Induction of heme oxygenase is a rapid, protective response in rhabdomyolysis in the rat

Induction of p16Ink4a Gene Expression in Heme Protein-Induced AKI and by Heme: Pathophysiologic Implications

Key Points

In heme protein–mediated AKI (HP-AKI), a senescence phenotype promptly occurs, and increased expression of p16Ink4a contributes to HP-AKI. Renal p16Ink4a expression is induced by hemoglobin, myoglobin, and heme in vivo and in renal epithelial cells exposed to heme in vitro . Impairing the binding or degradation of heme by hemopexin deficiency or heme oxygenase-1 deficiency, respectively, further upregulates p16Ink4a.

Background

Understanding the pathogenetic basis for AKI involves the study of ischemic and nephrotoxic models of AKI, the latter including heme protein–mediated AKI (HP-AKI). Recently, interest has grown regarding the role of senescence as a mechanism of kidney injury, including AKI. We examined whether senescence occurs in HP-AKI and potential inducers of and the role of a key driver of senescence, namely, p16Ink4a, in HP-AKI.

Methods

The long-established murine glycerol model of HP-AKI was used, and indices of senescence were examined. To evaluate the interaction of heme and p16Ink4a expression, murine models of genetic deficiency of hemopexin (HPX ) and heme oxygenase-1 (HO-1 ) were used. To determine the involvement of p16Ink4a in HP-AKI, the population of p16Ink4a-expressing cells was reduced using the INK-ATTAC model.

Results

Using multiple indices, a senescence phenotype appears in the kidney within hours after the induction of HP-AKI. This phenotype includes significant upregulation of p16Ink4a. p16Ink4a is upregulated in the kidney after the individual administration of myoglobin, hemoglobin, and heme, as well as in renal epithelial cells exposed to heme in vitro . Genetic deficiencies of HPX and HO-1 , which, independently, are expected to increase heme content in the kidney, exaggerate induction of p16Ink4a in the kidney and exacerbate HP-AKI, the latter shown in the present studies involving HPX −/− mice and in previous studies involving HO-1 −/− mice. Finally, reduction in the population of p16Ink4a-expressing cells in the kidney improves renal function in HP-AKI even within 24 hours.

Conclusions

The pathogenesis of HP-AKI involves senescence and the induction of p16Ink4a, the latter driven, in part, by hemoglobin, myoglobin, and heme.

Management of kidney injury in critically ill patients with earthquake-induced crush syndrome: A case series of 18 patients

İNTRODUCTION: It was aimed primarily to analyze the development of acute kidney injury (AKI) and treatment management in critically ill patients who developed rhabdomyolysis due to earthquake-related crush syndrome.

METHODS

We evaluated 18 patients with crush syndrome who were admitted to the intensive care unit (ICU) after the great earthquake in February 2023 in Turkey.

RESULTS

AKI occurred in 83% (n:15) of these patients after ICU admission (AKI-1; 16.6% [n:3], AKI-2; 16.6% [n:3], and AKI-3; 50% [n:9]). While the majority of patients who developed crush syndrome were treated with high volume intravenous hydration, only 33% (n:6) of all patients required renal replacement therapy. All patients who developed AKI had complete recovery in renal functions at the end of 2 months.

CONCLUSION

There is no need for routine renal replacement therapy in the treatment of AKI, which is frequently seen in patients with crush syndrome. Most can be treated with high volumes of intravenous fluid.

Tweak/Fn14 system is involved in rhabdomyolysis-induced acute kidney injury

BACKGROUND

Rhabdomyolysis is a severe clinical syndrome associated to acute kidney injury (AKI) and chronic kidney disease (CKD). TWEAK/Fn14 signaling axis regulates renal inflammation and tubular cell death. However, the functional role of TWEAK/Fn14 in rhabdomyolysis remains unknown.

METHODS

Rhabdomyolysis was induced in wild-type, TWEAK- and Fn14-deficient mice or mice treated with TWEAK blocking antibody. Renal injury, inflammation, fibrosis and cell death were assessed. Additionally, we performed in vivo and in vitro studies to explore the possible signalling pathways involved in Fn14 regulation.

FINDINGS

Fn14 renal expression was increased in mice with rhabdomyolysis, correlating with decline of renal function. Mechanistically, myoglobin (Mb) induced Fn14 expression via ERK and p38 pathway, whereas Nrf2 activation diminished Mb-mediated Fn14 upregulation in cultured renal cells. TWEAK or Fn14 genetic depletion ameliorated rhabdomyolysis-associated loss of renal function, histological damage, tubular cell death, inflammation, and expression of both tubular and endothelial injury markers. Deficiency of TWEAK or Fn14 also decreased long-term renal inflammation and fibrosis in mice with rhabdomyolysis. Finally, pharmacological treatment with a blocking TWEAK antibody diminished the expression of acute renal injury markers and cell death and lessened residual kidney fibrosis and chronic inflammation in rhabdomyolysis.

INTERPRETATION

TWEAK/Fn14 axis participates in the pathogenesis of rhabdomyolysis-AKI and subsequent AKI-CKD transition. Blockade of this signaling pathway may represent a promising therapeutic strategy for reducing rhabdomyolysis-mediated renal injury.

FUNDING

Spanish Ministry of Science and Innovation, ISCIII and Junta de Andalucía.

Arginase2 mediates contrast-induced acute kidney injury via facilitating nitrosative stress in tubular cells

Contrast-induced acute kidney injury(CI-AKI) is the third cause of AKI. Although tubular injury has been regarded as an important pathophysiology of CI-AKI, the underlying mechanism remains elusive. Here, we found arginase2(ARG2) accumulated in the tubules of CI-AKI mice, and was upregulated in iohexol treated kidney tubular cells and in blood samples of CI-AKI mice and patients, accompanied by increased nitrosative stress and apoptosis. However, all of the above were reversed in ARG2 knockout mice, as evidenced by the ameliorated kidney dysfunction and the tubular injury, and decreased nitrosative stress and apoptosis. Mechanistically, HO-1 upregulation could alleviate iohexol or ARG2 overexpression mediated nitrosative stress. Silencing and overexpressing ARG2 was able to upregulate and downregulate HO-1 expression, respectively, while HO-1 siRNA had no effect on ARG2 expression, indicating that ARG2 might inhibit HO-1 expression at the transcriptional level, which facilitated nitrosative stress during CI-AKI. Additionally, CREB1, a transcription factor, bound to the promoter region of ARG2 and stimulated its transcription. Similar findings were yielded in cisplatin- or vancomycin-induced AKI models. Taken together, ARG2 is a crucial target of CI-AKI, and activating CREB1/ARG2/HO-1 axis can mediate tubular injury by promoting nitrosative stress, highlighting potential therapeutic strategy for treating CI-AKI.

Hyperoxia Increases Kidney Injury During Renal Ischemia and Reperfusion in Mice

BACKGROUND

Renal ischemia and reperfusion (IR) contribute to perioperative acute kidney injury, and oxygen is a key regulator of this process. We hypothesized that oxygen administration during surgery and renal IR would impact postoperative kidney function and injury in mice.

METHODS

Mice were anesthetized, intubated, and mechanically ventilated with a fraction of inspired oxygen (F io2 ) 0.10 (hypoxia), 0.21 (normoxia), 0.60 (moderate hyperoxia), or 1.00 (severe hyperoxia) during 67 minutes of renal IR or sham IR surgery. Additional mice were treated before IR or sham IR surgery with 50 mg/kg tempol, a superoxide scavenger. At 24 hours, mice were sacrificed, and blood and kidney collected. We assessed and compared kidney function and injury across groups by measuring blood urea nitrogen (BUN, primary end point), renal histological injury, renal expression of neutrophil gelatinase-associated lipocalin (NGAL), and renal heme oxygenase 1 ( Ho-1 ), peroxisome proliferator-activated receptor gamma coactivator 1-α ( Pgc1-α ), and glutathione peroxidase 4 ( Gpx-4 ) transcripts, to explore potential mechanisms of any effect of oxygen.

RESULTS

Hyperoxia and hypoxia during renal IR surgery decreased renal function and increased kidney injury compared to normoxia. Baseline median (interquartile range) BUN was 22.2 mg/dL (18.4-26.0), and 24 hours after IR surgery, BUN was 17.5 mg/dL (95% confidence interval [CI], 1.3-38.4; P = .034) higher in moderate hyperoxia-treated animals, 51.8 mg/dL (95% CI, 24.9-74.8; P < .001) higher in severe hyperoxia-treated animals, and 64.9 mg/dL (95% CI, 41.2-80.3; P < .001) higher in hypoxia-treated animals compared to animals treated with normoxia ( P < .001, overall effect of hyperoxia). Hyperoxia-induced injury, but not hypoxia-induced injury, was attenuated by pretreatment with tempol. Histological injury scores, renal NGAL staining, and renal transcription of Ho-1 and suppression of Pgc1- α followed the same pattern as BUN, in relation to the effects of oxygen treatment.

CONCLUSIONS

In this controlled preclinical study of oxygen treatment during renal IR surgery, hyperoxia and hypoxia impaired renal function, increased renal injury, and impacted expression of genes that affect mitochondrial biogenesis and antioxidant response. These results might have implications for patients during surgery when high concentrations of oxygen are frequently administered, especially in cases involving renal IR.

