Anti-inflammatory effect of FK-506 on human skin mast cells

Investigation on the use of 0.3% tacrolimus lotion for canine atopic dermatitis: a pilot study

The efficacy of 0.3% tacrolimus lotion (maximum dosage: 0.3 mg kg-1 per day) for treatment of atopic dermatitis (AD) was evaluated. Systemic absorption and effects on complete blood cell counts (CBC) and chemistry panels were also investigated. Eight dogs were assigned randomly to either a tacrolimus or a vehicle lotion treatment group. Both owners and investigator were blinded to the treatment. After 4 weeks, there was a 2-week wash-out period and treatments were reversed. Owners scored pruritus weekly while the investigator scored pruritus and erythema at the beginning and end of each treatment period. Investigator scores for pruritus in the tacrolimus group significantly decreased by the end of the study (P = 0.03). Investigator scores for erythema in the tacrolimus group were significantly lower than those in the placebo group at the end of the study (P = 0.005). There was no difference between groups with respect to owner scores for pruritus. No changes in the CBC and chemistry panels were noted. Mean blood concentrations of tacrolimus were below toxic levels.

Efficacy and safety of tacrolimus ointment compared with that of hydrocortisone butyrate ointment in adult patients with atopic dermatitis

BACKGROUND

Vehicle-controlled studies have demonstrated the efficacy and safety of tacrolimus ointment for patients with atopic dermatitis.

OBJECTIVE

This study was undertaken to compare 0.03% and 0.1% tacrolimus ointment with 0.1% hydrocortisone-17-butyrate ointment, a midpotent to potent topical corticosteroid, in the treatment of adult patients with moderate-to-severe atopic dermatitis.

METHODS

Patients applied ointment twice daily to all affected areas for 3 weeks in this multicenter, randomized, double-blind, parallel-group study. The primary endpoint was the modified eczema area and severity index (mEASI) mean area under the curve as a percentage of baseline.

RESULTS

Five hundred seventy patients were randomized and received treatment. Discontinuations included 22 of 193 patients from the 0.03% tacrolimus group, 22 of 191 patients from the 0.1% tacrolimus group, and 17 of 186 patients from the hydrocortisone butyrate group. The median mEASI mean area under the curve as a percentage of baseline was 47.0%, 36.5%, and 36.1% for patients who received 0.03% tacrolimus, 0.1% tacrolimus, and 0.1% hydrocortisone butyrate, respectively. There was no statistically significant difference between 0.1% tacrolimus and 0.1% hydrocortisone butyrate; however, the lower improvement in mEASI for 0.03% tacrolimus was statistically significant when compared with 0.1% tacrolimus (P <.001) or hydrocortisone butyrate (P =.002). Skin burning and pruritus at the application site showed a higher incidence in the tacrolimus treatment groups than in the hydrocortisone butyrate group (P <.05). Laboratory parameters showed no treatment differences and no marked changes over time.

CONCLUSIONS

The efficacy of 0.1% tacrolimus ointment was similar to that of 0.1% hydrocortisone butyrate ointment and was lower for 0.03% tacrolimus ointment. No serious safety concerns were identified.

Tacrolimus: a review of its use for the management of dermatoses

The newly developed immunomodulator tacrolimus (FK506) is the first of a new class of agents that have enormous potential to change the way that dermatoses are treated and managed. Tacrolimus has been found to be active in a topical formulation with the latter exerting its effects by acting on the signal transduction pathways inside T cells and inhibiting gene transcription. The result is decreased responsiveness of T cells to antigens. Percutaneous absorption of tacrolimus is higher in diseased skin as opposed to healthy skin and, therefore, the drug will be taken in at progressively lower quantities as lesions heal. There is limited systemic absorption of tacrolimus over the course of therapy. The most extensive experience with tacrolimus has been in treating atopic dermatitis. In numerous trials, tacrolimus ointment 0.03-0.3% has shown to be effective in reducing the symptoms and severity of atopic dermatitis in adults and the paediatric population. Furthermore, there have been no significant toxic effects associated with topical therapy with tacrolimus. The most common complaint is that of local irritation after applying the ointment. This is generally transient and the patient is able to continue with therapy. The other dermatoses where tacrolimus has been used include contact dermatitis, psoriasis and pyoderma gangrenosum.

