Association between haptoglobin, hemopexin and mortality in adults with sepsis

A critical role for HNF4α in polymicrobial sepsis-associated metabolic reprogramming and death

In sepsis, limited food intake and increased energy expenditure induce a starvation response, which is compromised by a quick decline in the expression of hepatic PPARα, a transcription factor essential in intracellular catabolism of free fatty acids. The mechanism upstream of this PPARα downregulation is unknown. We found that sepsis causes a progressive hepatic loss-of-function of HNF4α, which has a strong impact on the expression of several important nuclear receptors, including PPARα. HNF4α depletion in hepatocytes dramatically increases sepsis lethality, steatosis, and organ damage and prevents an adequate response to IL6, which is critical for liver regeneration and survival. An HNF4α agonist protects against sepsis at all levels, irrespectively of bacterial loads, suggesting HNF4α is crucial in tolerance to sepsis. In conclusion, hepatic HNF4α activity is decreased during sepsis, causing PPARα downregulation, metabolic problems, and a disturbed IL6-mediated acute phase response. The findings provide new insights and therapeutic options in sepsis.

HAPTOGLOBIN DEPLETION DURING THE FIRST 7 DAYS OF VENO-VENOUS EXTRACORPOREAL MEMBRANE OXYGENATION THERAPY IS ASSOCIATED WITH INCREASED MORTALITY AND ADVERSE OUTCOMES IN PATIENTS WITH ACUTE RESPIRATORY DISTRESS SYNDROME

ABSTRACT

Background: Hemolysis is a frequent complication in patients with sepsis, ARDS, or extracorporeal membrane oxygenation (ECMO). Haptoglobin (Hp) can scavenge released cell-free hemoglobin (CFH). Hemolysis and low plasma concentrations of Hp may be independently associated with mortality in critically ill patients. Methods: This study used a retrospective analysis of 435 patients with ARDS and veno-venous ECMO therapy, admitted to a tertiary ARDS referral center (01/2007-12/2018). Hp depletion was defined as decrease in plasma Hp concentration <0.39 g/L within the first week after ECMO initiation. Patients with Hp depletion were compared to patients without Hp depletion. The primary endpoint was 28-day mortality. Secondary endpoints included organ dysfunction-free, renal replacement therapy-free, vasopressor-free, and ECMO-free composites. Results: Patients with Hp depletion (n = 269) had a significantly higher mortality 28 days after ECMO initiation compared to patients without Hp depletion (43.5% [95% CI 37.52-49.66] vs. 25.3% [19.03-32.74], P < 0.001). Furthermore, patients with Hp depletion had fewer organ dysfunction-free days (subdistribution hazard ratio [SHR] 0.35 [95% CI 0.25-0.50], P < 0.001), lower chances for successful weaning from renal replacement therapy (SHR 0.50 [0.32-0.79], P < 0.001), vasopressor therapy (SHR 0.39 [0.28-0.54], P < 0.001), and ECMO therapy (SHR 0.41 [0.30-0.57], P < 0.001) within 28 days after ECMO initiation. Patients with initial Hp <0.66 g/L had higher risks for Hp depletion than patients with initial Hp ≥0.66 g/L. Conclusion: Patients with Hp depletion within the first week of ECMO therapy might benefit from close monitoring of hemolysis with early detection and elimination of the underlying cause. They might be potential candidates for future Hp supplementation therapy to prevent overload of the CFH-scavenger system.

Hemopexin reverses activation of lung eIF2α and decreases mitochondrial injury in chlorine-exposed mice

We assessed the mechanisms by which nonencapsulated heme, released in the plasma of mice after exposure to chlorine (Cl2) gas, resulted in the initiation and propagation of acute lung injury. We exposed adult male and female C57BL/6 mice to Cl2 (500 ppm for 30 min), returned them to room air, and injected them intramuscularly with either human hemopexin (hHPX; 5 µg/g BW in 50-µL saline) or vehicle at 1 h post-exposure. Upon return to room air, Cl2-exposed mice, injected with vehicle, developed respiratory acidosis, increased concentrations of plasma proteins in the alveolar space, lung mitochondrial DNA injury, increased levels of free plasma heme, and major alterations of their lung proteome. hHPX injection mice mitigated the onset and development of lung and mitochondrial injury and the increase of plasma heme, reversed the Cl2-induced changes in 83 of 237 proteins in the lung proteome at 24 h post-exposure, and improved survival at 15 days post-exposure. Systems biology analysis of the lung global proteomics data showed that hHPX reversed changes in a number of key pathways including elF2 signaling, verified by Western blotting measurements. Recombinant human hemopexin, generated in tobacco plants, injected at 1 h post-Cl2 exposure, was equally effective in reversing acute lung and mtDNA injury. The results of this study offer new insights as to the mechanisms by which exposure to Cl2 results in acute lung injury and the therapeutic effects of hemopexin.NEW & NOTEWORTHY Herein, we demonstrate that exposure of mice to chlorine gas causes significant changes in the lung proteome 24 h post-exposure. Systems biology analysis of the proteomic data is consistent with damage to mitochondria and activation of eIF2, the master regulator of transcription and protein translation. Post-exposure injection of hemopexin, which scavenges free heme, attenuated mtDNA injury, eIF2α phosphorylation, decreased lung injury, and increased survival.

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.

UMI-77 Modulates the Complement Cascade Pathway and Inhibits Inflammatory Factor Storm in Sepsis Based on TMT Proteomics and Inflammation Array Glass Chip

Sepsis is a systemic inflammatory response syndrome caused by infection, which has no specific drug at present. UMI-77 can significantly improve the survival rate of septic mice; the detailed role of UMI-77 and its underlying mechanisms in sepsis are not clear. Inflammation array glass chip and proteomic analyses were performed to elucidate the latent mechanism of UMI-77 in the treatment of sepsis. The results showed that 7.0 mg/kg UMI-77 improved the 5 day survival rate in septic mice compared to the LPS group (60.964 vs 9.779%) and ameliorated the pathological conditions. Inflammation array glass chip analysis showed that sepsis treatment with UMI-77 may eventually through the suppression of the characteristic inflammatory storm-related cytokines such as KC, RANTES, LIX, IL-6, eotaxin, TARC, IL-1β, and so on. Proteomics analysis showed that 213 differential expression proteins and complement and coagulation cascades were significantly associated with the process for the UMI-77 treatment of sepsis. The top 10 proteins including Apoa2, Tgfb1, Serpinc1, Vtn, Apoa4, Cat, Hp, Serpinf2, Fgb, and Serpine1 were identified and verified, which play important roles in the mechanism of UMI-77 in the treatment of sepsis. Our findings indicate that UMI-77 exerts an antisepsis effect by modulating the complement cascade pathway and inhibiting inflammatory storm factors.

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.

Hemopexin Reverses Activation of Lung eIF2a and Decreases Mitochondrial Injury in Chlorine Exposed Mice

We assessed the mechanisms by which non-encapsulated heme, released in the plasma of mice post exposure to chlorine (Cl 2 ) gas, resulted in the initiation and propagation of acute lung injury. We exposed adult C57BL/6 male and female to Cl 2 (500 ppm for 30 min) in environmental chambers and returned them to room air and injected them intramuscularly with a single dose of human hemopexin (hHPX; 5 µg/ g BW), the most efficient scavenger of heme, 30-60 min post exposure. Concentrations of hHPX in plasma of air and Cl 2 exposed mice were 9081±900 vs. 1879± 293 at 6 h and 2966±463 vs. 1555±250 at 50 h post injection (ng/ml; X±1 SEM=3; p<0.01). Cl 2 exposed mice developed progressive acute lung injury post exposure characterized by increased concentrations of plasma heme, marked inflammatory response, respiratory acidosis and increased concentrations of plasma proteins in the alveolar space. Injection of hHPX decreased the onset of acute lung injury at 24 h post exposure; mean survival, for the saline and hHPX groups were 40 vs. 80% (P<0.001) at 15 d post exposure. Non-supervised global proteomics analysis of mouse lungs at 24 h post exposure, revealed the upregulation of 92 and downregulation of 145 lung proteins. Injection of hHPX at one h post exposure moderated the Cl 2 induced changes in eighty-three of these 237 lung proteins. System biology analysis of the global proteomics data showed that hHPX reversed changes in mitochondrial dysfunction and elF2 and integrin signaling. Western blot analysis of lung tissue showed significant increase of phosphorylated elF2 at 24 h post exposure in vehicle treated mice but normal levels in those injected with hHPX. Similarly, RT-PCR analysis of lung tissue showed that hHPX reversed the onset of mtDNA lesions. A form of recombinant human hemopexin generated in tobacco plants was equally effective in reversing acute lung and mtDNA injury. The results of this study offer new insights as to the mechanisms by which exposure to Cl 2 results in acute lung injury and to the therapeutic effects of hemopexin.

