Mechanisms of ischemic acute renal failure

Utilizing pathophysiological concepts of ischemia-reperfusion injury to design renoprotective strategies and therapeutic interventions for normothermic ex vivo kidney perfusion

Normothermic machine perfusion (NMP) has emerged as a promising tool for the preservation, viability assessment, and repair of deceased-donor kidneys prior to transplantation. These kidneys inevitably experience a period of ischemia during donation, which leads to ischemia-reperfusion injury when NMP is subsequently commenced. Ischemia-reperfusion injury has a major impact on the renal vasculature, metabolism, oxygenation, electrolyte balance, and acid-base homeostasis. With an increased understanding of the underlying pathophysiological mechanisms, renoprotective strategies and therapeutic interventions can be devised to minimize additional injury during normothermic reperfusion, ensure the safe implementation of NMP, and improve kidney quality. This review discusses the pathophysiological alterations in the vasculature, metabolism, oxygenation, electrolyte balance, and acid-base homeostasis of deceased-donor kidneys and delineates renoprotective strategies and therapeutic interventions to mitigate renal injury and improve kidney quality during NMP.

In vivo imaging of renal microvasculature in a murine ischemia-reperfusion injury model using optical coherence tomography angiography

Optical coherence tomography angiography (OCTA) provides three-dimensional structural and semiquantitative imaging of microvasculature in vivo. We developed an OCTA imaging protocol for a murine kidney ischemia-reperfusion injury (IRI) model to investigate the correlation between renal microvascular changes and ischemic damage. Mice were divided into mild and moderate IRI groups according to the duration of ischemia (10 and 35 mins, respectively). Each animal was imaged at baseline; during ischemia; and at 1, 15, 30, 45, and 60 mins after ischemia. Amplitude decorrelation OCTA images were constructed with 1.5-, 3.0-, and 5.8-ms interscan times, to calculate the semiquantitative flow index in the superficial (50-70 μm) and the deep (220-340 μm) capillaries of the renal cortex. The mild IRI group showed no significant flow index change in both the superfial and the deep layers. The moderate IRI group showed a significantly decreased flow index from 15 and 45 mins in the superficial and deep layers, respectively. Seven weeks after IRI induction, the moderate IRI group showed lower kidney function and higher collagen deposition than the mild IRI group. OCTA imaging of the murine IRI model revealed changes in superficial blood flow after ischemic injury. A more pronounced decrease in superficial blood flow than in deep blood flow was associated with sustained dysfunction after IRI. Further investigation on post-IRI renal microvascular response using OCTA may improve our understanding of the relationship between the degree of ischemic insult and kidney function.

Polyethylene glycol capped gold nanoparticles ameliorate renal ischemia-reperfusion injury in diabetic mice through AMPK-Nrf2 signaling pathway

The aim of this study is to investigate the protective effect of polyethylene glycol capped gold nanoparticles (PEG-AuNPs) on renal ischemia-reperfusion injury (I/R)-induced acute kidney injury (AKI) in diabetic mice via the activation of adenosine 5' monophosphate-activated protein kinase-nuclear factor erythroid-2-related factor-2 (AMPK-Nrf2) pathway. Diabetes was induced in male mice (12/group) by streptozotocin (50 mg/kg) for 5 consecutive days. After 4 weeks, the mice have intravenously received doses of PEG-AuNPs (40, 150, and 400 µg/kg body weight) for 3 consecutive days, and then animals were subjected to 30 min ischemia and 48 h reperfusion. Following the treatment with three different doses of PEG-AuNPs, the levels of blood urea nitrogen (BUN) and creatinine were reduced. Obvious reduction in renal tubular atrophy, glomerular damage, mitochondrial damage, and necrotic area were ultra-structurally detected, and renal interstitial inflammation and apoptosis were diminished. Moreover, PEG-AuNPs increased the recovering of damaged renal cells, suppressed significantly levels of malondialdehyde (MDA), downregulated significantly the level of inflammatory cytokines (TNF-α and IL-1β), and upregulated the AMPK-Nrf2 pathway. PEG-AuNPs exhibited a promising alternative therapeutic target for diabetic renal I/R-induced AKI through upregulation of AMPK/PI3K/AKT path which additionally stimulated Nrf2-regulated antioxidant enzymes in a dose-dependent manner.

Effects of dexmedetomidine on new oxidative stress markers on renal ischaemia-reperfusion injury in rats: thiol/disulphide homeostasis and the ischaemia-modified albumin

OBJECTIVES

This study investigated the effect of dexmedetomidine on the oxidant-antioxidant (thiol/disulphide) balance.

METHODS

A total of 24 rats were divided into four groups. The renal arteries in groups IR (ischaemia/reperfusion) and IR + D (ischaemia/reperfusion + dexmedetomidine) were clamped for 45 min and reperfused for 180 min. Groups D (Dexmedetomidine) and IR + D were administered 100 μg/kg dexmedetomidine. Oxidant-antioxidant (thiol/disulphide) levels were measured. Kidney tissue was examined histopathologically.

RESULTS

No statistically difference was found between the groups in terms of thiol-disulphide averages, while IMA, TOS and thiol-disulphide results showed a minimal decrease in Group IR + D compared to Group IR (p > 0.05). Tubular lesions and necrosis were found in 26-50% of tubules in Group IR. Tubular damage and necrosis in Group IR + D declined to 5-25% .

CONCLUSIONS

No statistically difference was found in the study where OSI index, thiol/disulphide balance and IMA were measured together as biochemical values.

Eplerenone reduces renal ischaemia/reperfusion injury by modulating Klotho, NF-κB and SIRT1/SIRT3/PGC-1α signalling pathways

OBJECTIVES

Acute kidney injury (AKI) is a sudden impairment in kidney function that is associated with high morbidity and mortality. Inflammation, oxidative stress, mitochondrial impairment and energy depletion, along with organ dysfunction are hallmarks of AKI. This study aimed to evaluate the effects of Eplerenone, an aldosterone receptor antagonist, on the kidney injury caused by ischaemia/reperfusion (I/R).

METHODS

Male Wistar rats (n = 24) were randomly allocated into four groups: sham, IR, Eplerenone and Eplerenone+IR. Rats in the two last groups 1 h before I/R induction, were treated with Eplerenone (100 mg/kg) via intraperitoneal injection. Protein levels of Klotho, heat shock protein 70 (HSP70), sirtuin1 (SIRT1), SIRT3 and peroxisome proliferator-activated receptor-gamma coactivator 1-α (PGC-1α) along with antioxidant, apoptotic (caspase 3, Bax and Bcl2) and inflammatory [nuclear factor kappa-B (NF-κB) p65, Interleukin-6 (IL-6), tumour necrosis factor-α (TNF-α) and cyclooxygenase-2 (COX-2)] factors were evaluated in the kidney tissues of the experimental groups.

KEY FINDINGS

Eplerenone pre-treatment significantly could improve IR-induced pathological changes and kidney function and increase the renal antioxidant factors compared to the IR group (P < 0.05). Furthermore, in the Eplerenone + IR group, significant elevation of the Klotho, SIRT1, SIRT3 and PGC-1α at the protein level was identified compared to the IR group. Eplerenone pretreatment could not only downregulate NF-κB signalling and its downstream inflammatory factors (IL-6, COX-2 and TNF-α) but also could decrease apoptotic factors (P ≤ 0.01).

CONCLUSIONS

The results recommended that Eplerenone exerts a protective effect against kidney IR injury by up-regulating Klotho, HSP70, sirtuins and PGC-1α to preserve mitochondrial function and cell survival. Moreover, it hinders renal inflammation by suppressing NF-κB signalling. These results offer insight into the prevention or treatment of AKI in the future.

