Gut microbiota-derived D-serine protects against acute kidney injury

A comparative study of blood and hippocampal D-serine change patterns in drug-naïve patients and animal models of depression

The dysfunction of the N-methyl-d-aspartate receptor (NMDAR) has been implicated in depression, and D‑serine, an endogenous co-agonist of NMDAR, plays a critical role in its function. However, the pattern and relationship of alterations in central and peripheral D‑serine concentrations in depression remain unclear. In this study, we conducted two parallel cross-sectional studies to investigate D‑serine alterations in depression. In the clinical study, we recruited drug-naïve patients with major depressive disorder (MDD) and age and sex-matched healthy controls to assess peripheral D‑serine levels in serum. In the preclinical study, a chronic social defeat stress (CSDS) mouse model of depression was used to measure both peripheral and hippocampal D‑serine levels, given the hippocampus's key role in depression. Our results revealed significantly higher levels of D‑serine and the D‑serine/L‑serine ratio in the serum of MDD patients compared to controls, while L‑serine levels showed no significant differences. Similarly, in the CSDS mouse model, serum D‑serine levels were also increased. However, hippocampal D‑serine and L‑serine levels were decreased in depressed mice compared to controls, with no significant correlation observed between blood and hippocampal D‑serine levels. These findings suggest a potential pattern of D‑serine concentrations between peripheral blood and the hippocampus in depression. However, the clinical implications of contrasting changes in D‑serine in the peripheral and central systems, as well as the underlying mechanisms, require further investigation.

Development of fluorescent probe for specific recognition of chiral alanine

Amino acids, the building blocks of life, exhibit significant chirality, whereas L-amino acids predominate in living organisms and play essential roles in protein synthesis and other biochemical processes. Although less abundant, D-amino acids play critical roles in forming bioactive compounds such as peptidoglycans in bacterial cell walls and find applications in the pharmaceutical industry and materials science. This study uses optical detection techniques to develop a chiral fluorescence sensor based on binaphthol (BINOL). We present the design and synthesis of the (R)-5 probe, which exhibits exclusive selectivity for D-alanine (Ala) among the 20 chiral amino acids, with a detection limit of 10.7 nM. The enantioselectivity of the probe was confirmed through fluorescence spectroscopy and visual inspection, demonstrating its potential for detecting and quantifying D-alanine (D-Ala) in biological samples. This work lays the foundation for developing sensitive diagnostic tools that rely on D-amino acid levels.

The microbiome and acute organ injury: focus on kidneys

The microbiome of critically ill patients is significantly altered by both effects of the illnesses and clinical interventions provided during intensive care. Studies have shown that manipulating the microbiome can prevent or modulate complications of critical illness in experimental models and preliminary clinical trials. This review aims to discuss general concepts about the microbiome, including mechanisms of modifying acute organ dysfunction. The focus will be on the effects of microbiome modulation during experimental acute kidney injury (excluding septic acute kidney injury) and comparison with other experimental acute organ injuries commonly seen in critically ill patients.

Fucoxanthin Ameliorates Kidney Injury by CCl4-Induced via Inhibiting Oxidative Stress, Suppressing Ferroptosis, and Modulating Gut Microbiota

Chemical-induced kidney injury represents a substantial health risk, with ferroptosis, a type of cell death caused by lipid peroxidation, playing a role in numerous kidney ailments. Fucoxanthin (Fx), a natural carotenoid known for its antioxidant capabilities, has shown promise in alleviating renal injury, but its exact mechanisms are yet to be fully understood. Carbon tetrachloride (CCl4) is recognized as a powerful nephrotoxic substance, and this study explores the therapeutic effects of Fx on oxidative stress, ferroptosis and intestinal microbiota in mouse kidneys subjected to CCl4 exposure. The mice were randomly assigned to control, model, colchicine groups (0.1 mg/kg/d), and Fx (50, 100 mg/kg/d) group and underwent related treatments for 4 weeks. Then, we evaluated their renal function, histological alterations in the kidneys, colon, and jejunum, and the levels of related proteins (i.e., Nrf2, GPX4, SLC7A11, HO-1, TFR1, NQO1, GCLM, FTL). Additionally, their gut microbiota was analyzed using 16S rRNA gene sequencing. The results showed that compared to the CCl4 group, Fx treatment led to lower serum creatinine and blood urea nitrogen levels, reduced malondialdehyde activity in kidneys and intestinal tissues, and increased activity of antioxidant enzymes. Fx also reduced dysbiosis and enhanced the diversity of intestinal flora. In summary, Fx reduced oxidative stress and ferroptosis and partially restored intestinal bacteria, thus improving CCl4-induced renal damage in mice. These results suggest Fx as a potential therapeutic option for kidney injuries related to oxidative stress. Further research is needed to clarify its precise mechanisms and potential clinical implications.

Navigating contradictions: Salmonella Typhimurium chemotactic responses to conflicting effector stimuli

Chemotaxis controls motility and colonization in many enteric pathogens, yet most studies have examined bacterial responses to single effectors in isolation. Previously, we reported that Salmonella Typhimurium uses the chemoreceptor Tsr to detect l-serine (L-Ser) in human blood serum, promoting invasion of damaged vasculature (Glenn et al., eLife 2024 1). Tsr also mediates sensing of indole, a microbiota-derived chemorepellent and bactericide proposed to protect against enteric infection by deterring pathogen colonization. The major biological reservoir of indole in the gut is feces, where it accumulates to millimolar levels. Here, we tested whether indole-rich human fecal material is protective against infection and found that exposure to feces instead enhances intestinal invasion in an explant model. Surprisingly, diverse non-typhoidal Salmonella serovars were strongly attracted to feces despite its high indole content. We found that while pure indole is a strong repellent sensed through Tsr, its effects are overridden in the presence of nutrient attractants, including l-Ser. Moreover, indole only minimally impairs growth in the presence of sufficient nutrients. Using video microscopy, we observed that Tsr integrates l-Ser and indole signals in real time, biasing bacterial movement based on the relative concentrations of attractant and repellent. We propose that this chemotactic compromise optimizes pathogen fitness by guiding bacteria to niches with a favorable l-Ser-to-indole ratio, balancing nutrient acquisition and avoidance of high microbial competitor density. These findings highlight the limitations of single-effector studies in predicting bacterial navigation in complex environments, where chemotaxis is shaped by the integration of multiple, often opposing, chemical cues.

The Potential Mechanism of D-Amino Acids - Mitochondria Axis in the Progression of Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a major complication of diabetes mellitus (DM) and stands out as the leading cause of end-stage renal disease worldwide. There is increasing evidence that mitochondrial dysfunction, including impaired mitochondrial biogenesis, dynamics, and oxidative stress, contributes to the development and progression of DKD. D-amino acids (D-AAs), which are enantiomers of L-AAs, have recently been detected in various living organisms and are acknowledged to play important roles in numerous physiological processes in the human body. Accumulating evidence demonstrates that D-AA levels in blood or urine could serve as useful biomarkers for reflecting renal function. The physiological roles of D-AAs are implicated in the regulation of cellular proliferation, oxidative stress, generation of reactive oxygen species (ROS), and innate immunity. This article reviews current evidence relating to D-AAs and mitochondrial dysfunction and proposes a potential interaction and contribution of the D-AAs-mitochondria axis in DKD pathophysiology and progression. This insight could provide novel therapeutic approaches for preventing or ameliorating DKD based on this biological axis.

