Biomedical subjects

James J M Greer

Publications and source records attributed to James J M Greer.

12 recordsLinked to original sources

PubMed2006

Sildenafil-mediated acute cardioprotection is independent of the NO/cGMP pathway.

Sildenafil, a potent inhibitor of phosphodiesterase type 5, has recently been investigated in animal models of myocardial ischemia-reperfusion (MI/R) injury. Previous studies have suggested that the protective effects of sildenafil are mediated via activation of endothelial nitric oxide (NO) synthesis (eNOS) and inducible NOS (iNOS). To further investigate the protective mechanism of sildenafil, we subjected wild-type, eNOS, and iNOS null animals to 30 min of myocardial ischemia and 24 h of reperfusion. Treatment with 0.06 mg/kg sildenafil 5 min before reperfusion significantly reduced myocardial infarct size in wild-type, eNOS null mice (eNOS(-/-)), and iNOS(-/-) animals. Additionally, the low dose utilized in this study did not alter myocardial cGMP. These results suggest that acute low-dose sildenafil-mediated cardioprotection is independent of eNOS, iNOS, and cGMP. In a second series of experiments, we investigated sildenafil in db/db diabetic mice subjected to MI/R. We found that sildenafil failed to protect diabetic mice against MI/R. However, NO(.) donor therapy was found to significantly protect against MI/R injury in both nondiabetic and diabetic mice, suggesting that protection could be conferred in diabetic mice and that the upstream modulator of soluble guanylyl cyclase, NO(.), may mediate protection independent of cGMP signaling. The present study suggests that further research is needed to delineate the precise mechanisms by which sildenafil exerts cardioprotection.

Acute Disease↗

PubMed2006

Low-dose simvastatin improves survival and ventricular function via eNOS in congestive heart failure.

3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors increase endothelial nitric oxide synthase (eNOS) activity by multiple mechanisms. We previously reported that genetic overexpression of eNOS improves survival and cardiac function in congestive heart failure (CHF). In the present study, we tested the hypothesis that low-dose treatment with an 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor exerts beneficial effects on survival and/or cardiac function in a murine model of CHF. Mice were subjected to permanent ligation of the left coronary artery and randomized to receive either saline vehicle or simvastatin (0.25 mg/kg) 2 h after myocardial infarction and daily (0.25 mg/kg) for 7 days, followed by 21 days of administration every other day for a total duration of 28 days. Myocardial infarct size was not reduced by simvastatin therapy (P = not significant between groups). Simvastatin treatment did significantly (P < 0.05) improve survival (45%) compared with vehicle treatment (25%). In addition, simvastatin treatment significantly improved (P < 0.01) left ventricular function and significantly (P < 0.01) abrogated cardiac hypertrophy and pulmonary edema compared with vehicle treatment. The protective effects of simvastatin were abrogated by delayed initiation of treatment or genetic ablation of eNOS. In conclusion, low-dose simvastatin therapy significantly improves survival and cardiac function and reduces both cardiac hypertrophy and pulmonary edema via an eNOS-dependent mechanism in a murine model of CHF.

Animals↗

PubMed2006

eNOS gene therapy exacerbates hepatic ischemia-reperfusion injury in diabetes: a role for eNOS uncoupling.

Previous studies indicate that endothelial nitric oxide synthase (eNOS) function is impaired in diabetes as a result of increased vascular generation of reactive oxygen species. We hypothesized that eNOS gene therapy would augment NO. bioavailability and protect against hepatic ischemia-reperfusion (I-R) injury in type 2 diabetes mellitus. We developed a transgenic (Tg) diabetic mouse in which eNOS is systemically overexpressed. We also examined the effects of hepatic eNOS adenovirus therapy in diabetic mice. Diabetic (db/db) and nondiabetic mice were subjected to hepatic I-R injury. In nondiabetic mice, genetic overexpression of eNOS (both eNOS-Tg and eNOS adenovirus) resulted in hepatoprotection. In contrast, hepatic I-R injury was significantly increased in the db/db eNOS-Tg mouse, as serum alanine aminotransaminase (ALT) levels were increased by 3.3-fold compared with diabetic controls. Similarly, eNOS adenovirus treatment resulted in a 3.2-fold increase in serum ALT levels as compared with diabetic controls. We determined that hepatic eNOS was dysfunctional in the db/db mouse and increased genetic expression of eNOS resulted in greater production of peroxynitrite. Treatment with the eNOS cofactor tetrahydrobiopterin (BH4) or the BH4 precursor sepiapterin resulted in a significant decrease in serum ALT levels following I-R injury. We present clear examples of the protective and injurious nature of NO. therapy in I-R. Our data indicate that eNOS exists in an "uncoupled" state in the setting of diabetes and that "recoupling" of the eNOS enzyme with cofactor therapy is beneficial.

