Suggestion of a deficient osteoblastic function in diabetes mellitus: the possible cause of osteopenia in diabetics

Novel insights into the complex architecture of osteoporosis molecular genetics

Osteoporosis is a prevalent osteodegenerative disease and silent killer linked to a decrease in bone mass and decline of bone microarchitecture, due to impaired bone matrix mineralization, raising the risk of fracture. Nevertheless, the process of bone matrix mineralization is still an unsolved mystery. Osteoporosis is a polygenic disorder associated with genetic and environmental risk factors; however, the majority of genes associated with osteoporosis remain largely unknown. Several signaling pathways regulate bone mass; therefore, dysregulation of a single signaling pathway leads to metabolic bone disease owing to high or low bone mass. Parathyroid hormone, core-binding factor α-1 (Cbfa1), Wnt/β-catenin, the receptor activator of the nuclear factor kappa-B (NF-κB) ligand (RANKL), myostatin, and osteogenic exercise signaling pathways play pivotal roles in the regulation of bone mass. The myostatin signaling pathway increases bone resorption by activating the RANKL signaling pathway, whereas osteogenic exercise inhibits myostatin and sclerostin while inducing irisin that consequentially activates the Cbfa1 and Wnt/β-catenin bone formation pathways. The aims of this review are to summarize what is known about osteoporosis-related signaling pathways; define the role of these pathways in osteoporosis drug discovery; focus light on the link between bone, muscle, pancreas, and adipose integrative physiology and osteoporosis; and underline the emerging role of osteogenic exercise in the prevention of, and care for, osteoporosis, obesity, and diabetes.

Effects of GLP-1 receptor analogue liraglutide and DPP-4 inhibitor vildagliptin on the bone metabolism in ApoE-/- mice

Background

It has been reported that glucagon-like peptide-1 (GLP-1) can alleviate diabetic osteoporosis (DOP). This study was to investigate the effects of GLP-1RA liraglutide and dipeptidyl peptdase-4 (DPP-4) inhibitor vildagliptin on the advanced glycation end products (AGEs)-induced bone injury in ApoE^-/- mice with euglycemia.

Methods

The bone markers OC, PINP, PTH, TRACP and CTX, the mRNA and protein expressions of RAGE in the femur, and the femoral morphology index were determined to evaluate whether the osteoporosis was improved by liraglutide or vildagliptin.

Results

AGEs adversely affected the bone metabolism, characterized by reduced OC and increased CTX. However, vildagliptin reduced AGEs and increased OC, and liraglutide significantly decreased AGEs and PTH. Both vildagliptin and liraglutide had no effects on the bone metrology and RAGE expression in the femurs of ApoE^-/- mice.

Conclusions

The elevated AGEs may exacerbate osteogenesis and increase bone resorption, and vildagliptin/liraglutide may improve bone metabolism.

Osteocalcin value to identify subclinical atherosclerosis over atherosclerotic cardiovascular disease (ASCVD) risk score in middle-aged and elderly Chinese asymptomatic men

BACKGROUND

Our study examined whether osteocalcin contributed to identifying carotid intima-media thickness (C-IMT) over the atherosclerotic cardiovascular disease (ASCVD) risk score.

METHODS

We recruited 618 middle-aged and elderly men from communities in Shanghai. Serum osteocalcin levels were determined using an electrochemiluminescence immunoassay. C-IMT was measured by ultrasonography.

RESULTS

The study included 245 men with low ASCVD risk and 373 men with moderate-to-high ASCVD risk. Serum osteocalcin levels were lower in the moderate-to-high risk vs. low risk men (p=0.042). Multivariate stepwise regression analysis showed that body mass index (BMI) and glycated hemoglobin were predictors for reduced osteocalcin levels (both p<0.001). Among all subjects, the proportion with an elevated C-IMT was higher in the low-osteocalcin group than in the high-osteocalcin group (p=0.042), and the significance of this result was greater when considering only subjects with a moderate-to-high ASCVD risk (p=0.011). The recognition rate of elevated C-IMT was superior with both low osteocalcin and moderate-to-high ASCVD risk vs. either parameter alone (p<0.001 and p=0.015, respectively). Osteocalcin was independently and inversely associated with elevated C-IMT after adjusting for the 10-year ASCVD risk score (p=0.004). The negative relationship remained statistically significant in subjects with a moderate-to-high ASCVD risk in particular (standardized β=-0.104, p=0.044).

CONCLUSIONS

In middle-aged and elderly men, serum osteocalcin levels strengthen identifying subclinical atherosclerosis over ASCVD risk score, especially among subjects with a moderate-to-high ASCVD risk.

Effect of Sodium-Glucose Co-transporter 2 Inhibitors on Bone Metabolism and Fracture Risk

The effect of anti-diabetic medications on bone metabolism has received increasing attention, considering that type 2 diabetes mellitus is a common metabolic disorder with adverse effects on bone metabolism. Sodium-glucose co-transporter 2 (SGLT2) inhibitors are novel anti-diabetic medications that prevent glucose resorption at the proximal convoluted tubules in the kidney, increasing urinary glucose excretion, and decreasing the blood glucose level. The superiority of SGLT2 inhibitors shows in reducing the glucose level independent of insulin secretion, lowering the risk of hypoglycemia, and improving cardiovascular outcomes. SGLT2 inhibitors have been associated with genital mycotic infections, increased risk of acute kidney injury, dehydration, orthostatic hypotension, and ketoacidosis. Moreover, the effect of SGLT2 inhibitors on bone metabolism and fracture risk has been widely taken into consideration. Our review summarizes the results of current studies investigating the effects of SGLT2 inhibitors on bone metabolism (possibly including increased bone turnover, disrupted bone microarchitecture, and reduced bone mineral density). Several mechanisms are probably involved, such as bone mineral losses due to the disturbed calcium and phosphate homeostasis, as confirmed by an increase in fibroblast growth factor 23 and parathyroid hormone levels and a decrease in 1,25-dihydroxyvitamin D levels. SGLT2 inhibitors might indirectly increase bone turnover by weight loss. Lowering the blood glucose level might ameliorate bone metabolism impairment in diabetes. The effect of SGLT2 inhibitors on bone fractures remains unclear. Evidence indicating the direct effect of SGLT2 inhibitors on fracture risk is lacking and increased falls probably contribute to fractures.

Serum Osteocalcin Levels in Children With Nonalcoholic Fatty Liver Disease

OBJECTIVES

The aim of the study was to investigate the relationship between osteocalcin and nonalcoholic fatty liver disease (NAFLD) in children with obesity.

METHOD

60 obese children with NAFLD were taken as a patient group and 60 obese children and normal liver with matching age, sex, and body mass index were taken as a control group. Anthropometric measurements, abdominal ultrasonography for diagnosis and grading of NAFLD, and laboratory investigations in the form of liver function tests, lipid profile, fasting serum glucose and insulin, and serum osteocalcin levels were done for all children. Patients with NAFLD were further divided into patients with metabolic syndrome (MS) and patients without MS.

RESULTS

Age of NAFLD children was (10.55 ± 2.71), 20 boys and 40 girls, whereas age of children in control group was (10.05 ± 3.51), 24 boys and 36 girls (P > 0.05). Patients with NAFLD showed significant increase in waist and hip circumference, alanine aminotransferase, alkaline phosphatase, total cholesterol, triglycerides, insulin resistance (IR), fasting serum glucose, and insulin, but lower serum osteocalcin level than control group. Serum osteocalcin level is inversely correlated with waist circumference, triglyceride, liver enzymes, fasting serum insulin, fasting serum glucose, IR, and grades of fatty liver. Increase in alanine aminotransferase, total cholesterol, triglycerides, fasting insulin, and IR went with increase in degree of hepatic steatosis. Serum osteocalcin level <44.5 ng/mL is a good predictor for severity of hepatic steatosis with sensitivity and specificity of 80%.

CONCLUSIONS

Osteocalcin plays an important role in glucose and lipid metabolism for protection against NAFLD occurrence and progression. Moreover, it could be a useful marker for progression of NAFLD in children with obesity.

Effect of Dipeptidyl Peptidase-4 Inhibitors on Bone Metabolism and the Possible Underlying Mechanisms

Diabetes mellitus has been demonstrated to be closely associated with osteoporosis. Accordingly, hypoglycemic therapy is considered effective in treating metabolic bone disease. Recently, the effects of dipeptidyl peptidase-4 (DPP-4) inhibitors, a new type of antidiabetic drug, on bone metabolism have been widely studied. This review mainly describes the effects of DPP-4 inhibitors on bone metabolism, including their effects on bone mineral density, bone quality, and fracture risk. In addition, the potential underlying mechanisms are discussed. Based on the current progress in this research field, DPP-4 inhibitors have been proved to reduce fracture risk. In addition, sitagliptin, a strong and highly selective DPP-4 inhibitor, showed its beneficial effects on bone metabolism by improving bone mineral density, bone quality, and bone markers. With regard to the potential underlying mechanisms, DPP-4 inhibitors may promote bone formation and reduce bone resorption through DPP-4 substrates and DPP-4-related energy metabolism. Vitamin D and other related signaling pathways also play a role in affecting bone metabolism. Although these assumptions are controversial, they provide a translational pharmacology approach for the clinical use of DPP-4 inhibitors in the treatment of metabolic diseases. Prior to the use of these drugs in clinic, further studies should be conducted to determine the appropriate type of DPP-4 inhibitor, the people who would benefit the most from this therapy, appropriate dose and duration, and the effects of the treatment.

