Molecular mechanisms and therapeutic interventions in acute kidney injury: a literature review

Acute kidney injury (AKI) is a clinical challenge characterized by elevated morbidity and a substantial impact on individual health and socioeconomic factors. A comprehensive examination of the molecular pathways behind AKI is essential for its prevention and management. In recent years, vigorous research in the domain of AKI has concentrated on pathophysiological characteristics, early identification, and therapeutic approaches across many aetiologies and highlighted the principal themes of oxidative stress, inflammatory response, apoptosis, necrosis, and immunological response. This review comprehensively reviewed the molecular mechanisms underlying AKI, including oxidative stress, inflammatory pathways, immune cell-mediated injury, activation of the renin-angiotensin-aldosterone (RAAS) system, mitochondrial damage and autophagy, apoptosis, necrosis, etc. Inflammatory pathways are involved in the injuries in all four structural components of the kidney. We also summarized therapeutic techniques and pharmacological agents associated with the aforementioned molecular pathways. This work aims to clarify the molecular mechanisms of AKI thoroughly, offer novel insights for further investigations of AKI, and facilitate the formulation of efficient therapeutic methods to avert the progression of AKI.

Integrated Analysis of Gene Expression and Immune Cell Infiltration Reveals Dysregulated Genes and miRNAs in Acute Kidney Injury

Acute Kidney Injury (AKI) is a multifaceted condition characterised by rapid deterioration of renal function, often precipitated by diverse etiologies. A comprehensive understanding of the molecular underpinnings of AKI is pivotal for identifying potential diagnostic markers and therapeutic targets. This study utilised bioinformatics to elucidate gene expression and immune infiltration in AKI. Publicly available mRNA and miRNA datasets were harnessed to discern differentially expressed genes (DEGs) and miRNAs in AKI. The CIBERSORT algorithm was employed to quantify immune cell infiltration in AKI samples. Functional enrichment analyses were conducted to unravel the implicated biological processes. Furthermore, the expression of identified genes and miRNAs was validated by quantitative real-time PCR in an AKI model. Our study revealed significant dysregulation of three genes (Aspn, Clec2h, Tmigd1) and two miRNAs (mmu-miR-21a-3p, mmu-miR-223-3p) in AKI, each with p < 0.0001. These molecular markers are implicated in immune responses, tissue remodelling, and inflammation. We observed notable disturbances in specific immune cells, including activated and immature dendritic cells, M1 macrophages, and subsets of T cells (Treg, Th1, Th17). These alterations correlated significantly with AKI pathology, with dendritic cells and M1 macrophages showing p < 0.01, and T cell subsets demonstrating p < 0.05. These results highlight the intricate involvement of the immune system in AKI and indicate significant enrichment of pathways related to immune response, inflammation, and tissue remodelling, pointing to their pivotal roles in AKI pathophysiology. Our study underscored the significance of immune cell infiltration and dysregulated gene and miRNA expression in AKI. The identified genes (Clec2h, Aspn, and Tmigd1) and miRNAs (mmu-miR-21a-3p and mmu-miR-223-3p) offer potential diagnostic markers and therapeutic avenues for AKI. Subsequent investigations targeting these genes and miRNAs, along with the elucidated pathways, may augment the clinical management and outcomes for AKI patients.

Association Between the Aggregate Index of Systemic Inflammation and Clinical Outcomes in Patients with Acute Myocardial Infarction: A Retrospective Study

Purpose

The Aggregate Index of Systemic Inflammation (AISI) has emerged as a novel marker for inflammation and prognosis, but its role in patients with acute myocardial infarction has not been studied. Therefore, this study aimed to investigate the impact of different AISI levels on the clinical outcomes of patients with acute myocardial infarction.

Patients and Methods

This study was a retrospective study, including 1044 patients with acute myocardial infarction (AMI) who were treated at the Fujian Medical University Affiliated Union Hospital, China from May 2017 to December 2022. The patients were divided into high and low AISI groups based on the median value (Q1 Group, ≤ 416.15, n=522; Q2 Group, ≥ 416.16, n=522), and the differences in baseline characteristics and clinical outcomes between the two groups were analyzed. The primary outcome included major adverse cardiovascular and cerebrovascular events (MACCEs), while the secondary outcomes included contrast-induced nephropathy (CIN) risk and all-cause rehospitalization rate.

Results

The findings of the single-factor analysis suggest that a significant association between high AISI levels and the occurrence of MACCEs in AMI patients. After adjusting for confounding factors, the results indicated that compared to Q1, patients in the Q2 group had a higher risk of all-cause mortality [adjusted odds ratio (aOR) 4.64; 95% CI 1.37-15.72; p=0.032], new-onset atrial fibrillation (aOR 1.75; 95% CI 1.02-3.00; p=0.047), and CIN (aOR 1.75; 95% CI 1.02-3.01; p=0.043), with all differences being statistically significant.

Conclusion

In the population of AMI patients, an elevated AISI level is significantly associated with an increased risk of cardiovascular death and can serve as an early marker for adverse prognosis.

Characteristics, Risk Factors, and Outcomes in Acute Kidney Injury Patients: A Retrospective Cross-Sectional Study, Palestine

BACKGROUND

Acute kidney injury (AKI) is a major medical problem affecting patients' quality of life and healthcare costs.

OBJECTIVES

This study evaluated the severity, risk factors, and outcomes of patients diagnosed with acute kidney injury (AKI), including community-acquired AKI (CA-AKI) and hospital-acquired AKI (HA-AKI), who were admitted to tertiary institutions in Palestine.

