Dietary Advanced Glycation End Products Have Sex- and Age-Dependent Effects on Vertebral Bone Microstructure and Mechanical Function in Mice

Development of heparinized and hepatocyte growth factor-coated acellular scaffolds using porcine carotid arteries

Tissue-engineered blood vessel substitutes have been developed due to the lack of suitable small-diameter vascular grafts. Xenogeneic extracellular matrix (ECM) scaffolds have the potential to provide an ideal source for off-the-shelf vascular grafts. In this study, porcine carotid arteries were used to develop ECM scaffolds by decellularization and coating with heparin and hepatocyte growth factor (HGF). After decellularization, cellular and nucleic materials were successfully removed with preservation of the main compositions (collagen, elastin, and basement membrane) of the native ECM. The ultimate tensile strength, suture strength, and burst pressure were significantly increased after cross-linking. Pore size distribution analysis revealed a porous structure within ECM scaffolds with a high distribution of pores larger than 10 μm. Heparinized scaffolds exhibited sustained release of heparin in vitro and showed potent anticoagulant activity by prolonging activated partial thromboplastin time. The scaffolds showed an enhanced HGF binding capacity as well as a constant release of HGF as a result of heparin modification. When implanted subcutaneously in rats, the modified scaffolds revealed good biocompatibility with enzyme degradation resistance, mitigated immune response, and anti-calcification. In conclusion, heparinized and HGF-coated acellular porcine carotid arteries may be a promising biological scaffold for tissue-engineered vascular grafts.

Advanced glycation end-product accumulation differs by location and sex in aged osteoarthritic human menisci

OBJECTIVE

There is a clear link between increasing age and meniscus degeneration, leading to increased injury, osteoarthritis (OA) progression, and often total knee replacement. Advanced glycation end-products (AGEs) are non-enzymatic crosslinks and adducts that accumulate in collagen with age, altering tissue mechanics and cell function, ultimately leading to increased injury and inflammation. AGEs, both fluorescent and non-fluorescent, play a central role in age-related degradation of tissues throughout the body; however, little is known about their role in meniscus degeneration. The objective of this study was to characterize changes in aged OA menisci, specifically evaluating zonal AGE accumulation, to gain a better understanding of changes that may lead to age-related meniscal degeneration.

METHOD

Deidentified human menisci (N = 48, 52-84 years old) were obtained from subjects undergoing total knee replacement. Changes in extracellular matrix (ECM) were assessed by gross morphology, confocal analysis, and biochemical assays. Deoxyribonucleic acid (DNA), glycosaminoglycan (GAG), collagen, and AGE accumulation were compared with patient age, zonal region, and patient sex.

RESULTS

There were minimal changes in DNA, GAG, and collagen concentration with age or zone. However, collagen fraying and AGEs increased with age, with more AGEs accumulating in the meniscal horns compared to the central body and in male menisci compared to females.

CONCLUSIONS

Overall, this work provides greater insights into regional changes that occur in human menisci with age and OA. These results suggest AGEs may play a role in the degeneration of the meniscus, with AGEs being a possible target to reduce age-related tears, degeneration, and OA progression.

Bone matrix quality in a developing high-fat diet mouse model is altered by RAGE deletion

Overweightness and obesity in adolescents are epidemics linked to chronic low-grade inflammation and elevated fracture risk. The increased fracture risk observed in overweight/obese adolescence contrasts the traditional concept that high body mass is protective against fracture, and thus highlights the need to determine why weight gain becomes detrimental to fracture during growth and maturity. The Receptor for Advanced Glycation End products (RAGE) is a central inflammatory regulator that can influence bone metabolism. It remains unknown how RAGE removal impacts skeletal fragility in overweightness/obesity, and whether increased fracture risk in adolescents could result from low-grade inflammation deteriorating bone quality. We characterized the multiscale structural, mechanical, and chemical properties of tibiae extracted from adolescent C57BL/6J (WT) and RAGE null (KO) mice fed either low-fat (LF) or high-fat (HF) diet for 12 weeks starting at 6 weeks of age using micro-computed tomography, strength, Raman spectroscopy, and nanoindentation. Overweight/obese WT HF mice possessed degraded mineral-crystal quality and increased matrix glycoxidation in the form of pentosidine and carboxymethyl-lysine, with HF diet in females only showing reduced cortical surface expansion and TMD independently of RAGE ablation. Furthermore, in contrast to males, HF diet in females led to more material damage and plastic deformation. RAGE KO mitigated glycoxidative matrix accumulation, preserved mineral quantity, and led to increased E/H ratio in females. Taken together, these results highlight the complex, multi-scale and sex-dependent relationships between bone quality and function under overweightness, and identifies RAGE-controlled glycoxidation as a target to potentially preserve matrix quality and mechanical integrity.

