Salicylic Acid Derivatives Inhibit Oxalate Production in Mouse Hepatocytes with Primary Hyperoxaluria Type 1

Searching glycolate oxidase inhibitors based on QSAR, molecular docking, and molecular dynamic simulation approaches

Primary hyperoxaluria type 1 (PHT1) treatment is mainly focused on inhibiting the enzyme glycolate oxidase, which plays a pivotal role in the production of glyoxylate, which undergoes oxidation to produce oxalate. When the renal secretion capacity exceeds, calcium oxalate forms stones that accumulate in the kidneys. In this respect, detailed QSAR analysis, molecular docking, and dynamics simulations of a series of inhibitors containing glycolic, glyoxylic, and salicylic acid groups have been performed employing different regression machine learning techniques. Three robust models with less than 9 descriptors-based on a tenfold cross (Q² _CV) and external (Q² _EXT) validation-were found i.e., MLR1 (Q² _CV = 0.893, Q² _EXT = 0.897), RF1 (Q² _CV = 0.889, Q² _EXT = 0.907), and IBK1 (Q² _CV = 0.891, Q² _EXT = 0.907). An ensemble model was built by averaging the predicted pIC₅₀ of the three models, obtaining a Q² _EXT = 0.933. Physicochemical properties such as charge, electronegativity, hardness, softness, van der Waals volume, and polarizability were considered as attributes to build the models. To get more insight into the potential biological activity of the compouds studied herein, docking and dynamic analysis were carried out, finding the hydrophobic and polar residues show important interactions with the ligands. A screening of the DrugBank database V.5.1.7 was performed, leading to the proposal of seven commercial drugs within the applicability domain of the models, that can be suggested as possible PHT1 treatment.

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.

CRISPR/Cas9-mediated knock-out of AGXT1 in HepG2 cells as a new in vitro model of Primary Hyperoxaluria Type 1

AGXT1 encodes alanine:glyoxylate aminotransferase 1 (AGT1), a liver peroxisomal pyridoxal 5'-phosphate dependent-enzyme whose deficit causes Primary Hyperoxaluria Type 1 (PH1). PH1 is a rare disease characterized by overproduction of oxalate, first leading to kidney stones formation, and possibly evolving to life-threatening systemic oxalosis. A minority of PH1 patients is responsive to pyridoxine, while the option for non-responders is liver-kidney transplantation. Therefore, huge efforts are currently focused on the identification of new therapies, including the promising approaches based on RNA silencing recently approved. Many PH1-associated mutations are missense and lead to a variety of kinetic and/or folding defects on AGT1. In this context, the availability of a reliable in vitro disease model would be essential to better understand the phenotype of known or newly-identified pathogenic variants as well as to test novel drug candidates. Here, we took advantage of the CRISPR/Cas9 technology to specifically knock-out AGXT1 in HepG2 cells, a hepatoma-derived cell model exhibiting a conserved glyoxylate metabolism. AGXT1-KO HepG2 displayed null AGT1 expression and significantly reduced transaminase activity leading to an enhanced secretion of oxalate upon glycolate challenge. Known pathogenic AGT1 variants expressed in AGXT1-KO HepG2 cells showed alteration in both protein levels and specific transaminase activity, as well as a partial mitochondrial mistargeting when associated with a common polymorphism. Notably, pyridoxine treatment was able to partially rescue activity and localization of clinically-responsive variants. Overall, our data validate AGXT1-KO HepG2 cells as a novel cellular model to investigate PH1 pathophysiology, and as a platform for drug discovery and development.

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.

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.

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.

Discovery of Novel, Potent Inhibitors of Hydroxy Acid Oxidase 1 (HAO1) Using DNA-Encoded Chemical Library Screening

Inhibition of hydroxy acid oxidase 1 (HAO1) is a strategy to mitigate the accumulation of toxic oxalate that results from reduced activity of alanine-glyoxylate aminotransferase (AGXT) in primary hyperoxaluria 1 (PH1) patients. DNA-Encoded Chemical Library (DECL) screening provided two novel chemical series of potent HAO1 inhibitors, represented by compounds 3-6. Compound 5 was further optimized via various structure-activity relationship (SAR) exploration methods to 29, a compound with improved potency and absorption, distribution, metabolism, and excretion (ADME)/pharmacokinetic (PK) properties. Since carboxylic acid-containing compounds are often poorly permeable and have potential active glucuronide metabolites, we undertook a brief, initial exploration of acid replacements with the aim of identifying non-acid-containing HAO1 inhibitors. Structure-based drug design initiated with Compound 5 led to the identification of a nonacid inhibitor of HAO1, 31, which has weaker potency and increased permeability.

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 therapeutic approaches in primary hyperoxaluria

Introduction: Currently, three types of primary hyperoxaluria (PH I-III) are known, all based on different gene-mutations affecting the glyoxylate metabolism in the liver. Disease hallmark is an increased endogenous oxalate production and thus massively elevated urinary excretion of oxalate and other type-specific metabolites. Hyperoxaluria induces the formation of calcium-oxalate kidney stones and/or nephrocalcinosis. In addition to that, a chronic inflammasome activation by hyperoxaluria per se, often leads to an early deterioration of kidney function, regularly resulting in end-stage renal disease (ESRD) at least in patients with type I PH. Except for vitamin B6 treatment in PH I, therapeutic regimen nowadays consists only of supportive measures, like significantly increased fluid intake and medication increasing the urinary solubility like alkaline citrate. Areas covered: Disease burden can be severe, and both clinicians and scientist are eager in finding new therapeutic approaches. The currently ongoing clinical studies and promising research in this field are reported in this paper. To present a complete overview, we searched electronic databases, like Clinical trial gov, National Center for Biotechnology Information PubMed, congress reports, press releases and personal information acquired at congresses and conventions. Searches were conducted using the following medical headings: (primary) hyperoxaluria, PH, therapy, treatment and research. Expert opinion: There is light on the horizon that new treatment options will be available in due time, as there are several promising therapeutic agents currently under investigation, some being at the first levels of drug development, but some already in ongoing clinical trials (phase I-III).