Animals↗

PubMed2006

Cardiomyocyte-specific overexpression of NO synthase-3 protects against myocardial ischemia-reperfusion injury.

OBJECTIVE: The protective effect of NO synthase-3 (eNOS)-derived NO in limiting myocardial ischemia-reperfusion (MI-R) injury is well established. We reported previously that systemic genetic overexpression of eNOS attenuates MI-R injury. The purpose of the current study was to investigate tissue-specific genetic overexpression of the human eNOS gene. METHODS AND RESULTS: To accomplish this, we used 2 distinct murine models of transgenic overexpression, a cardiomyocyte-specific eNOS overexpresser (CS eNOS-Tg) under the control of the alpha-myosin heavy chain promoter, and a systemic eNOS transgenic mouse (SYS eNOS-Tg) under control of the native eNOS promoter with an upstream endothelial enhancer element. Mice were subjected to 30 or 45 minutes of left coronary artery ischemia and 24 or 72 hours of reperfusion. CS eNOS-Tg mice displayed significantly decreased infarct size beyond that of mice with systemic overexpression. Additionally, CS eNOS-Tg mice exhibited better preservation of cardiac function compared with SYS eNOS-Tg mice after myocardial infarction. CONCLUSIONS: These results provide evidence that site-specific targeting of eNOS gene therapy may be more advantageous in limiting MI-R injury and subsequent cardiac dysfunction.

Animals↗

PubMed2006

Differential angiogenic regulation of experimental colitis.

Inflammatory bowel diseases (IBDs) are chronic inflammatory disorders of the intestinal tract with unknown multifactorial etiology that, among other things, result in alteration and dysfunction of the intestinal microvasculature. Clinical observations of increased colon microvascular density during IBD have been made. However, there have been no reports investigating the physiological or pathological importance of angiogenic stimulation during the development of intestinal inflammation. Here we report that the dextran sodium sulfate and CD4+CD45RBhigh T-cell transfer models of colitis stimulate angiogenesis that results in increased blood vessel density concomitant with increased histopathology, suggesting that the neovasculature contributes to tissue damage during colitis. We also show that leukocyte infiltration is an obligatory requirement for the stimulation of angiogenesis. The angiogenic response during experimental colitis was differentially regulated in that the production of various angiogenic mediators was diverse between the two models with only a small group of molecules being similarly controlled. Importantly, treatment with the anti-angiogenic agent thalidomide or ATN-161 significantly reduced angiogenic activity and associated tissue histopathology during experimental colitis. Our findings identify a direct pathological link between angiogenesis and the development of experimental colitis, representing a novel therapeutic target for IBD.

Angiogenesis Inhibitors↗

PubMed2005

Myocardial infarction and heart failure in the db/db diabetic mouse.

Clinical studies have reported that the incidence and severity of myocardial infarction is significantly greater in diabetics compared with nondiabetics after correction for all other risk factors. The majority of studies investigating the pathophysiology of myocardial ischemia-reperfusion injury have focused on otherwise healthy animals. At present, there is a paucity of experimental investigations on the pathophysiology of heart failure in diabetic animals. We hypothesized that the severity of myocardial reperfusion injury and the development of congestive heart failure would be markedly enhanced in the db/db diabetic mouse. Accordingly, we studied the effects of varying durations of in vivo myocardial ischemia and reperfusion on the incidence of heart failure in db/db diabetic mice. Nondiabetic and db/db diabetic mice (10 wk of age) were subjected to 30, 45, or 60 min of left coronary artery occlusion and 28 days of reperfusion. Survival at 24 h of reperfusion was 100% in nondiabetic mice subjected to 30 min of myocardial ischemia and 88% in nondiabetic mice subjected to 45 min of myocardial ischemia. In contrast, survival was 53% in db/db diabetic mice subjected to 30 min of myocardial ischemia and 44% in db/db mice after 45 min of myocardial ischemia. Prolonged survival in nondiabetic mice was not significantly attenuated when compared during the 28-day follow-up period with all groups experiencing >90% survival. Prolonged survival was significantly decreased in db/db mice after both 30 and 45 min of myocardial ischemia compared with sham controls. Furthermore, we observed a significant degree or left ventricular dilatation, cardiac hypertrophy, and cardiac contractile dysfunction in db/db mice subjected to 45 min of myocardial ischemia and 28 days reperfusion. In nondiabetic mice subjected to 45 min of myocardial ischemia, we failed to observe any changes in left ventricular dimensions or fractional shortening. These studies provide a feasible experimental model system for the investigation of heart failure secondary to acute myocardial infarction in the db/db diabetic mouse.

Animals↗

PubMed2005

HMG-CoA reductase inhibitors inhibit endothelial exocytosis and decrease myocardial infarct size.