Moderate exercise-induced dynamics on key sepsis-associated signaling pathways in the liver

BACKGROUND

There is a clear relationship between quantitative measures of fitness (e.g., VO₂ max) and outcomes after surgical procedures. Whether or not fitness is a modifiable risk factor and what underlying biological processes drive these changes are not known. The purpose of this study was to evaluate the moderate exercise training effect on sepsis outcomes (survival) as well as the hepatic biological response. We chose to study the liver because it plays a central role in the regulation of immune defense during systemic infection and receives blood flow directly from the origin of infection (gut) in the cecal ligation and puncture (CLP) model.

METHODS

We randomized 50 male (♂) and female (♀) Sprague-Dawley rats (10 weeks, 340 g) to 3 weeks of treadmill exercise training, performed CLP to induce polymicrobial "sepsis," and monitored survival for five days (Part I). In parallel (Part II), we randomized 60 rats to control/sedentary (G1), exercise (G2), exercise + sham surgery (G3), CLP/sepsis (G4), exercise + CLP [12 h (G5) and 24 h (G6)], euthanized at 12 or 24 h, and explored molecular pathways related to exercise and sepsis survival in hepatic tissue and serum.

RESULTS

Three weeks of exercise training significantly increased rat survival following CLP (polymicrobial sepsis). CLP increased inflammatory markers (e.g., TNF-a, IL-6), which were attenuated by exercise. Sepsis suppressed the SOD and Nrf2 expression, and exercise before sepsis restored SOD and Nrf2 levels near the baseline. CLP led to increased HIF1a expression and oxidative and nitrosative stress, the latter of which were attenuated by exercise. Haptoglobin expression levels were increased in CLP animals, which was significantly amplified in exercise + CLP (24 h) rats.

CONCLUSIONS

Moderate exercise training (3 weeks) increased the survival in rats exposed to CLP, which was associated with less inflammation, less oxidative and nitrosative stress, and activation of antioxidant defense pathways.

Safety and feasibility of the gene transfer of hemopexin for conditions with increased free heme

Heme is a fundamental molecule for several biological processes, but when released in the extracellular space such as in hemolytic diseases, it can be toxic to cells and tissues. Hemopexin (HPX) is a circulating protein responsible for removing free heme from the circulation, whose levels can be severely depleted in conditions such as sickle cell diseases. Accordingly, increasing HPX levels represents an attractive strategy to mitigate the deleterious effects of heme in these conditions. Gene transfer of liver-produced proteins with adeno-associated virus (AAV) has been shown to be an effective and safety strategy in animal and human studies mainly in hemophilia. Here, we report the feasibility of increasing HPX levels using an AAV8 vector expressing human HPX (hHPX). C57Bl mice were injected with escalating doses of our vector, and expression was assessed by enzyme immunoassay (ELISA), Western blot, and quantitative polymerase chain reaction (qPCR). In addition, the biological activity of transgenic hHPX was confirmed using two different models of heme challenge consisting of serial heme injections or phenylhydrazine-induced hemolysis. Sustained expression of hHPX was confirmed for up to 26 weeks in plasma. Expression was dose-dependent and not associated with clinical signs of toxicity. hHPX levels were significantly reduced by heme infusions and phenylhydrazine-induced hemolysis. No clinical toxicity or laboratory signs of liver damage were observed in preliminary short-term heme challenge studies. Our results confirm that long-term expression of hHPX is feasible and safe in mice, even in the presence of heme overload. Additional studies are needed to explore the effect of transgenic HPX protein in animal models of chronic hemolysis.

Potential of cell-free hemoglobin and haptoglobin as prognostic markers in patients with ARDS and treatment with veno-venous ECMO

BACKGROUND

Hemolysis is associated with increased mortality in patients with sepsis, ARDS, or therapy with extracorporeal membrane oxygenation (ECMO). To quantify a critical threshold of hemolysis in patients with ARDS and treatment with veno-venous ECMO, we aimed to identify cutoff values for cell-free hemoglobin (CFH) and haptoglobin (Hp) plasma concentrations associated with a significant increase in ICU mortality.

METHODS

Patients with ARDS admitted to a tertiary ARDS referral center between 01/2007 and 12/2018 and treatment with veno-venous ECMO were included. Cutoff values for mean CFH (mCFH) and mean Hp (mHp) plasma concentrations dividing the cohort into groups with significantly different ICU mortalities were calculated and patient characteristics were compared. A multiple logistic regression model with stepwise backward variable selection was included. In addition, cutoff values for vulnerable relative timespans for the respective CFH and Hp concentrations were calculated.

RESULTS

A quantitative cutoff value of 11 mg/dl for mCFH separated the cohort (n = 442) regarding ICU mortality (mCFH ≤ 11 mg/dl: 38%, [95%-CI: 32.22-43.93] (n = 277) vs. mCFH > 11 mg/dl: 70%, [61.99-76.47] (n = 165), p < 0.001). Analogously, a mHp cutoff value ≤ 0.39 g/l was associated with a significant increase in ICU mortality (mHp ≤ 0.39 g/l: 68.7%, [60.91-75.61] (n = 163) vs. mHp > 0.39 g/l: 38.7%, [33.01-44.72] (n = 279), p < 0.001). The independent association of ICU mortality with CFH and Hp cutoff values was confirmed by logistic regression adjusting for confounders (CFH Grouping: OR 3.77, [2.51-5.72], p < 0.001; Hp Grouping: OR 0.29, [0.19-0.43], p < 0.001). A significant increase in ICU mortality was observed when CFH plasma concentration exceeded the limit of 11 mg/dl on 13.3% of therapy days (≤ 13.3% of days with CFH > 11 mg/dl: 33%; [26.81-40.54] (n = 192) vs. > 13.3% of days with CFH > 11 mg/dl: 62%; [56.05-68.36] (n = 250), p < 0.001). Analogously, a mortality increase was detected when Hp plasma concentration remained ≤ 0.39 g/l for > 18.2% of therapy days (≤ 18.2% days with Hp ≤ 0.39 g/l: 27%; [19.80-35.14] (n = 138) vs. > 18.2% days with Hp ≤ 0.39 g/l: 60%; [54.43-65.70] (n = 304), p < 0.001).

CONCLUSIONS

Moderate hemolysis with mCFH-levels as low as 11 mg/dl impacts mortality in patients with ARDS and therapy with veno-venous ECMO. Furthermore, a cumulative dose effect should be considered indicated by the relative therapy days with CFH-concentrations > 11 mg/dl. In addition, also Hp plasma concentrations need consideration when the injurious effect of elevated CFH is evaluated.

Ultraviolet light oxidation of fresh hemoglobin eliminates aggregate formation seen in commercially sourced hemoglobin

Elevated levels of circulating cell-free hemoglobin (CFH) are an integral feature of several clinical conditions including sickle cell anemia, sepsis, hemodialysis and cardiopulmonary bypass. Oxidized (Fe3+, ferric) hemoglobin contributes to the pathophysiology of these disease states and is therefore widely studied in experimental models, many of which use commercially sourced CFH. In this study, we treated human endothelial cells with commercially sourced ferric hemoglobin and observed the appearance of dense cytoplasmic aggregates (CAgg) over time. These CAgg were intensely autofluorescent, altered intracellular structures (such as mitochondria), formed in multiple cell types and with different media composition, and formed regardless of the presence or absence of cells. An in-depth chemical analysis of these CAgg revealed that they contain inorganic components and are not pure hemoglobin. To oxidize freshly isolated hemoglobin without addition of an oxidizing agent, we developed a novel method to convert ferrous CFH to ferric CFH using ultraviolet light without the need for additional redox agents. Unlike commercial ferric hemoglobin, treatment of cells with the fresh ferric hemoglobin did not lead to CAgg formation. These studies suggest that commercially sourced CFH may contain stabilizers and additives which contribute to CAgg formation.

