"Point of no return" in unilateral renal ischemia reperfusion injury in mice.

BACKGROUND: In the past years evidence has been growing about the interconnection of chronic kidney disease and acute kidney injury. The underlying pathophysiological mechanisms remain unclear. We hypothesized, that a threshold ischemia time in unilateral ischemia/reperfusion injury sets an extent of ischemic tubule necrosis, which as "point of no return" leads to progressive injury. This progress is temporarily associated by increased markers of inflammation and results in fibrosis and atrophy of the ischemic kidney. METHODS: Acute tubule necrosis was induced by unilateral ischemia/reperfusion injury in male C57BL/6 N mice with different ischemia times (15, 25, 35, and 45 min). At multiple time points between 15 min and 5 weeks we assessed gene expression of markers for injury, inflammation, and fibrosis, histologically the injury of tubules, cell death (TUNEL), macrophages, neutrophil influx and kidney atrophy. RESULTS: Unilateral ischemia for 15 and 25 min induced upregulation of markers for injury after reperfusion for 24 h but no upregulation after 5 weeks. None of the markers for inflammation or fibrosis were upregulated after ischemia for 15 and 25 min at 24 h or 5 weeks on a gene expression level, except for Il-6. Ischemia for 35 and 45 min consistently induced upregulation of markers for inflammation, injury, and partially of fibrosis (Tgf-ß1 and Col1a1) at 24 h and 5 weeks. The threshold ischemia time for persistent injury of 35 min induced a temporal association of markers for inflammation and injury with peaks between 6 h and 7 d along the course of 10 d. This ischemia time also induced persistent cell death (TUNEL) throughout observation for 5 weeks with a peak at 6 h and progressing kidney atrophy beginning 7 d after ischemia. CONCLUSIONS: This study confirms the evidence of a threshold extent of ischemic injury in which markers of injury, inflammation and fibrosis do not decline to baseline but remain upregulated assessed in long term outcome (5 weeks). Excess of this threshold as "point of no return" leads to persistent cell death and progressing atrophy and is characterized by a temporal association of markers for inflammation and injury.

Maternal undernutrition aggravates renal tubular necrosis and interstitial fibrosis after unilateral ureteral obstruction in male rat offspring.

Maternal undernutrition is known to reduce glomerular number but it may also affect tubulointerstitium, capillary density, and response to oxidative stress. To investigate whether the latter elements are affected, we examined the response to unilateral ureteral obstruction (UUO), an established model of renal tubulointerstitial fibrosis, in the kidney of offspring from control and nutrient restricted rats. Six-week old male offspring from rats given food ad libitum (CON) and those subjected to 50% food restriction throughout pregnancy (NR) were subjected to UUO for 7 days. Body weight was significantly lower in NR. Systolic blood pressure and blood urea nitrogen increased similarly in CON and NR after UUO. Tubular necrosis in the obstructed kidney, on the other hand, was more extensive in NR. Also, the collagen area, a marker of fibrosis, of the obstructed kidney was significantly increased compared with the contralateral kidney only in NR. Capillary density was decreased similarly in the obstructed kidney of CON and NR compared with the contralateral kidney. Urine nitrate/nitrite, a marker of nitric oxide production, from the obstructed kidney was significantly increased in NR compared with CON. Nitrotyrosine, a marker of nitric oxide-mediated free radical injury, was increased in the obstructed kidney compared with the contralateral kidney in both CON and NR, but the extent was significantly greater in NR. In conclusion, more severe tubular necrosis and fibrosis after UUO was observed in NR, which was thought to be due to increased nitrosative stress.

Impact of Donor Age on the Outcomes of Kidney Transplantation From Deceased Donors With Histologic Acute Kidney Injury.

