207-nm UV light - a promising tool for safe low-cost reduction of surgical site infections. I: in vitro studies

Background

0.5% to 10% of clean surgeries result in surgical-site infections, and attempts to reduce this rate have had limited success. Germicidal UV lamps, with a broad wavelength spectrum from 200 to 400 nm are an effective bactericidal option against drug-resistant and drug-sensitive bacteria, but represent a health hazard to patient and staff. By contrast, because of its limited penetration, ∼200 nm far-UVC light is predicted to be effective in killing bacteria, but without the human health hazards to skin and eyes associated with conventional germicidal UV exposure.

Aims

The aim of this work was to test the biophysically-based hypothesis that ∼200 nm UV light is significantly cytotoxic to bacteria, but minimally cytotoxic or mutagenic to human cells either isolated or within tissues.

Methods

A Kr-Br excimer lamp was used, which produces 207-nm UV light, with a filter to remove higher-wavelength components. Comparisons were made with results from a conventional broad spectrum 254-nm UV germicidal lamp. First, cell inactivation vs. UV fluence data were generated for methicillin-resistant S. aureus (MRSA) bacteria and also for normal human fibroblasts. Second, yields of the main UV-associated pre-mutagenic DNA lesions (cyclobutane pyrimidine dimers and 6-4 photoproducts) were measured, for both UV radiations incident on 3-D human skin tissue.

Results

We found that 207-nm UV light kills MRSA efficiently but, unlike conventional germicidal UV lamps, produces little cell killing in human cells. In a 3-D human skin model, 207-nm UV light produced almost no pre-mutagenic UV-associated DNA lesions, in contrast to significant yields induced by a conventional germicidal UV lamp.

Conclusions

As predicted based on biophysical considerations, 207-nm light kills bacteria efficiently but does not appear to be significantly cytotoxic or mutagenic to human cells. Used appropriately, 207-nm light may have the potential for safely and inexpensively reducing surgical-site infection rates, including those of drug-resistant origin.

DNA damage in bone marrow cells induced by ultraviolet femtosecond laser irradiation

BACKGROUND DATA

Research on the damaging effect of ultraviolet (UV) laser irradiation on the DNA of live organisms is still scarce, although UV lasers are increasingly being used in therapeutics and surgical treatment.

OBJECTIVE

In this study we investigated the effect of new-generation 205-nm femtosecond solid-state laser irradiation on the DNA of murine bone marrow cells in vitro.

MATERIALS AND METHODS

Mouse bone marrow cells in distinct plates were exposed to different doses of 205-nm femtosecond laser irradiation. Single-cell gel electrophoresis, or comet, assay was used for DNA damage measurement.

RESULTS

Our study revealed intensity-dependent genotoxic, genotoxic-cytotoxic, or cytotoxic impact of laser irradiation. The lowest doses we used (0.0175-0.105 J/cm(2)) induced DNA photodamage in irradiated cells directly, medial doses (0.175 and 0.35 J/cm(2)) caused both direct damage of genetic material and irreversible injury of cell's structure whereas the highest doses (1.05-4.2 J/cm(2)) caused the death of most irradiated cells. It is worrisome that even comparatively low doses of irradiation were genotoxic. Exposure to the lowest-intensity irradiation (0.0175 J/cm(2)) caused a highly significant (p < 0.0001) increase in DNA strand breaks of bone marrow cells: the mean ± SEM %DNA score in the comet tail was 9.96 ± 0.56 compared with 3.58 ± 0.80 for controls. Investigation of the effects of low and medial intensities of irradiation showed a dosage-effect relationship of R(2) = 0.84, P < 0.01.

CONCLUSION

New-generation 205-nm femtosecond laser irradiation produced a genotoxic effect by inducing strand breaks in the DNA of murine bone marrow cells in vitro. Research on the possible genotoxic effects of this laser on corneal and skin epithelial cells in vivo is needed.

Process-Induced Cell Injury in Laser Direct Writing of Human Colon Cancer Cells

Matrix-assisted pulsed-laser evaporation direct-write has emerged as a promising technique for biological construct fabrication. The posttransfer cell viability in matrix-assisted pulsed-laser evaporation direct-write depends on various operating conditions such as the applied laser fluence. To date, the effects of operating conditions such as laser fluence, direct-writing height, and cell density on the posttransfer cell viability have not been well elucidated. This study investigates the effects of operating conditions on the posttransfer cell viability in laser direct writing of human colon cancer HT-29 cells. It has been observed that (1) the HT-29 cell viability decreases from 95% to 78% as the laser fluence increases from 258 to 1482 mJ/cm(2), and the posttransfer cell proliferation capacity does not vary significantly as the laser fluence changes; (2) the direct-writing height does not have noticeable effect on the posttransfer cell viability under low laser fluences (258 and 869 mJ/cm(2)). However, a larger height (such as 29.3 mm) led to an almost 8% viability improvement compared with that of 16.6 mm under a high laser fluence (1482 mJ/cm(2)); and (3) the posttransfer cell viability is not dependent on the cell density for a range from 1 × 10(6) to 1 × 10(7) cells/mL.

Histological Changes and Unscheduled DNA Synthesis in the Rabbit Cornea Following 213-nm, 193-nm, and 266-nm Irradiation

PURPOSE

To examine the acute outcome of corneal irradiation in adult rabbits for 193-, 213-, and 266-nm laser wavelengths.

METHODS

Animals were randomly allocated to one of three groups and were treated with 213-nm quintupled Nd:YAG laser, a 193-nm excimer laser, or a 266-nm quadrupled Nd:YAG laser (n = 6 per group, two exposure durations). Thermal damage was assessed histologically and the extent of DNA damage estimated by measuring unscheduled DNA synthesis in corneal epithelial and stromal cells using 3H thymidine autoradiography.