Association of skin autofluorescence with low bone density/osteoporosis and osteoporotic fractures in type 2 diabetes mellitus

BACKGROUND

Advanced glycation end products (AGEs) that abnormally accumulate in diabetic patients have been reported to damage bone health. We aimed to investigate the association between skin autofluorescence (SAF)-AGE_age (SAF - AGEs × age/100) and low bone density (LBD)/osteoporosis or major osteoporotic fractures (MOFs) in patients with type 2 diabetes mellitus (T2DM).

METHODS

This study was nested in the prospective REACTION (Risk Evaluation of Cancers in Chinese Diabetic Individuals) study and included 1214 eligible participants. SAF was used to measure skin AGEs (SAF-AGEs). Fracture events were determined by an in-person clinical follow-up. Binary logistic regression analysis, linear regression analysis, and a restricted cubic spline nested in logistic models were used to test outcomes.

RESULTS

The overall prevalence of LBD/osteoporosis in middle-aged or elderly T2DM patients was 35.7% (n = 434), and the overall incidence of MOFs was 10.5% (n = 116). Logistic analysis showed a significantly positive relationship between quartiles of SAF-AGE_age and the risk of LBD/osteoporosis (odds ratio [OR] 2.02, 95% CI 1.34-3.03; OR 3.63, CI 2.44-5.39; and OR 6.51, CI 4.34-9.78) for the multivariate-adjusted models, respectively. SAF-AGE_age was associated with MOFs with a multivariate-adjusted OR of 1.02 (CI 0.52-2.02), 2.42 (CI 1.32-4.46), and 2.70 (CI 1.48-4.91), respectively. Stratified analyses showed that SAF-AGE_age was significantly associated with MOFs only in females, nonsmokers, nondrinkers, individuals with lower body mass index, and those without LBD/osteoporosis. Linear regression analyses showed that higher SAF-AGEs were associated with a higher level of serum N-terminal propeptide of type I procollagen (s-PINP) and serum carboxy-terminal cross-linking peptide of type I collagen (s-CTX), with a multivariate-adjusted OR of 1.02 (CI 0.24-1.80) and 6.30 (CI 1.77-10.83), respectively.

CONCLUSIONS

In conclusion, SAF-AGE_age was positively associated with the prevalence of LBD/osteoporosis or MOFs in patients with T2DM. A positive association between SAF-AGEs and the level of s-PINP and s-CTX was found.

High fat diet causes inferior vertebral structure and function without disc degeneration in RAGE-KO mice

Back pain and spinal pathologies are associated with obesity in juveniles and adults, yet studies identifying causal relationships are lacking and none investigate sex differences. This study determined if high fat (HF) diet causes structural and functional changes to vertebrae and intervertebral discs (IVDs); if these changes are modulated in mice with systematic ablation for the receptor for advanced glycation endproducts (RAGE-KO); and if these changes are sex-dependent. Wild-type (WT) and RAGE-KO mice were fed a low fat (LF) or HF diet for 12 weeks starting at 6 weeks, representing the juvenile population. HF diet led to weight/fat gain, glucose intolerance, and increased cytokine levels (IL-5, MIG, and RANTES); with less fat gain in RAGE-KO females. Most importantly, HF diet reduced vertebral trabecular bone volume fraction and compressive and shear moduli, without a modifying effect of RAGE-KO, but with a more pronounced effect in females. HF diet caused reduced cortical area fraction only in WT males. Neither HF diet nor RAGE-KO affected IVD degeneration grade. Biomechanical properties of coccygeal motion segments were affected by RAGE-KO but not diet, with some interactions identified. In conclusion, HF diet resulted in inferior vertebral structure and function with some sex differences, no IVD degeneration, and few modifying effects of RAGE-KO. These structural and functional deficiencies with HF diet provide further evidence that diet can affect spinal structures and may increase the risk for spinal injury and degeneration with aging and additional stressors. Back pain and spinal pathologies are associated with obesity in juveniles and adults, yet studies identifying causal relationships are lacking and none investigate sex differences.

