The effect of photofrin on DNA strand breaks and base oxidation in HaCaT keratinocytes: a comet assay study

Photodynamic therapy (PDT) kills cells via the production of singlet oxygen and other reactive oxygen species. PDT causes chromosomal damage and mutation to cultured cells. However, DNA damage does not contribute to the phototoxic effect. To study the effect of Photofrin-PDT-induced DNA damage, we used the comet assay in combination with endonuclease III and formamidopyrimidine DNA glycosylase and a human keratinocyte cell line to investigate photogenotoxicity and its prevention by tocopherol (TOC). This study shows that PDT induced DNA damage in HaCaT cells at doses allowing cells to survive 7 days after irradiation. alpha-TOC did not prevent the acute cell lysis caused by Photofrin-PDT but did prevent Photofrin-PDT-induced DNA damage. However, the concentration of TOC that conferred protection (100 microM) was higher than is detected in human serum. Base oxidation was also measured using the comet assay. Although TOC could prevent frank DNA strand breaks caused by PDT, it was unable to decrease the level of base oxidation as revealed by enzyme-sensitive sites. It is suggested that the potential genotoxic risk from laser-PDT could be low, and that topical micro-TOC at a high concentration may be useful in preventing some types of DNA damage without preventing acute photolysis after Photofrin-PDT.     

The phototumorigenic fluoroquinolone lomefloxacin photosensitizes pyrimidine dimer formation in human keratinocytes in vitro

The fluoroquinolone antibiotic lomefloxacin is phototoxic, photogenotoxic, photomutagenic and photosensitizes tumorigenesis in mouse skin. We have used T4 endonuclease V to demonstrate that lomefloxacin photosensitizes pyrimidine dimer formation in a human keratinocyte line (HaCaT). A possible mechanism for this effect would be triplet-triplet energy transfer. However, there is indirect evidence that the lomefloxacin triplet yield is very low, making this reaction less likely. The finding that lomefloxacin photosensitizes production of highly mutagenic pyrimidine dimers correlates with its ability to initiate skin tumor formation in mice. Until the potential of other fluoroquinolones to photosensitize dimer formation is explored it may be unadvisable to prescribe these antibiotics to patients with defective DNA repair capacity (e.g. xeroderma pigmentosum).     

Simultaneous measurement of anomalous group-velocity dispersion and nonlinear coefficient in optical fibers using soliton-effect compression

We present a novel and simple method to measure both the value of the second-order dispersion coefficient and the nonlinear coefficient in optical fibers. This method is based on the higher-order soliton-effect pulse compression phenomenon and is valid for dispersion values greater than 0.5 ps/km/nm. A non-zero dispersion-shifted fiber, a standard single-mode fiber and a highly-dispersive highly-nonlinear fiber have been measured using this method.     

Environmentally stable picosecond ytterbium fiber laser with a broad tuning range

We demonstrate a widely tunable passively mode-locked fiber laser operating at a fundamental frequency of 80 MHz with an output power of 90 mW. The laser is capable of generating 5-ps pulses in the region 1010-1064 nm. A strong mode-locking mechanism promoted by frequency-shifted feedback allows us to operate in simultaneous Q-switched and mode-locked regimes and to obtain peak power in excess of 1.2 kW.     

Molecular view of the isothermal transformation of a stable glass to a liquid

We have used neutron reflectivity to measure translational motion on the nanometer length scale in exceptionally stable glasses of tris(naphthylbenzene). These glasses are prepared by vapor deposition onto a substrate held somewhat below the glass transition temperature (T(g) = 342 K). When the most stable samples are annealed at 345 K, no translational motion is observed on the 12 nm length scale for over 10,000 s and full mixing requires more than 60,000 s. For comparison, the equilibrium supercooled liquid mixes in 1000 s at this temperature and on this length scale. These measurements provide insight into the mechanism by which a stable glass transforms into a liquid. "Melting" of the stable glass appears to occur by the growth of liquid regions into the surrounding glassy matrix, perhaps by a surface-initiated growth process. At 345 K, translational motion in the stable glass is at least 100 times slower than motion in the supercooled liquid.     