Influence of uncontrolled diabetes mellitus on periodontal tissues during orthodontic tooth movement: a systematic review of animal studies

Diabetes mellitus (DM) may adversely affect periodontal tissues during orthodontic tooth movement (OTM). The aim of this review is to systematically analyze and review animal studies investigating the effect of DM on periodontal tissues during OTM. An electronic search was conducted via PubMed/Medline, Google Scholar, Embase, ISI Web of Knowledge, and Cochrane Central Register of Controlled Trials (CONTROL) using the keywords “diabetes,” “orthodontics,” and “tooth movement” for studies published between January 2000 and August 2016. After elimination of duplicate items, the primary search resulted in 89 articles. After exclusion of irrelevant articles on the basis of abstract and title, full texts of 25 articles were read to exclude additional irrelevant studies. Seven animal studies were included in this review for qualitative analysis. When compared to healthy animals, more bone resorption and diminished bone remodeling were observed in diabetic animals in all studies. Furthermore, DM decreased the rate of OTM in one study, but in another study, DM accelerated OTM. DM may adversely affect bone remodeling and tooth movement during application of orthodontic forces. However, a number of potential sources of bias and deficiencies in methodology are present in studies investigating the association between OTM and DM. Hence, more long-term and well-designed studies are required before the exact mechanism and impact of DM on outcomes of orthodontic treatment is understood.

Effect of targeted delivery of bone morphogenetic protein-2 on bone formation in type 1 diabetes

PURPOSE

Bone formation and healing are diminished in experimental type 1 diabetes. The present study investigated whether controlled local release of recombinant human bone morphogenetic protein 2 (rhBMP-2) stimulates bone defect healing in diabetes as a consequence of its anabolic effects on bone.

MATERIALS AND METHODS

Bilateral experimental circular bone defects were created in the temporal bones of 64 BALB/cByJ mice. Defects were treated with acellular collagen sponge plus 0.4 or 1.8 μg of rhBMP-2 per defect, and untreated defects served as controls. The healing of the defects over a 14-day period in diabetic and nondiabetic mice was analyzed histomorphometrically.

RESULTS

Diabetes inhibited bone formation in both untreated and BMP-treated bone defects. Controlled local release of rhBMP-2 significantly stimulated bone formation in diabetic animals, bringing it nearly to normal levels, and enhanced bone regeneration in normal animals.

CONCLUSION

Recombinant human BMP-2 may be beneficial in treating deficient intramembranous bone formation in diabetes.

Effects of diabetes on tooth movement and root resorption after orthodontic force application in rats

OBJECTIVE

To investigate the effects of diabetes on orthodontic tooth movement and orthodontically induced root resorption in rats.

SETTING AND SAMPLE POPULATION

Twenty-three 10-week-old male Sprague-Dawley rats divided into control (n = 7), diabetes (n = 9), and diabetes + insulin (n = 7) groups.

MATERIALS AND METHODS

Diabetes was induced by administering a single intraperitoneal injection of streptozotocin. Rats with a blood glucose level exceeding 250 mg/dl were assigned to the diabetes group. Insulin was administered daily to the diabetes + insulin group. A nickel-titanium closed-coil spring of 10 g was applied for 2 weeks to the maxillary left first molar in all rats to induce mesial tooth movement. Tooth movement was measured using microcomputed tomography images. To determine the quantity of root resorption, the mesial surfaces of the mesial and distal roots of the first molar were analyzed using both scanning electron microscopy and scanning laser microscopy.

RESULTS

After 2 weeks, the amount of tooth movement in the diabetic rats was lower than that in the control rats. Root resorption was also significantly lower in the diabetic rats. These responses of the rats caused by diabetes were mostly diminished by insulin administration.

CONCLUSIONS

Diabetes significantly reduced orthodontic tooth movement and orthodontically induced root resorption in rats. The regulation of blood glucose level through insulin administration largely reduced these abnormal responses to orthodontic force application.

The impact of diabetes and diabetes medications on bone health

Patients with type 2 diabetes mellitus (T2DM) have an increased risk of fragility fractures despite increased body weight and normal or higher bone mineral density. The mechanisms by which T2DM increases skeletal fragility are unclear. It is likely that a combination of factors, including a greater risk of falling, regional osteopenia, and impaired bone quality, contributes to the increased fracture risk. Drugs for the treatment of T2DM may also impact on the risk for fractures. For example, thiazolidinediones accelerate bone loss and increase the risk of fractures, particularly in older women. In contrast, metformin and sulfonylureas do not appear to have a negative effect on bone health and may, in fact, protect against fragility fracture. Animal models indicate a potential role for incretin hormones in bone metabolism, but there are only limited data on the impact of dipeptidyl peptidase-4 inhibitors and glucagon-like peptide-1 agonists on bone health in humans. Animal models also have demonstrated a role for amylin in bone metabolism, but clinical trials in patients with type 1 diabetes with an amylin analog (pramlintide) have not shown a significant impact on bone metabolism. The effects of insulin treatment on fracture risk are inconsistent with some studies showing an increased risk and others showing no effect. Finally, although there is limited information on the latest class of medications for the treatment of T2DM, the sodium-glucose co-transporter-2 inhibitors, these drugs do not seem to increase fracture risk. Because diabetes is an increasingly common chronic condition that can affect patients for many decades, further research into the effects of agents for the treatment of T2DM on bone metabolism is warranted. In this review, the physiological mechanisms and clinical impact of diabetes treatments on bone health and fracture risk in patients with T2DM are described.

Serum osteocalcin levels are inversely associated with plasma glucose and body mass index in healthy Chinese women

AIM

Osteocalcin, a biochemical marker of bone formation, has been suggested to be involved in the regulation of energy metabolism. The aim of this study was to investigate the possible association between serum osteocalcin and markers of glucose and lipid metabolism in a large sample of healthy Chinese women.

METHODS

A total of 2032 healthy Chinese women in Shanghai, aged 20-94 (including 1396 discovery-study subjects and 636 postmenopausal women for a reduplication analysis) were recruited. Their serum osteocalcin, calcium and the relevant measurements were analyzed. A Spearman correlation analysis was performed between osteocalcin and the other markers of energy metabolism including triglyceride, total cholesterol, fasting plasma glucose (FPG), serum insulin, body mass index and homeostasis model assessment-insulin resistance. Separate multiple regression analyses were performed with data from the discovery and reduplication subjects to determine whether serum osteocalcin concentration was an independent predictor of the glucose or lipid metabolism markers.

RESULTS

For the discovery-study subjects, serum osteocalcin was found to be negatively associated with weight (r=-0.08, P=0.002), BMI (-0.13, P<0.001) and FPG (r=-0.13, P=0.001). Similar results were also found in the reduplication subjects (weight: r=-0.19, P=0.016; BMI: r=-0.23, P=0.003; FPG: r=-0.28, P<0.001). In the multiple regression analysis, serum osteocalcin was revealed as a potential independent predictor for FPG (β=-0.07 and -0.210 for discovery and reduplication, respectively, P<0.01) and BMI (β=-0.127 and -0.299 for discovery and reduplication, respectively, P<0.01).

CONCLUSION

Serum osteocalcin is negatively associated with weight BMI and FPG in healthy Chinese women. Therefore, osteocalcin might contribute to obesity and diabetes.

Osteocalcin and vitamin D status are inversely associated with homeostatic model assessment of insulin resistance in Canadian Aboriginal and white women: the First Nations Bone Health Study

OBJECTIVE

Osteocalcin, a protein synthesized by osteoblasts, and vitamin D status have independently been implicated in energy metabolism and glucose regulation. This study was conducted to simultaneously explore the relationships among osteocalcin, vitamin D status and indicators of glucose metabolism and adiposity in a mixed-ethnicity cohort of adult women.

DESIGN

Cross-sectional.

METHODS

Aboriginal and white women (n=368) over 25 years of age (45.3±13.6 years) were studied for measures of osteocalcin and 25-hydroxy vitamin D [25(OH)D] plus glucose metabolism including glucose, insulin, C-peptide, hemoglobin A1c (HbA1c) and homeostatic model assessment of insulin resistance (HOMA-IR). Measures of adiposity included body mass index (BMI) plus total body fat and trunk fat from dual-energy X-ray absorptiometry.

RESULTS

Aboriginal women had higher BMI, fat and markers of dysglycemia. Osteocalcin was not different between groups, but 25(OH)D was lower in Aboriginal women. Osteocalcin was inversely related to all five parameters of glucose metabolism, whereas 25(OH)D was inversely related to insulin, C-peptide and HOMA-IR. After accounting for age, ethnicity or adiposity using regression analyses, glucose, HbA1c and HOMA-IR were inversely related to both osteocalcin and 25(OH)D. However, only 25(OH)D was inversely related to C-peptide, and neither osteocalcin nor 25(OH)D was related to insulin.

