Kidney toxicity accounts for a significant percentage of morbidity and drug candidate failure. Serum creatinine (SCr) and blood urea nitrogen (BUN) have been used to monitor kidney dysfunction for over a century but these markers are insensitive and non-specific. In multi-site preclinical rat toxicology studies the diagnostic performance of urinary kidney injury molecule-1 (Kim-1) was compared to traditional biomarkers as predictors of kidney tubular histopathologic changes, currently considered the “gold standard” of nephrotoxicity. In multiple models of kidney injury, urinary Kim-1 significantly outperformed SCr and BUN. The area under the receiver operating characteristic curve for Kim-1 was between 0.91 and 0.99 as compared to 0.79 to 0.9 for BUN and 0.73 to 0.85 for SCr. Thus urinary Kim-1 is the first injury biomarker of kidney toxicity qualified by the FDA and EMEA and is expected to significantly improve kidney safety monitoring.
Vaidya, Vishal S., Victoria Ramirez, Takaharu Ichimura, Norma A. Bobadilla, and Joseph V. Bonventre. Urinary kidney injury molecule-1: a sensitive quantitative biomarker for early detection of kidney tubular injury. sitive and specific biomarkers are needed to detect early kidney injury. The objective of the present work was to develop a sensitive quantitative urinary test to identify renal injury in the rodent to facilitate early assessment of pathophysiological influences and drug toxicity. Two mouse monoclonal antibodies were made against the purified ectodomain of kidney injury molecule-1 (Kim-1), and these were used to construct a sandwich Kim-1 ELISA. The assay range of this ELISA was 50 pg/ml to 5 ng/ml, with inter-and intra-assay variability of Ͻ10%. Urine samples were collected from rats treated with one of three doses of cisplatin (2.5, 5, or 7.5 mg/kg). At one day after each of the doses, there was an approximately three-to fivefold increase in the urine Kim-1 ectodomain, whereas other routinely used biomarkers measured in this study [plasma creatinine, blood urea nitrogen (BUN), urinary N-acetyl--glucosaminidase (NAG), glycosuria, proteinuria] lacked the sensitivity to show any sign of renal damage at this time point. When rats were subjected to increasing periods (10, 20, 30, or 45 min) of bilateral ischemia, there was an increasing amount of urinary Kim-1 detected. After only 10 min of bilateral ischemia, Kim-1 levels on day 1 were 10-fold higher (5 ng/ml) than control levels, whereas plasma creatinine and BUN were not increased and there was no glycosuria, increased proteinuria, or increased urinary NAG levels. Thus urinary Kim-1 levels serve as a noninvasive, rapid, sensitive, reproducible, and potentially high-throughput method to detect early kidney injury in pathophysiological studies and in preclinical drug development studies for risk-benefit profiling of pharmaceutical agents.
Pseudohypoaldosteronism type II is a salt-sensitive form of hypertension with hyperkalemia in humans caused by mutations in the with-no-lysine kinase 4 (WNK4). Several studies have shown that WNK4 modulates the activity of the renal Na + Cl − cotransporter, NCC. Because the renal consequences of WNK4 carrying pseudoaldosteronism type II mutations resemble the response to intravascular volume depletion (promotion of salt reabsorption without K + secretion), a condition that is associated with high angiotensin II (AngII) levels, it has been proposed that AngII signaling might affect WNK4 modulation of the NCC. In Xenopus laevis oocytes, WNK4 is required for modulation of NCC activity by AngII. To demonstrate that WNK4 is required in the AngII-mediated regulation of NCC in vivo, we used a total WNK4-knockout mouse strain (WNK4 −/− ). WNK4 mRNA and protein expression were absent in WNK4 −/− mice, which exhibited a mild Gitelman-like syndrome, with normal blood pressure, increased plasma renin activity, and reduced NCC expression and phosphorylation at T-58. Immunohistochemistry revealed normal morphology of the distal convoluted tubule with reduced NCC expression. Low-salt diet or infusion of AngII for 4 d induced phosphorylation of STE20/SPS1-related proline/alanine-rich kinase (SPAK) and of NCC at S-383 and T-58, respectively, in WNK4 +/+ but not WNK4 −/− mice. Thus, the absence of WNK4 in vivo precludes NCC and SPAK phosphorylation promoted by a low-salt diet or AngII infusion, suggesting that AngII action on the NCC occurs via a WNK4-SPAK-dependent signaling pathway. Additionally, stimulation of aldosterone secretion by AngII, but not by a high-K + diet, was impaired in WNK4 −/− mice. distal tubule | diuretics | thiazide | renin-angiotensin-aldosterone system
