ALLN-177, oral enzyme therapy for hyperoxaluria

OxDc-A0: an oral gastro-tolerant oxalate decarboxylase for treating secondary hyperoxaluria

Secondary hyperoxaluria is an acquired oxalate metabolic disorder characterized by increased urinary oxalate excretion. Reducing exogenous oxalate absorption through enzyme therapy represents a promising therapeutic strategy. However, the extremely acidic pH and protease-rich environment of the upper gastrointestinal tract pose major obstacles for the oral administration of protein therapeutics. OxDc-A0, a novel gastro-tolerant recombinant oxalate decarboxylase, can degrade oxalate in the stomach, thereby limiting the oxalate pool in the gastrointestinal tract and reducing oxalate absorption and urinary excretion. This study aimed to investigate the pharmacodynamics, pharmacokinetics, and safety profile of OxDc-A0 to assess its drug likeliness. The pharmacodynamics were evaluated in vitro and in hyperoxaluria beagle dog model induced by a high-oxalate diet. OxDc-A0 exhibited excellent gastric tolerance and significant efficacy in reducing urinary oxalate excretion in the dog model with hyperoxaluria. The safety of OxDc-A0 was evaluated in Sprague-Dawley rats, beagle dogs, and golden hamsters according to the guidelines for preclinical safety studies. No adverse effects were observed on the central nervous, cardiovascular, or respiratory system in rats or dogs treated orally with OxDc-A0 up to 37,500 U/kg. Pharmacokinetic studies showed that OxDc-A0 is non-systemically absorbed and is mainly distributed in the gastrointestinal tract. Toxicological studies showed that OxDc-A0 has excellent tolerance, with a NOAEL of 37,500 U/kg/day in both rats and dogs. The maximum tolerated dose was ≥ 105,000 U/kg in rats and ≥ 87,000 U/kg in dogs. Overall, OxDc-A0 shows great potential as a new drug candidate for treating secondary hyperoxaluria.

Enzymatic and structural properties of a novel oxalate decarboxylase BsOxdC from Bacillus safensis and its potential pH-dependent catalytic mechanism

Oxalate decarboxylase converts oxalate to formate and CO2 without requiring organic cofactors, making it biotechnologically relevant for applications in food, agriculture, and diagnostics. Its activity is highly dependent on pH; however, the pH-dependent catalytic mechanism remains poorly understood. This study identified a novel oxalate decarboxylase, BsOxdC, from Bacillus safensis and investigated its catalytic properties through heterologous expression and enzymatic assays. The purified BsOxdC efficiently degrades oxalate at an optimum temperature of 50 °C and a pH of 4.0, achieving a Vmax of 8.54 μmol/(min·mg). The apparent values of kcat, Km, and kcat/Km were 85.35 s-1, 4.67 μM, and 18.28 μM/s, respectively. The predicted structure of BsOxdC features two conserved cupin barrel folds at the N-terminal and C-terminal. Additionally, the docking model of the oxalate-BsOxdC complex is more stable than those of the formate-BsOxdC or acetate-BsOxdC complexes due to its lowest binding energy. In the open conformation of BsOxdC, the carboxyl group of the catalytic residue E181, located in the active loop S180E181N182S183T184, points away from both the oxalate and the active-site Mn ion. Simulations suggest that S180 and E181 interact with the substrate via ionic bonds and/or water bridges only at low pH (4.0), not at pH 8.0. Additionally, THR184 forms more molecular interactions with oxalate at pH 4.0 than at pH 8.0.

Opportunities in Primary and Enteric Hyperoxaluria at the Cross-Roads Between the Clinic and Laboratory

Hyperoxaluria is a condition in which there is a pathologic abundance of oxalate in the urine through either hepatic overproduction (primary hyperoxaluria [PH]) or excessive enteric absorption of dietary oxalate (enteric hyperoxaluria [EH]). Severity can vary with the most severe forms causing kidney failure and extrarenal manifestations. To address the current challenges and innovations in hyperoxaluria, the 14th International Hyperoxaluria Workshop convened in Perugia, Italy, bringing together international experts for focused presentation and discussion. The objective of the following report was to disseminate an overview of the proceedings and provide substrate for further thought. The format of this paper follows the format of the meeting, addressing, "PH type 1" (PH1) first, followed by "surgery, genetics, and ethics in PH", then "PH types 2 and 3," (PH2 and PH3) and, finally, "EH." Each session began with presentations of the current clinical challenges, followed by discussion of the latest advances in basic and translational research, and concluded with interactive discussions about prioritizing the future of research in the field to best serve the need of the patients.