Efficacy and safety of tacrolimus ointment compared with that of hydrocortisone acetate ointment in children with atopic dermatitis

BACKGROUND

Vehicle-controlled studies have demonstrated the efficacy and safety of tacrolimus ointment in the treatment of patients with atopic dermatitis (AD).

OBJECTIVE

This study was undertaken to compare 0.03% and 0.1% tacrolimus ointment with 1% hydrocortisone acetate ointment in children 2 to 15 years of age with moderate-to-severe AD.

METHODS

Treatment was twice daily to affected areas for 3 weeks in this multicenter, randomized, double-blind, parallel-group study. The primary endpoint was the modified eczema area and severity index (mEASI) mean area under the curve (mAUC) as a percentage of baseline.

RESULTS

Five hundred sixty patients were randomized and received at least one application of ointment. Discontinuations included 21 of 189 patients from the 0.03% tacrolimus group, 13 of 186 patients from the 0.1% tacrolimus group, and 20 of 185 patients from the hydrocortisone acetate group. The median mEASI mAUC as a percentage of baseline showed 0.03% and 0.1% tacrolimus to be significantly more effective than 1% hydrocortisone acetate (P <.001) and 0.1% tacrolimus to be more effective than 0.03% tacrolimus (P =.006). The mEASI mAUC as a percentage of baseline was 44.8%, 39.8%, and 64.0% for patients who received 0.03% tacrolimus, 0.1% tacrolimus, and 1% hydrocortisone acetate, respectively. Transient skin burning was the only adverse event to show a higher incidence in the tacrolimus treatment groups than in the hydrocortisone acetate group (P <.05). Laboratory parameters showed no treatment differences and no marked changes over time.

CONCLUSION

Tacrolimus, 0.03% and 0.1%, was significantly more effective than 1% hydrocortisone acetate and 0.1% tacrolimus was more effective than 0.03% tacrolimus in the treatment of moderate-to-severe AD in children. No safety concerns were identified.

Tacrolimus clinical studies for atopic dermatitis and other conditions

The first topical immunomodulator approved for human use, tacrolimus ointment (Protopic, Fujisawa, Healthcare, Inc, Deerfield, IL), has been shown to be effective and safe in the treatment of children (aged 2 years and older) and adults with atopic dermatitis (AD). Clinical trials conducted worldwide have involved 12,000 patients, with safety and efficacy data available for up to 3 years of treatment. In addition to its beneficial effects in the management of AD, topical tacrolimus has also been reported to be of benefit in other immunologically mediated skin diseases including: hand dermatitis, contact dermatitis, eyelid dermatitis, erosive lichen planus, steroid-induced rosacea, pyoderma gangrenosum, and graft-versus-host disease. This article reviews the clinical experience of topical tacrolimus in the treatment of AD and other skin conditions.

Pathophysiologic mechanisms in atopic dermatitis

Atopic dermatitis is a common, chronic inflammatory skin disease that frequently predates the development of asthma and/or allergic rhinoconjunctivitis. Recent studies have provided new insights into how the complex interrelationship of genetic, environmental, and immunologic factors may contribute to the development of atopic dermatitis. This article examines some of the factors involved in chronic cutaneous inflammation in this disease. Greater understanding of the mechanisms that underlie the pathophysiology of atopic dermatitis may lead to improved treatment strategies for this increasingly common skin disease.

Tacrolimus pharmacology and nonclinical studies: from FK506 to protopic

Tacrolimus (FK506) is a calcineurin inhibitor with potent immunomodulating properties. It has been marketed worldwide since 1993-1994 for the rejection of liver and kidney transplants (Prograf). The pharmacologic properties of tacrolimus resulted in its development as an ointment for the treatment of atopic dermatitis. An outline of nonclinical pharmacology studies that provided a rationale for this development is presented. The key nonclinical toxicology-safety studies that supported clinical efficacy/safety trials are also discussed. Taken collectively, these studies contributed to the marketing approval of 0.03% and 0.1% tacrolimus ointment (Protopic) as a first in class treatment for atopic dermatitis.

