title: Blockade of Thrombopoietin Reduces Organ Damage in Experimental Endotoxemia and Polymicrobial Sepsis.
abstract: OBJECTIVE
  Thrombopoietin (TPO), a growth factor primarily involved in thrombopoiesis may also have a role in the pathophysiology of sepsis. In patients with sepsis, indeed, TPO levels are markedly increased, with disease severity being the major independent determinant of TPO concentrations. Moreover, TPO increases and correlates with ex vivo indices of platelet activation in patients with burn injury upon sepsis development, and may contribute to depress cardiac contractility in septic shock. Still, the role of TPO in sepsis pathophysiology remains controversial, given the protective role of TPO in other experimental disease models, for instance in doxorubicin-induced cardiotoxicity and myocardial ischemia/reperfusion injury. The aim of our study was to define the contribution of TPO in the development of organ damage induced by endotoxemia or sepsis, and to investigate the effects of inhibiting TPO in these conditions.
  
  
  METHODS
  We synthesized a chimeric protein able to inhibit TPO, mTPOR-MBP, and studied its effect in two murine experimental models, acute endotoxemia and cecal ligation and puncture (CLP) model.
  
  
  RESULTS
  In both models, TPO levels markedly increased, from 289.80±27.87 pg/mL to 465.60±45.92 pg/mL at 3 hours in the LPS model (P<0.01), and from 265.00±26.02 pg/mL to 373.70±26.20 pg/mL in the CLP model (P<0.05), respectively. Paralleling TPO levels, also platelet-monocyte aggregates increased, from 32.86±2.48% to 46.13±1.39% at 3 hours in the LPS model (P<0.01), and from 43.68±1.69% to 56.52±4.66% in the CLP model (P<0.05). Blockade of TPO by mTPOR-MBP administration reduced histological damage in target organs, namely lung, liver, and gut. In particular, neutrophil infiltration and lung septal thickening were reduced from a score of 1.86±0.34 to 0.60±0.27 (P<0.01) and from 1.43±0.37 to 0.40±0.16 (P<0.05), respectively, in the LPS model at 3 hours, and from a score of 1.75±0.37 to 0.38±0.18 (P<0.01) and from 1.25±0.31 to 0.13±0.13 (P<0.001), respectively, in the CLP model. Similarly, the number of hepatic microabscesses was decreased from 14.14±1.41 to 3.64±0.56 in the LPS model at 3 hours (P<0.001), and from 1.71±0.29 to 0.13±0.13 in the CLP model (P<0.001). Finally, the diameter of intestinal villi decreased from 90.69±3.95 μm to 70.74±3.60 μm in the LPS model at 3 hours (P<0.01), and from 74.29±4.29 μm to 57.50±1.89 μm in the CLP model (P<0.01). This protective effect was associated with the blunting of the increase in platelet-monocyte adhesion, and, on the contrary, with increased platelet-neutrophil aggregates in the circulation, which may be related to decreased neutrophil sequestration into the inflamed tissues. Conversely, circulating cytokine levels were not significantly changed, in both models, by mTPOR-MBP administration.
  
  
  CONCLUSIONS
  Our results demonstrate that TPO participates in the development of organ damage induced by experimental endotoxemia or polymicrobial sepsis via a mechanism involving increased platelet-leukocyte adhesion, but not cytokine release, and suggest that blocking TPO may be useful in preventing organ damage in patients affected by systemic inflammatory response or sepsis.
authors.affiliation: Department of Medical Sciences, University of Turin, Turin, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Cuccurullo
authors.affiliation: Department of Medical Sciences, University of Turin, Turin, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Greco
authors.affiliation: Department of Medical Sciences, University of Turin, Turin, Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Lupia
authors.affiliation: Anatomia Patologica, San Lazzaro Hospital, Alba, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: De Giuli
authors.affiliation: Department of Medical Sciences, University of Turin, Turin, Italy.
authors.forename: Ornella
authors.initials: O
authors.lastname: Bosco
authors.affiliation: Department of Anaesthesiology and Critical Care, University of Turin, Turin, Italy.
authors.forename: Erica
authors.initials: E
authors.lastname: Martin-Conte
authors.affiliation: Department of Medical Sciences, University of Turin, Turin, Italy.
authors.forename: Tiziana
authors.initials: T
authors.lastname: Spatola
authors.affiliation: Department of Genetics, Biology and Biochemistry, University of Turin, Turin, Italy.
authors.forename: Emilia
authors.initials: E
authors.lastname: Turco
authors.affiliation: Department of Medical Sciences, University of Turin, Turin, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Montrucchio
mesh_terms: D000818:Animals; D019446:Endotoxemia / Q000188:drug therapy* / Q000378:metabolism; D006801:Humans; D008297:Male; D058619:Maltose-Binding Proteins / Q000235:genetics / Q000494:pharmacology*; D051379:Mice; D053628:Receptors, Thrombopoietin; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000494:pharmacology; D013926:Thrombopoietin / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D058619:Maltose-Binding Proteins; C481270:Mpl protein, mouse; D053628:Receptors, Thrombopoietin; D011993:Recombinant Fusion Proteins; D013926:Thrombopoietin