Development of coronary atherosclerosis in swine with severe hypercholesterolemia. Lack of influence of von Willebrand factor or acute intimal injury

Animal Models of Atherosclerosis-Supportive Notes and Tricks of the Trade

Atherosclerotic cardiovascular disease is a major cause of death among humans. Animal models have shown that cholesterol and inflammation are causatively involved in the disease process. Apolipoprotein B-containing lipoproteins elicit immune reactions and instigate inflammation in the vessel wall. Still, a treatment that is specific to vascular inflammation is lacking, which motivates continued in vivo investigations of the immune-vascular interactions that drive the disease. In this review, we distill old notions with emerging concepts into a contemporary understanding of vascular disease models. Pros and cons of different models are listed and the complex integrative interplay between cholesterol homeostasis, immune activation, and adaptations of the vascular system is discussed. Key limitations with atherosclerosis models are highlighted, and we suggest improvements that could accelerate progress in the field. However, excessively rigid experimental guidelines or limiting usage to certain animal models can be counterproductive. Continued work in improved models, as well as the development of new models, should be of great value in research and could aid the development of cardiovascular disease diagnostics and therapeutics of the future.

Tβ4 Increases Neovascularization and Cardiac Function in Chronic Myocardial Ischemia of Normo- and Hypercholesterolemic Pigs

Translations of new therapeutic options for cardiovascular disease from animal studies into a clinical setting have been hampered, in part by an improper reflection of a relevant patient population in animal models. In this study, we investigated the impact of thymosin β4 (Tβ4), which promotes collateralization and capillarization, during hypercholesterolemia, a known risk factor of coronary artery disease. Initial in vitro results highlighted an improved endothelial cell function upon Tβ4 treatment under control conditions and during hypercholesterolemic stress (scratch area [pixels]: oxidized low-density lipoprotein [oxLDL], 191,924 ± 7,717; and oxLDL + Tβ4, 105,621 ± 11,245). To mimic the common risk factor of hypercholesterolemia in vivo, pigs on regular (NC) or high-fat (HC) diet underwent chronic myocardial ischemia followed by recombinant adeno-associated virus (rAAV)-mediated transduction of Tβ4 or LacZ as a control. We show that Tβ4 overexpression improves capillarization and collateralization (collaterals: NC + rAAV.LacZ, 2.1 ± 0.5; NC + rAAV.Tβ4, 6.7 ± 0.5; HC + rAAV.LacZ, 3.0 ± 0.3; and HC + rAAV.Tβ4, 6.0 ± 0.4), ultimately leading to an improved myocardial function in both diet groups (ejection fraction [EF] at day 56 [%]: NC + rAAV.LacZ, 26 ± 1.1; NC + rAAV.Tβ4, 45 ± 1.5; HC + rAAV.LacZ, 26 ± 2.5; and HC + rAAV.Tβ4, 41 ± 2.6). These results demonstrate the potency of Tβ4 in a patient-relevant large animal model of chronic myocardial ischemia.

Development of Human-Like Advanced Coronary Plaques in Low-Density Lipoprotein Receptor Knockout Pigs and Justification for Statin Treatment Before Formation of Atherosclerotic Plaques

BACKGROUND

Although clinical trials have proved that statin can be used prophylactically against cardiovascular events, the direct effects of statin on plaque development are not well understood. We generated low-density lipoprotein receptor knockout (LDLR(-/-)) pigs to study the effects of early statin administration on development of atherosclerotic plaques, especially advanced plaques.

METHODS AND RESULTS

LDLR(-/-) pigs were generated by targeted deletion of exon 4 of the LDLR gene. Given a standard chow diet, LDLR(-/-) pigs showed atherosclerotic lesions starting at 6 months of age. When 3-month-old LDLR(-/-) pigs were fed a high-cholesterol, high-fat (HCHF) diet for 4 months (HCHF group), human-like advanced coronary plaques developed. We also fed 3-month-old LDLR(-/-) pigs an HCHF diet with pitavastatin for 4 months (Statin Prophylaxis Group). Although serum cholesterol concentrations did not differ significantly between the 2 groups, intravascular ultrasound revealed 52% reduced plaque volume in statin-treated pigs. Pathological examination revealed most lesions (87%) in the statin prophylaxis group were early-stage lesions, versus 45% in the HCHF diet group (P<0.01). Thin-cap fibroatheroma characterized 40% of the plaques in the HCHF diet group versus 8% in the statin prophylaxis group (P<0.01), intraplaque hemorrhage characterized 11% versus 1% (P<0.01), and calcification characterized 22% versus 1% (P<0.01).

