The type IV phosphodiesterase specific inhibitor mesopram inhibits experimental autoimmune encephalomyelitis in rodents

The Effects of PDE Inhibitors on Multiple Sclerosis: a Review of in vitro and in vivo Models

BACKGROUND

Multiple sclerosis (MS) is a chronic inflammatory and immune-mediated disease, whose current therapeutic means are mostly effective in the relapsing-remitting form of MS, where inflammation is still prominent, but fall short of preventing long term impairment. However, apart from inflammationmediated demyelination, autoimmune mechanisms play a major role in MS pathophysiology, constituting a promising pharmacological target. Phosphodiesterase (PDE) inhibitors have been approved for clinical use in psoriasis and have undergone trials suggesting their neuroprotective effects, rendering them eligible as an option for accessory MS therapy.

OBJECTIVE

In this review, we discuss the potential role of PDE inhibitors as a complementary MS therapy.

METHODS

We conducted a literature search through which we screened and comparatively assessed papers on the effects of PDE inhibitor use, both in vitro and in animal models of MS, taking into account a number of inclusion and exclusion criteria.

RESULTS

In vitro studies indicated that PDE inhibitors promote remyelination and axonal sustenance, while curbing inflammatory cell infiltration, hindering oligodendrocyte and neuronal loss and suppressing cytokine production. In vivo studies underlined that these agents alleviate symptoms and reduce disease scores in MS animal models.

CONCLUSION

PDE inhibitors proved to be effective in addressing various aspects of MS pathogenesis both in vitro and in vivo models. Given the latest clinical trials proving that the PDE4 inhibitor Ibudilast exerts neuroprotective effects in patients with progressive MS, research on this field should be intensified and selective PDE4 inhibitors with enhanced safety features should be seriously considered as prospective complementary MS therapy.

Propentofylline, phosphodiesterase and adenosine reuptake inhibitor modulates lymphocyte subsets and lymphocyte activity after in-vivo administration in non-immunized and SRBC-immunized mice

OBJECTIVES

The aim of the study was to investigate immunomodulatory effect of in-vivo administered propentofylline on the subsets and activity of murine lymphocytes.

METHODS

Propentofylline (3 mg/kg) was administered orally to 8-week-old Balb/c mice, once or six times at 12-h intervals. The lymphocyte subsets, regulatory T cells, IL-5 and TNF levels were determined 12 h and 24 h after a single dose or after the sixth dose of the drug in non-immunized mice. Humoral immune response in sheep red blood cells (SRBC)-immunized mice was determined 4, 7 and 14 days after immunization.

KEY FINDINGS

Propentofylline inhibited thymocyte maturation (increase in CD4^- CD8^- thymocyte subset and decrease in the percentage of CD4⁺ CD8⁺ thymocytes) and modulated the lymphocyte subsets in spleen and mesenteric lymph nodes. An increase in the absolute count and percentage of splenic regulatory T cells (CD4⁺ CD25⁺ Foxp3⁺ cells) was noticed 24 h after single administration of the drug. Propentofylline lowered serum level of IL-5 and did not affect TNF concentration. Only a weak inhibitory effect on anti-SRBC humoral immune response was observed.

CONCLUSIONS

Propentofylline administration induced inhibition of thymocyte maturation and an increase in Treg subset that might be beneficial for an inhibition of immune response.

Phosphodiesterase regulation of alcohol drinking in rodents

Alcohol use disorders are chronically relapsing conditions characterized by persistent drinking despite the negative impact on one's life. The difficulty of achieving and maintaining sobriety suggests that current treatments fail to fully address the underlying causes of alcohol use disorders. Identifying additional pathways controlling alcohol consumption may uncover novel targets for medication development to improve treatment options. One family of proteins recently implicated in the regulation of alcohol consumption is the cyclic nucleotide phosphodiesterases (PDEs). As an integral component in the regulation of the second messengers cyclic AMP and cyclic GMP, and thus their cognate signaling pathways, PDEs present intriguing targets for pharmacotherapies to combat alcohol use disorders. As activation of cAMP/cGMP-dependent signaling cascades can dampen alcohol intake, PDE inhibitors may provide a novel target for reducing excessive alcohol consumption, as has been proposed for PDE4 and PDE10A. This review highlights preclinical literature demonstrating the involvement of cyclic nucleotide-dependent signaling in neuronal and behavioral responses to alcohol, as well as detailing the capacity of various PDE inhibitors to modulate alcohol intake. Together these data provide a framework for evaluating the potential utility of PDE inhibitors as novel treatments for alcohol use disorders.