Drinkable in situ-forming tough hydrogels for gastrointestinal therapeutics

Pills are a cornerstone of medicine but can be challenging to swallow. While liquid formulations are easier to ingest, they lack the capacity to localize therapeutics with excipients nor act as controlled release devices. Here we describe drug formulations based on liquid in situ-forming tough (LIFT) hydrogels that bridge the advantages of solid and liquid dosage forms. LIFT hydrogels form directly in the stomach through sequential ingestion of a crosslinker solution of calcium and dithiol crosslinkers, followed by a drug-containing polymer solution of alginate and four-arm poly(ethylene glycol)-maleimide. We show that LIFT hydrogels robustly form in the stomachs of live rats and pigs, and are mechanically tough, biocompatible and safely cleared after 24 h. LIFT hydrogels deliver a total drug dose comparable to unencapsulated drug in a controlled manner, and protect encapsulated therapeutic enzymes and bacteria from gastric acid-mediated deactivation. Overall, LIFT hydrogels may expand access to advanced therapeutics for patients with difficulty swallowing.

Infant primary hyperoxaluria type 1 A case report and literature review

Primary hyperoxaluria (PH) is a rare autosomal recessive disorder, with PH type 1 (PH1) being the most common. It is primarily characterized by recurrent renal calculi, renal calcification, and can lead to acute renal failure. In infants, PH1 often results in early end-stage renal disease (ESRD) with a high mortality rate. This paper reports a case of an infant with acute renal failure in the Second Hospital of Shandong University who was diagnosed as PH1 using whole-exome sequencing, revealing a homozygous mutation in the AGXT gene (c.596-2A>G), which is reported here for the first time in the Chinese population. Previous literature indicates that urinary oxalate levels and stone composition can suggest PH1, with the gold standard for diagnosis being liver biopsy combined with alanine-glyoxylate aminotransferase (AGT) enzyme activity assessment. However, due to its convenience, AGXT gene sequencing has increasingly become the preferred diagnostic method. Conservative treatments for PH1 include adequate fluid intake, citrate, vitamin B6, and continuous renal replacement therapy, while liver transplantation is the only curative treatment. Infants with unexplained acute renal failure should be evaluated for PH1, with early detection of the level of urine oxalate and screening for genetic testing recommended.

Engineered microorganisms: A new direction in kidney stone prevention and treatment

Numerous studies have shown that intestinal and urinary tract flora are closely related to the formation of kidney stones. The removal of probiotics represented by lactic acid bacteria and the colonization of pathogenic bacteria can directly or indirectly promote the occurrence of kidney stones. However, currently existing natural probiotics have limitations. Synthetic biology is an emerging discipline in which cells or living organisms are genetically designed and modified to have biological functions that meet human needs, or even create new biological systems, and has now become a research hotspot in various fields. Using synthetic biology approaches of microbial engineering and biological redesign to enable probiotic bacteria to acquire new phenotypes or heterologous protein expression capabilities is an important part of synthetic biology research. Synthetic biology modification of microorganisms in the gut and urinary tract can effectively inhibit the development of kidney stones by a range of means, including direct degradation of metabolites that promote stone production or indirect regulation of flora homeostasis. This article reviews the research status of engineered microorganisms in the prevention and treatment of kidney stones, to provide a new and effective idea for the prevention and treatment of kidney stones.

Recent Advances of Oxalate Decarboxylase: Biochemical Characteristics, Catalysis Mechanisms, and Gene Expression and Regulation

Oxalate decarboxylase (OXDC) is a typical Mn2+/Mn3+ dependent metal enzyme and splits oxalate to formate and CO2 without any organic cofactors. Fungi and bacteria are the main organisms expressing the OXDC gene, but with a significantly different mechanism of gene expression and regulation. Many articles reported its potential applications in the clinical treatment of hyperoxaluria, low-oxalate food processing, degradation of oxalate salt deposits, oxalate acid diagnostics, biocontrol, biodemulsifier, and electrochemical oxidation. However, some questions still remain to be clarified about the role of substrate binding and/or protein environment in modulating the redox properties of enzyme-bound Mn(II)/Mn(III), the nature of dioxygen involved in the catalytic mechanism, and how OXDC acquires Mn(II) /Mn(III). This review mainly summarizes its biochemical and structure characteristics, gene expression and regulation, and catalysis mechanism. We also deep-mined oxalate decarboxylase gene data from National Center for Biotechnology Information to give some insights to explore new OXDC with diverse biochemical properties.

