Biomedical subjects

M M Kockx

Publications and source records attributed to M M Kockx.

At least 37 records · Page 2Linked to original sources

PubMed2000

The role of apoptosis in vascular disease.

Normal arteries are characterized by a low turnover of endothelial (EC) and smooth muscle cells (SMC). Different mechanisms protect the EC and SMC against apoptosis in the normal artery. In hypertension, SMC replication is increased but this is not counterbalanced by increased apoptosis, resulting in thickening of the media of arteries and arterioles. The significance of apoptosis in atherosclerosis depends on the stage of the plaque, localization and the cell types involved. Both macrophages and SMC undergo apoptosis in atherosclerotic plaques. Apoptosis of macrophages is mainly present in regions showing signs of DNA synthesis/repair. SMC apoptosis is mainly present in less cellular regions and is not associated with DNA synthesis/repair. Even in the early stages of atherosclerosis SMC become susceptible to apoptosis since they increase different pro-apoptotic factors. Moreover, recent data indicate that SMC may be killed by activated macrophages. The loss of the SMC can be detrimental for plaque stability since most of the interstitial collagen fibres, which are important for the tensile strength of the fibrous cap, are produced by SMC. Apoptosis of macrophages could be beneficial for plaque stability if apoptotic bodies were removed. Apoptotic cells that are not scavenged in the plaque activate thrombin, which could further induce intraplaque thrombosis. It can be concluded that apoptosis in primary atherosclerosis is detrimental since it could lead to plaque rupture and thrombosis. Recent data of our group indicate that apoptosis decreased after lipid lowering which could be important in the understanding of the cell biology of plaque stabilization.

Apoptosis↗

PubMed2000

Apoptosis in atherosclerosis: beneficial or detrimental?

Several groups have demonstrated apoptotic cell death in atherosclerotic plaques. The significance of apoptosis in atherosclerosis depends on the stage of the plaque, localization and the cell types involved. Both macrophages and smooth muscle cells undergo apoptosis in atherosclerotic plaques. Apoptosis of macrophages is mainly present in regions showing signs of DNA synthesis/repair. Smooth muscle cell apoptosis is mainly present in less cellular regions and is not associated with DNA synthesis/repair. Even in early stages of atherosclerosis smooth muscle cells become susceptible to undergoing apoptosis since they increase different pro-apoptotic factors. Moreover, recent data indicate that smooth muscle cells may be killed by activated macrophages. The loss of the smooth muscle cells can be detrimental for plaque stability since most of the interstitial collagen fibers, which are important for the tensile strength of the fibrous cap, are produced by SMC. Apoptosis of macrophages could be beneficial for plaque stability if apoptotic bodies are removed. Apoptotic cells that are not scavenged in the plaque activate thrombin which could further induce intraplaque thrombosis. It can be concluded that apoptosis in the primary atherosclerosis is detrimental since it could lead to plaque rupture and thrombosis. Recent data of our group indicate that apoptosis decreases after lipid lowering which could be important in our understanding of the cell biology of plaque stabilization.

Apoptosis↗

PubMed2000

Periadventitial inducible nitric oxide synthase expression and intimal thickening.

Positioning a silicone collar around the rabbit carotid artery induces a smooth muscle cell-rich intimal thickening. We investigated the localization of inducible nitric oxide synthase (iNOS) during thickening of the intima, the effect of iNOS inhibition on intimal thickness, and the effect of oxidized LDL (ox-LDL) on iNOS expression in the vessel wall. Collars were positioned for 18 hours or for 3, 7, or 14 days. Arterial cross sections were immunostained for iNOS, including naïve, sham-operated, and carotid arteries in which ox-LDL had been infused locally for 14 days. Furthermore, collars were connected to osmotic minipumps for local delivery (5 microL. h(-1), 14 days, n=12) of saline or the iNOS inhibitor L-N(6)-(1-iminoethyl)-lysine-HCl (L-NIL, 10 mmol/L). In the adventitia and the periadventitial granulation tissue of collared arteries, iNOS-positive macrophages and T lymphocytes were present from 18 hours onward. The media and intima were negative for iNOS. Reverse transcription-polymerase chain reaction revealed iNOS mRNA in collared but not in sham-operated arteries. Local inhibition of iNOS doubled the intimal thickness and decreased nitrotyrosine staining. Ox-LDL-treated arteries, which had a thicker intima, showed a pronounced influx of macrophages and T lymphocytes in all layers of the vessel wall, accompanied by iNOS expression in a subpopulation of these cells. Our study indicates that iNOS was not induced in intimal thickenings predominantly consisting of smooth muscle cells. However, iNOS was expressed in (peri)adventitial tissue and counteracted the progression of intimal thickening. Ox-LDL treatment was accompanied by an abundant influx of iNOS-positive macrophages and T lymphocytes in the vessel, but this could not prevent the progression of intimal thickening.

