Natalia Alvarenga Borges

Inflammasomes are cytoplasmic multiprotein complexes belonging to the innate immune system, playing a crucial role in responses to microbial infections and controlling mucosal immune responses and metabolic activities. The Nod-Like Pyrin Receptor Domain 3 (NLRP3) inflammasome is one of the most studied and may be a key element in the relationship between gut microbiota and systemic inflammation. Chronic non-communicable diseases have been closely associated with alterations in the gut microbiota (dysbiosis) and the activation of the inflammasome complex. Dysbiosis can expose the host to pathogenic microorganisms and their metabolites, thus triggering immune and inflammatory responses. This review discusses the importance of addressing the interaction between the gut microbiota and the NLRP3 inflammasome pathway and its possible effects on human health. Modulation of the intestinal microbiota may be a crucial factor in preventing and mitigating inflammation, and the NLRP3 inflammasome pathway appears to be substantially involved in this process.

Trimethylamine N‐oxide (TMAO) is a uremic toxin accumulated in patients with chronic kidney disease (CKD) and involved with atherosclerosis. TMAO is derived from the gut microbiota (nutrient fermentation) and is found in some fish and seafood. This pilot study evaluated the acute effects of cod fish, red meat, and vegetable meal consumption on plasma TMAO levels in nondialysis CKD patients. Patients (five women, three men, 72.5 [7.7] years, body mass index [BMI], 25.6 [1.4] kg/m², glomerular filtration rate, 32.5 [18.5] mL/min) consumed lunches containing codfish, red meat, and chickpeas, within a 7‐day interval between meals. TMAO plasma levels were assessed using the HPLC‐EM/EM method before and after the 4‐h meal challenge. Patients presented TMAO plasma levels of 9.06 µM. Consumption of codfish significantly increases the TMAO levels (to 23.5 µM, p < 0.001) compared to red meat and chickpeas. We conclude that codfish, compared to red meat and vegetable meal, provoked a transient elevation in TMAO levels in patients with CKD. Therefore, this result suggests that it is prudent to prescribe fish with low TMAO content for these patients. The response to ingesting TMAO‐rich foods in CKD patients needs more study.

Background The Nod-Like Receptor Pyrin domain-containing 3 (NLRP3) inflammasome is a critical sensor of bacterial signals and metabolites, initiating an inflammatory response. Chronic kidney disease (CKD) is often accompanied by systemic inflammation, which can be involved with gut dysbiosis. Considering this interplay, we aimed to explore the potential association between NLRP3 inflammasome expression and gut microbiota in CKD patients undergoing hemodialysis (HD). Methods and results This research comprises a cross-sectional pilot study involving twelve HD patients [59.2 ± 13.4 years, six women, BMI 26.6 ± 3.5 kg/m², 48.6 (20.1–77.2) months] on dialysis. The gut microbiota was evaluated by the 16 S ribosomal RNA gene. The mRNA expression of NLRP3 was assessed using real-time quantitative polymerase chain reaction (qPCR). Plasma levels of IL-1β were measured by ELISA. Fusobacteria and Fusobacterium negatively correlated with the mRNA expression levels of NLRP3 and IL-1β (p < 0.05). A positive correlation was observed between mRNA expression of NLRP3 and Lentisphaerae, Erysipelaloclostrium and Victivallis (p < 0.05). The relative abundances of Lentisphaerae, Spirochaetes, Abscicoccus, Colidextribacter, Desulfovibrio, Fournierella, Lawsonibacter, Ruminococcus, and Victivallis were positively correlated with IL-1β mRNA expression (p < 0.05). Regarding Archaea, IL-1β mRNA expression was positively correlated with Methanobrevibacter (p < 0.05). Conclusion In CKD patients undergoing hemodialysis, gut microbiota may be involved in NLRP3 activation and IL-1β expression, contributing to inflammation.