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.

Review of childhood genetic nephrolithiasis and nephrocalcinosis

Nephrolithiasis (NL) is a common condition worldwide. The incidence of NL and nephrocalcinosis (NC) has been increasing, along with their associated morbidity and economic burden. The etiology of NL and NC is multifactorial and includes both environmental components and genetic components, with multiple studies showing high heritability. Causative gene variants have been detected in up to 32% of children with NL and NC. Children with NL and NC are genotypically heterogenous, but often phenotypically relatively homogenous, and there are subsequently little data on the predictors of genetic childhood NL and NC. Most genetic diseases associated with NL and NC are secondary to hypercalciuria, including those secondary to hypercalcemia, renal phosphate wasting, renal magnesium wasting, distal renal tubular acidosis (RTA), proximal tubulopathies, mixed or variable tubulopathies, Bartter syndrome, hyperaldosteronism and pseudohyperaldosteronism, and hyperparathyroidism and hypoparathyroidism. The remaining minority of genetic diseases associated with NL and NC are secondary to hyperoxaluria, cystinuria, hyperuricosuria, xanthinuria, other metabolic disorders, and multifactorial etiologies. Genome-wide association studies (GWAS) in adults have identified multiple polygenic traits associated with NL and NC, often involving genes that are involved in calcium, phosphorus, magnesium, and vitamin D homeostasis. Compared to adults, there is a relative paucity of studies in children with NL and NC. This review aims to focus on the genetic component of NL and NC in children.

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.

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.

Randomized Placebo-Controlled Trial of Reloxaliase in Enteric Hyperoxaluria

BACKGROUND: Enteric hyperoxaluria is caused by increased intestinal oxalate absorption and can lead to kidney stones, chronic kidney disease, and kidney failure. Reloxaliase is an orally administered recombinant enzyme that degrades oxalate along the gastrointestinal tract, thereby preventing its absorption. METHODS: We randomly assigned participants with enteric hyperoxaluria to reloxaliase or placebo, three to five times per day with food for 4 weeks. The primary end point was percent change from baseline in 24-hour urinary oxalate (UOx) excretion during weeks 1 to 4. Secondary end points included the proportion of participants with more than a 20% reduction in 24-hour UOx and an efficacy assessment in the bariatric surgery subgroup. RESULTS: A total of 115 patients underwent randomization. The 24-hour UOx decreased from a baseline geometric mean of 83.2 to 67.4 mg/24 hr during weeks 1 to 4 in reloxaliase-treated participants. Corresponding data for placebo-treated participants were 84.2 to 78.1 mg/24 hr. Estimates from the mixed-effect model repeated-measures (MMRM) analysis showed a 22.6% reduction in geometric mean UOx during weeks 1 to 4 for reloxaliase and 9.7% for placebo, a difference of 14.3 percentage points (95% confidence interval [CI], 4.9 to 22.8; P=0.004). A 20% or greater reduction in 24-hour UOx was observed in 48.3% of reloxaliase-treated participants and 31.6% of placebo-treated participants (P=0.06). In the bariatric surgery subgroup, MMRM analysis showed a 21.2% reduction in geometric mean UOx for reloxaliase and a 6.0% reduction for placebo, for a difference of 16.2 percentage points (95% CI, 4.2% to 26.7%). Adverse events occurred in 69% of reloxaliase-treated participants versus 53% of individuals taking placebo and were most commonly gastrointestinal. All but one of the adverse events were grade 1 or 2 in severity; no reloxaliase-treated participants discontinued the study. CONCLUSIONS: Reloxaliase treatment for 4 weeks reduced UOx excretion in patients with enteric hyperoxaluria; adverse events were relatively common, but not dose-limiting. These data establish the foundation for a clinical trial to determine the impact of reloxaliase on nephrolithiasis in patients with enteric hyperoxaluria. (Funded by Allena Pharmaceuticals; ClinicalTrials.gov number, NCT03456830.)

Reloxaliase in Enteric Hyperoxaluria - The Recent Brake

Hyperoxaluria is defined as urinary oxalate (UOx) excretion greater than 0.5 mmol per day. Hyperoxaluria can result from genetic causes, and these are known as primary hyperoxalurias. Secondary hyperoxaluria results from high intake of oxalate-rich foods (e.g., chocolate, nuts, spinach), lack of calcium in the diet to bind oxalate in the gut, or oxalate malabsorption; these forms are termed enteric hyperoxaluria. Usually only primary and enteric hyperoxalurias lead to the complications of kidney stones, crystal nephropathy, chronic kidney disease (CKD), and systemic oxalosis.1.