The degenerative impact of hyperglycemia on the structure and mechanics of developing murine intervertebral discs

Introduction

Diabetes has long been implicated as a major risk factor for intervertebral disc (IVD) degeneration, interfering with molecular signaling and matrix biochemistry, which ultimately aggravates the progression of the disease. Glucose content has been previously shown to influence structural and compositional changes in engineered discs in vitro, impeding fiber formation and mechanical stability.

Methods

In this study, we investigated the impact of diabetic hyperglycemia on young IVDs by assessing biochemical composition, collagen fiber architecture, and mechanical behavior of discs harvested from 3- to 4-month-old db/db mouse caudal spines.

Results

We found that discs taken from diabetic mice with elevated blood glucose levels demonstrated an increase in total glycosaminoglycan and collagen content, but comparable advanced glycation end products (AGE) levels to wild-type discs. Diabetic discs also contained ill-defined boundaries between the nucleus pulposus and annulus fibrosus, with the latter showing a disorganized and unaligned collagen fiber network at this same boundary.

Conclusions

These compositional and structural changes had a detrimental effect on function, as the diabetic discs were twice as stiff as their wild-type counterparts and demonstrated a significant resistance to deformation. These results indicate that diabetes may predispose the young disc to DDD later in life by altering patterns of extracellular matrix deposition, fiber formation, and motion segment mechanics independently of AGE accumulation.

Advances in research on fat infiltration and lumbar intervertebral disc degeneration

Low back pain (LBP) is a disabling condition with no available cure, severely affecting patients' quality of life. Intervertebral disc degeneration (IVDD) is the leading cause of chronic low back pain (CLBP). IVDD is a common and recurrent condition in spine surgery. Disc degeneration is closely associated with intervertebral disc inflammation. The intervertebral disc is an avascular tissue in the human body. Transitioning from hematopoietic bone marrow to bone marrow fat may initiate an inflammatory response as we age, resulting in bone marrow lesions in vertebrae. In addition, the development of LBP is closely associated with spinal stability imbalance. An excellent functional state of paraspinal muscles (PSMs) plays a vital role in maintaining spinal stability. Studies have shown that the diminished function of PSMs is mainly associated with increased fat content, but whether the fat content of PSMs is related to the degree of disc degeneration is still under study. Given the vital role of PSMs lesions in CLBP, it is crucial to elucidate the interaction between PSMs changes and CLBP. Therefore, this article reviews the advances in the relationship and the underlying mechanisms between IVDD and PSMs fatty infiltration in patients with CLBP.

Non‐Obese MKR Mouse Model of Type 2 Diabetes Reveals Skeletal Alterations in Mineralization and Material Properties

Obesity is a common comorbidity of type 2 diabetes (T2D). Therefore, increased risk of fragility fractures in T2D is often confounded by the effects of obesity. This study was conducted to elucidate the mechanistic basis by which T2D alone leads to skeletal fragility. We hypothesized that obesity independent T2D would deteriorate bone's material quality by accumulating defects in the mineral matrix and undesired modifications in its organic matrix associated with increased oxidative stress and hyperglycemia. To test this hypothesis, we used 15‐week‐old male non‐obese mice with engineered muscle creatine kinase promoter/human dominant negative insulin growth factor 1 (IGF‐I) receptor (MKR) and FVB/N wild‐type (WT) controls (n = 12/group). MKR mice exhibit reduced insulin production and loss of glycemic control leading to diabetic hyperglycemia, verified by fasting blood glucose measurements (>250 mg/dL), without an increase in body weight. MKR mice showed a significant decrease in femoral radial geometry (cortical area, moment of inertia, cortical thickness, endosteal diameter, and periosteal diameter). Bone mineral density (BMD), as assessed by micro–computed tomography (μCT), remained unchanged; however, the quality of bone mineral was altered. In contrast to controls, MKR mice had significantly increased hydroxyapatite crystal thickness, measured by small‐angle X‐ray scattering, and elongated c‐axis length of the crystals evaluated by confocal Raman spectroscopy. There was an increase in changes in the organic matrix of MKR mice, associated with enhanced glycoxidation (carboxymethyl‐lysine [CML] and pentosidine) and overall glycation (fluorescent advanced glycation end products), both of which were associated with various measures of bone fragility. Moreover, increased CML formation positively correlated with elongated mineral crystal length, supporting the role of this negatively charged side chain to attract calcium ions, promote growth of hydroxyapatite, and build a physical link between mineral and collagen. Collectively, our results show, for the first time, changes in bone matrix in a non‐obese T2D model in which skeletal fragility is attributable to alterations in the mineral quality and undesired organic matrix modifications. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Experimental Animal Studies Support the Role of Dietary Advanced Glycation End Products in Health and Disease

