Urinary levels of pentosidine and the risk of fracture in postmenopausal women: the OFELY study

Advanced glycation and glycoxidation end products in bone

Hyperglycemia and oxidative stress, enhanced in diabetes and aging, result in excessive accumulation of advanced glycation and glycoxidation end products (AGEs/AGOEs) in bone. AGEs/AGOES are considered to be "the missing link" in explaining increased skeletal fragility with diabetes, aging, and osteoporosis where increased fracture risk cannot be solely explained by bone mass and/or fall incidences. AGEs/AGOEs disrupt bone turnover and deteriorate bone quality through alterations of organic matrix (collagen and non-collagenous proteins), mineral, and water content. AGEs and AGOEs are also associated with bone fragility in other conditions such as Alzheimer's disease, circadian rhythm disruption, and cancer. This review explains how AGEs and AGOEs accumulate in bone and impact bone quality and bone fracture, and how AGES/AGOEs are being targeted in preclinical and clinical investigations for inhibition or removal, and for prediction and management of diabetic, osteoporotic and insufficiency fractures.

Urinary pentosidine level is associated with the risk of fracture in community-dwelling older adults: a prospective observational study

A history of fracture in adulthood and urinary pentosidine levels were independently and significantly associated with fracture occurrence in this prospective observational study of community-dwelling older adults.

PURPOSE

This prospective observational study aimed to determine the factors associated with fragility fractures in community-dwelling older adults.

METHODS

Overall, 254 older adults who were participants of the Good Aging and Intervention Against Nursing Care and Activity Decline study in 2016 were included in this study. Grip strength, muscle mass, gait speed, calcaneal bone density, and the levels of parathyroid hormone, osteocalcin, 25-hydroxyvitamin D, total procollagen type I N-terminal propeptide, insulin-like growth factor-1 (IGF-1), tartrate-resistant acid phosphatase-5b, and urinary pentosidine were measured at baseline. Participants were classified as fracture ( +) or fracture (-) based on the data collected during a 5-year follow-up period.

RESULTS

Excluding those who were lost to follow-up during the observation period, 182 participants (64 men and 118 women, mean age: 74.2 years, range: 47-99 years) were included in the analysis. During the observation period, 23 patients experienced 24 new fractures. In univariate analysis, sex, height, weight, history of fracture in adulthood, baseline grip strength, muscle mass, bone density, and the levels of urinary pentosidine and IGF-1 at baseline were significantly different between patients who developed a fracture during follow-up and those who did not. In multivariate analysis, a history of fracture in adulthood and urinary pentosidine levels were independently and significantly associated with fracture occurrence.

CONCLUSION

High urine pentosidine levels and a history of fracture in adulthood are independent risk factors for fracture occurrence in community-dwelling older adults.

The AGE-RAGE Axis and the Pathophysiology of Multimorbidity in COPD

Chronic obstructive pulmonary disease (COPD) is a disease of the airways and lungs due to an enhanced inflammatory response, commonly caused by cigarette smoking. Patients with COPD are often multimorbid, as they commonly suffer from multiple chronic (inflammatory) conditions. This intensifies the burden of individual diseases, negatively affects quality of life, and complicates disease management. COPD and comorbidities share genetic and lifestyle-related risk factors and pathobiological mechanisms, including chronic inflammation and oxidative stress. The receptor for advanced glycation end products (RAGE) is an important driver of chronic inflammation. Advanced glycation end products (AGEs) are RAGE ligands that accumulate due to aging, inflammation, oxidative stress, and carbohydrate metabolism. AGEs cause further inflammation and oxidative stress through RAGE, but also through RAGE-independent mechanisms. This review describes the complexity of RAGE signaling and the causes of AGE accumulation, followed by a comprehensive overview of alterations reported on AGEs and RAGE in COPD and in important co-morbidities. Furthermore, it describes the mechanisms by which AGEs and RAGE contribute to the pathophysiology of individual disease conditions and how they execute crosstalk between organ systems. A section on therapeutic strategies that target AGEs and RAGE and could alleviate patients from multimorbid conditions using single therapeutics concludes this review.

