Monocyte Phosphodiesterase Abnormalities and Dysregulation of Lymphocyte Function in Atopic Dermatitis

Elemental exchange: Bioisosteric replacement of phosphorus by boron in drug design

Continuous efforts are being directed toward the employment of boron in drug design due to its advantages and unique characteristics including a plethora of target engagement modes, lower metabolism, and synthetic accessibility, among others. Phosphates are components of multiple drug molecules as well as clinical candidates, since they play a vital role in various biochemical functions, being components of nucleotides, energy currency- ATP as well as several enzyme cofactors. This review discusses the unique chemistry of boron functionalities as phosphate bioisosteres - "the boron-phosphorus elemental exchange strategy" as well as the superiority of boron groups over other commonly employed phosphate bioisosteres. Boron phosphate-mimetics have been utilized for the development of enzyme inhibitors as well as novel borononucleotides. Both the boron functionalities described in this review-boronic acids and benzoxaboroles-contain a boron connected to two oxygens and one carbon atom. The boron atom of these functional groups coordinates with a water molecule in the enzyme site forming a tetrahedral molecule which mimics the phosphate structure. Although boron phosphate-mimetic molecules - FDA-approved Crisaborole and phase II/III clinical candidate Acoziborole are products of the boron-phosphorus bioisosteric elemental exchange strategy, this technique is still in its infancy. The review aims to promote the use of this strategy in future medicinal chemistry projects.

New and Emerging Therapies for Pediatric Atopic Dermatitis

Atopic dermatitis (AD) is a chronic, inflammatory skin disease characterized by pruritus, inflammatory erythematous skin lesions, and skin-barrier defect. Current mainstay treatments of emollients, steroids, calcineurin inhibitors, and immunosuppressants have limited efficacy and potentially serious side effects. Recent advances and understanding of the pathogenesis of AD have resulted in new therapies that target specific pathways with increased efficacy and the potential for less systemic side effects. New FDA-approved therapies for AD are crisaborole and dupilumab. The JAK-STAT inhibitors (baricitinib, upadacitinib, PF-04965842, ASN002, tofacitinib, ruxolitinib, and delgocitinib) have the most promising results of the emerging therapies. Other drugs with potential include the aryl hydrocarbon receptor modulating agent tapinarof, the IL-4/IL-13 antagonists lebrikizumab and tralokinumab, and the IL-31Rα antagonist nemolizumab. In this review, new and emerging AD therapies will be discussed along with their mechanisms of action and their potential based on clinical study data.

Biological therapies for atopic dermatitis: An update

Severe atopic dermatitis, which affects both adults and children, is a debilitating disorder with a significant decline of patients' quality of life. Although aetiopathogenic factors are currently a topic of study and interpretation, the main features of atopic eczema are skin barrier disturbance and immune dysregulation. Severe refractory disease that fails to improve with conventional therapy may benefit from biologic therapy. Progress in understanding immunopathology of atopic dermatitis have allowed identification of therapeutic molecular targets in the field of biological therapy. We reviewed the different biological treatments with a focus on novel targeted agents: Systemic immunotherapy (Omalizumab, Dupilumab, Lebrikizumab, Tralokinumab, Nemolizumab, Ustekinumab, Fezakinumab, Tezepelumab, Apremilast, allergen specific immunotherapy), and topical agents (Tofacitinib, Crisaborole).

JAK/STAT inhibitors and other small molecule cytokine antagonists for the treatment of allergic disease

OBJECTIVE

To provide an overview of janus kinase (JAK), chemoattractant receptor homologous molecule expressed on T_H2 cells (CRTH2), and phosphodiesterase 4 (PDE4) inhibitors in allergic disorders.

DATA SOURCES

PubMed literature review.

STUDY SELECTIONS

Articles included in this review discuss the emerging mechanism of action of small molecule inhibitors and their use in the treatment of atopic dermatitis (AD), asthma, and allergic rhinitis (AR).

