Phosphodiesterase 4 inhibitors as novel anti-inflammatory agents

Update on the Pathogenesis and Therapy of Atopic Dermatitis

Atopic dermatitis (AD) is a common inflammatory skin disorder characterized by recurrent eczematous lesions and intense itch. Although it most often starts in infancy and affects children, it is also highly prevalent in adults. In this article, the main aspects of AD have been updated, with a focus on the pathogenetic and therapeutic aspects. The pathogenesis of AD is complex, and it is evident that a strong genetic predisposition, epidermal dysfunction, skin microbiome abnormalities, immune dysregulation, and the neuroimmune system are critical in AD development. Mutations in the genes associated with disrupted epidermal barrier, exaggerated pathological inflammation and inadequate antimicrobial peptides can promote enhanced Th2 inflammation and mediate pruritus. Current understanding of etiology highlights gut microbial diversity, NK cell deficiency, and different immunological phenotype with age and race. For topical anti-inflammatory treatment for mild-to-severe AD, phosphodiesterase 4 inhibitors (PDE-4), JAK inhibitors, and microbiome transplantation with Roseomonas mucosa provided more management selections. The treatment of moderate-to-severe AD has been limited to merely symptomatic and relatively nonspecific immunosuppressive approaches. In-depth understanding of the pathogenesis of AD has led to the development of innovative and targeted therapies, such as biologic agents targeting interleukin (IL)-4, IL-13 and JAK/STAT inhibitors. Other potential therapeutic agents for AD include agents targeting the T helper (Th) 22 and Th17/IL23 pathway. Antipruritic therapy and complementary probiotics therapy have also been reviewed.

Genome-Wide Association Analysis of Single-Breath DlCO

DlCO is a widely used pulmonary function test in clinical practice and a particularly useful measure for assessing patients with chronic obstructive pulmonary disease (COPD). We hypothesized that elucidating genetic determinants of DlCO could lead to better understanding of the genetic architecture of COPD. We estimated the heritability of DlCO using common genetic variants and performed genome-wide association analyses in four cohorts enriched for subjects with COPD (COPDGene [Genetic Epidemiology of COPD], NETT [National Emphysema Treatment Trial], GenKOLS [Genetics of Chronic Obstructive Lung Disease study], and TESRA [Treatment of Emphysema With a Gamma-Selective Retinoid Agonist study]) using a combined European ancestry white dataset and a COPDGene African American dataset. We assessed our genome-wide significant and suggestive associations for DlCO in previously reported genome-wide association studies of COPD and related traits. We also characterized associations of known COPD-associated variants and DlCO. We estimated the SNP-based heritability of DlCO in the European ancestry white population to be 22% (P = 0.0004). We identified three genome-wide significant associations with DlCO: variants near TGFB2, CHRNA3, and PDE11A loci (P < 5 × 10-8). In addition, 12 loci were suggestively associated with DlCO in European ancestry white (P < 1 × 10-5 in the combined analysis and P < 0.05 in both COPDGene and GenKOLS), including variants near NEGR1, CADM2, PCDH7, RETREG1, DACT2, NRG1, ANKRD18A, KRT86, NTN4, ARHGAP28, INSR, and PCBP3. Some DlCO-associated variants were also associated with COPD, emphysema, and/or spirometric values. Among 25 previously reported COPD loci, TGFB2, CHRNA3/CHRNA5, FAM13A, DSP, and CYP2A6 were associated with DlCO (P < 0.001). We identified several genetic loci that were significantly associated with DlCO and characterized effects of known COPD-associated loci on DlCO. These results could lead to better understanding of the heterogeneous nature of COPD.

Antipruritic mechanisms of topical E6005, a phosphodiesterase 4 inhibitor: inhibition of responses to proteinase-activated receptor 2 stimulation mediated by increase in intracellular cyclic AMP

BACKGROUND

Phosphodiesterase 4 (PDE4), which catalyses the conversion of cyclic adenosine 3',5'-monophosphate (cAMP) to 5'-AMP, plays a critical role in the pathogenesis of inflammatory disorders. Pruritus is the main symptom of dermatitides, such as atopic dermatitis, and is very difficult to control. Recent studies have shown that the activation of proteinase-activated receptor 2 (PAR2) is involved in pruritus in dermatoses in humans and rodents.

OBJECTIVE

To investigate the inhibitory effect of E6005, a topically effective PDE4 inhibitor, on PAR2-associated itching in mice.

METHODS

Mice were given an intradermal injection of SLIGRL-NH2 (100 nmol/site), a PAR2 agonist peptide, into the rostral part of the back. E6005 and 8-bromo-cAMP were applied topically and injected intradermally, respectively, to the same site. Scratching bouts were observed as an itch-related behavior, and firing activity of the cutaneous nerve was electrophysiologically recorded. Keratinocytes were isolated from the skin of neonatal mice and cultured for in vitro experiments. The concentrations of cAMP and leukotriene B4 (LTB4) were measured by enzyme immunoassay. The distribution of PDE4 subtypes in the skin was investigated by immunostaining.

RESULTS

Topical E6005 and intradermal 8-bromo-cAMP significantly inhibited SLIGRL-NH2-induced scratching and cutaneous nerve firing. Topical E6005 increased cutaneous cAMP content. Topical E6005 and intradermal 8-bromo-cAMP inhibited cutaneous LTB4 production induced by SLIGRL-NH2, which has been shown to elicit LTB4-mediated scratching. E6005 and 8-bromo-cAMP inhibited SLIGRL-NH2-induced LTB4 production in the cultured murine keratinocytes also. PDE4 subtypes were mainly expressed in keratinocytes and mast cells in the skin.

CONCLUSIONS

The results suggest that topical E6005 treatment inhibits PAR2-associated itching. Inhibition of LTB4 production mediated by an increase in cAMP may be partly involved in the antipruritic action of E6005.

The role of phosphodiesterase inhibitors in the management of pulmonary vascular diseases

Phosphodiesterase inhibitors (PDE) can be used as therapeutic agents for various diseases such as dementia, depression, schizophrenia and erectile dysfunction in men, as well as congestive heart failure, chronic obstructive pulmonary disease, rheumatoid arthritis, other inflammatory diseases, diabetes and various other conditions. In this review we will concentrate on one type of PDE, mainly PDE5 and its role in pulmonary vascular diseases.

Effectiveness of interleukin-1 receptor antagonist (Anakinra) on cerulein-induced experimental acute pancreatitis in rats

AIM

Acute pancreatitis (AP) is defined as an inflammatory disease of the pancreas. The purpose of this study was to examine the effectiveness of Anakinra on cerulein-induced experimental pancreatitis rat model by using the results of biochemical and histopathological findings.

MATERIALS AND METHODS

Cerulein was administered to induce AP in rats. Group 1 was the sham group. Subcutancerulein was injected to the rats in group 2 for experimental pancreatitis group. In groups 3 and 4, 100 and 50 mg/kg intraperitoneal Anakinra were injected after the induction of experimental pancreatitis by subcutaneous cerulein in rats, respectively. Lastly, in group 5, rats were injected with intraperitoneal saline and subcutan cerulean for placebo group. The following parameters were evaluated: histopathological score of pancreatitis, apoptotic index, amylase, lipase, TNF-α levels, IL-1β and the leukocyte count.

RESULTS

When the results of serum amylase, lipase, TNF-α and IL-1β levels, the leukocyte count, histopathologic scores and apoptotic indices of control group compared to the results of other groups, the differences exhibited statistical significance (all p < 0.05). On the other hand, when the results of fourth group compared with the results of third group, the data demonstrated statistical insignificance (p > 0.05). However, no any significant differences were found between the results of fourth and fifth groups (p > 0.05).

CONCLUSION

In the light of these results, cerulein is an appropriate agent for experimental AP rat model and Anakinra has a favorable therapeutic effect on acute experimental pancreatitis model. Moreover, Anakinra significantly decreases cerulein-related pancreatic tissue injury and pancreatic apoptosis.

