Hypoxic Kidney Research Articles

Tripterygium drug-loaded liposome alleviates renal function by promoting vascularization and inhibiting fibrosis.

Introduction: Tripterygium species have been traditionally used in Chinese medicine for treating various conditions. The aim of the study was to construct a drug-modified renal infarction targeting liposome (rTor-LIP) containing Tripterygium in order to improve the therapeutic effect on renal injury. Methods: rTor-LIP was prepared using the extruder method containing Tripterygium solution. The preparation was characterized by transmission electron microscopy, Marvin laser particle size analyzer, and Western blotting. In vitro experiments were conducted to verify the biocompatibility of rTor-LIP, and in vivo experiments were conducted to verify the therapeutic effect of rTor- LIP on renal injury. Results and discussion: The surface of rTor-LIP was regular and oval. In vitro results showed that after co-incubation with rTor-LIP, endothelial cells did not show significant apoptosis, and there were no significant abnormalities in the mitochondrial metabolism. The in vivo results showed that the morphology of endothelial cells in the rTor-LIP group was uniform and the cytoplasmic striations were clear, but the local striations had disappeared. Thus, rTor-LIP nano-targeted liposomes can effectively target hypoxic kidney tissue, providing a new idea for the treatment of renal infarction.

Shen-Shuai-II-Recipe inhibits tubular inflammation by PPARα-mediated fatty acid oxidation to attenuate fibroblast activation in fibrotic kidneys

BackgroundShen Shuai Ⅱ Recipe (SSR) is clinically used to treat chronic kidney diseases (CKDs) with remarkable efficacy and safety. In earlier research, we found the anti-inflammatory, antioxidant, and mitochondrial protective properties of SSR in hypoxic kidney injury model, which is closely related to its renal protection. Further work is needed to understand the underlying molecular mechanisms. PurposeFurther investigation of the mechanisms of action of SSR against renal interstitial fibrosis (RIF) building on previous research leads. MethodsRats receiving CKD model surgery were given with Fenofibrate or SSR once a day for eight weeks. In vitro, the NRK-52E cells were treated with SSR in the presence or absence of 10 μM Sc75741, 0.5 μM PMA, or 1 μM fenofibrate under 1% O2. The effects of SSR on NF-κB/NLRP3 inflammatory cascade, secretion of pro-inflammatory cytokines, fatty acid oxidation (FAO), and renal tubular injury were determined by immunoblotting, luminex liquid suspension chip assay, transmission electron microscopy, and Oil red O staining. Next, we delivered PPARα-interfering sequences to kidney tissue and NRK-52E cells by adeno-associated virus (AAV) injection and siRNA transfection methods. Finally, we evaluated the effect of renal tubular cells on fibroblast activation by co-culture method. ResultsSSR attenuated the release of IL-18, VEGF, and MCP1 cytokines, inhibited the activation of NF-κB/NLRP3 cascade, increased the PPARα, CPT-1α, CPT-2, ACADL, and MCAD protein expression, and improved the lipid accumulation. Further studies have demonstrated that one of the ways in which SSR suppresses the inflammatory response to protect renal tubular cells is through the restoration of PPARα-mediated FAO. In addition, by means of co-culture ways, the results demonstrated that SSR attenuated secretion of inflammatory mediators in NRK-52E cells by PPARα/NF-κB/NLRP3 pathway, thereby inhibiting renal fibroblast activation. ConclusionSSR inhibits RIF by suppressing inflammatory response of hypoxia-exposed RTECs through PPARα-mediated FAO.

Human proximal tubular epithelial cell-derived small extracellular vesicles mediate synchronized tubular ferroptosis in hypoxic kidney injury

