Volume 52 (9): 1141-1149, 2004 Copyright ©The Histochemical Society, Inc. More Fibrosis and Thrombotic Complications but Similar Expression Patterns of Markers for Coagulation and Inflammation in Symptomatic Plaques from DM2 Patients
Laboratory of Experimental Internal Medicine (DWS,AB,BEvA,HtC) and Department of Cardiovascular Pathology (HP,CMvdL,ACvdW), Academic Medical Center, Amsterdam; The Netherlands; Department of Clinical Chemistry, Free University, Amsterdam, The Netherlands (CGS); and Department of Internal Medicine and Cardiovascular Research Institute Maastricht, Academic Hospital and University of Maastricht, Maastricht, The Netherlands (HtC) Correspondence to: Dirkje W. Sommeijer, MD, Laboratory of Experimental Internal Medicine, G2-108, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. E-mail: d.w.sommeijer{at}amc.uva.nl
Objective: One of the possible pathological mechanisms behind the increased vascular injury in diabetes mellitus type 2 (DM2) is the formation of advanced glycation end products (AGEs). The aim of this study was to investigate whether the presence of AGEs and specific markers for coagulation and inflammation in symptomatic atherosclerotic plaques from DM2 patients differs from plaques from nondiabetics. Methods and results: Carotid atherectomies were obtained from DM2 patients (n=11) and controls without DM2 matched for age and other cardiovascular risk factors (n=12) who were treated for symptomatic carotid artery stenosis. Plaques were graded according to the American Heart Association classification of lesions. More fibrosis and more thrombotic complications (p=0.007) were observed in carotid atherectomies from DM2 patients. Percentages of immunostained smooth muscle cells and macrophages in the lesions, quantified planimetrically, did not differ between the two groups. No differences were found in the immunostaining for T cells, tissue factor (TF), endothelial protein C receptor (EPCR), nuclear factor B, and the AGE carboxymethyllysine. Conclusions: These findings demonstrate that DM2 is associated with increased plaque complications; however, a local changed presence of AGEs, TF, and EPCR seems not to be involved in this end stage of atherosclerosis. (J Histochem Cytochem 52:11411149, 2004)
Key Words: diabetes mellitus type 2 atherothrombotic complications atherectomy tissue factor endothelial protein C receptor advanced glycation end products nuclear factor
DIABETES MELLITUS TYPE 2 (DM2) is a risk factor for cardiovascular disease attributable to an accelerated process of atherosclerosis. An increasing body of evidence indicates that the presence of hyperglycemia is the primary causal factor for vascular complications in diabetic patients (Turner 1998
Tissue factor (TF) is a key player in initiating the activation of the coagulation cascade and is thought to be involved in the development of atherosclerosis and its thrombotic complications (Taubman et al. 1997
The endothelial protein C receptor (EPCR) plays a major role in the activation of the protein C anticoagulant pathway, which is an important mechanism in downregulating thrombus formation. It has been suggested that decreased expression of EPCR plays a role in the atherosclerotic process (Laszik et al. 2001
One of the signal transduction pathways that could play a role in the changed expression of coagulation factors by AGEs is the nuclear factor
Our hypothesis is that expression of TF and EPCR might be changed in diabetic atherosclerosis by an increased presence of AGEs. To test this hypothesis, we have immunohistochemically analyzed the presence and tissue localization of TF, EPCR, NF-
Patient Group For this study, a database was used that contained paraffin-embedded specimens of various arteries and veins from 244 patients who consecutively underwent peripheral vascular surgery at the Academic Medical Center (AMC), Amsterdam, The Netherlands, between 1994 and 1998. To use this database to compare specimens from patients with DM2 and controls, a nested case-control study was performed. First, a selection was made of all the vascular specimens of patients who had undergone carotid atherectomy because of symptomatic arterial stenosis. Second, carotid atherectomy specimens were selected from a subpopulation of patients with known DM2 at the time of intervention, treated with insulin and/or oral anti-diabetics (n=11). In addition, a matched control group (n=12) was selected, matched for coronary risk factors such as age, known hypertension [treated or known with hypertension (blood pressure >160/90 mmHg)], hypercholesterolemia [treated or known with hypercholesterolemia (total cholesterol >6 mmol/liter)], and smoking. For group characteristics, see Table 1. Informed consent was obtained before surgery, and the study was approved by the local ethical committee of the AMC.
