Blockade of Thrombopoietin Reduces Organ Damage in Experimental Endotoxemia and Polymicrobial Sepsis

Abstract

Background and PurposeThrombopoietin (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.MethodsWe 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.ResultsIn 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.ConclusionOur 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 block...

Blood platelets and sepsis pathophysiology: A new therapeutic prospect in critical ill patients?

“…The main regulator of platelet production, TPO, is elevated in sepsis and related to the platelet count [ 262 , 263 ], which may be linked to the reduction in platelet mass or stimulation of TPO production by inflammatory mediators. Experimental models show that TPO neutralization reduces the severity of organ damage [ 264 ]. However, in the clinics, the potential benefit of TPO administration in thrombocytopenic patients in sepsis has been recently suggested [ 265 ].…”

Expert consensus on the diagnosis and treatment of thrombocytopenia in adult critical care patients in China

“…It is mainly used to treat postchemotherapy thrombocytopenia, ITP, AA, and hepatitisassociated thrombocytopenia [87][88][89][90][91]. Some studies showed that for sepsis-associated thrombocytopenia, TPO treatment improved platelet count and reduced platelet transfusion [92]; however, other studies showed that blocking thrombopoietin reduced organ damage associated with sepsis [93]. Therefore, the role of TPO is still controversial in terms of improving the prognosis of sepsis.…”

Development of platelets during steady state and inflammation

“…In this activity, STAT3 may act in an opposing way to STAT1. [93,94] Up-regulated by endotoxin [95,96] and acute infections (bacterial and viral) [97] Regulates HSC and platelet-biased HSC quiescence [19,98,99,100] Supports MK colony formation; increases MK size and polyploidization [101,102] Stimulates platelet production in mice and in men [101,103] SCF c-Kit; PI3K/Akt, ras/ ERK, SFK, PLC/ IP3/Ca 2+ /PKC [104] Not changed during bacterial sepsis [105]; up-regulated by IL-1b…”