RESULTS

Allergic diseases represent a spectrum of diseases, including AD, asthma, and AR. For decades, these diseases have been primarily characterized by increased T_H2 signaling and downstream inflammation. In recent years, additional research has identified disease phenotypes and subsets of patients with non-Th2 mediated inflammation. The increasing heterogeneity of disease has prompted investigators to move away from wide-ranging treatment approaches with immunosuppressive agents, such as corticosteroids, to consider more targeted immunomodulatory approaches focused on specific pathways. In the past decade, inhibitors that target JAK signaling, PDE4, and CRTH2 have been explored for their potential activity in models of allergic disease and therapeutic benefit in clinical trials. Interestingly, although JAK inhibitors provide an opportunity to interfere with cytokine signaling and could be beneficial in a broad range of allergic diseases, current clinical trials are focused on the treatment of AD. Conversely, both PDE4 and CRTH2 inhibitors have been evaluated in a spectrum of allergic diseases. This review summarizes the varying degrees of success that these small molecules have demonstrated across allergic diseases.

CONCLUSION

Emerging therapies currently in development may provide more consistent benefit to patients with allergic diseases by specifically targeting inflammatory pathways important for disease pathogenesis.

Role of macrophages in the pathogenesis of atopic dermatitis

Atopic dermatitis (AD) is one of the most common and most intensively studied chronic inflammatory skin diseases. Several cofactors, such as an impaired skin barrier function, modifications of the immune system, and a complex genetic background, direct the course of AD. Within this complex network, macrophages play a pivotal role in enhanced susceptibility to cutaneous infections and act as central connecting components in the pathogenesis of AD on the cellular level. In AD, macrophages are known to accumulate in acutely and chronically inflamed skin. During the early and short inflammatory phase, macrophages exert proinflammatory functions like antigen-presenting phagocytosis and the production of inflammatory cytokines and growth factors that facilitate the resolution of inflammation. However, persistence of pro-inflammatory activity and altered function of macrophages result in the development of chronic inflammatory diseases such as AD. The exact mechanism of macrophages activation in these processes is not yet completely understood. Further studies should be performed to clarify the dysregulated mechanism of macrophages activation in AD, and this would allow us to target these cells with versatile functions for therapeutic purpose and improve and control the disease. In this paper, we highlight the new findings on dysregulated function of macrophages and the importance of these cells in the pathogenesis of AD in general and the contribution of these cells in enhanced susceptibility against microbial infections in particular.

Roflumilast attenuates allergen-induced inflammation in mild asthmatic subjects

Background

Phosphodiesterase 4 (PDE4) inhibitors increase intracellular cyclic adenosine monophosphate (cAMP), leading to regulation of inflammatory cell functions. Roflumilast is a potent and targeted PDE4 inhibitor. The objective of this study was to evaluate the effects of roflumilast on bronchoconstriction, airway hyperresponsiveness (AHR), and airway inflammation in mild asthmatic patients undergoing allergen inhalation challenge.

Methods

25 subjects with mild allergic asthma were randomized to oral roflumilast 500 mcg or placebo, once daily for 14 days in a double-blind, placebo-controlled, crossover study. Allergen challenge was performed on Day 14, and FEV₁ was measured until 7 h post challenge. Methacholine challenge was performed on Days 1 (pre-dose), 13 (24 h pre-allergen), and 15 (24 h post-allergen), and sputum induction was performed on Days 1, 13, 14 (7 h post-allergen), and 15.

Results

Roflumilast inhibited the allergen-induced late phase response compared to placebo; maximum % fall in FEV₁ (p = 0.02) and the area under the curve (p = 0.01). Roflumilast had a more impressive effect inhibiting allergen-induced sputum eosinophils, neutrophils, and eosinophil cationic protein (ECP) at 7 h post-allergen (all p = 0.02), and sputum neutrophils (p = 0.04), ECP (p = 0.02), neutrophil elastase (p = 0.0001) and AHR (p = 0.004) at 24 h post-allergen.

Conclusions

This study demonstrates a protective effect of roflumilast on allergen-induced airway inflammation. The observed attenuation of sputum eosinophils and neutrophils demonstrates the anti-inflammatory properties of PDE4 inhibition and supports the roles of both cell types in the development of late phase bronchoconstriction and AHR.

