Risk factors for fracture in adult kidney transplant recipients.

AIM: To determine the general and transplant-specific risk factors for fractures in kidney transplant recipients. METHODS: We conducted a cohort study of all adults who received a kidney-only transplant (n = 2723) in Ontario, Canada between 2002 and 2009. We used multivariable Cox proportional hazards regression to determine general and transplant-specific risk factors for major fractures (proximal humerus, forearm, hip, and clinical vertebral). The final model was established using the backward elimination strategy, selecting risk factors with a P-value ≤ 0.2 and forcing recipient age and sex into the model. We also assessed risk factors for other fracture locations (excluding major fractures, and fractures involving the skull, hands or feet). RESULTS: There were 132 major fractures in the follow-up (8.1 fractures per 1000 person-years). General risk factors associated with a greater risk of major fracture were older recipient age [adjusted hazard ratio (aHR) per 5-year increase 1.11, 95%CI: 1.03-1.19] and female sex (aHR = 1.81, 95%CI: 1.28-2.57). Transplant-specific risk factors associated with a greater risk of fracture included older donor age (5-year increase) (aHR = 1.09, 95%CI: 1.02-1.17) and end-stage renal disease (ESRD) caused by diabetes (aHR = 1.72, 95%CI: 1.09-2.72) or cystic kidney disease (aHR = 1.73, 95%CI: 1.08-2.78) (compared to glomerulonephritis as the reference cause). Risk factors across the two fracture locations were not consistent (major fracture locations vs other). Specifically, general risk factors associated with an increased risk of other fractures were diabetes and a fall with hospitalization prior to transplantation, while length of time on dialysis, and renal vascular disease and other causes of ESRD were the transplant-specific risk factors associated with a greater risk of other fractures. CONCLUSION: Both general and transplant-specific risk factors were associated with a higher risk of fractures in kidney transplant recipients. Results can be used for clinical prognostication.

Frequency of bone mineral density testing in adult kidney transplant recipients from Ontario, Canada: a population-based cohort study.

BACKGROUND: We lack consensus on the clinical value, frequency, and timing of bone mineral density (BMD) testing in kidney transplant recipients. This study sought to determine practice patterns in BMD testing across kidney transplant centres in Ontario, Canada, and to compare the frequency of testing in kidney transplant recipients to non-transplant reference groups. METHODS: Using healthcare databases from Ontario, Canada we conducted a population-based cohort study of adult kidney transplant recipients who received a transplant from 1994-2009. We used logistic regression to determine if there was a statistically significant difference across transplant centres in the decision to perform at least one BMD test after transplantation, adjusting for covariates that may influence a physician's decision to order a BMD test. We used the McNemar's test to compare the number of recipients who had at least one BMD test to non-transplant reference groups (matching on age, sex, and date of cohort entry). RESULTS: In the first 3 years after transplant, 4821 kidney transplant recipients underwent 4802 BMD tests (median 1 test per recipient, range 0 to 6 tests), costing $600,000 (2014 CAD equivalent dollars). Across the six centres, the proportion of recipients receiving at least one BMD test varied widely (ranging from 15.6 to 92.1 %; P < 0.001). Over half (58 %) of the recipients received at least one BMD test post-transplant, a value higher than two non-transplant reference groups (general population with a previous non-vertebral fracture [hip, forearm, proximal humerus], 13.8 %; general population with no previous non-vertebral fracture, 8.5 %; P value <0.001 for each of the comparisons). CONCLUSIONS: There is substantial practice variability in BMD testing after transplant. New high-quality information is needed to inform the utility, optimal timing, and frequency of BMD testing in kidney transplant recipients.

