Experimental approaches to antifungal chemotherapy

Octadecyl 3-(3, 5-di-tert-butyl-4-hydroxyphenyl) propanoate, an antifungal metabolite of Alcaligenes faecalis strain MT332429 optimized through response surface methodology

In the current study, a soil bacterial isolate F2 expressed a significant antagonistic activity against Candida albicans ATCC 10231 and Aspergillus niger clinical isolate confirmed through cross streak, dual culture, and agar well diffusion methods. The isolate F2 was identified using phenotypic and molecular approaches as Alcaligenes (A.) faecalis MT332429. The identification and structural characterization of the antifungal compound was performed using advanced spectroscopic techniques including UV absorbance, ¹H and ¹³C NMR and 2D NMR (COSY, HSQC, and HMBC) and was identified as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate. Response surface methodology (RSM) using a central composite design was employed to optimize the nutritional and cultural variables affecting the antifungal metabolite yield. The optimum conditions were found to be temperature 30 °C, agitation 150 rpm, glucose 1 g/l, peptone 2 g/l, and pH 8. A confirmatory experiment was performed to assess the accuracy of the optimization procedure, where an increase in the antifungal metabolite production by about 2.48-fold was obtained. To the best of our knowledge, this is the first report of octadecyl 3-(3, 5-di-tert-butyl-4-hydroxyphenyl) propanoate recovered from the culture broth of A. faecalis MT332429 with a promising antifungal activity along with its optimized production through RSM. KEY POINTS: • A novel soil bacterial isolate, F2, identified as Alcaligenes faecalis MT332429, showed significant antagonistic activity against Candida albicans ATCC 10231 and Aspergillus niger clinical isolate. • This stable fungicidal extracellular metabolite was identified as octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate. • Optimization using central composite design resulted in 2.48-fold increase in production reaching 213.82 μg/ml.

Antifungal agents of use in animal health--chemical, biochemical and pharmacological aspects

A limited number of antifungal agents is licensed for use in animals, however, many of those available for the treatment of mycoses in humans are used by veterinary practitioners. This review includes chemical aspects, spectra of activity, mechanisms of action and resistance, adverse reactions and drug interactions of the antifungals in current use.

Mathematical modelling of antifungal action

In this paper a simplified modelling approach indicated that yeast growth was inhibited by an antifungal drug according to an exponential function. In addition, the corresponding inhibition rate followed a hyperbolic function the parameters of which permit us to determine the percentage of maximum inhibition and the minimum inhibitory concentration for 80%. From the equation of a hyperbola it was also possible to calculate an affinity constant Kaff corresponding to the inverse of the concentration of antifungal drugs giving half the maximal inhibition. The affinity constant was demonstrated to be characteristic of the yeast strain and of the antifungal drug employed. Simulation of the mathematical modelling enabled determination of a theoretical inhibition level corresponding to strong concentrations of antifungal drugs which cannot be carried out for technical reasons (precipitates, opacity etc.). The interest of this mathematical modelling of growth and inhibition to predict the doses of antifungals which can act synergistically is discussed.

Progression of mouse buthionine sulfoximine cataracts in vitro is inhibited by thiols or ascorbate

Mouse lens cultures were employed to study the progression of cataracts initiated by injection of buthionine sulfoximine, an inhibitor of glutathione (GSH) biosynthesis. Culture of lenses removed from untreated mice on postnatal day 7, for 48 hr in the presence of 4 mm BSO, resulted in only limited cataractous changes. To enable substantial progression of cataracts in vitro, it was therefore necessary to pretreat the mice with BSO prior to lens culture. A single injection of BSO (4 nmol mg-1 lens), administered on day 7, resulted in >90% depletion of lens GSH within 3 days, but no visible cataractous changes. The clear lenses were incubated for 29+/-1 hr at 37 degrees C in Medium HL-1, supplemented with EGF, insulin and Ca2+, in the presence or absence of BSO, and were scored for cataract development by previously described criteria. In the absence of BSO, only 4 of 10 lenses developed large opacities. However, in the presence of 4 mm BSO, 40 out of 45 experimental lenses developed opacities affecting at least 50% of the lens visual field and were scored as stages 1C-4, depending upon the extent and density of the cataracts. In addition, three lenses had opacities involving 20-50% of the field (stage 1B). By contrast, less than 10% of lenses from untreated mice incubated in the absence of BSO developed opacities. The cataracts developed in 4 mm BSO were accompanied by reduction of lens glutathione levels to <0.010 nmol mg-1 lens. They were almost completely prevented by 1 mm ascorbate, 2 mm GSH, 2 mm GSH monoethyl ester and 2 mm cysteamine. GSH and GSH ester maintained lens glutathione content between 0.1 and 0.2 nmol mg-1 in the presence of BSO, whereas ascorbate did not prevent near-total GSH depletion. The prevention of cataracts by thiols and ascorbate was confirmed by lens Na/K ratios not significantly different from those in control lenses. The above combination of GSH depletion in vivo by a single injection of BSO, followed 3 days later with lens culture in the presence of BSO, may yield a useful system to elucidate and control the biochemical mechanisms involved in oxidative cataract induction by this GSH-depleting agent.

