Biomechanical Stimulation of Muscle Constructs Influences Phenotype of Bone Constructs by Modulating Myokine Secretion.

Diabetes is a chronic metabolic disorder that can lead to diabetic myopathy and bone diseases. The etiology of musculoskeletal complications in such metabolic disorders and the interplay between the muscular and osseous systems are not well understood. Exercise training promises to prevent diabetic myopathy and bone disease and offer protection. Although the muscle-bone interaction is largely biomechanical, the muscle secretome has significant implications for bone biology. Uncoupling effects of biophysical and biochemical stimuli on the adaptive response of bone during exercise training may offer therapeutic targets for diabetic bone disease. Here, we have developed an in vitro model to elucidate the effects of mechanical strain on myokine secretion and its impact on bone metabolism decoupled from physical stimuli. We developed bone constructs using cross-linked gelatin, which facilitated osteogenic differentiation of osteoprogenitor cells. Then muscle constructs were made from fibrin, which enabled myoblast differentiation and myotube formation. We investigated the myokine expression by muscle constructs under strain regimens replicating endurance (END) and high-intensity interval training (HIIT) in hyperglycemic conditions. In monocultures, both regimens induced higher expression of Il15 and Igf1, whereas END supported more myoblast differentiation and myotube maturation than HIIT. When co-cultured with bone constructs, HIIT regimen increased Glut4 expression in muscle constructs more than END, supporting higher glucose uptake. Likewise, the muscle constructs under the HIIT regimen promoted a healthier and more matured bone phenotype than END. Under static conditions, myostatin (Mstn) expression was significantly downregulated in muscle constructs co-cultured with bone constructs compared with monocultures. Together, our in vitro co-culture system allowed orthogonal manipulation of mechanical strain on muscle constructs while facilitating bone-muscle biochemical cross-talk. Such systems can provide an individualized microenvironment that allows decoupled biomechanical manipulation, help identify molecular targets, and develop engineered therapies for metabolic bone disease. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Pharmacologic Inhibition of Myostatin With a Myostatin Antibody Improves the Skeletal Muscle and Bone Phenotype of Male Insulin-Deficient Diabetic Mice.

Type 1 diabetes (T1D) is associated with low bone and muscle mass, increased fracture risk, and impaired skeletal muscle function. Myostatin, a myokine that is systemically elevated in humans with T1D, negatively regulates muscle mass and bone formation. We investigated whether pharmacologic myostatin inhibition in a mouse model of insulin-deficient, streptozotocin (STZ)-induced diabetes is protective for bone and skeletal muscle. DBA/2J male mice were injected with low-dose STZ (diabetic) or vehicle (non-diabetic). Subsequently, insulin or palmitate Linbits were implanted and myostatin (REGN647-MyoAb) or control (REGN1945-ConAb) antibody was administered for 8 weeks. Body composition and contractile muscle function were assessed in vivo. Systemic myostatin, P1NP, CTX-I, and glycated hemoglobin (HbA1c) were quantified, and gastrocnemii were weighed and analyzed for muscle fiber composition and gene expression of selected genes. Cortical and trabecular parameters were analyzed (micro-computed tomography evaluations of femur) and cortical bone strength was assessed (three-point bending test of femur diaphysis). In diabetic mice, the combination of insulin/MyoAb treatment resulted in significantly higher lean mass and gastrocnemius weight compared with MyoAb or insulin treatment alone. Similarly, higher raw torque was observed in skeletal muscle of insulin/MyoAb-treated diabetic mice compared with MyoAb or insulin treatment. Additionally, muscle fiber cross-sectional area (CSA) was lower with diabetes and the combination treatment with insulin/MyoAb significantly improved CSA in type II fibers. Insulin, MyoAb, or insulin/MyoAb treatment improved several parameters of trabecular architecture (eg, bone volume fraction [BV/TV], trabecular connectivity density [Conn.D]) and cortical structure (eg, cortical bone area [Ct. Ar.], minimum moment of inertia [Imin]) in diabetic mice. Lastly, cortical bone biomechanical properties (stiffness and yield force) were also improved with insulin or MyoAb treatment. In conclusion, pharmacologic myostatin inhibition is beneficial for muscle mass, muscle function, and bone properties in this mouse model of T1D and its effects are both independent and additive to the positive effects of insulin. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

"Exogenous" 5 Alpha Reductase Deficiency: A Case Report.

