Early Indicators of Atherosclerosis in People with HIV Are Linked to Inflammation, Improve with Antiretroviral Therapy

		SUMMARY: Several studies presented at the 17th Conference on Retroviruses and Opportunistic Infections (CROI 2010) last month in San Francisco looked at atherosclerosis and its precursors in people with HIV. Elevated levels of inflammation biomarkers and indicators of stepped-up T-cell activation were associated with thickening of artery walls, reduced dilating ability, and greater artery stiffness. Effective antiretroviral therapy (ART), however, appeared to slow atherosclerosis progression.

By Liz Highleyman

A growing body of evidence indicates that inflammation is associated with development of non-AIDS conditions such as cardiovascular disease in people with HIV.

Atherosclerosis ("hardening of the arteries") is a progressive inflammatory process in which artery walls thicken and lose their elasticity as they fill up with plaques made up of accumulated lipids, immune cells, calcium, and scar tissue fibers. Over time, this leads to impaired blood flow, which can ultimately result in a heart attack or stroke.

Carotid Artery Thickening

A research group at the University of California San Francisco (UCSF) including Steven Deeks, Priscilla Hsue, and Peter Hunt have extensively studied links between inflammation, immune activation, and cardiovascular risk factors. They presented multiple studies at CROI.

In an oral presentation (abstract 125), Hsue reported that people with HIV experience more rapid progression of atherosclerosis than uninfected individuals, especially as measured in a specific part of the carotid artery known as the bifurcation region.

Intima-media thickness (IMT), a commonly used early indicator of atherosclerosis, refers to thickness of the inner layers of the artery wall, where plaques accumulate. IMT is typically measured using ultrasound in the carotid arteries in the neck, but results can vary depending on whether a measurement is taken: in the main artery before it divides, in 1 of its 2 branches (the internal and external carotid), or at the bifurcation or "fork" where they split.

Lipids and other material collect more readily at the bifurcation due to changes in blood flow dynamics, and therefore it may be more susceptible to inflammation and show thickening sooner. However, the bifurcation region (sometimes referred to as the carotid bulb) is harder to measure, so researchers more often look at other sites.

The study included 263 HIV positive participants in the SCOPE cohort at San Francisco General Hospital; most (72%) were on antiretroviral therapy, 47% had suppressed viral load, the median current CD4 cell count was 433 cells/mm3, and the median nadir (lowest-ever) level was 150 cells/mm3. In addition, the investigators looked at 22 participants from a cohort of "elite controllers" who are able to maintain undetectable viral load without ART. There were also 40 HIV negative control subjects.

HIV positive participants had lower LDL (bad) cholesterol at baseline, but higher levels of triglycerides and the inflammation biomarker high-sensitivity C-reactive protein (CRP) compared with HIV negative control subjects. They were also more likely to smoke (68% vs 53%) and had more than twice the prevalence of high blood pressure, diabetes, and prior heart disease or strokes, but these differences did not reach statistical significance.

Results

	At baseline, IMT was greater among HIV positive people than HIV negative individuals, both overall (0.86 vs 0.71 mm) and in each carotid region.
	After a median 2 years of follow-up, overall IMT progression was significantly more rapid in HIV positive group (0.046 vs 0.012 per year).
	The difference remained significant after adjusting for traditional cardiovascular risk factors such as smoking.
	Among HIV positive participants, IMT progression was most evident in the bifurcation region, followed by the internal carotid and then the common carotid.
	The difference in progression between HIV positive and HIV negative people depended on measurement site:
	Largest difference in the bifurcation region (0.074 vs 0.013 mm/year, a significant difference); Smaller but still significant difference in the internal carotid (0.046 mm/year vs none); Not a statistically significant difference in the common carotid (0.074 vs 0.013 mm/year).
	Among people on suppressive ART and elite controllers, IMT progression was significantly greater only in the bifurcation region.
	CRP levels were more closely correlated with IMT progression in the bifurcation region.
	After adjusting for traditional risk factors and HIV status, CRP was independently associated with IMT progression in the bifurcation region.
	However, traditional cardiovascular risk factors were more predictive in other carotid regions.

Based on these findings, the researchers concluded, "HIV-related inflammation contributes to increased risk of atherosclerosis in the setting of HIV." They recommended that, "future studies of sub-clinical atherosclerosis in HIV-infected individuals should focus on the bifurcation region as a site of marked disease predilection."

Flow-mediated Dilation

In a related poster presentation (abstract 708), Hsue and colleagues looked at another indicator of atherosclerosis progression, flow-mediated dilation. This technique assesses the function of the endothelial lining of arteries by measuring how much an artery (typically the brachial artery in the upper arm) expands in response to changes in blood flow.

This study included 139 HIV positive people from the same SCOPE cohort who had suppressed viral load on ART, as well as 32 HIV negative control subjects. About half were smokers and about 40% had high blood pressure.

