CRISPR/Cas9-mediated metabolic pathway reprogramming in a novel humanized rat model ameliorates primary hyperoxaluria type 1

Preclinical evaluation of AGT mRNA replacement therapy for primary hyperoxaluria type I disease

Primary hyperoxaluria type 1 (PH1) is a rare inherited liver disorder caused by alanine glyoxylate aminotransferase (AGT) dysfunction, leading to accumulation of glyoxylate which is then converted into oxalate. Excessive oxalate results in kidney damage due to deposition of oxalate crystals. We have developed an mRNA-based protein replacement therapy for PH1 to restore normal glyoxylate to glycine metabolism. Sequence optimized human AGT mRNA (hAGT mRNA) was encapsulated in lipopolyplex (LPP) and produced functional AGT enzyme in peroxisomes. Pharmacokinetics and pharmacodynamics (PK/PD) were evaluated in vitro and in vivo. PK demonstrated that AGT mRNA and AGT protein maintained high expression levels for up to 48 hours. A single 2 mg/kg dose in AgxtQ84-/- rats achieved a 70% reduction in urinary oxalate. Toxicological assessment identified the highest nonserious toxic dose (HNSTD) as 2 mg/kg. These findings affirm the efficacy and safety of hAGT mRNA/LPP and support its clinical application in PH1 treatment.

Efficient and safe in vivo treatment of primary hyperoxaluria type 1 via LNP-CRISPR-Cas9-mediated glycolate oxidase disruption

Primary hyperoxaluria type 1 (PH1) is a severe genetic metabolic disorder caused by mutations in the AGXT gene, leading to defects in enzymes crucial for glyoxylate metabolism. PH1 is characterized by severe, potentially life-threatening manifestations due to excessive oxalate accumulation, which leads to calcium oxalate crystal deposits in the kidneys and, ultimately, renal failure and systemic oxalosis. Existing substrate reduction therapies, such as inhibition of liver-specific glycolate oxidase (GO) encoded by HAO1 using siRNA or CRISPR-Cas9 delivered by adeno-associated virus, either require repeated dosing or have raised safety concerns. To address these limitations, our study employed lipid nanoparticles (LNPs) for CRISPR-Cas9 delivery to rapidly generate a PH1 mouse model and validate the therapeutic efficacy of LNP-CRISPR-Cas9 targeting the Hao1 gene. The LNP-CRISPR-Cas9 system exhibited efficient editing of the Hao1 gene, significantly reducing GO expression and lowering urinary oxalate levels in treated PH1 mice. Notably, these effects persisted for 12 months with no significant off-target effects, liver-induced toxicity, or substantial immune responses, highlighting the approach's safety and specificity. Furthermore, the developed humanized mouse model validated the efficacy of our therapeutic strategy. These findings support LNP-CRISPR-Cas9 targeting HAO1 as a promising and safer alternative for PH1 treatment with a single administration.

All-in-one AAV-mediated Nrl gene inactivation rescues retinal degeneration in Pde6a mice

Retinitis pigmentosa (RP) is a complex group of inherited retinal diseases characterized by progressive death of photoreceptor cells and eventual blindness. Pde6a, which encodes a cGMP-specific phosphodiesterase, is a crucial pathogenic gene for autosomal recessive RP (RP43); there is no effective therapy for this form of RP. The compact CRISPR/Staphylococcus aureus Cas9 (CRISPR/SaCas9) system, which can be packaged into a single adeno-associated virus (AAV), holds promise for simplifying effective gene therapy. Here, we demonstrated that all-in-one AAV-SaCas9-mediated Nrl gene inactivation can efficiently prevent retinal degeneration in a RP mouse model with Pde6anmf363/nmf363 mutation. We screened single-guide RNAs capable of efficiently editing the mouse Nrl gene in N2a cells and then achieved effective gene editing by using a single AAV to codeliver SaCas9 and an optimal Nrl-sg2 into the mouse retina. Excitingly, in vivo inactivation of Nrl improved photoreceptor cell survival and rescued retinal function in treated Pde6a-deficient mice. Thus, we showed that a practical, gene-independent method, AAV-SaCas9-mediated Nrl inactivation, holds promise for future therapeutic applications in patients with RP.

