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Department of Internal Medicine, Division of Nephrology, University
Hospital, Albert-Ludwigs-University, Freiburg, Germany.
Department of Internal Medicine, Division of Endocrinology, University
Hospital, Albert-Ludwigs-University, Freiburg, Germany.
Department of Diagnostic Radiology, Division of Transplantation,
University Hospital, Albert-Ludwigs-University, Freiburg, Germany.
Department of Orthopedics, Division of Transplantation, University
Hospital, Albert-Ludwigs-University, Freiburg, Germany.
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Department of Surgery, Division of Transplantation, University Hospital,
Albert-Ludwigs-University, Freiburg, Germany.
¶
Department of Medical Biometrics, University Hospital,
Albert-Ludwigs-University, Freiburg, Germany.
Correspondence to Dr. Wolfgang Grotz, Department of Internal Medicine, Albert-Ludwigs-University Freiburg, Hugstetter Strasse 55, D-79106 Freiburg, Germany. Phone: 0761-270-3401; Fax: 0761-270-3232; E-mail: grotz{at}mm41.ukl.uni-freiburg.de
| Abstract |
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| Introduction |
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| Materials and Methods |
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Study Design
Eighty of 114 consecutive renal allograft recipients were randomized to
treatment or control (Figure
1). Patients had diet counseling to achieve an intake of at least
1000 mg of calcium per day. Patients with intolerance to dairy products were
supplemented with 500 mg of calcium (Calcium-Sandoz forte, Basel,
Switzerland). Treated patients received four intravenous bolus injections of
ibandronate (Bondronat, Roche, Weil am Rhein, Germany). Dosages were 1 mg
immediately before and 2 mg at 3, 6, and 9 mo after transplantation. The
dosing schedule is based on a previous study that investigated the effect of
different doses of ibandronate in postmenopausal osteoporosis
(12). The dose before
transplantation was reduced to account for renal insufficiency. The primary
end point was the change of bone mineral density after 12 mo. Graft outcome,
spinal deformities, fractures, body height, and hormonal and metabolic data
also were recorded.
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Bone Mineral Density Measurement
Bone mineral density was measured by dual energy x-ray absorptiometry
(DEXA-L Lunar) at lumbar spine (L1 to L4; spongy bone), femoral neck (spongy
and cortical bone), and midfemoral shaft (cortical bone) because of its
different admixture of cortical and trabecular bone. Results are expressed as
absolute values in gram hydroxylapatite per square centimeter
(g/cm2) and as relative values in number of SD below the expected
normal gender-, age-, and weight-adjusted bone mineral density value.
Calibration was performed daily. The precision error was 0.011
g/cm2. A standard set of lateral radiographs was obtained to select
radiographically intact lumbar vertebrae. The average bone mineral density of
vertebrae L2 to L4 was calculated.
Radiologic Measurements
At the end of the study, all x-rays were evaluated by a radiologist who was
blinded to the randomization. Anterior and posterior height of each lumbar
vertebra (L1 to L5) was measured. A new (incident) vertebral deformity was
defined as reduction of the sum of anterior and posterior height of each
lumbar vertebra greater than 5% between the baseline and follow-up radiographs
(13). A vertebral fracture was
defined as reduction of the anterior or posterior height greater than 20%
compared with the adjacent vertebrae. Body height was measured in the morning
at the same time for each patient.
Laboratory Measurements
Serum creatinine, alkaline phosphatase, serum phosphate, and serum calcium
were assayed with routine methods. Prolactin, follicle-stimulating hormone,
luteinizing hormone, and estradiol were measured by immunoradiometric magnetic
solid phase assays (MAIAclone; Biochem Immunosystems, Freiburg, Germany). Free
testosterone and DHEA-SO4 were measured by coated tube assays (coat a count;
DPC, Los Angeles, CA). Plasma intact parathyroid hormone was determined by
immunoradiometric assay (Allegro; Nichols Institute, Bad Nauheim, Germany),
25-hydroxycholecalciferol was measured by radioimmunometric assay
(25(OH)-vitamin D RIA, IBL, Hamburg, Germany), 1,25-hydroxycholecalciferol was
measured by radio receptor assay (1,25(OH)2-vitamin D radioreceptor
assay; Immundiagnostik, Bensheim, Germany), bone alkaline phosphatase was
determined by immunoradiometric assay (Ostase; Beckmann,
München, Germany), osteocalcin was measured by
enzyme-linked immunosorbent assay (Osteocalcin; IBL, Hamburg, Germany), and
pyridinoline and deoxypyridinoline were measured by HPLC after acid hydrolysis
of the urine samples (Pyridinium-Crosslinks; Biorad,
München, Germany). Normal values are provided in
Table 1.
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Comedication and Immunosuppressive Therapy
Patients with initial vitamin D deficiency below 15 ng/ml were supplemented
with a single dose of 10,000 U of cholecalciferol (11 patients in the
ibandronate and 8 patients in the control group; vitamin D levels are shown in
Table 1). Hormone replacement
therapy was continued (one postmenopausal woman in each group).
