Atherosclerosis: Known and unknown.

Atherosclerotic disease, such as myocardial infarction and stroke, is the number one killer worldwide. Atherosclerosis is considered to be caused by multiple factors, including genetic and environmental factors. In humans, it takes several decades until the clinical complications develop. There are many known risk factors for atherosclerosis, including hypercholesterolemia, hypertension, diabetes and smoking, which are involved in the pathogenesis of atherosclerosis; however, it is generally believed that atherosclerosis is vascular chronic inflammation initiated by interactions of these risk factors and arterial wall cells. In the past 30 years, the molecular mechanisms underlying the pathogenesis of atherosclerosis have been investigated extensively using genetically modified animals, and lipid-reducing drugs, such as statins, have been demonstrated as the most effective for the prevention and treatment of atherosclerosis. However, despite this progress, questions regarding the pathogenesis of atherosclerosis remain and there is a need to develop new animal models and novel therapeutics to treat patients who cannot be effectively treated by statins. In this review, we will focus on two topics of atherosclerosis, "pathology" and "pathogenesis," and discuss unanswered questions.

Treatment of atherosclerosis by traditional Chinese medicine: Questions and quandaries.

Atherosclerosis and its complications, such as myocardial infarction and stroke, are the major causes of morbidity and mortality, and development of effective therapies for both prevention and treatment of this disease is critically important. Currently, there are many drugs available for atherosclerotic disease, but the lipid-lowering drugs statins are still the first-choice for treatment of hypercholesterolemia, a major risk factor for atherosclerosis. On the other hand, traditional Chinese medicines, mainly Chinese herbal medicines (CHM), have been widely used in China and in other Asian countries for the treatment of atherosclerotic diseases. Although many CHMs have been reported to be effective for treating atherosclerotic diseases for more than two thousand years, there are still many difficulties for their use, such as lack of scientific evidence assessed by rigorous clinical trials, complicated components and unclear pharmacological mechanisms, which often hamper the widespread use of CHMs in Western countries. Due to these concerns, CHMs are usually considered as complimentary or alternative treatment for atherosclerotic diseases. In this review, we provide an overview of the pathophysiology of atherosclerosis viewed by Western and traditional Chinese medicine, summarize pros and cons on the efficacy of CHMs for atherosclerosis and discuss what is necessary for CHM use to spread to Western societies.

Motility and fertility of rabbit sperm cryopreserved using soybean lecithin as an alternative to egg yolk.

This study was conducted to investigate whether soy lecithin can be used as an alternative cryoprotectant to establish a procedure that does not require the use of egg yolk to cryopreserve rabbit strains. Semen from Japanese White rabbits was frozen with HEPES extender containing 20% egg yolk (EYH), 0.5% (Lec-0.5), 1.5% (Lec-1.5), 2.5% (Lec-2.5), or 3.5% (Lec-3.5; wt/vol) lecithin (type IV-S, ≥30%), and the motility of thawed sperm was analyzed. The sperm motility in the Lec-1.5 group was significantly higher than that in the Lec-2.5 and 3.5 groups and equivalent to the EYH group. From 17 rounds of artificial insemination with frozen-thawed sperm in the EYH and Lec-1.5 groups, 12 rabbits in both groups were pregnant (70.6%) and delivered offspring. The litter size was 3.3 in the EYH group and 5.1 in the Lec-1.5 group. These results indicate that soy lecithin can be used as a substitute for egg yolk as a cryoprotectant on the basis of motility and fertility of the frozen-thawed rabbit sperm and that 1.5% lecithin (type IV-S, ≥30%) in the semen extender was the optimum concentration for rabbit sperm cryopreservation.

Rabbit models for the study of human atherosclerosis: from pathophysiological mechanisms to translational medicine.

