Author: Michael Bukrinsky
Position: Professor
Institution: George Washington University
E-mail: mtmmib@gwumc.edu
Additional Authors: Dmitri Sviridov (Baker Heart Research Institute)
Submitted Date: November 30, 2006
Published Date: December 1, 2006
This comment was originally posted as a “Reader Response” on the publication date indicated above. All Reader Responses are now available as comments.

In their Perspectives article published in PLoS Medicine [1], Carr and Ory provide a fair review of our recent paper [2]. However, we believe their comment puts too much emphasis on the role of low high-density lipoprotein (HDL) cholesterol levels as a cause of atherosclerosis in HIV-infected patients. While HDL cholesterol levels are reduced in untreated HIV infection [3], and defects in reverse cholesterol transport (RCT) that we reported may well be a contributing factor to this abnormality, initiation of anti-retroviral therapy (ART) restores HDL levels [4]. Although dyslipidemia developing with prolonged use of anti-HIV drugs again lowers HDL cholesterol and in addition raises very low density lipoprotein (VLDL) and low density lipoprotein (LDL) levels [5], it is unlikely that HIV infection contributes significantly to these effects. Indeed, most of HDL comes from liver and intestine, which are responsible for maintaining plasma HDL levels [6], but neither hepatocytes nor enterocytes are infected by HIV. Also, the number of HIV-infected cells in treated patients is relatively low to account for any general changes in concentration of plasma lipoproteins.

We suggest a different model that provides a simple connection between HIV-induced impairment of the cellular step of RCT and pathogenesis of atherosclerosis. We propose that RCT-defective HIV-infected macrophages contribute to development of atherosclerosis in HIV patients by converting into foam cells and initiating plaque formation in the vessel wall. Indeed, specific inactivation of ABCA1 in macrophages has been shown to induce atherosclerosis in a mouse model independently from plasma HDL level [7]. Plaque formation through this mechanism can begin even on the background of normal HDL but would be greatly accelerated by dyslipidemia, a condition observed in ARV-treated HIV patients. Given that even fully suppressive HAART does not eliminate long-lived productive reservoirs of the virus and that macrophages are a likely potential component of these reservoirs [8], long-lived HIV-infected macrophages may contribute to atherosclerotic plaque formation long after initiation of HAART. Consistent with this hypothesis, it was found that majority of cardiovascular events in HIV-infected patients are 'one plaque' events [9].

Therefore, several lines of evidence indirectly implicate HIV-infected macrophages in pathogenesis of atherosclerosis in HIV patients. Future studies will determine the role of HIV-induced RCT impairment in this process and are expected to provide an understanding of connection between HIV infection and atherosclerosis and to identify novel treatment targets for both diseases.

References

1. Carr A, Ory D (2006) Does HIV Cause Cardiovascular Disease? PLoS Med 3: e496.
2. Mujawar Z, Rose H, Morrow MP, Pushkarsky T, Dubrovsky L, Mukhamedova N, Fu Y, Dart A, Orenstein JM, Bobryshev YV, Bukrinsky M, Sviridov D (2006) Human Immunodeficiency Virus Impairs Reverse Cholesterol Transport from Macrophages. PLoS Biol 4: e365.
3. Grunfeld C, Pang M, Doerrler W, Shigenaga JK, Jensen P, Feingold KR (1992) Lipids, lipoproteins, triglyceride clearance, and cytokines in human immunodeficiency virus infection and the acquired immunodeficiency syndrome. J Clin Endocrinol Metab 74: 1045-1052.
4. van der Valk M, Kastelein JJ, Murphy RL, van Leth F, Katlama C, Horban A, Glesby M, Behrens G, Clotet B, Stellato RK, Molhuizen HO, Reiss P (2001) Nevirapine-containing antiretroviral therapy in HIV-1 infected patients results in an anti-atherogenic lipid profile. Aids 15: 2407-2414.
5. Crook MA, Mir N (1999) Abnormal lipids and the acquired immunodeficiency syndrome: is there a problem and what should we do about it? Int J STD AIDS 10: 353-6.
6. Singaraja RR, van Eck M, Bissada N, Zimetti F, Collins HL, Hildebrand RB, Hayden A, Brunham LR, Kang MH, Fruchart JC, Van Berkel TJ, Parks JS, Staels B, Rothblat GH, Fievet C, Hayden MR (2006) Both hepatic and extrahepatic ABCA1 have discrete and essential functions in the maintenance of plasma high-density lipoprotein cholesterol levels in vivo. Circulation 114: 1301-1309.
7. Aiello RJ, Brees D, Bourassa PA, Royer L, Lindsey S, Coskran T, Haghpassand M, Francone OL (2002) Increased atherosclerosis in hyperlipidemic mice with inactivation of ABCA1 in macrophages. Arterioscler Thromb Vasc Biol 22: 630-637.
8. Pomerantz RJ (2003) Reservoirs, sanctuaries, and residual disease: the hiding spots of HIV-1. HIV Clin Trials 4: 137-143.
9. Stewart S, Wilkinson D, Becker A, Askew D, Ntyintyane L, McMurray JJ, Sliwa K (2006) Mapping the emergence of heart disease in a black, urban population in Africa: the Heart of Soweto Study. Int J Cardiol 108: 101-108.