Experimental Autoimmune Myasthenia Gravis (EAMG): from immunochemical characterization to therapeutic approaches

Myasthenia Gravis (MG) is an organ-specific autoimmune disease. In high percentage of patients there are autoantibodies to the nicotinic acetylcholine receptor (AChR) that attack AChR on muscle cells at the neuromuscular junction, resulting in muscle weakness. Experimental Autoimmune Myasthenia Gravis (EAMG) is an experimental model disease for MG. EAMG is induced in several animal species by immunization with acetylcholine receptor (AChR), usually isolated from the electric organ of electric fish, which is a rich source for this antigen. Our lab has been involved for several decades in research of AChR and of EAMG. The availability of an experimental autoimmune disease that mimics in many aspects the human disease, provides an excellent model system for elucidating the immunological nature and origin of MG, for studying various existing treatment modalities and for attempting the development of novel treatment approaches. In this review in honor of Michael Sela and Ruth Arnon, we report first on our early pioneering contributions to research on EAMG. These include the induction of EAMG in several animal species, early attempts for antigen-specific treatment for EAMG, elicitation and characterization of monoclonal antibodies and anti-idiotypic antibodies, measuring humoral and cellular AChR-specific immune responses in MG patient and more. In the second part of the review we discuss more recent studies from our lab towards developing and testing novel treatment approaches for myasthenia. These include antigen-dependent treatments aimed at specifically abrogating the humoral and cellular anti-AChR responses, as well as immunomodulatory approaches that could be used either alone, or in conjunction with antigen-specific treatments, or alternatively, serve as steroid-sparing agents.

PDE4 inhibition suppresses IL-17-associated immunity in dry eye disease

PURPOSE

To determine the effect of phosphodiesterase type-4 (PDE4) inhibition on IL-17-associated immunity in experimental dry eye disease (DED).

METHODS

Murine DED was induced, after which a PDE4 inhibitor (cilomilast), dexamethasone, cyclosporine, or a relevant vehicle was administered topically. Real-time PCR, immunohistochemical staining, and flow cytometry were employed to evaluate the immuno-inflammatory parameters of DED with a focus on IL-17-associated immunity. Corneal fluorescein staining (CFS) was performed to evaluate clinical disease progression.

RESULTS

DED induction increased proinflammatory cytokine expression, pathogenic immune cell infiltration, and CFS scores. Cilomilast significantly decreased the expression of TNF-α in the cornea (P ≤ 0.05) and IL-1α, IL-1β, and TNF-α in the conjunctiva (P ≤ 0.05) as compared with vehicle control. Cilomilast treatment markedly decreased the presence of CD11b+ antigen-presenting cells in the central and peripheral cornea (P ≤ 0.05), and led to decreased conjunctival expression of cytokines IL-6, IL-23, and IL-17 (P ≤ 0.05). Moreover, cilomilast decreased the expression of IL-17 and IL-23 in the draining lymph nodes (P ≤ 0.05). Topical cilomilast was significantly more effective than vehicle at reducing CFS scores (P ≤ 0.05). The therapeutic efficacy of cilomilast was comparable or superior to that of dexamethasone and cyclosporine in all tested measures.

CONCLUSIONS

Topical cilomilast suppresses the generation of IL-17-associated immunity in experimental DED.

Phosphodiesterase inhibitors. Part 1: Synthesis and structure-activity relationships of pyrazolopyridine-pyridazinone PDE inhibitors developed from ibudilast

Ibudilast [1-(2-isopropylpyrazolo[1,5-a]pyridin-3-yl)-2-methylpropan-1-one] is a nonselective phosphodiesterase inhibitor used clinically to treat asthma. Efforts to selectively develop the PDE3- and PDE4-inhibitory activity of ibudilast led to replacement of the isopropyl ketone by a pyridazinone heterocycle. Structure-activity relationship exploration in the resulting 6-(pyrazolo[1,5-a]pyridin-3-yl)pyridazin-3(2H)-ones revealed that the pyridazinone lactam functionality is a critical determinant for PDE3-inhibitory activity, with the nitrogen preferably unsubstituted. PDE4 inhibition is strongly promoted by introduction of a hydrophobic substituent at the pyridazinone N(2) centre and a methoxy group at C-7' in the pyrazolopyridine. Migration of the pyridazinone ring connection from the pyrazolopyridine 3'-centre to C-4' strongly enhances PDE4 inhibition. These studies establish a basis for development of potent PDE4-selective and dual PDE3/4-selective inhibitors derived from ibudilast.

Harnessing the clinical efficacy of phosphodiesterase 4 inhibitors in inflammatory lung diseases: dual-selective phosphodiesterase inhibitors and novel combination therapies

Phosphodiesterase (PDE) 4 inhibitors have been in development as a novel anti-inflammatory therapy for more than 20 years, with asthma and chronic obstructive pulmonary disease (COPD) being primary indications. Despite initial optimism, only one selective PDE4 inhibitor, roflumilast (Daxas (®)), has been approved for use in humans and available in Canada and the European Union in 2011 for the treatment of a specific population of patients with severe COPD. In many other cases, the development of PDE4 inhibitors of various structural classes has been discontinued due to lack of efficacy and/or dose-limiting adverse events. Indeed, for many of these compounds, it is likely that the maximum tolerated dose is either subtherapeutic or at the very bottom of the efficacy dose-response curve. Thus, a significant ongoing challenge that faces the pharmaceutical industry is to synthesize compounds with therapeutic ratios that are superior to roflumilast. Several strategies are being considered, but clinically effective compounds with an optimal pharmacophore have not, thus far, been reported. In this chapter, alternative means of harnessing the clinical efficacy of PDE4 inhibitors are described. These concepts are based on the assumption that additive or synergistic anti-inflammatory effects can be produced with inhibitors that target either two or more PDE families or with a PDE4 inhibitor in combination with other anti-inflammatory drugs such as a glucocorticoid.

Disposition of CP-671, 305, a selective phosphodiesterase 4 inhibitor in preclinical species

1. The disposition of (+)-2-[4-({[2-(benzo[1,3] dioxol-5-yloxy)-pyridine-3-carbonyl]-amino)-methyl)-3-fluoro-phenoxyl-propionic acid (CP-671,305), a potent and selective inhibitor of phosphodiesterase 4 (subtype D), was characterized in several animal species in support of its selection for preclinical safety studies and potential clinical development. 2. CP-671,305 demonstrates generally favourable pharmacokinetic properties in all species examined. Systemic plasma clearance after intravenous administration was low in Sprague-Dawley rats (9.60+/-1.16 ml min(-1) kg(-1)), beagle dogs (2.90+/-0.81 ml min(-1) kg(-1)) and cynomolgus monkeys (2.94+/-0.87ml min(-1) kg(-1)) resulting in plasma half-lives > 5 h. Moderate to high bioavailability in rats (43-80%), dogs (45%) and monkeys (26%) was observed after oral dosing. In rats, oral pharmacokinetics were dose dependent over the dose range studied (10 and 25 mgkg(-1)). 3. CP-671,305 was > 97% bound to plasma proteins in rat, dog, monkey and human. 4. The principal route of clearance of CP-671,305 in rats and dogs was by renal and biliary excretion of unchanged drug. This finding was consistent with CP-671,305 resistance towards metabolism in hepatocytes and NADPH-supplemented liver microsomes from preclinical species and human. 5. CP-671,305 did not exhibit competitive inhibition of the five major cytochrome P450 enzymes, namely CYP1A2, 2C9, 2C19, 2D6 and 3A4 (IC50's > 50 microM). Likewise, no time-dependent inactivation of the five major cytochrome P450 enzymes was discernible with CP-671,305. 6. Overall, the results indicate that the absorption, distribution, metabolism and excretion (ADME) profile of CP-671,305 is relatively consistent across preclinical species and predict potentially favourable pharmacokinetic properties in humans, supporting its selection for toxicity/safety assessment studies and possible investigations in humans.