Testosterone and dihydrotestosterone are significant drivers of male external genital development, and therefore teratogens that alter these hormone profiles have been hypothesized to cause aberrations in development. Here, we present the first case report of genitalia anomalies after prenatal exposure to spironolactone and dutasteride through 8-weeks of gestation. The patient was born with abnormal male external genitalia which was surgically managed. Long-term outcomes such as gender identity, sexual function, hormonal maturation through puberty, and fertility remain unknown. These numerous considerations necessitate multi-disciplinary management with close follow-up to address sexual, psychological, and anatomic concerns.

Bringing the Pediatric Endocrine Spanish Speaking Community Together: First Virtual Pediatric Endocrine Meeting in Low- and Middle-Income Countries in Central and South America.

BACKGROUND: Pediatric endocrinology is a specialty that is struggling worldwide to maintain adequately trained professionals. Pediatric endocrine care in Central America and Caribbean countries is often performed by pediatricians or adult endocrinologists due to the limited number of pediatric endocrinologists. These health care providers are seldom members of endocrine societies and frequently lack formal training in the field. OBJECTIVE: In this study, we describe the scope of a virtual conference in pediatric endocrinology and diabetes targeted to low- and middle-income countries to provide equal opportunities for access to medical education for health care professionals. METHODS: The virtual conference was sponsored by the Pediatric Endocrine Society (North America), Asociación Costarricense de Endocrinología (previously, Asociación Nacional Pro Estudio de la Diabetes, Endocrinología y Metabolismo), and Asociacion Centroamericana y del Caribe de Endocrinologia Pediátrica. The conference was free to participants and comprised 23 sessions that were either synchronous with ability for real-time interactive sessions or asynchronous sessions, where content was available online to access at their convenience. Topics included idiopathic short stature, polycystic ovarian syndrome, diabetes mellitus, telemedicine, Turner syndrome, congenital adrenal hyperplasia, obesity, central precocious puberty, and subclinical hypothyroidism. The participants were asked to evaluate the conference after its completion with a questionnaire. RESULTS: A total of 8 speakers from Spain, Canada, Costa Rica, and the United States delivered the virtual event to 668 health care professionals from Guatemala, Venezuela, Dominican Republic, Costa Rica, Ecuador, Peru, Uruguay, Mexico, Honduras, Argentina, the United States, Bolivia, Chile, Panama, El Salvador, Nicaragua, Paraguay, Belize, Spain, and Colombia. Name, profession, and country were fully disclosed by 410 (61.4%) of the 668 health care professionals. The profession or level of training of participants were as follows: pediatric endocrinologists (n=129, 19.3%), pediatricians (n=116, 17.4%), general practitioners (n=77, 11.5%), adult endocrinologists (n=34, 5.1%), medical students (n=23, 3.4%), residents in various specialties (n=14, 2.1%), and others (n=17, 2.6%). A total of 23 sessions were offered, most of which were bilingual (Spanish and English). Feedback from the evaluation questionnaire indicated that the content of the conference was very relevant to the participants' professional practice. Additionally, the participants reported that they were very satisfied with the organization, the web-based platform, and the sessions of the conference. CONCLUSIONS: Lack of accessibility to the latest and cutting-edge medical education in pediatric endocrinology and diabetes for medical professionals from low- and middle-income countries can be overcome with a virtual conference. Online availability, low cost, and easy-to-use technology were well received from the participants, who were overall very satisfied by the quality and the relevance of the sessions to their professional practice.

