The interplay between microbiota-dependent metabolite trimethylamine N-oxide, Transforming growth factor β/SMAD signaling and inflammasome activation in chronic kidney disease patients: A new mechanistic perspective

The gut microbiota derived metabolite trimethylamine N-oxide: Its important role in cancer and other diseases

An expanding body of research indicates a correlation between the gut microbiota and various diseases. Metabolites produced by the gut microbiota act as mediators between the gut microbiota and the host, interacting with multiple systems in the human body to regulate physiological or pathological functions. However, further investigation is still required to elucidate the underlying mechanisms. One such metabolite involved in choline metabolism by gut microbes is trimethylamine (TMA), which can traverse the intestinal epithelial barrier and enter the bloodstream, ultimately reaching the liver where it undergoes oxidation catalyzed by flavin-containing monooxygenase 3 (FMO3) to form trimethylamine N-oxide (TMAO). While some TMAO is eliminated through renal excretion, remaining amounts circulate in the bloodstream, leading to systemic inflammation, endoplasmic reticulum (ER) stress, mitochondrial stress, and disruption of normal physiological functions in humans. As a representative microbial metabolite originating from the gut, TMAO has significant potential both as a biomarker for monitoring disease occurrence and progression and for tailoring personalized treatment strategies for patients. This review provides an extensive overview of TMAO sources and its metabolism in human blood, as well as its impact on several major human diseases. Additionally, we explore the latest research areas related to TMAO along with future directions.

Lower Urinary Tract Inflammation and Infection: Key Microbiological and Immunological Aspects

The urinary system, primarily responsible for the filtration of blood and waste, is affected by several infectious and inflammatory conditions. Focusing on the lower tract, this review outlines the physiological and immune landscape of the urethra and bladder, addressing key immunological and microbiological aspects of important infectious/inflammatory conditions. The conditions addressed include urethritis, interstitial cystitis/bladder pain syndrome, urinary tract infections, and urosepsis. Key aspects of each condition are addressed, including epidemiology, pathophysiology, and clinical considerations. Finally, therapeutic options are outlined, highlighting gaps in the knowledge and novel therapeutic approaches.

Stimulator of interferon genes/Interferon regulatory factor 3 (STING-IRF3) and inflammasome-activation mediated pyroptosis biomarkers: a network of integrated pathways in diabetic nephropathy

Background

Diabetic Nephropathy (DN) is serious diabetic complication affecting the structure and function of the kidney. This study assessed the stimulator of interferon genes/ Interferon regulatory factor 3 (STING/IRF3) signaling pathway roles and inflammasome-activation mediated pyroptosis, being imperative pathways of inordinate importance in disease progression, in DN throughout its different stages.

Methods

45 Diabetic cases were categorized into three groups based on their albuminuric status as follow: Normoalbuminuric, Microalbuminuric and Macroalbuminuric diabetic groups and 15 healthy subjects as controls were included. We evaluated STING and absent in melanoma 2 (AIM2) messenger RNA (mRNA) expressions from whole blood using quantitative RT-PCR. Additionally, Serum levels of STING, AIM2, IRF3, Nod like receptor pyrins-3 (NLRP3), interleukin-1β (IL-1β) and caspase-1 were assessed by ELISA technique.

Results

The study documented that STING and AIM2 mRNA expressions had significantly increased in DN cases with highest value in macroalbuminuric diabetic groups (p < 0.001*). Parallel results were observed concerning serum STING, AIM2, IRF3, NLRP3, Caspase-1 in addition to IL-1β levels (p < 0.001*).

Conclusion

The study documented the forthcoming role of STING in DN progression and its positive correlation with inflammasome-activation mediated pyroptosis biomarkers throughout its three different stages; launching new horizons in DN pathogenesis by highlighting its role as a reliable prognostic biomarker.

Psoralen Alleviates Renal Fibrosis by Attenuating Inflammasome-Dependent NLRP3 Activation and Epithelial-Mesenchymal Transition in a Mouse Unilateral Ureteral Obstruction Model

The role of psoralen (PS), a major active component extracted from Psoralea corylifolia L. seed, in renal fibrosis is still unclear. Thus, the objective of this study was to evaluate the effects of PS on the development and progression of renal fibrosis induced by unilateral ureteral obstruction (UUO) in a mouse model. Mice were divided into four groups: PS (20 mg/kg, i.g., n = 5), PS + sham (n = 5), UUO (n = 10), and PS + UUO (n = 10). PS was intragastrically administered 24 h before UUO and continued afterwards for 7 days. All mice were killed 7 days post UUO. Severe tubular atrophy, tubular injury, and tubulointerstitial fibrosis (TIF) were significantly developed in UUO mice. A higher expression of transforming growth factor-β1 (TGF-β1) was accompanied by elevated levels of α-smooth muscle actin (α-SMA) and phosphorylated Smad2/3 (pSmad2/3) at 7 days post UUO. However, PS treatment reduced tubular injury, interstitial fibrosis, and the expression levels of TGF-β1, α-SMA, and pSmad2/3. Furthermore, the levels of macrophages (represented by F4/80 positive cells) and the inflammasome, reflected by inflammasome markers such as nucleotide-binding and oligomerization domain-like receptors protein 3 (NLRP3) and cleaved caspase1 (cCASP-1), were significantly decreased by PS treatment. These results suggest that PS merits further exploration as a therapeutic agent in the management of chronic kidney disease (CKD).

