Butyrate promotes kidney resilience through a coordinated kidney protective response in tubular cells.

Acute kidney injury (AKI) is common in hospitalized patients and increases short-term and long-term mortality. Treatment options for AKI are limited. Gut microbiota products such as the short-chain fatty acid butyrate have anti-inflammatory actions that may protect tissues, including the kidney, from injury. However, the molecular mechanisms of tissue protection by butyrate are poorly understood. Treatment with oral butyrate for two weeks prior to folic acid-induced AKI and during AKI improved kidney function and decreased tubular injury and kidney inflammation while stopping butyrate before AKI was not protective. Continuous butyrate preserved the expression of kidney protective factors such as Klotho, PGC-1α and Nlrp6 which were otherwise downregulated. In cultured tubular cells, butyrate blunted the maladaptive tubular cell response to a proinflammatory milieu, preserving the expression of kidney protective factors. Kidney protection afforded by this continuous butyrate schedule was confirmed in a second model of nephrotoxic AKI, cisplatin nephrotoxicity, where the expression of kidney protective factors was also preserved. To assess the contribution of preservation of kidney protective factors to kidney resilience, recombinant Klotho was administered to mice with cisplatin-AKI and shown to preserve the expression of PGC-1α and Nlrp6, decrease kidney inflammation and protect from AKI. In conclusion, butyrate promotes kidney resilience to AKI and decreases inflammation by preventing the downregulation of kidney protective genes such as Klotho. This information may be relevant to optimize antibiotic management during hospitalization.

Interaction of Fabry Disease and Diabetes Mellitus: Suboptimal Recruitment of Kidney Protective Factors.

Fabry disease is a lysosomal disease characterized by globotriaosylceramide (Gb3) accumulation. It may coexist with diabetes mellitus and both cause potentially lethal kidney end-organ damage. However, there is little information on their interaction with kidney disease. We have addressed the interaction between Fabry disease and diabetes in data mining of human kidney transcriptomics databases and in Fabry (Gla-/-) and wild type mice with or without streptozotocin-induced diabetes. Data mining was consistent with differential expression of genes encoding enzymes from the Gb3 metabolic pathway in human diabetic kidney disease, including upregulation of UGCG, the gene encoding the upstream and rate-limiting enzyme glucosyl ceramide synthase. Diabetic Fabry mice displayed the most severe kidney infiltration by F4/80+ macrophages, and a lower kidney expression of kidney protective genes (Pgc1α and Tfeb) than diabetic wild type mice, without a further increase in kidney fibrosis. Moreover, only diabetic Fabry mice developed kidney insufficiency and these mice with kidney insufficiency had a high expression of Ugcg. In conclusion, we found evidence of interaction between diabetes and Fabry disease that may increase the severity of the kidney phenotype through modulation of the Gb3 synthesis pathway and downregulation of kidney protective genes.

The transcription factor Fosl1 preserves Klotho expression and protects from acute kidney injury.

Increased expression of AP-1 transcription factor components has been reported in acute kidney injury (AKI). However, the role of specific components, such as Fosl1, in tubular cells or AKI is unknown. Upstream regulator analysis of murine nephrotoxic AKI transcriptomics identified AP-1 as highly upregulated. Among AP-1 canonical components, Fosl1 was found to be upregulated in two transcriptomics datasets from nephrotoxic murine AKI induced by folic acid or cisplatin and from proximal tubular cells exposed to TWEAK, a cytokine mediator of AKI. Fosl1 was minimally expressed in the kidneys of control uninjured mice. Increased Fosl1 protein was localized to proximal tubular cell nuclei in AKI. In human AKI, FOSL1 was found present in proximal tubular cells in kidney sections and in urine along with increased urinary FOSL1 mRNA. Selective Fosl1 deficiency in proximal tubular cells (Fosl1Δtub) increased the severity of murine cisplatin- or folate-induced AKI as characterized by lower kidney function, more severe kidney inflammation and Klotho downregulation. Indeed, elevated AP-1 activity was observed after cisplatin-induced AKI in Fosl1Δtub mice compared to wild-type mice. More severe Klotho downregulation preceded more severe kidney dysfunction. The Klotho promoter was enriched in Fosl1 binding sites and Fosl1 bound to the Klotho promoter in cisplatin-AKI. In cultured proximal tubular cells, Fosl1 targeting increased the proinflammatory response and downregulated Klotho. In vivo, recombinant Klotho administration protected Fosl1Δtub mice from cisplatin-AKI. Thus, increased proximal tubular Fosl1 expression during AKI is an adaptive response, preserves Klotho, and limits the severity of tubular cell injury and AKI.