Ten-Year Experience of a Global and Freely Accessible e-Learning Website for Pediatric Endocrinology and Diabetes.

The European Society for Paediatric Endocrinology (ESPE) interactive website, https://www.espe-elearning.org, was first published online in 2012. We describe the various applications of the content of the e-learning website that has been greatly expanded over the last 10 years. A large module on pediatric diabetes was added with the support of the International Society for Paediatric and Adolescent Diabetes (ISPAD). A separate multilingual module was created that focuses on frontline health care providers in limited resource settings. This module has been well received, particularly in targeted parts of the world. e-Learning may also be an opportunity to expand or tailor educational activities for learners according to their differing learning needs. The e-learning website provides guidelines for those interested in general pediatrics, neonatology, clinical genetics, and pediatric gynecology. We also describe various new applications such as master classes in the format of interactive video lectures and joint and complementary e-learning/e-consultation webinars. Finally, international certification was recently realized as e-learning courses were recognized by the European Accreditation Council for Continuing Medical Education (EACCME). As a result of the social distancing measures introduced to control the COVID-19 pandemic, digital education, whether individual or in a virtual classroom setting, has become even more important since e-learning can connect and engage individuals across geographic boundaries as well as those who live in remote areas. The future of education delivery may include hybrid learning strategies, which include in-person and e-learning platforms. Combined e-learning and e-consultation webinars illustrate how international academic institutions, learned medical specialty societies and networks are uniquely placed to deliver balanced, disease-oriented, and patient-centered e-learning education and at the same time provide expert consultation. Moreover, they are well equipped to maintain professional standards and to offer appropriate accreditation.

Emerging therapies for the treatment of rare pediatric bone disorders.

In recent years, new therapies for the treatment of rare pediatric bone disorders have emerged, guided by an increasing understanding of the genetic and molecular etiology of these diseases. Herein, we review three such disorders, impacted by debilitating deficits in bone mineralization or cartilage ossification, as well as the novel disease-modifying drugs that are now available to treat these conditions. Specifically, we discuss asfotase alfa, burosumab-twza, and vosoritide, for the treatment of hypophosphatasia, X-linked hypophosphatemia and achondroplasia, respectively. For each skeletal disorder, an overview of the clinical phenotype and natural history of disease is provided, along with a discussion of the clinical pharmacology, mechanism of action and FDA indication for the relevant medication. In each case, a brief review of clinical trial data supporting drug development for each medication is provided. Additionally, guidance as to drug dosing and long-term monitoring of adverse events and pediatric efficacy is presented, to aid the clinician seeking to utilize these novel therapies in their practice, or to become familiar with the healthcare expectations for children receiving these medications through specialized multidisciplinary clinics. The availability of these targeted therapies now significantly augments treatment options for conditions in which past therapy has relied upon less specific, symptomatic medical and orthopedic care.

Mouse models of type 1 diabetes and their use in skeletal research.

PURPOSE OF REVIEW: In this review, we describe the three primary mouse models of insulin-deficiency diabetes that have been used to study the effects of type 1 diabetes (T1D) on skeletal outcomes. These models include streptozotocin (chemically)-induced diabetes, autoimmune-mediated diabetes (the nonobese diabetes mouse), and a mutation in the insulin gene (the Akita mouse). We then describe the skeletal findings and/or skeletal phenotypes that have been delineated using these models. RECENT FINDINGS: Humans with T1D have decreased bone mineral density and an increased risk for fragility fracture. Mouse models of insulin-deficiency diabetes (hereafter denoted as T1D) in many ways recapitulate these skeletal deficits. Utilizing techniques of microcomputed tomography, bone histomorphometry, biomechanical testing and fracture modeling, bone biomarker analysis, and Raman spectroscopy, mouse models of T1D have demonstrated abnormalities in bone mineralization, bone microarchitecture, osteoblast function, abnormal bone turnover, and diminished biomechanical properties of bone. SUMMARY: Mouse models have provided significant insights into the underlying mechanisms involved in the abnormalities of bone observed in T1D in humans. These translational models have provided targets and pathways that may be modifiable to prevent skeletal complications of T1D.

