HIV-infected individuals have higher risk of developing atherosclerosis and myocardial infarction as observed in population-based observational studies.1,2 In addition to conventional cardiovascular risk factors,1,3 factors related to HIV infection, antiretroviral therapy (ART), and chronic inflammation, play significant roles in promoting atherosclerosis, although the pathogenic mechanisms have yet to be fully elucidated.1,4–7 At present, little data exist regarding the burden, risk factors, and pathogenic mechanisms for cardiovascular diseases among the HIV-infected individuals in Asian populations.8 Such information is urgently needed because of the large and growing number of patients put on treatment in the region. Extrapolation of data from other ethnic groups is considered inappropriate, as rates of atherosclerosis progression and the magnitude of impact of various contributory factors may be different.9,10
In this prospective, longitudinal study, we aim to investigate the progression and factors associated with atherosclerosis in an Asian HIV cohort. Clinical characteristics, metabolic profiles, inflammatory biomarkers, and body compositions were studied, and changes of carotid intima media thickness (cIMT) over time were measured. Such data can improve our understanding on the cardiovascular risks in the HIV-infected Asian patients and allow early evaluation and intervention of high-risk patients.
Study Design and Subjects
A prospective, longitudinal study was performed among adults attending the HIV Metabolic Clinic at the Prince of Wales Hospital, Hong Kong, a university-affiliated hospital receiving territory-wide referrals for screening and clinical management of metabolic diseases in HIV-infected individuals. The inclusion criteria were age ≥18 years, confirmed HIV infection, and Asian ethnicity. Exclusion criteria were acute HIV infection and refusal to consent. Informed, written consent was obtained from each study subject. Ethics approval was obtained from the institutional review boards of the Hospital Authority of Hong Kong and The Chinese University of Hong Kong.
Clinical Data Collection and Measurement of Metabolic Parameters and Inflammatory Biomarkers
A standardized research tool was designed to collect information on demographics, comorbidities, duration of HIV infection, medication history including ART exposure, CD4 count, and plasma viral load. Blood pressure, body weight, and waist circumference were recorded. The 10-year cardiovascular disease risk was calculated using Framingham risk score (FRS). Dyslipidemia was defined by total cholesterol level ≥6.2 mmol/L, high-density lipoprotein (HDL) cholesterol level ≤0.9 mmol/L, triglyceride level ≥2.3 mmol/L, or use of lipid-lowering drugs.5 All clinical assessments were performed at baseline and at 24 months; new cardiovascular events and clinical outcomes were recorded.
Peripheral blood samples were taken after a ≥8-hour fast for the measurement of total, HDL and LDL (low-density lipoprotein) cholesterol, triglyceride, LDL particle size (by lipoprotein electrophoresis), apolipoproteins A1 and B (by immunoassay), glucose, and insulin (by chemiluminescence) concentrations. Homeostasis model assessment of insulin resistance was calculated as fasting insulin concentration (mU/L) × fasting plasma glucose (mmol/L)/22.5. Based on literature findings,11 plasma concentrations of selected cytokines/chemokines and biomarkers for inflammation were measured, including: high-sensitive C reactive protein (IMMULITE high-sensitive CRP chemiluminescence immunoassay, Diagnostic Products Corp., Los Angeles, CA); CCL2/MCP-1, interleukin-6 (IL-6), interleukin-10 (IL-10), tumor-necrosis factor -α, soluble vascular cell adhesion molecule-1, and soluble intercellular adhesion molecule-1 (cytometric bead array reagent kit, BD Pharmingen, CA; with flow cytometry, FACSCalibur flow cytometer, BD Bioscience, CA; or ELISA reagent kits, R & D Systems, Minneapolis, MN)12; soluble phospholipase A2, myeloperoxidase, and adiponectin (using ELISA reagent kits from Cayman Chemical Company, MI; Bender Medsystems, Vienna, Austria; and Panomics, Inc., CA, respectively).13–15
Dual energy X-ray absorptiometry was performed using a Hologic QDR 4500A fan beam densitometer (Hologic, Inc., Bedford, MA), to measure total body fat, fat-free mass, regional fat in arms, legs, and trunk (in grams). Trunk fat and limb fat percentages were calculated using standard methods.16
