Nox4 in renal diseases: An update

Alpha lipoic acid attenuates iron induced oxidative acute kidney injury in rats

Iron has been implicated in oxidative tissue injury owing to its ability to generate reactive oxygen species (ROS). We investigated the reno-protective effects of alpha lipoic acid (ALA) by investigating its effects on the kidney isoform of NADPH oxidase (Nox4) and the specific signaling pathways, p38 MAPK and PI3K/Akt, which participate in apoptosis and survival, respectively. We established four groups of seven rats: control, 100 mg/kg ALA, 80 mg/kg iron sucrose (IS) and IS + ALA. IS and ALA were injected intravenously and rats were sacrificied after 6 h. The mRNA expression of the subunits of NADPH oxidase, Nox4 and p22phox; tumor necrosis factor-alpha (TNF-α); and kidney injury molecule-1 (KIM-1) were measured using quantitative real time polymerase chain reaction (qRT-PCR). Active caspase-3 protein expression was evaluated by immunostaining. Also, p38 MAPK and PI3K/Akt signaling pathways were analyzed using western blot. ALA suppressed the mRNA expression of Nox4, p22phox, TNF-α and KIM-1. Active caspase-3 protein expression induced by IS was decreased by ALA. ALA also suppressed p38 MAPK and activated the PI3K/Akt signaling pathway following IS administration. We found that ALA may be an effective strategy for preventing oxidative acute kidney injury caused by IS.

Nox4 Maintains Blood Pressure during Low Sodium Diet

The NADPH oxidase Nox4 is a hydrogen peroxide (H₂O₂)-producing enzyme, with the highest expression in the kidney. As the kidney is involved in volume and blood pressure control through sodium handling, we set out to determine the impact of a low sodium diet on these parameters in WT and Nox4-/- mice. Nox4 expression in the murine kidney was restricted to the proximal tubule. Nevertheless, low-sodium-induced weight loss and sodium sparing function was similar in WT and Nox4-/- mice, disputing an important function of renal Nox4 in sodium handling. In contrast, a low sodium diet resulted in a reduction in systolic blood pressure in Nox4-/- as compared to WT mice. This was associated with a selectively lower pressure to heart-rate ratio, as well as heart to body weight ratio. In general, a low sodium diet leads to activation of sympathetic tone and the renin angiotensin system, which subsequently increases peripheral resistance. Our observations suggest that the control by this system is attenuated in Nox4-/- mice, resulting in lower blood pressure in response to low sodium.

Dopamine D5 receptor-mediated decreases in mitochondrial reactive oxygen species production are cAMP and autophagy dependent

Overproduction of reactive oxygen species (ROS) plays an important role in the pathogenesis of hypertension. The dopamine D₅ receptor (D₅R) is known to decrease ROS production, but the mechanism is not completely understood. In HEK293 cells overexpressing D₅R, fenoldopam, an agonist of the two D₁-like receptors, D₁R and D₅R, decreased the production of mitochondria-derived ROS (mito-ROS). The fenoldopam-mediated decrease in mito-ROS production was mimicked by Sp-cAMPS but blocked by Rp-cAMPS. In human renal proximal tubule cells with DRD1 gene silencing to eliminate the confounding effect of D₁R, fenoldopam still decreased mito-ROS production. By contrast, Sch23390, a D₁R and D₅R antagonist, increased mito-ROS production in the absence of D₁R, D₅R is constitutively active. The fenoldopam-mediated inhibition of mito-ROS production may have been related to autophagy because fenoldopam increased the expression of the autophagy hallmark proteins, autophagy protein 5 (ATG5), and the microtubule-associated protein 1 light chain (LC)3-II. In the presence of chloroquine or spautin-1, inhibitors of autophagy, fenoldopam further increased ATG5 and LC3-II expression, indicating an important role of D₅R in the positive regulation of autophagy. However, when autophagy was inhibited, fenoldopam was unable to inhibit ROS production. Indeed, the levels of these autophagy hallmark proteins were decreased in the kidney cortices of Drd5^-/- mice. Moreover, ROS production was increased in mitochondria isolated from the kidney cortices of Drd5^-/- mice, relative to Drd5^+/+ littermates. In conclusion, D₅R-mediated activation of autophagy plays a role in the D₅R-mediated inhibition of mito-ROS production in the kidneys.

Sodium fluoride activates the extrinsic apoptosis via regulating NOX4/ROS-mediated p53/DR5 signaling pathway in lung cells both in vitro and in vivo

An extensive body of research has demonstrated that pulmonary toxicity induced by fluoride is related to cell apoptosis. Although induction of death receptor-initiated extrinsic apoptosis by sodium fluoride (NaF) has been reported, its mechanism of action is still not clearly defined. Herein, we found that NaF treatment induced activation of caspase-8 in BEAS-2B cells, resulting in apoptosis, which was markedly reduced by blocking caspase-8 using small interfering RNA (siRNA). In this study, we report that death receptor 5 (DR5), a major component of the extrinsic apoptotic pathway, is markedly induced upon NaF stimulation. Enhanced DR5 induction was necessary for the apoptotic effects of NaF, inasmuch as transfected BEAS-2B cells with DR5 siRNA attenuated NaF-induced caspase-8 activation in lung cells. Mechanism investigation indicated that the induction of DR5, following NaF exposure, was mediated by tumor protein 53 (p53)-dependent transcriptional activation. Notably, we demonstrated that NaF could induce a significant increase in intracellular reactive oxygen species (ROS) level derived from nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4). Specifically, NOX4 knockdown inhibited NaF-induced the activation of p53/DR5 axis by reducing NOX4-derived ROS production. Further in vivo investigation demonstrated that NOX4 deficiency markedly attenuates NaF-induced lung injury, apoptosis, and ROS levels in the lung. Moreover, the expressions of p53 and DR5 were significantly reduced after NaF treatment in NOX4 knockout mice compared with the wild type mice. Taken together, our findings provide a novel insight into for the pulmonary apoptosis in response to NaF exposure.

Receptor activator of NF-κB mediates podocyte injury in diabetic nephropathy

Receptor activator of NF-κB (RANK) expression is increased in podocytes of patients with diabetic nephropathy. However, the relevance of RANK to diabetic nephropathy pathobiology remains unclear. Here, to evaluate the role of podocyte RANK in the development of diabetic nephropathy, we generated a mouse model of podocyte-specific RANK depletion (RANK^-/-Cre T), and a model of podocyte-specific RANK overexpression (RANK TG), and induced diabetes in these mice with streptozotocin. We found that podocyte RANK depletion alleviated albuminuria, mesangial matrix expansion, and basement membrane thickening, while RANK overexpression aggravated these indices in streptozotocin-treated mice. Moreover, streptozotocin-triggered oxidative stress was increased in RANK overexpression but decreased in the RANK depleted mice. Particularly, the expression of NADPH oxidase 4, and its obligate partner, P22phox, were enhanced in RANK overexpression, but reduced in RANK depleted mice. In parallel, the transcription factor p65 was increased in the podocyte nuclei of RANK overexpressing mice but decreased in the RANK depleted mice. The relevant findings were largely replicated with high glucose-treated podocytes in vitro. Mechanistically, p65 could bind to the promoter regions of NADPH oxidase 4 and P22phox, and increased their respective gene promoter activity in podocytes, dependent on the levels of RANK. Taken together, these findings suggested that high glucose induced RANK in podocytes and caused the increase of NADPH oxidase 4 and P22phox via p65, possibly together with the cytokines TNF- α, MAC-2 and IL-1 β, resulting in podocyte injury. Thus, we found that podocyte RANK was induced in the diabetic milieu and RANK mediated the development of diabetic nephropathy, likely by promoting glomerular oxidative stress and proinflammatory cytokine production.

