The laboratory rabbit: an animal model of atherosclerosis research

 
 
The laboratory rabbit: an animal model
of atherosclerosis research

Amalia E. Yanni
The Laboratory of Experimental Surgery and Surgical Research, School of Medicine, National and
Kapodistrian University of Athens, Athens, Greece

Summary
The aim of the present mini review is to describe the laboratory rabbit, an animal that has
been widely used for the study of atherosclerosis, the leading cause of mortality in Western
society. Due to the fact that the rabbit exhibits hypercholesterolaemia within a few days
of an administration of a high cholesterol diet, it is very sensitive to the inducement of
atheromatic lesions. The administration of different types of diets can cause different types
of lesions. Although these lesions do not develop as tissue plaques, a great number of
researchers use this animal model to test the effectiveness of drugs because of their
similarity to human fatty streaks. The generation over recent years of transgenic rabbits
with alterations in speciŽ c genes is expected to help with the elucidation of the mecha-
nisms underlying the initial and developmental stages of the disease. The laboratory rabbit
is signiŽ cantly broadening our understanding on the pathogenesis of atherosclerosis.

Keywords    Laboratory animals; New Zealand white rabbits; high cholesterol diet;
atherosclerosis; transgenic rabbits

The growth of basic human knowledge in                                   Biomedical research is a huge effort that
the Ž elds of physiology, biochemistry, and                            demands much time and hard work, and the
molecular biology, and the consequent                                  devotion of many scientists. One of the
therapeutic potential, can be combined with                            most important contributions to this effort,
the use of laboratory animals in almost all                            which at many times has been an issue of
man’s research efforts. The use of laboratory                          argument, is the participation of animals in
animals is considered to be necessary today,                           laboratory experiments. It is historically
when alternatives cannot be used, for testing                          reported that Erasistratos from Alexandria
new surgical techniques, for the study of new                          (304–257 BC) made the Ž rst experiments
chemical and pharmaceutical substances and                             using live animals in order to study the
for the production of vaccines and antibodies.                         cardiac function in pigs (Karagiannakos
The use of cell culture lacks the complexity                           1994). A large number of scientists awarded
of real disease models, thus limiting the                              with the Nobel prize (Von Behring, Koch,
scope of any testable hypotheses.                                      Banding, Fleming, etc.) used animals in their
                                                                       experiments.
                                                                         The decision to work with laboratory
                                                                       animals must be made after considering and
                                                                       rejecting all the alternatives. All scientists
Correspondence to (Present address): Laboratory of                     must keep in mind that the animal is
Nutrition and Clinical Dietetics, Harokopio University,
El. Venizelou 70, 176 71, Athens, Greece                               probably to be killed in order to further the
E-mail: ayanni@hua.gr                                                  scientiŽ c research. Laboratory animals
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Accepted 1 March 2004                                          © Laboratory Animals Ltd. Laboratory Animals (2004) 38, 246–256
Laboratory rabbit and atherosclerosis                                                                                     247

should live under the best conditions and be                         The rabbit
handled with love and care. This is an
ethical obligation and imposes a sense of                            The European rabbit, Oryctolagus
responsibility to the animals as well as to                          cuniculus, along with the hare (genus Lepus)
the patients, because reliable research                              and the American cottontail rabbits (genus
results come from animals that are healthy                           Sylvilagus), belongs to the Leropidae family
and that live under appropriate conditions.                          of the Lagomorpha order (Okerman 1989a).
   This mini review refers to the laboratory                         The largest strain is called the ‘Flemish
rabbit, an animal that has been used in a                            Giant’, whose weight sometimes exceeds
large number of studies, especially in the                           9 kg. The smallest strain is the ‘Polish
Ž eld of atherosclerosis research. The use of                        rabbit’, which rarely reaches one kilogram.
rabbits in the study of atherosclerosis was                          Rabbits are classiŽ ed according to the type
Ž rst mentioned in 1908 (Ignatowski 1908).                           and colour of their hide. New Zealand white
Since then atheromatic lesions were mainly                           rabbits’ hair is thick and pure white; and
introduced by applying speciŽ c diets.                               that of California is thick and white, going
Among these, a high cholesterol diet is the                          dark at the end (Okerman 1989b).