MISE EN CONTEXTE: À ce jour, il n'existe aucun consensus sur la pertinence, au plan clinique, de demander une analyse de la densité minérale osseuse (DMO) chez les receveurs d'une greffe de rein, non plus que sur la fréquence ni le moment opportun pour y soumettre les patients après leur intervention. OBJECTIFS DE L'ÉTUDE: L'étude avait pour but d'établir un schéma de pratique pour la mesure de la DMO dans plusieurs centres de transplantation rénale en Ontario, au Canada. On a également voulu comparer la fréquence de ces analyses chez les patients ayant reçu une greffe rénale par rapport à un groupe de référence constitué de patients non transplantés. CADRE ET TYPE D'ÉTUDE: Il s'agit d'une étude rétrospective par cohorte représentative de la population, qui s'est tenue dans six centres de transplantation rénale en Ontario, au Canada. PATIENTS: Il s'agit d'une cohorte de patients ayant reçu une greffe du rein entre 1994 et 2009. MESURES: Les renseignements sur la fréquence, le coût total et les variations dans le nombre d'analyses de la DMO pour une période couvrant les trois années suivant la greffe ont été compilés dans chacun des six centres. La fréquence des analyses de la DMO chez les patients greffés a été comparée à la fréquence de ces mêmes tests pratiqués chez les sujets de groupes témoins, apparentés sur les plans de l'âge, du sexe et de la date de leur admission dans la cohorte, mais n'ayant pas subi une greffe du rein. MÉTHODE: L'analyse par régression logistique a été utilisée pour établir la présence de différences significatives du point de vue statistique entre les six centres de transplantation en regard de la décision d'effectuer au moins un test de DMO à la suite d'une greffe rénale. L'analyse a tenu compte des covariables qui pouvaient influencer les médecins traitants au moment de décider de procéder ou non à un test de DMO sur leurs patients greffés. Le test McNemar a été utilisé pour comparer le nombre de patients greffés ayant été soumis à une analyse de leur DMO par rapport au groupe témoin. RÉSULTATS: À l'intérieur d'une période de trois ans suivant leur transplantation, un total de 4802 analyses de DMO ont été demandées parmi les 4821 patients greffés du rein répertoriés dans les six centres participant à l'étude. La valeur médiane se situait à un test par patient sur une échelle allant de 0 à 6 tests par patient. Le coût total évalué pour ces 4802 analyses de DMO était de 600 000 CDN en 2014. La proportion de receveurs de greffe ayant été soumis à une analyse de leur DMO a fluctué considérablement d'un centre de transplantation à l'autre, avec des pourcentages variant de 15,6 % à 92,1 % (P < 0,001). Dans l'ensemble, on a analysé la DMO de plus de la moitié (58 %) des patients greffés au moins une fois après leur intervention. Ce résultat s'est avéré plus élevé que les pourcentages mesurés dans deux des groupes témoins non transplantés (valeur de P < 0,001 pour chaque cas) : un premier groupe constitué de gens qui avaient subi une fracture non vertébrale (hanche, avant-bras ou humérus proximal) par le passé (13,8 %) et un second groupe constitué de gens de la population générale n'ayant pas subi de fractures (8,5 %). LIMITES DE L'ÉTUDE: Les renseignements concernant les médicaments d'ordonnance administrés aux participants étaient incomplets et les valeurs de DMO étaient manquantes dans plusieurs cas. De plus, le faible taux de fractures subies par les participants ne permet pas d'établir une relation entre la valeur de DMO mesurée et le risque de fractures. CONCLUSIONS: Une variabilité importante a été constatée dans la pratique d'analyses de la DMO à la suite d'une transplantation rénale. Davantage de données sont nécessaires pour discuter de la pertinence d'effectuer ce test chez les receveurs de greffe rénale, ainsi que pour établir le moment opportun et la fréquence à laquelle les y soumettre après l'intervention.

Fracture Incidence in Adult Kidney Transplant Recipients.

BACKGROUND: It remains uncertain whether kidney transplant recipients are a high-risk group for fracture. METHODS: We conducted a cohort study using Ontario, Canada health care databases to estimate the 3-, 5- and 10-year cumulative incidence of nonvertebral fracture (proximal humerus, forearm, hip) in adult kidney transplant recipients between 1994 and 2009, stratifying by sex and age (<50 versus ≥50 years) at transplant. We also assessed the 3-year cumulative incidence of all fracture locations (excluding skull, toes, and fingers) and falls, 10-year cumulative incidence of hip fracture alone, and nonvertebral fracture incidence in recipients compared to nontransplant reference groups matched on age, sex, and cohort entry year. We studied 4821 recipients (median age, 50 years). RESULTS: Among the age and sex strata, female recipients aged 50 years or older had the highest 3-year cumulative incidence of nonvertebral fracture (3.1%; 95% confidence interval [95% CI], 2.1-4.4%). Recipients had a higher 3-year cumulative incidence of nonvertebral fracture (1.6%; 95% CI, 1.3-2.0%) compared to the general population with no previous nonvertebral fracture (0.5%; 95% CI, 0.4-0.6%; P < 0.0001) and nondialysis chronic kidney disease (1.1%; 95% CI, 0.9-1.2%; P = 0.03), but a lower fracture incidence than the general population with a previous nonvertebral fracture (2.3%; 95% CI, 1.9-2.8%; P = 0.007). The 10-year cumulative incidence of hip fracture in all recipients was 1.7% (≥3% defined as high risk in clinical guidelines). CONCLUSIONS: Kidney transplant recipients may have a lower fracture risk than previously suggested in the literature. Results inform our understanding of fracture incidence after kidney transplantation and how it compares to nontransplant populations.

Estimating osteoporotic fracture risk following a wrist fracture: a tale of two systems.

