Pathophysiology of acute kidney injury

Overexpression of augmenter of liver regeneration (ALR) mitigates the effect of H2O2-induced endoplasmic reticulum stress in renal tubule epithelial cells

Ischemia/reperfusion is a major cause of acute kidney injury and can induce apoptosis in renal epithelial tubule (HK-2) cells. Accumulating evidence indicates that endoplasmic reticulum (ER) stress is a major contributor to apoptosis in acute kidney injury. We previously reported that augmenter of liver regeneration (ALR) functions as an anti-apoptotic factor in H₂O₂-treated HK-2 cells although the precise mechanism underlying this action remains unclear. In the present study, we investigate the role of ALR in H₂O₂-induced ER stress-mediated apoptosis. We overexpressed ALR and established a H₂O₂-induced ER stress model in HK-2 cells. Overexpression of ALR reduced the level of reactive oxygen species and the rate of apoptosis in H₂O₂-treated HK-2 cells. Using confocal microscopy and western blot, we observed that ALR colocalized with the ER and mitochondria compartment. Moreover, ALR suppressed ER stress by maintaining the morphology of the ER and reducing the levels of the ER-related proteins, glucose-regulated protein 78 (GRP78), phospho-protein kinase-like ER kinase (p-PERK), phospho-eukaryotic initiation factor 2α (p-eIF2α) and C/EBP-homologous protein (CHOP) significantly (p < 0.05). Mechanistically, ALR promoted Bcl-2 expression and suppressed Bax and cleaved-caspase-3 expression significantly during ER-stress induced apoptosis (p < 0.05). Furthermore, ALR attenuated calcium release from the ER, and transfer to mitochondria, under ER stress. To conclude, ALR alleviates H₂O₂-induced ER stress-mediated apoptosis in HK-2 cells by suppressing ER stress response and by maintaining calcium homeostasis. Consequently, ALR may protect renal tubule epithelial cells from ischemia/reperfusion induced acute kidney injury.

Preconditioning strategies to prevent acute kidney injury

Acute kidney injury is a common clinical disorder resulting in significantly increased morbidity and mortality. However, despite extensive research, strategies for prevention or treatment are still lacking in routine clinical practice. Already decades ago, several preconditioning strategies (e. g. ischemic/hypoxic preconditioning and calorie restriction) have been published and their extraordinary effectiveness - especially in rodents - has raised the hope for powerful clinical tools to prevent acute kidney injury. However, the underlying mechanisms are still not completely understood and translation to the clinics has not been successful yet. In this review, the most attractive strategies and the current mechanistic concepts are introduced and discussed. Furthermore, we present clinical trials evaluating the feasibility of preconditioning in the clinical setting.

Chicken ovalbumin upstream promoter-transcription factor II protects against cisplatin-induced acute kidney injury

The chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) plays essential roles in organogenesis of embryos. Recently COUP-TFII is also implicated in several diseases in adults. Here we focus on the role of COUP-TFII in cisplatin-induced acute kidney injury (AKI). COUP-TFII was the most abundantly expressed in the kidney among organs. Male tamoxifen-inducible COUP-TFII-knockout mice or control mice were intraperitoneally treated with 30 mg/kg body weight of cisplatin at 12 weeks old to induce AKI. The kidney samples were subject to morphological studies, terminal deoxynucleotidyl transferase-mediated deoxyuridine nick-end labeling (TUNEL) assay, immunohistochemistry and RT-qPCR. Serum levels of creatinine, blood urea nitrogen (BUN) and tumor necrosis factor alpha (TNF-α) were measured. Administration of cisplatin induced a more severe AKI in adult COUP-TFII-knockout mice. An increase in dead cells in both the proximal tubules and thick ascending limb of Henle's loop (TAL) was observed in the knockout mouse kidney. The expression levels of COUP-TFII decreased in the TAL by cisplatin administration. There was no difference in the expression levels of transporter mRNAs responsible for cellular cisplatin uptake between control and knockout mouse kidney. COUP-TFII-knockout mice and COUP-TFII-depleted cells exhibited an elevation in TNF-α levels, suggesting the involvement of the TNF-α pathway. Chromatin immunoprecipitation showed that COUP-TFII was enriched in the potential binding site, suggesting that COUP-TFII might directly suppress the TNF-α gene at transcriptional level. These results indicate the involvement of COUP-TFII in the pathophysiology of AKI and COUP-TFII may be a potential therapeutic target for AKI.

Toxic Metal Implications on Agricultural Soils, Plants, Animals, Aquatic life and Human Health

The problem of environmental pollution is a global concern as it affects the entire ecosystem. There is a cyclic revolution of pollutants from industrial waste or anthropogenic sources into the environment, farmlands, plants, livestock and subsequently humans through the food chain. Most of the toxic metal cases in Africa and other developing nations are a result of industrialization coupled with poor effluent disposal and management. Due to widespread mining activities in South Africa, pollution is a common site with devastating consequences on the health of animals and humans likewise. In recent years, talks on toxic metal pollution had taken center stage in most scientific symposiums as a serious health concern. Very high levels of toxic metals have been reported in most parts of South African soils, plants, animals and water bodies due to pollution. Toxic metals such as Zinc (Zn), Lead (Pb), Aluminium (Al), Cadmium (Cd), Nickel (Ni), Iron (Fe), Manganese (Mn) and Arsenic (As) are major mining effluents from tailings which contaminate both the surface and underground water, soil and food, thus affecting biological function, endocrine systems and growth. Environmental toxicity in livestock is traceable to pesticides, agrochemicals and toxic metals. In this review, concerted efforts were made to condense the information contained in literature regarding toxic metal pollution and its implications in soil, water, plants, animals, marine life and human health.

Experimental rat model for acute tubular injury induced by high water hardness and high water fluoride: efficacy of primary preventive intervention by distilled water administration

Background

High water hardness associated with high water fluoride and the geographical distribution of Chronic Kidney Disease of unknown etiology (CKDu) in Sri Lanka are well correlated. We undertook this study to observe the effects of high water hardness with high fluoride on kidney and liver in rats and efficacy of distilled water in reducing the effects.

Methods

Test water sample with high water hardness and high fluoride was collected from Mihinthale region and normal water samples were collected from Kandy region. Twenty-four rats were randomly divided into 8 groups and water samples were introduced as follows as daily water supply. Four groups received normal water for 60 (N1) and 90 (N2) days and test water for 60 (T1) and 90 (T2) days. Other four groups received normal (N3) and test (T3) water for 60 days and followed by distilled water for additional 60 days and normal (N4) and test (T4) water for 90 days followed by distilled water for another 90 days. The rats were sacrificed following treatment. Serum samples were subjected to biochemical tests; serum creatinine, urea, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and elemental analysis. Histopathological examinations were carried out using kidney and liver samples.

Results

Test water treated groups were associated with acute tubular injury with loss of brush border and test water followed with distilled water treated groups maintained a better morphology with minimal loss of brush border. Serum creatinine levels in T1 and T2 groups and urea level in T2 group were significantly (p < 0.05) increased compared to control groups. After administration of distilled water, both parameters were significantly reduced in T4 group (p < 0.05) compared to T2. Serum AST activity was increased in T4 group (p < 0.05) compared to control group with no histopathological changes in liver tissues. The serum sodium levels were found to be much higher compared to the other electrolytes in test groups.

Conclusion

Hard water with high fluoride content resulted in acute tubular injury with a significant increase in serum levels of creatinine, urea and AST activity. These alterations were minimized by administering distilled water.

Fibroblast Growth Factor 2 Attenuates Renal Ischemia-Reperfusion Injury via Inhibition of Endoplasmic Reticulum Stress

Acute kidney injury (AKI) is a serious clinical disease that is mainly caused by renal ischemia-reperfusion (I/R) injury, sepsis, and nephrotoxic drugs. The pathologic mechanism of AKI is very complex and may involve oxidative stress, inflammatory response, autophagy, apoptosis, and endoplasmic reticulum (ER) stress. The basic fibroblast growth factor (FGF2) is a canonic member of the FGF family that plays a crucial role in various cellular processes, including organ development, wound healing, and tissue regeneration. However, few studies have reported the potential therapeutic effect of FGF2 in the repair of renal ischemic injury in the past two decades. In the present study, we investigated the protective effect of FGF2 on renal I/R injury using Sprague-Dawley and NRK-52E cells. Our results showed that FGF2 significantly attenuates the apoptosis of kidney tissues after I/R injury through the inhibition of excessive ER stress. Moreover, FGF2 also alleviated the excessive ER stress and apoptosis in cultured NRK-52E cells injured by tert-Butyl hydroperoxide (TBHP). Significantly, phosphatidylinositol 3-kinase (PI3K)-selective inhibitor LY294002 and mitogen-activated protein kinase kinase (MEK)-selective inhibitor U0126 were utilized in the present study to examine the protective mechanism of FGF2. Our in vitro experimental results confirmed that both LY294002 and U0126 largely abolished the protective effect of FGF2. Taken together, the findings of the present study indicated that FGF2 attenuates I/R-induced renal epithelial apoptosis by suppressing excessive ER stress via the activation of the PI3K/AKT and MEK-ERK1/2 signaling pathways.

