© 1995 American Heart Association, Inc.
Articles |
Elevated Concentrations of Plasma Lipids and Apolipoproteins B, C-III, and E Are Associated With the Progression of Coronary Artery Disease in Familial Hypercholesterolemic Swine
From the Departments of Genetics and Meat and Animal Science (J.H.-R., J.M.R., Z.H., J.R.), University of Wisconsin, Madison, and the Research Department (M.F.P., J. Von L.-R.), Pharmaceuticals Division, CIBA-GEIGY Corp, Summit, NJ.
Correspondence to Jan Rapacz, PhD, Immunogenetics Laboratory, University of Wisconsin-Madison, 666 Animal Sciences Bldg, 1675 Observatory Dr, Madison, WI 53706. E-mail rapacz@calshp.cals.wisc.edu.
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Abstract We reported earlier that a complex familial hypercholesterolemia (c-FHC) phenotype characterized by elevated levels of total plasma cholesterol (TC) and apoB and reduced levels of HDL cholesterol (HDL-C) and apoA-I is associated with the development of spontaneous atherosclerotic lesions in swine. In this study, we investigated concentrations of plasma lipids and apolipoproteins B, C-III, and E in six parental animals of two cholesterol concentration phenotypes and their 32 offspring, which segregated into high, intermediate, and normal cholesterol phenotypes. Subsequently, we compared the extent of atherosclerotic lesion development in coronary arteries to the concentrations of plasma lipids and apolipoproteins in the parents and two offspring per family. Mean concentrations for the high (n=23), intermediate (n=13), and normal (n=2) cholesterol level phenotypes at 4 months of age were TC, 316±62.2, 159±17.1, and 105±12 mg/dL; LDL cholesterol, 275±63.1, 113±16.4, and 67±18.4 mg/dL; HDL-C, 35±6.1, 41±5.7, and 33±6.4 mg/dL; triglycerides, 48±10.8, 39±8.0, and 29±5.7 mg/dL; apoB, 152±32.5, 80±7.2, and 48±5.7 mg/dL; apoC-III, 10±4.2, 8±1.7, and 3±0.1 mg/dL; and apoE, 17±3.4, 7±1.7, and 5±0.7 mg/dL, respectively. Histological analysis of the major coronary arteries from members of the three families showed considerable variation in the severity of lesions, ranging from foci of adaptive intimal thickening consisting of two to six layers of smooth muscle cells to advanced lesions containing necrotic cores, cholesterol clefts, calcification, and hemorrhage (type V). The most extensive lesions occurred only in animals of the high cholesterol phenotype (ie, c-FHC), in which the concentration of TC and apoB progressively increased after 4 months of age, apoC-III, apoE, and triglycerides increased or remained elevated, and HDL-C decreased, except for one animal. Data presented here show that the plasma cholesterol phenotypes in FHC animals are associated with levels of apolipoproteins B, C-III, and E and indicate that the increases in the studied parameters after 4 months of age correlate with the progression of coronary artery disease.