Probiotics for kidney disease.

Diet has long been known to influence the course of chronic kidney disease (CKD) and may even result in acute kidney injury (AKI). Diet may influence kidney disease through a direct impact of specific nutrients on the human body through modulation of the gut microbiota composition or through metabolites generated by the gut microbiota from ingested nutrients. The potential for interaction between diet, microbiota and CKD has fueled research into interventions aimed at modifying the microbiota to treat CKD. These interventions may include diet, probiotics, prebiotics, fecal microbiota transplant and other interventions that modulate the microbiota and its metabolome. A recent report identified Lactobacillus casei Zhang from traditional Chinese koumiss as a probiotic that may protect mice from AKI and CKD and slow CKD progression in humans. Potential mechanisms of action include modulation of the gut microbiota and increased availability of short-chain fatty acids with anti-inflammatory properties and of nicotinamide. However, the clinical relevance needs validation in large well-designed clinical trials.

Tubular Mitochondrial Dysfunction, Oxidative Stress, and Progression of Chronic Kidney Disease.

Acute kidney injury (AKI) and chronic kidney disease (CKD) are interconnected conditions, and CKD is projected to become the fifth leading global cause of death by 2040. New therapeutic approaches are needed. Mitochondrial dysfunction and oxidative stress have emerged as drivers of kidney injury in acute and chronic settings, promoting the AKI-to-CKD transition. In this work, we review the role of mitochondrial dysfunction and oxidative stress in AKI and CKD progression and discuss novel therapeutic approaches. Specifically, evidence for mitochondrial dysfunction in diverse models of AKI (nephrotoxicity, cytokine storm, and ischemia-reperfusion injury) and CKD (diabetic kidney disease, glomerulopathies) is discussed; the clinical implications of novel information on the key role of mitochondria-related transcriptional regulators peroxisome proliferator-activated receptor gamma coactivator 1-alpha, transcription factor EB (PGC-1α, TFEB), and carnitine palmitoyl-transferase 1A (CPT1A) in kidney disease are addressed; the current status of the clinical development of therapeutic approaches targeting mitochondria are updated; and barriers to the clinical development of mitochondria-targeted interventions are discussed, including the lack of clinical diagnostic tests that allow us to categorize the baseline renal mitochondrial dysfunction/mitochondrial oxidative stress and to monitor its response to therapeutic intervention. Finally, key milestones for further research are proposed.

Bone Marrow-Derived RIPK3 Mediates Kidney Inflammation in Acute Kidney Injury.

BACKGROUND: Receptor-interacting protein kinase 3 (RIPK3), a component of necroptosis pathways, may have an independent role in inflammation. It has been unclear which RIPK3-expressing cells are responsible for the anti-inflammatory effect of overall Ripk3 deficiency and whether Ripk3 deficiency protects against kidney inflammation occurring in the absence of tubular cell death. METHODS: We used chimeric mice with bone marrow from wild-type and Ripk3-knockout mice to explore RIPK3's contribution to kidney inflammation in the presence of folic acid-induced acute kidney injury AKI (FA-AKI) or absence of AKI and kidney cell death (as seen in systemic administration of the cytokine TNF-like weak inducer of apoptosis [TWEAK]). RESULTS: Tubular and interstitial cell RIPK3 expressions were increased in murine AKI. Ripk3 deficiency decreased NF-κB activation and kidney inflammation in FA-AKI but did not prevent kidney failure. In the chimeric mice, RIPK3-expressing bone marrow-derived cells were required for early inflammation in FA-AKI. The NLRP3 inflammasome was not involved in RIPK3's proinflammatory effect. Systemic TWEAK administration induced kidney inflammation in wild-type but not Ripk3-deficient mice. In cell cultures, TWEAK increased RIPK3 expression in bone marrow-derived macrophages and tubular cells. RIPK3 mediated TWEAK-induced NF-κB activation and inflammatory responses in bone marrow-derived macrophages and dendritic cells and in Jurkat T cells; however, in tubular cells, RIPK3 mediated only TWEAK-induced Il-6 expression. Furthermore, conditioned media from TWEAK-exposed wild-type macrophages, but not from Ripk3-deficient macrophages, promoted proinflammatory responses in cultured tubular cells. CONCLUSIONS: RIPK3 mediates kidney inflammation independently from tubular cell death. Specific targeting of bone marrow-derived RIPK3 may limit kidney inflammation without the potential adverse effects of systemic RIPK3 targeting.

