Xiao-Gai Yang

The permeability and cytotoxicity of insulin-mimetic vanadium compounds.

AbstractPurpose. The aim of this study was to investigate the mechanism of permeation and cytotoxicity of vanadium compounds, [VO(acac)2], [VO(ma)2], and vanadate. Methods. Absorptive transport were carried out in Caco-2 monolayers grown on transwell inserts. Vanadium was quantified using inductively coupled plasma atomic emission spectrometry (ICP-AES). The change of Caco-2 cells in the microvilli morphology and F-actin structure was visualized by transmission electron microscopy and confocal laser scanning microscopy. Results. The three vanadium compounds were taken up by Caco-2 cells via simple passive diffusion. [VO(acac)2] were mainly transcellularly transported and exhibited the highest apparent permeabilty coefficients (8.2 × 10-6 cm-1). The cell accumulation of [VO(acac)2] was found to be greater than that of [VO(ma)2], and vanadate caused much less accumulation than the other two compounds. Vanadium compounds induced intracellular reactive oxygen species, reduced the transepithelial electric resistance, caused morphological change in microvilli, and led to different perturbation of F-actin structure. Conclusions. The three compounds exhibited different permeability due to different diffusion process and cellular uptake. The toxicity of vanadium complexes on Caco-2 monolayer involved F-actin-related change of tight junction and impairment of microvilli. The toxicity was also related to elevated intracellular reactive oxygen species (ROS) and their cellular accumulation.

Membrane transport of vanadium compounds and the interaction with the erythrocyte membrane

In the present work, the membrane transport and the biotransformation of vanadate, bis(maltolato)oxovanadium (VO(ma)2), and vanadyl acetylacetonate (VO(acac)2) were investigated to explore the relationship with their insulin-like activity. Cellular uptake kinetics were performed by ICP-AES and EPR. The uptake of VO(acac)2 and VO(ma)2 by human erythrocytes showed intracellular vanadium level higher than NaVO3 and the membrane transport of these two vanadyl complexes was presumed to be via the passive diffusion mechanism. A fraction of vanadyl was oxidized to anionic vanadium(V) species and also entered the cells by the anion channel. The stability of VO(acac)2 and VO(ma)2 to oxidation in human erythrocyte membrane vesicles was investigated using EPR. VO(ma)2 was found to be more sensitive to oxidation than VO(acac)2 in aqueous buffer solution. However, in the presence of membrane vesicles, the oxidation of VO(ma)2 and VO(acac)2 was retarded and the differences between them became insignificant. Thus, the lifetime of vanadium complexes might be prolonged in physiological fluids. The interaction with membranes appears to be important in the stabilization of vanadyl complexes. Meanwhile, structural changes of membrane proteins were also observed. The higher uptake of the vanadyl complexes and the observed changes of membrane proteins might attribute to their insulin-mimetic mechanisms and toxicities.

Vanadium compounds discriminate hepatoma and normal hepatic cells by differential regulation of reactive oxygen species

Our previous study indicated that vanadium compounds can block cell cycle progression at the G1/S phase in human hepatoma HepG2 cells via a highly activated extracellular signal-regulated protein kinase (ERK) signal. To explore their differential action on normal cells, we investigated the response of an immortalized hepatic cell line, L02 cells. The results demonstrated that a higher concentration of vanadium compounds was needed to inhibit L02 proliferation, which was associated with S and G2/M cell cycle arrest. In addition, in contrast to insignificant reactive oxygen species (ROS) generation in HepG2 cells, all of the vanadium compounds resulted significant increases in both O2·− and H2O2 levels in L02 cells. At the same time, ERK and c-Jun N-terminal kinase (JNK) as well as cell division control protein 2 homolog (Cdc2) were found to be highly phosphorylated, which could be counteracted with the antioxidant N-acetylcysteine (NAC). The current study also demonstrated that both the ERK and the JNK pathways contributed to the cell cycle arrest induced by vanadium compounds in L02 cells. More importantly, it was found that although NAC can ameliorate the cytotoxicity of vanadium compounds in L02 cells, it did not decrease their cytotoxicity in HepG2 cells. It thus shed light on the potential therapeutic applications of vanadium compounds with antioxidants as synergistic agents to reduce their toxicities in human normal cells without affecting their antitumor activities in cancer cells.

