To investigate the pathophysiology of diabetic osteopenia, circulating levels and bone contents of bone gamma-carboxyglutamic acid-containing protein (BGP) were measured in streptozocin-induced diabetic rats . Plasma calcium and total protein were significantly decreased (P less than .01) in the diabetic group, and the plasma level of BGP in diabetic rats was 19.6 +/- 2.8 (mean +/- SE) ng/ml, which is significantly lower than the value of 89.2 +/- 14.0 ng/ml in control rats (P less than .01). Bone contents of calcium and hydroxyproline per femur were significantly decreased in the diabetic group (P less than .01), and the ratios of bone calcium to hydroxyproline were not different. Bone BGP content per femur in the diabetic group was 669 +/- 58 micrograms, which was also significantly lower compared with 1241 +/- 126 micrograms in control rats (P less than .01). The decreased bone content of BGP is consistent with the hypothesis that BGP synthesis is impaired in insulin-deficient diabetes. Because a relationship between plasma levels of BGP and bone turnover has been established, the low plasma BGP value suggests there is a decrease in bone turnover in diabetic rats. Therefore, we postulate that the low bone turnover is one of the pathological features of diabetic osteopenia and is at least partly responsible for the occurrence of this complication in diabetes mellitus.
In order to investigate the pathophysiology of anticonvulsant-induced osteopenia, circulating levels of bone gamma-carboxyglutamic acid-containing protein (Bone Gla Protein: BGP) and urinary excretion of BGP were measured in 16 children on chronic anticonvulsant therapy and in 12 control children. Using microdensitometry analysis, osteopenia was found in 25% of the anticonvulsant therapy group, but it was not observed in the control group. Serum BGP and A1-P levels were significantly increased in the anticonvulsant group compared with the control group (P less than 0.05 and P less than 0.01, respectively), and a positive correlation was found between serum BGP and A1-P levels (P less than 0.05). Urinary excretion of BGP and hydroxyproline showed an increase in the anticonvulsant group, but it was not statistically significant. On the other hand, there was no significant difference between the two groups in serum levels of vitamin D metabolites, PTH, calcitonin, Ca, or P or in urinary excretion of Ca or P. It is suggested, therefore, that the increased BGP level in children receiving anticonvulsant therapy is a reflection of high bone turnover due to anticonvulsant drug complications.
Circulating levels and bone contents of bone y-carboxyglutamic acid-containing protein in rat models of noninsulin-dependent diabetes mellitus. Acta Endocrinol 1993;128:69-73. ISSN 0001-5598 In order to investigate the pathophysiology of the diabetic osteopenia observed in non-insulin\x=req-\ dependent diabetes mellitus, the circulating levels and the bone contents of bone \g=g\-carboxyglutamic acid-containing protein (osteocalcin) were determined in rat models of non-insulin-dependent diabetes mellitus, neonatally streptozotocin-induced rats and in genetic Wistar fatty rats. In Wistar fatty rats the plasma level of osteocalcin was 8.1 \m=+-\0.8nmol/l, significantly lower than the value of 1 7.3 \m=+-\0.9nmol/l in their lean littermates (p < 0.001). Bone length, bone strength, and weight of powdered bone in Wistar fatty rats were significantly decreased compared to control rats (p<0.001, p<0.02 and p<0.001, respectively). Bone content of osteocalcin per femur in Wistar fatty rats was also significantly decreased compared to controls (p<0.001). In addition, plasma osteocalcin in neonatally streptozotocin-induced diabetic rats was 2.9\m=+-\0.3nmol/l, which was also significantly decreased compared to the value of 5.6\m=+-\0.5nmol/l in their controls (p<0.001). Since it has been established that the plasma level of osteocalcin is well related to bone formation and turnover, the low plasma values in these animal models suggest that bone formation and turnover are decreased in non-insulin-dependent diabetes mellitus. Low bone formation and turnover are, therefore, postulated to be one of the pathophysiological characteristics of the skeletal tissue in non-insulin-dependent diabetes mellitus, and to be at least in part responsible for the occurrence of this complication. Diabetic osteopenia has been recognized as one of the chronic complications of diabetes mellitus in patients with insulin-dependent diabetes mellitus (1-3) and in those with non-insulin-dependent diabetes mellitus (1, 4, 5). Although a negative calcium balance has been suggested to be characteristic of the diabetic state (3, 6) and altered mineral and vitamin D metabolism has been found to be associated with this complication (5, 7, 8), the exact mechanism responsible for the pathogenesis of diabetic osteopenia remains unclear.Bone y-carboxyglutamic acid-containing protein (osteocalcin) has been shown to be one of the major noncollagenous proteins in the extracellular bone matrix (9, 10). Recent studies have revealed that calcitriol stimu¬ lates osteocalcin synthesis in osteoblastic cells (11), and plasma osteocalcin levels have been found to be a sensitive marker for bone formation and turnover in patients with metabolic bone diseases (12). We have previously reported that both circulating levels and bone contents of osteocalcin are significantly decreased in streptozotocin (STZ)-induced insulin-dependent diabetic rats, which have the complication of osteopenia (13). Since decreased plasma osteocalcin levels have been similarly observed in human and...
Diabetic osteopenia has been known as one of the chronic complications of diabetes mellitus, and a decrease in bone turnover has been thought to be one of the pathophysiological characteristics of this complication. In order to investigate the effect of long-term insulin therapy on low bone turnover in diabetes, pancreas transplantation was performed on streptozotocin-induced diabetic rats. Plasma levels of bone γ-carboxyglutamic acid-containing protein(osteocalcin) in untreated diabetic rats were 0.9±0.1 (mean±sem) nmol/l, significantly lower than the value of 4.2±0.6 nmol/l in control rats (p<0.01). Pancreas transplantation reversed this decrease to 6.3±1.1 nmol/l, which was not significantly different from the value in control rats. The circulating levels of calcitriol were significantly decreased in the untreated diabetic group (p<0.01), and the decrease was fully reversed by pancreas transplantation. In addition, the decreases in bone length, strength and weight were also improved by the transplantation. This evidence clearly shows that the improvement of metabolic derangements in diabetes by insulin is essential for the prevention of deterioration in diabetic osteopenia. It is possible, therefore, that insulin exerts an indirect beneficial influence through the metabolic amelioration on the decreases in bone turnover and circulating osteocalcin in diabetes mellitus, or has a direct stimulatory effect on the osteoblasts via the insulin receptor since its presence has been shown recently in osteoblastic cells.
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