The ACVD task force on canine atopic dermatitis (XXII): nonsteroidal anti-inflammatory pharmacotherapy

The pharmacotherapy of canine atopic dermatitis has relied primarily on the use of glucocorticoids and anti-histamines. During the last decade, other anti-inflammatory drugs have been investigated in clinical trials. This paper will review the studies using misoprostol, cyclosporine, tacrolimus, phosphodiesterase inhibitors, capsaicin, leukotriene inhibitors and serotonin-reuptake inhibitors for treatment of dogs with atopic dermatitis. For each drug the mechanism of action, the rationale for use in atopic dermatitis, the clinical efficacy, reported adverse effects and strength of recommendation for treatment of canine atopic dermatitis are described. At the time of this writing, there is fair evidence to support the recommendation for using cyclosporine, misoprostol and pentoxifylline for treatment of canine atopic dermatitis. This recommendation can be strengthened by the performance of additional blinded randomized controlled trials with larger number of dogs. In contrast, there is insufficient evidence to recommend for or against treatment with tacrolimus, leukotriene inhibitors, serotonin-reuptake antagonists and capsaicin.

The ascomycin macrolactam pimecrolimus (Elidel, SDZ ASM 981) is a potent inhibitor of mediator release from human dermal mast cells and peripheral blood basophils

BACKGROUND

The ascomycin macrolactam pimecrolimus (Elidel, SDZ ASM 981) has recently been developed as a novel and cell-selective inhibitor of inflammatory cytokine secretion; it has fewer adverse effects than currently available drugs.

OBJECTIVE

In this study, we investigated the capacity of pimecrolimus to directly inhibit in vitro mediator release from human skin mast cells and basophils.

METHODS

Purified cutaneous mast cells or basophil-containing peripheral blood leukocytes were obtained from healthy human donors and preincubated with pimecrolimus (0.1 nmol/L to 1 micromol/L) in the absence or presence of its specific antagonist (rapamycin), cyclosporin A (100 nmol/L to 1 micromol/L), or dexamethasone (1 micromol/L) and then stimulated with anti-IgE or with calcium ionophore A23187 plus phorbol myristate acetate. Cell supernatants were kept for analysis of histamine, tryptase, LTC4, and TNF-alpha.

RESULTS

Pimecrolimus caused a strong and dose-dependent inhibition of anti-IgE--induced release of histamine from mast cells and basophils (maximally 73% and 82%, respectively, at 500 nmol/L pimecrolimus) and of mast cell tryptase (maximally 75%) and a less pronounced inhibition of LTC4 (maximally 32%) and of calcium ionophore plus phorbol myristate acetate--induced mast cell TNF-alpha release (90% maximum at 100 nmol/L pimecrolimus). In contrast, inhibition achieved during mast cell histamine release was maximally 60% with cyclosporin A and only 28% with dexamethasone.

CONCLUSION

These data demonstrate a marked inhibitory capacity of pimecrolimus on mediator release from human mast cells and basophils with a potency exceeding that of cyclosporin A and dexamethasone. Pimecrolimus might thus be expected to be effective in the treatment of mast cell-- and basophil-dependent diseases.

Topical tacrolimus for the treatment of inflammatory skin diseases

Chronic inflammatory skin disorders, such as atopic eczema, can cause considerable impairment of life quality. Their treatment is mainly driven by systemic or topical glucocorticosteroids which have the risk of many side effects. Recently, immunosuppressive macrolides which act via the inhibition of cytokine expression in T-lymphocytes have been shown to exert good therapeutic potency in inflammatory skin disorders. Cyclosporin, widely used in transplantation medicine, is also effective in psoriasis and atopic eczema but is not suitable for topical treatment. Tacrolimus (FK506) has been found to be 10-100 times more potent than cyclosporin and to penetrate skin much better due to a lower molecular weight. Initial clinical investigations have shown efficacy of topical tacrolimus in patients with atopic eczema. Large multi-centre studies have proven that long-term therapy with 0.03% and 0.1% tacrolimus ointment reveals effectiveness and safety both in adults and in children with severe atopic eczema. A burning sensation at the site of application is the most frequently observed local side effect. Relevant systemic adverse events were not detected. In Japan and the US, the drug is already licensed for the treatment of atopic eczema. The European admission for the pharmaceutical market is expected in the year 2002. Tacrolimus represents a milestone in topical therapy of inflammatory skin disorders which has so far been dominated by corticosteroid formulations and gives hope for the development of further topical immunosuppressive agents of its class in the future.

