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.

Apolipoprotein (apo-) B mRNA editing is the deamination of cytidine that creates a new termination codon and produces a truncated version of apo-B (apo-B48). The cytidine deaminase catalytic subunit [apo-B mRNA-editing enzyme catalytic polypeptide 1 (APOBEC-1)] of the multiprotein editing complex has been identified. We generated transgenic rabbits and mice expressing rabbit APOBEC-1 in their livers to determine whether hepatic expression would lower low density lipoprotein cholesterol concentrations. The apo-B mRNA from the livers of the transgenic mice and rabbit was extensively edited, and the transgenic animals had reduced concentrations of apo-B100 and low density lipoproteins compared with control animals. Unexpectedly, all of the transgenic mice and a transgenic rabbit had liver dysplasia, and many transgenic mice developed hepatocellular carcinomas. Many of the mouse livers were hyperplastic and filled with lipid. Other hepatic mRNAs with sequence motifs similar to apo-B mRNA were examined for this type of editing (i.e., cytidine deamination). One of these, tyrosine kinase, was edited in livers of transgenic mice but not of controls. This result demonstrates that other mRNAs can be edited by the overexpressed editing enzyme and suggests that aberrant editing of hepatic mRNAs involved in cell growth and regulation is the cause of the tumorigenesis. Finally, these findings compromise the potential use of APOBEC-1 for gene therapy to lower plasma levels of low density lipoproteins.

Atherosclerosis and its complications constitute the most common causes of death in Western societies and Japan. Although several theories or hypotheses about atherogenesis have been proposed during the past decades, none can completely explain the whole process of the pathogenesis of atherosclerosis because this disease is associated with multiple risk factors. In spite of this, the concept that atherosclerosis is a specific form of chronic inflammatory process resulting from interactions between plasma lipoproteins, cellular components ( monocyte/macrophages, T lymphocytes, endothelial cells and smooth muscle cells ) and the extracellular matrix of the arterial wall, is now well accepted. Histologically, atherosclerotic lesions from the early-stage ( fatty streak ) to more complicated lesions possess all the features of chronic inflammation. It has been demonstrated that atherogenic lipoproteins such as oxidized low density lipoprotein ( LDL ), remnant lipoprotein (β -VLDL) and lipoprotein [ Lp ] ( a ) play a critical role in the pro-inflammatory reaction, whereas high density lipoprotein ( HDL ), anti-atherogenic lipoproteins, exert anti-inflammatory functions. In cholesterol-fed animals, the earliest events in the arterial wall during atherogenesis are the adhesion of monocytes and lymphocytes to endothelial cells followed by the migration of these cells into the intima. It has been shown that these early events in atherosclerosis are triggered by the presence of high levels of atherogenic lipoproteins in the plasma and are mediated by inflammatory factors such as adhesion molecules and cytokines in the arterial wall. The development of genetically modified laboratory animals ( transgenic and knock-out mice and transgenic rabbits ) has provided a powerful approach for dissecting individual candidate genes and studying their cause-and-effect relationships in lesion formation and progression. The purpose of this article is to review the recent progress regarding the inflammatory processes during the development of atherosclerosis based on both human and experimental studies. In particular, we will address the mechanisms of atherogenic lipoproteins in terms of inflammatory reactions associated with hypercholesterolemia. Understanding the molecular mechanisms responsible for inflammatory reactions during atherogenesis may help us to develop novel therapeutic strategies to control, treat and prevent atherosclerosis in the future. J Atheroscler Thromb, 2003; 10: 63-71.

