Serum Trimethylamine N-Oxide Level Is Associated with Peripheral Arterial Stiffness in Advanced Non-Dialysis Chronic Kidney Disease Patients

The Gut-Kidney Axis in Chronic Kidney Diseases

The gut-kidney axis represents the complex interactions between the gut microbiota and kidney, which significantly impact the progression of chronic kidney disease (CKD) and overall patient health. In CKD patients, imbalances in the gut microbiota promote the production of uremic toxins, such as indoxyl sulfate and p-cresyl sulfate, which impair renal function and contribute to systemic inflammation. Mechanisms like endotoxemia, immune activation and oxidative stress worsen renal damage by activating pro-inflammatory and oxidative pathways. Insights into these mechanisms highlight the impact of gut-derived metabolites, bacterial translocation, and immune response changes on kidney health, suggesting new potential approaches for CKD treatment. Clinical applications, such as dietary interventions, prebiotics, probiotics and fecal microbiota transplantation, are promising in adjusting the gut microbiota to alleviate CKD symptoms and slow disease progression. Current research highlights the clinical relevance of the gut-kidney axis, but further study is essential to clarify these mechanisms' diagnostic biomarkers and optimize therapeutic interventions. This review emphasizes the importance of an integrated approach to CKD management, focusing on the gut microbiota as a therapeutic target to limit kidney injury.

The Association Between Serum Trimethylamine N-Oxide and Arterial Stiffness in Chronic Peritoneal Dialysis Patients: A Cross-Sectional Study

Trimethylamine N-oxide (TMAO), a gut microbiome-derived metabolite, participates in the atherogenesis and vascular stiffening that is closely linked with cardiovascular (CV) complications and related deaths in individuals with kidney failure undergoing peritoneal dialysis (PD) therapy. In these patients, arterial stiffness (AS) is also an indicator of adverse CV outcomes. This study assessed the correlation between serum TMAO concentration quantified with high-performance liquid chromatography and mass spectrometry and central AS measured by carotid-femoral pulse wave velocity (cfPWV) in patients with chronic PD. Of the 160 participants included, 23.8% had a cfPWV of ≥10 m/s, which fulfilled the AS criteria. Multivariable logistic regression analysis revealed that TMAO, age, and waist circumference were positively associated with AS. Multivariable stepwise linear regression showed that underlying diabetes, advanced age, waist circumference, systolic blood pressure, and logarithmic-transformed TMAO were independently correlated with cfPWV. The area under the receiver operating characteristic curve for TMAO in differentiating AS from non-AS was 0.737. In conclusion, serum TMAO level was significantly independently correlated with central AS among participants undergoing PD for end-stage kidney failure.

Research progress on the association between TMAO and vascular calcification in patients with chronic kidney disease

Vascular calcification (VC) is a common complication in patients with chronic kidney disease (CKD) and a major risk factor for increased cardiovascular mortality in patients with CKD. Its pathology and pathogenesis are complex and have not been fully elucidated. Trimethylamine N-oxide (TMAO) is an enteric-borne uremic toxin that has been found to play a role in the progression of VC. This article mainly reviews the metabolism of TMAO, the relationship between TMAO and VC in CKD patients, and possible treatments for TMAO, aiming to further explore the mechanism of VC occurrence in CKD patients and provide potential diagnostic and treatment strategies.

Low-Molecular-Weight Compounds Produced by the Intestinal Microbiota and Cardiovascular Disease

Cardiovascular disease is the main cause of mortality in industrialized countries, with over 500 million people affected worldwide. In this work, the roles of low-molecular-weight metabolites originating from the gut microbiome, such as short-chain fatty acids, hydrogen sulfide, trimethylamine, phenylacetic acid, secondary bile acids, indoles, different gases, neurotransmitters, vitamins, and complex lipids, are discussed in relation to their CVD-promoting or preventing activities. Molecules of mixed microbial and human hepatic origin, such as trimethylamine N-oxide and phenylacetylglutamine, are also presented. Finally, dietary agents with cardioprotective effects, such as probiotics, prebiotics, mono- and poly-unsaturated fatty acids, carotenoids, and polyphenols, are also discussed. A special emphasis is given to their gut microbiota-modulating properties.

Residual Kidney Function in Hemodialysis: Its Importance and Contribution to Improved Patient Outcomes

Individuals afflicted with advanced kidney dysfunction who require dialysis for medical management exhibit different degrees of native kidney function, called residual kidney function (RKF), ranging from nil to appreciable levels. The primary focus of this manuscript is to delve into the concept of RKF, a pivotal yet under-represented topic in nephrology. To begin, we unpack the definition and intrinsic nature of RKF. We then juxtapose the efficiency of RKF against that of hemodialysis in preserving homeostatic equilibrium and facilitating physiological functions. Given the complex interplay of RKF and overall patient health, we shed light on the extent of its influence on patient outcomes, particularly in those living with advanced kidney dysfunction and on dialysis. This manuscript subsequently presents methodologies and measures to assess RKF, concluding with the potential benefits of targeted interventions aimed at preserving RKF.

