The apolipoprotein epsilon2 allele and the severity of coronary artery disease in Type 2 diabetic patients

Apolipoprotein E in Cardiometabolic and Neurological Health and Diseases

A preponderance of evidence obtained from genetically modified mice and human population studies reveals the association of apolipoprotein E (apoE) deficiency and polymorphisms with pathogenesis of numerous chronic diseases, including atherosclerosis, obesity/diabetes, and Alzheimer’s disease. The human APOE gene is polymorphic with three major alleles, ε2, ε3 and ε4, encoding apoE2, apoE3, and apoE4, respectively. The APOE gene is expressed in many cell types, including hepatocytes, adipocytes, immune cells of the myeloid lineage, vascular smooth muscle cells, and in the brain. ApoE is present in subclasses of plasma lipoproteins, and it mediates the clearance of atherogenic lipoproteins from plasma circulation via its interaction with LDL receptor family proteins and heparan sulfate proteoglycans. Extracellular apoE also interacts with cell surface receptors and confers signaling events for cell regulation, while apoE expressed endogenously in various cell types regulates cell functions via autocrine and paracrine mechanisms. This review article focuses on lipoprotein transport-dependent and -independent mechanisms by which apoE deficiency or polymorphisms contribute to cardiovascular disease, metabolic disease, and neurological disorders.

Coronary Heart Disease in Type 2 Diabetes Mellitus: Genetic Factors and Their Mechanisms, Gene-Gene, and Gene-Environment Interactions in the Asian Populations

Asians are more susceptible to type 2 diabetes mellitus (T2D) and its coronary heart disease (CHD) complications than the Western populations, possibly due to genetic factors, higher degrees of obesity, insulin resistance, and endothelial dysfunction that could occur even in healthy individuals. The genetic factors and their mechanisms, along with gene-gene and gene-environment interactions associated with CHD in T2D Asians, are yet to be explored. Therefore, the objectives of this paper were to review the current evidence of genetic factors for CHD, summarize the proposed mechanisms of these genes and how they may associate with CHD risk, and review the gene-gene and gene-environment interactions in T2D Asians with CHD. The genetic factors can be grouped according to their involvement in the energy and lipoprotein metabolism, vascular and endothelial pathology, antioxidation, cell cycle regulation, DNA damage repair, hormonal regulation of glucose metabolism, as well as cytoskeletal function and intracellular transport. Meanwhile, interactions between single nucleotide polymorphisms (SNPs) from different genes, SNPs within a single gene, and genetic interaction with environmental factors including obesity, smoking habit, and hyperlipidemia could modify the gene's effect on the disease risk. Collectively, these factors illustrate the complexities of CHD in T2D, specifically among Asians.

Roles of Nutraceuticals and Functional Food in Prevention of Cardiovascular Disease

The chapter provides an overview of cardiovascular disease, a major cause of mortality worldwide. It relates economic and social impacts to the disease, especially in developing countries. One of the approaches to addressing this challenge is increasing awareness within society, through implementation of education programs. It is important for society to understand the types and roles of the risk factors leading to cardiovascular disease. Emphasis is on the role of functional food and nutraceuticals as dietary sources that could prevent development of cardiovascular disease. The chapter highlights roles of nutraceuticals and functional food sources from medical plants, seeds, berries, and tropical fruits in lowering risk factors. Key findings from trials conducted in Asia, China, Europe, and America provide supporting evidence for the importance of functional food to health, and its potential for modifying the level of risk factors related to cardiovascular diseases.

Distinct pro-inflammatory properties of myeloid cell-derived apolipoprotein E2 and E4 in atherosclerosis promotion

Polymorphisms in the apolipoprotein E (apoE) gene are risk factors for chronic inflammatory diseases including atherosclerosis. The gene product apoE is synthesized in many cell types and has both lipid transport–dependent and lipid transport–independent functions. Previous studies have shown that apoE expression in myeloid cells protects against atherogenesis in hypercholesterolemic ApoE^−/− mice. However, the mechanism of this protection is still unclear. Using human APOE gene replacement mice as models, this study showed that apoE2 and apoE4 expressed endogenously in myeloid cells enhanced the inflammatory response via mechanisms independent of plasma lipoprotein transport. The data revealed that apoE2-expressing myeloid cells contained higher intracellular cholesterol levels because of impaired efflux, causing increasing inflammasome activation and myelopoiesis. In contrast, intracellular cholesterol levels were not elevated in apoE4-expressing myeloid cells, and its proinflammatory property was found to be independent of inflammasome signaling and related to enhanced oxidative stress. When ApoE^−/− mice were reconstituted with bone marrow from various human APOE gene replacement mice, effective reduction of atherosclerosis was observed with marrow cells obtained from APOE3 but not APOE2 and APOE4 gene replacement mice. Taken together, these results documented that apoE2 and apoE4 expression in myeloid cells promotes inflammation via distinct mechanisms and promotes atherosclerosis in a plasma lipoprotein transport–independent manner.

