Heme protein-induced chronic renal inflammation: suppressive effect of induced heme oxygenase-1

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.

Genome-wide meta-analysis identifies new candidate genes for sickle cell disease nephropathy

Sickle cell disease nephropathy (SCDN), a common SCD complication, is strongly associated with mortality. Polygenic risk scores calculated from recent transethnic meta-analyses of urinary albumin-to-creatinine ratio and estimated glomerular filtration rate (eGFR) trended toward association with proteinuria and eGFR in SCD but the model fit was poor (R2 < 0.01), suggesting that there are likely unique genetic risk factors for SCDN. Therefore, we performed genome-wide association studies (GWAS) for 2 critical manifestations of SCDN, proteinuria and decreased eGFR, in 2 well-characterized adult SCD cohorts, representing, to the best of our knowledge, the largest SCDN sample to date. Meta-analysis identified 6 genome-wide significant associations (false discovery rate, q ≤ 0.05): 3 for proteinuria (CRYL1, VWF, and ADAMTS7) and 3 for eGFR (LRP1B, linc02288, and FPGT-TNNI3K/TNNI3K). These associations are independent of APOL1 risk and represent novel SCDN loci, many with evidence for regulatory function. Moreover, GWAS SNPs in CRYL1, VWF, ADAMTS7, and linc02288 are associated with gene expression in kidney and pathways important to both renal function and SCD biology, supporting the hypothesis that SCDN pathophysiology is distinct from other forms of kidney disease. Together, these findings provide new targets for functional follow-up that could be tested prospectively and potentially used to identify patients with SCD who are at risk, before onset of kidney dysfunction.

Nationwide study of eculizumab in paroxysmal nocturnal hemoglobinuria: Evaluation of treatment indications and outcomes

Eculizumab is an effective treatment for paroxysmal nocturnal hemoglobinuria (PNH). However, considering the risk of life-threatening meningococcal disease, life-long duration and costs, there are strict criteria for initiation of therapy. To evaluate the application and real-world effectiveness of eculizumab in the Netherlands, a multicenter retrospective cohort study was conducted: indications and treatment outcomes were collected for 105 Dutch PNH patients. In all patients, eculizumab was initiated conforming to indications as formulated in the Dutch PNH guideline. According to recently published response criteria, 23.4% of the patients had reached a complete hematological response, 53.2% a good or partial response, and 23.4% a minor response after 12 months of therapy. In the majority of patients the response remained stable during long-term follow-up. The degree and relevance of extravascular hemolysis significantly differed between response groups (p = 0.002). Improvements of EORTC-QLQc30 and FACIT-fatigue scores were observed, however patients reported lower scores than the general population. A detailed evaluation of 18 pregnancies during eculizumab showed no maternal or fetal deaths, and no thromboembolic events during pregnancy. This study demonstrates that the majority of patients benefit from eculizumab when adhering to the indications as formulated in the Dutch PNH guideline. However, novel therapies are needed to further improve real-world outcomes, such as hematological responses and quality of life.

Polymerized human cord hemoglobin assisted with ascorbic acid as a red blood cell substitute alleviating oxidative stress for blood transfusion

Introduction: Blood transfusion is widely used in clinical settings, where considerable efforts have been devoted to develop red blood cell substitutes to overcome blood shortage and safety concerns. Among the several kinds of artificial oxygen carriers, hemoglobin-based oxygen carriers are promising due to their inherent good oxygen-binding and -loading properties. However, difficulties in prone to oxidation, production of oxidative stress, and injury in organs limited their clinical utility. In this work, we report a red blood cell substitute composed of polymerized human cord hemoglobin (PolyCHb) assisted with ascorbic acid (AA) that alleviates oxidative stress for blood transfusion. Methods: In this study, the in vitro impacts of AA on the PolyCHb were evaluated by testing the circular dichroism, methemoglobin (MetHb) contents and oxygen binding affinity before and after the addition of AA. In the in vivo study, guinea pigs were subjected to a 50% exchange transfusion with PolyCHb and AA co-administration, followed by the collection of blood, urine, and kidney samples. The hemoglobin contents of the urine samples were analyzed, and histopathologic changes, lipid peroxidation, DNA peroxidation, and heme catabolic markers in the kidneys were evaluated. Results: After treating with AA, there was no effect on the secondary structure and oxygen binding affinity of the PolyCHb, while the MetHb content was kept at 55%, which was much lower than that without AA treating. Moreover, the reduction of PolyCHbFe3+ was significantly promoted, and the content of MetHb could be reduced from 100% to 51% within 3 h. In vivo study results showed that PolyCHb assisted with AA inhibited the formation of hemoglobinuria, upgraded the total antioxidant capacity and downgraded the superoxide dismutase activity of kidney tissue, and lowered the expression of biomarkers for oxidative stress, e.g., malondialdehyde (ET vs ET+AA: 4.03±0.26 μmol/mg vs 1.83±0.16 μmol/mg), 4-hydroxy-2-nonenal (ET vs ET+AA: 0.98±0.07 vs 0.57±0.04), 8-hydroxy 2 deoxyguanosine(ET vs ET+AA: 14.81±1.58 ng/ml vs 10.91±1.36 ng/ml), heme oxygenase 1 (ET vs ET+AA: 1.51±0.08 vs 1.18±0.05) and ferritin (ET vs ET+AA: 1.75±0.09 vs 1.32±0.04). The kidney histopathology results also demonstrated that kidney tissue damage was effectively alleviated. Conclusion: In conclusion, these comprehensive results provide evidence for the potential role of AA in controlling oxidative stress and organ injury in the kidneys induced by PolyCHb, and suggest that PolyCHb assisted with AA has promising application for blood transfusion.

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.

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.

The nephropathy of sickle cell trait and sickle cell disease

Sickle cell syndromes, including sickle cell disease (SCD) and sickle cell trait, are associated with multiple kidney abnormalities. Young patients with SCD have elevated effective renal plasma flow and glomerular filtration rates, which decrease to normal ranges in young adulthood and subnormal levels with advancing age. The pathophysiology of SCD-related nephropathy is multifactorial - oxidative stress, hyperfiltration and glomerular hypertension are all contributing factors. Albuminuria, which is an early clinical manifestation of glomerular damage, is common in individuals with SCD. Kidney function declines more rapidly in individuals with SCD than in those with sickle cell trait or in healthy individuals. Multiple genetic modifiers, including APOL1, HMOX1, HBA1 and HBA2 variants are also implicated in the development and progression of SCD-related nephropathy. Chronic kidney disease and rapid decline in estimated glomerular filtration rate are associated with increased mortality in adults with SCD. Renin-angiotensin-aldosterone system inhibitors are the standard of care treatment for albuminuria in SCD, despite a lack of controlled studies demonstrating their long-term efficacy. Multiple studies of novel therapeutic agents are ongoing, and patients with SCD and kidney failure should be evaluated for kidney transplantation. Given the high prevalence and severe consequences of kidney disease, additional studies are needed to elucidate the pathophysiology, natural history and treatment of SCD-related nephropathy.