Laboratory animal models play an important role in the study of human diseases. Using appropriate animals is critical not only for basic research but also for the development of therapeutics and diagnostic tools. Rabbits are widely used for the study of human atherosclerosis. Because rabbits have a unique feature of lipoprotein metabolism (like humans but unlike rodents) and are sensitive to a cholesterol diet, rabbit models have not only provided many insights into the pathogenesis and development of human atherosclerosis but also made a great contribution to translational research. In fact, rabbit was the first animal model used for studying human atherosclerosis, more than a century ago. Currently, three types of rabbit model are commonly used for the study of human atherosclerosis and lipid metabolism: (1) cholesterol-fed rabbits, (2) Watanabe heritable hyperlipidemic rabbits, analogous to human familial hypercholesterolemia due to genetic deficiency of LDL receptors, and (3) genetically modified (transgenic and knock-out) rabbits. Despite their importance, compared with the mouse, the most widely used laboratory animal model nowadays, the use of rabbit models is still limited. In this review, we focus on the features of rabbit lipoprotein metabolism and pathology of atherosclerotic lesions that make it the optimal model for human atherosclerotic disease, especially for the translational medicine. For the sake of clarity, the review is not an attempt to be completely inclusive, but instead attempts to summarize substantial information concisely and provide a guideline for experiments using rabbits.

Significance of 18 F-FDG PET and immunohistochemical GLUT-1 expression for cardiac myxoma.

Cardiac tumours are relatively rare and are difficult to diagnose merely with imaging techniques. We demonstrated an unusual case of left atrial myxoma, displaying the successful detection by positron emission tomography using 2-deoxy-2-[18 F] fluoro-D-glucose (18 F-FDG PET), correlated closely to more intense and enhanced immunoreactivity with glucose transporter-1 (GLUT-1) in a substantial number of cardiac myxoma cells. Further prospective studies are needed to validate the significance of 18 F-FDG PET findings for cardiac myxoma and the association with immunohistochemical GLUT-1 expression in its tumour cells, after collecting and investigating a larger number of surgical cases examined with both of them. VIRTUAL SLIDES: The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2991481941253449.

Effects of type III antifreeze protein on sperm and embryo cryopreservation in rabbit.

We investigated the effects of antifreeze protein (AFP) III supplementation on the cryopreservation of rabbit sperm cells and embryos. Ejaculated semen was collected from male Japanese white (JW) rabbits and divided into four AFP-supplemented groups (0.1 µg/ml, 1 µg/ml, 10 µg/ml, 100 µg/ml) and one control group with no AFP-supplementation. The semen samples were treated with egg-yolk HEPES extender containing 6% acetamide before the sperm was cooled from room temperature to 5 °C, then packed into sperm straws. The straws were frozen in steam of liquid nitrogen (LN2) and then preserved in the LN2. The motility of the sperm after thawing in 37 °C water was analyzed. The percentage of rapidly motile sperm in the 1 µg/ml AFP group was significantly higher than in the control group. Morulae were collected from female JW rabbits and divided into three AFP-supplemented groups (100 ng/ml, 500 ng/ml, 1000 ng/ml) and one control group. The morulae, immersed in an embryo-freezing solution (M199-HEPES containing 20% ethylene glycol, 20% dimethylsulfoxide, 10% fetal bovine serum and 0.25 M sucrose), were packed into open pulled embryo straws and vitrified in LN2. The frozen embryos were thawed in the embryo-freezing solution, and the rates of embryo survival and development to blastocyte stage were analyzed after incubation for 72 h. The development rate of the embryos in the 500 ng/ml AFP group was significantly higher than in the control group, but that in the 1000 ng/ml AFP group was significantly lower. In conclusion, the appropriate dose of AFP III increased the number of rapidly motile sperm and embryo survival following freezing and thawing. The results suggest that supplementation with AFP III can increase the efficiency of cryopreservation of rabbit sperm cells and embryos.

Effects of cholesterol-loaded cyclodextrins on the rate and the quality of motility in frozen and thawed rabbit sperm.

The motility of sperm after freezing and thawing is critical for effective cryopreservation. It is known that supplementation with cholesterol-loaded cyclodextrin (CLC) improves cryosurvival of sperm in various animals. To clarify the effects of supplementation with CLC on rabbit sperm motility after freezing and thawing, rabbit sperm motility was analyzed using a computer-assisted sperm analysis system. Sperm motility with CLC supplementation was 29.4 ± 9.6% (mean ± SD), which was significantly higher than that of controls (20.8 ± 7.1%, P<0.05). The curvilinear velocity of sperm with CLC exceeded that of controls, whereas the values for linearity and wobble were significantly lower in sperm with CLC compared with controls. After artificial insemination, 44.3% of recovered ova were fertilized in the CLC-supplemented group, which was higher than the percentage in the control group (36.4%). The results indicate that supplementation with CLC improves the rate and quality of motility in rabbit sperm after freezing and thawing, and would be advantageous for successful cryopreservation.

Intraductal fibroadenoma under the nipple in an 11-year-old female.

