Obesity-related changes in bone structural and material properties in hyperphagic OLETF rats and protection by voluntary wheel running

Biomineralization inspired 3D printed bioactive glass nanocomposite scaffolds orchestrate diabetic bone regeneration by remodeling micromilieu

Type II diabetes mellitus (TIIDM) remains a challenging clinical issue for both dentists and orthopedists. By virtue of persistent hyperglycemia and altered host metabolism, the pathologic diabetic micromilieu with chronic inflammation, advanced glycation end products accumulation, and attenuated biomineralization severely impairs bone regeneration efficiency. Aiming to "remodel" the pathologic diabetic micromilieu, we 3D-printed bioscaffolds composed of Sr-containing mesoporous bioactive glass nanoparticles (Sr-MBGNs) and gelatin methacrylate (GelMA). Sr-MBGNs act as a biomineralization precursor embedded in the GelMA-simulated extracellular matrix and release Sr, Ca, and Si ions enhancing osteogenic, angiogenic, and immunomodulatory properties. In addition to angiogenic and anti-inflammatory outcomes, this innovative design reveals that the nanocomposites can modulate extracellular matrix reconstruction and simulate biomineralization by activating lysyl oxidase to form healthy enzymatic crosslinked collagen, promoting cell focal adhesion, modulating osteoblast differentiation, and boosting the release of OCN, the noncollagenous proteins (intrafibrillar mineralization dependent), and thus orchestrating osteogenesis through the Kindlin-2/PTH1R/OCN axis. This 3D-printed bioscaffold provides a multifunctional biomineralization-inspired system that remodels the "barren" diabetic microenvironment and sheds light on the new bone regeneration approaches for TIIDM.

Local transplantation of GMSC-derived exosomes to promote vascularized diabetic wound healing by regulating the Wnt/β-catenin pathways

With the increasing number of diabetic patients, chronic wound healing remains a great challenge in clinical medicine. As one of the main components secreted by stem cells, the exosome is considered to be a promising candidate for promoting chronic wound healing. Here, gingival mesenchymal stem cell (GMSC)-derived exosomes (GMSC-Exo) were isolated and demonstrated to promote the proliferation, migration, and tube formation of human umbilical vein endothelial cells (HUVECs) by regulating the Wnt/β-catenin signaling pathway in a diabetic-mimicking high glucose environment. In order to deliver GMSCs-Exo to the target site and prolong their local retention, porous microspheres consisting of poly-lactic-co-glycolic acid (PLGA), amphiphilic block copolymer (PLLA-PEG-PLLA), nano-hydroxyapatite (nHAP), and poly-ε-l-lysine (EPL) coating were fabricated through a double emulsion method and following surface treatment, hereafter referred to as PHE microspheres. PHE microspheres loaded with GMSCs-Exo were implanted into the full-thickness skin wound of a diabetic mouse model, resulting in significant vascularized wound healing when compared to a control group only injected with GMSCs-Exo suspension or filled with PHE microspheres. These findings indicated that the GMSCs-Exo-loaded porous microspheres could efficiently treat diabetic wounds and have promising potential for future clinical translations.

Exercise and Diet: Uncovering Prospective Mediators of Skeletal Fragility in Bone and Marrow Adipose Tissue

PURPOSE OF REVIEW

To highlight recent basic, translational, and clinical works demonstrating exercise and diet regulation of marrow adipose tissue (MAT) and bone and how this informs current understanding of the relationship between marrow adiposity and musculoskeletal health.

RECENT FINDINGS

Marrow adipocytes accumulate in the bone in the setting of not only hypercaloric intake (calorie excess; e.g., diet-induced obesity) but also with hypocaloric intake (calorie restriction; e.g., anorexia), despite the fact that these states affect bone differently. With hypercaloric intake, bone quantity is largely unaffected, whereas with hypocaloric intake, bone quantity and quality are greatly diminished. Voluntary running exercise in rodents was found to lower MAT and promote bone in eucaloric and hypercaloric states, while degrading bone in hypocaloric states, suggesting differential modulation of MAT and bone, dependent upon whole-body energy status. Energy status alters bone metabolism and bioenergetics via substrate availability or excess, which plays a key role in the response of bone and MAT to mechanical stimuli. Marrow adipose tissue (MAT) is a fat depot with a potential role in-as well as responsivity to-whole-body energy metabolism. Understanding the localized function of this depot in bone cell bioenergetics and substrate storage, principally in the exercised state, will aid to uncover putative therapeutic targets for skeletal fragility.

