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Antifungal and antioxidant activity of fatty acid methyl esters from vegetable oils

ABSTRACT

Fatty acid methyl esters (FAMEs) were obtained from vegetable oils of soybean, corn and sunflower. The current study was focused on evaluating the antifungal activity of FAMEs mainly against Paracoccidioides spp., as well as testing the interaction of these compounds with commercial antifungal drugs and also their antioxidant potential. FAMEs presented small IC50 values (1.86-9.42 μg/mL). All three FAMEs tested showed antifungal activity against isolates of Paracoccidioides spp. with MIC values ranging from 15.6-500 µg/mL. Sunflower FAMEs exhibited antifungal activity that extended also to other genera, with an MIC of 15.6 μg/mL against Candida glabrata and C. krusei and 31.2 μg/mL against C. parapsilosis. FAMEs exhibited a synergetic effect with itraconazole. The antifungal activity of the FAMEs against isolates of Paracoccidioides spp. is likely due to the presence of methyl linoleate, the major compound present in all three FAMEs. The results obtained indicate the potential of FAMEs as sources for antifungal and antioxidant activity.

Key words:
antifungal; antioxidant; fatty acid methyl esters; vegetable oils

INTRODUCTION

Antioxidant compounds are capable of inhibiting or delaying lipid oxidation, which is associated with the appearance of degenerative or chronic diseases. Thus, antioxidants act to prevent or avoid incidence of cancer, diabetes, atherosclerosis, coronary heart disease and the aging process (Rufino et al. 2011RUFINO MSM, ALVES RE, FERNANDES FAN AND BRITO E. 2011. Free radical scavenging behavior of ten exotic tropical fruits extracts. Food Res Int 44: 2072-2075.). Natural substances with known antioxidant potential are phenolic compounds (flavonoids and phenolic acids), vitamins A, C, E and carotenoids which, in different proportions and quantities, can be obtained from foods of plant origin, such as vegetables, fruits, teas, herbs, beans and oil seeds (Ara and Nur 2009ARA N AND NUR H. 2009. In vitro antioxidant activity of methanolic leaves and flowers extracts of Lippia alba. Res J Medicine Med Sci 4: 107-110., Arnao et al. 2001ARNAO MB, CANO A AND ACOSTA M. 2001. The hydrophilic and lipophilic contribution to total antioxidant activity. Food Chem 73: 239-244.). Several studies have suggested that the development of chronic or degenerative diseases can be decreased with the regular consumption of vegetables or fruits (Chu et al. 2002CHU YF, SUN J, WU X AND LIU RH. 2002. Antioxidant and antiproliferative activities of common vegetables. J Agric Food Chem 50: 6910-6916.). Therefore, in recent years, the search for natural antioxidants, especially of plant origin, has greatly increased (Lima et al. 2010LIMA LARS, PIMENTA LPS AND BOAVENTURA MAD. 2010. Acetogenins from Annona cornifolia and their antioxidant capacity. Food Chem 122: 1129-1138.).

