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

Autophagy Regulates Putative Anion Transporter 1 Expression in Intestinal Epithelial Cells

Putative anion transporter 1 (PAT-1) is the key oxalate-secreting transporter in the intestine and therefore, maintaining its steady-state levels is critical for oxalate homeostasis. Autophagy is known to modulate the expression of intestinal solute transporters; however, its role in regulating PAT-1 has not been examined. Autophagy in Caco-2 cells was induced by either rapamycin treatment or by nutrient deprivation and assessed by conventional autophagy marker proteins. ATG7 (autophagy-related 7) protein expression was attenuated by ATG7-siRNA in Caco-2 cells or by utilising ATG7KO mice. PAT-1 protein levels in Caco-2 cells were significantly reduced by rapamycin or by nutrient deprivation at 48 and 72 h. Concomitantly, the LC3II/I ratio was increased, and p62 levels were significantly decreased, confirming the induction of autophagy. Nutrient deprivation for 6 h also caused a significant decrease in the surface levels of PAT-1. PAT-1 protein levels were increased by the siRNA-mediated ATG7 knockdown in Caco-2 cells and in the ileum of ATG7KO mice. In summary, Autophagy in intestinal epithelial cells modulates the basal levels of PAT-1 protein and may play a critical role in the maintenance of oxalate homeostasis.

High potency 3-carboxy-2-methylbenzofuran pendrin inhibitors as novel diuretics

Pendrin (SLC26A4) is an anion exchanger expressed in epithelial cells of kidney and lung. Pendrin inhibition is a potential treatment approach for edema, hypertension and inflammatory lung diseases. We have previously identified first-in-class pendrin inhibitors by high-throughput screening, albeit with low potency for pendrin inhibition (IC50 ∼10 μM). Here, we performed a de novo small molecule screen with follow-on structure-activity studies to identify more potent pendrin inhibitors. Screening of 50,000 synthetic small molecules identified four novel classes of pendrin inhibitors with diverse scaffolds, including 5-benzyloxy-2-methylbenzofurans, N-aryl urea substituted 5-methyltryptamines, N-aryl urea substituted anthranilic acids, and substituted N-benzyl 3-carboxyindoles. The most potent inhibitor from the initial screen, a 3-carboxy-2-methylbenzofuran (1a), had IC50 of 4.1 μM. Structure-activity studies using 732 benzofuran analogs identified 1d with IC50 ∼ 0.5 μM for pendrin inhibition. Selectivity studies showed that 1d has minimal or no activity against related ion channels/transporters including SLC26A3, SLC26A6 and CFTR at high concentrations. 1d administration to mice at 10 mg/kg had no effect on urine volume when used alone, but potentiated the diuretic effect of furosemide by 45 %. In conclusion, we have identified novel pendrin inhibitors with greatly improved potency and good in vivo efficacy. These compounds can be used as pharmacological tools to study the roles of pendrin, and potentially developed as drug candidates for edema, hypertension and lung diseases.

SLC26A3 (DRA, the Congenital Chloride Diarrhea Gene): A Novel Therapeutic Target for Diarrheal Diseases

Diarrhea associated with enteric infections, gut inflammation, and genetic defects poses a major health burden and results in significant morbidity and mortality. Impaired fluid and electrolyte absorption or secretion in the intestine are the hallmark of diarrhea. Electroneutral NaCl absorption in the mammalian GI tract involves the coupling of Na+/H+ and Cl-/HCO3- exchangers. SLC26A3 (Down Regulated in Adenoma, DRA) is the major anion exchanger involved in luminal Cl- absorption and HCO3- secretion. Mutations in the SLC26A3 gene cause a severe disease called congenital chloride diarrhea (CLD). Multiple studies have shown that DRA function or expression is downregulated in infectious diarrheal disorders caused by EPEC, C rodentium, Salmonella, Clostridioides difficile and Cryptosporidium parvum infection. In addition, DRA levels are severely depleted in colonic mucosa of IBD patients and in mouse models of IBD (eg, DSS, TNBS, adoptive T-cell transfer, anti-CD-40, and IL-10 KO colitis). In addition, genetic defects exhibiting diarrhea including microvillus inclusion disease (MVID), keratin-8 depletion, knock-out mouse models of transcriptional factors (eg, CDX-2 and HNF1α/1β) also exhibit severe down regulation of DRA. Also, recent studies have shown that DRA is not only critical for chloride absorption but also plays a key role in maintaining gut epithelial barrier integrity, microbiome composition, and has now emerged as an IBD susceptibility gene. In this review, we provide strong evidence that DRA may serve as a novel therapeutic target with dual benefits in not only correcting diarrheal phenotype but also improving gut barrier integrity and inflammation in pathogen infection or IBD.