IFC-305 attenuates renal ischemia-reperfusion injury by promoting the production of hydrogen sulfide (H2S) via suppressing the promoter methylation of cystathionine γ-lyase (CSE)

Renal ischemia-reperfusion (I/R) injury is characterized by elevated expression of homocysteine and decreased production of hydrogen sulfide (H₂S). Cystathionine γ-lyase (CSE) is a key factor in the onset of renal I/R injury, while IFC-305 can regulate the expression of CSE via epigenetic modification. Animal and cellular models of I/R were established in this work, followed by H&E staining to evaluate the extent of renal tissue injury under distinct conditions. Several methods, including ELISA, qPCR and Western blot, were used to analyze the levels of creatinine, CSE and H₂S in various I/R models. Bisulfite sequencing PCR was used to evaluate the level of DNA methylation. The severity of the renal injury was significantly elevated in I/R rats and alleviated by the IFC-305 treatment. The level of Hcy was increased in the renal tissue and peripheral blood of I/R rats, while the IFC-305 treatment inhibited the expression of homocysteine (Hcy). Mechanistically, the DNA methylation in the CSE promoter was dramatically enhanced in I/R rats and cells, while the IFC-305 treatment reduced the level of DNA methylation in the CSE promoter. Moreover, the IFC-305 increased the concentration of H₂S, which was reduced in I/R rats and cells. Finally, I/R rats and cells showed aberrantly high levels of MDA and superoxide, while the IFC-305 treatment reduced the levels of malondialdehyde (MDA) and superoxide. IFC-305, an adenosine derivative, promoted the production of H₂S and attenuated renal injury in cellular and animal models of renal I/R by modifying the methylation status of the CSE promoter.

MiRNA: Involvement of the MAPK Pathway in Ischemic Stroke. A Promising Therapeutic Target

Ischemic stroke (IS) is a cerebrovascular disease with a high rate of disability and mortality. It is classified as the second leading cause of death that arises from the sudden occlusion of small vessels in the brain with consequent lack of oxygen and nutrients in the brain tissue. Following an acute ischemic event, the cascade of events promotes the activation of multiple signaling pathways responsible for irreversible neuronal damage. The mitogen-activated protein kinase (MAPK) signaling pathway transmits signals from the cell membrane to the nucleus in response to different stimuli, regulating proliferation, differentiation, inflammation, and apoptosis. Several lines of evidence showed that MAPK is an important regulator of ischemic and hemorrhagic cerebral vascular disease; indeed, it can impair blood–brain barrier (BBB) integrity and exacerbate neuroinflammation through the release of pro-inflammatory mediators implementing neurovascular damage after ischemic stroke. This review aims to illustrate the miRNAs involved in the regulation of MAPK in IS, in order to highlight possible targets for potential neuroprotective treatments. We also discuss some miRNAs (miR), including miR-145, miR-137, miR-493, and miR-126, that are important as they modulate processes such as apoptosis, neuroinflammation, neurogenesis, and angiogenesis through the regulation of the MAPK pathway in cerebral IS. To date, limited drug therapies are available for the treatment of IS; therefore, it is necessary to implement preclinical and clinical studies aimed at discovering novel therapeutic approaches to minimize post-stroke neurological damage.

Renal Delivery of Pharmacologic Agents During Machine Perfusion to Prevent Ischaemia-Reperfusion Injury: From Murine Model to Clinical Trials

Donor organ shortage still remains a serious obstacle for the access of wait-list patients to kidney transplantation, the best treatment for End-Stage Kidney Disease (ESKD). To expand the number of transplants, the use of lower quality organs from older ECD or DCD donors has become an established routine but at the price of increased incidence of Primary Non-Function, Delay Graft Function and lower-long term graft survival. In the last years, several improvements have been made in the field of renal transplantation from surgical procedure to preservation strategies. To improve renal outcomes, research has focused on development of innovative and dynamic preservation techniques, in order to assess graft function and promote regeneration by pharmacological intervention before transplantation. This review provides an overview of the current knowledge of these new preservation strategies by machine perfusions and pharmacological interventions at different timing possibilities: in the organ donor, ex-vivo during perfusion machine reconditioning or after implementation in the recipient. We will report therapies as anti-oxidant and anti-inflammatory agents, senolytics agents, complement inhibitors, HDL, siRNA and H2S supplementation. Renal delivery of pharmacologic agents during preservation state provides a window of opportunity to treat the organ in an isolated manner and a crucial route of administration. Even if few studies have been reported of transplantation after ex-vivo drugs administration, targeting the biological pathway associated to kidney failure (i.e. oxidative stress, complement system, fibrosis) might be a promising therapeutic strategy to improve the quality of various donor organs and expand organ availability.

The Role and Mechanism of Histone Deacetylases in Acute Kidney Injury

Acute kidney injury (AKI) is a common clinical complication with an incidence of up to 8-18% in hospitalized patients. AKI is also a complication of COVID-19 patients and is associated with an increased risk of death. In recent years, numerous studies have suggested that epigenetic regulation is critically involved in the pathophysiological process and prognosis of AKI. Histone acetylation, one of the epigenetic regulations, is negatively regulated by histone deacetylases (HDACs). Increasing evidence indicates that HDACs play an important role in the pathophysiological development of AKI by regulation of apoptosis, inflammation, oxidative stress, fibrosis, cell survival, autophagy, ATP production, and mitochondrial biogenesis (MB). In this review, we summarize and discuss the role and mechanism of HDACs in the pathogenesis of AKI.

Effect of NAD+ boosting on kidney ischemia-reperfusion injury

Acute kidney injury (AKI) is associated with a very high mortality and an increased risk for progression to chronic kidney disease (CKD). Ischemia-reperfusion injury (IRI) is a model for AKI, which results in tubular damage, dysfunction of the mitochondria and autophagy, and in decreased cellular nicotinamide adenine dinucleotide (NAD⁺) with progressing fibrosis resulting in CKD. NAD⁺ is a co-enzyme for several proteins, including the NAD⁺ dependent sirtuins. NAD⁺ augmentation, e.g. by use of its precursor nicotinamide riboside (NR), improves mitochondrial homeostasis and organismal metabolism in many species. In the present investigation the effects of prophylactic administration of NR on IRI-induced AKI were studied in the rat. Bilateral IRI reduced kidney tissue NAD⁺, caused tubular damage, reduced α-Klotho (klotho), and altered autophagy flux. AKI initiated progression to CKD, as shown by induced profibrotic Periostin (postn) and Inhibin subunit beta-A, (activin A / Inhba), both 24 hours and 14 days after surgery. NR restored tissue NAD⁺ to that of the sham group, increased autophagy (reduced p62) and sirtuin1 (Sirt1) but did not ameliorate renal tubular damage and profibrotic genes in the 24 hours and 14 days IRI models. AKI induced NAD⁺ depletion and impaired autophagy, while augmentation of NAD⁺ by NR restored tissue NAD⁺ and increased autophagy, possibly serving as a protective response. However, prophylactic administration of NR did not ameliorate tubular damage of the IRI rats nor rescued the initiation of fibrosis in the long-term AKI to CKD model, which is a pivotal event in CKD pathogenesis.

MMP-9-mediated regulation of hypoxia-reperfusion injury-related neutrophil inflammation in an in vitro proximal tubular cell model

Background

Hypoxia-reperfusion (HR) and inflammation are causes of renal allograft injury. Pathological evidence has indicated that ischemia followed by reperfusion leads to the proteolysis and destruction of the extracellular matrix (ECM) in renal tubular epithelial cells. Matrix metalloproteinases (MMPs), such as MMP-2 and MMP-9, play roles in cleaving and reshaping the ECM. Acute accumulation of MMP-9 secreted from neutrophils promotes the incidence of inflammation and exacerbates graft trauma. Our goal was to investigate the activities of MMP-9/MMP-2 and their correlation with HR injury and neutrophil-related inflammation in renal proximal tubular cells.

Methods

This model was established by placing HK-2 cells under hypoxic conditions (5% CO₂, 1% O₂) for 6 h and then exposing them to reperfusion (5% CO₂, 21% O₂) for 12 h in a tri-gas incubator. The cell culture medium was collected for culturing polymorphonuclear leukocytes (PMNs). BB-94 (MMP-9 inhibitor) was added to the culture medium in the inhibitor group.