Causative or associative: A critical review of the role of advanced glycation end-products in bone fragility

The accumulation of advanced glycation end-products (AGEs) in the organic matrix of bone with aging and chronic disease such as diabetes is thought to increase fracture risk independently of bone mass. However, to date, there has not been a clinical trial to determine whether inhibiting the accumulation of AGEs is effective in preventing low-energy, fragility fractures. Moreover, unlike with cardiovascular or kidney disease, there are also no pre-clinical studies demonstrating that AGE inhibitors or breakers can prevent the age- or diabetes-related decrease in the ability of bone to resist fracture. In this review, we critically examine the case for a long-standing hypothesis that AGE accumulation in bone tissue degrades the toughening mechanisms by which bone resists fracture. Prior research into the role of AGEs in bone has primarily measured pentosidine, an AGE crosslink, or bulk fluorescence of hydrolysates of bone. While significant correlations exist between these measurements and mechanical properties of bone, multiple AGEs are both non-fluorescent and non-crosslinking. Since clinical studies are equivocal on whether circulating pentosidine is an indicator of elevated fracture risk, there needs to be a more complete understanding of the different types of AGEs including non-crosslinking adducts and multiple non-enzymatic crosslinks in bone extracellular matrix and their specific contributions to hindering fracture resistance (biophysical and biological). By doing so, effective strategies to target AGE accumulation in bone with minimal side effects could be investigated in pre-clinical and clinical studies that aim to prevent fragility fractures in conditions that bone mass is not the underlying culprit.

Greater Carboxy-Methyl-Lysine Is Associated With Increased Fracture Risk in Type 2 Diabetes

Accumulation of advanced glycation end-products (AGE) in bone alters collagen structure and function. Fluorescent AGEs are associated with fractures but less is known regarding non-fluorescent AGEs. We examined associations of carboxy-methyl-lysine (CML), with incident clinical and prevalent vertebral fractures by type 2 diabetes (T2D) status, in the Health, Aging, and Body Composition cohort of older adults. Incident clinical fractures and baseline vertebral fractures were assessed. Cox regression was used to analyze the associations between serum CML and clinical fracture incidence, and logistic regression for vertebral fracture prevalence. At baseline, mean ± standard deviation (SD) age was 73.7 ± 2.8 and 73.6 ± 2.9 years in T2D (n = 712) and non-diabetes (n = 2332), respectively. Baseline CML levels were higher in T2D than non-diabetes (893 ± 332 versus 771 ± 270 ng/mL, p < 0.0001). In multivariate models, greater CML was associated with higher risk of incident clinical fracture in T2D (hazard ratio [HR] 1.49; 95% confidence interval [CI], 1.24-1.79 per 1-SD increase in log CML) but not in non-diabetes (HR 1.03; 95% CI, 0.94-1.13; p for interaction = 0.001). This association was independent of bone mineral density (BMD), glycated hemoglobin (hemoglobin A1c), weight, weight loss, smoking, cystatin-C, and medication use. CML was not significantly associated with the odds of prevalent vertebral fractures in either group. In conclusion, higher CML levels are associated with increased risk of incident clinical fractures in T2D, independent of BMD. These results implicate CML in the pathogenesis of bone fragility in diabetes. © 2021 American Society for Bone and Mineral Research (ASBMR).

Advanced glycation endproducts and bone quality: practical implications for people with type 2 diabetes

PURPOSE OF REVIEW

Individuals with type 2 diabetes (T2D) are at increased risk of fracture, often despite normal bone density. This observation suggests deficits in bone quality in the setting of abnormal glucose homeostasis. The goal of this article is to review recent developments in our understanding of how advanced glycation end products (AGEs) are incorporated into the skeleton with resultant deleterious effects on bone health and structural integrity in patients with T2D.

RECENT FINDINGS

The adverse effects of skeletal AGE accumulation on bone remodeling and the ability of the bone to deform and absorb energy prior to fracture have been demonstrated both at the bench as well as in small human studies; however, questions remain as to how these findings might be better explored in large, population-based investigations.

SUMMARY

Hyperglycemia drives systemic, circulating AGE formation with subsequent accumulation in the bone tissue. In those with T2D, studies suggest that AGEs diminish fracture resistance, though larger clinical studies are needed to better define the direct role of longstanding AGE accumulation on bone strength in humans as well as to motivate potential interventions to reverse or disrupt skeletal AGE deposition with the goal of fracture prevention.