Diabetic Bone Disease and Diabetic Myopathy: Manifestations of the Impaired Muscle-Bone Unit in Type 1 Diabetes.

Type 1 diabetes is associated with complications affecting muscle and bone, with diabetic bone disease and diabetic myopathy becoming increasingly reported in the past few decades. This review is aimed at succinctly reviewing the literature on the current knowledge regarding these increasingly identified and possibly interconnected complications on the musculoskeletal system. Furthermore, this review summarizes several nonmechanical factors that could be mediating the development and progression of premature musculoskeletal decline in this population and discusses preventative measures to reduce the burden of diabetes on the musculoskeletal system.

Multilingual Global E-Learning Pediatric Endocrinology and Diabetes Curriculum for Front Line Health Care Providers in Resource-Limited Countries: Development Study.

BACKGROUND: Electronic learning (e-learning) is a widely accessible, low-cost option for learning remotely in various settings that allows interaction between an instructor and a learner. OBJECTIVE: We describe the development of a free and globally accessible multilingual e-learning module that provides education material on topics in pediatric endocrinology and diabetes and that is intended for first-line physicians and health workers but also trainees or medical specialists in resource-limited countries. METHODS: As complements to concise chapters, interactive vignettes were constructed, exemplifying clinical issues and pitfalls, with specific attention to the 3 levels of medical health care in resource-limited countries. The module is part of a large e-learning portal, ESPE e-learning, which is based on ILIAS (Integriertes Lern-, Informations- und Arbeitskooperations-System), an open-source web-based learning management system. Following a review by global experts, the content was translated by native French, Spanish, Swahili, and Chinese-speaking colleagues into their respective languages using a commercial web-based translation tool (SDL Trados Studio). RESULTS: Preliminary data suggest that the module is well received, particularly in targeted parts of the world and that active promotion to inform target users is warranted. CONCLUSIONS: The e-learning module is a free globally accessible multilingual up-to-date tool for use in resource-limited countries that has been utilized thus far with success. Widespread use will require dissemination of the tool on a global scale.

Canagliflozin, an SGLT2 inhibitor, corrects glycemic dysregulation in TallyHO model of T2D but only partially prevents bone deficits.

Higher fracture risk in type 2 diabetes (T2D) is attributed to disease-specific deficits in micro-structural and material properties of bone, although the primary cause is not yet established. The TallyHO (TH) mouse is a polygenic model of early-onset T2D and obesity analogous to adolescent-onset T2D in humans. Due to incomplete penetrance of the phenotype, ~25% of male TH mice never develop hyperglycemia, providing a strain-matched, non-diabetic control. Utilizing this model of T2D, we examined the impact of glucose-lowering therapy with canagliflozin (CANA) on diabetic bone. Male TH mice with or without hyperglycemia (High BG, Low BG) were monitored from ~8 to 20 weeks of age, and compared to age-matched, male, TH mice treated with CANA from ~8 to 20 weeks of age. At 20 weeks, untreated TH mice with high BG [High BG: 687 ± 106 mg/dL] exhibited lower body mass, decrements in cortical bone of the femur (decreased cross-sectional area and thickness; increased porosity) and in trabecular bone of the femur metaphysis and L6 vertebra (decreased bone volume fraction, thickness, and tissue mineral density), as well as decrements in cortical and vertebral bone strength (decreased yield force and ultimate force) when compared to untreated TH mice with low BG [Low BG: 290 ± 98 mg/dL; p < 0.0001]. CANA treatment was metabolically advantageous, normalizing body mass, BG and HbA1c to values comparable to the Low BG group. With drug-induced glycemic improvement, cortical area and thickness were significantly higher in the CANA than in the High BG group, but deficits in strength persisted with lower yield force and yield stress (partially independent of bone geometry) in the CANA group. Additionally, CANA only partially prevented the T2D-related loss in trabecular bone volume fraction. Taken together, these findings suggest that the ability of CANA to lower glucose and normalized glycemic control ameliorates diabetic bone disease but not fully.

