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AIDS:
doi: 10.1097/QAD.0b013e32832c4947
Clinical Science

First line zidovudine/lamivudine/lopinavir/ritonavir leads to greater bone loss compared to nevirapine/lopinavir/ritonavir

van Vonderen, Marit GAa,*; Lips, Paula; van Agtmael, Michiel Aa; Hassink, Elly AMb; Brinkman, Keesc; Geerlings, Suzanne Ed; Sutinen, Jussie; Ristola, Mattie; Danner, Sven Aa; Reiss, Peterd

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Author Information

aVU University Medical Center, Department of Internal Medicine, The Netherlands

bInternational Antiviral Therapy Evaluation Center, The Netherlands

cOnze Lieve Vrouwe Gasthuis, Department of Internal Medicine, The Netherlands

dAcademic Medical Center, Department of Infectious Diseases, Tropical Medicine and AIDS and Center for Infection and Immunity, Amsterdam, The Netherlands

eHelsinki University Central Hospital, Department of Internal Medicine, Helsinki, Finland.

* Current affiliation: Medisch Centrum Leeuwarden, Leeuwarden, The Netherlands.

Received 17 January, 2009

Revised 27 March, 2009

Accepted 30 March, 2009

Correspondence to M.G.A. van Vonderen, MD, VU University Medical Center, Department of Internal Medicine 4A35, PO Box 7057, 1007 MB Amsterdam, The Netherlands. E-mail: M.van.Vonderen@znb.nl

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Abstract

Objective: We studied changes in bone mineral density (BMD) and bone turnover after initiation of combination antiretroviral therapy (cART) and the contribution of zidovudine/lamivudine (ZDV/3TC) in particular.

Design: Randomized clinical trial comparing lopinavir/ritonavir(LPV/r) + ZDV/3TC with LPV/r + nevirapine (NVP) in 50 cART-naive men.

Methods: Dual energy X-ray absorptiometry (DXA) and quantitative computed tomography scans (QCT) were performed at baseline and 3, 12, and 24 months after cART initiation. Serum 25-hydroxy-vitamin D3, parathyroid hormone (PTH), osteocalcin, and urine deoxypyridinoline (DPD)/creatinine ratio were measured.

Results: BMD decreased rapidly in both femoral neck and lumbar spine after cART initiation. BMD loss during 24 months measured by DXA, but not by QCT, was greater in the ZDV/3TC/LPV/r group compared to the NVP/LPV/r group [femoral neck: −6.3% ± 1.0% (P < 0.0001) compared to −2.3% ± 0.9% (P = 0.01), between-group P = 0.0006); lumbar spine: −5.1% ± 0.8% (P < 0.0001) compared to −2.6% ± 0.7% (P = 0.0006), between-group P = 0.07]. Osteocalcin [+1.60 ± 0.32 (P < 0.0001) and +1.81 ± 0.29 (P < 0.0001) nmol/l] and the urine DPD/creatinine ratio [+1.35 ± 0.44 (P = 0.0029) and +1.19 ± 0.38 nmol/mmol (P = 0.0024)] increased in both groups over 24 months, with no significant difference between groups. PTH increased 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].

Conclusion: BMD in both femoral neck and lumbar spine decreased rapidly after initiation of cART, in parallel to an increase in bone turnover. The greater bone loss in the ZDV/3TC/LPV/r group compared to the NVP/LPV/r group suggests that ZDV/3TC contributes to this process. The PTH increase does not explain this greater bone loss.

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Introduction

An increased prevalence of reduced bone mineral density (BMD) has been reported among HIV-infected patients [1]. Longitudinal studies have generally observed a decrease in BMD after the initiation of combination antiretroviral therapy (cART) in cART-naïve patients [2–4]. However, prospective studies in cART-experienced patients have shown either an increase in or stable BMD over time [5–9], suggesting that BMD may stabilize after an initial decline after the start of cART. Recently, in a large population-based study, fracture prevalence was shown to be increased in HIV-infected patients compared to non-HIV-infected controls [10].

