Proceedings: Bone mineral determinations on long-term diabetics

An update on the potential role of C-peptide in diabetes and osteoporosis

PURPOSE

C-peptide secretion is deficient or absent in type 1 diabetes mellitus. It is well accepted that insulin replacement therapy cannot prevent the development of long-term diabetes-related complications, which can often be disabling or even life-threatening. Several cross-sectional investigations have suggested that residual C-peptide production in patients with type 1 diabetes mellitus would help prevent a number of complications. In animal models of diabetes and in patients with type 1 diabetes mellitus, C-peptide replacement improves renal function, skin and skeletal muscle blood flow, nerve conduction, glucose utilization, and other diabetes-related complications. Recent investigations suggest a new beneficial effect of C-peptide, which to date has never been studied. It is known that osteoporosis is the most prevalent short-term complication in type 1 diabetes mellitus. This review will highlight new insights into the pathophysiology and future therapeutic modalities for osteoporosis in individuals with diabetes.

METHODS

This review provides a concise summary of old and new insights into the role of C-peptide in diabetes-related complications.

RESULTS

The data suggest that C-peptide is a bioactive peptide, acting independently of insulin, which binds to a G-protein-coupled membrane binding site in different cell types. By triggering Ca²⁺-dependent intracellular signaling pathways, both Na⁺, K⁺-ATPase and endothelial nitric oxide synthase are activated. C-peptide may act on osteoblast cells by ERK 1/2 pathway activation, modulate collagen biosynthesis and RANKL expression. Furthermore, C-peptide-deficient postmenopausal women, not affected by diabetes, have a lower bone mineral density than those with normal C-peptide levels.

CONCLUSION

Taken together these studies encourage further investigations to elucidate the role of C-peptide in preventing bone loss in type 1 diabetes mellitus and in those individuals with C-peptide deficiency and osteoporosis.

MECHANISMS IN ENDOCRINOLOGY: Mechanisms and evaluation of bone fragility in type 1 diabetes mellitus

Subjects with type 1 diabetes mellitus (T1DM) have decreased bone mineral density and an up to sixfold increase in fracture risk. Yet bone fragility is not commonly regarded as another unique complication of diabetes. Both animals with experimentally induced insulin deficiency syndromes and patients with T1DM have impaired osteoblastic bone formation, with or without increased bone resorption. Insulin/IGF1 deficiency appears to be a major pathogenetic mechanism involved, along with glucose toxicity, marrow adiposity, inflammation, adipokine and other metabolic alterations that may all play a role on altering bone turnover. In turn, increasing physical activity in children with diabetes as well as good glycaemic control appears to provide some improvement of bone parameters, although robust clinical studies are still lacking. In this context, the role of osteoporosis drugs remains unknown.

Decreased bone ultrasound velocity in large-for-gestational-age infants

BACKGROUND

Bone speed of sound is a measure of bone breakability. There are few reports on bone mineral content in large for gestational age infants; most of them in infants of diabetic mothers. There are no data on bone speed of sound in large for gestational age infants of nondiabetic mothers.

OBJECTIVE

To test the hypothesis that large for gestational age infants of nondiabetic mothers have lower bone speed of sound than appropriate for gestational age infants.

DESIGN/METHODS

Bone speed of sound was measured within the first 96 hours of life at the right tibial midshaft in 25 singleton large for gestational age infants of non diabetic mothers and compared to appropriate for gestational age controls.

RESULTS

Bone speed of sound measured in large for gestational age infants of nondiabetic mothers was lower than in controls.

CONCLUSIONS

Large for gestational age infants of nondiabetic mothers have lower bone speed of sound than controls.

Corticosteroid-induced osteoporosis in patients with uveitis

AIMS

To estimate the prevalence of low bone density and osteoporosis in a population of patients with uveitis taking systemic steroid treatment; to clarify the risks of steroid-induced fracture and to suggest a protocol for the prevention and management of bone loss in patients with ophthalmic inflammatory disease.

