Involvement of cyclic AMP generation in the inhibition of respiratory burst by 2-phenyl-4-quinolone (YT-1) in rat neutrophils

Immunomodulatory Effects of Fluoroquinolones in Community-Acquired Pneumonia-Associated Acute Respiratory Distress Syndrome

Community-acquired pneumonia is reported as one of the infectious diseases that leads to the development of acute respiratory distress syndrome. The innate immune system is the first line of defence against microbial invasion; however, its dysregulation during infection, resulting in an increased pathogen load, stimulates the over-secretion of chemokines and pro-inflammatory cytokines. This phenomenon causes damage to the epithelial-endothelial barrier of the pulmonary alveoli and the leakage of the intravascular protein into the alveolar lumen. Fluoroquinolones are synthetic antimicrobial agents with immunomodulatory properties that can inhibit bacterial proliferation as well as exhibit anti-inflammatory activities. It has been demonstrated that the structure of fluoroquinolones, particularly those with a cyclopropyl group, exerts immunomodulatory effects. Its capability to inhibit phosphodiesterase activity leads to the accumulation of intracellular cAMP, which subsequently enhances PKA activity, resulting in the inhibition of transcriptional factor NF-κB and the activation of CREB. Another mechanism reported is the inhibition of TLR and ERK signalling pathways. Although the sequence of events has not been completely understood, significant progress has been made in comprehending the specific mechanisms underlying the immunomodulatory effects of fluoroquinolones. Here, we review the indirect immunomodulatory effects of FQs as an alternative to empirical therapy in patients diagnosed with community-acquired pneumonia.

Fluoroquinolones Suppress TGF-β and PMA-Induced MMP-9 Production in Cancer Cells: Implications in Repurposing Quinolone Antibiotics for Cancer Treatment

BACKGROUND

Fluoroquinolones (FQs) are potent antimicrobials with multiple effects on host cells and tissues. Although FQs can attenuate cancer invasion and metastasis, the underlying molecular mechanisms remain unclear. Matrix metalloproteinase-9 (MMP-9) has functional roles in tumor angiogenesis, invasion, and metastasis, and is associated with cancer progression and poor prognosis, suggesting that inhibitors of MMP-9 activity and transcription are prime candidates for cancer therapy. Despite numerous preclinical data supporting the use of MMP-9 inhibitors as anticancer drugs, the few available examples are not therapeutically useful due to low specificity and off-target effects. We examined the effects of FQs on MMP-9 production in cancer cells following transforming growth factor beta (TGF-β) and phorbol 12-myristate 13-acetate (PMA) stimulation.

EXPERIMENTAL APPROACHES

Using confluent cultures of HepG2 and A549 cells, the effects of FQs (ciprofloxacin, levofloxacin, clinafloxacin, gatifloxacin, and enrofloxacin) on TGF-β and PMA-induced MMP-9 mRNA expression and production were studied in RNA extracts and culture supernatants, respectively. FQs specifically abrogated TGF-β and PMA-induced MMP-9 levels and activity in a concentration and time-dependent manner, without affecting other MMPs or proteins involved in epithelial-mesenchymal transition. Additionally, FQs inhibited TGF-β and PMA-induced cell migration via p38 and cyclic AMP signaling pathways.

CONCLUSIONS AND IMPLICATIONS

Overall, we demonstrated that FQs inhibit cancer cell migration and invasion by downregulating MMP-9 expression and revealed the cellular mechanisms underlying their potential value in cancer treatment.

Effects of local anesthetics on the respiratory burst of cord blood neutrophils in vitro

BACKGROUND

Whether local anesthetics exert anti-inflammatory effects in fetal and newborn systemic neutrophils is unclear. The aim of the present study was to assess the effects of bupivacaine and lidocaine on the respiratory burst of cord blood neutrophils in vitro compared with adult cells.

METHODS

Whole cord blood (n = 12) and control adult blood samples (n = 7) were incubated with bupivacaine (0.0005, 0.005, 0.05, 1 mmol/l) and lidocaine (0.002, 0.02, 0.2, 4 mmol/l) for 1 and 4 h. The production of reactive oxygen species (ROS) by unstimulated neutrophils and the phorbol myristate acetate-induced oxidative burst were assessed by flow cytometry. A subset of neutrophils showing high fluorescence intensity (rho+) was analyzed separately.

