Human Immunodeficiency Virus infection, asymptomatic atherosclerosis, and inflammation: A candidate gene study

Abstract

Acquired Immunodeficiency Syndrome (AIDS) was identified more than 30 years ago. The challenges for the clinicians and Human Immunodeficiency Virus (HIV)-infected individuals have changed over the years. Nowadays, viral replication is suppressed with Antiretroviral Therapy (ART). ART prevents AIDS related complications and decreases morbidity and mortality in HIV-infected subjects. However, mortality rates among HIV-infected individuals remain 3-15 times higher than those observed in the general population. The excess of mortality observed among HIV-infected subjects can be partly attributed to HIV-related illnesses. However, more than half of the deaths observed among HIV-infected patients treated with ART are due to co-morbid disorders related to aging. It is nowadays considered that HIV-infected patients are aging prematurely. Multiple hypotheses have been made to explain this premature aging. Chronic systemic inflammation, reduced vascular endothelial reactivity, increased endovascular hypercoagulability and immune activation have been suggested as possible mechanisms. These processes are more prevalent in HIV-infected patients (treated and non-treated) than in the general population. Therefore, HIV-infected patients are prone to develop age-related diseases or co-morbidities. Among these co-morbidities, HIV-infected patients present increased cardiovascular risk, more prevalence of traditional cardiovascular risk factors and early onset of the atherosclerotic disease. However, the underlying mechanisms are not known yet. HIV-infection has been suggested as a potential contributor to atherosclerosis. Given the unique effects of HIV on the immune system, it is plausible to consider that HIV infection itself could be involved in atherosclerosis. The link between both may be the result of a generalized increase in the activity of the inflammatory pathways, especially the cytokine network. It is possible that these alterations in the inflammatory system may modulate the risk of atherosclerosis in HIV-infected individuals. These alterations may be caused by DNA sequence variants and/or by changes in the expression patterns of inflammatory pathway genes induced by the HIV-infection or by ART. The purpose of this study was to investigate the possible association between genetic variants and gene expression of genes involved in inflammation and cardiovascular risk measures in a cohort of HIV-infected subjects. The associations identified between genetic variants in the studied genes and CVR measures were modest. This suggests that SNPs may play a minor role and not be the underlying cause of the increased CVR observed in HIV-infected individuals. HIV-related CVD is probably influenced by non-genetic factors such as traditional CVR factors, the HIV-virus itself and by ART. The gene expression of the investigated genes is altered in HIV-related atherosclerotic disease. The findings regarding 5-LO pathway are the most relevant of this study. This part of the inflammatory pathway is important in the metabolism of lipids, which is closely related to atherosclerosis. To our knowledge this is the first study describing the implication of the 5-LO pathway in HIV-related atherosclerosis. Genetic variants in two key genes of this pathway (ALOX5 and ALOX5AP) were associated with HIV-related atherosclerosis. Although no differences were found in their gene expression, ART introduction reduced ALOX5AP gene expression levels, but not to the levels observed in uninfected controls justifying the importance of early ART initiation. Importantly, the 5-LO pathway interlinks lipid metabolism and inflammation and it is altered in HIV-infection. Thus, 5-LO pathway dysfunction may be critical in HIV-related atherosclerosis development. In summary, the findings reported in this thesis show that there is an intricate relationship among HIV-infection, antiretroviral treatment, atherosclerotic disease and the inflammatory pathway.