Animals↗

PubMed1999

Inducible nitric oxide synthase colocalizes with signs of lipid oxidation/peroxidation in human atherosclerotic plaques.

OBJECTIVE: Advanced human atherosclerotic plaques are characterized by the abundant presence of the autofluorescent non-soluble lipid pigment ceroid, consisting of oxidized lipoproteins. The aim of the present study was to examine the topographical and cellular distribution of inducible nitric oxide synthase (iNOS or NOS II) within different stages of atherosclerosis and its colocalization with ceroid deposits and nitrotyrosine. METHODS AND RESULTS: Different stages of atherosclerosis were studied by immunohistochemistry on whole-mount longitudinal sections of carotid endarterectomy specimens. In the adaptive intimal thickening the predominant cell type were smooth muscle cells. The fatty streaks contained both smooth muscle cells and macrophages with an extremely low NOS II immunoreactivity. The advanced atherosclerotic plaques however, showed a very dense infiltration by macrophages, of which a subpopulation expressed NOS II as a vesicular immunoreactivity in their cytoplasm. These were mainly present around the necrotic core, in association with ceroid accumulation and nitrotyrosine. Fluorescence quenching microscopy showed the presence of NOS II on autofluorescent ceroid vesicles in the macrophages. Large extracellular ceroid granules were not NOS II immunoreactive. NOS II mRNA was detected by RT-PCR and the protein by Western blot in the plaque tissue but not in mammary arteries used as controls. CONCLUSION: Ceroid, nitrotyrosine and NOS II colocalized in late stages of atherosclerosis and were found around the necrotic core in the plaque. This could suggest that NOS II expression in macrophages is involved in oxidation and peroxidation of lipids, leading to ceroid formation.

Aged↗

PubMed1999

Regression of cholesterol induced venous plaques after cholesterol withdrawal in rabbits.

Rabbits receiving a dietary cholesterol supplement of 0.5% develop atheromatous plaques in the systemic arteries, the pulmonary artery, the pulmonary veins and the venous cavities of the plexus pampiniformis in the funiculus spermaticus. Six months after the withdrawal of the cholesterol supplement the arterial lesions are still present, and show a fibrous transformation. This study is the first report of the total regression of the lesions in the particular venous localizations of the lungs and the plexus pampiniformis. The level of intraluminal pressure is discussed as the possible mechanism responsible for the diverging vascular reactivity.

Actins↗

PubMed1999

Intimal deposition of functional von Willebrand factor in atherogenesis.

During the formation of intimal thickening in normocholesterolemic rabbits, von Willebrand factor (vWF) is increased in the endothelial cells (ECs) and deposited in the intima. We investigated whether this also occurs during cholesterol-induced plaque formation, whether the synthesis of vWF increases, and whether this influences platelet adhesion. Rabbits were fed a cholesterol-rich (0.3%) diet for 26 weeks. Thereafter, half of the animals received a normal diet for another 26 weeks (cholesterol withdrawal). To induce intimal thickening in normocholesterolemic rabbits, collars were positioned around the carotid artery. Arterial segments were studied using immunohistochemistry, reverse transcription-polymerase chain reaction, electron microscopy, and platelet adhesion tests. Cholesterol treatment induced plaque formation in the aorta. The ECs had a cuboidal aspect, showed a dense immunoreactivity for vWF, a pronounced rough endoplasmic reticulum, and numerous Weibel-Palade bodies. There were subendothelial vWF deposits in the plaques and vWF mRNA was significantly increased as compared with controls. Similar changes were seen after collar-induced intimal thickening. After cholesterol withdrawal, both vWF mRNA and the ultrastructural morphology of the ECs normalized, and the vWF deposits disappeared from the plaque. Perfusion studies with anticoagulated rabbit blood over cross-sections of atherosclerotic aortas revealed increased vWF-mediated platelet adhesion in the subendothelial plaque region. Whereas rabbit platelets perfused through the lumen adhered to the same extent to de-endothelialized aortas of normocholesterolemic and atherosclerotic rabbits, vWF mediated platelet adhesion to endothelium was observed in atherosclerotic but not in normal aortas. Our results show an increased synthesis and (sub)endothelial presence of vWF after vascular injury, with functional consequences for platelet deposition on the vessel wall.