Urinary Cyclophilin A as Marker of Tubular Cell Death and Kidney Injury.

Background: Despite the term acute kidney injury (AKI), clinical biomarkers for AKI reflect function rather than injury and independent markers of injury are needed. Tubular cell death, including necroptotic cell death, is a key feature of AKI. Cyclophilin A (CypA) is an intracellular protein that has been reported to be released during necroptosis. We have now explored CypA as a potential marker for kidney injury in cultured tubular cells and in clinical settings of ischemia-reperfusion injury (IRI), characterized by limitations of current diagnostic criteria for AKI. Methods: CypA was analyzed in cultured human and murine proximal tubular epithelial cells exposed to chemical hypoxia, hypoxia/reoxygenation (H/R) or other cell death (apoptosis, necroptosis, ferroptosis) inducers. Urinary levels of CypA (uCypA) were analyzed in patients after nephron sparing surgery (NSS) in which the contralateral kidney is not disturbed and kidney grafts with initial function. Results: Intracellular CypA remained unchanged while supernatant CypA increased in parallel to cell death induction. uCypA levels were higher in NSS patients with renal artery clamping (that is, with NSS-IRI) than in no clamping (NSS-no IRI), and in kidney transplantation (KT) recipients (KT-IRI) even in the presence of preserved or improving kidney function, while this was not the case for urinary Neutrophil gelatinase-associated lipocalin (NGAL). Furthermore, higher uCypA levels in NSS patients were associated with longer surgery duration and the incidence of AKI increased from 10% when using serum creatinine (sCr) or urinary output criteria to 36% when using high uCypA levels in NNS clamping patients. Conclusions: CypA is released by kidney tubular cells during different forms of cell death, and uCypA increased during IRI-induced clinical kidney injury independently from kidney function parameters. Thus, uCypA is a potential biomarker of kidney injury, which is independent from decreased kidney function.

A multicenter blinded preclinical randomized controlled trial on Jak1/2 inhibition in MRL/MpJ-Faslpr mice with proliferative lupus nephritis predicts low effect size.

Data reproducibility and single-center bias are concerns in preclinical research and compromise translation from animal to human. Multicenter preclinical randomized controlled trials (pRCT) may reduce the gap between experimental studies and RCT and improve the predictability of results, for example Jak1/2 inhibition in lupus nephritis. To evaluate this, we conducted the first pRCT in the kidney domain at two Spanish and two German academic sites. Eligible MRL/MpJ-Faslpr mice (female, age13-14 weeks, stress scores of less than two and no visible tumor or signs of infection) were equally randomized to either oral treatment with the Jak1/2 inhibitor baricitinib or vehicle for four weeks. Central blinded histology analysis was performed at an independent fifth site. The primary endpoint was the urinary protein/creatinine ratio. Baricitinib treatment did not significantly affect proteinuria, histological markers of activity and chronicity, or the glomerular filtration rate but significantly improved plasma autoantibody levels and lymphadenopathy. Data heterogeneity was noted across the different centers referring in part to phenotype differences between MRL/MpJ-Faslpr mice bred at different sites, mimicking well patient phenotype diversity in lupus trials. Multicenter pRCT can overcome single-center bias at the cost of increasing variability and reducing effect size. Thus, our pRCT predicts a low effect size of baricitinib treatment on human lupus nephritis in heterogeneous study populations.

Ferroptosis and kidney disease / Ferroptosis y nefropatía

Cell death is a finely regulated process occurring through different pathways. Regulated cell death, either through apoptosis or regulated necrosis offers the possibility of therapeutic intervention. Necroptosis and ferroptosis are among the best studied forms of regulated necrosis in the context of kidney disease. We now review the current evidence supporting a role for ferroptosis in kidney disease and the implications of this knowledge for the design of novel therapeutic strategies. Ferroptosis is defined functionally, as a cell modality characterized by peroxidation of certain lipids, constitutively suppressed by GPX4 and inhibited by iron chelators and lipophilic antioxidants. There is functional evidence of the involvement of ferroptosis in diverse forms of kidneys disease. In a well characterized nephrotoxic acute kidney injury model, ferroptosis caused an initial wave of death, triggering an inflammatory response that in turn promoted necroptotic cell death that perpetuated kidney dysfunction. This suggests that ferroptosis inhibitors may be explored as prophylactic agents in clinical nephrotoxicity or ischemia-reperfusion injury such as during kidney transplantation. Transplantation offers the unique opportunity of using anti-ferroptosis agent ex vivo, thus avoiding bioavailability and in vivo pharmacokinetics and pharmacodynamics issues