A selective phosphodiesterase 4 (PDE4) inhibitor Zl-n-91 suppresses IL-17 production by human memory Th17 cells

Th17 cells are highly proinflammatory and involved in the immunopathogenesis of severe autoimmune diseases. Selective phosphodiesterase 4 (PDE4) inhibitors, which elevate intracellular cAMP by inhibiting the hydrolysis of cAMP, have been demonstrated to be an effective anti-inflammatory agent in airway inflammatory diseases. In the present study, we assessed the effect of a selective PDE4 inhibitor Zl-n-91 on IL-17 production by PBMCs and by purified CD4(+) T cells following stimulation. The results for the first time demonstrated that the addition of Zl-n-91 into cell cultures of PBMCs and purified CD4(+) T cells could result in the suppression of IL-17 production at the protein and mRNA levels. Further analysis indicated that Zl-n-91 had a direct inhibitory effect on the IL-17 production by memory Th17 cells via the suppression of activation, proliferation and division of CD4(+) T cells. Our data suggested that Zl-n-91 might have beneficial effects in the treatment of IL-17-related autoimmune diseases.

Berberine suppresses inflammatory agents-induced interleukin-1beta and tumor necrosis factor-alpha productions via the inhibition of IkappaB degradation in human lung cells

Pulmonary inflammation is a characteristic of many lung diseases. Increased levels of pro-inflammatory cytokines, such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), have been correlated with lung inflammation. In this study, we demonstrated that various inflammatory agents, including lipopolysaccharide, 12-o-tetradecanoylphorbol-13-acetate, hydrogen peroxide, okadaic acid and ceramide, were able to induce IL-1beta and TNF-alpha productions in human lung epithelial cells (A-549), fibroblasts (HFL1), and lymphoma cells (U-937). Berberine, the protoberberine alkaloid widely distributed in the plant kingdom, was capable of suppressing inflammatory agents-induced cytokine production in lung cells. Inhibition of cytokine production by berberine was dose-dependent and cell type-independent. Moreover, the suppression of berberine on the cytokine production resulted from the inhibition of inhibitory kappaB-alpha phosphorylation and degradation. In conclusion, our findings suggested the potential role of berberine in the treatment of pulmonary inflammation.

DNA Microarray in Search of New Drug Targets for Myasthenia Gravis

DNA microarray technology was used to identify new potential drug targets for myasthenia gravis (MG), to delineate genes involved in the pathogenesis of the disease and to possibly target their protein products for immunotherapy. In this study we compared the gene expression in lymph node cells (LNC) and muscles of rats with experimental autoimmune MG (EAMG) to those of control, healthy rats. Of the genes that were found to be deregulated in EAMG, we chose to elaborate on two gene systems: (a) The chemokine IFN-gamma-inducible protein 10 (IP-10, CXCL10), and its receptor (CXCR3) and (b) phosphodiesterases.

Dose-proportional intraindividual single- and repeated-dose pharmacokinetics of roflumilast, an oral, once-daily phosphodiesterase 4 inhibitor

The dose-proportional, intraindividual, single- and repeated-dose pharmacokinetics of roflumilast, an oral, once-daily phosphodiesterase 4 inhibitor under investigation for chronic obstructive pulmonary disease and asthma, was investigated in healthy subjects. In an open, randomized, 2-period, 2-sequence crossover study, 15 subjects received immediate-release tablets of roflumilast 250 or 500 microg as single (day 1) and as repeated, once-daily doses for 8 days (days 5-12). Dose-adjusted point estimates and 90% confidence intervals of test (500 microg)/reference (250 microg) ratios for AUC and Cmax of roflumilast and its pharmacologically active N-oxide metabolite after single and repeated dosing were all within the standard equivalence acceptance range (0.80, 1.25) indicating dose proportionality. The pharmacokinetic properties of both roflumilast dosage forms provide clinically relevant evidence of predictable, intraindividual total (AUC) and maximum (Cmax) exposure of roflumilast and roflumilast N-oxide. Repeated oral dosing with roflumilast 250 and 500 microg once daily was well tolerated.

Mitigation of stress-induced gastric mucosal lesions by a specific type IV phosphodiesterase inhibitor

Inhibition of type IV phosphodiesterase (PDE4) activity is beneficial in various inflammations. However, the effect of phosphodiesterase inhibitors on the development of stress-induced gastric mucosal lesions has not been reported. In the present study, we examined the effect of a specific PDE4 inhibitor (rolipram) on stress-induced gastric mucosal lesions. Rats were exposed to water-immersion stress with or without pretreatment with rolipram. Ulcer index and myeloperoxidase activity of the gastric mucosa were evaluated. Gastric mucosal lesions and mucosal myeloperoxidase activity were suppressed by treatment with rolipram without acid suppression. The effect of intraperitoneal administration of 2.5 mg/kg rolipram on suppression of mucosal lesions was almost equal to that of treatment with 200 mg/kg cimetidine. We demonstrated that a specific PDE4 inhibitor has a potent anti-ulcer effect presumably mediated by an increment in intracellular cAMP in inflammatory cells, in which this enzyme is abundantly and specifically expressed.

Local anti-inflammatory effect and behavioral studies on new PDE4 inhibitors

Phosphodiesterase 4 (PDE4) inhibitors are effective anti-inflammatory drugs, although some adverse effects are observed in animals and humans. These effects have forced researchers to find new PDE4 inhibitors with less adverse effects. We recently reported the synthesis of novel heterocyclic-fused pyridazinones that inhibit PDE4. As a first step in the study of the anti-inflammatory properties of these compounds, we studied the effects of local administration of these pyridazinone derivatives in a mouse model of acute inflammation. We found that 6-Benzyl-3-methyl-4-phenylpyrazolo[3,4-d]pyridazin-7(6H)-one (CC4), ethyl 6,7-dihydro-6-ethyl-3-methyl-7-oxo-4-phenyl-thieno[2,3-d]pyridazine-2-carboxylate (CC6) and ethyl 6,7-dihydro-6-ethyl-3-methyl-4-phenyl-1H-pyrrolo[2,3-d]pyridazine-2-carboxylate (CC12) reduced the paw edema induced by zymosan in mice as rolipram (the PDE4 inhibitor prototype with anti-inflammatory activity) and indomethacin did. It is well known that rolipram locally administered induces some adverse effects such as hyperalgesia. Thus, we studied this effect after local administration of CC4, CC6 and CC12 in the formalin test. We found that CC6 induced hyperalgesic effects, whereas CC4 and CC12 did not change the nociceptive threshold. Furthermore, we found that rolipram and CC6 reduced locomotor activity, whereas CC4 and CC12 did not change locomotor performance of the mice. Since CC4 and CC12 neither affected the nociceptive threshold nor changed the locomotor performance of mice, they appear more suitable than CC6 for future studies on animals and could be developed as an anti-inflammatory drug for humans.

Specific type IV phosphodiesterase inhibitor ameliorates cerulein-induced pancreatitis in rats

BACKGROUND AND AIMS

Type IV phosphodiesterase is a key enzyme to metabolize intracellular adenosine 3',5'-cyclic monophosphate (cAMP) expressed in inflammatory cells. The specific type IV phosphodiesterase inhibitor that increases intracellular cAMP is known to be potent suppressor of proinflammatory cytokines. However, the effect of phosphodiesterase inhibitors on the development of pancreatitis has not been well understood. In the present study, we examined the effect of a specific type IV phosphodiesterase inhibitor on experimentally induced pancreatitis.

METHODS

Severity of cerulein-induced pancreatitis and pancreatic proinflammatory cytokine levels were studied with or without pretreatment with a specific type IV phosphodiesterase inhibitor (rolipram) in Sprague-Dawley rats.