Lipid nanoparticle-mediated base-editing of the Hao1 gene achieves sustainable primary hyperoxaluria type 1 therapy in rats

Primary hyperoxaluria type 1 (PH1) is a severe hereditary disease, leading to the accumulation of oxalate in multiple organs, particularly the kidney. Hydroxyacid oxidase 1 (HAO1), a pivotal gene involved in oxalate production, is an approved target for the treatment of PH1. In this study, we demonstrated the discovery of several novel therapeutic sites of the Hao1 gene and the efficient editing of Hao1 c.290-2 A in vivo with lipid nanoparticles (LNP) delivered adenine base editing (ABE) mRNA. A single infusion of LNP-ABE resulted in a near-complete knockout of Hao1 in the liver, leading to the sustainable normalization of urinary oxalate (for at least 6 months) and complete rescue of the patho-physiology in PH1 rats. Additionally, a significant correlation between Hao1 editing efficiency and urinary oxalate levels was observed and over 60% Hao1 editing efficiency was required to achieve the normalization of urinary oxalate in PH1 rats. These findings suggest that the LNP-mediated base-editing of Hao1 c.290-2 A is an efficient and safe approach to PH1 therapy, highlighting its potential utility in clinical settings.

Gene editing in liver diseases

The deliberate and precise modification of the host genome using engineered nucleases represents a groundbreaking advancement in modern medicine. Several clinical trials employing these approaches to address metabolic liver disorders have been initiated, with recent remarkable outcomes observed in patients with transthyretin amyloidosis, highlighting the potential of these therapies. Recent technological improvements, particularly CRISPR Cas9-based technology, have revolutionized gene editing, enabling in vivo modification of the cellular genome for therapeutic purposes. These modifications include gene supplementation, correction, or silencing, offering a wide range of therapeutic possibilities. Moving forward, we anticipate witnessing the unfolding therapeutic potential of these strategies in the coming years. The aim of our review is to summarize preclinical data on gene editing in animal models of inherited liver diseases and the clinical data obtained thus far, emphasizing both therapeutic efficacy and potential limitations of these medical interventions.

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.

Genetically Engineered Microorganisms and Their Impact on Human Health

The emergence of antibiotic-resistant strains, the decreased effectiveness of conventional therapies, and the side effects have led researchers to seek a safer, more cost-effective, patient-friendly, and effective method that does not develop antibiotic resistance. With progress in synthetic biology and genetic engineering, genetically engineered microorganisms effective in treatment, prophylaxis, drug delivery, and diagnosis have been developed. The present study reviews the types of genetically engineered bacteria and phages, their impacts on diseases, cancer, and metabolic and inflammatory disorders, the biosynthesis of these modified strains, the route of administration, and their effects on the environment. We conclude that genetically engineered microorganisms can be considered promising candidates for adjunctive treatment of diseases and cancers.

In vivo base editing rescues primary hyperoxaluria type 1 in rats

Primary hyperoxaluria type 1 (PH1) is a childhood-onset autosomal recessive disease, characterized by nephrocalcinosis, multiple recurrent urinary calcium oxalate stones, and a high risk of progressive kidney damage. PH1 is caused by inherent genetic defects of the alanine glyoxylate aminotransferase (AGXT) gene. The in vivo repair of disease-causing genes was exceedingly inefficient before the invention of base editors which can efficiently introduce precisely targeted base alterations without double-strand DNA breaks. Adenine base editor (ABE) can precisely convert A·T to G·C with the assistance of specific guide RNA. Here, we demonstrated that systemic delivery of dual adeno-associated virus encoding a split-ABE8e could artificially repair 13% of the pathogenic allele in AgxtQ84X rats, a model of PH1, alleviating the disease phenotype. Specifically, ABE treatment partially restored the expression of alanine-glyoxylate-aminotransferase (AGT), reduced endogenous oxalate synthesis and alleviated calcium oxalate crystal deposition. Western blot and immunohistochemistry confirmed that ABE8e treatment restored AGT protein expression in hepatocytes. Moreover, the precise editing efficiency in the liver remained stable six months after treatment. Thus, our findings provided a prospect of in vivo base editing as a personalized and precise medicine for PH1 by directly correcting the mutant Agxt gene.