CONCLUSIONS

Results of our large animal experiment support statin prophylaxis before the occurrence of atherosclerosis. Early statin treatment appears to retard development of coronary artery atherosclerosis and ensure lesion stability. In addition, the LDLR(-/-) pigs we developed represent a large animal model of human-like advanced coronary plaque suitable for translational research.

Animal models of atherosclerosis

In this mini-review several commonly used animal models of atherosclerosis have been discussed. Among them, emphasis has been made on mice, rabbits, pigs and non-human primates. Although these animal models have played a significant role in our understanding of induction of atherosclerotic lesions, we still lack a reliable animal model for regression of the disease. Researchers have reported several genetically modified and transgenic animal models that replicate human atherosclerosis, however each of current animal models have some limitations. Among these animal models, the apolipoprotein (apo) E-knockout (KO) mice have been used extensively because they develop spontaneous atherosclerosis. Furthermore, atherosclerotic lesions developed in this model depending on experimental design may resemble humans’ stable and unstable atherosclerotic lesions. This mouse model of hypercholesterolemia and atherosclerosis has been also used to investigate the impact of oxidative stress and inflammation on atherogenesis. Low density lipoprotein (LDL)-r-KO mice are a model of human familial hypercholesterolemia. However, unlike apo E-KO mice, the LDL-r-KO mice do not develop spontaneous atherosclerosis. Both apo E-KO and LDL-r-KO mice have been employed to generate other relevant mouse models of cardiovascular disease through breeding strategies. In addition to mice, rabbits have been used extensively particularly to understand the mechanisms of cholesterol-induced atherosclerosis. The present review paper details the characteristics of animal models that are used in atherosclerosis research.

Porcine and canine von Willebrand factor and von Willebrand disease: hemostasis, thrombosis, and atherosclerosis studies

Use of animal models of inherited and induced von Willebrand factor (VWF) deficiency continues to advance the knowledge of VWF-related diseases: von Willebrand disease (VWD), thrombotic thrombocytopenic purpura (TTP), and coronary artery thrombosis. First, in humans, pigs, and dogs, VWF is essential for normal hemostasis; without VWF bleeding events are severe and can be fatal. Second, the ADAMTS13 cleavage site is preserved in all three species suggesting all use this mechanism for normal VWF multimer processing and that all are susceptible to TTP when ADAMTS13 function is reduced. Third, while the role of VWF in atherogenesis is debated, arterial thrombosis complicating atherosclerosis appears to be VWF-dependent. The differences in the VWF gene and protein between humans, pigs, and dogs are relatively few but important to consider in the design of VWF-focused experiments. These homologies and differences are reviewed in detail and their implications for research projects are discussed. The current status of porcine and canine VWD are also reviewed as well as their potential role in future studies of VWF-related disorders of hemostasis and thrombosis.

A monoclonal antibody against alphaVbeta3 integrin inhibits development of atherosclerotic lesions in diabetic pigs

