Genetic basis of lipoprotein disorders

An Overview of Atherosclerosis: A Look to the Future*

This overview briefly summarizes the cellular pathobiology of experimental atherosclerosis and is then followed by a consideration of how 3 major risk factors interact with the hypothesized pathogenetic process. First, since hemodynamics and blood flow influence the localization of atherosclerotic plaques, possible mechanisms and directions of research are considered. Secondly, the recent hypothesis relating the oxidation of LDL to several of the early processes of atherogenesis is briefly discussed in view of the fact that hyperlipidemia is a major risk factor. The possibility that subsets of LDL and lipoproteins other than LDL might be involved is also discussed. Family history is the last of the 3 contributors to atherosclerosis reviewed and some prototypes of gene abnormalities are considered. Finally, the needs and prospects of future research are summarized.

Different Susceptibilities between Apoe- and Ldlr-Deficient Mice to Inflammation-Associated Colorectal Carcinogenesis

Hypercholesterolemia resulting in atherosclerosis is associated with an increased risk of ischemic heart disease and colorectal cancer (CRC). However, the roles of apoliprotein (Apo) E (Apoe) and low-density lipoprotein (Ldl) receptor (Ldlr) in colorectal carcinogenesis have not yet been investigated. In this study, we examined the susceptibility of Apoe-deficient and Ldlr-deficient mice, which are genetic animal models of atherosclerosis to azoxymethane (AOM)/dextran sodium sulfate (DSS)-induced colorectal carcinogenesis. In Experiment 1, male Apoe-deficient (n = 20) and wild type (WT) mice (C57BL/6J, n = 21) were treated with a single intraperitoneal (i.p.) injection of AOM (10 mg/kg body weight) and then given 1.5% DSS in drinking water for seven days. They were maintained up to week 20 and sacrificed for the histopathological examination of colorectal tumors. The mRNA expression of cyclooxygenase (Cox)-2, inducible nitric oxide synthase (Nos2), tumor necrosis factor (Tnf)-α interleukin (Il)-1β, and Il-6 was assayed in the colorectal mucosa. In Experiment 2, male Ldlr-deficient (n = 14) and WT mice (C57BL/6J, n = 10) were given a single i.p. injection of AOM (10 mg/kg body weight) and then given 2% DSS in drinking water for seven days. They were sacrificed at week 20 to evaluate their colorectum histopathologically. In Experiment 1, the multiplicity of CRCs was significantly higher in the Apoe-deficient mice (2.75 ± 1.48) than in the WT mice (0.62 ± 0.67). The serum lipoprotein levels in the Apoe-deficient mice were also significantly higher than in the WT mice. In Experiment 2, the incidence (29%) and multiplicity (0.50 ± 0.94) of CRCs in the Ldlr mice were significantly lower than in the WT mice (80% incidence and 3.10 ± 2.38 multiplicity). The mRNA expression of two inducible enzymes and certain pro-inflammatory cytokines in the colorectum of each genotype was greater than in the respective WT mice. The values in the Apoe-deficient mice were much greater than in the Ldlr mice. These findings suggest that Apoe-deficient mice showed increased susceptibility to inflammation-associated colorectal carcinogenesis due to their high reactivity to inflammatory stimuli.

Apolipoprotein E genetic polymorphism, serum lipoprotein levels and breast cancer risk: A case-control study

The purpose of this study was to evaluate the association between apolipoprotein E (APOE) allelic frequency, serum lipoproteins and breast cancer (BC). We conducted a nested case-control study within a cohort including 47 cases and 165 controls. Polymerase chain reaction-restriction fragment length polymorphism analyses of the APOE polymorphism were performed. In general, participants with the genotype including alleles e2 and e3 tended to have lower serum triglycerides, total cholesterol and low-density lipoprotein cholesterol levels and higher high-density lipoprotein (HDL) cholesterol levels compared to participants homozygous for the e3 allele and participants heterozygous for the e3 and e4 alleles, respectively. BC patients exhibited higher mean levels of total serum cholesterol (P=0.070), dietary fat intake (P=0.020) and dietary cholesterol intake (P=0.017) compared to control subjects. The allelic distribution between the two groups revealed that the presence of the e2 allele was positively associated with the absence of BC, whereas the e4 allele was positively associated with the BC case group (P=0.019). The distribution of the APOE genotypes was not significantly different between cases and controls (P=0.172). The concomitant presence of the e2 and e4 alleles was positively associated with the absence of BC and e4/e4 homozygosity was positively associated with BC (P=0.021). Our findings suggested that APOE polymorphism plays an important role in the development of BC, particularly when associated with higher serum triglyceride levels.

Tamoxifen therapy in breast cancer: do apolipoprotein E genotype and menopausal state affect plasma lipid changes induced by the drug?

OBJECTIVE

This study examines the lipid profile change produced in response to tamoxifen (TAM) treatment, and its possible relationship with both apolipoprotein E genotype and menopausal state in patients with breast cancer.

METHODS

Blood samples were collected from 86 Spanish women with breast cancer before initiating TAM treatment and in the following 6, 12 and 18 months of treatment. Plasma lipid levels (total cholesterol, triglycerides, HDL-cholesterol and LDL-cholesterol) were determined using an automatic analyzer. Genotypes for apolipoprotein E (ApoE) were identified by PCR-RFLP using the HhaI enzyme.

RESULTS

In all patients, significant reductions in total cholesterol and LDL-cholesterol concentrations and a significant increase in triglyceride concentrations were observed after 6, 12, and 18 months of TAM treatment compared to baseline (p<0.01 for each time point). In the subset of APOE4-negative patients, triglyceride concentrations also significantly increased after 6, 12, and 18 months of treatment (p=0.019, p=0.045, p=0.001, respectively), while APOE4-positive patients showed no significant lipid changes at 12 and 18 months. However, after 18 months of TAM treatment the overall triglyceride concentrations had risen by 24.75% in APOE4-negative patients vs 29.9% in APOE4-positive patients. In postmenopausal women, significant reductions in total cholesterol, LDL-cholesterol and LDL/HDL ratios were observed at each time point (p<0.020 for each).

CONCLUSIONS

TAM treatment induced similar plasma triglyceride increases in patients with positive or negative APOE genotype. Compared to premenopausal patients, postmenopausal breast cancer patients showed a more beneficial lipid profile change in response to treatment.

RNA editing of the apolipoprotein B gene A mechanism to regulate the atherogenic potential of intestinal lipoproteins?

Apolipoprotein B (apo B) circulates in two distinct isomorphic forms, each the product of a single gene. The larger form, referred to as apo B-100, is the major protein of plasma low-density lipoproteins (LDLs) and is synthesized by the human liver. The smaller form, referred to as apo B-48, is produced in the small intestine as a result of a site-specific cytidine deamination, which alters a CAA codon, encoding glutamine in the unedited (apo B-100) mRNA to UAA, which specifies an in-frame stop codon. Apo B-48 lacks the domains involved in LDL receptor interaction and in complex formation with apolipoprotein(a). DNA sequence analysis of the gene that mediates this site-specific cytidine deamination suggests that apo B mRNA editing is an evolutionary adaptation to limit the atherogenic potential of intestinal lipoproteins.