Clinical, histological, and nanomechanical parameters of implants placed in healthy and metabolically compromised patients

OBJECTIVES

To evaluate the clinical outcomes, histological parameters, and bone nanomechanical properties around implants retrieved from healthy and metabolic syndrome (MS) patients.

METHODS

Twenty-four patients with edentulous mandibles (12/condition), received four implants between the mental foramina. An additional implant prototype was placed for retrieval histology. The following clinical outcomes were evaluated: insertion torque (IT), implant stability quotient (ISQ) values at baseline and after 60 days of healing, and implant survival. The prototype was retrieved after the healing and histologically processed for bone morphometric evaluation of bone-to-implant contact (%BIC) and bone area fraction occupancy (%BAFO), and bone nanoindentation to determine the elastic modulus (Em) and hardness (H). Descriptive statistical procedures and survival tests were used to analyze the data.

RESULTS

The final study population was comprised of 10 women and 11 men (∼64 years). A total of 105 implants were placed, 21 retrieved for histology. Implant survival rates were similar between groups (>99 %). Similarly, IT and ISQ analyses showed no significant association with systemic condition (p > 0.216). Histological micrographs depicted similar bone morphology, woven bone, for both conditions. While MS (33 ± 5.3 %) and healthy (39 ± 6.5 %) individuals showed no significant difference for %BIC (p = 0.116), significantly higher %BAFO was observed for healthy (45 ± 4.6 %) relative to MS (30 ± 3.8 %) (p < 0.001). No significant differences on bone nanomechanical properties was observed (p > 0.804).

CONCLUSIONS

Although no significant influence on clinical parameters and bone nanomechanical properties was observed, MS significantly reduced bone formation in the peri-implant area in the short-term.

CLINICAL SIGNIFICANCE

A lower amount of bone formation in the peri-implant area was observed in comparison to healthy patients, although the other short-term clinical outcomes were not significantly different. Considering the escalating prevalence of MS patients in need for implant treatment, it becomes crucial to understand bone-to-implant response to determine the ideal loading time in this population.

Obesity/Metabolic Syndrome and Diabetes Mellitus on Peri-implantitis

Literature has reported that up to 50% of dental implants may be affected by peri-implantitis, a bacteria-induced chronic inflammatory process, which promotes osteoclast-mediated bone resorption and inhibits bone formation, leading to progressive bone loss around implants. Current evidence points toward an increased risk for the development of peri-implantitis in both obesity/metabolic syndrome (MetS) and diabetes mellitus (DM) conditions relative to the healthy population. Currently, there is no effective treatment for peri-implantitis and the 50% prevalence in MetS and DM, along with its predicted increase in the worldwide population, presents a major concern in implant dentistry as hyperglycemic conditions are associated with bone-healing impairment; this may be through dysfunction of osteocalcin-induced glucose metabolism. The MetS/DM proinflammatory systemic condition and altered immune/microbiome response affect both catabolic and anabolic events of bone-healing that include increased osteoclastogenesis and compromised osteoblast activity, which could be explained by the dysfunction of insulin receptor that led to activation of signals related with osteoblast differentiation. Furthermore, chronic hyperglycemia along with associated micro- and macro-vascular ailments leads to delayed/impaired wound healing due to activation of pathways that are particularly important in initiating events linked to inflammation, oxidative stress, and cell apoptosis; this may be through deactivation of AKT/PKB protein, which possesses a pivotal role in drive survival and eNOS signaling. This review presents an overview of the local and systemic mechanisms synergistically affecting bone-healing impairment in MetS/DM individuals, as well as a rationale for hierarchical animal model selection, in an effort to characterize peri-implantitis disease and treatment.

Carbon Monoxide and Exercise Prevents Diet-Induced Obesity and Metabolic Dysregulation Without Affecting Bone

OBJECTIVE

Carbon monoxide (CO) may counteract obesity and metabolic dysfunction in rodents consuming high-fat diets, but the skeletal effects are not understood. This study investigated whether low-dose inhaled CO (250 ppm) with or without moderate intensity aerobic exercise (3 h/wk) would limit diet-induced obesity and metabolic dysregulation and preserve bone health.

METHODS

Obesity-resistant (OR) rats served as controls, and obesity-prone (OP) rats were randomized to sedentary, sedentary plus CO, exercise, or CO plus exercise. For 10 weeks, OP rats consumed a high-fat, high-sucrose diet, whereas OR rats consumed a low-fat control diet. Measurements included indicators of obesity and metabolism, bone turnover markers, femoral geometry and microarchitecture, bone mechanical properties, and tibial morphometry.