Atherosclerotic lesions develop and progress more rapidly in diabetic patients than in nondiabetic individuals. This may be caused by accelerated lesion formation in the high-glucose environment of diabetes. Smooth muscle cells (SMCs) cultured in high glucose are more responsive to growth factors such as insulin-like growth factor-1 (IGF-1). This enhanced response to IGF-1 is due in part to increased activation of the alpha(V)beta(3) integrin. We tested whether alpha(V)beta(3) integrin activation was increased in diabetic animals and whether an antibody to beta(3) would inhibit IGF-1 action and development of atherosclerosis. Eight male pigs were made diabetic with streptozotocin and fed a high-fat diet. A F(ab)(2) antibody fragment directed at beta(3) was infused into one femoral artery, whereas the other artery received control F(ab)(2) for 3.5 months. There was a 65 +/- 8% reduction in atherosclerotic lesion area in the arteries treated with F(ab)(2) antibody to beta(3). Phosphorylation of beta(3) was reduced by 75 +/- 18% in vessels treated with the antibody. Shc and mitogen-activated protein kinase phosphorylation, which are required for IGF-1-stimulated SMC proliferation, were also significantly reduced. We conclude that activation of IGF-1 receptor and alpha(V)beta(3)-linked signaling pathways accelerates atherosclerosis in diabetes and that administration of an antibody to beta(3) to diabetic pigs inhibits alpha(V)beta(3) activation, IGF-1-stimulated signaling, and atherosclerotic lesion development. This approach offers a potential therapeutic approach to the treatment of this disorder.

Protease-resistant insulin-like growth factor (IGF)-binding protein-4 inhibits IGF-I actions and neointimal expansion in a porcine model of neointimal hyperplasia

IGF-I has been shown to play a role in the progression of atherosclerosis in experimental animal models. IGF-binding protein-4 (IGFBP-4) binds to IGF-I and prevents its association with receptors. Overexpression of a protease-resistant form of IGFBP-4 has been shown to inhibit the ability of IGF-I to stimulate normal smooth muscle cell growth in mice. Based on these observations, we prepared a protease-resistant form of IGFBP-4 and infused it into hypercholesterolemic pigs. Infusion of the protease-resistant mutant inhibited lesion development by 53.3 +/- 6.1% (n = 6; P < 0.01). Control vessels that received an equimolar concentration of IGF-I and the protease-resistant IGFBP-4 showed no reduction in lesion size compared with control lesions that were infused with vehicle. Infusion of a nonmutated form of IGFBP-4 did not significantly inhibit lesion development. Proliferating cell nuclear antigen analysis showed that the mutant IGFBP-4 appeared to inhibit cell proliferation. The area occupied by extracellular matrix was also reduced proportionally compared with total lesion area. Immunoblotting revealed that the mutant IGFBP-4 remained intact, whereas the wild-type IGFBP-4 that was infused was proteolytically cleaved. Further analysis of the lesions revealed that a marker protein, IGFBP-5, whose synthesis is stimulated by IGF-I, was decreased in the lesions that received the protease-resistant, IGFBP-4 mutant, whereas there was no change in lesions that received wild-type IGFBP-4 or the mutant protein plus IGF-I. These findings clearly illustrate that infusion of protease-resistant IGFBP-4 into the perilesion environment results in inhibition of cell proliferation and attenuation of the development of neointima. The findings support the hypothesis that inhibiting IGFBP-4 proteolysis in the lesion microenvironment could be an effective means for regulating neointimal expansion.

von Willebrand factor and factor VIII as risk factors for arterial and venous thrombosis

Since the early 1990s attempts have been made to elucidate whether high concentrations of von Willebrand factor (VWF) and factor VIII (FVIII) in plasma are associated with an increased risk of thrombosis. Several prospective studies on the role of VWF in arterial thrombosis, mainly coronary heart disease, were performed in healthy individuals and patients with previous cardiovascular disease. Although the majority showed an association between high VWF levels and arterial thrombosis, others failed to confirm such findings. A smaller number of studies have evaluated FVIII, mainly for its association with venous thrombosis. Two prospective observations, together with several case-control studies, provided solid evidence of an association between high FVIII levels and a first or recurrent episode of venous thrombosis. On the whole, high levels of VWF and FVIII in plasma confer a moderately high risk of arterial and venous thrombosis, respectively. These findings have no therapeutic implication, but they should be taken into account in the assessment of the individual risk profile.

Porphyromonas gingivalis bacteremia induces coronary and aortic atherosclerosis in normocholesterolemic and hypercholesterolemic pigs

OBJECTIVES

The aim of this study was to determine whether recurrent intravenous injections with Porphyromonas gingivalis (P gingivalis), mimicking periodontitis-associated bacteremia, promotes coronary artery and aortic atherosclerosis in pigs.