Metabolic Regulations of Smilax china L. against β-Amyloid Toxicity in Caenorhabditis elegans

Smilax china L. (Chinaroot) is a natural herb that has multiple uses, such as being used to make tea and food. Both its roots and leaves have different uses due to their unique components. In this study, we analyzed the extract of S. china. roots using LC-HRMS and evaluated the neuroprotective effects and metabolic regulation of S. china on Caenorhabditis elegans. Chinaroot extract prolonged the life span of healthy nematodes, delayed the paralysis time of transgenic CL4176, and reduced the level of β-amyloid deposition in transgenic CL2006. The comprehensive analysis of metabolomics and qRT-PCR revealed that Chinaroot extract exerted neuroprotective effects through the valine, leucine and isoleucine degradation and fatty acid degradation pathways. Moreover, we first discovered that the expressions of T09B4.8, ech-7, and agxt-1 were linked to the neuroprotective effects of Chinaroot. The material exerted neuroprotective effects by modulating metabolic abnormalities in AD model C. elegans. Our study provides a new foundation for the development of functional food properties and functions.

Recent advances in therapeutic CRISPR-Cas9 genome editing: mechanisms and applications

Recently, clustered regularly interspaced palindromic repeats (CRISPR)-Cas9 derived editing tools had significantly improved our ability to make desired changes in the genome. Wild-type Cas9 protein recognizes the target genomic loci and induced local double strand breaks (DSBs) in the guidance of small RNA molecule. In mammalian cells, the DSBs are mainly repaired by endogenous non-homologous end joining (NHEJ) pathway, which is error prone and results in the formation of indels. The indels can be harnessed to interrupt gene coding sequences or regulation elements. The DSBs can also be fixed by homology directed repair (HDR) pathway to introduce desired changes, such as base substitution and fragment insertion, when proper donor templates are provided, albeit in a less efficient manner. Besides making DSBs, Cas9 protein can be mutated to serve as a DNA binding platform to recruit functional modulators to the target loci, performing local transcriptional regulation, epigenetic remolding, base editing or prime editing. These Cas9 derived editing tools, especially base editors and prime editors, can introduce precise changes into the target loci at a single-base resolution and in an efficient and irreversible manner. Such features make these editing tools very promising for therapeutic applications. This review focuses on the evolution and mechanisms of CRISPR-Cas9 derived editing tools and their applications in the field of gene therapy.

Lemon-Derived Extracellular Vesicle-like Nanoparticles Block the Progression of Kidney Stones by Antagonizing Endoplasmic Reticulum Stress in Renal Tubular Cells

Kidney stones, represented by the calcium oxalate (CaOx) type, are highly prevalent and recrudescent. Cumulative evidence shows regular consumption of lemonade intervenes with stone development. However, the detailed mechanism remains obscure. Here, extracellular vesicle-like nanoparticles (LEVNs) isolated from lemonade are demonstrated to traffick from the gut to the kidney, primarily enriched in tubule cells. Oral administration of LEVNs significantly alleviates the progression of kidney stones in rats. Mechanistically, in addition to altering the crystallization of CaOx toward a less stable subtype, LEVNs suppress the CaOx-induced endoplasmic reticulum stress response of tubule cells, as indicated by homeostasis of specific signaling molecules and restoration of subcellular function, thus indirectly inhibiting stone formation. To exercise this regulation, endocytosed LEVNs traffick along the microtubules throughout the cytoplasm and are eventually recruited into lysosomes. In conclusion, this study reveals a LEVNs-mediated mechanism against renal calculi and provides positive evidence for consumption of lemonade preventing stone formation.

Clinical trials and promising preclinical applications of CRISPR/Cas gene editing

Treatment of genetic disorders by genomic manipulation has been the unreachable goal of researchers for many decades. Although our understanding of the genetic basis of genetic diseases has advanced tremendously in the last few decades, the tools developed for genomic editing were not efficient and practical for their use in the clinical setting until now. The recent advancements in the research of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated protein (Cas) systems offered an easy and efficient way to edit the genome and accelerated the research on their potential use in the treatment of genetic disorders. In this review, we summarize the clinical trials that evaluate the CRISPR/Cas systems for treating different genetic diseases and highlight promising preclinical research on CRISPR/Cas mediated treatment of a great diversity of genetic disorders. Ultimately, we discuss the future of CRISPR/Cas mediated genome editing in genetic diseases.