METHODS

This retrospective cross-sectional study was conducted at multiple tertiary care hospitals in Palestine by reviewing patient charts from January 2020 to March 2023. The study included all patients aged ≥18 years who were admitted to the hospital and diagnosed with AKI at admission (CA-AKI) or who developed AKI 48 hours after admission (HA-AKI). Patients with incomplete medical records and those with no reported creatinine levels during their stay, pregnant women, kidney transplant patients, and end-stage renal disease patients were excluded. Data were analyzed using SPSS v22.0. The incidence of AKI in each group was compared using the chi-squared test.

RESULTS

This study included 259 participants. HA-AKI was present in 27.3% of the patients, while CA-AKI was 72.7%. The most common stage among patients was stage 3 (55.7%, HA-AKI) (42.9%, CA-AKI), and the most common comorbidity contributing to AKI was CKD. NSAIDs, ACE-I/ARBs, and DIURETICs were the most nephrotoxic drugs contributing to AKI. Patients with hyperphosphatemia, hyperkalemia, severe metabolic acidosis, or stage 3 AKI require renal replacement therapy. In addition, our findings revealed a significant association among AKI mortality, age, and heart disease.

CONCLUSION

CA-AKI was more prevalent than HA-AKI in Palestinian patients admitted for AKI. Risk factors for AKI included diabetes, CKD, and medications (antibiotics, NSAID, diuretics, and ACE-I/ARB). Preventive measures, medication management, and disease state management are necessary to minimize AKI during hospital admission or in the community.

Gut microbiota and acute kidney injury: immunological crosstalk link

The gut microbiota, often called the "forgotten organ," plays a crucial role in bidirectional communication with the host for optimal physiological function. This communication helps regulate the host's immunity and metabolism positively and negatively. Many factors influence microbiota homeostasis and subsequently lead to an immune system imbalance. The correlation between an unbalanced immune system and acute diseases such as acute kidney injury is not fully understood, and the role of gut microbiota in disease pathogenesis is still yet uncovered. This review summarizes our understanding of gut microbiota, focusing on the interactions between the host's immune system and the microbiome and their impact on acute kidney injury.

Natural products applied in acute kidney injury treatment: polymer matters

Acute kidney injury (AKI) is a global health threat due to its high morbidity and mortality. There is still a lack of effective therapeutic methods to deal with AKI clinically. Natural products with outstanding accessibility and bioactivity are potential candidates for AKI treatment. Natural product-based prodrugs or nano-structures with improved properties are frequently fabricated for maximizing bioavailability and decreasing side effects, in which natural polymers are selected as carriers, or natural drugs are loaded as cargos on designed polymers. In this review, the etiologies of AKI are briefly presented, and emerging natural products delivered rationally for AKI therapy, as either carriers or cargos, are both introduced. Moreover, the challenges of the future development of nature-based nanodrugs or prodrugs for AKI have also been discussed.

Acute Kidney Injury: Definition, Management, and Promising Therapeutic Target

Acute kidney injury (AKI) is caused by a sudden loss of renal function, resulting in the build-up of waste products and a significant increase in mortality and morbidity. It is commonly diagnosed in critically ill patients, with its occurrence estimated at up to 50% in patients hospitalized in the intensive critical unit. Despite ongoing efforts, the death rate associated with AKI has remained high over the past half-century. Thus, it is critical to investigate novel therapy options for preventing the epidemic. Many studies have found that inflammation and Toll-like receptor-4 (TLR-4) activation have a significant role in the pathogenesis of AKI. Noteworthy, challenges in the search for efficient pharmacological therapy for AKI have arisen due to the multifaceted origin and complexity of the clinical history of people with the disease. This article focuses on kidney injury's epidemiology, risk factors, and pathophysiological processes. Specifically, it focuses on the role of TLRs especially type 4 in disease development.

Engineered nanodrug targeting oxidative stress for treatment of acute kidney injury

Acute kidney injury (AKI) is a clinical syndrome characterized by a rapid decline in renal function, and is associated with a high risk of death. Many pathological changes happen in the process of AKI, including crucial alterations to oxidative stress levels. Numerous efforts have thus been made to develop effective medicines to scavenge excess reactive oxygen species (ROS). However, researchers have encountered several significant challenges, including unspecific biodistribution, high biotoxicity, and in vivo instability. To address these problems, engineered nanoparticles have been developed to target oxidative stress and treat AKI. This review thoroughly discusses the methods that empower nanodrugs to specifically target the glomerular filtration barrier and presents the latest achievements in engineering novel ROS-scavenging nanodrugs in clustered sections. The analysis of each study's breakthroughs and imperfections visualizes the progress made in developing effective nanodrugs with specific biodistribution and oxidative stress-targeting capabilities. This review fills the blank of a comprehensive outline over current progress in applying nanotechnology to treat AKI, providing potential insights for further research.

The predictive value of hematological inflammatory markers for acute kidney injury and mortality in adults with hemophagocytic Lymphohistiocytosis: A retrospective analysis of 585 patients

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is a rare immunological hyperactivation-related disease with a high mortality rate. The purpose of this study was to examine the relationship between complete blood count parameters and the occurrence of acute kidney injury (AKI) and mortality in patients with HLH.

METHODS

We included 585 adult patients with HLH. Logistic regression models for AKI and 28-day mortality were developed.

RESULTS

Multivariate logistic regression models revealed that hemoglobin (HB) ≤ 7.3 g/dl (adjusted OR, 1.651; 95% CI, 1.044-2.612), hemoglobin-to-red blood cell distribution width ratio (HRR) < 0.49 (adjusted OR, 1.692), neutrophil-to-lymphocyte ratio (NLR) ≥ 3.15 (adjusted OR, 1.697), and neutrophil-to-lymphocyte-platelet ratio (NLPR) ≥ 11.0 (adjusted OR, 1.608) were independent risk factors for the development of AKI. Moreover, lower platelet levels (31 × 109/L < platelets < 84 × 109/L, adjusted OR, 2.133; platelets ≤ 31 × 109/L, adjusted OR, 3.545) and higher red blood cell distribution width-to-platelet ratio (RPR) levels (0.20 < RPR < 0.54, adjusted OR, 2.595; RPR ≥ 0.54, adjusted OR, 4.307), lymphocytes ≤ 0.34 × 109/L (adjusted OR, 1.793), NLPR ≥ 11.0 (adjusted OR, 2.898), and the aggregate index of systemic inflammation (AISI) ≤ 7 (adjusted OR,1.778) were also independent risk factors for 28-day mortality. Furthermore, patients with AKI had a worse prognosis than those without AKI (P < 0.05).

