Relationship between increased cyclic AMP-phosphodiesterase activity and abnormal adenylyl cyclase regulation in leukocytes from patients with atopic dermatitis

Atopic dermatitis (AD) is characterized by a variety of abnormal physiologic and pharmacologic responses in the skin. Leukocyte abnormalities of the cyclic nucleotide system include increased cAMP phosphodiesterase (PDE) and adenylyl cyclase activities. We have evaluated the possibility that a defect of the inhibitory GTP-binding protein (Gi) might cause inadequate modulation of adenylyl cyclase activity in AD leukocytes. We carried out a series of studies assessing adenylyl cyclase and Gi subunits in monocyte membranes. Using both pertussis toxin ribosylation and direct monoclonal antibody labeling of Gi proteins, we have shown evidence for a decrease or possible absence of one of the Gi proteins in atopic monocyte membranes. A genetic defect or toxin-mediated abnormality in leukocyte membrane Gi could account for these findings. Increased cAMP degradation by PDE may be a compensatory mechanism for increased cAMP synthesis that is regulated by GTP-binding proteins. But this increased PDE activity also rendered AD leukocytes hypo-responsive to immunofunction regulatory signals mediated by cAMP.

Atopic dermatitis in infants and children

Atopic dermatitis is a common, chronic inflammatory skin disease triggered by a variety of irritative emotional and allergic factors. Education and simple prevention and maintenance measures such as proper moisturizing greatly reduce disease. Antibiotics and topical corticosteroids are therapeutic mainstays.

Tyrosinase gene mutations associated with type IB ("yellow") oculocutaneous albinism

We have identified three different tyrosinase gene mutant alleles in four unrelated patients with type IB ("yellow") oculocutaneous albinism (OCA) and thus have demonstrated that type IB OCA is allelic to type IA (tyrosinase negative) OCA. In an inbred Amish kindred, type IB OCA results from homozygosity for a Pro----Leu substitution at codon 406. In the second family, type IB OCA results from compound heterozygosity for a type IA OCA allele (codon 81 Pro----Leu) and a novel type IB allele (codon 275 Val----Phe). In the third patient, type IB OCA results from compound heterozygosity for the same type IB allele (codon 275 Val----Phe) and a novel type IB OCA allele. In a fourth patient, type IB OCA results from compound heterozygosity for the codon 81 type IA OCA allele and a type IB allele that contains no identifiable abnormalities; dysfunction of this type IB allele apparently results from a mutation either well within one of the large introns or at some distance from the tyrosinase gene. In vitro expression of the Amish type IB allele in nonpigmented HeLa cells demonstrates that the Pro----Leu substitution at codon 406 greatly reduces but does not abolish tyrosinase enzymatic activity, a finding consistent with the clinical phenotype.

Atopic dermatitis: new therapeutic considerations

Atopic dermatitis is a genetically determined inflammatory condition in which the primary defect is expressed in one or more hematopoietic cells that infiltrate the skin. It is a multifactorial disease with inflammation triggered by a variety of factors. Among these, atopic dermatitis has been experimentally induced and reproduced by emotional-stress interviews and food challenges only. The inflammatory events of atopic dermatitis appear to initiated by mast cells, but eosinophils, monocytes, and T lymphocytes (predominantly CD4) also are present in lesions. The secondary effects of inflammation are a dry, brittle stratum corneum and pruritus, causing excoriation and a lichenified epidermal layer resulting from chronic rubbing. Therapeutic approaches to atopic dermatitis may be directed at several points in the evolution of the disease. Agents including emollients are needed to preserve and restore the stratum corneum barrier, and effective antipruritics are required to reduce the self-inflicted damage to the involved skin. Various other agents may be needed to antagonize mediators or cytokines and to inhibit cytokine expression and release from lesional, immune-effector cells. Likewise, new phosphodiesterase inhibitors, calcium-active agents, and antiallergic drugs may be used to reduce the quantity and pathologic functioning of inflammatory infiltrating cells in the skin.

Airway responsiveness in atopic dermatitis

Twelve of 123 patients with atopic dermatitis (AD) were screened by questionnaire and spirometry for the absence of smoking, hay fever, and respiratory disorders. Seven of these 12 patients had a positive methacholine challenge test. None of eight patients with another skin disorder, psoriasis, screened in a similar fashion, had a positive methacholine challenge. We conclude that hyperresponsive airways are a frequent finding in patients with AD and that similar mechanisms may account for the cutaneous physiologic and pharmacologic abnormalities that have been observed in AD.