The pathophysiology of rhabdomyolysis in ungulates and rats: towards the development of a rodent model of capture myopathy

Capture myopathy (CM), which is associated with the capture and translocation of wildlife, is a life-threatening condition that causes noteworthy morbidity and mortality in captured animals. Such wildlife deaths have a significant impact on nature conservation efforts and the socio-economic wellbeing of communities reliant on ecotourism. Several strategies are used to minimise the adverse consequences associated with wildlife capture, especially in ungulates, but no successful preventative or curative measures have yet been developed. The primary cause of death in wild animals diagnosed with CM stems from kidney or multiple organ failure as secondary complications to capture-induced rhabdomyolysis. Ergo, the development of accurate and robust model frameworks is vital to improve our understanding of CM. Still, since CM-related complications are borne from biological and behavioural factors that may be unique to wildlife, e.g. skeletal muscle architecture or flighty nature, certain differences between the physiology and stress responses of wildlife and rodents need consideration in such endeavours. Therefore, the purpose of this review is to summarise some of the major etiological and pathological mechanisms of the condition as it is observed in wildlife and what is currently known of CM-like syndromes, i.e. rhabdomyolysis, in laboratory rats. Additionally, we will highlight some key aspects for consideration in the development and application of potential future rodent models.

The roles of heme oxygenase-1 in renal disease

Heme oxygenase (HO), a heat shock protein containing hemoglobin, is an important enzyme in heme catabolism. It is involved in cell homeostasis and has anti-inflammatory, antioxidant, anti-apoptosis, immunomodulation, and other functions. It is expressed at a modest level in most normal tissues. When the body suffers from ischemia hypoxia, injury, toxins, and other nociceptive stimuli, the expression increases, which can transform the oxidative microenvironment into an antioxidant environment to promote tissue recovery from damage. In recent years, research has continued to verify its value in a variety of human bodily systems. It is also regarded as a key target for the treatment of numerous disorders. With the advancement of studies, its significance in renal disease has gained increasing attention. It is thought to have a significant protective function in preventing acute kidney injury and delaying the progression of chronic renal diseases. Its protective mechanisms include anti-inflammatory, antioxidant, cell cycle regulation, apoptosis inhibition, hemodynamic regulation, and other aspects, which have been demonstrated in diverse animal models. Furthermore, as a protective factor, its potential therapeutic efficacy in renal disease has recently become a hot area of research. Although a large number of preclinical trials have confirmed its therapeutic potential in reducing kidney injury, due to the problems and side effects of HO-1 induction therapy, its efficacy and safety in clinical application need to be further explored. In this review, we summarize the current state of research on the mechanism, location, and treatment of HO and its relationship with various renal diseases.

Pre-conditioning of gingival epithelial cells with sub-apoptotic concentrations of curcumin prevents pro-inflammatory cytokine release

BACKGROUND AND OBJECTIVE

Plaque-induced gingival inflammation (gingivitis) is ubiquitous in humans. The epithelial barrier reacts to the presence of oral bacteria and induces inflammatory cascades. The objective of this study was to investigate the mechanism by which the small molecule micronutrient curcumin could decrease inflammatory response in vitro to oral bacterium heat-killed Fusobacterium nucleatum as curcumin could be a useful compound for combatting gingivitis already consumed by humans.

METHODS

H400 oral epithelial cell line was pre-conditioned with curcumin and the production of cytokines was measured by enzyme-linked immunosorbent assay (ELISA) and translocation of transcription factors was used to monitor inflammatory responses. Haem oxygenase (HO-1) expression and molecules that HO-1 releases were evaluated for their potential to reduce the quantity of cytokine production. Immunofluorescence microscopy and Western blotting were used to evaluate changes in transcription factor and enzyme location.

RESULTS

Pre-conditioning of H400 cells with a sub-apoptotic concentration of curcumin (20 μM) attenuated secretion of Granulocyte-Macrophage - Colony-Stimulating Factor (GM-CSF) and reduced NFkB nuclear translocation. This pre-conditioning caused an increase in nuclear Nrf2; an initial drop (at 8 h) followed by an adaptive increase (at 24 h) in glutathione; and an increase in haem oxygenase (HO-1) expression. Inhibition of HO-1 by SnPPIX prevented the curcumin-induced attenuation of GM-CSF production. HO-1 catalyses the breakdown of haem to carbon monoxide, free iron and biliverdin: the HO-1/CO anti-inflammatory pathway. Elevations in carbon monoxide, achieved using carbon monoxide releasing molecule-2 (CORM2) treatment alone abrogated F. nucleatum-induced cytokine production. Biliverdin is converted to bilirubin by biliverdin reductase (BVR). This pleiotropic protein was found to increase in cell membrane expression upon curcumin treatment.

CONCLUSION

Curcumin decreased inflammatory cytokine production induced by Fusobacterium nucleatum in H400 oral epithelial cells. The mechanism of action appears to be driven by the increase of haem oxygenase and the production of carbon monoxide.

Sesamol Attenuates Renal Inflammation and Arrests Reactive-Oxygen-Species-Mediated IL-1β Secretion via the HO-1-Induced Inhibition of the IKKα/NFκB Pathway In Vivo and In Vitro

Chronic nephritis leads to irreversible renal fibrosis, ultimately leading to chronic kidney disease (CKD) and death. Macrophage infiltration and interleukin 1β (IL-1β) upregulation are involved in inflammation-mediated renal fibrosis and CKD. Sesamol (SM), which is extracted from sesame seeds, has antioxidant and anti-inflammatory properties. We aimed to explore whether SM mitigates macrophage-mediated renal inflammation and its underlying mechanisms. ApoE^-/- mice were subjected to 5/6 nephrectomy (5/6 Nx) with or without the oral gavage of SM for eight weeks. Blood and urine samples and all the kidney remnants were collected for analysis. Additionally, THP-1 cells were used to explore the mechanism through which SM attenuates renal inflammation. Compared with the sham group, the 5/6 Nx ApoE^-/- mice exhibited a significant increase in the macrophage infiltration of the kidneys (nephritis), upregulation of IL-1β, generation of reactive oxygen species, reduced creatinine clearance, and renal fibrosis. However, the administration of SM significantly alleviated these effects. SM suppressed the H₂O₂-induced secretion of IL-1β from the THP-1 cells via the heme oxygenase-1-induced inhibition of the IKKα-NF-κB pathway. SM attenuated renal inflammation and arrested macrophage accumulation by inhibiting IKKα, revealing a novel mechanism of the therapeutic effects of SM on renal injury and offering a potential approach to CKD treatment.

Kynurenine/Aryl Hydrocarbon Receptor Modulates Mitochondria-Mediated Oxidative Stress and Neuronal Apoptosis in Experimental Intracerebral Hemorrhage

Aims: Oxidative stress and neuronal apoptosis play crucial roles in the pathological processes of secondary injury after intracerebral hemorrhage (ICH). Aryl hydrocarbon receptor (AHR), together with its endogenous ligand kynurenine, is known to mediate free radical accumulation and neuronal excitotoxicity in central nervous systems. Herein, we investigate the pathological roles of kynurenine/AHR after ICH. Results: Endogenous AHR knockout alleviated reactive oxygen species accumulation and neuronal apoptosis in ipsilateral hemisphere at 48 h after ICH in mice. The ICH insult resulted in an increase of total and nucleus AHR protein levels and AHR transcriptional activity. Inhibition of AHR provided both short- and long- term neurological benefits by attenuating mitochondria-mediated oxidative stress and neuronal apoptosis after ICH in mice. RhoA-Bax signaling activated mitochondrial death pathway and participated in deleterious actions of AHR. Finally, we reported that exogenous kynurenine aggravated AHR activation and mediated the brain mentioned earlier. Male animals were used in the experiments. Innovation: We show for the first time that kynurenine/AHR mediates mitochondria death and free radical accumulation, at least partially via the RhoA/Bax signaling pathway. Pharmacological antagonists of AHR and kynurenine may ameliorate neurobehavioral function and improve the prognosis of patients with ICH. Conclusion: Kynurenine/AHR may serve as a potential therapeutic target to attenuate mitochondria-mediated oxidative stress and neuronal cells impairment in patients with ICH. Antioxid. Redox Signal. 37, 1111-1129.

Heme Proteins and Kidney Injury: Beyond Rhabdomyolysis

Heme proteins, the stuff of life, represent an ingenious biologic strategy that capitalizes on the biochemical versatility of heme, and yet is one that avoids the inherent risks to cellular vitality posed by unfettered and promiscuously reactive heme. Heme proteins, however, may be a double-edged sword because they can damage the kidney in certain settings. Although such injury is often viewed mainly within the context of rhabdomyolysis and the nephrotoxicity of myoglobin, an increasing literature now attests to the fact that involvement of heme proteins in renal injury ranges well beyond the confines of this single disease (and its analog, hemolysis); indeed, through the release of the defining heme motif, destabilization of intracellular heme proteins may be a common pathway for acute kidney injury, in general, and irrespective of the underlying insult. This brief review outlines current understanding regarding processes underlying such heme protein-induced acute kidney injury (AKI) and chronic kidney disease (CKD). Topics covered include, among others, the basis for renal injury after the exposure of the kidney to and its incorporation of myoglobin and hemoglobin; auto-oxidation of myoglobin and hemoglobin; destabilization of heme proteins and the release of heme; heme/iron/oxidant pathways of renal injury; generation of reactive oxygen species and reactive nitrogen species by NOX, iNOS, and myeloperoxidase; and the role of circulating cell-free hemoglobin in AKI and CKD. Also covered are the characteristics of the kidney that render this organ uniquely vulnerable to injury after myolysis and hemolysis, and pathobiologic effects emanating from free, labile heme. Mechanisms that defend against the toxicity of heme proteins are discussed, and the review concludes by outlining the therapeutic strategies that have arisen from current understanding of mechanisms of renal injury caused by heme proteins and how such mechanisms may be interrupted.