cIMT was measured to provide estimates on atherosclerosis extent and progression.17 B-mode ultrasound examinations were performed with an Acuson 128XP/10 mainframe with a 7-MHz scanning frequency linear array transducer, or an ATL 3000 mainframe with a high-resolution, linear array scanner (medium frequency 7.5 MHz). All ultrasound systems used similar gain and depth settings. All scans were performed by an experienced physician after a predetermined, standardized scanning protocol for the right and left carotid arteries using images of the far wall of the distal 10 mm of the common carotid arteries. Three scanning angles, with the image focused on the posterior wall, were recorded from the angle showing the greatest distance between the lumen-intima interface and the media-adventitia interface. All scans were recorded on super-VHS videotape for subsequent off-line analysis by the same investigator, blinded to patients' clinical data, using an automatic computerized edge-detection and measurement system. The reported cIMT value represented the mean of measurements at both left and right carotid arteries. A carotid plaque was considered to be present when cIMT was >1.2 mm at any site. Annual rate of change of cIMT was calculated as the difference in cIMT divided by the interval (in years) between measurements.18
Statistical Analyses and Definitions
Chi square test with continuity correction, and the Student's t or Mann–Whitney U tests were applied for univariate comparisons according to data distribution. We analyzed variables that might predict greater progression of cIMT (defined as increment above the “upper tertile”) in logistic regression models; the unadjusted odds ratio (OR) and 95% confidence interval (95% CI) were reported for each of the explanatory variables. Predictive models constructed based on these significant variables, either alone or in combination, were then evaluated by the area under the curve of receiver operating characteristic analyses to determine their discriminative power on cIMT progression. Six models were eventually considered: (1) FRS alone; (2) limb fat percentage alone; (3) limb fat percentage and adiponectin; (4) limb fat percentage and LDL subclass pattern B; (5) limb fat percentage, LDL subclass pattern B, and adiponectin; and (6) limb fat percentage, LDL subclass pattern B, adiponectin, and FRS. In general, AUC ≥0.90, 0.80 to <0.90, 0.70 to <0.80, and <0.70 indicate “excellent,” “good,” “fair,” and “poor” performance, respectively.19 All probabilities were 2-tailed, and a P value of <0.05 was considered to indicate statistical significance. Statistical analysis was performed using PASW Statistics software, version 18.0.
Clinical Characteristics, Body Composition, Metabolic Profiles and Inflammatory Biomarkers
Sixty-one HIV-infected adult patients were recruited. Fifty-seven completed 24 months' follow-up (2 patients died, and 2 withdrew from the study). The mean age of this cohort was 49.8 ± 11.4 years, 89% men, 97% ethnic Chinese (remainder were South/South-east Asians), and 53% ever-active smokers. Median duration of HIV infection was 7 (Interquartile Range/IQR, 4.0–14.5) years, and 53% had history of AIDS-defining conditions; 97% were receiving ART at time of study entry (subsequently 100%). Among these, 61% were protease inhibitor-based, and 38% nonnucleoside reverse transcriptase inhibitor-based regimens; median duration of treatment was 4.8 (IQR 2.0–11.9) years. Mean CD4 count of patients was 484 ± 215 cells/μL, and 92% had undetectable plasma viral load at study entry. Thirty percent had hypertension, 39% had diabetes mellitus, and 85% had dyslipidemia. Baseline median (IQR) cIMT was 0.790 (0.705–0.890) mm and plaques were present in 47.5%. At 24 months, median (IQR) annual rate of change in cIMT was +0.0075 (0.0000–0.0163) mm/yr, and 18.8% developed new plaque among those who had none at baseline. In one patient, >70% stenosis at the internal carotid artery was diagnosed at baseline, who subsequently underwent angioplasty and stenting. There were 2 deaths in the HIV-infected cohort (3.3%); 1 patient had sudden cardiac death and the other died of metastatic cancer.
Factors Associated With Carotid IMT Progression
We found that lower limb fat percentage (unadjusted OR 0.877, 95% CI: 0.798 to 0.963, P = 0.006), lower adiponectin level (unadjusted OR 0.332, 95% CI: 0.119 to 0.926 per log increase, P = 0.035), and “LDL cholesterol subclass pattern type B” (unadjusted OR 2.824, 95% CI: 0.895 to 8.906, P = 0.077) were associated with greater progression in cIMT (Table 1), whereas duration of HIV infection and ART, nadir and baseline CD4 count, class of antiretroviral regimen, body weight, weight circumference, blood pressure, total/LDL/HDL-cholesterol, triglyceride, apolipoprotein A1/B, glucose, and insulin resistance were not.