CONCLUSIONS

These data from a unique mixed Aboriginal and white population suggest that both vitamin D and osteocalcin are involved in glucose control.

Low serum osteocalcin level is a potential marker for metabolic syndrome: results from a Chinese male population survey

Osteocalcin has been recognized as a bone-derived hormone to regulate energy metabolism recently. Little is known about the role of osteocalcin as regards metabolic syndrome (MetS) in a Chinese population. Components of MetS, osteocalcin, body mass index (BMI), and prevalence of MetS were assessed in 2344 men aged 20 to 69 years who participated in the population-based Fangchenggang Area Male Health and Examination Survey, which was carried out in Guangxi province of China from September 2009 to December 2009. Osteocalcin had a statistically significant positive correlation with high-density lipoprotein cholesterol and a negative relationship with blood pressure, glucose, triglycerides, waist circumference, and BMI after adjustment for age (all P < .001). The strongest correlation was observed between osteocalcin and BMI (r = -0.26). In a multivariate analysis, decreased odds ratios (ORs) for the MetS and its components as well were observed from the first to the fourth osteocalcin quartiles. After adjustment for BMI, the OR decreased substantially. Statistically significant difference still existed in MetS (OR, 1.77; 95% confidence interval [CI], 1.10-2.85), hypertriglyceridemia (OR, 1.66; 95% CI, 1.22-2.27), hyperglycemia (OR, 1.42; 95% CI, 1.05-1.92), and low high-density lipoprotein cholesterol (OR, 1.83; 95% CI, 1.03-3.24) when these risks were compared in the lowest quartile of osteocalcin levels with those in the highest quartile. In a Chinese male population, we firstly identified an inverse association of serum osteocalcin levels with MetS, independent from the well-known MetS risk factors. This may represent a further mechanism for the elevated cardiovascular disease or type 2 diabetes mellitus risk.

The relationship of serum osteocalcin concentration to insulin secretion, sensitivity, and disposal with hypocaloric diet and resistance training

CONTEXT

Bone has recently been described as exhibiting properties of an endocrine organ by producing osteocalcin that increases insulin sensitivity and secretion in animal models.

OBJECTIVE AND DESIGN

We aimed to evaluate circulating osteocalcin in association with insulin sensitivity and insulin secretion in three different studies in nondiabetic subjects: one cross-sectional study in 149 men (using minimal model), and two longitudinal studies in two independent groups (one formed by 26 women, and the other by 9 men and 11 women), after a mean of 7.3 and 16.8% weight loss, and after a mean of 8.7% weight loss plus regular exercise.

RESULTS

In the cross-sectional study, circulating osteocalcin was associated with insulin sensitivity, mainly in lean subjects, and with insulin secretion (only in lean subjects). A mean of 16.8%, but not 7.3% weight loss, led to significant increases in circulating osteocalcin. However, a mean of 8.7% weight loss plus regular exercise led to the more pronounced effects on the serum osteocalcin concentration, which increased in parallel to reduced visceral fat mass, unchanged thigh muscle mass, and increased leg strength and force. The postintervention serum levels of osteocalcin were associated with both insulin sensitivity (r = 0.49; P = 0.03) and fasting triglycerides (r = -0.54; P = 0.01). The change in visceral fat was the parameter that best predicted the change in serum osteocalcin, once age, body mass index, and insulin sensitivity changes were controlled for (P = 0.002).

CONCLUSION

Circulating osteocalcin could mediate the role of bone as an endocrine organ in humans.

Bone Turnover Markers in Patients with Type 2 Diabetes and Their Correlation with Glycosylated Haemoglobin Levels

The aim of this prospective, longitudinal study was to investigate, over a period of 12 months, the effects of metabolic control on bone turnover markers in patients with type 2 diabetes mellitus. The study included 17 male and 18 female patients with type 2 diabetes, aged 37 − 66 years. Mean follow-up period was 12 ± 1.2 months. Mean glycosylated haemoglobin (HbA1C) levels were 10.6% ± 1.6% at the start of the study and decreased to 7.7% ± 1.0% by the end of the study. Levels of the bone resorption markers, urinary deoxypyridinoline and N-telopeptide, were 28.6 ± 11.6 nmol/mmol creatinine and 93.6 ± 13.7 nmol bone collagen equivalents [BCE]/mmol creatinine, respectively, at the start of the study, and decreased significantly to 17.9 ± 7.1 nmol/mmol creatinine and 67.8 ± 12.8 nmol BCE/mmol creatinine, respectively, by the end of the study. Bone formation parameters also significantly decreased in parallel with HbA1c levels over the study period. It is concluded that effective management of metabolic disorder in patients with type 2 diabetes plays an important contribution to bone turnover improvement.

Osteoporosis among patients with type 1 and type 2 diabetes

Both diabetes and fractures are prevalent in adults. The relationship between diabetes and osteoporosis is complex and, although it has been investigated extensively, the subject remains controversial. While low bone mineral density (BMD) is consistently observed in type 1 diabetes, the relationship is less clear in type 2 diabetes, with some studies reporting modestly increased or unchanged BMD. Both type 1 and type 2 diabetes have been associated with a higher risk of fractures. Despite discrepancies between BMD and fracture rates, clinical trials uniformly support the fact that new bone formation and bone microarchitecture and, thus, bone quality, are altered in both types of diabetes. Although a causal association between diabetes and osteoporosis cannot be established on the basis of existing data, it is possible to conclude from many studies and from a better understanding of the physiopathology of diabetes that it can increase the risk of fractures through skeletal (decreased BMD and bone quality) and extraskeletal (increased risk of falls) factors. Even though osteoporosis screening or prophylactic treatment in all patients with type 1 and type 2 diabetes is not being recommended at present, such patient populations should be given general guidelines regarding calcium and vitamin D intakes, exercise and the avoidance of potential risk factors for osteoporosis. The extent of diagnostic and therapeutic interventions should be based on the individual's risk profile for fractures.

Association of lower serum cholesterol levels with higher risk of osteoporosis in type 2 diabetes

OBJECTIVE

To determine whether a correlation exists between bone mineral density and circulating lipoprotein levels and whether these variables are independently associated with osteoporosis in patients with type 2 diabetes.

METHODS

In a cross-sectional analysis, 159 patients with type 2 diabetes were compared with 70 patients without diabetes selected from an outpatient endocrinology clinic in a tertiary care institute during a 1-year period. Variables were gathered through history, physical examination, and laboratory findings, including blood chemistry studies and dual-energy x-ray absorptiometry.

RESULTS

Of the 229 study patients, 86 (37.6%) had osteoporosis. In the patients with diabetes, the mean +/- SD of age, weight, total cholesterol, and low-density lipoprotein (LDL) cholesterol in those with and without osteoporosis was 72.3 +/- 10.4 years versus 63.6 +/- 11.0 years, 74.2 +/- 14.4 kg versus 83.7 +/- 15.5 kg, 178.4 +/- 33.7 mg/dL versus 194.1 +/- 33.9 mg/dL, and 100.0 +/- 27.1 mg/dL versus 114.2 +/- 30.2 mg/dL, respectively (P<0.01 for all variables). After adjustment for other variables, multiple logistic regression analysis showed that the presence of diabetes was associated with a lower risk of osteoporosis. Similarly, older age and lower body weight, LDL levels, and serum calcium levels were independently associated with lumbar spine osteoporosis in patients with diabetes, in comparison with older age and lower weight in patients without diabetes. Lower weight and older age were associated with femoral neck and total hip osteoporosis in patients with diabetes, in comparison with only older age in patients without diabetes.

CONCLUSION

The presence of type 2 diabetes is associated with a lower risk of osteoporosis. In patients with type 2 diabetes, a lower LDL level is more likely to be associated with osteoporosis at the lumbar spine.

Effects of streptozotocin-induced diabetes mellitus on some bone turnover markers in the vertebrae of ovary-intact and ovariectomized adult rats

Diabetes mellitus and estrogen deficit are known causes of osteopenia in animal models as well as in humans. In the present work, the combined effect of ovariectomy and diabetes was investigated. Diabetes was induced in ovary-intact and ovariectomized female Wistar rats with a single injection (50 mg/kg body weight, i.p.) of streptozotocin. The rats were administered insulin (I) daily or 17-β estradiol (E2) on alternate days for a period of 35 days and sacrificed. Serum calcium (Ca2+), phosphorus (P), alkaline phosphatase (ALP), tartrate-resistant acid phosphatase (TRAP), vertebral ALP, collagen, and glycosaminoglycans were estimated. The levels of serum Ca2+and P increased in diabetic rats, but decreased after I or E2treatments. Serum ALP and TRAP activity increased in the ovary-intact and ovariectomized diabetic rats. Vertebral ALP activity increased in ovariectomized diabetic rats, but decreased in diabetic rats, which were treated with I or E2. In the vertebrae, TRAP activity was elevated as a result of diabetes, but this was prevented by insulin or estradiol. Diabetes induced a decrease in total collagen in the vertebrae, while I or E2treatment induced an increase. The levels of chondroitin sulphate and heparan sulphate decreased significantly in the vertebrae of both ovary-intact and ovariectomized diabetic rats, while hyaluronic acid increased. In conclusion, diabetes and ovariectomy each seem to affect the process of matrix formation and mineralization in the bone, and this is aggravated by the combination of diabetes and ovariectomy. The effects of I and E2were similar, and both hormones reversed the changes brought about by diabetes.

