Insulin-like growth factor-I in diabetes mellitus: its physiology, metabolic effects, and potential clinical utility

Identification of key genes modules linking diabetic retinopathy and circadian rhythm

Background

Diabetic retinopathy (DR) is a leading cause of vision loss worldwide. Recent studies highlighted the crucial impact of circadian rhythms (CR) on normal retinopathy in response to the external light cues. However, the role of circadian rhythms in DR pathogenesis and potential investigational drugs remains unclear.

Methods

To investigate the weather CR affects DR, differential expression analysis was employed to identify differentially expressed genes (DEGs) from the GEO database (GSE160306). Functional enrichment analysis was conducted to identify relevant signaling pathways. LASSO regression was utilized to screen pivotal genes. Weighted gene co-expression network anlaysis (WGCNA) was applied to identify different modules. Additionally, we use the Comparative Toxicogenomics Database (CTD) database to search key genes related to drugs or molecular compounds. The diabetic mouse model received three consecutive intraperitoneal injections of streptozotocin (STZ) during 3 successive days.

Results

We initially identified six key genes associated with circadian rhythm in DR, including COL6A3, IGFBP2, IGHG4, KLHDC7A, RPL26P30, and MYL6P4. Compared to normal tissue, the expression levels of COL6A3 and IGFB2 were significantly increased in DR model. Furthermore, we identified several signaling pathways, including death domain binding, insulin-like growth factor I binding, and proteasome binding. We also observed that COL6A3 was positively correlated with macrophages (cor=0.628296895, p=9.96E-08) and Th17 cells (cor=0.665120835, p=9.14E-09), while IGFBP2 showed a negatively correlated with Tgd (cor=-0.459953045, p=0.000247284) and Th2 cells (cor=-0.442269719, p=0.000452875). Finally, we identified four drugs associated with key genes: Resveratrol, Vitamin E, Streptozocin, and Sulindac.

Conclusion

Our findings revealed several key genes related to circadian rhythms and several relevant drugs in DR, providing a novel insight into the mechanism of DR and potential implications for future DR treatment. This study contributes to a better understanding of CR in DR and its implications for future therapeutic interventions.

Associations of Obesity Indices with Bone Mineral Densities and Risk of Osteoporosis Stratified Across Diabetic Vascular Disease in T2DM Patients

OBJECTIVE

To evaluate associations of obesity indices with bone mineral densities (BMD) and risk of osteoporosis in T2DM patients totally and stratified across presence of any diabetic cardiovascular complications.

METHODS

Cross-sectional analyses of baseline information on a cohort of 250 T2DM patients were conducted in Xiamen, China. Obesity indices included body weight, height, body mass index (BMI), waist and waist hip ratio (WHR). BMD was measured using dual-energy X-ray absorptiometry at three different sites, and osteoporosis was defined based on the minimum T-scores of BMD. Presence of any diabetic vascular complications was confirmed by checking their medical records histories.

RESULTS

Among the 250 T2DM patients, 50 (20.0%) were defined as osteoporosis. Multivariable linear regression and multivariable logistic regression analyses showed that igher obesity indices, including body weight, BMI and waist, but neither body height nor waist hip ratio, were positively associated with the minimum T-scores of BMD and had significantly decreased risk of osteoporosis. Stratified analyses across presence of any of diabetic vascular complications showed similar results for those with any of diabetic vascular complications, while no significant association between obesity indices and minimum T-scores of BMD was found for those without. Postmenopausal women (vs men) and ever drinking were significantly associated with increased risk of osteoporosis, and the adjusted odds ratios (95% CIs) were 5.165 (1.762-15.138, p = 0.003) and 3.789 (1.087-13.214, p = 0.037), respectively. None of metabolic profiles, including systolic and diastolic blood pressure, triglyceride, total cholesterol, high-density lipoprotein cholesterol, HbA1c and blood uric acid, was significantly associated with either minimum T-scores of BMD or risk of osteoporosis.

CONCLUSION

Associations of obesity indices with either BMD or risk of osteoporosis in T2DM patients varied by presence of any diabetic vascular complication and should be not interpreted as causal without considering the often-unmeasured effect modification by health status.

Association Between Uric Acid and Insulin-Like Growth Factor-1 in Type 2 Diabetes Mellitus

Objective

This research examined the relationship between uric acid (UA) and insulin-like growth factor-1 (IGF-1) in patients with type 2 diabetes mellitus (T2DM).

Methods

This study was a cross-sectional study that included 1230 Chinese patients with T2DM. We collected general information and laboratory indicators and calculated the standard deviation score of IGF-1 (IGF-1 SDS).

Results

The univariate analysis results demonstrated a significant positive relationship between UA levels and IGF-1 SDS (P<0.001). A nonlinear relationship was discovered between UA and IGF-1 SDS after adjusting for confounding factors. Multivariate piecewise linear regression showed that the levels of IGF-1 SDS increased when UA was <4.17 mg/dl (β 0.12,95% CI -0.04, 0.28; P=0.121) and decreased when UA was >4.17 mg/dl (β -0.38,95% CI -0.64, -0.12; P=0.004).

Conclusion

This study showed a nonlinear relationship between UA and IGF-1 in Chinese adults with T2DM. When the UA levels reached the inflection point, IGF-1 levels negatively correlated with the increase in UA. Further studies are needed to explore this relationship and mechanisms in the future.

Obesity and Bone Health: A Complex Link

So far, the connections between obesity and skeleton have been extensively explored, but the results are inconsistent. Obesity is thought to affect bone health through a variety of mechanisms, including body weight, fat volume, bone formation/resorption, proinflammatory cytokines together with bone marrow microenvironment. In this review, we will mainly describe the effects of adipokines secreted by white adipose tissue on bone cells, as well as the interaction between brown adipose tissue, bone marrow adipose tissue, and bone metabolism. Meanwhile, this review also reviews the evidence for the effects of adipose tissue and its distribution on bone mass and bone-related diseases, along with the correlation between different populations with obesity and bone health. And we describe changes in bone metabolism in patients with anorexia nervosa or type 2 diabetes. In summary, all of these findings show that the response of skeleton to obesity is complex and depends on diversified factors, such as mechanical loading, obesity type, the location of adipose tissue, gender, age, bone sites, and secreted cytokines, and that these factors may exert a primary function in bone health.

Short adult height increases the risk of end-stage renal disease in type 2 diabetes

OBJECTIVE

Although short adult height has been associated with an increasing variety of diseases and all-cause death, no reliable data exist on the association between adult height and end-stage renal disease (ESRD) in diabetic patients. We investigated the relationship between short adult height, development of ESRD, and mortality in type 2 diabetes mellitus (DM).

METHODS

This nationwide population-based cohort study analyzed clinical data from a total of 2,621,907 subjects aged ≥30 years with type 2 DM between January 1, 2009 and December 31, 2012, using the National Health Insurance Database in Korea.

RESULTS

During a 6.9-year follow-up period, 220,457 subjects (8.4%) died, and 28,704 subjects (1.1%) started dialysis. Short adult height significantly increased the incidence of ESRD and all-cause mortality in the overall cohort analysis. In multivariable Cox models, hazard ratios (HR) for the development of ESRD comparing the highest and lowest quartiles of adult height were 0.86 (95% CI 0.83-0.89). All-cause mortality also decreased with the highest height compared to patients with the lowest height, after fully adjusting for confounding variables (HR 0.79, 95% CI 0.78-0.81). Adult height had an inverse relationship to newly diagnosed ESRD (male: HR 0.86, 95% CI 0.83-0.90, female: HR 0.84, 95% CI 0.79-0.90) and all-cause mortality (male: HR 0.81, 95% CI 0.79-0.82, female: HR 0.80, 95% CI 0.78-0.82).

CONCLUSIONS

Short adult height is strongly associated with the increased risk of ESRD development and all-cause mortality in type 2 DM.

