Estrogen is renoprotective via a nonreceptor-dependent mechanism after cardiac arrest in vivo

Selective Activation of G Protein-coupled Estrogen Receptor 1 Attenuates Atherosclerosis

Atherosclerosis remains a leading contributor to cardiovascular disease-associated morbidity and mortality. Interestingly, atherosclerosis-associated mortality rate is higher in men than women. This suggested a protective role for estrogen in the cardiovasculature. These effects of estrogen were initially thought to be mediated by the classic estrogen receptors, ER alpha, and beta. However, genetic knockdown of these receptors did not abolish estrogen's vasculoprotective effects suggesting that the other membranous Gprotein coupled estrogen receptor, GPER1, maybe the actual mediator. Indeed, in addition to its role in vasotone regulation, this GPER1 appears to play important roles in regulating vascular smooth cell phenotype, a critical player in the onset of atherosclerosis. Moreover, GPER1-selective agonists appear to reduce LDL levels by promoting the expression of LDL receptors as well as potentiating LDL re-uptake in liver cells. Further evidence also show that GPER1 can downregulate Proprotein Convertase Subtilisin/ Kexin type 9, leading to suppression of LDL receptor breakdown. Here, we review how selective activation of GPER1 might prevent or suppress atherosclerosis, with less side effects than those of the non-selective estrogen.

Natural Killer Lymphocytes Mediate Renal Fibrosis Due to Acute Cardiorenal Syndrome

Key Points

Natural killer cells infiltrate the kidney after cardiac arrest and medial renal fibrosis Granzyme A is produced by natural killer cells and causes mesenchymal cell expansion and fibrosis in type 1 cardiorenal syndrome

Background

The AKI to CKD transition presents an opportunity for intervention to prevent CKD. Our laboratory developed a novel murine model of AKI-CKD transition and cardiac arrest/cardiopulmonary resuscitation (CA/CPR), in which all animals develop CKD at 7 weeks. The purpose of this study was to identify potential immune drivers of fibrosis after CA/CPR.

Methods

Cardiac arrest was induced by potassium chloride, and mice were resuscitated with chest compressions and epinephrine. The kidney immune landscape after CA/CPR was profiled using 11-color flow cytometry analysis and immunofluorescence. Immune cell-derived mediators of fibrosis were identified by analyzing data from three previously published single-cell or single-nuclear RNA sequencing studies. NRK49F fibroblasts were treated with granzyme A (GzA) in vitro , and then cell proliferation was quantified using 5-ethynyl-2′-deoxyuridine. GzA was pharmacologically inhibited both in vitro and in vivo .

Results

Immune cells infiltrated the kidney after CA/CPR, consisting primarily of innate immune cells, including monocytes/macrophages, neutrophils, and natural killer (NK) cells. NK cell infiltration immediately preceded mesenchymal cell expansion, which occurred starting 7 days after CA/CPR. Immune cells colocalized with mesenchymal cells, accumulating in the areas of fibrosis. Analysis of previously published single-cell or single-nuclear RNA sequencing data revealed GzA as a potential mediator of immune to mesenchymal communication. GzA administration to fibroblasts in vitro induced cell growth and proliferation. Pharmacologic blockade of GzA signaling in vivo attenuated fibrosis and improved renal function after CA/CPR.

Conclusions

Renal inflammation occurs during cardiorenal syndrome, which correlates with mesenchymal cell expansion. GzA, produced by NK cells, presents a novel therapeutic target to prevent the transition to CKD after AKI.

Activation of GPER1 in macrophages ameliorates UUO-induced renal fibrosis

Numerous studies have proven the critical role of macrophages in the renal fibrosis process. Notably, G Protein-coupled Estrogen Receptor 1 (GPER1), a novel estrogen receptor, has been shown to play a ubiquitous role in regulating macrophage activities and proinflammatory pathways. However, the precise role of GPER1 in macrophage-mediated renal fibrosis is unknown. In this study, we aimed to investigate the function of macrophage GPER1 in the UUO-induced renal fibrosis model. Compared to vehicle-treated ovariectomized (OVX) female and male unilateral ureteral obstruction (UUO) models, we observed that G-1 (GPER1 agonist)-treated OVX female and male UUO mice had fewer renal fibrotic lesions and less M1 and M2 macrophage infiltration in the kidney tissues. Conversely, Gper1 deletion in male UUO mice accelerated renal fibrosis and increased inflammation. In vitro studies also revealed that GPER1 activation reduced M0 macrophage polarization towards M1 or M2 phenotypes. The RNA-sequencing analysis and immunoblotting indicated that GPER1 activation was primarily involved in downregulating immune pathways activation and inactivating MAPK pathways. Tubular epithelial cells co-cultured with G-1-pretreated M1 macrophages exhibited fewer injuries and immune activation. In addition, fibroblasts co-cultured with G-1-pretreated M2 macrophages showed downregulated extracellular matrix expression. Overall, this is the first study to demonstrate the effect of GPER1 on macrophage-mediated renal fibrosis via inhibition of M1 and M2 macrophage activation. These findings indicate that GPER1 may be a promising therapeutic target for treating renal fibrosis.

Sex as a biological variable in acute kidney injury

PURPOSE OF REVIEW

The purpose of this review is to provide an overview of the preclinical and clinical studies investigating sex as a biological variable, as well as the impact of gender, on the development of and progression of acute kidney injury (AKI).

RECENT FINDINGS

Despite a matched degree of ischemia-reperfusion AKI based on measured glomerular filtration rates, male and female mice demonstrated important sex biases in cardiorenal outcomes (1). Although the 2012 Kidney Disease Improving Global Outcomes (KDIGO) Clinical Practice Guideline for AKI reported that female sex is associated with increased rates of hospital acquired AKI, subsequent meta-analyses do not show increased risk of AKI in women. Recent large scale, multicenter epidemiologic studies suggest males have higher rates of hospital acquired AKI. However, women have been consistently shown to have worse renal outcomes after AKI. There may be also be gender-based differences in presentation to care and management.

SUMMARY

Sex is an important biological variable in animal models of acute kidney injury. The impact of sex on AKI likely varies based on the etiology of AKI. Preclinical studies demonstrate the nuances of sex chromosomes, sex hormones and epigenetic factors on AKI, however these have not been well studied in humans. Gender may also impact processes of care, treatment and clinical outcomes related to AKI. The scientific rigor and reproducibility of translational studies benefit from the consideration of sex and gender.

Prunetin in a GPR30-dependent manner mitigates renal ischemia/reperfusion injury in rats via interrupting indoxyl sulfate/TLR4/TRIF, RIPK1/RIPK3/MLKL, and RIPK3/PGAM5/DRP-1 crosstalk

The potential health benefits of phytochemicals in preventing and treating diseases have gained increasing attention. Here, we proved that the methylated isoflavone prunetin possesses a reno-therapeutic effect against renal ischemia/reperfusion (I/R) insult by activating G protein-coupled receptor 30 (GPR30). After choosing the therapeutic dose of prunetin against renal I/R injury in the pilot study, male Sprague Dawley rats were allocated into 5 groups; viz., sham-operated (SO), SO injected with 1 mg/kg prunetin intraperitoneally for three successive days, untreated I/R, I/R treated with prunetin, and I/R treated with G-15, the selective GPR30 blocker, followed by prunetin. Treatment with prunetin reversed the I/R renal injury effect and majorly restored normal renal function and architecture. Mechanistically, prunetin restored the I/R-induced depletion of renal GPR30, an impact that was canceled by the pre-administration of G-15. Additionally, post-administration of prunetin normalized the boosted inflammatory markers indoxyl sulfate, TLR4, and TRIF and abrogated renal cell demise by suppressing necroptotic signaling, verified by the inactivation of p-RIPK1, p-RIPK3, and p-MLKL while normalizing the inhibited caspase-8. Besides, prunetin reversed the I/R-mediated mitochondrial fission by inhibiting the protein expression of PGMA5 and p-DRP-1. All these favorable impacts of prunetin were nullified by G-15. To sum up, prunetin exhibited a significant reno-therapeutic effect evidenced by the enhancement of renal morphology and function, the suppression of the inflammatory cascade indoxyl sulfate/TLR4/TRIF, which turns off the activated/phosphorylated necroptotic trajectory RIPK1/RIPK3/MLKL, while enhancing caspase-8. Additionally, prunetin opposed the mitochondrial fission pathway RIPK3/PGMA5/DRP-1, effects that are mediated via the activation of GPR30.

Connecting G protein-coupled estrogen receptor biomolecular mechanisms with the pathophysiology of preeclampsia: a review

BACKGROUND

Throughout the course of pregnancy, small maternal spiral arteries that are in contact with fetal tissue undergo structural remodeling, lose smooth muscle cells, and become less responsive to vasoconstrictors. Additionally, placental extravillous trophoblasts invade the maternal decidua to establish an interaction between the fetal placental villi with the maternal blood supply. When successful, this process enables the transport of oxygen, nutrients, and signaling molecules but an insufficiency leads to placental ischemia. In response, the placenta releases vasoactive factors that enter the maternal circulation and promote maternal cardiorenal dysfunction, a hallmark of preeclampsia (PE), the leading cause of maternal and fetal death. An underexplored mechanism in the development of PE is the impact of membrane-initiated estrogen signaling via the G protein-coupled estrogen receptor (GPER). Recent evidence indicates that GPER activation is associated with normal trophoblast invasion, placental angiogenesis/hypoxia, and regulation of uteroplacental vasodilation, and these mechanisms could explain part of the estrogen-induced control of uterine remodeling and placental development in pregnancy.