Gut microbiota and integrative traditional Chinese and western medicine in prevention and treatment of heart failure

BACKGROUND

Heart failure (HF) is the terminal stage of multiple cardiovascular diseases, with high mortality and morbidity. More and more studies have proved that gut microbiota may play a role in the process of HF, which is expected to become a new therapeutic target. The combination of traditional Chinese and Western medicine has vast therapeutic potential of complementation against HF.

PURPOSE

This manuscript expounds on the research progress of mechanisms of gut microbiota participating in the occurrence and prognosis of HF and the role of integrative traditional Chinese and Western medicine from 1987 to 2022. The combination of traditional Chinese and Western medicine in the prevention and treatment of HF from the perspective of gut microbiota has been discussed.

METHODS

Studies focusing on the effects and their mechanisms of gut microbiota in HF and the role of integrative traditional Chinese and Western medicine were identified and summarized, including contributions from February 1987 until August 2022. The investigation was carried out in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines. We searched PubMed, Embase, Cochrane Library, CNKI, Wanfang, and VIP databases up to April 2023 by using the relevant keywords and operators.

RESULTS

A total of 34 articles were finally included in this review.16 RCTs and 13 basic researches, and 3 clinical research studies involving 7 relevant outcome indicators(cardiac function evaluation index, changes in gut microbiota, inflammatory factors, metabolites of gut microbiota, serum nutritional index protein, quality of life score, intestinal permeability and all-cause mortality). Compared with healthy controls, serum TNF-α and TMAO levels were significantly higher in patients with heart failure [MD = 5.77, 95%CI(4.97, 6.56), p < 0.0001; SMD = 1.92, 95%CI(1.70, 2.14), p < 0.0001]. Escherichia coli and Thick-walled bacteria increased significantly [SMD = -0.99, 95%CI(-1.38, -0.61), p < 0.0001, SMD = 2.58, 95%CI(2.23, 2.93), p < 0.0001];The number of bacteroides and lactobacillus decreased [SMD = -2.29, 95%CI(-2.54, -2.04), p < 0.0001; SMD = -1.55, 95%CI(-1.8, -1.3), p < 0.0001]. There was no difference in bifidobacterium [SMD = 0.16, 95%CI(-0.22, 0.54), p = 0.42]. In the published literature, it is not difficult to see that most of the results are studied and proved based on animal experiments or clinical trials, involving the cellular level, while the mechanism and mode of action of the molecular biology of traditional Chinese medicine are less elaborated, which is related to the characteristics of multi-components and multi-targets of traditional Chinese medicine. The above are the shortcomings of published literature, which can also be the direction of future research.

CONCLUSION

Heart failure patients have decreased beneficial bacteria such as Bacillus mimics and Lactobacillus in the intestinal flora and increased harmful flora like thick-walled flora. And increase the inflammatory response of the body and the expression of trimethylamine oxide (TMAO) in the serum. And The prevention and treatment of integrative traditional Chinese and Western medicine against heart failure based on gut microbiota and its metabolites is a promising research direction.

Hedgehog signaling is a potential therapeutic target for vascular calcification

BACKGROUND

Patients with chronic kidney disease (CKD) suffered from vascular calcification (VC), one major contributor for their increased mortality rate. Hedgehog (Hh) signaling plays a crucial role in physiological bone mineralization and is associated with several cardiovascular diseases. However, the molecular changes underlying VC is ill defined and it remains unclear whether Hh signaling intervention affects VC.

METHODS

We constructed human primary vascular smooth muscle cell (VSMC) calcification model and performed RNA sequencing. Alizarin red staining and calcium content assay were conducted to identify the occurrence of VC. Three different R packages were applied to determine differentially expressed genes (DEGs). Enrichment analysis and protein-protein interaction (PPI) network analysis were carried out to explore the biological roles of DEGs. qRT-PCR assay was then applied to validate the expression of key genes. By using Connectivity Map (CMAP) analysis, several small molecular drugs targeting these key genes were obtained, including SAG (Hedgehog signaling activator) and cyclopamine (CPN) (Hedgehog signaling inhibitor), which were subsequently used to treat VSMC.

RESULTS

Obvious Alizarin red staining and increased calcium content identified the occurrence of VC. By integrating results from three R packages, we totally obtained 166 DEGs (86 up-regulated and 80 down-regulated), which were significantly enriched in ossification, osteoblast differentiation, and Hh signaling. PPI network analysis identified 10 key genes and CMAP analysis predicted several small molecular drugs targeting these key genes including chlorphenamine, isoeugenol, CPN and phenazopyridine. Notably, our in vitro experiment showed that SAG markedly alleviated VSMC calcification, whereas CPN significantly exacerbated VC.

CONCLUSIONS

Our research provided deeper insight to the pathogenesis of VC and indicated that targeting Hh signaling pathway may represent a potential and effective therapy for VC.

