Effect of cyclosporin A on bone mineral metabolism in experimental diabetes mellitus in the rat

Suppression of TLR4 prevents diabetic bone loss by regulating FTO-mediated m6A modification

Toll-like receptor-4 (TLR4) has been implicated in the development and progression of diabetic osteoporosis. However, the mechanisms underlying TLR4-regulated bone metabolism in diabetes are yet to be fully understood. Epigenetic modifications have been indicated as a possible mechanism leading to increased risk of osteoporosis and bone fracture. As N6-methyladenosine (m6A) is the most common epigenetic modification in eukaryotic mRNAs, we hypothesized that TLR4 regulates m6A modification in bone tissues of diabetic rats, thereby potentially explaining the pathogenesis of diabetic bone loss. m6A sequencing (m6A-seq) was performed in samples of the femur of TLR4-wild type (TLR4WT) and TLR4-knockout (TLR4KO) diabetic rats to identify genes with differential m6A modifications that may be associated with the bone loss phenotype. We found that in TLR4KO rats, the rapid weight loss of diabetic rats was prevented, and bone mineral density (BMD) was significantly increased. m6A-seq and Gene Ontology enrichment analysis revealed that m6A-modified genes in the femur of TLR4KO diabetic rats were associated with regulation of biological processes such as osteoclast differentiation. qRT-PCR analysis on the expression levels of the m6A-modified methyltransferases and demethylases demonstrated that only the m6A demethylase fat mass and obesity-associated protein（FTO）was decreased. Using an osteoclast cell model, we confirmed that TLR4-mediated osteoclast differentiation was induced by glycolipid toxicity via inhibition of FTO expression. Taken together, these results suggest that inhibition of TLR4 may prevent diabetic bone loss via regulation of FTO-mediated m6A modification.

Vitamin K₂ prevents hyperglycemia and cancellous osteopenia in rats with streptozotocin-induced type 1 diabetes

The purpose of the present study was to examine the effect of vitamin K₂ on cancellous and cortical bone mass in rats with streptozotocin (STZ)-induced type 1 diabetes. Twenty-seven male Sprague-Dawley rats aged 12 weeks were randomized by the weight-stratified method into the following three groups: age-matched control group, STZ + vehicle group, and STZ + vitamin K₂ group. STZ (40 + 50 mg/kg) was administered intravenously twice during the initial 1-week period. Vitamin K₂ (menatetrenone, 30 mg/kg) was administered orally 5 days a week. After 12 weeks of treatment, the serum glucose concentration and femoral length and weight were measured and histomorphometric analysis was performed on the cancellous and cortical bone of the distal femoral metaphysis and femoral diaphysis, respectively. STZ administration induced hyperglycemia and a decrease in femoral weight. The STZ + vehicle group also showed cancellous osteopenia due to a decrease in the number of osteoblasts/bone surface (N.Ob/BS) and the osteoblast surface (ObS)/BS without any significant changes in bone-resorption parameters, but it did not have a significant decrease in cortical bone mass. Administration of vitamin K₂ to STZ-treated rats prevented the development of hyperglycemia and a decrease in femoral weight. Vitamin K₂ also prevented cancellous osteopenia by inhibiting the decrease in N.Ob/BS and ObS/BS without significantly affecting bone-resorption parameters, but it did not significantly increase cortical bone mass. These results suggest that vitamin K₂ has beneficial effects on glucose concentration and cancellous bone mass in rats with STZ-induced type 1 diabetes.