Osteocalcin: A Potential Marker of Peripheral Arterial Stiffness in Hypertensive Patients

Background and Objectives: Brachial-ankle pulse wave velocity (baPWV) is an established independent risk factor for cardiovascular events, cardiovascular mortality, and all-cause mortality. Osteocalcin (OC) is recognized to be associated with vascular function. The present study assessed the correlation between serum OC levels and peripheral arterial stiffness (PAS) measured through baPWV in hypertensive patients. Materials and Methods: Fasting blood samples were collected from 120 hypertensive participants. The serum total OC levels were measured using a commercial enzyme-linked immunosorbent assay kit, whereas the baPWV device was used to detect PAS. The PAS group had left or right baPWV > 18.0 m/s. Results: Among the hypertensive patients, 24 (20.0%) were classified into the PAS group. The PAS group exhibited a significantly older age (p = 0.011), higher prevalence of diabetes (p = 0.010), systolic blood pressure (p = 0.019), levels of serum fasting glucose (p = 0.003), blood urea nitrogen (p = 0.024), creatinine (p = 0.004), C-reactive protein (p = 0.007), OC (p = 0.002), and lower estimated glomerular filtration rate (p = 0.004) than the non-PAS group. Age (odds ratio [OR]: 1.076, 95% CI: 1.004-1.153, p = 0.037) and serum OC level (OR: 1.797, 95% confidence interval (CI): 1.077-3.000, p = 0.025) were independent factors linked to PAS in hypertensive patients in the multivariate logistic regression analysis. Conclusions: Serum OC levels and older age are positively associated with PAS in hypertensive patients.

Serum Malondialdehyde-Modified Low-Density Lipoprotein as a Risk Marker for Peripheral Arterial Stiffness in Maintenance Hemodialysis Patients

Background and Objectives: Peripheral arterial stiffness (PAS), assessed by brachial-ankle pulse wave velocity (baPWV), is an independent biomarker of cardiovascular diseases (CVD) in patients on maintenance hemodialysis (HD). Malondialdehyde-modified low-density lipoprotein (MDA-LDL), an oxidative stress marker, has been linked to atherosclerosis and CVD. However, the association between serum MDA-LDL and PAS among HD patients has not been fully elucidated. This study aimed to examine the association of serum MDA-LDL with PAS in HD patients and to identify the optimal cutoff value of serum MDA-LDL for predicting PAS. Materials and Methods: A cross-sectional study was conducted in 100 HD patients. Serum MDA-LDL was quantified using an enzyme-linked immunosorbent assay (ELISA), and baPWV was measured using a volume plethysmographic device. Patients were divided into the PAS group (baPWV > 18.0 m/s) and the non-PAS group (baPWV ≤ 18.0 m/s). The associations of baPWV and other clinical and biochemical parameters with serum MDA-LDL were assessed by multivariable logistic regression analyses. A receiver operating characteristic (ROC) curve analysis was performed to determine the optimal cutoff value of serum MDA-LDL for predicting PAS. Results: In multivariable logistic regression analysis, higher serum MDA-LDL, older age, and higher serum C-reactive protein [odds ratios (ORs) and 95% confidence intervals: 1.014 (1.004-1.025), 1.044 (1.004-1.085) and 3.697 (1.149-11.893)] were significantly associated with PAS. In the ROC curve analysis, the optimal cutoff value of MDA-LDL for predicting PAS was 80.91 mg/dL, with a sensitivity of 79.25% and a specificity of 59.57%. Conclusions: Greater serum MDA-LDL levels, particularly ≥80.91 mg/dL, were independently associated with PAS in HD patients. The findings suggest that oxidative stress plays a crucial role in the pathogenesis of PAS, and targeting MDA-LDL may be a potential therapeutic strategy for reducing cardiovascular risk in HD patients.

Trimethylamine-N-oxide and cerebral stroke risk: A review

Trimethylamine-N-oxide (TMAO) is a gut microbiota-derived metabolite produced by the action of gut microbiota and the hepatic enzyme Flavin Mono‑oxygenase 3 (FMO3). TMAO level has a positive correlation with the risk of cardiovascular events, including stroke, and their level is influenced mainly by dietary choice and the action of liver enzyme FMO3. TMAO plays a role in the development of atherosclerosis plaque, which is one of the causative factors of the stroke event. Preclinical and clinical investigations on the TMAO and associated stroke risk, severity, and outcomes are summarised in this review. In addition, mechanisms of TMAO-driven vascular dysfunction are also discussed, such as inflammation, oxidative stress, thrombus and foam cell formation, altered cholesterol and bile acid metabolism, etc. Post-stroke inflammatory cascades involving activation of immune cells, i.e., microglia and astrocytes, result in Blood-brain-barrier (BBB) disruption, allowing TMAO to infiltrate the brain and further aggravate inflammation. This event occurs as a result of the activation of the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome pathway through the release of inflammatory cytokines and chemokines that further aggravate the BBB and initiate further recruitment of immune cells in the brain. Thus, it's likely that maintaining TMAO levels and associated gut microbiota could be a promising approach for treating and improving stroke complications.