Apolipoprotein E4 allele influences the response of plasma triglyceride levels to tamoxifen in breast cancer patients

BACKGROUND

Apolipoprotein E4 (APOE4) allele is an important risk factor for breast cancer and affects clearance of chylomicron remnants. Tamoxifen therapy increases serum triglyceride levels and sometimes inducing severe hypertriglyceridemia in breast cancer patients.

METHODS

Thirty-three women with breast cancer were recruited to examine the APOE polymorphism and fasting plasma lipid profiles before and after tamoxifen treatment for 6 months.

RESULTS

We found that plasma lipid profiles changed in accordance with the APOE4 allele after tamoxifen treatment for 6 months. Especially plasma triglyceride levels significantly decreased in the APOE4-positive patients (p=0.025), while there was no change in APOE4-negative patients (p=0.189). The total plasma cholesterol levels were reduced in APOE-4 positive patients after 6-month tamoxifen treatment (p=0.014). The levels of plasma low density lipoprotein cholesterol and high density lipoprotein cholesterol significantly decreased in both APOE4-negative and APOE4-positive patients.

CONCLUSIONS

These findings indicate that the effects of tamoxifen on plasma triglyceride levels are modified by APOE polymorphism. Breast cancer patients with APOE4 allele have low plasma triglyceride levels when receiving tamoxifen therapy. Therefore, we suggest that APOE gene polymorphism is a critical validation before tamoxifen treatment in breast cancer patients.

Association of high sensitive C-reactive protein with apolipoprotein E polymorphism in children and young adults: the Cardiovascular Risk in Young Finns Study

BACKGROUND

A relation between apolipoprotein E (APOE) genotypes and high sensitive C-reactive protein (hsCRP) has been observed in some studies with elderly subjects and different patient groups. We studied whether serum hsCRP levels are linked with common APOE (epsilon 2, epsilon 3, epsilon 4) polymorphism already in children and young adults.

METHODS

The study cohort included 1221 subjects participating in the Cardiovascular Risk in Young Finns Study at age 3-18 years at baseline in 1980. These subjects were reexamined at the 21-year follow-up at age 24-39 years in 2001. APOE phenotypes were examined in 1986, serum hsCRP was measured from fresh samples in 2001 and baseline hsCRP (in 1980) was measured from frozen samples in 2005.

RESULTS

Serum hsCRP was significantly associated with APOE phenotypes in children and young adults using multivariate analysis adjusted for age, body mass index, smoking, total cholesterol and low-density lipoprotein cholesterol. Male epsilon 4 carriers had significantly lower hsCRP levels both in childhood (p=0.003) and in adulthood (p=0.013). hsCRP increased in both phenotype classes (epsilon 4+ and epsilon 4-) during the 21-year follow-up. Female epsilon 4 carriers had lower hsCRP levels in childhood (p=0.032) but not in adulthood (p=0.995). An interaction effect between time and APOE phenotype (p=0.045) in relation to hsCRP was observed in females during the 21-year follow-up.

CONCLUSIONS

Common APOE polymorphism affects the level of circulating hsCRP already in children and young adults. Male APOE epsilon 4 carriers have consistently lower hsCRP levels. In females, APOE epsilon 4 carriers had lower hsCRP levels in childhood but not in adulthood.

Apolipoprotein E genotype and circulating interleukin-10 levels in patients with stable and unstable coronary artery disease

OBJECTIVES

This study was designed to assess the relation between apolipoprotein E (apoE) genotype and serum interleukin (IL)-10 levels in patients with acute coronary syndrome (ACS) and chronic stable angina (CSA).

BACKGROUND

Genetic variations in the apoE gene affect the risk for coronary artery disease (i.e., carriers of the e4 allele have an increased risk). Increased levels of C-reactive protein (CRP), an inflammatory marker, correlate with an increased risk of acute coronary events, whereas increased IL-10 concentrations have an atheroprotective role. Studies have reported a negative association between the apoE e4 allele and CRP levels.

METHODS

Apolipoprotein E genotypes were assessed in 166 consecutive ACS patients (119 men, mean age 68 years, interquartile range [IQR] 60 to 74 years) and 70 CSA patients (54 men, mean age 65 years, IQR 62 to 68 years). Serum IL-10 and CRP were assessed at study entry.

RESULTS

Analysis of covariance showed that genetic variation in the apoE gene locus significantly influences serum IL-10 levels in both ACS (p = 0.009) and CSA patients (p = 0.013). Among ACS patients, IL-10 levels were lower in E3/E4 carriers compared with E3/E3 carriers (p = 0.01) and marginally lower compared with E2/E3 carriers (p = 0.065). Among CSA patients, IL-10 levels were lower in E3/E4 carriers compared with E2/E3 carriers (p = 0.004) and marginally lower compared with E3/E3 carriers (p = 0.086).

CONCLUSIONS

The IL-10 concentrations differ in ACS and in CSA patients with different apoE genotypes. The e4 allele was associated with a trend toward lower IL-10 serum levels. Our results may provide an explanation of findings in previous studies that cardiovascular risk is higher in e4 carriers despite the presence of low CRP levels.

Association between the apolipoprotein E genotypes and breast cancer patients in Taiwanese

To display the association between the apolipoprotein E (APOE) genotypes and breast cancer patients, a cross sectional study including 291 patients and 148 controls was performed. The APOE genotypes were measured in all participants, and the pathological diagnosis, estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2 (HER-2) among breast cancer patients were collected. The results showed the APOE allele frequency in breast cancer patients was 11.7% epsilon2 carriers, 74.6% epsilon3 carriers and 13.7% epsilon4 carriers, and there was no significant difference when they were compared with those of the control group (15.5% epsilon2 carriers, 74.3% epsilon3 carriers and 10.1% epsilon4 carriers; p=0.342). Among the patients in pre-menopause, showed a higher frequency of epsilon2 carriers had the cancer site on the left than that of the epsilon3 carriers (78.6% versus 40.3%; p=0.019). Among breast cancer patients, there was no significant association between the APOE genotypes and menopausal status, pathological diagnosis, estrogen receptor, progesterone receptor, and HER-2. Our findings demonstrated that the APOE genotypes were not associated with breast cancer patients, and epsilon2 allele tended to induce breast cancer on the left site among those patients in pre-menopause.

Influences of apolipoprotein E polymorphism on the risk for breast cancer and HER2/neu status in Taiwan

Apolipoprotein E (APOE) polymorphism plays an important role in lipid metabolism. Preliminary evidence suggests that APOE genotype appears to be a risk factor for not only cardiovascular disease, but also Alzheimer's disease and cancer. We screened the APOE genotype in 290 breast cancer patients and 232 non-cancer controls and determined the relationship between APOE gene polymorphism and breast cancer in Taiwan. We found risk for breast cancer was associated with the APOE genotype (xi(2) = 8.652, p = 0.013). Carriers of the epsilon4 allele were more common in breast cancer cases than carriers of epsilon3 allele (p = 0.004, OR = 1.786, 95% CI: 1.197-2.664). In addition, the epsilon4 allele is also associated with HER2/neu negative status in breast cancer patients (p = 0.006, OR = 0.277, 95% CI: 0.111-0.693). No significant associations between APOE genotype and tumor grade, TN classification, progesterone receptor, estrogen receptor, lymphatic invasion, or recurrence of breast cancer were in evidence. These results suggest that the APOE epsilon4 allele may be a risk factor for breast cancer and correlates with HER2/neu negative status.