Pathophysiology of unilateral ischemia-reperfusion injury: importance of renal counterbalance and implications for the AKI-CKD transition

Unilateral ischemia-reperfusion (UIR) injury leads to progressive renal atrophy and tubulointerstitial fibrosis (TIF) and is commonly used to investigate the pathogenesis of the acute kidney injury-chronic kidney disease transition. Although it is well known that contralateral nephrectomy (CNX), even 2 wk post-UIR injury, can improve recovery, the physiological mechanisms and tubular signaling pathways mediating such improved recovery remain poorly defined. Here, we examined the renal hemodynamic and tubular signaling pathways associated with UIR injury and its reversal by CNX. Male Sprague-Dawley rats underwent left UIR or sham UIR and 2 wk later CNX or sham CNX. Blood pressure, left renal blood flow (RBF), and total glomerular filtration rate were assessed in conscious rats for 3 days before and over 2 wk after CNX or sham CNX. In the presence of a contralateral uninjured kidney, left RBF was lower (P < 0.05) from 2 to 4 wk following UIR (3.6 ± 0.3 mL/min) versus sham UIR (9.6 ± 0.3 mL/min). Without CNX, extensive renal atrophy, TIF, and tubule dedifferentiation, but minimal pimonidazole and hypoxia-inducible factor-1α positivity in tubules, were present at 4 wk post-UIR injury. Conversely, CNX led (P < 0.05) to sustained increases in left RBF (6.2 ± 0.6 mL/min) that preceded the increases in glomerular filtration rate. The CNX-induced improvement in renal function was associated with renal hypertrophy, more redifferentiated tubules, less TIF, and robust pimonidazole and hypoxia-inducible factor-1α staining in UIR injured kidneys. Thus, contrary to expectations, indexes of hypoxia are not observed with the extensive TIF at 4 wk post-UIR injury in the absence of CNX but are rather associated with the improved recovery of renal function and structure following CNX.

Defective Mitochondrial Fatty Acid Oxidation and Lipotoxicity in Kidney Diseases

The kidney is a highly metabolic organ and uses high levels of ATP to maintain electrolyte and acid-base homeostasis and reabsorb nutrients. Energy depletion is a critical factor in development and progression of various kidney diseases including acute kidney injury (AKI), chronic kidney disease (CKD), and diabetic and glomerular nephropathy. Mitochondrial fatty acid β-oxidation (FAO) serves as the preferred source of ATP in the kidney and its dysfunction results in ATP depletion and lipotoxicity to elicit tubular injury and inflammation and subsequent fibrosis progression. This review explores the current state of knowledge on the role of mitochondrial FAO dysfunction in the pathophysiology of kidney diseases including AKI and CKD and prospective views on developing therapeutic interventions based on mitochondrial energy metabolism.

Oral high dose vitamin B12 decreases renal superoxide and post-ischemia/reperfusion injury in mice

Renal ischemia/reperfusion injury (IRI) is a leading cause of acute kidney injury (AKI), a potentially fatal syndrome characterized by a rapid decline in kidney function. Excess production of superoxide contributes to the injury. We hypothesized that oral administration of a high dose of vitamin B12 (B12 - cyanocobalamin), which possesses a superoxide scavenging function, would protect kidneys against IRI and provide a safe means of treatment. Following unilateral renal IR surgery, C57BL/6J wild type (WT) mice were administered B12 via drinking water at a dose of 50 mg/L. After 5 days of the treatment, plasma B12 levels increased by 1.2-1.5x, and kidney B12 levels increased by 7-8x. IRI mice treated with B12 showed near normal renal function and morphology. Further, IRI-induced changes in RNA and protein markers of inflammation, fibrosis, apoptosis, and DNA damage response (DDR) were significantly attenuated by at least 50% compared to those in untreated mice. Moreover, the presence of B12 at 0.3 μM in the culture medium of mouse proximal tubular cells subjected to 3 hr of hypoxia followed by 1 hr of reperfusion in vitro showed similar protective effects, including increased cell viability and decreased reactive oxygen species (ROS) level. We conclude that a high dose of B12 protects against perfusion injury both in vivo and in vitro without observable adverse effects in mice and suggest that B12 merits evaluation as a treatment for I/R-mediated AKI in humans.

Renal Sympathetic Nerve-Derived Signaling in Acute and Chronic kidney Diseases

The kidney is innervated by afferent sensory and efferent sympathetic nerve fibers. Norepinephrine (NE) is the primary neurotransmitter for post-ganglionic sympathetic adrenergic nerves, and its signaling, regulated through adrenergic receptors (AR), modulates renal function and pathophysiology under disease conditions. Renal sympathetic overactivity and increased NE level are commonly seen in chronic kidney disease (CKD) and are critical factors in the progression of renal disease. Blockade of sympathetic nerve-derived signaling by renal denervation or AR blockade in clinical and experimental studies demonstrates that renal nerves and its downstream signaling contribute to progression of acute kidney injury (AKI) to CKD and fibrogenesis. This review summarizes our current knowledge of the role of renal sympathetic nerve and adrenergic receptors in AKI, AKI to CKD transition and CKDand provides new insights into the therapeutic potential of intervening in its signaling pathways.

Prenatal hypoxia increases susceptibility to kidney injury

Prenatal hypoxia is a gestational stressor that can result in developmental abnormalities or physiological reprogramming, and often decreases cellular capacity against secondary stress. When a developing fetus is exposed to hypoxia, blood flow is preferentially redirected to vital organs including the brain and heart over other organs including the kidney. Hypoxia-induced injury can lead to structural malformations in the kidney; however, even in the absence of structural lesions, hypoxia can physiologically reprogram the kidney leading to decreased function or increased susceptibility to injury. Our investigation in mice reveals that while prenatal hypoxia does not affect normal development of the kidneys, it primes the kidneys to have an increased susceptibility to kidney injury later in life. We found that our model does not develop structural abnormalities when prenatally exposed to modest 12% O2 as evident by normal histological characterization and gene expression analysis. Further, adult renal structure and function is comparable to mice exposed to ambient oxygen throughout nephrogenesis. However, after induction of kidney injury with a nephrotoxin (cisplatin), the offspring of mice housed in hypoxia exhibit significantly reduced renal function and proximal tubule damage following injury. We conclude that exposure to prenatal hypoxia in utero physiologically reprograms the kidneys leading to increased susceptibility to injury later in life.

Vagus Nerve Stimulation Ameliorates Renal Ischemia-Reperfusion Injury through Inhibiting NF-κB Activation and iNOS Protein Expression

OBJECTIVE

In renal ischemia/reperfusion injury (RIRI), nuclear factor κB (NF-κB (NF-κB (NF.

METHODS

Eighteen male Sprague-Dawley rats were randomly allocated into the sham group, the I/R group, and the VNS+I/R group, 6 rats per group. An RIRI model was induced by a right nephrectomy and blockade of the left renal pedicle vessels for 45 min. After 6 h of reperfusion, the blood samples and renal samples were collected. The VNS treatment was performed throughout the I/R process in the VNS+I/R group using specific parameters (20 Hz, 0.1 ms in duration, square waves) known to produce a small but reliable bradycardia. Blood was used for evaluation of renal function and inflammatory state. Renal injury was evaluated via TUNEL staining. Renal samples were harvested to evaluate renal oxidative stress, NF-κB (NF.

RESULTS

The VNS treatment reduces serum creatinine (Cr) and blood urea nitrogen (BUN) levels. Simultaneously, the levels of tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), and interleukin 1-beta (IL-1β) were significantly increased in the I/R group, but VNS treatment markedly ameliorated this inflammatory response. Furthermore, the VNS ameliorated oxidant stress and renal injury, indicated by a decrease in 3-nitrotyrosine (3-NT) formation and MDA and MPO levels and an increase in the SOD level compared to that in the I/R group. Finally, the VNS also significantly decreases NF-κB (NF.

CONCLUSION

Our findings indicate that NF-κB activation increased iNOS expression and promoted RIRI and that VNS treatment attenuated RIRI by inhibiting iNOS expression, oxidative stress, and inflammation via NF-κB inactivation.κB (NF-κB (NF.