CONCLUSION

Although the relevance of GPER in PE remains speculative, this review provides a summary of our current understanding on how GPER stimulation regulates some of the features of normal pregnancy and a potential link between its signaling network and uteroplacental dysfunction in PE. Synthesis of this information will facilitate the development of innovative treatment options.

G protein-coupled estrogen receptor 1 regulates renal endothelin-1 signaling system in a sex-specific manner

Demographic studies reveal lower prevalence of hypertension among premenopausal females compared to age-matched males. The kidney plays a central role in the maintenance of sodium (Na⁺) homeostasis and consequently blood pressure. Renal endothelin-1 (ET-1) is a pro-natriuretic peptide that contributes to sex differences in blood pressure regulation and Na⁺ homeostasis. We recently showed that activation of renal medullary G protein-coupled estrogen receptor 1 (GPER1) promotes ET-1-dependent natriuresis in female, but not male, rats. We hypothesized that GPER1 upregulates the renal ET-1 signaling system in females, but not males. To test our hypothesis, we determined the effect of GPER1 deletion on ET-1 and its downstream effectors in the renal cortex, outer and inner medulla obtained from 12-16-week-old female and male mice. GPER1 knockout (KO) mice and wildtype (WT) littermates were implanted with telemetry transmitters for blood pressure assessment, and we used metabolic cages to determine urinary Na⁺ excretion. GPER1 deletion did not significantly affect 24-h mean arterial pressure (MAP) nor urinary Na⁺ excretion. However, GPER1 deletion decreased urinary ET-1 excretion in females but not males. Of note, female WT mice had greater urinary ET-1 excretion than male WT littermates, whereas no sex differences were observed in GPER1 KO mice. GPER1 deletion increased inner medullary ET-1 peptide content in both sexes but increased outer medullary ET-1 content in females only. Cortical ET-1 content increased in response to GPER1 deletion in both sexes. Furthermore, GPER1 deletion notably increased inner medullary ET receptor A (ET_A) and decreased outer medullary ET receptor B (ET_B) mRNA expression in male, but not female, mice. We conclude that GPER1 is required for greater ET-1 excretion in females. Our data suggest that GPER1 is an upstream regulator of renal medullary ET-1 production and ET receptor expression in a sex-specific manner. Overall, our study identifies the role of GPER1 as a sex-specific upstream regulator of the renal ET-1 system.

Experimental models of acute kidney injury for translational research

Preclinical models of human disease provide powerful tools for therapeutic discovery but have limitations. This problem is especially apparent in the field of acute kidney injury (AKI), in which clinical trial failures have been attributed to inaccurate modelling performed largely in rodents. Multidisciplinary efforts such as the Kidney Precision Medicine Project are now starting to identify molecular subtypes of human AKI. In addition, over the past decade, there have been developments in human pluripotent stem cell-derived kidney organoids as well as zebrafish, rodent and large animal models of AKI. These organoid and AKI models are being deployed at different stages of preclinical therapeutic development. However, the traditionally siloed, preclinical investigator-driven approaches that have been used to evaluate AKI therapeutics to date rarely account for the limitations of the model systems used and have given rise to false expectations of clinical efficacy in patients with different AKI pathophysiologies. To address this problem, there is a need to develop more flexible and integrated approaches, involving teams of investigators with expertise in a range of different model systems, working closely with clinical investigators, to develop robust preclinical evidence to support more focused interventions in patients with AKI.

Accumulated Epinephrine Dose is Associated With Acute Kidney Injury Following Resuscitation in Adult Cardiac Arrest Patients

The goal of this study was to investigate the association between total epinephrine dosage during resuscitation and acute kidney injury after return of spontaneous circulation in patients with cardiac arrest. We performed a secondary analysis of previously published data on the resuscitation of cardiac arrest patients. Bivariate, multivariate logistic regression, and subgroup analyses were conducted to investigate the association between total epinephrine dosage during resuscitation and acute kidney injury after return of spontaneous circulation. A total of 312 eligible patients were included. The mean age of the patients was 60.8 ± 15.2 years. More than half of the patients were male (73.4%) and had an out-of-hospital cardiac arrest (61.9%). During resuscitation, 125, 81, and 106 patients received ≤2, 3 - 4, and ≥5 mg epinephrine, respectively. After return of spontaneous circulation, there were 165 patients (52.9%) and 147 patients (47.1%) with and without acute kidney injury, respectively. Both bivariate and multivariate analysis showed a statistically significant association between total epinephrine dosage and acute kidney injury. The subgroup analysis showed that the strength of the association between epinephrine dosage and acute kidney injury varied by location of cardiac arrest. Further multivariate regression analysis found that the association between epinephrine dosage and acute kidney injury was only observed in patients with in-hospital cardiac arrest after adjusting for multiple confounding factors. Compared with in-hospital cardiac arrest patients who received ≤2 mg of epinephrine, patients with 3–4 mg of epinephrine or ≥5 mg of epinephrine had adjusted odds ratios of 4.2 (95% confidence interval 1.0–18.4) and 11.3 (95% confidence interval 2.0–63.0), respectively, to develop acute kidney injury. Therefore, we concluded that a higher epinephrine dosage during resuscitation was associated with an increased incidence of acute kidney injury after return of spontaneous circulation in adult patients with in-hospital cardiac arrest.

The Neglected Price of Pediatric Acute Kidney Injury: Non-renal Implications

Preclinical models and emerging translational data suggest that acute kidney injury (AKI) has far reaching effects on all other major organ systems in the body. Common in critically ill children and adults, AKI is independently associated with worse short and long term morbidity, as well as mortality, in these vulnerable populations. Evidence exists in adult populations regarding the impact AKI has on life course. Recently, non-renal organ effects of AKI have been highlighted in pediatric AKI survivors. Given the unique pediatric considerations related to somatic growth and neurodevelopmental consequences, pediatric AKI has the potential to fundamentally alter life course outcomes. In this article, we highlight the challenging and complex interplay between AKI and the brain, heart, lungs, immune system, growth, functional status, and longitudinal outcomes. Specifically, we discuss the biologic basis for how AKI may contribute to neurologic injury and neurodevelopment, cardiac dysfunction, acute lung injury, immunoparalysis and increased risk of infections, diminished somatic growth, worsened functional status and health related quality of life, and finally the impact on young adult health and life course outcomes.

Role of HRTPT in kidney proximal epithelial cell regeneration: Integrative differential expression and pathway analyses using microarray and scRNA-seq

Damage to proximal tubules due to exposure to toxicants can lead to conditions such as acute kidney injury (AKI), chronic kidney disease (CKD) and ultimately end‐stage renal failure (ESRF). Studies have shown that kidney proximal epithelial cells can regenerate particularly after acute injury. In the previous study, we utilized an immortalized in vitro model of human renal proximal tubule epithelial cells, RPTEC/TERT1, to isolate HRTPT cell line that co‐expresses stem cell markers CD133 and CD24, and HREC24T cell line that expresses only CD24. HRTPT cells showed most of the key characteristics of stem/progenitor cells; however, HREC24T cells did not show any of these characteristics. The goal of this study was to further characterize and understand the global gene expression differences, upregulated pathways and gene interaction using scRNA‐seq in HRTPT cells. Affymetrix microarray analysis identified common gene sets and pathways specific to HRTPT and HREC24T cells analysed using DAVID, Reactome and Ingenuity software. Gene sets of HRTPT cells, in comparison with publicly available data set for CD133+ infant kidney, urine‐derived renal progenitor cells and human kidney‐derived epithelial proximal tubule cells showed substantial similarity in organization and interactions of the apical membrane. Single‐cell analysis of HRTPT cells identified unique gene clusters associated with CD133 and the 92 common gene sets from three data sets. In conclusion, the gene expression analysis identified a unique gene set for HRTPT cells and narrowed the co‐expressed gene set compared with other human renal–derived cell lines expressing CD133, which may provide deeper understanding in their role as progenitor/stem cells that participate in renal repair.

Sirtuin-3 mediates sex differences in kidney ischemia-reperfusion injury

Studies suggest that biological sex influences susceptibility to kidney diseases with males demonstrating greater risk for developing ischemic acute kidney injury (AKI). Sex-related differences in mitochondrial function and homeostasis exist, likely contributing to sexual dimorphism in kidney injury, but the mechanisms are not well characterized. Our observations reveal lower baseline expression of Sirtuin-3 (Sirt3, a major mitochondrial acetyltransferase) in the kidneys of male mice versus females. We tested the hypothesis that differential expression of kidney Sirt3 may mediate sexual dimorphism in AKI using a bilateral kidney ischemia-reperfusion injury (IRI) model and three transgenic mouse models: (1) mice with global transgenic overexpression of Sirt3; (2) mice with inducible, kidney tubule-specific Sirt3 knockdown (iKD); and (3) mice with global Sirt3 knockout. Low mitochondrial Sirt3 (mtSirt3) in males versus females is associated with development of kidney tubular epithelium vacuoles, increased mitochondrial ROS and susceptibility to IRI. Transgenic overexpression of Sirt3 in males protects against kidney IRI and development of tubular epithelium vacuoles. In both sexes, mice with partial kidney tubular epithelium-specific Sirt3 knockdown display intermediate - while global Sirt3 knockout mice display the highest susceptibility to IRI. Female Sirt3 iKD mice demonstrate decreased survival and kidney function after IRI indistinguishable from control males, abolishing the protective effects observed in females. Mechanistically, observed differences in kidney mtSirt3 are sex hormone-dependent; estradiol increases - while testosterone decreases mtSirt3 protein. Our results demonstrate that Sirt3 is an important contributor to the observed sex-related differences in IRI susceptibility, and a potential therapeutic target in the clinical management of AKI.

