Overall, 18% of the study subjects met the definition for metabolic syndrome as defined by National Cholesterol Education Program (NCEP) criteria. A higher proportion of the PI group (32%) had metabolic syndrome at baseline compared with the non-PI (18%) and HIV-negative groups (5%) (P = 0.003 and P < 0.0001, respectively). There were no significant trends over time within any group (P > 0.5).
At baseline, lipid-lowering therapy was being used by 13 subjects in the PI group, seven in the non-PI group, and by none in the HIV-negative group. Of the subjects not using lipid-lowering therapy at baseline, four subjects in the PI group, five of the non-PI group and two subjects in the HIV-negative group started new lipid-lowering therapy during follow-up. Lipid-lowering therapy was used more commonly in the combined HIV-positive groups compared with the HIV-negative group, with no significant difference between the two HIV groups. Use of lipid-lowering therapy was not associated with progression of IMT, although the small numbers of subjects may limit our power to detect an association.
The median rate of change in IMT in the PI group was 0.0096 mm/year, compared with 0.0058 and 0.0085 mm/year in the non-PI and HIV-negative groups, respectively (Fig. 1). The median paired difference in IMT change between the PI and non-PI subjects, 0.0027 mm/year, did not reach statistical significance (P = 0.19). When the HIV-positive groups were combined and compared with the HIV-negative group, the difference in progression was not statistically significant in a matched analysis (P = 0.71).
Univariate conditional logistic regression models for matched pairs data were used to explore the relationship between baseline variables of interest and progression in IMT. Higher total cholesterol (P = 0.02), higher non-HDL cholesterol (P = 0.02), and higher LDL cholesterol (P = 0.04) were individually associated with progression of carotid IMT. Within the groups of HIV-positive subjects, higher nadir CD4 cell count (> 200 versus ≤ 200 cells/μl; P = 0.04) was associated with progression. Multicovariate conditional logistic regression models for matched pairs data further explored the relationship between the covariates identified in the univariate analysis; covariates associated with progression were included (P ≤ 0.10, Table 2). Since total cholesterol, non-HDL cholesterol, and LDL cholesterol are highly correlated with each other, these covariates were considered separately: one model for each of the cholesterol covariates (best model determined by Akaike's information criterion). Considering all subjects, higher LDL cholesterol (P = 0.07) and higher homocysteine (P = 0.08) predicted progression of IMT. Among HIV-positive subjects, higher nadir CD4 cell count (> 200 versus ≤ 200 cells/μl; P = 0.04) and ritonavir use (P = 0.06) predicted progression. The results of the univariate and multicovariate models are summarized in Table 2.
In the overall study population, only higher homocysteine and LDL cholesterol predicted progression of carotid IMT. These observations suggest that, after control for traditional risk factors for atherosclerosis, HIV or treatment-related factors may be less important as contributors to progression of carotid IMT. This does not mean, however, that antiretroviral therapy may not contribute to IMT progression. Although there were few ritonavir users, given any two subjects in the same nadir CD4 cell count category, the subject taking ritonavir at baseline had a 14 times greater risk of progressing (defined as IMT increase of ≥ 0.0122 mm/year) relative to a subject not taking ritonavir.
There are several possible explanations for our negative findings in the context of previous studies. First, our study design allowed us better control for underlying cardiovascular risk factors than prior studies. The subjects enrolled in our study had a low cardiovascular risk profile since the study was focused on isolating the effect of HIV infection or PI use on risk for atherosclerosis. We excluded subjects with diabetes, prior coronary heart disease, or a family history of coronary heart disease because we felt these factors would be difficult to match within triads. It is possible that the risk for progression of atherosclerosis associated with PI therapy is most evident in those patients with a higher underlying cardiovascular risk. Second, the endpoints used vary across different studies; some studies have examined plaque or included additional segments of the carotid. Although other IMT assessment methods may account for the difference between our findings and those of others, studies that have used multiple segment measurements have reported results consistent with our data . It is possible that different factors influence the presence of plaque and carotid IMT. Third, in our longitudinal study, there appeared to be changes in lipid parameters over time within our PI group. Total and non-HDL cholesterol appeared to decline over time in the PI group, possibly because of the addition of lipid-lowering therapy as clinicians became aware of cardiovascular risk. Lipid-lowering therapy was utilized during follow-up by 17 subjects in the PI group and 12 in the non-PI group, which may have contributed to the rate of progression within these groups relative to the HIV-uninfected group, where only two subjects took lipid-lowering therapy. Fourth, although our study was powered to detect a difference of 0.02 mm/year in progression between groups, it is possible that the true difference is smaller and, therefore, would require a larger sample size. Our sample size enabled us to detect a clinically significant difference within the range described in other studies. Lastly, it is possible that the PI drugs used in our cohort have a lesser impact on lipid parameters and cardiovascular risk than the ones used in other studies. While our study suggested a possible relationship between ritonavir exposure and carotid IMT, only 30% of the subjects taking a PI were receiving a ritonavir-containing regimen at baseline. Our study was not designed to detect changes within the PI class and risk for progression of carotid IMT; however, this issue will be important to examine in future studies.