Recently, Chung et al. have reported the detailed clinicopathological features of an extremely rare case sharing similar histopathological characteristics with fibroadenomas, phyllodes tumours, intraductal papillomas or ductal adenomas, given the name of intraductal fibroadenomatosis, as an unusual variant of intracanalicular fibroadenoma. Herein we demonstrated a very unusual case of intraductal fibroadenoma of the breast with admixture of components of intracanalicular type fibroadenoma or benign phyllodes tumour and a smaller amount of intraductal papilloma, occupying the one duct and some adjacent ductules, presenting as a well-demarcated nodule.

Peroxiredoxin 4 protects against nonalcoholic steatohepatitis and type 2 diabetes in a nongenetic mouse model.

AIMS: Consumption of a high-fructose diet (HFrD) can induce the development of a metabolic syndrome, manifesting as nonalcoholic steatohepatitis (NASH) and/or type 2 diabetes mellitus (T2DM), via a process in which oxidative stress plays a critical role. Peroxiredoxin 4 (PRDX4) is a unique and only known secretory member of the PRDX antioxidant family. However, its putative roles in the development of NASH and/or T2DM have not been investigated. RESULTS: To elucidate the functions of PRDX4 in a metabolic syndrome, we established a nongenetic mouse model of T2DM by feeding mice a HFrD after injecting a relatively low dose of streptozotocin. Compared with wild-type (WT), human PRDX4 transgenic (Tg) mice exhibited significant improvements in insulin resistance, characterized by a lower glucose and insulin concentration and faster responses in glucose tolerance tests. The liver of Tg also showed less severe vesicular steatosis, inflammation, and fibrosis, along with lower lipid concentrations, lower levels of oxidative stress markers, more decreased expression of hepatic aminotransferase, and more reduced stellate cell activation than those in the WT liver, reminiscent of human early NASH. Hepatocyte apoptosis was also significantly repressed in Tg mice. By contrast, serum adiponectin levels and hepatic adiponectin receptor expression were significantly lower in WT mice, consistent with greater insulin resistance in the peripheral liver tissue compared with Tg mice. INNOVATION AND CONCLUSION: Our data for the first time show that PRDX4 may protect against NASH, T2DM, and the metabolic syndrome by ameliorating oxidative stress-induced injury.

Human apolipoprotein A-II protects against diet-induced atherosclerosis in transgenic rabbits.

OBJECTIVE: Apolipoprotein (apo) A-II is the second major apo of high-density lipoproteins, yet its pathophysiological roles in the development of atherosclerosis remain unknown. We aimed to examine whether apo A-II plays any role in atherogenesis and, if so, to elucidate the mechanism involved. METHODS AND RESULTS: We compared the susceptibility of human apo A-II transgenic (Tg) rabbits to cholesterol diet-induced atherosclerosis with non-Tg littermate rabbits. Tg rabbits developed significantly less aortic and coronary atherosclerosis than their non-Tg littermates, while total plasma cholesterol levels were similar. Atherosclerotic lesions of Tg rabbits were characterized by reduced macrophages and smooth muscle cells, and apo A-II immunoreactive proteins were frequently detected in the lesions. Tg rabbits exhibited low levels of plasma C-reactive protein and blood leukocytes compared with non-Tg rabbits, and high-density lipoproteins of Tg rabbit plasma exerted stronger cholesterol efflux activity and inhibitory effects on the inflammatory cytokine expression by macrophages in vitro than high-density lipoproteins isolated from non-Tg rabbits. In addition, ß-very-low-density lipoproteins of Tg rabbits were less sensitive to copper-induced oxidation than ß-very-low-density lipoproteins of non-Tg rabbits. CONCLUSIONS: These results suggest that enrichment of apo A-II in high-density lipoprotein particles has atheroprotective effects and apo A-II may become a target for the treatment of atherosclerosis.

Overexpression of peroxiredoxin 4 attenuates atherosclerosis in apolipoprotein E knockout mice.

