Fengxin Lu

Harvard University, Cambridge, Massachusetts, United States

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Publications (10)34.42 Total impact

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    [Show abstract] [Hide abstract] ABSTRACT: Plasmodium falciparum-induced severe malaria remains a continuing problem in endemic areas, with elevated morbidity and mortality. Drugs targeting mechanisms involved in severe malaria pathology, including cytoadhesion of infected red blood cells (RBCs) to host receptors and production of pro-inflammatory cytokines, are still necessary. Human C1-inhibitor (C1INH) is a multifunctional protease inhibitor that regulates coagulation, vascular permeability and inflammation with beneficial effects in inflammatory disease models including septic shock. We found that human C1INH at therapeutically relevant doses blocks severe malaria pathogenic processes by two distinct mechanisms. First, C1INH bound to glycan moieties within P. falciparum glycosylphosphatidylinositol (PfGPI) molecules on the parasite surface, inhibiting parasite RBC invasion and pro-inflammatory cytokine production by parasite-stimulated monocytes in vitro, and reducing parasitemia in a rodent model of experimental cerebral malaria (ECM) in vivo. Second, C1INH bound to host CD36 and Chondroitin Sulfate-A molecules, interfering with cytoadhesion of infected RBCs by competitive binding to these receptors in vitro, and reducing sequestration in specific tissues and protecting against ECM in vivo. This study places C1INH as a potential therapeutic antimalarial molecule able to interfere with severe disease etiology at multiple levels through specific interactions with both parasite PfGPIs and host cell receptors.
    Full-text · Article · Sep 2015 · The Journal of Infectious Diseases
  • [Show abstract] [Hide abstract] ABSTRACT: Background: Activation of the complement system has been demonstrated to be an important mechanism in the mediation of myocardial ischemia and reperfusion (MIR) injury. C1 inhibitor (C1INH) has been shown to be beneficial in experimental MIR models. The underlying mechanism of this effect has been assumed to result primarily from inhibition of complement system activation. We recently demonstrated that C1INH plays a direct role in suppression of leukocyte transmigration in the mouse intestinal ischemia and reperfusion model. The purpose of this study was to investigate the mechanism of the beneficial effect of C1INH in mouse MIR model. Methods: C57BL/6, C1INH-deficient (C1INH(-/-)), and C3-deficient mice (C3(-/-)) were subjected to 30-min (C57BL/6 and C1INH(-/-)) or 60-min (C3(-/-)) occlusion of the left anterior descending branch of the coronary artery followed by 4-h reperfusion. C1INH or reactive center cleaved inactive C1INH (iC1INH) was injected intravenously 5 min before reperfusion. Results: Myocardial infarct size relative to the area at risk or relative to left ventricular area was significantly reduced in C1INH-treated wild-type, C1INH(-/-), and C3(-/-) mice compared with vehicle-treated mice. MIR induced an increase in myocardial polymorphonuclear neutrophil accumulation and plasma cardiac specific troponin I levels in vehicle-treated MIR mice, while C1INH treatment significantly attenuated these effects. iC1INH had a similar protective effect. Conclusions: These results suggested that C1INH prevented MIR injury in mice and that this cardioprotective effect may not solely result from complement inhibition, but might be also contributed by inhibiting leukocyte recruitment into ischemic tissue, an effect that is not mediated via protease inhibition.
