Is strengthening the endothelial barrier a therapeutic strategy for Ebola?

Open AccessPublished:May 26, 2015DOI:https://doi.org/10.1016/j.ijid.2015.05.016

      1. Introduction

      In a provocative article published in this issue, Fedson and Rordam argue that statins and angiotensin II receptor blockers (ARBs) could be used as therapeutic agents in Ebola virus disease (EVD). The authors assert that the loss of vascular integrity represents a critical step in the pathophysiology of EVD, leading to hypovolemia and multi-organ failure. Since every blood vessel in the body is lined by endothelial cells and since, according to the authors, statins and ARBs work to maintain or enhance endothelial barrier integrity, these drugs might keep the patient alive long enough for the immune system to clear the virus. Essentially, this strategy seeks to modulate the host response to the infection rather than combating the virus itself. The authors point out that the loss of vascular integrity that is characteristic of human EVD is not reproduced in most animal models. Because of this, the authors note that the notion of targeting endothelial activation or leak in EVD has not been widely accepted. In this editorial we will address the biological plausibility of this approach and then address the clinical evidence of its efficacy.

      2. Biological plausibility

      The premise that the endothelium is critical to the pathogenesis of severe infections is not new. In animal models of bacterial sepsis, endothelial cell activation and increased endothelial permeability contribute to mortality.
      • Goldenberg N.M.
      • Steinberg B.E.
      • Slutsky A.S.
      • Lee W.L.
      Broken barriers: a new take on sepsis pathogenesis.
      • London N.R.
      • Zhu W.
      • Bozza F.A.
      • Smith M.C.
      • Greif D.M.
      • Sorensen L.K.
      • et al.
      Targeting Robo4-dependent Slit signaling to survive the cytokine storm in sepsis and influenza.
      Similar findings have been reported in certain viral infections.
      • Steinberg B.
      • Goldenberg N.
      • Lee W.
      Do viral infections mimic bacterial sepsis? The role of microvascular permeability: a review of mechanisms and methods.
      For instance, activation of the endothelium is critical to the pathogenesis of influenza,
      • Teijaro J.R.
      • Walsh K.B.
      • Cahalan S.
      • Fremgen D.M.
      • Roberts E.
      • Scott F.
      • et al.
      Endothelial cells are central orchestrators of cytokine amplification during influenza virus infection.
      and we and others have reported on the importance of lung endothelial barrier integrity in murine models of influenza virus- induced acute lung injury.
      • London N.R.
      • Zhu W.
      • Bozza F.A.
      • Smith M.C.
      • Greif D.M.
      • Sorensen L.K.
      • et al.
      Targeting Robo4-dependent Slit signaling to survive the cytokine storm in sepsis and influenza.
      • Armstrong S.M.
      • Wang C.
      • Tigdi J.
      • Si X.
      • Dumpit C.
      • Charles S.
      • et al.
      Influenza infects lung microvascular endothelium leading to microvascular leak: role of apoptosis and claudin-5.
      • Wang C.
      • Armstrong S.M.
      • Sugiyama M.G.
      • Tabuchi A.
      • Krauszman A.
      • Kuebler W.M.
      • et al.
      Influenza primes human lung microvascular endothelium to leak upon exposure to Staphylococcus aureus.
      Diarrhea and poor oral intake are major contributors to the hypovolemia that characterizes human cases of EVD;
      • Johnson D.W.
      • Sullivan J.N.
      • Piquette C.A.
      • Hewlett A.L.
      • Bailey K.L.
      • Smith P.W.
      • et al.
      Lessons learned: critical care management of patients with Ebola in the United States.
