Lan Yuan

Impaired mitochondrial function and oxidative stress in rat cortical neurons: implications for gadolinium-induced neurotoxicity.

Gadolinium (Gd), a rare-earth lanthanides metal, is widely utilized for various industrial and medical purposes, particularly in brain magnetic resonance imaging. However, its potential effects on the impairment of the central nervous system remain uncertain, especially with regard to the mitochondria, the potential primary target in metal-induced neural injury. This study investigates the effects of gadolinium on mitochondrial energy metabolism, ROS accumulation, and cell death toward cortical neurons. Results show that the metabolic activity of the mitochondria significantly decreased as early as 3h after exposure of cells to gadolinium chloride. Subsequently, significant elevation of intracellular ROS, decrease in ATP synthesis, depolarization of mitochondrial membrane potential, release of cytochrome c and activation of caspase-3 were observed. Following these changes, increased release of LDH into culture medium and DNA fragmentation were detected. Inhibition of both cytochrome c release and caspase-3 activation could significantly reduce Gd-induced neuron cell death. All these results suggest that gadolinium cause neuron cell apoptosis primarily by inhibiting mitochondrial function and inducing oxidative stress. The present work provides new insight into the toxicological mechanism of gadolinium in neurons.

Lanthanum enhances in vitro osteoblast differentiation via pertussis toxin‐sensitive gi protein and ERK signaling pathway

Converging lines of evidence suggest that lanthanum tends to deposit in bone. The influence of lanthanum ion (La3+) on osteoblast differentiation and the related mechanism are essential to understanding its effect on bone metabolism. In this study, La3+ treatment enhanced in vitro osteoblast differentiation as evidenced by promoting alkaline phosphatase (ALP) activity, osteocalcin (OC) secretion, and matrix mineralization. The expressions of osteoblast‐specific genes of Cbfa‐1, osteopontin (OPN), and bone sialoprotein (BSP) were all increased in the presence of La3+, but no change was observed in that of type I collagen (COL‐I). Further studies demonstrated that La3+ treatment enhanced phosphorylation of extracellular signal‐regulated kinase (ERK). Inhibition of ERK activation by U0126 suppressed the effects of La3+ on osteoblast activity. Moreover, pretreatment of the cells with pertussis toxin (PTx), a Gi protein inhibitor, suppressed the La3+‐enhanced ERK phosphorylation and osteoblast differentiation. These findings suggest that La3+ exposure enhances in vitro osteoblast differentiation and the effect depends on ERK phosphorylation via PTx‐sensitive Gi protein signaling. J. Cell. Biochem. 105: 1307–1315, 2008.

Cholestane-3β,5α,6β-triol inhibits osteoblastic differentiation and promotes apoptosis of rat bone marrow stromal cells

Converging lines of evidence suggest that oxidized lipids, long recognized as a risk factor in atherogenesis, also contribute to osteoporosis, but the underlying mechanism is not understood in detail. The effect of atherogenesis related factors including oxysterols on the differentiation and survival of marrow stromal cells (MSCs) would be very important in understanding the link between atherosclerosis and osteoporosis. In the present study, the effect of oxysterol cholestane‐3β,5α,6β‐triol (Triol) on osteoblastic differentiation and apoptosis of primary rat bone MSCs as well as the related mechanisms were studied. Triol inhibited MSCs osteoblastic differentiation as demonstrated by inhibition of alkaline phosphatase activity, osteocalcin secretion, and matrix mineralization. In the other aspect, Triol promoted MSCs apoptosis, as characterized by condensed or fragmented nuclei as well as active externalization of phosphatidyl serine to the cell surface. In addition, Triol was found to induce increases of intracellular Ca2+ and Ca2+‐dependent reactive oxygen species generation in MSCs. These effects were involved in the action of Triol on apoptosis, but not on osteoblastic differentiation of MSCs. These results suggested that Triol might contribute to the decreased bone formation by inhibition of osteoblastic differentiation and promotion of apoptosis of MSCs, providing insights about common factors underlying the pathogenesis of atherosclerosis and osteoporosis.

La3+-promoted proliferation is interconnected with apoptosis in NIH 3T3 cells.

