Vitamin C enhances differentiation of a continuous keratinocyte cell line (REK) into epidermis with normal stratum corneum ultrastructure and functional permeability barrier.

A continuous rat epidermal cell line (rat epidermal keratinocyte; REK) formed a morphologically well-organized epidermis in the absence of feeder cells when grown for 3 weeks on a collagen gel in culture inserts at an air-liquid interface, and developed a permeability barrier resembling that of human skin. By 2 weeks, an orthokeratinized epidermis evolved with the suprabasal layers exhibiting the differentiation markers keratin 10, involucrin, and filaggrin. Granular cells with keratohyalin granules and lamellar bodies, and corneocytes with cornified envelopes and tightly packed keratin filaments were present. Morphologically, vitamin C supplementation of the culture further enhanced the normal wavy pattern of the stratum corneum, the number of keratohyalin granules present, and the quantity and organization of intercellular lipid lamellae in the interstices of the stratum corneum. The morphological enhancements observed with vitamin C correlated with improved epidermal barrier function, as indicated by reduction of the permeation rates of tritiated corticosterone and mannitol, and transepidermal water loss, with values close to those of human skin. Moreover, filaggrin mRNA was increased by vitamin C, and western blots confirmed higher levels of profilaggrin and filaggrin, suggesting that vitamin C also influences keratinocyte differentiation in aspects other than the synthesis and organization of barrier lipids. The unique REK cell line in organotypic culture thus provides an easily maintained and reproducible model for studies on epidermal differentiation and transepidermal permeation.

Dynamic solid-state and tableting properties of four theophylline forms.

Relationships between solid-state, densification and compact properties of theophylline monohydrate (TMO), a mixture of forms (TMIX), and anhydrous polymorphs I (TA-I) and II (TA-II) were evaluated. Solid-state identification of powders and compacts was accomplished by powder X-ray diffraction. A compaction simulator was used to assess deformation behaviour of the powders and to prepare compacts. Porosity and tensile strength of the compacts were determined after 1,24, and 168 h of storage at 22% relative humidity. TA-II was stable, whereas TA-I, TMIX and TMO partially transformed to the TA-II form during storage. All theophylline modifications primarily deformed by plastic flow. Increased water content decreased resistance towards densification and deformation of TMIX and TMO when compared to TA-II or TA-I, demonstrating viscoelasticity. Permanent densification behaviours of TMIX and TMO approached to that of TA-II during storage. Tensile strength of the different theophylline forms were practically equal after 1 h of storage. Tensile strength and porosity of TMIX and TMO compacts increased during the storage. Dynamic solid-state transformations from TMO, TMIX and TA-I to TA-II were associated with parallel changes in their densification and compact properties. The extent of these changes was also dependent on the materials' water content.

Complexation with tolbutamide modifies the physicochemical and tableting properties of hydroxypropyl-beta-cyclodextrin.

The physicochemical and tableting properties of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and its tolbutamide (TBM) complex were studied. The kinetics of TBM/HP-beta-CD inclusion complex formation in solution were determined by the phase solubility method. Solid complexes were prepared by freeze-drying and spray-drying. Water sorption-desorption behaviour of the materials were studied and compacts were made using a compaction simulator. TBM and HP-beta-CD formed 1:1 inclusion complexes in aqueous solution with an apparent stability constant of 63 M(-1). HP-beta-CDs and TBM/HP-beta-CD complexes were amorphous whereas the freeze-dried and spray-dried TBMs were polymorphic forms II and I, respectively. Sorption-desorption studies showed that HP-beta-CDs were deliquescent at high relative humidities. TBM/HP-beta-CD complexes had slightly lower water contents at low relative humidities than the physical mixtures. However, at high humidities their water sorption and desorption behaviours were similar to those of corresponding physical mixtures, indicating a glass transition of the complexed materials. TBM/HP-beta-CD complexes demonstrated a worse compactability than similarly prepared HP-beta-CDs or physical mixtures. Also particle properties that resulted from these preparation methods affected the compactability of the materials. In conclusion, the physicochemical and tableting properties of HP-beta-CD were modified by complexation it with TBM.

Deformation behaviors of tolbutamide, hydroxypropyl-beta-cyclodextrin, and their dispersions.

PURPOSE: The deformation behaviors of compressed freeze-dried and spray-dried tolbutamide/hydroxypropyl-beta-cyclodextrin molecular dispersions were evaluated and compared with similarly prepared tolbutamides (TBM), hydroxypropyl-beta-cyclodextrins (HP-beta-CD) and as their physical dispersions. METHODS: TBM, HP-beta-CD, and their 1:1 molecular dispersions were prepared by freeze-drying and spray-drying, and physical dispersions of TBM and HP-beta-CD were blended. Deformation properties of the prepared materials were evaluated by using a compaction simulator and constants derived from Heckel plots. Molecular dynamics (MD) simulations were performed in order to gain a molecular-level view on the deformation behavior of TBM-HP-beta-CD inclusion complex. RESULTS: The freeze-dried TBM polymorphic form II was less prone to overall particle deformation than the spray-dried stable form I. Formation of molecular dispersions decreased the plastic and elastic behaviors of these materials. Also, the MD simulations showed a reduced molecular flexibility of the TBM-HP-beta-CD inclusion complex, as compared to HP-beta-CD. CONCLUSIONS: The formation of TBM and HP-beta-CD molecular dispersion resulted in more rigid molecular arrangements, which were less prone to deformation than either HP-beta-CDs or physical dispersions. The results showed how differing molecular, solid, particle, and powder state properties affect the deformation properties of the materials studied.