Oxalate, inflammasome, and progression of kidney disease

Catastrophic retinal vascular occlusion and vision loss due to crystal deposition in end-stage kidney disease treated with peritoneal dialysis

Purpose

To report two cases of catastrophic retinal vascular occlusion and crystalline retinopathy due to presumed oxalosis and hyperphosphatemia.

Observations

We describe two unrelated patients with end-stage kidney failure (ESKD) treated with peritoneal dialysis that developed rapid bilateral vision loss due to severe retinal vascular occlusion. Multi-modal retinal imaging studies demonstrated crystalline deposits. Plasma phosphorus and oxalate levels were markedly elevated compared to persons with normal kidney function. One patient harbored a heterozygous variant of unknown significance in the Alanine--Glyoxylate Aminotransferase (AGXT) gene. Intense hemodialysis and diet modification reduced phosphorus and oxalate levels.

Conclusions and importance

This report serves to raise awareness of hyperphosphatemia and oxalosis in dialysis patients to alert providers so that they can act to decrease the potential risk of vision loss.

Regulated cell death in chronic kidney disease: current evidence and future clinical perspectives

Chronic kidney disease (CKD) is the progressive loss of kidney function/structure over a period of at least 3 months. It is characterised histologically by the triad of cell loss, inflammation and fibrosis. This literature review focuses on the forms of cell death that trigger downstream inflammation and fibrosis, collectively called regulated cell death (RCD) pathways. Discrete forms of RCD have emerged as central mediators of CKD pathology. In particular, pathways of regulated necrosis - including mitochondrial permeability transition pore (mPTP)-mediated necrosis, necroptosis, ferroptosis and pyroptosis - have been shown to mediate kidney pathology directly or through the release of danger signals that trigger a pro-inflammatory response, further amplifying tissue injury in a cellular process called necroinflammation. Despite accumulating evidence in pre-clinical models, no clinical studies have yet targeted these RCD modes in human CKD. The review summarizes recent advances in our understanding of RCD pathways in CKD, looks at inter-relations between the pathways (with the emphasis on propagation of death signals) and the evidence for therapeutic targeting of molecules in the RCD pathways to prevent or treat CKD.

Mutation Characteristics of Primary Hyperoxaluria in the Chinese Population and Current International Diagnosis and Treatment Status

Background

Primary hyperoxaluria (PH) is a rare autosomal recessive disorder, mainly due to the increase in endogenous oxalate production, causing a series of clinical features such as kidney stones, nephrocalcinosis, progressive impairment of renal function, and systemic oxalosis. There are three common genetic causes of glycolate metabolism anomalies. Among them, PH type 1 is the most prevalent and severe type, and early end-stage renal failure often occurs.

Summary

This review summarizes PH through pathophysiology, genotype, clinical manifestation, diagnosis, and treatment options. And explore the characteristics of Chinese PH patients.

Key Messages

Diagnosis of this rare disease is based on clinical symptoms, urinary or blood oxalate concentrations, liver biopsy, and genetic testing. Currently, the main treatment is massive hydration, citrate inhibition of crystallization, dialysis, liver and kidney transplantation, and pyridoxine. Recently, RNA interference drugs have also been used. In addition, technologies such as gene editing and autologous liver cell transplantation are also being developed. C.815_816insGA and c.33_34insC mutation in the AGXT gene could be a common variant in Chinese PH1 population. Mutations at the end of exon 6 account for approximately 50% of all Chinese HOGA1 mutations. Currently, the treatment of PH in China still relies mainly on symptomatic and high-throughput dialysis, with poor prognosis (especially for PH1 patients).

Bacterial Degradation of Antinutrients in Foods: The Genomic Insight

Antinutrients, also known as anti-nutritional factors (ANFs), are compounds found in many plant-based foods that can limit the bioavailability of nutrients or can act as precursors to toxic substances. ANFs have controversial effects on human health, depending mainly on their concentration. While the positive effects of these compounds are well documented, the dangers they pose and the approaches to avoid them have not been discussed to the same extent. There is no dispute that many ANFs negatively alter the absorption of vitamins, minerals, and proteins in addition to inhibiting some enzyme activities, thus negatively affecting the bioavailability of nutrients in the human body. This review discusses the chemical properties, plant bioavailability, and deleterious effects of anti-minerals (phytates and oxalates), glycosides (cyanogenic glycosides and saponins), polyphenols (tannins), and proteinaceous ANFs (enzyme inhibitors and lectins). The focus of this study is on the possibility of controlling the amount of ANF in food through fermentation. An overview of the most common biochemical pathways for their microbial reduction is provided, showing the genetic basis of these phenomena, including the active enzymes, the optimal conditions of action, and some data on the regulation of their synthesis.

Management of Cardiovascular Diseases by Short-Chain Fatty Acid Postbiotics

PURPOSE OF REVIEW

Global health concerns persist in the realm of cardiovascular diseases (CVDs), necessitating innovative strategies for both prevention and treatment. This narrative review aims to explore the potential of short-chain fatty acids (SCFAs)-namely, acetate, propionate, and butyrate-as agents in the realm of postbiotics for the management of CVDs.

RECENT FINDINGS

We commence our discussion by elucidating the concept of postbiotics and their pivotal significance in mitigating various aspects of cardiovascular diseases. This review centers on a comprehensive examination of diverse SCFAs and their associated receptors, notably GPR41, GPR43, and GPR109a. In addition, we delve into the intricate cellular and pharmacological mechanisms through which these receptors operate, providing insights into their specific roles in managing cardiovascular conditions such as hypertension, atherosclerosis, heart failure, and stroke. The integration of current information in our analysis highlights the potential of both SCFAs and their receptors as a promising path for innovative therapeutic approaches in the field of cardiovascular health. The idea of postbiotics arises as an optimistic and inventive method, presenting new opportunities for preventing and treating cardiovascular diseases.

Pathophysiology and management of enteric hyperoxaluria

Enteric hyperoxaluria is a metabolic disorder resulting from conditions associated with fatty acid malabsorption and characterized by an increased urinary output of oxalate. Oxalate is excessively absorbed in the gut and then excreted in urine where it forms calcium oxalate crystals, inducing kidney stones formation and crystalline nephropathies. Enteric hyperoxaluria is probably underdiagnosed and may silently damage kidney function of patients affected by bowel diseases. Moreover, the prevalence of enteric hyperoxaluria has increased because of the development of bariatric surgical procedures. Therapeutic options are based on the treatment of the underlying disease, limitation of oxalate intakes, increase in calcium salts intakes but also increase in urine volume and correction of hypocitraturia. There are few data regarding the natural evolution of kidney stone events and chronic kidney disease in these patients, and there is a need for new treatments limiting kidney injury by calcium oxalate crystallization.

Oxalates: Dietary Oxalates and Kidney Inflammation: A Literature Review

This literature review explores the role of dietary oxalate in the development of chronic inflammatory kidney disease in middle-aged and older individuals. The authors pose the following questions: Is oxalate produced endogenously? If food sources contribute to chronic kidney disease and inflammation, what are those foods? What role do cultural food preparation and cooking play in denaturing food oxalates? The concentration of oxalates found within the body at any particular time is not limited to edible plants; normal human metabolic processes of breaking down ascorbic acid may create up to 30 mg of oxalate daily. Research supports urolithiasis as a common urologic disease in industrialized societies. Approximately 80% of kidney stones are composed of calcium oxalate, resulting in hyperoxaluria. Exogenous (originating outside the cell or organism) oxalate sources include ascorbic acid, amino acids, and glyoxal metabolism. Additional research estimates the daily endogenous (produced within the cell or organism) production of oxalate to be 10-25 mg. Suboptimal colonization of oxalate-degrading bacteria and malabsorptive disease are also contributing factors to the development of chronic kidney disease. Oxalate transcellular processes, though poorly understood, rely on multifunctional anion exchangers, and are currently being investigated. A review of research showed that normal human metabolic processes, including the breakdown of ascorbic acid, account for 35-55% of circulating oxalates and can create ≤30 mg of circulating serum oxalate daily. Glyoxylic acid accounts for 50-70% of circulating urinary oxalate in compromised individuals with liver glycation, bacterial insufficiencies, malabsorption, and anion exchange challenges. For persons with a family history of kidney stones, consumption of foods high in oxalates may be consumed in moderation, provided there is adequate calcium intake in the diet to decrease the absorption of oxalates from the meal ingested.