CONCLUSION

In patients with HLH, hematological parameters are of great value for the early identification of patients at high risk of AKI and 28-day mortality.

Single-cell RNA sequencing reveals the transcriptomic landscape of kidneys in patients with ischemic acute kidney injury

BACKGROUND

Ischemic acute kidney injury (AKI) is a common syndrome associated with considerable mortality and healthcare costs. Up to now, the underlying pathogenesis of ischemic AKI remains incompletely understood, and specific strategies for early diagnosis and treatment of ischemic AKI are still lacking. Here, this study aimed to define the transcriptomic landscape of AKI patients through single-cell RNA sequencing (scRNA-seq) analysis in kidneys.

METHODS

In this study, scRNA-seq technology was applied to kidneys from two ischemic AKI patients, and three human public scRNA-seq datasets were collected as controls. Differentially expressed genes (DEGs) and cell clusters of kidneys were determined. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, as well as the ligand-receptor interaction between cells, were performed. We also validated several DEGs expression in kidneys from human ischemic AKI and ischemia/reperfusion (I/R) injury induced AKI mice through immunohistochemistry staining.

RESULTS

15 distinct cell clusters were determined in kidney from subjects of ischemic AKI and control. The injured proximal tubules (PT) displayed a proapoptotic and proinflammatory phenotype. PT cells of ischemic AKI had up-regulation of novel pro-apoptotic genes including USP47 , RASSF4 , EBAG9 , IER3 , SASH1 , SEPTIN7 , and NUB1 , which have not been reported in ischemic AKI previously. Several hub genes were validated in kidneys from human AKI and renal I/R injury mice, respectively. Furthermore, PT highly expressed DEGs enriched in endoplasmic reticulum stress, autophagy, and retinoic acid-inducible gene I (RIG-I) signaling. DEGs overexpressed in other tubular cells were primarily enriched in nucleotide-binding and oligomerization domain (NOD)-like receptor signaling, estrogen signaling, interleukin (IL)-12 signaling, and IL-17 signaling. Overexpressed genes in kidney-resident immune cells including macrophages, natural killer T (NKT) cells, monocytes, and dendritic cells were associated with leukocyte activation, chemotaxis, cell adhesion, and complement activation. In addition, the ligand-receptor interactions analysis revealed prominent communications between macrophages and monocytes with other cells in the process of ischemic AKI.

CONCLUSION

Together, this study reveals distinct cell-specific transcriptomic atlas of kidney in ischemic AKI patients, altered signaling pathways, and potential cell-cell crosstalk in the development of AKI. These data reveal new insights into the pathogenesis and potential therapeutic strategies in ischemic AKI.

Apocynin abrogates methotrexate-induced nephrotoxicity: role of TLR4/NF-κB-p65/p38-MAPK, IL-6/STAT-3, PPAR-γ, and SIRT1/FOXO3 signaling pathways

The present study was designed to evaluate the potential renoprotective impacts of apocynin (APC) against nephrotoxicity induced by methotrexate (MTX) administration. To fulfill this aim, rats were allocated into four groups: control; APC (100 mg/kg/day; orally); MTX (20 mg/kg; single intraperitoneal dose at the end of the 5th day of the experiment); and APC +MTX (APC was given orally for 5 days before and 5 days after induction of renal toxicity by MTX). On the 11th day, samples were collected to estimate kidney function biomarkers, oxidative stress, pro-inflammatory cytokines, and other molecular targets. Compared to the MTX control group, treatment with APC significantly decreased urea, creatinine, and KIM-1 levels and improved kidney histological alterations. Furthermore, APC restored oxidant/antioxidant balance, as evidenced by a remarkable alleviation of MDA, GSH, SOD, and MPO levels. Additionally, the iNOS, NO, p-NF-κB-p65, Ace-NF-κB-p65, TLR4, p-p38-MAPK, p-JAK1, and p-STAT-3 expressions were reduced, while the IκBα, PPAR-γ, SIRT1, and FOXO3 expressions were significantly increased. In NRK-52E cells, MTX-induced cytotoxicity was protected by APC in a concentration-dependent manner. In addition, increased expression of p-STAT-3 and p-JAK1/2 levels were reduced in MTX-treated NRK-52E cells by APC. The in vitro experiments revealed that APC-protected MTX-mediated renal tubular epithelial cells were damaged by inhibiting the JAK/STAT3 pathway. Besides, our in vivo and in vitro results were confirmed by predicting computational pharmacology results using molecular docking and network pharmacology analysis. In conclusion, our findings proved that APC could be a good candidate for MTX-induced renal damage due to its strong antioxidative and anti-inflammatory bioactivities.

Development of Cell Therapies for Renal Disease and Regenerative Medicine

The incidence of renal disease is gradually increasing worldwide, and this condition has become a major public health problem because it is a trigger for many other chronic diseases. Cell therapies using multipotent mesenchymal stromal cells, hematopoietic stem cells, macrophages, and other cell types have been used to induce regeneration and provide a cure for acute and chronic kidney disease in experimental models. This review describes the advances in cell therapy protocols applied to acute and chronic kidney injuries and the attempts to apply these treatments in a clinical setting.