The functional interplay of lncRNA EGOT and HuR regulates hypoxia-induced autophagy in renal tubular cells

Autophagy, an important cellular homeostatic mechanism regulates cell survival under stress and protects against acute kidney injury. However, the role of long noncoding RNA (lncRNA) in autophagy regulation in renal tubular cells (HK-2) is unclear. The study was aimed to understand the importance of lncRNA in hypoxia-induced autophagy in HK-2 cells. LncRNA eosinophil granule ontogeny transcript (EGOT) was identified as autophagy-associated lncRNA under hypoxia. The lncRNA EGOT expression was significantly downregulated in renal tubular cells during hypoxia-induced autophagy. Gain- and loss-of-EGOT functional studies revealed that EGOT overexpression reduced autophagy by downregulation of ATG7, ATG16L1, LC3II expressions and LC 3 puncta while EGOT knockdown reversed the suppression of autophagy. Importantly, RNA-binding protein, (ELAVL1)/Hu antigen R (HuR) binds and stabilizes the EGOT expression under normoxia and ATG7/16L1 expressions under hypoxia. Furthermore, HuR mediated stabilization of ATG7/16L1 expressions under hypoxia causes a decline in EGOT levels and thereby promotes autophagy. Altogether, the study first reveals the functional interplay of lncRNA EGOT and HuR on the posttranscriptional regulation of the ATG7/16L1 expressions. Thus, the HuR/EGOT/ATG7/16L1 axis is crucial for hypoxia-induced autophagy in renal tubular cells.

Fibroblast Growth Factor 10 Attenuates Renal Damage by Regulating Endoplasmic Reticulum Stress After Ischemia-Reperfusion Injury

Renal ischemia–reperfusion (I/R) injury is a predominant cause of acute kidney injury (AKI), the pathologic mechanism of which is highly complex involving reactive oxygen species (ROS) accumulation, inflammatory response, autophagy, apoptosis as well as endoplasmic reticulum (ER) stress. Fibroblast growth factor 10 (FGF10), as a multifunctional growth factor, plays crucial roles in embryonic development, adult homeostasis, and regenerative medicine. Herein, we investigated the molecular pathways underlying the protective effect of FGF10 on renal I/R injury using Sprague–Dawley rats. Results showed that administration of FGF10 not only effectively inhibited I/R-induced activation of Caspase-3 and expression of Bax, but also alleviated I/R evoked expression of ER stress-related proteins in the kidney including CHOP, GRP78, XBP-1, and ATF-4 and ATF-6. The protective effect of FGF10 against apoptosis and ER stress was recapitulated by in vitro experiments using oxidative damaged NRK-52E cells induced by tert-Butyl hydroperoxide (TBHP). Significantly, U0126, a selective noncompetitive inhibitor of MAP kinase kinases (MKK), largely abolished the protective role of FGF10. Taken together, both in vivo and in vitro experiments indicated that FGF10 attenuates I/R-induced renal epithelial apoptosis by suppressing excessive ER stress, which is, at least partially, mediated by the activation of the MEK–ERK1/2 signaling pathway. Therefore, our present study revealed the therapeutic potential of FGF10 on renal I/R injury.

Urinary Extracellular Vesicles Carrying Klotho Improve the Recovery of Renal Function in an Acute Tubular Injury Model

Acute kidney injury, defined by a rapid deterioration of renal function, is a common complication in hospitalized patients. Among the recent therapeutic options, the use of extracellular vesicles (EVs) is considered a promising strategy. Here we propose a possible therapeutic use of renal-derived EVs isolated from normal urine (urine-derived EVs [uEVs]) in a murine model of acute injury generated by glycerol injection. uEVs accelerated renal recovery, stimulating tubular cell proliferation, reducing the expression of inflammatory and injury markers, and restoring endogenous Klotho loss. When intravenously injected, labeled uEVs localized within injured kidneys and transferred their microRNA cargo. Moreover, uEVs contained the reno-protective Klotho molecule. Murine uEVs derived from Klotho null mice lost the reno-protective effect observed using murine EVs from wild-type mice. This was regained when Klotho-negative murine uEVs were reconstituted with recombinant Klotho. Similarly, ineffective fibroblast EVs acquired reno-protection when engineered with human recombinant Klotho. Our results reveal a novel potential use of uEVs as a new therapeutic strategy for acute kidney injury, highlighting the presence and role of the reno-protective factor Klotho.

Extrahepatic Portal Venous Obstruction With Hepatic Enzyme Elevation Resembling Hepatitis in Patients With Cancer

BACKGROUND/AIM

Chemotherapy is often halted due to abnormal liver function resembling hepatitis. But the cause can be extrahepatic portal venous obstruction (EHPVO) with hepatic enzyme elevation rather than being an adverse effect of chemotherapy. We investigated EHPVO with hepatic enzyme elevation in patients with cancer.

PATIENTS AND METHODS

Data of these hospitalized patients with solid tumors between January 2013 and September 2017 were collected. The criteria for study inclusion were: (i) Extrahepatic malignancy; (ii) computed tomographic scans showing a tumor with external compression of the extrahepatic portal vein; and (iii) serum aminotransferase (AST) or alanine transaminase (ALT) level three times above the normal value.

RESULTS

Thirteen out of 377 (3%) patients developed EHPVO with hepatic enzyme elevation, as demonstrated from computed tomographic scan. Four cases (31%) also had vascular thrombosis (three portal vein and one inferior vena cava). Serum AST increased from 34±11 to 169±94 U/l. ALT increased from 9±38 to 177±104 U/l. There was no relationship of EHPVO with viral markers and cirrhosis. Six cases received chemotherapy with liver function improvement.

CONCLUSION

EHPVO occurred in patients with metastatic cancer, leading to hepatic enzyme elevation resembling hepatitis without hepatitis risk factors and cirrhosis. Before withholding chemotherapy due to hepatic enzyme elevation, the possibility of EHPVO should firstly be excluded.

Proximal tubule cyclophilin D regulates fatty acid oxidation in cisplatin-induced acute kidney injury

Regardless of the etiology, acute kidney injury involves aspects of mitochondrial dysfunction and ATP depletion. Fatty acid oxidation is the preferred energy source of the kidney and is inhibited during acute kidney injury. A pivotal role for the mitochondrial matrix protein, cyclophilin D in regulating overall cell metabolism is being unraveled. We hypothesize that mitochondrial interaction of proximal tubule cyclophilin D and the transcription factor PPARα modulate fatty acid beta-oxidation in cisplatin-induced acute kidney injury. Cisplatin injury resulted in histological and functional damage in the kidney with downregulation of fatty acid oxidation genes and increase of intrarenal lipid accumulation. However, proximal tubule-specific deletion of cyclophilin D protected the kidneys from the aforementioned effects. Mitochondrial translocation of PPARα, its binding to cyclophilin D, and sequestration led to inhibition of its nuclear translocation and transcription of PPARα-regulated fatty acid oxidation genes during cisplatin-induced acute kidney injury. Genetic or pharmacological inhibition of cyclophilin D preserved nuclear expression and transcriptional activity of PPARα and prevented the impairment of fatty acid oxidation and intracellular lipid accumulation. Docking analysis identified potential binding sites between PPARα and cyclophilin D. Thus, our results indicate that proximal tubule cyclophilin D elicits impaired mitochondrial fatty acid oxidation via mitochondrial interaction between cyclophilin D and PPARα. Hence, targeting their interaction may be a potential therapeutic strategy to prevent energy depletion, lipotoxicity and cell death in cisplatin-induced acute kidney injury.

CD154 Induces Interleukin-6 Secretion by Kidney Tubular Epithelial Cells under Hypoxic Conditions: Inhibition by Chloroquine

Inflammation is a major contributor to tubular epithelium injury in kidney disorders, and the involvement of blood platelets in driving inflammation is increasingly stressed. CD154, the ligand of CD40, is one of the mediators supporting platelet proinflammatory properties. Although hypoxia is an essential constituent of the inflammatory reaction, if and how platelets and CD154 regulate inflammation in hypoxic conditions remain unclear. Here, we studied the control by CD154 of the proinflammatory cytokine interleukin- (IL-) 6 secretion in short-term oxygen (O₂) deprivation conditions, using the HK-2 cell line as a kidney tubular epithelial cell (TEC) model. IL-6 secretion was markedly stimulated by CD154 after 1 to 3 hours of hypoxic stress. Both intracellular IL-6 expression and secretion were stimulated by CD154 and associated with a strong upregulation of IL-6 mRNA and increased transcription. Searching for inhibitors of CD154-mediated IL-6 production by HK-2 cells in hypoxic conditions, we observed that chloroquine, a drug that has been repurposed as an anti-inflammatory agent, alleviated this induction. Therefore, CD154 is a potent early stimulus for IL-6 secretion by TECs in O₂ deprivation conditions, a mechanism likely to take part in the deleterious inflammatory consequences of platelet activation in kidney tubular injury. The inhibition of CD154-induced IL-6 production by chloroquine suggests the potential usefulness of this drug as a therapeutic adjunct in conditions associated with acute kidney injury.

