Etiologies, Clinical Features, and Outcome of Oxalate Nephropathy

Determinants and impact of calcium oxalate crystal deposition on renal outcomes in acute kidney injury patients

OBJECTIVES

Calcium oxalate (CaOx) crystal deposition in acute kidney injury (AKI) patients is under recognized but impacts renal outcomes. This study investigates its determinants and effects.

METHODS

We studied 814 AKI patients with native kidney biopsies from 2011 to 2020, identifying CaOx crystal deposition severity (mild: <5, moderate: 5-10, severe: >10 crystals per section). We assessed factors like urinary oxalate, citrate, urate, electrolytes, pH, tubular calcification index, and SLC26A6 expression, comparing them with creatinine-matched AKI controls without oxalosis. We analyzed how these factors relate to CaOx severity and their impact on renal recovery (eGFR < 15 mL/min/1.73 m2 at 3-month follow-up).

RESULTS

CaOx crystal deposition was found in 3.9% of the AKI cohort (32 cases), with 72% due to nephrotoxic medication-induced tubulointerstitial nephritis. Diuretic use, higher urinary oxalate-to-citrate ratio induced by hypocitraturia, and tubular calcification index were significant contributors to moderate and/or severe CaOx deposition. Poor baseline renal function, low urinary chloride, high uric acid and urea nitrogen, tubular SLC26A6 overexpression, and glomerular sclerosis were also associated with moderate-to-severe CaOx deposition. Kidney recovery was delayed, with 43.8%, 31.2%, and 18.8% of patients having eGFR < 15 mL/min/1.73 m2 at 4, 12, and 24-week post-injury. Poor outcomes were linked to high urinary α1-microglobulin-to-creatinine (α1-MG/C) ratios and active tubular injury scores. Univariate analysis showed a strong link between this ratio and poor renal outcomes, independent of oxalosis severity.

CONCLUSIONS

In AKI, CaOx deposition is common despite declining GFR. Factors worsening tubular injury, not just oxalate-to-citrate ratios, are key to understanding impaired renal recovery.

Oxalate Nephropathy After Kidney Transplantation: Risk Factors and Outcomes of Two Phenotypes

Describing risk factors and outcomes in kidney transplant recipients with oxalate nephropathy (ON) may help elucidate the pathogenesis and guide treatment strategies. We used a large single-center database to identify patients with ON and categorized them into delayed graft function with ON (DGF-ON) and late ON. Incidence density sampling was used to select controls. A total of 37 ON cases were diagnosed between 1/2011 and 1/2021. DGF-ON (n = 13) was diagnosed in 1.05% of the DGF population. Pancreatic atrophy on imaging (36.4% vs. 2.9%, p = 0.002) and gastric bypass history (7.7% vs. 0%; p = 0.06) were more common in DGF-ON than with controls with DGF requiring biopsy but without evidence of ON. DGF-ON was not associated with worse graft survival (p = 0.98) or death-censored graft survival (p = 0.48). Late ON (n = 24) was diagnosed after a mean of 78.2 months. Late ON patients were older (mean age 55.1 vs. 48.4 years; p = 0.02), more likely to be women (61.7% vs. 37.5%; p = 0.03), have gastric bypass history (8.3% vs. 0.8%; p = 0.02) and pancreatic atrophy on imaging (38.9% vs. 13.3%; p = 0.02). Late ON was associated with an increased risk of graft failure (HR 2.0; p = 0.07) and death-censored graft loss (HR 2.5; p = 0.10). We describe two phenotypes of ON after kidney transplantation: DGF-ON and late ON. Our study is the first to our knowledge to evaluate DGF-ON with DGF controls without ON. Although limited by small sample size, DGF-ON was not associated with adverse outcomes when compared with controls. Late ON predicted worse allograft outcomes.

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.

Acute oxalate nephropathy: exploring the role of excess dietary oxalate intake

Acute oxalate nephropathy is a rare but important cause of severe acute kidney injury. We report here two cases presenting as unexplained AKI which were confirmed histologically to be due to acute oxalate nephropathy. Dietary oxalate or its precursor vitamin C was the cause of oxalate exposure in both of these cases. While one patient recovered, another continued to need dialysis and succumbed to underlying metastatic cancer. This cause should be suspected in all patients presenting with unexplained AKI, and detailed history about dietary intake of oxalate or vitamin C should be inquired.

