Crystal violet as an uncoupler of oxidative phosphorylation in rat liver mitochondria

Small-molecule compounds inhibiting S-phase kinase-associated protein 2: A review

S-phase kinase-associated protein 2 (Skp2) is a substrate-specific adaptor in Skp1-CUL1-ROC1-F-box E3 ubiquitin ligases and widely regarded as an oncogene. Therefore, Skp2 has remained as an active anticancer research topic since its discovery. Accordingly, the structure of Skp2 has been solved and numerous Skp2 inhibiting compounds have been identified. In this review, we would describe the structural features of Skp2, introduce the ubiquitination function of SCF^Skp2, and summarize the diverse natural and synthetic Skp2 inhibiting compounds reported to date. The IC₅₀ data of the Skp2 inhibitors or inhibiting compounds in various kinds of tumors at cellular levels implied that the cancer type, stage and pathological mechanisms should be taken into consideration when selecting Skp2-inhibiting compound for cancer treatment.

A contemporary overview on the enigma of managing recalcitrant or intractable post-operative otorrhoea following middle-ear surgery: perspectives, principles and practices

Background

A common problem in otological surgeries is the persistence of ear discharge in a patient who has undergone middle-ear reconstructive surgery, despite an intact graft. There is a dearth of knowledge in the literature on treatment strategies in such post-operative cases of recalcitrant otorrhoea.

Method

This was a retrospective observational descriptive study conducted on 45 patients who fitted the criteria for recalcitrant post-operative otorrhoea. All 45 patients showed no response to conservative treatment for 14 days from onset of discharge. Therefore, these patients were then given antiseptic ear drops.

Results

Thirty patients out of 45 showed a good response to antiseptic ear drops and achieved a dry ear at the end of the treatment.

Conclusion

In patients with recalcitrant otorrhoea with or without granulations after middle-ear reconstruction surgery, this study found that topical antiseptic ear drops, particularly those using boric acid powder, are more effective than topical antibiotic drops.

A protet-based, protonic charge transfer model of energy coupling in oxidative and photosynthetic phosphorylation

Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150-170mV; to achieve in vivo rates the imposed pmf must reach 200mV. The key question then is 'does the pmf generated by electron transport exceed 200mV, or even 170mV?' The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.

Adaptation and Therapeutic Exploitation of the Plasma Membrane of African Trypanosomes

African trypanosomes are highly divergent from their metazoan hosts, and as part of adaptation to a parasitic life style have developed a unique endomembrane system. The key virulence mechanism of many pathogens is successful immune evasion, to enable survival within a host, a feature that requires both genetic events and membrane transport mechanisms in African trypanosomes. Intracellular trafficking not only plays a role in immune evasion, but also in homeostasis of intracellular and extracellular compartments and interactions with the environment. Significantly, historical and recent work has unraveled some of the connections between these processes and highlighted how immune evasion mechanisms that are associated with adaptations to membrane trafficking may have, paradoxically, provided specific sensitivity to drugs. Here, we explore these advances in understanding the membrane composition of the trypanosome plasma membrane and organelles and provide a perspective for how transport could be exploited for therapeutic purposes.

The effect of gentian violet on human anterior lens epithelial cells

PURPOSE

To evaluate whether the gentian violet staining of the anterior lens capsule during the cataract surgery is cytotoxic for the human lens epithelial cells, as an indirect indication of possible toxicity towards the corneal endothelium and the safety of gentian violet application.

MATERIALS AND METHODS

Two groups of anterior lens capsules obtained during the cataract surgery, gentian violet stained and non-stained, were incubated with fluorescent dye Fura-2. Their fluorescence, upon excitation at 360 and 380 nm, was imaged to monitor changes in free intracellular calcium concentration ([Ca(2+)]i) in response to pharmacological stimulation by acetylcholine. The [Ca(2+)]i homeostasis is the indicator of cellular function. The changes in [Ca(2+)]i were compared between the two groups.

RESULTS

Epithelial cells responded to acetylcholine in both groups of capsules - gentian violet stained (n = 17) and non-stained ones (n = 33). No significant differences of the elicited responses were found in rise time (p = 0.89), decay time (p = 0.61) or amplitude of [Ca(2+)]i (p = 0.96 for 63× and p = 0.26 for 40× objectives) between the two groups of capsules (Student t test).