Inhibition of phosphodiesterase 4 reduces ethanol intake and preference in C57BL/6J mice

Some anti-inflammatory medications reduce alcohol consumption in rodent models. Inhibition of phosphodiesterases (PDE) increases cAMP and reduces inflammatory signaling. Rolipram, an inhibitor of PDE4, markedly reduced ethanol intake and preference in mice and reduced ethanol seeking and consumption in alcohol-preferring fawn-hooded rats (Hu et al., 2011; Wen et al., 2012). To determine if these effects were specific for PDE4, we compared nine PDE inhibitors with different subtype selectivity: propentofylline (nonspecific), vinpocetine (PDE1), olprinone, milrinone (PDE3), zaprinast (PDE5), rolipram, mesopram, piclamilast, and CDP840 (PDE4). Alcohol intake was measured in C57BL/6J male mice using 24-h two-bottle choice and two-bottle choice with limited (3-h) access to alcohol. Only the selective PDE4 inhibitors reduced ethanol intake and preference in the 24-h two-bottle choice test. For rolipram, piclamilast, and CDP840, this effect was observed after the first 6 h but not after the next 18 h. Mesopram, however, produced a long-lasting reduction of ethanol intake and preference. In the limited access test, rolipram, piclamilast, and mesopram reduced ethanol consumption and total fluid intake and did not change preference for ethanol, whereas CDP840 reduced both consumption and preference without altering total fluid intake. Our results provide novel evidence for a selective role of PDE4 in regulating ethanol drinking in mice. We suggest that inhibition of PDE4 may be an unexplored target for medication development to reduce excessive alcohol consumption.

Promotion of cAMP responsive element-binding protein activity ameliorates radiation-induced suppression of hippocampal neurogenesis in adult mice

This study was performed to examine whether elevated activity of cAMP responsive element-binding protein (CREB) attenuates the detrimental effects of acute gamma (γ) -irradiation on hippocampal neurogenesis and related functions. C57BL/6 male mice were treated with rolipram (1.25 mg/kg, i.p., twice a day for 5 consecutive days) to activate the cAMP/CREB pathway against cranial irradiation (2 Gy) , and were euthanized at 24 h post-irradiation. Exposure to γ-rays decreased both CREB phosphorylation and immunohistochemical markers for neurogenesis, including Ki-67 and doublecortin (DCX) , in the hippocampal dentate gyrus (DG) . However, the rolipram treatment protected from γ-irradiation-induced decreases of CREB phosphorylation, and Ki-67 and DCX immunoreactivity in the hippocampal DG. In an object recognition memory test, mice trained 24 h after acute γ-irradiation (2 Gy) showed significant memory impairment, which was attenuated by rolipram treatment. The results suggest that activation of CREB signaling ameliorates the detrimental effects of acute γ-irradiation on hippocampal neurogenesis and related functions in adult mice.

Modulation of Th1/Th2 cytokine production by selective and nonselective phosphodiesterase inhibitors administered to mice

Phosphodiesterase (PDE) inhibitors can modulate the functions of immune cells, including T lymphocytes, due to increased intracellular levels of cyclic nucleotides. The drugs (aminophylline, milrinone and sildenafil) were administered once or five times at 24 h intervals at the following doses: 20 mg/kg, i.m., 1 mg/kg, i.m. and 1 mg/kg, p.o., respectively. Th1 and Th2 cytokine levels (IL-2, IFN-γ, IL-4, IL-5, TNF) were determined 12, 24 or 72 h after the last administration of the drugs. A commercial BD™ Cytometric Bead Array Mouse Th1/Th2 Cytokine Kit (CBA) was used to determine the levels of Th1/Th2 cytokines in the serum. Neither of the PDE inhibitors under investigation administered once changed IFN-γ, TNF and IL-4 production. A single dose of aminophylline decreased the production of IL-2 (after 12 h). A single dose of milrinone did not affect Th1/Th2 cytokine secretion. Sildenafil administered once decreased the production of IL-2 (after 72 h). A temporary enhancement in the level of IL-5 was observed 12 h after a single dose of sildenafil. No changes in Th1 and Th2 cytokine production were observed after five doses of PDE inhibitors under investigation. These results indicate that nonstimulated lymphocytes Th1 and Th2 exhibited a slight sensitivity to aminophylline and sildenafil. The drugs under investigation were ineffective inhibitors of Th1/Th2 cytokine production.

Indomethacin-induced small intestinal injury is ameliorated by cilostazol, a specific PDE-3 inhibitor

BACKGROUND

Neutrophil migration, one of the major factors predisposing to nonsteroidal anti-inflammatory drugs (NSAIDs)-induced intestinal lesions, consists of several steps, including interaction with P-selectin from platelets. Cilostazol, a specific phosphodiesterase (PDE)-3 inhibitor, suppresses the expression of P-selectin from platelets and reduces interaction between platelets and leukocytes, leading to inflammatory amelioration in several disease models. We tried to clarify the therapeutic effectiveness of cilostazol for NSAID-induced small intestinal lesions.

SUBJECTS AND METHODS

1) Anti-PSGL-1 antibody (2 mg/kg) or cilostazol (100 mg/kg) was administered to mice one hour before Indomethacin (IND, 2.5 mg/kg) administration for 4 days to evaluate small intestinal lesions. 2) IND-induced migratory behaviors of neutrophils and platelets were evaluated in intestinal vessels by an intravital microscopy.