Gut-Derived Metabolite, Trimethylamine-N-oxide (TMAO) in Cardio-Metabolic Diseases: Detection, Mechanism, and Potential Therapeutics

Trimethylamine N-oxide (TMAO) is a biologically active gut microbiome-derived dietary metabolite. Recent studies have shown that high circulating plasma TMAO levels are closely associated with diseases such as atherosclerosis and hypertension, and metabolic disorders such as diabetes and hyperlipidemia, contributing to endothelial dysfunction. There is a growing interest to understand the mechanisms underlying TMAO-induced endothelial dysfunction in cardio-metabolic diseases. Endothelial dysfunction mediated by TMAO is mainly driven by inflammation and oxidative stress, which includes: (1) activation of foam cells; (2) upregulation of cytokines and adhesion molecules; (3) increased production of reactive oxygen species (ROS); (4) platelet hyperreactivity; and (5) reduced vascular tone. In this review, we summarize the potential roles of TMAO in inducing endothelial dysfunction and the mechanisms leading to the pathogenesis and progression of associated disease conditions. We also discuss the potential therapeutic strategies for the treatment of TMAO-induced endothelial dysfunction in cardio-metabolic diseases.

Modulation of Endothelial Function by TMAO, a Gut Microbiota-Derived Metabolite

Endothelial function is essential in the maintenance of systemic homeostasis, whose modulation strictly depends on the proper activity of tissue-specific angiocrine factors on the physiopathological mechanisms acting at both single and multi-organ levels. Several angiocrine factors take part in the vascular function itself by modulating vascular tone, inflammatory response, and thrombotic state. Recent evidence has outlined a strong relationship between endothelial factors and gut microbiota-derived molecules. In particular, the direct involvement of trimethylamine N-oxide (TMAO) in the development of endothelial dysfunction and its derived pathological outcomes, such as atherosclerosis, has come to light. Indeed, the role of TMAO in the modulation of factors strictly related to the development of endothelial dysfunction, such as nitric oxide, adhesion molecules (ICAM-1, VCAM-1, and selectins), and IL-6, has been widely accepted. The aim of this review is to present the latest studies that describe a direct role of TMAO in the modulation of angiocrine factors primarily involved in the development of vascular pathologies.

The Urinary Microbiome and Bladder Cancer

Bladder cancer is the 10th most common cancer worldwide. Approximately 75% of patients with bladder cancer will present with non-muscle invasive disease. Patients are usually treated with transurethral resection of bladder tumor (TURBT), in addition to adjuvant intravesical therapy (chemotherapy or anti-cancer immunotherapy with Bacillus Calmette Guerin- BCG) for those at intermediate-risk and high-risk of recurrence and progression. For many years, urine has been thought to be “sterile”; however, advanced microbiological and molecular techniques, including 16S ribosomal RNA (16S rRNA) sequencing, have negated that previous paradigm and confirmed the presence of a urinary microbiome. The urinary microbiome has been associated with several urological diseases, including interstitial cystitis, urgency urinary incontinence, neurogenic bladder dysfunction, and others. More recently, many reports are emerging about the role of the urinary microbiome in urothelial carcinogenesis, including gender disparity in bladder cancer and responses to treatments. The urinary microbiome may serve as a biomarker that can help with risk stratification as well as prediction of the response to intravesical therapies. However, the microbiome literature has been hampered by the lack of a unified standardized methodology for sample collection, type, preservation, processing, as well as bioinformatics analysis. Herein we describe and critique the literature on the association between urinary microbiome and bladder cancer and highlight some of the future directions.

Optimization of enzyme-linked immunosorbent assay kit protocol to detect trimethylamine N-oxide levels in humans

The serum level of trimethylamine N-oxide (TMAO), a gut microbiota metabolite associated with diabetes, cancer, inflammatory and neurological diseases, can be determined by the micro-enzyme-linked immunosorbent assay (ELISA) method. However, we had problems obtaining accurate standard curves with the original kit protocol from Bioassay Technology Laboratory. We aimed to acquire proper standard curves by modifying the kit protocol in this study. First, we evaluated the human TMAO ELISA kit protocols and other human ELISA kits. We maintained the incubation times longer and increased the wash cycle. Moreover, we incubated the standards containing biotinylated antibody in the wells alone. Then we washed the wells and added streptavidin-HRP for the second incubation step. The data of original and modified ELISA kit protocol were analyzed with Student's t-test. We measured higher absorbance with lower standard solution concentration in experiments that followed the original kit protocol. After investigating other human TMAO ELISA kits, we noticed that the SunRed Biotechnology Company and MyBioSource companies suggested similar protocols to the Bioassay Technology Laboratory company. The ELK Biotechnology ELISA protocol was different from others. However, since there is no biotinylated antibody in the standard solution in the ELK biotechnology kit, we changed some steps by examining other human ELISA protocols from different companies. After performing the modified protocol, we found that the absorbances of the standard solutions were consistent with their concentrations, and we obtained an accurate standard curve. Higher R2 values and lower absolute difference of standard concentrations were found in the modified kit protocol. The human TMAO ELISA protocol, which we modified in this study, will enable researchers to obtain more reliable results and prevent them from failing time and resources.