RESULTS

After 1 h incubation, local anesthetics decreased the respiratory burst in whole cord blood and adult neutrophils in a similar manner. At the clinically relevant concentration of 0.0005 mmol/l, bupivacaine was active, but its effect in cord blood cells could not be detected after 4 h. The cord blood rho+ cell subset was unresponsive to the inhibitory action of bupivacaine. In rho+ neutrophils, basal ROS production was stimulated by lidocaine at the lowest concentration tested.

CONCLUSION

Bupivacaine and lidocaine can decrease the respiratory burst in neutrophils of term newborns.

Design, synthesis, and mechanism of action of 2-(3-hydroxy-5-methoxyphenyl)-6-pyrrolidinylquinolin-4-one as a potent anticancer lead

New 6- (or 6,7-) substituted 2-(hydroxyl substituted phenyl)quinolin-4-one derivatives were synthesized and screened for antiproliferative effects against cancer cell lines. Structure-activity relationship correlations were established and the most promising compound 2-(3-hydroxy-5-methoxyphenyl)-6-pyrrolidin-1-ylquinolin-4-one (6h) exhibited strong inhibitory activity against various human cancer cell lines, particularly non-small cell lung cancer NCI-H522. Additional studies suggested a mechanism of action resembling that of the antimitotic drug vincristine. The presence of a C-ring OH group in 6h will allow this compound to be converted readily to a water soluble and physicochemically stable hydrophilic prodrug. Compound 6h is proposed as a new anticancer lead compound.

Malaria circumsporozoite protein inhibits the respiratory burst in Kupffer cells

After transmission by infected mosquitoes, malaria sporozoites rapidly travel to the liver. To infect hepatocytes, sporozoites traverse Kupffer cells, but surprisingly, the parasites are not killed by these resident macrophages of the liver. Here we show that Plasmodium sporozoites and recombinant circumsporozoite protein (CSP) suppress the respiratory burst in Kupffer cells. Sporozoites and CSP increased the intracellular concentration of cyclic adenosyl mono-phosphate (cAMP) and inositol 1,4,5-triphosphate in Kupffer cells, but not in hepatocytes or liver endothelia. Preincubation with cAMP analogues or inhibition of phosphodiesterase also inhibited the respiratory burst. By contrast, adenylyl cyclase inhibition abrogated the suppressive effect of sporozoites. Selective protein kinase A (PKA) inhibitors failed to reverse the CSP-mediated blockage and stimulation of the exchange protein directly activated by cAMP (EPAC), but not PKA inhibited the respiratory burst. Both blockage of the low-density lipoprotein receptor-related protein (LRP-1) with receptor-associated protein and elimination of cell surface proteoglycans inhibited the cAMP increase in Kupffer cells. We propose that by binding of CSP to LRP-1 and cell surface proteoglycans, malaria sporozoites induce a cAMP/EPAC-dependent, but PKA-independent signal transduction pathway that suppresses defence mechanisms in Kupffer cells. This allows the sporozoites to safely pass through these professional phagocytes and to develop inside neighbouring hepatocytes.

Role of PDE4 in superoxide anion generation through p44/42MAPK regulation: a cAMP and a PKA-independent mechanism

We investigated the generation of reactive oxygen species (ROS) from bronchoalveolar lavage (BAL) cells of either control or LPS-exposed rats and the effects of PDE4 inhibitors on ROS production. The PDE4 inhibitors, rolipram and Ariflo (cilomilast, SB 207499) dose-dependently (0.1-10 microm) inhibited fMLP-induced superoxide anion (O(2)(*-)) production (IC(50)s: 0.03 and 0.55 microm, respectively) in BAL cells of Wistar rats collected 3 h after an LPS-aerosol (200 micrograms ml(-1), 1 h). These BAL contained 85-95% neutrophils (BAL cells enriched in neutrophils). In contrast, BAL cells collected at the end of the challenge contained only macrophages and in these conditions, rolipram and Ariflo (0.1-10 microm) could only inhibit 25 and 45% of fMLP-induced O(2)(*-) release, respectively. We also observed that the inhibition of p44/42(MAPK) by PD98059 (1-10 microm) increased O(2)(*-) release by BAL cells enriched in neutrophils, but not by macrophages, and prevented the inhibition of O(2)(*-) production induced by PDE4 inhibitors. Western blot analysis showed that PDE4 inhibitors strongly activated p44/42(MAPK) in BAL cells enriched in neutrophils but not in macrophages. And in these cells, PDE4 and p44/42(MAPK) were co-immunoprecipitated by a polyclonal anti-PDE4 antibody. The following cell permeable-cAMP analogues, dbcAMP (10 microm-1 mm), 8-CPT-cAMP (1 mm) and 8-pMeOPT-2'-O-Me-cAMP (0.5 mm), could not reduce fMLP-induced O(2)(*-) production and both PKA inhibitors, PKA inhibitor 14-22 amide myristoylated (50 nm-1 microm) and H-89 (100 nm-1 microm), did not affect the decrease of O(2)(*-) release induced by PDE4 inhibitors in BAL cells enriched in neutrophils. These data suggest that PDE4 inhibitors decreased fMLP-induced O(2)(*-) release in BAL cells enriched in neutrophils but not in macrophages, through p44/42(MAPK) activation by a cAMP- and a PKA-independent mechanism.

