Cellular and immunologic features of carotid artery disease in man and experimental animal models

Distribution of atherosclerotic lesions in various arteries of WHHLMI rabbits, an animal model of familial hypercholesterolemia

In WHHLMI rabbits, arterial lesions develop spontaneously in various arteries even with standard chow. Here, we examined the development of arterial lesions in various arteries to demonstrate standard characteristics of arterial lesions in WHHLMI rabbits. For WHHLMI rabbits at 6, 12, 20, and 30 months of age, lesion areas and areas of arterial lumen surfaces were measured using image analysis software. Histopathological sections of arterial lesions were stained with elastic van Gieson staining. Arterial lesions developed around bifurcations and expanded with aging. In the aorta, atheromatous lesions were severe in the thoracic aorta but were mild in the distal part of the abdominal aorta. Carotid artery lesions progressed in the proximal region and at bifurcations, and the histopathological features were similar to those of coronary lesions. Pulmonary artery lesions contained many foam cells. Fibrous lesions were observed in the proximal and distal areas of the renal arteries, at the bifurcation of the iliac-femoral artery and mesenteric artery, and around the anastomosis of vertebral arteries. Lesions in the celiac artery contained foam cells and/or lipid droplets within fibrous lesions. In a pair of right and left arteries, the arterial lesions tended to progress more in the right artery. Gender did not affect analysis of arterial lesions. In conclusion, the arterial lesions expanded from bifurcations, and the morphological features of the arterial lesions varied depending on the type of artery. These results serve as reference data for arterial lesions in studies using WHHLMI rabbits.

Carotid artery disease: novel pathophysiological mechanisms identified by gene-expression profiling of peripheral blood

OBJECT

The pathogenesis of carotid artery stenosis (CAS) as well as the mechanisms underlying the different localisation of the atherosclerotic lesions remains poorly understood. We used microarray technology to identify novel systemic mediators that could contribute to CAS pathogenesis. Moreover, we compared gene-expression profile of CAS with that of patients affected by abdominal aortic aneurysm (AAA), previously published by our group.

METHODS AND RESULTS

By global gene-expression profiling in a pool of 10 CAS patients and 10 matched controls, we found 82 genes differentially expressed. Validation study in pools used for profiling and replication study in larger numbers of CAS patients (n = 40) and controls (n = 40) of 14 genes by real-time polymerase chain reaction (RT-PCR) confirmed microarray results. Fourteen out of 82 genes were similarly expressed in AAA patients. Gene ontology analysis identified a statistically significant enrichment in CAS of differentially expressed transcripts involved in immune response and oxygen transport. Whereas alteration of oxygen transport is a common tract of the two localisations, alteration of immune response in CAS and of lipid metabolic process in AAA represents distinctive tracts of the two atherosclerotic diseases.

CONCLUSIONS

We describe the systemic gene-expression profile of CAS, which provides an extensive list of potential molecular markers.

Suppression of hypercholesterolemic atherosclerosis by pentoxifylline and its mechanism

Reactive oxygen species (ROS) have been implicated in the development of hypercholesterolemic atherosclerosis. Hypercholesterolemia increases the levels of platelet activating factor (PAF) and cytokines which are known to stimulate granulocytes and endothelial cells to produce ROS. Pentoxifylline (PTX) is an inhibitor of cytokines and PAF and would reduce the generation of ROS by granulocytes and endothelial cells. PTX therefore would be expected to reduce the development of hypercholesterolemic atherosclerosis. New Zealand white female rabbits were assigned to four groups: Group I (n=12), control; Group II (n=5), PTX control (40 mg/kg body weight daily orally); Group III (n=13), 0.5% cholesterol; Group IV (n=9), 0.5% cholesterol+PTX (40 mg/kg body weight daily orally). Blood samples were collected before (0 time) and after 1 and 2 months on experimental diets for measurement of serum triglycerides (TG), total cholesterol (TC), LDL-C, HDL-C and serum malondialdehyde (MDA), a lipid peroxidation product. At the end of 2 months the aorta was removed for measurement of atherosclerotic plaques, MDA, and aortic tissue chemiluminescence (Ao-CL), a marker for antioxidant reserve. Rabbits in Group III developed atherosclerosis (56.61+/-6.90% of the intimal surface of aorta was covered with atherosclerotic plaques) which was associated with an increase in the serum TG, TC, LDL-C, HDL-C, TC/HDL-C, MDA and aortic MDA and antioxidant reserve. PTX reduced the development of atherosclerosis by 38.1% and this was associated with decreases in serum MDA by 32%, aortic MDA by 37%, and antioxidant reserve by 17.3% without changes in the serum lipids. These results suggest that ROS generated during hypercholesterolemia via cytokines and PAF may in part contribute to the development of hypercholesterolemic atherosclerosis and that suppression of production and activity of cytokines and PAF may reduce the development of hypercholesterolemic atherosclerosis.

