Folic acid-induced animal model of kidney disease

Hydrangea paniculata coumarins alleviate adriamycin-induced renal lipotoxicity through activating AMPK and inhibiting C/EBPβ

ETHNOPHARMACOLOGICAL RELEVANCE

Throughout Chinese history, Hydrangea paniculata Siebold has been utilized as a traditional medicinal herb to treat a variety of ailments associated to inflammation. In a number of immune-mediated kidney disorders, total coumarins extracted from Hydrangea paniculata (HP) have demonstrated a renal protective effect.

AIM OF THE STUDY

To investigate renal beneficial effect of HP on experimental Adriamycin nephropathy (AN), and further clarify whether reversing lipid metabolism abnormalities by HP contributes to its renoprotective effect and find out the underlying critical pathways.

MATERIALS AND METHODS

After establishment of rat AN model, HP was orally administrated for 6 weeks. Biochemical indicators related to kidney injury were determined. mRNAs sequencing using kidney tissues were performed to clarify the underlying mechanism. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis, western blot, molecular docking, and drug affinity responsive target stability (DARTS) assay was carried out to further explore and confirm pivotal molecular pathways and possible target by which HP and 7-hydroxylcoumarin (7-HC) played their renal protection effect via modulating lipid metabolism.

RESULTS

HP could significantly improve renal function, and restore renal tubular abnormal lipid metabolism and interstitial fibrosis in AN. In vitro study demonstrated that HP and its main metabolite 7-HC could reduce ADR-induced intracellular lipid deposition and fibrosis characteristics in renal tubular cells. Mechanically, HP and 7-HC can activate AMP-activated protein kinase (AMPK) via direct interaction, which contributes to its lipid metabolism modulation effect. Moreover, HP and 7-HC can inhibit fibrosis by inhibiting CCAAT/enhancer binding protein beta (C/EBPβ) expression in renal tubular cells. Normalization of lipid metabolism by HP and 7-HC further provided protection of mitochondrial structure integrity and inhibited the nuclear factor kappa-B (NF-κB) pathway. Long-term toxicity using beagle dogs proved the safety of HP after one-month administration.

CONCLUSION

Coumarin derivates from HP alleviate adriamycin-induced lipotoxicity and fibrosis in kidney through activating AMPK and inhibiting C/EBPβ.

WWP2 Regulates Renal Fibrosis and the Metabolic Reprogramming of Profibrotic Myofibroblasts

Key Points

Background

Renal fibrosis is a common pathologic end point in CKD that is challenging to reverse, and myofibroblasts are responsible for the accumulation of a fibrillar collagen–rich extracellular matrix. Recent studies have unveiled myofibroblasts' diversity in proliferative and fibrotic characteristics, which are linked to different metabolic states. We previously demonstrated the regulation of extracellular matrix genes and tissue fibrosis by WWP2, a multifunctional E3 ubiquitin–protein ligase. Here, we investigate WWP2 in renal fibrosis and in the metabolic reprograming of myofibroblasts in CKD.

Methods

We used kidney samples from patients with CKD and WWP2-null kidney disease mice models and leveraged single-cell RNA sequencing analysis to detail the cell-specific regulation of WWP2 in fibrotic kidneys. Experiments in primary cultured myofibroblasts by bulk-RNA sequencing, chromatin immunoprecipitation sequencing, metabolomics, and cellular metabolism assays were used to study the metabolic regulation of WWP2 and its downstream signaling.

Results

The tubulointerstitial expression of WWP2 was associated with fibrotic progression in patients with CKD and in murine kidney disease models. WWP2 deficiency promoted myofibroblast proliferation and halted profibrotic activation, reducing the severity of renal fibrosis in vivo. In renal myofibroblasts, WWP2 deficiency increased fatty acid oxidation and activated the pentose phosphate pathway, boosting mitochondrial respiration at the expense of glycolysis. WWP2 suppressed the transcription of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), a metabolic mediator of fibrotic response, and pharmacologic inhibition of PGC-1α partially abrogated the protective effects of WWP2 deficiency on myofibroblasts.

Conclusions

WWP2 regulates the metabolic reprogramming of profibrotic myofibroblasts by a WWP2-PGC-1α axis, and WWP2 deficiency protects against renal fibrosis in CKD.

Remimazolam attenuates inflammation and kidney fibrosis following folic acid injury

The transition of acute kidney injury (AKI) to chronic kidney disease (CKD) is characterized by intense inflammation and progressive fibrosis. Remimazolam is widely used for procedural sedation in intensive care units, such as AKI patients. Remimazolam has been shown to possess anti-inflammatory and organ-protective properties. However, the role of remimazolam in inflammation and renal fibrosis following AKI remains unclear. Here, we explored the effects of remimazolam on the inflammatory response and kidney fibrogenesis of mice subjected to folic acid (FA) injury. Our results showed that remimazolam treatment alleviated kidney damage and dysfunction. Mice treated with remimazolam presented less collagen deposition in FA-injured kidneys compared with FA controls, which was accompanied by a reduction of extracellular matrix proteins accumulation and fibroblasts activation. Furthermore, remimazolam treatment reduced inflammatory cells infiltration into the kidneys of mice with FA injury and inhibited proinflammatory or profibrotic molecules expression. Finally, remimazolam treatment impaired the activation of bone marrow-derived fibroblasts and blunted the transformation of macrophages to myofibroblasts in FA nephropathy. Additionally, the benzodiazepine receptor antagonist PK-11195 partially reversed the protective effect of remimazolam on the FA-injured kidneys. Overall, remimazolam attenuates the inflammatory response and renal fibrosis development following FA-induced AKI, which may be related to the peripheral benzodiazepine receptor pathway.