Novel insight into the feed conversion ratio in laying hens and construction of its prediction model

Feed efficiency (FE) is an important economic factor in poultry production, and feed conversion ratio (FCR) is one of the most widely used measures of FE. Factors associated with FCR include genetics, the environment, and other factors. However, the mechanisms responsible for FCR in chickens are still less well appreciated. In this study, we examined the pattern changes of FCR, then delved into understanding the mechanisms behind these variations from both genetic and environmental perspectives. Most interestingly, the FCR at the front section of henhouse exhibited the lowest value. Further investigation revealed that laying rate in the high FCR (HFCR) group was lower than that in the low FCR (LFCR) group (P < 0.05). Cortisol, total antioxidant capacity (TAOC), and IgG levels in the LFCR group were significantly lower than those in the HFCR group (P < 0.05), while BUN level was significantly higher than that in the HFCR group (P < 0.05). We identified a total of 67 and 10 differentially expressed genes (DEGs) associated with FCR in ovarian and small intestine tissues, respectively. Functional enrichment analysis of DEGs revealed that they might affect FCR by modulating genes associated with salivary secretion, ferroptosis, and mineral absorption. Moreover, values for relative humidity (RH), air velocity (AV), PM2.5, ammonia (NH3), and carbon dioxide (CO2) in the LFCR group were significantly lower than those in the HFCR group (P < 0.05). Conversely, value for light intensity (LI) in the LFCR group was significantly higher than that in the HFCR group (P < 0.05). Correlation analysis revealed a positive correlation between FCR and RH, AV, PM2.5, NH3, and CO2, and a negative correlation with LI. Finally, the FCR prediction model was successfully constructed based on multiple environmental variables using the random forest algorithm, providing a valuable tool for predicting FCR in chickens.

Screening of oxalate-degrading probiotics and preventive effect of Lactiplantibacillus plantarum AR1089 on kidney stones

Calcium oxalate stone is the main type of kidney stone, so far there is no specific drug treatment. Here, we screened for oxalate-degrading probiotics and evaluated the potential preventive effect of lactic acid bacteria in rats with hyperoxaluria-induced kidney stones. The oxalate degradation efficiencies of the probiotics were determined to be 5-20% by in vitro experiments, of which the degradation efficiencies of Lactiplantibacillus plantarum AR342 and L. plantarum AR1089 were 17.32% and 14.15%, respectively. Through animal experiments, we found that L. plantarum AR1089 significantly attenuated kidney injury, as demonstrated by improving renal dysfunction and renal fibrosis, lowering creatinine and urea nitrogen levels. L. plantarum AR1089 was also effective in decreasing the number of calcium oxalate crystals in the urine and kidneys as well as ameliorating oxidative stress as evidenced by lowering the level of MDA and decreasing the level of SOD and CAT. Moreover, supplementation of L. plantarum AR1089 inhibited renal crystalline deposition by down-regulating the expression of KIM-1, OPN and MCP-1, and prevented hyperoxaluria-induced kidney stones by regulating the gut microbiota. Taken together, the present study shows that oral administration of L. plantarum AR1089, by attenuating kidney injury and regulating gut microbiota, is a potential therapy to reduce calcium oxalate crystals and prevent the progression of kidney stones.

Magnesium for disease treatment and prevention: emerging mechanisms and opportunities

Magnesium (Mg2+) is a commonly used dietary supplement for the prevention and treatment of diseases. However, the efficacy and mechanisms of action of Mg2+ in most diseases have been controversial because of conflicting findings in earlier studies. Recent clinical and preclinical studies provide novel insights into the use of Mg2+ for the treatment and prevention of diseases affecting different organ systems. In this review, we provide an overview of recent clinical evidence for, and controversies over, the medical benefits of Mg2+. In addition, we critically discuss recent advances in understanding the mechanisms of action of Mg2+, which could enable the development of novel targeted therapies.