High glucose induces Nox4 expression and podocyte apoptosis through the Smad3/ezrin/PKA pathway

Podocytes are the major target in proteinuric kidney diseases such as diabetic nephropathy. The underlying molecular mechanisms by which high glucose (HG) results in podocyte damage remain unclear. This study investigated the regulatory role of Smad3, ezrin, and protein kinase A (PKA) in NADPH oxidase (Nox4) expression, reactive oxidative species (ROS) production, and apoptosis in HG-treated podocytes. A human podocyte cell line was cultured and differentiated, then treated with 30 mM HG. Apoptosis and intracellular ROS levels were assessed using TUNEL and DCF assays, respectively. Expressions of Nox4, phospho-Smad3^Ser423/425, phospho-PKA^Thr197, and phospho-ezrin^Thr567 were evaluated using western blotting. ELISA was used to quantify intracellular cAMP concentration and PKA activity. Knockdown assay was used to inhibit the expressions of Smad3, Nox4, and ezrin by lentiviral shRNA. In HG-treated podocytes, the level of phospho-Smad3^Ser423/425 and phospho-ezrin^Thr567 was increased significantly, which was accompanied by the reduction of cAMP and phospho-PKA^Thr197. HG-induced apoptosis was significantly prevented by the Smad3-inhibitor SIS3 or shRNA-Smad3. In podocytes expressing shRNA-ezrin or shRNA-Nox4, apoptosis was remarkably mitigated following HG treatment. HG-induced upregulation of phospho-ezrin^Thr567 and downregulation of phospho-PKA^Thr197 was significantly prevented by SIS3, shRNA-ezrin or shRNA-Smad3. Forskolin, a PKA activator, significantly inhibited HG-mediated upregulation of Nox4 expression, ROS generation, and apoptosis. Additionally, an increase in the ROS level was prohibited in HG-treated podocytes with the knockdown of Nox4, Smad3, or ezrin. Taken together, our findings provided evidence that Smad3-mediated ezrin activation upregulates Nox4 expression and ROS production, by suppressing PKA activity, which may at least in part contribute to HG-induced podocyte apoptosis.

Summary: The actin-membrane linker protein ezrin-related signaling plays a critical role in podocyte apoptosis through regulation of Nox4 expression and ROS production.

Inducible nitric oxide synthase (iNOS) mediates ethanol-induced redox imbalance and upregulation of inflammatory cytokines in the kidney

Overexpression of the inducible isoform of the enzyme nitric oxide synthase (iNOS) has been associated to pathological processes in the kidney. Ethanol consumption induces the renal expression of iNOS; however, the contribution of this enzyme to the deleterious effects of ethanol in the kidney remains elusive. We examined whether iNOS plays a role in the renal dysfunction and oxidative stress induced by ethanol consumption. With this purpose, male C57BL/6 wild-type (WT) or iNOS-deficient (iNOS^-/-) mice were treated with ethanol (20% v/v) for 10 weeks. Treatment with ethanol increased the expression of Nox4 as well as the concentration of thiobarbituric acid reactive substances and the levels of tumor necrosis factor α in the renal cortex of WT but not iNOS^-/- mice. Augmented serum levels of creatinine and increased systolic blood pressure were found in WT and iNOS^-/- mice treated with ethanol. WT mice treated with ethanol showed increased production of reactive oxygen species and myeloperoxidase activity, but these responses were attenuated in iNOS^-/- mice. We concluded that iNOS played a role in ethanol-induced oxidative stress and pro-inflammatory cytokine production in the kidney. These are mechanisms that may contribute to the renal toxicity induced by ethanol.

Long non-coding RNAs: A double-edged sword in aging kidney and renal disease

Aging as one of intrinsic biological processes is a risk factor for many chronic diseases. Kidney disease is a global problem and health care burden worldwide. The diagnosis of kidney disease is currently based on serum creatinine and urea levels. Novel biomarkers may improve diagnostic accuracy, thereby allowing early prevention and treatment. Over the past few years, advances in genome analyses have identified an emerging class of noncoding RNAs that play critical roles in the regulation of gene expression and epigenetic reprogramming. Long noncoding RNAs (lncRNAs) are pervasively transcribed in the genome and could bind DNA, RNA and protein. Emerging evidence has demonstrated that lncRNAs played an important role in all stages of kidney disease. To date, only some lncRNAs were well identified and characterized, but the complexity of multilevel regulation of transcriptional programs involved in these processes remains undefined. In this review, we summarized the lncRNA expression profiling of large-scale identified lncRNAs on kidney diseases including acute kidney injury, chronic kidney disease, diabetic nephropathy and kidney transplantation. We further discussed a number of annotated lncRNAs linking with complex etiology of kidney diseases. Finally, several lncRNAs were highlighted as diagnostic biomarkers and therapeutic targets. Targeting lncRNAs may represent a precise therapeutic strategy for progressive renal fibrosis.

Immunomodulatory role of reactive oxygen species and nitrogen species during T cell-driven neutrophil-enriched acute and chronic cutaneous delayed-type hypersensitivity reactions

Rationale: Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are important regulators of inflammation. The exact impact of ROS/RNS on cutaneous delayed-type hypersensitivity reaction (DTHR) is controversial. The aim of our study was to identify the dominant sources of ROS/RNS during acute and chronic trinitrochlorobenzene (TNCB)-induced cutaneous DTHR in mice with differently impaired ROS/RNS production. Methods: TNCB-sensitized wild-type, NADPH oxidase 2 (NOX2)- deficient (gp91^phox-/-), myeloperoxidase-deficient (MPO^-/-), and inducible nitric oxide synthase-deficient (iNOS^-/-) mice were challenged with TNCB on the right ear once to elicit acute DTHR and repetitively up to five times to induce chronic DTHR. We measured ear swelling responses and noninvasively assessed ROS/RNS production in vivo by employing the chemiluminescence optical imaging (OI) probe L-012. Additionally, we conducted extensive ex vivo analyses of inflamed ears focusing on ROS/RNS production and the biochemical and morphological consequences. Results: The in vivo L-012 OI of acute and chronic DTHR revealed completely abrogated ROS/RNS production in the ears of gp91^phox-/- mice, up to 90 % decreased ROS/RNS production in the ears of MPO^-/- mice and unaffected ROS/RNS production in the ears of iNOS^-/- mice. The DHR flow cytometry analysis of leukocytes derived from the ears with acute DTHR confirmed our in vivo L-012 OI results. Nevertheless, we observed no significant differences in the ear swelling responses among all the experimental groups. The histopathological analysis of the ears of gp91^phox-/- mice with acute DTHRs revealed slightly enhanced inflammation. In contrast, we observed a moderately reduced inflammatory immune response in the ears of gp91^phox-/- mice with chronic DTHR, while the inflamed ears of MPO^-/- mice exhibited the strongest inflammation. Analyses of lipid peroxidation, 8-hydroxy-2'deoxyguanosine levels, redox related metabolites and genomic expression of antioxidant proteins revealed similar oxidative stress in all experimental groups. Furthermore, inflamed ears of wild-type and gp91^phox-/- mice displayed neutrophil extracellular trap (NET) formation exclusively in acute but not chronic DTHR. Conclusions: MPO and NOX2 are the dominant sources of ROS/RNS in acute and chronic DTHR. Nevertheless, depletion of one primary source of ROS/RNS exhibited only marginal but conflicting impact on acute and chronic cutaneous DTHR. Thus, ROS/RNS are not a single entity, and each species has different properties at certain stages of the disease, resulting in different outcomes.