Navigating the Evolving Landscape of Primary Hyperoxaluria: Traditional Management Defied by the Rise of Novel Molecular Drugs

Primary hyperoxalurias (PHs) are inherited metabolic disorders marked by enzymatic cascade disruption, leading to excessive oxalate production that is subsequently excreted in the urine. Calcium oxalate deposition in the renal tubules and interstitium triggers renal injury, precipitating systemic oxalate build-up and subsequent secondary organ impairment. Recent explorations of novel therapeutic strategies have challenged and necessitated the reassessment of established management frameworks. The execution of diverse clinical trials across various medication classes has provided new insights and knowledge. With the evolution of PH treatments reaching a new milestone, prompt and accurate diagnosis is increasingly critical. Developing early, effective management and treatment plans is essential to improve the long-term quality of life for PH patients.

Plasma metabolomics reveals risk factors for lung adenocarcinoma

Background

Metabolic reprogramming plays a significant role in the advancement of lung adenocarcinoma (LUAD), yet the precise metabolic changes remain incompletely understood. This study aims to uncover metabolic indicators associated with the progression of LUAD.

Methods

A total of 1083 subjects were recruited, including 670 LUAD, 135 benign lung nodules (BLN) and 278 healthy controls (HC). Gas chromatography-mass spectrometry (GC/MS) was used to identify and quantify plasma metabolites. Odds ratios (ORs) were calculated to determine LUAD risk factors, and machine learning algorithms were utilized to differentiate LUAD from BLN.

Results

High levels of oxalate, glycolate, glycine, glyceric acid, aminomalonic acid, and creatinine were identified as risk factors for LUAD (adjusted ORs>1.2, P<0.03). Remarkably, oxalate emerged as a distinctive metabolic risk factor exhibiting a strong correlation with the progression of LUAD (adjusted OR=5.107, P<0.001; advanced-stage vs. early-stage). The Random Forest (RF) model demonstrated a high degree of efficacy in distinguishing between LUAD and BLN (accuracy = 1.00 and 0.73, F1-score= 1.00 and 0.79, and AUC = 1.00 and 0.76 in the training and validation sets, respectively). TCGA and GTEx gene expression data have shown that lactate dehydrogenase A (LDHA), a crucial enzyme involved in oxalate metabolism, is increasingly expressed in the progression of LUAD. High LDHA expression levels in LUAD patients are also linked to poor prognoses (HR=1.66, 95% CI=1.34-2.07, P<0.001).

Conclusions

This study reveals risk factors associated with LUAD.

Targeting the Liver with Nucleic Acid Therapeutics for the Treatment of Systemic Diseases of Liver Origin

Systemic diseases of liver origin (SDLO) are complex diseases in multiple organ systems, such as cardiovascular, musculoskeletal, endocrine, renal, respiratory, and sensory organ systems, caused by irregular liver metabolism and production of functional factors. Examples of such diseases discussed in this article include primary hyperoxaluria, familial hypercholesterolemia, acute hepatic porphyria, hereditary transthyretin amyloidosis, hemophilia, atherosclerotic cardiovascular diseases, α-1 antitrypsin deficiency-associated liver disease, and complement-mediated diseases. Nucleic acid therapeutics use nucleic acids and related compounds as therapeutic agents to alter gene expression for therapeutic purposes. The two most promising, fastest-growing classes of nucleic acid therapeutics are antisense oligonucleotides (ASOs) and small interfering RNAs (siRNAs). For each listed SDLO disease, this article discusses epidemiology, symptoms, genetic causes, current treatment options, and advantages and disadvantages of nucleic acid therapeutics by either ASO or siRNA drugs approved or under development. Furthermore, challenges and future perspectives on adverse drug reactions and toxicity of ASO and siRNA drugs for the treatment of SDLO diseases are also discussed. In summary, this review article will highlight the clinical advantages of nucleic acid therapeutics in targeting the liver for the treatment of SDLO diseases. SIGNIFICANCE STATEMENT: Systemic diseases of liver origin (SDLO) contain rare and common complex diseases caused by irregular functions of the liver. Nucleic acid therapeutics have shown promising clinical advantages to treat SDLO. This article aims to provide the most updated information on targeting the liver with antisense oligonucleotides and small interfering RNA drugs. The generated knowledge may stimulate further investigations in this growing field of new therapeutic entities for the treatment of SDLO, which currently have no or limited options for treatment.

Nephroprotective effect of PHYMIN-22 on ethylene glycol induced urolithiasis rat model

The present study was designed to evaluate the antiurolithiatic effect of PHYMIN-22 against ethylene glycol-induced urolithiasis in rats. Healthy Albino male rats with 200-230 g body weight were randomly divided into five groups, each with 5 animals, control group, EG group (0.75%), PHYMIN-22 treatment group (0.75% EG 14 days and 100 mg/kg PHYMIN-22 next 14 days), PHYMIN-22 drug control group (100 mg/kg) and cystone treatment group (0.75% EG 14 days and 750 mg/kg cystone next 14 days). Biochemical testing was adopted for measuring the blood and urine parameters, as well as the level of antioxidants including superoxide dismutase (SOD), Catalase (Cat), Glutathione peroxidase (GPx) and glutathione (GSH) in kidney tissues. Hematoxylin and eosin (HE) staining was utilized to observe the histopathological changes in the kidney tissue. End of the experiment the PHYMIN-22 treatment reduced the urine and serum calcium (p < 0.01; p < 0.01), oxalate (p < 0.01; p < 0.01), phosphate (p < 0.01; p < 0.01), uric acid (p < 0.001; p < 0.001), protein (p < 0.001; p < 0.001), and creatinine (p < 0.001; p < 0.001) respectively, serum indicators ALT (p < 0.001) and AST (p < 0.001) level and non-enzymic antioxidant GSH (p < 0.001) compared to EG induced urolithiasis animals (Diseased control group). PHYMIN-22 treatment significantly increased urine volume, pH, and body weight, and antioxidants include CAT (p < 0.001; p < 0.001), SOD (p ˃ 0.05; p < 0.05), and GPX (p < 0.01; p < 0.001) compared to Diseased control group animals. The effect of PHYMIN-22 on EG-induced urolithiasis animals could be by improving kidney function, normalizing the urine and serum parameters, maintaining the kidney antioxidants, eliminating crystal deposition, and excretion of unwanted ions from the kidney and urinary tract.

Oxalate (dys)Metabolism: Person-to-Person Variability, Kidney and Cardiometabolic Toxicity

Oxalate is a metabolic end-product whose systemic concentrations are highly variable among individuals. Genetic (primary hyperoxaluria) and non-genetic (e.g., diet, microbiota, renal and metabolic disease) reasons underlie elevated plasma concentrations and tissue accumulation of oxalate, which is toxic to the body. A classic example is the triad of primary hyperoxaluria, nephrolithiasis, and kidney injury. Lessons learned from this example suggest further investigation of other putative factors associated with oxalate dysmetabolism, namely the identification of precursors (glyoxylate, aromatic amino acids, glyoxal and vitamin C), the regulation of the endogenous pathways that produce oxalate, or the microbiota's contribution to oxalate systemic availability. The association between secondary nephrolithiasis and cardiovascular and metabolic diseases (hypertension, type 2 diabetes, and obesity) inspired the authors to perform this comprehensive review about oxalate dysmetabolism and its relation to cardiometabolic toxicity. This perspective may offer something substantial that helps advance understanding of effective management and draws attention to the novel class of treatments available in clinical practice.

Sel1-like proteins and peptides are the major Oxalobacter formigenes-derived factors stimulating oxalate transport by human intestinal epithelial cells

Kidney stones (KSs) are very common, excruciating, and associated with tremendous healthcare cost, chronic kidney disease (CKD), and kidney failure (KF). Most KSs are composed of calcium oxalate and small increases in urinary oxalate concentration significantly enhance the stone risk. Oxalate also potentially contributes to CKD progression, kidney disease-associated cardiovascular diseases, and poor renal allograft survival. This emphasizes the urgent need for plasma and urinary oxalate lowering therapies, which can be achieved by enhancing enteric oxalate secretion. We previously identified Oxalobacter formigenes (O. formigenes)-derived factors secreted in its culture-conditioned medium (CM), which stimulate oxalate transport by human intestinal Caco2-BBE (C2) cells and reduce urinary oxalate excretion in hyperoxaluric mice by enhancing colonic oxalate secretion. Given their remarkable therapeutic potential, we now identified Sel1-like proteins as the major O. formigenes-derived secreted factors using mass spectrometry and functional assays. Crystal structures for six proteins were determined to confirm structures and better understand functions. OxBSel1-14-derived small peptides P8 and P9 were identified as the major factors, with P8 + 9 closely recapitulating the CM's effects, acting through the oxalate transporters SLC26A2 and SLC26A6 and PKA activation. Besides C2 cells, P8 + 9 also stimulate oxalate transport by human ileal and colonic organoids, confirming that they work in human tissues. In conclusion, P8 and P9 peptides are identified as the major O. formigenes-derived secreted factors and they have significant therapeutic potential for hyperoxalemia, hyperoxaluria, and related disorders, impacting the outcomes of patients suffering from KSs, enteric hyperoxaluria, primary hyperoxaluria, CKD, KF, and renal transplant recipients.NEW & NOTEWORTHY We previously identified Oxalobacter formigenes-derived secreted factors stimulating oxalate transport by human intestinal epithelial cells in vitro and reducing urinary oxalate excretion in hyperoxaluric mice by enhancing colonic oxalate secretion. We now identified Sel1-like proteins and small peptides as the major secreted factors and they have significant therapeutic potential for hyperoxalemia and hyperoxaluria, impacting the outcomes of patients suffering from kidney stones, primary and secondary hyperoxaluria, chronic kidney disease, kidney failure, and renal transplant recipients.

