Insulin Resistance Negatively Influences the Muscle-Dependent IGF-1-Bone Mass Relationship in Premenarcheal Girls

Insulin resistance and skeletal health

PURPOSE OF REVIEW

Bone fragility is a complication of type 2 diabetes (T2D), and insulin resistance is suspected to contribute to diabetes-related bone deficits. This article provides an overview of emerging clinical research involving insulin resistance and bone health by summarizing recent publications, identifying existing knowledge gaps, and suggesting 'next steps' for this evolving field of research.

RECENT FINDINGS

Clinical studies in children and adults report greater bone density in people with increased insulin resistance, but these associations are often attenuated when adjusting for body size. Advancements in bone imaging methods allow for assessment of nuanced characteristics of bone quality and strength that extend beyond standard bone mineral density assessment methods. For example, several recent studies focusing on lumbar spine trabecular bone score, a relatively new measure of trabecular bone quality from dual-energy X-ray absorptiometry, have reported generally consistent inverse associations with insulin resistance. Longitudinal studies using advanced imaging methods capable of evaluating trabecular bone microstructure and strength, such as high-resolution peripheral quantitative computed tomography, are lacking. Studies in younger individuals are sparse, but emerging data suggest that peak bone mass attainment might be threatened by diabetes progression, and increased visceral fat, suppressed muscle-bone unit, advanced glycation end-products, sedentary lifestyle, and poor diet quality might contribute to diabetes effects on bone. Prospective studies during the transition from adolescence to young adulthood are required.

SUMMARY

Insulin resistance is a main feature of T2D, which is suspected to contribute to subclinical diabetes-related threats to bone health. Future clinical studies should focus on the critical years surrounding peak bone mass and peak bone strength attainment using contemporary imaging techniques.

Impact of Obesity on Bone Metabolism in Children

Obesity is an epidemic disease that can increase the incidence of type 2 diabetes, cardiovascular disease, malignancy, hypertension, and other health problems that affect the musculoskeletal system. There is a complex interaction between obesity and bone metabolism. In children with obesity, the peroxisome proliferator-activated receptor gamma pathway causes the differentiation of mesenchymal stem cells into adipocytes via osteoblasts, in which results in low bone mass and osteoporosis. Systemic inflammation in obesity has negative effects on bone metabolism. An increase in the number and size of adipose tissue and adipocytokines secreted from adipocytes affect the bone mass of the whole body with hormonal and biochemical effects. The skeletal effects of obesity are mediated by higher oxidative stress and increased production of proinflammatory cytokines. Osteoporosis due to obesity has increased morbidity and mortality in recent years, resulting in important health problems in developed and developing countries.

A Novel SNP in the Promoter Region of IGF1 Associated With Yunshang Black Goat Kidding Number via Promoting Transcription Activity by SP1

IGF1, a member of the insulin-like growth factor (IGF) superfamily, is also known as the growth-promoting factor (somatomedin C). IGF1 is involved in vertebrate growth and development, immunity, cell metabolism, reproduction, and breeding. However, there are relatively few studies on the relationship between IGF1 and goat reproduction. In this study, a new transcription factor SP1 bound to the IGF1 g. 64943050T>C promoted granulosa cell (GC) proliferation. A mutation g.64943050T>C located in the promoter region of IGF1 was identified. Association analysis revealed that the kidding number in the first and second litters and the average number of first three litters of the CC genotype (2.206 ± 0.044, 2.254 ± 0.056, and 2.251 ± 0.031) were significantly higher than those in the TC genotype (1.832 ± 0.049, 1.982 ± 0.06, and 1.921 ± 0.034) and TT genotype (1.860 ± 0.090, 1.968 ± 0.117, and 1.924 ± 0.062) (p < 0.05). The kidding number in the third litter of the CC genotype (2.355 ± 0.057) was significantly higher than that in the TT genotype (2.000 ± 0.107) (p < 0.05). Then, the function of this mutation was validated by the dual-luciferase reporter assay and EMSA. The results showed that the luciferase activity of IGF1-mutant-C was significantly higher than that of IGF1-Wild-T (p < 0.05). The EMSA also showed that the binding ability of IGF1-mutant-C was higher than that of IGF1-Wild-T (p < 0.05). Subsequently, the transcription factor SP1 was predicted to bind to the mutation of IGF1 (g.64943050T>C). Overexpression of SP1 promotes the expression of IGF1 in the primary granulosa cells (GCs). The results of the CCK-8 assay and the expression of GC proliferation factors (CDK4, cyclin D1, and cyclin D2) demonstrated that SP1 promoted GC proliferation by regulating IGF1 expression. Our results suggested that the IGF1 g.64943050T>C was significantly associated with the kidding number of Yunshang black goats, and SP1 as a transcription factor of IGF1 binding to the mutation T>C regulated the expression of IGF1. Furthermore, SP1 promoted goat GC proliferation by regulating the expression of IGF1, which provides a new insight for the goat fertility trait.