UNLABELLED: The WHO fracture risk assessment (FRAX) and Canadian Association of Radiologists and Osteoporosis Canada (CAROC) tools can both be used to determine an individual's 10-year risk of osteoporotic fracture. However, these tools differ in their risk calculation. For participants <65 years with a wrist fracture, FRAX provides a lower fracture risk estimate than CAROC resulting in fewer decisions to initiate therapy. PURPOSE: The purpose of the current report is to compare fracture risk prediction rates using the CAROC and the FRAX® tools. METHODS: Individuals ≥50 years with a distal radius fracture resulting from a fall from standing height or less were recruited from a single orthopedic clinic. Participants underwent a DXA scan of their lumbar spine and hip. Femoral neck (FN) bone mineral density (BMD) and fracture risk factors were used to determine each participant's 10-year fracture risk using both fracture risk assessment tools. Participants were categorized as low (<10 %), moderate (10-20 %), or high (>20 %) risk. Stratified by age (<65 years, >65 years), the proportion of participants in each category was compared between the tools. RESULTS: Analyses included 60 participants (mean age 65.7 ± 9.6 years). In those <65 years (n = 26), the proportion of individuals at low, moderate, and high risk differed between the FRAX and CAROC tools (p < 0.0001). FRAX categorized 69 % as low (CAROC 0 %) and 3 % as high (CAROC 12 %) risk. For individuals >65 years, almost all were at least at moderate risk (FRAX 79 %, CAROC 53 %), but fewer were at high risk using FRAX (18 vs. 47 %, p < 0.0003). CONCLUSION: For participants <65 years with a wrist fracture, FRAX provides a lower estimate of 10-year fracture risk than CAROC resulting in fewer decisions to initiate therapy. However, almost all participants >65 years were at moderate or high risk under both FRAX and CAROC and should at least be considered for pharmacotherapy.

Long-term changes in bone mineral density in kidney transplant recipients.

BACKGROUND: Alterations in bone mineral metabolism occur when kidney function declines and often continue after transplantation. We investigated long-term changes in bone mineral density (BMD) among kidney transplant recipients undergoing routine clinical BMD monitoring and management. METHODS: We identified adults receiving a kidney transplant in the province of Manitoba, Canada (1996-2011) who had greater than or equal to 2 posttransplant dual energy X-ray absorptiometry examinations. Bone mineral density was expressed as Z scores (standard deviation above/below sex-matched and age-matched reference data). The main outcome was the change in BMD. RESULTS: A total of 326 kidney transplant recipients were included (mean age, 45 years; 61% men). Recipients were followed up for an average of 8.2 years (766 follow-up dual energy X-ray absorptiometry measurements). At baseline (first scan; median, 0.5 years after transplantation), bone density was slightly below average for age and sex (mean Z scores: lumbar spine, -0.4 ± 1.6; femoral neck, -0.7 ± 1.1; total hip, -0.7 ± 1.1). At the second scan (mean, 2.7 years after first scan), mean bone density Z scores have increased (lumbar spine, -0.2 ± 1.6; femoral neck, -0.6 ± 1; total hip, -0.6 ± 1.1; matched, P < 0.01 at all sites). The only factor associated with a significant BMD change at all sites was osteoporosis treatment (BMD increase). Even after restricting the analysis to recipients who had not received osteoporosis treatment, final mean bone density (mean, 8.2 years after first scan) was average for age and sex (lumbar spine, +0.7 ± 1.6; femoral neck, -0.1 ± 1.1; total hip, 0.0 ± 1.1). CONCLUSION: With routine BMD monitoring and management, posttransplant bone density typically remains stable or improves with mean values that are average for age and sex.

Build better bones with exercise: protocol for a feasibility study of a multicenter randomized controlled trial of 12 months of home exercise in women with a vertebral fracture.

BACKGROUND: Our goal is to conduct a multicenter randomized controlled trial (RCT) to investigate whether exercise can reduce incident fractures compared with no intervention among women aged ≥65 years with a vertebral fracture. OBJECTIVES: This pilot study will determine the feasibility of recruitment, retention, and adherence for the proposed trial. DESIGN: The proposed RCT will be a pilot feasibility study with 1:1 randomization to exercise or attentional control groups. SETTING: Five Canadian sites (1 community hospital partnered with an academic center and 4 academic hospitals or centers affiliated with an academic center) and 2 Australian centers (1 academic hospital and 1 center for community primary care, geriatric, and rehabilitation services). PARTICIPANTS: One hundred sixty women aged ≥65 years with vertebral fracture at 5 Canadian and 2 Australian centers will be recruited. INTERVENTION: The Build Better Bones With Exercise (B3E) intervention includes exercise and behavioral counseling, delivered by a physical therapist in 6 home visits over 8 months, and monthly calls; participants are to exercise ≥3 times weekly. Controls will receive equal attention. MEASUREMENTS: Primary outcomes will include recruitment, retention, and adherence. Adherence to exercise will be assessed via calendar diary. Secondary outcomes will include physical function (lower extremity strength, mobility, and balance), posture, and falls. Additional secondary outcomes will include quality of life, pain, fall self-efficacy, behavior change variables, intervention cost, fractures, and adverse events. Analyses of feasibility objectives will be descriptive or based on estimates with 95% confidence intervals, where feasibility will be assessed relative to a priori criteria. Differences in secondary outcomes will be evaluated in intention-to-treat analyses via independent Student t tests, chi-square tests, or logistic regression. The Bonferroni method will be used to adjust the level of significance for secondary outcomes so the overall alpha level is .05. LIMITATIONS: No assessment of bone mineral density will be conducted. The proposed definitive trial will require a large sample size. CONCLUSIONS: The viability of a large-scale exercise trial in women with vertebral fractures will be evaluated, as well as the effects of a home exercise program on important secondary outcomes.

