Proteoglycan distribution in rat aortic wall following indwelling catheter injury

Effects of Preinjury Administration of Corticosteroids on Pseudointimal Hyperplasia and Cytokine Response in a Rat Model of Balloon Aortic Injury

Restenosis occurs in approximately one-third of patients with coronary or peripheral vascular disease who undergo balloon angioplasty or a surgical bypass procedure primarily because of the development of pseudointimal hyperplasia (PIH). Corticosteroids were effective in suppressing PIH in several experimental studies, but no clinical studies have been reported. To resolve this discrepancy, we studied the effects of preinjury administration of several doses of methylprednisolone (MP) at targeted times in a rat model of balloon aortic injury. Rats were given either no treatment or an intravenous injection of MP (0.5, 5.0, 50, or 500 mg/kg) 2 hours before aortic injury. Four hours later interleukin-6 (IL-6), IL-10, and macrophage migration inhibitory factor (MIF) concentrations in serum and tissue of injured aortas were assessed. Two weeks after injury, damaged aortas were harvested and studied histopathologically. Compared with results in controls, MP at a dose of 5 mg/kg significantly inhibited increases in plasma and tissue levels of IL-6 and significantly reduced the pseudointimal area, pseudointimal/medial area ratio, and proliferating cell nuclear antigen index in injured vessels. Administration of MP had no significant effect on the IL-10 or MIF level. Thus in a rat model of balloon aortic injury, preinjury administration of MP 5 mg/kg mitigated the development of PIH and cell proliferation and suppressed the postinjury increase in serum and tissue IL-6 concentrations. These results suggest that there is an appropriate dosage as well as appropriate timing for MP administration to suppress PIH.

Injury to the arterial wall of rabbits produces proteoglycan variants with enhanced low-density lipoprotein-binding property

The effect of arterial injury on proteoglycans (PG) and their ability to bind low-density lipoprotein (LDL) were studied in rabbits 12 weeks after balloon injury. Following biosynthetic labeling in an organ culture system, PG were isolated under dissociative conditions from deendothelialized areas (DEA), reendothelialized areas (REA), and uninjured areas (control) of the aortic tissue. DEA and REA tissues yielded 42-52% more PG and incorporated 39-67% more 35S-label into proteoglycans than control tissues. Ion-exchange chromatography of PG from DEA and REA tissues yielded PG-I, PG-II, and PG-III, while from control tissue only PG-I and PG-II. PG-II formed major portion (74-84%) of the isolated PG in all three tissue types. PGI preparations comprised entirely of heparan sulfate (HS)-PG of similar hydrodynamic size (Kav = 0.45-0.47). PG-II from DEA and REA tissues consisted of PGII-A (Kav = 0.02-0.04) and PGII-B (Kav = 0.32), while PG-II from control tissue contained only PGII-B with relatively smaller hydrodynamic size (Kav = 0.40). PGII-A preparations contained predominantly chondroitin sulfate (CS)-PG with no dermatan sulfate (DS); whereas PGII-B consisted mainly of CS/DS-PG, with relatively high proportion of DS in DEA and REA tissues vs. control tissue (50-54% vs. 43%). Further, the glycosaminoglycan chains of CS/DS-PG from DEA and REA tissues were 1.7-fold longer than those from control tissue. PG-III contained about 80% CS/DS-PG and 20% HS-PG; CS/DS-PG was similar to those found in PGII-B from DEA and REA tissues. HS-PG from PG-II and PG-III, unlike those from PG-I, was enriched with N-sulfated residues. PGI from all the three tissue types bound poorly to LDL. On the other hand, PGII-A, PGII-B, and PG-III from DEA and REA tissues showed enhanced ability to bind LDL, in that order. For example, the LDL-binding ability of PGII-B from DEA and REA was 2.9- to 3.1-fold above that from control tissue. Thus, arterial injury with or without regenerated endothelium produces proteoglycan variants with altered characteristics and enhanced LDL-binding ability.

