Effects of trypanocides on the fine structure of target organisms

Particularities of mitochondrial structure in parasitic protists (Apicomplexa and Kinetoplastida)

Without mitochondria, eukaryotic cells would depend entirely on anaerobic glycolysis for ATP generation. This also holds true for protists, both free-living and parasitic. Parasitic protists include agents of human and animal diseases that have a huge impact on world populations. In the phylum Apicomplexa, several species of Plasmodium cause malaria, whereas Toxoplasma gondii is a cosmopolite parasite found on all continents. Flagellates of the order Kinetoplastida include the genera Leishmania and Trypanosoma causative agents of human leishmaniasis and (depending on the species) African trypanosomiasis and Chagas disease. Although clearly distinct in many aspects, the members of these two groups bear a single and usually well developed mitochondrion. The single mitochondrion of Apicomplexa has a dense matrix and many cristae with a circular profile. The organelle is even more peculiar in the order Kinetoplastida, exhibiting a condensed network of DNA at a specific position, always close to the flagellar basal body. This arrangement is known as Kinetoplast and the name of the order derived from it. Kinetoplastids also bear glycosomes, peroxisomes that concentrate enzymes of the glycolytic cycle. Mitochondrial volume and activity is maximum when glycosomal is low and vice versa. In both Apicomplexa and trypanosomatids, mitochondria show particularities that are absent in other eukaryotic organisms. These peculiar features make them an attractive target for therapeutic drugs for the diseases they cause.

Diphenyl furans and aza analogs: effects of structural modification on in vitro activity, DNA binding, and accumulation and distribution in trypanosomes

Human African trypanosomiasis is a devastating disease with only a few treatment options, including pentamidine. Diamidine compounds such as pentamidine, DB75, and DB820 are potent antitrypanosomal compounds. Previous investigations have shown that diamidines accumulate to high concentrations in trypanosomes. However, the mechanism of action of this class of compounds remains unknown. A long-hypothesized mechanism of action has been binding to DNA and interference with DNA-associated enzymes. The fluorescent diamidines, DB75 and DB820, have been shown to localize not only in the DNA-containing nucleus and kinetoplast of trypanosomes but also to the acidocalcisomes. Here we investigate two series of analogs of DB75 and DB820 with various levels of in vitro antitrypanosomal activity to determine whether any correlation exists between trypanosome accumulation, distribution, and in vitro activity. Despite wide ranges of in vitro antitrypanosomal activity, all of the compounds investigated accumulated to millimolar concentrations in trypanosomes over a period of 8 h. Interestingly, some of the less potent compounds accumulated to concentrations much higher than those of more potent compounds. All of the compounds were localized to the DNA-containing nucleus and/or kinetoplast, and many were also found in the acidocalcisomes. Accumulation in the nucleus and kinetoplast should be important to the mechanism of action of these compounds. The acidocalcisomes may also play a role in the mechanism of action of these compounds. This investigation suggests that the extent of accumulation alone is not responsible for killing trypanosomes and that organelle-specific accumulation may not predict in vitro activity.

Cytotoxicity of (2,2':6',2''-terpyridine)platinum(II) complexes to Leishmania donovani, Trypanosoma cruzi, and Trypanosoma brucei

A range of (2,2':6',2''-terpyridine)platinum(II) complexes are shown to possess antiprotozoal activity in vitro against Leishmania donovani, Trypanosoma cruzi, and Trypanosoma brucei,the causative organisms of tropical diseases leishmaniasis and trypanosomiasis. The best compounds caused 100% and 78% inhibition of growth of the intracellular amastigote forms of L. donovani and T. cruzi, respectively, at a concentration of 1 microM and 100% inhibition of growth of the bloodstream trypomastigote forms of T. brucei at a concentration of 0.03 microM. The results obtained with complexes in which the fourth ligand to platinum(II) is capable of being substituted with a substitution inert hydroxyethanethiolate complex are compared. The ammine complexes show high antiprotozoal activity suggesting that the trans influence of the 2,2':6',2''-terpyridine ligand has a profound effect on the ease of displacement of the fourth ligand in (2,2':6',2'' -terpyridine)platinum(II) complexes, although nonbonded interaction between the ammine ligand and the 6 and 6' ' hydrogens probably also weakens the ligation to Pt(II).

