Abstract Background and Aims Ferroptosis is a regulated form of necrosis which is dependent on cellular iron and is characterized by the accumulation of lipid peroxides and failure of cellular antioxidant defences. We have previously described in vivo that ferroptosis is the primary cause of folic acid-induced acute kidney injury (FA-AKI) and that necroinflammation secondary to ferroptosis may further worsen kidney injury, since ferroptosis inhibition improved kidney function and decreased tubular cell death and oxidative stress. Acyl-CoA synthetase long-chain family member 4 (ACSL4) is involved in the incorporation of polyunsaturated fatty acid (PUFA) into membranes, while 15-Lipoxygenase (Alox15) catalyzes the regio- and enantioselective peroxidation of membrane-esterified PUFAs, forming the ultimate peroxidized species that induce ferroptosis. In the present work, we aim to explore the potential of both proteins as therapeutic targets in AKI, as well as the molecular characterization of kidney ferroptosis in cultured tubular cells. Method Animal model: Female 12- to 14-week-old C57BL/6J wild type mice received a single intraperitoneal (i.p) injection of folic acid or vehicle and were sacrificed 48 hours later. Troglitazone was intravenously administered for in vivo ACSL4 inhibition, and Compound 1 was i.p administered for in vivo ALOX15 inhibition. In vitro characterization of ferroptosis: HK2 human tubular kidney cells were incubated with arachidonic acid (AA) prior to sublethal RSL3 administration for sensitization to ferroptosis. We used Ferrostatin-1 (Fer-1) and Liproxstatin-1 (Lpx-1) as inhibitors of ferroptosis. The thiazolidinedione family members Rosiglitazone, Pioglitazone and Troglitazone were used as pharmacological inhibitors of ACSL4. We also performed transcriptional silencing of ACSL4 using a specific siRNA. Compound 1 and PD1646 were administered for in vitro Alox15 inhibition. Cellular lipid peroxidation was analyzed by flow cytometry with Bodipy 581/591 staining. To characterize the lipid signature of ferroptotic cells, supernatants were collected and 15-HETEs levels were measured by ELISA. Oxido-lipidomic analysis of ferroptotic cells was performed by LC-MS. Real Time PCR and Western Blot of whole kidneys and cultured cells were performed for the detection and quantification of ACSL4 and ALOX15. Cell death was assessed by measurement of cell viability (MTT assay) and cytotoxicity (LDH assay). Tissue cell death was assessed by TUNEL. Results Kidney transcriptomics identified Acsl4 as the most upregulated member of Acsl family during FA-AKI. This was validated at mRNA and protein levels. Supplementation with AA, the preferred ACSL4 substrate, sensitized HK2 tubular cells to ferroptosis under sublethal RSL3 conditions, and this was prevented with specific ferroptosis inhibitors Fer-1 and Lpx-1. Pharmacological inhibition of ACSL4 with Troglitazone and a specific siRNA protected from cell death and lipid peroxidation induced by co-stimulation of AA and RSL3 in HK2 cells. Likewise, ALOX15 proteins levels were also increased in FA-AKI at 48 hours. PD1646 and Compound 1, both used to inhibit ALOX15, protected from ferroptotic cell death and lipid peroxidation in HK2 cells. Lipidomic analysis on HK2 tubular cells stimulated with AA+RSL3 uncovered an increased content of key peroxidized lipid species involved in ferroptosis execution, which was alleviated by targeting ACSL4 or ALOX15. Additionally, renal function of FA-AKI in mice was improved by ACSL4 pharmacological inhibition with Troglitazone and with ALOX15 inhibition with Compound 1. Conclusion Our preliminary results suggest therapeutic potential of ACSL4 and ALOX15 as ferroptotic targes during AKI. High PUFA content sensitizes human tubular HK2 cells to cell death and lipid peroxidation in the presence of sublethal ferroptotic triggers, and this was prevented by targeting ACSL4 or ALOX15 both in vitro and in vivo in FA-AKI. Closely related lipid peroxide species were decreased by ACSL4 or ALOX15 inhibitors.

