoction can improve adenine-induced CRF in mice by remolding the structure of destructed gut microbiota community. Our findings shed light on the clinical application of SR decoction in nephropathy treatment.

Why Are Bifidobacteria Important for Infants?

The presence of Bifidobacterium species in the maternal vaginal and fecal microbiota is arguably an evolutionary trait that allows these organisms to be primary colonizers of the newborn intestinal tract. Their ability to utilize human milk oligosaccharides fosters their establishment as core health-promoting organisms throughout life. A reduction in their abundance in infants has been shown to increase the prevalence of obesity, diabetes, metabolic disorder, and all-cause mortality later in life. Probiotic strains have been developed as supplements for premature babies and to counter some of these ailments as well as to confer a range of health benefits. The ability to modulate the immune response and produce short-chain fatty acids, particularly acetate and butyrate, that strengthen the gut barrier and regulate the gut microbiome, makes Bifidobacterium a core component of a healthy infant through adulthood.

Short-Chain Fatty Acids Reduced Renal Calcium Oxalate Stones by Regulating the Expression of Intestinal Oxalate Transporter SLC26A6

Renal calcium oxalate (CaOx) stone is a common urologic disease with a high prevalence and recurrence rate. However, short-chain fatty acids (SCFAs) are less often reported in the prevention of urolithiasis. This study aimed to explore the effect of SCFAs on the renal CaOx stone formation and the underlying mechanisms. Ethylene glycol was used to induce renal CaOx crystals in rats. SCFAs (acetate, propionate, or butyrate) were added as supplements to the drinking water with or without antibiotics. Because intestinal oxalate transporters SLC26A6 and SLC26A3 regulate the excretion and absorption of oxalate in the intestine, we injected adeno-associated virus 9 (AAV9)-SLC26A6-shRNA (short hairpin RNA) and AAV9-SLC26A3 into the tail vein of rats to suppress SLC26A6 and overexpress SLC26A3 expression in the intestine, respectively, to explore the role of SLC26A3 and SLC26A6 (SLC26A3/6) in the reduction of renal CaOx crystals induced by SCFAs. Results showed that SCFAs reduced renal CaOx crystals and urinary oxalate levels but, however, increased the abundance of SCFA-producing bacteria and cecum SCFA levels. SCFA supplements still reduced renal crystals and urinary oxalate after gut microbiota depletion. Propionate and butyrate downregulated intestinal oxalate transporter SLC26A3 expression, while acetate and propionate upregulated SLC26A6 expression, both in vivo and in vitro. AAV9-SLC26A3 exerted a protective effect against renal crystals, while AAV9-SLC26A6-shRNA contributed to the renal crystal formation even though the SCFAs were supplemented. In conclusion, SCFAs could reduce urinary oxalate and renal CaOx stones through the oxalate transporter SLC26A6 in the intestine. SCFAs may be new supplements for preventing the formation of renal CaOx stones. IMPORTANCE Some studies found that the relative abundances of short-chain-fatty-acid (SCFA)-producing bacteria were lower in the gut microbiota of renal stone patients than healthy controls. Our previous study demonstrated that SCFAs could reduce the formation of renal calcium oxalate (CaOx) stones, but the mechanism is still unknown. In this study, we found that SCFAs (acetate, propionate, and butyrate) reduced the formation of renal calcium oxalate (CaOx) crystals and the level of urinary oxalate. Depleting gut microbiota increased the amount of renal crystals in model rats, and SCFA supplements reduced renal crystals and urinary oxalate after gut microbiota depletion. Intestinal oxalate transporter SLC26A6 was a direct target of SCFAs. Our findings suggested that SCFAs could reduce urinary oxalate and renal CaOx stones through the oxalate transporter SLC26A6 in the intestine. SCFAs may be new supplements for preventing the formation of renal CaOx stones.

The change of gut microbiota-derived short-chain fatty acids in diabetic kidney disease

Background

Previous studies found the dysbiosis of intestinal microbiota in diabetic kidney disease (DKD), especially the decreased SCFA‐producing bacteria. We aimed to investigate the concentration of the stool and serum short‐chain fatty acids (SCFAs), gut microbiota‐derived metabolites, in individuals with DKD and reveal the correlations between SCFAs and renal function.

Methods

A total of 30 participants with DKD, 30 participants with type 2 diabetes mellitus (DM), and 30 normal controls (NC) in HwaMei Hospital were recruited from 1/1/2018 to 12/31/2019. Participants with DKD were divided into low estimated glomerular filtration rate (eGFR)(eGFR<60ml/min, n=14) and high eGFR (eGFR≥60ml/min, n=16) subgroups. Stool and serum were measured for SCFAs with gas chromatograph‐mass spectrometry.