The finding that homocysteine and LDL cholesterol were independently associated with progression of carotid IMT is not surprising. Elevated levels of homocysteine have been implicated as a risk factor for vascular disease, including studies of carotid IMT [38–40]. Cross-sectional studies have suggested an association between PI therapy and elevated homocysteine ; however, results have been inconsistent and confounded by folate levels . In our study, median levels of homocysteine (7.6 μmol/l) in the 34 subjects who reported vitamin supplement use were significantly lower than the median (9.8 μmol/l) for the 88 non-users (P < 0.001). After control for vitamin use, the relationship between homocysteine and progression of IMT remained borderline significant.
In conclusion, in this well-matched cohort study, we did not detect a significant difference in the rate of progression of carotid IMT between PI-treated and non-PI-treated patients and between HIV-infected and matched HIV-uninfected controls. Although our study was small, we had adequate statistical power to detect a 0.01 mm/year difference in the rate of progression of carotid IMT. Larger prospective studies are needed to determine the precise contributions of specific antiretroviral agents to the progression of carotid IMT. As the long-term survival of the HIV-infected population continues to improve, it is important that physicians work closely with patients to reduce modifiable cardiovascular risk factors.
Site investigators: Susan Cahill (University of California, San Diego); Kathy Fox (University of Minnesota); Tomasa Maldonado, Suzette Chafey (University of California, Los Angeles); Kathleen Squires, Angela Grbic, Deborah Johnson (University of Southern California); Jeanne Conley (University of Washington); Cecilia Shikuma, Nancy Hanks (University of Hawaii); Joe Quinn (University of Pennsylvania); Michael Basar (Operational Support: Frontier Science and Technology Research Foundation, Inc.); Mira Madans (Social and Scientific Systems, Inc); Philip W. Anthony (Community Constituency Group of the AACTG).
1. Mulligan K, Grunfeld C, Tai VW, Algran H, Pang M, Chernoff DN, et al
. Hyperlipidemia and insulin resistance are induced by protease inhibitors
independent of changes in body composition in patients with HIV
infection. J Acquir Immun Defic Syndr 2000; 23:35–43.
2. Melroe NH, Kopaczewski J, Henry K, Huebsch J. Lipid abnormalities associated with protease inhibitors
. J Assoc Nurses AIDS Care 1999; 10:22–30.
3. Behrens G, Dejam A, Schmidt H, Balks HJ, Brabant G, Korner T, et al
. Impaired glucose tolerance, beta cell function and lipid metabolism in HIV
patients under treatment with protease inhibitors
. AIDS 1999; 13:F63–F70.
4. Berthold HK, Parhofer KG, Ritter MM, Addo M, Wasmuth JC, Schliefer K, et al
. Influence of protease inhibitor therapy on lipoprotein metabolism. J Intern Me 1999; 246:567–575.
5. Carr A, Samaras K, Burton S, Law M, Freund J, Chisholm DJ, et al
. A syndrome of peripheral lipodystrophy, hyperlipidaemia and insulin resistance due to HIV protease inhibitors
. AIDS 1998; 12:F51–F58.
6. Carr A, Samaras K, Thorisdottir A, Kaufmann GR, Chisholm DJ, Cooper DA. Diagnosis, prediction, and natural course of HIV
-1 protease-inhibitor-associated lipodystrophy, hyperlipidaemia, and diabetes mellitus: a cohort study. Lancet 1999; 353:2093–2099.
7. Mooser V, Carr A. Antiretroviral therapy-associated hyperlipidaemia in HIV
disease. Curr Opin Lipidol 2001; 12:313–319.