Animals↗

PubMed1999

Continuous perivascular L-arginine delivery increases total vessel area and reduces neointimal thickening after experimental balloon dilatation.

The aim of this study was to evaluate whether vascular remodeling and neointimal thickening occur after balloon dilatation of the nonatherosclerotic rabbit carotid artery, and whether both processes are influenced by continuous perivascular delivery of L-arginine or the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME). In the first experiment, histological and morphometric evaluation of arteries was performed at different time points after balloon dilatation: 10 minutes (n=7), and 1 (n=7), 2 (n=9), 3 (n=20), or 10 (n=5) weeks. Neointimal thickening progressively contributed to luminal narrowing for at least 10 weeks after angioplasty. During the first 2 weeks after dilatation, a significant decrease of the total vessel area was measured. Ten weeks after dilatation, both the neointimal and total vessel area were increased without further changing of the luminal area. In the second experiment, endothelial injured rabbits were randomly assigned to receive 2 weeks of continuous local perivascular physiological salt solution (n=6), L-arginine (n=8), or L-NAME (n=7), starting immediately after balloon dilatation (ie, local drug delivery during the first phase of the biphasic vascular remodeling process). Perivascular L-arginine delivery significantly reduced the neointimal area, despite an increased number of neointimal Ki-67-positive smooth muscle cells. Both the luminal area and total vessel area were significantly increased. Serum L-arginine levels remained unchanged. L-NAME administration had no effect on the neointimal area, nor on the luminal and total vessel area. Neointimal formation and biphasic vascular remodeling occur after experimental balloon dilatation of the nonatherosclerotic rabbit carotid artery, and can be influenced by continuous local perivascular delivery of L-arginine.

Animals↗

PubMed1998

Cell composition, replication, and apoptosis in atherosclerotic plaques after 6 months of cholesterol withdrawal.

Unstable human atherosclerotic plaques are characterized by a thin fibrous cap that contains few smooth muscle cells (SMCs) and numerous foam cells of macrophagic origin. Apoptosis of SMCs in the fibrous cap could destabilize the plaque and promote plaque rupture. In an experimental approach, we have studied apoptotic cell death and related proteins in atherosclerotic plaques of cholesterol-fed rabbits and examined the effects of cholesterol withdrawal. The induced atherosclerotic plaques at the thoracic aorta were composed of both fibromuscular tissue and foam cells. The presence of SMCs overlying macrophage accumulation was reminiscent of the structure of human atherosclerotic plaques. The plaques showed signs of cell replication and apoptotic cell death (1.8+/-0.5% terminal deoxynucleotidyl transferase end-labeling [TUNEL]-positive nuclei). Cell replication was confined mostly to the macrophages, whereas 34% of the TUNEL-labeled cells were SMCs. Both the macrophages and SMCs in the plaques expressed BAX, a proapoptotic protein of the BCL-2 family. After 6 months of cholesterol withdrawal, the thickness of the plaques in all localizations of the aorta was unchanged, but apoptosis was nearly absent (<0.1% of nuclei). Moreover, macrophages disappeared from the plaques, whereas the SMCs that remained present lost their lipid accumulation and strongly reduced their BAX expression. These changes were associated with a reduction of cell replication and increased deposition of fibrillar collagen fibers in the plaques, which pointed to plaque stabilization. In conclusion, the cell composition but not the thickness of atherosclerotic plaques was profoundly altered after a 6-month cholesterol withdrawal period. These changes were associated with a strong reduction of cell replication and apoptotic cell death. Moreover, the expression of the proapoptotic factor, BAX, was reduced in the remaining cells, which were mainly SMCs. These findings could help to explain the benefit of lipid-lowering therapy on plaque stabilization.