one which is used mostly. Due to the fact                              Studies on wild rabbits have proved that
that rabbit is very sensitive to the induce-                         these animals are quite selective in what
ment of atheromatic lesions through a high                           they eat and that a great variety of food is
cholesterol diet, the ‘cholesterol-fed rabbit’                       included in their diet. They prefer the
is deemed to be one of the most important                            tender, juicy parts of plants as the main
animal models for the study of atherosclero-                         portion of their diet and consume
sis. Different amounts of cholesterol in the                         indigestible parts of their food in small
diet (Bocan et al. 1993, Kolodgie et al. 1996),                      quantities that stimulate their intestine.
with or without a combination of oils                                Rabbits chew their food using their tongue
(Kolodgie et al. 1996, Ramjiganesh et al.                            elaborately, moving their jaw more than 120
2002, Yanni et al. 2003) and speciŽ c                                times per minute (Cortopassi & Muhl 1990,
proteins (Kritchevsky et al. 1977, West et al.                       Donnelly 1997).
1982, Terpstra et al. 1984), as well as                                The rabbit’s daily food intake constitutes
various durations of experimental studies                            almost 5% of its body weight, while the
(Hunt & Duncan 1985, Rogers & Karnovsky                              water consumption is about 10% of its body
1988), have been used in order to cause                              weight. Female animals are an exception
different types of lesions. The generation of                        during the period of suckling, when the
transgenic animals over recent years (Fan                            amount of water consumed depends on the
et al. 1994, Fan et al. 1995, Hoeg 1996, Shen                        number of offspring and the duration of
et al. 1996, Duverger et al. 1996a,b, Taylor                         suckling and sometimes exceeds one litre
1997, Taylor & Fan 1997, Brousseau & Hoeg                            per day. Rabbits hardly change their dietary
1999, Fan et al. 2001a,b) is expected to                             habits, and when they do the consumption
elucidate the mechanisms involved in the                             of food for a few days is less than the regular
pathogenesis of the disease.                                         level (Okerman 1989b). Changes in diet
   It is worthwhile mentioning that several                          should be done gradually in order to avoid
other animals have been used for the study                           intestine disorders.
of atherosclerosis, such as non-human                                  Among all strains of rabbits, the New
primates (Carey 1978), swine (Holvoet et al.                         Zealand with body weight of between 2 kg
1998) and mice (Breslow 1996). In particular,                        and 5 kg is the most used in the laboratory.
knock-out (i.e. apoE deŽ cient) mice and                             The New Zealand strain also appears in
transgenic (i.e. human apoB-100 expression)                          genetically altered strains, the most
mice are excellent alternatives to rabbits as                        important of which are the Watanabe,
models of atherosclerosis in developing                              St Tomas, and Houston RT which present
lesions with morphological similarity to                             genetic abnormalities in lipid metabolism
human atherosclerotic lesions (Breslow                               (Watanabe 1980, Kita et al. 1981, Armstrong
1996, Moghadasian et al. 2001).                                      1990).
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248                                                                                                     Yanni

   Gender differences provide an interesting                    Atherosclerosis and the New Zealand
Ž eld of observation, especially in the area                    white rabbit
of atherosclerosis. It has been shown that
the basal release of nitric oxide (NO),                         Atherosclerosis is the leading cause of
the endothelium derived vasodilator, is                         mortality in developed countries. A large
greater with endothelium intact aortic                          body of evidence suggests that high plasma
rings from female rabbits than from male                        cholesterol concentrations, especially of low
rabbits and depends on the circulating                          density lipoprotein (LDL) cholesterol, result
oestradiol concentration (Hayashi et al.                        in atherosclerotic lesion formation.