Skin Autofluorescence, a Noninvasive Biomarker for Advanced Glycation End-Products, Is Associated With Prevalent Vertebral and Major Osteoporotic Fractures: The Rotterdam Study

Advanced glycation end-products (AGEs), which bind to type 1 collagen in bone and skin, have been implicated in reduced bone quality. The AGE reader™ measures skin autofluorescence (SAF), which might be regarded as a marker of long-term accumulation of AGEs in tissues. We investigated the association of SAF with bone mineral density (BMD) and fractures in the general population. We studied 2853 individuals from the Rotterdam Study with available SAF measurements (median age, 74.1 years) and with data on prevalent major osteoporotic (MOFs: hip, humerus, wrist, clinical vertebral) and vertebral fractures (VFs: clinical + radiographic Genant's grade 2 and 3). Radiographs were assessed 4 to 5 years before SAF. Multivariate regression models were performed adjusted for age, sex, BMI, creatinine, smoking status, and presence of diabetes and additionally for BMD with interaction terms to test for effect modification. Prevalence of MOFs was 8.5% and of VFs 7%. SAF had a curvilinear association with prevalent MOFs and VFs and therefore, age-adjusted, sex stratified SAF quartiles were used. The odds ratio (OR) (95% confidence interval [CI]) of the second, third and fourth quartiles of SAF for MOFs were as follows: OR 1.60 (95% CI, 1.08-2.35; p = .02); OR 1.30 (95% CI, 0.89-1.97; p = .20), and OR 1.40 (95% CI, 0.95-2.10; p = .09), respectively, with first (lowest) quartile as reference. For VFs the ORs were as follows: OR 1.69 (95% CI, 1.08-2.64; p = .02), OR 1.74(95% CI, 1.11-2.71; p = .01), and OR 1.73 (95% CI, 1.12-2.73; p = .02) for second, third, and fourth quartiles, respectively. When comparing the top three quartiles combined with the first quartile, the OR (95% CI) for MOFs was 1.43 (95% CI, 1.04-2.00; p = .03) and for VFs was 1.72 (95% CI, 1.18-2.53; p = .005). Additional adjustment for BMD did not change the associations. In conclusion, there is evidence of presence of a threshold of skin AGEs below which there is distinctly lower prevalence of fractures. Longitudinal analyses are needed to confirm our cross-sectional findings. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Relationships between human cortical bone toughness and collagen cross-links on paired anatomical locations

Human cortical bone fracture processes depend on the internal porosity network down to the lacunar length scale. Recent results show that at the collagen scale, the maturation of collagen cross-links may have a negative influence on bone mechanical behavior. While the effect of pentosidine on human cortical bone toughness has been studied, the influence of mature and immature enzymatic cross-links has only been studied in relation to strength and work of fracture. Moreover, these relationships have not been studied on different paired anatomical locations. Thus, the aim of the current study was to assess the relationships between both enzymatic and non-enzymatic collagen cross-links and human cortical bone toughness, on four human paired anatomical locations. Single Edge Notched Bending toughness tests were performed for two loading conditions: a quasi-static standard condition, and a condition representative of a fall. These tests were done with 32 paired femoral diaphyses, femoral necks and radial diaphyses (18 women, age 81 ± 12 y.o.; 14 men, age 79 ± 8 y.o.). Collagen enzymatic and non-enzymatic crosslinks were measured on the same bones. Maturation of collagen was defined as the ratio between immature and mature cross-links (CX). The results show that there was a significant correlation between collagen cross-link maturation and bone toughness when gathering femoral and radial diaphyses, but not when considering each anatomical location individually. These results show that the influence of collagen enzymatic and non-enzymatic cross-links is minor when considering human cortical bone crack propagation mechanisms.

Changes of bone mineral density and serum pentosidine during a 27-month follow-up of monthly minodronate in osteoporotic patients

PURPOSE

Monthly regimen of minodronate for osteoporosis more than two years has not been reported yet. The aim of this study is to elucidate the effect of monthly minodronate (M-MIN) on bone mineral density (BMD) and serum pentosidine (Pen) during 27 months.

MATERIALS AND METHODS

The study consisted of 52 newly treated patients (73.3 ± 8.8 years) (new group) and 47 patients (75.9 ± 9.5 years) who were switched from either alendronate or risedronate (switch group). Monthly minodronate (50 mg/every 4 weeks) was administered for 27 months. Lumbar, femoral neck, and total hip BMDs and serum pentosidine were monitored at baseline and after 9, 18, and 27 months of treatment.