RESULTS

i) IND induced small intestinal lesions with an increase in MPO activity. Anti-PSGL-1 antibody and cilostazol ameliorated intestinal lesions along with suppression of MPO activity. ii) Intravital microscopy revealed that administration of IND increased migration of platelet-bearing neutrophils. Cilostazol treatment ameliorated neutrophil migration by blocking interaction between platelets and neutrophils.

CONCLUSION

Our results suggest that enhanced platelets-bearing neutrophil migration is critically involved in the pathogenesis of IND-induced small intestinal lesions and suggest a potential application of cilostazol for prevention of NSAID-induced small intestinal lesions.

Vinpocetine inhibits oligodendroglial precursor cell differentiation

BACKGROUND

In multiple sclerosis during periods of remission a limited degree of myelin repair can be observed mediated by oligodendroglial precursor cells. Phosphodiesterase inhibitors act as anti-inflammatory agents and might hold promise for future multiple sclerosis treatment.

AIMS

To investigate whether phosphodiesterase inhibitors could also influence myelin repair.

METHODS

We stimulated primary oligodendroglial precursor cells with cilostazol, rolipram and vinpocetine and assessed their effects on repair related cellular processes.

RESULTS

We found that vinpocetine exerted a strong negative effect on myelin expression while cilostazol and rolipram did not show such effects. In addition, vinpocetine decreased morphological complexities suggesting an overall negative impact on oligodendroglial cell maturation. We provide evidence that this is not mediated via a blockade of phosphodiesterase-1 but rather by inhibition of IĸB kinase.

CONCLUSION

These findings suggest that vinpocetine via IĸB inhibition exerts a strong negative impact on oligodendroglial cell maturation and may therefore provide the rationale to restrict its application during periods of remission in multiple sclerosis patients. This is of particular interest since vinpocetine is widely used as a health supplement thought to act as a cognitive and memory enhancer for healthy people and patients with neurological or muscle diseases.

Conditioning lesions before or after spinal cord injury recruit broad genetic mechanisms that sustain axonal regeneration: superiority to camp-mediated effects

Previous studies indicate that peripheral nerve conditioning lesions significantly enhance central axonal regeneration via modulation of cAMP-mediated mechanisms. To gain insight into the nature and temporal dependence of neural mechanisms underlying conditioning lesion effects on central axonal regeneration, we compared the efficacy of peripheral sciatic nerve crush lesions to cAMP elevations (in lumbar dorsal root ganglia) on central sensory axonal regeneration when administered either before or after cervical spinal cord lesions. We found significantly greater effects of conditioning lesions compared to cAMP elevations on central axonal regeneration when combined with cellular grafts at the lesion site and viral neurotrophin delivery; further, these effects persisted whether conditioning lesions were applied prior to or shortly after spinal cord injury. Indeed, conditioning lesions recruited extensively greater sets of genetic mechanisms of possible relevance to axonal regeneration compared to cAMP administration, and sustained these changes for significantly greater time periods through the post-lesion period. We conclude that cAMP-mediated mechanisms account for only a portion of the potency of conditioning lesions on central axonal regeneration, and that recruitment of broader genetic mechanisms can extend the effect and duration of cellular events that support axonal growth.

Modulating effects of nonselective and selective phosphodiesterase inhibitors on lymphocyte subsets and humoral immune response in mice

Phosphodiesterase (PDE) inhibitors can regulate the activity of immune cells by increasing intracellular levels of cyclic nucleotides. The aim of this study was to determine the effects of milrinone, a selective PDE3 inhibitor, sildenafil, a selective PDE5 inhibitor, and aminophylline, a nonselective PDE inhibitor, on lymphocyte subsets and humoral immune response in mice when administered in vivo. Aminophylline (20 mg/kg, i.m.), milrinone (1 mg/kg, i.m.) or sildenafil (1 mg/kg, p.o.) were administered to mice either once or five times at 24 h intervals. Some mice were immunized with a sheep red blood cell (SRBC) suspension administered i.p. either 2 h after the single dose or 2 h after the second of the five doses. In non-immunized mice treated five times with PDE inhibitors, the subsets of T lymphocytes in the thymus and T and B lymphocytes in the spleen and mesenteric lymph nodes were determined 12, 24 or 72 h after the last dose. The humoral immune response was determined on days 4, 7 and 14 after SRBC injection in SRBC-immunized mice treated with PDE inhibitors. A modulating effect of the drugs on lymphocyte subpopulations was observed. The greatest impact was observed in splenocyte subpopulations, and resulted in decreased percentages of B cells (CD19(+)) and increased percentages of T cells (CD3(+), CD4(+), CD8(+)). No effect or slight influence of the drugs on anti-SRBC hemagglutinins was observed, but the number of plaque-forming splenocytes was increased. The drugs under investigation did not show a significant immunosuppressive effect.