      • Schieffelin J.S.
      • Shaffer J.G.
      • Goba A.
      • Gbakie M.
      • Gire S.K.
      • Colubri A.
      • et al.
      Clinical illness and outcomes in patients with Ebola in Sierra Leone.
      however, the loss of endothelial barrier integrity may also contribute. While viral infection of the endothelium itself could conceivably cause endothelial leak, in vitro experiments,
      • Geisbert T.W.
      • Young H.A.
      • Jahrling P.B.
      • Davis K.J.
      • Larsen T.
      • Kagan E.
      • et al.
      Pathogenesis of Ebola hemorrhagic fever in primate models: evidence that hemorrhage is not a direct effect of virus-induced cytolysis of endothelial cells.
      as well as necropsy studies on cynomolgus monkeys
      • Ikegami T.
      • Miranda M.E.
      • Calaor A.B.
      • Manalo D.L.
      • Miranda N.J.
      • Niikura M.
      • et al.
      Histopathology of natural Ebola virus subtype Reston infection in cynomolgus macaques during the Philippine outbreak in 1996.
      and autopsy studies on human patients,
      • Martines R.B.
      • Ng D.L.
      • Greer P.W.
      • Rollin P.E.
      • Zaki S.R.
      Tissue and cellular tropism, pathology and pathogenesis of Ebola and Marburg viruses.
      suggest that this occurs only late in the disease. However, monocytes are an early target of the Ebola virus,
      • Bray M.
      • Geisbert T.W.
      Ebola virus: the role of macrophages and dendritic cells in the pathogenesis of Ebola hemorrhagic fever.
      and the massive activation of these cells and macrophages results in the secretion of pro-inflammatory cytokines
      • Baize S.
      • Leroy E.M.
      • Georges A.J.
      • Georges-Courbot M.C.
      • Capron M.
      • Bedjabaga I.
      • et al.
      Inflammatory responses in Ebola virus-infected patients.
      • Wauquier N.
      • Becquart P.
      • Padilla C.
      • Baize S.
      • Leroy E.M.
      Human fatal Zaire Ebola virus infection is associated with an aberrant innate immunity and with massive lymphocyte apoptosis.
      that can increase endothelial permeability. In addition, secreted Ebola virus glycoproteins have both direct and paracrine effects, including inducing endothelial cell activation, loss of cellular adhesion, and direct cytotoxicity.
      • Yang Z.
      • Delgado R.
      • Xu L.
      • Todd R.F.
      • Nabel E.G.
      • Sanchez A.
      • et al.
      Distinct cellular interactions of secreted and transmembrane Ebola virus glycoproteins.
      • Yang Z.Y.
      • Duckers H.J.
      • Sullivan N.J.
      • Sanchez A.
      • Nabel E.G.
      • Nabel G.J.
      Identification of the Ebola virus glycoprotein as the main viral determinant of vascular cell cytotoxicity and injury.
      • Simmons G.
      • Wool-Lewis R.J.
      • Baribaud F.
      • Netter R.C.
      • Bates P.
      Ebola virus glycoproteins induce global surface protein down-modulation and loss of cell adherence.
      • Escudero-Perez B.
      • Volchkova V.A.
      • Dolnik O.
      • Lawrence P.
      • Volchkov V.E.
      • Shed G.P.
      of Ebola virus triggers immune activation and increased vascular permeability.
      Finally, a recent study in mice reported that genes associated with endothelial signaling and vascular leakage correlated with resistance to a mouse-adapted strain of Ebola.
      • Rasmussen A.L.
      • Okumura A.
      • Ferris M.T.
      • Green R.
      • Feldmann F.
      • Kelly S.M.
      • et al.
      Host genetic diversity enables Ebola hemorrhagic fever pathogenesis and resistance.
      Together, these observations suggest an important and perhaps unappreciated role for the endothelium in the pathogenesis of EVD.

