Total plasma heme concentration increases after red blood cell transfusion and predicts mortality in critically ill medical patients

In-depth structure-function profiling of the complex formation between clotting factor VIII and heme

BACKGROUND AND AIMS

Blood disorders, such as sickle cell disease, and other clinical conditions are often accompanied by intravascular hemolytic events along with the development of severe coagulopathies. Hemolysis, in turn, leads to the accumulation of Fe(II/III)-protoporphyrin IX (heme) in the intravascular compartment, which can trigger a variety of proinflammatory and prothrombotic reactions. As such, heme binding to the blood coagulation proteins factor VIII (FVIII), fibrinogen, and activated protein C with functional consequences has been demonstrated earlier.

METHODS

We herein present an in-depth characterization of the FVIII-heme interaction at the molecular level and its (patho-)physiological relevance through the application of biochemical, biophysical, structural biology, bioinformatic, and diagnostic tools.

RESULTS

FVIII has a great heme-binding capacity with seven heme molecules associating with the protein. The respective binding sites were identified by investigating heme binding to FVIII-derived peptides in combination with molecular docking and dynamic simulation studies of the complex as well as cryo-electron microscopy, revealing three high-affinity and four moderate heme-binding motifs (HBMs). Furthermore, the relevance of the FVIII-heme complex formation was characterized in physiologically relevant assay systems, revealing a ~ 50 % inhibition of the FVIII cofactor activity even in the protein-rich environment of blood plasma.

CONCLUSION

Our study provides not only novel molecular insights into the FVIII-heme interaction and its physiological relevance, but also strongly suggests the reduction of the intrinsic pathway and the accentuation of the final clotting step (by, for example, fibrinogen crosslinking) in hemolytic conditions as well as a future perspective in the context of FVIII substitution therapy of hemorrhagic events in hemophilia A patients.

Plasma Nitric Oxide Consumption Is Elevated and Associated With Adverse Outcomes in Critically Ill Patients

OBJECTIVES

Impaired nitric oxide (NO) bioavailability may contribute to microvascular dysfunction in sepsis. Excessive plasma NO consumption has been attributed to scavenging by circulating cell-free hemoglobin. This may be a mechanism for NO deficiency in sepsis and critical illness. We hypothesized that plasma NO consumption is high in critically ill patients, particularly those with sepsis, acute respiratory distress syndrome (ARDS), shock, and in hospital nonsurvivors. We further hypothesized that plasma NO consumption is correlated with plasma cell-free hemoglobin concentration.

DESIGN

Retrospective cohort study.

SETTING

Adult ICUs of an academic medical center.

PATIENTS AND SUBJECTS

Three hundred sixty-two critically ill patients and 46 healthy control subjects.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Plasma NO consumption was measured using reductive chemiluminescence and cell-free hemoglobin was measured with a colorimetric assay. Mean (95% CI) plasma NO consumption (µM) was higher in critically ill patients versus healthy control subjects (3.9 [3.7-4.1] vs 2.1 [1.8-2.5]), septic versus nonseptic patients (4.1 [3.8-4.3] vs 3.6 [3.3-3.8]), ARDS versus non-ARDS patients (4.4 [4.0-4.9] vs 3.7 [3.6-3.9]), shock vs nonshock patients (4.4 [4.0-4.8] vs 3.6 [3.4-3.8]), and hospital nonsurvivors versus survivors (5.3 [4.4-6.4] vs 3.7 [3.6-3.9]). These relationships remained significant in multivariable analyses. Plasma cell-free hemoglobin was weakly correlated with plasma NO consumption.

CONCLUSIONS

Plasma NO consumption is elevated in critically ill patients and independently associated with sepsis, ARDS, shock, and hospital death. These data suggest that excessive intravascular NO scavenging characterizes sepsis and adverse outcomes of critical illness.

