Proximal tubule haptoglobin gene activation is an integral component of the acute kidney injury "stress response"

Digoxin-Mediated Inhibition of Potential Hypoxia-Related Angiogenic Repair in Modulated Electro-Hyperthermia (mEHT)-Treated Murine Triple-Negative Breast Cancer Model

Triple-negative breast cancer (TNBC) is a highly aggressive breast cancer type with no targeted therapy and hence limited treatment options. Modulated electrohyperthermia (mEHT) is a novel complementary therapy where a 13.56 MHz radiofrequency current targets cancer cells selectively, inducing tumor damage by thermal and electromagnetic effects. We observed severe vascular damage in mEHT-treated tumors and investigated the potential synergism between mEHT and inhibition of tumor vasculature recovery in our TNBC mouse model. 4T1/4T07 isografts were orthotopically inoculated and treated three to five times with mEHT. mEHT induced vascular damage 4-12 h after treatment, leading to tissue hypoxia detected at 24 h. Hypoxia in treated tumors induced an angiogenic recovery 24 h after the last treatment. Administration of the cardiac glycoside digoxin with the potential hypoxia-inducible factor 1-α (HIF1-α) and angiogenesis inhibitory effects could synergistically augment mEHT-mediated tumor damage and reduce tissue hypoxia signaling and consequent vascular recovery in mEHT-treated TNBC tumors. Conclusively, repeated mEHT induced vascular damage and hypoxic stress in TNBC that promoted vascular recovery. Inhibiting this hypoxic stress signaling enhanced the effectiveness of mEHT and may potentially enhance other forms of cancer treatment.

Differential renal proteomics analysis in a novel rat model of iodinated contrast-induced acute kidney injury

Contrast-induced acute kidney injury (CI-AKI), which occurs after the use of iodinated contrast media, has become the third leading cause of hospital-acquired acute kidney injury (AKI). It is associated with prolonged hospitalization and increased risks of end-stage renal disease and mortality. The pathogenesis of CI-AKI is unclear and effective treatments are lacking. By comparing different post-nephrectomy times and dehydration times, we constructed a new, short-course CI-AKI model using dehydration for 24 h two weeks after unilateral nephrectomy. We found that the low-osmolality contrast media iohexol caused more severe renal function decline, renal morphological damage, and mitochondrial ultrastructural alterations compared to the iso-osmolality contrast media iodixanol. The shotgun proteomics based on Tandem Mass Tag (TMT) was used to conduct proteomics research on renal tissue in the new CI-AKI model, and 604 distinct proteins were identified, mainly involving complement and coagulation cascade, COVID-19, PPAR signalling pathway, mineral absorption, cholesterol metabolism, ferroptosis, staphylococcus aureus infection, systemic lupus erythematosus, folate biosynthesis, and proximal tubule bicarbonate reclamation. Then, using parallel reaction monitoring (PRM), we validate 16 candidate proteins, of which five were novel candidates (Serpina1, Apoa1, F2, Plg, Hrg) previously unrelated to AKI and associated with an acute response as well as fibrinolysis. The pathway analysis and 16 candidate proteins may help to discover new mechanisms in the pathogenesis of CI-AKI, allowing for early diagnosis and outcome prediction.

Genome-Wide Association Analysis of Protein-Coding Variants in IgA Nephropathy

SIGNIFICANCE STATEMENT

Genome-wide association studies have identified nearly 20 IgA nephropathy susceptibility loci. However, most nonsynonymous coding variants, particularly ones that occur rarely or at a low frequency, have not been well investigated. The authors performed a chip-based association study of IgA nephropathy in 8529 patients with the disorder and 23,224 controls. They identified a rare variant in the gene encoding vascular endothelial growth factor A (VEGFA) that was significantly associated with a two-fold increased risk of IgA nephropathy, which was further confirmed by sequencing analysis. They also identified a novel common variant in PKD1L3 that was significantly associated with lower haptoglobin protein levels. This study, which was well-powered to detect low-frequency variants with moderate to large effect sizes, helps expand our understanding of the genetic basis of IgA nephropathy susceptibility.

BACKGROUND

Genome-wide association studies have identified nearly 20 susceptibility loci for IgA nephropathy. However, most nonsynonymous coding variants, particularly those occurring rarely or at a low frequency, have not been well investigated.

METHODS

We performed a three-stage exome chip-based association study of coding variants in 8529 patients with IgA nephropathy and 23,224 controls, all of Han Chinese ancestry. Sequencing analysis was conducted to investigate rare coding variants that were not covered by the exome chip. We used molecular dynamic simulation to characterize the effects of mutations of VEGFA on the protein's structure and function. We also explored the relationship between the identified variants and the risk of disease progression.

RESULTS

We discovered a novel rare nonsynonymous risk variant in VEGFA (odds ratio, 1.97; 95% confidence interval [95% CI], 1.61 to 2.41; P = 3.61×10 -11 ). Further sequencing of VEGFA revealed twice as many carriers of other rare variants in 2148 cases compared with 2732 controls. We also identified a common nonsynonymous risk variant in PKD1L3 (odds ratio, 1.16; 95% CI, 1.11 to 1.21; P = 1.43×10 -11 ), which was associated with lower haptoglobin protein levels. The rare VEGFA mutation could cause a conformational change and increase the binding affinity of VEGFA to its receptors. Furthermore, this variant was associated with the increased risk of kidney disease progression in IgA nephropathy (hazard ratio, 2.99; 95% CI, 1.09 to 8.21; P = 0.03).

CONCLUSIONS

Our study identified two novel risk variants for IgA nephropathy in VEGFA and PKD1L3 and helps expand our understanding of the genetic basis of IgA nephropathy susceptibility.

IL-6 mediates the hepatic acute phase response after prerenal azotemia in a clinically defined murine model

Prerenal azotemia (PRA) is a major cause of acute kidney injury and uncommonly studied in preclinical models. We sought to develop and characterize a novel model of PRA that meets the clinical definition: acute loss of glomerular filtration rate (GFR) that returns to baseline with resuscitation. Adult male C57BL/6J wild-type (WT) and IL-6-/- mice were studied. Intraperitoneal furosemide (4 mg) or vehicle was administered at time = 0 and 3 h to induce PRA from volume loss. Resuscitation began at 6 h with 1 mL intraperitoneal saline for four times for 36 h. Six hours after furosemide administration, measured glomerular filtration rate was 25% of baseline and returned to baseline after saline resuscitation at 48 h. After 6 h of PRA, plasma interleukin (IL)-6 was significantly increased, kidney and liver histology were normal, kidney and liver lactate were normal, and kidney injury molecule-1 immunofluorescence was negative. There were 327 differentially regulated genes upregulated in the liver, and the acute phase response was the most significantly upregulated pathway; 84 of the upregulated genes (25%) were suppressed in IL-6-/- mice, and the acute phase response was the most significantly suppressed pathway. Significantly upregulated genes and their proteins were also investigated and included serum amyloid A2, serum amyloid A1, lipocalin 2, chemokine (C-X-C motif) ligand 1, and haptoglobin; hepatic gene expression and plasma protein levels were all increased in wild-type PRA and were all reduced in IL-6-/- PRA. This work demonstrates previously unknown systemic effects of PRA that includes IL-6-mediated upregulation of the hepatic acute phase response.NEW & NOTEWORTHY Prerenal azotemia (PRA) accounts for a third of acute kidney injury (AKI) cases yet is rarely studied in preclinical models. We developed a clinically defined murine model of prerenal azotemia characterized by a 75% decrease in measured glomerular filtration rate (GFR), return of measured glomerular filtration rate to baseline with resuscitation, and absent tubular injury. Numerous systemic effects were observed, such as increased plasma interleukin-6 (IL-6) and upregulation of the hepatic acute phase response.