Glycyrol Alleviates Acute Kidney Injury by Inhibiting Ferroptsis

Acute kidney injury (AKI) is a common clinical problem with high morbidity and mortality. The discovery of ferroptosis has provided novel insights into the mechanisms underlying AKI and paves the way for developing ferroptosis-based approaches to treat AKI. Glycyrol (GC) is a representative coumarin compound isolated from licorice that demonstrates various pharmacological activities. However, its potential for a protective effect against kidney injury remains unknown. We hypothesized that GC might be able to protect against AKI via suppression of ferroptosis. This hypothesis was tested in a cell-culture model of RSL3-induced nephrocyte ferroptosis and a mouse model of folic acid-induced AKI. The results showed that GC exerted a significant protective effect against nephrocyte ferroptosis in vitro and was effective against folic acid-induced AKI in vivo, where it was mechanistically associated with suppressing HO-1-mediated heme degradation. Collectively, the findings of the present study support the hypothesis that GC holds considerable potential to be developed as a novel agent for treating ferroptosis-related AKI.

Assessment of Acute Kidney Injury using MRI

There has been growing interest in using quantitative magnetic resonance imaging (MRI) to describe and understand the pathophysiology of acute kidney injury (AKI). The ability to assess kidney blood flow, perfusion, oxygenation, and changes in tissue microstructure at repeated timepoints is hugely appealing, as this offers new possibilities to describe nature and severity of AKI, track the time-course to recovery or progression to chronic kidney disease (CKD), and may ultimately provide a method to noninvasively assess response to new therapies. This could have significant clinical implications considering that AKI is common (affecting more than 13 million people globally every year), harmful (associated with short and long-term morbidity and mortality), and currently lacks specific treatments. However, this is also a challenging area to study. After the kidney has been affected by an initial insult that leads to AKI, complex coexisting processes ensue, which may recover or can progress to CKD. There are various preclinical models of AKI (from which most of our current understanding derives), and these differ from each other but more importantly from clinical AKI. These aspects are fundamental to interpreting the results of the different AKI studies in which renal MRI has been used, which encompass different settings of AKI and a variety of MRI measures acquired at different timepoints. This review aims to provide a comprehensive description and interpretation of current studies (both preclinical and clinical) in which MRI has been used to assess AKI, and discuss future directions in the field. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 3.

CU06-1004 alleviates oxidative stress and inflammation on folic acid-induced acute kidney injury in mice

PURPOSE

Acute kidney injury (AKI) is characterized by reduced renal function, oxidative stress, inflammation, and renal fibrosis. CU06-1004, an endothelial cell dysfunction blocker, exhibits anti-inflammatory effects by reducing vascular permeability in pathological conditions. However, the potential effects of CU06-1004 on AKI have not been investigated. We investigated the renoprotective effect of CU06-1004 against oxidative stress, inflammation, and fibrotic changes in a folic acid-induced AKI model.

METHODS

AKI was induced by intraperitoneal injection of high dose (250 mg/kg) folic acid in mice. CU06-1004 was orally administered a low (10 mg/kg) or high dose (20 mg/kg).

RESULTS

CU06-1004 ameliorated folic acid-induced AKI by decreasing serum blood urea nitrogen and creatinine levels, mitigating histological abnormalities, and decreasing tubular injury markers such as kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin in folic acid-induced AKI mice. Additionally, CU06-1004 alleviated folic acid-induced oxidative stress by reducing 4-hydroxynonenal and malondialdehyde levels. Furthermore, it attenuated macrophage infiltration and suppressed the expression of the proinflammatory factors, including tumor necrosis factor-α, intercellular adhesion molecule-1, and vascular cell adhesion protein-1. Moreover, CU06-1004 mitigated folic acid-induced tubulointerstitial fibrosis by decreasing α-smooth muscle actin and transforming growth factor-β expression.

CONCLUSION

These findings suggest CU06-1004 as a potential therapeutic agent for folic acid-induced AKI.

A novel method for automated crystal visualization and quantification in murine folic acid-induced acute kidney injury

Folic acid (FA)-induced acute kidney injury (FA-AKI) is an increasingly prevalent rodent disease model involving the injection of a high dose of FA that culminates in renal FA crystal deposition and injury. However, the literature characterizing the FA-AKI model is sparse and dated in part due to the absence of a well-described methodology for the visualization and quantification of renal FA crystals. Using widely available materials and tools, we developed a straightforward and crystal-preserving histological protocol that can be coupled with automated imaging for renal FA crystal visualization and generated an automated macro for downstream crystal content quantification. The applicability of the method was demonstrated by characterizing the model in male and female C57BL6/JRj mice after 3 and 30 h of FA treatment. Kidneys from both sexes and timepoints showed a bimodal distribution of FA crystal deposition in the cortical and medullary regions while, compared with males, females exhibited higher renal FA crystal content at the 30-h timepoint accompanied by greater kidney weight and higher plasma urea. Despite comparable plasma phosphate concentrations, FA-AKI resulted in a substantially more elevated plasma intact fibroblast growth factor 23 (FGF23) in females, reflected by a similar pattern in osseous Fgf23 mRNA expression. Therefore, the presented method constitutes a valuable tool for the quantification of renal FA crystals, which can aid the mechanistic characterization of the FA-AKI model and serves as a means to control for confounding changes in FA crystallization when using the model for investigating early and prophylactic AKI therapeutic interventions.NEW & NOTEWORTHY Here, we describe a novel method for the visualization and quantification of renal folic acid (FA) crystals in the rodent FA-induced acute kidney injury (FA-AKI) model. The protocol involves a straightforward histological approach followed by fully automated imaging and quantification steps. Applicability was confirmed by showing that the FA-AKI model is sex-dependent. The method can serve as a tool to aid in characterizing FA-AKI and to control for studies investigating prophylactic therapeutic avenues using FA-AKI.