Scope: The uremic toxin trimethylamine N‐oxide (TMAO) accumulates in patients with chronic kidney disease (CKD) and is associated with its progression, cardiovascular disease, and other complications. The gut microbiota produces TMAO from substrates mainly found in red meat, eggs, and dairy. However, some saltwater fish also contain high levels of TMAO. Although fish consumption is generally linked to beneficial effects, its effects on CKD patients require further research. Methods and results: This study compares the effect of red meat and cod fish intake on TMAO plasma levels in CKD patients undergoing hemodialysis (HD). Participants received a single animal protein source (red meat vs. cod fish) for lunch and dinner for four consecutive days (each intervention), with a 2‐week washout period in between. TMAO plasma levels were analyzed using LC‐MS/MS. All 14 patients concluded the red meat intervention, while one refused to participate in the fish intervention. No significant difference in TMAO plasma levels was found post‐red meat (p = 0.21) or fish intervention (p = 0.91), as well as between groups (p = 0.43). Conclusion: In this study, 4 days of red meat and cod fish intake did not significantly impact TMAO levels in HD patients, while other factors may be associated with their circulating levels.

Gut dysbiosis, characterized by an imbalance in the gut microbiota, has emerged as a potential factor influencing CKD progression. This condition plays a crucial role in the gut-kidney axis, where changes in microbial composition can contribute to systemic inflammation and uremic toxin production and ultimately exacerbate kidney damage. Understanding the dynamics of the gut-kidney axis provides new insights into potential therapeutic strategies to mitigate CKD progression. Diet is the primary driver of gut microbiota composition. Therefore, an approach emphasizing healthy nutritional patterns is recommended for improving overall health, cardiovascular disease, and profoundly altered metabolic patterns in patients with CKD. Dietary modifications have been explored as therapeutic strategies targeting the microbiome to improve outcomes in CKD. An emerging therapeutic target is the production of dysmetabolites by the gut microbiota, which may help alleviate uremic and cardiovascular toxicity. In addition, future research should broaden the scope to include other microorganisms, such as fungi, archaea, and viruses. This expanded focus will enable a more comprehensive understanding of the gut-kidney axis and pave the way for more personalized and effective treatment strategies for patients with CKD. This review explores the role of lifestyle, particularly diet, in kidney health; highlights new gut microbiome therapies; and identifies research opportunities in CKD.

Introduction: Chronic kidney disease patients (CKD) have gut dysbiosis, which is related to the increased production of uremic toxins, contributing to the chronic inflammation. Metabolites from the gut microbiota appear to interact with transcription factors involved with immune response, inflammation, and oxidative stress. Cranberry (Vaccinium macrocarpon) is a fruit rich in bioactive compounds such as flavonoids, with potential prebiotic effects, thus potentially contributing positively to the modulation of the intestinal microbiota. Objective: To evaluate the effects of supplementation with dry cranberry extract on uremic toxins plasma levels and inflammation in non-dialysis CKD patients. Methods: In this randomized, double-blind, placebo-controlled clinical trial, thirty CKD patients (stages 3 and 4), received capsules containing cranberry dry extract (500 mg, standardized to 36mg of proanthocyanidins, twice a day) or placebo (500mg of cornstarch twice a day) for 2 months. Expression of PPAR-γ, Nuclear Factor kappa-B (NF-κB), and Nuclear erythroid factor 2 related to factor 2 (Nrf2) were evaluated using quantitative real-time PCR. The uremic toxins (indoxyl-sulfate, p-cresyl sulfate and indole-3-acetic acid) were determined by Reverse Phase High Performance Liquid Chromatography. Results: Twenty-seven patients completed the study (Cranberry Group: 54.4 ± 6.5 years, GFR 30.3 ± 7.4mL / min, BMI 29.8 ± 5.4kg / m2; Placebo Group: 57.8 ±5.6 years, GFR 35.7±11.5mL/min, BMI, 29.6±5.5kg/m2). PPAR-γ, NF-κB, and Nrf2 mRNA expression was not significantly different after the intervention in both groups. The treatment also did not alter the plasma levels of uremic toxins. Conclusions: Short-term cranberry dry extract supplementation did not promote significant changes in uremic toxins produced by the gut microbiota. In addition, no change in the expression of genes related to inflammation and oxidative stress were observed