Trial Registration

ClinicalTrials.gov: NCT01365533

Emerging drugs for atopic dermatitis

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease, affecting 10-20% of children and 2% of adults worldwide. Preventive treatment of AD consists of daily skin hydration and emollient therapy; but the majority of patients still require symptomatic treatment with topical corticosteroids and/or topical calcineurin inhibitors, both of which may be associated with potential long-term side effects. With increasing evidence supporting the role of skin barrier defects in the pathogenesis of AD, there is also a parallel increase in medications that claim to assist barrier repair. The current review discusses some exciting results with these medications, as well as the challenges that lie ahead of them. While barrier repair treatments offer some promise, there continues to be a need for safer anti-inflammatory medications. Some of these medications under investigation are phosphodiesterase-4 inhibitors, urocanic acid oxidation products and IL-4/IL-13 receptor blockers. The review also discusses anti-staphylococcal treatments including nanocrystalline silver cream, silver and antimicrobial-coated fabrics, and anti-itch treatments including mu-opiod receptor antagonists, chymase inhibitors and cannabinoid receptor agonists. These medications may become an integral part of AD therapy.

The genetics of atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is a complex genetic disorder influenced by environmental factors. The mode of inheritance and genes involved are not clear.

RESULTS

This report here is focusing on the current progress in searching the disease-susceptibility genes of AD via both the linkage studies and candidate gene approaches. Genome-wide linkage studies have identified multiple susceptibility loci on 3q and 17q. Candidate region linkage studies identify other susceptibility loci on 5q23-33, 11q13, and 13q12-14. At least 28 candidate genes have to date been verified in association studies, but only association with genes of interleukin (IL)-4, IL-13, IL-4RA, mast cell chymase, and serine protease inhibitor, kazal-type 5 have been replicated in more than two different studies. More halpotype tests and family-based association studies may help to shed more light for the candidate gene approach.

CONCLUSION

Determining the candidate susceptibility genes for AD is not only helping understanding the pathophysiology but also affecting the response to therapy, which is important in pharmacogenetics. The effect of environmental trigger may also have to be considered to elucidate the real face of the disease.

The role of PDE4 in pulmonary inflammation and goblet cell hyperplasia in allergic rats

Phosphodiesterase 4 (PDE4) has been suggested to a critical factor in the pathogenesis of inflammation by metabolizing cAMP in human leukocytes, endothelium and epithelium. The present study aimed at evaluating the PDE4 activity and expression, the relationship between the inflammation and cAMP- activity in the lungs, and potential interventions of PDE inhibitors and antiinflammatory drugs in the reduction of lung inflammation and goblet cell hyperplasia in allergic rats. The total leukocyte number and eosinophil number in bronchoalveolar lavegar fluid and infiltration of inflammatory cells in the perivascular and peribronchial spaces, structure changes and goblet cell hyperplasia in the OVA-sensitized and challenged allergic rats. A significant correlation was observed between the increases in cAMP-PDE activity and inflammation in the lung. Those OVA-induced changes were prevented by pretreatment with PDE inhibitor in a dose-related patterns and with glucocorticosteriod. We found an increase in the proportion of PDE4 and PDE4 gene expression, while a decrease in the proportion of PDE3 in the lung of the allergic rats. Incubation with different PDE inhibitors down-regulated OVA-induced cAMP hydrolysis. Our data suggest that PDE4C may play an important role in the airway inflammation, remodeling and goblet cell hyperplasia after repeated challenge of sensitized rats.

Upregulation of phosphodiesterase-4 in the lung of allergic rats

Inhibitors of phosphodiesterase-4 (PDE4) are efficacious for allergic asthma in animal models and have shown some efficacy in human asthma. Regulation of PDE4 in allergy and asthma has been widely investigated in blood leukocytes, with discrepant results. This study investigated PDE4 regulation in the lung in a rat model of allergic asthma. Ovalbumin sensitization and challenge significantly increased pulmonary resistance and lung interleukin (IL)-4 production. The increases in pulmonary resistance and IL-4 production were both suppressed by the PDE4-selective inhibitor rolipram or the corticosteroid drug dexamethasone. Furthermore, cAMP-PDE enzyme activity in the lung was also significantly increased by the sensitization and challenge. mRNA analysis confirmed that PDE4 gene expression was increased in the lung of the allergic rats. A highly significant correlation was observed between the increases in PDE activity and IL-4 production. Our data suggest, for the first time, that PDE4 may be upregulated in the lung and play a role in the pathogenesis of allergic asthma.

