Takashi Shimojo

Nitric Oxide Contributes to the Progression of Myocardial Damage in Experimental Autoimmune Myocarditis in Rats

BACKGROUND Excess amounts of NO produced by an inducible NO synthase (iNOS) in response to cytokines may be cytotoxic and can be destructive to tissue. We investigated the role of NO in the development of myocardial damage and the effects of aminoguanidine (AG), an inhibitor of iNOS, on experimental autoimmune myocarditis in rats. METHODS AND RESULTS Autoimmune myocarditis was induced in 20 Lewis rats by injection of porcine cardiac myosin. Ten of the 20 rats were administered AG. The severity of myocarditis was evaluated by measuring the size of myocarditic lesion and serum levels of CK-MB. Serum NO levels were determined using the Cd/Cu method. Tissue specimens were immunohistochemically examined for iNOS and nitrotyrosine. Histopathological study revealed extensive myocardial destruction and massive inflammatory cell infiltration in AG-untreated rats but only focal mononuclear cell infiltration in AG-treated rats. The mean percent areas of inflammatory lesions in the untreated and treated rats were 56 +/- 13% and 3 +/- 2%, respectively (P < .001). NO levels were 102 +/- 23 and 25 +/- 9 IU/L, respectively (P < .01). CK-MB levels were 68 +/- 13 and 16 +/- 13 nmol/L, respectively (P < .01). Superoxide production as measured with an ex vivo monitoring system was also significantly decreased in the treated rats. Nitrotyrosine relating to the generation of peroxynitrite was detected through immunostaining in the inflammatory lesions of untreated rats but not in those of treated rats. CONCLUSIONS Excess amounts of NO produced by iNOS appear to contribute to the progression of myocardial damage in myocarditis. AG may prove to be useful in the treatment of myocarditis.

Tenascin-C Modulates Adhesion of Cardiomyocytes to Extracellular Matrix during Tissue Remodeling after Myocardial Infarction

Tenascin-C (TNC), an extracellular matrix glycoprotein, plays important roles in tissue remodeling. TNC is not normally expressed in adults but reappears under pathologic conditions. The present study was designed to clarify the contribution of TNC to ventricular remodeling after myocardial infarction. We examined the expression of TNC after experimental myocardial infarction in the rat by immunohistochemistry and in situ hybridization. Within 24 hours of permanent coronary ligation, interstitial fibroblasts in the border zone started to express TNC mRNA. The expression of TNC was down-regulated on Day 7 and was no longer apparent by Day 14 after infarction. During the healing process, TNC protein and TNC-producing cells were found at the edges of the residual myocardium. Some of the TNC-producing cells were immunoreactive for α-smooth muscle actin. In culture, TNC increased the number of cardiomyocytes attached to laminin but inhibited the formation of focal contacts at costameres. The results indicate that during the acute phase after myocardial infarction, interstitial cells in the border zone synthesize TNC, which may loosen the strong adhesion of surviving cardiomyocytes to connective tissue and thereby facilitate tissue reorganization.

Hypertrophic cardiomyopathy in Noonan syndrome

Noonan syndrome, a well‐known multiple congenital anomalies syndrome, is frequently accompanied by cardiovascular diseases including hypertrophic cardiomyopathy (HCM). The incidence of HCM in Noonan syndrome is approximately 20–30% and one‐third of cases reveal ventricular outflow obstruction. HCM in Noonan syndrome is occasionally associated with a congenital heart defect, whereas classic HCM seldom accompanies cardiac malformations. Asymmetric septal hypertrophy and symmetric septal hypertrophy (concentric hypertrophy) can be observed both in HCM with Noonan syndrome and in classic HCM. but apical hypertrophy has not been reported in Noonan syndrome yet, although it appears in classic HCM. Congestive heart failure is the major cause of death in patients with HCM in Noonan syndrome, but cases of sudden death have also been reported. The histopathologic findings of ventricular myocardial tissue in HCM with Noonan syndrome are similar to those in classic HCM.

