Overexpression of DeltaFosB transcription factor(s) increases bone formation and inhibits adipogenesis.

Members of the AP-1 family of transcription factors participate in the regulation of bone cell proliferation and differentiation. We report here a potent AP-1-related regulator of osteoblast function: DeltaFosB, a naturally occurring truncated form of FosB that arises from alternative splicing of the fosB transcript and is expressed in osteoblasts. Overexpression of DeltaFosB in transgenic mice leads to increased bone formation throughout the skeleton and a continuous post-developmental increase in bone mass, leading to osteosclerosis. In contrast, DeltaFosB inhibits adipogenesis both in vivo and in vitro, and downregulates the expression of early markers of adipocyte differentiation. Because osteoblasts and adipocytes are thought to share a common precursor, it is concluded that DeltaFosB transcriptionally regulates osteoblastogenesis, possibly at the expense of adipogenesis.

Bone homeostasis in growth hormone receptor-null mice is restored by IGF-I but independent of Stat5.

Growth hormone (GH) regulates both bone growth and remodeling, but it is unclear whether these actions are mediated directly by the GH receptor (GHR) and/or IGF-I signaling. The actions of GH are transduced by the Jak/Stat signaling pathway via Stat5, which is thought to regulate IGF-I expression. To determine the respective roles of GHR and IGF-I in bone growth and remodeling, we examined bones of wild-type, GHR knockout (GHR(-/-)), Stat5ab(-/-), and GHR(-/-) mice treated with IGF-I. Reduced bone growth in GHR(-/-) mice, due to a premature reduction in chondrocyte proliferation and cortical bone growth, was detected after 2 weeks of age. Additionally, although trabecular bone volume was unchanged, bone turnover was significantly reduced in GHR(-/-) mice, indicating GH involvement in the high bone-turnover level during growth. IGF-I treatment almost completely rescued all effects of the GHR(-/-) on both bone growth and remodeling, supporting a direct effect of IGF-I on both osteoblasts and chondrocytes. Whereas bone length was reduced in Stat5ab(-/-) mice, there was no reduction in trabecular bone remodeling or growth-plate width as observed in GHR(-/-) mice, indicating that the effects of GH in bone may not involve Stat5 activation.

1-(5-oxohexyl)-3,7-Dimethylxanthine, a phosphodiesterase inhibitor, activates MAPK cascades and promotes osteoblast differentiation by a mechanism independent of PKA activation (pentoxifylline promotes osteoblast differentiation).

We have investigated the effect of 1-(5-oxohexyl)-3,7-dimethylxanthine or pentoxifylline (PeTx), a nonselective phosphodiesterase inhibitor, on osteoblastic differentiation in vitro by using two mesenchymal cell lines, C3H10T1/2 and C2C12, which are able to acquire the osteoblastic phenotype in the presence of bone morphogenetic protein-2 (BMP-2). PeTx induced the osteoblastic markers, osteocalcin and Osf2/Cbfa1, in C3H10T1/2 and C2C12 cells and enhanced BMP-2-induced expression of osteocalcin, Osf2/Cbfa1, and alkaline phosphatase. This activity was partially attributed to the fact that PeTx is able to enhance BMP-2-induced Smad1 transcriptional activity. Although PeTx clearly stimulates PKA in these cells, neither pretreatment of cells with the PKA inhibitor H89 nor transfection with the specific PKA inhibitor PKI prevented the induction or enhancement of osteoblast markers by PeTx, demonstrating that these effects were independent of PKA activation. On the other hand, PeTx induced the activation of ERK1/2 and p38 kinase pathways independently of the activation of PKA. Selective inhibitors of these MAPK cascades prevented the induction of osteoblastic markers in cells treated with PeTx, suggesting that the activation of these two pathways plays a role in the effect of PeTx on osteoblastic differentiation.

Characterization of specific low-density lipoprotein binding sites in human term placental microvillous membranes.

Purified microvillous membranes prepared from normal term human placenta were studied for their ability to bind specifically low-density lipoprotein (LDL). Electron microscopic examination of the membrane preparations revealed essentially microvilli-like structures, and the enzyme analyses a 14-17-fold enrichment in the membrane markers 5'-nucleotidase and alkaline phosphatase. The binding of [125I]LDL was dependent on time, temperature, pH and protein concentration; it was saturable with a low capacity (130.4 +/- 22.2 ng/mg of membrane protein) and presented a high affinity (apparent Ka 6.12 +/- 1.32 micrograms protein per ml). These high-affinity binding sites were specific for LDL (high-density lipoprotein induced less competition than unlabelled LDL) and were sensitive to pronase digestion. Unlike the binding of LDL to other tissues, the [125I]LDL binding to microvillous membranes did not require divalent cations. The presence of specific LDL receptors on the placental microvillous membranes, located at the effective site of exchange between the maternal blood and the placental tissue, supports the concept that human placenta utilizes LDL-cholesterol for its progesterone synthesis.

Low-density lipoprotein binding sites in the microvillous membranes of human placenta at different stages of gestation.

Microvillous membranes isolated from early gestation placentas (8-12 weeks of amenorrhoea) and from mid-term placentas (20-22 weeks of amenorrhoea) were used to study the specific binding of low-density lipoprotein (LDL) to the trophoblast. The purity of the microvillous preparations has been assessed by electron microscopy and by their enrichment in two membrane markers, 5'-nucleotidase and alkaline phosphatase. Evidence was presented demonstrating the existence of saturable binding sites for [125I]LDL in placental microvilli as early as 6 weeks of pregnancy. The apparent KD values for these binding sites have been determined by Scatchard analyses to be 6.98 +/- 0.83 and 6.57 +/- 0.81 micrograms protein LDL/ml, for early gestation and mid-term preparations, respectively. This apparent KD value was unaffected by a pretreatment of the membranes by heparin, as indicated by the mean values of 7.13 +/- 0.89 and 6.97 +/- 0.75 micrograms protein LDL/ml obtained for immature microvilli preincubated with or without heparin, respectively. Large variations of binding capacity were observed in each gestational age group and no significant difference was found between them. These results indicate that the LDL binding sites of the human placenta, located on the microvillous membranes, (i) are present as early as the 6th week of pregnancy, and (ii) display the same high affinity and specificity for LDL as those of the term trophoblast.