METHODS AND RESULTS

Pigs (n=36) fed low- or high-fat chow were divided into P gingivalis-sensitized and P gingivalis-challenged groups or P gingivalis-sensitized controls and saline-treated controls. Pigs were sensitized with 10(9) killed P gingivalis subcutaneously. Four weeks later all sensitized pigs in the group to be challenged started intravenous injections thrice weekly for 5 months with 10(6) to 10(7) colony forming units of P gingivalis while controls received saline. Anti-P gingivalis antibody, serum cholesterol, and complete blood counts were assayed monthly. Pigs were euthanized 2 weeks after the last injection, and coronary arteries and aortas were analyzed by histomorphometry and immunohistochemistry. Anti-P gingivalis antibody was increased by P gingivalis exposure. P gingivalis-challenged pigs developed a significantly greater amount of coronary and aortic atherosclerosis than controls in the normocholesterolemic group and nearly significant in the hypercholesterolemic group. P gingivalis was detected by polymerase chain reaction in arteries from most (94%, 16 of 17) P gingivalis-challenged pigs but not controls.

CONCLUSIONS

Recurrent P gingivalis bacteremia induces aortic and coronary lesions consistent with atherosclerosis in normocholesterolemic pigs and increases aortic and coronary atherosclerosis in hypercholesterolemic pigs.

Patients With Type 3 Severe von Willebrand Disease Are Not Protected Against Atherosclerosis

Background— The results of a number of studies in pigs and mice suggest that absence of von Willebrand factor (vWF) protects against the development of atherosclerosis. We studied whether patients with a complete deficiency of vWF (type 3 von Willebrand disease [vWD]) develop fewer atherosclerotic vessel wall changes than healthy controls.

Methods and Results— This study included 47 individuals with type 3 vWD and 84 healthy controls. Early atherosclerotic changes were assessed by measuring the thickness of the intima-media in the carotid and femoral arteries by B-mode ultrasonography. Advanced atherosclerotic changes were quantified by summing the maximal thickness of atherosclerotic plaques in the carotid and femoral arteries and were expressed as a plaque score. Established risk factors were determined to adjust for possible differences between the groups. We found no substantial difference in intima-media thickness between vWD patients and controls (adjusted difference for carotid artery 0.007 mm, 95% CI −0.022 to 0.036 mm; femoral artery 0.069 mm, 95% CI −0.056 to 0.19 mm). Similar proportions of patients and controls had atherosclerotic plaques (19% and 17%, respectively). No difference was found in the plaque score between groups (adjusted difference −0.22 mm, 95% CI −0.69 to 0.26). Among vWD patients, we found no effect of treatment with vWF concentrates on intima-media thickness or plaque score.

Conclusions— The results of this study indicate that vWF does not play a substantial role in human atherogenesis.

Beta3 integrin deficiency promotes atherosclerosis and pulmonary inflammation in high-fat-fed, hyperlipidemic mice

Hyperlipidemia promotes the chronic inflammatory disease atherosclerosis through poorly understood mechanisms. Atherogenic lipoproteins activate platelets, but it is unknown whether platelets contribute to early inflammatory atherosclerotic lesions. To address the role of platelet aggregation in diet-induced vascular disease, we studied beta3 integrin-deficient mice (lacking platelet integrin alphaIIbbeta3 and the widely expressed nonplatelet integrin alphavbeta3) in two models of atherosclerosis, apolipoprotein E (apoE)-null and low-density lipoprotein receptor (LDLR)-null mice. Unexpectedly, a high-fat, Western-type (but not a low-fat) diet caused death in two-thirds of the beta3-/-apoE-/- and half of the beta3-/-LDLR-/- mice due to noninfectious pneumonitis. In animals from both models surviving high-fat feeding, pneumonitis was absent, but aortic atherosclerosis was 2- to 6-fold greater in beta3-/- compared with beta+/+ littermates. Expression of CD36, CD40L, and CD40 was increased in lungs of beta3-/-LDLR-/- mice. Each was also increased in smooth muscle cells cultured from beta3-deficient mice and suppressed by retroviral reconstitution of beta3. These data show that the platelet defect caused by alphaIIbbeta3 deficiency does not impair atherosclerotic lesion initiation. They also suggest that alphavbeta3 has a suppressive effect on inflammation, the loss of which induces atherogenic mediators that are amplified by diet-induced hyperlipidemia.