      3. Evidence of efficacy

      In their article, Fedson and Rordam present data from a case series of approximately 100 consecutive patients in Sierra Leone treated for six or more days with a combination of atorvastatin 40 mg and irbesartan 150 mg daily. Remarkably, the authors report that “(o)nly two… died”. While intriguing, these observations must be interpreted cautiously. Importantly, no information is provided as to the oversight and consent processes and no control data are available—a particular shortcoming given that EVD mortality varies significantly in different clinical contexts.
      • Cenciarelli O.
      • Pietropaoli S.
      • Malizia A.
      • Carestia M.
      • D'Amico F.
      • Sassolini A.
      • et al.
      Ebola virus disease 2013–2014 outbreak in West Africa: an analysis of the epidemic spread and response.
      • Spencer C.
      Having and fighting Ebola—public health lessons from a clinician turned patient.
      The authors provide very little detail about these patients, making a critical appraisal of the results difficult. Other published case series emphasize the importance of adequate fluid and electrolyte replacement,
      • Schieffelin J.S.
      • Shaffer J.G.
      • Goba A.
      • Gbakie M.
      • Gire S.K.
      • Colubri A.
      • et al.
      Clinical illness and outcomes in patients with Ebola in Sierra Leone.
      and it is unclear whether statins and/or ARBs would confer additional benefit in the setting of optimal supportive care.
      Furthermore, we are unsure whether statins and ARBs can actually improve endothelial leak or activation in vivo. Statins have been suggested to have pleiotropic anti-inflammatory effects (reviewed by Tousoulis et al.
      • Tousoulis D.
      • Psarros C.
      • Demosthenous M.
      • Patel R.
      • Antoniades C.
      • Stefanadis C.
      Innate and adaptive inflammation as a therapeutic target in vascular disease: the emerging role of statins.
      ), including the ability to modulate endothelial activation in sepsis,
      • Kouroumichakis I.
      • Papanas N.
      • Proikaki S.
      • Zarogoulidis P.
      • Maltezos E.
      Statins in prevention and treatment of severe sepsis and septic shock.
      and observational trials initially suggested that statin therapy had a protective effect in this context (see meta-analysis by Wan et al.
      • Wan Y.D.
      • Sun T.W.
      • Kan Q.C.
      • Guan F.X.
      • Zhang S.G.
      Effect of statin therapy on mortality from infection and sepsis: a meta-analysis of randomized and observational studies.
      ). Unfortunately, randomized controlled trials do not support this hypothesis. Indeed, in the trial cited by Fedson and Rordam in which statin-naïve septic patients were treated with atorvastatin, there was no difference in the length of hospital stay or the mortality rate between treatment and control groups.
      • Patel J.M.
      • Snaith C.
      • Thickett D.R.
      • Linhartova L.
      • Melody T.
      • Hawkey P.
      • et al.
      Randomized double-blind placebo-controlled trial of 40 mg/day of atorvastatin in reducing the severity of sepsis in ward patients (ASEPSIS Trial).
      Other larger trials have shown that statins do not alter mortality
      • Kruger P.
      • Bailey M.
      • Bellomo R.
      • Cooper D.J.
      • Harward M.
      • Higgins A.
      • et al.
      A multicenter randomized trial of atorvastatin therapy in intensive care patients with severe sepsis.
      from sepsis or the acute respiratory distress syndrome.
      • McAuley D.F.
      • Laffey J.G.
      • O’Kane C.M.
      • Perkins G.D.
      • Mullan B.
      • Trinder T.J.
      • et al.