Results

Flow cytometry showed a significant increase in reactive oxygen species (ROS) levels in HK-2 cells from the HR injury group. MMP-9 expression was significantly increased and MMP-2 expression was significantly decreased in HK-2 cells from the HR group. MMP-9 and MPO expression were significantly increased in the HR group, while MPO expression was significantly decreased in the PMN inhibitor group.

Conclusions

The outcomes indicated that MMP-9 and MMP-2 are important components of an underlying pathophysiological mechanism of injury following HR. MMP-9 inhibition may be a potential approach to mitigateHR injury.

Sugar or Fat? Renal Tubular Metabolism Reviewed in Health and Disease

The kidney is a highly metabolically active organ that relies on specialized epithelial cells comprising the renal tubules to reabsorb most of the filtered water and solutes. Most of this reabsorption is mediated by the proximal tubules, and high amounts of energy are needed to facilitate solute movement. Thus, proximal tubules use fatty acid oxidation, which generates more adenosine triphosphate (ATP) than glucose metabolism, as its preferred metabolic pathway. After kidney injury, metabolism is altered, leading to decreased fatty acid oxidation and increased lactic acid generation. This review discusses how metabolism differs between the proximal and more distal tubular segments of the healthy nephron. In addition, metabolic changes in acute kidney injury and chronic kidney disease are discussed, as well as how these changes in metabolism may impact tubule repair and chronic kidney disease progression.

Localization and Maintenance of Engrafted Mesenchymal Stem Cells Administered via Renal Artery in Kidneys with Ischemia-Reperfusion Injury

Mesenchymal stem cells (MSCs) are a potential therapeutic tool for preventing the progression of acute kidney injury (AKI) to chronic kidney disease (CKD). Herein, we investigated the localization and maintenance of engrafted human bone marrow-derived MSCs in rats subjected to a renal ischemia-reperfusion injury (IRI) and compared the effectiveness of two intravascular injection routes via the renal artery or inferior vena cava. Renal artery injection of MSCs was more effective than intravenous injection at reducing IRI-induced renal fibrosis. Additionally, MSCs injected through the renal artery persisted in injured kidneys for over 21 days, whereas MSCs injected through the inferior vena cava survived for less than 7 days. This difference may be attributed to the antifibrotic effects of MSCs. Interestingly, MSCs injected through the renal artery were localized primarily in glomeruli until day 3 post-IRI, and they decreased in number thereafter. In contrast, the number of MSCs localized in tubular walls, and the interstitium increased gradually until day 21 post-IRI. This localization change may be related to areas of damage caused by IRI because ischemia-induced AKI leads to tubular cell damage. Taken together, these findings suggest renal artery injection of MSCs may be useful for preventing the progression of AKI to CKD.

The Protective Effect of Anthocyanins Extracted from Aronia Melanocarpa Berry in Renal Ischemia-Reperfusion Injury in Mice

Background

Our previous research showed the antioxidant activity of anthocyanins extracted from Aronia melanocarpa of black chokeberry in vitro. Ischemia acute kidney injury is a significant risk in developing progressive and deterioration of renal function leading to clinic chronic kidney disease. There were many attempts to protect the kidney against this progression of renal damage. Current study was designed to examine the effect of pretreatment with three anthocyanins named cyanidin-3-arabinoside, cyanidin-3-glucodise, and cyaniding-3-galactoside against acute ischemia-reperfusion injury in mouse kidney.

Methods

Acute renal injury model was initiated by 30 min clamping bilateral renal pedicle and followed by 24-hour reperfusion in C57Bl/6J mice. Four groups of mice were orally pretreated in 50 mg/g/12 h for two weeks with cyanidin-3-arabinoside, cyanidin-3-glucodise, and cyaniding-3-galactoside and anthocyanins (three-cyanidin mixture), respectively, sham-control group and the renal injury-untreated groups only with saline.

Results

The model resulted in renal dysfunction with high serum creatinine, blood urea nitrogen, and changes in proinflammatory cytokines (TNF-ɑ, IL-1β, IL-6, and MCP-1), renal oxidative stress (SOD, GSH, and CAT), lipid peroxidation (TBARS and MDA), and apoptosis (caspase-9). Pretreatment of two weeks resulted in different extent amelioration of renal dysfunction and tubular damage and suppression of proinflammatory cytokines, oxidative stress, lipid peroxidation, and apoptosis, thus suggesting that cyanidins are potentially effective in acute renal ischemia by the decrease of inflammation, oxidative stress, and lipid peroxidation, as well as apoptosis.

Conclusion

the current study provided the first attempt to investigate the role of anthocyanins purified from Aronia melanocarpa berry in amelioration of acute renal failure via antioxidant and cytoprotective effects.

Protective effect of cordycepin on experimental renal ischemia/reperfusion injury in rats

AIM

To date, various molecules have been investigated to reduce the effect of renal ischemia/reperfusion (I/R) injury. However, none have yet led to clinical use. The present study aimed to investigate the protective effect of cordycepin (C) on renal I/R injury in an experimental rat model.

MATERIALS AND METHODS

Twenty-four mature Sprague Dawley female rat was randomly divided into three groups: Sham, I/R, I/R+C. All animals underwent abdominal exploration. To induce I/R injury, an atraumatic vascular bulldog clamp was applied to the right renal pedicle for 60 minutes (ischemia) and later clamp was removed to allow reperfusion in all rats, except for the sham group. In the I/R + C group, 10 mg/kg C was administered intraperitoneally, immediately after reperfusion. After 4 hours of reperfusion, the experiment was terminated with right nephrectomy. Histological studies and biochemical analyses were performed on the right nephrectomy specimens. EGTI (endothelial, glomerular, tubulointerstitial) histopathology scoring and semi-quantitative analysis of renal cortical necrosis were used for histological analyses and superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), total oxidant status (TOS) for biochemical analyses.

RESULTS

Histopathological examination of the tissue damage revealed that all kidneys in the sham group were normal. The I/R group had higher histopathological scores than the I/R + C group. In the biochemical analysis of the tissues, SOD, MDA, TOS values were found to be statistically different in the I/R group compared to the I/R + C group (p: 0.004, 0.004, 0.001 respectively).

CONCLUSIONS

Intraperitoneal cordycepin injection following ischemia preserve renal tissue against oxidative stress in a rat model of renal I/R injury.

Renovascular effects of inorganic nitrate following ischemia-reperfusion of the kidney

BACKGROUND

Renal ischemia-reperfusion (IR) injury is a common cause of acute kidney injury (AKI), which is associated with oxidative stress and reduced nitric oxide (NO) bioactivity and increased risk of developing chronic kidney disease (CKD) and cardiovascular disease (CVD). New strategies that restore redox balance may have therapeutic implications during AKI and associated complications.

AIM

To investigate the therapeutic value of boosting the nitrate-nitrite-NO pathway during development of IR-induced renal and cardiovascular dysfunction.

METHODS

Male C57BL/6 J mice were given sodium nitrate (10 mg/kg, i. p) or vehicle 2 h prior to warm ischemia of the left kidney (45 min) followed by sodium nitrate supplementation in the drinking water (1 mmol/kg/day) for the following 2 weeks. Blood pressure and glomerular filtration rate were measured and blood and kidneys were collected and used for biochemical and histological analyses as well as renal vessel reactivity studies. Glomerular endothelial cells exposed to hypoxia-reoxygenation, with or without angiotensin II, were used for mechanistic studies.

RESULTS

IR was associated with reduced renal function and slightly elevated blood pressure, in combination with renal injuries, inflammation, endothelial dysfunction, increased Ang II levels and Ang II-mediated vasoreactivity, which were all ameliorated by nitrate. Moreover, treatment with nitrate (in vivo) and nitrite (in vitro) restored NO bioactivity and reduced mitochondrial oxidative stress and injuries.

