Primary hyperoxalurias: disorders of glyoxylate detoxification

Urinary Oxalate Excretion During Pregnancy in Primary Hyperoxaluria Type 1: A Report of 4 Cases

Primary hyperoxaluria (PH) is a rare genetic disorder characterized by excessive oxalate production because of specific gene defects. PH1 is the most prevalent type, causing recurrent kidney stone disease and often leading to chronic kidney disease and kidney failure. Our previous study suggested that pregnancy did not adversely affect kidney function in female patients with PH. In this study, we identified 4 PH1 cases with urinary oxalate (UOx) measurements during pregnancy from the Rare Kidney Stone Consortium and Oxalosis and Hyperoxaluria Foundation PH registry to investigate UOx levels during pregnancy in patients with PH1. The PH Registry is approved by the Institutional Review Board of Mayo Clinic (Rochester, MN). All 4 showed a decrease in UOx during pregnancy when compared with before pregnancy and after delivery. These findings contrast with those of the general population, in which the UOx tends to increase during pregnancy because of a simultaneous physiological increase in the glomerular filtration rate. Elucidating the mechanism underlying reduced UOx during pregnancy in PH1 could suggest novel PH therapies. These findings could also affect the clinical management and have implications regarding the safety of withholding novel PH1-directed molecular therapies that currently have uncertain safety profiles during pregnancy. We highlight the need for additional data on urinary changes in patients with PH and other populations while pregnant to clarify changes in UOx throughout pregnancy.

Ancient eukaryotic protein interactions illuminate modern genetic traits and disorders

All eukaryotes share a common ancestor from roughly 1.5 - 1.8 billion years ago, a single-celled, swimming microbe known as LECA, the Last Eukaryotic Common Ancestor. Nearly half of the genes in modern eukaryotes were present in LECA, and many current genetic diseases and traits stem from these ancient molecular systems. To better understand these systems, we compared genes across modern organisms and identified a core set of 10,092 shared protein-coding gene families likely present in LECA, a quarter of which are uncharacterized. We then integrated >26,000 mass spectrometry proteomics analyses from 31 species to infer how these proteins interact in higher-order complexes. The resulting interactome describes the biochemical organization of LECA, revealing both known and new assemblies. We analyzed these ancient protein interactions to find new human gene-disease relationships for bone density and congenital birth defects, demonstrating the value of ancestral protein interactions for guiding functional genetics today.

Restored glyoxylate metabolism after AGXT gene correction and direct reprogramming of primary hyperoxaluria type 1 fibroblasts

Primary hyperoxaluria type 1 (PH1) is a rare inherited metabolic disorder characterized by oxalate overproduction in the liver, resulting in renal damage. It is caused by mutations in the AGXT gene. Combined liver and kidney transplantation is currently the only permanent curative treatment. We combined locus-specific gene correction and hepatic direct cell reprogramming to generate autologous healthy induced hepatocytes (iHeps) from PH1 patient-derived fibroblasts. First, site-specific AGXT corrected cells were obtained by homology directed repair (HDR) assisted by CRISPR-Cas9, following two different strategies: accurate point mutation (c.731T>C) correction or knockin of an enhanced version of AGXT cDNA. Then, iHeps were generated, by overexpression of hepatic transcription factors. Generated AGXT-corrected iHeps showed hepatic gene expression profile and exhibited in vitro reversion of oxalate accumulation compared to non-edited PH1-derived iHeps. This strategy set up a potential alternative cellular source for liver cell replacement therapy and a personalized PH1 in vitro disease model.

Primary hyperoxaluria: Description of a new oral finding and review of literature

OBJECTIVES

Oro-dental manifestations of hyperoxaluria and dental management of affected patients are rarely reported in the literature. We describe a new oral presentation of primary hyperoxaluria (PH) and review relevant literature about oro-dental manifestations and management of dental complications of hyperoxaluria.

METHODS

A case report of a 44-year-old female who presented with symptoms of temporomandibular joint dysfunction due to hyperoxaluria was described according to the CARE guidelines. In addition, an extensive search of biomedical databases (PubMed, Medline, Google Scholar, and Embase) for articles describing oro-dental manifestations and/or dental management in patients with hyperoxaluria was performed using the key words ("oral" and/or "hyperoxaluria" and/or "dental" and/or "oxalosis"). Included articles were reviewed and data about patient demographics, disease type and stage, oral and dental manifestations, and dental treatment outcome were retrieved and analyzed.

RESULTS

A total of 14 articles describing the oral and dental manifestations in 15 patients with hyperoxaluria were included. Tooth mobility, root resorption, and radiographic alterations were consistently described in all cases. Oral manifestations were described mainly in PH at late stages, and only after the onset of chronic renal disease. Dental management in all reported cases was palliative and aimed to relive pain and treat periodontal infection. Tooth loss due to extraction or uncontrolled mobility was the ultimate outcome in almost all reported cases.

CONCLUSION

Oral and dental manifestations in hyperoxaluria are rarely reported in the literature. Management of tooth mobility and root resorption in hyperoxaluria is challenging and clinical guidelines and evidence-based recommendations are lacking. Early diagnosis and treatment of hyperoxaluria might be the only effective approach to prevent dental and periodontal complications of the disease.

Insights into the pathogenesis of primary hyperoxaluria type I from the structural dynamics of alanine:glyoxylate aminotransferase variants

Primary hyperoxaluria type I (PH1) is caused by deficient alanine:glyoxylate aminotransferase (AGT) activity. PH1-causing mutations in AGT lead to protein mistargeting and aggregation. Here, we use hydrogen-deuterium exchange (HDX) to characterize the wild-type (WT), the LM (a polymorphism frequent in PH1 patients) and the LM G170R (the most common mutation in PH1) variants of AGT. We provide the first experimental analysis of AGT structural dynamics, showing that stability is heterogeneous in the native state and providing a blueprint for frustrated regions with potentially functional relevance. The LM and LM G170R variants only show local destabilization. Enzymatic transamination of the pyridoxal 5-phosphate cofactor bound to AGT hardly affects stability. Our study, thus, supports that AGT misfolding is not caused by dramatic effects on structural dynamics.

Therapeutic targeting of HYPDH/PRODH2 with N-propargylglycine offers a Hyperoxaluria treatment opportunity

N-propargylglycine prevents 4-hydroxyproline catabolism in mouse liver and kidney. N-propargylglycine is a novel suicide inhibitor of PRODH2 and induces mitochondrial degradation of PRODH2. PRODH2 is selectively expressed in liver and kidney and contributes to primary hyperoxaluria (PH). Preclinical evaluation of N-propargylglycine efficacy as a new PH therapeutic is warranted.

Neuroprotective Effects and Therapeutic Potential of Dichloroacetate: Targeting Metabolic Disorders in Nervous System Diseases

Dichloroacetate (DCA) is an investigational drug used to treat lactic acidosis and malignant tumours. It works by inhibiting pyruvate dehydrogenase kinase and increasing the rate of glucose oxidation. Some studies have documented the neuroprotective benefits of DCA. By reviewing these studies, this paper shows that DCA has multiple pharmacological activities, including regulating metabolism, ameliorating oxidative stress, attenuating neuroinflammation, inhibiting apoptosis, decreasing autophagy, protecting the blood‒brain barrier, improving the function of endothelial progenitor cells, improving mitochondrial dynamics, and decreasing amyloid β-protein. In addition, DCA inhibits the enzyme that metabolizes it, which leads to peripheral neurotoxicity due to drug accumulation that may be solved by individualized drug delivery and nanovesicle delivery. In summary, in this review, we analyse the mechanisms of neuroprotection by DCA in different diseases and discuss the causes of and solutions to its adverse effects.