Cholesterol and apolipoprotein E in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia in North America and Europe. The incidence of the disease rises dramatically with age. AD is a complex multifactorial disorder that involves numerous susceptibility genes, but the exact pathogenesis and biochemical basis of AD is not well understood Cholesterol is receiving a great deal of attention as a potentially crucial factor in the etiology of AD. Almost all cholesterol in the brain is synthesized in the brain. Cholesterol exits the brain through the blood-brain barrier (BBB) in the form of apolipoprotein E (ApoE) or by first being converted to a more polar compound, 24(S)-hydroxycholesterol, which is elevated in individuals with AD. The key event leading to AD appears to be the formation and aggregation in the brain of amyloid beta (Abeta) peptide, a proteolytically derived product of amyloid precursor protein (APP). Cholesterol has been demonstrated to modulate processing of APP to Abeta. High levels of cholesterol are associated with increased risk of AD. Patients taking cholesterol-lowering statins have a lower prevalence of AD. ApoE, which transports cholesterol throughout the brain, exhibits an isoform-specific association with AD such that the E4 isoform, by unknown mechanisms, shifts the onset curve toward an earlier age.

Apolipoprotein E genotype and changes in serum lipids and maximal oxygen uptake with exercise training

Physical activity improves lipid levels by altering triglyceride (TG) metabolism. Apolipoprotein E (Apo E) facilitates TG clearance by mediating lipoprotein binding to hepatic receptors, but Apo E also has less defined roles in skeletal muscle and nervous tissue. This study examined if variants in Apo E genotype affect the lipid and physiologic response to exercise training. Seven centers genetically screened 566 individuals to recruit 120 subjects into 6 gender-specific cohorts equal for the most common Apo E genotypes: E2/3, E3/3, and E3/4. Anthropometics, exercise capacity (Vo(2)max), serum lipids, and post heparin (PH) plasma lipase activities were measured before and after 6 months of supervised exercise training. Difference in the response (Delta) to training among the Apo E genotypes was the primary outcome variable. Differences in pretraining serum lipids among the Apo E genotypes mimicked those observed in population studies: TGs were slightly higher in E2/3 subjects, whereas low-density lipoprotein (LDL)-cholesterol (C) was lower (P = not significant [NS] ). TGs decreased 11% with training for the entire cohort (P <.0001) and 7%, 12%, and 14% for the Apo E 2/3, 3/3 and 3/4 groups, respectively (P = NS for Delta). LDL-C did not change in the entire cohort, but decreased slightly in the 2/3 and 3/3 subjects and increased 4% in the 3/4 group (P = NS for Delta). High-density lipoprotein (HDL)-C increased 2% for the entire cohort (P =.06) due to a 6% increase in the 3/3 group (P =.07 for Delta). Total cholesterol (TC)/HDL and LDL/HDL decreased with training in the 2/3 and 3/3 groups, but increased in the 3/4 subjects and these responses differed among the genotypes (P <.05 for Delta). Vo(2)max increased 9% to 10% for the entire cohort, but only 5% in the 3/3 subjects versus 13% in the 2/3 and 3/4 groups and these differences were significantly different among the genotypes (P <.01 for Delta). This is the first prospective study to demonstrate that the serum lipid response to exercise training differs by Apo E genotype in a pattern consistent with known metabolic differences among the variants. Surprisingly, Apo E genotype also affected the increase in aerobic capacity produced by exercise training possibly via undefined effects on nerve and skeletal muscle function.

Apolipoprotein A-IV polymorphisms and diet-gene interactions

Apolipoprotein A-IV is a 46kDa glycoprotein that is synthesized by intestinal enterocytes and is incorporated into the surface of nascent chylomicrons. Considerable evidence suggests that apolipoprotein A-IV plays a role in intestinal lipid absorption and chylomicron assembly. We have proposed that polymorphisms that alter the interfacial behavior of apolipoprotein A-IV may modulate the physical properties and metabolic fate of plasma chylomicrons. Of the reported genetic polymorphisms of apolipoprotein A-IV, two, Q360H and T347S, are known to occur at high frequencies among the world populations. Biophysical studies have established that the Q360H isoprotein displays higher lipid affinity; conversely the T347S isoprotein is predicted to be less lipid avid. Recent studies have shown that the Q360H polymorphism is associated with increased postprandial hypertriglyceridemia, a reduced low-density lipoprotein response to dietary cholesterol in the setting of a moderate fat intake, an increased high-density lipoprotein response to changes in total dietary fat content, and lower body mass and adiposity; the T347S polymorphism appears to confer the opposite effects. Studies on the diet-gene interactions of other apolipoprotein A-IV alleles are needed, as are studies on the interactions between apolipoprotein A-IV alleles and other apolipoprotein polymorphisms.

Unique character and metabolism of high density lipoprotein (HDL) in fetus

Lipid and lipoprotein profiles, and enzymes for the lipid metabolism were compared between cord and adult blood. Consistent with previous reports, the major lipoprotein in cord blood was high-density lipoprotein (HDL), and that in adult blood was low-density lipoprotein (LDL). The level of apolipoprotein E (apo E) in cord blood was almost equivalent to that in adult blood, while other apolipoproteins and lipids were all lower than the adult level. In cord blood, apo E-rich HDL cholesterol represented more than 30% of total HDL cholesterol (around 11% in adult), and the concentration was about twice of that in adult blood. This apo E-rich HDL cholesterol was poorly esterified (E/T 56%) compared with that in adults (93%). The lecithin:cholesterol acyltransferase (LCAT) activity in cord blood was extremely low, while the activity and mass of cholesteryl ester transfer protein (CETP) were higher than those in adult blood. The apo E genotype did not show influences on total cholesterol, LDL cholesterol, total HDL cholesterol, and apo E rich HDL cholesterol levels in cord blood, as opposed to those in adult blood. The association of D442G mutation of the CETP gene with the increased HDL cholesterol in adult blood was not seen in cord blood. Rather, the mutation was associated with low total cholesterol and LDL cholesterol levels in cord blood. These results indicate that, in fetus, the character and metabolism of HDL, especially of apo E-rich HDL cholesterol, are distinct from those in adults.

Effects of dietary fat amount and saturation on the regulation of hepatic mRNA and plasma apolipoprotein A-I in rats