Clinicopathologic Characteristics, Etiologies, and Outcome of Secondary Oxalate Nephropathy

OBJECTIVE

To report the clinicopathologic characteristics, prognostic indicators, prognosis, and transplant outcome of secondary oxalate nephropathy (ON).

PATIENTS AND METHODS

We performed a retrospective analysis of 113 consecutive patients with secondary ON diagnosed at Mayo Clinic in Rochester, Minnesota, between January 1, 2001, and March 1, 2023.

RESULTS

The incidence of secondary ON among all native biopsies from Mayo Clinic patients over the study period (n=11,617) was 0.97%. ON was attributed to enteric hyperoxaluria in 60% of the 113 patients (68; most commonly Roux-en-Y gastric bypass), excessive ingestion of foods high in oxalate or oxalate precursors in 23% (26) (most commonly vitamin C), and idiopathic in 17% (19). Most patients presented with acute kidney injury (AKI) (particularly in the ingestion group) or AKI on chronic kidney disease, and 53% (60 of 113) were diabetic. Calcium oxalate crystals were accompanied by acute tubular injury, inflammation, and interstitial fibrosis and tubular atrophy. Concurrent pathologic conditions were present in 53% of the patients (60 of 113), most commonly diabetic nephropathy. After a median follow-up of 36 months, 27% of the patients (30 of 112) had kidney recovery, 19% (21 of 112) had persistent kidney dysfunction, 54% (61 of 112) had development of kidney failure, and 29% (32 of 112) died. The mean kidney survival was worse for patients with a concurrent pathologic lesion (30 months vs 96 months for those without a concurrent pathologic lesion; P<.001). Independent predictors of kidney failure were the degree of interstitial fibrosis and tubular atrophy and nadir estimated glomerular filtration rate but not the degree of crystal deposition. After a median follow-up of 58 months in 23 patients who received kidney transplant, 4 had graft loss (due to ON in 3). The 2-, 5-, and 10-year graft survivals were 90% (18 of 20), 79% (11 of 14), and 50% (6 of 12).

CONCLUSION

ON is a rare cause of AKI or AKI on chronic kidney disease. Most patients have comorbid pathologic conditions, particularly diabetic nephropathy, which worsen the prognosis. Recurrence in the renal allograft and graft loss may occur if hyperoxaluria is not controlled.

Oxalate nephropathy after pancreaticoduodenectomy: a case report

A 75-year-old male developed acute kidney injury KDIGO stage 3 a few weeks after Whipple surgery was performed for a distal cholangiocarcinoma. Kidney biopsy revealed oxalate nephropathy. This was attributed to post-Whipple malabsorption, poor compliance with pancreatic enzyme replacement therapy, and daily intake of vitamin C supplements. Pancreatic enzyme replacement therapy was resumed and calcium carbonate initiated, with an improvement in glomerular filtration rate. Unfortunately, due to oncological progression, best supportive care was initiated.We review the pathophysiology and conditions predisposing to secondary hyperoxaluria and oxalate nephropathy. This diagnosis should be considered among the main causes of acute kidney injury following pancreatectomy, with important therapeutic implications.

The Clinical and Pathological Characteristics of Patients with Oxalate Nephropathy

Key Points

Oxalate nephropathy is an underrecognized cause of CKD and ESKD We present one of the largest native oxalate nephropathy cohorts to date from a tertiary care institution in the United States Oxalate nephropathy has multiple etiologies and given its clinical course and poor prognosis, attention must be paid to screening for risk factors to guide prompt diagnosis and management

Background

Oxalate nephropathy (ON) is characterized by deposition of calcium oxalate crystals in the kidney and is commonly under-recognized. Causes of ON include primary hyperoxaluria, enteric hyperoxaluria, and ingestion of excess oxalate or its precursors.

Methods

We report the clinical and pathological characteristics of one of the largest series of native kidney ON to date, from January 2015 to March 2023 at the Cleveland Clinic.

Results

We identified 60 native biopsies with oxalate deposits and excluded patients with clinically insignificant biopsies (n =12) or lack of data (n =17). Thirty-one patients with native ON were described. The mean age at diagnosis was 66.2 years (±12.1), and 58.1% were female. 87.1% had hypertension, 58.1% had diabetes, 42% had nephrolithiasis, and 77.4% had underlying CKD, with a mean baseline creatinine of 1.8 mg/dl ±1.3.

