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.

End Point Considerations for Clinical Trials in Enteric Hyperoxaluria.

Enteric hyperoxaluria is a medical condition characterized by elevated urinary oxalate excretion due to increased gastrointestinal oxalate absorption. Causative features include fat malabsorption and/or increased intestinal permeability to oxalate. Enteric hyperoxaluria has long been known to cause nephrolithiasis and nephrocalcinosis, and, more recently, an association with CKD and kidney failure has been shown. Currently, there are no US Food and Drug Administration-approved therapies for enteric hyperoxaluria, and it is unclear what end points should be used to evaluate the efficacy of new drugs and biologics for this condition. This study represents work of a multidisciplinary group convened by the Kidney Health Initiative to review the evidence supporting potential end points for clinical trials in enteric hyperoxaluria. A potential clinical outcome is symptomatic kidney stone events. Potential surrogate end points include ( 1 ) an irreversible loss of kidney function as a surrogate for progression to kidney failure, ( 2 ) asymptomatic kidney stone growth/new stone formation observed on imaging as a surrogate for symptomatic kidney stone events, ( 3 ) urinary oxalate and urinary calcium oxalate supersaturation as surrogates for the development of symptomatic kidney stone events, and ( 4) plasma oxalate as a surrogate for the development of the clinical manifestations of systemic oxalosis. Unfortunately, because of gaps in the data, this Kidney Health Initiative workgroup was unable to provide definitive recommendations. Work is underway to obtain robust information that can be used to inform trial design and medical product development in this space.

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.

ePHex: a phase 3, double-blind, placebo-controlled, randomized study to evaluate long-term efficacy and safety of Oxalobacter formigenes in patients with primary hyperoxaluria.

BACKGROUND: Primary hyperoxalurias (PHs) are rare genetic diseases that increase the endogenous level of oxalate, a waste metabolite excreted predominantly by the kidneys and also the gut. Treatments aim to improve oxalate excretion, or reduce oxalate generation, to prevent kidney function deterioration. Oxalobacter formigenes is an oxalate metabolizing bacterium. This Phase III, double-blind, placebo-controlled randomized trial investigated the effectiveness of orally administered Oxabact™, a lyophilized O. formigenes formulation, at reducing plasma oxalate levels in patients suffering from PH. METHODS: Subjects (≥ 2 years of age) with a diagnosis of PH and maintained but suboptimal kidney function (mean estimated glomerular filtration rate at baseline < 90 mL/min/1.73 m2) were eligible to participate. Subjects were randomized to receive Oxabact or placebo twice daily for 52 weeks. Change from baseline in plasma oxalate concentration at Week 52 was the primary study endpoint. RESULTS: Forty-three subjects were screened, 25 were recruited and one was discontinued. At Week 52, O. formigenes was established in the gut of subjects receiving Oxabact. Despite decreasing plasma oxalate level in subjects treated with Oxabact, and stable/increased levels with placebo, there was no significant difference between groups in the primary outcome (Least Squares mean estimate of treatment difference was - 3.80 µmol/L; 95% CI: - 7.83, 0.23; p-value = 0.064). Kidney function remained stable in both treatments. CONCLUSIONS: Oxabact treatment may have stabilized/reduced plasma oxalate versus a rise with placebo, but the difference over 12 months was not statistically significant (p = 0.06). A subtle effect observed with Oxabact suggests that O. formigenes may aid in preventing kidney stones. A higher resolution version of the Graphical abstract is available as Supplementary information.

Bone marrow oxalosis with pancytopenia in a patient with short bowel syndrome: Report of a case and review of the literature.

Systemic oxalosis is a condition in which calcium oxalate crystals deposit into various bodily tissues. Although this may occur as the result of a rare primary syndrome in which an error of glyoxylate metabolism causes an overproduction of oxalate, it is more often seen as a secondary process characterized by increased enteric oxalate absorption. Here, we describe a patient with short bowel syndrome on long-term parenteral nutrition support who developed a unique manifestation of systemic oxalosis, leading to deposition of oxalate crystals within the bone marrow contributing to pancytopenia. In this report, in addition to reviewing the literature on this presumably rare manifestation of oxalosis, we also discuss its pathogenesis in the setting of short bowel syndrome and its management, including prevention.

What treatments reduce kidney stone risk in patients with bowel disease?

