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Biochemical and morphological effects of polyamine biosynthesis inhibitors on Trichophyton and Microsporum
1Department of Biology, College of Arts and Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg 24061.
Abstract:
The minimum inhibitory concentrations (MICs) of three known irreversible inhibitors of polyamine synthesis, alpha-difluoromethylornithine (DFMO) and monofluoromethyldehydroornithine methylester (MFMOme), inhibitors of ornithine decarboxylase (ODC) and alpha-difluoromethylarginine (DFMA), an inhibitor of arginine decarboxylase (ADC), were determined for 10 species of dermatophytic fungi. Trichophyton species were generally more sensitive to these inhibitors than Microsporum species. Both genera produced arginase, and treatment of members of either genus with DFMO or DFMA resulted in an inhibition of ODC activity and a depletion of cellular polyamines. However, conversion of labelled DFMA to DFMO, either in vivo or in vitro, could not be demonstrated in spite of both genera producing arginase. The ultrastructure of cells cultured in the presence of either DFMO or DFMA was similar, and revealed disruption of calcium metabolism, an increase in mitochondrial number and alterations to membrane systems. DFMA and DFMO also inhibited sporulation in Microsporum gypseum. Our findings indicate that DFMO limits the growth of dermatophytes by direct inhibition of ODC and lowering of cellular polyamine levels; in contrast, DFMA inhibits polyamine synthesis in an unspecified manner as ADC activity was undetected.
Insights
Alpha-difluoromethylornithine (DFMO) and alpha-difluoromethylarginine (DFMA) inhibit fungal growth by disrupting polyamine synthesis. DFMO directly targets ornithine decarboxylase (ODC), while DFMA
Area of Science:
- Medical Mycology
- Biochemistry
- Antimicrobial Agents
Background:
- Polyamines are essential for fungal growth and development.
- Inhibitors of polyamine synthesis, such as DFMO and DFMA, are potential antifungal agents.
- Dermatophytic fungi are a common cause of superficial fungal infections.
Purpose of the Study:
- To determine the minimum inhibitory concentrations (MICs) of DFMO and DFMA against dermatophytic fungi.
- To investigate the mechanism of action of these inhibitors on fungal polyamine synthesis.
- To assess the effects of these inhibitors on fungal ultrastructure and sporulation.
Main Methods:
- Determination of MICs for 10 dermatophyte species.
- Measurement of ornithine decarboxylase (ODC) and arginine decarboxylase (ADC) activities.
- Analysis of cellular polyamine levels and in vitro/in vivo conversion of labeled DFMA.
- Ultrastructural examination of fungal cells and assessment of sporulation.
Main Results:
- Trichophyton species were more sensitive to DFMO and DFMA than Microsporum species.
- DFMO and DFMA inhibited ODC activity and depleted cellular polyamines in both genera.
- No conversion of DFMA to DFMO was observed, despite arginase production.
- Cellular ultrastructure showed disrupted calcium metabolism, increased mitochondria, and altered membranes.
- DFMA and DFMO inhibited sporulation in Microsporum gypseum.
Conclusions:
- DFMO inhibits dermatophyte growth by directly inhibiting ODC and lowering polyamine levels.
- DFMA inhibits polyamine synthesis through an uncharacterized mechanism, as ADC activity was undetected.
- These inhibitors affect fungal cell metabolism and structure, suggesting potential as antifungal therapies.