Editorial for the Special Issue: Pathophysiology of Chronic Kidney Disease and Its Complications.

Chronic kidney disease (CKD) is a risk factor for end-stage kidney disease, requiring renal replacement therapy [...].

SGLT2 inhibitor dapagliflozin protects the kidney in a murine model of Balkan nephropathy.

Proximal tubular uptake of aristolochic acid (AA) forms aristolactam (AL)-DNA adducts, which cause a p53/p21-mediated DNA damage response and acute tubular injury. Recurrent AA exposure causes kidney function loss and fibrosis in humans (Balkan endemic nephropathy) and mice and is a model of (acute kidney injury) AKI to chronic kidney disease (CKD) transition. Inhibitors of the proximal tubule sodium-glucose transporter SGLT2 can protect against CKD progression, but their effect on AA-induced kidney injury remains unknown. C57BL/6J mice (15-wk-old) were administered vehicle or AA every 3 days for 3 wk (10 and 3 mg/kg ip in females and males, respectively). Dapagliflozin (dapa, 0.01 g/kg diet) or vehicle was initiated 7 days prior to AA injections. All dapa effects were sex independent, including a robust glycosuria. Dapa lowered urinary kidney-injury molecule 1 (KIM-1) and albumin (both normalized to creatinine) after the last AA injection and kidney mRNA expression of early DNA damage response markers (p53 and p21) 3 wk later at the study end. Dapa also attenuated AA-induced increases in plasma creatinine as well as AA-induced up-regulation of renal pro-senescence, pro-inflammatory and pro-fibrotic genes, and kidney collagen staining. When assessed 1 day after a single AA injection, dapa pretreatment attenuated AL-DNA adduct formation by 10 and 20% in kidney and liver, respectively, associated with reduced p21 expression. Initiating dapa application after the last AA injection also improved kidney outcome but in a less robust manner. In conclusion, the first evidence is presented that pretreatment with an SGLT2 inhibitor can attenuate the AA-induced DNA damage response and subsequent nephropathy.NEW & NOTEWORTHY Recurrent exposure to aristolochic acid (AA) causes kidney function loss and fibrosis in mice and in humans, e.g., in the form of the endemic Balkan nephropathy. Inhibitors of the proximal tubule sodium-glucose transporter SGLT2 can protect against CKD progression, but their effect on AA-induced kidney injury remains unknown. Here we provide the first evidence in a murine model that pretreatment with an SGLT2 inhibitor can attenuate the AA-induced DNA damage response and subsequent nephropathy.

CRRT 2023 Meeting: Targeting Amino Acid Transport to Improve Acute Kidney Injury Outcome.

BACKGROUND: In acute kidney injury (AKI), proximal tubules are a primary site of injury, resulting in significant alterations in amino acid transport and metabolism. However, little is known about the therapeutic potential of targeting amino acid transporters. Here, we briefly review the first experimental evidence that targeting the sodium-coupled amino acid transporter SLC6A19 (B0AT1) can improve AKI outcome. SUMMARY: SLC6A19 is expressed in the small intestine and early proximal tubules, where it absorbs and reabsorbs most of the ingested and filtered neutral amino acids, respectively. Systemic SLC6A19 deficiency alleviates renal cellular senescence and suppresses subsequent inflammation and fibrosis in a murine model of aristolochic acid-induced nephropathy, which targets the proximal tubule. The underlying mechanisms remain to be determined, but potentially may include reduced tubular workload, an inhibitory effect on SGLT2, downstream shift in transport and preconditioning of late proximal tubules, and induction of a fasting-like phenotype and lowering tubular accumulation of branched-chain amino acids, which all can promote tubular health.

Japanese clinical practice patterns of primary nephrotic syndrome 2021: a web-based questionnaire survey of certified nephrologists.