Effects of Tolvaptan on Oxidative Stress in ADPKD: A Molecular Biological Approach

Autosomal dominant polycystic disease (ADPKD) is the most frequent monogenic kidney disease. It causes progressive renal failure, endothelial dysfunction, and hypertension, all of which are strictly linked to oxidative stress (OxSt). Treatment with tolvaptan is known to slow the renal deterioration rate, but not all the molecular mechanisms involved in this effect are well-established. We evaluated the OxSt state in untreated ADPKD patients compared to that in tolvaptan-treated ADPKD patients and healthy subjects. OxSt was assessed in nine patients for each group in terms of mononuclear cell p22^phox protein expression, NADPH oxidase key subunit, MYPT-1 phosphorylation state, marker of Rho kinase activity (Western blot) and heme oxygenase (HO)-1, induced and protective against OxSt (ELISA). p22^phox protein expression was higher in untreated ADPKD patients compared to treated patients and controls: 1.42 ± 0.11 vs. 0.86 ± 0.15 d.u., p = 0.015, vs. 0.53 ± 0.11 d.u., p < 0.001, respectively. The same was observed for phosphorylated MYPT-1: 0.96 ± 0.28 vs. 0.68 ± 0.09 d.u., p = 0.013 and vs. 0.47 ± 0.13 d.u., p < 0.001, respectively, while the HO-1 expression of untreated patients was significantly lower compared to that of treated patients and controls: 5.33 ± 3.34 vs. 2.08 ± 0.79 ng/mL, p = 0.012, vs. 1.97 ± 1.22 ng/mL, p = 0.012, respectively. Tolvaptan-treated ADPKD patients have reduced OxSt levels compared to untreated patients. This effect may contribute to the slowing of renal function loss observed with tolvaptan treatment.

New Insights into the Pivotal Role of Iron/Heme Metabolism in TLR4/NF-κB Signaling-Mediated Inflammatory Responses in Human Monocytes

Iron metabolism and heme biosynthesis are essential processes in cells during the energy cycle. Alteration in these processes could create an inflammatory condition, which results in tumorigenesis. Studies are conducted on the exact role of iron/heme metabolism in induced inflammatory conditions. This study used lipopolysaccharide (LPS)- or high-glucose-induced inflammation conditions in THP-1 cells to study how iron/heme metabolism participates in inflammatory responses. Here, we used iron and heme assays for measuring total iron and heme. We also used flow cytometry and Western blotting to analyze molecular responses. Our results demonstrated that adding LPS or high-glucose induced iron formation and heme synthesis and elevated the expression levels of proteins responsible for iron metabolism and heme synthesis. We then found that further addition of heme or 5-aminolevulinic acid (ALA) increased heme biosynthesis and promoted inflammatory responses by upregulating TLR4/NF-κB and inflammatory cytokine expressions. We also demonstrated the inhibition of heme synthesis using succinylacetone (SA). Moreover, N-MMP inhibited LPS- or high-glucose-induced inflammatory responses by inhibiting TLR4/NF-κB signaling. Hence, iron/heme metabolism checkpoints could be considered a target for treating inflammatory conditions.

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.

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.

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 Pivotal Role of Oxidative Stress in the Pathophysiology of Cardiovascular-Renal Remodeling in Kidney Disease

The excessive activation of the renin-angiotensin system in kidney disease leads to alteration of intracellular pathways which concur altogether to the induction of cardiovascular and renal remodeling, exposing these patients since the very beginning of the renal injury to chronic kidney disease and progression to end stage renal disease, a very harmful and life threatening clinical condition. Oxidative stress plays a pivotal role in the pathophysiology of renal injury and cardiovascular-renal remodeling, the long-term consequence of its effect. This review will examine the role of oxidative stress in the most significant pathways involved in cardiovascular and renal remodeling with a focus on the detrimental effects of oxidative stress-mediated renal abnormalities on the progression of the disease and of its complications. Food for thoughts on possible therapeutic target are proposed on the basis of experimental evidences.

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.

The Worst Things in Life are Free: The Role of Free Heme in Sickle Cell Disease

Hemolysis is a pathological feature of several diseases of diverse etiology such as hereditary anemias, malaria, and sepsis. A major complication of hemolysis involves the release of large quantities of hemoglobin into the blood circulation and the subsequent generation of harmful metabolites like labile heme. Protective mechanisms like haptoglobin-hemoglobin and hemopexin-heme binding, and heme oxygenase-1 enzymatic degradation of heme limit the toxicity of the hemolysis-related molecules. The capacity of these protective systems is exceeded in hemolytic diseases, resulting in high residual levels of hemolysis products in the circulation, which pose a great oxidative and proinflammatory risk. Sickle cell disease (SCD) features a prominent hemolytic anemia which impacts the phenotypic variability and disease severity. Not only is circulating heme a potent oxidative molecule, but it can act as an erythrocytic danger-associated molecular pattern (eDAMP) molecule which contributes to a proinflammatory state, promoting sickle complications such as vaso-occlusion and acute lung injury. Exposure to extracellular heme in SCD can also augment the expression of placental growth factor (PlGF) and interleukin-6 (IL-6), with important consequences to enthothelin-1 (ET-1) secretion and pulmonary hypertension, and potentially the development of renal and cardiac dysfunction. This review focuses on heme-induced mechanisms that are implicated in disease pathways, mainly in SCD. A special emphasis is given to heme-induced PlGF and IL-6 related mechanisms and their role in SCD disease progression.

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.

Heme as Possible Contributing Factor in the Evolvement of Shiga-Toxin Escherichia coli Induced Hemolytic-Uremic Syndrome

Shiga-toxin (Stx)-producing Escherichia coli hemolytic-uremic syndrome (STEC-HUS) is one of the most common causes of acute kidney injury in children. Stx-mediated endothelial injury initiates the cascade leading to thrombotic microangiopathy (TMA), still the exact pathogenesis remains elusive. Interestingly, there is wide variability in clinical presentation and outcome. One explanation for this could be the enhancement of TMA through other factors. We hypothesize that heme, as released during extensive hemolysis, contributes to the etiology of TMA. Plasma levels of heme and its scavenger hemopexin and degrading enzyme heme-oxygenase-1 (HO-1) were measured in 48 STEC-HUS patients. Subsequently, the effect of these disease-specific heme concentrations, in combination with Stx, was assessed on primary human glomerular microvascular endothelial cells (HGMVECs). Significantly elevated plasma heme levels up to 21.2 µM were found in STEC-HUS patients compared to controls and were inversely correlated with low or depleted plasma hemopexin levels (R² −0.74). Plasma levels of HO-1 are significantly elevated compared to controls. Interestingly, especially patients with high heme levels (n = 12, heme levels above 75 quartile range) had high plasma HO-1 levels with median of 332.5 (86–720) ng/ml (p = 0.008). Furthermore, heme is internalized leading to a significant increase in reactive oxygen species production and stimulated both nuclear translocation of NF-κB and increased levels of its target gene (tissue factor). In conclusion, we are the first to show elevated heme levels in patients with STEC-HUS. These increased heme levels mediate endothelial injury by promoting oxidative stress and a pro-inflammatory and pro-thrombotic state. Hence, heme may be a contributing and driving factor in the pathogenesis of STEC-HUS and could potentially amplify the cascade leading to TMA.