The mechanisms for reduced BMD in HIV-infected patients have not been fully elucidated. HIV proteins have been shown to modulate osteoblast function and development [11], and may also affect osteoclastogenesis [12]. Persistent proinflammatory activation in HIV infection has been associated with disturbed bone formation and resorption [13]. Other traditional risk factors frequently found in HIV-infected patients, including low body weight, hypogonadism and a high smoking prevalence, may also play a role [14]. The contribution of antiretroviral drugs to reduced BMD in HIV-infected patients is a controversial issue. In-vitro evidence suggests that different protease inhibitors have heterogeneous effects on bone [15,16]. Among the nucleoside reverse transcriptase inhibitors (NRTI), zidovudine, lamivudine and didanosine have been shown to enhance osteoclastogenesis [17], whereas tenofovir has been associated with decreased BMD [17], potentially due to renal phosphate wasting, a mineralization defect and, ultimately, osteomalacia [18]. Prospective randomized trials investigating the effects of initiation of different antiretroviral drugs on bone mineral metabolism are scarce and have mainly focused on the role of protease inhibitors and tenofovir [3,4].

We aimed to explore the role of zidovudine and lamivudine (ZDV/3TC) on BMD and bone metabolism in patients initiating cART. We performed sequential BMD measurements of the femoral neck and lumbar spine and of serum and urine markers of bone metabolism in a randomized clinical trial, comparing a thymidine analogue (TA)-NRTI sparing regimen of nevirapine with lopinavir/ritonavir with a TA-NRTI containing regimen of ZDV/3TC combined with lopinavir/ritonavir in prior cART-naïve patients. We hypothesized that bone loss would be greater in patients using ZDV/3TC than in patients in the TA-NRTI sparing group. We currently report the results of the planned primary analysis after 24 months follow-up.

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Patients and methods

Study design and patients

The MEDICLAS (Metabolic Effects of DIfferent CLasses of AntiretroviralS) trial is a multicenter, single-blinded, randomized trial of 36 months duration comparing the TA-NRTI-containing regimen of zidovudine/lamivudine [ZDV/3TC, 300/150 mg twice daily (b.i.d.)] + lopinavir/ritonavir (LPV/r, 400/100 mg b.i.d.) with the TA-NRTI-sparing regimen of nevirapine (NVP, 200 mg b.i.d.) + LPV/r (533/133 mg b.i.d.) [19]. To compensate for an increased LPV/r clearance resulting from NVP-associated hepatic enzyme induction, an increased dose of LPV/r was used in combination with NVP to aim for comparable therapeutic LPV plasma concentrations in both trial arms. The main objective of the trial is to assess and compare the impact of both treatments on body fat distribution and metabolic complications. Patients were included between February 2003 and June 2005, complete 24-month follow-up ended in June 2007.

Eligible patients were antiretroviral-naïve HIV-1-infected men, 18–70 years old, with an indication to start cART according to international and national guidelines in each participating country. Individuals with severe obesity (BMI > 35 kg/m2), diabetes mellitus, a history of hyperlipidemia, or use of lipid-lowering drugs, nandrolone or testosterone, were excluded. Patients were recruited from HIV treatment centers in the Netherlands, Spain, Finland and the United Kingdom. The study was approved by the ethics committees of all participating centers, and each patient provided written informed consent prior to study entry.

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Randomization procedure

At the central study-coordinating center a treatment allocation sequence (1: 1 for ZVD/3TC + LPV/r and NVP + LPV/r) was generated using the minimization variable BMI (BMI ≤ 25 kg/m2 versus > 25 kg/m2).

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Procedures

Primary outcome measure was BMD, measured by dual energy X-ray absorptiometry (DXA) in all participants and quantitative computed tomography (QCT) scans in those recruited in the Netherlands, Finland and the United Kingdom at baseline and 3, 12, 24 and 36 months after start of treatment. DXA scans were performed in the Hospital Clinic, Barcelona for Spanish participants, and in the VU University Medical Center and Academic Medical Center, Amsterdam for all other participants. QCT scans were performed in the Academic Medical Center at the same timepoints as DXA scans. At the same timepoints, secondary outcome measures serum and urine markers of bone turnover were assessed in all participants, and body fat distribution was measured as previously described [19]. Limb and trunk fat were quantified by DXA (Hologic QDR-4500W, software version whole body v8.26A:5). A standardized single slice abdominal CT-scan was performed from which the surface area of visceral (VAT), subcutaneous (SAT), and total adipose tissue (TAT) was determined. Plasma HIV-1 RNA measurements, CD4 cells, adverse events and lactate levels were monitored at baseline, after 1 and 3 months of treatment, and every three months thereafter. LPV concentration was analysed centrally at baseline and after 3, 12 and 24 months.