CONCLUSIONS

The staining of the anterior lens capsule with gentian violet during phacoemulsification in concentration of 0.01%, does not have detectable cytotoxic effects, which would affect the [Ca(2+)]i homeostasis in lens epithelial cells. The data, if extrapolated to corneal endothelium, exposed to the same concentration, suggest that gentian violet in concentration of 0.01% is safe as an adjunct for capsule visualization in cataract surgery.

Rosamines targeting the cancer oxidative phosphorylation pathway

Reprogramming of energy metabolism is pivotal to cancer, so mitochondria are potential targets for anticancer therapy. A prior study has demonstrated the anti-proliferative activity of a new class of mitochondria-targeting rosamines. This present study describes in vitro cytotoxicity of second-generation rosamine analogs, their mode of action, and their in vivo efficacies in a tumor allografted mouse model. Here, we showed that these compounds exhibited potent cytotoxicity (average IC₅₀<0.5 µM), inhibited Complex II and ATP synthase activities of the mitochondrial oxidative phosphorylation pathway and induced loss of mitochondrial transmembrane potential. A NCI-60 cell lines screen further indicated that rosamine analogs 4 and 5 exhibited potent antiproliferative effects with Log₁₀GI₅₀ = −7 (GI₅₀ = 0.1 µM) and were more effective against a colorectal cancer sub-panel than other cell lines. Preliminary in vivo studies on 4T1 murine breast cancer-bearing female BALB/c mice indicated that treatment with analog 5 in a single dosing of 5 mg/kg or a schedule dosing of 3 mg/kg once every 2 days for 6 times (q2d×6) exhibited only minimal induction of tumor growth delay. Our results suggest that rosamine analogs may be further developed as mitochondrial targeting agents. Without a doubt proper strategies need to be devised to enhance tumor uptake of rosamines, i.e. by integration to carrier molecules for better therapeutic outcome.

Gentian violet: a 19th century drug re-emerges in the 21st century

Gentian violet (GV) has a long and varied history as a medicinal agent. Historically used as an antibacterial and antifungal, recent reports have shown its utility as an antitypranosomal, antiviral and anti-angiogenic agent. The objective of this article is to summarize evidence regarding the efficacy and safety of GV use in dermatology. Recent discoveries have found novel targets of GV, namely NADPH oxidase in mammalian cells and thioredoxin reductase 2 in bacterial, fungal and parasitic cells. These discoveries have expanded the use of GV in the 21st century. Given that GV is well tolerated, effective and inexpensive, its use in dermatology is predicted to increase.

Malachite green toxicity assessed on Asian catfish primary cultures of peripheral blood mononuclear cells by a proteomic analysis

The potential genotoxic and carcinogenic properties reported for malachite green (MG) and the frequent detection of MG residues in fish and fish products, despite the ban of MG, have recently generated great concern. Additional toxicological data are required for a better understanding of the mechanism of action and a more comprehensive risk assessment for the exposure of fish to this fungicide. To date, the use of fish peripheral blood mononuclear cells (PBMCs) has not been exploited as a tool in the assessment of the toxicity of chemicals. However, PBMCs are exposed to toxicants and can be easily collected by blood sampling. The present study aims at better understanding the effects of MG by a proteomic analysis of primary cultured PBMC from the Asian catfish, Pangasianodon hypophthalmus, exposed to MG. The two lowest concentrations of 1 and 10 ppb were selected based on the MTS (water soluble tetrazolium salts) cytotoxicity test. Using a proteomic analysis (2D-DIGE), we showed that 109 proteins displayed significant changes in abundance in PBMC exposed during 48 h to MG. Most of these proteins were successfully identified by nano LC-MS/MS and validated through the Peptide and Protein Prophet of Scaffold™ software, but only 19 different proteins were considered corresponding to a single identification per spot. Our data suggest that low concentrations of MG could affect the mitochondrial metabolic functions, impair some signal transduction cascades and normal cell division, stimulate DNA repair and disorganize the cytoskeleton. Altogether, these results confirm that the mitochondrion is a target of MG toxicity. Further studies on the identified proteins are needed to better understand the mechanisms of MG toxicity in fish produced for human consumption.

