The potential role of Na-K-ATPase and its signaling in the development of anemia in chronic kidney disease

Interplay between the Redox System and Renal Tubular Transport

The kidney plays a critical role in maintaining the homeostasis of body fluid by filtration of metabolic wastes and reabsorption of nutrients. Due to the overload, a vast of energy is required through aerobic metabolism, which inevitably leads to the generation of reactive oxygen species (ROS) in the kidney. Under unstressed conditions, ROS are counteracted by antioxidant systems and maintained at low levels, which are involved in signal transduction and physiological processes. Accumulating evidence indicates that the reduction-oxidation (redox) system interacts with renal tubular transport. Redox imbalance or dysfunction of tubular transport leads to renal disease. Here, we discuss the ROS and antioxidant systems in the kidney and outline the metabolic dysfunction that is a common feature of renal disease. Importantly, we describe the key molecules involved in renal tubular transport and their relationship to the redox system and, finally, summarize the impact of their dysregulation on the pathogenesis and progression of acute and chronic kidney disease.

Exposure to low dose of Bisphenol A (BPA) intensifies kidney oxidative stress, inflammatory factors expression and modulates Angiotensin II signaling under hypertensive milieu

Humans are constantly exposed to low concentrations of ubiquitous environmental pollutant, Bisphenol A (BPA). Due to the prevalence of hypertension (one of the major risk factors of cardiovascular disease [CVD]) in the population, it is necessary to explore the adverse effect of BPA under hypertension associated pathogenic milieu. The current study exposed the Nω-nitro-l-arginine methyl ester (L-NAME) induced hypertensive Wistar rats to low dose BPA (50 μg/kg) for 30 days period. In tissue samples immunohistochemistry, real-time quantitative polymerase chain reaction and enzymatic assays were conducted. Moreover, studies on primary kidney cell culture were employed to explore the impact of low dose of BPA exposure at nanomolar level (20-80 nM range) on renal cells through various fluorescence assays. The observed results illustrate that BPA exposure potentiates/aggravates hypertension induced tissue abnormalities (renal fibrosis), oxidative stress (ROS generation), elevated angiotensin-converting enzyme activity, malfunction of the antioxidant and tricarboxylic acid cycle enzymes, tissue lipid abnormalities and inflammatory factor expression (both messenger RNA and protein level of TNF-α and IL-6). Further, in vitro exposure of nM levels of BPA to primary kidney cells modulates oxidative stress (both superoxide and total ROS), mitochondrial physiology (reduced mitochondrial transmembrane potential-∆ψm) and lipid peroxidation in a dose dependent manner. In addition, angiotensin II induced ROS generation was aggravated further by BPA during coexposure in kidney cells. Therefore, during risk assessment, a precise investigation on BPA exposure in hypertensive (CVD vulnerable) populations is highly suggested.

Normalization of the ATP1A1 Signalosome Rescinds Epigenetic Modifications and Induces Cell Autophagy in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide. In metabolic dysfunction-associated steatohepatitis (MASH)-related HCC, cellular redox imbalance from metabolic disturbances leads to dysregulation of the α1-subunit of the Na/K-ATPase (ATP1A1) signalosome. We have recently reported that the normalization of this pathway exhibited tumor suppressor activity in MASH-HCC. We hypothesized that dysregulated signaling from the ATP1A1, mediated by cellular metabolic stress, promotes aberrant epigenetic modifications including abnormal post-translational histone modifications and dysfunctional autophagic activity, leading to HCC development and progression. Increased H3K9 acetylation (H3K9ac) and H3K9 tri-methylation (H3K9me3) were observed in human HCC cell lines, HCC-xenograft and MASH-HCC mouse models, and epigenetic changes were associated with decreased cell autophagy in HCC cell lines. Inhibition of the pro-autophagic transcription factor FoxO1 was associated with elevated protein carbonylation and decreased levels of reduced glutathione (GSH). In contrast, normalization of the ATP1A1 signaling significantly decreased H3K9ac and H3K9me3, in vitro and in vivo, with concomitant nuclear localization of FoxO1, heightening cell autophagy and cancer-cell apoptotic activities in treated HCC cell lines. Our results showed the critical role of the ATP1A1 signalosome in HCC development and progression through epigenetic modifications and impaired cell autophagy activity, highlighting the importance of the ATP1A1 pathway as a potential therapeutic target for HCC.

Development and validation of a nomogram for assessment postoperative sodium disturbance in PAs patients: a retrospective cohort study

Background

Pituitary adenomas (PAs) are neuroendocrine tumors located in the sellar region. Surgery, being the primary treatment option for most PAs, is known to cause disruptions in sodium metabolism.

Objective

To develop and validate a nomogram for assessment the incidence of postoperative sodium disturbance (SD) in patients with PAs.

Methods

In this retrospective study, 208 patients with PAs who underwent resection surgery between 2013 and 2020 were included. Various demographic characteristics, clinical features and laboratory data were analyzed as potential predictors of postoperative sodium disturbance (SD). LASSO regression were used to identify independent preoperative variables associated with SD. Logistic regression was employed to calculate odds ratios (ORs) and 95% confidence intervals (CIs). A nomogram was constructed to visualize these results and evaluated using metrics such as the area under the curve (AUC) for discrimination, the Hosmer-Lemeshow test for calibration and decision curve for usefulness assessment.