A selective phosphodiesterase-4 inhibitor reduces leukocyte infiltration, oxidative processes, and tissue damage after spinal cord injury

We tested the hypothesis that a selective phosphodiesterase type 4 inhibitor (PDE4-I; IC486051) would attenuate early inflammatory and oxidative processes following spinal cord injury (SCI) when delivered during the first 3 days after injury. Rats receiving a moderately severe thoracic-clip-compression SCI were treated with the PDE4-I (0.5, 1.0, and 3.0 mg/kg IV) in bolus doses from 2-60 h post-injury. Doses at 0.5 mg/kg and 1.0 mg/kg significantly decreased myeloperoxidase (MPO) enzymatic activity (neutrophils), expression of a neutrophil-associated protein and of ED-1 (macrophages), and estimates of lipid peroxidation in cord lesion homogenates at 24 h and 72 h post-injury by 25-40%. The 3.0 mg/kg dose had small or no effects on these measures. The PDE4-I treatment (0.5 or 1.0 mg/kg) reduced expression of the oxidative enzymes gp91(phox), inducible nitric oxide synthase, and cyclooxygenase-2, and diminished free radical generation by up to 40%. Treatment with 0.5 mg/kg PDE4-I improved motor function (as assessed by the Basso-Beattie-Bresnahan scale) significantly from 4-8 weeks after SCI (average difference 1.3 points). Mechanical allodynia elicited from the hindpaw decreased by up to 25%. The PDE4-I treatment also increased white matter volume near the lesion at 8 weeks after SCI. In conclusion, the PDE4-I reduced key markers of oxidative stress and leukocyte infiltration, producing cellular protection, locomotor improvements, and a reduction in neuropathic pain. Early inhibition of PDE4 is neuroprotective after SCI when given acutely and briefly at sufficient doses.

Suppression of encephalitogenic T-cell responses by cilostazol is associated with upregulation of regulatory T cells

Cilostazol is a specific phosphodiesterase III inhibitor. Recent data show that cilostazol has anti-inflammatory effects and administration of cilostazol ameliorates experimental autoimmune encephalomyelitis (EAE). In this study, we used a mouse EAE model to explore the role of cilostazol in Th1 and Th17 cell-mediated immune responses. We found that cilostazol suppressed mitogen or antigen-induced T-cell responses and Th17 cell differentiation in vitro, which correlated with enhanced Treg-cell responses. Beginning of oral administration of cilostazol at the onset of EAE significantly inhibited encephalitogenic T cells, reduced the levels of inflammatory cytokines in the central nervous system, and ameliorated the severity of EAE. Moreover, administration of cilostazol markedly enhanced Treg-cell response in vivo. Cilostazol, therefore, may exert its therapeutic effects through upregulation of Treg-cell activity.

Effects of the phosphodiesterase IV inhibitor rolipram on Th1 and Th2 immune responses in mice

The present study was designed to investigate the effect of the phosphodiesterase IV inhibitor rolipram on Th1 and Th2 immune responses in mice. Mice were immunized subcutaneously at the base of the tail with ovalbumin (OVA) emulsified with complete Freund's adjuvant (day 0) and were treated daily with oral administration of various doses of rolipram from days 0 to 20. On day 21, production of anti-OVA IgG and proliferative responses to the antigen were determined. Anti-OVA IgG2a and interferon-γ (IFN-γ), as indicators of Th1 responses, and anti-OVA IgG1 and interleukin-10 (IL-10), as indicators of Th2 responses, were also measured. The results showed that treatment with rolipram failed to affect the production of OVA-specific IgG but decreased the proliferation of spleen cells to the antigen. Its inhibitory effect on these immune responses was correlated with a marked decrease in IFN-γ but not IL-10 production, although neither anti-OVA IgG2a nor IgG1 production was affected by rolipram. These results suggest that rolipram may preferentially inhibit Th1 responses more effectively than Th2 responses. Administration of rolipram resulted in suppression of antigen (OVA)-induced arthritis in mice. The suppression of joint inflammation by rolipram was associated with the inhibition of the OVA-specific proliferative responses of spleen cells and IFN-γ secretion. These results indicate that rolipram may be effective in regulating Th1-mediated diseases such as rheumatoid arthritis.

Involvement of phosphodiesterases in autoimmune diseases

We have previously shown that several phosphodiesterase (PDE) subtypes are up-regulated in muscles and lymph node cells (LNC) of rats with experimental autoimmune myasthenia gravis (EAMG). In the present study we investigated PDE expression during the course of EAMG and experimental allergic encephalomyelitis (EAE) and found that the up-regulated expression of selected PDE subtypes in both experimental models is correlated with disease severity. In EAMG, PDE expression is correlated also with muscle damage. A similar up-regulation of PDE was also observed in the respective human diseases, MG and multiple sclerosis (MS). Our findings suggest that change in PDE expression levels is a general phenomenon in autoimmune diseases and may also be used as a marker for disease severity.