      Simvastatin in the acute respiratory distress syndrome.
      Several meta-analyses now suggest that statins do not have clinically significant effects on the outcome of severe infection.
      • Wan Y.D.
      • Sun T.W.
      • Kan Q.C.
      • Guan F.X.
      • Zhang S.G.
      Effect of statin therapy on mortality from infection and sepsis: a meta-analysis of randomized and observational studies.
      • Thomas G.
      • Hraiech S.
      • Loundou A.
      • Truwit J.
      • Kruger P.
      • McAuley D.F.
      • et al.
      Statin therapy in critically-ill patients with severe sepsis: a review and meta-analysis of randomized clinical trials.
      • Deshpande A.
      • Pasupuleti V.
      • Rothberg M.B.
      Statin therapy and mortality from sepsis: a meta-analysis of randomized trials.
      The literature on ARBs as modulators of endothelial permeability is not as complete. Angiotensin II has potent effects on the vascular endothelium (reviewed by Salgado et al.
      • Salgado D.R.
      • Rocco J.R.
      • Silva E.
      • Vincent J.L.
      Modulation of the renin–angiotensin–aldosterone system in sepsis: a new therapeutic approach?.
      ); for instance, in rat tissue, angiotensin II modulates vascular leak,
      • Newton C.R.
      • Curran B.
      • Victorino G.P.
      Angiotensin II type 1 receptor activation increases microvascular permeability via a calcium dependent process.
      while mice deficient in Angiotensin Converting Enzyme, the enzyme that generates angiotensin II, exhibit reduced susceptibility to acute lung injury.
      • Imai Y.
      • Kuba K.
      • Rao S.
      • Huan Y.
      • Guo F.
      • Guan B.
      • et al.
      Angiotensin-converting enzyme 2 protects from severe acute lung failure.
      Consistent with these findings, ARBs have been shown to have lung-protective effects in a murine model of sepsis.
      • Shen L.
      • Mo H.
      • Cai L.
      • Kong T.
      • Zheng W.
      • Ye J.
      • et al.
      Losartan prevents sepsis-induced acute lung injury and decreases activation of nuclear factor κB and mitogen-activated protein kinases.
      However, there are no data from randomized controlled trials in humans with sepsis or lung injury. Human genetic studies suggest that a polymorphism that would be expected to attenuate angiotensin II signaling is actually associated with lower blood pressure and increased mortality from sepsis.
      • Nakada T.A.
      • Russell J.A.
      • Boyd J.H.
      • McLaughlin L.
      • Nakada E.
      • Thair S.A.
      • et al.
      Association of angiotensin II type 1 receptor-associated protein gene polymorphism with increased mortality in septic shock.
      From a practical standpoint, ARBs could be dangerous in severe infections, as inhibition of angiotensin II signaling could contribute to renal insult
      • Plataki M.
      • Kashani K.
      • Cabello-Garza J.
      • Maldonado F.
      • Kashyap R.
      • Kor D.J.
      • et al.
      Predictors of acute kidney injury in septic shock patients: an observational cohort study.
      and hemodynamic instability.
      • Salgado D.R.
      • Rocco J.R.
      • Silva E.
      • Vincent J.L.
      Modulation of the renin–angiotensin–aldosterone system in sepsis: a new therapeutic approach?.
      Ultimately, the efficacy of statins and ARBs for EVD cannot be properly evaluated without a formal, well-designed clinical trial. Nonetheless, modulation of the endothelial response to Ebola infection is a potentially promising approach that merits further investigation. Finally, the development of better animal models for Ebola-mediated vascular leak could be an important next step towards the development of future therapeutics.