RESULTS

Administration of rolipram clearly ameliorated severity of pancreatitis evaluated by edema, serum amylase (P<0.05), and lipase levels (P<0.05) in rats. Also, the level of pancreatic proinflammatory cytokine (interleukin-1beta (IL-1beta)) was significantly reduced when rats were treated with rolipram prior cerulein injection (P<0.05).

CONCLUSIONS

Our results demonstrated that intracellular cAMP and pancreatic proinflammatory cytokine level, which are regulated by type IV phosphodiesterase, might play an important role in the pathogenesis of acute pancreatitis.

Synthesis of 4-Aryl-2-pyrrolidones and β-Aryl-γ-amino-butyric Acid (GABA) Analogues by Heck Arylation of 3-Pyrrolines with Arenediazonium Tetrafluoroborates. Synthesis of (±)-Rolipram on a Multigram Scale and Chromatographic Resolution by Semipreparative Chiral Simulated Moving Bed Chromatography

We report herein a new, practical, and economic synthesis of the phosphodiesterase inhibitor Rolipram on a multigram scale as well as the synthesis of new 4-aryl pyrrolidones and beta-aryl-gamma-amino butyric acids (GABA derivatives) employing an efficient Heck-Matsuda arylation of 3-pyrroline with aryldiazonium tetrafluoroborates. Racemic Rolipram was resolved into its enantiomers using chiral simulated moving bed chromatography having the low-cost microcrystalline cellulose triacetate as a chiral stationary phase.

Expression, intracellular distribution and basis for lack of catalytic activity of the PDE4A7 isoform encoded by the human PDE4A cAMP-specific phosphodiesterase gene

PDE4A7 is an isoform encoded by the human PDE4A cAMP-specific phosphodiesterase gene that fails to hydrolyse cAMP and whose transcripts are widely expressed. Removal of either the N- or C-terminal unique portions of PDE4A7 did not reconstitute catalytic activity, showing that they did not exert a chronic inhibitory effect. A chimera (Hyb2), formed by swapping the unique N-terminal portion of PDE4A7 with that of the active PDE4A4C form, was not catalytically active. However, one formed (Hyb1) by swapping the unique C-terminal portion of PDE4A7 with that common to all active PDE4 isoforms was catalytically active. Compared with the active PDE4A4B isoform, Hyb1 exhibited a similar K(m) value for cAMP and IC50 value for rolipram inhibition, but was less sensitive to inhibition by Ro-20-1724 and denbufylline, and considerably more sensitive to thermal denaturation. The unique C-terminal region of PDE4A7 was unable to support an active catalytic unit, whereas its unique N-terminal region can. The N-terminal portion of the PDE4 catalytic unit is essential for catalytic activity and can be supplied by either highly conserved sequence found in active PDE4 isoforms from all four PDE4 subfamilies or the unique N-terminal portion of PDE4A7. A discrete portion of the conserved C-terminal region in active PDE4A isoforms underpins their aberrant migration on SDS/PAGE. Unlike active PDE4A isoforms, PDE4A7 is exclusively localized to the P1 particulate fraction in cells. A region located within the C-terminal portion of active PDE4 isoforms prevents such exclusive targeting. Three functional regions in PDE4A isoforms are identified, which influence catalytic activity, subcellular targeting and conformational status.

Synthesis and biological evaluation of neutrophilic inflammation inhibitors

In several non-infectious human diseases, such as ulcerous colitis, rheumatoid arthritis, chronic obstructive pulmonary disease (COPD), the extravasal recruitment of neutrophils plays a crucial role in the development of tissue damage, which, when persistent, can lead to the irreversible organ dysfunction. The neutrophil activation is controlled by a number of intracellular pathways, particularly by a cAMP-dependent protein kinase A (PKA) which also acts on phosphodiesterase IV (PDE4) gene stimulating the synthesis of this enzyme, able to transform cAMP to inactive AMP. PDE4 inhibitors enhance intracellular cAMP and decrease inflammatory cell activation. Several 3-cyclopentyloxy-4-methoxybenzaldehyde and 3-cyclopentyloxy-4-methoxybenzoic acid derivatives were synthesized and studied by us to evaluate their ability to inhibit the superoxide anion production in human neutrophils. These compounds were found able to inhibit the neutrophil activation and some of them increased the cAMP level on tumor necrosis factor-alpha-stimulated neutrophils. Moreover, they also inhibited selectively the human PDE4 enzyme, although they are less potent than the reference compound Rolipram. We report here synthesis, biological studies and some SAR considerations concerning the above mentioned compounds.

Subacute toxicity and toxicokinetics of CJ-10882, a type IV phosphodiesterase inhibitor, after 4-week repeated oral administration in dogs

The subacute toxicity and toxicokinetics of a type IV phosphodiesterase inhibitor, CJ-10882, were evaluated after single (on the 1st day) and 4-week (on the 27th day) oral administration of the drug, in doses of 0 (to serve as a control), 2, 10 and 50 mg/kg/day, to male and female dogs (n=3 for male and female dogs for each dose). During the test period, clinical signs, mortality, body weight, food consumption, ophthalmoscopy, urinalysis, hematology, serum biochemistry, gross findings, organ weight and histopathology were examined. The 4-week repeated oral doses of CJ-10882 resulted in salivation, vomiting, and atrophy of the thymus. The absolute toxic dose was 50 mg/kg/day and the level at which no adverse effects were observed was 2 mg/kg/day for male and female dogs. There were no significant gender differences in the pharmacokinetic parameters of CJ-10882 for each dose after both single and 4-week oral administration. The pharmacokinetic parameters of CJ-10882 were dose independent after a single oral administration; the time to reach a peak plasma concentration (T(max)) and the dose-normalized area under the plasma concentration-time curve from time zero to 8 h in plasma (AUC(0-8 h)) were not significantly different among three doses. The accumulation of CJ-10882 after 4-week oral administration was not notable at the toxic dose of 50 mg/kg/day. For example, after 4-week administration, the dose-normalized AUC(0-8 h) value at 50 mg/kg/day (0.132 microg h/ml) was not significantly greater than that at 10 mg/kg/day (0.131 microg h/ml). After 4-week oral administration, the dose-normalized C(max) and AUC(0-8 h) at 50 mg/kg/day were not significantly higher and greater, respectively, than those after the single oral administration.

Occupancy of the catalytic site of the PDE4A4 cyclic AMP phosphodiesterase by rolipram triggers the dynamic redistribution of this specific isoform in living cells through a cyclic AMP independent process

In cells transfected to express wild-type PDE4A4 cAMP phosphodiesterase (PDE), the PDE4 selective inhibitor rolipram caused PDE4A4 to relocalise so as to form accretion foci. This process was followed in detail in living cells using a PDE4A4 chimera formed with Green Fluorescent Protein (GFP). The same pattern of behaviour was also seen in chimeras of PDE4A4 formed with various proteins and peptides, including LimK, RhoC, FRB and the V5-6His tag. Maximal PDE4A4 foci formation, occurred over a period of about 10 h, was dose-dependent on rolipram and was reversible upon washout of rolipram. Inhibition of protein synthesis, using cycloheximide, but not PKA activity with H89, inhibited foci generation. Foci formation was elicited by Ro20-1724 and RS25344 but not by either Ariflo or RP73401, showing that not all PDE4 selective inhibitors had this effect. Ariflo and RP73401 dose-dependently antagonised rolipram-induced foci formation and dispersed rolipram pre-formed foci as did the adenylyl cyclase activator, forskolin. Foci formation showed specificity for PDE4A4 and its rodent homologue, PDE4A5, as it was not triggered in living cells expressing the PDE4B2, PDE4C2, PDE4D3 and PDE4D5 isoforms as GFP chimeras. Altered foci formation was seen in the Deltab-LR2-PDE4A4 construct, which deleted a region within LRZ, showing that appropriate linkage between the N-terminal portion of PDE4A4 and the catalytic unit of PDE4A4 was needed for foci formation. Certain single point mutations within the PDE4A4 catalytic site (His505Asn, His506Asn and Val475Asp) were shown to ablate foci formation but still allow rolipram inhibition of PDE4A4 catalytic activity. We suggest that the binding of certain, but not all, PDE4 selective inhibitors to PDE4A4 induces a conformational change in this isoform by 'inside-out' signalling that causes it to redistribute in the cell. Displacing foci-forming inhibitors with either cAMP or inhibitors that do not form foci can antagonise this effect. Specificity of this effect for PDE4A4 and its homologue PDE4A5 suggests that interplay between the catalytic site and the unique N-terminal region of these isoforms is required. Thus, certain PDE4 selective inhibitors may exert effects on PDE4A4 that extend beyond simple catalytic inhibition. These require protein synthesis and may lead to redistribution of PDE4A4 and any associated proteins. Foci formation of PDE4A4 may be of use in probing for conformational changes in this isoform and for sub-categorising PDE4 selective inhibitors.