METHODS

Bone densitometry was performed on 129 adult patients with prednisolone-treated uveitis from four centres. Information on uveitis diagnosis, associated risk factors, steroid dosage and treatment duration, prophylaxis and management, was collected. Juveniles, patients with scleritis and those who had used deflazacort, were excluded.

RESULTS

Steroid treatment time varied from 13 weeks to 31 years, and the total dosage from 1.29 g to 166.5 g. Twenty-six percent of patients also used one or more immunosuppressives. Forty-eight percent had additional risk factors for bone loss. Bone density was abnormally low in 44.2%, and 15.5% had osteoporosis. Osteoporosis was substantially more common in males (20.6%, all under 60 yrs) than in females (9.8%). Seven symptomatic fractures occurred in patients on treatment. Bone loss correlated with total steroid dose, mean dose, duration of treatment and the presence of pre-existing risk factors.

CONCLUSIONS

The prevalence of steroid-induced osteoporosis and fracture is low for patients with uveitis but young males are at risk. Patients at high risk should be identified, and prophylaxis and treatment should be used as required. The guideline of the National Osteoporosis Society is recommended as a management protocol.

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.

Anabolic effects of insulin on bone suggest a role for chromium picolinate in preservation of bone density

Activation of osteoclasts by parathyroid hormone (PTH) is mediated by PTH stimulation of osteoblasts, and is dependent on a PTH-induced rise in protein kinase C activity. Physiological levels of insulin reduce the ability of PTH to activate protein kinase C in osteoblasts, suggesting that insulin may be a physiological antagonist of bone resorption. In addition, insulin is known to promote collagen production by osteoblasts. These findings imply that efficient insulin activity may exert an anabolic effect on bone, and rationalize the many clinical studies demonstrating reduced bone density in Type I diabetes. Recently, the insulin-sensitizing nutrient chromium picolinate has been found to reduce urinary excretion of hydroxyproline and calcium in postmenopausal women, presumably indicative of a reduced rate of bone resorption. This nutrient also raised serum levels of dehydroepiandrosterone-sulfate, which may play a physiological role in the preservation of postmenopausal bone density. The impact of chromium picolinate (alone or in conjunction with calcium and other micronutrients) on bone metabolism and bone density, merits further evaluation in controlled studies.

Whole body composition and regional bone mass in women with insulin-dependent diabetes mellitus

OBJECTIVE

Reduced bone mass has been reported in adult patients with insulin-dependent diabetes mellitus but there are few data on bone density in the axial skeleton or on whole body composition in this group. The aim of this study was to determine whether whole body and regional bone mass are normal in middle-aged women with insulin-dependent diabetes mellitus.

DESIGN

Total and regional bone mass were measured in 24 post-menopausal women aged 43-69 years (mean 56.3) with insulin-dependent diabetes, recruited during routine clinic attendance. Results were compared with those obtained from 24 age and weight-matched community-based post-menopausal women.

MEASUREMENTS

Whole body bone mineral content and bone mass in the lumbar spine and femoral neck were measured by dual energy X-ray absorptiometry on a Lunar DPX.

RESULTS

Whole body bone mineral content was significantly lower in the diabetic women than in community-based controls (P = 0.02). There was no significant difference between the two groups in whole body bone density or lumbar spine bone density. Mean bone density in the femur was lower in the patient group at all sites assessed (femoral trochanter P = 0.003, femoral neck, P = 0.057). Values for all regional bone density measurements in the diabetic women were within the Lunar reference range (mean +/- 2 SD) and at all sites the mean value was close to 100% of the sex and age-matched reference value. There was no correlation between duration or control of diabetes and bone mass at any site.

CONCLUSIONS

Insulin-dependent diabetes mellitus in middle-aged women is associated with small reductions in total body bone mineral content and in femoral bone density; the clinical significance of these findings in terms of subsequent fracture risk remains to be established. No evidence was found in this study for a reduction in whole body or lumbar spine bone density.

