Sepsis-induced cardiac dysfunction: Pathophysiology and experimental treatments
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The severity of cardiac dysfunction predicts mortality in septic patients. In this thesis, I have investigated the pathophysiology and the novel therapeutic strategy to attenuate cardiac dysfunction in experimental sepsis. I have developed a model of cardiac dysfunction caused by lipopolysaccharide (LPS)/peptidoglycan (PepG) co-administration or polymicrobial sepsis in young and old, male and female mice. There is good evidence that females tolerate sepsis better than males. Here, I have demonstrated for the first time that the cardiac dysfunction caused by sepsis was less pronounced in female than in male mice; this protection was associated with cardiac activation of a pro-survival pathway [Akt and endothelial nitric oxide synthase], and the decreased activation of a pro-inflammatory signalling pathway [nuclear factor (NF)-κB]. Patients with chronic kidney disease (CKD) requiring dialysis have a higher risk of sepsis and a 100-fold higher mortality. Activation of NF-κB is associated with sepsis-induced cardiac dysfunction and NF-κB is activated by IκB kinase (IKK). Here, I have shown that 5/6th nephrectomy for 8 weeks caused a small, but significant, cardiomyopathy, cardiac activation of NF-κB and expression of inducible nitric oxide synthase (iNOS). When subjected to LPS or polymicrobial sepsis, CKD mice exhibited exacerbation of cardiac dysfunction and cardiac activation of NF-κB and iNOS expression, which were attenuated by a specific IKK inhibitor (IKK 16). Thus, selective inhibition of IKK may represent a novel therapeutic approach for the sepsis-induced cardiac dysfunction in CKD patients. Activation of transient receptor potential vanilloid receptor type 1 (TRPV1) improves outcome in sepsis/endotoxaemia. The identity of the endogenous activators of TRPV1 and the role of the channel in the cardiac dysfunction caused by sepsis/endotoxaemia is unknown. Here, I have shown that activation of TRPV1 by 12-(S)-HpETE and 20-HETE (potent ligands of TRPV1) leads to the release of calcitonin gene-related peptide (downstream mediator of TRPV1 activation), which protects the heart against the cardiac dysfunction caused by LPS.
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