Administration of Human Non-Diabetic Mesenchymal Stromal Cells to a Murine Model of Diabetic Fracture Repair: A Pilot Study

Individuals living with type 1 diabetes mellitus may experience an increased risk of long bone fracture. These fractures are often slow to heal, resulting in delayed reunion or non-union. It is reasonable to theorize that the underlying cause of these diabetes-associated osteopathies is faulty repair dynamics as a result of compromised bone marrow progenitor cell function. Here it was hypothesized that the administration of non-diabetic, human adult bone marrow-derived mesenchymal stromal cells (MSCs) would enhance diabetic fracture healing. Human MSCs were locally introduced to femur fractures in streptozotocin-induced diabetic mice, and the quality of de novo bone was assessed eight weeks later. Biodistribution analysis demonstrated that the cells remained in situ for three days following administration. Bone bridging was evident in all animals. However, a large reparative callus was retained, indicating non-union. µCT analysis elucidated comparable callus dimensions, bone mineral density, bone volume/total volume, and volume of mature bone in all groups that received cells as compared to the saline-treated controls. Four-point bending evaluation of flexural strength, flexural modulus, and total energy to re-fracture did not indicate a statistically significant change as a result of cellular administration. An ex vivo lymphocytic proliferation recall assay indicated that the xenogeneic administration of human cells did not result in an immune response by the murine recipient. Due to this dataset, the administration of non-diabetic bone marrow-derived MSCs did not support fracture healing in this pilot study.

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.

Assessment using serum insulin-like growth factor-I and bone mineral density is useful for detecting prevalent vertebral fractures in patients with type 2 diabetes mellitus

Bone mineral density (BMD) is less useful for evaluating fracture risk in type 2 diabetes. This study showed for the first time that combined evaluation by serum insulin-like growth factor-I and BMD is useful to assess the risk of vertebral fracture in postmenopausal women and men with type 2 diabetes.

INTRODUCTION

BMD is less useful for evaluating fracture risk in type 2 diabetes mellitus (T2DM). We aimed to examine the usefulness of combined evaluation by BMD and serum insulin-like growth factor-I (IGF-I) to assess the risk of vertebral fracture (VF) in T2DM.

METHODS

In this cross-sectional study, 412 postmenopausal women and 582 men with T2DM, whose BMD, bone turnover markers, and serum IGF-I were measured, were enrolled. The association of BMD alone, serum IGF-I alone, and combined assessment by BMD and IGF-I with the presence of VF was examined.

RESULTS

Multiple logistic regression analyses showed that IGF-I as well as BMD T-score at lumbar (L) and femoral neck (FN) were significantly associated with VF except for IGF-I in men, respectively. Receiver operating characteristic curves showed that the cutoff values of IGF-I, L T-score and FN T-score were 127 ng/mL, - 1.78, and - 2.02 in postmenopausal women and 127 ng/mL, - 1.67, and - 1.24 in men. Based on the cutoff vales, the subjects were divided into four categories. The category of lower IGF-I and lower T-scores had a significant increased risk of VF compared to higher IGF-I and higher T-scores both in postmenopausal women and in men. The sensitivity and specificity of the combined assessment to detect VF were better compared to using BMD alone or IGF-I alone.

CONCLUSIONS

This is the first study to show that in addition to BMD measurement, the assessment using serum IGF-I is useful to estimate the prevalence of VF in patients with T2DM.

Diabetes Mellitus-induced Bone Fragility

Accumulating evidence has shown that the risk of osteoporotic fractures is increased in patients with diabetes mellitus (DM). Thus, DM-induced bone fragility has been recently recognized as a diabetic complication. Because the fracture risk is independent of the reduction in bone mineral density, deterioration of the bone quality may be the main cause of bone fragility. Although its mechanism remains poorly understood, accumulated collagen cross-links of advanced glycation end-products (AGEs) and dysfunctions of osteoblast and osteocyte may be involved. Previous studies have suggested that various diabetes-related factors, such as chronic hyperglycemia, insulin, insulin-like growth factor-I, AGEs, and homocysteine, are associated with the risk of bone fragility caused by impaired bone formation and bone remodeling. Furthermore, several anti-diabetic drugs are known to affect bone metabolism and fracture risk. We herein review the association between DM and fracture risk as well as the mechanism of DM-induced bone fragility based on recent evidence.

Interaction between bone and glucose metabolism [Review]

Accumulating evidence has shown that bone and glucose metabolism are closely associated with each other. Since the risk of osteoporotic fractures is increased in patients with diabetes mellitus (DM), osteoporosis is recently recognized as one of diabetic complications, called DM-induced bone fragility. Previous studies showed that collagen cross-links of advanced glycation end products (AGEs) and dysfunctions of osteoblast and osteocyte are involved in DM-induced bone fragility. Circulating levels of AGEs and homocysteine are increased in patients with DM, and they directly impair the functions of osteoblast and osteocyte, resulting in decreased bone formation and bone remodeling. On the other hand, bone is recently recognized as an endocrine organ. Previous studies based on in vitro and animal studies showed that osteocalcin, which is specifically expressed in osteoblasts and secreted into the circulation, may regulate glucose homeostasis. Although several clinical studies reported the relationship between osteocalcin and glucose metabolism, further large-scale and intervention studies are necessary to confirm the beneficial effects of osteocalcin on glucose metabolism in human. It has been shown that adenosine monophosphate-activated protein kinase (AMPK), an intracellular energy sensor, is involved in bone metabolism. Adiponectin and metformin stimulate osteocalcin expression and the differentiation of osteoblasts via AMPK activation. Also, AMPK activation protects against oxidative stress-induced apoptosis of osteocytes. These findings suggest that AMPK in osteoblasts and osteocytes may be a therapeutic target for DM-induced bone fragility.

Bone Cell Bioenergetics and Skeletal Energy Homeostasis

The rising incidence of metabolic diseases worldwide has prompted renewed interest in the study of intermediary metabolism and cellular bioenergetics. The application of modern biochemical methods for quantitating fuel substrate metabolism with advanced mouse genetic approaches has greatly increased understanding of the mechanisms that integrate energy metabolism in the whole organism. Examination of the intermediary metabolism of skeletal cells has been sparked by a series of unanticipated observations in genetically modified mice that suggest the existence of novel endocrine pathways through which bone cells communicate their energy status to other centers of metabolic control. The recognition of this expanded role of the skeleton has in turn led to new lines of inquiry directed at defining the fuel requirements and bioenergetic properties of bone cells. This article provides a comprehensive review of historical and contemporary studies on the metabolic properties of bone cells and the mechanisms that control energy substrate utilization and bioenergetics. Special attention is devoted to identifying gaps in our current understanding of this new area of skeletal biology that will require additional research to better define the physiological significance of skeletal cell bioenergetics in human health and disease.

Decreased Serum Insulin-like Growth Factor-I is a Risk Factor for Non-vertebral Fractures in Diabetic Postmenopausal Women

Objective Previous studies have shown that serum insulin-like growth factor-I (IGF-I) is involved in diabetes-related bone fragility. Although lower serum levels of IGF-I are reported to be associated with a higher risk of vertebral fractures in patients with type 2 diabetes, it is unknown whether or not the serum level of IGF-I is associated with the incidence of non-vertebral fractures. Methods We investigated the relationships between the serum levels of IGF-I and the incidence of non-vertebral osteoporotic fractures in 188 men and 168 postmenopausal women with type 2 diabetes. Results A multiple logistic regression analysis adjusted for age, duration of diabetes, observation period, body mass index, HbA1c, serum creatinine, and the bone mineral density at the lumbar spine showed that the serum IGF-I level was significantly and inversely associated with the incidence of non-vertebral osteoporotic fractures in postmenopausal women (odds ratio =0.48, 95% confidential interval [CI] 0.23-0.99 per SD increase; p=0.047), but not in men. Moreover, the inverse association between the serum IGF-I level and the incidence of non-vertebral fractures remained significant after additional adjustment for insulin use, and the serum calcium and phosphate levels (odds ratio =0.48, 95% CI 0.23-0.99 per SD increase; p=0.046). Conclusion This is the first study to show that decreased serum IGF-I levels are associated with a higher risk of non-vertebral osteoporotic fractures in postmenopausal women with type 2 diabetes. Serum IGF-I could be a useful marker for assessing the incidence of osteoporotic fractures.

Hair follicle characteristics as early marker of Type 2 Diabetes

Type 2 Diabetes mellitus (DM2) includes a continuum of metabolic disorders characterized by hyperglycemia that causes several chronic long-term complications such as coronary artery disease, peripheral arterial disease, nephropathy, and neuropathy. The hair follicle could reveal signs of early vascular impairment, yet its relationship to early metabolic injuries has been largely ignored. We propose that in earlier stages of the continuum of DM2-related metabolic disorders, a group of susceptible patients who do not yet meet the diagnostic criteria to be considered as persons with DM2 may present chronic vascular impairment and end organ damage, including hair follicle damage, which can be evaluated to identify an early risk marker. This hypothesis is based in the association found between insulin resistance and alopecia in non-diabetic persons, and the hair loss on the lower limbs as a manifestation of long-term peripheral arterial disease among subjects with DM2. In order to test this hypothesis, studies are required to evaluate if hair follicle characteristics are related to and can predict hyperglycemic complications, and if they do so, which feature of the hair follicle, such as hair growth, best characterizes such DM2-related conditions. If this hypothesis were proven to be true, significant advances towards a personalized approach for early prevention strategies and management of DM2 would be made. By focusing on the hair follicles, early stages of metabolic-related organ damage could be identified using non-invasive low-cost techniques. In so doing, this approach could provide early identification of DM2-susceptible individuals and lead to the early initiation of adequate primary prevention strategies to reduce or avoid the onset of large internal organ damage.