PURPOSE: Kidney transplantation from elderly donors with acute kidney injury (AKI) has increased recently due to donor shortage, but the safety and prognosis are not well known. We examined the effect of donor age on the outcomes of kidney transplantation (KT) from donors with histologic AKI. MATERIALS AND METHODS: We retrospectively analyzed the medical records of 59 deceased-donor KTs with acute tubular necrosis (ATN) on preimplantation donor kidney biopsy between March 2012 and October 2017. Histologic evaluations of ATN, inflammation, glomerulosclerosis (GS), interstitial fibrosis, tubular atrophy, and arterial sclerosis were performed. RESULTS: Twenty and 39 recipients received kidneys from elderly (> 60, 68.9 ± 5.0 years) and young (≤ 60, 45.9 ± 9.6 years) donors with ATN, respectively. Among the elderly donors, significantly increased donor creatinine was observed in only 44% donors, and there were more diabetic patients and women and a higher proportion of GS than among the young donors. Six months after KT, estimated glomerular filtration rate was significantly lower in recipients who received kidneys from elderly donors compared to young donors. Donor creatinine level and AKI severity did not significantly affect the recipient outcomes in either group. However, the presence of ATN and GS were significant factors that exacerbated renal outcomes after KT from elderly donors only. On multivariate analysis, severe ATN was the strongest independent predictor of elderly recipient renal function. CONCLUSIONS: Histologic injury may predict renal outcomes in KT from elderly donors. A donor allocation protocol including preimplantation renal histology should be established for KT from elderly donors.

Human Alpha-1-Antitrypsin (hAAT) therapy reduces renal dysfunction and acute tubular necrosis in a murine model of bilateral kidney ischemia-reperfusion injury.

Several lines of evidence have demonstrated the anti-inflammatory and cytoprotective effects of alpha-1-antitrypsin (AAT), the major serum serine protease inhibitor. The aim of the present study was to investigate the effects of human AAT (hAAT) monotherapy during the early and recovery phase of ischemia-induced acute kidney injury. Mild renal ischemia-reperfusion (I/R) injury was induced in male C57Bl/6 mice by bilateral clamping of the renal artery and vein for 20 min. hAAT (80 mg/kg, Prolastin®) was administered daily intraperitoneally (i.p.) from day -1 until day 7 after surgery. Control animals received the same amount of human serum albumin (hAlb). Plasma, urine and kidneys were collected at 2h, 1, 2, 3, 8 and 15 days after reperfusion for histological and biochemical analysis. hAAT partially preserved renal function and tubular integrity after induction of bilateral kidney I/R injury, which was accompanied with reduced renal influx of macrophages and a significant decrease of neutrophil gelatinase-associated lipocalin (NGAL) protein levels in urine and plasma. During the recovery phase, hAAT significantly decreased kidney injury molecule-1 (KIM-1) protein levels in urine but showed no significant effect on renal fibrosis. Although the observed effect size of hAAT administration was limited and therefore the clinical relevance of our findings should be evaluated carefully, these data support the potential of this natural protein to ameliorate ischemic and inflammatory conditions.

Role of Oxidative Stress in Drug-Induced Kidney Injury.

The kidney plays a primary role in maintaining homeostasis and detoxification of numerous hydrophilic xenobiotics as well as endogenous compounds. Because the kidney is exposed to a larger proportion and higher concentration of drugs and toxins than other organs through the secretion of ionic drugs by tubular organic ion transporters across the luminal membranes of renal tubular epithelial cells, and through the reabsorption of filtered toxins into the lumen of the tubule, these cells are at greater risk for injury. In fact, drug-induced kidney injury is a serious problem in clinical practice and accounts for roughly 20% of cases of acute kidney injury (AKI) among hospitalized patients. Therefore, its early detection is becoming more important. Usually, drug-induced AKI consists of two patterns of renal injury: acute tubular necrosis (ATN) and acute interstitial nephritis (AIN). Whereas AIN develops from medications that incite an allergic reaction, ATN develops from direct toxicity on tubular epithelial cells. Among several cellular mechanisms underlying ATN, oxidative stress plays an important role in progression to ATN by activation of inflammatory response via proinflammatory cytokine release and inflammatory cell accumulation in tissues. This review provides an overview of drugs associated with AKI, the role of oxidative stress in drug-induced AKI, and a biomarker for drug-induced AKI focusing on oxidative stress.

Remote Ischemic Preconditioning and Contrast-Induced Nephropathy: A Systematic Review.