Folic acid antioxidant supplementation to binge drinking adolescent rats improves hydric-saline balance and blood pressure, but fails to increase renal NO availability and glomerular filtration rate

Binge drinking (BD) is an especially pro-oxidant pattern of alcohol consumption, particularly widespread in the adolescent population. In the kidneys, it affects the glomerular filtration rate (GFR), leading to high blood pressure. BD exposure also disrupts folic acid (FA) homeostasis and its antioxidant properties. The aim of this study is to test a FA supplementation as an effective therapy against the oxidative, nitrosative, and apoptotic damage as well as the renal function alteration occurred after BD in adolescence. Four groups of adolescent rats were used: control, BD (exposed to intraperitoneal alcohol), control FA-supplemented group and BD FA-supplemented group. Dietary FA content in control groups was 2 ppm, and 8 ppm in supplemented groups. BD provoked an oxidative imbalance in the kidneys by dysregulating antioxidant enzymes and increasing the enzyme NADPH oxidase 4 (NOX4), which led to an increase in caspase-9. BD also altered the renal nitrosative status affecting the expression of the three nitric oxide (NO) synthase (NOS) isoforms, leading to a decrease in NO levels. Functionally, BD produced a hydric-electrolytic imbalance, a low GFR and an increase in blood pressure. FA supplementation to BD adolescent rats improved the oxidative, nitrosative, and apoptotic balance, recovering the hydric-electrolytic equilibrium and blood pressure. However, neither NO levels nor GFR were recovered, showing in this study for the first time that NO availability in the kidneys plays a crucial role in GFR regulation that the antioxidant effects of FA cannot repair.

ACSS2 gene variants determine kidney disease risk by controlling de novo lipogenesis in kidney tubules

Worldwide, over 800 million people are affected by kidney disease, yet its pathogenesis remains elusive, hindering the development of novel therapeutics. In this study, we used kidney-specific expression of quantitative traits and single-nucleus open chromatin analysis to show that genetic variants linked to kidney dysfunction on chromosome 20 target the acyl-CoA synthetase short-chain family 2 (ACSS2). By generating ACSS2-KO mice, we demonstrated their protection from kidney fibrosis in multiple disease models. Our analysis of primary tubular cells revealed that ACSS2 regulated de novo lipogenesis (DNL), causing NADPH depletion and increasing ROS levels, ultimately leading to NLRP3-dependent pyroptosis. Additionally, we discovered that pharmacological inhibition or genetic ablation of fatty acid synthase safeguarded kidney cells against profibrotic gene expression and prevented kidney disease in mice. Lipid accumulation and the expression of genes related to DNL were elevated in the kidneys of patients with fibrosis. Our findings pinpoint ACSS2 as a critical kidney disease gene and reveal the role of DNL in kidney disease.

HDAC3 aberration-incurred GPX4 suppression drives renal ferroptosis and AKI-CKD progression

Acute kidney injury (AKI) progression to chronic kidney disease (CKD) represents a unique renal disease setting characterized by early renal cellular injury and regulated cell death, and later renal fibrosis, of which the critical role and nature of ferroptosis are only partially understood. Here, we report that renal tubular epithelial ferroptosis caused by HDAC3 (histone deacetylase 3) aberration and the resultant GPX4 suppression drives AKI-CKD progression. In mouse models of AKI-CKD transition induced by nephrotoxic aristolochic acid (AA) and folic acid (FA), renal tubular epithelial ferroptosis occurred early that coincided with preferential HDAC3 elevation and marked suppression of a core anti-ferroptosis enzyme GPX4 (glutathione peroxidase 4). Intriguingly, genetic Hdac3 knockout or administration of a HDAC3-selective inhibitor RGFP966 effectively mitigated the GPX4 suppression, ferroptosis and the fibrosis-associated renal functional loss. In cultured tubular epithelial cells, HDAC3 over-expression or inhibition inversely affected GPX4 abundances. Further analysis revealed that Gpx4 promoter contains a typical binding motif of transcription factor KLF5 (Kruppel-like factor 5). HDAC3 and KLF5 inducibly associated and bound to Gpx4 promoter upon AA treatment, leading to local histone hypoacetylation and GPX4 transactivation inhibition, which was blocked by RGFP966 and a KLF5 inhibitor ML264, respectively, suggesting that KLF5 co-regulated the HDAC3-incurred Gpx4 transcription inhibition. More importantly, in AKI-CKD mice receiving a GPX4 inactivator RSL3, the anti-ferroptosis and renoprotective effects of RGFP966 were largely abrogated, indicating that GPX4 is an essential downstream mediator of the HDAC3 aberration and renal ferroptosis during AKI-CKD transition. Together, our study identified a critical epigenetic pathway of ferroptosis during AKI-CKD transition and suggested that the strategies preserving GPX4 by HDAC3 inhibition are potentially effective to reduce renal ferroptosis and slow AKI-CKD progression.

Epidermal growth factor receptor activation is essential for kidney fibrosis development

Fibrosis is the progressive accumulation of excess extracellular matrix and can cause organ failure. Fibrosis can affect nearly every organ including kidney and there is no specific treatment currently. Although Epidermal Growth Factor Receptor (EGFR) signaling pathway has been implicated in development of kidney fibrosis, underlying mechanisms by which EGFR itself mediates kidney fibrosis have not been elucidated. We find that EGFR expression increases in interstitial myofibroblasts in human and mouse fibrotic kidneys. Selective EGFR deletion in the fibroblast/pericyte population inhibits interstitial fibrosis in response to unilateral ureteral obstruction, ischemia or nephrotoxins. In vivo and in vitro studies and single-nucleus RNA sequencing analysis demonstrate that EGFR activation does not induce myofibroblast transformation but is necessary for the initial pericyte/fibroblast migration and proliferation prior to subsequent myofibroblast transformation by TGF-ß or other profibrotic factors. These findings may also provide insight into development of fibrosis in other organs and in other conditions.