Cellular Senescence in Kidney Fibrosis: Pathologic Significance and Therapeutic Strategies

Age-related disorders such as chronic kidney disease (CKD) are increasingly prevalent globally and pose unprecedented challenges. In many aspects, CKD can be viewed as a state of accelerated and premature aging. Aging kidney and CKD share many common characteristic features with increased cellular senescence, a conserved program characterized by an irreversible cell cycle arrest with altered transcriptome and secretome. While developmental senescence and acute senescence may positively contribute to the fine-tuning of embryogenesis and injury repair, chronic senescence, when unresolved promptly, plays a crucial role in kidney fibrogenesis and CKD progression. Senescent cells elicit their fibrogenic actions primarily by secreting an assortment of inflammatory and profibrotic factors known as the senescence-associated secretory phenotype (SASP). Increasing evidence indicates that senescent cells could be a promising new target for therapeutic intervention known as senotherapy, which includes depleting senescent cells, modulating SASP and restoration of senescence inhibitors. In this review, we discuss current understanding of the role and mechanism of cellular senescence in kidney fibrosis. We also highlight potential options of targeting senescent cells for the treatment of CKD.

Kahweol Ameliorates Cisplatin-Induced Acute Kidney Injury through Pleiotropic Effects in Mice

Cisplatin is an effective chemotherapeutic agent, but its clinical use is frequently limited by its nephrotoxicity. The pathogenesis of cisplatin-induced acute kidney injury (AKI) remains incompletely understood, but oxidative stress, tubular cell death, and inflammation are considered important contributors to cisplatin-induced renal injury. Kahweol is a natural diterpene extracted from coffee beans and has been shown to possess anti-oxidative and anti-inflammatory properties. However, its role in cisplatin-induced nephrotoxicity remains undetermined. Therefore, we investigated whether kahweol exerts a protective effect against cisplatin-induced renal injury. Additionally, its mechanisms were also examined. Administration of kahweol attenuated renal dysfunction and histopathological damage together with inhibition of oxidative stress in cisplatin-injected mice. Increased expression of nicotinamide adenine dinucleotide phosphate oxidase 4 and decreased expression of manganese superoxide dismutase and catalase after cisplatin treatment were significantly reversed by kahweol. Moreover, kahweol inhibited cisplatin-induced apoptosis and necroptosis in the kidneys. Finally, kahweol reduced inflammatory cytokine production and immune cell accumulation together with suppression of nuclear factor kappa-B pathway and downregulation of vascular adhesion molecules. Together, these results suggest that kahweol ameliorates cisplatin-induced renal injury via its pleiotropic effects and might be a potential preventive option against cisplatin-induced nephrotoxicity.

Antioxidative, Antiapoptotic, and Anti-Inflammatory Effects of Apamin in a Murine Model of Lipopolysaccharide-Induced Acute Kidney Injury

Sepsis is the major cause of acute kidney injury (AKI) in severely ill patients, but only limited therapeutic options are available. During sepsis, lipopolysaccharide (LPS), an endotoxin derived from bacteria, activates signaling cascades involved in inflammatory responses and tissue injury. Apamin is a component of bee venom and has been shown to exert antioxidative, antiapoptotic, and anti-inflammatory activities. However, the effect of apamin on LPS-induced AKI has not been elucidated. Here, we show that apamin treatment significantly ameliorated renal dysfunction and histological injury, especially tubular injury, in LPS-injected mice. Apamin also suppressed LPS-induced oxidative stress through modulating the expression of nicotinamide adenine dinucleotide phosphate oxidase 4 and heme oxygenase-1. Moreover, tubular cell apoptosis with caspase-3 activation in LPS-injected mice was significantly attenuated by apamin. Apamin also inhibited cytokine production and immune cell accumulation, suppressed toll-like receptor 4 pathway, and downregulated vascular adhesion molecules. Taken together, these results suggest that apamin ameliorates LPS-induced renal injury through inhibiting oxidative stress, apoptosis of tubular epithelial cells, and inflammation. Apamin might be a potential therapeutic option for septic AKI.

Polydatin attenuates renal fibrosis in diabetic mice through regulating the Cx32-Nox4 signaling pathway

We previously found that polydatin could attenuate renal oxidative stress in diabetic mice and improve renal fibrosis. Recent evidence shows that NADPH oxidase 4 (Nox4)-derived reactive oxygen species (ROS) contribute to inflammatory and fibrotic processes in diabetic kidneys. In this study we investigated whether polydatin attenuated renal fibrosis by regulating Nox4 in vitro and in vivo. In high glucose-treated rat glomerular mesangial cells, polydatin significantly decreased the protein levels of Nox4 by promoting its K48-linked polyubiquitination, thus inhibited the production of ROS, and eventually decreasing the expression of fibronectin (FN) and intercellular adhesion molecule-1 (ICAM-1), the main factors that exacerbate diabetic renal fibrosis. Overexpression of Nox4 abolished the inhibitory effects of polydatin on FN and ICAM-1 expression. In addition, the expression of Connexin32 (Cx32) was significantly decreased, which was restored by polydatin treatment. Cx32 interacted with Nox4 and reduced its protein levels. Knockdown of Cx32 abolished the inhibitory effects of polydatin on the expression of FN and ICAM-1. In the kidneys of streptozocin-induced diabetic mice, administration of polydatin (100 mg·kg-1·d-1, ig, 6 days a week for 12 weeks) increased Cx32 expression and reduced Nox4 expression, decreased renal oxidative stress levels and the expression of fibrotic factors, eventually attenuating renal injury and fibrosis. In conclusion, polydatin promotes K48-linked polyubiquitination and degradation of Nox4 by restoring Cx32 expression, thereby decreasing renal oxidative stress levels and ultimately ameliorating the pathological progress of diabetic renal fibrosis. Thus, polydatin reduces renal oxidative stress levels and attenuates diabetic renal fibrosis through regulating the Cx32-Nox4 signaling pathway.

Ellagic Acid Ameliorates Renal Ischemic-Reperfusion Injury Through NOX4/JAK/STAT Signaling Pathway

Ellagic acid (EA), a natural polyphenolic compound, has been proved to possess multiple biological activities including alleviating ischemic-reperfusion (I/R) injury. The aim of this current study was to investigate whether EA alleviates I/R injury via regulating inflammatory signaling pathway. Rats were subjected to ischemic-reperfusion (I/R) injury and given orally with different doses of EA before surgery. H&E staining, ELISA assay, and biochemical index analysis were performed to evaluate renal injury and inflammatory factors. Oxidative stress level was detected by DCFH-DA staining and corresponding assay kits. In addition, TUNEL assay and flow cytometric assay were applied for exploring the apoptosis of tissue and cells, respectively. Western blot assay was used to assess protein expressions in tissue and cells. The results showed that EA attenuated the renal I/R injury and reserved renal cell function in vivo. The levels of TNF-a, IL-1β, IL-6, and MCP-1, oxidative stress level, and apoptosis were suppressed in EA-treated rats. Mechanistic studies showed that EA suppressed the phosphorylation of JAK1, JAK2, and STAT1 and reduced the NOX4 level. EA reduced apoptosis, hypoxia-induced inflammatory response, and ROS levels. Moreover, overexpression of NOX4 reversed the protective function with NOX4 inhibition, indicating that the effect of EA against renal IRI or cell hypoxia/reoxygenation might mainly depend on NOX4. The results suggest that EA exerts the renoprotective effect via suppressing NOX4/JAK/STAT signaling pathway, which may be a novel potential therapy for the treatment of acute kidney injury in clinic.