Phosphodiesterase 4 inhibitors reduce human dendritic cell inflammatory cytokine production and Th1-polarizing capacity

Inhibitors of cAMP-specific phosphodiesterase (PDE) 4 have been shown to inhibit inflammatory mediator release and T cell proliferation, and are considered candidate therapies for T(h)1-mediated diseases. However, little is known about how PDE4 inhibitors influence dendritic cells (DC), the cells responsible for the priming of naive T(h) cells. Therefore, we investigated the PDE profile of monocyte-derived DC, and whether PDE4 inhibitors modulate DC cytokine production and T cell-polarizing capacity. We mainly found cAMP-specific PDE4 enzymatic activity in both immature and mature DC. In contrast to monocytes that mainly express PDE4B, we found that PDE4A is the predominant PDE4 subtype present in DC. Immature DC showed reduced ability to produce IL-12p70 and tumor necrosis factor (TNF)-alpha upon lipopolysaccharide or CD40 ligand (CD40L) stimulation in the presence of PDE4 inhibitors, whereas cytokine production upon CD40L stimulation of fully mature DC in the presence of PDE4 inhibitors was not affected. Exposure to PDE4 inhibitors for 2 days during DC maturation did not influence T cell-stimulatory capacity or acquisition of a mature phenotype, but increased the expression of the chemokine receptor CXCR4. Furthermore, DC matured in the presence of PDE4 inhibitors showed reduced capacity to produce IL-12p70 and TNF-alpha upon subsequent CD40L stimulation. Using these PDE4 inhibitor-matured DC to stimulate naive T cells resulted in a reduction of IFN-gamma-producing (T(h)1) cells. These findings indicate that PDE4 inhibitors can affect T cell responses by acting at the DC level and may increase our understanding of the therapeutic implication of PDE4 inhibitors for T(h)1-mediated disorders.

The effect of the PDE-4 inhibitor (cipamfylline) in two human models of irritant contact dermatitis

BACKGROUND

New therapeutic approaches have to be considered in the treatment of irritant contact dermatitis (ICD). Recently, phosphodiesterase 4 (PDE-4) inhibitors have been introduced as nonsteroidal, antiinflammatory agents. These agents inhibit the secretion of the cytokines thought to be involved in the pathogenesis of ICD. We investigated the effect of a new selective PDE-4 inhibitor (cipamfylline) in human models using single and repeated exposures to an irritant in a blind, randomized pilot study with healthy volunteers. We compared the effect of cipamfylline ointment with a strong corticosteroid (betamethasone-17-valerate) and with a placebo ointment.

METHODS

Ten volunteers were patch tested at four investigation sites with sodium dodecyl sulphate (1%) for 24 h. In a model that simulates chronic damage, 11 volunteers were patch tested with sodium dodecyl sulphate (0.2%) for 4 h daily for four consecutive days. The investigation sites were treated once a day with the above-mentioned agents. One site was left untreated. We used erythema scoring, measurements of transepidermal water loss (TEWL) and several immunohistochemical markers for epidermal proliferation and differentiation.

RESULTS

Repeated application revealed that betamethasone-17-valerate caused a statistically significant reduction in erythema and TEWL compared to cipamfylline and placebo. We also observed a significant suppression of proliferating cells and cytokeratin 16 expression at sites treated with betamethasone compared to the other sites. In the model for acute ICD, no significant differences were seen between the investigated sites.

CONCLUSIONS

Our results show that betamethasone-17-valerate may modulate the response in ICD. In this human model of ICD we could not confirm the efficacy of cipamfylline. Clinical studies are needed before the effect of PDE-4 inhibitors in ICD can be refuted with certainty.

PDE4 cAMP phosphodiesterases: modular enzymes that orchestrate signalling cross-talk, desensitization and compartmentalization

cAMP is a second messenger that controls many key cellular functions. The only way to inactivate cAMP is to degrade it through the action of cAMP phosphodiesterases (PDEs). PDEs are thus poised to play a key regulatory role. PDE4 cAMP-specific phosphodiesterases appear to have specific functions with selective inhibitors serving as potent anti-inflammatory agents. The recent elucidation of the structure of the PDE4 catalytic unit allows for molecular insight into the mode of catalysis as well as substrate and inhibitor selectivity. The four PDE4 genes encode over 16 isoforms, each of which is characterized by a unique N-terminal region. PDE4 isoforms play a pivotal role in controlling functionally and spatially distinct pools of cAMP by virtue of their unique intracellular targeting. Targeting occurs by association with proteins, such as arrestins, SRC family tyrosyl kinases, A-kinase anchoring proteins ('AKAPs') and receptor for activated C kinase 1 ('RACK1'), and, in the case of isoform PDE4A1, by a specific interaction (TAPAS-1) with phosphatidic acid. PDE4 isoforms are 'designed' to be regulated by extracellular-signal-related protein kinase (ERK), which binds to anchor sites on the PDE4 catalytic domain that it phosphorylates. The upstream conserved region 1 (UCR1) and 2 (UCR2) modules that abut the PDE4 catalytic unit confer regulatory functions by orchestrating the functional outcome of phosphorylation by cAMP-dependent protein kinase ('PKA') and ERK. PDE4 enzymes stand at a crossroads that allows them to integrate various signalling pathways with that of cAMP in spatially distinct compartments.

Design, synthesis and structure-activity relationships of a series of 9-substituted adenine derivatives as selective phosphodiesterase type-4 inhibitors

Adenine derivatives substituted in position 9 have been demonstrated to have potent cyclic nucleotide phosphodiesterase (PDE) inhibition properties with high selectivity toward PDE-4. Starting from our initial lead compound 9-(2-fluorobenzyl)-N(6)-methyl-2-trifluoromethyladenine (4, NCS613), we designed and synthesized a new series of 9-substituted derivatives for developing structure-activity relationship studies. This new series of derivatives showed increased potencies and better selectivity profiles. Structural modifications were achieved in parallel on three different positions of the adenine ring, and led to the following observations: (i) introduction of a lipophilic substituent such as trifluoromethyl, n-propyl group or iodine in the C-2 position is favourable for both the PDE-4 inhibitory activity and the selectivity towards other isoenzymes; (ii) functionalization of the N9 benzyl group with a 2-methoxy substituent led to remarkably more active compounds; (iii) replacement of the N(6)-methylamino moiety by other amino groups is detrimental to the activity. Among all derivatives prepared, the 9-(2-methoxybenzyl)-N(6)-methyl-2-trifluoromethyladenine (9r), 9-(2-methoxybenzyl)-N(6)-methyl-2-n-propyladenine (9s), and the 2-iodo-9-(2-methoxybenzyl)-N(6)-methyladenine (13b) were found to be the most potent inhibitors within this series (PDE-4-IC(50)=1.4, 7.0, and 0.096 nM, respectively). Compared to our reference compound 4, which showed an IC(50) of 42 nM, the derivative 13b was found 450-fold more potent. Moreover, 2-iodo-9-(2-methoxybenzyl)-N(6)-methyladenine (13b) and 9-(2-methoxybenzyl)-N(6)-methyl-2-trifluoromethyladenine (9r), were at least 50000-150000 times more selective for the PDE-4 than for the other PDE families. Additionally, these new derivatives showed improved efficiency in inhibiting the TNFalpha release from mononuclear cells from healthy subjects (e.g. adenines 7l, 9s and 13b). Thus, compounds 7l, 9r, 9s and 13b are among the most potent and selective PDE-4 inhibitors reported so far and represent very promising pharmacological tools for a better understanding of the signal transduction involving cyclic AMP within the cell: this pathway is implicated in the physiology and the pathophysiology of inflammation, asthma and autoimmune disorders.