Integrative proteomic profiling of lung tissues and blood in acute respiratory distress syndrome

Introduction

Acute respiratory distress syndrome and acute lung injury (ARDS/ALI) still lack a recognized diagnostic test and pharmacologic treatments that target the underlying pathology.

Methods

To explore the sensitive non-invasive biomarkers associated with pathological changes in the lung of direct ARDS/ALI, we performed an integrative proteomic analysis of lung and blood samples from lipopolysaccharide (LPS)-induced ARDS mice and COVID-19-related ARDS patients. The common differentially expressed proteins (DEPs) were identified based on combined proteomic analysis of serum and lung samples in direct ARDS mice model. The clinical value of the common DEPs was validated in lung and plasma proteomics in cases of COVID-19-related ARDS.

Results

We identified 368 DEPs in serum and 504 in lung samples from LPS-induced ARDS mice. Gene ontology (GO) classification and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that these DEPs in lung tissues were primarily enriched in pathways, including IL-17 and B cell receptor signaling pathways, and the response to stimuli. In contrast, DEPs in the serum were mostly involved in metabolic pathways and cellular processes. Through network analysis of protein-protein interactions (PPI), we identified diverse clusters of DEPs in the lung and serum samples. We further identified 50 commonly upregulated and 10 commonly downregulated DEPs in the lung and serum samples. Internal validation with a parallel-reacted monitor (PRM) and external validation in the Gene Expression Omnibus (GEO) datasets further showed these confirmed DEPs. We then validated these proteins in the proteomics of patients with ARDS and identified six proteins (HP, LTA4H, S100A9, SAA1, SAA2, and SERPINA3) with good clinical diagnostic and prognostic value.

Discussion

These proteins can be viewed as sensitive and non-invasive biomarkers associated with lung pathological changes in the blood and could potentially serve as targets for the early detection and treatment of direct ARDS especially in hyperinflammatory subphenotype.

Hemopexin accumulates in kidneys and worsens acute kidney injury by causing hemoglobin deposition and exacerbation of iron toxicity in proximal tubules

Hemopexin, a heme scavenging protein, accumulates in the kidneys during acute kidney injury (AKI). However, the function of this accumulated hemopexin in the kidney is unclear. In both the cisplatin-induced and the unilateral kidney ischemia-reperfusion injury models of AKI, we found accumulation of hemoglobin and hemopexin in the kidneys localized to the proximal tubules. Next, hemopexin wild-type and knockout mice were compared in both AKI models and hemopexin wild type mice had significantly worse kidney injury. Furthermore, there was increased kidney expression of kidney injury molecule-1 (a biomarker of AKI) and heme oxygenase-1 (an indicator of oxidative stress) in hemopexin wild type compared with knockout mice in both models of AKI. Next, the interaction of hemopexin and hemoglobin in vitro was investigated using cultured proximal tubular cells. Co-incubation of hemopexin with hemoglobin resulted in hemoglobin deposition and exaggerated hemoglobin-induced injury. Deferoxamine, an iron chelator, and ferrostatin-1, a ferroptosis inhibitor, inhibited this deleterious effect of hemoglobin and hemopexin in proximal tubular cells, implicating iron toxicity in the mechanism of hemopexin mediated injury. Furthermore, the protective effect of deferoxamine in cisplatin-induced AKI was apparent in hemopexin wild type, but not in hemopexin knockout mice, further implicating hemopexin as a mediator of iron toxicity in AKI. Thus, our findings demonstrate that hemopexin accumulates in the kidneys and worsens kidney injury in AKI by increasing hemoglobin deposition on proximal tubular cells to exaggerate hemoglobin-induced cell injury.

Quantitative Proteogenomic Characterization of Inflamed Murine Colon Tissue Using an Integrated Discovery, Verification, and Validation Proteogenomic Workflow

Chronic inflammation of the colon causes genomic and/or transcriptomic events, which can lead to expression of non-canonical protein sequences contributing to oncogenesis. To better understand these mechanisms, Rag2^−/−Il10^−/− mice were infected with Helicobacter hepaticus to induce chronic inflammation of the cecum and the colon. Transcriptomic data from harvested proximal colon samples were used to generate a customized FASTA database containing non-canonical protein sequences. Using a proteogenomic approach, mass spectrometry data for proximal colon proteins were searched against this custom FASTA database using the Galaxy for Proteomics (Galaxy-P) platform. In addition to the increased abundance in inflammatory response proteins, we also discovered several non-canonical peptide sequences derived from unique proteoforms. We confirmed the veracity of these novel sequences using an automated bioinformatics verification workflow with targeted MS-based assays for peptide validation. Our bioinformatics discovery workflow identified 235 putative non-canonical peptide sequences, of which 58 were verified with high confidence and 39 were validated in targeted proteomics assays. This study provides insights into challenges faced when identifying non-canonical peptides using a proteogenomics approach and demonstrates an integrated workflow addressing these challenges. Our bioinformatic discovery and verification workflow is publicly available and accessible via the Galaxy platform and should be valuable in non-canonical peptide identification using proteogenomics.

Rapid Evaluation of the Extent of Haptoglobin Glycosylation Using Orthogonal Intact-Mass MS Approaches and Multivariate Analysis

Intact-mass measurements are becoming increasingly popular in mass spectrometry (MS) based protein characterization, as they allow the entire complement of proteoforms to be evaluated within a relatively short time. However, applications of this approach are currently limited to systems exhibiting relatively modest degrees of structural diversity, as the high extent of heterogeneity frequently prevents straightforward MS measurements. Incorporation of limited charge reduction into electrospray ionization (ESI) MS is an elegant way to obtain meaningful information on most heterogeneous systems, yielding not only the average mass of the protein but also the mass range populated by the entire complement of proteoforms. Application of this approach to characterization of two different phenotypes of haptoglobin (1-1 and 2-1) provides evidence of a significant difference in their extent of glycosylation (with the glycan load of phenotype 2-1 being notably lighter) despite a significant overlap of their ionic signals. More detailed characterization of their glycosylation patterns is enabled by the recently introduced technique of cross-path reactive chromatography (XP-RC) with online MS detection, which combines chromatographic separation with in-line reduction of disulfide bonds to generate metastable haptoglobin subunits. Application of XP-RC to both haptoglobin phenotypes confirms that no modifications are present within their light chains and provides a wealth of information on glycosylation patterns of the heavy chains. N-Glycosylation patterns of both haptoglobin phenotypes were found to be consistent with bi- and triantennary structures of complex type that exhibit significant level of fucosylation and sialylation. However, multivariate analysis of haptoglobin 1-1 reveals higher number of the triantennary structures, in comparison to haptoglobin 2-1, as well as a higher extent of fucosylation. The glycosylation patterns deduced from the XP-RC/MS measurements are in agreement with the conclusions of the intact-mass analysis supplemented by limited charge reduction, suggesting that the latter technique can be employed in situations when fast assessment of protein heterogeneity is needed (e.g., process analytical technology applications).

Towards a biological definition of ARDS: are treatable traits the solution?

The pathophysiology of acute respiratory distress syndrome (ARDS) includes the accumulation of protein-rich pulmonary edema in the air spaces and interstitial areas of the lung, variable degrees of epithelial injury, variable degrees of endothelial barrier disruption, transmigration of leukocytes, alongside impaired fluid and ion clearance. These pathophysiological features are different between patients contributing to substantial biological heterogeneity. In this context, it is perhaps unsurprising that a wide range of pharmacological interventions targeting these pathophysiological processes have failed to improve patient outcomes. In this manuscript, our goal is to provide a narrative summary of the potential methods to capture the underlying biological heterogeneity of ARDS and discuss how this information could inform future ARDS redefinitions. We discuss what biological tests are available to identify patients with any of the following predominant biological patterns: (1) epithelial and/or endothelial injury, (2) protein rich pulmonary edema and (3) systemic or within lung inflammatory responses.

