Intracellular Calcium, Myosin Light Chain Phosphorylation, and Contractile Force in Experimental Cerebral Vasospasm:

2014 Williams Harvey Lecture: importance of coronary vasomotion abnormalities-from bench to bedside

Coronary vasomotion abnormalities play important roles in the pathogenesis of ischaemic heart disease, in which endothelial dysfunction and coronary artery spasm are substantially involved. Endothelial vasodilator functions are heterogeneous depending on the vessel size, with relatively greater role of nitric oxide (NO) in conduit arteries and predominant role of endothelium-derived hyperpolarizing factor (EDHF) in resistance arteries, where endothelium-derived hydrogen peroxide serves as an important EDHF. The functions of NO synthases in the endothelium are also heterogeneous with multiple mechanisms involved, accounting for the diverse functions of the endothelium in vasomotor as well as metabolic modulations. Cardiovascular abnormalities and metabolic phenotypes become evident when all three NO synthases are deleted, suggesting the importance of both NO and EDHF. Coronary artery spasm plays important roles in the pathogenesis of a wide range of ischaemic heart disease. The central mechanism of the spasm is hypercontraction of vascular smooth muscle cells (VSMCs), but not endothelial dysfunction, where activation of Rho-kinase, a molecular switch of VSMC contraction, plays a major role through inhibition of myosin light-chain phosphatase. The Rho-kinase pathway is also involved in the pathogenesis of a wide range of cardiovascular diseases and new Rho-kinase inhibitors are under development for various indications. The registry study by the Japanese Coronary Spasm Association has demonstrated many important aspects of vasospastic angina. The ongoing international registry study of vasospastic angina in six nations should elucidate the unknown aspects of the disorder. Coronary vasomotion abnormalities appear to be an important therapeutic target in cardiovascular medicine.

Endothelial function and coronary spastic angina

Coronary spasm plays an important role in the pathogenesis of not only variant angina but also coronary heart disease in general including acute coronary syndromes, especially in the Japanese population. The vascular endothelium has been reported to be a multifunctional organ whose integrity is essential for normal vascular physiology. Vascular endothelial dysfunction can be a critical factor in the pathogenesis of ischemic heart disease. Acetylcholine and methacholine cause vasodilation by endothelium-derived relaxing factor when the endothelium is functioning normally, whereas they cause vasoconstriction when the endothelium is removed or damaged. Coronary spasm can be induced by a variety of stimuli with different mechanisms of action, including acetylcholine and methacholine. Patients with coronary spasm may have a disturbance in endothelial function as well as local hyperreactivity of the coronary arteries.

Subarachnoid hemorrhage: a preventable disease with a heritable component

BACKGROUND AND PURPOSE

Subarachnoid hemorrhage (SAH) caused by ruptured intracranial aneurysm affects approximately 16 000 Americans annually, and almost 40% of affected patients die within 30 days despite the best current therapy. Prevention of SAH is therefore of paramount importance. We present a preliminary analysis of risk factors for SAH from our population-based, case-control study.

METHODS

Cases were prospectively collected and matched 2:1 by age, race, and gender to controls using random digit dialing. Personal risk factor history, family history, neuroimaging data, and genetic samples were obtained. Univariate and bivariate analyses were performed and population-attributable risks estimated. Multivariable analysis was performed using conditional logistic regression.

RESULTS

Between June 1997 and February 2000, 107 cases and 197 controls were enrolled. In bivariate analyses, a large proportion of population-attributable risk for SAH could be explained by modifiable risk factors: smoking, hypertension, and heavy alcohol use. In multivariable analysis, current cigarette smoking, history of hypertension, frequent alcohol use, lower body mass index, and a family history of a relative with SAH or intracranial aneurysm were found to be significant, independent risk factors for SAH.

CONCLUSION

Our data confirm previous reports that SAH clusters within some families independent of environmental risk factors, suggesting that SAH has a significant genetic component. Yet, even among families at increased risk of SAH, smoking cessation, treatment of hypertension, and reduced alcohol intake may substantially decrease SAH risk. The independent associations with heavy alcohol use and low body mass index with SAH may be confounded by smoking and require further study.

The protein kinase inhibitor fasudil protects against ischemic myocardial injury induced by endothelin-1 in the rabbit

Endothelin-1 (ET-1) induces severe pathologic conditions such as coronary spasm followed by vasospastic angina pectoris and acute myocardial infarction. The related pathophysiologic mechanisms have remained obscure. Endothelin-1 receptor (ET(A) and ET(B)) is reported to couple with several types of G protein-involved pathways that participate in phospholipase C activation and atrial myofibrils organization into sarcomeric units. Here we demonstrate that ET-1 induces histologic and pathologic dysfunction in the rabbit myocardium and that such pathologic events are prevented by the Rho-kinase inhibitor fasudil. Although the bolus injection of ET-1 (1.4 nmol/kg) via the auricular vein of the rabbit induced only transient T-wave elevation, irreversible, severe histologic changes were observed in papillary muscles of the ventricle, and multifocal myocardial necrosis with infiltration of neutrophils and macrophages in the left ventricle occurred. Oral administration of fasudil (10 mg/kg) significantly reduced the occurrence of myocardial injury determinants, whereas conventional Ca2+ channel blockers (nifedipine, diltiazem) and a K+ channel opener (nicorandil; 10 mg/kg, p.o. each) showed a lesser or no effect on such determinants. These results suggest that ET-1 induces severe myocardial dysfunction based not only on the occurrence of vasospastic ischemia but also on its direct effects on the myocardium.