Detection of Fast Decliner of Diabetic Kidney Disease Using Chiral Amino Acid Profiling: A Pilot Study

Biomarkers for the prediction of diabetic kidney disease are still unsatisfactory. Although D-amino acids have been shown to reflect kidney conditions, their efficacy in treating diabetic kidney disease (DKD) has not been demonstrated. This study explored the potential role of D-amino acids as progression markers for DKD, an aspect not addressed previously. We performed comprehensive D-amino acid measurements and collected the longitudinal estimated glomerular filtration rate (eGFR) data of 135 patients. We defined fast decliners (FDs) as patients exhibiting >10% decline from baseline eGFR per year and compared the D-amino acid levels of FDs and non-FDs. Then, we verified that D-amino acids could predict FDs independent of creatinine levels. In patients with diabetic kidney disease, D-serine, D-alanine, and D-proline were only detected in the blood, while 15 D-amino acids were detected in the urine. Using supervised orthogonal partial least squares analysis, blood D-serine and urine D-amino acid levels were identified as features characterizing diabetic kidney disease. Baseline blood D-serine levels and ratios did not differ between the FD and non-FD groups; however, short-term changes in blood D-serine levels differed. This study emphasized the significance of D-serine as a prognostic marker for DKD, an aspect not identified in previous research.

The Application of L-Serine-Incorporated Gelatin Sponge into the Calvarial Defect of the Ovariectomized Rats

BACKGROUND

Osteoporosis, characterized by decreased bone mineral density due to an imbalance between osteoblast and osteoclast activity, poses significant challenges in bone healing, particularly in postmenopausal women. Current treatments, such as bisphosphonates, are effective but associated with adverse effects like medication-related osteonecrosis of the jaw, necessitating safer alternatives.

METHODS

This study investigated the use of L-serine-incorporated gelatin sponges for bone regeneration in calvarial defects in an ovariectomized rat model of osteoporosis. Thirty rats were divided into three groups: a control group, a group treated with a gelatin sponge containing an amino acid mixture, and a group treated with a gelatin sponge containing L-serine. Bone regeneration was assessed using micro-computed tomography (micro-CT) and histological analyses.

RESULTS

The L-serine group showed a significant increase in bone volume (BV) and bone area compared to the control and amino acid groups. The bone volume to total volume (BV/TV) ratio was also significantly higher in the L-serine group. Immunohistochemical analysis demonstrated that L-serine treatment suppressed the expression of cathepsin K, a marker of osteoclast activity, while increasing serine racemase activity.

CONCLUSION

These findings suggest that L-serine-incorporated gelatin sponges not only enhance bone formation but also inhibit osteoclast-mediated bone resorption, providing a promising and safer alternative to current therapies for osteoporosis-related bone defects. Further research is needed to explore its clinical applications in human patients.

Effect of D-amino acid metabolic enzyme deficiency on cancer development-diffuse large B-cell lymphoma onset and gene expression analyses in DASPO-knockout mice

The relationship between D-AA metabolic enzymes and cancer development remains unclear. We aimed to investigate this relationship using mice deficient in D-AA-related metabolic enzymes. We examined mice lacking these enzymes for approximately 900 days and the effects of altered D-AA metabolism on cancer development based on lifespan, pathological findings, and gene expression. The lifespan of female DASPO -knockout (DASPO-/-) mice was shorter than that of the other group mice; furthermore, these mice showed tumor-like masses in the liver, spleen, and small intestine. A pathological diagnosis of diffuse large B-cell lymphoma (DLBCL) was made. RNA sequencing of the liver samples showed specific alterations in the expression of 71 genes in DASPO-/- mice compared with that in wild-type B6 mice; RGS 1, MTSS1, and SMARCD 1 were identified as DLBCL-related genes. Patients with DLBCL exhibiting low DASPO expression demonstrated a shorter survival period than those showing high expression. However, the role of DASPO in DLBCL development is unclear. Therefore, future research should focus on B cells. DASPO may serve as novel biomarkers and therapeutic targets in cancer.

Chiral Amino Acids Mediate Mitochondria-Dependent Apoptosis of Human Proximal Tubular Epithelial Cells Under Oxidative Stress

Amino acids are the basic structural units of life, and their intake levels affect disease and health. In the case of renal disease, alterations in amino acid metabolism can be used not only as a clinical indicator of renal disease but also as a therapeutic strategy. However, the biological roles and molecular mechanisms of natural chiral amino acids in human proximal tubular epithelial cells (HK-2) remain unclear. In this study, cell viability assays revealed that chiral acidic amino acids (Glu and Asp) and aromatic amino acids (Trp and Phe) inhibited cell growth. The molecular mechanisms indicated that cell growth was closely related to ROS levels. Specifically, chiral Glu, Asp, Trp, and Phe induced oxidative stress and mitochondria-dependent apoptosis in HK-2 cells. This was manifested by elevated levels of intracellular ROS, 8-OHdG, and MDA, increased activities of antioxidant enzymes CAT, SOD, and GPx, decreased mitochondrial membrane potential, increased cytoplasmic Ca2+ concentration, and cell acidification. The expression levels of apoptosis-related molecules Caspase-9, Caspase-3, Cyt-C, and Bax were increased, and the expression level of anti-apoptotic molecule Bcl-2 was decreased. Moreover, L-Glu, D-Asp, L-Trp, and D-Phe exhibited a more pronounced inhibition of cell growth and elicited more substantial alterations in gene expression compared to the other configurations.

Lymphocytes and innate immune cells in acute kidney injury and repair

Acute kidney injury (AKI) is a common and serious disease entity that affects native kidneys and allografts but for which no specific treatments exist. Complex intrarenal inflammatory processes driven by lymphocytes and innate immune cells have key roles in the development and progression of AKI. Many studies have focused on prevention of early injury in AKI. However, most patients with AKI present after injury is already established. Increasing research is therefore focusing on mechanisms of renal repair following AKI and prevention of progression from AKI to chronic kidney disease. CD4+ and CD8+ T cells, B cells and neutrophils are probably involved in the development and progression of AKI, whereas regulatory T cells, double-negative T cells and type 2 innate lymphoid cells have protective roles. Several immune cells, such as macrophages and natural killer T cells, can have both deleterious and protective effects, depending on their subtype and/or the stage of AKI. The immune system not only participates in injury and repair processes during AKI but also has a role in mediating AKI-induced distant organ dysfunction. Targeted manipulation of immune cells is a promising therapeutic strategy to improve AKI outcomes.

Amino acid metabolism in kidney health and disease

Amino acids form peptides and proteins and are therefore considered the main building blocks of life. The kidney has an important but under-appreciated role in the synthesis, degradation, filtration, reabsorption and excretion of amino acids, acting to retain useful metabolites while excreting potentially harmful and waste products from amino acid metabolism. A complex network of kidney transporters and enzymes guides these processes and moderates the competing concentrations of various metabolites and amino acid products. Kidney amino acid metabolism contributes to gluconeogenesis, nitrogen clearance, acid-base metabolism and provision of fuel for tricarboxylic acid cycle and urea cycle intermediates, and is thus a central hub for homeostasis. Conversely, kidney disease affects the levels and metabolism of a variety of amino acids. Here, we review the metabolic role of the kidney in amino acid metabolism and describe how different diseases of the kidney lead to aberrations in amino acid metabolism. Improved understanding of the metabolic and communication routes that are affected by disease could provide new mechanistic insights into the pathogenesis of kidney diseases and potentially enable targeted dietary or pharmacological interventions.

Gut microbiome and metabolites mediate the benefits of caloric restriction in mice after acute kidney injury

The role of gut microbiome in acute kidney injury (AKI) is increasing recognized. Caloric restriction (CR) has been shown to enhance the resistance to ischemia/reperfusion injury to the kidneys in rodents. Nonetheless, it is unknown whether intestinal microbiota mediated CR protection against ischemic/reperfusion-induced injury (IRI) in the kidneys. Herein, we showed that CR ameliorated IRI-elicited renal dysfunction, oxidative stress, apoptosis, and inflammation, along with enhanced intestinal barrier function. In addition, gut microbiota depletion blocked the favorable effects of CR in AKI mice. 16S rRNA and metabolomics analysis showed that CR enriched the gut commensal Parabacteroides goldsteinii (P. goldsteinii) and upregulated the level of serum metabolite dodecafluorpentan. Intestinal colonization of P. goldsteinii and oral administration of dodecafluorpentan showed the similar beneficial effects as CR in AKI mice. RNA sequencing and experimental data revealed that dodecafluorpentan protected against AKI-induced renal injury by antagonizing oxidative burst and NFκB-induced NLRP3 inflammasome activation. In addition, we screened and found that Hamaudol improved renal insufficiency by boosting the growth of P. goldsteinii. Our results shed light on the role of intestinal microbiota P. goldsteinii and serum metabolites dodecafluorpentan in CR benefits to AKI.