Role of Toll-like receptor 4 in intravascular hemolysis-mediated injury

Massive intravascular hemolysis is a common characteristic of several pathologies. It is associated with the release of large quantities of heme into the circulation, promoting injury in vulnerable organs, mainly kidney, liver, and spleen. Heme activates Toll-like receptor 4 (TLR4), a key regulator of the inflammatory response; however, the role of TLR4 in hemolysis and whether inhibition of this receptor may protect from heme-mediated injury are unknown. We induced intravascular hemolysis by injection of phenylhydrazine in wildtype and Tlr4-knockout mice. In this model, we analyzed physiological parameters, histological damage, inflammation and cell death in kidney, liver, and spleen. We also evaluated whether heme-mediated-inflammatory effects were prevented by TLR4 inhibition with the compound TAK-242, both in vivo and in vitro. Induction of massive hemolysis elicited acute kidney injury characterized by loss of renal function, morphological alterations of the tubular epithelium, cell death, and inflammation. These pathological effects were significantly ameliorated in the TLR4-deficient mice and in wildtype mice treated with TAK-242. In vitro studies showed that TAK-242 pretreatment reduced heme-mediated inflammation by inhibiting the TLR4/NF-κB (nuclear factor kappa B) axis. However, analysis in liver and spleen indicated that TLR4 deficiency did not protect against the toxic accumulation of heme in these organs. In conclusion, TLR4 is a key molecule involved in the renal inflammatory response triggered by massive intravascular hemolysis. TLR4 inhibition may be a potential therapeutic approach to prevent renal damage in patients suffering from hemolysis. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Prominent Mitochondrial Injury as an Early Event in Heme Protein-Induced Acute Kidney Injury

Background

Mitochondrial injury occurs in and underlies acute kidney injury (AKI) caused by ischemia-reperfusion and other forms of renal injury. However, to date, a comprehensive analysis of this issue has not been undertaken in heme protein-induced AKI (HP-AKI). We examined key aspects of mitochondrial function, expression of proteins relevant to mitochondrial quality control, and mitochondrial ultrastructure in HP-AKI, along with responses to heme in renal proximal tubule epithelial cells.

Methods

The long-established murine glycerol model of HP-AKI was examined at 8 and 24 hours after HP-AKI. Indices of mitochondrial function (ATP and NAD+), expression of proteins relevant to mitochondrial dynamics, mitochondrial ultrastructure, and relevant gene/protein expression in heme-exposed renal proximal tubule epithelial cells in vitro were examined.

Results

ATP and NAD+ content and the NAD+/NADH ratio were all reduced in HP-AKI. Expression of relevant proteins indicate that mitochondrial biogenesis (PGC-1α, NRF1, and TFAM) and fusion (MFN2) were impaired, as was expression of key proteins involved in the integrity of outer and inner mitochondrial membranes (VDAC, Tom20, and Tim23). Conversely, marked upregulation of proteins involved in mitochondrial fission (DRP1) occurred. Ultrastructural studies, including novel 3D imaging, indicate profound changes in mitochondrial structure, including mitochondrial fragmentation, mitochondrial swelling, and misshapen mitochondrial cristae; mitophagy was also observed. Exposure of renal proximal tubule epithelial cells to heme in vitro recapitulated suppression of PGC-1α (mitochondrial biogenesis) and upregulation of p-DRP1 (mitochondrial fission).

Conclusions

Modern concepts pertaining to AKI apply to HP-AKI. This study validates the investigation of novel, clinically relevant therapies such as NAD+-boosting agents and mitoprotective agents in HP-AKI.

Advance of genetically modified pigs in xeno-transplantation

As the standard of living improves, chronic diseases and end-stage organ failure have been a regular occurrence in human beings. Organ transplantation has become one of the hopes in the fight against chronic diseases and end-stage organ failure. However, organs available for transplantation are far from sufficient to meet the demand, leading to a major organ shortage crisis. To solve this problem, researchers have turned to pigs as their target since pigs have many advantages as xenograft donors. Pigs are considered the ideal organ donor for human xenotransplantation, but direct transplantation of porcine organs to humans faces many obstacles, such as hyperacute rejection, acute humoral xenograft rejection, coagulation dysregulation, inflammatory response, coagulation dysregulation, and endogenous porcine retroviral infection. Many transgenic strategies have been developed to overcome these obstacles. This review provides an overview of current advances in genetically modified pigs for xenotransplantation. Future genetic engineering-based delivery of safe and effective organs and tissues for xenotransplantation remains our goal.

Oxidant- induced preconditioning: A pharmacologic approach for triggering renal 'self defense'

Acute kidney injury (AKI) is a common event, occurring in ~5% and ~35% of hospitalized and ICU patients, respectively. The development of AKI portends an increased risk of morbidity, mortality, prolonged hospitalization, and subsequent development of chronic kidney disease (CKD). Given these facts, a multitude of experimental studies have addressed potential methods for inducing AKI prevention in high-risk patients. However, successful clinical translation of promising experimental data has remained elusive. Over the past decade, our laboratory has focused on developing a method for safely triggering AKI protection by inducing "kidney preconditioning" in mice by the intravenous administration of a combination of Fe sucrose (FeS) + tin protoporphyrin (SnPP). These agents induce mild, but short lived, 'oxidant stress' which synergistically activate a number of kidney 'self-defense' pathways (e.g., Nrf2, ferritin, IL-10). Within 18-24 h of Fe/SnPP administration, marked protection against diverse forms of experimental toxic and ischemic AKI results. FeS/SnPP-mediated reductions in kidney injury can also indirectly decrease injury in other organs by mitigating the so called "organ cross talk" phenomenon. Given these promising experimental data, three phase 1b clinical trials were undertaken in healthy subjects and patients with stage 3 or 4 CKD. These studies demonstrated that FeS/SnPP were well tolerated and that they up-regulated the cytoprotective Nrf2, ferritin, and IL-10 pathways. Two subsequent phase 2 trials, conducted in patients undergoing 'on-pump' cardiovascular surgery or in patients hospitalized with COVID 19, confirmed FeS/SnPP safety. Furthermore, interim data analyses revealed statistically significant improvements in several clinical parameters. The goals of this review are to: (i) briefly discuss the historical background of renal "preconditioning"; (ii) present the experimental data that support the concept of FeS/SnPP- induced organ protection; and (iii) discuss the initial results of clinical trials that suggest the potential clinical utility of an 'oxidant preconditioning' strategy.

Molecular Mechanisms of Rhabdomyolysis-Induced Kidney Injury: From Bench to Bedside

Rhabdomyolysis-induced acute kidney injury (RIAKI) occurs following damage to the muscular sarcolemma sheath, resulting in the leakage of myoglobin and other metabolites that cause kidney damage. Currently, the sole recommended clinical treatment for RIAKI is aggressive fluid resuscitation, but other potential therapies, including pretreatments for those at risk for developing RIAKI, are under investigation. This review outlines the mechanisms and clinical significance of RIAKI, investigational treatments and their specific targets, and the status of ongoing research trials.

Identification of Cytoprotective Small-Molecule Inducers of Heme-Oxygenase-1

Acute kidney injury (AKI) is a major public health concern with significant morbidity and mortality and no current treatments beyond supportive care and dialysis. Preclinical studies have suggested that heme-oxygenase-1 (HO-1), an enzyme that catalyzes the breakdown of heme, has promise as a potential therapeutic target for AKI. Clinical trials involving HO-1 products (biliverdin, carbon monoxide, and iron), however, have not progressed beyond the Phase ½ level. We identified small-molecule inducers of HO-1 that enable us to exploit the full therapeutic potential of HO-1, the combination of its products, and yet-undefined effects of the enzyme system. Through cell-based, high-throughput screens for induction of HO-1 driven by the human HO-1 promoter/enhancer, we identified two novel small molecules and broxaldine (an FDA-approved drug) for further consideration as candidate compounds exhibiting an Emax ≥70% of 5 µM hemin and EC50 <10 µM. RNA sequencing identified shared binding motifs to NRF2, a transcription factor known to regulate antioxidant genes, including HMOX1. In vitro, the cytoprotective function of the candidates was assessed against cisplatin-induced cytotoxicity and apoptosis. In vivo, delivery of a candidate compound induced HO-1 expression in the kidneys of mice. This study serves as the basis for further development of small-molecule HO-1 inducers as preventative or therapeutic interventions for a variety of pathologies, including AKI.

