Caspase inhibition reduces cardiac myocyte dyshomeostasis and improves cardiac contractile function after major burn injury.

In the heart, thermal injury activates a group of intracellular cysteine proteases known as caspases, which have been suggested to contribute to myocyte inflammation and dyshomeostasis. In this study, Sprague-Dawley rats were given either a third-degree burn over 40% total body surface area plus conventional fluid resuscitation or sham burn injury. Experimental groups included 1) sham burn given vehicle, 400 microl DMSO; 2) sham burn given Q-VD-OPh (6 mg/kg), a highly specific and stable caspase inhibitor, 24 and 1 h prior to sham burn; 3) burn given vehicle, DMSO as above; 4) burn given Q-VD-OPh (6 mg/kg) 24 and 1 h prior to burn. Twenty-four hours postburn, hearts were harvested and studied with regard to myocardial intracellular sodium concentration, intracellular pH, ATP, and phosphocreatine (23Na/31P nuclear magnetic resonance); myocardial caspase-1, -3,and -8 expression; myocyte Na+ (fluorescent indicator, sodium-binding benzofurzan isophthalate); myocyte secretion of TNF-alpha, IL-1beta, IL-6, and IL-10; and myocardial performance (Langendorff). Burn injury treated with vehicle alone produced increased myocardial expression of caspase-1, -3, and -8, myocyte Na+ loading, cytokine secretion, and myocardial contractile depression; cellular pH, ATP, and phosphocreatine were stable. Q-VD-OPh treatment in burned rats attenuated myocardial caspase expression, prevented burn-related myocardial Na+ loading, attenuated myocyte cytokine responses, and improved myocardial contraction and relaxation. The present data suggest that signaling through myocardial caspases plays a pivotal role in burn-related myocyte sodium dyshomeostasis and myocyte inflammation, perhaps contributing to burn-related contractile dysfunction.

Sepsis and burn complicated by sepsis alter cardiac transporter expression.

UNLABELLED: Sepsis alone and burn complicated by sepsis produce significant cardiac dysfunction. Since calcium handling by the cardiomyocyte is essential for cardiac function, one mechanism for cardiac abnormalities may be calcium dyshomeostasis. We hypothesized that sepsis and burn plus sepsis alter cardiac calcium transporter expression. Sprague-Dawley rats were divided into: (1) control, (2) sepsis (intratracheal S. Pneumoniae, 4x10(6) CFU), and (3) burn (40% TBSA) plus sepsis. Myocyte [Ca(2+)](i) and [Na(+)](i) were quantified with Fura-2 AM and SBFI, respectively. Western blot analysis of rat hearts used antibodies against the sarcoplasmic reticular Ca(2+) ATPase (SERCA), the L-type calcium channel, the Na(+)/Ca(2+) exchanger or the Na(+)/K(+) ATPase. RESULTS: Sepsis in the presence and absence of burn trauma increased [Ca(2+)](i) and [Na(+)](i). SERCA expression was decreased in the sepsis and burn plus sepsis groups while calcium channel expression was transiently increased in these sepsis groups. Na(+)/Ca(2+) exchanger expression exhibited a biphasic pattern of altered expression. Sepsis and burn plus sepsis reduced Na(+)/K(+) ATPase protein levels. These data suggest that altered transporter expression produce cardiomyocyte calcium and sodium loading and may contribute to sepsis-mediated cardiac contractile dysfunction.

Sodium/hydrogen exchange activity in sepsis and in sepsis complicated by previous injury: 31P and 23Na NMR study.