Complement Inhibition Therapy and Dialytic Strategies in Paroxysmal Nocturnal Hemoglobinuria: The Nephrologist's Opinion

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare clonal disease that presents an estimated incidence of 1.3 cases per million per year, with a prevalence of 15.9 cases per million. It is characterized by hemolysis, bone marrow dysfunction with peripheral blood cytopenia, hypercoagulability, thrombosis, renal impairment and arterial and pulmonary hypertension. Hemolysis and subsequent hemosiderin accumulation in tubular epithelium cells induce tubular atrophy and interstitial fibrosis. The origin of PNH is the somatic mutation in the X-linked phosphatidylinositol glycan class A (PIG-A) gene located on Xp22: this condition leads to the production of clonal blood cells with a deficiency in those surface proteins that protect against the lytic action of the activated complement system. Despite the increased knowledge of this syndrome, therapies for PNH were still only experimental and symptomatic, until the introduction of the C5 complement blockade agent Eculizumab. A second generation of anti-complement agents is currently under investigation, representing future promising therapeutic strategies for patients affected by PNH. In the case of chronic hemolysis and renal iron deposition, a multidisciplinary approach should be considered to avoid or treat acute tubular injury or acute kidney injury (AKI). New promising perspectives derive from complement inhibitors and iron chelators, as well as more invasive treatments such as immunoadsorption or the use of dedicated hemodialysis filters in the presence of AKI.

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.

Heme as a target for protection against doxorubicin-induced apoptosis in H9c2 cardiomyocytes

Heme homeostasis is of vital importance to many biological processes associated with cell redox activity. However, the role of heme in the doxorubicin (DOX)-induced cardiotoxicity is still not clear. The aim of the present study was to test the hypothesis that heme is related to the DOX-induced oxidative stress and inhibition of heme expression may protect H9c2 cardiomyocytes against DOX-induced cardiotoxicity. For the evaluation of heme changing under doxorubicin treatment, H9c2 cells were treated with 0.5, 1, 2, and 4 mg/mL doxorubicin respectively. H9c2 cells were divided into 5 groups: Control group (cells were cultured without intervention), DOX group (cells were treated with 2 mg/mL doxorubicin for 6 h), Heme depletion+DOX group (cells were cultured with heme-depleted serum media, 0.5 mM succinylacetone and 2 mg/mL doxorubicin), Heme group (cells were treated with 30 μM heme), and Heme depletion+DOX+Heme group. Apoptotic cells were detected by flow cytometry with Annexin V-FITC/PI. The intracellular oxidant levels were measured by DCFH-DA fluorescence. The levels of heme were detected by ELISA. Doxorubicin significantly increased intracellular heme level from 5013 ± 187 ng/mL to the highest level of 11,720 ± 107 ng/mL, as well as the intracellular oxidants and cell apoptosis rate elevated by the increase of doxorubicin concentration. Heme depletion can significantly suppress the DOX-induced apoptosis from 39.8 ± 0.5% to 20.8 ± 0.5% (p < 0.001). Re-supplemented with exogenous heme partially but significantly restored the DOX-induced apoptosis. Heme plays an important role in doxorubicin toxicity-induced cardiomyocyte injury. By appropriate reduction in the accumulation of free heme in cardiomyocytes, doxorubicin-induced cardiotoxicity may be alleviated.

Analysis of clinical characteristics of 92 patients with paroxysmal nocturnal hemoglobinuria: A single institution experience in China

Objectives

We performed a retrospective analysis to investigate the clinical characteristics and therapeutic strategies of Chinese paroxysmal nocturnal hemoglobinuria (PNH) patients, and assessed the efficacy and safety of glucocorticoid in PNH patients.

Methods

The clinical data of 92 PNH cases in our hospital were analyzed, including clinical manifestation, laboratory examination, treatment efficacy, and survival.

Results

The main clinical manifestations of these patients included hemoglobinuria, anemia, fatigue, dyspnea, headache, abdominal pain, and erectile dysfunction. Glucocorticoid is still the first‐line treatment for PNH patients to control hemolytic attack, and the short‐term remission rate (12 months) is 79.01% (64/81). Meanwhile, the overall survival (OS) of 10 years after diagnosis was estimated as 70.77% (46/65). Moreover, Cox proportional risk model for multivariate analysis showed that the increase in LDH multiple, thrombosis complications, and complicated with bone marrow failure were the independent adverse prognostic factors affecting the survival of PNH patients.

Conclusion

Paroxysmal nocturnal hemoglobinuria patients in mainland China have various clinical features, while lower incidences of thrombosis and renal damage. Thrombosis and bone marrow failure are two complications with worse prognosis.

Mechanisms of haemolysis-induced kidney injury

Intravascular haemolysis is a fundamental feature of chronic hereditary and acquired haemolytic anaemias, including those associated with haemoglobinopathies, complement disorders and infectious diseases such as malaria. Destabilization of red blood cells (RBCs) within the vasculature results in systemic inflammation, vasomotor dysfunction, thrombophilia and proliferative vasculopathy. The haemoprotein scavengers haptoglobin and haemopexin act to limit circulating levels of free haemoglobin, haem and iron - potentially toxic species that are released from injured RBCs. However, these adaptive defence systems can fail owing to ongoing intravascular disintegration of RBCs. Induction of the haem-degrading enzyme haem oxygenase 1 (HO1) - and potentially HO2 - represents a response to, and endogenous defence against, large amounts of cellular haem; however, this system can also become saturated. A frequent adverse consequence of massive and/or chronic haemolysis is kidney injury, which contributes to the morbidity and mortality of chronic haemolytic diseases. Intravascular destruction of RBCs and the resulting accumulation of haemoproteins can induce kidney injury via a number of mechanisms, including oxidative stress and cytotoxicity pathways, through the formation of intratubular casts and through direct as well as indirect proinflammatory effects, the latter via the activation of neutrophils and monocytes. Understanding of the detailed pathophysiology of haemolysis-induced kidney injury offers opportunities for the design and implementation of new therapeutic strategies to counteract the unfavourable and potentially fatal effects of haemolysis on the kidney.