FRAX predicts fracture risk in kidney transplant recipients.

BACKGROUND: The World Health Organization Fracture Risk Assessment Tool (FRAX) estimates the 10-year fracture probability. We assessed the prognostic value of FRAX in kidney transplant recipients, as its utility in recipients is unknown. METHODS: We considered 458 individuals (mean age 45 years, 64% men) who received a kidney transplant in the province of Manitoba, Canada at the time of their first bone mineral density (BMD) test posttransplant (mean 1.1 years posttransplant; transplant years 1996-2011). FRAX probabilities were calculated from baseline information (age, sex, clinical risk factors, with or without BMD). Recipients were followed a mean of 6.4 years (interquartile range 3.0-10.0 years) after cohort entry for an incident major osteoporotic fracture. RESULTS: In follow-up, 21 (4.6%) recipients experienced a major osteoporotic fracture. The observed 10-year major osteoporotic fracture risk of 6.3% (95% CI, 3.4-9.2%) was concordant with FRAX predictions (5.0% with BMD, 5.6% without BMD). Major osteoporotic fracture scores showed significant fracture prediction (hazard ratio per standard deviation, FRAX without BMD 1.66, 95% CI, 1.10-2.50; FRAX with BMD 1.64, 95% CI, 1.07-2.51). Area under the curve (AUC) for incident major osteoporotic fracture discrimination (AUC: FRAX with BMD 0.62, 95% CI, 0.50-0.74) was similar to the general population. CONCLUSIONS: FRAX scores categorized most kidney transplant recipients as a low-risk fracture group, and the low observed fracture rates were consistent with the 10-year fracture predictions. FRAX showed modest fracture prediction and discrimination similar to the general population. Independent validation is needed before clinicians can routinely use FRAX in kidney transplant recipients.

The three-year incidence of fracture in chronic kidney disease.

Knowing a person's fracture risk according to their kidney function, gender, and age may influence clinical management and decision-making. Using healthcare databases from Ontario, Canada, we conducted a cohort study of 679,114 adults of 40 years and over (mean age 62 years) stratified at cohort entry by estimated glomerular filtration rate ((eGFR) 60 and over, 45-59, 30-44, 15-29, and under 15 ml/min per 1.73 m(2)), gender, and age (40-65 and over 65 years). The primary outcome was the 3-year cumulative incidence of fracture (proportion of adults who fractured (hip, forearm, pelvis, or proximal humerus) at least once within 3-years of follow-up). Additional analyses examined the fracture incidence per 1000 person-years, hip fracture alone, stratification by prior fracture, stratification by eGFR and proteinuria, and 3-year cumulative incidence of falls with hospitalization. The 3-year cumulative incidence of fracture significantly increased in a graded manner in adults with a lower eGFR for both genders and both age groups. The 3-year cumulative incidence of fracture in women over 65 years of age across the 5 eGFR groups were 4.3%, 5.8%, 6.5%, 7.8%, and 9.6%, respectively. Corresponding estimates for men over 65 years were 1.6%, 2.0%, 2.7%, 3.8%, and 5.0%, respectively. Similar graded relationships were found for falls with hospitalization and additional analyses. Thus, many adults with chronic kidney disease will fall and fracture. Results can be used for prognostication and guidance of sample size requirements for fracture prevention trials.

Appropriate osteoporosis treatment by family physicians in response to FRAX vs CAROC reporting: results from a randomized controlled trial.

