Periodic Charging of Individual Molecules Coupled to the Motion of an Atomic Force Microscopy Tip.

Individual molecules at the edges of self-assembled islands grown on Ag(111) can be deliberately switched in their charge state with the electric field from a scanning-probe tip. Close to the threshold voltage for a charge state transition, periodic switching of the charge is directly driven by the cantilever motion in frequency-modulated atomic force microscopy (AFM), as can be deduced from the signature in the measured frequency shift. In this regime, the integrated frequency shift yields the tip-sample force that is due to a single additional electron. Further, the signature of the dynamic charging response provides information on the electronic coupling of the molecule to the substrate. In analogy to previous experiments on quantum dots, this may also be used in the future to access excited state properties of single molecules from AFM experiments.

Keratinocyte-derived cytokines after photodynamic therapy and their paracrine induction of matrix metalloproteinases in fibroblasts.

BACKGROUND: Recent studies have shown that collagen-degrading matrix metalloproteinase (MMP)-1 and MMP-3 are produced by fibroblasts in response to photodynamic therapy (PDT) with 5-aminolaevulinic acid (ALA) and are considered to be involved in the antisclerotic effects of ALA-PDT observed in the treatment of localized scleroderma. OBJECTIVES: As the primary target of topical PDT is epidermal keratinocytes, we studied the indirect participation of keratinocytes in the production of MMPs and collagen by dermal fibroblasts. METHODS: Keratinocytes were treated with sublethal doses of ALA (100 micromol L(-1)) and red light. The conditioned media were collected 24 h after PDT and primary human fibroblasts were exposed to these media for 6-48 h. Further, a coculture model, keratinocytes seeded on to collagen type IV-coated transwells in the upper chamber and fibroblasts in the lower chamber, was used to study paracrine effects of keratinocytes after PDT. RESULTS: Keratinocyte supernatants after PDT showed a significant, up to 10-fold increase of interleukin (IL)-1alpha and a 2.5-fold increase of tumour necrosis factor-alpha as determined by enzyme-linked immunosorbent assay, while IL-6, MMP-1 and MMP-3 were not altered significantly. Fibroblasts treated with keratinocyte-conditioned media after PDT showed an induction of MMP-1 and MMP-3 protein levels up to threefold in both models used, suggesting that ALA-PDT modulates MMP-1 and MMP-3 production via indirect mechanisms. Collagen type I mRNA expression by fibroblasts was not altered significantly in either model. The addition of an IL-1 receptor antagonist to the keratinocyte-conditioned media completely inhibited the induction of MMP-1 and MMP-3 in stimulated fibroblasts, suggesting that IL-1 is mainly responsible for the observed paracrine effects. CONCLUSIONS: We present evidence that PDT can trigger MMP production in dermal fibroblasts not only directly as has been already shown, but also by an indirect paracrine loop mediated by soluble factors released by epidermal keratinocytes.

Indocyanine green (ICG) and laser irradiation induce photooxidation.

The cellular uptake and subcellular localization of indocyanine green (ICG; absorption band 700-850 nm), and cell survival and ultrastructural changes following ICG-mediated phototherapy were investigated in vitro in four different cell lines derived from human skin (SCL1 and SCL2 squamous cell carcinoma, HaCaT keratinocytes and N1 fibroblasts). The cellular uptake of ICG (1-50 microM, incubation times 1, 4, 24 h) was saturable, highly cumulative and could be inhibited by the addition of 250 microM bromosulphophthalein indicating the involvement of the organic anion transporting polypeptide (OATP). For HaCaT cells, the maximum cellular uptake (Vmax) and the Michaelis constant (K(m)) were 9.9 +/- 1.1 mM and 47 +/- 16 microM, respectively, following a 24-h incubation with ICG. Fluorescence microscopy revealed a cytoplasmic distribution of ICG, probably bound to glutathione S-transferase. Following irradiation with a cw-diode laser (805 nm, 80 mW/cm2) at doses of 24 or 48 J/cm2, the phototoxicity was determined using the MTT assay as a measure of cell viability. For all cell lines, ICG concentrations above 25 microM produced a significant phototoxic effect. The EC50, of ICG for HaCaT cells following irradiation at 24 J/cm2 was 20.1 +/- 3.9 microM. Growth curves showed that even HaCaT cells treated at the EC50 were killed within a week following treatment. Electron microscopy 1 h after ICG-mediated phototherapy revealed cytoplasmic vesiculation, dilation of the rough endoplasmic reticulum, the Golgi complex and the perinuclear cisternae and the beginning of chromatin condensation in the nucleus. These ultrastructural findings are not consistent with a photothermal action of ICG-mediated phototherapy. Taken together with those of previous studies by our group these results support photooxidation as a major cell-killing mechanism.