RESULTS

A high-fat, high-sucrose diet led to obesity, hyperinsulinemia, and hyperleptinemia, without impacting bone. CO alone led only to a modest reduction in weight gain. Exercise attenuated weight gain and improved the metabolic profile; however, bone fragility increased. Combined CO and exercise led to body mass reduction and a metabolic state similar to control OR rats and prevented the exercise-induced increase in bone fragility.

CONCLUSIONS

CO and aerobic exercise training prevent obesity and metabolic sequelae of nutrient excess while stabilizing bone physiology.

Effects of activated vitamin D, alfacalcidol, and low-intensity aerobic exercise on osteopenia and muscle atrophy in type 2 diabetes mellitus model rats

Diabetes mellitus causes secondary osteoporosis and muscle atrophy. The ability of alfacalcidol (ALF) and exercise (Exe) to inhibit osteoporosis and muscle atrophy in type 2 diabetes mellitus (T2DM) model rats was examined. Twenty-week-old Otsuka Long-Evans Tokushima Fatty rats were randomized to ALF (orally 0.1 μg/kg/day), Exe (treadmill exercise at 10 m/min, 60 min/day, 5 days/week), Comb (ALF and Exe), and Cont (T2DM control treated with vehicle and no exercise) groups (n = 8–10 per group). Sedentary Long-Evans Tokushima Otsuka rats were used as a non-hyperphagic control. After treatment for 2 or 6 weeks, blood glucose (BG) levels, cross-sectional area (CSA) of tibialis anterior muscle fibers, femoral bone mineral density (BMD), and relative quantities of muscle anabolic markers (Pax7, MyoD, and myogenin) and catabolic markers (Atrogin-1, MuRF1, and REDD1) of the soleus muscle assessed by real-time polymerase chain reaction assays were measured. Exe and Comb treatments for 6 weeks decreased BG levels compared with those of the Cont group. ALF, Exe, and Comb treatments for 2 and 6 weeks recovered the CSA compared with that of the Cont group. ALF and Comb treatments for 6 weeks increased femoral BMDs compared with those of the Cont group. After 2 weeks of treatment, Comb treatment increased MyoD expression and decreased MuRF1 expression. ALF or Exe monotherapy significantly decreased Atrogin-1 or MuRF1 expression after 2 weeks of treatment, respectively. After 6 weeks of treatment, ALF and Comb treatments decreased Atrogin-1 and REDD1. These results demonstrate that a combination of ALF and Exe improved CSA from the early phase of treatment by stimulating skeletal muscle differentiation and suppressing muscle catabolic genes. Improvements in BG, BMD, and CSA were observed as long-term effects of the combination therapy. Continued suppression of muscle catabolic genes was observed as a background to these effects.

Soy protein improves tibial whole-bone and tissue-level biomechanical properties in ovariectomized and ovary-intact, low-fit female rats

BACKGROUND

Osteoporosis and related fractures, decreased physical activity, and metabolic dysfunction are serious health concerns for postmenopausal women. Soy protein might counter the negative effects of menopause on bone and metabolic health due to the additive or synergistic effects of its bioactive components.

OBJECTIVE

To evaluate the effects of ovariectomy (OVX) and a soy-protein diet (SOY) on bone outcomes in female, low-capacity running (LCR) rats selectively bred for low aerobic fitness as a model of menopause.

METHODS

At 27 weeks of age, LCR rats (N = 40) underwent OVX or sham (SHAM) surgery and were randomized to one of two isocaloric and isonitrogenous plant-protein-based dietary treatments: 1) soy-protein (SOY; soybean meal); or, 2) control (CON, corn-gluten meal), resulting in four treatment groups. During the 30-week dietary intervention, animals were provided ad libitum access to food and water; body weight and food intake were measured weekly. At completion of the 30-week intervention, body composition was measured using EchoMRI; animals were fasted overnight, euthanized, and blood and hindlimbs collected. Plasma markers of bone formation (osteocalcin, OC; N-terminal propeptide of type I procollagen, P1NP) and resorption (tartrate-resistant acid phosphatase, TRAP5b; C-terminal telopeptide of type I collagen, CTx) were measured using ELISA. Tibial trabecular microarchitecture and cortical geometry were evaluated using μCT; and torsional loading to failure was used to assess cortical biomechanical properties. Advanced glycation end-product (AGE) content of the femur was measured using a fluorimetric assay, and was expressed relative to collagen content measured by a colorimetric OH-proline assay. Two-factor ANOVA or ANOVCA was used to test for significant main and interactive effects of ovarian status (OV STAT: OVX vs. SHAM) and DIET (SOY vs. CON); final body weight was included as a covariate for body-weight-dependent cortical geometry and biomechanical properties.