[Pharmacological profile and clinical effect of tacrolimus ointment (Protopic ointment) for atopic dermatitis]

Atopic dermatitis (AD) is thought to be induced by a complex of various allergic reactions and T cells are implicated in its etiology. Since tacrolimus strongly inhibits T cell activation, tacrolimus ointment has been developed as a novel drug for AD throughout the world. Tacrolimus inhibits mast cell and eosinophil activation and antigen presenting activity of Langerhans cells in vitro. In the in vivo experimental animal models of AD, such as contact and spontaneous dermatitis in mice and repeated hapten treated skin inflammation in rats, tacrolimus ointment showed inhibitory activity. In clinical studies with AD patients in Japan, USA and Europe, tacrolimus ointment showed a marked effect. In comparative studies in Japan, it showed the same efficacy as a strong class steroid ointment on eczema at the trunk and extremities and superior efficacy at the face and neck compared to a medium class steroid. The most prominent adverse event is experienced at the local application site with reactions such as a burning sensation and erythema. Systemic side effects were rarely observed. While there is a possibility of skin infections when using tacrolimus, skin atrophy, even after long term treatment, was not observed. Thus tacrolimus ointment could be an efficient alternative to steroid ointment for AD.

Human epidermal Langerhans' cells are targets for the immunosuppressive macrolide tacrolimus (FK506)

BACKGROUND

The immunosuppressive macrolide tacrolimus (FK506) has been shown to inhibit allergic contact dermatitis in animal models as well as in human beings. More recently, successful treatment of atopic dermatitis with an ointment containing tacrolimus has been reported.

OBJECTIVES

We explored the effects of this compound on epidermal Langerhans' cells (LCs), which are known to play an important pathophysiologic role in inflammatory skin diseases.

METHODS

The expression of the intracellular FK506 binding protein (FKBP12) was monitored on freshly isolated and cultured epidermal LCs. Phenotyping and functional exploration of LCs treated with different concentrations of tacrolimus and beta-methasone valerate (betaMv) were performed.

RESULTS

FKBP12 is expressed in freshly isolated LCs but is lost while they are maturating into mature dendritic cells. Tacrolimus inhibited the expression of IL-2R (CD25) and of the costimulatory molecules CD80 (B7.1) and CD40. Expression of MHC class I and II was also affected, whereas CD86 (B7.2) expression was not altered. In contrast, betaMv strongly increased the expression of CD25. Paradoxically, while decreasing CD40 and MHC class I expression, betaMv significantly increased the expression of MHC class II, CD80, and CD86 on cultured LCs but impaired their allostimulatory activity. Tacrolimus was about 100 times more potent than betaMv at inhibiting LC stimulatory function.

CONCLUSION

Tacrolimus can exert immunopharmacologic alterations on LCs, which may account, at least in part, for the therapeutic effect of this compound in eczematous skin diseases.

Nonclinical and early clinical development of tacrolimus ointment for the treatment of atopic dermatitis

Tacrolimus ointment, formulated for the treatment of atopic dermatitis, is the first in a class of topical immunomodulators. Its mechanism of action is based on calcineurin inhibition, which results in suppression of antigen-specific T-cell activation and inhibition of inflammatory cytokine release. Animal and human studies have shown that topically applied tacrolimus is minimally absorbed into the systemic circulation, the fraction that is absorbed is extensively distributed, and tacrolimus does not accumulate in tissues following repeated topical application. In addition, tacrolimus ointment is not inherently irritating, sensitizing, phototoxic, or photoallergenic when applied to intact skin. Unlike some topical corticosteroids, tacrolimus ointment does not cause a decrease in collagen synthesis or skin thickness, nor does it produce skin abnormalities or depigmentation. In animal studies, repeated daily application of tacrolimus ointment up to 1 year is associated with dermal findings similar to those following vehicle application (mild to moderate dermal irritation and microscopic findings of acanthosis, hyperkeratosis, and superficial inflammation). In a 52-week study with Yucatan micropigs, no noteworthy macroscopic or microscopic changes (either dermal or systemic) related to the application of tacrolimus ointment (0.03% to 0.3% concentrations) were observed. Tacrolimus ointment was shown to be safe and effective in phase 2 and early phase 3 studies. Significant improvements in atopic dermatitis were observed in the majority of patients treated with tacrolimus ointment. The most common adverse events associated with its use were a transient burning sensation and pruritus at the site of application. Blood tacrolimus concentrations were below the limit of quantitation in most patients.

