Changes in vitamin D and parathyroid hormone metabolism in incident pediatric Crohn's disease

BACKGROUND

Prior studies of vitamin D metabolism in Crohn's disease (CD) did not include controls or examine changes following diagnosis. This study examined associations among 25-hydroxyvitamin D [25(OH)D], 1,25-dihydroxyvitamin D [1,25(OH)(2)D], and parathyroid hormone (PTH) levels in incident pediatric CD, compared with controls, and following diagnosis.

METHODS

Serum vitamin D and PTH were measured at diagnosis (n = 78), 6, 12, and a median of 43 months (n = 52) later in CD participants, and once in 221 controls. Multivariate regression was used to examine baseline associations and quasi-least squares regression to assess subsequent changes.

RESULTS

At diagnosis, 42% of CD participants were 25(OH)D-deficient (<20 ng/mL). The odds ratio for deficiency was 2.1 (95% confidence interval [CI]: 1.1, 3.9; P < 0.05) vs. controls, adjusted for age, race, and season. 1,25(OH)(2)D was lower in CD vs. controls (P < 0.05), adjusted for 25(OH)D, tumor necrosis factor alpha (TNF-α), and PTH. TNF-α was associated with lower 1,25(OH)(2)D (P < 0.05), and the positive association between PTH and 1,25(OH)(2)D in controls was absent in CD (interaction P = 0.02). Among participants with 25(OH)D <30 ng/mL, CD was associated with lower PTH (P < 0.05) vs. controls. Following diagnosis, 25(OH)D and 1,25(OH)(2)D improved (P < 0.001). At the final visit, 3% were 25(OH)D-deficient, PTH was no longer low relative to 25(OH)D, and 1,25(OH)(2)D was significantly elevated (P < 0.001) compared with controls.

CONCLUSIONS

Incident CD was associated with 25(OH)D and 1,25(OH)2D deficiency and a relative hypoparathyroidism that resolved following diagnosis. Inflammatory cytokine suppression of PTH and renal 1-α-hyroxylase may contribute to these alterations.

Risk of hip fracture associated with hepatitis C virus infection and hepatitis C/human immunodeficiency virus coinfection

Hepatitis C virus (HCV) infection has been associated with reduced bone mineral density, but its association with fracture rates is unknown, particularly in the setting of human immunodeficiency virus (HIV) coinfection. Our aims were to determine whether persons with HCV infection alone are at increased risk for hip fracture, compared to uninfected individuals, and to examine whether the risk of hip fracture is higher among HCV/HIV-coinfected persons, compared to those with HCV alone, those with HIV alone, and those uninfected with either virus. We conducted a cohort study in 36,950 HCV/HIV-coinfected, 276,901 HCV-monoinfected, 95,827 HIV-monoinfected, and 3,110,904 HCV/HIV-uninfected persons within the U.S. Medicaid populations of California, Florida, New York, Ohio, and Pennsylvania (1999-2005). Incidence rates of hip fracture were lowest among uninfected persons (1.29 events/1,000 person-years), increased with the presence of either HIV infection (1.95 events/1,000 person-years) or HCV infection (2.69 events/1,000 person-years), and were highest among HCV/HIV-coinfected individuals (3.06 events/1,000 person-years). HCV/HIV coinfection was associated with an increased relative hazard (adjusted hazard ratio [HR] [95% confidence interval; CI]) of hip fracture, compared to HCV-monoinfected (HR, 1.38; 95% CI: 1.25-1.53), HIV-monoinfected (females: HR, 1.76; 95% CI: 1.44-2.16; males: HR, 1.36; 95% CI: 1.20-1.55), and HCV/HIV-uninfected persons (females: HR, 2.65; 95% CI: 2.21-3.17; males: HR, 2.20; 95% CI: 1.97-2.47). HCV monoinfection was associated with an increased risk of hip fracture, compared to uninfected individuals, and the relative increase was highest in the youngest age groups (females, 18-39 years: HR, 3.56; 95% CI: 2.93-4.32; males, 18-39 years: HR, 2.40; 95% CI: 2.02-2.84).

CONCLUSION

Among Medicaid enrollees, HCV/HIV coinfection was associated with increased rates of hip fracture, compared to HCV-monoinfected, HIV-monoinfected, and HCV/HIV-uninfected persons. HCV-monoinfected patients had an increased risk of hip fracture, compared to uninfected individuals.

Body composition analysis in the pediatric population

Body composition analysis has become a useful tool in both clinical and research settings. Its use in the pediatric population is complicated by the rapid periods of growth and physical development that are characteristic of infancy, childhood, and adolescence. A thorough understanding of the changing nature of body composition during this time is essential for choosing the most appropriate measurement technique for a given individual, population, or clinical question. Growing evidence suggests that tissues such as fat, muscle, and bone are intimately involved in the regulation of whole body energy metabolism. This knowledge, when coupled with advancements in imaging techniques such as MRI and PET-CT, offers the possibility of developing new models of "functional" body composition. These models may prove to be especially important when assessing malnutrition and metabolic risk in patients with chronic disease.