Abstract Background and Aims Receptor-interacting protein kinase 3 (RIPK3) is traditionally involved in necroptosis, a regulated necrosis pathway which has been observed in diseases associated to cell death and inflammation. However, RIPK3 has been also associated to inflammatory responses independent of necroptosis. In previous studies we demonstrated that RIPK3 deficiency does not prevent renal injury but protects from inflammation in folic acid-induced AKI (FA-AKI), suggesting a proinflammatory role independently of cell death. In the present work, we aim to explore the role of RIPK3 in kidney injury and inflammation induced by a cytokine storm. Method Lipopolysaccharide (LPS) was used to induce cytokine storm-AKI in mice. For this, female 12- to 14-week-old wild type (WT), RIPK3-KO, MLKL-KO or NRLP3-KO C57BL/6J mice received a single intraperitoneal (i.p) injection of LPS 5 mg/kg or vehicle and were sacrificed 1h, 4h and 24 hours later. To generate chimera mice, WT and Ripk3-KO receptor mice were irradiated to deplete the autologous bone marrow (BM). BM was extracted from the femur and tibia of donor WT or Ripk3-KO mice, and 107 cells were transferred to irradiated receptor mice by intravenous injection. After 1 month, LPS-AKI was induced. Plasma was collected to assess kidney function. Kidneys were collected for RNA, protein studies, and histologic studies. Additionally, a WT group received 1.65 mg/kg of the necroptosis inhibitor Necrostatin-1 (Nec1) i.p. prior to LPS to evaluate the impact of necroptosis pathway. Liver, lungs and heart were also collected to assess the systemic inflammatory response. Additionally, cultured murine immortalized tubular MCT cells, and primary tubular cells, bone marrow dendritic cells (BMDC) and bone marrow derived macrophages (BMDM) isolated from WT and Ripk3-KO mice were studied. Cells were stimulated with 100 ng/ml LPS for 6h and RNA was studied. To analyze the impact of the inflammatory response on tubular cells, supernatants from LPS-stimulated BMDM and BMDC were collected and used to stimulate MCT cells. RNA expression was studied by RT-PCR and protein expression by Western Blotting. Results The kidney expression of RIPK3 mRNA and protein was upregulated in cytokine storm-AKI in mice, while Ripk3 deficiency improved survival and renal function, with less expression of proinflammatory cytokines and inflammatory infiltrate. Necroptosis did not seem to be implicated in cytokine storm-AKI, since neither Nec1 nor genetic MLKL ablation offered protection on renal function. Systemic inflammation in non-kidney organs was also milder with Ripk3 deficiency. In addition, inflammasome-related proteins were upregulated in cytokine storm-AKI, and this was reduced in Ripk3-KO mice. However, Nlrp3-deficient mice developed kidney injury and inflammation after LPS injection. Next, we explored the role of RIPK3 in BM-derived cells in cytokine storm-AKI by generating chimera mice. In this context, WT mice with Ripk3 deficient BM exhibited less inflammation and better renal function. This supports that RIPK3 from BM cells mediates kidney inflammation and injury during cytokine storm-AKI. In cultured cells, LPS induced RIPK3 expression in BMDMs but not in tubular cells, and RIPK3 mediated IL-6 expression in BMDMs but not in tubular cells. Moreover, IL-6 and conditioned media from LPS-exposed WT macrophages promoted proinflammatory responses in cultured tubular cells, that was partially ameliorated for RIPK3-KO LPS-macrophage conditioned medium. Conclusion In conclusion, RIPK3 mediates kidney injury and systemic inflammation induced by a cytokine storm independently of the necroptosis pathway. These results identify RIPK3 as a therapeutic target for renal inflammatory diseases.