Phosphodiesterase-4 inhibitors in the treatment of inflammatory lung disease

Phosphodiesterases (PDE) belong to an important family of proteins that regulate the intracellular levels of cyclic nucleotide second messengers. Targeting PDE with selective inhibitors may offer novel therapeutic strategies in the treatment of various conditions, and in the context of respiratory disease these include asthma and chronic obstructive pulmonary disease (COPD). The rationale for such an approach stems, in part, from the clinical efficacy of theophylline, an orally active drug that is purportedly a nonselective PDE inhibitor. In addition, intracellular cyclic adenosine monophosphate (cAMP) levels regulate the function of many of the cells thought to contribute to the pathogenesis of respiratory diseases such as asthma and COPD, and these cells also selectively express PDE4. This has offered pharmaceutical companies the opportunity to selectively targeting these enzymes for the treatment of these diseases. Finally, the success of targeting PDE5 in the treatment of erectile dysfunction provides clinical proof of concept for the targeting of PDE in disease. Whether a 'Viagra' of the airways can be found for the treatment of asthma and COPD remains to be seen, but positive results from recent clinical studies examining the efficacy of selective PDE4 inhibitors such as cilomilast and roflumilast offer some optimism. However, one of the major issues to be resolved is the tolerability profile associated with this drug class that is a consequence of PDE4 inhibition. While cilomilast and roflumilast have low emetic potential they are not free from emesis and various strategies are being investigated in the hope of developing a PDE4 inhibitor without this adverse effect.

The pathogenesis of atopic eczema

Atopic eczema is associated with a genetic predisposition to dysregulation of the immune system. T lymphocytes differentiate towards the Th2 type with promotion of immunoglobulin E antibodies. Allergic responses to environmental allergens develop and microbes, including staphylococci and pityrosporum yeasts, may contribute to the inflammatory process.

Randomized comparison of the type 4 phosphodiesterase inhibitor cipamfylline cream, cream vehicle and hydrocortisone 17-butyrate cream for the treatment of atopic dermatitis

BACKGROUND

Therapeutic options to treat atopic dermatitis are limited. Leukocytes from atopic patients have an abnormally high activity of cyclic adenosine monophosphate (AMP)-phosphodiesterase (PDE), which can be normalized in vitro by PDE inhibitors. Cipamfylline is a new potent and selective inhibitor of PDE-4.

OBJECTIVES

To compare the efficacy and safety of up to 14 days' topical treatment with cipamfylline (0.15%) cream with vehicle and with hydrocortisone 17-butyrate (0.1%) cream.

PATIENTS AND METHODS

International, multicentre, prospective, randomized double-blind, left-right studies of cipamfylline vs. vehicle and cipamfylline vs. hydrocortisone 17-butyrate in adult patients with stable symmetrical atopic dermatitis on the arms.

RESULTS

Both cipamfylline and hydrocortisone 17-butyrate reduced the Total Severity Score significantly (P < 0.001). The reduction with cipamfylline was significantly greater than that with vehicle (difference vehicle-cipamfylline 1.67 95% confidence interval (CI) 1.06, 2.28; P < 0.001) and was significantly less than with hydrocortisone 17-butyrate (difference hydrocortisone-cipamfylline -2.10 95% CI -2.93, -1.27; P < 0.001). Investigator and patient assessments of the overall treatment response showed a similar picture.

CONCLUSIONS

Cipamfylline cream is significantly more effective than vehicle, but significantly less effective than hydrocortisone 17-butyrate cream in the treatment of atopic dermatitis.

Expression of IL-18 mRNA and secretion of IL-18 are reduced in monocytes from patients with atopic dermatitis

BACKGROUND

IL-18 has been found to be an IFN-gamma-inducing factor that plays an important role in T(H)1 cell activation. Recently, IL-18 has also been found to enhance a T(H)2 cellular response in a specific setting.

OBJECTIVE

The aim of this study was to elucidate the role of monocytes and soluble factors, with special focus on IL-18, in the pathogenesis of atopic dermatitis (AD).

METHODS

The release of cytokines from PBMCs and purified monocytes was measured through use of ELISA; mRNA expression was evaluated by RT-PCR. The results from patients with AD were compared with those from healthy controls.

RESULTS

IL-18 secretion was reduced in both unstimulated and lipopolysaccharide-stimulated monocytes from patients with AD. The mRNA expression of IL-18 and IL-1 beta-converting enzyme was significantly reduced in unstimulated monocytes from patients with AD (P <.03 and P <.01, respectively). Patients with AD had an elevated secretion of prostaglandin E(2) (PGE(2)) from unstimulated PBMCs (P <.001). The anti-PGE(2) antibody reversed the suppressive effect of PGE(2) on IL-18 secretion in unstimulated PBMCs from patients with AD.