1992). Accordingly, it has been reported                        Oxidized LDL (oxLDL) particles are a potent
that female animals are less prone                              atherogenic agent (Ross 1993, Glass &
to diet-induced atherosclerotic                                 Witztum 2001, Libby 2002). In ammation is
lesions than male animals (Holm                                 thought to be the link between hyperlipi-
et al. 1998). The protection of the females                     daemia and atherosclerosis (Ross 1993,
is explained by the presence of higher                          Glass & Witztum 2001, Libby 2002). After
oestrogen concentrations and depends on                         the initiation of a high cholesterol diet,
the state of the arterial endothelium                           endothelial cells express various adhesion
(Holm et al. 1998).                                             molecules leading to the attachment of
   Laboratory rabbits have quite different                      leucocytes to the endothelium. The vascular
nutrient needs from rabbits that are sold                       cell adhesion molecule-1 (VCAM-1) plays
commercially. Laboratory animals are usually                    a major role in binding, particularly of
adults and are kept for extended periods.                       monocytes and T-lymphocytes, the main
A proper diet is used mainly to avoid                           cell types of early atherosclerotic lesions.
obesity and kidney disorders. Obesity can be                    After their adhesion to endothelial cells,
prevented by limiting the amount of food                        monocytes migrate to subendothelial space,
intake to a level sufŽ cient for the suste-                     where they differentiate to macrophages.
nance of the animal.                                            Macrophages express scavenger receptors
   The food the laboratory animals are                          that bind oxLDL particles, without feedback
provided with must contain all the                              control by intracellular cholesterol levels.
necessary dietary nutrients, be preserved for                   Under these conditions, the cytoplasm of
extended periods, and be easy to use. It is                     macrophages becomes full of lipid droplets
usually supplied in the form of pellets                         consisting mainly of cholesterol esters, and
which contain mainly grain and other                            the subsequent development of macrophage
ingredients in the form of a homogenous                         ‘foam cells’ takes place. The accumulation
mixture, so that the animals are not able to                    of foam cells results in the formation of
choose some ingredients and ignore others.                      fatty streaks, the earliest observable
Dry food, which can be preserved for a long                     abnormality of the vessel wall. These cells
time, about 4 months, is easy to use and has                    produce cytokines and reactive oxygen
a low cost (Tuffery 1996). Typical laboratory                   species, which enhance the in ammatory
chow diets contain 15% protein, 40–50%                          process. As the process continues, the
carbohydrate, 2% vegetable fat, and 15–25%                      formation of a more complex lesion occurs.
Ž bre.                                                          Smooth muscle cells immigrate from the
   In the international literature the                          medial layer into the subendothelial space
biochemical parameter values of the blood                       where they may proliferate, ingest modiŽ ed
of laboratory rabbit show great deviation.                      lipoproteins and contribute to lesion devel-
This deviation is attributed to many factors                    opment. As smooth muscle cells secrete
such as the collection and preparation of                       extracellular matrix proteins, fatty streaks
the sample, the analytical methods and the                      may progress to Ž brous plaque, yielding
reagents used, as well as factors concerning                    to the narrowing of the aortic lumen.
the animals such as age, breed, strain, sex,                    Advanced lesions occur with rupture of the
diet, living conditions and handling                            plaque, which allows blood components to
(Wolford et al. 1986).                                          come into contact with plaque lipids and
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Laboratory Animals (2004) 38
Laboratory rabbit and atherosclerosis                                                                                     249

tissue factor, resulting in the formation of a                       are characterized by the presence of foam
thrombus (Ross 1993, Glass & Witztum                                 cells originating from macrophages.
2001, Libby 2002, Libby & Aikawa 2002).                              Although these early lesions are similar to
If a thrombus is occlusive, it will lead to                          human fatty streaks, they do not develop as
myocardial infarction. As plaque rupture is                          tissue plaques, which are the trademarks of
the main clinical complication, stabilization                        atherosclerosis in humans (Kolodgie et al.
of the plaque is crucial. Dietary lipid lower-                       1996). Long-term experiments using diets
ing has been shown to reduce macrophage                              high in cholesterol are discouraging, because
penetration and the lipid content of plaque                          high hepatotoxicity does not allow the ani-
and to increase collagen and the expression                          mal to survive. In addition, massive in am-
of smooth muscle cell content, resulting                             mation in the body does not re ect human
in plaque stabilization, in rabbits (Aikawa                          pathophysiology. Despite these restrictions,
1998a,b) and miniature pigs (Verhamme                                a great number of researchers use this
et al. 2002).                                                        animal model to test the effectiveness of
   The rabbit is the most widely used animal                         drugs on the development of fatty streaks.
in atherosclerosis research. Ignatowski                              These lesions are present in people from all
(1908) Ž rst mentioned the use of rabbit.                            nations and are considered insigniŽ cant.