Gender differences and survival after an out-of-hospital cardiac arrest: a systematic review and meta-analysis

Patients who experience out-of-hospital cardiac arrest (OHCA) have unacceptably high mortality rates. It remains unclear whether gender has an association with survival in this regard. Hence, we aimed to investigate the association between gender and survival by conducting a systematic review and meta-analysis. The databases of PubMed, Embase, and Cochrane Database of Systematic Reviews were searched from inception to 17 March, 2020. Studies assessing the association between gender and survival to discharge or 30-day survival after OHCA were included. Two reviewers independently assessed the eligibility of the identified studies. The random-effects model was used to pool data, and the outcome was reported as odds ratios (ORs) and 95% confidence intervals, as the relative measure of association. Twenty-three eligible studies enrolling 897,805 patients were included in this systematic review. Overall, women were older and less likely to experience arrest in public places. When arrest occurred, women had less initial shockable rhythm, were less likely to be witnessed by bystanders, and were less likely provided with CPR compared with men. After admission, women underwent less coronary angiography, percutaneous coronary angiography, and targeted temperature management therapy. Eleven studies with ORs were pooled, showing a significant survival benefit in women (OR = 1.08, p < 0.05, I² = 52.3%). In the subgroup analysis, both premenopausal women (< 50 years) (OR = 1.42, p < 0.001, I² = 0%) and postmenopausal women (≥ 50 years) (OR = 1.07, p < 0.05, I² = 16.4%) had higher odds of survival compared with age-matched men. Despite the unfavorable factors, the pooled results showed a significant survival benefit in women after OHCA, especially in premenopausal women.

A prediction model of delayed graft function in deceased donor for renal transplant: a multi-center study from China

Background

Kidneys obtained from deceased donors increase the incidence of delayed graft function (DGF) after renal transplantation. Here we investigated the influence of the risk factors of donors with DGF, and developed a donor risk scoring system for DGF prediction.

Methods

This retrospective study was conducted in 1807 deceased kidney donors and 3599 recipients who received donor kidneys via transplants in 29 centers in China. We quantified DGF associations with donor clinical characteristics. A donor risk scoring system was developed and validated using an independent sample set.

Results

The incidence of DGF from donors was 19.0%. Six of the donor characteristics analyzed, i.e., age, cause of death, history of hypertension, terminal serum creatinine, persistence of hypotension, and cardiopulmonary resuscitation (CPR) time were risk factors for DGF. A 49-point scoring system of donor risk was established for DGF prediction and exhibited a superior degree of discrimination. External validation of DGF prediction revealed area under the receiver-operating characteristic (AUC) curves of 0.7552.

Conclusions

Our study determined the deceased donor risk factors related to DGF after renal transplantation pertinent to the Chinese cohort. The scoring system developed here had superior diagnostic significance and consistency and can be used by clinicians to make evidence-based decisions on the quality of kidneys from deceased donors and guide renal transplantation therapy.

Estrogen and estrogen receptors in kidney diseases

Acute kidney injury (AKI) and chronic kidney disease (CKD) are posing great threats to global health within this century. Studies have suggested that estrogen and estrogen receptors (ERs) play important roles in many physiological processes in the kidney. For instance, they are crucial in maintaining mitochondrial homeostasis and modulating endothelin-1 (ET-1) system in the kidney. Estrogen takes part in the kidney repair and regeneration via its receptors. Estrogen also participates in the regulation of phosphorus homeostasis via its receptors in the proximal tubule. The ERα polymorphisms have been associated with the susceptibilities and outcomes of several renal diseases. As a consequence, the altered or dysregulated estrogen/ERs signaling pathways may contribute to a variety of kidney diseases, including various causes-induced AKI, diabetic kidney disease (DKD), lupus nephritis (LN), IgA nephropathy (IgAN), CKD complications, etc. Experimental and clinical studies have shown that targeting estrogen/ERs signaling pathways might have protective effects against certain renal disorders. However, many unsolved problems still exist in knowledge regarding the roles of estrogen and ERs in distinct kidney diseases. Further research is needed to shed light on this area and to enable the discovery of pathway-specific therapies for kidney diseases.

A novel ultrasound-guided mouse model of sudden cardiac arrest

AIM

Mouse models of sudden cardiac arrest are limited by challenges with surgical technique and obtaining reliable venous access. To overcome this limitation, we sought to develop a simplified method in the mouse that uses ultrasound-guided injection of potassium chloride directly into the heart.

METHODS

Potassium chloride was delivered directly into the left ventricular cavity under ultrasound guidance in intubated mice, resulting in immediate asystole. Mice were resuscitated with injection of epinephrine and manual chest compressions and evaluated for survival, body temperature, cardiac function, kidney damage, and diffuse tissue injury.

RESULTS

The direct injection sudden cardiac arrest model causes rapid asystole with high surgical survival rates and short surgical duration. Sudden cardiac arrest mice with 8-min of asystole have significant cardiac dysfunction at 24 hours and high lethality within the first seven days, where after cardiac function begins to improve. Sudden cardiac arrest mice have secondary organ damage, including significant kidney injury but no significant change to neurologic function.

CONCLUSIONS

Ultrasound-guided direct injection of potassium chloride allows for rapid and reliable cardiac arrest in the mouse that mirrors human pathology without the need for intravenous access. This technique will improve investigators' ability to study the mechanisms underlying post-arrest changes in a mouse model.

G protein-coupled estrogen receptor 1 as a novel regulator of blood pressure

The mechanisms underlying hypertension are multifaceted and incompletely understood. New evidence suggests that G protein-coupled estrogen receptor 1 (GPER1) mediates protective actions within the cardiovascular and renal systems. This mini-review focuses on recent advancements in our understanding of the vascular, renal, and cardiac GPER1-mediated mechanisms that influence blood pressure regulation. We emphasize clinical and basic evidence that suggests GPER1 as a novel target to aid therapeutic strategies for hypertension. Furthermore, we discuss current controversies and challenges facing GPER1-related research.

Sex-dependent mechanisms involved in renal tolerance to ischemia-reperfusion: Role of inflammation and histone H3 citrullination

Ischemia-reperfusion (I/R) injury, an inevitable result of kidney transplantation, triggers early inflammatory events that affect graft viability. Evidence from human transplantation and preclinical models of I/R suggests that a female hormonal environment positively influences the ability to recover from ischemic injury. However, the mechanisms behind these effects remain mostly unexplored. Here, we studied the influence of sex on pro-inflammatory mediators involved in the pathophysiology of acute I/R injury in male, female, and female ovariectomized (OVX) Wistar rats that underwent unilateral renal ischemia for 45 min, followed by 24 h of reperfusion. We found improved renal function, reduced cytokine expression, and decreased infiltration of myeloperoxidase-positive cells in females after I/R, when compared to their male and female OVX counterparts. Remarkably, citrullination of histone H3 was exacerbated in serum and renal tubules of females after I/R. In contrast, we observed lower levels of citrullinated histone H3 in male and female OVX rats in response to I/R, mostly in neutrophil extracellular traps. Our results demonstrate that female sex promotes renal I/R tolerance by attenuating pro-inflammatory mediators involved in I/R-induced damage.

Sex differences in redox homeostasis in renal disease

Sex differences in redox signaling in the kidney present new challenges and opportunities for understanding the physiology and pathophysiology of the kidney. This review will focus on reactive oxygen species, immune-related signaling pathways and endothelin-1 as potential mediators of sex-differences in redox homeostasis in the kidney. Additionally, this review will highlight male-female differences in redox signaling in several major cardiovascular and renal disorders namely acute kidney injury, diabetic nephropathy, kidney stone disease and salt-sensitive hypertension. Furthermore, we will discuss the contribution of redox signaling in the pathogenesis of postmenopausal hypertension and preeclampsia.