FK506 suppresses neutrophil chemoattractant production by peripheral blood mononuclear cells

To understand the mechanism of action of FK506 (Tacrolimus) on neutrophil chemotaxis, we examined its effect on human neutrophil chemotaxis and neutrophil chemoattractant production by peripheral blood mononuclear cells. FK506 and cyclosporin A had no direct suppressive effect on neutrophil chemotaxis induced by interleukin-8, leukotriene B(4), complement 5a (C5a), zymosan-activated serum and formyl-Met-Leu-Phe (fMLP). FK506 and cyclosporin A only slightly suppressed the chemotactic activity of platelet-activating factor (PAF). Dexamethasone did not inhibit the chemotactic activity of any chemoattractant. The supernatant of peripheral blood mononuclear cells stimulated with anti-CD3 and CD2 antibodies induced neutrophil chemotaxis. FK506 and cyclosporin A suppressed the chemotactic activity of the supernatant in parallel to the suppression of interleukin-8 production by peripheral blood mononuclear cells. Anti-interleukin-8 antibody completely suppressed the chemotactic activity of the supernatant without drugs. These studies indicate that FK506 may exert a beneficial effect on human inflammatory diseases by suppressing neutrophil chemotaxis secondary to inhibition of chemoattractant (for example, interleukin-8) production by leukocytes.

Applications of tacrolimus for the treatment of skin disorders

During the last decades, systemic and topical glucocorticosteroids assumed a dominant role in immunosuppressive therapy in dermatology. However, their administration is limited because of numerous adverse effects. Consequently, there is a large need for alternative non-steroidal anti-inflammatory therapeutics with a superior risk/benefit ratio. In recent years, a new class of anti-inflammatories, the macrolide lactones, has attracted special interest. During the last decade, a member of this class, tacrolimus, proved to be a powerful suppressor of the immune system. Introduced into clinical practice to prevent allograft rejection, it is now routinely used in organ transplantation. Recently, several placebo-controlled multicenter studies showed the therapeutic efficiency of systemic and topical tacrolimus in common inflammatory skin diseases such as psoriasis and atopic eczema.Short-term tacrolimus ointment therapy disclosed significant efficacy vs. placebo and a safety profile with only few local side effects in patients with atopic eczema. Further clinical trials including greater extent of exposure (experienced by children), and comparison between tacrolimus ointment and glucocorticosteroids are being conducted and the results will show whether this drug opens a new era in the treatment of inflammatory skin disorders. The aim of this review is to summarize the current knowledge regarding the pharmacokinetic properties, adverse effects and therapeutic indications of tacrolimus in dermatology.

FK506 inhibition of histamine release and cytokine production by mast cells and basophils

Histamine release and cytokine production by mast cells and basophils are thought to be closely involved in the pathogenesis of allergic diseases. Some reports show that FK506 (tacrolimus hydrate) inhibited histamine release and cytokine production by mast cells and basophils. However, as the effects of FK506 has not been compared with those of clinically used drugs in those reports, the clinical relevancy of FK506 inhibition remained unclear. In this paper, we compared the actions of FK506 with those of steroids or disodium cromoglycate (DSCG) which has been clinically used. FK506 inhibited histamine release by Brown-Norway rat peritoneal mast cells more potently than steroids and especially DSCG. FK506 also inhibited histamine release by a mast rat basophilic leukemia (RBL)-1 cell line and human peripheral blood basophils, whereas steroids failed to inhibit histamine release by human basophils. FK506 as well as steroids inhibited TNF-alpha and IL-4 production by RBL-1 cells. FK506 was therefore more effective than steroids and DSCG in inhibiting histamine release, and it also had the ability of inhibiting cytokine production by mast cells as steroids do. We concluded that FK506 might regulate allergic diseases via these actions, judging from the viewpoint of clinical relevancy.