    No preview · Article · Jun 2012 · Cardiovascular pathology: the official journal of the Society for Cardiovascular Pathology
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    Alvin E Davis · Fengxin Lu · Pedro Mejia
    [Show abstract] [Hide abstract] ABSTRACT: C1 inhibitor (C1INH) is a serpin that regulates both complement and contact (kallikrein-kinin) system activation. It consists of a serpin domain that is highly homologous to other serpins and an amino terminal non-serpin mucin-like domain. Deficiency of C1INH results in hereditary angioedema, a disease characterised by episodes of angioedema of the skin or the mucosa of the gastrointestinal tract or the oropharynx. Although early data suggested that angioedema was mediated via complement system activation, the preponderance of the data indicate that bradykinin is the mediator. In the past few years, it has become apparent that C1INH has additional anti-inflammatory functions independent of protease inhibition. These include interactions with leukocytes that may result in enhanced phagocytosis, with endothelial cells via E- and P-selectins that interfere with leukocyte rolling and in turn results in suppression of transmigration of leukocytes across the endothelium, and interactions with extracellular matrix components that may serve to concentrate C1INH at sites of inflammation. In addition, C1INH suppresses gram negative sepsis and endotoxin shock, partly via direct interaction with endotoxin that interferes with its interaction with macrophages, thereby suppressing tumour necrosis factor-a and other inflammatory mediators. C1INH treatment improves outcome in a number of disease models, including sepsis and other bacterial infections, possibly malaria, ischaemia-reperfusion injury (intestinal, hepatic, muscle, cardiac, brain), hyper-acute transplant rejection, and other inflammatory disease models. Recent data suggest that this effectiveness is the result of mechanisms that do not require protease inhibition, in addition to both complement and contact system activation.
    Full-text · Article · Nov 2010 · Thrombosis and Haemostasis
  • [Show abstract] [Hide abstract] ABSTRACT: The complement and contact systems may be involved in the pathophysiological process of inflammatory bowel disease (IBD). C1 inhibitor (C1INH) is the most important inhibitor of both the complement and contact systems. We evaluated the role of these systems and the effect of both active and inactive forms of C1INH (iC1INH) in dextran sulfate sodium (DSS)-induced colitis mouse model. Three percent DSS was used in drinking water to induce colitis in complement C3-deficient (C3(-/-)) mice, bradykinin type 2 receptor deficient (Bk(2)R(-/-)) mice, and C57BL/6 mice. After ten days DSS exposure, C3(-/-) mice exhibited markedly less weight loss than wild-type (WT) mice (12 +/- 3.3% vs. 30 +/- 1.2%, P < 0.05) and developed a milder disease-activity index (DAI), histological score, colon shortening, and myeloperoxidase (MPO) elevation (P < 0.05, respectively). The Bk(2)R(-/-) mice were not protected from the disease. Seven-day treatment with either native C1INH or iC1INH reduced the severity of the disease in WT mice, as indicated by decreased weight loss (15 +/- 1.8%, 14 +/- 2.1% vs. 30 +/- 1.2%, P < 0.05, respectively), DAI, intestinal tissue damage, and MPO elevation compared with untreated WT DSS control mice (P < 0.05, respectively). These findings suggest that complement plays a role in the development of DSS-induced colitis and that blockade of the complement system might be useful for the acute phase of IBD treatment. C1INH, however, leads to an amelioration of DSS-induced colitis via a mechanism that does not involve the inhibition of complement or contact system activation but does result in significant suppression of leukocyte infiltration.
    No preview · Article · Mar 2010 · AJP Gastrointestinal and Liver Physiology
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    Alvin E. Davis · Pedro Mejia · Fengxin Lu
    [Show abstract] [Hide abstract] ABSTRACT: Broadly speaking, C1 inhibitor plays important roles in the regulation of vascular permeability and in the suppression of inflammation. Vascular permeability control is exerted largely through inhibition of two of the proteases involved in the generation of bradykinin, factor XIIa and plasma kallikrein (the plasma kallikrein–kinin system). Anti-inflammatory functions, however, are exerted via several activities including inhibition of complement system proteases (C1r, C1s, MASP2) and the plasma kallikrein–kinin system proteases, in addition to interactions with a number of different proteins, cells and infectious agents. These more recently described, as yet incompletely characterized, activities serve several potential functions, including concentration of C1 inhibitor at sites of inflammation, inhibition of alternative complement pathway activation, inhibition of the biologic activities of gram negative endotoxin, enhancement of bacterial phagocytosis and killing, and suppression of the influx of leukocytes into a site of inflammation. C1 inhibitor has been shown to be therapeutically useful in a variety of animal models of inflammatory diseases, including gram negative bacterial sepsis and endotoxin shock, suppression of hyperacute transplant rejection, and treatment of a variety of ischemia-reperfusion injuries (heart, intestine, skeletal muscle, liver, brain). In humans, early data appear particularly promising in myocardial reperfusion injury. The mechanism (or mechanisms) of the effect of C1 inhibitor in these conditions is (are) not completely clear, but involve inhibition of complement and contact system activation, in addition to variable contributions from other C1 inhibitor activities that do not involve protease inhibition.