Sweet, bloody consumption - what we eat and how it affects vascular ageing, the BBB and kidney health in CKD

In today's industrialized society food consumption has changed immensely toward heightened red meat intake and use of artificial sweeteners instead of grains and vegetables or sugar, respectively. These dietary changes affect public health in general through an increased incidence of metabolic diseases like diabetes and obesity, with a further elevated risk for cardiorenal complications. Research shows that high red meat intake and artificial sweeteners ingestion can alter the microbial composition and further intestinal wall barrier permeability allowing increased transmission of uremic toxins like p-cresyl sulfate, indoxyl sulfate, trimethylamine n-oxide and phenylacetylglutamine into the blood stream causing an array of pathophysiological effects especially as a strain on the kidneys, since they are responsible for clearing out the toxins. In this review, we address how the burden of the Western diet affects the gut microbiome in altering the microbial composition and increasing the gut permeability for uremic toxins and the detrimental effects thereof on early vascular aging, the kidney per se and the blood-brain barrier, in addition to the potential implications for dietary changes/interventions to preserve the health issues related to chronic diseases in future.

From heart failure and kidney dysfunction to cardiorenal syndrome: TMAO may be a bridge

The study of trimethylamine oxide (TMAO), a metabolite of gut microbiota, and heart failure and chronic kidney disease has made preliminary achievements and been summarized by many researchers, but its research in the field of cardiorenal syndrome is just beginning. TMAO is derived from the trimethylamine (TMA) that is produced by the gut microbiota after consumption of carnitine and choline and is then transformed by flavin-containing monooxygenase (FMO) in the liver. Numerous research results have shown that TMAO not only participates in the pathophysiological progression of heart and renal diseases but also significantly affects outcomes in chronic heart failure (CHF) and chronic kidney disease (CKD), besides influencing the general health of populations. Elevated circulating TMAO levels are associated with adverse cardiovascular events such as HF, myocardial infarction, and stroke, patients with CKD have a poor prognosis as well. However, no study has confirmed an association between TMAO and cardiorenal syndrome (CRS). As a syndrome in which heart and kidney diseases intersect, CRS is often overlooked by clinicians. Here, we summarize the research on TMAO in HF and kidney disease and review the existing biomarkers of CRS. At the same time, we introduced the relationship between exercise and gut microbiota, and appropriately explored the possible mechanisms by which exercise affects gut microbiota. Finally, we discuss whether TMAO can serve as a biomarker of CRS, with the aim of providing new strategies for the detection, prognostic, and treatment evaluation of CRS.

Serum Trimethylamine N-Oxide Level Is Positively Associated with Aortic Stiffness Measured by Carotid-Femoral Pulse Wave Velocity in Patients Undergoing Maintenance Hemodialysis

Trimethylamine N-oxide (TMAO) is a biomarker that is effective in predicting major adverse cardiovascular (CV) events. Age-related vascular problems are significantly affected by aortic stiffness (AS), which is independently linked to CV morbidity and mortality. This study aimed to determine the association between serum TMAO levels and carotid-femoral pulse wave velocity (cfPWV) in patients receiving hemodialysis (HD) therapy. In total, 115 patients with HD were enrolled in this study. The AS group included patients whose cfPWV was >10 m/s. Using high-performance liquid chromatography and mass spectrometry, the levels of serum TMAO were measured. The AS group included 42 (36.5%) patients, and compared with the non-AS group, the rates of diabetes, hypertension, older age, systolic blood pressure, serum glucose, and TMAO levels were high. In the multivariate logistic regression analysis, serum TMAO and age were independently linked with AS after correcting for the factors significantly associated with AS. Following multivariate stepwise linear regression analysis, serum TMAO in these individuals was found to be strongly correlated with cfPWV values (p < 0.001). In patients on chronic HD, serum TMAO level is an independent measure of AS and strongly correlated with cfPWV.

Study on the effect of periodontitis on renal tissue in atherosclerotic mice

BACKGROUND AND OBJECTIVE

Periodontitis is immune inflammatory disease, atherosclerosis (AS) and chronic kidney disease (CKD) are two common systemic diseases. Periodontitis promotes AS and CKD, and CKD interacts with AS. The objective of this animal study was to evaluate the changes of kidney when periodontitis and atherosclerosis exist separately and the degenerative effects of periodontitis on the kidney in atherosclerotic mice.

