Towards the revival of alkaline phosphatase for the management of bone disease, mortality and hip fractures

Predisposing factors for a second fragile hip fracture in a population of 1130 patients with hip fractures, treated at Oulu University Hospital in 2013-2016: a retrospective study

OBJECTIVE

The life-time risk of a second fragile hip fracture is 8.4%, but the risk factors that predispose to a second hip fracture remain unresolved. This study aimed to define risk factors that predisposed patients to a second hip fracture.

METHODS

For this retrospective study, we retrieved clinical data on 1130 patients with fragile hip fractures (67.2% female, mean age: 79.3 years) that underwent surgery at the Oulu University Hospital in 2013-2016. These data included the fracture risk assessment score (measured with the FRAX tool), the bone-mass T-score, laboratory values, ambulatory capacity, and the time of death.

RESULTS

In this population, 12.4% of patients sustained a second hip fracture. The predisposing factors for a second hip fracture were: female (p = 0.016), a high FRAX score (p = 0.020), and low physical capacity (p < 0.001). The vitamin D level recommended for treating osteoporosis (i.e., vitamin D > 75 nmol/l) was observed in only 24% of patients, and 42% of patients had ionized calcium levels below the reference range. According to the level of the cross-linked carboxy-terminal telopeptide of type I collagen (ICTP), 37% of patients did not have high bone turnover. We found a positive correlation between age and ICTP (p = 0.001). The risk of death was higher after the second hip fracture (p = 0.005), but we found no difference in age between patients with first and second hip fractures (p = 0.11).

CONCLUSION

After a hip fracture, a second hip fracture is a well-known risk. Nevertheless, we found that only one-third of patients with a second hip fracture had used anti-osteoporosis medication at any time previously. These findings suggested that second hip fractures were most likely to occur in patients with osteopenic T-score values, in women more often than men, and in patients with high FRAX scores and low ambulatory capacity.

Bone mineral density progression following long-term simultaneous pancreas-kidney transplantation in type-1 diabetes

INTRODUCTION

Simultaneous pancreas-kidney transplantation (SPKT) has demonstrated favorable impact on the progression of chronic complications in type-1 diabetes (T1D) and terminal chronic kidney disease (CKD). However, some CKD mineral and bone disorders (CKD-MBD) may persist, even after transplantation. There are only a few studies addressing the long-term progression of bone mineral density (BMD) in these patients. Our aim was to assess baseline BMD and long-term progression and consequences in patients with T1D undergoing SPKT.

METHODS

A retrospective cohort included patients undergoing SPKT in our tertiary center between 2000 and 2017. BMD progression was assessed on dual X-ray absorptiometry (DXA). Only patients with baseline data and a minimum follow-up of 2 years were included.

RESULTS

Seventy-three patients were included, 53.4% male, with a median age at SPKT of 35 years (interquartile range [IQR] 31; 39). At transplantation, the median T-scores for the lumbar spine (LS) and femoral neck (FN) were -1.6 (IQR -2.6; -1.1) and --2.1 (IQR -2.7; -1.6), respectively. Seventy-five percent of patients presented low BMD (osteopenia or osteoporosis) in the LS and 90% in the FN, with 33% osteoporosis in the LS and 36% in the FN. On multivariate analysis, male gender (odds ratio [OR] 10.82, 95% confidence interval (CI) 2.88-40.70) and low body-mass index (BMI) (OR 0.73, 95% CI 0.55-0.97) were significantly associated with lumbar but not femoral osteoporosis. At long-term follow-up, BMD significantly improved in the LS (ΔT-score +0.41, P<0.001) and FN (ΔT-score +0.29, P=0.01), at a median 4 years after SPKT. Twelve (16.4%) and 9 (12.3%) patients showed persistent FN and LS osteoporosis, respectively. Multivariate linear regression showed that high BMI was predictive of improvement in BMD.

CONCLUSIONS

This study demonstrated severe skeletal fragility in T1D patients with terminal CKD undergoing SPKT, more than a quarter of whom showed osteoporosis. The significant improvement in BMD may result from metabolic correction by SPKT and from physiological skeleton mineralization, which continues in this age group. BMD progression was positively associated with BMI, due to improved nutritional balance after transplantation.

