Muscarinic receptors participation in angiogenic response induced by macrophages from mammary adenocarcinoma-bearing mice.

INTRODUCTION: The role of macrophages in tumor progression has generated contradictory evidence. We had previously demonstrated the ability of peritoneal macrophages from LMM3 murine mammary adenocarcinoma-bearing mice (TMps) to increase the angiogenicity of LMM3 tumor cells, mainly through polyamine synthesis. Here we investigate the ability of the parasympathetic nervous system to modulate angiogenesis induced by TMps through the activation of the muscarinic acetylcholine receptor (mAchR). METHODS: Peritoneal macrophages from female BALB/c mice bearing a 7-day LMM3 tumor were inoculated intradermally (3 x 10(5) cells per site) into syngeneic mice. Before inoculation, TMps were stimulated with the muscarinic agonist carbachol in the absence or presence of different muscarinic antagonists or enzyme inhibitors. Angiogenesis was evaluated by counting vessels per square millimeter of skin. The expression of mAchR, arginase and cyclo-oxygenase (COX) isoforms was analyzed by Western blotting. Arginase and COX activities were evaluated by urea and prostaglandin E2 (PGE2) production, respectively. RESULTS: TMps, which stimulate neovascularization, express functional mAchR, because carbachol-treated TMps potently increased new blood vessels formation. This response was completely blocked by preincubating TMps with pirenzepine and 4-diphenylacetoxy-N-methylpiperidine (4-DAMP), M1 and M3 receptor antagonists, and partly by the M2 receptor antagonist methoctramine. M1 receptor activation by carbachol in TMps triggers neovascularization through arginase products because Nomega-hydroxy-L-arginine reversed the agonist action. Preincubation of TMps with methoctramine partly prevented carbachol-stimulated urea formation. In addition, COX-derived liberation of PGE2 is responsible for the promotion of TMps angiogenic activity by M3 receptor. We also detected a higher expression of vascular endothelial growth factor (VEGF) in TMps than in macrophages from normal mice. Carbachol significantly increased VEGF expression in TMps, and this effect was totally reversed by methoctramine and pirenzepine. Arginase and COX inhibitors partly decreased VEGF derived from TMps. CONCLUSION: TMps themselves induce a potent angiogenic response that is augmented by carbachol action. mAchR activation triggers arginine metabolism, PGE2 synthesis and VEGF production, promoting neovascularization.

Different mechanisms lead to the angiogenic process induced by three adenocarcinoma cell lines.

Neoangiogenesis is essential for tumor and metastasis growth, but this complex process does not follow the same activation pathway, at least in tumor cell lines originated from different murine mammary adenocarcinomas. LMM3 cells were the most potent to stimulate new blood vessel formation. This response was significantly reduced by preincubating cells with indomethacin and NS-398, non-selective cyclooxygenase (COX) and COX-2 selective inhibitors, respectively. COX-1 and COX-2 isoenzymes were both highly expressed in LMM3 cells, and we observed that indomethacin was more effective than NS-398 to inhibit prostaglandin E2 (PGE2) synthesis. In addition, nitric oxide synthase (NOS) inhibitors, Nomega monomethyl L-arginine and aminoguanidine, also reduced LMM3-induced angiogenesis and nitric oxide (NO) synthesis as well. NOS2 > NOS3 proteins and arginase II isoform were detected in LMM3 cells by Western blot. The latter enzyme was also involved in the LMM3 neovascular response, since the arginase inhibitor, Nomega hydroxy L-arginine reduced the angiogenic cascade. On the other hand, parental LM3 cells were able to stimulate neovascularization via COX-1 and arginase products since only indomethacin and Nomega hydroxy L-arginine, which diminished PGE2 and urea synthesis, respectively, also reduced angiogenesis. In turn, LM2 cells angiogenic response could be due in fact to PGE2-induced VEGF liberation that stimulated neoangiogenesis at very low levels of NO.

Arginine metabolic pathways involved in the modulation of tumor-induced angiogenesis by macrophages.

Neovascularization, an essential step for tumor progression and metastasis development, can be modulated by the presence of macrophages (Mps) in the tumor microenvironment. The ability of Mps to regulate the angiogenicity of the LMM3 tumor cell line was studied. Peritoneal Mps from LMM3 tumor-bearing mice (TMps) potentiate in vivo LMM3 angiogenicity. These results were confirmed by CD31 immunoblotting assays. The activity of TMps depended on nitric oxide synthase (NOS) and arginase (A) activity. By immunoblotting we evidenced that AI and AII isoforms were up-regulated in TMps while the inducible and neuronal NOS isoforms were highly expressed in normal Mps. TMps might positively modulate tumor growth by stimulating angiogenic cascade mainly through polyamine synthesis.

Nitric oxide synthase, arginase and cyclooxygenase are involved in muscarinic receptor activation in different murine mammary adenocarcinoma cell lines.

