Decreased Serum Insulin-like Growth Factor-I is a Risk Factor for Non-vertebral Fractures in Diabetic Postmenopausal Women

Biochemical Markers of Bone Fragility in Patients with Diabetes. A Narrative Review by the IOF and the ECTS

CONTEXT

The risk of fragility fractures is increased in both type 1 and type 2 diabetes. Numerous biochemical markers reflecting bone and/or glucose metabolism have been evaluated in this context. This review summarizes current data on biochemical markers in relation to bone fragility and fracture risk in diabetes.

METHODS

Literature review by a group of experts from the International Osteoporosis Foundation (IOF) and European Calcified Tissue Society (ECTS) focusing on biochemical markers, diabetes, diabetes treatments and bone in adults.

RESULTS

Although bone resorption and bone formation markers are low and poorly predictive of fracture risk in diabetes, osteoporosis drugs seem to change bone turnover markers in diabetics similarly to non-diabetics, with similar reductions in fracture risk. Several other biochemical markers related to bone and glucose metabolism have been correlated with BMD and/or fracture risk in diabetes, including osteocyte-related markers such as sclerostin, HbA1c and advanced glycation end products (AGEs), inflammatory markers and adipokines, as well as IGF-1 and calciotropic hormones.

CONCLUSION

Several biochemical markers and hormonal levels related to bone and/or glucose metabolism have been associated with skeletal parameters in diabetes. Currently, only HbA1c levels seem to provide a reliable estimate of fracture risk, while bone turnover markers could be used to monitor the effects of anti-osteoporosis therapy.

Fracture risk assessment in diabetes mellitus

Growing evidence suggests that diabetes mellitus is associated with an increased risk of fracture. Bone intrinsic factors (such as accumulation of glycation end products, low bone turnover, and bone microstructural changes) and extrinsic factors (such as hypoglycemia caused by treatment, diabetes peripheral neuropathy, muscle weakness, visual impairment, and some hypoglycemic agents affecting bone metabolism) probably contribute to damage of bone strength and the increased risk of fragility fracture. Traditionally, bone mineral density (BMD) measured by dual x-ray absorptiometry (DXA) is considered to be the gold standard for assessing osteoporosis. However, it cannot fully capture the changes in bone strength and often underestimates the risk of fracture in diabetes. The fracture risk assessment tool is easy to operate, giving it a certain edge in assessing fracture risk in diabetes. However, some parameters need to be regulated or replaced to improve the sensitivity of the tool. Trabecular bone score, a noninvasive tool, indirectly evaluates bone microstructure by analyzing the texture sparsity of trabecular bone, which is based on the pixel gray level of DXA. Trabecular bone score combined with BMD can effectively improve the prediction ability of fracture risk. Quantitative computed tomography is another noninvasive examination of bone microstructure. High-resolution peripheral quantitative computed tomography can measure volume bone mineral density. Quantitative computed tomography combined with microstructure finite element analysis can evaluate the mechanical properties of bones. Considering the invasive nature, the use of microindentation and histomorphometry is limited in clinical settings. Some studies found that the changes in bone turnover markers in diabetes might be associated with fracture risk, but further studies are needed to confirm this. This review focused on summarizing the current development of these assessment tools in diabetes so as to provide references for clinical practice. Moreover, these tools can reduce the occurrence of fragility fractures in diabetes through early detection and intervention.

Sex-specific associations of serum insulin-like growth factor-1 with bone density and risk of fractures in Chinese patients with type 2 diabetes

We evaluated the associations of serum insulin-like growth factor-1 (IGF-1) with bone mineral density (BMD) and risk of fractures in Chinese patients with type 2 diabetes (T2D). We found positive associations between IGF-I and BMD and negative associations between IGF-I and all three modified 10-year probabilities of MOFs and HFs in men, but not in women.

INTRODUCTION

The objective was to investigate the associations of serum insulin-like growth factor-1 (IGF-1) with bone mineral density (BMD) and risk of fractures in Chinese patients with type 2 diabetes (T2D) in each gender.