Canadian guidelines recommend either the FRAX or the Canadian Association of Radiologists and Osteoporosis Canada (CAROC) fracture risk assessment tools to report 10-yr fracture risk as low (<10%), moderate (10%-20%) or high (>20%). It is unknown whether one reporting system is more effective in helping family physicians (FPs) identify individuals who require treatment. Individuals ≥50 yr old with a distal radius fracture and no previous osteoporosis diagnosis or treatment were recruited. Participants underwent a dual-energy x-ray absorptiometry scan and answered questions about fracture risk factors. Participants' FPs were randomized to receive either a FRAX report or the standard CAROC-derived bone mineral density report currently used by the institution. Only the FRAX report included statements regarding treatment recommendations. Within 3 mo, all participants were asked about follow-up care by their FP, and treatment recommendations were compared with an osteoporosis specialist. Sixty participants were enrolled (31 to FRAX and 29 to CAROC). Kappa statistics of agreement in treatment recommendation were 0.64 for FRAX and 0.32 for bone mineral density. The FRAX report was preferred by FPs and resulted in better postfracture follow-up and treatment that agreed more closely with a specialist. Either the clear statement of fracture risk or the specific statement of treatment recommendations on the FRAX report may have supported FPs to make better treatment decisions.

Fracture risk in kidney transplant recipients: a systematic review.

BACKGROUND: Fractures in men and women after kidney transplantation are associated with morbidity (including acute and chronic pain), mortality, and high economic costs. METHODS: We systematically reviewed cohort studies that provided estimates on incidence and risk factors for fracture in kidney transplant recipients. We abstracted data in duplicate and assessed the methodological quality of each study on a 17-point scale (17 representing the highest quality). RESULTS: We screened 2715 articles, reviewed 81, and included 10 studies totaling 262,678 recipients (study mean, 26,268 recipients; range, 61-77,430). The average follow-up ranged from 1.7 to 5.3 years. The study quality scores ranged from 8 to 13. Fracture sites varied by study resulting in a highly variable incidence rate ranging from 3.3 to 99.6 fractures per 1000 person-years. Similarly, the 5-year cumulative incidence for fracture varied ranging from 0.85% to 27%. Common factors associated with an increased fracture risk were older age, female sex, the presence of diabetes, and receipt of dialysis before transplantation. Other less common but statistically significant risk factors were a previous history of fracture and receipt of a kidney from a deceased (vs. living) donor. CONCLUSIONS: There is poor consensus on the incidence and risk factors for fractures in kidney transplant recipients. Previous studies vary substantially in quality, fracture definitions, and the characteristics of recipients studied. Future research should clarify fracture incidence and risk, which will inform the design of future prevention trials and guide prognostication.

Bone and mineral metabolism and fibroblast growth factor 23 levels after kidney donation.

BACKGROUND: Living kidney donation offers a unique setting to study changes in phosphate and vitamin D homeostasis attributable to mild isolated decreases in estimated glomerular filtration rate (eGFR). STUDY DESIGN: Cross-sectional study. SETTING & PARTICIPANTS: 198 living kidney donors and 98 nondonor controls from 9 transplant centers across 3 countries. For donors, median time after donation was 5.3 years. At assessment, donors had a lower eGFR than controls (73 vs 98 mL/min/1.73 m(2)). PREDICTOR: Living kidney donation (mildly decreased eGFR). OUTCOMES: Biochemical markers of chronic kidney disease-mineral and bone disorder. MEASUREMENTS: Serum creatinine, total serum calcium, serum and urine inorganic phosphate, plasma intact parathyroid hormone, serum calcidiol and calcitriol, renal fractional excretion of inorganic phosphate, and intact serum fibroblast growth factor 23 (FGF-23). RESULTS: Serum FGF-23 levels were significantly higher in donors (38.1 vs 29.7 pg/mL; P < 0.001). For every 10-mL/min/1.73 m(2) decrease in eGFR, FGF-23 level was higher by 3.2 (95% CI, 2.0-4.4) pg/mL. Compared with controls, donors showed higher renal tubular fractional excretion of inorganic phosphate (17.8% vs 12.3%; P < 0.001), lower serum phosphate (0.97 vs 1.02 mmol/L; P = 0.03), and lower serum calcitriol values (63 vs 77 pmol/L; P < 0.001). Serum calcium levels were not significantly different between the 2 groups. Plasma intact parathyroid hormone levels were significantly higher in donors (5.7 vs 5.0 pmol/L; P = 0.03), but were not correlated with FGF-23 or calcitriol levels. LIMITATIONS: Enrollment of a small proportion of past donors at participating centers; assessment of only postdonation values; unable to assess seasonal variation or other temporal patterns in biochemical markers; assessment of kidney function was based on eGFR, not measured GFR. CONCLUSIONS: The FGF-23 pathway may be activated in living kidney donors who show early biochemical changes compatible with chronic kidney disease-mineral and bone disorder. Whether these changes influence bone mineral density and fracture rates warrants consideration.

Osteoporosis Canada 2010 guidelines for the assessment of fracture risk.