Sequence-selective binding to DNA of bis(amidinophenoxy)alkanes related to propamidine and pentamidine

The DNA sequences targeted by a complete homologous series of aromatic diamidines have been determined at single-nucleotide resolution via protection from cutting by the endonucleases DNase I, DNase II and micrococcal nuclease. Propamidine, pentamidine and to a lesser extent hexamidine bind selectively to nucleotide sequences composed of at least four consecutive A-T base pairs. In contrast, the binding to DNA of butamidine, heptamidine, octamidine and nonamidine is poorly sequence-selective. Sequences composed of only three consecutive A-T base pairs do not afford a potential binding site for propamidine or the longer homologues, and none of the drugs tolerate the presence of a G-C base pair within the binding site. Experiments with DNA molecules containing inosine in place of guanosine and 2,6-diaminopurine in place of adenine reveal that the lack of binding of propamidine to GC-containing sites is attributable to an obstructive effect of the exocyclic 2-amino group of guanosine. The present data support the view that the local conformation of the double helix (in particular the width of the minor groove) plays a dominant role in the binding reaction and that the capacity of diamidines to recognize AT-rich sequences selectively varies considerably depending on the length of the alkyl chain. The evidence indicates that binding to AT-tracts in DNA must play a role in the biological activity of these diamidines, but there is no simple correlation between binding and pharmacological efficacy.

Uptake of diamidine drugs by the P2 nucleoside transporter in melarsen-sensitive and -resistant Trypanosoma brucei brucei

The African trypanosome, Trypanosoma brucei brucei, possesses at least two nucleoside transporter systems designated P1 and P2, the latter being implicated in the selective uptake of melaminophenyl arsenical drugs. Since arsenical-resistant trypanosomes show cross-resistance in vivo to aromatic diamidines, we have investigated whether these drugs are also substrates for the P2 nucleoside transporter. In melarsen-sensitive T. b. brucei, the diamidines, including the commonly used trypanocides, pentamidine and berenil, were found to abrogate lysis induced by the P2 transport of melarsen oxide in vitro. Measurement of [ring-3H]pentamidine transport in melarsen-sensitive T. b. brucei, demonstrated that uptake is carrier-mediated, with a Km of 0.84 microM and a Vmax of 9.35 pmol s-1 (10(8) cells)-1. Pentamidine transport appears to be P2-mediated in these cells, as pentamidine strongly inhibited uptake of [2',5',8-3H]adenosine by the P2 transporter, with a Ki of 0.56 microM. Furthermore, [ring-3H]pentamidine transport was blocked by a number of P2 transporter substrates and inhibitors, as well as by other diamidine drugs. Analysis of the uptake of pentamidine and other diamidines in melarsen-resistant trypanosomes in vitro and in vivo, which also show differential levels of resistance to these compounds in vivo, indicated that P2 transport was altered in these cells and that accumulation of these drugs was markedly reduced.

Gel electrophoretic analysis of cellular and secreted proteins from resting and activated rat alveolar macrophages treated with pentamidine isethionate

Pneumocystic carinii pneumonia, which is a major cause of death among patients suffering from acquired immunodeficiency syndrome, has often been treated successfully with pentamidine isethionate. This study examines pentamidine effects on cellular and secreted proteins from rat alveolar macrophages by two-dimensional gel electrophoresis and computerized image analysis. Over 100 secreted proteins were detected by fluorography. Fluorography showed pentamidine diminished tumor necrosis factor and interleukin-1 release along with other proteins. Effects of combined bacterial lipopolysaccharide and pentamidine were more pronounced on secreted versus cellular proteins in protein amount and pattern difference. Thus pentamidine exhibited a general repressive effect on cellular and secreted protein expression in resting and activated macrophages.

