Prevalence of angiographically significant stenosis in patients with chest pain and an elevated troponin Is level and normal creatine kinase and creatine kinase-MB levels

Exploration of the polar microenvironment around the reactive cysteine in rabbit muscle creatine kinase

The polar microenvironment around the reactive Cys283 of rabbit muscle creatine kinase was explored using kinetic analysis of substrates reaction in the presence of modifiers. In the present study, three specific sulphydryl reagents, 5,5'-dithiobis(2-nitrobenzoic acid), 6,6'-dithiodinicotinic acid and 2,2'-dithiodipyridine, were applied as modifiers to react with Cys283 of creatine kinase. The inactivation kinetics of creatine kinase by the modifiers was analyzed. The microscopic rate constants for reactions of the modifiers with free enzyme and enzyme-substrate complexes were also determined. The results suggested that the inactivation rate of creatine kinase by 5,5'-dithiobis(2-nitrobenzoic acid) was the fastest, followed by 6,6'-dithiodinicotinic acid and then 2,2'-dithiodipyridine. Interestingly, 5,5'-dithiobis(2-nitrobenzoic acid) and 6,6'-dithiodinicotinic acid functioned as non-complexing modifiers, while 2,2'-dithiodipyridine did a complexing modifier. The results here indicated that the electrophilic group was predominant around Cys283, and that the presence of substrates seemed to have different effects on the inactivation reactions of creatine kinase by the three modifiers. Furthermore, the findings in this study may provide a novel explanation for the low pKa value of Cys283.

Sodium barbital is a slow reversible inactivator of rabbit-muscle creatine kinase

As a depressant of the central nervous system, the clinical effect of sodium barbital has been extensively studied. Here we report on sodium barbital as an inhibitor of rabbit-muscle creatine kinase (CK), which plays a significant role in energy homeostasis in the muscles. Although sodium barbital gradually inhibits the activity of CK with increased concentration, the inhibition effect can be completely reversed by dilution, indicating that the inactivation process is reversible. Detailed kinetics analysis, according to a previously presented theory, indicates that sodium barbital functions as a non complexing inhibitor, and its inhibition effect on CK is a slow reversible inactivation. In this study, a kinetic model of the substrate reaction is presented, and the microscopic rate constants for the reaction of sodium barbital with the free enzyme and the enzyme-substrate complexes are determined. Kinetic analysis reveals that sodium barbital might compete with both creatine and ATP, but mainly with creatine, to inhibit the activity of CK. The results suggest that CK might be a target for sodium barbital in vivo.

Lipoprotein(a) levels in patients with unstable angina and their relationship with atherothrombosis and myocardial damage

The aim of the study was to compare lipoprotein(a) [Lp(a)] levels in patients with cTroponin-I (cTn-I)-positive or -negative unstable angina and to investigate their relationship with atherothrombosis. A total of 202 consecutive patients were enrolled in the study. Lp(a), fibrinogen, plasminogen, PAI-1 and t-PA levels were measured and C-reactive protein (CRP) assays were performed on admission for all patients, and venous blood samples were drawn 12 and 24 h later for cTn-I measurements. The patients were divided into cTn-I-negative (cTn-I < 1 ng/ml) and -positive (cTn-I > or = 1 ng/ml) unstable angina groups. Lp(a) levels of the cTn-I-positive patients were higher than those of the cTn-I-negative patients (52.9 +/- 6.0 and 15.7 +/- 2.5 mg/dl, p < 0.0001). There was a positive correlation between Lp(a) and cTn-I levels (r = 0.692; p = 0.0001). Increase in coagulation activity and impairment in fibrinolytic activity were significant in the cTn-I-positive patients. Elevated Lp(a) levels may have a role in the development of myocardial damage in patients with unstable angina.

[Usefulness of troponin I for predicting systolic dysfunction in acute coronary syndromes. Results of a prospective and quantitative study]

The relationship between troponin I and systolic function (quantitative contrast ventriculography) was evaluated in 137 consecutive patients with a first acute coronary syndrome (60 with and 77 without ST elevation). In general, a larger troponin I peak value was related with a more depressed ejection fraction and poorer regional systolic function (p < 0.0001). Nevertheless, this correlation was weaker than expected, especially in those cases without ST-segment elevation, suggesting that other factors apart from systolic dysfunction must be taken into account in order to explain the worse prognosis of those patients with increased serum levels of this marker of myocardial damage.

The contemporary management of acute myocardial infarction

The contemporary management of acute myocardial infarction continues to evolve rapidly. The ultimate goal of therapy is timely, complete, and sustained myocardial reperfusion. There is a powerful time-dependent effect on mortality, and thus the balance between the time and likelihood of maximal reperfusion is crucial in deciding whether to use primary percutaneous balloon angioplasty or thrombolysis as the initial reperfusion strategy. Newer thrombolytic agents allow for equivalent coronary reperfusion compared with the standard accelerated alteplase (tPA) regimen with the advantage of easier dosing regimens. Low molecular weight heparin has been shown to be superior to unfractionated heparin and likely will be the standard of care in the near future. The use of glycoprotein IIb/IIIa inhibitors has been shown to decrease the short- and long-term complication rates in patients with acute coronary syndromes treated medically and with percutaneous coronary interventions; however, the choice of the optimal agent and dosing regimen in various clinical settings remains controversial. Combination therapy with low-dose fibrinolytics, glycoprotein IIb/IIIa inhibitors, and low molecular weight heparin, with or without subsequent early planned percutaneous coronary interventions, may provide the optimal strategy for maximal coronary reperfusion, but the results of large, randomized mortality trials currently underway need to be analyzed. Risk stratification will continue to play a major role in determining which patients should receive a specific therapy. The care of the patient with an acute myocardial infarction will continue to be a challenge requiring the proper selection from the vast pharmaceutic and interventional options available.