Structural Determinants of Opioid Activity in the Orvinols and Related Structures. Ethers of 7,8‐Cyclopenta‐Fused Analogs of Buprenorphine

A series of ethers of 7,8‐cyclopenta‐fused analogs of the orvinols related to buprenorphine were prepared and evaluated in opioid‐binding and functional assays. Comparison of the ethyl ethers 4b and 5b with the parent alcohols 4a and 5a , respectively, in both the (5′R) (=5′β) and (5′S) (=5′α) series, shows that the 20‐OH group in the orvinols (corresponding to 5′‐OH of 4 and 5 ) is not crucial for opioid activity, although in the [³⁵S]GTPγS assay, the 5′β‐ethyl ether 4b had 80‐fold greater κ‐agonist potency than its epimer 5b . Increasing the size of the 5′β‐OR group has a major effect on μ‐agonist efficacy and potency, a more modest effect on δ‐efficacy, and no effect on κ‐activity. These data show that μ‐ and δ‐agonist efficacy is favoured by lipophilic binding in the area occupied by the ^tBu in the lowest‐energy conformation of buprenorphine, and that κ‐agonist binding may involve interaction with an H‐bond‐donor group in that region.     

In vitro phototoxicity of nifedipine: sequential induction of toxic and non-toxic photoproducts with UVA radiation.

Anecdotal reports suggest that the dihydropyridine calcium antagonist, nifedipine (NIF), may be phototoxic in human skin. We have studied NIF phototoxicity in vitro using UVA fluorescent tubes (Sylvania PUVA). NIF was phototoxic to Candida albicans and induced photohaemolysis both with NIF present during irradiation and with pre-irradiated drug. In V79 hamster fibroblasts, NIF (10 micrograms ml-1) was phototoxic MTT assay) 24 h after irradiation (0-112 kJ m-2); at 7.5 kJ m-2, about 70% of cells were damaged whilst at 37.5 kJ m-2, only about 45% of cells were damaged. A similar pattern was seen with pre-irradiated NIF. Absorption spectroscopy showed that the NIF absorption maximum (Amax approximately 340 nm) blue-shifted to 314 nm at low UVA doses (7.5 kJ m-2 or less) and red-shifted to 345 nm at higher doses (isosbestic point, 325 nm). Thin layer chromatography of irradiated NIF showed a single photoproduct (PP1; Amax approximately 314 nm) formed at 7.5 kJ m-2 or less which disappeared at higher UVA doses to give further photoproducts. PP1 was highly dark toxic to V79 cells (50% damage at about 5 micrograms ml-1) but PP1 pre-irradiated with UVA was non-toxic. Preliminary gas chromatography-mass spectroscopy studies suggest that PP1 is the nitroso derivative of NIF. These results indicate that NIF phototoxicity in vitro is partially mediated by initial formation of a toxic photoproduct (PP1) but, paradoxically, subsequent UVA irradiation may reduce phototoxicity. The NIF concentrations required to induce in vitro phototoxicity are much greater than therapeutic plasma levels. Unless there is skin accumulation of NIF or PP1, our in vitro results suggest that NIF may not be an important skin-photosensitizing agent in vivo.     

Monotonely Cauchy locally-solid topologies

The lattice of monotonely Cauchy (=pre-Lebesgue) locally solid topologies on a given lattice-ordered group is studied. Indentifying topologies agreeing on order bounded sets this lattice becomes a complete Boolean algebra isomorphic to the subalgebra of the lattice's complemented members and realizable as a Boolean algebra of order projections. Some consequences of these results are indicated.Work done while Tim Traynor was visiting professor at University of Napoli sponsored by CNR-Italia.