Bone mineral content of the third lumbar vertebra during 18 months of prednisolone treatment for giant cell arteritis

Altogether forty-four patients with giant cell arteritis (GCA) were randomly allocated to either daily morning or alternate-day administration of prednisolone. The BMC of the third lumbar vertebra was determined using dual photon absorptiometry. At least ten measurements were performed in each patient during a period of 18 months. During the course of treatment there was no significant change of the mean BMC in either group compared to the pre-treatment value. The changes of BMC were independent of such potentially explanatory variables as cumulative dose of prednisolone, initial BMC, sex and body weight. Corticosteroid treatment in patients with GCA, in the doses used by us, does not appear to cause excessive bone loss.

Calcium metabolism in diabetes mellitus: effect of improved blood glucose control

Reduced bone mass occurring with increased frequency in diabetes mellitus has been attributed to poor blood glucose control but the pathogenetic mechanisms remain unknown. To evaluate the role of calcium metabolism, 59 patients with diabetes and normal renal function (22 Type 1, 37 Type 2) were studied. In all patients plasma calcium (Ca), serum phosphate (PO4), serum parathyroid hormone (PTH), and 24-h urinary calcium (uCa) were determined under both poor and improved control (for at least 7 days) as ascertained by four blood glucose determinations daily. Improvement of blood glucose control (p = 0.001) was associated with reduction of uCa both in Type 1 (6.9 +/- 1 vs 4.9 +/- 0.9 mmol day-1, mean +/- SEM, p = 0.02) and in Type 2 patients (4.2 +/- 0.4 vs 3.2 +/- 0.4 mmol day-1, mean +/- SEM, p = 0.002). Considerably more Type 1 patients (10 out of 22) had PTH values below the detection limit (1.5 pmol l-1) during poor than during improved control (2 out of 22). Comparison between the two types of diabetes showed that in Type 1 under poor control, Ca and PTH were lower (p = 0.03), while uCa was higher (p = 0.003), and after improved control, only uCa continued to be higher (p = 0.035). These findings suggest that increased uCa excretion in association with 'functional hypoparathyroidism' (especially in Type 1 diabetes) is observed during poor blood glucose control, and may be one of the factors leading to reduced bone mass in diabetes mellitus.

Bone mineral density measured by dual energy x-ray absorptiometry in patients with non-insulin-dependent diabetes mellitus

Because of the previous controversial findings in diabetic patients with older methodologies, we assessed bone mineral density (BMD) in 78 patients (38 males and 40 females) with non-insulin-dependent diabetes mellitus using dual energy x-ray absorptiometry (DEXA). BMD was measured in lumbar vertebrae (L2-4). The BMD of each patient was calculated as the percentage of the mean value (%BMD) obtained from a healthy control group matched for sex and age. The %BMD of the patients with diabetes was about 100% for females and 96% for males, as compared with BMD of normal controls. The %BMD of the patients with diabetes was significantly correlated with body mass index and urinary C peptide level, and inversely correlated with age and duration of diabetes within 20 years. No relationships were found between %BMD and serum calcium, phosphorus, or glycosylated hemoglobin A1C levels. These observations suggest that metabolic abnormalities associated with diabetes mellitus alter the BMD, and that such factors as duration of the disease and deficit in insulin secretion are risk factors for decreased BMD.

