Soluble (Pro)Renin Receptor as a Negative Regulator of NCC (Na + -Cl – Cotransporter) Activity

NCC (Na + -Cl − cotransporter), uniquely located at the distal convoluted tubule (DCT), is the target of thiazide diuretics and critically involved in renal handling of both Na + and K + . However, the mechanism of how NCC activity is regulated remains incompletely understood. Here, we report a novel role of PRR ([pro]renin receptor) and its cleavage product sPRR (soluble PRR) via S1P (site-1 protease) as negative regulators of NCC during high-salt or high K + loading. Under basal condition, mice with DCT-specific deletion of PRR (DCT PRR KO) exhibited modest hypertension associated with reduced urinary Na + , K + , and Cl − excretion due to increased NCC activity. Following a high-salt diet, DCT PRR KO mice exhibited a ≈25 mm Hg increase of mean arterial pressure contrasting to salt resistance in the floxed controls. The null mice also exhibited impaired kaliuresis and hyperkalemia after high K + intake. This phenotype was recapitulated by treatment of C57/BL6 mice with S1P inhibitor PF429242. In cultured Flp-In T-REx 293 NCC cells, S1P-derived sPRR directly dephosphorylated NCC via activation of AT1R (angiotensin II receptor type 1). Taken together, the present study has demonstrated that S1P-derived sPRR via AT1R negatively regulates NCC activity in the DCT to render salt resistance and to promote K + excretion.

Magnesium Metabolism in Chronic Alcohol-Use Disorder: Meta-Analysis and Systematic Review

Chronic alcohol-use disorder has been imputed as a possible cause of dietary magnesium depletion. The purpose of this study was to assess the prevalence of hypomagnesemia in chronic alcohol-use disorder, and to provide information on intracellular magnesium and on its renal handling. We carried out a structured literature search up to November 2020, which returned 2719 potentially relevant records. After excluding non-significant records, 25 were retained for the final analysis. The meta-analysis disclosed that both total and ionized circulating magnesium are markedly reduced in chronic alcohol-use disorder. The funnel plot and the Egger’s test did not disclose significant publication bias. The I2-test demonstrated significant statistical heterogeneity between studies. We also found that the skeletal muscle magnesium content is reduced and the kidney’s normal response to hypomagnesemia is blunted. In conclusion, magnesium depletion is common in chronic alcohol-use disorder. Furthermore, the kidney plays a crucial role in the development of magnesium depletion.

Renal Handling of Albumin—From Early Findings to Current Concepts

Albumin is the main protein of blood plasma, lymph, cerebrospinal and interstitial fluid. The protein participates in a variety of important biological functions, such as maintenance of proper colloidal osmotic pressure, transport of important metabolites and antioxidant action. Synthesis of albumin takes place mainly in the liver, and its catabolism occurs mostly in vascular endothelium of muscle, skin and liver, as well as in the kidney tubular epithelium. Long-lasting investigation in this area has delineated the principal route of its catabolism involving glomerular filtration, tubular endocytic uptake via the multiligand scavenger receptor tandem—megalin and cubilin-amnionless complex, as well as lysosomal degradation to amino acids. However, the research of the last few decades indicates that also additional mechanisms may operate in this process to some extent. Direct uptake of albumin in glomerular podocytes via receptor for crystallizable region of immunoglobulins (neonatal FC receptor) was demonstrated. Additionally, luminal recycling of short peptides into the bloodstream and/or back into tubular lumen or transcytosis of whole molecules was suggested. The article discusses the molecular aspects of these processes and presents the major findings and controversies arising in the light of the research concerning the last decade. Their better characterization is essential for further research into pathophysiology of proteinuric renal failure and development of effective therapeutic strategies.

Fluid-induced harm in the hospital: look beyond volume and start considering sodium. From physiology towards recommendations for daily practice in hospitalized adults

Purpose Iatrogenic fluid overload is a potential side effect of intravenous fluid therapy in the hospital. Little attention has been paid to sodium administration as a separate cause of harm. With this narrative review, we aim to substantiate the hypothesis that a considerable amount of fluid-induced harm is caused not only by fluid volume, but also by the sodium that is administered to hospitalized patients. Methods We show how a regular dietary sodium intake is easily surpassed by the substantial amounts of sodium that are administered during typical hospital stays. The most significant sodium burdens are caused by isotonic maintenance fluid therapy and by fluid creep, defined as the large volume unintentionally administered to patients in the form of dissolved medication. In a section on physiology, we elaborate on the limited renal handling of an acute sodium load. We demonstrate how the subsequent retention of water is an energy-demanding, catabolic process and how free water is needed to excrete large burdens of sodium. We quantify the effect size of sodium-induced fluid retention and discuss its potential clinical impact. Finally, we propose preventive measures, discuss the benefits and risks of low-sodium maintenance fluid therapy, and explore options for reducing the amount of sodium caused by fluid creep. Conclusion The sodium burdens caused by isotonic maintenance fluids and fluid creep are responsible for an additional and avoidable derailment of fluid balance, with presumed clinical consequences. Moreover, the handling of sodium overload is characterized by increased catabolism. Easy and effective measures for reducing sodium load and fluid retention include choosing a hypotonic rather than isotonic maintenance fluid strategy (or avoiding these fluids when enough free water is provided through other sources) and dissolving as many medications as possible in glucose 5%.