Review: Insulin-like growth factor-related proteins and diabetic complications

The insulin-like growth factor system and, in particular, insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-1 (IGFBP-1) are dysregulated in type 1 and type 2 diabetes. Serum IGF-I levels are low in both forms of diabetes, and this may be in part genetically determined. It is possible that the reduced serum levels of IGF-I are involved in the development of microvascular and macrovascular complications. Fasting serum IGFBP-1 levels are usually low in early type 2 diabetic patients with insulin resistance and hyperinsulinaemia but may be raised in patients with particularly poor glycaemic control and severe beta-cell failure. Treatment with IGF-I/binding protein complexes has been shown to improve glycaemic control in conjunction with insulin and may in future have a place in the treatment of diabetes, potentially to prevent diabetic complications. Serum IGFBP-1 determination may have utility in the assessment of cardiovascular risk and as an indicator for insulin resistance.

Growth hormone and ocular dysfunction: Endocrine, paracrine or autocrine etiologies?

The eye is a target site for GH action and growth hormone has been implicated in diabetic retinopathy and other ocular dysfunctions. However, while this could reflect the hypersecretion of pituitary GH, the expression of the GH gene is now known to occur in ocular tissues and it could thus also reflect excess GH production within the eye itself. The possibility that ocular dysfunctions might arise from endocrine, autocrine or paracrine etiologies of GH overexpression is therefore the focus of this brief review.

Deep sea minerals prolong life span of streptozotocin-induced diabetic rats by compensatory augmentation of the IGF-I-survival signaling and inhibition of apoptosis

Consumption of deep sea minerals (DSM), such as magnesium, calcium, and potassium, is known to reduce hypercholesterolemia-induced myocardial hypertrophy and cardiac-apoptosis and provide protection against cardiovascular diseases. Heart diseases develop as a lethal complication among diabetic patients usually due to hyperglycemia-induced cardiac-apoptosis that causes severe cardiac-damages, heart failure, and reduced life expectancy. In this study, we investigated the potential of DSM and its related cardio-protection to increase the life expectancy in diabetic rats. In this study, a heart failure rat model was developed by using streptozotocin (65 mg kg(-1) ) IP injection. Different doses of DSM-1× (37 mg kg(-1) day(-1) ), 2× (74 mg kg(-1) day(-1) ) and 3× (111 mg kg(-1) day(-1) ), were administered to the rats through gavages for 4 weeks. The positive effects of DSM on the survival rate of diabetes rats were determined with respect to the corresponding effects of MgSO4 . Further, to understand the mechanism by which DSM enhances the survival of diabetic rats, their potential to regulate cardiac-apoptosis and control cardiac-dysfunction were examined. Echocardiogram, tissue staining, TUNEL assay, and Western blotting assay were used to investigate modulations in the myocardial contractile function and related signaling protein expression. The results showed that DSM regulate apoptosis and complement the cardiomyocyte proliferation by enhancing survival mechanisms. Moreover DSM significantly reduced the mortality rate and enhanced the survival rate of diabetic rats. Experimental results show that DSM administration can be an effective strategy to improve the life expectancy of diabetic subjects by improving cardiac-cell proliferation and by controlling cardiac-apoptosis and associated cardiac-dysfunction. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 769-781, 2016.

Neurotrophins and cognitive functions in T1D compared with healthy controls: effects of a high-intensity exercise

Exercise is known to have beneficial effects on cognitive function. This effect is greatly favored by an exercise-induced increase in neurotrophic factors, such as brain-derived neurotrophic factor (BDNF) and insulin-like growth factor-1 (IGF-1), especially with high-intensity exercises (HIE). As a complication of type 1 diabetes (T1D), a cognitive decline may occur, mostly ascribed to hypoglycaemia and chronic hyperglycaemia. Therefore, the purpose of this study was to examine the effects of acute HIE on cognitive function and neurotrophins in T1D and matched controls. Ten trained T1D (8 males, 2 females) participants and their matched (by age, sex, fitness level) controls were evaluated on 2 occasions after familiarization: a maximal test to exhaustion and an HIE bout (10 intervals of 60 s at 90% of their maximal wattage followed by 60 s at 50 W). Cognitive tests and analyses of serum BDNF, IGF-1, and free insulin were performed before and after HIE and following 30 min of recovery. At baseline, cognitive performance was better in the controls compared with the T1D participants (p < 0.05). After exercise, no significant differences in cognitive performance were detected. BDNF levels were significantly higher and IGF-1 levels were significantly lower in T1D compared with the control group (p < 0.05) at all time points. Exercise increased BDNF and IGF-1 levels in a comparable percentage in both groups (p < 0.05). In conclusion, although resting levels of serum BDNF and IGF-1 were altered by T1D, comparable increasing effects on BDNF and IGF-1 in T1D and healthy participants were found. Therefore, regularly repeating acute HIE could be a promising strategy for brain health in T1D.

Osteocalcin, adipokines and their associations with glucose metabolism in type 1 diabetes

To determine osteocalcin (OC) and adipokines in type 1 diabetes (T1D) and healthy controls, and to explore possible associations between glucose and bone metabolism, body composition and adipokines. Serum levels of total OC, undercarboxylated (UC-OC), leptin, adiponectin, and other parameters of glucose and bone metabolism were measured in 128 patients with T1D (mean duration 21.2years) and in 77 healthy controls, matched for gender, age, and body mass index (BMI). Partial correlations (adjusted for age and gender) with parameters of body composition (BMI, fat body mass [derived from bone mineral density scans]), glycaemic control (hemoglobin A1c (HbA1c), daily insulin dose in T1D), skeletal homeostasis (osteoprotegerin (OPG), receptor activator of NF-κB ligand (RANKL), all measured in serum), and serum insulin-like growth factor 1 (IGF-1) were also examined. Independent predictors of total and UC-OC were then explored. Total OC was lower in males with T1D (16.3±6.4 vs. 22.2±9.9ng/ml; p=0.001), whereas UC-OC did not show group differences. Adiponectin was higher in T1D patients, both for males and females (8.9±6.6 vs. 5.7±2.5μg/ml; p=0.004 and 13.8±6.4 vs. 8.8±4.0μg/ml; p<0.001). IGF-1 was lower only in females with T1D (146.6±68.8 vs. 203.0±74.4ng/ml; p<0.001). BMI and fat body mass were similar in T1D and controls. In T1D patients, total OC was inversely correlated with BMI and HbA1c, and UC-OC inversely correlated with HbA1c. In T1D patients, leptin positively correlated with BMI, fat body mass and daily insulin dose, while adiponectin inversely correlated with BMI and daily insulin dose. Multivariate regression modelling showed that determinants of higher total OC levels were male gender (p=0.04, ß-coefficient=2.865) and lower HbA1c (p=0.04, ß-coefficient=-0.117), whereas determinants of UC-OC levels were T1D (p=0.016, ß-coefficient=2.015), higher IGF-1 (p=0.004, ß-coefficient=0.011) and lower HbA1c (p=0.011, ß-coefficient=- 0.061). Total OC and UC-OC are associated with good glycaemic control in T1D, with gender-specific differences for total-OC. The association of leptin and adiponectin with glycaemic control, as observed in controls, does not seem to be a feature in T1D, although both adipokines appear to be related to the insulin demand. This article is part of a Special Issue entitled "Bone and diabetes".

Protective effect of Danggui (Radix Angelicae Sinensis) on angiotensin II-induced apoptosis in H9c2 cardiomyoblast cells

BACKGROUND

Danggui (Radix Angelicae Sinensis) is an herb often used in Traditional Chinese medicine. It is used to promote blood flow and has been used in the treatment of myocardial ischemia-reperfusion injury in animal models. Angiotensin II (Ang II) has been shown to play important roles in mediating cardiovascular diseases, and may cause cardiac hypertrophy and apoptosis. This study aimed to investigate whether Danggui has protective effects on Ang II-induced apoptosis in H9c2 cardiomyoblast cells and study the mechanisms involved.

