Diet induced mild hypercholesterolemia in pigs: local and systemic inflammation, effects on vascular injury - rescue by high-dose statin treatment.

OBJECTIVE: The aim of the present study was to comprehensively evaluate systemic and local inflammation as well as progression of vascular inflammation in normal and mechanically injured vessels in a large animal model of mild hypercholesterolemia. Our aim was also to test the effect of high-dose statin treatment on these processes. METHODS: Pigs were kept for 120 days on a standard diet (SD, n=7), high-cholesterol diet (HCD, n=7) or high-cholesterol diet with Atorvastatin starting after 50 days (STATIN, n=7). Left carotid artery balloon injury was conducted in all groups after 60 days of diet treatment. Biochemical analysis together with evaluation of blood and tissue markers of vascular injury and inflammation were performed in all groups at the end of experiment. RESULTS: HCD compared to SD induced systemic inflammation demonstrated by increased number of circulating monocytes and lymphocytes. HCD compared to SD induced also local inflammation demonstrated by adipocyte hypertrophy and infiltration of T-lymphocytes in abdominal white adipose tissue, activation of hepatic stellate cells with infiltration of T- and B-lymphocytes and macrophages in the liver and increased macrophage content in lung parenchyma. These changes were accompanied by increased Intima/Media thickness, stenosis, matrix deposition and activated T-cell infiltrates in injured but not in uninjured contralateral carotid artery as we previously reported. The treatment with high-dose statin attenuated all aspects of systemic and local inflammation as well as pathological changes in injured carotid artery. CONCLUSIONS: Diet related mild hypercholesterolemia induce systemic and local inflammation in the liver, lung and adipose tissue that coincide with enhanced inflammation of injured vessel but is without deleterious effect on uninjured vessels. High dose statin attenuated systemic and local inflammation and protected injured vessels. However, finding exact role of reduced systemic and remote inflammation in vascular protection requires further studies.

Heme oxygenase-1 inhibition prevents intimal hyperplasia enhancing nitric oxide-dependent apoptosis of vascular smooth muscle cells.

Heme oxygenase-1 (HO-1, encoded by the HMOX1 gene) and inducible nitric oxide synthase (iNOS) have been implicated in vascular disease; however the role of these genes remains unclear. Therefore, we studied the mechanism by which iNOS-derived nitric oxide (NO) affects the intimal hyperplasia (IH) formation in relation to HO-1. We show, in a model of balloon injury in rats, that the suppression of vascular smooth muscle cells (VSMC) proliferation by NO required HO-1, while induction of apoptosis of the VSMC by NO does not involve HO-1. To better clarify the molecular mechanism of this finding, we used Hmox1(+/+) and Hmox1(-/-) VSMC exposed to NO. In Hmox1(+/+) VSMC, NO is antiproliferative (up to 34% inhibition) and it is associated to an increase of apoptosis (up to 35%) due to a decrease of X-linked inhibitor of apoptosis protein (XIAP) expression level and to the activation of caspase-3. In the absence of HO-1 (Hmox1(-/-) VSMC) apoptosis was significantly greater (69% p<0.01 vs. Hmox1(+/+) VSMC) demonstrating that HO-1 attenuated the pro-apoptotic effect of NO on VSMC. In the context of IH, the pro-apoptotic effect of NO on VSMC is increased in the absence of HO-1 and exerts therapeutic effects with a significant reduction in IH.

Pathogenetic role of hypercholesterolemia in a novel preclinical model of vascular injury in pigs.

OBJECTIVE: Most strategies against intimal hyperplasia developed in several preclinical models failed in terms of clinical application, often due to a discrepancy between animal and human disease. The aim of this study was to setup for the first time a porcine vascular injury model with mild hypercholesterolemia able to significantly increase the degree of stenosis resembling human settings and investigate the pathogenetic role of hypercholesterolemia on protective genes and inflammatory response affecting matrix deposition and cell proliferation. METHODS: Pigs were fed with standard (SD, n=7) or high-cholesterol diet (HCD, n=7) for 120 days. A balloon angioplasty injury was induced in carotid arteries. RESULTS: Hypercholesterolemia induced a mild significant increase of total and LDL cholesterolemia. HCD significantly increased the degree of stenosis (48+/-3% vs. 13+/-4%, p=0.001), with induction of cell proliferation, matrix deposition, TGF-beta1/TGFbetaRII and MMP2 expression and reduction of collagen. The reduced expression of the protective gene heme oxygenase-1 and inducible-nitric oxide synthase in HCD was associated to a systemic inflammation with a significant increase in circulating leukocytes, serum IFN-gamma and TNF-alpha and a local inflammatory response with an increase of CD3-positive cell infiltrates. There was a significant correlation between CD3 infiltrates and the degree of stenosis. CONCLUSION: We developed for the first time a porcine vascular injury model with mild hypercholesterolemia able to significantly increase the degree of stenosis and showed the pathogenetic role of hypercholesterolemia on intimal hyperplasia. New therapeutical strategies to prevent restenosis can be tested in this preclinical hypercholesterolemic model resembling human disease.