The role of antihistamines in atopic dermatitis

Although several lines of evidence support a role for histamine in the pathogenesis of atopic dermatitis, antihistamines have generally offered only marginal therapeutic benefit. The efficacy of the classic antihistamines has been severely limited by sedative effects, demonstrating the need for improved, nonsedating agents. Multifunctional antihistamines, or third-generation "antiallergic" drugs, appear to offer a variety of advantages beyond their ability to inhibit histamine release, such as inhibition of mediator release and interference with eosinophil migration. Double-blind studies of high-dose regimens are needed to help clarify the therapeutic efficacy of these antiallergic drugs.

Immunologic aspects of atopic dermatitis

The immunology of atopic dermatitis is complex, multilayered, and multifaceted. In one realm are the IgE-mediated, type I hypersensitivity reactions that can be elicited in at least 80% of patients. A second realm is that associated with cell-mediated immunity and delayed-type hypersensitivity (type IV) reactions. Scattered between these immunologic paradigms are the various splinters: immune complex abnormalities, putative late-phase reactions, and cutaneous basophil hypersensitivity. The inflammatory lesion of atopic dermatitis probably is a composite of the many model reactions that investigators have glimpsed but never resolved into a reasonable concept.

Thymopentin therapy reduces the clinical severity of atopic dermatitis

One hundred patients with moderate to severe atopic dermatitis were entered into a two-center, double-blind trial. Patients were randomized to receive either thymopentin (Timunox, n = 48) or placebo (n = 52), administered as daily subcutaneous injections for 6 weeks. Clinical extent of disease and severity parameters were measured at baseline and at regular time intervals during the study. Both the placebo- and thymopentin-treated groups demonstrated a progressive and statistically significant (p less than 0.001) decline in the overall severity of their disease, but reduction in the clinical severity score was higher in the thymopentin-treated group and statistically significant (p = 0.04) in comparison with the placebo-treated group after 6 weeks of treatment. Of the individual symptoms comprising the total severity score, pruritus (p = 0.02) and erythema (p = 0.04) were reduced significantly when thymopentin therapy was compared to placebo therapy. In addition, both the extent of body involvement and severity index (a combined severity/extent index) were significantly reduced after 6 weeks in the thymopentin-treated group in comparison to the placebo-treated group (p = 0.04). There were no serious adverse experiences in either treatment group. We conclude that treatment with thymopentin is safe and offers significant therapeutic promise for atopic dermatitis.

A frequent tyrosinase gene mutation in classic, tyrosinase-negative (type IA) oculocutaneous albinism

We have identified a tyrosinase gene mutation in several patients with classic, tyrosinase-negative (type IA) oculocutaneous albinism. This mutation, which results in a proline----leucine substitution at codon 81 of the tyrosinase polypeptide (EC 1.14.18.1), was observed in 20% (6 of 30) of oculocutaneous albinism alleles from independent probands, but it was not observed in any normal individuals. This mutation thus appears to be a frequent cause of tyrosinase-negative oculocutaneous albinism.

Atopic dermatitis

AD is a complex, multifactorial, cutaneous manifestation of the atopic diathesis. Observations from bone marrow transplantation cases have shown transmission of the disease from atopic donors [30] and indicate that the basic defect is carried in immune and inflammatory cells which infiltrate skin lesions. Mast cells appear to be important in the initiation of inflammatory events and eosinophils may have an important role in perpetuating the response. New evidence suggests that IL-4 may be a crucial factor controlling mast cells as well as IgE production in allergic disease. The significance of the Fc&RII/CD23 in regulating IgE synthesis and its role in Langerhans' cell/antigen interactions in atopic dermatitis represents an intriguing area in need of further study.

Phosphodiesterase and immune dysfunction in atopic dermatitis

Atopic dermatitis and the other atopic conditions occur as a result of direct or indirect influences from cells of hematopoietic origin. Cellular immune abnormalities have been described, but appear to be secondary to cutaneous inflammation in atopic dermatitis. Pharmacophysiologic abnormalities are numerous and may relate to defective cyclic nucleotide metabolism in circulating and infiltrating leukocytes. A consistent leukocyte abnormality is elevated cyclic AMP-phosphodiesterase. This enzyme abnormality results in reduced intracellular cyclic AMP, creating a net permissive effect upon cell function. Phosphodiesterase inhibitors have been demonstrated to reduce abnormal histamine release and IgE production by cultured leukocytes. Studies of phosphodiesterase and associated defects in atopic leukocytes may lead to delineation of basic pathogenetic mechanisms as well as providing the potential for therapeutic targeting.

