Adenosine mediated lung mast cell degranulation in the mouse

Adenosine has been implicated to play a role in inflammatory processes associated with asthma. Most notable is adenosine's ability to potentiate mediator release from mast cells. Mast cells are bone marrow derived inflammatory cells that can release mediators that have both immediate and chronic effects on airway constriction and inflammation. Most physiological roles of adenosine are mediated through adenosine receptors. Four subtypes of adenosine receptors have been identified, A1, A2A, A2B and A 3. The mechanisms by which adenosine can influence the release of mediators from lung tissue mast cells is not understood due to lack of in vivo models. Mice deficient in the enzyme adenosine deaminase (ADA) have been generated. ADA controls the levels of adenosine in tissues and cells, and consequently, adenosine accumulates in the lungs of ADA-deficient mice. ADA-deficient mice develop features seen in asthmatics, including lung eosinophilia and mucus hypersecretion. In addition, lung tissue mast cell degranulation was associated with elevated adenosine in ADA-deficient lungs and can be prevented by ADA enzyme therapy. We established primary murine lung mast cell cultures, and used real time RT-PCR and immunofluorescence to demonstrate that A 2A, A2B and A3 receptors are expressed on murine lung mast cells. Studies using selective adenosine receptor agonists and antagonists and A3 receptor deficient (A3−/−) mast cells suggested that activation of A3 receptors could induce mast cell mediator release in vitro. Furthermore, this mediator release was associated with increases in intracellular Ca++ that appeared to be mediated through a Gi and PI3K pathway. In addition, nebulized A3 receptor agonist directly induced lung mast cell degranulation in wild type mice while having no effect in A3−/− mice. These results demonstrate that the A3 receptor plays an important role in adenosine mediated murine lung mast cell degranulation. Therefore, the A3 adenosine receptor and its signaling pathways may represent novel therapeutic targets for the treatment and prevention of asthma. ^

Synaptotagmin-2 controls regulated exocytosis but not other secretory responses of mast cells.

Mast cell degranulation is a highly regulated, calcium-dependent process, which is important for the acute release of inflammatory mediators during the course of many pathological conditions. We previously found that Synaptotagmin-2, a calcium sensor in neuronal exocytosis, was expressed in a mast cell line. We postulated that this protein may be involved in the control of mast cell-regulated exocytosis, and we generated Synaptotagmin-2 knock-out mice to test our hypothesis. Mast cells from this mutant animal conferred an abnormally decreased passive cutaneous anaphylaxis reaction on mast cell-deficient mice that correlated with a specific defect in mast cell-regulated exocytosis, leaving constitutive exocytosis and nonexocytic mast cell effector responses intact. This defect was not secondary to abnormalities in the development, maturation, migration, morphology, synthesis, and storage of inflammatory mediators, or intracellular calcium transients of the mast cells. Unlike neurons, the lack of Synaptotagmin-2 in mast cells was not associated with increased spontaneous exocytosis.

Early stages of experimental colon carcinogenesis inhibit mast cell-dependent mucosal immune function of the distal colon

Inhibition of local host immune reactions is one mechanism contributing to tumor progression. To determine if alterations in local immune functioning occur during colon carcinogenesis, a model mucosal immune response, type I hypersensitivity against the intestinal parasite Trichinella spiralis, was first characterized in normal mice and then examined during experimental colon carcinogenesis. Segments of sensitized colon mounted in Ussing chambers and challenged with T. spiralis-derived antigen resulted in a rise in short-circuit current ($\rm\Delta I\sb{sc}$) that was antigen-specific and inhibited by furosemide, implicating epithelial Cl$\sp-$ secretion as the ionic mechanism. The immune-regulated Cl$\sp-$ secretion by colonic epithelial cells required the presence of mast cells with surface IgE. Inhibition of potential anaphylactic mediators with various pharmacological agents in vitro implicated prostaglandins and leukotrienes as the principal mediators of the antigen-induced $\rm\Delta I\sb{sc}$, with 5-hydroxytryptamine also playing a role. Distal colon from immune mice fed an aspirin-containing diet (800 mg/kg powdered diet) ad libitum for 6 wk had a decreased response to antigen, confirming the major role of prostaglandins in generating the colonic I$\sb{\rm sc}$. To determine the effects of early stages of colon carcinogenesis on this mucosal immune response, mice were immunized with T. spiralis 1 day after or 8 wk prior to the first of 6 weekly injections of the procarcinogen 1,2-dimethylhydrazine (DMH). Responsiveness to antigenic challenge was suppressed in the distal colon 4-6 wk after the final injection of DMH. One injection of DMH was not sufficient to inhibit antigen responsiveness. The colonic epithelium remained sensitive to direct stimulation by exogenous Cl$\sp-$ secretagogues. Decreased antigen-induced $\rm\Delta I\sb{sc}$ in the distal colon was not due to systemic immune suppression by DMH, as the proximal colon and jejunum maintained responsiveness to antigen. Also, rejection of a secondary T. spiralis infection from the small intestine was not altered. Tumors eventually developed 25-30 wk after the final injection of DMH only in the distal portions of the colon. These results suggest that early stages of DMH-induced colon carcinogenesis manipulate the microenvironment such that mucosal immune function, as measured by immune-regulated Cl$\sp-$ secretion, is suppressed in the distal colon, but not in other regions of the gut. Future elucidation of the mechanisms by which this localized inhibition of immune-mediated ion transport occurs may provide possible clues to the microenvironmental changes necessary for tumor progression in the distal colon. ^

Generation of an hTERT-restricted, CMV-augmented oncolytic adenovirus capable of tumor-specific transgene expression: Development, characterization, and optimization

Current shortcomings in cancer therapy require the generation of new, broadly applicable, potent, targeted treatments. Here, an adenovirus is engineered to replicate specifically in cells with active human telomerase promotion using a modified hTERT promoter, fused to a CMV promoter element. The virus was also modified to contain a visible reporter transgene, GFP. The virus, Ad/hTC-GFP-E1 was characterized in vitro and demonstrated tumor specific activity both by dose and over time course experiments in a variety of cell lines. In vivo, Ad/hTC-GFP-E1 was affected at suppressing tumor growth and providing a survival benefit without causing any measurable toxicity. To increase the host range of the vector, the fiber region was modified to contain an RGD-motif. The vector, AdRGD/hTC-GFP-E1, was recharacterized in vitro, revealing heightened levels of infectivity and toxicity however maintaining a therapeutic window between cancer and normal cell toxicity. AdRGD/hTC-GFP-E1 was administered in vivo by limb perfusion and was observed to be tumor specific both in expression and replication. To further enhance the efficacy of viral vectors in lung delivery, asthma medications were investigated for their abilities to enhance transgene delivery and expression. A combination of bronchodilators, mast cell inhibitors, and mucolytic agents was devised which demonstrated fold increases in expression in immunocompetent mouse lungs as single agents and more homogenous, intense levels of expression when done in combination of all agents. To characterize the methods in which some cancers are resistant or may become resistant to oncolytic treatments, several small molecule inhibitors of metabolic pathways were applied in combination with oncolytic infection in vitro. SP600125 and PD 98059, respective JNK and ERK inhibitors, successfully suppressed oncolytic toxicity, however did not affect infectivity or transgene expression of Ad/hTC-GFP-E1. JNK and ERK inhibition did significantly suppress viral replication, however, as analyzed by lysate transfer and titration assays. In contrast, SB 203580, an inhibitor for p38, did not demonstrate any protective effects with infected cells. Flow cytometric analysis indicated a possible correlation with G1 arrest and suppressed viral production, however more compounds must be investigated to clarify this observation. ^