Streptozotocin, type I diabetes severity and bone

As many as 50% of adults with type I (T1) diabetes exhibit bone loss and are at increased risk for fractures. Therapeutic development to prevent bone loss and/or restore lost bone in T1 diabetic patients requires knowledge of the molecular mechanisms accounting for the bone pathology. Because cell culture models alone cannot fully address the systemic/metabolic complexity of T1 diabetes, animal models are critical. A variety of models exist including spontaneous and pharmacologically induced T1 diabetic rodents. In this paper, we discuss the streptozotocin (STZ)-induced T1 diabetic mouse model and examine dose-dependent effects on disease severity and bone. Five daily injections of either 40 or 60 mg/kg STZ induce bone pathologies similar to spontaneously diabetic mouse and rat models and to human T1 diabetic bone pathology. Specifically, bone volume, mineral apposition rate, and osteocalcin serum and tibia messenger RNA levels are decreased. In contrast, bone marrow adiposity and aP2 expression are increased with either dose. However, high-dose STZ caused a more rapid elevation of blood glucose levels and a greater magnitude of change in body mass, fat pad mass, and bone gene expression (osteocalcin, aP2). An increase in cathepsin K and in the ratio of RANKL/OPG was noted in high-dose STZ mice, suggesting the possibility that severe diabetes could increase osteoclast activity, something not seen with lower doses. This may contribute to some of the disparity between existing studies regarding the role of osteoclasts in diabetic bone pathology. Examination of kidney and liver toxicity indicate that the high STZ dose causes some liver inflammation. In summary, the multiple low-dose STZ mouse model exhibits a similar bone phenotype to spontaneous models, has low toxicity, and serves as a useful tool for examining mechanisms of T1 diabetic bone loss.

Understanding the pathology and mechanisms of type I diabetic bone loss

Type I (T1) diabetes, also called insulin dependent diabetes mellitus (IDDM), is characterized by little or no insulin production and hyperglycemia. One of the less well known complications of T1-diabetes is bone loss which occurs in humans and animal models. This complication is receiving increased attention because T1-diabetics are living longer due to better therapeutics, and are faced with their existing health concerns being compounded by complications associated with aging, such as osteoporosis. Both male and female, endochondrial and intra-membranous, and axial and appendicular bones are susceptible to T1-diabetic bone loss. Exact mechanisms accounting for T1-diabetic bone loss are not known. Existing data indicate that the bone defect in T1-diabetes is anabolic rather than catabolic, suggesting that anabolic therapeutics may be more effective in preventing bone loss. Potential contributors to T1-diabetic suppression of bone formation are discussed in this review and include: increased marrow adiposity, hyperlipidemia, reduced insulin signaling, hyperglycemia, inflammation, altered adipokine and endocrine factors, increased cell death, and altered metabolism. Differences between T1-diabetic- and age-associated bone loss underlie the importance of condition specific, individualized treatments for osteoporosis. Optimizing therapies that prevent bone loss or restore bone density will allow T1-diabetic patients to live longer with strong healthy bones.

Bone loss and increased bone adiposity in spontaneous and pharmacologically induced diabetic mice

Insulin-dependent diabetes mellitus (IDDM) is associated with increased risk of osteopenia/osteoporosis in humans. The mechanisms accounting for diabetic bone loss remain unclear. Pharmacologic inducers of IDDM, such as streptozotocin, mimic key aspects of diabetes in rodents, allow analysis at the onset of diabetes, and induce diabetes in genetically modified mice. However, side effects of streptozotocin, unrelated to diabetes, can complicate data interpretation. The nonobese diabetic (NOD) mouse model develops diabetes spontaneously without external influences, negating side effects of inducing agents. Unfortunately, in this model the onset of diabetes is unpredictable, occurs in a minority of male mice, and can only be studied in a single mouse strain. To validate the relevance of the more flexible streptozotocin-induced diabetes model for studying diabetes-associated bone loss, we compared its phenotype to the spontaneously diabetic NOD model. Both models exhibited hyperglycemia and loss of body, fat pad, and muscle weight. Furthermore, these genetically different and distinct models of diabetes induction demonstrated similar bone phenotypes marked by significant trabecular bone loss and increased bone marrow adiposity. Correspondingly, both diabetic models exhibited decreased osteocalcin mRNA and increased adipocyte fatty acid-binding protein 2 mRNA levels in isolated tibias and calvaria. Taken together, multiple streptozotocin injection-induced diabetes is a valid model for understanding the acute and chronic pathophysiologic responses to diabetes and their mechanisms in bone.