Pentamidine congeners. 3. Crystal structure and molecular modeling studies of trans-1,4-bis(4-amidinophenoxy)-2-butene

X-ray diffraction was used to confirm the geometry of trans-1,4-bis(4-amidinophenoxy)-2-butene dihydrochloride dihydrate (trans-butenamidine). trans-Butenamidine is a semirigid analogue of pentamidine that has demonstrated good anti-Pneumocystis carinii activity in rats. Molecular modeling studies revealed that unlike pentamidine or propamidine, trans-butenamidine does not discriminate between AT and TA sequences in its binding to the minor groove of DNA. Crystal data: [C18H22N4O2(2+)][Cl(-)]2[H2O]2, triclinic space group, P1, a = 9.443(1) A, b = 11.400(1) A, c = 11.919(1) A, alpha = 62.19(1) degree, beta = 81.10(1) degree, gamma = 72.19(1) degree, V = 1080.3(3) A3, Z = 2, R = 0.054 for 1149 observed reflections with I > 3 sigma (1).

Health effects and exposure assessment of aerosolized pentamidine handlers

Nurses administering aerosolized pentamidine (AP) were studied to determine any effect AP may be having on their health. Exposure was determined by each nurse's self-report of treatment given as recorded in a daily log and personal and area pentamidine sampling. Outcome measures were self-reported symptoms recorded in a daily log and peak expiratory flow rates (PEFR) and cross-shift and cross-week pulmonary function tests (PFTs). Results revealed no dose-response effect of pentamidine exposure on cross-shift and cross-week PFTs. However, declines in cross-shift PEFRs, diffusion capacities, and increased symptom complaints were observed for a subset of the study population. This suggested that outcomes were modulated by host factors (history of hay fever and allergy) as well as exposure doses. Treatment both efficacy in containing fugitive AP aerosol was also corroborated as a means of minimizing worker exposure.

Pentamidine Congeners 1: Synthesis of Cis- and Trans-Butamidine Analogues As Anti-Pneumocystis carinii Pneumonia Agents

Butamidine analogues possessing unsaturation in the ether bridge between the bisamidinophenyl or bisimidazolinophenyl functionalities have been synthesized as semirigid congeners of pentamidine. These compounds demonstrated good anti-P. carinii pueumonia activity in a rat model of the disease.

Efficacy of engineering controls in reducing occupational exposure to aerosolized pentamidine

Aerosolized pentamidine administration may pose potential risks to health care workers exposed to fugitive drug and to infectious respiratory pathogens (eg, tuberculosis) generated by pentamidine-induced cough. Classic infection control methods may be applied to this problem, although the effectiveness of these measures in mitigating environmental pentamidine exposure is unknown. Lack of data fully characterizing pentamidine's mechanism of action or potential mutagenicity, carcinogenicity, or teratogenicity raises concern and suggests worker exposed and environmental contamination be minimized. We report herein on the efficacy of an aerosol containment hood in containing fugitive pentamidine aerosol during administration.

Pentamidine: a review

With the advent of the acquired immunodeficiency syndrome (AIDS), the therapeutic importance of pentamidine isethionate has increased greatly. This review summarizes the pharmacology, clinical experience in the treatment of Pneumocystis carinii pneumonia, and toxicity of pentamidine. Data are conflicting as to whether pentamidine is more or less effective than trimethoprim-sulfamethoxazole (TMP-SX) for the treatment of P carinii pneumonia in individuals with AIDS, but due to its toxicity and expense, it is considered as second-line therapy for P carinii pneumonia by many authorities. Hypoglycemia has been encountered in up to 27%, and nephrotoxicity in 25%, of treatment courses with pentamidine. In an attempt to circumvent the toxicities associated with parenteral administration, aerosolized delivery has been evaluated for both therapy and prevention of P carinii pneumonia. Aerosolized pentamidine, on the basis of early clinical results, convenience, and low toxicity, is being used extensively to prevent P carinii pneumonia in individuals at high risk. Relapses occur, however, and pneumothorax may be more common in those using this form of prophylaxis. Aerosolized pentamidine should not be used as sole therapy for acute P carinii pneumonia.

Lipid peroxidation as a component in trypanocidal drug action

A representative range of trypanocides was examined for ability to induce lipid peroxidation in Trypanosoma rhodesiense in vitro. Because of drug interference, thiobarbituric acid (TBA) chromogen production and diene conjugation U.V. absorbance assay methods were less satisfactory that GLC analysis of polyenoic fatty acid loss. Docosohexanoic acid (22:6) content was specifically reduced to a highly significant degree by treatment with Ethidium or the lipid-soluble 4-demethoxydaunorubicin.

