Persistent oxidative stress following renal ischemia-reperfusion injury increases ANG II hemodynamic and fibrotic activity

Gut microbial metabolites SCFAs and chronic kidney disease

The global incidence of Chronic Kidney Disease (CKD) is steadily escalating, with discernible linkage to the intricate terrain of intestinal microecology. The intestinal microbiota orchestrates a dynamic equilibrium in the organism, metabolizing dietary-derived compounds, a process which profoundly impacts human health. Among these compounds, short-chain fatty acids (SCFAs), which result from microbial metabolic processes, play a versatile role in influencing host energy homeostasis, immune function, and intermicrobial signaling, etc. SCFAs emerge as pivotal risk factors influencing CKD's development and prognosis. This paper review elucidates the impact of gut microbial metabolites, specifically SCFAs, on CKD, highlighting their role in modulating host inflammatory responses, oxidative stress, cellular autophagy, the immune milieu, and signaling cascades. An in-depth comprehension of the interplay between SCFAs and kidney disease pathogenesis may pave the way for their utilization as biomarkers for CKD progression and prognosis or as novel adjunctive therapeutic strategies.

Impaired hemodynamic renal reserve response following recovery from established acute kidney injury and improvement by hydrodynamic isotonic fluid delivery

Renal reserve capacity may be compromised following recovery from acute kidney injury (AKI) and could be used to identify impaired renal function in the face of restored glomerular filtration rate (GFR) or plasma creatinine. To investigate the loss of hemodynamic renal reserve responses following recovery in a model of AKI, rats were subjected to left unilateral renal ischemia-reperfusion (I/R) injury and contralateral nephrectomy and allowed to recover for 5 wk. Some rats were treated 24 h post-I/R by hydrodynamic isotonic fluid delivery (AKI-HIFD) of saline through the renal vein, previously shown to improve recovery and inflammation relative to control rats that received saline through the vena cava (AKI-VC). At 5 wk after surgery, plasma creatinine and GFR recovered to levels observed in uninephrectomized sham controls. Baseline renal blood flow (RBF) was not different between AKI or sham groups, but infusion of l-arginine (7.5 mg/kg/min) significantly increased RBF in sham controls, whereas the RBF response to l-arginine was significantly reduced in AKI-VC rats relative to sham rats (22.6 ± 2.2% vs. 13.8 ± 1.8%, P < 0.05). RBF responses were partially protected in AKI-HIFD rats relative to AKI-VC rats (17.0 ± 2.2%) and were not significantly different from sham rats. Capillary rarefaction observed in AKI-VC rats was significantly protected in AKI-HIFD rats. There was also a significant increase in T helper 17 cell infiltration and interstitial fibrosis in AKI-VC rats versus sham rats, which was not present in AKI-HIFD rats. These data suggest that recovery from AKI results in impaired hemodynamic reserve and that associated CKD progression may be mitigated by HIFD in the early post-AKI period.NEW & NOTEWORTHY Despite the apparent recovery of renal filtration function following acute kidney injury (AKI) in rats, the renal hemodynamic reserve response is significantly attenuated, suggesting that clinical evaluation of this parameter may provide information on the potential development of chronic kidney disease. Treatments such as hydrodynamic isotonic fluid delivery, or other treatments in the early post-AKI period, could minimize chronic inflammation or loss of microvessels with the potential to promote a more favorable outcome on long-term function.

The Association Between Serum Glutathione Peroxidase-3 Concentration and Risk of Acute Kidney Injury After Cardiac Surgery: A Nested Case-Control Study

Oxidative stress has an integral role in the pathophysiology of cardiac surgery-associated acute kidney injury (CSA-AKI). Glutathione peroxidase 3 (GPx3) is an important antioxidant enzyme in circulation and is mainly secreted by the kidney. This study aimed to evaluate the relation between GPx3 protein and CSA-AKI. This study is a nested case-control study in Zhongshan Hospital affiliated with Fudan University. We examined serum samples from 80 CSA-AKI patients and 80 age- and gender-matched non-AKI patients who underwent cardiac surgery. AKI was defined according to Kidney Disease: Improving Global Outcomes (KDIGO) 2012 criteria. We measured serum GPx3 concentration using the enzyme-linked immunosorbent assay. GPx3 ratio is the ratio of preoperative and 6 hours postoperative of GPx3 protein concentration. We applied dose-response relation analyses to odds ratio in different GPx3 ratio levels and integrated it into the logistic model to predict the risk of AKI. The receiver operating characteristic curve and area under the curve (AUC) was used to assess the prediction models. Postoperative serum GPx3 concentrations were significantly lower in the AKI group compared with the non-AKI group (1.78 ± 0.33 vs 2.03 ± 0.27, p <0.001). Malondialdehyde was higher in the AKI than in the non-AKI group (17.74 ± 8.65 vs 7.48 ± 4.59, p <0.001). The AKI risk increased in a dose-dependent manner, which was flat in the first half of the GPx3 ratio and then tended to be faster. The peaking odds ratio of CSA-AKI was 2.615 at the GPx3 ratio of 1.21 to 1.40. The AUC value to predict CSA-AKI only included the GPx3 ratio was 72.3%. After gradually integrating other covariates (body mass index, aortic crossclamp time, and cardiopulmonary bypass), the model showed an AUC of 82.6%. The serum GPx3 concentration was significantly lower in the CSA-AKI group. GPx3 ratio has a good predictive value for CSA-AKI, which may be a potential early diagnostic marker for AKI.

Recovery after AKI: Effects on outcomes over 15 years

PURPOSE

To examine the effect of kidney recovery on mortality, dialysis and kidney transplantation up to 15 years after AKI.

MATERIALS AND METHODS

We studied 29,726 survivors of critical illness and compared these outcomes stratified by AKI and recovery status at hospital discharge. Kidney recovery was defined as a return of serum creatinine to ≤150% of baseline without dialysis prior to hospital discharge.

RESULTS

Overall AKI occurred in 59.2% in which two thirds developed stage 2-3 AKI. Recovery rate of AKI at hospital discharge was 80.8%. Patients who did not recover experienced the worst 15-year mortality compared to those who recovered and those without AKI (57.8% vs 45.2% vs 30.3%, p < 0.001). This pattern was also found in subgroups of patients with suspected sepsis-associated (57.1% vs 47.9% vs 36.5%, p < 0.001) and cardiac surgery-associated AKI (60.1% vs 41.8% vs 25.9%, p < 0.001). The rates of dialysis and transplantation at 15 years were low and not associated with recovery status.

CONCLUSIONS

Recovery of AKI in critically ill patients at hospital discharge had an effect on long-term mortality for up to 15 years. These results have implications for acute care, follow-up and choice of endpoints for clinical trials.

Acute kidney injury in diabetes mellitus: Epidemiology, diagnostic, and therapeutic concepts

Acute kidney injury (AKI) and diabetes mellitus (DM) are public health problems that cause a high socioeconomic burden worldwide. In recent years, the landscape of AKI etiology has shifted: Emerging evidence has demonstrated that DM is an independent risk factor for the onset of AKI, while an alternative perspective considers AKI as a bona fide complication of DM. Therefore, it is necessary to systematically characterize the features of AKI in DM. In this review, we summarized the epidemiology of AKI in DM. While focusing on circulation- and tissue-specific microenvironment changes after DM, we described the active cellular and molecular mechanisms of increased kidney susceptibility to AKI under DM stress. We also reviewed the current diagnostic and therapeutic strategies for AKI in DM recommended in the clinic. Updated recognition of the epidemiology, pathophysiology, diagnosis, and medications of AKI in DM is believed to reveal a path to mitigate the frequency of AKI and DM comorbidity that will ultimately improve the quality of life in DM patients.

Vitamin D-vitamin D receptor alleviates oxidative stress in ischemic acute kidney injury via upregulating glutathione peroxidase 3

Vitamin D receptor was previously reported to be protective in acute kidney injury (AKI) with the mechanism unclear, while the role of renal localized glutathione peroxidase 3 (GPX3) was not illustrated. The present study aims to investigate the role of GPX3 as well as its correlation with vitamin D-vitamin D receptor (VD-VDR) in ischemia-reperfusion (I/R)-induced renal oxidative stress injury. We showed that the expression of GPX3 and VDR were consistently decreased in renal tissues of I/R-related AKI patients and mice models. VDR agonist paricalcitol could reverse GPX3 expression and inhibit oxidative stress in I/R mice or hypoxia-reoxygenation (H/R) insulted HK-2 cells. VDR deficiency resulted in aggregated oxidative stress and severer renal injury accompanied by further decreased renal GPX3, while tubular-specific VDR overexpression remarkably reduced I/R-induced renal injury with recovered GPX3 in mice. Neither serum selenium nor selenoprotein P was affected by paricalcitol administration nor Vdr modification in vivo. In addition, inhibiting GPX3 abrogated the protective effects of VD-VDR in HK-2 cells, while GPX3 overexpression remarkably attenuated H/R-induced oxidative stress and apoptosis. Mechanistic probing revealed the GPX3 as a VDR transcriptional target. Our present work revealed that loss of renal GPX3 may be a hallmark that promotes renal oxidative stress injury and VD-VDR could protect against I/R-induced renal injury via inhibition of oxidative stress partly by trans-regulating GPX3. In addition, maintenance of renal GPX3 could be a therapeutic strategy for ischemic AKI.