AIM: A growing body of evidence has shown that increased formation of oxidized molecules and reactive oxygen species within the vasculature (i.e., the extracellular space) plays a crucial role in the initiation and progression of atherosclerosis and in the formation of unstable plaques. Peroxiredoxin 4 (PRDX4) is the only known secretory member of the antioxidant PRDX family. However, the relationship between PRDX4 and susceptibility to atherosclerosis has remained unclear. RESULTS: To define the role of PRDX4 in hyperlipidemia-induced atherosclerosis, we generated hPRDX4 transgenic (Tg) and apolipoprotein E (apoE) knockout mice (hPRDX4(+/+)/apoE(-/-)). After feeding the mice a high-cholesterol diet, they showed fewer atheromatous plaques, less T-lymphocyte infiltration, lower levels of oxidative stress markers, less necrosis, a larger number of smooth muscle cells, and a larger amount of collagen, resulting in thickened fibrous cap formation and possible stable plaque phenotype as compared with apoE(-/-) mice. We also detected greater suppression of apoptosis and decreased Bax expression in hPRDX4(+/+)/apoE(-/-) mice than in apoE(-/-) mice. Bone marrow transplantation from hPRDX4(+/+) donors to apoE(-/-) mice confirmed the antiatherogenic aspects of PRDX4, revealing significantly suppressed atherosclerotic progression. INNOVATION: In this study, we demonstrated for the first time that PRDX4 suppressed the development of atherosclerosis in apoE(-/-) mice fed a high-cholesterol diet. CONCLUSION: These data indicate that PRDX4 is an antiatherogenic factor and, by suppressing oxidative damage and apoptosis, that it may protect against the formation of vulnerable (unstable) plaques.

Histamine deficiency decreases atherosclerosis and inflammatory response in apolipoprotein E knockout mice independently of serum cholesterol level.

OBJECTIVE: Histamine and histamine receptors are found in atherosclerotic lesions, and their signaling and subsequent proatherogenic or proinflammatory gene expression are involved in atherogenesis. In the present study, we generated apolipoprotein E (apoE) and histamine synthesizing histidine decarboxylase double knockout (DKO) mice on a C57BL/6J (wild-type mice) background to clarify the roles of histamine in atherosclerosis. METHODS AND RESULTS: Wild-type, apoE knockout (KO), and DKO mice were fed a high-cholesterol diet to analyze hyperlipidemia-induced atherosclerosis. Compared with wild-type mice, apoE-KO mice showed increased expression of histamine and its receptors, corresponding to increased atherosclerotic lesion areas and expression of inflammatory regulators, such as nuclear factor-κB, scavenger receptors, inflammatory cytokines, and matrix metalloproteinases. Histamine deficiency after deletion of histidine decarboxylase reduced atherosclerotic areas and expression of a range of the inflammation regulatory genes, but serum cholesterol levels of DKO mice were higher than those of apoE-KO mice. CONCLUSIONS: These results indicate that histamine is involved in the development of atherosclerosis in apoE-KO mice by regulating gene expression of inflammatory modulators, an action that appears to be independent of serum cholesterol levels. In addition to acute inflammatory response, histamine participates in chronic inflammation, such as hyperlipidemia-induced atherosclerosis, and might be a novel therapeutic target for the treatment of atherosclerosis.

Histamine regulation in glucose and lipid metabolism via histamine receptors: model for nonalcoholic steatohepatitis in mice.

Histamine has been proposed to be an important regulator of energy intake and expenditure. The aim of this study was to evaluate histamine regulation of glucose and lipid metabolism and development of nonalcoholic steatohepatitis (NASH) with a hyperlipidemic diet. Histamine regulation of glucose and lipid metabolism, adipocytokine production, and development of hyperlipidemia-induced hepatic injury were studied in histamine H1 (H1R(-/-)) and H2 (H2R(-/-)) receptor knockout and wild-type mice. H1R(-/-) mice showed mildly increased insulin resistance. In contrast, H2R(-/-) mice manifested profound insulin resistance and glucose intolerance. High-fat/high-cholesterol feeding enhanced insulin resistance and glucose intolerance. Studies with two-deoxy-2-[(18)F]-fluoro-d-glucose and positron emission tomography showed a brain glucose allocation in H1R(-/-) mice. In addition, severe NASH with hypoadiponectinemia as well as hepatic triglyceride and free cholesterol accumulation and increased blood hepatic enzymes were observed in H2R(-/-) mice. H1R(-/-) mice showed an obese phenotype with visceral adiposity, hyperleptinemia, and less severe hepatic steatosis and inflammation with increased hepatic triglyceride. These data suggest that H1R and H2R signaling may regulate glucose and lipid metabolism and development of hyperlipidemia-induced NASH.