Results

	People with HIV had significantly lower -- that is, worse -- endothelium-dependent flow-mediated dilation compared with uninfected people (4.1% vs 5.2%).
	This finding remained significant after adjusting for traditional cardiovascular risk factors.
	Use of abacavir (Ziagen, also in the Epzicom and Trizivir coformulations) was associated with impaired flow-mediated dilation.
	Protease inhibitor exposure and overall duration of ART, however, were not significant predictors of impaired dilation.
	CD4 count was also not significantly linked to impaired flow-mediated dilation.
	HIV positive people on ART had a higher median CRP level than HIV negative individuals.
	CRP was independently associated with HIV infection after adjusting for traditional cardiovascular risk factors.
	In the HIV positive group, higher CRP was a stronger predictor of impaired flow-mediated dilation than older age, but the opposite was true for HIV negative people.

In this study the investigators concluded, "CRP -- a measure of inflammation -- was more predictive of impaired endothelial function than traditional risk factors in this population."

"These findings suggest that even patients doing well on combination antiretroviral therapy (as defined by viral load) may be at increased risk for cardiovascular disease, and that chronic inflammation in the setting of treated HIV disease likely contributes to this increased risk," they continued. "Our findings also argue for an independent role of direct drug toxicity in driving early cardiovascular disease."

T-Cell Activation and Senescence

Robert Kaplan, along with members of the UCSF team and others (abstract 709) looked at the relationship between carotid IMT and carotid distensibility (ability to expand) and immune activation in HIV positive and at-risk HIV women from the Women's Interagency HIV Study (WIHS) cohort.

The study included 28 HIV positive women on ART with undetectable viral load, 46 HIV positive women on ART but with detectable virus, 41 untreated HIV positive women, and 43 HIV negative women.

T-cell status was determined according to the proportion of T-cells carrying the CD38+ and HLA-DR+ immune activation markers or the CD57+ and/or CD28- senescence markers. Senescence refers to exhaust of a cell's ability to proliferate.

Results

	CD4 and CD8 T-cell activation was significantly greater among HIV positive women (of all treatment or response statuses) compared with HIV negative women.
	Women on ART with suppressed HIV had significantly lower T-cell activation than either treated but detectable or untreated HIV positive women.
	However, even after a median 6 years on ART, T-cell activation did not fall to the level of the HIV negative women.
	Greater T-cell activation was associated with lower CD4 cell counts.
	Among HIV positive women, increased levels of CD4 and CD8 T-cell activation and senescence markers were independently associated with reduced carotid distensibility.
	Greater CD4 and CD8 T-cell activation were associated with carotid lesions (defined as > 1.5mm carotid IMT) as measured in the right common carotid artery, internal carotid artery, and carotid bifurcation.
	In a multivariate analysis adjusting for age and ART status, T-cell status was an independently predicted higher risk of IMT lesions:
	CD4 T-cell activation: hazard ratio (HR) 1.6, or 60% increased risk; CD8 T-cell activation: HR 2.0, or twice the risk; CD8 T-cell senescence: HR 1.9.
	Among HIV negative women, however, there was no observed association between CD4 or CD8 T-cell status and carotid IMT or distensibility.

"Among HIV-infected women, T-cell activation was associated with markers of sub-clinical carotid artery disease after adjustment for multiple confounders," the investigators summarized. "These associations of T-cell activation and senescence with carotid artery parameters were not observed in a population of HIV-uninfected controls who were studied using identical methods and who had comparable cardiovascular risk factor profiles."

"Collectively, these observations are consistent with a model in which untreated
HIV infection results in immune activation, accelerated immunologic aging and the emergence of a population of potentially dysfunctional immunosenescent T-Cells," they concluded. "Antiretroviral therapy-mediated suppression of HIV replication may only partially reverse or prevent this process. The presence of a large population of activated and/or senescent T-cells may be causally associated with premature onset of cardiovascular disease."

ART and Atherosclerosis Progression

Jason Baker and fellow investigators with the Centers for Disease Control and Prevention's SUN Study (abstract 126) evaluated changes in carotid IMT and their relationship with ART.

This observational cohort included HIV positive people in four U.S. cities enrolled during the modern ART era (2004-2006). Most (78%) were men and the median age was 42 years. Overall, the group was at low risk for progression to AIDS; 78% were on ART (about evenly divided between NNRTIs and protease inhibitors), 71% had a viral load below 400 copies/mL, and the median CD4 cell count was near normal at 481 cells/mm3 (though the nadir was about 200 cells/mm3).

Many had traditional cardiovascular risk factors, but overall they were considered at relatively low risk for cardiovascular disease. About 40% were smokers and about 30% had high blood pressure or metabolic syndrome. Total and LDL cholesterol levels were generally within recommended ranges. The median Framingham Risk Score was also low at 2, but 30% had a score of 5 or higher.

The researchers used ultrasound to measure IMT in the common carotid artery at study entry and 2 years later. They then conducted an analysis to determine factors associated with carotid artery thickening.