Glycosaminoglycan synthesis by smooth muscle cells of differing phenotype and their response to endothelial cell conditioned medium

The synthesis of glycosaminoglycans (GAG) by contractile and irreversible synthetic phenotypes of vascular smooth muscle cells (SMC), and their response to endothelial cell conditioned medium (ECCM), has been investigated. Contractile SMC, (with a high volume fraction of myofilaments) were obtained by culturing freshly isolated rabbit aortic SMC for 3 days in primary culture. Irreversible synthetic SMC (with a low volume fraction of myofilaments) were obtained by serially passaging SMC to achieve more than 5 cumulative population doublings. In fresh medium both phenotypes produced significant amounts of GAG, but irreversible synthetic cells were more than twice as active on a per cell and cell volume basis. The proportions of individual GAG also changed with change in phenotype. Hyaluronic acid (HA) was the predominant GAG (78%) synthesised by contractile SMC but was significantly reduced (47%) in the irreversible synthetic cells with a corresponding increase in sulphated GAG (SGAG). The changed levels in GAG synthesis were independent of SMC growth. Both phenotypes responded to ECCM from bovine endothelial cells (EC) and significantly increased their synthesis of GAG and by the same relative amounts (50-100%). This response was density dependent, with ECCM from low and high density cultures of EC producing maximal responses and EC of intermediate densities producing minimal increases. Furthermore, dense cultures of EC preferentially stimulated SGAG. These findings show that an increase in synthesis of SMC GAG, and especially sulphated GAG as is found in atherosclerosis, may occur either through a change in phenotype or through endothelial mediated stimulation of GAG synthesis by either phenotype.

Endothelial cell stimulation of smooth muscle glycosaminoglycan synthesis can be accounted for by transforming growth factor beta activity

Endothelial cell conditioned medium (ECCM) contains a factor which markedly stimulates smooth muscle cell (SMC) glycosaminoglycan (GAG) synthesis. We report here that the factor responsible is transforming growth factor beta (TGF-beta) as assessed by (1) protease and thiol sensitivity, (2) heat and acid enhancement of ECCM activity, and (3) neutralisation of ECCM activity by anti-TGF-beta-immunoglobulin. Anti-TGF-beta-neutralisation was effective against increases in both sulphated and non-sulphated GAG. Previous studies showed that ECCM from EC of varying densities stimulated individual GAG to varying degrees. ECCM from low density EC preferentially stimulated hyaluronic acid (HA) whereas ECCM from intermediate and high density cultures stimulated increasing amounts of sulphated GAG. Exposure of SMC to varying concentrations of TGF-beta produced a similar pattern Exposure of SMC to varying concentrations of TGF-beta produced a similar pattern of response. Very low amounts of TGF-beta (less than 10-500 pg/10 cells) stimulated a marked and significant increase in HA synthesis. Increase in chondroitin sulphate 4/6 was most marked at TGF-beta levels from 500-1000 pg/10(6) cells. At levels above 1000 pg/10(6) cells both HA and sulphated GAG synthesis decreased but still remained elevated above controls. These findings indicate that TGF-beta alone can account for the changes in SMC GAG synthesis stimulated by ECCM. It was also found, however, that heat-treated SMC conditioned medium stimulated SMC GAG synthesis, thus SMC may contribute to the control of their own GAG synthesis through autocrine TGF-beta activity.

