To evaluate morphologic and metabolic abnormalities among vertically HIV infected children/youth, we performed a cross-sectional study within the PACTG. To our knowledge, this is the largest survey in HIV-infected children/youth that uses objective measurements of both metabolic and morphologic outcomes and features a carefully selected control group.
We observed a high prevalence of dyslipidemia in those with HIV infection, particularly those on PI-containing regimens, consistent with other studies in HIV-infected children/youth[16
]. Using a cutpoint of 130 mg/dL, fasting levels of triglyceride were elevated in 52% and 20% of HIV infected children in the PI and non-PI groups, respectively. Abnormalities in total (29%), non-HDL (24%), LDL (19%) and HDL (10%) cholesterol were also frequently observed in the PI group. Differences between the HIVpos and HIVneg subjects remained significant after adjusting for race/ethnicity, Tanner stage, gender, BMI z-score and CDC classification. In models that also included ART exposure history, longer exposure to PIs in the current regimen was associated with dyslipidemia (higher total, LDL, non-HDL cholesterol and triglycerides and lower HDL-C) as well as glucose abnormalities (2-hour insulin and glucose). When the effects of nelfinavir and ritonavir were included in these models, ritonavir exposure had greater effects on total, non-HDL and triglycerides than nelfinavir.
Dyslipidemia, particularly LDL-C >130 mg/dL, has been associated with an elevated risk of CVD in adults[43
], and dyslipidemic children are more likely than their normolipidemic counterparts to be dyslipidemic as adults[39
]. In addition, elevations in total and LDL-C and reduced levels of HDL-C are associated with the presence of early atherosclerotic lesions in adolescents and children[39
]. Indeed, carotid intima media thickness was found to be higher in HIV-infected children, who also had higher levels of total and non-HDL-C and triglycerides, relative to seronegative controls matched for age, gender, race, and BMI[12
]. The risk of CVD is further elevated in certain racial/ethnic groups and in those with a family history[44
]. In the United States, HIV infection disproportionately affects African-American and Hispanic children/youth[47
], who may bear increased risk for CVD. Over a third of our HIV-infected subjects had a family history of CVD, 26% had family members with hyperlipidemia, and 37% with type 2 diabetes. Although not significantly different from the controls, elevated hsCRP levels were observed almost twice as frequently in HIV-infected children/youth. In addition, almost half of our subjects reported exercising less than once a week and approximately one-third watched television for more than 3 hours daily. Inactivity and television viewing have been associated with increased risk of obesity in HIVneg children[48
]. This combination of factors suggests that these children are at high risk of developing CVD and should be closely monitored. Until specific guidelines are developed for monitoring metabolic and morphologic changes in HIV infected children, published guidelines for adults can be followed[7
]. Increased emphasis should be also placed on identifying effective ways to not just improve eating and exercise habits but also prevent children/youth from beginning to smoke cigarettes.
In contrast to the high prevalence of dyslipidemia, abnormal fasting or 2-h glucose values were relatively uncommon in all groups. Although impaired fasting glucose or glucose intolerance are observed frequently in obese children and adolescents[50
], these abnormalities occur rarely, if at all, in nonobese children and adolescents[51
], a group that would be more comparable to those in this study. It should be noted that although we saw no clinically relevant differences in fasting glucose, insulin levels were approximately 40% higher in both HIV-infected groups, consistent with other studies in which fasting insulin, but not glucose, was higher in HIV-pos children[14
]. We also found that ritonavir use was significantly associated with increasing 2-hour (but not fasting) values for glucose, insulin, and C-peptide. Thus, this dynamic test revealed an association that was not evident in fasting measurements. Overall, our results and those of others provide evidence of developing insulin resistance and, potentially, increasing risk of diabetes, which could contribute to overall risk for CVD as exposure to ART lengthens.
