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Author(s): William D. Wood [sup.1] , Ayah Elmaghrabi [sup.1] , Garrett Gotway [sup.2] , Matthias T. F. Wolf [sup.1] Author Affiliations: (1) grid.267313.2, 0000 0000 9482 7121, Pediatric Nephrology, University [...], Background Cobalamin C (cblC), a vitamin B12 processing protein, plays a crucial role in metabolism for the conversion of homocysteine to methionine and methylmalonyl-CoA to succinyl-CoA. CblC deficiency, an inborn error of cobalamin processing, is a rare cause of atypical hemolytic-uremic syndrome (aHUS) and results in hyperhomocysteinemia and methylmalonic aciduria. Both substances are thought to contribute to thrombotic microangiopathy (TMA) in cblC deficiency patients. However, the roles of homocysteine and methylmalonic acid (MMA) in these patients remain unclear. We want to shed more light on the contributions of homocysteine and MMA levels as contributing factors for thrombotic microangiopathy (TMA)/aHUS by a follow-up of a cblC deficiency patient over 6 years. Case diagnosis A 27-day-old Hispanic female presented with abnormal C3-carnitine on her newborn screen, poor feeding, decreased activity, and oligouria. She was diagnosed with cblC deficiency after laboratory results revealed elevated serum homocysteine, and serum MMA along with genetic testing showing a homozygous pathogenic frameshift variant in MMACHC. The patient developed aHUS and acute kidney injury (AKI), which resolved after appropriate therapy. Over 6 years, she continued to have normal kidney function with no thrombocytopenia despite persistently elevated homocysteine and MMA levels. Conclusion We question the roles of homocysteine and MMA as causative of aHUS/TMA in cblC deficiency as they remained elevated during follow-up but did not result in aHUS/TMA or AKI. Hyperhomocysteinemia and/or MMA caused by other metabolic diseases do not result in aHUS/TMA or AKI. This suggests that other nephrotoxic factors may trigger aHUS/TMA in cblC patients.

Author(s): Anthony J. Bleyer [sup.1] [sup.2] , Matthias T. Wolf [sup.3] , Kendrah O. Kidd [sup.1] [sup.2] , Martina Zivna [sup.2] , Stanislav Kmoch [sup.1] [sup.2] Author Affiliations: (1) grid.241167.7, [...], Autosomal dominant tubulointerstitial kidney disease (ADTKD) refers to a group of disorders with a bland urinary sediment, slowly progressive chronic kidney disease (CKD), and autosomal dominant inheritance. Due to advances in genetic diagnosis, ADTKD is becoming increasingly recognized as a cause of CKD in both children and adults. ADTKD-REN presents in childhood with mild hypotension, CKD, hyperkalemia, acidosis, and anemia. ADTKD-UMOD is associated with gout and CKD that may present in adolescence and slowly progresses to kidney failure. HNF1[beta] mutations often present in childhood with anatomic abnormalities such as multicystic or dysplastic kidneys, as well as CKD and a number of other extra-kidney manifestations. ADTKD-MUC1 is less common in childhood, and progressive CKD is its sole clinical manifestation, usually beginning in the late teenage years. This review describes the pathophysiology, genetics, clinical characteristics, diagnosis, and treatment of the different forms of ADTKD, with an emphasis on diagnosis. We also present data on kidney function in children with ADTKD from the Wake Forest Rare Inherited Kidney Disease Registry.