Roles of Nutraceuticals and Functional Food in Prevention of Cardiovascular Disease

The chapter provides an overview of cardiovascular disease, a major cause of mortality worldwide. It relates economic and social impacts to the disease, especially in developing countries. One of the approaches to addressing this challenge is increasing awareness within society, through implementation of education programs. It is important for society to understand the types and roles of the risk factors leading to cardiovascular disease. Emphasis is on the role of functional food and nutraceuticals as dietary sources that could prevent development of cardiovascular disease. The chapter highlights roles of nutraceuticals and functional food sources from medical plants, seeds, berries, and tropical fruits in lowering risk factors. Key findings from trials conducted in Asia, China, Europe, and America provide supporting evidence for the importance of functional food to health, and its potential for modifying the level of risk factors related to cardiovascular diseases.

Apolipoprotein E2 accentuates postprandial inflammation and diet-induced obesity to promote hyperinsulinemia in mice

Genetic studies have revealed the association between the ε2 allele of the apolipoprotein E (apoE) gene and greater risk of metabolic diseases. This study compared C57BL/6 mice in which the endogenous mouse gene has been replaced by the human APOE2 or APOE3 gene (APOE2 and APOE3 mice) to identify the mechanism underlying the relationship between ε2 and obesity and diabetes. In comparison with APOE3 mice, the APOE2 mice had elevated fasting plasma lipid and insulin levels and displayed prolonged postprandial hyperlipidemia accompanied by increased granulocyte number and inflammation 2 h after being fed a lipid-rich meal. In comparison with APOE3 mice, the APOE2 mice also showed increased adiposity when maintained on a Western-type, high-fat, high-cholesterol diet. Adipose tissue dysfunction with increased macrophage infiltration, abundant crown-like structures, and inflammation were also observed in adipose tissues of APOE2 mice. The severe adipocyte dysfunction and tissue inflammation corresponded with the robust hyperinsulinemia observed in APOE2 mice after being fed the Western-type diet. Taken together, these data showed that impaired plasma clearance of apoE2-containing, triglyceride-rich lipoproteins promotes lipid redistribution to neutrophils and adipocytes to accentuate inflammation and adiposity, thereby accelerating the development of hyperinsulinemia that will ultimately lead to advanced metabolic diseases.

ApoE isoforms, treatment of diabetes and the risk of coronary heart disease

AIM

To analyze the risk of coronary heart disease in patients with type 2 diabetes mellitus (T2DM) receiving standard medical treatment.

METHODS

We performed a retrospective chart analysis of 269 middle-aged patients (age 45-64 years, mean age, 53.9 ± 5.5 years) with T2DM and without atherosclerotic cardiovascular events who underwent typing to determine their apolipoprotein E (apoE) isoforms. The apoE isoforms were determined using isoelectric focusing, followed by immunoblotting. We retrospectively evaluated the charts of the 269 patients, recorded between their first visit to the hospital (the study's start point, between 1987 and 1992) and the occurrence of an atherosclerotic cardiovascular event (the study's endpoint) or January 2004, whichever came first. The age-adjusted mean values and the prevalences of covariates were calculated to compare the laboratory data among the apoE phenotypes. To investigate the association of risk factors with the incidence of coronary heart disease during the follow-up period, monovariate and multivariate Cox regression models were used.

RESULTS

At enrollment, the mean serum low density lipoprotein (LDL) cholesterol levels were lowest (2.92 ± 0.89 mmol/L) among the subjects with apoE2 (apoE2/2 or apoE2/3) and highest (3.52 ± 0.77 mmol/L) among the subjects with apoE4 (apoE3/4 or apoE4/4). No significant differences in mean age or the percentage of smokers were observed among the three groups. Furthermore, no significant differences were observed in the systolic and diastolic blood pressures, body mass index, HbA1c level or serum triglyceride levels among the three groups. There were 47 cases of coronary heart disease over 3285 person-years of follow-up. An age-adjusted multivariate Cox proportional model identified diabetic retinopathy (hazard ratio, 2.38, 95% CI: 1.28-4.43, P = 0.006), a high systolic blood pressure (hazard ratio, 1.04, 95% CI: 1.02-1.06, P < 0.001) and high HbA1c values (hazard ratio, 1.19, 95% CI: 1.02-1.38, P = 0.0029), but not the LDL cholesterol value at enrollment (hazard ratio, 1.01, 95% CI: 0.97-1.05, P = 0.77) nor the specific apoE isoform, as significant predictors of coronary heart disease.