Oxidative Stress in the Pathophysiology of Kidney Disease: Implications for Noninvasive Monitoring and Identification of Biomarkers

Kidney disease represents a serious global health problem. One of the main concerns is its late diagnosis, only feasible in a progressed disease state. The lack of a clinical manifestation in the early stages and the fact that the commonly measured parameters of renal function are markedly reduced only during advanced stages of the disease are the main cause. Changes at the molecular level of the kidney tissue occur even before nitrogenous substances, such as creatinine and urea, start to accumulate in the blood. Renal proximal tubules contain a large number of mitochondria and are critical for the energy-demanding process of reabsorption of water and solutes. Mitochondria are the largest producers of oxygen radicals, which, in turn, increase the susceptibility of kidneys to oxidative stress-induced damage. Free radicals and prooxidants produced during acute or chronic kidney injury may further aggravate the course of the disease and play a role in the pathogenesis of subsequent complications. Prevention might be the solution in CKD, but patients are often reluctant to undergo preventive examinations. Noninvasive markers and the possibility to obtain samples at home might help to increase compliance. This review will provide an overview of the possible uses of markers of oxidative status in noninvasive biofluids in patients with renal disease.

Animal Models of Diabetes-Associated Renal Injury

Diabetic nephropathy (DN) is the main factor leading to end-stage renal disease (ESRD) and subsequent morbidity and mortality. Importantly, the prevalence of DN is continuously increasing in developed countries. Many rodent models of type 1 and type 2 diabetes have been established to elucidate the pathogenesis of diabetes and examine novel therapies against DN. These models are developed by chemical, surgical, genetic, drug, and diet/nutrition interventions or combination of two or more methods. The main characteristics of DN including a decrease in renal function, albuminuria and mesangiolysis, mesangial expansion, and nodular glomerulosclerosis should be exhibited by an animal model of DN. However, a rodent model possessing all of the abovementioned features of human DN has not yet been developed. Furthermore, mice of different genetic backgrounds and strains show different levels of susceptibility to DN with respect to albuminuria and development of glomerular and tubulointerstitial lesions. Therefore, the type of diabetes, development of nephropathy, duration of the study, cost of maintaining and breeding, and animals' mortality rate are important factors that might be affected by the type of DN model. In this review, we discuss the pros and cons of different rodent models of diabetes that are being used to study DN.

Evaluation of the Risk Factors for Acute Kidney Injury in Neonates Exposed to Antenatal Indomethacin

OBJECTIVE

Evidence is limited about important maternal and neonatal risk factors that affect neonatal renal function. The incidence of acute kidney injury (AKI) and identification of associated risk factors in neonates exposed to antenatal indomethacin was studied.

METHODS

A retrospective cohort of neonates exposed to antenatal indomethacin within 1 week of delivery was analyzed for development of AKI up to 15 days of life. Adjusted hazard ratios (HRs) and 95% CIs for AKI risk were calculated in time-dependent Cox proportional hazards models.

RESULTS

Among 143 neonates with mean gestational age of 28.3 ± 2.4 weeks, AKI occurred in 62 (43.3%), lasting a median duration of 144 hours (IQR, 72-216 hours). Neonates with AKI had greater exposure to postnatal NSAIDs (48.4% vs 9.9%, p < 0.001) and inotropes (37.1% vs 3.7%, p < 0.001) compared with neonates without AKI. In multivariable-adjusted models, increased AKI risk was observed with antenatal indomethacin doses received within 24 to 48 hours (HR, 1.6; 95% CI, 1.28-1.94; p = 0.036) and <24 hours (HR, 2.33; 95% CI, 1.17-4.64; p = 0.016) prior to delivery. Further, postnatal NSAIDs (HR, 2.8; 95% CI, 1.03-7.61; p = 0.044), patent ductus arteriosus (HR, 4.04; 95% CI, 1.27-12.89; p = 0.018), and bloodstream infection (HR, 3.01; 95% CI, 1.37-6.60; p = 0.006) were associated significantly with increased risk of AKI following antenatal indomethacin. Neonates with AKI experienced more bloodstream infection, severe intraventricular hemorrhage, patent ductus arteriosus, respiratory distress syndrome, and longer hospitalization.

CONCLUSIONS

Extended risk of AKI with antenatal indomethacin deserves clinical attention among this population at an already increased AKI risk.

Reno-protection of Urine-derived Stem Cells in A Chronic Kidney Disease Rat Model Induced by Renal Ischemia and Nephrotoxicity

Purpose: Drug-induced nephrotoxicity can occur in patients with pre-existing renal dysfunction or renal ischemia, potentially leading to chronic kidney disease (CKD) and end-stage renal disease (ESRD). Prompt treatment of CKD and the related side effects is critical in preventing progression to ESRD. The goal of this study was to demonstrate the therapeutic potential of urine-derived stem cells (USC) to treat chronic kidney disease-induced by nephrotoxic drugs and renal ischemia.

Materials and methods: Human USC were collected, expanded and characterized by flow cytometry. A CKD model was induced by creating an ischemia-reperfusion injury and gentamicin administration. Twenty-eight adult immunodeficient rats were divided into three groups: PBS-treated group (n=9), USC-treated group (n=9), and sham group with age-matched control animals (n=10). Cell suspension of USC (5 x 10⁶ / 100µl / kidney) or PBS was injected bilaterally into the renal parenchyma 9 weeks after CKD model creation. Renal function was evaluated by collection blood and urine samples to measure serum creatinine and glomerulus filtration rate. The kidneys were harvested 12 weeks after cell injection. Histologically, the extent of glomerulosclerosis and tubular atrophy, the amount of collagen deposition, interstitial fibrosis, inflammatory monocyte infiltration, and expression of transforming growth factor beta 1 (TGF-ß1), and superoxide dismutase 1 (SOD-1) were examined.

Results: USC expressed renal parietal epithelial cells (CD24, CD29 and CD44). Renal function, measured by GFR and serum Cr in USC-treated group were significantly improved compared to PBS-treated animals (p<0.05). The degree of glomerular sclerosis and atrophic renal tubules, the amount of fibrosis, and monocyte infiltration significantly decreased in USC-treated group compared to the PBS group (p<0.05). The level of TGF-ß1 expression in renal tissues was also significantly lower in the PBS group, while the level of SOD-1 expression was significantly elevated in the USC group, compared to PBS group (p<0.05).

Conclusions: The present study demonstrates the nephron-protective effect of USC on renal function via anti-inflammatory, anti-oxidative stress, and anti-fibrotic activity in a dual-injury CKD rat model. This provides an alternative treatment for CKD in certain clinical situations, such as instances where CKD is due to drug-induced nephrotoxicity and renal ischemia.

Tubular and Glomerular Biomarkers of Acute Kidney Injury in Newborns

BACKGROUND

Acute Kidney Injury (AKI) is a sudden decrease in kidney function. In the early period, the highest percentage of AKI occurs among newborns hospitalized in the neonatal intensive care units, especially premature neonates. The prognosis of AKI depends on the type and severity of the cause of an injury, the accuracy and the time of diagnosis and treatment. The concentration of serum creatinine is still the main diagnostic test, although it changes in the course of AKI later than glomerular filtration rate GFR. In addition, the reliability of the determination of creatinine level is limited because it depends on many factors. New studies have presented other, more useful laboratory markers of renal function that can be measured in serum and/or in urine.

OBJECTIVE

The aim of the work was to present the latest data about tubular and glomerular biomarkers of acute kidney injury in newborns.

METHODS

We undertook a structured search of bibliographic databases for peer-reviewed research literature by using focused review topics. According to the conceptual framework, the main idea of research literature has been summarized and presented in this study.

RESULTS

The concentrations of some novel biomarkers are higher in serum and/or urine of term and preterm newborns with AKI, especially in the course of perinatal asphyxia.

CONCLUSION

In this systematic review of the literature, we have highlighted the usefulness of biomarkers in predicting tubular and/or glomerular injury in newborns. However, novel biomarkers need to prove their clinical applicability, accuracy, and cost-effectiveness prior to their implementation in clinical practice.

Novel Variants of Angiotensin Converting Enzyme-2 of Shorter Molecular Size to Target the Kidney Renin Angiotensin System

ACE2 is a monocarboxypeptidase which generates Angiotensin (1-7) from Angiotensin II (1-8). Attempts to target the kidney Renin Angiotensin System using native ACE2 to treat kidney disease are hampered by its large molecular size, 100 kDa, which precludes its glomerular filtration and subsequent tubular uptake. Here, we show that both urine and kidney lysates are capable of digesting native ACE2 into shorter proteins of ~60-75 kDa and then demonstrate that they are enzymatically very active. We then truncated the native ACE2 by design from the C-terminus to generate two short recombinant (r)ACE2 variants (1-605 and 1-619AA). These two truncates have a molecular size of ~70 kDa, as expected from the amino acid sequence and as shown by Western blot. ACE2 enzyme activity, measured using a specific substrate, was higher than that of the native rACE2 (1-740 AA). When infused to mice with genetic ACE2 deficiency, a single i.v. injection of 1-619 resulted in detectable ACE2 activity in urine, whereas infusion of the native ACE2 did not. Moreover, ACE2 activity was recovered in harvested kidneys from ACE2-deficient mice infused with 1-619, but not in controls (23.1 ± 4.3 RFU/µg creatinine/h and 1.96 ± 0.73 RFU/µg protein/hr, respectively). In addition, the kidneys of ACE2-null mice infused with 1-619 studied ex vivo formed more Ang (1-7) from exogenous Ang II than those infused with vehicle (AUC 8555 ± 1933 vs. 3439 ± 753 ng/mL, respectively, p < 0.05) further demonstrating the functional effect of increasing kidney ACE2 activity after the infusion of our short ACE2 1-619 variant. We conclude that our novel short recombinant ACE2 variants undergo glomerular filtration, which is associated with kidney uptake of enzymatically active proteins that can enhance the formation of Ang (1-7) from Ang II. These small ACE2 variants may offer a potentially useful approach to target kidney RAS overactivity to combat kidney injury.