Muscle and serum myostatin expression in type 1 diabetes.

Type 1 diabetes (T1D) has been reported to negatively affect the health of skeletal muscle, though the underlying mechanisms are unknown. Myostatin, a myokine whose increased expression is associated with muscle-wasting diseases, has not been reported in humans with T1D but has been demonstrated to be elevated in preclinical diabetes models. Thus, the purpose of this study was to determine if there is an elevated expression of myostatin in the serum and skeletal muscle of persons with T1D compared to controls. Secondarily, we aimed to explore relationships between myostatin expression and clinically important metrics (e.g., HbA1c , strength, lean mass) in women and men with (N = 31)/without T1D (N = 24) between 18 and 72 years old. Body composition, baseline strength, blood sample and vastus lateralis muscle biopsy were evaluated. Serum, but not muscle, myostatin expression was significantly elevated in those with T1D versus controls, and to a greater degree in T1D women than T1D men. Serum myostatin levels were not significantly associated with HbA1c nor disease duration. A significant correlation between serum myostatin expression and maximal voluntary contraction (MVC) and body fat mass was demonstrated in control subjects, but these correlations did not reach significance in those with T1D (MVC: R = 0.64 controls vs. R = 0.37 T1D; Body fat: R = -0.52 controls/R = -0.02 T1D). Collectively, serum myostatin was correlated with lean mass (R = 0.45), and while this trend was noted in both groups separately, neither reached statistical significance (R = 0.47 controls/R = 0.33 T1D). Overall, while those with T1D exhibited elevated serum myostatin levels (particularly females) myostatin expression was not correlated with clinically relevant metrics despite some of these relationships existing in controls (e.g., lean/fat mass). Future studies will be needed to fully understand the mechanisms underlying increased myostatin in T1D, with relationships to insulin dosing being particularly important to elucidate.

Postnatal loss of the insulin receptor in osteoprogenitor cells does not impart a metabolic phenotype.

The relationship between osteoblast-specific insulin signaling, osteocalcin activation and gluco-metabolic homeostasis has proven to be complex and potentially inconsistent across animal-model systems and in humans. Moreover, the impact of postnatally acquired, osteoblast-specific insulin deficiency on the pancreas-to-skeleton-to-pancreas circuit has not been studied. To explore this relationship, we created a model of postnatal elimination of insulin signaling in osteoprogenitors. Osteoprogenitor-selective ablation of the insulin receptor was induced after ~10 weeks of age in IRl°x/lox/Osx-Cre+/- genotypic male and female mice (designated postnatal-OIRKO). At ~21 weeks of age, mice were then phenotypically and metabolically characterized. Postnatal-OIRKO mice demonstrated a significant reduction in circulating concentrations of undercarboxylated osteocalcin (ucOC), in both males and females compared with control littermates. However, no differences were observed between postnatal-OIRKO and control mice in: body composition (lean or fat mass); fasting serum insulin; HbA1c; glucose dynamics during glucose tolerance testing; or in pancreatic islet area or islet morphology, demonstrating that while ucOC is impacted by insulin signaling in osteoprogenitors, there appears to be little to no relationship between osteocalcin, or its derivative (ucOC), and glucose homeostasis in this model.

Constitutive activation of MEK1 in osteoprogenitors increases strength of bone despite impairing mineralization.