[Maternal and neonatal effects of remifentanil for general anaesthesia for Caesarean delivery]. / Répercussions maternelles et néonatales de l'anesthésie générale par rémifentanil pour césarienne programmée.

OBJECTIVE: Opioids are routinely omitted at the induction of general anesthesia for Caesarean delivery because of the risks of respiratory neonatal depression. The short-acting opioid remifentanil may afford advantages at the induction and surgical stimulation, without subsequent neonatal depression. PATIENTS AND METHODS: In this double-blinded study, 40 at term women undergoing elective Caesarean section and requiring general anaesthesia were allocated randomly to receive either remifentanil (0,5 microg/kg) at the induction of anaesthesia (G1, n=20) or placebo (G2, n=20). Induction of anaesthesia was performed with propofol 2 mg/kg and succinylcholine 1 mg/kg. Anaesthesia was maintained with nitrous oxide in oxygen (50/50%, v/v), propofol (100 microg/kg/min), remifentanil (0.2 microg/kg/min) and atracurium. Neonates were assessed by using Apgar scores, possible respiratory depression, with or without ventilation in the mask or intubation and umbilical cord blood gas (artery: UA and vein: UV). Values are expressed as mean values +/-SD. Pearson's Chi squared and t-test were used for statistical analysis P<0.05 was considered significant. RESULTS: Maternal systolic pressure, mean pressure and heart rate were significantly higher in G1 at induction. Apgar scores, heart and respiratory rate were similar between groups. Seven episodes of respiratory depressions were noted (3 in G1, 4 in G2). Five neonates required only brief assisted ventilation by face-mask (2 in G1, 3 in G2). CONCLUSION: Remifentanil (0.5 microg/kg) at the induction of anaesthesia in elective Caesarean section under general anaesthesia can be used without subsequent neonatal depression. However, we believe that further research is necessary to extrapolate these results to a pregnancy carrying an acutely distressed foetus.

Postcoital contraception: myth or reality?

PIP: In preparation for a clinical trial of an antiprogesterone molecule as a postcoital contraceptive method, the authors reviewed the available research on the effectiveness of use of high-dose estrogen and combined estrogen-progesterone preparations for this purpose. The medical literature for the period 1971-87 included 5 studies on the former and 5 studies on the latter regimens that involved over 500 subjects. In each of these studies, the failure rate was calculated by dividing the number of observed pregnancies by the total number of women enrolled. The authors computed true failure rates for the 10 studies in 2 different ways. First, the failure rate derived from the number of reported pregnancies was divided by the number of expected pregnancies according to Tietze's probability of pregnancy. Second, the true failure rate derived from Dixon's table was calculated. Since the latter approach requires data on the date of the intercourse that resulted in pregnancy, it could not be applied to all 10 studies. The 5 studies on the efficacy of high-dose estrogen as a postcoital contraceptive reported failure rates below 1%. However, the authors' recalculations indicated failure rates as high as 48% (Tietze) or 16% (Dixon). COmbined estrogen-progesterone was reported to produce a failure rate of 0.16-5%. Here, the true failure rate was as high as 4.2-100% (Tietze) or 5.9-44% (Dixon). The implication of these recalculations is that use of the total number of women enrolled as the denominator produces a substantially lower failure rate than the number of women potentially pregnant. Given the potential for underestimation of the efficacy of postcoital contraceptives, more prospective controlled studies are urged.^ieng

Effect of trimegestone alone or in combination with estradiol on bone mass and bone turnover in an adult rat model of osteopenia.

The effects of trimegestone (1 mg/kg/day orally), a novel norpregnane progestin, and 17 beta-estradiol (10 micrograms/kg/day subcutaneously), alone and in combination, on bone mass and turnover were investigated using an experimental model of osteoporosis involving ovariectomized rats. An equivalent dose (1 mg/kg/day orally) or norethisterone was used as a reference progestin. Six-month-old rats were ovariectomized and left untreated for 2 months to allow the development of osteopenia. Treatment with a progestin, alone or in combination with estradiol, was then started and continued for 2 months. Bone was assessed by a combination of static and dynamic histomorphometric measurements, by densitometry and by the use of biochemical markers of bone turnover. Ovariectomy induced a pronounced uterine atrophy, which was reversed by estradiol. Trimegestone effectively counteracted the uterotropic effect of estradiol, whilst norethisterone showed a less pronounced antagonistic effect. A severe osteopenia was established in the initial 2 months after ovariectomy, and further bone loss occurred during the 2-month treatment period in animals not receiving estradiol. This effect was associated with a marked increase in both biochemical and dynamic histomorphometric markers of bone turnover, reflecting in an imbalance between resorption and formation. 17 beta-estradiol given alone prevented further bone loss, but neither trimegestone nor norethisterone alone had a beneficial effect on bone mass and turnover. When given in combination with 17 beta-estradiol, however, trimegestone significantly improved its effect on bone mass and turnover. This effect was more potent than that induced by combined 17 beta-estradiol and norethisterone therapy. We conclude that trimegestone, when combined with 17 beta-estradiol, is a more effective progestin than norethisterone in preventing bone loss in adult ovariectomized rats.