OBJECTIVE: Sepsis or septic shock occurs frequently in sick and injured patients and is associated with a significant mortality. Myocardial contractile dysfunction has been proposed to be a major determinant of sepsis-related mortality. This study was directed to examine the role of Na/H exchange activity in myocardial defects after sepsis or after sepsis complicated by a previous burn injury. DESIGN: Laboratory study. SETTING: University research laboratory. SUBJECTS: Sprague-Dawley rats (300-350 g, males). INTERVENTIONS: Cardiac function, cellular Na and Ca, myocardial pH, and high-energy phosphates were examined in perfused hearts harvested after sepsis alone (intratracheal Streptococcus pneumoniae, 0.4 mL of 1 x 10 CFU/mL), after sepsis complicated by previous burn injury (40% total body surface area), and after amiloride (a selective inhibitor of Na/H exchange) treatment of either sepsis alone or sepsis plus burn. MEASUREMENTS AND RESULTS: The ratio of Na signal from the intracellular compartment (Nai) compared with an external standard (monitored by Na-NMR spectroscopy, TmDOTP shift reagent) increased by 70% in sepsis alone and by 41% in sepsis complicated by previous burn injury compared with shams. Cardiac adenosine triphosphate and intracellular pH (P nuclear magnetic resonance spectroscopy) were unchanged by sepsis or sepsis plus burn. Left ventricular pressure and maximal change in pressure over time were reduced after sepsis or after sepsis plus burn injury. Amiloride treatment in either sepsis or sepsis complicated by a previous burn injury prevented myocardial Na and Ca accumulation, attenuated sepsis-related lactic acidosis, and improved left ventricular function. CONCLUSION: Our results suggest that sepsis-related cardiac dysfunction is mediated, in part, by Na/H exchange activity, and inhibition of Na/H exchange activity improves cardiac function after sepsis alone or sepsis complicated by a previous injury.

Activation of stress-responsive pathways by the sympathetic nervous system in burn trauma.

We have shown previously that bum trauma activates the stress responsive proteins, p38 mitogen-activated protein kinase (MAPK), c-jun NH2-terminal kinase (JNK), and NF-kappaB, and we have shown further that p38 MAPK is an important mediator of cardiomyocyte TNF-alpha secretion and cardiac dysfunction in burn trauma. Since burn trauma causes a rise in circulating catecholamine levels, we hypothesized that this increased sympathetic activity may function as an upstream activator of the p38 MARK pathway in burn trauma. This study determined whether the alpha1-adrenergic receptor ligand phenylephrine could mimic burn trauma activation of p38 MAPK, JNK, and NF-kappaB nuclear translocation; and the effect of the alpha1-adrenergic receptor antagonist prazosin on either phenylephrine or burn-mediated activation of the stress response pathway was examined. Sprague Dawley rats were divided into seven groups: Group 1, controls; Group 2, phenylephrine-treated (2 microg/kg, i.v.) control rats; Group 3, phenylephrine-treated plus prazosin-treated (1 mg/kg, i.v.) control rats; additional rats were given burn over 40% total body surface area (TBSA) and received vehicle (1 mL of 2% sucrose, p.o.) plus fluid resuscitation (Group 4), while in Group 5, burn rats were given prazosin (1 mg/kg, p.o.) plus fluid resuscitation. In Groups 6 and 7, sham-burned rats were given either vehicle (1 mL of 2% sucrose, p.o.) or prazosin (1 mg/kg, p.o.) to provide appropriate controls. Administration of phenylephrine to rats caused a significant activation of cardiac p38 MAPK/JNK activities (Western blot) and cardiac NF-kappaB nuclear translocation (electrophoretic mobility shift assay, EMSA). Prazosin blocked phenylephrine mediated changes in p38 MAPK/JNK activities. Burn trauma activated cardiac p38 MAPK/JNK and NF-kappaB, increased TNF-alpha secretion by cardiomyocytes, and impaired cardiac function. Prazosin treatment in burns interrupted the burn-mediated signaling cascade, decreasing TNF-alpha secretion by cardiomyocytes and preventing post-burn cardiac contractile dysfunction. Thus, burn trauma-related sympathetic activity likely activates the stress-responsive cascade, which regulates myocardial TNF-alpha transcription/translation and culminates in cardiac contraction and relaxation defects.