Recent clinical studies have revealed that a somatic mutation in MAP2K1, causing constitutive activation of MEK1 in osteogenic cells, occurs in melorheostotic bone disease in humans. We have generated a mouse model which expresses an activated form of MEK1 (MEK1DD) specifically in osteoprogenitors postnatally. The skeletal phenotype of these mice recapitulates many features of melorheostosis observed in humans, including extra-cortical bone formation, abundant osteoid formation, decreased mineral density, and increased porosity. Paradoxically, in both humans and mice, MEK1 activation in osteoprogenitors results in bone that is not structurally compromised, but is hardened and stronger, which would not be predicted based on tissue and matrix properties. Thus, a specific activating mutation in MEK1, expressed only by osteoprogenitors postnatally, can have a significant impact on bone strength through complex alterations in whole bone geometry, bone micro-structure, and bone matrix.

TLR4 Promotes and DAP12 Limits Obesity-Induced Osteoarthritis in Aged Female Mice.

Aging and female sex are the strongest risk factors for nontraumatic osteoarthritis (OA); whereas obesity is a modifiable risk factor accelerating OA. Prior studies indicate that the innate immune receptor toll-like receptor 4 (TLR4) mediates obesity-induced metabolic inflammation and cartilage catabolism via recognition of damage-associated molecular patterns and is increased with aging in OA joints. TLR4 responses are limited by innate immunoreceptor adapter protein DNAX-activating protein of 12kDA (DAP12). We undertook this study to test the hypothesis that TLR4 promotes, whereas DAP12 limits, obesity-accelerated OA in aged female mice. We fed 13- to 15-month-old female WT, TLR4 KO, and DAP12 KO mice a high-fat diet (HFD) or a control diet for 12 weeks, and changes in body composition, glucose tolerance, serum cytokines, and insulin levels were compared. Knee OA was evaluated by histopathology and µCT. Infrapatellar fat pads (IFPs) were analyzed by histomorphometry and F4/80+ crown-like structures were quantified. IFPs and synovium gene expression were analyzed using a targeted insulin resistance and inflammation array. All HFD-treated mice became obese, but only WT and TLR4 KO mice developed glucose intolerance. HFD induced cartilage catabolism in WT and DAP12 KO female mice, but not in TLR4 KO mice. Gene-expression analysis of IFPs and synovium showed significant differences in insulin signaling, adipokines, and inflammation between genotypes and diets. Unlike young mice, systemic inflammation was not induced by HFD in the older female mice independent of genotype. Our findings support the conclusion that TLR4 promotes and DAP12 limits HFD-induced cartilage catabolism in middle-aged female mice.

Diabetes pharmacotherapy and effects on the musculoskeletal system.

Persons with type 1 or type 2 diabetes have a significantly higher fracture risk than age-matched persons without diabetes, attributed to disease-specific deficits in the microarchitecture and material properties of bone tissue. Therefore, independent effects of diabetes drugs on skeletal integrity are vitally important. Studies of incretin-based therapies have shown divergent effects of different agents on fracture risk, including detrimental, beneficial, and neutral effects. The sulfonylurea class of drugs, owing to its hypoglycemic potential, is thought to amplify the risk of fall-related fractures, particularly in the elderly. Other agents such as the biguanides may, in fact, be osteo-anabolic. In contrast, despite similarly expected anabolic properties of insulin, data suggests that insulin pharmacotherapy itself, particularly in type 2 diabetes, may be a risk factor for fracture, negatively associated with determinants of bone quality and bone strength. Finally, sodium-dependent glucose co-transporter 2 inhibitors have been associated with an increased risk of atypical fractures in select populations, and possibly with an increase in lower extremity amputation with specific SGLT2I drugs. The role of skeletal muscle, as a potential mediator and determinant of bone quality, is also a relevant area of exploration. Currently, data regarding the impact of glucose lowering medications on diabetes-related muscle atrophy is more limited, although preclinical studies suggest that various hypoglycemic agents may have either aggravating (sulfonylureas, glinides) or repairing (thiazolidinediones, biguanides, incretins) effects on skeletal muscle atrophy, thereby influencing bone quality. Hence, the therapeutic efficacy of each hypoglycemic agent must also be evaluated in light of its impact, alone or in combination, on musculoskeletal health, when determining an individualized treatment approach. Moreover, the effect of newer medications (potentially seeking expanded clinical indication into the pediatric age range) on the growing skeleton is largely unknown. Herein, we review the available literature regarding effects of diabetes pharmacotherapy, by drug class and/or by clinical indication, on the musculoskeletal health of persons with diabetes.