Osteoporosis after bariatric surgery is an increasing health concern as the rate of bariatric surgery has risen. In animal studies mimicking bariatric procedures, bone disease, together with decreased serum levels of Ca2+, Mg2+ and the gastric hormone Ghrelin were described. Ghrelin regulates metabolism by binding to and activating the growth hormone secretagogue receptor (GHSR) which is also expressed in the kidney. As calcium and magnesium are key components of bone, we tested the hypothesis that Ghrelin-deficiency contributes to osteoporosis via reduced upregulation of the renal calcium channel TRPV5 and the heteromeric magnesium channel TRPM6/7. We expressed GHSR with TRPV5 or TRPM6/7 channel in HEK293 cells and treated them with purified Ghrelin. Whole-cell current density was analyzed by patch-clamp recording. Nephron-specific gene expression was performed by tubular microdissection followed by qPCR in wild-type (WT) mice, and immunofluorescent imaging of GHSR-eGFP mice. Tubular magnesium homeostasis was analyzed in GHSR-null and WT mice at baseline and after caloric restriction. After Ghrelin exposure, whole-cell current density did not change for TRPV5 but increased for TRPM6/7 in a dose-dependent fashion. Applying the Ghrelin-mimetic (D-Trp7, Ala8,D-Phe10)-α-MSH (6-11) amide without and with the GHSR antagonist (D-Lys3)-GHRP6, we confirmed the stimulatory role of Ghrelin towards TRPM6/7. As GHSR initiates downstream signaling via protein kinase A (PKA), we found that the PKA inhibitor H89 abrogated TRPM6/7 stimulation by Ghrelin. Similarly, transfected Gαs, but not the Gαs mutant Q227L, nor Gαi2, Gαq, or Gα13 upregulated TRPM6/7 current density. In microdissected TALs and DCTs similar levels of GHSR mRNA were detected. In contrast, TRPM6 mRNA was expressed in the DCT and also detected in the TAL at 25% expression compared to DCT. Immunofluorescent studies using reporter GHSR-eGFP mice showed a strong eGFP signal in the TAL but surprisingly displayed no eGFP signal in the DCT. In 3-, 6-, and 9-month-old GHSR-null and WT mice, baseline serum magnesium was not significantly different, but 24-h urinary magnesium excretion was elevated in 9-month-old GHSR-null mice. In calorically restricted GHSR-null mice, we detected excess urinary magnesium excretion and reduced serum magnesium levels compared to WT mice. The kidneys from calorically restricted WT mice showed upregulated gene expression of magnesiotropic genes Hnf1b, Cldn-16, Cldn-19, Fxyd-2b, and Parvalbumin compared to GHSR-null mice. Our in vitro studies show that Ghrelin stimulates TRPM6/7 via GHSR and Gαs-PKA signaling. The murine studies are consistent with Ghrelin-GHSR signaling inducing reduced urinary magnesium excretion, particularly in calorically restricted mice when Ghrelin levels are elevated. This effect may be mediated by Ghrelin-upregulation of TRPM6 in the TAL and/or upregulation of other magnesiotropic genes. We postulate that rising Ghrelin levels with hunger contribute to increased renal Mg2+ reabsorption to compensate for lack of enteral Mg2+ uptake. [ABSTRACT FROM AUTHOR]

The cochlearols and ganocochlearins are natural products with unique antifibrotic and renoprotective activities in models of kidney disease. They represent compelling lead compounds for pharmacological intervention against kidney disease, often characterized by renal fibrosis. We report a four-step synthesis of (±)-cochlearol T ( 1 ) and the first reported syntheses of (±)-ganocochlearin A ( 2 ) and (±)-cochlearol Y ( 3 ) through a strategy that includes a Robinson annulation and unexpected oxidative aromatization. We also access tricyclic intermediate 12 that represents a formal synthesis of ganocins A-C and ganocochlearins C-D. We investigated the activity of these synthesized compounds in vitro by inducing fibrosis in a human kidney cell line with TGF-β1. The effect on fibrosis was assessed by qPCR and Western blot studies. We detected significantly lower mRNA gene and protein expression of fibrosis markers for all three natural products., Competing Interests: The authors declare no competing financial interest., (© 2024 American Chemical Society.)

Osteoporosis after bariatric surgery is an increasing health concern as the rate of bariatric surgery has risen. In animal studies mimicking bariatric procedures, bone disease, together with decreased serum levels of Ca 2+ , Mg 2+ and the gastric hormone Ghrelin were described. Ghrelin regulates metabolism by binding to and activating the growth hormone secretagogue receptor (GHSR) which is also expressed in the kidney. As calcium and magnesium are key components of bone, we tested the hypothesis that Ghrelin-deficiency contributes to osteoporosis via reduced upregulation of the renal calcium channel TRPV5 and the heteromeric magnesium channel TRPM6/7. We expressed GHSR with TRPV5 or TRPM6/7 channel in HEK293 cells and treated them with purified Ghrelin. Whole-cell current density was analyzed by patch-clamp recording. Nephron-specific gene expression was performed by tubular microdissection followed by qPCR in wild-type (WT) mice, and immunofluorescent imaging of GHSR-eGFP mice. Tubular magnesium homeostasis was analyzed in GHSR-null and WT mice at baseline and after caloric restriction. After Ghrelin exposure, whole-cell current density did not change for TRPV5 but increased for TRPM6/7 in a dose-dependent fashion. Applying the Ghrelin-mimetic (D-Trp 7 , Ala 8 ,D-Phe 10 )-α-MSH (6-11) amide without and with the GHSR antagonist (D-Lys 3 )-GHRP6, we confirmed the stimulatory role of Ghrelin towards TRPM6/7. As GHSR initiates downstream signaling via protein kinase A (PKA), we found that the PKA inhibitor H89 abrogated TRPM6/7 stimulation by Ghrelin. Similarly, transfected Gα s , but not the Gα s mutant Q227L, nor Gα i2 , Gα q , or Gα 13 upregulated TRPM6/7 current density. In microdissected TALs and DCTs similar levels of GHSR mRNA were detected. In contrast, TRPM6 mRNA was expressed in the DCT and also detected in the TAL at 25% expression compared to DCT. Immunofluorescent studies using reporter GHSR-eGFP mice showed a strong eGFP signal in the TAL but surprisingly displayed no eGFP signal in the DCT. In 3-, 6-, and 9-month-old GHSR-null and WT mice, baseline serum magnesium was not significantly different, but 24-h urinary magnesium excretion was elevated in 9-month-old GHSR-null mice. In calorically restricted GHSR-null mice, we detected excess urinary magnesium excretion and reduced serum magnesium levels compared to WT mice. The kidneys from calorically restricted WT mice showed upregulated gene expression of magnesiotropic genes Hnf1b , Cldn-16 , Cldn-19 , Fxyd-2b , and Parvalbumin compared to GHSR-null mice. Our in vitro studies show that Ghrelin stimulates TRPM6/7 via GHSR and Gα s -PKA signaling. The murine studies are consistent with Ghrelin-GHSR signaling inducing reduced urinary magnesium excretion, particularly in calorically restricted mice when Ghrelin levels are elevated. This effect may be mediated by Ghrelin-upregulation of TRPM6 in the TAL and/or upregulation of other magnesiotropic genes. We postulate that rising Ghrelin levels with hunger contribute to increased renal Mg 2+ reabsorption to compensate for lack of enteral Mg 2+ uptake., Competing Interests: JMZ owns stock in Eli Lilly, Novo Nordisk, and Medtronic. The other authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Nie, Zhang, Bal, Duran, An, Zigman, Baum, Hiremath, Marciano and Wolf.)