The effects of the amount of dietary fat and saturation together with cholesterol both on hepatic apolipoprotein A-I gene mRNA levels and on plasma levels of this apolipoprotein were studied in male rats. To achieve these goals, seven groups of male Wistar rats were established: control group (n=5) consuming chow diet; cholesterol group (n=4) fed on a chow diet containing 0.1% (w/w) cholesterol; coco group (n=5) fed on a chow diet containing 0.1% (w/w) cholesterol and 40% coconut oil; corn group (n=5) fed on a chow diet containing 0.1% (w/w) cholesterol and 40% corn oil; and three olive groups consuming a chow diet containing 0.1% (w/w) cholesterol and percentages of 5 (n=5), 10 (n=4) and 40% (n=5), respectively, of olive oil. Animals were kept on these diets for 2 months and then sacrificed for lipoprotein, apolipoprotein and hepatic mRNA analysis. Dietary cholesterol by itself was hypercholesterolemic when compared to chow diet, an effect that was mainly due to an increase in LDL-cholesterol. Corn oil had a hypocholesterolemic action, whether compared to chow or to cholesterol diet, due to a reduction in HDL-cholesterol as well as LDL-cholesterol. HDL-cholesterol levels of 40% olive oil diet were lower than those corresponding to coconut oil and higher than those found in corn oil diet. When compared to control or cholesterol diets, plasma apoA-I concentration appeared significantly increased in coconut and 40% olive oil diets. Coconut oil or corn oil diets did not induce any significant change in apoA-I mRNA compared to control or cholesterol diets. Compared to cholesterol diet, 40 and 10% olive oil diets induced a significant increase in the expression of this message. A positive and significant (r=0.97, P<0.01) correlation between plasma apolipoprotein A-I concentration and its hepatic mRNA, was observed when the amount of dietary olive oil was 40% (w/w). A significant negative (r=-0.97, P<0.01) correlation was found in the corn oil group and no significant association was observed in the remaining groups. Based on the increased plasma levels in coconut oil and in high percentage olive oil diets, and the differences between these two diets for mRNA expression, it can be concluded that different fatty acid containing diets regulate apolipoprotein A-I through different mechanisms, and these mechanisms could be modulated by the fat intake.

Apolipoprotein E genetic polymorphism, serum lipoproteins, and breast cancer risk

Apolipoprotein E (apoE) is a polymorphic gene involved in lipid metabolism with three common variant alleles (epsilon2, epsilon3, and epsilon4). The epsilon4 allele has been associated with elevated levels of cholesterol as well as greater risk of coronary heart disease and Alzheimer's disease. In this case-control study we examined whether apoE genotype affected the association between serum lipids and breast cancer risk. In a subset of a study in western New York, 260 women with incident, primary breast cancer and 332 community controls were interviewed and provided blood samples. Polymerase chain reaction-restriction fragment length polymorphism analyses of the apoE polymorphism were performed. Participants were classified as apoE2 (epsilon2, epsilon2 or epsilon2, epsilon3), apoE3 (epsilon3, epsilon3), or apoE4 (epsilon4, epsilon4 or epsilon4, epsilon3). No unconditional logistic regression was used to compute adjusted odds ratios (ORs) and 95% confidence intervals (CI). Compared with women with the apoE3 genotype, there were no associations with risk for women with the apoE2 (OR=1.0; 95% CI=0. 91-1.64) or apoE4 genotype (OR=0.97; 95% CI=0.63-1.54). Higher serum levels of total cholesterol, HDL cholesterol, and LDL cholesterol were not associated with risk, either in the total sample or among subgroups of women defined by apoE genotype. Women with the highest serum triglyceride levels had an increase in risk (OR=1.63; 95% CI=1. 03-2.59) compared to women with the lowest levels. This effect was not apparent among women with the apoE2 or apoE3 genotype, but much stronger among women with the apoE4 genotype (OR=4.69; 95% CI=1. 49-14.7). These data suggest that the apoE4 genotype may modify the association between serum triglycerides and breast cancer risk.

Lipoprotein-genotype associations in Trinidadian neonates

OBJECTIVES

We hypothesized that common variation in the angiotensinogen (AGT), beta-3-adrenergic receptor, intestinal fatty acid-binding protein, serum paraoxonase, paraoxonase-2, hepatic lipase, apolipoprotein E (APOE), and Werner helicase (WRN) genes would be associated with variation in biochemical phenotypes in a previously unstudied neonatal sample.

DESIGN AND METHODS

We examined associations of both nongenetic and genetic variables with plasma lipoprotein traits in neonates from Trinidad.

RESULTS

Among nongenetic variables, we found significant associations between plasma concentrations of: 1) lipoprotein(a) [Lp(a)] and both ethnicity (p = 0.037) and birth weight (p = 0.001); 2) total cholesterol and gender (p = 0.010); 3) triglyceride and birth weight (p = 0.035); and 4) apolipoprotein AI and gender (p = 0.016). Among genetic variables, we found that: 1) common variation on chromosome 1q in AGT codon 235 was significantly associated with variation in plasma apolipoproteins AI (p<0.0001) and B (p = 0.013); 2) common variation in WRN at codon 1367 was significantly associated with variation in plasma Lp(a) (p<0.0001); and 3) common variation in APOE at codons 112 and 158 was significantly associated with variation in plasma triglycerides (p = 0.013).

CONCLUSIONS

The associations with AGT and WRN are novel and may have resulted either from a direct influence of the genetic variants or through linkage disequilibrium with other functional loci, such as the familial combined hyperlipidemia locus on chromosome 1q in the case of AGT. Despite the fact that there are some limitations in making determinations from cord blood, the results suggest that there may be genetic determinants of plasma lipoproteins in neonates.

The Lipoprotein Lipase HindIII Polymorphism: Association with Total Cholesterol and LDL-Cholesterol, but not with HDL and Triglycerides in 342 Females

Background: Lipoprotein lipase (LPL) is the rate-limiting enzyme in the hydrolysis of core triglycerides in chylomicrons and VLDL.

Methods: We investigated the association between the HindIII polymorphism of the LPL gene and fasting glucose, lipid, and lipoprotein concentrations in 683 Caucasians. We first stabilized the study subjects, using an 8-day diet and exercise intervention program before obtaining blood samples. The use of this standardization period reduced the variance of all glucose and lipid concentrations.

Results: In our study, the HindIII allele frequencies for females and males were 0.29 and 0.34 for H− and 0.71 and 0.66 for H+, respectively. We found in females, but not in males, a significant association between the HindIII genotype and total cholesterol (P = 0.007) and LDL-cholesterol (P = 0.018), with females homozygous for the rare H− allele having the lowest, heterozygotes (H−/+) having intermediate, and women homozygous for the common H+ allele having the highest of each of these lipid traits. With regard to triglycerides, HDL-cholesterol, and glucose, no significant effect of the HindIII genotype was noted in either gender.

Conclusions: These results suggest that in a gender-specific manner, the rare LPLHindIII H− allele has a cholesterol-lowering and, therefore, potentially cardioprotective effect compared with the common H+ allele.

The apolipoprotein E phenotype has a strong influence on tracking of serum cholesterol and lipoprotein levels in children: a follow-up study from birth to the age of 11 years