Paracoccidioidomycosis (PCM) is a systemic mycosis caused by fungi of the genus Paracoccidioides, and two species are known, P. brasiliensis and P. lutzii. PCM is a disease limited to Latin America and is a common cause of deaths from fungal diseases. PCM is the eighth most important cause of mortality from chronic infectious diseases reaching rates of 1.65 deaths per 106 habitants (Bocca et al. 2013BOCCA AL, AMARAL AC, TEIXEIRA MM, SATO PK, SHIKANAI-YASUDA MA AND SOARES FELIPE MS. 2013. Paracoccidioidomycosis: eco-epidemiology, taxonomy and clinical and therapeutic issues. Future Microbiol 8: 1177-1191. , Coutinho et al. 2002COUTINHO ZF, SILVA D, LAZÉRA M, PETRI V, OLIVEIRA RM, SABROZA PC AND WANKE B. 2002. Paracoccidioidomycosis mortality in Brazil (1980-1995). Cad Saúde Pública RJ 18: 1441-1454., Prado et al. 2009PRADO M, SILVA MB, LAURENTI R, TRAVASSOS LR AND TABORDA CP. 2009. Mortality due to systemic mycoses as a primary cause of death or in association with AIDS in Brazil: a review from 1996 to 2006. Mem Inst Oswaldo Cruz 104: 513-521.). There are some drugs available to treat PCM; itraconazole therapy is the first choice to control the mild to moderate clinical forms but this therapy is not easily available in most of the endemic regions. Consequently, sulfamethoxazole-trimethoprim (SMX-THT) is a useful option; this drug is freely distributed by the Brazilian Ministry of Health. The main disadvantage of SMX-THT is the need for long-term treatment (more than 12 months) in moderate and severe cases which can lead patients to abandon treatment (Brummer et al. 1993BRUMMER E, CASTANEDA E AND RESTREPO A. 1993. Paracoccidioidomycosis: an update. Clin Microbiol Rev 6: 89-117., Paniago et al. 2003PANIAGO AM, AGUIAR JI, AGUIAR ES, CUNHA RV, PEREIRA GROL, LONDERO AT AND WANKE B. 2003. Paracoccidioidomycosis: a clinical and epidemiological study of 422 cases observed in Mato Grosso do Sul. Rev Soc Bras Med Trop 36: 455-459. , Travassos et al. 2008TRAVASSOS LR, TABORDA CP AND COLOMBO AL. 2008. Treatment options for paracoccidioidomycosis and new strategies investigated. Expert Rev Anti-Infect Ther 6: 251-262.). Amphotericin B therapy is the best choice for severe cases of PCM, but toxicity, mainly nephrotoxicity, is related to this drug which will sometimes require discontinuation of this therapy (de Oliveira et al. 2015, Ferreira 2009FERREIRA MS. 2009. Paracoccidioidomycosis. Paediatr Respir Rev. 10: 161-165., Shikanai-Yasuda 2015). Relapses, a common event in PCM patients, associated with toxicity represent an unresolved problem in the conventional therapeutic approach (Travassos et al. 2008, Travassos and Taborda 2012). Due to these facts it is necessary to research new drugs that are safer, more effective and cheaper and with shorter periods of therapy for the treatment of PCM.

Fatty acids are the most abundant component of oils, the most commonly found being stearic, palmitic, oleic, linoleic and linolenic acids (Cabral 2005CABRAL GA. 2005. Lipids as bioeffectors in the immune system. Life Sci 77: 1699-1710.). The antibacterial and antifungal properties of vegetable oils are reported in the literature, these being especially attributed to the presence of fatty acids (Desbois and Smith 2010DESBOIS AP AND SMITH VJ. 2010. Antibacterial free fatty acids: activities, mechanisms of action and biotechnological potential. Appl Microbiol Biotechnol 85: 1629-1642, Erdemoglu and Kusmenoglu 2003ERDEMOGLU N AND KUSMENOGLU S. 2003. Fatty acid composition of Zygophyllum fabago seeds. Chem Nat Compd 39: 595-596. ). However, some works done with methyl esters showed their potential as antifungals (Abdelillah et al. 2013ABDELILLAH A, HOUCINE B, HALIMA D, MERIEM CS, IMANE Z, EDDINE SD, ABDALLAH M AND DAOUDI CS. 2013. Evaluation of antifungal activity of free fatty acids methyl esters fraction isolated from Algerian Linum usitatissimum L. seeds against toxigenic Aspergillus. Asian Pac J Trop Biomed 3: 443-448., Agoramoorthy et al. 2007AGORAMOORTHY G, CHANDRASEKARAN M, VENKATESALU V AND HSU MJ. 2007. Antibacterial and antifungal activities of fatty acid methyl esters of the blind-your-eye mangrove from India. Braz J Microbiol 38: 739-742., Chandrasekaran et al. 2011CHANDRASEKARAN M, SENTHILKUMAR A AND VENKATESALU V. 2011. Antibacterial and antifungal efficacy of fatty acid methyl esters from the leaves of Sesuvium portulacastrum L. Eur Rev Med Pharmacol Sci 15: 775-780., Golebiowiski et al. 2013, Lima et al. 2011LIMA LARS, JOHANN S, CISALPINO PS, PIMENTA LPS AND BOAVENTURA MAD. 2011. In vitro antifungal activity of fatty acid methyl esters of the seeds of Annona cornifolia A. St. Hil. (Annonaceae) against pathogenic fungus Paracoccidioides brasiliensis. Rev Soc Bras Med Trop 44: 777-780.), but these works are still scarce, so it is important to test these compounds. Fatty acid methyl esters (FAMEs) are obtained from vegetable oils. This work is focused on evaluating the antifungal activity of FAMEs from vegetable oils against Paracoccidioides spp., and also antioxidant potential by the scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals.