Determinants on urinary excretion of oxalate and other key factors related to urolithiasis among patients with chronic kidney disease: a single center study

PURPOSE

Urolithiasis is a known risk factor for chronic kidney disease (CKD). However, how CKD might affect the risk of incidence of urolithiasis is not widely studied.

METHODS

Urinary excretion of oxalate as well as other key factors related to urolithiasis was analyzed in a single center study of 572 patients with biopsy-proven kidney disease.

RESULTS

The mean age of the cohort was 44.9 years and 60% were males. The mean eGFR was 65.9 ml/min/1.73 m2. Median urinary excretion of oxalate was 14.7 (10.4-19.1) mg/24-h and associated with current urolithiasis (OR 12.744, 95% CI: 1.564-103.873 per one logarithm transformed unit of urinary oxalate excretion). Oxalate excretion was not associated with eGFR and urinary protein excretion. Oxalate excretion was higher in patients with ischemia nephropathy as compared with patients with glomerular nephropathy and tubulointerstitial nephropathy (16.4 vs 14.8 vs 12.0 mg, p = 0.018). And ischemia nephropathy (p = 0.027) was associated with urinary oxalate excretion on adjusted linear regression analysis. Urinary excretion of calcium and uric acid was correlated with eGFR and urinary protein excretion (all p < 0.001), with ischemia nephropathy and tubulointerstitial nephropathy associated with uric acid excretion (both p < 0.01) as well. Citrate excretion was correlated with eGFR (p < 0.001) on adjusted linear regression.

CONCLUSION

Excretion of oxalate and other key factors related to urolithiasis was differentially associated with eGFR, urinary protein, and pathological changes in CKD patients. The influence of these intrinsic traits of the underlining kidney disease should be considered when evaluating urolithiasis risk in patients with CKD.

Oxalate Homeostasis in Non-Stone-Forming Chronic Kidney Disease: A Review of Key Findings and Perspectives

Chronic kidney disease (CKD) is a significant global public health concern associated with high morbidity and mortality rates. The maintenance of oxalate homeostasis plays a critical role in preserving kidney health, particularly in the context of CKD. Although the relationship between oxalate and kidney stone formation has been extensively investigated, our understanding of oxalate homeostasis in non-stone-forming CKD remains limited. This review aims to present an updated analysis of the existing literature, focusing on the intricate mechanisms involved in oxalate homeostasis in patients with CKD. Furthermore, it explores the key factors that influence oxalate accumulation and discusses the potential role of oxalate in CKD progression and prognosis. The review also emphasizes the significance of the gut-kidney axis in CKD oxalate homeostasis and provides an overview of current therapeutic strategies, as well as potential future approaches. By consolidating important findings and perspectives, this review offers a comprehensive understanding of the present knowledge in this field and identifies promising avenues for further research.

Research progress on renal calculus associate with inborn error of metabolism

Renal calculus is a common disease with complex etiology and high recurrence rate. Recent studies have revealed that gene mutations may lead to metabolic defects which are associated with the formation of renal calculus, and single gene mutation is involved in relative high proportion of renal calculus. Gene mutations cause changes in enzyme function, metabolic pathway, ion transport, and receptor sensitivity, causing defects in oxalic acid metabolism, cystine metabolism, calcium ion metabolism, or purine metabolism, which may lead to the formation of renal calculus. The hereditary conditions associated with renal calculus include primary hyperoxaluria, cystinuria, Dent disease, familial hypomagnesemia with hypercalciuria and nephrocalcinosis, Bartter syndrome, primary distal renal tubular acidosis, infant hypercalcemia, hereditary hypophosphatemic rickets with hypercalciuria, adenine phosphoribosyltransferase deficiency, hypoxanthine-guanine phosphoribosyltransferase deficiency, and hereditary xanthinuria. This article reviews the research progress on renal calculus associated with inborn error of metabolism, to provide reference for early screening, diagnosis, treatment, prevention and recurrence of renal calculus.

Oxalate homeostasis

Oxalate homeostasis is maintained through a delicate balance between endogenous sources, exogenous supply and excretion from the body. Novel studies have shed light on the essential roles of metabolic pathways, the microbiome, epithelial oxalate transporters, and adequate oxalate excretion to maintain oxalate homeostasis. In patients with primary or secondary hyperoxaluria, nephrolithiasis, acute or chronic oxalate nephropathy, or chronic kidney disease irrespective of aetiology, one or more of these elements are disrupted. The consequent impairment in oxalate homeostasis can trigger localized and systemic inflammation, progressive kidney disease and cardiovascular complications, including sudden cardiac death. Although kidney replacement therapy is the standard method for controlling elevated plasma oxalate concentrations in patients with kidney failure requiring dialysis, more research is needed to define effective elimination strategies at earlier stages of kidney disease. Beyond well-known interventions (such as dietary modifications), novel therapeutics (such as small interfering RNA gene silencers, recombinant oxalate-degrading enzymes and oxalate-degrading bacterial strains) hold promise to improve the outlook of patients with oxalate-related diseases. In addition, experimental evidence suggests that anti-inflammatory medications might represent another approach to mitigating or resolving oxalate-induced conditions.

Secondary oxalate nephropathy and kidney transplantation

PURPOSE OF REVIEW

Secondary hyperoxaluria is associated with poor kidney allograft outcomes after the kidney transplant. Calcium oxalate (CaOx) deposition is common in early allograft biopsies leading to acute tubular necrosis and poor kidney allograft function. Though treatment options for secondary hyperoxaluria are limited, it is crucial to identify patients at increased risk of oxalate nephropathy after the transplant.

RECENT FINDINGS

Recent data suggest that significant changes in renal replacement therapies and dietary modifications in high-risk patients can prevent kidney allograft damage from the calcium oxalate deposition leading to improve allograft outcomes.

SUMMARY

The accurate and timely diagnosis of secondary oxalate nephropathy in kidney transplant recipients is paramount to preserving graft function in the long-term. This review will discuss the incidence, risk factors, prevention, and management of oxalate nephropathy in the kidney allograft.

Diet Management of Patients with Chronic Kidney Disease in Bariatric Surgery

Morbid obesity is considered a civilization disease of the 21st century. Not only does obesity increase mortality, but it is also the most important cause of the shortening life expectancy in the modern world. Obesity is associated with many metabolic abnormalities: dyslipidemia, hyperglycemia, cardiovascular diseases, and others. An increasing number of patients diagnosed with chronic kidney disease (CKD) are obese. Numerous additional disorders associated with impaired kidney function make it difficult to conduct slimming therapy and may also be associated with a greater number of complications than in people with normal kidney function. Currently available treatments for obesity include lifestyle modification, pharmacotherapy, and bariatric surgery (BS). There are no precise recommendations on how to reduce excess body weight in patients with CKD treated conservatively, undergoing chronic dialysis, or after kidney transplantation. The aim of this study was to analyze studies on the bariatric treatment of obesity in this group of people, as well as to compare the recommendations typical for bariatrics and CKD.

Dietary oxalate-calcium balance and the incidence of hypertension and chronic kidney disease: a prospective study among an Asian population

Background

The potential effects of dietary oxalate (Ox) intake on cardio-renal function have remained unestablished. We evaluated the effect of usual Ox intake and its interaction with dietary calcium (Ca) on incident hypertension (HTN) and chronic kidney disease (CKD).

Methods

Adult men and women, free of HTN and CKD at baseline (2006–2008), were recruited. Dietary intakes were assessed using a validated food frequency questionnaire, and the outcomes were documented up to 2014–2017. Multivariate Cox proportional hazard regression models were used to estimate the development of HTN and CKD in relation to Ox intakes. Repeated-measures generalized estimating equation (GEE) linear regression models were used to assess possible effect of Ox-intake on the estimated glomerular filtration rate (eGFR) and blood pressure levels over eight years.