      Acknowledgements

      Research in WLL's laboratory is supported by the Canadian Institutes of Health Research (MOP130564).
      Conflict of interest:.

      References

        • Goldenberg N.M.
        • Steinberg B.E.
        • Slutsky A.S.
        • Lee W.L.
        Broken barriers: a new take on sepsis pathogenesis.
        Sci Transl Med. 2011; 3: 88ps25
        • London N.R.
        • Zhu W.
        • Bozza F.A.
        • Smith M.C.
        • Greif D.M.
        • Sorensen L.K.
        • et al.
        Targeting Robo4-dependent Slit signaling to survive the cytokine storm in sepsis and influenza.
        Sci Transl Med. 2010; 2: 23ra19
        • Steinberg B.
        • Goldenberg N.
        • Lee W.
        Do viral infections mimic bacterial sepsis? The role of microvascular permeability: a review of mechanisms and methods.
        Antiviral Res. 2012; 93: 2-15
        • Teijaro J.R.
        • Walsh K.B.
        • Cahalan S.
        • Fremgen D.M.
        • Roberts E.
        • Scott F.
        • et al.
        Endothelial cells are central orchestrators of cytokine amplification during influenza virus infection.
        Cell. 2011; 146: 980-991
        • Armstrong S.M.
        • Wang C.
        • Tigdi J.
        • Si X.
        • Dumpit C.
        • Charles S.
        • et al.
        Influenza infects lung microvascular endothelium leading to microvascular leak: role of apoptosis and claudin-5.
        PLoS One. 2012; 7: e47323
        • Wang C.
        • Armstrong S.M.
        • Sugiyama M.G.
        • Tabuchi A.
        • Krauszman A.
        • Kuebler W.M.
        • et al.
        Influenza primes human lung microvascular endothelium to leak upon exposure to Staphylococcus aureus.
        Am J Respir Cell Mol Biol. 2015 Feb 18; ([Epub ahead of print])
        • Johnson D.W.
        • Sullivan J.N.
        • Piquette C.A.
        • Hewlett A.L.
        • Bailey K.L.
        • Smith P.W.
        • et al.
        Lessons learned: critical care management of patients with Ebola in the United States.
        Crit Care Med. 2015; 43: 1157-1164
        • Schieffelin J.S.
        • Shaffer J.G.
        • Goba A.
        • Gbakie M.
        • Gire S.K.
        • Colubri A.
        • et al.
        Clinical illness and outcomes in patients with Ebola in Sierra Leone.
        N Engl J Med. 2014; 371: 2092-2100
        • Geisbert T.W.
        • Young H.A.
        • Jahrling P.B.
        • Davis K.J.
        • Larsen T.
        • Kagan E.
        • et al.
        Pathogenesis of Ebola hemorrhagic fever in primate models: evidence that hemorrhage is not a direct effect of virus-induced cytolysis of endothelial cells.
        Am J Pathol. 2003; 163: 2371-2382
        • Ikegami T.
        • Miranda M.E.
        • Calaor A.B.
        • Manalo D.L.
        • Miranda N.J.
        • Niikura M.
        • et al.
        Histopathology of natural Ebola virus subtype Reston infection in cynomolgus macaques during the Philippine outbreak in 1996.
        Exp Anim. 2002; 51: 447-455
        • Martines R.B.
        • Ng D.L.
        • Greer P.W.
        • Rollin P.E.
        • Zaki S.R.
        Tissue and cellular tropism, pathology and pathogenesis of Ebola and Marburg viruses.
        J Pathol. 2015; 235: 153-174
        • Bray M.
        • Geisbert T.W.
        Ebola virus: the role of macrophages and dendritic cells in the pathogenesis of Ebola hemorrhagic fever.
        Int J Biochem Cell Biol. 2005; 37: 1560-1566
        • Baize S.
        • Leroy E.M.
        • Georges A.J.
        • Georges-Courbot M.C.
        • Capron M.
        • Bedjabaga I.
        • et al.
        Inflammatory responses in Ebola virus-infected patients.
        Clin Exp Immunol. 2002; 128: 163-168
        • Wauquier N.
        • Becquart P.
        • Padilla C.
        • Baize S.
        • Leroy E.M.
        Human fatal Zaire Ebola virus infection is associated with an aberrant innate immunity and with massive lymphocyte apoptosis.
        PLoS Negl Trop Dis. 2010; 4: e837
        • Yang Z.
        • Delgado R.
        • Xu L.
        • Todd R.F.
        • Nabel E.G.
        • Sanchez A.
        • et al.
        Distinct cellular interactions of secreted and transmembrane Ebola virus glycoproteins.
        Science. 1998; 279: 1034-1037
        • Yang Z.Y.
        • Duckers H.J.
        • Sullivan N.J.
        • Sanchez A.
        • Nabel E.G.
        • Nabel G.J.
        Identification of the Ebola virus glycoprotein as the main viral determinant of vascular cell cytotoxicity and injury.
        Nat Med. 2000; 6: 886-889
        • Simmons G.
        • Wool-Lewis R.J.
        • Baribaud F.
        • Netter R.C.
        • Bates P.
        Ebola virus glycoproteins induce global surface protein down-modulation and loss of cell adherence.
        J Virol. 2002; 76: 2518-2528