Vitamin D, metabolic dyslipidemia, and metabolic syndrome in rheumatoid arthritis

PURPOSE

Vitamin D deficiency is a potential risk factor for cardiometabolic disease. We investigated the associations between vitamin D and dyslipidemia and the metabolic syndrome in patients with rheumatoid arthritis, a group at high risk for cardiovascular disease.

METHODS

Serum 25(OH)vitamin D and lipoprotein levels were measured at baseline in a random sample of 499 participants, ages 18-85 years, enrolled in a randomized trial of golimumab (GOlimumab Before Employing methotrexate as the First-line Option in the treatment of Rheumatoid arthritis of Early onset or GO-BEFORE Trial). Participants had rheumatoid arthritis with active disease, and were naïve to methotrexate and biologic therapies. Multivariable linear regression was performed to assess associations between vitamin D levels and lipoprotein fractions. Multivariable logistic regression was performed to determine the odds of hyperlipidemia and the metabolic syndrome in participants with vitamin D deficiency (<20 ng/mL).

RESULTS

In multivariable linear regression, vitamin D levels (per 10 ng/mL) were associated inversely with low-density lipoprotein (β: -0.029 [-0.049, -0.0091], P=.004) and triglyceride (β: -0.094 [-0.15, -0.039] P=.001) levels, adjusted for demographic, cardiovascular, and disease-specific variables. Vitamin D and high-density lipoprotein levels were not associated in univariate or multivariate analyses. Vitamin D deficiency was associated independently with an increased odds of hyperlipidemia (odds ratio 1.72; 95% confidence interval, 1.10-2.45; P=.014) and metabolic syndrome (odds ratio 3.45; 95% confidence interval, 1.75-6.80; P <.001) in adjusted models.

CONCLUSIONS

In conclusion, vitamin D deficiency was associated with the metabolic syndrome and dyslipidemia in rheumatoid arthritis, suggesting a potential role in cardiovascular disease risk. Large-scale, prospective studies are needed to determine if vitamin D supplementation improves lipoprotein levels and reduces cardiovascular risk in rheumatoid arthritis.

Longitudinal assessment of bone density and structure in childhood survivors of acute lymphoblastic leukemia without cranial radiation

PURPOSE

Children with acute lymphoblastic leukemia (ALL) are at risk for impaired bone accrual. This peripheral quantitative computed tomography study assessed changes in bone mineral density (BMD) and structure after completion of ALL treatment.

METHODS

Fifty ALL participants, ages 5-22 yr, were enrolled within 2 yr (median 0.8 yr) after completing ALL therapy. Tibia peripheral quantitative computed tomography scans were performed at enrollment and 12 months later. Age-, sex-, and race-specific Z-scores for trabecular BMD (TrabBMD), cortical BMD (CortBMD), and cortical area (CortArea) were generated based on more than 650 reference participants. Multivariable linear regression models examined determinants of changes in Z-scores.

RESULTS

At enrollment, mean TrabBMD (-1.03±1.34) and CortBMD (-0.84±1.05) Z-scores were low (both P<0.001) compared with reference participants. TrabBMD and CortBMD Z-scores increased to -0.58±1.41 and -0.51±0.91 over 1 yr, respectively (both P<0.001). Changes in cortical outcomes varied according to the interval since completion of therapy. Among those enrolled less than 6 months after therapy, CortArea Z-scores increased and CortBMD Z-scores decreased (both P<0.01). Among those enrolled 6 months or more after therapy, CortArea Z-scores did not change and CortBMD Z-scores increased (P<0.01). Changes in CortArea and CortBMD Z-scores were inversely associated (r=-0.32, P<0.001). Cumulative glucocorticoid exposure, leukemia risk status, and antimetabolite chemotherapy were not associated with outcomes.

CONCLUSION

TrabBMD was low after completion of ALL therapy and improved significantly. Early increases in cortical dimensions were associated with declines in CortBMD; however, participants further from ALL therapy demonstrated stable cortical dimensions and increases in CortBMD, potentially reflecting the time necessary to mineralize newly formed bone.

Associations between vitamin D, disease activity, and clinical response to therapy in rheumatoid arthritis

OBJECTIVES

Vitamin D deficiency is a potential risk factor for autoimmunity. Prior studies of the association between vitamin D levels and rheumatoid arthritis (RA) disease activity have yielded conflicting results.

METHODS

Serum 25(OH)vitamin D levels were measured at baseline in 499 participants with active RA, ages 18-85 years, enrolled in a randomised clinical trial of golimumab (Go-Before Trial). Subjects were methotrexate and biologic therapy naïve. Multivariable linear regression was used to assess associations between vitamin D levels and disease activity scores (DAS28), van der Heijde-Sharp (vdHS) erosion scores, and serum inflammatory markers. Generalised estimating equations were used to evaluate the associations between vitamin D status and the response to therapy over 52 weeks, using the DAS28 and ACR response.

RESULTS

Forty-eight percent of participants were vitamin D deficient, defined as serum 25(OH)vitamin D <20 ng/mL. Deficiency was not associated with greater DAS28 (β-0.021 [95% CI -0.22, 0.18]), adjusted for age, race, sex, BMI, disease duration and glomerular filtration rate. Vitamin D deficiency was not associated with baseline vdHS scores or inflammatory markers in adjusted or unadjusted models. There was no association between baseline vitamin D deficiency and change in DAS28 (β = -0.024 [-0.30, 0.25]), proportion meeting ACR response (OR 0.82 [0.56, 1.20]), or radiographic progression at 52 weeks (OR 0.91 [0.59-1.40]).