BACKGROUND: The use of imaging is increasing in clinical practice either for diagnosis or intervention. In these aims, contrast medium (CM) is widely used. However, CM administration can induce contrast-induced nephropathy (CIN). The incidence of CIN varies from 2% to 50% depending on patient risk factors, and CIN is the third cause of renal insufficiency. To date, methods such as hyperhydration to prevent CIN have a low level of evidence. Remote ischemic preconditioning (RIPC), which has already proved its efficiency in the cardiology field, seems to be a promising technique for CIN prevention. The aim of this work was to carry out a systematic review of the literature of the randomized clinical studies on RIPC in the prevention of CIN in man. METHODS: We conducted a systematic review of randomized clinical studies on the RIPC in the prevention of CIN in man. Documentary sources were PubMed articles published until June 2015. Randomized clinical trials of RIPC in preventing CIN in human were reviewed. RESULTS: Five articles were selected for the analysis. One article studied the impact of RIPC in a population at high risk of CIN, whereas the other 4 analyzed populations at low, moderate or unknown risk of CIN. In 4 studies, except the later one, the risk of CIN was based on the Mehran score that was previously published. In the high-risk population, a decrease in the incidence of CIN was found in the RIPC group compared with the control group (12% against 40%; P = 0.002). Among the 3 other studies using the Mehran's score, one also demonstrated the interest of such a procedure in a subgroup of high-risk patients. A second one found a low incidence of CIN in the RIPC group ([5 of 47; 10%] as compared with a control group [17 of 47; 36%] P = 0.003) in patients at the low risk of CIN. In another low-risk population, a significant lower level of a biological marker (liver-type fatty acid-binding protein) that assesses a renal impairment was found in the RIPC compared with the control group. CONCLUSIONS: Only 5 studies were found in this search, which may constitute a limitation. However, RIPC appears as a promising method to prevent CIN since it is a noninvasive, low cost, easy, and safe method. More randomized controlled trials are needed to confirm these preliminary results.

Presence of arteriolar hyalinosis in post-reperfusion biopsies represents an additional risk to ischaemic injury in renal transplant.

AIM: The role of post-reperfusion biopsy findings as a predictor of early and long-term graft function and survival is still a target of research. METHODS: We analyzed data from 136 post-reperfusion biopsies performed in deceased donor renal transplanted patients from November 2008 to May 2012. We analyzed the presence of acute tubular necrosis (ATN), arteriolar hyalinosis (AH), intimal thickness (IT), interstitial fibrosis (IF) and glomerulosclerosis (GS). We also analyzed the impact of donor features on the following outcomes: delayed graft function (DGF) and chronic allograft dysfunction defined as eGFR < 60 mL/min at 1 year. RESULTS: The mean donor age was 41 years, 26% of whom were extended criteria donors (ECD), 33% had hypertension and 50% had cerebral vascular accident (CVA) as the cause of death. ATN was present in 87% of these biopsies, AH in 31%, IF in 21%, IT in 27% and GS in 32%. DGF occurred in 80% and chronic allograft dysfunction was present in 53%. AH was the only histological finding associated with DGF and chronic allograft dysfunction at 1 year. Patients with AH had a lower eGFR at 1 year than patients without it (49.8 mL/min × 64.5 mL/min, P = 0.02). In the multivariate analysis, risk variables for development of chronic graft dysfunction were male sex (odds ratio [OR] = 3.159 [CI: 1.22-8.16]; P = 0.018), acute rejection (OR = 8.91 [CI: 2.21-35.92]; P = 0.002), donor hypertension (OR = 2.94 [CI: 1.10-7.84]; P = 0.031), AH (OR = 3.96 [CI: 1.46-10.70]; P = 0.007) and eGFR at discharge (OR = 0.96 [CI: 0.93-0.98]; P = 0.005). In multivariate analysis, risk factors for AH were donor age ≥ 50 years (OR = 2.46 [CI: 1.10-5.44]; P = 0.027) and CVA as the cause of donor death (OR = 2.33 [CI: 1.05-5.15]; P = 0.007). CONCLUSION: The presence of AH in post-reperfusion biopsies is a marker of ageing and vascular disease and was associated with DGF and a one year poorer renal function. AH in donor biopsies superimposed to long ischaemic time is a predictor of renal function. The management of immunosuppression based on the presence of AH in post-reperfusion biopsy could be useful to improve long term graft function.

Renal Klotho expression in patients with acute kidney injury is associated with the severity of the injury.