The role of cell-free hemoglobin and haptoglobin in acute kidney injury in critically ill adults with ARDS and therapy with VV ECMO

Background

Increased plasma concentrations of circulating cell-free hemoglobin (CFH) are supposed to contribute to the multifactorial etiology of acute kidney injury (AKI) in critically ill patients while the CFH-scavenger haptoglobin might play a protective role. We evaluated the association of CFH and haptoglobin with AKI in patients with an acute respiratory distress syndrome (ARDS) requiring therapy with VV ECMO.

Methods

Patients with CFH and haptoglobin measurements before initiation of ECMO therapy were identified from a cohort of 1044 ARDS patients and grouped into three CFH concentration groups using a risk stratification. The primary objective was to assess the association of CFH and haptoglobin with KDIGO stage 3 AKI. Further objectives included the identification of a target haptoglobin concentration to protect from CFH-associated AKI.

Measurements and main results

Two hundred seventy-three patients fulfilled the inclusion criteria. Of those, 154 patients (56.4%) had AKI at ECMO initiation. The incidence of AKI increased stepwise with increasing concentrations of CFH reaching a plateau at 15 mg/dl. Compared to patients with low [< 5 mg/dl] CFH concentrations, patients with moderate [5–14 mg/dl] and high [≥ 15 mg/dl] CFH concentrations had a three- and five-fold increased risk for AKI (adjusted odds ratio [OR] moderate vs. low, 2.69 [95% CI, 1.25–5.95], P = 0.012; and OR high vs. low, 5.47 [2.00–15.9], P = 0.001). Among patients with increased CFH concentrations, haptoglobin plasma levels were lower in patients with AKI compared to patients without AKI. A haptoglobin concentration greater than 2.7 g/l in the moderate and 2.4 g/l in the high CFH group was identified as clinical cutoff value to protect from CFH-associated AKI (sensitivity 89.5% [95% CI, 83–96] and 90.2% [80–97], respectively).

Conclusions

In critically ill patients with ARDS requiring therapy with VV ECMO, an increased plasma concentration of CFH was identified as independent risk factor for AKI. Among patients with increased CFH concentrations, higher plasma haptoglobin concentrations might protect from CFH-associated AKI and should be subject of future research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03894-5.

Mortality at 180-days is affected by serum haptoglobin levels in septic patients with high magnitude serum high mobility group box-1 levels

Aim

High mobility group box‐1 (HMGB1) is a lethal mediator of sepsis that binds to haptoglobin (Hp) and is associated with its prognosis. We investigated the effect of the combination of HMGB1 and Hp on sepsis prognosis.

Methods

This single‐center, retrospective study registered 78 patients with sepsis according to Sepsis‐3 criteria on day 1 of diagnosis from July 2016 to November 2018. We divided the patients into four groups according to the serum concentration of 6.2 ng/mL HMGB1 and the median value of Hp. The 180‐day mortality rates and cytokine concentrations of the low and high HMGB1 groups were compared.

Results

There was no difference in the 180‐day mortality rate between the low Hp group and the high Hp group in the low HMGB1 group (P = 0.691). In the high HMGB1 group, a statistically significant difference was found between the low Hp group and the high Hp group (P = 0.002). In the high HMGB1 group, high Hp was associated with a better prognosis in univariate analysis (odds ratio, 0.131; 95% confidence interval [CI], 0.027–0.629; P = 0.011), and multivariate analysis (adjusted odds ratio, 0.086; 95% CI, 0.013–0.582; P = 0.009). In addition, in the high HMGB1 group, interleukin‐8 levels were significantly higher in the low Hp group than in the high Hp group (P = 0.004).

Conclusion

Patients with sepsis‐induced high serum HMGB1 levels and low serum Hp levels could have a poor long‐term prognosis.

Serum haptoglobin concentration and liver enzyme activity as indicators of systemic inflammatory response syndrome and survival of sick calves

Background

Increased concentration of haptoglobin (Hp) in serum is associated with survival of critically ill humans and horses. High serum activity of liver‐derived enzyme is associated with sepsis in children and foals.

Hypothesis/Objectives

Investigate whether admission serum Hp and glutamic dehydrogenase (GLDH) are associated with systemic inflammatory response syndrome (SIRS) and survival of sick calves.

Animals

One hundred two calves.

Methods

Retrospective cross‐sectional study. Electronic medical records from all calves <30 days of age admitted to a teaching hospital for 8 years were reviewed. The signalment, clinicopathological findings, the presence of SIRS, final diagnosis, hospitalization time and outcome were recorded. A Cox proportional hazard ratio (HzR) were calculated to assess the association between clinicopathological variables and survival to discharge.

Results

Serum Hp concentrations were similar between SIRS (0.29 g/L; range, 0.05‐3.6) and non‐SIRS calves (0.22 g/L; range, 0‐4.2; P = .62). GLDH activity was similar between SIRS (12 U/L; range, 1‐1025) and non‐SIRS calves (9 U/L; range, 2‐137; P = .2). Absent suckle reflex (HzR: 6.44, 95% CI: 1.44‐28.86), heart rate (HR) < 100 beats per minute (bpm; HzR: 12.2; 95% CI: 2.54‐58.62), HR > 140 bpm (HzR: 3.59, 95% CI: 1.05‐12.33), neutrophil count <1.7 × 10⁹/L (HzR: 7.36; 95% CI: 2.03‐26.66) and increased gamma‐glutamyl transferase activity (every 50‐unit, HzR: 1.12; 95% CI: 1.03‐1.21) were predictive of nonsurvival.

Conclusions and Clinical Importance

The use of Hp and GLDH for prediction of survival in sick calves cannot be recommended at this time.

The Effects of a Meldonium Pre-Treatment on the Course of the Faecal-Induced Sepsis in Rats

Sepsis is a life-threatening condition caused by the dysregulated and overwhelming response to infection, accompanied by an exaggerated pro-inflammatory state and lipid metabolism disturbance leading to sequential organ failure. Meldonium is an anti-ischemic and anti-inflammatory agent which negatively interferes with lipid metabolism by shifting energy production from fatty acid oxidation to glycolysis, as a less oxygen-demanding pathway. Thus, we investigated the effects of a four-week meldonium pre-treatment on faecal-induced sepsis in Sprague-Dawley male rats. Surprisingly, under septic conditions, meldonium increased animal mortality rate compared with the meldonium non-treated group. However, analysis of the tissue oxidative status did not provide support for the detrimental effects of meldonium, nor did the analysis of the tissue inflammatory status showing anti-inflammatory, anti-apoptotic, and anti-necrotic effects of meldonium. After performing tissue lipidomic analysis, we concluded that the potential cause of the meldonium harmful effect is to be found in the overall decreased lipid metabolism. The present study underlines the importance of uninterrupted energy production in sepsis, closely drawing attention to the possible harmful effects of lipid-mobilization impairment caused by certain therapeutics. This could lead to the much-needed revision of the existing guidelines in the clinical treatment of sepsis while paving the way for discovering new therapeutic approaches.

Halogen-Induced Chemical Injury to the Mammalian Cardiopulmonary Systems

The halogens chlorine (Cl₂) and bromine (Br₂) are highly reactive oxidizing elements with widespread industrial applications and a history of development and use as chemical weapons. When inhaled, depending on the dose and duration of exposure, they cause acute and chronic injury to both the lungs and systemic organs that may result in the development of chronic changes (such as fibrosis) and death from cardiopulmonary failure. A number of conditions, such as viral infections, coexposure to other toxic gases, and pregnancy increase susceptibility to halogens significantly. Herein we review their danger to public health, their mechanisms of action, and the development of pharmacological agents that when administered post-exposure decrease morbidity and mortality.

AICAR decreases acute lung injury by phosphorylating AMPK and upregulating heme oxygenase-1

INTRODUCTION

Herein we investigated the mechanisms by which 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR), an activator of adenosine monophosphate (AMP)-activated protein kinase (AMPK), administered to mice post exposure to bromine (Br₂), decreases lung injury and mortality.