MATERIALS AND METHODS

CHEMICALS

Soybean, corn and sunflower vegetable oils were obtained from ABC Industry, Trade SA and Caramuru Foods SA (Brazil), respectively. All PA and HPLC grade reagents used were purchased from Vetec (Brazil) and Sigma (St. Louis, USA), respectively. Amphotericin B, 2,6-bis(1,1-dimethylethyl)-4-methylphenol (BHT), DPPH, 2’,7’-dichlorofluorescein diacetate, ascorbic acid (AA), methyl palmitate, methyl stearate, methyl oleate, methyl linoleate, methyl linolenate, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, synthetic medium RPMI and morpholine propanesulfonic acid (MOPS) from Sigma-Aldrich (St. Louis, MO, USA). Dihidrorhodamine 123 was obtained from Invitrogen (USA). Sabouraud dextrose agar was purchased from Oxoid (Basingstoke, UK), SMX-THT from Roche (Rio de Janeiro, Brazil) and fluconazole from Pfizer Pharmaceutical (USA).

PREPARATION OF METHYL ESTERS

Vegetable oils (1 g) were refluxed with 1.0 mol/L methanolic sodium hydroxide solution for 30 min and then extracted with ethyl ether. The aqueous phase was acidified with 1.0 mol/L hydrochloric acid solution and extracted with ethyl ether. The organic phase was dissolved in hexane and then refluxed with 2% v/v sulfuric acid methanolic solution for 60 min. After extraction and solvent elimination FAMEs were obtained (Lima et al. 2011LIMA LARS, JOHANN S, CISALPINO PS, PIMENTA LPS AND BOAVENTURA MAD. 2011. In vitro antifungal activity of fatty acid methyl esters of the seeds of Annona cornifolia A. St. Hil. (Annonaceae) against pathogenic fungus Paracoccidioides brasiliensis. Rev Soc Bras Med Trop 44: 777-780.).

ANALYSIS OF METHYL ESTERS BY GAS CHROMATOGRAPHY-MASS SPECTROMETRY (GC-MS)

Analysis of FAMEs by GC-MS was performed on Shimadzu CG-MS QP5050A apparatus, using impact electron at 1.2 kV, helium as the carrier gas and a Supelco PTE-5 column (30 m × 0.25 mm, df 0.25 μm). The temperature was maintained at 120 °C and programmed to 300 °C with increments of 5 °C/min; injection and detector temperatures were 230 °C. The split ratio was 1/10. The mass range was 40-500 m/z and flow rate was 2 mL/min. FAMEs were identified by using the NIST 2.0 Library database search and by comparison of their retention times with those of standards.