Background Receptor-interacting protein kinase 3 (RIPK3), a component of necroptosis pathways, may have an independent role in inflammation. It has been unclear which RIPK3-expressing cells are responsible for the anti-inflammatory effect of overall Ripk3 deficiency and whether Ripk3 deficiency protects against kidney inflammation occurring in the absence of tubular cell death. Methods We used chimeric mice with bone marrow from wild-type and Ripk3-knockout mice to explore RIPK39s contribution to kidney inflammation in the presence of folic acid-induced acute kidney injury AKI (FA-AKI) or absence of AKI and kidney cell death (as seen in systemic administration of the cytokine TNFlike weak inducer of apoptosis [TWEAK]). Results Tubular and interstitial cell RIPK3 expressions were increased in murine AKI. Ripk3 deficiency decreased NF- kB activation and kidney inflammation in FA-AKI but did not prevent kidney failure. In the chimeric mice, RIPK3-expressing bone marrow-derived cells were required for early inflammation in FA-AKI. The NLRP3 inflammasome was not involved in RIPK39s proinflammatory effect. Systemic TWEAK administration induced kidney inflammation in wild-type but not Ripk3-deficient mice. In cell cultures, TWEAK increased RIPK3 expression in bone marrow-derived macrophages and tubular cells. RIPK3 mediated TWEAK-induced NF- kB activation and inflammatory responses in bone marrow-derived macrophages and dendritic cells and in Jurkat T cells; however, in tubular cells, RIPK3 mediated only TWEAKinduced Il-6 expression. Furthermore, conditioned media from TWEAK-exposed wild-type macrophages, but not from Ripk3-deficient macrophages, promoted proinflammatory responses in cultured tubular cells. Conclusions RIPK3 mediates kidney inflammation independently from tubular cell death. Specific targeting of bone marrow-derived RIPK3 may limit kidney inflammation without the potential adverse effects of systemic RIPK3 targeting.

Ferroptosis, a form of regulated necrosis characterized by peroxidation of lipids such as arachidonic acid‐containing phosphatidylethanolamine (PE), contributes to the pathogenesis of acute kidney injury (AKI). We have characterized the kidney lipidome in an experimental nephrotoxic AKI induced in mice using folic acid and assessed the impact of the ferroptosis inhibitor Ferrostatin‐1. Matrix‐assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) was used to assess kidney lipidomics and it discriminated between glomeruli, medulla, and cortex in control kidneys, AKI kidneys, and AKI + Ferrostatin‐1 kidneys. Out of 139 lipid species from 16 classes identified, 29 (20.5%) showed significant differences between control and AKI at 48 h. Total PE and lyso‐sulfatide species decreased, while phosphatidylinositol (PI) species increased in AKI. Dysregulated mRNA levels for Pemt, Pgs1, Cdipt, and Tamm41, relevant to lipid metabolism, were in line with the lipid changes observed. Ferrostatin‐1 prevented AKI and some AKI‐associated changes in lipid levels, such as the decrease in PE and lyso‐sulfatide species, without changing the gene expression of lipid metabolism enzymes. In conclusion, changes in the kidney lipid composition during nephrotoxic AKI are associated with differential gene expression of lipid metabolism enzymes and are partially prevented by Ferrostatin‐1. © 2022 The Pathological Society of Great Britain and Ireland.