Results

Dietary Ox intakes were positively associated with incident CKD (HR = 2.59, 95% CI = 1.46–4.64) and HTN (HR = 1.79, 95% CI = 1.05–3.04). Compared to high-Ca consumers, subjects who had lower Ca intakes (< 990 vs. 1580 mg/d) had a higher incidence of CKD and HTN (HR = 2.43, 95% CI = 1.06–5.55, and HR = 1.72, 95% CI = 0.76–3.78). Participants with higher intakes of Ox (> 220 vs. < 150 mg/d) had lower eGFR values (75.3, 95% CI = 75.0–76.5 vs. 77.3, 95% CI = 76.6–78.1 mL/min/1.73m², P_time×group = 0.004) and higher SBP levels (112, 95% CI = 111–113 vs. 109, 95% CI = 108–110 mmHg, P_time×group = 0.007) overtime.

Conclusion

Higher dietary Ox intake may increase the risk of HTN and CKD. The relation between dietary Ox and risk of HTN and CKD seems to be varied by Ca intake, and subjects with lower Ca intakes may be more burdened by excessive amounts of dietary Ox.

Hypoxic human proximal tubular epithelial cells undergo ferroptosis and elicit an NLRP3 inflammasome response in CD1c+ dendritic cells

Inflammasomes are multiprotein platforms responsible for the release of pro-inflammatory cytokines interleukin (IL)-1β and IL-18. Mouse studies have identified inflammasome activation within dendritic cells (DC) as pivotal for driving tubulointerstitial fibrosis and inflammation, the hallmarks of chronic kidney disease (CKD). However, translation of this work to human CKD remains limited. Here, we examined the complex tubular cell death pathways mediating inflammasome activation in human kidney DC and, thus, CKD progression. Ex vivo patient-derived proximal tubular epithelial cells (PTEC) cultured under hypoxic (1% O₂) conditions modelling the CKD microenvironment showed characteristics of ferroptotic cell death, including mitochondrial dysfunction, reductions in the lipid repair enzyme glutathione peroxidase 4 (GPX4) and increases in lipid peroxidation by-product 4-hydroxynonenal (4-HNE) compared with normoxic PTEC. The addition of ferroptosis inhibitor, ferrostatin-1, significantly reduced hypoxic PTEC death. Human CD1c⁺ DC activated in the presence of hypoxic PTEC displayed significantly increased production of inflammasome-dependent cytokines IL-1β and IL-18. Treatment of co-cultures with VX-765 (caspase-1/4 inhibitor) and MCC950 (NLRP3 inflammasome inhibitor) significantly attenuated IL-1β/IL-18 levels, supporting an NLRP3 inflammasome-dependent DC response. In line with these in vitro findings, in situ immunolabelling of human fibrotic kidney tissue revealed a significant accumulation of tubulointerstitial CD1c⁺ DC containing active inflammasome (ASC) specks adjacent to ferroptotic PTEC. These data establish ferroptosis as the primary pattern of PTEC necrosis under the hypoxic conditions of CKD. Moreover, this study identifies NLRP3 inflammasome signalling driven by complex tubulointerstitial PTEC-DC interactions as a key checkpoint for therapeutic targeting in human CKD.

Acute oxalate nephropathy: A potential cause of acute kidney injury in diabetes mellitus—A case series from a single center

Background

Acute oxalate nephropathy (AON) is an uncommon condition that causes acute kidney injury (AKI), characterized by the massive deposition of calcium oxalate crystals in the renal parenchyma. In previous studies, urinary oxalate excretion has been found to be increased in patients with diabetes mellitus (DM). Here, we report a case series of diabetic patients with AKI with biopsy-proven AON, aiming to alert physicians to the potential of AON as a trigger of AKI in diabetic patients in clinical practice.

Materials and methods

Cases with pathological diagnosis of AON who presented with AKI clinically and had DM between January 2016 and December 2020 were retrospectively enrolled. Their clinical and pathological manifestations, treatment, and prognosis were collected.

Results

Six male patients with biopsy-proven AON out of a total of 5,883 native kidney biopsies were identified, aged 58.3 ± 9.1 years at the time of kidney biopsy. Only one patient who had received Roux-en-Y gastric bypass surgery took oxalate-rich food before the onset of the disease. None of them had clinical features of enteric malabsorption. Three patients were currently on renin-angiotensin system inhibitor treatment for hypertension, and 5 of them received non-steroidal anti-inflammatory drugs. Three patients presented with oliguria and 4 patients needed dialysis at the beginning with none requiring dialysis at discharge. Four patients received a course of corticosteroid treatment empirically. Among them, two patients had estimated glomerular filtration rate (eGFR) recovered to over 60 ml/min/1.73 m2, while the other two patients remained with kidney dysfunction at the last follow-up. In two patients without corticosteroid treatment, one patient fully recovered with eGFR over 90 ml/min/1.73 m2 and the other patient remained with kidney dysfunction at the last follow-up.

Conclusion

AON might be a rare but potentially trigger of AKI in patients with DM. A kidney biopsy could help physicians to make the correct diagnosis. The proper treatment to alleviate oxalate-induced injury needs to be further studied.

The Role of Inflammasomes in Mediating Urological Disease: A Short Literature Review

Inflammasome dysfunction may be responsible for underlying inflammatory diseases, which include renal and urological pathologies. Five inflammasomes have been described, including nucleotide-binding domain leucine-rich repeat (NLR), NL pyrin domain containing receptor 1(NLPR1), NLRP3, NLR and caspase recruitment domain containing receptor 4 (NLRC4), and the AIM2-like receptor. The purpose of this study was to review literature sources regarding how innate immunity and inflammasomes contribute to urologic disease and infection. A literature search of PubMed/MEDLINE, EMBASE and Google Scholar articles. Articles were selected for review if their content included (1) inflammasomes and (2) urology in the adult population. The initiation of specific cytokine cascades, which include IL-1β and IL-18, appear responsible for a repertoire of urologic pathologies. Inflammation mediates a wide range of uropathies (urologic disorders and infections) which are found in the bladder, prostate, or kidney and inflammasomes appear to be particularly responsible for urological and renal pathologies. Understanding the role of inflammasomes in urologic disorders can help improve treatment and overall quality of life in patients with these disorders.

The association between platelet-lymphocyte ratio and the risk of all-cause mortality in chronic kidney disease: a systematic review and meta-analysis

BACKGROUND

Chronic kidney disease (CKD) patients have high levels of inflammatory mediators. These inflammatory mediators contribute to the increased risk of cardiovascular events and all-cause mortality. Platelet-lymphocyte ratio (PLR) has recently been recognized as a novel inflammatory marker and has been shown to be associated with the prognosis in CKD patients. However, the quality of these studies varies and their results are controversial. The purpose of this meta-analysis was to investigate the relationship between PLR and all-cause mortality in CKD patients.

METHODS

A systematic literature search of PubMed, EMBASE, CENTRAL and ISI Web of Science was conducted. The databases were searched from their inception dates up to the latest issue (31 October 2021). Two reviewers independently searched the databases and screened studies. Data were extracted using a standardized collection form. Meta-analysis was performed to compare PLR values between CKD and non-CKD patients, and to investigate the association between PLR and all-cause mortality in CKD patients. This meta-analysis is reported in adherence to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).

RESULTS

A total of 11 studies involving 4244 participants were selected. The pooled data indicated that PLR values were significantly higher in CKD patients than non-CKD controls (weighted mean difference = 21.6, 95% CI 17.39-25.81, p < 0.01), and PLR is associated with an increased risk of all-cause mortality in CKD patients (hazard ratio = 2.49, 95% CI 1.78-3.49, p < 0.01).

CONCLUSIONS

Patients with CKD have higher PLR values compared to non-CKD patients. Meanwhile, PLR values were highly associated with all-cause mortality in CKD patients. PLR is a valid predictor as a clinically accessible indicator for patients with CKD.

Pathophysiology and Management of Hyperoxaluria and Oxalate Nephropathy: A Review

Hyperoxaluria results from either inherited disorders of glyoxylate metabolism leading to hepatic oxalate overproduction (primary hyperoxaluria), or increased intestinal oxalate absorption (secondary hyperoxaluria). Hyperoxaluria may lead to urinary supersaturation of calcium oxalate and crystal formation, causing urolithiasis and deposition of calcium oxalate crystals in the kidney parenchyma, a condition termed oxalate nephropathy. Considerable progress has been made in the understanding of pathophysiological mechanisms leading to hyperoxaluria and oxalate nephropathy, whose diagnosis is frequently delayed and prognosis too often poor. Fortunately, novel promising targeted therapeutic approaches are on the horizon in patients with primary hyperoxaluria. Patients with secondary hyperoxaluria frequently have long-standing hyperoxaluria-enabling conditions, a fact suggesting the role of triggers of acute kidney injury such as dehydration. Current standard of care in these patients includes management of the underlying cause, high fluid intake, and use of calcium supplements. Overall, prompt recognition of hyperoxaluria and associated oxalate nephropathy is crucial because optimal management may improve outcomes.

