Pimecrolimus

Pimecrolimus blocks T-lymphocyte activation pathway by inhibiting calcineurin function. ^[1] Pimecrolimus prevents the release of cytokines and pro-inflammatory mediators from mast cells. Pimecrolimus binds to macrophilin-12, the pimecrolimusmacrophilin complex then binds to the cytosolic enzyme calcineurin phosphatase. The pimecrolimus-macrophilin complex prevents the dephosphorylation of the cytoplasmic component of the nuclear factor of activated T cells by inhibiting the action of calcineurin. Pimecrolimus inhibits not only the transcription and synthesis of cytokines from mast cells, but also the release of preformed mediators serotonin and β-hexosaminidase by the inhibition of Fc∈-RI-mediated degranulation and secretion. Pimecrolimus treatment causes a strong down-regulation of the expression of mRNA for genes associated with the macrolactam target pathway and inflammation. ^[2]

The proliferation rate of melanocytes was determined using a colorimetric MTT assay. Melanocytes were plated in 96-well microplates, and each well was pretreated with 100 µl of different concentrations (1, 10, 100, 1,000 nM) of pimecrolimus for 3 days. Then, 50 µL of 5 mg/mL 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) solution was added to each well. The resulting formazan was dissolved with 150 µL dimethylsulfoxide. The absorbance of the samples was measured at a wavelength of 490 nm.

Pimecrolimus is found to be as effective as cyclosporine A following oral ingestion and slightly superior after subcutaneous administration in mice. Pimecrolimus contrasts cyclosporine A and tacrolimus by inhibiting ongoing secondary inflammatory response, but not impairing the primary immune response in allergic contact dermatitis in mice. ^[2] Pimecrolimus is as effective as the high-potency corticosteroid clobetasol-17-propionate in a pig model of allergic contact dermatitis (ACD). Pimecrolimus also effectively reduces skin inflammation and pruritus in hypomagnesemic hairless rats, a model that mimics acute signs of atopic dermatitis. Pimecrolimus shows only a low potential to impair systemic immune responses when compared with tacrolimus as shown in rats in (1) the localized graft-versus-host reaction, (2) the antibody formation to sheep red blood cells, and (3) kidney transplantation.^[3]