The increased incidence of obesity, diabetes mellitus, aging, and associated comorbidities indicates the interplay between genetic and environmental influences. Several dietary components have been identified to play a role in the pathogenesis of the so-called "modern diseases", and their complications including advanced glycation end products (AGEs), which are generated during the food preparation and processing. Diet-derived advanced glycation end products (dAGEs) can be absorbed in the gastrointestinal system and contribute to the total body AGEs' homeostasis, partially excreted in the urine, while a significant amount accumulates to various tissues. Various in vitro, in vivo, and clinical studies support that dAGEs play an important role in health and disease, in a similar way to those endogenously formed. Animal studies using wild type, as well as experimental, animal models have shown that dAGEs contribute significantly to the pathogenesis of various diseases and their complications, and are involved in the changes related to the aging process. In addition, they support that dAGEs' restriction reduces insulin resistance, oxidative stress, and inflammation; restores immune alterations; and prevents or delays the progression of aging, obesity, diabetes mellitus, and their complications. These data can be extrapolated in humans and strongly support that dAGEs' restriction should be considered as an alternative therapeutic intervention.

Complications in the spine associated with type 2 diabetes: The role of advanced glycation end-products

Type 2 diabetes mellitus (T2D) is an increasingly prevalent disease with numerous comorbidities including many in the spine. T2D is strongly linked with vertebral fractures, intervertebral disc (IVD) degeneration, and severe chronic spinal pain. Yet the causative mechanism for these musculoskeletal impairments remains unclear. The chronic hyperglycemic state in T2D promotes the formation of advanced glycation end-products (AGEs) in tissues, and the accumulation of AGEs may play a role in musculoskeletal complications by modifying the extracellular matrix, impairing cellular homeostasis, and perpetuating an inflammatory cascade via its receptor (RAGE). The AGE and RAGE associated alterations in extracellular matrix composition and morphological features of the vertebral bodies and IVDs are likely contributors to the incidence and severity of spinal pathologies in T2D. This review will broadly examine the effects of AGEs on tissues in the spine in the context of T2D, with an emphasis on the changes in the vertebrae and the IVD. Along with the clinical and epidemiological findings, we will provide an overview of preclinical rodent models of T2D that exhibit deficits in the IVD and vertebral bone. Elucidating the role of AGEs and RAGE will be crucial for understanding the disease mechanisms and translation therapies of musculoskeletal pathologies in T2D.

Dietary AGEs as Exogenous Boosters of Inflammation

Most chronic modern non-transmissible diseases seem to begin as the result of low-grade inflammation extending over prolonged periods of time. The importance of diet as a source of many pro-inflammatory compounds that could create and sustain such a low-grade inflammatory state cannot be ignored, particularly since we are constantly exposed to them during the day. The focus of this review is on specific components of the diet associated with inflammation, specifically advanced glycation end products (AGEs) that form during thermal processing of food. AGEs are also generated in the body in normal physiology and are widely recognized as increased in diabetes, but many people are unaware of the potential importance of exogenous AGEs ingested in food. We review experimental models, epidemiologic data, and small clinical trials that suggest an important association between dietary intake of these compounds and development of an inflammatory and pro-oxidative state that is conducive to chronic diseases. We compare dietary intake of AGEs with other widely known dietary patterns, such as the Mediterranean and the Dietary Approaches to Stop Hypertension (DASH) diets, as well as the Dietary Inflammation Index (DII). Finally, we delineate in detail the pathophysiological mechanisms induced by dietary AGEs, both direct (i.e., non-receptor-mediated) and indirect (receptor-mediated).