Immunosuppressive therapies attenuate paraquat-induced renal dysfunction by suppressing inflammatory responses and lipid peroxidation

Although paraquat (PQ) induces oxidative damage and inflammatory responses in the lungs, the mechanism underlying PQ-induced acute kidney injury in patients is unclear. Immunosuppressive therapy with glucocorticoids and the immunosuppressant cyclophosphamide (CP) has been employed to treat patients with PQ poisoning. This study examined whether PQ could concurrently cause renal injury, inflammatory responses, and oxidative damage in the kidneys, and whether CP and dexamethasone (DEX) could suppress PQ-induced alterations. Mice were assigned to eight groups: Control, PQ, DEX, PQ plus DEX, CP, PQ plus CP, DEX plus CP, and PQ plus DEX with CP. DEX, CP, and DEX plus CP reversed PQ-induced renal injury, as indicated by urinary albumin-to-creatinine ratios and urea nitrogen levels in serum. The treatments also attenuated PQ-induced renal infiltration of leukocytes and macrophages and induction of the Il6, Tnf, Icam, Cxcl2, Tlr4, and Tlr9 genes encoding the inflammatory mediators in the kidneys. However, DEX only partially suppressed the macrophage infiltration, whereas DEX plus CP provided stronger protection than DEX or CP alone for the induction of Il6 and Cxcl2. Moreover, through the detection of F2-isoprostanes (F2-IsoPs) and isofurans in the kidneys and lungs and F2-IsoPs in the plasma and urine, the therapies were found to suppress PQ-induced lipid peroxidation, although DEX was less effective. Finally, PQ decreased ubiquinol-9:ubiquinone-9 ratios in the kidneys. This effect of PQ was not found under CP treatment, but the ratio was lower than that of the control group. Our findings suggest that the suppression of PQ-induced inflammatory responses by DEX and CP in the kidneys can mitigate oxidative damage and acute kidney injury.

Pathophysiology of Acute Kidney Injury in Critical Illness: A Narrative Review

Acute kidney injury (AKI) is a syndrome that entails a rapid decline in kidney function with or without injury. The consequences of AKI among acutely ill patients are dire and lead to higher mortality, morbidity, and healthcare cost. To prevent AKI and its short and long-term repercussions, understanding its pathophysiology is essential. Depending on the baseline kidney histology and function reserves, the number of kidney insults, and the intensity of each insult, the clinical presentation of AKI may differ. While many factors are capable of inducing renal injury, they can be categorized into a few processes. The three primary processes reported in the literature are hemodynamic changes, inflammatory reactions, and nephrotoxicity. The majority of patients with AKI will suffer from more than one during their development and/or progression of AKI. Moreover, the development of one usually leads to the instigation of another. Thus, the interactions and progression between these mechanisms may determine the severity and duration of the AKI. Other factors such as organ crosstalk and how our concurrent therapies interact with these mechanisms complicate the pathophysiology of the progression of the AKI even further. In this narrative review article, we describe these three main pathophysiological processes that lead to the development and progression of AKI. © 2022 American Physiological Society. Compr Physiol 12: 1-14, 2022.

Melatonin Alleviates Acute Kidney Injury by Inhibiting NRF2/Slc7a11 Axis-Mediated Ferroptosis

Acute kidney injury (AKI) is still a puzzling clinical problem; its pathophysiology is not completely understood. Up to now, an effective treatment for AKI is lacking. Ferroptosis is a novel form of regulated cell death characterized by the lethal accumulation of lipid hydroperoxides that are dependent on iron and reactive oxygen species and mitochondrial dysfunction. Recently, ferroptosis was shown to play a vital role in AKI such as ischemia-reperfusion kidney injury and folic acid-induced AKI. Melatonin (MT) is an antioxidant that regulates the sleep-wake cycle. While the therapeutic effect of melatonin on AKI has been reported, its mechanism for the treatment of renal ferroptosis remains unclear. We found that melatonin treatment significantly alleviated the serum biochemistry index and histopathological alterations in vivo AKI models induced by bilateral renal artery ischemia reperfusion and folic acid in mice. Ferroptosis induced by hypoxia and reoxygenation or erastin (Era) in mouse tubular epithelial cells (MTEC) was also rescued by melatonin treatment. RNA sequence analysis of ferroptosis-related genes showed that melatonin affects oxidative stress responses by inhibiting hypoxia and reoxygenation- (HR-) mediated downregulation of NRF2 and upregulation of Slc7a11 in MTEC. Specific knockdown of NRF2 increased the sensitivity of cells to ferroptosis, and melatonin failed to protect against ferroptosis in the HR condition. Together, our data indicate that melatonin prevents ferroptosis in AKI by acting on the NRF2/Slc7a11 axis.

The Role of Circadian Clock Genes in Critical Illness: The Potential Role of Translational Clock Gene Therapies for Targeting Inflammation, Mitochondrial Function, and Muscle Mass in Intensive Care

The Earth's 24-h planetary rotation, with predictable light and heat cycles, has driven profound evolutionary adaptation, with prominent impacts on physiological mechanisms important for surviving critical illness. Pathways of interest include inflammation, mitochondrial function, energy metabolism, hypoxic signaling, apoptosis, and defenses against reactive oxygen species. Regulation of these by the cellular circadian clock (BMAL-1 and its network) has an important influence on pulmonary inflammation; ventilator-associated lung injury; septic shock; brain injury, including vasospasm; and overall mortality in both animals and humans. Whether it is cytokines, the inflammasome, or mitochondrial biogenesis, circadian medicine represents exciting opportunities for translational therapy in intensive care, which is currently lacking. Circadian medicine also represents a link to metabolic determinants of outcome, such as diabetes and cardiovascular disease. More than ever, we are appreciating the problem of circadian desynchrony in intensive care. This review explores the rationale and evidence for the importance of the circadian clock in surviving critical illness.