BACKGROUND: With the publication of the "Evidence-Based Clinical Practice Guideline for Nephrotic Syndrome 2020," we examined nephrologists' adherence to the recommendations of four of its clinical questions (CQs). METHODS: This was a cross-sectional web-based survey conducted between November and December 2021. The target population comprised nephrologists certified by the Japanese Society of Nephrology who were recruited using convenience sampling. The participants answered six items regarding the four CQs about adult patients with nephrotic syndrome and their characteristics. RESULTS: In total, 434 respondents worked in at least 306 facilities, of whom 386 (88.9%) provided outpatient care for primary nephrotic syndrome. Of these patients, 179 (41.2%) answered that they would not measure anti- phospholipase A2 receptor antibody levels in cases of suspected primary membranous nephropathy (MN) in which kidney biopsy was not possible (CQ1). Regarding immunosuppressants as maintenance therapy after relapse of minimal change nephrotic syndrome (CQ2), cyclosporine was the most common choice (290 [72.5%] and 300 [75.0%] of 400 respondents after the first and second relapses, respectively). The most common treatment for steroid-resistant cases of primary focal segmental glomerulosclerosis (CQ3) was cyclosporine (323 of 387, 83.5%). For the initial treatment of primary MN with nephrotic-range proteinuria (CQ4), corticosteroid monotherapy was the most common choice (240 of 403, 59.6%), followed by corticosteroid and cyclosporine (114, 28.3%). CONCLUSION: Gaps in recommendations and practices regarding serodiagnosis and treatment of MN (i.e., CQ1 and 4) are observed, suggesting the need to address the barriers to their insurance reimbursement and the lack of evidence behind them.

Marked reduction of proteinuria after removal of a growth hormone-producing pituitary adenoma in a patient with focal segmental glomerulosclerosis: a case report and literature review.

Focal segmental glomerulosclerosis is a rare complication of acromegaly. A 74-year-old man was found to have acromegaly features such as enlargement of the forehead, nose, and hands. Laboratory tests showed a urine protein/creatinine ratio of 3.16 g/gCr and serum creatinine of 1.34 mg/dL. The levels of growth hormone and insulin-like growth factor I were markedly elevated, and the growth hormone level was not suppressed after 75 g oral glucose loading. Magnetic resonance imaging revealed a pituitary tumor with a diameter of 1.2 cm. Renal biopsy confirmed the diagnosis of focal segmental glomerulosclerosis. Transsphenoidal resection of the pituitary tumor led to remission of acromegaly and reduction in proteinuria highlighting the causal link between growth hormone overproduction and proteinuria. Treatment of acromegaly may be effective for acromegaly-associated focal segmental glomerulosclerosis.

The Pathophysiological Basis of Diabetic Kidney Protection by Inhibition of SGLT2 and SGLT1.

SGLT2 inhibitors can protect the kidneys of patients with and without type 2 diabetes mellitus and slow the progression towards end-stage kidney disease. Blocking tubular SGLT2 and spilling glucose into the urine, which triggers a metabolic counter-regulation similar to fasting, provides unique benefits, not only as an anti-hyperglycemic strategy. These include a low hypoglycemia risk and a shift from carbohydrate to lipid utilization and mild ketogenesis, thereby reducing body weight and providing an additional energy source. SGLT2 inhibitors counteract hyperreabsorption in the early proximal tubule, which acutely lowers glomerular pressure and filtration and thereby reduces the physical stress on the filtration barrier, the filtration of tubule-toxic compounds, and the oxygen demand for tubular reabsorption. This improves cortical oxygenation, which, together with lesser tubular gluco-toxicity and improved mitochondrial function and autophagy, can reduce pro-inflammatory, pro-senescence, and pro-fibrotic signaling and preserve tubular function and GFR in the long-term. By shifting transport downstream, SGLT2 inhibitors more equally distribute the transport burden along the nephron and may mimic systemic hypoxia to stimulate erythropoiesis, which improves oxygen delivery to the kidney and other organs. SGLT1 inhibition improves glucose homeostasis by delaying intestinal glucose absorption and by increasing the release of gastrointestinal incretins. Combined SGLT1 and SGLT2 inhibition has additive effects on renal glucose excretion and blood glucose control. SGLT1 in the macula densa senses luminal glucose, which affects glomerular hemodynamics and has implications for blood pressure control. More studies are needed to better define the therapeutic potential of SGLT1 inhibition to protect the kidney, alone or in combination with SGLT2 inhibition.

Tissue Factor, Thrombosis, and Chronic Kidney Disease.