Omega-3 fatty acids ameliorate doxorubicin-induced cardiorenal toxicity: In-vivo regulation of oxidative stress, apoptosis and renal Nox4, and in-vitro preservation of the cytotoxic efficacy

This study examines the protective effects of omega-3 fatty acids (OMG), a frequently used nutritional therapy in cancer patients, against doxorubicin (DOX)-induced acute cardiorenal toxicity in rats, and evaluates the cytotoxic activity of DOX when used with OMG against breast cancer cell line. Five groups of rats were treated for 4 consecutive weeks with vehicle (groups I & II), or OMG (25, 50 or 100 mg/kg/day, po; groups III, IV & V, respectively). After twenty-four hours, the last four groups were injected with DOX (200 mg/kg, ip). In DOX-treated rats, the altered ECG, serum cardiac and renal function biomarkers, and histopathological features indicated the induction of cardiorenal toxicity. Increased oxidative and apoptotic markers in both organs was observed, with elevated renal contents of NADPH-oxidase-4 (Nox4) and renin. OMG pretreatment improved those DOX-induced impairments in a dose-dependent manner, and showed antioxidant and antiapoptotic effects with regulation of renal Nox4 expression. The in-vitro study showed preservation of the cytotoxic activity of DOX on MCF7 cell line in the presence of OMG. The data suggests OMG for protection against acute DOX-induced cardiorenal damage without affecting the latter antitumor activity. It proposes regulation of oxidative stress, Nox4 activity and apoptosis as contributing protective mechanisms.

Caffeine Targets G6PDH to Disrupt Redox Homeostasis and Inhibit Renal Cell Carcinoma Proliferation

Glucose-6-phosphate dehydrogenase (G6PDH) is the rate-limiting enzyme in the pentose phosphate pathway (PPP) and plays a crucial role in the maintenance of redox homeostasis by producing nicotinamide adenine dinucleotide phosphate (NADPH), the major intracellular reductant. G6PDH has been shown to be a biomarker and potential therapeutic target for renal cell carcinoma (RCC). Here, we report a previously unknown biochemical mechanism through which caffeine, a well-known natural small molecule, regulates G6PDH activity to disrupt cellular redox homeostasis and suppress RCC development and progression. We found that caffeine can inhibit G6PDH enzymatic activity. Mechanistically, caffeine directly binds to G6PDH with high affinity (K _D = 0.1923 μM) and competes with the coenzyme NADP⁺ for G6PDH binding, as demonstrated by the decreased binding affinities of G6PDH for its coenzyme and substrate. Molecular docking studies revealed that caffeine binds to G6PDH at the structural NADP⁺ binding site, and chemical cross-linking analysis demonstrated that caffeine inhibits the formation of dimeric G6PDH. G6PDH inhibition abrogated the inhibitory effects of caffeine on RCC cell growth. Moreover, inhibition of G6PDH activity by caffeine led to a reduction in the intracellular levels of NADPH and reactive oxygen species (ROS), and altered the expression of redox-related proteins in RCC cells. Accordingly, caffeine could inhibit tumor growth through inhibition of G6PDH activity in vivo. Taken together, these results demonstrated that caffeine can target G6PDH to disrupt redox homeostasis and inhibit RCC tumor growth, and has potential as a therapeutic agent for the treatment of RCC.

Critical Role for AMPK in Metabolic Disease-Induced Chronic Kidney Disease

Chronic kidney disease (CKD) is prevalent in 9.1% of the global population and is a significant public health problem associated with increased morbidity and mortality. CKD is associated with highly prevalent physiological and metabolic disturbances such as hypertension, obesity, insulin resistance, cardiovascular disease, and aging, which are also risk factors for CKD pathogenesis and progression. Podocytes and proximal tubular cells of the kidney strongly express AMP-activated protein kinase (AMPK). AMPK plays essential roles in glucose and lipid metabolism, cell survival, growth, and inflammation. Thus, metabolic disease-induced renal diseases like obesity-related and diabetic chronic kidney disease demonstrate dysregulated AMPK in the kidney. Activating AMPK ameliorates the pathological and phenotypical features of both diseases. As a metabolic sensor, AMPK regulates active tubular transport and helps renal cells to survive low energy states. AMPK also exerts a key role in mitochondrial homeostasis and is known to regulate autophagy in mammalian cells. While the nutrient-sensing role of AMPK is critical in determining the fate of renal cells, the role of AMPK in kidney autophagy and mitochondrial quality control leading to pathology in metabolic disease-related CKD is not very clear and needs further investigation. This review highlights the crucial role of AMPK in renal cell dysfunction associated with metabolic diseases and aims to expand therapeutic strategies by understanding the molecular and cellular processes underlying CKD.

Methylation-dependent antioxidant-redox imbalance regulates hypertensive kidney injury in aging

The prevalence of hypertension increases with age, and oxidative stress is a major contributing factor to the pathogenesis of hypertension-induced kidney damage in aging. The nicotinamide adenine dinucleotide phosphate (NADPH) family is one of the major sources of reactive oxygen species (ROS) generation, and several NADPH oxidase isoforms are highly expressed in the kidney. Although epigenetic protein modification plays a role in organ injury, the methylation of the oxidant-antioxidant defense system and their role in hypertension-induced kidney damage in aging remains underexplored. The present study investigated the role of NADPH oxidase 4, superoxide dismutases (SODs), catalase, and NOS in Ang-II induced kidney damage in aging. Wild type (WT, C57BL/6J) mice aged 12-14 and 75-78 weeks were used and treated with or without Ang-II (1000 ng/kg/min) for 4 weeks with control mice receiving saline. Aged mice with or without Ang-II exhibited higher mean BP, lower renal blood flow, and decreased renal vascular density compared to young mice. While superoxide, 4-HNE, p22^phox, Nox4, iNOS were increased in the aged kidney, the expression of eNOS, MnSOD, CuSOD, catalase, Sirt1, and -3 as well as the ratio of GSH/GSSG, and activities of SODs and catalase were decreased compared to young control mice. The changes further deteriorated with Ang-II treatment. In Ang-II treated aged mice, the expressions of DNMTs were increased and associated with increased methylation of SODs, Sirt1, and Nox4. We conclude that hypermethylation of antioxidant enzymes in the aged kidney during hypertension worsens redox imbalance leading to kidney damage.