CONCLUSIONS

Vitamin D levels were not associated with RA disease activity, inflammatory markers, or vdHS scores at baseline. Furthermore, there was no association between baseline vitamin D level and response to therapy or radiographic progression.

Assessment of dual-energy X-ray absorptiometry measures of bone health in pediatric chronic kidney disease

BACKGROUND

Dual-energy X-ray absorptiometry (DXA) techniques are limited in childhood chronic kidney disease (CKD) by the confounding effect of short stature and opposing parathyroid hormone effects on trabecular and cortical bone. Peripheral quantitative computed tomography (pQCT) is not subject to these limitations.

METHODS

Lumbar spine (LS) and whole-body (WB) DXA and tibia pQCT scans were obtained in 88 stage 4-5 CKD and >650 healthy participants, ages 5-21 years. Sex- and race-specific Z-scores were generated for bone mineral density (BMD) and bone mineral content (BMC) by DXA, relative to age and adjusted for height Z-score (LS-BMD-Z and WB-BMC-Z), and compared to pQCT Z-scores for trabecular BMD (TrabBMD-Z) for age and cortical BMC (CortBMC-Z) for age and tibia length.

RESULTS

LS-BMD-Z [0.50 (95% C.I. 0.28, 0.73), p<0.0001] and TrabBMD-Z [0.53 (0.27, 0.79), p<0.0001] were greater in CKD, and WB-BMC-Z [-0.36 (-0.53, -0.19), p<0.0001] and CortBMC-Z [-0.48 (-0.70, -0.27), p<0.0001] were lower, compared to reference participants. Z-scores were correlated at trabecular (LS-BMD-Z and TrabBMD-Z: R=0.36) and cortical (WB-BMC-Z and CortBMC-Z: R=0.64) sites in CKD; similar to correlations in reference participants.

CONCLUSIONS

Lumbar spine and whole-body DXA suggested greater trabecular BMD and lower cortical BMC in CKD, consistent with pQCT results; however, correlations were modest. Studies are needed to identify methods that predict fracture in childhood CKD.

Estimating GFR among participants in the Chronic Renal Insufficiency Cohort (CRIC) Study

BACKGROUND

Glomerular filtration rate (GFR) is considered the best measure of kidney function, but repeated assessment is not feasible in most research studies.

STUDY DESIGN

Cross-sectional study of 1,433 participants in the Chronic Renal Insufficiency Cohort (CRIC) Study (ie, the GFR subcohort) to derive an internal GFR estimating equation using a split-sample approach.

SETTING & PARTICIPANTS

Adults from 7 US metropolitan areas with mild to moderate chronic kidney disease; 48% had diabetes and 37% were black.

INDEX TEST

CRIC GFR estimating equation.

REFERENCE TEST OR OUTCOME

Urinary (125)I-iothalamate clearance testing (measured GFR [mGFR]).

OTHER MEASUREMENTS

Laboratory measures, including serum creatinine and cystatin C, and anthropometrics.

RESULTS

In the validation data set, the model that included serum creatinine level, serum cystatin C level, age, sex, and race was the most parsimonious and similarly predictive of mGFR compared with a model additionally including bioelectrical impedance analysis phase angle, CRIC clinical center, and 24-hour urinary creatinine excretion. Specifically, root mean square errors for the separate models were 0.207 versus 0.202, respectively. Performance of the CRIC GFR estimating equation was most accurate for the subgroups of younger participants, men, nonblacks, non-Hispanics, those without diabetes, those with body mass index <30 kg/m(2), those with higher 24-hour urine creatinine excretion, those with lower high-sensitivity C-reactive protein levels, and those with higher mGFRs.

LIMITATIONS

Urinary clearance of (125)I-iothalamate is an imperfect measure of true GFR; cystatin C level is not standardized to certified reference material; lack of external validation; small sample sizes limit analyses of subgroup-specific predictors.

CONCLUSIONS

The CRIC GFR estimating equation predicts mGFR accurately in the CRIC cohort using serum creatinine and cystatin C levels, age, sex, and race. Its performance was best in younger and healthier participants.

Fibroblast growth factor 23 and Inflammation in CKD

BACKGROUND AND OBJECTIVES

Levels of fibroblast growth factor 23 (FGF23) and inflammatory markers are commonly elevated in CKD, and each is associated with adverse clinical outcomes. This study tested the hypothesis that FGF23 is independently associated with inflammation in CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The association between levels of FGF23 and the inflammatory markers IL-6, C-reactive protein (CRP), TNF-α, and fibrinogen was assessed in a cross-sectional analysis of 3879 participants enrolled in the Chronic Renal Insufficiency Cohort (CRIC) study between June 2003 and September 2008.