Cell death‑related molecules and targets in the progression of urolithiasis (Review)

Urolithiasis is a high‑incidence disease caused by calcium oxalate (mainly), uric acid, calcium phosphate, struvite, apatite, cystine and other stones. The development of kidney stones is closely related to renal tubule cell damage and crystal adhesion and aggregation. Cell death, comprising the core steps of cell damage, can be classified into various types (i.e., apoptosis, ferroptosis, necroptosis and pyroptosis). Different crystal types, concentrations, morphologies and sizes cause tubular cell damage via the regulation of different forms of cell death. Oxidative stress caused by high oxalate or crystal concentrations is considered to be a precursor to a variety of types of cell death. In addition, complex crosstalk exists among numerous signaling pathways and their key molecules in various types of cell death. Urolithiasis is considered a metabolic disorder, and tricarboxylic acid cycle‑related molecules, such as citrate and succinate, are closely related to cell death and the inhibition of stone development. However, a literature review of the associations between kidney stone development, metabolism and various types of cell death is currently lacking, at least to the best of our knowledge. Thus, the present review summarizes the major advances in the understanding of regulated cell death and urolithiasis progression.

Substituted 4-methylcoumarin inhibitors of SLC26A3 (DRA) for treatment of constipation and hyperoxaluria

SLC26A3, also known as downregulated in adenoma (DRA), is an anion (Cl-, HCO3- and oxalate) exchanger in the luminal membrane of intestinal epithelial cells. Loss of DRA function in mice and humans causes congenital chloride-losing diarrhea and reduces urinary excretion of oxalate, a major constituent of kidney stones. Thus, inhibition of DRA is a potential treatment approach for constipation and calcium oxalate kidney stones. High-throughput screening previously identified 4,8-dimethylcoumarins (4a-4c) as DRA inhibitors, with lead candidate 4b having an IC50 of 40-50 nM for DRA inhibition. Here, we explored the effects of varying substituents at the 8-position, and replacing 8-methyl by 5-methyl (4e-4h). A focused library of 17 substituted compounds (4d-4t) was synthesized with good yield and purity. Compounds were tested for DRA inhibition potency using Fischer rat thyroid cells stably expressing DRA and a halide-sensitive YFP. Structure-activity analysis revealed that 8-bromo- (4m-4p) and 8-fluoro-coumarins (4q-4t) were slightly less potent than the corresponding 8-chloro analogs, demonstrating that the size of methyl or chloro substituents at the coumarin 8 position affects the potency. An analog containing 8-chlorocoumarin (4k) had ∼2-fold improved potency (IC50 25 nM) compared with the original lead candidate 4b. 5,8-Dimethylcoumarins were active against DRA, but with much lower potency than 4,8-disubstituted coumarins. In mice, orally administered 4k at 10 mg kg-1 reduced constipation and normalized stool water content in a loperamide-induced constipation model with comparable efficacy to 4b. Pharmacokinetic analysis of orally administered 4k at 10 mg kg-1 in mice indicated serum levels of >10 μM for at least six hours after single dose. This study expands SAR knowledge of 4,8-disubstituted coumarin inhibitors of DRA as novel drug candidates for constipation and kidney stones.

Pathophysiology and management of enteric hyperoxaluria

Enteric hyperoxaluria is a metabolic disorder resulting from conditions associated with fatty acid malabsorption and characterized by an increased urinary output of oxalate. Oxalate is excessively absorbed in the gut and then excreted in urine where it forms calcium oxalate crystals, inducing kidney stones formation and crystalline nephropathies. Enteric hyperoxaluria is probably underdiagnosed and may silently damage kidney function of patients affected by bowel diseases. Moreover, the prevalence of enteric hyperoxaluria has increased because of the development of bariatric surgical procedures. Therapeutic options are based on the treatment of the underlying disease, limitation of oxalate intakes, increase in calcium salts intakes but also increase in urine volume and correction of hypocitraturia. There are few data regarding the natural evolution of kidney stone events and chronic kidney disease in these patients, and there is a need for new treatments limiting kidney injury by calcium oxalate crystallization.