Although ritonavir has long been recognized as a major factor in PI-associated dyslipidemia[54
], our results and other recent studies point to an emerging role in insulin resistance as well. For example, in the Multicenter AIDS Cohort Study, ritonavir was the only PI associated with increased incidence of diabetes or hyperglycemia[48
]. In addition, a study in healthy HIV-uninfected volunteers demonstrated that 4 weeks of exposure to ritonavir, in either a therapeutic or boosting dose combined with lopinavir, decreased insulin sensitivity[56
]. The significant relationships of exposure to didanosine with fasting C-peptide and triglycerides are consistent with the recent observation that didanosine was associated with increased risk of diabetes in a large cohort study of HIV-infected adults[58
Our DXA results demonstrated that both groups of HIV-infected subjects had significantly lower mean Z-scores for limb fat, which is consistent with observations from other cross-sectional studies that employed an objective measure of fat distribution[59
] or clinical criteria to define lipoatrophy[20
]. The extent to which this is due to impaired growth trajectories in vertically infected youth[31
], or specific effects of ART on fat distribution cannot be discerned. The cross-sectional study design also prevents us from stating whether the difference is a result of specific fat loss or failure to accrue fat at the expected rates. Given the concerns about disfigurement and forced disclosure of HIV status among adults with lipoatrophy, low levels of extremity fat among HIV-infected children/youth may become an important factor in adherence to ART and may warrant interventions. Notably, a recent study demonstrated that substitution of tenofovir for d4T and an NNRTI for a PI in HIV-infected children with lipoatrophy normalized the rate of fat accrual in HIV-infected children[60
Predicted mean Z-scores for trunk fat were, if anything, lower than those in HIVneg controls, which is consistent with studies that did not match for BMI[60
]. A limitation is that DXA cannot distinguish between visceral and subcutaneous fat. Use of computed tomography in one study revealed no difference between PI-treated and PI-naïve HIV-pos children in either visceral or subcutaneous fat[17
]. Other studies using magnetic resonance imaging have identified subgroups of HIV-infected children and adolescents with higher-than-normal volumes of visceral fat[59
]. Given evidence of reduced levels of limb fat in the HIV-infected groups in this study, it is possible there may have been concomitant reduction in or impaired accrual of subcutaneous fat in the central region with relative sparing or even accumulation of visceral fat in these groups. The implications of conserved visceral fat on long-term cardiovascular risk are unknown.
We cannot account for the effects of delayed puberty or impeded growth trajectories in this analysis, but it is notable that Z-scores for LBM in both HIV-pos groups were not different from HIVneg. Thus, it appears that the lower weight and BMI in the HIV-infected groups was entirely attributable to differences in fat, primarily in the extremities. This pattern is strikingly different from that seen in vertically HIV-infected children studied before the HAART era, who were reported to have significantly lower levels of LBM with relative sparing of fat[64
A strength of our study is that it featured a recruitment strategy that was designed to balance the groups with regard to gender, race, and Tanner stage. However, like all cross-sectional studies, our study has several important limitations. Although the two HIV-infected groups were similar with regard to current CD4 count or viral load, the PI group showed evidence of more extensive disease history and had longer exposure to NNRTIs. In addition, although our HIVneg and HIVpos subjects were chosen from similar backgrounds, we cannot exclude differences in important potential confounders. Our random selection procedures were designed to provide a representative sample of HIV-infected children/youth from sites and minimize selection bias, but about 40% of these candidates declined to participate. The reasons for refusal are unknown but if related to outcome measures, our sample may be biased. Although the LOESS Z-scores calculated relative to the study HIVneg yielded similar results to those from NHANES IV data when available, our Z-scores were based on a comparatively small number of subjects. As stated earlier, with the large number of outcomes reported, some statistically significant results may occur by chance. Finally, the fact that only 55% of the targeted enrollment was achieved in the non-PI group may have impaired our ability to detect associations between metabolic alterations among subjects on non-PI containing regimens and the potential role of individual NNRTIs in these alterations. The greater reliance on PI-based regimens in this population may reflect the challenges of managing the disease in this population with a long history of exposure to ART.
In summary, the current study included a randomized sampling design and comprehensive assessment of metabolic and morphologic alterations using objective techniques in a large group of vertically HIV-infected children and youth and seronegative controls. It revealed a high prevalence of dyslipidemia and evidence of reduced peripheral fat among the HIV—infected children. Ritonavir was associated with increased risk of dyslipidemia and altered glucose metabolism. These factors may combine to increase risk of CVD in children who are likely to be facing a lifetime of exposure to ART. Our data underscore the need for promoting lifestyles (diet, exercise, reduced television watching, smoking cessation) that decrease cardiovascular risk[65
]. Further, they provide a rationale for continuing efforts to untangle the role of HIV infection and its treatment from genetic, developmental and lifestyle factors, which is essential to understanding basic pathophysiologic mechanisms and for the design of appropriate interventions to reverse or minimize progression of these complications.