Animals↗

PubMed1998

Apoptosis and related proteins in different stages of human atherosclerotic plaques.

BACKGROUND: The transition of a fatty streak into an atherosclerotic plaque is characterized by the appearance of focal and diffuse regions of cell death. We have investigated the distribution of apoptotic cell death and apoptosis-related proteins in early and advanced atherosclerotic lesions. METHODS AND RESULTS: Human atherosclerotic plaques were studied by whole-mount carotid endarterectomy specimens (n=18). This approach allowed comparison of adaptive intimal thickenings, fatty streaks, and advanced atherosclerotic plaques of the same patient. The fatty streaks differed from adaptive intimal thickenings by the presence of BAX (P<0.01), a proapoptotic protein of the BCL-2 family. Both regions were composed mainly of smooth muscle cells (SMCs), and macrophage infiltration was low and not different. Apoptosis, as detected by DNA in situ end labeling (terminal deoxynucleotidyl transferase end labeling [TUNEL] and in situ nick translation) was not present in these regions. Apoptosis of SMCs and macrophages, however, was present in advanced atherosclerotic plaques that were present mainly in the carotid sinus. A dense infiltration of macrophages (5.8+/-3% surface area) was present in these advanced atherosclerotic plaques. Cytoplasmic remnants of apoptotic SMCs, enclosed by a cage of thickened basal lamina, were TUNEL negative and remained present in the plaques as matrix vesicles. CONCLUSIONS: We conclude that SMCs within human fatty streaks express BAX, which increases the susceptibility of these cells to undergo apoptosis. The localization of these susceptible SMCs in the deep layer of the fatty streaks could be important in our understanding of the transition of fatty streaks into atherosclerotic plaques, which are characterized by regions of cell death. Matrix vesicles are BAX-immunoreactive cytoplasmic remnants of fragmented SMCs that can calcify and may be considered the graves of SMCs that have died in the plaques.

Aged↗

PubMed1998

Exposure to oxidized low-density lipoprotein in vivo enhances intimal thickening and selectively impairs endothelium-dependent dilation in the rabbit.

OBJECTIVES: Based on in vitro studies, oxidized low-density lipoprotein (oxLDL) has been implicated in atherogenesis and the associated deficiency in endothelium-dependent relaxation. The aim of this study was to investigate the effects of in vivo exposure to oxLDL on intimal thickening and relaxing behaviour. METHODS: Intimal thickening was evoked by the placement of silicone collars around the carotid arteries of the rabbit for 3 or 14 days. OxLDL (Cu(2+)-oxidized, 7 micron/h) or the vehicle phosphate-buffered saline (PBS) was infused in the collars via subdermally implanted osmotic minipumps. RESULTS: The collared vessels receiving PBS developed discrete intimal thickening after 14 days (intima/media (I/M) ratio 11 +/- 2%). OxLDL infusion resulted in intimal thickening after 3 days and significantly enhanced the intimal thickness by 14 days (I/M ratio 98 +/- 16%). Collaring alone for 3 or 14 days and 3 days exposure to oxLDL did not impair the endothelium-dependent relaxations to acetylcholine or calcium ionophore, nor to the NO donors glyceryl trinitrate (GTN) and S-nitroso-N-acetylpenicillamine (SNAP). However, the sensitivity to acetylcholine was decreased after exposure to oxLDL for 14 days (-logEC50 oxLDL 6.95 +/- 0.11 vs. 7.52 +/- 0.11 collar alone) and the maximal relaxation to the endothelium-dependent agonist was reduced by 50%, this in the presence of a virtually intact endothelium. Complete relaxation was still obtained with the nitric oxide donors. CONCLUSION: Our results show for the first time that local vascular exposure to oxLDL in vivo promotes intimal thickening and inhibits endothelium-dependent dilation, thereby supporting an active role for oxLDL in the morphological and functional changes observed in atherosclerotic blood vessels.

Acetylcholine↗

PubMed1998

Apoptosis in the atherosclerotic plaque: quantitative and qualitative aspects.