Urinary proteome of dogs with renal disease secondary to leishmaniosis

Canine leishmaniosis is frequently associated with the development of renal disease. Its pathogenesis is complex and not fully understood. For this reason, this study aimed to describe the urinary proteome, and identify possible new biomarkers in dogs with kidney disease secondary to leishmaniosis. Urine samples were collected from 20 dogs, 5 from healthy dogs, and 15 from stages Leishvet III and IV. Urine samples were analyzed by UHPLC-MS/MS. The data are available via ProteomeXchange with identifier PXD029165. A total of 951 proteins were obtained. After bioinformatic analysis, 93 urinary proteins were altered in the study group. Enrichment analysis performed on these proteins showed an overrepresentation of the complement activation pathway, among others. Finally, 12 discriminant variables were found in dogs with renal disease secondary to leishmaniosis, highlighting C4a anaphylatoxin, apolipoprotein A-I, haptoglobin, leucine-rich alpha-2-glycoprotein 1, and beta-2-microglobulin. This study is the first to describe the urinary proteomics of dogs with renal disease caused by leishmaniosis, and it provides new possible biomarkers for the diagnosis and monitoring of this disease.

A New Role of Acute Phase Proteins: Local Production Is an Ancient, General Stress-Response System of Mammalian Cells

The prevailing general view of acute-phase proteins (APPs) is that they are produced by the liver in response to the stress of the body as part of a systemic acute-phase response. We demonstrated a coordinated, local production of these proteins upon cell stress by the stressed cells. The local, stress-induced APP production has been demonstrated in different tissues (kidney, breast cancer) and with different stressors (hypoxia, fibrosis and electromagnetic heat). Thus, this local acute-phase response (APR) seems to be a universal mechanism. APP production is an ancient defense mechanism observed in nematodes and fruit flies as well. Local APP production at the tissue level is also supported by sporadic literature data for single proteins; however, the complex, coordinated, local appearance of this stress response has been first demonstrated only recently. Although a number of literature data are available for the local production of single acute-phase proteins, their interpretation as a local, coordinated stress response is new. A better understanding of the role of APPs in cellular stress response may also be of diagnostic/prognostic and therapeutic significance.

Cellular and molecular pathways underlying the nephrotoxicity of gadolinium

Mounting evidence on the short- and long-term adverse effects associated with gadolinium [Gd (III)]-based contrast agents used in magnetic resonance imaging have emerged in the past three decades. Safety issues arise from the release of Gd (III) from chelates and its deposition in tissues, which is exacerbated in patients with renal disease, since the kidney is the major excretion organ of most of these agents. This study aimed at unveiling the cellular and molecular mechanisms of nephrotoxicity of Gd (III), using an in vitro model of human proximal tubular cells (HK-2 cell line). Cell viability declined in a concentration- and time-dependent manner after exposure to GdCl3·6H2O. The estimated inhibitory concentrations (ICs) eliciting 1 to 50% of cell death, after 24 h of exposure, ranged from 3.4 to 340.5 µM. At toxic concentrations, exposure to Gd (III) led to disruption of the oxidative status, mitochondrial dysfunction, cell death by apoptosis, switching to necrosis at higher levels, and autophagic activation. Disturbance of the lipid metabolism was already observed at low-toxicity ICs, with accumulation of lipid droplets, and upregulation of genes related to both lipogenesis and lipolysis. Gd (III)-exposure, even at the subtoxic IC01, increased the expression of modulators of various signaling pathways involved in the development and progression of renal disease, including inflammation, hypoxia and fibrosis. Our results give new insights into the mechanisms underlying the nephrotoxic potential of Gd (III) and highlight the need to further clarify the risks versus benefits of the Gd (III)-based contrast agents currently in use.

The Role of Alpha-1-Acid Glycoprotein in the Diagnosis and Treatment of Crush Syndrome-Induced Acute Kidney Injury

BACKGROUND

Crush syndrome (CS) is the most common cause of deaths following earthquakes and other disasters. The pathogenesis of CS has yet to be fully elucidated. Thus, clinical choice of ideal drug treatments for CS remains deficient.

METHODS AND RESULTS

In this study, we first evaluated the relation between extrusion force and the severities of CS. Rats were exposed to different extrusion forces: 1 kg, 3 kg, 5 kg, and 8 kg, respectively. Survival rates, crushed muscle tissue edema, serum biochemical parameters, and histopathological staining were used to assess severity. Our results showed that there were no statistical differences in survival rate or changes in thigh circumference among the different extrusion forces groups. However, serum levels of potassium, creatine kinase, blood urea nitrogen, creatinine, and myoglobin were elevated at 12- and 24-h post-decompression in 5 kg and 8 kg groups, compared with 1 kg and 3 kg groups. Histopathological staining demonstrated that the degree of organ damage to kidney, muscle, and lung tissues correlated with increasing extrusion force. We next analyzed changes in serum protein profiles in 3 kg or 5 kg extrusion pressure groups. A total of 76 proteins (20 upregulated, 56 downregulated) were found to be altered at all three time points (0, 12, and 72 h) post-decompression, compared with the control group. Three common upregulated proteins alpha-1-acid glycoprotein (α1-AGP), neutrophil gelatinase-associated lipocalin (NGAL), and Haptoglobin were selected for validation of increased expression. α1-AGP was explored as a treatment for CS-induced acute kidney injury (AKI). Intraperitoneal injection of α1-AGP protected kidneys from CS-induced AKI by regulating TNF-α and IL-6 production, attenuating neutrophil recruitment, and reducing renal cell apoptosis.

CONCLUSION

Our findings demonstrated that the severity of crush injury is causally related to extrusion pressure and increase in blood serum markers. Our identification of the biomarker and treatment candidate, α1-AGP, suggests its implication in predicting the severity of CS and its use as a mediator of CS-induced AKI, respectively.

Development of a sensitive and reliable ELISA kit of urinary haptoglobin to predict progress of diabetic kidney disease

AIMS

Urinary haptoglobin (UHp) is a potential biomarker for predicting progress of diabetic kidney disease (DKD) to remedy the defects of currently used urinary albumin. The clinical application of UHp is however limited, owing to the extremely low level in urine. This study aims to establish an enzyme-linked immunosorbent assay (ELISA) kit specifically for detecting UHp in urine samples of patients with diabetes and DKD.

MATERIALS AND METHODS

Supersensitive human haptoglobin antibodies were generated for ELISA kit development, and the sensitivity, specificity and reproducibility of the kit was evaluated. This kit was used to detect UHp in 246 healthy individuals and 83 patients with type 2 diabetes (T2D). The interference of blood haptoglobin genotypes on UHp measurement was analysed.

RESULTS

The UHp ELISA kit had a standard curve ranging from 5 to 200 ng/ml. The low detection limit was 0.11 ng/ml. The coefficients of variation of intra- and interassay were 5.5% and 8.3%, respectively. The kit showed high accuracy with 100.9% mean recovery rate, and linearity R²  = 0.999. The reference range of UHp was 0-42.3 ng/g creatinine (0-Q95) in the healthy individuals. UHp level was significantly higher in T2D patients with microalbuminuria and macroalbuminuria than that in T2D without microalbuminuria (p < 0.01). The UHp concentration measured by this kit was not affected by haptoglobin genotypes.

CONCLUSIONS

We have generated an ELISA kit to accurately detect UHp levels, which is potentially a reliable biomarker of DKD.