Functional consequence of myeloid ferritin heavy chain on acute and chronic effects of rhabdomyolysis-induced kidney injury

Acute kidney injury (AKI) is a serious complication of rhabdomyolysis that significantly impacts survival. Myoglobin released from the damaged muscle accumulates in the kidney, causing heme iron-mediated oxidative stress, tubular cell death, and inflammation. In response to injury, myeloid cells, specifically neutrophils and macrophages, infiltrate the kidneys, and mediate response to injury. Ferritin, comprised of ferritin light chain and ferritin heavy chain (FtH), is vital for intracellular iron handling. Given the dominant role of macrophages and heme-iron burden in the pathogenesis of rhabdomyolysis, we studied the functional role of myeloid FtH in rhabdomyolysis-induced AKI and subsequent fibrosis. Using two models of rhabdomyolysis induced AKI, we found that during the acute phase, myeloid FtH deletion did not impact rhabdomyolysis-induced kidney injury, cell death or cell proliferation, suggesting that tubular heme burden is the dominant injury mechanism. We also determined that, while the kidney architecture was markedly improved after 28 days, tubular casts persisted in the kidneys, suggesting sustained damage or incomplete recovery. We further showed that rhabdomyolysis resulted in an abundance of disparate intra-renal immune cell populations, such that myeloid populations dominated during the acute phase and lymphoid populations dominated in the chronic phase. Fibrotic remodeling was induced in both genotypes at 7 days post-injury but continued to progress only in wild-type mice. This was accompanied by an increase in expression of pro-fibrogenic and immunomodulatory proteins, such as transforming growth factor-β, S100A8, and tumor necrosis factor-α. Taken together, we found that while the initial injury response to heme burden was similar, myeloid FtH deficiency was associated with lesser interstitial fibrosis. Future studies are warranted to determine whether this differential fibrotic remodeling will render these animals more susceptible to a second AKI insult or progress to chronic kidney disease at an accelerated pace.

Effect of Cisplatin on Renal Iron Homeostasis Components: Implication in Nephropathy

Cisplatin is an important chemotherapeutic drug for the treatment of solid tumors but often causes nephropathy as part of the off-target toxicity. Iron accumulation and related damage were implicated in cisplatin-induced kidney injury. However, the role of cisplatin in the renal iron sensing mechanism and its target genes responsible for iron uptake, storage, and release have not been investigated. Cellular iron homeostasis is controlled by the interaction of iron regulatory proteins (IRP1 and IRP2) and iron-responsive elements (IREs) present in the untranslated regions of iron transport and storage components. Here, we report that cisplatin does not influence the expressions of IRP targets such as transferrin receptor-1 (TfR1), divalent metal transporter-1 (DMT1), and ferroportin in renal cells despite the increased heme oxygenase-1 (HO-1) level. Ferritin subunits (Ft-H and Ft-L) are elevated in different magnitudes due to the increased mRNA expression. Intriguingly, a higher expression of Ft-L mRNA is detected than that of Ft-H mRNA. The inability of cisplatin in altering the IRE-IRP interaction is confirmed by examining IRE-containing luciferase activity, RNA electrophoretic mobility shift assay, and activation of IRPs. The labile iron pool is depleted but reversed by silencing of either Ft-H or Ft-L, suggesting increased iron storage by ferritin. Silencing of Ft-H or Ft-L promotes cell death, suggesting that ferritin acts to protect the renal cells from cisplatin-mediated toxicity. A differential increase of transcripts and equivalent increase of proteins of Ft-H and Ft-L and unaltered TfR1 and DMT1 transcripts are found in the kidneys of cisplatin-treated rats along with iron accumulation. Our results reveal that cisplatin does not influence the IRE-IRP interaction despite alteration of the cellular iron pool in renal cells. This insensitivity of the IRE-IRP system may be implicated in the accumulation of iron to contribute to cisplatin-induced nephropathy.

Lipocalin-2, S100A8/A9, and cystatin C: Potential predictive biomarkers of cardiovascular complications in COVID-19

Severe coronavirus (SARS-COV-2) infection often leads to systemic inflammation accompanied by cardiovascular complications including venous thromboembolism (VTE). However, it is largely undefined if inflammatory markers such as lipocalin-2 (LNC2), calprotectin (S100A8/A9), and cystatin C (CST3), previously linked with VTE, play roles in cardiovascular complications and advancement of COVID-19 severity. To investigate the same, hospitalized moderate and severe (presented pneumonia and required intensive care) COVID-19 patients were recruited. The levels of plasma LNC2, S100A8/A9, CST3, myoglobin, and cardiac Troponin I (cTnI) were assessed through enzyme-linked immunosorbent assay (ELISA). The investigation revealed a significantly upregulated level of plasma LNC2 at the moderate stage of SARS-CoV-2 infection. In contrast, the levels of S100A8/A9 and CST3 in moderate patients were comparable to healthy controls; however, a profound induction was observed only in severe COVID-19 patients. The tissue injury marker myoglobin was unchanged in moderate patients; however, a significantly elevated level was observed in the critically ill COVID-19 patients. In contrast, cTnI level was unchanged both in moderate and severe patients. Analysis revealed a positive correlation between the levels of S100A8/A9 and CST3 with myoglobin in COVID-19. In silico analysis predicted interactions of S100A8/A9 with toll-like receptor 4 (TLR-4), MyD88 LY96, and LCN2 with several other inflammatory mediators including MMP2, MMP9, TIMP1, and interleukins (IL-6, IL-17A, and IL-10). In summary, early induction of LCN2 likely plays a role in advancing the COVID-19 severity. A positive correlation of S100A8/A9 and CST3 with myoglobin suggests that these proteins may serve as predictive biomarkers for thromboembolism and tissue injury in COVID-19.

Renal hypoxia-HIF-PHD-EPO signaling in transition metal nephrotoxicity: friend or foe?

The kidney is the main organ that senses changes in systemic oxygen tension, but it is also the key detoxification, transit and excretion site of transition metals (TMs). Pivotal to oxygen sensing are prolyl-hydroxylases (PHDs), which hydroxylate specific residues in hypoxia-inducible factors (HIFs), key transcription factors that orchestrate responses to hypoxia, such as induction of erythropoietin (EPO). The essential TM ion Fe is a key component and regulator of the hypoxia–PHD–HIF–EPO (HPHE) signaling axis, which governs erythropoiesis, angiogenesis, anaerobic metabolism, adaptation, survival and proliferation, and hence cell and body homeostasis. However, inadequate concentrations of essential TMs or entry of non-essential TMs in organisms cause toxicity and disrupt health. Non-essential TMs are toxic because they enter cells and displace essential TMs by ionic and molecular mimicry, e. g. in metalloproteins. Here, we review the molecular mechanisms of HPHE interactions with TMs (Fe, Co, Ni, Cd, Cr, and Pt) as well as their implications in renal physiology, pathophysiology and toxicology. Some TMs, such as Fe and Co, may activate renal HPHE signaling, which may be beneficial under some circumstances, for example, by mitigating renal injuries from other causes, but may also promote pathologies, such as renal cancer development and metastasis. Yet some other TMs appear to disrupt renal HPHE signaling, contributing to the complex picture of TM (nephro-)toxicity. Strikingly, despite a wealth of literature on the topic, current knowledge lacks a deeper molecular understanding of TM interaction with HPHE signaling, in particular in the kidney. This precludes rationale preventive and therapeutic approaches to TM nephrotoxicity, although recently activators of HPHE signaling have become available for therapy.

Protective effect of tin chloride on rhabdomyolysis-induced acute kidney injury in rats

The heme component of myoglobin plays a crucial role in the pathogenesis of rhabdomyolysis-associated acute kidney injury (RM-AKI). Heme oxiganenase-1 (HO-1) is the rate-limiting enzyme of heme catabolism, and its metabolites, iron, biliverdin, and carbon monoxide, have antioxidant properties. Tin chloride (SnCl₂) is a kidney specific HO-1 inducer. In this study, we examined whether the induction of HO-1 in the kidney by SnCl_₂ pretreatment ameliorates RM-AKI in rats and if the effect is due to the degradation of excess renal free heme. We developed an RM-AKI rat (male Sprague-Dawley rats) model by injecting glycerol (Gly) in the hind limbs. RM-AKI rats were pretreated with saline or SnCl_₂ or additional SnMP (tin mesoporphyrin, a specific HO inhibitor) followed by Gly treatment. Serum blood urea nitrogen (BUN) and creatinine (Crea) were measured as indicators of renal function. Renal free heme level was assessed based on the levels of δ-aminolevulinate synthase (ALAS1), a heme biosynthetic enzyme, and nuclear BTB and CNC homology 1 (Bach1), an inhibitory transcription factor of HO-1. Elevated free heme levels lead to decreases in ALAS1 and nuclear Bach1. After 24 h of Gly injection, serum BUN and Crea levels in saline-pretreated rats were significantly higher than those in untreated control rats. In contrast, SnCl_₂-pretreated rats showed no significant increase in the indices. However, additional treatment of SnMP abolished the beneficial effect of SnCl_₂. Renal ALAS1 mRNA levels and renal nuclear Bach1 protein levels in the saline pretreated rats were significantly lower than those in control rats 3 h after Gly injection. In contrast, the levels in SnCl₂-pretreated rats were not altered. The findings indicate that SnCl₂ pretreatment confers protection against RM-AKI by virtue of HO-1 induction in the renal system, at least in part through excess free heme degradation.

