Apoptosis and Proliferation of Cardiomyocytes and Interstitial Mononuclear Cells: Association With Rejection and Macrophage Infiltration

Stimulation of Cardiomyocyte Regeneratory Reactions under Conditions of Cytopathic Hypercholesterolemia

The regeneratory reactions of cardiomyocytes in the heart under conditions of cytopathic exposure to hypercholesterolemia and during verapamil treatment were studied by immunohistochemical detection of proliferation marker Ki-67 and evaluation of cardiomyocyte count. A 30-day exposure of rats to atherogenic diet led to an increase of Ki-67+ cardiomyocytes by 14.5-16.7 times (p<0.05). The Ki-67 label index in cardiomyocytes remained higher than normally (8-9-fold; p<0.05) after 64 days. It remained elevated (8-11-fold; p<0.05) after verapamil treatment. Evaluation of cardiomyocyte count and of their nuclear status detected various regeneratory strategies: increase of the total cardiomyocyte count, with increase of the percentage of mononuclear cardiomyocytes (particularly in response to verapamil in group 1 rats); decrease of total cardiomyocyte count with increase of the percentage of multinuclear cardiomyocytes (particularly in group 2 rats in response to verapamil).

Proliferative activity of cadriomyocytes in chronic hypercholesterolemia

We studied proliferative activity of cardiomyocytes (using proliferation marker Ki-67) and compared it with their total number in the heart under conditions of experimental chronic hypercholesterolemia and its combination with hypothyroidism. It was found that Ki-67-positive cells are primarily located in the subepicardial layer near the heart base in both intact and experimental animals. Replicative cardiomyocyte pool in intact rats constituted 1.67 ± 0.33‰ of the total cardiomyocyte population; after 68-day atherogenic diet with exogenous cholesterol alone, the replicative cardiomyocyte pool decreased by 16 % (to 1.40 ± 0.24‰). Treatment with mercazolil against the background of exogenous cholesterol increased this parameter by 40 % (to 2.33 ± 0.88‰). Changes in replicative activity of cardiomyocytes correlated with their total number in the heart and organ weight. We conclude that replicative cardiomyocyte pool primarily includes non-terminally differentiated cardiomyocytes (small mononuclear cardiomyocytes) and their proliferation maintains the total number of cardiomyocytes in the heart under conditions of cytopathic influences and provides the basis for physiological and reparative regeneration of the myocardium.

The comparison of the effects of Bretschneider's histidine-tryptophan-ketoglutarate and conventional crystalloid cardioplegia on pediatric myocardium at tissue level

Cardioplegic arrest is one of the most common myocardial protection strategies. A wide variety of cardioplegic solutions are routinely being used. There is an ongoing discussion about the relative effectiveness of these solutions considering myocardial protection. This study aims to investigate the hypothesis that the use of histidine-tryptophan-ketoglutarate (HTK) cardioplegia leads to decreased ischemic damage on myocardium compared with the use of conventional crystalloid cardioplegia. The study population was 32 patients operated on at Başkent University, Department of Cardiovascular Surgery for congenital heart diseases. The first group of 16 patients received conventional crystalloid cardioplegia (KK group) which is a modification of St. Thomas' solution, while the second group of 16 patients received HTK solution (HTK group). The echocardiographic measurements and the laboratory values of the patients were taken as the clinical variables. Right ventricular biopsies were taken from every patient before and after cardioplegic arrest. These biopsies were histopathologically examined for apoptosis using caspase-3 antigen and cell proliferation using Ki-67 antigen. The statistical analysis revealed no significant difference between the two groups regarding the clinical variables, apoptotic indices and proliferation indices. The apoptotic indices in the postcardioplegic arrest biopsies positively correlated with aortic clamp time in the KK group but not in the HTK group. Liver function tests on postoperative day 1 positively correlated with aortic clamp time in both groups. On postoperative day 2, this correlation was sustained in the KK group and ceased in HTK group. The difference in the correlation of apoptotic indices and liver function tests between the groups is accepted as a supportive finding for HTK solution. However, it can be postulated that when the aortic clamp times are similar to those in the present study, the clinical manifestation of the difference between the two solutions would not be significant.

Genetic or pharmaceutical blockade of phosphoinositide 3-kinase p110δ prevents chronic rejection of heart allografts

Chronic rejection is the major cause of long-term heart allograft failure, characterized by tissue infiltration by recipient T cells with indirect allospecificity. Phosphoinositol-3-kinase p110δ is a key mediator of T cell receptor signaling, regulating both T cell activation and migration of primed T cells to non-lymphoid antigen-rich tissue. We investigated the effect of genetic or pharmacologic inactivation of PI3K p110δ on the development of chronic allograft rejection in a murine model in which HY-mismatched male hearts were transplanted into female recipients. We show that suppression of p110δ activity significantly attenuates the development of chronic rejection of heart grafts in the absence of any additional immunosuppressive treatment by impairing the localization of antigen-specific T cells to the grafts, while not inducing specific T cell tolerance. p110δ pharmacologic inactivation is effective when initiated after transplantation. Targeting p110δ activity might be a viable strategy for the treatment of heart chronic rejection in humans.