CONCLUSIONS

Decreased IL-18 production, together with a significantly reduced IL-18 and ICE mRNA expression in unstimulated monocytes and elevated PGE(2) secretion from PBMCs, was associated with the pathogenesis of AD.

Regulatory roles of adenylate cyclase and cyclic nucleotide phosphodiesterases 1 and 4 in interleukin-13 production by activated human T cells

We studied the activities of 3',5'-adenosine-cyclic monophosphate (cAMP)- synthesizing adenylate cyclase (AC) and cAMP-hydrolyzing cyclic nucleotide phosphodiesterase (PDE) in phytohemagglutinin (PHA)- or anti-CD3 plus anti-CD28-stimulated human T cells, and examined their roles in interleukin-13 (IL-13) production. The AC inhibitor MDL 12,330A [cis-N-(2-phenylcyclopentyl)azacyclotridec-1-en-2-amine hydrochloride] completely blocked PHA- or anti-CD3/CD28-induced IL-13 production. The PDE 1 inhibitor 8-methoxymethyl-3-isobutyl-1-methylxanthine or the PDE4 inhibitor rolipram partially inhibited IL-13 production, and the addition of both resulted in 100 or 85% inhibition in PHA- or anti-CD3/CD28-stimulated T cells, respectively. AC in T cells was transiently activated 5 min after stimuli, followed by the transient activation of PDE4 at 30 min. PDE1 activity, undetectable in resting T cells, was detected 3 hr after stimuli, and then increased gradually. Although PDE1-, 2-, 3-, and 4-independent PDE activity was low (< or = 15% of total), it began to increase 3 hr after anti-CD3/CD28; the increase was blocked by PDE7 antisense oligonucleotide, and such an increase was not induced by PHA. PHA or anti-CD3/CD28 induced PDE1B mRNA expression, undetectable in resting T cells. PDE4 mRNA level in T cells was not altered by either stimulus. PDE7 mRNA expression was detected in resting T cells, and was enhanced by anti-CD3/CD28, but not by PHA. The cAMP level of T cells increased 5 min after stimuli, returned to the basal level at 2 hr, and then continued to decrease. These results suggest that PHA or anti-CD3/CD28 initially (< or = 5 min) increases cAMP in T cells via AC, then reverses the increase via PDE4 (< or = 2 hr), and in the later phase (> 2 hr) further decreases cAMP via PDE1. Both the time-dependent increase and decrease of cAMP may be required for IL-13 production.

Systemic therapy of atopic dermatitis

Atopic dermatitis is a chronic, relapsing, inflammatory skin disease. Topical therapy is the mainstay, but patients with widespread moderate to severe atopic dermatitis may require systemic therapy. Immunosuppressants, immune response modifiers, antihistamines and antibiotics are among the classes of systemic medications frequently used to treat extensive atopic dermatitis; the indications and scientific support for the use of these and other less commonly used medications will be reviewed in this article.

Atopic dermatitis: pathogenetic mechanisms

Atopic dermatitis (AD) is a chronic inflammatory skin disease with increasing incidence and socio-economical relevance. The diagnosis is made on clinical grounds and different diagnostic criteria sets have been established. The majority of all AD cases is associated with a sensitization to environmental allergens and increased serum IgE (so-called extrinsic AD), but about 10--30% of all cases suffer from the so-called intrinsic AD, which obviously lacks any link to the classical atopic diathesis. The genetic background of AD has been investigated by target gene approach by different groups with mostly contradictory results for each of the genes under study. An imbalance in the spectrum of Th1/Th2 responses, a disturbed prostaglandin metabolism, intrinsic defects in keratinocyte function, delayed eosinophil apoptosis, IgE-mediated facilitated antigen presentation by epidermal dendritic cells, a two phase model of the inflammatory response and staphylococcal superantigen effects are among the currently studied pathogenetical aspects of extrinsic AD, which are reviewed in this paper.