Future of Uremic Toxin Management

During the progression of chronic kidney disease (CKD), the retention of uremic toxins plays a key role in the development of uremic syndrome. Knowledge about the nature and biological impact of uremic toxins has grown exponentially over the past decades. However, the science on reducing the concentration and effects of uremic toxins has not advanced in parallel. Additionally, the focus has remained for too long on dialysis strategies, which only benefit the small fraction of people with CKD who suffer from advanced kidney disease, whereas uremic toxicity effects are only partially prevented. This article reviews recent research on alternative methods to counteract uremic toxicity, emphasizing options that are also beneficial in the earlier stages of CKD, with a focus on both established methods and approaches which are still under investigation or at the experimental stage. We will consequently discuss the preservation of kidney function, the prevention of cardiovascular damage, gastro-intestinal interventions, including diet and biotics, and pharmacologic interventions. In the final part, we also review alternative options for extracorporeal uremic toxin removal. The future will reveal which of these options are valid for further development and evidence-based assessment, hopefully leading to a more sustainable treatment model for CKD than the current one.

Gut bacteria: an etiological agent in human pathological conditions

Through complex interactions with the host's immune and physiological systems, gut bacteria play a critical role as etiological agents in a variety of human diseases, having an impact that extends beyond their mere presence and affects the onset, progression, and severity of the disease. Gaining a comprehensive understanding of these microbial interactions is crucial to improving our understanding of disease pathogenesis and creating tailored treatment methods. Correcting microbial imbalances may open new avenues for disease prevention and treatment approaches, according to preliminary data. The gut microbiota exerts an integral part in the pathogenesis of numerous health conditions, including metabolic, neurological, renal, cardiovascular, and gastrointestinal problems as well as COVID-19, according to recent studies. The crucial significance of the microbiome in disease pathogenesis is highlighted by this role, which is comparable to that of hereditary variables. This review investigates the etiological contributions of the gut microbiome to human diseases, its interactions with the host, and the development of prospective therapeutic approaches. To fully harness the benefits of gut microbiome dynamics for improving human health, future research should address existing methodological challenges and deepen our knowledge of microbial interactions.

Gut Microbiota and Neonatal Acute Kidney Injury

OBJECTIVE

 To characterize the relationship between gut microbiota and neonatal acute kidney injury biomarkers based on the gut-kidney axis.

STUDY DESIGN

 The Pubmed database was primarily searched to include relevant literature on gut microbiota and neonatal acute kidney injury biomarkers, which was subsequently organized and analyzed and a manuscript was written.

RESULTS

 Gut microbiota was associated with neonatal acute kidney injury biomarkers. These biomarkers included TIMP-2, IGFBP-7, VEGF, calbindin, GST, B2MG, ghrelin, and clusterin.

CONCLUSION

 The gut microbiota is strongly associated with neonatal acute kidney injury biomarkers, and controlling the gut microbiota may be a potential target for ameliorating neonatal acute kidney injury.

KEY POINTS

· There is a bidirectional association between gut microbiota and AKI.. · Gut microbiota is closely associated with biomarkers of nAKI.. · Manipulation of gut microbiota may improve nAKI..

Physiology, Pathophysiology and Clinical Relevance of D-Amino Acids Dynamics: From Neurochemistry to Pharmacotherapy

Over three decades ago, two independent groups of investigators identified free D-aspartic and later D-serine in specific brain nuclei and endocrine glands. This finding revealed a novel, non-proteinogenic role of these molecules. Moreover, the finding that aged proteins from the human eye crystallin, teeth, bone, blood vessels or the brain incorporate D-aspartic acids to specific primary protein sequences fostered the hypothesis that aging might be related to D-amino acid isomerization of body proteins. The experimental confirmation that schizophrenia and neurodegenerative diseases modify plasma free D-amino acids or tissue levelsnurtured the opportunity of using D-amino acids as therapeutic agents for several disease treatments, a strategy that prompted the successful current application of D-amino acids to human medicine.

Urinary D-asparagine level is decreased by the presence of glioblastoma

Gliomas, particularly glioblastomas (GBMs), pose significant challenges due to their aggressiveness and poor prognosis. Early detection through biomarkers is critical for improving outcomes. This study aimed to identify novel biomarkers for gliomas, particularly GBMs, using chiral amino acid profiling. We used chiral amino acid analysis to measure amino acid L- and D-isomer levels in resected tissues (tumor and non-tumor), blood, and urine from 33 patients with primary gliomas and 24 healthy volunteers. The levels of D-amino acid oxidase (DAO), a D-amino acid-degrading enzyme, were evaluated to investigate the D-amino acid metabolism in brain tissue. The GBM mouse model was created by transplanting GBM cells into the brain to confirm whether gliomas affect blood and urine chiral amino acid profiles. We also assessed whether D-amino acids produced by GBM cells are involved in cell proliferation. D-asparagine (D-Asn) levels were higher and DAO expression was lower in glioma than in non-glioma tissues. Blood and urinary D-Asn levels were lower in patients with GBM than in healthy volunteers (p < 0.001), increasing after GBM removal (p < 0.05). Urinary D-Asn levels differentiated between healthy volunteers and patients with GBM (area under the curve: 0.93, sensitivity: 0.88, specificity: 0.92). GBM mouse model validated the decrease of urinary D-Asn in GBM. GBM cells used D-Asn for cell proliferation. Gliomas induce alterations in chiral amino acid profiles, affecting blood and urine levels. Urinary D-Asn emerges as a promising diagnostic biomarker for gliomas, reflecting tumor presence and severity.

Urinary D-amino acid profiles in cats with chronic kidney disease

Chronic kidney disease (CKD) is highly prevalent in domestic cats. This study aimed to compare urinary D-amino acid levels between control and CKD-afflicted cats as a novel noninvasive method for assessing CKD. Cats were divided into control and CKD stage II groups in accordance with the International Renal Interest Society guidelines. The urinary DL-amino acid levels of the cats were analyzed using chiral tandem liquid chromatography-tandem mass spectrometry, and their medical records were investigated. The CKD group had considerably lower urinary D-amino acid concentrations and enantiomeric ratios than the control group. The total urinary D-amino acid contents significantly correlated with blood parameters (creatinine and urea nitrogen). These findings may contribute towards the detection of CKD stage II in domestic cats.

Bifidobacterium bifidum alleviates adenine-induced acute kidney injury in mice by improving intestinal barrier function

Acute kidney injury (AKI) is a kind of critical kidney disease characterized by tubular injury, rapid decline of renal function and renal inflammation, with high clinical incidence. AKI has been shown to be associated with dysregulation of the gut microbiota and impaired intestinal barrier. Bifidobacterium has a positive impact on the treatment of many diseases. However, little is known about the role and mechanism of Bifidobacterium in AKI. Based on previous experiments, Bifidobacterium bifidum FL228.1 and FL276.1, which can relieve intestinal inflammation, and Bifidobacterium bifidum ZL.1, which has anti-inflammatory potential, were screened. This study aimed to investigate the effects of Bifidobacterium bifidum FL228.1, FL276.1 and ZL.1 on AKI, focusing on their role in the gut microbiota composition and intestinal barrier function. Our results showed that Bifidobacterium bifidum FL228.1, FL276.1 and ZL.1 effectively improved kidney function in mice with AKI by regulating the gut microbiota dysregulation, inhibiting intestinal inflammation and rebuilding the intestinal mucosal barrier. In addition, intervention with probiotics turned the gut microbiota disturbance caused by AKI into a normalized trend, reversed the adverse outcome of microbiota imbalance, and increased the abundance of potentially beneficial bacteria Bifidobacterium and Faecalibaculum. In summary, Bifidobacterium bifidum FL228.1, FL276.1, and ZL.1 alleviate adenine-induced AKI based on the gut-kidney axis. Although their mechanisms of action are different, their effect on alleviating AKI is almost the same.