La muerte celular es un proceso minuciosamente regulado que se desarrolla a través de diferentes vías. La muerte celular regulada, ya sea mediante apoptosis o necrosis regulada, ofrece la posibilidad de introducir una intervención terapéutica. La necroptosis y la ferroptosis se encuentran entre las formas mejor estudiadas de necrosis regulada en el contexto de la nefropatía. Revisamos los datos actuales que avalan que la ferroptosis desempeña una función en la nefropatía y las repercusiones que tiene este conocimiento en el diseño de nuevas estrategias terapéuticas. La ferroptosis se define de forma funcional como una modalidad celular caracterizada por la peroxidación de ciertos lípidos, constitutivamente suprimida por GPX4 e inhibida por quelantes férricos y antioxidantes lipofílicos. Existen datos probatorios funcionales de la implicación de la ferroptosis en diversas formas de nefropatía. En un modelo de lesión renal aguda nefrotóxica bien caracterizado, la ferroptosis provocó una ola inicial de muerte, la cual desencadenó una respuesta inflamatoria que a su vez promovió la muerte celular necroptótica que perpetuó la disfunción renal. Esto sugiere que los inhibidores de la ferroptosis pueden explorarse como agentes profilácticos en la nefrotoxicidad clínica o en la lesión por isquemia-reperfusión, como durante un trasplante de riñón. Los trasplantes ofrecen una oportunidad única para el uso de agentes inhibidores de la ferroptosis ex vivo, con lo que se evitarían los problemas de biodisponibilidad y los problemas de farmacocinética y farmacodinámica in vivo

Ferroptosis and kidney disease.

Cell death is a finely regulated process occurring through different pathways. Regulated cell death, either through apoptosis or regulated necrosis offers the possibility of therapeutic intervention. Necroptosis and ferroptosis are among the best studied forms of regulated necrosis in the context of kidney disease. We now review the current evidence supporting a role for ferroptosis in kidney disease and the implications of this knowledge for the design of novel therapeutic strategies. Ferroptosis is defined functionally, as a cell modality characterized by peroxidation of certain lipids, constitutively suppressed by GPX4 and inhibited by iron chelators and lipophilic antioxidants. There is functional evidence of the involvement of ferroptosis in diverse forms of kidneys disease. In a well characterized nephrotoxic acute kidney injury model, ferroptosis caused an initial wave of death, triggering an inflammatory response that in turn promoted necroptotic cell death that perpetuated kidney dysfunction. This suggests that ferroptosis inhibitors may be explored as prophylactic agents in clinical nephrotoxicity or ischemia-reperfusion injury such as during kidney transplantation. Transplantation offers the unique opportunity of using anti-ferroptosis agent ex vivo, thus avoiding bioavailability and in vivo pharmacokinetics and pharmacodynamics issues.

Megalin/lipoprotein receptor-related protein 2 autoimmunity and kidney disease.

In this issue of Clinical Kidney Journal, Gamayo et al. describe two cases of anti-low-density lipoprotein receptor-related protein 2 (LRP2) nephropathy. This is a recently described entity that has features of both tubulointerstitial disease and segmental membranous nephropathy. The originality of the present report consists of the association of a disease thought to be rare (only 13 in prior described patients, 11 in the past year) with B-cell lymphoproliferative disease. Together with the finding of a third case among 224 elderly patients studied, this raises the issue of the underdiagnoses of LRP2 nephropathy, on top of the potential association to B-cell malignancy. We now put these findings in context within the wider frame of autoimmunity against megalin/LRP2 and related antigens such as Fx1A and CD69.

Epigenetic Modifiers as Potential Therapeutic Targets in Diabetic Kidney Disease.