Altered mechanical behavior of demineralized bone following therapeutic radiation

Post-radiotherapy (RTx) bone fragility fractures are a late-onset complication occurring in bone within or underlying the radiation field. These fractures are difficult to predict, as patients do not present with local osteopenia. Using a murine hindlimb RTx model, we previously documented decreased mineralized bone strength and fracture toughness, but alterations in material properties of the organic bone matrix are largely unknown. In this study, 4 days of fractionated hindlimb irradiation (4 × 5 Gy) or Sham irradiation was administered in a mouse model (BALB/cJ, end points: 0, 4, 8, and 12 weeks, n = 15/group/end point). Following demineralization, the viscoelastic stress relaxation, and monotonic tensile mechanical properties of tibiae were determined. Irradiated tibiae demonstrated an immediate (day after last radiation fraction) and sustained (4, 8, 12 weeks) increase in stress relaxation compared to the Sham group, with a 4.4% decrease in equilibrium stress (p < .017). While tensile strength was not different between groups, irradiated tibiae had a lower elastic modulus (-5%, p = .027) and energy to failure (-12.2%, p = .012) with monotonic loading. Gel electrophoresis showed that therapeutic irradiation (4 × 5 Gy) does not result in collagen fragmentation, while irradiation at a common sterilization dose (25 kGy) extensively fragmented collagen. These results suggest that altered collagen mechanical behavior has a role in postirradiation bone fragility, but this can occur without detectable collagen fragmentation. Statement of Clinical Significance: Therapeutic irradiation alters bone organic matrix mechanics and which contribute to diminished fatigue strength, but this does not occur via collagen fragmentation.

Advanced glycation end products cause RAGE-dependent annulus fibrosus collagen disruption and loss identified using in situ second harmonic generation imaging in mice intervertebral disk in vivo and in organ culture models

Aging and diabetes are associated with increased low-back pain and intervertebral disk (IVD) degeneration yet causal mechanisms remain uncertain. Advanced glycation end products (AGEs), which accumulate in IVDs from aging and are implicated in diabetes-related disorders, alter collagen and induce proinflammatory conditions. A need exists for methods that assess IVD collagen quality and degradation in order to better characterize specific structural changes in IVDs due to AGE accumulation and to identify roles for the receptor for AGEs (RAGE). We used multiphoton microscopy with second harmonic generation (SHG), collagen-hybridizing peptide (CHP), and image analysis methods to characterize effects of AGEs and RAGE on collagen quality and quantity in IVD annulus fibrosus (AF). First, we used SHG imaging on thin sections with an in vivo dietary mouse model and determined that high-AGE (H-AGE) diets increased AF fibril disruption and collagen degradation resulting in decreased total collagen content, suggesting an early degenerative cascade. Next, we used in situ SHG imaging with an ex vivo IVD organ culture model of AGE challenge on wild type and RAGE-knockout (RAGE-KO) mice and determined that early degenerative changes to collagen quality and degradation were RAGE dependent. We conclude that AGE accumulation leads to RAGE-dependent collagen disruption in the AF and can initiate molecular and tissue level collagen disruption. Furthermore, SHG and CHP analyzes were sensitive to collagenous alterations at multiple hierarchical levels due to AGE and may be useful in identifying additional contributors to collagen damage in IVD degeneration processes.

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.

Kinematic Changes in a Mouse Model of Penetrating Hippocampal Injury and Their Recovery After Intranasal Administration of Endometrial Mesenchymal Stem Cell-Derived Extracellular Vesicles

Locomotion speed changes appear following hippocampal injury. We used a hippocampal penetrating brain injury mouse model to analyze other kinematic changes. We found a significant decrease in locomotion speed in both open-field and tunnel walk tests. We described a new quantitative method that allows us to analyze and compare the displacement curves between mice steps. In the tunnel walk, we marked mice with indelible ink on the knee, ankle, and metatarsus of the left and right hindlimbs to evaluate both in every step. Animals with hippocampal damage exhibit slower locomotion speed in both hindlimbs. In contrast, in the cortical injured group, we observed significant speed decrease only in the right hindlimb. We found changes in the displacement patterns after hippocampal injury. Mesenchymal stem cell-derived extracellular vesicles had been used for the treatment of several diseases in animal models. Here, we evaluated the effects of intranasal administration of endometrial mesenchymal stem cell-derived extracellular vesicles on the outcome after the hippocampal injury. We report the presence of vascular endothelial growth factor, granulocyte–macrophage colony-stimulating factor, and interleukin 6 in these vesicles. We observed locomotion speed and displacement pattern preservation in mice after vesicle treatment. These mice had lower pyknotic cells percentage and a smaller damaged area in comparison with the nontreated group, probably due to angiogenesis, wound repair, and inflammation decrease. Our results build up on the evidence of the hippocampal role in walk control and suggest that the extracellular vesicles could confer neuroprotection to the damaged hippocampus.