Hypoxia is the key pathobiological trigger of tubular oxidative stress and cell death that drives the transition of acute kidney injury (AKI) to chronic kidney disease (CKD). The mitochondrial-rich proximal tubular epithelial cells (PTEC) are uniquely sensitive to hypoxia and thus, are pivotal in propagating the sustained tubular loss of AKI-to-CKD transition. Here, we examined the role of PTEC-derived small extracellular vesicles (sEV) in propagating the ‘wave of tubular death’.Ex vivo patient-derived PTEC were cultured under normoxia (21 % O2) and hypoxia (1 % O2) on Transwell inserts for isolation and analysis of sEV secreted from apical versus basolateral PTEC surfaces. Increased numbers of sEV were secreted from the apical surface of hypoxic PTEC compared with normoxic PTEC. No differences in basolateral sEV numbers were observed between culture conditions. Biological pathway analysis of hypoxic-apical sEV cargo identified distinct miRNAs linked with cellular injury pathways. In functional assays, hypoxic-apical sEV selectively induced ferroptotic cell death (↓glutathione peroxidase-4, ↑lipid peroxidation) in autologous PTEC compared with normoxic-apical sEV. The addition of ferroptosis inhibitors, ferrostatin-1 and baicalein, attenuated PTEC ferroptosis. RNAse A pretreatment of hypoxic-apical sEV also abrogated PTEC ferroptosis, demonstrating a role for sEV RNA in ferroptotic ‘wave of death’ signalling. In line with these in vitro findings, in situ immunolabelling of diagnostic kidney biopsies from AKI patients with clinical progression to CKD (AKI-to-CKD transition) showed evidence of ferroptosis propagation (increased numbers of ACSL4+ PTEC), while urine-derived sEV (usEV) from these ‘AKI-to-CKD transition’ patients triggered PTEC ferroptosis (↑lipid peroxidation) in functional studies.Our data establish PTEC-derived apical sEV and their intravesicular RNA as mediators of tubular lipid peroxidation and ferroptosis in hypoxic kidney injury. This concept of how tubular pathology is propagated from the initiating insult into a ‘wave of death’ provides novel therapeutic check-points for targeting AKI-to-CKD transition.

Opioids and the kidney: two sides of the same coin.

Renal dysfunction, including acute renal failure (ARF) and chronic kidney disease (CKD), continues to present significant health challenges, with renal ischemia-reperfusion injury (IRI) being a pivotal factor in their development and progression. This condition, notably impacting kidney transplantation outcomes, underscores the urgent need for innovative therapeutic interventions. The role of opioid agonists in this context, however, remains a subject of considerable debate. Current reviews tend to offer limited perspectives, focusing predominantly on either the protective or detrimental effects of opioids in isolation. Our review addresses this gap through a thorough and comprehensive evaluation of the existing literature, providing a balanced examination of the dualistic nature of opioids' influence on renal health. We delve into both the nephroprotective and nephrotoxic aspects of opioids, dissecting the complex interactions and paradoxical effects that embody the "two sides of the same coin" phenomenon. This comprehensive analysis is vital for understanding the intricate roles of opioids in renal pathophysiology, potentially informing the development of novel therapeutic strategies for preventing or treating hypoxic kidney injury.

Untargeted metabolomics analysis on kidney tissues from mice reveals potential hypoxia biomarkers

Chronic hypoxia may have a huge impact on the cardiovascular and renal systems. Advancements in microscopy, metabolomics, and bioinformatics provide opportunities to identify new biomarkers. In this study, we aimed at elucidating the metabolic alterations in kidney tissues induced by chronic hypoxia using untargeted metabolomic analyses. Reverse phase ultrahigh performance liquid chromatography-mass spectroscopy/mass spectroscopy (RP–UPLC–MS/MS) and hydrophilic interaction liquid chromatography (HILIC)–UPLC–MS/MS methods with positive and negative ion mode electrospray ionization were used for metabolic profiling. The metabolomic profiling revealed an increase in metabolites related to carnitine synthesis and purine metabolism. Additionally, there was a notable increase in bilirubin. Heme, N-acetyl-l-aspartic acid, thyroxine, and 3-beta-Hydroxy-5-cholestenoate were found to be significantly downregulated. 3-beta-Hydroxy-5-cholestenoate was downregulated more significantly in male than female kidneys. Trichome Staining also showed remarkable kidney fibrosis in mice subjected to chronic hypoxia. Our study offers potential intracellular metabolite signatures for hypoxic kidneys.

Anemia and Hypoxia Impact on Chronic Kidney Disease Onset and Progression: Review and Updates.