Inhibitory effects of vesnarinone in the progression of myocardial damage in experimental autoimmune myocarditis in rats

OBJECTIVES Vesnarinone, a positive inotropic and immunomodulatory agent, diminishes nitric oxide (NO) levels by suppressing the induction of inducible NO synthase (iNOS) expressed in cytokine-stimulated macrophages and cardiomyocytes. We examined whether vesnarinone exerts inhibitory effects on the progression of myocardial damage in experimental autoimmune myocarditis in rats through suppression of iNOS. METHODS Myocarditis was induced in 30 Lewis rats by injection of porcine cardiac myosin and vesnarinone was orally administered to 20 of the 30 rats. On day 21 after immunization (the climax of inflammation), the hemodynamics were examined and the severity of myocarditis was evaluated by determining the area ratio (%) [affected/entire area] of myocardial lesions in histological sections. Levels of serum CK-MB, NOx (NO2(-)+NO3-), TNF-alpha and IL-1 beta, and cyclic GMP, iNOS mRNA, TNF-alpha and IL-1 beta in heart tissues were determined. Expression of iNOS and TNF-alpha protein were examined by immunohistochemical methods. RESULTS Histopathological examination revealed extensive myocardial destruction and massive infiltration of inflammatory cells in the vesnarinone-untreated rats. The area ratio of the lesions in the treated rats was significantly lower than that in the untreated ones. Levels of CK-MB, NOx, cyclic GMP, cytokines and iNOS mRNA were significantly lower in the vesnarinone-treated rats. Infiltrating macrophages and cardiomyocytes in the untreated rats showed much higher levels of expression of iNOS and TNF-alpha than those in the vesnarinone-treated rats. CONCLUSIONS Vesnarinone may prove to be useful in the treatment of myocarditis by attenuating NO production through suppression of iNOS induced by cytokines.

Participation of nitric oxide and peroxynitrite in the development of myocardial tissue damage in acute myocardial infarction.

Many factors, including superoxides, contribute to tissue damage in acute myocardial infarction (AMI). Excess nitric oxide (NO) produced by inducible NO synthase (iNOS) has also been reported to participate in myocardial injury associated with AMI, but its exact role remains unclear. To elucidate the role of NO and peroxynitrite in the pathogenesis of myocardial injury associated with AMI, we examined the expression of iNOS in the autopsied specimens of the left ventricle obtained from 15 patients with AMI and five with old MI by immunohistochemistry using an anti-iNOS polyclonal antibody. The distribution of nitrotyrosine was also examined immunohistochemically. In patients who died from 12 hours to 3 weeks after the infarction, positive immunoreactivity for iNOS was observed in residual myocytes, macrophages, and vascular endothelial cells in the peri-infarcted area. Degenerating myocytes in that area in all of that group showing positive staining for iNOS were also stained positive for anti-nitrotyrosine antibody selfsame. These findings were not observed in the myocardial specimens obtained from patients who died within 12 hours after the onset of AMI, showing a minimal number of inflammatory cells, or in the specimens from patients with an old myocardial infarction, which showed scar tissue and no cellular infiltration. Inducible NOS and nitrotyrosine were expressed in damaged myocardium from patients with AMI, suggesting that the NO radical and peroxynitrite are involved in the pathogenesis of myocardial damage.

726-1 Expression of Inducible Nitric Oxide Synthase in the Myocardium of Acute Myocarditis – A Serial Cardiac Biopsy Study

In endotoxin shock, hypotension and impaired myocardial contractility may be caused by increased nitric oxide (NO) formed by inducible NO synthase (iNOS) which is induced by cytokines and bacterial lipopolysaccarides. We have investigated whether iNOS is expressed in serially biopsied samples from the right ventricle of 20 cases of acute myocarditis by immunohistochemistry and in situ hybridization. Distinct iNOS immunoreactivity was observed in cardiomyocytes, endothelial cells, vascular smooth muscle cells and macrephages in all cases during acute active stage, in which cardiac function was severely impaired. Immunoelectron microscopic distribution of iNOS was evident in the cytosol of these cells. However, little staining was disclosed in the myocardium during the convalescent stage, showing normal cardiac function. The distribution of myocytes with elevated iNOS mRNA concentration was identical to that of these immunoreactive cells. Conclusions The present study shows the expression of human myocardial iNOS in acute myocarditis, suggesting that the enhanced production of NO by iNOS is cytotoxic and accounts, in part, for myocardial injury and reduced myocardial contractility during acute illness.