METHODS

We evaluated the effect of Danggui on Ang II-induced apoptosis in an in vitro model. H9c2 cardiomyoblast cells were cultured in serum-free medium for 4 hr, then treated with Danggui (50, 100 μg/ml) 1 hr pre- or post-Ang II treatment. After a further 23 hr of culture, cells were harvested for analyses with assays for apoptosis markers and cell signaling pathways.

RESULTS

Our results showed that Ang II induced upregulation of pro-apoptotic Bad, instability of the mitochondria membrane potential, cytochrome c release, caspase-9 and caspase-3 activation and cardiomyocyte apoptosis. Pre- or post-treatment with Danggui reversed all of the above Ang II-induced apoptotic effects in H9c2 cells. Furthermore, the JNK (SP600125) inhibitor completely blocked Danggui inhibition of caspase-3 activation in Ang II-treated H9c2 cells.

CONCLUSIONS

Our results showed that Danggui either pre-treatment or post-treatment highly attenuated the Ang II-induced apoptosis in cardiomyoblast cells. The findings demonstrated that the anti-apoptosis effect of Danggui is mediated by JNK and PI3k inhibitors.

The inhibition effects of insulin on BMP2-induced muscle heterotopic ossification

Bone morphogenetic proteins (BMPs) play an important role in regulating osteoblastic differentiation and bone formation. But the diffuse of BMPs into muscle tissues around bone injury sites often leads to heterotopic ossification, which has been regarded as one of major side-effects of BMP implementation in bone defect patients. It raises great demands for exploring effective methods that preventing BMP-induced heterotopic ossification while not interrupting the osteoinductive activity of BMPs for in situ bone defect repair. Here we found insulin, a positive regulator for bone regeneration, inhibited BMP2-induced muscle heterotopic ossification by suppressing the expression of bone transcription factor Osterix. By analyzing downstream molecules of insulin pathway, we found AKT/mTOR/GSK3 signaling was responsible for the inhibition of insulin on BMP2-induced ossification, and GSK3 inhibitor SB216763 attenuated BMP2-induced muscle heterotopic ossification. The data might shed light on developing effective clinical therapy for inhibiting muscle heterotopic ossification when BMPs were used bone defect repair.

Tsc2 is a molecular checkpoint controlling osteoblast development and glucose homeostasis

Insulin signaling in osteoblasts regulates global energy balance by stimulating the production of osteocalcin, a bone-derived protein that promotes insulin production and action. To identify the signaling pathways in osteoblasts that mediate insulin's effects on bone and energy metabolism, we examined the function of the tuberous sclerosis 2 (Tsc2) protein, a key target important in coordinating nutrient signaling. Here, we show that loss of Tsc2 in osteoblasts constitutively activates mTOR and destabilizes Irs1, causing osteoblasts to differentiate poorly and become resistant to insulin. Young Tsc2 mutant mice demonstrate hypoglycemia with increased levels of insulin and undercarboxylated osteocalcin. However, with age, Tsc2 mutants develop metabolic features similar to mice lacking the insulin receptor in the osteoblast, including peripheral adiposity, hyperglycemia, and decreased pancreatic β cell mass. These metabolic abnormalities appear to result from chronic elevations in undercarboxylated osteocalcin that lead to downregulation of the osteocalcin receptor and desensitization of the β cell to this hormone. Removal of a single mTOR allele from the Tsc2 mutant mice largely normalizes the bone and metabolic abnormalities. Together, these findings suggest that Tsc2 serves as a key checkpoint in the osteoblast that is required for proper insulin signaling and acts to ensure normal bone acquisition and energy homeostasis.

Osteo-promoting effects of insulin-like growth factor I (IGF-I) in a mouse model of type 1 diabetes

OBJECTIVE

Using a streptozotocin (STZ)-induced mouse model of type 1 diabetes (T1D), we have previously demonstrated that long-term diabetes inhibits regenerative bone formation during tibial distraction osteogenesis (DO) and perturbs skeletal integrity by decreasing cortical thickness, bone mineral density and bone's resistance to fracture. Because long-standing T1D is also associated with a deficiency of insulin-like growth factor I (IGF-I), we examined the effects of systemic IGF-I treatment on skeletal microarchitecture and strength, as well as on bone formation in diabetic mice.

RESEARCH DESIGN AND METHODS

Streptozotocin-induced diabetic or control mice were treated with recombinant human IGF-I (rhIGF-I, 1.5mg/kg/day as subcutaneous infusion) or vehicle throughout a 14day DO procedure. Thereafter, trunk blood was assayed for glucose, insulin, rhIGF-I, mouse IGF-I and leptin. Bone formation in distracted tibiae was quantified. Effects on cortical bone strength and trabecular bone architecture were assessed by μCT analysis and three-point bend testing of contralateral femurs.

RESULTS

New bone formation during DO was reduced in diabetic mice but significantly improved with rhIGF-I treatment. The contralateral femurs of diabetic mice demonstrated significant reductions in trabecular thickness, yield strength and peak force of cortical bone, which were improved with rhIGF-I treatment. rhIGF-I also reduced intracortical porosity in control mice. However, treatment with rhIGF-I did not normalize serum glucose, or correct concurrent deficiencies of insulin or leptin seen in diabetes.

CONCLUSIONS

These findings demonstrate that despite persistent hyperglycemia, rhIGF-I promoted new bone formation and improved biomechanical properties of bone in a model of T1D, suggesting that it may be useful as a fracture preventative in this disease.

Assessment of Maxillary and Mandibular Bone Density in Controlled Type II Diabetes: A Computed Tomography Study

This study was undertaken to compare the bone density in nondiabetic and controlled type II diabetes patients using spiral computed tomography. A group of 40 edentulous men, comprising of 20 nondiabetics and 20 controlled type II diabetics between the ages of 50-65 years, were enrolled in the study. Glycemic control of the diabetic patients was assessed by glycosylated hemoglobin level. The controlled diabetic group had an HbA1c level between 6.1-8%. A radiographic stent was prepared by using chemically cured resin. Bone densities at trabecular, buccal, and lingual cortical regions of maxillary and mandibular edentulous arches were measured by a tomography machine. Mean bone density measurements were recorded in Hounsfield units. The data thus obtained from 10 sites of maxillary and mandibular arches were tabulated and analyzed using SPSS statistical software. This study showed no significant changes in bone density between the controlled diabetic and nondiabetic subjects. Within the limitation of this study, it can be concluded that bone density does not seem to be affected in controlled type II diabetics.

DNA-PK phosphorylation of IGFBP-3 is required to prevent apoptosis in retinal endothelial cells cultured in high glucose

PURPOSE

The goal of this study was to determine whether Compound 49b stimulates insulin-like growth factor binding protein-3 (IGFBP-3) activation in retinal endothelial cells (REC) through DNA-dependent protein kinase (DNA-PK).

METHODS

REC were grown in a normal glucose (5 mM) or high glucose medium (25 mM). Some cells were transfected with protein kinase A (PKA) siRNA, following treatment with 50 nM Compound 49b, a novel β-adrenergic receptor agonist. Cell proteins were extracted and analyzed for DNA-PK expression by Western blotting. Additional cells were treated with or without NU7441 (a specific DNA-PK inhibitor) prior to Compound 49b treatment. Cell lysates were processed for IGFBP-3 ELISA analyses and Western blotting to measure casein kinase 2 (CK2). Immunoprecipitation for total and phospho-IGFBP-3, cell proliferation and cell death measurements were done after transfection with the S(156)A IGFBP-3 mutation (key phosphorylation site involved in DNA-PK) plasmid DNA.

RESULTS

Compound 49b required DNA-PK to activate IGFBP-3 in REC. IGFBP-3 activation was significantly reduced following treatment with either the DNA-PK inhibitor or following transfection with the IGFBP-3 S(156)A mutant plasmid (P < 0.05). Significant increases in cell death and decreases in cell proliferation were also observed in cells transfected with the IGFBP-3 S(156)A mutant plasmid (P < 0.05). Casein kinase levels were not altered after treatment with NU7741 or Compound 49b.

CONCLUSIONS

Our findings suggest Compound 49b induces DNA-PK levels through PKA activity. DNA-PK is required for Compound 49b-induced IGFBP-3 expression, leading to inhibition of REC cell death.