Interaction Between Intrinsic Renal Cells and Immune Cells in the Progression of Acute Kidney Injury

A growing number of studies have confirmed that immune cells play various key roles in the pathophysiology of acute kidney injury (AKI) development. After the resident immune cells and intrinsic renal cells are damaged by ischemia and hypoxia, drugs and toxins, more immune cells will be recruited to infiltrate through the release of chemokines, while the intrinsic cells promote macrophage polarity conversion, and the immune cells will promote various programmed deaths, phenotypic conversion and cycle arrest of the intrinsic cells, ultimately leading to renal impairment and fibrosis. In the complex and dynamic immune microenvironment of AKI, the bidirectional interaction between immune cells and intrinsic renal cells affects the prognosis of the kidney and the progression of fibrosis, and determines the ultimate fate of the kidney.

Protective effects of berberine on various kidney diseases: Emphasis on the promising effects and the underlined molecular mechanisms

Berberine (BBR) is a pentacyclic benzylisoquinoline alkaloid that can be found in diversity of medicinal plants. BBR has a wide range of pharmacological bioactivities, in addition when administrated orally, it has a broad safety margin. It has been used as an antidiarrheal, antimicrobial, and anti-diabetic drug in Ayurvedic and Chinese medicine. Several scholars have found that BBR has promising renoprotective effects against different renal illnesses, including diabetic nephropathy, renal fibrosis, renal ischemia, renal aging, and renal stones. Also, it has renoprotective effects against nephrotoxicity induced by chemotherapy, heavy metal, aminoglycosides, NSAID, and others. These effects imply that BBR has an evolving therapeutic potential against acute renal failure and chronic renal diseases. Hence, we report herein the beneficial therapeutic renoprotective properties of BBR, as well as the highlighted molecular mechanism. In conclusion, the studies discussed throughout this review will afford a comprehensive overview about renoprotective effect of BBR and its therapeutic impact on different renal diseases.

Indoleamine 2,3 Dioxygenase 1-The Potential Link between the Innate Immunity and the Ischemia-Reperfusion-Induced Acute Kidney Injury?

Ischemia-reperfusion injury (IRI) is of the most common causes of acute kidney injury (AKI); nevertheless, the mechanisms responsible for both early kidney injury and the reparative phase are not fully recognised. The inflammatory response following ischemia is characterised by the crosstalk between cells belonging to the innate immune system-dendritic cells (DCs), macrophages, neutrophils, natural killer (NK) cells, and renal tubular epithelial cells (RTECs). A tough inflammatory response can damage the renal tissue; it may also have a protective effect leading to the repair after IRI. Indoleamine 2,3 dioxygenase 1 (IDO1), the principal enzyme of the kynurenine pathway (KP), has a broad spectrum of immunological activity from stimulation to immunosuppressive activity in inflamed areas. IDO1 expression occurs in cells of the innate immunity and RTECs during IRI, resulting in local tryptophan (TRP) depletion and generation of kynurenines, and both of these mechanisms contribute to the immunosuppressive effect. Nonetheless, it is unknown if the above mechanism can play a harmful or preventive role in IRI-induced AKI. Despite the scarcity of literature in this field, the current review attempts to present a possible role of IDO1 activation in the regulation of the innate immune system in IRI-induced AKI.

Three-Dimensional Visualization With Tissue Clearing Uncovers Dynamic Alterations of Renal Resident Mononuclear Phagocytes After Acute Kidney Injury

Traditional histologic methods are limited in detecting dynamic changes in immune cells during acute kidney injury (AKI). Recently, optical tissue clearing combined with multiphoton microscopy (MPM) or light sheet fluorescence microscopy (LSFM) has become an emerging method for deep tissue evaluation and three-dimensional visualization. These new approaches have helped expand our understanding of tissue injury and repair processes, including tracing the changes in immune cells. We designed this study to investigate the morphological and functional alterations of renal mononuclear phagocytes (MNPs) in lipopolysaccharide (LPS)-induced AKI using renal clearing in CD11c-YFP mice. We also evaluated the effect of the NLRP3 inhibitor MCC950 to determine whether NLRP3 inhibition attenuates the activation of CD11c+ cells in an LPS-induced AKI model. Transverse sectioned whole mouse kidney imaging by LSFM showed that CD11c+ cells were mainly distributed in the cortex, especially the tubulointerstitial area. The number of CD11c+ cells was significantly more densely interspersed, particularly in periglomerular and perivascular lesions, in the saline-treated LPS-exposed kidney than in the control kidney. Deep imaging of the kidney cortex by MPM demonstrated an increased number of CD11c+ cells in the saline-treated LPS group compared with the control group. This quantitative alteration of CD11c+ cells in AKI was accompanied by morphological changes at high resolution, showing an increased number and level of dendrites. These morphological and behavioral changes in the saline-treated LPS group were accompanied by increased MHC class II and CD86 on CD11c-YFP+ cells. MCC950 attenuated the activation of CD11c+ cells after AKI and improved renal function. In conclusion, wide and deep three-dimensional visualization using MPM or LSFM combined with kidney clearing uncovers dynamic changes of renal MNPs, which are directly linked to renal function in AKI.

RORC gene polymorphism is associated with acute kidney injury following cardiac surgery

BACKGROUND

Acute kidney injury (AKI) is a common complication of cardiopulmonary bypass (CPB), associated with increased mortality in surgical patients. It is well-proven that Th17 and its hallmark cytokine, IL-17, contribute to AKI development. Since the RAR-related orphan receptor C (RORC) gene is a master regulator of the Th17 differentiation, we aimed to evaluate the association between its polymorphisms, CPB-AKI and plasma IL-17 levels among Iranian patients undergoing CPB.

METHOD

Totally, 138 patients undergoing CPB in Bandar Abbas, Iran, were enrolled. The allele and genotype frequencies of the selected SNPs were determined using PCR-SSP. IL-17 serum level was determined using an enzyme-linked immunosorbent assay.