Association between amoxicillin administration and outcomes in critically ill patients with acute kidney injury

Purpose

This study assessed the effect of amoxicillin on outcomes in intensive care unit (ICU) patients with acute kidney injury (AKI), focusing on mortality rates and acute kidney disease (AKD) occurrence.

Materials and Methods

We conducted a retrospective cohort analysis utilizing data from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database. The study included intensive care unit patients diagnosed with AKI to assess the effects of post-admission amoxicillin administration on 30-day and 90-day mortality rates and acute kidney disease incidence. We employed Cox proportional hazards models, propensity score matching, and inverse probability of treatment weighting to control for potential confounders.

Results

Among 24,650 AKI patients, 676 (2.7%) received amoxicillin. The results indicated significantly lower mortality rates at 30 days (hazard ratio [HR] 0.54, 95% confidence interval [CI] 0.42-0.69) and 90 days (HR 0.64, 95% CI 0.52-0.77) in the amoxicillin group compared to non-recipients. Additionally, amoxicillin administration was associated with a reduced incidence of AKD (HR 0.49, 95% CI 0.36-0.65) but resulted in a modestly increased length of hospital stay (mean difference [MD] 1.95 days, 95% CI 1.15-2.75). A dose‒response relationship was evident, with higher doses (>875 mg) further decreasing mortality rates. Subgroup analysis revealed consistent benefits across most patient groups.

Conclusion

Amoxicillin administration following ICU admission in patients with AKI was associated with improved survival rates and a lower incidence of AKD, highlighting its potential as a therapeutic measure for AKI management.

Effects of d-alanine Intake on Amino Acid Metabolism and Kidney Function in Healthy Adults: A Multicenter, Randomized Pilot Study

Background

d-alanine administration prevented kidney damage in a murine acute kidney injury model. Further data are needed on the influence of d-alanine on kidney function in humans.

Objective

This study investigated the effects of d-alanine intake on amino acid metabolism and kidney function in healthy volunteers.

Methods

This multicenter pilot study randomly assigned individuals from the general Japanese population to receive 3 g or 6 g of d-alanine intake per day for 7 d in a 1:1 ratio. The primary endpoint was the mean change in plasma and urine d-alanine levels from baseline to 7 d after intake. The secondary endpoints were mean changes in kidney function and other clinical factors. Safety was assessed by evaluating adverse events and clinical parameters.

Results

We randomly assigned 24 participants to the 3-g (n = 12) and 6-g d-alanine (n = 12) groups. The mean baseline estimated glomerular filtration rate (eGFR) was 73 mL/min/1.73 m2. The mean plasma d-alanine concentration increased from baseline by 77.5 ± 34.3 and 192.1 ± 80.9 nmol/mL in the 3-g and 6-g d-alanine groups (both p < 0.0001), respectively, in a dose-dependent manner (between-group difference: 114.6 nmol/mL; 95% CI: 62.1-167.2; P = 0.0002). A similar increase was observed for the urine d-alanine to creatinine ratio. The mean eGFR was elevated by 5.7 ± 8.8 mL/min/1.73 m2 in the 6-g d-alanine group (P = 0.045) but did not significantly change in the 3-g d-alanine group. Nonserious adverse events were reported in 11 participants.

Conclusions

d-alanine intake increased plasma and urine d-alanine levels and was well tolerated in participants with normal kidney function. These results will be useful in future trials investigating the effects of d-alanine intake on kidney disease progression in patients with chronic kidney disease.This trial was registered at the UMIN Clinical Trials Registry as UMIN000051466.

Investigating gut microbiota-blood and urine metabolite correlations in early sepsis-induced acute kidney injury: insights from targeted KEGG analyses

Background

The interplay between gut microbiota and metabolites in the early stages of sepsis-induced acute kidney injury (SA-AKI) is not yet clearly understood. This study explores the characteristics and interactions of gut microbiota, and blood and urinary metabolites in patients with SA-AKI.

Methods

Utilizing a prospective observational approach, we conducted comparative analyses of gut microbiota and metabolites via metabolomics and metagenomics in individuals diagnosed with SA-AKI compared to those without AKI (NCT06197828). Pearson correlations were used to identify associations between microbiota, metabolites, and clinical indicators. The Comprehensive Antibiotic Resistance Database was employed to detect antibiotic resistance genes (ARGs), while Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways informed on metabolic processes and microbial resistance patterns.

Results

Our study included analysis of four patients with SA-AKI and five without AKI. Significant disparities in bacterial composition were observed, illustrated by diversity indices (Shannon index: 2.0 ± 0.4 vs. 1.4 ± 0.6, P = 0.230; Simpson index: 0.8 ± 0.1 vs. 0.6 ± 0.2, P = 0.494) between the SA-AKI group and the non-AKI group. N6, N6, N6-Trimethyl-L-lysine was detected in both blood and urine metabolites, and also showed significant correlations with specific gut microbiota (Campylobacter hominis and Bacteroides caccae, R > 0, P < 0.05). Both blood and urine metabolites were enriched in the lysine degradation pathway. We also identified the citrate cycle (TCA cycle) as a KEGG pathway enriched in sets of differentially expressed ARGs in the gut microbiota, which exhibits an association with lysine degradation.

Conclusions

Significant differences in gut microbiota and metabolites were observed between the SA-AKI and non-AKI groups, uncovering potential biomarkers and metabolic changes linked to SA-AKI. The lysine degradation pathway may serve as a crucial link connecting gut microbiota and metabolites.

A fast and efficient liquid chromatography-tandem mass spectrometry method for measuring l- and d-amino acids in the urine of patients with immunoglobulin A nephropathy

Immunoglobulin nephropathy (IgAN) stands as the most prevalent primary glomerular nephropathy globally, typically diagnosed through an invasive renal biopsy. Emerging research suggests the significant involvement of chiral amino acids in kidney disease progression. This study introduces a nonderivative LC-tandem mass spectrometry approach, offering efficient separation outcomes within 15 min for identifying chiral amino acids in human urine samples. Subsequently, using this method, the analysis of l- and d-amino acids in the urine of both patients with IgAN and healthy individuals was conducted. Fourteen d-amino acids and 20 l-amino acids were identified in the urine samples obtained from 17 patients with IgAN and 21 healthy individuals. The results indicated notable variances in the concentrations of both l- and d-amino acids between the IgAN and healthy control groups. In contrast to the healthy group, the IgAN group exhibited higher mean urine concentrations of most l-amino acids and lower concentrations of d-amino acids. Furthermore, correlations between amino acids and clinical markers were investigated. These results propose a novel method for monitoring trace amino acids in urine samples and introduce a new concept for potential markers of IgAN.

Multifunctional enzymes related to amino acid metabolism in bacteria

In bacteria, d-amino acids are primarily synthesized from l-amino acids by amino acid racemases, but some bacteria use d-amino acid aminotransferases to synthesize d-amino acids. d-Amino acids are peptidoglycan components in the cell wall involved in several physiological processes, such as bacterial growth, biofilm dispersal, and peptidoglycan metabolism. Therefore, their metabolism and physiological roles have attracted increasing attention. Recently, we identified novel bacterial d-amino acid metabolic pathways, which involve amino acid racemases, with broad substrate specificity, as well as multifunctional enzymes with d-amino acid-metabolizing activity. Here, I review these multifunctional enzymes and their related d- and l-amino acid metabolic pathways in Escherichia coli and the hyperthermophile Thermotoga maritima.