Using area under the curve of receiver operating characteristic analyses, the combination of limb fat percentage, “LDL cholesterol subclass pattern type B” and adiponectin level best predicted cIMT progression, with an AUC value of 0.80 (95% CI: 0.68 to 0.91, P < 0.001) (Fig. 1). The FRS, when applied alone, had a poor predictive value (AUC 0.52, 95% CI: 0.36 to 0.67, P = 0.834); and it did not further improve prediction when added to the above combination.
Our study showed that Asian HIV-infected individuals receiving ART had progression of atherosclerosis at a magnitude similar to other ethnic groups. We found that limb fat percentage, LDL cholesterol subclass pattern and adiponectin level were potentially useful predictive tools to identify at-risk individuals.
To our knowledge, this is the first study to document progression of atherosclerosis in Asian/Chinese HIV patients with carotid imaging, thus provide important data to guide subsequent, larger-scale research. Our results showed that annual progression of cIMT was 0.0075 mm/yr among Asian/Chinese HIV-infected individuals. This was similar in magnitude to studies performed in other ethnic groups.20,21 Our results add that IMT progression can be evident in the older patient group with metabolic conditions (mean age of this cohort was 50 ± 11 years), which is a rapidly expanding population in the ART era.
Multiple population-based studies have reported higher risks of myocardial infarction and stroke among HIV patients, which could not be fully explained by conventional cardiovascular risk factors alone.1,2,22,23 Assessments based on conventional risk factors such as FRS often underestimate the cardiovascular risks in HIV-infected individuals.1 Our findings suggest that the predictive performance of FRS may be even worse in Chinese subjects.24 Instead, we identified lipodystrophy (lower limb fat percentage), small LDL particle size (“subclass pattern B”), and hypoadiponectinemia were associated with atherosclerosis progression in this population, and that their combination provided best predictive accuracy.
Body fat composition changes or lipodystrophy in HIV patients have been linked to risk of cardiovascular diseases.25,26 In several cross-sectional studies, increased carotid IMT are reported among patients with lipodystrophy, although longitudinal data on progression is limited.22,27–29 Alterations in adipocyte biology lead to local and systemic proinflammatory changes and excessive free fatty-acid release through lipolysis; and these complex processes may in turn promote insulin resistance and atherosclerosis.26,29 Smaller LDL particles more readily infiltrate arterial tissues, and have lower affinity for LDL receptors and higher oxidative susceptibility.30 The “lipid triad” of smaller LDL particle size, low HDL cholesterol, and elevated triglycerides can lead to premature atherosclerosis and coronary disease.30,31 Hypoadiponectinemia has been linked to diabetes, hypertension, and cardiovascular diseases in obese individuals, and shown to correlate with IMT progression in different ethnic populations, including Chinese.32–34 Adiponectin exerts cardioprotective effects via antiapoptotic and antioxidative mechanisms, counteraction of endothelial dysfunction, and enhancement of tissue insulin sensitivity.32 Lower adiponectin level may indicate visceral fat accumulation,35 a pathogenic process known to be significant in Asian populations.36 In HIV patients, adiponectin production is reduced because of interplay of direct viral effect, antiretrovirals, and lipodsytrophy.26 Our finding suggests that it might contribute to atherosclerosis progression, which is supported by a recent study showing increased coronary artery stenosis in HIV-infected men with hypoadiponectinemia.35
The strength of this study include its longitudinal design, and comprehensive evaluation of key metabolic, inflammatory, and body composition parameters, and their effects on carotid IMT changes. It is limited by a small sample size and a relatively short duration of follow-up, as such, cardiovascular events/outcomes and the impacts of different ART regimens21 cannot be adequately addressed. Although the older age and presence of risk factors in this cohort may somewhat limit the generalizability of our results (patients were from a HIV Metabolic Clinic), with the aging HIV population worldwide and their frequent metabolic comorbidities, longitudinal data in such patient group are of practical importance.37
In conclusion, our study showed that HIV-infected, ART-treated Asian/Chinese patients have significant degree of atherosclerosis progression. Limb fat percentage, LDL-particle size, and adiponectin level, but not the conventional risk assessment alone, can help to identify at-risk patients for early evaluation and intervention.
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