Alkaline phosphatase

About: Alkaline phosphatase is a research topic. Over the lifetime, 20218 publications have been published within this topic receiving 540547 citations. The topic is also known as: Alkaline_phosphatase & IPR001952.

Matrix-induced endochondral bone differentiation: Influence of hypophysectomy, growth hormone, and thyroid-stimulating hormone

Abstract: The influence of hypophysectomy (hypox), GH, and TSH on the discrete phases of matrix-induced endochondral bone differentiation was investigated [3H]Thymidine incorporation by proliferating mesenchymal cells on day 3 was inhibited by hypox, but was corrected by GH administration On day 7, 35SO4 incorporation into cartilage proteoglycans was reduced by hypox, but was restored to values higher than controls by GH Calcification of cartilage and bone was monitored by alkaline phosphatase activity, 45Ca incorporation into bone mineral, and total calcium Alkaline phosphatase levels were maximal on day 11 in the controls and declined thereafter; however, the activity of alkaline phosphatase remained elevated in hypox recipients Hypox reduced and delayed the rate and extent of calcification, as reflected by 45Ca incorporation and total calcium, respectively The administration of GH and TSH alone and in combination restored 45Ca incorporation to control values in tibial metaphyses but not in the matrix-induc

Estrogen Regulation of Human Osteoblastic Cell Proliferation and Differentiation

Abstract: Estrogen (E2) has been shown to prevent bone loss among postmenopausal women. The molecular mechanism(s) by which this is accomplished is not clear. The discovery of E2 receptor (ER) in osteoblasts and osteoclasts has implicated these cells as direct targets for E2. Previous studies on the effects of E2 on osteoblastic cells in vitro or in organ culture present conflicting results, possibly due to heterogeneity in cell types, stage of differentiation, ER levels, and/or species differences. The effects of E2 on gene expression during various stages of human osteoblast cell differentiation has not been investigated extensively. In this study we employed a newly developed human fetal osteoblastic cell line (hFOB/ER9) that contains high levels of ER to examine the effects of E2 on osteoblast proliferation and differentiation. The basal levels and E2 effects on the expression of various extracellular matrix proteins were also characterized throughout different stages of differentiation. These stages include a proliferative/relatively undifferentiated stage (day 6), a matrix maturation stage (days 10-14), and a mineralization/calcified nodule stage (day 18). During the stage of rapid cell proliferation, E2 treatment of hFOB/ER9 cells resulted in a dose-dependent decrease in [3H]thymidine incorporation to a maximum of 72% compared to the vehicle control value. Treatment of hFOB/ER9 cells with 10(-9) M E2 for 48 h resulted in an increase in alkaline phosphatase (AP) activity throughout cell differentiation. The magnitude of AP induction varied from approximately 200-500%. In contrast, E2 decreased osteocalcin protein levels to a minimum of 54% compared to the vehicle control value. The steady state messenger RNA levels for AP increased and osteocalcin decreased after E2 treatment, similar to the responses observed at the protein level. At all stages, there was little or no effect of E2 on type I collagen protein levels or osteonectin steady state messenger RNA levels. The E2 responses on hFOB/ER9 cell matrix protein expression and cell proliferation were mediated through the ER, as cultures cotreated with a 100-fold molar excess of a type II anti-E2 (ICI 182,780) abrogated these effects. These results support the hypothesis that E2 does have an effect on osteoblastic differentiation by decreasing hFOB/ER9 cell proliferation and differentially regulating extracellular matrix expression.

Alkaline sphingomyelinase activity is decreased in human colorectal carcinoma

Abstract: BACKGROUND: The metabolism of sphingomyelin generates important signals regulating cell proliferation and apoptosis. Previous studies found that the administration of colon carcinoma carcinogen was associated with an accumulation of membrane sphingomyelin, and that dietary sphingomyelin inhibited promotion of experimental colon carcinoma in mice, indicating that the abnormal metabolism of sphingomyelin is linked to colon carcinoma development. However, the changes in sphingomyelinase (SMase) activity in colon carcinoma have not been directly studied. The authors identified, specifically in the intestine, a distinctive alkaline SMase that differs from the known acidic and neutral SMases. The functions and clinical implications of the enzyme are unknown. This study examined the changes in all three SMase activities in human colorectal carcinoma. METHODS: Tissue samples were taken from colorectal carcinoma and normal mucosa from 18 patients. After homogenization, the activities of acidic, neutral, and alkaline SMase, as well as ceramidase and alkaline phosphatase, were determined. The enzyme activities in cancer tissue were compared with normal tissue from the same patients. RESULTS: In the normal tissue, there is an activity gradient from the ascending colon to the rectum for neutral and alkaline SMases but not for acidic SMase. In colorectal carcinoma, alkaline SMase activity was preferentially decreased by 75%, whereas acidic and neutral SMase activity decreased by 30% and 50%, respectively. No changes could be found for either ceramidase or alkaline phosphatase activity. CONCLUSIONS: Alkaline SMase activity preferentially decreases in human colorectal carcinoma, suggesting a regulatory role of the enzyme in colon mucosa cell proliferation.

Reactive oxygen species derived from Nox4 mediate BMP2 gene transcription and osteoblast differentiation.

Abstract: BMP-2 (bone morphogenetic protein-2) promotes differentiation of osteoblast precursor cells to mature osteoblasts that form healthy bone. In the present study, we demonstrate a novel mechanism of BMP-2-induced osteoblast differentiation. The antioxidant NAC (N-acetyl-L-cysteine) and the flavoprotein enzyme NAD(P)H oxidase inhibitor DPI (diphenyleneiodonium) prevented BMP-2-stimulated alkaline phosphatase expression and mineralized bone nodule formation in mouse 2T3 pre-osteoblasts. BMP-2 elicited a rapid generation of ROS (reactive oxygen species) concomitant with increased activation of NAD(P)H oxidase. NAC and DPI inhibited BMP-2-induced ROS production and NAD(P)H oxidase activity respectively. NAD(P)H oxidases display structurally similar catalytic subunits (Nox1-5) with differential expression in various cells. We demonstrate that 2T3 pre-osteoblasts predominantly express the Nox4 isotype of NAD(P)H oxidase. To extend this finding, we tested the functional effects of Nox4. Adenovirus-mediated expression of dominant-negative Nox4 inhibited BMP-2-induced alkaline phosphatase expression. BMP-2 promotes expression of BMP-2 for maintenance of the osteoblast phenotype. NAC and DPI significantly blocked BMP-2-stimulated expression of BMP2 mRNA and protein due to a decrease in BMP2 gene transcription. Dominant-negative Nox4 also mimicked this effect of NAC and DPI. Our results provide the first evidence for a new signalling pathway linking BMP-2-stimulated Nox4-derived physiological ROS to BMP-2 expression and osteoblast differentiation.