Synergistic actions of insulin-sensitive and Sirt1-mediated pathways in the differentiation of mouse embryonic stem cells to osteoblast

Murine embryonic stem cells (mESCs) have the potential to differentiate into almost any type of cell, and hence, represent a useful biological resource for tissue engineering. The differentiation of mESCs into osteoblasts in vitro is usually dampened by simultaneous differentiation of adipocytes. Insulin exerts a profound effect on bone development through increased differentiation of osteoblasts and concurrent formation of adipocytes. Comparatively, Sirt1, which plays a crucial role in osteoblast differentiation, has been reported to down regulate adipocyte formation during osteoblast differentiation. This study analyzed the combined effects of insulin and Sirt1 on the differentiation of osteoblasts. Osteoblast differentiation was quantified by estimating the accumulation of mineralized matrix and expression of osteogenic genes. The present data show that the simultaneous action of the insulin and Sirt1-mediated pathways increased the efficiency of osteoblast differentiation. When the cells were tested for ALP activity and Alizarin red staining, there was a respective increase of ~180% and ~166% (P<0.05) compared to the control. Furthermore, the mRNA expression patterns of osteoprotegerin, osterix, runx2, and osteopontin were increased by 3.6, 2.3, 1.8, and 1.7-fold, respectively, with a concomitant decrease in the mRNA expression levels of adipocyte marker genes. Interestingly, blocking the effects of both Sirt1 and insulin resulted in decreased osteoblastogenesis (60%) and subsequent increased adipocyte differentiation (195%) (P<0.05). Moreover, immunoblotting analysis demonstrated that this activation was via an Akt-dependent pathway. In conclusion, the present data suggests an enhanced process of osteoblast differentiation that can be exploited further to improve mESC differentiation.

Determinants of undercarboxylated and carboxylated osteocalcin concentrations in type 1 diabetes

To determine whether undercarboxylated osteocalcin (UC-OC) or gamma-carboxyglutamic-carboxylated-type osteocalcin (GLA-OC) concentrations deviate from normal in type 1 diabetes (T1D), serum levels were compared between 115 subjects with T1D and 55 age-matched healthy controls. UC-OC and GLA-OC concentrations were similar between groups; however, in T1D, UC-OC correlated positively with markers of insulin exposure, either endogenously produced or exogenously administered.

INTRODUCTION

A study was conducted to determine whether dysregulation of circulating concentrations of UC-OC or GLA-OC occurs in patients with type 1 diabetes, a condition of insulin deficiency without insulin resistance.

METHODS

We measured serum concentrations of UC-OC and GLA-OC in 115 subjects with T1D, ages 14-40 years, and in 55 age-matched healthy control subjects. Relationships between UC-OC and GLA-OC concentrations and patient characteristics (gender and age), indices of glycemic control (hemoglobin A1c (HbA1c), fasting plasma glucose, C-peptide concentration, 3-day average glucose measured by a continuous glucose sensor, total daily insulin dose) and circulating indices of skeletal homeostasis (total calcium, 25-OH vitamin D, parathyroid hormone, insulin-like growth factor 1 (IGF-1), type 1 collagen degradation fragments (CTX), adiponectin, leptin) were examined. Between group differences in the concentrations of UC-OC and GLA-OC were the main outcome measures.

RESULTS

Although adiponectin levels were higher in the T1D group, between-group comparisons did not reveal statistically significant differences in concentration of UC-OC, GLA-OC, CTX or leptin between the T1D and control populations. Instead, by multivariate regression modeling, UC-OC was correlated with younger age (p < 0.001), higher CTX (p < 0.001), lower HbA1c (p = 0.013), and higher IGF-1 (p = 0.086). Moreover, within the T1D subgroup, UC-OC was positively correlated with C-peptide/glucose ratio (reflecting endogenous insulin secretion), with IGF-1 (reflecting intra-portal insulin sufficiency), and with total daily insulin dose.

CONCLUSIONS

In T1D, UC-OC appears to correlate positively with markers of insulin exposure, either endogenously produced or exogenously administered.

Exercise training enhances cardiac IGFI-R/PI3K/Akt and Bcl-2 family associated pro-survival pathways in streptozotocin-induced diabetic rats

BACKGROUND

Increased myocyte apoptosis in diabetic hearts has been previously reported. The purpose of this study was to evaluate the effects of exercise training on cardiac survival pathways in streptozotocin (STZ)-induced diabetic rats.

METHODS

Forty-eight male Wistar rats were randomly divided into control group (Control), STZ-induced (65 mg/kg, i.p.) diabetes (DM), and DM rats with moderate aerobic exercise training (DM-EX) on a treadmill 60 min/day, 5 days/week, for 10 weeks. Histopathological analysis, positive TUNEL assays and Western blotting were performed on the excised cardiac left ventricles from all three groups.

RESULTS

The components of cardiac survival pathway (insulin-like growth factor I (IGFI), IGFI-receptor (IGFI-R), phosphatidylinositol 3'-kinase (PI3K), and Akt) and the pro-survival Bcl-2 family proteins (Bcl-2, Bcl-xL, and p-BAD) were all significantly decreased in the DM group compared with the Control group whereas they were increased in the DM-EX group. In addition, the abnormal myocardial architecture, enlarged interstitial space and increased cardiac TUNEL-positive apoptotic cells were observed in the DM group, but they were reduced in the DM-EX group. The apoptotic key component, caspase-3, was significantly increased in the DM group relative to the Control group whereas it was decreased in the DM-EX group.

CONCLUSIONS

Exercise training enhances cardiac IGFI-R/PI3K/Akt and Bcl-2 family associated pro-survival pathways, which provides one of the new beneficial effects for exercise training in diabetes.

Novel functions for insulin in bone

The insulin-like growth factors (IGF) evolved in lower animals to enable a wide range of physiologic processes, including smell, food consumption, metabolism, growth, reproduction, and dormancy. These functions were accomplished by the actions of multiple related ligands that activated a common transmembrane receptor protein. In higher organisms, including mammals, the insulin and IGF ligands and their receptors evolved to function in a more circumscribed fashion. The contemporary model assigns IGFs as central regulators of cell proliferation, survival, and organism growth, whereas insulin's action dominates at the level of regulation of fuel accumulation, storage, and energy expenditure. Such a simplistic paradigm, however, obscures the fact that insulin and IGF-1 continue to exert overlapping roles in several physiologic processes. Indeed, recent studies have identified previously unappreciated skeletal actions of insulin, which suggests that insulin-responsive bone cells participate in the regulation of global energy homeostasis. These findings raise intriguing questions on the nature of the fuel sensing and processing mechanisms in bone and their relative importance to overall energy homeostasis in mammals. Answers to these questions should ultimately improve the ability to diagnose and manage patients with metabolic diseases such as diabetes and osteoporosis.

Noninsulin pharmacological management of type 1 diabetes mellitus

The injectable nature and other shortcomings of insulin have stimulated interest in studying the noninsulin pharmacological therapies to manage type 1 diabetes mellitus (T1DM). The purpose of this study is to conduct a systematic literature review of noninsulin pharmacological therapies for the management of T1DM. For this, the following PubMed search was conducted: Diabetes Mellitus, Type 1/therapy"[Mesh]

LIMITS

Review Sort by: Publication Date. After applying various inclusion and exclusion criteria, a total of 63 studies were reviewed. Based on this review, noninsulin pharmacological therapies can be divided into following classes: (1) Insulin-sensitizing agents (biguanides and thiazolidinediones), (2) gastrointestinal nutrient absorption modulators (α-Glucosidase inhibitors and amylin), (3) immunotherapeutic agents, (4) incretin-based therapies, (5) recombinant human insulin-like growth factors, and (6) other promising therapeutics. Some of these are already used either as monotherapy or adjuvant to insulin, whereas, to manage T1DM, the benefits and risks of the others are still under evaluation. Nonetheless, insulin still remains the cornerstone to manage the T1DM.

Bone density, body composition, and markers of bone remodeling in type 1 diabetic patients

OBJECTIVE

To assess bone mineral density (BMD), body composition by dual X-ray absorptiometry (DXA), and various biochemical markers of bone growth and resorption in a group of children with type 1 diabetes mellitus (T1DM).

PATIENTS AND METHODS

The study included 47 patients with T1DM and 30 age- and sex-matched controls. Anthropometric measurements, biochemical markers for bone formation, bone resorption and DXA were done for all patients and controls.