Characterization of the Oxidative Stress in Renal Ischemia/Reperfusion-Induced Cardiorenal Syndrome Type 3

In kidney disease (KD), several factors released into the bloodstream can induce a series of changes in the heart, leading to a wide variety of clinical situations called cardiorenal syndrome (CRS). Reactive oxygen species (ROS) play an important role in the signaling and progression of systemic inflammatory conditions, as observed in KD. The aim of the present study was to characterize the redox balance in renal ischemia/reperfusion-induced cardiac remodeling. C57BL/6 male mice were subjected to occlusion of the left renal pedicle, unilateral, for 60 min, followed by reperfusion for 8 and 15 days, respectively. The following redox balance components were evaluated: catalase (CAT), superoxide dismutase (SOD), total antioxidant capacity (FRAP), NADPH oxidase (NOX), nitric oxide synthase (NOS), hydrogen peroxide (H₂O₂), and the tissue bioavailability of nitric oxide (NO) such as S-nitrosothiol (RSNO) and nitrite (NO₂⁻). The results indicated a process of renoprotection in both kidneys, indicated by the reduction of cellular damage and some oxidant agents. We also observed an increase in the activity of antioxidant enzymes, such as SOD, and an increase in NO bioavailability. In the heart, we noticed an increase in the activity of NOX and NOS, together with increased cell damage on day 8, followed by a reduction in protein damage on day 15. The present study concludes that the kidneys and heart undergo distinct processes of damage and repair at the analyzed times, since the heart is a secondary target of ischemic kidney injury. These results are important for a better understanding of the cellular mechanisms involved in CRS.

Morroniside Inhibits H2O2-Induced Podocyte Apoptosis by Down-Regulating NOX4 Expression Controlled by Autophagy In Vitro

Podocyte apoptosis is the common pathological basis for the progression of various kidney diseases. The overexpression of NOX4, a key enzyme involved in oxidative stress, has been proved to participate in the occurrence of podocyte apoptosis. Autophagy is a kind of adaptive response of cells under stress. However, as a “double-edged sword”, the effect of autophagy on apoptosis in different cells and conditions is complex and variable, which has not been fully explained yet. Morroniside, extracted from the traditional medicinal plant Cornus officinalis, has remarkable antioxidant and anti-apoptosis effects, and has been proven to inhibit the overexpression of NOX4 in kidney tissue. Therefore, H₂O₂ was used in this study to explore the effects of autophagy on podocyte NOX4 overexpression and apoptosis induced by oxidative stress, as well as the protection mechanism of morroniside in podocytes. The results showed that the autophagy activator rapamycin, as well as the autophagy inhibitor chloroquine, could induce podocyte apoptosis cultured in normal condition, and chloroquine could also significantly increase the NOX4 expression. The NOX4 expression and apoptosis rate of podocytes increased after H₂O₂ treatment, the expression of LC3-II decreased, and the expressions of p62, mTOR, and p-mTOR increased. The intervention of morroniside and rapamycin improved autophagy activity and inhibited NOX4 overexpression and apoptosis induced by H₂O₂. And chloroquine reversed the inhibitory effect of morroniside on NOX4 overexpression and podocyte apoptosis. Taken together, our results suggest that the expression level of NOX4 in podocytes is regulated by autophagy activity. Morroniside can reduce oxidative stress induced podocyte apoptosis by restoring the damaged autophagy flux and inhibit the overexpression of NOX4.

NOX4-dependent regulation of ENaC in hypertension and diabetic kidney disease

NADPH oxidase 4 (NOX4) is the most abundant NOX isoform in the kidney; however, its importance for renal function has only recently emerged. The NOX4-dependent pathway regulates many factors essential for proper sodium handling in the distal nephron. However, the functional significance of this pathway in the control of sodium reabsorption during the initiation of chronic kidney disease is not established. The goal of this study was to test Nox4-dependent ENaC regulation in two models: SS hypertension and STZ-induced type 1 diabetes. First, we showed that genetic ablation of Nox4 in Dahl salt-sensitive (SS) rat attenuated a high-salt (HS)-induced increase in epithelial Na⁺ channel (ENaC) activity in the cortical collecting duct. We also found that H₂ O₂ upregulated ENaC activity, and H₂ O₂ production was reduced in both the renal cortex and medulla in SS^Nox4-/- rats fed an HS diet. Second, in the streptozotocin model of hyperglycemia-induced renal injury ENaC activity in hyperglycemic animals was elevated in SS but not SS^Nox4-/- rats. NaCl cotransporter (NCC) expression was increased compared to healthy controls, while expression values between SS and SS^Nox4-/- groups were similar. These data emphasize a critical contribution of the NOX4-mediated pathway in maladaptive upregulation of ENaC-mediated sodium reabsorption in the distal nephron in the conditions of HS- and hyperglycemia-induced kidney injury.

Alcohol promotes renal fibrosis by activating Nox2/4-mediated DNA methylation of Smad7

Alcohol consumption causes renal injury and compromises kidney function. The underlying mechanism of the alcoholic kidney disease remains largely unknown. In the present study, an alcoholic renal fibrosis animal model was first employed which mice received liquid diet containing alcohol for 4 to 12 weeks. The Masson's Trichrome staining analysis showed that kidney fibrosis increased at week 8 and 12 in the animal model that was further confirmed by albumin assay, Western blot, immunostaining and real-time PCR of fibrotic indexes (collagen I and α-SMA). In vitro analysis also confirmed that alcohol significantly induced fibrotic response (collagen I and α-SMA) in HK2 tubular epithelial cells. Importantly, both in vivo and in vitro studies showed alcohol treatments decreased Smad7 and activated Smad3. We further determined how the alcohol affected the balance of Smad7 (inhibitory Smad) and Smad3 (regulatory Smad). Genome-wide methylation sequencing showed an increased DNA methylation of many genes and bisulfite sequencing analysis showed an increased DNA methylation of Smad7 after alcohol ingestion. We also found DNA methylation of Smad7 was mediated by DNMT1 in ethyl alcohol (EtOH)-treated HK2 cells. Knockdown of Nox2 or Nox4 decreased DNMT1 and rebalanced Smad7/Smad3 axis, and thereby relieved EtOH-induced fibrotic response. The inhibition of reactive oxygen species by the intraperitoneal injection of apocynin attenuated renal fibrosis and restored renal function in the alcoholic mice. Collectively, we established novel in vivo and in vitro alcoholic kidney fibrosis models and found that alcohol induces renal fibrosis by activating oxidative stress-induced DNA methylation of Smad7. Suppression of Nox-mediated oxidative stress may be a potential therapy for long-term alcohol abuse-induced kidney fibrosis.

Rutaecarpine derivative Cpd-6c alleviates acute kidney injury by targeting PDE4B, a key enzyme mediating inflammation in cisplatin nephropathy

Acute kidney injury (AKI), characterized by a rapid decline in renal function, is triggered by an acute inflammatory response that leads to kidney damage. An effective treatment for AKI is lacking. Using in vitro and in vivo AKI models, our laboratory has identified a series of anti-inflammatory molecules and their derivatives. In the current study, we identified the protective role of rutaecarpine (Ru) on renal tubules. We obtained a series of 3-aromatic sulphonamide-substituted Ru derivatives exhibiting enhanced renoprotective and anti-inflammatory function. We identified Compound-6c(Cpd-6c) as having the best activity and examined its protective effect against cisplatin nephropathy both in vivo and in vitro in cisplatin-stimulated tubular epithelial cells (TECs). Our results showed that Cpd-6c restored renal function more effectively than Ru, as evidenced by reduced blood urea nitrogen and serum creatinine levels in mice. Cpd-6c alleviated tubular injury, as shown by PAS staining and molecular analysis of kidney injury molecule-1 (KIM-1), with both prevention and treatment protocols in cisplatin-treated mice. Moreover, Cpd-6c decreased kidney inflammation, oxidative stress and programmed cell death. These results have also been confirmed in cisplatin-treated TECs. Using web-prediction algorithms, molecular docking, and cellular thermal shift assay (CETSA), we identified phosphodiesterase 4B (PDE4B) as a Cpd-6c target. In addition, we firstly found that PDE4B was up-regulated significantly in the serum of AKI patients. After identifying the function of PDE4B in cisplatin-treated tubular epithelial cells by siRNA transfection or PDE4 inhibitor rolipram, we showed that Cpd-6c treatment did not protect against cisplatin-induced injury in PDE4B knockdown TECs, thus indicating that Cpd-6c exerts its renoprotective and anti-oxidative effects via the PDE4B-dependent pathway. Collectively, Cpd-6c might serve as a potential therapeutic agent for AKI and PDE4B may be highly involved in the initiation and progression of AKI.