We examined how physicians made therapeutic choices to decrease stone risk in patients with bowel disease without colon resection, many of whom have enteric hyperoxaluria (EH), at a single clinic. We analyzed clinic records and 24-h urine collections before and after the first clinic visit, among 100 stone formers with bowel disease. We used multivariate linear regression and t tests to compare effects of fluid intake, alkali supplementation, and oxalate-focused interventions on urine characteristics. Patients advised to increase fluid intake had lower initial urine volumes (L/day; 1.3 ± 0.5 vs. 1.7 ± 0.7) and increased volume more than those not so advised (0.7 ± 0.6 vs. 0.3 ± 0.6 p = 0.03; intervention vs. non-intervention). Calcium oxalate supersaturation (CaOx SS) fell (95% CI -4.3 to -0.8). Alkali supplementation increased urine pH (0.34 ± 0.53 vs. 0.22 ± 0.55, p = 0.26) and urine citrate (mg/d; 83 ± 256 vs. 98 ± 166, p = 0.74). Patients advised to reduce oxalate (mg/day) absorption had higher urine oxalate at baseline (88 ± 44 vs. 50 ± 26) which was unchanged on follow-up (88 (baseline) vs. 91 (follow-up), p = 0.90). Neither alkali (95% CI -1.4 to 2.1) nor oxalate-focused advice (95% CI -1.2 to 2.3) lowered CaOx SS. Physicians chose treatments based on baseline urine characteristics. Advice to increase fluid intake increased urine volume and decreased CaOx SS. Alkali and oxalate interventions were ineffective.

Dietary Management of Chronic Kidney Disease and Secondary Hyperoxaluria in Patients with Short Bowel Syndrome and Type 3 Intestinal Failure.

Short gut syndrome can lead to type 3 intestinal failure, and nutrition and hydration can only be achieved with parenteral nutrition (PN). While this is a lifesaving intervention, it carries short- and long-term complications leading to complex comorbidities, including chronic kidney disease. Through a patient with devastating inflammatory bowel disease's journey, this review article illustrates the effect of short gut and PN on kidney function, focusing on secondary hyperoxaluria and acute precipitants of glomerular filtration. In extensive small bowel resections colon in continuity promotes fluid reabsorption and hydration but predisposes to hyperoxaluria and stone disease through the impaired gut permeability and fat absorption. It is fundamental, therefore, for dietary intervention to maintain nutrition and prevent clinical deterioration (i.e., sarcopenia) but also to limit the progression of renal stone disease. Adaptation of both enteral and parenteral nutrition needs to be individualised, keeping in consideration not only patient comorbidities (short gut and jejunostomy, cirrhosis secondary to PN) but also patients' wishes and lifestyle. A balanced multidisciplinary team (renal physician, gastroenterologist, dietician, clinical biochemist, pharmacist, etc.) plays a core role in managing complex patients, such as the one described in this review, to improve care and overall outcomes.

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.

[Interferent RNA treatment: Example of primary hyperoxaluria]. / Traitement par ARN interférent : exemple de l'hyperoxalurie primitive.

Primary hyperoxalurias are rare disease with autosomal recessive inheritance; they often lead to kidney failure and can lead to life-threatening conditions, especially in early onset forms. There are three types, responding to distinct enzyme deficits. Type 1 represents 85% of cases and results from an enzyme deficiency (alanine-glyoxylate aminotransferase) in the peroxisomes of the liver, causing hyperoxaluria leading to urolithiasis with or without nephrocalcinosis. As glomerular filtration decreases, a systemic overload appears and spares no organ. Treatment has hitherto been based on combined liver and kidney transplantation, with significant mortality and morbidity. The recent introduction of interfering RNA treatments opens up new perspectives. By blocking an enzymatic synthesis (glycolate oxidase or lacticodehydrogenase a) upstream of the deficit that causes the disease, oxaluria normalizes and the tolerance of the drug (administered by injection every 1 to 3 months) is good. This strategy will help prevent kidney failure in patients treated early and avoid liver transplantation in those who are diagnosed at an advanced stage of kidney failure.

Nedosiran Dramatically Reduces Serum Oxalate in Dialysis-Dependent Primary Hyperoxaluria 1: A Compassionate Use Case Report.

Primary hyperoxaluria 1 (PH1) is a devastating condition involving recurrent urolithiasis, early end-stage renal disease and multisystemic deposition of calcium oxalate crystals. Treatment options for PH1 are limited, inevitably requiring transplantation, usually combined kidney and liver transplant. Here we report successful compassionate use of Nedosiran, an RNA interference targeting lactate dehydrogenase, in an index patient. Monthly Nedosiran injections led to dramatically decreased plasma oxalate levels, decreased frequency of weekly hemodialysis sessions from 6 to 3, and deferral of combined kidney and liver transplant. Nedosiran represents a novel and impactful potential therapeutic for PH1 patients with end-stage renal disease.

Pathophysiology and Treatment of Enteric Hyperoxaluria.