Chronic kidney disease (CKD) is caused by hypoxia in the renal tissue, leading to inflammation and increased migration of pathogenic cells. Studies showed that leukocytes directly sense hypoxia and respond by initiating gene transcription, encoding the 2-integrin adhesion molecules. Moreover, other mechanisms participate in hypoxia, including anemia. CKD-associated anemia is common, which induces and worsens hypoxia, contributing to CKD progression. Anemia correction can slow CKD progression, but it should be cautiously approached. In this comprehensive review, the underlying pathophysiology mechanisms and the impact of renal tissue hypoxia and anemia in CKD onset and progression will be reviewed and discussed in detail. Searching for the latest updates in PubMed Central, Medline, PubMed database, Google Scholar, and Google search engines were conducted for original studies, including cross-sectional studies, cohort studies, clinical trials, and review articles using different keywords, phrases, and texts such as "CKD progression, anemia in CKD, CKD, anemia effect on CKD progression, anemia effect on CKD progression, and hypoxia and CKD progression". Kidney tissue hypoxia and anemia have an impact on CKD onset and progression. Hypoxia causes nephron cell death, enhancing fibrosis by increasing interstitium protein deposition, inflammatory cell activation, and apoptosis. Severe anemia correction improves life quality and may delay CKD progression. Detection and avoidance of the risk factors of hypoxia prevent recurrent acute kidney injury (AKI) and reduce the CKD rate. A better understanding of kidney hypoxia would prevent AKI and CKD and leadto new therapeutic strategies.

Development of renal fibrosis in patients with chronic kidney disease: Mechanisms, biomarkers, and clinical implications

CKD is a global health concern with significant implications for patients' well-being, morbidity, and mortality. The underlying mechanism of CKD development often involves progressive interstitial fibrosis. Understanding the processes and factors influencing fibrogenesis is crucial. This review aims to analyze recent literature on the pathophysiological mechanisms, early diagnosis, prevention, and treatment of renal fibrosis in CKD patients. It explores various aspects of kidney fibrogenesis, highlighting key pathogenic factors and signaling pathways that warrant further investigation.
 The review emphasizes the potential of urinary uromodulin (uUmod) as a biomarker for early renal fibrosis diagnosis and delves into the role of anemia, kidney hypoxia, vitamin D, and unique aspects of fibrosis development in diabetic kidney disease patients. Furthermore, it underscores the importance of inhibiting the renin-angiotensin-aldosterone system (RAAS) as a strategy for fibrosis prevention and attenuation.

7-LB: Sodium–Glucose Cotransporter-2 Inhibitors (SGLT2i) Decrease Kidney Oxygen Consumption in Adults with Type 2 Diabetes (T2D)—A Randomized Clinical Trial Using 11C-Acetate Positron Emission Tomography (PET) Imaging

Kidney hypoxia has been proposed as key pathophysiological mechanism in the development of chronic kidney disease, potentially stemming from a mismatch between oxygen delivery and oxygen consumption. SGLT2i are kidney protective drugs that initially lower glomerular filtration rate (GFR). Accordingly, we hypothesized that SGLT2i lower kidney oxygen consumption by reducing GFR and associated tubular workload. Twenty adults with T2D (sex 80% male, age 68±6 years, BMI 30±4 kg/m2, HbA1c 7.5±0.9%, eGFR 76 ± 11 mL/min/1.73m2) received a 4-week treatment with SGLT2i ertugliflozin (ERTU) and matched placebo (PLB) in a randomized, double-blind cross-over study. Participants were treated with metformin and received maximal tolerable dose of an angiotensin receptor blocker. Whole-kidney oxygen consumption (Kmono) was measured by PET using 11C-acetate. GFR was measured by gold-standard iohexol clearance. Tubular sodium transport (TNa) was calculated by kidney sodium load (([arterial Na]*mGFR) - urinary sodium excretion). Kidney efficiency calculated as TNa/ Kmono. GFR was lower during ERTU (94 ± 14 mL/min) vs. PLB (99 ± 15 mL/min) treatment (p=0.02). Kmono was 0.086 ± 0.006 min-1 during ERTU and 0.091 ± 0.009 min-1 during PLB (p<0.01). Kidney sodium load (12.9 ± 1.90 vs 13.7 ± 2.22 mmol/min) and TNa (12.7 ± 1.87 vs 13.6 ± 2.18 mmol/min) were lower during ERTU (p=0.02 for both), while urinary sodium excretion (p=0.1) and TNa/ Kmono remained unchanged (p=0.7). TNa strongly associated with Kmono (r=0.50; p<0.0001). In conclusion, SGLT2i lowers mGFR, TNa, and kidney oxygen consumption, potentially decreasing hypoxia risk. SGLT2i treatment did not lower overall kidney efficiency, despite the ATP efficiency of cortical sodium transport. Additional data on cortex and medulla-specific oxygen consumption and multiparametric kidney MRI data will be presented at ADA. Disclosure A. Hesp: None. L. I. P. Snel: None. P. Schober: None. L. A. Schwarte: None. R. Boellaard: None. P. Bjornstad: Advisory Panel; AstraZeneca. Consultant; Bayer Inc., Bristol-Myers Squibb Company. Advisory Panel; Novo Nordisk, Lilly, Horizon Therapeutics plc, Boehringer Ingelheim (Canada) Ltd., LG Chem. D. van Raalte: Consultant; Boehringer Ingelheim and Eli Lilly Alliance, AstraZeneca, Merck & Co., Inc. Research Support; Boehringer Ingelheim and Eli Lilly Alliance, AstraZeneca, Merck & Co., Inc. Funding MSD