The mean creatinine at biopsy was 5.2 mg/dl ±1.7. Kidney biopsies showed abundant calcium oxalate crystal deposits, and 27 of 31 biopsies had additional diagnoses, the most common of which were acute tubular injury n =17 (54.8%) and diabetic glomerulosclerosis n =7 (22.6%). Severe and moderate interstitial fibrosis was present in 38.7% (n =12) and 51.6% (n =16) of biopsies, respectively. Ten had a single etiology of ON, ten had a multifactorial etiology (both enteric hyperoxaluria and high precursor intake), and 11 had an unclear etiology. Notably, only seven patients had a history of gastric bypass.

The mean duration of follow-up was 26.8 months, and 26 patients had follow-up data >1 year. Of these, 21 required dialysis, and five were dialysis-free at presentation. Five of the 26 were deceased at 1 year, with 12 patients (38.7%) deceased at last follow-up. Seventeen patients received targeted management, while nine patients did not receive targeted treatment, and all nine required hemodialysis. More patients (31.6%) had vitamin C intake after the coronavirus disease 2019 pandemic (2020–2023) versus 16.7% before 2020.

Conclusions

ON presents as AKI or acute on CKD. The prognosis is poor with most patients requiring dialysis at presentation with high morbidity and mortality. Clinicians need to be aware of the risk factors associated with ON to aid prompt diagnosis and management.

Podcast

This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/K360/2024_01_26_KID0000000000000340.mp3

Oxalate Nephropathy: A Case Report of Acute Kidney Injury Due to Juice Diet

Oxalate nephropathy occurs due to the deposition of calcium oxalate crystals in kidney tubules and/or the interstitium as a part of primary or secondary hyperoxaluria. Secondary oxalate nephropathy can occur even with moderately high doses of ascorbic acid intake under yet unidentified clinical circumstances. Vitamin C, although traditionally considered an antioxidant, leads to the formation of superoxide and subsequent generation of reactive oxidant species at pharmacologic concentrations. Ascorbic acid is partly converted to oxalic acid, which is responsible for deposition and renal tubular injury. We report a case of a diabetic patient with normal kidney function who was put on a juice diet for a week due to upper gastrointestinal bleeding. He developed acute kidney injury due to biopsy-proven oxalate nephropathy requiring dialysis. Though he was lost to follow-up after two weeks on dialysis, he was expected to have only a slow recovery or become dependent on dialysis given his age, comorbidities, and extent of tubular involvement. Hence, caution should be exercised before supplementing vitamin C either in its natural form or as a drug. Risk factors for secondary oxalate nephropathy due to excessive intake of oxalate or its precursor are likely to be age, diabetes, dehydration, and underlying chronic kidney disease. Most of the patients do not have a complete recovery of kidney function, and many become dependent on dialysis.

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.

Purslane-induced oxalate nephropathy: case report and literature review

BACKGROUND

The kidney is particularly vulnerable to toxins due to its abundant blood supply, active tubular reabsorption, and medullary interstitial concentration. Currently, calcium phosphate-induced and calcium oxalate-induced nephropathies are the most common crystalline nephropathies. Hyperoxaluria may lead to kidney stones and progressive kidney disease due to calcium oxalate deposition leading to oxalate nephropathy. Hyperoxaluria can be primary or secondary. Primary hyperoxaluria is an autosomal recessive disease that usually develops in childhood, whereas secondary hyperoxaluria is observed following excessive oxalate intake or reduced excretion, with no difference in age of onset. Oxalate nephropathy may be overlooked, and the diagnosis is often delayed or missed owning to the physician's inadequate awareness of its etiology and pathogenesis. Herein, we discuss the pathogenesis of hyperoxaluria with two case reports, and our report may be helpful to make appropriate treatment plans in clinical settings in the future.

CASE PRESENTATION

We report two cases of acute kidney injury, which were considered to be due to oxalate nephropathy in the setting of purslane (portulaca oleracea) ingestion. The two patients were elderly and presented with oliguria, nausea, vomiting, and clinical manifestations of acute kidney injury requiring renal replacement therapy. One patient underwent an ultrasound-guided renal biopsy, which showed acute tubulointerstitial injury and partial tubular oxalate deposition. Both patients underwent hemodialysis and were discharged following improvement in creatinine levels.

CONCLUSIONS

Our report illustrates two cases of acute oxalate nephropathy in the setting of high dietary consumption of purslane. If a renal biopsy shows calcium oxalate crystals and acute tubular injury, oxalate nephropathy should be considered and the secondary causes of hyperoxaluria should be eliminated.