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 Yin and Yang of Alarmins in Regulation of Acute Kidney Injury

Acute kidney injury (AKI) is a major clinical burden affecting 20 to 50% of hospitalized and intensive care patients. Irrespective of the initiating factors, the immune system plays a major role in amplifying the disease pathogenesis with certain immune cells contributing to renal damage, whereas others offer protection and facilitate recovery. Alarmins are small molecules and proteins that include granulysins, high-mobility group box 1 protein, interleukin (IL)-1α, IL-16, IL-33, heat shock proteins, the Ca++ binding S100 proteins, adenosine triphosphate, and uric acid. Alarmins are mostly intracellular molecules, and their release to the extracellular milieu signals cellular stress or damage, generally leading to the recruitment of the cells of the immune system. Early studies indicated a pro-inflammatory role for the alarmins by contributing to immune-system dysregulation and worsening of AKI. However, recent developments demonstrate anti-inflammatory mechanisms of certain alarmins or alarmin-sensing receptors, which may participate in the prevention, resolution, and repair of AKI. This dual function of alarmins is intriguing and has confounded the role of alarmins in AKI. In this study, we review the contribution of various alarmins to the pathogenesis of AKI in experimental and clinical studies. We also analyze the approaches for the therapeutic utilization of alarmins for AKI.

The circadian clock gene Bmal1 facilitates cisplatin-induced renal injury and hepatization

Cisplatin is one of the most potent chemotherapy drugs to treat cancers, but its clinical application remains limited due to severe nephrotoxicity. Several approaches have been developed to minimize such side effects, notably including chronotherapy, a well-known strategy based on the circadian clock. However, the component of the circadian clock machinery that particularly responses to the cisplatin stimulation remains unknown, including its functions in cisplatin-induced renal injury. In our present study, we demonstrated that Bmal1, as a key clock gene, was induced by the cisplatin stimulation in the mouse kidney and cultured human HK-2 renal cells. Gain- and loss-of-function studies indicated that Bmal1 facilitated cisplatin-induced renal injury both in vivo and in vitro, by aggravating the cell apoptotic process. More importantly, RNA-seq analysis revealed that Bmal1 triggered the expression of hallmark genes involved in renal hepatization, a critical event accompanied by the injury. At the molecular level, Bmal1 activated the transcription of hepatization-associated genes through direct recruitment to the E-box motifs of their promoters. Our findings suggest that Bmal1, a pivotal mediator induced renal injury in response to cisplatin treatment, and the therapeutic intervention targeting Bmal1 in the kidney may be a promising strategy to minimize the toxic side-effects of cisplatin in its clinical applications.

The Role of Biomarkers in Acute Kidney Injury

Several biomarkers have been developed to detect acute kidney injury (AKI) and predict outcomes. Most AKI biomarkers have been shown to be expressed before serum creatinine and to be more sensitive and specific than urine output. Only a few studies have examined how implementation can change clinical outcomes. A second generation of AKI biomarkers have been developed. These markers, including tissue inhibitor of metalloproteinases-2 (TIMP-2) and insulinlike growth factor-binding protein 7 (IGFBP7), have obtained regulatory approval in many countries based on large, rigorous clinical studies and small, single-centered trials and have begun to establish clinical utility.

Association of Urine Haptoglobin With Risk of All-Cause and Cause-Specific Mortality in Individuals With Type 2 Diabetes: A Transethnic Collaborative Work

OBJECTIVE

Haptoglobin is an acute-phase reactant with pleiotropic functions. We aimed to study whether urine haptoglobin may predict risk of mortality in people with type 2 diabetes.

RESEARCH DESIGN AND METHODS

We employed a transethnic approach with a cohort of Asian origin (Singapore) (N = 2,061) and a cohort of European origin (France) (N = 1,438) included in the study. We used survival analyses to study the association of urine haptoglobin with risk of all-cause and cause-specific mortality.

RESULTS

A total of 365 and 525 deaths were registered in the Singapore cohort (median follow-up 7.5 years [interquartile range 3.5-12.8]) and French SURDIAGENE cohort (median follow-up 6.8 years [interquartile range 4.3-10.5], respectively. Singapore participants with urine haptoglobin in quartiles 2 to 4 had higher risk for all-cause mortality compared with quartile 1 (unadjusted hazard ratio [HR] 1.47 [95% CI 1.02-2.11], 2.28 [1.62-3.21], and 4.64 [3.39-6.35], respectively). The association remained significant in quartile 4 after multiple adjustments (1.68 [1.15-2.45]). Similarly, participants in the French cohort with haptoglobin in quartile 4 had significantly higher hazards for all-cause mortality compared with quartile 1 (unadjusted HR 2.67 [2.09-3.42] and adjusted HR 1.49 [1.14-1.96]). In both cohorts, participants in quartile 4 had a higher risk of mortality attributable to cardiovascular disease and infection but not malignant tumor.

CONCLUSIONS

Urine haptoglobin predicts risk of mortality independent of traditional risk factors, suggesting that it may potentially be a novel biomarker for risk of mortality in patients with type 2 diabetes.

Extensive Changes in Transcriptomic "Fingerprints" and Immunological Cells in the Large Organs of Patients Dying of Acute Septic Shock and Multiple Organ Failure Caused by Neisseria meningitidis

Background: Patients developing meningococcal septic shock reveal levels of Neisseria meningitidis (10⁶-10⁸/mL) and endotoxin (10¹-10³ EU/mL) in the circulation and organs, leading to acute cardiovascular, pulmonary and renal failure, coagulopathy and a high case fatality rate within 24 h. Objective: To investigate transcriptional profiles in heart, lungs, kidneys, liver, and spleen and immunostain key inflammatory cells and proteins in post mortem formalin-fixed, paraffin-embedded (FFPE) tissue samples from meningococcal septic shock patients. Patients and Methods: Total RNA was isolated from FFPE and fresh frozen (FF) tissue samples from five patients and two controls (acute non-infectious death). Differential expression of genes was detected using Affymetrix microarray analysis. Lung and heart tissue samples were immunostained for T-and B cells, macrophages, neutrophils and the inflammatory markers PAI-1 and MCP-1. Inflammatory mediators were quantified in lysates from FF tissues. Results: The transcriptional profiles showed a complex pattern of protein-coding and non-coding RNAs with significant regulation of pathways associated with organismal death, cell death and survival, leukocyte migration, cellular movement, proliferation of cells, cell-to-cell signaling, immune cell trafficking, and inflammatory responses in an organ-specific clustering manner. The canonical pathways including acute phase response-, EIF2-, TREM1-, IL-6-, HMBG1-, PPAR signaling, and LXR/RXR activation were associated with acute heart, pulmonary, and renal failure. Fewer genes were regulated in the liver and particularly in the spleen. The main upstream regulators were TNF, IL-1β, IL-6, RICTOR, miR-6739-3p, and CD3. Increased numbers of inflammatory cells (CD68+, MPO+, CD3+, and CD20+) were found in lungs and heart. PAI-1 inhibiting fibrinolysis and MCP-1 attracting leukocyte were found significantly present in the septic tissue samples compared to the controls. Conclusions: FFPE tissue samples can be suitable for gene expression studies as well as immunostaining of specific cells or molecules. The most pronounced gene expression patterns were found in the organs with highest levels of Neisseria meningitidis DNA. Thousands of protein-coding and non-coding RNA transcripts were altered in lungs, heart and kidneys. We identified specific biomarker panels both protein-coding and non-coding RNA transcripts, which differed from organ to organ. Involvement of many genes and pathways add up and the combined effect induce organ failure.

The Acute Phase Response Is a Prominent Renal Proteome Change in Sepsis in Mice

(1) Background: Sepsis-induced acute kidney injury (AKI) is the most common form of acute kidney injury (AKI). We studied the temporal profile of the sepsis-induced renal proteome changes. (2) Methods: Male mice were injected intraperitoneally with bacterial lipopolysaccharide (LPS) or saline (control). Renal proteome was studied by LC-MS/MS (ProteomeXchange: PXD014664) at the early phase (EP, 1.5 and 6 h after 40 mg/kg LPS) and the late phase (LP, 24 and 48 h after 10 mg/kg LPS) of LPS-induced AKI. Renal mRNA expression of acute phase proteins (APP) was assessed by qPCR. (3) Results: Renal proteome change was milder in EP vs. LP. APPs dominated the proteome in LP (proteins upregulated at least 4-fold (APPs/all): EP, 1.5 h: 0/10, 6 h: 1/10; LP, 24 h: 22/47, 48 h: 17/44). Lipocalin-2, complement C3, fibrinogen, haptoglobin and hemopexin were the most upregulated APPs. Renal mRNA expression preceded the APP changes with peak effects at 24 h, and indicated renal production of the majority of APPs. (4) Conclusions: Gene expression analysis revealed local production of APPs that commenced a few hours post injection and peaked at 24 h. This is the first demonstration of a massive, complex and coordinated acute phase response of the kidney involving several proteins not identified previously.