RESULTS

OVX had significantly greater CTx than SHAM; SOY did not affect bone turnover markers. OVX adversely affected trabecular microarchitecture as evidenced by reduced BV/TV, trabecular thickness (Tb.Th), trabecular number (Tb.N), and connectivity density (Conn.D), and by increased trabecular separation (Tb.Sp) and structural model index (SMI). SOY increased BV/TV only in ovary-intact animals. There was no effect of OVX or SOY on tibial cortical geometry. In SHAM and OVX rats, SOY significantly improved whole-bone strength and stiffness; SOY also increased tissue-level stiffness and tended to increase tissue-level strength (p = 0.067). There was no effect of OVX or SOY on AGE content.

CONCLUSION

Soy protein improved cortical bone biomechanical properties in female low-fit rats, regardless of ovarian hormone status.

Complex interplay among adiposity, insulin resistance and bone health

Obesity and osteoporosis are common public health problems. Paradoxically, while obesity is associated with higher bone density, type 2 diabetic obese individuals have an increased fracture risk. Although obesity and insulin resistance co-exist, some obese individuals remain insulin-sensitive. We suggest that the apparent paradox relating obesity, bone density and fracture risk in type 2 diabetes may be at least partly influenced by differences in bone strength and quality between insulin-resistant and insulin-sensitive obese individuals. In this review, we focus on the complex interplay between, adiposity, insulin resistance and osteoporotic fracture risk and suggest that this is an important area of study that has implications for individually tailored and targeted treatment to prevent osteoporotic fracture in obese type 2 diabetic individuals.

Soy Protein Isolate Suppresses Bone Resorption and Improves Trabecular Microarchitecture in Spontaneously Hyperphagic, Rapidly Growing Male OLETF Rats

BACKGROUND

Traditionally, milk proteins have been recommended for skeletal health; recently, soy proteins have emerged as popular alternatives. Excess adiposity appears detrimental to skeletal health, as obese adolescents have increased fracture rates compared with healthy controls. However, soy protein effects on skeletal health during excess adiposity remain unknown.

OBJECTIVE

The study objective was to examine the effects of isocaloric diets containing milk protein isolate (MPI), soy protein isolate (SPI), or a 50/50 combination (MIX) as the sole protein source on metabolic health indicators and bone outcomes in rapidly growing, hyperphagic, male Otsuka Long Evans Tokushima Fatty (OLETF) rats.

METHODS

OLETF rats, aged 4 wk, were randomly assigned to 3 treatment groups (MPI, SPI, or MIX, n = 20 per group) and provided with access to experimental diets ad libitum for 16 wk.

RESULTS

Body mass did not differ between the groups, but SPI had lower percentage body fat than MPI (P = 0.026). Insulin was lower in MPI than in MIX (P = 0.033) or SPI (P = 0.044), but fasting blood glucose was not different between the groups. SPI significantly reduced serum cholesterol compared with MPI (P = 0.001) and MIX (P = 0.002). N-terminal propeptide of type I collagen (P1NP) was higher in MIX than MPI (P = 0.05); C-terminal telopeptide of type 1 collagen (CTx) was higher in MPI than SPI (P < 0.001) and MIX (P < 0.001); the P1NP to CTx ratio was significantly higher in SPI and MIX than in MPI (P < 0.001). Trabecular separation was reduced in SPI compared with MPI (P = 0.030) and MIX (P = 0.008); trabecular number was increased in SPI compared with MIX (P = 0.038). No differences were seen in cortical geometry and biomechanical properties.

CONCLUSIONS

In the context of excess adiposity, soy- and milk-based proteins have comparable effects on cortical bone geometry and biomechanical properties, whereas soy-based proteins favorably affect the trabecular microarchitecture, and the combination of both proteins may offer additional benefits to bone remodeling in rapidly growing male OLETF rats.