Heme oxygenase-nitric oxide crosstalk-mediated iron homeostasis in plants under oxidative stress

Plant growth under abiotic stress conditions significantly enhances intracellular generation of reactive oxygen species (ROS). Oxidative status of plant cells is directly affected by the modulation of iron homeostasis. Among mammals and plants, heme oxygenase-1 (HO-1) is a well-known antioxidant enzyme. It catalyzes oxygenation of heme, thereby producing Fe²⁺, CO and biliverdin as byproducts. The antioxidant potential of HO-1 is primarily due to its catalytic reaction byproducts. Biliverdin and bilirubin possess conjugated π-electrons which escalate the ability of these biomolecules to scavenge free radicals. CO also enhances the ROS scavenging ability of plants cells by upregulating catalase and peroxidase activity. Enhanced expression of HO-1 in plants under oxidative stress accompanies sequestration of iron in specialized iron storage proteins localized in plastids and mitochondria, namely ferritin for Fe³⁺ storage and frataxin for storage of Fe-S clusters, respectively. Nitric oxide (NO) crosstalks with HO-1 at multiple levels, more so in plants under oxidative stress, in order to maintain intracellular iron status. Formation of dinitrosyl-iron complexes (DNICs) significantly prevents Fenton reaction during oxidative stress. DNICs also release NO upon dissociation in target cells over long distance in plants. They also function as antioxidants against superoxide anions and lipidic free radicals. A number of NO-modulated transcription factors also facilitate iron homeostasis in plant cells. Plants facing oxidative stress exhibit modulation of lateral root formation by HO-1 through NO and auxin-dependent pathways. The present review provides an in-depth analysis of the structure-function relationship of HO-1 in plants and mammals, correlating them with their adaptive mechanisms of survival under stress.

Divergent roles of haptoglobin and hemopexin deficiency for disease progression of Shiga-toxin-induced hemolytic-uremic syndrome in mice

Thrombotic microangiopathy, hemolysis and acute kidney injury are typical clinical characteristics of hemolytic-uremic syndrome (HUS), which is predominantly caused by Shiga-toxin-producing Escherichia coli. Free heme aggravates organ damage in life-threatening infections, even with a low degree of systemic hemolysis. Therefore, we hypothesized that the presence of the hemoglobin- and the heme-scavenging proteins, haptoglobin and hemopexin, respectively impacts outcome and kidney pathology in HUS. Here, we investigated the effect of haptoglobin and hemopexin deficiency (haptoglobin^-/-, hemopexin^-/-) and haptoglobin treatment in a murine model of HUS-like disease. Seven-day survival was decreased in haptoglobin^-/- (25%) compared to wild type mice (71.4%), whereas all hemopexin^-/- mice survived. Shiga-toxin-challenged hemopexin^-/- mice showed decreased kidney inflammation and attenuated thrombotic microangiopathy, indicated by reduced neutrophil recruitment and platelet deposition. These observations were associated with supranormal haptoglobin plasma levels in hemopexin^-/- mice. Low dose haptoglobin administration to Shiga-toxin-challenged wild type mice attenuated kidney platelet deposition and neutrophil recruitment, suggesting that haptoglobin at least partially contributes to the beneficial effects. Surrogate parameters of hemolysis were elevated in Shiga-toxin-challenged wild type and haptoglobin^-/- mice, while signs for hepatic hemoglobin degradation like heme oxygenase-1, ferritin and CD163 expression were only increased in Shiga-toxin-challenged wild type mice. In line with this observation, haptoglobin^-/- mice displayed tubular iron deposition as an indicator for kidney hemoglobin degradation. Thus, haptoglobin and hemopexin deficiency play divergent roles in Shiga-toxin-mediated HUS, suggesting haptoglobin is involved, and hemopexin is redundant for the resolution of HUS pathology.

Carbon Monoxide in Renal Physiology, Pathogenesis and Treatment of Renal Disease

Carbon monoxide (CO) is one of the endogenous gaseous messengers or gasotransmitters, and is a paramount mediator in physiological and disease conditions. In this review, we focus on the functions of CO in normal and pathological renal physiology. We discuss endogenous renal CO production and signaling in the normal kidney, the characteristic of CO-releasing molecules (CORMs) modalities, and outline its regulatory functions in renal physiology. This article summarizes the mechanisms as well as the effect of CO in the evolving field of renal diseases. We predict numerous innovative CO applications forevolvingcutting-edge scholarly work in the future.

Cilastatin Ameliorates Rhabdomyolysis-induced AKI in Mice

BACKGROUND

Rhabdomyolysis, the destruction of skeletal muscle, is a significant cause of AKI and death in the context of natural disaster and armed conflict. Rhabdomyolysis may also initiate CKD. Development of specific pharmacologic therapy is desirable because supportive care is nearly impossible in austere environments. Myoglobin, the principal cause of rhabdomyolysis-related AKI, undergoes megalin-mediated endocytosis in proximal tubule cells, a process that specifically injures these cells.

METHODS

To investigate whether megalin is protective in a mouse model of rhabdomyolysis-induced AKI, we used male C57BL/6 mice and mice (14-32 weeks old) with proximal tubule-specific deletion of megalin. We used a well-characterized rhabdomyolysis model, injection of 50% glycerol in normal saline preceded by water deprivation.

RESULTS

Inducible proximal tubule-specific deletion of megalin was highly protective in this mouse model of rhabdomyolysis-induced AKI. The megalin knockout mice demonstrated preserved GFR, reduced proximal tubule injury (as indicated by kidney injury molecule-1), and reduced renal apoptosis 24 hours after injury. These effects were accompanied by increased urinary myoglobin clearance. Unlike littermate controls, the megalin-deficient mice also did not develop progressive GFR decline and persistent new proteinuria. Administration of the pharmacologic megalin inhibitor cilastatin to wild-type mice recapitulated the renoprotective effects of megalin deletion. This cilastatin-mediated renoprotective effect was dependent on megalin. Cilastatin administration caused selective proteinuria and inhibition of tubular myoglobin uptake similar to that caused by megalin deletion.

CONCLUSIONS

We conclude that megalin plays a critical role in rhabdomyolysis-induced AKI, and megalin interference and inhibition ameliorate rhabdomyolysis-induced AKI. Further investigation of megalin inhibition may inform translational investigation of a novel potential therapy.

Forced running-induced rhabdomyolysis in the Sprague-Dawley rat: towards a rodent model of capture myopathy

Capture myopathy (CM) is a metabolic disease associated with mortality in mass boma captured (MBC) wildlife. The condition is induced by the forced pursuit, capturing, and restraint of wild animals, although its causal biology remains to be confirmed. A core feature of MBC-CM is rhabdomyolysis, which is associated with myoglobinuria and hyperthermia. Towards developing a translational model of CM-associated rhabdomyolysis, we investigated forced treadmill running to induce physical exhaustion and trigger rhabdomyolysis in Sprague Dawley (SD) rats. Twenty-four (24) SD rats (12 per sex) were subjected to treadmill habituation in a speed-tiered approach. Forty-eight hours after the last habituation session, one strenuous exercise (SE) session was performed at 75% of the theoretical VO_2MAX (30 m/min) until animals reached physical exhaustion. Core and skin surface temperatures were measured before the SE session and after rats reached exhaustion, after which a 1-h-cumulative urine sample was collected, and the myoglobin content assayed. We show that most SE, but not control-exposed (non-exercise) rats presented with myoglobinuria, while core and surface body temperatures in both male and female rats were significantly higher post-exercise. This pre-clinical model framework shows potential for investigating the pathophysiology of MBC-CM.

Immunomodulatory Effects of Heme Oxygenase-1 in Kidney Disease

Kidney disease is a general term for heterogeneous damage that affects the function and the structure of the kidneys. The rising incidence of kidney diseases represents a considerable burden on the healthcare system, so the development of new drugs and the identification of novel therapeutic targets are urgently needed. The pathophysiology of kidney diseases is complex and involves multiple processes, including inflammation, autophagy, cell-cycle progression, and oxidative stress. Heme oxygenase-1 (HO-1), an enzyme involved in the process of heme degradation, has attracted widespread attention in recent years due to its cytoprotective properties. As an enzyme with known anti-oxidative functions, HO-1 plays an indispensable role in the regulation of oxidative stress and is involved in the pathogenesis of several kidney diseases. Moreover, current studies have revealed that HO-1 can affect cell proliferation, cell maturation, and other metabolic processes, thereby altering the function of immune cells. Many strategies, such as the administration of HO-1-overexpressing macrophages, use of phytochemicals, and carbon monoxide-based therapies, have been developed to target HO-1 in a variety of nephropathological animal models, indicating that HO-1 is a promising protein for the treatment of kidney diseases. Here, we briefly review the effects of HO-1 induction on specific immune cell populations with the aim of exploring the potential therapeutic roles of HO-1 and designing HO-1-based therapeutic strategies for the treatment of kidney diseases.

Iron deficiency exacerbates cisplatin- or rhabdomyolysis-induced acute kidney injury through promoting iron-catalyzed oxidative damage

Iron deficiency is the most common micronutrient deficiency worldwide. While iron deficiency is known to suppress embryonic organogenesis, its effect on the adult organ in the context of clinically relevant damage has not been considered. Here we report that iron deficiency is a risk factor for nephrotoxic intrinsic acute kidney injury of the nephron (iAKI). Iron deficiency exacerbated cisplatin-induced iAKI by markedly increasing non-heme catalytic iron and Nox4 protein which together catalyze production of hydroxyl radicals followed by protein and DNA oxidation, apoptosis and ferroptosis. Crosstalk between non-heme catalytic iron/Nox4 and downstream oxidative damage generated a mutual amplification cycle that facilitated rapid progression of cisplatin-induced iAKI. Iron deficiency also exacerbated a second model of iAKI, rhabdomyolysis, via increasing catalytic heme-iron. Heme-iron induced lipid peroxidation and DNA oxidation by interacting with Nox4-independent mechanisms, promoting p53/p21 activity and cellular senescence. Our data suggests that correcting iron deficiency and/or targeting specific catalytic iron species are strategies to mitigate iAKI in a wide range of patients with diverse forms of kidney injury.

