Effects of Arsenic on Osteoblast Differentiation in Vitro and on Bone Mineral Density and Microstructure in Rats

Abstract

Background: Arsenic is a ubiquitous toxic element and is known to contaminate drinking water in many countries. Several epidemiological studies have shown that arsenic exposure augments the risk of bone disorders. However, the detailed effect and mechanism of inorganic arsenic on osteoblast differentiation of bone marrow stromal cells and bone loss still remain unclear.Objectives: We investigated the effects and mechanism of arsenic on osteoblast differentiation in vitro and evaluated bone mineral density (BMD) and bone microstructure in rats at doses relevant to human exposure from drinking water.Methods: We used a cell model of rat primary bone marrow stromal cells (BMSCs) and a rat model of long-term exposure with arsenic-contaminated drinking water, and determined bone microstructure and BMD in rats by microcomputed tomography (μCT).Results: We observed significant attenuation of osteoblast differentiation after exposure of BMSCs to arsenic trioxide (0.5 or 1 μM). After arsenic treatment during differentiation, expression of runt-related transcription factor-2 (Runx2), bone morphogenetic protein-2 (BMP-2), and osteocalcin in BMSCs was inhibited and phosphorylation of enhanced extracellular signal-regulated kinase (ERK) was increased. These altered differentiation-related molecules could be reversed by the ERK inhibitor PD98059. Exposure of rats to arsenic trioxide (0.05 or 0.5 ppm) in drinking water for 12 weeks altered BMD and microstructure, decreased Runx2 expression, and increased ERK phosphorylation in bones. In BMSCs isolated from arsenic-treated rats, osteoblast differentiation was inhibited.Conclusions: Our results suggest that arsenic is capable of inhibiting osteoblast differentiation of BMSCs via an ERK-dependent signaling pathway and thus increasing bone loss.Citation: Wu CT, Lu TY, Chan DC, Tsai KS, Yang RS, Liu SH. 2014. Effects of arsenic on osteoblast differentiation in vitro and on bone mineral density and microstructure in rats. Environ Health Perspect 122:559–565; http://dx.doi.org/10.1289/ehp.1307832

Height and blood chemistry in adults with a history of developmental arsenic poisoning from contaminated milk powder

“…Because phosphate is crucial for bone growth and mineralization (Penido and Alon 2012), lack of phosphate due to substitution by arsenic may have led to shorter height among the exposed participants. Indeed, arsenic may affect bone metabolism, as shown in experimental studies (Aybar Odstrcil et al 2010;Hu et al 2012;Szymczyk et al 2006;Wu et al 2014), and arsenic exposure inhibits endochondral ossification and osteoblast differentiation (Aybar Odstrcil et al 2010;Wu et al 2014). In humans, chronic exposure is associated with diminished bone mass density in adult males (Akbal et al 2014).…”

“…Further, a prospective cohort study from Bangladesh suggests an inverse association between early-life arsenic exposure from contaminated drinking water and children's growth during infancy (Gardner et al 2013;Saha et al 2012). Growth inhibition due to arsenic exposure has been supported by laboratory animal studies that show decreased body length and femur length (Hu et al 2012), as well as decreased bone mass density (Wu et al 2014). A cross-sectional study of adult males reported an inverse association between environmental arsenic exposure and bone mass density (Akbal et al 2014).…”

“…A cross-sectional study of adult males reported an inverse association between environmental arsenic exposure and bone mass density (Akbal et al 2014). In vitro studies have reported arsenic-induced decreased mineralization of osteoblasts in primary cell cultures (Hu et al 2012), decreased osteoblast differentiation (Wu et al 2014), and increased differentiation of preosteoclasts (Szymczyk et al 2006). Arsenate likely substitutes phosphate in the skeletal apatite crystals (Lindgren et al 1982), and arsenic exposure causes a decreased expression of alkaline phosphatase (ALP) (Hu et al 2012), an enzyme that hydrolyzes pyrophosphate and provides inorganic phosphate needed for bone mineralization (Millan 2013).…”

In Vivo Exposure to Inorganic Arsenic Alters Differentiation-Specific Gene Expression of Adipose-Derived Mesenchymal Stem/Stromal Cells in C57BL/6J Mouse Model

“…Little evidence exists on how iAs exposure impacts osteogenesis, however, other arsenical compounds such as arsenic trioxide decrease osteogenesis in bone marrow stromal cells following exposure (Wu et al, 2014), which suggests these differentiation processes may be influenced by environmental contaminants such as iAs. Interestingly, unlike adipogenesis, osteogenesis, and chondrogenesis showed a strikingly similar response to increasing iAs concentrations, showing a concentration-dependent decrease in the expression of several differentiation markers.…”

“…This was partly due to a host of evidence cumulating in arsenic being designated as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC, 2012), which suggested that exposure was directly linked to the risk of developing cancer within humans. However, iAs also has been shown to play a role in the dysfunction of regenerative capacity in muscles (Ambrosio et al, 2014) and bone (Wu et al, 2014), suggesting detrimental effects on stem/progenitor cell populations in these tissues.…”