Parenterial iron sucrose-induced renal preconditioning: differential ferritin heavy and light chain expression in plasma, urine, and internal organs

Experimental data suggest that iron sucrose (FeS) injection, used either alone or in combination with other prooxidants, can induce "renal preconditioning," in part by upregulating cytoprotective ferritin levels. However, the rapidity, degree, composition (heavy vs. light chain), and renal ferritin changes after FeS administration in humans remain to be defined. To address these issues, healthy human volunteers (n = 9) and patients with stage 3-4 chronic kidney disease(n = 9) were injected once with FeS (120, 240, or 360 mg). Plasma ferritin was measured from 0 to 8 days postinjection as an overall index of ferritin generation. Urinary ferritin served as a "biomarker" of renal ferritin production. FeS induced rapid (≤2 h), dose-dependent, plasma ferritin increases in all study participants, peaking at approximately three to five times baseline within 24-48 h. Significant urinary ferritin increases (~3 times), without dose-dependent increases in albuminuria, neutrophil gelatinase-associated lipocalin, or N-acetyl-β-d-glucosaminidase excretion, were observed. Western blot analysis with ferritin heavy chain (Fhc)- and light chain (Flc)-specific antibodies demonstrated that FeS raised plasma Flc but not Fhc levels. Conversely, FeS increased both Fhc and Flc in urine. To assess sites of FeS-induced ferritin generation, organs from FeS-treated mice were probed for Fhc, Flc, and their mRNAs. FeS predominantly raised hepatic Flc. Conversely, marked Fhc and Flc elevations developed in the kidney and spleen. No cardiopulmonary ferritin increases occurred. Ferritin mRNAs remained unchanged throughout, implying posttranscriptional ferritin production. We conclude that FeS induces rapid, dramatic, and differential Fhc and Flc upregulation in organs. Renal Fhc and Flc increases, in the absence of nephrotoxicity, suggest potential FeS utility as a clinical renal "preconditioning" agent.

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.

Proteomics analysis of blood plasma in HIV-infected patients with chronic kidney disease

BACKGROUND

Patients treated for human immunodeficiency virus (HIV) infection are prone to developing chronic kidney disease (CKD). Current methods used in assessing kidney function suffer inaccuracy in HIV-infected patients. This study aims to identify biomarkers that could complement existing methods of kidney assessment among HIV-infected subjects.

METHODS

Plasma protein profiling was performed for HIV patients with CKD presented with negative/trace proteinuria (non-proteinuric) (n = 8) and their matched non-CKD controls, using two-dimensional gel electrophoresis (2DE); selected protein candidates were identified using mass spectrometry. Subsequently, altered plasma abundance of protein candidates were verified using Western blotting in HIV-infected subjects with non-proteinuric CKD (n = 8), proteinuric CKD (n = 5), and their matched non-CKD controls, as well as in HIV-uninfected subjects with impaired kidney function (n = 3) and their matched controls.

RESULTS

Analysis of 2DE found significantly altered abundance of five protein candidates between HIV-infected patients with non-proteinuric CKD and without CKD: alpha-1-microglobulin (A1M), serum albumin (ALB), zinc-alpha-2-glycoprotein (AZGP1), haptoglobin (HP), and retinol binding protein (RBP4). Western blotting showed an increased abundance of A1M and HP in HIV-infected patients with non-proteinuric CKD compared to their non-CKD controls, whereas A1M, AZGP1, and RBP4 were significantly increased in HIV-infected patients with proteinuric CKD compared to their non-CKD controls. Such pattern was not found in HIV-uninfected subjects with impaired kidney function.

CONCLUSION

The data suggests four proteins that may be used as biomarkers of CKD in HIV-infected patients. Further validation in a larger cohort of HIV-infected patients is necessary for assessing the clinical use of these proposed biomarkers for CKD.

Rat models of colistin nephrotoxicity: previous experimental researches and future perspectives

Colistin is an old antibiotic, which is abandoned decades ago because of high nephrotoxicity rates. However, it is reintroduced to clinical medicine due to lack of newly discovered antibiotics and is still widely used for the treatment of resistant gram-negative infections. Discovering mechanisms to reduce nephrotoxicity risk is of significant importance since exposed patients may have many other factors that alter kidney functions. Several agents were evaluated in animal models of colistin nephrotoxicity as a means to prevent kidney injury. Considerable heterogeneity exists in terms of reporting colistin dosing and experimental designs. This issue leads clinicians to face difficulties in designing studies and sometimes may lead to report dosing strategies inadequately. Here, we present a review according to animal models of colistin nephrotoxicity using data gathered from previous experiments to draw attention on possible complexities that researchers may encounter.

Mechanisms Underlying Increased TIMP2 and IGFBP7 Urinary Excretion in Experimental AKI

BACKGROUND

Recent clinical data support the utility/superiority of a new AKI biomarker ("NephroCheck"), the arithmetic product of urinary TIMP × IGFBP7 concentrations. However, the pathophysiologic basis for its utility remains ill defined.

METHODS

To clarify this issue, CD-1 mice were subjected to either nephrotoxic (glycerol, maleate) or ischemic AKI. Urinary TIMP2/IGFBP7 concentrations were determined at 4 and 18 hours postinjury and compared with urinary albumin levels. Gene transcription was assessed by measuring renal cortical and/or medullary TIMP2/IGFBP7 mRNAs (4 and 18 hours after AKI induction). For comparison, the mRNAs of three renal "stress" biomarkers (NGAL, heme oxygenase 1, and p21) were assessed. Renal cortical TIMP2/IGFBP7 protein was gauged by ELISA. Proximal tubule-specific TIMP2/IGFBP7 was assessed by immunohistochemistry.

RESULTS

Each AKI model induced prompt (4 hours) and marked urinary TIMP2/IGFBP7 increases without an increase in renal cortical concentrations. Furthermore, TIMP2/IGFBP7 mRNAs remained at normal levels. Endotoxemia also failed to increase TIMP2/IGFBP7 mRNAs. In contrast, each AKI model provoked massive NGAL, HO-1, and p21 mRNA increases, confirming that a renal "stress response" had occurred. Urinary albumin rose up to 100-fold and strongly correlated (r=0.87-0.91) with urinary TIMP2/IGFBP7 concentrations. Immunohistochemistry showed progressive TIMP2/IGFBP7 losses from injured proximal tubule cells. Competitive inhibition of endocytic protein reabsorption in normal mice tripled urinary TIMP2/IGFBP7 levels, confirming this pathway's role in determining urinary excretion.

CONCLUSIONS

AKI-induced urinary TIMP2/IGFBP7 elevations are not due to stress-induced gene transcription. Rather, increased filtration, decreased tubule reabsorption, and proximal tubule cell TIMP2/IGFBP7 urinary leakage seem to be the most likely mechanisms.

