Hemoglobin induces cytotoxic damage of glycine-preserved renal tubules

Research progress on the pathogenesis of AKI complicated by ECMO

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) stands as a pivotal intervention for patients grappling with cardiopulmonary insufficiency. However, alongside its therapeutic benefits, ECMO carries the risk of complications, with acute kidney injury (AKI) emerging as a significant concern. The precise pathophysiological underpinnings of AKI in the context of ECMO remain incompletely elucidated.

METHODS

A comprehensive literature review was conducted to explore the epidemiology and pathophysiological mechanisms underlying the utilization of ECMO in the management of AKI.

RESULTS

ECMO initiates a multifaceted cascade of inflammatory reactions, encompassing complement activation, endothelial dysfunction, white blood cell activation, and cytokine release. Furthermore, factors such as renal hypoperfusion, ischemia-reperfusion injury, hemolysis, and fluid overload exacerbate AKI. Specifically, veno-arterial ECMO (VA-ECMO) may directly induce renal hypoperfusion, whereas veno-venous ECMO (VV-ECMO) predominantly impacts pulmonary function, indirectly influencing renal function.

CONCLUSION

While ECMO offers significant therapeutic advantages, AKI persists as a potentially fatal complication. A thorough comprehension of the pathogenesis underlying ECMO-associated AKI is imperative for effective prevention and management strategies. Moreover, additional research is warranted to delineate the incidence of AKI secondary to ECMO and to refine clinical approaches accordingly.

Cell-Free Hemoglobin in Acute Kidney Injury after Lung Transplantation and Experimental Renal Ischemia/Reperfusion

Cell-free hemoglobin (CFH), a pro-oxidant and cytotoxic compound that is released in hemolysis, has been associated with nephrotoxicity. Lung transplantation (LuTx) is a clinical condition with a high incidence of acute kidney injury (AKI). In this study, we investigated the plasma levels of CFH and haptoglobin, a CFH-binding serum protein, in prospectively enrolled LuTx patients (n = 20) with and without AKI. LuTx patients with postoperative AKI had higher CFH plasma levels at the end of surgery compared with no-AKI patients, and CFH correlated with serum creatinine at 48 h. Moreover, CFH levels inversely correlated with haptoglobin levels, which were significantly reduced at the end of surgery in LuTx patients with AKI. Because multiple other factors can contribute to AKI development in the complex clinical setting of LuTx, we next investigated the role of exogenous CFH administration in a mouse model of mild bilateral renal ischemia reperfusion injury (IRI). Exogenous administration of CFH after reperfusion caused overt AKI with creatinine increase, tubular injury, and enhanced markers of renal inflammation compared with vehicle-treated animals. In conclusion, CFH is a possible factor contributing to postoperative AKI after LuTx and promotes AKI in an experimental model of mild transient renal ischemia. Targeting CFH might be a therapeutic option to prevent AKI after LuTx.

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

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

Independent risk factors and the long-term outcomes for postoperative continuous renal replacement treatment in patients who underwent emergency surgery for type a acute aortic dissection

Objective

The study objective was to investigate the incidence and risk factors of continuous renal replacement therapy (CRRT) in patients undergoing emergency surgery for type A acute aortic dissection (TA-AAD) and evaluate the perioperative and long-term outcomes.

Methods

From January 2014 to December 2018, 712 consecutive patients were enrolled in the study. These patients were divided into two groups according to whether or not needed postoperative CRRT: the CRRT group vs the control group. Univariate analysis and binary logistic regression analysis were used to analyze the risk factors of CRRT. To avoid the selection bias and confounders, baseline characteristics were matched for propensity scores. Kaplan-Meier curves were generated to provide survival estimates at postoperative points in time.

Results

Before propensity score matching, univariate analysis showed that there were significant differences in age, preoperative hypertension, pericardial effusion, preoperative serum creatinine (sCr), intraoperative need for combined coronary artery bypass grafting (CABG) or mitral valve or tricuspid valve surgery, cardiopulmonary bypass (CPB) time, extracorporeal circulation assistant time, aortic cross-clamp time, drainage volume 24 h after surgery and ventilator time between two groups. All were higher in the CRRT group (P < 0.05). These risk factors were included in binary logistic regression. It showed that preoperative sCr and CPB time were independent risk factors for CRRT patients undergoing surgery for TA-AAD. And there were significant differences regarding 30-day mortality (P < 0.001) and long-term overall cumulative survival (P < 0.001) with up to a 6-year follow-up. After propensity scoring, 29 pairs (58 patients) were successfully matched. Among these patients, the analysis showed that CPB time was still significantly longer in the CRRT group (P = 0.004), and the 30-day mortality rate was also higher in this group (44.8% vs 10.3%; P = 0.003).