The Non-invasive Diagnosis of Bone Disorders in CKD

Abnormal bone metabolism is an integral part of the chronic kidney disease-mineral bone disorder (CKD-MBD). For several reasons, the difficult bone compartment was neglected for some time, but there has been renewed interest as a result of the conception of bone as a new endocrine organ, the increasing recognition of the cross-talk between bone and vessels, and, especially, the very high risk of osteoporotic fractures (and associated mortality) demonstrated in patients with CKD. Therefore, it has been acknowledged in different guidelines that action is needed in respect of fracture risk assessment and the diagnosis and treatment of osteoporosis in the context of CKD and CKD-MBD, even beyond renal osteodystrophy. These updated guidelines clearly underline the need to improve a non-invasive approach to these bone disorders in order to guide treatment decisions aimed at not only controlling CKD-MBD but also decreasing the risk of fracture. In this report, we review the current role of the most often clinically used or promising biochemical circulating biomarkers such as parathyroid hormone, alkaline phosphatases, and other biochemical markers of bone activity as alternatives to some aspects of bone histomorphometry. We also mention the potential role of classic and new imaging techniques for CKD patients. Information on many aspects is still scarce and heterogeneous, but many of us consider that it is indeed time for action, recognizing our definitely limited ability to base certain treatment decisions only on our current non-comprehensive knowledge.

Serum alkaline phosphatase and the risk of coronary heart disease, stroke and all-cause mortality: Tehran Lipid and Glucose Study

OBJECTIVES

To investigate the association of alkaline phosphatase (ALP) levels with the risk of the composite end point of cardiovascular disease (CVD), and all-cause mortality as well as each of them separately.

DESIGN

Prospective cohort study.

SETTING

Within the framework of the Tehran Lipid and Glucose Study (TLGS) cohort, participants were followed from baseline examination (1999-2001) until March 2014.

PARTICIPANTS

A total of 2578 participants, aged ≥30 years free of prevalent CVD at baseline examination.

PRIMARY OUTCOME

The main outcome measures were composite end point of coronary heart disease (CHD), stroke, all-cause mortality and each per se.

RESULTS

During a median follow-up of 11.3 years, 369, 68, 420, 170 and 495 participants experienced CHD, stroke, CVD, all-cause mortality and the composite outcome, respectively. In the multivariable Cox regression models, the adjusted HRs (95% CI) for mentioned events per one SD increase in ALP level after full adjustment were 1.11 (1.01 to 1.22), 1.20 (0.97 to 1.49, p=0.058), 1.10 (1.01 to 1.21), 1.16 (1.01 to 1.33) and 1.11 (1.02 to 1.21), respectively. Furthermore, participants with ALP levels in the highest tertile had significant adjusted HRs (95% CI) for stroke (1.88 (1.00 to 3.61)), CVD (1.30 (1.01 to 1.68)) and composite outcome (1.27 (1.00 to 1.61)). The cut-off value of ALP ≥199 IU/L for predicting composite outcome was derived using Youden's index, based on which this cut-off point was associated with significant risk of 80%, 26%, 43% and 26% for incident stroke, CVD, all-cause mortality and composite outcome. Additionally, no improvement was seen in the predictive ability of traditional risk factors models after adding ALP values, considering the levels of Akaike information criterion, C-index and Net Reclassification Index.

CONCLUSION

Independent associations between ALP levels and the risks of CVD and mortality events were shown, despite the fact that adding the data of ALP to known risk factors did not improve the prediction of these events.

Alkaline Phosphatases in the Complex Chronic Kidney Disease-Mineral and Bone Disorders

