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Published on: April 7, 2011
Metabolism of 5-methoxypsoralen by Saccharomyces cerevisiae
E Morichetti1, C Ceragioli, E Cundari
1Istituto di Mutagenesi e Differenziamento C.N.R., Pisa, Italy.
Abstract:
Incubation of methoxypsoralen (5-MOP) in the presence of diploid yeast cells (Saccharomyces cerevisiae) before UV-A exposure leads to an incubation-time dependent decrease of photoinduced genotoxic effects. The reduction in photoinduced genotoxicity is stronger in cells grown in the presence of 20% glucose and containing high levels of cytochrome P-450 than in cells grown in the presence of 0.5% glucose and containing undetectable levels of cytochrome P-450. Inhibition of P-450 activity by specific inhibitors, such as tetrahydrofuran and metyrapone, strongly affects the observed decrease in 5-MOP genotoxicity, indicating the involvement of P-450 in 5-MOP metabolism. As demonstrated by spectrophotometric and chromatographic (HPLC) analysis during incubation of 5-MOP with P-450 containing yeast cells, 5-MOP gradually disappears from the cell supernatant of the incubation mixture. The reduction in the chromatographic peak corresponding to 5-MOP is accompanied by the appearance of a new peak that probably corresponds to a metabolite. As shown by the use of P-450 specific inhibitors, the metabolite appears to be due to P-450 mediated 5-MOP metabolisation. Its UV absorption spectrum suggests an alteration of the pyrone moiety of the 5-MOP molecule.
Insights
Methoxypsoralen (5-MOP) incubation with yeast cells before UV-A exposure reduces genotoxicity. This protective effect is linked to cytochrome P-450 metabolism of 5-MOP.
Area of Science:
- Biochemistry
- Molecular Biology
- Photobiology
Background:
- Methoxypsoralen (5-MOP) is a photosensitizing agent.
- UV-A exposure in the presence of 5-MOP can induce genotoxic effects.
- Yeast cells (Saccharomyces cerevisiae) can be used as a model system.
Purpose of the Study:
- To investigate the effect of 5-MOP incubation with yeast cells prior to UV-A exposure on photoinduced genotoxicity.
- To explore the role of cytochrome P-450 in the metabolism of 5-MOP and its influence on genotoxicity.
Main Methods:
- Incubation of diploid yeast cells with 5-MOP.
- UV-A irradiation.
- Assessing genotoxic effects.
- Culturing yeast cells in media with varying glucose concentrations (0.5% vs. 20%).
- Using cytochrome P-450 inhibitors (tetrahydrofuran, metyrapone).
- Spectrophotometric and High-Performance Liquid Chromatography (HPLC) analysis.
Main Results:
- Incubation time with 5-MOP before UV-A exposure decreased photoinduced genotoxicity in a time-dependent manner.
- The reduction in genotoxicity was more pronounced in yeast cells with high cytochrome P-450 levels (grown in 20% glucose).
- Inhibition of cytochrome P-450 activity reduced the protective effect against 5-MOP genotoxicity.
- HPLC and spectrophotometry showed the disappearance of 5-MOP and the appearance of a metabolite, indicating P-450 mediated metabolism.
- The metabolite's UV spectrum suggested an alteration in the pyrone moiety of 5-MOP.
Conclusions:
- Cytochrome P-450 plays a significant role in the metabolism of 5-MOP in yeast cells.
- Metabolism of 5-MOP by cytochrome P-450 leads to a reduction in its photoinduced genotoxicity.
- Yeast cells expressing cytochrome P-450 can metabolize 5-MOP, mitigating its harmful effects.
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