New therapeutics for primary hyperoxaluria type 1

PURPOSE OF REVIEW

Primary hyperoxaluria type 1 (PH1) is a rare genetic disorder that causes hepatic overproduction of oxalate and, often, nephrocalcinosis, nephrolithiasis, chronic kidney disease, and kidney failure. The purpose of the review is to provide an update on current emerging therapies for the treatment of PH1.

RECENT FINDINGS

Use of ribonucleic acid interference (RNAi) therapeutics that target the liver to block production of key enzymes along pathways that generate oxalate is a promising approach. Available evidence supports the efficacy of both Lumasiran (targeting glycolate oxidase) and Nedosiran (targeting hepatic lactate dehydrogenase (LDHa)) to reduce urinary oxalate excretion in PH1. The efficacy of alternative approaches including stiripentol (an anticonvulsant drug that also targets LDHa), lanthanum (a potential gastrointestinal oxalate binder), and Oxalobacter formigenes (a bacterium that can degrade oxalate within the gastrointestinal tract and may also increase its secretion from blood) are all also under study. Genetic editing tools including clustered regularly interspaced short palindromic repeats/Cas9 are also in preclinical study as a potential PH1 therapeutic.

SUMMARY

Novel treatments can reduce the plasma oxalate concentration and urinary oxalate excretion in PH1 patients. Thus, it is possible these approaches will reduce the need for combined kidney and liver transplantation to significantly decrease the morbidity and mortality of affected patients.

Engineered probiotics

Engineered probiotics are a kind of new microorganisms produced by modifying original probiotics through gene editing. With the continuous development of tools and technology progresses, engineering renovation of probiotics are becoming more diverse and more feasible. In the past few years there have been some advances in the development of engineered probiotics that will benefit humankind. This review briefly introduces the theoretical basis of gene editing technology and focuses on some recent engineered probiotics researches, including inflammatory bowel disease, bacterial infection, tumor and metabolic diseases. It is hoped that it can provide help for the further development of genetically modified microorganisms, stimulate the potential of engineered probiotics to treat intractable diseases, and provide new ideas for the diagnosis of some diseases or some industrial production.

Gene editing and its applications in biomedicine

The steady progress in genome editing, especially genome editing based on the use of clustered regularly interspaced short palindromic repeats (CRISPR) and programmable nucleases to make precise modifications to genetic material, has provided enormous opportunities to advance biomedical research and promote human health. The application of these technologies in basic biomedical research has yielded significant advances in identifying and studying key molecular targets relevant to human diseases and their treatment. The clinical translation of genome editing techniques offers unprecedented biomedical engineering capabilities in the diagnosis, prevention, and treatment of disease or disability. Here, we provide a general summary of emerging biomedical applications of genome editing, including open challenges. We also summarize the tools of genome editing and the insights derived from their applications, hoping to accelerate new discoveries and therapies in biomedicine.

Recent Advances in the Production of Genome-Edited Rats

The rat is an important animal model for understanding gene function and developing human disease models. Knocking out a gene function in rats was difficult until recently, when a series of genome editing (GE) technologies, including zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and the type II bacterial clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated Cas9 (CRISPR/Cas9) systems were successfully applied for gene modification (as exemplified by gene-specific knockout and knock-in) in the endogenous target genes of various organisms including rats. Owing to its simple application for gene modification and its ease of use, the CRISPR/Cas9 system is now commonly used worldwide. The most important aspect of this process is the selection of the method used to deliver GE components to rat embryos. In earlier stages, the microinjection (MI) of GE components into the cytoplasm and/or nuclei of a zygote was frequently employed. However, this method is associated with the use of an expensive manipulator system, the skills required to operate it, and the egg transfer (ET) of MI-treated embryos to recipient females for further development. In vitro electroporation (EP) of zygotes is next recognized as a simple and rapid method to introduce GE components to produce GE animals. Furthermore, in vitro transduction of rat embryos with adeno-associated viruses is potentially effective for obtaining GE rats. However, these two approaches also require ET. The use of gene-engineered embryonic stem cells or spermatogonial stem cells appears to be of interest to obtain GE rats; however, the procedure itself is difficult and laborious. Genome-editing via oviductal nucleic acids delivery (GONAD) (or improved GONAD (i-GONAD)) is a novel method allowing for the in situ production of GE zygotes existing within the oviductal lumen. This can be performed by the simple intraoviductal injection of GE components and subsequent in vivo EP toward the injected oviducts and does not require ET. In this review, we describe the development of various approaches for producing GE rats together with an assessment of their technical advantages and limitations, and present new GE-related technologies and current achievements using those rats in relation to human diseases.