Hemoglobinuria in the Early Poststem-Cell-Transplant Period: Risk Factors and Association with Outcomes

Background

Information on risk factors of hemoglobinuria after hematopoietic stem-cell transplant (HSCT) and its association with AKI, mortality, and engraftment is limited.

Methods

We conducted a retrospective cohort study on all consecutive adults that underwent HSCT from January 6, 1999, to November 6, 2017. The study included 6039 patients that underwent bone marrow transplantation (BMT), umbilical cord blood, and peripheral blood stem-cell transplantation (PBSCT).

Results

Early post-HSCT, AKI occurred in 393 (7%) patients, and 52 (0.9%) patients had post-HSCT hemoglobinuria. Post-HSCT hemoglobinuria was associated with graft type (BMT+Cord), underlying disease (lymphoma, acute leukemia), and fludarabine-based conditioning regimen. Post-HSCT hemoglobinuria was associated with early (48-72 hours) post-HSCT AKI. Graft type (BMT+Cord) was associated with AKI among patients with hemoglobinuria. AKI in patients with hemoglobinuria was associated with delayed platelet engraftment and delayed WBC engraftment but not 100-day mortality.

Conclusion

Close monitoring is recommended in this patient group to facilitate a good engraftment outcome.

Upregulation of hemeoxygenase enzymes HO-1 and HO-2 following ischemia-reperfusion injury in connection with experimental cardiac arrest and cardiopulmonary resuscitation: Neuroprotective effects of methylene blue

Oxidative stress plays an important role in neuronal injuries after cardiac arrest. Increased production of carbon monoxide (CO) by the enzyme hemeoxygenase (HO) in the brain is induced by the oxidative stress. HO is present in the CNS in two isoforms, namely the inducible HO-1 and the constitutive HO-2. Elevated levels of serum HO-1 occurs in cardiac arrest patients and upregulation of HO-1 in cardiac arrest is seen in the neurons. However, the role of HO-2 in cardiac arrest is not well known. In this review involvement of HO-1 and HO-2 enzymes in the porcine brain following cardiac arrest and resuscitation is discussed based on our own observations. In addition, neuroprotective role of methylene blue- an antioxidant dye on alterations in HO under in cardiac arrest is also presented. The biochemical findings of HO-1 and HO-2 enzymes using ELISA were further confirmed by immunocytochemical approach to localize selective regional alterations in cardiac arrest. Our observations are the first to show that cardiac arrest followed by successful cardiopulmonary resuscitation results in significant alteration in cerebral concentrations of HO-1 and HO-2 levels indicating a prominent role of CO in brain pathology and methylene blue during CPR followed by induced hypothermia leading to superior neuroprotection after return of spontaneous circulation (ROSC), not reported earlier.

Adapting decarbonylation chemistry for the development of prodrugs capable of in vivo delivery of carbon monoxide utilizing sweeteners as carrier molecules

Carbon monoxide as an endogenous signaling molecule exhibits pharmacological efficacy in various animal models of organ injury. To address the difficulty in using CO gas as a therapeutic agent for widespread applications, we are interested in developing CO prodrugs through bioreversible caging of CO in an organic compound. Specifically, we have explored the decarboxylation-decarbonylation chemistry of 1,2-dicarbonyl compounds. Examination and optimization of factors favorable for maximal CO release under physiological conditions led to organic CO prodrugs using non-calorific sweeteners as leaving groups attached to the 1,2-dicarbonyl core. Attaching a leaving group with appropriate properties promotes the desired hydrolysis-decarboxylation-decarbonylation sequence of reactions that leads to CO generation. One such CO prodrug was selected to recapitulate the anti-inflammatory effects of CO against LPS-induced TNF-α production in cell culture studies. Oral administration in mice elevated COHb levels to the safe and efficacious levels established in various preclinical and clinical studies. Furthermore, its pharmacological efficacy was demonstrated in mouse models of acute kidney injury. These studies demonstrate the potential of these prodrugs with benign carriers as orally active CO-based therapeutics. This represents the very first example of orally active organic CO prodrugs with a benign carrier that is an FDA-approved sweetener with demonstrated safety profiles in vivo.

Heme Burden and Ensuing Mechanisms That Protect the Kidney: Insights from Bench and Bedside

With iron at its core, the tetrapyrrole heme ring is a cardinal prosthetic group made up of many proteins that participate in a wide array of cellular functions and metabolism. Once released, due to its pro-oxidant properties, free heme in sufficient amounts can result in injurious effects to the kidney and other organs. Heme oxygenase-1 (HO-1) has evolved to promptly attend to such injurious potential by facilitating degradation of heme into equimolar amounts of carbon monoxide, iron, and biliverdin. HO-1 induction is a beneficial response to tissue injury in diverse animal models of diseases, including those that affect the kidney. These protective attributes are mainly due to: (i) prompt degradation of heme leading to restraining potential hazardous effects of free heme, and (ii) generation of byproducts that along with induction of ferritin have proven beneficial in a number of pathological conditions. This review will focus on describing clinical aspects of some of the conditions with the unifying end-result of increased heme burden and will discuss the molecular mechanisms that ensue to protect the kidneys.

The NRF2 stimulating agent, tin protoporphyrin, activates protective cytokine pathways in healthy human subjects and in patients with chronic kidney disease

BACKGROUND

Tin protoporphyrin (SnPP), a heme oxygenase 1 (HO-1) inhibitor, triggers adaptive tissue responses that confer potent protection against acute renal- and extra-renal tissue injuries. This effect is mediated, in part, via SnPP-induced activation of the cytoprotective Nrf2 pathway. However, it remains unclear as to whether SnPP can also upregulate humoral cytokine defenses, either in healthy human subjects or in patients with CKD. If so, then systemically derived cytokines could contribute SnPP-induced tissue protection.

METHODS

SnPP (90 mg IV) was administered over 2 hr to six healthy human volunteers (HVs) and 12 subjects with stage 3-4 CKD. Plasma samples were obtained from baseline upto 72 hr post injection. Two representative anti-inflammatory cytokines (IL-10, TGFβ1), and a pro-inflammatory cytokine (TNF-α), were assayed. Because IL-6 has been shown to induce tissue preconditioning, its plasma concentrations were also assessed. In complementary mouse experiments, SnPP effects on renal, splenic, and hepatic IL-10, IL-6, TGFβ1, and TNF-α production (as gauged by their mRNAs) were tested. Tissue HO-1 mRNA served as an Nrf2 activation marker.

RESULTS

SnPP induced marked (~5-7x) increases in plasma IL-10 and IL-6 concentrations within 24-48 hr, and to equal degrees in HVs and CKD patients. SnPP modestly raised plasma TGFβ1 without impacting plasma TNF-α levels. In mouse experiments, SnPP did not affect IL-6, IL-10, TNF-α, or TGFβ1 mRNAs in kidney despite marked renal Nrf2 activation. Conversely, SnPP increased splenic IL-10 and hepatic IL-6/TGFβ1 mRNA levels, suggesting these organs as sites of extra-renal cytokine generation.

CONCLUSIONS

SnPP can trigger cytoprotective cytokine production, most likely in extra-renal tissues. With ready glomerular cytokine filtration, extra-renal/renal "organ cross talk" can result. Thus, humoral factors seemingly can contribute to SnPP's cytoprotective effects.

Nature's marvels endowed in gaseous molecules I: Carbon monoxide and its physiological and therapeutic roles

Nature has endowed gaseous molecules such as O2, CO2, CO, NO, H2S, and N2 with critical and diverse roles in sustaining life, from supplying energy needed to power life and building blocks for life's physical structure to mediating and coordinating cellular functions. In this article, we give a brief introduction of the complex functions of the various gaseous molecules in life and then focus on carbon monoxide as a specific example of an endogenously produced signaling molecule to highlight the importance of this class of molecules. The past twenty years have seen much progress in understanding CO's mechanism(s) of action and pharmacological effects as well as in developing delivery methods for easy administration. One remarkable trait of CO is its pleiotropic effects that have few parallels, except perhaps its sister gaseous signaling molecules such as nitric oxide and hydrogen sulfide. This review will delve into the sophistication of CO-mediated signaling as well as its validated pharmacological functions and possible therapeutic applications.

Heme Oxygenase 1: A Defensive Mediator in Kidney Diseases

The incidence of kidney disease is rising, constituting a significant burden on the healthcare system and making identification of new therapeutic targets increasingly urgent. The heme oxygenase (HO) system performs an important function in the regulation of oxidative stress and inflammation and, via these mechanisms, is thought to play a role in the prevention of non-specific injuries following acute renal failure or resulting from chronic kidney disease. The expression of HO-1 is strongly inducible by a wide range of stimuli in the kidney, consequent to the kidney's filtration role which means HO-1 is exposed to a wide range of endogenous and exogenous molecules, and it has been shown to be protective in a variety of nephropathological animal models. Interestingly, the positive effect of HO-1 occurs in both hemolysis- and rhabdomyolysis-dominated diseases, where the kidney is extensively exposed to heme (a major HO-1 inducer), as well as in non-heme-dependent diseases such as hypertension, diabetic nephropathy or progression to end-stage renal disease. This highlights the complexity of HO-1's functions, which is also illustrated by the fact that, despite the abundance of preclinical data, no drug targeting HO-1 has so far been translated into clinical use. The objective of this review is to assess current knowledge relating HO-1's role in the kidney and its potential interest as a nephroprotection agent. The potential therapeutic openings will be presented, in particular through the identification of clinical trials targeting this enzyme or its products.