Lanthanum ion (La3+) has been reported to affect proliferation or apoptosis of different cells. In the present study, La3+ was confirmed to promote both proliferation and apoptosis of NIH 3T3 cells at the same concentrations. La3+ was shown to promote proliferation by helping the cells to pass through the G1/S restriction point and enter S phase, however, the proliferating cells induced by incubation with La3+ eventually underwent apoptosis. The proliferation and apoptosis of NIH 3T3 cells induced by La3+ were well correlated with cell cycle alterations. La3+ caused the phosphorylation of extracellular signal‐regulated kinase (ERK) 1/2; while inhibition of ERK phosphorylation by 2′‐amino‐3′‐methoxyflavone (PD98059) suppressed both proliferation and apoptosis induced by La3+. Based on the above experimental results, we postulated that La3+‐promoted proliferation of NIH 3T3 cells could be interconnected with the cell apoptosis, possibly through cell cycle machinery. Our results thus support the recent hypothesis that proliferation and apoptosis of cell are intrinsically coordinated.

Gadolinium triggers unfolded protein responses (UPRs) in primary cultured rat cortical astrocytes via promotion of an influx of extracellular Ca2

Gadolinium (Gd) and its complexes are utilized widely in industrial and clinical diagnoses. As a rare earth metal ion, free gadolinium (Gd3+) in the human body poses neurotoxic risks during its in vivo release and retention. In the central nervous system, astrocytes play a pivotal role in processing toxic metal ions. The present study evaluates the effects of Gd on cellular calcium homeostasis, a common mechanism that causes cell death, and on unfolded protein responses (UPRs), a mechanism for cell survival in response to toxic stimuli in mammalian cells. The experimental results indicate that the influx of extracellular Ca2+ increases greatly after the exposure of astrocytes to Gd; however, no cell deaths were observed. Further evidence suggests the up-regulated expression of the endoplasmic reticulum (ER)-resident chaperone protein GRP78 by ER stress-mediated signal transductions, specifically the activation of ATF6, eIF2a, and IRE1. These results suggest that Gd promotes Ca2+ influx, thus triggering UPRs, which can be closely associated to the resistance of astrocytes to Gd-induced cytotoxicity.

Endothelial cell and macrophage regulation of vascular smooth muscle cell calcification modulated by cholestane-3β, 5α, 6β-triol

The cellular and molecular mechanisms that mediate vascular calcification remain poorly understood. In our previous study, oxysterol cholestane‐3β, 5α, 6β‐triol (Triol) was shown to promote vascular smooth muscle cells (VSMCs) calcification. In this study, by using direct coculture, non‐contact transwell coculture, and culture with conditioned media, we investigated the roles of endothelial cells (ECs) and macrophages in the regulation of VSMCs calcification in the absence or presence of Triol. In vitro calcification was induced by incubation of VSMCs with β‐glycerophosphate. The results showed that ECs inhibited VSMCs calcification, as manifested by the reduction of calcium deposition in extracellular matrix. This effect of ECs on calcification was via the secreted soluble factors. Furthermore, the stimulation of ECs by Triol had no influence on ECs inhibition of calcification. On the other hand, macrophages promoted VSMCs calcification via the secreted soluble factors such as reactive oxygen species, which was further enhanced by Triol. Our results supported the roles for ECs and macrophages in vascular calcification, modulated by oxysterols in atherosclerotic plaque.

Comparison of intestinal absorption of two insulin-mimic vanadyl complexes using Caco-2 monolayers as model system

Intestinal absorption of two oxovanadium complexes, vanadyl acetylacetonate (VO(acac)2) and bis-(maltolato)-oxovanadium (VO(ma)2), has been compared using Caco-2 monolayers as a model system. The two compounds are similar in chemical structures but different in glucose-lowering effects. Our experimental results show that they are both transported via passive diffusion with apparent permeabilty coefficients (apical → basolateral) of (82.0 ± 6.7)×10−7 and (14.6 ± 0.7) ×10−7 cm · s−1 respectively. This suggests that absorptivity of VO(acac)2 is much higher than that of VO(ma)2. This difference may be related to the metabolism of either compound, or its ligand, or both in the course of the transport. However, This difference in absorption will cause the great difference in bioavailability, which might account for better efficacy of VO(acac)2 than VO(ma)2 as the insulin-mimic agent.