Different effects of insulin and insulin-like growth factors I and II on osteoprogenitors and adipocyte progenitors in fetal rat bone cell populations

We investigated the effects of insulin (1-1,000 nM), insulin-like growth factor (IGF)-I, and IGF-II (3-100 nM each) alone or together with 10 nM dexamethasone (DEX) or 10 nM 1,25-dihydroxyvitamin D(3) (1,25[OH](2)D(3)) on proliferation and differentiation of adipocyte and osteoblast progenitors in bone cell populations derived from fetal rat calvaria. The effects on differentiation were evaluated by counting the number of bone or osteoid nodules and adipocyte colonies and the effects on proliferation, by measuring their size by image analysis. The types of cells studied were 1,25(OH)(2)D(3)- and DEX-responsive adipocyte progenitors and DEX-dependent and independent osteoprogenitors. Both IGF-I and IGF-II stimulated osteoprogenitor differentiation both alone and in the presence of DEX, while insulin stimulated osteoprogenitor differentiation only in the absence of DEX. Neither IGF-I/-II nor insulin affected proliferation of osteoprogenitors. Insulin had little effect on adipocyte differentiation by itself but strongly stimulated differentiation in the presence of either 1,25(OH)(2)D(3) or DEX, while IGF-II stimulated adipocyte differentiation in both the absence and presence of 1,25(OH)(2)D(3) or DEX. IGF-I by itself or in the presence of DEX strongly stimulated adipocyte cell differentiation but had little effect in the presence of 1,25(OH)(2)D(3). Our results demonstrate that insulin, IGF-II, and IGF-I have specific and different effects on the differentiation and proliferation of different groups of progenitor cells.

Is insulin an anabolic agent in bone? Dissecting the diabetic bone for clues

Diabetic osteoporosis is increasingly recognized as a significant comorbidity of type 1 diabetes mellitus. In contrast, type 2 diabetes mellitus is more commonly associated with modest increases in bone mineral density for age. Despite this dichotomy, clinical, in vivo, and in vitro data uniformly support the concept that new bone formation as well as bone microarchitectural integrity are altered in the diabetic state, leading to an increased risk for fragility fracture and inadequate bone regeneration following injury. In this review, we examine the contribution that insulin, as a potential anabolic agent in bone, may make to the pathophysiology of diabetic bone disease. Specifically, we have assimilated human and animal data examining the effects of endogenous insulin production, exogenous insulin administration, insulin sensitivity, and insulin signaling on bone. In so doing, we present evidence that insulin, acting as an anabolic agent in bone, can preserve and increase bone density and bone strength, presumably through direct and/or indirect effects on bone formation.

Increased bone adiposity and peroxisomal proliferator-activated receptor-gamma2 expression in type I diabetic mice

Decreased bone mass, osteoporosis, and increased fracture rates are common skeletal complications in patients with insulin-dependent diabetes mellitus (IDDM; type I diabetes). IDDM develops from little or no insulin production and is marked by elevated blood glucose levels and weight loss. In this study we use a streptozotocin-induced diabetic mouse model to examine the effect of type I diabetes on bone. Histology and microcomputed tomography demonstrate that adult diabetic mice, exhibiting increased plasma glucose and osmolality, have decreased trabecular bone mineral content compared with controls. Bone resorption could not completely account for this effect, because resorption markers (tartrate-resistant acid phosphatase 5b, urinary deoxypyridinoline excretion, and tartrate-resistant acid phosphatase 5 mRNA) are unchanged or reduced at 2 and/or 4 wk after diabetes induction. However, osteocalcin mRNA (a marker of late-stage osteoblast differentiation) and dynamic parameters of bone formation were decreased in diabetic tibias, whereas osteoblast number and runx2 and alkaline phosphatase mRNA levels did not differ. These findings suggest that the final stages of osteoblast maturation and function are suppressed. We also propose a second mechanism contributing to diabetic bone loss: increased marrow adiposity. This is supported by increased expression of adipocyte markers [peroxisome proliferator-activated receptor gamma2, resistin, and adipocyte fatty acid binding protein (alphaP2)] and the appearance of lipid-dense adipocytes in diabetic tibias. In contrast to bone marrow, adipose stores at other sites are depleted in diabetic mice, as indicated by decreased body, liver, and peripheral adipose tissue weights. These findings suggest that IDDM contributes to bone loss through changes in marrow composition resulting in decreased mature osteoblasts and increased adipose accumulation.