Effects of voluntary running exercise on bone histology in type 2 diabetic rats

The incidence of obesity in children and adolescents, which may lead to type 2 diabetes, is increasing. Exercise is recommended to prevent and improve diabetes. However, little is known about the bone marrow environment at the onset of diabetes in the young, and it is unclear whether exercise training is useful for maintaining bone homeostasis, such as mechanical and histological properties. Thus, this study clarified the histological properties of bone and whether exercise contributes to maintaining bone homeostasis at the onset of type 2 diabetes in rats. Four-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF; n = 21) rats as a diabetic model and Long-Evans Tokushima Otsuka (LETO; n = 18) rats as a control were assigned randomly to four groups: the OLETF sedentary group (O-Sed; n = 11), OLETF exercise group (O-Ex; n = 10), LETO sedentary group (L-Sed; n = 9), and LETO exercise group (L-Ex; n = 9). All rats in the exercise group were allowed free access to a steel running wheel for 20 weeks (5-25 weeks of age). In the glucose tolerance test, blood glucose level was higher in the O-Sed group than that in the L-Sed and L-Ex groups, and was markedly suppressed by the voluntary running exercise of O-Ex rats. The energy to fracture and the two-dimensional bone volume at 25 weeks of age did not differ significantly among the groups, though the maximum breaking force and stiffness were lower in OLETF rats. However, bone marrow fat volume was greater in O-Sed than that in L-Sed and L-Ex rats, and was markedly suppressed by wheel running in the O-Ex rats. Our results indicate that exercise has beneficial effects not only for preventing diabetes but also on normal bone remodeling at an early age.

Does a Treadmill Running Exercise Contribute to Preventing Deterioration of Bone Mineral Density and Bone Quality of the Femur in KK-Ay Mice, a Type 2 Diabetic Animal Model?

Although it has been recently shown that type 2 diabetics have an increased risk of hip fracture, the effects of exercise therapy to prevent this have not been clarified. We examined whether a treadmill running exercise contributes to the bone mineral density (BMD) and bone microarchitecture of the femur and what kind of exercise intensity and duration are optimum in type 2 diabetes mellitus using KK-Ay diabetic mice. The mice were divided into two running groups, one fast speed and short duration (FS), the other slow speed and long duration (SL), and a group of controls with no running (CO). The running exercise was started when the mice were 8 weeks of age, and continued once a day 5 days per week for 10 weeks. Ten weeks after the start of the running exercise, the BMD of the proximal region and mid-diaphysis in the SL were significantly higher in comparison with that in the CO, whereas there was no difference in bone microarchitecture among the three groups. Blood glucose, insulin levels, and visceral fat contents in the SL were significantly lower than those in the CO and FS. Bone resorption protein and C-reactive protein levels in the SL were significantly lower than those in the CO. These results suggest that slow, long duration loading is better for both bone and glycemic control than fast, short duration loading in type 2 diabetes.

Obesity and type 2 diabetes, not a diet high in fat, sucrose, and cholesterol, negatively impacts bone outcomes in the hyperphagic Otsuka Long Evans Tokushima Fatty rat

BACKGROUND

Obesity and type 2 diabetes (T2D) increase fracture risk; however, the association between obesity/T2D may be confounded by consumption of a diet high in fat, sucrose, and cholesterol (HFSC).

OBJECTIVE

The study objective was to determine the main and interactive effects of obesity/T2D and a HFSC diet on bone outcomes using hyperphagic Otuska Long Evans Tokushima Fatty (OLETF) rats and normophagic Long Evans Tokushima Otsuka (LETO) controls.

METHODS

At 8weeks of age, male OLETF and LETO rats were randomized to either a control (CON, 10 en% from fat as soybean oil) or HFSC (45 en% from fat as soybean oil/lard, 17 en% sucrose, and 1wt%) diet, resulting in four treatment groups. At 32weeks, total body bone mineral content (BMC) and density (BMD) and body composition were measured by dual-energy X-ray absorptiometry, followed by euthanasia and collection of blood and tibiae. Bone turnover markers and sclerostin were measured using ELISA. Trabecular microarchitecture of the proximal tibia and geometry of the tibia mid-diaphysis were measured using microcomputed tomography; whole-bone and tissue-level biomechanical properties were evaluated using torsional loading of the tibia. Two-factor ANOVA was used to determine main and interactive effects of diet (CON vs. HFSC) and obesity/T2D (OLETF vs. LETO) on bone outcomes.

RESULTS

Hyperphagic OLEFT rats had greater final body mass, body fat, and fasting glucose than normophagic LETO, with no effect of diet. Total body BMC and serum markers of bone formation were decreased, and bone resorption and sclerostin were increased in obese/T2D OLETF rats. Trabecular bone volume and microarchitecture were adversely affected by obesity/T2D, but not diet. Whole-bone and tissue-level biomechanical properties of the tibia were not affected by obesity/T2D; the HFSC diet improved biomechanical properties only in LETO rats.