Genetic Polymorphisms of IGF1 and IGF1R Genes and Their Effects on Growth Traits in Hulun Buir Sheep

The identification of candidate genes and genetic variations associated with growth traits is important for sheep breeding. Insulin like growth factor 1 (IGF1) and insulin like growth factor 1 receptor (IGF1R) are well-accepted candidate genes that affect animal growth and development. The current study attempted to assess the association between IGF1 and IGF1R genetic polymorphisms and growth traits in Hulun Buir sheep. To achieve this goal, we first identified three and ten single nucleotide polymorphisms (SNPs) in exons of IGF1 and IGF1R in Hulun Buir sheep and then constructed six haplotypes of IGF1R based on linkage disequilibrium, respectively. Association studies were performed between SNPs and haplotypes of IGF1 and IGF1R with twelve growth traits in a population encompassing 229 Hulun Buir sheep using a general linear model. Our result indicated three SNPs in IGF1 were significantly associated with four growth traits (p < 0.05). In IGF1R, three SNPs and two haplotype blocks were significantly associated with twelve growth traits (p < 0.05). The combined haplotype H5H5 and H5H6 in IGF1R showed the strong association with 12 superior growth traits in Hulun Buir sheep (p < 0.05). In conclusion, we identified SNPs and haplotype combinations associated with the growth traits, which provided genetic resources for marker-assisted selection (MAS) in Hulun Buir sheep breeding.

Relationship between IGF-1 and body weight in inflammatory bowel diseases: Cellular and molecular mechanisms involved

Inflammatory bowel diseases (IBD), represented by ulcerative colitis (UC) and Crohn's disease (CD), are characterized by chronic inflammation of the gastrointestinal tract, what leads to diarrhea, malnutrition, and weight loss. Depression of the growth hormone-insulin-like growth factor-1 axis (GH-IGF-1 axis) could be responsible of these symptoms. We demonstrate that long-term treatment (54 weeks) of adult CD patients with adalimumab (ADA) results in a decrease in serum IGF-1 without changes in serum IGF-1 binding protein (IGF1BP4). These results prompted us to conduct a preclinical study to test the efficiency of IGF-1 in the medication for experimental colitis. IGF-1 treatment of rats with DSS-induced colitis has a beneficial effect on the following circulating biochemical parameters: glucose, albumin, and total protein levels. In this experimental group we also observed healthy maintenance of colon size, body weight, and lean mass in comparison with the DSS-only group. Histological analysis revealed restoration of the mucosal barrier with the IGF-1 treatment, which was characterized by healthy quantities of mucin production, structural maintenance of adherers junctions (AJs), recuperation of E-cadherin and β-catenin levels and decrease in infiltrating immune cells and in metalloproteinase-2 levels. The experimentally induced colitis caused activation of apoptosis markers, including cleaved caspase 3, caspase 8, and PARP and decreases cell-cycle checkpoint activators including phosphorylated Rb, cyclin E, and E2F1. The IGF-1 treatment inhibited cyclin E depletion and partially protects PARP levels. The beneficial effects of IGF-1 in experimental colitis could be explained by a re-sensitization of the IGF-1/IRS-1/AKT cascade to exogenous IGF-1. Given these results, we postulate that IGF-1 treatment of IBD patients could prove to be successful in reducing disease pathology.

Effect of fasting hyperglycemia and insulin resistance on bone turnover markers in children aged 9-11 years

AIM

Impaired regulation of glucose metabolism in childhood adversely affects bone health. We assessed the effect of fasting hyperglycemia and insulin resistance on bone turnover markers in prepubertal children with normal glycemia (<100 mg/dL) and fasting hyperglycemia (100-125 mg/dL).

METHODS

Glucose, hemoglobin A1c, IGF-I (insulin-like growth factor I), iP1NP (N-terminal propeptide of type I procollagen), CTX-1 (C-terminal telopeptide of type I collagen) and insulin were measured. Bone turnover index (BTI) and HOMA-IR (homeostasis model assessment) were calculated.

RESULTS

Bone resorption marker (CTX) levels were decreased by 26.5% in boys with hyperglycemia, though only 7% in girls. Hyperglycemia had no effect on the bone formation marker iP1NP. IGF-1, the best predictor of bone marker variance accounted for 25% of iP1NP and 5% of CTX variance. Girls presented significantly higher BTI indicating the predominance of bone formation over resorption. Insulin resistance significantly decreased CTX. In girls, HOMA-IR and IGF-1 predicted 15% of CTX variance.

CONSLUSIONS

Fasting hyperglycemia and insulin resistance in children impact bone turnover suppressing bone resorption. Hyperglycemia decreased resorption, particularly in boys, while suppression of resorption by insulin resistance was more pronounced in girls. We suggest that the progression of disturbances accompanying prediabetes, may interfere with bone modelling and be deleterious to bone quality in later life.

A narrative review of skeletal muscle atrophy in critically ill children: pathogenesis and chronic sequelae

Muscle wasting is now recognized as a growing, debilitating problem in critically ill adults, resulting in long-term deficits in function and an impaired quality of life. Ultrasonography has demonstrated decreases in skeletal muscle size during pediatric critical illness, although variations exist. However, muscle protein turnover patterns during pediatric critical illness are unclear. Understanding muscle protein turnover during critical illness is important in guiding interventions to reduce muscle wasting. The aim of this review was to explore the possible protein synthesis and breakdown patterns in pediatric critical illness. Muscle protein turnover studies in critically ill children are lacking, with the exception of those with burn injuries. Children with burn injuries demonstrate an elevation in both muscle protein breakdown (MPB) and synthesis during critical illness. Extrapolations from animal models and whole-body protein turnover studies in children suggest that children may be more dependent on anabolic factors (e.g., nutrition and growth factors), and may experience greater muscle degradation in response to insults than adults. Yet, children, particularly the younger ones, are more responsive to anabolic agents, suggesting modifiable muscle wasting during critical illness. There is a lack of evidence for muscle wasting in critically ill children and its correlation with outcomes, possibly due to current available methods to study muscle protein turnover in children-most of which are invasive or tedious. In summary, children may experience muscle wasting during critical illness, which may be more reversible by the appropriate anabolic agents than adults. Age appears an important determinant of skeletal muscle turnover. Less invasive methods to study muscle protein turnover and associations with long-term outcome would strengthen the evidence for muscle wasting in critically ill children.