RESULTS

In the new condition, lumbar, neck, and total hip BMDs increased significantly by 9.07%, 3.15%, and 3.06%, respectively. Only the lumbar BMD significantly increased in the switch condition. Serum Pen increased in both groups in a time-dependent manner. In the group switch, multivariate logistic regression analysis revealed that the initial change in serum intact procollagen type I N-terminal propeptide (P1NP) at 9 months was an independent predictor of changes in neck and total hip BMDs at 27 months (OR = 1.039, 95% CI 1.003-1.077, p = 0.032 for neck and OR = 1.055, 95% CI 1.009-1.104, p = 0.020 for total hip).

CONCLUSIONS

Monthly minodronate treatment increased BMDs in newly treated patients over 27 months. Serum Pen increased with M-MIN therapy, possibly indicating prolonged bone turnover. The initial 9-month changes in serum P1NP predicted the 27-month changes in hip BMDs when M-MIN replaced alendronate or risedronate.

Serum and bone pentosidine in patients with low impact hip fractures and in patients with advanced osteoarthritis

Background

Femoral neck fractures are a common occurrence in patients suffering from osteoporosis, while intracapsular hip fracture is rare in cases of osteoarthritis of the hip. Previous histomorphometric studies have emphasized the association between bone microarchitecture and the risk of low-impact fractures in osteoarthritis and osteoporosis patients. However, the strength of bone material is also a function of composition of organic bone matrix. In order to compare tissue material properties in these two clinical conditions, serum and bone pentosidine, a non-enzymatic collagen crosslinking element, was measured in patients who suffered a low-impact fracture, and in patients with advanced osteoarthritis.

Methods

The patient population consisted of 70 patients who underwent hemiarthroplasty surgery for a femoral neck fracture, and 41 patients with advanced hip joint osteoarthritis without a history of low- impact fracture, who were indicated for total hip joint replacement. Pentosidine content was analyzed in bone samples and in serum obtained from fracture and osteoarthritis patients using high performance liquid chromatography.

Results

Serum and bone concentrations of pentosidine were higher in subjects with hip fractures compared with osteoarthritis after adjustment for age, sex, weight, serum creatinine, and diabetes. A significant positive correlation was found between bone and serum pentosidine in fractured cases. A comparable relationship was also demonstrated for pentosidine levels in serum and bone relative to differentiation of fracture and osteoarthritis cases.

Conclusions

Serum pentosidine can be considered a potential biomarker for identification of subjects with impaired bone quality and bone strength.

Serum pentosidine levels after 3 years of bisphosphonate treatment in post-menopausal osteoporotic women

The present study measured changes in plasma pentosidine and bone turnover markers in elderly patients with osteoporosis treated using bisphosphonate. The relationship between pentosidine and bone turnover markers and bone mineral density (BMD) was investigated. This study consisted of post-menopausal osteoporotic women who could be treated using bisphosphonate for 3 years were included in the present analysis. The study population consisted of 58 cases, all women, ranging in age from 53 to 86 years (mean, 67.1 years). Bisphosphonate treatment significantly increased BMD of the lumbar spine to 0.914 ± 0.141 g/cm(2) and BMD of the femoral neck to 0.708 ± 0.086 g/cm(2) after 3 years (p < 0.001 versus baseline). The mean BAP level was 27.3 ± 8.3 U/L in patients at baseline. After bisphosphonate treatment, BAP significantly decreased to 18.1 ± 7.2 U/L at 3 years (p < 0.001). Urinary NTX also decreased after bisphosphonate treatment. After 3 years of treatment, urinary NTX significantly decreased from 50.0 ± 19.0 nmol BCE/mmol Cr to 24.6 ± 10.2 nmol BCE/mmol Cr at 3 years (p < 0.001). Serum pentosidine levels were 0.0413 ± 0.0094 μg/mL at baseline and 0.0413 ± 0.0122 μg/mL after 3 years. They were not significantly changed by bisphosphonate treatment. Serum pentosidine levels were not changed by treatment with bisphosphonates. Thus, serum pentosidine may not be suitable as a marker of bone quality after 3 years of bisphosphonate treatment.