Absence of muscarinic cholinergic airway responses in mice deficient in the cyclic nucleotide phosphodiesterase PDE4D

Muscarinic cholinergic signaling plays an essential role in the control of the normal airway functions and in the development of pulmonary pathologies including asthma. In this paper we demonstrate that the airways of mice deficient in a cAMP-specific phosphodiesterase (PDE4D) are no longer responsive to cholinergic stimulation. Airway hyperreactivity that follows exposure to antigen was also abolished in PDE4D(-/-) mice, despite an apparently normal lung inflammatory infiltration. The loss of cholinergic responsiveness was specific to the airway, not observed in the heart, and was associated with a loss of signaling through muscarinic receptors with an inability to decrease cAMP accumulation. These findings demonstrate that the PDE4D gene plays an essential role in cAMP homeostasis and cholinergic stimulation of the airway, and in the development of hyperreactivity. In view of the therapeutic potentials of PDE4 inhibitors, our findings provide the rationale for novel strategies that target a single PDE isoenzyme.

The high-affinity IgE receptor (FcepsilonRI) blocks apoptosis in normal human monocytes

Monocytes have a limited life span, and their homeostasis is regulated by apoptosis in vivo. When cultured in the absence of appropriate exogenous stimuli, they undergo apoptosis, but under the influence of survival signals, these cells differentiate into macrophages or dendritic cells. Here we show that ligation of the high-affinity IgE receptor (FcepsilonRI) on human monocytes from nonatopic individuals markedly reduces apoptosis induced by serum deprivation or by CD95/Fas ligation. Aggregation of FcepsilonRI reduces its own expression but fails to modulate CD95/Fas expression. In contrast, FcepsilonRI ligation enhances the expression of the antiapoptotic molecules Bcl-2 and Bcl-xL, but not Mcl-1, in monocytes. Incubation of unstimulated cells with culture supernatants of FcepsilonRI-activated monocytes prolongs their life span, whereas CD95/Fas expression remains unaffected. The incidence of apoptosis is restored considerably when the supernatant is depleted of TNF-alpha, whereas elimination of IL-1beta, GM-CSF, or IL-12 has no effect. These results indicate that FcepsilonRI mediates signals preventing monocyte apoptosis directly by increasing the levels of Bcl-2 and Bcl-xL, and indirectly by means of TNF-alpha in an autocrine and paracrine fashion. This process may contribute to the establishment of chronic allergic disorders such as atopic dermatitis.

Phosphodiesterase 4 (PDE4) inhibitors in asthma and chronic obstructive pulmonary disease (COPD)

Phosphodiesterases (PDE) are a family of enzymes responsible for the metabolism of the intracellular second messengers cyclic AMP and cyclic GMP. PDE4 is a cyclic AMP specific PDE that is the major if not sole cyclic AMP metabolizing enzymes found in inflammatory and immune cells, and contributes significantly to cyclic AMP metabolism in smooth muscles. Based on its cellular and tissue distribution and the demonstration that selective inhibitors of this isozyme reduce bronchoconstriction in animals and suppress the activation of inflammatory cells, PDE4 has become an important molecular target for the development of novel therapies for asthma and COPD. This chapter will review the evidence demonstrating the ability of PDE4 inhibitors to modify airway obstruction, airway inflammation and airway remodelling and hyperreactivity, will present some preliminary findings obtained with theses compounds in clinical trials and and will discuss experimental approaches designed to identify novel compounds that maintain the beneficial activity of the initial selective PDE4 inhibitors but with a reduced tendency of elicit the gastrointestinal side effects observed with this class of compounds.

Mechanisms of deficient interferon-gamma production in atopic diseases

BACKGROUND

The mechanisms responsible for an imbalanced cytokine response in atopic diseases are still not understood. While impaired interferon-gamma (IFN-gamma) production may be the result of a pathological T-cell/antigen-presenting cell (APC) interaction, evidence was provided that the T cell itself may have an intrinsic defect to produce IFN-gamma.

OBJECTIVE

To clarify whether impaired IFN-gamma production by T cells from patients with atopic dermatitis (AD) represents an intrinsic defect in producing IFN-gamma.

METHODS

Effector T cells were generated from CD4+ CD45RA+-naive precursors from patients with AD and healthy control individuals by activation with anti-CD3+ anti-CD28 MoAbs. Following restimulation, IFN-gamma production was measured by ELISA and flow cytometry.

RESULTS

IFN-gamma production by atopic T cells was decreased compared with healthy T cells. IL-12 present at priming or high doses of IL-2 during the culture period, even in the absence of IL-12, completely restored IFN-gamma production. Conversion of naive CD45RA+ to CD45R0+ effector cells did not differ between atopic and healthy donors' T cells.

CONCLUSION

Impaired IFN-gamma production by T cells from atopic individuals is not the result of an intrinsic, genetically fixed, defect to produce sufficient amounts of IFN-gamma. The data provides evidence that correction of an impaired TH1 response in AD may be successful at the precursor T cell level.