RESULTS

FGF23 correlated directly with IL-6 (r=0.4), CRP (r=0.2), TNF-α (r=0.4), and fibrinogen (r=0.3; P<0.001 for each). In univariate and multivariable-adjusted linear regression analyses, natural log (ln) transformed FGF23 was significantly associated with lnIL-6, lnCRP, lnTNF-α, and fibrinogen (P<0.001 for each). Each unit higher lnFGF23 was associated with severe inflammation, defined as levels of all inflammatory markers in the highest 25th percentile, in univariate (odds ratio [OR], 2.4 [95% confidence interval (CI), 2.0-2.9]) and multivariable-adjusted (OR, 2.0 [95% CI, 1.6-2.5]) logistic regression analyses. Ascending FGF23 quartiles were independently associated with severe inflammation (OR, 5.6 for the highest versus lowest FGF23 quartile [95% CI, 2.3-13.9]; P for trend < 0.001).

CONCLUSIONS

Higher FGF23 levels are independently associated with higher levels of inflammatory markers in patients with CKD and with significantly greater odds of severe inflammation. Future studies should evaluate whether inflammation modifies the association between FGF23 and adverse outcomes in CKD.

Earlier onset and greater severity of disordered mineral metabolism in diabetic patients with chronic kidney disease

OBJECTIVE

Disordered mineral metabolism is a common complication of chronic kidney disease (CKD) and a novel risk factor for CKD progression, cardiovascular disease, and mortality. Although diabetes is the leading cause of CKD and is associated with worse clinical outcomes than other etiologies, few studies have evaluated mineral metabolism in CKD according to diabetes status.

RESEARCH DESIGN AND METHODS

Using the Chronic Renal Insufficiency Cohort Study, we tested the hypothesis that diabetes is independently associated with lower serum calcium and higher serum phosphate, parathyroid hormone (PTH), and fibroblast growth factor 23 (FGF23).

RESULTS

Compared with participants without diabetes (n = 1,936), those with diabetes (n = 1,820) were more likely to have lower estimated glomerular filtration rate (eGFR), lower serum albumin, and higher urinary protein excretion (all P < 0.001). Unadjusted serum phosphate, PTH, and FGF23 levels were higher and calcium was lower among those with compared with those without diabetes (all P < 0.001). After multivariate adjustment, diabetes remained a significant predictor of serum phosphate, PTH, and FGF23 but not calcium. The eGFR cut point at which 50% of participants met criteria for secondary hyperparathyroidism or elevated FGF23 was higher in participants with diabetes compared with those without (PTH: eGFR 30-39 vs. 20-29, P < 0.001; FGF23: eGFR 50-59 vs. 40-49, P < 0.001).

CONCLUSIONS

Disordered mineral metabolism begins earlier in the course of CKD and is more severe among CKD patients with compared with those without diabetes. Future studies should explore mechanisms for these differences and whether they contribute to excess risks of adverse clinical outcomes among diabetic patients with CKD.

Micro-MR imaging-based computational biomechanics demonstrates reduction in cortical and trabecular bone strength after renal transplantation

PURPOSE

To examine the ability of three-dimensional micro-magnetic resonance (MR) imaging-based computational biomechanics to detect mechanical alterations in trabecular bone and cortical bone in the distal tibia of incident renal transplant recipients 6 months after renal transplantation and compare them with bone mineral density (BMD) outcomes.

MATERIALS AND METHODS

The study was approved by the institutional review board and complied with HIPAA guidelines. Written informed consent was obtained from all subjects. Micro-MR imaging of distal tibial metaphysis was performed within 2 weeks after renal transplantation (baseline) and 6 months later in 49 participants (24 female; median age, 44 years; range, 19-61 years) with a clinical 1.5-T whole-body imager using a modified three-dimensional fast large-angle spin-echo pulse sequence. Micro-finite-element models for cortical bone, trabecular bone, and whole-bone section were generated from each image by delineating the endosteal and periosteal boundaries. Mechanical parameters (stiffness and failure load) were estimated with simulated uniaxial compression tests on the micro-finite-element models. Structural parameters (trabecular bone volume fraction [BV/TV, bone volume to total volume ratio], trabecular thickness [TbTh], and cortical thickness [CtTh]) were computed from micro-MR images. Total hip and spine areal BMD were determined with dual-energy x-ray absorptiometry (DXA). Parameters obtained at the follow-up were compared with the baseline values by using parametric or nonparametric tests depending on the normality of data.

RESULTS

All mechanical parameters were significantly lower at 6 months compared with baseline. Decreases in cortical bone, trabecular bone, and whole-bone stiffness were 3.7% (P = .03), 4.9% (P = .03), and 4.3% (P = .003), respectively. Decreases in cortical bone, trabecular bone, and whole-bone failure strength were 7.6% (P = .0003), 6.0% (P = .004), and 5.6% (P = .0004), respectively. Conventional structural measures, BV/TV, TbTh, and CtTh, did not change significantly. Spine BMD decreased by 2.9% (P < .0001), while hip BMD did not change significantly at DXA.

CONCLUSION

MR imaging-based micro-finite-element analysis suggests that stiffness and failure strength of the distal tibia decrease over a 6-month interval after renal transplantation.