CONCLUSIONS

Acute treatment with inorganic nitrate prior to renal ischemia may serve as a novel therapeutic approach to prevent AKI and CKD and associated risk of developing cardiovascular dysfunction.

H2S- and NO-releasing gasotransmitter platform: A crosstalk signaling pathway in the treatment of acute kidney injury

Acute kidney injury (AKI) is a syndrome affecting most patients hospitalized due to kidney disease; it accounts for 15 % of patients hospitalized in intensive care units worldwide. AKI is mainly caused by ischemia and reperfusion (IR) injury, which temporarily obstructs the blood flow, increases inflammation processes and induces oxidative stress. AKI treatments available nowadays present notable disadvantages, mostly for patients with other comorbidities. Thus, it is important to investigate different approaches to help minimizing side effects such as the ones observed in patients subjected to the aforementioned treatments. Therefore, the aim of the current review is to highlight the potential of two endogenous gasotransmitters - hydrogen sulfide (H₂S) and nitric oxide (NO) - and their crosstalk in AKI treatment. Both H₂S and NO are endogenous signalling molecules involved in several physiological and pathophysiological processes, such as the ones taking place in the renal system. Overall, these molecules act by decreasing inflammation, controlling reactive oxygen species (ROS) concentrations, activating/inactivating pro-inflammatory cytokines, as well as promoting vasodilation and decreasing apoptosis, hypertrophy and autophagy. Since these gasotransmitters are found in gaseous state at environmental conditions, they can be directly applied by inhalation, or in combination with H₂S and NO donors, which are compounds capable of releasing these molecules at biological conditions, thus enabling higher stability and slow release of NO and H₂S. Moreover, the combination between these donor compounds and nanomaterials has the potential to enable targeted treatments, reduce side effects and increase the potential of H₂S and NO. Finally, it is essential highlighting challenges to, and perspectives in, pharmacological applications of H₂S and NO to treat AKI, mainly in combination with nanoparticulated delivery platforms.

NOX1 Inhibition Attenuates Kidney Ischemia-Reperfusion Injury via Inhibition of ROS-Mediated ERK Signaling

The protective effects of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) 1 inhibition against kidney ischemia-reperfusion injury (IRI) remain uncertain. The bilateral kidney pedicles of C57BL/6 mice were clamped for 30 min to induce IRI. Madin–Darby Canine Kidney (MDCK) cells were incubated with H₂O₂ (1.4 mM) for 1 h to induce oxidative stress. ML171, a selective NOX1 inhibitor, and siRNA against NOX1 were treated to inhibit NOX1. NOX expression, oxidative stress, apoptosis assay, and mitogen-activated protein kinase (MAPK) pathway were evaluated. The kidney function deteriorated and the production of reactive oxygen species (ROS), including intracellular H₂O₂ production, increased due to IRI, whereas IRI-mediated kidney dysfunction and ROS generation were significantly attenuated by ML171. H₂O₂ evoked the changes in oxidative stress enzymes such as SOD2 and GPX in MDCK cells, which was mitigated by ML171. Treatment with ML171 and transfection with siRNA against NOX1 decreased the upregulation of NOX1 and NOX4 induced by H₂O₂ in MDCK cells. ML171 decreased caspase-3 activity, the Bcl-2/Bax ratio, and TUNEL-positive tubule cells in IRI mice and H₂O₂-treated MDCK cells. Among the MAPK pathways, ML171 affected ERK signaling by ERK phosphorylation in kidney tissues and tubular cells. NOX1-selective inhibition attenuated kidney IRI via inhibition of ROS-mediated ERK signaling.

The effect of tramadol on oxidative stress total antioxidant levels in rats with renal ischemia-reperfusion injury

OBJECTIVE

To evaluate the protective effect of tramadol on renal tissue in rats with induced renal ischemia-reperfusion injury (I/R injury), and its effects on oxidative stress.

MATERIAL AND METHODS

Thirty adult, male Wistar rats weighing 250-300 g were selected as subjects. Rats were randomized into 3 groups: group 1, sham; group 2, renal I/R injury; and group 3, renal I/R+Tramadol. In order to obtain ischemia in groups 2 and 3, renal artery was clamped for 1 h. Total oxidant status (TOS) and total antioxidant capacity (TAC) were analyzed using biochemical assays in the serum samples.

RESULTS

TOS values were measured as 1.68±0.4 in group 1, 3.35±1.0 in group 2, and 3.49±0.9 in group 3. When group 1 was compared with group 2 and group 3, the TOS values of group 1 were significantly lower (p<0.05), whereas there was no difference between group 2 and group 3 (p>0.05). TAC values were measured as 1.65±1.4 in group 1, 1.85±0.1 in group 2, and 2.79±0.6 in group 3. The antioxidant status of group 1 was not significantly different from that of group 2 (p>0.05), whereas there was a significant difference between group 1 and group 3 (p>0.05).

CONCLUSIONS

Tramadol has positive effects on antioxidant levels in renal I/R injury. We think that tramadol may be used in patients who underwent renal surgery and have I/R injury risk. There is a need for studies on this subject including human series.

Signaling through tumor necrosis receptor 2 induces stem cell marker in CD133+ regenerating tubular epithelial cells in acute cell-mediated rejection of human renal allografts

Tumor necrosis factor receptor 2 (TNFR2) is strongly upregulated on renal tubular epithelial cells by acute cell-mediated rejection (ACR. In human kidney organ culture, TNFR2 signaling both upregulates TNFR2 expression and promotes cell cycle entry of tubular epithelial cells. We find significantly more cells express CD133 mRNA and protein, a putative stem cell marker, in allograft biopsy samples with ACR compared to acute tubular injury without rejection or pretransplant "normal kidney" biopsy samples. Of CD133⁺ cells, ~85% are within injured tubules and ~15% are interstitial. Both populations express stem cell marker TRA-1-60 and TNFR2, but only tubular CD133⁺ cells express proximal tubular markers megalin and aquaporin-1. TNFR2⁺ CD133⁺ cells in tubules express proliferation marker phospho-histone H3^S10 (pH3^S10 ). Tubular epithelial cells in normal kidney organ cultures respond to TNFR2 signaling by expressing CD133 mRNA and protein, stem cell marker TRA-1-60, and pH3^S10 within 3 hours of treatment. This rapid response time suggests that CD133⁺ cells in regenerating tubules of kidneys undergoing ACR represent proliferating tubular epithelial cells with TNFR2-induced stem cell markers rather than expansion of resident stem cells. Infiltrating host mononuclear cells are a likely source of TNF as these changes are absent in acute tubular injury .

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.

Preventive effects of fraxin on ischemia/reperfusion-induced acute kidney injury in rats

AIM

Kidney ischemia reperfusion (IR) injury is an important health problem resulting in acute kidney failure. The oxidative stress and inflammatory process are the underlying mechanisms of IR injury. It has been purposed in this study to research the possible protective effects of fraxin on kidney injury induced by IR.

MATERIAL AND METHODS

32 Sprague Dawley male rats were divided into 4 groups. The groups were organized as follows; sham, IR, IR + fraxin 10 mg/kg, and IR + 50 mg/kg fraxin groups. Some oxidant, antioxidant and inflammatory parameters were evaluated in kidney tissues removed at the end of our experimental study.

KEY FINDINGS

It was detected that the oxidant and proinflammatory markers increased and antioxidant parameters decreased in IR group but the results significantly reversed in treatment groups compared to IR group. And also, 8-OHdG, NF-κB, HAVCR1 immunopositivities were at severe levels and these results attenuated in IR fraxin + 10 mg/kg, and IR + fraxin 50 mg/kg groups.

SIGNIFICANCE

These presented results have shown that fraxin performed protective effects against kidney injury induced by IR.