Many research groups, mainly Russian, have                           There are studies supporting the suggestion
studied atherosclerosis using rabbits as labo-                       that human lesions in late stages are similar
ratory animals. The studies were designed to                         to those caused in rabbits when a diet low
compare the experimentally-caused lesions                            in cholesterol is administered for extended
to the usual atheromatic lesions noticed in                          periods (Adams et al. 1982).
human vessels. Researchers have tested                                  In order to induce more advanced lesions
different methods of causing these lesions                           in the thoracic and abdominal aorta, a high
such as various diets, or injections of adren-                       cholesterol diet can be combined with a
aline, bacteria or toxins (Finking & Hanke                           single or double balloon injury (Abela et al.
1997).                                                               1995, Skinner et al. 1995, Aikawa et al.
   Anitschkow and Chalatow discovered that                           1998b, Worthley et al. 2000). Balloon injury
rabbits with atherosclerosis exhibit an                              accelerates the formation of atheromatic
accumulation of cholesterol in their liver.                          lesions and produces plaques with a lipid
Anitschkow came to the conclusion that                               core covered by a Ž brous cap with a high
atherosclerosis results from the content of                          amount of smooth muscle cells. These
cholesterol in foods. He began experiment-                           lesions in the rabbit aorta are more similar
ing with foods rich in cholesterol and                               to human atherosclerotic lesions than those
suggested that the extent of the damage                              produced by feeding rabbits with a high
caused by atherosclerosis is proportional to                         cholesterol diet alone (Aikawa et al. 1998a,b).
the amount of cholesterol consumed                                   It has been shown that, although female
(Finking & Hanke 1997).                                              rabbits accumulate less cholesterol in
   Among the animals that have been                                  undamaged aorta than do male rabbits, this
studied, the rabbit is the only one that has                         atheroprotection does not exist in the
the tendency to exhibit hypercholestero-                             balloon-injured aorta (Holm et al. 1998).
laemia within a few days of the administra-                             The hypercholesterolaemia induced in the
tion of a high cholesterol diet (Bocan et al.                        rabbit through diet is caused by the accumu-
1993). The normal range of plasma choles-                            lation of exogenous cholesterol. Rabbits are
terol in the New Zealand white rabbits is                            prone to the inducement of atherosclerosis
low (average 1.3 mmol/l) (Finking & Hanke                            through diet, since they cannot increase the
1997), but it can increase by up to 2 to 8                           excretion of sterols (Kolodgie et al. 1996).
times after the administration of a diet                             As a result, liver produces increased quanti-
enriched with 0.1–2% cholesterol, within                             ties of lipoproteins rich in cholesterol esters
the Ž rst 20 days (Bocan et al. 1993).                               that enter the blood circulation. LDL and
   Under these conditions, the cholesterol                           b -VLDL, the atherogenic lipoproteins, are
level increases rapidly and the early lesions                         the main transporters of cholesterol in
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250                                                                                                       Yanni

plasma. They remain in the blood                                Macrophages are the main cells that ingest
circulation for an extended time (Kolodgie                      lipids during fatty streak formation but
et al. 1996). Studies have shown that LDL                       these are not the only cells capable of
remains extensively in the blood vessels of                     accumulating lipid. Endothelial cells also
cholesterol-fed rabbits. The duration of the                    contain lipid droplets (Rosenfeld et al. 1987).
diet is proportional to the time that LDL                       However, the fatty streak is a potentially
remains in the blood (Tozer & Carew 1997).                      reversible lesion (Badimon et al. 1990, Ross
The areas of the blood vessels prone to                         1993, Aikawa et al. 2001).