Prednisone-induced osteopenia in beagles: variable effects mediated by differential suppression of bone formation

To examine the mechanism of glucocorticoid-induced osteopenia and the basis for variable bone loss after glucocorticoid administration, we gave prednisone (1.3 mg.kg-1.day-1) to normal male dogs (n = 15) for 29 wk to attempt induction of osteopenia. Compared with age-matched control dogs (n = 14), prednisone treatment rapidly decreased spinal bone density by 4.3%, as assessed by quantitative digital radiography, and reduced trabecular bone volume by 14.6%, as measured by quantitative histomorphology of iliac crest bone specimens. Bone loss was attenuated in prednisone-treated dogs after prolonged treatment (greater than 12 wk). Prednisone treatment resulted in diminished bone formation rates (15 +/- 3.4 vs. 47 +/- 4.5 microns/yr) and activation frequency (0.4 +/- 0.1 vs. 1.3 +/- 0.2/day). These findings indicate that suppression of osteoblastic function and recruitment is the primary histological abnormality mediating glucocorticoid-induced osteopenia in beagles. In contrast, prednisone administration had no effect on bone resorption or serum concentrations of parathyroid hormone and 1,25-dihydroxyvitamin D, which suggests that these factors are not essential for prednisone-induced bone loss. Moreover, 33% of beagles were totally resistant to glucocorticoid-induced osteopenia. Such heterogeneity of bone loss was associated with variable suppressive effects of prednisone on osteoblastic function, as evidenced by greater bone formation rates and activation frequency in prednisone-resistant animals. Collectively, these observations suggest that glucocorticoid-induced bone loss results from a dynamic interplay between steroid-mediated suppression of osteoblastic function and recruitment and undefined compensatory factors that ameliorate the effects of glucocorticoids on osteoblastic precursors.

Bone mineral density of the lumbar vertebrae in children and adolescents with insulin-dependent diabetes mellitus

To test the hypothesis that bone mineral density (BMD) is lower in children with insulin-dependent diabetes mellitus (IDDM), we measured BMD of the lumbar vertebrae (L-2 to L-4) by dual-photon absorptiometry in 31 boys and 25 girls, mean age 12.3 years, with IDDM of varying clinical duration (range 0.1 to 14.8 years). Mean standard deviation scores (z scores) were determined for L-2-L-4 BMD, weight, height, weight percentile, and weight-adjusted L-2-L-4 BMD index (L-2-L-4 BMD/weight), with reference data from a previously described white, nondiabetic, age-matched control group (n = 221). Compared with nondiabetic control subjects, male patients with short-term IDDM and all female patients with IDDM did not have significantly different L-2-L-4 BMD, weight, weight percentile, height, or BMD index. Boys with IDDM longer than 1 year had significantly lower weight, weight percentile, and height than did age-matched control subjects. When L-2-L-4 BMD of boys with long-term diabetes was corrected for weight, the L-2-L-4 BMD index was significantly greater than that of control subjects, indicating that weight was disproportionately lower than BMD. There were no significant linear correlations between metabolic control and L-2-L-4 BMD. When L-2-L-4 BMD was adjusted for differences in body weight, spinal BMD values in children with IDDM were not lower than in control subjects. These findings indicate that in children with IDDM, as in previously studied nondiabetic youths, body weight and spinal BMD are highly correlated; although BMD is reduced in some children with diabetes, the reduction parallels reductions in growth, and may simply reflect a normal response of the skeleton to a lower weight-bearing load.

Bone mineral density in diabetes mellitus

In the present study bone mineral content (BMC) was measured at 1/3 and 1/10 the length of the radius from the distal end in 100 adult diabetic subjects (55 females, 45 males, 54 insulin-dependent [IDD], 46 non-insulin-dependent [NIDD]), using single photon absorptiometry. Each individual BMC value in the diabetics was first compared to normal BMC values for age obtained in our laboratory from 500 non-diabetic subjects. BMC in the diabetics was within the normal range (M +/- 2 SD) with respect to sex and age. Data from IDD and NIDD males, under and over 50 years of age, and of IDD and NIDD females, pre- and postmenopausal, were compared with the respective control group data after matching each diabetic subject to a non-diabetic one of identical age and menstrual history and of comparable body mass index. In each group BMC in the diabetic subjects was found not to be statistically different from BMC in the control ones. Correlation analysis was carried out between BMC and endocrine or metabolic parameters obtained in 52 of the diabetic patients. BMC in diabetic subjects was not correlated with plasma levels of hormones (thyroid hormones, cortisol, 17-beta-estradiol, testosterone), Ca, P or alkaline phosphatase activity. It was inversely correlated with urinary Ca and P in NIDD women and with urinary Ca in NIDD men. No relationship was found between BMC and the metabolic control of diabetes (evaluated by basal glycemia, 2h-post-prandial glycemia and glycosylated hemoglobin).