Idiopathic Oxalate Nephropathy Leading to End-Stage Kidney Disease: A Case Report

Oxalate nephropathy represents a frequently overlooked etiology of renal failure, characterized by the deposition of calcium oxalate crystals within the renal parenchyma. This progressive form of kidney disease is marked by a significant increase in serum creatinine (Cr) level accompanied by evidence of oxalate crystal deposition on renal biopsy causing tubular obstruction and tubular injury leading to fibrosis. In all instances of oxalate nephropathy, examination of stones consistently exhibits multiple birefringent calcium oxalate crystals under polarized light. This case report details the clinical course of a patient who initially presented with progressively worsening renal function and ultimately developed end-stage kidney disease (ESKD) as a consequence of idiopathic hyperoxaluria.

Acute Kidney Injury and Hair-Straightening Products: A Case Series

RATIONALE & OBJECTIVE

Keratin-based hair-straightening treatment is a popular hair-styling method. The majority of keratin-based hair-straightening products in Israel contain glycolic acid derivatives, which are considered safe when used topically. Systemic absorption of these products is possible, and anecdotal reports have described kidney toxicity associated with their use. We report a series of cases of severe acute kidney injury (AKI) following use of hair-straightening treatment in Israel during the past several years.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

We retrospectively identified 26 patients from 14 medical centers in Israel who experienced severe AKI and reported prior treatment with hair-straightening products in 2019-2022.

FINDINGS

The 26 patients described had a median age of 28.5 (range, 14-58) years and experienced severe AKI following a hair-straightening procedure. The most common symptoms at presentation were nausea, vomiting, and abdominal pain. Scalp rash was noted in 10 (38%) patients. Two patients experienced a recurrent episode of AKI following a repeat hair-straightening treatment. Seven patients underwent kidney biopsies, which demonstrated intratubular calcium oxalate deposition in 6 and microcalcification in tubular cells in 1. In all biopsies, signs of acute tubular injury were present, and an interstitial infiltrate was noted in 4 cases. Three patients required temporary dialysis.

LIMITATIONS

Retrospective uncontrolled study, small number of kidney biopsies.

CONCLUSIONS

This series describes cases of AKI with prior exposure to hair-straightening treatments. Acute oxalate nephropathy was the dominant finding on kidney biopsies, which may be related to absorption of glycolic acid derivatives and their metabolism to oxalate. This case series suggests a potential underrecognized cause of AKI in the young healthy population. Further studies are needed to confirm this association and to assess the extent of this phenomenon as well as its pathogenesis.

Oxalate nephropathy in an elderly patient with newly diagnosed celiac disease - a case report

Oxalate nephropathy, due to secondary hyperoxaluria has widely been described in gastrointestinal diseases. However, reports of oxalate nephropathy in newly diagnosed celiac disease are rare. A 72-year-old Caucasian male presented to the hospital with abdominal discomfort and acute renal insufficiency with a creatinine of 290 µmol/L. The clinical course, laboratory results and urinalysis were suspect for tubular injury. Renal biopsy showed calcium oxalate depositions. Elevated plasma and urine oxalate levels established the diagnosis oxalate nephropathy. The abdominal complaints with steatorrhea and positive anti-tissue transglutaminase antibodies were diagnosed as celiac disease, which was confirmed after duodenal biopsies. Treatment with prednisone, and gluten-free, low oxalate and normal calcium diet, lowered the plasma oxalate levels and improved his renal function. Decreased absorption of free fatty acids can lead to increased free oxalate in the colon due to the binding of free fatty acids to calcium, preventing the formation of the less absorbable calcium oxalate in the colon. Oxalate dispositions in the kidney can lead to acute tubular injury and chronic renal insufficiency. Celiac disease is therefore one of the intestinal diseases that can lead to hyperoxaluria and oxalate nephropathy.

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.

A Case of Oxalate Nephropathy Associated With Prolonged Cholecystostomy Tube Placement

Oxalate nephropathy is a rare pathology that can be difficult to diagnose. It results from calcium oxalate crystals that are deposited in the renal interstitium or renal tubules. Once the deposition ensues, a multitude of complications can occur, including renal failure. One etiology for oxalate nephropathy is a lack of biliary acid. The diagnosis of oxalate nephropathy is typically based on visualization of oxalate crystals in the renal tubules on biopsy, and treatment based on the etiology can range from simple removal of the offending agent or a change in diet to liver/kidney transplant in the setting of primary hyperoxaluria. This report discusses a case of severe oxalate nephropathy related to long-term cholecystostomy tube placement resulting in a deficiency of biliary acid.

