In multivariate analyses, HIV-infected women had significantly lower CIMT than HIV-uninfected women (adjusted mean difference in CIMT = −12 μm, 95% confidence interval, −23 to −2 μm, P = 0.02), after adjustment for age, race, education, income level, family history of MI, current smoking, alcohol consumption, opiate use, injection drug use, and study site (Table 2). This association was attenuated and not statistically significant after additional adjustment for metabolic variables including history of diabetes, lipid levels and hyperlipidemic therapy, BMI, and blood pressure. In men, CIMT did not differ significantly between HIV-infected and HIV-uninfected groups, although the point estimates suggested that as in women, HIV-infected men appeared to have lower CIMT. Carotid lesions were not significantly associated with HIV infection in either sex**.
No association was observed between the most recent CD4+ T-cell count and mean CIMT (data not shown). Multivariate-adjusted analyses indicated a significant 70–100% increase in the prevalence of carotid lesions among HIV-infected individuals with CD4+ T-cell count below 200 cells/μl, as compared with HIV-uninfected individuals (Table 3). Results were similar after additional adjustment for metabolic CVD risk factors (Table 3) and after excluding from the analysis HIV-infected individuals who had never been treated with antiretroviral therapies (data not shown). In additional analyses, which incorporated historical data on CD4+ T-cell count and AIDS, neither the lowest measured CD4+ T-cell count nor prior AIDS defining illness was associated with CIMT or lesions. The most recent or peak HIV viral load measurement was not associated with CIMT or lesions.
Compared with women, men had longer median cumulative duration of antiretroviral drug exposure (including protease inhibitors, NNRTI, and NRTI) (Table 4). Among men, we observed an association between longer duration of protease inhibitor exposure and increased prevalence ratio for carotid lesions (adjusted prevalence ratio per 2 years of protease inhibitor use = 1.11, 95% confidence interval, 1.00–1.24, P = 0.05), although this association was not significant after further adjustment for metabolic risk factors (P = 0.08) (Table 4). In contrast to the results in men, no significant association between duration of protease inhibitor use and carotid lesions was found in women. Further, NRTI and NNRTI use were not significantly associated with carotid lesions among women or men, and no associations were observed between duration of antiretroviral therapy and mean CIMT (data not shown).
Analyses conducted among all study participants showed significant associations between subclinical carotid atherosclerosis and age, African–American race/ethnicity, smoking, diabetes, BMI, blood pressure, and lipids (Table 5). The presence of carotid lesions was associated with increased CIMT among both HIV-infected women (adjusted ΔCIMT = 34 μm, 95% confidence interval, 16–56, P < 0.001) and HIV-infected men (adjusted ΔCIMT = 46 μm, 95% confidence interval, 22–73, P < 0.001).
This study did not confirm the presence of increased mean CIMT among HIV-infected as compared with HIV-uninfected individuals, as has been previously reported [5,6]. However, we did find that the frequency of carotid lesions (IMT > 1.5mm) was significantly increased among HIV-infected men and women with evidence of more advanced HIV disease. Compared with HIV-uninfected persons, the adjusted prevalence of carotid lesions was 70–100% higher in HIV-infected persons who had a recent CD4+ T-cell count measurement below 200 cells/μl. These findings are consistent with prior evidence that low CD4+ T-cell count may increase the risk of CVD in HIV-infected populations [5,30]. Prior studies have also suggested increased risks of incident CVD events with each additional year of combination antiretroviral therapy, particularly for regimens that include protease inhibitors [1,2]. Our data, based on a surrogate marker for CVD, provide little support for the conclusion that increased atherosclerotic vascular disease is associated with longer duration of protease inhibitor therapy. There was no evidence of such an association among women, and among men a possible association between protease inhibitor use and carotid lesions was weak and not significant in multivariate models. This study among two large population-based HIV cohorts has several strengths, including extensive data on an array of potential confounders and metabolic risk mediators, and the inclusion of HIV-uninfected comparison groups who were recruited using comparable methods and from similar venues as the HIV-infected individuals and who also had HIV risk behaviors (e.g., injection drug use, receipt of blood products, high-risk sexual practices).