Cellular and molecular mechanisms of coronary artery spasm: lessons from animal models

Coronary artery spasm plays an important role in the pathogenesis of a wide variety of ischemic heart diseases, especially in the Japanese population. Because coronary artery spasm can be induced by a variety of stimuli with different mechanisms of action, the occurrence of the spasm appears to be due to the local hyperreactivity of the coronary artery rather than to an enhanced stimulation with a single mechanism of action. Several lines of evidence indicate that coronary artery spasm is caused primarily by smooth muscle hypercontraction whereas the contribution of endothelial dysfunction may be minimal. In order to elucidate the cellular and molecular mechanisms of the spasm, porcine models of the spasm were developed. In the first model with balloon injury and high-cholesterol feeding, a close topological correlation between the early atherosclerotic lesions and the spastic sites was noted, whereas in the second model with an inflammatory cytokine the potential importance of coronary inflammatory changes, especially at the adventitia, was noted. Subsequent studies in vivo and in vitro demonstrated that protein kinase C (PKC) and Rho-kinase are substantially involved in the intracellular mechanism of the spasm, resulting in increases in the mono- and diphosphorylations of myosin light chain (MLC). Furthermore, molecular biological analyses demonstrated that Rho-kinase is upregulated at the spastic site (at all levels, including mRNA, protein, and activity), resulting in the inhibition of MLC phosphatase through the phosphorylation of its myosin binding subunit and thereby causing the increase in MLC phosphorylations. Preliminary results also suggest that the long-term inhibition of Rho-kinase is effective in inhibiting the development of arteriosclerotic vascular lesions in several porcine models. Thus, Rho-kinase could be regarded as a novel therapeutic target for coronary arteriosclerosis in general and coronary artery spasm in particular.

H-series protein kinase inhibitors and potential clinical applications

During the course of generating derivatives of N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide, a synthetic calmodulin inhibitor, we came across several analogues with shorter alkyl chains that exhibited inhibition of serine/threonine protein kinase activities in an ATP-competitive manner. Certain derivatives proved to be selective inhibitors of protein kinases useful for elucidation of relevant functions of the enzymes. One of them turned out to be a unique vasodilator that preferentially suppresses delayed cerebral vasospasm, a critical complication of subarachnoid hemorrhage, without significant changes in systemic blood pressure. The compound in question, 1-(5-isoquinolinesulfonyl)-homopiperazine, was identified from sequential development of protein kinase inhibitors with isoquinolinesulfonyl structures, which occupy the adenine pocket of the ATP-binding site of the enzyme. It recently has been proposed that the target kinase responsible for vasodilation by 1-(5-isoquinolinesulfonyl)-homopiperazine may be Rho-kinase, which regulates phosphorylation of myosin light chains and vasocontraction. Because protein phosphorylation plays important roles in regulation of various cellular functions, the foregoing is a good example of current progress in the development of protein kinase inhibitors with potential clinical applications.

Generation of the catalytic fragment of protein kinase C alpha in vasospastic canine basilar artery

In previous studies of topical application of calphostin C, a specific inhibitor of the regulatory domain of protein kinase C (PKC), and calpeptin, a selective inhibitor of calpain, to spastic canine basilar artery (BA) researchers have suggested that the catalytic fragment of PKC (known as PKM) is probably formed by a limited proteolysis of continuously activated μ-calpain, but there has been no direct evidence for PKM formation in vasospasm. The present immunoblot study with anti-PKC-alpha antibody shows a significant decrease in cytosolic 80-kD PKC-alpha and a concomitantly significant increase in membrane PKC-alpha in the spastic canine BA. In addition, an immunoblot study in which cleavage site-directed antibodies were used demonstrated a significant increase in immunoreactive 45-kD PKM. The changes in membrane PKC-alpha and PKM were enhanced with the lapse of time after subarachnoid hemorrhage. The cleavage site-directed antibodies distinguish the proteolyzed from the unproteolyzed forms of PKC for in situ analyses of enzyme regulation mediated by proteolysis. The data indicate that PKC-alpha in spastic canine BA is translocated to the cell membrane, where PKC-alpha is rapidly cleaved into PKM as a result of proteolysis of the isozyme by μ-calpain but not by m-calpain. The authors hypothesize that μ-calpain is continuously activated in spastic canine BA and produces PKM by limited proteolysis of PKC-alpha.