Oxalic acid degradation in wood-rotting fungi. Searching for a new source of oxalate oxidase

Oxalate oxidase (EC 1.2.3.4) is an oxalate-decomposing enzyme predominantly found in plants but also described in basidiomycete fungi. In this study, we investigated 23 fungi to determine their capability of oxalic acid degradation. After analyzing their secretomes for the products of the oxalic acid-degrading enzyme activity, three groups were distinguished among the fungi studied. The first group comprised nine fungi classified as oxalate oxidase producers, as their secretome pattern revealed an increase in the hydrogen peroxide concentration, no formic acid, and a reduction in the oxalic acid content. The second group of fungi comprised eight fungi described as oxalate decarboxylase producers characterized by an increase in the formic acid level associated with a decrease in the oxalate content in their secretomes. In the secretomes of the third group of six fungi, no increase in formic acid or hydrogen peroxide contents was observed but a decline in the oxalate level was found. The intracellular activity of OXO in the mycelia of Schizophyllum commune, Trametes hirsuta, Gloeophyllum trabeum, Abortiporus biennis, Cerrena unicolor, Ceriosporopsis mediosetigera, Trametes sanguinea, Ceriporiopsis subvermispora, and Laetiporus sulphureus was confirmed by a spectrophotometric assay.

Increased Rates of Supplement-Associated Oxalate Nephropathy During COVID-19 Pandemic

Introduction

Causes of secondary oxalate nephropathy include enteric dysfunction and excessive intake of oxalate or oxalate precursors. During the COVID-19 pandemic, there has been a dramatic rise in sales of supplements and vitamin C, during which time we observed an apparent increase in the proportion of ingestion-associated oxalate nephropathy.

Methods

We retrospectively reviewed secondary oxalate nephropathy and compared pre-pandemic (2018–2019) and pandemic (2020–early 2022) time periods.

Results

We identified 35 patients with kidney biopsy proven (30 native, 5 allograft) oxalate nephropathy at a single academic institution. Supplement-associated oxalate nephropathy comprised a significantly higher proportion of cases during COVID-19 pandemic compared with the preceding 2 years (44% vs. 0%, P = 0.002), and was associated with use of vitamin C, dietary changes, and supplements. Oxalate nephropathy in the kidney allograft, in contrast, remained associated with enteric hyperoxaluria, antibiotic use, and dehydration. Many patients had diabetes mellitus (57%), hypertension (40%) and/or pre-existing chronic kidney disease (CKD, 49%). Of 9 patients in which the potentially causative ingestion was identified and removed, 8 experienced improvement in kidney function.

Conclusion

There was a shift toward supplements rather than enteric hyperoxaluria as a leading cause of secondary oxalate nephropathy during the COVID-19 pandemic. Kidney outcomes are better than those observed for enteric hyperoxaluria, if the offending agent is identified and removed.

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.

Ferrostatin‑1 alleviates oxalate‑induced renal tubular epithelial cell injury, fibrosis and calcium oxalate stone formation by inhibiting ferroptosis

The present study aimed to evaluate the role and mechanism of ferrostatin-1 (Fer-1) in oxalate (Ox)-induced renal tubular epithelial cell injury, fibrosis, and calcium oxalate (CaOx) stone formation. A CaOx model in mice kidneys was established via intraperitoneal injection of 80 mg/kg glyoxylic acid for 14 days. The mice were randomly divided into three groups (n=6), namely, the control (Con), the CaOx group, and the CaOx + Fer-1 group. Cultured human renal tubular epithelial cells (HK-2 cells) were randomly divided into three groups (n=3), namely, the control (Con), the Ox group, and the Ox + Fer-1 group. The levels of heme oxygenase 1 (HO-1), superoxide dismutase 2 (SOD2), glutathione peroxidase 4 (GPX4), and solute carrier family 7 member 11 (SLC7A11) were assessed by immunofluorescence and western blot analysis. Renal tubular injury and apoptosis were evaluated by H&E and TUNEL staining. Kidney interstitial fibrosis was evaluated by Masson and Sirius red staining, and the levels of E-cadherin, vimentin and α-SMA were detected by immunofluorescence or western blot analysis. Mitochondrial structure was observed using a transmission electron microscope. The levels of reactive oxygen species (ROS) were determined by flow cytometry and CaOx stone formation was evaluated by von Kossa staining. The results revealed that in comparison with the Con group, mitochondrial injury under glyoxylic acid treatment was observed by TEM. The expression of GPX4 and SLC7A11 in the CaOx and Ox groups was downregulated (P<0.05), whereas the expression of HO-1 and SOD2 was upregulated (P<0.05). Renal tissue damage, apoptosis of renal tubular epithelial cells, and interstitial fibrosis were increased in the CaOx and Ox groups (P<0.05). In comparison with the CaOx or Ox group, the expression of GPX4 and SLC7A11 in the CaOx + Fer-1 or Ox + Fer-1 group was upregulated (P<0.05), whereas that of HO-1 and SOD2 was downregulated (P<0.05). Renal tissue damage, apoptosis of renal tubular epithelial cells and interstitial fibrosis were decreased following Fer-1 treatment (P<0.05). The ROS level was also decreased following Fer-1 treatment. Moreover, CaOx stone formation was decreased in the CaOx + Fer-1 group (P<0.05). In conclusion, Fer-1 alleviated Ox-induced renal tubular epithelial cell injury, fibrosis, and CaOx stone formation by inhibiting ferroptosis.

