Growth inhibition of pathogenic yeast isolates by alpha-difluoromethylornithine: an inhibition of ornithine decarboxylase

Spermidine-analogous triamines suppressed the growth of Candida albicans

We examined the antifungal activity of various synthetic triamines on several fungi. Among various triamines having a general structure H2N(CH2)aNH(CH2)bNH2 (a=2-5, b=3-8), some triamines (a=4 or 5) showed inhibitory effect on the growth of Candida albicans and C. tropicalis. Determination of the minimum inhibitory concentrations (MICs) of these triamines on C. albicans showed that triamine 4-8 (a=4, b=8) and triamine 5-8 had strong antifungal activity. Further analysis revealed that the antifungal effect of triamine 4-8 was fungistatic and the antifungal effect was diminished by the addition of spermidine, a physiological triamine, to the medium. These results suggested that triamine 4-8 is antagonistic to spermidine and the antifungal activity is due to the suppression of the action of intrinsic polyamines. On the agar medium, C. albicans formed microcolonies even in the presence of triamine 4-8 by long cultivation. We then observed the form of C. albicans using microscope and found that the cells cultivated with triamine 4-8 were round, similar to the yeast form, while most of the cells on the agar medium without triamine 4-8 were hyphal form. Subsequently, we investigated the synergistic effect of two compounds with triamine 4-8, cyclohexylamine and dl-α-difluoromethylornithine which are inhibitors of enzymes involving in the biosynthesis of physiological polyamines such as spermidine. The results showed that the antifungal activity of triamine 4-8 increased by the addition of these enzyme inhibitors.

Biogenic amines in rhizobia and legume root nodules

Root-nodule bacteria (rhizobia) are of great importance for nitrogen acquisition through symbiotic nitrogen fixation in a wide variety of leguminous plants. These bacteria differ from most other soil microorganisms by taking dual forms, i.e. a free-living form in soils and a symbiotic form inside of host legumes. Therefore, they should have a versatile strategy for survival, whether inhabiting soils or root nodules formed through rhizobia-legume interactions. Rhizobia generally contain large amounts of the biogenic amine homospermidine, an analog of spermidine which is an essential cellular component in most living systems. The external pH, salinity and a rapid change in osmolarity are thought to be significant environmental factors affecting the persistence of rhizobia. The present review describes the regulation of homospermidine biosynthesis in response to environmental stress and its possible functional role in rhizobia. Legume root nodules, an alternative habitat of rhizobia, usually contain a variety of biogenic amines besides homospermidine and the occurrence of some of these amines is closely associated with rhizobial infections. In the second half of this review, novel biogenic amines found in certain legume root nodules and the mechanism of their synthesis involving cooperation between the rhizobia and host legume cells are also described.

Trichomonas vaginalis: characterization of ornithine decarboxylase

Ornithine decarboxylase (ODC), the lead enzyme in polyamine biosynthesis, was partially purified from Trichomonas vaginalis and its kinetic properties were studied. The enzyme appears to be of special significance in this anaerobic parasite, since the arginine dihydrolase pathway generates ATP as well as putrescine from arginine. ODC from T. vaginalis had a broad substrate specificity, decarboxylating ornithine (100%), lysine (1.0%) and arginine (0.1%). The enzyme had a pH optimum of 6.5, a temperature optimum of 37 degrees C and was pyridoxal 5'-phosphate-dependent. Attempts to separate ornithine- from lysine-decarboxylating activity by thermal-stability and pH-optima curves were not successful. Although Km values for ornithine and lysine were 109 and 91 microM respectively, and the Vmax values for these substrates were 1282 and 13 nmol/min per mg of protein respectively, the most important intracellular substrate is ornithine, since intracellular ornithine levels are 3.5 times those of lysine and extracellular putrescine levels are 7.5 times those of cadaverine. Ornithine was also an effective inhibitor of lysine-decarboxylating activity (Ki 150 microM), whereas lysine was relatively ineffective as inhibitor of ornithine-decarboxylating activity (Ki 14.5 mM). Crude ODC activity was localized (86%) in the 43,000 g supernatant and 3303-fold purification was obtained by (NH4)2SO4 salting and DEAE-Sephacel, agarose-gel and hydroxyapatite chromatography steps. The enzyme bound difluoro[3H]methylornithine ([3H]DFMO) with a ratio of drug bound to activity of 2500 fmol/unit, where 1 unit corresponds to 1 nmol of CO2 released from ornithine/min. The enzyme had a native M(r) of 210000 (gel filtration), with a subunit M(r) of 55,000 (by SDS/PAGE), suggesting that the trichomonad enzyme is a tetramer. From the subunit M(r) and binding ratio of DFMO, there is about 137 ng of ODC per mg of T. vaginalis protein (0.013%). The significant amount of ODC protein present supports the view that putrescine synthesis in T. vaginalis plays an important role in the metabolism of the parasite.

Polyamine depletion and growth inhibition of Cryptococcus neoformans by alpha-difluoromethylornithine and cyclohexylamine

The ability of two known inhibitors of polyamine synthesis alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (ODC), and cyclohexylamine, an inhibitor of spermidine synthase, to inhibit the in vitro growth and polyamine synthesis of clinical isolates of Cryptococcus neoformans was examined. Treatment of C. neoformans with either DFMO or cyclohexylamine resulted in depletion of cellular polyamines and inhibition of growth. Cryptococcus neoformans was shown to lack detectable spermine and to require high concentrations of spermidine, but not putrescine, for growth. The growth inhibition by DFMO and cyclohexylamine was reversed by exogenous polyamines. These findings document the ability of cyclohexylamine and DFMO to inhibit polyamine synthesis and growth in clinically important isolates of C. neoformans.

Eflornithine. A new drug in the treatment of sleeping sickness

Eflornithine (alpha-difluoromethylornithine; DFMO) is a recently developed drug against African trypanosomiasis (sleeping sickness). After a short description of trypanosomiasis and the current treatment, the mechanism of action of eflornithine is discussed, some clinical data is given and attention is paid to recently discovered analogues of eflornithine. Some examples of combination therapy with eflornithine and possible applications are mentioned.