Pyrrolidine dithiocarbamate reduces alloxan-induced kidney damage by decreasing nox4, inducible nitric oxide synthase, and metalloproteinase-2

We examined the effect of the NFκB inhibitor pyrrolidine-1-carbodithioic acid (PDTC) on inducible nitric oxide synthase (iNOS), matrix metalloproteinase-2 (MMP-2) activity, and oxidative and inflammatory kidney damage in alloxan-induced diabetes. Two weeks after diabetes induction (alloxan-130 mg/kg), control and diabetic rats received PDTC (100 mg/kg) or vehicle for 8 weeks. Body weight, glycemia, urea, and creatinine were measured. Kidney changes were measured in hematoxylin/eosin sections and ED1 by immunohistochemistry. Kidney thiobarbituric acid reactive substances (TBARS), superoxide anion (O2-), and nitrate/nitrite (NOx) levels, and catalase and superoxide dismutase (SOD) activities were analyzed. Also, kidney nox4 and iNOS expression, and NFkB nuclear translocation were measured by western blot, and MMP-2 by zymography. Glycemia and urea increased in alloxan rats, which were not modified by PDTC treatment. However, PDTC attenuated kidney structural alterations and macrophage infiltration in diabetic rats. While diabetes increased both TBARS and O₂^- levels, PDTC treatment reduced TBARS in diabetic and O₂^- in control kidneys. A decrease in NO_x levels was found in diabetic kidneys, which was prevented by PDTC. Diabetes reduced catalase activity, and PDTC increased catalase and SOD activities in both control and diabetic kidneys. PDTC treatment reduced MMP-2 activity and iNOS and p65 NFκB nuclear expression found increased in diabetic kidneys. Our results show that the NFκB inhibitor PDTC reduces renal damage through reduction of Nox4, iNOS, macrophages, and MMP-2 in the alloxan-induced diabetic model. These findings suggest that PDTC inhibits alloxan kidney damage via antioxidative and anti-inflammatory mechanisms.

Empagliflozin attenuates acute kidney injury after myocardial infarction in diabetic rats

Acute kidney injury (AKI) predicts poor prognosis in patients with acute myocardial infarction (MI) and diabetes mellitus (DM) is an independent risk factor of AKI. Recent clinical studies have shown the beneficial effects of sodium-glucose cotransporter 2 (SGLT2) inhibitors on cardiovascular and renal outcomes in patients with DM. We recently reported that canagliflozin normalized susceptibility of diabetic rats to AKI after acute MI via β-hydroxybutyrate-mediated suppression of NOX expression. Here we examined whether the same renoprotective effect is shared by empagliflozin. Serum creatinine levels were not changed by MI induced by coronary artery occlusion in LETO, non-diabetic control rats, and OLETF, obese type 2 diabetic rats. However, immunohistochemistry revealed that MI increased renal expression of NGAL and KIM-1, early markers of tubular injury, by 3.2-fold and 2.6-fold, respectively, in OLETF. These increases in injury markers were not observed in LETO. Pretreatment with empagliflozin of OLETF for 2 weeks improved hyperglycemia, increased blood β-hydroxybutyrate level, and suppressed MI-induced expression of NGAL and KIM-1. Empagliflozin suppressed upregulation of NOX2 and NOX4 in the kidney of OLETF. Taken together with the results of our previous study, it was concluded that treatment with the SGLT2 inhibitor protects the diabetic kidney from MI-induced AKI.

7-Hydroxycoumarin protects against cisplatin-induced acute kidney injury by inhibiting necroptosis and promoting Sox9-mediated tubular epithelial cell proliferation

BACKGROUND

7-Hydroxycoumarin (7-HC), also known as umbelliferon, is commonly found in Chinese herbs (e.g. Eucommiae Cortex, Prunellae Spica, Radix Angelicae Biseratae). Previous laboratory studies have indicated that 7-HC has anti-inflammatory, anti-oxidative, and anti-tumor effects. Cisplatin is a widely used chemotherapeutic agent for cancer. Nephrotoxicity is one of the limiting side effects of cisplatin use.

PURPOSE

This study aimed to evaluate the renoprotective effect of 7-HC in a cisplatin-induced acute kidney injury (AKI) mouse model.

METHODS

AKI was induced in male C57BL/6 mice (aged 6-8 weeks) by a single intraperitoneal injection of cisplatin at 20 mg/kg. The mice received 7-HC at 30, 60, and 90 mg/kg intraperitoneally before or after cisplatin administration. Renal function, necroptosis, and cell proliferation were measured. Mechanisms underlying the reno-protective effect of 7-HC were explored in renal tubular epithelial cells treated with or without cisplatin.

RESULTS

In-vivo experiments showed that 7-HC significantly improved the loss in kidney function induced by cisplatin, as indicated by lower levels of serum creatinine and blood urea nitrogen, in AKI mice. Consistent herewith, cisplatin-induced tubular damage was alleviated by 7-HC as shown by morphological (periodic acid-Schiff staining) and kidney injury marker (KIM-1) analyses. We found that 7-HC suppressed renal necroptosis via the RIPK1/RIPK3/MLKL pathway and accelerated renal repair as evidenced by the upregulation of cyclin D1 in cisplatin-induced nephropathy. In-vitro experiments showed that knockdown of Sox9 attenuated the suppressive effect of 7-HC on KIM-1 and reversed the stimulatory effect of 7-HC on cyclin D1 expression in cisplatin-treated HK-2 cells, indicating that 7-HC may protect against AKI via a Sox9-dependent mechanism.

CONCLUSION

7-HC inhibits cisplatin-induced AKI by suppressing RIPK1/RIPK3/MLKL-mediated necroptosis and promoting Sox9-mediated tubular epithelial cell proliferation. 7-HC may serve as a preventive and therapeutic agent for AKI.

Smad3 promotes AKI sensitivity in diabetic mice via interaction with p53 and induction of NOX4-dependent ROS production

The incidence and severity of acute kidney injury (AKI) is increased yearly in diabetic patients. Although the mechanisms for this remain unclear, the prevention of AKI in diabetic nephropathy is feasible and of value. As we detected highly activation of TGF-β/Smad3 signaling in both human biopsy and mouse model of diabetic nephropathy, we hypothesized that Smad3 activation in diabetic kidneys may increase AKI sensitivity. We tested our hypothesis in vitro using TGF-β type II receptor (TGF-βRII) disrupted tubular epithelial cells (TECs) and in vivo in mice with streptozotocin (STZ)-induced diabetic nephropathy before the induction of ischemia/reperfusion (I/R) injury. We found that high glucose (HG)-cultured TECs showed increased inflammation, apoptosis and oxidative stress following hypoxia/reoxygenation (H/R) injury. Disruption of TGF-βRII attenuated cell injury induced by H/R in HG-treated TECs. Consistently, Smad3 knockdown in diabetic kidney attenuated I/R-induced AKI. Mechanistically, Smad3 binds to p53 and enhances p53 activity in cells treated with HG and H/R, which may lead to TECs apoptosis. Additionally, ChIP assay showed that Smad3 bound with the promoter region of NOX4 and induced ROS production and inflammation. In conclusion, our results demonstrate that Smad3 promotes AKI susceptibility in diabetic mice by interacting with p53 and NOX4.