Immunopharmacology of human mast cells and basophils

Human mast cells and basophils play a key role in the pathogenesis of several immunological and inflammatory disorders, not only by producing inflammatory and fibrogenic mediators, but also by directly (CD40 ligand) and indirectly secreting various cytokines and chemokines. Studies carried out to evaluate the effects of drugs that modulate the release of mediators and cytokines from these cells have contributed to clarifying the biochemical mechanism by which immunological and non-immunological stimuli activate these cells. Significant differences have been documented between human mast cells and basophils as regard the pharmacological agents that modulate the release of mediators, between mast cells isolated from different anatomical sites, and between compounds of the same class of drugs. Efforts to gain insight into the biochemical events occurring during immunological activation of mast cells and basophils could lead to the identification of new biochemical targets for therapeutic interventions in several immunological disorders.

Effect of tacrolimus hydrate (FK506) ointment on spontaneous dermatitis in NC/Nga mice

The effect of tacrolimus hydrate (FK506) ointment on spontaneous dermatitis in NC/Nga (NC) mice was examined. FK506 ointment (0.1-1%) suppressed the development of dermatitis and was also therapeutically effective against established dermatitis. Increases in CD4-positive T cells (helper T cells), mast cells, eosinophils and immunostaining of interleukin (IL)-4, IL-5 and IgE were confirmed in the skin of the NC mice, and FK506 ointment suppressed all of these changes. Increased plasma IgE was also confirmed in the NC mice, and treatment with FK506 ointment reduced the plasma IgE level. These results suggested that FK506 suppressed the dermatitis by inhibiting the activation of inflammatory cells and by blocking the cytokine network in the skin of the NC mice. The commercially available steroid ointments showed only marginal effect on the development of dermatitis and showed some signs of side effects such as alopecia or atrophy of the skin. The effect of the steroids might have been masked by these side effects because the steroids showed similar inhibitory effects on the skin histopathological changes and the increase of plasma IgE. From these results, FK506 ointment can be expected to be a useful drug for atopic dermatitis.

Milestones in the biology and pharmacology of H1-receptor antagonists

Daniele Bovet's pioneering discovery that a series of compounds possessing anti-histamine activity reduced the symptoms of anaphylaxis provided the proof that histamine plays a pivotal role as a mediator of allergic reactions. Basophils and mast cells are the major sources of histamine in man and they are thus one of the primary effector cells of allergic inflammation. Some H1-receptor antagonists possess a variety of antiinflammatory activity to H1 antagonism in vitro and in vivo. This promising area should be explored further and much remains to be done in the evaluation of the immunomodulatory effects of anti-histamines.

Effects of FK506 and cyclosporin A on proliferation, histamine release and phenotype of murine mast cells

Using mouse peritoneal cavity mast cells, we investigated the effects of FK506 and cyclosporin A (CsA) on cell proliferation and histamine release induced by anti-IgE antibody, calcium ionophore (A23 187), or neuropeptide (substance P). Both FK506 and CsA inhibited cytokine-dependent mast cell proliferation in a dose-dependent manner. The inhibitory effects of these compounds on mast cell proliferation was reversible; the removal of the chemicals from the incubation medium resulted in the reinitiation of mast cell proliferation. Flow cytometric analysis suggested that the inhibitory effect of FK506 and CsA was mostly due to G1/S boundary block, although a significant number of G2-arrested cells were also observed following FK506 treatment. Both FK506- and CsA-treated mast cells showed a similar inhibition of histamine release induced by A23187. However, CsA at higher concentrations inhibited the histamine release induced by anti-IgE antibody or substance P more markedly than FK506. Cellular histamine content was decreased by CsA treatment while FK506 had no effect. The staining properties of peritoneal mast cells changed from connective tissue-type mast cell-like to mucosal mast cell-like during CsA treatment but not during FK506 treatment. Thus FK506 and CsA have different effects on mast cell proliferation as well as histamine release, that might be associated with a phenotypic change of the cells during culture.

Human synovial mast cells. I. Ultrastructural in situ and in vitro immunologic characterization

OBJECTIVE

To examine the ultrastructure of human synovial mast cells in situ, to identify immunologic and nonimmunologic stimuli that activate these cells in vitro, and to quantify a number of preformed and de novo-synthesized mediators.