Several laboratories have demonstrated the presence of apoptotic cell death in atherosclerotic plaques. Apoptosis occurs in at least 2 stages. The final "execution" phase, which includes DNA fragmentation, is brief ( approximately 6 hours) and irreversible and can be detected by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) technique. The TUNEL technique is only selective (rather than specific) for apoptotic nuclei, because these contain a far greater degree of DNA fragmentation than do nonapoptotic nuclei. Nonapoptotic cell nuclei that show high levels of RNA synthesis and splicing can also be labeled. This could explain the large variation in the reported percentages of TUNEL-positive nuclei in the plaques. Therefore, the TUNEL technique should be combined with additional techniques, such as markers of transcription and morphological criteria. Recent studies indicate that human fatty streaks differ from adaptive intimal thickenings by the presence of cells containing pro-apoptotic proteins. However, apoptotic cell death is present only in advanced atherosclerotic plaques that show a dense macrophage infiltration. This indicates that although both smooth muscle cells and macrophages within the human fatty streaks become susceptible to apoptosis, additional factors (mainly macrophage- and lipid-derived factors) are necessary to terminate the cell death pathway.

Animals↗

PubMed1998

Role of polymorphonuclear leukocytes in collar-induced intimal thickening in the rabbit carotid artery.

In this study, the involvement of polymorphonuclear leukocytes (PMNs) in the development of intimal thickening was investigated. A fibromuscular intima was induced by placing a silicone collar around the rabbit carotid artery for 3 days or 2 weeks; the contralateral artery was sham operated. Rabbits received placebo treatments (groups 1 and 3), granulocyte-colony stimulating factor (group 2; G-CSF, 20 microg x kg(-1) x d(-1), delivered by subcutaneous osmotic pumps), or an anti-CD18 monoclonal antibody (group 4; 1.5 mg/kg i.v.). The G-CSF treatment raised the peripheral PMN count 5- to 12-fold but had no effect on intimal thickening on day 3, 12, or 14. A single injection of anti-CD18 prevented PMN extravasation 6 hours after collar implantation without influencing intimal hyperplasia on day 14. Repeated daily administration of anti-CD18 strongly bound to CD18 on peripheral PMNs and inhibited both PMN-dependent plasma extravasation in the skin and accumulation of CD14-immunoreactive leukocytes in the intima and media. However, anti-CD18 did not suppress early intimal thickening or accumulation of alpha-smooth muscle actin-immunoreactive cells by day 3. It thus appears that the PMN influx in the intima and media evoked by the perivascular collar is of little functional relevance to the subsequent smooth muscle cell migration and intimal thickening in this model.

Animals↗

PubMed1998

Vascular remodeling in varicose veins.

The present study describes the histopathologic aspects of varicose (n=29; mean age, 52 +/- 12 years) and normal saphenous veins (n=17; mean age, 51 +/- 12 years) of patients from a similar age group. We focused on the changes that occur in the circular layer of the venous wall. We examined the venous walls by light microscopy and transmission electronmicroscopy. A semiquantitative grading system was used to assess the smooth muscle cell (SMC) hypertrophy and the change that occurs in the elastin pattern. The volume densities (Vv) of SMC and collagen were measured as well as the diameter of the SMC, and the nuclei of SMC per fixed area were counted. The varicose vein wall differed from the normal saphenous vein by the presence of hypertrophic SMC as well as disorganized elastin patterns. A correlation between the hypertrophic SMC and an abnormal elastin pattern was observed (r=0.658, p<0.001). Ultrastructurally, the SMC show prominent microherniations and vesicles that bud from the cell. These vesicles contain microfilaments and microtubuli, although no other organelles could be detected. The elastin fibers are disrupted from the hypertrophic SMC. No significant difference could be detected in both the Vv of SMC and the Vv of collagen. The diameter of the SMC in the varicose vein (d=9.45 +/- 1.22 microm) differs significantly from that in the normal saphenous vein (d=6.22 +/- 1.47 microm) (p<0.001). Also, the nuclei of SMC per fixed area differs significantly between the varicose (87 +/- 18) and nonvaricose (117 +/- 24) veins (p<0.001). We conclude that the cellular hypertrophy of the SMC and the microherniations could be the basis for disruption of the elastin fibers connected to the SMC in varicose veins. Disrupted connections between SMC and elastin fibers could in turn induce the weakness of the venous wall observed in varicose vein disease.