Dietary Advanced Glycation End-Products (dAGEs) Intake and Bone Health: A Cross-Sectional Analysis in the Rotterdam Study

Animal studies suggest a role for dietary advanced glycation end-products (dAGEs) in bone health, but human studies on dAGEs in relation to bone are lacking. We aimed to study whether dAGEs intake is associated with the parameters of bone strength namely, bone mineral density (BMD), prevalent vertebral (VFs), and major osteoporotic fractures (MOFs = hip, wrist, proximal humerus, and clinical VFs). 3949 participants (mean age 66.7 ± 10.5 years) were included from a Rotterdam study for whom Carboxymethyllysine (CML—a dietary AGE) was estimated from food frequency questionnaires combined with dAGEs databases. Multivariable linear and logistic regression models were performed adjusting for age, sex, energy intake, dietary quality, physical activity, diabetes, smoking, renal function, and cohort effect and for models on fractures, subsequently for BMD. We observed no association of CML with BMD at both femoral neck (β = −0.006; p = 0.70) and lumbar spine (β = −0.013; p = 0.38). A higher intake of CML was linearly associated with VFs (Odds ratio, OR = 1.16, 95% CI (1.02–1.32) and a similar but non-significant trend with MOFs (OR = 1.12 (0.98–1.27). Additional adjustment for BMD did not change the associations. Our results imply a positive association between dietary intake of CML and VFs independent of BMD. Future studies are needed in order to elucidate whether associations found are causal.

The BALB/c mouse as a preclinical model of the age-related deterioration in the lumbar vertebra

The likelihood of experiencing an osteoporotic fracture of one or more vertebral bodies increases with age, and this increase is not solely due to sex steroid deficiency. For the purpose of assessing the effectiveness of novel therapeutic strategies in the prevention of vertebral fractures among the elderly, we hypothesized that the BALB/c mouse model of aging phenocopies the age-related decrease in human VB strength. To test this hypothesis, we assessed the age-related changes in trabecular architecture of the L6 VB, with respect to those in the distal femur metaphysis, between 6-mo. (young adulthood, n = 20/sex) and 20-mo. of age (old age, n = 18/sex) and then determined how well the architectural characteristics, volumetric bone mineral density (vBMD), and predicted failure force from μCT-derived finite element analysis (μFEA) with linear elastic failure criteria explained the age-related variance in VB strength, which was the ultimate force during quasi-static loading of the VB in compression. While there was a pronounced age-related deterioration in trabecular architecture in the distal femur metaphysis of female and male BALB/c mice, the decrease in trabecular bone volume fraction and trabecular number between 6-mo. and 20-mo. of age occurred in male mice, but not in female mice. As such, the VB strength was lower with age in males only. Nonetheless, BV/TV and volumetric bone mineral density (vBMD) positively correlated with the ultimate compressive force of the L6 VB for both females and males. Whether using a fixed homogeneous distribution of tissue modulus (E_t = 18 GPa) or a heterogeneous distribution of E_t based on a positive relationship with TMD, the predicted failure force of the VB was not independent of age, thereby suggesting linear μFEA may not be a suitable replacement for mechanical-based measurements of strength with respect to age-related changes. Overall, the BALB/c mouse model of aging mimics the age-related in decline in human VB strength when comparing 6-mo. and 20-mo. old male mice. The decrease in VB strength in female mice may occur over a different age range.

Advanced glycation end products and their ratio to soluble receptor are associated with limitations in physical functioning only in women: results from the CARLA cohort

BACKGROUND

Advanced glycation end products (AGEs), modifications of proteins or amino acids, are increasingly produced and accumulated with age-related diseases. Recent studies suggested that the ratio of AGEs and their soluble receptor (sRAGE) is a more accurate biomarker for age-related diseases than each separately. We aim to investigate whether this also applies for physical functioning in a broad age-spectrum.

METHODS

AGE and sRAGE levels, and physical functioning (SF-12 questionnaire) of 967 men and 812 women (45-83 years) were measured in the CARLA study. We used ordinal logistic regression to examine associations between AGEs, sRAGE, and AGE/sRAGE ratio with physical functioning in sex- and age-stratified models.