Transmission of the effect of an antifungal agent within a single hypha

A micro-compartment culture method was devised in which a single hypha of Rhizopus stolonifer growing on an agar section traversed an antifungal non-diffusible barrier to another agar section; thus the local environment of the distal or proximal part of the hypha could be controlled independently. The responses in terms of hyphal extension of the test fungus to local application of amphotericin B in this culture system were estimated by using an automatic analysing system. After hyphae had traversed the barrier, distal application of amphotericin B caused no appreciable effect on the proximal hyphae. In contrast, proximal application of amphotericin B caused inhibition of the extension of distal hyphae. The reversal of polarized cytoplasmic streaming also occurred during the inhibition of distal hyphal extension. The extents of inhibition of the distal hyphal extension and the cytoplasmic streaming were dependent upon the hyphal distance between the amphotericin B application site and the hyphal tip. These results show that the effect of an antifungal agent on a hypha depends on the region of the hypha exposed. Cytoplasmic streaming may play key role in the transmission of antifungal effects within a single hypha.

Oral carriage of Candida in healthy and HIV-seropositive persons

The prevalence of oral colonization with Candida species was studied in 28 HIV-seropositive and 28 healthy persons. Candida was cultured from 75% and 68% of HIV-positive and control persons, respectively, with a significantly higher density carriage in the HIV-seropositive group. Positive smears were seen in 39% of all patients. Candida albicans was the most frequently isolated species with Biotype 1 accounting for 56% of the isolates. Resistance to antifungal agents was seen in Candida strains isolated from both groups.

Alteration of the permeability of the human erythrocyte membrane to cations by liposome-incorporated amphotericin B

Some effects of liposome-incorporated amphotericin B on the permeability of the human erythrocyte membrane to potassium and sodium ions is reported. The influence of cholesterol and amphotericin B in causing a shift towards smaller and larger liposomes, respectively, is also described. Phosphatidylcholine liposomes containing amphotericin B in a molar ratio of 7.4 +/- 0.1 (mean +/- SD) antibiotic to 1000 phospholipid reduced the initial rates of K+ and Na+ transport across the erythrocyte membrane to 40 +/- 2.6% and 0%, respectively, of their rates in the presence of comparable concentrations of free amphotericin B. Amphotericin B incorporated into liposomes (8.2 +/- 0.15 mumol antibiotic per 1000 mumol total lipid) composed of cholesterol and phosphatidylcholine (in a molar ratio of 3:7) reduced the initial rate of K+ transport to 19 +/- 0.8% of its value measured in the presence of a comparable concentration of free antibiotic. These results suggest that liposomes containing specified amounts of amphotericin B, especially liposomes also containing cholesterol in addition to phosphatidylcholine, could be used as a method of controlling K+ transport across the erythrocyte and possibly other types of cellular membranes, thereby limiting antibiotic toxicity to some mammalian tissues.