Increased incidence of vertebral fracture in older female hemodialyzed patients with type 2 diabetes mellitus

Bone disease in hemodialysis (HD) patients with type 2 diabetes mellitus (DM) is characterized by low bone turnover (Inaba M, et al. Am J Kidney Dis 2002; 39:1261-1269), although their bone quality is yet to be determined. The present study was designed to examine whether the prevalence of vertebral fracture in female HD patients with type 2 DM, age 65 years and older, might be increased, and the relation of this fracture to bone mineral density (BMD) determined by dual X-ray absorptiometry (DXA), since few data are available on the effect of DM on bone strength at lumbar spine. The prevalence of vertebral fracture in type 2 DM HD patients was 32.3%, which was greater than that of non-DM HD patients (13.3%) when adjusted for age and HD duration. Logistic regression analysis elucidated the presence of DM and age as independent risk factors for an increased prevalence of vertebral fracture in HD patients. In non-DM HD patients, those with vertebral fracture showed age significantly higher and BMD in either lumbar spine or distal one third of radius significantly lower than the respective value in those without fracture. However, in DM HD patients, neither BMD in lumbar spine nor distal one third of radius was significantly lower in those with vertebral fracture than in those without. Furthermore, age did not differ significantly between DM HD patients with and without fracture. In conclusion, female type 2 DM HD patients, age 65 years and older, showed significantly higher incidence of vertebral fracture than non-DM HD patients. Although age and low BMD emerged as independent risk factors for vertebral fracture in non-DM HD patients, those factors failed to be a risk factor in DM HD patients, suggesting that BMD determined by DXA might not be reliable in assessing bone strength in DM HD patients.

Bone metabolism in male patients with type 2 diabetes

Few reports are available on bone turnover in type 2 diabetes. Impaired bone turnover in type 2 diabetes appears to result from decreased bone formation. Studies also suggest that poor glycaemic control in type 2 diabetes may contribute to osteopaenia. The aim of this study was to investigate biochemical markers of bone turnover in males with poorly controlled type 2 diabetes and look for correlations with glycaemic control and gonadal and hypophyseal hormonal axis. Consecutive male patients with poorly controlled type 2 diabetes and attending the internal medicine department during a period of 6 months were enrolled. The patients were receiving oral hypoglycaemic agents (metformin or sulphonylureas or both). None of the patients had any evidence of macroangiopathy, nephropathy or neuropathy. Only two patients had proliferative retinopathy. Serum osteocalcin, crosslaps (C-telopeptide, CTx), parathyroid hormone (PTH), testosterone, oestrogen, prolactin, follicle-stimulating hormone (FSH) and luteinising hormone (LH) were measured in 35 patients and 35 controls. The mean age of the study population was 53.7 (10.3) years (range: 50.2-57.3) and the mean disease duration was 8.6 (6.0) years (range: 6.5-10.7). No differences between patients and controls were observed in serum calcium, phosphorus, creatinine, albumin, PTH, CTx, oestrogen, testosterone, LH, FSH, prolactin and urinary calcium. Patients had lower serum levels of osteocalcin than controls with a significant statistical difference [15.3 (4.1) vs 18.3 (5.3), p=0.012]. There was a negative significant statistical correlation between CTx levels and HbA1c (r=-0.41, p< 0.05). Our study suggested that bone formation is altered in type 2 diabetes and that bone turnover is affected by glycaemic control status.

(n-3) fatty acids reduce the release of prostaglandin E2 from bone but do not affect bone mass in obese (fa/fa) and lean Zucker rats

Childhood obesity is prevalent and linked to the development of Type 2 diabetes mellitus (DM) and poor bone health. Some PUFA enhance bone mass and thus may improve bone health in obese children. The study objective was to determine the effects of dietary (n-6) compared with (n-3) essential PUFA and long-chain PUFA (LCPUFA) on bone in an obese and insulin-resistant state. Male fa/fa (n = 48) and lean Zucker rats (n = 48) were fed diets containing safflower oil [SO, high (n-6) PUFA], flaxseed oil [FXO, high (n-3) PUFA], or menhaden oil [MO, high (n-3) LCPUFA] for 9 wk. Measurements included the following: femur bone area (BA), mineral content (BMC), density (BMD), morphometry and ex vivo release of prostaglandin E(2) (PGE(2)); plasma osteocalcin and C-terminal telopeptides of type I collagen. Differences among groups were detected using 2-way ANOVA. Genotype effects in the fa/fa rats included lower femoral weight, length, BA, and BMC, as well as femoral head and proximal epiphysis widths compared with the lean rats, but BMD was not affected. Femur BA, BMC, and BMD did not differ among the dietary groups, but diaphysis width was elevated in the MO group and PGE(2) release was reduced by the FXO and MO diets. No genotype x diet interactions were observed. These data indicate that the fa/fa Zucker rat is at risk for low bone mass and that dietary (n-3) FA effectively reduce PGE(2) release. Whether reduced PGE(2) will support optimal peak bone mass during childhood and conserve bone mass with aging warrants investigation.

Collagen type I prevents glyoxal-induced apoptosis in osteoblastic cells cultured on titanium alloy

Advanced glycation end products (AGEs) irreversibly cross-link proteins with sugars and accumulate at a higher age and in diabetes, processes which can interfere with the integration of implants into the tissue. Glyoxal is a highly reactive glycating agent involved in the formation of AGEs and is known to induce apoptosis, as revealed by the upregulation of caspase-3 and fractin (caspase-3 being a key enzyme activated during the late stage of apoptosis and fractin being a caspase-cleaved actin fragment). In this study, we investigated the influence of collagen type I coating on the cytotoxic effect of glyoxal on rat calvarial osteoblastic cells and on human osteosarcoma cells (Saos-2) grown on titanium alloy, Ti6Al4V. Activation of caspase-3 and fractin was measured by counting immunohistochemically stained cells and by flow cytometry with propidium iodide (detection of the apoptosis indicating a sub-G1 peak). Our results showed an increased number of apoptotic osteoblasts after incubation with glyoxal on Ti6Al4V discs. However, the number of apoptotic cells on collagen-coated titanium was significantly smaller than on uncoated titanium after the same treatment. The present findings demonstrate that osteoblasts treated with glyoxal undergo apoptosis, whereas collagen type I coating of titanium alloys (used for implants) has an antiapoptotic function.

A role for advanced glycation end products in diminished bone healing in type 1 diabetes

The effect of type 1 diabetes on bone healing and bone formation in standardized craniotomy defects created in BALB/cByJ mice was determined. The hypothesis that advanced glycation end products (AGEs) contribute to diminished bone healing in diabetes was evaluated by assessing for the presence of the receptor for advanced glycation end products (RAGE) by immunohistochemistry in healing craniotomy defects in diabetic animals. The effect of local application of a known RAGE protein ligand, N(epsilon)-(carboxymethyl)lysine (CML)-mouse serum albumin (MSA), on craniotomy defect healing in normal animals was then assessed and compared to the effects of control MSA. Finally, evidence in support of the expression of RAGE mRNA and protein in osteoblastic cells was obtained. The results indicated that craniotomy defects in diabetic animals healed approximately 40% of the degree to which they healed in nondiabetic animals (P < 0.05). RAGE was expressed at higher levels in healing bone tissues in diabetic compared to control animals. Further studies in nondiabetic animals indicated that bone healing was reduced by 63 and 42% in lesions treated with 900 and 90 micro g CML-MSA, respectively, compared to in animals treated with MSA alone (P < 0.05). Evidence for the expression of RAGE was obtained in mouse and rat osteoblastic cultures. These results support the contribution of AGEs to diminished bone healing in type 1 diabetes, possibly mediated by RAGE.

Effect of streptozotocin-induced diabetes mellitus on alveolar bone deposition in the rat

Effects of diabetes on alveolar bone remodelling were assessed by quantitative histology and a chronological lead-labelling technique. Experimental diabetes was induced by a single dose of 40 mg/kg of streptozotocin. Remodelling of the alveolar wall surrounding the root of mandibular first molar was studied in control rats fed ad libitum, and in diabetic and insulin-treated diabetic rats 24 days after the induction of diabetes. The volumes of bone formation on the mesial side of the alveolar wall were evaluated over a 10-day period by chronological lead-labelling and computer image analysis. For a histometric measure of bone-resorption, the number of osteoclasts along the distal surface of the alveolar wall was counted. The volume of bone formed and the number of osteoclasts were significantly lower in the diabetic rats than in the controls, but insulin treatment of diabetic rats normalised these histomorphometric measures of bone turnover. These results demonstrate that streptozotocin-induced diabetes mellitus reduces the rate of bone turnover in the alveolar wall surrounding the root, which reduction is corrected by treatment with insulin.