DPPH RADICAL-SCAVENGING ASSAY

The radical-scavenging ability of FAMEs was analyzed compared to standards BHT and AA based on reaction with DPPH radicals. The DPPH method was adapted for use with microplates (Araújo et al. 2013ARAÚJO SG, PINTO MEA, SILVA NL, SANTOS FJL, CASTRO AHF AND LIMA LARS. 2013. Antioxidant and allelopathic activities of extract and fractions from Rosmarinus officinalis. BBR - Biochem Biotechnol Rep 2: 35-43. ). A solution of DPPH (0.002% w/v) was prepared in 80% methanol. Exactly 75 μL of sample or standard (1, 10, 100, 250 and 500 μg/mL) was added to 150 μL of DPPH, and the microplate was then covered and left in the dark (once) at room temperature (25 °C); 80% methanol was used for baseline correction. The absorbance was measured in a spectrophotometer (BioTek Power Wave XS2/US) at 517 nm, after 30 min. Scavenging ability was calculated by the following equation (Burda and Oleszek 2001BURDA S AND OLESZEK W. 2001. Antioxidant and antiradical activities of flavonoids. J Agric Food Chem 49: 2774-2779.): , where Abscontrol = absorbance of DPPH radicals and Abssample = absorbance of samples or standards + DPPH. The antioxidant activity was expressed as IC50 (concentration of samples necessary to inhibit by 50% the formation of DPPH radicals, in μg/mL). Probit analysis (Finney 1980FINNEY DJ. 1980. Probit analysis, a statical treatment of the sigmoid response curve, Cambridge: University Press, 333 p.) was used to calculate the IC50 values. All assays were performed in triplicate.

CULTURE AND MAINTENANCE OF THE FUNGAL ISOLATES

In this study we used eight isolates of Paracoccidioides brasiliensis representing the three phylogenetic species (PS1, PS2 and PS3) and three isolates of P. lutzii, members of the collection of the Microorganism-Host Interaction Laboratory, Biological Science Institute of Universidade Federal de Minas Gerais (UFMG). Paracoccidioides spp. were maintained in YPD (yeast, peptone and dextrose) and subcultures were performed after 7 days of growth at 37 °C. Candida albicans ATCC 18804, C. glabrata ATCC 2001, C. krusei ATCC 200298, C. parapsilosis ATCC 22019, C. tropicalis ATCC 22019, Cryptococcus gattii ATCC 24065 and C. neoformans ATCC 24067 were used in the biological assays. The species of Candida and Cryptococcus were stored frozen at −80 °C.

The inoculum of Paracoccidioides was done according Hahn and Hamdan (2000HAHN RC AND HAMDAN JS. 2000. Effects of amphotericin B and three azole derivatives on the lipids of yeast cells of Paracoccidioides brasiliensis. Antimicrob Agents Chemother 44: 1997-2000.). The resulting suspensions were diluted in RPMI 1640 (1 : 10) to obtain the final inoculum with 1-5 × 105 yeasts/mL (Cruz et al. 2013CRUZ RC, WERNECK SMC, OLIVEIRA CS, SANTOS PC, SOARES BM, SANTOS DA AND CISALPINO PS. 2013. Influence of different media, incubation times, and temperatures for determining the MICs of seven antifungal agents against Paracoccidioides brasiliensis by microdilution. J Clin Microbiol 51: 436-443.). For Candida spp. and Cryptococcus spp., the inoculum was obtained with a final concentration of 0.5-2.5 × 103 cells/mL for susceptibility testing (CLSI 2008).

ANTIFUNGAL ACTIVITY

The antifungal activity was evaluated by the minimal inhibitory concentration (MIC) in accordance with the guidelines from the CLSI M27-A3 document (CLSI 2008). The MIC for Paracoccidioides was performed according to the method described by Johann et al. (2010JOHANN S, CISALPINO PS, WATANABE GA, COTA BB, DE SIQUEIRA EP, PIZZOLATTI MG, ZANI CL AND DE RESENDE MA. 2010. Antifungal activity of extracts of some plants used in the Brazilian traditional medicine against the pathogenic fungus Paracoccidioides brasiliensis. Pharm Biol 48: 388-396.). FAMEs were tested in the range of 2000-7.81 μg/mL, amphotericin B was tested in the range of 1-0.008 μg/mL and SMX-THT (4.49 × 10−3 to 2.3 μmol/mL) was tested in the range of 600-4.6 μg/mL. The MIC values correspond to the lowest concentrations that did not allow for the detection of any visual fungal growth. All assays were performed in triplicate and repeated at least once.