Regulating mitochondrial metabolism by targeting pyruvate dehydrogenase with dichloroacetate, a metabolic messenger

Dichloroacetate (DCA) is a naturally occurring xenobiotic that has been used as an investigational drug for over 50 years. Originally found to lower blood glucose levels and alter fat metabolism in diabetic rats, this small molecule was found to serve primarily as a pyruvate dehydrogenase kinase inhibitor. Pyruvate dehydrogenase kinase inhibits pyruvate dehydrogenase complex, the catalyst for oxidative decarboxylation of pyruvate to produce acetyl coenzyme A. Several congenital and acquired disease states share a similar pathobiology with respect to glucose homeostasis under distress that leads to a preferential shift from the more efficient oxidative phosphorylation to glycolysis. By reversing this process, DCA can increase available energy and reduce lactic acidosis. The purpose of this review is to examine the literature surrounding this metabolic messenger as it presents exciting opportunities for future investigation and clinical application in therapy including cancer, metabolic disorders, cerebral ischemia, trauma, and sepsis.

Oxalate as a potent promoter of kidney stone formation

Kidney stones are among the most prevalent urological diseases, with a high incidence and recurrence rate. Treating kidney stones has been greatly improved by the development of various minimally invasive techniques. Currently, stone treatment is relatively mature. However, most current treatment methods are limited to stones and cannot effectively reduce their incidence and recurrence. Therefore, preventing disease occurrence, development, and recurrence after treatment, has become an urgent issue. The etiology and pathogenesis of stone formation are key factors in resolving this issue. More than 80% of kidney stones are calcium oxalate stones. Several studies have studied the formation mechanism of stones from the metabolism of urinary calcium, but there are few studies on oxalate, which plays an equally important role in stone formation. Oxalate and calcium play equally important roles in calcium oxalate stones, whereas the metabolism and excretion disorders of oxalate play a crucial role in their occurrence. Therefore, starting from the relationship between renal calculi and oxalate metabolism, this work reviews the occurrence of renal calculi, oxalate absorption, metabolism, and excretion mechanisms, focusing on the key role of SLC26A6 in oxalate excretion and the regulatory mechanism of SLC26A6 in oxalate transport. This review provides some new clues for the mechanism of kidney stones from the perspective of oxalate to improve the understanding of the role of oxalate in the formation of kidney stones and to provide suggestions for reducing the incidence and recurrence rate of kidney stones.

Mitochondrial DNA Supplementation of Oocytes Has Downstream Effects on the Transcriptional Profiles of Sus scrofa Adult Tissues with High mtDNA Copy Number

Oocytes can be supplemented with extra copies of mitochondrial DNA (mtDNA) to enhance developmental outcome. Pigs generated through supplementation with mtDNA derived from either sister (autologous) or third-party (heterologous) oocytes have been shown to exhibit only minor differences in growth, physiological and biochemical assessments, and health and well-being do not appear affected. However, it remains to be determined whether changes in gene expression identified during preimplantation development persisted and affected the gene expression of adult tissues indicative of high mtDNA copy number. It is also unknown if autologous and heterologous mtDNA supplementation resulted in different patterns of gene expression. Our transcriptome analyses revealed that genes involved in immune response and glyoxylate metabolism were commonly affected in brain, heart and liver tissues by mtDNA supplementation. The source of mtDNA influenced the expression of genes associated with oxidative phosphorylation (OXPHOS), suggesting a link between the use of third-party mtDNA and OXPHOS. We observed a significant difference in parental allele-specific imprinted gene expression in mtDNA-supplemented-derived pigs, with shifts to biallelic expression with no effect on expression levels. Overall, mtDNA supplementation influences the expression of genes in important biological processes in adult tissues. Consequently, it is important to determine the effect of these changes on animal development and health.

Effect of liver transplantation with primary hyperoxaluria type 1: Five case reports and review of literature

BACKGROUND

Primary hyperoxaluria type 1 (PH1) is a rare autosomal recessive disease stemming from a deficiency in liver-specific alanine-glyoxylate aminotransferase, resulting in increased endogenous oxalate deposition and end-stage renal disease. Organ transplantation is the only effective treatment. However, its approach and timing remain controversial.

CASE SUMMARY

We retrospectively analyzed 5 patients diagnosed with PH1 from the Liver Transplant Center of the Beijing Friendship Hospital from March 2017 to December 2020. Our cohort included 4 males and 1 female. The median age at onset was 4.0 years (range: 1.0-5.0), age at diagnosis was 12.2 years (range: 6.7-23.5), age at liver transplantation (LT) was 12.2 years (range: 7.0-25.1), and the follow-up time was 26.3 mo (range: 12.8-40.1). All patients had delayed diagnosis, and 3 patients had progressed to end-stage renal disease by the time they were diagnosed. Two patients received preemptive LT; their estimated glomerular filtration rate was maintained at > 120 mL/min/1.73 m², indicating a better prognosis. Three patients received sequential liver and kidney transplantation. After transplantation, serum and urinary oxalate decreased, and liver function recovered. At the last follow-up, the estimated glomerular filtration rates of the latter 3 patients were 179, 52 and 21 mL/min/1.73 m².

CONCLUSION

Different transplantation strategies should be adopted for patients based on their renal function stage. Preemptive-LT offers a good therapeutic approach for PH1.

Molecular Mechanisms, Genotype-Phenotype Correlations and Patient-Specific Treatments in Inherited Metabolic Diseases

Advances in DNA sequencing technologies are revealing a vast genetic heterogeneity in human population, which may predispose to metabolic alterations if the activity of metabolic enzymes is affected [...].

PHYOX2: a pivotal randomized study of nedosiran in primary hyperoxaluria type 1 or 2

Nedosiran is an investigational RNA interference agent designed to inhibit expression of hepatic lactate dehydrogenase, the enzyme thought responsible for the terminal step of oxalate synthesis. Oxalate overproduction is the hallmark of all genetic subtypes of primary hyperoxaluria (PH). In this double-blind, placebo-controlled study, we randomly assigned (2:1) 35 participants with PH1 (n = 29) or PH2 (n = 6) with eGFR ≥30 mL/min/1.73 m² to subcutaneous nedosiran or placebo once monthly for 6 months. The area under the curve (AUC) of percent reduction from baseline in 24-hour urinary oxalate (Uox) excretion (primary endpoint), between day 90-180, was significantly greater with nedosiran vs placebo (least squares mean [SE], +3507 [788] vs -1664 [1190], respectively; difference, 5172; 95% CI 2929-7414; P < 0.001). A greater proportion of participants receiving nedosiran vs placebo achieved normal or near-normal (<0.60 mmol/24 hours; <1.3 × ULN) Uox excretion on ≥2 consecutive visits starting at day 90 (50% vs 0; P = 0.002); this effect was mirrored in the nedosiran-treated PH1 subgroup (64.7% vs 0; P < 0.001). The PH1 subgroup maintained a sustained Uox reduction while on nedosiran, whereas no consistent effect was seen in the PH2 subgroup. Nedosiran-treated participants with PH1 also showed a significant reduction in plasma oxalate versus placebo (P = 0.017). Nedosiran was generally safe and well tolerated. In the nedosiran arm, the incidence of injection-site reactions was 9% (all mild and self-limiting). In conclusion, participants with PH1 receiving nedosiran had clinically meaningful reductions in Uox, the mediator of kidney damage in PH.

The interplay between nonalcoholic fatty liver disease and atherosclerotic cardiovascular disease

Therapeutic approaches that lower circulating low-density lipoprotein (LDL)-cholesterol significantly reduced the burden of cardiovascular disease over the last decades. However, the persistent rise in the obesity epidemic is beginning to reverse this decline. Alongside obesity, the incidence of nonalcoholic fatty liver disease (NAFLD) has substantially increased in the last three decades. Currently, approximately one third of world population is affected by NAFLD. Notably, the presence of NAFLD and particularly its more severe form, nonalcoholic steatohepatitis (NASH), serves as an independent risk factor for atherosclerotic cardiovascular disease (ASCVD), thus, raising interest in the relationship between these two diseases. Importantly, ASCVD is the major cause of death in patients with NASH independent of traditional risk factors. Nevertheless, the pathophysiology linking NAFLD/NASH with ASCVD remains poorly understood. While dyslipidemia is a common risk factor underlying both diseases, therapies that lower circulating LDL-cholesterol are largely ineffective against NASH. While there are no approved pharmacological therapies for NASH, some of the most advanced drug candidates exacerbate atherogenic dyslipidemia, raising concerns regarding their adverse cardiovascular consequences. In this review, we address current gaps in our understanding of the mechanisms linking NAFLD/NASH and ASCVD, explore strategies to simultaneously model these diseases, evaluate emerging biomarkers that may be useful to diagnose the presence of both diseases, and discuss investigational approaches and ongoing clinical trials that potentially target both diseases.