RESULTS

For the 193- and 213-nm groups, irradiation did not induce thermal damage. Moreover, cells displaying unscheduled DNA synthesis represented < 4% of the total cell numbers with no difference between groups (P > .05). By contrast, the 266-nm laser led to stromal melting and vacuolation; unscheduled DNA synthesis levels were elevated over the other groups (P < .05).

CONCLUSIONS

Corneal laser ablation with the 213-nm Nd:YAG laser resulted in similarly low levels of thermal and DNA damage to those produced using the clinically accepted 193-nm excimer laser.

Scattering phenomena effects on growth of 308-nm laser-irradiated bacteria in suspension

In this study we analyzed the effect of 308-nm laser exposure on recovery of irradiated Staphylococcus epidermidis held in liquid after irradiation and before plating. Coexistence of bacterial growth inhibition and stimulation phenomena was observed. Under certain conditions, bacterial recovery was about fivefold higher in irradiated samples than in the controls. The available evidence suggests that the growth inhibition was due to the bactericidal activity of the 308-nm wavelength light, whereas the growth stimulation effect was associated with broadband radiation generated by scattering phenomena in the bacterial suspensions. Spectroscopic investigations revealed that the nutrient broth plays a decisive role in the scattering of laser radiation within the suspension.

Fluence and mutagenic side effects of excimer laser radiation applied in ophthalmology in human lymphocytes in vitro

PURPOSE

To investigate the influence of different fluences in 193 and 248 nm excimer laser radiation on the yields of chromatid and chromosome aberrations induced in human lymphocytes in vitro.

METHOD

Heparinized human blood was exposed to 193 or 248 nm excimer laser radiation. The fluence was gradually increased from 21 to 400 mJ/cm2 in 193 nm (constant total energy of 250 J) and from 150 to 377 mJ/cm2 in 248 nm radiation (constant total energy of 500 J). Chromatid and chromosome aberrations were then analysed microscopically.

RESULTS

The yields of chromatid breaks and achromatic lesions depend on the fluence per pulse. This dependence contains a linear component, indicating a threshold of about 70 mJ/cm2 fluence in 193 nm and of about 250 mJ/cm2 fluence in 248 nm laser radiation. An increase of the yield of dicentric chromosomes could only be observed at the highest fluence tested (377 mJ/cm2) in the 248 nm series. Over 126 mJ/cm2 in 193 nm radiation no lymphocytes could be cultured and therefore no aberrations could be found.

CONCLUSIONS

Our findings show that the fluence of 193 nm and of 248 nm excimer laser radiation has an effect on the yields of chromatid breaks and achromatic lesions in human lymphocytes under in vitro conditions.

Photochemistry of DNA and related biomolecules: quantum yields and consequences of photoionization

The reactions of nucleic acids and constituents, which can be induced by laser UV irradiation, are described. Emphasis is placed on the quantum yields of various stable photoproducts of DNA and model compounds upon irradiation at 193, 248, 254 or 266 nm. In particular, those quantum yields and processes are discussed which involve photoionization as the initial step and occur in aqueous solution under well defined conditions, e.g. type of atmosphere. The efficiencies of some photoproducts, with respect to photoionization using irradiation at 193 or 248 nm, are presented. Radical cations of nucleobases are important sources of damage of biological substrates since they can cause lesions other than dimers and adducts, e.g. strand breakage, abasic sites, crosslinks or inactivation of plasmid and chromosomal DNA. While competing photoreactions, such as hydration, dimerization or adduct formation, diminish the selectivity of the photoionization method, a combination with model studies on pyrimidine- and purine-containing constituents of DNA has brought about an enhanced insight into the reaction mechanisms. The knowledge concerning the lethal events in plasmid and cellular DNA has been greatly improved by correlation with the chemical effects obtained by gamma-radiolysis, vacuum-UV (< 190 nm) and low-intensity irradiation at 254 nm.

DNA damage in cultured human skin fibroblasts exposed to excimer laser radiation

Ultraviolet excimer lasers are being considered for use in a variety of refractive and therapeutic procedures, the long-term biologic consequences of which are unknown. The effect of sublethal doses of 193-nm laser radiation on cellular DNA was examined in cultured human skin fibroblasts. In contrast to 248 nm, treatments with the 193-nm laser radiation below 70 J/m2 did not cause significant pyrimidine dimer formation in the skin cells. This was indicated by the lack of excision repair activities (unscheduled DNA synthesis assay), and further demonstrated by direct analysis of pyrimidine dimers in DNA from irradiated cells. However, a low level of unscheduled DNA synthesis could be detected following irradiation at 193 nm with 70 J/m2. Both the 193-nm and 248-nm radiation were able to induce chromosomal aberrations, as indicated by a micronucleus assay. A dose-dependent increase in micronuclei frequency was observed 48 and 72 h after laser irradiation. These results indicate that exposure of actively replicating human skin fibroblasts to sublethal doses of either 193- or 248-nm laser radiation can result in genotoxicity.

Excimer-laser-induced fluorescence of rabbit cornea: radiometric measurement through the cornea

The laser-induced fluorescence spectrum of rabbit cornea irradiated at ablative intensities was measured. This system directly measured the radiant exposure of fluorescence transmitted through the cornea when the anterior surface of the cornea was irradiated by an ArF excimer laser. Evidence of changing spectral characteristics as a function of total laser dose suggests photochemical changes in the cornea may be occurring. Results are compared with previous data of laser-induced fluorescence in other models and detection schemes.