RESULTS

Rs9017 GG genotype and G allele were associated with increased risk of CPB-AKI (OR = 3, 95% CI = 1.4-6.6 and OR = 2.3, 95% CI = 1.3-3.9, respectively) while A allele was protective against the disease (OR = 0.4, 95% CI = 0.3-0.7, p = .02). There was not a statistically significant interaction between the three genotypes of rs9017 and AKI disease with IL-17 serum level before (p = .9) and after (p = .6) the operation. The IL-17 serum level before surgery was significantly higher in patients carrying GG genotype compared to GA genotype (p = .017).

CONCLUSION

Our results showed that the rs9017 GG genotype was associated with an increased level of IL-17 and risk of CBP-AKI in the Iranian population. Our current results suggest that the rs9017 GG genotype could be a probable predictor of AKI after cardiac surgery.

Novel lncRNA XLOC_032768 protects against renal tubular epithelial cells apoptosis in renal ischemia-reperfusion injury by regulating FNDC3B/TGF-β1

Renal ischemia–reperfusion injury is a leading cause of acute kidney injury, but its underlying mechanism remains poorly understood and effective therapies are still lacking. Here, we identified lncRNA XLOC_032768 as a novel target in renal ischemia–reperfusion injury by analyzing differentially expressed genes of the transcriptome data. PCR results show that XLOC_032768 was markedly downregulated in the kidney during renal ischemia–reperfusion in mice and in cultured kidney cells during hypoxia. Upon induction in vitro, XLOC_032768 overexpression repressed the expression of fibronectin type III domain containing 3B (FNDC3B) and tubular epithelial cells apoptosis. Administration of XLOC_032768 preserved FNDC3B expression and attenuated renal tubular epithelial cells apoptosis, resulting in protection against kidney injury in mice. Knockdown of FNDC3B markedly reduced the expression of TGF-β1 and apoptosis of renal tubular cells. Thus, XLOC_032768/FNDC3B/TGF-β1signaling pathway in ischemia–reperfusion injury may be targeted for therapy.

Acute kidney injury in the critically ill: an updated review on pathophysiology and management

Acute kidney injury (AKI) is now recognized as a heterogeneous syndrome that not only affects acute morbidity and mortality, but also a patient’s long-term prognosis. In this narrative review, an update on various aspects of AKI in critically ill patients will be provided. Focus will be on prediction and early detection of AKI (e.g., the role of biomarkers to identify high-risk patients and the use of machine learning to predict AKI), aspects of pathophysiology and progress in the recognition of different phenotypes of AKI, as well as an update on nephrotoxicity and organ cross-talk. In addition, prevention of AKI (focusing on fluid management, kidney perfusion pressure, and the choice of vasopressor) and supportive treatment of AKI is discussed. Finally, post-AKI risk of long-term sequelae including incident or progression of chronic kidney disease, cardiovascular events and mortality, will be addressed.

Separated parabiont reveals the fate and lifespan of peripheral-derived immune cells in normal and ischaemia-induced injured kidneys

Immune cell infiltration plays a key role in acute kidney injury (AKI) to chronic kidney disease (CKD) progression. T lymphocytes, neutrophils, monocytes/macrophages and other immune cells regulate inflammation, tissue remodelling and repair. To determine the kinetics of accumulation of various immune cell populations, we established an animal model combining parabiosis and separation surgery to explore the fate and lifespan of peripheral leucocytes that migrate to the kidney. We found that peripheral T lymphocytes could survive for a long time (more than 14 days), whereas peripheral neutrophils survived for a short time in both healthy and ischaemia-induced damaged kidneys. Nearly half of the peripheral-derived macrophages disappeared after 14 days in normal kidneys, while their existing time in the inflammatory kidneys was prolonged. A fraction of F4/80^high macrophages were renewed from the circulating monocyte pool. In addition, we found that after renal ischaemia reperfusion, neutrophils increased significantly in the early phase, and T lymphocytes mainly accumulated in the late stage, whereas macrophages infiltrated throughout AKI-CKD progression and were sustained longer in injured as opposed to normal kidneys. In conclusion, peripheral-derived macrophages, T lymphocytes and neutrophils exhibit different lifespans in the kidney, which may play different roles during AKI-CKD progression.

Chess Not Checkers: Complexities Within the Myeloid Response to the Acute Kidney Injury Syndrome

Immune dysregulation in acute kidney injury (AKI) is an area of intense interest which promises to enhance our understanding of the disease and how to manage it. Macrophages are a heterogeneous and dynamic population of immune cells that carry out multiple functions in tissue, ranging from maintenance to inflammation. As key sentinels of their environment and the major immune population in the uninjured kidney, macrophages are poised to play an important role in the establishment and pathogenesis of AKI. These cells have a profound capacity to orchestrate downstream immune responses and likely participate in skewing the kidney environment toward either pathogenic inflammation or injury resolution. A clear understanding of macrophage and myeloid cell dynamics in the development of AKI will provide valuable insight into disease pathogenesis and options for intervention. This review considers evidence in the literature that speaks to the role and regulation of macrophages and myeloid cells in AKI. We also highlight barriers or knowledge gaps that need to be addressed as the field advances.