Contractile and cytoskeletal proteins of smooth muscle cells in rat, rabbit, and human arteries

The aim of this study was to determine whether similar populations of smooth muscle cells, in relation to contractile and cytoskeletal proteins, are present in normal and diseased human coronary arteries and normal and injured rat and rabbit arteries. Rat aortae and rabbit carotid arteries were de-endothelialised and the resulting neointimal thickening examined at set time points 2-24 weeks later. Immunohistochemistry revealed that arteries had three distinct populations of cells in respect to alpha-smooth muscle actin, smooth muscle myosin heavy chain and vimentin (staining intensities '-', '+' or '++' for each protein), but only two populations in respect to desmin ('-' and '+'). The different populations of cells were found in the neointima at all times after injury, in human atherosclerotic plaque and in the media of diseased, injured and uninjured vessels, although in different proportions. It was concluded that arteries of the human, rat and rabbit have cells with a wide spectrum of contractile and cytoskeletal proteins. Expression of the different proteins did not reflect the state of the artery after injury or during the disease process, and was not associated with the expansion of a subset of cells within the artery wall.

A combined histochemical and double immunohistochemical labeling protocol for simultaneous evaluation of four cellular markers in restenotic arteries

We designed an effective quadruple staining protocol that combines histochemistry (HC) and double-labeling immunohistochemistry (IHC: IHC) to stain simultaneously several different morphological features and cell types in vascular lesions. Morphometric image analysis to quantitate vascular wall thickening, lumen area, and proliferating smooth muscle cells on consecutive serial sections is adequate, but morphometric precision and dependable cellular characterization and co-localization could be obtained if analyses are performed on one tissue section. The development of a neointima in the rat carotid artery was induced by angioplasty with a balloon catheter. Tissues were stained for elastin by a modified van Gieson method, then processed for double-labeling IHC:IHC for proliferating cell nuclear antigen and smooth muscle actin followed by hematoxylin staining. The four resulting tissue stains labeled elastin filaments black, proliferating nuclei brown, smooth muscle actin red and nonproliferating nuclei blue. Our staining protocol improved the descriptive and quantitative analysis of relation between smooth muscle cell proliferation and protein expression. Also, neointimal thickening could be measured to analyze its relation to cellular proliferation. Providing one slide with four stains maximizes the information from a single slice of tissue, reduces slide preparation and analysis time, and overcomes the restriction of tissue sample availability. This technique can be applied to a wide spectrum of morphologic and morphometric studies.

Dexamethasone and enalapril suppress intimal hyperplasia individually but have no synergistic effect

Vascular injury is associated with complex interactions that lead to development of intimal hyperplasia (IH). We have demonstrated previously that the corticosteroid dexamethasone and the ACE-inhibitor enalapril are effective in suppressing the development of IH. We hypothesize that due to distinctly different pharmacologic mechanisms of action, a synergistic effect would be expected if these agents were given in combination. Forty New Zealand White rabbits underwent balloon catheter denudation of the carotid artery. Animals were divided into four equal treatment groups and received daily intramuscular injections: Group 1, saline; Group 2, enalapril 0.07 mg/kg, Group 3, dexamethasone 0.125 mg/kg; and Group 4, enalapril 0.07 mg/kg plus dexamethasone 0.125 mg/kg. Vessels were harvested at 12 weeks and intimal hyperplasia was measured as a ratio of the absolute area of IH to the normalized area enclosed by the internal elastic lamina (IH/IEL). Mean values for IH/IEL are expressed as a percent (SD): Group 1, 32.31 (14.9); Group 2, 9.47 (2.11); Group 3, 5.40 (4.14); and Group 4, 8.49 (4.27). All treatment groups demonstrated significant suppression of IH compared to the control group (p < 0.01); dexamethasone was more effective than enalapril (p = 0.01). There was no statistical difference in IH suppression between respective agents and the combination group (p > 0.10). Coadministration of dexamethasone and enalapril provides no advantage over single-agent therapy in suppressing the development of IH, suggesting that maximal suppression is obtained with single-agent treatment or that these agents affect IH through a common pathway.

Ischemia-Induced Transplant Arteriosclerosis in the Rat

The effect of cold graft ischemia time on the development of transplant arteriosclerosis was investigated. Aorta grafts from DA or PVG rats were stored in a cold perfusion solution for 1, 4, or 24 hours before being orthotopically transplanted to PVG recipients. After observation times ranging from 2 to 8 weeks, the grafts were examined for various cell populations. Regional changes in the intima and media layers were measured by using an image analysis system. The arteriosclerosis-like changes seen in syngeneic grafts with the longest ischemia time could be almost as prominent as those seen in the al-logeneic transplants. The magnitude of the regional intima changes in the syngeneic group correlated well with the ischemia time and in the allogeneic group with the observation time. The cell composition found in the intima and media of the allogeneic vessels consisted of macrophages, T-lymphocytes, MHC class II-expressing cells, and smooth muscle cells, whereas the syngeneic grafts contained almost exclusively smooth muscle cells and macro-phages. We therefore conclude that the damage due to prolonged cold ischemia time is sufficient to cause pronounced graft arteriosclerosis. The patho-physiological mechanism leading to ischemia-induced arteriosclerosis is different from the one seen in the allogeneic situation. (Arterio-scler Throtnb Vase Biol . 1995;15:145-155.)