Successful percutaneous transluminal coronary angioplasty for acute myocardial infarction in von Willebrand's disease

An elderly woman with mild von Willebrand's disease presented with acute myocardial infarction. Percutaneous transluminal coronary angioplasty, to mechanically disrupt the thrombus without anticoagulation, was successfully undertaken. Haemostatic cover was also avoided.

Endothelial von Willebrand factor recruits platelets to atherosclerosis-prone sites in response to hypercholesterolemia

Platelets are thought to play a causal role during atherogenesis. Platelet-endothelial interactions in vivo and their molecular mechanisms under shear are, however, incompletely characterized. Here, an in vivo platelet homing assay was used in hypercholesterolemic rabbits to track platelet adhesion to plaque predilection sites. The role of platelet versus aortic endothelial cell (EC) activation was studied in an ex vivo flow chamber. Pathways of human platelet immobilization were detailed during in vitro perfusion studies. In rabbits, a 0.125% cholesterol diet induced no lesions within 3 months, but fatty streaks were found after 12 months. ECs at segmental arteries of 3- month rabbits expressed more von Willebrand factor (VWF) and recruited 5-fold more platelets than controls (P <.05, n = 5 and 4, respectively). The 3-month ostia had an increased likelihood to recruit platelets compared to control ostia (56% versus 18%, P <.0001, n = 89 and 63, respectively). Ex vivo, the adhesion of 3-month platelets to 3-month aortas was 8.4-fold increased compared to control studies (P <.01, n = 7 and 5, respectively). In vitro, endothelial VWF-platelet glycoprotein (GP) Ib and platelet P-selectin- endothelial P-selectin glycoprotein ligand 1 interactions accounted in combination for 83% of translocation and 90% of adhesion (P <.01, n = 4) of activated human platelets to activated human ECs. Platelet tethering was mainly mediated by platelet GPIb alpha, whereas platelet GPIIb/IIIa contributed 20% to arrest (P <.05). In conclusion, hypercholesterolemia primes platelets for recruitment via VWF, GPIb alpha, and P-selectin to lesion-prone sites, before lesions are detectable.

Advances in experimental dyslipidemia and atherosclerosis

Among the models of dyslipidemia and atherosclerosis, a number of wild-type, naturally defective, and genetically modified animals (rabbits, mice, pigeons, dogs, pigs, and monkeys) have been characterized. In particular, their similarities to and differences from humans in respect to relevant biochemical, physiologic, and pathologic conditions have been evaluated. Features of atherosclerotic lesions and their specific relationship to plasma lipoprotein particles have been critically reviewed and summarized. All animal models studied have limitations: the most significant advantages and disadvantages of using a specific animal species are outlined here. New insights in lipid metabolism and genetic background with regard to variations in pathogenesis of dyslipidemia-associated atherogenesis have also been reviewed. Evidence suggests that among wild-type species, strains of White Carneau pigeons and Watanabe Heritable Hyperlipidemic and St. Thomas's Hospital rabbits are preferable to the cholesterol-fed wild-type animal species in dyslipidemia and atherosclerosis research. Evidence for the usefulness of both wild-type and transgenic animals in studying the involvement of inflammatory pathways and Chlamydia pneumoniae infection in pathogenesis of atherosclerosis has also been summarized. Transgenic mice and rabbits are excellent tools for studying specific gene-related disorders. However, despite these significant achievements in animal experimentation, there are no suitable animal models for several rare types of fatal dyslipidemia-associated disorders such as phytosterolemia and cerebrotendinous xanthomatosis. An excellent model of diabetic atherosclerosis is unavailable. The question of reversibility of atherosclerosis still remains unanswered. Further work is needed to overcome these deficiencies.