Assessment of compound hepatotoxicity using human plateable cryopreserved hepatocytes in a 1536-well-plate format

Hepatotoxicity is a major concern for both drug development and toxicological evaluation of environmental chemicals. The assessment of compound-induced hepatotoxicity has traditionally relied on in vivo testing; however, it is being replaced by human in vitro models due to an emphasis on the reduction of animal testing and species-specific differences. Since most cell lines and hybridomas lack the full complement of enzymes at physiological levels found in the liver, primary hepatocytes are the gold standard to study liver toxicities in vitro due to the retention of most of their in vivo activities. Here, we optimized a cell viability assay using plateable cryopreserved human hepatocytes in a 1536-well-plate format. The assay was validated by deriving inhibitory concentration at 50% values for 12 known compounds, including tamoxifen, staurosporine, and phenylmercuric acetate, with regard to hepatotoxicity and general cytotoxicity using multiple hepatocyte donors. The assay performed well, and the cytotoxicity of these compounds was confirmed in comparison to HepG2 cells. This is the first study to report the reliability of using plateable cryopreserved human hepatocytes for cytotoxicity studies in a 1536-well-plate format. These results suggest that plateable cryopreserved human hepatocytes can be scaled up for screening a large compound library and may be amenable to other hepatocytic assays such as metabolic or drug safety studies.

Gentian violet and ferric ammonium citrate disrupt Pseudomonas aeruginosa biofilms

OBJECTIVE/HYPOTHESIS

Bacterial biofilms are resistant to antibiotics and may contribute to persistent infections including chronic otitis media and cholesteatoma. Discovery of substances to disrupt biofilms is necessary to treat these chronic infections. Gentian violet (GV) and ferric ammonium citrate (FAC) were tested against Pseudomonas aeruginosa biofilms to determine if either substance can reduce biofilm volume.

STUDY DESIGN

The biofilm volume and planktonic growth of PAO1 and otopathogenic P. aeruginosa (OPPA8) isolated from an infected cholesteatoma was measured in the presence of GV or FAC.

METHODS

OPPA8 and PAO1 expressing a green fluorescent protein plasmid (pMRP9-1) was inoculated into a glass flow chamber. Biofilms were grown under low flow conditions for 48 hours and subsequently exposed to either GV or FAC for an additional 24 hours. Biofilm formation was visualized by confocal laser microscopy and biofilm volume was assayed by measuring fluorescence. Planktonic cultures were grown under standard conditions with GV or FAC. Statistical analysis was performed by Student t test and one-way ANOVA.

RESULTS

GV reduced PAO1 and OPPA8 biofilm volume (P < .01). GV delayed the onset and rate of logarithmic growth in both strains. FAC reduced OPPA8 biofilm volume (P < .01), but did not effect of PAO1 biofilms. FAC had no effect on planktonic growth.

CONCLUSIONS

The efficacy of GV in disrupting biofilms in vitro suggests that it may disrupt biofilms in vivo. The effect of FAC on Pseudomonas aeruginosa biofilms is strain dependent. Strain differences in response to increasing iron concentration and biofilm morphology stress the importance of studying clinically isolated strains in testing antibiofilm agents.

Effect of molecular structure on the performance of triarylmethane dyes as therapeutic agents for photochemical purging of autologous bone marrow grafts from residual tumor cells

Extensively conjugated cationic molecules with appropriate structural features naturally accumulate into the mitochondria of living cells, a phenomenon typically more prominent in tumor than in normal cells. Because a variety of tumor cells also retain pertinent cationic structures for longer periods of time compared with normal cells, mitochondrial targeting has been proposed as a selective therapeutic strategy of relevance for both chemotherapy and photochemotherapy of neoplastic diseases. Here we report that the triarylmethane dye crystal violet stains cell mitochondria with efficiency and selectivity, and is a promising candidate for photochemotherapy applications. Crystal violet exhibits pronounced phototoxicity toward L1210 leukemia cells but comparatively small toxic effects toward normal hematopoietic cells (murine granulocyte-macrophage progenitors, CFU-GM). On the basis of a comparative examination of chemical, photochemical, and phototoxic properties of crystal violet and other triarylmethane dyes, we have identified interdependencies between molecular structure, and selective phototoxicity toward tumor cells. These structure-activity relationships represent useful guidelines for the development of novel purging protocols to promote selective elimination of residual tumor cells from autologous bone marrow grafts with minimum toxicity to normal hematopoietic stem cells.