Osteoporosis Canada's 2010 Clinical Practice Guidelines for the Diagnosis and Management of Osteoporosis in Canada focus on the clinical impact of fragility fractures, and on the assessment and management of women and men at high risk for fragility fracture. These guidelines now integrate a 10-year absolute fracture risk prediction into an overall management approach by using validated risk assessment tools. There currently is a large gap between optimal practices and those that are now being provided to Canadians with osteoporosis. These guidelines are part of a concerted effort to close this gap. Key changes from the 2002 guidelines of interest and relevance to radiologists are highlighted in this report.

Reducing the risk of re-fracture in the dialysis population: is it time to consider therapy with PTH analogues?

Dialysis patients are at high risk for fracture, with published rates in excess of a 20% probability of fracture over the next 10 years of dialysis. Unfortunately, there is no accepted methodology for quantifying this risk in advance of the first fracture; conventional bone densitometry performs unreliably in this role, in contrast to its utility in elderly patients with osteoporosis. The KDIGO clinical guidelines emphasize the importance of bone turnover in the development of renal osteodystrophy with high bone turnover strongly associated with uncontrolled secondary hyperparathyroidism, and adynamic bone disease (ABD) defined as a very low bone turnover state associated with functional hypoparathyroidism. It is likely that fractures occur in association with both extremes of uremic bone turnover, in addition to the known risk factors for developing osteoporosis prior to an individual developing end-stage renal failure. No systematic evidence has been forthcoming on therapy to reduce the risk of re-fracture after a dialysis patient presents with a first fracture. Anti-resorptive therapy might be effective in high turnover uremic bone disease and has been demonstrably effective in reducing fracture risk in osteoporotic patients, but there is only post hoc evidence that cinacalcet might reduce the incidence of fractures, and almost no evidence on outcomes from the use of bisphosphonates in dialysis patients. Fractures associated with ABD present a particular challenge. Although aluminum intoxication has been an important cause of skeletal fracturing in the past, this is a rare event today, when nonaluminum containing dietary phosphate binders are routinely prescribed. We suggest that the use of an anabolic agent would be a more plausible approach to the management of ABD (rather than anti-resorptive agents) and propose that a "proof-of-concept" trial with a PTH analogue such as teriparatide should be considered for these patients.

Functional analysis of a type 1 parathyroid hormone receptor intracellular tail mutant [KRK(484-6)AAA]: effects on second messenger generation and cellular targeting.

The parathyroid hormone receptor type 1 (PTHR1) is activated by parathyroid hormone (PTH) and PTH-related protein (PTHrP) and primarily signals via intracellular pathways involving adenylyl cyclase and phospholipase C. The intracellular tail domain of the PTHR1 contributes to G protein subunit coupling that is important for second messenger signalling. In addition, the intracellular domain has a potential nuclear localization sequence (NLS) that, if functional, could point to an intracrine role for the receptor. In the present study, we have utilized 2 sets of constructs that employ either a [KRK(484-486)AAA](3Ala) mutation in the putative NLS or the non-mutant counterpart and included (a) the full-length rat PTHR1 with FLAG and c-myc epitope tags at the N-terminus and C-terminus, respectively (designated as PTHR1(3Ala)-TAG and PTHR1-TAG); and (b) only the putative NLS-containing intracellular domain (471-488), with green fluorescent protein (GFP) fused to the C-terminus (designated as GFP-(3Ala)471-488 or GFP-471-488). Porcine kidney LLC-PK1 cells stably expressing the PTHR1(3Ala)-TAG exhibited reduced signalling via both cAMP and cytosolic calcium transients in spite of greater cell surface expression relative to cells expressing PTHR1-TAG. We also examined the ability of the intracellular tail to influence the cellular localization of a heterologous protein. LLC-PK1 cells transiently transfected with GFP-471-488, exhibited increased fluorescence within the nucleus, relative to cells transfected with GFP alone that was not observed when cells were transiently transfected with the mutated construct, GFP-(3Ala)471-488. However, LLC-PK1 cells transiently transfected with either the full-length PTHR1-TAG or the PTHR1(3Ala)-TAG constructs did not exhibit nuclear localization of these receptors. Moreover, mouse osteoblast-like cells (MC3T3-E1) transiently expressing PTHR1-TAG also failed to demonstrate nuclear localization, although both full-length PTHR1 constructs exhibited plasma membrane immunofluorescence in both cell lines. Thus, the 484-486 sequence is critical for the full signalling responsiveness of the intact PTHR1, but the putative nuclear localization signal may not function as such within the intact receptor.

10-year probability of recurrent fractures following wrist and other osteoporotic fractures in a large clinical cohort: an analysis from the Manitoba Bone Density Program.