Three-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors protect the vasculature from inflammation and atherosclerosis by cholesterol dependent and cholesterol independent mechanisms. We hypothesized that HMG-CoA reductase inhibitors decrease exocytosis of Weibel-Palade bodies, endothelial cell granules whose contents promote thrombosis and vascular inflammation. We pretreated human aortic endothelial cells with simvastatin for 24 hours, then stimulated the cells with thrombin, and measured the amount of vWF released into the media. We then measured the effect of simvastatin on myocardial infarction in mice. Simvastatin decreased thrombin-stimulated Weibel-Palade body exocytosis by 89%. Simvastatin inhibited exocytosis in part by increasing synthesis of nitric oxide (NO), which S-nitrosylated N-ethylmaleimide sensitive factor (NSF), a critical regulator of exocytosis. Simvastatin treatment attenuated myocardial infarct size by 58% in wild-type but not eNOS knockout mice. Furthermore, simvastatin decreased endothelial exocytosis and neutrophil infiltration into ischemic-reperfused myocardium, which was mediated in part by P-selectin contained in Weibel-Palade bodies. However, simvastatin did not affect exocytosis and inflammation in myocardial infarcts of eNOS knockout mice. Inhibition of endothelial exocytosis is a novel mechanism by which HMG-CoA reductase inhibitors may reduce vascular inflammation, inhibit thrombosis, and protect the ischemic myocardium. These findings may explain part of the pleiotropic effects of statin therapy for patients with cardiovascular disease.

Animals↗

PubMed2005

Cytoprotective effects of nitrite during in vivo ischemia-reperfusion of the heart and liver.

Nitrite represents a circulating and tissue storage form of NO whose bioactivation is mediated by the enzymatic action of xanthine oxidoreductase, nonenzymatic disproportionation, and reduction by deoxyhemoglobin, myoglobin, and tissue heme proteins. Because the rate of NO generation from nitrite is linearly dependent on reductions in oxygen and pH levels, we hypothesized that nitrite would be reduced to NO in ischemic tissue and exert NO-dependent protective effects. Solutions of sodium nitrite were administered in the setting of hepatic and cardiac ischemia-reperfusion (I/R) injury in mice. In hepatic I/R, nitrite exerted profound dose-dependent protective effects on cellular necrosis and apoptosis, with highly significant protective effects observed at near-physiological nitrite concentrations. In myocardial I/R injury, nitrite reduced cardiac infarct size by 67%. Consistent with hypoxia-dependent nitrite bioactivation, nitrite was reduced to NO, S-nitrosothiols, N-nitros-amines, and iron-nitrosylated heme proteins within 1-30 minutes of reperfusion. Nitrite-mediated protection of both the liver and the heart was dependent on NO generation and independent of eNOS and heme oxygenase-1 enzyme activities. These results suggest that nitrite is a biological storage reserve of NO subserving a critical function in tissue protection from ischemic injury. These studies reveal an unexpected and novel therapy for diseases such as myocardial infarction, organ preservation and transplantation, and shock states.

Animals↗

PubMed2004

Deficiency of iNOS does not attenuate severe congestive heart failure in mice.

Inducible nitric oxide synthase (iNOS) has been implicated in the pathophysiology of congestive heart failure (CHF). Given the extensive evidence supporting this concept, we hypothesized that iNOS deficiency (iNOS(-/-)) would attenuate the severity of CHF in mice. Mice were subjected to permanent occlusion [myocardial infarction (MI)] of the proximal left anterior descending coronary artery to produce CHF. Cardiac function was assessed in vivo using echocardiography and ultraminiature ventricular pressure catheters. Sham wild-type (n = 17), sham iNOS(-/-) (n = 8), MI wild-type (n = 56), and MI iNOS(-/-) (n = 48) mice were subjected to MI (or sham MI) and followed for 1 mo. Deficiency of iNOS did not alter survival during CHF compared with wild type (35% vs. 32%, P = not significant). Furthermore, fractional shortening and cardiac output were not significantly different between wild-type (9.6 +/- 2.0% and 441 +/- 20 microl.min(-1).g(-1)) and iNOS(-/-) (9.8 +/- 1.3% and 471 +/- 26 microl.min(-1).g(-1)) mice. The extent of cardiac hypertrophy and pulmonary edema was also similar between wild-type and iNOS(-/-) mice. None of the indexes demonstrated any significant differences between iNOS(-/-) and wild-type mice subjected to MI. These findings indicate that deficiency of iNOS does not significantly affect severe CHF in mice after MI.

Animals↗

PubMed2003

Endothelial nitric oxide synthase overexpression attenuates myocardial reperfusion injury.

