Growth hormone cannot enhance the recovery of dexamethasone-induced osteopenia after withdrawal in young female wistar rats

Dietary 2-oxoglutarate prevents bone loss caused by neonatal treatment with maximal dexamethasone dose

Synthetic glucocorticoids (GCs) are widely used in the variety of dosages for treatment of premature infants with chronic lung disease, respiratory distress syndrome, allergies, asthma, and other inflammatory and autoimmune conditions. Yet, adverse effects such as glucocorticoid-induced osteoporosis and growth retardation are recognized. Conversely, 2-oxoglutarate (2-Ox), a precursor of glutamine, glutamate, and collagen amino acids, exerts protective effects on bone development. Our aim was to elucidate the effect of dietary administered 2-Ox on bone loss caused by neonatal treatment with clinically relevant maximal therapeutic dexamethasone (Dex) dose. Long bones of neonatal female piglets receiving Dex, Dex+2-Ox, or untreated were examined through measurements of mechanical properties, density, mineralization, geometry, histomorphometry, and histology. Selected hormones, bone turnover, and growth markers were also analyzed. Neonatal administration of clinically relevant maximal dose of Dex alone led to over 30% decrease in bone mass and the ultimate strength ( P < 0.001 for all). The length (13 and 7% for femur and humerus, respectively) and other geometrical parameters (13-45%) decreased compared to the control ( P < 0.001 for all). Dex impaired bone growth and caused hormonal imbalance. Dietary 2-Ox prevented Dex influence and vast majority of assessed bone parameters were restored almost to the control level. Piglets receiving 2-Ox had heavier, denser, and stronger bones; higher levels of growth hormone and osteocalcin concentration; and preserved microarchitecture of trabecular bone compared to the Dex group. 2-Ox administered postnatally had a potential to maintain bone structure of animals simultaneously treated with maximal therapeutic doses of Dex, which, in our opinion, may open up a new opportunity in developing combined treatment for children treated with GCs. Impact statement The present study has showed, for the first time, that dietary 2-oxoglutarate (2-Ox) administered postnatally has a potential to improve/maintain bone structure of animals simultaneously treated with maximal therapeutic doses of dexamethasone (Dex). It may open the new direction in searching and developing combined treatment for children treated with glucocorticoids (GCs) since growing group of children is exposed to synthetic GCs and adverse effects such as glucocorticoid-induced osteoporosis and growth retardation are recognized. Currently proposed combined therapies have numerous side effects. Thus, this study proposed a new direction in combined therapies utilizing dietary supplementation with glutamine derivative. Impairment caused by Dex in presented long bones animal model was prevented by dietary supplementation with 2-Ox and vast majority of assessed bone parameters were restored almost to the control level. These results support previous thesis on the regulatory mechanism of nutrient utilization regulated by glutamine derivatives and enrich the nutritional science.

Early toxicology signal generation in the mouse

The rat has been the preferred rodent toxicology species since before regulatory requirements have been in place, and there exists in the pharmaceutical industry and the regulatory agencies a significant amount of historical data for the rat. The resulting experience base with the rat makes the possibility of replacing it with the mouse for regulated toxicology studies untenable for all but the most extreme circumstances. However, toxicologists are very familiar with the mouse as a model for chronic carcinogenicity studies, and there exist multiple preclinical mouse models of disease. The authors evaluated the use of the mouse for early in vivo toxicology signal generation and prioritization of small molecule lead compounds prior to nomination of a development candidate. In five-day oral gavage studies with three test agents in the mouse, the authors were able to identify the same dose-limiting toxicities as those identified in the rat, including examples of compound-mediated hemolysis as well as microscopic lesions in the alimentary canal, kidney, and pancreas. Performing early signal generation studies in the mouse allows for earlier assessment of the safety liabilities of small molecules, requires significantly less compound, and allows evaluation of more compounds earlier in the project's life cycle.

Bone development of suckling piglets after prenatal, neonatal or perinatal treatment with dexamethasone

In mammals, the release from growth-inhibiting conditions results in catch-up growth. To investigate animal evidence for whether prenatal dexamethasone (DEX) treatment leads to the development of growth restriction especially reduced mineralization of skeleton, and release from it leads to the phenomenon of catch-up, piglets were prenatally exposed to DEX (3.0 mg/sow per day(-2)) during the last 24 days of prenatal life and tested further in two different ways: discontinued at birth and continued administration of DEX (0.5 mg/kg day(-2)) to piglets through 30 days of neonatal life. Using dual energy X-ray absorptiometry methods, bone mineral density (BMD) and bone mineral content (BMC) were measured. The three-point bending test was applied to determine the mechanical properties of the bones. Furthermore, geometric properties of the bones were assessed. Serum concentration of osteocalcin (OC) was determined. Histomorphological analysis of the ribs was also performed. The consequences of neonate DEX treatment and in utero DEX exposure were reflected in a dramatic decrease of BMD, BMC and blood serum OC concentration and geometric parameters of piglets' bones. Prenatal action of DEX during the last 24 days of pregnancy resulted in continued neonatal modification of bone tissues, thus diminishing bone quality, and negatively influenced structural development and mechanical properties, finally increasing the risk of fractures of ribs and limb bones. Prenatal DEX treatment limited to the last 24 days of foetal life did not reduce the term birth weight and the growth of suckling piglets followed up to 30 days of neonatal life, and catch-up in bone mineralization did not occur.