Reactive-oxygen-species-mediated Cdc25C degradation results in differential antiproliferative activities of vanadate, tungstate, and molybdate in the PC-3 human prostate cancer cell line

The differential antiproliferative effects of vanadate, tungstate, and molybdate on human prostate cancer cell line PC-3 were compared and the underlying mechanisms were investigated. The results demonstrate that all of the three oxoanions can cause G2/M cell cycle arrest, which is evidenced by the increase in the level of phosphorylated Cdc2 at its inactive Tyr-15 site. Moreover, even if the difference in cellular uptake among the three oxoanions is excluded from the possible factors affecting their antiproliferative activity, vanadate exerted a much more potent effect in PC-3 cells than the other two oxoanions. Our results also reveal that reactive oxygen species (ROS)-mediated degradation of Cdc25C rather than Cdc25A or Cdc25B is responsible for vanadate-induced G2/M cell cycle arrest. We propose a possible mechanism to clarify the differential effect of the three oxoanions in biological systems beyond just considering that they are structural analogs of phosphate. We suggest that ROS formation is unlikely to be involved in the biological function of tungstate and molybdate, whereas the redox properties of vanadium may be important factors for it to exert pharmacological effects. Further, given the evidence from epidemiology studies of the association between diabetes and prostate cancer, the possibility of vanadate as a good candidate as both an antidiabetic and an anticancer agent or a chemopreventive agent is indicated.

Gadolinium-containing bioparticles as an active entity to promote cell cycle progression in mouse embryo fibroblast NIH3T3 cells

In the present study, we demonstrated that gadolinium-containing particles formed in cell culture medium acted as a biologically active entity to mediate cell cycle progression in NIH3T3 cells. The particles were observed to accumulate at the cell surface by scanning electron microscopy. Energy-dispersive X-ray analysis was undertaken and confirmed that gadolinium was incorporated in the agglomerated particles. Moreover, the smaller gadolinium particles exhibited a stronger cell-cycle-promoting effect than the larger ones, but they shared the common signaling pathways. Both extracellular signal regulated kinase and phosphatidylinositol 3-kinase signaling pathways were activated by gadolinium-containing particles and may account for their proliferation-promoting effect on NIH3T3 cells. Furthermore, the study showed that the free gadolinium ion released from gadolinium-containing particles may be responsible for the proliferation effect. This study will be helpful to clarify the biological effect of the insoluble species formed from Gd3+ as well as other multivalent metal ions under physiological conditions and will help to improve their medical applications.

Gadolinium-promoted cell cycle progression with enhanced S-phase entry via activation of both ERK and PI3K signaling pathways in NIH 3T3 cells

The aim of this study was to investigate whether Gd is able to exert the proliferation-promoting effect and to explore its possible underlying mechanism. We showed that Gd promoted cell cycle progression with increased S-phase entry in a concentration- and time-dependent manner in NIH 3T3 cells. The effect was further evidenced by the expressions of key proteins in driving cells through the G1/S transition point of the cell cycle. In the presence of Gd, the protein levels of cyclins D, E, and A were dramatically increased and demonstrated a characteristically temporal pattern of sequential mitotic events. Additionally, the levels of phosphorylated retinoblastoma protein were also significantly increased at certain time periods. To further elucidate the underlying mechanism, extracellular signal-regulated kinase and phosphatidylinositol 3-kinase signaling pathways were assessed. Both pathways were activated by Gd. Moreover, the levels of cyclin D and cyclin A were evaluated after the addition of the pharmacological inhibitors at early and late G1 phases, correspondingly, to reveal the contribution of the two pathways in the Gd-promoted G1/S transition. It showed that both pathways were needed for Gd-promoted cell cycle progression. The results presented here provide novel evidence to advance knowledge leading to further understanding of the mechanisms of both cell growth and death caused by Gd and may be helpful for more rational application of Gd-based compounds in the future.