Increased concentrations of neopterin in carotid atherosclerosis

Activation of T-cells and macrophages may play a role in the pathogenesis of atherosclerosis. Therefore, serum concentrations of the immune activation markers neopterin and soluble interleukin-2 receptor were compared with routine laboratory parameters, candidate risk variables and degree of carotid atherosclerosis. Study subjects were 561 individuals (293 men and 268 women) aged between 50 and 79 years who were enrolled in a cross-sectional community based study (Ischemic Heart Disease and Stroke Prevention Study, Bruneck, Italy). Extent of carotid atherosclerosis was quantitated by an ultrasound B-mode procedure based scoring system. Detailed physical examination and quantification of laboratory and candidate risk variables were performed. By univariate as well as multivariate statistical analyses, serum concentrations of neopterin but not soluble interleukin-2 receptor were significantly higher in subjects with carotid atherosclerosis (men, 8.5 +/- 2.7 nmol/l neopterin; women, 9.6 +/- 3.3) than in those without (men, 6.7 +/- 2.3, P < 0.0001; women, 7.5 +/- 2.3, P < 0.0001). The data show that the macrophage-derived immune activation marker neopterin is closely correlated with the extent of carotid atherosclerosis. Chronic activation of immune cells, preferentially of macrophages, may play a key role in atherogenesis and/or progression of atherosclerosis.

Polymorphonuclear leukocytes and monocytes/macrophages in the pathogenesis of cerebral ischemia and stroke

BACKGROUND

The extent to which polymorphonuclear leukocytes and monocytes/macrophages contribute to the pathobiology of cerebral ischemia and stroke is an issue of long-standing contradiction and controversy. Recent developments in the ability to selectively modify leukocyte adhesion with antiadhesion antibodies and the potential clinical application of this therapeutic approach have spurred a resurgence of experimental studies examining the role of leukocytes in cerebral ischemia and stroke.

SUMMARY OF REVIEW

We review studies examining leukocyte accumulation, initiation of thrombosis, and exacerbation of ischemic brain injury in stroke, and we examine other proposed contributions of leukocytes to cerebrovascular pathophysiology.

CONCLUSIONS

The importance of specific characteristics of a given ischemia model and of underlying stroke risk factors in determining the degree of leukocyte involvement and effectiveness of therapies directed against these cells is discussed.

The synergistic effect of hypercholesterolemia and mechanical injury on intimal hyperplasia

In an attempt to clarify data obtained from animal models of intimal hyperplasia, we used New Zealand white rabbits, a standardized balloon catheter injury model, and a 0.25% cholesterol supplemented diet. The effects of mechanical injury and hypercholesterolemia separately and combined were determined at the carotid and iliac positions at 12 weeks. En-face planimetry of lesioned intima and measurement of transverse intima-to-media thickness were taken as indices of intimal hyperplasia. No animals received antiplatelet agents or postoperative anticoagulation and all vessels remained patent. Neither procedure alone resulted in statistically significant lesion increase. However, combinations of injury and cholesterol resulted in statistically significant and synergistic lesion enhancement. The quantitative data, coupled with distinctive features noted on scanning electron microscopy and transmission electron microscopy, showed separate and synergistic effects of mechanical injury and cholesterol diet on intimal lesions in this model. Additionally, these effects must be considered in evaluation of animal models of intimal hyperplasia and atherosclerosis. Furthermore, this may help dissect mechanisms of failed revascularizations.

Interferon-gamma inhibits arterial stenosis after injury

BACKGROUND

Arterial injury initiates a proliferative response among the smooth muscle cells of the artery. This leads to the formation of a thickened intima that may reduce the diameter of the arterial lumen. Such intimal lesions often develop after vascular surgery and angioplastic procedures. Previous cell culture studies have shown that the lymphokine, interferon-gamma (gIFN), inhibits smooth muscle cell proliferation.

METHODS AND RESULTS

We therefore tested whether administration of exogenous gIFN could inhibit the development of intimal lesions. Rat carotid arteries were denuded with a balloon catheter, resulting in the formation of a standardized intimal lesion. The animals were then treated with recombinant rat gIFN at 200,000 units (approximately 400,000 units or 100 micrograms/kg body wt) administered parenterally once daily for 7 days. Autoradiographic analysis of 3H-thymidine incorporation revealed that gIFN reduced the early smooth muscle replication by approximately 75%. gIFN treatment for 1 week resulted in a 50% reduction of intimal cross-section area at 2 weeks after injury when compared to control rats injected with buffer alone. The difference in lesion development persisted in rats analyzed 10 weeks after injury, suggesting that proliferative events during the first week determine the long-term development of the intima. Inhibition of lesion development was accompanied by expression of the class II histocompatibility (Ia) gene, RT1B, suggesting that both were directly related to the administration of gIFN.

CONCLUSIONS

These results show that gIFN is a potent inhibitor of the formation of arterial proliferative lesions in vivo. It is possible that gIFN could be useful in preventing arterial stenosis after surgery and angioplasty in man.