ASSESSMENT OF DRUG INTERACTIONS

The assessment of drug interactions of FAMEs and positive controls (amphotericin B, SMX-THT and itraconazole) were performed according to the described methods (Pyun and Shin 2006PYUN MS AND SHIN S. 2006. Antifungal effects of the volatile oils from Allium plants against Trichophyton species and synergism of the oil with ketoconazole. Phytomedicine 13: 394-400., White et al. 1996WHITE RL, BURGESS DS, MANDURURU M AND BOSSO JA. 1996. Comparison of three different in vitro methods of detecting synergy: time kill, checkboard, and E-test. Antimicrob Agents Chemother 40: 1914-1918.), using eight serial dilutions of each compound. These dilutions were added to 96-well plates in several combinations of concentrations of the two compounds tested. After that, a suspension of Pb-18, done according to the MIC test, was added to all wells of the plate and cultured for 14 days. The fractional inhibitory concentration (FIC) was obtained by dividing the MIC of the positive control in the presence of FAMEs by the MIC of the positive control alone. The FIC of FAMEs was calculated in the same way. The FIC index (FICI) was obtained by adding both FICs. Synergistic activity was observed when the FICI was ≤ 0.5, an indifferent effect in the range 0.5 < FICI < 2.0 and an antagonistic effect when the FICI was > 2.0.

CELLULAR REACTIVE OXYGEN SPECIES (ROS)

The P. brasiliensis Pb-18 was cultured in YPD agar during days at 37 ºC. Microplate wells received 100 μL inoculum containing 1 x 105 cfu/mL in RPMI medium without phenol red, and then the probes were added. Briefly, the probe for reactive oxygen species (ROS) (2’,7’-dichlorofluorescein diacetate) and reactive nitrogen species (RNS) (dihidrorhodamine 123) were prepared in methanol and PBS, respectively, at 100 μM and 20 μL were distributed to each well for a final concentration of 10 μM. Hydrogen peroxide (4M) was included as a control. The drug treatment solutions were evaluated at the respective MIC, in a final volume of 200 μL. The plates were incubated at 37 ºC in the dark. After 120 hour, the fluorescence was measured with a fluorometer (Biotek Synergy 2 SL Luminescence Microplate Reader/US) using excitation at 485 nm and emission wavelengths of 530 nm.

STATISTICAL ANALYSIS

Student’s t test was utilized to evaluate the statistical difference between the control group and the group exposed to FAMEs. To evaluate the statistical difference between the three FAMEs tested we used the Newman-Keuls test and ANOVA (1 way) to cellular ROS. A P value < 0.05 was considered statistically significant. The analyses were performed using Prisma 5.0 software.

RESULTS AND DISCUSSION

ANTIOXIDANT ACTIVITY

In this study, FAMEs obtained from vegetable oils were investigated by GC-MS. The analysis by GC-MS revealed a high percentage of unsaturated methyl esters (83.95-88.33%) as compared to saturated methyl esters (11.67-16.05%). In samples, methyl oleate and methyl linoleate were detected as the major unsaturated methyl esters. Methyl palmitate was the most abundant among the saturated methyl esters, followed by methyl stearate (Table I).

TABLE I
Composition and percentages of fatty acid methyl esters (FAMEs).

The scavenging effect on DPPH radicals of FAMEs from vegetable oils is presented in Figure 1. FAMEs, BHT and AA revealed an inhibitory effect in a concentration-dependent manner. FAMEs were more effective in scavenging DPPH radicals than AA at a concentration of 1 μg/mL and BHT at concentrations of 1 and 10 μg/mL. FAMEs showed IC50 values of 1.86, 9.42 and 3.33 μg/mL for soybean, corn and sunflower oils, respectively, lower than BHT (16.36 μg/mL; P < 0.05), but higher than AA (1.62 μg/mL; P < 0.05). FAMEs obtained from Annona cornifolia seeds also presented antioxidant activity, with IC50 = 3.83 μg/mL (Lima et al. 2012LIMA LARS, ALVES TMA, ZANI CL, PIMENTA LPS AND BOAVENTURA MAD. 2012. Antioxidant and cytotoxic potential of fatty acid methyl esters from the seeds of Annona cornifolia A. St. -Hil. (Annonaceae). Food Res Int 43: 873-875.). Soybean and sunflower FAMEs were more active than the FAMEs of Annona cornifolia.

