Experimental models of accelerated atherosclerosis syndromes

Effect of chondroitin sulphate in a rabbit model of atherosclerosis aggravated by chronic arthritis

BACKGROUND AND PURPOSE

Among the agents employed to manage osteoarthritis, chondroitin sulphate (CS) is a natural glycosaminoglycan with an anti-inflammatory effect on joint cells. CS might also influence the inflammatory component of atherosclerosis. Our aim was to examine the effect of CS administration on vascular injury and on markers of systemic inflammation in a rabbit model of atherosclerosis aggravated by systemic inflammation provoked by chronic antigen-induced arthritis.

EXPERIMENTAL APPROACH

Atherosclerosis was induced in rabbits by maintaining them on a hyperlipidaemic diet after producing an endothelial lesion in the femoral arteries. Simultaneously, chronic arthritis was induced in these animals by repeated intraarticular injections of ovalbumin in previously immunized rabbits. A group of these rabbits were treated prophylactically with CS (100 mg kg(-1)day(-1)) and when the animals were killed, serum and peripheral blood mononuclear cells (PBMC) were isolated. Furthermore, femoral arteries and thoracic aorta were used for gene expression studies and histological examination.

KEY RESULTS

CS administration reduced the concentration of the proinflammatory molecules C-reactive protein and IL-6 in serum. Likewise, CS inhibited the expression of CCL2/monocyte chemoattractant protein (MCP)-1 and cyclooxygenase (COX)-2 in PBMC, and reduced the nuclear translocation of nuclear factor-kappaB. In the femoral lesion, CS also diminished the expression of CCL2 and COX-2, as well as the ratio of the intima/media thickness. Moreover, CS decreased the percentage of rabbits with atherosclerosis and chronic arthritis that developed vascular lesions in the aorta.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that CS treatment may to some extent impede the progression of atherosclerosis.

Cryopreservation alters antigenicity of allografts in a porcine model of transplant vasculopathy

The need for arterial grafts in coronary surgery to complement autologous vessels has generated interest in cryopreservation of small diameter allografts. We evaluated functional and histologic changes occurring in cryopreserved allografts 3 months after porcine femoral artery transplants.

METHODS

Twenty recipient and 15 donor pigs included a control group of 16 fresh and 12 cryopreserved nonimplant arteries were used. Fresh (n=5) and cryopreserved (n=5) autografts were implanted to assess cryopreservation effects in the absence of rejection. Fresh allografts with or without treatment with cyclosporine (CsA) (n=6 of 8) and cryopreserved allografts with or without treatment with CsA (n=6 of 10) were performed to study the antigenicity of cryopreserved allografts. Arteries were stained with hematoxylin and eosin, Masson's trichrome, and orcein for morphometric analyses and immunostained to identify endothelial cells, smooth muscle cells, T lymphocytes, and macrophages.

RESULTS

Among nonimplant arteries, cryopreservation reduced alpha-actin expression and increased the luminal area. All implanted autografts were patent. Cryopreserved autografts showed reduced alpha-actin expression and developed intimal hyperplasia compared to fresh autografts. Treatment with CsA improved the patency of fresh allografts from 0% to 83% (P <.01) and of cryopreserved allografts from 40% to 100% (P <.05). Cryopreserved allografts showed substantial intimal hyperplasia, and fresh allografts had more T lymphocyte infiltration in the intimal layer with aneurysmal dilatation.

CONCLUSIONS

Cryopreservation reduces the deposition of inflammatory cells and prevents the thrombosis or aneurysmal lesions observed in fresh allografts. Therefore, cryopreservation modifies the antigenicity of vascular allografts.

Hyperphosphatemia aggravates cardiac fibrosis and microvascular disease in experimental uremia

BACKGROUND

Hyperphosphatemia is a known predictor of cardiovascular death and specifically of cardiac death in hemodialysis patients. The pathomechanisms involved have not been completely clarified. While a number of observations suggest an important role of hyperphosphatemia and positive calcium balance on atherosclerosis and calcification of the coronary conduit arteries, independent effects on postcoronary microvessels and on cardiac fibrosis have not been excluded.