Recognizing and managing clinical problems in atopic dermatitis

Atopic dermatitis is a pruritic, inflammatory cutaneous disorder found most frequently among patients with a personal or family history of atopic disease. A primary defect is found in bone marrow cells. The most consistent abnormality relates to the overproduction of IgE. Pharmacophysiologic abnormalities include abnormal vascular responses, abnormal sweating responses, and a reduced threshold for itch. In addition, seven of 12 patients with pure atopic dermatitis with no respiratory disease have an abnormal methacholine inhalation test. There is an abnormal response of leukocyte cyclic AMP to a variety of adenylate cyclase stimulants. Characteristic histological findings are interepidermal edema, called spongiosis, which is consistent with a composite of late-phase and delayed hypersensitivity. The brittle stratum corneum can be treated with hydration, a commonly neglected aspect of management. An overlooked complication is herpes simplex infection of the eye. Overall management includes stress control, treating allergenic trigger factors, topical steroids, systemic antibiotics, antihistamines, ultraviolet light, and hospitalization in severe cases.

Itraconazole therapy for recalcitrant dermatophyte infections

Five patients with recurrent Trichophyton rubrum infections had become unresponsive to topical and oral antifungal therapy. These patients were treated in an open trial of itraconazole, a new oral antifungal medication. Each patient responded promptly to therapy within 1 month and showed marked improvement at the end of 3 to 6 months of therapy. Complete clearing of toenail infections was not achieved in this limited trial and recurrences occurred in the four patients who had toenail infections. The drug was well tolerated and no adverse effects were observed. Itraconazole appears to be an effective drug for relief of clinical aspects of recalcitrant dermatophyte infections. Long-term safety and prevention of recurrence remain to be established.

Altered leukocyte protein kinase activity in atopic dermatitis

Previous studies have demonstrated elevated cyclic-AMP-specific phosphodiesterase (PDE) activity in mononuclear leukocytes (MNL) from patients with atopic dermatitis (AD). We questioned whether increased kinase activation could account for this observation. In these studies, we measured abnormally lower basal calcium/phospholipid-dependent protein kinase (PK-C) phosphorylation in MNL from patients with AD. Basal cAMP-dependent protein kinase (PK-A) phosphorylation was concomitantly higher in MNL from patients with AD. These results are in agreement with earlier reports that PK-A activity may have a negative influence on PK-C activity in certain cell systems. Stimulation with the H1-histamine agonist, thiazolylethylamine (TEA), of MNL from normal donors but not patients with AD, resulted in statistically significant increases in PK-C phosphorylation. This implies receptor down regulation or functional desensitization in AD cells. Altered basal protein kinase phosphorylation and abnormal response to selective histamine agonists seen in MNL from patients with AD could explain elevated PDE activity.

Clinical effects of diaper types on the skin of normal infants and infants with atopic dermatitis

Cloth diapers, cellulose core diapers (conventional disposable diapers), and cellulose core diapers containing absorbent gelling material were examined for their effects on diaper rash and skin microbiology of normal infants and infants with atopic dermatitis in a 26-week double-blind clinical trial. Infants with atopic dermatitis wearing the diapers containing absorbent gelling material had significantly lower diaper rash grades than infants with atopic dermatitis wearing cloth diapers at five of eight grading visits. Infants with atopic dermatitis wearing conventional cellulose core diapers had statistically less rash at one of eight visits. There was no statistically significant difference between diaper types at three of the eight visits. At no time did the cloth group have less diaper rash than the conventional cellulose or absorbent gelling material disposable diaper group. A statistical correlation between the severity of general atopic dermatitis outside the diaper area and the diaper rash condition under the diaper occurred only in the atopic dermatitis group wearing cloth diapers. Isolation of microorganisms from the intact, uninvolved skin surface both inside and outside the diaper showed no biologically significant changes in the presence or numbers of selected skin organisms. Repeated isolation, at multiple grading visits of Staphylococcus aureus from uncompromised skin inside the diaper area was infrequent but correlated with the diagnosis of atopic dermatitis when observed.

