Cardiovascular disease (CVD) deaths are an important cause of mortality in HIV-infected patients. As a prediction of cardiovascular outcome, carotid intima media thickness (CIMT) has been shown as an independent predictor of CVD events . We read with great interest the study by Stein et al. in which they report that treatment-naïve HIV-infected individuals randomized to an initial antiretroviral therapy (ART) regimen including atazanavir/ritonavir (ATV/r) experienced slower progression of CIMT than those assigned darunavir/ritonavir (DRV/r) or raltegravir. Accordingly, we conducted retrospective analysis of the longitudinal Hawaii Aging with HIV Cardiovascular Study to assess the relationship of ATV/r on CIMT in a cohort of HIV-infected individuals on stable ART. Additionally, the baseline plasma biomarkers and total serum bilirubin were analyzed for differences between participants currently receiving ATV/r compared with participants not on ATV/r. Group differences between participants receiving ATV/r versus those not taking ATV/r were assessed using multivariable regression.
A total of 62 study participants enrolled in the Hawaii Aging with HIV Cardiovascular Study had available CIMT measures at baseline and year 2. A total of 11 study participants (18%) were receiving ATV/r and 51 (82%) were not receiving ATV/r (non-ATV/r). In the non-ATV/r group, 55% were on non-nucleoside reverse transcriptase inhibitors, 18% were on a protease inhibitors other than ritonavir as a booster, and none were on an integrase inhibitor. Entry criteria for the cohort required study participants to be on stable ART for at least 3 months, and 82% of these study participants were virologically suppressed with a plasma HIV RNA level of less than 50 copies/ml on ATV/r and 82% were suppressed on non-ATV/r. The median CD4 cell count was 370 cells/μl (Q1: 249, Q3 : 612) for the ATV/r group and 502 (349, 660) cells/μl for the non-ATV/r group (P = 0.10). Baseline median Framingham Risk Score were: ATV/r 0.03 (0.01, 0.14), non-nucleoside reverse transcriptase inhibitors 0.04 (0.02, 0.14), and protease inhibitors 0.08 (0.04, 0.20) (P = 0.53). Median duration on ART did not differ between the ATV/r and non-ATV/r groups, 14.2 years (6.4, 14.6) versus 12.6 years (7.8, 16.2), respectively. The median increase in CIMT over 2 years was 0.009 mm (0.005, 0.022) for the ATV/r group compared with 0.022 mm (0.013, 0.034) in the non-ATV/r group (P < 0.001). ATV/r use continued to be associated with slower CIMT progression compared with the non-ATV/r group after adjusting for age, sex, hypertension, diabetes mellitus, current smoking status, low-density lipoprotein cholesterol, and systolic blood pressure (P = 0.012) (Table 1).
The rate of CIMT change was similar to the findings presented by the A5260 study. Interestingly, we also found a significant correlation between increasing baseline total serum bilirubin level and reduced CIMT progression (Table 1). The A5260 study reported a significant reduction in CIMT with bilirubin as a binary cut-off point of 0.6 mg/dl at weeks 4 and 24, with similar trends seen for higher cut-off points. Bilirubin has an antioxidant effect as well as an association with reduced inflammation . The antioxidant and anti-inflammatory effects of bilirubin metabolism have been reported with lower serum IL-6, C-reactive protein (CRP), and serum amyloid P (SAP) level [4–6]. In our study, log total bilirubin levels correlated with log SAP (r = −0.329, P = 0.009) and log CRP (r = −0.288, P = 0.023), but not with other biomarkers such as IL-6, matrix metalloproteinase-9, tissue plasminogen activator inhibitor-1, soluble intercellular adhesion molecule, soluble vascular cell adhesion molecule, myeloperoxidase, monocyte chemoattractant protein-1, acute phase protein (Serum amyloid A, vascular endothelial growth factor). Total bilirubin was also negatively correlated with the intermediate (CD14++CD16+) monocyte subset (r = −0.267, P = 0.048). None of these baseline biomarkers or intermediate monocyte subsets were associated with change in CIMT . The article by Stein et al. did not report on the correlations between bilirubin, biomarkers, and monocyte subsets. Although there were no direct associations with biomarkers and monocyte subsets, we still speculate a potential role of total bilirubin in slowing CIMT progression. Hereditary conditions such as Gilbert syndrome, where serum bilirubin levels in these individuals are elevated, are reported to have much lower rates of ischemic heart disease compared with the general population . A cardioprotective role of bilirubin, heme oxygenase, and UDP-glucuronosyltransferase has been speculated . This retrospective study is limited by its small sample size and nonrandomized design. Despite these differences, our findings have important implications and suggestions for future research. Our data demonstrated similar CIMT findings with ATV/r as in the A5260 study. The exact mechanism of ATV/r on CIMT progression remains unclear, but total serum bilirubin may play a potential role in modifying CVD risk.
This work was supported by the National Institutes of Health grants U54RR026136, U54MD007584, R21 N5080656-01A1, and R01HL095135.
Conflicts of interest
There are no conflicts of interest.
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