Un nuevo paradigma en el fracaso renal agudo

El fracaso renal agudo es una de las patologías con las que más ha avanzado el conocimiento médico y, sin embargo, menos se ha modificado el tratamiento o el pronóstico. Con un crecimiento anual de un 25%, el fracaso renal afecta a más de trece millones de personas en el mundo cada año. Cuando aparece en un paciente hospitalizado por otro motivo, aumenta la duración de la estancia media en casi cuatro días. La mortalidad por fracaso renal agudo es mayor que la mortalidad combinada por cáncer de mama, cáncer de próstata, insuficiencia cardíaca y diabetes. Varios factores pueden estar contribuyendo a esta epidemia mundial que afecta por igual, aunque por distintas causas, a los países del primer mundo tanto como a los subdesarrollados. - El envejecimiento de la población. - La aparición de gérmenes más agresivos y resistentes que requieren tratamientos más nefrotóxicos. - El aumento de la fragilidad en los pacientes seleccionados para tratamientos quirúrgicos, oncológicos y antibióticos cada vez más exigentes. - El aumento de prevalencia de enfermedades crónicas con un riesgo cardiovascular progresivamente mayor y proporcional al nivel de inflamación.

Analysis of the critical determinants of renal medullary oxygenation

We have previously developed a three-dimensional computational model of oxygen transport in the renal medulla. In the present study, we used this model to quantify the sensitivity of renal medullary oxygenation to four of its major known determinants: medullary blood flow (MBF), medullary oxygen consumption rate (V̇o2,M), hemoglobin (Hb) concentration in the blood, and renal perfusion pressure. We also examined medullary oxygenation under special conditions of hydropenia, extracellular fluid volume expansion by infusion of isotonic saline, and hemodilution during cardiopulmonary bypass. Under baseline (normal) conditions, the average medullary tissue Po2 predicted for the whole renal medulla was ~30 mmHg. The periphery of the interbundle region in the outer medulla was identified as the most hypoxic region in the renal medulla, which demonstrates that the model prediction is qualitatively accurate. Medullary oxygenation was most sensitive to changes in renal perfusion pressure followed by Hb, MBF, and V̇o2,M, in that order. The medullary oxygenation also became sensitized by prohypoxic changes in other parameters, leading to a greater fall in medullary tissue Po2 when multiple parameters changed simultaneously. Hydropenia did not induce a significant change in medullary oxygenation compared with the baseline state, while volume expansion resulted in a large increase in inner medulla tissue Po2 (by ~15 mmHg). Under conditions of cardiopulmonary bypass, the renal medulla became severely hypoxic, due to hemodilution, with one-third of the outer stripe of outer medulla tissue having a Po2 of <5 mmHg.

The role of CD47 in pathogenesis and treatment of renal ischemia reperfusion injury

Ischemia reperfusion (IR) injury is a process defined by the temporary loss of blood flow and tissue perfusion followed later by restoration of the same. Brief periods of IR can be tolerated with little permanent deficit, but sensitivity varies for different target cells and tissues. Ischemia reperfusion injuries have multiple causes including peripheral vascular disease and surgical interventions that disrupt soft tissue and organ perfusion as occurs in general and reconstructive surgery. Ischemia reperfusion injury is especially prominent in organ transplantation where substantial effort has been focused on protecting the transplanted organ from the consequences of IR. A number of factors mediate IR injury including the production of reactive oxygen species and inflammatory cell infiltration and activation. In the kidney, IR injury is a major cause of acute injury and secondary loss of renal function. Transplant-initiated renal IR is also a stimulus for innate and adaptive immune-mediated transplant dysfunction. The cell surface molecule CD47 negatively modulates cell and tissue responses to stress through limitation of specific homeostatic pathways and initiation of cell death pathways. Herein, a summary of the maladaptive activities of renal CD47 will be considered as well as the possible therapeutic benefit of interfering with CD47 to limit renal IR.

A Melanin-Based Natural Antioxidant Defense Nanosystem for Theranostic Application in Acute Kidney Injury

Acute kidney injury (AKI) is frequently associated with oxidative stress and causes high mortality annually in clinics. Nanotechnology-mediated antioxidative therapy is emerging as a novel strategy for the treatment of AKI. Herein, a novel biomedical use of the endogenous biopolymer melanin as a theranostic natural antioxidant defense nanoplatform for AKI is reported. In this study, ultrasmall Mn2+-chelated melanin (MMP) nanoparticles are easily prepared via a simple coordination and self-assembly strategy, and further incorporated with polyethylene glycol (MMPP). In vitro experiments reveal the ability of MMPP nanoparticles to scavenge multiple toxic reactive oxygen species (ROS) and suppress ROS-induced oxidative stress. Additionally, in vivo results from a murine AKI model demonstrate preferential renal uptake of MMPP nanoparticles and a subsequent robust antioxidative response with negligible side effects according to positron emission tomography/magnetic resonance (PET/MR) bimodal imaging and treatment assessment. These results indicate that the effectiveness of MMPP nanoparticles for treating AKI suggests the potential efficacy of melanin as a natural theranostic antioxidant nanoplatform for AKI, as well as other ROS-related diseases.

Acute kidney injury and adverse outcomes of critical illness: correlation or causation?

Critically ill patients who develop acute kidney injury (AKI) are more than twice as likely to die in hospital. However, it is not clear to what extent AKI is the cause of excess mortality, or merely a correlate of illness severity. The Bradford Hill criteria for causality (plausibility, temporality, magnitude, specificity, analogy, experiment & coherence, biological gradient and consistency) were applied to assess the extent to which AKI may be causative in adverse short-term outcomes of critical illness.

Plausible mechanisms exist to explain increased risk of death after AKI, both from direct pathophysiological effects of renal dysfunction and mechanisms of organ cross-talk in multiple-organ failure. The temporal relationship between increased mortality following AKI is consistent with its pathophysiology. AKI is associated with substantially increased mortality, an association that persists after accounting for known confounders. A biological gradient exists between increasing severity of AKI and increasing short-term mortality. This graded association shares similar features to the increased mortality observed in ARDS; an analogous condition with a multifactorial aetiology. Evidence for the outcomes of AKI from retrospective cohort studies and experimental animal models is coherent however both of these forms of evidence have intrinsic biases and shortcomings. The relationship between AKI and risk of death is maintained across a range of patient ages, comorbidities and underlying diagnoses.

In conclusion many features of the relationship between AKI and short-term mortality suggest causality. Prevention and mitigation of AKI and its complications are valid targets for studies seeking to improve short-term survival in critical care.

Oxidative stress as a potential target in acute kidney injury

Background

Acute kidney injury (AKI) is a major problem for health systems being directly related to short and long-term morbidity and mortality. In the last years, the incidence of AKI has been increasing. AKI and chronic kidney disease (CKD) are closely interconnected, with a growing rate of CKD linked to repeated and severe episodes of AKI. AKI and CKD can occur also secondary to imbalanced oxidative stress (OS) reactions, inflammation, and apoptosis. The kidney is particularly sensitive to OS. OS is known as a crucial pathogenetic factor in cellular damage, with a direct role in initiation, development, and progression of AKI. The aim of this review is to focus on the pathogenetic role of OS in AKI in order to gain a better understanding. We exposed the potential relationships between OS and the perturbation of renal function and we also presented the redox-dependent factors that can contribute to early kidney injury. In the last decades, promising advances have been made in understanding the pathophysiology of AKI and its consequences, but more studies are needed in order to develop new therapies that can address OS and oxidative damage in early stages of AKI.

Methods

We searched PubMed for relevant articles published up to May 2019. In this review we incorporated data from different types of studies, including observational and experimental, both in vivo and in vitro, studies that provided information about OS in the pathophysiology of AKI.

Results

The results show that OS plays a major key role in the initiation and development of AKI, providing the chance to find new targets that can be therapeutically addressed.