CPUY192018, a potent inhibitor of the Keap1-Nrf2 protein-protein interaction, alleviates renal inflammation in mice by restricting oxidative stress and NF-κB activation

The Keap1-Nrf2-ARE pathway regulates the constitutive and inducible transcription of various genes that encode detoxification enzymes, antioxidant proteins and anti-inflammatory proteins and has pivotal roles in the defence against cellular oxidative stress. In this study, we investigated the therapeutic potential of CPUY192018, a potent small-molecule inhibitor of the Keap1-Nrf2 protein-protein interaction (PPI), in renal inflammation. In human proximal tubular epithelial HK-2 cells, CPUY192018 treatment significantly increased Nrf2 protein level and Nrf2 nuclear translocation, which enhanced Nrf2-ARE transcription capacity and the downstream protein content in a Nrf2 dependent manner. In lipopolysaccharide (LPS)-challenged human HK-2 cells, CPUY192018 exhibited cytoprotective effects by enhancing the Nrf2-ARE regulated antioxidant system and diminished the LPS-induced inflammatory response by hindering the ROS-mediated activation of the NF-κB pathway. In the LPS-induced mouse model of chronic renal inflammation, by activating Nrf2, CPUY192018 treatment balanced renal oxidative stress and suppressed inflammatory responses. Hence, administration of CPUY192018 reduced kidney damage and ameliorated pathological alterations of the glomerulus. Taken together, our study suggested that small-molecule Keap1-Nrf2 PPI inhibitors can activate the Nrf2-based cytoprotective system and protect the kidney from inflammatory injury, raising a potential application of Keap1-Nrf2 PPI inhibitors in the treatment of inflammatory kidney disorders.

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CPUY192018 activated Nrf2-ARE pathway to protect against LPS-induced renal inflammation both in cells and in vivo.

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CPUY192018 also inhibited NF-κB involved inflammatory response both in cells and kidney.

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The development of Keap1-Nrf2 PPI inhibitors may create treatment options for kidney diseases with reduced off-target effects.

Heme oxygenase-1 repeat polymorphism in septic acute kidney injury

Acute kidney injury (AKI) is a syndrome that frequently affects the critically ill. Recently, an increased number of dinucleotide repeats in the HMOX1 gene were reported to associate with development of AKI in cardiac surgery. We aimed to test the replicability of this finding in a Finnish cohort of critically ill septic patients. This multicenter study was part of the national FINNAKI study. We genotyped 300 patients with severe AKI (KDIGO 2 or 3) and 353 controls without AKI (KDIGO 0) for the guanine–thymine (GTn) repeat in the promoter region of the HMOX1 gene. The allele calling was based on the number of repeats, the cut off being 27 repeats in the S–L (short to long) classification, and 27 and 34 repeats for the S–M–L₂ (short to medium to very long) classification. The plasma concentrations of heme oxygenase-1 (HO-1) enzyme were measured on admission. The allele distribution in our patients was similar to that published previously, with peaks at 23 and 30 repeats. The S-allele increases AKI risk. An adjusted OR was 1.30 for each S-allele in an additive genetic model (95% CI 1.01–1.66; p = 0.041). Alleles with a repeat number greater than 34 were significantly associated with lower HO-1 concentration (p<0.001). In septic patients, we report an association between a short repeat in HMOX1 and AKI risk.

Renal control of disease tolerance to malaria

Malaria, the disease caused by Plasmodium spp. infection, remains a major global cause of morbidity and mortality. Host protection from malaria relies on immune-driven resistance mechanisms that kill Plasmodium However, these mechanisms are not sufficient per se to avoid the development of severe forms of disease. This is accomplished instead via the establishment of disease tolerance to malaria, a defense strategy that does not target Plasmodium directly. Here we demonstrate that the establishment of disease tolerance to malaria relies on a tissue damage-control mechanism that operates specifically in renal proximal tubule epithelial cells (RPTEC). This protective response relies on the induction of heme oxygenase-1 (HMOX1; HO-1) and ferritin H chain (FTH) via a mechanism that involves the transcription-factor nuclear-factor E2-related factor-2 (NRF2). As it accumulates in plasma and urine during the blood stage of Plasmodium infection, labile heme is detoxified in RPTEC by HO-1 and FTH, preventing the development of acute kidney injury, a clinical hallmark of severe malaria.

Oxidative stress and the altered reaction to it in Fabry disease: A possible target for cardiovascular-renal remodeling?

BACKGROUND

Fabry disease is characterized by deficient expression/activity of α-GalA with consequent lysosomal accumulation in various organs of its substrate Gb3. Despite enzyme replacement therapy, Fabry disease progresses with serious myocardial, cerebral and renal manifestations. Gb3 accumulation may induce oxidative stress (OxSt), production of inflammatory cytokines and reduction of nitric oxide, which may impact on Fabry disease's clinical manifestations.

METHODS

OxSt status was characterized in 10 patients compared with 10 healthy subjects via protein expression of p22phox, subunit of NADH/NADPH oxidase, (Western blot), Heme oxygenase (HO)-1 levels (ELISA), antioxidant/anti-inflammatory, lipid peroxidation as malondialdehyde (MDA) production (colorimetric assay), phosphorylation state of Extracellular Signal Regulated Kinase (ERK)1/2 and Myosin Phosphatase Target Protein (MYPT)-1 (Western blot), marker of Rho kinase activation, both involved in OxSt signaling. Cardiac left ventricular (LV) mass was also evaluated (M-mode echocardiography).

RESULTS

LV mass was higher in Fabry's males (123.72±2.03SEM g/m2) and females (132.09±6.72g/m2). p22phox expression was also higher in patients (1.04±0.09 d.u. vs 0.54±0.05 d.u. p<0.01) as well as MDA levels (54.51±3.97 vs 30.05±7.11 nmol/mL p = 0.01) while HO-1 was reduced (8.84±0.79 vs 14.03±1.23 ng/mL, p<0.02). MYPT-1's phosphorylation was increased in patients (0.52±0.11 d.u. vs 0.03±0.08 d.u., p<0.01) while phosphorylation of ERK1/2 was reduced (0.91±0.08 d.u. vs 1.53±0.17 d.u., p = 0.004).

CONCLUSIONS

This study documents OxSt activation and the altered reaction to it in Fabry patients. Cardiac remodeling, Rho kinase signaling activation and reduction of protective HO-1 might suggest that, in addition to enzyme replacement therapy, OxSt inhibition by either pharmacological or nutritional measures, is likely to prove useful for the prevention/treatment of Fabry patients' cardiovascular-renal remodeling.