Alkaline phosphatases (APs) remove the phosphate (dephosphorylation) needed in multiple metabolic processes (from many molecules such as proteins, nucleotides, or pyrophosphate). Therefore, APs are important for bone mineralization but paradoxically they can also be deleterious for other processes, such as vascular calcification and the increasingly known cross-talk between bone and vessels. A proper balance between beneficial and harmful activities is further complicated in the context of chronic kidney disease (CKD). In this narrative review, we will briefly update the complexity of the enzyme, including its different isoforms such as the bone-specific alkaline phosphatase or the most recently discovered B1x. We will also analyze the correlations and potential discrepancies with parathyroid hormone and bone turnover and, most importantly, the valuable recent associations of AP's with cardiovascular disease and/or vascular calcification, and survival. Finally, a basic knowledge of the synthetic and degradation pathways of APs promises to open new therapeutic strategies for the treatment of the CKD-Mineral and Bone Disorder (CKD-MBD) in the near future, as well as for other processes such as sepsis, acute kidney injury, inflammation, endothelial dysfunction, metabolic syndrome or, in diabetes, cardiovascular complications. However, no studies have been done using APs as a primary therapeutic target for clinical outcomes, and therefore, AP's levels cannot yet be used alone as an isolated primary target in the treatment of CKD-MBD. Nonetheless, its diagnostic and prognostic potential should be underlined.

High Serum Alkaline Phosphatase, Hypercalcaemia, Race, and Mortality in South African Maintenance Haemodialysis Patients

Objective. To determine the association between serum total alkaline phosphatase (TAP) and mortality in African maintenance haemodialysis patients (MHD). Patients and Methods. The study enrolled a total of 213 patients on MHD from two dialysis centers in Johannesburg between January 2009 and March 2016. Patients were categorized into a low TAP group (≤112 U/L) versus a high TAP group (>112 U/L) based on a median TAP of 112 U/L. Results. During the follow-up period of 7 years, there were 55 (25.8%) deaths. After adjusting for cofounders such as age, other markers of bone disorder, and comorbidity (diabetes mellitus), patients in the high TAP group had significantly higher risk of death compared to patients in the low TAP group (hazard ratio, 2.50; 95% CI 1.24-5.01, P = 0.01). Similarly, serum calcium >2.75 mmol/L was associated with increased risk of death compared to patients within levels of 2.10-2.37 mmol/L (HR 6.34, 95% CI 1.40-28.76; P = 0.02). The HR for death in white patients compared to black patients was 6.88; 95% CI 1.82-25.88; P = 0.004. Conclusion. High levels of serum alkaline phosphatase, hypercalcaemia, and white race are associated with increased risk of death in MHD patients.

Changes in bone mineral density following long-term simultaneous pancreas-kidney transplantation

The symptoms of chronic renal disease-related mineral and bone disease improve significantly in patients after successful simultaneous pancreas-kidney transplantation (SPKT); however, bone pathology is still present even after many post-transplant years. The aim of this study was to analyze the bone densitometry in different periods after SPKT. Three-point densitometry was performed with the dual-energy X-ray absorptiometry (DXA) technique. Serum levels of alkaline phosphatase (ALP), total serum calcium, phosphate and parathyroid hormone were analyzed as markers of mineral metabolism. The study population consisted of 48 patients (28 females, 20 males) with a mean age of 35 ± 6 years and mean 24 ± 6 years of prior diabetes. Mean period of maintenance dialysis was 36 ± 26 months. The median time from SPKT and DXA measurement was 0.53, 26.2 and 41.9 months, respectively. Based on the DXA technique, 35.4 % of patients were categorized as having osteoporosis at the lumbar spine and 39.6 % at the femoral neck. Patients with diagnosed osteoporosis had significantly higher levels of ALP (OR = 1.5; 95 % CI = 1.1-2.2; p < 0.05 at the lumbar spine; OR = 1.4; 95 % CI = 1.0-1.9; p < 0.05 at the femoral neck). In addition, subjects with lumbar osteoporosis were characterized by a significantly lower body mass index (BMI) (OR = 0.5; 95 % CI = 0.3-0.9; p < 0.05). In the long-term follow-up, BMD increased significantly at the lumbar spine (T-score -1.86 ± 1.07 to -1.08 ± 0.89) and femoral neck (T-score -2.12 ± 0.78 to -1.63 ± 0.65). A multivariate linear model identified a BMI increase as a significant factor associated with improvement in BMD. Results of our study led us to conclude that, according to three-point densitometry, BMD among patients with functioning kidney and pancreas grafts improved. Increased serum levels of ALP were significantly associated with a decrease in BMD, suggesting a higher risk of osteoporosis. BMI gain was predictive of BMD improvement.