Results

The DKD group showed markedly lower levels of fecal acetate, propionate, and butyrate versus NC (p<0.001, p<0.001, p=0.018, respectively) [1027.32(784.21–1357.90)]vs[2064.59(1561.82–2637.44)]μg/g,[929.53(493.65–1344.26)]vs[1684.57(1110.54–2324.69)]μg/g,[851.39(409.57–1611.65)] vs[1440.74(1004.15–2594.73)]μg/g, respectively, and the lowest fecal total SCFAs concentration among the groups. DKD group also had a lower serum caproate concentration than that with diabetes (p=0.020)[0.57(0.47–0.61)]vs[0.65(0.53–0.79)]μmol/L. In the univariate regression analysis, fecal and serum acetate correlated with eGFR (OR=1.013, p=0.072; OR=1.017, p=0.032). The correlation between serum total SCFAs and eGFR showed statistical significance (OR=1.019, p=0.024) unadjusted and a borderline significance (OR=1.024, p=0.063) when adjusted for Hb and LDL. The decrease in serum acetate and total SCFAs were found of borderline significant difference in both subgroups (p=0.055, p=0.050).

Conclusion

This study provides evidence that in individuals with DKD, serum and fecal SCFAs levels (fecal level in particular) were lowered, and there was a negative correlation between SCFAs and renal function.

The Role of the Gut Microbiome in Diabetes and Obesity-Related Kidney Disease

Diabetic kidney disease (DKD) is a progressive disorder, which is increasing globally in prevalence due to the increased incidence of obesity and diabetes mellitus. Despite optimal clinical management, a significant number of patients with diabetes develop DKD. Hence, hitherto unrecognized factors are likely to be involved in the initiation and progression of DKD. An extensive number of studies have demonstrated the role of microbiota in health and disease. Dysregulation in the microbiota resulting in a deficiency of short chain fatty acids (SCFAs) such as propionate, acetate, and butyrate, by-products of healthy gut microbiota metabolism, have been demonstrated in obesity, type 1 and type 2 diabetes. However, it is not clear to date whether such changes in the microbiota are causative or merely associated with the diseases. It is also not clear which microbiota have protective effects on humans. Few studies have investigated the centrality of reduced SCFA in DKD development and progression or the potential therapeutic effects of supplemental SCFAs on insulin resistance, inflammation, and metabolic changes. SCFA receptors are expressed in the kidneys, and emerging data have demonstrated that intestinal dysbiosis activates the renal renin-angiotensin system, which contributes to the development of DKD. In this review, we will summarize the complex relationship between the gut microbiota and the kidney, examine the evidence for the role of gut dysbiosis in diabetes and obesity-related kidney disease, and explore the mechanisms involved. In addition, we will describe the role of potential therapies that modulate the gut microbiota to prevent or reduce kidney disease progression.

Acetate ameliorates nephrotoxicity in streptozotocin-nicotinamide-induced diabetic rats: Involvement of xanthine oxidase activity

Impaired renal function is a common complication of diabetes mellitus (DM) that often degenerates to cardiovascular disease, contributing to high morbidity and reduced survival worldwide. Short chain fatty acids (SCFAs), including acetate has shown potential benefits in glycemic or metabolic regulation but its effect on diabetes-associated renal toxicity/impairment is not clear. Herein, we investigated the hypothesis that acetate would ameliorate renal toxicity, accompanying DM, possibly by suppression of xanthine oxidase (XO) activity. Adult male Wistar rats (230-260 g) were allotted into groups (n = 6/group) namely: control (vehicle; po), sodium acetate (NaAc)-treated (200 mg/kg), diabetic with or without NaAc groups. DM was induced by intraperitoneal injection of streptozotocin 65 mg/kg after a dose of nicotinamide (110 mg/kg). Diabetic animals showed increased fasting glucose and insulin, renal triglyceride, total cholesterol, atherogenic lipid, malondialdehyde, XO, tissue necrosis factor-α, uric acid, interleukin-6, aspartate transaminase/alanine aminotransferase ratio, gamma-glutamyl transferase and decreased glutathione and nitric oxide concentration. The renal tissue was characterized with disrupted tissue architecture, enlarged Bowman's space, congested glomeruli and adherence of abnormal segments of tuft to Bowman's capsule with consequent elevated serum creatinine and urea concentration. However, these alterations were attenuated by NaAc. The study demonstrates that acetate ameliorates diabetes-induced nephrotoxicity, which is associated with suppressed XO and its accompanied pro-inflammatory mediators. Therefore, SCFAs, acetate would be a promising dietary-derived therapeutic agent for the prevention and management of diabetes-associated renal disturbances.