Design and rationale for an open-label, randomized, controlled pilot trial to evaluate the changes in blood uremic toxins in patients with chronic kidney disease by dietary therapy with sake lees

BACKGROUND

Patients with chronic kidney disease (CKD) reportedly show dysbiosis, which is the imbalance of gut microbiome. Dysbiosis increases the uremic toxin level in the intestine, and uremic toxins transfer into the blood, causing CKD progression. Sake lees, a traditional Japanese fermented food, may help reduce uremic toxins by altering the gut microbiome. Additionally, D-alanine, which is present in sake lees, may have a renoprotective effect. The present pilot study aims to evaluate the effect of adding sake lees to the standard CKD dietary therapy in reducing blood uremic toxins.

METHODS

This pilot study is a single-center, open-label, randomized controlled trial. Twenty-four patients with CKD will be enrolled and allocated 1:1 to the intervention and control groups. The intervention group will receive standard CKD dietary therapy with an additional intake of 50 g of sake lees per day for 8 weeks, whereas the control group will only receive standard CKD dietary therapy. The primary endpoint is the change in serum indoxyl sulfate after 8 weeks. The secondary endpoint is the plasma D-alanine and fecal microbiome changes.

CONCLUSION

This pilot study provides insight into the development of a new diet focused on gut microbiome and D-amino acids in patients with CKD.

CLINICAL TRIAL REGISTRATION

This protocol was approved by the Clinical Trial Review Board of Kanazawa University Hospital on October 27, 2022 (2022-001 [6139]) and available to the public on the website of the Japan Registry of Clinical Trials on November 22, 2022 (jRCT1040220095).

Research progress in the role of gut microbiota in acute kidney injury

Acute kidney injury (AKI) remains a global public health problem with high incidence, high mortality rates, expensive medical costs, and limited treatment options. AKI can further progress to chronic kidney disease (CKD) and eventually end-stage renal disease (ESRD). Previous studies have shown that trauma, adverse drug reactions, surgery, and other factors are closely associated with AKI. With further in-depth exploration, the role of gut microbiota in AKI is gradually revealed. After AKI occurs, there are changes in the composition of gut microbiota, leading to disruption of the intestinal barrier, intestinal immune response, and bacterial translocation. Meanwhile, metabolites of gut microbiota can exacerbate the progression of AKI. Therefore, elucidating the specific mechanisms by which gut microbiota is involved in the occurrence and development of AKI can provide new insights from the perspective of intestinal microbiota for the prevention and treatment of AKI.

Protective effect of D‐Cys on renal function in mice with chronic kidney disease

MTT assay The chirality of amino acids affects their physiological functions. Recent studies uncovered potential physiological effects of D‐amino acids (D‐AAs) in nephropathy. Here, we explored the protective effects of exogenous D‐AAs on chronic kidney disease (CKD). First, by the 3‐(4,5‐dimethylthiazol‐2‐YI)‐2,5‐diphenyltetrazolium bromide (MTT) assay it was found that among the four D‐AAs studied (D‐glutamate (D‐Glu), D‐aspartic acid (D‐Asp) being the highest content in fermented yogurt, and D‐alanine (D‐Ala), D‐cysteine (D‐Cys), amino acids with renal protective potential), D‐Cys most significantly enhanced the viability of hypoxia‐induced injured HK‐2 cells, even better than its L‐analog, L‐Cys. Mitochondrial function analyzed by JC‐1 assay showed that 10 and 100 mM D‐Cys can significantly reduce the green/red fluorescence intensity by 16.1% (p < .001) and 17.6% (p < .001), respectively, in injured HK‐2 cells. Next, the in vivo protective effect of D‐Cys on adenine‐induced CKD mice was studied. The results indicated that the administration of D‐Cys decreased the serum creatinine and urea nitrogen levels by at least 15.5% and 11.8%, respectively, and significantly protected renal function in the CKD mice. Further analysis found that the administration of D‐Cys induced increased water intake in CKD mice, which is beneficial for the clearance of 2,8‐dihydroxyadenine, thereby attenuating the destruction of renal tissue structure. Moreover, H2S produced from D‐Cys resisted oxidative stress and inhibited inflammation, thus slowing down the process of renal fibrosis. In summary, this study verified the protective effect of D‐Cys on renal function and tissue structure in CKD mice, and propounded a new field of application for the utilization of D‐AAs.

d -Alanine Affects the Circadian Clock to Regulate Glucose Metabolism in the Kidney

Key Points

d -Alanine affects the circadian clock to regulate gluconeogenesis in the kidney. d -Alanine itself has a clear intrinsic circadian rhythm, which is regulated by urinary excretion, and acts on the circadian rhythm. d -Alanine is a signal activator for circadian rhythm and gluconeogenesis through circadian transcriptional network.

Background

The aberrant glucose circadian rhythm is associated with the pathogenesis of diabetes. Similar to glucose metabolism in the kidney and liver, d -alanine, a rare enantiomer of alanine, shows circadian alteration, although the effect of d- alanine on glucose metabolism has not been explored. Here, we show that d- alanine acts on the circadian clock and affects glucose metabolism in the kidney.

Methods

The blood and urinary levels of d -alanine in mice were measured using two-dimensional high-performance liquid chromatography system. Metabolic effects of d -alanine were analyzed in mice and in primary culture of kidney proximal tubular cells from mice. Behavioral and gene expression analyses of circadian rhythm were performed using mice bred under constant darkness.

Results

d- Alanine levels in blood exhibited a clear intrinsic circadian rhythm. Since this rhythm was regulated by the kidney through urinary excretion, we examined the effect of d -alanine on the kidney. In the kidney, d -alanine induced the expressions of genes involved in gluconeogenesis and circadian rhythm. Treatment of d- alanine mediated glucose production in mice. Ex vivo glucose production assay demonstrated that the treatment of d -alanine induced glucose production in primary culture of kidney proximal tubular cells, where d -amino acids are known to be reabsorbed, but not in that of liver cells. Gluconeogenetic effect of d -alanine has an intraday variation, and this effect was in part mediated through circadian transcriptional network. Under constant darkness, treatment of d- alanine normalized the circadian cycle of behavior and kidney gene expressions.

Conclusions

d- Alanine induces gluconeogenesis in the kidney and adjusts the period of the circadian clock. Normalization of circadian cycle by d -alanine may provide the therapeutic options for life style–related diseases and shift workers.

Biosynthesis and Degradation of Free D-Amino Acids and Their Physiological Roles in the Periphery and Endocrine Glands

It was long believed that D-amino acids were either unnatural isomers or laboratory artifacts, and that the important functions of amino acids were exerted only by L-amino acids. However, recent investigations have revealed a variety of D-amino acids in mammals that play important roles in physiological functions, including free D-serine and D-aspartate that are crucial in the central nervous system. The functions of several D-amino acids in the periphery and endocrine glands are also receiving increasing attention. Here, we present an overview of recent advances in elucidating the physiological roles of D-amino acids, especially in the periphery and endocrine glands.

Gut-derived 4-hydroxyphenylacetic acid attenuates sepsis-induced acute kidney injury by upregulating ARC to inhibit necroptosis

BACKGROUND

Studies have found that the plasma content of gut-derived 4-hydroxyphenylacetic acid (4-HPA) was significantly increased in septic patients. However, the mechanism of 4-HPA elevation during sepsis and its relationship with sepsis-induced acute kidney injury (SAKI) remain unclear.

METHODS

Cecal ligation and puncture (CLP) was performed in C57BL/6 mice to establish the SAKI animal model. Human renal tubular epithelial (HK-2) cells stimulated with lipopolysaccharide were used to establish the SAKI cell model. The widely targeted metabolomics was applied to analyze the renal metabolite changes after CLP. Proteomics was used to explore potential target proteins regulated by 4-HPA. The blood sample of clinical sepsis patients was collected to examine the 4-HPA content.

RESULTS

We found that renal gut-derived 4-HPA levels were significantly increased after CLP. The high permeability of intestinal barrier after sepsis contributed to the dramatic increase of renal 4-HPA. Intriguingly, we demonstrated that exogenous 4-HPA administration could further significantly reduce CLP-induced increases in serum creatinine, urea nitrogen, and cystatin C, inhibit renal pathological damage and apoptosis, and improve the survival of mice. Mechanistically, 4-HPA inhibited necroptosis in renal tubular epithelial cells by upregulating the protein expression of apoptosis repressor with caspase recruitment domain (ARC) and enhancing the interaction between ARC and receptor-interacting protein kinase 1 (RIPK1).