Significance Statement In autosomal dominant polycystic kidney disease (ADPKD), interstitial inflammation promotes cyst progression. TWEAK is a TNF superfamily cytokine that regulates inflammatory responses, and its receptor, Fn14, is expressed in nephron epithelium. This paper describes TWEAK’s role in ADPKD and its potential as a therapeutic target. The Fn14/TWEAK axis is upregulated in human and mouse polycystic kidneys, and TWEAK administration in mice accelerates cyst progression, whereas anti-TWEAK treatment slows cyst growth, improving kidney function and survival. Anti-TWEAK antibodies restore several ADPKD-related pathways, such as proliferation and NF- κ B; slightly reduces fibrosis and apoptosis; and indirectly decreases macrophage recruitment. These findings identify the TWEAK signaling pathway as a new disease mechanism in ADPKD and a new possible therapeutic approach. Background In autosomal dominant polycystic kidney disease (ADPKD), cyst development and enlargement lead to ESKD. Macrophage recruitment and interstitial inflammation promote cyst growth. TWEAK is a TNF superfamily (TNFSF) cytokine that regulates inflammatory responses, cell proliferation, and cell death, and its receptor Fn14 (TNFRSF12a) is expressed in macrophage and nephron epithelia. Methods To evaluate the role of the TWEAK signaling pathway in cystic disease, we evaluated Fn14 expression in human and in an orthologous murine model of ADPKD. We also explored the cystic response to TWEAK signaling pathway activation and inhibition by peritoneal injection. Results Meta-analysis of published animal-model data of cystic disease reveals mRNA upregulation of several components of the TWEAK signaling pathway. We also observed that TWEAK and Fn14 were overexpressed in mouse ADPKD kidney cysts, and TWEAK was significantly high in urine and cystic fluid from patients with ADPKD. TWEAK administration induced cystogenesis and increased cystic growth, worsening the phenotype in a murine ADPKD model. Anti-TWEAK antibodies significantly slowed the progression of ADPKD, preserved renal function, and improved survival. Furthermore, the anti-TWEAK cystogenesis reduction is related to decreased cell proliferation–related MAPK signaling, decreased NF- κ B pathway activation, a slight reduction of fibrosis and apoptosis, and an indirect decrease in macrophage recruitment. Conclusions This study identifies the TWEAK signaling pathway as a new disease mechanism involved in cystogenesis and cystic growth and may lead to a new therapeutic approach in ADPKD.

Background: Despite the term acute kidney injury (AKI), clinical biomarkers for AKI reflect function rather than injury and independent markers of injury are needed. Tubular cell death, including necroptotic cell death, is a key feature of AKI. Cyclophilin A (CypA) is an intracellular protein that has been reported to be released during necroptosis. We have now explored CypA as a potential marker for kidney injury in cultured tubular cells and in clinical settings of ischemia-reperfusion injury (IRI), characterized by limitations of current diagnostic criteria for AKI. Methods: CypA was analyzed in cultured human and murine proximal tubular epithelial cells exposed to chemical hypoxia, hypoxia/reoxygenation (H/R) or other cell death (apoptosis, necroptosis, ferroptosis) inducers. Urinary levels of CypA (uCypA) were analyzed in patients after nephron sparing surgery (NSS) in which the contralateral kidney is not disturbed and kidney grafts with initial function. Results: Intracellular CypA remained unchanged while supernatant CypA increased in parallel to cell death induction. uCypA levels were higher in NSS patients with renal artery clamping (that is, with NSS-IRI) than in no clamping (NSS-no IRI), and in kidney transplantation (KT) recipients (KT-IRI) even in the presence of preserved or improving kidney function, while this was not the case for urinary Neutrophil gelatinase-associated lipocalin (NGAL). Furthermore, higher uCypA levels in NSS patients were associated with longer surgery duration and the incidence of AKI increased from 10% when using serum creatinine (sCr) or urinary output criteria to 36% when using high uCypA levels in NNS clamping patients. Conclusions: CypA is released by kidney tubular cells during different forms of cell death, and uCypA increased during IRI-induced clinical kidney injury independently from kidney function parameters. Thus, uCypA is a potential biomarker of kidney injury, which is independent from decreased kidney function.