To elucidate the precise metabolic roles of hepatic lipase (HL), a human HL cDNA in a liver-specific expression vector was used to generate transgenic lines in the rabbit, an animal that normally expresses low levels of this enzyme. HL was detected in the plasma of all rabbits only after the aministration ofheparin; HL activity in transgenic rabbits was found at levels up to 80-fold greater than that in nontransgenic littermates. This increase in enzyme activity was associated with as much as a 5-fold decrease in total plasma cholesterol levels. Expression of the transgene resulted in a dramatic reduction in the level of large high density lipoproteins (HDL1 (6).Studies in vitro indicate that HL possesses both triglyceride hydrolase and phospholipase activities, and it has a high affinity for HDL particles (1). Administration of specific antibodies against HL in cats, rats, and monkeys indicated a role for this enzyme in the conversion of very low density lipoprotein (VLDL) remnants to low density lipoproteins (LDL) (7-9), in the metabolism of apolipoprotein (apo) B48-containing lipoproteins (10-12), and in the conversion of HDL2 to HDL3 (13,14). These findings are consistent with the phenotype of HL deficiency in human subjects. This disorder, in which the premature development of atherosclerosis is a cardinal feature, is characterized by elevated total plasma triglycerides and cholesterol corresponding to an increase in the amount of triglyceride-rich . However, the precise role of HL in lipoprotein metabolism remains unclear.To elucidate the physiological roles of HL, we generated transgenic rabbits that express human HL only in the liver, a major site of metabolic activity. The rabbit was selected as a model for studying HL functions because it has naturally decreased activity of this enzyme; it has about 1/10th as much activity as that of the rat (18, 19). Our results demonstrate that HL plays a key rate-limiting role in both IDL andThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 8724HDL metabolism; it has dramatic effects on the distribution and composition of these particles in plasma, with concomitant effects on plasma cholesterol levels. To our knowledge, this study is the first report of transgenic rabbits that overexpress an enzyme involved in lipid metabolism. MATERIALS AND METHODSCreation of the Human HL Constructs. Vectors designed for liver-specific expression contained sequences from the human apoE gene: 3 kb (plivhHL1) or 5 kb (plivhHL2) of 5'-flanking sequence, the first exon, first intron, the first six nucleotides (a nontranslated portion) of the second exon, a polylinker for cDNA insertion, the distal 92 nucleotides in the noncoding region of the fourth exon, the proximal 114 nucleotides of 3'-flanking sequence (20), and the hepatic control region (21, 22) of the apoE/C

Objective-Coronary heart disease is the most common cause of death in developed countries. However, there are no suitable animal models that mimic spontaneous myocardial infarction in humans. In this study, we attempted to obtain a rabbit strain with spontaneous myocardial infarction by selective breeding of coronary atherosclerosis-prone Watanabe heritable hyperlipidemic (WHHL) rabbits, designated as WHHLMI rabbits. Methods and Results-WHHLMI rabbits were characterized by the high incidence of fatal myocardial infarction at ages 11 to 35 months, being increased from 23% to 97% after the selective breeding. The ECG on WHHLMI rabbits showed a typical feature of myocardial infarction. Histological examination of hearts from suddenly deceased WHHLMI rabbits revealed old myocardial infarction accompanied by fresh myocardial lesions. The culprit coronary arteries exhibited severe atheromatous plaques (Ͼ90% lumen area stenosis), suggesting that coronary atherosclerosis is responsible for myocardial infarction observed in WHHLMI rabbits. In addition, the coronary plaques showed vulnerable features including macrophage-rich thin cap and large necrotic core. Conclusions-To the best of our knowledge, this is the first report of spontaneous myocardial infarction in rabbits, and it is suggested that this WHHLMI rabbit strain will be a useful animal model to study human myocardial infarction. Key Words: coronary atherosclerosis Ⅲ myocardial infarction Ⅲ vulnerable plaque Ⅲ WHHLMI rabbit C oronary heart disease is the major cause of death in developed countries. However, there are no suitable animal models for human myocardial infarction. It is essential to develop animal models for myocardial infarction to reveal its mechanisms and to develop new therapeutic interventions. Although several genetically modified mouse models with hypercholesterolemia and atherosclerosis have been reported, 1-3 coronary atherosclerosis and subsequent myocardial lesions resembling those of humans have not been documented, possibly because of the difference in lipoprotein metabolism between humans and mice. 4,5 In addition, the mouse is small in size, which may hamper its use in many surgical manipulations and therapeutic interventions. Therefore, there is a need to develop a relatively large animal model for the study of myocardial infarction. Until now, such an ideal model (eg, rabbits) with spontaneous myocardial infarction has not been established.In 1980, our institute developed Watanabe heritable hyperlipidemic (WHHL) rabbits as a suitable animal model for human familial hypercholesterolemia and atherosclerosis. 6 Based on this strain, we additionally developed coronary atherosclerosisprone WHHL rabbits, a variant strain, which have higher low-density lipoprotein cholesterol and typical coronary atheromatous plaques similar to those of humans. 7 However, the incidence of spontaneous myocardial infarction in coronary atherosclerosis-prone WHHL rabbits was extremely low, which limits their use in the study of myocardial infarction. Since 1994...