METHODS

This was a cross-sectional, retrospective study that included men over 50 years and postmenopausal women with T2D without medical conditions or medications known to significantly affect BMD or serum IGF-I levels. Data of IGF-1, bone metabolism markers, lumbar spine (LS), femoral neck (FN), and total hip (TH) BMD were obtained; 10-year probability of major osteoporotic fractures (MOFs) and hip fractures (HFs) was calculated and modified with rheumatoid arthritis, femoral neck T-score, and age. Correlations of IGF-1 levels with bone metabolism and risk of fractures were statistically analyzed in men and women, respectively.

RESULTS

A total of 391 patients, including 226 men and 165 women, were included. The age, serum fasting C-peptide, glycosylated hemoglobin (HbA1c), bone formation marker, and all three modified 10-year probabilities of MOFs and HFs were higher in women than those in men (all p < 0.05). The levels of 25 hydroxyvitamin D (25OHD), IGF-1, and BMD were lower in women than those in men (all p < 0.05). In men, IGF-1 was positively correlated with FN and TH BMD (FN BMD: r = 0.267, p < 0.001; TH BMD: r = 0.235, p < 0.001) and negatively correlated with all three modified 10-year probabilities of MOFs (RA-modified MOFs: r = - 0.289, p < 0.001; age-modified MOFs: r = - 0.237, p < 0.001; FN T-score-modified MOFs: r = - 0.280, p < 0.001) and HFs (RA-modified HFs: r = - 0.291, p < 0.001; age-modified HFs: r = - 0.271, p < 0.001; FN T-score-modified HFs: r = - 0.270, p < 0.001), while no significant correlations were found between serum IGF-I and BMD and three modified 10-year probability in women.

CONCLUSIONS

According to this study, we found sex differences in the associations of serum IGF-1 with BMD and risk of fractures in Chinese patients with T2D. These results suggested that increasing serum IGF-1 might be a clinical target for protecting fractures in T2D, especially in men.

Obesity and Bone Health: A Complex Link

So far, the connections between obesity and skeleton have been extensively explored, but the results are inconsistent. Obesity is thought to affect bone health through a variety of mechanisms, including body weight, fat volume, bone formation/resorption, proinflammatory cytokines together with bone marrow microenvironment. In this review, we will mainly describe the effects of adipokines secreted by white adipose tissue on bone cells, as well as the interaction between brown adipose tissue, bone marrow adipose tissue, and bone metabolism. Meanwhile, this review also reviews the evidence for the effects of adipose tissue and its distribution on bone mass and bone-related diseases, along with the correlation between different populations with obesity and bone health. And we describe changes in bone metabolism in patients with anorexia nervosa or type 2 diabetes. In summary, all of these findings show that the response of skeleton to obesity is complex and depends on diversified factors, such as mechanical loading, obesity type, the location of adipose tissue, gender, age, bone sites, and secreted cytokines, and that these factors may exert a primary function in bone health.

Diabetes Mellitus and Osteoporosis Correlation: Challenges and Hopes

Diabetes and osteoporosis are two common diseases with different complications. Despite different therapeutic strategies, managing these diseases and reducing their burden have not been satisfactory, especially when they appear one after the other. In this review, we aimed to clarify the similarity, common etiology and possible common adjunctive therapies of these two major diseases and designate the known molecular pattern observed in them. Based on different experimental findings, we want to illuminate that interestingly similar pathways lead to diabetes and osteoporosis. Meanwhile, there are a few drugs involved in the treatment of both diseases, which most of the time act in the same line but sometimes with opposing results. Considering the correlation between diabetes and osteoporosis, more efficient management of both diseases, in conditions of concomitant incidence or cause and effect condition, is required.

Falls and Fractures in Diabetes-More than Bone Fragility

PURPOSE OF REVIEW

Based on a systematic literature search, we performed a comprehensive review of risk factors for falls and fractures in patients with diabetes.