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.

Synthesis and anti-inflammatory activity of phthalimide derivatives, designed as new thalidomide analogues

This paper describes the synthesis and anti-inflammatory activity of new N-phenyl-phthalimide sulfonamides (3a-e) and the isosters N-phenyl-phthalimide amides (4a-e), designed as hybrids of thalidomide (1) and aryl sulfonamide phosphodiesterase inhibitor (2). In these series, compound 3e (LASSBio 468), having a sulfonyl-thiomorpholine moiety, showed potent inhibitory activity on LPS-induced neutrophil recruitment with ED(50)=2.5mg kg(-1), which was correlated with its inhibitory effect on TNF-alpha level.

Redox regulation of pro-inflammatory cytokines and IkappaB-alpha/NF-kappaB nuclear translocation and activation

Reduction-oxidation (redox) state constitutes such a potential signaling mechanism for the regulation of an inflammatory signal associated with oxidative stress. Exposure of alveolar epithelial cells to ascending DeltapO(2) regimen+/-reactive oxygen species (ROS)-generating systems induced a dose-dependent release of interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha. Similarly, the Escherichia coli-derived lipopolysaccharide-endotoxin (LPS) up-regulated cytokine biosynthesis in a dose- and time-dependent manner. Irreversible inhibition of gamma-glutamylcysteine synthetase, the rate-limiting enzyme in the biosynthesis of glutathione (GSH), by L-buthionine-(S,R)-sulfoximine (BSO), induced the accumulation of ROS and augmented DeltapO(2) and LPS-mediated release of cytokines. Analysis of the molecular mechanism implicated revealed an inhibitory-kappaB (IkappaB-alpha)/nuclear factor-kappaB (NF-kappaB)-independent pathway in mediating redox-dependent regulation of inflammatory cytokines. BSO stabilized cytosolic IkappaB-alpha and down-regulated its phosphorylation, thereby blockading NF-kappaB activation, yet it augmented cytokine secretion. Glutathione depletion is associated with the augmentation of oxidative stress-mediated inflammatory state in a ROS-dependent mechanism and the IkappaB-alpha/NF-kappaB pathway is redox-sensitive but differentially involved in regulating redox-dependent regulation of cytokines.

Nuclear factor (NF)-kappa B blockade attenuates but does not abrogate LPS-mediated interleukin (IL)-1 beta biosynthesis in alveolar epithelial cells

The role that the nuclear factor (NF)-kappa B plays in regulating the biosynthesis of interleukin (IL)-1 beta, an inflammatory cytokine, has been investigated in vitro. Irreversible inhibition of the proteasome complex by carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG-132; 1-50 microM) had no inhibitory effect on lipopolysaccharide (LPS)-mediated IL-1 beta biosynthesis. Furthermore, selective inhibition of NF-kappa B by the action of caffeic acid phenylethyl ester (CAPE; 1-100 microM) and sulfasalazine (SSA; 0.1-10 mM), a potent and irreversible inhibitor of NF-kappa B, partially attenuated but did not abolish LPS-dependent IL-1 beta secretion. Incorporation of a selectively permeant inhibitor of NF-kappa B, SN-50 (1-20 microM), a peptide which contains the nuclear localization sequence (NLS) for the p50 NF-kappa B subunit and the amino-terminal sequence of Kaposi fibroblast growth factor to promote cell permeability, attenuated in a dose-dependent manner LPS-mediated release of IL-1 beta. It is concluded that the NF-kapp B pathway is partially implicated and its blockade attenuates but does not abrogate LPS-dependent IL-1 beta biosynthesis in alveolar epithelial cells.

Rolipram inhibits leukocyte-endothelial cell interactions in vivo through P- and E-selectin downregulation

1. Rolipram, a selective phosphodiesterase (PDE) type 4 inhibitor, was used to characterize leukocyte recruitment mechanisms in models of acute and subacute inflammation. Intravital microscopy within the rat mesenteric microcirculation was employed. 2. Mesentery superfusion with PAF (0.1 microM) induced a significant increase in leukocyte rolling flux, adhesion and emigration at 60 min. Rolipram pretreatment, markedly inhibited these parameters by 100, 95 and 95% respectively. 3. Similar effects were observed when the mesentery was superfused with LPS (1 microg ml(-1)) for the same time period and these leukocyte parameters were nearly abrogated by rolipram pretreatment. 4. LPS exposure of the mesentery for 4 h caused a greater increase in leukocyte rolling flux, adhesion and emigration which were inhibited by rolipram administration by 51, 71 and 81% respectively. 5. Immunohistochemistry revealed a significant increase in P-selectin expression after 60 min superfusion with PAF which was attenuated by rolipram. 6. LPS exposure of the mesentery for 4 h caused a significant increase in P- and E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression. Rolipram pretreatment down-regulated both P- and E-selectin expression but had no effect on ICAM-1 and VCAM-1 expression. 7. Significant increases in plasma cyclic AMP levels were detected at 4.5 h after rolipram administration. 8. In conclusion, we have demonstrated that rolipram is a potent in vivo inhibitor of leukocyte-endothelial cell interactions. The effects observed are mediated through endothelial P- and E-selectin downregulation. Therefore, selective PDE-4 inhibitors may be useful in the control of different inflammatory disorders.

Recombinant TNF-alpha mediated regulation of the I kappa B-alpha/NF-kappa B signaling pathway: evidence for the enhancement of pro- and anti-inflammatory cytokines in alveolar epithelial cells

The signaling transduction mechanism mediated by tumor necrosis factor-alpha (TNF-alpha) in the alveolar epithelium is not well characterized. It was subsequently hypothesized that recombinant murine TNF-alpha (rmTNF-alpha) selectively regulates the inhibitory kappa B (I kappa B-alpha)/nuclear factor-kappa B (NF-kappa B) pathway and interferes with the endogenous biosynthesis of pro-inflammatory (stimulatory) and anti-inflammatory (inhibitory) cytokines. The cytokine rmTNF-alpha induced, in a time- and dose-dependent manner, the degradation of I kappa B-alpha within the cytosolic compartment, an effect associated with up-regulating its phosphorylation. This allowed the biphasic regulation of selective NF-kappa B subunit nuclear translocation, thereby mediating a dual excitatory mechanism on NF-kappa B activation. The immunoregulatory effect of rmTNF-alpha was associated with a time-dependent induction of pro-inflammatory [interleukin (IL)-1 beta, IL-6 and TNF-alpha] and anti-inflammatory (IL-10) cytokine biosynthesis. These results indicate a novel involvement of an I kappa B-alpha/NF-kappa B-sensitive pathway mediating the effect of TNF-alpha, which is associated with an autocrine, endogenous mechanism mediating the regulation of cytokine signaling.