Osteoporosis-associated fracture and diabetes

Osteoporosis and diabetes mellitus are chronic diseases with significant associated morbidity and mortality. Recent evidence suggests that both type 1 and type 2 diabetes are associated with an increased fracture risk. Fracture as a complication of diabetes must be considered when evaluating and treating patients with diabetes.

Circulating levels of carboxy‐methyl‐lysine (CML) are associated with hip fracture risk: the Cardiovascular Health Study

Advanced glycation end products (AGE) in bone tissue are associated with impaired biomechanical properties and increased fracture risk. Here we examine whether serum levels of the AGE carboxy‐methyl‐lysine (CML) are associated with risk of hip fracture.We followed 3373 participants from the Cardiovascular Health Study (age 78 years; range, 68–102 years; 39.8% male) for a median of 9.22 years (range, 0.01–12.07 years). Rates of incident hip fracture were calculated by quartiles of baseline CML levels, and hazard ratios were adjusted for covariates associated with hip fracture risk. A subcohort of 1315 participants had bone mineral density (BMD)measurement. There were 348 hip fractures during follow‐up, with incidence rates of hip fracture by CML quartiles of 0.94, 1.34, 1.18, and 1.69 per 100 participant‐years. The unadjusted hazard ratio of hip fracture increased with each 1 SD increase (189 ng/mL) of CML level (hazard ratio, 1.27; 95% confidence interval [CI], 1.16–1.40]; p<0.001). Sequential adjustment for age, gender, race/ethnicity,body mass index (BMI), smoking, alcohol consumption, prevalent coronary heart disease (CHD), energy expenditure, and estimated glomerular filtration rate (based on cystatin C), moderately attenuated the hazard ratio for fracture (1.17; 95% CI, 1.05–1.31; p=0.006).In the cohort with BMD testing, total hip BMD was not significantly associated with CML levels. We conclude that increasing levels of CML are associated with hip fracture risk in older adults, independent of hip BMD. These results implicate AGE in the pathogenesis of hip fractures.

Plasma level of homocysteine associated with severe vertebral fracture in postmenopausal women

The aim of this cross-sectional cohort study was to clarify risk factors for severe vertebral fractures in postmenopausal Japanese women. Subjects were ambulatory volunteers age over 50 years who were recruited from a population of outpatients at a primary care institute. At registration, age, body mass index (BMI), bone mineral density (BMD), and present illness were investigated. Biochemical parameters including urinary levels of type I collagen cross-linked N-telopeptides (NTXs), and pentosidine and plasma levels of homocysteine were measured. Values were compared with different fracture grades (grade 0-3). A total of 1,475 postmenopausal women (66.6 ± 9.0 years) were included in the present study. Distributions of vertebral fracture grades were grade 1, 137 cases (9.3 %); grade 2, 124 cases (8.4 %); and grade 3, 162 cases (11.0 %). Age, BMI, BMD, NTX, pentosidine, and homocysteine were significantly associated with vertebral fracture in unadjusted analysis. In addition, a higher prevalence of hypertension was observed in patients with severe fracture. When comparing vertebral fracture grade 0 versus grade 2-3 by multiple regression analysis, pentosidine and homocysteine levels were a significant risk for moderate/severe vertebral fracture (odds ratio [OR] = 1.17, 95 % confidence interval [CI] 1.00-1.38, p = 0.049; OR = 1.22, 95 % CI 1.03-1.46, p = 0.013). Homocysteine levels were also a significant risk when comparing vertebral fracture grade 0 versus grade 3 (OR = 1.27, 95 % CI 1.04-1.58, p = 0.021). Plasma level of homocysteine was an independent risk for severe vertebral fractures.

Overweight/obesity and underweight are both risk factors for osteoporotic fractures at different sites in Japanese postmenopausal women

This cohort study of 1,614 postmenopausal Japanese women followed for 6.7 years showed that overweight/obesity and underweight are both risk factors for fractures at different sites. Fracture risk assessment may be improved if fracture sites are taken into account and BMI is categorized.

INTRODUCTION

The effect of body mass index (BMI) on fracture at a given level of bone mineral density (BMD) is controversial, since varying associations between BMI and fracture sites have been reported.