Key Words: swine • familial hypercholesterolemia • atherosclerosis • animal model • apolipoproteins
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Introduction |
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Elevated levels of LDL cholesterol (LDL-C), triglycerides (TG), and apoB and reduced levels of HDL cholesterol (HDL-C) and apoA-I are the most frequently observed characteristics in familial lipid and lipoprotein disorders associated with premature coronary artery disease.1 2 3 4 5 Since all apolipoproteins play a role in the formation of lipoprotein particles and perform various functions in lipoprotein metabolism, apoC-III and apoE have also been found to be associated with familial dyslipidemias.6 7
ApoC-III is known to play a role in the metabolism of TG-rich lipoproteins by inhibiting lipolysis and uptake of TG-rich lipoprotein particles.8 9 10 11 ApoC-III levels are correlated with plasma TG concentrations, and severalfold increases of apoC-III have been found in human hyperlipidemias.12 13 14 15 16
ApoE, which is present in different classes of lipoproteins, is an important protein involved in cholesterol transport in the plasma and serves as a ligand for LDL (apoB, E) receptors.17 ApoE concentrations were shown to be significantly higher in familial hypercholesterolemia (FH) heterozygotes compared with normal human subjects,15 and genetic variants of apoE are associated with type III hypercholesterolemia.18 19
FHC in swine was originally described as endogenous hyperbetalipoproteinemia and hypercholesterolemia.20 Although FHC was first identified in animals homozygous for the Lpb5 (apoB) allele, the majority of Lpb5/5 swine were normolipidemic. Mean plasma total cholesterol (TC) concentration in the serum of FHC animals fed a low-fat, low-cholesterol diet was originally 176.5±63.3 mg/dL, compared with 81.4±14.3 mg/dL in normolipidemic Lpbnon5 swine.20 21 Cholesterol concentrations and intraindividual variations increased in the FHC population during the following decade, and the phenotypic heterogeneity was suggestive of at least three cholesterol concentration phenotypes; hence, complex FHC (c-FHC) may be a combination of the three phenotypes.22 23 Genetic studies led to the isolation of the first major monogenic subphenotype (TC, 223±24.7 mg/dL) exhibiting the recessive mode of inheritance, designated FHC-r, which is not linked to the apoB locus.22 Plasma of c-FHC swine is characterized by fourfold and 4.7-fold increases in TC and apoB, respectively, and 1.5-fold decreases in HDL-C and apoA-I, resulting in a 14:1 ratio of TC to HDL-C.24
All animals expressing the c-FHC phenotype develop complex atherosclerotic lesions in the three major coronary arteries; these lesions show necrotic cores, calcification, neovascularization, and intraplaque hemorrhage that closely mimic advanced human atherosclerosis.25 26 In contrast to c-FHC, normolipidemic animals of Lpbnon5 genotypes show normal vascular morphology. However, lesion development in FHC (TC, 185 to 445 mg/dL) varied from preatheromatous lesions to complicated, ruptured lesions with myocardial infarct and areas of myocardial ischemia. The severity of lesions was not always correlated with TC at 4 months of age, nor were hypercholesterolemia and advanced atherosclerosis exclusive to swine of the Lpb5/5 genotype.25 26 Variations in lesion severity as well as lipoprotein profiles complicated comparative analysis of the relation of dyslipidemia with coronary artery disease and warranted additional investigations.
In this study we took advantage of the development of isospecific antibodies to apoC-III and apoE as well as the opportunity of having plasma samples and hearts of six mature or aging breeder pigs and their preselected mature offspring representing different cholesterol phenotypes and apoB genotypes. The animals were primarily of the high (c-FHC) and intermediate (c-FHCxnormocholesterolemic crosses) TC levels. The aim of this study was to enhance information on FHC and its relation with the progression of coronary artery disease by correlating concentrations and transmission of plasma lipids and apolipoproteins with lesion development in coronary arteries.
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Animals
Swine used in this study were derived from the Immunogenetic Project Herd (IPH), University of Wisconsin, and represent a strain propagated for several generations that exhibits polygenic FHC when fed a low-cholesterol (65 mg/d), low-fat (6%) diet (University of Wisconsin Diet).24 Plasma or sera from all IPH swine are routinely phenotyped and genotyped for Lpb, Lpr, and Lpu alloimmunological lipoprotein polymorphisms27 28 and tested periodically for apoB, TC, HDL-C, and TG.