Short wave ultraviolet laser energy in porcine coronary arteries: medial cell death and neointimal formation

BACKGROUND AND OBJECTIVE

Smooth muscle cell migration and proliferation from arterial media into the neointima are major factors in the restenosis process following coronary angioplasty. Because short wave ultraviolet (UV) radiation is cytotoxic for rat carotid artery smooth muscle cells, the aims of this study were to determine the effects of short wave UV irradiation on normal pig coronary arteries and to evaluate the efficacy of UV laser energy for reducing neointimal hyperplasia (NI).

STUDY DESIGN/MATERIALS AND METHODS

In 13 pigs fed a normal diet, 37 coronary arteries were studied. UV laser light (275 nm) was applied in escalating doses from 0-16,353 mJ/cm2 via fiberoptic through a 20 mm PTCA balloon catheter. The pigs were euthanized at 21 days and histologic analysis performed. Arterial media was rendered acellular (ACM) in 20 of 33 irradiated coronary arteries (61%). The minimum UV energy density inducing ACM was 1348 mJ/cm2. The fraction of acellular media to internal elastic lamina length (ACM/IEL) was 0.79 +/- 0.29.

RESULTS

No statistically significant difference was found between NI thickness at normal media sites (NM) vs. ACM sites (0.17 +/- 0.14 mm vs. 0.16 +/- 0.17 mm). No correlation was found between UV dose and NI formation (r = 0.307, P = 0.08).

CONCLUSION

Short wave UV irradiation induces ACM in normal porcine coronary arteries. Induction of acellular media is not associated with a reduction of NI formation in this porcine coronary model.

von Willebrand factor does not influence atherogenesis in arteries subjected to altered shear stress

The role of von Willebrand factor (vWF) in arterial neointimal formation that develops in arteries with altered shear stress was investigated using normal, heterozygous, and homozygous von Willebrand disease pigs (ie, vWD, or lacking vWF) that were fed normal pig chow. Shear stress was applied to carotid and femoral arteries with a Goldblatt clamp for 14 days, producing a > or = 80% stenosis. Neointimal lesion size was measured by computer-assisted morphometry. Expression of proliferative cell nuclear antigen (PCNA) by neointimial and medial cells was used as a relative index of proliferative activity. For shear-stressed arteries, there was no significant difference in the number of smooth muscle cell layers in the lesion, lesion size, and percent of PCNA-positive neointimal or medial cells among normal, heterozygous, and homozygous vWD pigs (P> or =.1, ANOVA). Lesions in pigs that expressed vWF (normals and heterozygotes) contained large amounts of vWF in the neointima, whereas lesions in vWD pigs had no detectable vWF. Moreover, no foam cells were detected in the lesions. Thus, the absence of vWF apparently does not alter the size of lesions in shear-stressed arteries in vWD pigs or the number of neointimal or medial cells expressing PCNA. Mechanism(s) involved with shear-induced modulation of smooth muscle cell proliferation, then, can operate independently of vWF in normolipemic pigs.

Familial and diet-induced hypercholesterolemia in swine. Lipid, ApoB, and ApoA-I concentrations and distributions in plasma and lipoprotein subfractions