RESULTS

Higher levels of AGEs and AGE/sRAGE ratio were associated with lower physical functioning only in women, even after consideration of classical lifestyle and age-related factors (education, BMI, smoking, alcohol consumption, diet, creatinine clearance, diabetes mellitus, lipid lowering and antihypertensive drugs) (odds ratio (OR) =0.86, 95%confidence interval = 0.74-0.98 and OR = 0.86, 95%CI = 0.75-0.98 for AGEs and AGE/sRAGE ratio respectively). We could not demonstrate a significant difference across age.

CONCLUSIONS

We showed a sex-specific association between physical functioning and AGEs and AGE/sRAGE, but no stronger associations of the latter with physical functioning. Further investigation is needed in the pathophysiology of this association.

Bone Strength Is Improved with Genistein Treatment in Mice with Diet-Induced Obesity

BACKGROUND

High caloric intake of saturated fat and refined sugars accelerates the development of obesity and diabetes and increases bone fracture risk. Some evidence suggests that consumption of a diet rich in phytoestrogens like genistein has the potential to strengthen bone biomechanical properties. Its bone-strengthening properties may mitigate fracture risk associated with metabolic conditions like obesity and diabetes, especially when combined with exercise.

OBJECTIVE

In this study, we test the effects of genistein, exercise training, and combination treatment on biomechanical properties of cortical bone in mice fed a high-fat, high-sugar (HFHS) diet.

METHODS

Eighty C67BL6 mice (40 females, 40 males) aged 6 wk were treated for 12 wk with an HFHS diet containing 60% fat and drinking water with 4.2 g/L sugar (55% sucrose, 45% fructose). Subgroups of the mice were also treated with genistein and/or moderate exercise (treadmill running). Genistein was incorporated into the HFHS diet (600 mg genistein/kg HFHS) and exercise was performed daily for 30 min, 5 d/wk (n = 10 females, 10 males per group). Three-point bending mechanical testing and quantitative fluorescence microscopy were conducted on femurs to measure bone strength and matrix quality.

RESULTS

Mechanical testing revealed HFHS-fed mice treated with genistein, either alone or combined with exercise, had femurs that exhibited increased postyield displacement and reduced stiffness during 3-point bending in comparison with mice only treated with the HFHS diet. Femurs of genistein-treated mice also exhibited greater ultimate force required to achieve fracture. Quantitative fluorescence showed genistein reduced advanced glycation end product accumulation in bone matrix. Exercise treatment alone had no effect.

CONCLUSIONS

Treatment with genistein, either alone or in combination with exercise, improves fracture resistance in mice fed an HFHS diet by improving bone matrix quality and increasing bone strength.

Elevated glycohemoglobin HbA1c is associated with low back pain in nonoverweight diabetics

BACKGROUND CONTEXT

Low back pain (LBP) is a common complaint in clinical practice of multifactorial origin. Although obesity has been thought to contribute to LBP primarily by altering the distribution of mechanical loads on the spine, the additional contribution of obesity-related conditions such as diabetes mellitus (DM) to LBP has not been thoroughly examined.

PURPOSE

To determine if there is a relationship between DM and LBP that is independent of body mass index (BMI) in a large cohort of adult survey participants.

STUDY DESIGN

Retrospective analysis of prospectively collected National Health and Nutrition Examination Survey (NHANES) data to characterize associations between LBP, DM, and BMI in adults subdivided into 6 subpopulations: normal weight (BMI 18.5-25), overweight (BMI 25-30), and obese (BMI >30) diabetics and nondiabetics. Diabetes was defined with glycohemoglobin A1c (HbA1c) ≥6.5%.

PATIENT SAMPLE

11,756 participants from NHANES cohort.

OUTCOME MEASURES

Percentage of LBP reported.

METHODS

LBP reported in the 1999-2004 miscellaneous pain NHANES questionnaire was the dependent variable examined. Covariates included HbA1c, BMI, age, and family income ratio to poverty as continuous variables as well as race, gender, and smoking as binary variables. Individuals were further subdivided by weight class and diabetes status. Regression and graphical analyses were performed on the study population as a whole and also on subpopulations.

