wow
Complement is an important mediator of vascular injury following oxidative stress. We recently demonstrated that complement activation following endothelial oxidative stress is mediated by mannose-binding lectin (MBL) and activation of the lectin complement pathway. Here, we investigated whether nine plant lectins which have a binding profile similar to that of MBL competitively inhibit MBL deposition and subsequent complement activation following human umbilical vein endothelial cell (HUVEC) oxidative stress. HUVEC oxidative stress (1% O2, 24 hr) significantly increased Ulex europaeus agglutinin II (UEA-II) binding by 72 ± 9% compared to normoxic cells. UEA-II inhibited MBL binding to HUVEC in a concentration-dependent manner following oxidative stress. Further, MBL inhibited UEA-II binding to HUVEC in a concentration-dependent manner following oxidative stress, suggesting a common ligand. UEA-II ( 100 µmol/L) did not attenuate the hemolytic activity, nor did it inhibit C3a des Arg formation from alternative or classical complement pathway-specific hemolytic assays. C3 deposition (measured by ELISA) following HUVEC oxidative stress was inhibited by UEA-II in a concentration-dependent manner (IC50 = 10 pmol/L). UEA-II inhibited C3 and MBL co-localization (confocal microscopy) in a concentration-dependent manner on HUVEC following oxidative stress (IC50 1 pmol/L). Finally, UEA-II significantly inhibited complement-dependent neutrophil chemotaxis, but failed to inhibit fMLP-mediated chemotaxis, following endothelial oxidative stress. These data demonstrate that UEA-II is a novel, potent inhibitor of human MBL deposition and complement activation following human endothelial oxidative stress.
Endothelial cells are important in the regulation of coagulation, vascular permeability, vasomotor tone and inflammation. Oxidative stress may result in complement activation and endothelial dysfunction. Endothelial dysfunction and complement activation are thought to be involved in human pathology including myocardial infarction (Weisman et al. 1990; Tsao et al. 1990), lung injury (Bless et al. 1999), sepsis (Czermak et al. 1999), and gut ischemia (Siegfried et al. 1992). Indeed, inhibition of complement attenuates tissue injury in patients undergoing cardiopulmonary bypass (Fitch et al. 1999) and in several experimental models of human disease (Weisman et al. 1990; Vakeva et al. 1998; Zhou et al. 2000). Complement is known to interact with the vascular endothelium and initiate a variety of pro-inflammatory signals, including leukocyte adhesion molecule expression, pro-inflammatory cytokine secretion, and loss of endothelium-dependent relaxation (Stahl et al. 1995; Kilgore et al. 1996; Collard et al. 1999; Buerke et al. 1998). Thus, the development of complement inhibitors may reduce endothelial dysfunction and tissue injury in a variety of clinical settings.
During the early stages of reperfusion of ischemic tissue, complement activation is known to occur initially at the endothelial cell (Weisman et al. 1990). We recently demonstrated that mannose-binding lectin (MBL) deposition and lectin complement pathway activation occurs on human endothelial cells following oxidative stress (Collard et al. 2000). MBL is a C-type lectin whose binding is calcium-dependent and has a high specificity to N-acetyl-D-glucosamine (GlcNAc), mannose or their oligomers (Thiel et al. 1997). Although the molecular mechanism by which oxidative stress increases MBL binding to endothelial cells is at present unclear, hypoxia alters endothelial protein synthesis and surface expression (Ogawa et al. 1991; Weinhouse et al. 1993; Dore-Duffy et al. 1999). Other lectins derived from plant sources have binding profiles similar to that of MBL. In the present study we investigated whether endothelial oxidative stress increases the binding of plant lectins displaying saccharide specificity similar to that of human MBL. We also investigated whether these lectins could be used to inhibit human MBL binding and lectin complement pathway activation following endothelial oxidative stress. We found that the plant lectin Ulex europaeus agglutinin II (UEA-II) significantly attenuates human MBL binding, lectin complement pathway activation, and the resulting complement-dependent neutrophil chemotaxis following endothelial oxidative stress.