RESULTS

Of our diabetes patients, seven (16.7 %), three (7.3 %), and 17 (41.5%) met diagnostic criteria for osteopenia at the right femur, lumbar spine and total body, respectively. On the other hand, osteoporosis as defined by the WHO criteria was diagnosed in 21 patients (51.2%) at the total body by DXA. Lean body mass and lean fat ratio were lower, while, total fat mass, abdominal fat%, soft tissue fat mass%, and fat/lean ratio were higher in diabetics compared to controls. Also, our patients showed lower serum osteocalcin, osteoprotegerin, procollagen type 1, and higher urinary deoxypyridinoline. Pubertal (diabetics and controls) have higher BMD and BMC than prepubertal.

CONCLUSION

Diabetic patients had a low BMD after adjustment (Z score), low bone formation and high bone resorption markers. Diabetes control and increase in BMI leads to a decrease in the incidence of low bone mineral density. Diabetes causes an increase in body fat especially abdominal fat which leads to an increase in insulin resistance and decrease in lean mass.

Serum insulin-like growth factor-I is a marker for assessing the severity of vertebral fractures in postmenopausal women with type 2 diabetes mellitus

Although previous studies indicated that serum insulin-like growth factor-I (IGF-I) was inversely associated with the presence of vertebral fractures (VFs), little is known whether serum IGF-I is associated with multiple VFs. We report that serum IGF-I could be clinically useful for assessing the severity of VFs in type 2 diabetic postmenopausal women.

INTRODUCTION

The number of VFs is associated with the mobility and mortality of the elderly people. Although serum IGF-I is inversely associated with the presence of VFs, little is known about the relationship between serum IGF-I and multiple VFs.

METHODS

In this cross-sectional study, we recruited 479 men and 334 postmenopausal women with type 2 diabetes mellitus and measured serum IGF-I, bone mineral density, and bone turnover markers. Lateral X-ray films of the thoracic and lumbar spine were taken to diagnose the VF.

RESULTS

In postmenopausal women, serum IGF-I level was decreased when the number of VFs was increased [no VFs; 138 ± 51 ng/ml (mean ± SD) vs. one VF; 119 ± 42 (p = 0.006), two VFs; 103 ± 39 (p = 0.002), and three and more VFs; 91 ± 40 (p < 0.001)]. Multiple logistic regression analysis adjusted for age, duration of diabetes, body mass index, serum creatinine, and HbA(1c) showed that serum IGF-I level was inversely associated with the presence of one VF [odds ratio (OR) = 0.67, p = 0.029], two VFs (OR = 0.40, p = 0.017), as well as three and more VFs (OR = 0.27, p = 0.005). These associations were still significant after the additional adjustment for BMD at the lumbar spine. In contrast, no significant association of serum IGF-I level with VFs was found in men.

CONCLUSIONS

Serum IGF-I level was inversely associated with the number of prevalent VFs in postmenopausal women with type 2 diabetes, suggesting that serum IGF-I could be clinically useful for assessing the severity of VFs in the population.

GLUT4 in murine bone growth: from uptake and translocation to proliferation and differentiation

Skeletal growth, taking place in the cartilaginous growth plates of long bones, consumes high levels of glucose for both metabolic and anabolic purposes. We previously showed that Glut4 is present in growing bone and is decreased in diabetes. In the present study, we examined the hypothesis that in bone, GLUT4 gene expression and function are regulated via the IGF-I receptor (IGF-IR) and that Glut4 plays an important role in bone growth. Insulin and IGF-I actions on skeletal growth and glucose uptake were determined using mandibular condyle (MC) organ cultures and MC-derived primary cell cultures (MCDC). Chondrogenesis was determined by following proliferation and differentiation activities using immunohistochemical (IHC) analysis of proliferating cell nuclear antigen and type II collagen expression, respectively. Overall condylar growth was assessed morphometrically. GLUT4 mRNA and protein levels were determined using in situ hybridization and IHC, respectively. Glut4 translocation to the cell membrane was assessed using confocal microscopy analysis of GFP-Glut4 fusion-transfected cells and immunogold and electron microscopy on MC sections; glucose uptake was assayed by 2-deoxyglucose (2-DOG) uptake. Both IGF-I and insulin-stimulated glucose uptake in MCDC, with IGF-I being tenfold more potent than insulin. Blockage of IGF-IR abrogated both IGF-I- and insulin-induced chondrogenesis and glucose metabolism. IGF-I, but not insulin, induced Glut4 translocation to the plasma membrane. Additionally, insulin induced both GLUT4 and IGF-IR gene expression and improved condylar growth in insulin receptor knockout mice-derived MC. Moreover, silencing of GLUT4 gene in MCDC culture abolished both IGF-I-induced glucose uptake and chondrocytic proliferation and differentiation. In growing bone, the IGF-IR pathway stimulates Glut4 translocation and enhances glucose uptake. Moreover, intact Glut4 cellular levels and translocation machinery are essential for early skeletal growth.

Bone metabolism and fracture risk in type 2 diabetes mellitus [Review]

Osteoporosis and type 2 diabetes mellitus (T2DM) are now prevalent in aging and westernized societies, and adversely affect the health of the elderly people by causing fractures and vascular complications, respectively. Recent experimental and clinical studies show that both disorders are etiologically related to each other through the actions of osteocalcin and adiponectin. Meta-analyses of multiple clinical studies show that hip fracture risk of T2DM patients is increased to 1.4 to 1.7-folds, although BMD of the patients is not diminished. Vertebral fracture risk of T2DM patients is also increased, and BMD is not useful for assessing its risk. These findings suggest that bone fragility in T2DM depends on bone quality deterioration rather than bone mass reduction. Thus, surrogate markers are needed to replace the insensitivity of BMD in assessing fracture risks of T2DM patients. Markers related to advanced glycation end products as well as insulin-like growth factor-I may be such candidates, because these substances were experimentally shown to modulate bone quality in DM. In practice, it is important for physicians to assess fracture risk in T2DM patients by evaluating prior VFs and fracture histories using spine X-ray and interview, respectively, until the usefulness of surrogate markers is established.

Bone fragility in type 2 diabetes mellitus

The number of patients with osteoporosis or type 2 diabetes mellitus (T2DM) is increasing in aging and westernized societies. Both disorders predispose elderly people to disabling conditions by causing fractures and vascular complications, respectively. It is well documented that bone metabolism and glucose/fat metabolism are etiologically related to each other through osteocalcin action and Wnt signaling. Bone fragility in T2DM, which is not reflected by bone mineral density (BMD), depends on bone quality deterioration rather than bone mass reduction. Thus, surrogate markers are needed to replace the insensitivity of BMD in assessing fracture risks of T2DM patients. Pentosidine, the endogenous secretory receptor for advanced glycation endproducts, and insulin-like growth factor-I seem to be such candidates, although further studies are required to clarify whether or not these markers could predict the occurrence of new fractures of T2DM patients in a prospective fashion.

Insulin receptor signaling in osteoblasts regulates postnatal bone acquisition and body composition

Global energy balance in mammals is controlled by the actions of circulating hormones that coordinate fuel production and utilization in metabolically active tissues. Bone-derived osteocalcin, in its undercarboxylated, hormonal form, regulates fat deposition and is a potent insulin secretagogue. Here, we show that insulin receptor (IR) signaling in osteoblasts controls osteoblast development and osteocalcin expression by suppressing the Runx2 inhibitor Twist2. Mice lacking IR in osteoblasts have low circulating undercarboxylated osteocalcin and reduced bone acquisition due to decreased bone formation and deficient numbers of osteoblasts. With age, these mice develop marked peripheral adiposity and hyperglycemia accompanied by severe glucose intolerance and insulin resistance. The metabolic abnormalities in these mice are improved by infusion of undercarboxylated osteocalcin. These results indicate the existence of a bone-pancreas endocrine loop through which insulin signaling in the osteoblast ensures osteoblast differentiation and stimulates osteocalcin production, which in turn regulates insulin sensitivity and pancreatic insulin secretion.