Assessment of circulating extracellular vesicles from calorie‐restricted mice and humans in ischaemic injury models

AbstractCalorie restriction (CR) and fasting affect lifespan, disease susceptibility and response to acute injury across multiple animal models, including ischaemic injuries such as myocardial infarction or kidney hypoxia. The cargo and function of circulating extracellular vesicles (EV) respond to changes in host physiology, including exercise, injury, and other interventions. Thus, we hypothesised that EVs induced following CR may reflect some of the beneficial properties of CR itself. In a pilot study, EVs were isolated from mice following 21 days of 30 % CR, and from eight human donors after 72 h water‐only fasting. EV size, concentration and morphology were profiled by NTA, western blot and cryoEM, and their function was assessed using multiple assays related to ischaemic diseases. We found that EVs from post‐fasting samples better protected cardiac cells from hypoxia/reperfusion (H/R) injury compared to pre‐fasting EVs. However, there was no difference when used to treat H/R‐injured kidney epithelial cells. Post‐fasting derived EVs slowed the rate of fibroblast migration and slightly reduced macrophage inflammatory gene expression compared to pre‐fasting derived EVs. Lastly, we compared miRNA cargos of pre‐ and post‐fasting human serum EVs and found significant changes in a small number of miRNAs. We conclude that fasting appears to influence EV cargo and function, with varied effects worthy of further exploration.

Designing a Brightness-Restored Rhodamine Derivative by the Ortho-Compensation Effect for Assessing Drug-Induced Acute Kidney Injury.

Effective monitoring of essential bioindicators with high-contrast fluorescence imaging is highly crucial to reveal the pathological progression of diseases. However, most reported probes based on asymmetric amino-rhodamine (ARh) derivatives are often limited in practical application due to the low signal-to-noise ratios. Herein, a new fluorophore, 3-methoxy-amino-rhodamine (3-MeOARh), with improved fluorescence quantum yield (0.51 in EtOH) is designed and synthesized by introducing methoxy group in the ortho-position of amino in asymmetric amino-rhodamine. Notably, the good properties of the ortho-compensation effect further effectively enable the construction of an activatable probe with a high signal-to-noise ratio. As a proof of concept, the probe (3-MeOARh-NTR) was successfully synthesized for nitroreductase detection with high selectivity, excellent sensitivity, and good stability. More importantly, the relationship between drug-induced kidney hypoxia and elevated nitroreductase concentration was first uncovered in living tissues through high-contrast imaging. Therefore, the study presents the activatable probe for kidney hypoxia imaging while highlighting the 3-MeOARh structure with a satisfactory signal-to-noise ratio. It is believed that 3-MeOARh can serve as an efficient platform for activatable probe construction to reveal the pathological progression of different diseases.