Diabetic kidney disease is one of the fastest growing causes of death worldwide. Epigenetic regulators control gene expression and are potential therapeutic targets. There is functional interventional evidence for a role of DNA methylation and the histone post-translational modifications-histone methylation, acetylation and crotonylation-in the pathogenesis of kidney disease, including diabetic kidney disease. Readers of epigenetic marks, such as bromodomain and extra terminal (BET) proteins, are also therapeutic targets. Thus, the BD2 selective BET inhibitor apabetalone was the first epigenetic regulator to undergo phase-3 clinical trials in diabetic kidney disease with an endpoint of kidney function. The direct therapeutic modulation of epigenetic features is possible through pharmacological modulators of the specific enzymes involved and through the therapeutic use of the required substrates. Of further interest is the characterization of potential indirect effects of nephroprotective drugs on epigenetic regulation. Thus, SGLT2 inhibitors increase the circulating and tissue levels of ß-hydroxybutyrate, a molecule that generates a specific histone modification, ß-hydroxybutyrylation, which has been associated with the beneficial health effects of fasting. To what extent this impact on epigenetic regulation may underlie or contribute to the so-far unclear molecular mechanisms of cardio- and nephroprotection offered by SGLT2 inhibitors merits further in-depth studies.

The Contribution of Histone Crotonylation to Tissue Health and Disease: Focus on Kidney Health.

Acute kidney injury (AKI) and chronic kidney disease (CKD) are the most severe consequences of kidney injury. They are interconnected syndromes as CKD predisposes to AKI and AKI may accelerate CKD progression. Despite their growing impact on the global burden of disease, there is no satisfactory treatment for AKI and current therapeutic approaches to CKD remain suboptimal. Recent research has focused on the therapeutic target potential of epigenetic regulation of gene expression, including non-coding RNAs and the covalent modifications of histones and DNA. Indeed, several drugs targeting histone modifications are in clinical use or undergoing clinical trials. Acyl-lysine histone modifications (e.g. methylation, acetylation, and crotonylation) have modulated experimental kidney injury. Most recently, increased histone lysine crotonylation (Kcr) was observed during experimental AKI and could be reproduced in cultured tubular cells exposed to inflammatory stress triggered by the cytokine TWEAK. The degree of kidney histone crotonylation was modulated by crotonate availability and crotonate supplementation protected from nephrotoxic AKI. We now review the functional relevance of histone crotonylation in kidney disease and other pathophysiological contexts, as well as the implications for the development of novel therapeutic approaches. These studies provide insights into the overall role of histone crotonylation in health and disease.

Albuminuria Downregulation of the Anti-Aging Factor Klotho: The Missing Link Potentially Explaining the Association of Pathological Albuminuria with Premature Death.

Ten percent of the adult population has chronic kidney disease (CKD), which is diagnosed when the glomerular filtration rate (GFR) is below 60 mL/min per 1.73 m2 or when albuminuria is above 30 mg/day. The numerical thresholds were chosen because they are associated with an increased risk of CKD progression or premature death within a wider scenario of accelerated aging. Indeed, CKD is one of the fastest growing causes of death worldwide. A decreased GFR is associated with the accumulation of uraemic toxins that may promote tissue and organ damage. However, CKD may be diagnosed when the GFR is completely normal, as long as there is pathological albuminuria. A key unanswered question to stem the rise of CKD-associated deaths is whether the association between isolated albuminuria (when the GFR is normal) and premature death is causal. The recent demonstration that albuminuria per se directly suppresses the production of the anti-aging factor Klotho by kidney tubular cells may be one of the first steps to address the causality of the albuminuria-premature death-accelerated aging association. This hypothesis should be tested in interventional studies that should draw from translational science advances. Thus, the observation that albuminuria decreases Klotho production through epigenetic mechanisms implies that Klotho downregulation may persist after the correction of albuminuria, and innovative therapeutic approaches are needed to restore Klotho production. On the basis of recent literature, these may include manipulation of NF-kappaB regulators such as B cell lymphoma 3 protein (BCL-3), and epigenetic regulators such as histone deacetylases, or the repurposing of drugs such as pentoxifylline.

Molecular pathways driving omeprazole nephrotoxicity.