Genetic markers for urine haptoglobin is associated with decline in renal function in type 2 diabetes in East Asians

Urine haptoglobin (uHP) level prospectively predicts diabetic kidney disease (DKD) progression. Here, we aim to identify genetic determinants of uHP level and evaluate association with renal function in East Asians (EA) with type 2 diabetes (T2D). Genome-wide association study (GWAS) among 805 [236 Chinese (discovery) and 569 (57 Malay and 512 Chinese) (validation)] found that rs75444904/kgp16506790 variant was robustly associated with uHP level (MetaP = 1.21 × 10^-60). rs75444904 correlates well with plasma HP protein levels and multimerization in EA but was not in perfect LD (r² = 0.911 in Chinese, r² = 0.536 in Malay) and is monomorphic in Europeans (1000 G data). Conditional probability analysis indicated weakening of effects but residual significant associations between rs75444904 and uHP when adjusted on HP structural variant (MetaP = 8.22 × 10^-7). The rs75444904 variant was associated with DKD progression (OR = 1.77, P = 0.014) independent of traditional risk factors. In an additional validation-cohort of EA (410 end-stage renal disease (ESRD) cases and 1308 controls), rs75444904 was associated with ESRD (OR = 1.22, P = 0.036). Furthermore, increased risk of DKD progression (OR = 2.09, P = 0.007) with elevated uHP level through Mendelian randomisation analysis provide support for potential causal role of uHP in DKD progression in EA. However, further replication of our findings in larger study populations is warranted.

Macrophages in Renal Injury and Repair

Acute kidney injury (AKI) is a growing global health concern, yet no treatment is currently available to prevent it or to promote kidney repair after injury. Animal models demonstrate that the macrophage is a major contributor to the inflammatory response to AKI. Emerging data from human biopsies also corroborate the presence of macrophages in AKI and their persistence in progressive chronic kidney disease. Macrophages are phagocytic innate immune cells that are important mediators of tissue homeostasis and host defense. In response to tissue injury, macrophages become activated based on specific signals from the damaged microenvironment. The activation and functional state of the macrophage depends on the stage of tissue injury and repair, reflecting a dynamic and diverse spectrum of macrophage phenotypes. In this review, we highlight our current understanding of the mechanisms by which macrophages contribute to injury and repair after AKI.

Effects of arginine vasopressin on the urine proteome in rats

Biomarkers are the measurable changes associated with a physiological or pathophysiological process. The content of urine frequently changes because it is not controlled by homeostatic mechanisms, and these alterations can be a source of biomarkers. However, urine is affected by many factors. In this study, vasoconstrictor and antidiuretic arginine vasopressin (AVP) were infused into rats using an osmotic pump. The rats’ urinary proteome after one week of infusion was analyzed by label-free LC-MS/MS. A total of 408 proteins were identified; among these proteins, eight and 10 proteins had significantly altered expression in the low and high dose groups, respectively, compared with the control group using the one-way ANOVA analysis followed by post hoc analysis with the least significant difference (LSD) test or Dunnett’s T3 test. Three differential proteins were described in prior studies as related to AVP physiological processes, and nine differential proteins are known disease biomarkers. Sixteen of the 17 differential proteins have human orthologs. These results suggest that we should consider the effects of AVP on urinary proteins in future urinary disease biomarker researches. The study data provide clues regarding underlying mechanisms associated with AVP for future physiological researches on AVP. This study provide a sensitive changes associated with AVP. However, the limitation of this result is that the candidate biomarkers should be further verified and filtered. Large clinical samples must be examined to verify the differential proteins identified in this study before these proteins are used as biomarkers for pathological AVP increased diseases, such as syndrome of inappropriate antidiuretic hormone secretion (SIADH).

Genotypic and phenotypic characterization of G6PD deficiency in Bengali adults with severe and uncomplicated malaria

BACKGROUND

Control of malaria increasingly involves administration of 8-aminoquinolines, with accompanying risk of haemolysis in individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Few data on the prevalence and genotypic basis of G6PD deficiency are available from Bangladesh, where malaria remains a major problem in the South (Chittagong Division). The aim of this study was to determine the prevalence of G6PD deficiency, and associated G6PD genotypes, in adults with falciparum malaria in southern Bangladesh.

METHODS

G6PD status was assessed via a combination of fluorescent spot testing (FST) and genotyping in 141 Bengali patients admitted with falciparum malaria to two centres in Chittagong Division from 2012 to 2014. In addition, an analysis of genomic data from 1000 Genomes Project was carried out among five healthy Indian subcontinent populations.

RESULTS

One male patient with uncomplicated malaria was found to have G6PD deficiency on FST and a genotype associated with deficiency (hemizygous Orissa variant). In addition, there were two female patients heterozygous for deficiency variants (Orissa and Kerala-Kalyan). These three patients had a relatively long duration of symptoms prior to admission compared to G6PD normal cases, possibly suggesting an interaction with parasite multiplication rate. In addition, one of 27 healthy local controls was deficient on FST and hemizygous for the Mahidol variant of G6PD deficiency. Examination of 1000 Genomes Project sequencing data across the Indian subcontinent showed that 19/723 chromosomes (2.63%) carried a variant associated with deficiency. In the Bengali from Bangladesh 1000 Genomes population, three of 130 chromosomes (2.31%) carried deficient alleles; this included single chromosomes carrying the Kerala-Kalyan and Orissa variants.

CONCLUSIONS

In line with other recent work, G6PD deficiency is uncommon in Bengalis in Bangladesh. Further studies of particular ethnic groups are needed to evaluate the potential risk of wide deployment of primaquine in malaria control efforts in Bangladesh.

An evaluation of the antioxidant protein α1-microglobulin as a renal tubular cytoprotectant

α1-Microglobulin (A1M) is a low-molecular-weight heme-binding antioxidant protein that is readily filtered by the glomerulus and reabsorbed by proximal tubules. Given these properties, recombinant A1M (rA1M) has been proposed as a renal antioxidant and therapeutic agent. However, little direct evidence to support this hypothesis exists. Hence, we have sought “proof of concept” in this regard. Cultured proximal tubule (HK-2) cells or isolated mouse proximal tubule segments were challenged with a variety of prooxidant insults: 1) hemin, 2) myoglobin; 3) “catalytic” iron, 4) H2O2/Fenton reagents, 5) a Ca2+ ionophore, 6) antimycin A, or 7) hypoxia (with or without rA1M treatment). HK-2 injury was gauged by the percent lactate dehydrogenase release and 4,5-(dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide uptake. In vivo protection was sought in rA1M-treated mice subjected to 1) graded myohemoglobinura (2, 4, 8, or 9 ml/kg glycerol injection), 2) purified myoglobinemia/uria, or 3) endotoxemia. In vivo injury was assessed by blood urea nitrogen, creatinine, and the expression of redox-sensitive genes (heme oxygenase-1, neutrophil gelatinase-associated lipocalin, and monocyte chemoattractant protein-1 mRNAs). Although rA1M totally blocked in vitro hemin toxicity, equimolar albumin (another heme binder) or 10% serum induced equal protection. rA1M failed to mitigate any nonhemin forms of either in vitro or in vivo injury. A1M appeared to be rapidly degraded within proximal tubules (by Western blot analysis). Surprisingly, rA1M exerted select injury-promoting effects (increased in vitro catalytic iron/antimycin toxicities and increased in vivo monocyte chemoattractant protein-1/neutrophil gelatinase-associated lipocalin mRNA expression after glycerol or endotoxin injection). We conclude that rA1M has questionable utility as a renal antioxidant/cytoprotective agent, particularly in the presence of larger amounts of competitive free heme (e.g., albumin) binders.

Acute phase proteins as promising biomarkers: Perspectives and limitations for human and veterinary medicine

Acute phase proteins (APPs) are highly conserved plasma proteins that are increasingly secreted by the liver in response to a variety of injuries, independently of their location and cause. APPs favor the systemic regulation of defense, coagulation, proteolysis, and tissue repair. Various APPs have been applied as general diagnostic parameters for a long time. Through proteomic techniques, more and more APPs have been discovered to be differentially altered. Since they are not consistently explainable by a stereotypic hepatic expression of sets of APPs, most of these results have unfortunately been neglected or attributed to the nonspecificity of the acute phase reaction. Moreover, it appears that various extrahepatic tissues are also able to express APPs. These extrahepatic APPs show focally specific roles in tissue homeostasis and repair and are released primarily into interstitial and distal fluids. Since these focal proteins might leak into the circulatory system, mixtures of hepatic and extrahepatic APP species can be expected in blood. Hence, a selective alteration of parts of APPs might be expected. There are several hints on multiple molecular forms and fragments of tissue-derived APPs. These differences offer the chance for multiple selective determinations. Thus, specific proteoforms might indeed serve as tissue-specific disease indicators.

