Polyamine Depletion Following Exposure to DL‐α‐Difluoromethylornithine Both In Vivo and In Vitro Initiates Morphological Alterations and Mitochondrial Activation in a Monomorphic Strain of Trypanosoma brucei brucei

Abstract

DL-alpha-difluoromethylornithine (DFMO), a specific irreversible inhibitor of ornithine decarboxylase (ODC), rapidly depletes cells of intracellular putrescine. When administered to animals and humans, DFMO cures acute infections of trypanosomiasis. In order to determine if the mechanism of drug action is related to initiation of transformation and biochemical alterations subsequent to polyamine depletion, trypanosome morphology and mitochondrial activation were studied in a monomorphic strain of Trypanosoma brucei brucei. Exposure of trypanosomes to DFMO in vivo in infected rodents or in vitro in culture resulted in a depletion of intracellular putrescine and a cessation of cell division without specific cytotoxicity. These events were followed by a transformation of the long slender bloodstream form to a short stumpy form via an intermediate morphology. Putrescine, the product of the ODC reaction, abrogates this effect. When introduced into SDM-79 medium, the intermediate form is capable of further transformation to an "insect" procyclic trypomastigote whereas the long slender form and short stumpy form are not. Short stumpy forms are incapable of binary fission and have lost their infectivity for the vertebrate host. In addition, the mitochondrial marker enzyme, NAD diaphorase, was found only in the short stumpy and intermediate forms. We hypothesize that the short stumpy phenotype may not be a viable stage in the natural transformation of the trypanosome from its mammalian host to the insect vector.

Ornithine Decarboxylase of Stagonospora (Septoria) nodorum Is Required for Virulence toward Wheat

“…ODC is an effective therapeutic target in the treatment of human protozoal pathogens (5-9) and has been proposed as a target in treatment of certain cancers and in the eradication of economically damaging plant pathogenic fungi (10). Inhibition of the polyamine biosynthetic enzyme ODC using the specific and highly potent inhibitor, di-fluoromethylornithine (DFMO) (11), is an effective therapy in treatment of Trypanosomiasis and other diseases caused by Plasmodia, Giardia, and Leishmania (5)(6)(7)(8)(9).…”

Developmental aspects of uridine addition within mitochondrial transcripts of Trypanosoma brucei.

“…In stocks of T. brucei which do not spontaneously * Corresponding author. differentiate to stumpy forms, difluoromethylornithine (DFMO) treatment of slender forms results in a stumpy morphology (1,4,8,11) and a transcript abundance pattern which is very similar to that of spontaneously occurring stumpy forms (8). Polyadenylation is also differentially regulated between life cycle stages, with a larger proportion of mitochondrial transcripts being polyadenylated in procyclic forms than in slender ones (21).…”

Protein methylases in Trypanosoma brucei brucei: activities and response to dl- -difluoromethylornithine

“…In contrast, the activity of protein methylase I1 consistently increased in trypanosomes exposed to DFMO. The differential activities of these enzymes when trypanosomes are exposed to DFMO suggests that these enzymes are under tight control by either the substrate, or the product, or the substrate/product ratio, a significant property for any control mechanism which might participate in the rapid changes of transformation which accompany DFMO administration (Giffin et al, 1986;Giffin & McCann, 1989).…”

“…The production of hypermethylated end-products due to an elevated methylation index and increased activity of protein methylase I1 is one possible mechanism for the major morphological and biochemical changes observed in T. b. brucei cells undergoing DFMO treatment (Bacchi et al, 1983;de Gee et al, 1984;Giffin et al, 1986;Giffin & McCann, 1989). These events feature the development of stumpy forms from slender blood forms and activation of the quiescent mitochondria1 genome to produce cytochromes and other respiratory proteins (Giffin & McCann, 1989;Bienen et al, 1983;Feagin et al, 1986).…”