Mg2+ supplementation treats secretory diarrhea in mice by activating calcium-sensing receptor in intestinal epithelial cells

Cholera is a global health problem with no targeted therapies. The Ca2+-sensing receptor (CaSR) is a regulator of intestinal ion transport and a therapeutic target for diarrhea, and Ca2+ is considered its main agonist. We found that increasing extracellular Ca2+ had a minimal effect on forskolin-induced Cl- secretion in human intestinal epithelial T84 cells. However, extracellular Mg2+, an often-neglected CaSR agonist, suppressed forskolin-induced Cl- secretion in T84 cells by 65% at physiological levels seen in stool (10 mM). The effect of Mg2+ occurred via the CaSR/Gq signaling that led to cAMP hydrolysis. Mg2+ (10 mM) also suppressed Cl- secretion induced by cholera toxin, heat-stable E. coli enterotoxin, and vasoactive intestinal peptide by 50%. In mouse intestinal closed loops, luminal Mg2+ treatment (20 mM) inhibited cholera toxin-induced fluid accumulation by 40%. In a mouse intestinal perfusion model of cholera, addition of 10 mM Mg2+ to the perfusate reversed net fluid transport from secretion to absorption. These results suggest that Mg2+ is the key CaSR activator in mouse and human intestinal epithelia at physiological levels in stool. Since stool Mg2+ concentrations in patients with cholera are essentially zero, oral Mg2+ supplementation, alone or in an oral rehydration solution, could be a potential therapy for cholera and other cyclic nucleotide-mediated secretory diarrheas.

SLC26 Anion Transporters

Solute carrier family 26 (SLC26) is a family of functionally diverse anion transporters found in all kingdoms of life. Anions transported by SLC26 proteins include chloride, bicarbonate, and sulfate, but also small organic dicarboxylates such as fumarate and oxalate. The human genome encodes ten functional homologs, several of which are causally associated with severe human diseases, highlighting their physiological importance. Here, we review novel insights into the structure and function of SLC26 proteins and summarize the physiological relevance of human members.

Selective isoxazolopyrimidine PAT1 (SLC26A6) inhibitors for therapy of intestinal disorders

A loss of prosecretory Cl- channel CFTR activity in the intestine is considered as the key cause of gastrointestinal problems in cystic fibrosis (CF): meconium ileus, distal intestinal obstruction syndrome (DIOS) and constipation. Since CFTR modulators have minimal effects on gastrointestinal symptoms, there is an unmet need for novel treatments for CF-associated gastrointestinal disorders. Meconium ileus and DIOS mainly affect the ileum (distal small intestine). SLC26A6 (putative anion transporter 1, PAT1) is a Cl-/HCO3- exchanger at the luminal membrane of small intestinal epithelial cells which facilitates Cl- and fluid absorption. We recently identified first-in-class PAT1 inhibitors by high-throughput screening. Isoxazolopyrimidine PAT1inh-A01 was a hit compound, which had low potency (IC50 5.2 μM) for SLC26A6 inhibition precluding further preclinical development. Here we performed structure-activity relationship studies to optimize isoxazolopyrimidine SLC26A6 inhibitors and tested a potent inhibitor in mouse models of intestinal fluid absorption. Structure-activity studies of 377 isoxazolopyrimidine analogs identified PAT1inh-A0030 (ethyl 4-(benzyl(methyl)amino)-3-methylisoxazolo[5,4-d]pyrimidine-6-carboxylate) as the most potent SLC26A6 inhibitor with a 1.0 μM IC50. Selectivity studies showed that PAT1inh-A030 has no activity on relevant ion transporters/channels (SLC26A3, SLC26A4, SLC26A9, CFTR, TMEM16A). In a closed-loop model of intestinal fluid absorption, intraluminal PAT1inh-A0030 treatment inhibited fluid absorption in the ileum of wild-type and CF mice (CftrdelF508/delF508) with >90% prevention of a decrease in loop fluid volume and loop weight/length ratio at 30 minutes. These results suggest that SLC26A6 is the key transporter mediating Cl- and fluid absorption in the ileum and SLC26A6 inhibitors are novel drug candidates for treatment of CF-associated small intestinal disorders.

