Analysis of the Association Between Apolipoprotein E Polymorphism and Cardiovascular Risk Factors in an Elderly Population with Longevity

Helena Augustin Schwanke, Ivana Beatrice Mânica da Cruz, Ney Furhmann Leal, Rosane Scheibe, Yukio Moriguchi, Emílio Hideyuki Moriguchi

Objective – To establish the allelic and genotypic frequencies related to apolipoprotein E (ApoE) polymor- phism and association of the genotypes with risk factors and cardiovascular morbidity in an elderly population with longevity.

An increasing number of genetic polymorphisms has been associated with the susceptibility to cardiovascular di- seases, such as the apolipoprotein E (ApoE) gene. Studies have shown that the E4 allelic variant is associated with the mechanisms of development of atherosclerosis, dementia, and, more recently, with the risk of bone fractures 1-5.

Methods - We analyzed 70 elderly patients aged 80 years or more who were part of the Projeto Veranópolis. We used the gene amplification technique through the poly- merase chain reaction-restriction fragment length poly- morphism (PCR-RFLP) and cleavage with the restriction enzyme Hha I to identify the ApoE genotypes. The most fre- quent genotypes were compared considering biological variables and cardiovascular risks and morbidity.

The first genetic studies in cardiology was that of the association between ApoE polymorphism and coronary artery disease 6. Apolipoprotein E participates in the me- tabolism of lipoproteins and plays a significant role in the transport of the cholesterol molecule [1- ligand of the LDL receptor; 2 - activator of enzymes like hepatic lipase; 3 – he- patic production of very low density lipoprotein (VLDL)] 7,8. In addition, this protein is related to immunoregulation and neurobiological routes (neuronal repair, remodeling, and protection). Apolipoprotein E is mainly synthesized in the liver (> 90%), but also in other tissues, such as the bowel, brain, lungs, kidneys, and macrophages, and secreted as a glycosylated protein. Apolipoprotein E polymorphism is located in the long arm of chromosome 19. Point changes are the molecular features of this polymorphism in the nitrogen bases, causing the replacement of 1 amino acid in the 112 and l58 positions of the peptide chain. The 3 most common isoforms are as follows: E2 (cysteine/cysteine), E3 (cystei- ne/arginine), and E4 (arginine/arginine). Of the 3 isoforms, E3 is the most frequently reported in the literature in the ge- neral population and E4 is rare in the centenarian popula- tion. The allelic frequency of ApoE varies in the populations because the polymorphism of its locus ranges from 16% to 53% according to the population. Therefore, different phe- notypes of ApoE exist, and they result from 6 genotypes as follows: 3 homozygous (E2E2, E3E3, and E4E4), and 3 hete- rozygous (E2E3, E3E4, and E2E4). Apolipoprotein E poly- morphism changes protein both in its structure and func- tion. The E2 isoform generates a protein whose binding to the LDL receptor is defective (in the rare situation of ho-

Results - The frequencies of the E2, E3, and E4 alleles were 0.05, 0.84, and 0.11, respectively, and of the genotypes were as follows: E3E3 (0.70), E3E4 (0.22), E2E3 (0.06), and E2E2 (0.02). Individuals with the E3E4 had a mean age greater than those with the E3E3. No association was observed between the genotypes and the variables analy- zed, except for obesity, which was associated with the E3E3 genotype. Individuals with the E3E4 genotype had high levels of LDL-cholesterol and fibrinogen as compared with those with the E3E3 genotype.

Conclusion - The results suggest that the E4E4 genoty- pe may be associated with early mortality. A balance between the protective or neutral factors and the cardiovascular risk factors may occur among the individuals with different geno- types, attenuating the negative effects of the E4 allele.

Faculdade de Medicina da Pontifícia Universidade Católica do Rio Grande do Sul Mailing address: Ivana Beatrice Mânica da Cruz - Instituto de Geriatria e Gerontologia da PUCRS - Av. Ipiranga, 6690 - 3o andar - 90610-000 Porto Alegre, RS, Brazil - E-mail: emoriguchi@pucrs.br English version by Stela Maris C. e Gandour

mozygosis and in the presence of other factors, such as diabetes mellitus, it may generate the type III Fredrickson dyslipidemia or dysbetalipoproteinemia). On the other hand, the E4 isoform generates a protein whose affinity for the LDL receptor is 4 times greater than that for LDL itself 1-5,9. Popula- tion studies have shown that the serum levels of LDL-choles- terol (LDL-c) and apolipoprotein B (ApoB) are higher in in- dividuals with the E4 allele, intermediate in individuals with the E3 allele, and lower in individuals with the E2 allele 10,11.

A few studies have also associated the presence of the E2 allele with greater longevity, because a higher fre- quency of that allele is observed in nonagenarians and cen- tenarians 12,13. These results, however, have not been repro- duced in all the populations studied, and they seem not to follow a universal pattern. Excluding the possible methodolo- gical problems associated with this type of study reviewed by Marian 5 and Mansur 6, one of the hypotheses to be con- sidered is that in chronic and degenerative diseases with a multifactorial origin, the set of genetic variations of a popu- lation associated with the social and environmental surro- undings of the same population and with the processes re- lated to biogerontology (biology of aging) can be responsi- ble for the varied results, which have been found so far. Therefore, additional investigations about the impact of certain genetic polymorphisms, about the traditional risk factors for the development of cardiovascular diseases, and especially the coronary arteries and aging are required in individuals with longevity (> 80 years).

individuals of Italian heritage within that age bracket living in the municipality of Veranópolis in 1998.