Successful Treatment of Primary Hyperoxaluria Type 2 with a Combined Liver and Kidney Transplant

Characterization of CHK-336, A First-in-Class, Liver-Targeted, Small-Molecule Lactate Dehydrogenase Inhibitor for Hyperoxaluria Treatment

Key Points

Background

Primary hyperoxalurias (PH) 1–3 are genetic diseases defined by elevated hepatic oxalate production and higher incidence of calcium oxalate kidney stones and potentially kidney failure. There are two approved agents available for PH1, and there are no approved therapies for PH2 or PH3. Lactate dehydrogenase A catalyzes the final step in hepatic oxalate synthesis and represents a potential therapeutic target for PH and other forms of hyperoxaluria associated with increased oxalate production.

Methods

Potent and selective lactate dehydrogenase (LDH) inhibitors with liver-targeted tissue distribution were identified and characterized in enzymatic, cellular, and in vivo models.

Results

We identified CHK-336, a novel oral small-molecule that demonstrates potent and selective inhibition of the human LDH enzyme and its activity in hepatocyte assays across multiple species, including hepatocytes isolated from PH1 mice. CHK-336 demonstrated a favorable liver distribution profile in mice, rats, and monkeys that was dependent on hepatic uptake by organic anion-transporting polypeptide transporters and target-mediated drug binding. In a rat pharmacodynamic model, CHK-336 inhibited conversion of 13C2-glycolate to 13C2-oxalate in a dose-dependent manner. In a PH1 mouse model, once-daily oral dosing of CHK-336 produced robust and dose-dependent reductions in urinary oxalate to the normal range. Seven days of treatment with CHK-336 also resulted in a significant reduction in urinary oxalate in a PH2 mouse model.

Conclusions

In conclusion, CHK-336 is a potent, liver-targeted, small-molecule LDH inhibitor that suppressed urinary oxalate production in a rat pharmacodynamic model and mouse models of PH1 and PH2.

Evaluation for genetic disease in kidney transplant candidates: A practice resource

The increasing availability of clinically approved genetic tests for kidney disease has spurred the growth in the use of these tests in kidney transplant practice. Neither the testing options nor the patient population where this should be deployed has been defined, and its value in kidney transplant evaluation has not been demonstrated. Transplant providers may not always be aware of the limitations of genetic testing and may need guidance on comprehending test results and providing counsel, as many centers do not have easy access to a renal genetic counselor or a clinical geneticist. In this practice resource, a working group of nephrologists, geneticists, and a genetic counselor provide a pragmatic, tailored approach to genetic testing, advocating for its use only where the genetic diagnosis or its exclusion can impact the choices available for transplantation or posttransplant management or the workup of living donor candidates at increased risk for heritable disease.

Second transplantation after kidney graft loss in primary hyperoxaluria type 2: a pedigree study and mutation analysis

BACKGROUND

Primary hyperoxaluria type 2 (PH2) is a rare disorder caused by GRHPR mutations. Research on the mutation spectrum and pedigree of PH2 helps in comprehending its pathogenesis and clinical outcomes, guiding clinical diagnosis and treatment.

METHODS

We report a case of PH2 with a three-generational pedigree. The GRHPR genotypes of the family members were confirmed by Sanger sequencing. Urine and blood samples were collected for biochemical analysis. Computational analysis was performed to assess the pathogenicity of the mutations. Cellular experiments based on site-directed mutagenesis were conducted to confirm the effect of mutations on GRHPR expression, activity, and subcellular localization.

RESULTS

The proband underwent her first kidney transplantation in 2015, and experienced recurrent urinary tract infections and urolithiasis postoperatively. Graft failure occurred in 2018. Whole exome sequencing identified compound heterozygous GRHPR mutations p.G160E/p.P203Rfs*7. The patient underwent a second kidney transplantation in 2019 and maintained good graft function with urine dilution measures. Notably, her brother and sister carried the same mutations; however, only the proband progressed to renal failure. Computational analysis suggested that p.G160E reduced the affinity of GRHPR for coenzymes. Cellular experiments indicated that p.G160E reduced GRHPR activity (p < 0.001), whereas p.P203Rfs*7 not only suppressed expression (p < 0.001) and reduced activity (p < 0.001), but also facilitated protein aggregation. Based on our results, the variant p.G160E was classified as 'pathogenic' according to ACMG guidelines.

CONCLUSIONS

Our findings suggest that treatment strategies for the long-term prevention of oxalate nephropathy should be developed for patients with PH2 receiving isolated kidney transplantation. Moreover, the pathogenicity of the compound heterozygous GRHPR mutations p.G160E/p.P203Rfs*7 was also validated.

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.

A molecular journey on the pathogenesis of primary hyperoxaluria

PURPOSE OF REVIEW

Primary hyperoxalurias (PHs) are rare disorders caused by the deficit of liver enzymes involved in glyoxylate metabolism. Their main hallmark is the increased excretion of oxalate leading to the deposition of calcium oxalate stones in the urinary tract. This review describes the molecular aspects of PHs and their relevance for the clinical management of patients.

RECENT FINDINGS

Recently, the study of PHs pathogenesis has received great attention. The development of novel in vitro and in vivo models has allowed to elucidate how inherited mutations lead to enzyme deficit, as well as to confirm the pathogenicity of newly-identified mutations. In addition, a better knowledge of the metabolic consequences in disorders of liver glyoxylate detoxification has been crucial to identify the key players in liver oxalate production, thus leading to the identification and validation of new drug targets.

SUMMARY

The research on PHs at basic, translational and clinical level has improved our knowledge on the critical factors that modulate disease severity and the response to the available treatments, leading to the development of new drugs, either in preclinical stage or, very recently, approved for patient treatment.

Clinical features and mutational spectrum of Chinese patients with primary hyperoxaluria type 2

Primary hyperoxaluria type 2 (PH2) is a rare hereditary disease that causes nephrolithiasis, nephrocalcinosis and kidney failure. This study aimed to investigate the clinical features and mutational spectrum of Chinese patients with PH2. A retrospective cohort study was performed on PH2 patients admitted to our center over seven years. We also systematically reviewed all the articles on Chinese PH2 patients published from January 2000 to May 2023 and conducted a meta-analysis. A total of 25 PH2 patients (10 from our center and 15 from published studies) were included in this study. The median age of onset in patients from our center was 8.50 (1.00, 24.00) years, and 50% were male. Among the full cohort of 25 Chinese patients, the median age of onset was 8.00 (0.40, 26.00) years, and 64% of them were male. Seven patients progressed to end-stage kidney disease, with a median age of 27.50 (12, 31) years. The cumulative renal survival rates were 100%, 91.67%, 45.83% and 30.56% at 10, 20, 30 and 40 years of age, respectively. A total of 18 different variants were identified, and c.864_865del was the dominant variant, accounting for 57.69% of the total alleles. Patients who were heterozygous for c.864_865del were more susceptible to nephrocalcinosis than those who were homozygous for c.864_865del and those harboring other mutations (83.33% versus 33.3% and 0%, respectively) (p = 0.025). The clinical features and mutational spectrum of Chinese PH2 patients were described. This study helps to expand awareness of the phenotypes and genotypes of Chinese PH2 patients and contributes to the improvement of diagnostic and treatment strategies for PH2 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.