Innate Immune Responses and Osteoarthritis.

PURPOSE OF THE REVIEW: Osteoarthritis (OA) is a chronic, painful joint disease that affects approximately 40% of adults over 70 year. Age is the strongest predictor of OA, while obesity is considered the primary preventable risk factor for OA. Both conditions are associated with abnormal innate immune inflammatory responses that contribute to OA progression and are the focus of this review. RECENT FINDINGS: Recent studies have identified risk factors for OA progression including increased innate immune responses secondary to aging-associated myeloid skewing, obesity-related myeloid activation, and synovial tissue hyperplasia with activated macrophage infiltration. Toll-like receptor (TLR)4-induced catabolic responses also play a significant role in OA. The complex interplay between obesity and aging-associated macrophage activation, pro-inflammatory cytokine production from TLR-driven responses, and adipokines leads to a vicious cycle of synovial hyperplasia, macrophage activation, cartilage catabolism, infrapatellar fat pad fibrosis, and joint destruction.

Preserving and restoring bone with continuous insulin infusion therapy in a mouse model of type 1 diabetes.

Those with type 1 diabetes (T1D) are more likely to suffer a fracture than age- and sex-matched individuals without diabetes, despite daily insulin therapy. In rodent studies examining the effect of bone- or glucose-targeting therapies on preventing the T1D-related decrease in bone strength, insulin co-therapy is often not included, despite the known importance of insulin signaling to bone mass accrual. Therefore, working toward a relevant pre-clinical model of diabetic bone disease, we assessed the effect of continuous subcutaneous insulin infusion (CSII) therapy at escalating doses on preserving bone and the effect of delayed CSII on rescuing the T1D-related bone deterioration in an established murine model of T1D. Osmotic minipumps were implanted in male DBA/2 J mice 2 weeks (prevention study) and 6 weeks (rescue study) after the first injection of streptozotocin (STZ) to deliver insulin at 0, 0.0625, 0.125, or 0.25 IU/day (prevention study; n = 4-5 per dose) and 0 or 0.25 IU/day (rescue study; n = 10 per group). CSII lasted 4 weeks in both studies, which also included age-matched, non-diabetic DBA/2 J mice (n = 8-12 per study). As the insulin dose increased, blood glucose decreased, body weight increased, a serum maker of bone resorption decreased, and a serum marker of bone formation increased such that each end-point characteristic was linearly correlated with dose. There were insulin dose-dependent relationships (femur diaphysis) with cross-sectional area of cortical bone and cortical thickness (micro-computed tomography) as well as structural strength (peak force endured by the mid-shaft during three-point bending). Likewise, trabecular bone volume fraction (BV/TV), thickness, and number (distal femur metaphysis) increased as the insulin dose increased. Delayed CSII improved glycated hemoglobin (HbA1c), but blood glucose levels remained relatively high (well above non-diabetic levels). Interestingly, it returned the resorption and formation markers to similar levels as those seen in non-T1D control mice. This apparent return after 4 weeks of CSII translated to a partial rescue of the structural strength of the femur mid-shaft. Delayed CSII also increased Tb.Th to levels seen in non-T1D controls but did not fully restore BV/TV. The use of exogenous insulin should be considered in pre-clinical studies investigating the effect of T1D on bone as insulin therapy maintains bone structure without necessarily lowering glucose below diabetic levels.