Cationic uncouplers of oxidative phosphorylation are inducers of mitochondrial permeability transition

To determine whether cationic uncouplers of oxidative phosphorylation induce permeability transition in mitochondria, the effects of the divalent cationic sulfhydryl cross-linker copper-o-phenanthroline (Cu(OP)2) and the cyanine dye tri-S-C4(5) on rat liver mitochondria were examined. Like Ca2+, they accelerated mitochondrial respiration with succinate and induced mitochondrial swelling when inorganic phosphate (Pi) was present in the incubation medium. The acceleration of respiration and swelling were inhibited by the SH-reagent N-ethylmaleimide, and by the specific permeability transition inhibitor cyclosporin A (CsA). In addition, these cations, like Ca2+, induced release of ADP entrapped in the mitochondrial matrix space, and the morphological change of mitochondria induced by these cations was essentially the same as that induced by Ca2+. It is concluded that the uncoupling actions of Cu(OP)2 and tri-S-C4(5) are due to induction of permeability transition in the inner mitochondrial membrane.

The Saccharomyces cerevisiae MFS superfamily SGE1 gene confers resistance to cationic dyes

A gene from Saccharomyces cerevisiae whose overexpression confers resistance to 10-N-nonyl acridine orange (NAO) has been isolated. This cationic dye binds acidic phospholipids and more specifically cardiolipin (Petit, J. M., Maftah, A., Ratinaud, M. H. and Julien, R. Eur. J. Biochem. 209, 267-273, 1992). The isolated gene was found to be identical to SGE1, a partial multicopy suppressor of the gal11 mutation (Amakasu, H., Suzuki, Y., Nishizawa, M. and Fukasawa, T. Genetics 134, 675-683, 1993), that also confers crystal violet resistance to a supersensitive strain (Ehrenhofer-Murray, A. E., Wurgler, F. E. and Sengstag, C. Mol. Gen. Genet. 244, 287-294, 1994). The data presented in this paper show that the SGE1 gene product, a member of the major facilitator superfamily, confers a pleiotropic drug-resistance phenotype when present in high copy number. The results also demonstrate that Sge1p acts as an extrusion permease whose specificity seems restricted to dye molecules possessing a large unsaturated domain that stabilizes a permanent positive charge such as NAO, crystal violet, ethidium bromide or malachite green.

In vivo interference of paromomycin with mitochondrial activity of Leishmania

Paromomycin is an aminocyclitol aminoglycoside antibiotic used for the treatment of leishmaniasis. In view of the central role of mitochondria in cellular energetics and metabolism, its effect on in vivo mitochondrial activities of Leishmania donovani promastigotes-the parasite flagellate form-was investigated. The approach used flow cytometry, amperometric measure of O2 consumption, and, as a global estimate of mitochondrial dehydrogenases, thiazolyl blue reduction (MTT test); some in vitro controls were also made. When added to promastigote cultures for 24-72 h at 150-200 microM (= LC50), paromomycin doubled the generation time, inhibited respiration, and lowered its associated electric potential difference across mitochondrial membranes, as measured by rhodamine 123 fluorescence. The chemical analogue neomycin was ineffective. Furthermore, the in vivo mitochondrial dehydrogenase activities were lower, seemingly because of the shortage of respiratory substrates. Indeed, succinate addition to paromomycin-treated cultures partly restored mitochondrial membrane potential. However, no immediate effect of paromomycin on respiration was observed, neither inhibition of redox chain nor increase of membrane permeability (uncoupling). It is proposed that paromomycin acts at a metabolic level upstream of the respiratory chain itself. This would have the observed delayed consequence because the cell energy supply would progressively decline since it depends upon the proton gradient-viz., membrane potential-generated by respiration. In conclusion, paromomycin is an antibiotic affecting the cell's energetic metabolism; the respiratory dysfunction it induces may be a crucial aspect of its action against Leishmania and possibly other cells.

Protonophoric activity of ellipticine and isomers across the energy-transducing membrane of mitochondria

Ellipticine is an antitumor alkaloid capable of uncoupling mitochondrial oxidative phosphorylation. It behaves as a lipophilic weak base with pK = 7.40. We have investigated its molecular mode of action using several of its isomers with pK ranging between 5.8 and 7.7 and ellipticinium, which is a permanent cationic derivative. The effects of these molecules on mitochondrial oxygen uptake and transmembrane potential were compared at different pHs. Ellipticinium exhibited very low effects on both respiratory rate and membrane potential. By contrast, protonable derivatives showed maximal stimulation of oxygen uptake and depolarizing effects when the pH of the medium was close to the drug pK. These effects were lowered when the transmembrane delta pH was dissipated, which indicates that the neutral form of the drug is implicated in the uncoupling mechanism. In addition, protonable derivatives of ellipticine display a linear relationship between oxidation rate and transmembrane potential, which suggests that the uncoupling properties of these molecules result from a protonophoric mechanism. From these results, the following cyclic protonophoric mechanism is proposed for protonable ellipticines: (i) electrophoretical accumulation of the protonated form; (ii) deprotonation at the matrix interface; (iii) diffusion outwards; and (iv) reprotonation at the external interface.