Genetic assessment in primary hyperoxaluria: why it matters

Accurate diagnosis of primary hyperoxaluria (PH) has important therapeutic consequences. Since biochemical assessment can be unreliable, genetic testing is a crucial diagnostic tool for patients with PH to define the disease type. Patients with PH type 1 (PH1) have a worse prognosis than those with other PH types, despite the same extent of oxalate excretion. The relation between genotype and clinical phenotype in PH1 is extremely heterogeneous with respect to age of first symptoms and development of kidney failure. Some mutations are significantly linked to pyridoxine-sensitivity in PH1, such as homozygosity for p.G170R and p.F152I combined with a common polymorphism. Although patients with these mutations display on average better outcomes, they may also present with CKD stage 5 in infancy. In vitro studies suggest pyridoxine-sensitivity for some other mutations, but confirmatory clinical data are lacking (p.G47R, p.G161R, p.I56N/major allele) or scarce (p.I244T). These studies also suggest that other vitamin B6 derivatives than pyridoxine may be more effective and should be a focus for clinical testing. PH patients displaying the same mutation, even within one family, may have completely different clinical outcomes. This discordance may be caused by environmental or genetic factors that are unrelated to the effect of the causative mutation(s). No relation between genotype and clinical or biochemical phenotypes have been found so far in PH types 2 and 3. This manuscript reviews the current knowledge on the genetic background of the three types of primary hyperoxaluria and its impact on clinical management, including prenatal diagnosis.

Phosphorylation of Thr9 Affects the Folding Landscape of the N-Terminal Segment of Human AGT Enhancing Protein Aggregation of Disease-Causing Mutants

The mutations G170R and I244T are the most common disease cause in primary hyperoxaluria type I (PH1). These mutations cause the misfolding of the AGT protein in the minor allele AGT-LM that contains the P11L polymorphism, which may affect the folding of the N-terminal segment (NTT-AGT). The NTT-AGT is phosphorylated at T9, although the role of this event in PH1 is unknown. In this work, phosphorylation of T9 was mimicked by introducing the T9E mutation in the NTT-AGT peptide and the full-length protein. The NTT-AGT conformational landscape was studied by circular dichroism, NMR, and statistical mechanical methods. Functional and stability effects on the full-length AGT protein were characterized by spectroscopic methods. The T9E and P11L mutations together reshaped the conformational landscape of the isolated NTT-AGT peptide by stabilizing ordered conformations. In the context of the full-length AGT protein, the T9E mutation had no effect on the overall AGT function or conformation, but enhanced aggregation of the minor allele (LM) protein and synergized with the mutations G170R and I244T. Our findings indicate that phosphorylation of T9 may affect the conformation of the NTT-AGT and synergize with PH1-causing mutations to promote aggregation in a genotype-specific manner. Phosphorylation should be considered a novel regulatory mechanism in PH1 pathogenesis.

HOGA1 gene pathogenic variants in primary hyperoxaluria type III: Spectrum of pathogenic sequence variants, and phenotypic association

Primary hyperoxalurias (PH) are a group of rare heterogeneous disorders characterized by deficiencies in glyoxylate metabolism. To date, three genes have been identified to cause three types of PH (I, II, and III). The HOGA1 gene caused type III in around 10% of the PH cases. Disease-associated pathogenic variants have been reported from several populations and a comprehensive spectrum of these mutations and genotype-phenotype correlation has never been presented. In this study, we describe new cases of the HOGA1 gene pathogenic variants identified in our population. We report the first case of ESKD with successful kidney transplantation with 5 years of follow-up. Furthermore, a comprehensive overview of PH type III associated HOGA1 gene variants was carried out. Compiling the data from the literature, we reviewed 57 distinct HOGA1 gene pathogenic variants in 175 patients worldwide. The majority of reported variants are missense variants that predicted a loss of function mechanism as the underlying pathology. There has been evidence of the presence of founder mutations in several populations like Europeans, Ashkenazi Jews, Arab, and Chinese populations. No significant genotype-phenotype correlation was identified concerning the ages of onset of the disease and biochemical and metabolic parameters. Nephrocalcinosis was rare in patients with disease-associated variants. Most of the patients were presented with urolithiasis early in life; only five cases reported disease progression after the second decade of life. The establishment of impairment of renal function in 8% of all the reported cases makes this type a relatively severe form of primary hyperoxaluria, not a benign etiology as suggested previously.

Characterization of zearalenone-induced hepatotoxicity and its mechanisms by transcriptomics in zebrafish model

Zearalenone is a mycotoxin produced by several species of Fusarium fungi, which contaminates crop and cereal products worldwide. It is widely distributed and can be transported from agricultural fields to the aquatic environment via soil run-off. Zearalenone exposure can cause serious health problems to humans and animals, including estrogenic, immunotoxic, and xenogenic effects. Though its hepatotoxicity has been reported by few studies, the underlying mechanisms are yet to be investigated. This study aimed to comprehensively evaluate the hepatotoxic effects of zearalenone and its molecular mechanism in the zebrafish model system. First, we found zearalenone exposure can cause liver injury, as evidenced by reduced liver size, decreased liver-specific fluorescence, increased aspartate aminotransferase (AST) activity, delayed yolk sac absorption and lipid accumulation. Then, RNA sequencing (RNA-seq) was performed using dissected zebrafish fry liver, which found genes involved in oxidation and reduction were significantly enriched. Quantitative real-time PCR further confirmed the dysregulated expression of several antioxidant enzymes. Additionally, lipid peroxidation was proved by increased malondialdehyde (MDA) production and gene expression at the mRNA level. In contrast to the previous study, apoptosis was likely decreased in response to zearalenone exposure. Last, glucuronidation and amino acid metabolism were also disrupted by zearalenone. Our results revealed the complex mechanism of zearalenone-induced hepatotoxicity, which is a valuable contribution to a more comprehensive understanding of the toxicity of zearalenone.

Clinical and molecular characterization of a large primary hyperoxaluria cohort from Saudi Arabia: a retrospective study

BACKGROUND

Primary hyperoxalurias (PHs) constitute rare disorders resulting in abnormal glyoxalate metabolism. PH-associated phenotypes range from progressive nephrocalcinosis and/or recurrent urolithiasis to early kidney failure.

METHODS

A retrospective study was conducted for patients with confirmed PH diagnoses from three tertiary centers in Saudi Arabia. Detailed clinical molecular diagnosis was performed for 25 affected individuals. Whole exome sequencing (WES)-based molecular diagnosis was performed for all affected individuals.

RESULTS

The male:female ratio was 52% male (n = 13) and 48% female (n = 12), and consanguinity was present in 88%. Nephrolithiasis and/or nephrocalcinosis were present in all patients. Kidney stones were present in 72%, nephrocalcinosis in 60%, hematuria in 32%, proteinuria in 16%, abdominal pain in 36%, developmental delay in 8%, and chronic kidney disease stage 5 (CKD stage 5) was observed in 28% of the patients. The most common PH disorder was type I caused by variants in the AGXT gene, accounting for 56%. The GRHPR gene variants were identified in 4 patients, 16% of the total cases. Seven patients did not reveal any associated variants. Missense variants were the most commonly observed variants (48%), followed by frame-shift duplication variants (28%).

CONCLUSIONS

Characterization of the genetic and clinical aspects of PH in this unique population provides direction for improved patient management and further research. A higher resolution version of the Graphical abstract is available as Supplementary information.