Histomorphometric evaluation of the effect of doxycycline on the healing of bone defects in experimental diabetes mellitus: a pilot study

PURPOSE

Bone healing is impaired in diabetes mellitus, particularly due to increased collagen breakdown. Recently, tetracyclines have been used to treat experimental bone defects because they have anticollagenolytic properties, and positive effects on the healing process have been obtained. The objective of this study was to develop a computer-assisted histomorphometric technique to quantitatively determine the amount of regenerating bone within experimental bone defects in a diabetic rodent model.

MATERIALS AND METHODS

This study examined the effects of systemic doxycycline administration on the healing of tibial bone defects in healthy albino rats and in experimentally induced diabetic rats. Twenty-four female albino rats were assigned to 4 groups: diabetic, diabetic plus doxycycline, control, or control plus doxycycline. The standardized bone defects were histomorphometrically examined 10 and 30 days postoperatively. Histomorphometric analysis of the amount of new bone formation was performed using the Zeiss Vision image analysis program KS 400 (Kontron Elektron GmbH, Eching, Germany).

RESULTS

At 10 days of healing, the diabetic groups exhibited inferior healing compared with the control groups in terms of the amount of new bone formation within the defects. However, the effect of doxycycline administration to the diabetic and control groups was not statistically different. At 30 days of healing, there were no statistically significant differences between the amount of newly formed bone in any of the groups.

CONCLUSIONS

This study found that doxycycline administration did not significantly alter the amount of new bone formation during the healing of bone defects in control and diabetic rats.

Impaired secretion of parathyroid hormone, but not refractoriness of osteoblast, is a major mechanism of low bone turnover in hemodialyzed patients with diabetes mellitus

Diabetic bone disease is characterized by low bone turnover resulting from either impaired secretion of parathyroid hormone (PTH) or refractoriness of osteoblasts to PTH. The present study was performed to elucidate which factor contributes more to the reduction in bone turnover by comparison between 64 hemodialyzed patients with diabetes mellitus and 106 hemodialyzed patients without diabetes mellitus. Only men were enrolled to avoid the influence of the menstrual cycle on bone metabolism. Serum intact PTH (iPTH) levels were significantly lower in hemodialyzed patients with diabetes than those without diabetes, although no significant difference existed in age, duration of hemodialysis therapy, or serum calcium or phosphate levels. Of the biochemical markers measured, serum intact osteocalcin (iOC) and deoxypyridinoline levels were significantly lower in patients with diabetes, although serum bone-specific alkaline phosphatase (BAP) and pyridinoline levels did not differ significantly between the two groups of patients. When patients were restricted to those with serum iPTH levels greater than 180 pg/mL, this parameter correlated significantly in a positive manner with both serum iOC and BAP levels and negatively with bone mineral density at distal radius 1/3. Regression slopes between iPTH levels and these parameters were not significantly different between the two groups of patients, indicating the absence of refractoriness of bone to PTH in patients with diabetes. In conclusion, our findings suggest that impaired PTH secretion, but not refractoriness of osteoblasts to PTH, may be responsible for the low bone turnover in hemodialyzed patients with diabetes.

The biomechanical integrity of bone in experimental diabetes

Patients with diabetes mellitus incur a higher incidence of fractures compared to healthy individuals. This suggests that the structural integrity of the skeletal system may be compromised. To examine the biomechanical consequences of diabetes, we studied the structural integrity of the femur and tibia of rats with streptozotocin-induced diabetes. The induction of diabetes was confirmed by measuring blood glucose levels (>300 mg/dl). Seven-weeks following the establishment of diabetes, the animals were euthanized and the hind limbs removed. The femur and tibia of each hind limb were excised, and prepared for three point bending test on an Instron Materials Testing System. The results revealed a 37% decrease in maximum load (breaking strength) of the femur of diabetic rats when compared to controls. The diabetic femurs had 25% less deformation at maximum load compared to controls. Similarly, energy absorption capacity to yield point and toughness were reduced by 27 and 34%, respectively, in the diabetic femur. A 38% increase in the bending stiffness was observed in the femurs of diabetic rats. Similar results were obtained with the tibias of both groups. Measurement at the break point revealed that the bones of diabetic rats bore significantly less load, deformation and energy absorption capacity than controls. Overall, our findings warrant the conclusion that the diabetic state is associated with mechanical deterioration of bone, resulting in bones with inferior biomechanical integrity.

Impaired secretion of parathyroid hormone is coherent to diabetic hemodialyzed patients

Diabetic bone disease is characterized by low bone turnover resulting from impaired secretion of parathyroid hormone (PTH). However, it was suggested that the difference in duration of hemodialysis (HD) therapy and age of patients between HD patients with and without diabetes mellitus (DM) may be responsible for a significant reduction in serum intact PTH (iPTH) level in HD patients with DM. The present study showed that although such major factors affecting PTH secretion as age, sex, HD duration, and serum calcium, phosphate, and magnesium levels did not differ significantly between HD patients with and without DM, serum iPTH levels were still significantly lower in HD patients with than without DM. Among biochemical markers for bone metabolism, serum levels of intact osteocalcin (iOC) and deoxypyridinoline (DPD) were significantly lower in HD patients with than without DM, whereas serum bone-specific alkaline phosphatase, pyridinoline, and beta-crosslaps did not differ significantly between the two groups of patients. In summary, our findings indicate that PTH secretion may be significantly impaired in HD patients with DM compared with those without DM, and serum iOC and DPD are bone markers sensitive enough to detect low bone turnover in HD patients with DM.

Bone mineral density at time of clinical diagnosis of adult-onset type 1 diabetes mellitus

OBJECTIVE

To study bone mineral density (BMD) and bone remodeling factors at the time of diagnosis of adult-onset type 1 diabetes mellitus (DM).

METHODS

In 22 men and 10 women, who ranged in age from 20 to 39 years, a study was undertaken promptly after diagnosis of type 1 DM (on the basis of criteria established by the World Health Organization). Before any treatment, the clinical history, glycemia, ketonuria, basal and glucagon-stimulated C-peptide levels, islet cell antibodies (ICA), glutamic acid decarboxylase autoantibodies (GADA), and bone remodeling variables were recorded for all the study subjects. Dual-energy x-ray absorptiometry (Hologic QDR1000) was performed to measure BMD in the lumbar spine (LS), femoral neck (FN), and Ward's triangle.

RESULTS

Of the 32 patients, 24 (75%) showed positive levels of ICA or GADA (or both), whereas 8 (25%) tested negative. The BMD values-Z-scores (standard deviation [SD] adjusted for age and sex)-were lower among the patients with DM than in a matched healthy population in both the LS (-0.61 +/- 1.23 SD; P = 0.008) and the FN (-0.38 +/- 1.00 SD; P = 0.003). Twelve patients had a T-score between -2.5 SD and -1 SD in the LS, and 14 had the same scores in the FN and were classified as having osteopenia. A correlation was found between BMD values and C-peptide levels in the LS (r = 0.231; P = 0.02) and the FN (r = 0.27; P = 0.01). The BMD values did not correlate with bone remodeling markers, hemoglobin A1c, or immunologic variables.

CONCLUSION

We found reduced bone mass in patients with type 1 DM at the time of the clinical diagnosis. A high percentage of patients with DM have osteopenia, which may not, therefore, be a late complication of type 1 DM. These findings need to be confirmed in larger studies.

The effects of high levels of glucose and insulin on type I collagen synthesis in mature human odontoblasts and pulp tissue in vitro

High levels of dietary sucrose affect the metabolism of the pulp-dentin complex and enhance the caries process in dentin. The high-sucrose diet reduces dentin formation in young rats (Tjäderhane et al., 1994; Hietala and Larmas, 1995; Tjäderhane, 1996) and in pups of rat dams fed high-sucrose diet during lactation (Pekkala et al., 2000a). However, the mechanisms behind the effects are unknown. A direct effect of elevated blood glucose or an indirect effect via insulin has been suggested. We investigated the effects of high glucose and insulin on type I collagen synthesis in human odontoblasts and pulp tissue in vitro, using an organ culture method for functional post-mitotic odontoblasts. Odontoblasts and pulp tissue were cultured separately for 10 days in DMEM with 15% FBS containing additional glucose (G) (4.45 g/L) or insulin (I) (0.6 microgram/mL) or both together (GI). We evaluated type I collagen synthesis with RIA, measuring the level of N-terminal propeptide of type I collagen (PINP) secreted into the culture media. PINP secretion decreased in odontoblasts and pulp tissue in G and GI groups when compared with the control and insulin samples (p = 0.001 in both groups in the pulp samples). Insulin alone did not affect PINP secretion distinctly. The results indicate that high levels of glucose, but not insulin, directly down-regulate the type I collagen synthesis in young, differentiated human odontoblasts and pulp tissue. Insulin does not affect the inhibitory effect of high sucrose. These in vitro findings indicate that the high-sucrose diet may alter odontoblast function independently of insulin.