Evaluation of antifungal activity of antimycotics by automatic analyzing system

Antifungal activity of several antimycotics has been evaluated using an automatic analyzing system (AAS), which is composed of a specially designed reaction vessel, microscopic observation system, image analyzing system, and computer program for automatic tracing of hypha growth. The agar plate was prepared on the ceiling of the reaction vessel, and spore mass of a fungus (Aspergillus niger) was inoculated onto it. After the preincubation at 28 degrees C for 24 h the reaction vessel was set on a microscope stage and connected to the liquid flow system. An appropriate hypha was selected for the measurement of growth process during the following steps: first contact with saline for 30 min for the adaptation, the second contact with same saline for 30 min, contact with saline containing an antimycotic substance for 60 min, and contact with flushing saline for 60 min. During a sequence of these steps, the apical tip of a growing hypha displayed on a TV monitor was followed automatically. The dynamic response of hypha to an agent was analyzed by several parameters. Morphological changes of the hypha caused by respective agents were recorded on VTR for further analysis. By using this system, the antifungal activity of antimycotics could be quantitatively determined within several hours.

Evaluation of antifungal volatile compounds on the basis of the elongation rate of a single hypha

A novel method is proposed for the evaluation of the activity of an antifungal agent administered as a gas. This system is composed of a batch-flow type reaction vessel, a gas flow system, and a microscopic observation system. The agar plate was prepared on the ceiling of the reaction vessel, and the mycelium of a fungus (Aspergillus niger or Rhizoctonia solani) was inoculated onto it. After preincubation at 25 degrees C for 24 h, the reaction vessel was connected to the gas flow system. An appropriate hypha was selected, and its elongation rate was measured. Then a sample holder containing an antifungal compound was inserted into the reaction vessel from the side hole to saturate the atmosphere inside with its vapor. The retardation or inhibition of the hypha elongation was observed on a television monitor and recorded on a video tape recorder. The antifungal compound was then removed, and the reaction vessel was flushed with air. If the hypha lived, it began to elongate again. By this method, antifungal activity of seven odor compounds could be evaluated quantitatively within several hours.

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.

An evaluation of the acute in vivo toxicity of benzylidenechroman-4-ones, 1-thiobenzylidenechroman-4-ones and benzylidenetetralones

A series of new compounds were evaluated for acute in vivo toxicity. Their synthesis and antifungal activity have previously been described by us. The naturally occurring class of compounds to which they belong - the benzylidenechroman-4-ones - have been identified as a potential source of new antifungal agents. These compounds were found to be less toxic, as judged by acute toxicity, than existing commercially available antifungals. A number of conclusions can be drawn about the relationship of structural changes in this series of compounds to increases or decreases in acute toxicity.

A double-blind clinical trial of fenticonazole (2%) spray versus naftifine (1%) spray in patients with cutaneous mycoses

A multi-centre, double-blind trial was carried out in 100 patients with cutaneous mycotic infections, confirmed by direct microscopy and/or culture, to compare the efficacy and tolerability of spray formulations of 2% fenticonazole and 1% naftifine. On entry, patients were allocated at random to receive once daily topical applications of one or other drug over a period of 2 to 4 weeks, treatment being stopped when patients had recovered or substantially improved. Clinical and mycological assessments were made before (baseline), at weekly intervals during treatment and, if possible, 2 to 3 weeks after the end of treatment (drug-free period). Treatment was continued for 19.25 days with fenticonazole and 19.62 days with naftifine. All patients had positive mycological findings on entry. The most frequently isolated pathogens were dermatophytes, mainly Trichophyton rubrum; however, Candida albicans was present in 33.3% of patients in the fenticonazole group and in 20.8% of those treated with naftifine. At the end of treatment, only 3 (6.3%) and 5 (10.4%) patients, respectively, of the 48 patients assessed in each group still had positive mycological findings. Assessments of symptoms indicated comparable, significant improvement in both groups, and at the end of treatment the overall opinion of doctors and patients was that about 90% of patients were cured or greatly improved. The end of the drug-free period evaluation showed that, of the patients assessed as cured or greatly improved at the end of treatment, only 1 (3.2%) patient who had received fenticonazole and 2 (6.3%) who had received naftifine were confirmed mycologically as having relapsed.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term treatment of vaginal candidiasis with fenticonazole ovules: a three-dose schedule comparative trial