the lesion selectively accumulate these                            In rabbits, lesion morphology is altered
atherogenic lipoproteins from circulation,                      by the percentage of cholesterol added to
thus causing atherosclerotic lesions                            the diet and the duration of the diet (Bocan
(Kolodgie et al. 1996).                                         et al. 1993, Kolodgie et al. 1996, Finking &
   The intima of the normal rabbit aorta                        Hanke 1997). Diets that are short in
consists of a layer of endothelial cells lining                 duration and with a percentage of cholesterol
the aortic lumen. Under this, there is another                  of more than 2% cause hypercholestero-
layer consisting of connective tissue and                       laemia, and atherosclerotic lesions rich in
ground substances, which occasionally                           foam cells originate from macrophages. On
contains smooth muscle cells. Studies with                      the opposite side, a diet with a low choles-
electronic microscopy showed that lipid                         terol content and long duration causes
droplets rarely appear in endothelial and                       atherosclerotic lesions, which are rich in
smooth muscle cells. The intima is separated                    smooth muscle cells and contain choles-
from the media by internal elastic lamina                       terol deposits leading to atherosclerotic
(Skepper & Kapagoda 1996). Lipoproteins                         lesions more similar to those of humans
penetrate the endothelium of blood vessels                      (Kolodgie et al. 1996). It has been shown
at a rate reversely proportional to the                         that more advanced lesions can be formed
lipoprotein diameter. These rates increase                      not with continuous but with intermittent
along with the atherosclerotic extent. The                      atherogenic diets (Kolodgie et al. 1996).
amount of lipoproteins that are metabolized                     When the percentage of cholesterol in the
by the cells of the vessel wall is higher in                    diet is higher than 0.15%, cholesterol
the areas of atheromatic lesions and dimin-                     esters are detected in the lesion (Kolodgie
ishes with the administration of oestrogens                     et al. 1996). In other studies (Cornhill &
or antioxidants (Carew et al. 1987, Kita                        Roach 1974, Cornhill & Roach 1976,
et al. 1987, Yamacoshi et al. 1999).                            Kritchevsky et al. 1977, West et al. 1982,
Lipoproteins are degraded by macrophage                         Hunt & Duncan 1985, Rogers & Karnovsky
foam cells (Rosenfeld et al. 1991).                             1988) diets enriched with casein, 0.2%
   In rabbits (as well as in other animal mod-                  cholesterol and 19% butterfat have been
els), the earliest detectable cellular events                   provided to the animals for long periods
are an increase in leukocyte margination                        (from 6 to 60 months) in order to cause
and endothelial penetration and the forma-                      advanced atheromatic lesions. Some
tion of macrophage-derived intimal foam                         studies support the suggestion that the
cells (Rosenfeld et al. 1987, Faquri &                          formation of advanced lesions depends on
Dicorleto 1993). Scanning electron                              the age of the animal. Old rabbits (3–4.5
microscopy has elucidated that after                            years old) exhibit Ž brotic plaques while
3 weeks of a diet enriched with 0.2%                            young rabbits (4 months old) do not have
cholesterol, adherent leukocytes are                            such advanced lesions (Spagnoli et al.
observed adjacent to branches in the arch,                      1991). However, the percentage of
thoracic and upper abdominal aortas. By 3–5                     cholesterol in the diet and the duration of
weeks with the same diet, numerous foam                         the diet depend on the study. If the study
cells are found in the subendothelial space                     focuses on fatty streak initiation, a diet
and constitute the developing fatty streak in                   enriched with 0.25% (w/w) cholesterol and
the same locations that adherent monocytes                      of a duration of 4 weeks is appropriate
were earlier observed (Rosenfeld et al. 1987).                  (Yanni et al. 2003). A diet enriched with
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Laboratory Animals (2004) 38
Laboratory rabbit and atherosclerosis                                                                                     251

1% (w/w) cholesterol maintained for 12                                  The genetically altered strains of the
weeks can cause lesions rich in foam cells                           New Zealand white rabbit are also used
originated from macrophages and smooth                               extensively. The Watanabe rabbit (Watanabe
muscle cells (Boger et al. 1998). A low level                        heritable hyperlipidemic rabbit, WHHL)
of cholesterol feeding with a high duration                          constitutes a laboratory animal suitable for
of the diet (i.e. 0.25% for 8 months) causes                         the understanding of the pathology of the
advanced atheromatic lesions (Kolodgie                               human familial hypercholesterolaemia of
et al. 1996). Diets of long periods where                            type IIa (Fredrickson). This animal exhibits
1–2% percentage of cholesterol is supple-                            a genetic deprivation of functional LDL
mented usually lead to high mortality rates                          receptors and a dissimilar distribution of
of the animals.                                                      cholesterol amongst the lipoprotein classes.