Serum osteocalcin/bone-specific alkaline phosphatase ratio is a predictor for the presence of vertebral fractures in men with type 2 diabetes

We examined whether or not BMD or bone markers were useful for assessing the risk of vertebral fractures in 248 Japanese men with type 2 diabetes. We analyzed the relationships between bone markers (osteocalcin [OC], bone-specific alkaline phosphatase [BAP], urinary N-terminal cross-linked telopeptide of type-I collagen) or BMD and HbA(1c), urinary C-peptide, insulin-like growth factor-I (IGF-I), parathyroid hormone, 1,25(OH)(2) vitamin D, and the presence of prevalent vertebral fractures. Multiple regression analysis adjusted for age, body height, weight, duration of diabetes, and serum creatinine showed that serum OC and OC/BAP ratio were correlated negatively with HbA(1c) (P < 0.01) and positively with IGF-I (P < 0.01). Multivariate logistic regression analysis adjusted for the above parameters showed that serum OC/BAP ratio was inversely associated with the presence of vertebral fractures (odds ratio = 0.695, P < 0.05). This association was still significant after additional adjustment for lumbar or femoral neck BMD. Our results suggest that poor diabetic control and lower IGF-I level are linked to impaired bone formation and resultant reduction in OC/BAP ratio in men with type 2 diabetes. The OC/BAP ratio could be clinically useful for assessing the risk of vertebral fractures independent of BMD in diabetic men.

IGF-1 and IGF-binding proteins and bone mass, geometry, and strength: relation to metabolic control in adolescent girls with type 1 diabetes

Children and adolescents with poorly controlled type 1 diabetes mellitus (T1DM) are at risk for decreased bone mass. Growth hormone (GH) and its mediator, IGF-1, promote skeletal growth. Recent observations have suggested that children and adolescents with T1DM are at risk for decreased bone mineral acquisition. We examined the relationships between metabolic control, IGF-1 and its binding proteins (IGFBP-1, -3, -5), and bone mass in T1DM in adolescent girls 12-15 yr of age with T1DM (n = 11) and matched controls (n = 10). Subjects were admitted overnight and given a standardized diet. Periodic blood samples were obtained, and bone measurements were performed. Serum GH, IGFBP-1 and -5, glycosylated hemoglobin (HbA(1c)), glucose, and urine magnesium levels were higher and IGF-1 values were lower in T1DM compared with controls (p < 0.05). Whole body BMC/bone area (BA), femoral neck areal BMD (aBMD) and bone mineral apparent density (BMAD), and tibia cortical BMC were lower in T1DM (p < 0.05). Poor diabetes control predicted lower IGF-1 (r(2) = 0.21) and greater IGFBP-1 (r(2) = 0.39), IGFBP-5 (r(2) = 0.38), and bone-specific alkaline phosphatase (BALP; r(2) = 0.41, p < 0.05). Higher urine magnesium excretion predicted an overall shorter, lighter skeleton, and lower tibia cortical bone size, mineral, and density (r(2) = 0.44-0.75, p < 0.05). In the T1DM cohort, earlier age at diagnosis was predictive of lower IGF-1, higher urine magnesium excretion, and lighter, thinner cortical bone (r(2) >or=0.45, p < 0.01). We conclude that poor metabolic control alters the GH/IGF-1 axis, whereas greater urine magnesium excretion may reflect subtle changes in renal function and/or glucosuria leading to altered bone size and density in adolescent girls with T1DM.

Seropositivity to celiac antigens in asymptomatic children with type 1 diabetes mellitus: association with weight, height, and bone mineralization

BACKGROUND

Screening for celiac disease (CD) in children with diabetes is controversial because no studies have demonstrated metabolic complications in asymptomatic, seropositive subjects or beneficial effects of dietary intervention.

OBJECTIVE

We hypothesized that seropositivity to celiac antigens is associated with decreased growth and bone mineralization in asymptomatic diabetic children.

DESIGN/METHODS

Asymptomatic diabetic children were screened for seropositivity to tissue transglutaminase. Villous atrophy was assessed by small bowel biopsy in a subset of seropositive subjects. We compared measures of growth and bone mineralization in 30 seropositive subjects, and 34 matched seronegative controls.

RESULTS

Relative to seronegative controls, the seropositive subjects had reductions in insulin-like growth factor (IGF) binding protein 3 z scores (p < 0.05) and bone mineral density (BMD) z scores (p = 0.05). Weight, body mass index, IGF-I, and bone mineral apparent density (BMAD) z scores were marginally lower, but height z scores were comparable. Seropositive patients with severe villous atrophy had lower weight (-0.91 SDs), height (-1.1 SDs), BMD (-2.0 SDs), and BMAD (-2.0 SDs) z scores and significant increases in parathyroid hormone (all p < 0.05). Four patients with severe villous atrophy maintained strict gluten restriction for at least 12 months. Gluten restriction increased BMD and BMAD z scores.

CONCLUSIONS

High-titer seropositivity to celiac antigens is associated with reductions in weight and BMD in diabetic children, justifying screening of high-risk patients. Results suggest that biopsy is required to confirm the diagnosis and assess the severity of CD; those with severe villous atrophy are more likely to have growth failure and osteopenia. Gluten restriction may reverse these complications.

Diabetes mellitus and prostate cancer risk

BACKGROUND

Epidemiological evidence suggests that diabetes mellitus (DM) is associated with a decrease in risk for prostate cancer (PCa). The objective of this study was to examine the association between PCa risk and several characteristics of DM (duration, age at diagnosis, treatment) in data from two population-based, case-control studies of PCa.

METHODS

PCa cases (n = 1,752), and controls (n = 1,644) were residents of King County, Washington identified using the Surveillance, Epidemiology, and End Results Seattle-Puget Sound cancer registry and random digit dialing, respectively. The majority of PCa patients had localized stage disease (78%). Using self-reported on DM, logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (95% CI) for associations between DM characteristics and PCa risk.

RESULTS

After adjustment for confounding factors, DM status was not significantly associated with PCa risk (OR = 0.98; 95% CI = 0.76-1.27). However, early-onset DM (diagnosed before age 30) showed a significant inverse association with PCa risk (OR = 0.27; 95% CI = 0.07-0.97). Time since DM diagnosis (median = 6 years) and DM treatment types (i.e., diet changes, oral medications, and insulin) did not show significant associations with PCa risk.

CONCLUSIONS

These data suggest that DM is not associated with PCa risk; however, early-onset DM, possibly reflecting insulin dependent DM (type 1), may be an important component of the previously reported inverse association between DM on PCa risk, but these findings are based on a small number of observations and require further investigation.

Serum insulin-like growth factor-I level is associated with the presence of vertebral fractures in postmenopausal women with type 2 diabetes mellitus

Multivariate logistic regression analysis showed that serum IGF-I level was significantly lower in postmenopausal diabetic women with vertebral fractures than in those without fractures. Serum IGF-I level could be clinically useful for assessing the risk of vertebral fractures independent of BMD in postmenopausal women with type 2 diabetes.

INTRODUCTION

We investigated the relationships among serum IGF-I and C-peptide levels, BMD, and vertebral fractures in postmenopausal women with type 2 diabetes.

METHODS

A total of 131 postmenopausal women with type 2 diabetes were consecutively recruited, and radiographic and biochemical characteristics were collected.

RESULTS

Either IGF-I or C-peptide was not correlated with BMD at any site or bone metabolic markers, such as osteocalcin (OC) and urinary N-terminal cross-linked telopeptide of type-I collagen (uNTX). However, serum IGF-I level was significantly lower in subjects with vertebral fractures than in those without fractures (mean +/- SD: 106.9 +/- 50.0 vs. 142.8 +/- 50.8 ng/ml, p = 0.0006). When multivariate logistic regression analysis was performed with the presence of vertebral fractures as a dependent variable and serum IGF-I adjusted for the parameters described above as independent variables, IGF-I was selected as an index affecting the presence of vertebral fractures [odds ratio = 0.436, 95% confidential interval 0.234-0.814 per SD increase, p = 0.0092]. This significance was almost the same after additional adjustment for lumbar BMD or C-peptide.

CONCLUSIONS

Serum IGF-I level could be clinically useful for assessing the risk of vertebral fractures independent of BMD in postmenopausal women with type 2 diabetes.

Efficacy and safety of mecasermin rinfabate

There has been interest in using recombinant human (rh) insulin-like growth factor (IGF)-I (rhIGF-I) to treat short stature, either alone or in combination with its binding protein (insulin-like growth factor binding protein [IGFBP]-3). IGF-I has been shown to increase growth velocity in children with IGF deficiency, either as a result of growth hormone insensitivity syndrome (GHIS) or IGF gene deletion. However, there have been adverse events, particularly hypoglycaemia, reported with administration of unbound rhIGF-I. In addition, the serum half-life of unbound rhIGF-I is shorter when administered to patients with GHIS, who have low serum concentrations of its binding proteins IGFBP-3 and acid-labile subunit (ALS), than when administered to normal volunteers or to the patient with an IGF-I gene deletion (who had normal levels of IGFBP-3). iPlex (mecasermin rinfabate), an equimolar mixture of IGF-I and its binding protein IGFBP-3, was developed to prolong the half-life and to counteract acute adverse events (particularly hypoglycaemia) associated with administration of IGF-I. Although there are no published data on the efficacy of mecasermin rinfabate in treating growth disorders, it does appear that mecasermin rinfabate has a longer half-life in patients with GHIS than unbound IGF-I, and fewer reports of adverse events (including hypoglycaemia) when administered to patients with diabetes.