Systematic review of the nuclear factor erythroid 2-related factor 2 (NRF2) system in human chronic kidney disease: alterations, interventions, and relation to morbidity

BACKGROUND

NRF2 and its effectors NAD(P)H:quinoneoxidoreductase 1 (NQO1) and heme oxygenase 1 (HO-1) are of interest in kidney disease. We therefore reviewed studies about their status in patients with chronic kidney disease (CKD).

METHODS

We undertook systematic searches of PubMed and EMBASE databases. Alterations of NRF2, NQO1 and HO-1 in CKD, their responses to interventions and their relation to clinically relevant parameters were reported.

RESULTS

We identified 1373 articles, of which 32 studies met the inclusion criteria. NRF2 levels were decreased in the majority of analyses of CKD patients. Half of the analyses showed a similar or increased NQO1 level vs. control, whereas NQO1 was decreased in half of the analyses. Most of the studies reported either an increased or similar HO-1 level in CKD patients compared to controls. For patients with CKD stages 1-4, studies reported positive correlations to markers of kidney disease severity. Also, positive associations of NQO1/HO-1 levels to inflammation and comorbidities were reported. One third of the studies showed discordant changes between gene expression and protein level of NRF2 system components. Two thirds of intervention studies (50% dietary, such as using resistant starch) reported an increase of NRF2, NQO1, or HO-1.

CONCLUSIONS

In patients with CKD, NRF2 expression was downregulated, while NQO1 and HO-1 showed varying alterations related to inflammation, comorbidities, and severity of kidney damage. Interventions that increased NRF2 system components were described, but their effectiveness and clinical relevance require further clinical studies of high quality. Research on gene expression together with protein analyses is indispensable to understand NRF2 system alterations in CKD.

Regulation of Complement Activation by Heme Oxygenase-1 (HO-1) in Kidney Injury

Heme oxygenase is a cytoprotective enzyme with strong antioxidant and anti-apoptotic properties. Its cytoprotective role is mainly attributed to its enzymatic activity, which involves the degradation of heme to biliverdin with simultaneous release of carbon monoxide (CO). Recent studies uncovered a new cytoprotective role for heme oxygenase-1 (HO-1) by identifying a regulatory role on the complement control protein decay-accelerating factor. This is a key complement regulatory protein preventing dysregulation or overactivation of complement cascades that can cause kidney injury. Cell-specific targeting of HO-1 induction may, therefore, be a novel approach to attenuate complement-dependent forms of kidney disease.

Acute kidney injury induced by glycerol is worsened by orchiectomy and attenuated by testosterone replacement

Although several studies have demonstrated that the male gender represents an independent risk factor for renal disease, evidence shows that androgens exert renal protective actions. The findings are controversial and no studies have evaluated the effects of orchiectomy and testosterone replacement on glycerol-induced renal injury. Male Wistar rats were submitted to orchiectomy or sham surgery and divided into four groups: SC, sham control rats injected with NaCl; SG, sham rats injected with glycerol; OG, orchiectomized rats injected with glycerol; OGT, orchiectomized rats injected with glycerol and testosterone. Testosterone was administered daily for 14 days in the OGT group. After 11 days of testosterone replacement in the OGT group, SC rats were submitted to a saline injection, while SG, OG and OGT rats received glycerol. All rats were euthanized three days after injections. OG rats presented higher serum creatinine and urea, and sodium excretion, compared to SC and SG, while testosterone attenuated these changes. Acute tubular necrosis was also mitigated by testosterone. Renal immunostaining for macrophages, lymphocytes and NF-κB was higher in OG compared to SC and SG. In addition, renal interleukin-1β, Caspase 3 and AT1 gene expression was higher in OG rats compared to SG. Testosterone attenuated these alterations, except the NF-κB immunostaining. The renal NO was lower in OG rats compared to SG. Only the OG rats presented decreases in serum NO and renal HO-1, and increased TNF-α, angiotensinogen and AT1 expression compared to SC. We conclude that orchiectomy worsened glycerol-induced kidney injury, while testosterone attenuated this renal damage.

New insights into the role of heme oxygenase-1 in acute kidney injury

Acute kidney injury (AKI) is attended by injury-related biomarkers appearing in the urine and serum, decreased urine output, and impaired glomerular filtration rate. AKI causes increased morbidity and mortality and can progress to chronic kidney disease and end-stage kidney failure. AKI is without specific therapies and is managed by supported care. Heme oxygenase-1 (HO-1) is a cytoprotective, inducible enzyme that degrades toxic free heme released from destabilized heme proteins and, during this process, releases beneficial by-products such as carbon monoxide and biliverdin/bilirubin and promotes ferritin synthesis. HO-1 induction protects against assorted renal insults as demonstrated by in vitro and preclinical models. This review summarizes the advances in understanding of the protection conferred by HO-1 in AKI, how HO-1 can be induced including via its transcription factor Nrf2, and HO-1 induction as a therapeutic strategy.

Effects of Single and Repeated Oral Doses of Ochratoxin A on the Lipid Peroxidation and Antioxidant Defense Systems in Mouse Kidneys

Ochratoxin-A (OTA) is a carcinogenic and nephrotoxic mycotoxin, which may cause health problems in humans and animals, and it is a contaminant in foods and feeds. The purpose of the present study is to evaluate the effect of oral OTA exposure on the antioxidant defense and lipid peroxidation in the kidney. In vivo administration of OTA in CD1, male mice (1 or 10 mg/kg body weight in a single oral dose for 24 h and repeated daily oral dose for 72 h or repeated daily oral dose of 0.5 mg/kg bodyweight for 21 days) resulted in a significant elevation of OTA levels in blood plasma. Some histopathological alterations, transcriptional changes in the glutathione system, and oxidative stress response-related genes were also found. In the renal cortex, the activity of the glutathione-system-related enzymes and certain metabolites of the lipid peroxidation (conjugated dienes, trienes, and thiobarbituric reactive substances) also changed.

α1-Microglobulin (A1M) Protects Human Proximal Tubule Epithelial Cells from Heme-Induced Damage In Vitro

Oxidative stress is associated with many renal disorders, both acute and chronic, and has also been described to contribute to the disease progression. Therefore, oxidative stress is a potential therapeutic target. The human antioxidant α₁-microglobulin (A1M) is a plasma and tissue protein with heme-binding, radical-scavenging and reductase activities. A1M can be internalized by cells, localized to the mitochondria and protect mitochondrial function. Due to its small size, A1M is filtered from the blood into the glomeruli, and taken up by the renal tubular epithelial cells. A1M has previously been described to reduce renal damage in animal models of preeclampsia, radiotherapy and rhabdomyolysis, and is proposed as a pharmacological agent for the treatment of kidney damage. In this paper, we examined the in vitro protective effects of recombinant human A1M (rA1M) in human proximal tubule epithelial cells. Moreover, rA1M was found to protect against heme-induced cell-death both in primary cells (RPTEC) and in a cell-line (HK-2). Expression of stress-related genes was upregulated in both cell cultures in response to heme exposure, as measured by qPCR and confirmed with in situ hybridization in HK-2 cells, whereas co-treatment with rA1M counteracted the upregulation. Mitochondrial respiration, analyzed with the Seahorse extracellular flux analyzer, was compromised following exposure to heme, but preserved by co-treatment with rA1M. Finally, heme addition to RPTE cells induced an upregulation of the endogenous cellular expression of A1M, via activation of the nuclear factor erythroid 2-related factor 2 (Nrf2)-pathway. Overall, data suggest that A1M/rA1M protects against stress-induced damage to tubule epithelial cells that, at least partly, can be attributed to maintaining mitochondrial function.

Genetic Polymorphisms Complicate COVID-19 Therapy: Pivotal Role of HO-1 in Cytokine Storm

Coronaviruses are very large RNA viruses that originate in animal reservoirs and include severe acute respiratory distress syndrome (SARS) and Middle East respiratory syndrome (MERS) and other inconsequential coronaviruses from human reservoirs like the common cold. SARS-CoV-2, the virus that causes COVID-19 and is believed to originate from bat, quickly spread into a global pandemic. This RNA virus has a special affinity for porphyrins. It invades the cell at the angiotensin converting enzyme-2 (ACE-2) receptor and binds to hemoproteins, resulting in a severe systemic inflammatory response, particularly in high ACE-2 organs like the lungs, heart, and kidney, resulting in systemic disease. The inflammatory response manifested by increased cytokine levels and reactive oxygen species results in inhibition of heme oxygenase (HO-1), with a subsequent loss of cytoprotection. This has been seen in other viral illness like human immunodeficiency virus (HIV), Ebola, and SARS/MERS. There are a number of medications that have been tried with some showing early clinical promise. This illness disproportionately affects patients with obesity, a chronic inflammatory disease with a baseline excess of cytokines. The majority of the medications used in the treatment of COVID-19 are metabolized by cytochrome P450 (CYP) enzymes, primarily CYP2D6. This is further complicated by genetic polymorphisms of CYP2D6, HO-1, ACE, and ACE-2. There is a potential role for HO-1 upregulation to treat/prevent cytokine storm. Current therapy must focus on antivirals and heme oxygenase upregulation. Vaccine development will be the only magic bullet.