Pilot testing for long-term impact of glycerol-induced acute kidney injury on oxalate homeostasis in rats

Abstract. There is a general lack of research on the long-term effects of acute kidney injury (AKI) on oxalate-degrading bacteria (ODB) and their total oxalate-degrading activity (ODA) in fecal microbiota. In the present pilot study, we separately evaluated the changes in the ODB number and their total ODA in fecal microbiota at 3-time points after glycerol-induced AKI. In addition, we assessed the interactions between AKI-induced renal histopathological changes and ODB, total fecal ODA, and plasma and urine oxalate concentrations in rats. Methods. The male Wistar rats (200-300 g, n = 20) on oxalate-free diet were randomly divided into 2 groups. After 24-h of water deprivation, experimental group 1 (n = 10) received an intramuscular injection of 50% glycerol (10 ml/kg of body weight), and group 2 (n = 10) served as a control. The numbers of ODB (incubated in a highly selective Oxalate Medium and determined using the culture method), total fecal ODA and urinary oxalate (UOx) excretion were measured after injection on days 8, 22 and 70. The method of redoximetric titration with a KMnO4 solution was adopted to evaluate total ODA in fecal microbiota. Renal injury was assessed by histopathology examination, serum creatinine plasma oxalic acid (POx) concentration and daily proteinuria levels after removing the animals from the experiment on day 70. Results. After glycerol injection on days 8 and 22, no differences were found in the numbers of ODB, their total fecal ODA, and UOx excretion level between the experimental and control groups. However, after AKI initiation on day 70, the numbers of ODB, total fecal ODA, and daily UOx excretion were significantly lower in the experimental group as compared with the control group. In addition, in 10 weeks following AKI, the number of ODB had a direct correlation with UOx excretion and an inverse correlation with POx and serum creatinine concentrations and daily proteinuria. Total ODA in fecal microbiota was directly associated with the percentage of renal interstitial fibrosis and the average glomerular volumes in the experimental rats. Conclusions: AKI had long-term negative effects on the quantitative and qualitative characteristics of ODB in fecal microbiota in rats. Moreover, the results of our study confirmed an increasing trend in total fecal ODA according to the aggravation of renal interstitial fibrosis and glomerular volume in rats’ kidneys. Further studies are warranted to gain more insight into the mechanism of oxalate homeostasis impairment in AKI.

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.

Chaga mushroom-induced oxalate nephropathy that clinically manifested as nephrotic syndrome: A case report

RATIONALE

The Chaga mushroom (Hymenochaetaceae, Inonotus obliquus) is a fungus belonging to the Hymenochaetaceae family. It is parasitic on birch and other tree species. Chaga mushrooms are rich in various vitamins, minerals, and nutrients. Some people consider these mushrooms medicinal as they have been reported to suppress cancer progression through anti-inflammatory and antioxidant effects. However, recent studies have reported that excessive ingestion of Chaga mushrooms can cause acute oxalate nephropathy.

PATIENT CONCERNS

A 69-year-old man who ingested Chaga mushroom powder (10-15 g per day) and vitamin C (500 mg per day) for the past 3 months developed acute kidney injury (AKI) with the clinical manifestations of nephrotic syndrome (NS).

DIAGNOSIS

Pathological findings showed focal acute tubular injury and the deposition of calcium oxalate crystals in the tubules. Light microscopy showed interstitial fibrosis and tubular atrophy, and electron microscopy showed the effacement of the foot processes in podocytes. Based on these results, the diagnosis was acute oxalate nephropathy accompanied by minimal change disease (MCD).

