Our results show a significant relationship between new-onset diabetes and exposure to cART, with this effect being mainly related to exposure to stavudine. However, exposures to zidovudine and didanosine were also associated with an increased risk, whereas exposures to ritonavir and nevirapine were both associated with a reduced risk of diabetes. Our findings are consistent with those of two other cohort studies that showed a similar relationship between exposure to stavudine and incidence of diabetes (2
). We found a lower incidence of new-onset diabetes than in the Multicenter AIDS Cohort Study (MACS) (5.72 per 1,000 PYFU vs. 47 and 17 per 1,000 PYFU among individuals receiving or not receiving cART) (2
). This difference could be related to different size and demographic compositions of both cohorts as the MACS involved white males exclusively, who were likely to be exposed to the typical North American diet and who were older and had higher BMI than the D:A:D participants. In addition, in the MACS a single elevated fasting blood glucose measurement was sufficient to establish a diagnosis of diabetes, a less stringent criterion than that used in our study. Importantly, in the MACS, fasting glucose levels were obtained as part of the assessments at predefined cohort visits, whereas in our cohort the validation of diabetes as an end point is dependent on the actual screening policy for glucose intolerance and diabetes, which is in place in each of the 212 treatment units contributing data to D:A:D, which undoubtedly differs between centers.
The association between diabetes/insulin resistance and stavudine/zidovudine might be explained through an indirect mechanism, i.e., lipoatrophy, a state that is associated with insulin resistance. The increased lipolysis observed in patients with lipoatrophy actually reflects their adipose tissue being insulin resistant. Lipolysis leads to increased circulating free fatty acids, which may reinforce insulin resistance in the liver and skeletal muscles (4
However, clinical evidence for a direct effect of thymidine analog nucleoside reverse transcriptase inhibitors (NRTIs) on insulin sensitivity is also emerging. Antiretroviral therapy-naive subjects randomly assigned to stavudine- and didanosine-based therapy had a significant increase in homeostasis model assessment of insulin resistance at 1 month, whereas there was no change in those randomly assigned to abacavir and lamivudine (5
). Exposure to stavudine and didanosine is associated with greater lipoatrophy, illustrating the link between drug-related lipoatrophy and insulin resistance (2
). Stavudine exposure leads to depletion of mitochondrial DNA content, which may result in mitochondrial dysfunction. A recent study performed in healthy volunteers demonstrated that a 1-month exposure to stavudine reduces insulin sensitivity in parallel with a 58% reduction in muscle mitochondrial DNA, suggesting that mitochondrial dysfunction and insulin sensitivity were linked (7
). Several studies in HIV-uninfected individuals have suggested that mitochondrial dysfunction precedes the onset of diabetes in insulin-resistant offspring of patients with type 2 diabetes. Alterations of several genes involved in mitochondrial oxidative phosphorylation have been identified in muscle samples of patients with type 2 diabetes and impaired glucose tolerance (8
The other risk factors for diabetes identified in our study included male sex, older age, greater BMI, and black race, largely consistent with other studies in both the HIV-uninfected and HIV-infected populations (11
). Current smoking status appeared to be marginally protective, contradicting some studies but consistent with results from the Multiple Risk Factor Intervention Trial (MR-FIT) for the reduction of CVD (12
). The lower incidence of diabetes in recent calendar years could be inherent to the study design, i.e., follow-up of a closed cohort in which the patients at risk (i.e., susceptible to develop an end point) experience this relatively soon after enrollment, reducing the subsequent risk in the cohort. It is also possible that the movement away from “old” drugs, particularly stavudine, toward alternative agents that are not associated with lipoatrophy development and have a lesser or no effect on mitochondria may partially explain this finding.