Fe(II)-Targeted PET/19F MRI Dual-Modal Molecular Imaging Probe for Early Evaluation of Anticancer Drug-Induced Acute Kidney Injury

Ferroptosis, an iron-dependent regulated cell death, has been emerging as an early mechanism in anticancer drug-induced acute kidney injury (AKI) that may benefit therapeutic intervention. However, the lack of molecular imaging methods for in vivo detection of ferroptosis restricts the early diagnosis of anticancer drug-induced AKI. Herein, we developed a PET/19F MRI dual-modal imaging probe for the monitoring of ferroptosis in AKI by chemically conjugating the Fe(II)-sensitive artemisinin (Art) motif and macrocyclic ligand 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) to the CF3-modified polyhedral oligomeric silsesquioxane (POSS) clusters, denoted as the PAD probe. The PAD probe could be converted into PA*D in the presence of Fe(II) ions and subsequently be intercepted by biological macromolecules nearby, thereby enhancing the retention effect in ferroptotic cells and tissues. After labeling with 68Ga isotopes, the 68Ga-labeled PAD probe in cisplatin (CDDP)-induced AKI mice displayed a significantly higher renal uptake level than that in normal mice. Moreover, the PAD probe with a precise chemical structure, relatively high 19F content, and single 19F resonance frequency allowed for interference-free and high-performance19F MRI that could detect the onset of CDDP-induced AKI at least 24 h earlier than the typical clinical/preclinical assays. Our study provides a robust dual-modal molecular imaging tool for the early diagnosis and mechanistic investigation of various ferroptosis-related diseases.

Animal Models of Kidney Disease: Challenges and Perspectives

Kidney disease is highly prevalent and affects approximately 850 million people worldwide. It is also associated with high morbidity and mortality, and current therapies are incurable and often ineffective. Animal models are indispensable for understanding the pathophysiology of various kidney diseases and for preclinically testing novel remedies. In the last two decades, rodents continue to be the most used models for imitating human kidney diseases, largely because of the increasing availability of many unique genetically modified mice. Despite many limitations and pitfalls, animal models play an essential and irreplaceable role in gaining novel insights into the mechanisms, pathologies, and therapeutic targets of kidney disease. In this review, we highlight commonly used animal models of kidney diseases by focusing on experimental AKI, CKD, and diabetic kidney disease. We briefly summarize the pathological characteristics, advantages, and drawbacks of some widely used models. Emerging animal models such as mini pig, salamander, zebrafish, and drosophila, as well as human-derived kidney organoids and kidney-on-a-chip are also discussed. Undoubtedly, careful selection and utilization of appropriate animal models is of vital importance in deciphering the mechanisms underlying nephropathies and evaluating the efficacy of new treatment options. Such studies will provide a solid foundation for future diagnosis, prevention, and treatment of human kidney diseases.

Restoring glomerular filtration rate by sulforaphane modulates ERK1/2/JNK/p38MAPK, IRF3/iNOS, Nrf2/HO-1 signaling pathways against folic acid-induced acute renal injury in rats

BACKGROUND

Folic acid (FA)-induced acute renal injury (AKI) is a commonly and highly reproducible model used to study AKI. The current study aims to evaluate the possible protective effects of sulforaphane (SFN) against FA-induced renal damage and explore the underlying molecular mechanism.

METHODS

The animals were divided into four groups (6 rats/group) as follows: normal group (received vehicle, p.o.), FA group (received 250 mg/kg, i.p.), SFN low dose group (received 15 mg/kg, p.o. plus FA 250 mg/kg, i.p.), SFN high dose group (30 mg/kg, p.o. plus FA 250 mg/kg, i.p.). At the end of the experiment, serum samples and kidney tissues were obtained to perform biochemical, molecular, and histopathological investigations.

RESULTS

The present study showed that FA-caused AKI was confirmed by a significant elevation of kidney function biomarkers serum levels accompanied by an observation of histopathologic changes. Interestingly, SFN-administration significantly improved kidney function, reduced oxidative stress markers; MDA, NADPH oxidase, MPO, iNOS with up-regulation of GSH, GCLM, GPX4, SOD, NQO1, HO-1 and Nrf2 levels. SFN also downregulated proinflammatory markers. The results also demonstrated the anti-apoptotic effect of SFN through its ability to increase the antiapoptotic Bcl-2 protein and to decrease caspase-3. Moreover, SFN significantly decreased the relative expression of JNK, ERK-1/2, IRF3, and p38MAPK as compared to the FA-nephrotoxic group.

CONCLUSION

The present study revealed that SFN possess an antioxidant, anti-inflammatory and antiapoptotic activity by modulating caspase-3, Bcl-2, ERK1/2, JNK, GCLM, NQO1, GPX4, Nrf2, HO-1 and P38 signaling pathways in a dose dependent manner which provides a potential therapeutic strategy for preventing FA-induced AKI.

The impact of hypoxia-inducible factors in the pathogenesis of kidney diseases: a link through cell metabolism

Kidneys are sensitive to disturbances in oxygen homeostasis. Hypoxia and activation of the hypoxia-inducible factor (HIF) pathway alter the expression of genes involved in the metabolism of renal and immune cells, interfering with their functioning. Whether the transcriptional activity of HIF protects the kidneys or participates in the pathogenesis of renal diseases is unclear. Several studies have indicated that HIF signaling promotes fibrosis in experimental models of kidney disease. Other reports showed a protective effect of HIF activation on kidney inflammation and injury. In addition to the direct effect of HIF on the kidneys, experimental evidence indicates that HIF-mediated metabolic shift activates inflammatory cells, supporting the HIF cascade as a link between lung or gut damage and worsening of renal disease. Although hypoxia and HIF activation are present in several scenarios of renal diseases, further investigations are needed to clarify whether interfering with the HIF pathway is beneficial in different pathological contexts.

TJ-17 (Goreisan) mitigates renal fibrosis in a mouse model of folic acid-induced chronic kidney disease

BACKGROUND AND PURPOSE

TJ-17 (Goreisan), a traditional Japanese Kampo medicine, has been generally used to treat edema, such as heart failure, due to its diuretic effect. In the present study, we investigate the effects of TJ-17 on chronic kidney disease (CKD).

METHODS

We the preventive action of TJ-17 against acute kidney injury (AKI) transition to CKD in vivo using a folic acid (FA)-induced mouse model. Mice were treated with food containing TJ-17 at 48 h after FA intraperitoneal injection (AKI phase).