Omeprazole, a proton pump inhibitor used to treat peptic ulcer and gastroesophageal reflux disease, has been associated to chronic kidney disease and acute interstitial nephritis. However, whether omeprazole is toxic to renal cells is unknown. Omeprazole has a lethal effect over some cancer cells, and cell death is a key process in kidney disease. Thus, we evaluated the potential lethal effect of omeprazole over tubular cells. Omeprazole induced dose-dependent cell death in human and murine proximal tubular cell lines and in human primary proximal tubular cell cultures. Increased cell death was observed at the high concentrations used in cancer cell studies and also at lower concentrations similar to those in peptic ulcer patient serum. Cell death induced by omeprazole had features of necrosis such as annexin V/7-AAD staining, LDH release, vacuolization and irregular chromatin condensation. Weak activation of caspase-3 was observed but inhibitors of caspases (zVAD), necroptosis (Necrostatin-1) or ferroptosis (Ferrostatin-1) did not prevent omeprazole-induced death. However, omeprazole promoted a strong oxidative stress response affecting mitochondria and lysosomes and the antioxidant N-acetyl-cysteine reduced oxidative stress and cell death. By contrast, iron overload increased cell death. An adaptive increase in the antiapoptotic protein BclxL failed to protect cells. In mice, parenteral omeprazole increased tubular cell death and the expression of NGAL and HO-1, markers of renal injury and oxidative stress, respectively. In conclusion, omeprazole nephrotoxicity may be related to induction of oxidative stress and renal tubular cell death.

Acute kidney injury (AKI) and chronic kidney disease (CKD) are the most severe consequences of kidney injury. They are interconnected syndromes as CKD predisposes to AKI and AKI may accelerate CKD progression. Despite their growing impact on the global burden of disease, there is no satisfactory treatment for AKI and current therapeutic approaches to CKD remain suboptimal. Recent research has focused on the therapeutic target potential of epigenetic regulation of gene expression, including non-coding RNAs and the covalent modifications of histones and DNA. Indeed, several drugs targeting histone modifications are in clinical use or undergoing clinical trials. Acyl-lysine histone modifications (e.g. methylation, acetylation, and crotonylation) have modulated experimental kidney injury. Most recently, increased histone lysine crotonylation (Kcr) was observed during experimental AKI and could be reproduced in cultured tubular cells exposed to inflammatory stress triggered by the cytokine TWEAK. The degree of kidney histone crotonylation was modulated by crotonate availability and crotonate supplementation protected from nephrotoxic AKI. We now review the functional relevance of histone crotonylation in kidney disease and other pathophysiological contexts, as well as the implications for the development of novel therapeutic approaches. These studies provide insights into the overall role of histone crotonylation in health and disease.

Diabetic kidney disease is one of the fastest growing causes of death worldwide. Epigenetic regulators control gene expression and are potential therapeutic targets. There is functional interventional evidence for a role of DNA methylation and the histone post-translational modifications-histone methylation, acetylation and crotonylation-in the pathogenesis of kidney disease, including diabetic kidney disease. Readers of epigenetic marks, such as bromodomain and extra terminal (BET) proteins, are also therapeutic targets. Thus, the BD2 selective BET inhibitor apabetalone was the first epigenetic regulator to undergo phase-3 clinical trials in diabetic kidney disease with an endpoint of kidney function. The direct therapeutic modulation of epigenetic features is possible through pharmacological modulators of the specific enzymes involved and through the therapeutic use of the required substrates. Of further interest is the characterization of potential indirect effects of nephroprotective drugs on epigenetic regulation. Thus, SGLT2 inhibitors increase the circulating and tissue levels of β-hydroxybutyrate, a molecule that generates a specific histone modification, β-hydroxybutyrylation, which has been associated with the beneficial health effects of fasting. To what extent this impact on epigenetic regulation may underlie or contribute to the so-far unclear molecular mechanisms of cardio- and nephroprotection offered by SGLT2 inhibitors merits further in-depth studies.