Oxalate Homeostasis in Non-Stone-Forming Chronic Kidney Disease: A Review of Key Findings and Perspectives

Chronic kidney disease (CKD) is a significant global public health concern associated with high morbidity and mortality rates. The maintenance of oxalate homeostasis plays a critical role in preserving kidney health, particularly in the context of CKD. Although the relationship between oxalate and kidney stone formation has been extensively investigated, our understanding of oxalate homeostasis in non-stone-forming CKD remains limited. This review aims to present an updated analysis of the existing literature, focusing on the intricate mechanisms involved in oxalate homeostasis in patients with CKD. Furthermore, it explores the key factors that influence oxalate accumulation and discusses the potential role of oxalate in CKD progression and prognosis. The review also emphasizes the significance of the gut-kidney axis in CKD oxalate homeostasis and provides an overview of current therapeutic strategies, as well as potential future approaches. By consolidating important findings and perspectives, this review offers a comprehensive understanding of the present knowledge in this field and identifies promising avenues for further research.

SLC26 family: a new insight for kidney stone disease

The solute-linked carrier 26 (SLC26) protein family is comprised of multifunctional transporters of substrates that include oxalate, sulphate, and chloride. Disorders of oxalate homeostasis cause hyperoxalemia and hyperoxaluria, leading to urinary calcium oxalate precipitation and urolithogenesis. SLC26 proteins are aberrantly expressed during kidney stone formation, and consequently may present therapeutic targets. SLC26 protein inhibitors are in preclinical development. In this review, we integrate the findings of recent reports with clinical data to highlight the role of SLC26 proteins in oxalate metabolism during urolithogenesis, and discuss limitations of current studies and potential directions for future research.

Small molecule inhibitors of intestinal epithelial anion exchanger SLC26A3 (DRA) with a luminal, extracellular site of action

The anion exchanger protein SLC26A3 (down-regulated in adenoma, DRA) is expressed in the luminal membrane of intestinal epithelial cells in colon, where it facilitates the absorption of Cl^- and oxalate. We previously identified a 4,8-dimethylcoumarin class of SLC26A3 inhibitors that act from the SLC26A3 cytoplasmic surface, and demonstrated their efficacy in mouse models of constipation and hyperoxaluria. Here, screening of 50,000 new compounds and 1740 chemical analogs of active compounds from the primary screen produced five novel classes of SLC26A3-selective inhibitors (1,3-dioxoisoindoline-amides; N-(5-sulfamoyl-1,3,4-thiadiazol-2-yl)acetamides; thiazolo-pyrimidin-5-ones; 3-carboxy-2-phenylbenzofurans and benzoxazin-4-ones) with IC₅₀ down to 100 nM. Kinetic washout and onset of action studies revealed an extracellular site of action for the thiazolo-pyrimidin-5-one and 3-carboxy-2-phenylbenzofuran inhibitors. Molecular docking computations revealed putative binding sites for these inhibitors. In a loperamide model of constipation in mice, orally administered 7-(2-chloro-phenoxymethyl)-3-phenyl-thiazolo [3,2-a]pyrimidin-5-one (3a) significantly increased stool weight, pellet number and water content. SLC26A3 inhibitors with an extracellular site of action offer the possibility of creating non-absorbable, luminally acting inhibitors with minimal systemic exposure following oral administration. Our findings also suggest that inhibitors of related SLC26 anion transporters with an extracellular site of action might be identified for pharmacological modulation of selected epithelial ion transport processes.

Oxalate homeostasis

Oxalate homeostasis is maintained through a delicate balance between endogenous sources, exogenous supply and excretion from the body. Novel studies have shed light on the essential roles of metabolic pathways, the microbiome, epithelial oxalate transporters, and adequate oxalate excretion to maintain oxalate homeostasis. In patients with primary or secondary hyperoxaluria, nephrolithiasis, acute or chronic oxalate nephropathy, or chronic kidney disease irrespective of aetiology, one or more of these elements are disrupted. The consequent impairment in oxalate homeostasis can trigger localized and systemic inflammation, progressive kidney disease and cardiovascular complications, including sudden cardiac death. Although kidney replacement therapy is the standard method for controlling elevated plasma oxalate concentrations in patients with kidney failure requiring dialysis, more research is needed to define effective elimination strategies at earlier stages of kidney disease. Beyond well-known interventions (such as dietary modifications), novel therapeutics (such as small interfering RNA gene silencers, recombinant oxalate-degrading enzymes and oxalate-degrading bacterial strains) hold promise to improve the outlook of patients with oxalate-related diseases. In addition, experimental evidence suggests that anti-inflammatory medications might represent another approach to mitigating or resolving oxalate-induced conditions.