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Smad3 activation in diabetic kidneys may increase AKI sensitivity.

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Blockade of Smad3 in diabetic kidney may both prevent AKI and CKD progression.

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Smad3 interacts with p53 to enhance TECs apoptosis.

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Smad3 binds with promoter region of NOX4 to induce ROS production and inflammation.

Maximum reproductive lifespan correlates with CD33rSIGLEC gene number: Implications for NADPH oxidase-derived reactive oxygen species in aging

Humans and orcas are among the very rare species that have a prolonged post-reproductive lifespan (PRLS), during which the aging process continues. Reactive oxygen species (ROS) derived from mitochondria and from the NADPH oxidase (NOX) enzymes of innate immune cells are known to contribute to aging, with the former thought to be dominant. CD33-related-Siglecs are immune receptors that recognize self-associated-molecular-patterns and modulate NOX-derived-ROS. We herewith demonstrate a strong correlation of lifespan with CD33rSIGLEC gene number in 26 species, independent of body weight or phylogeny. The correlation is stronger when considering total CD33rSIGLEC gene number rather than those encoding inhibitory and activating subsets, suggesting that lifetime balancing of ROS is important. Combining independent lines of evidence including the short half-life and spontaneous activation of neutrophils, we calculate that even without inter-current inflammation, a major source of lifetime ROS exposure may actually be neutrophil NOX-derived. However, genomes of human supercentenarians (>110 years) do not harbor a significantly higher number of functional CD33rSIGLEC genes. Instead, lifespan correlation with CD33rSIGLEC gene number was markedly strengthened by excluding the post-reproductive lifespan of humans and orcas (R2  = 0.83; P < .0001). Thus, CD33rSIGLEC modulation of ROS likely contributes to maximum reproductive lifespan, but other unknown mechanisms could be important to PRLS.

Conservation of glucagon like peptide-1 level with liraglutide and linagilptin protects the kidney against angiotensin II-induced tissue fibrosis in rats

This study tested the hypothesis that the enhancement of glucagon-like peptide-1 (GLP-1) level through either exogenous supply of GLP-1 agonist, liraglutide or prevention of endogenous GLP-1 degradation with dipeptidyl peptidease-4 inhibitor, lingaliptin ameliorates angiotensin II (Ang II)-induced renal fibrosis. Sprague-Dawley rats were randomly divided into four groups: 0.9% saline or Ang II (500 ng/kg/min) was infused with osmotic minipumps for 4 weeks, defined as sham and Ang II groups. In drug treated groups, liraglutide (0.3 mg/kg) was injected subcutaneously twice daily or linagliptin (8 mg/kg) was administered daily via oral gavage during Ang II infusion. Compared with Ang II stimulation, liraglutide or linagliptin comparatively down-regulated the protein level of the AT₁ receptor, and up-regulated the AT₂ receptor, as identified by a reduced AT₁/AT₂ ratio (all p < 0.05), consistent with less locally-expressed AT₁ receptor and enhanced AT₂ receptor in the glomerular capillaries and proximal tubules of the renal cortex. Furthermore, both drugs significantly increased the expression of GLP-1 receptor and attenuated the protein levels of TLR4, NOX4 and IL-6. The populations of macrophages and α-SMA expressing myofibroblasts decreased with treatment of liraglutide and linagliptin, in coincidence with the reduced expression of phosphor-Smad2/3, Smad4, TGFβ1, and up-regulated Smad7. Along with these modulations, renal morphology was preserved and synthesis of fibronectin/collagen I was down-regulated, as identified by small collagen-rich area in the renal cortex. These results suggest that the preservation of GLP-1 level using liraglutide or linagliptin might be considered as an add-on therapeutic option for inhibiting Ang II induced renal fibrosis and failure.

Follistatin Protects Against Glomerular Mesangial Cell Apoptosis and Oxidative Stress to Ameliorate Chronic Kidney Disease

Aims: Interventions to inhibit oxidative stress and apoptosis, important pathogenic contributors toward the progression of chronic kidney disease (CKD), are not well established. Here, we investigated the role of a transforming growth factor beta (TGFβ) superfamily neutralizing protein, follistatin (FST), in the regulation of apoptosis and oxidative stress in glomerular mesangial cells (MCs) and in the progression of CKD. Results: The endoplasmic reticulum (ER) stress inducer thapsigargin (Tg), known to cause MC apoptosis, led to a post-translational increase in the expression of FST. Recombinant FST protected, whereas FST downregulation augmented, Tg-induced apoptosis without affecting Ca²⁺ release or ER stress induction. Although activins are the primary ligands neutralized by FST, their inhibition with neutralizing antibodies did not affect Tg-induced apoptosis. Instead, FST protected against Tg-induced apoptosis through neutralization of reactive oxygen species (ROS) independently of its ability to neutralize activins. Importantly, administration of FST to mice with CKD protected against renal cell apoptosis and oxidative stress. This was associated with improved kidney function, reduced albuminuria, and attenuation of fibrosis. Innovation and Conclusion: Independent of its activin neutralizing ability, FST protected against Tg-induced apoptosis through neutralization of ROS and consequent suppression of oxidative stress, seen both in vitro and in vivo. Importantly, FST also ameliorated fibrosis and improved kidney function in CKD. FST is, thus, a novel potential therapeutic agent for delaying the progression of CKD. Antioxid. Redox Signal. 31, 551-571.

Redox signaling in aging kidney and opportunity for therapeutic intervention through natural products

Kidney diseases are serious public problems with high morbidity and mortality in the general population and heavily retard renal function with aging regardless of the cause. Although myriad strategies have been assigned to prevent or harness disease progression, unfortunately, thus far, there is a paucity of effective therapies partly due to an insufficient knowledge of underlying pathological mechanisms, indicating deeper studies are urgently needed. Additionally, natural products are increasingly recognized as an alternative source for disease intervention owing to the potent safety and efficacy, which might be exploited for novel drug discovery. In this review, we primarily expatiate the new advances on mediators that might be amenable to targeting aging kidney and kidney diseases, including nicotinamide adenine dinucleotide phosphate oxidase (NOX), transforming growth factor-β (TGF-β), renin-angiotensin system (RAS), nuclear factor-erythroid 2 related factor 2 (Nrf2), peroxisome proliferator-activated γ receptor (PPARγ), advanced glycation endproducts (AGEs) as well as microRNAs and vitagenes. Of note, we conclude by highlighting some natural products which have the potential to facilitate the development of novel treatment for patients with myriad renal diseases.