Previous studies indicate that deficiency of endothelial nitric oxide (NO) synthase (eNOS)-derived NO exacerbates myocardial reperfusion injury. We hypothesized that overexpression of eNOS would reduce the extent of myocardial ischemia-reperfusion (MI/R) injury. We investigated two distinct strains of transgenic (TG) mice overexpressing the eNOS gene (eNOS TG). Bovine eNOS was overexpressed in one strain (eNOS TG-Kobe), whereas the human eNOS gene was overexpressed in the other strain (eNOS TG-RT). Non-TG (NTG) and eNOS TG mice were subjected to 30 min of coronary artery occlusion followed by 24 h of reperfusion, and the extent of myocardial infarction was determined. Myocardial infarct size was reduced by 33% in the eNOS TG-Kobe strain (P < 0.05 vs. NTG) and by 32% in the eNOS TG-RT strain (P < 0.05 vs. NTG). However, postischemic cardiac function (cardiac output, fractional shortening) was not improved in the eNOS TG-Kobe mouse at 24 h of reperfusion [P = not significant (NS) vs. NTG]. In additional studies, eNOS TG-Kobe mice were subjected to 30 min of myocardial infarction and 7 days of reperfusion. Fractional shortening and the first derivative of left ventricular pressure were measured in eNOS TG-Kobe and NTG mice, and no significant differences in contractility were observed (P = NS) between the eNOS TG mice and NTG controls. Left ventricular end-diastolic pressure was significantly (P < 0.05 vs. NTG) reduced in the eNOS TG-Kobe strain at 7 days of reperfusion. The cardioprotective effects of eNOS overexpression on myocardial infarct size were ablated by Nomega-nitro-l-arginine methyl ester (300 mg/kg) pretreatment. Thus genetic overexpression of eNOS in mice attenuates myocardial infarction after MI/R but fails to significantly protect against postischemic myocardial contractile dysfunction in mice.

Alkenes↗

PubMed2003

Endothelial nitric oxide synthase overexpression attenuates congestive heart failure in mice.

Congestive heart failure results in cardiovascular dysfunction and diminished vascular nitric oxide (NO) production. We hypothesized that overexpression of endothelial NO synthase (eNOS) within the endothelium would reduce the extent of contractile dysfunction in a murine model of infarct-induced congestive heart failure. We generated transgenic (TG) mice overexpressing the human eNOS gene. The TG mice displayed significantly enhanced eNOS protein levels and eNOS activity levels (10- to 12-fold greater) in the aorta and the coronary vasculature. Non-TG (NTg) and eNOS TG mice were subjected to permanent left anterior descending coronary artery occlusion and then observed for 1 mo. We assessed cardiac function in vivo by using echocardiography and ultraminiature ventricular pressure catheters. Myocardial infarct size was similar between study groups (approximately 70% of the risk zone). Survival was increased by 43% in the eNOS TG mice compared with NTg (P < 0.05). Fractional shortening and cardiac output were also significantly (P < 0.05) greater in the eNOS TG than in NTg. Interestingly, pulmonary edema was evident only in NTg mice, and no evidence of pulmonary edema was observed in the eNOS TG mice. Thus, targeted overexpression of the eNOS gene within the vascular endothelium in mice attenuates both cardiac and pulmonary dysfunction and dramatically improves survival during severe congestive heart failure.

Animals↗

PubMed2003

Endothelial cell overexpression of fas ligand attenuates ischemia-reperfusion injury in the heart.

Fas ligand (FasL) is a member of tumor necrosis factor family that induces apoptosis in target cells that express Fas. The function of FasL during inflammation remains controversial. In this study, we examined the role of vascular endothelial FasL during acute myocardial ischemia-reperfusion that is closely associated with inflammation. Transgenic mouse lines were established that overexpress human FasL on endothelium under the control of the vascular endothelial cadherin promoter. Expression of FasL transgene was detected at both mRNA and protein levels, and functional transgene-encoded FasL protein was specifically expressed on the surface of vascular endothelial cells. Transgenic mice developed normally and had normal hearts. When subjected to 30 min of myocardial ischemia and 72 h of reperfusion, myocardial infarct size was reduced by 42% in the transgenic mice compared with nontransgenic littermates (p < 0.05). Moreover, hemodynamic data demonstrated that transgenic hearts performed better following ischemia and reperfusion compared with nontransgenic hearts. Myocardial neutrophil infiltration was reduced by 54% after 6 h of reperfusion in transgenic hearts (p < 0.01). Neutrophil depletion prior to ischemia-reperfusion injury led to smaller infarcts that were not different between transgenic and nontransgenic mice, suggesting that endothelial FasL may attenuate ischemia-reperfusion injury by abating the inflammatory response. These results indicate that vascular endothelial FasL may exert potent anti-inflammatory actions in the setting of myocardial ischemia-reperfusion injury.

Animals↗