Chronic GPER1 Activation Protects Against Oxidative Stress-Induced Cardiomyoblast Death via Preservation of Mitochondrial Integrity and Deactivation of Mammalian Sterile-20-Like Kinase/Yes-Associated Protein Pathway

Introduction: Estrogen (17β-estradiol, E2) is well-known to induce cardioprotective effects against ischemia/reperfusion (I/R) injury. We recently reported that acute application of E2 at the onset of reperfusion in vivo induces cardioprotective effects against I/R injury via activation of its non-steroidal receptor, G protein-coupled estrogen receptor 1 (GPER1). Here, we investigated the impact and mechanism underlying chronic GPER1 activation in cultured H9c2 rat cardiomyoblasts. Methods: H9c2 rat cardiomyoblasts were cultured and pretreated with the cytotoxic agent H₂O₂ for 24 h and incubated in the presence of vehicle (control), GPER1 agonists E2 and G1, or GPER1 agonists supplemented with G15 (GPER1 antagonist) for 48 or 96 h. After treatment, cells were collected to measure the rate of cell death and viability using flow cytometry and Calcein AM assay or MTT assay, respectively. The resistance to opening of the mitochondrial permeability transition pore (mPTP), the mitochondrial membrane potential, and ATP production was assessed using fluorescence microscopy, and the mitochondrial structural integrity was observed with electron microscopy. The levels of the phosphorylation of mammalian sterile-20-like kinase (MST1) and yes-associated protein (YAP) were assessed by Western blot analysis in whole-cell lysate, while the expression levels of mitochondrial biogenesis genes, YAP target genes, and proapoptotic genes were measured by qRT-PCR. Results: We found that after H₂O₂ treatment, chronic E2/G1 treatment decreased cell death effect was associated with the prevention of the S phase of the cell cycle arrest compared to control. In the mitochondria, chronic E2/G1 activation treatment preserved the cristae morphology, and increased resistance to opening of mPTP, but with little change to mitochondrial fusion/fission. Additionally, chronic E2/G1 treatment predominantly reduced phosphorylation of MST1 and YAP, as well as increased MST1 and YAP protein levels. E2 treatment also upregulated the expression levels of TGF-β and PGC-1α mRNAs and downregulated PUMA and Bim mRNAs. Except for ATP production, all the E2 or G1 effects were prevented by the cotreatment with the GPER1 antagonist, G15. Conclusion: Together, these results indicate that chronic GPER1 activation with its agonists E2 or G1 treatment protects H9c2 cardiomyoblasts against oxidative stress-induced cell death and increases cell viability by preserving mitochondrial structure and function as well as delaying the opening of mPTP. These chronic GPER1 effects are associated with the deactivation of the non-canonical MST1/YAP mechanism that leads to genetic upregulation of cell growth genes (CTGF, CYR61, PGC-1α, and ANKRD1), and downregulation of proapoptotic genes (PUMA and Bim).

Mitochondrial connexin 43 in sex-dependent myocardial responses and estrogen-mediated cardiac protection following acute ischemia/reperfusion injury

Preserving mitochondrial activity is crucial in rescuing cardiac function following acute myocardial ischemia/reperfusion (I/R). The sex difference in myocardial functional recovery has been observed after I/R. Given the key role of mitochondrial connexin43 (Cx43) in cardiac protection initiated by ischemic preconditioning, we aimed to determine the implication of mitochondrial Cx43 in sex-related myocardial responses and to examine the effect of estrogen (17β-estradiol, E2) on Cx43, particularly mitochondrial Cx43-involved cardiac protection following I/R. Mouse primary cardiomyocytes and isolated mouse hearts (from males, females, ovariectomized females, and doxycycline-inducible Tnnt2-controlled Cx43 knockout without or with acute post-ischemic E2 treatment) were subjected to simulated I/R in culture or Langendorff I/R (25-min warm ischemia/40-min reperfusion), respectively. Mitochondrial membrane potential and mitochondrial superoxide production were measured in cardiomyocytes. Myocardial function and infarct size were determined. Cx43 and its isoform, Gja1-20k, were assessed in mitochondria. Immunoelectron microscopy and co-immunoprecipitation were also used to examine mitochondrial Cx43 and its interaction with estrogen receptor-α by E2 in mitochondria, respectively. There were sex disparities in stress-induced cardiomyocyte mitochondrial function. E2 partially restored mitochondrial activity in cardiomyocytes following acute injury. Post-ischemia infusion of E2 improved functional recovery and reduced infarct size with increased Cx43 content and phosphorylation in mitochondria. Ablation of cardiac Cx43 aggravated mitochondrial damage and abolished E2-mediated cardiac protection during I/R. Female mice were more resistant to myocardial I/R than age-matched males with greater protective role of mitochondrial Cx43 in female hearts. Post-ischemic E2 usage augmented mitochondrial Cx43 content and phosphorylation, increased mitochondrial Gja1-20k, and showed cardiac protection.

The acute kidney injury to chronic kidney disease transition in a mouse model of acute cardiorenal syndrome emphasizes the role of inflammation

Acute cardiorenal syndrome is a common complication of acute cardiovascular disease. Studies of acute kidney injury (AKI) to chronic kidney disease (CKD) transition, including patients suffering acute cardiovascular disease, report high rates of CKD development. Therefore, acute cardiorenal syndrome associates with CKD, but no study has established causation. To define this we used a murine cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) model or sham procedure on male mice. CA was induced with potassium chloride while CPR consisted of chest compressions and epinephrine eight minutes later. Two weeks after AKI was induced by CA/CPR, the measured glomerular filtration rate (GFR) was not different from sham. However, after seven weeks the mice developed CKD, recapitulating clinical observations. One day, and one, two, and seven weeks after CA/CPR, the GFR was measured, and renal tissue sections were evaluated for various indices of injury and inflammation. One day after CA/CPR, acute cardiorenal syndrome was indicated by a significant reduction of the mean GFR (649 in sham, vs. 25 μL/min/100g in CA/CPR animals), KIM-1 positive tubules, and acute tubular necrosis. Renal inflammation developed, with F4/80 positive and CD3-positive cells infiltrating the kidney one day and one week after CA/CPR, respectively. Although there was functional recovery with normalization of GFR two weeks after CA/CPR, deposition of tubulointerstitial matrix proteins α-smooth muscle actin and fibrillin-1 progressed, along with a significantly reduced mean GFR (623 in sham vs. 409 μL/min/100g in CA/CPR animals), proteinuria, increased tissue transforming growth factor-β, and fibrosis establishing the development of CKD seven weeks after CA/CPR. Thus, murine CA/CPR, a model of acute cardiorenal syndrome, causes an AKI-CKD transition likely due to prolonged renal inflammation.

The Effect of Zinc Deficiency and Supplementation on Elements in the Kidney Tissue of Ovariectomized Rats: Histopathologic Changes

The objective of the present study is to determine the effects of zinc deficiency in and zinc supplementation to ovariectomized rats on some elements in kidney tissue. The study included 40 Sprague-Dawley type adult female rats. The experimental animals were randomized into four groups with equal numbers as follows: Group 1: Control (10). Group 2: Ovariectomized control (10). Group 3: Ovariectomized + zinc supplemented (10). Group 4: Ovariectomized + zinc deficient (10). After the animals were decapitated at the end of the experiment, element levels were determined by Atomic Emission (ICP-AES) as mg/g/wet tissue for calcium, phosphate, zinc, aluminum, copper, iron, lithium, and manganese and μg/g/wet tissue for magnesium in the kidney tissue. Additionally, the tissue samples were subjected to a histopathologic assessment. An examination of the study results showed that ovariectomy significantly reduced calcium, phosphorus, and zinc levels, while zinc supplementation to the rats following ovariectomy restored the reduced element levels to normal (0.10 ± 0.03, 0.85 ± 0.16, 0.11 ± 0.03 vs 0.19 ± 0.06, 1.86 ± 0.18, 0.52 ± 0.05). Group 4, which was both ovariectomized and fed on a zinc-deficient diet, had significantly lower aluminum, copper, and lithium values. Calcification, inflammation, and sclerotic changes in group 4, the group which was fed on a zinc-deficient diet, were greater in comparison to other groups (p < 0.05). Results of the study suggest that ovariectomy + zinc deficiency leads to calcification, inflammation, and sclerotic changes in renal tissue and significantly reduces element levels, whereas zinc supplementation after ovariectomy restores the lowered element levels to normal.

Glomerular filtrate proteins in acute cardiorenal syndrome

Acute cardiorenal syndrome (CRS-1) is a morbid complication of acute cardiovascular disease. Heart-to-kidney signals transmitted by "cardiorenal connectors" have been postulated, but investigation into CRS-1 has been limited by technical limitations and a paucity of models. To address these limitations, we developed a translational model of CRS-1, cardiac arrest and cardiopulmonary resuscitation (CA/CPR), and now report findings from nanoscale mass spectrometry proteomic exploration of glomerular filtrate 2 hours after CA/CPR or sham procedure. Filtrate acquisition was confirmed by imaging, molecular weight and charge distribution, and exclusion of protein specific to surrounding cells. Filtration of proteins specific to the heart was detected following CA/CPR and confirmed with mass spectrometry performed using urine collections from mice with deficient tubular endocytosis. Cardiac LIM protein was a CA/CPR-specific filtrate component. Cardiac arrest induced plasma release of cardiac LIM protein in mice and critically ill human cardiac arrest survivors, and administration of recombinant cardiac LIM protein to mice altered renal function. These findings demonstrate that glomerular filtrate is accessible to nanoscale proteomics and elucidate the population of proteins filtered 2 hours after CA/CPR. The identification of cardiac-specific proteins in renal filtrate suggests a novel signaling mechanism in CRS-1. We expect these findings to advance understanding of CRS-1.