Nuclear factor-kappa B-independent regulation of lipopolysaccharide-mediated interleukin-6 biosynthesis

The possible involvement of nuclear factor (NF)-kappa B in mediating the regulation of interleukin (IL)-6 biosynthesis in response to E. coli-derived lipopolysaccharide-endotoxin (LPS) was investigated in vitro. In alveolar epithelial cells, irreversible inhibition of the proteasome complex by carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG-132; 1-50 muM) did not affect LPS-mediated IL-6 secretion. Whereas the selective inhibition of the NF-kappa B pathway by the action of caffeic acid phenyl ethyl ester (CAPE; 1-100 microM) attenuated LPS-dependent IL-6 production at 100 muM, sulfasalazine (SSA; 0.1--10 mM), a potent and irreversible inhibitor of NF-kappa B, did not inhibit LPS-dependent IL-6 secretion. Incorporation of a selectively permeant inhibitor of NF-kappa B, SN-50 (1-20 microM), a peptide which contains the nuclear localization sequence (NLS) for the p50 NF-kappa B subunit and the amino-terminal sequence of Kaposi fibroblast growth factor to promote cell permeability, did not reduce LPS-mediated release of IL-6. These data indicate a NF-kappa B-independent pathway mediating LPS-dependent regulation of IL-6 biosynthesis in the airway epithelium.

Synthesis of 4-(8-benzo[1,2,5]oxadiazol-5-yl-[1,7]naphthyridine-6-yl)-benzoic acid: a potent and selective phosphodiesterase type 4D inhibitor

The synthesis of a 6,8-disubstituted 1,7-naphthyridine 1 and its characterization as a potent and selective phosphodiesterase type 4D inhibitor (IC(50)=1.5nM) are described. The compound inhibited TNFalpha-release from human peripheral blood mononuclear cells and was orally active in a model of adjuvant-induced arthritis in rats.

The involvement of L-gamma-glutamyl-L-cysteinyl-glycine (glutathione/GSH) in the mechanism of redox signaling mediating MAPK(p38)-dependent regulation of pro-inflammatory cytokine production

Redox regulation of mitogen-activated protein kinase (MAPK(p38))-mediated pro-inflammatory cytokine production is not well characterized in the alveolar epithelium. It was hypothesized that the involvement of the MAPK(p38) pathway in regulating lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF)-alpha and interleukin-6 secretion is redox-sensitive and affected by NAC, an antioxidant and a precursor of glutathione, and L-buthionine-(S,R)-sulfoximine, an irreversible inhibitor of gamma-glutamylcysteine synthetase, the rate-limiting enzyme in GSH biosynthesis. Exposure of fetal alveolar type II epithelial cells to Escherichia coli-derived LPS induced, in a time-dependent manner, the phosphorylation/activation of MAPK(p38) (peak at 15min). In addition, LPS up-regulated the phosphorylation of MAPK(p38) in a dose-dependent manner. The effect of LPS on the MAPK(p38) pathway was associated with the activation of MAPK-activated protein kinase, which phosphorylated the small 27kDa heat-shock protein (Hsp27). LPS induced the phosphorylation of Hsp27 in a time- and dose-dependent manner. Selective blockage of the MAPK(p38) pathway by a pyridinyl-imidazole (SB-203580) abrogated LPS-induced release of TNF-alpha and IL-6. Pre-treatment with NAC reduced LPS-mediated secretion of TNF-alpha and IL-6. Incubation of cells with NAC induced intracellular accumulation of GSH, but reduced the concentration of GSSG. On the other hand, pre-treatment with BSO augmented LPS-mediated secretion of TNF-alpha and IL-6. In addition, BSO induced intracellular accumulation of GSSG, but reduced the concentration of GSH. Whereas NAC blocked the phosphorylation/activation of MAPK(p38), BSO amplified the LPS-mediated effect on MAPK(p38). These results indicated that intracellular redox signaling plays an important role in regulating LPS-induced activation of the MAPK(p38) pathway and MAPK(p38)-mediated regulation of LPS-dependent inflammatory cytokine production in the alveolar epithelium.

Redox/ROS regulation of lipopolysaccharide-induced mitogen-activated protein kinase (MAPK) activation and MAPK-mediated TNF-alpha biosynthesis

Redox and ROS regulation of MAPK-mediated TNF-alpha biosynthesis is not well characterized. It was hypothesized that the involvement of the MAPK pathway in regulating LPS-mediated TNF-alpha secretion is redox-dependent, NF-kappaB-sensitive and attenuated by N-acetyl-L-cysteine (NAC) and other antioxidants. In alveolar epithelial cells, LPS induced a time- and dose-dependent phosphorylation of MAPK(p38). This was associated with the activation of MAPK-activated protein kinase, which phosphorylated the small heat-shock protein, Hsp27. MAPK(p38) inhibition (SB-203580) abrogated LPS-induced TNF-alpha production. MAPK(ERK) blockade (PD-98059) attenuated TNF-alpha secretion, an effect synergistically amplified in the presence of SB-203580. Regulation of NF-kappaB by selective inhibitors revealed that this pathway is partially involved in regulating LPS-mediated TNF-alpha secretion. Whereas the proteasome inhibitor, MG-132, had no effect on LPS-mediated TNF-alpha production, CAPE, sulfasalazine and SN-50, a cell-permeant NF-kappaB inhibitor, attenuated but did not abrogate TNF-alpha biosynthesis. LPS up-regulated ROS, an effect abrogated by 4'-hydroxy-3'-methoxy-acetophenone and NAC, which reduced TNF-alpha secretion, induced the accumulation of GSH, reduced the concentration of GSSG, and blockaded the phosphorylation/activation of MAPK(p38) pathway. ROS induced MAPK(p38) phosphorylation and selective antioxidants, including the permeant GSH precursor, gamma-GCE, reduced ROS-dependent MAPK(p38) phosphorylation. These results indicate that the MAPK pathway and MAPK-mediated regulation of TNF-alpha production is redox-dependent, GSH-mediated and requires, at least in part, a NF-kappaB/ROS-sensitive mechanism.

Amiloride blockades lipopolysaccharide-induced proinflammatory cytokine biosynthesis in an IkappaB-alpha/NF-kappaB-dependent mechanism. Evidence for the amplification of an antiinflammatory pathway in the alveolar epithelium

It has been previously reported that amiloride suppresses inflammatory cytokine biosynthesis. However, the molecular mechanism involved has yet to be ascertained. Therefore, the immunoregulatory potential mediated by amiloride and the underlying signaling transduction pathway was investigated. Exposure of alveolar epithelial cells to amiloride or its analog, 5-(N,N-hexamethylene)-amiloride (HMA), reduced, in a dose-dependent manner, lipopolysaccharide (LPS)-induced secretion of interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha. This inhibitory effect was associated with the augmentation of a counter antiinflammatory response, mediated by IL-6 and IL-10. Analysis of the mechanism implicated revealed the involvement of an inhibitory kappaB (IkappaB-alpha)/nuclear factor kappaB (NF- kappaB)-sensitive pathway. Amiloride and HMA suppressed the phosphorylation of IkappaB-alpha mediated by LPS, thereby allowing its cytosolic accumulation. Furthermore, both inhibitors interfered with the nuclear translocation of selective NF-kappaB subunits, an effect associated with blockading the DNA-binding activity of NF-kappaB. Recombinant IL-10 blockaded LPS-induced biosynthesis of IL-1beta and TNF-alpha and reduced NF-kappaB activation. Immunoneutralization of endogenous IL-10 reversed the inhibitory effect of amiloride on proinflammatory cytokines and restored the DNA-binding activity of NF-kappaB. These results indicate that amiloride acts as a novel dual immunoregulator in the alveolar epithelium: it downregulates an inflammatory signal and at the same time upregulates an antiinflammatory response. This biphasic effect is IL-10 sensitive and is associated with the selective targeting of the IkappaB-alpha/NF-kappaB signaling transduction pathway.