Omeprazole, a proton pump inhibitor used to treat peptic ulcer and gastroesophageal reflux disease, has been associated to chronic kidney disease and acute interstitial nephritis. However, whether omeprazole is toxic to renal cells is unknown. Omeprazole has a lethal effect over some cancer cells, and cell death is a key process in kidney disease. Thus, we evaluated the potential lethal effect of omeprazole over tubular cells. Omeprazole induced dose-dependent cell death in human and murine proximal tubular cell lines and in human primary proximal tubular cell cultures. Increased cell death was observed at the high concentrations used in cancer cell studies and also at lower concentrations similar to those in peptic ulcer patient serum. Cell death induced by omeprazole had features of necrosis such as annexin V/7-AAD staining, LDH release, vacuolization and irregular chromatin condensation. Weak activation of caspase-3 was observed but inhibitors of caspases (zVAD), necroptosis (Necrostatin-1) or ferroptosis (Ferrostatin-1) did not prevent omeprazole-induced death. However, omeprazole promoted a strong oxidative stress response affecting mitochondria and lysosomes and the antioxidant N-acetyl-cysteine reduced oxidative stress and cell death. By contrast, iron overload increased cell death. An adaptive increase in the antiapoptotic protein BclxL failed to protect cells. In mice, parenteral omeprazole increased tubular cell death and the expression of NGAL and HO-1, markers of renal injury and oxidative stress, respectively. In conclusion, omeprazole nephrotoxicity may be related to induction of oxidative stress and renal tubular cell death.

PGC-1α deficiency causes spontaneous kidney inflammation and increases the severity of nephrotoxic AKI.

PGC-1α (peroxisome proliferator-activated receptor gamma coactivator-1α, PPARGC1A) regulates the expression of genes involved in energy homeostasis and mitochondrial biogenesis. Here we identify inactivation of the transcriptional regulator PGC-1α as a landmark for experimental nephrotoxic acute kidney injury (AKI) and describe the in vivo consequences of PGC-1α deficiency over inflammation and cell death in kidney injury. Kidney transcriptomic analyses of WT mice with folic acid-induced AKI revealed 1398 up- and 1627 downregulated genes. Upstream transcriptional regulator analyses pointed to PGC-1α as the transcription factor potentially driving the observed expression changes with the highest reduction in activity. Reduced PGC-1α expression was shared by human kidney injury. Ppargc1a-/- mice had spontaneous subclinical kidney injury characterized by tubulointerstitial inflammation and increased Ngal expression. Upon AKI, Ppargc1a-/- mice had lower survival and more severe loss of renal function, tubular injury, and reduction in expression of mitochondrial PGC-1α-dependent genes in the kidney, and an earlier decrease in mitochondrial mass than WT mice. Additionally, surviving Ppargc1a-/- mice showed higher rates of tubular cell death, compensatory proliferation, expression of proinflammatory cytokines, NF-κB activation, and interstitial inflammatory cell infiltration. Specifically, Ppargc1a-/- mice displayed increased M1 and decreased M2 responses and expression of the anti-inflammatory cytokine IL-10. In cultured renal tubular cells, PGC-1α targeting promoted spontaneous cell death and proinflammatory responses. In conclusion, PGC-1α inactivation is a key driver of the gene expression response in nephrotoxic AKI and PGC-1α deficiency promotes a spontaneous inflammatory kidney response that is magnified during AKI. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Increased urinary osmolyte excretion indicates chronic kidney disease severity and progression rate.

Background: Chronic kidney disease (CKD) is a recognized global health problem. While some CKD patients remain stable after initial diagnosis, others can rapidly progress towards end-stage renal disease (ESRD). This makes biomarkers capable of detecting progressive forms of CKD extremely valuable, especially in non-invasive biofluids such as urine. Screening for metabolite markers using non-targeted metabolomic techniques like nuclear magnetic resonance spectroscopy is increasingly applied to CKD research. Methods: A cohort of CKD patients (n = 227) with estimated glomerular filtration rates (eGFRs) ranging from 9.4-130 mL/min/1.73 m2 was evaluated and urine metabolite profiles were characterized in relation to declining eGFR. Nested in this cohort, a retrospective subset (n = 57) was investigated for prognostic metabolite markers of CKD progression, independent of baseline eGFR. A transcriptomic analysis of murine models of renal failure was performed to validate selected metabolomic findings. Results: General linear modeling revealed 11 urinary metabolites with significant associations to reduced eGFR. Linear modelling specifically showed that increased urine concentrations of betaine (P < 0.05) and myo-inositol (P < 0.05) are significant prognostic markers of CKD progression. Conclusions: Renal organic osmolytes, betaine and myo-inositol play a critical role in protecting renal cells from hyperosmotic stress. Kidney tissue transcriptomics of murine preclinical experimentation identified decreased expression of Slc6a12 and Slc5a11 mRNA in renal tissue consistent with defective tubular transport of these osmolytes. Imbalances in renal osmolyte regulation lead to increased renal cell damage and thus more progressive forms of CKD. Increases in renal osmolytes in urine could provide clinical diagnostic and prognostic information on CKD outcomes.