A ketogenic diet attenuates acute and chronic ischemic kidney injury and reduces markers of oxidative stress and inflammation

BACKGROUND

Ischemic kidney injury is a common clinical condition resulting from transient interruption of the kidney's normal blood flow, leading to oxidative stress, inflammation, and kidney dysfunction. The ketogenic diet (KD), a low-carbohydrate, high-fat diet that stimulates endogenous ketone body production, has potent antioxidant and anti-inflammatory effects in distinct tissues and might thus protect the kidney against ischemia and reperfusion (IR) injury.

MAIN METHODS

Male Wistar rats were fed a KD or a control diet (CD) for three days before analyzing metabolic parameters or testing nephroprotection. We used two different models of kidney IR injury and conducted biochemical, histological, and Western blot analyses at 24 h and two weeks after surgery.

KEY FINDINGS

Acute KD feeding caused protein acetylation, liver AMPK activation, and increased resistance to IR-induced kidney injury. At 24 h after IR, rats on KD presented reduced tubular damage and improved kidney functioning compared to rats fed with a CD. KD attenuated oxidative damage (protein nitration, 4-HNE adducts, and 8-OHdG), increased antioxidant defenses (GPx and SOD activity), and reduced inflammatory intermediates (IL6, TNFα, MCP1), p50 NF-κB expression, and cellular infiltration. Also, KD prevented interstitial fibrosis development at two weeks, up-regulation of HSP70, and chronic Klotho deficiency.

SIGNIFICANCE

Our findings demonstrate for the first time that short-term KD increases tolerance to experimental kidney ischemia, opening the opportunity for future therapeutic exploration of a dietary preconditioning strategy to convey kidney protection in the clinic.

Female and male mice have differential longterm cardiorenal outcomes following a matched degree of ischemia-reperfusion acute kidney injury

Acute kidney injury (AKI) is common in patients, causes systemic sequelae, and predisposes patients to long-term cardiovascular disease. To date, studies of the effects of AKI on cardiovascular outcomes have only been performed in male mice. We recently demonstrated that male mice developed diastolic dysfunction, hypertension and reduced cardiac ATP levels versus sham 1 year after AKI. The effects of female sex on long-term cardiac outcomes after AKI are unknown. Therefore, we examined the 1-year cardiorenal outcomes following a single episode of bilateral renal ischemia-reperfusion injury in female C57BL/6 mice using a model with similar severity of AKI and performed concomitantly to recently published male cohorts. To match the severity of AKI between male and female mice, females received 34 min of ischemia time compared to 25 min in males. Serial renal function, echocardiograms and blood pressure assessments were performed throughout the 1-year study. Renal histology, and cardiac and plasma metabolomics and mitochondrial function in the heart and kidney were evaluated at 1 year. Measured glomerular filtration rates (GFR) were similar between male and female mice throughout the 1-year study period. One year after AKI, female mice had preserved diastolic function, normal blood pressure, and preserved levels of cardiac ATP. Compared to males, females demonstrated pathway enrichment in arginine metabolism and amino acid related energy production in both the heart and plasma, and glutathione in the plasma. Cardiac mitochondrial respiration in Complex I of the electron transport chain demonstrated improved mitochondrial function in females compared to males, regardless of AKI or sham. This is the first study to examine the long-term cardiac effects of AKI on female mice and indicate that there are important sex-related cardiorenal differences. The role of female sex in cardiovascular outcomes after AKI merits further investigation.

PARK7 Protects Against Chronic Kidney Injury and Renal Fibrosis by Inducing SOD2 to Reduce Oxidative Stress

Renal fibrosis is the final common pathway to chronic kidney diseases regardless of etiology. Parkinson disease protein 7 (PARK7) is a multifunctional protein involved in various cellular processes, but its pathophysiological role in kidneys remain largely unknown. Here, we have determined the role of PARK7 in renal fibrosis and have further elucidated the underlying mechanisms by using the in vivo mouse model of unilateral ureteric obstruction (UUO) and the in vitro model of transforming growth factor-b (TGFB1) treatment of cultured kidney proximal tubular cells. PARK7 decreased markedly in atrophic kidney tubules in UUO mice, and Park7 deficiency aggravated UUO-induced renal fibrosis, tubular cell apoptosis, ROS production and inflammation. In vitro, TGFB1 treatment induced fibrotic changes in renal tubular cells, which was accompanied by alterations of PARK7. Park7 knockdown exacerbated TGFB1-induced fibrotic changes, cell apoptosis and ROS production, whereas Park7 overexpression or treatment with ND-13 (a PARK7-derived peptide) attenuated these TGFB1-induced changes. Mechanistically, PARK7 translocated into the nucleus of renal tubular cells following TGFB1 treatment or UUO, where it induced the expression of SOD2, an antioxidant enzyme. Taken together, these results indicate that PARK7 protects against chronic kidney injury and renal fibrosis by inducing SOD2 to reduce oxidative stress in tubular cells.

Restoration of afferent arteriolar autoregulatory behavior in ischemia-reperfusion injury in rat kidneys

Renal autoregulation is critical in maintaining stable renal blood flow (RBF) and glomerular filtration rate (GFR). Renal ischemia-reperfusion (IR)-induced kidney injury is characterized by reduced RBF and GFR. The mechanisms contributing to renal microvascular dysfunction in IR have not been fully determined. We hypothesized that increased reactive oxygen species (ROS) contributed to impaired renal autoregulatory capability in IR rats. Afferent arteriolar autoregulatory behavior was assessed using the blood-perfused juxtamedullary nephron preparation. IR was induced by 60 min of bilateral renal artery occlusion followed by 24 h of reperfusion. Afferent arterioles from sham rats exhibited normal autoregulatory behavior. Stepwise increases in perfusion pressure caused pressure-dependent vasoconstriction to 65 ± 3% of baseline diameter (13.2 ± 0.4 μm) at 170 mmHg. In contrast, pressure-mediated vasoconstriction was markedly attenuated in IR rats. Baseline diameter averaged 11.7 ± 0.5 µm and remained between 90% and 101% of baseline over 65-170 mmHg, indicating impaired autoregulatory function. Acute antioxidant administration (tempol or apocynin) to IR kidneys for 20 min increased baseline diameter and improved autoregulatory capability, such that the pressure-diameter profiles were indistinguishable from those of sham kidneys. Furthermore, the addition of polyethylene glycol superoxide dismutase or polyethylene glycol-catalase to the perfusate blood also restored afferent arteriolar autoregulatory responsiveness in IR rats, indicating the involvement of superoxide and/or hydrogen peroxide. IR elevated mRNA expression of NADPH oxidase subunits and monocyte chemoattractant protein-1 in renal tissue homogenates, and this was prevented by tempol pretreatment. These results suggest that ROS accumulation, likely involving superoxide and/or hydrogen peroxide, impairs renal autoregulation in IR rats in a reversible fashion.NEW & NOTEWORTHY Renal ischemia-reperfusion (IR) leads to renal microvascular dysfunction manifested by impaired afferent arteriolar autoregulatory efficiency. Acute administration of scavengers of reactive oxygen species, polyethylene glycol-superoxide dismutase, or polyethylene glycol-catalase following renal IR restored afferent arteriolar autoregulatory capability in IR rats, indicating that renal IR led to reversible impairment of afferent arteriolar autoregulatory capability. Intervention with antioxidant treatment following IR may improve outcomes in patients by preserving renovascular autoregulatory function and potentially preventing the progression to chronic kidney disease after acute kidney injury.

Acute Kidney Injury Results in Long-Term Diastolic Dysfunction That Is Prevented by Histone Deacetylase Inhibition

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This is the first long-term (1-year) study to evaluate both the kidney and systemic sequelae of acute kidney injury in mice.

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Serial kidney function was measured via transcutaneous glomerular filtration rate.

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AKI resulted in diastolic dysfunction, followed by hypertension. Ejection fraction was preserved. One year after AKI, cardiac ATP levels were reduced compared with sham controls.

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Mice treated with the histone deacetylase inhibitor, ITF2357, maintained normal diastolic function normal blood pressure, and normal cardiac ATP after AKI.

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Metabolomics data suggest that treatment with ITF2357 preserves pathways related to energy metabolism.

Growing epidemiological data demonstrate that acute kidney injury (AKI) is associated with long-term cardiovascular morbidity and mortality. Here, the authors present a 1-year study of cardiorenal outcomes following bilateral ischemia-reperfusion injury in male mice. These data suggest that AKI causes long-term dysfunction in the cardiac metabolome, which is associated with diastolic dysfunction and hypertension. Mice treated with the histone deacetylase inhibitor, ITF2357, had preservation of cardiac function and remained normotensive throughout the study. ITF2357 did not protect against the development of kidney fibrosis after AKI.

