Cardiomyocyte-Specific Overexpression of Nitric Oxide Synthase 3 Prevents Myocardial Dysfunction in Murine Models of Septic Shock

Abstract

Abstract-Myocardial dysfunction contributes to the high mortality of patients with endotoxemia. Although nitric oxide (NO) has been implicated in the pathogenesis of septic cardiovascular dysfunction, the role of myocardial NO synthase 3 (NOS3) remains incompletely defined. Here we show that mice with cardiomyocyte-specific NOS3 overexpression (NOS3TG) are protected from myocardial dysfunction and death associated with endotoxemia. Endotoxin induced more marked impairment of Ca 2ϩ transients and cellular contraction in wild-type than in NOS3TG cardiomyocytes, in part, because of greater total sarcoplasmic reticulum Ca 2ϩ load and myofilament sensitivity to Ca 2ϩ in the latter during endotoxemia. Endotoxin increased reactive oxygen species production in wild-type but not NOS3TG hearts, in part, because of increased xanthine oxidase activity. Inhibition of NOS by N G -nitro-L-arginine-methyl ester restored the ability of endotoxin to increase reactive oxygen species production and xanthine oxidase activity in NOS3TG hearts to the levels measured in endotoxin-challenged wild-type hearts. Allopurinol, a xanthine oxidase inhibitor, attenuated endotoxin-induced reactive oxygen species accumulation and myocardial dysfunction in wild-type mice. The protective effects of cardiomyocyte NOS3 on myocardial function and survival were further confirmed in a murine model of polymicrobial sepsis. These results suggest that increased myocardial NO levels attenuate endotoxin-induced reactive oxygen species production and increase total sarcoplasmic reticulum Ca 2ϩ load and myofilament sensitivity to Ca 2ϩ , thereby reducing myocardial dysfunction and mortality in murine models of septic shock. Key Words: nitric oxide Ⅲ endotoxin Ⅲ reactive oxygen species Ⅲ calcium handling Ⅲ myofilament S eptic shock is a complex syndrome that claims more than 200 000 lives per year in the United States. 1 Endotoxemia occurs frequently in septic shock, and severe manifestations of this syndrome include cardiac depression. 2 Although cytokines and nitric oxide (NO) have been implicated in the pathogenesis of septic shock, the underlying mechanisms of myocardial depression of sepsis remains incompletely understood.High levels of NO produced by NO synthase 2 (NOS2) contribute to the systemic hypotension and myocardial dysfunction associated with sepsis. 3 However, despite the prominent role of NOS2 in cardiovascular dysfunction of sepsis, clinical trials using NOS inhibitors that are not isoform specific have been associated with increased mortality in septic patients, presumably caused by further impairment of cardiac function. 4 Although these observations indirectly suggest that NOS1 and/or NOS3 may have beneficial effects on myocardial function in sepsis, other studies using NOS isoform-deficient mice reported variable results. For instance, NOS3-deficient mice (NOS3 Ϫ/Ϫ ) were reported to have higher mortality at 1 day after endotoxin challenge compared with wild-type (WT) mice. 5 In contrast, another study showed that endotoxin-induced hypoten...

sGCα1β1attenuates cardiac dysfunction and mortality in murine inflammatory shock models

“…A saline-filled catheter was inserted into the left carotid artery for infusion of saline (2 ml/h). For measurement of cardiac function, the chest was opened, and a pressure-volume conductance catheter (model SPR-839, Millar Instruments, Houston, TX) was introduced through the apex into the left ventricle (LV), as described previously (25). Heart rate (HR), LV end-systolic and end-diastolic pressures (LVESP and LVEDP, respectively), and LV volumes were measured.…”

“…Furthermore, all cells with a resting sarcomere length Ͻ1.65 m were excluded. Measurements of sarcomere shortening (cell shortening, as a percentage of diastolic length) and intracellular Ca 2ϩ (⌬Cai, measured as the difference between the peak systolicto-diastolic fura 2 ratios) were performed simultaneously and as described previously (25). Briefly, isolated cardiac cells were loaded with the membrane-permeable Ca 2ϩ indicator fura 2-AM (Molecular Probes; 1 mol/l, 25 min) and superfused with a physiological solution containing (in mmol/l) 137 NaCl, 5.4 KCl, 1.2 Ca 2ϩ , 0.5 MgCl2, 10 HEPES, and 5.5 and 0.5 probenecid (to improve fura 2-AM retention), with pH titrated to 7.4 with NaOH.…”

“…However, NOS2-derived NO has also been found to have protective effects in TNF-induced (9) and endotoxin-induced (59) shock models, curbing oxidative stress and apoptosis. Similarly, increased NO levels, associated with overexpression of NOS3 in cardiomyocytes, attenuated myocardial dysfunction in mice challenged with endotoxin (25). However, NOS3-derived NO was also shown to have adverse cardiovascular effects in endotoxin-induced (13) and anaphylactic (7,10) shock models.…”

Inhibition of NADPH oxidase 2 (NOX2) prevents sepsis-induced cardiomyopathy by improving calcium handling and mitochondrial function

“…Studies of human blood metabolites show that LPS injection correlates with the abnormalities seen in sepsis (8). A variety of mechanisms have been proposed to explain cardiomyopathy during sepsis, including increased reactive oxygen species (ROS) as an important part of the pathophysiology (9,10). Mitochondrial dysfunction has been a consistent finding in sepsis models, with decreased mitochondrial oxidative phosphorylation and decreased transcription of mitochondrial genes (11)(12)(13).…”

Ulinastatin and Septic Cardiac Dysfunction

“…This suggested that nNOS wasn't always harmful to sepsis, it may have a protective role (Cui et al 2007). Moreover, mice with a cardiomyocyte-specific over expression of endothelial nitric oxide synthase (eNOS) was also partially protected against both endotoxemia and polymicrobial sepsis (Ichinose et al 2006).Why does these phenomenon happen? Maybe a research team can give a reasonable answer.…”