Mitochondrial dysfunction in acute kidney injury and sex-specific implications

The kidney is one of the most energy-demanding organs in the human body, and the maintenance of mitochondrial homeostasis is central to kidney function. Recent advances have led to a greater appreciation of how mitochondrial dysfunction contributes to the pathogenesis of AKI, from decreased ATP production, to enhanced mitochondrial oxidative stress, cell necrosis and apoptosis. Accumulating evidence suggests sexual dimorphism in the response to AKI with males demonstrating greater risk for developing ischemia-reperfusion and sepsis-induced kidney injury. In contrast, females may be more susceptible to nephrotoxic-AKI. There are important sex-related differences in mitochondrial respiration, biogenesis and dynamics that likely contribute to the observed sexual dimorphism in AKI. Sex hormones mediate many of these differences with multiple preclinical studies demonstrating the renoprotective actions of estrogen in many rodent models of AKI. Estrogenic control of mitochondrial biogenesis, function and reactive oxygen species (ROS) generation is discussed. Furthermore, the potential role for sex chromosomes in mediating sex differences in AKI is examined. Novel animal models such as the "four core genotypes" (FCG) mouse model provide us with important tools to study sex chromosome effects in kidney health and disease. By understanding the influences of sexual dimorphism or sex hormones on mitochondrial homeostasis and disease manifestations, we may be able to identify novel therapeutic targets and improve existing treatment options for AKI.

The role of Sigma-1 receptor in sex-specific heat shock response in an experimental rat model of renal ischaemia/reperfusion injury

We previously showed that female rats are more protected against renal ischaemia/reperfusion (I/R) injury than males, which is partly attributed to their more pronounced heat shock response. We recently described that Sigma-1 receptor (S1R) activation improves postischaemic survival and renal function. 17β-estradiol activates S1R, thus here we investigated the role of sex-specific S1R activation and heat shock response in severe renal I/R injury. Proximal tubular cells were treated with 17β-estradiol, which caused direct S1R activation and subsequent induction of heat shock response. Uninephrectomized female, male and ovariectomized female (Ovx) Wistar rats were subjected to 50-min renal ischaemia followed by 2 (T2) and 24 (T24) hours of reperfusion. At T24 renal functional, impairment was less severe and structural damage was less prominent in females versus males or Ovx. Postischaemic increase in S1R, pAkt, HSF-1, HSP72 levels were detected as early as at T2, while pHSP27 was elevated later at T24. Abundance of heat shock proteins was higher in healthy female rats and remained higher at T2 and T24 (female versus male or Ovx; resp.). We propose a S1R-dependent mechanism, which contributes to the relative renoprotection of females after I/R injury by enhancing the heat shock response.

Postischemic application of estrogen ameliorates myocardial damage in an in vivo mouse model

BACKGROUND

Cardioprotection provided by estrogen has been recognized for many years. It is noteworthy that most of these studies employ a means of preinjury application in experimental research and the preventive usage in clinical studies. Compared to pretreatment, postischemic administration of estrogen will be more practical in treating myocardial ischemia. On the other hand, defect in circadian clock gene period2 (Per2) has been shown to aggravate ischemia-induced heart damage. Given that Per2 expression decreases as a consequence of menopause, in this study, we aim to determine (1) potential improvement of myocardial function by postischemic administration of 17β-estradiol (E2) using an in vivo mouse myocardial ischemia/reperfusion (I/R) model and (2) the role of E2 in regulating myocardial Per2 expression following I/R.

METHODS

Thirty-minute occlusion of left anterior descending artery followed by 24-h reperfusion was performed on adult C57BL ovariectomized female mice. Groups (n = 3-6/group) were as follows: (1) Sham, (2) I/R + vehicle, and (3) I/R + E2. Vehicle or 0.5 mg/kg of E2 was subcutaneously injected right after 30-min ischemia. Following 24-h reperfusion, myocardial function was determined. Heart tissue was collected for analysis of cleaved caspase-3 and Per2 expression by Western blotting, as well as proinflammatory cytokine production (IL-1β, IL-6, and TNF-α) by enzyme-linked immunosorbent assay.

RESULTS

I/R significantly impaired left ventricular function and increased myocardial levels of active caspase-3, IL-1β, and IL-6. Importantly, postischemic treatment of E2 markedly restored I/R-depressed myocardial function, reduced caspase-3 activation, and decreased proinflammatory cytokine production (IL-1β, IL-6, and TNF-α). Intriguingly, a trend of the decreased Per2 level was observed in ovariectomized female hearts subjected to I/R, whereas E2 treatment upregulated myocardial Per2 expression.

CONCLUSIONS

Our study represents the initial evidence that postischemic administration of E2 effectively preserves the myocardium against I/R injury and this protective effect of E2 may involve upregulation of Per2 in ischemic heart.

Parp1 protects against Aag-dependent alkylation-induced nephrotoxicity in a sex-dependent manner

Nephrotoxicity is a common toxic side-effect of chemotherapeutic alkylating agents. Although the base excision repair (BER) pathway is essential in repairing DNA alkylation damage, under certain conditions the initiation of BER produces toxic repair intermediates that damage healthy tissues. We have shown that the alkyladenine DNA glycosylase, Aag (a.k.a. Mpg), an enzyme that initiates BER, mediates alkylation-induced whole-animal lethality and cytotoxicity in the pancreas, spleen, retina, and cerebellum, but not in the kidney. Cytotoxicity in both wild-type and Aag-transgenic mice (AagTg) was abrogated in the absence of Poly(ADP-ribose) polymerase-1 (Parp1). Here we report that Parp1-deficient mice expressing increased Aag (AagTg/Parp1^−/−) develop sex-dependent kidney failure upon exposure to the alkylating agent, methyl methanesulfonate (MMS), and suffer increased whole-animal lethality compared to AagTg and wild-type mice. Macroscopic, histological, electron microscopic and immunohistochemical analyses revealed morphological kidney damage including dilated tubules, proteinaceous casts, vacuolation, collapse of the glomerular tuft, and deterioration of podocyte structure. Moreover, mice exhibited clinical signs of kidney disease indicating functional damage, including elevated blood nitrogen urea and creatinine, hypoproteinemia and proteinuria. Pharmacological Parp inhibition in AagTg mice also resulted in sensitivity to MMS-induced nephrotoxicity. These findings provide in vivo evidence that Parp1 modulates Aag-dependent MMS-induced nephrotoxicity in a sex-dependent manner and highlight the critical roles that Aag-initiated BER and Parp1 may play in determining the side-effects of chemotherapeutic alkylating agents.

17β-Estradiol Accelerated Renal Tubule Regeneration in Male Rats After Ischemia/Reperfusion-Induced Acute Kidney Injury

Ischemic/reperfusion injury (IRI) is the most common cause of acute kidney injury (AKI). Murine studies report that pretreatment with 17β-estradiol protects against AKI using multiple mechanisms, but how 17β-estradiol is involved in regenerating tubular cells is unknown. To visualize the kidney injury and repair, we used 17β-estradiol to treat rats with postischemic acute kidney injury. AKI was induced by clamping the renal pedicle for 90 minutes 2 weeks after a unilateral nephrectomy. Rats were treated with an intravenous injection of 17β-estradiol or vehicle immediately after reperfusion. Kidney injury was assessed by measuring biochemical and histopathological changes. Immunohistochemical staining of vimentin, proliferating cell nuclear antigen (PCNA), and E-cadherin were used to assess dedifferentiation, proliferation, and redifferentiation. Rats treated with 17β-estradiol had less kidney injury than did vehicle-treated rats post-IRI day 1. The number of PCNA-positive (PCNA) cells was significantly higher in post-IRI kidneys on day 1 in 17β-estradiol-treated rats. Moreover, vimentin and E-cadherin cells, which were interpreted as regeneration markers, were expressed earlier and significantly more copiously in 17β-estradiol-treated rats. We hypothesize that 17β-estradiol attenuates IRI-induced AKI by reducing inflammation and accelerating injured tubular cell regeneration.

Effects of erythropoietin receptor activity on angiogenesis, tubular injury, and fibrosis in acute kidney injury: a "U-shaped" relationship

The erythropoietin receptor (EpoR) is widely expressed but its renoprotective action is unexplored. To examine the role of EpoR in vivo in the kidney, we induced acute kidney injury (AKI) by ischemia-reperfusion in mice with different EpoR bioactivities in the kidney. EpoR bioactivity was reduced by knockin of wild-type human EpoR, which is hypofunctional relative to murine EpoR, and a renal tubule-specific EpoR knockout. These mice had lower EPO/EpoR activity and lower autophagy flux in renal tubules. Upon AKI induction, they exhibited worse renal function and structural damage, more apoptosis at the acute stage (<7 days), and slower recovery with more tubulointerstitial fibrosis at the subacute stage (14 days). In contrast, mice with hyperactive EpoR signaling from knockin of a constitutively active human EpoR had higher autophagic flux, milder kidney damage, and better renal function at the acute stage but, surprisingly, worse tubulointerstitial fibrosis and renal function at the subacute stage. Either excess or deficient EpoR activity in the kidney was associated with abnormal peritubular capillaries and tubular hypoxia, creating a "U-shaped" relationship. The direct effects of EpoR on tubular cells were confirmed in vitro by a hydrogen peroxide model using primary cultured proximal tubule cells with different EpoR activities. In summary, normal erythropoietin (EPO)/EpoR signaling in renal tubules provides defense against renal tubular injury maintains the autophagy-apoptosis balance and peritubular capillary integrity. High and low EPO/EpoR bioactivities both lead to vascular defect, and high EpoR activity overides the tubular protective effects in AKI recovery.