Discussion

Acute kidney injury represents a major health issue that is still not fully understood. Research in this area still provides new useful data that can help obtain a better management of the patient. OS represents a major focus point in many studies, and a better understanding of its implications in AKI might offer the chance to fight new therapeutic strategies.

Urine neutrophil gelatinase-associated lipocalin to diagnose and characterize acute kidney injury in dogs

BACKGROUND

Urine neutrophil gelatinase-associated lipocalin (NGAL) is a promising biomarker of acute kidney injury (AKI) in dogs.

OBJECTIVES

To evaluate the utility of urinary NGAL for characterizing AKI according to volume responsiveness, presence of inflammation and sepsis, and prognosis.

ANIMALS

Dogs with AKI (n = 76) and healthy controls (n = 10).

METHODS

Prospective study. Clinical and clinicopathologic data including absolute urine NGAL concentration (uNGAL) and NGAL normalized to urine creatinine concentration (uNGALC) were measured upon admission. Dogs were graded according to International Renal Interest Society (IRIS) AKI guidelines and compared based on AKI features: volume-responsive (VR-) AKI vs. intrinsic (I-) AKI based on IRIS criteria; VR-AKI and I-AKI based on urine chemistry; inflammatory versus noninflammatory; septic versus nonseptic; and survivors versus nonsurvivors. Nonparametric statistics were calculated, and significance set at P < .05.

RESULTS

Urinary NGAL was significantly higher in dogs with AKI compared to controls, regardless of AKI grade. Urinary NGAL did not differ between dogs with VR-AKI and I-AKI based on IRIS criteria, whereas higher uNGALC was recorded in dogs with I-AKI based on urine chemistry. Urinary NGAL was significantly higher in dogs with inflammatory AKI, whereas no difference with respect to sepsis or outcome was identified.

CONCLUSIONS AND CLINICAL IMPORTANCE

Urinary NGAL is a sensitive marker for AKI in dogs, but its specificity is affected by systemic inflammation. Increased urinary NGAL in both I-AKI and VR-AKI also suggests the presence of tubular damage in transient AKI. Combining urine chemistry data with IRIS criteria could facilitate AKI characterization in dogs.

Nucleophosmin Phosphorylation as a Diagnostic and Therapeutic Target for Ischemic AKI

Background Ischemic AKI lacks a urinary marker for early diagnosis and an effective therapy. Differential nucleophosmin (NPM) phosphorylation is a potential early marker of ischemic renal cell injury and a therapeutic target.Methods Differential NPM phosphorylation was assessed by mass spectrometry in NPM harvested from murine and human primary renal epithelial cells, fresh kidney tissue, and urine before and after ischemic injury. The biologic behavior and toxicity of NPM was assessed using phospho-NPM mutant proteins that either mimic stress-induced or normal NPM phosphorylation. Peptides designed to interfere with NPM function were used to explore NPM as a therapeutic target.Results Within hours of stress, virtually identical phosphorylation changes were detected at distinct serine/threonine sites in NPM harvested from primary renal cells, tissue, and urine. A phosphomimic NPM protein that replicated phosphorylation under stress localized to the cytosol, formed monomers that interacted with Bax, a cell death protein, coaccumulated with Bax in isolated mitochondria, and significantly increased cell death after stress; wild-type NPM or a phosphomimic NPM with a normal phosphorylation configuration did not. Three renal targeted peptides designed to interfere with NPM at distinct functional sites significantly protected against cell death, and a single dose of one peptide administered several hours after ischemia that would be lethal in untreated mice significantly reduced AKI severity and improved survival.Conclusions These findings establish phosphorylated NPM as a potential early marker of ischemic AKI that links early diagnosis with effective therapeutic interventions.

Periostin Promotes Cell Proliferation and Macrophage Polarization to Drive Repair after AKI

BACKGROUND

The matricellular protein periostin has been associated with CKD progression in animal models and human biopsy specimens. Periostin functions by interacting with extracellular matrix components to drive collagen fibrillogenesis and remodeling or by signaling through cell-surface integrin receptors to promote cell adhesion, migration, and proliferation. However, its role in AKI is unknown.

METHODS

We used mice with conditional tubule-specific overexpression of periostin or knockout mice lacking periostin expression in the renal ischemia-reperfusion injury model, and primary cultures of isolated tubular cells in a hypoxia-reoxygenation model.

RESULTS

Tubular epithelial cells showed strong production of periostin during the repair phase of ischemia reperfusion. Periostin overexpression protected mice from renal injury compared with controls, whereas knockout mice showed increased tubular injury and deteriorated renal function. Periostin interacted with its receptor, integrin-β1, to inhibit tubular cell cycle arrest and apoptosis in in vivo and in vitro models. After ischemia-reperfusion injury, periostin-overexpressing mice exhibited diminished expression of proinflammatory molecules and had more F4/80⁺ macrophages compared with knockout mice. Macrophages from periostin-overexpressing mice showed increased proliferation and expression of proregenerative factors after ischemia-reperfusion injury, whereas knockout mice exhibited the opposite. Coculturing a macrophage cell line with hypoxia-treated primary tubules overexpressing periostin, or treating such macrophages with recombinant periostin, directly induced macrophage proliferation and expression of proregenerative molecules.

CONCLUSIONS

In contrast to the detrimental role of periostin in CKD, we discovered a protective role of periostin in AKI. Our findings suggest periostin may be a novel and important mediator of mechanisms controlling renal repair after AKI.

Ursolic acid exhibits anti-inflammatory effects through blocking TLR4-MyD88 pathway mediated by autophagy

There is an urgent need for effective treatments to reduce the large and growing burden of acute kidney injury (AKI) and its consequences. Inflammation is believed to play a vital role in the pathophysiology of AKI. Macrophage autophagy is considered protective against inflammation. Previous study discovered that ursolic acid (UA), a natural pentacyclic triterpene carboxylic acid found in many plants as apples, bilberries, cranberries and so on, promoted cancer cell autophagy. In the present study, we aimed to explore the effect of UA on ameliorating AKI and the role of macrophage autophagy in the context of inflammation. The data from in vivo experiments showed that pretreatment of mice with UA significantly suppressed xylene-induced ear oedema as well as protected against LPS-induced AKI. Related mechanisms were further studied through in vitro experiment. As expected, UA decreased inflammatory factors TNF-α, IL-6 and IL-1β secretion in macrophages in response to lipopolysaccharide (LPS) stimulation. Furthermore, UA blocked LPS-induced TLR4/MyD88 pathway. More importantly, enhanced autophagy of macrophages by UA through increasing the expression of both LC3B and Beclin-1 led to alter macrophage function. What is more, similar to UA, autophagy inhibitor 3-MA obviously decreased inflammation factors releases hinting the vital role of autophagy in regulating inflammation. In all, above study suggested that UA is a potential anti-inflammatory natural compound for treating AKI by inducing autophagy.

Magnetization Transfer Imaging Is Unaffected by Decreases in Renal Perfusion in Swine

OBJECTIVES

Multiparametric renal magnetic resonance imaging (MRI), including diffusion-weighted imaging, magnetic resonance elastography, and magnetization transfer imaging (MTI), is valuable in the noninvasive assessment of renal fibrosis. However, hemodynamic changes in diseased kidneys may impede their ability to measure renal fibrosis. Because MTI assesses directly tissue content of macromolecules, we test the hypothesis that MTI would be insensitive to renal hemodynamic changes in swine kidneys with acute graded ischemia.

MATERIALS AND METHODS

Seven domestic pigs underwent placement of an inflatable silicone cuff around the right renal artery to induce graded renal ischemia. Multiparametric MRI was performed at baseline, 50%, 75%, and 100% renal artery stenosis as well as reperfusion. Measurements included regional perfusion, R2*, apparent diffusion coefficient (ADC), stiffness, and magnetization transfer ratio (MTR) using arterial spin-labeled MRI, blood oxygenation-dependent MRI, diffusion-weighted imaging, magnetic resonance elastography, and MTI, respectively. Histology was performed to rule out renal fibrosis.

RESULTS

During graded ischemia, decreases in renal perfusion were accompanied with elevated R2*, decreased ADC, and stiffness, whereas no statistically significant changes were observed in the MTR. No fibrosis was detected by histology. After release of the obstruction, renal perfusion showed only partial recovery, associated with return of kidney R2*, ADC, and stiffness to baseline levels, whereas cortical MTR decreased slightly.

CONCLUSIONS

Renal MTI is insensitive to decreases in renal perfusion and may offer reliable assessment of renal structural changes.