RESULTS

Histological analysis, as well as renal function and renal injury markers, deteriorated in mice with FA-induced CKD and were ameliorated by TJ-17 treatment. Increased levels of inflammatory cytokines and macrophage infiltration were also alleviated in mice treated with TJ-17. Renal fibrosis, a crucial factor in CKD, was induced by FA administration and inhibited by TJ-17 treatment. Pretreatment with TJ-17 did not exert an inhibitory effect on FA-induced AKI. The increase in urinary volume in FA-induced CKD mice was ameliorated by TJ-17 treatment, with a concurrent correction of reduced aquaporins expression in the kidney.

CONCLUSION

TJ-17 may have a novel preventive effect against inflammation, oxidative stress, and fibrosis, contributing to innovation in the treatment of CKD.

CCN2 Activates RIPK3, NLRP3 Inflammasome, and NRF2/Oxidative Pathways Linked to Kidney Inflammation

Inflammation is a key characteristic of both acute and chronic kidney diseases. Preclinical data suggest the involvement of the NLRP3/Inflammasome, receptor-interacting protein kinase-3 (RIPK3), and NRF2/oxidative pathways in the regulation of kidney inflammation. Cellular communication network factor 2 (CCN2, also called CTGF in the past) is an established fibrotic biomarker and a well-known mediator of kidney damage. CCN2 was shown to be involved in kidney damage through the regulation of proinflammatory and profibrotic responses. However, to date, the potential role of the NLRP3/RIPK3/NRF2 pathways in CCN2 actions has not been evaluated. In experimental acute kidney injury induced with folic acid in mice, CCN2 deficiency diminished renal inflammatory cell infiltration (monocytes/macrophages and T lymphocytes) as well as the upregulation of proinflammatory genes and the activation of NLRP3/Inflammasome-related components and specific cytokine products, such as IL-1β. Moreover, the NRF2/oxidative pathway was deregulated. Systemic administration of CCN2 to C57BL/6 mice induced kidney immune cell infiltration and activated the NLRP3 pathway. RIPK3 deficiency diminished the CCN2-induced renal upregulation of proinflammatory mediators and prevented NLRP3 modulation. These data suggest that CCN2 plays a fundamental role in sterile inflammation and acute kidney injury by modulating the RIKP3/NLRP3/NRF2 inflammatory pathways.

The Road from AKI to CKD: Molecular Mechanisms and Therapeutic Targets of Ferroptosis

Acute kidney injury (AKI) is a prevalent pathological condition that is characterized by a precipitous decline in renal function. In recent years, a growing body of studies have demonstrated that renal maladaptation following AKI results in chronic kidney disease (CKD). Therefore, targeting the transition of AKI to CKD displays excellent therapeutic potential. However, the mechanism of AKI to CKD is mediated by multifactor, and there is still a lack of effective treatments. Ferroptosis, a novel nonapoptotic form of cell death, is believed to have a role in the AKI to CKD progression. In this study, we retrospectively examined the history and characteristics of ferroptosis, summarized ferroptosis's research progress in AKI and CKD, and discussed how ferroptosis participates in regulating the pathological mechanism in the progression of AKI to CKD. Furthermore, we highlighted the limitations of present research and projected the future evolution of ferroptosis. We hope this work will provide clues for further studies of ferroptosis in AKI to CKD and contribute to the study of effective therapeutic targets to prevent the progression of kidney diseases.

Direct mapping of kidney function by DCE-MRI urography using a tetrazinanone organic radical contrast agent

Chronic kidney disease (CKD) and acute kidney injury (AKI) are ongoing global health burdens. Glomerular filtration rate (GFR) is the gold standard measure of kidney function, with clinical estimates providing a global assessment of kidney health without spatial information of kidney- or region-specific dysfunction. The addition of dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) to the anatomical imaging already performed would yield a 'one-stop-shop' for renal assessment in cases of suspected AKI and CKD. Towards urography by DCE-MRI, we evaluated a class of nitrogen-centered organic radicals known as verdazyls, which are extremely stable even in highly reducing environments. A glucose-modified verdazyl, glucoverdazyl, provided contrast limited to kidney and bladder, affording functional kidney evaluation in mouse models of unilateral ureteral obstruction (UUO) and folic acid-induced nephropathy (FAN). Imaging outcomes correlated with histology and hematology assessing kidney dysfunction, and glucoverdazyl clearance rates were found to be a reliable surrogate measure of GFR.

Ferroptosis: A new mechanism of traditional Chinese medicine compounds for treating acute kidney injury

Acute kidney injury (AKI) is a major health concern owing to its high morbidity and mortality rates, to which there are no drugs or treatment methods, except for renal replacement therapy. Therefore, identifying novel therapeutic targets and drugs for treating AKI is urgent. Ferroptosis is an iron-dependent and lipid-peroxidation-driven regulatory form of cell death and is closely associated with the occurrence and development of AKI. Traditional Chinese medicine (TCM) has unique advantages in treating AKI due to its natural origin and efficacy. In this review, we summarize the mechanisms underlying ferroptosis and its role in AKI, and TCM compounds that play essential roles in the prevention and treatment of AKI by inhibiting ferroptosis. This review suggests ferroptosis as a potential therapeutic target for AKI, and that TCM compounds show broad prospects in the treatment of AKI by targeting ferroptosis.

Renal-Protective Roles of Lipoic Acid in Kidney Disease

The kidney is a crucial organ that eliminates metabolic waste and reabsorbs nutritious elements. It also participates in the regulation of blood pressure, maintenance of electrolyte balance and blood pH homeostasis, as well as erythropoiesis and vitamin D maturation. Due to such a heavy workload, the kidney is an energy-demanding organ and is constantly exposed to endogenous and exogenous insults, leading to the development of either acute kidney injury (AKI) or chronic kidney disease (CKD). Nevertheless, there are no therapeutic managements to treat AKI or CKD effectively. Therefore, novel therapeutic approaches for fighting kidney injury are urgently needed. This review article discusses the role of α-lipoic acid (ALA) in preventing and treating kidney diseases. We focus on various animal models of kidney injury by which the underlying renoprotective mechanisms of ALA have been unraveled. The animal models covered include diabetic nephropathy, sepsis-induced kidney injury, renal ischemic injury, unilateral ureteral obstruction, and kidney injuries induced by folic acid and metals such as cisplatin, cadmium, and iron. We highlight the common mechanisms of ALA’s renal protective actions that include decreasing oxidative damage, increasing antioxidant capacities, counteracting inflammation, mitigating renal fibrosis, and attenuating nephron cell death. It is by these mechanisms that ALA achieves its biological function of alleviating kidney injury and improving kidney function. Nevertheless, we also point out that more comprehensive, preclinical, and clinical studies will be needed to make ALA a better therapeutic agent for targeting kidney disorders.