8. Friis-Moller N, Weber R, Reiss P, Thiebaut R, Kirk O, d’Arminio Monforte A, et al
. Cardiovascular disease risk factors in HIV
patients: association with antiretroviral therapy. Results from the DAD study. AIDS 2003; 17:1179–1193.
9. Riddler SA, Smit E, Cole SR, Li R, Chmiel JS, Dobs A, et al
. Impact of HIV
infection and HAART on serum lipids in men. JAMA 2003; 289:2978–2982.
10. Grunfeld C, Pang M, Doerrler W, Shigenaga JK, Jensen P, Feingold KR. Lipids, lipoproteins, triglyceride clearance, and cytokines in human immunodeficiency virus infection and the acquired immunodeficiency syndrome. J Clin Endocrinol Metab 1992; 74:1045–1052.
11. Dubé MP. Disorders of glucose metabolism in patients infected with human immunodeficiency virus. Clin Infect Dis 2000; 31:1467–1475.
12. Caron M, Auclair M, Vigouroux C, Glorian M, Forest C, Capeau J. The HIV
protease inhibitor indinavir impairs sterol regulatory element-binding protein-1 intranuclear localization, inhibits preadipocyte differentiation, and induces insulin resistance. Diabetes 2001; 50:1378–1388.
13. Miller KD, Jones E, Yanovski JA, Shankar R, Feuerstein I, Falloon J. Visceral abdominal-fat accumulation associated with use of indinavir. Lancet 1998; 351:871–875.
14. Shor Posner G, Basit A, Lu Y, Cabrejos C, Chang J, Fletcher M, et al
. Hypocholesterolemia is associated with immune dysfunction in early human immunodeficiency virus-1 infection. Am J Med 1993; 94:515–519.
15. Giorgi JV, Liu Z, Hultin LE, Cumberland WG, Hennessey K, Detels R. Elevated levels of CD38+CD8+ T cells in HIV
infection add to the prognostic value of low CD4+ T cell levels: results of 6 years of follow-up. The Los Angeles Center, Multicenter AIDS Cohort Study. J Acquir Immune Defic Syndr 1993; 6:904–912.
16. Henry K, Zackin R, Dubé M, Hammer S, Sprecher D, Currier J. C-Reactive protein levels over time and cardiovascular risk in HIV
-infected individuals suppressed on an indinavir-based regimen: AIDS Clinical Trials Group 5056s. AIDS 2004; 18:2434–2437.
17. Dolan SE, Hadigan C, Killilea KM, Sullivan MP, Hemphill L, Lees RS, et al
. Increased cardiovascular disease risk indices in HIV
-infected women. J Acquir Immune Defic Syndr 2005; 39:44–54.
18. Lau B, Sharrett AR, Kingsley LA, Post W, Palella FJ, Visscher B, et al
. C-reactive protein is a marker for human immunodeficiency virus disease progression. Arch Intern Med 2006; 166:64–70.
19. Holmberg SD, Moorman AC, Greenberg AE. Trends in rates of myocardial infarction among patients with HIV
. N Engl J Med 2004; 350:730–732.
20. Mary-Krause M, Cotte L, Simon A, Partisani M, Costagliola D. Increased risk of myocardial infarction with duration of protease inhibitor therapy in HIV
-infected men. AIDS 2001; 17:2479–2486.
21. Friis-Moller N, Sabin CA, Weber R, d’Arminio Monforte A, El-Sadr WM, Reiss P, et al
. Combination antiretroviral therapy and the risk of myocardial infarction. N Engl J Med 2003; 349:1993–2003.
22. Currier JS, Kendall MA, Zackin R, Henry WK, Alston-Smith B, Torriani FJ, et al
. Carotid artery
intima–media thickness and HIV
infection: traditional risk factors overshadow impact of protease inhibitor exposure. AIDS 2005; 19:927–933.
23. Hodis H, Mack W, Lobo R, Shoupe D, Sevanian A, Mahrer P, et al
. Estrogen in the prevention of atherosclerosis: a randomized, double-blind, placebo-controlled trial. Ann Intern Med 2001; 135:939–953.
24. Hodis H, Mack W, LaBree L, Selzer RH, Liu CR, Liu CH, et al
. The role of carotid arterial intima–media thickness in predicting clinical coronary events. Ann Intern Med
25. Selzer RH, Hodis HN, Kwong-Fu H, Mack WJ, Lee PL, Liu CR, et al
. Evaluation of computerized edge tracking for quantifying intima-media thickness
of the common carotid artery
from B-mode ultrasound images. Atherosclerosis 1994; 111:1–11.