Lithium targeting of AMPK protects against cisplatin-induced acute kidney injury by enhancing autophagy in renal proximal tubular epithelial cells

Autophagy has been demonstrated to be vital for kidney homeostasis and is centrally implicated in the pathogenesis of cisplatin-induced acute kidney injury (AKI). Lithium is a potent autophagy inducer in a number of cell types. However, it remains uncertain whether its autophagic activity is associated with a beneficial effect on renal tubular cells in AKI. This study aimed to examine the effect of lithium on renal autophagy in cisplatin-induced AKI. Mice or renal proximal tubular epithelial cells in culture were exposed to cisplatin-induced acute injury in the presence or absence of lithium treatment. AKI or tubular cell injury was evaluated, and cell signaling associated with autophagy was examined. Lithium pretreatment prominently ameliorated acute renal tubular damage in mice exposed to cisplatin insult, associated with enhanced autophagy in renal tubules, as assessed by measuring microtubule-associated protein 1A/1B-light chain 3 (LC3)BII/I expression and autophagosome formation. Consistently, in cisplatin-injured renal tubular cells in vitro, lithium enhanced autophagic activities, improved cell viability, and attenuated cell death. Mechanistically, lithium triggered AMPK-α phosphorylation and activation, which in turn positively correlated with the induced expression of autophagy-related molecules, like mammalian target of rapamycin and LC3BII/I. AMPK-α activation is likely required for lithium-induced tubular cell autophagy and protection in cisplatin-induced AKI because blockade of AMPK-α phosphorylation by compound C markedly abrogated lithium-induced autophagosome formation and mitigated the protective effect of lithium on AKI. Our findings suggest that lithium represents a promising therapeutic strategy for protecting renal tubular cells against cisplatin-induced AKI by enhancing autophagy via AMPK-α activation.-Bao, H., Zhang, Q., Liu, X., Song, Y., Li, X., Wang, Z., Li, C., Peng, A., Gong, R. Lithium targeting of AMPK protects against cisplatin-induced acute kidney injury by enhancing autophagy in renal proximal tubular epithelial cells.

Kidney-based in vitro models for drug-induced toxicity testing

The kidney is frequently involved in adverse effects caused by exposure to foreign compounds, including drugs. An early prediction of those effects is crucial for allowing novel, safe drugs entering the market. Yet, in current pharmacotherapy, drug-induced nephrotoxicity accounts for up to 25% of the reported serious adverse effects, of which one-third is attributed to antimicrobials use. Adverse drug effects can be due to direct toxicity, for instance as a result of kidney-specific determinants, or indirectly by, e.g., vascular effects or crystals deposition. Currently used in vitro assays do not adequately predict in vivo observed effects, predominantly due to an inadequate preservation of the organs' microenvironment in the models applied. The kidney is highly complex, composed of a filter unit and a tubular segment, together containing over 20 different cell types. The tubular epithelium is highly polarized, and the maintenance of this polarity is critical for optimal functioning and response to environmental signals. Cell polarity is dependent on communication between cells, which includes paracrine and autocrine signals, as well as biomechanic and chemotactic processes. These processes all influence kidney cell proliferation, migration, and differentiation. For drug disposition studies, this microenvironment is essential for prediction of toxic responses. This review provides an overview of drug-induced injuries to the kidney, details on relevant and translational biomarkers, and advances in 3D cultures of human renal cells, including organoids and kidney-on-a-chip platforms.

AMPK Activation Promotes Tight Junction Assembly in Intestinal Epithelial Caco-2 Cells

The AMP-activated protein kinase (AMPK) is principally known as a major regulator of cellular energy status, but it has been recently shown to play a key structural role in cell-cell junctions. The aim of this study was to evaluate the impact of AMPK activation on the reassembly of tight junctions in intestinal epithelial Caco-2 cells. We generated Caco-2 cells invalidated for AMPK α1/α2 (AMPK dKO) by CRISPR/Cas9 technology and evaluated the effect of the direct AMPK activator 991 on the reassembly of tight junctions following a calcium switch assay. We analyzed the integrity of the epithelial barrier by measuring the trans-epithelial electrical resistance (TEER), the paracellular permeability, and quantification of zonula occludens 1 (ZO-1) deposit at plasma membrane by immunofluorescence. Here, we demonstrated that AMPK deletion induced a delay in tight junction reassembly and relocalization at the plasma membrane during calcium switch, leading to impairments in the establishment of TEER and paracellular permeability. We also showed that 991-induced AMPK activation accelerated the reassembly and reorganization of tight junctions, improved the development of TEER and paracellular permeability after calcium switch. Thus, our results show that AMPK activation ensures a better recovery of epithelial barrier function following injury.

Neprilysin, the kidney brush border neutral proteinase: a possible potential target for ischemic renal injury

Neprilysin (NEP) is an endogenously induced peptidase for modulating production and degradation of various peptides in humans. It is most abundantly present in kidney and regulates the intrinsic renal homeostatic mechanism. Recently, drugs inhibiting NEP have been approved for the use in heart failure. In the context of increased prevalence of ischemia associated renal failure, NEP could be an attractive target for treating kidney failure. In the kidney, targeting NEP may possess potential benefits as well as adverse consequences. The unfavorable outcomes of NEP are mainly attributed to the degradation of the natriuretic peptides (NPs). NPs are involved in the inhibition of the renin-angiotensin-aldosterone system (RAAS) and activation of the sympathetic system contributing to the tubular and glomerular injury. In contrary, NEP exerts the beneficial effect by converting angiotensin-1 (Ang I) to angiotensin-(1-7) (Ang-(1-7)), thus activating MAS-related G-protein coupled receptor. MAS receptor antagonizes angiotensin type I receptor (AT-1R), reduces reactive oxygen species (ROS) and inflammation, thus ameliorating renal injury. However, the association of NEP with complex cascades of renal ischemia remains vague. Therefore, there is a need to evaluate the putative mechanism of NEP and its overlap with other signaling cascades in conditions of renal ischemia.

Evaluation with endothelial nitric oxide synthase (eNOS) immunoreactivity of the protective role of astaxanthin on hepatorenal injury of remote organs caused by ischaemia reperfusion of the lower extremities

Introduction

Ischemia and following reperfusion triggers local and systemic damage with the involvement of free oxygen radicals and inflammatory mediators. Although blood flow saves extremity from necrosis,multi organ dysfunction may progress and cause death of the patient.

Aim

The study aims to examine the effect of astaxanthin (AST) on the prevention of remote tissue injury resulting from lower extremity ischaemia–reperfusion (I/R). To elucidate the potential hepatoprotective and renoprotective effects of AST, in addition to histopathological findings, the intrahepatic and intrarenal kinetics of endothelial nitric oxide synthase (eNOS) during I/R were determined by using the immunohistochemical method.

Material and methods

Twenty-eight male Wistar albino rats were divided into four groups. For the control group, only the anaesthesia procedure (2 h) was conducted without I/R. In the I/R group, 2 h of reperfusion was conducted following ischaemia under anaesthesia. For the I/R group + AST, 7 days prior to ischaemia, 125 mg/kg AST was given with gavage, and 2 h of ischaemia and 2 h of reperfusion were conducted under anaesthesia. Following necropsy, liver and kidney tissue samples were fixed in 10% buffered formalin for 48 h for histopathological and immunohistochemical investigation.

Results

The histological analysis revealed that severe I/R hepatorenal injury such as inflammatory cell infiltration, dilatation in sinusoids and lumen of tubuli, congestion in glomerular capillaries, degeneration in hepatocyte and epithelial cells of tubuli, and necrosis was ameliorated by AST. Immunohistochemical studies showed that the I/R-induced elevation in eNOS expression was reduced by AST treatment.

Conclusions

In the case of acute lower extremity I/R, AST decreased the ischaemic injury in liver and renal tissues by protecting the microcirculation and providing a cytoprotective effect with vasodilatation.

Molecular optical imaging probes for early diagnosis of drug-induced acute kidney injury

Drug-induced acute kidney injury (AKI) with a high morbidity and mortality is poorly diagnosed in hospitals and deficiently evaluated in drug discovery. Here, we report the development of molecular renal probes (MRPs) with high renal clearance efficiency for in vivo optical imaging of drug-induced AKI. MRPs specifically activate their near-infrared fluorescence or chemiluminescence signals towards the prodromal biomarkers of AKI including the superoxide anion, N-acetyl-β-D-glucosaminidase and caspase-3, enabling an example of longitudinal imaging of multiple molecular events in the kidneys of living mice. Importantly, they in situ report the sequential occurrence of oxidative stress, lysosomal damage and cellular apoptosis, which precedes clinical manifestation of AKI (decreased glomerular filtration). Such an active imaging mechanism allows MRPs to non-invasively detect the onset of cisplatin-induced AKI at least 36 h earlier than the existing imaging methods. MRPs can also act as exogenous tracers for optical urinalysis that outperforms typical clinical/preclinical assays, demonstrating their clinical promise for early diagnosis of AKI.