Small molecule inhibitor of intestinal anion exchanger SLC26A3 for therapy of hyperoxaluria and nephrolithiasis

Nephrolithiasis is a common and recurrent disease affecting 9% of the US population. Hyperoxaluria is major risk factor for calcium oxalate kidney stones, which constitute two-thirds of all kidney stones. SLC26A3 (DRA, downregulated in adenoma) is an anion exchanger of chloride, bicarbonate, and oxalate thought to facilitate intestinal oxalate absorption, as evidenced by approximately 70% reduced urine oxalate excretion in knockout mice. We previously identified a small-molecule SLC26A3 inhibitor (DRA_inh-A270) that selectively inhibited SLC26A3-mediated chloride/bicarbonate exchange (IC₅₀ ~ 35 nM) and, as found here, oxalate/chloride exchange (IC₅₀ ~ 60 nM). In colonic closed loops in mice, luminal DRA_inh-A270 inhibited oxalate absorption by 70%. Following oral sodium oxalate loading in mice, DRA_inh-A270 largely prevented the 2.5-fold increase in urine oxalate/creatinine ratio. In a mouse model of oxalate nephropathy produced by a high-oxalate low-calcium diet, vehicle-treated mice developed marked hyperoxaluria with elevated serum creatinine, renal calcium oxalate crystal deposition, and renal injury, which were largely prevented by DRA_inh-A270 (10 mg/kg twice daily). DRA_inh-A270 administered over 7 days to healthy mice did not show significant toxicity. Our findings support a major role of SLC26A3 in intestinal oxalate absorption and suggest the therapeutic utility of SLC26A3 inhibition for treatment of hyperoxaluria and prevention of calcium oxalate nephrolithiasis.

Primary hyperoxaluria type 1: novel therapies at a glance

Primary hyperoxaluria type 1 (PH1) is a rare and severe autosomal recessive disease of oxalate metabolism, resulting from a mutation in the AGXT gene that encodes the hepatic peroxisomal enzyme alanine–glyoxylate aminotransferase (AGT). Until recently, treatment of PH1 was supportive, consisting of intensive hyperhydration, use of crystallization inhibitors (citrate and neutral phosphorus), in a subset of responsive PH1 patients’ pharmacologic doses of vitamin B6 (pyridoxine), and kidney and liver transplantation when patients progressed to kidney failure. Treatment approaches have been similar for PH2 caused by mutations in hepatic glyoxylate reductase/hydroxypyruvate reductase (GR/HPR), although pyridoxine does not have any benefit in this group. PH3 is caused by mutations of mitochondrial 4-hydroxy-2-oxoglutarate aldolase (HOGA1) and was the most recently described. Kidney failure appears less common in PH3, although kidney stones occur as frequently as in PH1 and PH2. Oxalate metabolism in the liver is complex. Novel therapies based on RNA interference (RNAi) have recently emerged to modulate these pathways, designed to deplete substrate for enzymes upstream and decrease/avoid oxalate production. Two hepatic enzymes have been targeted to date in PH: glycolate oxidase (GO) with lumasiran and lactate dehydrogenase A (LDH-A) with nedosiran. Lumasiran was approved for the treatment of PH1 in 2020 by both the European Medicines Agency and the Food and Drug Administration, whilst clinical trials with nedosiran are ongoing. Results with the two RNAi therapies demonstrate a significant reduction of urinary oxalate excretion in PH1 patients, but long-term data on efficacy (preservation of kidney function, decreased stone events) and safety remain to be established. Nevertheless, the hepatically targeted RNAi approach represents a potential ‘game changer’ in the field of PH1, bringing hope to families and patients that they may be able to avoid liver and/or kidney transplantation in the future and suffer fewer stone events, perhaps with less strict therapeutic regimens. Pharmacological compounds directly inhibiting GO or LDH are also under development and could be of special interest in developing countries where RNAi therapies may not be readily available in the near future. Approaches to manipulate the intestinal microbiome with a goal to increase oxalate degradation or to stimulate secretion of oxalate into the intestine from plasma are also under development. Overall, we appear to be entering a new phase of PH treatment, with an array of promising approaches emerging that will need optimization and evaluation to establish long-term efficacy and safety.

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.

