# Hyperlipidemic Rabbit Models for Anti-Atherosclerotic Drug Development
## 2 Hyperlipidemic Rabbit Models
### Spontaneous Hyperlipidemic Rabbits  
#### 2.2.1 Watanabe Heritable Hyperlipidemic (WHHL) Rabbits  
The WHHL rabbit was established by Dr. [PERSON] in the 1970s at Kobe University in Japan [21; 22] and is often used as a model of human familial hypercholesterolemiaia (FH). FH is an autosomal dominant genetic disorder characterized by elevated plasma LDL levels due to LDLR dysfunctions [23]. WHHL rabbits are genetically deficient in LDLR functions, therefore, even on a normal standard diet, they showed hyperlipidemia (plasma TC, 385-518 mg/dL, and TG, 304-511 mg/dL), being 10-fold and 8-fold higher than normal wild-type rabbits [22]. Serum lipoproteins characterized by electrophoresis exhibited elevated \(\beta\)-lipoprotein with a broad \(\beta\)-pattern and diminished \(\alpha\)-lipoprotein in WHHL rabbits. [PERSON] et al. demonstrated that WHHL rabbits have a dysfunctional LDLR with an in-frame deletion of 12 nucleotides that eliminate four amino acids from the ligand-binding domain of the LDLR. Mutant LDLRs cannot transport to the cell surface at a normal rate [24]. The dysfunction of the LDLR in WHHL rabbits results in a loss of the hepatic uptake of LDL and subsequent elevation of the plasma LDL levels similar to human FH [25; 26; 27]. Age-related changes in plasma lipids were observed in WHHL rabbits [22; 28]. Compared with 3-month-old juvenile rabbits, 24-month-old rabbits showed a 45% decrease in TC (916 at 3 months to 508 mg/dL at 24 months) and a 42% decrease in LDL-C (680 at 3 months to 393 mg/dL at 24 months) [28]. [PERSON] et al. compared plasma TC levels in heterozygous WHHL rabbits and NZW rabbits on a cholesterol diet for 24 weeks. On a 0.5% cholesterol  
Figure 1: Hypercholesterolia and representative aortic atherosclerosis of cholesterol-fed rabbits. (**A**) Plasma total cholesterol (TC) levels of wild-type rabbits fed either a normal standard diet or a cholesterol diet containing 0.3% cholesterol and 3% soybean oil for 16 weeks. Mean \(\pm\) SD (\(n\) = 4–20). (**B**) Aortic gross lesion stained with Sudan IV can be seen in rabbits fed a cholesterol diet (right).  
diet, plasma TC levels in heterozygous WHHL rabbits were significantly higher than those in NZW rabbits (\(\approx\)2000 in WHHL vs. \(\approx\)1000 mg/dL in NZW rabbits). However, on a 1% cholesterol diet, plasma TC levels reached a peak (\(\approx\)3000 mg/dL) at eight weeks in both rabbits without significant differences between the two groups [29].  
Besides spontaneous hypercholesterolemia and atherosclerosis, WHHL rabbits exhibited other metabolic abnormalities including insulin resistance [30] and visceral fat accumulation [31]. Some WHHL rabbits (also designated as myocardial infarction-prone Watanabe heritable hyperlipidemic, WHHLMI) developed coronary atherosclerosis and myocardial infarction [8; 32; 33]. To obtain a myocardial infarction-prone colony, WHHL rabbits with severe coronary atherosclerosis, myocardial infarction, and relatively higher plasma TC levels were selected and bred. Selective breeding was carried out for five to seven generations. WHHLMI rabbits exhibit 93% of coronary stenosis and 97% of myocardial infarction, whereas the corresponding values are 60% and 23% in original WHHL rabbits [32].