RECENT FINDINGS

Patients with diabetes have an increased risk of fractures partly explained by increased bone fragility. Several risk factors as altered body composition including sarcopenia and obesity, impaired postural control, gait deficits, neuropathy, cardiovascular disease, and other co-morbidities are considered to increase the risk of falling. Diabetes and bone fragility is well studied, but new thresholds for fracture assessment should be considered. In general, the risk factors for falls in patients with diabetes are well documented in several studies. However, the fall mechanisms among diabetic patients have only been assessed in few studies. Thus, a gab of knowledge exits and may influence the current understanding and treatment, in order to reduce the risk of falling and thereby prevent fractures.

A scoring assessment tool for the risk of vertebral fractures in patients with type 2 diabetes mellitus

BACKGROUND

Development of assessment tool for fracture risk is an urgent task, because bone mineral density (BMD) is less useful for evaluating fracture risk in type 2 diabetes mellitus (T2DM).

SUBJECTS AND METHODS

In total, 808 T2DM patients were enrolled in this cross-sectional study. To develop a scoring assessment tool using clinical risks for vertebral fracture (VF), we evaluated which variables were associated with VF by logistic regression analysis, and categorized these variables based on cut-off values obtained by using receiver operating characteristic (ROC) curves. For calculation of the score, the relative weight of the factors was determined, and a tentative score was assigned. Then, cut-off point of the score was examined to predict VF.

RESULTS

Logistic regression analyses showed that age, diabetes duration, body mass index (BMI), serum albumin, and T score at femoral neck (FN-T score) were associated with VF risk. Parameter estimates for each risk factor obtained by logistic analyses were converted to risk scores (maximum score 23). ROC analysis showed that 8.5 was the cut-off value for detecting VF. Multiple logistic regression analysis adjusted for confounding factors showed that score ≥9 was significantly associated with an increased risk of prevalent VF (odds ratio 1.99, 95% confidence interval 1.22-3.24, p = 0.006).

CONCLUSIONS

This is the first study to show that a scoring assessment tool using age, duration of diabetes, BMI, serum albumin, and FN-T score is useful to estimate VF risk in patients with T2DM, being more sensitive than BMD alone in detecting bone fragility.

Aqueous Extract of Mori Folium Exerts Bone Protective Effect Through Regulation of Calcium and Redox Homeostasis via PTH/VDR/CaBP and AGEs/RAGE/Nox4/NF-κB Signaling in Diabetic Rats