Histomorphometric evaluation of the influence of the diabetic metabolic state on bone defect healing depending on the defect size in spontaneously diabetic BB/OK rats

Insulin-dependent type 1 diabetes mellitus (IDDM) has been shown to alter the properties of bone and impair bone repair in both humans and animals. The objective of this study was the detailed histomorphometric evaluation of the influence of the diabetic metabolic state on bone formation and remodeling during bone defect healing depending on the defect size in spontaneously diabetic BB/O(ttawa)K(arlsburg) rats, a rat strain that represents a close homology to IDDM in man. Based on blood-glucose values at the time of surgery, postoperative blood-glucose course, and postoperative insulin requirements, 80 spontaneously diabetic BB/OK rats were divided into groups with well-compensated or poorly compensated metabolic state. Forty LEW.1A rats served as normoglycemic controls. Using a Kirschner wire, bone defects of different sizes were created proximal to the knee joint space in both femora. Ten animals from each group were killed on postoperative days 7, 14, 24, and 42, and specimens were processed undecalcified for quantitative bone histomorphometry. In terms of bone histomorphometry, our study did not show any differences in bone defect healing between the groups where the defect size was 0.4 mm. Larger bone defects (0.8 mm) only showed significant differences in the structural calculations after the 24th postoperative day exclusively in poorly compensated diabetic rats compared to well-compensated diabetic and control rats (P < 0.05 or P < 0.01). In bone defect sizes more than 1.2 mm, severe mineralization disorders occurred within the first 14 days exclusively in rats with poorly compensated diabetic metabolic state with a highly significant (P < 0.001) or significant (P < 0.01) decrease of all fluorochrome-based parameters of mineralization, apposition, formation, and timing of mineralization in comparison to spontaneously diabetic rats with well-compensated diabetic metabolic state and control rats. These results demonstrate that the bone repair of minor bone defects (0.4 mm) is independent of the diabetic metabolic state in spontaneously diabetic BB/OK rats. In larger bone defects (more than 0.8 mm), the bone defect healing in spontaneously diabetic BB/OK rats is impaired exclusively in poorly compensated diabetic metabolic states. This study suggests that strictly controlled insulin treatment resulting in a well-compensated diabetic metabolic state will ameliorate the impaired histomorphometric parameters of IDDM bone defect healing.

Disorders associated with acute rapid and severe bone loss

We describe a constellation of bone diseases characterized by the common feature of acute, rapid, and severe bone loss accompanied by dramatic fracture rates. These disorders are poorly recognized, resulting mainly from systemic diseases, frailty, immobilization, and immunosuppressive drugs, such as glucocorticoids and the calcineurin inhibitors. The opportunity to prevent or treat fractures is commonly missed because they are often not detected. Ideally, patients need to be identified early and preventative therapy initiated promptly to avoid the rapid bone loss and fractures. The most effective therapy at present seems to be the bisphosphonates, particularly when bone resorption is predominant. However, more severe forms of bone loss that result from an osteoblastic defect and reduced bone formation may benefit potentially more from newer anabolic agents, such as recombinant human parathyroid hormone (rhPTH).

A histomorphological investigation of the effect of cyclosporin on trabecular bone of the rat mandibular condyle

The effect of cyclosporin A (CSA) on the condylar trabecular bone was evaluated by microscopy. Twenty, 5-week-old male Sprague-Dawley rats were divided into a treated and a control group. Animals in the treated group received CSA, 15 mg/kg body weight, by gastric feeding daily for 4 weeks; controls received the vehicle only. Five animals from each group were killed at the end of weeks 2 and 4. After histological processing, 10 tissue sections from the mid-part of the mandibular condyle were examined. Generally, a histopathological osteopenia was observed around the condyle after CSA treatment, especially at the end of week 4. In the control animals, the trabecular bone volume steadily increased from weeks 2 to 4 (from 0.46+/-0.07 to 0.61+/-0.07 mm(3)/mm(3)). However, the bone volume was significantly less in the CSA group than in the control group at both times (0.33+/-0.02 vs 0.46+/-0.07 and 0.26+/-0.07 vs 0.61+/-0.07 mm(3)/mm(3) for CSA vs control group at the end of weeks 2 and 4, respectively). Conversely, an increased marrow volume was observed in the CSA group at both these times (0.60+/-0.02 vs 0.42+/-0.08 and 0.71+/-0.06 vs 0.31+/-0.06 mm(3)/mm(3) for CSA vs control group at the end of weeks 2 and 4, respectively). Decreases were also observed in trabecular thickness, osteoid seam width, osteoid volume and cortical bone width. Because trabecular bone mass, osteoid mass and cortical bone thickness all showed a decrease after CSA at both times, an inhibitory effect of CSA on trabecular bone formation in the mandibular condyle is proposed.