Biochemical and immunologic mechanisms in atopic dermatitis: new targets for emerging therapies

The immunologic and pharmacophysiologic features of atopic dermatitis have stimulated research seeking to identify relevant effector cells and mediators that characterize chronic skin inflammation. The theory that unifies the various abnormalities associated with atopic dermatitis suggests that hematopoietic cells carrying abnormal genetic expressions of atopy cause clinical disease once they infiltrate the skin and mucosa. The proposed underlying mechanism may be either abnormalities in cyclic nucleotide regulation of marrow-derived cells or allergenic overstimulation that causes secondary abnormalities. The primacy of one mechanism over the other remains unresolved, but this does not obviate their value in identifying two novel therapeutic targets: phosphodiesterase inhibition and immune-intervention alternatives to corticosteroids. New type IV phosphodiesterase inhibitors are proving promising in topical formulations, as are inhibitors of calcineurin, such as FK506 and SDZ ASM 981, an ascomycin macrolactam derivative that in early clinical research appears to offer the potency of a corticosteroid without its adverse side effects. The promising clinical trial profiles of these new topical agents may result in alternative therapies providing potent anti-inflammatory activity without the adverse effects that limit corticosteroid use.

Cyclic-3',5'-nucleotide phosphodiesterase isozymes in cell biology and pathophysiology of the kidney

Investigations of recent years revealed that isozymes of cyclic-3', 5'-nucleotide phosphodiesterase (PDE) are a critically important component of the cyclic-3',5'-adenosine monophosphate (cAMP) protein kinase A (PKA) signaling pathway. The superfamily of cyclic-3', 5'-phosphodiesterase (PDE) isozymes consists of at least nine gene families (types): PDE1 to PDE9. Some PDE families are very diverse and consist of several subtypes and numerous PDE isoform-splice variants. PDE isozymes differ in molecular structure, catalytic properties, intracellular regulation and location, and sensitivity to selective inhibitors, as well as differential expression in various cell types. A number of type-specific "second-generation" PDE inhibitors have been developed. Current evidence indicates that PDE isozymes play a role in several pathobiologic processes in kidney cells. In rat mesangial cells, PDE3 and PDE4 compartmentalize cAMP signaling to the PDE3-linked cAMP-PKA pathway that modulates mitogenesis and PDE4-linked cAMP-PKA pathway that modulates generation of reactive oxygen species. Administration of selective PDE isozyme inhibitors in vivo suppresses proteinuria and pathologic changes in experimental anti-Thy-1.1 mesangial proliferative glomerulonephritis in rats. Increased activity of PDE5 (and perhaps also PDE9) in glomeruli and in cells of collecting ducts in sodium-retaining states, such as nephrotic syndrome, accounts for renal resistance to atriopeptin; diminished ability to excrete sodium can be corrected by administration of the selective PDE5 inhibitor zaprinast. Anomalously high PDE4 activity in collecting ducts is a basis of unresponsiveness to vasopressin in mice with hereditary nephrogenic diabetes insipidus. Apparently, PDE isozymes apparently also play an important role in the pathogenesis of acute renal failure of different origins. Administration of PDE isozyme-selective inhibitors suppresses some components of immune responses to allograft transplant and improves preservation and survival of transplanted organ. PDE isozymes are a target for action of numerous novel selective PDE inhibitors, which are key components in the design of novel "signal transduction" pharmacotherapies of kidney diseases.

Phosphodiesterase profile of human B lymphocytes from normal and atopic donors and the effects of PDE inhibition on B cell proliferation