Figure 1
DPPH radical-scavenging ability of fatty acid methyl esters (FAMEs) at five different concentrations (1, 10, 100, 250 and 500 μg/mL). Values represent averages ± standard deviations for triplicate experiments. BHT: 2,6-bis(1,1-dimethylethyl)-4-methylphenol; AA: ascorbic acid.

ANTIFUNGAL ACTIVITY

The antifungal activity of FAMEs obtained from vegetable oils was evaluated against 18 fungal strains of clinical interest (Table II). Results showed that all FAMEs tested showed antifungal activity against the isolates of Paracoccidioides tested, with values between 15.6 and 500 µg/mL. Paracoccidioides brasiliensis Penguin showed more susceptibility to soybean and sunflower FAMEs with an MIC value of 15.6 µg/mL, but this isolate was less susceptible to corn FAMEs (MIC = 500 µg/mL). For P. lutzii, isolate 1578 was most susceptible to the FAMEs tested in the present study. Moreover, FAMEs (soybean, corn and sunflower) showed better activity than SMX-THT (P = 0.0001) against the isolates of P. brasiliensis Pb-18, Pb-608, Pb-1017, Pb-9673 and P. lutzii 01. SMX-THT is used in the treatment of PCM, mainly in endemic regions where other therapy (such as itraconazole) is not easily available; consequently, therapy consisting of SMX-THT is a useful option (de Oliveira et al. 2015, Shikanai-Yasuda 2015). The difference in antifungal activity between different FAMEs, against 11 isolates of Paracoccidioides spp., is not statistically significant (P < 0.05). MIC values found for SMX-THT and amphotericin B against the isolates of Paracoccidioides were statistically significant when compared with FAMEs (P = 0.0001).

TABLE II
Minimal inhibitory concentration (MIC) of FAMEs against 18 clinically important fungi.

It is interesting to note that when we tested the susceptibility of other fungus genera we observed that only sunflower FAMEs showed activity under the conditions tested in the present study (Table II). This antifungal activity (sunflower FAMEs) was more pronounced against C. krusei, C. glabrata and C. parapsilosis with MIC values of 15.6, 15.6 and 31.2 µg/mL, respectively.

TABLE III
Minimal inhibitory concentration (MIC) of standards of fatty acids and methyl esters against important fungi.

Few works reporting the biological activity of FAMEs against pathogenic fungi are found in the literature. Twelve clinical strains of the fungus P. brasiliensis were susceptible to FAMEs from seeds of A. cornifolia, with MICs in the range between 3.4 and 55.5 µg/mL (Lima et al. 2011LIMA LARS, JOHANN S, CISALPINO PS, PIMENTA LPS AND BOAVENTURA MAD. 2011. In vitro antifungal activity of fatty acid methyl esters of the seeds of Annona cornifolia A. St. Hil. (Annonaceae) against pathogenic fungus Paracoccidioides brasiliensis. Rev Soc Bras Med Trop 44: 777-780.). The FAME extract of Excoecaria agallocha presented antifungal activity against Candida albicans, C. krusei, C. parapsilosis and Candida tropicalis (Agoramoorthy et al. 2007AGORAMOORTHY G, CHANDRASEKARAN M, VENKATESALU V AND HSU MJ. 2007. Antibacterial and antifungal activities of fatty acid methyl esters of the blind-your-eye mangrove from India. Braz J Microbiol 38: 739-742.). Golebiowiski et al. (2013) reported the antifungal activity of FAMEs from Calliphora vomitoria against entomopathogenic fungi, protecting this ectoparasite against entomopathogenic microorganisms present in its habitat. Furthermore, these authors showed that when individual FAMEs were tested they presented weak antifungal activity, but the mixture of FAMEs found in living forms of C. vomitoria was more active. These experiments are in agreement with those of the present study where the mixture of FAMEs presented antifungal activity.