Conclusion

CRRT after TA-AAD is common and worsened short- and long- term mortality. The preoperative sCr and CPB time are independent risk factors for postoperative CRRT patients. Shorten the CPB time as much as possible is recommended to reduce the risk of CRRT after the operation.

Anticoagulant-related nephropathy in a patient with IgA nephropathy

Anticoagulant-related nephropathy is a type of acute kidney injury caused by overcoagulation. We describe a case of an 84-year-old man with arterial hypertension, coronary heart disease and atrial fibrillation treated with acenocoumarol, who presented with haematoproteinuria and acute kidney injury during a phase of excessive anticoagulation. In addition to IgA nephropathy, renal biopsy also revealed acute tubular necrosis, red blood cell casts and positive iron staining in tubular cells. After this acute episode, renal function improved and proteinuria decreased below the nephrotic range.

Ulinastatin Protects against Acute Kidney Injury in Infant Piglets Model Undergoing Surgery on Hypothermic Low-Flow Cardiopulmonary Bypass

Objective

Infants are more vulnerable to kidney injuries induced by inflammatory response syndrome and ischemia-reperfusion injury following cardiopulmonary bypass especially with prolonged hypothermic low-flow (HLF). This study aims to evaluate the protective role of ulinastatin, an anti-inflammatory agent, against acute kidney injuries in infant piglets model undergoing surgery on HLF cardiopulmonary bypass.

Methods

Eighteen general-type infant piglets were randomly separated into the ulinastatin group (Group U, n = 6), the control group (Group C, n = 6), and the sham operation group (Group S, n = 6), and anaesthetized. The groups U and C received following experimental procedure: median thoracotomy, routine CPB and HLF, and finally weaned from CPB. The group S only underwent sham median thoracotomy. Ulinastatin at a dose of 5,000 units/kg body weight and a certain volume of saline were administrated to animals of the groups U and C at the beginning of CPB and at aortic declamping, respectively. Venous blood samples were collected at 3 different time points: after anesthesia induction in all experimental groups, 5 minutes, and 120 minutes after CPB in the Groups U and C. Markers for inflammation and acute kidney injury were tested in the collected plasma. N-acetyl-β-D-glucosaminidase (NAG) from urine, markers of oxidative stress injury and TUNEL-positive cells in kidney tissues were also detected.

Results

The expressions of plasma inflammatory markers and acute kidney injury markers increased both in Group U and Group C at 5 min and 120 min after CPB. Also, numbers of TUNEL-positive cells and oxidative stress markers in kidney rose in both groups. At the time point of 120-min after CPB, compared with the Group C, some plasma inflammatory and acute kidney injury markers as well as TUNEL-positive cells and oxidative stress markers in kidney were significantly reduced in the Group U. Histologic analyses showed that HLF promoted acute tubular necrosis and dilatation.

Conclusions

HLF cardiopulmonary bypass surgery could intensify systemic inflammatory responses and oxidative stress on infant piglets, thus causing acute kidney injury. Ulinastatin might reduce such inflammatory response and oxidative stress and the extent of kidney injury.

Altered iron homeostasis in an animal model of hypertensive nephropathy: stroke-prone rats

BACKGROUND AND AIM

Iron is the most abundant metal in mammalian cells, and plays a pivotal role in many metabolic processes. Dysregulated iron homeostasis is involved in the cause of a number of pathological processes including renal diseases.