26. Selzer RH, Mack WJ, Lee PL, Kwong-Fu H, Hodis HN. Improved common carotid elasticity and intima–media thickness measurements from computer analysis of sequential ultrasound frames. Atherosclerosis 2001; 154:185–193.
27. Lehmann E. Nonparametrics: Statistical Methods based on Ranks. San Francisco: Holden-Day; 1975.
28. Seminari E, Pan A, Voltini G, Carnevale G, Maserati R, Minoli L, et al
. Assessment of atherosclerosis using carotid ultrasonography in a cohort of HIV
-positive patients treated with protease inhibitors
. Atherosclerosis 2002; 162:433–438.
29. Mercie P, Thiebaut R, Lavignolle V, Pellegrin JL, Yvorra-Vives MC, Morlat P, et al
. Evaluation of cardiovascular risk factors in HIV
-1 infected patients using carotid intima–media thickness measurement. Ann Med 2002; 34:55–63.
30. Maggi P, Serio G, Epifani G, Fiorentino G, Saracino A, Fico C, et al
. Premature lesions of the carotid vessels in HIV
-1-infected patients treated with protease inhibitors
. AIDS 2000; 14:F123–F128.
31. Depairon M, Chessex S, Sudre P, Rodondi N, Doser N, Chave JP, et al
. Premature atherosclerosis in HIV
-infected individuals: focus on protease inhibitor therapy. AIDS 2001; 15:329–334.
32. Chironi G, Escaut L, Gariepy J, Cogny A, Teicher E, Monsuez JJ, et al
. Brief report: carotid intima–media thickness in heavily pretreated HIV
-infected patients. J Acquir Immune Defic Syndr 2003; 32:490–493.
33. Jerico C, Knobel H, Calvo N, Sorli ML, Guelar A, Gimeno-Bayon JL, et al
. Subclinical carotid atherosclerosis in HIV
-infected patients: role of combination antiretroviral therapy. Stroke 2006; 37:812–817.
34. Mercie P, Thiebaut R, Aurillac-Lavignolle V, Pellegrin JL, Yvorra-Vives MC, Cipriano C, et al
. Carotid intima–media thickness is slightly increased over time in HIV
-1-infected patients. HIV
Med 2005; 6:380–387.
35. Hsue PY, Lo JC, Franklin A, Bolger AF, Martin JN, Deeks SG, et al
. Progression of atherosclerosis as assessed by carotid intima–media thickness in patients with HIV
infection. Circulation 2004; 109:1603–1608.
36. de Saint Martin L, Vandhuick O, Guillo P, Bellein V, Bressollette L, Roudaut N, et al
. Premature atherosclerosis in HIV
positive patients and cumulated time of exposure to antiretroviral therapy (SHIVA study). Atherosclerosis 2006; 185:361–367.
37. Mangili A, Gerrior J, Tang AM, O’Leary DH, Polak JK, Schaefer EJ, et al
. Risk of cardiovascular disease in a cohort of HIV
-infected adults: a study using carotid intima-media thickness
and coronary artery calcium score. Clin Infect Dis 2006; 43:1482–1489.
38. Homocysteine Studies Collaboration. Homocysteine and risk of ischemic heart disease and stroke: a meta-analysis. JAMA
39. Ford ES, Smith SJ, Stroup DF, Steinberg KK, Mueller PW, Thacker SB. Homocyst(e)ine and cardiovascular disease: a systematic review of the evidence with special emphasis on case–control studies and nested case–control studies. Int J Epidemiol 2002; 31:59–70.
40. Willinek WA, Ludwig M, Lennarz M, Holler T, Stumpe KO. High-normal serum homocysteine concentrations are associated with an increased risk of early atherosclerotic carotid artery
wall lesions in healthy subjects. J Hypertens 2000; 18:425–430.
41. Bernasconi E, Uhr M, Magenta L, Ranno A, Telenti A. Homocysteinaemia in HIV
-infected patients treated with highly active antiretroviral therapy. AIDS 2001; 15:1081–1082.
42. Uccelli MC, Torti C, Lapadula G, Labate L, Cologni G, Tirelli V, et al
. Influence of folate serum concentration on plasma homocysteine levels in HIV
-positive patients exposed to protease inhibitors
undergoing HAART. Ann Nutr Metab 2006; 50:247–252.