The impact of SGLT2 inhibitors, compared with insulin, on diabetic bone disease in a mouse model of type 1 diabetes.

Skeletal co-morbidities in type 1 diabetes include an increased risk for fracture and delayed fracture healing, which are intertwined with disease duration and the presence of other diabetic complications. As such, chronic hyperglycemia is undoubtedly a major contributor to these outcomes, despite standard insulin-replacement therapy. Therefore, using the streptozotocin (STZ)-induced model of hypoinsulinemic hyperglycemia in DBA/2J male mice, we compared the effects of two glucose lowering therapies on the fracture resistance of bone and markers of bone turnover. Twelve week-old diabetic (DM) mice were treated for 9weeks with: 1) oral canagliflozin (CANA, dose range ~10-16mg/kg/day), an inhibitor of the renal sodium-dependent glucose co-transporter type 2 (SGLT2); 2) subcutaneous insulin, via minipump (INS, 0.125units/day); 3) co-therapy (CANA+INS); or 4) no treatment (STZ, without therapy). These groups were also compared to non-diabetic control groups. Untreated diabetic mice experienced increased bone resorption and significant deficits in cortical and trabecular bone that contributed to structural weakness of the femur mid-shaft and the lumbar vertebra, as determined by three-point bending and compression tests, respectively. Treatment with either canagliflozin or insulin alone only partially rectified hyperglycemia and the diabetic bone phenotype. However, when used in combination, normalization of glycemic control was achieved, and a prevention of the DM-related deterioration in bone microarchitecture and bone strength occurred, due to additive effects of canagliflozin and insulin. Nevertheless, CANA-treated mice, whether diabetic or non-diabetic, demonstrated an increase in urinary calcium loss; FGF23 was also increased in CANA-treated DM mice. These findings could herald ongoing bone mineral losses following CANA exposure, suggesting that certain CANA-induced skeletal consequences might detract from therapeutic improvements in glycemic control, as they relate to diabetic bone disease.

Effects of Type 1 Diabetes on Osteoblasts, Osteocytes, and Osteoclasts.

PURPOSE OF REVIEW: To describe the effects of type 1 diabetes on bone cells. RECENT FINDINGS: Type 1 diabetes (T1D) is associated with low bone mineral density, increased risk of fractures, and poor fracture healing. Its effects on the skeleton were primarily attributed to impaired bone formation, but recent data suggests that bone remodeling and resorption are also compromised. The hyperglycemic and inflammatory environment associated with T1D impacts osteoblasts, osteocytes, and osteoclasts. The mechanisms involved are complex; insulinopenia, pro-inflammatory cytokine production, and alterations in gene expression are a few of the contributing factors leading to poor osteoblast activity and survival and, therefore, poor bone formation. In addition, the observed sclerostin level increase accompanied by decreased osteocyte number and enhanced osteoclast activity in T1D results in uncoupling of bone remodeling. T1D negatively impacts osteoblasts and osteocytes, whereas its effects on osteoclasts are not well characterized, although the limited studies available indicate increased osteoclast activity, favoring bone resorption.

Air displacement plethysmography: cradle to grave.

Differences in body composition are associated with increased disease risk in various stages of life. Despite numerous available methods in assessing body composition (air displacement plethysmography, dual-energy X-ray absorptiometry, bioelectrical impedance, hydrometry, and magnetic resonance imaging), due to innate technical limitations, the ability for one singular method to track body composition over the life span (ie, infancy to adulthood) is challenging and imperfect. The primary goal of this review is to determine if there are body composition methods that can accurately track body composition from infancy into adulthood. After careful consideration and taking into account the best available scientific evidence, we feel air displacement plethysmography is the best instrument at this time for tracking body composition, starting in infancy and forward into adulthood, partly because it is the only "practical" clinical tool currently available for use during infancy.