Tensile strain and altered synovial tissue metabolism in human knee osteoarthritis

Synovium is critical for maintaining joint homeostasis and may contribute to mechanobiological responses during joint movement. We investigated mechanobiological responses of whole synovium from patients with late-stage knee osteoarthritis (OA). Synovium samples were collected during total knee arthroplasty and assigned to histopathology or cyclic 10% tensile strain loading, including (1) static (control); (2) low-frequency (0.3 Hz); and iii) high-frequency (1.0 Hz) for 30-min. After 6-h incubation, tissues were bisected for RNA isolation and immunostaining (3-nitrotyrosine; 3-NT). RNA sequencing was analyzed for differentially expressed genes and pathway enrichment. Cytokines and lactate were measured in conditioned media. Compared to controls, low-frequency strain induced enrichment of pathways related to interferon response, Fc-receptor signaling, and cell metabolism. High-frequency strain induced enrichment of pathways related to NOD-like receptor signaling, high metabolic demand, and redox signaling/stress. Metabolic and redox cell stress was confirmed by increased release of lactate into conditioned media and increased 3-NT formation in the synovial lining. Late-stage OA synovial tissue responses to tensile strain include frequency-dependent increases in inflammatory signaling, metabolism, and redox biology. Based on these findings, we speculate that some synovial mechanobiological responses to strain may be beneficial, but OA likely disturbs synovial homeostasis leading to aberrant responses to mechanical stimuli, which requires further validation.

Chitosan Derivatives as Nanocarriers for hLDHA Inhibitors Delivery to Hepatic Cells: A Selective Strategy for Targeting Primary Hyperoxaluria Diseases

Primary hyperoxalurias (PHs) are a group of inherited alterations of the hepatic glyoxylate metabolism that result in an excess of oxalate production by the oxidation of glyoxylate by the human lactate dehydrogenase A enzyme (hLDHA). The selective liver inhibition of this enzyme is one of the therapeutic strategies followed in the treatment of this disease. Even though several efforts have been recently performed using gene silencing by the RNA interference approach, small-molecule inhibitors that selectively reach hepatocytes are preferred since they present the advantages of a lower production cost and better pharmacological properties. In that sense, the design, synthesis, and physicochemical characterization by NMR, FTIR, DLS and TEM of two nanocarriers based on chitosan conjugates (1, non-redox-sensitive; 2, redox-sensitive) have been performed to (i) achieve the selective transport of hLDHA inhibitors into hepatocytes and (ii) their disruption once they reach the hepatocytes cytosol. Polymer 2 self-assembled into micelles in water and showed high drug loadings (19.8-24.5%) and encapsulation efficiencies (31.9-40.8%) for the hLDHA inhibitors (I-III) tested. The non-redox-sensitive micelle 1 remained stable under different glutathione (GSH) concentrations (10 μM and 10 mM), and just a residual release of the inhibitor encapsulated was observed (less than 10%). On the other hand, micelle 2 was sufficiently stable under in vitro physiological conditions (10 μM, GSH) but it quickly disassembled under the simulated reducing conditions present inside hepatocytes (10 mM GSH), achieving a 60% release of the hLDHA inhibitor encapsulated after 24 h, confirming the responsiveness of the developed carrier to the high levels of intracellular GSH.

Lactate dehydrogenase A inhibitors with a 2,8-dioxabicyclo[3.3.1]nonane scaffold: A contribution to molecular therapies for primary hyperoxalurias

Human lactate dehydrogenase A (hLDHA) is one of the main enzymes involved in the pathway of oxalate synthesis in human liver and seems to contribute to the pathogenesis of disorders with endogenous oxalate overproduction, such as primary hyperoxaluria (PH), a rare life-threatening genetic disease. Recent published results on the knockdown of LDHA gene expression as a safe strategy to ameliorate oxalate build-up in PH patients are encouraging for an approach of hLDHA inhibition by small molecules as a potential pharmacological treatment. Thus, we now report on the synthesis and hLDHA inhibitory activity of a new family of compounds with 2,8-dioxabicyclo[3.3.1]nonane core (23-42), a series of twenty analogues to A-type proanthocyanidin natural products. Nine of them (25-27, 29-34) have shown IC₅₀ values in the range of 8.7-26.7 µM, based on a UV spectrophotometric assay, where the hLDHA inhibition is measured according to the decrease in absorbance of the cofactor β-NADH (340 nm). Compounds 25, 29, and 31 were the most active hLDHA inhibitors. In addition, the inhibitory activities of those nine compounds against the hLDHB isoform were also evaluated, finding that all of them were more selective inhibitors of hLDHA versus hLDHB. Among them, compounds 32 and 34 showed the highest selectivity. Moreover, the most active hLDHA inhibitors (25, 29, 31) were evaluated for their ability to decrease the oxalate production by hyperoxaluric mouse hepatocytes (PH1, PH2 and PH3) in vitro, and the relative oxalate output at 24 h was 16% and 19 % for compounds 25 and 31, respectively, in Hoga1^-/- mouse primary hepatocyte cells (a model for PH3). These values improve those of the reference compound used (stiripentol). Compounds 25 and 31 have in common the presence of two hydroxyl groups at rings B and D and an electron-withdrawing group (NO₂ or Br) at ring A, pointing to the structural features to be taken into account in future structural optimization.

Identification of Human Alanine-Glyoxylate Aminotransferase Ligands as Pharmacological Chaperones for Variants Associated with Primary Hyperoxaluria Type 1

Primary hyperoxaluria type I (PH1) is a rare kidney disease due to the deficit of alanine:glyoxylate aminotransferase (AGT), a pyridoxal-5′-phosphate-dependent enzyme responsible for liver glyoxylate detoxification, which in turn prevents oxalate formation and precipitation as kidney stones. Many PH1-associated missense mutations cause AGT misfolding. Therefore, the use of pharmacological chaperones (PCs), small molecules that promote correct folding, represents a useful therapeutic option. To identify ligands acting as PCs for AGT, we first performed a small screening of commercially available compounds. We tested each molecule by a dual approach aimed at defining the inhibition potency on purified proteins and the chaperone activity in cells expressing a misfolded variant associated with PH1. We then performed a chemical optimization campaign and tested the resulting synthetic molecules using the same approach. Overall, the results allowed us to identify a promising hit compound for AGT and draw conclusions about the requirements for optimal PC activity.

Improving Treatment Options for Primary Hyperoxaluria

The primary hyperoxalurias are three rare inborn errors of the glyoxylate metabolism in the liver, which lead to massively increased endogenous oxalate production, thus elevating urinary oxalate excretion and, based on that, recurrent urolithiasis and/or progressive nephrocalcinosis. Frequently, especially in type 1 primary hyperoxaluria, early end-stage renal failure occurs. Treatment possibilities are scare, namely, hyperhydration and alkaline citrate medication. In type 1 primary hyperoxaluria, vitamin B₆, though, is helpful in patients with specific missense or mistargeting mutations. In those vitamin B₆ responsive, urinary oxalate excretion and concomitantly urinary glycolate is significantly decreased, or even normalized. In patients non-responsive to vitamin B₆, RNA interference medication is now available. Lumasiran^® is already available on prescription and targets the messenger RNA of glycolate oxidase, thus blocking the conversion of glycolate into glyoxylate, hence decreasing oxalate, but increasing glycolate production. Nedosiran blocks liver-specific lactate dehydrogenase A and thus the final step of oxalate production. Similar to vitamin B₆ treatment, where both RNA interference urinary oxalate excretion can be (near) normalized and plasma oxalate decreases, however, urinary and plasma glycolate increases with lumasiran treatment. Future treatment possibilities are on the horizon, for example, substrate reduction therapy with small molecules or gene editing, induced pluripotent stem cell-derived autologous hepatocyte-like cell transplantation, or gene therapy with newly developed vector technologies. This review provides an overview of current and especially new and future treatment options.