Interpretation of body mass index in children with CKD

BACKGROUND AND OBJECTIVES

Clinical practice guidelines recommend that body mass index (BMI) in children with CKD be expressed relative to height-age (BMI-height-age-z) rather than chronologic age (BMI-age-z) to account for delayed growth and sexual maturation. This approach has not been validated. This study sought to (1) compare children who have CKD with healthy children regarding the relationships between BMI-age-z and each of relative lean mass (LM) and adiposity and (2) determine whether BMI-height-age-z reflects relative LM and adiposity in CKD in the same way that BMI-age-z does in healthy children.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a cross-sectional study, dual-energy x-ray absorptiometry was used to assess whole-body fat mass (FM) and LM in 143 participants with CKD and 958 healthy participants (age, 5-21 years); FM and LM were expressed as sex-specific Z-scores relative to height (LM-height-z, FM-height-z), with healthy participants as the reference. BMI-age-z and BMI-height-age-z were determined using the 2000 Centers for Disease Control and Prevention reference data.

RESULTS

Compared with healthy children of the same sex, age, race, and BMI-age-z, LM-height-z was significantly higher in males with all CKD stages (by 0.41-0.43 SDs) and in females with mild to moderate CKD (by 0.38 SD); FM-height-z was significantly higher in both males (by 0.26 SD) and females (by 0.52 SD) with severe CKD. Underestimation of relative LM and adiposity was improved by expressing BMI relative to height-age.

CONCLUSIONS

In children with CKD, BMI-height-age-z reflects relative LM and adiposity in the same way that BMI-age-z does in healthy children.

Bone density and cortical structure after pediatric renal transplantation

The impact of renal transplantation on trabecular and cortical bone mineral density (BMD) and cortical structure is unknown. We obtained quantitative computed tomography scans of the tibia in pediatric renal transplant recipients at transplantation and 3, 6, and 12 months; 58 recipients completed at least two visits. We used more than 700 reference participants to generate Z-scores for trabecular BMD, cortical BMD, section modulus (a summary measure of cortical dimensions and strength), and muscle and fat area. At baseline, compared with reference participants, renal transplant recipients had significantly lower mean section modulus and muscle area; trabecular BMD was significantly greater than reference participants only in transplant recipients younger than 13 years. After transplantation, trabecular BMD decreased significantly in association with greater glucocorticoid exposure. Cortical BMD increased significantly in association with greater glucocorticoid exposure and greater decreases in parathyroid hormone levels. Muscle and fat area both increased significantly, but section modulus did not improve. At 12 months, transplantation associated with significantly lower section modulus and greater fat area compared with reference participants. Muscle area and cortical BMD did not differ significantly between transplant recipients and reference participants. Trabecular BMD was no longer significantly elevated in younger recipients and was low in older recipients. Pediatric renal transplant associated with persistent deficits in section modulus, despite recovery of muscle, and low trabecular BMD in older recipients. Future studies should determine the implications of these data on fracture risk and identify strategies to improve bone density and structure.

Bone density and structure in long-term survivors of pediatric allogeneic hematopoietic stem cell transplantation

Children requiring allogeneic hematopoietic stem cell transplantation (alloHSCT) have multiple risk factors for impaired bone accrual. The impact of alloHSCT on volumetric bone mineral density (vBMD) and cortical structure has not been addressed. Tibia peripheral quantitative computed tomography (pQCT) scans were obtained in 55 alloHSCT recipients, ages 5 to 26 years, a median of 7 (range, 3-16) years after alloHSCT. pQCT outcomes were converted to sex- and race- specific Z-scores relative to age based on reference data in >700 concurrent healthy participants. Cortical section modulus (Zp; a summary measure of cortical bone structure and strength), and muscle and fat area Z-scores were further adjusted for tibia length for age Z-scores. AlloHSCT survivors had lower height Z-scores (-1.21 ± 1.25 versus 0.23 ± 0.92; p < 0.001), versus reference participants; BMI Z-scores did not differ. AlloHSCT survivors had lower trabecular vBMD (-1.05; 95% confidence interval [CI], -1.33 to -0.78; p < 0.001), cortical Zp (-0.63; 95% CI, -0.91 to -0.35; p < 0.001), and muscle (-1.01; 95% CI, -1.30 to -0.72; p < 0.001) Z-scores and greater fat (0.82; 95% CI, 0.54-1.11; p < 0.001) Z-scores, versus reference participants. Adjustment for muscle deficits eliminated Zp deficits in alloHSCT. Total body irradiation (TBI) was associated with lower trabecular vBMD (-1.30 ± 1.40 versus -0.49 ± 0.88; p = 0.01) and muscle (-1.34 ± 1.42 versus -0.34 ± 0.87; p < 0.01) Z-scores. Growth hormone deficiency (GHD) was associated with lower Zp Z-scores (-1.64 ± 2.47 versus -0.28 ± 1.24; p = 0.05); however, muscle differences were not significant (-1.69 ± 1.84 versus -0.78 ± 1.01; p = 0.09). History of graft versus host disease was not associated with pQCT outcomes. In summary, alloHSCT was associated with significant deficits in trabecular vBMD, cortical geometry, and muscle area years after transplantation. TBI and GHD were significant risk factors for musculoskeletal deficits. Future studies are needed to determine the metabolic and fracture implications of these deficits, and to identify therapies to improve bone accrual following alloHSCT during childhood.