The role of gut-dependent molecule trimethylamine N-oxide as a novel target for the treatment of chronic kidney disease

Trimethylamine N-oxide (TMAO) is an intestinal uremic toxin molecule mainly excreted by the kidney. Therefore, the plasma TMAO concentration is significantly increased in chronic kidney disease (CKD) patients, and plasma TMAO can be cleared by dialysis. Furthermore, TMAO damage the kidney mainly through three mechanisms: oxidative stress, inflammation and endoplasmic reticulum stress. Clinical experiments have indicated that higher TMAO levels are strongly related to the elevated incidence and mortality of cardiovascular (CV) events in CKD patients. Moreover, experimental data have shown that high levels of TMAO directly aggravate atherosclerosis, thrombosis and enhance myocardial contractility, resulting in myocardial ischemia and stroke. Specially, there are currently four potential ways to reduce blood TMAO concentration or block the effect of TMAO, including reducing the intake of trimethylamine (TMA) precursors in the diet, regulating the intestinal flora to reduce TMA production, interrupting the role of flavin-dependent monooxygenase isoforms (FMOs) to reduce the generation of TMAO, and blocking the TMAO receptor protein kinase R-like endoplasmic reticulum kinase (PERK). We hope that more clinical studies and clinicians will focus on clinical treatment to reduce the concentration of TMAO and alleviate renal damage.

Chronic kidney disease and NLRP3 inflammasome: Pathogenesis, development and targeted therapeutic strategies

Chronic kidney disease (CKD) is a global health concern and public health priority. The condition often involves inflammation due to the accumulation of toxins and the reduced clearance of inflammatory cytokines, leading to gradual loss of kidney function. Because of the tremendous burden of CKD, finding effective treatment strategies against inflammation is crucial. Substantial evidence suggests an association between kidney disease and the inflammasome. As a well-known multiprotein signaling complex, the NLR family pyrin domain containing 3 (NLRP3) inflammasome plays an important role in inducing renal inflammation and fibrosis. Small molecule inhibitors targeting the NLRP3 inflammasome are potential agents for the treatment of CKD.The NLRP3 inflammasome activation amplifies the inflammation response, promoting pyroptotic cell death. Thus, it may contribute to the onset and progression of CKD, but the mechanism behind inflammasome activation in CKD remains obscure.In this review, we summarized recent findings on the role of the NLRP3 inflammasome in CKD and new strategies targeting the NLRP3 inflammasome.

Intestinal Flora Derived Metabolites Affect the Occurrence and Development of Cardiovascular Disease

In recent years, increasing evidence has shown that the gut microbiota and their metabolites play a pivotal role in human health and diseases, especially the cardiovascular diseases (CVDs). Intestinal flora imbalance (changes in the composition and function of intestinal flora) accelerates the progression of CVDs. The intestinal flora breaks down the food ingested by the host into a series of metabolically active products, including trimethylamine N-Oxide (TMAO), short-chain fatty acids (SCFAs), primary and secondary bile acids, tryptophan and indole derivatives, phenylacetylglutamine (PAGln) and branched chain amino acids (BCAA). These metabolites participate in the occurrence and development of CVDs via abnormally activating these signaling pathways more swiftly when the gut barrier integrity is broken down. This review focuses on the production and metabolism of TMAO and SCFAs. At the same time, we summarize the roles of intestinal flora metabolites in the occurrence and development of coronary heart disease and hypertension, pulmonary hypertension and other CVDs. The theories of "gut-lung axis" and "gut-heart axis" are provided, aiming to explore the potential targets for the treatment of CVDs based on the roles of the intestinal flora in the CVDs.

C3aR contributes to unilateral ureteral obstruction-induced renal interstitial fibrosis via the activation of the NLRP3 inflammasome

AIMS

Complement component 3a and its receptor (C3a/C3aR) and nucleotide-binding oligomerization domain-like receptor protein-3 (NLRP3) inflammasome are involved in the pathogenesis of renal interstitial fibrosis (RIF). However, the mechanisms have not been clearly illuminated. This study aimed to elucidate the roles of C3aR and the NLRP3 inflammasome involved in unilateral ureteral obstruction (UUO)-induced renal interstitial fibrosis.

MAIN METHODS

UUO models were established using male C57BL/6 wild-type (WT) mice and age-matched C3aR-deficient mice. MCC950, an inhibitor of the NLRP3 inflammasome, was intraperitoneally injected in UUO mice. Blood samples were collected to quantify serum creatinine and urea. Kidney samples were collected for hematoxylin-eosin (HE), Masson, and immunohistochemistry staining, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay, and Western blotting.

KEY FINDINGS

Renal function, renal fibrosis, and renal inflammation in WT mice were aggravated with longer periods of UUO. C3aR deficiency improved renal function and attenuated renal fibrosis and the activation of the NLRP3 inflammasome in UUO mice. Renal function and renal fibrosis in UUO mice were attenuated after NLRP3 inflammasome inhibition; however, the expression of C3aR did not change.