Design and Synthesis of New Pyrimidine-Quinolone Hybrids as Novel hLDHA Inhibitors

A battery of novel pyrimidine-quinolone hybrids was designed by docking scaffold replacement as lactate dehydrogenase A (hLDHA) inhibitors. Structures with different linkers between the pyrimidine and quinolone scaffolds (10-21 and 24−31) were studied in silico, and those with the 2-aminophenylsulfide (U-shaped) and 4-aminophenylsulfide linkers (24−31) were finally selected. These new pyrimidine-quinolone hybrids (24−31)(a−c) were easily synthesized in good to excellent yields by a green catalyst-free microwave-assisted aromatic nucleophilic substitution reaction between 3-(((2/4-aminophenyl)thio)methyl)quinolin-2(1H)-ones 22/23(a−c) and 4-aryl-2-chloropyrimidines (1−4). The inhibitory activity against hLDHA of the synthesized hybrids was evaluated, resulting IC50 values of the U-shaped hybrids 24−27(a−c) much better than the ones of the 1,4-linked hybrids 28−31(a−c). From these results, a preliminary structure−activity relationship (SAR) was established, which enabled the design of novel 1,3-linked pyrimidine-quinolone hybrids (33−36)(a−c). Compounds 35(a−c), the most promising ones, were synthesized and evaluated, fitting the experimental results with the predictions from docking analysis. In this way, we obtained novel pyrimidine-quinolone hybrids (25a, 25b, and 35a) with good IC50 values (<20 μM) and developed a preliminary SAR.

Progress with RNA Interference for the Treatment of Primary Hyperoxaluria

Over the last few years, US Food and Drug Administration-approved drugs using RNA interference have come to the market. Many have treated liver-specific diseases utilizing N-acetyl galactosamine conjugation because of its effective delivery and limited off-target effects. The autosomal recessive disorder primary hyperoxaluria, specifically type 1, has benefited from these developments. Primary hyperoxaluria arises from mutations in the enzymes involved in endogenous oxalate synthesis. The severity of disease varies but can result in kidney failure and systemic oxalosis. Until recently, the treatment options were limited and focused primarily on supportive treatments, pyridoxine use in a subset of patients with primary hyperoxaluria type 1, and liver-kidney transplants in those who progressed to kidney failure. Two genes have been targeted with RNA interference; lumasiran targets glycolate oxidase and nedosiran targets lactate dehydrogenase A. Lumasiran was recently approved in the treatment of primary hyperoxaluria type 1 and nedosiran is in the approval process. Unfortunately, despite initial hopes that nedosiran may also be a treatment option for primary hyperoxaluria types 2 and 3, initial data suggest otherwise. The use of RNA interference liver-specific targeting for the treatment of primary hyperoxaluria type 1 will likely transform the natural history of the disease.

In vivo CRISPR-Cas9 inhibition of hepatic LDH as treatment of primary hyperoxaluria

Genome-editing strategies, especially CRISPR-Cas9 systems, have substantially increased the efficiency of innovative therapeutic approaches for monogenic diseases such as primary hyperoxalurias (PHs). We have previously demonstrated that inhibition of glycolate oxidase using CRISPR-Cas9 systems represents a promising therapeutic option for PH type I (PH1). Here, we extended our work evaluating the efficacy of liver-specific inhibition of lactate dehydrogenase (LDH), a key enzyme responsible for converting glyoxylate to oxalate; this strategy would not be limited to PH1, being applicable to other PH subtypes. In this work, we demonstrate a liver-specific inhibition of LDH that resulted in a drastic reduction of LDH levels in the liver of PH1 and PH3 mice after a single-dose delivery of AAV8 vectors expressing the CRISPR-Cas9 system, resulting in reduced urine oxalate levels and kidney damage without signs of toxicity. Deep sequencing analysis revealed that this approach was safe and specific, with no off-targets detected in the liver of treated animals and no on-target/off-tissue events. Altogether, our data provide evidence that in vivo genome editing using CRISPR-Cas9 systems would represent a valuable tool for improved therapeutic approaches for PH.

Modern therapeutic approaches to liver-related disorders

The liver is a key production and processing site that is essential for health. Liver dysfunction can result in both systemic and liver-specific diseases. To combat these diseases, genetic approaches have been developed that have high liver tropism and are based on gene addition/editing or gene silencing. The gene addition/editing approach has yielded encouraging clinical data on the use of viral vectors in patients with haemophilia, as well as neuromuscular diseases, and has led to trials for liver-related disorders. However, the immune response and the long-term stability of exogenous expression remain important challenges. Gene editing and mRNA therapy have yielded first in-human proof-of-concept therapeutics and vaccines, but the road to the treatment of liver-related disorders remains long. Gene silencing is accomplished primarily via antisense oligonucleotides and small-interfering RNAs (siRNAs). siRNA modification with N-acetyl galactosamine results in hepatocellular-specific targeting and catapulted the liver to the centre of siRNA research. Several siRNA drugs for liver-related disorders have recently been approved, and the pipeline of drugs under investigation is crowded. Loss-of-function mutations might also be treated with enzyme substitution therapy. This review summarises current genetic approaches as well as key enzyme substitution therapies, focusing on recently approved compounds, potential adverse effects, and future challenges. Collectively, these recent advances place the liver at the forefront of precision medicine for metabolic and genetic diseases and are expected to transform the care and treatment of patients with both liver-specific and systemic diseases.

Novel Starting Points for Human Glycolate Oxidase Inhibitors, Revealed by Crystallography-Based Fragment Screening

Primary hyperoxaluria type I (PH1) is caused by AGXT gene mutations that decrease the functional activity of alanine:glyoxylate aminotransferase. A build-up of the enzyme’s substrate, glyoxylate, results in excessive deposition of calcium oxalate crystals in the renal tract, leading to debilitating renal failure. Oxidation of glycolate by glycolate oxidase (or hydroxy acid oxidase 1, HAO1) is a major cellular source of glyoxylate, and siRNA studies have shown phenotypic rescue of PH1 by the knockdown of HAO1, representing a promising inhibitor target. Here, we report the discovery and optimization of six low-molecular-weight fragments, identified by crystallography-based fragment screening, that bind to two different sites on the HAO1 structure: at the active site and an allosteric pocket above the active site. The active site fragments expand known scaffolds for substrate-mimetic inhibitors to include more chemically attractive molecules. The allosteric fragments represent the first report of non-orthosteric inhibition of any hydroxy acid oxidase and hold significant promise for improving inhibitor selectivity. The fragment hits were verified to bind and inhibit HAO1 in solution by fluorescence-based activity assay and surface plasmon resonance. Further optimization cycle by crystallography and biophysical assays have generated two hit compounds of micromolar (44 and 158 µM) potency that do not compete with the substrate and provide attractive starting points for the development of potent and selective HAO1 inhibitors.

Cats with Genetic Variants of AGXT2 Respond Differently to a Dietary Intervention Known to Reduce the Risk of Calcium Oxalate Stone Formation