    Full-text · Article · Oct 2008 · Molecular Immunology
  • No preview · Article · Oct 2008 · Molecular Immunology
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    [Show abstract] [Hide abstract] ABSTRACT: Complement activation and neutrophil stimulation are two major components in events leading to ischemia and reperfusion (IR) injury. C1 inhibitor (C1INH) inhibits activation of each of the three pathways of complement activation and of the contact system. It is also endowed with anti-inflammatory properties that are independent of protease inhibition. The goal of these studies was to investigate the role and mechanism of C1INH in alleviating IR-induced intestinal injury. C57BL/6, C1INH-deficient (C1INH(-/-)), bradykinin type 2 receptor-deficient (Bk2R(-/-)), and C3-deficient mice (C3(-/-)) were randomized into three groups: sham operated control, IR, and IR + C1INH-treated groups. Ischemia was generated by occlusion of the superior mesenteric artery followed by reperfusion. C1INH or reactive center-cleaved inactive C1INH (iC1INH) was injected intravenously before reperfusion. IR resulted in intestinal injury in C57BL/6, C1INH(-/-), Bk2R(-/-), and C3(-/-) mice with significantly increased neutrophil infiltration into intestinal tissue. In each mouse strain, C1INH treatment reduced intestinal tissue injury and attenuated leukocyte infiltration compared with the untreated IR group. C1INH inhibited leukocyte rolling in the mesenteric veins of both C57BL/6 and C3-deficient mice subjected to IR. C1INH treatment also improved the survival rate of C57BL/6 and C1INH(-/-) mice following IR. Similar findings were observed in the IR animals treated with iC1INH. These studies emphasize the therapeutic benefit of C1INH in preventing intestinal injury caused by IR. In addition to the protective activities mediated via inhibition of the complement system, these studies indicate that C1INH also plays a direct role in suppression of leukocyte transmigration into reperfused tissue.
    Full-text · Article · Oct 2008 · AJP Gastrointestinal and Liver Physiology
  • No preview · Conference Paper · Oct 2008
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    [Show abstract] [Hide abstract] ABSTRACT: C1 inhibitor (C1INH) protects mice from lethal Gram-negative bacterial LPS-induced endotoxin shock and blocks the binding of LPS to the murine macrophage cell line, RAW 264.7, via an interaction with lipid A. Using the cecal ligation and puncture (CLP) model for sepsis in mice, treatment with C1INH improved survival in comparison with untreated controls. The effect was not solely the result of inhibition of complement and contact system activation because reactive center-cleaved, inactive C1INH (iC1INH) also was effective. In vivo, C1INH and iC1INH both reduced the number of viable bacteria in the blood and peritoneal fluid and accelerated killing of bacteria by blood neutrophils and peritoneal macrophages. In vitro, C1INH bound to bacteria cultured from blood or peritoneal fluid of mice with CLP-induced sepsis, but had no direct effect on bacterial growth. However, both C1INH and iC1INH enhanced the bactericidal activity of blood neutrophils and peritoneal exudate leukocytes. C1INH-deficient mice (C1INH-/- mice) subjected to CLP had a higher mortality than did wild-type littermate mice. Survival of C1INH-/- mice was significantly increased with two doses of C1INH, one given immediately following CLP, and the second at 6 h post-CLP. C1INH may be important in protection from sepsis through enhancement of bacterial uptake by, and/or bactericidal capacity of, phagocytes. Treatment with C1INH may provide a useful additional therapeutic approach in some patients with peritonitis and/or sepsis.
    Full-text · Article · Oct 2007 · The Journal of Immunology
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