SIGNIFICANCE

Our data revealed that C3aR may aggravate RIF by regulating the activation of the NLRP3 inflammasome (particularly regulating inflammasome assembly) in renal tubular epithelial cells in the UUO model.

Implications of trimethylamine N-oxide (TMAO) and Betaine in Human Health: Beyond Being Osmoprotective Compounds

Osmolytes are naturally occurring small molecular weight organic molecules, which are accumulated in large amounts in all life forms to maintain the stability of cellular proteins and hence preserve their functions during adverse environmental conditions. Trimethylamine N-oxide (TMAO) and N,N,N-trimethylglycine (betaine) are methylamine osmolytes that have been extensively studied for their diverse roles in humans and have demonstrated opposing relations with human health. These osmolytes are obtained from food and synthesized endogenously using dietary constituents like choline and carnitine. Especially, gut microbiota plays a vital role in TMAO synthesis and contributes significantly to plasma TMAO levels. The elevated plasma TMAO has been reported to be correlated with the pathogenesis of numerous human diseases, including cardiovascular disease, heart failure, kidney diseases, metabolic syndrome, etc.; Hence, TMAO has been recognized as a novel biomarker for the detection/prediction of several human diseases. In contrast, betaine acts as a methyl donor in one-carbon metabolism, maintains cellular S-adenosylmethionine levels, and protects the cells from the harmful effects of increased plasma homocysteine. Betaine also demonstrates antioxidant and anti-inflammatory activities and has a promising therapeutic value in several human diseases, including homocystinuria and fatty liver disease. The present review examines the multifarious functions of TMAO and betaine with possible molecular mechanisms towards a better understanding of their emerging and diverging functions with probable implications in the prevention, diagnosis, and treatment of human diseases.

Blood-brain barrier and gut barrier dysfunction in chronic kidney disease with a focus on circulating biomarkers and tight junction proteins

Kidney failure and associated uraemia have implications for the cardiovascular system, brain, and blood–brain barrier (BBB). We aim to examine BBB disruption, by assessing brain-derived neurotropic factor (BDNF), neuron-specific enolase (NSE) levels, and gut-blood barrier (GBB) disruption by trimethylamine N-oxide (TMAO), in chronic kidney disease (CKD) patients. Additionally, endothelial tight-junction protein expressions and modulation via TMAO were assessed. Serum from chronic kidney disease (CKD) female and male haemodialysis (HD) patients, and controls, were used to measure BDNF and NSE by enzyme-linked immunosorbent assays, and TMAO by mass spectrometry. Immunofluorescent staining of subcutaneous fat biopsies from kidney transplant recipients, and controls, were used to measure microvascular expression of tight-junction proteins (claudin-5, occludin, JAM-1), and control microvasculature for TMAO effects. HD patients versus controls, had significantly lower and higher serum levels of BDNF and NSE, respectively. In CKD biopsies versus controls, reduced expression of claudin-5, occludin, and JAM-1 were observed. Incubation with TMAO significantly decreased expression of all tight-junction proteins in the microvasculature. Uraemia affects BBB and GBB resulting in altered levels of circulating NSE, BDNF and TMAO, respectively, and it also reduces expression of tight-junction proteins that confer BBB maintenance. TMAO serves as a potential candidate to alter BBB integrity in CKD.

Modulating gut dysbiosis and mitochondrial dysfunction in oxazolone-induced ulcerative colitis: the restorative effects of β-glucan and/or celastrol

Objectives

Microbiome–Mitochondria interaction is gaining a significant attention; thus, studying its mechanism emerges as a must to provide restorative lines in managing diseases. The aim is to study the mechanistic effects of β-Glucan and/or Celastrol in oxazolone-induced ulcerative colitis (UC).

Methods

75 Wistar rats were allocated into 5 equal groups. Group I: control group. Group II: UC group, Group III: β-Glucan-treated UC group, Group IV: Celastrol-treated UC group & Group V: mutual treatment group. All groups were subjected to the detection of free fatty acid receptor 2 (FFAR-2) and peroxisome proliferator-activated receptor gamma co-activator1α (PGC-1α) mRNA gene expressions. Citrate synthase (CS) activity, mitochondrial membrane potential (MMP), ATP concentration, reactive oxygen species (ROS) were detected. Trimethylamine N-oxide (TMAO) concentration was measured.

Results

After treatment we monitored significant upregulation of FFAR-2 and PGC-1α mRNA expression. Likewise, ATP level and CS activity were significantly increased. On the contrary, there was a significant lessening in ROS and TMAO levels with improvement of MMP.

Conclusion

Mutual use of β- Glucan and Celastrol had a greater effect than each alone against UC, which is considered a novel finding highlighting the ameliorative effects of this combined treatment in modulating Microbiome/Mitochondria axis, thus launching promising avenues for UC.