Modulation of Dickkopf-1 attenuates glucocorticoid induction of osteoblast apoptosis, adipocytic differentiation, and bone mass loss

Long-term glucocorticoid treatment impairs the survival and bone formation of osteogenic cells, leading to bone mass loss. The Wnt inhibitor Dickkopf-1 (DKK1) acts as a potent bone-remodeling factor that mediates several types of skeletal disorders. Whereas excess glucocorticoid is known to disturb Wnt signaling in osteogenic cells, modulation of the skeletally deleterious effects of DKK1 to alleviate glucocorticoid induction of bone loss has not been tested. In this study, knockdown of DKK1 expression by end-capped phosphorothioate DKK1 antisense oligonucleotide (DKK1-AS) abrogated dexamethasone suppression of alkaline phosphatase activity and osteocalcin expression in MC3T3-E1 preosteoblasts. Exogenous DKK1-AS treatment alleviated dexamethasone suppression of mineral density, trabecular bone volume, osteoblast surface, and bone formation rate in bone tissue and ex vivo osteogenesis of primary bone-marrow mesenchymal cells. The DKK1-AS inhibited adipocyte volume in the marrow cavity of steroid-treated bone tissue. Immunohistochemical observation revealed that DKK1-AS abrogated dexamethasone-induced DKK1 expression and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling of osteoblasts adjacent to trabecular bone. Knocking down DKK1 abrogated dexamethasone-modulated expression of nuclear beta-catenin and phosphorylated Ser(473)-Akt and survival of osteoblasts and adipocytic differentiation of mesenchymal progenitor cell cultures. Taken together, knocking down DKK1 alleviated the deleterious effect of glucocorticoid on bone microstructure. The DKK1-AS treatment appeared to protect bone tissue by modulating beta-catenin and Akt-mediated survival as well as the osteogenic and adipogenic activities of glucocorticoid-stressed osteoprogenitor cells. Interference with the osteogenesis-inhibitory action of DKK1 has therapeutic potential for preventing glucocorticoid induction of osteopenia.

Regulation of insulin-like growth factor binding protein-5, four and a half lim-2, and a disintegrin and metalloprotease-9 expression in osteoblasts

The roles of insulin-like growth factors (IGFs) in regulating growth and their modulation by six IGF binding proteins (IGFBP) are well established. IGFBP-5, the most abundant IGFBP stored in bone, is an important regulator of bone formation via IGF-dependent and -independent mechanisms. Two new proteins, four and a half lim (FHL)-2, a transcription modulator that interacts with IGFBP-5, and a disintegrin and metalloprotease (ADAM)-9, an IGFBP-5 protease, have been identified as potential regulators of IGFBP-5 action in bone. We tested the hypothesis that agents which modulate bone formation by regulating IGFBP-5 expression would also regulate FHL-2 and ADAM-9 expression in a coordinated manner. We evaluated the expression of IGFBP-5, FHL-2, and ADAM-9 by real-time reverse transcriptase (RT)-PCR during differentiation of mouse bone marrow stromal cells into osteoblasts and in response to treatment with bone formation modulators in the LSaOS human osteosarcoma cell line. IGFBP-5 and FHL-2 increased 4.3- and 3.0-fold (P < or = 0.01), respectively, during osteoblast differentiation. Dexamethasone (Dex), an inhibitor of bone formation, decreased IGFBP-5 and FHL-2 and increased ADAM-9 in LSaOS cells (P < or = 0.05). Bone morphogenic protein (BMP)-7, a stimulator of bone formation, increased IGFBP-5 and decreased ADAM-9 (P<0.01). To determine if BMP-7 would eliminate Dex inhibition of IGFBP-5, cells were treated with Dex+BMP-7. The BMP-7-induced increase in IGFBP-5 was reduced, but not eliminated, in the presence of Dex (P < or = 0.01), indicating that BMP-7 and Dex may regulate IGFBP-5 via different mechanisms. Transforming growth factor (TGF)-beta, a stimulator of bone formation, increased IGFBP-5 and FHL-2 expression (P < or = 0.01). IGF-I and TNF-alpha decreased expression of ADAM-9 (P<0.05). In conclusion, our findings are consistent with the hypothesis that FHL-2 and ADAM-9 are important modulators of IGFBP-5 actions and are, in part, regulated in a coordinated manner in bone.