MATERIALS AND METHODS

A total of 40 male Apoe-/- mice were randomly divided into four groups: control (NC), periodontitis (PD), AS and AS with PD (AS + PD). AS was induced by high-fat diet feeding, and PD was induced by injection of Porphyromonas gingivalis-Lipopolysaccharide (P.g-LPS) (endotoxin suspension) into the buccal side of mouse maxillary molars. The right maxilla of mice was scanned with micro-CT to evaluate alveolar bone loss; aortic tissue was stained with HE and Oil-Red O to evaluate arterial plaque formation; serum was collected to detect the changes of blood lipids and serum renal function parameters (blood urea nitrogen [BUN], serum creatinine [Scr]); renal histopathological changes were evaluated by HE staining (glomerular and tubular damage scores), PAS staining (glomerular Mesangial matrix index) and Masson staining (percentage of renal fibrosis area); qRT-PCR and ELISA were used to evaluate the expression of renal inflammatory cytokines (tumor necrosis factor-α, Interleukin-1β, neutrophil surface marker Ly6G).

RESULTS

The amount of alveolar bone loss: PD group was significantly higher than NC group (p < .05); AS + PD group was higher than PD group, the difference was not statistically significant. Atherosclerotic plaque formation and serum lipid changes: AS group were significantly worse than NC group (p < .05), and AS + PD group were worse than AS group. The results of the corresponding qualitative and quantitative analyses of kidney tissue in experimental animals gradually deteriorated in the NC group, PD group, AS group and AS + PD group and worsened sequentially. Renal function parameters: the content of BUN in AS group was higher than that in PD group, the difference was not statistically significant; Scr in AS group was significantly higher than that in PD group (p < .05); the contents of BUN and Scr in AS + PD group were higher than those in AS group, the difference was not statistically significant. Glomerular and tubular damage scores: AS group were higher than PD group, the difference was not statistically significant; AS + PD group were significantly higher than AS group (p < .001). The ratio of glomerular mesangial matrix to glomerular area and the percentage of renal fibrosis area: AS group were significantly higher than PD group (p < .001), and AS + PD group were significantly higher than AS group (p < .001). Expression of inflammatory cytokines: AS group was higher than PD group, the difference was not statistically significant; AS + PD group was significantly higher than AS group (p < .05).

CONCLUSION

Both PD and AS can aggravate the inflammatory stress of kidney tissue and cause the damage of kidney tissue, and the inflammatory increase and damage effect of AS is stronger; PD can promote kidney damage of atherosclerotic mice by aggravating the renal inflammation in atherosclerotic mice; renal function parameters were not completely synchronized with the changes of renal inflammation and histopathology in each group of mice; PD can promote AS, periodontal inflammation in mice with AS is more severe, and the special changes of blood lipids in mice with AS are closely related to the above results.

Dietary choline, via gut microbe- generated trimethylamine-N- oxide, aggravates chronic kidney disease-induced cardiac dysfunction by inhibiting hypoxia-induced factor 1α

Chronic kidney disease (CKD) is a global public health problem that shortens lifespan primarily by increasing the risk of cardiovascular diseases. Trimethylamine-N-oxide (TMAO), a gut microbiota-derived toxin produced by metabolizing high-choline or carnitine foods, is associated with cardiovascular events in patients with CKD. Although the deleterious effect of TMAO on CKD-induced cardiac injury has been confirmed by various researches, the mechanisms remain unclear. Here, we tested the hypothesis that TMAO aggravates CKD-induced cardiac injury and explores the potential mechanism. CD1 mice underwent 5/6 nephrectomy to induce CKD, and then fed with a diet supplemented with choline (1.2% total) for 8 weeks. Serum TMAO levels were elevated in CKD mice compared with SHAM group, and higher TMAO levels were found in choline-supplemented CKD mice compared with CKD group. Dietary choline aggravated CKD-induced cardiac dysfunction, and reducing TMAO levels via medicinal charcoal tablets improved cardiac dysfunction. RNA-seq analysis revealed that dietary choline affected cardiac angiogenesis in CKD mice. Reduced cardiac capillary density and expressions of angiogenesis-related genes were observed in choline-treated CKD mice. Furthermore, dietary choline inhibited cardiac Hif-1α protein level in CKD mice, and Hif-1α stabilizer FG-4592 could improve cardiac angiogenesis and dysfunction in CKD mice on a high-choline diet. In conclusion, these data indicate that dietary choline, via gut microbe-generated TMAO, inhibits cardiac angiogenesis by reducing Hif-1α protein level, ultimately aggravates cardiac dysfunction in CKD mice.