The extent to which an individual maintains his position relative to the rest of the population is called tracking. The objective of this study was to examine the effect of the apolipoprotein E (apoE) phenotype on the tracking of serum cholesterol and lipoproteins from birth to the age of 11 y. In a longitudinal follow-up study of healthy children, concentrations of total serum cholesterol and triglyceride were determined at birth (n = 193), and at the ages of 2 (n = 192), 4 (n = 192), 6 (n = 190), 9 (n = 188), and 12 mo (n = 196), and 5 (n = 162) and 11 y (n = 153). Concentrations of total HDL, HDL2, and HDL3, VLDL, and LDL cholesterol were determined at 2, 6, 9, and 12 mo (n = 36), and 5 (n = 162) and 11 y (n = 153). The apoE phenotype was determined in 151 children. The children had the following apoE phenotypes: 4 had type 4/4 and 40 type 3/4 (group apoE4), 94 had type 3/3 (group apoE3), and 11 had type 2/3 and 2 type 2/4 (group apoE2). The correlation coefficients for total cholesterol levels during childhood compared with the level at 11 y of age were: 0.03 at birth, 0.26 (p < 0.001) at 2 mo, 0.24 (p < 0.001) at 4 mo, 0.24 (p < 0.001) at 6 mo, 0.28 (p < 0.001) at 9 mo, 0.41 (p < 0.001) at 12 mo, and 0.60 (p < 0.001) at 5 y. When the children were divided into three groups according to their apoE phenotypes, these three groups had the following correlation coefficients at 4 mo, 12 mo, or 5 y of age compared with the level at the age of 11 y; group apoE2: r = 0.65 (p < 0.01), r = 0.59 (p < 0.01), and r = 0.72 (p < 0.01); group apoE3: r = 0.27 (p < 0.01), 0.43 (p < 0.001), and r = 0.64 (p < 0.001); and group apoE4: r = 0.14 (p = NS), r = 0.33 (p < 0.05), and 0.42 (p < 0.01). The apoE phenotype also strongly influenced the tracking of the LDL cholesterol levels; the correlation coefficients between 5 and 11 y of age were for group apoE2 r = 0.84 (p < 0.001), for group apoE3 r = 0.70 (p < 0.001), and for group apoE4 r = 0.37 (p < 0.05). Our results indicate that the apoE phenotype strongly influences the tracking of lipids. The children having apoE 2/3, 2/4, and 3/3 phenotypes maintained their relative cholesterol and lipoprotein levels better than the others throughout the first 11 y of age. Because the apoE phenotype strongly affects the tracking of serum cholesterol, the usefulness of cholesterol screening in predicting future cholesterol values should be analyzed, keeping the apoE phenotype in mind.

Common genomic variation in the APOC3 promoter associated with variation in plasma lipoproteins

We hypothesized that common genomic variation that affected the expression and/or function of the products of the APOC3, APOE, FABP2, and PON1 genes would be associated with variation in biochemical phenotypes in a previously unstudied human sample. We determined genotypes of functional genomic variants of APOC3, APOE, FABP2, and PON1 in 509 adult aboriginal Canadians from an isolated community in Northern Ontario. We tested for genotype associations with plasma lipoprotein traits. We found that (1) common variation at nucleotide -455 of the APOC3 promoter was associated with variation in plasma triglycerides (P = .006) and (2) common variation of APOE determining plasma isoforms of apo E was associated with variation in plasma apo B (P = .009). Analysis of subjects classed by APOC3 markers showed that homozygosity for presence of a C at nucleotide -455 and a T at nucleotide -482 was associated with significantly increased plasma triglycerides in both men and women. Furthermore, this allele was approximately twice as frequent in subjects within the highest quartile of plasma triglycerides as in subjects within the lowest quartile. Since the DNA variation detected by the APOC3 markers affects in vitro expression of the gene product, it is possible that the marker itself caused the associations. However, the associations could also have resulted from linkage disequilibrium with other functional variants in APOC3 or the closely linked APOA1 and/or APOA4 genes.

Common genomic variants associated with variation in plasma lipoproteins in young aboriginal Canadians

We hypothesized that common genomic variants would be associated with variation in lipoprotein phenotypes in young subjects. We determined genotypes of FABP2, PON, APOC3, and APOE in 188 aboriginal Canadians, aged 9 to 17 years. We found that 13 of 32 possible genotype-phenotype associations were significant: (1) the FABP2 codon 54 genotype was associated with variation in plasma triglycerides (P = .045); (2) the PON codon 192 genotype was associated with variation in plasma total and LDL cholesterol and apoB (P = .0099, P = .0088, and P = .016, respectively); (3) the APOC3 insulin-response-element genotype was associated with variation in plasma triglycerides, HDL cholesterol, apoA-I, the total cholesterol to HDL cholesterol ratio, and the apoB to apoA-I ratio (P = .0014, P = .0069, P = .045, P = .0021, and P = .0081, respectively); and (4) the APOE restriction isotype was associated with variation in plasma LDL cholesterol, apoB, the total cholesterol to HDL cholesterol ratio, and the apoB to apoA-I ratio (P = .025, P = .034, P = .045, and P = .047, respectively). The average young age and relative absence of age-dependent secondary environmental factors could have eased the identification of small genetic effects on lipoprotein phenotypes in this study sample.

Effects of a major gene for apolipoprotein A-I concentration are thyroid hormone dependent in Mexican Americans

Apolipoprotein A-I (apoA-I) is the principal protein component of HDL cholesterol. The thyroid hormone triiodothryonine (T3) is known to be a potent mediator of expression of the apoA-I structural gene (APOA1). Using complex segregation analysis, we detected a major gene influencing plasma concentration of apoA-I and examined its interaction with T3 serum level in Mexican Americans participating in the San Antonio Family Heart Study. Strong evidence for a major locus with two alleles (A and a) determining apoA-I level was obtained when interaction with T3 was allowed. The major gene appears not to be linked to the APOA1 structural locus. Genotypes differed significantly in their relationships to T3 level. The AA and Aa genotypes showed a positive relationship with T3 level, while the rarer aa homozygote showed a strong negative relationship with T3. The relative variance in apoA-I concentration due to this major gene varied from 56% to 18%, depending on T3 level. On average, the major gene accounts for 30% of apoA-I variation, and shared-household effects account for an additional 11%. These findings suggest that thyroid hormone has an important role in the genetic control of lipoprotein metabolism.

Genetic factors in lipoprotein metabolism. Analysis of a genetic cross between inbred mouse strains NZB/BINJ and SM/J using a complete linkage map approach

A genetic cross was constructed from two parental inbred strains of mice, NZB/BINJ and SM/J, which differ markedly in their plasma lipoprotein levels. Plasma lipid and apolipoprotein values were measured in 184 F2 progeny on a normal chow diet and on an atherogenic diet. Genetic markers were typed at 126 loci spanning all chromosomes except the Y. Statistical analysis revealed significant linkage or suggestive linkage of lipoprotein levels with markers on a number of chromosomes. Chromosome 1 markers were linked to levels of total cholesterol (lod 5.9) and high density lipoprotein (HDL) cholesterol (lod 8.1), chromosome 5 markers were linked to levels of total cholesterol (lod 6.7) and HDL cholesterol (lod 5.6), and chromosome 7 markers were linked to levels of total plasma triglycerides (lod 5.1) and free fatty acids (lod 5.6). Plasma apoAII levels were linked to the apoAII gene (lod score 19.6) and were highly correlated with plasma HDL cholesterol levels (r = 0.63, P = 0.0001), indicating that apoAII expression influences HDL cholesterol levels. Molecular studies suggested that structural differences in the apoAII polypeptide of the two strains may contribute to differences in clearance of the protein.

Single-strand conformational polymorphisms (SSCP): studies of the genetic polymorphisms of exon 4 of apolipoprotein C III

OBJECTIVE

We used single-strand conformational polymorphism (SSCP). To screen for mutations/polymorphisms in exon 4 of the apolipoprotein C III in 45 patients with hypertriglyceridemia and 46 control individuals, single-strand conformational polymorphism was investigated using restriction endonuclease and amplification refractory mutations systems (ARMS).

RESULTS

SSCP identified six patterns corresponding to six genotypes. We confirmed that the different genotypes result from the two polymorphic sites at positions 3175 and 3206 of the apo C III gene. Only three of four possible haplotypes were found in the study population. This resulted in the identification of 6 of the 10 possible genotypes.