The Human Microbiome in Chronic Kidney Disease: A Double-Edged Sword

Chronic kidney disease (CKD) is an increasing global health burden. Current treatments for CKD include therapeutics to target factors that contribute to CKD progression, including renin–angiotensin–aldosterone system inhibitors, and drugs to control blood pressure and proteinuria control. Recently, associations between chronic disease processes and the human microbiota and its metabolites have been demonstrated. Dysbiosis—a change in the microbial diversity—has been observed in patients with CKD. The relationship between CKD and dysbiosis is bidirectional; gut-derived metabolites and toxins affect the progression of CKD, and the uremic milieu affects the microbiota. The accumulation of microbial metabolites and toxins is linked to the loss of kidney functions and increased mortality risk, yet renoprotective metabolites such as short-chain fatty acids and bile acids help restore kidney functions and increase the survival rate in CKD patients. Specific dietary interventions to alter the gut microbiome could improve clinical outcomes in patients with CKD. Low-protein and high-fiber diets increase the abundance of bacteria that produce short-chain fatty acids and anti-inflammatory bacteria. Fluctuations in the urinary microbiome are linked to increased susceptibility to infection and antibiotic resistance. In this review, we describe the potential role of the gut, urinary and blood microbiome in CKD pathophysiology and assess the feasibility of modulating the gut microbiota as a therapeutic tool for treating CKD.

Advances in the Progression and Prognosis Biomarkers of Chronic Kidney Disease

Chronic kidney disease (CKD) is one of the increasingly serious public health concerns worldwide; the global burden of CKD is increasingly due to high morbidity and mortality. At present, there are three key problems in the clinical treatment and management of CKD. First, the current diagnostic indicators, such as proteinuria and serum creatinine, are greatly interfered by the physiological conditions of patients, and the changes in the indicator level are not synchronized with renal damage. Second, the established diagnosis of suspected CKD still depends on biopsy, which is not suitable for contraindication patients, is also traumatic, and is not sensitive to early progression. Finally, the prognosis of CKD is affected by many factors; hence, it is ineviatble to develop effective biomarkers to predict CKD prognosis and improve the prognosis through early intervention. Accurate progression monitoring and prognosis improvement of CKD are extremely significant for improving the clinical treatment and management of CKD and reducing the social burden. Therefore, biomarkers reported in recent years, which could play important roles in accurate progression monitoring and prognosis improvement of CKD, were concluded and highlighted in this review article that aims to provide a reference for both the construction of CKD precision therapy system and the pharmaceutical research and development.

Effects of Serum Metabolites on the Pancreatic Transcriptome in Acute Acalculous Cholecystitis

Background

To provide a basis for the diagnosis and treatment of acalculous biliary pancreatitis, this study investigated the impact of serum metabolites on the pancreatic transcriptome in acute acalculous cholecystitis (AAC).

Methods

Fourteen rabbits were randomly divided into two groups (a normal control group of 7 rabbits and an AAC group of 7 rabbits), blood was collected from the 14 rabbits, and metabolomic analysis was performed through ¹H NMR. Two pancreatic tissue chips of the AAC group and the normal control group were prepared and sequenced. We utilized the limma package of R software, the DAVID database, the STRING database, Cytoscape software, and the CFinder analysis tool to perform differential expression gene analysis, gene function enrichment analysis, protein interaction network (PPI) construction, and network module mining, and we performed gene enrichment analysis in each module.

Results

Serum metabolism analysis showed that in AAC, the metabolism of sugar, lipids, and protein, that is, the three major nutrients, was affected to varying degrees, and levels of serum trimethylamine N-oxide (TMAO) increased. Bioinformatic methods were utilized to identify a total of 183 differentially expressed genes and 3 key genes. Enrichment analysis showed that differentially expressed genes were significantly enriched in cation transport, the inflammatory response, the NF-κB pathway, and the cancer signaling pathway.

Conclusion

Metabolomic analysis and functional analysis of 3 key genes demonstrated that abnormal serum metabolites affected the pancreatic transcriptome and induced a sensitive state of inflammation in the pancreas. These metabolites may represent important targets for future research on the pathogenesis, clinical diagnosis, and treatment of noncalculous biliary pancreatitis.

The Nutritional Supplement L-Alpha Glycerylphosphorylcholine Promotes Atherosclerosis

L-alpha glycerylphosphorylcholine (GPC), a nutritional supplement, has been demonstrated to improve neurological function. However, a new study suggests that GPC supplementation increases incident stroke risk thus its potential adverse effects warrant further investigation. Here we show that GPC promotes atherosclerosis in hyperlipidemic Apoe-/- mice. GPC can be metabolized to trimethylamine N-oxide, a pro-atherogenic agent, suggesting a potential molecular mechanism underlying the observed atherosclerosis progression. GPC supplementation shifted the gut microbial community structure, characterized by increased abundance of Parabacteroides, Ruminococcus, and Bacteroides and decreased abundance of Akkermansia, Lactobacillus, and Roseburia, as determined by 16S rRNA gene sequencing. These data are consistent with a reduction in fecal and cecal short chain fatty acids in GPC-fed mice. Additionally, we found that GPC supplementation led to an increased relative abundance of choline trimethylamine lyase (cutC)-encoding bacteria via qPCR. Interrogation of host inflammatory signaling showed that GPC supplementation increased expression of the proinflammatory effectors CXCL13 and TIMP-1 and activated NF-κB and MAPK signaling pathways in human coronary artery endothelial cells. Finally, targeted and untargeted metabolomic analysis of murine plasma revealed additional metabolites associated with GPC supplementation and atherosclerosis. In summary, our results show GPC promotes atherosclerosis through multiple mechanisms and that caution should be applied when using GPC as a nutritional supplement.