CONCLUSIONS

Obesity/T2D, regardless of diet, negatively impacted the balance between bone formation and resorption and trabecular bone volume and microarchitecture in OLETF rats.

Exercise initiated after the onset of insulin resistance improves trabecular microarchitecture and cortical bone biomechanics of the tibia in hyperphagic Otsuka Long Evans Tokushima Fatty rats

The present study extends our previous findings that exercise, which prevents the onset of insulin resistance and type 2 diabetes (T2D), also prevents the detrimental effects of T2D on whole-bone and tissue-level strength. Our objective was to determine whether exercise improves bone's structural and material properties if insulin resistance is already present in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat. The OLETF rat is hyperphagic due to a loss-of-function mutation in cholecystokinin-1 receptor (CCK-1 receptor), which leads to progressive obesity, insulin resistance and T2D after the majority of skeletal growth is complete. Because exercise reduces body mass, which is a significant determinant of bone strength, we used a body-mass-matched caloric-restricted control to isolate body-mass-independent effects of exercise on bone. Eight-wk old, male OLETF rats were fed ad libitum until onset of hyperglycemia (20weeks of age), at which time they were randomly assigned to three groups: ad libitum fed, sedentary (O-SED); ad libitum fed, treadmill running (O-EX); or, sedentary, mild caloric restriction to match body mass of O-EX (O-CR). Long-Evans Tokushima Otsuka rats served as the normophagic, normoglycemic controls (L-SED). At 32weeks of age, O-SED rats had T2D as evidenced by hyperglycemia and a significant reduction in fasting insulin compared to OLETFs at 20weeks of age. O-SED rats also had reduced total body bone mineral content (BMC), increased C-terminal telopeptide of type I collagen (CTx)/tartrate resistant acid phosphatase isoform 5b (TRAP5b), decreased N-terminal propeptide of type I procollagen (P1NP), reduced percent cancellous bone volume (BV/TV), trabecular number (Tb.N) and increased trabecular separation (Tb.Sp) and structural model index (SMI) of the proximal tibia compared to L-SED. T2D also adversely affected biomechanical properties of the tibial diaphysis, and serum sclerostin was increased and β-catenin, runt-related transcription factor 2 (Runx2) and insulin-like growth factor-I (IGF-I) protein expression in bone were reduced in O-SED vs. L-SED. O-EX or O-CR had greater total body bone mineral density (BMD) and BMC, and BV/TV, Tb.N, Tb.Sp, and SMI compared to O-SED. O-EX had lower CTx and CR greater P1NP relative to O-SED. O-EX, not O-CR, had greater cortical thickness and area, and improved whole-bone and tissue-level biomechanical properties associated with a 4-fold increase in cortical bone β-catenin protein expression vs. O-SED. In summary, EX or CR initiated after the onset of insulin resistance preserved cancellous bone volume and structure, and EX elicited additional benefits in cortical bone.

Mechanical signals protect stem cell lineage selection, preserving the bone and muscle phenotypes in obesity

The incidence of obesity is rapidly rising, increasing morbidity and mortality rates worldwide. Associated comorbidities include type 2 diabetes, heart disease, fatty liver disease, and cancer. The impact of excess fat on musculoskeletal health is still unclear, although it is associated with increased fracture risk and a decline in muscular function. The complexity of obesity makes understanding the etiology of bone and muscle abnormalities difficult. Exercise is an effective and commonly prescribed nonpharmacological treatment option, but it can be difficult or unsafe for the frail, elderly, and morbidly obese. Exercise alternatives, such as low-intensity vibration (LIV), have potential for improving musculoskeletal health, particularly in conditions with excess fat. LIV has been shown to influence bone marrow mesenchymal stem cell differentiation toward higher-order tissues (i.e., bone) and away from fat. While the exact mechanisms are not fully understood, recent studies utilizing LIV both at the bench and in the clinic have demonstrated some efficacy. Here, we discuss the current literature investigating the effects of obesity on bone, muscle, and bone marrow and how exercise and LIV can be used as effective treatments for combating the negative effects in the presence of excess fat.