Primary hyperoxaluria type 1: pathophysiology and genetics

Primary hyperoxaluria type 1 (PH1) is a rare genetic form of calcium oxalate kidney stone disease. It is caused by a deficiency in the liver-specific enzyme, alanine:glyoxylate aminotransferase (AGT), a pyridoxal-5'-phosphate (PLP)-dependent enzyme involved in the metabolism of glyoxylate. The excessive endogenous synthesis of oxalate that ensues leads to hyperoxaluria, and the crystallization of the poorly soluble calcium salt of oxalate is responsible for a severe kidney stone disease, which can progress to end-stage renal disease, systemic deposition of oxalate and death. Knowledge about metabolic precursors of glyoxylate and oxalate, molecular pathology of AGT and analytical methods for diagnosis and clinical assessment have allowed a better understanding of the mechanisms underlying PH1 and opened the door to new therapeutic strategies.

Dietary oxalate to calcium ratio and incident cardiovascular events: a 10-year follow-up among an Asian population

Background and aim

The potential cardiovascular impact of usual intakes of oxalate (Ox) is uninvestigated. We evaluated the effect of dietary Ox and its interaction with dietary calcium (Ca) on incident cardiovascular disease (CVD).

Methods

We included 2966 adult men and women aged 19–84 y without known CVD during baseline enrollment (2006–2008) of the Tehran Lipid and Glucose Study. Dietary intakes were assessed using a validated FFQ, and incident CVD (i.e., coronary heart disease, stroke, and CVD mortality) were documented through March 2018.

Results

A 7.1% incident of CVD occurred during a median follow-up of 10.6 y. After multivariable adjustment for traditional risk factors and key dietary nutrients, including total fat and fiber, Ox intakes ≥220 mg/d increased incident CVD (HR T3 vs. T1 = 1.47, 95% CI = 1.02–2.12). This association was potentiated (HR T3 vs. T1 = 2.42, 95% CI = 1.19–4.89) in subjects who had a lower intake of Ca (< 981 mg/d); in a low-Ca diet, an even lower amount of dietary Ox (second tertile, 148–220 mg/d) was related to increased CVD events by 92% (HR = 1.92, 95% CI = 1.00–3.70). No association was observed between dietary Ox and CVD events in the presence of medium- and high levels of Ca intakes. The critical cut-off point of Ox-to-Ca for predicting CVD events was 0.14, which was related to an increased risk of CVD by 37% (HR = 1.37, 95% CI = 1.02–1.84).

Conclusion

Higher dietary Ox intake appeared to be associated with a modestly elevated risk of incident CVD, especially in a diet with a lower amount of Ca.

Oxalate Balance in Peritoneal Dialysis Patients: A Potential Role of Dialysis-related Peritonitis

BACKGROUND

Little evidence is available on oxalate balance in peritoneal dialysis (PD) patients.

PATIENTS AND METHODS

We performed a cross-sectional observational pilot study with 62 adult PD patients to document oxalate balance and explore its association with PD-related peritonitis. Plasma oxalate concentration, levels of oxalate excretion in 24-h urine, and peritoneal dialysis effluent were evaluated. The peritoneal oxalate transport status and renal and peritoneal oxalate clearances were calculated according to the PD-related peritonitis history.

RESULTS

PD patients with a history of peritonitis had a statistically significantly lower peritoneal oxalate clearance, daily peritoneal oxalate excretion, and overall oxalate removal rate compared with the peritonitis-free PD patients. They had a 4-fold risk of plasma oxalic acid increase, and even a single episode of dialysis-related peritonitis resulted in plasma oxalate elevation.

CONCLUSION

Peritoneal oxalate clearance plays an important role in oxalate balance in PD patients and, therefore, dialysis-related peritonitis is a significant predictor for hyperoxalemia. Further well-designed clinical trials need to be undertaken before the association between peritonitis and oxalate balance in PD patients is more clearly understood.

Plasma oxalic acid and cardiovascular risk in end-stage renal disease patients: a prospective, observational cohort pilot study

BACKGROUND/AIMS

It was hypothesized that oxalate might be strongly involved in atherogenesis and the inflammatory pathway that could result in an increased risk of cardiovascular disease (CVD) in end-stage renal disease (ESRD) patients. Therefore, this study aimed to address two primary research questions: to characterize the lipid profile and the pattern of pro-inflammatory cytokines according to plasma oxalic acid (POx) concentration in ESRD patients; to evaluate the potential role of elevated POx concentration in the development of CVD risk.

METHODS

A total of 73 participants were enrolled in this prospective, observational cohort pilot study. Among them, there were 50 ESRD patients and 23 healthy volunteers. The lipid profile and the pro-inflammatory cytokines were analyzed according to the distribution of POx concentration into tertiles. After the clinical examination, 29 hemodialysis patients and 21 peritoneal dialysis patients without prevalent CVD were observed for CVD events for 2 years. The Cox regression analysis and a set of different types of sensitivity analyses were used to determine whether elevated POx was associated with an increased risk of CVD.

RESULTS

An increasing trend in the atherogenic lipoprotein fractions and the pro-inflammatory markers as well as a linear decrease in high-density lipoprotein was significantly associated with elevated POx. POx concentration ≥ 62.9 μmol/L was significantly associated with CVD events independently of other examined CVD risk factors.

CONCLUSION

This pilot study firstly demonstrated a potential contribution of POx to atherogenesis, inflammation and CVD risk in ESRD patients.

Perspectives in primary hyperoxaluria - historical, current and future clinical interventions

Primary hyperoxalurias are a devastating family of diseases leading to multisystem oxalate deposition, nephrolithiasis, nephrocalcinosis and end-stage renal disease. Traditional treatment paradigms are limited to conservative management, dialysis and combined transplantation of the kidney and liver, of which the liver is the primary source of oxalate production. However, transplantation is associated with many potential complications, including operative risks, graft rejection, post-transplant organ failure, as well as lifelong immunosuppressive medications and their adverse effects. New therapeutics being developed for primary hyperoxalurias take advantage of biochemical knowledge about oxalate synthesis and metabolism, and seek to specifically target these pathways with the goal of decreasing the accumulation and deposition of oxalate in the body.

Primary hyperoxalurias are a devastating family of diseases that eventually lead to end-stage renal disease. In this Review, Shee and Stoller discuss current treatment paradigms for primary hyperoxalurias, new therapeutics and their mechanisms of action, and future directions for novel research in the field.

Primary hyperoxalurias (PHs) are a devastating family of rare, autosomal-recessive genetic disorders that lead to multisystem oxalate deposition, nephrolithiasis, nephrocalcinosis and end-stage renal disease.

Traditional treatment paradigms are limited to conservative management, dialysis and inevitably transplantation of the kidney and liver, which is associated with high morbidity and the need for lifelong immunosuppression.

New therapeutics being developed for PHs take advantage of biochemical knowledge about oxalate synthesis and metabolism to specifically target these pathways, with the goal of decreasing the accumulation and deposition of plasma oxalate in the body.

New therapeutics can be divided into classes, and include substrate reduction therapy, intestinal oxalate degradation, chaperone therapy, enzyme restoration therapy and targeting of the inflammasome.

Lumasiran, a mRNA therapeutic targeting glycolate oxidase, was the first primary hyperoxaluria-specific therapeutic approved by the European Medicines Agency and the FDA in 2020.

Future work includes further clinical trials for promising therapeutics in the pipeline, identification of biomarkers of response to PH-directed therapy, optimization of drug development and delivery of new therapeutics.

Cashew-Induced Oxalate Nephropathy: A Rare Cause of Acute Renal Failure

We present a rare case of cashew-induced oxalate nephropathy in a 69 year old veteran male with history of type 2 diabetes mellitus, nephrolithiasis, and undiagnosed chronic kidney disease (CKD). Oxalate nephropathy is a rare cause of acute renal failure with poor prognosis. The various causes of oxalate nephropathy are categorized as primary or secondary hyperoxaluria. Primary hyperoxaluria is caused by genetic mutation in genes involved in the metabolism of glyoxylate. Secondary hyperoxaluria is caused by mal-absorptive state, excessive intake of oxalate-rich diet, inflammatory diseases, and medications such as orlistat and antibiotics. Diet-induced oxalate nephropathy is often identified after unexplained acute kidney injury in patients with underlying CKD. Definitive diagnosis requires renal biopsy as laboratory tests are non-specific. A simple dietary history in CKD patients during routine primary care visit may lead to early diagnosis and lead to prevention of acute renal failure and progression of renal disease.

