Changes Over Time in Lipids
In the DC arm, the cumulative numbers of patients resuming ART were 1 (0.6%), 20 (12.8%), 40 (25.6%), and 61 (39.1%) by months 1, 2, 4, and 8, respectively. Figure 1 shows lipid changes over the first 8 months. Changes in lipids after interruption of ART were rapid. In the DC arm, TC, LDL-c, HDL-c, and TG fell substantially by month 1, with some further decline subsequently. Maximum declines were observed at month 1 for LDL-c, month 2 for TC and HDL-c, and month 4 for TG. There was little change over time in the TC/HDL-c ratio. In the VS arm, changes in lipids were smaller: moderate declines occurred in TC, LDL-c, and HDL-c, with little change in TC/HDL-c ratio and TG. At month 1, declines in TC, LDL-C, HDL-C, and TG were significantly greater in the DC compared with VS arm (Table 2): estimated DC versus VS mean differences (mg/dL) adjusted for baseline (95% CI) were −21.2 (−28.4 to −14.0) for TC, −7.1 (−12.5 to −1.7) for LDL-c, −3.4 (−5.0 to −1.7) for HDL-c; and the percentage difference (95% CI) for TG was -17.6% (−24.9% to −8.4%) (P ≤ 0.01 for all). There was no significant difference in TC/HDL-c ratio [DC versus VS difference: −0.10 (95% CI: −0.59 to 0.38), P = 0.67].
Changes in Lipoprotein Particle Subclasses
Table 3 shows baseline values and changes at month 1 in lipoprotein particle subclasses. Compared with the VS arm, there were declines in total VLDL-p and in VLDL subclasses in the DC arm at month 1; differences were significant for total, large, and medium VLDL-p (P ≤ 0.01). The percentage difference (95% CI) for DC versus VS was -19.4% (−26.7% to −11.4%) for total VLDL-p, −27.3% (−44.3% to −5.1%) for large VLDL-p, and -28.7% (−39.6% to −15.9%) for medium VLDL-p. There were no significant differences between arms in total LDL-p [percentage difference (95% CI): −3.8% (−8.6%, to +1.3%)], small LDL-p [−5.0% (−16.5% to +8.6%)], or other LDL-p subclasses. Total HDL-p and medium HDL-p declined in the DC arm relative to the VS arm [percentage differences (95% CI): −9.6% (−13.5% to −5.6%) for total and -39.9% (−59.3% to −11.3%) for medium HDL-p; P ≤ 0.01]. There was no significant difference between arms for small HDL-p, (−4.6% [−13.4% to +5.1%] P = 0.35), or for large HDL-p, VLDL-p, LDL-p, or HDL-p size.
Baseline and Changes in Lipids and Lipoprotein Particle Subclasses According to Demographic and Treatment Factors
Baseline lipids varied according to several demographic and treatment factors. Among the 332 subjects overall, mean HDL-c was lower among men (41.7 mg/dL) than women (48.2 mg/dL); TG levels were higher among men than women (5.24 versus 5.01 log mg/dL), and among subjects aged ≥45 years compared with <45 years (5.28 versus 5.05 log mg/dL); LDL-c was higher among white subjects compared with others (115.5 versus 107.6 mg/dL). Subjects taking nonnucleoside reverse transcriptase inhibitor-based treatment had higher HDL-c than those taking protease inhibitor-based treatment (46.4 versus 40.8 mg/dL). Compared with others, subjects taking lipid-lowering drugs had considerably higher TC (218.8 and 189.4 mg/dL for subjects on and off lipid-lowering drugs, respectively), LDL-c (120.3 and 107.8 mg/dL) and TG (5.51 and 5.08 log mg/dL; P < 0.05 for all two sample t-tests).
Table 4 shows baseline-adjusted DC versus VS differences in lipids at month 1, according to demographic and treatment factors. The declines in TC, LDL-c, and HDL-c in the DC arm relative to the VS arm tended to be greater among men compared with women, among older compared with younger subjects, and among white subjects compared with those of other ethnicity. Among the subgroup of 275 subjects taking either a protease inhibitor-based or nonnucleoside reverse transcriptase inhibitor-based ART regimen, there was no evidence that changes in lipids varied according to class of ART. However, changes in TC and LDL-c in the DC versus VS arm were much greater in subjects taking lipid-lowering drugs at baseline compared with those not taking these drugs. For TC, the baseline-adjusted DC versus VS differences in means (mg/dL) were -32.7 and −15.8 for subjects who were and were not taking lipid-lowering drugs, respectively; the corresponding differences in means for LDL-c were -18.0 and -3.6 (P < 0.05 for both interactions). Interaction tests were also performed for the following lipid particle measures: total, large, and medium VLDL-p and total and medium HDL-p, as significant differences between arms at month 1 had been found for these parameters. No significant interactions of randomized group with demographic factors, class of ART or lipid-lowering drug use were found (P > 0.05; data not shown).