BACKGROUND/AIMS: The potential physiologic roles of Klotho in acute kidney injury (AKI) have recently been demonstrated in animal models. However, to date, there have been no human studies investigating the expression of renal Klotho in AKI. METHODS: We retrospectively collected biopsy specimens and clinical data of AKI patients between January 2001 and December 2012. Klotho expression was determined by immunohistochemical staining, and the clinical-pathological correlation was examined. RESULTS: Among the 34 patients diagnosed with acute tubular necrosis or acute tubulointerstitial nephritis, 21 patients without chronic histological lesions were included. The mean age was 37.3 ± 18.5 years and the mean peak creatinine level was 8.2 ± 5.5 mg/dL. In total, 10 patients (47.6%) received temporary renal replacement therapy (RRT); however, 17 patients (81%) showed functional recovery with creatinine levels of < 1.3 mg/dL after 1 month. The intensity of Klotho expression was scored as a percentage of Klotho-positive area. The renal Klotho score showed a significant negative correlation with the initial or peak creatinine level. When the patients were divided into three groups according to the Klotho score (low, middle, high), the low group had a significantly higher peak creatinine level and a more frequent requirement for RRT. However, the Klotho score was not a significant predictor of renal recovery. CONCLUSIONS: The results demonstrated that renal Klotho expression in humans decreased significantly according to the severity of AKI, regardless of the etiology, and that low expression was associated with a poor short-term outcome.

Survey of acute kidney injury and related risk factors of mortality in hospitalized patients in a third-level urban hospital of Shanghai.

OBJECTIVE: The main aim of this study is to investigate the incidence and prognosis of acute kidney injury (AKI) and to clarify the risk factors associated with the prognosis of AKI in hospitalized patients. METHOD: All patients hospitalized from January 1st to December 31st 2012 in Ren Ji Hospital, School of Medicine Shanghai Jiao Tong University were screened by the Lab Administration Network. All the patients with an intact medical history of AKI according to the Acute Kidney Injury Network (AKIN) were enrolled in the study cohort. AKI's incidence and etiology, as well as the patient's characteristics and prognosis, were retrospectively analyzed. Logistic regression analysis was used to investigate the risk factors on the patient prognosis and renal outcome. RESULTS: 934 AKI patients were enrolled. The incidence of AKI in hospitalized patients was 2.41%. The ratio of males to females of patients was 1.88:1 and the mean age was 60.82 ± 16.94. The incidence of AKI increased with increase in age. Among hospitalized patients, 63.4% were from the surgical department, 35.4% from the internal medicine department, and 1.2% from the obstetric and gynecologic department. Regarding the cause of AKI, pre-renal AKI, acute tubular necrosis (ATN), acute glomerulonephritis and vasculitis (AGV), acute interstitial nephritis (AIN), and post-renal AKI contributed with 51.7, 37.7, 3.8, 3.5, and 3.3%, respectively. The survival rate on the day 28 after AKI was 71.8%. In addition, 65.7% patients got complete renal recovery, while 16.9% got partial renal recovery and 17.4% got renal loss. The mortality of AKI in hospitalized patients at Stage I, Stage II and Stage III was 24.8, 31.2 and 43.7%, respectively. Multivariate Logistic regression analysis showed that use of nephrotoxic drugs, [Odds Ratio (OR) = 2.313], hypotension in the previous week (OR = 4.482), oliguria (OR = 5.267), the number of extra-renal organ failures (OR = 1.376), and need for renal replacement therapy (RRT) (OR = 4.221) were independent risk factors for mortality. The number of extra-renal organ failures (OR = 1.529) and RRT (OR = 2.117) were independent risk factors for renal loss. CONCLUSION: AKI is one of the most common complications in hospitalized patients. The mortality is high and renal prognosis is poor after AKI. The prognosis is closely associated with the severity of AKI. Nephrotoxic drugs, hypotension within the last week, oliguria, the number of extra-renal organ failures, and RRT are independent risk factors for mortality, while the number of extra-renal organ failures and RRT are independent risk factors for renal loss.

Resistance index measured by Doppler ultrasound as a predictor of graft function after kidney transplantation.