Protective Role of Nrf2 in Renal Disease

Chronic kidney disease (CKD) is one of the fastest-growing causes of death and is predicted to become by 2040 the fifth global cause of death. CKD is characterized by increased oxidative stress and chronic inflammation. However, therapies to slow or prevent CKD progression remain an unmet need. Nrf2 (nuclear factor erythroid 2-related factor 2) is a transcription factor that plays a key role in protection against oxidative stress and regulation of the inflammatory response. Consequently, the use of compounds targeting Nrf2 has generated growing interest for nephrologists. Pre-clinical and clinical studies have demonstrated that Nrf2-inducing strategies prevent CKD progression and protect from acute kidney injury (AKI). In this article, we review current knowledge on the protective mechanisms mediated by Nrf2 against kidney injury, novel therapeutic strategies to induce Nrf2 activation, and the status of ongoing clinical trials targeting Nrf2 in renal diseases.

Acute Kidney Injury: A Bona Fide Complication of Diabetes

The landscape of kidney disease in diabetes has shifted. The classical dogma of "diabetic nephropathy" progressing through stages of albuminuria, leading to decline in glomerular filtration rate and end-stage kidney disease (ESKD), has been replaced by a more nuanced understanding of the complex and heterogeneous nature of kidney disease in diabetes. Paralleling this evolution, standardized definitions have resulted in a growing appreciation that acute kidney injury (AKI) is increasing in its incidence rapidly and that people with diabetes are much more likely to develop AKI than people without diabetes. Here, I propose that AKI should be considered a complication of diabetes alongside other complications that similarly do not fit neatly into the historical microvascular/macrovascular paradigm. In this article, we take a look at the evidence indicating that diabetes is a major risk factor for AKI and we review the causes of this increased risk. We consider the long-term implications of AKI in diabetes and its potential contribution to the future development of chronic kidney disease, ESKD, and mortality. Finally, we look toward the future at strategies to better identify people at risk for AKI and to develop new approaches to improve AKI outcomes. Recognizing AKI as a bona fide complication of diabetes should open up new avenues for investigation that may ultimately improve the outlook for people living with diabetes and at risk for kidney disease.

Extracellular Vesicles Derived from Induced Pluripotent Stem Cells Promote Renoprotection in Acute Kidney Injury Model

Induced pluripotent stem cells (iPSC) have been the focus of several studies due to their wide range of application, including in cellular therapy. The use of iPSC in regenerative medicine is limited by their tumorigenic potential. Extracellular vesicles (EV) derived from stem cells have been shown to support renal recovery after injury. However, no investigation has explored the potential of iPSC-EV in the treatment of kidney diseases. To evaluate this potential, we submitted renal tubule cells to hypoxia-reoxygenation injury, and we analyzed cell death rate and changes in functional mitochondria mass. An in vivo model of ischemia-reperfusion injury was used to evaluate morphological and functional alterations. Gene array profile was applied to investigate the mechanism involved in iPSC-EV effects. In addition, EV derived from adipose mesenchymal cells (ASC-EV) were also used to compare the potential of iPSC-EV in support of tissue recovery. The results showed that iPSC-EV were capable of reducing cell death and inflammatory response with similar efficacy than ASC-EV. Moreover, iPSC-EV protected functional mitochondria and regulated several genes associated with oxidative stress. Taken together, these results show that iPSC can be an alternative source of EV in the treatment of different aspects of kidney disease.

Effects of single and dual RAAS blockade therapy on progressive kidney disease transition to CKD in rats

Ischemic reperfusion (I/R) is the primary cause of acute kidney injury (AKI) in hospitalized patients. Although AKI resolution occurs in few days, it predisposes kidneys to progressive renal injury. Previously, administration of rennin-angiotensin-aldosterone system (RAAS) blocker spironolactone in acute phase was reported to attenuate various manifestations of chronic kidney disease (CKD) in rats. The present study investigates the effects of RAAS blockade during progressive kidney disease (30 days onwards) on CKD outcomes in rodent model of I/R injury. CKD was induced by clamping both renal pedicles for 45 min followed by 90 days of reperfusion in rats. Single and dual RAAS blocker therapy was initiated at 30 days post-I/R injury and continued until the end of the study period. Evaluation of proteinuria and creatinine levels was done every 30 days in various study groups. Assessment of CKD was done by analyzing renal tissue oxidative stress, inflammatory biomarker levels, and histological changes after 90 days of I/R injury. After 90 days, I/R rat kidneys displayed hypertrophy, reduced body weight, increased oxidative stress, elevated inflammatory biomarker levels, and histological abnormalities such as glomerulosclerosis, mesangial expansion, and tubulointerstitial fibrosis. Treatment with losartan or spironolactone alone significantly reduced various CKD-associated features. Remarkably, combined treatment with dual RAAS blocker in low dose or high dose exhibited highest beneficial effects on various parameters in CKD model, with low-dose combination showing fewer side effects. Therefore, we propose that combined low-dose RAAS blockade therapy might serve as a better therapeutic approach for retarding progressive kidney disease transition to CKD.

Molecular Interactions Between Reactive Oxygen Species and Autophagy in Kidney Disease

Reactive oxygen species (ROS) are highly reactive signaling molecules that maintain redox homeostasis in mammalian cells. Dysregulation of redox homeostasis under pathological conditions results in excessive generation of ROS, culminating in oxidative stress and the associated oxidative damage of cellular components. ROS and oxidative stress play a vital role in the pathogenesis of acute kidney injury and chronic kidney disease, and it is well documented that increased oxidative stress in patients enhances the progression of renal diseases. Oxidative stress activates autophagy, which facilitates cellular adaptation and diminishes oxidative damage by degrading and recycling intracellular oxidized and damaged macromolecules and dysfunctional organelles. In this review, we report the current understanding of the molecular regulation of autophagy in response to oxidative stress in general and in the pathogenesis of kidney diseases. We summarize how the molecular interactions between ROS and autophagy involve ROS-mediated activation of autophagy and autophagy-mediated reduction of oxidative stress. In particular, we describe how ROS impact various signaling pathways of autophagy, including mTORC1-ULK1, AMPK-mTORC1-ULK1, and Keap1-Nrf2-p62, as well as selective autophagy including mitophagy and pexophagy. Precise elucidation of the molecular mechanisms of interactions between ROS and autophagy in the pathogenesis of renal diseases may identify novel targets for development of drugs for preventing renal injury.

Normothermic Machine Perfusion Protects Against Liver Ischemia-Reperfusion Injury During Reduced-Size Liver Transplantation in Pigs

Background

Normothermic machine perfusion (NMP) preservation is superior to cold preservation during reduced-size liver transplantation (RSLT) in pigs. However, the mechanism of this protective effect has not been explained. We aimed to compare the effects of NMP preservation with that of cold preservation (CS) in protecting against ischemia-reperfusion injury (IRI) during RSLT in pigs.

Material/Methods

Twenty-four healthy Bama miniature pigs were randomized into 2 groups: 1) the NMP group in which donor livers harvested without warm ischemia time and cardiac activity were connected to the NMP system to reduce liver size under normothermic conditions, and 2) the CS group in which donor livers harvested without warm ischemia time and cardiac activity were perfused using the University of Wisconsin (UW) solution and then preserved in the 0–4°C UW solution to reduce liver size under cold conditions. Livers were then transplanted without veno-venous bypass. Amounts of bile secretion for the NMP groups were recorded hourly. The serological indices were measured. Expressions of cytochrome C, caspase 3, and NF-κB p65 in liver tissue were observed.

Results

The levels of bile secretions were gradually diminished from 16.50±2.66 mL/h before splitting to 6.35±1.24 mL/h after splitting. With the exception of TNF-α on postoperative day 2, overall, levels of TNF-α, IL-1, IL-6, and MDA were significantly lower in the NMP group versus CS group for all 5 days postoperatively. Finally, cytochrome C, caspase 3, and NF-κB p65 expressions were all significantly suppressed in the NMP group as compared with the CS group.

Conclusions

MP preservation is superior to cold preservation in protecting against liver IRI during RSLT in pigs.

Fiend and friend in the renin angiotensin system: An insight on acute kidney injury

Besides assisting the maintenance of blood pressure and sodium homeostasis, the renin-angiotensin system (RAS) plays a pivotal role in pathogenesis of acute kidney injury (AKI). The RAS is equipped with two arms i) the pressor arm composed of Angiotensin II (Ang II)/Angiotensin converting enzyme (ACE)/Angiotensin II type 1 receptor (AT1R) also called conventional RAS, and ii) the depressor arm consisting of Angiotensin (1-7) (Ang 1-7)/Angiotensin converting enzyme 2 (ACE2)/MasR known as non-conventional RAS. Activation of conventional RAS triggers oxidative stress, inflammatory, hypertrophic, apoptotic, and pro-fibrotic signaling cascades which promote AKI. The preclinical and clinical studies have reported beneficial as well as deleterious effects of RAS blockage either by angiotensin receptor blocker or ACE inhibitor in AKI. On the contrary, the depressor arm opposes the conventional RAS, has beneficial effects on the kidney but has been less explored in pathogenesis of AKI. This review focuses on significance of RAS in pathogenesis of AKI and provides better understanding of novel and possible therapeutic approaches to combat AKI.