Molecular cloning, expression, and functional features of IGF1 splice variants in sheep

Insulin-like growth factor 1 (IGF1), also known as somatomedin C, is essential for the regulation of animal growth and development. In many species, the IGF1 gene can be alternatively spliced into multiple transcripts, encoding different pre-pro-IGF1 proteins. However, the exact alternative splicing patterns of IGF1 and the sequence information of different splice variants in sheep are still unclear. In this study, four splice variants (class 1-Ea, class 1-Eb, class 2-Ea, and class 2-Eb) were obtained, but no IGF1 Ec, similar to that found in other species, was discovered. Bioinformatics analysis showed that the four splice variants shared the same mature peptide (70 amino acids) and possessed distinct signal peptides and E peptides. Tissue expression analysis indicated that the four splice variants were broadly expressed in all tested tissues and were most abundantly expressed in the liver. In most tissues and stages, the expression of class 1-Ea was highest, and the expression of other splice variants was low. Overall, levels of the four IGF1 splice variants at the fetal and lamb stages were higher than those at the adult stage. Overexpression of the four splice variants significantly increased fibroblast proliferation and inhibited apoptosis (P < 0.05). In contrast, silencing IGF1 Ea or IGF1 Eb with siRNA significantly inhibited proliferation and promoted apoptosis (P < 0.05). Among the four splice variants, class 1-Ea had a more evident effect on cell proliferation and apoptosis. In summary, the four ovine IGF1 splice variants have different structures and expression patterns and might have different biological functions.

Impact of Lean Body Mass and Insulin Sensitivity on the IGF-1-Bone Mass Axis in Adolescence: the EPICOM Study

CONTEXT

Insulin-like growth factor-1 (IGF-1) is involved in the growth of muscle and bone mass and contributes to glucose homeostasis. The offspring of mothers with diabetes during pregnancy have an increased risk of insulin resistance (IR).

OBJECTIVE

We hypothesized that bone mass was decreased in the offspring of mothers with type 1 diabetes (T1D), and that the IGF-1-bone mass relationship would be negatively influenced by IR.

DESIGN

Data from the Epigenetic, Genetic and Environmental Effects on Growth, Metabolism and Cognitive Functions in Offspring of Women with Type 1 Diabetes (EPICOM) study performed from 2012 to 2013 were included.

SETTING

This work is a follow-up study of a nationwide register study.

PATIENTS

A total of 278 adolescent index offspring whose mothers had T1D and 303 matched controls were studied.

MAIN OUTCOME MEASURE

Bone mineral content (BMC) determined by a dual-energy x-ray absorptiometry scan and the interaction with IGF-1 and insulin sensitivity were measured.

RESULTS

There was no difference in BMC, bone mineral density, height (SD score [SDS]), or BMC/height between index and control offspring. IGF-1 (SDS) did not differ between the groups but insulin-like growth factor-binding protein 3 (SDS) was higher in index boys compared to controls (B = .31 [95% CI, 0.06-0.57], P = .02). The statistical path analysis showed that IGF-1 predicted BMC/height (B = .24 [95% CI, 0.02-0.45], P = .03), but lean mass was a mediator of this. IGF-1 and the homeostatic model assessment of IR were positively associated (B = .75 [95% CI, 0.37-1.12], P < .001). There was no moderating effect of the interaction between IR and IGF-1 on lean mass in the entire cohort (B = .005 [95% CI, -0.03 to 0.04], P = .81) or when analyzing index cases and controls separately.

CONCLUSION

We found that lean mass was an intermediary factor in the IGF-1-bone mass relationship in a large cohort of adolescents, and this relationship was not moderated by IR.

Association of Insulin Resistance and β-cell Function With Bone Turnover Biomarkers in Dysglycemia Patients

BACKGROUND

The interrelation between glucose and bone metabolism is complex and has not been fully revealed. This study aimed to investigate the association between insulin resistance, β-cell function and bone turnover biomarker levels among participants with abnormal glycometabolism.

METHODS

A total of 5277 subjects were involved through a cross-sectional study (METAL study, http://www.chictr.org.cn, ChiCTR1800017573) in Shanghai, China. Homeostasis model assessment of insulin resistance (HOMA-IR) and β-cell dysfunction (HOMA-%β) were applied to elucidate the nexus between β-C-terminal telopeptide (β-CTX), intact N-terminal propeptide of type I collagen (P1NP) and osteocalcin (OC). β-CTX, OC and P1NP were detected by chemiluminescence.