Introduction: Trimethylamine N-oxide (TMAO) is a uremic toxin linked to the development and progression of cardiovascular disease that accumulates in chronic kidney disease (CKD) patients. In humans, TMAO is produced by the gut microbiota through bacteria fermentation of substrates such as carnitine, particularly present in red meat. In addition, some species of fish are high in TMAO. Although fish is associated with health benefits and cardiovascular protection, the impact of intake of fish rich in TMAO levels in patients with CKD needs to be investigated. Objective: to evaluate the effect of red meat and fish intake on plasma levels of TMAO in patients with CKD in HD. Methods: A crossover clinical trial with a washout period was conducted in 14 individuals undergoing HD. Patients were allocated into two groups, according to their respective dialysis days. The patients received a single animal protein source (red meat vs. fish) at lunch and dinner for four consecutive days (each intervention). The meals were prepared considering an offer of 1.2g of protein/kg of body weight, and the other nutrients were offered according to each participant’s nutritional requirements. The patients received 8 lunch boxes to take home, and after this period, a washout was carried out for two weeks, and then the interventions were reversed. TMAO plasma levels were analyzed by Liquid Chromatography coupled with Mass Spectrometry. Results: All 14 patients underwent the red meat intervention, while 1 patient refused to participate in the fish intervention [9 men, 5 women, age: 49 (IQR=29) years, BMI: 26.1 (IQR=6.7) kg/m2]. No significant difference in TMAO plasma levels were found post red meat intervention (p=0.21) or fish intervention (p=0.91). TMAO levels correlated with age (r=0.542; p=0.003), waist circumference (r=0.483; p=0.02) and post-dialysis urea (r=0.404; p=0.04). Conclusion: In this study, red meat and fish intake for 4 days was not able to significantly impact the TMAO levels in HD patients, while other factors may be associated with its circulating levels. Further studies addressing different animal protein sources with a larger sample size are needed to improve nutritional guidance for patients with CKD.

Background: Propolis possesses many bioactive compounds that could modulate the gut microbiota and reduce the production of uremic toxins in patients with chronic kidney disease (CKD) undergoing hemodialysis (HD). This clinical trial aimed to evaluate the effects of propolis on the gut microbiota profile and uremic toxin plasma levels in HD patients. These are secondary analyses from a previous double-blind, randomized clinical study, with 42 patients divided into two groups: the placebo and propolis group received 400 mg of green propolis extract/day for eight weeks. Indole-3 acetic acid (IAA), indoxyl sulfate (IS), and p-cresyl sulfate (p-CS) plasma levels were evaluated by reversed-phase liquid chromatography, and cytokines were investigated using the multiplex assay (Bio-Plex Magpix^®). The fecal microbiota composition was analyzed in a subgroup of patients (n = 6) using a commercial kit for fecal DNA extraction. The V4 region of the 16S rRNA gene was then amplified by the polymerase chain reaction (PCR) using short-read sequencing on the Illumina NovaSeq PE250 platform in a subgroup. Forty-one patients completed the study, 20 in the placebo group and 21 in the propolis group. There was a positive correlation between IAA and TNF-α (r = 0.53, p = 0.01), IL-2 (r = 0.66, p = 0.002), and between pCS and IL-7 (r = 0.46, p = 0.04) at the baseline. No significant changes were observed in the values of uremic toxins after the intervention. Despite not being significant, microbial evenness and observed richness increased following the propolis intervention. Counts of the Fusobacteria species showed a positive correlation with IS, while counts of Firmicutes, Lentisphaerae, and Proteobacteria phyla were negatively correlated with IS. Two months of propolis supplementation did not reduce the plasma levels of uremic toxins (IAA, IS, and p-CS) or change the fecal microbiota.

The gut microbiota performs several crucial roles in a holobiont with its host, including immune regulation, nutrient absorption, synthesis, and defense against external pathogens, significantly influencing host physiology. Disruption of the gut microbiota has been linked to various chronic conditions, including cardiovascular, kidney, liver, respiratory, and intestinal diseases. Studying how animals adapt their gut microbiota across their life course at different life stages and under the dynamics of extreme environmental conditions can provide valuable insights from the natural world into how the microbiota modulates host biology, with a view to translating these into treatments or preventative measures for human diseases. By modulating the gut microbiota, opportunities to address many complications associated with chronic diseases appear. Such a biomimetic approach holds promise for exploring new strategies in healthcare and disease management.