METHODS

We conducted an ultrastructural study of synovial mast cells in situ and performed immunoelectron microscopy localization of tryptase and chymase. Isolated synovial mast cells were analyzed biochemically, immunologically, and functionally in vitro and compared with cells from human lung, heart, and skin.

RESULTS

Ultrastructural study of synovial tissue revealed mast cells with homogeneously dense, scrolled, crystal, and mixed granules, and lipid bodies in the cytoplasm. A small percentage of mast cells showed evidence of degranulation. Immunoelectron microscopy demonstrated the subcellular localization of tryptase and chymase over granules of > 90% of the mast cells, which were of the MCTC subtype. Isolated synovial mast cells released histamine in response to immunologic (anti-IgE and anti-Fc epsilon receptor I [anti-Fc epsilon RI]) and nonimmunologic (substance P, recombinant human stem cell factor, and 48/80) stimuli, but did not respond to recombinant human C5a in vitro. Synovial mast cells differed from those isolated from other human tissues, in a variety of immunologic and biochemical features. There was a linear correlation between the percentage of histamine secretion and tryptase release (r = 0.79, P < 0.001) induced by cross-linking of Fc epsilon RI. Cross-linking of IgE with anti-IgE on synovial mast cells induced de novo synthesis of prostaglandin D2 (mean +/- SEM 87.5 +/- 4.9 ng/10(6) cells) and of leukotriene C4 (57.6 +/- 17.8 ng/10(6) cells).

CONCLUSION

Mast cells ultrastructurally characterized in situ in synovial tissue were seen to differ from mast cells previously isolated from other human tissues. This raises the possibility that the local microenviroment influences their phenotype. Isolation of mast cells from human synovia can be useful for studying their role and their mediators in patients with arthritis.

FK506 in the treatment of inflammatory skin disease: promises and perspectives

The immunosuppressive macrolide drug FK506 is currently gaining increasing importance in dermatopharmacology. Here, Gunter Michel and colleagues summarize the current state of research into the molecular mechanisms responsible for the functional modulation of cell types other than T cells, particularly epidermal cells, by this drug.

The effects of cyclosporin A and FK506 on proliferation and IL-8 production of cultured human keratinocytes

The present study was conducted to determine whether cyclosporin A (CsA) and FK506 could be effective in inhibiting the proliferation and cytokine secretion of normal human epidermal keratinocytes (NHEK). NHEK proliferation in the presence of CsA and FK506 at the concentrations 10(-9) to 10(-5) M at 24 and 48 h time points was measured colorimetrically by the MTS assay. CsA had inhibitory effects from 10(-6) to 10(-5) M, while FK506 had no effect, except for toxicity at the very highest concentrations (5 x 10(-6) M and higher). NHEK cells spontaneously secrete IL-8 (243.4 +/- 55.5 pg/ml), and this baseline level was augmented by TNF-alpha alone, or synergistically by TNF-alpha and IFN-gamma, which are thought to be secreted by T cells. Neither CsA nor FK506 had any significant effect on either spontaneous or cytokine-stimulated keratinocyte IL-8 production. Therefore, it is most likely that the two drugs indirectly inhibit the keratinocyte inflammatory response through their actions on T cells or other immunocompetent cells.

FK506: therapeutic effects on lupus dermatoses in autoimmune-prone MRL/Mp-lpr/lpr mice

The effects of FK506, a new immunosuppressive agent, on the development of lupus dermatoses were investigated in the autoimmune-prone MRL/Mp-lpr/lpr (MRL/lpr) mouse, which is an animal model for the spontaneous development of skin lesions similar to those of human lupus erythematosus (LE). FK506 reduced the incidence of skin lesions, lupus nephritis, the titre of serum anti-double-stranded DNA antibodies and the massive T cell proliferation. The incidence and magnitude of IgG deposition at the dermoepidermal junction were not changed. These results suggest that FK506 is a promising immunosuppressive agent for the control of autoimmune skin diseases.