Effects of exercise and disuse on bone remodeling, bone mass, and biomechanical competence in spontaneously diabetic female rats

Diabetes is associated with low bone formation. In this study we investigate the effect of additional or reduced mechanical loading on indices of bone formation and resorption, bone mass, and biomechanical properties in spontaneously diabetic BB rats. Female diabetic (mean age 13 weeks) and age-matched control rats were each allocated to three experimental groups: no-intervention; supervised running exercise program (Ex); and unloading induced by unilateral sciatic neurectomy (USN). The study period was 8 weeks. We measured biochemical parameters of bone formation (plasma osteocalcin) and resorption (urinary deoxypyridinoline [Dpd]); bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) at middiaphyseal and metaphyseal regions of the femur; histomorphometry of the proximal tibial metaphysis (PTM); and biomechanical properties of the femur (neck, diaphysis, and metaphysis) and lumbar vertebra (L-5). In nondiabetic rats, Ex did not affect parameters of bone formation/resorption and BMD, and had little effect on biomechanical properties. USN increased Dpd excretion, whereas there was a decreased trabecular bone formation rate (BFR) on morphometry of PTM in both paralyzed and intact limbs. Compared with intact limbs, paralyzed limbs of USN rats showed decreased trabecular bone volume at the PTM, and decreased BMD and biomechanical properties at the distal femoral metaphysis (DFM) and, to a lesser extent, femoral neck. Diabetic rats of the three experimental groups had low plasma osteocalcin levels and Dpd excretion, as well as low BFR on morphometry. The BMD and biomechanical properties of both femur and L-5 were unchanged in diabetic rats. Diabetic Ex rats, however, showed a lower maximum load and stress at DFM than control Ex rats. Diabetic USN rats showed no increase in Dpd excretion; their paralyzed limbs showed decreased maximum load at DFM, but there was no significant decrease in trabecular bone volume at PTM or BMD at DFM. Thus, the running exercise does not affect low bone formation in diabetic rats; however, trabecular bone loss caused by disuse is less pronounced in diabetic rats, probably as a result of low bone resorption.

Additive effects of estrogen deficiency and diabetes on bone mineral density in rats

We investigated the combined effects of estrogen deficiency and diabetes on bone mineral density (BMD) and bone metabolism in rats. Ten-week-old, female rats were randomly divided into four groups: controls (C), an ovariectomized group (O), a streptozotocin-induced diabetic group (S), and a combined ovariectomy and streptozotocin-induced diabetic group (OS). The BMD of the lumbar spine and the femur were measured before grouping and at 23 weeks old. At the end of the experiment, blood samples were obtained via cardiac puncture, and bone gla protein (BGP), tartrate-resistant acid phosphatase (TRAP) and 1,25-dihydroxyvitamin D levels were measured. The rats in the C, O, S, and OS groups, in that order, had higher levels of BMD of the lumbar spine and femur at 23 weeks of age. The BGP levels in the S and OS groups were significantly lower than in C and O groups. Significantly higher 1,25-dihydroxyvitamin D was observed in the O group compared with the C, S and OS groups. No differences were obtained in TRAP among four groups. Our data suggest that the combined effects of estrogen deficiency and diabetes on BMD are not synergistic or counteractive but additive.

Skeletal effects of low-dose cyclosporin A in aged male rats: lack of relationship to serum testosterone levels

The aim of this study was to investigate the skeletal effects of cyclosporin A (CsA) in a dose range relevant to clinical medicine in lumbar vertebral cancellous bone of aged male rats and to correlate these effects with possible changes in serum testosterone levels. Thirty-one 18-month-old male Wistar rats were divided into four weight-matched groups and subcutaneously injected with either 0, 1, 3, or 5 mg of CsA/kg of body weight three times per week After 4 weeks of treatment, all rats were killed after in vivo fluorochrome labeling and the first lumbar vertebrae analyzed by quantitative histomorphometry. Serum was analyzed for total calcium, creatinine, alkaline phosphatase, osteocalcin, parathyroid hormone, total testosterone, and CsA levels. CsA administration resulted in a dose-dependent increase in serum osteocalcin levels and in histomorphometric indices of cancellous bone turnover in the axial skeleton. Furthermore, CsA-treated rats showed a deterioration of vertebral cancellous bone structure with increased discontinuity of the trabecular bone network due to trabecular plate perforations. Serum testosterone levels were not significantly changed by CsA treatment and were uncorrelated to all biochemical or histomorphometric indices of bone turnover. We conclude that the 4-week administration of CsA at doses that are close to those used in transplantation patients induced high turnover osteopenia in the axial skeleton of aged, 18-month-old male rats, and that these effects were likely not mediated by changes in serum testosterone levels.