Carbon monoxide: An emerging therapy for acute kidney injury

Treating acute kidney injury (AKI) represents an important unmet medical need both in terms of the seriousness of this medical problem and the number of patients. There is also a large untapped market opportunity in treating AKI. Over the years, there has been much effort in search of therapeutics with minimal success. However, over the same time period, new understanding of the underlying pathobiology and molecular mechanisms of kidney injury have undoubtedly helped the search for new therapeutics. Along this line, carbon monoxide (CO) has emerged as a promising therapeutic agent because of its demonstrated cytoprotective, and immunomodulatory effects. CO has also been shown to sensitize cancer, but not normal cells, to chemotherapy. This is particularly important in treating cisplatin-induced AKI, a common clinical problem that develops in patients receiving cisplatin therapies for a number of different solid organ malignancies. This review will examine and make the case that CO be developed into a therapeutic agent against AKI.

The protective effect of human adiposederived mesenchymal stem cells on cisplatin-induced nephrotoxicity is dependent on their level of expression of heme oxygenase-1

The therapeutic efficacy of adipose mesenchymal stem cells (Ad-MSCs) for acute kidney injury (AKI) has been investigated extensively, and the anti-apoptotic, anti-inflammatory, and proangiogenic effects of heme oxygenase-1 (HO-1) reportedly ameliorate AKI. We hypothesized that the therapeutic efficacy of Ad-MSCs is dependent on their expression level of HO-1. The viability and migration ability of cisplatin-treated human renal proximal tubular epithelial cells were assessed. Sprague–Dawley rats were divided into control, cisplatin (10 mg/kg), and cisplatin plus Ad MSCs (with high and low HO-1 expression) groups. The HO-1 expression level in hAd-MSCs increased with increasing passage number, peaking at passage 4 and decreasing thereafter. The viability and migratory ability of hAd-MSCs with high HO-1 expression were greater than those of hAd-MSCs with low HO-1 expression. Renal tubular toxicity in cisplatin-treated rats was ameliorated by administration of hAd-MSCs with high HO-1 expression, although the levels of blood urea nitrogen and serum creatinine did not differ according to the level of HO-1 expression. The magnitude of reactive oxygen species induced DNA damage was lower in hAd-MSCs with high HO-1 expression than in those with low HO-1 expression. Administration of hAd-MSCs significantly suppressed cisplatin induced apoptosis. Also, hAd-MSCs with high HO-1 expression were more resistant to cisplatin-induced apoptosis than were those with low HO-1 expression. hAd MSCs with high HO-1 expression have therapeutic potential for cisplatin induced nephrotoxicity, based on our in vitro and in vivo results. These findings will facilitate the development of novel therapeutic strategies for cisplatin-induced AKI.

ArrhythmoGenoPharmacoTherapy

This review is focusing on the understanding of various factors and components governing and controlling the occurrence of ventricular arrhythmias including (i) the role of various ion channel-related changes in the action potential (AP), (ii) electrocardiograms (ECGs), (iii) some important arrhythmogenic mediators of reperfusion, and pharmacological approaches to their attenuation. The transmembrane potential in myocardial cells is depending on the cellular concentrations of several ions including sodium, calcium, and potassium on both sides of the cell membrane and active or inactive stages of ion channels. The movements of Na+, K+, and Ca2+ via cell membranes produce various currents that provoke AP, determining the cardiac cycle and heart function. A specific channel has its own type of gate, and it is opening and closing under specific transmembrane voltage, ionic, or metabolic conditions. APs of sinoatrial (SA) node, atrioventricular (AV) node, and Purkinje cells determine the pacemaker activity (depolarization phase 4) of the heart, leading to the surface manifestation, registration, and evaluation of ECG waves in both animal models and humans. AP and ECG changes are key factors in arrhythmogenesis, and the analysis of these changes serve for the clarification of the mechanisms of antiarrhythmic drugs. The classification of antiarrhythmic drugs may be based on their electrophysiological properties emphasizing the connection between basic electrophysiological activities and antiarrhythmic properties. The review also summarizes some important mechanisms of ventricular arrhythmias in the ischemic/reperfused myocardium and permits an assessment of antiarrhythmic potential of drugs used for pharmacotherapy under experimental and clinical conditions.

A Pharmacologic "Stress Test" for Assessing Select Antioxidant Defenses in Patients with CKD

BACKGROUND AND OBJECTIVES

Oxidative stress is a hallmark and mediator of CKD. Diminished antioxidant defenses are thought to be partly responsible. However, there is currently no way to prospectively assess antioxidant defenses in humans. Tin protoporphyrin (SnPP) induces mild, transient oxidant stress in mice, triggering increased expression of select antioxidant proteins (e.g., heme oxygenase 1 [HO-1], NAD[P]H dehydrogenase [quinone] 1 [NQO1], ferritin, p21). Hence, we tested the hypothesis that SnPP can also variably increase these proteins in humans and can thus serve as a pharmacologic "stress test" for gauging gene responsiveness and antioxidant reserves.

DESIGN

, setting, participants, & measurementsA total of 18 healthy volunteers and 24 participants with stage 3 CKD (n=12; eGFR 30-59 ml/min per 1.73 m²) or stage 4 CKD (n=12; eGFR 15-29 ml/min per 1.73 m²) were injected once with SnPP (9, 27, or 90 mg). Plasma and/or urinary antioxidant proteins were measured at baseline and for up to 4 days post-SnPP dosing. Kidney safety was gauged by serial measurements of BUN, creatinine, eGFR, albuminuria, and four urinary AKI biomarkers (kidney injury molecule 1, neutrophil gelatinase-associated lipocalin, cystatin C, and N-acetyl glucosaminidase).

RESULTS

Plasma HO-1, ferritin, p21, and NQO1 were all elevated at baseline in CKD participants. Plasma HO-1 and urine NQO1 levels each inversely correlated with eGFR (r=-0.85 to -0.95). All four proteins manifested statistically significant dose- and time-dependent elevations after SnPP injection. However, marked intersubject differences were observed. p21 responses to high-dose SnPP and HO-1 responses to low-dose SnPP were significantly suppressed in participants with CKD versus healthy volunteers. SnPP was well tolerated by all participants, and no evidence of nephrotoxicity was observed.

CONCLUSIONS

SnPP can be safely administered and, after its injection, the resulting changes in plasma HO-1, NQO1, ferritin, and p21 concentrations can provide information as to antioxidant gene responsiveness/reserves in subjects with and without kidney disease.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

A Study with RBT-1, in Healthy Volunteers and Subjects with Stage 3-4 Chronic Kidney Disease, NCT0363002 and NCT03893799.

Ferritins in Kidney Disease

Ferritins are evolutionarily conserved proteins that regulate cellular iron metabolism. It is the only intracellular protein that is capable of storing large quantities of iron. Although the ratio of different subunits determines the iron content of each ferritin molecule, the exact mechanism that dictates organization of these subunits still is unclear. In this review, we address renal ferritin expression and its implication in kidney disease. Specifically, we address the role of ferritin subunits in preventing kidney injury and also promoting tolerance against infection-associated kidney injury. We describe functions for ferritin that are independent of its ability to ferroxidize and store iron. We further discuss the implications of ferritin in body fluids, including blood and urine, during inflammation and kidney disease. Although there are several in-depth review articles on ferritin in the context of iron metabolism, we chose to focus on the role of ferritin particularly in kidney health and disease and highlight unanswered questions in the field.

Antithrombotic effects of heme-degrading and heme-binding proteins

In the murine venous thrombosis model induced by ligation of the inferior vena cava (IVCL), genetic deficiency of heme oxygenase-1 (HO-1) increases clot size. This study examined whether induction of HO-1 or administration of its products reduces thrombosis. Venous HO-1 upregulation by gene delivery reduced clot size, as did products of HO activity, biliverdin, and carbon monoxide. Induction of HO-1 by hemin reduced clot formation, clot size, and upregulation of plasminogen activator inhibitor-1 (PAI-1) that occurs in the IVCL model, while leaving urokinase plasminogen activator (uPA) and tissue plasminogen activator (tPA) expression unaltered. The reductive effect of hemin on clot size required HO activity. The IVCL model exhibited relatively high concentrations of heme that peaked just before maximum clot size, then declined as clot size decreased. Administration of hemin decreased heme concentration in the IVCL model. HO-2 mRNA was induced twofold in the IVCL model (vs. 40-fold HO-1 induction), but clot size was not increased in HO-2^-/- mice compared with HO-2^+/+ mice. Hemopexin, the major heme-binding protein, was induced in the IVCL model, and clot size was increased in hemopexin^-/- mice compared with hemopexin^+/+ mice. We conclude that in the IVCL model, the heme-degrading protein HO-1 and HO products inhibit thrombus formation, as does the heme-binding protein, hemopexin. The reductive effects of hemin administration require HO activity and are mediated, in part, by reducing PAI-1 upregulation in the IVCL model. We speculate that HO-1, HO, and hemopexin reduce clot size by restraining the increase in clot concentration of heme (now recognized as a procoagulant) that otherwise occurs.NEW & NOTEWORTHY This study provides conclusive evidence that two proteins, one heme-degrading and the other heme-binding, inhibit clot formation. This may serve as a new therapeutic strategy in preventing and treating venous thromboembolic disease.