The study on lipids and apolipoproteins included three sires, three dams, and their 32 offspring of different cholesterol concentration phenotypes and lipoprotein genotypes. Histological study of the coronary arteries included the six parental animals and six offspring, two per family, selected originally as prospective breeders at 6 months of age. Cholesterol phenotypes of the studied animals were determined at 4 months of age, the earliest time after birth with full penetrance and expressivity of the FHC-r and c-FHC phenotypes.29
The six parental animals were of two cholesterol phenotypes: three high (H; TC, 395±87 mg/dL) and three intermediate (I; TC, 158±18.8 mg/dL). They were assigned to three matings representing three phenotypic combinations: HxH, HxI, and IxI. Breeders of the HxH mating type were of the apoB heterozygous genotype (Lpb2/5 and Lpb3/8); their TC and apoB levels resembled the c-FHC phenotype, while the breeders of the HxI and IxI matings were of the Lpb5/5 homozygous genotype. The three breeders of the intermediate TC phenotype represented the F1 generation that was obtained from crosses of the high cholesterol phenotype (ie, c-FHC) animals to normocholesterolemic mates.
Lipid Measurements
Total plasma cholesterol, HDL-C, and TG were determined by
enzymatic procedures24 using Sigma diagnostic kits. LDL-C
was calculated by subtracting HDL-C and VLDL cholesterol (VLDL-C) from
TC.30 VLDL-C (d<1.006 g/mL) was measured in
the plasma of 12 animals at 4 months of age, with a mean±SD of
4.65±1.6 mg/dL; hence, 5 mg/dL was specified as VLDL-C.
Apolipoprotein Measurements
Apolipoproteins were measured by the single radial
immunodiffusion test.20 31 Standardizations of apoB and
apoA-I have been published.24 32 Antibodies to apoC-III
and apoE were prepared by using high-performance liquid chromatography
(HPLC)–purified apoC-III from delipidated VLDL and a gel slice from a
two-dimensional sodium dodecyl sulfate–polyacrylamide gel for apoE.
ApoC-III and apoE standards were used from HPLC-purified apoVLDL (ie,
delipidated VLDL). Both standards were subjected to amino acid
composition and analysis, and their protein concentrations were
calculated by using the Lowry33 method with bovine serum
albumin as the primary protein standard.
To establish the regression equation for apoC-III and apoE, both standards were tested four times on three different plates, with 1, 2, 3, 4, and 5 µL for apoC-III (16 mg/dL) and 2, 3, 4, 5, and 6 µL for apoE (13 mg/dL). The regression equation for apoC-III was y=-14.829+1.0036e-2x (r=.986) and for apoE, y=-8.9345+8.1309e-3x (r=.976). The coefficient of variation was 0.1% to 2.7% for intra-assay and 1.8% to 5.2% for interassay. From this, 1.2% for intra-assay and 6% for interassay variation of apoC-III and apoE were adapted as the limit of chance variation between duplicate values for an experimental sample. The plates were photographed and enlarged x10 by an HS Opaque 1000 Projector to measure the diameter of the precipitation ring. The apoC-III and apoE protein concentrations in each sample were calculated by using the area (x) in the regression equation.
Coronary Artery Tissue Collection
Twelve pigs (three sets of parents and two offspring per family)
ranging in age from 14 to 60 months were killed by intramuscular
injections of ketamine and xylazine (procedures approved by the
Research Animal Care Committee, University of Wisconsin), and the
hearts were immersion fixed in 10% phosphate-buffered formalin. The
three major coronary arteries (left anterior descending, left
circumflex, and right coronary) were excised from the heart, cut
cross-sectionally into segments 5 mm apart, and
processed.25 26 At least nine cross-sections per coronary
artery were stained with hematoxylin and eosin. Calcium was identified
on selected sections by using the Von Kossa silver stain.
Immunohistochemistry was also performed on selected sections by using
the biotinylated lectin Conconavalin A (Vector) to identify
macrophages. Photographs were made from the most advanced lesions of
animals found to have occlusive atherosclerosis and from the most
representative segments of the coronary arteries of animals
found to have normal morphology or intimal thickening but no advanced
atherosclerotic lesions. Lesions were classified as type I through type
VI according to a system first described by Stary34 and
more recently by Fuster,35 who described both plaque
composition and the risk of plaque rupture. Plaques of types IV, V, and
VI were considered to be advanced lesions. Intimal thickening
consisting of two to six layers of longitudinally oriented smooth
muscle cells were noted as adaptive intimal thickening and considered
to be normal.36 37
Statistical Methods
Data were analyzed with the general linear model procedure of
ANOVA using the statistical package SAS (Statistical
Analysis Software). The least-significant difference was used for all
possible comparisons of mean concentrations of all parameters among the
three groups. Data are mean±SD unless otherwise specified.