METHODS

Male Sprague-Dawley rats were sham operated (N = 14) or subtotally nephrectomized (SNX, N = 17) and subsequently placed on low phosphorus (0.08% w/w) and high phosphorus (1.2% w/w) diet under pair-feeding conditions. After 8 weeks, serum chemistry and inhibitory parathyroid hormone (iPTH) were measured, and the hearts were harvested using perfusion fixation. Arteriolar thickness and volume density of the interstitium (excluding vessels) were quantitated using stereologic techniques.

RESULTS

In SNX animals with moderate renal failure serum phosphorus concentrations were higher than in sham-operated controls on low phosphorus diet (1.7 +/- 0.37 mmol/L) and were significantly higher in SNX + high phosphorus diet (2.33 +/- 0.23 mmol/L) compared to SNX + low phosphorus diet (1.95 +/- 0.32 mmol/L; P < 0.05). In sham-operated controls, dietary phosphorus content had no effect on cardiac morphologic indices. In contrast, in SNX + high phosphorus diet the index of interstitial cardiac fibrosis was significantly higher (3.22 +/- 0.44%) than in SNX + low phosphorus (2.75 +/- 0.46%) or in sham-operated controls (2.5 +/- 0.05% on high phosphorus and 2.4 +/- 0.89 on low phosphorus, respectively). In SNX + high phosphorus (14.0 +/- 9.0 microm), but not in SNX + low phosphorus (9.2 +/- 4.5 microm), arterial wall thickness was significantly higher compared to sham-operated controls (10.2 +/- 5.1 on high phosphorus and 9.8 +/- 5.0 micro;m on low phosphorus, respectively). The data were confirmed in an independent repeat experiment.

CONCLUSION

High dietary phosphorus and hyperphosphatemia have significant effects on cardiac fibrosis and arterial wall thickening. Such abnormalities of cardiac architecture may be relevant for the increased cardiac risk in hyperphosphatemic uremic patients.

[Effect of cAMP on the function of endothelial cells and fibromuscular proliferation after the injury of the carotid and coronary arteries in a porcine model]

INTRODUCTION AND OBJECTIVE

Reendothelization of damaged blood vessels protects against the vascular injury response. We evaluated in vivo whether a systemic increase in cAMP accelerates reendothelization and attenuates intimal hyperplasia in injured swine carotid and coronary arteries.

METHODS

Both carotid arteries of 10 swines were subjected to balloon injury. Five animals had been treated with 2 ml (10 mg) of Forskolin, an activator of the adenylate cyclase, and another 5 with 2 ml of saline solution. These animals were sacrificed at day 8, and carotid artery reendothelization was evaluated. The descendent coronary (DC) artery of another 19 pigs was injured by atherotome. Nine animals had been treated with 2 ml of Forskolin, and another 10 with 2 ml of saline solution. These animals were sacrificed at day 28, with myointimal proliferation and arterial geometric remodelation being evaluated. Likewise, in these animals intracellular cAMP levels were measured at baseline and 28 and 60 minutes after saline solution or Forskolin administration and 90 min after arterial injury.

RESULTS

Eight days after balloon injury, carotid artery reendothelization was greater in the Forskolin-treated group compared with the control group (p = 0.02), and the number of CD31 positive cells was statistically increased in the treated group (38 +/- 11 cells) versus controls (11 +/- 9 cells). Although the degree of vascular injury caused by atherotome was similar in all of the arteries in the control group, restenosis was only observed in 40% of these animals. Correlation analysis demonstrated that intracellular cAMP may condition arterial geometric remodeling and the diameter of the lumen after vascular injury.

CONCLUSION

Our results suggest that cAMP may promote reendothelization and attenuate fibromuscular proliferation.