Coagulation abnormalities are common in chronic kidney disease (CKD). Tissue factor (TF, factor III) is a master regulator of the extrinsic coagulation system, activating downstream coagulation proteases, such as factor Xa and thrombin, and promoting fibrin formation. TF and coagulation proteases also activate protease-activated receptors (PARs) and are implicated in various organ injuries. Recent studies have shown the mechanisms by which thrombotic tendency is increased under CKD-specific conditions. Uremic toxins, such as indoxyl sulfate and kynurenine, are accumulated in CKD and activate TF and coagulation; in addition, the TF-coagulation protease-PAR pathway enhances inflammation and fibrosis, thereby exacerbating renal injury. Herein, we review the recent research studies to understand the role of TF in increasing the thrombotic risk and CKD progression.

Aristolochic acid-induced nephropathy is attenuated in mice lacking the neutral amino acid transporter B0AT1 (Slc6a19).

B0AT1 (Slc6a19) mediates absorption of neutral amino acids in the small intestine and in the kidneys, where it is primarily expressed in early proximal tubules (S1-S2). To determine the role of B0AT1 in nephropathy induced by aristolochic acid (AA), which targets the proximal tubule, littermate female B0AT1-deficient (Slc6a19-/-), heterozygous (Slc6a19+/-), and wild-type (WT) mice were administered AA (10 mg/kg ip) or vehicle every 3 days for 3 wk, and analyses were performed after the last injection or 3 wk later. Vehicle-treated mice lacking Slc6a19 showed normal body and kidney weight and plasma creatinine versus WT mice. The urinary glucose-to-creatinine ratio (UGCR) and urinary albumin-to-creatinine ratio (UACR) were two to four times higher in vehicle-treated Slc6a19-/- versus WT mice, associated with lesser expression of early proximal transporters Na+-glucose cotransporter 2 and megalin, respectively. AA caused tubular injury independently of B0AT1, including robust increases in cortical mRNA expression of p53, p21, and hepatitis A virus cellular receptor 1 (Havcr1), downregulation of related proximal tubule amino acid transporters B0AT2 (Slc6a15), B0AT3 (Slc6a18), and Slc7a9, and modest histological tubular damage and a rise in plasma creatinine. Absence of B0AT1, however, attenuated AA-induced cortical upregulation of mRNA markers of senescence (p16), inflammation [lipocalin 2 (Lcn2), C-C motif chemokine ligand 2 (Ccl2), and C-C motif chemokine receptor 2 (Ccr2)], and fibrosis [tissue inhibitor of metallopeptidase 1 (Timp1), transforming growth factor-ß1 (Tgfb1), and collagen type I-α1 (Col1a1)], associated with lesser fibrosis staining, lesser suppression of proximal tubular organic anion transporter 1, restoration of Na+-glucose cotransporter 2 expression, and prevention of the AA-induced fivefold increase in the urinary albumin-to-creatinine ratio observed in WT mice. The data suggest that proximal tubular B0AT1 is important for the physiology of renal glucose and albumin retention but potentially deleterious for the kidney response following AA-induced kidney injury.NEW & NOTEWORTHY Based on insights from studies manipulating glucose transport, the hypothesis has been proposed that inhibiting intestinal uptake or renal reabsorption of energy substrates has unique therapeutic potential to improve metabolic disease and kidney outcome in response to injury. The present study takes this idea to B0AT1, the major transporter for neutral amino acids in the intestine and kidney, and shows that its absence attenuates aristolochic acid-induced nephropathy.

Glomerulonephritis Associated with Infective Endocarditis Showing Serological Positivity for PR3-anti-neutrophil Cytoplasmic Antibody and Anti-glomerular Basement Membrane Antibody.

We herein report a case of crescentic glomerulonephritis (GN) associated with infective endocarditis (IE). A 61-year-old-woman presented with a fever and renal dysfunction and was diagnosed with IE. The patient was positive for proteinase 3-anti-neutrophil cytoplasmic antibody (PR3-ANCA) and anti-glomerular basement membrane (GBM) antibodies. Renal biopsy findings showed crescentic GN with isolated deposition of C3c, a serum conversion product of complement C3. Given these clinical findings, the patient was diagnosed with infective endocardis (IE)-associated GN. Antibiotic therapy was continued without immunosuppressive agents. After the initiation of the antibiotics, the fever resolved, and the renal function gradually recovered. This case highlights the notion that laboratory findings should be carefully evaluated with reference to other findings.