METHODS

We exposed male C57BL/6 mice as well as heme oxygenase-1 deficient (HO-1^-/-) and corresponding WT littermate mice to Br₂ (600 ppm for 45 or 30 min respectively) gas in environmental chambers and returned them to room air. AICAR was administered 6 h post-exposure (10 mg·kg^-1, IP). We assessed survival, indices of lung injury, high mobility group box 1 (HMGB1) in the plasma, HO-1 levels in lung tissues and phosphorylation of AMPK and its upstream liver kinase B1 (LKB1). Rat lung Type II epithelial cells (L2) and human club-like epithelial cells (H441) were also exposed to Br₂ (100 ppm for 10 min). Twenty-four h later we measured apoptosis and necrosis, AMPK and LKB1 phosphorylation and HO-1 expression.

RESULTS

There was a marked downregulation of phosphorylated AMPK and LKB1 in both lung tissues and L2 and H441 cells post-exposure. AICAR increased survival in C57BL/6 but not in HO-1^-/- mice. Additionally, in WT mice AICAR decreased lung injury and restored pAMPK and pLKB1 to control levels and increased HO-1 levels in both lung tissues and cells exposed to Br_2. Treatment of L2 and H441 cells with siRNAs against Nrf2 or HO-1 abrogated the protective effects of AICAR.

CONCLUSIONS

Our data indicate that the primary mechanism for the protective action of AICAR in toxic gas injury is by upregulating lung HO-1 levels.

Toxic effects of cell-free hemoglobin on the microvascular endothelium: implications for pulmonary and nonpulmonary organ dysfunction

Levels of circulating cell-free hemoglobin are elevated during hemolytic and inflammatory diseases and contribute to organ dysfunction and severity of illness. Though several studies have investigated the contribution of hemoglobin to tissue injury, the precise signaling mechanisms of hemoglobin-mediated endothelial dysfunction in the lung and other organs are not yet completely understood. The purpose of this review is to highlight the knowledge gained thus far and the need for further investigation regarding hemoglobin-mediated endothelial inflammation and injury to develop novel therapeutic strategies targeting the damaging effects of cell-free hemoglobin.

Iron homeostasis and disorders revisited in the sepsis

Sepsis is a life-threatening condition caused by a dysregulated host-response to inflammation, although it currently lacks a fully elucidated pathobiology. Iron is a crucial trace element that is essential for fundamental processes in both humans and bacteria. During sepsis, iron metabolism is altered, including increased iron transport and uptake into cells and decreased iron export. The intracellular sequestration of iron limits its availability to circulating pathogens, which serves as a conservative strategy against the pathogens. Although iron retention has been showed to have protective protect effects, an increase in labile iron may cause oxidative injury and cell death (e.g., pyroptosis, ferroptosis) as the condition progresses. Moreover, iron disorders are substantial and correlate with the severity of sepsis. This also suggests that iron may be useful as a diagnostic marker for evaluating the severity and predicting the outcome of the disease. Further knowledge about these disorders could help in evaluating how drugs targeting iron homeostasis can be optimally applied to improve the treatment of patients with sepsis. Here, we present a comprehensive review of recent advances in the understanding of iron metabolism, focusing on the regulatory mechanisms and iron-mediated injury in sepsis.

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

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

Hemopexin: A Novel Anti-inflammatory Marker for Distinguishing COPD From Asthma

Purpose

Systemic inflammatory biomarkers can improve diagnosis and assessment of chronic obstructive pulmonary disease (COPD) and asthma. We aimed to validate an airway disease biomarker panel of 4 systemic inflammatory biomarkers, α2-macroglobulin, ceruloplasmin, haptoglobin and hemopexin, to establish their relationship to airway disease diagnosis and inflammatory phenotypes and to identify an optimized biomarker panel for disease differentiation.

Methods

Participants with COPD or asthma were classified by inflammatory phenotypes. Immunoassay methods were used to measure levels of validation biomarkers in the sera of participants with disease and non-respiratory disease controls. Markers were analyzed individually and in combination for disease differentiation and compared to established biomarkers (C-reactive protein, interleukin-6, and white blood cell/blood eosinophil count).

Results

The study population comprised of 141 COPD, 127 severe asthma, 54 mild-moderate asthma and 71 control participants. Significant differences in ceruloplasmin, haptoglobin and hemopexin levels between disease groups and between systemic inflammatory phenotypes were observed. However, no differences were found between airway inflammatory phenotypes. Hemopexin was the best performing individual biomarker and could diagnose COPD versus control participants (area under the curve [AUC], 98.3%; 95% confidence interval [CI], 96.7%–99.9%) and differentiate COPD from asthmatic participants (AUC, 97.0%; 95% CI, 95.4%–98.6%), outperforming established biomarkers. A biomarker panel, including hemopexin, haptoglobin and other established biomarkers, could diagnose asthma versus control participants (AUC, 87.5%; 95% CI, 82.8%–92.2%).

Conclusions

Hemopexin can be a novel biomarker with superior diagnostic ability in differentiating COPD and asthma. We propose an anti-inflammatory axis between the airways and systemic circulation, in which hemopexin is a protective component in airway disease.

Apohemoglobin-haptoglobin complex attenuates the pathobiology of circulating acellular hemoglobin and heme

Haptoglobin (Hp) is the plasma protein that binds and clears cell-free hemoglobin (Hb), whereas apohemoglobin (apoHb, i.e., Hb devoid of heme) can bind heme. Therefore, the apoHb-Hp protein complex should facilitate holoHb-apoHb αβ-dimer exchange and apoHb-heme intercalation. Thus, we hypothesized that apoHb-Hp could facilitate both Hb and heme clearance, which, if not alleviated, could have severe microcirculatory consequences. In this study, we characterized apoHb-Hp and Hb/heme ligand interactions and assessed their in vivo consequences. Hb exchange and heme binding with the apoHb-Hp complex was studied with transfer assays using size-exclusion high-performance liquid chromatography coupled with UV-visible spectrophotometry. Exchange/transfer experiments were conducted in guinea pigs dosed with Hb or heme-albumin followed by a challenge with equimolar amounts of apoHb-Hp. Finally, systemic and microcirculatory parameters were studied in hamsters instrumented with a dorsal window chamber via intravital microscopy. In vitro and in vivo Hb exchange and heme transfer experiments demonstrated proof-of-concept Hb/heme ligand transfer to apoHb-Hp. Dosing with the apoHb-Hp complex reversed Hb- and heme-induced systemic hypertension and microvascular vasoconstriction, reduced microvascular blood flow, and diminished functional capillary density. Therefore, this study highlights the apoHb-Hp complex as a novel therapeutic strategy to attenuate the adverse systemic and microvascular responses to intravascular Hb and heme exposure.NEW & NOTEWORTHY This study highlights the apoHb-Hp complex as a novel therapeutic strategy to attenuate the adverse systemic and microvascular responses to intravascular Hb and heme exposure. In vitro and in vivo Hb exchange and heme transfer experiments demonstrated proof-of-concept Hb/heme ligand transfer to apoHb-Hp. The apoHb-Hp complex reverses Hb- and heme-induced systemic hypertension and microvascular vasoconstriction, preserves microvascular blood flow, and functional capillary density. In summary, the unique properties of the apoHb-Hp complex prevent adverse systemic and microvascular responses to Hb and heme-albumin exposure and introduce a novel therapeutic approach to facilitate simultaneous removal of extracellular Hb and heme.

Haptoglobin Therapeutics and Compartmentalization of Cell-Free Hemoglobin Toxicity

Hemolysis and accumulation of cell-free hemoglobin (Hb) in the circulation or in confined tissue compartments such as the subarachnoid space is an important driver of disease. Haptoglobin is the Hb binding and clearance protein in human plasma and an efficient antagonist of Hb toxicity resulting from physiological red blood cell turnover. However, endogenous concentrations of haptoglobin are insufficient to provide protection against Hb-driven disease processes in conditions such as sickle cell anemia, sepsis, transfusion reactions, medical-device associated hemolysis, or after a subarachnoid hemorrhage. As a result, there is increasing interest in developing haptoglobin therapeutics to target 'toxic' cell-free Hb exposures. Here, we discuss key concepts of Hb toxicity and provide a perspective on the use of haptoglobin as a therapeutic protein.

