The novel findings of greatest clinical significance in this study are that favorable lipid changes (increased HDL and decreased total-HDL cholesterol ratio z scores) are associated with immune reconstitution and improved GH sensitivity in HIV-infected children who begin or change ART regimens. There was also a trend toward higher HDL cholesterol z score with higher CD4% cell counts at study entry, giving additional credence to the association. In addition, a greater increase in apolipoprotein A1 z score was associated with improved IGF-1 and a trend toward the same with improved CD4%, emphasizing the favorable change in lipid profiles with greater GH sensitivity and immune reconstitution. It is important to note that despite the mean increases in LDL and total cholesterol experienced by these children, the HDL also increased such that there was not a worsening of the cardiovascular risk as measured by total-HDL cholesterol ratio. Accordingly, we were unable to prove our hypothesis that abnormalities in lipid profiles would increase in prevalence in these children. The decrease in HDL abnormalities paralleled the increase in abnormal total cholesterol levels and resulted in a statistically insignificant decrease in the percentage of children with an abnormal total-HDL cholesterol ratio. The hypothesis that treatment-naive patients would have an increased prevalence of lipid abnormalities at entry compared with population-based norms, however, was true, but we were surprised to find that the difference was related to abnormally low HDL cholesterol in the infected children and consequently higher total-HDL cholesterol ratios.
Increases in HDL cholesterol have been described in ART-treated children,26
a finding that we confirmed. We did not, however, find an association of increased total cholesterol with improvements in CD4% counts reported recently in both HAART-treated children9
and adult women.27
Rather, our findings are similar to those from a study in HIV-infected adults in which greater HDL cholesterol was associated with higher CD4+
We did find a relationship between immune reconstitution and LDL cholesterol only during the first 24 weeks of the study, an association that has been seen in adults.28
It is not clear what biological differences in children would cause a net favorable change in lipid profile with improvements in CD4% not previously noted in adults.
In multivariate analysis, the total cholesterol concentration at baseline in our population was associated with a history of PI use, suggesting a deleterious effect of PI therapy that has been described in multiple previous studies.2,7,28–31
Moreover, we noted that dual NNRTI-PI–based therapy during the study resulted in greater total-HDL cholesterol ratio increases than NNRTI- or than PI-based therapy, suggesting a potential synergistic effect. Greater triglyceride increase was also seen in our study with combined NNRTI and PI therapy, whereas PI therapy without NNRTI use was associated only with greater triglyceride increase at 24 weeks. Greater changes in triglycerides with ART regimens that contain both an NNRTI and a PI compared with regimens that contain just 1 but not both of these drug classes have been previously described.32
Viral suppression was related in multivariate analysis to greater increases in total cholesterol, concurring with the previous report in children of an association between hypercholesterolemia and an undetectable VL.8
Taken together with the finding that the total cholesterol at entry was actually below that of matched population-based control subjects, perhaps viral replication itself interferes with cholesterol metabolism. There is increasing evidence for this concept from in vitro studies. Of particular interest is the recent report that intracellular lipid metabolism is dysregulated in HIV-infected macro-phages.33
It may be that viral suppression unmasks the effect of increased cholesterol related to drug therapy, or it may be a marker for improved adherence and therefore greater ART exposure.
There was a statistically significant increase in insulin and insulin resistance as measured by HOMA-IR in the children our study and a change in fasting blood glucose that approached statistical significance. Unfortunately, there are not available comparison values from NHANES to measure whether these changes were greater than might be expected in the general population. Although there was not a statistically significant change in the number of children with frankly abnormal values (and thus our hypothesis was not confirmed), the mean (SD) increase of HOMA-IR at 48 weeks by 0.48 (1.14 µIU/mL per mmol/L) and the increase in the prevalence of abnormal glucose tolerance as defined by HOMA-IR >3.16 from 1% at entry to 8% at 48 weeks suggest that development of glucose intolerance even in prepubertal children may be of concern and needs additional investigation. We did not identify risk factors for increased insulin resistance with any of the variables in our multivariate analysis, other than cholesterol intake. Previous reports are contradictory regarding whether insulin sensitivity is altered with PI therapy in this age group.30,31
We previously reported that children in this study did not increase their BMI or percentage of body fat z
suggesting that greater adiposity is unlikely to account for the increase in insulin and HOMA-IR that was seen. The greater increase in insulin resistance associated with excessive cholesterol consumption in this study may suggest that the development of insulin resistance could be prevented, in part, by a heart-healthy diet.
We previously reported that IGF-1 increased over time in a greater number of children in P1010 than would be expected by chance and that these increases were associated with improvements in muscle mass.34,35
This analysis further notes that greater HDL cholesterol and apolipoprotein A1 and lower total-HDL cholesterol ratio concentrations, both at entry and over time, were associated with normal IGF-1 concentrations, confirming our hypothesis. These findings suggest that GH sensitivity is likely related to improved lipid profiles as well as improved anabolism. The improved lipid metabolism that was seen in lipodystrophic HIV-infected adults who were treated with physiologic GH replacement supports the link between GH resistance (or deficiency) and dyslipidemias. 36
This study had several limitations. It is likely the HIV-infected children in our study differed from the overall US population represented in NHANES data in ways for which we could not adjust, such as socioeconomic status, parental health, etc. Furthermore, measures of insulin resistance were not obtained in NHANES, so we had no comparison group for these analytes. Apolipoprotein z
values from NHANES were obtained from a publication, rather than derived directly from the data. NHANES itself is a cross-sectional data set and not ideal for comparison of longitudinal data. Longitudinal reference data would allow for calculation of z
scores for changes in lipids, etc. We did not have a comparison group of HIV-infected children who were not beginning or changing therapy, so clearly the associations noted are not necessarily causally related and may be different in children who are on long-term therapy. The children in our study also began diverse ART regimens, limiting the power to detect changes that may be associated with specific ART agents or classes. Because therapy on study was not independent of therapy before the study, some caution must be taken when noting associations with the combination of ART classes taken during follow-up. We also cannot be certain that changes that are associated with normalization of IGF-1 are specifically attributable to improved GH sensitivity, although GH insensitivity has been previously demonstrated in HIV-infected children.37
Associations do not demonstrate causality; furthermore, there could be other causes of increased IGF-1, such as an increase in GH secretion. Although we have focused on specific hypotheses concerning the associations between lipid profiles and insulin resistance and improvements in immune status, viral suppression, and ART classes, there remains a risk for inflated type I error rate as a result of multiple comparisons. The major strengths of the study include a sample size larger than most prospective studies of children that have evaluated metabolic changes in this population, evaluation before and after ART initiation or change, and measured indices of the GH axis in addition to those of insulin resistance and lipids.