Increasing CNS noradrenaline reduces EAE severity

The endogenous neurotransmitter noradrenaline (NA) is known to exert potent anti-inflammatory effects in glial cells, as well as provide neuroprotection against excitatory and inflammatory stimuli. These properties raise the possibility that increasing levels of NA in the central nervous system (CNS) could provide benefit in neurological diseases and conditions containing an inflammatory component. In the current study, we tested this possibility by examining the consequences of selectively modulating CNS NA levels on the development of clinical signs in experimental autoimmune encephalomyelitis (EAE). In mice immunized with myelin oligodendrocyte glycoprotein peptide to develop a chronic disease, pretreatment to selectively deplete CNS NA levels exacerbated clinical scores. Elevation of NA levels using the selective NA reuptake inhibitor atomoxetine did not affect clinical scores, while treatment of immunized mice with the synthetic NA precursor L-threo-3,4-dihydroxyphenylserine (L-DOPS) prevented further worsening. In contrast, treatment of mice with a combination of atomoxetine and L-DOPS led to significant improvement in clinical scores as compared to the control group. The combined treatment reduced astrocyte activation in the molecular layer of the cerebellum as assessed by staining for glial fibrillary protein but did not affect Th1 or Th17 type cytokine production from splenic T cells. These data suggest that selective elevation of CNS NA levels could provide benefit in EAE and multiple sclerosis without influencing peripheral immune responses.

Cilostazol, a specific PDE-3 inhibitor, ameliorates chronic ileitis via suppression of interaction of platelets with monocytes

Excessive migration of monocytes to a site of intestinal inflammation contributes to tissue damage in Crohn's disease. It is known that cilostazol, a specific phosphodiesterase-3 (PDE-3) inhibitor of platelets, decreases monocyte recruitment to intestinal mucosa through suppression of platelet-monocyte interactions. The objective of this study was to clarify whether cilostazol ameliorates murine ileitis by suppression of monocyte migration. Significant inflammation was induced in the ileum of SAMP1/Yit mice at 23 wk of age after piroxicam treatment for 3 wk. Weight of the terminal ileum of mice was significantly greater with inflammatory cell infiltration in SAMP1/Yit mice than in control mice (AKR-J). Treatment of SAMP1/Yit mice with cilostazol-containing food (200 ppm) for 3 wk significantly attenuated the increase in intestinal weight and the histological changes, including invasion of F4/80-positive macrophages. A significant increase in migration of monocytes and platelets to microvessels of the ileal mucosa was observed in SAMP/Yit mice in vivo by using an intravital fluorescence microscope. Pretreatment with cilostazol significantly attenuated the increased migration of monocytes, possibly through suppression of platelet-monocyte interactions. In conclusion, a PDE-3 inhibitor ameliorates murine ileitis through attenuating migration of monocytes to the intestinal mucosa, suggesting a potential usefulness of antiplatelet drugs for treatment of Crohn's disease.

Selective phosphodiesterase-3 inhibitor cilostazol ameliorates experimental autoimmune encephalomyelitis

We investigated the possible therapeutic effect of cilostazol, a specific inhibitor of phosphodiesterase-3, for experimental autoimmune encephalomyelitis (EAE). Mice affected with EAE induced by inoculation with MOG(35-55) were fed with cilostazol or vehicle control. The clinical EAE scores of the cilostazol-fed mice were lower than those of the controls. Serum level of soluble intercellular adhesion molecule-1 was significantly lower in the cilostazol-fed mice than in the controls. In the recall responses with MOG(35-55), proliferation and IFN-gamma production by lymphocytes from cilostazol-fed mice were significantly reduced. Cilostazol may exhibit repressive effects on EAE by reducing the antigen-specific T-cell response and decreasing the expression of the adhesion molecules. Cilostazol is a hopeful choice for the treatment of multiple sclerosis.

Acetamide-45 inhibited hyperresponsiveness and airway inflammation in mice partly depending on phosphodiesterase activity suppression

AIM

Asthma is characterized as a chronic inflammatory disorder of the airways. Phosphodiesterases (PDE), which hydrolyze cAMP, are considered to play important roles in asthma. We previously reported that acetamide-45 could inhibit cAMP-PDE activity, and histamine- and methacholine-induced contractions of isolated guinea pig trachea. The purpose of this study is to determine whether this agent could suppress allergic-induced airway hyperresponsiveness (AHR) and airway inflammation in allergic mice.

METHODS

A mouse model for asthma was used to investigate acetamide-45 on the airway lesions compared with glucocorticoids. The study was conducted on mice sensitized and challenged with ovalbumin and the whole body plethysmography was carried out to assess AHR. The bronchoalveolar lavage (BAL) histopathology was examined.

RESULTS

We found that acetamide-45 significantly inhibited the enhanced hyperresponsiveness and eosinophil recruitment in airways with elimination of cAMP-PDE activity in lung tissue. Elevated IL-4 and IL-5 in bronchoalveolar lavage fluid (BALF) in asthmatic mice were markedly decreased.

CONCLUSION

Our results indicate that the agent has a potential role in inflammatory disease.

