Influence of blood sampling procedure on plasma concentrations of matrix metalloproteinases and their tissue inhibitors.

1. Plasma levels of matrix metalloproteinases (MMP) and tissue inhibitors of metalloproteinases (TIMP) are potential markers of many diseases involving extracellular matrix remodelling such as hypertension. Our aim was to determine whether the anticoagulant used to collect plasma and several freeze-thaw cycles may influence the accuracy of plasma MMP and TIMP determinations. 2. Plasma samples of 18 healthy volunteers were collected on three anticoagulants: heparinate, citrate and EDTA. For each anticoagulant, we compared: (i) MMP-2 and MMP-9 levels using gelatin zymography and TIMP-1 and TIMP-2 concentrations using enzyme-linked immunosorbent assay; (ii) intra- and interassay coefficients of variation (CV); and (iii) MMP and TIMP levels after up to five freeze-thaw cycles. 3. The choice of anticoagulant influenced TIMP-2 and TIMP-1 concentrations (TIMP-2, P < 0.0001; paired comparisons, citrate vs EDTA, P < 0.0001; EDTA vs heparin, P < 0.0001; citrate vs heparin, P < 0.0001; TIMP-1, P < 0.001; paired comparisons, citrate vs EDTA, P = 0.10; EDTA vs heparin, P < 0.01; citrate vs heparin, P < 0.0001), but not those of MMP. We observed a bias with heparinate for TIMP-2, TIMP-1 and MMP-9 determinations. The anticoagulant did not influence intra-assay or interassay CV. Performing freeze-thaw cycles led to alterations in the TIMP-1 plasma levels (P < 0.0001), regardless of the anticoagulant used, whereas MMP and TIMP-2 concentrations were not significantly affected. 4. Anticoagulant influences the measured levels of MMP and TIMP in plasma and should be systematically reported. However, it does not influence the reproducibility of the measurements. Repeated freeze-thaw cycles alter the measurement of TIMP-1 levels and should be avoided.

Reduced immunoregulatory CD31+ T cells in patients with atherosclerotic abdominal aortic aneurysm.

BACKGROUND: Cell-mediated immunity is considered to contribute to the pathogenesis of abdominal aortic aneurysms (AAA). In particular, infiltrating macrophages and CD8+ T lymphocytes participate in the destruction of the aortic wall extracellular matrix and smooth muscle cells. We surmise that these pathological events are controlled by circulating regulatory lymphocytes. METHODS AND RESULTS: Circulating CD4+/CD31+ cells were reduced in AAA patients (n=80, 8.9+/-0.6%) as compared with controls (n=69, 13.7+/-0.8%; P<0.001) and inversely proportional to AAA size. Exclusion of the aneurysm by an endoprothesis did not affect CD31+ T cell values. Reduction of blood CD4+/CD31+ cells was not attributable to their enrichment in AAA tissue. In contrast, CD8+/CD31+ cells were slightly reduced in the blood while increased in the aneurysmal tissue (29.2+/-0.5 versus 20.2+/-4.7% in blood, n=6; P<0.05). Remarkably, high percentages of CD4+/CD31+ cells were able to regulate proliferation and cytokine production of CD8+ lymphocytes, as well as CD8+ cell-mediated cytotoxicity of aortic smooth muscle cells (P<0.01). Finally, CD4+/CD31+ cells reduced the production and activity of metalloproteinase-9 by lipopolysaccharide-stimulated macrophages. CONCLUSIONS: Circulating CD4+/CD31+ T cells regulate macrophage and CD8+ T cell activation and effector function in the arterial wall. Their reduction might promote the development of AAA.

Compliance of abdominal aortic aneurysms evaluated by tissue Doppler imaging: correlation with aneurysm size.

OBJECTIVES: Several studies have shown that an increase in abdominal aortic aneurysm (AAA) growth rate occurs when the diameter reaches 40 to 50 mm. AAA expansion is related to remodeling of the parietal extracellular matrix. The parietal mechanisms involved in this critical phase of sudden increase remain unexplained. Analysis of AAA wall movements and determination of AAA compliance may provide information about the constitution of the arterial wall. If a change in parietal wall motion somewhere between 40 and 50 mm could be shown, this would contribute to the understanding of the growth of AAA. Furthermore, it would provide a valuable additional parameter for AAA monitoring. This study had two aims: first, to evaluate the relationship between AAA compliance and maximum diameter using the tissue Doppler imaging system; and second, to test the hypothesis of a change in AAA behavior at around 45 mm in diameter. METHODS: Fifty-six patients with AAA (mean diameter, 39 mm) were prospectively investigated using the tissue Doppler imaging system, which provides information concerning arterial wall motion. Maximum mean segmental dilation (MMSD), segmental compliance, pressure strain elastic modulus (Ep), and stiffness were determined and related to the maximum diameter of AAA. Results After natural log transformation of all variables, there was a significant positive linear relationship between maximum diameter and both MMSD (P < .001) and segmental compliance (P < .001) but not with Ep or stiffness (P = .37 and .22, respectively). MMSD and segmental compliance were significantly higher in AAA > or = 45 mm than in AAA < 45 mm (P < .0002 and <. 004, respectively). Ep and stiffness tended to decrease in larger AAAs, but this was not statistically significant (P < .43 and .24, respectively). Dispersion of Ep and stiffness values seemed to be wider among AAA < 45 mm compared with those > or = 45 mm. CONCLUSION: Compliance parameters can easily be measured during routine AAA ultrasound monitoring using the tissue Doppler imaging system. The study showed an increase in MMSD and segmental compliance as well as a nonsignificant trend toward increased distensibility (decreased Ep and stiffness) with increased AAA diameter. A change in dispersion of AAA distensibility may appear around 45 mm in diameter, but a larger study will be needed to clarify this.

Compliance of abdominal aortic aneurysms: evaluation of tissue Doppler imaging.

Expansion of abdominal aortic aneurysms (AAA) is due to remodeling of the parietal extra-cellular matrix and may lead to rupture. This remodeling is reflected by compliance which may be an indicator of AAA behavior and thus useful for clinicians. Tissue Doppler Imaging (TDI) is an ultrasonographic modality which allows wall motion measurements along an arterial segment. It has previously been evaluated in normal aortas and was then evaluated in thirty-five patients with AAA. Mean values (+/-standard deviation) characterizing maximum diameter AAA compliance were dilation 809 mum (+/-465), strain 2.2% (+/-1), pressure strain elastic modulus 3.94 10(5) Pa [3.25; 4.8] and stiffness 28.8 [24; 34.5], last values being expressed as geometric mean [interquartile range]. They were in accordance with those previously obtained with other systems. Segmental parameter values were maximum mean segmental dilation 534 mum (+/-305) and segmental compliance 14.6 (+/-8.3) 10(-2) mum/Pa. Reproducibility was appropriate for clinical studies. The TDI system is simple and reliable for measurement of AAA compliance, and compliance can easily be recorded during routine ultrasound control.