M A Mackanos | PubMed Health

PubMed2006

Cellular tolerance to pulsed hyperthermia.

Transient heating of tissues leading to cellular stress or death is very common in medicine and biology. In procedures involving a mild (below 70 degrees C) and prolonged (minutes) heating, such as hyperthermal tumor therapy, the cellular response to thermal stress is relatively well studied. However, there is practically no data on cell viability at higher temperatures and shorter exposures, while the demand for this knowledge is growing. Two main reasons motivate this research: (i) a growing number of laser therapies and surgical procedures involving pulsed heating, and (ii) cellular viability data at short exposures to high temperatures provide a unique insight into the understanding of processes leading to thermally induced cellular death. We designed a technique and performed a study of cell viability under pulses of heat from 0.3 to 100 ms in duration with peak temperatures as high as 130 degrees C. We found that the threshold of cellular death in this range can be accurately approximated by the Arrhenius law with the activation energy of 1 eV, a significantly lower value than was reported in studies based on multisecond exposures.

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PubMed2001

In vivo optical imaging of expression of vascular endothelial growth factor following laser incision in skin.

BACKGROUND AND OBJECTIVE: Laser-tissue interaction studies have focused on laser-induced secondary effects on tissue and the postmortem histological analysis of laser wounds. In this study we addressed wound healing and possible impairment of wound healing due to collateral tissue damage by in vivo imaging of gene expression. STUDY DESIGN/MATERIALS AND METHODS: We used a transgenic mouse model containing a VEGF promoter driving a GFP reporter gene to image VEGF expression in vivo. Twenty-two mice received two full thickness incisions in the dorsal skin: one with the Free Electron Laser (lambda = 6.45 microm, 52.9 mJ/mm(2)) and one with a scalpel. Mice were imaged for GFP expression at 3 days, 1, 2, 3, and 4 weeks. Confocal microscopic imaging was performed at 2 weeks. RESULTS: Peak GFP expression was seen at 2-3 weeks and was localized in fibroblasts. FEL lesions showed more total GFP expression than scalpel lesions but this was only statistically significant (P < 0.05) at 2 and 4 weeks. The full-width half-max (FWHM) of the GFP expression was always larger for the FEL lesion compared to the scalpel lesion but was only statistically significant (P < 0.05) at 2 and 3 weeks. At 2 weeks the extent of the GFP expression in the laser lesion was on average 55 microm beyond that seen in the scalpel lesion but correlated with the number of laser passes. CONCLUSIONS: Feasibility of using transgenic mice carrying photoactive reporter genes for studying cellular process of laser-inflicted wound repair in a noninvasive, in vivo manner was shown. GFP expression mediated by the VEGF promoter in fibroblast showed minimal impairment of wound healing due to the laser.

Animals↗