The Na ؉ :K ؉ :2Cl ؊ cotransporter (NKCC2) is the target of loop diuretics and is mutated in Bartter's syndrome, a heterogeneous autosomal recessive disease that impairs salt reabsorption in the kidney's thick ascending limb (TAL). Despite the importance of this cation/chloride cotransporter (CCC), the mechanisms that underlie its regulation are largely unknown. Here, we show that intracellular chloride depletion in Xenopus laevis oocytes, achieved by either coexpression of the K-Cl cotransporter KCC2 or low-chloride hypotonic stress, activates NKCC2 by promoting the phosphorylation of three highly conserved threonines (96, 101, and 111) in the amino terminus. Elimination of these residues renders NKCC2 unresponsive to reductions of [Cl ؊ ]i. The chloride-sensitive activation of NKCC2 requires the interaction of two serine-threonine kinases, WNK3 (related to WNK1 and WNK4, genes mutated in a Mendelian form of hypertension) and SPAK (a Ste20-type kinase known to interact with and phosphorylate other CCCs). WNK3 is positioned upstream of SPAK and appears to be the chloridesensitive kinase. Elimination of WNK3's unique SPAK-binding motif prevents its activation of NKCC2, as does the mutation of threonines 96, 101, and 111. A catalytically inactive WNK3 mutant also completely prevents NKCC2 activation by intracellular chloride depletion. Together these data reveal a chloride-sensing mechanism that regulates NKCC2 and provide insight into how increases in the level of intracellular chloride in TAL cells, as seen in certain pathological states, could drastically impair renal salt reabsorption.ion transport ͉ loop of Henle ͉ protein serine-threonine kinases ͉ hypertension ͉ diuretics
Mutations in the kinase WNK4 cause pseudohypoaldosteronism type II (PHAII), a syndrome featuring hypertension and high serum K ؉ levels (hyperkalemia). WNK4 has distinct functional states that regulate the balance between renal salt reabsorption and K ؉ secretion by modulating the activities of renal transporters and channels, including the Na-Cl cotransporter NCC and the K ؉ channel ROMK. WNK4's functions could enable differential responses to intravascular volume depletion (hypovolemia) and hyperkalemia. Because hypovolemia is uniquely associated with high angiotensin II (AngII) levels, AngII signaling might modulate WNK4 activity. We show that AngII signaling in Xenopus oocytes increases NCC activity by abrogating WNK4's inhibition of NCC but does not alter WNK4's inhibition of ROMK. This effect requires AngII, its receptor AT1R, and WNK4, and is prevented by the AT1R inhibitor losartan. NCC activity is also increased by WNK4 harboring mutations found in PHAII, and this activity cannot be further augmented by AngII signaling, consistent with PHAII mutations providing constitutive activation of the signaling pathway between AT1R and NCC. AngII's effect on NCC is also dependent on the kinase SPAK because dominant-negative SPAK or elimination of the SPAK binding motif in NCC prevent activation of NCC by AngII signaling. These effects extend to mammalian cells. AngII increases phosphorylation of specific sites on SPAK and NCC that are necessary for activation of each in mpkDCT cells. These findings place WNK4 in the signaling pathway between AngII and NCC, and provide a mechanism by which hypovolemia maximizes renal salt reabsoprtion without concomitantly increasing K ؉ secretion.angiotensin II receptor ͉ hypertension ͉ distal convoluted tubule ͉ salt reabsorption ͉ thiazide A ldosterone is released from the adrenal glomerulosa in 2 different physiologic conditions: intravascular volume depletion and hyperkalemia. In the former, aldosterone promotes maximal renal Na-Cl reabsorption to preserve and restore intravascular volume, whereas in the latter renal K ϩ secretion is maximized. Classical explanations for these alternative responses have focused on acute changes in solute delivery to the distal nephron. For example, in volume depletion there is enhanced proximal reabsorption of Na ϩ , which reduces the distal electrogenic reabsorption of Na ϩ via the epithelial sodium channel (ENaC) that is required to establish the electrical gradient necessary for K ϩ secretion.The rare autosomal dominant disease pseudohypoaldosteronism type II (PHAII) suggests there must be additional components that regulate the balance between renal salt reabsorption and potassium secretion. Patients with PHAII have chloridedependent hypertension and hyperkalemia despite otherwise normal renal function and normal aldosterone secretion, suggesting that they constitutively reabsorb Na-Cl at the expense of impaired K ϩ secretion. Missense mutations in the serinethreonine kinase WNK4 have been shown to cause PHAII (1). Subsequent studies in X...