Insulin-Stimulated Bone Blood Flow and Bone Biomechanical Properties Are Compromised in Obese, Type 2 Diabetic OLETF Rats

Type 2 diabetes (T2D) increases skeletal fragility and fracture risk; however, the underlying mechanisms remain to be identified. Impaired bone vascular function, in particular insulin‐stimulated vasodilation and blood flow is a potential, yet unexplored mechanism. The purpose of this study was to determine the effects of T2D on femoral biomechanical properties, trabecular microarchitecture, and insulin‐stimulated bone vasodilation by comparison of hyperphagic Otsuka Long‐Evans Tokushima Fatty (OLETF) rats with normoglycemic control OLETF rats. Four‐week old, male OLETF rats were randomized to two groups: type 2 diabetes (O‐T2D) or normoglycemic control (O‐CON). O‐T2D were allowed ad libitum access to a rodent chow diet and O‐CON underwent moderate caloric restriction (30% restriction relative to intake of O‐T2D) to maintain normal body weight (BW) and glycemia until 40 weeks of age. Hyperphagic O‐T2D rats had significantly greater BW, body fat, and blood glucose than O‐CON. Total cross‐sectional area (Tt.Ar), cortical area (Ct.Ar), Ct.Ar/Tt.Ar, and polar moment of inertia of the mid‐diaphyseal femur adjusted for BW were greater in O‐T2D rats versus O‐CON. Whole‐bone biomechanical properties of the femur assessed by torsional loading to failure did not differ between O‐T2D and O‐CON, but tissue‐level strength and stiffness adjusted for BW were reduced in O‐T2D relative to O‐CON. Micro–computed tomography (μCT) of the distal epiphysis showed that O‐T2D rats had reduced percent bone volume, trabecular number, and connectivity density, and greater trabecular spacing compared with O‐CON. Basal tibial blood flow assessed by microsphere infusion was similar in O‐T2D and O‐CON, but the blood flow response to insulin stimulation in both the proximal epiphysis and diaphyseal marrow was lesser in O‐T2D compared to O‐CON. In summary, impaired insulin‐stimulated bone blood flow is associated with deleterious changes in bone trabecular microarchitecture and cortical biomechanical properties in T2D, suggesting that vascular dysfunction might play a causal role in diabetic bone fragility. © 2017 The Authors. JBMR Plus Published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Exercise improves femoral whole-bone and tissue-level biomechanical properties in hyperphagic OLETF rats

An often-overlooked comorbidity of type 2 diabetes (T2D) is increased fracture risk. Since traditional T2D therapies focus solely on glucose homeostasis, there is an increased need for effective treatment strategies that improve both metabolic and bone health. The current study evaluated if previously reported protective effects of exercise (EX) on cortical bone geometry and biomechanical properties are due to the prevention of obesity compared with obese Otsuka Long-Evans Tokushima Fatty (OLETF) rats or the unique skeletal effects of exercise. Four-week-old male OLETF rats were randomly assigned to 1 of 3 groups, each fed a standard rodent chow diet until 40 weeks of age: ad libitum-fed sedentary (O-SED), ad libitum-fed EX (O-EX), or a control group body-weight-matched to the O-EX group by caloric restriction (O-CR). Ad libitum-fed sedentary Long-Evans Tokushima Otsuka (L-SED) rats were used as a lean control. EX or CR prevented the excess body mass accumulation and elevated HbA1c observed in O-SED. Total-body bone mineral density was greater in O-EX than O-CR, but similar to L-SED and O-SED. O-EX and O-CR had lower osteocalcin and TRAP5b than O-SED and L-SED. EX or CR prevented the ∼3-fold increase in CTx in O-SED versus L-SED. EX increased femoral cortical mass accumulation and expansion at the mid-diaphysis compared with O-CR. EX or CR significantly increased tissue-level stiffness and strength compared with O-SED and L-SED, but O-EX had greater whole-bone stiffness than all other groups. In summary, EX has distinct advantages over CR for improving bone biomechanical properties in hyperphagic OLETF rats.

