PubMed: 29956069

Mechanisms of Hemolysis During Sepsis.
Effenberger-Neidnicht K | Hartmann M

Evidence 7859c0a72a

Another pathogenic mechanism involves the release of iron from cell-free hemoglobin with consecutive radical formation, which in turn can modify lipids, proteins, and DNA, leading to inflammation [39].

Evidence 21377b888e

Lipid A alone, however, does not appear to affect the osmotic resistance of red blood cells [127].

Evidence d40e6115a7

Hemodynamics will be impaired, which on the one hand can lead to the production of oxygen radicals and thus directly to tissue damage.

Evidence 8c2058216b

However, 6 years later, Heyes and co-workers demonstrated in an experimental study in rats that infusions of thrombin induce DIC accompanied with hemolysis and schistocytosis [89].

Evidence 31de443f8c

Recently, using a rat model of lipopolysaccharide (LPS)-induced systemic inflammation, our own collaboration could show that argatroban (a specific direct thrombin inhibitor and consequently an inhibitor of coagulation) abolishes DIC, schistocyte formation, and hemolysis.

Evidence 726d0f2629

Eryptosis is tightly regulated and triggered by a wide range of (endogenous) mediators and stimuli such as calcium signaling, ceramide formation, complement activation, energy depletion, eicosanoid release, hemolysin, and heme [140–142].

Evidence e60b311c50

Interestingly, inhibition of coagulation is capable of diminishing DIC and hemolysis but not antiplatelet therapy—treatment with eptifibatide (an antiplatelet drug of the glycoprotein IIb/IIIa inhibitor class) failed to reduce LPS-induced DIC, schistocyte formation, and hemolysis.

Evidence 1244624422

Without sufficient glucose supply, red blood cells will starve and perish and cytoplasmic components will release. Hemolysis will be the consequence [120].

Evidence a682b1ef6a

Recently, our own collaboration could show that moderate glucose supply reduces hemolysis in rats treated with LPS to induce systemic inflammation [121].

Evidence c2fa336ac0

In infectious diseases, such as malaria and sepsis, high amounts of cell-free hemoglobin and heme were found [8], suggesting that hemolysis during sepsis and systemic inflammation is of pathophysiological relevance.

Evidence dc49e54d8d

Heme released from cell-free hemoglobin has been described to be an activator of TLR-4 [39, 41, 42].

Evidence 26f39c3428

Heme/TLR-4 signaling, moreover, was found to activate NF-κB and trigger vaso-occlusion [42].

Evidence 858200b69b

Cell-free hemoglobin and its prosthetic group heme can contribute to organ dysfunction and death [1–4, 9–12]; the pathological mechanisms include nitric oxide consumption, vasoconstriction, oxidative injury to lipid membranes, activation of the transcription factor NF-κB, endothelial injury as well as iron-driven oxidative inhibition of glucose metabolism[10–14].

Evidence c9bb0950d0

Already in 1941, Macfarlane and collaborators described hemolysis due to loss of lecithin from the red blood cell membrane in consequence of an infection with Clostridium perfingens [128, 130].

Evidence 510c125146

In animal experiments, the administration of lipopolysaccharide (LPS) to induce systemic inflammation leads to a significant increase in plasma concentration of cell-free hemoglobin as well [5–8].

Evidence cb06dd875e

Due to these properties, LPS can easily be incorporated into the membrane of (red blood) cells, alter their membrane properties, and thus promote cell death [123, 124].

Evidence c05cd9fb64

We found, moreover, a decreased osmotic resistance and membrane stiffness of washed red blood cells treated with LPS [80, 81].

Evidence 45a0b256bc

One crucial factor in pathogenesis of systemic inflammation/sepsis is an impaired microcirculation [99].

Evidence 603b0d9057

The cause of sepsis is primarily an exaggerated, generalized inflammatory response to an extrinsic stimulus. Mechanistically, so-called PAMPs (pathogen-associated molecular patterns) lead to the activation of pattern recognition receptors (PRRs) such as tolllike receptors (TLRs) and C-type lectin receptors (CLRs) [28, 29].

Evidence 2922fa5118

This study further supports the concept that fibrin deposition in the blood vessels as a result of DIC might contribute to red blood cell fragmentation and, in turn, hemolysis [89].

Evidence b8d899d06a

Moreover, longer storage duration of red blood cells is associated with an increased risk of acute lung injury in patients with sepsis [63].

Evidence ab36e412bf

Some pathogens are capable of causing hemolysis by cytolytic toxins.

Evidence c3e212b406

During DIC, fibrin strands within the fibrin mesh formed could cut red blood cells, resulting in the formation of schistocytes (strongly deformed red blood cells or fragments of red blood cells) and the release of hemoglobin.

