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

Decoding the Phosphatase Code: Regulation of Cell Proliferation by Calcineurin

Calcineurin, a calcium-dependent serine/threonine phosphatase, integrates the alterations in intracellular calcium levels into downstream signaling pathways by regulating the phosphorylation states of several targets. Intracellular Ca²⁺ is essential for normal cellular physiology and cell cycle progression at certain critical stages of the cell cycle. Recently, it was reported that calcineurin is activated in a variety of cancers. Given that abnormalities in calcineurin signaling can lead to malignant growth and cancer, the calcineurin signaling pathway could be a potential target for cancer treatment. For example, NFAT, a typical substrate of calcineurin, activates the genes that promote cell proliferation. Furthermore, cyclin D1 and estrogen receptors are dephosphorylated and stabilized by calcineurin, leading to cell proliferation. In this review, we focus on the cell proliferative functions and regulatory mechanisms of calcineurin and summarize the various substrates of calcineurin. We also describe recent advances regarding dysregulation of the calcineurin activity in cancer cells. We hope that this review will provide new insights into the potential role of calcineurin in cancer development.

Calcineurin regulates cyclin D1 stability through dephosphorylation at T286

The Calcineurin/NFAT (nuclear factor of activated T cells) pathway plays an essential role in the tumorigenic and metastatic properties in breast cancer. The molecular mechanism of the antiproliferative effect of calcineurin inhibition, however, is poorly understood. We found that calcineurin inhibition delayed cell cycle progression at G1/S, and promoted cyclin D1 degradation by inhibiting dephosphorylation at T286. Importantly, overexpression of cyclin D1 partially rescued delayed G1/S progression, thereby revealing cyclin D1 as a key factor downstream of calcineurin inhibition. Cyclin D1 upregulation is observed in human invasive breast cancers, and our findings indicate that dysregulation of T286 phosphorylation could play a role in this phenomenon. We therefore propose that targeting site specific phosphorylation of cyclin D1 could be a potential strategy for clinical intervention of invasive breast cancer.

Sustained Release of Immunosuppressant by Nanoparticle-anchoring Hydrogel Scaffold Improved the Survival of Transplanted Stem Cells and Tissue Regeneration

The outcome of scaffold-based stem cell transplantation remains unsatisfied due to the poor survival of transplanted cells. One of the major hurdles associated with the stem cell survival is the immune rejection, which can be effectively reduced by the use of immunosuppressant. However, ideal localized and sustained release of immunosuppressant is difficult to be realized, because it is arduous to hold the drug delivery system within scaffold for a long period of time. In the present study, the sustained release of immunosuppressant for the purpose of improving the survival of stem cells was successfully realized by a nanoparticle-anchoring hydrogel scaffold we developed.

Methods: Poly (lactic-co-glycolic acid) (PLGA) nanoparticles were modified with RADA16 (RNPs), a self-assembling peptide, and then anchored to a RADA16 hydrogel (RNPs + Gel). The immobilization of RNPs in hydrogel was measured in vitro and in vivo, including the Brownian motion and cumulative leakage of RNPs and the in vivo retention of injected RNPs with hydrogel. Tacrolimus, as a typical immunosuppressant, was encapsulated in RNPs (T-RNPs) that were anchored to the hydrogel and its release behavior were studied. Endothelial progenitor cells (EPCs), as model stem cells, were cultured in the T-RNPs-anchoring hydrogel to test the immune-suppressing effect. The cytotoxicity of the scaffold against EPCs was also measured compared with free tacrolimus-loaded hydrogel. The therapeutic efficacy of the scaffold laden with EPCs on the hind limb ischemia was further evaluated in mice.

Results: The Brownian motion and cumulative leakage of RNPs were significantly decreased compared with the un-modified nanoparticles (NPs). The in vivo retention of injected RNPs with hydrogel was obviously longer than that of NPs with hydrogel. The release of tacrolimus from T-RNPs + Gel could be sustained for 28 days. Compared with free tacrolimus-loaded hydrogel, the immune responses were significantly reduced and the survival of EPCs was greatly improved both in vitro and in vivo. The results of histological evaluation, including accumulation of immune cells and deposition of anti-graft antibodies, further revealed significantly lessened immune rejection in T-RNPs-anchoring hydrogel group compared with other groups. In pharmacodynamics study, the scaffold laden with EPCs was applied to treat hind limb ischemia in mice and significantly promoted the blood perfusion (~91 % versus ~36 % in control group).

Conclusion: The nanoparticle-anchoring hydrogel scaffold is promising for localized immunosuppressant release, thereby can enhance the survival of transplanted cells and finally lead to successful tissue regeneration.

Emerging drugs for ocular allergy

Ocular allergy is a common condition that usually affects the conjunctiva of the eye and is, therefore, often referred to as allergic conjunctivitis. The severity of the disease can range from mild itching and redness, as seen in seasonal allergic conjunctivitis, to the more severe, sight-threatening forms such as vernal and atopic keratoconjunctivitis. The central mechanism in the pathogenesis of these diseases is IgE-mediated mast cell degranulation and activation of T lymphocytes, eosinophils and conjunctival structural cells. The pharmacotherapy of allergic conjunctivitis consists of several classes of drugs: antihistamines, mast cell stabilisers, dual-acting agents and corticosteroids. None of the available drugs completely abolishes the development of ocular allergy. For this reason, new topical antiallergic/anti-inflammatory agents are currently and continually under clinical trials. This review provides a background to ocular allergic diseases, the medical need for therapy and current and potential new treatments.