Double-edged functions of hemopexin in hematological related diseases: from basic mechanisms to clinical application

It is now understood that hemolysis and the subsequent release of heme into circulation play a critical role in driving the progression of various diseases. Hemopexin (HPX), a heme-binding protein with the highest affinity for heme in plasma, serves as an effective antagonist against heme toxicity resulting from severe acute or chronic hemolysis. In the present study, changes in HPX concentration were characterized at different stages of hemolytic diseases, underscoring its potential as a biomarker for assessing disease progression and prognosis. In many heme overload-driven conditions, such as sickle cell disease, transfusion-induced hemolysis, and sepsis, endogenous HPX levels are often insufficient to provide protection. Consequently, there is growing interest in developing HPX therapeutics to mitigate toxic heme exposure. Strategies include HPX supplementation when endogenous levels are depleted and enhancing HPX's functionality through modifications, offering a potent defense against heme toxicity. It is worth noting that HPX may also exert deleterious effects under certain circumstances. This review aims to provide a comprehensive overview of HPX's roles in the progression and prognosis of hematological diseases. It highlights HPX-based clinical therapies for different hematological disorders, discusses advancements in HPX production and modification technologies, and offers a theoretical basis for the clinical application of HPX.

Monosodium urate crystals alter the circadian clock in macrophages leading to loss of NLRP3 inflammasome repression: Implications for timing of the gout flare

Gout is caused by monosodium urate (MSU) crystal deposition within joints. This leads to acute episodes of inflammation ("gout flares") driven by NLRP3 inflammasome activation in macrophages. Gout flares are frequently present during late night/early morning. The reason for this timing is unclear. Recent evidence suggests the NLRP3 inflammasome is under circadian control. The purpose of this study was to determine whether MSU crystals cause changes in the circadian clock in macrophages leading to time-of-day differences in NLRP3 inflammasome activation. Levels of circadian clock components were measured in undifferentiated "monocytic" and PMA-differentiated "macrophagic" THP-1 cells cultured with/without MSU crystals. Caspase-1 activity was measured to assess NLRP3 inflammasome activity. MSU crystal exposure resulted in minimal effects on clock genes in THP-1 monocytes but BMAL1, CRY1, PER2, and REV-ERBα showed altered expression with reduced protein levels of BMAL1 and REV-ERBα in THP-1 macrophages. REV-ERBα activation or BMAL1 over-expression resulted in reduced MSU crystal-induced caspase-1 activity. BMAL1 knockdown resulted in a further increase in MSU crystal-induced caspase-1 activity, but only at times of day when BMAL1 levels were naturally high. MSU crystal-induced NLRP3 inflammasome activation was greatest at the time of day when BMAL1 levels were naturally low. MSU crystals alter the expression of circadian clock components in THP-1 macrophages leading to loss of BMAL1 and REV-ERBα-mediated repression of NLRP3 inflammasome activity and time-of-day differences in susceptibility to inflammasome activation. Our findings suggest that the nocturnal risk of gout flare is at least partially a consequence of altered circadian control of immune cell function.

Heme b inhibits class III adenylyl cyclases

Acidic lipid extracts from mouse liver, kidney, heart, brain, and lung inhibited human pseudoheterodimeric adenylyl cyclases (hACs) expressed in HEK293 cells. Using an acidic lipid extract from bovine lung, a combined MS- and bioassay-guided fractionation identified heme b as inhibitor of membrane-bound ACs. IC₅₀ concentrations were 8-12 μM for the hAC isoforms. Hemopexin and bacterial hemophore attenuated heme b inhibition of hAC5. Structurally related compounds, such as hematin, protoporphyrin IX, and biliverdin, were significantly less effective. Monomeric bacterial class III ACs (mycobacterial ACs Rv1625c; Rv3645; Rv1264; cyanobacterial AC CyaG) were inhibited by heme b with similar efficiency. Surprisingly, structurally related chlorophyll a similarly inhibited hAC5. Heme b inhibited isoproterenol-stimulated cAMP accumulation in HEK293 cells. Using cortical membranes from mouse brain hemin efficiently and reversibly inhibited basal and Gsα-stimulated AC activity. The physiological relevance of heme b inhibition of the cAMP generating system in certain pathologies is discussed.