Investigations on the influence of the parasympathetic nervous system via muscarinic signaling in tumor progression have produced contradictory evidence. We investigated the expression of muscarinic acetylcholine receptors (mAchR) and their intracellular transduction pathways, in two murine mammary adenocarcinoma cell lines, LM3 and LM2 in comparison with the normal murine mammary epithelial cell line: NMuMG. Saturation binding assays with the tritiated muscarinic antagonist quinuclidinyl benzilate ([3H]-QNB) indicate that LM3 cells express higher amounts of mAchR than LM2 cells. Muscarinic receptor activation with carbachol (CARB) enhanced basal production of citrulline to a greater extent in LM3 cells than in LM2 cells. The nitric oxide synthase (NOS) inhibitor, NGmono-methyl-L-arginine (L-NMMA), blunted this effect only in LM3 cells while in LM2 cells the action of CARB was blocked by Nomega hydroxy-L-arginine (L-OH-Arg), which is known to inhibit the arginase pathway. Atropine blocks the action of CARB in both cell lines. Additionally, mAchR activation stimulates prostaglandin E2 (PGE2) synthesis only in LM2 cells. NMuMG cells show detectable basal amounts of nitric oxide and PGE2, but they did not respond to CARB. Binding experiments confirm the absence of mAchR in these cells. The findings indicate that mAchR expression in tumor cells, and its control on arginine metabolism, via NOS/arginase, and on PGE2 synthesis by COX activation, could be a switch on mechanism that might lead mammary cells from normal to malignant phenotype. Moreover, mAchR coupling to distinct effectors might be associated with differences in aggressiveness of tumor cells.

Reactivity of tumor-draining lymph nodes and the nitric oxide pathway.

Regional lymph nodes are important in the generation of tumor-directed immune responses. The relationship between nitric oxide synthase (NOS) expression and the biological behavior of tumor-draining lymph node (TDLNs) cells in vivo was determined using a spontaneously arising BALB/c mammary adenocarcinoma S13. We first demonstrated a reduction of tumor size and tumor-induced angiogenesis by blocking NOS activity in vivo. TDLNs harvested from tumor-bearing mice (TBM) on day 16 after tumor implant, showed enhanced NOS activity and NOS expression compared to control nodes. Identification of the NOS isoforms present in TDLNs resulted in expression of neuronal NOS (nNOS), endothelial NOS (eNOS) and absence of inducible NOS (iNOS). TDLN cells admixed with tumor cells and inoculated into normal mice (Winn assay) induced a reduction of tumor growth although, when inoculated alone, were able to induce the formation of new blood vessels (angiogenesis). Our data indicate that the in vivo antitumor activity of TDLN cells is modulated by a balance between angiogenesis and antitumor effectors. In our model, when trafficking of leukocytes is obviated, the control of tumor growth by TDLN cells can be explained in part by an antitumor activity great enough to exceed the angiogenic component elicited by the same cells, leading to a reduction of tumor size.

Inmunorregulación del crecimiento tumoral en un sistema murino / Immunoregulation of tumor growth in a murine model

Estudiamos la regulación del crecimiento tumoral y metastásico tanto por el propio tumor como por el sistema inmune, en un modelo murino. Sobrenadantes de cultivo de esplenocitos de portadores de tumor exacerban el crecimiento del propio tumor. Esta actividad desaparece luego de la cirugía tumoral pero con una cinética diferente dependendo de si el tumor es precoz o avanzado al tiempo de la cirugía. Las poblaciones esplénicas involucradas en la exacerbación varían durante el crecimiento del tumor mientras que las responsables de inducción de angiogénesis son siempre de naturaleza T. Con respecto de la autorregulación tumoral, encontramos que diferentes formas de antígenos tumorales (extractos tumorales, sobrenadantes de cultivo de células tumorales, células tumorales formolizadas) aumentan la diseminación metastásica, pero esta actividad está mediada por el sistema inmune del huésped. Por el contrario, sobrenadantes de cultivo de células tumorales no inducen exacerbación del tumor primario. Las células tumorales fueron tratadas con un modificador de membrana con la expectativa de alterar la respuesta inmune antitumoral

Inmunorregulación del crecimiento tumoral en un sistema murino / Immunoregulation of tumor growth in a murine model

Estudiamos la regulación del crecimiento tumoral y metastásico tanto por el propio tumor como por el sistema inmune, en un modelo murino. Sobrenadantes de cultivo de esplenocitos de portadores de tumor exacerban el crecimiento del propio tumor. Esta actividad desaparece luego de la cirugía tumoral pero con una cinética diferente dependendo de si el tumor es precoz o avanzado al tiempo de la cirugía. Las poblaciones esplénicas involucradas en la exacerbación varían durante el crecimiento del tumor mientras que las responsables de inducción de angiogénesis son siempre de naturaleza T. Con respecto de la autorregulación tumoral, encontramos que diferentes formas de antígenos tumorales (extractos tumorales, sobrenadantes de cultivo de células tumorales, células tumorales formolizadas) aumentan la diseminación metastásica, pero esta actividad está mediada por el sistema inmune del huésped. Por el contrario, sobrenadantes de cultivo de células tumorales no inducen exacerbación del tumor primario. Las células tumorales fueron tratadas con un modificador de membrana con la expectativa de alterar la respuesta inmune antitumoral (AU)