Low levels of high-density lipoproteins (HDLs) may constitute an independent risk factor that may be as important as elevated low-density lipoproteins (LDLs) in coronary artery disease (CAD). Concentrations and distributions of lipids, apolipoprotein (apo) B, and apoA-I in the plasma and lipoprotein subfractions of two groups of swine, one with familial hypercholesterolemia (FHC) and the other with diet-induced hypercholesterolemia (DHC), were examined. Normolipidemic (NL) animals served as controls. All pigs carried the Lpb5 apoB mutation, which is known to influence the formation of atherosclerotic lesions. Mean concentrations of serum total cholesterol in NL, DHC, and FHC were 80.0 +/- 9.3, 774.3 +/- 54.5, and 316.5 +/- 36.1 mg/dL, respectively; HDL cholesterol (HDL-C), 33.5 +/- 1.9, 137.0 +/- 9.9, and 22.3 +/- 2.2 mg/dL; triglycerides, 33.0 +/- 16.3, 40.3 +/- 11.7, and 56.8 +/- 7.2 mg/dL; apoB, 35.7 +/- 3.1, 142.0 +/- 4.8, and 169.3 +/- 13.9 mg/dL; and apoA-I, 62.4 +/- 9.3, 170.9 +/- 6.9, and 42.6 +/- 4.8 mg/dL. The distributions of total cholesterol, apoB, and apoA-I in plasma lipoprotein subfractions were also examined. Compared with NL, FHC had fourfold and 4.7-fold increases in total cholesterol and apoB, respectively, distributed in the lower densities (d < 1.043 g/mL), and low HDL-C and apoA-I levels, resulting in a high total cholesterol/HDL-C ratio (14.4:1) and elevated triglyceride levels. DHC was characterized by 10-fold and fourfold increases in total cholesterol and apoB, respectively, resulting in an LDL particle highly enriched in cholesterol, a fourfold increase of HDL-C, an almost threefold increase in apoA-I, and a normal triglyceride level.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of neointimal hyperplasia by coronary angioplasty balloon overinflation: comparison of feeder pigs to Yucatan minipigs

We evaluated the use of simple balloon overinflation to induce neointimal hyperplasia in a porcine model of coronary artery restenosis. By using standard percutaneous transluminal coronary angioplasty techniques, left anterior descending (LAD) and/or left circumflex (LCX) coronary arteries of either juvenile feeder pigs or adult Yucatan minipigs were intentionally overinflated. Four weeks later, resultant neointimal hyperplastic responses (neointima/media area; NI/M) were quantitated morphometrically. At all ballooned sites neointimal hyperplasia occurred only when the internal elastic lamina (IEL) was ruptured; the degree of hyperplasia correlated directly with the injury index, that is, the percentage of IEL circumference that fractured (r = 0.74; n = 25; p < 0.05). Despite similar injury indexes in the LAD bed, there was a trend (p = 0.07; analysis of variance) toward greater NI/M ratios in the Yucatan minipig versus the feeder pig group (1.14 +/- 0.21 vs 0.73 +/- 0.09, n = 7/group). We found no such trend in the LCX bed, where the injury index (25.7% +/- 3.5%) was significantly greater than that of the LAD (18.2% +/- 1.2%, p < 0.05). If variations in balloon-induced vascular injury are accounted for, the technique of balloon overinflation of coronary arteries should prove useful in testing potential antirestenotic agents in either adult or juvenile pigs.

Coronary atherosclerosis in the pig. Induced plaque injury and platelet response

The thrombogenic potential of atherosclerotic diet-induced coronary atherosclerotic plaques was investigated in normal swine and in bleeder swine with homozygous von Willebrand disease. Fourteen paired normal and bleeder swine were placed on a 1% cholesterol diet for 1 to 16 weeks. Serum cholesterol was elevated in all animals at sacrifice. Foam cell deposits developed in all major epicardial coronary arteries, and lesions progressed over time from small subendothelial foam cell deposits to fibrous cap lesions that contained foam cells, elastic fibers, collagen, degenerative material, and smooth muscle cells. Balloon catheter injury resulted in platelet deposition, largely in a monolayer or as small platelet clumps devoid of fibrin. Lipid debris was present in injured areas of the subendothelium but did not induce thrombus formation. When the injury involved the media, platelet-fibrin thrombi were formed. Lipid was not present in these thrombi. Morphometric analysis of platelet deposition on ballooned atherosclerotic vessels showed similar numbers of platelets in both phenotypes. However, the attached platelets in bleeder pigs showed significantly less spreading than did those in the normal animals. The results show that injury to intimal foam cell and mixed cellular lesions in coronary arteries of cholesterol-fed swine does not promote the development of platelet-fibrin thrombus formation. In contrast, when the injury extended to the media, mixed thrombi were formed.

von Willebrand factor and occlusive arterial thrombosis. A study in normal and von Willebrand's disease pigs with diet-induced hypercholesterolemia and atherosclerosis