CONCLUSION

Under standard medical treatment of diabetes, including the control of LDL cholesterol levels, the apoE4 isoform was not associated with coronary heart disease among T2DM patients.

Butyrylcholinesterase K variant and the APOE-epsilon 4 allele work in synergy to increase the risk of coronary artery disease especially in diabetic patients

We have previously shown that butyrylcholinesterase-K (BCHE-K, G1615A/Ala539Thr) variant increases the risk of coronary artery disease (CAD). In addition, we have found that the presence of APOE-epsilon 4 allele augments the risk of CAD in patients with type II diabetes mellitus (T2DM/CAD). Here we explored the concomitant presences of two alleles of the BCHE-K and APOE-epsilon 4 in increasing the risk of CAD or diabetes in T2DM patients with or without CAD and CAD patients without T2DM. This case-control study comprised 631 subjects undergoing their first coronary angiography. They were matched and randomly assigned into four groups: type II diabetic patients with no sign of CAD (T2DM), type II diabetic patients with CAD/ND (T2DM/CAD), CAD patients with no sign of diabetes (CAD/ND), and healthy individuals (NCAD/ND). BCHE-K variant and APOE genotypes were detected by PCR-RFLP and serum lipid level was measured enzymatically. We found that BCHE-K and APOE-epsilon 4 allele act synergistically to increase the risk of CAD in both T2DM, non-diabetic and total CAD (TCAD = T2DM/CAD + CAD/ND) individuals. The level of synergy 1.5 and 1.2 fold are higher in CAD patients (OR = 4.5; P = 0.011) with T2DM than the non-diabetic CAD patients (OR = 3.07; P = 0.024) and TCAD patients (OR = 3.74; P = 0.018), respectively. The CAD subjects with and without T2DM and TCAD patients carrying both APOE-epsilon 4 allele and BCHE-K had significantly lower plasma HDL-C (P values = 0.008, 0.047, and 0.036, respectively) and higher plasma LDL-C (P values = 0.025, 0.048, and 0.04, respectively), than that of the control carriers both APOE-epsilon 4 and BCHE-K. We have found that BCHE-K and APOE-epsilon 4 allele not only act synergistically to increase the risk of CAD, particularly in T2DM subjects in population from western Iran, who have high levels of LDL-C and low levels of HDL-C, suggesting that a specific therapeutic intervention should be considered for these particular groups of patients.

Type 2 diabetes mellitus and its renal complications in relation to apolipoprotein E gene polymorphism

The apolipoprotein E (APOE) epsilon2 allele is reported to be associated with greater risk of renal impairment in type 2 diabetes. Relationships among APOE polymorphisms, renal impairment, and biochemical parameters were explored. A prospective study of 405 consenting Chinese type 2 diabetic patients [mean age +/- standard deviation (SD): 59.2 +/- 10.3 years] without advanced complications at entry was conducted. APOE genotyping and measurement of plasma biomarkers of oxidative stress and antioxidants were performed at entry. HbA1C, plasma glucose, lipids, creatinine, urine albumin/creatinine, and blood pressure were measured at entry and at up to 4 years of follow-up. APOE allelic frequencies were in Hardy-Weinberg equilibrium. Odds ratios of albuminuria at entry and/or during follow-up for different APOE groups were not significantly different. The non-epsilon2 (epsilon3/3, epsilon3/4, epsilon4/4) group had significantly greater plasma ascorbate (51.6 +/- 20.1 mumol/L) than the epsilon2 (epsilon2/2, epsilon2/3) group (44.5 +/- 16.2 mumol/L, P = 0.021), but higher plasma ascorbate levels did not seem to decrease the risk of renal impairment in the non-epsilon2 group. Baseline plasma lipid-standardized alpha-tocopherol levels were least in epsilon2 subjects with persistent albuminuria (3.6 +/- 1.1 mumol/mmol of total cholesterol plus triglycerides, P = 0.008) compared with epsilon2 subjects who had no albuminuria at entry or during follow-up (4.5 +/- 0.8 mumol/mmol of total cholesterol plus triglycerides). The APOE epsilon2 allele does not seem to be associated with increased risk of renal impairment in Chinese type 2 diabetic patients. Plasma lipid-standardized alpha-tocopherol may play a role in determining risk of renal dysfunction in type 2 diabetes.

The presence of apolipoprotein epsilon4 and epsilon2 alleles augments the risk of coronary artery disease in type 2 diabetic patients

OBJECTIVE

It has been suggested that there is a relationship between apolipoprotein E polymorphism and the severity of coronary artery disease in type II diabetes mellitus (T2DM). The current study specifically aimed to examine whether APOE polymorphism in association with serum lipids-lipoproteins level is a risk factor for developing coronary artery disease (CAD) in diabetic patients living in western of Iran.