Changes in vitamin D binding protein and vitamin D concentrations associated with liver transplantation

BACKGROUND

Vitamin D deficiency is associated with fractures, infections and death. Liver disease impairs vitamin D and vitamin D binding protein (DBP) metabolism.

AIMS

We aimed to determine the impact of liver transplantation on vitamin D, particularly on DBP and free vitamin D concentrations.

METHODS

Serum 25(OH)D, 1,25(OH)(2) D and DBP concentrations were measured in 202 adults before liver transplantation and 3 months later in 155. Free vitamin D concentrations were estimated from these values. Risk factors for 25(OH)D deficiency (<20 ng/ml) and low 1,25(OH)(2) D (<20 pg/ml) were examined with logistic regression, and changes in concentrations following transplantation with linear regression.

RESULTS

Pretransplant, 84% were 25(OH)D deficient, 13% had 25(OH)D concentrations <2.5 ng/ml, and 77% had low 1,25(OH)(2) D. Model for end-stage liver disease score ≥ 20 (P < 0.005) and hypoalbuminemia (P < 0.005) were associated with low 25(OH)D and 1,25(OH)(2) D concentrations. Following transplantation, 25(OH)D concentrations increased a median of 17.8 ng/ml (P < 0.001). Albumin increased from a median of 2.7 to 3.8 g/dl (P < 0.001) and DBP from 8.6 to 23.8 mg/dl (P < 0.001). Changes in total 25(OH)D were positively and independently associated with changes in DBP (P < 0.05) and albumin (P < 0.001). Free 25(OH)D concentrations rose from 6.0 to 9.7 pg/ml (P < 0.001). In contrast, total 1,25(OH)(2)D concentrations rose only by 4.3 pg/ml (P < 0.001) and free 1,25(OH)(2D concentrations declined (P < 0.001).

CONCLUSIONS

Serum total and free 25(OH)D and DBP concentrations rose substantially following transplantation, while 1,25(OH)(2) D concentrations showed modest changes and free 1,25(OH)(2) D decreased. Studies of the effects of vitamin D status on diverse transplant complications are needed.

Reduced fracture risk with early corticosteroid withdrawal after kidney transplant

Corticosteroid use after kidney transplantation results in severe bone loss and high fracture risk. Although corticosteroid withdrawal in the early posttransplant period has been associated with bone mass preservation, there are no published data regarding corticosteroid withdrawal and risk of fracture. We hypothesized lower fracture incidence in patients discharged from the hospital without than with corticosteroids after transplantation. From the United States Renal Data System (USRDS), 77, 430 patients were identified who received their first kidney transplant from 2000 to 2006. Fracture incidence leading to hospitalization was determined from 2000 to 2007; discharge immunosuppression was determined from United Networks for Organ Sharing forms. Time-to-event analyses were used to evaluate fracture risk. Median (interquartile range) follow-up was 1448 (808-2061) days. There were 2395 fractures during follow-up; fracture incidence rates were 0.008 and 0.0058 per patient-year for recipients discharged with and without corticosteroid, respectively. Corticosteroid withdrawal was associated with a 31% fracture risk reduction (HR 0.69; 95% CI 0.59-0.81). Fractures associated with hospitalization are significantly lower with regimens that withdraw corticosteroid. As this study likely underestimates overall fracture incidence, prospective studies are needed to determine differences in overall fracture risk in patients managed with and without corticosteroids after kidney transplantation.

Exposure to CYP3A4-inducing and CYP3A4-non-inducing antiepileptic agents and the risk of fractures

PURPOSE

To evaluate whether exposure to Cytochrome P450, family 3, subfamily A, polypeptide 4 (CYP3A4)-inducing antiepileptics increases fracture risk compared to CYP3A4-non-inducing antiepileptics.

METHODS

We performed a retrospective cohort study of initiators of antiepileptic agents using a UK medical record database (The Health Improvement Network) from 1995 to 2007. We considered an antiepileptic user an initiator if he or she had not received a prescription for an antiepileptic agent within the first year after entry in the database. Proportional hazards regression was used to calculate hazard ratios for fracture during long-term (≥ 6 months) exposure to CYP3A4 inducing versus CYP3A4 non-inducing antiepileptics.

RESULTS

We identified 4077 initiators of CYP3A4-inducing antiepileptics and 6433 initiators of CYP3A4-non-inducing antiepileptics with at least 6 months of antiepileptic exposure. During 6006 person-years exposed to CYP3A4-inducing antiepileptics, 118 fractures were identified for an incidence rate of 1.96 (95% confidence interval (CI): 1.63-2.35) fractures per 100 person-years. During 7184 person-years exposed to CYP3A4-non-inducing antiepileptics, 127 fractures were identified, for an incidence rate of 1.77 (95% CI: 1.47-2.10) fractures per 100 person-years. The adjusted hazard ratio for CYP3A4-inducing antiepileptic versus CYP3A4-non-inducing antiepileptic was 1.21 (95% CI: 0.93-1.56). No duration-response relationship was evident.