Medical Treatment and Prevention of Urinary Stone Disease

The pathophysiology underlying urinary stone formation remains an area of active investigation. There are many pharmacotherapies aimed at optimizing metabolic factors and reducing urinary supersaturation of stone components that play an important role in urinary stone prevention. In addition, medical expulsive therapy for ureteral stones and medical dissolution therapy for uric acid-based urinary stones are helpful treatment tools and are used alongside surgical treatments in the management of urinary stones.

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.

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.

High Oxalate Concentrations Correlate with Increased Risk for Sudden Cardiac Death in Dialysis Patients

BACKGROUND

The clinical significance of accumulating toxic terminal metabolites such as oxalate in patients with kidney failure is not well understood.

METHODS

To evaluate serum oxalate concentrations and risk of all-cause mortality and cardiovascular events in a cohort of patients with kidney failure requiring chronic dialysis, we performed a post-hoc analysis of the randomized German Diabetes Dialysis (4D) Study; this study included 1255 European patients on hemodialysis with diabetes followed-up for a median of 4 years. The results obtained via Cox proportional hazards models were confirmed by competing risk regression and restricted cubic spline modeling in the 4D Study cohort and validated in a separate cohort of 104 US patients on dialysis after a median follow-up of 2.5 years.

RESULTS

A total of 1108 patients had baseline oxalate measurements, with a median oxalate concentration of 42.4 µM. During follow-up, 548 patients died, including 139 (25.4%) from sudden cardiac death. A total of 413 patients reached the primary composite cardiovascular end point (cardiac death, nonfatal myocardial infarction, and fatal or nonfatal stroke). Patients in the highest oxalate quartile (≥59.7 µM) had a 40% increased risk for cardiovascular events (adjusted hazard ratio [aHR], 1.40; 95% confidence interval [95% CI], 1.08 to 1.81) and a 62% increased risk of sudden cardiac death (aHR, 1.62; 95% CI, 1.03 to 2.56), compared with those in the lowest quartile (≤29.6 µM). The associations remained when accounting for competing risks and with oxalate as a continuous variable.

CONCLUSIONS

Elevated serum oxalate is a novel risk factor for cardiovascular events and sudden cardiac death in patients on dialysis. Further studies are warranted to test whether oxalate-lowering strategies improve cardiovascular mortality in patients on dialysis.

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.

Contribution of Dietary Oxalate and Oxalate Precursors to Urinary Oxalate Excretion

Kidney stone disease is increasing in prevalence, and the most common stone composition is calcium oxalate. Dietary oxalate intake and endogenous production of oxalate are important in the pathophysiology of calcium oxalate stone disease. The impact of dietary oxalate intake on urinary oxalate excretion and kidney stone disease risk has been assessed through large cohort studies as well as smaller studies with dietary control. Net gastrointestinal oxalate absorption influences urinary oxalate excretion. Oxalate-degrading bacteria in the gut microbiome, especially Oxalobacter formigenes, may mitigate stone risk through reducing net oxalate absorption. Ascorbic acid (vitamin C) is the main dietary precursor for endogenous production of oxalate with several other compounds playing a lesser role. Renal handling of oxalate and, potentially, renal synthesis of oxalate may contribute to stone formation. In this review, we discuss dietary oxalate and precursors of oxalate, their pertinent physiology in humans, and what is known about their role in kidney stone disease.

Subsequent urinary stone events are predicted by the magnitude of urinary oxalate excretion in enteric hyperoxaluria

 

Data directly demonstrating the relationship between urinary oxalate (UOx) excretion and stone events in those with enteric hyperoxaluria (EH) are limited. Therefore, we assessed the relationship between UOx excretion and risk of kidney stone events in a retrospective population-based EH cohort. In all, 297 patients from Olmsted County, Minnesota were identified with EH based upon having a 24-h UOx ≥40 mg/24 h preceded by a diagnosis or procedure associated with malabsorption. Diagnostic codes and urologic procedures consistent with kidney stones during follow-up after baseline UOx were considered a new stone event. Logistic regression and accelerated failure time modeling were performed as a function of UOx excretion to predict the probability of new stone event and the annual rate of stone events, respectively, with adjustment for urine calcium and citrate. Mean ± standard deviation age was 51.4 ± 11.4 years and 68% were female. Median (interquartile range) UOx was 55.4 (46.6-73.0) mg/24 h and 81 patients had one or more stone event during a median follow-up time of 4.9 (2.8-7.8) years. Higher UOx was associated with a higher probability of developing a stone event (P < 0.01) and predicted an increased annual risk of kidney stones (P = 0.001). Estimates derived from these analyses suggest that a 20% decrease in UOx is associated with 25% reduction in the annual odds of a future stone event. Thus, these data demonstrate an association between baseline UOx and stone events in EH patients and highlight the potential benefit of strategies to reduce UOx in this patient group.

