Influence of Viscosity and Magnetoviscous Effect on the Performance of a Magnetic Fluid Seal in a Water Environment

<p>The magnetic fluid seal is one of the most successful applications of magnetic fluids. The theory of magnetic fluid seals in liquid environments has not been developed. This work mainly presents an experimental study of the influence of viscosity and magnetoviscous effects on the performance of a magnetic fluid seal in a water environment. Three engine oil–based magnetic fluids of different viscosities and similar saturation magnetization values were prepared and a multistage magnetic seal structure was designed. The magnetoviscous effect of the magnetic fluids under different working conditions was measured with an advanced rotational rheometer. An experimental platform and a multistage magnetic seal structure were designed for the critical pressure value and durability tests. The experimental results show that the viscosity of a magnetic fluid is a decisive factor in its sealing performance under a water environment and a discussion is presented that can explain the experimental results qualitatively.</p

The mTOR/p70S6K/ RPS6/4E-BP1 signaling pathway was involved in T2A-induced inhibition of HIF-1α.

<p>(A) The MDA-MB-231 cells were treated without or with various concentrations of T2A for 24 hours under normoxic and hypoxic conditions. Whole cell extracts were prepared from cells and subjected to Western blot assay using antibodies against phospho-mTOR (p-mTOR), mTOR, p70S6 Kinase(p70S6K), p-p70S6K (Thr421/Ser424), p-p70S6K(Thr389), S6 Ribosomal Protein (RPS6), p-RPS6(Ser235/236), p-RPS6(Ser240/244), 4E-BP1, and p-4E-BP1(Thr37/46). (B) Cells were pretreated with rapamycin (20 nM) for 2 hours, followed by T2A treatment (20 μM) under normoxic or hypoxic conditions as described above. Whole cell extracts were analyzed by Western blot using antibodies as indicated. (C) VEGF in the supernatant was evaluated using ELISA. Error bars represent means ± SD (n = 3). Values of cells treated with T2A and rapamycin were significantly reduced compared to values obtained from cells treated with T2A alone based on Student’s t-test; **<i>P</i> <0.01.</p

T2A inhibited angiogenesis and tumor growth <i>in vivo</i>.

<p>Xenograft mouse models on the back of nude mice were established using human MDA-MB-231 cells (2 × 10⁶). Tumor mice were treated with T2A or vehicle as described in the Methods section. Tumor growth and body weight of mice were measured once a week. (A) Average tumor volume of vehicle control mice and mice treated with T2A. Values of tumor volume from the T2A-treated group were significantly reducted compared with those from mice of the control group based on Student’s t test; *<i>P</i> < 0.05 or **<i>P</i> < 0.01. (B) Body weight of mice during the eight weeks of T2A treatment. (C) Representative tumors from the control and T2A-treated groups. (D) Average hemoglobin levels in tumor tissues from 4 vehicle control and 4 T2A-treated mice. **<i>P</i> < 0.01 compared with vehicle control. (E) Representative tumor sections were immunostaining by using CD31 antibody. Scale bar represents 20 μm. (F) Microvessel density (MVD) was counted the CD31-positive blood vessels per field (400 × magnification) from four replicate tumor sections. **<i>P</i> < 0.01 compared with vehicle control. (G) Total cellular RNA were extracted from tumors in 4 vehicle control and 4 T2A-treated mice and the VEGF mRNA level was evaluated using real-time PCR. **<i>P</i> < 0.01 compared with vehicle control. (H) Tumors from 1 vehicle control mouse and 1 T2A-treated mice were surgically removed and homogenized. Whole tumor lysates were prepared and subjected to Western blot assay using antibodies as indicated.</p

T2A inhibited HIF-1α expression in MDA-MB-231 and MCF-7 cells.

<p>(A and B) The MDA-MB-231 and MCF-7 cells were treated without or with various concentrations of T2A for 16 hours and then subjected to hypoxia, or remained in normoxia for an additional 8 hours. Whole cell extracts (WCE) and nuclear extracts (NE) were prepared from cells and subjected to Western blot assay using antibodies against HIF-1α, HIF-2α, HIF-1β, and β-actin. (C) Cells were fixed, permeabilized, and processed for immunofluorescence labeling with anti-Tubulin (Red) and anti-HIF-1α (green) antibodies. Nuclei were counterstained with 0.1 μg/ml DAPI (blue). Scale bar represents 10 μm.</p

T2A inhibited HIF-1α expression through the inhibition of protein synthesis rather than the promotion of HIF-1α degradation.

<p>(A) The MDA-MB-231 cells were cultured under normoxic or hypoxic conditions for 8 hours, then pretreated without or with 20 μM T2A for 30 minutes, followed by treatment without or with 20 μM cycloheximide (CHX) for various intervals as indicated. Upper panel: after treatment, whole cell extracts were analyzed by Western blot using antibodies against HIF-1α and β-actin. Lower panel: quantification of the HIF-1α by densitometry following normalization to the β-actin level. The HIF-1α protein levels in untreated or T2A-treated cells were arbitrarily given the value of 100%. (B) Cells were labeled with [³⁵S]methionine as described in the Methods section and chased for the indicated periods (h) in the presence or absence of T2A under normoxic or hypoxic conditions. Upper panel: equal amounts of proteins from each cell lysate were subjected to immunoprecipitation and then separated in SDS-PAGE and examined by autoradiography following normalization to the control. Lower panel: quantification of the autoradiographic HIF-1α signal by densitometry. (C) Cells were pretreated with either vehicle or 20 μM T2A for 16 hours and then subjected to hypoxia, or remained in normoxia for an additional 8 hours. Subsequently, cells were labeled with [³⁵S]methionine in the presence or absence of 20 μM T2A for the indicated time. Upper panel: Equal amounts of proteins were subjected to immunoprecipitation and then separated in SDS-PAGE and examined by autoradiography. Lower panel: quantification of the autoradiographic HIF-1α signal by densitometry. (D) Cells were pretreated with the proteasome inhibitor MG132 (10 μM) for 2 hours, followed by T2A treatment (20 μM) under normoxic or hypoxic conditions as described above. Whole cell extracts were analyzed by Western blot using antibodies against HIF-1α and β-actin.</p