Activation of A2A adenosine receptors inhibits expression of alpha 4/beta 1 integrin (very late antigen-4) on stimulated human neutrophils

The alpha 4/beta 1 integrin very late antigen-4 (CD49d/CD29) is up-regulated on circulating neutrophils of septic patients. Although no individual agent mimics this effect of sepsis, we now report that following priming of human neutrophils with lipopolysaccharide or tumor necrosis factor alpha (TNF-alpha), addition of formyl-Met-Leu-Phe (fMLP) results in a "stimulated", sepsis-like, four- to fivefold rise in CD49d expression. TNF/fMLP stimulation also produced a similar increase in CD49d-mediated adhesion of neutrophils to a vascular cell adhesion molecule-1 (VCAM-1)-coated surface. Adenosine is a naturally occurring, anti-inflammatory mediator released from injured or inflamed tissues. We observed that stimulated neutrophil CD49d expression was decreased by activation of A(2A) adenosine receptors (A(2A)AR) with the selective agonist 4-[3-[6-amino-9-(5-ethylcarbamoyl-3,4-dihydroxy-tetrahydro-furan-2-yl)-9H-purin-2-yl]-prop-2-ynyl]-cyclohexanecarboxylicacid methyl ester (ATL146e; EC(50)=6.4 nM). ATL146e (100 nM) also reduced the fraction of stimulated neutrophils that adhered to VCAM-1 from 38 +/- 6% to 27 +/- 5%. Inhibition of CD49d expression was equally inhibited by ATL146e, added before or after TNF priming, and was reversed by incubation with the A(2A)AR-selective antagonist 4-[2-[7-amino-2-(2-furyl) (1, 2, 4)triazolo(2,3-a) (1, 3, 5)triazin-5-yl-amino]ethyl]-phenol (ZM241385; 100 nM). A suboptimal ATL146e concentration (1 nM) combined with the type IV phosphodiesterase inhibitor rolipram (100 nM) synergistically decreased stimulated CD49d expression by >50%. The cyclic adenosine monophosphate (cAMP)-dependent kinase [protein kinase A (PKA)] inhibitor H-89 (10 microM) reversed the effect of ATL146e on stimulated CD49d expression. Other means of increasing cAMP in neutrophils also decreased stimulated CD49d expression. We conclude that adenosine binding to A(2A)AR counteracts stimulation of neutrophil CD49d integrin expression and neutrophil binding to VCAM-1 via a cAMP/PKA-mediated pathway.

Immunomodulatory effects of quinolones

We review data on the in-vitro, ex-vivo, in-vivo, and clinical effects of fluoroquinolones on the synthesis of cytokines and their mechanisms of immunomodulation. In general, most fluoroquinolone derivatives superinduce in-vitro interleukin 2 synthesis but inhibit synthesis of interleukin 1 and tumour necrosis factor (TNF)alpha; furthermore, they enhance significantly the synthesis of colony-stimulating factors (CSF). Fluoroquinolones affect in-vivo cellular and humoral immunity by attenuating cytokine responses. Interleukins 10 and 12 have an important role in the functional differentiation of immunocompetent cells and trigger the initiation of the acquired immune response. In addition, certain fluoroquinolones were seen to enhance haematopoiesis by increasing the concentrations of CSF in the lung as well as in the bone marrow and shaft. Those fluoroquinolones exerting significant effects on haematopoiesis were those with a cyclopropyl moiety at position N1 of their quinolone core structure. Mechanisms that could explain the various immunomodulatory effects of fluoroquinolones include: (1) an effect on intracellular cyclic adenosine-3',5'-monophosphate and phosphodiesterases; (2) an effect on transcription factors such as nuclear factor (NF)kappaB, activator protein 1, NF-interleukin-6 and nuclear factor of activated T cells; and (3) a triggering effect on the eukaryotic equivalent of bacterial SOS response with its ensuing intracellular events. Further studies are required, especially in the clinical setting to exploit fully the potential of the immunomodulatory effect of fluoroquinolones during, for example, immunosuppression, chronic airway inflammatory diseases, and sinusitis.

