Novel Therapeutic Approaches for Experimental Trauma-Haemorrhage.

Abstract

Haemorrhagic shock (HS) is commonly associated with trauma. Severe haemorrhage causes hypoperfusion of tissues resulting in a global ischaemic state, and resuscitation is performed to restore circulating volume. However, the return of oxygen to ischaemic tissues causes the induction of a systemic inflammatory response, which contributes to cell death leading to organ failure. In trauma patients, failure of more than four organs is linked to certain mortality, highlighting the need for interventions that may reduce or prevent the deterioration in organ function. The aim of this thesis was to investigate the effect of therapeutic approaches on the organ injury and dysfunction induced by HS. Briefly, male Wistar rats were subjected to haemorrhage by withdrawal of blood to reduce the mean arterial pressure to 35 ± 5 mmHg for 90 min. Followed by resuscitation with 20 ml/kg Ringer’s lactate for 10 min and 50% of the shed blood for 50 min. Organ function was determined 4 h after the onset of resuscitation. This model was used to investigate the effect of three different interventions on the organ injury and dysfunction induced. In the first study, administration of bone marrow-derived mononuclear cells (BMMNCs) upon resuscitation resulted in (1) significant attenuation of the organ injury and dysfunction associated with HS, and (2) restoration of the activation of the Akt pro-survival pathway. It is possible that these beneficial effects are mediated by paracrine mediators secreted by BMMNCs, which modulate this pathway, however injection of large numbers of cells is not practical in the acute setting of trauma. Therefore, in the next study erythropoietin (EPO) was used as a daily pre-treatment for three days prior to the induction of haemorrhage, as EPO is a known stimulus of endothelial progenitor cell (EPC) mobilisation. EPO pre-treatment resulted in (1) significant attenuation of the organ injury and dysfunction associated with HS, (2) mobilisation of EPCs (CD34+/flk-1+), and (3) activation of the Akt pro-survival pathway with enhanced activation of eNOS. However, when used clinically EPO is associated with an increased risk of thrombotic events, therefore in the final study a non-erythropoietic analogue of EPO was investigated. Treatment with pyroglutamate helix B surface peptide (pHBSP) resulted in (1) significant attenuation of the organ injury and dysfunction associated with HS, and (2) activation of the Akt pro-survival pathway with enhanced activation of both eNOS and STAT3. Additionally, late pHBSP treatment, up to 60 min after the onset of resuscitation, exerted the highest degree of protection. The findings of this thesis support the view that modulation of the Akt pro-survival pathway is a potential therapeutic target in the treatment of the ischaemia-reperfusion injury associated with severe haemorrhage and resuscitation.