Horizons in pharmacologic intervention in allergic contact dermatitis

The treatment of allergic contact dermatitis remains a major challenge. Current management strategies consist of elimination of the allergen when possible and therapy for symptoms with topical or systemic corticosteroids. With increasing exposure of the human skin to environmental antigens and haptens, more selective treatment options are needed. Advances in the elucidation of the skin immune system and of the cellular and molecular events in immunologic processes may allow targeted methods of controlling delayed hypersensitivity reactions. This review focuses on mechanisms of established therapeutic agents and new developments, such as FK 506 (tacrolimus), pentoxifylline, and vitamin D3 derivative, for suppression of any phase of allergic contact dermatitis.

A role for mast cells in the progression of Duchenne muscular dystrophy? Correlations in dystrophin-deficient humans, dogs, and mice

Dystrophin deficiency has been shown to be the underlying cause of Duchenne muscular dystrophy. Although dystrophin-deficient homologous animal models have been identified (dog, mouse, and cat), the clinical expression of the biochemical defect is species-specific. Thus, while the genetics and biochemistry of Duchenne dystrophy is understood, the pathophysiological cascade leading to muscle weakness in only humans and dogs remains obscure. To begin to dissect the pathophysiology at the histological level, we undertook a systematic study of mast cells in normal and dystrophin-deficient muscle. Mast cells have been implicated in the development of fibrosis in other disorders, and progressive fibrosis has been hypothesized to mediate the failure of muscle regeneration in human and dog dystrophin deficiency. Our results show a strong correlation between mast cell content and localization, and the clinico-histopathological progression in humans, dogs and mice. The mast cell increases were disease specific: other dystrophic myopathies with normal dystrophin generally did not show substantial increases in mast cell content or degranulation. Our data suggest that mast cell accumulation and degranulation may cause the grouped necrosis characteristic of dystrophin deficiency in all species.

Tacrolimus. A review of its pharmacology, and therapeutic potential in hepatic and renal transplantation

Tacrolimus (FK 506) is a macrolide immunosuppressant which possesses similar but more potent immunosuppressant properties compared with cyclosporin, inhibiting cell-mediated and humoral immune responses. Like cyclosporin, tacrolimus demonstrates considerable interindividual variation in its pharmacokinetic profile. This has caused difficulty in defining the optimum dosage regimen and has highlighted the usefulness of therapeutic drug monitoring. Most clinical studies with tacrolimus have neither been published in their entirety nor subjected to extensive peer review; there is also a paucity of published randomised investigations of tacrolimus versus cyclosporin, particularly in renal transplantation. Despite these drawbacks, tacrolimus has shown notable efficacy as a rescue or primary immunosuppressant therapy when combined with corticosteroids in adult and paediatric recipients following liver or kidney transplantation. Indeed, graft salvage rates in patients experiencing rejection or drug-related toxicity were > or = 50%, although data in renal transplantation are limited. Compared with cyclosporin as a primary immunosuppressant, tacrolimus showed comparable or greater patient/graft survival rates in liver allograft recipients (where cost savings associated with reduced hospitalisation costs were evident in one study), and comparable patient/graft survival in patients following kidney transplantation. Worthy of note was the efficacy of tacrolimus as a primary immunosuppressant in patients who received en bloc kidney allografts. The incidence of rejection was largely reduced following rescue therapy with tacrolimus and was generally lower (notably for refractory rejection) than that observed for cyclosporin, at least in liver allograft recipients. This was reflected in less need for adjunct immunotherapy including antilymphocyte preparations for the treatment of rejection episodes. The potential for reduction or withdrawal of corticosteroid therapy with tacrolimus appears to be a distinct advantage compared with cyclosporin, and this may be enhanced by the reduced incidence of infectious complications and of hypertension and hypercholesterolaemia reported by some investigators. In other respects, however, the tolerability profile of tacrolimus appears to be broadly similar to that of cyclosporin. Against this background, preliminary data indicate that tacrolimus provides a valuable therapeutic alternative to retransplantation in patients experiencing liver or kidney graft rejection or drug-related toxicity. Pending confirmation of initial randomised studies and preliminary results from large randomised investigations, tacrolimus may well be considered as an alternative primary immunosuppressant to cyclosporin in hepatic (particularly) and renal transplantation. Furthermore, the steroid-sparing effects of tacrolimus, although of benefit to all patient groups, may prove to be of particular worth in children and in en bloc kidney recipients. In these patients tacrolimus may well emerge as the drug of choice.(ABSTRACT TRUNCATED AT 400 WORDS)