Localization of phosphodiesterase-4 isoforms in the medulla and nodose ganglion of the squirrel monkey

Pre-clinical and clinical studies are currently underway to evaluate the potential of phosphodiesterase-4 (PDE4) inhibitors for the treatment of chronic obstructive pulmonary disease and other inflammatory conditions of the airways. The most common side effect associated with this class of compounds is emesis. The squirrel monkey provides a model for evaluating the efficacy of PDE4 inhibitors and their emetic potential. The distribution of three PDE4 isoforms (A, C and D) has been investigated in the squirrel monkey medulla and nodose ganglion to determine which isoform(s) could be responsible for the emetic adverse effects. The distribution of PDE4 isoforms was delineated using immunohistochemistry with antibodies specific for PDE4A, PDE4C and PDE4D and by in situ hybridization with isoform-selective riboprobes. PDE4A was present in the medulla where expression was mostly restricted to glial cells and the vasculature. PDE4C was not detected in either the medulla or nodose ganglion. Finally, the PDE4D isoform was localized to neurons in the nodose ganglion and found through many structures of medulla including the area postrema, neurons of the nucleus tractus solitarius and locus coeruleus. These data are consistent with a role for PDE4D in the emetic response.

Anti-TNF-alpha properties of new 9-benzyladenine derivatives with selective phosphodiesterase-4- inhibiting properties

In inflammatory cells, intracellular cAMP concentration is regulated by cyclic nucleotide phosphodiesterases 4. Therefore, PDE4 inhibition appears as a rational goal for treating acute or chronic inflammatory diseases. Selective PDE4 inhibitors have been developed, but due to unwanted side effects, search for new selective PDE4-inhibitors had to be pursued. Recently, Boichot et al. (J. Pharmacol. Exp. Ther. (2000) 292, 647-653) showed that 9-benzyladenine derivatives are selective PDE4 inhibitors. In vivo data in animals suggested that they may induce fewer side effects (emesis). We examined the effects of new 9-benzyladenines on TNF-alpha, interleukin (IL)-1beta, IL-6 and IL-8 production by lipopolysaccharide-activated peripheral blood mononuclear cells, and compared them to other PDEs inhibitors. Selected potent 9-benzyladenines, strongly inhibited TNF-alpha production. Interleukin-1beta, IL-6, and IL-8 production was not significantly affected. Our results suggest that some of these new adenines (i.e., NCS 675 and NCS 700), may be potential therapeutic candidates for the treatment of inflammatory diseases.

Nuclear factor-kappab blockade attenuates but does not abrogate lipopolysaccharide-dependent tumor necrosis factor-alpha biosynthesis in alveolar epithelial cells

We have investigated the role that the nuclear factor (NF)-kappaB plays in regulating the biosynthesis of tumor necrosis factor (TNF)-alpha, an inflammatory cytokine. Irreversible inhibition of the proteasome complex by carbobenzoxy-l-leucyl-l-leucyl-l-leucinal (MG-132; 1-50 microM) had no inhibitory effect on LPS-mediated TNF-alpha biosynthesis. Furthermore, selective inhibition of NF-kappaB by the action of caffeic acid phenylethyl ester (CAPE; 1-100 microM) and sulfasalazine (SSA; 0.1-10 mM), a potent and irreversible inhibitor of NF-kappaB, partially attenuated, but did not abolish, LPS-dependent TNF-alpha secretion. Incorporation of a selectively permeant inhibitor of NF-kappaB, SN-50 (1-20 microM), a peptide which contains the nuclear localization sequence (NLS) for the p50 NF-kappaB subunit, and the amino-terminal sequence of Kaposi fibroblast growth factor to promote cell permeability, attenuated in a dose-dependent manner LPS-mediated release of TNF-alpha. It is concluded that the NF-kappaB pathway is partially implicated and that its blockade attenuates, but does not abrogate, LPS-dependent TNF-alpha biosynthesis in alveolar epithelial cells.

The biphasic immunoregulation of pyrimidylpiperazine (Y-40138) is IL-10 sensitive and requires NF-kappa B targeting in the alveolar epithelium

1. Pyrimidylpiperazine (Y-40138), a synthetic derivative of N-[1-(4-([4-(pyrimidin-2-yl)piperazin-1-yl]methyl)phenyl)cyclopropyl] acetamide, is a novel dual regulator of pro- and anti-inflammatory cytokines in vivo. The aim of the present study was to determine the signal transduction mechanisms implicated in vitro. 2. In alveolar epithelial cells, pre-treatment (30 min) with Y-40138 reduced LPS-induced biosynthesis of IL-1 beta, IL-6 and TNF-alpha, an effect paralleled by up-regulating an anti-inflammatory counter-loop mediated through IL-10. 3. This differential regulation of pro- and anti-inflammatory signals was accompanied by an inhibition of the nuclear localization of selective NF-kappa B subunits, particularly NF-kappa B(1) (p50), RelA (p65), the major transactivating member of the Rel family, RelB (p68) and c-Rel (p75). In addition, Y-40138 blockaded, in a dose-dependent manner, the LPS-induced nuclear activation of NF-kappa B. 4. Analysis of the upstream pathway involved in Y-40138-dependent retardation of LPS-induced NF-kappa B translocation/activation revealed the involvement of an I kappa B-alpha sensitive pathway. Pre-treatment with Y-40138 ameliorated LPS-induced degradation of I kappa B-alpha in the cytosolic compartment and retarded its phosphorylation, suggesting the involvement of an upstream kinase. 5. Recombinant IL-10 (0 -- 10 ng ml(-1)) blockaded, in a dose-dependent manner, LPS-induced biosynthesis of IL-1 beta, IL-6 and TNF-alpha. Furthermore, rhIL-10 reduced the DNA binding activity of NF-kappa B. Immunoneutralization of endogenous IL-10 by a polyclonal alpha IL-10 (5 microg ml(-1)) reversed the inhibitory effect of Y-40138 on pro-inflammatory cytokines and partially restored the DNA binding activity of NF-kappa B. 6. These results indicate that Y-40138 mediated dual immunoregulation of pro- and anti-inflammatory cytokines is IL-10 sensitive and mediated through the I kappa B-alpha/NF-kappa B signal transduction pathway.

cAMP signalling in Trypanosoma brucei

Cyclic AMP was the first second messenger to be identified. After five decades of research, much is currently known about its biological functions and clinical implications. Several components of the cAMP signalling pathways, such as the G-protein coupled receptors and the phosphodiesterases, have become sensitive and specific drug targets for a host of clinical applications. Surprisingly, very little effort has been invested so far into the study of cAMP signalling in parasites, and its significance in host/parasite interaction. Our laboratory has embarked on a study of cAMP signalling in Trypanosoma brucei. A newly identified adenylyl cyclase, GRESAG4.4B, a member of a small family of closely related genes, is being used as a model molecule for investigating the mechanisms which control cyclase activity in the T. brucei cell. On the other hand, a number of genes for different families of cAMP-specific phosphodiesterases have been identified and characterised. One enzyme, TbPDE1, is coded for by a single-copy gene. Knock-outs of this gene display an almost normal phenotype in culture, indicating that TbPDE1 is not an essential enzyme under culture conditions. A second phosphodiesterase which is being studied in detail, TbPDE2A, is clearly different from TbPDE1, and it is coded for by a member of a small gene family containing about six similar, but non-identical genes. TbPDE2A, as TbPDE1, is specific for cAMP. In its N-terminal, it contains a GAF domain which may represent an allosteric cGMP-binding site. The other members of the TbPDE2 family all exhibit strongly conserved catalytic domains, but vary widely in their N-terminal regulatory domains. With regard to downstream signalling by the cAMP generated through the interplay of adenylyl cyclases and phosphodiesterases, we have recently identified a single-copy gene (TbRSU1) which codes for a putative regulatory subunit of the cAMP-regulated protein kinase A. This protein exhibits considerable similarity with its mammalian counterparts. Immunoprecipitation co-precipitates a protein kinase activity with the characteristics of protein kinase A.