Notch Signaling in Kidney Development, Maintenance, and Disease

Kidney development involves formation of nephrons intricately aligned with the vasculature and connected to a branched network of collecting ducts. Notch signaling plays multiple roles during kidney development involving the formation of nephrons composed of diverse epithelial cell types arranged into tubular segments, all the while maintaining a nephron progenitor niche. Here, we review the roles of Notch signaling identified from rodent kidney development and injury studies, while discussing human kidney diseases associated with aberrant Notch signaling. We also review Notch signaling requirement in maintenance of mature kidney epithelial cell states and speculate that Notch activity regulation mediates certain renal physiologic adaptations.

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.

Potentiating Renal Regeneration Using Mesenchymal Stem Cells

BACKGROUND

The potential of a mesenchymal stem cell (MSC) therapy to accelerate the repair of ischemically damaged human kidneys during 24 hours of warm perfusion was evaluated. The hypothesis was that by administering MSC directly to the renal tissue, there would be an improved opportunity for cellular repair mediated by intrarenal paracrine effects.

METHODS

Studies were performed using the exsanguinous metabolic support (EMS) tissue-engineering platform. Five pairs of human kidney allografts from donation after circulatory death donors were studied. One human kidney was EMS perfused for 24 hours (control), whereas its paired kidney was EMS perfused with MSC (1 × 10). The kidneys were evaluated for DNA synthesis, cytokine/chemokine synthesis, cytoskeletal regeneration, and mitosis.

RESULTS

Treatment with MSC resulted in reduced inflammatory cytokines synthesized by the kidneys. Mesenchymal stem cell treatment led to a significant increase in the synthesis of adenosine triphosphate and growth factors resulting in normalization of metabolism and the cytoskeleton. Toluidine Blue staining of MSC-treated kidneys demonstrated a significant increase in the number of renal cells undergoing mitosis (26%) compared with EMS perfusion alone.

CONCLUSIONS

To our knowledge, our work is the first to have demonstrated actual renal regeneration while ischemically damaged human kidneys are perfused ex vivo for 24 hours. The observed regeneration entails: increased synthesis of adenosine triphosphate, a reduced inflammatory response, increased synthesis of growth factors, normalization of the cytoskeleton and mitosis. The ability to regenerate renal tissue ex vivo sufficiently to result in immediate function could revolutionize transplantation by solving the chronic organ shortage.

Rapid Identification of Ischemic Injury in Renal Tissue by Mass-Spectrometry Imaging

The increasing analytical speed of mass-spectrometry imaging (MSI) has led to growing interest in the medical field. Acute kidney injury is a severe disease with high morbidity and mortality. No reliable cut-offs are known to estimate the severity of acute kidney injury. Thus, there is a need for new tools to rapidly and accurately assess acute ischemia, which is of clinical importance in intensive care and in kidney transplantation. We investigated the value of MSI to assess acute ischemic kidney tissue in a porcine model. A perfusion model was developed where paired kidneys received warm (severe) or cold (minor) ischemia ( n = 8 per group). First, ischemic tissue damage was systematically assessed by two blinded pathologists. Second, MALDI-MSI of kidney tissues was performed to study the spatial distributions and compositions of lipids in the tissues. Histopathological examination revealed no significant difference between kidneys, whereas MALDI-MSI was capable of a detailed discrimination of severe and mild ischemia by differential expression of characteristic lipid-degradation products throughout the tissue within 2 h. In particular, lysolipids, including lysocardiolipins, lysophosphatidylcholines, and lysophosphatidylinositol, were dramatically elevated after severe ischemia. This study demonstrates the significant potential of MSI to differentiate and identify molecular patterns of early ischemic injury in a clinically acceptable time frame. The observed changes highlight the underlying biochemical processes of acute ischemic kidney injury and provide a molecular classification tool that can be deployed in assessment of acute ischemic kidney injury.

The renoprotective effects of naringin and trimetazidine on renal ischemia/reperfusion injury in rats through inhibition of apoptosis and downregulation of micoRNA-10a

Renal Ischemia-Reperfusion (IR) injury occurs due to circulatory shock and renal transplantation, leading to mortality and morbidity worldwide. The primary purpose of the current study was to evaluate the renoprotective effects of the naringin (NAR) and trimetazidine (TMZ) on IR injury, renal hemodynamics, antioxidant capacity, microRNA-10a, and expression of apoptosis factors. Forty rats were divided into five groups randomly: Sham, IR injury, (TMZ, 5 mg/kg), (NAR pretreatment, 100 mg/kg), and TMZ plus NAR. The sham group underwent the identical surgical procedure as the other groups, except for the application of clamps. After anesthesia, IR injury was induced by 45 min of ischemia, followed by reperfusion for 4 h. Tissue and blood samples were collected for evaluation of renal function, antioxidant activity and, biochemical and molecular parameters. Administration of the NAR, TMZ, and their combination decreased the plasma level of microRNA-10a, caspase-3, and Bcl-2 associated x protein (Bax) mRNA expression, but increased the B- cell lymphoma 2 (Bcl-2) mRNA expression in the kidney tissue. In addition, antioxidant activity, renal blood flow, creatinine clearance (C_Cr), and fractional excretion of sodium (FE_Na) were improved. The NAR, TMZ, and their combination can prevent renal I/R injury through promotion of the level of antioxidant enzymes, as well as decrease of microRNA-10a and anti-apoptosis properties. Our data also suggest that NAR, TMZ, or their combination might be beneficial as potent therapeutic factors against renal IR injury.

8-Br-cADPR, a TRPM2 ion channel antagonist, inhibits renal ischemia-reperfusion injury

The transient receptor potential melastatin-2 (TRPM2) channel belongs to the transient receptor potential channel superfamily and is a cation channel permeable to Na⁺ and Ca ²⁺ . The TRPM2 ion channel is expressed in the kidney and can be activated by various molecules such as hydrogen peroxide, calcium, and cyclic adenosine diphosphate (ADP)-ribose (cADPR) that are produced during acute kidney injury. In this study, we investigated the role of 8-bromo-cyclic ADP-ribose (8-Br-cADPR; a cADPR antagonist) in renal ischemia-reperfusion injury using biochemical and histopathological parameters. CD38, cADPR, tumor necrosis factor-α, interleukin-1β, and myeloperoxidase (inflammatory markers), urea and creatinine, hydrogen peroxide (oxidant), and catalase (antioxidant enzyme) levels that increase with ischemia-reperfusion injury decreased in the groups treated with 8-Br-cADPR. In addition, renin levels were elevated in the groups treated with 8-Br-cADPR. Histopathological examination revealed that 8-Br-cADPR reduced renal damage and the expression of caspase-3 and TRPM2. Our results suggest that the inhibition of TRPM2 ion channel may be a new treatment modality for ischemic acute kidney injury.

EGF Receptor-Dependent YAP Activation Is Important for Renal Recovery from AKI

BACKGROUND

Increasing evidence indicates that renal recovery from AKI stems from dedifferentiation and proliferation of surviving tubule epithelial cells. Both EGF receptor (EGFR) and the Hippo signaling pathway are implicated in cell proliferation and differentiation, and previous studies showed that activation of EGFR in renal proximal tubule epithelial cells (RPTCs) plays a critical role in recovery from ischemia-reperfusion injury (IRI). In this study, we explored RPTC activation of Yes-associated protein (YAP) and transcriptional coactivator with PDZ binding motif (TAZ), two key downstream effectors of the Hippo pathway, and their potential involvement in recovery from AKI.

METHODS

We used immunofluorescence to examine YAP expression in kidney biopsy samples from patients with clinical AKI and controls (patients with minimal change disease). Studies of RPTC activation of YAP and TAZ used cultured human RPTCs that were exposed to hypoxia-reoxygenation as well as knockout mice (with inducible deletions of Yap, Taz, or both occurring specifically in RPTCs) that were subjected to bilateral IRI.