Cytochemical changes in a human arterial proteoglycan related to atherosclerosis

The cuprolinic blue (CB) staining method has been used to visualize and characterize proteoglycans (PG) in the extracellular matrix (ECM) of normal and atherosclerotic human arteries. Arterial tissues of 13 individuals (1-83 years of age) were obtained by autopsy. For electron microscopic visualization of PGs staining with CB was performed in the presence of a critical electrolyte concentration of 0.3 M MgCl2. Under these conditions CB selectively interacts with the polysulfated glycosaminoglycan (GAG) side chains of the molecules. Removal of PG side chains by GAG-degrading enzymes prior to CB staining selectively prevented the formation of chondroitin sulfate (CS)-rich and dermatan sulfate (DS)-rich PG-CB precipitates. The DS-rich type of PG is mainly associated with collagen fibrils, the CS-rich type of PG is preferentially localized in nonfibrous areas of the ECM (soluble matrix). When normal arterial tissues are compared with those affected by atherosclerosis quantitative and qualitative changes of PG-CB precipitates are detected. In fibrous plaques a strong accumulation of a large CS-rich type of precipitate close by smooth muscle cells (SMC) and foam cells is observed. In addition, these precipitates are significantly longer in fibrous plaques than in adjacent normal media (116 nm vs. 100 nm; P less than 0.001). This alteration is independent of the age of the donor. Small DS-rich PG-CB precipitates associated with collagen fibrils show strong variations in their length, but not a significant tendency towards elongated precipitates in atherosclerosis. The present results demonstrate that ultracytochemical and morphometric analysis are useful in providing information on the diverse types, locations, interactions, and possibly of molecular changes of PGs in normal and atherosclerotic human arteries.

Cell biology of arterial proteoglycans

Although proteoglycans constitute a minor component of vascular tissue, these molecules have been shown to influence a number of arterial properties such as viscoelasticity, permeability, lipid metabolism, hemostasis, and thrombosis. A hallmark of early and late atherosclerosis is the accumulation of proteoglycans in the intimal lesions. Yet, it is not clear why this accumulation occurs. This article reviews the classes of proteoglycans synthesized by the two major cell types of the arterial wall--the endothelial and smooth muscle cell. Detailed consideration is then given to the modulation of proteoglycan metabolism and the role that proteoglycans play in a number of cellular events such as adhesion, migration, and proliferation--important processes in both the development and the pathogenesis of blood vessels. Last, the involvement of proteoglycans in two critical vascular wall processes--hemostasis and lipid metabolism--is reviewed, because these events pertain to atherogenesis. This review emphasizes the importance of proteoglycans in regulating several key events in normal and pathophysiological processes in the vascular tissue.

Proteoglycan composition of rabbit arterial wall under conditions of experimentally induced atherosclerosis

The concentration and composition of proteoglycans (PG) of the neointima developed following balloon catheter removal of aortic endothelium in rabbits, were assessed. PG were extracted from the aortic intimal-medial tissues with 4 M guanidinium chloride in the presence of protease inhibitors and purified subsequently by cesium chloride gradient ultracentrifugation and fractionation by high-performance liquid chromatography (HPLC). PG so obtained was analysed for its protein, cholesterol and glycosaminoglycan (GAG) content. For the characterization of the GAG moiety, an exhaustive proteolytic digestion was done. The GAG were then recovered by ethanolic precipitation and their relative distribution was determined after a selective enzymatic digestion using specific enzymes. Results show a significant increase in the amount of PG in the areas of the injured arterial wall covered by regenerated endothelium. In addition, changes in the composition of GAG were also found in the PG isolated from experimental animals when compared to PG isolated from normal aorta. A marked increase in the content of chondroitin sulfates and dermatan sulfate of injured tissue was seen. Hyaluronic acid content also changed in response to de-endothelialization and cholesterol feeding, but only moderately. The content of heparan sulfate remained unaffected in experimental tissues. Furthermore, cholesterol feeding aggravated the injury-induced increment of GAG. These findings are consistent with previously reported morphological observations, and correlate well with reports that arterial injury and cholesterol feeding act synergistically in the evolution of the atherosclerotic lesion and provide further evidence that the interaction of lipid and PG of the arterial wall may be of particular importance to our comprehension of the pathogenesis of atherosclerosis.