RESULTS

HOMA-IR was negatively associated with β-CTX, P1NP and OC (regression coefficient (β) -0.044 (-0.053, -0.035), Q4vsQ1; β -7.340 (-9.130, -5.550), Q4vsQ1 and β -2.885 (-3.357, -2.412), Q4vsQ1, respectively, all P for trend <0.001). HOMA-%β was positively associated with β-CTX, P1NP and OC (β 0.022 (0.014, 0.031), Q4vsQ1; β 6.951 (5.300, 8.602), Q4vsQ1 and β 1.361 (0.921, 1.800), Q4vsQ1, respectively, all P for trend <0.001).

CONCLUSIONS

Our results support that lower bone turnover biomarker (β-CTX, P1NP and OC) levels were associated with a combination of higher prevalence of insulin resistance and worse β-cell function among dysglycemia patients. It is feasible to detect bone turnover in diabetes or hyperglycemia patients to predict the risk of osteoporosis and fracture, relieve patients' pain and reduce the expenses of long-term cure.

Insulin-like growth factor-1 status is associated with insulin resistance in young patients with spinal muscular atrophy

Insulin-like growth factor-1 (IGF-1) is an anabolic hormone with myotrophic effects on muscle tissue. Patients with spinal muscular atrophy (SMA) sustain early-onset sarcopenia, which contributes to an increased prevalence of insulin resistance. Our aim was to determine the IGF-1 status in 5q-SMA patients and its association with insulin resistance. Real-life clinical and laboratory data of 34 patients (15 males; age 3 months-24 years) included: anthropometric measurements [weight, height/length, body mass index or weight-to-length ratio, delta-height standard deviation score (∆Ht SDS) as the difference between height/length SDS and mid-parental height (MPHt) SDS] and laboratory measurements [Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) and IGF-1]. HOMA-IR levels categorized patients as insulin-resistant [HOMA-IR ≥1.9 (n = 20)] or insulin-sensitive [HOMA-IR <1.9 (n = 14)]. The collective height/length SDS was -0.29±1.34 and ∆Ht SDS was -0.11±1.47. IGF-1 levels were within the normal population range for all patients. Insulin-resistant patients had higher IGF-1 SDS levels compared to insulin-sensitive patients (0.87±0.78 vs. -0.67±0.96, respectively, P<0.001). The IGF-1 SDS was significantly associated with HOMA-IR for all subjects (r = 0.547, P = 0.001), and linear growth parameters (height/length SDS, ∆Ht SDS) were significantly associated with IGF-1 SDS in the insulin-resistant subgroup (r = 0.649, P = 0.002 and r = 0.605, P = 0.005, respectively). Our findings suggest that IGF-1 status is associated with insulin resistance in patients with early-onset sarcopenia.

Sex-Specific Muscular Mediation of the Relationship Between Physical Activity and Cortical Bone in Young Adults

Muscle mass is a commonly cited mediator of the relationship between physical activity (PA) and bone, representing the mechanical forces generated during PA. However, neuromuscular properties (eg, peak force) also account for unique portions of variance in skeletal outcomes. We used serial multiple mediation to explore the intermediary role of muscle mass and force in the relationships between cortical bone and moderate-to-vigorous intensity PA (MVPA). In a cross-sectional sample of young adults (n = 147, 19.7 ± 0.7 years old, 52.4% female) cortical diaphyseal bone was assessed via peripheral quantitative computed tomography at the mid-tibia. Peak isokinetic torque in knee extension was assessed via Biodex dynamometer. Thigh fat-free soft tissue (FFST) mass, assessed via dual-energy X-ray absorptiometry, represented the muscular aspect of tibial mechanical forces. Habitual MVPA was assessed objectively over 7 days using Actigraph GT3X+ accelerometers. Participants exceeded MVPA guidelines (89.14 ± 27.29 min/day), with males performing 44.5% more vigorous-intensity activity relative to females (p < 0.05). Males had greater knee extension torque and thigh FFST mass compared to females (55.3%, and 34.2%, respectively, all p < 0.05). In combined-sex models, controlling for tibia length and age, MVPA was associated with strength strain index (pSSI) through two indirect pathways: (i) thigh FFST mass (b = 1.11 ± 0.37; 95% CI, 0.47 to 1.93), and (i) thigh FFST mass and knee extensor torque in sequence (b = 0.30 ± 0.16; 95% CI, 0.09 to 0.73). However, in sex-specific models MVPA was associated with pSSI indirectly through its relationship with knee extensor torque in males (b = 0.78 ± 0.48; 95% CI, 0.04 to 2.02) and thigh FFST mass in females (b = 1.12 ± 0.50; 95% CI, 0.37 to 2.46). Bootstrapped CIs confirmed these mediation pathways. The relationship between MVPA and cortical structure appears to be mediated by muscle in young adults, with potential sex-differences in the muscular pathway. If confirmed, these findings may highlight novel avenues for the promotion of bone strength in young adults. © 2019 American Society for Bone and Mineral Research.

Relationship of cardiometabolic risk biomarkers with DXA and pQCT bone health outcomes in young girls

BACKGROUND

Excess weight exerts the positive effect of mechanical loading on bone during development whereas obesity-related metabolic dysfunction may have a detrimental impact. In adults, the presence of metabolic syndrome and type 2 diabetes has been associated with compromised bone density, quality, and strength, and an increased incidence of fractures. The few studies that have investigated the role of cardio-metabolic disease risk biomarkers (CMR) on bone strength in children have given conflicting results. The aim of this study was to assess the combined and independent relationships of cardio-metabolic biomarkers with total body and regional bone parameters in young girls.