Inhibition of protein synthesis and amino acid transport by crystal violet in Trypanosoma cruzi

[35S]methionine incorporation into proteins of either T. cruzi epimastigotes or trypomastigotes was drastically inhibited by low concentrations of crystal violet in a dose-dependent manner. This inhibition was not due to ATP depletion since cellular ATP levels did not change significantly after incubation of epimastigotes with 50 microM crystal violet for similar periods of time, and was unaffected by changes in the extracellular free calcium concentration. Although crystal violet was able to inhibit protein synthesis in a cell-free system from T. cruzi epimastigotes, half maximal inhibition was at 1 mM, a concentration three orders of magnitude higher than those that inhibited protein synthesis in intact cells. On the other hand, crystal violet was able to inhibit total [35S]methionine uptake at similar concentrations to those that inhibited protein synthesis while addition of increasing concentrations of cold methionine to the incubation medium protected the cells against crystal violet inhibition. Crystal violet also inhibited total [3H]proline uptake thus indicating that it has a general inhibitory effect upon the transport of amino acids, and not specifically upon methionine. These results indicate that inhibition of protein synthesis by crystal violet is probably due to inhibition of amino acid uptake.

Inhibition of Trypanosoma cruzi trypanothione reductase by crystal violet

A trypanothione reductase activity is present in all the main differentiation stages of Trypanosoma cruzi, amastigotes having the highest activity, and trypomastigotes the lowest. Trypanothione reductase could not be induced in epimastigotes exposed to H2O2. The trypanocidal drug crystal violet was a potent inhibitor of T. cruzi trypanothione reductase in vitro. The inhibition was competitive with respect to trypanothione with a Ki of 5.3 +/- 0.5 microM, uncompetitive with NADPH, and increased below pH 7.0 and above pH 8.0. Crystal violet, however, was not able to decrease the level of total reduced thiols in intact cells. Dihydrotrypanothione but not reduced glutathione, protected the enzyme from inhibition by crystal violet.

Disruption of Ca2+ homeostasis in Trypanosoma cruzi by crystal violet

We have demonstrated previously that crystal violet induces a rapid, dose-related collapse of the inner mitochondrial membrane potential of Trypanosoma cruzi epimastigotes. In this work, we show that crystal violet-induced dissipation of the membrane potential was accompanied by an efflux of Ca2+ from the mitochondria. In addition, crystal violet inhibited the ATP-dependent, oligomycin-, and antimycin A-insensitive Ca2+ uptake by digitonin-permeabilized epimastigotes. Crystal violet also induced Ca2+ release from the mitochondria and endoplasmic reticulum of digitonin-permeabilized trypomastigotes. Furthermore, crystal violet inhibited Ca2+ uptake and the (Ca(2+)-Mg2+)-ATPase of a highly enriched plasma membrane fraction of epimastigotes, thus indicating an inhibition of other calcium transport mechanisms of the cells. Disruption of Ca2+ homeostasis by crystal violet may be a key process leading to trypanosome cell injury by this drug.

The lipophilic weak base (Z)-5-methyl-2-[2-(1-naphthyl)ethenyl]-4-piperidinopyridine (AU-1421) is a potent protonophore type cationic uncoupler of oxidative phosphorylation in mitochondria

The lipophilic weak base AU-1421 acts as a simple protonophoric uncoupler of oxidative phosphorylation in rat liver mitochondria judging from the following observations. In the absence of any carrier lipophilic anions or P(i), AU-1421 stimulated the rate of state 4 respiration maximally about 7-fold at a concentration of 30 nmol/mg mitochondrial protein. At the same maximum effective concentration, it also inhibited ATP synthesis, released oligomycin-inhibited state 3 respiration, dissipated the proton motive force in the energized state, and activated latent H(+)-ATPase. AU-1421 also allowed proton conduction in both mitochondrial membranes and liposomes. These actions of AU-1421 resemble those of the typical anionic uncoupler SF6847. A marked difference between the two was, however, that ATPase activation by AU-1421 was not suppressed at higher concentrations of AU-1421, whereas ATPase activated by SF6847 was suppressed on increase of the SF6847 concentration. The finding that this simple protonophoric cation acts as an uncoupler at a micromolar concentration is significant, because all true (i.e., protonophore type) uncouplers known so far are anionic not cationic. Thus, AU-1421 is a unique uncoupler of the protonophore type.

