Glucosaminylmuramyl dipeptide (GMDP) modulates endothelial cell activities in vitro but has no effect on angiogenesis in vivo

Anti-tumor effect of Liqi, a traditional Chinese medicine prescription, in tumor bearing mice

Background

Liqi, an herbal preparation used in traditional Chinese medicine, has been used to treat cancer in China for centuries. We investigated the anti-tumor effects of liqi and their mechanisms in mice that had been xenografted with tumors.

Methods

Sarcoma 180 tumor, Lewis lung carcinoma, and SGC-7901 cells were implanted in BALB/c mice, C57BL/6 mice, and BALB/c nude mice, respectively. Liqi was administered to subgroups of these mice. The tumor weight and size were measured. Cell cycle analysis and T lymphocyte subsets were determined by flow cytometry. The activity of NK cells and TNF was tested using cytotoxicity assay on YAC-1 cells and L929 cells, respectively, and the activity of IL-2 was tested with an IL-2-dependent CTLL-2 cell proliferation assay. Platelet aggregation was monitored by measuring electric impedance, and the levels of thromboxane A2 (TXA₂) and prostacyclin (PGI₂) in blood were measured by ¹²⁵I-TXB₂ and ¹²⁵I-Keto-PGF_1α radioimmunoassay.

Results

The results showed that liqi inhibited tumor growth in tumor-implanted mice and arrested the cell proliferation in the G0/G1 phase and reduced the portion of cells in S and G2/M phase for SGC-7901 cells. Liqi increased the activity of NK cells and TNF-α, stimulated IL-2 production and activity, and regulated T lymphocyte subpopulations. Liqi inhibited the Lewis lung carcinoma metastasis by inhibiting platelet aggregation and normalizing the balance between TXA₂ and PGI₂.

Conclusion

All these findings demonstrated that liqi has an anti-tumor effect in vivo. The mechanism may be related to immune regulation and anticoagulation effects.

Establishment of a cell-based assay to screen regulators of the hypoxia-inducible factor-1-dependent vascular endothelial growth factor promoter

In this study, we established a drug screening system based on transcriptional regulation of vascular endothelial growth factor (VEGF) under hypoxia-inducible factor-1alpha control. We cloned the neomycin-resistance gene into the plasmid GL (pGL)3-promoter vector to generate the pGL3-promoter-neo vector. The 3 copies of the 47-bp fragment that contained the hypoxia response element of VEGF were synthesized and inserted in front of the minimal promoter of the pGL3-promoter-neo vector to generate p3HRE-luc-neo. The recombinant reporter gene vectors were transfected into EAhy926 cells, and stable cell lines were obtained. The positive cell line was selected for its ability to express luciferase in response to hypoxia. We demonstrated that CoCl(2) significantly enhances luciferase activity in a concentration-dependent fashion. We then optimized the cell density and incubation time under hypoxia which were used to screen. The assay exhibited a low background and was an ideal model for high-throughput screening for human VEGF regulators.

Effect of Hydroxysafflor yellow A on human umbilical vein endothelial cells under hypoxia

Hydroxysafflor yellow A (HSYA), is a component of the flower, Carthamus tinctorius L. In this study, we investigated its effect on Human Umbilical Vein Endothelial Cells (HUVECs) under hypoxia. We evaluated cell viability using the MTT kit. The cell cycle distribution was analyzed by PI staining flow cytometric analysis. PI AnnexinV-FITC detection and the TUNEL assay were performed to evaluate the apoptosis rate. Nitric oxide (NO) generation in cell supernatant was measured by the Griess assay. RT-PCR, Western blot and Immunocytochemistry analysis were used to evaluate the changes of Bcl-2, Bax, p53 and eNOS. Our data showed that HSYA inhibited cell apoptosis and cell cycle G1 arrest induced by hypoxia. HSYA treatment increased the Bcl-2/Bax ratio of protein and mRNA, reduced p53 protein expression in cell nucleus. In addition, HSYA enhanced the NO content of cell supernatant under hypoxia, accompanied with upregulating eNOS mRNA expression and protein level. Taken together, these results demonstrate that HSYA could protect HUVECs from hypoxia induced injuries by inhibiting cell apoptosis and cell cycle arrest. These findings have partly revealed the molecular mechanism of HSYA on treating of ischemic heart disease. We expected our experiments might provide some clues for further research.