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Mean Concentrations of Lipids and Apolipoproteins, Their Ratios, and Correlations
Table 1
shows mean concentrations of lipids,
apolipoproteins, and selected ratios in the sera of all members of the
three families (n=38) at 4 months of age, representing the
three cholesterol concentration phenotypes. The correlations of TC and
TG with the remaining variables for all members at 4 months of age and
for 12 selected members at 4 months and death are shown in Table 2. TC in animals of the high phenotype group ranged from
234 to 464 mg/dL, in the intermediate from 136 to 194 mg/dL, and in the
normal from 96 to 113 mg/dL. The concentrations of LDL-C, apoB, apoE,
and TG were 4.1-, 3.2-, 3.4- (P<.001), and 1.7-fold
(P<.05) higher in the high cholesterol phenotype group than
in the normal group, while the increases observed in the intermediate
group were 1.7-, 1.7-, 1.4-, and 1.2-fold higher, respectively.
ApoC-III levels differed nonsignificantly between the high and
intermediate groups (10 versus 8 mg/dL, respectively) but were
significantly lower in the normal group (3 mg/dL; P<.05).
The HDL-C levels were similar in the high and normal groups, but 17%
and 24% (P<.05) higher, respectively, in the
intermediate group. The ratios of LDL-C/HDL-C and LDL-C/
apoB were higher in the high group (P<.001) than in
the intermediate and normal groups.
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LDL-C, TG, apoB, apoC-III, and apoE concentrations were positively correlated with TC level at 4 months of age; HDL showed a negative correlation with TC. The correlation values at the time of death for the 12 animals used in the coronary artery study remained similar to the 4-month values for LDL-C, apoB, apoC-III, and apoE, increased for TG, and decreased for HDL-C. TG and apoC-III showed the highest correlation at death.
Concentration and Segregation of Plasma Lipids and
Apolipoproteins
Table 3 shows concentrations of plasma lipids and
apolipoproteins at 4 months of age and death.
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Of the three mating types used in this study, the parents of family 1 were of the high (HxH) cholesterol phenotype, although their cholesterol levels differed considerably (TC, 423 and 297 mg/dL for male and female, respectively) at 4 months of age. They produced a litter of 12 offspring, all expressing the parental high cholesterol phenotype (TC, 292±45.4 mg/dL, n=12). In the sire (1-1) the lipid and apolipoprotein parameters decreased between 4 and 48 months of age, except for TG, while in the dam (1-2) these parameters increased between 4 and 60 months of age, with the exception of apoC-III and apoE, which remained stable. The two offspring showed the high cholesterol phenotype, but of different expression: female 1-3, with the higher TC level, showed a marked increase of all parameters (except HDL-C) from 4 to 26 months of age, while her sister 1-4 demonstrated stable apolipoprotein and lipid levels at 4 and 42 months of age except for a decrease in apoE and HDL-C. The parents were heterozygous for apoB allotypic polymorphism, Lpb2/5 and Lpb3/8, and their 12 offspring segregated into four LDL genotypes: Lpb2/3, Lpb2/8, Lpb3/5, and Lpb5/8 (not shown). The two offspring selected for this study were of the Lpb2/3 genotype.