METHODS

A total of 1,614 postmenopausal Japanese women were followed for 6.7 years in a hospital-based cohort study. Endpoints included incident vertebral, femoral neck, and long-bone fractures. Rate ratios were estimated by Poisson regression models adjusted for age, diabetes mellitus, BMD, prior fracture, back pain, and treatment by estrogen.

RESULTS

Over a mean follow-up period of 6.7 years, a total of 254 clinical and 335 morphometric vertebral fractures, 48 femoral neck fractures, and 159 long-bone fractures were observed. Incidence rates of vertebral fracture in underweight and normal weight women were significantly lower than overweight or obese women by 0.45 (95 % confidence interval: 0.32 to 0.63) and 0.61 (0.50 to 0.74), respectively, if BMD and other risk factors were adjusted, and by 0.66 (0.48 to 0.90) and 0.70 (0.58 to 0.84) if only BMD was not adjusted. Incidence rates of femoral neck and long-bone fractures in the underweight group were higher than the overweight/obese group by 2.15 (0.73 to 6.34) and 1.51 (0.82 to 2.77) and were similar between normal weight and overweight/obesity.

CONCLUSIONS

Overweight/obesity and underweight are both risk factors for fractures at different sites. Fracture risk assessment may be improved if fracture sites are taken into account and BMI is categorized.

The contribution of collagen crosslinks to bone strength

Collagen crosslinking is a major post-translational modification of collagen which has important roles in determining the biomechanical competence of bone. Crosslinks can be divided into enzymatic lysil oxidase-mediated and non-enzymatic glycation-induced (advanced glycation end products, AGE) molecules. In addition, collagen in bone can also undergo spontaneous isomerization and racemization of the aspartic acid residues with the C-telopeptide (CTX), leading to the formation of two isomers namely α (newly formed collagen) and β (matured isomerized collagen) CTX. Several in vitro and ex vivo studies, relating the bone content of these crosslinks with bone strength, have shown that they contributed to the mechanical competence of trabecular and cortical bone-mainly on the post-yield properties-in part independent of the bone mineral content. In addition, AGEs such as pentosidine have been reported to alter the formation and propagation of microdamage by making the bone more brittle. The bone content of AGEs and isomerization can also be modified by antiresorptive and anabolic therapies. They may thus explain part of the antifracture efficacy of these treatments. The main challenge consists in the transposition of these in vitro/ex vivo studies to clinical applications for the development of a non-invasive biomarker, as none of currently identified collagen crosslinks (both enzymatic and nonenzymatic) is bone specific. Nevertheless, serum or urine levels of pentosidine and the ratio of α/β CTX have been reported to predict fracture risk in postmenopausal women, in men and in patients with type 2 diabetes.

The contribution of the extracellular matrix to the fracture resistance of bone

The likelihood of suffering a bone fracture is not solely predicated on areal bone mineral density. As people age, there are numerous changes to the skeleton occurring at multiple length scales (from millimeters to submicron scales) that reduce the ability of bone to resist fracture. Herein is a review of the current knowledge about the role of the extracellular matrix (ECM) in this resistance, with emphasis on engineering principles that characterize fracture resistance beyond bone strength to include bone toughness and fracture toughness. These measurements of the capacity to dissipate energy and to resist crack propagation during failure precipitously decline with age. An age-related loss in collagen integrity is strongly associated with decreases in these mechanical properties. One potential cause for this deleterious change in the ECM is an increase in advanced glycation end products, which accumulate with aging through nonenzymatic collagen crosslinking. Potential regulators and diagnostic tools of the ECM with respect to fracture resistance are also discussed.

Skin advanced glycation end-product accumulation is negatively associated with calcaneal osteo-sono assessment index among non-diabetic adult Japanese men

This study aims to determine the relationship between advanced glycation end-product (AGE) accumulation in skin tissue and bone strength, assessed by quantitative ultrasound, among healthy adult Japanese men. The results of the study suggest that men with higher AGE accumulation in skin tissue have a lower osteo-sono assessment index.

INTRODUCTION

AGE accumulate in bone collagen with age and diabetes and decrease the mechanical properties of bone. Although increased AGE levels are associated with fractures among diabetic patients and elderly women, it is unclear whether a relationship between increased AGE levels and bone strength is present in apparently healthy adult males. The aim of this study was to determine the relationship between AGE accumulation in tissue and the mechanical properties of bone among adult Japanese men, using quantitative ultrasound as a surrogate measure of the latter.

