Taka-aki Okabe

Therapy with granulocyte colony-stimulating factor in the chronic stage, but not in the acute stage, improves experimental autoimmune myocarditis in rats via nitric oxide

We systematically investigated serial efficacy of granulocyte colony-stimulating factor (G-CSF) therapy upon experimental autoimmune myocarditis (EAM) in rats treated with and without the inhibition of nitric oxide (NO) with the analyses of tissue regeneration. G-CSF could mobilize multipotent progenitor cells of bone marrow into the peripheral blood and may improve ventricular function. A rat model of porcine myosin-induced EAM was used. After the immunization of myosin, G-CSF (10 microg/kg/day) or saline was injected intraperitoneally on days 0-21 in experiment 1 and on days 21-42 in experiment 2. Additional myosin-immunized rats were orally given 25 mg/kg/day of N(G)-nitro-L-arginine methylester (L-NAME), an inhibitor of nitric oxide synthase (NOS), in each experiment (each group; n=8-21). Serum cytokines and peripheral blood cell counts were measured in each group. In experiment 1, G-CSF treatment aggravated cardiac pathology associated with increased macrophage inflammatory protein-2 (MIP-2) and interleukin-6 (IL-6) levels and enhanced superoxide production. In experiment 2, G-CSF treatment reduced the severity of myocarditis with increased capillary density and improved left ventricular ejection fraction. In the rats with EAM treated with G-CSF associated with oral L-NAME treatment in experiment 2, the severity of myocarditis was not reduced. Myocardial c-kit(+) cells were demonstrated only in G-CSF-treated group in experiment 2 but not in other groups. G-CSF has differential effects on EAM in rats associated with the modulation of cytokine network. The overwhelming superoxide production by G-CSF administration in the acute stage may worsen the disease. G-CSF therapy improved cardiac function via NO system in a rat model of myocarditis in the chronic stage, but not in the acute stage, possibly through the myocardial regeneration and acceleration of healing process.

L‐arginine ameliorates experimental autoimmune myocarditis by maintaining extracellular matrix and reducing cytotoxic activity of lymphocytes

It was previously shown that administration of the nitric oxide synthase inhibitor NG‐nitro‐l‐arginine methyl ester (l‐NAME) aggravated murine viral myocarditis by increasing myocardial virus titres. Experimental autoimmune myocarditis in mice and rats mimics human fulminant myocarditis. The effects of l‐arginine, a precursor of nitric oxide, upon heart failure in experimental autoimmune myocarditis were evaluated. Dietary l‐arginine (l‐arginine group) and l‐arginine plus NG‐nitro‐l‐arginine methyl ester (l‐arginine + l‐NAME group) were administered to C57BL/6 mice immunized with porcine cardiac myosin over 3 weeks. An untreated myocarditis group was prepared. Cardiac damage was less in the l‐arginine group compared with the other two groups, as was incidence of heart failure. In addition, extracellular matrix change was less prominent in the l‐arginine group. Plasma concentrations of nitric oxide were elevated in the l‐arginine group. Cytotoxic activities of lymphocytes were lower in l‐arginine group than in other two groups. l‐arginine treatment may be effective in preventing the development of heart failure in experimental myocarditis by maintaining extracellular matrix and reducing the cytotoxic activity of lymphocytes.

Naloxone, an opiate receptor antagonist, ameliorates acute experimental autoimmune myocarditis by reducing cytotoxic activities.

Little is known about effects of naloxone, an opiate receptor antagonist, upon experimental autoimmune myocarditis (EAM) in mice. The aim of the present study was to test the effects of naloxone upon EAM in mice. Four-week-old C57BL/6 mice were injected with porcine cardiac myosin. Naloxone 1 mg/kg/day was given intraperitoneally daily on days 0 to 21 in experiment I (acute stage) and on days 21 to 42 in experiment II (chronic stage). For the analysis of endogenous opiate and neurohumoral system, plasma β-endorphin and cytokines were measured. The cytotoxic activity of lymphocytes was determined by 51Cr-release assay. Naloxone reversed hypotension produced by massive myocardial injury in experiment I. In experiment I, the severity of cardiac pathology and inflammatory cytokines were decreased in the naloxone-treated group associated with higher β-endorphin level compared with the untreated group. In addition, naloxone induced a shift from Th1 cytokine toward Th2 cytokine balance. Thus, cytotoxic activities of lymphocytes against EL-4 tumor cells were lower in the treated group than in the untreated group in experiment I, but not in experiment II. Naloxone is beneficial for heart failure caused by EAM in the acute stage, but not in the chronic stage, due to decreasing cytotoxic activities of lymphocytes and to its neurohumoral modulating effects.