Current approaches in CRISPR-Cas9 mediated gene editing for biomedical and therapeutic applications

A single gene mutation can cause a number of human diseases that affect quality of life. Until the development of clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein (Cas) systems, it was challenging to correct a gene mutation to avoid disease by reverting phenotypes. The advent of CRISPR technology has changed the field of gene editing, given its simplicity and intrinsic programmability, surpassing the limitations of both zinc-finger nuclease and transcription activator-like effector nuclease and becoming the method of choice for therapeutic gene editing by overcoming the bottlenecks of conventional gene-editing techniques. Currently, there is no commercially available medicinal cure to correct a gene mutation that corrects and reverses the abnormality of a gene's function. Devising reprogramming strategies for faithful recapitulation of normal phenotypes is a crucial aspect for directing the reprogrammed cells toward clinical trials. The CRISPR-Cas9 system has been promising as a tool for correcting gene mutations in maladies including blood disorders and muscular degeneration as well as neurological, cardiovascular, renal, genetic, stem cell, and optical diseases. In this review, we highlight recent developments and utilization of the CRISPR-Cas9 system in correcting or generating gene mutations to create model organisms to develop deeper insights into diseases, rescue normal gene functionality, and curb the progression of a disease.

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.

CRISPR Systems Suitable for Single AAV Vector Delivery

CRISPR (clustered regularly interspaced short palindromic repeats)/Cas gene editing is a revolutionary technology that can enable the correction of genetic mutations in vivo, providing great promise as a therapeutic intervention for inherited diseases. Adeno-associated viral (AAV) vectors are a potential vehicle for delivering CRISPR/Cas. However, they are restricted by their limited packaging capacity. Identifying smaller Cas orthologs that can be packaged, along with the required guide RNA elements, into a single AAV would be an important optimization for CRISPR/Cas gene editing. Expanding the options of Cas proteins that can be delivered by a single AAV not only increases translational application but also expands the genetic sites that can be targeted for editing. This review considers the benefits and current scope of small Cas protein orthologs that are suitable for gene editing approaches using single AAV vector delivery.

Advances in Genome Editing and Application to the Generation of Genetically Modified Rat Models

The rat has been extensively used as a small animal model. Many genetically engineered rat models have emerged in the last two decades, and the advent of gene-specific nucleases has accelerated their generation in recent years. This review covers the techniques and advances used to generate genetically engineered rat lines and their application to the development of rat models more broadly, such as conditional knockouts and reporter gene strains. In addition, genome-editing techniques that remain to be explored in the rat are discussed. The review also focuses more particularly on two areas in which extensive work has been done: human genetic diseases and immune system analysis. Models are thoroughly described in these two areas and highlight the competitive advantages of rat models over available corresponding mouse versions. The objective of this review is to provide a comprehensive description of the advantages and potential of rat models for addressing specific scientific questions and to characterize the best genome-engineering tools for developing new projects.

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.

Generation and characterization of a novel rat model of primary hyperoxaluria type 1 with a nonsense mutation in alanine-glyoxylate aminotransferase gene