1. CD19+ B lymphocytes were purified from the peripheral blood of normal and atopic subjects to analyse and compare the phosphodiesterase (PDE) activity profile, PDE mRNA expression and the importance of PDE activity for the regulation of B cell function. 2. The majority of cyclic AMP hydrolyzing activity of human B cells was cytosolic PDE4, followed by cytosolic PDE7-like activity; marginal PDE3 activity was found only in the particulate B cell fraction. PDE1, PDE2 and PDE5 activities were not detected. 3. By cDNA-PCR analysis mRNA of the PDE4 subtypes A, B (splice variant PDE4B2) and D were detected. In addition, a weak signal for PDE3A was found. 4. No differences in PDE activities or mRNA expression of PDE subtypes were found in B cells from either normal or atopic subjects. 5. Stimulation of B lymphocytes with the polyclonal stimulus lipopolysaccharide (LPS) induced a proliferative response in a time- and concentration-dependent manner, which was increased in the presence of interleukin-4 (IL-4). PDE4 inhibitors (rolipram, piclamilast) led to an increase in the cellular cyclic AMP concentration and to an augmentation of proliferation, whereas a PDE3 inhibitor (motapizone) was ineffective, which is in accordance with the PDE profile found. The proliferation enhancing effect of the PDE4 inhibitors was partly mimicked by the cyclic AMP analogues dibutyryl (db) cyclic AMP and 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole-3',5'-cyclic monophosphorothioate, Sp-isomer (dcl-cBIMPS), respectively. However, at concentrations exceeding 100 microM db-cyclic AMP suppressed B lymphocyte proliferation, probably as a result of cytotoxicity. Prostaglandin E2 (PGE2, 1 microM) and forskolin (10 microM) did not affect B cell proliferation, even when given in combination with rolipram. 6. Inhibition of protein kinase A (PKA) by differentially acting selective inhibitors (KT 5720, Rp-8-Br-cyclic AMPS) decreased the proliferative response of control cells and reversed the proliferation enhancing effects of rolipram. 7. Importantly, PDE4 activity in LPS/IL-4-activated B lymphocytes decreased by about 50% compared to unstimulated control values. 8. We conclude that an increase in cyclic AMP, mediated by down-regulation of PDE4 activity, is involved in the stimulation of B cell proliferation in response to LPS/IL-4. B cell proliferation in response to a mitogenic stimulus can be further enhanced by pharmacological elevation of cyclic AMP.

Critical evaluation of food and mite allergy in the management of atopic dermatitis

The subject of allergic causation of atopic dermatitis (AD) has been a source of controversy for over sixty years. While there is general agreement of allergen-induced asthma and allergic rhinoconjunctivitis, AD lesions cannot be readily or consistently induced by foods and inhalants. The most consistent perturbators of atopic conditions are irritants, probably reflecting the consistent inflammatory cell hyper-reactivity due to elevated cyclic AMP-phosphodiesterase activity. The immunologic reactions are another manifestation of that general cellular dysregulation.

Phenotypic differences between human blood monocyte subpopulations in psoriasis and atopic dermatitis

Peripheral blood monocytes seem to be of importance in the initiation and maintenance of cutaneous inflammatory disorders such as psoriasis and atopic dermatitis. Functional abnormalities of monocytes have been observed in both diseases. We sought to determine whether these abnormalities are reflected by an altered phenotypic expression of functionally active surface molecules. Peripheral blood monocyte subsets varying in cellular density and cell size from patients with psoriasis and atopic dermatitis were investigated using FACS analysis employing a panel of monoclonal antibodies (CD14, CD16, HLA-DR, HLA-DO, Fc epsilon RII, IL-2R, ICAM-1, CR3). Furthermore, the modulation of expression by interferon-gamma in monocyte subsets from patients was compared to normal controls. The results show that HLA-DR and -DQ expression on monocyte subsets in psoriatic patients was significantly decreased; "large" monocytes expressed significantly less HLA-DR than "small" monocyte subpopulations. Decreased HLA-DR and -DQ expression could be upregulated by incubation of psoriatic monocytes with IFN gamma. In atopic dermatitis, a different phenotype pattern of monocyte subsets was demonstrated: HLA-DR expression and HLA-DQ expression were both decreased in both "large" and "small" monocytes as compared to normal controls. However, there were no significant differences in HLA-DR and HLA-DQ expression between "large" and "small" monocyte subpopulations in atopic dermatitis. Moreover, the ICAM-1 and IL-2R expression of "large" and "small" monocyte subpopulations was significantly decreased in atopic patients from levels in normal controls and psoriatic patients. The altered expression of HLA-DR, -DQ ICAM-1 and IL-2R could be upregulated by incubation of atopic monocytes with IFN gamma. In addition, there was a significant increase in the percentage of monocytes in the differential count of patients with psoriasis or atopic dermatitis. We conclude that the differential phenotype pattern of surface molecules on monocytes in psoriasis and atopic dermatitis may reflect an abnormal monocyte maturation/differentiation state. This may explain the functional abnormalities of monocytes observed in patients with psoriasis and atopic dermatitis.