The Role of Circulating Cell-Free Hemoglobin in Sepsis-Associated Acute Kidney Injury

Sepsis is a heterogeneous clinical syndrome that is complicated commonly by acute kidney injury (sepsis-AKI). Currently, no approved pharmacologic therapies exist to either prevent sepsis-AKI or to treat sepsis-AKI once it occurs. A growing body of evidence supports a connection between red blood cell biology and sepsis-AKI. Increased levels of circulating cell-free hemoglobin (CFH) released from red blood cells during hemolysis are common during sepsis and can contribute to sepsis-AKI through several mechanisms including tubular obstruction, nitric oxide depletion, oxidative injury, and proinflammatory signaling. A number of potential pharmacologic therapies targeting CFH in sepsis have been identified including haptoglobin, hemopexin, and acetaminophen, and early phase clinical trials have suggested that acetaminophen may have beneficial effects on lipid peroxidation and kidney function in patients with sepsis. Bedside measurement of CFH levels may facilitate predictive enrichment for future clinical trials of CFH-targeted therapeutics. However, rapid and reliable bedside tests for plasma CFH will be required for such trials to move forward.

Cell-free hemoglobin increases inflammation, lung apoptosis, and microvascular permeability in murine polymicrobial sepsis

Increased endothelial permeability is central to the pathogenesis of sepsis and leads to organ dysfunction and death but the endogenous mechanisms that drive increased endothelial permeability are not completely understood. We previously reported that cell-free hemoglobin (CFH), elevated in 80% of patients with sepsis, increases lung microvascular permeability in an ex vivo human lung model and cultured endothelial cells. In this study, we augmented a murine model of polymicrobial sepsis with elevated circulating CFH to test the hypothesis that CFH increases microvascular endothelial permeability by inducing endothelial apoptosis. Mice were treated with an intraperitoneal injection of cecal slurry with or without a single intravenous injection of CFH. Severity of illness, mortality, systemic and lung inflammation, endothelial injury and dysfunction and lung apoptosis were measured at selected time points. We found that CFH added to CS increased sepsis mortality, plasma inflammatory cytokines as well as lung apoptosis, edema and inflammation without affecting large vessel reactivity or vascular injury marker concentrations. These results suggest that CFH is an endogenous mediator of increased endothelial permeability and apoptosis in sepsis and may be a promising therapeutic target.

Agomelatine could prevent brain and cerebellum injury against LPS-induced neuroinflammation in rats

Sepsis, systemic hyper-inflammatory immune response, causes the increase of morbidity and mortality rates due to multi-organ diseases such as neurotoxicity. Lipopolysaccharide (LPS) induces inflammation, oxidative stress and apoptosis to cause brain damage. We aimed to evaluate the antioxidant, anti-inflammatory and antiapoptotic effects of Agomelatine (AGM) on LPS induced brain damage via NF-kB signaling. Twenty-four animals were divided into three groups as control, LPS (5 mg/kg) and LPS + AGM (20 mg/kg). Six hours after the all administrations, rats were sacrificed, brain tissues were collected for biochemical, histopathological and immunohistochemical analysis. In LPS group; total oxidant status (TOS), OSI index, Caspase-8 (Cas-8), NF-kß levels increased and Total antioxidant status (TAS) levels decreased biochemically and Cas-8, haptoglobin and IL-10 expressions increased and sirtuin-1 (SIRT-1) levels decreased immunohistochemically. AGM treatment reversed these parameters except haptoglobin levels in hippocampus and SIRT-1 levels in cerebellum. Besides, AGM treatment blocked the phosphorylation of NF-kB biochemically and ameliorated increased the levels of hyperemia, edema and degenerative changes histopathologically. In conclusion, AGM enhanced SIRT-1 levels to negatively regulate the transcription and activation of p-NF-kB/p65 which caused to ameliorate inflammation, oxidative stress and apoptosis.

Malaria in Pregnancy and Adverse Birth Outcomes: New Mechanisms and Therapeutic Opportunities

Malaria infection during pregnancy is associated with adverse birth outcomes but underlying mechanisms are poorly understood. Here, we discuss the impact of malaria in pregnancy on three pathways that are important regulators of healthy pregnancy outcomes: L-arginine-nitric oxide biogenesis, complement activation, and the heme axis. These pathways are not mutually exclusive, and they collectively create a proinflammatory, antiangiogenic milieu at the maternal-fetal interface that interferes with placental function and development. We hypothesize that targeting these host-response pathways would mitigate the burden of adverse birth outcomes attributable to malaria in pregnancy.

Haptoglobin-2 variant increases susceptibility to acute respiratory distress syndrome during sepsis

Acute respiratory distress syndrome (ARDS) is an inflammatory lung disorder that frequently complicates critical illness and commonly occurs in sepsis. Although numerous clinical and environmental risk factors exist, not all patients with risk factors develop ARDS, raising the possibility of genetic underpinnings for ARDS susceptibility. We have previously reported that circulating cell-free hemoglobin (CFH) is elevated during sepsis, and higher levels predict worse outcomes. Excess CFH is rapidly scavenged by haptoglobin (Hp). A common HP genetic variant, HP2, is unique to humans and is common in many populations worldwide. HP2 haptoglobin has reduced ability to inhibit CFH-mediated inflammation and oxidative stress compared with the alternative HP1. We hypothesized that HP2 increases ARDS susceptibility during sepsis when plasma CFH levels are elevated. In a murine model of sepsis with elevated CFH, transgenic mice homozygous for Hp2 had increased lung inflammation, pulmonary vascular permeability, lung apoptosis, and mortality compared with wild-type mice. We then tested the clinical relevance of our findings in 496 septic critically ill adults, finding that HP2 increased ARDS susceptibility after controlling for clinical risk factors and plasma CFH. These observations identify HP2 as a potentially novel genetic ARDS risk factor during sepsis and may have important implications in the study and treatment of ARDS.

Cell-free hemoglobin augments acute kidney injury during experimental sepsis

Acute kidney injury is a common complication of severe sepsis and contributes to high mortality. The molecular mechanisms of acute kidney injury during sepsis are not fully understood. Because hemoproteins, including myoglobin and hemoglobin, are known to mediate kidney injury during rhabdomyolysis, we hypothesized that cell-free hemoglobin (CFH) would exacerbate acute kidney injury during sepsis. Sepsis was induced in mice by intraperitoneal injection of cecal slurry (CS). To mimic elevated levels of CFH observed during human sepsis, mice also received a retroorbital injection of CFH or dextrose control. Four groups of mice were analyzed: sham treated (sham), CFH alone, CS alone, and CS + CFH. The addition of CFH to CS reduced 48-h survival compared with CS alone (67% vs. 97%, P = 0.001) and increased the severity of illness. After 24 and 48 h, CS + CFH mice had a reduced glomerular filtration rate from baseline, whereas sham, CFH, and CS mice maintained baseline glomerular filtration rate. Biomarkers of acute kidney injury, neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1), were markedly elevated in CS+CFH compared with CS (8-fold for NGAL and 2.4-fold for KIM-1, P < 0.002 for each) after 48 h. Histological examination showed a trend toward increased tubular injury in CS + CFH-exposed kidneys compared with CS-exposed kidneys. However, there were similar levels of renal oxidative injury and apoptosis in the CS + CFH group compared with the CS group. Kidney levels of multiple proinflammatory cytokines were similar between CS and CS + CFH groups. Human renal tubule cells (HK-2) exposed to CFH demonstrated increased cytotoxicity. Together, these results show that CFH exacerbates acute kidney injury in a mouse model of experimental sepsis, potentially through increased renal tubular injury.