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Dual energy X-ray absorptiometry

BMD of the lumbar vertebrae (L1-L4) and hip (femoral neck) were measured by DXA (Hologic QDR-4500W, Hologic Inc., Bedford, Massachusetts, USA). BMD was defined as bone mineral content, divided by the surface of the projected bone area, expressed in g/cm2. T-scores and Z-scores were calculated using hip reference values based on the National Health and Nutrition Examination Survey (NHANES III) and Hologic reference values for the lumbar spine (L1-L4). The T-score is the patient's BMD expressed as the number of standard deviations difference from the mean BMD of the 30-year old reference population (of the same sex), the Z-score is the patient's BMD expressed as the number of standard deviations difference from the mean of the age-matched reference population. As defined by the World Health Organization, a BMD T-score of minus 2.5 or less was classified as osteoporosis and a BMD T-score between −1 and −2.5 as osteopenia. Scans were analyzed by radiology staff blinded to allocated treatment.

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Quantitative computed tomography scans

A cross-sectional CT scan (Mx8000 4-slice CT-scanner, Philips Medical Systems, Best, The Netherlands) of the abdomen at the level of the lumbar spine was performed. A solid calcium hydroxyapatite QCT reference phantom (QCT-5000, Image Analysis Inc, Columbia, Kentucky, USA) was placed beneath the patient's lower back. This phantom contains four cylinders of calciumhydroxyapatite with different concentrations (0, 50, 100, and 200 mg/cm3). A lateral scout image standardized the location of slices at the mid L2 and L3 vertebrae. Standardized scanning specifics were set at 120 kV, 100 mAs, 10 mm slice thickness and a field-of-view between 300 and 500 mm. Elliptical regions of interest (ROIs) were manually defined in the images in the region of the trabecular bone of each vertebral body; the mean CT-number (in Houndsfield Units) within each ROI was calculated. Mean CT-numbers of the cylinders of calciumhydroxyapatite within the reference phantom were determined likewise. The mean CT-number of the trabecular bone of each vertebra was converted into bone density in mg/cm3 calciumhydroxyapatite by comparing both sets of measurements [20]. All scans were analyzed by two blinded investigators.

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Markers of calcium metabolism and bone turnover

25-hydroxy-vitamin D3 was measured by a competitive binding protein assay (Diasorin, Stillwater, Minnesota, USA). The intraassay and interassay coefficients of variation were 9 and 10%, respectively. Parathyroid hormone (PTH) was measured by an immunometric assay (Abbott Laboratories, Abbott Park, Illinois, USA). The intraassay and interassay coefficients of variation were both 5%. Osteocalcin, a marker of bone formation, was measured by an immunometric assay (Biosource, Nivelles, Belgium), with an intraassay and interassay coefficient of variation of less than 5 and 7%, respectively. Urine deoxypyridinoline (DPD), a marker of bone resorption, was measured by a competitive immunoassay (Immulite 2500, Siemens, California, USA). The intraassay and interassay coefficients of variation were both 10%. The ratio of urine deoxypyridinoline to urine creatinine (in nmol/mmol creatinine) was calculated.

25-hydroxy-vitamin D3 and PTH were measured at baseline and after 24 months, all other markers were performed at all study visits.

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Statistical analysis

Analyses were by intention-to-treat, including all randomized patients who received at least one dose of allocated treatment. BMD was a prespecified secondary outcome of the study, albeit the study was not powered specifically to look at changes in BMD. Within-group changes, between-group differences in overall course and between-group differences at study visits were analyzed by mixed model repeated measures analysis with correction for differences in baseline values. A second longitudinal analysis of BMD by DXA was performed with adjustment for local changes in fat and lean mass. Data are presented as estimated means ± standard error of the mean. Data that were not analyzed longitudinally were compared between groups using Mann–Whitney U tests and chi squared/Fisher exact tests (where applicable). The correlations between baseline to 24 months changes in markers of bone metabolism and changes in bone mineral density were calculated by Pearson correlation analysis. Alpha less than 0.05 was considered statistically significant. SAS version 9.2 (SAS Institute, Cary, North Carolina, USA) (for the longitudinal analysis) and SPSS statistical software version 15.0 (SPSS Inc, Chicago, Illinois, USA) were used for the analyses.

