Carotid artery intima–media thickness
Common and bifurcation CIMTs were 0.64 (0.59–0.70) and 0.74 (0.65–0.82) mm, respectively (Figs 1 and 2). In univariate analyses, CCA and bifurcation CIMT were associated with classic CVD risk factors (nominal P < 0.05). Higher CIMT was associated with older age, non-Hispanic ethnicity, medium/high FRS, higher SBP and DBP, higher total cholesterol, LDL cholesterol and non-HDL cholesterol, longer smoking history, higher fasting glucose (CCA only), higher measures of body size and composition (BMI, weight, height, waist circumference, limb fat, trunk fat, visceral adipose tissue, subcutaneous adipose tissue, total abdominal adipose tissue, total body fat, total body lean mass and upper extremity fat), lower estimated glomerular filtration rate (eGFR) and presence of metabolic syndrome. Higher CIMT also was associated with higher levels of total and small LDL particles, small HDL particles (bifurcation only), lower pro-inflammatory HDL and higher leptin. There was some evidence of associations with HIV-1 disease; lower baseline HIV-1 RNA was associated with higher CIMT, prior AIDS diagnosis (CCA only) and longer time since HIV diagnosis (bifurcation only). Of note, significant associations between CIMT and CD4 cell count were not observed. A longer smoking history was associated with increasing age (P = 0.021).
In multivariable analyses, independent associations with increasing CCA CIMT (Fig. 2a) were observed for older age, larger body size and higher levels of small LDL particles as well as non-Hispanic black race/ethnicity (compared with White). Independent associations with increasing bifurcation CIMT were similar (Fig. 2b) and were observed for older age, larger body size and LDL cholesterol, with positive trends as indicated. In a separate model, moderate/high FRS was independently associated with CCA (P = 0.004) but not bifurcation (P = 0.100) CIMT (data not shown).
Carotid artery lesions
There were 27 (8%) individuals who had carotid artery lesions (Fig. 2c). Individuals with lesions tended to be older (48 versus 34 years, P < 0.001) and were more likely to have moderate/high FRS (41 compared with 11%, P < 0.001); 44% of those with lesions were at least 50 years old (P < 0.001, data not shown) and 41% with lesions had moderate/high FRS of at least 6% (P < 0.001, data not shown). In univariate analyses, presence of carotid artery lesions was associated (nominal P < 0.05) with older age, higher SBP and DBP, presence of metabolic syndrome, higher small LDL particles, higher levels of visceral adipose tissue, higher levels of interleukin-6 and lower HIV-RNA. In adjusted analyses, age, level of interleukin-6, presence of metabolic syndrome and lower HIV-1 RNA level remained independently associated with the presence of lesions (Fig. 2c).
Brachial artery flow-mediated dilation and diameter
Median FMD was 4.5 (3.0–6.3)% (Figs. 1 and 3). In univariate analyses, higher maximum FMD (indicative of lower CVD risk) was associated (nominal P < 0.05) with younger age, lower FRS, higher measures of body composition (BMI, trunk fat, upper extremity fat, total body fat), shorter height, smaller brachial artery diameter, higher levels of interleukin-6 and higher HIV-1 RNA. In multivariable analyses (Fig. 3a), independent associations with higher FMD were observed for smaller brachial artery diameter, increasing weight and decreasing height. In a separate model, moderate/high FRS was independently associated with lower FMD (P = 0.035, data not shown).
Given the strong dependence of FMD on brachial artery diameter, the latter associations were explored in detail. In univariate analyses, larger diameter (indicative of a higher CVD risk) was associated (nominal P < 0.05) with older age, male sex, lower baseline HIV-1 RNA, higher baseline CD4 cell count, medium/high FRS, higher SBP and DBP, metabolic syndrome, higher measures of body size and composition (BMI, weight, height, mid-waist circumference, trunk fat, total body fat, total body lean mass, visceral adipose tissue, subcutaneous adipose tissue and total abdominal adipose tissue), higher glucose, higher creatinine, higher levels of small LDL and HDL particles, and lower levels of pro-inflammatory HDL and interleukin-6. Of note, the association of brachial artery diameter and total body lean mass was much stronger (ρ = 0.47, P < 0.001) than its associations with height, weight, BMI and waist circumference (ρ = 0.23–0.35) and any fat depot (ρ = 0.04–0.14). Lean body mass was strongly associated with height (ρ = 0.63) and weight (ρ = 0.80) (both P < 0.001). In multivariable analyses (Fig. 3b), independent associations with larger brachial artery diameter were observed for increasing age, weight, male sex, fasting glucose and lower HIV-1 RNA level.