: Chronic kidney disease (CKD) is one of the fastest growing causes of death worldwide, emphasizing the need to develop novel therapeutic approaches. CKD predisposes to acute kidney injury (AKI) and AKI favors CKD progression. Mitochondrial derangements are common features of both AKI and CKD and mitochondria-targeting therapies are under study as nephroprotective agents. PGC-1α is a master regulator of mitochondrial biogenesis and an attractive therapeutic target. Low PGC-1α levels and decreased transcription of its gene targets have been observed in both preclinical AKI (nephrotoxic, endotoxemia, and ischemia-reperfusion) and in experimental and human CKD, most notably diabetic nephropathy. In mice, PGC-1α deficiency was associated with subclinical CKD and predisposition to AKI while PGC-1α overexpression in tubular cells protected from AKI of diverse causes. Several therapeutic strategies may increase kidney PGC-1α activity and have been successfully tested in animal models. These include AMP-activated protein kinase (AMPK) activators, phosphodiesterase (PDE) inhibitors, and anti-TWEAK antibodies. In conclusion, low PGC-1α activity appears to be a common feature of AKI and CKD and recent characterization of nephroprotective approaches that increase PGC-1α activity may pave the way for nephroprotective strategies potentially effective in both AKI and CKD.

Cell death is a finely regulated process occurring through different pathways. Regulated cell death, either through apoptosis or regulated necrosis offers the possibility of therapeutic intervention. Necroptosis and ferroptosis are among the best studied forms of regulated necrosis in the context of kidney disease. We now review the current evidence supporting a role for ferroptosis in kidney disease and the implications of this knowledge for the design of novel therapeutic strategies. Ferroptosis is defined functionally, as a cell modality characterized by peroxidation of certain lipids, constitutively suppressed by GPX4 and inhibited by iron chelators and lipophilic antioxidants. There is functional evidence of the involvement of ferroptosis in diverse forms of kidneys disease. In a well characterized nephrotoxic acute kidney injury model, ferroptosis caused an initial wave of death, triggering an inflammatory response that in turn promoted necroptotic cell death that perpetuated kidney dysfunction. This suggests that ferroptosis inhibitors may be explored as prophylactic agents in clinical nephrotoxicity or ischemia–reperfusion injury such as during kidney transplantation. Transplantation offers the unique opportunity of using anti-ferroptosis agent ex vivo, thus avoiding bioavailability and in vivo pharmacokinetics and pharmacodynamics issues.

PGC-1α (peroxisome proliferator-activated receptor gamma coactivator-1α, PPARGC1A) regulates the expression of genes involved in energy homeostasis and mitochondrial biogenesis. Here we identify inactivation of the transcriptional regulator PGC-1α as a landmark for experimental nephrotoxic acute kidney injury (AKI) and describe the in vivo consequences of PGC-1α deficiency over inflammation and cell death in kidney injury. Kidney transcriptomic analyses of WT mice with folic acid-induced AKI revealed 1398 up- and 1627 downregulated genes. Upstream transcriptional regulator analyses pointed to PGC-1α as the transcription factor potentially driving the observed expression changes with the highest reduction in activity. Reduced PGC-1α expression was shared by human kidney injury. Ppargc1a-/- mice had spontaneous subclinical kidney injury characterized by tubulointerstitial inflammation and increased Ngal expression. Upon AKI, Ppargc1a-/- mice had lower survival and more severe loss of renal function, tubular injury, and reduction in expression of mitochondrial PGC-1α-dependent genes in the kidney, and an earlier decrease in mitochondrial mass than WT mice. Additionally, surviving Ppargc1a-/- mice showed higher rates of tubular cell death, compensatory proliferation, expression of proinflammatory cytokines, NF-κB activation, and interstitial inflammatory cell infiltration. Specifically, Ppargc1a-/- mice displayed increased M1 and decreased M2 responses and expression of the anti-inflammatory cytokine IL-10. In cultured renal tubular cells, PGC-1α targeting promoted spontaneous cell death and proinflammatory responses. In conclusion, PGC-1α inactivation is a key driver of the gene expression response in nephrotoxic AKI and PGC-1α deficiency promotes a spontaneous inflammatory kidney response that is magnified during AKI. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Acute kidney injury is a common complication of rhabdomyolysis. A better understanding of this syndrome may be useful to identify novel therapeutic targets because there is no specific treatment so far. Ferroptosis is an iron-dependent form of regulated nonapoptotic cell death that is involved in renal injury. In this study, we investigated whether ferroptosis is associated with rhabdomyolysis-mediated renal damage, and we studied the therapeutic effect of curcumin, a powerful antioxidant with renoprotective properties. Induction of rhabdomyolysis in mice increased serum creatinine levels, endothelial damage, inflammatory chemokines, and cytokine expression, alteration of redox balance (increased lipid peroxidation and decreased antioxidant defenses), and tubular cell death. Treatment with curcumin initiated before or after rhabdomyolysis induction ameliorated all these pathologic and molecular alterations. Although apoptosis or receptor-interacting protein kinase (RIPK)3-mediated necroptosis were activated in rhabdomyolysis, our results suggest a key role of ferroptosis. Thus, treatment with ferrostatin 1, a ferroptosis inhibitor, improved renal function in glycerol-injected mice, whereas no beneficial effects were observed with the pan-caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-(O-methyl)-fluoromethylketone or in RIPK3-deficient mice. In cultured renal tubular cells, myoglobin (Mb) induced ferroptosis-sensitive cell death that was also inhibited by curcumin. Mechanistic in vitro studies showed that curcumin reduced Mb-mediated inflammation and oxidative stress by inhibiting the TLR4/NF-κB axis and activating the cytoprotective enzyme heme oxygenase 1. Our findings are the first to demonstrate the involvement of ferroptosis in rhabdomyolysis-associated renal damage and its sensitivity to curcumin treatment. Therefore, curcumin may be a potential therapeutic approach for patients with this syndrome.-Guerrero-Hue, M., García-Caballero, C., Palomino-Antolín, A., Rubio-Navarro, A., Vázquez-Carballo, C., Herencia, C., Martín-Sanchez, D., Farré-Alins, V., Egea, J., Cannata, P., Praga, M., Ortiz, A., Egido, J., Sanz, A. B., Moreno, J. A. Curcumin reduces renal damage associated with rhabdomyolysis by decreasing ferroptosis-mediated cell death.

Epigenetics refers to heritable changes in gene expression patterns not caused by an altered nucleotide sequence, and includes non-coding RNAs and covalent modifications of DNA and histones. This review focuses on functional evidence for the involvement of DNA and histone epigenetic modifications in the pathogenesis of kidney disease and the potential therapeutic implications. There is evidence of activation of epigenetic regulatory mechanisms in acute kidney injury (AKI), chronic kidney disease (CKD) and the AKI-to-CKD transition of diverse aetiologies, including ischaemia-reperfusion injury, nephrotoxicity, ureteral obstruction, diabetes, glomerulonephritis and polycystic kidney disease. A beneficial in vivo effect over preclinical kidney injury has been reported for drugs that decrease DNA methylation by either inhibiting DNA methylation (e.g. 5-azacytidine and decitabine) or activating DNA demethylation (e.g. hydralazine), decrease histone methylation by inhibiting histone methyltransferases, increase histone acetylation by inhibiting histone deacetylases (HDACs, e.g. valproic acid, vorinostat, entinostat), increase histone crotonylation (crotonate) or interfere with histone modification readers [e.g. inhibits of bromodomain and extra-terminal proteins (BET)]. Most preclinical studies addressed CKD or the AKI-to-CKD transition. Crotonate administration protected from nephrotoxic AKI, but evidence is conflicting on DNA methylation inhibitors for preclinical AKI. Several drugs targeting epigenetic regulators are in clinical development or use, most of them for malignancy. The BET inhibitor apabetalone is in Phase 3 trials for atherosclerosis, kidney function being a secondary endpoint, but nephrotoxicity was reported for DNA and HDAC inhibitors. While research into epigenetic modulators may provide novel therapies for kidney disease, caution should be exercised based on the clinical nephrotoxicity of some drugs.