Soft X-ray microscopy for probing of topical tacrolimus delivery via micelles

Abstract

The penetration of topically applied tacrolimus formulated in micelles into murine skin is reported, measured by X-ray microscopy. Tacrolimus and micelles are probed for the first time by this high spatial resolution technique by element-selective excitation in the C 1s-and O 1s-regimes. This method allows selective detection of the distribution and penetration depth of drugs and carrier molecules into biologic tissues. It is observed that small, but distinct quantities of the drug and micelles, acting as a drug carrier, penetrate the stratum corneum. A comparison is made with the paraffin-based commercial tacrolimus ointment Protopic ® , where local drug concentrations show to be low. A slight increase in local drug concentration in the stratum corneum is observed, if tacrolimus is formulated in micelles, as compared to Protopic ® . This underscores the importance of the drug formulations for effective drug delivery. Time-resolved penetration shows presence of drug in the stratum corneum 100 min after formulation application, with penetration to deeper skin layers at 1000 min. High resolution micrographs give indications for a penetration pathway along the lipid membranes between corneocytes, but also suggest that the compound may penetrate corneocytes.

Improved Skin Permeability after Topical Treatment with Serine Protease: Probing the Penetration of Rapamycin by Scanning Transmission X-ray Microscopy

“…Finally, they were embedded in EPON resin (Serva, Heidelberg, Germany) and cut into 200–300 nm slices with an area of typically 500 μm × 500 μm using an ultramicrotome, similar to previous work. 24 − 26 , 28 , 45 − 47 The samples were deposited on silicon nitride (Si 3 N 4 ) windows (thickness: 100 nm, Silson, UK). All samples were characterized by optical microscopy (MM-400/LU, Nikon) prior to the STXM studies for selecting distinct regions to be investigated.…”

“…Similar to previous work, this pretreatment was performed to model the enzymatic activity, cytokine environment, and barrier alteration typical of inflamed skin. , The samples were treated with a cotton swab for removing the formulation still sticking to the skin surface and subsequently prepared for STXM studies by fixation in 2.5% glutaraldehyde and 1% cacodylate buffer. Finally, they were embedded in EPON resin (Serva, Heidelberg, Germany) and cut into 200–300 nm slices with an area of typically 500 μm × 500 μm using an ultramicrotome, similar to previous work. − ,,− The samples were deposited on silicon nitride (Si 3 N 4 ) windows (thickness: 100 nm, Silson, UK). All samples were characterized by optical microscopy (MM-400/LU, Nikon) prior to the STXM studies for selecting distinct regions to be investigated.…”

Characterization and In Vitro and In Vivo Evaluation of Tacrolimus-Loaded Poly(ε-Caprolactone) Nanocapsules for the Management of Atopic Dermatitis

“…Physicochemically, TAC shows a high molecular mass of 822 Da, pKa 1 = 2.94; pKa 2 = 9.95; pKa 3 = 14.07; log P of 3.96 ± 0.83; and melting point in the range 126-129 • C. It is insoluble in water (4-12 µg/mL), slightly soluble in saturated hydrocarbons, and highly soluble in lipids and organic solvents such as methanol, ethanol, acetone, and propylene glycol (PPG). TAC is available as white crystals and sold as capsules, injectables, and ointments for topical application [10][11][12][13][14].…”

Dermal Delivery of the High-Molecular-Weight Drug Tacrolimus by Means of Polyglycerol-Based Nanogels

“…Thus, several aspects indicate that new alternative formulations could result in significant improvements of current therapeutic strategies. Consequently, new formulations for the delivery of tacrolimus into the skin have been investigated in the last years, including lipid-based nanocarriers [14], liposomes [15], micelles [16,17,18], or transferosomes [19]. In all these works, the investigated nanocarrier formulation improved skin penetration of tacrolimus with respect to the marketed formulation.…”

“…In most previous studies, tacrolimus penetration was investigated using animal skin [18,27], which is anatomically and immunologically different from human skin, with little consideration of skin barrier impairment or skin inflammatory status. In this study, we used excised human skin from two distinct anatomical regions, breast as well as abdomen, and different methods to induce barrier disruption and inflammatory reactions.…”