Magnesium (Mg 2+ ) is the second most common intracellular cation and the fourth most abundant element on earth. However, Mg 2+ is a frequently overlooked electrolyte and often not measured in patients. While hypomagnesemia is common in 15% of the general population, hypermagnesemia is typically only found in preeclamptic women after Mg 2+ therapy and in patients with ESRD. Mild to moderate hypomagnesemia has been associated with hypertension, metabolic syndrome, type 2 diabetes mellitus, CKD, and cancer. Nutritional Mg 2+ intake and enteral Mg 2+ absorption are important for Mg 2+ homeostasis, but the kidneys are the key regulators of Mg 2+ homeostasis by limiting urinary excretion to less than 4% while the gastrointestinal tract loses over 50% of the Mg 2+ intake in the feces. Here, we review the physiological relevance of Mg 2+ , the current knowledge of Mg 2+ absorption in the kidneys and the gut, the different causes of hypomagnesemia, and a diagnostic approach on how to assess Mg 2+ status. We highlight the latest discoveries of monogenetic conditions causing hypomagnesemia, which have enhanced our understanding of tubular Mg 2+ absorption. We will also discuss external and iatrogenic causes of hypomagnesemia and advances in the treatment of hypomagnesemia., (Copyright © 2022 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.)

Background: Treatment with the aminoglycoside antibiotic gentamicin can be associated with severe adverse effects, including renal Ca 2+ wasting. The underlying mechanism is unknown but it has been proposed to involve activation of the Ca 2+ -sensing receptor (CaSR) in the thick ascending limb, which would increase expression of claudin-14 (CLDN14) and limit Ca 2+ reabsorption. However, no direct evidence for this hypothesis has been presented., Methods: We studied the effect of gentamicin in vivo using mouse models with impaired Ca 2+ reabsorption in the proximal tubule and the thick ascending limb. We used a Cldn14 promoter luciferase reporter assay to study CaSR activation and investigated the effect of gentamicin on activity of the distal nephron Ca 2+ channel transient receptor potential vanilloid 5 (TRPV5), as determined by patch clamp in HEK293 cells., Results: Gentamicin increased urinary Ca 2+ excretion in wild-type mice after acute and chronic administration. This calciuretic effect was unaltered in mice with genetic CaSR overactivation and was present in furosemide-treated animals, whereas the calciuretic effect in Cldn14 -/- mice and mice with impaired proximal tubular Ca 2+ reabsorption (claudin-2 [CLDN2]-deficient Cldn2 -/- mice) was equivalent to that of wild-type mice. In vitro , gentamicin failed to activate the CaSR. In contrast, patch clamp analysis revealed that gentamicin strongly inhibited rabbit and human TRPV5 activity and chronic gentamicin administration downregulated distal nephron Ca 2+ transporters., Conclusions: Gentamicin does not cause hypercalciuria via activation of the CaSR-CLDN14 pathway or by interfering with proximal tubular CLDN2-dependent Ca 2+ reabsorption. Instead, gentamicin blocks distal Ca 2+ reabsorption by direct inhibition of the Ca 2+ channel TRPV5. These findings offer new insights into Ca 2+ wasting in patients treated with gentamicin., (Copyright © 2022 by the American Society of Nephrology.)