Cyclic AMP enhances resolution of allergic pleurisy by promoting inflammatory cell apoptosis via inhibition of PI3K/Akt and NF-kappaB.

Selective and timely induction of apoptosis is an effective means of resolving inflammation. The effects and putative mechanisms by which cyclic AMP (cAMP) modulates leukocyte apoptosis in vivo are still unclear. The present study aims at identifying intracellular pathways underlying the ability of cAMP elevating agents to resolve eosinophilic inflammation in a model of allergic pleurisy in mice. Ovalbumin (OVA) challenge of immunized mice induced eosinophil recruitment that peaked at 24h and persisted till 48h. Treatment with the PDE4 inhibitor rolipram, cAMP mimetic db-cAMP or adenylate cyclase activator forskolin, at 24h after antigen-challenge resulted in profound resolution of eosinophilic inflammation, without a decrease of mononuclear cell numbers. There was a concomitant increase in number of apoptotic cells in the pleural cavity. The effects of rolipram and db-cAMP were inhibited by the PKA inhibitor H89. Inhibition of PI3K/Akt or NF-kappaB induced resolution of inflammation that was associated with increased apoptosis. OVA-challenge resulted in a time-dependent activation of Akt and NF-kappaB, which was blocked by treatment with rolipram or PI3K/Akt pathway inhibitors. Thus, cAMP elevating agents resolve established eosinophilic inflammation by inducing leukocyte apoptosis. Mechanistically, the actions of cAMP are dependent on PKA and target a PI3K/Akt-dependent NF-kappaB survival pathway.

Cyclic GMP protein kinase activity is reduced in thyroxine-induced hypertrophic cardiac myocytes.

1. We tested the hypothesis that the cGMP-dependent protein kinase has major negative functional effects in cardiac myocytes and that the importance of this pathway is reduced in thyroxine (T4; 0.5 mg/kg per day for 16 days) hypertrophic myocytes. 2. Using isolated ventricular myocytes from control (n = 7) and T4-treated (n = 9) rabbit hypertrophic hearts, myocyte shortening was studied with a video edge detector. Oxygen consumption was measured using O2 electrodes. Protein phosphorylation was measured autoradiographically. 3. Data were collected following treatment with: (i) 8-(4-chlorophenylthio)guanosine-3',5'-monophosphate (PCPT; 10-7 or 10-5 mol/L); (ii) 8-bromo-cAMP (10-5 mol/L) followed by PCPT; (iii) beta-phenyl-1,N2-etheno-8-bromoguanosine-3',5'-monophosphorothioate, SP-isomer (SP; 10-7 or 10-5 mol/L); or (iv) 8-bromo-cAMP (10-5 mol/L) followed by SP. 4. There were no significant differences between groups in baseline percentage shortening (Pcs; 4.9 +/- 0.2 vs 5.6 +/- 0.4% for control and T4 groups, respectively) and maximal rate of shortening (Rs; 64.8 +/- 5.9 vs 79.9 +/- 7.1 micro m/ s for control and T4 groups, respectively). Both SP and PCPT decreased Pcs (-43 vs-21% for control and T4 groups, respectively) and Rs (-36 vs-22% for control and T4 groups, respectively), but the effect was significantly reduced in T4 myocytes. 8-Bromo-cAMP similarly increased Pcs (28 vs 23% for control and T4 groups, respectively) and Rs (20 vs 19% for control and T4 groups, respectively). After 8-bromo-cAMP, SP and PCPT decreased Pcs (-34%) and Rs (-29%) less in the control group. However, the effects of these drugs were not altered in T4 myocytes (Pcs -24%; Rs -22%). Both PCPT and cAMP phosphorylated the same five protein bands. In T4 myocytes, these five bands were enhanced less. 5. We conclude that, in control ventricular myocytes, the cGMP-dependent protein kinase exerted major negative functional effects but, in T4-induced hypertrophic myocytes, the importance of this pathway was reduced and the interaction between cAMP and the cGMP protein kinase was diminished.

Evidence for an inhibitory role of cyclic AMP in the control of juvenile hormone biosynthesis by cockroach corpora allata.

High levels of cyclic AMP were found in the corpora allata of adult female Diploptera punctata. The adenylate cyclase activator forskolin caused a rapid, reversible and dose-dependent accumulation of cAMP in the corpora allata in vitro. The sensitivity of the corpora allata to forskolin was low when juvenile hormone (JH) synthetic activity was high, and vice versa. Incubation of corpora allata with compounds which cause or mimic elevated intracellular cAMP levels (forskolin, 3-isobutyl-1-methylxanthine, 8-bromo-cAMP) led to a rapid and dose-dependent inhibition of juvenile hormone synthesis. Glands from day 5 virgin females were more sensitive to forskolin than glands from mated females of the same age. The results suggest that a cAMP second messenger system may be responsible for the intracellular transduction of inhibitory signals to the corpora allata of D. punctata.