Long-term risk of adverse outcomes after acute kidney injury: a systematic review and meta-analysis of cohort studies using consensus definitions of exposure

Reliable estimates of the long-term outcomes of acute kidney injury (AKI) are needed to inform clinical practice and guide allocation of health care resources. This systematic review and meta-analysis aimed to quantify the association between AKI and chronic kidney disease (CKD), end-stage kidney disease (ESKD), and death. Systematic searches were performed through EMBASE, MEDLINE, and grey literature sources to identify cohort studies in hospitalized adults that used standardized definitions for AKI, included a non-exposed comparator, and followed patients for at least 1 year. Risk of bias was assessed by the Newcastle-Ottawa Scale. Random effects meta-analyses were performed to pool risk estimates; subgroup, sensitivity, and meta-regression analyses were used to investigate heterogeneity. Of 4973 citations, 82 studies (comprising 2,017,437 participants) were eligible for inclusion. Common sources of bias included incomplete reporting of outcome data, missing biochemical values, and inadequate adjustment for confounders. Individuals with AKI were at increased risk of new or progressive CKD (HR 2.67, 95% CI 1.99-3.58; 17.76 versus 7.59 cases per 100 person-years), ESKD (HR 4.81, 95% CI 3.04-7.62; 0.47 versus 0.08 cases per 100 person-years), and death (HR 1.80, 95% CI 1.61-2.02; 13.19 versus 7.26 deaths per 100 person-years). A gradient of risk across increasing AKI stages was demonstrated for all outcomes. For mortality, the magnitude of risk was also modified by clinical setting, baseline kidney function, diabetes, and coronary heart disease. These findings establish the poor long-term outcomes of AKI while highlighting the importance of injury severity and clinical setting in the estimation of risk.

P53 in kidney injury and repair: Mechanism and therapeutic potentials

Acute kidney injury (AKI) is a major kidney disease with poor clinical outcome. Besides its acute consequence of high mortality, AKI may also contribute significantly to the occurrence and progression of chronic kidney diseases (CKD). Accumulating evidence has demonstrated that maladaptive and incomplete kidney repair after AKI leads to the development of renal fibrosis and, ultimately, CKD. p53, a well-known tumor suppressor, plays a critical role in AKI and subsequent kidney repair through the regulation of various cell biologic processes, including apoptosis, cell cycle arrest, and autophagy. Despite the notable progress in deciphering the involvement of p53 in kidney injury and repair, the underlying mechanisms of p53 in these pathological processes remain largely unknown. Further investigation in this area is essential for the application of p53 as therapeutic target to prevent and treat AKI or impede its progression to CKD. In this review, we summarize the recent advances in understanding p53 regulation of AKI and kidney repair, pinpoint the potential of p53 as a therapeutic target, and present future research interests and directions.

Interleukin 1 receptor (IL-1R1) activation exacerbates toxin-induced acute kidney injury

Acute kidney injury (AKI) is a leading cause of morbidity and mortality. Drug-induced/toxic AKI can be caused by a number of therapeutic agents. Cisplatin is an effective chemotherapeutic agent whose administration is limited by significant nephrotoxicity. Therapies to prevent cisplatin-induced AKI are lacking. Although tumor necrosis factor-α (TNF) plays a key role in the pathogenesis of cisplatin nephrotoxicity, the innate immune signaling pathways that trigger TNF generation in this context require elucidation. In this regard, sterile injury triggers the release and activation of both isoforms of interleukin(IL)-1, IL-1α and IL-1β. In turn, stimulation of the interleukin-1 receptor (IL-1R1) by these ligands engages a proinflammatory signaling cascade that induces TNF induction. We therefore hypothesized that IL-1R1 activation exacerbates cisplatin-induced AKI by inducing TNF production, thereby augmenting inflammatory signals between kidney parenchymal cells and infiltrating myeloid cells. IL-1R1+/+ (WT) and IL-1R1-/- (KO) mice were subjected to cisplatin-induced AKI. Compared with WT mice, IL-1R1 KO mice had attenuated AKI as measured by serum creatinine and BUN, renal NGAL mRNA levels, and blinded histological analysis of kidney pathology. In the cisplatin-injured kidney, IL-1R1 KO mice had diminished levels of whole kidney TNF, and fewer Ly6G-expressing neutrophils. In addition, an unbiased machine learning analysis of intrarenal immune cells revealed a diminished number of CD11bint/CD11cint myeloid cells in IL-1R1 KO injured kidneys compared with IL-1R1 WT kidneys. Following cisplatin, IL-1R1 KO kidneys, compared with WTs, had fewer TNF-producing: macrophages, CD11bint/CD11cint cells, and neutrophils, consistent with an effect of IL-1R1 to polarize intrarenal myeloid cells toward a proinflammatory phenotype. Interruption of IL-1-dependent signaling pathways warrants further evaluation to decrease nephrotoxicity during cisplatin therapy.

Absence of renal hypoxia in the subacute phase of severe renal ischemia-reperfusion injury

Tissue hypoxia has been proposed as an important event in renal ischemia-reperfusion injury (IRI), particularly during the period of ischemia and in the immediate hours following reperfusion. However, little is known about renal oxygenation during the subacute phase of IRI. We employed four different methods to assess the temporal and spatial changes in tissue oxygenation during the subacute phase (24 h and 5 days after reperfusion) of a severe form of renal IRI in rats. We hypothesized that the kidney is hypoxic 24 h and 5 days after an hour of bilateral renal ischemia, driven by a disturbed balance between renal oxygen delivery (Do₂) and oxygen consumption (V̇o₂). Renal Do₂ was not significantly reduced in the subacute phase of IRI. In contrast, renal V̇o₂ was 55% less 24 h after reperfusion and 49% less 5 days after reperfusion than after sham ischemia. Inner medullary tissue Po₂, measured by radiotelemetry, was 25 ± 12% (mean ± SE) greater 24 h after ischemia than after sham ischemia. By 5 days after reperfusion, tissue Po₂ was similar to that in rats subjected to sham ischemia. Tissue Po₂ measured by Clark electrode was consistently greater 24 h, but not 5 days, after ischemia than after sham ischemia. Cellular hypoxia, assessed by pimonidazole adduct immunohistochemistry, was largely absent at both time points, and tissue levels of hypoxia-inducible factors were downregulated following renal ischemia. Thus, in this model of severe IRI, tissue hypoxia does not appear to be an obligatory event during the subacute phase, likely because of the markedly reduced oxygen consumption.

Schisantherin A protects renal tubular epithelial cells from hypoxia/reoxygenation injury through the activation of PI3K/Akt signaling pathway

Schisantherin A (SchA), a dibenzocyclooctadiene lignan isolated from the fruit of Schisandra sphenanthera, was reported to possess anti-inflammatory and antioxidant activities. However, its protective effect against renal ischemia-reperfusion (I/R) injury in human renal tubular epithelial cells subjected to hypoxia/reoxygenation (H/R) has never been studied. Thus, herein, we investigated the effect of SchA on renal I/R injury in vitro. Our results demonstrated that SchA pretreatment significantly improved HK-2 cell viability exposed to H/R. Pretreatment with SchA markedly inhibited the levels of reactive oxygen species and malondialdehyde, as well as suppressed the production of tumor necrosis factor-α (TNF-α), interleukin-1β, and interleukin-6 in H/R-stimulated HK-2 cells. In addition, SchA also suppressed H/R-induced HK-2 cell apoptosis. Furthermore, this protective effect of SchA was mediated through the PI3K/Akt signaling pathway in HK-2 cells. These findings showed that SchA may exert a protective effect on renal tubular epithelial cells against H/R injury through the activation of PI3K/Akt signaling pathway.

Acute Kidney Injury and Progression of Diabetic Kidney Disease

Diabetic kidney disease, commonly termed diabetic nephropathy (DN), is the most common cause of end-stage kidney disease (ESKD) worldwide. The characteristic histopathology of DN includes glomerular basement membrane thickening, mesangial expansion, nodular glomerular sclerosis, and tubulointerstitial fibrosis. Diabetes is associated with a number of metabolic derangements, such as reactive oxygen species overproduction, hypoxic state, mitochondrial dysfunction, and inflammation. In the past few decades, our knowledge of DN has advanced considerably although much needs to be learned. The traditional paradigm of glomerulus-centered pathophysiology has expanded to the tubule-interstitium, the immune response and inflammation. Biomarkers of proximal tubule injury have been shown to correlate with DN progression, independent of traditional glomerular injury biomarkers such as albuminuria. In this review, we summarize mechanisms of increased susceptibility to acute kidney injury in diabetes mellitus and the roles played by many kidney cell types to facilitate maladaptive responses leading to chronic and end-stage kidney disease.