The Effects of Gum Acacia on the Composition of the Gut Microbiome and Plasma Levels of Short-Chain Fatty Acids in a Rat Model of Chronic Kidney Disease

Chronic kidney disease (CKD) may be fatal for its victims and is an important long-term public health problem. The complicated medical procedures and diet restrictions to which patients with CKD are subjected alter the gut microbiome in an adverse manner, favoring over-accumulation of proteolytic bacteria that produce ammonia and other toxic substances. The present study aimed to investigate the effect of GA on 1) the composition of the gut microbiome and 2) on plasma levels of short-chain fatty acids. Male Wister rats were divided into four groups (six each) and treated for 4 weeks based on the following: control, dietary adenine (0.75%, w/w) to induce CKD, GA in the drinking water (15%, w/v), and both adenine and GA. At the end of the treatment period, plasma, urine, and fecal samples were collected for determination of several biochemical indicators of renal function and plasma levels of short-chain fatty acids (SCFAs) as well as characterization of the gut microbiome. Dietary adenine induced the typical signs of CKD, i.e., loss of body weight and impairment of renal function, while GA alleviated these effects. The intestine of the rats with CKD contained an elevated abundance of pathogenic Proteobacteria, Actinobacteria, and Verrucomicrobia but lowered proportions of Lactobacillaceae belonging to the Firmicutes phylum. Plasma levels of propionate and butyrate were lowered by dietary adenine and restored by GA. A negative association (Spearman's p-value ≤ 0.01, r ≤ 0.5) was observed between Firmicutes and plasma creatinine, urea, urine N-acetyl-beta-D-glucosaminidase (NAG) and albumin. Phylum Proteobacteria on the other hand was positively associated with these markers while Phylum Bacteroidetes was positively associated with plasma SCFAs. In conclusion, the adverse changes in the composition of the gut microbiome, plasma levels of SCFAs, and biochemical indicators of renal function observed in the rats with CKD induced by dietary adenine were mitigated by GA. These findings are indicative of a link between uremia and the composition of the microbiome in connection with this disease. Dietary administration of GA to patients with CKD may improve their renal function via modulating the composition of their microbiome-a finding that certainly warrants further investigation.

The role of short-chain fatty acids in intestinal barrier function, inflammation, oxidative stress, and colonic carcinogenesis

Short-chain fatty acids (SCFAs), mainly including acetate, propionate, and butyrate, are metabolites produced during the bacterial fermentation of dietary fiber in the intestinal tract. They are believed to be essential factors affecting host health. Most in vitro and ex vivo studies have shown that SCFAs affect the regulation of inflammation, carcinogenesis, intestinal barrier function, and oxidative stress, but convincing evidence in humans is still lacking. Two major SCFA signaling mechanisms have been identified: promotion of histone acetylation and activation of G-protein-coupled receptors. In this review, we introduce the production and metabolic characteristics of SCFAs, summarize the potential effects of SCFAs on the four aspects mentioned above and the possible mechanisms. SCFAs have been reported to exert a wide spectrum of positive effects and have a high potential for therapeutic use in human-related diseases.

Clinical utility of characterizing intestinal flora in septic kidney injury

The incidence of septic acute kidney injury (AKI) is increasing, it has become a major threat to human health because of its acute onset, poor prognosis, and high hospital costs. The most common cause of AKI in critical-care units is sepsis. Septic AKI is a complex and multi-factorial process; its pathogenesis is not fully understood. In sepsis, the destruction of mucosal barriers, intestinal flora disorders, intestinal ischemia/reperfusion injury, use of antibiotics, and lack of intestinal nutrients lead to an inflammatory reactions that in turn affects the metabolism and immunity of the host. Such changes further influence the occurrence and development of AKI. New technology is enabling various detection methods for intestinal flora. Clinical application of these methods in septic renal injury is expected to clarify the relationship among pathogenesis, disease progression mechanism, and intestinal flora.