This study was completed to evaluate a genotype-specific nutritional intervention for reducing the risk of calcium oxalate stone formation. Serum metabolomic profiles and genotypes of 445 cats in the colony at Hill’s Pet Nutrition, Inc (Topeka, KS, USA)were assessed in a genome-wide association study, and revealed an association between genetic variants of alanine-glyoxylate aminotransferase 2 (AGXT2) and 2-oxoarginine. The most significant single nucleotide polymorphisms (SNP) associated with 2-oxoarginine was at position chrA1:212069607, [G/A] (p < 3.687 × 10−17). This SNP explained approximately 15% of the variance in 2-oxoarginine concentrations. The distribution of genotype frequencies was 0.07 AA, 0.39 AG, and 0.54 GG, with a mean relative 2-oxoarginine concentration for each genotype of 0.45 AA, 0.92 AG, and 1.27 GG, indicating a subtractive effect of the minor allele (A). Serum concentrations of two AGXT2 substrates, symmetric/asymmetric dimethylarginines (SDMA/ADMA) and β-aminoisobutyrate (BAIB) were also strongly associated with SNP chrA1:212069607 (p < 1.43 × 10−12 and p < 2.30 × 10−14, respectively). These two AGXT2 substrates were increased with the minor allele (A), indicating that the variant of the AGXT2 gene results in decreased aminotransferase activity. Additionally, the lifetime history of stone incidence showed that cats with the AA variant of AGXT2 SNP had a 2.515× increased incidence of stones compared with cats having the GG variant (p = 0.019). In a subsequent study assessing AGXT2 genotypes, cats (n = 10 GG, 4 AG, 9 AA) were fed control or test food (containing betaine at 0.500%, and the botanicals green tea, fenugreek and tulsi at 0.25, 0.025, and 0.0015%, respectively) in a cross-over study design. Stone risk analysis was conducted on urine samples after feeding control or test food for 28 days each. A calcium oxalate titration test (COT) was performed to assess the amount of added Ox−2 (per L) required to initiate calcium oxalate crystal formation. Cats with the GG variant of the AGXT2 SNP required more added oxalate to initiate urine crystal formation after consuming test food compared with control food, indicating a decreased risk of oxalate crystal formation in GG cats. In addition, urine oxalate concentrations showed an overall effect of test food independent of genotype (p = 0.0009), which resulted in lower oxalate concentrations after consuming test food compared with control food. These data indicate that cats with the GG-specific variant of AGXT2 should benefit from a reduced risk of calcium oxalate stone formation after consuming a betaine and botanical dietary enhancement.

Glyoxylate protects against cyanide toxicity through metabolic modulation

Although cyanide's biological effects are pleiotropic, its most obvious effects are as a metabolic poison. Cyanide potently inhibits cytochrome c oxidase and potentially other metabolic enzymes, thereby unleashing a cascade of metabolic perturbations that are believed to cause lethality. From systematic screens of human metabolites using a zebrafish model of cyanide toxicity, we have identified the TCA-derived small molecule glyoxylate as a potential cyanide countermeasure. Following cyanide exposure, treatment with glyoxylate in both mammalian and non-mammalian animal models confers resistance to cyanide toxicity with greater efficacy and faster kinetics than known cyanide scavengers. Glyoxylate-mediated cyanide resistance is accompanied by rapid pyruvate consumption without an accompanying increase in lactate concentration. Lactate dehydrogenase is required for this effect which distinguishes the mechanism of glyoxylate rescue as distinct from countermeasures based solely on chemical cyanide scavenging. Our metabolic data together support the hypothesis that glyoxylate confers survival at least in part by reversing the cyanide-induced redox imbalances in the cytosol and mitochondria. The data presented herein represent the identification of a potential cyanide countermeasure operating through a novel mechanism of metabolic modulation.

Combined effect of polyacrylic acid and vitamin E in preventing calcium oxalate crystal deposition in the kidneys of experimental hyperoxaluric rats

Our study explores the combined effect of polyacrylic acid and vitamin E as prophylactic and curative agent against ethylene glycol (EG) induced calcium oxalate stone formation in Wistar rats. Male Wistar rats (54) were divided into nine groups, including control. The experimental groups were equally segregated into two for preventive study (4) and curative study (4). Urolithiasis was induced with 0.75% (v/v) EG in drinking water. Polyacrylic acid (10 mg/kg) and vitamin E (300 IU/day) were supplemented from day 1 for preventive and day 30 for curative studies. Restoration of urinary lithogenic factors (calcium, oxalate, phosphate, citrate and magnesium) and renal function (urea and creatinine in serum) by intervening agents were accomplished compared to urolithic rats (P < .001). Abnormal localization and increased expression of Tamm-Horsfall Protein, osteopontin and transferrin were observed in the kidneys of urolithic rats (P < .001) from immunohistochemistry and immunoblotting analysis. Polyacrylic acid and vitamin E supplementation have regulated the expression of the urinary macromolecules. Pro-inflammatory cytokines in kidney were significantly reduced (P < .001) by the intervening agents compared to urolithic rats. Therefore, polyacrylic acid and vitamin E in combination could be a potential formulation for better management of urolithiasis.

Beauvericin (BEA) and enniatin B (ENNB)-induced impairment of mitochondria and lysosomes - Potential sources of intracellular reactive iron triggering ferroptosis in Atlantic salmon primary hepatocytes

Beauvericin (BEA) and enniatin B (ENNB) are emerging mycotoxins frequently detected in plant-based fish feed. With ionophoric properties, they have shown cytotoxic potential in mammalian models. Sensitivity in fish is still largely unknown. Primary hepatocytes isolated from Atlantic salmon (Salmo salar) were used as a model and exposed to BEA and ENNB (0.05-10 μM) for 48 h. Microscopy, evaluation of cell viability, total ATP, total H₂O₂, total iron content, total Gpx enzyme activity, and RNA sequencing were used to characterize the toxicodynamics of BEA and ENNB. Both mycotoxins became cytotoxic at ≥ 5 μM, causing condensation of the hepatocytes followed by formation of blister-like protrusions on the cell's membrane. RNA sequencing analysis at sub-cytotoxic levels indicated BEA and ENNB exposed hepatocytes to experience increased energy expenditure, elevated oxidative stress, and iron homeostasis disturbances sensitizing the hepatocytes to ferroptosis. The present study provides valuable knowledge disclosing the toxic action of these mycotoxins in Atlantic salmon primary hepatocytes.

The Potential of CRISPR/Cas9 Gene Editing as a Treatment Strategy for Inherited Diseases

Clustered regularly interspaced short palindromic repeats (CRISPR) is a promising innovative technology for genomic editing that offers scientists the chance to edit DNA structures and change gene function. It has several possible uses consisting of editing inherited deficiencies, treating, and reducing the spread of disorders. Recently, reports have demonstrated the creation of synthetic RNA molecules and supplying them alongside Cas9 into genome of eukaryotes, since distinct specific regions of the genome can be manipulated and targeted. The therapeutic potential of CRISPR/Cas9 technology is great, especially in gene therapy, in which a patient-specific mutation is genetically edited, or in the treating of human disorders that are untreatable with traditional treatments. This review focused on numerous, in vivo, in vitro, and ex vivo uses of the CRISPR/Cas9 technology in human inherited diseases, discovering the capability of this versatile in medicine and examining some of the main limitations for its upcoming use in patients. In addition to introducing a brief impression of the biology of the CRISPR/Cas9 scheme and its mechanisms, we presented the utmost recent progress in the uses of CRISPR/Cas9 technology in editing and treating of human genetic diseases.

Oxalate Flux Across the Intestine: Contributions from Membrane Transporters

Epithelial oxalate transport is fundamental to the role occupied by the gastrointestinal (GI) tract in oxalate homeostasis. The absorption of dietary oxalate, together with its secretion into the intestine, and degradation by the gut microbiota, can all influence the excretion of this nonfunctional terminal metabolite in the urine. Knowledge of the transport mechanisms is relevant to understanding the pathophysiology of hyperoxaluria, a risk factor in kidney stone formation, for which the intestine also offers a potential means of treatment. The following discussion presents an expansive review of intestinal oxalate transport. We begin with an overview of the fate of oxalate, focusing on the sources, rates, and locations of absorption and secretion along the GI tract. We then consider the mechanisms and pathways of transport across the epithelial barrier, discussing the transcellular, and paracellular components. There is an emphasis on the membrane-bound anion transporters, in particular, those belonging to the large multifunctional Slc26 gene family, many of which are expressed throughout the GI tract, and we summarize what is currently known about their participation in oxalate transport. In the final section, we examine the physiological stimuli proposed to be involved in regulating some of these pathways, encompassing intestinal adaptations in response to chronic kidney disease, metabolic acid-base disorders, obesity, and following gastric bypass surgery. There is also an update on research into the probiotic, Oxalobacter formigenes, and the basis of its unique interaction with the gut epithelium. © 2021 American Physiological Society. Compr Physiol 11:1-41, 2021.

