Bone mineral density of the lumbar spine
At baseline, eight of 22 (36.4%) patients in the ZDV/3TC/LPV/r group and seven of 26 (26.9%) in the NVP/LPV/r group had lumbar spine osteopenia. One patient in the ZDV/3TC/LPV/r group (4.5%) and two in the NVP/LPV/r group (7.7%) had lumbar spine osteoporosis.
As was the case for the femur, lumbar spine BMD decreased significantly in both groups after cART initiation, there was a trend for this decrease to be greater in the ZDV/3TC/LPV/r group compared to the NVP/LPV/r group (−5.1% ± 0.8% (P < 0.0001) and −2.6% ± 0.7% (P = 0.0006), respectively, between-group P = 0.07) (Table 2, Fig. 2). Patients in the ZDV/3TC/LPV/r group had significantly lower lumbar spine BMD after 24 months than patients in the NVP/LPV/r group (between-group difference 0.025 ± 0.01 g/cm2, P = 0.01). After 24 months, six of 18 (33.3%) patients in the ZDV/3TC/LPV/r group and eight of 22 (36.4%) in the NVP/LPV/r group had lumbar spine osteopenia (P = 0.97). Three patients, two in the ZDV/3TC/LPV/r group and one in the NVP/LPV/r group, developed lumbar spine osteoporosis over 24 months; two patients with osteoporosis at baseline dropped out of the study.
Lumbar spine BMD measured by QCT also declined significantly in both groups over 24 months. However, in contrast to DXA scan results, no difference in BMD decrease was observed between groups. At level L2, the BMD decrease was 10.9 ± 2.9 mg/cm3 (6.0 ± 2.0%, P = 0.003) in the ZDV/3TC/LPV/r group and 11.5 ± 3.0 mg/cm3 (7.7 ± 2.1%, P = 0.003) in the NVP/LPV/r group, between-group P = 0.65. At level L3, these differences were 10.5 ± 2.6 mg/cm3 (5.9 ± 1.7%, P = 0.001) and 13.3 ± 2.7 mg/cm3 (9.2 ± 1.8%, P < 0.0001) for the ZDV/3TC/LPV/r and NVP/LPV/r groups, respectively, between-group P = 0.66.
A greater decrease in lumbar spine BMD by DEXA was significantly correlated with a decrease in serum 25-hydroxy-vitamin D (correlation coefficient 0.43, P = 0.009), and a greater decrease in lumbar spine BMD by QCT was significantly correlated with an increase in parathyroid hormone (correlation coefficients 0.42 (P = 0.017) and 0.42 (P = 0.018) for levels L2 and L3, respectively).
Analysis adjusted for body composition changes
All longitudinal analyses of BMD measured by DXA scans were repeated after adjustment for changes in soft tissue surrounding the measured bone site. For the femur, adjustments were made for changes in total leg fat and lean mass, and for the lumbar spine, adjustments were made for changes in trunk fat and lean mass. Separate adjustments were also made for changes in body weight. These adjustments did not change the results of the analyses described earlier (data not shown).
Markers of bone metabolism
Osteocalcin increased significantly in both groups over 24 months (+1.60 ± 0.32 (P < 0.0001) and +1.81 ± 0.29 (P < 0.0001) nmol/l for the ZDV/3TC/LPV/r and NVP/LPV/r groups, respectively), with no significant difference between the groups, overall or at any timepoint (Table 2). The ratio of urine deoxypyridinoline to urine creatinine also increased significantly over 24 months in both groups (+1.35 ± 0.44 nmol/mmol (P = 0.0029) and +1.19 ± 0.38 nmol/mmol (P = 0.0024) for the ZDV/3TC/LPV/r and NVP/LPV/r groups, respectively), between-group P = 0.41. Serum 25-hydroxy-vitamin D and serum calcium (corrected for albumin) did not change over time in either of the groups. PTH increased significantly in both groups, but to a greater degree in the NVP/LPV/r group (+2.0 ± 0.31 pmol/l (P < 0.0001) compared to +0.81 ± 0.33 pmol/l (P = 0.021) in the ZDV/3TC/LPV/r group, (between-group P = 0.009). After 24 months, PTH was significantly higher in patients in the NVP/LPV/r group than in those treated with ZDV/3TC/LPV/r (between-group difference 1.24 ± 0.34 pmol/l (P = 0.0009). Concurrently, a significant decline in serum phosphate was observed in the NVP/LPV/r group (−0.10 ± 0.04 mmol/l (P = 0.011)), whereas no overall change occurred in this parameter in patients in the ZDV/3TC/LPV/r group.