Results

	Over 2 years of follow-up, the overall median common carotid IMT increased from 0.710 mm at baseline to 0.720 mm (a median increase of +0.013 mm).
	The largest proportion of patients, however, showed no change.
	Participants with consistently suppressed viral load at all study visits showed a significantly smaller IMT increase than those with 1 measurements above 400 copies/mL (+0.011 vs +0.019 mm).
	NNRTI use was associated with a significantly smaller IMT increase compared with protease inhibitors (+0.009 vs +0.016 mm).
	However, there was not a significant difference between patients who took abacavir and those who used tenofovir (Viread, also in the Truvada and Atripla coformulations) (+0.015 vs +0.013 mm).
	After adjusting for traditional cardiovascular risk factors, the following factors predicted smaller increases in caroid IMT (all statistically significant):
	Baseline viral load suppression (difference of -0.010 mm); Persistent viral suppression during follow-up (difference of -0.014 mm); ART use at baseline (difference of 0.009 mm).
	Older age and being overweight were also independently associated with larger IMT increases:
	Each additional 10 years of age increased carotid IMT by a further 0.005 mm. Body mass index > 25 increased IMT by 0.013 mm.
	In this study, however, the high-sensitivity CRP as not a significant predictor of increased carotid IMT.

"Maintaining a suppressed HIV viral load decreased progression of sub-clinical atherosclerosis (carotid IMT)," the investigators concluded. "Factors related to both HIV infection and the type of antiretroviral therapy independently associate with the rate of carotid IMT progression."

Early ART and Arterial Stiffness

Finally, Jennifer Ho and colleagues from the UCSF team (abstract 707) looked at whether earlier initiation of HIV therapy -- above the 350 cells/mm3 threshold in effect at the time of the study -- might reduce cardiovascular risk.

This analysis included men on ART with undetectable plasma HIV RNA chosen from the SCOPE cohort (who start ART during chronic infection) and the OPTIONS study (who started ART within 6 months after HIV diagnosis).

Participants underwent non-invasive assessment of arterial stiffness using pulse wave analysis to determine the augmentation index and carotid-femoral pulse wave velocity, a sensitive measure of cardiovascular risk.

Results

	In unadjusted analyses, predictors of arterial stiffness included age, blood pressure, diabetes, current CD4 T-cell count, and having nadir CD4 count < 350 cells/mm3 (all P < 0.05).
	After adjusting for traditional cardiovascular risk factors (age, blood pressure, diabetes, elevated cholesterol, smoking) and HIV status, only having a lowest-ever CD4 cell count < 350 -- that is, below the treatment threshold -- was independently associated with increased pulse wave velocity and augmentation index.
	Neither ART use overall nor exposure to protease inhibitors was associated with greater arterial stiffness.

"Among treated HIV-infected individuals, both traditional cardiovascular risk factors as well as a low nadir CD4+ T-cell counts are associated with arterial stiffness as assessed by augmentation index and pulse wave velocity," the investigators concluded. "Our data suggest that cardiovascular risk among HIV-infected individuals could be reduced through early initiation of antiretroviral therapy, before CD4+ T-cell counts are depressed."

Studies 125, 707, and 708: University of California at San Francisco and San Francisco General Hospital, San Francisco, CA.

Study 709: Albert Einstein College of Medicine, Bronx, NY; University of California, San Francisco, CA; Rush University Medical Center, Chicago, IL; Johns Hopkins University, Baltimore, MD; University of Southern California, Los Angeles, CA.

Study 126: University of Minnesota, Hennepin County Med Ctr, Minneapolis, MN; CDC, Atlanta, GA; Univ of Southern California, Los Angeles, CA; Washington Univ, St Louis, MO; Los Angeles Biomed Res Inst at Harbor-UCLA, Torrance, CA.

3/12/10

References

P Hsue, P Hunt, A Schnell, and others. Rapid Progression of Atherosclerosis at the Carotid Bifurcation Is Linked to Inflammation in HIV-infected Patients. 17th Conference on Retroviruses & Opportunistic Infections (CROI 2010). San Francisco. February 16-19, 2010. Abstract 125.

P Hsue, P Hunt, A Schnell, and others. Inflammation Is Associated with Endothelial Dysfunction among Individuals with Treated and Suppressed HIV Infection. 17th Conference on Retroviruses & Opportunistic Infections (CROI 2010). San Francisco. February 16-19, 2010. Abstract 708.

R Kaplan, E Sinclair, A Landay, and others. T Cell Senescence and T Cell Activation Predict Carotid Atherosclerosis in HIV-infected Women. 17th Conference on Retroviruses & Opportunistic Infections (CROI 2010). San Francisco. February 16-19, 2010. (Abstract 709).

J Baker, K Henry, P Patel, and others (CDC Study Investigators). Progression of Carotid Intima-media Thickness in a Contemporary HIV Cohort. 17th Conference on Retroviruses & Opportunistic Infections (CROI 2010). San Francisco. February 16-19, 2010. Abstract 126.

J Ho, S Deeks, F Hecht, and others. Earlier Initiation of ART in HIV-infected Individuals Is Associated with Reduced Arterial Stiffness. 17th Conference on Retroviruses & Opportunistic Infections (CROI 2010). San Francisco. February 16-19, 2010. Abstract 707.