METHODS

In 306, 9-12 year old girls, measures of whole body fat and lean mass, areal bone mineral density (aBMD), bone mineral content (BMC), and bone area (BA) were obtained by dual-energy x-ray absorptiometry (DXA). Bone mineral density (vBMD), geometry, and strength of metaphyseal and diaphyseal regions of the femur and tibia and a diaphyseal region of the radius were measured using peripheral quantitative computed tomography (pQCT). Fasting serum measures of CMRs included, fasting glucose, insulin, homeostatic model assessment for insulin resistance (HOMA-IR), high-density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), triglyceride (TG), systolic and diastolic blood pressure (SBP and DBP), and C-reactive protein (CRP). Multiple linear regression was used to assess the independent associations of a single CMR with total body and peripheral measures of bone strength after controlling for the other CMRs, plus total body soft tissue, and other relevant covariates. Also, a standardized total CMR composite score, calculated by standardizing to z-scores and then summing z-scores of each CMR biomarker, was regressed with total body and regional bone measures to assess the relationship of a cluster of risk factors with bone health.

RESULTS

Total CMR composite score had inverse associations (p < 0.001) with DXA total BMC and BA. Inverse associations (p < 0.05) of CMR risk score with pQCT regional bone measures occurred with total and trabecular BA at the 4% tibia. Of the individual CMRs, HOMA-IR and CRP were significant predictors of total body bone measures by DXA accounting for ~1-5% of the variance in BMC, BA, and/or aBMD. HOMA-IR was the main predictor of regional pQCT bone outcomes, accounting for the most variance in trabecular vBMD (2.6%) and BSI (3.8%) at the 4% tibia. Most markers of dyslipidemia (TG, HDL-C, LDL-C) and hypertension (SBP, DBP) were not associated (p > 0.05) with any total body or regional bone outcomes with the exception of the inverse relationship of LDL-C with total and trabecular BA and the positive relationship of DBP with cortical vBMD at the radius.

CONCLUSION

Of the obesity-related metabolic impairments, insulin resistance and chronic inflammation may compromise whole body bone development in young girls. In particular, trabecular bone, such as that found at the metaphysis of long bones, may be more susceptible to the detrimental effects associated with obesity-related metabolic dysfunction.

Effect of cardiometabolic risk factors on the relationship between adiposity and bone mass in girls

BACKGROUND/OBJECTIVE

Childhood obesity has been separately associated with cardiometabolic risk factors (CMRs) and increased risk of fracture. However, both augmented and compromised bone mass have been reported among overweight/obese children. Metabolic dysfunction, often co-existing with obesity, may explain the discrepancy in previous studies. The aim of this study was to examine whether the relationship between adiposity and dual-energy X-ray absorptiometry (DXA) derived bone mass differed in young girls with and without CMR(s).

SUBJECTS/METHODS

Whole-body bone and body composition measures by DXA and measures of CMR (fasting glucose, high-density lipoprotein cholesterol (HDL-C), triglyceride (TG), systolic and diastolic blood pressure, waist circumference (WC)) were obtained from 307, 9- to 12-year-old girls. Girls with 1 or ≥ 2 CMR(s) were considered to be at risk (vs. no CMR). Multiple linear regression was used to test the relationship of total fat mass with total body bone mineral content (BMC) after controlling for height, lean mass, CMR risk, and other potential confounders.

RESULTS

There was a significant interaction between CMR risk and total body fat mass. When girls were stratified by CMR group, all groups had a significant positive relationship between fat mass and BMC (p < 0.05), however, girls with ≥ 2 CMRs had a lower BMC for a given level of body fat. Total body fat was not significantly related to bone mineral density (p > 0.05).

CONCLUSION

Fat mass has a positive relationship with BMC even after controlling for lean mass. However, the positive relationship of fat mass with BMC may be attenuated if multiple CMRs are present.

Association of Insulin Resistance with Lower Bone Volume and Strength Index of the Proximal Femur in Nondiabetic Postmenopausal Women

Background

Type 2 diabetes mellitus is associated with an increased risk of osteoporotic fracture despite relatively preserved bone mineral density (BMD). Although this paradox might be attributed to the influence of insulin resistance (IR) on bone structure and material properties, the association of IR with femur bone geometry and strength indices remains unclear.

Methods

Using data from the Cardiovascular and Metabolic Disease Etiology Research Center cohort study, we conducted a cross-sectional analysis among nondiabetic postmenopausal women. IR was estimated using the homeostasis model assessment of IR (HOMA-IR). Compartment-specific volumetric BMD (vBMD) and bone volume of proximal femur were measured using quantitative computed tomography. The compressive strength index (CSI), section modulus (Z), and buckling ratio of the femoral neck were calculated as bone strength indices.

Results

Among 1,008 subjects (mean age, 57.3 years; body mass index [BMI], 23.6 kg/m²), BMI, waist circumference, and vBMD of the femoral neck and total hip increased in a linear trend from the lowest (<1.37) to highest (≥2.27) HOMA-IR quartile (P<0.05 for all). The HOMA-IR showed an independent negative association with total bone volume (standardized β=−0.12), cortical volume (β=−0.05), CSI (β=−0.013), and Z (β=−0.017; P<0.05 for all) of the femoral neck after adjustment for age, weight, height, physical activity, and vitamin D and high-sensitivity C-reactive protein levels. However, the association between HOMA-IR and vBMD was attenuated in the adjusted model (femoral neck, β=0.94; P=0.548).