INTERVENTIONS

The patient's kidney function did not improve with supportive care, such as hydration and blood pressure control. Thus, we recommended hemodialysis and the administration of a high dose of steroids (intravenous hydrocortisone 500 mg twice a day for 3 days and oral prednisolone at 1 mg/kg).

OUTCOMES

The patient's kidney function recovered just 1 month after the start of treatment, and the MCD was completely remitted.

LESSONS

In cases of AKI with an unknown cause, it is important to closely observe the patient's medication history, and it is recommended to perform kidney biopsy. Furthermore, this study showed that active dialysis and high-dose steroid treatment can restore kidney function in patients with AKI caused by acute oxalate nephropathy with MCD.

Oxalobacter formigenes treatment confers protective effects in a rat model of primary hyperoxaluria by preventing renal calcium oxalate deposition

In primary hyperoxaluria, increased hepatic oxalate production sometimes leads to severe nephrocalcinosis and early end-stage kidney disease. Oral administration of Oxalobacter formigenes (O. formigenes), an oxalate-degrading bacterium, is thought to derive oxalate from systemic sources by inducing net enteric oxalate secretion. Here, the impact of O. formigenes on nephrocalcinosis was investigated in an ethylene glycol rat model mimicking hepatic oxalate overproduction in primary hyperoxaluria. Eighteen rats were administered ethylene glycol (0.75% in drinking water) for 6 weeks, of which 9 were treated by oral gavage with O. formigenes and 9 received vehicle. Five control rats did not receive ethylene glycol or O. formigenes. Plasma and urinary oxalate levels, calcium oxalate crystalluria, urinary volume, fluid intake, and serum creatinine were monitored during the study. On killing, nephrocalcinosis was quantified. Ethylene glycol intake induced pronounced hyperoxalemia, hyperoxaluria, calcium oxalate crystalluria and nephrocalcinosis. Concomitant O. formigenes treatment partially prevented the ethylene glycol-induced increase in plasma oxalate and completely prevented nephrocalcinosis. Urinary oxalate excretion was not reduced by O. formigenes treatment. Nevertheless, absence of crystals in renal tissue of O. formigenes-treated ethylene glycol animals indicates that the propensity for oxalate to crystallize in the kidneys was reduced compared to non-treated animals. This is supported by the lower plasma oxalate concentrations in O. formigenes-treated animals. This study shows a beneficial effect of O. formigenes treatment on ethylene glycol-induced hyperoxalemia and nephrocalcinosis, and thus supports a possible beneficial effect of O. formigenes in primary hyperoxaluria.

Oxalate nephropathy: a review

This review describes the clinical and pathological features of oxalate nephropathy (ON), defined as a syndrome of decreased renal function associated with deposition of calcium oxalate crystals in kidney tubules. We review the different causes of hyperoxaluria, including primary hyperoxaluria, enteric hyperoxaluria and ingestion-related hyperoxaluria. Recent case series of biopsy-proven ON are reviewed in detail, as well as the implications of these series. The possibility of antibiotic use predisposing to ON is discussed. Therapies for hyperoxaluria and ON are reviewed with an emphasis on newer treatments available and in development. Promising research avenues to explore in this area are discussed.

Detection and localization of calcium oxalate in kidney using synchrotron deep ultraviolet fluorescence microscopy

Renal oxalosis is a rare cause of renal failure whose diagnosis can be challenging. Synchrotron deep ultraviolet (UV) fluorescence was assayed to improve oxalosis detection on kidney biopsies spatial resolution and sensitivity compared with the Fourier transform infrared microspectroscopy gold standard. The fluorescence spectrum of synthetic mono-, di- and tri-hydrated calcium oxalate was investigated using a microspectrometer coupled to the synchrotron UV beamline DISCO, Synchrotron SOLEIL, France. The obtained spectra were used to detect oxalocalcic crystals in a case control study of 42 human kidney biopsies including 19 renal oxalosis due to primary (PHO, n = 11) and secondary hyperoxaluria (SHO, n = 8), seven samples from PHO patients who received combined kidney and liver transplants, and 16 controls. For all oxalocalcic hydrates samples, a fluorescence signal is detected at 420 nm. These spectra were used to identify standard oxalocalcic crystals in patients with PHO or SHO. They also revealed micrometric crystallites as well as non-aggregated oxalate accumulation in tubular cells. A nine-points histological score was established for the diagnosis of renal oxalosis with 100% specificity (76-100) and a 73% sensitivity (43-90). Oxalate tubular accumulation and higher histological score were correlated to lower estimated glomerular filtration rate and higher urinary oxalate over creatinine ratio.