The Role of Ketone Bodies in Various Animal Models of Kidney Disease

The kidney is a vital organ that carries out significant metabolic functions in our body. Due to the complexity of its role, the kidney is also susceptible to many disease conditions, such as acute kidney injury (AKI) and chronic kidney disease (CKD). Despite the prevalence and our increased understanding of the pathophysiology of both AKI and CKD as well as the transition of AKI to CKD, no well-established therapeutics have been applied clinically to these conditions, rendering an urgent need for a novel potential therapeutic target to be developed. In this article, we reviewed the function of ketone bodies in some common kidney conditions, such as drug-induced nephrotoxicity, ischemia and reperfusion injury, fibrosis development, diabetic kidney disease, kidney aging, hypertension, and CKD progression. All the selected studies reviewed were performed in animal models by primarily utilizing rodents, which also provide invaluable sources for future clinical applications. Ketone bodies have shown significant renal protective properties via attenuation of oxidative stress, increased expression of anti-inflammatory proteins, gene regulation, and a reduction of apoptosis of renal cells. A physiological level of ketone bodies could be achieved by fasting, a ketogenic diet, and an exogenous ketone supplement. Finally, the limitations of the long-term ketogenic diet were also discussed.

FGFR regulator Memo1 is dispensable for FGF23 expression by osteoblasts during folic acid-driven kidney injury

Loss of the mediator Of cell motility 1 (Memo1) in mice caused kidney disease and a bone disease with diminished osteoblast and osteoclast biomarkers in serum, resembling alterations occurring in adynamic bone disease in humans with chronic kidney disease or in Klotho-deficient mice. Here, we investigated whether Memo1 expression in osteoblasts is required for normal bone structure and FGF23 expression. We deleted Memo1 in the osteoblast-osteocyte lineage in Memo fl/fl mice using a Cre under Col1a1 promotor to obtain osteoblast-specific knockout (obKO) mice. We studied organs by micro-computed tomography, qPCR, and western blot. We challenged mice with folic acid for acute kidney injury (AKI) and analyzed organs. Memo obKO were viable without changes in gross anatomy, serum electrolytes, or circulating FGF23 concentrations compared to controls. Memo1 expression was blunted in bones of Memo obKO, whereas it remained unchanged in other organs. Micro-CT revealed no differences between genotypes in bone structure of vertebrae, femur, and tibia. During AKI, Fgf23 expression in calvaria, and renal transcriptional changes were comparable between genotypes. However, renal injury marker expression, circulating FGF23, and parathyroid hormone revealed a sex difference with more severely affected females than males of either genotype. The present data imply that Memo1 in osteoblasts is dispensable for bone structure and expression of Fgf23. Moreover, we found evidence of potential sex differences in murine folic acid nephropathy similar to other experimental models of renal injury that are important to consider when using this experimental model of renal injury.

Impact of Vancomycin Loading Doses and Dose Escalation on Glomerular Function and Kidney Injury Biomarkers in a Translational Rat Model

Vancomycin-induced kidney injury is common, and outcomes in humans are well predicted by animal models. This study employed our translational rat model to investigate temporal changes in the glomerular filtration rate (GFR) and correlations with kidney injury biomarkers related to various vancomycin dosing strategies. First, Sprague-Dawley rats received allometrically scaled loading doses or standard doses. Rats that received a loading dose had low GFRs and increased urinary injury biomarkers (kidney injury molecule 1 [KIM-1] and clusterin) that persisted through day 2 compared to those that did not receive a loading dose. Second, we compared low and high allometrically scaled vancomycin doses to a positive acute kidney injury control of high-dose folic acid. Rats in both the low- and high-dose vancomycin groups had higher GFRs on all dosing days than the positive-control group. When the two vancomycin groups were compared, rats that received the low dose had significantly higher GFRs on days 1, 2, and 4. Compared to low-dose vancomycin, the KIM-1 was elevated among rats in the high-dose group on dosing day 3. The GFR correlated most closely with the urinary injury biomarker KIM-1 on all experimental days. Vancomycin loading doses were associated with significant losses of kidney function and elevations of urinary injury biomarkers. In our translational rat model, both the degree of kidney function decline and urinary biomarker increases corresponded to the magnitude of the vancomycin dose (i.e., a higher dose resulted in worse outcomes).

Formononetin ameliorates ferroptosis-associated fibrosis in renal tubular epithelial cells and in mice with chronic kidney disease by suppressing the Smad3/ATF3/SLC7A11 signaling

AIMS

Chronic kidney disease (CKD) is characterized by interstitial fibrosis, while limited treatment drugs are available. Ferroptosis is a newly identified process that can trigger tubular atrophy and fibrosis. The aim of this study is to investigate the effects of formononetin (FN), a bioflavonoid, on ferroptosis and renal fibrosis.

MAIN METHODS

In vivo experiments, unilateral ureteral obstruction (UUO)- and folic acid (FA, 250 mg/kg)-induced CKD models were constructed in C57BL/6 mice of 6-8 weeks old, followed by the administration with 40 mg/kg/day FN by gavage. For in vitro experiments, ferroptosis was induced with RSL3 or erastin in primary mouse renal tubular epithelial cells (TECs), followed by the addition of indicated concentrations of FN. Then, the levels of ferroptosis and fibrosis were analyzed. The translocation of Smad3, ATF3, and Nrf2 from the cytoplasm to the nucleus was checked by western blotting. The interaction of Smad3 and ATF3 was detected by Co-immunoprecipitation.