Attenuation of MPTP neurotoxicity by rolipram, a specific inhibitor of phosphodiesterase IV

Rolipram, a specific inhibitor of the phosphodiesterase IV (PDE IV), has recently been shown to exert neuroprotective effects in an Alzheimer transgenic mouse model and in hypoxic-ischemic damage in the rat brain. It activates the cAMP-dependent protein kinase (PKA)/cAMP regulatory element-binding protein (CREB) signaling pathway and it inhibits inflammation. We tested the neuroprotective effects of the specific PDE IV inhibitor rolipram in C57BL/6 mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We found that rolipram administered at 1.25 mg/kg or 2.5 mg/kg doses significantly attenuated MPTP-induced dopamine depletion in the striatum, and reduced the loss of tyrosine hydroxylase-positive neurons in the substantia nigra. There was a bell-shaped dose effect with greater efficacy at the 1.25 mg/kg dose than 2.5 mg/kg and a higher dose of rolipram, 5 mg/kg, had no protective effect and even increased the mortality of animals when co-administered with MPTP. Rolipram did not interact with MPTP in its absorption into the brain and in its metabolism to 1-methyl-4-phenylpyridinium (MPP(+)). Our data show a neuroprotective effect of the PDE IV specific inhibitor rolipram against dopaminergic neuron degeneration, suggesting that PDE IV inhibitors might be a potential treatment for Parkinson's disease.

Effect of Rolipram, a Phosphodiesterase IV Inhibitor, on Allergic Footpad Swelling using Various Adjuvants in Mice

We studied the effect of rolipram, a phosphodiesterase (PDE) IV inhibitor, on allergic footpad swelling in mice. For this study, varying adjuvants including complete Freund's adjuvant (CFA), incomplete Freund's adjuvant (IFA) and Imject Alum (Alum) were used because the extent of antigen-specifically induced T helper type 1 (Th1) and Th2 responses had been shown to depend on adjuvants used. To induce allergic footpad swelling, we immunized mice with ovalbumin (OVA) emulsified in either CFA or IFA, dissolved in Alum or in phosphate-buffered saline (PBS) as a control (day 0), followed by subcutaneous injection of the antigen into footpads on day 21. Rolipram was given orally to the animals daily from days 0-20. Results showed that treatment with rolipram was followed by an increase in early swelling at 0.5 h and a decrease in late swelling at 6 and 24 h in the CFA group. In the IFA group, rolipram significantly enhanced swelling at, but not after, 30 min. In the Alum and the PBS groups, the PDE inhibitor failed to affect the OVA-specific footpad reaction at all times examined. Treatment of the CFA and IFA groups with rolipram significantly inhibited the production of the Th1 antibody anti-OVA immunoglobulin G2a (IgG2a), and the drug enhanced Th2 cell-dependent anti-OVA IgE production. In both groups, rolipram also enhanced the secretion of Th2 cytokines including interleukin-4 (IL-4) and IL-10. These findings suggest that rolipram may facilitate early allergic footpad swelling mediated by Th2 immune responses, while the late phase of swelling associated with Th1 responses may be attenuated by the PDE IV inhibitor.

Cyclic nucleotide phosphodiesterases and their role in immunomodulatory responses: advances in the development of specific phosphodiesterase inhibitors

The activity of phosphodiesterases (PDEs) is associated with a wide variety of diseases and an intense effort toward the development of specific PDEs inhibitors has been generated for the last years. They are the enzymes responsible for the hydrolysis of intracellular cyclic adenosine and guanosine monophosphate, and their complexity, as well as their different functional role, makes these enzymes a very attractive therapeutic target. This review is focused on the role of PDEs played on immunomodulatory processes and the advance on the development of specific inhibitors, covering PDEs mainly related to the regulation of autoimmune processes, PDE4 and PDE7. The review also highlights the novel structural classes of PDE4 and PDE7 inhibitors, and the therapeutic potential that combined PDE4/PDE7 inhibitors offer as immunomodulatory agents.

PDE4 inhibitors as new anti-inflammatory drugs: effects on cell trafficking and cell adhesion molecules expression

Phosphodiesterase 4 (PDE4) is a major cyclic AMP-hydrolyzing enzyme in inflammatory and immunomodulatory cells. The wide range of inflammatory mechanisms under control by PDE4 points to this isoenzyme as an attractive target for new anti-inflammatory drugs. Selective inhibitors of PDE4 have demonstrated a broad spectrum of anti-inflammatory activities including the inhibition of cellular trafficking and microvascular leakage, cytokine and chemokine release from inflammatory cells, reactive oxygen species production, and cell adhesion molecule expression in a variety of in vitro and in vivo experimental models. The initially detected side effects, mainly nausea and emesis, appear at least partially overcome by the 'second generation' PDE4 inhibitors, some of which like roflumilast and cilomilast are in the later stages of clinical development for treatment of chronic obstructive pulmonary disease. These new drugs may also offer opportunities for treatment of other inflammatory diseases.

Alternatives to current disease-modifying treatment in MS: what do we need and what can we expect in the future?