There was no overall significant difference in serum lactate levels between the groups, although there was a transient increase of 0.6 ± 0.22 mmol/l (P = 0.008) over the first 12 months in the ZDV/3TC/LPV/r group leading to a difference of 0.58 ± 0.27 mmol/l (P = 0.035) between groups at 12 months.
Osteopenia and osteoporosis are increasingly being reported among HIV-infected patients. To our knowledge, this is the first prospective study comparing a ZDV/3TC-containing with a ZDV/3TC-sparing regimen investigating changes in BMD and bone turnover after treatment initiation in cART-naive HIV-infected patients. Our findings confirm the high prevalence of osteopenia , already present prior to start of cART. We observed a rapid BMD decrease in both femoral neck and lumbar spine after initiation of cART. The BMD loss measured by DXA was significantly greater in patients randomized to ZDV/3TC/LPV/r compared to those using NVP/LPV/r. In both groups, lumbar spine bone loss appeared to stabilize in the second year of treatment, whereas in the femoral neck progressive bone loss was observed in the second year in the ZDV/3TC/LPV/r group only. Furthermore, markers of bone formation (osteocalcin), and bone resorption (urine DPD/creatinine ratio) increased significantly after cART initiation in all patients, indicating an increase in bone turnover.
Our finding that patients treated with ZDV/3TC/LPV/r had significantly greater bone loss compared to those using NVP/LPV/r suggests that ZDV/3TC contributes to bone loss in patients initiating cART. This result is somewhat consistent with another study in which patients using ZDV-containing regimens or stavudine-containing regimens had a small but significant total body BMD decrease during 104 weeks follow-up, whereas those switching to abacavir had stable BMD . Both zidovudine and lamivudine have been shown to enhance osteoclastogenesis , potentially leading to bone loss. Lactic acidemia due to NRTI-related mitochondrial dysfunction has also been suggested to play a role in reduced (total body) BMD in HIV-infected patients . Another study in which patients switching to low-dose stavudine had improvement in mitochondrial indices and stable BMD, whereas those continuing full dose stavudine had significant bone loss after 48 weeks, may also support this hypothesis . In our study, lactate levels did not differ significantly between the two groups over time. However, the transient significant increase in lactate in the ZDV/3TC/LPV/r group in the first year, concurrent with the greatest bone loss, could suggest that lactic acidemia plays a role.
Alternatively, a protective effect of NVP may theoretically explain the difference in bone loss between the groups, although we are not aware of any clinical or in-vitro evidence supporting this theory.
The degree of bone loss over 24 months in the ZDV/3TC/LPV/r group is comparable to that observed in patients starting the same regimen in a small 48-week trial . In that study, patients using ZDV/3TC with abacavir had significantly less BMD decrease than those using ZDV/3TC/LPV/r, suggesting a contribution of LPV/r to bone loss. Other studies on the role of protease inhibitors, including LPV/r, in bone loss have had conflicting results [24,25]. As all patients in our study used LPV/r, and LPV exposure was not significantly different between groups, we cannot draw any conclusions concerning the role of this protease inhibitor in the observed BMD changes.
The difference in decrease of lumbar spine BMD between groups was only visible when measured by DXA and not by QCT scan. There are several potential explanations for this apparent contrast. First, QCT scan measured the central part of the vertebral body, that is, trabecular bone, whereas DXA scan cannot differentiate between trabecular and cortical bone. Our findings therefore suggest that cortical bone is mainly affected in the ZDV/3TC/LPV/r group, whereas trabecular bone loss was similar in both groups. A histomorphometric study of bone biopsies could confirm this hypothesis. Another possible explanation for this discrepancy may be underestimation of BMD by DXA scan, which can occur when the ratio of fat to lean tissue decreases in the area surrounding the bone, as may be the case in our patients [26,27]. As adjustment of analyses for local fat and lean mass did not change the results, this does not appear to be the most likely explanation for the observed differences.