Adult↗

PubMed1998

RNA synthesis and splicing interferes with DNA in situ end labeling techniques used to detect apoptosis.

The detection of DNA fragmentation by the use of the TUNEL technique has become a standard technique for the detection of apoptosis in tissue sections. DNA cleavage, detected by the TUNEL technique, is the last irreversible stage of the apoptosis cascade. When the nuclear DNA is cleaved in oligonucleosomal-sized fragments, processes such as transcription are completely abolished. The values of apoptotic cell death that were obtained for atherosclerotic plaques by the TUNEL technique ranged from less than 2% up to 60%. The latter value would indicate that plaques are in an imminent state of collapse, which is certainly not the case. Other factors that could result in TUNEL labeling have to be considered. Therefore, we developed a co-localization system and studied TUNEL labeling together with markers of RNA transcription and splicing. The present study demonstrates that, besides apoptotic nuclei, non-apoptotic nuclei that show signs of active gene transcription are labeled by the TUNEL technique. The fact that the TUNEL technique is not specific for the executive phase of apoptosis is not surprising, as the technique is only selective (rather than specific) for apoptotic nuclei as these contain a far greater degree of DNA fragmentation than non-apoptotic nuclei. Therefore, we think that the TUNEL technique should be combined with additional techniques, such as markers of transcription and morphological criteria.

Apoptosis↗

PubMed1998

Apoptosis in atherogenesis: implications for plaque destabilization.

Atherosclerotic plaques in coronary arteries are composed of a crescent-shaped mass of lipids separated from the lumen by a fibrous cap. Loss of smooth muscle cells (SMCs) in the fibrous cap could have serious consequences, since SMCs are the only cells in the cap that can synthesize collagen fibres type I and III. These fibres maintain the tensile strength of the fibrous cap. The role of cell loss and apoptotic cell death in the progression of atherosclerosis has received renewed attention recently in the literature. The large variability in the reported values for the percentage of apoptotic cells in plaques can be explained by the aspecificity of the TUNEL technique used to detect apoptosis. Despite this variability, there is no doubt that both SMCs and macrophages can die in plaques through apoptosis. The significance of macrophage apoptosis is very different from that of SMC apoptosis. Increased apoptosis of SMCs in the vulnerable regions of the plaque can result in weakening of the fibrous cap, whereas increased macrophage apoptosis can lead to plaque stabilization through decreased breakdown of collagen. Cytoplasmic remnants of apoptotic SMCs often remain in the plaque as matrix vesicles. These small calcium-containing vesicles could initiate plaque calcification.

Animals↗

PubMed1997

The effect of chronic treatment with NO donors during intimal thickening and fatty streak formation.

Intimal thickening in arteries is considered as a site of predilection for atherosclerosis. We investigated whether oral application of the nitric oxide (NO) donors SPM-5185 (N-nitratopivaloyl-S-(N'-acetylalanyl)-cysteine ethylester, 10 mg/kg body weight/b.i.d.) and molsidomine (pro-drug of 3-morpholino-sydnonimine (SIN-1), 10 mg/kg body weight/day) can retard intimal thickening and changes in vascular reactivity induced by a silicone collar positioned around the carotid artery of rabbits. Intimal thickening was significantly inhibited by SPM-5185 (cross-sectional area 18 +/- 6 vs. 44 +/- 10 x 10(-3) mm2; P < 0.05), but not by molsidomine (28 +/- 6 vs. 35 +/- 9 x 10(-3) mm2), which is a donor of both NO and superoxide anions. In organ chamber studies collaring was associated with a decreased sensitivity to acetylcholine (ACh). SPM-5185 evoked a tendency towards normalization of the pD2 of ACh in collared arteries. We also investigated whether chronic nitric oxide (NO) treatment affected vascular reactivity and fatty streak development in the rabbit aorta. During 16 weeks rabbits received 150 g/day of a standard diet, or diets with 0.3% cholesterol, with 0.02% molsidomine (10 mg/kg body weight/day) or with the combination. The NO donor enhanced the area of fatty streaks, without affecting hypercholesterolemia. Moreover, it desensitized the smooth muscle cells of the rabbit aorta to vasodilators acting via the cytoplasmic guanylate cyclase and suppressed the capacity of the endothelial cells to release NO in response to muscarinic receptor stimulation. This suggested that chronic exposure to large quantities of NO caused a negative feedback, with selective decreases of both the endothelial capacity to generate NO and the responsiveness to vasodilators operating via cyclic GMP. In conclusion, we demonstrated that exogenous NO can decrease intimal hyperplasia in vivo. However, prolonged in vivo treatment with a donor of NO enhanced atherosclerosis in hypercholesterolemic rabbits.