The thrombotic response of atherosclerotic arteries to stenosis and injury was studied in 14 pigs, eight normal and six with von Willebrand's disease (vWD). Atherosclerosis was produced by feeding a 1% to 2% cholesterol diet for 24 weeks. Both groups of pigs developed severe hypercholesterolemia, greater than five times baseline values. Coronary atherosclerosis was detected in all vWD pigs and in all but one normal pig and was not significantly different between groups. At sacrifice under general anesthesia, a Goldblatt clamp (GC) was positioned around the left anterior descending coronary (LAD) and carotid arteries to produce a stenotic segment, which was pinch-injured with needle holders. A 20 MHz Doppler velocity crystal was placed distal to the GC to detect cyclic flow reductions or permanent cessation of flow velocity indicative of occlusive thrombosis. In the phenotypically normal pigs with diet-induced atherosclerosis, occlusive thrombosis was detected in seven of seven LAD and seven of seven carotid arteries. In atherosclerotic vWD pigs, occlusive thrombosis failed to form in six LAD and 10 carotid arteries (p less than 0.003, Wilcoxon rank sum test). Scanning electron micrographs demonstrated platelet-fibrin microthrombi in both groups of pigs; only phenotypically normal pigs had occlusive thrombi. Von Willebrand factor is essential for the development of occlusive thrombosis and appears to support the progression of a mixed microthrombus to an occlusive thrombus.

Effect of repeated endotoxin treatment and hypercholesterolemia on preatherosclerotic lesions in weaned pigs. Part II. Lipid and glycosaminoglycan analysis of intima and inner media

We compared the effects of mild hypercholesterolemia and repeated endotoxin infusions on the biochemical composition of aortic intima and inner media of 24 piglets divided into 4 groups 5 days after weaning: controls on normal diet (group I); normal diet and endotoxin (group II); fat-supplemented diet (group III); and fat-supplemented diet and endotoxin (group IV). It was found that mild hypercholesterolemia increased the concentration of arterial esterified cholesterol and the relative amount of the fraction containing chondroitin sulphates A and C in total glycosaminoglycans. Endotoxin infusions partly prevented the increase of serum cholesterol caused by the fat-supplemented diet but had no independent effect on the arterial biochemical composition; nor did they affect the biochemical changes caused by hypercholesterolemia. When the results of all groups were combined, chondroitin sulphates A and C showed a significant positive correlation with the concentration of arterial esterified cholesterol and the percentage of linoleic acid in arterial cholesteryl esters. Serum total cholesterol did not correlate with arterial cholesterol fractions, but the ratio of high density lipoprotein-cholesterol to total serum cholesterol showed a negative association with arterial esterified cholesterol. The present findings indicate that (1) mild hypercholesterolemia is atherogenic in young piglets, and (2) changes in arterial glycosaminoglycan composition might be one of the earliest biochemical alterations in atherogenesis.

Effect of repeated endotoxin treatment and hypercholesterolemia on preatherosclerotic lesions in weaned pigs. Part 1. Scanning and transmission electron microscopic study

Endothelial cell damage is considered to be the primary event in atherogenesis. In this study we compared the effects of mild hypercholesterolemia and repeated E. coli endotoxin infusions on the endothelial cells of the coronary arteries of the pig. We divided 24 pigs into 4 groups: I: controls on normal diet; II: normal diet and endotoxin treatment; III: fat-supplemented diet; IV: fat-supplemented diet and endotoxin treatment. The animals on a fat-supplemented diet showed the most frequent and most severe endothelial cell damage. The damage was less when this diet was combined with endotoxin treatment. Endotoxin reduced the serum total cholesterol level (P less than 0.01). The cholesterol level correlated very significantly (P less than 0.001) with endothelial damage of the coronary arteries. Mild hypercholesterolemia (s-cholesterol 5.68 mmol/l, controls 2.28 mmol/l) was thus associated with toxic effects in the endothelial cells. The E. coli endotoxin infusions did not have any cumulative effect on the lesions.