In the second family, of the IxH mating type, the sire (2-1) was of the intermediate while the dam (2-2) was of the high cholesterol phenotype (TC, 168 and 464 mg/dL, respectively). They produced a litter of 11 offspring that segregated into high (TC, 353±61.2 mg/dL, n=4) and intermediate (TC, 152±8.1 mg/dL, n=7; not shown) cholesterol concentration phenotypes. The sire showed a decrease in apolipoprotein and lipid levels at 33 months of age. Although the dam expressed very high concentrations of all parameters at 4 months of age, except for TG, these values decreased by 27 months of age. Their two offspring studied, a female (2-3) and a male (2-4), expressed the high and intermediate TC phenotypes, respectively. The female showed an increase of all parameters (except HDL-C) from 4 to 23 months of age, which contrasted with the changes observed in her mother. The male showed a profile similar to his father, except for HDL-C.
Both parents (3-1 and 3-2) of family 3 were of the intermediate (IxI) cholesterol phenotype (TC, 136 and 169 mg/dL, respectively). Their litter of nine offspring segregated into three phenotypes: high (TC, 301±48 mg/dL, n=4), intermediate (173±17.7 mg/dL, n=3), and normal (105±12 mg/dL, n=2). The parents showed reduced levels of all lipids and apolipoproteins with age, except for HDL-C in the sire and TG in the dam. Of the two offspring studied (3-3 and 3-4), one expressed the intermediate and the other the high cholesterol concentration phenotype, respectively. Female 3-3 showed a relatively stable lipid and apolipoprotein profile between 4 and 24 months of age, except for HDL-C and TG, while female 3-4 exhibited an increase of all parameters between 4 and 24 months of age, except for apoE and HDL-C.
Morphology of Coronary Arteries and Number of Advanced
Atherosclerotic Lesions
The pedigrees of the three families used for studies of coronary
artery lesions are shown in Fig 1 and photomicrographs
illustrating the most advanced coronary lesion found in each animal are
shown in Figs 2, 3, and 4.
Data on the number of advanced coronary lesions (types IV, V, and VI)
detected in the left anterior descending, left circumflex, and right
coronary arteries are presented in Table 3
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males; and 
, females.
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The sire of family 1 (48 months of age) had advanced atherosclerotic
lesions in six of 31 coronary artery sites sampled (Table 3). These
lesions were of the fibrous type and contained cholesterol clefts and
calcification (Fig 2, panel 1-1). In the dam at 60 months of age
advanced lesions (type V) were observed diffused throughout the major
coronary arteries in 46 of 53 artery segments sampled (Table 3);
lesions contained necrotic cores, cholesterol clefts, calcification,
inflammatory cells, and intraplaque hemorrhage (Fig 2, panel 1-2). An
area of previous myocardial infarct was also observed. The two
offspring (panels 1-3 and 1-4) demonstrated a markedly different
propensity for lesion development. Female 1-3 at 26 months of age
showed advanced atherosclerotic lesions in nine of 36 coronary artery
segments sampled (Table 3), which were of types IV and V (Fig 2, panel
1-3), and resembled those seen in her mother (Fig 2, panel 1-2). In
contrast, no advanced atherosclerosis was observed in her sister at 42
months of age, although macrophage-rich, fatty streak type II lesions
were commonly observed on the luminal aspect of adaptive intimal
thickenings (Fig 2, panel 1-4).
The sire of family 2 (33 months of age) exhibited normal morphology
with occasional foci of adaptive intimal thickening consisting of two
to three layers of longitudinally oriented smooth muscle cells (Fig 3,
panel 2-1). The dam at 54 months of age exhibited five advanced type IV
atherosclerotic lesions in the 31 coronary artery segments sampled
(Table 3); lesions contained necrotic cores, cholesterol clefts,
inflammatory cells, infiltrates, calcification, and fibrous caps (Fig 3, panel 2-2). One offspring (2-3) at 23 months of age demonstrated
advanced lesion formation in 15 of 27 sites sampled (Table 3); lesions
contained necrotic cores, inflammatory cells, and calcification (Fig 3,
panel 2-3). Offspring 2-3 exhibited more extensive lesions at 23 months
than those observed in her mother at 54 months of age, while her
brother (2-4) at 14 months of age exhibited only fatty streak type II
lesions (Fig 3, panel 2-4).