INTRODUCTION: Doppler ultrasound (US) has become the primary imaging technique for the evaluation of renal transplants. It provides information about the intrarenal resistance index (RI). A high RI is seen in every form of graft dysfunction. In this article, we review the utility of sonography, particularly the intrarenal RI measured early after renal transplant, as a predictor of acute and chronic clinical outcome in patients. RESULTS: RI is a valuable marker to determine graft function and related vascular complications. It reveals a strong correlation with serum creatinine levels measured days after transplant. Its elevation is typical for acute tubular necrosis and can be used to predict its duration. An RI >1 (absent end-diastolic flow) seen in the first weeks after transplant is associated with impaired renal graft recovery. In addition, it is an early predictor of chronic allograft nephropathy (even correlated with biopsy results), which will allow a change in therapy. CONCLUSIONS: RI measured serially in the early period after kidney transplantation is a valuable marker for determining renal graft function. It is also useful for demonstrating various types of graft dysfunction; however, it cannot differentiate between them. In recent studies, extrarenal factors in kidney transplantation (eg, recipient's age) may significantly influence RI in the recipient, demonstrating that RI depends on the vascular characteristics of the recipient and not on the graft itself.

Power doppler sonography in early renal transplantation: does it differentiate acute graft rejection from acute tubular necrosis?

To evaluate the role of power Doppler in the identification and differentiation between acute renal transplant rejection and acute tubular necrosis (ATN), we studied 67 live donor renal transplant recipients. All patients were examined by spectral and power Doppler sonography. Assessment of cortical perfusion (CP) by power Doppler was subjective, using our grading score system: P0 (normal CP); homogenous cortical blush extending to the capsule, P1 (reduced CP); cortical vascular cut-off at interlobular level, P2 (markedly reduced CP); scattered cortical color flow at the interlobar level. Renal biopsies were performed during acute graft dysfunction. Pathological diagnoses were based on Banff classification 1997. The Mann- Whitney test was used to test the difference between CP grades with respect to serum creatinine (SCr), and resistive index (RI). For 38 episodes of acute graft rejection grade I, power Doppler showed that CP was P1 and RI ranging from 0.78 to 0.89. For 21 episodes of acute graft rejection grade II, power Doppler showed that CP was P1, with RI ranging from 0.88 to >1. Only one case of grade III rejection had a CP of P2. Twelve biopsies of ATN had CP of P0 and RI ranging from 0.80 to 0.89 There was a statistically significant correlation between CP grading and SCr (P <0.01) as well as between CP grading and RI (P <0.05). CP grading had a higher sensitivity in the detection of early acute rejection compared with RI and cross-sectional area measurements. We conclude that power Doppler is a non-invasive sensitive technique that may help in the detection and differentiation between acute renal transplant rejection and ATN, particularly in the early post-transplantation period.

Glomerular haemodynamics, the renal sympathetic nervous system and sepsis-induced acute kidney injury.

BACKGROUND: To describe recent insights into glomerular haemodynamics in septic acute kidney injury (AKI). METHODS: We reviewed the literature with particular emphasis on recent findings in animal experiments and human studies in relation to renal macro- and micro-renal haemodynamics during septic AKI. RESULTS: The dominant paradigm is that septic AKI is due to decreased renal perfusion with ischaemic loss of glomerular filtration rate (GFR), ischaemic tubular cell injury and acute tubular necrosis (ATN). However, recent experimental and human studies challenge this view of the pathogenesis of septic AKI. In addition, rapid post-mortem and experimental histological studies do not support ATN as the histological substrate of septic AKI. Finally, more recent experimental evidence suggests that changes in the glomerular and peri-glomerular haemodynamics provide a more likely explanation for the loss of GFR seen in the early phases of septic AKI. CONCLUSIONS: Despite a long-standing paradigm that septic AKI is due to renal hypo-perfusion and associated ATN, experimental and human studies increasingly suggest that changes in the state of the glomerular and peri-glomerular micro-vasculature are a more likely additional explanation for this condition.

Effects of Schizolobium parahyba extract on experimental Bothrops venom-induced acute kidney injury.

