Percentage body fat was 30% higher in women than in men not only at baseline, but also at final evaluation, due to the similar gain in fat mass in both sexes during HAART (Fig. 2).
There was a moderate correlation between serum leptin levels and body fat mass in both HIV-infected men and women at baseline (r = 0.64 and r = 0.68, respectively, P < 0.02 for both sexes). Positive correlations between the gain in serum leptin levels and in fat mass were noted only in women during HAART (r = 0.63, P < 0.03).
In contrast, baseline serum insulin levels did not correlate with baseline fat mass (r = 0.34 in men, r = 0.24 in women, P > 0.05 for both sexes), and the increase in serum insulin did not correlate with the gain in fat mass during therapy (r = 0.35 in men, r = 0.25 in women, P > 0.05 for both sexes).
Dyslipidaemia and asymptomatic atherosclerotic lesions are more frequent in HIV-positive patients than in healthy controls [17,26,27]. The risk to these patients of developing cardiovascular complications may increase further during long-term use of antiviral therapy .
As female sex protects from cardiovascular disease in HIV-seronegative subjects, we set out to study prospectively sex-differences in metabolic side-effects of a newly initiated HAART regimen, in particular to evaluate whether female sex is protective in this setting.
In good agreement with previous findings, HIV-infected patients had lower baseline levels of HDL than healthy age-matched controls  (Table 1), whereas levels of LDL (Table 1) and total cholesterol were not different from control values. The latter finding is possibly due to the relatively good immune and the adequate nutritional status of our HIV-patients, who were also free of opportunistic infections or wasting.
Hence, the baseline LDL : HDL ratio, an established indicator of cardiovascular risk, was higher in HIV-patients than in controls, and higher in HIV-infected men than HIV-infected women (Fig. 1). The less favourable lipid profiles in our male patients before the start of HAART mirror nicely what is seen in the general population, i.e. the well-known increased risk for cardiovascular disease in men as compared with women [9,29]. Thus, HIV-infected women seem to be naturally better ‘protected’ from the pro-atherogenic effects of HIV-infection per se than are men.
However, after initiation of a combined antiretroviral therapy, LDL : HDL ratios increased only in our female HIV patients (Fig. 1) due to increases in LDL (Table 2). As a consequence, the baseline sex difference in the LDL : HDL ratio finally disappeared (Fig. 1). Hence, women seemed to have ‘lost’ part of their natural protection from cardiovascular disease.
Baseline levels of serum triglycerides and insulin were similar between sexes as in a normal population, whereas serum leptin concentrations were trend-wise (> 30%) higher in female than in male patients. Although the magnitude of this sex difference was not significant, it was comparable to the degree of sex differences in leptin levels in a healthy population.
Antiretroviral therapy increased serum triglycerides, insulin and leptin levels predominantly in our female, and to a lesser extent in our male HIV patients (Fig. 2, Table 2). Even though we were not surprised to find rising leptin levels during HAART [30,31], we had not necessarily expected sharper increases in the female patients as compared with the male HIV-infected patients. Of note, the twofold increase in serum leptin levels in women (Fig. 2) is rather pronounced in view of animal studies, showing that induction of inflammation by lethal doses of endotoxin increased leptin levels only 2.5-fold .
Interestingly, HIV-infected men and women gained fat mass to comparable extents, but the increase in leptin and insulin levels was clearly more pronounced in the female patients (Fig. 2). Yet, we found a moderate correlation between the increase in leptin levels and the gain in fat mass in our female patients, but not in male patients. The moderate degree of correlation, however, indicates that the preferential increase in leptin levels in women was not solely dependent on the increase in fat mass. This is in line with previous findings indicating that circulating leptin levels do not correlate directly with weight changes in HIV-infected patients or reflect exclusively adipose tissue mass [33–35].
In view of several previous reports, peripheral insulin resistance could be an explanation for the elevations in serum insulin in these patients . Higher insulin concentrations may then have contributed to the increase in serum leptin levels, independently of body fat mass [37–39]. Finally, lower energy expenditure after successful antiretroviral treatment  may have been associated with an increase in leptin concentrations in this HIV-infected population .
Endothelial cell damage is present early in HIV infection, but the understanding of markers and mechanisms remains incomplete . It has been reported that HIV may infect vascular EC directly , and induce shedding of adhesion molecules from the cell surface, possibly due to oxidative stress . In addition, HIV and various opportunistic pathogens may exert indirect deleterious effects on EC, conceivably via pro-inflammatory cytokines.
Serum cE-selectin is a specific endothelial activation marker, which can indicate HIV-associated vascular inflammation , and/or atherosclerosis and the consecutive development of cardiovascular disease [18,52,53].
In this study, HIV-infected patients had higher baseline levels of cE-selectin than healthy controls confirming a previous cross-sectional study . HIV-infected male patients had almost 50% higher baseline levels of cE-selectin than female patients (Fig. 1) as would be expected from healthy controls [54,55]. The preserved sex differences in baseline cE-selectin levels in HIV infection may indicate that female sex protects against endothelial activation in HIV-infected individuals.
However, during HAART, serum cE-selectin levels declined in the male, but not in the female patients (Fig. 2), despite similar reductions in viral load. As a consequence, sex differences in cE-selectin were no longer apparent 6 months after initiation of HAART (P > 0.05, Fig. 2). This may be interpreted as evidence that HAART suppressed immunological/inflammatory processes in EC less effectively in female patients than in male patients.
A limitation of this study is that the question of whether the observed metabolic disturbances were related specifically to the use of PI could not be addressed in this setting. Indeed, previous studies on the association of metabolic changes with certain components of combinational regimens have produced inconsistent data. Whereas disturbances in lipid metabolism have been reported during HIV-therapy without PI , ‘switch studies’ have indicated that cholesterol and triglyceride levels fall when PI-containing therapy is discontinued . Furthermore, PI have been shown to increase concentrations of serum triglycerides and atherogenic lipoproteins even in healthy volunteers . Only very recently, in vitro experiments have shown a direct and dose-dependent influence of PI on insulin-stimulated glucose uptake in adipocytes .
As it cannot be ruled out completely that the stage of disease also influenced metabolic changes to a certain extent, only HIV and AIDS patients who were in very good clinical condition were enrolled in the study.
However, to answer more comprehensively the question of whether there is a cause and effect relationship between the use of PI-containing HAART and metabolic disturbances would require a comparison of (at least) two groups of patients, one receiving a PI-based regimen and the other receiving a non-NRTI in combination with two NRTI.
In summary, adverse metabolic effects of a HAART regimen were more pronounced in women than in men in this study. Female patients exhibited more distinct increases in serum levels of LDL, LDL : HDL, triglycerides, insulin and leptin decreased more in men than in women. Hence, female HIV-infected patients seem to loose part of their natural protection from atherosclerosis during antiretroviral therapy.
Further studies are necessary to determine whether these pro-atherogenic effects are related specifically to PI and whether in women non-NRTI-based regimens are as effective as PI-based regimens immunologically and virologically and with fewer adverse metabolic effects.
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