Immunosuppressive therapy consisted of cyclosporine dosed to a blood level of
120 to 180 ng/ml; prednisone 100 mg for 5 d, 50 mg for 5 d, 25 mg for 10 d,
and tapered to 5 mg after 1 yr; and mycophenolate mofetil 2 g/d. Patients who
were receiving kidneys from unrelated living donors were treated additionally
with antilymphocyte globulin for 10 d. Acute rejections were treated with
three boluses of 500 mg of prednisone. Refractory cases received a 10-d course
of antilymphocyte globulin.
Acute Rejections
Acute rejections were clinically suspected when one or more of the
following criteria were present: increase in size and/or decrease in
tenderness of the graft and increase in serum creatinine and/or decrease in
urine volume after exclusion of other reasons
(14). Clinically suspected
rejections were confirmed by biopsy (Department of Pathology, University
Freiburg). When a biopsy was not possible, patients were considered to have
acute rejection when there was a positive response to prednisone bolus therapy
(decrease in serum creatinine and increase in urine volume).
Statistical Analyses
Sample sizes were calculated for an assumed 5% difference in bone mineral
density, an SD of 7.5, a power of 80%, and a two-sided level of significance
of 0.05, assuming a 10% loss of patients. The
2 test was used
for qualitative variables, and the Mann-Whitney U test was used for
quantitative variables. ANOVA for repeated measurements was used for the
investigation of bone mineral density values using treatment groups as
covariate. Dropouts were not included in the analysis. Missing values were not
substituted. The impact of metabolic parameters on the treatment effect was
studied by introducing the corresponding covariate and by analysis of the
ANOVA interaction term. Multivariate analysis was performed with stepwise
backward elimination procedure. Results are presented as means ±
SD.
| Results |
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Bone Measurements
Progression of osteoporosis after transplantation was prevented by
ibandronate (lumbar spine, -0.9 ± 6.1% from baseline; femoral neck,
+0.5 ± 5.2%; and midfemoral shaft, +2.7 ± 12.2%). In control
subjects, the greatest bone loss occurred during the first 6 mo. After 1 yr,
bone mineral density of control subjects had decreased at lumbar spine (-6.5
± 5.4% from baseline), femoral neck (-7.7 ± 6.5%), and
midfemoral shaft (-4.0 ± 10.9%). Ibandronate-treated patients and
control subjects differed significantly (lumbar spine, P < 0.0001;
femoral neck, P < 0.0001; midfemoral shaft, P = 0.024
[ANOVA]; Figure 2).
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Subgroup analysis was done for antirejection therapy, gender, menopause, age, level of parathyroid hormone, and vitamin D supplementation. Patients with rejection had a significantly higher cumulative dose of prednisone as compared with patients without rejections (7362 ± 903 mg versus 5920 ± 999 mg). Patients with rejection demonstrated significant benefit when treated with ibandronate (n = 11) as compared with control subjects (n = 22) at the femoral neck (-1.1 ± 6.9% versus -8.6 ± 6.1%; P = 0.0025; Figure 3). Similar changes were seen at the two other sites; however, differences did not approach significance (lumbar spine, -1.7 ± 8.1% versus -5.7 ± 4.9% [P = 0.118]; midfemoral shaft, +0.8 ± 15.1% versus -7.2 ± 11.3% [P = 0.251]). A similar benefit of ibandronate treatment was observed in patients without rejection (lumbar spine, -0.5 ± 5.2% versus -7.8 ± 6.0% [P = 0.0002]; femoral neck, +1.3 ± 4.4% versus -6.3 ± 7.0% [P = 0.0002]; midfemoral shaft, +3.5 ± 10.8% versus +1.0 ± 8.4% [P = 0.204]). Ibandronate protected bone loss in all other subgroups and measured sites except lumbar spine of post-menopausal women (n = 5). Furthermore, ibandronate was the strongest predictor of bone loss at lumbar spine (P < 0.0001) and femoral neck (P < 0.0001) in multivariate analysis using all hormonal metabolic data before transplantation and graft function at the end of the study. Especially parathyroid hormone value or serum creatinine did not influence the results. Twenty-five patients (ibandronate, n = 13; control subjects, n = 12) were followed for a second year. Without further osteoporosis treatment, bone mineral density remained stable or increased slightly in both groups.
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Spinal deformities developed less frequently in the ibandronate group (7 patients with 7 deformities versus 12 patients with 23 deformities; P = 0.047 for deformities). On ibandronate, fewer patients lost body height (12 versus 21; P = 0.033). Mean height loss was 0.5 ± 1.0 cm versus 1.1 ± 1.0 cm (P = 0.049). One vertebral and one arm fracture occurred in each group.
Graft Outcome
Graft function at the end of the study was comparable (serum creatinine:
ibandronate, 115 ± 40 µmol/L; controls, 142 ± 100 µmol/L;
P = 0.136). Eleven rejection episodes occurred in the ibandronate
group compared with 22 episodes in control subjects (P = 0.009;
Table 4).