In an unblinded, randomized parallel group trial three different therapeutic dose schedules of fenticonazole (vaginal ovules) were compared in the treatment of vaginal candidiasis. A total of 60 patients, aged 17-71 years, affected by mycologically confirmed symptomatic vaginal candidiasis were included and randomly allocated to three treatment groups: 200 mg daily, for 3 days; 600 mg in a single administration; and 1000 mg in a single administration. Therapeutic efficacy was assessed by microbiological and clinical criteria 7 days after the end of the treatment. All mycologically cured patients were re-checked, microbiologically and clinically, 2 weeks after the end of treatment to identify and evaluate possible relapses. The results obtained indicate that vaginal application of fenticonazole ovules is highly effective in producing both symptomatic relief and mycological sterilization of vaginal swabs in 75-85% of treated patients. No relapses were noted at the time of re-check. The three administration schedules tested appear to be equally effective and well tolerated. In one case only of the group given 200 mg and two cases of those given 1000 mg, a local burning sensation was noted. These results show that short-term treatment of vaginal candidiasis with fenticonazole ovules is effective and well tolerated.

Antimicrobial activity of protoanemonin, a lactone from ranunculaceous plants

Protoanemonin, a component of Ranunculus bulbosus, was tested as an antifungal agent on selected strains of dermatophytes and yeasts. The minimum inhibitory concentrations ranged from 2.0 to 7.5 X 10(-4) M and the minimum lethal concentrations from 3.8 X 10(-4) M to greater than 1.0 X 10(-3) M. The most sensitive dermatophyte tested was Epidermophyton floccosum, and the most sensitive yeast Rhodotorula glutinis. The effects of different culture media and of light on the sensitivity of Rhodotorula glutinis to protoanemonin were also tested. Structural analogies between protoanemonin and other cytotoxic unsaturated lactones, and the reversal by the amino acid cysteine of the antifungal action suggest a possible mechanism of action.

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

A large body of evidence exists suggesting that polyamines can play essential roles in cellular growth and differentiation. We examined the ability of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, the major rate-limiting enzyme in polyamine biosynthesis, to inhibit the growth of Candida albicans, C. tropicalis, and C. parapsilosis. Substantial growth-inhibition was observed for all three species at DFMO concentrations ranging from 1 to 100 mM. C. tropicalis was significantly more susceptible to DFMO than C. albicans or C. parapsilosis. Depletion of cellular polyamine pools was seen in all 3 species following exposure to DFMO and polyamine depletion enhanced the susceptibility of the organisms to DFMO. The action of DFMO was specifically antagonized by exogenous polyamines. These data suggest that polyamines are important in the growth of Candida spp. and that inhibitors of polyamine biosynthesis may be useful as antifungal agents.

Hormonal factors in vaginal candidiasis in rats

The hormonal status of rats affected vaginal infection with Candida albicans. Four hours after infection viable counts were higher and germ tubes were longer in those animals in estrous than in other animals. However, the infection was not maintained with the change in epithelial cell type which occurred as part of the estrous cycle. Estrogen dosing following ovariectomy predisposed toward infection, while progesterone dosing did not. In rats injected with progesterone, germ tube clumping was seen, leukocytes were present, and elimination occurred before hyphal growth was evident. In rats injected with estrogen, however, infection was maintained, with hyphal growth extending throughout the cornified epithelial layer. Vaginal washings from rats dosed with estrogen promoted elongation of germ tubes in vitro to a greater extent than washings from other rats. Preincubation of blastospores in progesterone and subsequent infection of rats in pseudoestrous promoted clumping of germ tubes in the vagina. Strains of C. albicans varied in their virulence, which correlated with their ability to produce germ tubes in vitro. Loss of virulence occurred on subculture of a clinical isolate.

Inhibition of growth and uptake of amino acids in the yeast, Candida parapsilosis, by ambruticin

The antifungal antibiotic, ambruticin, inhibits growth of Candida parapsilosis and reduces its ability to take up amino acids. Increasing growth temperature from 30 degrees C to 39 degrees C leads to a 100-fold decrease in the minimum growth inhibitory concentration. Ambruticin is 20 times more effective at pH 5 than at pH 8 and exponentially growing cultures are much less susceptible than stationary phase cells. The activity of ambruticin is also dependent on the presence of certain exogenous nutrients. When acetate or succinate (10 mM) are included in the incubation medium, ambruticin has little effect on amino acid uptake. Glucose, mannose and glycerol do not decrease the efficacy of ambruticin. Ambruticin probably inhibits growth by reducing the utilization of exogenous and intracellular carbohydrates. This leads to a fall in energy production within the cell which can be monitored as a reduction in the activity of energy-dependent transport systems.