BACKGROUND

Data directly demonstrating the relationship between urinary oxalate (UOx) excretion and stone events in those with enteric hyperoxaluria (EH) are limited.

METHODS

We assessed the relationship between UOx excretion and risk of kidney stone events in a retrospective population-based EH cohort. In all, 297 patients from Olmsted County, Minnesota were identified with EH based upon having a 24-h UOx ≥40 mg/24 h preceded by a diagnosis or procedure associated with malabsorption. Diagnostic codes and urologic procedures consistent with kidney stones during follow-up after baseline UOx were considered a new stone event. Logistic regression and accelerated failure time modeling were performed as a function of UOx excretion to predict the probability of new stone event and the annual rate of stone events, respectively, with adjustment for urine calcium and citrate.

RESULTS

Mean ± SD age was 51.4 ± 11.4 years and 68% were female. Median (interquartile range) UOx was 55.4 (46.6-73.0) mg/24 h and 81 patients had ≥1 stone event during a median follow-up time of 4.9 (2.8-7.8) years. Higher UOx was associated with a higher probability of developing a stone event (P < 0.01) and predicted an increased annual risk of kidney stones (P = 0.001). Estimates derived from these analyses suggest that a 20% decrease in UOx is associated with 25% reduction in the annual odds of a future stone event.

CONCLUSIONS

These data demonstrate an association between baseline UOx and stone events in EH patients and highlight the potential benefit of strategies to reduce UOx in this patient group.

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.

Urinary oxalate as a potential mediator of kidney disease in diabetes mellitus and obesity

PURPOSE OF REVIEW

Hyperoxaluria can cause kidney disease through multiple mechanisms, including tubular obstruction from calcium oxalate crystals, sterile inflammation, and tubular epithelial cell injury. Hyperoxaluria is also observed in individuals with diabetes mellitus and obesity, which are in turn risk factors for chronic kidney disease (CKD). Whether hyperoxaluria is a potential mediator of increased risk of CKD in diabetes mellitus and obesity is unknown.

RECENT FINDINGS

Individuals with diabetes have increased levels of plasma glyoxal (a protein glycation product) and glyoxylate, both of which are precursors for oxalate. Increased gut absorption of oxalate in obesity may be because of obesity-associated inflammation. A recent study in individuals with CKD found that higher 24 h urinary oxalate excretion was independently associated with increased risk of kidney disease progression, especially in individuals with diabetes and obesity.

SUMMARY

Both diabetes mellitus and obesity are associated with higher urinary oxalate excretion through distinct mechanisms. Hyperoxaluria could be a mechanism by which kidney disease develops in individuals with diabetes mellitus or obesity and could also contribute to progressive loss of renal function. Future research on pharmacologic or dietary measures to limit oxalate absorption or generation are required to test whether lowering urinary oxalate excretion is beneficial in preventing kidney disease development and progression in diabetes mellitus and obesity.

Risk of Kidney Stones: Influence of Dietary Factors, Dietary Patterns, and Vegetarian-Vegan Diets

Nephrolithiasis is a common medical condition influenced by multiple environmental factors, including diet. Since nutritional habits play a relevant role in the genesis and recurrence of kidney stones disease, dietary manipulation has become a fundamental tool for the medical management of nephrolithiasis. Dietary advice aims to reduce the majority of lithogenic risk factors, reducing the supersaturation of urine, mainly for calcium oxalate, calcium phosphate, and uric acid. For this purpose, current guidelines recommend increasing fluid intake, maintaining a balanced calcium intake, reducing dietary intake of sodium and animal proteins, and increasing intake of fruits and fibers. In this review, we analyzed the effects of each dietary factor on nephrolithiasis incidence and recurrence rate. Available scientific evidence agrees on the harmful effects of high meat/animal protein intake and low calcium diets, whereas high content of fruits and vegetables associated with a balanced intake of low-fat dairy products carries the lowest risk for incident kidney stones. Furthermore, a balanced vegetarian diet with dairy products seems to be the most protective diet for kidney stone patients. Since no study prospectively examined the effects of vegan diets on nephrolithiasis risk factors, more scientific work should be made to define the best diet for different kidney stone phenotypes.