Combined iron sucrose and protoporphyrin treatment protects against ischemic and toxin-mediated acute renal failure

Tissue preconditioning, whereby various short-term stressors initiate organ resistance to subsequent injury, is well recognized. However, clinical preconditioning of the kidney for protection against acute kidney injury (AKI) has not been established. Here we tested whether a pro-oxidant agent, iron sucrose, combined with a protoporphyrin (Sn protoporphyrin), can induce preconditioning and protect against acute renal failure. Mice were pretreated with iron sucrose, protoporphyrin, cyanocobalamin, iron sucrose and protoporphyrin, or iron sucrose and cyanocobalamin. Eighteen hours later, ischemic, maleate, or glycerol models of AKI were induced, and its severity was assessed the following day (blood urea nitrogen, plasma creatinine concentrations; post-ischemic histology). Agent impact on cytoprotective gene expression (heme oxygenase 1, hepcidin, haptoglobin, hemopexin, α1-antitrypsin, α1-microglobulin, IL-10) was assessed as renal mRNA and protein levels. AKI-associated myocardial injury was gauged by plasma troponin I levels. Combination agent administration upregulated multiple cytoprotective genes and, unlike single agent administration, conferred marked protection against each tested model of acute renal failure. Heme oxygenase was shown to be a marked contributor to this cytoprotective effect. Preconditioning also blunted AKI-induced cardiac troponin release. Thus, iron sucrose and protoporphyrin administration can upregulate diverse cytoprotective genes and protect against acute renal failure. Associated cardiac protection implies potential relevance to both AKI and its associated adverse downstream effects.

Marked protection against acute renal and hepatic injury after nitrited myoglobin + tin protoporphyrin administration

The phenomenon known as renal "ischemic preconditioning," whereby an initial ischemic insult induces resistance against subsequent kidney damage, has been well established in the experimental literature. However, a clinically applicable way to safely recapitulate this state has not been defined. We hypothesized that a unique combination of agents (nitrited myoglobin [N-Mgb] + tin protoporphyrin [SnPP]) can achieve these ends safely and synergistically, increasing cytoprotective proteins (eg, heme oxygenase 1 [HO-1], interleukin 10 [IL-10], and haptoglobin) in kidney cells. To test this hypothesis, CD-1 mice received 1 mg of N-Mgb and 1 μmol of SnPP, either alone or in combination. Renal cortical HO-1, haptoglobin, and IL-10 gene expressions (messenger RNA [mRNA], protein levels) were determined 4 and 18 hours later. Cytoresistance to 3 forms of acute kidney injury (AKI; glycerol-induced rhabdomyolysis, maleate nephrotoxicity, and postischemic AKI progression to chronic kidney disease [CKD]) was assessed. To ascertain whether cytoresistance might emerge in extrarenal organs, hepatic HO-1, IL-10, and haptoglobin levels were also measured, and resistance to 25 minutes of hepatic ischemia-reperfusion injury and hepatotoxicity (intraperitoneal glycerol injection) was sought. N-Mgb + SnPP induced additive or synergistic increases in renal HO-1, haptoglobin, and IL-10 mRNA and protein levels (up to 20-fold) without inducing any apparent renal or extrarenal damage. After 18 hours of post-treatment, marked or complete protection against glycerol-induced AKI, maleate-induced AKI, and postischemic AKI progression to CKD had emerged. Combined N-Mgb + SnPP was more protective than either agent alone (assessed in glycerol model). N-Mgb + SnPP also upregulated cytoprotective pathways in liver and induced marked protection against both hepatic ischemia-reperfusion and toxic liver damage. In conclusion, we posit that "preconditioning" with combined administration of N-Mgb + SnPP represents a promising approach for protecting against diverse forms of renal and nonrenal (hepatic) forms of tissue damage.

Epigenetic profiles of pre-diabetes transitioning to type 2 diabetes and nephropathy

AIM: To examine DNA methylation profiles in a longitudinal comparison of pre-diabetes mellitus (Pre-DM) subjects who transitioned to type 2 diabetes mellitus (T2DM).

METHODS: We performed DNA methylation study in bisulphite converted DNA from Pre-DM (n = 11) at baseline and at their transition to T2DM using Illumina Infinium HumanMethylation27 BeadChip, that enables the query of 27578 individual cytosines at CpG loci throughout the genome, which are focused on the promoter regions of 14495 genes.

RESULTS: There were 694 CpG sites hypomethylated and 174 CpG sites hypermethylated in progression from Pre-DM to T2DM, representing putative genes involved in glucose and fructose metabolism, inflammation, oxidative and mitochondrial stress, and fatty acid metabolism. These results suggest that this high throughput platform is able to identify hundreds of prospective CpG sites associated with diverse genes that may reflect differences in Pre-DM compared with T2DM. In addition, there were CpG hypomethylation changes associated with a number of genes that may be associated with development of complications of diabetes, such as nephropathy. These hypomethylation changes were observed in all of the subjects.

CONCLUSION: These data suggest that some epigenomic changes that may be involved in the progression of diabetes and/or the development of complications may be apparent at the Pre-DM state or during the transition to diabetes. Hypomethylation of a number of genes related to kidney function may be an early marker for developing diabetic nephropathy.

Inflammatory triggers of acute rejection of organ allografts

Solid organ transplantation is a vital therapy for end stage diseases. Decades of research have established that components of the adaptive immune system are critical for transplant rejection, but the role of the innate immune system in organ transplantation is just emerging. Accumulating evidence indicates that the innate immune system is activated at the time of organ implantation by the release of endogenous inflammatory triggers. This review discusses the nature of these triggers in organ transplantation and also potential mediators that may enhance inflammation resolution after organ implantation.

Effects of diuretics on urinary proteins

Biomarker is the measurable change associated with a physiological or pathophysiological process. Unlike blood which has mechanisms to keep the internal environment homeostatic, urine is more likely to reflect changes of the body. As a result, urine is likely to be a better biomarker source than blood. However, since the urinary proteome is affected by many factors, including diuretics, careful evaluation of those effects is necessary if urinary proteomics is used for biomarker discovery. The human orthologs of most of these 14 proteins affected are stable in the healthy human urinary proteome, and 10 of them are reported as disease biomarkers. Thus, our results suggest that the effects of diuretics deserve more attention in future urinary protein biomarker studies. Moreover, the distinct effects of diuretics on the urinary proteome may provide clues to the mechanisms of diuretics.

A two-stage spin cartridge for integrated protein precipitation, digestion and SDS removal in a comparative bottom-up proteomics workflow

Protein precipitation with organic solvent is an effective means of depleting contaminants such as sodium dodecyl sulfate (SDS), while maintaining high analyte recovery. Here, we report the use of a disposable two-stage spin cartridge to facilitate isolation of the precipitated protein, with subsequent enzyme digestion and peptide cleanup in the cartridge. An upper filtration cartridge retains over 95% of the protein (10 μg BSA), with 99.75% detergent depleted from a sample initially containing 2% SDS. Following precipitation, a plug attached to the base of the filtration cartridge retains the solution to enable tryptic digestion in the vial, while a solid phase extraction cartridge attached to the base of the filter facilitates peptide cleanup post-digestion. A GELFrEE fractionated Escherichia coli proteome extract processed with the spin cartridge yields similar protein identifications compared to controls (226 vs 216 for control), and with an increased number of unique peptides (1753 vs 1554 for control). The device is applied to proteome characterization of rat kidneys experiencing a surgically induced ureteral tract obstruction, revealing several statistically altered proteins, consistent with the morphology and expected pathophysiology of the disease.