RESULTS

YAP was activated in RPTCs in kidneys from post-AKI patients and post-IRI mouse kidneys. Inhibition of the interaction of YAP and the TEA domain (TEAD) transcription factor complex by verteporfin or conditional deletion of YAP in RPTCs delayed renal functional and structural recovery from IRI, whereas TAZ deletion had no effect. Activation of the EGFR-PI3K-Akt pathway in response to IRI signaled YAP activation, which promoted cell cycle progression.

CONCLUSIONS

This study shows that EGFR-PI3K-Akt-dependent YAP activation plays an essential role in mediating epithelial cell regeneration during kidney recovery from AKI.

Hepatorenal protection during renal ischemia by quercetin and remote ischemic perconditioning

BACKGROUND

Pathogenesis of renal ischemia/reperfusion injury (IRI) involves oxidative stress response in the kidney and remote organs. Both quercetin and remote ischemic perconditioning (RIPerC) can protect partially against IRI. This study determined whether combined quercetin and RIPerC could provide an augmented hepatorenal protection against renal IRI.

MATERIALS AND METHODS

I/R was induced by clamping renal arteries for 45 min followed by 24-h reperfusion. RIPerC consisted of four cycles of 2 min of left femoral artery ischemia followed by 3 min of reperfusion administered at the beginning of renal ischemia. Rats were divided into five groups: sham, I/R, RIPerC, quercetin (Q + I/R), and combined quercetin and RIPerC (Q + RIPerC). At the end of reperfusion period, blood, urine, and tissue samples were collected.

RESULTS

I/R caused kidney dysfunction, as proved by significant decrease in creatinine clearance, and a significant increase in liver functional indicators as evidenced by increased plasma alanine aminotransferase and aspartate aminotransferase activity. This was accompanied by a decrease of glutathione peroxidase and catalase activities with an increase of malondialdehyde levels and histological damages in renal and hepatic tissues. Treatment with RIPerC and quercetin reduced all these changes. However, the measure of improvements was enhanced by combined quercetin and RIPerC treatment.

CONCLUSIONS

This study demonstrated protective effects of quercetin and RIPerC strategy on the both kidney and liver after renal I/R. The results suggest that combined quercetin and RIPerC provides an enhanced protection against renal IRI by reduction of lipid peroxidation and augmentation of antioxidant systems.

Can Tissue Cilia Lengths and Urine Cilia Proteins Be Markers of Kidney Diseases?

The primary cilium is an organelle which consists of a microtubule in the core and a surrounding cilia membrane, and has long been recognized as a “vestigial organelle”. However, new evidence demonstrates that the primary cilium has a notable effect on signal transduction in the cell and is associated with some genetic and non-genetic diseases. In the kidney, the primary cilium protrudes into the Bowman's space and the tubular lumen from the apical side of epithelial cells. The length of primary cilia is dynamically altered during the normal cell cycle, being shortened by retraction into the cell body at the entry of cell division and elongated at differentiation. Furthermore, the length of primary cilia is also dynamically changed in the cells, as a result and/or cause, during the progression of various kidney diseases including acute kidney injury and chronic kidney disease. Notably, recent data has demonstrated that the shortening of the primary cilium in the cell is associated with fragmentation, apart from retraction into the cell body, in the progression of diseases and that the fragmented primary cilia are released into the urine. This data reveals that the alteration of primary cilia length could be related to the progression of diseases. This review will consider if primary cilia length alteration is associated with the progression of kidney diseases and if the length of tissue primary cilia and the presence or increase of cilia proteins in the urine is indicative of kidney diseases.

Ischemic acute kidney injury and klotho in renal transplantation

Post-transplant ischemic acute kidney injury (AKI), secondary to ischemia reperfusion injury (IRI), is a major problem influencing on the short and long term graft and patient survival. Many molecular and cellular modifications are observed during IRI, for example, tissue damage result production of reactive oxygen species (ROS), cytokines, chemokines, and leukocytes recruitment which are activated by NF-κB (nuclear factor kappa B) signaling pathway. Therefore, inhibiting these processes can significantly protect renal parenchyma from tissue damage. Klotho protein, mainly produced in distal convoluted tubules (DCT), is an anti-senescence protein. There is increasing evidence to confirm a relationship between Klotho levels and renal allograft function. Many studies have also demonstrated that expression of the Klotho gene would be down regulated with IRI, so it will be used as an early biomarker for acute kidney injury after renal transplantation. Other studies suggest that Klotho may have a renoprotective effect for attenuating of kidney injury. In this review, we will discuss pathophysiology of IRI-induced acute kidney injury and its relation with klotho level in renal transplantation procedure.

Anti-inflammatory Effects of Valproic Acid in a Rat Model of Renal Ischemia/Reperfusion Injury: Alteration in Cytokine Profile

Valporic acid (VPA) has been implicated to have anti-inflammatory and anti-oxidant activities in several ischemic/reperfusion (I/R) injury models. This study intended to evaluate whether VPA could affect the inflammatory/anti-inflammatory cytokines balance and severity of renal I/R injury in rat. I/R injury was induced in two groups of animals, vehicle normal saline and VPA-treated (IP injection, 150 mg/kg) rats, by 45 min occlusion of both left and right renal arteries followed by 3, 24 and 120 h reperfusion in separate groups. After each time point, kidneys and blood samples were collected for cytokine genes (TNF-α, IL-1β, IL-10 and TGF-β) expression analysis and histological examinations in the kidney tissues. Serum creatinine levels were measured for evaluation of renal function. We observed significantly downregulated mRNA expressions for IL-1β and TNF-α in blood and tissue samples 24 and 120 h post I/R injury in VPA-treated animals compared to control groups (P < 0.0001). On the other hand, mRNA expression levels for IL-10 and TGF-β were significantly increased in the blood samples from VPA-treated animals at two time points after I/R injury (P < 0.0001) and at 120 h in tissue samples (P < 0.001). Histopathology analysis showed downgraded ischemic changes in VPA group compared to sham control. Also, decreased serum creatinine levels were observed in VPA-treated animals particularly 120 h post I/R injury (P < 0.0001) that was correlated with less pathological changes in this group. Our results indicate that VPA can attenuate pro-inflammatory responses and augment the anti-inflammatory condition in favor of faster renal recovery from ischemic changes and improved renal function after renal I/R injury.

Berberine nanoparticles protects tubular epithelial cells from renal ischemia-reperfusion injury

Renal ischemia-reperfusion (I/R) injury is one of the most common causes of acute renal failure, the prognosis of which remains poor and there still lacks of effective therapeutics available in the clinic. This study aimed at investigating the effects of Berberine nanoparticles (BBR-NP) on the ischemia-reperfusion injury of renal tubular epithelial cells and underlying the mechanisms. Our results showed that in a rat model of renal I/R injury, BBR and BBR-NP protected renal against injury both functionally (as assessed by serum urea nitrogen and creatinine level) and morphologically (as assessed by HE staining, transmission electron microscopy and TUNEL staining) in a dose-dependent manner, with the effects of BBR-NP superior to BBR alone. Mechanism investigation showed that BBR-NP reversed oxidative stress and subsequent apoptosis of renal cells, as demonstrated by the decreased expression of proteins involved in the oxidative stress and mitochondrial stress pathways. In conclusion, our study showed that BBR-NP is superior to BBR alone in protecting renal against I/R injury and explored the underlying mechanisms, which should be tested in further studies and might give impetus to the development of novel therapeutics based on BBR-NP against renal I/R.

