Possible role of prostaglandins in the pathogenesis of cardiomyopathies

Molecular mechanisms in endothelial regulation of cardiac function

Endothelium is now recognized as a massive, regionally specific, multifunctional organ. Given its strategic anatomic location between the circulating blood components and the vascular smooth muscle or the cardiac muscle, it is a biologically significant interface whose dysfunction can be a critical factor in various pathological conditions. Two types of endothelial cells are recognized in the heart, the endocardial endothelial (EE) cells and the microvascular endothelial cells (MVE). Both produce common autacoids and share similar roles in signal transduction induced by neurotransmitters, hormones or mechanical stimuli. They are however two distinct cell populations with dissimilar embryological origin, cytoskeletal organization, receptor mediated functions and electrophysiological properties. Both the MVE and EE are modulators of cardiac performance. Myocardial contraction may be modulated by cardioactive agents such as nitric oxide, prostanoids, endothelin, natriuretic peptides, angiotensin II, kinins, reactive oxygen species and adenyl purines released from the cardiac endothelium. Two mechanisms have been proposed for the signal transduction from EE to the underlying myocytes: stimulus-secretion-contraction coupling and blood-heart barrier. Nitric oxide, bradykinin and myofilament desensitizing agent are probably important in short-term regulation of myocardial functions. Endothelin and Angiotensin II are probably involved in long-term regulation. Besides its sensory function and paracrine modulation of myocardial performance, EE as a blood-heart barrier could be of significance for the ionic homeostasis of the cardiac interstitium. In cardiac diseases, the damage to EE or MVE leading to failure of the endothelial cells to perform its regulatory and modulator functions may have serious consequences. A better understanding of the endothelial signaling pathways in cardiac physiology and pathophysiology may lead to the development of novel therapeutic strategies.

Doxorubicin and mechanical performance of cardiac trabeculae after acute and chronic treatment: a review

Doxorubicin, a very potent and often used anti-cancer drug, has a wide spectrum of biological activity. Classic studies have demonstrated that doxorubicin and other members of the anthracycline family intercalate with DNA and partially uncoil the double-stranded helix. Doxorubicin has a high affinity for cell nuclei: as much as 60% of the total intracellular amount of doxorubicin is found in the nucleus. Once binding to DNA occurs, several consequences may ensue. The binding of anthracyclines to DNA inhibits DNA polymerase and nucleic acid synthesis. In addition, anthracyclines are known to stabilize the otherwise cleavable complex between DNA and homodimeric topoisomerase II enzyme subunits, resulting in the formation of protein-linked DNA double strand breaks. In tumor cells, these anthracycline-induced perturbations are believed to result in a final common pathway of endonucleolytic DNA fragmentation known as apoptosis. Because proliferation is an important determinant of tumor growth, interference with the genome is regarded as the primary cause of the anti-tumor action of doxorubicin. Intercalation with DNA may not be important in the cardiotoxicity associated with doxorubicin therapy (see next section), because cardiac cell proliferation in humans stops after 2 months of age. This review is focussed on the effects of doxorubicin on mechanical performance in skinned cardiac trabeculae after acute and chronic administration of doxorubicin. We look especially at the mechanical performance and the molecular changes observed and related to mechanical performance.

Doxorubicin interacts directly with skinned single skeletal muscle fibres

The effect of doxorubicin, a highly effective anticancer agent, on the contractile apparatus of skinned single muscle fibres was tested in a concentration of 1 microM. Sarcomere length was set and held at 2 microns. Doxorubicin induced an increase in tension dependent on the Ca2+ concentration and time of incubation. The rise was up to 25% at [Ca2+] 40 microM. A parallel, small but significant shift of the calcium sensitivity curve, the relation between normalized tension and the negative logarithm of [Ca2+], the pCa, was observed. The results of this study suggest a direct interaction of doxorubicin with the actin myosin structure, possibly by an effect on myosin-ATP activity.

Cod liver oil does not reduce ventricular extrasystoles after myocardial infarction

Previous work has shown that in experimental animal models a lower incidence of arrhythmias and sudden death was observed if the animals were fed cod liver oil or fish oil. After a 48-h control period starting, on average, 8 days after the onset of symptoms, 18 men who were recovering from acute myocardial infarction were given 20 ml d-1 cod liver oil for 6 weeks, either immediately after the control period, weeks 0-6 (n = 10), or during weeks 6-12 (n = 8). Forty-eight-hour Holter monitoring was carried out before cod liver oil administration and at the end of weeks 6 and 12. The eicosapentaenoic acid content of plasma phospholipids was increased by 230% during cod liver oil administration. However, no significant change was observed in the 24-h prevalence of ventricular extrasystoles or other arrhythmias during the study period. The mean ln number of ventricular extrasystoles was 2.95 +/- 0.51 (+/- SEM) during cod liver oil ingestion and 2.63 +/- 0.30 when not taking cod liver oil.

Biochemical interactions of ethanol with the arachidonic acid cascade

A rapidly increasing scientific literature now supports the possibility of an alcohol-prostaglandin interaction. This chapter reviews evidence for both direct and indirect biochemical interactions between ethanol and the metabolism of arachidonic acid and several related compounds. Much of the present data is based on pharmacological manipulation of prostaglandin (PG) levels by potent nonsteroid anti-inflammatory agents such as indomethacin. Indomethacin markedly alters the behavioral response to ethanol, particularly in the mouse model. These data suggest that PGs are involved in the behavioral response to acute ethanol exposure in the mouse. In other animal models, alcohol has been reported to alter blood platelet metabolism of arachidonic acid, to suppress the enzymatic degradation of PGs, and to alter the response of the adenyl cyclase system to several hormones including PGs of the "E" series. In humans, both the stimulation and inhibition of PG synthesis is reported to aid the treatment of various aspects of alcoholism. Further, PGs are reported to protect against alcohol-induced fatty liver, and both PGs and arachidonic acid protect the gastric mucosa against ethanol-induced lesions. Certainly the residual consequences of acute, excessive ethanol consumption are commonly treated with a prostaglandin synthesis inhibitor. The material in this chapter is an attempt to review the data and to discuss the molecular mechanism underlying these observations.