RESULTS

Increasing HbA1c did not increase the odds of reporting LBP in the full cohort. However, multivariate logistic regression of the 6 subpopulations revealed that the odds of LBP significantly increased with increasing HbA1c levels in normal weight diabetics. No other subpopulations reported significant relationships between LBP and HbA1c. LBP was also significantly associated with BMI for normal weight diabetics and also for obese subjects regardless of their DM status.

CONCLUSIONS

LBP is significantly related to DM status, but this relationship is complex and may interact with BMI. These results support the concept that LBP may be improved in normal weight diabetic subjects with improved glycemic control and weight loss, and that all obese LBP subjects may benefit from improved weight loss alone.

Dietary advanced glycation end-product consumption leads to mechanical stiffening of murine intervertebral discs

Back pain is a leading cause of disability and is strongly associated with intervertebral disc (IVD) degeneration. Reducing structural disruption and catabolism in IVD degeneration remains an important clinical challenge. Pro-oxidant and structure-modifying advanced glycation end-products (AGEs) contribute to obesity and diabetes, which are associated with increased back pain, and accumulate in tissues due to hyperglycemia or ingestion of foods processed at high heat. Collagen-rich IVDs are particularly susceptible to AGE accumulation due to their slow metabolic rates, yet it is unclear whether dietary AGEs can cross the endplates to accumulate in IVDs. A dietary mouse model was used to test the hypothesis that chronic consumption of high AGE diets results in sex-specific IVD structural disruption and functional changes. High AGE diet resulted in AGE accumulation in IVDs and increased IVD compressive stiffness, torque range and failure torque, particularly for females. These biomechanical changes were likely caused by significantly increased AGE crosslinking in the annulus fibrosus, measured by multiphoton imaging. Increased collagen damage measured with collagen hybridizing peptide did not appear to influence biomechanical properties and may be a risk factor as these animals age. The greater influence of high AGE diet on females is an important area of future investigation that may involve AGE receptors known to interact with estrogen. We conclude that high AGE diets can be a source for IVD crosslinking and collagen damage known to be important in IVD degeneration. Dietary modifications and interventions that reduce AGEs warrant further investigation and may be particularly important for diabetics, in whom AGEs accumulate more rapidly.

Summary: Dietary AGEs lead to sex-specific intervertebral disc structural and functional changes and may be targeted for promoting spinal health, especially in diabetes, in which AGEs form rapidly.

Contributions of Material Properties and Structure to Increased Bone Fragility for a Given Bone Mass in the UCD-T2DM Rat Model of Type 2 Diabetes

Adults with type 2 diabetes (T2D) have a higher fracture risk for a given bone quantity, but the mechanisms remain unclear. Using a rat model of polygenic obese T2D, we demonstrate that diabetes significantly reduces whole-bone strength for a given bone mass (μCT-derived BMC), and we quantify the roles of T2D-induced deficits in material properties versus bone structure; ie, geometry and microarchitecture. Lumbar vertebrae and ulnae were harvested from 6-month-old lean Sprague-Dawley rats, obese Sprague-Dawley rats, and diabetic obese UCD-T2DM rats (diabetic for 69 ± 7 days; blood glucose >200 mg/dL). Both obese rats and those with diabetes had reduced whole-bone strength for a given BMC. In obese rats, this was attributable to structural deficits, whereas in UCD-T2DM rats, this was attributable to structural deficits and to deficits in tissue material properties. For the vertebra, deficits in bone structure included thinner and more rod-like trabeculae; for the ulnae, these deficits included inefficient distribution of bone mass to resist bending. Deficits in ulnar material properties in UCD-T2DM rats were associated with increased non-enzymatic crosslinking and impaired collagen fibril deformation. Specifically, small-angle X-ray scattering revealed that diabetes reduced collagen fibril ultimate strain by 40%, and those changes coincided with significant reductions in the elastic, yield, and ultimate tensile properties of the bone tissue. Importantly, the biomechanical effects of these material property deficits were substantial. Prescribing diabetes-specific tissue yield strains in high-resolution finite element models reduced whole-bone strength by a similar amount (and in some cases a 3.4-fold greater amount) as the structural deficits. These findings provide insight into factors that increase bone fragility for a given bone mass in T2D; not only does diabetes associate with less biomechanically efficient bone structure, but diabetes also reduces tissue ductility by limiting collagen fibril deformation, and in doing so, reduces the maximum load capacity of the bone. © 2018 American Society for Bone and Mineral Research.