A replica plating technique for in vitro study of susceptibility of Candida albicans to miconazole, econazole and ketoconazole: some data for standardization

We report our studies in vitro on the activity of ketoconazole (KZ), econazole and miconazole on 115 isolates of Candida albicans of clinical origin tested by an agar dilution method with three different culture media: yeast morphology agar, Sabouraud maltose agar and Casitone agar (CA). The antifungal effects of the imidazole compounds (IC) were strongest in CA. Eighty percent of the strains were inhibited by 0.1 micrograms/ml of KZ, the most active drug. The frequent appearance of "veil growth" at higher concentrations of the IC made the exact determination of the minimal inhibitory concentration (MIC) difficult. Microscopic examination of the growth on plates at the highest drug dilutions was performed and the results compared with a replica plating technique of IC plates on other plates with antibiotic-free media. The following were observed: a) a residual capacity of cell division of Candida strains even in the presence of high antifungal concentrations to which they are considered sensitive; and b) a certain viability (7% of the cases) of some fungal cells in the residual growth, particularly in those strains with higher conventional MIC. A standardized methodology is needed for the clinical evaluation of the susceptibility tests of Candida to the imidazolic compounds.

Allylamine derivatives: new class of synthetic antifungal agents inhibiting fungal squalene epoxidase

A new class of synthetic antifungal agents, the allylamines , has been developed by modification of naftifine , a topical antimycotic. SF 86-327, the most effective of these compounds so far, is highly active in vitro against a wide range of fungi and exceeds clinical standards in the oral and topical treatment of guinea pig dermatophytoses. SF 86-327 is a powerful specific inhibitor of fungal squalene epoxidase, a key enzyme in sterol biosynthesis.

Liposomal amphotericin B is toxic to fungal cells but not to mammalian cells

Amphotericin B is an efficacious but extremely toxic anti fungal drug. Recently it has been shown that the incorporation of Amphotericin B in multilamellar liposomes results in a marked reduction in drug toxicity in mice with no loss of anti fungal potency. Until now, the mechanistic basis of the enhanced therapeutic index of liposomal Amphotericin B has been unclear. In this report, however, we show that the in vivo effects can be mimicked in vitro where free but not liposomal Amphotericin B causes lysis of erythrocytes while both free and liposomal drug kill fungal cells. These results suggest that the markedly improved therapeutic index of liposomal Amphotericin B is largely due to a fundamental alteration in the ability of the drug to interact with mammalian cell membranes rather than to alterations in pharmacokinetics or drug distribution.

A direct comparison of oral treatments with BAY-n-7133, BAY-1-9139 and ketoconazole in experimental murine coccidioidomycosis

Two new experimental antifungal azole drugs were compared with ketoconazole for the management of experimental murine coccidioidomycosis. The first, BAY-n-7133, a triazole, was superior to the second, BAY-1-9139, an imidazole derivative. Neither BAY drug was as effective as ketoconazole in early fulminant coccidioidomycosis of mice, in later disseminated disease and in deep-seated chronic disease. A possible limitation of BAY-n-7133 in the mouse model was its reported capacity to induce enzyme changes that accelerated its clearance from serum. Induction of such an enzyme response in human beings has been reported not to occur.

Disseminate sporotrichosis of skin and bone cured with 5-fluorocytosine: Photosensitivity as a complication

Disseminate cutaneous and osseous sporotrichosis is reported in a patient who failed to respond to 6 months of iodide therapy. Although the patient showed improvement on a 2-month course of amphotericin B, he experienced a fulminant relapse 12 days after the amphotericin B was stopped. Cure was achieved after 6 months of 5-fluorocytosine (8 gm/day) in conjunction with amphotericin B (total, 4.8 gm). The fluorocytosine was continued for an entire year. Two years after all treatment was discontinued the patient remained in good health. The only complication was a marked photosensitivity associated with the 5-fluorocytosine therapy. This is the second case of such photosensitivity in the literature.