Cyclic nucleotide function in trachealis muscle of dogs with and without airway hyperresponsiveness

We examined basal adenosine 3',5'-cyclic monophosphate (cAMP) levels, isoproterenol (ISO)-stimulated cAMP responses, basal cAMP, and guanosine 3',5'-cyclic monophosphate (cGMP) phosphodiesterase (PDE) activities and protein-kinase (PK) activities in trachealis muscle from five Basenji-greyhound (BG) and four greyhound dogs to determine whether the inverse relationship between in vivo and in vitro airway responsiveness could be due to altered cyclic nucleotide metabolism. Basal cAMP levels were not significantly different (PNS) in muscle from BG (11.6 +/- 0.53 pmol/mg protein) and greyhound dogs (10.30 +/- 1.60 pmol/mg protein). The cAMP responses to stimulation with ISO were enhanced in BG compared with greyhound dogs. The low Michaelis constant (1) for Km-cAMP PDE activity (Km = 0.63 microM) was significantly less (P less than 0.005) in BG dogs (1.54 +/- 0.28 pmol.min-1.mg protein-1) than greyhounds (11.76 +/- 2.48). Endogenously active PK activity was significantly greater (P less than 0.005) in BG (54.74 +/- 5.39 pmol.min-1.mg protein-1) than in greyhound dogs (15.50 +/0 2.20). Increases in PK activity with 5 microM cAMP added were not significantly different between BG (14.79 +/- 6.00) and greyhound dogs (7.04 +/- 2.14). Approximately 90% of both endogenous PK activity and cAMP-activated PK activity in BG and greyhound dogs was inhibited by a cAMP-dependent PK inhibitor (PKI'). These data suggest that decreased cyclic nucleotide degradation due to decreased cyclic nucleotide PDE activity with increased PK could account for the in vitro hyporesponsiveness of airway smooth muscle in BG dogs as a protective adaptive mechanism.

Histamine induced elevation of cyclic AMP phosphodiesterase activity in human monocytes

We have previously reported histamine desensitization of human blood mononuclear leukocytes resulting in reduced cAMP responses to beta-adrenergic agonists, histamine and prostaglandin E1. This heterologous desensitization occurred at low, micromolar histamine concentrations and was accompanied by elevation of cAMP-phosphodiesterase (PDE) activity in these cells. We have now investigated the activity of PDE in the lymphocyte and monocyte fractions of mononuclear leukocytes to determine the site of histamine effect. PDE activity per cell was higher in monocytes (0.075 +/- 0.070 units) than lymphocytes (0.026 +/- 0.08) units). Monocytes responded to 10(-6) M histamine stimulation with a much greater increase in PDE activity (0.354 +/- 0.1 units) than did lymphocytes (0.047 +/- 0.015 units). Histamine receptor studies, using thiazolylethylamine and chlorpheniramine as H1-agonist and antagonist respectively and dimaprit and cimetidine as H2-agonists and antagonists respectively, indicated that the histamine stimulation of PDE activity is mediated predominantly through H1 histamine receptor in the monocytes and the H1 receptor in the lymphocytes. Previously histamine had been thought to increase cyclic AMP by acting on H2 receptors to activate adenylate cyclase. Our studies show that stimulation of H1 or H2 receptors by low histamine concentration can cause the opposite effect i.e. increased catabolism and a net reduction in cAMP levels. The localization of this effect predominantly to monocytes indicates a potentially important mechanism for histamine action on immune regulation.

Substance P-induced histamine release in human cutaneous mast cells

Substance P is an undecapeptide found in multiple sites throughout the central and peripheral nervous systems including small unmyelinated (type C) cutaneous nerve fibers. Previous studies demonstrated that antidromic stimulation results in substance P (SP) release from nerve endings, SP stimulates histamine release (HR) from rat mast cells in vitro, and intradermal SP in humans produces wheals identical to those induced by histamine. These studies suggest a possible role for SP as a link between neurologic events and cutaneous mast cell-mediated reactions. We therefore investigated SP-induced HR in an in vitro preparation of human skin mast cells. Human foreskin sections were incubated with varying concentrations of SP. Histamine was assayed using automated fluorimetry and release was calculated as a percentage of total tissue histamine. Substance P caused dose-dependent HR over a range from 10(-5) M (1.3%) to 5 X 10(-4) M (25.1%). Histamine release was optimal at 3 mM calcium and was blocked by pretreatment with calcium chelation. Naloxone failed to block HR. These studies suggest that HR from skin mast cells by SP may play a role in neural modulation of poorly understood inflammatory skin conditions.

[Changed phosphodiesterase activity of leukocytes in atopic eczema]

Leukocytes of patients with atopic eczema exhibit a variety of biochemical abnormalities, particularly an alteration in cyclic nucleotide metabolism. The basic defect is an elevation of phosphodiesterase activity in these cells, which leads to a diminished modulation of cellular immune function by cAMP. This, in turn, leads to an elevation of IgE synthesis and enhanced release of inflammatory mediators from mast cells and basophils. The phosphodiesterase defect offers new approaches to the treatment of atopic eczema.