In a contemporary cohort of HIV-infected ART-naive individuals without advanced HIV disease, ultrasonographic measures of CVD risk were more strongly associated with traditional risk factors such as ageing, body size and lipoprotein measurements, rather than CD4 cell count, viral replication, inflammatory markers and cytokines. Several aspects of this study and findings are notable and important for understanding CVD risk in contemporary patients with HIV infection. This is the first large study to evaluate CVD risk among HIV-infected, but treatment-naive individuals ready to initiate ART. Given the complex interplay between HIV infection and treatment on CVD risk factors and CVD risk, understanding the associations with arterial disease prior to ART initiation is important for understanding why patients with HIV infection appear to be at an increased CVD risk compared with HIV-negative individuals. This is the only study of its kind to simultaneously evaluate CIMT and FMD along with multiple, putative markers of CVD risk, including advanced lipoprotein testing, inflammatory markers, immune activation and HIV disease activity. Its multicentre nature with strict quality control enhanced the reliability of the data and our ability to identify associations. A medium or high 10-year predicted CVD risk was associated with increased CIMT in the common and bifurcation carotid artery segments, more carotid artery lesions, lower brachial artery FMD and larger brachial artery diameter, each of the ultrasound measures of increased CVD risk, demonstrating the internal validity of our findings.
By demonstrating that modifiable risk factors such as increased body size and lipoprotein measures are the major associates of increased CIMT, carotid artery lesions and impaired FMD, these parameters can be targeted for early preventive lifestyle and, if necessary, pharmacological interventions to reduce future CVD risk in patients initiating ART. Indeed, a recent randomized clinical trial demonstrated that a focused dietary intervention significantly reduced LDL cholesterol in HIV-infected patients beginning their first ART regimen , the magnitude of which would be expected to significantly reduce long-term CVD risk. AIDS Clinical Trials Group Study A5078, a longitudinal, observational investigation showed that in cross-section, traditional risk factors overshadowed the impact of HIV protease inhibitor exposure, and that progression of CCA CIMT was similar among age and risk factor matched individuals with and without HIV infection [23,24]. Our results confirm and extend these findings, showing that traditional CVD risk factors, but not markers of inflammation and HIV disease activity, are strongly associated with bifurcation CIMT, carotid artery lesions and brachial artery FMD in a low CVD risk population.
Despite a wide range of CD4 cell counts among our participants, CD4 cell counts were not independently associated with any ultrasonographic marker of CVD risk. This may be due to the relatively small sample size, as within the larger sample sizes of the Multicenter AIDS Cohort Study and the Women's Interagency HIV Study, a CD4 cell count of less than 200 cells/μl was independently associated with increased carotid artery lesion prevalence and with increased carotid arterial stiffness in HIV-infected versus HIV-uninfected individuals [17,25]. However, these individuals were older than those in our study and most were ART-experienced. It has been hypothesized that starting ART in individuals with higher cell counts would reduce CVD risk .
The effects of HIV viral load on arterial function and disease are less clear. Lower HIV loads were weakly associated with carotid artery lesions, but neither CIMT measure. Higher viral loads were associated with smaller brachial artery diameters, but not worse FMD. Active infection may invalidate the observational association between smaller arteries and lower CVD risk, perhaps because of sympathetic activation and attendant vasoconstriction . Indeed, higher viral loads were associated with higher heart rates. In ACTG Study A5152s, a randomized clinical trial of three ART regimens in treatment-naive patients, effective ART improved FMD, reduced heart rates and increased brachial artery diameters . Improvement in FMD was related to the reduction in HIV load, indicating that treating HIV infection improves endothelial function and relieves vasoconstriction that accompanies untreated HIV infection . In the Study to Understand the Natural History of HIV/AIDS in the ERA of Effective Therapy, suppression of plasma HIV-1 RNA viral load to less than 400 copies/ml was associated with decreased progression of CCA CIMT over a 2-year period . The possibility of increased CVD risk with treatment interruption was observed in the SMART study . Therefore, treatment of HIV infection may reduce CVD risk, as does treatment of CVD risk factors.
Limitations of this study include the absence of an HIV-negative or HIV treatment-experienced control group and the young age of the participants, who on average, were at a low CVD risk. Although this is the largest study, to date, describing CVD risk among treatment-naive HIV-infected individuals, it still is relatively small and underpowered for detecting modest risk factor associations with our CVD risk markers, especially considering the high intraindividual and/or measurement variability of some of the markers we studied. Also, this was a cross-sectional analysis; longitudinal follow-up, which is in progress, may be even more informative.
Given these limitations, the absence of significant associations between inflammation and the arterial measurements in this study does not exclude a role for inflammation and immune activation as contributors to CVD risk in patients with HIV. The association between increasing interleukin-6 levels and the prevalence of carotid artery lesions was the only independent association between any inflammatory marker and adipocytokine with a vascular marker that we evaluated. The meaning of this finding is unclear; however, higher interleukin-6 levels have been linked to increased mortality in individuals with HIV. It is possible that other unmeasured markers of inflammation or immune activation may be more strongly associated with vascular disease. In recent studies, CD4 and CD8 T-cell activation and CD8 T-cell senescence were associated with increased carotid artery lesion prevalence and increased carotid arterial stiffness in HIV-infected individuals [18,29].