Decreased osteoblast activity in spontaneously diabetic rats. In vivo studies on the pathogenesis

Diabetes in both humans and rats is accompanied by low bone formation, which is presumably caused by serum-borne factors. To explore its pathogenesis, we carried out experiments in diabetic and nondiabetic BB rats, using plasma osteocalcin concentrations (OC) as a marker for osteoblast activity. In nondiabetic rats, the i.v. infusion of glucose (30%, 4 d) did not change OC; s.c. insulin infusion (4 U/d, 14 d) reduced OC by 27% (p < 0.01). In diabetic rats, OC were decreased from the first day of glycosuria (71 +/- 5% of paired controls), declining exponentially to 24 +/- 3% after 5 wk. Insulin infusion (1, 2, and 3 U/d, 14 d) produced gradual restoration of OC. OC were better correlated with insulin-like growth factor-I (IGF-I) than with insulin levels in these experiments. OC were dramatically increased 4 d after adrenalectomy (ADX) in all diabetic rats (73 +/- 8 vs 22 +/- 4 micrograms/L before ADX; p < 0.001), but not if corticosterone was administered. Ligand blotting of IGF binding proteins showed a marked decrease in two bands (44-49 and 32-35 kDa) 10-14 d after diabetes onset; the density of these bands was increased, but not normalized after ADX. Thus, decreased osteoblast activity is present from the onset of diabetes, is dependent on endogenous corticosterone, and cannot be reproduced by hyperglycemia in nondiabetic rats.

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.

Effects of long-term diabetes and/or high-dose 17 beta-estradiol on bone formation, bone mineral density, and strength in ovariectomized rats

Long-term diabetes in female rats preserves the bone mineral density (BMD) but impairs the strength of the femur. In this study, we have compared the effects of diabetes and high-dose 17 beta-estradiol (E2), two conditions of low bone formation, in ovariectomized (ovx) rats. Spontaneously diabetic BB rats were ovx 0-3 days after onset, and nondiabetic ovx littermates were used as controls; the rats were either untreated or treated with E2 (30 micrograms/day, subcutaneously), for 6 or 12 weeks (n = 9 in each of the eight groups). Analysis included: plasma 1,25-dihydroxyvitamin D3, insulin-like growth factor-I (IGF-I), and osteocalcin concentrations; histomorphometry of the proximal tibial metaphysis (PTM); and DXA and biomechanical testing of the femur. Both E2 treatment and diabetes markedly lowered plasma IGF-I and osteocalcin concentrations, as well as dynamic morphometric parameters of bone formation in the PTM. Plasma IGF-I and osteocalcin were correlated (R2 = 0.55; p < 0.0001). E2 treatment in both control and diabetic ovx rats increased the trabecular bone volume in the PTM and the BMD in the metaphysis of the distal femur; there was no difference between control and diabetic rats, however. The diaphyseal area and BMC were decreased in E2-treated or/and diabetic ovx rats, but the diaphyseal BMD remained unchanged compared with untreated ovx rats. The biomechanical properties of the whole femur (strength, angular deformation, and stiffness) were decreased in E2-treated and diabetic E2-treated ovx rats after 12 weeks. The data indicate that in situations of chronic low bone formation, whole bone strength does not reflect total BMD but correlates better with bone size and bone mineral content measurements.