Coagulation, Protease-Activated Receptors, and Diabetic Kidney Disease: Lessons from eNOS-Deficient Mice.

Endothelial nitric oxide synthase (eNOS) dysfunction is known to exacerbate the progression and prognosis of diabetic kidney disease (DKD). One of the mechanisms through which this is achieved is that low eNOS levels are associated with hypercoagulability, which promotes kidney injury. In the extrinsic coagulation cascade, the tissue factor (factor III) and downstream coagulation factors, such as active factor X (FXa), exacerbate inflammation through activation of the protease-activated receptors (PARs). Recently, it has been shown that the lack of or reduced eNOS expression in diabetic mice, as a model of advanced DKD, increases renal tissue factor levels and PAR1 and 2 expression in their kidneys. Furthermore, pharmaceutical inhibition or genetic deletion of coagulation factors or PARs ameliorated inflammation in DKD in mice lacking eNOS. In this review, we summarize the relationship between eNOS, coagulation, and PARs and propose a novel therapeutic option for the management of patients with DKD.

Myeloid cell-derived coagulation tissue factor is associated with renal tubular damage in mice fed an adenine diet.

Patients with chronic kidney disease (CKD) commonly exhibit hypercoagulability. Increased levels of uremic toxins cause thrombogenicity by increasing tissue factor (TF) expression and activating the extrinsic coagulation cascade. TF is induced in monocytes and macrophages under pathological conditions, such as inflammatory diseases. However, the role of monocyte myeloid cell TF in CKD progression remains unclear. We aimed to clarify this issue, and the present study found that patients with CKD had elevated levels of D-dimer, a marker of fibrin degradation, which was associated with decreased estimated glomerular filtration rate and increased serum levels of uremic toxins, such as indoxyl sulfate. In vitro studies showed that several uremic toxins increased cellular TF levels in monocytic THP-1 cells. Mice with TF specifically deleted in myeloid cells were fed an adenine diet to cause uremic kidney injury. Myeloid TF deletion reduced tubular injury and pro-inflammatory gene expression in the kidneys of adenine-induced CKD but did not improve renal function as measured by plasma creatinine or blood urea nitrogen. Collectively, our findings suggest a novel concept of pathogenesis of coagulation-mediated kidney injury, in which elevated TF levels in monocytes under uremic conditions is partly involved in the development of CKD.

A Novel Mutation in LMX1B (p.Pro219Ala) Causes Focal Segmental Glomerulosclerosis with Alport Syndrome-like Phenotype.

A 69-year-old woman presented with mild renal dysfunction, proteinuria, and sensorineural hearing loss. A renal biopsy showed focal segmental glomerulosclerosis with thinning of the glomerular basement membrane. There was a positive family history of end-stage kidney disease and hearing loss. Although Alport syndrome was suspected from these features, a genetic test using next-generation sequencer identified a novel missense mutation in LMX1B, c.655C>G: p. (Pro219Ala). In silico analyses predicted the pathogenicity of the mutation. Thus, the present case was diagnosed as LMX1B-associated nephropathy presenting with Alport syndrome-like phenotype, expanding the disease spectrum of LMX1B nephropathy.

Spontaneous remission of minimal change nephrotic syndrome in an elderly man.

Minimal change nephrotic syndrome (MCNS) cases achieving spontaneous remission without external factors are rarely reported. We report a case of MCNS that achieved spontaneous remission without external factors that triggered its onset. An 82-year-old male patient was admitted to the hospital for close examination of nephrotic syndrome. Renal biopsy was performed and MCNS was diagnosed. Owing to the patient's age and history of foot and microvascular arteriovenous thrombosis, we did not start immunosuppressive drugs, including steroids, and opted for conservative management. After conservative treatment, proteinuria gradually decreased, and the patient achieved complete remission. Given that the patient had a history of urinary protein and thrombosis, recurrence of MCNS was considered again this time. In addition, the involvement of external factors that trigger the onset of MCNS was not found. In conclusion, in elderly-onset MCNS, clinicians generally hesitate to initiate treatment with an immunosuppressive drug, containing steroids, because of its many complications. Thus, our data provide valuable insight into MCNS.