Are disease duration and degree of functional impairment determinants of bone loss in rheumatoid arthritis?

One hundred and five patients with rheumatoid arthritis treated with a variety of antirheumatic drugs, excepting glucocorticoids, were stratified according to the degree of functional impairment (functional classes I to IV) and duration of the disease (0-3 years; 4-8 years; and greater than 8 years). The variables investigated were distal forearm bone mineral content (BMC), biochemical markers of bone formation: serum alkaline phosphatase and serum bone gamma-carboxyglutamic acid containing protein (BGP) and biochemical markers of bone resorption: fasting urinary calcium and fasting urinary hydroxyproline. Significant relationships were found between BMC and functional impairment and duration of the disease. Indices of bone formation and bone resorption rose with increasing functional impairment, particularly those of bone resorption. It is concluded that disability induces osteopenia in rheumatoid arthritis by increasing the bone turnover with a more marked increased in resorption than in the formation processes. The effect of the disease duration is merely that of adding more years of functional impairment.

The effect of glucocorticoids on bone mass in rheumatoid arthritis patients. Influence of menopausal state

We studied 97 patients with definite or classic rheumatoid arthritis (RA). Fifty-four patients (19 premenopausal women, 25 postmenopausal women, and 10 men) had been treated with low-dose glucocorticoids for at least 12 months (mean dose less than 10 mg/day). The remaining 43 patients (15 premenopausal women, 17 postmenopausal women, and 11 men) had been treated with penicillamine, and served as a patient control group. The distal forearm bone mineral content (BMC) was measured in all patients by single photon absorptiometry using 125I, and the total body bone mineral (TBBM) was measured in 61 patients by dual photon absorptiometry using 153Gd. Compared with normal controls, both treatment groups had significantly decreased BMC and TBBM (0.01 less than P less than 0.001). When the patients were stratified according to pre- and postmenopausal state, we found significantly lower BMC and TBBM values in the premenopausal glucocorticoid-treated women than in penicillamine-treated women. However, no differences in BMC and TBBM values were found in the corresponding postmenopausal groups. In the premenopausal women treated with glucocorticoids, the duration of treatment and cumulative dose correlated with BMC. No such correlations were found in the postmenopausal women. We conclude that 1) RA is associated with loss of bone mass, 2) systemic glucocorticoid treatment further aggravates the bone loss, 3) in postmenopausal RA patients, the bone loss resulting from menopause and from the disease itself is not accelerated by low-dose glucocorticoids, and 4) in premenopausal RA patients, however, the bone mass is significantly affected by glucocorticoid treatment. We therefore suggest that these factors be considered when prescribing glucocorticoids, in order to minimize the bone loss.

Evaluation of factors associated with glucocorticoid-induced osteopenia in patients with rheumatic diseases

In 161 ambulatory rheumatic disease patients receiving long-term prednisone therapy, diaphyseal mass (DM) and metaphyseal mass (MM) of the forearm were measured by single photon absorptiometry, and bone radiographs were reviewed when available. Multivariate analysis of treatment and patient characteristics demonstrated that glucocorticoid-induced osteopenia (defined as an elevated DM:MM ratio) and bone fractures occurred with similar frequency in patients of each sex, in whites and blacks, in patients with various rheumatic diseases, and in patients receiving different regimens of prednisone therapy. However, large cumulative doses of prednisone were associated with elevated DM:MM ratios as well as with bone fractures, and menopause or age greater than or equal to 50 years (males or females) was associated with bone fractures. We conclude that long-term therapy with various prednisone regimens results in glucocorticoid-induced osteopenia and fractures. This affect is cumulative, occurs in all patient groups, and results in more bone fractures in certain groups.