Investigation of the cellular mechanism of inhibition of formyl-methionyl-leucyl-phenylalanine-induced superoxide anion generation in rat neutrophils by 2-benzyloxybenzaldehyde

The inhibition of formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide anion (O2(.-)) generation by 2-benzyloxybenzaldehyde (CCY1a) was investigated in rat neutrophils, and the underlying mechanism of this inhibition was assessed. CCY1a concentration-dependently inhibited O2(.-) generation (IC(50)=18.5+/-4.3 microM). In cell-free systems, CCY1a failed to alter O2(.-) generation during dihydroxyfumaric acid autoxidation, in phorbol 12-myristate 13-acetate (PMA)-activated neutrophil particulate NADPH oxidase preparations, or during arachidonic acid-induced NADPH oxidase activation. CCY1a increased cellular cyclic AMP (cAMP) levels in a time- and concentration-dependent manner, and this cAMP-elevating effect was inhibited by the adenylyl cyclase inhibitor 9-(tetrahydro-2'-furyl)adenine (SQ22536), adenosine deaminase (ADA), and the adenosine receptor antagonist 8-(p-sulfophenyl)theophylline. In neutrophils, inhibition of O2(.-) generation by CCY1a was partially reversed by the protein kinase A inhibitor (9R,10S,12S)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-l][1,6]benzodiazocine-10-carboxylic acid, hexyl ester (KT5720). CCY1a did not affect fMLP-induced p38 mitogen-activated protein kinase phosphorylation, but concentration-dependently attenuated the phosphorylation of extracellular signal-regulated kinase (ERK) and Akt (IC(50) about 31.3 and 19.4 microM, respectively). The plateau phase, but not the initial spike, of fMLP-induced [Ca2+](i) changes was inhibited by CCY1a in a concentration-dependent manner. CCY1a inhibition of Ca2+ entry, ERK, and Akt phosphorylation was not prevented by SQ22536 or ADA. fMLP-induced phospholipase D (PLD) activation was inhibited by CCY1a (IC(50)=13.9+/-2.0 microM). ADA and KT5720 did not prevent the inhibition of PLD activation by CCY1a. Collectively, these results indicate that the inhibition by CCY1a of fMLP-induced O2(.-) generation in rat neutrophils can probably be attributed to the increase in cAMP levels, and to the blockade of Ca2+ entry, suppression of Akt, and PLD activation via cAMP-independent mechanisms.

DMSO-treated HL60 cells: a model of neutrophil-like cells mainly expressing PDE4B subtype

The human promyelocytic HL60 cells acquired a neutrophilic phenotype after a 7- to 10-day DMSO treatment. Fc gammaRII was up-regulated. Fc gammaRI was also up-regulated by an additional IFN-gamma treatment. These cells are able to produce O2*- by NADPH oxidase activation in the presence of immune complexes or phorbol-12-myristate-13-acetate (PMA). A change of their PDE4 subtype profile was also observed: PDE4B was the predominant isoenzyme, PDE4D was down-regulated and PDE4A was no longer detectable. Additionally, the more NADPH oxidase was activated by PMA, the less PDE4A was expressed, suggesting that NADPH oxidase activity could be used as a surrogate marker of PDE4A down-regulation. Rolipram and Ariflo (cilomilast), two selective PDE4 inhibitors, dose-dependently inhibited receptor-coupled activation of superoxide. These results suggest that PDE4B is the main subtype involved in regulating superoxide induced by Fc gammaRs activation. Furthermore, these cells, expressing almost exclusively PDE4B subtype, could be useful to identify selective PDE4B inhibitors.