METHODS AND RESULTS

Longitudinal MRI scans of salt-loaded spontaneously hypertensive stroke-prone rats (SHRSP), an animal model that spontaneously develops hypertensive nephropathy, showed a decrease in renal and hepatic T2 SI (a sign of iron accumulation) of, respectively, 42.3 ± 2.5% (P < 0.01) and 60.4 ± 15.1% (P < 0.01) in comparison with SHRSP fed a standard diet. This was accompanied by the development of renal inflammation and oxidative stress (as evaluated by immunohistochemical and proteomic analyses), mitochondrial dysfunction, massive proteinuria and sustained intravascular hemolysis with the subsequent depletion of plasma haptoglobin, which was responsible for the renal uptake of hemoglobin and iron accumulation. In order to investigate the role of iron in these pathological processes, we subcutaneously treated the salt-loaded rats with the iron chelator deferoxamine (200 mg/kg per day). The pharmacological treatment prevented iron tissue accumulation, as indicated by the increase in renal and hepatic T2 SI of, respectively, 120.0 ± 10.1% (P < 0.01) and 73.9 ± 4.4% (P < 0.01) in comparison with salt-loaded rats treated with vehicle alone. Deferoxamine also preserved renal morphology and function, the renal infiltration of ED-1-positive macrophages/monocytes, and the expression of MCP-1 and TGF-β mRNA, reduced the level of reactive oxygen species, and improved the activity of mitochondrial cytochrome c oxidase.

CONCLUSION

These findings suggest that iron dysmetabolism is involved in the development of hypertensive nephropathy in SHRSP.

Warfarin-related nephropathy in a patient with mild IgA nephropathy on dabigatran and aspirin

Dabigatran is a direct thrombin inhibitor used as an alternative to warfarin for long-term anticoagulation. We describe a patient who developed acute kidney injury (AKI) in the setting of warfarin conversion to dabigatran, and a renal biopsy demonstrating acute tubular injury. Although the patient had undiagnosed IgA nephropathy that may have predisposed him to bleeding, AKI was due to heme-associated tubular injury. We propose that severe hematuria in patients with underlying glomerular pathology treated with either dabigatran or warfarin may lead to toxic tubular injury through the accumulation of heme-proteins.

Multidrug donor preconditioning protects steatotic liver grafts against ischemia-reperfusion injury

BACKGROUND

Graft dysfunction of steatotic livers (SL) still remains a major challenge in liver transplantation. Different mechanisms are thought to be involved in the impaired tolerance of SL to ischemia-reperfusion injury. Thus, different pharmacologic strategies may need to be combined to effectively protect SL and to reduce graft dysfunction after transplantation. Therefore, we analyzed the effectiveness of a multidrug donor preconditioning (MDDP) procedure to protect SL from cold ischemia-reperfusion injury.

METHODS

Liver steatosis was induced by a high-carbohydrate, fat-free diet. A total of 24 Sprague-Dawley rats were divided into 3 groups (n = 8 each), including a control group with nonsteatotic livers (Con), a vehicle-treated SL group (SL-Con), and a SL group undergoing MDDP (SL-MDDP), including pentoxyphylline, glycine, deferoxamine, N-acetylcysteine, erythropoietin, melatonin, and simvastatin. MDDP was applied before liver perfusion with 4°C histidine-tryptophan-ketoglutarate (HTK) solution and organ harvest. After 24 hours of cold storage in HTK, postischemic reperfusion was performed in an isolated liver reperfusion model using 37°C Krebs-Henseleit bicarbonate buffer.

RESULTS

After 60 minutes of reperfusion, SL showed a significant reduction of bile flow as well as a marked increase of liver enzyme levels and apoptotic cell death compared with Con. This was associated with an increased malondialdehyde formation, interleukin-1 production, and leukocytic tissue infiltration. MDDP completely abolished the inflammatory response and was capable of significantly reducing parenchymal dysfunction and injury.

CONCLUSIONS

MDDP decreases SL injury after cold storage and reperfusion. The concept of MDDP as a simple and safe preoperative regime, thus may be of interest in clinical use, expanding the donor pool from marginal donors.

Split-liver procedure and inflammatory response: improvement by pharmacological preconditioning

BACKGROUND

Final outcome of split-liver (SL) transplantation is impaired due to an increased rate of vascular complications and primary non-function. Herein, we hypothesized that an in situ split-liver procedure induces an inflammatory response and a deterioration of graft quality. We further studied whether graft quality can be improved by pharmacologic preconditioning.