Bacterial-Induced Blood Pressure Reduction: Mechanisms for the Treatment of Hypertension via the Gut

Hypertension is a major risk factor for the development of cardiovascular disease. As more research into the gut microbiome emerges, we are finding increasing evidence to support that these microbes may have significant positive and negative effects on blood pressure and associated disorders. The bacterial-derived metabolites that are produced in the gut are capable of widespread effects to several tissue types and organs in the body. It is clear that the extensive metabolic function that is lost with gut dysbiosis is unlikely to be replenished with a single metabolite or bacterial strain. Instead, combinations of bacteria and concomitant therapies will provide a more well-rounded solution to manage hypertension. The bioactive molecules that are recognized in this review will inform on ideal characteristics of candidate bacteria and provide direction for future research on the gut microbiome in hypertension.

Novel therapeutic approaches for the primary hyperoxalurias

Loss-of-function mutations in three genes, involved in the metabolic pathway of glyoxylate, result in increased oxalate production and its crystallization in the form of calcium oxalate. This leads to three forms of primary hyperoxaluria-an early-onset inherited kidney disease with wide phenotypic variability ranging from isolated kidney stone events to stage 5 chronic kidney disease in infancy. This review provides a description of metabolic processes resulting in oxalate overproduction and summarizes basic therapeutic approaches. Unfortunately, current treatment of primary hyperoxaluria does not allow the prevention of loss of kidney function or to substantially diminish other symptoms in most patients. However, latest breakthroughs in biotechnology provide new promising directions for drug development. Some of them have already progressed to the level of clinical trials; others are just at the stage of proof of concept. Here we review the most advanced technologies including those that have been harnessed as possible therapeutic modalities.

A Sodium Oxalate-Rich Diet Induces Chronic Kidney Disease and Cardiac Dysfunction in Rats

Chronic kidney disease (CKD) is a worldwide public health issue affecting 14% of the general population. However, research focusing on CKD mechanisms/treatment is limited because of a lack of animal models recapitulating the disease physiopathology, including its complications. We analyzed the effects of a three-week diet rich in sodium oxalate (OXA diet) on rats and showed that, compared to controls, rats developed a stable CKD with a 60% reduction in glomerular filtration rate, elevated blood urea levels and proteinuria. Histological analyses revealed massive cortical disorganization, tubular atrophy and fibrosis. Males and females were sensitive to the OXA diet, but decreasing the diet period to one week led to GFR significance but not stable diminution. Rats treated with the OXA diet also displayed classical CKD complications such as elevated blood pressure and reduced hematocrit. Functional cardiac analyses revealed that the OXA diet triggered significant cardiac dysfunction. Altogether, our results showed the feasibility of using a convenient and non-invasive strategy to induce CKD and its classical systemic complications in rats. This model, which avoids kidney mass loss or acute toxicity, has strong potential for research into CKD mechanisms and novel therapies, which could protect and postpone the use of dialysis or transplantation.

Hydroxycitrate prevents calcium oxalate crystallization and kidney injury in a nephrolithiasis rat model

Hydroxycitrate (HCA) is a derivative of citric acid, and previous studies of HCA have revealed its ability to inhibit the formation of calcium oxalate crystals in vitro. To date, there has been little evidence proving that HCA has the same effectiveness in vivo. The present study was designed to investigate the ameliorating effect of HCA on calcium oxalate deposition and renal impairment in a male rat model. Male Sprague-Dawley rats were randomly divided into four groups: a control group, a model group (glyoxalic acid), a CA group (glyoxalic acid + CA), and an HCA group (glyoxalic acid + HCA). Kidney stone formation was induced by injection of glyoxalic acid (60 mg/kg). The results showed that serum and urinary parameters were significantly improved by HCA treatment. In addition, differences in the formation of calcium oxalate crystals between groups were observed, and HCA was superior to CA in inhibiting crystal accumulation. The ultrastructure of renal tubules and glomeruli occurred in the model group, and the above lesions were significantly reduced in the HCA group. Both OPN and SOD expression levels were promoted by HCA, while CA only promoted OPN. In this article, we provided data on whether HCA affected kidney stones and the expression levels of OPN and SOD in a male rat model.

TRPV1 Hyperfunction Contributes to Renal Inflammation in Oxalate Nephropathy

Inflammation worsens oxalate nephropathy by exacerbating tubular damage. The transient receptor potential vanilloid 1 (TRPV1) channel is present in kidney and has a polymodal sensing ability. Here, we tested whether TRPV1 plays a role in hyperoxaluria-induced renal inflammation. In TRPV1-expressed proximal tubular cells LLC-PK₁, oxalate could induce cell damage in a time- and dose-dependent manner; this was associated with increased arachidonate 12-lipoxygenase (ALOX12) expression and synthesis of endovanilloid 12(S)-hydroxyeicosatetraenoic acid for TRPV1 activation. Inhibition of ALOX12 or TRPV1 attenuated oxalate-mediated cell damage. We further showed that increases in intracellular Ca²⁺ and protein kinase C α activation are downstream of TRPV1 for NADPH oxidase 4 upregulation and reactive oxygen species formation. These trigger tubular cell inflammation via increased NLR family pyrin domain-containing 3 expression, caspase-1 activation, and interleukin (IL)-1β release, and were alleviated by TRPV1 inhibition. Male hyperoxaluric rats demonstrated urinary supersaturation, tubular damage, and oxidative stress in a time-dependent manner. Chronic TRPV1 inhibition did not affect hyperoxaluria and urinary supersaturation, but markedly reduced tubular damage and calcium oxalate crystal deposition by lowering oxidative stress and inflammatory signaling. Taking all these results together, we conclude that TRPV1 hyperfunction contributes to oxalate-induced renal inflammation. Blunting TRPV1 function attenuates hyperoxaluric nephropathy.

Evaluation of a high-performance liquid chromatography method for urinary oxalate determination and investigation regarding the pediatric reference interval of spot urinary oxalate to creatinine ratio for screening of primary hyperoxaluria

BACKGROUND

Urinary oxalate can provide important clues for the screening and monitoring of children with primary hyperoxaluria (PH), which is a potentially life-threatening condition. However, little effort has been devoted to improve the oxalate assay in recent years. We have proposed a reliable and cost-effective high-performance liquid chromatography (HPLC) method for urinary oxalate determination.

METHODS

Urine specimens were centrifuged after one-step derivatization, and the supernatants were subjected to HPLC analysis.

RESULTS

The method was validated with consistent linearity from 0.0625 to 2.0 mmol/L with coefficients of variation ≤7.73%, good recovery, low carryover, satisfactory sample stability, and analytical specificity. The lower limit of quantification and the limit of detection were 0.03130 and 0.0156 mmol/L, respectively. Imprecision values were ≤2.92% and ≤16.6% for externally and internally produced controls, respectively. The pediatric reference interval of spot urinary oxalate to creatinine ratios was established together with its application in screening of PH in patients with renal diseases, revealing its successful deployment in our laboratory.

CONCLUSIONS

This reliable HPLC method could serve as a significant tool to determine urinary oxalate levels for screening and monitoring of children with PH in routine clinical laboratories.

Vitexin exerts protective effects against calcium oxalate crystal-induced kidney pyroptosis in vivo and in vitro

BACKGROUND

Nephrolithiasis is a common urinary disease with a high recurrence rate of secondary stone formation. Several mechanisms are involved in the onset and recurrence of nephrolithiasis, e.g., oxidative stress, inflammation, apoptosis, and epithelial-mesenchymal transition (EMT). Vitexin, a flavonoid monomer derived from medicinal plants that exert many biological effects including anti-inflammatory and anticancer effects, has not been investigated in nephrolithiasis studies. Moreover, pyroptosis, a form of programmed cell death resulting from inflammasome-associated caspase activation, has not been studied in mice with nephrolithiasis.

PURPOSE

We aimed to investigate the protective effect and underlying mechanisms of vitexin in nephrolithiasis, and the related role of pyroptosis in vivo and in vitro.

METHODS

Mouse models of nephrolithiasis were established via intraperitoneal injection of glyoxylate, and cell models of tubular epithelial cells and macrophages were established using calcium oxalate monohydrate (COM). Crystal deposition and kidney tissue injury were evaluated by hematoxylin and eosin, and von Kossa staining. Renal oxidative stress indexes including malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH), and catalase (CAT), were analyzed. The renal expression of interleukin-1 beta (IL-1β), gasdermin D (GSDMD), osteopontin (OPN), CD44, and monocyte chemotactic protein 1 (MCP-1), and EMT-related proteins in renal tubular epithelial cells was assessed. Cell viability and the apoptosis ratio were evaluated.