Decreased bone mineral density and bone formation markers shortly after diagnosis of clinical type 1 diabetes mellitus

We recently demonstrated that children with type 1 diabetes mellitus (DM) have decreased lumbar spine bone mineral density (BMD) as early as four years after clinical diagnosis of the disease. In order to determine whether osteopenia is already present in patients very early on after diagnosis of clinical DM, we evaluated the bone mineral status of a group of newly diagnosed children (5.8 +/- 1.5 mo after diagnosis). We studied 23 prepubertal children (7 M, 16 F) with a mean chronological age of 9.5 +/- 2.2 yr and a mean glycosylated hemoglobin of 8.9 +/- 2.4%. Lumbar spine and femoral neck BMD were measured by dual X-ray absorptiometry, while bone turnover was assessed by the determination of the serum concentration of the carboxy-terminal propeptide of type I collagen (PICP) and the carboxy-terminal cross-linked telopeptide of type I collagen (N-telopeptide). Results were compared to those of age, height, and pubertal status matched controls. Lumbar spine BMD Z-scores were decreased in patients compared to controls (Z-scores of -0.89 +/- 1.2, with 10 of 22 patients showing values >1 SD below the mean). When lumbar spine Z-scores were analyzed in those patients with <3 months or > or =3 months since diagnosis of DM a significant difference was noticed between groups (-0.648 +/- 1.12 vs -1.267 +/- 1.17; p <0.02). No significant differences were noted in femoral neck BMD and total BMD between groups. Serum PICP levels were decreased when compared to controls (233.6 +/- 39.3 vs 375.9 +/- 50.7 microg/l; p <0.002), while serum N-telopeptide concentrations, although increased, were not significantly different (9.3 +/- 1.3 vs 5.7 +/- 1.5 microg/l). In summary, early on after the diagnosis of type 1 DM, children present with decreased lumbar spine BMD and decreased bone formation markers.

Osteopenia in insulin-dependent diabetes mellitus; prevalence and aspects of pathophysiology

The objective was to evaluate the prevalence and severity of osteopenia in patients with uncomplicated insulin-dependent diabetes mellitus (IDDM) and to obtain more information on the pathophysiology of diabetic osteopenia. In 35 patients with uncomplicated IDDM (21 men and 14 women; age 37.6+/-9.9 yr; duration of disease 8.5+/-3.5 years) bone mineral density was measured by dual energy X-ray absorptiometry (DEXA). In addition, markers of bone formation [plasma insulin-like growth factor I (IGF-I), serum alkaline phosphatase (ALP), serum bone alkaline phosphatase (BAP) and serum osteocalcin] and bone resorption [urinary excretion of calcium and of the cross-linked N-telopeptide of type 1 collagen, both corrected for the excretion of creatinine] were measured in the diabetic patients and in 33 healthy controls, matched for sex, age, height, weight and body mass index (BMI). In 67% of the diabetic men and 57% of the diabetic women osteopenia of the femoral neck and/or the lumbar spine (T-value < or = -1 SD) was present. Fourteen percent of the male patients, but none of the female patients, met the criteria for osteoporosis (T-value < or = -2.5 SD). In the whole group of diabetic patients the mean plasma IGF-I level tended to be lower (p<0.10) as compared to that in the controls. In the diabetic patients with femoral neck osteopenia, the mean plasma IGF-I level was significantly lower (p<0.05) than in those without osteopenia at this site. There were no differences in the mean serum ALP, BAP and osteocalcin levels between the diabetic patients and the controls, nor between the diabetic patients with and without femoral neck osteopenia. Considering only the male diabetic patients, significantly lower mean plasma IGF-I (-26%), serum ALP (-24%) and serum osteocalcin (-38%) levels were present in the patients with femoral neck osteopenia than in those without osteopenia at this site, suggesting lowered bone formation. The bone resorption markers were similar in all (sub)groups of diabetic patients and not different between diabetic patients and controls. Bone mineral density (BMD) did not correlate with plasma levels of glycosylated hemoglobin (HbA1c). BMD values were not related to any of the bone resorption or formation markers, except for plasma IGF-I both in the femoral neck (r=+0.38, p=0.026) and the lumbar spine (r=+0.34, p=0.043). Our data demonstrate that at least in male patients with IDDM, osteopenia is the consequence of a lowered bone formation with a predominance of bone resorption over formation.

HMG-CoA reductase inhibitors increase BMD in type 2 diabetes mellitus patients

Recently, it was reported that 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors increased bone mineral density (BMD) in mice. We studied the effect of HMG-CoA reductase inhibitors on BMD of type 2 diabetes mellitus by a retrospective review of medical records. Sixty-nine type 2 diabetic patients were included. The control group (n = 33) did not take HMG-CoA reductase inhibitors. The treatment group (n = 36) was administered either lovastatin, pravastatin, or simvastatin. BMD of the spine, femoral neck, femoral trochanter, and total hip were measured by dual-energy X-ray absorptiometry. There were no significant differences between control and treatment groups in age, sex, body mass index, glycemic control, and serum insulin levels. In the control group, BMD of the spine significantly decreased (from 1.116 +/- 0.165 to 1.081 +/- 0.178 g/cm2) after 14 months. In the treatment group, BMD of the femoral neck significantly increased (from 0.853 +/- 0.139 to 0.878 +/- 0.147 g/cm2) after 15 months. In male subjects treated with HMG-CoA reductase inhibitors, there was a significant increase in BMD of the femoral neck and femoral trochanter (from 0.899 +/- 0.139 to 0.934 +/- 0.139 and from 0.801 +/- 0.145 to 0.833 +/- 0.167 g/cm2, respectively), but in female subjects, only BMD of the femoral neck increased (from 0.819 +/- 0.132 to 0.834 +/- 0.143 g/cm2). Percentage increments of BMD of the femoral neck, femoral wards triangle, femoral trochanter, and total hip in the treatment group were significantly higher than in the control group (2.32% vs. -0.99, 1.77% vs. -1.25%, 1.40% vs. -1.21%, 0.88% vs. -1.03%, respectively). The proportion of subjects who had an increase in BMD of the spine and total hip more than two percentages was significantly larger in the treatment group than in the control group (30.6% vs. 15.2% and 30.6% vs. 9.1%, respectively). The increased increment in BMD of the treatment group was significantly greater than those in the control group after adjustment for age and body mass index (P < 0.05). These results suggest that HMG-CoA reductase inhibitors may increase BMD of the femur in male patients with type 2 diabetes mellitus.

Streptozotocin-induced diabetes: significant changes in the kinetic properties of the soluble form of rat bone alkaline phosphatase

A soluble form of an alkaline phosphatase, obtained from the osseous plate of streptozotocin-induced diabetic rats, was purified 90-fold with a yield of 26%. The calculated Mr of the purified enzyme was 80,000 by denaturing polyacrylamide gel electrophoresis and 160,000 by gel filtration on Sephacryl S-300, suggesting a dimeric structure for its native form. In the absence of metal ions, the p-nitrophenylphosphatase activity of the purified enzyme was 4223.1 U/mg. Magnesium or calcium ion concentrations up to 2 mM increased the specific activity of the enzyme to 9896.5 and 10,796.2 U/mg, respectively. The enzyme was stimulated to a lesser extent by MnCl2 (5390.1 U/mg) and CoCl2 (5088.2 U/mg). The purified soluble alkaline phosphatase showed a broad substrate specificity, and among the less hydrolyzed substrates were pyrophosphate (1517.6 U/mg) and bis-p-nitrophenylphosphate (499.6 U/mg). The enzyme was relatively stable at 45 degrees for periods as long as 180 min, but was denatured rapidly above 50 degrees, following first order kinetics with T1/2 values ranging from 3.5 to 57.7 min. The results reported herein suggested that the soluble form of alkaline phosphatase from streptozotocin-induced diabetic rats had its kinetic properties altered, apparently as a consequence of changes in metal-binding properties.

Calcium metabolism in adolescents and young adults with type 1 diabetes mellitus without and with persistent microalbuminuria

Alterations in calcium metabolism can be demonstrated in the course of insulin-dependent diabetes mellitus. In order to clarify if the presence of persistent microalbuminuria (MA) can affect the main parameters of calcium metabolism, we studied 22 diabetic adolescents and young adults with persistent MA and compared them with 24 patients without MA and 24 healthy controls. Mean values of serum calcium, phosphorus and magnesium were similar in diabetic children and young adults without persistent MA and in controls. In addition, the mean values of PTH and 25-OHD, 1,25 (OH)2D3 and OC did not differ between these diabetics and controls. Diabetics with persistent MA showed no significant difference from the values of either controls or the group of diabetics without persistent MA for the mean values of serum calcium, phosphorus and magnesium and PTH. In contrast, diabetics with persistent MA had significantly (p<0.01) lower 25-OHD (26.5+/-5.2 ng/ml) and 1,25 (OH)2D3 (24.7+/-5.6 pg/ml) as well as OC levels (9.8+/-2.5 ng/ml; p<0.001) than controls (38.1+/-4.9 ng/ml, 40.7+/-6.4 pg/ml and 16.5+/-5.8 ng/ml, respectively) and subjects with normoalbuminuria (36.0+/-4.5 ng/ml, 38.8+/-8.9 pg/ml and 14.5+/-3.2 ng/ml). In conclusion, our study suggests that abnormalities in 25-OHD, 1,25(OH)2D3 and OC can be present in diabetic adolescents and young adults with incipient nephropathy.