The increases in serum osteocalcin and the urinary DPD/creatinine ratio in all patients indicate an increase in bone turnover after initiation of cART. High bone turnover usually leads to increased bone loss, as is seen for instance in the menopausal state and hyper (para)thyroidism. Our findings are in agreement with the only other longitudinal study that measured markers of bone metabolism in patients initiating cART . In the pre-HAART era, HIV-infected patients were generally observed to have low-serum osteocalcin concentrations [28–30], consistent with a low-bone formation rate, and high levels of bone resorption markers . In addition to direct effects of HIV proteins on osteoblasts and osteoclasts, chronic inflammation may play a role, and various cytokines are known to increase osteoclast activity [31,32] and inhibit bone formation [33,34]. Suppression of HIV and the accompanying chronic inflammatory response may reverse or ameliorate some of these processes. Unfortunately, the design of our study does not enable us to distinguish whether and to what extent these changes may be due to the suppression of HIV or to any direct effects of antiretroviral drugs.
cART-naive HIV-infected patients have been shown to have relatively low levels of PTH . Various mechanisms have been suggested, including suppression of PTH secretion by TNF-alpha, and parathyroiditis due to HIV . An increase in PTH after start of cART is therefore not an unexpected finding, and is in agreement with a previous study . The increase in PTH may explain part of the bone loss, as suggested by the significant correlation between the decrease in lumbar spine BMD and PTH increase, possibly in combination with low vitamin D3 levels. The greater increase of PTH in the NVP/LPV/r group however remains unexplained, especially as this group had less bone loss than the ZVD/3TC/LPV group, suggesting that the PTH increase does not explain the difference in bone loss between the two groups.
Previous studies have shown that the relative risk of fracture for a BMD decrease of one standard deviation below age-adjusted mean (Z-score) is approximately 2–2.5 [36,37]. Although these studies were performed in a different population, these results suggest that the observed BMD changes in our study may eventually increase the risk of osteoporotic fractures. In particular, the 0.5 SD BMD loss in the lumbar spine in the ZDV/3TC/LPV/r group can be calculated to correspond to an approximately 50–60% greater relative fracture risk, whereas in the NVP/LPV/r arm this risk would be around 30% greater. As the absolute fracture risk is low in this age category, a clinically significant difference may only become apparent after longer follow-up with older age.
The main limitation of our study is the limited sample size. Smaller differences in markers of bone turnover, which might have been expected considering the observed differences in bone loss between groups, may therefore have remained undetected. Another potential limitation is that DXA scans were performed at different sites and were not analyzed centrally.
In conclusion, we demonstrated a rapid BMD decrease in both femoral neck and lumbar spine after initiation of cART, in parallel to an increase in bone turnover. The loss of BMD was significantly greater in the ZDV/3TC/LPV/r group compared to the NVP/LPV/r group, suggesting that ZDV/3TC contributes to this process, the mechanism of which remains to be elucidated.
We are indebted to Ingrid Knufman for her excellent assistance and to Kees van Kuijk and Henk Venema for the analysis and interpretation of the quantitative CT scans.
We gratefully acknowledge the contribution of the following investigators and research nurses to coordinate the study in their respective sites:
K. Brinkman, A. Carroll, F.A.P. Claessen, O. Debnam, W. Dorama, A. van Eeden, L. Elsenburg, P.H.J. Frissen, S.E. Geerlings, L. Gelinck, L. Hegeman, N. Hulshoff, R.W. ten Kate, A. Kritsos, F.P. Kroon, S. Lowe, R.M. Perenboom, M. Ristola, M. Schoemaker, W.E.M. Schouten, L. Schrijnders, J. Stadwijk, J. Sutinen, J. Tesselaar, H. Wiggers, M. Youle.
Author contributions: M.vV. contributed to the conception and design of the study, the acquisition, analysis and interpretation of the data, and the drafting and revising of the article. P.L. contributed to the analysis and interpretation of the data and the drafting and revising of the article. M.vA. contributed to the analysis and interpretation of the data and the revising of the article. E.H. contributed to the analysis and interpretation of the data and the revision of the article. K.B., S.G., J.S. and M.R. contributed to the acquisition and interpretation of the data and the revision of the manuscript. S.D. contributed to the conception and design of the study, the interpretation of the data and the revision of the manuscript. P.R. contributed to the conception and design of the study, the acquisition, analysis and interpretation of the data and the drafting and revising of the manuscript. All authors approved the final version of the manuscript.
Financial support: This study was sponsored by an independent scientific grant from Abbott International and Boehringer Ingelheim Corporate. The sponsors were involved in the design of the study and in the review of the manuscript, but not in the conduct of the study, collection, management, analysis and interpretation of the data; preparation and approval of the manuscript; or decision to submit for publication.(ClinicalTrials.gov number: NCT 00122226, http://www.clinicaltrials.gov).
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Keywords:© 2009 Lippincott Williams & Wilkins, Inc.
acquired immune deficiency syndrome; HIV; nucleoside reverse transcriptase inhibitors bone mineral density; osteoporosis