Two patients in the treatment group had early graft loss as a result of renal vein thrombosis (pediatric en bloc kidneys). Histology of the explanted kidneys showed no signs of acute rejection. Two patients from the treatment group and three patients from the control group died as a result of infectious complications.
Metabolic Data and Side Effects
Changes in metabolic parameters after transplantation were comparable in
both groups (Table 1). Three
patients on ibandronate reported side effects in temporal relation to
ibandronate administration (bone pain, flatulence). No side effects were
reported in the control group. No patient withdrew from the study as a result
of side effects.
| Discussion |
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Bisphosphonates are favorable compounds because of the few side effects and efficacy in both genders. They are incorporated into the bone and exert a variety of molecular mechanisms to inhibit osteoclast activity and bone resorption (26). There are various bisphosphonates that demonstrate great differences in their potency, route of administration, and effect on lymphocytes (27). Ibandronate was selected for its high potency and the possibility of intravenous injection. A schedule of four single injections (at transplantation and at 3, 6, and 9 mo thereafter) was used to improve compliance.
In the present study, ibandronate prevented posttransplantation loss of both spongy and cortical bone. Lumbar spine, femoral neck, and midfemoral shaft showed consistent results. Subgroup analysis showed only one possible exception. In the small subgroup of postmenopausal women (n = 5), bone loss was seen at lumbar spine but not at femoral neck and midfemoral shaft. It is possible that in these patients, higher doses of ibandronate or addition of estrogen is necessary for inhibition of posttransplantation osteoporosis.
The positive effect of ibandronate on bone mineral density was not accompanied by a reduction of the fracture rate within the 1-yr period. Nevertheless, vertebral deformities were reduced by 70% and decrease of body height by 53% in the ibandronate group. Bisphosphonates have been reported to reduce fracture rate in postmenopausal osteoporosis, which represents a different mechanism of bone loss, however (28,29).
It may be of concern that bisphosphonates aggravate preexistent low-turnover bone disease. In contrast to the situation before transplantation, posttransplantation osteoporosis is a high-turnover bone disease (30,31), making this possibility unlikely. However, bisphosphonates may worsen preexisting hyperparathyroidism (22), which was not observed in the present study. Initial elevated parathyroid hormone levels decreased during the study course and were not different between the ibandronate and control groups.
Interpretation of bone mass change in treatment studies should be done on the background of bone remodeling transient (32,33). The volume of bone involved in remodeling has low bone mineral density. Any drug that inhibits bone remodeling therefore shows an increase of bone mineral density. This apparent increase may be caused by reduction of the remodeling space and not by true biologic gain in bone mass. Because in our study bone mineral density did not decrease after withdrawal of ibandronate, our data reflect a real treatment benefit.
The effect of ibandronate after transplantation could result from reducing initial accelerated bone resorption, when bone formation is low. Our metabolic and bone mineral density data suggest that 6 to 12 mo after transplantation, a new equilibrium between resorption and formation is reestablished since deoxypyridinoline (bone resorption) decreased and bone alkaline phosphatase (bone formation) increased to the normal range during the first year after transplantation. Loss of bone mineral density did slow after 6 mo and showed a continuing, slow bone gain between 12 and 24 mo in both groups. Therefore, it seems that prophylactic treatment of the initial posttransplantation bone loss can be limited to the first year after transplantation. The necessary medication costs of 632 Euros per patient are substantially less than costs of fractures expected in the entire posttransplantation period.
An interesting aspect of our study is the association of reduced incidence of acute rejections and ibandronate treatment. At first glance, this seems surprising and one might suspect a statistical type 1 error. However, there is another explanation. Macrophages play a central role in acute rejection and are still not sufficiently targeted by classical immunosuppressive drugs. Because macrophages and osteoclasts are derived from a common bone marrow progenitor cell, agents that inhibit osteoclasts also inhibit macrophages. Such an immunoinhibitory effect was already shown for alendronate in vitro, where it interfered with T-cell function by inhibiting antigen-presenting cells (34). Ibandronate is even more potent than alendronate, and its effects probably are enhanced when given to patients with renal insufficiency in whom the circulating half-life is longer. Other explanations, such as differences of donor-recipient incompatibilities between groups, were excluded. The observation that bisphosphonates are able to reduce incidence of acute rejections is supported by data of various animal studies in which clodronate reduced acute graft rejection after cornea, heart, pancreas, and small bowel transplantation (35,36,37,38).
The decreased incidence of rejection episodes in the ibandronate group might have been a potentially confounding variable. Even though not significant, the cumulative dose of corticosteroids was lower in our ibandronate group and could have been responsible for the beneficial effect of ibandronate. This explanation is not supported by a subgroup analysis of patients with and without rejections. Although patients with rejections had received significantly higher cumulative doses of corticosteroids than patients without rejections, ibandronate showed also a clear beneficial effect on bone loss in patients with and without rejection.
Taken together, four injections of ibandronate at 3-mo intervals are sufficient to prevent progression of posttransplantation osteoporosis. A favorable effect of ibandronate on graft tolerance is observed; however, its exact mechanism of action needs to be confirmed in further studies.
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