Pathophysiology of Unstable Angina

Role of pro-/anti-inflammatory cytokines and their correlation with established risk factors in South Indians with coronary artery disease

Cytokines are responsible for the modulation of immunological and inflammatory processes and play a significant role in the pathogenesis of coronary artery disease. We estimated the levels of pro-/anti-inflammatory cytokines in South Indian patients with coronary artery disease. The study population comprised of groups 1-3: 100 patients each with acute myocardial infarction, unstable angina, and stable angina, respectively, and group 4 (100 healthy controls). Cytokine levels (interleukin-6, interleukin-8, interleukin-10, and tumor necrosis factor-alpha) were estimated by enzyme-linked immunosorbent assay (ELISA). Interleukin-6, interleukin-8, and tumor necrosis factor-alpha levels were significantly higher in patients from groups 1 and 2, than in group 3 and controls. Acute myocardial infarction patients exhibited higher serum levels of interleukin-10 compared with other groups and control subjects. Patients with unstable angina had significantly lower interleukin-10 concentrations than those with stable angina. The ratios of pro-/anti-inflammatory cytokines in all the study groups increased significantly when patients with unstable angina were compared to other groups. In patients with acute myocardial infarction, interleukin-10 and tumor necrosis factor-alpha levels showed significant correlation with established risk factors such as body mass index, blood pressure, and lipid levels. Acute myocardial infarction patients show elevation in proinflammatory and anti-inflammatory cytokines, while unstable angina is associated with low levels of serum interleukin-10. Higher levels of anti-inflammatory cytokine interleukin-10 may be needed to provide protection in unstable angina. These cytokines are markers of coronary artery disease and may be used for the identification of high-risk patients with unstable angina/acute myocardial infarction.

Anti-inflammatory cytokine profile in acute coronary syndromes: behavior of interleukin-10 in association with serum metalloproteinases and proinflammatory cytokines

BACKGROUND

The anti-inflammatory cytokine interleukin-10 (IL-10) downregulates the production of metalloproteinases (MMPs) and upregulates the production of their tissue inhibitors (TIMPs). The aim of this study was to assess the levels of IL-10 in patients with acute myocardial infarction (AMI) and unstable angina (UA), as well as to investigate the relationship of circulating IL-10 with the levels of MMPs (MMP-1, -2, -9), their tissue inhibitor (TIMP-1), pro-inflammatory cytokines (IL-6, tumor necrosis factor (TNF)-alpha) and serum lipids in the same patient population.

METHODS

Serum MMP-1, -2, -9, TIMP-1, IL-6, TNF-alpha and IL-10 were measured by ELISA assays in 23 patients with AMI and 20 patients with UA after their hospital admission, as well as in 16 healthy controls subjects. The lipid profile was assessed by measuring the serum levels of total cholesterol, HDL-cholesterol, LDL-cholesterol and triglycerides.

RESULTS

AMI patients exhibited significantly higher serum levels of IL-10 as compared with those of UA patients and healthy controls (both P=0.005). In contrast, there was no significant difference in IL-10 levels between UA patients and healthy controls. In AMI patients there was a statistically significant positive correlation of serum IL-10 with the levels of MMP-9 (rho=0.588, P=0.003), IL-6 (rho=0.502, P=0.015) and HDL-cholesterol (rho=0.697, P<0.001), as well as a significant negative correlation with the levels of triglycerides (rho=-0.417, P=0.048).

CONCLUSIONS

Our results suggest that UA is associated with low serum activity of IL-10, while a significant elevation of this anti-inflammatory cytokine accompanies the peripheral immune responses of AMI. This observation indicates that different patterns of inflammatory reactions are implicated in the pathophysiology of two clinical conditions.

Histopathology of plaque rupture

Plaque disruption occurs during the development of atherosclerotic lesions. During certain circumstances it may result in thrombosis and subsequent development of acute coronary syndromes. Several characteristics of the plaque appear to be associated with plaque disruption, including a large lipid rich core, superficial plaque inflammation, and a thin fibrous cap. The importance of these and other plaque components are discussed in this article.

Nitroglycerin-inhibited whole blood aggregation is partially mediated by calcitonin gene-related peptide -- a neurogenic mechanism

1. The role of the vasculature and calcitonin gene-related peptide (CGRP) in nitroglycerin (NTG)-mediated platelet inhibition was studied. 2. In vitro incubations of CGRP in whole blood induced a dose-dependent inhibition of platelet aggregation with an IC50 of 62.1 nM. 3. The platelet inhibition induced by CGRP was blocked by co-incubation of 0.53 microM CGRP8-37, as well as 30 microM N(G)-nitro-monomethyl-L-arginine (L-NMMA). 4. In a separate group of experiments, 100 nM NTG in rat whole blood (WB) induced platelet inhibition of 6.0 +/- 1.3% (mean +/- s.d.), which was enhanced to 77.6+/-3.5% by the addition of rat aortic tissue (AT) (P<0.001). The inclusion of CGRP8-37 with NTG and AT in WB reduced platelet inhibition to 31.6+6.8% (P<0.01). Incubation of WB and AT with 30 microM L-NMMA reduced NTG-induced inhibition of platelet aggregation to 26.4+/-4.2% (P<0.001). 5. It is concluded that vascular tissue contributes to the antiplatelet mechanism of action of NTG. Furthermore, NTG apparently evokes the release of CGRP from vascular tissue and this neuropeptide contributes to the antiplatelet actions of NTG. 6. The antiplatelet activity of CGRP in whole blood is mediated primarily through the activation of nitric oxide synthase.

Unstable angina. Strategies to minimize myocardial injury

The primary goals in treatment of unstable angina are to relieve pain and prevent or limit myocardial infarction or ischemia. Patients with distinct, rapid progression of their usual angina pattern should be admitted to a coronary care unit and given heparin and intravenous nitrates as well as aspirin. Cardioselective beta blockers should also be administered when there are no contraindications. Intravenous thrombolytic agents are indicated in patients with objective evidence of ischemia who fit criteria for this therapy. However, thrombolysis is not advocated for routine treatment of unstable angina. Percutaneous transluminal coronary angioplasty or coronary artery bypass grafting should be considered--depending on the location, age, and morphology of the culprit lesion and the degree of left ventricular dysfunction--in patients who have refractory or recurrent ischemia despite aggressive medical therapy. However, in general, high-technology interventions are not a substitute for long-term regimens, such as risk-factor and lifestyle modification, daily aspirin, and pharmacologic therapies aimed at maximizing cardiac function.