ABSTRACT
Diabetes is associated with increased formation of advanced glycation end products (AGEs), which have been implicated in micro and macrovascular complications of diabetes. Our earlier reports showed proangiogenic effect of AGE-bovine serum albumin (BSA). In order to understand the mechanism of AGE-mediated angiogenesis, the possibility of involvement of peroxisome prolifeator activated receptor (PPAR) , a ligand activated transcription factor was examined. The angiogenic effect was studied in chick chorio allantoic membrane (CAM) and by analyzing angiogenic markers in human umbilical vein endothelial cells (HUVECs) in culture. The involvement of PPAR was investigated using synthetic PPAR agonist GW 1929 and antagonist GW 9662 and by RT-PCR. In CAM assay, PPAR antagonist GW 9662 reversed the AGE-induced effect on vascularity. In HUVECs in culture, GW 9662 reversed the effect of AGE-BSA and decreased the expression of CD 31, E-Selectin and VEGF. RT-PCR analysis showed that treatment with AGE-BSA caused upregulation of PPAR mRNA levels. The reversal of the effect of AGE on angiogenesis by treatment with PPAR antagonists and up-regulation of PPAR gene in HUVECs treated with AGE-BSA suggested the possible involvement of PPAR -dependent downstream pathway in mediating the angiogenic effect of AGE.
Subject(s)
Angiogenesis Inducing Agents/metabolism , Anilides/pharmacology , Animals , Platelet Endothelial Cell Adhesion Molecule-1/drug effects , Platelet Endothelial Cell Adhesion Molecule-1/metabolism , Benzophenones/pharmacology , Cells, Cultured , Chick Embryo , Chorioallantoic Membrane/drug effects , Chorioallantoic Membrane/metabolism , Diabetes Mellitus/metabolism , E-Selectin/metabolism , /pharmacology , Human Umbilical Vein Endothelial Cells/metabolism , PPAR gamma/antagonists & inhibitors , PPAR gamma/antagonists & inhibitors , PPAR gamma/drug effects , PPAR gamma/metabolism , RNA/drug effects , RNA/metabolism , Tyrosine/analogs & derivatives , Tyrosine/pharmacology , Vascular Endothelial Growth Factor A/drug effects , Vascular Endothelial Growth Factor A/metabolismABSTRACT
Resistance to anticancer drugs is a major cause of failure of many therapeutic protocols. A variety of mechanisms have been proposed to explain this phenomenon. The exact mechanism depends upon the drug of interest as well as the tumor type treated. While studying a cell line selected for its resistance to cisplatin we noted that the cells expressed a >25,000-fold collateral resistance to methotrexate. Given the magnitude of this resistance we elected to investigate this intriguing collateral resistance. From a series of investigations we have identified an alteration in a membrane protein of the resistant cell as compared to the sensitive cells that could be the primary mechanism of resistance. Our studies reviewed here indicate decreased tyrosine phosphorylation of a protein (molecular mass = 66) in the resistant cells, which results in little or no transfer of methotrexate from the medium into the cell. Since this is a relatively novel function for tyrosine phosphorylation, this information may provide insight into possible pharmacological approaches to modify therapeutic regimens by analyzing the status of this protein in tumor samples for a better survival of the cancer patients