The new disease produced by severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) represents a major pandemic event nowadays. Since its origin in China in December 2019, there is compelling evidence that novel SARS-CoV-2 is a highly transmissible virus, and it is associated to a broad clinical spectrum going from subclinical presentation to severe respiratory distress and multiorgan failure. Like other coronaviruses, SARS-CoV-2 recognizes human angiotensin-converting enzyme 2 as a cellular receptor that allows it to infect different host cells and likely disrupts renin-angiotensin-aldosterone system homeostasis. Particularly, a considerable incidence of many renal abnormalities associated to COVID-19 has been reported, including proteinuria, hematuria, and acute kidney injury. Moreover, it has been recently demonstrated that SARS-CoV-2 can infect podocytes and tubular epithelial cells, which could contribute to the development of the aforementioned renal abnormalities. In this review, we discuss the biological aspects of SARS-CoV-2 infection, how understanding current knowledge about SARS-CoV-2 infection may partly explain the involvement of the kidneys in the pathophysiology of COVID-19, and what questions have arisen and remain to be explored.
Our data show that aldosterone plays an important role as a mediator of renal injury induced by CsA. Thus, mineralocorticoid receptor blockade may be a potential strategy to prevent CsA nephrotoxicity.
SLC12A cation͞Cl ؊ cotransporters are mutated in human disease, are targets of diuretics, and are collectively involved in the regulation of cell volume, neuronal excitability, and blood pressure. This gene family has two major branches with different physiological functions and inverse regulation: K-Cl cotransporters (KCC1-KCC4) mediate cellular Cl ؊ efflux, are inhibited by phosphorylation, and are activated by dephosphorylation; Na-(K)-Cl cotransporters (NCC and NKCC1͞2) mediate cellular Cl ؊ influx and are activated by phosphorylation. A single kinase͞phosphatase pathway is thought to coordinate the activities of these cotransporters in a given cell; however, the mechanisms involved are as yet unknown. We previously demonstrated that WNK3, a paralog of serine-threonine kinases mutated in hereditary hypertension, is coexpressed with several cation͞Cl ؊ cotransporters and regulates their activity. Here, we show that WNK3 completely prevents the cell swelling-induced activation of KCC1-KCC4 in Xenopus oocytes. In contrast, catalytically inactive WNK3 abolishes the cell shrinkage-induced inhibition of KCC1-KCC4, resulting in a >100-fold stimulation of K-Cl cotransport during conditions in which transport is normally inactive. This activation is completely abolished by calyculin A and cyclosporine A, inhibitors of protein phosphatase 1 and 2B, respectively. Wild-type WNK3 activates Na-(K)-Cl cotransporters by increasing their phosphorylation, and catalytically inactive kinase inhibits Na-(K)-Cl cotransporters by decreasing their phosphorylation, such that our data suggest that WNK3 is a crucial component of the kinase͞phosphatase signaling pathway that coordinately regulates the Cl ؊ influx and efflux branches of the SLC12A cotransporter family.ion transport ͉ protein serine-threonine kinases ͉ hypertension ͉ cell volume regulation
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