Overexpression of peroxiredoxin 4 protects against high-dose streptozotocin-induced diabetes by suppressing oxidative stress and cytokines in transgenic mice.

Peroxiredoxin 4 (PRDX4) is one of a newly discovered family of antioxidative proteins. We generated human PRDX4 (hPRDX4) transgenic (Tg) mice, displaying a high level of hPRDX4 expression in the pancreatic islets, and then focused on the functions of PRDX4 in a type 1 diabetes mellitus (T1DM) model using a single high dose of streptozotocin (SHDS). After SHDS-injection, Tg mice showed significantly less hyperglycemia and hypoinsulinemia and a much faster response on glucose tolerance test than wild-type (WT) mice. Morphologic and immunohistochemical observation revealed that the pancreatic islet areas of Tg mice were larger along with less CD3-positive lymphocyte infiltration compared with WT mice. Upon comparison between these two mouse models, ß-cell apoptosis was also repressed, and reversely, ß-cell proliferation was enhanced in Tg mice. Real-time RT-PCR demonstrated that the expression of many inflammatory-related molecules and their receptors and transcription factors were significantly downregulated in Tg mice. These data indicate that PRDX4 can protect pancreatic islet ß-cells against injury caused by SHDS-induced insulitis, which strongly suggests that oxidative stress plays an essential role in SHDS-induced diabetes. This study, for the first time, implicates that PRDX4 has a pivotal protective function against diabetes progression in this T1DM model.

Human C-reactive protein does not promote atherosclerosis in transgenic rabbits.

BACKGROUND: Although there is a statistically significant association between modestly raised baseline plasma C-reactive protein (CRP) values and future cardiovascular events, the debate is still unsettled in regard to whether CRP plays a causal role in the pathogenesis of atherosclerosis. METHODS AND RESULTS: We generated 2 lines of transgenic (Tg) rabbits expressing human CRP (hCRP). The plasma levels of hCRP in hCRP-Tg-1 and hCRP-Tg-2 rabbits were 0.4+/-0.13 (n=14) and 57.8+/-20.6 mg/L (n=12), respectively. In addition, hCRP isolated from Tg rabbit plasma exhibited the ability to activate the rabbit complement. To define the role of hCRP in atherosclerosis, we compared the susceptibility of hCRP-Tg rabbits to cholesterol-rich diet-induced aortic and coronary atherosclerosis with that of non-Tg rabbits. After being fed with a cholesterol-rich diet for 16 weeks, Tg and non-Tg rabbits developed similar hypercholesterolemia and lesion sizes in both aortic and coronary arteries. Immunohistochemical staining and Western blotting revealed that hCRP was indeed present in the lesions but did not affect macrophage accumulation and smooth muscle cell proliferation of the lesions. CONCLUSIONS: Neither high nor low plasma concentrations of hCRP affected aortic or coronary atherosclerosis lesion formation in hCRP-Tg rabbits.

Expression of human apoAII in transgenic rabbits leads to dyslipidemia: a new model for combined hyperlipidemia.

OBJECTIVE: Apolipoprotein AII (apoAII) is the second major apolipoprotein in high-density lipoprotein (HDL). However, the physiological functions of apoAII in lipoprotein metabolism have not been fully elucidated. METHODS AND RESULTS: We generated human apoAII transgenic (Tg) rabbits, a species that normally does not have an endogenous apoAII gene. Plasma levels of human apoAII in Tg rabbits were approximately 30 mg/dL, similar to the plasma levels in healthy humans. The expression of human apoAII in Tg rabbits resulted in increased levels of plasma triglycerides, total cholesterol, and phospholipids accompanied by a marked reduction in HDL-cholesterol levels compared with non-Tg littermates. Analysis of lipoprotein fractions showed that hyperlipidemia exhibited by Tg rabbits was caused by elevated levels of very-low-density lipoproteins (VLDL) and intermediate-density lipoproteins. Furthermore, postheparin lipoprotein lipase activity significantly decreased in Tg rabbits compared with non-Tg rabbits. CONCLUSIONS: These results indicate that apoAII plays an important role in both VLDL and HDL metabolism, possibly through the inhibition of lipoprotein lipase activity. ApoAII Tg rabbits may become a new model for the study of human familial combined hyperlipidemia.

Genetic podocyte lineage reveals progressive podocytopenia with parietal cell hyperplasia in a murine model of cellular/collapsing focal segmental glomerulosclerosis.