Glutathione Peroxidase 3 Delivered by hiPSC-MSCs Ameliorated Hepatic IR Injury via Inhibition of Hepatic Senescence

Background and Aims: Down-regulation of GPx3 accelerated hepatic senescence, which further caused overwhelming inflammation and severe liver graft injury. MSCs derived from human induced pluripotent stem cells (hiPSC-MSCs) have been developed as more efficient delivery vehicle with the property of injury tropism. Here, we aimed to explore the suppressive role of GPx3 in hepatic IR injury using novel delivery system of hiPSC-MSCs.

Methods: The mice IR injury model with partial hepatectomy was established. The engineered hiPSC-MSCs delivering GPx3 was constructed. All the mice were segregated into three groups. hiPSC-MSC-GPx3, hiPSC-MSC-pCDH (vector control) or PBS were injected via portal vein after reperfusion. Liver injury was evaluated by histological and serological test. Hepatic apoptosis was detected by Tunel staining and remnant liver regeneration was assessed by Ki67 staining. The role of hepatic senescence in liver graft injury was evaluated in rat orthotopic liver transplantation model. The suppressive effect of GPx3 on hepatic senescence was examined in mice IR injury model and confirmed in vitro. Hepatic senescence was detected by SA-β-Gal and P^16/ink4a staining.

Results: GPx3 can be successfully delivered by hiPSC-MSCs into liver tissues. Histological examination showed that hiPSC-MSC-GPx3 treatment significantly ameliorated hepatic IR injury post-operation. Significantly lower LDH (891.43±98.45 mU/mL, P<0.05) and AST (305.77±36.22 IU/L, P<0.01) were observed in hiPSC-MSC-GPx3 group compared with control groups. Less apoptotic hepatocytes were observed and the remnant liver regeneration was more active in hiPSC-MSC-GPx3 group. In rat orthotopic liver transplantation model, more senescent hepatocytes were observed in small-for-size liver graft, in which GPx3 expression was significantly compromised. In mice IR injury model, hiPSC-MSC-GPx3 significantly suppressed hepatic senescence. In addition, rGPx3 inhibited cellular senescence of liver cells in a dose dependent manner. Four candidate genes (CD44, Nox4, IFNG, SERPERINB2) were identified to be responsible for suppressive effect of GPx3 on hepatic senescence.

Conclusion: Engineered hiPSC-MSCs delivering GPx3 ameliorated hepatic IR injury via inhibition of hepatic senescence.

Acute Kidney Injury and Risk of Incident Heart Failure Among US Veterans

BACKGROUND

Acute kidney injury (AKI) is common and associated with poor outcomes. Heart failure is a leading cause of cardiovascular disease among patients with chronic kidney disease. The relationship between AKI and heart failure remains unknown and may identify a novel mechanistic link between kidney and cardiovascular disease.

STUDY DESIGN

Observational study.

SETTING & PARTICIPANTS

We studied a national cohort of 300,868 hospitalized US veterans (2004-2011) without a history of heart failure.

PREDICTOR

AKI was the predictor and was defined as a 0.3-mg/dL or 50% increase in serum creatinine concentration from baseline to the peak hospital value. Patients with and without AKI were matched (1:1) on 28 in- and outpatient covariates using optimal Mahalanobis distance matching.

OUTCOMES

Incident heart failure was defined as 1 or more hospitalization or 2 or more outpatient visits with a diagnosis of heart failure within 2 years through 2013.

RESULTS

There were 150,434 matched pairs in the study. Patients with and without AKI during the index hospitalization were well matched, with a median preadmission estimated glomerular filtration rate of 69mL/min/1.73m². The overall incidence rate of heart failure was 27.8 (95% CI, 19.3-39.9) per 1,000 person-years. The incidence rate was higher in those with compared with those without AKI: 30.8 (95% CI, 21.8-43.5) and 24.9 (95% CI, 16.9-36.5) per 1,000 person-years, respectively. In multivariable models, AKI was associated with 23% increased risk for incident heart failure (HR, 1.23; 95% CI, 1.19-1.27).

LIMITATIONS

Study population was primarily men, reflecting patients seen at Veterans Affairs hospitals.

CONCLUSIONS

AKI is an independent risk factor for incident heart failure. Future studies to identify underlying mechanisms and modifiable risk factors are needed.

Hyperpolarized 13 C magnetic resonance evaluation of renal ischemia reperfusion injury in a murine model

Acute kidney injury (AKI) is a major risk factor for the development of chronic kidney disease (CKD). Persistent oxidative stress and mitochondrial dysfunction are implicated across diverse forms of AKI and in the transition to CKD. In this study, we applied hyperpolarized (HP) ¹³ C dehydroascorbate (DHA) and ¹³ C pyruvate magnetic resonance spectroscopy (MRS) to investigate the renal redox capacity and mitochondrial pyruvate dehydrogenase (PDH) activity, respectively, in a murine model of AKI at baseline and 7 days after unilateral ischemia reperfusion injury (IRI). Compared with the contralateral sham-operated kidneys, the kidneys subjected to IRI showed a significant decrease in the HP ¹³ C vitamin C/(vitamin C + DHA) ratio, consistent with a decrease in redox capacity. The kidneys subjected to IRI also showed a significant decrease in the HP ¹³ C bicarbonate/pyruvate ratio, consistent with impaired PDH activity. The IRI kidneys showed a significantly higher HP ¹³ C lactate/pyruvate ratio at day 7 compared with baseline, although the ¹³ C lactate/pyruvate ratio was not significantly different between the IRI and contralateral sham-operated kidneys at day 7. Arterial spin labeling magnetic resonance imaging (MRI) demonstrated significantly reduced perfusion in the IRI kidneys. Renal tissue analysis showed corresponding increased reactive oxygen species (ROS) and reduced PDH activity in the IRI kidneys. Our results show the feasibility of HP ¹³ C MRS for the non-invasive assessment of oxidative stress and mitochondrial PDH activity following renal IRI.

Atorvastatin alleviates iodinated contrast media-induced cytotoxicity in human proximal renal tubular epithelial cells

Contrast media (CM)-induced nephropathy (CIN) is a serious complication of intravascularly applied radiocontrast media. At present, no drugs have been approved for the prevention of CIN. The present study aimed to explore the effects and potential mechanisms of atorvastatin on iodinated CM-induced cytotoxicity in the human proximal renal tubular epithelial cells. The cytotoxic effect of iohexol (50, 100 and 200 mg I/ml) and the protective effect of atorvastatin pretreatment (1, 20 and 40 µM) were assessed. The cytotoxicity of iohexol was evaluated via the MTT cell viability and lactate dehydrogenase assays. The amount of apoptotic cells was determined by flow cytometry. Morphological changes in HK-2 cells were observed via transmission electron microscopy. The mRNA expression of NOX4 and p22phox was measured through reverse transcription-quantitative polymerase chain reaction analysis. The cytotoxicity was induced by iohexol in HK-2 cells. Atorvastatin was identified to significantly alleviate the suppression of cell viability induced by iohexol. Notably, 40 µM atorvastatin also significantly reduced the mRNA expression of intracellular NOX4 and p22phox, and the percentage of apoptotic cells. Furthermore, morphological changes characteristic of injured cells were alleviated by atorvastatin pretreatment. These results suggest that atorvastatin exhibits a protective effect on HK-2 cells against iohexol-induced cytotoxicity through the downregulation of NOX4 and p22phox. Thus, atorvastatin is a potential therapeutic agent for the prevention of CIN and required further study.

Targeting the KEAP1-NRF2 System to Prevent Kidney Disease Progression

BACKGROUND

Nuclear factor erythroid 2-related factor 2 (NRF2) is a critical transcription factor for the antioxidative stress response and it activates a variety of cytoprotective genes related to redox and detoxification. NRF2 activity is regulated by the oxidative-stress sensor molecule Kelch-like ECH-associated protein 1 (KEAP1) that induces proteasomal degradation of NRF2 through ubiquitinating NRF2 under unstressed conditions. Because oxidative stress is a major pathogenic and aggravating factor for kidney diseases, the KEAP1-NRF2 system has been proposed to be a therapeutic target for renal protection.