Multiple biomarkers of sepsis identified by novel time-lapse proteomics of patient serum

Serum components of sepsis patients vary with the severity of infection, the resulting inflammatory response, per individual, and even over time. Tracking these changes is crucial in properly treating sepsis. Hence, several blood-derived biomarkers have been studied for their potential in assessing sepsis severity. However, the classical approach of selecting individual biomarkers is problematic in terms of accuracy and efficiency. We therefore present a novel approach for detecting biomarkers using longitudinal proteomics data. This does not require a predetermined set of proteins and can therefore reveal previously unknown related proteins. Our approach involves examining changes over time of both protein abundance and post-translational modifications in serum, using two-dimensional gel electrophoresis (2D-PAGE). 2D-PAGE was conducted using serum from n = 20 patients, collected at five time points, starting from the onset of sepsis. Changes in protein spots were examined using 49 spots for which the signal intensity changed by at least two-fold over time. These were then screened for significant spikes or dips in intensity that occurred exclusively in patients with adverse outcome. Individual level variation was handled by a mixed effects model. Finally, for each time transition, partial correlations between spots were estimated through a Gaussian graphical model (GGM) based on the ridge penalty. Identifications of spots of interest by tandem mass spectrometry revealed that many were either known biomarkers for inflammation (complement components), or had previously been suggested as biomarkers for kidney failure (haptoglobin) or liver failure (ceruloplasmin). The latter two are common complications in severe sepsis. In the GGM, many of the tightly connected spots shared known biological functions or even belonged to the same protein; including hemoglobin chains and acute phase proteins. Altogether, these results suggest that our screening method can successfully identify biomarkers for disease states and cluster biologically related proteins using longitudinal proteomics data derived from 2D-PAGE.

Lipid metabolism impairment in patients with sepsis secondary to hospital acquired pneumonia, a proteomic analysis

Background

Sepsis is a dysregulated host response to infection and a major cause of death worldwide. Respiratory tract infections account for most sepsis cases and depending on the place of acquisition, i.e., community or hospital acquired infection, differ in etiology, antimicrobial resistance and outcomes. Accordingly, the host response may be different in septic patients secondary to community-acquired pneumonia and hospital acquired pneumonia (HAP). Proteomic analysis is a useful approach to evaluate broad alterations in biological pathways that take place during sepsis. Here we evaluated plasma proteome changes in sepsis secondary to HAP.

Methods

Plasma samples were obtained from patients (n = 27) at admission and after 7 days of follow-up, and were analyzed according to the patients’ outcomes. The patients’ proteome profiles were compared with healthy volunteers (n = 23). Pooled plasma samples were labeled with isobaric tag for relative and absolute quantitationand analyzed by LC–MS/MS. We used bioinformatics tools to find altered functions and pathways. Results were validated using biochemical estimations and ELISA tests.

Results

We identified 159 altered proteins in septic patients; most of them were common when comparing patients’ outcomes, both at admission and after 7 days. The top altered biological processes were acute inflammatory response, response to wounding, blood coagulation and homeostasis. Lipid metabolism emerged as the main altered function in patients, with HDL as a central node in the network analysis, interacting with downregulated proteins, such as APOA4, APOB, APOC1, APOL1, SAA4 and PON1. Validation tests showed reduced plasma levels of total cholesterol, HDL-C, LDL-C, non-HDL cholesterol, apolipoproteins ApoA1 and ApoB100, and Paraoxonase 1 in HAP patients.

Conclusion

Proteomic analysis pointed to impairment of lipid metabolism as a major change in septic patients secondary to HAP, which was further validated by the reduced levels of cholesterol moieties and apolipoproteins in plasma. Our results stress the involvement of lipids in the pathogenesis of sepsis, which is in accordance with previous reports supporting the role of lipid moieties in pathogen toxin clearance and in modulating inflammatory responses.

Electronic supplementary material

The online version of this article (10.1186/s12014-019-9252-2) contains supplementary material, which is available to authorized users.

Safe coordinated trafficking of heme and iron with copper maintain cell homeostasis: modules from the hemopexin system

Studies with patients, animal models of human disease and hemopexin null mice have shown that the heme-binding protein hemopexin is vital for the protection of a variety of cell types and tissues against heme toxicity. The presence of hemopexin in all biological fluids examined to date indicates wide roles in abrogating heme toxicity in human tissues; and, thus, is clinically relevant. Heme-hemopexin endocytosis leads to coordinated trafficking of heme, iron and copper as heme traffics from endosomes to heme oxygenases (HOs) in the smooth endoplasmic reticulum and to the nucleus. This is safe redox-metal trafficking, without oxidative stress, as iron released from heme catabolism by HOs as well as copper taken up with heme-hemopexin move through the cell. To our knowledge, this coordinated metal trafficking has been described only for the hemopexin system and differs from the cell's response to non-protein bound heme, which can be toxic. We propose that defining how cells respond to heme-hemopexin endocytosis, a natural cytoprotective system, will aid our understanding of how cells adapt as they safely respond to increases in heme, Fe(II) and copper. This is relevant for many genetic hemolytic diseases and conditions, stroke and hemorrhage as well as neurodegeneration. Such analyses will help to define a pattern of events that can be utilized to characterize how dysfunctional redox and transition metal handling is linked to the development of pathology in disease states such as Alzheimer's disease when metal homeostasis is not restored; and potentially provide novel targets and approaches to improve therapies.

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

BACKGROUND

Relationships between red blood cell (RBC) transfusion, circulating cell-free heme, and clinical outcomes in critically ill transfusion recipients are incompletely understood. The goal of this study was to determine whether total plasma heme increases after RBC transfusion and predicts mortality in critically ill patients.

STUDY DESIGN AND METHODS

This was a prospective cohort study of 111 consecutive medical intensive care patients requiring RBC transfusion. Cell-free heme was measured in RBC units before transfusion and in the patients' plasma before and after transfusion.

RESULTS

Total plasma heme levels increased in response to transfusion, from a median (interquartile range [IQR]) of 35 (26-76) μmol/L to 47 (35-73) μmol/L (p < 0.001). Posttransfusion total plasma heme was higher in nonsurvivors (54 [35-136] μmol/L) versus survivors (44 [31-65] μmol/L, p = 0.03). Posttransfusion total plasma heme predicted hospital mortality (odds ratio [95% confidence interval] per quartile increase in posttransfusion plasma heme, 1.76 [1.17-2.66]; p = 0.007). Posttransfusion total plasma heme was not correlated with RBC unit storage duration and weakly correlated with RBC unit cell-free heme concentration.

CONCLUSIONS

Total plasma heme concentration increases in critically ill patients after RBC transfusion and is independently associated with mortality. This transfusion-associated increase in total plasma heme is not fully explained by RBC unit storage age or cell-free heme content. Additional studies are warranted to define mechanisms of transfusion-related plasma heme accumulation and test prevention strategies.

Ferritin Light Chain Confers Protection Against Sepsis-Induced Inflammation and Organ Injury

Despite the prevalence and recognition of its detrimental impact, clinical complications of sepsis remain a major challenge. Here, we investigated the effects of myeloid ferritin heavy chain (FtH) in regulating the pathogenic sequelae of sepsis. We demonstrate that deletion of myeloid FtH leads to protection against lipopolysaccharide-induced endotoxemia and cecal ligation and puncture (CLP)-induced model of sepsis as evidenced by reduced cytokine levels, multi-organ dysfunction and mortality. We identified that such protection is predominantly mediated by the compensatory increase in circulating ferritin (ferritin light chain; FtL) in the absence of myeloid FtH. Our in vitro and in vivo studies indicate that prior exposure to ferritin light chain restrains an otherwise dysregulated response to infection. These findings are mediated by an inhibitory action of FtL on NF-κB activation, a key signaling pathway that is implicated in the pathogenesis of sepsis. We further identified that LPS mediated activation of MAPK pathways, specifically, JNK, and ERK were also reduced with FtL pre-treatment. Taken together, our findings elucidate a crucial immunomodulatory function for circulating ferritin that challenges the traditional view of this protein as a mere marker of body iron stores. Accordingly, these findings will stimulate investigations to the adaptive nature of this protein in diverse clinical settings.