Hypoxia-Induced Kidney Injury in Newborn Rats

Exposure to hypoxia during the early postnatal period can have adverse effects on vital organs. Neonatal Sprague-Dawley rats housed in a hypoxic chamber were compared to those in a normoxic chamber from postnatal days 0 to 7. Arterial blood was collected to evaluate renal function and hypoxia. Kidney morphology and fibrosis were evaluated using staining methods and immunoblotting. In the kidneys of the hypoxic group, protein expressions of hypoxia-inducible factor-1 were higher than those in the normoxic group. Hypoxic rats had higher levels of hematocrit, serum creatinine, and lactate than normoxic rats. Body weight was reduced, and protein loss of kidney tissue was observed in hypoxic rats compared to normoxic rats. Histologically, hypoxic rats showed glomerular atrophy and tubular injury. Renal fibrosis with collagen fiber deposition was observed in the hypoxic group. The expression of nicotinamide adenine dinucleotide phosphate oxidases was enhanced in the kidneys of hypoxic rats. Proteins involved in apoptosis were upregulated in the kidneys of hypoxic rats. An increase in the expression of pro-inflammatory cytokines was also observed in the kidneys of hypoxic rats. Hypoxic kidney injury in neonatal rats was associated with oxidative stress, inflammation, apoptosis, and fibrosis.

Hypoxia Sensing of β-Adrenergic Receptor Is Regulated by Endosomal PI3Kγ.

Impaired beta-adrenergic receptor (β1 and β2AR) function following hypoxia underlies ischemic heart failure/stroke. Activation of PI3Kγ (phosphoinositide 3-kinase γ) by beta-adrenergic receptor leads to feedback regulation of the receptor by hindering beta-adrenergic receptor dephosphorylation through inhibition of PP2A (protein phosphatase 2A). However, little is known about PI3Kγ feedback mechanism in regulating hypoxia-mediated β1 and β2AR dysfunction and cardiac remodeling. Human embryonic kidney 293 cells or mouse adult cardiomyocytes and C57BL/6 (WT) or PI3Kγ knockout (KO) mice were subjected to hypoxia. Cardiac plasma membranes and endosomes were isolated and evaluated for β1 and β2AR density and function, PI3Kγ activity and β1 and β2AR-associated PP2A activity. Metabolic labeling was performed to assess β1 and β2AR phosphorylation and epinephrine/norepinephrine levels measured post-hypoxia. Hypoxia increased β1 and β2AR phosphorylation, reduced cAMP, and led to endosomal accumulation of phosphorylated β2ARs in human embryonic kidney 293 cells and WT cardiomyocytes. Acute hypoxia in WT mice resulted in cardiac remodeling and loss of adenylyl cyclase activity associated with increased β1 and β2AR phosphorylation. This was agonist-independent as plasma and cardiac epinephrine and norepinephrine levels were unaltered. Unexpectedly, PI3Kγ activity was selectively increased in the endosomes of human embryonic kidney 293 cells and WT hearts post-hypoxia. Endosomal β1- and β2AR-associated PP2A activity was inhibited upon hypoxia in human embryonic kidney 293 cells and WT hearts showing regulation of beta-adrenergic receptors by PI3Kγ. This was accompanied with phosphorylation of endogenous inhibitor of protein phosphatase 2A whose phosphorylation by PI3Kγ inhibits PP2A. Increased β1 and β2AR-associated PP2A activity, decreased beta-adrenergic receptor phosphorylation, and normalized cardiac function was observed in PI3Kγ KO mice despite hypoxia. Compared to WT, PI3Kγ KO mice had preserved cardiac response to challenge with β1AR-selective agonist dobutamine post-hypoxia. Agonist-independent activation of PI3Kγ underlies hypoxia sensing as its ablation leads to reduction in β1- and β2AR phosphorylation and amelioration of cardiac dysfunction.

Tubular Epithelial Cell HMGB1 Promotes AKI-CKD Transition by Sensitizing Cycling Tubular Cells to Oxidative Stress: A Rationale for Targeting HMGB1 during AKI Recovery.