Lack of Endothelial Nitric Oxide Synthase Accelerates Ectopic Calcification in Uremic Mice Fed an Adenine and High Phosphorus Diet.

Ectopic calcification is a risk of cardiovascular disease in chronic kidney disease (CKD) patients, and impaired endothelial nitric oxide synthase (eNOS) is involved in the CKD complications. However, whether eNOS dysfunction is a cause of ectopic calcification in CKD remains to be elucidated. To address this issue, we investigated the role of eNOS in ectopic calcification in mice with renal injury caused by an adenine and high-phosphorus (Ade + HP) diet. DBA/2J mice, a calcification-sensitive strain, were fed Ade + HP for 3 weeks. Expression levels of eNOS-related genes were reduced significantly in their calcified aorta. C57BL/6J is a calcification-resistant strain, and wild-type mice showed mild calcified lesions in the aorta and kidney when given an Ade + HP diet for 4 weeks. In contrast, a lack of eNOS led to the development of severe aortic calcification accompanied by an increase in runt-related transcription factor 2, an osteochondrogenic marker. Increased renal calcium deposition and the tubular injury score were remarkable in mice lacking eNOS-fed Ade + HP. Exacerbation of ectopic calcification by a lack of eNOS is associated with increased oxidative stress markers such as nicotinamide adenine dinucleotide phosphate oxidases. In conclusion, eNOS is critically important in preventing ectopic calcification. Therefore, the maintenance of eNOS is useful to reduce cardiovascular disease events and to improve prognosis in CKD patients.

The effect of aldosterone on adiposity - The role of glucose absorption in the small intestine.

We have previously demonstrated that manipulation of the renin angiotensin system (RAS) has large effects on digestive efficiency. However, the effects of aldosterone on body weight, adiposity, and glucose absorption in the intestine remains unknown. We here demonstrated that lack of aldosterone synthase (ASKO) in mice did not affect adiposity. In contrast, mice administered with aldosterone were resistant to diet-induced obesity. This is due to gastrointestinal loss of dietary glucose. As expected, ASKO mice had increased glucose absorption, whereas mice administered with aldosterone had reduced glucose absorption in the small intestine. Furthermore, the level of protein expression of sodium glucose transporter 1 (SGLT1) in the mucosa of the jejunum was higher in ASKO mice, and lower in mice administered with aldosterone than control mice. Our findings indicate that aldosterone plays an important role on SGLT-1-mediated glucose absorption in the small intestine.

Protease-activated receptor 2 contributes to placental development and fetal growth in mice.

BACKGROUND: Protease-activated receptor 2 (PAR2) is activated by serine proteases such as coagulation tissue factor/VIIa complex, factor Xa or trypsin and is pro-angiogenic in several disease models. Impaired angiogenesis in placenta causes placental dysfunction and fetal growth restriction. PAR2 is expressed in the placenta trophoblast. However, the role of PAR2 in pregnancy remains unknown. OBJECTIVE: The present study aimed to examine the role of PAR2 in placental development and fetal growth using a murine model. METHODS: PAR2-/- or PAR2+/+ mice in the ICR background were used. Female PAR2-/- mice were mated with male PAR2-/- mice, and female PAR2+/+ mice were mated with male PAR2+/+ mice to obtain PAR2-/- and PAR2+/+ fetuses, respectively. The day a virginal plug was observed in the morning was determined as 0.5-day post-coitum (dpc). Pregnant mice were sacrificed on 13.5 or 18.5 dpc to collect samples. RESULTS: A deficiency of PAR2 significantly reduced the fetal and placental weight and impaired placental labyrinth development in mice on 18.5 dpc. Collagen IV expression in placenta labyrinth was smaller in PAR2 knockout mice compared to that of wild-type mice. A deficiency of PAR2 also reduced the expression levels of genes related to angiogenesis and coagulation in placenta. CONCLUSION: Our data suggest that PAR2 is required for fetal growth and angiogenesis in the placenta and is thus important for a normal pregnancy.