   In the rabbit, lesions are distributed pre-                       In these animals, the atherosclerotic process
dominantly in the aortic arch and thoracic                           begins in utero (Rosenfeld et al. 1987,
aorta, at the origins of intercostal arteries                        Aliev & Burnstock 1998). The lesions
and, to a lesser extent, in the abdominal                            progress with age and serum cholesterol is
aorta. In humans, plaques are more abun-                             mainly found in LDL and to a lower extent
dant in the abdominal aorta enriched with                            in IDL particles (Aliev & Burnstock 1998).
smooth muscle cells, and usually have a                                 According to studies regarding the use of
Ž brous cap (Taylor & Fan 1997). However,                            the rabbit as a laboratory animal in athero-
the rabbit provides an excellent model of                            sclerosis research, it appears that atheroscle-
plaque rupture, when used in conjunction                             rotic lesions are more difŽ cult to regress in
with Russell’s viper venom. The use of                               the rabbit than in other laboratory animals
Russell’s viper venom was initially proposed                         such as primates. One reason is the extended
by Contantinides and Chakravarti (1961)                              time needed for the plasma cholesterol to
and provides one of the few animal models                            return to normal levels after the interrup-
of acute plaque disruption and thrombosis.                           tion of a high cholesterol diet. This may
Additionally, pharmacological triggering                             be responsible for the progression of the
in combination with balloon injury results                           athrerosclerotic lesions that already exist
in the formation of plaques that are similar                         and their regression afterwards (Gupta et al.
to those found in human coronary arteries                            1970). However, it is possible for regression
(Johnstone et al. 2001).                                             to take place, and this has also been shown
   Rabbits are more prone to the inducement                          to be independent of cholesterol levels. In
of atherosclerosis with high cholesterol                             particular, the administration of HDL plas-
diets than are mice and rats. Most rodents                           ma fraction in cholesterol-fed rabbits leads
are highly resistant, a phenomenon that can                          to the signiŽ cant regression of established
be attributed to low cholesteryl ester trans-                        atherosclerotic lesions (Badimon et al.
fer protein (CETP) activity that leads to a                          1990). In humans, HDL restores endothelial
high concentration of high density lipopro-                          function in hypercholesterolaemic men
tein (HDL) cholesterol (Moghadasian et al.                           (Spieker et al. 2002), while the administra-
2001). However, certain strains of mice,                             tion of apoA-1 has been shown to regress
such as C57BL/6, develop atherosclerotic                             coronary atherosclerosis (Nissen et al. 2003).
lesions when they are exposed to an                                     The extent of atherosclerosis in the rabbit
appropriate diet. In particular, when these                          aorta can be quantiŽ ed by the measurement
animals are fed with a very high cholesterol,                        of oil red O-stained intimal foam cells
high-fat diet supplemented with cholic acid                          (Rogers & Karnovsky 1988, Yanni et al.
for many months, several layers of foam                              2003), and of the surface of sudanophilic
cells appear in the subendothelial space                             lesions (Kolodgie et al. 1996), and by
(Breslow 1996). Primates exhibit variations                          immunohistochemical analysis (Boger et al.