SUMMARY

Oxidative-stress molecules, such as reactive oxygen species, accumulate in the kidneys of animal models for acute kidney injury (AKI), in which NRF2 is transiently and slightly activated. Genetic or pharmacological enhancement of NRF2 activity in the renal tubules significantly ameliorates damage related to AKI and prevents AKI progression to chronic kidney disease (CKD) by reducing oxidative stress. These beneficial effects of NRF2 activation highlight the KEAP1-NRF2 system as an important target for kidney disease treatment. However, a phase-3 clinical trial of a KEAP1 inhibitor for patients with stage 4 CKD and type-2 diabetes mellitus (T2DM) was terminated due to the occurrence of cardiovascular events. Because recent basic studies have accumulated positive effects of KEAP1 inhibitors in moderate stages of CKD, phase-2 trials have been restarted. The data from the ongoing projects demonstrate that a KEAP1 inhibitor improves the glomerular filtration rate in patients with stage 3 CKD and T2DM without safety concerns. Key Message: The KEAP1-NRF2 system is one of the most promising therapeutic targets for kidney disease, and KEAP1 inhibitors could be part of critical therapies for kidney disease.

Stop adding insult to injury-identifying and managing risk factors for the progression of acute kidney injury in children

Acute kidney injury (AKI) is common in children admitted to hospital. Whilst some recover normal kidney function following an acute kidney insult, a significant proportion experience long-term sequelae. The aim of this review is to summarize current understanding of the processes that can lead to sequelae following AKI. Kidney injury, repair, recovery and progression are described. Risk factors for progression are outlined, and potential strategies to stratify the risk of progression in children with AKI are discussed. Clinical management priorities to minimize sequelae are suggested. Looking ahead, novel therapeutic targets are discussed with the potential to accelerate adaptive repair and ameliorate the progression and sequelae of AKI in the future.

IL-17 mediates neutrophil infiltration and renal fibrosis following recovery from ischemia reperfusion: compensatory role of natural killer cells in athymic rats

T cells have been implicated in the pathogenesis of acute kidney injury (AKI) and its progression to chronic kidney disease (CKD). Previous studies suggest that Th17 cells participate during the AKI-to-CKD transition, and inhibition of T cell activity by mycophenolate mofetil (MMF) or losartan attenuates the development of fibrosis following AKI. We hypothesized that T cell-deficient rats may have reduced levels of IL-17 cytokine leading to decreased fibrosis following AKI. Renal ischemis-reperfusion (I/R) was performed on T cell-deficient athymic rats (Foxn1^rnu-/rnu-) and control euthymic rats (Foxn1^rnu-/+), and CKD progression was hastened by unilateral nephrectomy at day 33 and subsequent exposure to 4.0% sodium diet. Renal fibrosis developed in euthymic rats and was reduced by MMF treatment. Athymic rats exhibited a similar degree of fibrosis, but this was unaffected by MMF treatment. FACS analysis demonstrated that the number of IL-17⁺ cells was similar between postischemic athymic vs. euthymic rats. The source of IL-17 production in euthymic rats was predominately from conventional T cells (CD3⁺/CD161^-). In the absence of conventional T cells in athymic rats, a compensatory pathway involving natural killer cells (CD3^-/CD161⁺) was the primary source of IL-17. Blockade of IL-17 activity using IL-17Rc receptor significantly decreased fibrosis and neutrophil recruitment in both euthymic and athymic rats compared with vehicle-treated controls. Taken together, these data suggest that IL-17 secretion participates in the pathogenesis of AKI-induced fibrosis possibly via the recruitment of neutrophils and that the source of IL-17 may be from either conventional T cells or NK cells.

High serum creatinine nonlinearity: a renal vital sign?

Patients with chronic kidney disease (CKD) may have nonlinear serum creatinine concentration (SC) trajectories, especially as CKD progresses. Variability in SC is associated with renal failure and death. However, present methods for measuring SC variability are unsatisfactory because they blend information about SC slope and variance. We propose an improved method for defining and calculating a patient's SC slope and variance so that they are mathematically distinct, and we test these methods in a large sample of US veterans, examining the correlation of SC slope and SC nonlinearity (SCNL) and the association of SCNL with time to stage 4 CKD (CKD4) and death. We found a strong correlation between SCNL and rate of CKD progression, time to CKD4, and time to death, even in patients with normal renal function. We therefore argue that SCNL may be a measure of renal autoregulatory dysfunction that provides an early warning sign for CKD progression.

Progression after AKI: Understanding Maladaptive Repair Processes to Predict and Identify Therapeutic Treatments

Recent clinical studies indicate a strong link between AKI and progression of CKD. The increasing prevalence of AKI must compel the nephrology community to consider the long-term ramifications of this syndrome. Considerable gaps in knowledge exist regarding the connection between AKI and CKD. The 13th Acute Dialysis Quality Initiative meeting entitled "Therapeutic Targets of Human Acute Kidney Injury: Harmonizing Human and Experimental Animal Acute Kidney Injury" convened in April of 2014 and assigned a working group to focus on issues related to progression after AKI. This article provides a summary of the key conclusions and recommendations of the group, including an emphasis on terminology related to injury and repair processes for both clinical and preclinical studies, elucidation of pathophysiologic alterations of AKI, identification of potential treatment strategies, identification of patients predisposed to progression, and potential management strategies.

Th-17 cell activation in response to high salt following acute kidney injury is associated with progressive fibrosis and attenuated by AT-1R antagonism

Exposure of rats to elevated dietary salt following recovery from acute kidney injury (AKI) accelerates the transition to chronic kidney disease (CKD), and is dependent on lymphocyte activity. Here we tested whether high salt diet triggers lymphocyte activation in postischemic kidneys to worsen renal inflammation and fibrosis. Male Sprague-Dawley rats on a 0.4% salt diet were subjected to left unilateral ischemia-reperfusion and allowed to recover for 5 weeks. This resulted in a mild elevation of CD4(+) T cells relative to sham animals. Contralateral unilateral nephrectomy and elevated dietary salt (4%) for 4 extra weeks hastened CKD and interstitial fibrosis. Activated T cells were increased in the kidney threefold after 4 weeks of elevated dietary salt exposure relative to post-AKI rats before salt feeding. The T cell subset was largely positive for IL-17, indicative of Th-17 cells. Because angiotensin II activity may influence lymphocyte activation, injured rats were given the AT1R antagonist, losartan, along with high salt diet. This significantly reduced the number of renal Th-17 cells to levels of sham rats, and significantly reduced the salt-induced increase in fibrosis to about half. In vitro studies in AKI-primed CD4(+) T cells indicated that angiotensin II and extracellular sodium enhanced, and losartan inhibited, IL-17 expression. Thus, dietary salt modulates immune cell activity in postischemic recovering kidneys because of the activity of local RAS, suggesting the participation of these cells in CKD progression post-AKI.

Unilateral Renal Ischemia as a Model of Acute Kidney Injury and Renal Fibrosis in Cats

The objectives of this study were to define the acute and chronic effects of 1-hour unilateral in vivo renal ischemia on renal function and histology in cats. Twenty-one adult purpose-bred research cats were anesthetized, and 1 kidney underwent renal artery and vein occlusion for 1 hour. Serum creatinine and urea concentrations, urine protein:creatinine ratio, urine-specific gravity, glomerular filtration rate, hematocrit, platelet concentration and function, and white blood cell count were measured at baseline and variable time points after ischemia. Renal histopathology was evaluated on days 3, 6, 12, 21, 42, and 70 postischemia; changes in smooth muscle actin and interstitial collagen were examined. Following ischemia, whole animal glomerular filtration rate was significantly reduced (57% of baseline on day 6; P < .05). At the early time points, the ischemic kidneys exhibited severe acute epithelial necrosis accompanied by evidence of regeneration of tubules predominantly within the corticomedullary junction. At later periods, postischemic kidneys had evidence of tubular atrophy and interstitial inflammation with significantly more smooth muscle actin and interstitial collagen staining and interstitial fibrosis when compared with the contralateral control kidneys. This study characterizes the course of ischemic acute kidney injury in cats and demonstrates that ischemic acute kidney injury triggers chronic fibrosis, interstitial inflammation, and tubular atrophy in feline kidneys. These late changes are typical of those observed in cats with naturally occurring chronic kidney disease.

Failed Tubule Recovery, AKI-CKD Transition, and Kidney Disease Progression

The transition of AKI to CKD has major clinical significance. As reviewed here, recent studies show that a subpopulation of dedifferentiated, proliferating tubules recovering from AKI undergo pathologic growth arrest, fail to redifferentiate, and become atrophic. These abnormal tubules exhibit persistent, unregulated, and progressively increasing profibrotic signaling along multiple pathways. Paracrine products derived therefrom perturb normal interactions between peritubular capillary endothelium and pericyte-like fibroblasts, leading to myofibroblast transformation, proliferation, and fibrosis as well as capillary disintegration and rarefaction. Although signals from injured endothelium and inflammatory/immune cells also contribute, tubule injury alone is sufficient to produce the interstitial pathology required for fibrosis. Localized hypoxia produced by microvascular pathology may also prevent tubule recovery. However, fibrosis is not intrinsically progressive, and microvascular pathology develops strictly around damaged tubules; thus, additional deterioration of kidney structure after the transition of AKI to CKD requires new acute injury or other mechanisms of progression. Indeed, experiments using an acute-on-chronic injury model suggest that additional loss of parenchyma caused by failed repair of AKI in kidneys with prior renal mass reduction triggers hemodynamically mediated processes that damage glomeruli to cause progression. Continued investigation of these pathologic mechanisms should reveal options for preventing renal disease progression after AKI.