CONCLUSIONS

SSCP is a useful method to screen for both known and unknown mutations/polymorphisms and should have increasing applications in clinical laboratories involved with the study of genetic markers of a wide variety of diseases.

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

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.

Detection and treatment of elevated blood lipids and other risk factors for coronary artery disease in youth

The early lesions of atherosclerosis in youth are strongly related to antemortem levels of total and low-density lipoprotein (LDL) cholesterol, very low density lipoprotein (VLDL) cholesterol, and triglyceride to ponderal index and to blood pressure. The major apolipoproteins of LDL and high-density lipoprotein (HDL), apoB and apoA1 respectively, and levels of Lp(a) lipoprotein are often abnormal in children born in a family with premature coronary artery disease (CAD). Other risk factors for CAD include obesity, high blood pressure, cigarette smoking, diabetes mellitus, positive family history of CAD, and physical inactivity. Children from families with premature CAD, dyslipidemia, or hypertension, and/or two other risk factors should have a lipoprotein profile determined. Treatment begins with a diet low in total fat, saturated fat, and cholesterol, combined with treatment of overnutrition and obesity, if necessary, and regular habits of aerobic physical activity. Children with inherited disorders of LDL metabolism may require the addition of lipid-lowering therapy. The early detection and treatment of youth at risk for premature CAD offer the greatest promise to decrease morbidity and mortality.

Genetic cholesteryl ester transfer protein deficiency caused by two prevalent mutations as a major determinant of increased levels of high density lipoprotein cholesterol

Genetic determinants of HDL cholesterol (HDL-C) levels in the general population are poorly understood. We previously described plasma cholesteryl ester transfer protein (CETP) deficiency due to an intron 14 G(+1)-to-A mutation(Int14 A) in several families with very high HDL-C levels in Japan. Subjects with HDL-C > or = 100 mg/dl (n = 130) were screened by PCR single strand conformational polymorphism analysis of the CETP gene. Two other mutations were identified by DNA sequencing or primer-mediated restriction map modification of PCR products: a novel intron 14 splice donor site mutation caused by a T insertion at position +3 from the exon14/intron14 boundary (Int14 T) and a missense mutation (Asp442 to Gly) within exon 15 (D442G). The Int14 T mutation was only found in one family. However, the D442G and Int14 A mutations were highly prevalent in subjects with HDL-C > or = 60 mg/dl, with combined allele frequencies of 9%, 12%, 21% and 43% for HDL-C 60-79, 80-99, 100-119, and > or = 120 mg/dl, respectively. Furthermore, prevalences of the D442G and Int14 A mutations were extremely high in a general sample of Japanese men (n = 236), with heterozygote frequencies of 7% and 2%, respectively. These two mutations accounted for about 10% of the total variance of HDL-C in this population. The phenotype in a genetic compound heterozygote (Int14 T and Int14 A) was similar to that of Int14 A homozygotes (no detectable CETP and markedly increased HDL-C), indicating that the Int14 T produces a null allele. In four D442G homozygotes, mean HDL-C levels (86 +/- 26 mg/dl) were lower than in Int14 A homozygotes (158 +/- 35 mg/dl), reflecting residual CETP activity in plasma. In 47 D442G heterozygotes, mean HDL-C levels were 91 +/- 23 mg/dl, similar to the level in D442G homozygotes, and significantly greater than mean HDL-C levels in Int14 A heterozygotes (69 +/- 15 mg/dl). Thus, the D442G mutation acts differently to the null mutations with weaker effects on HDL in the homozygous state and stronger effects in the heterozygotes, suggesting dominant expression of a partially defective allele. CETP deficiency, reflecting two prevalent mutations (D442G and Int14 A), is the first example of a genetic deficiency state which is sufficiently common to explain a significant fraction of the variation in HDL-C in the general population.

Attenuated hypercholesterolemic response to a high-cholesterol diet in subjects heterozygous for the apolipoprotein A-IV-2 allele

BACKGROUND

Previous studies have suggested that the variant apolipoprotein (apo) allele apo A-IV-2 may influence the response of the plasma cholesterol concentration to dietary cholesterol.

METHODS

We measured plasma lipids and lipoproteins in 11 subjects who were heterozygous for the apo A-IV-2 allele (apo A-IV-1/2 heterozygotes) and a control group of 12 subjects who were homozygous for the common apo A-IV allele (apo A-IV-1/1 homozygotes) in an outpatient dietary-modification study. (Approximately one in seven persons in the United States is a heterozygote.) The subjects consumed a low-cholesterol diet (about 200 mg [0.5 mmol] of cholesterol per day) during a two-week run-in period; daily cholesterol intake was then increased to approximately 1100 mg (2.8 mmol) by the addition of four egg yolks per day.

RESULTS

The fat intake and the ratio of polyunsaturated to saturated fat were similar in the two groups throughout the study. After three weeks of egg intake, the mean plasma total cholesterol increased by 22 mg per deciliter (0.57 mmol per liter) in the apo A-IV-1/1 group, but by only 6 mg per deciliter (0.15 mmol per liter) in the apo A-IV-1/2 group (P = 0.05). The mean plasma low-density lipoprotein cholesterol increased by 19 mg per deciliter (0.49 mmol per liter) in the apo A-IV-1/1 group, but by only 1 mg per deciliter (0.03 mmol per liter) in the apo A-IV-1/2 group (P = 0.03). There were no changes in the plasma triglyceride or high-density lipoprotein cholesterol concentrations in either group.

CONCLUSIONS

The apo A-IV-2 allele attenuates the hypercholesterolemic response to the short-term ingestion of a very-high-cholesterol diet and may partially account for the heterogeneous response to dietary cholesterol. However, cholesterol intake in this study was more than twice that of the general population; whether the apo A-IV-2 allele alters responsiveness at lower levels of cholesterol intake remains to be determined.

DNA polymorphisms at the locus for human cholesteryl ester transfer protein (CETP) are associated with macro- and microangiopathy in non-insulin-dependent diabetes mellitus

The effect of variation at the cholesteryl ester transfer protein (CETP) gene locus and in the apolipoprotein (apo) AI-CIII-AIV gene cluster on the susceptibility of individuals with non-insulin-dependent diabetes mellitus (NIDDM) to atherosclerotic vascular disease was studied in 136 male and 122 female patients with NIDDM. The prevalence of myocardial infarction was high (38%) in patients with the EcoNI genotype 2-2 of the CETP gene locus (= 2-2; subjects homozygous for the absence of the restriction site) compared with patients with the genotype 1-1 (= 1-1; subjects homozygous for the presence of the restriction site) (18%, p < 0.02). The prevalence of any evidence of coronary heart disease (CHD) (presence of ischaemic ECG changes or definite myocardial infarction) was high in 2-2 (73%) compared with the genotype 1-2 (= 1-2; heterozygous for the presence of the restriction site) (52%, p < 0.02) and genotype 1-1 (p = 0.06). CHD was more prevalent in men with 2-2 (70%) than in those with 1-1 (42%, p < 0.05), but in women no significant differences were found in the prevalences of CHD between the EcoNI genotypes. Neuropathy was more often present in the patients with 2-2 (31%) than in those with 1-1 (12%, p < 0.02) or 1-2 (14%, p < 0.01). Plasma total cholesterol and total- and VLDL-triglycerides were higher in women with the EcoNI genotype 1-1 than in those with the genotype 1-2. In men no significant differences in plasma lipids were found. In addition, the prevalence of cerebrovascular disease was high (21%) in the patients with the genotype 1-1 of the TaqIB polymorphism compared with the genotype 2-2 (6%, p < 0.02). None of the alleles defined by four polymorphisms in the apo AI-CIII-AIV gene region were associated with an increased risk for macroangiopathy. The PstI polymorphism had an effect on plasma triglyceride levels. At the CETP locus one pair of loci (TaqIB and EcoNI) and three pairs of loci at the apo AI-CIII-AIV gene cluster (SacI and MspI, SacI and PvuII and MspI and PvuII) showed significant allelic association. In conclusion, the variation of CETP locus modulates the risk for diabetic complications in patients with NIDDM and the effect seems to be different between men and women. In contrast, the AI-CIII-AIV gene cluster polymorphisms seem not to be related to the risk of CHD in NIDDM.(ABSTRACT TRUNCATED AT 400 WORDS)