Ginsenoside Rg1 protects human renal tubular epithelial cells from lipopolysaccharide-induced apoptosis and inflammation damage

Ginsenoside Rg1, one of the most notable active components of Panax ginseng, has been widely reported to exert anti-inflammatory actions. This study aimed to reveal whether ginsenoside Rg1 also exhibits beneficial roles against lipopolysaccharide (LPS)-induced apoptosis and inflammation in human renal tubular epithelial cells, and to evaluate the potential role of the component on tubulointerstitial nephritis treatment. HK-2 cells were treated with various doses of ginsenoside Rg1 (0, 50, 100, 150, and 200 μM) in the absence or presence of 5 μg/mL LPS. Thereafter, CCK-8 assay, flow cytometry, western blot, migration assay, reactive oxygen species (ROS) assay, and ELISA were carried out to respectively assess cell viability, apoptosis, migration, ROS activity, and the release of inflammatory cytokines. As a result, ginsenoside Rg1 protected HK-2 cells from LPS-induced injury, as cell viability was increased, cell apoptosis was decreased, and the release of MCP-1, IL-1β, IL-6, and TNF-α was reduced. Ginsenoside Rg1 functioned to HK-2 cells in a dose-dependent manner, and the 150 μM dose exhibited the most protective functions. Ginsenoside Rg1 had no significant impact on cell migration and ROS activity, while it alleviated LPS-induced ROS release and migration impairment. Furthermore, the down-regulations of p-PI3K, p-AKT, and up-regulations of PTEN, p-IκBα, p-p65, Bcl-3 induced by LPS were recovered to some extent after ginsenoside Rg1 treatment. In conclusion, ginsenoside Rg1 protects HK-2 cells against LPS-induced inflammation and apoptosis via activation of the PI3K/AKT pathway and suppression of NF-κB pathway.

Angiotensinogen as a biomarker of acute kidney injury

Early recognition of acute kidney injury (AKI) is critical to prevent its associated complications as well as its progression to long term adverse outcomes like chronic kidney disease. A growing body of evidence from both laboratory and clinical studies suggests that inflammation is a key factor contributing to the progression of AKI regardless of the initiating event. Biomarkers of inflammation are therefore of interest in the evaluation of AKI pathogenesis and prognosis. There is evidence that the renin angiotensin aldosterone system is activated in AKI, which leads to an increase in angiotensin II (Ang II) formation within the kidney. Ang II activates pro-inflammatory and pro-fibrotic pathways that likely contribute to the progression of AKI. Angiotensinogen is the parent polypeptide from which angiotensin peptides are formed and its stability in urine makes it a more convenient marker of renin angiotensin system activity than direct measurement of Ang II in urine specimens, which would provide more direct information. The potential utility of urinary angiotensinogen as a biomarker of AKI is discussed in light of emerging data showing a strong predictive value of AKI progression, particularly in the setting of decompensated heart failure. The prognostic significance of urinary angiotensinogen as an AKI biomarker strongly suggests a role for renin-angiotensin system activation in modulating the severity of AKI and its outcomes.

3D printed conformal microfluidics for isolation and profiling of biomarkers from whole organs

The ability to interface microfluidic devices with native complex biological architectures, such as whole organs, has the potential to shift the paradigm for the study and analysis of biological tissue. Here, we show 3D printing can be used to fabricate bio-inspired conformal microfluidic devices that directly interface with the surface of whole organs. Structured-light scanning techniques enabled the 3D topographical matching of microfluidic device geometry to porcine kidney anatomy. Our studies show molecular species are spontaneously transferred from the organ cortex to the conformal microfluidic device in the presence of fluid flow through the organ-conforming microchannel. Large animal studies using porcine kidneys (n = 32 organs) revealed the profile of molecular species in the organ-conforming microfluidic stream was dependent on the organ preservation conditions. Enzyme-linked immunosorbent assay (ELISA) studies revealed conformal microfluidic devices isolate clinically relevant metabolic and pathophysiological biomarkers from whole organs, including heat shock protein 70 (HSP-70) and kidney injury molecule-1 (KIM-1), which were detected in the microfluidic device as high as 409 and 12 pg mL^-1, respectively. Overall, these results show conformal microfluidic devices enable a novel minimally invasive 'microfluidic biopsy' technique for isolation and profiling of biomarkers from whole organs within a clinically relevant interval. This achievement could shift the paradigm for whole organ preservation and assessment, thereby helping to relieve the organ shortage crisis through increased availability and quality of donor organs. Ultimately, this work provides a major advance in microfluidics through the design and manufacturing of organ-conforming microfluidic devices and a novel technique for microfluidic-based analysis of whole organs.

Dietary nitrate attenuates renal ischemia-reperfusion injuries by modulation of immune responses and reduction of oxidative stress

Ischemia-reperfusion (IR) injury involves complex pathological processes in which reduction of nitric oxide (NO) bioavailability is suggested as a key factor. Inorganic nitrate can form NO in vivo via NO synthase-independent pathways and may thus provide beneficial effects during IR. Herein we evaluated the effects of dietary nitrate supplementation in a renal IR model. Male mice (C57BL/6J) were fed nitrate-supplemented chow (1.0mmol/kg/day) or standard chow for two weeks prior to 30min ischemia and during the reperfusion period. Unilateral renal IR caused profound tubular and glomerular damage in the ischemic kidney. Renal function, assessed by plasma creatinine levels, glomerular filtration rate and renal plasma flow, was also impaired after IR. All these pathologies were significantly improved by nitrate. Mechanistically, nitrate treatment reduced renal superoxide generation, pro-inflammatory cytokines (IL-1β, IL-6 and IL-12 p70) and macrophage infiltration in the kidney. Moreover, nitrate reduced mRNA expression of pro-inflammatory cytokines and chemo attractors, while increasing anti-inflammatory cytokines in the injured kidney. In another cohort of mice, two weeks of nitrate supplementation lowered superoxide generation and IL-6 expression in bone marrow-derived macrophages. Our study demonstrates protective effect of dietary nitrate in renal IR injury that may be mediated via modulation of oxidative stress and inflammatory responses. These novel findings suggest that nitrate supplementation deserve further exploration as a potential treatment in patients at high risk of renal IR injury.

Matrix Metalloproteinases in Kidney Disease: Role in Pathogenesis and Potential as a Therapeutic Target

Matrix metalloproteinases (MMPs) are large family of proteinases. In addition to a fundamental role in the remodeling of the extracellular matrix, they also cleave a number of cell surface proteins and are involved in multiple cellular processes. MMP activity is regulated via numerous mechanisms, including inhibition by endogenous tissue inhibitors of metalloproteinases (TIMPs). Similar to MMPs, a role for TIMPs has been established in multiple cell signaling pathways. Aberrant expression of MMPs and TIMPS in renal pathophysiology has long been recognized, and with the generation of specific knockout mice, the mechanistic role of several MMPs and TIMPs is becoming more understood and has revealed both pathogenic and protective roles. This chapter will focus on the expression and localization of MMPs and TIMPs in the kidney, as well as summarizing the current information linking these proteins to acute kidney injury and chronic kidney disease. In addition, we will summarize studies suggesting that MMPs and TIMPs may be biomarkers of renal dysfunction and represent novel therapeutic targets to attenuate kidney disease.

Histone deacetylase–mediated silencing of AMWAP expression contributes to cisplatin nephrotoxicity

Cisplatin-induced acute kidney injury is a serious problem in cancer patients during treatment of solid tumors. Currently, there are no therapies available to treat or prevent cisplatin nephrotoxicity. Since histone deacetylase (HDAC) inhibition augments cisplatin anti-tumor activity, we tested whether HDAC inhibitors can prevent cisplatin-induced nephrotoxicity and determined the underlying mechanism. Cisplatin upregulated the expression of several HDACs in the kidney. Inhibition of HDAC with clinically used trichostatin A suppressed cisplatin-induced kidney injury, inflammation, and epithelial cell apoptosis. Moreover, trichostatin A upregulated the novel anti-inflammatory protein, activated microglia/macrophage WAP domain protein (AMWAP), in epithelial cells which was enhanced with cisplatin treatment. Interestingly, HDAC1 and -2 specific inhibitors are sufficient to potently upregulate AMWAP in epithelial cells. Administration of recombinant AMWAP or its epithelial cell-specific overexpression reduced cisplatin-induced kidney dysfunction. Moreover, AMWAP treatment suppressed epithelial cell apoptosis, and siRNA-based knockdown of AMWAP expression abolished trichostatin A-mediated suppression of epithelial cell apoptosis in vitro. Thus, HDAC-mediated silencing of AMWAP may contribute to cisplatin nephrotoxicity. Hence, HDAC1 and -2 specific inhibitors or AMWAP could be useful therapeutic agents for the prevention of cisplatin nephrotoxicity.