Heme induces intestinal epithelial cell ferroptosis via mitochondrial dysfunction in transfusion-associated necrotizing enterocolitis

Transfusion-associated necrotising enterocolitis (TANEC) is a life-threatening disease with a poor prognosis in preterm infants. This study explored whether and how heme induces ferroptosis in TANEC gut injury. A TANEC mouse model and a cell culture system for heme and Caco-2 cells were established. Ferroptosis was assessed by measuring iron and malondialdehyde (MDA) levels and mitochondrial morphology in intestinal tissues and Caco-2 cells. Mitochondrial dysfunction was evaluated by measuring mitochondrial reactive oxygen species (ROS) production and membrane potential using JC-1. The intestinal injury grade was higher in the anemia-transfusion group than in the control group (p < .0001). Higher intestinal iron concentration (p < .0001), elevated levels of lipid peroxidation MDA (p = .0021), and ferroptotic mitochondrial morphological changes were found in mice of the anemia-transfusion group; specific ferroptosis inhibitor could alleviate anemia-transfusion gut injury, suggesting that ferroptosis play a role in the TANEC gut injury. Next, we explored whether heme released by hemolysis of erythrocytes induces ferroptosis in intestinal epithelial cells in vitro. The viability of Caco-2 cells significantly decreased after heme treatment (p < .0001). Iron accumulation, MDA elevated levels, and mitochondrial dysfunction also existed in the co-culture system, which ferroptosis inhibitors could reduce. In summary, ferroptosis was discovered in TANEC, and heme could induce ferroptosis in intestinal epithelial cells via mitochondrial dysfunction. Heme-inducing ferroptosis may be a possible mechanism and therapeutic target for TANEC.

Impact of perioperative blood transfusions on postoperative renal function and survival after resection of colorectal liver metastases

Background and aims

Recent studies focusing on thoracic surgery suggest postoperative kidney injury depending on the amount of perioperative blood transfusions. Data investigating similar effects after resection of colorectal liver metastases (CRLM) are not available. Aim of this study was therefore to evaluate the influence of perioperative blood transfusions on postoperative renal function and survival after resection of CRLM.

Methods

Seven hundred twenty-seven cases of liver resection for CRLM were retrospectively analyzed. Renal function was measured via estimated glomerular filtration rate (eGFR) and a postoperative decline of ≥ 10% was considered substantial. Potential influences on postoperative kidney function were assessed using univariable and multivariable logistic regression analyses. Cox-regression analyses were performed to estimate the impact on overall survival (OS).

Results

Preoperative impaired kidney function (p = 0.001, OR 2.477) and transfusion of > 2 units of packed red blood cells (PRBC) (p = 0.046; OR 1.638) were independently associated with an increased risk for ≥ 10% loss of renal function. Neither a pre-existing renal impairment, nor the additional loss of renal function were associated with reduced survival. Chemotherapies in the context of primary colorectal cancer treatment (p = 0.002), age > 70 years at liver resection (p = 0.005), number (p = 0.001), and size of metastases > 50 mm (p = 0.018), duration of resection > 120 min (p = 0.006) and transfusions of > 2 units of PRBC (p = 0.039) showed a negative independent influence on OS.

Conclusion

The results demonstrate a negative impact of perioperative blood transfusions on the postoperative renal function and OS. Hence, efforts to reduce blood transfusions should be intensified.

Perioperative Transfusion is Related to the Length of Hospital Stays in Primary Liver Cancer Patients

Purpose

Blood loss may be corrected with red blood cell transfusion, but may ultimately contribute to negative impacts. This study was a retrospective analysis to assess the impact of perioperative blood transfusion on hospital stay days in liver cancer patients.

Methods

We retrospectively examined data from patients with primary liver cancer who underwent curative resection. Patients were divided into perioperative blood transfusion (PBT) and non-PBT groups. Data were given as means and SDs for continuous variables and as counts and percentage for categorical variables. The correlation between blood transfusion and hospital stay days was analyzed by Fisher's exact test. Multivariable logistic regression analyses were used to identify independent predictors of length of hospital stays.