Clinical Outcomes and Histological Patterns in Oxalate Nephropathy due to Enteric and Nonenteric Risk Factors

INTRODUCTION

Current knowledge of risk factors and renal histologic patterns of oxalate nephropathy (ON) not due to primary hyperoxaluria (PH) has been limited to small case series and case reports. Thus, we analyzed and compared clinical risk factors, histologic characteristics, and renal outcomes of patients with biopsy-confirmed ON among a cohort of patients with enteric and nonenteric risk factors.

METHODS

A clinical data repository of native kidney pathology reports from 2009 to 2020 at all Mayo Clinic sites was used to identify 421 ON cases.

RESULTS

After excluding cases in transplanted kidneys or due to PH, 64 cases remained. Enteric risk factors were present in 30 and nonenteric in 34. Roux-en-Y gastric bypass (17) and pancreatic insufficiency (6) were most common in the enteric hyperoxaluria group. In the nonenteric group, vitamin C (7) and dietary oxalate (7) were common, while no apparent risk was noted in 16. Acute kidney injury (AKI) stage III at the time of diagnosis was present in 60%, and 40.6% required dialysis. Patients in the nonenteric group had more interstitial inflammation (p = 0.01), and a greater number of tubules contained intratubular calcium oxalate (CaOx) crystals (p = 0.001) than the nonenteric group. Patients in the enteric group were more likely to have baseline chronic kidney disease (CKD) (p = 0.02) and moderate-to-severe tubulointerstitial fibrosis and atrophy (IFTA) (OR 3.49, p = 0.02). After a median follow-up of 10 months, 39% were dialysis dependent, 11% received a kidney transplant, and 32% died. On univariate analysis, >10 tubules with CaOx crystals, baseline CKD, and AKI requiring dialysis correlated with the risk of dialysis, transplant, or death. On multivariate analysis, only AKI requiring dialysis correlated with adverse renal outcomes.

CONCLUSION

This is the largest cohort study of ON not due to PH. Histologic features differ in patients with enteric versus nonenteric risks. Patients in the enteric group are more likely to have baseline CKD and significant IFTA, while patients in the nonenteric group were more likely to have a greater number of tubules with CaOx crystals and corresponding interstitial inflammation. AKI requiring dialysis at the time of diagnosis was the single most significant predictor of adverse renal outcome.

Secondary Oxalate Nephropathy: Causes and Clinicopathological Characteristics of a Case Series

INTRODUCTION

Secondary oxalate nephropathy (OxN) is associated with a variety of causes and has not been well characterized in Chinese population. To investigate the etiology, clinicopathological features, and outcomes of secondary OxN, we report a case series from a single center in China.

METHODS

A retrospective analysis of 68 patients diagnosed with secondary OxN by renal biopsy from January 2013 to February 2019 in Jinling Hospital was performed.

RESULTS

Secondary OxN accounted for 0.23% of the renal biopsies and 2.31% of patients who received renal biopsies due to acute kidney injury (AKI). A total of 49 men and 19 women with an average age of 51.6 ± 11.8 years were enrolled. The most common cause was iatrogenic medication, followed by oxalate-rich diet and industry exposure. Stage 1, 2, and 3 AKI and AKI on chronic kidney disease (ACKD) were found in 4.4, 8.8, 69.1, and 17.6% of the patients, respectively. The peak serum creatinine during hospitalization was 8.62 ± 4.67 mg/dL. The median urinary oxalate excretion was 51.5 (23.2-147.1) mg/24 h. Kidney biopsy showed extensive calcium oxalate crystal deposits with acute tubulointerstitial nephritis. Thirty-four patients (50.0%) required renal replacement therapy. At the end of a follow-up that lasted 8.7 (0.1-72.1) months, 81.0% of patients achieved renal function recovery in 50 (14-432) days. Patients with renal function recovery had a lower rate of ACKD, a higher level of hemoglobin, a lower level of urine lysozyme, and a lower degree of interstitial fibrosis/tubular atrophy, interstitial inflammation, and global glomerulosclerosis than those in the nonrecovery group.

CONCLUSIONS

In this case series of secondary OxN, the most common cause was iatrogenic medication, and it presented with AKI or ACKD. Half of the patients required renal replacement therapy, and in most of them, the renal function was reversible. Renal biopsy played an important role in diagnosis and prognosis evaluation.

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.

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.