Haptoglobin improves acute phase response and endotoxin tolerance in response to bacterial LPS

Sepsis is characterized by delayed acute phase response and lowered immune tolerance in patients. Acute phase serum proteins, like Haptoglobin (Hp), have been associated with increased mortality in bacteria mediated acute lung inflammation and sepsis in neonates. However, it's direct role in modulating the immune response by regulating pro-inflammatory mediators leading to immune tolerant state and if gender affects its expression levels during bacterial infection, especially in blood has not been fully explored. To understand its specific role in endotoxin-mediated immune response, we investigated the correlation between the rise in Hp levels on bacterial infection and its influence on the expression of pro-inflammatory mediators in male and female Whole blood (WHB) and PBMCs. Here, we observed pathogen-specific and gender-specific expression of Hp. Gonadal steroid hormones differentially influenced the Hp expression in LPS-induced WHB, where the addition of Estrogen increased Hp expression, with suppression of TNFα, in both genders. Further on evaluating, the influence of Hp on TNFα expression in endotoxin tolerance (ET), we show that increased Hp levels directly reduced TNFα expression in ET models. Interestingly, blockade of secreted Hp significantly reversed the (ET) state, confirmed by a significant rise in TNFα expression in both ex vivo and in vitro ET models, indicating a possible feedback inhibition by Hp on inflammatory mediators like TNFα. We also investigated the role of PKCδ in the regulation of LPS induced secretion of acute phase proteins (Hp) in serum, where inhibition of PKCδ, reduced secretion of anti-microbial proteins in response to LPS shown by restored bacterial growth. These findings clearly highlight the crucial role of Hp in maintaining immune tolerance via suppressing the pro-inflammatory mediators and also in preventing bacterial proliferation in blood during infection.

Heme Induces Endoplasmic Reticulum Stress (HIER Stress) in Human Aortic Smooth Muscle Cells

Accumulation of damaged or misfolded proteins resulted from oxidative protein modification induces endoplasmic reticulum (ER) stress by activating the pathways of unfolded protein response. In pathologic hemolytic conditions, extracellular free hemoglobin is submitted to rapid oxidation causing heme release. Resident cells of atherosclerotic lesions, after intraplaque hemorrhage, are exposed to heme leading to oxidative injury. Therefore, we raised the question whether heme can also provoke ER stress. Smooth muscle cells are one of the key players of atherogenesis; thus, human aortic smooth muscle cells (HAoSMCs) were selected as a model cell to reveal the possible link between heme and ER stress. Using immunoblotting, quantitative polymerase chain reaction and immunocytochemistry, we quantitated the markers of ER stress. These were: phosphorylated eIF2α, Activating transcription factor-4 (ATF4), DNA-damage-inducible transcript 3 (also known as C/EBP homology protein, termed CHOP), X-box binding protein-1 (XBP1), Activating transcription factor-6 (ATF6), GRP78 (glucose-regulated protein, 78kDa) and heme responsive genes heme oxygenase-1 and ferritin. In addition, immunohistochemistry was performed on human carotid artery specimens from patients who had undergone carotid endarterectomy. We demonstrate that heme increases the phosphorylation of eiF2α in HAoSMCs and the expression of ATF4. Heme also enhances the splicing of XBP1 and the proteolytic cleavage of ATF6. Consequently, there is up-regulation of target genes increasing both mRNA and protein levels of CHOP and GRP78. However, TGFβ and collagen type I decreased. When the heme binding proteins, alpha-1-microglobulin (A1M) and hemopexin (Hpx) are present in cell media, the ER stress provoked by heme is inhibited. ER stress pathways are also retarded by the antioxidant N-acetyl cysteine (NAC) indicating that reactive oxygen species are involved in heme-induced ER stress. Consistent with these findings, elevated expression of the ER stress marker GRP78 and CHOP were observed in smooth muscle cells of complicated lesions with hemorrhage compared to either atheromas or healthy arteries. In conclusion, heme triggers ER stress in a time- and dose-dependent manner in HAoSMCs. A1M and Hpx as well as NAC effectively hamper heme-induced ER stress, supporting their use as a potential therapeutic approach to reverse such a deleterious effects of heme toxicity.

Haptoglobin improves shock, lung injury, and survival in canine pneumonia

During the last half-century, numerous antiinflammatory agents were tested in dozens of clinical trials and have proven ineffective for treating septic shock. The observation in multiple studies that cell-free hemoglobin (CFH) levels are elevated during clinical sepsis and that the degree of increase correlates with higher mortality suggests an alternative approach. Human haptoglobin binds CFH with high affinity and, therefore, can potentially reduce iron availability and oxidative activity. CFH levels are elevated over approximately 24-48 hours in our antibiotic-treated canine model of S. aureus pneumonia that simulates the cardiovascular abnormalities of human septic shock. In this 96-hour model, resuscitative treatments, mechanical ventilation, sedation, and continuous care are translatable to management in human intensive care units. We found, in this S. aureus pneumonia model inducing septic shock, that commercial human haptoglobin concentrate infusions over 48-hours bind canine CFH, increase CFH clearance, and lower circulating iron. Over the 96-hour study, this treatment was associated with an improved metabolic profile (pH, lactate), less lung injury, reversal of shock, and increased survival. Haptoglobin binding compartmentalized CFH to the intravascular space. This observation, in combination with increasing CFHs clearance, reduced available iron as a potential source of bacterial nutrition while decreasing the ability for CFH and iron to cause extravascular oxidative tissue injury. In contrast, haptoglobin therapy had no measurable antiinflammatory effect on elevations in proinflammatory C-reactive protein and cytokine levels. Haptoglobin therapy enhances normal host defense mechanisms in contrast to previously studied antiinflammatory sepsis therapies, making it a biologically plausible novel approach to treat septic shock.

Relationship between Anaemia, Haemolysis, Inflammation and Haem Oxygenase-1 at Admission with Sepsis: a pilot study

Upregulation of haem oxygenase-1 (HO-1), due to haemolysis and/or inflammation, can lead to impaired immune function. Anaemia is common among sepsis patients, but the consequences of sepsis-associated anaemia are poorly understood. Here, our objective was to determine the prevalence and extent of anaemia, haemolysis, inflammation, and HO-1 induction after early hospital admission. We hypothesised that inflammation- or infection-induced haemolysis contributes to sepsis-associated anaemia and that this will lead to expression of HO-1. In this study, plasma obtained from seventy adult patients within 12 hours of admission to intensive care due to sepsis were analysed for anaemia, haemolysis and inflammatory markers by ELISA and microbead array. The majority (82.6%) of patients were anaemic with evidence of haemolysis (raised haem, haptoglobin, haemopexin, and HO-1 concentrations). Interestingly, concentrations of both haemoglobin and IL-10 were moderately positively correlated with HO-1 concentration (Hb: r = 0.32, p = 0.007; IL-10 r = 0.39, p = 0.0008) whereas HO-1 concentration was weakly negatively correlated with haemopexin (r = −0.23, p = 0.055). Anaemia, while common, was not associated with HO-1 concentration. After adjusting for confounding, HO-1 induction appears to be associated primarily with IL-10 concentration rather than haemolysis. Disease severity at diagnosis was correlated with early plasma IL-10 (r = 0.35, p = 0.003) and HO-1 (r = 0.24, p = 0.048) concentrations. Notably, admission levels of haem, HO-1, and IL-10 were indicators of survival.

Hemoglobin metabolism by-products are associated with an inflammatory response in patients with hemorrhagic stroke

Objective

To evaluate the relationships of brain iron and heme with the inflammatory response of the systemic and central nervous systems and to investigate the role of defensive systems against the toxicity of iron and heme in the central nervous system.

Methods

We assessed a prospective cohort of patients presenting with intracerebral and subarachnoid hemorrhage. We assayed plasma and cerebrospinal fluid samples for the presence of iron, heme, hemopexin, haptoglobin, enolase, S100-β and cytokines for the first three days following hemorrhagic stroke. We also analyzed the dynamic changes in these components within both fluids and their relationship with early mortality rates.

Results

Hemopexin and haptoglobin concentrations were nearly negligible in the brain after intracerebral and subarachnoid hemorrhage. Cerebrospinal fluid iron and heme concentrations correlated with a pro-inflammatory response in the central nervous system, and plasmatic and cerebrospinal fluid inflammatory profiles on the third day after hemorrhagic stroke were related to early mortality rates. Interleukin 4 levels within the cerebrospinal fluid during the first 24 hours after hemorrhagic stroke were found to be higher in survivors than in non-survivors.

Conclusion

Iron and heme are associated with a pro-inflammatory response in the central nervous system following hemorrhagic stroke, and protections against hemoglobin and heme are lacking within the human brain. Patient inflammatory profiles were associated with a poorer prognosis, and local anti-inflammatory responses appeared to have a protective role.