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Rat Heterotopic Abdominal Heart/Single-lung Transplantation in a Volume-loaded Configuration

Herein, we describe a novel technique for heterotopic abdominal heart-lung transplantation (HAHLT) in rats. The configuration of the transplant graft ...

UBC James Hogg Research Center, St. Paul's Hospital

Hypotension and hypoperfusion during septic shock may contribute to tissue hypoxia and the intramyocardial inflammatory response that results in myocardial dysfunction. Therefore, we hypothesized that crystalloid or colloid resuscitation may alter myocardial dysfunction.

Albumin resuscitation increases cardiomyocyte contractility and decreases nitric oxide synthase II expression in rat endotoxemia.

The transmembrane receptor family of Toll-like receptors (TLRs) may play a role in initiating early inflammatory and functional responses to danger signals arising from ischemia-reperfusion and inflammatory stimuli. We determined whether Toll-like receptors are expressed in cardiac tissue and whether stimulation with cognate ligands would result in a pro-inflammatory response and decreased cardiomyocyte contractility.

Toll-like receptor stimulation in cardiomyoctes decreases contractility and initiates an NF-kappaB dependent inflammatory response.

Fluid resuscitation to improve delivery of oxygen to vital organs is a principal clinical intervention for septic patients. We previously reported that albumin resuscitation in rat endotoxemia improved contractility in isolated cardiomyocytes, but whether this effect occurs in vivo is unknown. We hypothesized that albumin resuscitation would improve decreased ventricular contractility and myocardial tissue oxygenation in vivo.

Albumin resuscitation improves ventricular contractility and myocardial tissue oxygenation in rat endotoxemia.

Cardiovascular dysfunction as a result of sepsis is the leading cause of death in the critically ill. Cardiomyocytes respond to infectious pathogens with a Toll-like receptor-initiated proinflammatory response in conjunction with a decrease in contractility, although the downstream events linking Toll-like receptor activation and reduced cardiac contractility remain to be elucidated. Using microarray analysis of cardiac tissue exposed to systemic lipopolysaccharide (LPS), we discovered that 2 small calcium-regulating proteins (S100A8 and S100A9) are highly upregulated. HL-1 cardiomyocytes, isolated primary cardiomyocytes, and live mice were exposed to LPS, whereas beating HL-1 cells had S100A8 and S100A9 overexpressed and their calcium flux quantified. Using in vivo microbubble technology, we delivered S100A8 and S100A9 to normal mouse hearts; using the same technology, we inhibited S100A9 production in mouse hearts and subsequently exposed them to LPS. Coimmunoprecipitation of S100A8 and S100A9 identified interaction with RAGE (the receptor for advanced glycation end products), the cardiac function and postreceptor signaling of which were investigated. HL-1 cardiomyocytes, isolated primary cardiomyocytes, and whole hearts exposed to LPS have large increases in S100A8 and S100A9. Cardiac overexpression of S100A8 and S100A9 led to a RAGE-dependent decrease in calcium flux and, in the intact mouse, to a decreased cardiac ejection fraction, whereas knockdown of S100A9 attenuated LPS-induced cardiac dysfunction. Cardiomyocytes exposed to LPS express S100A8 and S100A9, leading to a RAGE-mediated decrease in cardiomyocyte contractility. This finding provides a novel mechanistic link between circulating pathogen-associated molecular products and subsequent cardiac dysfunction.

S100A8 and S100A9 mediate endotoxin-induced cardiomyocyte dysfunction via the receptor for advanced glycation end products.

The early use of vasopressors in sepsis has been associated with a decrease in immune activation independent of hemodynamic effects, although the mechanism behind this remains unclear. We hypothesize that low dose vasopressin will reduce the pulmonary inflammation associated with sepsis. Our aims were to (1) determine whether vasopressin reduces lipopolysaccharide (LPS)-induced pulmonary inflammation and (2) determine which vasopressin receptor is responsible for pulmonary immune modulation. Mice were treated with intraperitoneal LPS to induce both systemic and pulmonary inflammation. Vasopressin or saline was infused via peritoneal pump and interleukin 6 (IL-6) in lung and serum was measured at 6h. NF-kappaB activation as was determined in the lung through immunoblotting total and phospho-IkappaB. Hemodynamic data was also obtained at the 6h mark. In a separate series of experiments mice received both LPS and vasopressin infusion following pretreatment with vasopressin receptor antagonists to V1R, V2R and OTR. Low dose LPS dramatically raises both serum IL-6 and pulmonary levels of IL-6 and phospho-IkappaB despite no significant changes in mean arterial pressure at 6h. Compared to saline, vasopressin infusion significantly decreases both the pulmonary IL-6 levels and phospho-IkappaB in LPS treated mice without raising arterial pressure. Pretreatment with V2R antagonist results in complete attenuation of vasopressin's immunosuppressive effects, with restoration of pulmonary IL-6 and phospho-IkappaB levels to those seen with LPS alone.

Vasopressin decreases sepsis-induced pulmonary inflammation through the V2R.

Arginine vasopressin is a vasoactive drug commonly used in distributive shock states including mixed shock with a cardiac component. However, the direct effect of arginine vasopressin on the function of the ischemia/reperfusion injured heart has not been clearly elucidated.

Low-dose vasopressin infusion results in increased mortality and cardiac dysfunction following ischemia-reperfusion injury in mice.

Toll-like receptors (TLRs) are expressed on cardiomyocytes and recognize pathogen-associated molecular patterns. Whether endogenous molecules produced by tissue injury (damage associated molecular patterns, DAMPs) can induce cardiomyocyte inflammation via TLR signalling pathways and/or reduce cardiomyocyte contractility is unknown.

Extracellular heat shock protein 70 induces cardiomyocyte inflammation and contractile dysfunction via TLR2.

We have recently described that Notch activates nitric oxide (NO) signaling in the embryonic endocardium. Both Notch signaling and NO signaling have been shown to be important during adult arteriogenesis. Notch has been shown to be required for remodeling of the collateral vessels, whereas NO is required for the initial vasodilatory response to ischemia. Whether Notch also has an impact on the vasodilatory phase of arteriogenesis after ischemia is not known. We tested the hypothesis that endothelial cell-Notch function is required for NO induction and vasodilation, in response to ischemia in the adult vasculature.

Yingjin Wang

UBC James Hogg Research Center, St. Paul's Hospital

Rat Heterotopic Abdominal Heart/Single-lung Transplantation in a Volume-loaded Configuration