Polyamine Catabolism in Acute Kidney Injury

Acute kidney injury (AKI) refers to an abrupt decrease in kidney function. It affects approximately 7% of all hospitalized patients and almost 35% of intensive care patients. Mortality from acute kidney injury remains high, particularly in critically ill patients, where it can be more than 50%. The primary causes of AKI include ischemia/reperfusion (I/R), sepsis, or nephrotoxicity; however, AKI patients may present with a complicated etiology where many of the aforementioned conditions co-exist. Multiple bio-markers associated with renal damage, as well as metabolic and signal transduction pathways that are involved in the mediation of renal dysfunction have been identified as a result of the examination of models, patient samples, and clinical data of AKI of disparate etiologies. These discoveries have enhanced our ability to diagnose AKIs and to begin to elucidate the mechanisms involved in their pathogenesis. Studies in our laboratory revealed that the expression and activity of spermine/spermidine N1-acetyltransferase (SAT1), the rate-limiting enzyme in polyamine back conversion, were enhanced in kidneys of rats after I/R injury. Additional studies revealed that the expression of spermine oxidase (SMOX), another critical enzyme in polyamine catabolism, is also elevated in the kidney and other organs subjected to I/R, septic, toxic, and traumatic injuries. The maladaptive role of polyamine catabolism in the mediation of AKI and other injuries has been clearly demonstrated. This review will examine the biochemical and mechanistic basis of tissue damage brought about by enhanced polyamine degradation and discuss the potential of therapeutic interventions that target polyamine catabolic enzymes or their byproducts for the treatment of AKI.

Mechanisms Underlying Exacerbation of Osmotic Nephrosis Caused by Pre-existing Kidney Injury

Osmotic nephrosis, a disease caused by intravenous infusion of various fluids such as hypertonic sucrose and isotonic polysaccharide-based plasma volume expanders, exhibits specific histopathological features, including vacuolated and swollen proximal tubules, ie, "clear tubules". Pre-existing kidney injury exacerbates this condition, resulting in major clinical problems. However, the underlying mechanisms are unclear. Animal models often yield results that are directly translatable to humans. Therefore, in this study, we performed detailed histopathological analyses of the formation of clear tubules in rats treated with gentamicin or ischemia/reperfusion (IR) operation followed by dextran administration. The results showed that clear tubules may originate from regenerative tubules. Additionally, we classified regenerative tubules into 3 categories based on their development, with a particular focus on the middle and late stages. Comprehensive microarray and real-time polymerase chain reaction analyses of mRNA extracted from regenerative tubules at each stage using laser microdissection revealed that regenerative tubules in the middle stage showed an imbalance between dextran absorption and metabolism, resulting in accumulation of dextran, particularly in the cytoplasm of the tubules. Overall, our findings demonstrated that clear tubules originated from regenerated tubules and that tubules at the middle stage became clear tubules because of an imbalance during their development. This could explain why osmotic nephrosis is exacerbated in the presence of kidney lesions.

Oxidative Stress and Renal Fibrosis: Mechanisms and Therapies

Oxidative stress results from the disruption of the redox system marked by a notable overproduction of reactive oxygen species. There are four major sources of reactive oxygen species, including NADPH oxidases, mitochondria, nitric oxide synthases, and xanthine oxidases. It is well known that renal abnormalities trigger the production of reactive oxygen species by diverse mechanisms under various pathologic stimuli, such as acute kidney injury, chronic kidney disease, nephrotic syndrome, and metabolic disturbances. Mutually, accumulating evidences have identified that oxidative stress plays an essential role in tubulointerstitial fibrosis by myofibroblast activation as well as in glomerulosclerosis by mesangial sclerosis, podocyte abnormality, and parietal epithelial cell injury. Given the involvement of oxidative stress in renal fibrosis, therapies targeting oxidative stress seem promising in renal fibrosis management. In this review, we sketch the updated knowledge of the mechanisms of oxidative stress generation during renal diseases, the pathogenic processes of oxidative stress elicited renal fibrosis and treatments targeting oxidative stress during tubulointerstitial fibrosis and glomerulosclerosis.

Determinants of preferential renal accumulation of synthetic polymers in acute kidney injury

Acute kidney injury (AKI) is a major kidney disease associated with high mortality and morbidity. AKI may lead to chronic kidney disease and end-stage renal disease. Currently, the management of AKI is mainly focused on supportive treatments. Previous studies showed macromolecular delivery systems as a promising method to target AKI, but little is known about how physicochemical properties affect the renal accumulation of polymers in ischemia-reperfusion AKI. In this study, a panel of fluorescently labeled polymers with a range of molecular weights and net charge was synthesized by living radical polymerization. By testing biodistribution of the polymers in unilateral ischemia-reperfusion mouse model of AKI, the results showed that negatively charged and neutral polymers had the greatest potential for selectively accumulating in I/R kidneys. The polymers passed through glomerulus and were retained in proximal tubular cells for up to 24 h after injection. The results obtained in the unilateral model were validated in a bilateral ischemic-reperfusion model. This study demonstrates for the first time that polymers with specific physicochemical characteristics exhibit promising ability to accumulate in the injured AKI kidney, providing initial insights on their use as polymeric drug delivery systems in AKI.

The Potential for Renal Injury Elicited by Physical Work in the Heat

An epidemic of chronic kidney disease (CKD) is occurring in laborers who undertake physical work in hot conditions. Rodent data indicate that heat exposure causes kidney injury, and when this injury is regularly repeated it can elicit CKD. Studies in humans demonstrate that a single bout of exercise in the heat increases biomarkers of acute kidney injury (AKI). Elevations in AKI biomarkers in this context likely reflect an increased susceptibility of the kidneys to AKI. Data largely derived from animal models indicate that the mechanism(s) by which exercise in the heat may increase the risk of AKI is multifactorial. For instance, heat-related reductions in renal blood flow may provoke heterogenous intrarenal blood flow. This can promote localized ischemia, hypoxemia and ATP depletion in renal tubular cells, which could be exacerbated by increased sodium reabsorption. Heightened fructokinase pathway activity likely exacerbates ATP depletion occurring secondary to intrarenal fructose production and hyperuricemia. Collectively, these responses can promote inflammation and oxidative stress, thereby increasing the risk of AKI. Equivalent mechanistic evidence in humans is lacking. Such an understanding could inform the development of countermeasures to safeguard the renal health of laborers who regularly engage in physical work in hot environments.

The role of platelets in acute kidney injury

Acute kidney injury (AKI), a major public health problem associated with high mortality and increased risk of progression towards end-stage renal disease, is characterized by the activation of intra-renal haemostatic and inflammatory processes. Platelets, which are present in high numbers in the circulation and can rapidly release a broad spectrum of bioactive mediators, are important acute modulators of inflammation and haemostasis, as they are the first cells to arrive at sites of acute injury, where they interact with endothelial cells and leukocytes. Diminished control of platelet reactivity by endothelial cells and/or an increased release of platelet-activating mediators can lead to uncontrolled platelet activation in AKI. As increased platelet sequestration and increased expression levels of the markers P-selectin, thromboxane A₂, CC-chemokine ligand 5 and platelet factor 4 on platelets have been reported in kidneys following AKI, platelet activation likely plays a part in AKI pathology. Results from animal models and some clinical studies highlight the potential of antiplatelet therapies in the preservation of renal function in the context of AKI, but as current strategies also affect other cell types and non-platelet-derived mediators, additional studies are required to further elucidate the extent of platelet contribution to the pathology of AKI and to determine the best therapeutic approach by which to specifically target related pathogenic pathways.

Chronic exposure to hypoxia attenuates renal injury and innate immunity activation in the remnant kidney model

Hypoxia is thought to influence the pathogenesis of chronic kidney disease, but direct evidence that prolonged exposure to tissue hypoxia initiates or aggravates chronic kidney disease is lacking. We tested this hypothesis by chronically exposing normal rats and rats with 5/6 nephrectomy (Nx) to hypoxia. In addition, we investigated whether such effect of hypoxia would involve activation of innate immunity. Adult male Munich-Wistar rats underwent Nx (n = 54) or sham surgery (sham; n = 52). Twenty-six sham rats and 26 Nx rats remained in normoxia, whereas 26 sham rats and 28 Nx rats were kept in a normobaric hypoxia chamber (12% O₂) for 8 wk. Hypoxia was confirmed by immunohistochemistry for pimonidazole. Hypoxia was confined to the medullary area in sham + normoxia rats and spread to the cortical area in sham + hypoxia rats, without changing the peritubular capillary density. Exposure to hypoxia promoted no renal injury or elevation of the content of IL-1β or Toll-like receptor 4 in sham rats. In Nx, hypoxia also extended to the cortical area without ameliorating the peritubular capillary rarefaction but, unexpectedly, attenuated hypertension, inflammation, innate immunity activation, renal injury, and oxidative stress. The present study, in disagreement with current concepts, shows evidence that hypoxia exerts a renoprotective effect in the Nx model instead of acting as a factor of renal injury. The mechanisms for this unexpected beneficial effect are unclear and may involve NF-κB inhibition, amelioration of oxidative stress, and limitation of angiotensin II production by the renal tissue.