BACKGROUND AND PURPOSESphingosine-1-phosphate (S1P) has been shown to be involved in the asthmatic disease as well in preclinical mouse experimental models of this disease. The aim of this study was to understand the mechanism(s) underlying S1P effects on the lung. EXPERIMENTAL APPROACHBALB/c, mast cell-deficient and Nude mice were injected with S1P (s.c.) on days 0 and 7. Functional, molecular and cellular studies were performed. KEY RESULTSS1P administration to BALB/c mice increased airway smooth muscle reactivity, mucus production, PGD2, IgE, IL-4 and IL-13 release. These features were associated to a higher recruitment of mast cells to the lung. Mast cell-deficient Kit W-sh/W-sh mice injected with S1P did not display airway smooth muscle hyper-reactivity. However, lung inflammation and IgE production were still present. Treatment in vivo with the anti-CD23 antibody B3B4, which blocks IgE production, inhibited both S1P-induced airway smooth muscle reactivity in vitro and lung inflammation. S1P administration to Nude mice did not elicit airway smooth muscle hyper-reactivity and lung inflammation. Naïve (untreated) mice subjected to the adoptive transfer of CD4+ T-cells harvested from S1P-treated mice presented all the features elicited by S1P in the lung. CONCLUSIONS AND IMPLICATIONSS1P triggers a cascade of events that sequentially involves T-cells, IgE and mast cells reproducing several asthma-like features. This model may represent a useful tool for defining the role of S1P in the mechanism of action of currently-used drugs as well as in the development of new therapeutic approaches for asthma-like diseases. AbbreviationsCFSE, carboxyfluoresceindiacetate, succinimidyl ester; FcεRI, high affinity IgE receptor; H&E, haematoxylin and eosin; PAS, periodic acid/Alcian blue/Schiff; S1P, sphingosine-1-phosphate; SPK, sphingosine kinase BJP British Journal of Pharmacology

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Sphingosine-1-phosphate (S1P) has been widely associated with inflammation-based lung pathologies. Because B cells play a critical role as antigen-presenting and/or Ig-producing cells during asthmatic conditions, we wanted to dissect the role of these cells in S1P-dependent airway hyperreactivity and inflammation. Mice were sensitized to ovalbumin or exposed to S1P. Ovalbumin sensitization caused airway hyperreactivity coupled to an increased lung infiltration of B cells, which was significantly reduced after the inhibition of sphingosine kinases I/II. Similarly, the sole administration of S1P increased bronchial reactivity compared with vehicle and was accompanied by a higher influx of B cells in a time-dependent manner. This effect was associated with higher levels of IL-13, transforming growth factor-β, IL-10, and T regulatory cells. In addition, isolated S1P-derived lung B cells increased CD4(+) and CD8(+) T cell proliferation in vitro, and their suppressive nature at Day 14 was associated with the higher release of transforming growth factor-β and IL-10 when they were cocultured. Therefore, to prove the role of B cells in S1P-mediated airway inflammation, and because CD20 expression, contrary to major hystocompatibility complex I and major hystocompatibility complex II, was up-regulated at Day 14, CD20(+) B cells were depleted by means of a specific monoclonal antibody. The absence of CD20(+) B cells increased airway reactivity and inflammation in S1P-treated mice compared with control mice. These data imply that sphingosine kinase/S1P-mediated airway inflammation is countered by B cells via the induction of an immune-suppressive environment to reduce asthma-like outcomes in mice.

Studies were made on COMT and MAO activity in rats 2, 4, 6, 12 and 24 h after intraperitoneal treatment with 8 and 60 mg/kg doses of tetrahydropapaveroline (THP), and 10 and 20 days after treatment with 8 mg/kg/day. Results suggested COMT activity inhibition only after 2 h of treatment. Experiments were also performed on THP and salsolinol methylation capacity in vitro. Results showed that both alkaloids use COMT enzymes for methylation and can also act as competitive inhibitors of COMT and MAO activity.

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