Focal segmental glomerulosclerosis (FSGS) is a progressive renal disease, and the glomerular visceral cell hyperplasia typically observed in cellular/collapsing FSGS is an important pathological factor in disease progression. However, the cellular features that promote FSGS currently remain obscure. To determine both the origin and phenotypic alterations in hyperplastic cells in cellular/collapsing FSGS, the present study used a previously described FSGS model in p21-deficient mice with visceral cell hyperplasia and identified the podocyte lineage by genetic tagging. The p21-deficient mice with nephropathy showed significantly higher urinary protein levels, extracapillary hyperplastic indices on day 5, and glomerular sclerosis indices on day 14 than wild-type controls. X-gal staining and immunohistochemistry for podocyte and parietal epithelial cell (PEC) markers revealed progressive podocytopenia with capillary collapse accompanied by PEC hyperplasia leading to FSGS. In our investigation, non-tagged cells expressed neither WT1 nor nestin. Ki-67, a proliferation marker, was rarely associated with podocytes but was expressed at high levels in PECs. Both terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and electron microscopy failed to show evidence of significant podocyte apoptosis on days 5 and 14. These findings suggest that extensive podocyte loss and simultaneous PEC hyperplasia is an actual pathology that may contribute to the progression of cellular/collapsing FSGS in this mouse model. Additionally, this is the first study to demonstrate the regulatory role of p21 in the PEC cell cycle.

Temporal and quantitative analysis of expression of metalloproteinases (MMPs) and their endogenous inhibitors in atherosclerotic lesions.

Matrix metalloproteinases (MMPs) play an important role in the pathogenesis of vascular diseases, such as atherosclerosis, plaque rupture and aneurysms. Although several MMPs have been demonstrated in the lesions of atherosclerosis, their expression profiles during the initiation and progression of lesions have not been fully determined. We hypothesized that the expression of various MMPs, along with their endogenous inhibitors, may be differentially regulated dependent upon the lesion progression. Therefore, we made a temporal and quantitative analysis of the mRNA and protein expression of MMPs and tissue inhibitors of metalloproteinases expressed in the different stages of atherosclerotic lesions of rabbits and humans. We found that MMP-1, MMP-12 and MMP-13 expression was nearly absent in the normal arterial wall, but was remarkably increased with lesion progression. Furthermore, the expression of these MMPs in the lesions was closely associated with intimal macrophages and monocyte chemoattractant protein-1 expression, suggesting that the intimal macrophages are the major source of production of these MMPs. MMP-3 and MT1-MMP were also significantly upregulated in the early-stage lesions and fatty streaks compared to the normal aortas of rabbits. Our results indicate that MMP-1, -12, and -13 derived from intimal macrophages may play a pivotal role in both lesion initiation and progression, and therefore are potential therapeutic targets for the treatment of plaque rupture and aneurysm formation.

Matrix metalloproteinase 12 accelerates the initiation of atherosclerosis and stimulates the progression of fatty streaks to fibrous plaques in transgenic rabbits.

Whether fatty streaks are directly followed by fibrous plaque formation in atherosclerosis remains controversial. Disruption of the basement membrane and elastic layers is thought to be essential for this process. Matrix metalloproteinase 12 (MMP-12) can degrade a broad spectrum of substrates, but the role of MMP-12 in the early stage of atherosclerosis is unclear. To investigate MMP-12 function in the initiation and progression of atherosclerosis, we investigated macrophage migration and elastolysis in relation to fatty streaks in human MMP-12 transgenic (hMMP-12 Tg) rabbits. Fatty streaks in hMMP-12 Tg rabbits fed a 1% cholesterol diet for 6 weeks (cholesterol-induced model of atherosclerosis) were more pronounced and were associated with more significant degradation of the internal elastic layer compared with wild-type (WT) animals. Numbers of infiltrating macrophages and smooth muscle cells in the lesions were increased in hMMP-12 Tg compared with WT animals. In both cuff- and ligation-induced models of atherosclerosis, smooth muscle cell-predominant atherosclerotic lesions were elevated with significant elastolysis of the internal elastic lamina in Tg compared with WT animals; "microelastolytic sites" were recognized before formation of the neointima in the cuff model only. These results indicate that MMP-12 may be critical to the initiation and progression of atherosclerosis via degradation of the elastic layers and/or basement membrane. Therefore, a specific MMP-12 inhibitor might prove useful for the treatment of progressive atherosclerosis.