The Microbiome’s Function in Disorders of the Urinary Bladder

The introduction of next generation sequencing techniques has enabled the characterization of the urinary tract microbiome, which resulted in the rejection of the long-held notion of urinary bladder sterility. Since the discovery and confirmation of the human bladder microbiome, an increasing number of studies have defined this microbial community and understand better its relationship to urinary pathologies. The composition of microbial communities in the urinary tract is linked to a variety of urinary diseases. The purpose of this review is to provide an overview of current information about the urinary microbiome and diseases as well as the development of novel treatment methods.

Intestinal Fibrosis and Gut Microbiota: Clues From Other Organs

Fibrosis is a complex and difficult to elucidate pathological process with no available therapies. Growing evidence implicates intestinal microbiota in the occurrence and development of fibrosis, and the potential mechanisms involved in different organs have been explored in several studies. In this review, we summarize the causative and preventive effects of gut microbiota on intestinal fibrosis, as well as the relationships between gut microbiota and fibrosis in other organs. Interestingly, several colonized microbes are associated with fibrosis via their structural components and metabolic products. They may also play essential roles in regulating inflammation and fibroblast activation or differentiation, which modulates extracellular matrix formation. While the relationships between intestinal fibrosis and gut microbiota remain unclear, lessons can be drawn from the effects of gut microbiota on hepatic, cardiac, nephritic, and pulmonary fibrosis. Various intestinal microbes alterations have been detected in different fibrotic organs; however, the results were heterogeneous. Mechanisms by which the intestinal microbiota regulate fibrotic processes in other organs, such as novel metabolic products or specific microbes, are also discussed. The specific microbiota associated with fibrosis in other organs could instruct future studies aiming to discover prospective mechanisms regulating intestinal fibrosis.

The microbiome and host mucosal interactions in urinary tract diseases

The urinary tract consists of the bladder, ureters, and kidneys, and is an essential organ system for filtration and excretion of waste products and maintaining systemic homeostasis. In this capacity, the urinary tract is impacted by its interactions with other mucosal sites, including the genitourinary and gastrointestinal systems. Each of these sites harbors diverse ecosystems of microbes termed the microbiota, that regulates complex interactions with the local and systemic immune system. It remains unclear whether changes in the microbiota and associated metabolites may be a consequence or a driver of urinary tract diseases. Here, we review the current literature, investigating the impact of the microbiota on the urinary tract in homeostasis and disease including urinary stones, acute kidney injury, chronic kidney disease, and urinary tract infection. We propose new avenues for exploration of the urinary microbiome using emerging technology and discuss the potential of microbiome-based medicine for urinary tract conditions.

Urinary Microbiome: Yin and Yang of the Urinary Tract

The application of next generation sequencing techniques has allowed the characterization of the urinary tract microbiome and has led to the rejection of the pre-established concept of sterility in the urinary bladder. Not only have microbial communities in the urinary tract been implicated in the maintenance of health but alterations in their composition have also been associated with different urinary pathologies, such as urinary tract infections (UTI). Therefore, the study of the urinary microbiome in healthy individuals, as well as its involvement in disease through the proliferation of opportunistic pathogens, could open a potential field of study, leading to new insights into prevention, diagnosis and treatment strategies for urinary pathologies. In this review we present an overview of the current state of knowledge about the urinary microbiome in health and disease, as well as its involvement in the development of new therapeutic strategies.

Phosphate, Microbiota and CKD

Phosphate is a key uremic toxin associated with adverse outcomes. As chronic kidney disease (CKD) progresses, the kidney capacity to excrete excess dietary phosphate decreases, triggering compensatory endocrine responses that drive CKD-mineral and bone disorder (CKD-MBD). Eventually, hyperphosphatemia develops, and low phosphate diet and phosphate binders are prescribed. Recent data have identified a potential role of the gut microbiota in mineral bone disorders. Thus, parathyroid hormone (PTH) only caused bone loss in mice whose microbiota was enriched in the Th17 cell-inducing taxa segmented filamentous bacteria. Furthermore, the microbiota was required for PTH to stimulate bone formation and increase bone mass, and this was dependent on bacterial production of the short-chain fatty acid butyrate. We review current knowledge on the relationship between phosphate, microbiota and CKD-MBD. Topics include microbial bioactive compounds of special interest in CKD, the impact of dietary phosphate and phosphate binders on the gut microbiota, the modulation of CKD-MBD by the microbiota and the potential therapeutic use of microbiota to treat CKD-MBD through the clinical translation of concepts from other fields of science such as the optimization of phosphorus utilization and the use of phosphate-accumulating organisms.