Tissue Processing and Histomorphology Carotid atherectomies were obtained and immediately fixed in 4% buffered formalin after surgical removal. Tissues were routinely processed for paraffin embedding, and sections were serially cut at 5 µm from each specimen. Per atherectomy sample, one to three sites were available for testing (total control sites, n=17; total diabetes sites, n=13). To evaluate the morphology of atherosclerotic plaques, one section was stained with hematoxylin and eosin and one with elastic van Gieson. The severity of plaque formation was graded according to the American Heart Association (AHA) classification: type I lesion, intimal thickening with an increase in macrophages and formation of scattered macrophage foam cells; type II, fatty streak consisting of layers of macrophage foam cells and lipid-laden smooth muscle cells (SMCs); type III, preatheroma, potentially symptom producing; type IV, atheroma with a more disruptive core of extracellular lipid; type Va, fibroatheroma, lipid core containing thick layers of fibrous connective tissue; type Vb, largely calcified plaque; type Vc, plaque consists mainly of fibrous connective tissue with little or no accumulated lipid or calcium; type VI, complicated plaque with fissure, hematoma, and thrombus (Stary et al. 1995
Immunohistochemistry
Morphometric Analysis Results of anti- -actin and anti-CD68 antibodies were planimetrically quantified using image analysis software (Image Pro Plus; Media Cybernetics, Inc., Silver Spring, MD) on a personal computer connected with a video-mounted microscope. The total tissue area of each immunostained tissue section was outlined manually on the video screen and measured. Tissue areas of the immunopositive stained areas in the section were measured automatically using gray scale detection with a fixed threshold. Subsequently, SMCs and macrophage areas were calculated as percentages of the total tissue area.
For evaluation of CD3, NF- Observers were blinded to the clinical status of the patients.
Statistical Analysis
Patient Group For patient characteristics, see Table 1. There were no significant differences between diabetic patients and control patients with regard to age, gender, hypercholesterolemia, hypertension, and smoking. The average serum glucose levels of the diabetic patients (173.6 ± 19.3 mg/dl) were significantly higher than those of the control patients (109.4 ± 4.0 mg/dl) (p=0.004).
Morphological Features of Atherectomies
Immunohistochemistry of TF, EPCR, NF- B, and CMLNo differences were observed in the presence of TF, EPCR, NF- B, and CML staining in lesions from DM2 patients and controls (Table 4). Staining for CML varied widely from nearly absent to strong throughout the different plaques. However, no differences were found between DM2 patients and controls. CML was located in SMCs, macrophages, and the extracellular matrix (Figures 3C and 4C)
. Staining for TF was located in SMCs and macrophages (Figure 4B). In 87% of the plaques, colocalization of CML and TF in macrophages was observed, using two adjacent sections. There was no difference in the number of patients showing colocalization of CML and TF between the diabetic and nondiabetic groups. EPCR staining of the atherosclerotic plaque endothelium was weakly positive in endothelium of all atherosclerotic plaques (Figure 5B). EPCR staining in microvessel endothelium ranged from absent to weakly positive (Figure 5A). There were no differences in EPCR staining of the plaque endothelium or the microvessel endothelium in the DM2 group compared with the control group (Table 4). In nearly all atherectomies, only weak NF- B-p65 staining was observed, mainly located in SMCs, macrophages, and endothelial cells (Figures 3D and 4D). To identify the activation of NF- B, we used an antibody specifically against activated NF- B (MAB3026). A weak staining pattern of activated NF- B was observed, which was located in nuclei of SMCs, macrophages, and endothelial cells (Figure 6)
. No difference in staining was observed between diabetic and control plaques (Table 4).
Hyperglycemia is considered to play a major role in diabetic cardiovascular disease. In particular, the formation of AGEs appears to be an important mediator of hyperglycemia-induced vascular injury (Brownlee et al. 1988 B was observed.
The lack of difference in AGE staining in the present study might be explained by the symptomatic, end-stage atherosclerosis that was studied and is in agreement with earlier studies that reported that AGEs are associated with atherosclerotic lesions regardless of the presence of diabetes (Niwa et al. 1997
TF, the main initiator of the coagulation cascade, is widely expressed in atherosclerotic plaques and is thought to play a role in the development of acute arterial thrombosis. In agreement with earlier observations (Taubman et al. 1997
Activation of the NF-
EPCR expression was found to be decreased in endothelial cells covering atherosclerotic lesions compared with the expression in endothelial cells in control arteries (Laszik et al. 2001 In summary, we found a significantly higher number of fibrotic lesions and lesions with thrombotic complications in plaques from DM2 patients. However, we did not find evidence that this could be related to the increased presence of AGEs and the changed expression of coagulation proteins in diabetic atherosclerotic lesions. It may be that in this end stage of atherosclerosis, no more local differences in the presence of these proteins can be distinguished, although they might have played a role in an earlier stage of the process. Preexisting differences in the expression of coagulation and inflammation markers may have been obscured by the advanced stage of atherosclerosis. Thus, to elucidate the question of whether DM2 leads to a changed expression of inflammation and coagulation markers and whether this plays a role in the accelerated atherosclerotic process, studies of less advanced presymptomatic atherosclerotic lesions may be necessary.
HtC is a Clinical Established Investigator of the Netherlands Heart Foundation. CGS is financially supported by a grant from the Diabetes Fonds Nederland. We thank Angelique P.A. Groot from the Laboratory for Experimental Internal Medicine (AMC) and Wilfried P. Meun from the Department of Pathology (AMC) for their excellent technical assistance.
1 Present address: Department of Clinical Research, Centocor, Leiden, The Netherlands. Received for publication November 18, 2003; accepted April 13, 2004
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