Several anesthetics, but not diethyl ether, cause marked elevation of serum parathyroid hormone concentration in rats

The effects of anesthetics on serum parathyroid hormone (PTH) concentrations were determined by a new homologous two-site immunoradiometric assay for rat PTH. Serum PTH concentrations (mean +/- SE) from ether-anesthetized rats (14.7 +/- 1.5 pg/ml, n = 22) were not significantly different from those of decapitated unanesthetized female rats (13.0 +/- 1.8 pg/ml, n = 21). Serum PTH concentrations in pg/ml (n = 4-14) for other anesthetics tested were: ketamine, 12.5 +/- 1.1; Na pentobarbital, 23.3 +/- 2.4; methoxyflurane (inhalation), 42.2 +/- 6.8; and xylazine combined with ketamine, 51.4 +/- 11.3 pg/ml. The latter two concentrations were significantly (p < 0.001) higher than the values for all other anesthetics and decapitation. Elevation of serum PTH induced by pentobarbital or ketamine + xylazine increased with time under anesthesia. Neither serum Ca2+ concentrations nor pH differed among any of the groups. We conclude that anesthesia induced by pentobarbital, methoxyflurane, or ketamine + xylazine in rats leads to a marked elevation of serum PTH levels that appears to be related to the duration of anesthesia and not due to any measurable fall in serum Ca2+.

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)

Rapamycin: a bone sparing immunosuppressant?

Immunosuppressant therpay is associated with osteoporosis both clinically, post-transplantation, and experimentally. In rats, cyclosporin A (CsA) and FK506 induce a state of high turnover rapid bone loss. After 14 days of administration in immunosuppressive doses, the more recently discovered immunosuppressant, rapamycin, resulted in no change of cancellous bone volume. A longer study over 28 days has now been carried out; contrasting the new drug with CsA and FK506. Sixty, 10-week-old Sprague-Dawley rats were randomly divided into five groups of 12 rats each. The first group served as an aging control. The remaining four groups received, by daily gavage, a combined vehicle placebo, CsA 15 mg/kg, FK506 5 mg/kg, and rapamycin 2.5 mg/kg, respectively. CsA- and FK506-treated rats, but not those treated with rapamycin, demonstrated high turnover osteoporosis with raised serum 1,25(OH)2D (p < 0.05) and elevated serum osteocalcin (p < 0.05). The trabecular bone area was decreased by 66% (p < 0.01) in the CsA group and 56% (p < 0.05) in the FK506-treated group compared with the control animals. The CsA- and the rapamycin-treated groups failed to gain weight and developed severe hyperglycemia (> 20 mmol/l, p < 0.001) by day 14 but which largely resolved by day 28. Unlike the groups treated with CsA and FK506, rapamycin-treated rats had no loss of trabecular bone volume but there was increased modeling and remodeling and a decreased longitudinal growth rate. Rapamycin may thus confer a distinct advantage over the established immunosuppressants in not reducing bone volume in the short term.(ABSTRACT TRUNCATED AT 250 WORDS)

Amylin increases bone volume but cannot ameliorate diabetic osteopenia

Amylin is normally secreted in a regulated fashion by the pancreatic beta-cells in parallel with insulin and has been reported to have bone-conserving properties. Type I diabetes mellitus results in a low-turnover osteopenia in the presence of decreased amylin, which is in contrast to type II diabetes where less bone loss, in the presence of high amylin levels, occurs. We investigated the effects of amylin on bone mineral metabolism in normal and diabetic (streptozotocin-induced) rats, in order to ascertain whether amylin would modify the streptozotocin-induced diabetic osteopenia. Ten-week-old male Sprague-Dawley rats were randomized as follows: group A (n = 18) received normal saline; group B (n = 18) received amylin; group C, diabetic rats (n = 23), received normal saline; and group D, diabetic rats (n = 23), received amylin. Amylin (100 pmol/100 g b.w.) was administered by a daily subcutaneous injection. Double calcein-labeled tibiae were removed for histomorphometric analysis followed sacrifice on day 19. Results showed no difference in blood ionized calcium between groups. Blood glucose remained above 600 mg/dl in the diabetic animals and was not affected by the administration of amylin. Serum osteocalcin, insulin-like growth factor-1 (IGF-1), parathyroid hormone (PTH), and 1,25 dihydroxyvitamin D [1,25(OH)2D] were significantly lower in the diabetic rats compared with control group A by day 19. Amylin produced higher levels of serum osteocalcin in group B on day 9 (P < 0.05) compared with controls but returned to control values (group A) by day 19; no such change occurred in the diabetic group.(ABSTRACT TRUNCATED AT 250 WORDS)