The coronary arteries of both parents of family 3 appeared normal with
occasional foci of adaptive intimal thickening at 51 and 27 months of
age for father and mother, respectively (Fig 4, panels 3-1 and 3-2).
The coronary arteries from one offspring showed normal morphology at 24
months (Fig 4, panel 3-3), while the coronary arteries of her sister at
the same age exhibited advanced atherosclerotic lesions in 10 of 32
artery segments sampled (Table 3). These lesions (type IV) contained
necrotic cores, calcification, and fibrous caps (Fig 4, panel 3-4).
Results from histological analysis of the coronary arteries showed
that the progression of the lesions correlated well with the
concentrations of plasma parameters at the age of death.
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Discussion |
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Data presented in earlier reports indicate that the swine model of FHC is unique and of interest for elucidating human dyslipidemias and atherosclerosis. This was demonstrated by showing that the profile of the essential plasma lipids and apolipoproteins in c-FHC bears marked resemblance to familial combined hyperlipidemia,24 the most common and atherogenic type among human familial dyslipidemias, and by presenting histological evidence for the development of spontaneous advanced coronary atherosclerosis, including myocardial infarction.25 26 However, the interindividual and intraindividual variations together with a suggestive polygenic nature of the c-FHC phenotype and its relation to the lesion progression have significantly hindered progress in elucidating the etiology of this disorder.
In this study, we have continued investigations on quantitative characterization of the two main lipids (TC and TG) and apolipoproteins B, C-III, and E in plasma collected at 4 months of age and from adult animals at the time of death and examined the correlation of the plasma parameters with the progression of coronary atherosclerosis using family members of two generations composed of c-FHC animals and their crosses and intercrosses.
Among several new observations of interest are data showing that apoC-III and apoE are highly elevated and correlated with the concentrations of TC, LDL-C, and apoB in the plasma of the studied FHC animals. The observed alterations bear significant resemblance to human dyslipidemias.38 Also of interest are data on the detection of three patterns of intraindividual variations (increasing, relatively stable, or decreasing) in plasma constituent concentrations between 4 months of age and mature age and their association with the progression of lesion development. In addition, we showed that the F1 generation (c-FHCxnormocholesterolemic), which was heterozygous for the c-FHC gene(s), appeared resistant to advanced lesion development in spite of moderately elevated cholesterol concentrations, which corresponds to the effect of a single dose of a major gene transmitted in the codominant manner.
The observed apoC-III and apoE elevations revealed additional resemblances to human dyslipidemias. Whether these apolipoproteins contribute to the FHC phenotype through their associations with apoB lipoproteins known in humans as distinct apoB-containing lipoprotein families remains to be determined. The concept of apoB-containing lipoproteins was established by Alaupovic38 through immunological separation of VLDL and LDL into five particles identifiable by their apolipoprotein composition (for review, see Reference 3838 ). The significance of the particle concept as an underlying cause in metabolic disorders is best expressed in preliminary data from metabolic and functional studies of the apoB-containing particles in hyperlipidemic and normolipidemic subjects, suggesting that it is not the qualitative differences of the apoB families but the concentration and distribution profile that reflect the defective metabolism of specific apoB-containing particles; eg, an excess of lipoproteins with apoB/C-III and apoB/C-III/E over apoB and apoB/E particles in the buoyant LDL suggests impairment in the metabolism of TG-rich lipoproteins.