IGF-1 is an independent risk factor for anemia in diabetic pre-dialysis patients

BACKGROUND

We investigated whether the presence of diabetes mellitus (DM) was related to the degree of the anemia in predialytic patients with renal failure and what was the most relevant factor for anemia in patients with chronic kidney disease (CKD) from DM (DM-CKD).

METHODS

Seventy seven patients (47 predialytic patients with long-term type 2 DM (DM-CKD) and 30 predialytic patients whose disease was due to other causes (non DM-CKD)) were enrolled in this study. The blood hemoglobin (Hb) and hematocrit, and the creatinine, ferritin, vitamin B12, folate, iron, LDH, albumin, hs-CRP, intact-PTH, erythropoietin, leptin and Insulin-like growth factor I (IGF-1) levels were measured using standard methods. The estimated GFR was calculated using the abbreviated MDRD equation.

RESULTS

The two groups did not significantly differ as to age, gender, the serum creatinine level and the inflammatory status. The Hb level was significantly lower in the DM-CKD patients than that in the non DM-CKD patients (8.5+/-1.7 g/dL vs 9.6+/-1.6 g/dL, respectively, p=0.01). The Hb level was significantly lower in the DM-CKD patients who were being treated with ACE inhibitors (the DM-ACE patients) than that in the non DM-CKD patients who were being treated with ACE inhibitors (the non DM-ACE patients) (8.5+/-1.5 g/dL vs 10.8+/-1.6 g/dL, respectively, p=0.001). Multiple regression analysis indicated that serum IGF-1 concentration was independently associated with the Hb level (beta=0.425, p=0.02) in the DM-CKD patients.

CONCLUSIONS

The Hb concentration was significantly lower in the DM-CKD patients than that in the non DM-CKD patients. It was independently associated with the serum IGF-1 concentration in the DM-CKD patients.

Evidence for distinct effects of GH and IGF-I in the metabolic syndrome

AIMS

The metabolic syndrome is a cluster of cardiovascular risk factors which include central obesity, dyslipidaemia, glucose intolerance and hypertension. These risk factors are common in patients with growth hormone (GH) deficiency, suggesting a role for the somatotropic axis in the development of metabolic syndrome.

METHODS

We used factor analysis to investigate the relationships linking serum levels of GH and insulin-like growth factor I (IGF-I) to metabolic syndrome variables (high-density lipoprotein cholesterol, triglycerides, fasting glucose, blood pressure and waist circumference). We studied 359 men and 388 women from the Data from an Epidemiological Study on the Insulin Resistance syndrome (DESIR). Their age range was 30-64 years.

RESULTS

Three independent latent factors explained 61% of the total variance in women and four factors explained 73% in men. In both men and women, IGF-I showed a strong positive correlation with the lipid factor and a negative correlation with the obesity/glucose factor. In women, GH showed a strong negative correlation with the obesity/glucose factor but not the lipid factor. In men, GH was unrelated to the lipid and obesity/glucose factors. The blood pressure factor was not related to GH or IGF-I. In contrast with IGF-I, GH was significantly lower in women with metabolic syndrome (1575 +/- 449 pg/ml) than in the other women (2121 +/- 520 pg/ml, P = 0.002). No significant difference was observed in men for GH or IGF-I.

CONCLUSION

Our results support a link between the somatotropic axis and several features of the metabolic syndrome, and suggest distinct effects of GH and IGF-I on these parameters.

Association of serum levels of IGF-I and IGFBP-1 with renal function in patients with type 2 diabetes mellitus

OBJECTIVE

Our aim was to determine whether serum Insulin-like growth factor-I (IGF-I) and Insulin-like growth factor binding protein-1 (IGFBP-1) levels were different between type 2 diabetic patients and non-diabetic control group. We also aimed to establish any relationship that might exist between the serum IGF-I and IGFBP-1 levels with the urinary albumin excretion (UAE), creatinine clearance and urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion (as a marker of renal tubular dysfunction) and other parameters (such as age, duration of diabetes, treatment, etc.) in patients with type 2 diabetes mellitus (DM).

DESIGN

Fifty-nine type 2 diabetic patients and thirty-one non-diabetic controls were included in this study.

RESULTS

Mean serum IGF-I levels in diabetic patients were lower than the non-diabetic controls (158+/-12 vs. 287+/-26microg/l), (p<0.001). Serum IGFBP-1 levels were also higher in type 2 diabetic patients compared to the control group (67+/-5 vs. 35+/-4microg/l), (p<0.001). No relationship was obtained between IGF-I and IGFBP-1 levels with neither UAE nor urinary NAG excretion. A significant negative relationship was observed between creatinine clearance and serum IGFBP-1 level (r=-0.39, p=0.004). In multiple regression analysis IGF-I was independently and negatively associated with age and insulin treatment. On the other hand, IGFBP-1 was negatively related with creatinine clearance and positively related with the duration of diabetes.

CONCLUSION

These results suggest that type 2 DM leads to a decrease in the IGF-I while elevating the IGFBP-1 levels. Further studies are needed to clarify a potential role of increased levels of IGFBP-1 in decreased creatinine clearance in type 2 DM.

Effects of short-term physical training on the liver IGF-I in diabetic rats

To investigate the influence of short-term physical training on IGF-I concentrations in diabetic rats, male wistar rats were distributed into four groups: sedentary control, trained control, sedentary diabetic and trained diabetic. Diabetes was induced by Alloxan (32 mg/kg b.w.) and training protocol consisted of swimming 1 h/day, 5 days/week, during 4 weeks, supporting 5% b.w. At the end of this period, rats were sacrificed and blood was collected for determinations of serum glucose, insulin, albumin, IGF-I and hematocrit. Liver samples were used to determine glycogen, protein, DNA and IGF-I concentrations. Diabetes reduced insulin and IGF-I concentrations in blood and liver protein, ratio protein/DNA and IGF-I concentrations in liver and increased glycemia. Physical training reduced serum glucose and recovered hepatic glycogen stores in diabetic rats and reduced serum and liver IGF-I concentrations. In conclusion, short-term physical training improved the metabolic conditions of diabetic rats, despite of impairing liver and blood IGF-I concentrations.

TISSUE-SPECIFIC REGULATION OF INSULIN-LIKE GROWTH FACTORS AND INSULIN-LIKE GROWTH FACTOR BINDING PROTEINS IN MALE DIABETIC RATS IN VIVO AND IN VITRO

1. Insulin-like growth factors (IGFs) are associated with the development of diabetes mellitus. The liver, kidney and heart have been implicated as important organs in the onset of diabetes mellitus. However, the effect of diabetes on the IGF system in these organs has not been fully described. Thus, we investigated changes in IGF-I, IGF-II and IGF binding proteins (IGFBPs) in male steptozotocin-induced diabetic rats, as well as in a high glucose-induced in vitro model. 2. Serum levels of IGF-I were decreased, but the levels of IGF-II were increased, in diabetic rats compared with controls. The expression of IGFBP-3 in the serum was markedly decreased; in contrast, the expression of IGFBP-1 and -2 was increased in diabetic rats. The expression of IGF-I, IGF-II, IGFBP-1, IGFBP-2, IGFBP-3 and IGFBP-4 in the liver of the diabetic group was similar to that in the serum of diabetic rats. 3. In heart tissue of the diabetic group, IGF-I levels were decreased, but IGF-II levels were increased. In addition, the expression of IGFBP-3, IGFBP-1 and IGFBP-2 was decreased in diabetic rats. 4. In the kidney of the diabetic group, IGF-I and IGF-II levels were increased. There was only slight expression of IGFBP-3 in the kidney and this was not altered in diabetic rats. Levels of IGFBP-1 and -2 were markedly increased in the kidney of diabetic rats. 5. Insulin treatment recovered the changes in expression of IGF-I, IGF-II and IGFBPs in the serum, liver, heart and kidney. In the liver, heart and kidney, the expression of the insulin receptor was increased in male diabetic rats. 6. In conclusion, diabetes tissue-specifically alters the IGF system in the liver, heart and kidney in rats; this effect can be recovered by insulin treatment.