Cells undergoing necrosis release extracellular high mobility group box (HMGB)-1, which triggers sterile inflammation upon AKI in mice. Neither deletion of HMGB1 from tubular epithelial cells, nor HMGB1 antagonism with small molecules, affects initial ischemic tubular necrosis and immediate GFR loss upon unilateral ischemia/reperfusion injury (IRI). On the contrary, tubular cell-specific HMGB1 deficiency, and even late-onset pharmacological HMGB1 inhibition, increased functional and structural recovery from AKI, indicating that intracellular HMGB1 partially counters the effects of extracellular HMGB1. In vitro studies indicate that intracellular HMGB1 decreases resilience of tubular cells from prolonged ischemic stress, as in unilateral IRI. Intracellular HMGB1 is a potential target to enhance kidney regeneration and to improve long-term prognosis in AKI. Late diagnosis is a hurdle for treatment of AKI, but targeting AKI-CKD transition may improve outcomes. High mobility group box-1 (HMGB1) is a nuclear regulator of transcription and a driver of necroinflammation in AKI. We hypothesized that HMGB1 would also modulate AKI-CKD transition in other ways. We conducted single-cell transcriptome analysis of human and mouse AKI and mouse in vivo and in vitro studies with tubular cell-specific depletion of Hmgb1 and HMGB1 antagonists. HMGB1 was ubiquitously expressed in kidney cells. Preemptive HMGB1 antagonism with glycyrrhizic acid (Gly) and ethyl pyruvate (EP) did not affect postischemic AKI but attenuated AKI-CKD transition in a model of persistent kidney hypoxia. Consistently, tubular Hmgb1 depletion in Pax8 rtTA, TetO Cre, Hmgb1fl/fl mice did not protect from AKI, but from AKI-CKD transition. In vitro studies confirmed that absence of HMGB1 or HMGB1 inhibition with Gly and EP does not affect ischemic necrosis of growth-arrested differentiated tubular cells but increased the resilience of cycling tubular cells that survived the acute injury to oxidative stress. This effect persisted when neutralizing extracellular HMGB1 with 2G7. Consistently, late-onset HMGB1 blockade with EP started after the peak of ischemic AKI in mice prevented AKI-CKD transition, even when 2G7 blocked extracellular HMGB1. Treatment of AKI could become feasible when ( 1 ) focusing on long-term outcomes of AKI; ( 2 ) targeting AKI-CKD transition with drugs initiated after the AKI peak; and ( 3 ) targeting with drugs that block HMGB1 in intracellular and extracellular compartments.

Hypervolemia suppresses dilutional anaemic injury in a rat model of haemodilution.

Haemodilution leads to complications in clinical practice. It is exactly unknown whether this damage is caused by the fluid or by the stretching of the vascular bed. We aimed to compare two different haemodilution techniques at the same anaemic level. Normovolemic or hypervolemic haemodilution was performed on twelve adult male Wistar rats. In the normovolemic procedure, blood was withdrawn and instantaneously administered with similar amounts of 6% hydroxyethyl starch (HES 130/0.4). Fluid was administered without withdrawing blood in the hypervolemic procedure. In both models, a 25% haematocrit level was targeted and kept at this level for 90 min to deepen the anaemia effect. Besides haemodynamics measurement, renal function (creatinine, blood urea nitrogen) and injury (tissue norepinephrine, malondialdehyde) were evaluated. Also, systemic hypoxia (lactate), oxidative stress (malondialdehyde, ischaemia-modified albumin), inflammation (tumour necrosis factor-alpha [TNF-α]), osmotic stress, adrenal stress (norepinephrine, epinephrine), and vascular stretching (atrial natriuretic peptide [ANP]) were assessed. Arterial pressure in the normovolemic group was lower than in the hypervolemic group. Serum creatinine, blood urea nitrogen, and lactate levels were higher in the normovolemic group. Tissue norepinephrine and malondialdehyde levels were higher in the normovolemic group. Serum ANP, malondialdehyde, ischaemia-modified albumin, free haemoglobin, syndecan-1, and TNF-α were higher in both groups compared to respective baseline. Normovolemic haemodilution may lead to hypoxic kidney injury. The hypervolemic state may be advantageous if fluid is to be administered. Thus, the effect of the fluid itself can be relatively masked.