Disease-modifying treatments (DMTs) for multiple sclerosis (MS) are now widely available, and their beneficial effects on relapse rates, magnetic resonance imaging outcomes and, in some cases, relapse-related disability have been shown in numerous clinical studies. However, as these treatments are only partially effective in halting the MS disease process, the search for improved treatment regimens and novel therapies must continue. Strategies to improve our therapeutic armamentarium have to take into account the different phases or parts of the pathogenesis of the disease. Available treatments address systemic immune dysfunction, blood-brain barrier permeability and the inflammatory process in the central nervous system. Currently, patients who fail to respond adequately to first-line DMTs are often considered as candidates for intensive immunosuppression with cytostatic agents or even autologous stem cell transplantation. However, new approaches are being developed. Combination therapies offer an alternative approach that may have considerable potential to improve therapeutic yield and, although likely to present considerable challenges in terms of trial design, this certainly seems to be a logical step forward in view of the complex pathology of MS. Several new drugs are also being developed with the aim of providing more effective, convenient and/or specific modulation of the inflammatory component of the disease. These treatments include humanised monoclonal antibodies such as the anti-VLA-4 antibody natalizumab, inhibitors of intracellular activation, signalling pathways and T-cell proliferation, and oral immunomodulators such as sirolimus, teriflunomide or statins. There remains, however, an urgent need for treatments that protect against demyelination and axonal loss, or promote remyelination/regeneration. Due to the chronicity of MS, the therapeutic window for neuroprotective agents is wider than that following stroke or acute spinal cord injury, and may therefore allow the use of some drugs that have proven disappointing in other situations. Novel potential neuroprotective agents such as alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid antagonists and ion-channel blockers will be entering Phase II trials in MS in the near future, and it is hoped that these agents will mark the start of a new era for DMTs for MS.

The phosphodiesterase PDE4B limits cAMP-associated PI3K/AKT-dependent apoptosis in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is a common and often fatal malignancy. Advances in the treatment of this disease will require the identification of novel therapeutic targets. We previously defined an expression signature of outcome in DLBCL and found that the phosphodiesterase PDE4B was overexpressed in fatal/refractory tumors. Phosphodiesterase 4B (PDE4B) inactivates the second messenger cyclic adenosine 3',5' monophosphate (cAMP) and abrogates its inhibitory effects in B lymphocytes. Hence, DLBCLs that express high PDE4B levels may be resistant to cAMP-induced apoptosis, contributing to their less favorable outcome. Herein, we confirmed the risk-related expression of PDE4B in an independent series of primary DLBCLs and defined the enzyme's role in modulating cAMP-induced apoptosis in parental DLBCL cell lines or those reconstituted with wild-type or mutant PDE4B. The cAMP-mediated apoptosis of DLBCLs was largely independent of the previously described cAMP effectors, protein kinase A (PKA) and exchange protein directly activated by cAMP (EPAC), but associated with inhibition of the phosphatidylinositol 3-kinase (PI3K)/AKT pathway. The central role of AKT in this process was confirmed by expressing constitutively active mutants of this kinase in DLBCL cells. Our findings highlight the important role of cAMP signaling in DLBCL and suggest that clinically relevant PDE4 and PI3K/AKT inhibitors might be useful in the treatment of DLBCL and additional B-lymphoid malignancies with increased PDE4B expression.

Effects of dialkoxylphenyl compounds with oxime group on macrophage function and the proliferation of lymphocytes

Dialkoxyphenyl compounds have been reported to possess anti-inflammatory activity through inhibition of phosphodieseterase (PDE) type IV. In this study, a series of derivatives of dialkoxyphenyl compounds with an oxime group, which is generally known to be one of the biologically active functional groups, were prepared and evaluated for their ability to inhibit the production of inflammatory mediators in activated macrophages and the proliferation of lymphocytes. The structure-activity relationship (SAR) study with 12 compounds on tumour necrosis factor (TNF)-alpha inhibition, analysed by the oxime geometry and different size of spacers between the oxime and phenyl group, indicated that there might be at least three possible hydrogen bonding sites in the inhibitor binding pocket of PDE IV. Of them, compound 6 clearly displayed the highest inhibitory effect on in-vitro TNF-alpha production from lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Compound 6 also suppressed in-vivo TNF-alpha release from LPS-primed mice, a level comparable with that of the standard PDE IV inhibitor, rolipram. In addition, oxime compounds also significantly inhibited both nitric oxide production from activated RAW264.7 cells and T lymphocyte proliferation elicited by concanavalin A but not IL-2. The data suggest that the oxime group may act as a functional group, capable of interacting with the inhibitor-binding pocket of target PDE IV. Therefore, it is conceivable that compound 6 may have the potential either to be developed as a new anti-inflammatory drug or to be used to develop more potent analogues.

Phosphodiesterase inhibitors suppress IL-12 production with microglia and T helper 1 development

The effects of phosphodiesterase inhibitors (PDEIs) on interleukin (IL)-12 production by microglia, antigen-presenting cells in the central nervous system (CNS), were examined to learn how they affect T cell differentiation in the CNS. PDEIs significantly suppressed the microglial IL-12 production, as determined by reverse transcriptase-polymerase chain reaction for IL-12 p35 and p40 mRNA expression and by an ELISA specific for IL-12 functional heterodimer, p70. In addition, the PDEI ibudilast also suppressed interferon-gamma, but not IL-4 or IL-10, production by myelin oligodendrocyte glycoprotein (MOG)-specific T cells reactivated with MOG in the presence of microglia. Thus, PDEIs may also suppress differentiation of T helper 1 (Th1) in the CNS. PDEIs can be of use for future therapeutic strategy to treat Th1-mediated diseases, such as multiple sclerosis.

