The cohort displayed a dyslipidaemic profile commonly seen with long-term PI-containing HAART, with elevated cholesterol (7.6 ± 1.5 mmol/L) and triglyceride [4.0 (5.3) mmol/l] concentrations. Both groups were well matched for baseline total cholesterol, HDL- and non-HDL-cholesterol (Table 2).
Although HDL-cholesterol, glucose and insulin values were within the normal range, triglycerides were lower in the pravastatin group and, based on the HOMA-IR index, the pravastatin group was more insulin resistant than the placebo group (Table 2). There were no significant, between-group differences in change in HDL-cholesterol, triglycerides, glucose, insulin or HOMA-IR (Table 2) and no correlations between baseline triglycerides or HOMA-IR and AUC change in cholesterol from week 4.
At baseline, groups were well matched for body mass index (BMI), total and regional body fat, lean mass and BMI, as assessed by DEXA. On CT, the pravastatin group had more visceral abdominal fat (VAT) than the placebo group, with a correspondingly higher VAT: subcutaneous fat ratio (Table 2). Subjects randomized to pravastatin experienced greater increases in subcutaneous fat compared to the control group (Table 2), with both limb fat on DEXA and subcutaneous fat on CT increasing significantly more in the pravastatin group than control group [+0.72 (1.55) versus +0.19 (0.48) kg; P < 0.04 and +5.2 (8.7) versus −1.3 (13.7) cm2; P = 0.02 respectively). Overall, the pravastatin group experienced 13.7 (27.9)% increase in limb fat versus 4.8 (12.6)% change in the placebo group during the 12 weeks of study drug (Fig. 3). Use of pravastatin remained the strongest predictor of change in limb fat when corrected for potential confounders (age, AIDS diagnoses, presence of lipoatrophy, current use of NNRTI, tNRTIs or lopinavir, duration of exposure to PI, NRTI or tNRTI, time since last exposure to tNRTI and baseline triglycerides, insuslin, HOMA and %FMD). There was no significant correlation between change in limb fat and TWAUC change in cholesterol from either week 0 or week 4, regardless of whether the analysis included the entire cohort or either of the randomized groups. There were no significant differences in change in BMI, trunk fat, VAT or percentage intra-abdominal fat between randomized groups.
Cardiovascular parameters were measured at week 4 and 16. Apart from %FMD and PAI-1, which were lower and higher respectively in the pravastatin group than in the placebo group, the groups were well matched for other measures of cardiovascular risk (Table 2). Week 4 endothelial function, assessed using %FMD, was generally impaired [median %FMD for the cohort, 4.3% (3.6), reference range, 8–11% ]. Apart from homocysteine, which decreased more in the pravastatin group compared to placebo, there were no between-group differences in change in %FMD, blood pressure or other serum markers of cardiovascular risk (Table 2). There were no significant correlations between week 4% FMD or PAI-1 and AUC change from week 4 total cholesterol.
This is among the first randomized, placebo-controlled studies on the use of statins in the setting of HAART-associated dyslipidaemia that examines all of the relevant clinical and laboratory markers of HIV-associated lipodystrophy, of which dyslipidaemia is an important component. Twelve weeks' treatment with pravastatin resulted in a modest 11% decrease in cholesterol concentrations. Compared to previously published studies of pravastatin use in the setting of HAART, our subjects were slightly older (47 versus 41–44 years [17,20,24]) and all were male (100% versus 77–100% [17,20,23,24]). The effect of pravastatin on total cholesterol in our study (11% reduction) was somewhat less than that reported in previous studies (reductions ranging between 17 and 25% [20,23,24,34]) but is consistent with a recent report of HIV-infected subjects treated with lipid-lowering therapy in which a subgroup receiving pravastatin experienced reductions of 12% . We believe these differences to be related to the higher percentage of subjects in our study receiving HAART regimens containing ritonavir-boosted PI (91%) compared to previous studies (47–61% where data are available [20,23,24,34]) and the higher baseline cholesterol values observed in our subjects [median baseline cholesterol 7.6 (1.7) mmol/l] compared to several similar studies [17,20,24]. Although one could argue that those with greater baseline cholesterol concentrations should have the potential for greater decreases, if these higher baseline cholesterol values reflect a greater perturbation of cholesterol homeostasis, potential therapeutic interventions may be less effective.