KEY FINDINGS

FN dramatically ameliorated tubular injury along with reduced expression of the profibrotic genes including α-SMA, Col1a1, and fibronectin in both two CKD mouse models and RSL3/erastin-treated TECs. Furthermore, FN administration also significantly suppressed ferroptosis, as evidenced by increased expression of SLC7A11 and GPX4, and decreased levels of 4-HNE. In mechanism, FN disrupted the interaction between Smad3 and ATF3, resulting in the blocking of their translocation from the cytoplasm to the nucleus. In addition, FN also promoted the separation of the Nrf2/Keap1 complex and enhanced Nrf2 nuclear accumulation.

SIGNIFICANCE

FN alleviates CKD by impeding ferroptosis-associated fibrosis by suppressing the Smad3/ATF3/SLC7A11 signaling and could serve as a candidate therapeutic drug for CKD.

Higher Concentrations of Folic Acid Cause Oxidative Stress, Acute Cytotoxicity, and Long-Term Fibrogenic Changes in Kidney Epithelial Cells

Kidney fibrosis is a common step during chronic kidney disease (CKD), and its incidence has been increasing worldwide. Aberrant recovery after repeated acute kidney injury leads to fibrosis. The mechanism of fibrogenic changes in the kidney is not fully understood. Folic acid-induced kidney fibrosis in mice is an established in vivo model to study kidney fibrosis, but the mechanism is poorly understood. Moreover, the effect of higher concentrations of folic acid on kidney epithelial cells in vitro has not yet been studied. Oxidative stress is a common property of nephrotoxicants. Therefore, this study evaluated the role of folic acid-induced oxidative stress in fibrogenic changes by using the in vitro renal proximal tubular epithelial cell culture model. To obtain comprehensive and robust data, three different cell lines derived from human and mouse kidney epithelium were treated with higher concentrations of folic acid for both acute and long-term durations, and the effects were determined at the cellular and molecular levels. The result of cell viability by the MTT assay and the measurement of reactive oxygen species (ROS) levels by the DCF assay revealed that folic acid caused cytotoxicity and increased levels of ROS in acute exposure. The cotreatment with antioxidant N-acetyl cysteine (NAC) protected the cytotoxic effect, suggesting the role of folic acid-induced oxidative stress in cytotoxicity. In contrast, the long-term exposure to folic acid caused increased growth, DNA damage, and changes in the expression of marker genes for EMT, fibrosis, oxidative stress, and oxidative DNA damage. Some of these changes, particularly the acute effects, were abrogated by cotreatment with antioxidant NAC. In summary, the novel findings of this study suggest that higher concentrations of folic acid-induced oxidative stress act as the driver of cytotoxicity as an acute effect and of fibrotic changes as a long-term effect in kidney epithelial cells.

Crosstalk between TBK1/IKKε and the type I interferon pathway contributes to tubulointerstitial inflammation and kidney tubular injury

The type I interferon (TI-IFN) pathway regulates innate immunity, inflammation, and apoptosis during infection. However, the contribution of the TI-IFN pathway or upstream signaling pathways to tubular injury in kidney disease is poorly understood. Upon observing evidence of activation of upstream regulators of the TI-IFN pathway in a transcriptomics analysis of murine kidney tubulointerstitial injury, we have now addressed the impact of the TI-IFN and upstream signaling pathways on kidney tubulointerstitial injury. In cultured tubular cells and kidney tissue, IFNα/β binding to IFNAR activated the TI-IFN pathway and recruited antiviral interferon-stimulated genes (ISG) and NF-κB-associated proinflammatory responses. TWEAK and lipopolysaccharide (LPS) signaled through TBK1/IKKε and IRF3 to activate both ISGs and NF-κB. In addition, TWEAK recruited TLR4 to stimulate TBK1/IKKε-dependent ISG and inflammatory responses. Dual pharmacological inhibition of TBK1/IKKε with amlexanox decreased TWEAK- or LPS-induced ISG and cytokine responses, as well as cell death induced by a complex inflammatory milieu that included TWEAK. TBK1 or IRF3 siRNA prevented the TWEAK-induced ISG and inflammatory gene expression while IKKε siRNA did not. In vivo, kidney IFNAR and IFNβ were increased in murine LPS and folic acid nephrotoxicity while IFNAR was increased in human kidney biopsies with tubulointerstitial damage. Inhibition of TBK1/IKKε with amlexanox or IFNAR neutralization decreased TI-IFN pathway activation and protected from kidney injury induced by folic acid or LPS. In conclusion, TI-IFNs, TWEAK, and LPS engage interrelated proinflammatory and antiviral responses in tubular cells. Moreover, inhibition of TBK1/IKKε with amlexanox, and IFNAR targeting, may protect from tubulointerstitial kidney injury.

Pharmacological Inhibition of S100A4 Attenuates Fibroblast Activation and Renal Fibrosis

The TGF-β/Smad3 signaling pathway is an important process in the pathogenesis of kidney fibrosis. However, the molecular mechanisms are not completely elucidated. The current study examined the functional role of S100A4 in regulating TGF-β/Smad3 signaling in fibroblast activation and kidney fibrosis development. S100A4 was upregulated in the kidney in a murine model of renal fibrosis induced by folic acid nephropathy. Further, S100A4 was predominant in the tubulointerstitial cells of the kidney. Pharmacological inhibition of S100A4 with niclosamide significantly attenuated fibroblast activation, decreased collagen content, and reduced extracellular matrix protein expression in folic acid nephropathy. Overexpression of S100A4 in cultured renal fibroblasts significantly facilitated TGF-β1-induced activation of fibroblasts by increasing the expression of α-SMA, collagen-1 and fibronectin. In contrast, S100A4 knockdown prevented TGF-β1-induced activation of fibroblast and transcriptional activity of Smad3. Mechanistically, S100A4 interacts with Smad3 to stabilize the Smad3/Smad4 complex and promotes their translocation to the nucleus. In conclusion, S100A4 facilitates TGF-β signaling via interaction with Smad3 and promotes kidney fibrosis development. Manipulating S100A4 may provide a beneficial therapeutic strategy for chronic kidney disease.