Mitochondria, oxidative damage, and inflammation in Parkinson's disease

The pathogenesis of Parkinson's disease (PD) remains obscure, but there is increasing evidence that impairment of mitochondrial function, oxidative damage, and inflammation are contributing factors. The present paper reviews the experimental and clinical evidence implicating these processes in PD. There is substantial evidence that there is a deficiency of complex I activity of the mitochondrial electron transport chain in PD. There is also evidence for increased numbers of activated microglia in both PD postmortem tissue as well as in animal models of PD. Impaired mitochondrial function and activated microglia may both contribute to oxidative damage in PD. A number of therapies targeting inflammation and mitochondrial dysfunction are efficacious in the MPTP model of PD. Of these, coenzyme Q(10) appears to be particularly promising based on the results of a recent phase 2 clinical trial in which it significantly slowed the progression of PD.

The specific type-4 phosphodiesterase inhibitor mesopram alleviates experimental colitis in mice

Mesopram, a specific inhibitor of type-4 phosphodiesterase, decreases the synthesis of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma). In the present study, we investigated the effect of mesopram in dextran sulfate sodium (DSS)-induced murine colitis. In the preventive model, colitis was induced by DSS simultaneously with the application of mesopram in BALB/c mice. In the therapeutic model, colitis was induced in BALB/c mice by DSS over 7 days. At day 8, DSS was discontinued, and treatment was started. Mesopram was applied intraperitoneally or orally. The clinical score was calculated daily during the course of each study. Post mortem, colon length, histologic score, and expression of TNF-alpha and IFN-gamma in colons were determined. In the preventive model, mesopram significantly reduced the maximal clinical score, decreased colon shortening, and the histologic score. A dose finding study, using the preventive model, showed that most clinical and post mortem benefit was achieved with 50 mg/kg mesopram compared with 2 and 10 mg/kg. In the therapeutic model, i.p. mesopram treatment led to a significant reduction of clinical score. Both, i.p. and p.o. mesopram significantly reversed DSS-induced colon shortening and reduced the ex vivo colonic production of IFN-gamma. We conclude that the specific type-4 phosphodiesterase inhibitor mesopram ameliorates murine colitis both in a preventive and a therapeutic setting.

Update on the therapeutic potential of PDE4 inhibitors

Phosphodiesterase (PDE) enzymes are responsible for the inactiviation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Phosphodiesterase 4 (PDE4) is a cAMP specific phosphodiesterase expressed in inflammatory cells such as eosinophils. Inhibition of PDE4 results in an elevation of cAMP in these cells, which in turn downregulates the inflammatory response. The anti-inflammatory effects of PDE4 inhibitors have been well documented both in vitro and in vivo in a range of animal models. The potential use of PDE4 inhibitors as anti-inflammatory agents for the treatment of diseases such as asthma, chronic obstructive pulmonary disease (COPD) and multiple sclerosis (MS), has received considerable attention from the pharmaceutical industry but to date, there are no selective PDE4 inhibitors on the market. Early PDE4 inhibitors, such as rolipram suffered from dose limiting side effects, including nausea and emesis, which severely restricted their therapeutic utility. Second generation compounds such as cilomilast have been identified with reduced side effect liability. Indeed, cilomilast is showing good therapeutic effects in clinical trials for asthma and COPD and represents the most advanced selective PDE4 inhibitor for any indication. The utility of this class of inhibitor in other inflammatory diseases is less well advanced. However, data in animal models of rheumatoid arthritis (RA) and MS suggests that there is also significant potential for PDE4 inhibitors as treatments for these diseases and the results of clinical trials in these disease areas are eagerly awaited.

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.

Administration of pentoxifylline during allergen sensitization dissociates pulmonary allergic inflammation from airway hyperresponsiveness

Asthma, a chronic inflammatory disease characterized by intermittent, reversible airflow obstruction and airway hyperresponsiveness (AHR), is classically characterized by an excess of Th2 cytokines (IL-13, IL-4) and depletion of Th1 cytokines (IFN-gamma, IL-12). Recent studies indicating an important role for Th1 immunity in the development of AHR with allergic inflammation suggest that Th1/Th2 balance may be important in determining the association of AHR with allergic inflammation. We hypothesized that administration of pentoxifylline (PTX), a phosphodiesterase inhibitor known to inhibit Th1 cytokine production, during allergen (OVA) sensitization and challenge would lead to attenuation of AHR in a murine model of allergic pulmonary inflammation. We found that PTX treatment led to attenuation of AHR when administered at the time of allergen sensitization without affecting other hallmarks of pulmonary allergic inflammation. Attenuation of AHR with PTX treatment was found in the presence of elevated bronchoalveolar lavage fluid levels of the Th2 cytokine IL-13 and decreased levels of the Th1 cytokine IFN-gamma. PTX treatment during allergen sensitization leads to a divergence of AHR and pulmonary inflammation following allergen challenge.