Isometamidium in pigs: disposition kinetics, tissue residues and adverse reactions

The disposition and adverse effects of the anti-trypanosomal drug isometamidium in pigs were evaluated. Following intramuscular administration of the drug at doses of 0.5, 15 and 35 mg kg-1, the drug was rapidly absorbed within 15 to 30 minutes to reach maximum plasma concentrations of 12 to 477 (n = 6), 302 to 655 (n = 4) and 1620 (n = 1) ng ml-1, respectively. No drug was detectable in plasma (less than 5 ng ml-1) 24 hours after drug administration at the three doses used. The half-lives of disappearance of the drug from plasma during the terminal phase were 7.12 h for the pigs given a dose of 15 mg kg-1, and 7.20 h for the pig which received a dose of 35 mg kg-1. At all the intramuscular injection sites, high drug concentrations were found six weeks after administration. The most dramatic adverse reactions observed were: one death after intramuscular administration at a dose of 35 mg kg-1 to two animals, and two deaths after intravenous administration at a dose of 2 mg kg-1 to two animals. For all these cases, the immediate cause of death was acute cardiovascular collapse. Biochemical analyses and gross and histological examinations showed that the animals that tolerated the high doses of 15 and 35 mg kg-1 given intramuscularly had extensive and severe tissue damage at the injection sites. Significant increases in plasma gamma-glutamyltransferase and alanine aminotransferase following drug administration suggested a degree of hepatobiliary damage.

[African trypanosomes: parasites with protective mechanisms]

African trypanosomes have developed protective mechanisms in order to escape from their hosts' immune attack. New cell surface antigens become sequentially expressed during a chronic infection providing the parasites continuously with immunologically altered faces. The trypanosomal genome contains a considerable repertoire of different genes coding for the surface antigens; they become separately activated and expressed by a variety of novel molecular processes. In addition, the trypanosomal cell surface participates in the protection of the parasites against non-immune defense mechanisms of the host.

Parasitic infections: therapeutic considerations

Parasitic infections are a problem even in developed countries. Since the agents used to treat these infections are infrequently used, most physicians are unfamiliar with antiparasitic compounds. The activity, mode of action, and use of antiparasitic agents is reviewed.

Trypanocidal and antitumour activity of platinum-metal and platinum-metal-drug dual-function complexes

A number of antitumour platinum-metal complexes related to cis-platin showed trypanocidal activity against Trypanosoma rhodesiense in vitro but not in vivo. New platinum- and rhodium-metal complexes of diamidine and plenanthridinium trypanocides are described which showed higher therapeutic indices than the parent drugs, due to increased activity in the former drug type and decreased toxicity in the latter. Some evidence of potentiation of antitumour activity was noted in these drug complexes. At the ultrastructural level, complex-treated trypanosomes showed a number of nuclear effects and other lesions specifically attributable to platinum-metal action. Some of the lesions were similar to those induced by cis-platin in tumour cells.

Localization of phosphatases in Trypanosoma rhodesiense

Phosphatase activity in Trypanosoma rhodesiense has been examined histochemically by light and electron microscopy and by enzymatic assay in homogenate fractions. Using a method with lead as capture ion, acid phosphatase was found in lysosome-like vesicles and in the flagellar pocket. No alkaline adenosine triphosphatase (ATPase) was detectable by this method. Direct assay of p-nitrophenylphosphatase activity in homogenate fractions showed that acid phosphatase activity was strongly membrane-bound, but that activity at pH 9 was minimal in both soluble and particulate fractions. "Endogenous" ATPase activity was localized specifically and reproducibly in the mitochondrial membranes and under the plasma membrane of he flagellum. This nonenzymic reaction product could not be eradicated by glycerol extraction or glucose depletion. Unlike the membrane staining, which was manifest only after lead treatment, heat-resistant electron-dense material was found in the matrix of lysosomal vesicles in trypanosomes fixed in glutaraldehyde only and not subjected to further treatment with heavy metal reagents. X-ray emission analysis showed the presence of calcium and phosphorus, indicating that the matrix might have a phosphate storage function.