MATERIAL AND METHODS

SL-procedure was performed in rats. One group (SL-HPP; n = 8) was pretreated according to a defined protocol [Homburg preconditioning protocol (HPP)], including pentoxyphylline, glycine, deferoxamine, N-acetylcysteine, erythropoietin, melatonin, and simvastatin. A second SL group (SL-Con; n = 8) received NaCl. Untreated non-SL served as controls (Sham; n = 8). Cytokines release, leukocyte invasion, endothelial activation and liver morphology were studied directly after liver harvest and after 8 h cold storage. Lung tissue was studied to determine remote injury.

RESULTS

The SL-procedure induced an increase of TNF-α concentration, intercellular-adhesion-molecule 1 (ICAM-1) expression, leukocytic-tissue infiltration and vacuolization. This was associated with an increased number of apoptotic hepatocytes. HPP reduced TNF-α release, ICAM-1 expression, the number of infiltrated leukocytes, as well as hepatocellular vacuolization and apoptosis. In lung tissue, the SL-procedure caused an increased IL-1 and IL-6 concentration and leukocyte infiltration.

CONCLUSIONS

HPP was capable of abrogating cytokine-mediated leukocytic response. Pharmacologic preconditioning of liver donors prevents the SL procedure-mediated inflammatory response, resulting in an improved graft quality.

Multidrug donor preconditioning prevents cold liver preservation and reperfusion injury

PURPOSE

Primary graft dysfunction still represents a major challenge in liver transplantation. We herein studied in an isolated rat liver perfusion model whether a multidrug donor preconditioning (MDDP) can not only reduce but also completely prevent cold ischemia-reperfusion injury.

METHODS

MDDP included curcumin, simvastatin, N-acetylcysteine, erythropoietin, pentoxyphylline, melatonin, glycine, and methylprednisolone. Postischemic reperfusion was performed after 24 h cold storage in histidine-tryptophan-ketoglutarate solution with 37°C Krebs Henseleit bicarbonate buffer.

RESULTS

Cold hepatic ischemia-reperfusion resulted in a massive K(+) release, protein loss, and aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase elevation. This was associated with increased malondialdehyde formation, enhanced tumor necrosis factor-alpha and interleukin-6 production, pronounced leukocytic tissue infiltration, and apoptotic cell death.

CONCLUSIONS

MDDP abolished the inflammation response and was capable of completely preventing the manifestation of parenchymal injury. Thus, MDDP potentiates the protective effects reported after single-drug donor preconditioning and may therefore be an interesting approach to improve the outcome in clinical liver transplantation.

Increase in plasma free haemoglobin during cardiopulmonary bypass in heart valve surgery: assessment of renal dysfunction by RIFLE classification

Heart valve surgery carries a high risk of renal insufficiency as an independent risk factor due to prolonged cardiopulmonary bypass. Multiple causes of cardiopulmonary bypass-associated renal damage have been described, and haemoglobin-induced renal injury is presently being investigated. Forty-three patients scheduled for heart valve surgery (mostly combined) were enrolled in the prospective study. Plasma free haemoglobin (PFH) levels were evaluated by photocolorimetric measurement at the start of procedures (t(0)) and before the end of extracorporeal circulation (t(1)). A statistically significant increase in PFH levels during cardiopulmonary bypass was detected [median values (interquartile range) - t(0): 62.0 (53.4) mg/L, t(1): 320.4 (352.2) mg/L], P < 0.001. A significant regression relationship between the duration of cardiopulmonary bypass and the increased PFH was found (Spearman's correlation coefficient 0.628, P < 0.001). In some elderly patients, the tendency towards a high release of PFH during cardiopulmonary bypass was more pronounced, but the overall association between age and PFH levels was of borderline significance (P = 0.077). The correlation between PFH and post-operative serum creatinine was low and non-significant, but the latter correlated highly with the pre-operative serum creatinine values (Spearman's correlation coefficient reached values of 0.6-0.7, P < 0.001). Patients were classified according to the Risk of renal failure, Injury to the kidney, Failure of kidney function, Loss of kidney function and End-stage renal failure (RIFLE) classification for acute renal dysfunction during post-operative days 1 - 4; the influence of PFH levels at t(1) on the consequent RIFLE classification was not proven (P=0.648), but 4 patients in the Injury category had shown a higher median value of PFH (433.6 mg/L) in comparison with the others (29 patients with no acute renal dysfunction - 313.7 mg/L, 10 patients at Risk - 330.1 mg/L).