Our finding that low CD4+ T-cell count is a vascular risk factor among HIV-infected individuals is supported by previous observational data  and by secondary analyses from the FIRST/CPCRA 058 clinical trial . In the Strategies for Management of Antiretroviral Therapy (SMART) trial, HIV-infected individuals randomized to episodic antiretroviral therapy (e.g., ‘drug conservation’ arm) guided by the CD4+ T-cell count had reduced CD4+ T-cell count and increased risk of major CVD events as compared with those randomized to continuous therapy . The main results from SMART appear to be consistent with our finding that immunosuppression was associated with increased atherosclerosis, although subsequent analyses from SMART found that high (not low) CD4+ T-cell count was a predictor of increased CVD risk in the drug-conservation arm . The association between low CD4+ T-cell count may plausibly be explained by chronic inflammation  or specific pathogen exposures  in immunosuppressed HIV-infected individuals.
Prior data have suggested that use of antiretroviral therapy may increase CVD risk among HIV-infected adults [1,2], although this is not entirely consistent with other studies, some of which were based on subclinical rather than clinical CVD [8–10]. The Data Collection on Adverse Events of Anti-HIV Drugs (DAD) Study Group , a large collaborative study of HIV-infected cohorts, reported an adjusted 16% increase in the relative hazard of incident MI with each additional year of protease inhibitor based combination antiretroviral treatment. The present study did not find consistent evidence for an association between antiretroviral therapies and atherosclerosis. There was no association whatsoever between the use of protease inhibitors or other antiretroviral therapies and atherosclerosis in women. Among men, a possible association between longer duration of protease inhibitor based therapy and increased risk of carotid artery lesions was observed, but this finding was nonsignificant in adjusted models. The possible reasons why the association between antiretroviral therapies and atherosclerosis would differ by sex are unclear. This may reflect random subgroup differences; poorer drug adherence or less aggressive antiretroviral therapy among women as compared with men; the younger age of women as compared with men in the study; or lower susceptibility to atherosclerosis among women than among men. However, the lack of clear and consistent findings in this study is evidence against the hypothesis that antiretroviral medications are an important cause of vascular disease.
Although we found evidence that men and women with low CD4+ T-cell count have increased occurrence of atherosclerotic lesions, the present study also suggested that overall carotid wall thickness (i.e., mean CIMT) was significantly lower among HIV-infected women than among HIV-uninfected women (with a similar trend in men). A possible explanation may be that HIV infection is associated with favorable levels of some vascular risk factors including total cholesterol, LDL-C, blood pressure, and BMI [14,19,34,35]. Consistent with this proposed mechanism, we found that the association between HIV infection and reduced CIMT was attenuated through adjustment for metabolic variables. We note that our observation of both more frequent carotid lesions and lower mean CIMT in the HIV-infected population is strikingly similar to the findings from carotid ultrasound studies of other inflammatory and immune-related conditions. For example, women with systemic lupus erythematosus  and rheumatoid arthritis  have increased prevalence of carotid lesions, but reduced mean CIMT, compared with healthy controls. Histologic studies of carotid plaques in HIV-infected individuals show extensive inflammatory infiltration of the vascular wall, more similar to arteritis than to classical atheroma , which is further evidence of an atypical vascular disease phenotype in the HIV-infected population.