Antioxidant supplements as a novel mean for blocking recurrent heat stress-induced kidney damage following rehydration with fructose-containing beverages

Recently repeated heat stress and dehydration have been reported to cause oxidative stress and kidney damage that is enhanced by rehydrating with fructose solutions. We hypothesized that antioxidants might provide a novel way to prevent kidney damage. To test this hypothesis, mild heat stress was induced by exposing rats to 37 °C during 1 h in a closed chamber. The supplementation with water-soluble antioxidants (Antiox), ascorbic acid 1% plus N-acetyl cysteine 600 mg/L was done either in the 10% fructose 2 h rehydration fluid immediately after heat stress (Fructose 10% + Antiox), and/or in the tap water (Water + Antiox) for the remainder of the day, or in both fluids. After 4 weeks, control rats exposed to heat with fructose rehydration developed impaired renal function, tubular injury, intrarenal oxidative stress, a reduction in Nrf2-Keap1 antioxidant pathway, stimulation of vasopressin and the intrarenal polyol-fructokinase pathway. In contrast, dosing the antioxidants in the tap water (i.e., before the heat exposure and rehydration with fructose) preserved renal function, prevented renal tubule dysfunction and avoided the increase in systemic blood pressure. These effects were likely due to the amplification of the antioxidant defenses through increased Nrf2 nuclear translocation stimulated by the antioxidants and by the prevention of polyol fructokinase pathway overactivation. More studies to understand the mechanisms implicated in this pathology are warranted as there is recent evidence that they may be operating in humans as well.

RIPK1 inhibitor Cpd-71 attenuates renal dysfunction in cisplatin-treated mice via attenuating necroptosis, inflammation and oxidative stress

Acute kidney injury (AKI) is a destructive clinical condition induced by multiple insults including ischemic reperfusion, nephrotoxic drugs and sepsis. It is characterized by a sudden decline in renal function, in addition to excessive inflammation, oxidative stress and programmed cell death of renal tubular epithelial cells. RIPK1-mediated necroptosis plays an important role in AKI. In the present study, we evaluated the treatment effects of Compound-71 (Cpd-71), a novel RIPK1 inhibitor, by comparing with Necrostatin-1 (Nec-1), a classic RIPK1 inhibitor, which has several drawbacks like the narrow structure–activity relationship (SAR) profile, moderate potency and non-ideal pharmacokinetic properties, in vivo and in vitro. Our results showed that pretreatment of Cpd-71 attenuated cisplatin-induced renal injury, restored renal function and suppressed renal inflammation, oxidative stress and cell necroptosis. In addition, Cpd-71 inhibited renal damage while reducing the up-regulated serum creatinine (Cr) and blood urea nitrogen (BUN) levels in established AKI mice model. Consistently, we confirmed that Cpd-71 exhibited more effectively suppressive effect on cisplatin-induced renal tubular cell necroptosis than Nec-1, by physically binding to the allosteric type III ligand binding site of RIPK1, thereby reduced RIPK1 kinase activity, RIPK1/RIPK3 complex formation and phosphor-MLKL membrane translocation by molecular docking, Western blot, co-immunoprecipitation and cellular thermal shift assay (CETSA). Taken together, we currently showed that targeting RIPK1 with Cpd-71 may serve as a promising clinical candidate for AKI treatment.

Mitochondrial Activity and Skeletal Muscle Insulin Resistance in Kidney Disease

Insulin resistance is a key feature of the metabolic syndrome, a cluster of medical disorders that together increase the chance of developing type 2 diabetes and cardiovascular disease. In turn, type 2 diabetes may cause complications such as diabetic kidney disease (DKD). Obesity is a major risk factor for developing systemic insulin resistance, and skeletal muscle is the first tissue in susceptible individuals to lose its insulin responsiveness. Interestingly, lean individuals are not immune to insulin resistance either. Non-obese, non-diabetic subjects with chronic kidney disease (CKD), for example, exhibit insulin resistance at the very onset of CKD, even before clinical symptoms of renal failure are clear. This uraemic insulin resistance contributes to the muscle weakness and muscle wasting that many CKD patients face, especially during the later stages of the disease. Bioenergetic failure has been associated with the loss of skeletal muscle insulin sensitivity in obesity and uraemia, as well as in the development of kidney disease and its sarcopenic complications. In this mini review, we evaluate how mitochondrial activity of different renal cell types changes during DKD progression, and discuss the controversial role of oxidative stress and mitochondrial reactive oxygen species in DKD. We also compare the involvement of skeletal muscle mitochondria in uraemic and obesity-related muscle insulin resistance.

Novel Regulators and Targets of Redox Signaling in Pulmonary Vasculature

Dysregulated redox signaling in pulmonary vasculature is central to the development of pulmonary arterial hypertension (PAH) and lung injury. Modulators of reactive oxygen species (ROS) production and downstream signaling targets are critical for mediating the physiological or pathological effects of ROS. Understanding the complex interactions between the modulators and signaling targets of ROS is essential for developing novel strategies to prevent or attenuate lung pathologies. In this review, we discuss recent studies on the modulators and targets of ROS in pulmonary endothelial and smooth muscle cells, their cellular effects, and the disease conditions associated with dysregulated redox signaling.

NOX5: Molecular biology and pathophysiology

NEW FINDINGS

What is the topic of this review? This review provides a comprehensive overview of Nox5 from basic biology to human disease and highlights unique features of this Nox isoform What advances does it highlight? Major advances in Nox5 biology relate to crystallization of the molecule and new insights into the pathophysiological role of Nox5. Recent discoveries have unravelled the crystal structure of Nox5, the first Nox isoform to be crystalized. This provides new opportunities to develop drugs or small molecules targeted to Nox5 in an isoform-specific manner, possibly for therapeutic use. Moreover genome wide association studies (GWAS) identified Nox5 as a new blood pressure-associated gene and studies in mice expressing human Nox5 in a cell-specific manner have provided new information about the (patho) physiological role of Nox5 in the cardiovascular system and kidneys. Nox5 seems to be important in the regulation of vascular contraction and kidney function. In cardiovascular disease and diabetic nephropathy, Nox5 activity is increased and this is associated with increased production of reactive oxygen species and oxidative stress implicated in tissue damage.

ABSTRACT

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Nox), comprise seven family members (Nox1-Nox5 and dual oxidase 1 and 2) and are major producers of reactive oxygen species in mammalian cells. Reactive oxygen species are crucially involved in cell signalling and function. All Noxs share structural homology comprising six transmembrane domains with two haem-binding regions and an NADPH-binding region on the intracellular C-terminus, whereas their regulatory systems, mechanisms of activation and tissue distribution differ. This explains the diverse function of Noxs. Of the Noxs, NOX5 is unique in that rodents lack the gene, it is regulated by Ca2+ , it does not require NADPH oxidase subunits for its activation, and it is not glycosylated. NOX5 localizes in the perinuclear and endoplasmic reticulum regions of cells and traffics to the cell membrane upon activation. It is tightly regulated through numerous post-translational modifications and is activated by vasoactive agents, growth factors and pro-inflammatory cytokines. The exact pathophysiological significance of NOX5 remains unclear, but it seems to be important in the physiological regulation of sperm motility, vascular contraction and lymphocyte differentiation, and NOX5 hyperactivation has been implicated in cardiovascular disease, kidney injury and cancer. The field of NOX5 biology is still in its infancy, but with new insights into its biochemistry and cellular regulation, discovery of the NOX5 crystal structure and genome-wide association studies implicating NOX5 in disease, the time is now ripe to advance NOX5 research. This review provides a comprehensive overview of our current understanding of NOX5, from basic biology to human disease, and highlights the unique characteristics of this enigmatic Nox isoform.