Dyslipoproteinemia and other risk factors for atherosclerosis in children and adolescents

The early lesions of atherosclerosis in youth are strongly related to antemortem levels of total and low density lipoprotein (LDL) cholesterol, very low density lipoprotein (VLDL) cholesterol, and triglyceride, to ponderal index and to systolic and diastolic blood pressure. The major apolipoproteins of LDL and high density lipoprotein (HDL), apo B and apo A1, respectively, as well as levels of Lp(a) lipoprotein are often abnormal in children born to a parent with coronary artery disease (CAD). Other risk factors for CAD include obesity, high blood pressure, cigarette smoking, diabetes mellitus, positive family history of CAD and physical inactivity. Children from families with premature CAD, familial dyslipidemia or hypertension, and/or two other risk factors should have a lipoprotein profile determined. The first form of treatment is a diet low in total fat, saturated fat and cholesterol, combined with treatment of overnutrition and obesity, if necessary, and regular habits of aerobic physical activity. Children with inherited disorders of LDL metabolism may require the addition of lipid lowering therapy. The early detection and treatment of youth at risk for premature CAD offers the greatest promise to decrease morbidity and mortality.

Complex segregation analysis provides evidence for a major gene acting on serum triglyceride levels in 55 British families with familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) was first described as an autosomal dominant inherited trait with primary action on triglyceride levels and secondary effects on cholesterol metabolism. This conclusion has since been questioned by several groups despite subsequent supportive biochemical and metabolic studies. To reexplore the genetics of FCHL, we assembled 55 families from the United Kingdom comprising 559 persons ascertained through probands with both hypercholesterolemia and hypertriglyceridemia. The results of univariate complex segregation analysis were consistent with a major gene acting on triglyceride and explaining two thirds of the genetic variability and 20% of the phenotypic variance in triglyceride levels. Univariate analysis did not identify a major genetic component acting on cholesterol levels. Bivariate segregation analysis rejected a major gene model. We also reexamined the original FCHL pedigrees collected by Goldstein et al and obtained results similar to those in the UK families. The prospects for mapping putative major genes determining triglyceride levels in FCHL patients by linkage analysis are discussed.

Differential effect of dietary fat saturation and cholesterol on hepatic apolipoprotein gene expression in rats

The effects of dietary cholesterol and fat saturation on hepatic apolipoprotein A-I, A-II, A-IV, B, C-I, C-III, E and LDL receptor mRNA levels were studied in male rats. Animals were maintained for 2 months on a high fat diet (40% w/w) containing 0.1% cholesterol. Two groups of control animals received either chow diet or chow plus 0.1% cholesterol, while experimental groups received as their fat supplement coconut, corn or olive oil. Olive oil fed animals had higher levels of hepatic apo A-I than the control cholesterol group (1.6 +/- 0.3 vs. 0.8 +/- 0.2). Apo E mRNA levels were 50% and 72% higher in animals consuming the saturated (coconut) and unsaturated (corn and olive) fat diet than the control cholesterol group. Apo B and apo C-I mRNA levels were not affected by the experimental conditions. Apo A-IV mRNA increased between 66% and 127% in groups in which cholesterol was present. LDL receptor mRNA increased 2 times in the corn fed group compared with the control groups. These results indicate that the expression of genes coding for products involved in lipoprotein metabolism have a differential susceptibility to dietary fat saturation and cholesterol.

DNA variants at the LPL gene locus associate with angiographically defined severity of atherosclerosis and serum lipoprotein levels in a Welsh population

Coronary artery disease (CAD) patients (n = 235), comprising minimal (CAD-, n = 124) and severe (CAD+, n = 111) CAD, were recruited on the basis of their angiographic scores. Male control subjects (n = 123) were selected randomly from the Caerphilly Heart Study cohort. Subjects were genotyped for the Ser447-Ter mutation and HindIII/Pvu II restriction fragment length polymorphisms of the lipoprotein lipase gene and investigated for associations with severity and development of CAD and lipid and lipoprotein levels. The Ser447-Ter mutation showed no significant associations with CAD or dyslipidemia but was related to favorable lipid and lipoprotein profiles. The H2H2 genotype (P < .05) and H2 allele (P = .05) were significantly more frequent in CAD+ versus CAD- and control subjects versus CAD-. H2H2 subjects, among the entire male cohort, had significantly higher levels of apolipoprotein B (P = .0002), total cholesterol (P < .004), and triglycerides (P < .04) than alternative genotypes. P2P2 associated with significantly lower high-density lipoprotein cholesterol levels (P < .01). The H2 allele had most significant associations with raised apolipoprotein B levels compared with other biochemical parameters. Our data suggest that the H2 allele may be a linkage marker for an etiologic mutation for dyslipidemia and the severity and development of atherosclerosis; this is not the Ser447-Ter mutation.

A gene-gender interaction affecting plasma lipoproteins in a genetic isolate

The Hutterite Brethren are a genetic isolate characterized by high indices of relatedness and a communal agrarian lifestyle. We hypothesized that variation in their apolipoprotein (apo) E and lipoprotein lipase (LPL) genes would be associated with variation in fasting plasma lipoproteins. We measured plasma lipids, lipoproteins, and apolipoproteins and analyzed DNA for genotypes of apoE and LPL in 803 Hutterites. We observed that apoE and LPL genotypes were significantly associated with variations in plasma total cholesterol, low-density lipoprotein (LDL) cholesterol, and apoB. When the data were subdivided by sex, apoE genotype was associated with plasma apoB-related traits in men, but LPL genotype was not. In contrast, LPL genotype was associated with plasma apoB-related traits in women, including triglycerides and LDL cholesterol. After accounting for age, body mass index, and colony of origin, the variation in these variables was much more significantly associated with LDL genotype than with apoE genotype in women but not in men. The association of LPL variation with plasma lipoproteins in women suggests that the functional effects of important structural elements within, flanking, or proximal to the LPL gene on chromosome 8p22 may be sex related.