Evidence c42dadde81

Essential for the development of DIC during sepsis is the so-called pro-coagulatory shift of the endothelial cells, caused among others by an increased expression of tissue factor and adhesion molecules especially by damaged endothelial cells [87].

Evidence 74786d061c

However, also the anaphylatoxins C3a and C5a may lead to cellular and organ disturbances [75].

Evidence 4b3db9729d

Ultimately, activation of the complement cascade results in formation of the terminal complement complex C5b-9, the so-called membrane attack complex, and consequently a pore formation resulting in osmotic lysis of the target [71]. In the case of red blood cells, hemolysis will result.

Evidence e833a411e6

During extravascular hemolysis, the IgG-coated red blood cells are degraded in the so-called reticuloendothelial systems such as liver, spleen, and lymph nodes.

Evidence 1b7bad2d99

The earliest documented effect of PFTs is their ability to rapidly kill red blood cells through osmotic lysis.

Evidence b4286cb755

In recent years, it has also been shown that toll-like receptors and other pattern recognition receptors are activated not only by extrinsic factors but also by intrinsic stimuli (so called damage-associated molecular patterns, DAMPs) that are released when the host cell is damaged [27, 29].

Evidence 1ffc7cddc2

The cytokines released can further lead to pronounced peripheral vasodilation with arterial hypotension by activating the inducible nitric oxide (NO) synthase (iNOS) and the subsequent formation of NO [30].

Evidence 4ddae796fa

Furthermore, a massive release of cytokines will shift the balance between pro- and anti-coagulatory factors in the blood, which will lead to increased coagulation of the blood (coagulopathy).

Evidence 3b556f7e7b

Inhibition of the terminal complement cascade by eculizumab (inhibits the cleavage of C5 into C5a und C5b and thus the formation of the membrane attack complex 8, MAC C5b-C9) for the treatment of hemolytic paroxymal nocturnal hemoglobinuria (PNH) significantly prevented PNH-related symptoms in patients including abnormal thrombophilia, red blood cell destruction, and the extent of hemolysis [76].

Evidence 40134edddf

In a case report, Bull and Kuhn presented the pathogenesis of microangiopathic hemolytic anemia in a patient with an infiltrating adenocarcinoma [88]. In that patient, they found large numbers of micro-clots composed of fine fibrin strands in his vasculature.

Evidence 2c4ebb54ff

It is crucial, hence, to further investigate the mechanisms of sepsis-induced hemolysis with the aim of deriving possible therapeutic principles. Herein, we collected the most important previously known triggers of hemolysis during sepsis, which are (1) transfusion reactions and complement activation, (2) disseminated intravascular coagulation, (3) capillary stopped-flow, (4) restriction of glucose to red blood cells, (5) changes in red blood cell membrane properties, (6) hemolytic pathogens, and (7) red blood cell apoptosis.

Evidence 6bfb2a37cf

Thus, the complement system may be causally involved in the onset of hemolysis during sepsis [74] by directly damaging the red blood cells upon activation as a result of detecting pathogen structures [73].

Evidence 62eac5ca3b

If glucose consumption further exceeds glucose production or uptake, finally hypoglycemia occurs [118].

Evidence 76cc983602

Extravascular hemolysis, however, results from Rh incompatibility of red blood cells [72] and is complement independent [71].

Evidence 14c87661cf

Nevertheless, the crosstalk between glucose and heme metabolism in sepsis is bidirectional since an excessive accumulation of cell-free heme following hemolysis influences the glucose metabolism by iron-driven oxidative inhibition of the glucose-6-phosphatase (a liver enzymes being important for endogenous glucose production via gluconeogenesis and glycogenolysis) [14].

Evidence b847f8edf3

Similar to HUS, during sepsis an activation not just of the complement system but also of the coagulation system has been described (essentially in consequence of the so-called pro-coagulant shift of the endothelial cells), which offers us the next possible cause of hemolysis during sepsis: destruction of the red blood cells in the fibrin mesh.

Evidence a09ee98ae9

Most hemolytic transfusion reactions^ can be attributed to ABO antibodies (ABO incompatibility of red blood cells) leading to intravascular hemolysis [69, 70] as a consequence of robust complement activation [71].

Evidence 31f411f9ff

On the other hand, eryptosis is associated with anemia, microcirculatory derangement, and thrombosis [142, 144].

Evidence eaa052f1e1

A higher glucose requirement is covered, then, by increased glycogenolysis and gluconeogenesis [37, 118].

Evidence 41d7e922ab

Finally, a bi-directional crosstalk between hemolysis and coagulation was postulated with induction of tissue factor by cell-free hemoglobin as potentially central mechanism for hemolysis to trigger coagulation [87].