An Escherichia coli FdrA Variant Derived from Syntrophic Coculture with a Methanogen Increases Succinate Production Due to Changes in Allantoin Degradation

Wild-type Escherichia coli was adapted to syntrophic growth with Methanobacterium formicicum for glycerol fermentation over 44 weeks. Succinate production by E. coli started to increase in the early stages of syntrophic growth. Genetic analysis of the cultured E. coli population by pooled sequencing at eight time points suggests that (i) rapid evolution occurred through repeated emergence of mutators that introduced a large number of nucleotide variants and (ii) many mutators increased to high frequencies but remained polymorphic throughout the continuous cultivation. The evolved E. coli populations exhibited gains both in fitness and succinate production, but only for growth under glycerol fermentation with M. formicicum (the condition for this laboratory evolution) and not under other growth conditions. The mutant alleles of the 69 single nucleotide polymorphisms (SNPs) identified in the adapted E. coli populations were constructed individually in the ancestral wild-type E. coli. We analyzed the phenotypic changes caused by 84 variants, including 15 nonsense variants, and found that FdrA_D296Y was the most significant variant leading to increased succinate production. Transcription of fdrA was induced under anaerobic allantoin degradation conditions, and FdrA was shown to play a crucial role in oxamate production. The FdrA_D296Y variant increased glyoxylate conversion to malate by accelerating oxamate production, which promotes carbon flow through the C4 branch, leading to increased succinate production.

IMPORTANCE Here, we demonstrate the ability of E. coli to perform glycerol fermentation in coculture with the methanogen M. formicicum to produce succinate. We found that the production of succinate by E. coli significantly increased during successive cocultivation. Genomic DNA sequencing, evaluation of relative fitness, and construction of SNPs were performed, from which FdrA_D296Y was identified as the most significant variant to enable increased succinate production by E. coli. The function of FdrA is uncertain. In this study, experiments with gene expression assays and metabolic analysis showed for the first time that FdrA could be the “orphan enzyme” oxamate:carbamoyltransferase in anaerobic allantoin degradation. Furthermore, we demonstrate that the anaerobic allantoin degradation pathway is linked to succinate production via the glyoxylate pathway during glycerol fermentation.

[Histopathological diagnosis of an intoxication]

Ethylene glycol poisoning is relatively rare, with around a hundred cases reported each year in France. Its diagnosis is often challenging and delayed because of a several hours' free interval between ingestion of the toxic and the onset of the first symptoms. Ethylene glycol is a colorless and odorless liquid primarily found in automotive coolants, whose toxicity is linked to its hepatic metabolites. Histologically, ethylene glycol poisoning is characterized by abundant tissular deposits of calcium oxalate crystals. Under polarized light, these crystals appear birefringent and iridescent. Their microscopic appearance and their distribution are pathognomonic of oxalosis. Due to its frequent misleading presentation, the diagnosis of ethylene glycol poisoning is sometimes only made after an autopsy. Hereafter, we report the case of a 59-year-old man diagnosed with ethylene glycol intoxication after a post-mortem histopathological examination of organs.

Novel therapeutic approaches for the primary hyperoxalurias

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

Effects of Workers Exposure to Nanoparticles Studied by NMR Metabolomics

In this study, the effects of occupational exposure to nanoparticles (NPs) were studied by NMR metabolomics. Exhaled breath condensate (EBC) and blood plasma samples were obtained from a research nanoparticles-processing unit at a national research university. The samples were taken from three groups of subjects: samples from workers exposed to nanoparticles collected before and after shift, and from controls not exposed to NPs. Altogether, 60 1H NMR spectra of exhaled breath condensate (EBC) samples and 60 1H NMR spectra of blood plasma samples were analysed, 20 in each group. The metabolites identified together with binning data were subjected to multivariate statistical analysis, which provided clear discrimination of the groups studied. Statistically significant metabolites responsible for group separation served as a foundation for analysis of impaired metabolic pathways. It was found that the acute effect of NPs exposure is mainly reflected in the pathways related to the production of antioxidants and other protective species, while the chronic effect is manifested mainly in the alteration of glutamine and glutamate metabolism, and the purine metabolism pathway.

Structural and chemical heterogeneities of primary hyperoxaluria kidney stones from pediatric patients

OBJECTIVE

Calcium oxalate stones are the most common type among stone-forming patients and in some cases result from predisposed genetic conditions. In this work, we examined the differences in structure and chemical composition between oxalate stones from patients from three groups: 1) pediatric patients that were genetically predisposed (primary hyperoxaluria) to form stones (PPH); 2) control pediatric patients that did not have such genetic predisposition (PN-PH); 3) adult patients that formed oxalate stones without the genetic predisposition (A-CaOx). A variety of instrumental analyses were conducted to identify physicochemical properties of stones characteristic of predisposed pediatric (PPH), pediatric hyperoxaluria (PN-PH), and adult (A-CaOx) patient populations.

METHODS

Genetic variants of 16 stone-forming patients were determined using whole-exome gene sequencing. Components of stones from PPH (n = 6), PN-PH (n = 5), and A-CaOx (n = 5) groups were identified using Fourier transform infrared (FTIR) spectroscopy. Stone morphology and density were evaluated using high resolution X-ray computed tomography (micro-XCT). Stone microstructure and elemental composition were mapped with scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy, respectively.

RESULTS

Calcium oxalate bipyramidal crystals were found on stones from all groups. Stones from PPH patients with PH types I and II were composed of calcium oxalate monohydrate (COM) with relatively uniform mineral density (1224 ± 277 mg/cc) and distinct smooth surfaces. By contrast, micro-spherical calcium phosphate particles were found only on PN-PH stones, which also showed a broader range of mineral densities (1266 ± 342 mg/cc). Stones from the PN-PH group also contained phosphorus (P), which was absent in NP-PH stones. A-CaOx stones were of significantly lower mineral density (645 ± 237 mg/cc) than pediatric stones and were more heterogeneous in their elemental composition.

CONCLUSION

Unique structural and compositional characteristics were identified in stones from pediatric patients with primary hyperoxaluria. These include the absence of phosphorus, a narrower mineral density distribution, and a uniform elemental composition compared to stones from pediatric patients without the genetic predisposition. Thus, characterization of stones at the macro- and micro-scales in combination with genetic testing of patients can provide insights and accurate diagnosis to develop a treatment plan for effective patient care.

Clinical analysis of 13 children with primary hyperoxaluria type 1

A retrospective statistical analysis of primary hyperoxaluria type 1 (PH1) in children from June 2016 to May 2019 was carried out to discover its clinical and molecular biological characteristics. Patients were divided into two groups (infant and noninfant) according to clinic type. There were 13 pediatric patients (male:female = 6:7) with PH1 in the cohort from 11 families (four of which were biological siblings from two families), whose median age of symptom onset was 12 months and median confirmed diagnosis age was 14 months. Infant type (6 patients) was the most common type. The infant type mortality rate (100%) was higher than the noninfant (14.3%) (p = 0.029). The incidence of renal failure in infant patients was 67%, while the noninfant was 14.3%. 8 of 10 patients with nephrocalcinosis (NC) (76.92%, 10/13) were diagnosed by radiological imaging examinations, including X-ray (3 patients), CT (4 patients) and MRI (1 patient). NC was an independent risk factor for renal insufficiency [OR 3.33, 95% CI (0.7-1.2)], p < 0.05). Nine types of AGXT gene mutations were found; 1 type, c.190A > T, were first reported here. The most common AGXT gene mutation was c.679_680del, which occurred in exon 6 (5 patients). The infant type is the most common type of pediatric PH, with a relatively higher ratio of renal failure at symptom onset and poor prognosis. NC is an independent risk factor leading to renal failure, and radiological imaging examination is recommended for patients with abnormal ultrasound examination to identify NC. AGXT gene detection is important for the diagnosis and treatment of PH1 in children.