Renal function is associated with plasma trimethylamine-N-oxide, choline, L-carnitine and betaine: a pilot study

INTRODUCTION

Chronic kidney disease (CKD) is characterized by decreased glomerular filtration rate (GFR) due to a variety of causes. Most patients remain undiagnosed at early stage of CKD and proceed to end stage CKD due to unawareness and lacking of efficient biomarkers. Trimethylamine-N-oxide (TMAO) and its predecessor products: choline, L-carnitine and betaine are associated with reduced renal function. However, whether the combined variation of the four metabolites could contribute in prediction and stratification of impaired glomerular function in Chinese CKD patients is unknown. Our aim is to investigate the associations of plasma TMAO, choline, L-carnitine and betaine with glomerular filtration in CKD patients.

MATERIALS AND METHODS

A total of 65 CKD patients and 64 healthy controls were enrolled in this study. Fasting plasma metabolites were detected using liquid chromatography-based method.

RESULTS

Plasma TMAO, choline, betaine and L-carnitine levels were differentially correlated with eGFR. The four metabolites were independently associated with CKD after adjustment for multiple traditional risk factors. The combination of the four metabolites had good performance at discriminating CKD from healthy controls (AUC = 0.96) as well as discriminating low eGFR from high eGFR in CKD (AUC = 0.96).

CONCLUSION

Combinations of TMAO and its precursors were associated with glomerular function and might be utilized in evaluation of CKD.

Impact of trimethylamine N-oxide (TMAO) metaorganismal pathway on cardiovascular disease

Host-microbes interaction plays a crucial role in cardiovascular disease (CVD) pathogenesis, mechanistically via metaorganismal pathways. The trimethylamine N-oxide (TMAO) metaorganismal pathway is the most deeply investigated one, which comprises trimethylamine precursors, such as choline, trimethylamine lyase, trimethylamine, host liver FMO3, TMAO, and downstream effectors involving unfolded protein response (UPR), NF-κB and NLRP3 inflammasome. Accumulating data from clinical investigations of CVD patient cohorts and rodent models have supported the critical role of this metaorganismal pathway in the pathogenesis of CVD. We summarize an array of significant animal studies especially for arthrosclerosis with an emphasis on downstream molecular effectors of this metaorganismal pathway. We highlight clinical investigations of the prognostic value of plasma TMAO levels in predicting prospective risk for future major adverse cardiac events (MACE) indicated by composite end points of myocardial infarction (MI), stroke, heart failure (HF), other ischemic cardiovascular events, or death. Further, we discuss the latest advances of preclinical models targeting the gut microbiota trimethylamine lyase of the TMAO metaorganismal pathway for CVD intervention, as well as the catalog of gut microbiota TMA lyase genes and microbes in the human gut as the prerequisite for potential clinical intervention. In-depth characterization of TMAO metaorganismal pathway holds great promise for CVD clinical metagenomics, diagnostics and therapeutics.

Contribution of TGF-Beta-Mediated NLRP3-HMGB1 Activation to Tubulointerstitial Fibrosis in Rat With Angiotensin II-Induced Chronic Kidney Disease

Fibrosis is a common phenotype that often leads to the progression of blood pressure-induced chronic kidney disease (CKD). TGF-beta plays an important role in promoting pathogenesis, and NLRP3 is a critical mediator in the progression of blood pressure-induced CKD. However, the pathophysiological roles of the TGF-beta-mediated NLRP3 pathway in modulating fibrosis in blood pressure-induced CKD have not been elucidated. The present study aims to investigate the contribution of TGF-beta-mediated NLRP3 inflammasome to renal fibrosis in rats with high blood pressure. By treating rats with angiotensin II (Ang II) for 14 days, we observed the development of fibrosis, characterized by epithelial-mesenchymal transition (EMT) markers [alpha-smooth muscle actin (alpha-SMA), MMP-2, and MMP-9]. Immunohistochemical analysis further revealed that TGF-beta and NLRP3 inflammasome activation [high-mobility group box 1 (HMGB1), IL-1beta, and NLRP3] were significantly upregulated in the kidney of rats with Ang II-induced hypertension. Interestingly, we observed that Ang II could not increase the production of NLRP3 proteins, but TGF-beta could induce NLRP3 protein expression in cultured NRK-52E cells. Furthermore, we speculated that TGF-beta played a pathogenic role in Ang II-induced CKD because TGF-beta induced the activation of NLRP3 inflammasomes and Gasdermin D cleavage expression. We also proved that the pharmacological inhibition of NLRP3 by ISO caused a decrease in TGF-beta-induced NLRP3 inflammasome activation and the expression of EMT markers (alpha-SMA and CollagenI) and Gasdermin D cleavage. Collectively, these results suggest that TGF-beta-mediated NLRP3 inflammasome activation may cause the release of HMGB1 and an increase in Gasdermin D cleavage in NRK-52E, thereby contributing to renal fibrosis in Ang II-induced CKD. These findings provide novel insights into the pathogenic role of NLRP3 in CKD associated with high blood pressure.

Gut Microbiota and Renal Injury

Renal injury, especially chronic kidney disease (CKD), is closely associated with gut microbiota. It is well known that renal injury development could cause enteric microbial compositional disruption. On the other hand, gut microbial composition, as well as their function, would directly influence the renal disease progression. Here, in the present chapter, we will summarize the crosstalk between intestinal microbiota and renal disease and discuss some potential therapeutic approaches based on this topic.