in the site of lesions, their availability is                        1998). Recently, non-invasive magnetic
restricted, their cost is very high, and                             resonance imaging (MRI) has been used for
specialist knowledge is needed for appropri-                         the study of vascular lesions. MRI accurately
ate handling (Moghadasian et al. 2001).                              quantiŽ es and documents changes in the
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                                                                                                  Laboratory Animals (2004) 38
252                                                                                                      Yanni

composition of atherosclerotic plaque and it                    concentration was about one-third that of
can be used for the monitoring of athero-                       the control group (Brousseau & Hoeg 1999).
sclerosis progression and regression in vivo.                      Another model of transgenic rabbits is
The method is advantageous because serial                       that of human apoB-100. Analysis of plasma
studies may be performed in response to                         lipid concentration in these rabbits has
interventional therapies (Worthley et al.                       revealed that total plasma cholesterol and
2000, Helft et al. 2002).                                       triglyceride levels are 2- to 3-fold higher
                                                                than those observed in age-, sex- and
                                                                diet-matched non-transgenic littermates,
                                                                whereas those of HDL cholesterol are
Transgenic rabbit models
                                                                markedly reduced (Fan et al. 1995,
The use of transgenic rabbit models for the                     Brousseau & Hoeg 1999).
elucidation of the mechanisms involved in                          The overexpression of lipoprotein lipase
the pathogenesis of the disease is a new area                   (LPL) in transgenic rabbits in uences all
of great interest. Already transgenic rabbits                   classes of lipoproteins. These rabbits are
with altered expression of speciŽ c genes                       highly resistant to diet-induced hypercholes-
have been generated.                                            terolaemia and atherosclerosis (Fan et al.
  In 1996, Duverger et al. generated New                        2001a). Increased LPL activity leads to a
Zealand white rabbits that expressed human                      reduction of plasma triglycerides concentra-
apoA-1 in the liver and examined the in u-                     tion especially in VLDL and IDL. It is still
ence of increased apoA-1 expression on                          unknown whether the protection against
susceptibility to atherosclerosis. The results                  atherosclerotic lesions may be attributed to
showed that the apoA-1 transgenic group                         the enhancement of remnant clearance in
had signiŽ cant decreases in atherosclerotic                    the liver, except from the lipid lowering
lesion areas compared to the control group.                     effects of the enzyme.
Infusion of HDL has been shown to regress                          In 1996, Shen and co-workers showed that
previously established atherosclerotic                          the overexpression of 15-lipoxygenase in
lesions in the cholesterol-fed rabbit model                     monocytes/macrophages protects against
(Badimon et al. 1990), and recently the                         lipid deposition in the vessel wall during
administration of apoA-1 has been shown                         early atherogenesis. The results of that study
to regress atherosclerotic coronary lesions                     were unexpected, since 15-lipoxygenase is
in humans (Nissen et al. 2003).                                 considered to be responsible for the oxidative
  Lecithin-cholesterol acyl transferase                         modiŽ cation of LDL.
(LCAT) is an enzyme that plays a very                              Finally, the development of transgenic
important role in cholesterol and HDL                           WHHL rabbits that express human
metabolism. Transgenic rabbits overexpress-                     apolipoprotein(a) which assembles into Lp(a)
ing human LCAT showed markedly reduced                          in plasma, shows more extensive advanced
atherosclerosis compared to control rabbits,                    atherosclerotic lesions in the transgenic
when fed a high cholesterol diet (Hoeg                          animals compared to controls. It is impor-
1996). This phenomenon was attributed not                       tant to mention that Lp(a) in transgenic
only to the elevated HDL cholesterol levels                     WHHL rabbits leads to advanced lesions
in transgenic animals but also to the accel-                    consisting of atheroma, Ž broatheroma and
erated catabolism of LDL apo B-100 relative                     calciŽ cation, and in cholesterol-fed apo(a)
to controls.                                                    transgenic animals leads to a signiŽ cant
  In 1994, Fan and co-workers generated                         increase in the area of sudanophilic lesions
transgenic rabbits overexpressing human                         (Fan et al. 2001b).