METHODS

Skin autofluorescence (AF), which is a noninvasive method for measuring tissue AGEs, and osteo-sono assessment index (OSI), which is determined by quantitative ultrasound, were measured in 193 adult Japanese men (median age 43 years; interquartile range 37.0-55.0 years).

RESULTS

Adjusted for age, BMI, calcium intake, physical activity, smoking status, and education level, log-transformed skin AF had a negative association with log-transformed OSI (β = -0.218, P < 0.01). Adjusted geometric means (95% CI) for OSI across the tertiles of skin AF were 2.81 (2.75-2.87) for the lowest tertile, 2.81 (2.74-2.87) for the middle tertile, and 2.66 (2.61-2.73) for the highest tertile; thus, OSI for the highest skin AF appeared to be 5.0% lower than that for the lowest and middle skin AF tertiles (P < 0.01).

CONCLUSION

Among apparently healthy adult Japanese men, those with higher skin AF had a lower OSI, indicating a relationship between AGE accumulation and bone strength. A long-term prospective study is required to clarify the causality.

The role of bone turnover markers in monitoring treatment in postmenopausal osteoporosis

Bone metabolism is assessed using biochemical bone turnover markers (BTM). BTM reflect the metabolic effect of drugs on bone turnover, help to establish the lowest dose inducing the largest change in the BTM, predict treatment-related reduction in fracture risk, and are helpful in bridging studies. Changes in BTM during anti-osteoporotic therapy depend on the cellular mechanism of action of the drug, degree of change in bone turnover rate and route of administration. BTM help to establish the optimal dose of anti-osteoporotic drugs because treatment-related changes in BTM are more rapid compared with change in BMD. A greater decrease in BTM levels during the first year of tantiresorptive treatment is associated with greater antifracture efficacy over 3 years. According to preliminary data, measurement of BTM can improve persistence with anti-resorptive treatment. The use of BTM to monitor anti-osteoporotic therapy in "real life" is limited at this stage.

Use of Bone Turnover Markers in Clinical Osteoporosis Assessment in Women: Current Issues and Future Options

Monitoring bone turnover of the adult and aging skeleton is essential for optimal treatment of bone metabolic diseases, such as postmenopausal osteoporosis. Diagnosis of osteoporosis is based solely on dual-emission x-ray absorptiometry-based measurements of bone mineral density. However, within the last 20 years, biochemical markers of bone turnover have been implemented to a larger degree, and especially within the field of drug development. Numerous clinical studies have underscored that the markers have promise in terms of predicting patients at high risk of losing bone, future fracture events and importantly also the fracture efficacy of drugs in development. Furthermore, while classical methods often require years to monitor the changes, the bone turnover markers do so within a shorter time span. The aims of this article are to provide an update on the different biochemical markers of bone turnover, and to give an overview of their applications in epidemiological and clinical research especially in women. The main emphasis will be on their utility in clinical trials testing the efficacy of drugs for the treatment of osteoporosis, and their ability to supplement bone mass measurements. Finally, recent evidence suggests that biochemical markers may provide information on bone age that may indirectly relate to bone quality, and this is discussed together with future possibilities for measuring bone quality using bone turnover markers. In summary, a more targeted use of biomarkers could assist in the identification of high-risk patients, the process of drug discovery and monitoring of the efficacy of osteoporosis treatment in clinical settings.

Urinary pentosidine improves risk classification using fracture risk assessment tools for postmenopausal women

We investigated whether measurement of pentosidine, in addition to the conventional risk assessment tool, the Fracture and Immobilization Score (FRISC), improves early identification of fracture cases. A total of 765 postmenopausal Japanese women with baseline measurement of urinary pentosidine were followed in a hospital-based cohort study. Endpoints were incidence of vertebral fracture, incidence of long bone fracture, and incidence of long bone and vertebral fracture. To assess the effect of pentosidine on fracture risk, we fitted multivariate Cox regression models adjusted for age, body weight, diabetes mellitus, lumbar BMD, prior fracture, and presence of back pain. To explore potential nonlinear relationships, we fitted a multivariate generalized additive model. To assess the discriminatory power of pentosidine, we performed receiver operating characteristic analysis. The hazard ratios for a 1 SD increase in pentosidine were 1.18 (95% CI 1.05-1.33, p < 0.01) for vertebral fracture and 1.20 (95% CI 1.07-1.33, p < 0.01) for long bone and vertebral fractures. The relationship was approximately linear, and there was no indication of the presence of a threshold. The C statistics were 0.732 (95% CI 0.686-0.778) for the model with both pentosidine and the 10-year risk and 0.702 (95% CI 0.654-0.750) for the 10-year risk alone. Eighty-three subjects (11%) in the whole cohort were in the highest quartile of pentosidine, although their 10-year risks were less than 15% and included 17 incident vertebral fracture cases. Urinary pentosidine improves risk classification using conventional risk assessment tools. Optimal clinical strategies of diagnosis and treatment remain uncertain and in need of additional investigation.