GPER-novel membrane oestrogen receptor

The recent discovery of the G protein-coupled oestrogen receptor (GPER) presents new challenges and opportunities for understanding the physiology, pathophysiology and pharmacology of many diseases. This review will focus on the expression and function of GPER in hypertension, kidney disease, atherosclerosis, vascular remodelling, heart failure, reproduction, metabolic disorders, cancer, environmental health and menopause. Furthermore, this review will highlight the potential of GPER as a therapeutic target.

Correlation of Impedance Threshold Device use during cardiopulmonary resuscitation with post-cardiac arrest Acute Kidney Injury

PURPOSE

To assess whether use of Impedance Threshold Device (ITD) during cardiopulmonary resuscitation (CPR) reduces the degree of post-cardiac arrest Acute Kidney Injury (AKI), as a result of improved hemodynamics, in a porcine model of ventricular fibrillation (VF) cardiac arrest.

METHODS

After 8 min of untreated cardiac arrest, the animals were resuscitated either with active compression-decompression (ACD) CPR plus a sham ITD (control group, n=8) or with ACD-CPR plus an active ITD (ITD group, n=8). Adrenaline was administered every 4 min and electrical defibrillation was attempted every 2 min until return of spontaneous circulation (ROSC) or asystole. After ROSC the animals were monitored for 6 h under general anesthesia and then returned to their cages for a 48 h observation, before euthanasia. Two novel biomarkers, Neutrophil Gelatinase-Associated Lipocalin (NGAL) in plasma and Interleukin-18 (IL-18) in urine, were measured at 2 h, 4 h, 6 h, 24 h and 48 h post-ROSC, in order to assess the degree of AKI.

RESULTS

ROSC was observed in 7 (87.5%) animals treated with the sham valve and 8 (100%) animals treated with the active valve (P=NS). However, more than twice as many animals survived at 48 h in the ITD group (n=8, 100%) compared to the control group (n=3, 37.5%). Urine IL-18 and plasma NGAL levels were augmented post-ROSC in both groups, but they were significantly higher in the control group compared with the ITD group, at all measured time points.

CONCLUSION

Use of ITD during ACD-CPR improved hemodynamic parameters, increased 48 h survival and decreased the degree of post-cardiac arrest AKI in the resuscitated animals.

Determination of renal function and injury using near-infrared fluorimetry in experimental cardiorenal syndrome

Cardiorenal syndrome type 1 causes acute kidney injury but is poorly understood; animal models and diagnostic aids are lacking. Robust noninvasive measurements of glomerular filtration rate are required for injury models and clinical use. Several have been described but are untested in translational models and suffer from biologic interference. We developed a mouse model of cardiorenal syndrome and tested the novel near-infrared fluorophore ZW800-1 to assess renal and cardiac function. We performed murine cardiac arrest and cardiopulmonary resuscitation followed by transthoracic echocardiography, 2 and 24 h later. Transcutaneous fluorescence of ZW800-1 bolus dispersion and clearance was assessed with whole animal imaging and compared with glomerular filtration rate (GFR; inulin clearance), tubular cell death (using unbiased stereology), and serum creatinine. Correlation, Bland-Altman, and polar analyses were used to compare GFR with ZW800-1 clearance. Cardiac arrest and cardiopulmonary resuscitation caused reversible cardiac failure, halving fractional shortening of the left ventricle (n = 12, P = 0.03). Acute kidney injury resulted with near-zero GFR and sixfold increase in serum creatinine 24 h later (n = 16, P < 0.01). ZW800-1 biodistribution and clearance were exclusively renal. ZW800-1 t_1/2 and clearance correlated with GFR (r = 0.92, n = 31, P < 0.0001). ZW800-1 fluorescence was reduced in cardiac arrest, and cardiopulmonary resuscitation-treated mice compared with sham animals 810 s after injection (P < 0.01) and bolus time-dispersion curves demonstrated that ZW800-1 fluorescence dispersion correlated with left ventricular function (r = 0.74, P < 0.01). Cardiac arrest and cardiopulmonary resuscitation lead to experimental cardiorenal syndrome type 1. ZW800-1, a small near-infrared fluorophore being developed for clinical intraoperative imaging, is favorable for evaluating cardiac and renal function noninvasively.

Renal Doppler and Novel Biomarkers to Assess Acute Kidney Injury in a Swine Model of Ventricular Fibrillation Cardiac Arrest

Background:

Majority of the research on cardiac arrest (CA) have focused on post-CA brain injury and myocardial dysfunction, the renal dysfunction and acute kidney injury (AKI) in other critical illnesses after CA have not been well described. This study was designed to assess AKI with renal Doppler and novel AKI biomarkers in a swine model of ventricular fibrillation cardiac arrest (VFCA).

Methods:

Thirty healthy piglets were divided into VFCA group (n = 22) and Sham group (n = 8) in a blinded manner. Mean arterial pressure, heart rate, and cardiac output were recorded continuously. Cardiac arrest (CA) was induced by programmed electric stimulation in the VFCA group, and then cardiopulmonary resuscitation was performed. Twenty piglets returned of spontaneous circulation (ROSC) and received intensive care. Blood and urine samples were collected for AKI biomarkers testing, and Color Doppler flow imaging was performed at baseline, 6 h, 12 h, and 24 h, respectively after ROSC. At ROSC 24 h, the animals were sacrificed and a semi-quantitative evaluation of pathologic kidney injury was performed.

Results:

In the VFCA group, corrected resistive index (cRI) increased from 0.47 ± 0.03 to 0.64 ± 0.06, and pulsatility index (PI) decreased from 0.82 ± 0.03 to 0.68 ± 0.04 after ROSC. Cystatin C (CysC) in both serum and urine samples increased at ROSC 6 h, but neutrophil gelatinase-associated lipocalin (NGAL) in serum increased to 5.34 ± 1.68 ng/ml at ROSC 6 h, and then decreased to 3.16 ± 0.69 ng/ml at ROSC 24 h while CysC increasing constantly. According to the renal histopathology, 18 of 20 animals suffered from kidney injury. The grade of renal injury was highly correlated with RI, cRI, NGAL, and CysC. Linear regression equation was established: Grade of renal injury = 0.002 × serum CysC + 6.489 × PI + 4.544 × cRI – 8.358 (r² = 0.698, F = 18.506, P < 0.001).

Conclusions:

AKI is common in post-CA syndrome. Renal Doppler and novel AKI biomarkers in serum and urine are of significant importance as early predictors of post-CA AKI.

Renoprotective approaches and strategies in acute kidney injury

Acute kidney injury (AKI) is a major renal disease associated with high mortality rate and increasing prevalence. Decades of research have suggested numerous chemical and biological agents with beneficial effects in AKI. In addition, cell therapy and molecular targeting have been explored for reducing kidney tissue damage and promoting kidney repair or recovery from AKI. Mechanistically, these approaches may mitigate oxidative stress, inflammation, cell death, and mitochondrial and other organellar damage, or activate cytoprotective mechanisms such as autophagy and pro-survival factors. However, none of these findings has been successfully translated into clinical treatment of AKI. In this review, we analyze these findings and propose experimental strategies for the identification of renoprotective agents or methods with clinical potential. Moreover, we propose the consideration of combination therapy by targeting multiple targets in AKI.

Improved renal ischemia tolerance in females influences kidney transplantation outcomes

Experimentally, females show an improved ability to recover from ischemia-reperfusion injury (IRI) compared with males; however, this sex-dependent response is less established in humans. Here, we developed a series of murine renal ischemia and transplant models to investigate sex-specific effects on recovery after IRI. We found that IRI tolerance is profoundly increased in female mice compared with that observed in male mice and discovered an intermediate phenotype after neutering of either sex. Transplantation of adult kidneys from either sex into a recipient of the opposite sex followed by ischemia at a remote time resulted in ischemia recovery that reflected the sex of the recipient, not the donor, revealing that the host sex determines recovery. Likewise, renal IRI was exacerbated in female estrogen receptor α-KO mice, while female mice receiving supplemental estrogen before ischemia were protected. We examined data from the United Network for Organ Sharing (UNOS) to determine whether there is an association between sex and delayed graft function (DGF) in patients who received deceased donor renal transplants. A multivariable logistic regression analysis determined that there was a greater association with DGF in male recipients than in female recipients. Together, our results demonstrate that sex affects renal IRI tolerance in mice and humans and indicate that estrogen administration has potential as a therapeutic intervention to clinically improve ischemia tolerance.

The Protective Effect of γ-aminobutyric Acid on Kidney Injury Induced by Renal Ischemia-reperfusion in Ovariectomized Estradiol-treated Rats

Background:

Renal ischemia-reperfusion injury (IRI) is one of the most important causes of kidney injury, which is possibly gender-related. This study was designed to investigate the role of γ-aminobutyric acid (GABA) against IRI in ovariectomized estradiol-treated rats.

Methods:

Thirty-five ovariectomized Wistar rats were used in six experimental groups. The first three groups did not subject to estradiol treatment and assigned as sham-operated, control, and GABA-treated groups. GABA (50 μmol/kg) and saline were injected in the treated and control groups 30 min before the surgery, respectively. The second three groups received the same treatments but received estradiol valerate (500 μg/kg, intramuscularly) 3 days prior to the surgery. The IRI was induced in the control and treated groups by clamping the renal artery for 45 min and then 24 h of reperfusion. All animals were sacrificed for the measurements.