BACKGROUND: Wrist fractures are the most prevalent type of fracture occurring in postmenopausal women. We sought to contrast the probability of recurrent osteoporotic fractures after a primary wrist fracture with other important primary fracture sites. METHODS: A historical cohort study comprising 21,432 women 45 years or older referred for bone mineral density (BMD) testing. Longitudinal health service records were assessed for the presence of fracture codes before and after BMD testing (359,737 person-years of observation). RESULTS: A total of 2652 women (12.4%) experienced a primary fracture (wrist, vertebra, humerus, hip) prior to BMD testing, of which wrist fractures were the largest single group (1225 [46.2%]). The adjusted hazard ratio (HR) for recurrent osteoporotic fracture following a primary wrist fracture (HR, 1.58; 95% confidence interval [CI], 1.29-1.93) was lower than for other primary fractures (HR, 2.66; 95% CI, 2.30-3.08). Primary wrist fractures were not significantly associated with subsequent hip fractures (adjusted HR, 1.29; 95% CI, 0.88-1.89), whereas other primary fracture sites were individually and collectively significant predictors of future hip fractures (HR, 1.72; 95% CI, 1.31-2.26). The 10-year probability of any recurrent fracture after a primary wrist fracture was 14.2% (95% CI, 11.9%-16.5%), which was significantly less than for other primary fractures (spine, 25.7%; hip, 24.9%; humerus, 23.7%; P < .001 for all comparisons vs wrist) but greater than in those without prior fractures (10.8%; P < .001). The relationship between BMD and fracture risk was much stronger after a primary wrist fracture (HR, 2.20 per standard deviation; 95% CI, 1.70-2.80) than after other primary osteoporotic fractures (HR, 1.21; 95% CI, 1.05-1.40), reflecting the dominance of the other fracture information over BMD. CONCLUSIONS: Wrist fractures are the most common of the clinical osteoporotic fractures in patients referred for BMD testing. However, the risk of recurrent fractures in the 10 years following a wrist fracture is substantially lower than that following other osteoporotic fractures, although it remains significantly higher than for those who have yet to experience a fracture.

Re-exposure to mismatched HLA class I is a significant risk factor for graft loss: multivariable analysis of 259 kidney retransplants.

BACKGROUND: Kidney retransplants carry increased immunologic risk. One possible contributor to this risk may be re-exposure to human leukocyte antigens (HLA) common to a previous donor but foreign to the recipient. Conflicting publications have assessed this risk, so to examine our experience 259 kidney retransplants were analyzed. METHODS: A retrospective cohort of retransplant patients from 1973 to 2005 with minimum 12 months follow up was examined. Using multivariable modeling, important confounders were controlled for identifying factors significantly affecting graft survival. RESULTS: Re-exposure to HLA class I (HLA-A or B) antigens, peak panel reactive antibodies and donor source were the most important determinants of allograft survival, despite a negative conventional or anti-human globulin-augmented T cell crossmatch. We failed to demonstrate that recipient re-exposure to HLA class II (HLA-DR) or positive B cell crossmatch were associated with adverse outcomes. Sample size and molecular versus serologic methods may have influenced the former, while inability to determine antibody specificities may have influenced the latter. Controlling for other variables, the adjusted risk of graft loss associated with re-exposure to HLA class I increased by 71% (P=0.006) and occurred early, consistent with recall of memory cytotoxic T lymphocyte or antibody responses. CONCLUSIONS: Kidney recipients re-exposed to mismatched HLA class I antigens appear to be at heightened risk of early graft loss. Such patients may benefit from pretransplant identification of donor specific antibodies using solid phase methods and heightened vigilance for acute rejection. Future studies may indicate whether more intensive immunosuppression for these patients is warranted.

Expression of PTH1R constructs in LLC-PK1 cells: protein nuclear targeting is mediated by the PTH1R NLS.

This study demonstrates that the PTH1R NLS can target a fusion protein to the nucleus, and that this is blocked by sequences downstream of the NLS. GFP fused to the NLS showed a significant increase in nuclear targeting compared to GFP alone or GFP fused to a peptide of the same length. In previous studies, we demonstrated that the type I PTH/PTHrP receptor (PTH1R) localizes to the nucleus of cells within rat liver, kidney, uterus, ovary and gut. Similarly, nuclear localization of the PTH1R was observed in the cultured osteoblast-like cells MC3T3-E1, UMR106, ROS 17/2.8 and SaOS-2. We have identified a putative bipartite nuclear localization signal (NLS), from residues 471-488 in the protein sequence of the PTH1R. In this study, several PTH1R constructs were made in the Enhanced Green Fluorescent Protein (EGFP) expression vector (Clontech), transiently transfected into LLC-PK1 Clone 46 cells, and the resultant fusion protein expression followed by fluorescence microscopy. This particular clone of LLC-PK1 shows no biochemical response in vitro to parathyroid hormone. Constructs included the entire PTH1R sequence (PTH1R-GFP), the putative NLS fused to the C-terminus of GFP (GFP-NLS) or the NLS through to the C-terminus of the PTH1R fused to GFP (GFP-NLSCT). Deconvolution fluorescence microscopy of cells transfected with PTH1R-GFP showed abundant fluorescent signal throughout the cells with distinctly fluorescing plasma membranes. These cells also exhibited an increase in cAMP production in response to (0-10(-8) M) hPTH(1-34), with an increase in cAMP from 11 fmol/mug of protein to 101 fmol/microg. In contrast, cells transfected with the GFP-NLS construct showed significant nuclear sequestration of fluorescence as compared to GFP alone, GFP-NLSCT, or a short amino acid sequence fused to GFP (GFP-FFVAIYCFCNGEVQAEI). These results indicate that the NLS at residues 471-488 of the mature rat PTH1R is functional and plays a role in targeting the PTH1R the nucleus, also the addition of GFP to the C-terminus of the PTH1R still allows cAMP generation which will be useful for further studies.

