Cardiovascular Effect And Mechanism Of Interleukin-2 In Rat

Since interleukin-2 (IL-2) was discovered by Morgan in 1976, it has been studied intensively by scientists in many countries. But as a key immune regulator, its study has been limited within the fields of immunology and immunotherapy. Immunotherapy with IL-2 demonstrated clinical activity in the treatment of advanced renal cell carcinoma and malignant melanoma. Unfortunately, intravenous administration of IL-2 is associated with relevant cardiovascular side effects, for example, hypotension (70% of incidence), fluid retention, and myocardial toxicity. Cardiac arrhythmias have been reported in 14-21% of patients undergoing IL-2 therapy. Other major cardiotoxic effects reported included myocardial infarction, myocarditis, and cardiomyopathy. Cardiovascular toxicity is the main dose limiting effect of IL-2 immunotherapy. On the other hand, more and more clinical reports showed that the system of IL-2/IL-2R is closely related with the severity degree of cardiovascular diseases. However, the cardiovascular effect and underlying mechanisms have not been elucidated.Objectives1) To study the effects of IL-2 in the cultured neonatal rat cardiomyocytes, the isolated papillary muscles and the isolated Langendorff perfused rat hearts;2) To investigate the role of nitric oxide (NO) and endogenous catecholamine, norpinephrine (NE) on the action of IL-2 in the isolated rat myocardium;3) To explore the effects and mechanism of IL-2 on the positive effect of isoproterenol (ISO) in the isolated rat cardiomyocytes, and the roles of Gs protein, adenylyl cyclase (AC) and cAMP in the cross-talk of two signal transduction pathways;4) To explore the effect and mechanism of iron on the vasodilating effect of IL-2 in the isolated aortic ring, and investigate the roles of NO synthase, calcium release from sarcoplasmic reticulum and inward rectifier potassium channel in the modulation of ferric ammonium citrate (FAC).Methods1) The left ventricular developed pressure (LVDP), left ventricular end-diastolic pressure (LVEDP), premature ventricular contraction (PVC), heart rate (HR.) and coronary flow (CF) were recorded in isolated Langendorff perfused rat hearts.2) The average contractile force, systolic duration and the 1/2 diastolic duration were measured in the isolated papillary muscles.3) Enzymatically isolated cardiomyocytes were used. [Ca2+]j transients were determined with a fluorometric ratio method by using fura-2/AM as Ca2+ indicators.4) The spontaneously beating rate of the neonatal rat cardiomyocyte was recorded.5) Thoracic arteries were used in evaluation of vascular effect of IL-2.ResultsPart 1: Effects of interleukin-2 on the isolated myocardium1) Effects of interleukin-2 on the spontaneously beating rate of the neonatal rat cardiomyocytes IL-2 at 0.5 U/ml did not alter the spontaneously beating rate of the neonatal rat cardiomyocytes (p>0.05). The beating rate of the neonatal rat cardiomyocyte was reduced by 24.40%, 24.59%, 29.80% and 42.10% after exposed to IL-2 at concentrations of 2.5, 10, 50 and 200 U/ml, respectively. Heat inactivated IL-2 did not change the spontaneously beating rate of the neonatal rat cardiomyocytes at all (p>0.05 vs control).2) Effects of IL-2 on the isolated rat papillary muscle IL-2 at 0.5 U/ml did not alter the average contractile force of the papillary muscle (p>0.05). However, the average contractile force of the papillary muscle was decreased by 20.61%, 26.80%, 38.60% and 47.57% after exposed to IL-2 at concentrations of 2.5, 10, 50 and 200 U/ml, respectively. In addition, IL-2 at 50 U/ml and 200 U/ml reduced the systolic duration to (81.07±9.21) % and (74.45±7.27) % of pre-drug values, respectively (p<0.05). IL-2 at same doses prolonged the 1/2 diastolic duration to (133.57±28.90) % and (144.05±23.99) % of pre-drug values, respectively (p<0.05 vs control). Heat inactivated IL-2 had no effect on the isolated rat papillary muscle (p>0.05 vs control).3) Effects of...