Dual effect of hemin on renal ischemia-reperfusion injury

Acute kidney injury (AKI) is a major public health concern, which is contributing to serious hospital complications, chronic kidney disease (CKD) and even death. Renal ischemia-reperfusion injury (IRI) remains a leading cause of AKI. The stress-responsive enzyme, heme oxygenase-1 (HO-1) mediates protection against renal IRI and may be preventively induced using hemin prior to renal insult. This HO-1 induction pathway called hemin preconditioning is largely known to be effective. Therefore, HO-1 might be an interesting therapeutic target in case of predictable AKI (e.g. partial nephrectomy or renal transplantation). However, the use of hemin to mitigate established AKI remains poorly characterized. Mice underwent bilateral renal IRI for 26 min or sham surgery. After surgical procedure, animals were injected either with hemin (5 mg/kg) or vehicle. Twenty-four hours later, mice were sacrificed. Despite strong HO-1 induction, hemin-treated mice exhibited significant renal damage and oxidative stress as compared to vehicle-treated mice. Interestingly, higher dose of hemin is associated with more severe IRI-induced AKI in a dose-dependent relation. To determine whether hemin preconditioning remains efficient to dampen postoperative hemin-amplified IRI-induced AKI, we pretreated mice either with hemin (5 mg/kg) or vehicle 24 h prior to surgical procedure. Then, all mice (hemin- and vehicle-pretreated) received postoperative injection of hemin (5 mg/kg) to amplify IRI-induced AKI. In comparison to vehicle, prior administration of hemin to renal IRI mitigated hemin-amplified IRI-induced AKI as attested by fewer renal damage, inflammation and oxidative stress. In conclusion, hemin may have a dual effect on renal IRI, protective or deleterious, depending on the timing of its administration.

Hematuria as a risk factor for progression of chronic kidney disease and death: findings from the Chronic Renal Insufficiency Cohort (CRIC) Study

BACKGROUND

Hematuria is associated with chronic kidney disease (CKD), but has rarely been examined as a risk factor for CKD progression. We explored whether individuals with hematuria had worse outcomes compared to those without hematuria in the CRIC Study.

METHODS

Participants were a racially and ethnically diverse group of adults (21 to 74 years), with moderate CKD. Presence of hematuria (positive dipstick) from a single urine sample was the primary predictor. Outcomes included a 50% or greater reduction in eGFR from baseline, ESRD, and death, over a median follow-up of 7.3 years, analyzed using Cox Proportional Hazards models. Net reclassification indices (NRI) and C statistics were calculated to evaluate their predictive performance.

RESULTS

Hematuria was observed in 1145 (29%) of a total of 3272 participants at baseline. Individuals with hematuria were more likely to be Hispanic (22% vs. 9.5%, respectively), have diabetes (56% vs. 48%), lower mean eGFR (40.2 vs. 45.3 ml/min/1.73 m2), and higher levels of urinary albumin > 1.0 g/day (36% vs. 10%). In multivariable-adjusted analysis, individuals with hematuria had a greater risk for all outcomes during the first 2 years of follow-up: Halving of eGFR or ESRD (HR Year 1: 1.68, Year 2: 1.36), ESRD (Year 1: 1.71, Year 2: 1.39) and death (Year 1:1.92, Year 2: 1.77), and these associations were attenuated, thereafter. Based on NRIs and C-statistics, no clear improvement in the ability to improve prediction of study outcomes was observed when hematuria was included in multivariable models.

CONCLUSION

In a large adult cohort with CKD, hematuria was associated with a significantly higher risk of CKD progression and death in the first 2 years of follow-up but did not improve risk prediction.

Endogenous hepcidin synthesis protects the distal nephron against hemin and hemoglobin mediated necroptosis

Hemoglobinuria is associated with kidney injury in various hemolytic pathologies. Currently, there is no treatment available and its pathophysiology is not completely understood. Here we studied the potential detrimental effects of hemoglobin (Hb) exposure to the distal nephron (DN). Involvement of the DN in Hb kidney injury was suggested by the induction of renal hepcidin synthesis (p < 0.001) in mice repeatedly injected with intravenous Hb. Moreover, the hepcidin induction was associated with a decline in urinary kidney injury markers 24p3/NGAL and KIM1, suggesting a role for hepcidin in protection against Hb kidney injury. We demonstrated that uptake of Hb in the mouse cortical collecting duct cells (mCCDcl1) is mediated by multi-protein ligand receptor 24p3R, as indicated by a significant 90% reduction in Hb uptake (p < 0.001) after 24p3R silencing. Moreover, incubation of mCCDcl1 cells with Hb or hemin for 4 or 24 h resulted in hepcidin synthesis and increased mRNA expression of markers for oxidative, inflammatory and ER stress, but no cell death as indicated by apoptosis staining. A protective role for cellular hepcidin against Hb-induced injury was demonstrated by aggravation of oxidative, inflammatory and ER stress after 4 h Hb or hemin incubation in hepcidin silenced mCCDcl1 cells. Hepcidin silencing potentiated hemin-mediated cell death that could be diminished by co-incubation of Nec-1, suggesting that endogenous hepcidin prevents necroptosis. Combined, these results demonstrate that renal hepcidin synthesis protects the DN against hemin and hemoglobin-mediated injury.

Role of TLR4 signaling in the nephrotoxicity of heme and heme proteins

Destabilized heme proteins release heme, and free heme is toxic. Heme is now recognized as an agonist for the Toll-like receptor-4 (TLR4) receptor. This study examined whether the TLR4 receptor mediates the nephrotoxicity of heme, specifically, the effects of heme on renal blood flow and inflammatory responses. We blocked TLR4 signaling by the specific antagonist TAK-242. Intravenous administration of heme to mice promptly reduced renal blood flow, an effect attenuated by TAK-242. In vitro, TAK-242 reduced heme-elicited activation of NF-κB and its downstream gene monocyte chemoattractant protein-1(MCP-1); in contrast, TAK-242 failed to reduce heme-induced activation of the anti-inflammatory transcription factor Nrf2 and its downstream gene heme oxygenase-1 (HO-1). TAK-242 did not reduce heme-induced renal MCP-1 upregulation in vivo. TAK-242 did not reduce dysfunction and histological injury in the glycerol model of heme protein-induced acute kidney injury (AKI), findings corroborated by studies in TLR4+/+ and TLR4-/- mice. We conclude that 1) acute heme-mediated renal vasoconstriction occurs through TLR4 signaling; 2) proinflammatory effects of heme in renal epithelial cells involve TLR4 signaling, whereas the anti-inflammatory effects of heme do not; 3) TLR4 signaling does not mediate the proinflammatory effects of heme in the kidney; and 4) major mechanisms underlying glycerol-induced, heme protein-mediated AKI do not involve TLR4 signaling. These findings in the glycerol model are in stark contrast with findings in virtually all other AKI models studied to date and emphasize the importance of TLR4-independent pathways of heme protein-mediated injury in this model. Finally, these studies urge caution when using observations derived in vitro to predict what occurs in vivo.