Results:

The serum levels of creatinine and blood urea nitrogen, kidney weight, and kidney tissue damage score significantly increased in the IRI rats (P < 0.05). GABA significantly decreased the aforementioned parameters (P < 0.05). The uterus weight increased significantly in rats that received estradiol (P < 0.05). Serum and kidney levels of nitrite (nitric oxide metabolite) did not alter significantly. Serum level of malondialdehyde increased significantly in the ovariectomized rats exposed to IRI (P < 0.05).

Conclusions:

It seems that GABA improved IRI in ovariectomized rats. Estradiol was also nephroprotective against IRI. However, co-administration of estradiol and GABA could not protect the kidney against IRI.

Effect of gender on outcome of out of hospital cardiac arrest in the Resuscitation Outcomes Consortium

INTRODUCTION

This study examined the relationship between gender and outcomes of non-traumatic out-of-hospital cardiac arrest (OHCA).

METHODS

All eligible, consecutive, non-traumatic Emergency Medical Services (EMS) treated OHCA patients in the Resuscitation Outcomes Consortium between December 2005 and May 2007. Patient age was analyzed as a continuous variable and stratified in two age cohorts: 15-45 and >55 years of age (yoa). Unadjusted and adjusted (based on Utstein characteristics) chi square tests and logistic regression models were employed to examine the relationship between gender, age, and survival outcomes.

RESULTS

This study enrolled 14,690 patients: of which 36.4% were women with a mean age of 68.3 and 63.6% of them men with a mean age of 64.2. Women survived to hospital discharge less often than men (6.4% vs. 9.1%, p<0.001); the unadjusted OR was 0.69, 95%CI: 0.60, 0.77 whereas when adjusted for all Utstein predictors the difference was not significant (OR: 1.16, 95%CI: 0.98, 1.36, p=0.07). The adjusted survival rate for younger women (15-45 yoa) was 11.1% vs. 9.8% for younger men (OR: 1.66, 95%CI: 1.04, 2.64, p=0.03) but no difference in discharge rates was observed in the >55 cohort (OR: 0.94, 95%CI: 0.78, 1.15, p=0.57).

CONCLUSIONS

Women who suffer OHCAs have lower rates of survival and have unfavourable Utstein predictors. When survival is adjusted for these predictors survival is similar between men and women except in younger women suggesting that age modifies the association of gender and survival from OHCA; a result that supports a protective hormonal effect among premenopausal women.

Estrogen administered after cardiac arrest and cardiopulmonary resuscitation ameliorates acute kidney injury in a sex- and age-specific manner

Introduction

There is a sex difference in the risk of ischemic acute kidney injury (AKI), and estrogen mediates the protective effect of female sex. We previously demonstrated that preprocedural chronic restoration of physiologic estrogen to ovariectomized female mice ameliorated AKI after cardiac arrest and cardiopulmonary resuscitation (CA/CPR). In the present study, we hypothesized that male mice and aged female mice would benefit from estrogen administration after CA/CPR. We tested the effect of estrogen in a clinically relevant manner by administrating it after CA/CPR.

Methods

CA/CPR was performed in young (10–15 weeks), middle-aged (43–48 weeks), and aged (78–87 weeks) C57BL/6 male and female mice. Mice received intravenous 17β-estradiol or vehicle 15 min after resuscitation. Serum chemistries and unbiased stereological assessment of renal injury were completed 24 h after CA. Regional renal cortical blood flow was measured by a laser Doppler, and renal levels of estrogen receptor alpha (ERα) and G protein-coupled estrogen receptor (GPER) were evaluated with immunoblotting.

Results

Post-arrest estrogen administration reduced injury in young males without significant changes in renal blood flow (percentage reduction compared with vehicle: serum urea nitrogen, 30 %; serum creatinine (sCr), 41 %; volume of necrotic tubules (VNT), 31 %; P < 0.05). In contrast, estrogen did not affect any outcomes in young females. In aged mice, estrogen significantly reduced sCr (80 %) and VNT (73 %) in males and VNT (51 %) in females. Serum estrogen levels in aged female mice after CA/CPR were the same as levels in male mice. With age, renal ERα was upregulated in females.

Conclusions

Estrogen administration after resuscitation from CA ameliorates renal injury in young males and aged mice in both sexes. Because injury was small, young females were not affected. The protective effect of exogenous estrogen may be detectable with loss of endogenous estrogen in aged females and could be mediated by differences in renal ERs. Post-arrest estrogen administration is renoprotective in a sex- and age-dependent manner.

G Protein-Coupled Estrogen Receptor 1 Mediates Acute Estrogen-Induced Cardioprotection via MEK/ERK/GSK-3β Pathway after Ischemia/Reperfusion

Three types of estrogen receptors (ER) exist in the heart, Esr1, Esr2 and the G protein-coupled estrogen receptor 1, Gper1. However, their relative importance in mediating estrogen protective action is unknown. We found that, in the male mouse ventricle, Gper1 transcripts are three- and seventeen-fold more abundant than Esr1 and Esr2 mRNAs, respectively. Analysis of the three ER knockouts (Esr1^-/-, Esr2^-/- and Gper1^-/-) showed that only the Gper1^-/- hearts lost their ability to be protected by 40 nM estrogen as measured by heart function, infarct size and mitochondrial Ca²⁺ overload, an index of mitochondrial permeability transition pore (mPTP) activity. Analysis of Akt, ERK_1/2 and GSK-3β salvage kinases uncovered Akt and ERK_1/2 transient activation by estrogen whose phosphorylation increased during the first 5 min of non-ischemic perfusion. All these increase in phosphorylation effects were abrogated in Gper1^-/-. Inhibition of MEK_1/2/ERK_1/2 (1 μM U0126) and PI-3K/Akt (10 μM LY294002) signaling showed that the MEK_1/2/ERK_1/2 pathway via GSK-3β exclusively was responsible for cardioprotection as an addition of U0126 prevented estrogen-induced GSK-3β increased phosphorylation, resistance to mitochondrial Ca²⁺-overload, functional recovery and protection against infarction. Further, inhibiting PKC translocation (1 μM chelerythrin-chloride) abolished estrogen-induced cardioprotection. These data indicate that estrogen-Gper1 acute coupling plays a key role in cardioprotection against ischemia/reperfusion injury in male mouse via a cascade involving PKC translocation, ERK_1/2/GSK-3β phosphorylation leading to the inhibition of the mPTP opening.

What have we learned about GPER function in physiology and disease from knockout mice?

Estrogens, predominantly 17β-estradiol, exert diverse effects throughout the body in both normal and pathophysiology, during development and in reproductive, metabolic, endocrine, cardiovascular, nervous, musculoskeletal and immune systems. Estrogen and its receptors also play important roles in carcinogenesis and therapy, particularly for breast cancer. In addition to the classical nuclear estrogen receptors (ERα and ERβ) that traditionally mediate predominantly genomic signaling, the G protein-coupled estrogen receptor GPER has become recognized as a critical mediator of rapid signaling in response to estrogen. Mouse models, and in particular knockout (KO) mice, represent an important approach to understand the functions of receptors in normal physiology and disease. Whereas ERα KO mice display multiple significant defects in reproduction and mammary gland development, ERβ KO phenotypes are more limited, and GPER KO exhibit no reproductive deficits. However, the study of GPER KO mice over the last six years has revealed that GPER deficiency results in multiple physiological alterations including obesity, cardiovascular dysfunction, insulin resistance and glucose intolerance. In addition, the lack of estrogen-mediated effects in numerous tissues of GPER KO mice, studied in vivo or ex vivo, including those of the cardiovascular, endocrine, nervous and immune systems, reveals GPER as a genuine mediator of estrogen action. Importantly, GPER KO mice have also demonstrated roles for GPER in breast carcinogenesis and metastasis. In combination with the supporting effects of GPER-selective ligands and GPER knockdown approaches, GPER KO mice demonstrate the therapeutic potential of targeting GPER activity in diseases as diverse as obesity, diabetes, multiple sclerosis, hypertension, atherosclerosis, myocardial infarction, stroke and cancer.

Preventive role of estradiol on kidney injury induced by renal ischemia-reperfusion in male and female rats

Background:

Renal ischemia-reperfusion (RIR) is the main cause of renal failure. The incidence of RIR injury seems to be gender-related due to female sex hormone; estrogen. This study was designed to investigate the protective role of estrogen against RIR injury in male and ovariectomized female rats.

Methods:

Thirty-nine Wistar rats were used in this study as male and ovariectomized female rats in the sham-operated, RIR, and estradiol-treated plus RIR groups. The RIR was induced by clamping the renal vessels for 45 min and then 24 h of reperfusion. All animals finally were sacrificed for the measurements.

Results:

The serum levels of creatinine and blood urea nitrogen and kidney tissue damage score significantly increased in both male and female RIR rats (P < 0.05). Estradiol however significantly attenuated theses parameters (P < 0.05) toward normal levels in female (P < 0.05), but not in male rats. Kidney weight increased in both genders and estradiol intensified it in the male rats (P < 0.05). Uterus weight was increased by estradiol in female rats (P < 0.05) and testis weight did not alter in male rats.

Conclusions:

Estradiol demonstrated a protective role against RIR injury in female rats; however, estradiol as an antioxidant could not protect the male kidney from RIR injury.