Conclusions

Elevated HOMA-IR was associated with lower cortical bone volume and bone strength indices in nondiabetic postmenopausal women, independent of age and body size.

Body fat mass, lean body mass and associated biomarkers as determinants of bone mineral density in children 6-8years of age - The Physical Activity and Nutrition in Children (PANIC) study

Lean body mass (LM) has been positively associated with bone mineral density (BMD) in children and adolescents, but the relationship between body fat mass (FM) and BMD remains controversial. Several biomarkers secreted by adipose tissue, skeletal muscle, or bone may affect bone metabolism and BMD. We investigated the associations of LM, FM, and such biomarkers with BMD in children. We studied a population sample of 472 prepubertal Finnish children (227 girls, 245 boys) aged 6-8years. We assessed BMD, LM, and FM using whole-body dual-energy x-ray absorptiometry and analysed several biomarkers from fasting blood samples. We studied the associations of LM, FM, and the biomarkers with BMD of the whole body excluding the head using linear regression analysis. LM (standardized regression coefficient β=0.708, p<0.001), FM (β=0.358, p<0.001), and irisin (β=0.079, p=0.048) were positive correlates for BMD adjusted for age, sex, and height in all children. These associations remained statistically significant after further adjustment for LM or FM. The positive associations of dehydroepiandrosterone sulphate (DHEAS), insulin, homeostatic model assessment for insulin resistance (HOMA-IR), leptin, free leptin index, and high-sensitivity C-reactive protein and the negative association of leptin receptor with BMD were explained by FM. The positive associations of DHEAS and HOMA-IR with BMD were also explained by LM. Serum 25-hydroxyvitamin D was a positive correlate for BMD adjusted for age, sex, and height and after further adjustment for FM but not for LM. LM and FM were positive correlates for BMD also in girls and boys separately. In girls, insulin, HOMA-IR, leptin, and free leptin index were positively and leptin receptor was negatively associated with BMD adjusted for age, height, and LM. After adjustment for age, height, and FM, none of the biomarkers was associated with BMD. In boys, leptin and free leptin index were positively and leptin receptor was negatively associated with BMD adjusted for age, height, and LM. After adjustment for age, height and FM, 25(OH)D was positively and IGF-1 and leptin were negatively associated with BMD. FM strongly modified the association between leptin and BMD. LM but also FM were strong, independent positive correlates for BMD in all children, girls, and boys. Irisin was positively and independently associated with BMD in all children. The associations of other biomarkers with BMD were explained by LM or FM.

Increases in IGF-1 After Anti-TNF-α Therapy Are Associated With Bone and Muscle Accrual in Pediatric Crohn Disease

CONTEXT

Low levels of insulinlike growth factor 1 (IGF-1) in pediatric and adolescent Crohn disease (CD) likely contribute to bone and muscle deficits.

OBJECTIVE

Assess changes in IGF-1 levels and associations with bone and muscle accrual following initiation of anti-tumor necrosis factor α (TNF-α) therapy in pediatric and adolescent CD.

DESIGN AND PARTICIPANTS

Participants (n = 75, age 5 to 21 years) with CD were enrolled in a prospective cohort study; 63 completed the 12-month visit.

MAIN OUTCOME MEASURES

IGF-1 levels at baseline and 10 weeks, as well as dual-energy x-ray absorptiometry (DXA) and tibia peripheral quantitative computed tomography (pQCT) measures of bone and muscle at baseline and 12 months after initiation of anti-TNF-α therapy. Outcomes were expressed as sex-specific z scores.

RESULTS

IGF-1 z scores increased from a median (interquartile range) of -1.0 (-1.58 to -0.17) to -0.36 (-1.04 to 0.36) over 10 weeks (P < 0.001). Lesser disease severity and systemic inflammation, as well as greater estradiol z scores (in girls), was significantly associated with greater IGF-1 z scores over time. DXA whole-body bone mineral content, leg lean mass, and total hip and femoral neck bone mineral density (BMD) z scores were low at baseline (P < 0.0001 vs reference data) and increased significantly (P < 0.001) over 12 months. Greater increases in IGF-1 z scores over 10 weeks predicted improvement in DXA bone and muscle outcomes and pQCT trabecular BMD and cortical area. Adjustment for changes in muscle mass markedly attenuated the associations between IGF-1 levels and bone outcomes.

CONCLUSIONS

Short-term improvements in IGF-1 z scores predicted recovery of bone and muscle outcomes following initiation of anti-TNF-α therapy in pediatric CD. These data suggest that disease effects on growth hormone metabolism contribute to musculoskeletal deficits in CD.