CONCLUSIONS

The increase of gut-derived 4-HPA in the kidney after sepsis could play a protective effect in SAKI by upregulating ARC to inhibit necroptosis.

The AKI-to-CKD Transition: The Role of Uremic Toxins

After acute kidney injury (AKI), renal function continues to deteriorate in some patients. In a pro-inflammatory and profibrotic environment, the proximal tubules are subject to maladaptive repair. In the AKI-to-CKD transition, impaired recovery from AKI reduces tubular and glomerular filtration and leads to chronic kidney disease (CKD). Reduced kidney secretion capacity is characterized by the plasma accumulation of biologically active molecules, referred to as uremic toxins (UTs). These toxins have a role in the development of neurological, cardiovascular, bone, and renal complications of CKD. However, UTs might also cause CKD as well as be the consequence. Recent studies have shown that these molecules accumulate early in AKI and contribute to the establishment of this pro-inflammatory and profibrotic environment in the kidney. The objective of the present work was to review the mechanisms of UT toxicity that potentially contribute to the AKI-to-CKD transition in each renal compartment.

D-Serine as a sensor and effector of the kidney

D-Serine, a rare enantiomer of serine, is a biomarker of kidney disease and function. The level of D-serine in the human body is precisely regulated through the urinary clearance of the kidney, and its clearance serves as a new measure of glomerular filtration rate with a lower bias than creatinine clearance. D-Serine also has a direct effect on the kidneys and mediates the cellular proliferation of tubular cells via mTOR signaling and induces kidney remodeling as a compensatory reaction to the loss of kidney mass. In living kidney donors, the removal of the kidney results in an increase in blood D-serine level, which in turn accelerates kidney remodeling and augments kidney clearance, thus reducing blood levels of D-serine. This feedback system strictly controls D-serine levels in the body. The function of D-serine as a biomarker and modulator of kidney function will be the basis of precision medicine for kidney diseases.

Gut microbiota and neonatal acute kidney injury biomarkers

One of the most frequent issues in newborns is acute kidney injury (AKI), which can lengthen their hospital stay or potentially raise their chance of dying. The gut-kidney axis establishes a bidirectional interplay between gut microbiota and kidney illness, particularly AKI, and demonstrates the importance of gut microbiota to host health. Since the ability to predict neonatal AKI using blood creatinine and urine output as evaluation parameters is somewhat constrained, a number of interesting biomarkers have been developed. There are few in-depth studies on the relationships between these neonatal AKI indicators and gut microbiota. In order to gain fresh insights into the gut-kidney axis of neonatal AKI, this review is based on the gut-kidney axis and describes relationships between gut microbiota and neonatal AKI biomarkers.

Probiotics in septic acute kidney injury, a double blind, randomized control trial

INTRODUCTION

During acute kidney injury (AKI) due to sepsis, the intestinal microbiota changes to dysbiosis, which affects the kidney function recovery (KFR) and amplifies the injury. Therefore, the administration of probiotics could improve dysbiosis and thereby increase the probability of KFR.

METHODS

In this double-blind clinical trial, patients with AKI associated with sepsis were randomized (1:1) to receive probiotics or placebo for 7 consecutive days, with the objectives of evaluate the effect on KFR, mortality, kidney replacement therapy (KRT), urea, urine volume, serum electrolytes and adverse events at day 7.

RESULTS

From February 2019 to March 2022, a total of 92 patients were randomized, 48 to the Probiotic and 44 to Placebo group. When comparing with placebo, those in the Probiotics did not observe a higher KFR (HR 0.93, 0.52-1.68, p = 0.81), nor was there a benefit in mortality at 6 months (95% CI 0.32-1.04, p = 0.06). With probiotics, urea values decreased significantly, an event not observed with placebo (from 154 to 80 mg/dl, p = 0.04 and from 130 to 109 mg/dl, p = 0.09, respectively). Urinary volume, need for KRT, electrolyte abnormalities, and adverse events were similar between groups. (ClinicalTrial.gov NCT03877081) (registered 03/15/2019).

CONCLUSION

In AKI related to sepsis, probiotics for 7 consecutive days did not increase the probability of KFR, nor did other variables related to clinical improvement, although they were safe.

Microbiome modulation after severe acute kidney injury accelerates functional recovery and decreases kidney fibrosis

Targeting gut microbiota has shown promise to prevent experimental acute kidney injury (AKI). However, this has not been studied in relation to accelerating recovery and preventing fibrosis. Here, we found that modifying gut microbiota with an antibiotic administered after severe ischemic kidney injury in mice, particularly with amoxicillin, accelerated recovery. These indices of recovery included increased glomerular filtration rate, diminution of kidney fibrosis, and reduction of kidney profibrotic gene expression. Amoxicillin was found to increase stool Alistipes, Odoribacter and Stomatobaculum species while significantly depleting Holdemanella and Anaeroplasma. Specifically, amoxicillin treatment reduced kidney CD4+T cells, interleukin (IL)-17 +CD4+T cells, and tumor necrosis factor-α double negative T cells while it increased CD8+T cells and PD1+CD8+T cells. Amoxicillin also increased gut lamina propria CD4+T cells while decreasing CD8+T and IL-17+CD4+T cells. Amoxicillin did not accelerate repair in germ-free or CD8-deficient mice, demonstrating microbiome and CD8+T lymphocytes dependence for amoxicillin protective effects. However, amoxicillin remained effective in CD4-deficient mice. Fecal microbiota transplantation from amoxicillin-treated to germ-free mice reduced kidney fibrosis and increased Foxp3+CD8+T cells. Amoxicillin pre-treatment protected mice against kidney bilateral ischemia reperfusion injury but not cisplatin-induced AKI. Thus, modification of gut bacteria with amoxicillin after severe ischemic AKI is a promising novel therapeutic approach to accelerate recovery of kidney function and mitigate the progression of AKI to chronic kidney disease.

Association Between Risperidone Use and Kidney Function Decline in Patients with Schizophrenia: A Retrospective Cohort Study

PURPOSE

Several D-amino acids have been shown to be protective against kidney injury in mice. Risperidone, a currently used atypical antipsychotic agent for schizophrenia, is also known to inhibit the activity of D-amino acid oxidase, which degrades certain D-amino acids. Based on the hypothesis that risperidone would prevent kidney disease progression, this study investigated the association between risperidone use and kidney function decline in patients with schizophrenia.

METHODS

This retrospective cohort study included patients who were diagnosed with schizophrenia and had data available from two or more serum creatinine measurements between April 1, 2010, and March 31, 2020. Patients who used risperidone for at least 30 days were included in the risperidone group, whereas those who had no record of risperidone use were included in the control group. Cox regression models were used to evaluate the risk for 40% decline in estimated glomerular filtration rate (eGFR) in patients treated with risperidone compared to that in the control group.

FINDINGS

Overall, 212 patients used risperidone and 1468 patients had no record of risperidone use. The mean age was 55 years, 759 (45%) of the patients were male, and the mean eGFR at baseline was 88 mL/min/1.73 m2. The mean age in the risperidone group was less than that in the control group (52 vs 56 years); other baseline characteristics were comparable between the two groups. During a mean follow-up of 1.6 years, 267 patients (16%) had a 40% eGFR decline. The incidence rate of 40% eGFR decline was lower in the risperidone group than in the control group (60 vs 104 per 1000 person-years). After adjustment for baseline age, sex, and eGFR, risperidone use was associated with a decreased risk for 40% eGFR decline (hazard ratio = 0.54; 95% CI, 0.33-0.87; P = 0.01).

IMPLICATIONS

Risperidone use may be associated with decreased risk for kidney function decline in patients with schizophrenia. Further studies are warranted to validate these findings.