Multifaceted roles of Toll-like receptors in acute kidney injury

Toll-like receptors (TLRs) are a family of pattern recognition receptors (PRRs) in the first line defense system of our bodies; they are widely expressed on leukocytes and kidney epithelial cells. Infections due to pathogens or danger signals from injured tissues often activate several TLRs and these receptors mediate their signal transduction through the activation of transcription factors that regulate the expression of cytokine interleukin-1β (IL-1β), type I interferons (IFNs), and nuclear factor kappa light chain enhancer of activated B cells (NF-κB) dependent cytokines and chemokines. Acute kidney injury (AKI) involves early Toll-like receptors driven immunopathology, while resolution of inflammation is needed for rapid regeneration of injured tubular cells. Despite their well known function in the progression of inflammation; interestingly, activation of TLRs also has been implicated in renal epithelial repair through the induction of certain interleukins and improvement in autophagy mechanism. Studies have found that although the blockade of TLRs during the early injury phase of renal tissues prevented tubular necrosis, suppression of interleukins production and impaired kidney regeneration due to their blockade has been observed during the healing phase of tissue. Taken together, these results suggest that the two danger response programs of renal cells i.e. renal inflammation and regeneration may link at the level of TLRs. This review aims to emphasize on the role of TLRs signaling in different acute kidney injury phases. Understanding of these pathways may turn out to be effective as therapeutic option for kidney diseases.

Toll-Like Receptors in Acute Kidney Injury

Acute kidney injury (AKI) is an important health problem, affecting 13.3 million individuals/year. It is associated with increased mortality, mainly in low- and middle-income countries, where renal replacement therapy is limited. Moreover, survivors show adverse long-term outcomes, including increased risk of developing recurrent AKI bouts, cardiovascular events, and chronic kidney disease. However, there are no specific treatments to decrease the adverse consequences of AKI. Epidemiological and preclinical studies show the pathological role of inflammation in AKI, not only at the acute phase but also in the progression to chronic kidney disease. Toll-like receptors (TLRs) are key regulators of the inflammatory response and have been associated to many cellular processes activated during AKI. For that reason, a number of anti-inflammatory agents targeting TLRs have been analyzed in preclinical studies to decrease renal damage during AKI. In this review, we updated recent knowledge about the role of TLRs, mainly TLR4, in the initiation and development of AKI as well as novel compounds targeting these molecules to diminish kidney injury associated to this pathological condition.

Bruton's tyrosine kinase inhibition attenuates oxidative stress in systemic immune cells and renal compartment during sepsis-induced acute kidney injury in mice

Sepsis is a life-threatening condition which affects multiple organs including the kidney. Sepsis-induced acute kidney injury (AKI) is a major health burden throughout the globe. Pathogenesis of sepsis-induced AKI is complex; however, it involves both innate and adaptive immune cells such as B cells, T cells, dendritic cells (DCs), macrophages, and neutrophils. Bruton's tyrosine kinase (BTK) is reportedly involved in inflammatory and oxidative signaling in different immune cells, however its contribution with respect to sepsis-induced AKI has not been delineated. This study attempted to investigate the role of BTK and its inhibition on oxidizing enzymes NADPH oxidase (NOX-2) and inducible nitric oxide synthase (iNOS) in DCs, neutrophils, and B cells during AKI. Our data reveal that BTK is activated in DCs, neutrophils, and B cells which causes an increase in AKI associated biochemical markers such as serum creatinine/blood urea nitrogen, renal myeloperoxidase activity, and histopathological disturbances in renal tubular structures. Activation of BTK causes upregulation of NOX-2/iNOS/nitrotyrosine in these immune cells and kidney. Treatment with BTK inhibitor, Ibrutinib causes attenuation in AKI associated dysfunction in biochemical parameters (serum creatinine/blood urea nitrogen, renal myeloperoxidase activity) and oxidative stress in immune cells and kidney (iNOS/NOX2/lipid peroxides/nitrotyrosine/protein carbonyls). In summary, the current investigation reveals a compelling role of BTK signaling in sepsis-induced AKI which is evident from amelioration of AKI associated renal dysfunction after its inhibition.

The role of Nrf2 in acute kidney injury: Novel molecular mechanisms and therapeutic approaches

Acute kidney injury (AKI) is a common clinical syndrome that is related to high morbidity and mortality. Oxidative stress, including the production of reactive oxygen species (ROS), appears to be the main element in the occurrence of AKI and the cause of the progression of chronic kidney disease (CKD) into end-stage renal disease (ESRD). Nuclear factor erythroid 2 related factor 2 (Nrf2) is a significant regulator of redox balance that has been shown to improve kidney disease by eliminating ROS. To date, researchers have found that the use of Nrf2-activated compounds can effectively reduce ROS, thereby preventing or retarding the progression of various types of AKI. In this review, we summarized the molecular mechanisms of Nrf2 and ROS in AKI and described the latest findings on the therapeutic potential of Nrf2 activators in various types of AKI.

Autophagy and Inflammation Regulation in Acute Kidney Injury

Autophagy at an appropriate juncture in the cell cycle exerts protective effects in acute kidney injury (AKI), whereas abnormal autophagy may lead to cell death. Inflammatory response plays a pivotal role in the pathophysiological process of kidney injury and repair during AKI. Several studies have reported an interaction between autophagy and inflammation in the pathogenesis of AKI. This review outlines recent advances in the investigation of the role of autophagy in inflammatory response regulation based on the following aspects. (1) Autophagy inhibits inflammatory responses induced in AKI through the regulation of mTOR and AMPK pathways and the inhibition of inflammasomes activation. (2) Autophagy can also help in the regulation of inflammatory responses through the nuclear factor kappa B pathway, which is beneficial to the recovery of kidney tissues. These studies reviewed here provide better insight into the mechanisms underlying the protective effects of the autophagy-inflammatory pathway. Through this review, we suggest that the autophagy-inflammatory pathway may serve as an alternative target for the treatment of AKI.