BACKGROUND: Venom-induced acute kidney injury (AKI) is a frequent complication of Bothrops snakebite with relevant morbidity and mortality. The aim of this study was to assess the effects of Schizolobium parahyba (SP) extract, a natural medicine with presumed anti-Bothrops venom effects, in an experimental model of Bothrops jararaca venom (BV)-induced AKI. METHODOLOGY: Groups of 8 to 10 rats received infusions of 0.9% saline (control, C), SP 2 mg/kg, BV 0.25 mg/kg and BV immediately followed by SP (treatment, T) in the doses already described. After the respective infusions, animals were assessed for their glomerular filtration rate (GFR, inulin clearance), renal blood flow (RBF, Doppler), blood pressure (BP, intra-arterial transducer), renal vascular resistance (RVR), urinary osmolality (UO, freezing point), urinary neutrophil gelatinase-associated lipocalin (NGAL, enzyme-linked immunosorbent assay [ELISA]), lactate dehydrogenase (LDH, kinetic method), hematocrit (Hct, microhematocrit), fibrinogen (Fi, Klauss modified) and blinded renal histology (acute tubular necrosis score). PRINCIPAL FINDINGS: BV caused significant decreases in GFR, RBF, UO, HcT and Fi; significant increases in RVR, NGAL and LDH; and acute tubular necrosis. SP did not prevent these changes; instead, it caused a significant decrease in GFR when used alone. CONCLUSION: SP administered simultaneously with BV, in an approximate 10∶1 concentration, did not prevent BV-induced AKI, hemolysis and fibrinogen consumption. SP used alone caused a decrease in GFR.

Acute oxalate nephropathy associated with Clostridium difficile colitis.

We report the case of a 69-year-old man who presented with acute kidney injury in the setting of community-acquired Clostridium difficile-associated diarrhea and biopsy-proven acute oxalate nephropathy. We discuss potential mechanisms, including increased colonic permeability to oxalate. We conclude that C difficile-associated diarrhea is a potential cause of acute oxalate nephropathy.

Preconditioning with triiodothyronine improves the clinical signs and acute tubular necrosis induced by ischemia/reperfusion in rats.

BACKGROUND: Renal ischemia/reperfusion (I/R) injury is manifested by acute renal failure (ARF) and acute tubular necrosis (ATN). The aim of this study was to evaluate the effectiveness of preconditioning with 3, 3, 5 triiodothyronine (T3) to prevent I/R renal injury. METHODOLOGY/PRINCIPAL FINDINGS: The rats were divided into four groups: sham-operated, placebo-treated (SO-P), sham-operated T3- treated (SO- T3), I/R-injured placebo-treated (IR-P), and I/R-injured T3-treated (IR- T3) groups. At 24 h before ischemia, the animals received a single dose of T3 (100 µg/kg). Renal function and plasma, urinary, and tissue variables were studied at 4, 24, and 48 h of reperfusion, including biochemical, oxidative stress, and inflammation variables, PARP-1 immunohistochemical expression, and ATN morphology. In comparison to the SO groups, the IR-P groups had higher plasma urea and creatinine levels and greater proteinuria (at all reperfusion times) and also showed: increased oxidative stress-related plasma, urinary, and tissue variables; higher plasma levels of IL6 (proinflammatory cytokine); increased glomerular and tubular nuclear PARP-1 expression; and a greater degree of ATN. The IR-T3 group showed a marked reduction in all of these variables, especially at 48 h of reperfusion. No significant differences were observed between SO-P and SO-T3 groups. CONCLUSIONS: This study demonstrates that preconditioning rats with a single dose of T3 improves the clinical signs and ATN of renal I/R injury. These beneficial effects are accompanied by reductions in oxidative stress, inflammation, and renal PARP-1 expression, indicating that this sequence of factors plays an important role in the ATN induced by I/R injury.

Kielin/chordin-like protein attenuates both acute and chronic renal injury.

The secreted kielin/chordin-like (KCP) protein, one of a family of cysteine-rich proteins, suppresses TGF-ß signaling by sequestering the ligand from its receptor, but it enhances bone morphogenetic protein (BMP) signaling by promoting ligand-receptor interactions. Given the critical roles for TGF-ß and BMP proteins in enhancing or suppressing renal interstitial fibrosis, respectively, we examined whether secreted KCP could attenuate renal fibrosis in mouse models of chronic and acute disease. Transgenic mice that express KCP in adult kidneys showed significantly less expression of collagen IV, α-smooth muscle actin, and other markers of disease progression in the unilateral ureteral obstruction model of renal interstitial fibrosis. In the folic acid nephrotoxicity model of acute tubular necrosis, mice expressing KCP survived high doses of folic acid that were lethal for wild-type mice. With a lower dose of folic acid, mice expressing KCP exhibited improved renal recovery compared with wild-type mice. Thus, these data suggest that extracellular regulation of the TGF-ß/BMP signaling axis by KCP, and by extension possibly other cysteine-rich domain proteins, can attenuate both acute and chronic renal injury.

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.