Urea transporter and its specific and nonspecific inhibitors: State of the art and pharmacological perspective

KCNJ16-depleted kidney organoids recapitulate tubulopathy and lipid recovery upon statins treatment

BACKGROUND

The KCNJ16 gene has been associated with a novel kidney tubulopathy phenotype, viz. disturbed acid-base homeostasis, hypokalemia and altered renal salt transport. KCNJ16 encodes for Kir5.1, which together with Kir4.1 constitutes a potassium channel located at kidney tubular cell basolateral membranes. Preclinical studies provided mechanistic links between Kir5.1 and tubulopathy, however, the disease pathology remains poorly understood. Here, we aimed at generating and characterizing a novel advanced in vitro human kidney model that recapitulates the disease phenotype to investigate further the pathophysiological mechanisms underlying the tubulopathy and potential therapeutic interventions.

METHODS

We used CRISPR/Cas9 to generate KCNJ16 mutant (KCNJ16+/- and KCNJ16-/-) cell lines from healthy human induced pluripotent stem cells (iPSC) KCNJ16 control (KCNJ16WT). The iPSCs were differentiated following an optimized protocol into kidney organoids in an air-liquid interface.

RESULTS

KCNJ16-depleted kidney organoids showed transcriptomic and potential functional impairment of key voltage-dependent electrolyte and water-balance transporters. We observed cysts formation, lipid droplet accumulation and fibrosis upon Kir5.1 function loss. Furthermore, a large scale, glutamine tracer flux metabolomics analysis demonstrated that KCNJ16-/- organoids display TCA cycle and lipid metabolism impairments. Drug screening revealed that treatment with statins, particularly the combination of simvastatin and C75, prevented lipid droplet accumulation and collagen-I deposition in KCNJ16-/- kidney organoids.

CONCLUSIONS

Mature kidney organoids represent a relevant in vitro model for investigating the function of Kir5.1. We discovered novel molecular targets for this genetic tubulopathy and identified statins as a potential therapeutic strategy for KCNJ16 defects in the kidney.

Structural characterization of human urea transporters UT-A and UT-B and their inhibition

In this study, we present the structures of human urea transporters UT-A and UT-B to characterize them at molecular level and to detail the mechanism of UT-B inhibition by its selective inhibitor, UTBinh-14. High-resolution structures of both transporters establish the structural basis for the inhibitor's selectivity to UT-B, and the identification of multiple binding sites for the inhibitor will aid with the development of drug lead molecules targeting both transporters. Our study also discovers phospholipids associating with the urea transporters by combining structural observations, native MS, and lipidomics analysis. These insights improve our understanding of urea transporter function at a molecular level and provide a blueprint for a structure-guided design of therapeutics targeting these transporters.

Prepubertal to adulthood exposure to low doses of glyphosate-based herbicide increases the expression of the Havcr1 (Kim1) biomarker and causes mild kidney alterations

Glyphosate is a nonselective and postemergent herbicide used to combat weeds in several crops, which raises concerns about risks to human health since residues are detected in urine, human milk, surface water and several types of food. Feces and urine are the major routes of elimination of glyphosate, making the kidney a sensitive target for the development of toxicity. In fact, farmers are at high risk of developing chronic kidney disease. In this sense, this study aims to investigate kidney function by measuring the serum levels of urea and creatinine, examining the histological morphology, and analyzing the mRNA expression of genes related to tubular transport of ions, urea and urates and the biomarker of kidney disease Kim1, and the levels of lead in the kidney in male Wistar rats orally exposed to low levels of glyphosate-based herbicide (GBH: 0, 0.5 or 5 mg/kg) from weaning to adult life by gavage. GBH0.5 showed reduced serum urea concentration, presence of tubulointerstitial swelling and mononuclear cell infiltration into the interstitium, increased gene expression of Kim1 and reduced gene expression of Slc14a1. GBH5 showed reduced serum urea and increased serum creatinine concentrations, tubulointerstitial swelling, interstitial fibrosis, and reduced expression of Trpm6 and Trpv5. Exposure to GBH did not affect the levels of Pb in the kidneys of animals. In conclusion, glyphosate at low doses may cause mild kidney damage. It is necessary to evaluate whether the long-term effects of this constant injury may contribute to the development of chronic kidney disease of uncertain etiology.

A critical analysis of urea transporter B inhibitors: molecular fingerprints, pharmacophore features for the development of next-generation diuretics

Urea transporter is a membrane transport protein. It is involved in the transferring of urea across the cell membrane in humans. Along with urea transporter A, urea transporter B (UT-B) is also responsible for the management of urea concentration and blood pressure of human. The inhibitors of urea transporters have already generated a huge attention to be developed as alternate safe class of diuretic. Unlike conventional diuretics, these inhibitors are suitable for long-term therapy without hampering the precious electrolyte imbalance in the human body. In this study, UT-B inhibitors were analysed by using multi-chemometric modelling approaches. The possible pharmacophore features along with favourable and unfavourable sub-structural fingerprints for UT-B inhibition are extracted. This information will guide the medicinal chemist to design potent UT-B inhibitors in future.