Abnormal cell calcium concentrations in cultured bone cells obtained from femurs of obese and noninsulin-dependent diabetic rats

Beneficial Effect of Cissus quadrangularis Linn. on Osteopenia Associated with Streptozotocin-Induced Type 1 Diabetes Mellitus in Male Wistar Rats

Petroleum ether fraction of Cissus quadrangularis (PECQ) impact on the development of osteopenia in type 1 diabetic rat model has been evaluated. Diabetic rats were treated orally with two doses of PECQ. Another group of diabetic rats were treated with subcutaneous injection of synthetic human insulin. The cortical and trabecular bone thickness and bone strength were significantly decreased in diabetic rats. Treatment with two doses of PECQ significantly prevented these changes in diabetic rats. However, PECQ treatment (two doses) did not alter the glycemic levels in these diabetic rats. Increased levels of serum alkaline phosphatase (ALP), tartrate-resistant acid phosphatase (TRAP), and hydroxyproline were noted in diabetic rats when compared to normal control rats. The two doses of PECQ treatment further improved the serum ALP levels and significantly decreased the serum levels of TRAP and hydroxyproline. The effects of PECQ treatment on histological, biomechanical, and biochemical parameters are comparable to those of insulin. Since PECQ improves the bone health in hyperglycemic conditions by enhancing the cortical and trabecular bone growth and altering the circulating bone markers, it could be used as an effective therapy against diabetes-associated bone disorders.

Disordered osteoclast formation in RAGE-deficient mouse establishes an essential role for RAGE in diabetes related bone loss

The mechanisms underlying diabetes-mediated bone loss are not well defined. It has been reported that the advanced glycation endproducts (AGEs) and receptor for AGEs (RAGEs) are involved in diabetic complications. Here, mice deficient in RAGE were used as a model for investigating the effects of RAGE on bone mass. We found that RAGE-/- mice have a significantly increased bone mass and bone biomechanical strength and a decreased number of osteoclasts compared to wild-type mice. The serum levels of IL-6 and bone breakdown marker pyridinoline were significantly decreased in RAGE-/- mice. RAGE-/- mice maintain bone mass following ovariectomy, whereas wild-type mice lose bone mass. Furthermore, osteoclast-like cells do express RAGE mRNA. Our data therefore indicate that RAGE serves as a positive factor to regulate the osteoclast formation, directly implicates a role for RAGE in diabetes-promoted bone destruction, and documents that the AGE-RAGE interaction may account for diabetes associated bone loss.

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.

The effects of diabetes mellitus on the material properties of human metatarsal bones

While some investigations have focused on the effect of diabetes on the material properties of connective tissue in both the human and animal model, no study to date has investigated the effects of the disease process on human metatarsal bones. This investigation compared the material properties of human metatarsal bones from young diabetic donors (51.3 +/- 8 years) and older nondiabetic donors (72.3 +/- 10 years). The results demonstrated no significant differences between the two groups. This would seem to suggest that the effects of aging are comparable to the effects of diabetes on the structural integrity of human metatarsal bones.

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.

Influence of calcium channel blocker treatment on the mechanical properties of diabetic rat myocardium

The objective of this investigation was to determine whether calcium channel blocker (CCB) treatment effectively restores normal baseline mechanical function in diabetic myocardium and to evaluate its effect on the interval-strength relationship. Wistar rats were made diabetic with streptozotocin (55 mg/kg, IV). Left-ventricular papillary muscles from normal and diabetic (10 weeks) rats were superfused with Tyrode's solution at 30 degrees C. A subgroup of diabetic and normal animals received daily injections of verapamil or nifedipine (10 mg/kg, IP; 8 weeks) to compare the effectiveness of a phenylalkylamine to a dihydropyridine in reversing diabetes-induced contractile dysfunction in vitro. Muscles were electrically stimulated at 0.5 Hz with suprathreshold stimuli, and the following parameters were measured: peak tension developed, time to-peak tension, time-to-90% relaxation, and the maximum velocities of tension development and decay. Experimental diabetes was characterized by: severe hyperglycemia, hepatomegaly, reduced body weight gain, cardiomegaly, and increased plasma phospholipid levels. In addition, baseline values of peak tension developed, time to-peak tension, and time-to-90% relaxation were significantly greater in muscles from diabetic animals. Chronic nifedipine treatment reduced hyperglycemia and plasma phospholipid levels, normalized body weight gain, and reduced both heart and liver sizes in diabetic animals. Nifedipine treatment completely reversed diabetes-induced prolongation in both time-to-peak tension and time-to-90% relaxation. In diabetic myocardium, a slightly positive component was present in the interval-strength relationship between 0.01 and 1 Hz, resulting in a rightward shift in the entire curve across a wide range of stimulation frequencies (0.01-5 Hz). This positive component was absent in muscles from diabetic animals treated with both CCBs, and verapamil produced a leftward shift in the frequency response curve. The results of this study suggest that chronic nifedipine treatment may be more effective than verapamil in restoring normal baseline myocardial mechanical function, reducing hyperglycemia and hyperlipidemia, as well as attenuating both cardiac and liver enlargement in experimental diabetes. In contrast, verapamil treatment tended to normalize more effectively the inotropic response to changes in stimulation frequency in diabetic myocardium.