Finally, this study sheds insight into the interaction between brachial artery size and FMD. FMD is lower in individuals with larger arteries; however, it is unclear whether this is merely a mathematical function of brachial artery size being in the denominator of the formula for calculating FMD, or whether it represents pathophysiology related to larger patients having risk factors associated with increasing body size and adiposity. Contemporaneous measurement of body composition helped us show that lean body mass was associated much more strongly with brachial artery size than any fat depot or adiposity measure. Lean body mass was associated with height and weight, indicating that the association between increased brachial artery size and CVD risk is not due to adiposity; arteries are larger in bigger people with greater muscle mass.
Participants in this study reflect contemporary patients with HIV initiating their first ART regimen. They have notably less advanced HIV disease than in historical cohorts, even more recent ART-naive cohorts such as in ACTG Study A5224s . Contemporary patients starting ART not only have higher CD4 cell counts and a shorter duration of HIV infection but also have a different burden of traditional risk factors than historical cohorts. They tend to be younger, have lower (albeit still excessive) rates of smoking and lower triglycerides, but they are heavier and have higher BMIs. The changing demographics and CVD risk burden of HIV-infected patients initiating ART further complicates efforts to understand predictors of CVD risk in patients with HIV.
In a large, contemporary cohort of HIV-infected ART-naive individuals, ultrasonographic measures of CVD risk were more strongly associated with traditional risk factors than CD4 cell count, viral replication and inflammatory markers. Increasing age, body size and lipoprotein measures were most consistently associated with CIMT and brachial artery FMD. Efforts to prevent excessive weight gain and improve lipoproteins are likely to reduce CVD risk in HIV-infected ART-naive patients.
J.H.S. was responsible for and contributed to the conception, design, obtained funding, conduct of study, data analysis, draft of manuscript and critical revision of manuscript.
T.B.B. contributed to thedesign, conduct of study and critical revision of manuscript.
H.J.R. contributed to the design, conduct of study, data analysis and critical revision of manuscript.
Y.C. was responsible for conduct of study, data analysis and critical revision of manuscript.
M.Y. was responsible for conduct of study and critical revision of manuscript.
E.L.-B. was responsible for conduct of study and critical revision of manuscript.
G.A.McC. was contributed to design, conduct of study and critical revision of manuscript.
M.P.D. wcontributed to conduct of study and critical revision of manuscript.
R.L.M. wacontributed toconduct of study and critical revision of manuscript.
H.N.H. was responsible for design, conduct of study and critical revision of manuscript.
J.S.C. was responsible for and contributed to the conception, design, obtained funding, conduct of study, data analysis and critical revision of manuscript.
The project described was supported by Award Number U01AI068636 from the National Institute of Allergy and Infectious Diseases and supported by National Institute of Mental Health (NIMH), and the National Institute of Dental and Craniofacial Research (NIDCR). This research also was supported by NIH grants HL095132, HL095126, AI 068636, AI068634, AI69471 and AI56933 from the National Heart, Lung, and Blood Institute and the National Institute of Allergy and Infectious Diseases.
The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Allergy and Infectious Diseases or the National Institutes of Health.
The following ACTUs participated in this study: 103 – Beth Israel Deaconess Medical Center ACTG CRS 6; 107 – Brigham and Women's Hospital ACTG CRS 5; 201 – Johns Hopkins Adult AIDS CRS 11; 401 – NY University HIV/AIDS CRS 11; 601 – UCLA CARE Center CRS 8; 603 – Harbor-UCLA Med. Ctr. CRS 24; 801 – UCSF AIDS CRS 4; 1001 – University of Pittsburgh CRS 4; 1101 – University of Rochester ACTG CRS 4; 1108 – AIDS Care CRS 8; 1201 – USC CRS 30; 1401 – University of Washington AIDS CRS 18; 1601 – Duke University Medical Cener Adult CRS 3; 2101 – Washington U CRS 23; 2301 – Ohio State University AIDS CRS 9; 2401 – Univ. of Cincinnati CRS 28; 2501 - Case Western Reserve CRS 12; 2503 – MetroHealth CRS 1; 2701 – Northwestern University CRS 23; 2702 – Rush University Medical Center ACTG CRS 8; 3201 – UNC AIDS CRS 15; 3652 – Vanderbilt Therapeutics CRS 17; 5802 – Ponce de Leon Center CRS 3; 6101 – University of Colorado Hospital CRS 40; 31473 – Houston AIDS Research Team CRS 10; and 31477 – New Jersey Medical School – Adult Clinical Research Ctr. CRS 9.
The assistance of the ACTG Statistical and Data Analysis Center and the ACTG Optimization of Antiretroviral Therapy Committee, as well as the clinical trials support from Social and Scientific Systems, Inc. are appreciated.
Conflicts of interest
Regarding the content of this article, there are no conflicts of interest to disclose. The disclosures of each author are reported separately.
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Keywords:© 2013 Lippincott Williams & Wilkins, Inc.
atherosclerosis; carotid arteries; endothelial function; HIV; inflammation