Acetylcholine↗

PubMed1997

Possible mechanisms of collar-induced intimal thickening.

The positioning of a soft silicone collar around the rabbit carotid artery induces intimal thickening. We investigated to which extent occlusion of the vasa vasorum, damage of the perivascular nerve network, and/or changes in blood flow velocity contribute to intimal thickening. To this end, collars with different bores (diameter of inlet and outlet) were positioned around the carotid artery of male rabbits for 14 days. In another experiment, 75% of the wall of fitting collars was removed (open collar). In the midcollar region, the cross-sectional area of the intima reached a maximum (72 +/- 14 mm2/1000) when the endings of the collar fitted the artery closely. Removal of the side wall of these fitting collars reduced intimal thickening by 90%. Examination of unoperated carotid arteries never showed penetration of the adventitia or the media by vasa vasorum. The perivascular neuronal network in the region surrounded by a closed or an open collar was almost completely lost as compared with the zones outside the collar. Both the closed and open collar slightly bent the artery and increased the peak systolic velocity, measured with pulsed color Doppler after 6 hours, to a similar extent as compared with the proximal zone outside the collar. After 2 weeks, the peak systolic velocity within both the closed and open collar was partly normalized and was statistically not different from the proximal zone outside the collar. In conclusion, the geometry of the collar influenced the extent of intimal thickening, whereby more intimal thickening was obtained with a collar whose endings fit the carotid artery, rather than with a loose collar. Moreover, a closed structure was essential. The results obtained with the open collar exclude occlusion of vasa vasorum, damage of the perivascular neuronal network, kinking of the artery, and changes in blood flow velocity as major factors in the collar-induced intimal thickening. Our findings are consistent with the possibility that intimal thickening is the consequence of the combination of both vascular injury and hindrance of transmural flow by the collar. The obstruction of transmural fluid transport may then lead to retention of toxic metabolites, and/or cytokines within the segment enclosed by the collar.

Animals↗

PubMed1997

Local application of LDL promotes intimal thickening in the collared carotid artery of the rabbit.

Oxidized LDL (oxLDL) has been implicated in atherogenesis on the basis of in vitro studies and is present in atherosclerotic lesions. The aim of this study was to investigate the effects of LDL and oxLDL on intimal thickening in vivo. Intimal thickening was evoked by the placement of silicone collars around the carotid arteries of rabbits for 2 weeks. The collars were connected to osmotic minipumps containing LDL (7 micrograms h-1, n = 16 arteries), oxLDL (Cu2+ oxidized, 7 micrograms h-1, n = 16), or phosphate-buffered saline (5 microL h-1, n = 16). Segments proximal to the collars served as controls. Collar placement without lipoprotein application resulted in the appearance of alpha-SMC actin-immunoreactive cells in the intima, thereby increasing the intimal thickness from 5 +/- 1 to 26 +/- 5 microns. The perivascular infusion of LDL or oxLDL within the collar significantly enhanced the development of the intima ninefold and sevenfold, respectively. The large intimas resulting from lipoprotein exposure were infiltrated by macrophages and T lymphocytes, and the intimal collagen area was increased from 5 +/- 2% in the discrete collar-induced intima to approximately 20% in the lipoprotein-evoked lesions. In conclusion, the local vascular application of LDL, oxidized in vitro or possibly in vivo, elicited an inflammatory-fibroproliferative response characteristic of arteriosclerotic lesions, thereby demonstrating an active role for this class of lipoproteins in the disease process.

Animals↗