Precision-cut kidney slices (PCKS) to study development of renal fibrosis and efficacy of drug targeting ex vivo

Renal fibrosis is a serious clinical problem resulting in the greatest need for renal replacement therapy. No adequate preventive or curative therapy is available that could be clinically used to target renal fibrosis specifically. The search for new efficacious treatment strategies is therefore warranted. Although in vitro models using homogeneous cell populations have contributed to the understanding of the pathogenetic mechanisms involved in renal fibrosis, these models poorly mimic the complex in vivo milieu. Therefore, we here evaluated a precision-cut kidney slice (PCKS) model as a new, multicellular ex vivo model to study the development of fibrosis and its prevention using anti-fibrotic compounds. Precision-cut slices (200-300 μm thickness) were prepared from healthy C57BL/6 mouse kidneys using a Krumdieck tissue slicer. To induce changes mimicking the fibrotic process, slices were incubated with TGFβ1 (5 ng/ml) for 48 h in the presence or absence of the anti-fibrotic cytokine IFNγ (1 µg/ml) or an IFNγ conjugate targeted to PDGFRβ (PPB-PEG-IFNγ). Following culture, tissue viability (ATP-content) and expression of α-SMA, fibronectin, collagen I and collagen III were determined using real-time PCR and immunohistochemistry. Slices remained viable up to 72 h of incubation, and no significant effects of TGFβ1 and IFNγ on viability were observed. TGFβ1 markedly increased α-SMA, fibronectin and collagen I mRNA and protein expression levels. IFNγ and PPB-PEG-IFNγ significantly reduced TGFβ1-induced fibronectin, collagen I and collagen III mRNA expression, which was confirmed by immunohistochemistry. The PKCS model is a novel tool to test the pathophysiology of fibrosis and to screen the efficacy of anti-fibrotic drugs ex vivo in a multicellular and pro-fibrotic milieu. A major advantage of the slice model is that it can be used not only for animal but also for (fibrotic) human kidney tissue.

Drug Discovery Collection: TGFβ induces renal fibrosis in ex vivo cultured precision-cut kidney slices, which can be attenuated by IFNγ.

Mild ischemic injury leads to long-term alterations in the kidney: amelioration by spironolactone administration

Administration of the mineralocorticoid receptor antagonist spironolactone prevents the development of chronic kidney disease (CKD) after a severe ischemic injury. However, whether brief periods of ischemia lead to CKD and whether spironolactone administration after ischemia may be a useful therapeutic strategy to prevent the gradual deterioration of structure and function remains unexplored. Nineteen male Wistar rats were divided into four groups: rats that underwent renal bilateral ischemia for 10, 20, or 45 min were compared with sham operated rats. Additionally, thirteen male Wistar rats that underwent renal bilateral ischemia for 20 min were divided into an untreated ischemic group (I) and two groups receiving spironolactone, 20 mg/kg by gavage, at either 0 (Sp0) or 1.5-h after ischemia (Sp1.5). The rats were followed up and studied after 9 months. Mild (20 min) and severe (45 min) ischemia induced a progressive increase in proteinuria at varying magnitudes, whereas minor ischemia (10 min) did not modify proteinuria. CKD induced by moderate ischemia was characterized by renal hypertrophy and tubulointerstitial fibrosis. These effects were associated with activation of the transforming growth factor β (TGFβ) signaling pathway and up-regulation of endothelin receptor A (ETA) and alpha smooth muscle actin (αSMA). Spironolactone treatment immediately or 1.5-h after the ischemic insult prevented the onset of these disorders. Our results show that moderate ischemic insult leads to long-term structural and molecular changes that may compromise renal function in later stages. Additionally, we demonstrate that spironolactone administration after mild ischemia prevents this detrimental effect.

Nox and renal disease

Since the first demonstration of Nox enzyme expression in the kidney in the early 1990s and the subsequent identification of Nox4, or RENOX, a decade later, it has become apparent that the Nox family of reactive oxygen species (ROS) generating enzymes plays an integral role in the normal physiological function of the kidney. As our knowledge of Nox expression patterns and functions in various structures and specialized cell types within the kidney grows, so does the realization that Nox-derived oxidative stress contributes significantly to a wide variety of renal pathologies through their ability to modify lipids and proteins, damage DNA and activate transcriptional programmes. Diverse studies demonstrate key roles for Nox-derived ROS in kidney fibrosis, particularly in settings of chronic renal disease such as diabetic nephropathy. As the most abundant Nox family member in the kidney, much emphasis has been placed on the role of Nox4 in this setting. However, an ever growing body of work continues to uncover key roles for other Nox family members, not only in diabetic kidney disease, but in a diverse array of renal pathological conditions. The objective of the present review is to highlight the latest novel developments in renal Nox biology with an emphasis not only on diabetic nephropathy but many of the other renal disease contexts where oxidative stress is implicated.

L-FABP: A novel biomarker of kidney disease

Human liver-type fatty acid-binding protein (hL-FABP), which is found in both the normal and the diseased human kidney, has been observed to bind free fatty acids. Recently, the predictive and prognostic value of L-FABP in kidney diseases has attracted considerable attention. Numerous studies have demonstrated that L-FABP is a promising biomarker of several kidney diseases, and it has also been shown to attenuate renal injury. We performed a literature review regarding the ability of L-FABP to identify patients at risk of developing kidney diseases, including acute kidney injury (AKI) and chronic kidney disease (CKD) and to protect the kidneys in the course of kidney disease.

RGS4 inhibits angiotensin II signaling and macrophage localization during renal reperfusion injury independent of vasospasm

Vascular inflammation is a major contributor to the severity of acute kidney injury. In the context of vasospasm-independent reperfusion injury we studied the potential anti-inflammatory role of the Gα-related RGS protein, RGS4. Transgenic RGS4 mice were resistant to 25 minute injury, although post-ischemic renal arteriolar diameter was equal to the wild type early after injury. A 10 minute unilateral injury was performed to study reperfusion without vasospasm. Eighteen hours after injury blood flow was decreased in the inner cortex of wild type mice with preservation of tubular architecture. Angiotensin II levels in the kidneys of wild type and transgenic mice were elevated in a sub-vasoconstrictive range 12 and 18 hours after injury. Angiotensin II stimulated pre-glomerular vascular smooth muscle cells (VSMC) to secrete the macrophage chemoattractant, RANTES; a process decreased by angiotensin II R2 (AT2) inhibition. However, RANTES increased when RGS4 expression was suppressed implicating Gα protein activation in an AT2-RGS4-dependent pathway. RGS4 function, specific to VSMC, was tested in a conditional VSMC-specific RGS4 knockout showing high macrophage density by T2 MRI compared to transgenic and non-transgenic mice after the 10 minute injury. Arteriolar diameter of this knockout was unchanged at successive time points after injury. Thus, RGS4 expression, specific to renal VSMC, inhibits angiotensin II-mediated cytokine signaling and macrophage recruitment during reperfusion, distinct from vasomotor regulation.

Comparative study on the protective role of vitamin C and L-arginine in experimental renal ischemia reperfusion in adult rats

Ischemia reperfusion (I/R) injury is a main cause of transplanted kidney dysfunction and rejection. Reactive oxygen species (ROS) play a causal role in cellular damage induced by I/R. Antioxidant vitamins and Nitric oxide (NO) were postulated to play renoprotective effects against I/R. This study compares the protective effects of vitamin C with that of the nitric oxide donor, L-arginine, on renal I/R injury in adult rats. The study was performed on 50 adult Wistar rats of both sexes, divided into 5 groups: I: Control group, receive daily intraperitoneal (i.p.) saline for 3 days. II: Renal I/R group, received i.p saline for 3 days and subjected to renal I/R. III: L-arginine Pretreated, 400 mg/kg/day i.p. for 3 days prior to I/R. IV: Vitamin C Pretreated, 500 mg/kg/day i.p. 24 hours prior to I/R. V: combined L-arginine and Vitamin C Pretreated, exposed to Renal I/R group. At the end of the experiment, plasma urea and creatinine were determined. Kidney tissue malondialdehyde (MDA), NO, catalase and superoxide dismutase (SOD) activity were measured and kidneys were examined histologically.

RESULTS

I/R group showed significant increase in plasma urea, creatinine, and renal MDA, and a significant decrease in renal catalase with marked necrotic epithelial cells and infiltration by inflammatory cells in kidney section compared to the control group. All the treated groups showed significant decrease in urea, creatinine, and MDA, and a significant increase in catalase with less histopathological changes in kidney sections compared to I/R group. However, significant improvements in urea, MDA, and catalase were found in vitamin C pretreated and combined treated groups than L-arginine pretreated group.