The Nicotinamide/Streptozotocin Rodent Model of Type 2 Diabetes: Renal Pathophysiology and Redox Imbalance Features

Diabetic nephropathy (DN) is a common complication of diabetes mellitus. While there has been a great advance in our understanding of the pathogenesis of DN, no effective managements of this chronic kidney disease are currently available. Therefore, continuing to elucidate the underlying biochemical and molecular mechanisms of DN remains a constant need. In this regard, animal models of diabetes are indispensable tools. This review article highlights a widely used rodent model of non-obese type 2 diabetes induced by nicotinamide (NA) and streptozotocin (STZ). The mechanism underlying diabetes induction by combining the two chemicals involves blunting the toxic effect of STZ by NA so that only a percentage of β cells are destroyed and the remaining viable β cells can still respond to glucose stimulation. This NA-STZ animal model, as a platform for the testing of numerous antidiabetic and renoprotective materials, is also discussed. In comparison with other type 2 diabetic animal models, such as high-fat-diet/STZ models and genetically engineered rodent models, the NA-STZ model is non-obese and is less time-consuming and less expensive to create. Given that this unique model mimics certain pathological features of human DN, this model should continue to find its applications in the field of diabetes research.

Cisplatin-Induced Kidney Toxicity: Potential Roles of Major NAD+-Dependent Enzymes and Plant-Derived Natural Products

Cisplatin is an FDA approved anti-cancer drug that is widely used for the treatment of a variety of solid tumors. However, the severe adverse effects of cisplatin, particularly kidney toxicity, restrict its clinical and medication applications. The major mechanisms of cisplatin-induced renal toxicity involve oxidative stress, inflammation, and renal fibrosis, which are covered in this short review. In particular, we review the underlying mechanisms of cisplatin kidney injury in the context of NAD⁺-dependent redox enzymes including mitochondrial complex I, NAD kinase, CD38, sirtuins, poly-ADP ribosylase polymerase, and nicotinamide nucleotide transhydrogenase (NNT) and their potential contributing roles in the amelioration of cisplatin-induced kidney injury conferred by natural products derived from plants. We also cover general procedures used to create animal models of cisplatin-induced kidney injury involving mice and rats. We highlight the fact that more studies will be needed to dissect the role of each NAD⁺-dependent redox enzyme and its involvement in modulating cisplatin-induced kidney injury, in conjunction with intensive research in NAD⁺ redox biology and the protective effects of natural products against cisplatin-induced kidney injury.

A Retinol Derivative Inhibits SARS-CoV-2 Infection by Interrupting Spike-Mediated Cellular Entry

Retinoids, a group of compounds including vitamin A and its active metabolite all- trans retinoic acid (ATRA), regulate serial physiological activity in multiple organ systems, such as cell growth, differentiation, and apoptosis. The ATRA analogues reported to date include more than 4,000 natural and synthetic molecules that are structurally and/or functionally related to ATRA.

Immunometabolic rewiring of tubular epithelial cells in kidney disease

Kidney tubular epithelial cells (TECs) have a crucial role in the damage and repair response to acute and chronic injury. To adequately respond to constant changes in the environment, TECs have considerable bioenergetic needs, which are supported by metabolic pathways. Although little is known about TEC metabolism, a number of ground-breaking studies have shown that defective glucose metabolism or fatty acid oxidation in the kidney has a key role in the response to kidney injury. Imbalanced use of these metabolic pathways can predispose TECs to apoptosis and dedifferentiation, and contribute to lipotoxicity and kidney injury. The accumulation of lipids and aberrant metabolic adaptations of TECs during kidney disease can also be driven by receptors of the innate immune system. Similar to their actions in innate immune cells, pattern recognition receptors regulate the metabolic rewiring of TECs, causing cellular dysfunction and lipid accumulation. TECs should therefore be considered a specialized cell type - like cells of the innate immune system - that is subject to regulation by immunometabolism. Targeting energy metabolism in TECs could represent a strategy for metabolically reprogramming the kidney and promoting kidney repair.

5-Methyltetrahydrofolate Attenuates Oxidative Stress and Improves Kidney Function in Acute Kidney Injury through Activation of Nrf2 and Antioxidant Defense

Oxidative stress is a major mediator of adverse outcomes in acute kidney injury (AKI). Deficiency of micronutrients, such as folate, is common in AKI. Our previous study reported that AKI impaired kidney reabsorption of folate and decreased plasma folate level in rats. The present study investigated the effect of 5-methyltetrahydrofolate (5-MTHF), a biologically active form of folate/folic acid, on AKI-impaired kidney function and oxidative stress. Sprague-Dawley rats developed AKI after kidney ischemia (45 min) and reperfusion (24 h). Injection of 5-MTHF (3 µg/kg body weight) improved kidney function and attenuated oxidative stress with a restoration of glutathione and a reduction of lipid peroxidation in the kidney. Injection of 5-MTHF activated transcription factor Nrf2 and increased the expression of glutathione synthesizing enzymes, superoxide dismutase-1 and heme oxygenase-1 in the kidney. Simulated ischemia-reperfusion through hypoxia-reoxygenation increased oxidative stress in proximal tubular cells. Incubation of cells with 5-MTHF alleviated cell injury and increased antioxidant enzyme expression and intracellular glutathione levels. Inhibition of Nrf2 expression through siRNA transfection abolished the effect of 5-MTHF against oxidative stress. These results suggest that low-dose folic acid can improve kidney function through activation of Nrf2 and restoration of antioxidant defence. Micronutrient supplements may improve clinical outcomes in AKI.

Imaging mass spectrometry differentiates the effects of doxorubicin formulations on non-targeted tissues

Imaging mass spectrometry indicated a wide range of chemical disturbances in a model of non-targeted organs of rats treated with different formulations of doxorubicin and enabled the differentiation of drug formulation-specific effects.