Prevention of renal osteodystrophy in peritoneal dialysis

BACKGROUND

Renal osteodystrophy (ROD) is still one of the major long-term complications in end-stage renal disease leading to considerable morbidity. Despite some progress in understanding the pathogenesis of secondary hyperparathyroidism (sHPT) during recent years, prevention and treatment of ROD is still suboptimal, requiring surgical parathyroidectomy in 6 to 10% of all patients on dialysis after 10 years. In addition, the spectrum of bone lesions has changed, with non-aluminum-related adynamic bone disease (ABD) found in up to 43% of peritoneal dialysis (PD) patients.

METHODS

Current recommendations concerning prevention of ROD in PD based on the literature and personal recent data were reviewed. The focus is on (i) the importance of early prophylactic intervention to prevent parathyroid gland hyperplasia, (ii) the pathogenesis of ABD, and (iii) the role of metabolic acidosis in ROD.

RESULTS

There is ample evidence that sHPT starts early during the course of renal failure and results from both hypersecretion of PTH by parathyroid cells and glandular hyperplasia. As shown by experimental and clinical studies, established parathyroid cell hyperplasia is hardly reversible by pharmacological means, and therefore prevention of parathyroid cell proliferation needs to start early. Recent data from randomized trials document the efficacy and safety of low dose active vitamin D (0.125 to 0.25 microgram/day) and/or an oral calcium substitute to prevent progression of sHPT in patients with mild to moderate renal failure. Since little is known about the pathogenesis, natural course and clinical impact of ABD in PD, specific therapeutic concepts have not yet been generated. Diabetes and advanced age are established risk factors, whereas the role of calcium and vitamin D overtreatment or the type of dialysis (PD vs. HD) are still controversial. Currently no evidence for different functional behavior of the parathyroids in ABD and sHPT has been found. The role of circulating or local factors such as cytokines, growth factors or the presence of advanced glycation end-product (AGE)-modified matrix proteins for the pathogenesis of either type of ROD deserves further investigation. Avoiding oversuppression of parathyroid gland and the use of low calcium dialysate may help prevent ABD. There is growing evidence that a correction of metabolic acidosis will influence ROD by both direct effects on the bone and on parathyroid cell function. New dialysate composition for CAPD with a high HCO3 concentration will allow normalization of acid-based metabolism in PD patients. Their effects on ROD under long term conditions remain to be determined.

CONCLUSION

Therapeutic efforts should aim to prevent the development of parathyroid gland hyperplasia and sHPT early during the course of renal failure, and should include the use of low dose vitamin D therapy and oral calcium substitution as well as correction of metabolic acidosis. Concerning ABD, more information is needed regarding the causes and consequences of this type of bone lesion to develop a more specific therapy.

Secondary osteoporosis

Generalized osteoporosis currently represents a heterogeneous group of conditions with many different causes and pathogenetic mechanisms, that often are variably associated. The term "secondary" is applied to all patients with osteoporosis in whom the identifiable causal factors are other than menopause and aging. In this heterogeneous group of conditions, produced by many different pathogenetic mechanisms, a negative bone balance may be variably associated with low, normal or increased bone remodeling states. A consistent group of secondary osteoporosis is related to endocrinological or iatrogenic causes. Exogenous hypercortisolism may be considered an important risk factor for secondary osteoporosis in the community, and probably glucocorticoid-induced osteoporosis is the most common type of secondary osteoporosis. Supraphysiological doses of corticosteroids cause two abnormalities in bone metabolism: a relative increase in bone resorption, and a relative reduction in bone formation. Bone loss, mostly of trabecular bone, with its resultant fractures is the most incapacitating consequence of osteoporosis. The estimated incidence of fractures in patients prescribed corticosteroid is 30% to 50%. Osteoporosis is considered one of the potentially serious side effects of heparin therapy. The occurrence of heparin-induced osteoporosis appeared to be strictly related to the length of treatment (over 4-5 months), and the dosage (15,000 U or more daily), but the pathogenesis is poorly understood. It has been suggested that heparin could cause an increase in bone resorption by increasing the number of differentiated osteoclasts, and by enhancing the activity of individual osteoclasts. Hyperthyroidism is frequently associated with loss of trabecular and cortical bone; the enhanced bone turnover that develops in thyrotoxicosis is characterized by an increase in the number of osteoclasts and resorption sites, and an increase in the ratio of resorptive to formative bone surfaces, with the net result of bone loss. Despite these findings, the occurrence of pathological fractures in patients with hyperthyroidism is relatively low, and probably due to the fact that deficiencies in bone mass may be reversed by treatment of the thyroid disease. Most, but not all, studies on insulin-dependent diabetes mellitus (IDDM) report an association with osteopenia. In IDDM, the extent of bone loss is usually slight, which helps explain the discrepancy between the frequency of decreased bone mineral density, and the frequency of osteoporotic fractures in long-standing diabetes. Contradictory results have been obtained in non-insulin-dependent diabetes mellitus (NIDDM) patients. Increased rates of bone loss at the radius and lumbar spine were demonstrated either in patients with two-thirds gastric resection and Billroth II reconstruction, or in those with one-third resection and Billroth I anastomosis, and the metabolic bone disease following gastrectomy may consist also of osteomalacia or mixed pattern of osteoporosis-osteomalacia, with secondary hyperparathyroidism. Miscellaneous causes of secondary osteoporosis are also immobilization, pregnancy and lactation, and alcohol abuse.

Decreased lumbar spine bone mass and low bone turnover in children and adolescents with insulin dependent diabetes mellitus followed longitudinally

The effects of insulin dependent diabetes mellitus (IDDM) on bone metabolism are still not well defined. We evaluated total bone mineral content (TBMC) and bone mineral density (BMD) at the lumbar spine and femoral neck using dual X-ray absorptiometry in 26 IDDM children (15 M, 11 F) with a mean chronological age of 12.1+/-3.1 yr (range 7.1-14.2 yr). Duration of diabetes was 4.3+/-2.9 yr, with a mean glycosylated hemoglobin of 9.2+/-0.4%. BMD and TBMC standard deviation scores (Z-scores) were determined by comparing our results to controls matched for age, sex and pubertal status. BMD and bone formation and resorption markers were determined at the beginning of the study and after one year of follow up. Mean lumbar spine Z-score was -1.06+/-0.2, with negative values in 24 of 26 children (92.6%); 14/26 patients (53.8%) had a lumbar spine Z-score >1.0 SD below the mean. Mean lumbar spine Z-score remained unchanged after one year of follow up (-1.02+/-0.3). No significant differences were obtained in femoral neck BMD or TBMC between groups. No correlation was observed between lumbar spine BMD Z-scores and duration of IDDM or degree of diabetes control, as assessed by the mean glycosylated hemoglobin. Daily urinary calcium excretion was elevated in our patients initially and after one year of follow up; however, no correlation was obtained between lumbar spine BMD and 24 h urinary calcium excretion. Carboxy-terminal propeptide of type 1 collagen values and levels of urinary cross-linked N-telopeptides of type 1 collagen in the diabetic children were significantly lower than those of the matched controls. Osteoblastic activity as assessed by serum osteocalcin and by the carboxy-terminal propeptide of type I collagen and bone resorption as measured by cross-linked N-telopeptides of type 1 collagen did not correlate with the lumbar spine Z-scores. When IDDM patients were subdivided into males and females and into children with more than or less than 2 yr duration of diabetes since diagnosis, no differences between groups were found. These results suggest that insulin dependent diabetes in children is associated with low bone turnover resulting in a deficit in bone mass which may be manifested as osteopenia in the growing bone. This defect is already present in trabecular bone early on in the disease and seems not to be related to glycemic control.

Nonenzymatic glycation of type I collagen modifies interaction with UMR 201-10B preosteoblastic cells

Advanced glycation endproduct (AGE), whose formation is accelerated on long lived extracellular matrix proteins in diabetes, is implicated in diabetic complications in various tissues. Type I collagen is the predominant matrix protein of bone and plays an important role in bone cell-matrix interactions. We have previously reported the accelerated accumulation of AGE collagen in bone tissue in diabetes mellitus (DM), in which reduced bone mineral density was observed. In addition, when cultures of mature primary rat osteoblasts were plated onto an in vitro AGE-modified collagen substrate, they showed altered cell functions, in terms of alkaline phosphatase (ALP) activity, osteocalcin secretion, and nodule formation (J Bone Miner Res 11:931-937; 1996). To determine whether AGE collagen might also affect differentiation of preosteoblasts, we compared the effects of plating the preosteoblastic UMR 201-10B cell line onto AGE-modified collagen with plating onto unmodified collagen. The latter had been shown previously to promote differentiation of UMR 201 cells. We have also explored whether these effects might be partly mediated by the transforming growth factor beta (TGF-beta) receptor. Growth of UMR 201-10B cells on a type I collagen substrate significantly inhibited cell growth and retinoic acid (RA)-induced upregulation of ALP activity, compared to cells on plastic. These inhibitory effects were reduced by prior glycation of collagen, in a dose-dependent manner with respect to AGE content. Unmodified collagen stimulated production of osteopontin mRNA, which was reduced by AGE modification to levels attained in cells on plastic. Growth on control collagen inhibited TGF-beta type II receptor binding in 10B cells, while this inhibition was reduced by AGE modification. These data suggest that glycation of collagen interferes with specific interaction(s) between UMR 201-10B cells and collagen. Based on our previous results in UMR 201 cells, these results would be compatible with the notion that glycated collagen has reduced ability to promote differentiation of preosteoblasts to mature osteoblasts. These data further suggest that collagen-mediated events in these cells may be at least in part mediated by regulation of the TGF-beta receptor expression.