Enteric hyperoxaluria is a distinct entity that can occur as a result of a diverse set of gastrointestinal disorders that promote fat malabsorption. This, in turn, leads to excess absorption of dietary oxalate and increased urinary oxalate excretion. Hyperoxaluria increases the risk of kidney stones and, in more severe cases, CKD and even kidney failure. The prevalence of enteric hyperoxaluria has increased over recent decades, largely because of the increased use of malabsorptive bariatric surgical procedures for medically complicated obesity. This systematic review of enteric hyperoxaluria was completed as part of a Kidney Health Initiative-sponsored project to describe enteric hyperoxaluria pathophysiology, causes, outcomes, and therapies. Current therapeutic options are limited to correcting the underlying gastrointestinal disorder, intensive dietary modifications, and use of calcium salts to bind oxalate in the gut. Evidence for the effect of these treatments on clinically significant outcomes, including kidney stone events or CKD, is currently lacking. Thus, further research is needed to better define the precise factors that influence risk of adverse outcomes, the long-term efficacy of available treatment strategies, and to develop new therapeutic approaches.

Long-term outcomes of peritoneal dialysis started in infants below 6 months of age: An experience from two tertiary centres.

BACKGROUND: Little data are available for infants who started renal replacement therapy before 6 months of age. Because of extra-renal comorbidities and uncertain outcomes, whether renal replacement therapy in neonates is justified remains debatable. METHODS: We performed a retrospective analysis of all patients who began chronic peritoneal dialysis below 6 months between 2007 and 2017 in two tertiary centres. Results are presented as median (min;max). RESULTS: Seventeen patients (10 boys) were included (8 prenatal diagnoses, 6 premies), with the following diagnoses: congenital anomalies of kidney and urinary tract (n=9), oxalosis (n=5), congenital nephrotic syndrome (n=2) and renal vein thrombosis (n=1). Five patients had associated comorbidities. At peritoneal dialysis initiation, age was 2.6 (0.1;5.9) months, height-standard deviation score (SDS) -1.3 (-5.7;1.6) and weight-SDS -1.4 (-3.6;0.6). Peritoneal dialysis duration was 12 (2;32) months, and at peritoneal dialysis discontinuation height-SDS was -1.0 (-4.3;0.7) weight-SDS -0.7 (-3.2;0.2), parathyroid hormone 123 (44;1540) ng/L, and hemoglobin 110 (73;174) g/L. During the first 6 months of peritoneal dialysis, the median time of hospitalisation stay was 69 (15;182) days. Ten patients presented a total of 27 peritonitis episodes. Reasons for peritoneal dialysis discontinuation were switch to hemodialysis (n=6), transplantation (n=6), recovery of renal function (n=2) and death (n=1). After a follow-up of 4.3 (1.7;10.3) years, 12 patients were transplanted, 2 patients were still on peritoneal dialysis, 2 patients were dialysis free with severe chronic kidney disease and 1 patient had died. Seven patients displayed neurodevelopmental delay, of whom five needed special schooling. CONCLUSION: We confirm that most infants starting peritoneal dialysis before 6 months of age will be successfully transplanted and will have a favourable growth outcome. Their quality of life will be impacted by recurrent hospitalisations and neurodevelopmental delay is frequent.

Impact of Phyllantus niruri and Lactobacillus amylovorus SGL 14 in a mouse model of dietary hyperoxaluria.

Hyperoxaluria is a pathological condition which affects long-term health of kidneys. The present study evaluates the impact of the combination of Lactobacillus amylovorus SGL 14 and the plant extract Phyllantus niruri (namely Phyllantin 14™) on dietary hyperoxaluria. Safety and efficacy of Phyllantin 14 have been evaluated in vivo. Mice C57BL6 fed a high-oxalate diet were compared to mice fed the same diet administered with Phyllantin 14 by gavage for 6 weeks. Control mice were fed a standard diet without oxalate. No adverse effects were associated to Phyllantin 14 supplementation, supporting its safety. Mice fed a high-oxalate diet developed significant hyperoxaluria and those administered with Phyllantin 14 showed a reduced level of urinary oxalate and a lower oxalate-to-creatinine ratio. Soluble and insoluble caecal oxalate were significantly lower in treated group, a finding in agreement with the colonisation study, i.e. mice were colonised with SGL 14 after 3 weeks. Microbiota analysis demonstrated that both oxalate diet and Phyllantin 14 can differently modulate the microbiota. In conclusion, our findings suggest that Phyllantin 14 supplementation represents a potential supportive approach for reducing urinary oxalate and/or for enhancing the efficacy of existing treatments.

Investigational Therapies for Primary Hyperoxaluria.

Recent years have brought exciting new insights in the field of primary hyperoxaluria (PH), both on a basic research level as well as through the progress of novel therapeutics in clinical development. To date, very few supportive measures are available for patients suffering from PH, which, together with the severity of the disorder, make disease management challenging. Basic and clinical research and development efforts range from correcting the underlying gene mutations, preventing calcium oxalate crystal-induced kidney damage, to the administration of probiotics favoring the intestinal secretion of excess oxalate. In this review, current advances in the development of those strategies are presented and discussed.