RESULTS

In vivo, vitexin alleviated crystal deposition and kidney tissue injury, and decreased the level of MDA, and increased the levels of SOD, GSH, and CAT. Vitexin also reduced the levels of the pyroptosis-related proteins GSDMD, NLRP3, cleaved caspase-1, and mature IL-1β, which were elevated in mice with nephrolithiasis, and repressed apoptosis and the expression of OPN and CD44. Moreover, vitexin mitigated F4/80-positive macrophage infiltration and MCP-1 expression in the kidneys. Furthermore, an in vitro study showed that vitexin increased the viability of HK-2 cells and THP-1-derived macrophages, which was impaired by treatment with COM crystals, decreased the medium lactate dehydrogenase (LDH) level, and inhibited the expression of pyroptosis-related proteins in HK-2 cells and macrophages. Vitexin repressed EMT of HK-2 cells, with increased expression of pan-cytokeratin (Pan-ck) and decreased expression of Vimentin and alpha-smooth muscle actin (α-SMA), and downregulated the Wnt/β-catenin pathway. Moreover, vitexin suppressed tumor necrosis factor-α (TNF-α) and IL-1β mRNA expression, which was upregulated by COM in macrophages.

CONCLUSION

Vitexin exerts protective effects against nephrolithiasis by inhibiting pyroptosis activation, apoptosis, EMT, and macrophage infiltration. In addition, GSDMD-related pyroptosis mediates nephrolithiasis.

Plant-Based Milk Alternatives and Risk Factors for Kidney Stones and Chronic Kidney Disease

OBJECTIVE

Patients with kidney stones are counseled to eat a diet low in animal protein, sodium, and oxalate and rich in fruits and vegetables, with a modest amount of calcium, usually from dairy products. Restriction of sodium, potassium, and oxalate may also be recommended in patients with chronic kidney disease. Recently, plant-based diets have gained popularity owing to health, environmental, and animal welfare considerations. Our objective was to compare concentrations of ingredients important for kidney stones and chronic kidney disease in popular brands of milk alternatives.

DESIGN AND METHODS

Sodium, calcium, and potassium contents were obtained from nutrition labels. The oxalate content was measured by ion chromatography coupled with mass spectrometry.

RESULTS

The calcium content is highest in macadamia followed by soy, almond, rice, and dairy milk; it is lowest in cashew, hazelnut, and coconut milk. Almond milk has the highest oxalate concentration, followed by cashew, hazelnut, and soy. Coconut and flax milk have undetectable oxalate levels; coconut milk also has comparatively low sodium, calcium, and potassium, while flax milk has the most sodium. Overall, oat milk has the most similar parameters to dairy milk (moderate calcium, potassium and sodium with low oxalate). Rice, macadamia, and soy milk also have similar parameters to dairy milk.

CONCLUSION

As consumption of plant-based dairy substitutes increases, it is important for healthcare providers and patients with renal conditions to be aware of their nutritional composition. Oat, macadamia, rice, and soy milk compare favorably in terms of kidney stone risk factors with dairy milk, whereas almond and cashew milk have more potential stone risk factors. Coconut milk may be a favorable dairy substitute for patients with chronic kidney disease based on low potassium, sodium, and oxalate. Further study is warranted to determine the effect of plant-based milk alternatives on urine chemistry.

Critically ill, tubular injury, delayed early recovery: characteristics of acute kidney disease with renal oxalosis

Objects

This study aimed to analyze the clinicopathological features of acute kidney disease (AKD) with renal oxalosis.

Methods

Data for biopsy-proven AKD with oxalosis diagnosed from Jan 2011 to Oct 2018 was collected. The underlying diseases, dietary habits, clinical and pathological characteristics of newly emerging kidney disease were analyzed. The long-term renal prognosis was observed.

Results

A total of 23 patients were included, comprised of 18 men and 5 women with a mean age of 51.6 ± 15.9 years. The peak Scr was 669.9 ± 299.8 μmol/L, and 95.7% of patients had stage 3 acute kidney injury (AKI). Drug-induced tubulointerstitial nephritis (TIN) was the most common cause (65.2%) of AKD, followed by severe nephrotic syndrome (17.4%). All patients had pathological changes indicating TIN, and 11 patients were complicated with the newly emerging glomerular disease (GD). The risk of oxalosis caused by increased enterogenous oxalate absorption accounted for only 26.1%, and others came from new kidney diseases. The majority (75%) of abundant (medium to severe) oxalosis occurred in patients without GD. There were no significant differences in the score for tubular injury (T-IS) and interstitial inflammation with different severities of oxalosis. Rate of Scr decrease (ΔScr%) at 2 weeks was negatively correlated with the severity of oxalosis (R = −0.542, p = 0.037), score for T-IS (R = −0.553, p = 0.033), and age (R = −0.736, p = 0.002). The decrease in Scr at 4 weeks was correlated with T-IS (R = −0.433), but had no correlation with oxalosis.

Conclusions

The present findings revealed that 95.7% of AKD with secondary renal oxalosis occurred in critically ill patients. AKD from tubular injury was the prominent cause. Severe oxalosis contributed to delayed early recovery of AKD.

Gut-kidney axis in oxalate homeostasis

PURPOSE OF REVIEW

The gut-kidney axis plays a critical role in oxalate homeostasis, and better understanding of oxalate transport regulatory mechanisms is essential for developing novel therapies.

RECENT FINDINGS

Oxalate potentially contributes to chronic kidney disease (CKD) progression, CKD - and end stage renal disease (ESRD)-associated cardiovascular diseases, polycystic kidney disease (PKD) progression, and/or poor renal allograft survival, emphasizing the need for plasma and urinary oxalate lowering therapies. One promising strategy would be to enhance the bowel's ability to secrete oxalate, which might be facilitated by the following findings. Oxalobacter formigenes (O. formigenes)-derived factors recapitulate O. formigenes colonization effects by reducing urinary oxalate excretion in hyperoxaluric mice by inducing colonic oxalate secretion. Protein kinase A activation stimulates intestinal oxalate transport by enhancing the surface expression of the oxalate transporter SLC26A6 (A6). Glycosylation also stimulates A6-mediated oxalate transport. The colon adapts to chronic acidosis in rats through increased colonic oxalate secretion as previously reported in CKD rats, and A6-mediated enteric oxalate secretion is critical in reducing the body oxalate burden in CKD mice. Intestinal oxalate transport is negatively regulated by proinflammatory cytokines and cholinergic, purinergic, and adenosinergic signaling.

SUMMARY

These findings could facilitate the development of novel therapeutics for hyperoxalemia, hyperoxaluria, and related disorders if similar regulatory mechanisms are confirmed in humans.

Evaluation of transporter expression in HK-2 cells after exposure to free and ester-bound 3-MCPD

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3-Monochloropropane-1,2-diol (3-MCPD) and its fatty acid esters have the potential to induce nephrotoxicity.

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We used an in vitro cellular model of human proximal tubule cells to test the effects of 3-MCPD compound exposures on transporter gene expression.

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3-MCPD-related nephrotoxicity could be associated with indirect modes of action relating to aquaporin homeostasis.

3-Monochloropropane-1,2-diol (3-MCPD) is a food processing contaminant in some infant formula products and other foods in the United States. Although rodent studies have demonstrated that 3-MCPD and its palmitic esters have the potential to induce nephrotoxicity, our recent human cell culture studies using the human renal proximal tubule cell line HK-2 have not strongly supported this finding. Considering this disparity, we sought to examine whether changes in transporter gene expression on proximal tubule cells could be modulated by these compounds and allow us to glean mechanistic information on a possible indirect path to proximal tubule injury in vivo. If fundamental processes like water and solute transport could be disrupted by 3-MCPD compounds, then a new avenue of toxicity could be further explored in both infant and adult models. In our current study, we used HK-2 cells as an in vitro cellular model of human proximal tubule cells to investigate the effects of low (10 μM) and high (100 μM) 3-MCPD compound exposures to these cells for 24 hours (h) on the expression of 20 transporter genes that are known to be relevant to proximal tubules. Although we detected consistent upregulation of AQP1 expression at the RNA transcript level following HK-2 treatment with both low and high doses of several ester-bound 3-MCPD compounds, these increases were not associated with statistically significant elevations in their protein expression levels. Moreover, we observed a lack of modulation of other members of the AQP protein family that are known to be expressed by human proximal tubule cells. Overall, our study suggests the possibility that 3-MCPD-related nephrotoxicity could be associated with indirect modes of action relating to aquaporin homeostasis, but additional studies with other human-derived models would be pertinent to further explore these findings and to better understand transporter expression differences under different stages of proximal tubule development.