Why is inorganic phosphate necessary for uncoupling of oxidative phosphorylation by Cd2+ in rat liver mitochondria?

The phosphate (Pi)-dependent uncoupling action of Cd2+ in oxidative phosphorylation in rat liver mitochondria was studied mainly in terms of Pi transport. Cd2+ at 2 microM caused full uncoupling in the presence of 10 mM Pi, but no uncoupling in the absence of Pi. Cd2+ released state 4 respiration after a certain lag-time, and then the respiration increased progressively with time. After its addition, Cd2+ was taken up by mitochondria in a similar period to the lag time before respiratory release. KIH-201, a potent and specific inhibitor of Pi transport via the Pi/H+ symporter, abolished the uncoupling completely. Cd2+ caused dissipation of the electric transmembrane potential (delta psi) and swelling of mitochondria in a Pi-dependent manner. Uncoupling by Cd2+ was found to take place in parallel with the uptake of Pi into mitochondria via the Pi/H+ symporter, suggesting that the uncoupling was due to acceleration of H+ influx through the Pi/H+ symporter activated by Cd2+.

Tricyclic drugs reduce proton motive force in Leishmania donovani promastigotes

Tricyclic compounds have been suggested as potential anti-leishmanial drugs. We have studied the effect of tricyclic drugs on several cellular functions in L. donovani promastigotes. Imipramine inhibits proline transport and reduces delta pH and cellular ATP at relatively high concentrations (IC50 = 50-80 microM). High concentrations of imipramine are also required to kill L. donovani promastigotes (LD50 greater than 50 microM). The presence of a chlorine atom in the side ring of either imipramine or promazine results in a three-fold increase in both IC50 and LD50 values. Tricyclic compounds in which the nitrogen in the middle ring was substituted with a carbon atom (amitryptyline and chlorprothixene) are most effective in causing cell death and in decreasing proline transport and delta pH (IC50 congruent to 5 microM), whereas depletion of cellular ATP requires a higher drug concentration (IC50 = 12 microM). Transchlorprothixene has IC50 values for proline transport, delta pH and cellular ATP that are similar to those of amitriptyline, whereas the cis isomer is less active. Imipramine, chlomipramine and chlorpromazine decrease the membrane potential in promastigotes. There is a direct correlation between inhibition of membrane transport of proline and the size of the membrane potential at various concentrations of the drugs. Taken together, the multiple effects of the tricyclic drugs on cellular functions in Leishmania suggest that the drugs cause cellular death by non-specific mechanisms, probably involving a general increase in membrane permeability.

The metabolism and mode of action of gentian violet

Gentian violet has been used in medicine for almost 100 years: as an antiseptic for external use, as an antihelminthic agent by oral administration, and more recently, as a blood additive to prevent transmission of Chagas' disease. To date, no serious side effects have been reported when used externally. However, oral administration can cause gastrointestinal irritation, and intravenous injection can cause depression in the white blood cell count. Surprisingly, no acute toxic side effects were reported after administration of large amounts of gentian violet-treated blood. No studies have been done on long-term effects (chronic toxicity, carcinogenicity) of gentian violet-treated blood either in humans or in laboratory animals. Gentian violet is a mutagen, a mitotic poison, and a clastogen. The carcinogenic effects of gentian violet in rodents have been reported recently. In addition, a number of triphenylmethane-classed dyes, of which gentian violet is a member, have been recognized as animal and human carcinogens. A photodynamic action of gentian violet, apparently mediated by a free-radical mechanism, has been described in bacteria and in T. cruzi. However, the main target of gentian violet toxicity in the dark is the mitochondrion. Gentian violet is actively demethylated by liver microsomes from different animals and is reduced to leucogentian violet by intestinal microflora. Although the first process may represent a detoxication reaction, the second pathway may have toxicological significance because the completely demethylated derivative leucopararosaniline has been demonstrated to be carcinogenic in rats. A free-radical derivative of gentian violet is also formed by the action of rat liver microsomes, but whether this radical is involved in the cytotoxic effects of gentian violet in mammalian cells remains to be elucidated. Other pathways of gentian violet metabolism have recently been investigated that involve its oxidative N-demethylation by peroxidases. The N-demethylation of gentian violet by prostaglandin synthetase deserves further study. In this regard, the PGS system is being studied as an alternative activating pathway in xenobiotic metabolism because some carcinogenic intermediates can be formed during this cooxidation reaction.