Purpose: The present study is aimed to explore whether the aqueous extract of Mori Folium (MF) exhibits bone protective effect by regulating calcium and redox homeostasis in diabetic rats, and to identify the signaling pathways involved in this process. Methods: Diabetic rats were established using high-sugar and high-fat diet and streptozotocin (STZ) (30 mg/kg for 3 consecutive days). The serum levels of osteocalcin (OC), insulin-like growth factor-1 (IGF-1), tartrate-resistant acid phosphatase (TRAP), phosphorus (P), calcium (Ca), 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], parathormone (PTH), advanced glycation end products (AGEs), superoxide dismutase (SOD), and malondialdehyde (MDA), total antioxidant capacity (TAC), 8-hydroxy-2'-deoxyguanosine (8-OH-dG), and interleukin 6 (IL-6) were determined by ELISA or biochemical assays. Histopathological alterations in the femurs were evaluated by the stainings of hematoxylin-eosin (H&E) and alizarin red S. In addition, femoral strength was detected by a three-point bending assay, bone microstructure was detected with micro-computer tomography. Bone material properties were examined by Fourier-transform infrared spectroscopy. Furthermore, the expressions of IGF-1, runt-related transcription factor 2 (Runx2), osteoprotegerin (OPG), receptor activator of nuclear factor kappa-B ligand (RANKL), cathepsin K, AGEs, receptor of advanced glycation end products (RAGE), NADPH oxidase 4 (Nox4), and nuclear factor kappa-B (NF-κB) in the femurs and tibias, and the alterations in the levels of calcium-binding protein-28k (CaBP-28k), transient receptor potential V6 (TRPV6), and vitamin D receptor (VDR) in the kidneys and duodenums were determined by western blot and immunohistochemical analysis. Results: Treatment of diabetic rats with MF aqueous extract induces an increase in the levels of OC and IGF-1 as well as a decrease in TRAP level in serum. MF treatment also upregulates the expression of OPG, downregulates the expressions of AGEs, RAGE, Nox4, NF-κB, and RANKL, which leads to improve bone microstructure and strength exhibited by an increase in cortical area ratio, cortical thickness, and trabecular area ratio as well as ultimate load, elastic modulus, and bending stress in the femurs and tibias of diabetic rats. In addition, MF aqueous extract preserves bone material properties by decreasing the ratio of fatty acid/collagen and increasing the ratio of mineral/matrix in the femurs of diabetic rats. Moreover, MF treatment increases the levels of P, Ca, and 1,25(OH)2D3, and decreases the level of PTH in the serum, as well as upregulates the expressions of TRPV6 and VDR in the duodenums and CaBP-28k in the kidneys of diabetic rats. Additionally, MF has ability of rebuilding redox homeostasis and eliminating inflammatory stress by increasing the levels of SOD and TAC as well as decreasing the levels of IL-6, AGEs, MDA, and 8-OH-dG. Conclusions: MF treatment may improve bone quality through maintenance of calcium homeostasis via regulating the PTH/VDR/CaBP signaling, and elimination of oxidative stress via regulating the AGEs/RAGE/Nox4/NF-κB signaling. These results may suggest the potential of MF in preventing the development of diabetic osteoporosis.

Assessment using serum insulin-like growth factor-I and bone mineral density is useful for detecting prevalent vertebral fractures in patients with type 2 diabetes mellitus

Bone mineral density (BMD) is less useful for evaluating fracture risk in type 2 diabetes. This study showed for the first time that combined evaluation by serum insulin-like growth factor-I and BMD is useful to assess the risk of vertebral fracture in postmenopausal women and men with type 2 diabetes.

INTRODUCTION

BMD is less useful for evaluating fracture risk in type 2 diabetes mellitus (T2DM). We aimed to examine the usefulness of combined evaluation by BMD and serum insulin-like growth factor-I (IGF-I) to assess the risk of vertebral fracture (VF) in T2DM.

METHODS

In this cross-sectional study, 412 postmenopausal women and 582 men with T2DM, whose BMD, bone turnover markers, and serum IGF-I were measured, were enrolled. The association of BMD alone, serum IGF-I alone, and combined assessment by BMD and IGF-I with the presence of VF was examined.

RESULTS

Multiple logistic regression analyses showed that IGF-I as well as BMD T-score at lumbar (L) and femoral neck (FN) were significantly associated with VF except for IGF-I in men, respectively. Receiver operating characteristic curves showed that the cutoff values of IGF-I, L T-score and FN T-score were 127 ng/mL, - 1.78, and - 2.02 in postmenopausal women and 127 ng/mL, - 1.67, and - 1.24 in men. Based on the cutoff vales, the subjects were divided into four categories. The category of lower IGF-I and lower T-scores had a significant increased risk of VF compared to higher IGF-I and higher T-scores both in postmenopausal women and in men. The sensitivity and specificity of the combined assessment to detect VF were better compared to using BMD alone or IGF-I alone.

CONCLUSIONS

This is the first study to show that in addition to BMD measurement, the assessment using serum IGF-I is useful to estimate the prevalence of VF in patients with T2DM.