CONCLUSION

Oxidative stress is the primary element involved in renal I/R injury. So, antioxidants play an important renoprotective effects than NO donors.

Angiotensin II removes kidney resistance conferred by ischemic preconditioning

Ischemic preconditioning (IPC) by ischemia/reperfusion (I/R) renders resistance to the kidney. Strong IPC triggers kidney fibrosis, which is involved in angiotensin II (AngII) and its type 1 receptor (AT1R) signaling. Here, we investigated the role of AngII/AT1R signal pathway in the resistance of IPC kidneys to subsequent I/R injury. IPC of kidneys was generated by 30 minutes of bilateral renal ischemia and 8 days of reperfusion. Sham-operation was performed to generate control (non-IPC) mice. To examine the roles of AngII and AT1R in IPC kidneys to subsequent I/R, IPC kidneys were subjected to either 30 minutes of bilateral kidney ischemia or sham-operation following treatment with AngII, losartan (AT1R blocker), or AngII plus losartan. IPC kidneys showed fibrotic changes, decreased AngII, and increased AT1R expression. I/R dramatically increased plasma creatinine concentrations in non-IPC mice, but not in IPC mice. AngII treatment in IPC mice resulted in enhanced morphological damage, oxidative stress, and inflammatory responses, with functional impairment, whereas losartan treatment reversed these effects. However, AngII treatment in non-IPC mice did not change I/R-induced injury. AngII abolished the resistance of IPC kidneys to subsequent I/R via the enhancement of oxidative stress and inflammatory responses, suggesting that the AngII/AT1R signaling pathway is associated with outcome in injury-experienced kidney.

Recruitment and subsequent proliferation of bone marrow-derived cells in the postischemic kidney are important to the progression of fibrosis

Acute kidney injury (AKI) is an independent risk factor of the development of chronic kidney disease. Kidney fibrosis is a typical feature of chronic kidney disease and is characterized as an expansion of the interstitium due to increases in extracellular matrix molecules and interstitial cells caused by accumulations of extrarenal cells and by the proliferation or differentiation of intrarenal cells. However, the role of bone marrow-derived cells (BMDCs) in AKI-induced kidney fibrosis remains to be defined. Here, we investigated the role of BMDCs in kidney fibrosis after ischemia-reperfusion injury (IRI)-induced AKI in green fluorescent protein (GFP)-expressing bone marrow chimeric mice. IRI resulted in severe fibrotic changes in kidney tissues and dramatically increased interstitial cell numbers. Furthermore, GFP-expressing BMDCs accounted for >80% of interstitial cells in fibrotic kidneys. Interstitial GFP-expressing cells expressed α-smooth muscle actin (a myofibroblast marker), fibroblast-specific protein-1 (a fibroblast marker), collagen type III, and F4/80 (a macrophage marker). Over 20% of interstitial cells were bromodeoxyuridine-incorporating (proliferating) cells, and of these, 80% cells were GFP-expressing BMDCs. Daily treatment of IRI mice with apocynin (a NADPH oxidase inhibitor that functions as an antioxidant) from the day after surgery until euthanization slightly inhibited these changes with a small reduction of fibrosis. Taken together, our findings show that BMDCs make a major contribution to IRI-induced fibrosis due to their infiltration, subsequent differentiation, and proliferation in injured kidneys, suggesting that BMDCs be considered an important target for the treatment of kidney fibrosis.

Renal oxygenation in acute renal ischemia-reperfusion injury

Tissue hypoxia has been demonstrated, in both the renal cortex and medulla, during the acute phase of reperfusion after ischemia induced by occlusion of the aorta upstream from the kidney. However, there are also recent clinical observations indicating relatively well preserved oxygenation in the nonfunctional transplanted kidney. To test whether severe acute kidney injury can occur in the absence of widespread renal tissue hypoxia, we measured cortical and inner medullary tissue Po2 as well as total renal O2 delivery (Do2) and O2 consumption (Vo2) during the first 2 h of reperfusion after 60 min of occlusion of the renal artery in anesthetized rats. To perform this experiment, we used a new method for measuring kidney Do2 and Vo2 that relies on implantation of fluorescence optodes in the femoral artery and renal vein. We were unable to detect reductions in renal cortical or inner medullary tissue Po2 during reperfusion after ischemia localized to the kidney. This is likely explained by the observation that Vo2 (-57%) was reduced by at least as much as Do2 (-45%), due to a large reduction in glomerular filtration (-94%). However, localized tissue hypoxia, as evidence by pimonidazole adduct immunohistochemistry, was detected in kidneys subjected to ischemia and reperfusion, particularly in, but not exclusive to, the outer medulla. Thus, cellular hypoxia, particularly in the outer medulla, may still be present during reperfusion even when reductions in tissue Po2 are not detected in the cortex or inner medulla.

Mineralocorticoid receptor blockade reduced oxidative stress in renal transplant recipients: a double-blind, randomized pilot study

BACKGROUND

Previous experimental studies from our laboratory have demonstrated that aldosterone plays a central role in renal ischemic processes. This study was designed to evaluate the effect of mineralocorticoid receptor blockade in renal transplant recipients from living donors.

METHODS

20 adult kidney transplant recipients from living donors were included in a double-blind, randomized, placebo-controlled clinical pilot study that compared spironolactone and placebo. Placebo or spironolactone (25 mg) was administered 1 day before and 3 days posttransplantation. Renal function and urinary kidney injury molecule-1, interleukin-18, and heat shock protein 72 as well as urinary hydrogen peroxide (H2O2) levels were quantified.

RESULTS

No significant differences were seen between the groups studied regarding age, gender, indication for kidney transplantation, residual renal function, renal replacement therapy, or warm and cold ischemia periods. In contrast, spironolactone administration significantly reduced the oxidative stress assessed by the urinary H2O2 excretion, in spite of no differences in renal function or reduction in tubular injury biomarkers.

CONCLUSIONS

The findings of this exploratory study strongly suggest that aldosterone promotes oxidative stress and that the administration of spironolactone reduces the production of urinary H2O2 as a result of lesser formation of surrogate reactive oxygen species secondary to the ischemia-reperfusion phenomenon.

Remifentanil protects liver against ischemia/reperfusion injury through activation of anti-apoptotic pathways

BACKGROUND

Remifentanil protects against ischemia/reperfusion (I/R)-induced organ injury, although its underlying mechanism remains elusive. This study was designed to examine the protective effect of remifentanil preconditioning, if any, against hepatic I/R injury in rats and the underlying mechanism involved.

MATERIALS AND METHODS

Adult Sprague-Dawley rats were randomly divided into sham operation (S group), ischemia/reperfusion (I/R group), and remifentanil preconditioning (R group) groups. Rats in the I/R group were subjected to a partial (70%) hepatic ischemia for 45 min, followed by 1 h, 3 h, and 6 h of reperfusion. Rats in the R group received venous injection of remifentanil (2 μg/kg/min) from 30 min prior to hepatic ischemia to the end of ischemia. Hepatic morphology and apoptosis were examined. Markers of liver damage, oxidative stress, and inflammation were evaluated. Mitochondrial function was assessed using mitochondrial membrane potential and appearance of mitochondrial swelling.

RESULTS

Compared with the S group, rats in the I/R group displayed a massive degenerative death in liver tissues and significantly enhanced cell apoptosis. Remifentanil preconditioning significantly reduced I/R-induced hepatocyte apoptosis. In addition, remifentanil protected against I/R-induced mitochondrial swelling and loss of membrane potential. Remifentanil preconditioning inhibited I/R-induced increases in tumor necrosis factor α, intercellular adhesion molecule 1, and nuclear factor κB p65 levels in liver tissues. Remifentanil preconditioning also inhibited the loss in superoxide dismutase and rise in malondialdehyde levels in liver tissues going through I/R injury.

CONCLUSIONS

Our data revealed that remifentanil preconditioning may turn on multiple cellular pathways in hepatocytes to protect the liver from I/R injury by alleviating hepatic apoptosis.

Chronic kidney disease following acute kidney injury-risk and outcomes

In the past two decades, a substantial increase in the incidence of acute kidney injury (AKI) and kidney injury requiring dialysis has occurred in North America. This increase has coincided with an increase in the incidence of end-stage renal disease (ESRD), which has exceeded that expected based upon the prevalence of chronic kidney disease (CKD). In order to better understand the association between these conditions, there has been a proliferation of studies that have examined the risks of incident and progressive CKD following AKI. Animal studies have shown that failed differentiation of epithelial cells following renal ischaemia-reperfusion injury might lead to tubulointerstitial fibrosis, supporting a biological mechanism linking AKI and CKD. Strong and consistent associations between AKI and incident CKD, progression of CKD and incident ESRD have also been shown in epidemiological studies. In this Review, we summarize the wealth of available data on the relationship between AKI and CKD, and discuss the implications of these findings for the long-term clinical management of patients following AKI. We also identify areas of active investigation and future directions for research.