Proteoglycan distribution in catheter-induced aortic lesions in normolipaemic rabbits. An ultrastructural study

The aortic lesions induced in normal-fed rabbits by an indwelling catheter were examined for changes in lipid content shown by oil red O-stained sections and associated proteoglycan distribution and ultrastructural changes by transmission electron microscopy of ruthenium red-stained sections, during an 8-week period of regression. Compared to normal aorta there was a highly significant increase in proteoglycan in lipid-containing lesions, which was also associated with the presence of regenerated endothelium. In the lesions which had regressed in terms of size and lipid content, the proteoglycan concentration, especially in superficial regions, was significantly reduced compared to early lesions and was similar to that seen in the normal vessel. Proteoglycan concentration decreased before lipid content of lesions was reduced. Proteoglycan was not associated with lipid-containing macrophages. These observations support the hypothesis that an increased glycosaminoglycan concentration is associated with lipid deposition in the vessel wall in response to injury in the absence of hyperlipaemia.

Glycosaminoglycan composition and biosynthesis in the endothelium-covered neointima of de-endothelialized rabbit aorta

The biosynthesis and composition of glycosaminoglycans (GAG) in the endothelium-covered neointima, formed in response to de-endothelialization of the rabbit aorta by a balloon catheter, was examined. The [14C]glucosamine incorporation into GAG during an in vitro incubation with intimal-medial tissue was monitored periodically up to 24 hr. The GAG were isolated after an exhaustive proteolytic digestion with pronase and protease followed by ethanolic precipitation at 4 degrees C. Electrophoretic migration on cellulose acetate paper was compared for identification. The distribution of GAG was determined after a selective enzymatic digestion of isolated GAG using specific enzymes. Heparan sulfates were estimated after nitrous acid treatment. The concentration of GAG was measured spectrophotometrically by forming colored complexes with Alcian blue dye. In addition, the specific activity (dpm/microgram GAG) and the rate of GAG synthesis (ng/mg dry defatted tissue/day) were determined. The results indicate that the rate of GAG synthesis by de-endothelialized neointima (DEA) was twice that of intact aorta (control). In the re-endothelialized neointima (REA), the GAG synthetic rate was three times more than in control. However, the release of GAG into medium from REA accounts for only 25% of the GAG synthesized by this tissue type, and the release from DEA accounts for 60% of the synthesized GAG. Similarly, a threefold increase in the GAG concentration in REA compared to control was found. The relative distribution as chondroitin-6-sulfate (C6S), chondroitin-4-sulfate (C4S), dermatan sulfate (DS), heparan sulfate (HS) and hyaluronic acid (HA) was markedly altered in the injured neointima. There was an increase in chondroitin sulfates (CS) and DS concomitant with a decrease in HS. It is concluded that injury to aortic endothelium induces stimulation of GAG synthesis in the arterial wall. Furthermore, the greater release of GAG from DEA, compared to control and REA, suggests that endothelium may function as a "reverse" barrier in the neointima covered by regenerated endothelium.

Proteoglycans in human atherosclerotic lesions--a pilot qualitative and quantitative study by ruthenium red

A pilot study was carried out to test whether normal human aorta and aortic atherosclerotic lesions obtained at post-mortem examination were suitable for the demonstration of proteoglycans (PGs) by ruthenium red (RR) staining, and whether by this method qualitative and quantitative differences of PGs might be detectable in various types of lesions and between lesions and the normal aortic intima. The results indicate that the PGs of the above tissues obtained at post mortem were clearly visualized by electron microscopy using the RR-indicator and were thus suitable for quantitative and qualitative evaluation. Of the RR-positive granules only those 20 nm and larger were assessed. RR-granules measuring 20-50 nm were present in normal intima and media, in increased concentration in the innermost part of the mixed fatty-gelatinous lesion, and in a decreased concentration in the fibrous cap of an atherosclerotic plaque. The same RR-granules were observed in a fatty streak and in addition 50-100 nm granules were present in this type of lesion; the overall RR-granule-concentration was reduced here. Granules of both sizes were interconnected by filamentous network. The differential presence of the large (and hitherto unreported) as well as the smaller granules in the various lesions is briefly discussed in the light of the present-day knowledge of tissue-PGs, and the importance of an examination in situ of the compound PGs-complexes in their native form, is emphasized.