Oxalobacter formigenes treatment combined with intensive dialysis lowers plasma oxalate and halts disease progression in a patient with severe infantile oxalosis.

BACKGROUND: Infantile oxalosis, the most devastating form of primary hyperoxaluria type 1 (PH1), often leads to end-stage renal disease (ESRD) during the first weeks to months of life. CASE-DIAGNOSIS: Here, we report the outcome of the therapeutic use of Oxalobacter formigenes (Oxabact OC5; OxThera AB, Stockholm, Sweden) in a female infant with PH1 who exhibited severely elevated plasma oxalate (Pox) levels, pronounced nephrocalcinosis, anuretic end-stage renal disease, and retinal oxalate deposits. Following the diagnosis of PH1 at an age of 8 weeks, a combined regimen of daily peritoneal dialysis, daily pyridoxine treatment and hemodialysis (3 times a week) was unable to reduce the pronounced hyperoxalemia. After the addition of Oxalobacter formigenes therapy to the otherwise unchanged treatment regimen, Pox levels first stabilized and subsequently declined from 130 µmol/L to around 80 µmol/L. Nephrocalcinosis and retinal deposits stabilized. Oxalobacter formigenes treatment was well-tolerated and no related adverse events were observed. The patient showed nearly age-appropriate growth and development and received successful combined liver-kidney transplantation at the age of two years. CONCLUSIONS: Treatment with O. formigenes combined with intensive dialysis led to reduction of Pox, stabilization of systemic oxalosis, and improvement in the clinical disease course. O. formigenes treatment may be an option for reduction of oxalosis in infantile patients with insufficient response to conservative treatments until combined liver-kidney transplantation can be performed.

Future treatments for hyperoxaluria.

PURPOSE OF REVIEW: The review of potential therapies in the treatment of hyperoxaluria is timely, given the current excitement with clinical trials and the mounting evidence of the importance of oxalate in both kidney stone and chronic kidney disease. RECENT FINDINGS: Given the significant contribution of both endogenous and dietary oxalate to urinary oxalate excretions, it is not surprising therapeutic targets are being studied in both pathways. This article covers the existing data on endogenous and dietary oxalate and the current targets in these pathways. SUMMARY: In the near future, there will likely be therapies targeting both endogenous and dietary oxalate, especially in subsets of kidney stone formers.

Educational review: role of the pediatric nephrologists in the work-up and management of kidney stones.

BACKGROUND: The incidence of nephrolithiasis in children and adolescents is increasing and appears to double every 10 years. The most important role of the pediatric nephrologist is to diagnose and modify various metabolic and non-metabolic risk factors, as well as prevent long-term complications especially in the case of recurrent nephrolithiasis. OBJECTIVE: The purpose of this review is to summarize the existing literature on the etiology and management of pediatric nephrolithiasis. RESULTS: The incidence of kidney stones is increasing; dietary and environmental factors are probably the main causes for this increased incidence. In most pediatric patients, the etiology for the kidney stones can be identified. Metabolic factors, such as hypercalciuria and hypocitraturia, urinary tract infection, and urinary stasis, constitute leading causes. Herein, we review the etiologies, diagnostic work-up, and treatment options for the most prevalent causes of kidney stones. The detrimental effects of excessive dietary sodium, reduced fluid intake, and the benefits of plant-based over animal-based protein consumption on urinary crystal formation are discussed. We also review the long-term complications. CONCLUSIONS: Pediatric nephrologists have an important role in the diagnostic work-up and prevention of recurring nephrolithiasis.

Secondary hyperoxaluria due to pancreatic insufficiency.

BACKGROUND: In this article, we present two cases of patients with acute renal insufficiency with a history of exocrine pancreatic insufficiency. In one case, this was caused by pancreaticoduodenectomy; in the other, by alcohol abuse. Neither patient had considerable proteinuria or haematuria. Their renal biopsies showed tubulopathy with widespread oxalate crystals, characterised by their birefringence in light microscopy. Restricting oxalate intake and prescribing oxalate binding agents reduced serum oxalate levels. Renal function partially recovered in both patients. Oxalate nephropathy is associated with exocrine pancreatic insufficiency, gastric and pancreatic surgery, and inflammatory bowel disease. Normally, dietary calcium binds oxalate to form calcium oxalate, which is excreted in the stool. In patients with pancreatic insufficiency, fatty acids bind calcium instead, allowing oxalate to be absorbed in the colon. The resulting hyperoxaluria can cause oxalate crystal formation, tubulopathy, and renal insufficiency. Treatment relies on decreasing the amount of absorbable oxalate in the intestinal lumen, as well as lowering urinary oxalate concentrations. CONCLUSION: Secondary hyperoxaluria is a common cause of renal insufficiency and should be considered in patients with a medical history of pancreatic insufficiency and progressive kidney injury.