Diabetes Mellitus-induced Bone Fragility

Accumulating evidence has shown that the risk of osteoporotic fractures is increased in patients with diabetes mellitus (DM). Thus, DM-induced bone fragility has been recently recognized as a diabetic complication. Because the fracture risk is independent of the reduction in bone mineral density, deterioration of the bone quality may be the main cause of bone fragility. Although its mechanism remains poorly understood, accumulated collagen cross-links of advanced glycation end-products (AGEs) and dysfunctions of osteoblast and osteocyte may be involved. Previous studies have suggested that various diabetes-related factors, such as chronic hyperglycemia, insulin, insulin-like growth factor-I, AGEs, and homocysteine, are associated with the risk of bone fragility caused by impaired bone formation and bone remodeling. Furthermore, several anti-diabetic drugs are known to affect bone metabolism and fracture risk. We herein review the association between DM and fracture risk as well as the mechanism of DM-induced bone fragility based on recent evidence.

Skeletal Fragility in Type 2 Diabetes Mellitus

Type 2 diabetes (T2D) is associated with an increased risk of fracture, which has been reported in several epidemiological studies. However, bone mineral density in T2D is increased and underestimates the fracture risk. Common risk factors for fracture do not fully explain the increased fracture risk observed in patients with T2D. We propose that the pathogenesis of increased fracture risk in T2D is due to low bone turnover caused by osteocyte dysfunction resulting in bone microcracks and fractures. Increased levels of sclerostin may mediate the low bone turnover and may be a novel marker of increased fracture risk, although further research is needed. An impaired incretin response in T2D may also affect bone turnover. Accumulation of advanced glycosylation endproducts may also impair bone strength. Concerning antidiabetic medication, the glitazones are detrimental to bone health and associated with increased fracture risk, and the sulphonylureas may increase fracture risk by causing hypoglycemia. So far, the results on the effect of other antidiabetics are ambiguous. No specific guideline for the management of bone disease in T2D is available and current evidence on the effects of antiosteoporotic medication in T2D is sparse. The aim of this review is to collate current evidence of the pathogenesis, detection and treatment of diabetic bone disease.

Assessment of bone quality in patients with diabetes mellitus

Substantial evidence exists that diabetes mellitus is associated with an increased risk of osteoporotic fractures. Low bone strength as well as bone extrinsic factors are probably contributing to the increased bone fragility in diabetes. Bone density and quality are important determinants of bone strength. Although bone mineral density (BMD) and the fracture risk assessment tool (FRAX) are very useful clinical tools in assessing bone strength, they may underestimate the fracture risk in diabetes mellitus. Through advances in new technologies such as trabecular bone score (TBS) and peripheral quantitative computed tomography (pQCT), we can better assess the bone quality and fracture risk of patients with diabetes mellitus. Invasive assessments such as microindentation and histomorphometry have been great complement to the existing bone analysis techniques. Bone turnover markers have been found to be altered in diabetes mellitus patients and may be associated with fractures. This review will give a brief summary of the current development and clinical uses of these assessments.

Managing and maintaining bone mineral density in diabetes patients with pharmacotherapy

INTRODUCTION

The population of patients with osteoporosis and diabetes is increasing as the aging population increases. Loss of bone mineral density occurs in patients with diabetes, but is not always a priority in the practice setting. The aim of this review is to discuss clinical considerations when managing osteoporosis in patients with diabetes. Areas covered: The pathophysiology of decreased bone mineral density in patients with diabetes is discussed. Additionally, diabetic risk factors for fracture, such as hypoglycemia, the National Osteoporosis Foundation recommendations for osteoporosis, and secondary causes of osteoporosis, including disease and medication related causes, are discussed. Furthermore, recommendations for antihyperglycemic agents, thiazolidinediones, canagliflozin, insulin, metformin, and sitagliptin are discussed due to their effects on bone mineral density. Expert opinion: Even though diabetes is an important risk factor for osteoporosis, assessing bone health in diabetic patients is often overlooked. Ensuring adequate prevention and treatment strategies for osteoporosis is vitally important with our diabetic patients as the population ages. T-scores and FRAX scores likely underrepresent a diabetic patients risk for fracture, and this should be taken into consideration in treatment decisions. Future studies are needed to determine optimal pharmacologic treatment of hyperglycemia in this population.