Gut microbiota and chronic kidney disease: evidences and mechanisms that mediate a new communication in the gastrointestinal-renal axis

Chronic kidney disease (CKD) represents a growing public health problem associated with loss of kidney function and cardiovascular disease (CVD), the main leading cause of morbidity and mortality in CKD. It is well established that CKD is associated with gut dysbiosis. Over the past few years, there has been a growing interest in studying the composition of the gut microbiota in patients with CKD as well as the mechanisms by which gut dysbiosis contributes to CKD progression, in order to identify possible therapeutic targets to improve the morbidity and survival in CKD. The purpose of this review is to explore the clinical evidence and the mechanisms involved in the gut-kidney crosstalk as well as the possible interventions to restore a normal balance of the gut microbiota in CKD. It is well known that the influence of the gut microbiota on the gut-kidney axis acts in a reciprocal way: on the one hand, CKD significantly modifies the composition and functions of the gut microbiota. On the other hand, gut microbiota is able to manipulate the processes leading to CKD onset and progression through inflammatory, endocrine, and neurologic pathways. Understanding the complex interaction between these two organs (gut microbiota and kidney) may provide novel nephroprotective interventions to prevent the progression of CKD by targeting the gut microbiota. The review is divided into three main sections: evidences from clinical studies about the existence of a gut microbiota dysbiosis in CKD; the complex mechanisms that explain the bidirectional relationship between CKD and gut dysbiosis; and reports regarding the effects of prebiotic, probiotic, and synbiotic supplementation to restore gut microbiota balance in CKD.

The Association Between Changes in Plasma Short-Chain Fatty Acid Concentrations and Hypertension in Children With Chronic Kidney Disease

Background: Some children with chronic kidney disease (CKD) develop hypertension faster than others. This may be attributable to endothelial dysfunction, among other reasons. Short-chain fatty acids (SCFAs), that is, acetate, butyrate, and propionate, are known for reducing cardiovascular risks via preserving endothelial function. This study aimed to investigate the association between changes in plasma SCFA concentrations and in cardiovascular and endothelial parameters in children with CKD. Methods: In total, 105 children and adolescents who met the CKD criteria were enrolled in this study, and 65 patients aged >6 years were divided into two groups based on the ambulatory BP measurements. The parameters of plasma SCFAs, endothelial function and morphology, and echocardiography were examined at the index visit and followed up after 1 year. Results: We observed that 27.69% of 65 patients developed hypertension during the study period. Plasma acetate increased by 22.75 μM in the stable group (P < 0.001), whereas there was no change in the worsened BP group. The index higher plasma butyrate was positively correlated with worsened BP (adjusted odd ratio, 1.381; P = 0.013). At the follow-up, plasma butyrate decreased by 2.12 and 4.41 μM in the stable and worsened BP groups, respectively (P < 0.001). In 105 subjects, higher index plasma propionate was positively correlated with decreasing ejection fraction (adjusted odd ratio, 1.281; P = 0.046). Conclusions: Plasma acetate seemed to play a role in preventing hypertension in children with CKD. However, the index plasma propionate and butyrate concentrations seemed to imply the development of cardiovascular problems in our 1-year study.

Analysis of serum metabolomics among biopsy-proven diabetic nephropathy, type 2 diabetes mellitus and healthy controls

Type 2 diabetes mellitus (T₂DM) has a rising prevalence and diabetic nephropathy (DN) is a major complication of T₂DM. Metabolomics could provide novel insights into the pathogenesis, so we aimed to explore serum metabolomic profiles from DN to T₂DM. Serum samples were collected from 14 biopsy-proven DNs, 14 age/gender-matched T₂DMs without renal diseases (DM), 14 age/gender-matched healthy controls (CTRL) and household contacts of DM group (HH). Serum metabolomics was analyzed by untargeted liquid chromatography-tandem mass spectrometry (LC/MS) assays. There were a total of 1470 metabolites identified from all serum samples. 45 metabolites with significantly different intensity were found between DN and DM, e.g., biliverdin and taurine were reduced while l-arginine was increased in DN comparing to DM. DN could be distinguished from age/gender matched DM patients by l-arginine (AUC = 0.824) or taurine levels (AUC = 0.789). The metabolic pathways affected by metabolite distinctions between DN and DM also existed, among which taurine and hypotaurine metabolism exhibited the highest pathway impact. l-Methionine, deethylatrazine, l-tryptophan and fumaric acid were reduced in DM comparing with those of CTRL, but had no different intensity in DM and HH groups. The changes were demonstrated in the metabolomic profiles of biopsy-proven DN compared to DM. Biopsy-proven DN patients could be distinguished from age/gender matched DM by l-arginine or taurine levels in serum metabolomic profiles. Taurine and hypotaurine metabolism pathway had the highest impact in pathway set enrichment analysis, which potentially affected the pathogenesis of DN from T₂DM.

Metabolites between healthy controls (CTRL)/type 2 diabetes mellitus without renal diseases (DM), and DM/diabetic nephropathy (DN).