We have shown earlier that the increase in buoyant LDL in FHC plasma accounts for the difference in TC and apoB between FHC and normolipidemic swine.24 32 In addition, the LDL of Lpb5 animals showed defective binding to the LDL receptor39 and a delayed plasma clearance.40 In this study, we confirmed that the hypercholesterolemia in FHC swine is highly variable20 21 23 27 and, most importantly, that it is not exclusive to the Lpb5 apoB allele.26 Comparative studies on the profile of apoC-III and apoE in progress (J.H.-R. and J.R., unpublished data, 1994) indicate that their elevations in FHC plasma are reflected in the buoyant LDL subfraction (d<1.043 g/mL), which may imply that in swine FHC, as in human dyslipidemia, apoC-III could be primarily in the apoB/C-III and apoB/C-III/E complexes. These alterations in FHC may reflect an impaired metabolism of apoB/C-III and apoB/C-III/E particles and contribute significantly to the observed dyslipoproteinemia that is linked to spontaneous atherosclerosis. Human studies have shown that the apoC-III heparin precipitate (apoC-III present in LDL) was a predominant risk factor linked to the severity of lesions.41
The detection of the three patterns of intraindividual variations in lipid and apolipoprotein concentrations observed between 4 months and mature age among examined FHC swine, primarily females, was an unexpected finding since only one pattern, similar for both FHC and normolipidemic swine, was observed in earlier studies.29 Recent examination of additional FHC swine confirmed the existence of the three patterns in males (J.R. and J.H.-R., unpublished data, 1994). The original pattern was characterized by a gradual decline in TC and apoB concentrations with age that occurred at a slower rate in females than in males.29
Comparative analysis of the pattern of intraindividual variations with the advancement of lesions showed a clear association, indicating that the observed lipid patterns are better predictors of the extent of lesion progression than the cholesterol estimate made at the time of its full penetrance at 4 to 6 months of age.21 22 25 26 29 Thus the rate of lesion progression in swine expressing FHC appears highly correlated with the course of alteration in concentrations of lipids and apolipoproteins B, C-III, and E. However, the small number of animals used makes speculation difficult as to whether the nature of modulation or regulation of intraindividual variation observed is more physiological or genetic. It remains to be determined whether other minor genes, a late penetrance (12 months of age) of the third genetic dyslipidemia phenotype (type III), and/or changes in steroid hormones have modifying effects on the intraindividual variation of the affected variables.
Our study also took advantage of opportunities to investigate patterns of transmission of the studied lipid and apolipoprotein variables by analyzing their phenotypic distributions in offspring from three types of matings. While the number of animals is too small for quantitative statistical evaluation, and the cholesterol distribution phenotypes of the six breeders showed considerable variability that was probably polygenic, the relative comparison of the transmission patterns in the three litters is indicative of mendelian segregation. The observed segregation into 1, 2, or 3 phenotypic distribution classes in families 1, 2, and 3, respectively, is compatible with a hypothesis that the main effect on the observed distributions was by one major codominant allele (temporarily designated FHC-D). A relatively high correlation between TC and the remaining variables seems to indicate that this allele has a strong pleiotropic effect.
Phenotypic heterogeneity was not limited to lipids and apolipoproteins but was also reflected in the degree of severity and number of complicated lesions. Complex lesions resembling advanced human atherosclerosis were common in the three major coronary arteries of the high cholesterol phenotype (c-FHC) and contained necrotic cores, fibrous caps, neovascularization, and intraplaque hemorrhage. Although the number of animals studied is small, three of the seven animals of the high cholesterol concentration phenotype, demonstrating an increase in plasma lipids and apolipoproteins after 4 months of age, exhibited a greater number of advanced lesions at 2 years of age than the remaining two animals at greater than 4 years of age in which these parameters decreased. Animals with TC <240 mg/dL showed no advanced lesions. Thus, the FHC swine represent the first animal model that develops coronary artery disease with myocardial infarction and ischemia without the interventions of vascular injury or diet induction.
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Acknowledgments |
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This study was supported in part by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, and by the National Institutes of Health (grant HL44900) to Dr Rapacz. We thank P. Crump for the help with the statistical analysis of the data and Scott Kirk, Terry Timm, David Jensen, Jane Gahlman, and Todd Dybevik for their help in collecting blood samples and tissues and for the care of the animals. This is paper No. 3413 from the Department of Genetics. We appreciate the reviewer's comments and suggestions.
Received November 30, 1994; accepted February 20, 1995.
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