Urinary pentosidine and plasma homocysteine levels at baseline predict future fractures in osteoporosis patients under bisphosphonate treatment

To clarify what kind of risk factors predict incident fractures in patients treated with bisphosphonates, the authors investigated the relationship between baseline characteristics and incident vertebral fracture in Japanese osteoporosis patients undergoing bisphosphonate treatment. This was a multi-center follow-up study conducted at three centers, in which a total of 251 Japanese patients with osteoporosis (mean age 70.5 years) from the three centers were followed for 3.2 ± 2.0 years. Baseline data, including pre-existing fractures, bone mineral density in the lumbar spine (LBMD), bone metabolic markers, urinary pentosidine, and plasma homocysteine, were evaluated. Changes in LBMD, bone turnover markers, and incident fractures after the treatment were followed. Sixty-one patients developed incident vertebral fractures; this group of patients was older and had lower LBMD, a higher prevalent vertebral fracture number, and higher homocysteine and pentosidine levels than patients who did not develop incident vertebral fractures. Changes in LBMD, urinary N-terminal telopeptides of type I collagen (NTX), and bone-derived alkaline phosphatase showed no significant association with the occurrence of vertebral fractures. Cox's proportional hazard model demonstrated that age, prevalent fracture, pentosidine, and homocysteine were independent predictors of the incident vertebral fracture rate under bisphosphonate treatment. Higher baseline levels of pentosidine and homocysteine in osteoporosis patients are potential risk factors for incident vertebral fractures when these patients are treated with bisphosphonates. Further clarification is needed to explain why such patients have higher fracture susceptibility.

Collagen cross-links as a determinant of bone quality: a possible explanation for bone fragility in aging, osteoporosis, and diabetes mellitus

Collagen cross-linking, a major post-translational modification of collagen, plays important roles in the biological and biomechanical features of bone. Collagen cross-links can be divided into lysyl hydroxylase and lysyloxidase-mediated enzymatic immature divalent cross-links,mature trivalent pyridinoline and pyrrole cross-links, and glycation- or oxidation-induced non-enzymatic cross-links(advanced glycation end products) such as glucosepane and pentosidine. These types of cross-links differ in the mechanism of formation and in function. Material properties of newly synthesized collagen matrix may differ in tissue maturity and senescence from older matrix in terms of crosslink formation. Additionally, newly synthesized matrix in osteoporotic patients or diabetic patients may not necessarily be as well-made as age-matched healthy subjects. Data have accumulated that collagen cross-link formation affects not only the mineralization process but also microdamage formation. Consequently, collagen cross-linking is thought to affect the mechanical properties of bone. Furthermore,recent basic and clinical investigations of collagen cross-links seem to face a new era. For instance, serum or urine pentosidine levels are now being used to estimate future fracture risk in osteoporosis and diabetes. In this review, we describe age-related changes in collagen cross-links in bone and abnormalities of cross-links in osteoporosis and diabetes that have been reported in the literature.

Advanced Glycation End-products and Bone Fractures

Bone does not turn over uniformly, and becomes susceptible to post-translational modification by non-enzymatic glycation (NEG). NEG of bone causes the formation of advanced glycation end-products (AGEs) and this process is accelerated with aging, diabetes and antiresorptive postmenopausal osteoporosis therapy. Due to the elevated incidence of fracture associated with aging and diabetes, several studies have attempted to measure and evaluate AGEs as biomarkers for fracture risk. Here current methods of estimating AGEs in bone by liquid chromatography and fluorometric assay are summarized and the relationships between AGEs and fracture properties at whole bone, apparent tissue and matrix levels are discussed.