Obese Versus Normal-Weight Late-Adolescent Females have Inferior Trabecular Bone Microarchitecture: A Pilot Case-Control Study

Though still a topic of debate, the position that skeletal health is compromised with obesity has received support in the pediatric and adult literature. The limited data relating specifically to trabecular bone microarchitecture, however, have been relatively inconsistent. The aim of this pilot cross-sectional case-control study was to compare trabecular bone microarchitecture between obese (OB) and normal-weight (NW) late-adolescent females. A secondary aim was to compare diaphyseal cortical bone outcomes between these two groups. Twenty-four non-Hispanic white females, ages 18-19 years, were recruited into OB (n = 12) or NW (n = 12) groups based on pre-specified criteria for percent body fat (≥32 vs. <30, respectively), body mass index (>90th vs. 20th-79th, respectively), and waist circumference (≥90th vs. 25th-75th, respectively). Participants were also individually matched on age, height, and oral contraceptive use. Using magnetic resonance imaging, trabecular bone microarchitecture was assessed at the distal radius and proximal tibia metaphysis, and cortical bone architecture was assessed at the mid-radius and mid-tibia diaphysis. OB versus NW had lower apparent trabecular thickness (radius and tibia), higher apparent trabecular separation (radius), and lower apparent bone volume to total volume (radius; all P < 0.050). Some differences in radius and tibia trabecular bone microarchitecture were retained after adjusting for insulin resistance or age at menarche. Mid-radius and mid-tibia cortical bone volume and estimated strength were lower in the OB compared to NW after adjusting for fat-free soft tissue mass (all P < 0.050). These trabecular and cortical bone deficits might contribute to the increased fracture risk in obese youth.

Insulin Resistance and the IGF-I-Cortical Bone Relationship in Children Ages 9 to 13 Years

IGF-I is a pivotal hormone in pediatric musculoskeletal development. Although recent data suggest that the role of IGF-I in total body lean mass and total body bone mass accrual may be compromised in children with insulin resistance, cortical bone geometric outcomes have not been studied in this context. Therefore, we explored the influence of insulin resistance on the relationship between IGF-I and cortical bone in children. A secondary aim was to examine the influence of insulin resistance on the lean mass-dependent relationship between IGF-I and cortical bone. Children were otherwise healthy, early adolescent black and white boys and girls (ages 9 to 13 years) and were classified as having high (n = 147) or normal (n = 168) insulin resistance based on the homeostasis model assessment of insulin resistance (HOMA-IR). Cortical bone at the tibia diaphysis (66% site) and total body fat-free soft tissue mass (FFST) were measured by peripheral quantitative computed tomography (pQCT) and dual-energy X-ray absorptiometry (DXA), respectively. IGF-I, insulin, and glucose were measured in fasting sera and HOMA-IR was calculated. Children with high HOMA-IR had greater unadjusted IGF-I (p < 0.001). HOMA-IR was a negative predictor of cortical bone mineral content, cortical bone area (Ct.Ar), and polar strength strain index (pSSI; all p ≤ 0.01) after adjusting for race, sex, age, maturation, fat mass, and FFST. IGF-I was a positive predictor of most musculoskeletal endpoints (all p < 0.05) after adjusting for race, sex, age, and maturation. However, these relationships were moderated by HOMA-IR (p_Interaction  < 0.05). FFST positively correlated with most cortical bone outcomes (all p < 0.05). Path analyses demonstrated a positive relationship between IGF-I and Ct.Ar via FFST in the total cohort (β_{Indirect Effect} = 0.321, p < 0.001). However, this relationship was moderated in the children with high (β_{Indirect Effect} = 0.200, p < 0.001) versus normal (β_{Indirect Effect} = 0.408, p < 0.001) HOMA-IR. These data implicate insulin resistance as a potential suppressor of IGF-I-dependent cortical bone development, though prospective studies are needed. © 2017 American Society for Bone and Mineral Research.

Metabolic milieu associates with impaired skeletal characteristics in obesity

High leptin concentration, low-grade inflammation, and insulin resistance often coexist in obese subjects; this adverse metabolic milieu may be the main culprit for increased fracture risk and impaired bone quality seen in patients with type 2 diabetes. We examined the associations of leptin, hs (high sensitivity)- CRP and insulin resistance with bone turnover markers (BTMs) and bone characteristics in 55 young obese adults (median BMI 40 kg/m²) and 65 non-obese controls. Mean age of the subjects was 19.5 ± 2.5 years (mean ± SD). Concentrations of leptin, adiponectin, hs-CRP, MMP-8 and TIMP-1, fasting plasma glucose and insulin (to calculate HOMA), BTMs (BAP, P1NP, CTX-1, and TRAC5b) were measured. Bone characteristics were determined with pQCT at radius and tibia, and with DXA for central sites. Leptin, hs-CRP and HOMA correlated inversely with BTMs: the partial coefficients were 1.5–1.9 fold higher in males than in females. After adjusting for age, BMI, and other endocrine factors, leptin displayed an independent effect in males on radial bone mass (p = 0.019), tibial trabecular density (p = 0.025) and total hip BMD (p = 0.043), with lower densities in males with high leptin. In females, the model adjusting for age, BMI, and other endocrine factors, revealed that hs-CRP had independent effects on radial bone mass (p = 0.034) and lumbar spine BMD (p = 0.016), women with high hs-CRP having lower values. Partial correlations of adiponectin and TIMP-1 with bone characteristics were discrepant; MMP-8 showed no associations. In conclusion, in young obese adults and their controls, leptin, hs-CRP and HOMA associate inversely with BTMs and bone characteristics. Leptin appears to be the key independent effector in males, whereas hs-CRP displayed a predominant role in females.

Insulin Resistance Is Associated With Smaller Cortical Bone Size in Nondiabetic Men at the Age of Peak Bone Mass

CONTEXT

In type 2 diabetes mellitus, fracture risk is increased despite preserved areal bone mineral density. Although this apparent paradox may in part be explained by insulin resistance affecting bone structure and/or material properties, few studies have investigated the association between insulin resistance and bone geometry.