Linkage between the APOB gene and serum ApoB levels in a large pedigree from the Bogalusa Heart Study

Maximum likelihood linkage analyses were performed to test for linkage between serum apoB levels and several candidate gene markers including apolipoprotein B, lipoprotein lipase, hepatic lipase, cholesterol ester transfer protein, and apolipoprotein AI in a large pedigree. Parameters of general Mendelian inheritance derived from maximum likelihood segregation analysis of the serum apoB levels were used in the linkage analysis. The highest two-point lod score between the quantitative trait and a marker defined by a single restriction digest was 1.86 at recombination fraction (theta) = 0. This was observed for linkage between serum apoB levels and the presence or absence of a PvuII digestion site in the apoB gene. Linkage between serum apoB levels and polymorphisms of the apoB gene defined by the two restriction digests EcoR1 and PvuII was supported by a lod score of 3.30, while inclusion of VNTR typings led to a lod score of 2.33. None of the other candidate genes gave positive evidence of linkage.

Role of preclinical cardiovascular disease in the evolution from risk factor exposure to development of morbid events

Conventional risk factors (especially high arterial pressure, elevated cholesterol and glucose levels, and cigarette smoking) are useful predictors of morbid atherosclerotic and hypertensive events, and their control variably reduces the incidence of events. However, both the ability to predict risk and the ability to reduce it by modification of established risk factors are limited. These limitations occur in part because the progression from risk factor exposure to morbid events depends on the variable likelihood that individuals exposed to the same risk factors will progress through two stages: the development of asymptomatic or "preclinical" anatomic and functional cardiovascular disease in response to standard risk factors and other variables, and the precipitation of morbid events by progression of preclinical disease or by the action of additional "triggering" mechanisms in the presence of preclinical disease. Advances in diagnostic methodology now make possible accurate noninvasive detection in many asymptomatic individuals of preclinical disease such as left ventricular hypertrophy, carotid atherosclerosis, and renal dysfunction. Progress in elucidating stimuli to left ventricular hypertrophy and systemic atherosclerosis suggests that focusing research separately on these two stages of disease evolution is a fruitful strategy. The closer relation of measures of preclinical disease than risk factors with the subsequent risk of complications indicates that their detection improves clinical risk stratification. However, critical testing of whether clinical outcome is improved or treatment cost is lowered by basing antihypertensive or antihyperlipidemic treatment decisions in part on the presence of preclinical cardiovascular disease is needed before this strategy is adopted on a widespread scale.

The apolipoprotein E gene and the serum low-density lipoprotein cholesterol response to dietary fiber

Our goal was to determine whether differences in apolipoprotein E (apo E) influenced the response to dietary changes aimed at reducing serum cholesterol levels, especially increases in fiber. Apo E phenotype and genotype were determined in 43 men and 24 women who had previously taken part in parallel 2-week metabolic dietary studies involving either wheat bran or oat bran supplementation at a level of 6.8 g fiber/1,000 kcal. Fasting blood lipid measurements had been made at the beginning and end of the 2-week metabolic period. Reductions in low-density lipoprotein (LDL) cholesterol levels across both oat and wheat bran diets were significantly different depending on the E allele (P = .048). The LDL cholesterol level reduction for E2 carriers (0.60 +/- 0.14 mmol/L, n = 13) was greater than that for E3 homozygotes (0.21 +/- 0.07 mmol/L, n = 38; P = .014) and E4 carriers (0.28 +/- 0.12 mmol/L, n = 16; P = .09). Only the change in dietary fiber on the oat bran diet was related significantly to the decrease in LDL cholesterol levels (r = -.47, P = .007; n = 32). No such relationship was seen on the wheat bran diet (r = -.010, P = .59; n = 33). Carriers of the E2 allele appear to be more responsive than noncarriers to a dietary change involving increased fiber intake. The data also support a lipid-lowering advantage of oat bran over wheat bran. Current dietary recommendations to reduce serum lipid levels may vary in effectiveness depending on distribution of apo E alleles in the different populations studied.

Low-density lipoprotein cholesterol responsiveness to diet in normolipidemic subjects

Both apolipoprotein E genotype (apo E) and diet predict very-low-density (VLDL-C) and low-density lipoprotein cholesterol (LDL-C) levels. In a retrospective pooled analysis of six studies, we sought to identify the predictors of VLDL-C and LDL-C change, or "responsiveness," to a diet crossover. "Response" to diet was studied in 67 normolipidemic subjects of common apo E genotype. Subjects were fed two contrasting, metabolically controlled diets: one had a low polyunsaturated to saturated fatty acid ratio (P:S), and the other had a high P:S ratio. Multiple blood samples were analyzed for VLDL-C and LDL-C levels at the end of each metabolic diet period, and values were averaged and differences were calculated. Despite adjustment for significant predictors across the component studies, a wide range of LDL-C responsiveness was found, with an average decrease of 28 mg/dL. Multivariate regression analysis was used to identify the most significant predictors of LDL-C response to the diet crossover. All dietary and clinical variables were entered by stepwise regression for potential inclusion in a "best-fit" model. The degree of change in saturated fat content and age were the most significant predictors of LDL-C responsiveness. Neither dietary cholesterol nor apo E phenotype were significant predictors of responsiveness. The most LDL-C-responsive subjects were older and required smaller reductions in dietary saturated fat levels than did less-responsive subjects to achieve a comparable reduction in LDL-C levels. Multiple regression analysis suggested a precursor-product relationship between VLDL-C and LDL-C responsiveness.

Influence of the apoA-II gene locus on HDL levels and fatty streak development in mice

Previous studies have shown that distal mouse chromosome 1 contains the apolipoprotein AII (apoAII) gene, encoding the second most abundant apolipoprotein in high density lipoproteins (HDLs), as well as a gene termed Ath-1 that controls aortic fatty streak development and HDL cholesterol levels in response to a high-fat, high-cholesterol diet. We report genetic studies confirming that the genes are distinct. Using molecular markers for mouse chromosome 1, we have further mapped the two genes, and our results indicate that they are separated by a minimum of 2 cM. We also report evidence that in mice on a low-fat chow diet, the apoAII gene locus influences HDL cholesterol levels. Thus, statistical analysis of two sets of recombinant inbred strains revealed concordant segregation patterns of HDL cholesterol levels and the apoAII gene locus. The effect of apoAII expression on HDL cholesterol levels was further tested by using a congenic strain that exhibits increased apoAII synthesis in comparison to the background strain. The results support the concept that increased synthesis of apoAII results in increased HDL cholesterol levels. Unexpectedly, increased expression of apoAII appeared to promote rather than retard aortic fatty streak development.

Gene-environment interactions in atherosclerosis

The importance of environment and genetics working together to shape an individual's risk for atherosclerosis seems intuitively obvious. However, it is only recently that research strategies have begun to evolve that attempt to answer questions related to apportionment of risk that is due to specific environmental and genetic factors. These factors may impact upon risk either singly or, more likely, through a complex interaction that affects the metabolic history of the whole organism. Because the genetic bases of lipid and lipoprotein metabolism have been well-studied, and because of the epidemiologic and pathobiochemical associations between genetic disorders of lipid metabolism and atherosclerosis, researchers have searched for gene-environment interactions within animal and human systems in which the phenotype is defined by some index of lipoprotein metabolism. From work done in the lipoprotein area to this point a clear case can be made for: 1) the genetic influence over the phenotypic response to an environmental stimulus; 2) the environmental modulation of the phenotypic expression of severe genetic defects. In the realm of gene-environment interactions that affect lipoprotein phenotype, diet is the best-studied environmental factor.