Results

The incidence of SD was 44.23% (92 cases out of 208). Six preoperative factors, including sex, types of PAs, phosphocreatine kinase (CK), serum iron (Fe), free fatty acids (NEFA) and mean corpuscular volume (MCV), were identified for constructing a predictive nomogram. The nomogram showed high accuracy, with AUC values of 0.851 (95% CI [0.799-0.923]) and 0.771 (95% CI [0.681-0.861]) in the training and validation datasets, respectively. Calibration assessment and decision curve analysis confirmed its good agreement and clinical utility.

Conclusion

A practical and effective nomogram for predicting SD after PAs surgery is presented in this study.

The Na+,K+-ATPase and its stoichiometric ratio: some thermodynamic speculations

 Almost seventy years after its discovery, the sodium-potassium adenosine triphosphatase (the sodium pump) located in the cell plasma membrane remains a source of novel mechanistic and physiologic findings. A noteworthy feature of this enzyme/transporter is its robust stoichiometric ratio under physiological conditions: it sequentially counter-transports three sodium ions and two potassium ions against their electrochemical potential gradients per each hydrolyzed ATP molecule. Here we summarize some present knowledge about the sodium pump and its physiological roles, and speculate whether energetic constraints may have played a role in the evolutionary selection of its characteristic stoichiometric ratio.

Blockage of the Na-K-ATPase signaling-mediated oxidant amplification loop elongates red blood cell half-life and ameliorates uremic anemia induced by 5/6th PNx in C57BL/6 mice

We have previously demonstrated that the Na-K-ATPase signaling-mediated oxidant amplification loop contributes to experimental uremic cardiomyopathy and anemia induced by 5/6th partial nephrectomy (PNx). This process can be ameliorated by systemic administration of the peptide pNaKtide, which was designed to block this oxidant amplification loop. The present study demonstrated that the PNx-induced anemia is characterized by marked decreases in red blood cell (RBC) survival as assessed by biotinylated RBC clearance and eryptosis as assessed by annexin V binding. No significant change in iron homeostasis was observed. Examination of plasma samples demonstrated that PNx induced significant increases in systemic oxidant stress as assessed by protein carbonylation, plasma erythropoietin concentration, and blood urea nitrogen. Systemic administration of pNaKtide, but not NaKtide (pNaKtide without the TAT leader sequence) and a scramble "pNaKtide" (sc-pNaKtide), led to the normalization of hematocrit, RBC survival, and plasma protein carbonylation. Administration of the three peptides had no significant effect on PNx-induced increases in plasma erythropoietin and blood urea nitrogen without notable changes in iron metabolism. These data indicate that blockage of the Na-K-ATPase signaling-mediated oxidant amplification loop ameliorates the anemia of experimental renal failure by increasing RBC survival.NEW & NOTEWORTHY The anemia of CKD is multifactorial, and the current treatment based primarily on stimulating bone marrow production of RBCs with erythropoietin or erythropoietin analogs is unsatisfactory. In a murine model of CKD that is complicated by anemia, blockade of Na-K-ATPase signaling with a specific peptide (pNaKtide) ameliorated the anemia primarily by increasing RBC survival. Should these results be confirmed in patients, this strategy may allow for novel and potentially additive strategies to treat the anemia of CKD.

Coordinated Contribution of NADPH Oxidase- and Mitochondria-Derived Reactive Oxygen Species in Metabolic Syndrome and Its Implication in Renal Dysfunction

Metabolic syndrome (MetS), a complex of interrelated risk factors for cardiovascular disease and diabetes, is comprised of central obesity (increased waist circumference), hyperglycemia, dyslipidemia (high triglyceride blood levels, low high-density lipoprotein blood levels), and increased blood pressure. Oxidative stress, caused by the imbalance between pro-oxidant and endogenous antioxidant systems, is the primary pathological basis of MetS. The major sources of reactive oxygen species (ROS) associated with MetS are nicotinamide-adenine dinucleotide phosphate (NADPH) oxidases and mitochondria. In this review, we summarize the current knowledge regarding the generation of ROS from NADPH oxidases and mitochondria, discuss the NADPH oxidase- and mitochondria-derived ROS signaling and pathophysiological effects, and the interplay between these two major sources of ROS, which leads to chronic inflammation, adipocyte proliferation, insulin resistance, and other metabolic abnormalities. The mechanisms linking MetS and chronic kidney disease are not well known. The role of NADPH oxidases and mitochondria in renal injury in the setting of MetS, particularly the influence of the pyruvate dehydrogenase complex in oxidative stress, inflammation, and subsequent renal injury, is highlighted. Understanding the molecular mechanism(s) underlying MetS may lead to novel therapeutic approaches by targeting the pyruvate dehydrogenase complex in MetS and prevent its sequelae of chronic cardiovascular and renal diseases.