Maintenance of renal function in a patient with a history of acute paroxysmal nocturnal hemoglobinuria-associated kidney injury

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, life-threatening blood disorder characterized by intravascular hemolysis, thrombosis and bone marrow failure. Acute kidney injury, including acute renal failure, have been reported in patients with PNH. We report the case of a 36-year-old male patient with PNH who developed acute kidney injury following an infection of undetermined diagnosis. Although hemolysis was initially controlled and renal function stabilized following packed red blood cell transfusion and empirical levofloxacin and prednisone, he later experienced recurrent episodes of hemolysis and hematuria requiring monthly red blood cell support. Given the high risk of thromboembolic events, treatment with standard-dose eculizumab was started. The patient's hematologic values improved, renal function was maintained, and no thromboembolic events occurred.

Renal involvement in paroxysmal nocturnal hemoglobinuria: an update on clinical features, pathophysiology and treatment

OBJECTIVES

The present review summarizes the available knowledge regarding acute and chronic kidney dysfunction in patients with paroxysmal nocturnal hemoglobinuria (PNH) focusing on its clinical features, pathophysiology and treatment.

METHODS

A thorough PubMed search was performed using as main keywords: 'paroxysmal nocturnal hemoglobinuria', 'acute kidney injury', 'chronic kidney disease' and 'eculizumab'.

RESULTS

PNH's etiopathogenesis is based on acquired mutations that lead to the reduction or absence of CD55 and CD59 complement regulators, which are responsible for some of the disease's major clinical features, like intravascular hemolysis, cytopenias and thrombosis. PNH is often underdiagnosed, mainly due to its occasional mild manifestations and to its ability to mimic other severe clinical conditions. Various mechanisms have been proposed for the kidney damage attributed to the release of cell-free heme and free iron, including inflammatory response, oxidative stress, nitric oxide depletion, renal ischemia, membrane damage and apoptosis. Eculizumab, a terminal complement inhibitor, provides a safe and effective treatment option, especially when it is initiated early in the presence of kidney damage.

DISCUSSION

Kidney injury is a poorly investigated clinical feature of PNH that affects a significant portion of patients. Increased awareness is needed by physicians to recognize the early signs and symptoms of acute and chronic renal insufficiency, so as to initiate the necessary therapy. It is also important to re-evaluation of PNH-specific treatments during the course of the disease.

CONCLUSION

Understanding the difficult but at the same time impressive mechanisms behind PNH remains a challenge for treating physicians.

Diseases of complement dysregulation-an overview

Atypical hemolytic uremic syndrome (aHUS), C3 glomerulopathy (C3G), and paroxysmal nocturnal hemoglobinuria (PNH) are prototypical disorders of complement dysregulation. Although complement overactivation is common to all, cell surface alternative pathway dysregulation (aHUS), fluid phase alternative pathway dysregulation (C3G), or terminal pathway dysregulation (PNH) predominates resulting in the very different phenotypes seen in these diseases. The mechanism underlying the dysregulation also varies with predominant acquired autoimmune (C3G), somatic mutations (PNH), or inherited germline mutations (aHUS) predisposing to disease. Eculizumab has revolutionized the treatment of PNH and aHUS although has been less successful in C3G. With the next generation of complement therapeutic in late stage development, these archetypal complement diseases will provide the initial targets.

Podocytes are new cellular targets of haemoglobin-mediated renal damage

Recurrent and massive intravascular haemolysis induces proteinuria, glomerulosclerosis, and progressive impairment of renal function, suggesting podocyte injury. However, the effects of haemoglobin (Hb) on podocytes remain unexplored. Our results show that cultured human podocytes or podocytes isolated from murine glomeruli bound and endocytosed Hb through the megalin-cubilin receptor system, thus resulting in increased intracellular Hb catabolism, oxidative stress, activation of the intrinsic apoptosis pathway, and altered podocyte morphology, with decreased expression of the slit diaphragm proteins nephrin and synaptopodin. Hb uptake activated nuclear factor erythroid-2-related factor 2 (Nrf2) and induced expression of the Nrf2-related antioxidant proteins haem oxygenase-1 (HO-1) and ferritin. Nrf2 activation and Hb staining was observed in podocytes of mice with intravascular haemolysis. These mice developed proteinuria and showed podocyte injury, characterized by foot process effacement, decreased synaptopodin and nephrin expression, and podocyte apoptosis. These pathological effects were enhanced in Nrf2-deficient mice, whereas Nrf2 activation with sulphoraphane protected podocytes against Hb toxicity both in vivo and in vitro. Supporting the translational significance of our findings, we observed podocyte damage and podocytes stained for Hb, HO-1, ferritin and phosphorylated Nrf2 in renal sections and urinary sediments of patients with massive intravascular haemolysis, such as atypical haemolytic uraemic syndrome and paroxysmal nocturnal haemoglobinuria. In conclusion, podocytes take up Hb both in vitro and during intravascular haemolysis, promoting oxidative stress, podocyte dysfunction, and apoptosis. Nrf2 may be a potential therapeutic target to prevent loss of renal function in patients with intravascular haemolysis. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Measuring in vivo responses to endogenous and exogenous oxidative stress using a novel haem oxygenase 1 reporter mouse

Key points

Haem oxygenase 1 (Hmox1) is a cytoprotective enzyme with anti‐inflammatory and anti‐oxidant properties that is induced in response to multiple noxious environmental stimuli and disease states.

Tools to enable its expression to be monitored in vivo have been unavailable until now.

In a new Hmox1 reporter model we provide high‐fidelity, single‐cell resolution blueprints for Hmox1 expression throughout the body of mice.

We show for the first time that Hmox1 is constitutively expressed at barrier tissues at the interface between the internal and external environments, and that it is highly induced in muscle cells during systemic inflammation.

These data suggest novel biological insights into the role of Hmox1 and pave the way for the use of the model to study the role of environmental stress in disease pathology.

Abstract

Hmox1 protein holds great promise as a biomarker of in vivo stress responses as it is highly induced in stressed or damaged cells. However, Hmox1 expression patterns have thus far only been available in simple model organisms with limited relevance to humans. We now report a new Hmox1 reporter line that makes it possible to obtain this information in mice, a premiere model system for studying human disease and toxicology. Using a state‐of‐the‐art strategy, we expressed multiple complementary reporter molecules from the murine Hmox1 locus, including firefly luciferase, to allow long‐term, non‐invasive imaging of Hmox1 expression, and β‐galactosidase for high‐resolution mapping of expression patterns post‐mortem. We validated the model by confirming the fidelity of reporter expression, and its responsiveness to oxidative and inflammatory stimuli. In addition to providing blueprints for Hmox1 expression in mice that provide novel biological insights, this work paves the way for the broad application of this model to establish cellular stresses induced by endogenous processes and those resulting from exposure to drugs and environmental agents. It will also enable studies on the role of oxidative stress in the pathogenesis of disease and its prevention.