Analysis of D-amino acid in Japanese post-fermented tea, Ishizuchi-kurocha

The D-amino acid content of Ishizuchi-kurocha, a post-fermented tea produced in Ehime, Japan, was measured. Ishizuchi-kurocha mainly contains D-glutamic acid and D-alanine, but it also contains a small amount of D-aspartic acid. Two types of lactic acid bacteria, Lactiplantibacillus plantarum and Levilactobacillus brevis, are the main species involved in lactic acid fermentation during the tea fermentation process. Therefore, the D-amino acid-producing abilities of strains of these two species isolated from Ishizuchi-kurocha were examined. Specifically, the production of D-aspartic acid, D-alanine, and D-glutamic acid by L. brevis and L. plantarum strains was observed. The amount of D-aspartic acid produced by L. plantarum was low. D-glutamine was detected in culture supernatant but not in bacterial cells. D-arginine was detected in bacterial cells of the L. plantarum strains but not in the culture supernatant. Both the L. brevis and L. plantarum strains possessed at least three kinds of putative racemase genes: alanine racemase, glutamate racemase, and aspartate racemase. However, their expression and enzyme activity remain unknown. L. plantarum and L. brevis could play an important role in the production of D-amino acids in Ishizuchi-kurocha. In fact, Ishizuchi-kurocha is expected to possess the effective physiological activities of D-amino acids.

Metabolomic interplay between gut microbiome and plasma metabolome in cardiac surgery-associated acute kidney injury

RATIONALE

Cardiac surgery-associated acute kidney injury (CSA-AKI) is a prevalent complication of cardiac surgery, which may be associated with a great risk of developing chronic kidney disease and mortality. This study aimed to investigate the possible links between gut microbiota metabolism and CSA-AKI.

METHODS

A prospective cohort of patients who underwent cardiac surgery was continuously recruited, who were further divided into CSA-AKI group and Non-AKI group based on clinical outcomes. Their faecal and plasma samples were collected before surgery and were separately analysed by nontargeted and targeted metabolomics. The differential metabolites related to CSA-AKI were screened out using statistical methods, and altered metabolic pathways were determined by examining the Kyoto Encyclopedia of Genes and Genomes database.

RESULTS

Nearly 1000 faecal metabolites were detected through high-resolution mass spectrometry (MS) and bioinformatics at high and mid confidence levels, and 49 differential metabolites at high confidence level may perform essential biological functions and provide potential diagnostic indicators. Compared with the Non-AKI group, the patients in the CSA-AKI group displayed dramatic changes in gut microbiota metabolism, including amino acid metabolism, nicotinate and nicotinamide metabolism, purine metabolism and ATP-binding cassette (ABC) transporters. Meanwhile, 188 plasma metabolites were identified and quantified by tandem MS, and 34 differential plasma metabolites were screened out between the two groups using univariate statistical analysis. These differential plasma metabolites were primarily enriched in the following metabolic pathways: sulphur metabolism, amino acid biosynthesis, tryptophan metabolism and ABC transporters. Furthermore, the content of indole metabolites in the faecal and plasma samples of the CSA-AKI group was higher than that of the Non-AKI group.

CONCLUSIONS

Patients with CSA-AKI may have dysbiosis of their intestinal microbiota and metabolic abnormalities in their gut system before cardiac surgery. Thus, some metabolites and related metabolic pathways may be potential biomarkers and new therapeutic targets for the disease.

Gut Protective Effect from D-Methionine or Butyric Acid against DSS and Carrageenan-Induced Ulcerative Colitis

Microbiome dysbiosis resulting in altered metabolite profiles may be associated with certain diseases, including inflammatory bowel diseases (IBD), which are characterized by active intestinal inflammation. Several studies have indicated the beneficial anti-inflammatory effect of metabolites from gut microbiota, such as short-chain fatty acids (SCFAs) and/or D-amino acids in IBD therapy, through orally administered dietary supplements. In the present study, the potential gut protective effects of d-methionine (D-Met) and/or butyric acid (BA) have been investigated in an IBD mouse model. We have also built an IBD mouse model, which was cost-effectively induced with low molecular weight DSS and kappa-carrageenan. Our findings revealed that D-Met and/or BA supplementation resulted in the attenuation of the disease condition as well as the suppression of several inflammation-related gene expressions in the IBD mouse model. The data shown here may suggest a promising therapeutic potential for improving symptoms of gut inflammation with an impact on IBD therapy. However, molecular metabolisms need to be further explored.

d-Serine agonism of GluN1-GluN3 NMDA receptors regulates the activity of enteric neurons and coordinates gut motility

The enteric nervous system (ENS) is a complex network of diverse molecularly defined classes of neurons embedded in the gastrointestinal wall and responsible for controlling the major functions of the gut. As in the central nervous system, the vast array of ENS neurons is interconnected by chemical synapses. Despite several studies reporting the expression of ionotropic glutamate receptors in the ENS, their roles in the gut remain elusive. Here, by using an array of immunohistochemistry, molecular profiling and functional assays, we uncover a new role for d-serine (d-Ser) and non-conventional GluN1-GluN3 N-methyl d-aspartate receptors (NMDARs) in regulating ENS functions. We demonstrate that d-Ser is produced by serine racemase (SR) expressed in enteric neurons. By using both in situ patch clamp recording and calcium imaging, we show that d-Ser alone acts as an excitatory neurotransmitter in the ENS independently of the conventional GluN1-GluN2 NMDARs. Instead, d-Ser directly gates the non-conventional GluN1-GluN3 NMDARs in enteric neurons from both mouse and guinea-pig. Pharmacological inhibition or potentiation of GluN1-GluN3 NMDARs had opposite effects on mouse colonic motor activities, while genetically driven loss of SR impairs gut transit and fluid content of pellet output. Our results demonstrate the existence of native GluN1-GluN3 NMDARs in enteric neurons and open new perspectives on the exploration of excitatory d-Ser receptors in gut function and diseases.

Acute kidney injury and distant organ dysfunction-network system analysis

Acute kidney injury (AKI) occurs in about half of critically ill patients and associates with high in-hospital mortality, increased long-term mortality post-discharge and subsequent progression to chronic kidney disease. Numerous clinical studies have shown that AKI is often complicated by dysfunction of distant organs, which is a cause of the high mortality associated with AKI. Experimental studies have elucidated many mechanisms of AKI-induced distant organ injury, which include inflammatory cytokines, oxidative stress and immune responses. This review will provide an update on evidence of organ crosstalk and potential therapeutics for AKI-induced organ injuries, and present the new concept of a systemic organ network to balance homeostasis and inflammation that goes beyond kidney-crosstalk with a single distant organ.

Evaluation of the contribution of gut microbiome dysbiosis to cardiac surgery-associated acute kidney injury by comparative metagenome analysis

Introduction

Cardiac surgery-associated acute kidney injury (CSA-AKI) is a common hospital-acquired AKI that carries a grave disease burden. Recently, gut-kidney crosstalk has greatly changed our understanding of the pathogenesis of kidney diseases. However, the relationship between gut microbial dysbiosis and CSA-AKI remains unclear. The purpose of this study was to investigate the possible contributions of gut microbiota alterations in CSA-AKI patients

Methods

Patients undergoing cardiac surgery were enrolled and divided into acute kidney injury (AKI) and Non-AKI groups. Faecal samples were collected before the operation. Shotgun metagenomic sequencing was performed to identify the taxonomic composition of the intestinal microbiome. All groups were statistically compared with alpha- and beta-diversity analysis, and linear discriminant analysis effect size (LEfSe) analysis was performed.

Results

A total of 70 individuals comprising 35 AKI and 35 Non_AKI were enrolled in the study. There was no significant difference between the AKI and Non_AKI groups with respect to the alpha-and beta-diversity of the Shannon index, Simpson or Chao1 index values except with respect to functional pathways (p &lt; 0.05). However, the relative abundance of top 10 gut microbiota in CSA-AKI was different from the Non_AKI group. Interestingly, both LEfSe and multivariate analysis confirmed that the species Escherichia coli, Rothia mucilaginosa, and Clostridium_innocuum were associated with CSA-AKI. Moreover, correlation heat map indicated that altered pathways and disrupted function could be attributed to disturbances of gut microbiota involving Escherichia_coli.