Metabolomics of a mouse model of preeclampsia induced by overexpressing soluble fms-like tyrosine kinase 1.

Preeclampsia (PE) is a leading cause of maternal morbidity and mortality. Nicotinamide has beneficial effects on PE. In this study, we evaluated the effect of nicotinamide on placental development using a PE mouse model. To generate the PE model, a recombinant adenovirus to overproduce soluble fms-like tyrosine kinase 1 (sFlt-1) was administered to mice (Jcl:ICR) at 8.5 day post-coitum (dpc). Plasma and placenta samples were harvested at 12.5 dpc. Fetal and placental weight was significantly decreased at 12.5 dpc in PE mice. Plasma and placental acylcarnitine levels were significantly higher in PE mice than those in control mice. Glycolysis was accelerated and glucose metabolic flow was altered with hypoxia, leading to ATP shortage in the labyrinth of PE mice. In PE mice, ATP production was diminished, and fatty acid oxidation was accelerated in the placenta, consequently, blood carnitine and acylcarnitine levels were increased. The mitochondrial morphology in BeWo cells was impaired under hypoxia. Nicotinamide treatment reversed fetal growth restriction, placental development, and altered metabolic flow in the early stage in PE. In addition, nicotinamide normalized impaired mitochondrial morphology. Hence, targeting this metabolic alteration in the placenta using nicotinamide may serve as a potential therapeutic approach for PE treatment.

Questionnaire survey on the prescription of renal replacement therapy for acute phase patients on maintenance dialysis who developed cerebrovascular disease.

BACKGROUND: There is limited information about acute phase renal replacement therapy (RRT) for maintenance hemodialysis patients after the onset of cerebrovascular disease. This study aimed to investigate which modality of renal replacement therapy is currently selected in practice. METHODS: We conducted a mail-based survey in 317 dialysis facilities that were certified by three academic societies that focus on dialysis, neurology, and neurosurgery in Japan. RESULTS: We received responses from 103 facilities (32.5%). In cases of cerebral infarction (CI) and intracerebral hemorrhage (ICH), more than 80% of the facilities selected only intermittent RRT, and 22.3% (CI)/8.7% (ICH) of the facilities selected intermittent HD which is the same setting in normal conditions. Although continuous hemodiafiltration and peritoneal dialysis are recommended in the Japanese guidelines, these were selected in only a few facilities: 16.5% and 0% in CI, 16.5% and 1% in ICH, respectively. RRT on the day of onset tended to be avoided, irrespective of the duration following the last HD session. Furthermore, physicians preferred to modify anticoagulants and reduce dialysis performance in the acute phase. CONCLUSION: This questionnaire survey uncovered a gap between guidelines and actual practice, even in hospitals accredited as educational facility, which is a novel and important finding. Further studies with larger sample sizes are needed to determine the optimal modality of RRT for the acute phase of cerebrovascular disease.

Effects of the oral adsorbent AST-120 on fecal p-cresol and indole levels and on the gut microbiota composition.

In chronic kidney disease, elevated levels of circulating uremic toxins are associated with a variety of symptoms and organ dysfunction. Indoxyl sulfate (IS) and p-cresyl sulfate (pCS) are microbiota-derived metabolites and representative uremic toxins. We have previously shown that the oral adsorbent AST-120 profoundly reduced pCS compared to IS in adenine-induced renal failure in mice. However, the mechanisms of the different attenuation effects of AST-120 between IS and pCS are unclear. To clarify the difference of AST-120 on IS and pCS, we investigated the levels of fecal indole and p-cresol, the respective precursors of IS and pCS, and examined the influence on the gut microbiota. Although fecal indole was detected in all groups analyzed, fecal p-cresol was not detected in AST-120 treatment groups. In genus level, a total of 23 organisms were significantly changed by renal failure or AST-120 treatment. Especially, AST-120 reduced the abundance of Erysipelotrichaceae uncultured and Clostridium sensu stricto 1, which have a gene involved in p-cresol production. Our findings suggest that, in addition to the adsorption of the uremic toxin precursors, AST-120 affects the abundance of some gut microbiota in normal and renal failure conditions, thereby explaining the different attenuation effects on IS and pCS.