Evidence bc13077452

One of the mechanisms by which cell-free hemoglobin exerts its detrimental effects is its ability to effectively scavenge nitric oxide (NO), which in turn leads to perfusion disorders and an increased arterial and pulmonary arterial pressure [39, 40].

Evidence 18ba2569b9

Thus, the intravenous administration of hemoglobin in LPS-pretreated mice leads to a higher TNF- α concentration and an increased mortality; in turn, these effects could be inhibited by hemoglobin antibodies [33, 34].

Evidence dacbca5a81

Heme released from cell-free hemoglobin on oxidation is bound by hemopexin and degraded by hepatocytes in the liver [12].

Evidence 21f8e1484c

Vinchi and co-workers proved that the hemoglobin scavenger hemopexin prevents from hepatic microvascular stasis induced by intravascular hemolysis (using a mouse model of heme overloadin wild-typemicecomparedtohemopexin-nullmice) [116].

Evidence ead063a153

Lipopolysaccharide (LPS)—the main constituent of the outer cell wall of Gram-negative bacteria—is known to bind to the pathogen recognition receptor TLR-4 and to activate the innate immune and hemostatic systems.

Evidence e1e5e1a294

Once cell-free hemoglobin was bound by its scavenger haptoglobin, the resulting haptoglobin–hemoglobin complex will bind to CD163 on the surface of macrophages/monocytes to initiate endocytosis and degradation of the complex [12, 39].

Evidence d1de605828

Normally, cellfree hemoglobin will dimerize and rapidly be bound by its hemoglobin scavengers haptoglobin and hemopexin [12].

Evidence 319c883ae0

The same applies to hemolysin. For one thing, the pore-forming toxin hemolysin is one the pathogens’ tools of causing hemolysis or releasing hemoglobin and poorly available iron [139]; then again it trigger eryptosis, one mechanism of protecting against hemolysis [142].

Evidence 6c73761a72

From hemolytic uremic syndrome (HUS), we know that damage to the endothelium (endothelial lesions) might be the primary cause of hemolysis.

Evidence 4f7bccfbef

During HUS, endothelial lesions cause a complement dependent activation of immune response and local thrombus formation—attachment of fibrin and platelets to the endothelial lesions and consequently disseminated intravascular coagulation (DIC)—and further mechanical destruction of the red blood cells in the fibrin mesh resulting in hemolysis [82].

Evidence 20ae626383

There are various studies that show a relationship between microvascular stasis and intravascular hemolysis. Already in 1940, Mumme described that renal stasis causes hemolysis [108].

Evidence 1c90462279

On the other hand, impaired microcirculation in the tissue usually causes local ischemia (circulatory disorders and lack of oxygen in the tissue) and often results in multiple organ failure [31].

Evidence 00548f72df

They concluded that intravascular coagulation must be the most likely cause of this microangiopathic hemolytic anemia.

Evidence e13292e1eb

A severe sepsis further was defined as sepsis with organ dysfunction and a septic shock as severe sepsis with cardiovascular collapse that does not respond to fluid intake [23].

Evidence c8e3b75b7b

DIC is characterized by a systemic intravascular coagulation, formation of microvascular thrombi, insufficiently compensated consumption of platelets and coagulation factors, and eventually bleeding tendency [84].

Evidence 0a331a0875

Sepsis/systemic inflammation is frequently associated with disseminated intravascular coagulation (DIC) being a predictor of mortality in septic patients [84, 85].

Evidence c79e5e7fed

Thus, hemolysis can act as a kind of amplifier of the complex response to an infection or injury [8, 15] and worsen the outcome from animals and patients with systemic inflammation, sepsis, or trauma [1–4, 10].

Evidence 720e60e0c2

Crucial for a sepsis, thus, was the presence of at least two of four criteria of a systemic inflammatory response syndrome (SIRS), which includes (1) fever (≥ 38.0 °C) or hypothermia (≤ 36.0 °C), (2) tachycardia (heart rate ≥ 90/min), (3) tachypnea (frequency ≥ 20/min) or hyperventilation, and (4) leukocytosis (white blood cells ≥ 12,000/mm3) or leukopenia (white blood cells ≤ 4000/mm3).

Evidence 40ffcebd23

Both clinical [1–4] and experimental [5–8] studies have shown that sepsis and systemic inflammation lead to a massive release of hemoglobin from red blood cells (hemolysis) being accompanied with an increased risk of death [1–4, 8, 9].

Evidence de0c56d19c

Furthermore, fibrinolysis (dissolution of a blood clot) is also regularly inhibited in the early stages of sepsis [86].


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