Sodium Pentosan Polysulfate Reduced Renal Ischemia-Reperfusion-Induced Oxidative Stress and Inflammatory Responses in an Experimental Animal Model

Acute kidney injury (AKI) remains an independent risk factor for mortality and morbidity after vascular surgery (affecting the renal arteries) or aortic surgery (requiring suprarenal aortic clamping). These types of vascular surgery produce renal ischemia/reperfusion (I/R) injury, a common cause of AKI. The present studies aimed at monitoring the course of renal I/R injury at the cellular level and investigating the efficacy of long-term preoperative and single-shot intraoperative administration of sodium pentosan polysulfate (PPS) to protect renal tissue from acute I/R injury both in native and diabetic kidneys in rats. Western blot analyses of the proapoptotic (bax) and antiapoptotic (bcl-2) signaling pathways, as well as the extent of DNA damage (phospho-p53), were performed. Oxidative stress followed upon the termination of malondialdehyde, reduced glutathione, thiol group, and superoxide dismutase plasma levels. Inflammatory changes were measured by the determination of serum tumor necrosis factor-α and interleukin-1 levels. Morphological changes were detected by histological examinations. Our results showed that the long-term administration of PPS has an advantage in reducing I/R kidney injury in diabetic rats, while high-dose, single-shot parenteral administration of PPS prior to revascularization might be useful in nondiabetic rats.

Mitochondrial NADP+-Dependent Isocitrate Dehydrogenase Deficiency Exacerbates Mitochondrial and Cell Damage after Kidney Ischemia-Reperfusion Injury

Mitochondrial NADP⁺-dependent isocitrate dehydrogenase (IDH2) catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate, synthesizing NADPH, which is essential for mitochondrial redox balance. Ischemia-reperfusion (I/R) is one of most common causes of AKI. I/R disrupts the mitochondrial redox balance, resulting in oxidative damage to mitochondria and cells. Here, we investigated the role of IDH2 in I/R-induced AKI. I/R injury in mice led to the inactivation of IDH2 in kidney tubule cells. Idh2 gene deletion exacerbated the I/R-induced increase in plasma creatinine and BUN levels and the histologic evidence of tubule injury, and augmented the reduction of NADPH levels and the increase in oxidative stress observed in the kidney after I/R. Furthermore, Idh2 gene deletion exacerbated I/R-induced mitochondrial dysfunction and morphologic fragmentation, resulting in severe apoptosis in kidney tubule cells. In cultured mouse kidney proximal tubule cells, Idh2 gene downregulation enhanced the mitochondrial damage and apoptosis induced by treatment with hydrogen peroxide. This study demonstrates that Idh2 gene deletion exacerbates mitochondrial damage and tubular cell death via increased oxidative stress, suggesting that IDH2 is an important mitochondrial antioxidant enzyme that protects cells from I/R insult.

Oxidant Mechanisms in Renal Injury and Disease

SIGNIFICANCE

A common link between all forms of acute and chronic kidney injuries, regardless of species, is enhanced generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) during injury/disease progression. While low levels of ROS and RNS are required for prosurvival signaling, cell proliferation and growth, and vasoreactivity regulation, an imbalance of ROS and RNS generation and elimination leads to inflammation, cell death, tissue damage, and disease/injury progression.

RECENT ADVANCES

Many aspects of renal oxidative stress still require investigation, including clarification of the mechanisms which prompt ROS/RNS generation and subsequent renal damage. However, we currently have a basic understanding of the major features of oxidative stress pathology and its link to kidney injury/disease, which this review summarizes.

CRITICAL ISSUES

The review summarizes the critical sources of oxidative stress in the kidney during injury/disease, including generation of ROS and RNS from mitochondria, NADPH oxidase, and inducible nitric oxide synthase. The review next summarizes the renal antioxidant systems that protect against oxidative stress, including superoxide dismutase and catalase, the glutathione and thioredoxin systems, and others. Next, we describe how oxidative stress affects kidney function and promotes damage in every nephron segment, including the renal vessels, glomeruli, and tubules.

FUTURE DIRECTIONS

Despite the limited success associated with the application of antioxidants for treatment of kidney injury/disease thus far, preventing the generation and accumulation of ROS and RNS provides an ideal target for potential therapeutic treatments. The review discusses the shortcomings of antioxidant treatments previously used and the potential promise of new ones. Antioxid. Redox Signal. 25, 119-146.

Regulation of necrotic cell death: p53, PARP1 and cyclophilin D-overlapping pathways of regulated necrosis?

In contrast to apoptosis and autophagy, necrotic cell death was considered to be a random, passive cell death without definable mediators. However, this dogma has been challenged by recent developments suggesting that necrotic cell death can also be a regulated process. Regulated necrosis includes multiple cell death modalities such as necroptosis, parthanatos, ferroptosis, pyroptosis, and mitochondrial permeability transition pore (MPTP)-mediated necrosis. Several distinctive executive molecules, particularly residing on the mitochondrial inner and outer membrane, amalgamating to form the MPTP have been defined. The c-subunit of the F1F0ATP synthase on the inner membrane and Bax/Bak on the outer membrane are considered to be the long sought components that form the MPTP. Opening of the MPTP results in loss of mitochondrial inner membrane potential, disruption of ATP production, increased ROS production, organelle swelling, mitochondrial dysfunction and consequent necrosis. Cyclophilin D, along with adenine nucleotide translocator and the phosphate carrier are considered to be important regulators involved in the opening of MPTP. Increased production of ROS can further trigger other necrotic pathways mediated through molecules such as PARP1, leading to irreversible cell damage. This review examines the roles of PARP1 and cyclophilin D in necrotic cell death. The hierarchical role of p53 in regulation and integration of key components of signaling pathway to elicit MPTP-mediated necrosis and ferroptosis is explored. In the context of recent insights, the indistinct role of necroptosis signaling in tubular necrosis after ischemic kidney injury is scrutinized. We conclude by discussing the participation of p53, PARP1 and cyclophilin D and their overlapping pathways to elicit MPTP-mediated necrosis and ferroptosis in acute kidney injury.

Pioglitazone ameliorates renal ischemia reperfusion injury through NMDA receptor antagonism in rats

The present study investigated the role of N-methyl-D-aspartate (NMDA) receptors in pioglitazone-mediated protection against renal ischemia reperfusion injury (IRI) in rats. Male wistar rats were subjected to 40 min of bilateral renal ischemia followed by reperfusion for 24 h to induce kidney injury. The renal damage was evaluated by measuring serum creatinine, creatinine clearance, blood urea nitrogen, uric acid, electrolytes, and microproteinuria in rats. Oxidative stress in renal tissues was quantified in terms of myeloperoxidase activity, thiobarbituric acid reactive substances, superoxide anion generation, and reduced glutathione level. Hematoxylin-eosin and periodic acid Schiff staining of renal tissues were performed to observe histological changes. Pioglitazone (20 and 40 mg/kg) was administered 1 h prior to ischemia in rats. In separate groups, NMDA agonists, glutamic acid (200 mg/kg), and spermidine (20 mg/kg) were administered 1 h prior to pioglitazone treatment, followed by renal IRI in rats. Ischemia reperfusion resulted in marked renal damage with significant changes in serum and urine parameters along with marked oxidative stress and histological changes in kidneys. Pioglitazone treatment afforded anti-oxidant effect and renoprotection in a dose-dependent manner in rats. Pioglitazone-mediated renoprotection was attenuated by glutamic acid and spermidine pretreatment in rats, which indicated the role of NMDA receptors in pioglitazone-mediated protection. It is concluded that NMDA antagonism serves as one of the mechanisms in pioglitazone-mediated protection against renal IRI in rats.