The plant lectins specific for GlcNAc, mannose or their oligomers used in this study are listed in Table 1. As shown in Figure 1, of the lectins screened, only UEA-II demonstrated a significant (P < 0.05) increase in binding to HUVEC following oxidative stress compared to normoxic cells. This observation is analogous to our recent finding that endothelial oxidative stress increases human MBL binding (Collard et al. 2000), as both UEA-II and MBL are calcium-dependent lectins with a high specificity for GlcNAc and its oligomers. The binding of UEA-II was unique, since the lectins LEA, STL, and WGA did not increase their binding to HUVEC following oxidative stress, yet have specificity for GlcNAc and its oligomers.
ok.. so. minus 1000 cool points if you actually read that. HOWEVER. it means that they are looking at preventing immune mediated responses and secondary inflammation damage to endothelial cells (that line the blood vessels) caused by complement fixation. Complement is a complex of 30 some proteins that normally circulate in blood plasma as an inactive complex. When antibodies (made by white blood cells) bind antigen (bacteria, virus, etc..) it releases an enzyme that initiates the complement cascade in a chain reaction (C1 to C9 and various sub-units as C3a and C3b). Once antibodies bind "target cells" or bad guys, complement destroys them. (Complement is non specific so it can bind to good cells too, where it causes the damage). These different complement sub-units all have different functions, but C3 is the most abundant in the complement system and some of the subunits of C3 such as C3b bind glycoprotein on cell surfaces. Any cells with C3b bound to their surfaces are targeted by white corpuscles and are phagocytized or eaten by the corpuscles which leads to more inflammation. C3a, another C3 subunit binds to other white blood cells, called basophils and mast cells, and causes them to release histamine (think of allergies here) which can lead to anaphylaxis and death. Besides cell lyses, complement causes a whole host of immune (think inflammation) responses as increased permeability of blood vessel walls, chemotaxis (drawing other white cells to the site), and triggers easy clotting of blood. Anyway it’s a complex system of interactions and you probably don't want to read a book about it. Basically, what the mad scientists are working on is a drug to prevent vascular damage which leads to vascular occlusion by blood clots and ultimately heat attack. You have probably read all the stuff on the link of chronic inflammation and heart attack. There are all kinds of lectins, but I think they are looking at a specific lectin found in plants (or some organism) that prevents all this by blocking C3b from binding to cell surfaces in the first place. Lectins bind sugars (glyco) in glycoprotiens so their lectin would compete with complement components for the glycoprotien sites on the cell surface and stop the accidental damage to vessel epithelial cells by the immune response and prevent a cardiac event in the long term. Anyway it’s a biochemical mechanism to prevent vascular inflammation, the most common cause of cardiac arrest.
w00t
i sound smart
Endothelial cells are important in the regulation of coagulation, vascular permeability, vasomotor tone and inflammation. Oxidative stress may result in complement activation and endothelial dysfunction. Endothelial dysfunction and complement activation are thought to be involved in human pathology including myocardial infarction (Weisman et al. 1990; Tsao et al. 1990), lung injury (Bless et al. 1999), sepsis (Czermak et al. 1999), and gut ischemia (Siegfried et al. 1992). Indeed, inhibition of complement attenuates tissue injury in patients undergoing cardiopulmonary bypass (Fitch et al. 1999) and in several experimental models of human disease (Weisman et al. 1990; Vakeva et al. 1998; Zhou et al. 2000). Complement is known to interact with the vascular endothelium and initiate a variety of pro-inflammatory signals, including leukocyte adhesion molecule expression, pro-inflammatory cytokine secretion, and loss of endothelium-dependent relaxation (Stahl et al. 1995; Kilgore et al. 1996; Collard et al. 1999; Buerke et al. 1998). Thus, the development of complement inhibitors may reduce endothelial dysfunction and tissue injury in a variety of clinical settings.