Bis(acetylacetonato)-oxidovanadium(IV) and sodium metavanadate inhibit cell proliferation via ROS-induced sustained MAPK/ERK activation but with elevated AKT activity in human pancreatic cancer AsPC-1 cells

In this study, the antiproliferative effect of bis(acetylacetonato)-oxidovanadium(IV) and sodium metavanadate and the underlying mechanisms were investigated in human pancreatic cancer cell line AsPC-1. The results showed that both exhibited an antiproliferative effect through inducing G2/M cell cycle arrest and can also cause elevation of reactive oxygen species (ROS) levels in cells. Moreover, the two vanadium compounds induced the activation of both PI3K/AKT and MAPK/ERK signaling pathways dose- and time-dependently, which could be counteracted with the antioxidant N-acetylcysteine. In the presence of MEK-1 inhibitor, the degradation of Cdc25C, inactivation of Cdc2 and accumulation of p21 were relieved. However, the treatment of AKT inhibitor did not cause any significant effect. Therefore, it demonstrated that the ROS-induced sustained MAPK/ERK activation rather than AKT contributed to vanadium compounds-induced G2/M cell cycle arrest. The current results also exhibited that the two vanadium compounds did not induce a sustained increase of ROS generation, but the level of ROS reached a plateau instead. The results revealed that an intracellular feedback loop may be against the elevated ROS level induced by vanadate or VO(acac)2, evidenced by the increased GSH content, the unchanged level at the expression of antioxidant enzymes. Therefore, vanadium compounds can be regarded as a novel type of anticancer drugs through the prolonged activation of MAPK/ERK pathway but retained AKT activity. The present results provided a proof-of-concept evidence that vanadium-based compounds may have the potential as both antidiabetic and antipancreatic cancer agents to prevent or treat patients suffering from both diseases.

Binding of vanadium compounds perturbs conformation and aggregation state of insulin

Abstract The interactions between zinc-free insulin and vanadium compounds, NaVO3, VO(acac)2 and VO(ma)2, have been investigated by fluorescence spectroscopy, circular dichroism (CD) and Fourier-transformed infrared (FT-IR) spectroscopy. The results showed that binding of vanadium compounds produced a static quenching of the intrinsic fluorescence of insulin. The apparent association constants were determined to be (0.17 ± 0.01) × 104 L·mol−1 for NaVO3, (2.8 ± 0.2) × 104 L·mol−1 for VO(acac)2, and (4.0 ± 0.1) × 104 L·mol−1 for VO(ma)2, respectively. The light scattering intensity of insulin decreased upon incubation with the vanadium compounds, suggesting the disaggregation of insulin. The attenuation of the band at 273 nm of insulin CD spectra also supported the disaggregation of insulin observed above. A new band at 1650-1653cm−1 appeared in the FT-IR spectra of insulin upon incubation with the vanadium compounds, indicating the formation of an α-helix structure at B (9–19) motif. This α-helix structure...

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.

9. Health Benefits of Vanadium and Its Potential as an Anticancer Agent

Vanadium compounds have been known to have beneficial therapeutic properties since the turn of the century, but it was not until 1965 when it was discovered that those effects could be extended to treating cancer. Some vanadium compounds can combat common markers of cancer, which include metabolic processes that are important to initiating and developing the phenotypes of cancer. It is appropriate to consider vanadium as a treatment option due to the similarities in some of the metabolic pathways utilized by both diabetes and cancer and therefore is among the few drugs that are effective against more than one disease. The development of vanadium compounds as protein phosphatase inhibitors for the treatment of diabetes may be useful for potential applications as an anticancer agent. Furthermore, the ability of vanadium to redox cycle is also important for biological properties and is involved in the pathways of reactive oxygen species. Early agents including vanadocene and peroxovanadium compounds have been investigated in detail, and the results can be used to gain a better understanding of how some vanadium compounds are modifying the metabolic pathways potentially developing cancer. Considering the importance of coordination chemistry to biological responses, it is likely that proper consideration of compound formulation will improve the efficacy of the drug. Future development of vanadium-based drugs should include consideration of drug formulation at earlier stages of drug development.