Primary hyperoxaluria type 1 (PH1) is a severe inherited disorder caused by a genetic defect in alanine-glyoxylate aminotransferase (AGXT), which results in recurrent urolithiasis and renal failure. Animal models that precisely reflect human PH1 phenotypes are lacking. We aimed to develop a novel PH1 rat model and study the mechanisms involved in PH1 deterioration. One cell stage Sprague-Dawley embryos were injected with the CRISPR/Cas9 system to introduce a Q84X mutation in Agxt. Liver tissues were harvested to determine Agxt expression. Urine oxalate, crystals, and electrolyte levels in Agxt^Q84X and wild-type (WT) littermates were evaluated. Kidney tissues were used for Pizzolato staining and kidney injury evaluation. Data showed that Agxt mRNA and protein were absent in Agxt^Q84X rats. At 4 and 24 wk, Agxt^Q84X rats displayed 2.1- and 2.9-fold higher urinary oxalate levels, respectively, compared with WT littermates. As a result, calcium oxalate (CaOx) crystals in urine were revealed in all Agxt^Q84X rats but in none of the WT rats. We also observed bladder stones in 36.4% of Agxt^Q84X rats, of which 44.4% had renal CaOx deposition. Moreover, the elevated serum urea and creatinine levels indicated the impaired renal function in Agxt^Q84X rats. Further investigation revealed significantly increased expression of inflammation-, necroptosis-, and fibrosis-related genes in the kidneys of Agxt^Q84X rats with spontaneous renal CaOx deposition, indicating that these pathways are involved in PH1 deterioration. Collectively, these results suggest that this rat model has broad applicability in mechanistic studies and innovative therapeutics development for PH1 and other kidney stone diseases.NEW & NOTEWORTHY Primary hyperoxaluria type 1 is a severe inherited disorder that results in recurrent urolithiasis and renal failure. We generated an alanine-glyoxylate aminotransferase (Agxt)^Q84X nonsense mutant rat model that displayed an early onset of hyperoxaluria, spontaneous renal CaOx precipitation, bladder stone, and kidney injuries. Our results suggest an interaction of renal CaOx crystals with the activation of inflammation-, fibrosis-, and necroptosis-related pathways. In all, the Agxt^Q84X rat strain has broad applicability in mechanistic studies and the development of innovative therapeutics.

Transplantation for Primary Hyperoxaluria Type 1: Designing New Strategies in the Era of Promising Therapeutic Perspectives

Primary hyperoxaluria type 1 (PH1) is an autosomal recessive disease caused by the functional defect of alanine-glyoxylate aminotransferase that results in the overproduction of oxalate. It can be devastating especially for kidneys, leading to end-stage renal disease (ESRD) during the first 2 to 3 decades of life in most patients. Consequently, many PH1 patients need kidney transplantation. However, because PH1 is caused by a liver enzyme deficiency, the only cure of the metabolic defect is liver transplantation. Thus, current transplant strategies to treat PH1 patients with ESRD include dual liver-kidney transplantation. However, the morbidity and mortality associated with liver transplantation make these strategies far from optimal. Fortunately, a therapeutic revolution is looming. Indeed, innovative drugs are being currently tested in clinical trials, and preliminary data show impressive efficacy to reduce the hepatic overproduction of oxalate. Hopefully, with these therapies, liver transplantation will no longer be necessary. However, some patients with progressing renal disease or those who will be diagnosed with PH1 at an advanced stage of chronic kidney disease will ultimately need kidney transplantation. Here we review the current knowledge on this subject and discuss the future of kidney transplant management in PH1 patients in the era of novel therapies.

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.

Effect of alanine supplementation on oxalate synthesis

The Primary Hyperoxalurias (PH) are rare disorders of metabolism leading to excessive endogenous synthesis of oxalate and recurring calcium oxalate kidney stones. Alanine glyoxylate aminotransferase (AGT), deficient in PH type 1, is a key enzyme in limiting glyoxylate oxidation to oxalate. The affinity of AGT for its co-substrate, alanine, is low suggesting that its metabolic activity could be sub-optimal in vivo. To test this hypothesis, we examined the effect of L-alanine supplementation on oxalate synthesis in cell culture and in mouse models of Primary Hyperoxaluria Type 1 (Agxt KO), Type 2 (Grhpr KO) and in wild-type mice. Our results demonstrated that increasing L-alanine in cells decreased synthesis of oxalate and increased viability of cells expressing GO and AGT when incubated with glycolate. In both wild type and Grhpr KO male and female mice, supplementation with 10% dietary L-alanine significantly decreased urinary oxalate excretion ~30% compared to baseline levels. This study demonstrates that increasing the availability of L-alanine can increase the metabolic efficiency of AGT and reduce oxalate synthesis.