Glycolate combats massive oxidative stress by restoring redox potential in Caenorhabditis elegans

Upon exposure to excessive reactive oxygen species (ROS), organismal survival depends on the strength of the endogenous antioxidant defense barriers that prevent mitochondrial and cellular deterioration. Previously, we showed that glycolic acid can restore the mitochondrial membrane potential of C. elegans treated with paraquat, an oxidant that produces superoxide and other ROS species, including hydrogen peroxide. Here, we demonstrate that glycolate fully suppresses the deleterious effects of peroxide on mitochondrial activity and growth in worms. This endogenous compound acts by entering serine/glycine metabolism. In this way, conversion of glycolate into glycine and serine ameliorates the drastically decreased NADPH/NADP+ and GSH/GSSG ratios induced by H2O2 treatment. Our results reveal the central role of serine/glycine metabolism as a major provider of reducing equivalents to maintain cellular antioxidant systems and the fundamental function of glycolate as a natural antioxidant that improves cell fitness and survival.

Small Molecule-Based Enzyme Inhibitors in the Treatment of Primary Hyperoxalurias

Primary hyperoxalurias (PHs) are a group of inherited alterations of the hepatic glyoxylate metabolism. PHs classification based on gene mutations parallel a variety of enzymatic defects, and all involve the harmful accumulation of calcium oxalate crystals that produce systemic damage. These geographically widespread rare diseases have a deep impact in the life quality of the patients. Until recently, treatments were limited to palliative measures and kidney/liver transplants in the most severe forms. Efforts made to develop pharmacological treatments succeeded with the biotechnological agent lumasiran, a siRNA product against glycolate oxidase, which has become the first effective therapy to treat PH1. However, small molecule drugs have classically been preferred since they benefit from experience and have better pharmacological properties. The development of small molecule inhibitors designed against key enzymes of glyoxylate metabolism is on the focus of research. Enzyme inhibitors are successful and widely used in several diseases and their pharmacokinetic advantages are well known. In PHs, effective enzymatic targets have been determined and characterized for drug design and interesting inhibitory activities have been achieved both in vitro and in vivo. This review describes the most recent advances towards the development of small molecule enzyme inhibitors in the treatment of PHs, introducing the multi-target approach as a more effective and safe therapeutic option.

Novel mutations in response to vitamin B6 in primary hyperoxaluria type 1 after only kidney transplantation: a case report

Recently, the mainstream curative treatment for primary hyperoxaluria type 1 (PH1) is combined liver and kidney transplantation, and only kidney transplantation is considered ineffective for most PH1 patients. Furthermore, vitamin B6 (B6) is the only permitted drug available for treatment. However, except for specific mutations such as G170R and F152I in gene AGXT, data of B6 effect on other mutations are lacking. Insufficient research has evaluated the efficacy of the combination of kidney transplantation and B6 treatment in the therapeutic strategy in PH1 patients. Here, we report a case of a 52-year-old male with frequent stone events and end-stage renal diseases (ESRD), and subsequently undergone kidney transplantation. Sudden rising of serum creatinine within two months after the transplantation. After gene sequencing, the mutations of A186V, R197Q, and I340M were presented in gene AGXT. Therefore, the patient was diagnosed with PH1. B6 administration was attempted during the period of waiting for liver transplantation. Four-week oral B6 therapy (50 mg tid) reduced the serum creatinine of the patient from 194 to 145 µmol/L, which revealed that the patient probably responded to B6 treatment. At the almost three-year follow-up, the patient's serum creatinine remained reduced (130 µmol/L), without urinary oxalate excretion. In this case, we established a positive effect, even a beneficial result, of the use of B6 as a retrospective therapeutic choice in PH1 treatment after kidney transplantation.

The metabolic importance of the overlooked asparaginase II pathway

The asparaginase II pathway consists of an asparagine transaminase [l-asparagine + α-keto acid ⇆ α-ketosuccinamate + l-amino acid] coupled to ω-amidase [α-ketosuccinamate + H₂O → oxaloacetate + NH₄⁺]. The net reaction is: l-asparagine + α-keto acid + H₂O → oxaloacetate + l-amino acid + NH₄⁺. Thus, in the presence of a suitable α-keto acid substrate, the asparaginase II pathway generates anaplerotic oxaloacetate at the expense of readily dispensable asparagine. Several studies have shown that the asparaginase II pathway is important in photorespiration in plants. However, since its discovery in rat tissues in the 1950s, this pathway has been almost completely ignored as a conduit for asparagine metabolism in mammals. Several mammalian transaminases can catalyze transamination of asparagine, one of which - alanine-glyoxylate aminotransferase type 1 (AGT1) - is important in glyoxylate metabolism. Glyoxylate is a precursor of oxalate which, in the form of its calcium salt, is a major contributor to the formation of kidney stones. Thus, transamination of glyoxylate with asparagine may be physiologically important for the removal of potentially toxic glyoxylate. Asparaginase has been the mainstay treatment for certain childhood leukemias. We suggest that an inhibitor of ω-amidase may potentiate the therapeutic benefits of asparaginase treatment.

Knockdown of lactate dehydrogenase by adeno-associated virus-delivered CRISPR/Cas9 system alleviates primary hyperoxaluria type 1

BACKGROUND

Primary hyperoxaluria type 1 (PH1) is a rare genetic disorder caused by endogenous overproduction of hepatic oxalate, leading to hyperoxaluria, recurrent calcium oxalate kidney stones, and end-stage renal disease. Lactate dehydrogenase (LDH) is an ideal target for diminishing oxalate production as it is responsible for glyoxylate to oxalate conversion in the liver, the last step of oxalate metabolism. Here, we investigated the therapeutic efficacy and potential side effects of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology to ameliorate PH1 via specifically disrupting the hepatic LDH.

METHODS

Pheochromocytoma (PC12) cells were used to assess the efficacy of cleavage of single-guide RNAs in vitro. PH1 neonatal rats were injected with a single administration of adeno-associated virus to deliver the CRISPR/Cas9 system that targeted LDH. Three weeks after injection, a liver biopsy was performed to detect LDH expression, liver injury, and liver metabolomics. Urinary oxalate was regularly monitored, and renal calcium oxalate deposition was evaluated after 4 weeks of 0.5% ethylene glycol challenge. After 6 months of treatment, animals were euthanized, and ex-liver organs were harvested for toxicity analysis.

RESULTS

The Ldha gene was specifically knocked out in 20% of the liver cells of PH1 rats in the treatment group, leading to a 50% lower LDH expression than that in the control group. Compared to the control groups, urinary oxalate levels were significantly decreased, and renal calcium oxalate precipitation was largely mitigated in the treatment group throughout the entire 6-month study period. While no CRISPR/Cas9-associated off-target edits or hepatotoxicity were detected, we observed mild metabolic changes in the liver tricarboxylic acid (TCA) and glycolysis pathways.

CONCLUSIONS

CRISPR/Cas9-mediated LDH disruption may represent an applicable new strategy for alleviating PH1 for its long-lasting effect and low editorial efficiency requirements.

Deleterious AGXT Missense Variant Associated with Type 1 Primary Hyperoxaluria (PH1) in Zwartbles Sheep

Severe oxalate nephropathy has been previously reported in sheep and is mostly associated with excessive oxalate in the diet. However, a rare native Dutch breed (Zwartbles) seems to be predisposed to an inherited juvenile form of primary hyperoxaluria and no causative genetic variant has been described so far. This study aims to characterize the phenotype and genetic etiology of the inherited metabolic disease observed in several purebred Zwartbles sheep. Affected animals present with a wide range of clinical signs including condition loss, inappetence, malaise, and, occasionally, respiratory signs, as well as an apparent sudden unexpected death. Histopathology revealed widespread oxalate crystal deposition in kidneys of the cases. Whole-genome sequencing of two affected sheep identified a missense variant in the ovine AGXT gene (c.584G>A; p.Cys195Tyr). Variants in AGXT are known to cause type I primary hyperoxaluria in dogs and humans. Herein, we present evidence that the observed clinicopathological phenotype can be described as a form of ovine type I primary hyperoxaluria. This disorder is explained by a breed-specific recessively inherited pathogenic AGXT variant. Genetic testing enables selection against this fatal disorder in Zwartbles sheep as well as more precise diagnosis in animals with similar clinical phenotype. Our results have been incorporated in the Online Mendelian Inheritance in Animals (OMIA) database (OMIA 001672-9940).