OBJECTIVE

We aimed to explore this association in a cohort of nondiabetic men at the age of peak bone mass.

DESIGN, SETTING, AND PARTICIPANTS

Nine hundred ninety-six nondiabetic men aged 25 to 45 years were recruited in a cross-sectional, population-based sibling pair study at a university research center.

MAIN OUTCOME MEASURES

Insulin resistance was evaluated using the homeostasis model assessment of insulin resistance (HOMA-IR), with insulin and glucose measured from fasting serum samples. Bone geometry was assessed using peripheral quantitative computed tomography at the distal radius and the radial and tibial shafts.

RESULTS

In age-, height-, and weight-adjusted analyses, HOMA-IR was inversely associated with trabecular area at the distal radius and with cortical area, periosteal and endosteal circumference, and polar strength strain index at the radial and tibial shafts (β ≤ -0.13, P < 0.001). These associations remained essentially unchanged after additional adjustment for dual-energy X-ray absorptiometry-derived body composition, bone turnover markers, muscle size or function measurements, or adiponectin, leptin, insulin-like growth factor 1, or sex steroid levels.

CONCLUSION

In this cohort of nondiabetic men at the age of peak bone mass, insulin resistance is inversely associated with trabecular and cortical bone size. These associations persist after adjustment for body composition, muscle size or function, or sex steroid levels, suggesting an independent effect of insulin resistance on bone geometry.

Bone Density in the Obese Child: Clinical Considerations and Diagnostic Challenges

The prevalence of obesity in children has reached epidemic proportions. Concern about bone health in obese children, in part, derives from the potentially increased fracture risk associated with obesity. Additional risk factors that affect bone mineral accretion, may also contribute to obesity, such as low physical activity and nutritional factors. Consequences of obesity, such as inflammation, insulin resistance, and non-alcoholic fatty liver disease, may also affect bone mineral acquisition, especially during the adolescent years when rapid increases in bone contribute to attaining peak bone mass. Further, numerous pediatric health conditions are associated with excess adiposity, altered body composition, or endocrine disturbances that can affect bone accretion. Thus, there is a multitude of reasons for considering clinical assessment of bone health in an obese child. Multiple diagnostic challenges affect the measurement of bone density and its interpretation. These include greater precision error, difficulty in positioning, and the effects of increased lean and fat tissue on bone health outcomes. Future research is required to address these issues to improve bone health assessment in obese children.

Insulin and bone health in young adults: The mediator role of lean mass

BACKGROUND

The positive relationship between lean mass (LM) and bone health is well known, but a positive association between insulin and LM has also been described. Insulin has some anabolic properties on bone through the stimulation of osteoblast differentiation, yet the role of LM as a confounder or mediator in this relationship remains uncertain.

OBJECTIVE

To examine whether the association between insulin levels and bone health is mediated by LM.

METHODS

A cross-sectional study was conducted at the Castilla La Mancha University (Spain) involving 466 young adults (113 young men; 19.5±2.3 years). LM and total-body bone mineral content (BMC) were measured by dual energy x-ray absorptiometry, and insulin was measured in fasting serum samples.

RESULTS

Young adults with high total LM had higher values of total-body BMC than their peers after controlling for age and sex, this relationship persisted after adjusting for insulin levels (p<0.001). In mediation analyses, insulin levels were positively associated with total-body BMC (b = 0.05; p<0.001) and total LM acted as an intermediate variable, attenuating the association between insulin levels and total-body BMC (b = -31.98; p>0.05) as indicated by Sobel test values for indirect effect (z = 4.43; p<0.001).

CONCLUSIONS

LM plays an important role in the relationship between insulin levels and bone health, in such a way that while increases in LM have a positive influence on bone health, they are also negatively associated with insulin levels.

Associations among osteocalcin, leptin and metabolic health in children ages 9-13 years in the United States

Background

This study aimed to investigate the relationships among osteocalcin, leptin and metabolic health outcomes in children ages 9–13 years.

Methods

This was a cross-sectional analysis of baseline data from 161 boys and 157 girls (ages 9–13 years) who previously participated in a double-blinded randomized placebo controlled trial of vitamin D supplementation. Relationships among fasting serum total osteocalcin (tOC), undercarboxylated osteocalcin (ucOC), leptin, and metabolic health outcomes were analyzed.

Results

Approximately 52% of study participants were obese based on percent body fat cutoffs (>25% for boys and >32% for girls) and about 5% had fasting serum glucose within the prediabetic range (i.e. 100 to 125 mg/dL). Serum tOC was not correlated with leptin, glucose, insulin, HOMA-IR, or HOMA-β after adjusting for percent body fat. However, serum ucOC negatively correlated with leptin (partial r = −0.16; p = 0.04) and glucose (partial r = −0.16; p = 0.04) after adjustment for percent body fat. Leptin was a positive predictor of insulin, glucose, HOMA-IR, and HOMA-β after adjusting for age, sex and percent body fat (all p < 0.001).

Conclusions

These data depict an inverse relationship between leptin and various metabolic health outcomes in children. However, the notion that tOC or ucOC link fat with energy metabolism in healthy children was not supported.

Clinical trial registration number

NCT00931580.