Decreased activity of (Ca2+ + Mg2+)-adenosine triphosphatase (ATPase) and a hormone-specific defect in insulin regulation of ATPase in kidney basolateral membranes from obese fa/fa rats

The plasma membrane enzyme (Ca2+ + Mg2+)-adenosine triphosphatase (ATPase) is hormonally regulated and may participate in Ca2+ signaling by removing excess Ca2+ from the cell. Therefore, observations of a hormone-specific loss of insulin stimulation of ATPase in kidney membranes from non-insulin-dependent diabetic (NIDDM) rats may reflect their insulin-resistant state. Consequently, to evaluate whether additional insulin-resistant conditions are associated with impaired function of ATPase and with loss of regulation of the enzyme by insulin, studies were extended to investigate (Ca2+ + Mg2+)-ATPase activities and hormonal regulation of the enzyme in kidney basolateral membranes from obese and lean Zucker rats. (Ca2+ + Mg2+)-ATPase activity was lower in membranes from obese rats compared with lean rats. Maximal velocity (Vmax) of the enzyme activity was 29.2 +/- 2.6 nmol Pi/mg/min in obese rats versus 57.2 +/- 6.5 in lean rats (P < .05). However, the affinity of the enzyme for Ca2+ was similar in obese and lean rats (Km Ca2+, 0.23 +/- 0.025 v 0.23 +/- 0.032 mumol/L Ca2+). Also, the Km for ATP of the enzyme was similar in membranes from obese and lean rats. Insulin, parathyroid hormone (PTH), and cyclic adenosine monophosphate (cAMP) stimulated the ATPase activity in membranes from lean rats in a dose-dependent manner (15% to 28%). Also, the protein kinase C (PKC) stimulator 12-O-tetradecanoyl phorbol-13-acetate (TPA) increased the ATPase activity in membranes from lean rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone mineral density in the femur and lumbar vertebrae decreases after twelve weeks of diabetes in spontaneously diabetic-prone BB/Worcester rats

The accumulated data indicate that bone mineral density (BMD) is decreased in humans with insulin-dependent diabetes mellitus. The purpose of this study was to prospectively determine sequential lumbar and femoral BMD utilizing dual energy X-ray absorptiometry in rats that spontaneously become diabetic to determine if weight and blood glucose control would prevent the diabetes-related bone mass changes. BMD of the lumbar spine and femur was measured prior to the onset of diabetes and at 3-week intervals after the diagnosis of diabetes for 12 weeks in 14 diabetes-prone BB/Wor rats (DP) and eight diabetes-resistant BB/Wor control rats (DR). At 12 weeks, the lumbar (0.238 +/- 0.013 vs 0.262 +/- 0.007 g/cm2, P < 0.001) and femoral (0.313 +/- 0.013 vs 0.343 +/- 0.013 g/cm2, P < 0.001) BMD were significantly lower in the DP rats despite significantly greater body weights (387 +/- 26 vs 329 +/- 46 g, P < 0.001) and plasma glucose levels of only 178 mg/dl. There was no difference in plasma values of calcium, phosphorus, osteocalcin, or tartrate-resistant acid phosphatase between groups or differences in osteoblast numbers in histologic sections. There was a significant (P < 0.001) decrease in plasma creatinine in the diabetic animals. The results indicate that in this animal model of type I diabetes, spine and femoral BMD do not increase comparable to control despite weight and blood glucose control. This would suggest that the diabetic condition itself affects bone mass in the absence of weight loss and poor blood glucose control.

Diabetes mellitus: a disease of abnormal cellular calcium metabolism?

Although the pathogenesis of the diabetes mellitus syndrome remains poorly understood, both insulin-dependent diabetes mellitus and non-insulin-dependent diabetes mellitus predispose the individual to a similar spectrum of complications, including hypertension, macrovascular and microvascular disease, cataracts cardiomyopathy, neuropathy, and premature aging, suggesting that these complications develop along a pathway common to both diabetic conditions. Yet not all diabetic persons are affected by all of these complications or to the same degree. What causes this marked variability in the clinical manifestations of the diabetes syndrome remains an enigma. Accumulating data from animal models of diabetes and from studying patients with diabetes reveal that intracellular calcium levels are increased in most tissues. The activities of the membrane, adenosine triphosphatase (ATPase) associated cation pumps, which determine intracellular calcium level (i.e., calcium-ATPase and [sodium + potassium]-ATPase), are also altered. The nature of the alteration is often tissue specific and may depend on the level of blood glucose or insulin, or both. In this review we discuss the potential contribution of these changes in intracellular calcium regulation, whether acquired or genetically determined, to the pathogenesis of the diabetes syndrome, to the abnormalities in insulin secretion and action (mainly in non-insulin-dependent diabetes), and to the complications of both diabetes syndromes. Altered intracellular calcium metabolism may represent a common, underlying abnormality linking the metabolic, cardiovascular, ocular, and neural manifestations of the diabetic disease process.

Role of cellular calcium metabolism in abnormal glucose metabolism and diabetic hypertension

The prevalence of hypertension in patients with non-insulin-dependent diabetes mellitus (NIDDM) is considerably higher than in the non-diabetic population. Insulin resistance may contribute to this increased prevalence. Abnormal cellular calcium (Ca2+) homeostasis may link insulin resistance and high blood pressure in patients with NIDDM. Observations of abnormal cellular Ca2+ homeostasis in animal models of NIDDM and obesity as well as in diabetic patients are consistent with this hypothesis. Abnormalities in cellular Ca2+ homeostasis are also found in hypertensive animals and humans. Alterations in cell membrane phospholipid content and distribution may be the primary cause of abnormal plasma membrane Ca2+ fluxes in patients with NIDDM and hypertension.