Peak Bone Mass and Quantitative Ultrasound Bone Properties in Young Adulthood: A Study in the PEAK-25 Cohort of Women

Peak bone mass is normally reached in the third decade of life. Previously, in the population-based PEAK-25 cohort (n = 1061, age 25.5 ± 0.2), we demonstrated that bone mineral density in the population-based PEAK-25 cohort is comparatively high; therefore, this study aimed to determine if the calcaneus microarchitecture mirrored this. In the process, we describe normative quantitative ultrasound (QUS) values for 25-yr-old women and the relationship between QUS values and extremes of body weight. QUS variables speed of sound (SOS), broadband ultrasound attenuation (BUA), and stiffness index were measured. Young adult values were based on the manufacturer-supplied QUS reference values. Analyses were performed in the cohort as a whole, and additionally, to understand the relationship between body weight and QUS values in young women, the variables were categorized into octiles for weight or body mass index (BMI) and the lowest and highest octiles were compared. In the cohort, SOS values, reflecting bone density, were higher (108 ± 18%), whereas BUA values, reflecting bone complexity, were lower (90 ± 14%) compared to the young adult reference population. SOS did not correlate with body weight or BMI. In the cohort, overall correlations between BUA weight, and BMI were small and positive (Pearson's r coefficients 0.261 and 0.197, respectively; p < 0.001), although in the low-weight group, r coefficients were higher (r = 0.313 and 0.268; p < 0.05). In contrast, in the high-weight group, correlation with BUA values tended to be small, negative, and nonsignificant. Correlation between QUS and dual-energy X-ray absorptiometry-measured bone mineral density was low to moderate and significant at all skeletal sites (r = 0.37-0.52). Whereas coefficients tended to be higher in the low-weight group, the reverse was apparent for the low-BMI group. In these 25-yr-old women, a comparatively high dual-energy X-ray absorptiometry-measured bone mass is offset by less complex bone structures assessed by QUS. This may have implications for later osteoporosis assessment and future fracture risk.

Palmitic Acid Reduces Circulating Bone Formation Markers in Obese Animals and Impairs Osteoblast Activity via C16-Ceramide Accumulation

Obesity and impaired lipid metabolism increase circulating and local fatty acid (FA) levels. Our previous studies showed that a high high-saturated -fat diet induced greater bone loss in mice than a high high-unsaturated-fat diet due to increased osteoclast numbers and activity. The impact of elevated FA levels on osteoblasts is not yet clear. We induced obesity in 4 week old male mice using a palmitic acid (PA)- or oleic acid (OA)-enriched high fat high-fat diet (HFD) (20 % of calories from FA), and compared them to mice on a normal (R) caloric diet (10 % of calories from FA). We collected serum to determine FA and bone metabolism marker levels. Primary osteoblasts were isolated; cultured in PA, OA, or control (C) medium; and assessed for mineralization activity, gene expression, and ceramide levels. Obese animals in the PA and OA groups had significantly lower serum levels of bone formation markers P1NP and OC compared to normal weight animals (*p < 0.001), with the lowest marker levels in animals on an PA-enriched HFD (*p < 0.001). Accordingly, elevated levels of PA significantly reduced osteoblast mineralization activity in vitro (*p < 0.05). Elevated PA intake significantly increased C16 ceramide accumulation. This accumulation was preventable through inhibition of SPT2 (serine palmitoyl transferase 2) using myriocin. Elevated levels of PA reduce osteoblast function in vitro and bone formation markers in vivo. Our findings suggest that saturated PA can compromise bone health by affecting osteoblasts, and identify a potential mechanism through which obesity promotes bone loss.

Plasma osteoprotegerin levels are inversely associated with nonalcoholic fatty liver disease in patients with type 2 diabetes: A case-control study in China

OBJECTIVE

Osteoprotegerin (OPG), a soluble member of the tumor necrosis factor (TNF) receptor superfamily, is a decoy receptor for the receptor activator of nucleus factor-κB ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL). OPG has an effect on systemic insulin sensitivity and glucose homeostasis. The objective of this study was to evaluate the relationship between plasma osteoprotegerin (OPG) levels and nonalcoholic fatty liver disease (NAFLD) in patients with type 2 diabetes.

MATERIALS/METHODS

A case-control study was performed with 746 patients with type 2 diabetes. Of the study population, 367 patients had B-mode ultrasound-proven NAFLD and 379 were controls. The plasma OPG levels were measured using ELISA methods. NAFLD was diagnosed by hepatic ultrasound after the exclusion of alcohol abuse and other liver diseases.

RESULTS

The OPG levels were significantly decreased in patients with NAFLD (2.3±1.1μg/L vs. 2.8±1.3μg/L, p=3.75×10(5)) compared to controls. Pearson correlation analysis showed that the OPG levels were associated with age and systolic blood pressure (both p<0.05). The participants in the lowest OPG quartile had a significantly increased risk for NAFLD (OR=3.49, 95% CI 1.86-6.94) after adjusting for potential cofounders.

CONCLUSIONS

The plasma OPG level is negatively associated with NAFLD independent of potential cofounders.