Type 1 parathyroid hormone receptor (PTH1R) nuclear trafficking: regulation of PTH1R nuclear-cytoplasmic shuttling by importin-alpha/beta and chromosomal region maintenance 1/exportin 1.

The type 1 PTH/PTH-related peptide receptor (PTH1R) is a class B G protein-coupled receptor that demonstrates immunoreactivity in the nucleus as well as cytoplasm of target cells. Our previous studies on the PTH1R have shown that it associates with the importin family of transport regulatory proteins. To investigate the role of the importins in PTH1R nuclear import, we used small interfering (si)RNA technology to knock down the expression of importin-beta in the mouse osteoblast-like cell line, MC3T3-E1. Immunofluorescence microscopy as well as ligand blotting for PTH1R in nuclear fractions of importin-beta siRNA-treated cells demonstrated a decrease in nuclear localization of the PTH1R in comparison with control cells. Under normal culture conditions, PTH1R is present in both the nucleus and cytoplasm of cells. Serum starvation favors nuclear localization of PTH1R, whereas returning cells to serum or treatment with PTH-related peptide induced its cytoplasmic localization. To address the nuclear export of PTH1R, interactions between PTH1R and chromosomal region maintenance 1 (CRM1) were investigated. PTH1R and CRM1 coimmunoprecipitated from MC3T3-E1 cells, suggesting that CRM1 and PTH1R form a complex in vivo. After treatment with leptomycin B, a specific inhibitor of CRM1-mediated nuclear export, PTH1R accumulated in the nucleus. Taken together, our studies show that PTH1R shuttles from the nucleus to the cytoplasm under normal physiological conditions and that this nuclear-cytoplasmic transport is dependent upon importin-alpha/beta and CRM1.

Effects of a one-month treatment with PTH(1-34) on bone formation on cancellous, endocortical, and periosteal surfaces of the human ilium.

UNLABELLED: Using bone histomorphometry, we found that a 1-month treatment with PTH(1-34) [hPTH(1-34)] stimulated new bone formation on cancellous, endocortical, and periosteal bone surfaces. Enhanced bone formation was associated with an increase in osteoblast apoptosis. INTRODUCTION: The precise mechanisms by which hPTH(1-34) increases bone mass and improves bone structure are unclear. Using bone histomorphometry, we studied the early effects of treating postmenopausal women with osteoporosis with hPTH(1-34). MATERIALS AND METHODS: Tetracycline-labeled iliac crest bone biopsies were obtained from 27 postmenopausal women with osteoporosis who were treated for 1 month with hPTH(1-34), 50 microg daily subcutaneously. The results were compared with tetracycline-labeled biopsies from a representative control group of 13 postmenopausal women with osteoporosis. RESULTS: The bone formation rate on the cancellous and endocortical surfaces was higher in hPTH(1-34)-treated women than in control women by factors of 4.5 and 5.0, respectively. We also showed a 4-fold increase in bone formation rate on the periosteal surface, suggesting that hPTH(1-34) has the potential to increase bone diameter in humans. On the cancellous and endocortical surfaces, the increased bone formation rate was primarily caused by stimulation of formation in ongoing remodeling units, with a modest amount of increased formation on previously quiescent surfaces. hPTH(1-34)-stimulated bone formation was associated with an increase in osteoblast apoptosis, which may reflect enhanced turnover of the osteoblast population and may contribute to the anabolic action of hPTH(1-34). CONCLUSIONS: These findings provide new insight into the cellular basis by which hPTH(1-34) improves cancellous and cortical bone architecture and geometry in patients with osteoporosis.

Management of osteoporosis in men: an update and case example.

In 2002, Osteoporosis Canada published clinical practice guidelines for the diagnosis and management of osteoporosis. The current paper supplements that guideline and provides a review and synthesis of the current literature on the diagnosis and management of osteoporosis in men.