Haem oxygenase 1 (Hmox1) is a cytoprotective enzyme with anti‐inflammatory and anti‐oxidant properties that is induced in response to multiple noxious environmental stimuli and disease states.

Tools to enable its expression to be monitored in vivo have been unavailable until now.

In a new Hmox1 reporter model we provide high‐fidelity, single‐cell resolution blueprints for Hmox1 expression throughout the body of mice.

We show for the first time that Hmox1 is constitutively expressed at barrier tissues at the interface between the internal and external environments, and that it is highly induced in muscle cells during systemic inflammation.

These data suggest novel biological insights into the role of Hmox1 and pave the way for the use of the model to study the role of environmental stress in disease pathology.

AKI on CKD: heightened injury, suppressed repair, and the underlying mechanisms

Acute kidney injury (AKI) and chronic kidney disease (CKD) are interconnected. Although AKI-to-CKD transition has been intensively studied, the information of AKI on CKD is very limited. Nonetheless, AKI, when occurring in patients with CKD, is known to be more severe and difficult to recover. CKD is associated with significant changes in cell signaling in kidney tissues, including the activation of transforming growth factor-β, p53, hypoxia-inducible factor, and major developmental pathways. At the cellular level, CKD is characterized by mitochondrial dysfunction, oxidative stress, and aberrant autophagy. At the tissue level, CKD is characterized by chronic inflammation and vascular dysfunction. These pathologic changes may contribute to the heightened sensitivity of, and nonrecovery from, AKI in patients with CKD.

Presence of acute and chronic renal failure in patients with paroxysmal nocturnal hemoglobinuria: results of a retrospective analysis from the Spanish PNH Registry

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, life-threatening blood disease. With the advent of eculizumab treatment, renal function has substantially improved, although no data from real-world clinical practice are available. An observational, retrospective, multicenter study was conducted in Spain on clinical data obtained from outpatient visits of patients with PNH (Spanish PNH Registry) who had experienced acute (ARF) or chronic (CRF) renal failure. Of the 128 patients registered (April 2014), 60 were diagnosed with classic PNH. Twenty-seven (45.0%) patients with a mean age of 48.5 (±16.2) years had renal failure, ARF or CRF, and were included in this study. Near half of the patients (n = 13; 48.1%) presented with ARF alone, 33.3% (n = 9) had CRF with episodes of ARF, while 18.5% (n = 5) were diagnosed with CRF alone. For patients with diagnosis of PNH and renal failure (n = 27), the median time to the first ARF episode was 6.5 (CI 95%; 2.2, 14.9) years, whereas the median to the diagnosis of CRF was 14.5 (CI 95%; 3.8, 19.2) years after the diagnosis of PNH. Patients with ARF (n = 22) were treated with eculizumab and did not experience new episodes of ARF, except for one patient with sepsis. Of the patients with CRF, two received treatment without experiencing further episodes of ARF. Sixteen patients who completed treatment (11 with ARF and 5 with ARF + CRF) recovered from the episode of ARF or from CRF. Of the remaining patients treated with eculizumab, one patient improved from stages III to II, three patients stabilized without showing disease progression, and one patient progressed from stages III to IV. Treatment with eculizumab in PNH patients has beneficial effects on renal function, preventing ARF and progression to CRF.

Plasma heme-induced renal toxicity is related to a capillary rarefaction

Severe hypertension can lead to malignant hypertension (MH) with renal thrombotic microangiopathy and hemolysis. The role of plasma heme release in this setting is unknown. We aimed at evaluating the effect of a mild plasma heme increase by hemin administration in angiotensin II (AngII)-mediated hypertensive rats. Prevalence of MH and blood pressure values were similar in AngII and AngII + hemin groups. MH rats displayed a decreased renal blood flow (RBF), increased renal vascular resistances (RVR), and increased aorta and interlobar arteries remodeling with a severe renal microcirculation assessed by peritubular capillaries (PTC) rarefaction. Hemin-treated rats with or without AngII displayed also a decreased RBF and increased RVR explained only by PCT rarefaction. In AngII rats, RBF was similar to controls (with increased RVR). PTC density appeared strongly correlated to tubular damage score (rho = -0.65, p < 0.0001) and also renal Heme Oygenase-1 (HO-1) mRNA (rho = -0.67, p < 0.0001). HO-1 was expressed in PTC and renal tubules in MH rats, but only in PTC in other groups. In conclusion, though increased plasma heme does not play a role in triggering or aggravating MH, heme release appears as a relevant toxic mediator leading to renal impairment, primarily through PTC endothelial dysfunction rather than direct tubular toxicity.

Proximal tubule-targeted heme oxygenase-1 in cisplatin-induced acute kidney injury

Heme oxygenase-1 (HO-1) is a cytoprotective enzyme that catalyzes the breakdown of heme to biliverdin, carbon monoxide, and iron. The beneficial effects of HO-1 expression are not merely due to degradation of the pro-oxidant heme but are also credited to the by-products that have potent, protective effects, including antioxidant, anti-inflammatory, and prosurvival properties. This is well reflected in the preclinical animal models of injury in both renal and nonrenal settings. However, excessive accumulation of the by-products can be deleterious and lead to mitochondrial toxicity and oxidative stress. Therefore, use of the HO system in alleviating injury merits a targeted approach. Based on the higher susceptibility of the proximal tubule segment of the nephron to injury, we generated transgenic mice using cre-lox technology to enable manipulation of HO-1 (deletion or overexpression) in a cell-specific manner. We demonstrate the validity and feasibility of these mice by breeding them with proximal tubule-specific Cre transgenic mice. Similar to previous reports using chemical modulators and global transgenic mice, we demonstrate that whereas deletion of HO-1, specifically in the proximal tubules, aggravates structural and functional damage during cisplatin nephrotoxicity, selective overexpression of HO-1 in proximal tubules is protective. At the cellular level, cleaved caspase-3 expression, a marker of apoptosis, and p38 signaling were modulated by HO-1. Use of these transgenic mice will aid in the evaluation of the effects of cell-specific HO-1 expression in response to injury and assist in the generation of targeted approaches that will enhance recovery with reduced, unwarranted adverse effects.