Recent Advances in the Role of Natural Killer Cells in Acute Kidney Injury

Growing evidence is revealing a central role for natural killer (NK) cells, cytotoxic cells belonging to the broad family of innate lymphoid cells (ILCs), in acute and chronic forms of renal disease. NK cell effector functions include both the recognition and elimination of virus-infected and tumor cells and the capability of sensing pathogens through Toll-like receptor (TLR) engagement. Notably, they also display immune regulatory properties, exerted thanks to their ability to secrete cytokines/chemokines and to establish interactions with different innate and adaptive immune cells. Therefore, because of their multiple functions, NK cells may have a major pathogenic role in acute kidney injury (AKI), and a better understanding of the molecular mechanisms driving NK cell activation in AKI and their downstream interactions with intrinsic renal cells and infiltrating immune cells could help to identify new potential biomarkers and to select clinically valuable novel therapeutic targets. In this review, we discuss the current literature regarding the potential involvement of NK cells in AKI.

Mesenchymal Stromal Cell Uses for Acute Kidney Injury-Current Available Data and Future Perspectives: A Mini-Review

There is growing evidence concerning the potential use of mesenchymal stromal cells (MSCs) for different tissue injuries. Initially, the intended physiological use of MSCs was due to their ability to differentiate and replace damaged cells. However, MSCs have multiple effects, including being able to significantly modulate immunological responses. MSCs are currently being tested for neurodegenerative diseases, graft vs. host disease, kidney injury, and other chronic unremitting tissue damage. Using MSCs in acute tissue damage is only now being studied. Acute kidney injury (AKI) is a common cause of morbidity and mortality. After the primary insult, overactivation of the immune system culminates in additional secondary potentially permanent kidney damage. MSCs have the potential to ameliorate the secondary damage, and recent studies have shed important light on their mechanisms of action. This article summarizes the basics of MSCs therapy, the newly discovered mechanisms of action, and their potential application in the setting of AKI.

Regulation of Innate Lymphoid Cells in Acute Kidney Injury: Crosstalk between Cannabidiol and GILZ

Innate lymphoid cells (ILCs) have emerged as largely tissue-resident archetypal cells of the immune system. We tested the hypotheses that renal ischemia-reperfusion injury (IRI) is a contributing factor to polarization of ILCs and that glucocorticoid-induced leucine zipper (GILZ) and cannabidiol regulate them in this condition. Mice subjected to unilateral renal IRI were treated with the following agents before restoration of renal blood flow: cannabidiol, DMSO, transactivator of transcription- (TAT-) GILZ, or the TAT peptide. Thereafter, kidney cells were prepared for flow cytometry analyses. Sham kidneys treated with either cannabidiol or TAT-GILZ displayed similar frequencies of each subset of ILCs compared to DMSO or TAT, respectively. Renal IRI increased ILC1s and ILC3s but reduced ILC2s compared to the sham group. Cannabidiol or TAT-GILZ treatment of IRI kidneys reversed this pattern as evidenced by reduced ILC1s and ILC3s but increased ILC2s compared to their DMSO- or TAT-treated counterparts. While TAT-GILZ treatment did not significantly affect cells positive for cannabinoid receptors subtype 2 (CB2+), cannabidiol treatment increased frequency of both CB2+ and GILZ-positive (GILZ+) cells of IRI kidneys. Subsequent studies showed that IRI reduced GILZ+ subsets of ILCs, an effect less marked for ILC2s. Treatment with cannabidiol increased frequencies of each subset of GILZ+ ILCs, but the effect was more marked for ILC2s. Indeed, cannabidiol treatment increased CB2+ GILZ+ ILC2s. Collectively, the results indicate that both cannabidiol and GILZ regulate ILC frequency and phenotype, in acute kidney injury, and that the effects of cannabidiol likely relate to modulation of endogenous GILZ.

Complete blood count in acute kidney injury prediction: a narrative review

Acute kidney injury (AKI) is a complex syndrome defined by a decrease in renal function. The incidence of AKI has raised in the past decades, and it is associated with negative impact in patient outcomes in the short and long term. Considering the impact of AKI on patient prognosis, research has focused on methods to assess patients at risk for developing AKI, diagnose subclinical AKI, and on prevention and treatment strategies, for which it is crucial an understanding of pathophysiology the of AKI. In this review, we discuss the use of easily available parameters found in a complete blood count to detect patients at risk for developing AKI, to provide an early diagnosis of AKI, and to predict associated patient outcomes.

Cardio-renal safety of non-steroidal anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most widely used therapeutic class in clinical medicine. These are sub-divided based on their selectivity for inhibition of cyclooxygenase (COX) isoforms (COX-1 and COX-2) into: (1) non-selective (ns-NSAIDs), and (2) selective NSAIDs (s-NSAIDs) with preferential inhibition of COX-2 isozyme. The safety and pathophysiology of NSAIDs on the renal and cardiovascular systems have continued to evolve over the years following short- and long-term treatment in both preclinical models and humans. This review summarizes major learnings on cardiac and renal complications associated with pharmaceutical inhibition of COX-1 and COX-2 with focus on preclinical to clinical translatability of cardio-renal data.

Kidney Pathophysiology, Toxicology, and Drug-Induced Injury in Drug Development

Anatomically, the kidneys are paired, bean-shaped (in most mammals), excretory organs that lie in the retroperitoneum. High blood flow to the kidneys, together with high oxygen consumption, makes them more vulnerable to exposure, via the circulation, and subsequent injury related to high concentrations of xenobiotics and chemicals. In preclinical drug development and safety assessment of new investigational drugs, changes in kidney structure and/or function following drug administration in experimental laboratory animals need to be put in context with interspecies differences in kidney functional anatomy, physiology, spontaneous pathologies, and toxicopathological responses to injury. In addition, translation to human relevance to avoid premature drug termination from development is vital. Thus, detection and characterization of kidney toxicity in preclinical species and human relevance will depend on the preclinical safety testing strategy and collective weight-of-evidence approach including new investigational drug mechanism of action (MOA), preclinical and clinical interspecies differences, and MOA relevance to humans. This review describes kidney macroscopic and microscopic functional anatomy, physiology, pathophysiology, toxicology, and drug-induced kidney toxicities in safety risk assessment and drug development.