Prevalence of decreased bone mass in rheumatoid arthritis. Relation to anti-inflammatory treatment

The bone mineral content (BMC) in both forearms (highly correlated to total body calcium) was measured by photon absorptiometry in a representative sample of rheumatoid arthritis outpatients comprising 129 patients treated with either gold salts (n = 29), penicillamine (n = 61), prednisone (n = 24), or other anti-RA drugs (n = 15). The mean BMC value was 84% of normal (p less than 0.001) with the lowest mean value in the group treated with prednisone (73% of normal). The patients as a group had hypocalcaemia (p less than 0.001), raised serum alkaline phosphatase (p less than 0.001), and normal urinary excretion rates of calcium and hydroxyproline. These results indicate that RA patients have disturbances in their calcium and bone metabolism.

Steroid-induced fractures and bone loss in patients with asthma

To study the association between bone disease and long-term steroid administration in asthmatics, we reviewed the hospital records of 128 patients over 40 years of age who had taken daily or alternate-day adrenal corticosteroids for at least a year and compared them with the records of 54 other asthmatics of similar age who had not required long-term administration of steroids. We found evidence in the records of a total of 58 fractures of the ribs or vertebrae in 14 of the patients who had received long-term steroid treatment (11 per cent) and no evidence of fractures in the patients who had not received long-term treatment. We also prospectively studied 30 hospitalized asthmatic patients between 20 and 70 years of age who had been screened for medications (other than steroids) or complicating diseases known to affect bone mineralization. Eight of 19 asthmatic patients receiving long-term steroid therapy had rib or vertebral fractures, whereas none of 11 matched patients not receiving such therapy had fractures. Furthermore, bone-density measurements of the distal and proximal radius by photon absorptiometry revealed that the trabecular, but not the cortical, bone mass was below normal in the former group of patients but not in the latter. Within the long-term steroid group, there was no significant correlation between bone density and dose or duration of steroid treatment. We conclude that long-term steroid therapy in asthmatic patients is associated with decreased trabecular bone density and an increased prevalence of rib and vertebral fractures.

Corticosteroid-induced bone loss. A longitudinal study of alternate day therapy in patients with bronchial asthma using quantitative computed tomography

Treatment with corticosteroids can produce osteoporosis. It is generally held that bone loss occurs when steroids are administered daily, but recent findings indicate that bone may also be lost on alternate day therapy. Cortical and trabecular bone, which may be affected differently, can be assessed independently, by quantitative computed tomography. This technique has been applied to the appendicular skeleton in following 20 patients with bronchial asthma during one year of chronic alternate day corticosteroid therapy. The trabecular bone loss was considerable; prednisone 25 mg on alternate days caused an average reduction in trabecular bone of 3.5% over one year. Bone loss was dose- and age-dependent. Young patients on 50 mg/2 days lost up to 17% trabecular bone in one year. Cortical bone was not significantly affected over the same period.

Vitamin D deficiency inhibits pancreatic secretion of insulin

The effects of a vitamin D deficiency on insulin and glucagon release was determined in the isolated perfused rat pancreas by radioimmunoassay of the secreted proteins. During a 30-minute period of perfusion with glucose and arginine, pancreases from vitamin D-deficient rats exhibited a 48 percent reduction in insulin secretion compared to that for pancreases from vitamin D-deficient rats that had been replenished with vitamin D. Vitamin D status had no effect on pancreatic glucagon secretion. This result, along with the previously demonstrated presence in the pancreas of a vitamin D-dependent calcium-binding protein and cytosol receptor for the hormonal form of vitamin D, 1,25-dihydroxyvitamin D3, indicates an important role for vitamin D in the endocrine functioning of the pancreas.