Role of OATP4C1 in Renal Handling of Remdesivir and its Nucleoside Analog GS-441524: The First Approved Drug for Patients with COVID-19

Purpose. Remdesivir and its active metabolite are predominantly eliminated via renal route; however, information regarding renal uptake transporters is limited. In the present study, the interaction of remdesivir and its nucleoside analog GS-441524 with OATP4C1 was evaluated to provide the detailed information about its renal handling. Methods. We used HK-2 cells, a proximal tubular cell line derived from normal kidney, to confirm the transport of remdesivir and GS-441524. To assess the involvement of OATP4C1 in handling remdesivir and GS-441524, the uptake study of remdesivir and GS-441524 was performed by using OATP4C1-overexpressing Madin-Darby canine kidney II (MDCKII) cells. Moreover, we also evaluated the IC50 and Ki value of remdesivir. Results. The time-dependent remdesivir uptake in HK-2 cells was observed. The results of inhibition study using OATs and OCT2 inhibitors and OATP4C1 knockdown suggested the involvement of renal drug transporter OATP4C1. Remdesivir was taken up by OATP4C1/MDCKII cells. OATP4C1-mediated uptake of remdesivir increased linearly up to 10 min and reached a steady state at 30 min. Remdesivir inhibited OATP4C1-mediated transport in a concentration-dependent manner with the IC50 and apparent Ki values of 42 ± 7.8 μM and 37 ± 6.9 μM, respectively. Conclusions. We have provided novel information about renal handling of remdesivir. Furthermore, we evaluated the potential drug interaction via OATP4C1 by calculating the Ki value of remdesivir. OATP4C1 may play a pivotal role in remdesivir therapy for COVID-19, particularly in patients with kidney injury.

Effect of Experimental Fanconi Syndrome on Tubular Reabsorption of Lithium in Rats

Lithium, administered to patients of bipolar disorders, is mainly excreted into urine, and tubular reabsorption at the proximal tubule is involved in the renal handling of lithium. In this study, we examined the renal excretion of lithium in rats with Fanconi syndrome, characterized by defects of transports of various compounds at the proximal tubules, induced by maleic acid. After maleic acid was intravenously injected, mannitol and lithium chloride were infused in turn. Using samples of plasma and bladder urine during the mannitol infusion, renal parameters were determined. Pharmacokinetic parameters of lithium were obtained using samples during the lithium chloride infusion. Maleic acid decreased creatinine clearance and increased the fractional excretion of glucose and phosphate, suggesting the induction of Fanconi syndrome. In rats with Fanconi syndrome, plasma concentration of lithium was increased, and its renal clearance was decreased. No effect on the fractional excretion of lithium was exhibited. This study represents that the tubular reabsorption of lithium was impaired to the same degree with glomerular filtration in rats with experimental Fanconi syndrome and that the dysfunction of the tubular reabsorption of glucose and phosphate was more severe. It is possible that Fanconi syndrome inhibited the reabsorption of lithium at the proximal tubule and facilitated the reabsorption of lithium from the loop of Henle to the collecting duct.

Deranged Coagulation Profile Secondary to Cefazolin Use: Case Report

Cefazolin is a widely used first-generation cephalosporin. While generally well tolerated, several case reports have described severe coagulopathy induced by intravenous (IV) cefazolin. This was seen particularly in patients with impaired renal function, where antibiotic choice is limited and may require specific dose adjustments. Altered renal handling of antibiotics and their metabolites may potentiate toxicity and side effects. We report a case of a 72-year-old Chinese man who had been treated for methicillin-sensitive staphylococcus aureus (MSSA, coagulase-positive) infective endocarditis with cefazolin and, consequently, developed significantly elevated international normalised ratio (INR) while on therapy. This resolved within 48 h after cessation of cefazolin and administration of oral vitamin K. Malnourished patients with pre-existing or acute kidney injury may be at an increased risk of cefazolin-related coagulopathy.

Effect of sodium-glucose cotransporter-2 inhibitors on renal handling of electrolytes

Sodium-glucose cotransporter-2 inhibitors (SGLT2i) are the latest introduction into the armamentarium of diabetes care in the present decade. By virtue of their beneficial effects, such as blood pressure-lowering, bodyweight reduction and significant renal and cardioprotective effects which extends beyond their glycaemic control effects, SGLT2i have become one of the most preferred oral antihyperglycaemic agents of recent times. However, they can influence tubular handling of electrolytes that can result in some electrolyte disturbances such as alteration in the serum levels of magnesium, potassium and phosphate levels. Some of these changes are mild or transient and may not have significant clinical implications. The underlying putative mechanism(s) responsible for disturbances of electrolytes are yet to be deciphered. In this review, we aim to describe electrolytes and acid–base abnormalities due to SGLT2i as well as to elucidate the underlying mechanism.