CONCLUSIONS

Our results do not support the hypothesis that CYP3A4 induction by antiepileptic agents increases the fracture risk. Further research will be needed to evaluate whether mechanisms other than CYP3A4 induction might explain some of the elevated risk of fractures associated with long-term use of antiepileptic agents.

On the significance of motion degradation in high-resolution 3D μMRI of trabecular bone

RATIONALE AND OBJECTIVES

Subtle subject movement during high-resolution three-dimensional micro-magnetic resonance imaging of trabecular bone (TB) causes blurring, thereby rendering the data unreliable for quantitative analysis. In this work, the effects of translational and rotational motion displacements were evaluated qualitatively and quantitatively.

MATERIALS AND METHODS

In experiment 1, motion was induced by applying various simulated and previously observed in vivo trajectories as phase shifts to k-space or rotation angles to k-space segments of a virtually motion-free data set. In experiment 2, images that were visually free of motion artifacts from two groups of 10 healthy individuals, differing in age, were selected to probe the effects of motion on TB parameters. In both experiments, images were rated for motion severity, and the scores were compared to a focus criterion, the normalized gradient squared.

RESULTS

Strong correlations were observed between the motion quality scores and the corresponding normalized gradient squared values (R(2) = 0.52-0.64, P < .01). The results from experiment 1 demonstrated consistently lower image quality and alterations in structural parameters of 9% to 45% with increased amplitude of displacements. In experiment 2, the significant differences in structural parameter group means of the motion-free images were lost upon motion degradation. Autofocusing, a postprocessing correction method, partially recovered the sharpness of the original motion-free images in 13 of 20 subjects.

CONCLUSIONS

Quantitative TB structural measures are highly sensitive to subtle motion-induced degradation, which adversely affects precision and statistical power. The results underscore the influence of subject movement in high-resolution three-dimensional micro-magnetic resonance imaging and its correction for TB structure analysis.

Correlates of osteoprotegerin and association with aortic pulse wave velocity in patients with chronic kidney disease

BACKGROUND AND OBJECTIVES

Osteoprotegerin (OPG), a cytokine that regulates bone resorption, has been implicated in the process of vascular calcification and stiffness.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Serum OPG was measured in 351 participants with chronic kidney disease (CKD) from one site of the Chronic Renal Insufficiency Cohort Study. Cortical bone mineral content (BMC) was measured by quantitative computed tomography in the tibia. Multivariable linear regression was used to test the association between serum OPG and traditional cardiovascular risk factors, measures of abnormal bone and mineral metabolism, and pulse wave velocity.

RESULTS

Higher serum OPG levels were associated with older age, female gender, greater systolic BP, lower estimated GFR, and lower serum albumin. OPG was not associated with measures of abnormal bone or mineral metabolism including serum phosphorus, albumin-corrected serum calcium, intact parathyroid hormone, bone-specific alkaline phosphatase, or cortical BMC. Among 226 participants with concurrent aortic pulse wave velocity measurements, increasing tertiles of serum OPG were associated with higher aortic pulse wave velocity after adjustment for demographics, traditional vascular risk factors, and nontraditional risk factors such as estimated GFR, albuminuria, serum phosphate, corrected serum calcium, presence of secondary hyperparathyroidism, serum albumin, and C-reactive protein or after additional adjustment for cortical BMC in a subset (n = 161).

CONCLUSIONS

These data support a strong relationship between serum OPG and arterial stiffness independent of many potential confounders including traditional cardiovascular risk factors, abnormal bone and mineral metabolism, and inflammation.

Volumetric bone mineral density and bone structure in childhood chronic kidney disease

Chronic kidney disease (CKD) is associated with increased fracture risk and skeletal deformities. The impact of CKD on volumetric bone mineral density (vBMD) and cortical dimensions during growth is unknown. Tibia quantitative computed tomographic scans were obtained in 156 children with CKD [69 stages 2 to 3, 51 stages 4 to 5, and 36 stage 5D (dialysis)] and 831 healthy participants aged 5 to 21 years. Sex-, race-, and age- or tibia length-specific Z-scores were generated for trabecular BMD (TrabBMD), cortical BMD (CortBMD), cortical area (CortArea) and endosteal circumference (EndoC). Greater CKD severity was associated with a higher TrabBMD Z-score in younger participants (p < .001) compared with healthy children; this association was attenuated in older participants (interaction p < .001). Mean CortArea Z-score was lower (p < .01) in CKD 4-5 [-0.49, 95% confidence interval (CI) -0.80, -0.18)] and CKD 5D (-0.49, 95% CI -0.83, -0.15) compared with healthy children. Among CKD participants, parathyroid hormone (PTH) levels were positively associated with TrabBMD Z-score (p < .01), and this association was significantly attenuated in older participants (interaction p < .05). Higher levels of PTH and biomarkers of bone formation (bone-specific alkaline phosphatase) and resorption (serum C-terminal telopeptide of type 1 collagen) were associated with lower CortBMD and CortArea Z-scores and greater EndoC Z-score (r = 0.18-0.36, all p ≤ .02). CortBMD Z-score was significantly lower in CKD participants with PTH levels above versus below the upper limit of the Kidney Disease Outcome Quality Initiative (KDOQI) CKD stage-specific target range: -0.46 ± 1.29 versus 0.12 ± 1.14 (p < .01). In summary, childhood CKD and secondary hyperparathyroidism were associated with significant reductions in cortical area and CortBMD and greater TrabBMD in younger children. Future studies are needed to establish the fracture implications of these alterations and to determine if cortical and trabecular abnormalities are reversible.