METHODS

The APOE genotypes were detected by PCR-RFLP in 152 angiographically documented diabetic CAD patients, 262 non-diabetic (ND) individuals with CAD and 300 unrelated controls (normal coronary artery cases without diabetes) and serum lipid level was measured enzymatically.

RESULTS

The APOE-epsilon4 and epsilon2 allele frequencies were significantly higher in the CAD/T2DM and CAD/ND patients than in the control group (p<0.001). Our study demonstrated a significant association between APOE polymorphism and the level of plasma lipids with CAD/T2DM (p=0.001) and CAD/ND (p=0.026) patients. The CAD subjects with T2DM and ND patients carrying APOE-epsilon4 allele had lower plasma HDL-C level (p<0.001), (p=0.008) but had higher plasma LDL-C (p=0.01), total cholesterol (p=0.002), (p=0.03) and TG (p<0.001), (p=0.042) than that of the APOE-epsilon3 carriers, respectively. However, carriers of APOE-epsilon2 had significantly higher levels of plasma TG only. OR of APOE-epsilon4 and epsilon2 alleles in CAD/T2DM and CAD/ND patients were found to be 2.98 (p=0.001),1.86 (p=0.001), 2 (p=0.001), and 1.65 (p=0.001), respectively.

CONCLUSIONS

The major finding of the present case-control study is that T2DM patients carrying APOE-epsilon2 and epsilon4 alleles have a higher risk of developing CAD than ND patients in the western population of Iran, with APOE-epsilon4 being more closely associated with CAD than the APOE-epsilon2 allele. These results indicated that carriers of APOE-epsilon4 allele have a distinct plasma lipids profile and carrier of this allele with low levels of HDL-C and with high levels of LDL-C may be susceptible to CAD and myocardial infarction specially in diabetic patients. This suggests that a therapeutic modality should be considered for these patients.

Apolipoprotein E polymorphism and atherosclerosis

The relationship between apolipoprotein (apo) E and vascular disease has been the subject of a considerable amount of research. However, this relationship is far from clearly defined. This deficiency appears to be due to a multitude of factors. Among these are differences in ethnicity, age (and possibly gender), diagnostic criteria, and environmental factors (eg, diet and smoking) that have contributed to the contradictory findings. Several diseases and their treatment may also influence this relationship. There are also documented interactions between apo E genotypes and other genes or vascular risk factors. One possible clinically relevant application of identifying the apo E genotype could be to assess the response to a particular drug treatment. It may also be that apo E polymorphism will become a good predictor of vascular death (eg, from myocardial infarction or stroke) rather than an indicator of the risk of developing vascular disease but without an acute ischemic event. More research is required to define the place of apo E genotyping in the management of vascular disease in its various forms. Whatever the future brings, the evaluation of apo E genotypes will need to be rapid, cheap, and technically undemanding before this investigation becomes widely available and clinically relevant.

Association of apolipoprotein E polymorphism with myocardial infarction in Greek patients with coronary artery disease

Studies in several populations have indicated that genetic variation at the apolipoprotein E (apoE) structural locus influences the risk of coronary artery disease (CAD) and myocardial infarction (MI). This study aimed at investigating whether apoE polymorphism has an allelic and/or genotypic impact on the risk of MI in Greek patients with CAD. We compared apoE gene polymorphism in a group of patients with angiographically confirmed CAD but not MI [CAD/MI (-)-group, n = 143] and a group of age and sex-matched CAD patients who had experienced a non-fatal Ml [CAD/MI (+)-group, n = 124]. The patients were also compared with a group of healthy younger individuals (n = 240) with no family history of CAD. The apoE genotype distribution differed significantly between the two groups of CAD patients (p = 0.02). The epsilon2 allele was 5.3-fold less frequent in the CAD/ MI (+)-group compared with the CAD/MI (-)-group (1.2% vs. 6.3%, p = 0.01). The frequency of the epsilon2 allele in healthy subjects was 8.1%, which is 6.8-fold higher than in CAD/MI (+)-patients (p = 0.001) and twice as high compared with all CAD patients (p = 0.02). No differences in epsilon4 allele frequencies were observed between CAD/MI (+)- and CAD/MI (-)-patients (10.9% vs. 9.8%), or between patients with CAD and healthy subjects (10.3% vs. 10.2%). In summary, the epsilon4 allele was not found to be associated with an increased risk for CAD or MI. In contrast, a negative association of the epsilon2 allele with Ml was observed among Greek patients with CAD.