Appearance of Heterogeneous Macrophages During Development of Isoproterenol-Induced Rat Myocardial Fibrosis

Macrophages appearing in lesions are polarized toward M1 (for inflammation) and M2 (for anti-inflammation/fibrosis) types. We analyzed immunophenotypes of macrophages appearing in myocardial lesion in rats injected once with isoproterenol (10 mg/kg body weight). Inflammation following myocardial necrosis on day 1 was seen with a peak on days 3 and 5, and thereafter, reparative fibrosis developed on days 7 to 28. CD68⁺ M1 macrophages were seen in the early stages of injury and inflammatory on days 1 to 7, and thereafter, CD163⁺ M2 macrophages increased in the late stages of fibrosis on days 7 to 28. There was the polarization of M1 and M2 macrophages. The kinetics of macrophages reacting to Iba-1 and Galectin-3 was similar to that of M1 macrophages, indicating that Iba1- and Gal-3-positive macrophages might have functions of M1 type. Double immunofluorescence revealed that CD204- and MHC class II-positive macrophages are polarized toward M1 and M2 types, respectively. CCR2 messenger RNA expression is transiently elevated on day 1. Since CCR2 is a marker of blood monocytes, M1 macrophages might be recruited from blood monocytes. Collectively, macrophages expressing heterogeneous immunophenotypes participate in myocardial fibrosis. These findings would be useful for understanding the pathogenesis of myocardial fibrosis and analyzing myocardial toxicity.

Cardioprotective Effect of Olive Oil Against Ischemia Reperfusion-induced Cardiac Arrhythmia in Isolated Diabetic Rat Heart

Background

Olive oil is rich in monounsaturated fatty acids and has been reported for a variety of beneficial cardiovascular effects, including blood pressure lowering, anti-platelet, anti-diabetic, and anti-inflammatory effects. Diabetes is a major risk factor for cardiac dysfunctions, and olive oil prevents diabetes-induced adverse myocardial remodeling.

Objective

The study aimed to evaluate the effects of olive oil against streptozotocin-induced cardiac dysfunction in animal models of diabetes and ischemia and reperfusion (I/R)-induced cardiac arrhythmias.

Methods

Diabetes was induced in male rats with a single intraperitoneal injection of streptozotocin (60 mg/kg i.p), rats were treated for five, 15, or 56 days with olive oil (1 ml/kg p.o). Control animals received saline. Blood glucose and body weight were monitored every two weeks. At the end of the treatment, rats were sacrificed and hearts were isolated for mounting on Langedorff’s apparatus. The effect of olive oil on oxidative stress and histopathological changes in the cardiac tissues were studied.

Results

The initial blood glucose and body weight were not significantly different in the control and olive-treated animals. Streptozotocin (60 mg/kg i.p) caused a significant increase in the blood glucose of animals as compared to saline-treated animals. The control, saline-treated diabetic animals exhibited a 100% incidence of I/R-induced ventricular fibrillation, which was reduced to 0% with olive oil treatment. The protective effects of olive oil were evident after 15 and 56 days of treatment. Diltiazem, a calcium channel blocker (1 µm/L) showed similar results and protected the I/R-induced cardiac disorders. The cardiac tissues isolated from diabetic rats exhibited marked pathological changes in the cardiomyocytes, including decreased glutathione (GSH) and increased oxidative stress (malondialdehyde; MDA). Pretreatment of animals with olive oil (1 ml/kg p.o) increased GSH and decreased MDA levels. Olive oil also improved the diabetic-induced histopathological changes in the cardiomyocytes.

Conclusion

Olive oil possesses cardiac protective properties against I/R-induced cardiac arrhythmias in rats. It attenuated oxidative stress and diabetes-induced histopathological changes in cardiac tissues. The observed cardiac protectiveness of olive oil in the present investigation may be related to its antioxidant potential.

Regional activation of the immediate-early response gene c-fos in infarcted rat hearts

Regional infarction of the left ventricle is followed by hypertrophy of the viable myocardium. This compensatory growth of cardiac myocytes requires induction of gene transcription and synthesis of proteins. In this study, we examined the expression of the immediate-early response gene c-fos following ligation of the left coronary artery in rat hearts. RNase protection assay demonstrated a rapid increase in the c-fos mRNA level in the ventricular myocardium. After two days of infarction, the c-fos expression was attenuated and was comparable to that observed in sham-operated control hearts. In situ tissue distribution of Fos protein-like immunoreactivity revealed the appearance of positively stained cells adjacent to the lateral border of the ischaemic myocardium, in the left ventricular subendocardial areas, in the papillary muscles of the left ventricle, in the proximity of great transmural vessels, and focally in the normo-perfused subepicardial myocardium. Double staining using antibodies recognizing the Fos protein and alpha-actinin, confirmed that the accumulation of nuclear Fos protein-like immunoreactivity was mainly seen in the cardiac myocytes. However, double staining of the Fos protein and Hoechst DNA labelling showed that detectable immunoreactivity occurred only in a limited proportion of the total nuclei present in these myocardial regions. Moreover, the regions showing c-fos activation correspond to the areas in which the appearance of subsequent growth responses are most pronounced following myocardial infarction. The present results therefore indicate that an early and regional c-fos activation is taking place in viable cardiac myocytes following left coronary artery ligation, and that c-fos is a possible regulating factor of sequential events leading to altered pattern of gene expression and protein synthesis in the hypertrophying heart.