Short communication: Acute hypoxia does not alter mitochondrial abundance in naked mole-rats

Hypoxia poses a significant energetic challenge and most species exhibit metabolic remodelling when exposed to prolonged hypoxia. One component of this remodelling is mitochondrial biogenesis/mitophagy, which alter mitochondrial abundance and helps to adjust metabolic throughput to match changes in energy demands in hypoxia. However, how acute hypoxia impacts mitochondrial abundance in hypoxia-tolerant species is poorly understood. To help address this gap, we exposed hypoxia-tolerant naked mole-rats to 3 h of normoxia or acute hypoxia (5% O2) and measured changes in mitochondrial abundance using two well-established markers: citrate synthase (CS) enzyme activity and mitochondrial DNA (mtDNA) abundance. We found that neither marker changed with hypoxia in brain, liver, or kidney, suggesting that mitochondrial biogenesis is not initiated during acute hypoxia in these tissues. Conversely in skeletal muscle, the ratio of CS activity to total protein decreased 50% with hypoxia. However, this change was likely driven by an increase in soluble protein density in hypoxia because CS activity was unchanged relative to wet tissue weight and the mtDNA copy number was unchanged. To confirm this, we examined skeletal muscle mitochondria using transmission electron microscopy and found no change in mitochondrial volume density. Taken together with previous studies of mitochondrial respiratory function, our present findings suggest that naked mole-rats primarily rely on tissue-specific functional remodelling of metabolic pathways and mitochondrial respiratory throughput, and not physical changes in mitochondrial number or volume, to adjust to short-term hypoxic exposure.

Delayed Graft Function in Kidney Transplant: Risk Factors, Consequences and Prevention Strategies.

Background. Delayed graft function is a frequent complication of kidney transplantation that requires dialysis in the first week posttransplant. Materials and Methods. We searched for the most relevant articles in the National Institutes of Health library of medicine, as well as in transplantation, pharmacologic, and nephrological journals. Results. The main factors that may influence the development of delayed graft function (DGF) are ischemia–reperfusion injury, the source and the quality of the donated kidney, and the clinical management of the recipient. The pathophysiology of ischemia–reperfusion injury is complex and involves kidney hypoxia related to the duration of warm and cold ischemia, as well as the harmful effects of blood reperfusion on tubular epithelial cells and endothelial cells. Ischemia–reperfusion injury is more frequent and severe in kidneys from deceased donors than in those from living donors. Of great importance is the quality and function of the donated kidney. Kidneys from living donors and those with normal function can provide better results. In the peri-operative management of the recipient, great attention should be paid to hemodynamic stability and blood pressure; nephrotoxic medicaments should be avoided. Over time, patients with DGF may present lower graft function and survival compared to transplant recipients without DGF. Maladaptation repair, mitochondrial dysfunction, and acute rejection may explain the worse long-term outcome in patients with DGF. Many different strategies meant to prevent DGF have been evaluated, but only prolonged perfusion of dopamine and hypothermic machine perfusion have proven to be of some benefit. Whenever possible, a preemptive transplant from living donor should be preferred.

Proximal tubular epithelia-specific transcriptomics of diabetic mice treated with dapagliflozin

Based on recent clinical trials using sodium-glucose co-transporter 2 inhibitor (SGLT2i) demonstrating the significant improvement of outcomes of diabetic kidney disease (DKD), the paradigm shift from “glomerulocentric” to “tubule centric” pathophysiology in DKD progression has been highlighted. Several responsible mechanisms for renoprotective effects by SGLT2i have been proposed recently, but the changes in proximal tubule-specific gene expression by SGLT2i in diabetic mice have not been elucidated. We report the analysis of the proximal tubular-specific pathway, demonstrating the downregulation of oxidative phosphorylation in dapagliflozin-treated db/db mice, a type 2 diabetic model. After 8-week treatment of dapagliflozin for db/db mice having a proximal tubule-specific tdTomato reporter, tdTomato-positive cells were isolated by FACS. Pathway analysis of RNA sequencing of isolated tubular epithelia revealed that oxidative phosphorylation was downregulated in dapagliflozin-treated mice. However, depletion of renal tissue ATP content in db/db mice was ameliorated by dapagliflozin administration. Pimonidazole staining demonstrated renal cortical tissue hypoxia in db/db mice, which was improved by dapagliflozin administration. This study suggests that dapagliflozin can ameliorate the excessive oxygen and ATP consumption, and subsequent tissue hypoxia in the diabetic kidney, which may explain, in part, the responsible mechanisms of the renoprotective effects of dapagliflozin.