Results

Totally 206/1031 patients (20.3%) were given perioperative transfusion. The mean length of hospital stay was 17.8 days in PBT and 13.9 days in non-PBT groups. Our multivariable logistic regression showed transfusion, total bilirubin, indirect bilirubin, and the ratio of albumin to bilirubin were all indicators of the length of hospital stay days. Perioperative transfusion was also associated with prolonged length of hospital stays (95% CI: 0.395-0.811, p = 0.002). Transfusion also affected intrinsic coagulation factors (activated partial thromboplastin time, fibrinogen, platelet), inflammatory index (neutrocyte to lymphocyte ratio, monocyte), albumin and bilirubin levels.

Conclusion

Perioperative transfusion of blood was associated with a significantly increased length of hospital stays probably via changing intrinsic coagulation and inflammatory factors and bilirubin levels in plasma.

Heme cytotoxicity is the consequence of endoplasmic reticulum stress in atherosclerotic plaque progression

Hemorrhage and hemolysis with subsequent heme release are implicated in many pathologies. Endothelial cells (ECs) encounter large amount of free heme after hemolysis and are at risk of damage from exogenous heme. Here we show that hemorrhage aggravates endoplasmic reticulum (ER) stress in human carotid artery plaques compared to healthy controls or atheromas without hemorrhage as demonstrated by RNA sequencing and immunohistochemistry. In EC cultures, heme also induces ER stress. In contrast, if cultured ECs are pulsed with heme arginate, cells become resistant to heme-induced ER (HIER) stress that is associated with heme oxygenase-1 (HO-1) and ferritin induction. Knocking down HO-1, HO-2, biliverdin reductase, and ferritin show that HO-1 is the ultimate cytoprotectant in acute HIER stress. Carbon monoxide-releasing molecules (CORMs) but not bilirubin protects cultured ECs from HIER stress via HO-1 induction, at least in part. Knocking down HO-1 aggravates heme-induced cell death that cannot be counterbalanced with any known cell death inhibitors. We conclude that endothelium and perhaps other cell types can be protected from HIER stress by induction of HO-1, and heme-induced cell death occurs via HIER stress that is potentially involved in the pathogenesis of diverse pathologies with hemolysis and hemorrhage including atherosclerosis.

Linking Labile Heme with Thrombosis

Thrombosis is one of the leading causes of death worldwide. As such, it also occurs as one of the major complications in hemolytic diseases, like hemolytic uremic syndrome, hemorrhage and sickle cell disease. Under these conditions, red blood cell lysis finally leads to the release of large amounts of labile heme into the vascular compartment. This, in turn, can trigger oxidative stress and proinflammatory reactions. Moreover, the heme-induced activation of the blood coagulation system was suggested as a mechanism for the initiation of thrombotic events under hemolytic conditions. Studies of heme infusion and subsequent thrombotic reactions support this assumption. Furthermore, several direct effects of heme on different cellular and protein components of the blood coagulation system were reported. However, these effects are controversially discussed or not yet fully understood. This review summarizes the existing reports on heme and its interference in coagulation processes, emphasizing the relevance of considering heme in the context of the treatment of thrombosis in patients with hemolytic disorders.

Heme Determination and Quantification Methods and Their Suitability for Practical Applications and Everyday Use

Many research institutions, clinical diagnostic laboratories, and blood banks are desperately searching for a possibility to identify and quantify heme in different physiological and pathological settings as well as various research applications. The reasons for this are the toxicity of the heme and the fact that it acts as a hemolytic and pro-inflammatory molecule. Heme only exerts these severe and undesired effects when it is not incorporated in hemoproteins. Upon release from the hemoproteins, it enters a biologically available state (labile heme), in which it is loosely associated with proteins, lipids, nucleic acids, or other molecules. While the current methods and procedures for quantitative determination of heme have been used for many years in different settings, their value is limited by the challenging chemical properties of heme. A major cause of inadequate quantification is the separation of labile and permanently bound heme and its high aggregation potential. Thus, none of the current methods are utilized as a generally applicable, standardized approach. The aim of this Feature is to describe and summarize the most common and frequently used chemical, analytical, and biochemical methods for the quantitative determination of heme. Based on this overview, the most promising approaches for future solutions to heme quantification are highlighted.