Conclusion

Dysbiosis of the intestinal microbiota in preoperative stool affects susceptibility to CSA-AKI, indicating the crucial role of key microbial players in the development of CSA-AKI. This work provides valuable knowledge for further study of the contribution of gut microbiota in CSA-AKI.

Intestinal microbiome diversity of diabetic and non-diabetic kidney disease: Current status and future perspective

A significant portion of the health burden of diabetic kidney disease (DKD) is caused by both type 1 and type 2 diabetes which leads to morbidity and mortality globally. It is one of the most common diabetic complications characterized by loss of renal function with high prevalence, often leading to acute kidney disease (AKD). Inflammation triggered by gut microbiota is commonly associated with the development of DKD. Interactions between the gut microbiota and the host are correlated in maintaining metabolic and inflammatory homeostasis. However, the fundamental processes through which the gut microbiota affects the onset and progression of DKD are mainly unknown. In this narrative review, we summarised the potential role of the gut microbiome, their pathogenicity between diabetic and non-diabetic kidney disease (NDKD), and their impact on host immunity. A well-established association has already been seen between gut microbiota, diabetes and kidney disease. The gut-kidney interrelationship is confirmed by mounting evidence linking gut dysbiosis to DKD, however, it is still unclear what is the real cause of gut dysbiosis, the development of DKD, and its progression. In addition, we also try to distinguish novel biomarkers for early detection of DKD and the possible therapies that can be used to regulate the gut microbiota and improve the host immune response. This early detection and new therapies will help clinicians for better management of the disease and help improve patient outcomes.

The Molecular Mechanism and Therapeutic Strategy of Cardiorenal Syndrome Type 3

Cardiorenal syndrome type 3 (CRS3) is defined as acute kidney injury (AKI)-induced acute cardiac dysfunction, characterized by high morbidity and mortality. CRS3 often occurs in elderly patients with AKI who need intensive care. Approximately 70% of AKI patients develop into CRS3. CRS3 may also progress towards chronic kidney disease (CKD) and chronic cardiovascular disease (CVD). However, there is currently no effective treatment. Although the major intermediate factors that can mediate cardiac dysfunction remain elusive, recent studies have summarized the AKI biomarkers, identified direct mechanisms, including mitochondrial dysfunction, inflammation, oxidative stress, apoptosis and activation of the sympathetic nervous system (SNS) and renin-angiotensin-aldosterone system (RAAS), inflammasome, as well as indirect mechanisms such as fluid overload, electrolyte imbalances, acidemia and uremic toxins, which are involved in the pathophysiological changes of CRS3. This study reviews the main pathological characteristics, underlying molecular mechanisms, and potential therapeutic strategies of CRS3. Mitochondrial dysfunction and inflammatory factors have been identified as the key initiators and abnormal links between the impaired heart and kidney, which contribute to the formation of a vicious circle, ultimately accelerating the progression of CRS3. Therefore, targeting mitochondrial dysfunction, antioxidants, Klotho, melatonin, gene therapy, stem cells, exosomes, nanodrugs, intestinal microbiota and Traditional Chinese Medicine may serve as promising therapeutic approaches against CRS3.

Fecal Microbiota Transplantation in Reducing Uremic Toxins Accumulation in Kidney Disease: Current Understanding and Future Perspectives

During the past decades, the gut microbiome emerged as a key player in kidney disease. Dysbiosis-related uremic toxins together with pro-inflammatory mediators are the main factors in a deteriorating kidney function. The toxicity of uremic compounds has been well-documented in a plethora of pathophysiological mechanisms in kidney disease, such as cardiovascular injury (CVI), metabolic dysfunction, and inflammation. Accumulating data on the detrimental effect of uremic solutes in kidney disease supported the development of many strategies to restore eubiosis. Fecal microbiota transplantation (FMT) spread as an encouraging treatment for different dysbiosis-associated disorders. In this scenario, flourishing studies indicate that fecal transplantation could represent a novel treatment to reduce the uremic toxins accumulation. Here, we present the state-of-the-art concerning the application of FMT on kidney disease to restore eubiosis and reverse the retention of uremic toxins.

Ion channels and channelopathies in glomeruli

An essential step in renal function entails the formation of an ultrafiltrate that is delivered to the renal tubules for subsequent processing. This process, known as glomerular filtration, is controlled by intrinsic regulatory systems and by paracrine, neuronal, and endocrine signals that converge onto glomerular cells. In addition, the characteristics of glomerular fluid flow, such as the glomerular filtration rate and the glomerular filtration fraction, play an important role in determining blood flow to the rest of the kidney. Consequently, disease processes that initially affect glomeruli are the most likely to lead to end-stage kidney failure. The cells that comprise the glomerular filter, especially podocytes and mesangial cells, express many different types of ion channels that regulate intrinsic aspects of cell function and cellular responses to the local environment, such as changes in glomerular capillary pressure. Dysregulation of glomerular ion channels, such as changes in TRPC6, can lead to devastating glomerular diseases, and a number of channels, including TRPC6, TRPC5, and various ionotropic receptors, are promising targets for drug development. This review discusses glomerular structure and glomerular disease processes. It also describes the types of plasma membrane ion channels that have been identified in glomerular cells, the physiological and pathophysiological contexts in which they operate, and the pathways by which they are regulated and dysregulated. The contributions of these channels to glomerular disease processes, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, as well as the development of drugs that target these channels are also discussed.

Increased levels of oral Streptococcus-derived D-alanine in patients with chronic kidney disease and diabetes mellitus

The number of patients on hemodialysis is increasing globally; diabetes mellitus (DM) complications is the major cause of hemodialysis in patients with chronic kidney disease (CKD). The D-amino acid (AA) profile is altered in patients with CKD; however, it has not been studied in patients with CKD and DM. Furthermore, bacteria responsible for altering the D-AA profile are not well understood. Therefore, we examined the D-AA profiles and associated bacteria in patients with CKD, with and without DM. We enrolled 12 healthy controls and 54 patients with CKD, with and without DM, and determined their salivary, stool, plasma, and urine chiral AA levels using two-dimensional high-performance liquid chromatography. We performed 16S rRNA gene sequencing analysis of the oral and gut microbiota to determine the association between the abundance of bacterial species and D-AA levels. Plasma D-alanine and D-serine levels were higher in patients with CKD than in healthy adults (p < 0.01), and plasma D-alanine levels were higher in patients with CKD and DM than in those without DM. The abundance of salivary Streptococcus, which produced D-alanine, increased in patients with CKD and DM and was positively correlated with plasma D-alanine levels. Patients with CKD and DM had unique oral microbiota and D-alanine profiles. Plasma D-alanine is a potential biomarker for patients with CKD and DM.

The central role of the gut in intensive care

Critically ill patients undergo early impairment of their gut microbiota (GM) due to routine antibiotic therapies and other environmental factors leading to intestinal dysbiosis. The GM establishes connections with the rest of the human body along several axes representing critical inter-organ crosstalks that, once disrupted, play a major role in the pathophysiology of numerous diseases and their complications. Key players in this communication are GM metabolites such as short-chain fatty acids and bile acids, neurotransmitters, hormones, interleukins, and toxins. Intensivists juggle at the crossroad of multiple connections between the intestine and the rest of the body. Harnessing the GM in ICU could improve the management of several challenges, such as infections, traumatic brain injury, heart failure, kidney injury, and liver dysfunction. The study of molecular pathways affected by the GM in different clinical conditions is still at an early stage, and evidence in critically ill patients is lacking. This review aims to describe dysbiosis in critical illness and provide intensivists with a perspective on the potential as adjuvant strategies (e.g., nutrition, probiotics, prebiotics and synbiotics supplementation, adsorbent charcoal, beta-lactamase, and fecal microbiota transplantation) to modulate the GM in ICU patients and attempt to restore eubiosis.