Albumin downregulates Klotho in tubular cells.

Background: Kidney tubular cells are the main sources of Klotho, a protein with phosphaturic action. Genetic Klotho deficiency causes premature cardiovascular aging in mice. Human chronic kidney disease (CKD) is characterized by acquired Klotho deficiency. Despite the lack of uremic toxin accumulation, Category G1 CKD [(normal glomerular filtration rate (GFR)] is already associated with decreased Klotho and with premature cardiovascular aging. Methods: We have explored whether albuminuria, a criterion to diagnose CKD when GFR is normal, may directly decrease Klotho expression in human CKD, preclinical models and cultured tubular cells. Results: In a CKD cohort, albuminuria correlated with serum phosphate after adjustment for GFR, age and sex. In this regard, urinary Klotho was decreased in patients with pathological albuminuria but preserved GFR. Proteinuria induced in rats by puromycin aminonucleoside and in mice by albumin overload was associated with interstitial inflammation and reduced total kidney Klotho messenger ribonucleic acid (mRNA) expression. Western blot disclosed reduced kidney Klotho protein in proteinuric rats and mice and immunohistochemistry localized the reduced kidney Klotho expression to tubular cells in proteinuric animals. In cultured murine and human tubular cells, albumin directly decreased Klotho mRNA and protein expression. This was inhibited by trichostatin A, an inhibitor of histone deacetylases, but unlike cytokine-induced Klotho downregulation, not by inhibitors of nuclear factor kappa-light-chain-enhancer of activated B cells. Conclusions: In conclusion, albumin directly decreases Klotho expression in cultured tubular cells. This may explain, or at least contribute to, the decrease in Klotho and promote fibroblast growth factor 23 resistance in early CKD categories, as observed in preclinical and clinical proteinuric kidney disease.

Urine metabolomics insight into acute kidney injury point to oxidative stress disruptions in energy generation and H2S availability.

Acute kidney injury (AKI) is one of the main complications in acute care medicine and a risk factor for chronic kidney disease (CKD). AKI incidence has increased; however, its diagnosis has limitations and physiopathological mechanisms are underexplored. We investigated urine samples, aiming to identify major metabolite changes during human AKI evolution. Metabolic signatures found were further explored for a potential link to severity of injury. Twenty-four control subjects and 38 hospitalized patients with AKI were recruited and urine samples were collected at the time of diagnosis, during follow-up and at discharge. Nuclear magnetic resonance (NMR) was used in a first discovery phase for identifying potential metabolic differences. Target metabolites of interest were confirmed by liquid chromatography-mass spectrometry (LC-MS/MS) in an independent group. Underlying metabolic defects were further explored by kidney transcriptomics of murine toxic AKI. Urinary 2-hydroxybutyric acid, pantothenic acid, and hippuric acid were significantly downregulated and urinary N-acetylneuraminic acid, phosphoethanolamine, and serine were upregulated during AKI. Hippuric acid, phosphoethanolamine, and serine showed further downregulation/upregulation depending on the metabolite in acute tubular necrosis (ATN) AKI compared to prerenal AKI. Kidney transcriptomics disclosed decreased expression of cystathionase, cystathionine-ß-synthase, and ethanolamine-phosphate cytidylyltransferase, and increased N-acetylneuraminate synthase as the potentially underlying cause of changes in urinary metabolites. A urinary metabolite panel identified AKI patients and provided insight into intrarenal events. A urine fingerprint made up of six metabolites may be related to pathophysiological changes in oxidative stress, energy generation, and H2S availability associated with AKI. KEY MESSAGES: The urinary metabolome reflects AKI evolution and severity of injury. Kidney transcriptomics revealed enzymatic expression changes. Enzymatic expression changes may be the potentially underlying cause of changes in urine metabolites. Identified metabolite changes link oxidative stress, energy generation, and H2S availability to AKI.