Expression of allograft inflammatory factor-1 is a marker of activated human vascular smooth muscle cells and arterial injury

The cytokine-induced activation and proliferation of medial vascular smooth muscle cells (VSMCs) leading to intimal hyperplasia is one of the most critical cellular events in the formation of transplant arteriopathy and balloon angioplasty-induced restenosis. Allograft inflammatory factor-1 (AIF-1) is a calcium-binding protein that we have previously shown to be expressed in balloon angioplasty-injured rat carotid arteries. We hypothesized that AIF-1 expression may be associated with the VSMC response to injury. In this study, we examined AIF-1 expression in immunologic and mechanical models of arterial injury. Reverse transcription-polymerase chain reaction and Western analysis demonstrated that AIF-1 is acutely and transiently expressed in aortic medial smooth muscle cells of rat cardiac allografts, with mRNA and protein peaking at 3 to 7 days after transplant and declining by 10 days after transplant. Immunohistochemical analysis identified abundant AIF-1 in the medial VSMCs of these vessels. Immunohistochemical analysis of balloon angioplasty-injured swine coronary arteries also demonstrates an acute AIF-1 expression detectable by 24 hours and continuing up to 14 days after the procedure. AIF-1 in these vessels also localizes to the medial VSMCs and cells of the developing neointima. AIF-1 protein is not expressed in quiescent cultured human VSMCs but is induced in cells challenged with various inflammatory cytokines, primarily by interferon-gamma, interleukin-1beta, and T-cell-conditioned media. Transfection and overexpression of AIF-1 in human VSMCs result in enhanced growth of these cells. Taken together, these data indicate that AIF-1 expression is associated with vascular trauma and suggest that this protein may play a role in VSMC activation subsequent to arterial injury.

Nanoparticulate delivery system of a tyrphostin for the treatment of restenosis

Restenosis, the principal complication of percutaneous transluminal coronary angioplasty is responsible for the 35-40% long-term failure rate following coronary revascularization. The neointimal formation, a morphological substrate of restenosis, is dependent on smooth muscle cells (SMC) proliferation and migration. Signal transduction through the platelet-derived growth factor (PDGF)/PDGF receptors system is involved in the process of post-angioplasty restenosis. The unsuccessful attempts to control restenosis by systemic pharmacological interventions have prompted many researchers to look for more promising therapeutic approaches such as local drug delivery. Tyrphostins are low molecular weight inhibitors of protein tyrosine kinases. We assessed the release kinetics and in vivo effects of nanoparticles containing PDGF-Receptor beta (PDGFRbeta) tyrphostin inhibitor, AG-1295. AG-1295-loaded poly(DL-lactide) (PLA) nanoparticles were prepared by spontaneous emulsification/solvent displacement technique. In vitro release rate and the impact of drug/polymer ratio on the nanoparticle size were determined. The degree of tyrosine phosphorylation was assessed by Western blot with phosphotyrosine-specific antibody in rat SMC extracts. Several bands characteristic of PDGF BB-stimulated SMC disappeared or weakened following tyrphostin treatment. Local intraluminal delivery of AG-1295-loaded PLA nanoparticles to the injured rat carotid artery had no effect on proliferative activity in medial and neointimal compartments of angioplastisized arteries, indicating a primary antimigration effect of AG-1295 on medial SMC.

Towards the prevention of vein graft failure

Improved outcome after coronary bypass surgery over the last decade has been attributed largely to the increasing use of arterial conduits and their superior patency rates over that of saphenous vein grafts. In spite of this trend, autologous saphenous vein has remained an important and convenient conduit for a variety of operative scenarios, and is still used for more than 70% of grafts. As a result, vein graft failure continues to represent a significant clinical and economic burden upon the health care service. Between 15 to 30% of saphenous vein grafts occlude within the first year of surgery, increasing to over 50% after 10 years. By this time, more than 10% of patients will require further intervention to alleviate symptoms arising from occluded grafts and progression of native disease. Graft occlusion arises either from early thrombosis or the later onset of 'vein graft disease' and subsequent atherosclerotic changes.