hepatic lipase. The susceptibility of the
hepatic lipase transgenic rabbit to
atherosclerosis has been determined
                                                                Commentary
(Taylor & Fan 1997). In these animals the
response to dietary cholesterol was                             Laboratory animals have been extensively
attenuated, and the plasma cholesterol                          used in biomedical research. Among these,
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Laboratory Animals (2004) 38
Laboratory rabbit and atherosclerosis                                                                                     253

the rabbit has participated in a large number                        Aikawa M, Rabkin E, Okada Y, Voglic SJ, Clinton SK,
of studies concerning atherosclerosis                                  Brinckerhoff CE, Sukhova GK, Libby P (1998a)
                                                                       Lipid lowering by diet reduces matrix metallopro-
research. Especially, the cholesterol-fed
                                                                       teinase activity and increases collagen content of
rabbit is an animal model which has been                               rabbit atheroma: a potential mechanism of lesion
widely used for the elucidation of the                                 stabilization. Circulation 97, 2433–44
mechanisms involved in the pathogenesis                              Aikawa M, Rabkin E, Voglic SJ, Shing H, Nagai R,
of the disease. It has contributed to the                              Schoen FJ, Libby P (1998b) Lipid lowering pro-
understanding of the effects of drugs and                              motes accumulation of mature smooth muscle
food constituents with therapeutic properties                          cells expressing smooth muscle myosin heavy
                                                                       chain isoforms in rabbit atheroma. Circulation
(Cooke et al. 1992, Bocan et al. 1994, Tsao et
                                                                       Research 83, 1015–26
al. 1994, Harbo & Christiansen 1996,                                 Aliev G, Burnstock G (1998) Watanabe rabbits with
Aikawa et al. 1998a,b, Bode-Boger et al.                               heritable hypercholesterolaemia: a model of
1998, Boger et al. 1998, Yamacoshi et al.                              atherosclerosis. Histology and Histopathology
1999, Aikawa et al. 2001, Yanni et al. 2003).                          13, 797–817
   The transgenic animals that have been                             Armstrong, ML (1990) Animal models of atheroscle-
generated are expected to shed light on the                            rosis. Atherosclerosis 85, 15–23
                                                                     Badimon JJ, Badimon L, Fuster V (1990) Regression
pathogenesis of atherosclerosis at the                                 of atherosclerotic lesions by high density lipopro-
molecular level (Fan et al. 1994, Fan et al.                           tein plasma fraction in the cholesterol-fed rabbit.
1995, Duverger et al. 1996a,b, Hoeg 1996,                              Journal of Clinical Investigation 85, 1234–41
Shen et al. 1996, Taylor 1997, Taylor & Fan                          Bocan TM, Mueller SB, Mazur MJ, Uhlendorf, PD,
1997, Brousseau & Hoeg 1999, Fan et al.                                Brown EQ, Kieft KA (1993) The relationship
2001a,b) and to elucidate the cause-and-                               between the degree of dietary-induced hypercho-
                                                                       lesterolemia in the rabbit and atherosclerotic
effect relationships in lesion formation and
                                                                       lesion formation. Atherosclerosis 102, 9–22
progression. In the future these models may                          Bocan TMA, Mazur MJ, Mueller SB, Brown EQ,
prove or disprove the suggested potential                              Sliskovic DR, O’Brien PM, Creswell MW, Lee H,
mechanisms.                                                            Uhlendorf PD, Roth BD, Newton RS (1994)
   The laboratory rabbit combined with                                 Antiatherosclerotic activity of inhibitors of
different methods of lesion induction                                  3-hydroxy-3-methylglutaryl coenzyme A reductase
remains a very important model for the                                 in cholesterol-fed rabbits: a biochemical and mor-
                                                                       phological evaluation. Atherosclerosis 111, 127–42
study of atherosclerosis and can help
                                                                     Bode-Boger SM, Boger RH, Kienke S, Bohme M,
immensely the research into, and Ž ghting                              Phivthongam L, Tsikas D, Frolich JC (1998)
of, a disease that is considered a plague for                          Chronic dietary supplementation with L-arginine
all humanity.                                                          inhibits platelet aggregation and thromboxane A2
                                                                       synthesis in hypercholesterolemic rabbits in vivo.
                                                                       Cardiovascular Research 37, 756–64
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