The cross-sectional nature of the present study is an important limitation because use of antiretroviral medications, CD4+ T-cell cell counts, HIV viral loads, and CVD risk mediators such as lipid levels are dynamic variables that change over time. Although vascular measurements were only performed at a single timepoint, we did make use of extensive longitudinal data on medication use and other HIV-related variables collected as part of the WIHS and MACS core protocols. This is an observational study, and it is possible that associations of HIV infection, medications, and other HIV-related variables with subclinical carotid atherosclerosis may not accurately represent causal relationships. As this study was conducted after the initial reports linking specific antiretroviral therapies with metabolic disorders and CVD, channeling bias may have affected our results. This would have lead to an underestimation of the risks associated with these therapies, if they tended to be avoided in patients known to be at high vascular risk. As noted, the HIV-uninfected comparison groups had similar characteristics and were recruited using similar methods as the HIV-infected groups, albeit it is possible that relevant behaviors, comorbidities, social factors, healthcare access, and other health-related practices may not have been balanced between the groups. For technical reasons related to a concurrent study of coronary calcium , men younger than 40 years were excluded from the study, which is a limitation, as this group represents a large fraction of the HIV-infected population. Likewise, our study excluded individuals with preexisting CVD, who may be susceptible to adverse effects of HIV infection or therapies. Finally, this was a study of subclinical atherosclerosis measures rather than hard CVD events. Although the carotid ultrasound protocol is a well validated measure of atherosclerosis and predictor of clinical cardiovascular events, other mechanisms such as increased coagulation or impaired endothelial function may also lead to vascular events in HIV-infected populations .
In conclusion, we found that HIV-infected women and men with a low CD4+ T-cell count had a significantly increased prevalence of subclinical carotid artery lesions. Use of antiretroviral therapies had no consistent association with atherosclerosis in this study. These findings emphasize that the association of antiretroviral therapy use and other HIV-related variables with atherosclerosis needs to be studied further.
Data in this study were collected by the Women's Interagency HIV Study (WIHS) Collaborative Study Group with centers (Principal Investigators) at New York City/Bronx Consortium (Kathryn Anastos); Brooklyn, New York (Howard Minkoff); Washington, District of Columbia Metropolitan Consortium (Mary Young); The Connie Wofsy Study Consortium of Northern California (Ruth Greenblatt); Los Angeles County/Southern California Consortium (Alexandra Levine); Chicago Consortium (Mardge Cohen); Data Coordinating Center (Stephen Gange). MACS centers (Principal Investigators) at The Johns Hopkins University Bloomberg School of Public Health (Joseph B. Margolick, Lisa Jacobson), Howard Brown Health Center and Northwestern University Medical School (John Phair), University of California, Los Angeles (Roger Detels), and University of Pittsburgh (Charles Rinaldo). The WIHS is funded by the National Institute of Allergy and Infectious Diseases (UO1-AI-35004, UO1-AI-31834, UO1-AI-34994, UO1-AI-34989, UO1-AI-34993, and UO1-AI-42590) and by the National Institute of Child Health and Human Development (UO1-HD-32632). The study is co- funded by the National Cancer Institute, the National Institute on Drug Abuse, and the National Institute on Deafness and Other Communication Disorders. Funding is also provided by the National Center for Research Resources (MO1-RR-00071, MO1-RR-00079, MO1-RR-00083). The MACS is funded by the National Institute of Allergy and Infectious Diseases, with additional supplemental funding from the National Cancer Institute and the National Heart, Lung and Blood Institute. UO1-AI-35042, 5-MO1-RR-00722 (GCRC), UO1-AI-35043, UO1-AI-37984, UO1-AI-35039, UO1-AI-35040, UO1-AI-37613, UO1-AI-35041. Also supported by NIH/NHLBI grant 1R01HL083760-01 (to R.C.K.) and grant M01RR-023942-01 from the National Center for Research Resources (NIH/NCRR). Conception of the study: Kaplan, Kingsley, and Gange. Collection of study data: Kingsley, Lazar, Anastos, Tien, and Hodis. Statistical analyses: Kaplan, Gange, Benning, and Jacobson. Interpretation of study data: Kaplan, Kingsley, Gange, Benning, Jacobson, Lazar, Anastos, Tien, Sharrett, and Hodis. Drafting of the manuscript: Kaplan. Critical revision of the manuscript: Kaplan, Kingsley, Gange, Benning, Jacobson, Lazar, Anastos, Tien, Sharrett, and Hodis. Acquisition of study funding: Kaplan, Kingsley, Gange, Jacobson, Anastos, and Hodis.
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