Metabolic Syndrome and β-Oxidation of Long-Chain Fatty Acids in the Brain, Heart, and Kidney Mitochondria.

We present evidence that metabolic syndrome (MetS) represents the postreproductive stage of the human postembryonic ontogenesis. Accordingly, the genes governing this stage experience relatively weak evolutionary selection pressure, thus representing the metabolic phenotype of distant ancestors with β-oxidation of long-chain fatty acids (FAs) as the primary energy source. Mitochondria oxidize at high-rate FAs only when succinate, glutamate, or pyruvate are present. The heart and brain mitochondria work at a wide range of functional loads and possess an intrinsic inhibition of complex II to prevent oxidative stress at periods of low functional activity. Kidney mitochondria constantly work at a high rate and lack inhibition of complex II. We suggest that in people with MetS, oxidative stress is the central mechanism of the heart and brain pathologies. Oxidative stress is a secondary pathogenetic mechanism in the kidney, while the primary mechanisms are kidney hypoxia caused by persistent hyperglycemia and hypertension. Current evidence suggests that most of the nongenetic pathologies associated with MetS originate from the inconsistencies between the metabolic phenotype acquired after the transition to the postreproductive stage and excessive consumption of food rich in carbohydrates and a sedentary lifestyle.

Thyroid hormone increases oxygen metabolism causing intrarenal tissue hypoxia; a pathway to kidney disease.

The proposed mechanisms for the development of nephropathy are many, complex and often overlapping. Although recent literature strongly supports a role of kidney hypoxia as an independent pathway to nephropathy, the evidence remains inconclusive since the role of hypoxia is difficult to differentiate from confounding factors such as hyperglycemia, hypertension and oxidative stress. By increasing kidney oxygen consumption using triiodothyronine (T3) and, thus, avoiding these confounding factors, the aim of the present study was to investigate renal hypoxia per se as a causal pathway for the development of nephropathy. Healthy Sprague-Dawley rats were treated with T3 (10 μg/kg/day) and the angiotensin II AT1-receptor antagonist candesartan (1 mg/kg in drinking water) to eliminate effects of T3-induced renin release; and compared to a candesartan treated control group. After 7 weeks of treatment in vivo kidney function, oxygen metabolism and mitochondrial function were evaluated. T3 did not affect glomerular filtration rate or renal blood flow, but increased total kidney oxygen consumption resulting in cortical hypoxia. Nephropathy, demonstrated as albuminuria and tubulointerstitial fibrosis, developed in T3-treated animals. Mitochondria uncoupling mediated by uncoupling protein 2 and the adenosine nucleotide transporter was demonstrated as a mechanism causing the increased kidney oxygen consumption. Importantly, blood glucose levels, mean arterial blood pressure and oxidative stress levels were not affected by T3. In conclusion, the present study provides further evidence for increased kidney oxygen consumption causing intrarenal tissue hypoxia, as a causal pathway for development of nephropathy.

Hypoxia-Inducible Factors and Burn-Associated Acute Kidney Injury-A New Paradigm?

O2 deprivation induces stress in living cells linked to free-radical accumulation and oxidative stress (OS) development. Hypoxia is established when the overall oxygen pressure is less than 40 mmHg in cells or tissues. However, tissues and cells have different degrees of hypoxia. Hypoxia or low O2 tension may be present in both physiological (during embryonic development) and pathological circumstances (ischemia, wound healing, and cancer). Meanwhile, the kidneys are major energy-consuming organs, being second only to the heart, with an increased mitochondrial content and O2 consumption. Furthermore, hypoxia-inducible factors (HIFs) are the key players that orchestrate the mammalian response to hypoxia. HIFs adapt cells to low oxygen concentrations by regulating transcriptional programs involved in erythropoiesis, angiogenesis, and metabolism. On the other hand, one of the life-threatening complications of severe burns is acute kidney injury (AKI). The dreaded functional consequence of AKI is an acute decline in renal function. Taking all these aspects into consideration, the aim of this review is to describe the role and underline the importance of HIFs in the development of AKI in patients with severe burns, because kidney hypoxia is constant in the presence of severe burns, and HIFs are major players in the adaptative response of all tissues to hypoxia.