Sex- and gender-specific research priorities in cardiovascular resuscitation: proceedings from the 2014 Academic Emergency Medicine Consensus Conference Cardiovascular Resuscitation Research Workgroup

Significant sex and gender differences in both physiology and psychology are readily acknowledged between men and women; however, data are lacking regarding differences in their responses to injury and treatment and in their ultimate recovery and survival. These variations remain particularly poorly defined within the field of cardiovascular resuscitation. A better understanding of the interaction between these important factors may soon allow us to dramatically improve outcomes in disease processes that currently carry a dismal prognosis, such as sudden cardiac arrest. As part of the 2014 Academic Emergency Medicine consensus conference "Gender-Specific Research in Emergency Medicine: Investigate, Understand, and Translate How Gender Affects Patient Outcomes," our group sought to identify key research questions and knowledge gaps pertaining to both sex and gender in cardiac resuscitation that could be answered in the near future to inform our understanding of these important issues. We combined a monthly teleconference meeting of interdisciplinary stakeholders from largely academic institutions with a focused interest in cardiovascular outcomes research, an extensive review of the existing literature, and an open breakout session discussion on the recommendations at the consensus conference to establish a prioritization of the knowledge gaps and relevant research questions in this area. We identified six priority research areas: 1) out-of-hospital cardiac arrest epidemiology and outcome, 2) customized resuscitation drugs, 3) treatment role for sex steroids, 4) targeted temperature management and hypothermia, 5) withdrawal of care after cardiac arrest, and 6) cardiopulmonary resuscitation training and implementation. We believe that exploring these key topics and identifying relevant questions may directly lead to improved understanding of sex- and gender-specific issues seen in cardiac resuscitation and ultimately improved patient outcomes.

Estrogen-mediated renoprotection following cardiac arrest and cardiopulmonary resuscitation is robust to GPR30 gene deletion

Introduction

Acute kidney injury is a serious,sexually dimorphic perioperative complication, primarily attributed to hypoperfusion. We previously found that estradiol is renoprotective after cardiac arrest and cardiopulmonary resuscitation in ovariectomized female mice. Additionally, we found that neither estrogen receptor alpha nor beta mediated this effect. We hypothesized that the G protein estrogen receptor (GPR30) mediates the renoprotective effect of estrogen.

Methods

Ovariectomized female and gonadally intact male wild-type and GPR30 gene-deleted mice were treated with either vehicle or 17β-estradiol for 7 days, then subjected to cardiac arrest and cardiopulmonary resuscitation. Twenty four hours later, serum creatinine and urea nitrogen were measured, and histologic renal injury was evaluated by unbiased stereology.

Results

In both males and females, GPR30 gene deletion was associated with reduced serum creatinine regardless of treatment. Estrogen treatment of GPR30 gene-deleted males and females was associated with increased preprocedural weight. In ovariectomized female mice, estrogen treatment did not alter resuscitation, but was renoprotective regardless of GPR30 gene deletion. In males, estrogen reduced the time-to-resuscitate and epinephrine required. In wild-type male mice, serum creatinine was reduced, but neither serum urea nitrogen nor histologic outcomes were affected by estrogen treatment. In GPR30 gene-deleted males, estrogen did not alter renal outcomes. Similarly, renal injury was not affected by G1 therapy of ovariectomized female wild-type mice.

Conclusion

Treatment with 17β-estradiol is renoprotective after whole-body ischemia-reperfusion in ovariectomized female mice irrespective of GPR30 gene deletion. Treatment with the GPR30 agonist G1 did not alter renal outcome in females. We conclude GPR30 does not mediate the renoprotective effect of estrogen in ovariectomized female mice. In males, estrogen therapy was not renoprotective. Estrogen treatment of GPR30 gene-deleted mice was associated with increased preprocedural weight in both sexes. Of significance to further investigation, GPR30 gene deletion was associated with reduced serum creatinine, regardless of treatment.

Serum estradiol levels predict survival and acute kidney injury in patients with septic shock--a prospective study

Sex hormones have diverse immunomodulatory effects that may be involved in the pathogenesis of sepsis. However, the roles of serum sex hormones in predicting outcomes and the severity of organ dysfunction, especially acute kidney injury (AKI), in septic shock patients remains controversial. We prospectively enrolled 107 clinically diagnosed pneumonia-related septic shock patients and serum sex hormone levels were measured on the day of shock onset. The aim of the present study was to investigate the predictive values of serum sex hormones levels for 28-day mortality and organs dysfunction, especially AKI. Compared with survivors, serum levels of progesterone (p<0.001) and estradiol (p<0.001) were significantly elevated in non-survivors. In multivariate Cox regression analysis, serum level of estradiol >40 pg/mL (p = 0.047) and APACHE II score ≥25 (p = <0.001) were found to be independent predictors of day 28 mortality. Inclusion of estradiol levels further enhanced the ability of APACHE II scores to predict survival in patients with high mortality risk. A serum level of estradiol >40 pg/mL was also an independent predictor of concomitant AKI (p = 0.002) and correlated well with severity of renal dysfunction using RIFLE classification. Elevated serum estradiol levels also predicted the development of new AKI within 28 days of shock onset (p = 0.013). In conclusion, serum estradiol levels appear to have value in predicting 28-day mortality in septic shock patients. Increased serum estradiol levels are associated with higher severity of concomitant AKI and predict development of new AKI.

Extracranial hypothermia during cardiac arrest and cardiopulmonary resuscitation is neuroprotective in vivo

There is increasing evidence that ischemic brain injury is modulated by peripheral signaling. Peripheral organ ischemia can induce brain inflammation and injury. We therefore hypothesized that brain injury sustained after cardiac arrest (CA) is influenced by peripheral organ ischemia and that peripheral organ protection can reduce brain injury after CA and cardiopulmonary resuscitation (CPR). Male C57Bl/6 mice were subjected to CA/CPR. Brain temperature was maintained at 37.5°C ± 0.0°C in all animals. Body temperature was maintained at 35.1°C ± 0.1°C (normothermia) or 28.8°C ± 1.5°C (extracranial hypothermia [ExHy]) during CA. Body temperature after resuscitation was maintained at 35°C in all animals. Behavioral testing was performed at 1, 3, 5, and 7 days after CA/CPR. Either 3 or 7 days after CA/CPR, blood was analyzed for serum urea nitrogen, creatinine, alanine aminotransferase, aspartate aminotransferase, and interleukin-1β; mice were euthanized; and brains were sectioned. CA/CPR caused peripheral organ and brain injury. ExHy animals experienced transient reduction in brain temperature after resuscitation (2.1°C ± 0.5°C for 4 minutes). Surprisingly, ExHy did not change peripheral organ damage. In contrast, hippocampal injury was reduced at 3 days after CA/CPR in ExHy animals (22.4% ± 6.2% vs. 45.7% ± 9.1%, p=0.04, n=15/group). This study has two main findings. Hypothermia limited to CA does not reduce peripheral organ injury. This unexpected finding suggests that after brief ischemia, such as during CA/CPR, signaling or events after reperfusion may be more injurious than those during the ischemic period. Second, peripheral organ hypothermia during CA reduces hippocampal injury independent of peripheral organ protection. While it is possible that this protection is due to subtle differences in brain temperature during early reperfusion, we speculate that additional mechanisms may be involved. Our findings add to the growing understanding of brain-body cross-talk by suggesting that peripheral interventions can protect the brain even if peripheral organ injury is not altered.

Anatomical location and redistribution of G protein-coupled estrogen receptor-1 during the estrus cycle in mouse kidney and specific binding to estrogens but not aldosterone

Prior studies have linked renoprotective effects of estrogens to G-protein-coupled estrogen receptor-1 (GPER-1) and suggest that aldosterone may also activate GPER-1. Here, the role of GPER-1 in murine renal tissue was further evaluated by examining its anatomical distribution, subcellular distribution and steroid binding specificity. Dual immunofluorescent staining using position-specific markers showed that GPER-1 immunoreactivity primarily resides in distal convoluted tubules and the Loop of Henle (stained with Tamm-Horsfall Protein-1). Lower GPER-1 expression was observed in proximal convoluted tubules marked with megalin, and GPER-1 was not detected in collecting ducts. Plasma membrane fractions prepared from whole kidney tissue or HEK293 cells expressing recombinant human GPER-1 (HEK-GPER-1) displayed high-affinity, specific [(3)H]-17β-estradiol ([(3)H]-E2) binding, but no specific [(3)H]-aldosterone binding. In contrast, cytosolic preparations exhibited specific binding to [(3)H]-aldosterone but not to [(3)H]-E2, consistent with the subcellular distribution of GPER-1 and mineralocorticoid receptor (MR) in these preparations. Aldosterone and MR antagonists, spironolactone and eplerenone, failed to compete for specific [(3)H]-E2 binding to membranes of HEK-GPER-1 cells. Furthermore, aldosterone did not increase [(35)S]-GTP-γS binding to membranes of HEK-GPER-1 cells, indicating that it is not involved in G protein signaling mediated through GPER-1. During the secretory phases of the estrus cycle, GPER-1 is upregulated on cortical epithelia and localized to the basolateral surface during proestrus and redistributed intracellularly during estrus. GPER-1 is down-modulated during luteal phases of the estrus cycle with significantly less receptor on the surface of renal epithelia. Our results demonstrate that GPER-1 is associated with specific estrogen binding and not aldosterone binding and that GPER-1 expression is modulated during the estrus cycle which may suggest a physiological role for GPER-1 in the kidney during reproduction.