BIOLOGICAL SIGNIFICANCE

Conventionally, protein precipitation involves extended centrifugation to pellet the sample, with careful pipetting to remove the supernatant without disturbing the pellet. The method is not only time consuming but is highly subject to the skill of the individual, particularly at lower protein concentrations where the pellet may not be visible. As such, protein precipitation is often overlooked in proteomics, favoring column-based approaches to concentrate or purify samples. Here, all aspects of sample manipulation are integrated into a simple disposable cartridge. The device enables SDS depletion, sample preconcentration, resolubilization, derivatization, digestion, and peptide cleanup in a highly repeatable and easily multiplexed format. The device is ideally suited for comparative proteome studies. Antenatal hydronephrosis is a congenital disorder affecting 1-5% of all pregnancies, and can require surgical intervention to avoid loss of renal function. Using our device, we investigated the impact of hydronephrosis on the kidneys in a surgically induced animal model of the disease. Proteome analysis points to decreased metabolic activity in the obstructed kidney, with upregulation of proteins involved in cytoskeletal organization. This article is part of a Special Issue entitled: Protein dynamics in health and disease. Guest Editors: Pierre Thibault and Anne-Claude Gingras.

Acute hepatic ischemic-reperfusion injury induces a renal cortical "stress response," renal "cytoresistance," and an endotoxin hyperresponsive state

Hepatic ischemic-reperfusion injury (HIRI) is considered a risk factor for clinical acute kidney injury (AKI). However, HIRI's impact on renal tubular cell homeostasis and subsequent injury responses remain ill-defined. To explore this issue, 30-45 min of partial HIRI was induced in CD-1 mice. Sham-operated or normal mice served as controls. Renal changes and superimposed injury responses (glycerol-induced AKI; endotoxemia) were assessed 2-18 h later. HIRI induced mild azotemia (blood urea nitrogen ∼45 mg/dl) in the absence of renal histologic injury or proteinuria, implying a "prerenal" state. However, marked renal cortical, and isolated proximal tubule, cytoprotective "stress protein" gene induction (neutrophil gelatinase-associated lipocalin, heme oxygenase-1, hemopexin, hepcidin), and increased Toll-like receptor 4 (TLR4) expression resulted (protein/mRNA levels). Ischemia caused release of hepatic heme-based proteins (e.g., cytochrome c) into the circulation. This corresponded with renal cortical oxidant stress (malondialdehyde increases). That hepatic derived factors can evoke redox-sensitive "stress protein" induction was implied by the following: peritoneal dialysate from HIRI mice, soluble hepatic extract, or exogenous cytochrome c each induced the above stress protein(s) either in vivo or in cultured tubule cells. Functional significance of HIRI-induced renal "preconditioning" was indicated by the following: 1) HIRI conferred virtually complete morphologic protection against glycerol-induced AKI (in the absence of hyperbilirubinemia) and 2) HIRI-induced TLR4 upregulation led to a renal endotoxin hyperresponsive state (excess TNF-α/MCP-1 gene induction). In conclusion, HIRI can evoke "renal preconditioning," likely due, in part, to hepatic release of pro-oxidant factors (e.g., cytochrome c) into the systemic circulation. The resulting renal changes can impact subsequent AKI susceptibility and TLR4 pathway-mediated stress.

Rapid renal alpha-1 antitrypsin gene induction in experimental and clinical acute kidney injury

Alpha-1-antitrypsin (AAT) is a hepatic stress protein with protease inhibitor activity. Recent evidence indicates that ischemic or toxic injury can evoke selective changes within kidney that resemble a hepatic phenotype. Hence, we tested the following: i) Does acute kidney injury (AKI) up-regulate the normally renal silent AAT gene? ii) Does rapid urinary AAT excretion result? And iii) Can AAT's anti-protease/anti-neutrophil elastase (NE) activity protect injured proximal tubule cells? CD-1 mice were subjected to ischemic or nephrotoxic (glycerol, maleate, cisplatin) AKI. Renal functional and biochemical assessments were made 4–72 hrs later. Rapidly following injury, 5–10 fold renal cortical and isolated proximal tubule AAT mRNA and protein increases occurred. These were paralleled by rapid (>100 fold) increases in urinary AAT excretion. AKI also induced marked increases in renal cortical/isolated proximal tubule NE mRNA. However, sharp NE protein levels declines resulted, which strikingly correlated (r, −0.94) with rising AAT protein levels (reflecting NE complexing by AAT/destruction). NE addition to HK-2 cells evoked ∼95% cell death. AAT completely blocked this NE toxicity, as well as Fe induced oxidant HK-2 cell attack. Translational relevance of experimental AAT gene induction was indicated by ∼100–1000 fold urinary AAT increases in 22 AKI patients (matching urine NGAL increases). We conclude: i) AKI rapidly up-regulates the renal cortical/proximal tubule AAT gene; ii) NE gene induction also results; iii) AAT can confer cytoprotection, potentially by blocking/reducing cytotoxic NE accumulation; and iv) marked increases in urinary AAT excretion in AKI patients implies clinical relevance of the AKI- AAT induction pathway.

Effects of three commonly-used diuretics on the urinary proteome

Biomarker is the measurable change associated with a physiological or pathophysiological process. Unlike blood which has mechanisms to keep the internal environment homeostatic, urine is more likely to reflect changes of the body. As a result, urine is likely to be a better biomarker source than blood. However, since the urinary proteome is affected by many factors, including diuretics, careful evaluation of those effects is necessary if urinary proteomics is used for biomarker discovery. Here, we evaluated the effects of three commonly-used diuretics (furosemide, F; hydrochlorothiazide, H; and spirolactone, S) on the urinary proteome in rats. Urine samples were collected before and after intragastric administration of diuretics at therapeutic doses and the proteomes were analyzed using label-free liquid chromatography-tandem mass spectrometry (LC-MS/MS). Based on the criteria of P≤0.05, a fold change ≥2, a spectral count ≥5, and false positive rate (FDR) ≤1%, 14 proteins (seven for F, five for H, and two for S) were identified by Progenesis LC-MS. The human orthologs of most of these 14 proteins are stable in the healthy human urinary proteome, and ten of them are reported as disease biomarkers. Thus, our results suggest that the effects of diuretics deserve more attention in future urinary protein biomarker studies. Moreover, the distinct effects of diuretics on the urinary proteome may provide clues to the mechanisms of diuretics.

How to find a prognostic biomarker for progressive diabetic nephropathy

As a prognostic biomarker for progression of diabetic nephropathy, albuminuria fails in terms of sensitivity and specificity. Better urinary or plasma biomarkers are needed that can predict which diabetic patients are at highest risk for progression. Bhensdadia et al. report proteomic investigations that identified urinary haptoglobin as a potential prognostic biomarker for progressive diabetic nephropathy. Although as a single marker urinary haptoglobin adds little to albuminuria, together the two appear to provide better diagnostic accuracy than albuminuria alone.

Red Blood Cell Distribution Width Level: A Predictive Marker for Early Detection and Monitoring of Diabetic Nephropathy Progression

Chronic inflammation may be one of the factors that contribute to the development of diabetic nephropathy (DN). However, erythropoiesis, erythrocyte circulatory half-life and erythrocyte deformability may be influenced by inflammation. Thus, red blood cell distribution width (RDW) levels increase in inflammatory conditions. We investigated the RDW values and related factors in patients with uncomplicated type 2 diabetes mellitus (DM) and diabetic patients with DN. We carried out a retrospective study on patients with type 2 DM admitted to our hospital. Subjects were divided into three groups. Group 1 consisted of healthy subjects. Group 2 consisted of patients with uncomplicated type 2 DM. Patients with various stages of DN were included in Group 3. The RDW values in group 1 subjects were significantly lower than those in group 2 and 3 patients (p<0.05). The RDW values of group 3 patients were higher than those in the other two groups (p<0.05). While the RDW values had positive correlation with blood pressure, serum creatinine, HbA1c, body mass index, proteinuria, platelet (PLT), triglyceride, low density lipoprotein (LDL), total cholesterol (TC), and fasting blood glucose (r values: 0.95, 0.72, 0.56, 0.86, 0.82, 0.76, 0.88, 0.84, 0.88, 0.86, respectively) (p<0.05 for all), there was negative correlation between estimated glomerular filtration rate (eGFR), albumin, high density lipoprotein (HDL) and RDW levels (r values: −0.92, −0. 88, −0.78, respectively) (p value < 0.05 for all).