        • Escudero-Perez B.
        • Volchkova V.A.
        • Dolnik O.
        • Lawrence P.
        • Volchkov V.E.
        • Shed G.P.
        of Ebola virus triggers immune activation and increased vascular permeability.
        PLoS Pathog. 2014; 10: e1004509
        • Rasmussen A.L.
        • Okumura A.
        • Ferris M.T.
        • Green R.
        • Feldmann F.
        • Kelly S.M.
        • et al.
        Host genetic diversity enables Ebola hemorrhagic fever pathogenesis and resistance.
        Science. 2014; 346: 987-991
        • Cenciarelli O.
        • Pietropaoli S.
        • Malizia A.
        • Carestia M.
        • D'Amico F.
        • Sassolini A.
        • et al.
        Ebola virus disease 2013–2014 outbreak in West Africa: an analysis of the epidemic spread and response.
        Int J Microbiol. 2015; 2015: 769121
        • Spencer C.
        Having and fighting Ebola—public health lessons from a clinician turned patient.
        N Engl J Med. 2015; 372: 1089-1091
        • Tousoulis D.
        • Psarros C.
        • Demosthenous M.
        • Patel R.
        • Antoniades C.
        • Stefanadis C.
        Innate and adaptive inflammation as a therapeutic target in vascular disease: the emerging role of statins.
        J Am Coll Cardiol. 2014; 63: 2491-2502
        • Kouroumichakis I.
        • Papanas N.
        • Proikaki S.
        • Zarogoulidis P.
        • Maltezos E.
        Statins in prevention and treatment of severe sepsis and septic shock.
        Eur J Intern Med. 2011; 22: 125-133
        • Wan Y.D.
        • Sun T.W.
        • Kan Q.C.
        • Guan F.X.
        • Zhang S.G.
        Effect of statin therapy on mortality from infection and sepsis: a meta-analysis of randomized and observational studies.
        Crit Care. 2014; 18: R71
        • Patel J.M.
        • Snaith C.
        • Thickett D.R.
        • Linhartova L.
        • Melody T.
        • Hawkey P.
        • et al.
        Randomized double-blind placebo-controlled trial of 40 mg/day of atorvastatin in reducing the severity of sepsis in ward patients (ASEPSIS Trial).
        Crit Care. 2012; 16: R231
        • Kruger P.
        • Bailey M.
        • Bellomo R.
        • Cooper D.J.
        • Harward M.
        • Higgins A.
        • et al.
        A multicenter randomized trial of atorvastatin therapy in intensive care patients with severe sepsis.
        Am J Respir Crit Care Med. 2013; 187: 743-750
        • McAuley D.F.
        • Laffey J.G.
        • O’Kane C.M.
        • Perkins G.D.
        • Mullan B.
        • Trinder T.J.
        • et al.
        Simvastatin in the acute respiratory distress syndrome.
        N Engl J Med. 2014; 371: 1695-1703
        • Thomas G.
        • Hraiech S.
        • Loundou A.
        • Truwit J.
        • Kruger P.
        • McAuley D.F.
        • et al.
        Statin therapy in critically-ill patients with severe sepsis: a review and meta-analysis of randomized clinical trials.
        Minerva Anestesiol. 2015 Feb 18; ([Epub ahead of print])
        • Deshpande A.
        • Pasupuleti V.
        • Rothberg M.B.
        Statin therapy and mortality from sepsis: a meta-analysis of randomized trials.
        Am J Med. 2015; 128 (410–7.e1)
        • Salgado D.R.
        • Rocco J.R.
        • Silva E.
        • Vincent J.L.
        Modulation of the renin–angiotensin–aldosterone system in sepsis: a new therapeutic approach?.
        Expert Opin Ther Targets. 2010; 14: 11-20
        • Newton C.R.
        • Curran B.
        • Victorino G.P.
        Angiotensin II type 1 receptor activation increases microvascular permeability via a calcium dependent process.
        J Surg Res. 2005; 123: 33-39
        • Imai Y.
        • Kuba K.
        • Rao S.
        • Huan Y.
        • Guo F.
        • Guan B.
        • et al.
        Angiotensin-converting enzyme 2 protects from severe acute lung failure.
        Nature. 2005; 436: 112-116
        • Shen L.
        • Mo H.
        • Cai L.
        • Kong T.
        • Zheng W.
        • Ye J.
        • et al.
        Losartan prevents sepsis-induced acute lung injury and decreases activation of nuclear factor κB and mitogen-activated protein kinases.
        Shock. 2009; 31: 500-506
        • Nakada T.A.
        • Russell J.A.
        • Boyd J.H.
        • McLaughlin L.
        • Nakada E.
        • Thair S.A.
        • et al.
        Association of angiotensin II type 1 receptor-associated protein gene polymorphism with increased mortality in septic shock.
        Crit Care Med. 2011; 39: 1641-1648
        • Plataki M.
        • Kashani K.
        • Cabello-Garza J.
        • Maldonado F.
        • Kashyap R.
        • Kor D.J.
        • et al.
        Predictors of acute kidney injury in septic shock patients: an observational cohort study.
        Clin J Am Soc Nephrol. 2011; 6: 1744-1751