Review on Inflammation Markers in Chronic Kidney Disease

Chronic kidney disease (CKD) is one of the major health problems of the modern age. It represents an important public health challenge with an ever-lasting rising prevalence, which reached almost 700 million by the year 2017. Therefore, it is very important to identify patients at risk for CKD development and discover risk factors that cause the progression of the disease. Several studies have tackled this conundrum in recent years, novel markers have been identified, and new insights into the pathogenesis of CKD have been gained. This review summarizes the evidence on markers of inflammation and their role in the development and progression of CKD. It will focus primarily on cytokines, chemokines, and cell adhesion molecules. Nevertheless, further large, multicenter studies are needed to establish the role of these markers and confirm possible treatment options in everyday clinical practice.

6,7-Dihydroxycoumarin ameliorates crystal-induced necroptosis during crystal nephropathies by inhibiting MLKL phosphorylation

AIMS

Mineralization of crystalline particles and the formation of renal calculi contribute to the pathogenesis of crystal nephropathies. Several recent studies on the biology of crystal handling implicated intrarenal crystal deposition-induced necroinflammation in their pathogenesis. We hypothesized that 6,7-dihydroxycoumarin (DHC) inhibit intrarenal crystal cytotoxicity and necroinflammation, and ameliorate crystal-induced chronic kidney disease (CKD).

MAIN METHODS

An unbiased high content screening coupled with fluorescence microscopy was used to identify compounds that inhibit CaOx crystal cytotoxicity. The ligand-protein interactions were identified using computational models e.g. molecular docking and molecular dynamics simulations. Furthermore, mice and rat models of oxalate-induced CKD were used for in-vivo studies. Renal injury, crystal deposition, and fibrosis were assessed by histology analysis. Western blots were used to quantify the protein expression. Data were expressed as boxplots and analyzed using one way ANOVA.

KEY FINDINGS

An unbiased high-content screening in-vitro identified 6,7-DHC as a promising candidate. Further, 6,7-DHC protected human and mouse cells from calcium oxalate (CaOx) crystal-induced necroptosis in-vitro as well as mice and rats from oxalate-induced CKD in either preventive or therapeutic manner. Computational modeling demonstrated that 6,7-DHC interact with MLKL, the key protein in the necroptosis machinery, and inhibit its phosphorylation by ATP, which was evident in both in-vitro and in-vivo analyses.

SIGNIFICANCE

Together, our results indicate that 6,7-DHC possesses a novel pharmacological property as a MLKL inhibitor and could serve as a lead molecule for further development of coumarin-based novel MLKL inhibitors. Furthermore, our data identify 6,7-DHC as a novel therapeutic strategy to combat crystal nephropathies.

Reversibility of oxalate nephropathy in a kidney transplant recipient with prior gastric bypass surgery

Bariatric surgery is an acknowledged treatment for obesity and related comorbidities with beneficial effects on kidney function. However, bariatric surgery can also lead to secondary hyperoxaluria and oxalate nephropathy, resulting in end-stage kidney disease in both native and transplanted kidneys. We present a 66-year-old man who was in need of dialysis 3 months after kidney transplantation due to recurrent oxalate nephropathy. Intensified haemodialysis together with increased liquid intake, dietary restrictions of oxalate and fat and supplementation with calcium citrate and a bile acid binder were applied. Graft function improved and the patient did not require dialysis during the following 8 months.

Plasma oxalate and eGFR are correlated in primary hyperoxaluria patients with maintained kidney function-data from three placebo-controlled studies

BACKGROUND

In patients with primary hyperoxaluria (PH), endogenous oxalate overproduction increases urinary oxalate excretion, leading to compromised kidney function and often kidney failure. Highly elevated plasma oxalate (Pox) is associated with systemic oxalate deposition in patients with PH and severe chronic kidney disease (CKD). The relationship between Pox and estimated glomerular filtration rate (eGFR) in patients with preserved kidney function, however, is not well established. Our analysis aimed to investigate a potential correlation between these parameters in PH patients from three randomized, placebo-controlled trials (studies OC3-DB-01, OC3-DB-02, and OC5-DB-01).

METHODS

Baseline data from patients with a PH diagnosis (type 1, 2, or 3) and eGFR > 40 mL/min/1.73 m² were analyzed for a correlation between eGFR and Pox using Spearman's rank and Pearson's correlation coefficients. Data were analyzed by individual study and additionally were pooled for Studies OC3-DB-02 and OC5-DB-01 in which the same Pox assay was used.

RESULTS

A total of 106 patients were analyzed. A statistically significant inverse Spearman's correlation between eGFR and Pox was observed across all analyses; correlation coefficients were - 0.44 in study OC3-DB-01, - 0.55 in study OC3-DB-02, - 0.51 in study OC5-DB-01, and - 0.49 in the pooled studies (p < 0.0064).

CONCLUSIONS

Baseline evaluations showed a moderate and statistically significant inverse correlation between eGFR and Pox in patients with PH already at early stages of CKD (stages 1-3b), demonstrating that a correlation is present before substantial loss in kidney function occurs.

Association of neutrophil-to-lymphocyte ratio and risk of cardiovascular or all-cause mortality in chronic kidney disease: a meta-analysis

BACKGROUND

It is currently controversial whether neutrophil-to-lymphocyte ratio (NLR) has a prognostic role in patients with chronic kidney disease (CKD). We aimed to investigate whether NLR was an independent predictor of cardiovascular or all-cause mortality in CKD patients with or without hemodialysis by performing a meta-analysis.

METHODS

Pubmed, Embase, and Cochrane Library databases are systematically searched for relevant literature that investigated NLR and subsequent cardiovascular or all-cause mortality risk in CKD with or without dialysis. Pooled hazard risk (HR) with 95% confidence interval (CI) was calculated for the high vs. low NLR category.

RESULTS

A total of thirteen studies enrolling 116,709 patients were identified and analyzed. In summary, high NLR was associated with an increased risk of all-cause mortality (HR 1.93, 95% CI 1.87-2.00; P < 0.00001) and cardiovascular mortality (HR 1.45, 95% CI 1.18-1.79, P < 0.001). Subgroup analysis indicated that high NLR are independently associated with all-cause mortality risk in dialysis patients (HR 1.94, 95% CI 1.87-2.01; P < 0.00001).

CONCLUSIONS

This meta-analysis indicates a high NLR is related to all-cause mortality and cardiovascular mortality in patients with chronic kidney disease. Dialysis patients with high NLR are candidates at high risk of mortality to allow for earlier interventions. Further large scale and more rigorously designed studies are warranted to confirm the prognostic value of NLR in the different stages of CKD.

Dietary Oxalate Intake and Kidney Outcomes

Oxalate is both a plant-derived molecule and a terminal toxic metabolite with no known physiological function in humans. It is predominantly eliminated by the kidneys through glomerular filtration and tubular secretion. Regardless of the cause, the increased load of dietary oxalate presented to the kidneys has been linked to different kidney-related conditions and injuries, including calcium oxalate nephrolithiasis, acute and chronic kidney disease. In this paper, we review the current literature on the association between dietary oxalate intake and kidney outcomes.

Long-term in vitro effects of exposing the human HK-2 proximal tubule cell line to 3-monochloropropane-1,2-diol

3-Monochloropropane-1,2-diol (3-MCPD) is a food processing contaminant in the U.S. food supply, detected in infant formula. In vivo rodent model studies have identified a variety of possible adverse outcomes from 3-MCPD exposure including renal effects like increased kidney weights, tubular hyperplasia, kidney tubular necrosis, and chronic progressive nephropathy. Given the lack of available in vivo toxicological assessments of 3-MCPD in humans and the limited availability of in vitro human cell studies, the health effects of 3-MCPD remain unclear. We used in vitro human proximal tubule cells represented by the HK-2 cell line to compare short- and long-term consequences to continuous exposure to this compound. After periodic lengths of exposure (0-100 mM) ranging from 1 to 16 days, we evaluated cell viability, mitochondrial integrity, oxidative stress, and a specific biomarker of proximal tubule injury, Kidney Injury Molecule-1 (KIM-1). Overall, we found that free 3-MCPD was generally more toxic at high concentrations or extended durations of exposure, but that its overall ability to induce cell injury was limited in this in vitro system. Further experiments will be needed to conduct a comprehensive safety assessment in infants who may be exposed to 3-MCPD through consumption of infant formula, as human renal physiology changes significantly during development.