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Results

Patient characteristics

Fifty patients were included in the study; 23 were randomly assigned to ZDV/3TC/LPV/r and 27 to NVP/LPV/r (Fig. 1). The groups had comparable baseline demographic and HIV disease characteristics (Table 1). Antiretroviral therapy was modified in eight patients. In the ZDV/3TC/LPV/r group, one patient switched from ZDV to tenofovir after 3 months for anemia, one switched to tenofovir/lamivudine/efavirenz after 4 months for anemia and hypercholesterolemia and one patient switched from LPV/r to NVP for hypercholesterolemia after 17 months. In the NVP/LPV/r group, two patients switched to ZDV/3TC/NVP, one after 3 months for diarrhea and one after 24 months at his own request. In three other patients NVP was replaced by efavirenz because of hepatotoxicity and/or rash after 1, 2 and 5 months, respectively. Data of all patients switching medication were included in the analysis. An analysis in which patients who switched antiretroviral medication were excluded yielded essentially the same results as the analyses described below. No fractures were reported during the trial period. None of the patients used corticosteroid therapy at baseline and none of the patients received any treatment for low-bone mineral density during the study.

Fig. 1
Fig. 1
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Table 1
Table 1
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Body composition, virology, immunology and lopinavir concentrations

Body composition changes and virologic and immunologic responses to cART were reported previously [19]. In summary, patients in the ZDV/3TC/LPV/r group had a progressive decline in limb fat after the first 3 months, whereas limb fat increased in patients randomized to NVP/LPV/r. Trunk fat increased in both groups, but VAT increased in patients on ZDV/3TC/LPV/r only. Patients in both groups had similar immunologic and virologic responses to cART. The median CD4 cell increase over 24 months was 280 (205–455) and 308 (191–410) × 106 cells/l in the ZDV/3TC/LPV/r group and NVP/LPV/r group, respectively. At 24 months, 17/22 (77%) of the patients in the ZDV/3TC/LPV/r group and 21/26 (80%) in the NVP/LPV/r group had plasma HIV-RNA less than 50 copies/ml. After 24 months there was a trend for the LPV concentration to be greater in the NVP/LPV/r group (8.0 (4.0–9.3) mg/l compared with 5.5 (3.8–6.9) mg/l for the ZDV/3TC/LPV/r group (P = 0.065).

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Bone mineral density of the femoral neck

At baseline, six of 22 (27.3%) patients in the ZDV/3TC/LPV/r group and eight of 26 (30.8%) in the NVP/LPV/r group had femoral neck osteopenia One patient in the ZDV/3TC/LPV/r group (4.5%) and none in the NVP/LPV/r group had femoral neck osteoporosis. Femoral neck BMD decreased significantly in both groups after cART initiation, but this decrease was significantly greater in the ZDV/3TC/LPV/r group compared to the NVP/LPV/r group (loss of 6.3% ± 1.0% (P < 0.0001) and 2.3% ± 0.9% (P = 0.01), respectively, between-group P = 0.0006) (Table 2, Fig. 2). After 24 months, patients in the ZDV/3TC/LPV/r group had significantly lower femoral neck BMD compared to patients in the NVP/LPV/r group (between-group difference 0.036 ± 0.01 g/cm2, P = 0.0006). After 24 months, seven of 18 (38.9%) patients in the ZDV/3TC/LPV/r group and nine of 21 (40.9%) in the NVP/LPV/r group had osteopenia (P = 0.58); no patients had osteoporosis in either group. The patient with osteoporosis at baseline dropped out of the study after 3 months. Changes in femoral neck BMD did not correlate significantly with any changes in markers of bone metabolism.

Table 2
Table 2
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Fig. 2
Fig. 2
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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).

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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).

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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.

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Discussion

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 [1], 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 [21]. Both zidovudine and lamivudine have been shown to enhance osteoclastogenesis [17], 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 [22]. 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 [23]. 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 [4]. 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 [13]. 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 [30]. 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 [35]. Various mechanisms have been suggested, including suppression of PTH secretion by TNF-alpha, and parathyroiditis due to HIV [35]. An increase in PTH after start of cART is therefore not an unexpected finding, and is in agreement with a previous study [13]. 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.

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Acknowledgements

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:

acquired immune deficiency syndrome; HIV; nucleoside reverse transcriptase inhibitors bone mineral density; osteoporosis

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