'Biologic memory' in response to acute kidney injury: cytoresistance, toll-like receptor hyper-responsiveness and the onset of progressive renal disease

Following the induction of ischemic or toxin-mediated acute kidney injury (AKI), cellular adaptations occur that 're-program' how the kidney responds to future superimposed insults. This re-programming is not simply a short-lived phenomenon; rather it can persist for many weeks, implying that a state of 'biologic memory' has emerged. These changes can be both adaptive and maladaptive in nature and they can co-exist in time. A beneficial adaptation is the emergence of acquired cytoresistance, whereby a number of physiologic responses develop that serve to protect the kidney against further ischemic or nephrotoxic attack. Conversely, some changes are maladaptive, such as a predisposition to Gram-negative or Gram-positive bacteremia due to a renal tubular up-regulation of toll-like receptor responses. This latter change culminates in exaggerated cytokine production, and with efflux into the systemic circulation, extra-renal tissue injury can result (so-called 'organ cross talk'). Another maladaptive response is a persistent up-regulation of pro-inflammatory, pro-fibrotic and vasoconstrictive genes, culminating in progressive renal injury and ultimately end-stage renal failure. The mechanisms by which this biologic re-programming, or biologic memory, is imparted remain subjects for considerable debate. However, injury-induced, and stable, epigenetic remodeling at pro-inflammatory/pro-fibrotic genes seems likely to be involved. The goal of this editorial is to highlight that the so-called 'maintenance phase' of acute renal failure is not a static one, somewhere between injury induction and the onset of repair. Rather, this period is one in which the induction of 'biologic memory' can ultimately impact renal functional recovery, extra-renal injury and the possible transition of AKI into chronic, progressive renal disease.

New insights in intestinal ischemia-reperfusion injury: implications for intestinal transplantation

PURPOSE OF REVIEW

Ischemia-reperfusion injury is inevitable during intestinal transplantation and can negatively affect the transplant outcome. Here, an overview is provided of the recent advances in the pathophysiological mechanisms of intestinal ischemia-reperfusion injury and how this may impact graft survival.

RECENT FINDINGS

The intestine hosts a wide range of microorganisms and its mucosa is heavily populated by immune cells. Intestinal ischemia-reperfusion results in the disruption of the epithelial lining, affecting also protective Paneth cells (antimicrobials) and goblet cells (mucus), and creates a more hostile intraluminal microenvironment. Consequently, both damage-associated molecular patterns as well as pathogen-associated molecular patterns are released from injured tissue and exogenous microorganisms, respectively. These 'danger' signals may synergistically activate the innate immune system. Exaggerated innate immune responses, involving neutrophils, mast cells, platelets, dendritic cells, as well as Toll-like receptors and complement proteins, may shape the adaptive T-cell response, thereby triggering the destructive alloimmune response toward the graft and resulting in transplant rejection.

SUMMARY

Innate immune activation as a consequence of ischemia-reperfusion injury may compromise engraftment of the intestine. More dedicated research is required to further establish this concept in man and to design more effective therapeutic strategies to better tolerize intestinal grafts.

Age sensitizes the kidney to heme protein-induced acute kidney injury

Age increases the risk for ischemic acute kidney injury (AKI). We questioned whether a similar age-dependent injury occurs following exposure to hemoglobin, a known nephrotoxin. Old mice (~16 mo old), but not young mice (~6 mo old), when administered hemoglobin, exhibited marked elevation in blood urea nitrogen (BUN) and serum creatinine, and acute tubular necrosis with prominent tubular cast formation. The aged kidney exhibited induction of heme oxygenase-1 (HO-1) and other genes/proteins that may protect against heme-mediated renal injury, including ferritin, ferroportin, haptoglobin, and hemopexin. Old mice did not evince induction of HO-2 mRNA by hemoglobin, whereas a modest induction of HO-2 mRNA was observed in young mice. To determine the functional significance of HO-2 in heme protein-induced AKI, we administered hemoglobin to relatively young HO-2(+/+) and HO-2(-/-) mice: HO-2(-/-) mice, compared with HO-2(+/+) mice, exhibited greater renal dysfunction and histologic injury when administered hemoglobin. In addition to failing to elicit a protective system such as HO-2 in response to hemoglobin, old mice exhibited an exaggerated maladaptive response typified by markedly greater induction of the nephrotoxic cytokine IL-6 (130-fold increase vs. 10-fold increase in mRNA in young mice). We conclude that aged mice, unlike relatively younger mice, are exquisitely sensitive to the nephrotoxicity of hemoglobin, an effect attended by a failure to induce HO-2 mRNA and a fulminant upregulation of IL-6. Age thus markedly augments the sensitivity of the kidney to heme proteins, and HO-2 confers resistance to such insults.

Renal cortical hemopexin accumulation in response to acute kidney injury

Hemopexin (Hpx) is a liver-generated acute phase reactant that binds and neutralizes prooxidant free heme. This study tested whether acute kidney injury (AKI) triggers renal Hpx accumulation, potentially impacting heme Fe-mediated tubular injury. Mice were subjected to glycerol, cisplatin, ischemia-reperfusion (I/R), or endotoxemic [lipopolysaccharide (LPS)] AKI. In each instance, 3- to 30-fold renal cortical and isolated proximal tubule segment (PTS) Hpx increases resulted. Although renal cortex and PTS showed variable Hpx mRNA increases, due, in part, to increased mRNA stability, mRNA levels did not correlate with renal Hpx protein accumulation. Conversely, AKI evoked three- to fourfold increases in hepatic Hpx gene induction, which corresponded with three- to fourfold plasma Hpx increases. Renal immunohistochemistry, and increased urinary Hpx excretion, indicated that circulating Hpx gains tubule luminal/urinary access, followed by proximal tubule endocytic uptake. Paradoxically, in cultured renal cells (HK-2, HEK-293), Fe depletion, and not free heme excess, increased Hpx mRNA. LPS acutely increased HK-2 cell Hpx mRNA. This finding, coupled with observations that LPS evoked ∼30-fold greater renal Hpx mRNA increases than any other AKI model, suggests that inflammation, not heme exposure, activates the renal Hpx gene. Each form of AKI evoked early increases in circulating free heme, which subsequently fell to subnormal levels as plasma Hpx rose. In addition, purified Hpx blunted free Fe-mediated HK-2 cell death. In sum, these data indicated that AKI-associated hepatic stress generates Hpx, which gains renal tubule access. Given its ability to bind free heme and mitigate free Fe toxicity, Hpx loading can potentially confer cytoprotective effects.

Mouse model of ischemic acute kidney injury: technical notes and tricks

Renal ischemia-reperfusion leads to acute kidney injury (AKI), a major kidney disease associated with an increasing prevalence and high mortality rates. A variety of experimental models, both in vitro and in vivo, have been used to study the pathogenic mechanisms of ischemic AKI and to test renoprotective strategies. Among them, the mouse model of renal clamping is popular, mainly due to the availability of transgenic models and the relatively small animal size for drug testing. However, the mouse model is generally less stable, resulting in notable variations in results. Here, we describe a detailed protocol of the mouse model of bilateral renal ischemia-reperfusion. We share the lessons and experiences gained from our laboratory in the past decade. We further discuss the technical issues that account for the variability of this model and offer relevant solutions, which may help other investigators to establish a well-controlled, reliable animal model of ischemic AKI.