Validation of The Health Improvement Network (THIN) database for epidemiologic studies of chronic kidney disease

PURPOSE

Chronic kidney disease (CKD) is a prevalent and important outcome and covariate in pharmacoepidemiology. The Health Improvement Network (THIN) in the UK represents a unique resource for population-based studies of CKD. We compiled a valid list of Read codes to identify subjects with moderate to advanced CKD.

METHODS

A cross-sectional validation study was performed to identify codes that best define CKD Stages 3-5. All subjects with at least one non-zero measure of serum creatinine after 1 January 2002 were included. Estimated glomerular filtration rate (eGFR) was calculated according to the Schwartz formula for subjects aged < 18 years and the Modification of Diet in Renal Disease formula for subjects aged ≥ 18 years. CKD was defined as an eGFR <60 mL/minute/1.73 m² on at least two occasions, more than 90 days apart.

RESULTS

The laboratory definition identified 230,426 subjects with CKD, for a period prevalence in 2008 of 4.56% (95%CI, 4.54-4.58). A list of 45 Read codes was compiled, which yielded a positive predictive value of 88.9% (95%CI, 88.7-89.1), sensitivity of 48.8%, negative predictive value of 86.5%, and specificity of 98.2%. Of the 11.1% of subjects with a code who did not meet the laboratory definition, 83.6% had at least one eGFR <60. The most commonly used code was for CKD Stage 3.

CONCLUSIONS

The proposed list of codes can be used to accurately identify CKD when serum creatinine data are limited. The most sensitive approach for the detection of CKD is to use this list to supplement creatinine measures.

Discriminants of prevalent fractures in chronic kidney disease

Patients with chronic kidney disease (CKD) have higher rates of fracture than the general population. Increased bone remodeling, leading to microarchitectural deterioration and increased fragility, may accompany declining kidney function, but there are no reliable methods to identify patients at increased risk for fracture. In this cross-sectional study of 82 patients with predialysis CKD, high-resolution imaging revealed that the 23 patients with current fractures had significantly lower areal density at the femoral neck; total, cortical, and trabecular volumetric bone density; cortical area and thickness; and trabecular thickness. Compared with levels in the lowest tertile, higher levels of osteocalcin, procollagen type-1 N-terminal propeptide, and tartrate-resistant acid phosphatase 5b were associated with higher odds of fracture, even after adjustment for femoral neck T-score. Discrimination of fracture prevalence was best with a femoral neck T-score of -2.0 or less and a value in the upper two tertiles for osteocalcin, procollagen type-1 N-terminal propeptide, or tartrate-resistant acid phosphatase 5b; these values corresponded to the upper half of the normal premenopausal reference range. In summary, these cross-sectional data suggest that measurement of bone turnover markers may increase the diagnostic accuracy of densitometry to identify patients with CKD at high risk for fracture.

Mechanical loads and cortical bone geometry in healthy children and young adults

Muscle and bone form a functional unit. While muscle size is a useful surrogate of mechanical load on bone, the independent contributions to bone strength of muscle force, muscle size, gravitational load (body weight), and physical activity have not been assessed. Three hundred twenty-one healthy participants (32% black, 47% male), aged 5-35 years were assessed. Peak dorsiflexion muscle torque (ft-lbs) of the ankle was assessed using isometric dynamometry. Tibia peripheral quantitative computed tomography measures included polar section modulus (Zp; mm(3)), periosteal and endosteal circumference (mm), cortical area (mm(2)), and volumetric bone mineral density (vBMD; mg/cm(3)) at the 38% site, and muscle cross-sectional area (CSA; mm(2)), at the 66% site. Physical activity (average hours per week) was assessed by questionnaire. Log linear regression was used to assess determinants of muscle specific force (MSF; torque relative to muscle CSA) and Zp adjusted for age and tibia length. MSF was greater in blacks than whites (p<0.05) and lower in females than males (p<0.001). Zp was greater in blacks than whites (p=0.002) in Tanner stages 1-4, but the difference was attenuated in Tanner 5 (interaction, p=0.02); R(2)=0.87. Muscle CSA, muscle torque, body weight, and physical activity were added to the model and each load covariate was independently and significantly (all, p<0.02) associated with Zp (R(2)=0.92), periosteal circumference, and cortical area. Inclusion of these measures attenuated but did not eliminate the significant race differences. Only muscle CSA was positively associated with endosteal circumference, while none of the load covariates were associated with vBMD. In conclusion, bone geometry is associated with several factors that define the mechanical load on bone, independent of age, tibia length, maturation, race, and sex. Race differences in Zp were not explained by these measures of mechanical load. Given that inclusion of muscle torque, body weight, and physical activity resulted in a nominal increase in the R(2), muscle size is an adequate surrogate for the mechanical load on bone in healthy participants.