Tetracycline prevents cancellous bone loss and maintains near-normal rates of bone formation in streptozotocin diabetic rats

The skeletal consequences of streptozotocin-induced (STZ) diabetes in the rat are characterized by decreased bone formation and, consequently, reductions in bone mass. Given the ability of tetracyclines to inhibit the breakdown of connective tissue collagen in experimental diabetes (and in other diseases), we examined the potential of this drug to prevent the osteopenia associated with STZ diabetes. To evaluate drug efficacy, the cortical and trabecular bone histomorphometry were analyzed and compared between vehicle-treated control and diabetic rats and control and diabetic rats treated orally with 20 mg/day of minocycline, a semisynthetic tetracycline. In addition, blood and urine glucose, body weight change, tibia lengths, cortical bone densities, and bone ash content were compared. At the end of the 26 day experimental period, diabetic (D) and minocycline-treated diabetic (MTD) rats were polyuric with reduced body weights and significantly elevated blood and urinary glucose levels (p < 0.01). Compared to control (C) and minocycline-treated control (MTC) animals, the periosteal and cancellous bone formation in the D rats had virtually ceased (p < 0.001), and the cancellous bone mass in the tibial metaphysis was reduced 47% (p < 0.01). In contrast, bone formation rates in the MTD animals were increased compared to the D rats (p < 0.001), while cancellous bone areas in the MTD animals were essentially equivalent to those observed in the C and MTC groups. Moreover, growth plate thickness, reduced 43% in the D rats, was preserved in the diabetic animals treated with minocycline. These results demonstrate that minocycline treatment of the streptozotocin diabetic rat maintains normal bone formation, normalizes growth plate thickness, and prevents cancellous bone loss.

Bone mineral metabolism is normal in non-insulin-dependent diabetes mellitus

Because of the previous controversial findings in non-insulin-dependent diabetes mellitus (NIDDM), we measured bone-mineral density (BMD) by two different methods, studied biochemical markers of bone remodeling and calciotropic hormones (parathyroid hormone and calcitonin) in women with NIDDM, and compared the results with age-matched controls. Forty-seven women with NIDDM and 252 healthy nondiabetic women as controls were recruited for this study. BMD was measured by dual X-ray absorptiometry (DEXA) and by quantitative computed tomography (QCT). Biochemical markers of bone remodeling included plasma alkaline phosphatase (AP), osteocalcin (BGP), tartrate-resistant acid phosphatase (TRAP), parathyroid hormone (PTH), calcitonin (CT), and 24-h urine calcium, hydroxyproline. Diabetic patients were more obese with a higher body-mass index (BMI) than controls. Bone mass was normal in NIDDM, both by DEXA and by QCT. Biochemical markers of bone remodeling, PTH and CT were also normal. There was no statistical correlation between bone mass and any of the other measurements studied. There is no evidence that NIDDM produces any change in bone metabolism or mass.

Role of nonenzymatic glycosylation of type I collagen in diabetic osteopenia

Formation of advanced glycation end products (AGEs) in extracellular matrix (ECM) is implicated in the development of chronic diabetic complications. However, the involvement of AGEs in diabetic bone disease has not been well established. We have examined whether AGEs are increased in the bone collagen of streptozotocin-induced diabetic rats in vivo and whether glycation of type I collagen affects the functions of osteoblastic cells in vitro. During 12 weeks of observation, AGEs in collagen extracted from the tibiae of diabetic rats increased in a time-dependent manner and were significantly higher than controls at every time point. In vitro, the incubation of collagen with glucose-6-phosphate resulted in a time-dependent increase of AGEs. When osteoblastic cells isolated from fetal rat calvaria were cultured on AGE-modified type I collagen, it dose-dependently inhibited phenotypic expressions of osteoblasts. Among osteoblastic parameters, nodule formation was the most sensitive, being inhibited by approximately 70% by the glycation of collagen for only 1 week. Alkaline phosphatase activity and osteocalcin secretion were inhibited by 20-30% and 15-70%, respectively, by the glycation of collagen for 1-5 weeks. These results indicate that AGE-modified collagen affects osteoblastic cell differentiation and function in vitro and suggest that similar changes occurring in vivo may contribute to diabetic osteopenia.

Treatment of osteopenia in children with insulin-dependent diabetes mellitus: the effect of 1 alpha-hydroxyvitamin D3

Twelve children (8 boys and 4 girls) with insulin-dependent diabetes mellitus (IDDM), aged 9-15 years, received 1 alpha-hydroxyvitamin D3 (1 alpha-OHD3) in a dose of 0.05 microgram/kg per day for 1 year. Duration of disease varied between 2.8 and 9 years. Bone density was determined in the distal third of forearm using single photon absorptiometry, and was expressed as standard scores (+/- SD) with respect to sex- and age-matched controls. Bone density measurements and ultrasound studies of the kidneys were performed at 0, 6 and 12 months. Serum calcium, ionized calcium, phosphorus, magnesium, creatinine, alkaline phosphatase, glycosylated haemoglobin in morning blood samples and urinary Ca, P, Mg, and hydroxyproline were regularly determined. One patient was excluded from the study because of hypercalciuria and one because of lack of compliance. Bone density increased significantly after 6 and 12 months of 1 alpha-OHD3 administration (P = 0.015, P < 0.001 respectively). None of the biochemical parameters changed significantly.

CONCLUSION

Osteopenia is not uncommon in children and adolescents with IDDM. In 10 children with IDDM and osteopenia the administration of 1 alpha-OHD3 for 1 year corrected bone loss.

Influence of high glucose on 1,25-dihydroxyvitamin D3-induced effect on human osteoblast-like MG-63 cells

Impaired bone formation due to defective osteoblast function, as reflected in a decreased serum osteocalcin (OC) concentration in the patients with diabetes, has been implicated in the development of diabetic osteopenia. The role of hyperglycemia in this decrease in serum OC concentration was investigated. 1,25-dihydroxyvitamin D3 (1,25[OH]2D3), an active form of vitamin D3, stimulated OC secretion from the human osteosarcoma cell line MG-63 in a dose-dependent manner. Exposure of the cells to high concentrations of glucose for 7 days significantly impaired 1,25(OH)2D3-induced OC secretion as compared with that observed with cells maintained under normal glucose (5.5 mM) or high mannitol conditions. The inhibitory effect of glucose was in a dose-dependent manner up to 55 mM. High glucose (55 mM) also attenuated the 1,25(OH)2D3-induced increase in OC mRNA abundance in MG-63 cells, suggesting that the inhibition of the 1,25(OH)2D3-induced increase in OC secretion by exposure to a high concentration of glucose was, at least in part, mediated at the transcriptional level. High glucose significantly decreased the number of 1,25(OH)2D3 receptors in MG-63 cells, without any change in the dissociation constant for 1,25(OH)2D3; this effect was not mimicked by high mannitol, indicating specificity for glucose. These observations suggest that a high glucose concentration significantly impairs the ability of osteoblastic cells to synthesize OC in response to 1,25(OH)2D3 by reducing 1,25(OH)2D3 receptor number, and that impaired cell function caused by sustained exposure to high glucose contributes to the defect in bone formation observed in the patients with diabetic osteopenia.

Development of secondary hyperparathyroidism and bone disease in diabetic rats with renal failure

Renal osteodystrophy in diabetic patients on maintenance hemodialysis is characterized by a higher prevalence of low bone turnover and is associated with a relative deficiency of parathyroid hormone (PTH) as compared with non-diabetic hemodialysis patients. The goal of the study was to evaluate how diabetes affected the development of secondary hyperparathyroidism (2 degrees HPT) and bone disease in azotemic rats. Three groups of 5/6 nephrectomized, pair-fed male Wistar rats maintained on a high phosphorus (1.2%) diet were studied: (1) the control group, non-diabetic azotemic rats (NDR); and two streptozotocin-induced diabetic azotemic groups, (2) poorly-controlled diabetic rats (PCDR) which received only enough NPH insulin to maintain the blood glucose between 300 and 400 mg/dl, and (3) well-controlled insulin-treated diabetic rats (IDR) which received a continuous insulin infusion for 14 days via a subcutaneously implanted miniosmotic pump. Serum calcium, phosphorus and creatinine levels were similar among the three groups. Blood glucose levels were greater in the PCDR group than the IDR and NDR groups (358 +/- 11 vs. 83 +/- 9 and 87 +/- 8 mg/dl, respectively; P < 0.001). Rats in the PCDR group weighed less at sacrifice as compared with the IDR and NDR groups (P < 0.05). Serum PTH levels (normal 47 +/- 2 pg/ml) were elevated, but not different among the three groups (136 +/- 34, 147 +/- 21 and 98 +/- 8 pg/ml in the PDCR, IDR and NDR groups, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)