losartan-potassium and anandamide

Anandamide (ANA) is an endogenous ligand for the cannabinoid receptors Cb1 and Cb2 that is able to synergistically stimulate the proliferation of hematopoietic growth factor-dependent blood cells in serum-free culture. To elucidate the mechanisms by which ANA enhances the proliferative responses of hematopoietic cells, we investigated the ANA-mediated effects on proliferation, cell cycling, apoptosis and intracellular signaling of erythropoietin-stimulated 32D/EPO cells.. 32D/EPO cells were cultured serum free to determine the effects of EPO and anandamide on these cells. Proliferation was analyzed by tritiated thymidine incorporation. Apoptosis as well as cell cycle analysis was carried out by flow cytometry. MAPKinase activation was determined by Western blotting, using phospho-specific MAPK antibodies.. Simultaneous addition of erythropoietin (EPO) and ANA enhanced DNA synthesis and increased 32D/EPO cell numbers in serum-free culture. Interestingly, ANA did not alter the G1/S transition but it accelerated each of the successive cell cycle phases of EPO-stimulated 32D/EPO cells. Percentages of apoptotic 32D/EPO cells were equally low in cultures supplemented with EPO alone or a combination of EPO and ANA. Both cultures showed enhanced activation of two mitogen-activated protein kinases, namely, extracellular factor responsive kinases 1 and 2 (ERK1/2), as well as the MAPK-target gene protein c-Fos. This fully correlated with the synergistic stimulation of proliferation of 32D/EPO cells by EPO and ANA. ANA had no effect on EPO-induced STAT-5 activation of 32D/EPO cells. Experiments with the Cb2 receptor-specific antagonist SR144528 demonstrated that the synergistic stimulation of proliferation by ANA was partially Cb2 receptor-mediated.. These data suggest that the positive effects of ANA on the erythropoietin-induced proliferation of 32D/EPO cells are mediated by receptor-dependent as well as receptor-independent mechanisms, both of which involve activation of the mitogen-activated protein kinases, ERK1/2.

Topics: Animals; Apoptosis; Arachidonic Acids; Camphanes; Cell Cycle; Cell Line; Culture Media, Serum-Free; DNA Replication; DNA-Binding Proteins; Drug Synergism; Endocannabinoids; Enzyme Activation; Erythropoietin; Genes, fos; Mice; Milk Proteins; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Polyunsaturated Alkamides; Proto-Oncogene Proteins c-fos; Pyrazoles; Receptors, Cannabinoid; Receptors, Drug; RNA, Messenger; Signal Transduction; STAT5 Transcription Factor; Trans-Activators; Up-Regulation

We recently demonstrated that the gene encoding the peripheral cannabinoid receptor (Cb2) may be a proto-oncogene involved in murine myeloid leukemias. We show here that Cb2 may have a role in hematopoietic development. RNAse protection analysis showed that Cb2 is normally expressed in spleen and thymus. Cb2 mRNA is also expressed in 45 of 51 cell lines of distinct hematopoietic lineages, ie, myeloid, macrophage, mast, B-lymphoid, T-lymphoid, and erythroid cells. The effect of the fatty acid anandamide, an endogenous ligand for cannabinoid receptors, on primary murine marrow cells and hematopoietic growth factor (HGF)-dependent cell lines was then investigated. In vitro colony cultures of normal mouse bone marrow cells showed anandamide to potentiate interleukin-3 (IL-3)-induced colony growth markedly. Whereas HGFs alone stimulate proliferation of the various cell lines in serum-free culture only weakly, anandamide enhances the proliferative response of the cell lines to HGFs profoundly. This was apparent for responses induced by IL-3, granulocyte-macrophage colony-stimulating factor, granulocyte colony-stimulating factor, and erythropoietin. Anandamide was already effective at concentrations as low as 0.1 to 0.3 micromol/L and plateau effects were reached at 0.3 to 3 micromol/L. The addition of anandamide as single growth factor had no effect. The costimulatory effect of anandamide was not evident when cells were cultured with fetal calf serum (FCS), suggesting that FCS contains anandamide or another ligand capable of activating the peripheral cannabinoid receptor. Other cannabinoid ligands did not enhance the proliferative responsiveness of hematopoietic cells to HGFs. Transfection experiments of Cb2 in myeloid 32D cells showed that anandamide specifically activates proliferation through activation of the peripheral cannabinoid receptor. Anandamide appears to be a novel and synergistic growth stimulator for hematopoietic cells.

Topics: Animals; Arachidonic Acids; Bone Marrow Cells; Cannabinoids; Cell Division; Culture Media, Serum-Free; Drug Synergism; Endocannabinoids; Erythropoietin; Granulocyte Colony-Stimulating Factor; Granulocyte-Macrophage Colony-Stimulating Factor; Growth Substances; Hematopoietic Stem Cells; Interleukin-3; Ligands; Mice; Polyunsaturated Alkamides; Receptors, Cannabinoid; Receptors, Drug; RNA, Messenger