Alleviation of apoptosis of bone marrow-derived mesenchymal stem cells in the acute injured kidney by heme oxygenase-1 gene modification

Bone marrow-derived mesenchymal stem cells (BMSCs) transplantation is beneficial for the treatment of acute kidney injury (AKI), but the poor survival of BMSCs limits the repair effect. The oxidative stress in the AKI microenvironment is regarded as the main reason. Considering the potent anti-oxidant ability of heme oxygenase-1 (HO-1), HO-1 overexpression in BMSCs can be expected to improve the survival of BMSCs and correspondingly enhance the AKI repair effect. Here, BMSCs are transfected with pLV-HO-1/eGFP and pLV-eGFP by the lentivirus vector to get HO-1-BMSCs and eGFP-BMSCs, respectively. Ischemia/reperfusion-AKI kidney homogenate supernatant (KHS) is prepared for treating BMSCs, eGFP-BMSCs and HO-1-BMSCs. AKI-KHS results in a high inhibitory rate of BMSCs growth and a high proportion of TUNEL positive BMSCs, while HO-1 overexpression inverses this phenomenon and re-establishes the antioxidant and oxidant balance in HO-1-BMSCs. Phosphorylations of p53 and p38 mitogen-activated protein kinases (p38 MAPK) in HO-1-BMSCs decrease. Lower levels of monocyte chemotactic protein 1, tumor necrosis factor-α and interleukin 1β are also observed in supernatant of HO-1-BMSCs. The in vivo study shows that HO-1 overexpression sharply decreases the apoptosis of BMSCs in the injured kidney, and correspondingly the renal function of the AKI rats improves significantly. In conclusion, BMSCs with HO-1 overexpression suggests a better survival in the I/R-AKI microenvironment and a better kidney repair effect. The anti-oxidant effect via the inactivations of the downstream p53 and p38MAPK in BMSCs and the anti-inflammation could be the mechanisms. It provides a novel approach for the cell-based AKI-therapy.

Genetic variants and cell-free hemoglobin processing in sickle cell nephropathy

Intravascular hemolysis and hemoglobinuria are associated with sickle cell nephropathy. ApoL1 is involved in cell-free hemoglobin scavenging through association with haptoglobin-related protein. APOL1 G1/G2 variants are the strongest genetic predictors of kidney disease in the general African-American population. A single report associated APOL1 G1/G2 with sickle cell nephropathy. In 221 patients with sickle cell disease at the University of Illinois at Chicago, we replicated the finding of an association of APOL1 G1/G2 with proteinuria, specifically with urine albumin concentration (β=1.1, P=0.003), observed an even stronger association with hemoglobinuria (OR=2.5, P=4.3×10(-6)), and also replicated the finding of an association with hemoglobinuria in 487 patients from the Walk-Treatment of Pulmonary Hypertension and Sickle cell Disease with Sildenafil Therapy study (OR=2.6, P=0.003). In 25 University of Illinois sickle cell disease patients, concentrations of urine kidney injury molecule-1 correlated with urine cell-free hemoglobin concentrations (r=0.59, P=0.002). Exposing human proximal tubular cells to increasing cell-free hemoglobin led to increasing concentrations of supernatant kidney injury molecule-1 (P=0.01), reduced viability (P=0.01) and induction of HMOX1 and SOD2. HMOX1 rs743811 associated with chronic kidney disease stage (OR=3.0, P=0.0001) in the University of Illinois cohort and end-stage renal disease (OR=10.0, P=0.0003) in the Walk-Treatment of Pulmonary Hypertension and Sickle cell Disease with Sildenafil Therapy cohort. Longer HMOX1 GT-tandem repeats (>25) were associated with lower estimated glomerular filtration rate in the University of Illinois cohort (P=0.01). Our findings point to an association of APOL1 G1/G2 with kidney disease in sickle cell disease, possibly through increased risk of hemoglobinuria, and associations of HMOX1 variants with kidney disease, possibly through reduced protection of the kidney from hemoglobin-mediated toxicity.

Pathogenesis of glomerular haematuria

Haematuria was known as a benign hallmark of some glomerular diseases, but over the last decade, new evidences pointed its negative implications on kidney disease progression. Cytotoxic effects of oxidative stress induced by hemoglobin, heme, or iron released from red blood cells may account for the tubular injury observed in human biopsy specimens. However, the precise mechanisms responsible for haematuria remain unclear. The presence of red blood cells (RBCs) with irregular contours and shape in the urine indicates RBCs egression from the glomerular capillary into the urinary space. Therefore glomerular haematuria may be a marker of glomerular filtration barrier dysfunction or damage. In this review we describe some key issues regarding epidemiology and pathogenesis of haematuric diseases as well as their renal morphological findings.

Use of surface-enhanced Raman scattering as a prognostic indicator of acute kidney transplant rejection

We report an early, noninvasive and rapid prognostic method of predicting potential acute kidney dysfunction using surface-enhanced Raman scattering (SERS). Our analysis was performed on urine samples collected prospectively from 58 kidney transplant patients using a He-Ne laser (632.8 nm) as the excitation source. All abnormal kidney function episodes (three acute rejections and two acute kidney failures that were eventually diagnosed independently by clinical biopsy) consistently exhibited unique SERS spectral features in just one day following the transplant surgery. These results suggested that SERS analysis provides an early and more specific indication to kidney function than the clinically used biomarker, serum creatinine (sCr).

Sickle cell disease: renal manifestations and mechanisms

Sickle cell disease (SCD) substantially alters renal structure and function, and causes various renal syndromes and diseases. Such diverse renal outcomes reflect the uniquely complex vascular pathobiology of SCD and the propensity of red blood cells to sickle in the renal medulla because of its hypoxic, acidotic, and hyperosmolar conditions. Renal complications and involvement in sickle cell nephropathy (SCN) include altered haemodynamics, hypertrophy, assorted glomerulopathies, chronic kidney disease, acute kidney injury, impaired urinary concentrating ability, distal nephron dysfunction, haematuria, and increased risks of urinary tract infections and renal medullary carcinoma. SCN largely reflects an underlying vasculopathy characterized by cortical hyperperfusion, medullary hypoperfusion, and an increased, stress-induced vasoconstrictive response. Renal involvement is usually more severe in homozygous disease (sickle cell anaemia, HbSS) than in compound heterozygous types of SCD (for example HbSC and HbSβ(+)-thalassaemia), and is typically mild, albeit prevalent, in the heterozygous state (sickle cell trait, HbAS). Renal involvement contributes substantially to the diminished life expectancy of patients with SCD, accounting for 16-18% of mortality. As improved clinical care promotes survival into adulthood, SCN imposes a growing burden on both individual health and health system costs. This Review addresses the renal manifestations of SCD and focuses on their underlying mechanisms.

Anticomplement C5 therapy with eculizumab for the treatment of paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome

The complement inhibitor eculizumab is a humanized monoclonal antibody against C5. It was developed to specifically target cleavage of C5 thus preventing release of C5a and activation of the terminal pathway. Paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS) are 2 diseases with distinctly different underlying molecular mechanisms. In PNH, progeny of hematopoietic stem cells that harbor somatic mutations lead to a population of peripheral blood cells that are deficient in complement regulators resulting in hemolysis and thrombosis. In aHUS, germline mutations in complement proteins or their regulators fail to protect the glomerular endothelium from complement activation resulting in thrombotic microangiopathy and renal failure. Critical to the development of either disease is activation of the terminal complement pathway. Understanding this step has led to the study of eculizumab as a treatment for these diseases. In clinical trials, eculizumab is proven to be effective and safe in PNH and aHUS.