An absolute decrease of < 1 mmol/l was observed with pravastatin, and only seven (21%) subjects, spread across both arms, achieved cholesterol values < 6mmol/l with only four subjects, two from each group, achieving a week 16 cholesterol value < 5.5 mmol/l. Together with the absence of non-lipid statin effects, with no significant changes in %FMD or most atherothrombotic markers, these data raise doubt as to the clinical consequences of such small decreases in cholesterol concentrations on the risk of CVD at a population level in HIV-infected patients on PI therapy. However, individual patients with significant numbers of co-existing cardiovascular risk factors may still receive clinical benefit from reductions in total and non-HDL cholesterol, no matter how small.
Homocysteine levels decreased significantly with pravastatin treatment. Although decreases in homocysteine are thought to be cardioprotective and in vitro, statins may modulate release of homocysteine from peripheral blood mononuclear cells , decreases in homocysteine with statin use have not been consistently shown in clinical studies of hyperlipidaemia  and further investigations are required to confirm this finding in a HIV-infected PI-treated population.
Both the active and placebo groups experienced decreases in cholesterol concentrations during this study. The reasons for the change in the placebo group may be explained either by dietary effect, or a regression to mean, not uncommonly observed in randomized studies. The latter explanation is favoured as no individual dietary component significantly changed over the course of the study.
The changes in subcutaneous fat observed with this study were surprising given that, unlike rosiglitazone, which has been investigated in this setting [37–39], pravastatin use has not been previously reported to have effects on subcutaneous fat mass. However, the finding is consistent across measures (with both CT and DEXA showing changes in subcutaneous and peripheral fat without significant changes in central or visceral fat).
Several mechanisms could underlie the observed increases in subcutaneous fat. As HMG Co-A is metabolized through the proteasome, inhibition of the proteasome by PI could lead to abnormally elevated levels of active intracellular HMG Co-A and blunt the normal negative feedback of accumulated intracellular cholesterol on intracellular HMG Co-A activity. In vitro, depletion of intracellular cholesterol in mouse adipocytes results in upregulation of sterol regulatory element-binding protein 2 (SREBP-2), a nuclear transcription factor which stimulates expression of genes involved in cholesterol syntheses (HMG-CoA synthase) and uptake (LDL receptor) . By directly inhibiting HMG Co-A reductase, rather than relying on proteasomal degradation, cholesterol depletion resulting from statin use could result in increased cell-surface LDL-receptor expression and increased uptake of circulating lipid into tissues such as adipose tissue, causing increase in size of adipocyte depots. Further studies, both in vitro and in vivo are required to test this hypothesis. Although diet may play a potential role, we think this less likely, both for the reasons described above, and as previous studies of dietary intervention alone have been disappointing .
Regardless of the mechanism involved, the increases in limb fat observed are clinically significant when compared to other strategies previously used to increase limb fat in treated HIV-infected patients . The strategy of switching away from a tNRTI has resulted in some of the most significant durable changes in limb fat observed to date . When compared to the MITOX study, which observed a mean increase of 0.39 kg over a 24-week period , use of pravastatin was associated with a much greater increase, with a median increase of 0.72 kg over a 12-week period of treatment. However, unlike the strategy of switching away from tNRTI to increase limb fat, the use of pravastatin does not place limits on the use of specific antiretrovirals and should be less likely to introduce risks seen with switch strategies such as virological failure or new ART side effects. However, further research is needed to determine if the improvements observed with pravastatin use will continue, or persist in those receiving PI or tNRTI.
This single-centre study does have limitations. Although 12 weeks' therapy with pravastatin had relatively modest effects total cholesterol, it is doubtful whether prolonged exposure to pravastatin would change this outcome, given the rapid effect observed in other hypercholesterolaemic populations [26,27]. The observed changes in limb fat were part of the secondary endpoints and therefore the study was not primarily designed to test the effect of pravastatin on limb fat. This is reflected in the absence of objective body composition data at week 0 when the dietary assessment and advice was started. In addition, that the study was not designed or powered around the secondary endpoints makes it difficult to draw definite conclusions based on specific negative results. Because of the make-up of our clinical population, we did not test the effect of pravastatin in women, non-Caucasian populations, or in those with normal cholesterol concentrations.
Despite this, this study provides valuable information as to the role of pravastatin for the treatment of hyperlipidaemia in HIV-infected men treated with ritonavir-boosted PI. The results suggest that, as a general strategy, the effect of pravastatin on cholesterol concentrations in this patient group is limited. Despite this, the drug is well tolerated and may have a role in CVD prevention in specific at-risk groups, and its effects on limb fat mass, although novel, are encouraging and should be further investigated in larger randomized prospective studies.
We thank the subjects for their time and commitment to the study and Dr Matthew Law from the National Centre in HIV Epidemiology and Clinical Research for statistical advice.
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