Hydroxysafflor yellow A enhances survival of vascular endothelial cells under hypoxia via upregulation of the HIF-1 alpha-VEGF pathway and regulation of Bcl-2/Bax

Hydroxysafflor yellow A (HSYA) is a component of the flower Carthamus tinctorius L. The present investigation determines whether HSYA can modify the effects of hypoxia on vascular endothelial cells (EC) and its mechanisms. Human EC line (EAhy926) viability was determined using the MTT assay. EC cycle phase distribution was done with PI staining and flow cytometric analysis, and EC apoptosis was done by AnnexinV-FITC detection and the TUNEL assay. The protein levels of VEGF, Bcl-2, Bax, and HIF-1 alpha were determined by ELISA or Western blot analysis, and the mRNA expression of these genes by RT-PCR analysis. HIF-1 alpha transcriptional activity was measured using a reporter gene assay. HSYA improved cell viability under hypoxia in a concentration-dependent manner by attenuating its cycle arrest and inhibiting its apoptosis. HSYA upregulated the bcl-2/bax ratio, which is downregulated under hypoxia, increased VEGF protein concentration and VEGF mRNA expression and enhanced HIF-1 alpha protein accumulation and its transcriptional activity. In conclusion, HSAY could enhance the survival of ECs under hypoxia, which may be correlated with its effect of upregulating the bcl-2/bax ratio and promoting HIF-1 alpha protein accumulation, which increases VEGF. These findings provide evidence for the mechanisms by which HSYA maintains EC survival under hypoxia.

CD105 prevents apoptosis in hypoxic endothelial cells

CD105, a marker of endothelial cells, is abundantly expressed in tissues undergoing angiogenesis and is a receptor for transforming growth factorbeta. The pivotal role of CD105 in the vascular system was demonstrated by the severe vascular defects that occur in CD105-knockout mice, but the exact mechanisms for CD105 regulation of vascular development have not been fully elucidated. In light of the function of CD105 and the importance of hypoxia in neovascularisation, we speculated that CD105 is involved in hypoxia-initiated angiogenesis. Using tissue-cultured human microvascular endothelial cells, we have investigated the effects of hypoxic stress on CD105 gene expression. Hypoxia induced a significant increase in membrane-bound and secreted CD105 protein levels. CD105 mRNA and promoter activity were also markedly elevated, the latter returning to the basal level after 16 hours of hypoxic stress. Hypoxia induced cell cycle arrest at the G0/G1 phases and massive cell apoptosis after 24 hours through a reduction in the Bcl-2 to Bax ratio, downregulation of Bcl-XL and Mcl-1, and upregulation of caspase-3 and caspase-8. The consequence of CD105 upregulation was revealed using an antisense approach and a TUNEL assay. Suppression of CD105 increased cell apoptosis under hypoxic stress in the absence of TGFbeta1. Furthermore, hypoxia and TGFbeta1 synergistically induced apoptosis in the CD105-deficient cells but not in the control cells. We conclude that hypoxia is a potent stimulus for CD105 gene expression in vascular endothelial cells, which in turn attenuates cell apoptosis and thus contributes to angiogenesis.

CD105 antagonizes the inhibitory signaling of transforming growth factor beta1 on human vascular endothelial cells

CD105 (endoglin), a receptor for transforming growth factor beta (TGFbeta), is highly expressed in tissue-cultured, activated endothelial cells in vitro and in tissues undergoing angiogenesis in vivo. The absence of CD105 in knockout mice leads to their death from defective vascular development, but the role of CD105 in the modulation of angiogenesis has not been elucidated. TGFbeta1 is a well-recognized regulator of angiogenesis. Using an antisense approach, we have shown that inhibition of CD105 protein translation in cultured human endothelial cells enhances the ability of TGFbeta1 to suppress growth and migration in these cells. The ability of endothelial cells to form capillary tubes was evaluated by the use of a 3-dimensional collagen matrix system where TGFbeta1 not only reduced the length of capillary-like structures, but also caused massive mortality in CD105-deficient cells compared to control cultures. These results provide direct evidence that CD105 antagonizes the inhibitory effects of TGFbeta1 on human vascular endothelial cells and that normal cellular levels of CD105 are required for the formation of new blood vessels.