Recognition of the molecular mechanisms of keratinocyte participation in normal skin homeostasis and in pathogenesis may lead to creation of more effective tools for topical application of cosmetics, cosmeceutics and drugs to a particular location within the skin for prevention and therapy of many skin disorders and diseases. For this purpose, the PAMAM G3 dendrimer with amide linkages of 9 biotin molecules and 10 molecules of pyridoxal phosphate (BC-PAMAM) was constructed, and its biological properties and cellular uptake and localization were investigated in the HaCaT keratinocytes. BC-PAMAM is nontoxic for HaCaT cells, as estimated by two assays (Neutral Red and tetrazolium salt reduction, XTT), and revealed low apoptosis induction at up to 50 µM concentration. Fluorescent labeled BC-PAMAM accumulates in HaCaT cells with high efficiency in a concentration–dependent manner. Its mitochondrial localization, estimated as Mander’s colocalization coefficient, is substantially lower than the native PAMAM, and that correlates with its cytotoxicity. The only undesirable, but significant inhibitory effect on cell mobility, evaluated by the wound healing test, was observed at 10 µM BC-PAMAM. The important anti-inflammatory action of BC-PAMAM was clearly documented by decreased production of total IL-1α, assayed with an ELISA test with unstimulated and stimulated by bacterial antigens (LPS and GroEL) HaCaT cells. Thus, it is expected that the biotin pyridoxal phosphate conjugated PAMAM may be considered as a potential carrier for safe delivery of vitamins and drugs into the epidermis.
The intracellular localization and colocalization of a fluorescently labeled G3 amine-terminated cationic polyamidoamine (PAMAM) dendrimer and its biotin–pyridoxal (BC-PAMAM) bioconjugate were investigated in a concentration-dependent manner in normal human fibroblast (BJ) and squamous epithelial carcinoma (SCC-15) cell lines. After 24 hours treatment, both cell lines revealed different patterns of intracellular dendrimer accumulation depending on their cytotoxic effects. Cancer cells exhibited much higher (20-fold) tolerance for native PAMAM treatment than fibroblasts, whereas BC-PAMAM was significantly toxic only for fibroblasts at 50 µM concentration. Fibroblasts accumulated the native and bioconjugated dendrimers in a concentration-dependent manner at nontoxic range of concentration, with significantly lower bioconjugate loading. After reaching the cytotoxicity level, fluorescein isothiocyanate-PAMAM accumulation remains at high, comparable level. In cancer cells, native PAMAM loading at higher, but not cytotoxic concentrations, was kept at constant level with a sharp increase at toxic concentration. Mander’s coefficient calculated for fibroblasts and cancer cells confirmed more efficient native PAMAM penetration as compared to BC-PAMAM. Significant differences in nuclear dendrimer penetration were observed for both cell lines. In cancer cells, PAMAM signals amounted to ~25%–35% of the total nuclei area at all investigated concentrations, with lower level (15%–25%) observed for BC-PAMAM. In fibroblasts, the dendrimer nuclear signal amounted to 15% at nontoxic and up to 70% at toxic concentrations, whereas BC-PAMAM remained at a lower concentration-dependent level (0.3%–20%). Mitochondrial localization of PAMAM and BC-PAMAM revealed similar patterns in both cell lines, depending on the extracellular dendrimer concentration, and presented significantly lower signals from BC-PAMAM, which correlated well with the cytotoxicity.
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