During the early stages of reperfusion of ischemic tissue, complement activation is known to occur initially at the endothelial cell (Weisman et al. 1990). We recently demonstrated that mannose-binding lectin (MBL) deposition and lectin complement pathway activation occurs on human endothelial cells following oxidative stress (Collard et al. 2000). MBL is a C-type lectin whose binding is calcium-dependent and has a high specificity to N-acetyl-D-glucosamine (GlcNAc), mannose or their oligomers (Thiel et al. 1997). Although the molecular mechanism by which oxidative stress increases MBL binding to endothelial cells is at present unclear, hypoxia alters endothelial protein synthesis and surface expression (Ogawa et al. 1991; Weinhouse et al. 1993; Dore-Duffy et al. 1999). Other lectins derived from plant sources have binding profiles similar to that of MBL. In the present study we investigated whether endothelial oxidative stress increases the binding of plant lectins displaying saccharide specificity similar to that of human MBL. We also investigated whether these lectins could be used to inhibit human MBL binding and lectin complement pathway activation following endothelial oxidative stress. We found that the plant lectin Ulex europaeus agglutinin II (UEA-II) significantly attenuates human MBL binding, lectin complement pathway activation, and the resulting complement-dependent neutrophil chemotaxis following endothelial oxidative stress.
The plant lectins specific for GlcNAc, mannose or their oligomers used in this study are listed in Table 1. As shown in Figure 1, of the lectins screened, only UEA-II demonstrated a significant (P < 0.05) increase in binding to HUVEC following oxidative stress compared to normoxic cells. This observation is analogous to our recent finding that endothelial oxidative stress increases human MBL binding (Collard et al. 2000), as both UEA-II and MBL are calcium-dependent lectins with a high specificity for GlcNAc and its oligomers. The binding of UEA-II was unique, since the lectins LEA, STL, and WGA did not increase their binding to HUVEC following oxidative stress, yet have specificity for GlcNAc and its oligomers.
ok.. so. minus 1000 cool points if you actually read that. HOWEVER. it means that they are looking at preventing immune mediated responses and secondary inflammation damage to endothelial cells (that line the blood vessels) caused by complement fixation. Complement is a complex of 30 some proteins that normally circulate in blood plasma as an inactive complex. When antibodies (made by white blood cells) bind antigen (bacteria, virus, etc..) it releases an enzyme that initiates the complement cascade in a chain reaction (C1 to C9 and various sub-units as C3a and C3b). Once antibodies bind "target cells" or bad guys, complement destroys them. (Complement is non specific so it can bind to good cells too, where it causes the damage). These different complement sub-units all have different functions, but C3 is the most abundant in the complement system and some of the subunits of C3 such as C3b bind glycoprotein on cell surfaces. Any cells with C3b bound to their surfaces are targeted by white corpuscles and are phagocytized or eaten by the corpuscles which leads to more inflammation. C3a, another C3 subunit binds to other white blood cells, called basophils and mast cells, and causes them to release histamine (think of allergies here) which can lead to anaphylaxis and death. Besides cell lyses, complement causes a whole host of immune (think inflammation) responses as increased permeability of blood vessel walls, chemotaxis (drawing other white cells to the site), and triggers easy clotting of blood. Anyway it’s a complex system of interactions and you probably don't want to read a book about it. Basically, what the mad scientists are working on is a drug to prevent vascular damage which leads to vascular occlusion by blood clots and ultimately heat attack. You have probably read all the stuff on the link of chronic inflammation and heart attack. There are all kinds of lectins, but I think they are looking at a specific lectin found in plants (or some organism) that prevents all this by blocking C3b from binding to cell surfaces in the first place. Lectins bind sugars (glyco) in glycoprotiens so their lectin would compete with complement components for the glycoprotien sites on the cell surface and stop the accidental damage to vessel epithelial cells by the immune response and prevent a cardiac event in the long term. Anyway it’s a biochemical mechanism to prevent vascular inflammation, the most common cause of cardiac arrest.
w00t
i sound smart