Association of Changes in Lipids and Lipid Particle Subclasses With Changes in Inflammatory Markers, Coagulation Markers, and Viral Load After ART Interruption
Table 5 shows the association between 1-month changes in lipids and 1-month changes in inflammatory and coagulation markers and viral load, in the DC arm only. The strongest associations were with D-dimer and viral load: changes in TC, LDL-c, and HDL-c were negatively correlated with changes in D-dimer and viral load (r = −0.40 to r = −0.24). In other words, after ART interruption, decreases in lipids were associated with increases in viral load and D-dimer. Weak to moderate negative associations were apparent between changes in TC, LDL-c, and HDL-c and changes in IL-6 and amyloid A. There were similar negative associations with lipoprotein particles in the DC arm: change in large VLDL-p was negatively associated with change in viral load (r = −0.25); change in total LDL-p was negatively associated with changes in amyloid A (r = −0.24) and viral load (r = −0.21); change in total HDL-p was negatively associated with change in D-dimer (r = −0.41), F1.2 (r = −0.26), amyloid A (r = −0.37), hsCRP (r = −0.31), IL-6 (r = −0.41), and viral load (r = −0.34); change in small HDL-p was negatively associated with change in amyloid A (r = −0.23) and IL-6 (r = −0.30).
We examined the effect of ART interruption on lipids and lipoprotein particle subclasses in a randomized comparison with subjects remaining on ART. ART interruption resulted in rapid and substantial declines in TC, LDL-c, HDL-c, and TG, but had little net effect on the TC/HDL-c ratio. There were no significant changes in LDL-p subclasses. There were declines in total, large, and medium VLDL-p and total and medium HDL-p, but no change in small HDL-p.
The major strengths of this study are the randomized nature of the comparison and the comprehensive ascertainment of lipid parameters. We focused on 1-month changes, which were not diluted by DC patients resuming ART. There are some limitations. Baseline TC, HDL-c, LDL-c, and TG were measured in serum, with subsequent measurements in plasma. Previous studies suggest that serum lipid values tend to be consistently higher than plasma values by about 2%-3% for TC and 3%-5% for TG.19,20 There is less evidence of a consistent serum/plasma difference for HDL-c. Therefore, in our study, declines in usual lipids from baseline to month 1 will tend to be slightly overestimated. Serum/plasma differences probably contribute to the declines in TC, LDL-c, and HDL-c observed at month 1 in the VS arm, although they do not seem to fully explain the declines (mean values declined by 6%-11%, Table 1). Our primary analysis involving comparisons between randomized groups should be unaffected by serum/plasma differences. Nonfasting lipid measurement may result in increased variability of TG and some underestimation of TG changes and associations with other factors but should have minimal impact on the other lipid measures.19
Previous randomized21-25 and nonrandomized studies26-31 have assessed changes in conventional lipids during a single ART interruption or during a strategy of repeated interruptions. Most were small (<50 individuals interrupting ART),21,22,26,27,29-31 some only reported on defined lipid abnormalities,27,29 few considered HDL-c,25,26,31 and none considered lipoprotein particle subclasses. Most previous studies suggested declines compared with baseline (of varying magnitudes) in TC21,22,24,25,27 (and/or LDL-c24,27) and TG21,22,27 during ART interruption. Of 3 studies measuring HDL-c,25,26,31 only 1 found a significant decline on treatment interruption,31 but all were relatively small. Two of 4 trials failed to show significant differences in any lipid measure between interruption and continuation arms.22,23 The comparison between studies is complicated by their different interruption/resumption strategies, the differing time points for lipid endpoints and the ART status of patients at this time. Changes in conventional lipids at year 1 in the SMART trial have been reported previously,10 but 40% of DC subjects had resumed ART. The present results show that mean lipids declines were substantially greater at month 1 than year 1 (19%, 110%, and 130% greater for TC, LDL-c, and HDL-c, respectively among DC subjects on ART at baseline.) This is in part due to attenuation of lipid changes over time as patients resumed ART, but it also demonstrates that lipid changes were rapid, with much of the decline occurring within the first month.