Our data do not show a significant relationship between cumulative exposure to protease inhibitors and new-onset diabetes. This result is in line with a recent study in protease inhibitor–exposed women, which showed that cumulative exposure to protease inhibitors was not associated with incidence of diabetes, whereas cumulative exposure to NRTIs was (3
). Antiretroviral regimens that include protease inhibitors for the treatment of HIV-1 have been associated with new-onset diabetes and insulin resistance (13
). Reversal of hyperglycemia after protease inhibitor withdrawal, onset of hyperinsulinemia before measurable body composition changes in protease inhibitor recipients, and improvements in insulin sensitivity after substitution of protease inhibitors by the NNRTI nevirapine or the NRTI abacavir all suggest a direct effect of protease inhibitors on reducing insulin sensitivity in HIV-infected patients (15
). In our study, we focused on the cumulative effect of exposure to antiretroviral drugs. Data from other studies suggest that the effect of indinavir on insulin resistance is an acute onset effect rather than a cumulative or long-term effect and that this effect is reversible after drug discontinuation. The acute effect seen with indinavir in human volunteers on insulin resistance is limited in size and not on the order of magnitude of the relationship seen with lipodystrophy. The Swiss HIV Cohort Study showed recently that new-onset diabetes was independently associated with current exposure to indinavir, lamivudine-stavudine, didanosine-stavudine, and didanosine-tenofovir; other protease inhibitors and NRTIs also showed trends (17
). In a preliminary analysis, we tested whether current use of indinavir or other protease inhibitors was associated with the risk of developing diabetes, finding that current indinavir exposure was an additional risk factor for diabetes in our dataset. Additional analyses are planned to quantify this effect. The apparent slightly protective effect of ritonavir should be viewed cautiously; it could reflect the increasing use of more recent ritonavir-boosted protease inhibitor regimens with less impact on insulin sensitivity.
Total cholesterol, HDL cholesterol, and triglyceride levels were all associated with new-onset diabetes after adjustment for demographic and clinical factors as well as for stavudine exposure, but adjustment for lipid parameters only slightly reduced the relationship between stavudine and diabetes. This relationship could be due to a common pathophysiological mechanism leading to both lipid disorders and diabetes. Alternatively, lipolysis and increased serum free fatty acids have been documented in HIV-positive individuals. Excess free fatty acids in the circulation may reduce insulin sensitivity through inappropriate lipid storage in muscle and liver, resulting in impaired glucose utilization and insulin-mediated inhibition of glucogenolysis and gluconeogenesis (6
Clinically observed lipodystrophy was also significantly associated with new-onset diabetes in accordance with previous studies showing that abnormal body fat distribution in HIV-positive individuals is strongly associated with insulin resistance and/or glucose intolerance, with excess trunk or visceral fat being, as in the general population, a risk factor for insulin resistance among those with HIV infection. In addition, insulin resistance is itself independently associated with fat loss in HIV-positive individuals (4
Our data confirm previous findings on the relationship between new-onset diabetes and exposure to stavudine (but also zidovudine and didanosine), increased total cholesterol, decreased HDL cholesterol, and increased triglycerides. Interestingly, relationships for those parameters remained significant after adjustment for all other available risk factors. The large size of this cohort provides greater power to detect findings that other cohorts may be insufficiently powered to detect. However, it is possible that some of these results may reflect chance findings. There are several limitations of the study that should be considered: first, cohort studies such as ours cannot formally determine causality. However, they do permit an association between drug exposure and incidence of diabetes to be established and our findings are both consistent with those of other cohorts and biologically plausible. Second, factors such as treatment interruptions or changes in adherence are not taken into account because of the complex treatment patterns in this population. Finally, although we recognize that standardized assessments of lipodystrophy would have been preferable, this is unrealistic to achieve in a large multicohort collaboration such as this.
The relationship between new-onset diabetes and exposure to stavudine (and other NRTIs) and lipodystrophy is a striking finding, particularly as adjustment for lipodystrophy did not modify the relationship between stavudine and diabetes. It is plausible that stavudine and other NRTIs directly contribute to insulin resistance and diabetes, apart from any indirect effect by way of lipodystrophy development. It should also be noted that our binary categorization of lipodystrophy may provide a relatively blunt tool with which to perform statistical adjustment; adjustment for the degree to which lipodystrophy is present (rather than just its presence or absence) may explain a higher proportion of the effect of stavudine. However, this level of information on lipodystrophy is rarely collected.