Ocular Allergic Disease: Mechanisms, Disease Sub-types, Treatment

Ocular allergy refers to a variety of hypersensitivity disorders that affect the lid, conjunctiva, and/or cornea. Its incidence is estimated at over 20% of the general population in the United States. This review will discuss the various forms of ocular allergy, their pathophysiology, clinical presentation, and treatment. New frontiers in mechanisms, therapy, and management in the office are emphasized throughout.

Effects of immunomodulators on airways hyperresponsiveness to adenosine induced in actively sensitised Brown Norway rats by exposure to allergen

We have recently demonstrated a marked and selective augmentation of the bronchoconstrictor response to adenosine in actively sensitised Brown Norway (BN) rats challenged with ovalbumin (OA). The augmented response is mediated by 5-hydroxytryptamine (5-HT) released as a consequence of mast cell activation. We describe here the effects of budesonide, a clinically used glucocorticosteroid, IMM125, a hydroxyethyl derivative of D-serine-cyclosporine, MLD987, a close analogue of ascomycin and SAR943, a rapamycin derivative, on the hyperresponsiveness to adenosine induced in actively sensitised BN rats by exposure to allergen. Bronchoconstrictor responses to adenosine elicited 3 h following intratracheal (i.t.) instillation of OA, 0.3 mg kg(-1) were reduced dose-dependently by budesonide, IMM125, and MLD987, given i.t. 25 and 1 h prior to allergen challenge. In contrast, SAR943 had no effect on responses to adenosine. Responses to methacholine and 5-HT were minimally affected by these agents. Bronchoconstrictor responses to bradykinin were dose-dependently reduced by budesonide, but unaffected following IMM125, MLD987 or SAR943 pre-treatment. Challenge with OA at a dose of 0.3 mg kg(-1), induced increases in bronchoalveolar lavage (BAL) fluid, leukocyte numbers, eosinophil peroxidase (EPO) and myeloperoxidase (MPO) activities and protein concentration measured 24 h post challenge. Budesonide (1 mg kg(-1) given i.t. 25 and 1 h prior to OA challenge) induced reductions in the BAL fluid parameters of inflammation; IMM125 and MLD987, at a dose of 1 mg kg(-1) had no significant effect whereas SAR943 reduced lymphocyte numbers. Thus, budesonide, IMM125 and MLD987 block the hyperresponsiveness to adenosine induced by allergen challenge in sensitised rats. In the case of budesonide the effect is associated with a powerful, generalised anti-inflammatory effect although an effect directly on the mast cells is also likely. With IMM125 and MLD987, the effect is seen at doses that are not anti-inflammatory and may reflect direct suppression of mast cell activation by these agents.

Role of mast cells in antigen-induced airway inflammation and bronchial hyperresponsiveness in rats

The participation of mast cells in the induction of antigen-induced airway inflammation and bronchial hyperresponsiveness (BHR) to acetylcholine (ACh) was investigated using pharmacological agents and mast cell-deficient rats (Ws/Ws). A significant increase in the number of leukocytes in bronchoalveolar lavage fluid (BALF) and bronchial responsiveness to ACh were observed 24 h after antigen (ovalbumin) challenge in sensitized Brown-Norway (BN) rats. Disodium cromoglycate and terfenadine did not inhibit antigen-induced airway inflammation and BHR in sensitized BN rats. In contrast, cyclosporin A (CyA), FK-506 and prednisolone significantly inhibited antigen-induced airway inflammation and BHR in sensitized BN rats. In addition, disodium cromoglycate, terfenadine and prednisolone, but not CyA and FK-506, inhibited homologous passive cutaneous anaphylaxis in rats. Furthermore, a significant increase in the number of leukocytes in BALF and BHR was also observed in Ws/Ws rats 24 h after inhalation of antigen; however, the magnitude of BHR in Ws/Ws rats was lower than that in the congenic rats. These findings suggest that mast cells play a partial role in the development of antigen-induced BHR in rats and that the induction of BHR is barely suppressed by mast cell stabilizing agents.

The use of two immunosuppressive drugs, cyclosporin A and tacrolimus, to inhibit virus replication and apoptosis in cells infected with feline immunodeficiency virus

An in vitro model of acute and chronic infections with feline immunodeficiency virus (FIV) was used to examine the effect of two immunosuppressive agents, cyclosporin A (CsA) and tacrolimus (also known as FK506), on the inhibition of the replication of the virus and of apoptosis. Both drugs significantly suppressed virus production in a dose-dependent manner in acutely and chronically infected cells. The ability of FK506 to inhibit virus replication was much lower than that of CsA, and was accompanied by marked antiproliferative activity. Treatment of infected cells with either CsA or FK506 did not affect the rise of free intracellular Ca2+ but did protect the cells against apoptosis. Thus, the antiviral activity of CsA and FK506 makes these compounds promising candidates for the development of drugs suitable for the treatment of AIDS.

Inhibitory effect of 1 alpha,25-dihydroxyvitamin D3 on mast cell proliferation and A23187-induced histamine release, also accompanied by a decreased c-kit receptor

Using mouse peritoneal mast cells, we investigated the effects of 1 alpha,25-dihydroxyvitamin D3 (calcitriol) on mast cell proliferation and histamine release. Calcitriol did not affect IL-3/IL-4-dependent mast cell proliferation, but it selectively inhibited stem cell factor-dependent mast cell proliferation and colony formation. Immunohistochemical and immunoblot analyses revealed that calcitriol treatment reduced expression of purified peritoneal mast cell c-kit protein. Using a mast cell line, MC/9, both c-kit protein and c-kit mRNA transcript were seen to be reduced following calcitriol treatment. Calcitriol also reduced histamine release induced by calcium ionophore A23187. In contrast, anti-IgE antibody-dependent histamine release was not affected by calcitriol. Our results indicate that calcitriol inhibits mast cell proliferation and A23187-induced histamine release that might be associated with a decreased expression of c-kit receptor.