It is believed that information on lipoprotein particle subclasses measured by NMR may improve CHD risk assessment compared with standard lipid measures alone. Findings from non-HIV studies are inconclusive, but there is evidence that number of LDL particles, total LDL-p, small LDL-p, and smaller LDL size are positively associated with CHD,11-16 in some cases independently of chemically measured LDL-c.12-14,16 In addition, several studies have found an inverse association between small HDL-p and CHD.13,15 There is very little information from HIV-infected individuals. In cross-sectional analysis of the Multicenter AIDS Cohort Study, men on ART were judged to have an “atherogenic lipoprotein profile”: higher small LDL-p and total VLDL-p and lower large LDL-p and total HDL-p compared with HIV-negative men.32 In contrast, HIV-positive ART-naive men had lower small LDL-p compared with HIV-negative men. The declines on treatment interruption observed in this present study in total VLDL-p and HDL-p would be consistent with results from Multicenter AIDS Cohort Study and with reversal of lipid changes induced by ART. However, although we observed a clear decline in chemically measured LDL-c in DC compared with VS arms, the difference between arms in NMR total LDL-p was not significant, and there were no differences in LDL-p subclasses. The association between lipoprotein particle subclasses and cardiovascular risk has recently been assessed in a nested case-control study within SMART; this analysis found that, of the NMR measures, small and large HDL-p had the strongest (inverse) associated with cardiovascular events.33 Overall, the short-term changes in lipid parameters associated with interruption of ART in this analysis suggest little net effect on coronary risk. The reduction in LDL-c was offset by the decline in HDL-c; in addition, small LDL-p and small HDL-p, the NMR subclasses most consistently linked with CHD risk, did not differ between DC and VS arms.
We did not find greater reductions in TC and LDL-c in those stopping protease inhibitors or greater reductions in HDL-c among those stopping nonnucleoside reverse transcriptase inhibitors, as might be expected.3-7 As drugs within each class differ in their effect on different lipid fractions,3-7,34,35 this may be due to variations in specific drugs used, variations in duration of use, or differences in the nucleoside component of the regimen. Lipid changes on ART interruption tended to be greater among subgroups with higher baseline lipid levels (men, older subjects, white subjects and particularly those taking lipid-lowering drugs); differences were somewhat attenuated when assessed in terms of percentage change, using analysis on the log scale (data not shown). The considerably greater declines in TC and LDL-c among subjects on lipid-lowering drugs compared with other subjects may also be due to interactions between ART and lipid-lowering agents.36 DC versus VS differences in lipids and lipoprotein particle subclasses were similar after exclusion of subjects taking lipid-lowering drugs at baseline (data not shown).
HIV replication is associated with endothelial dysfunction and activation of inflammatory and coagulation pathways37,38 In the SMART trial, interruption of ART resulted in substantial increases in IL-6 and D-dimer at month 1.17 These present results show that, in the DC arm, greater increases in D-dimer, IL-6, and amyloid A were associated with greater declines in TC, LDL-c, and HDL-c, although there was no association with hsCRP. These correlations were strongest for D-dimer. Similar moderate negative associations were observed between changes in viral load and changes in TC, LDL-c, and HDL-c. Changes in various NMR lipid measures (particularly total and small HDL-p) were also negatively associated with changes in viral load and some inflammatory and coagulation markers. The associations with viral load were the most consistent. The pattern of rapid changes in lipids was similar to that observed for viral load: the percentage of subjects with viral load ≤400 copies per milliliter fell from 72% at baseline to 6% at 2 months in the DC arm overall.9 These results suggest that lipid declines may be closely linked to the sudden increase in viral replication and perhaps associated activation and inflammation, on interruption of ART. Possibly it is these acute changes, rather than the specific antiretrovirals used, that are the dominating factors in determining short-term lipid changes when treatment is stopped.
Structured or CD4-guided treatment interruption strategies were once considered as a means of reducing toxicity associated with long-term ART-in particular, reversing drug-induced increases in TC. The SMART trial showed that CD4-guided treatment interruption resulted in increased risk of AIDS and severe non-AIDS morbidity. This assessment of short-term changes in lipids and lipoprotein particle concentrations among subjects on ART at baseline suggests that although TC changes associated with ART use seem to be rapidly reversed on treatment interruption, the overall lipid profile is not favorably influenced. Short-term changes in lipid parameters were not associated with class of ART and may be linked to increases in viral replication, inflammation, and coagulation.
We would like to acknowledge the SMART participants, the SMART study team (N Engl J Med. 2006;355:2294-2295 for list of investigators) and the INSIGHT Executive Committee.
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Keywords:© 2010 Lippincott Williams & Wilkins, Inc.
antiretroviral therapy interruption; coagulation markers; inflammatory markers; lipids; lipoprotein particle subclasses