In the present work we also tested the antifungal activity of standards of the methyl esters which were present in the FAMEs (Table III). Of these methyl esters tested only methyl linoleate showed antifungal activity against P. brasiliensis (Pb-18), with an MIC value of 62.5 µg/mL (Table III). It is interesting to note that sunflower FAMEs had a higher percentage of methyl linoleate (65.93%) and also presented better antifungal activity, with 54.54% of isolates of Paracoccidioides tested with an MIC value ≤ 62.5 µg/mL. The other two FAMEs tested also followed this pattern; soybean FAMEs containing 55.67% methyl linoleate showed antifungal activity with an MIC value ≤ 62.5 µg/mL for 36.36% of isolates of Paracoccidioides tested and corn FAMEs (48.38% methyl linoleate) with 27.27% of isolates tested with an MIC value ≤ 62.5 µg/mL. Probably, methyl linoleate is responsible for the antifungal activity of the FAMEs studied, because it is also present in a greater concentration in all the FAMEs tested (Table I). In present work we also observed the production of reactive oxygen (ROS) by methyl linoleate, sunflower and corn FAMEs (Figure 2) with production significantly compared to the control group (P. brasiliensis 18 without treatment) (P < 0.05). Methyl linoleate is able to produce hydroperoxide (Yamamoto et al. 1984YAMAMOTO Y, HAGA S, NIKI E AND KAMIYA Y. 1984. Oxidation of lipids. V. Oxidation of Methyl Linoleate in aqueous dispersion. Bull Chem Sot Jpn 57: 1260-1264.) and probably this property is responsible for the antifungal activity of this compound in the present work. Therefore the ROS production could be related with antifungal activity of sunflower and corn FAMEs and methyl linoleate compound present in these FAMEs could be responsible for ROS production.

Figure 2
Production of reactive oxygen species (ROS) in Paracoccidioides brasiliensis after treatment with FAMEs and methyl linoleate. Treatments with Corn and Sunflower FAMEs increased ROS production significantly compared to the control group (P < 0.05) One-way analysis of variance (ANOVA) and Kruskal-Wallis multiple-comparison tests.

Methyl linoleate has already been tested against inhibition of the in vitro proliferation of human tumor cell lines; this compound showed antiproliferative activity with an IC50 of 250 µg/mL, but not induction of differentiation. This is an interesting finding, because 5-fluorouracil is also a known antitumor compound that does not induce differentiation and is currently used as an antifungal (Lampronti et al. 2003LAMPRONTI I, MARTELLO D, BIANCHI N, BORGATTI M, LAMBERTINI E, PIVA R, JABBAR S, CHOUDHURI MSK, KHAN TH AND GAMBARI R. 2003. In vitro antiproliferative effects on human tumor cell lines of extracts from the Bangladeshi medicinal plant Aegle marmelos Correa. Phytomedicine 10: 300-308.).

In the present work we also tested the antifungal activity of standards of fatty acids (Table III) because these compounds were present in the oils (sunflower, soybean and corn oils) that originated the FAMEs. Although two of these compounds (oleic acid and linoleic acid) exhibited interesting antifungal activity against Pb-18, the oils did not present activity (data not shown).

To explore the possibility of developing more powerful combination therapies of FAMEs with other antifungal drugs, a checkerboard micro-titer test was carried out. FAMEs showed an antagonistic effect with amphotericin B and an indifferent effect with SMX-THT (Table IV). FAMEs showed a synergetic effect with itraconazole. This illustrates one important result, because it could lead to the development of a new combination therapy using lower concentrations of itraconazole in a shorter treatment time, which would reduce the side effects of patients. Itraconazole interferes in ergosterol synthesis, leading to cell membrane perturbation (Odds et al. 2003ODDS FC, BROWN AJP AND GOW NAR. 2003. Antifungal agents: mechanisms of action. Trends Microbiol 11: 272-279.). Alteration in membrane permeability could allow increased concentrations of FAMEs to penetrate the cell, resulting in cell death.

TABLE IV
Fractional inhibitory concentration (FIC) and FIC index (FICI) of FAMEs against Paracoccidioides brasiliensis isolate Pb-18.

CONCLUSIONS

In the search for new drugs with antifungal and antioxidant properties, FAMEs (obtained from vegetable oils of soybean, corn and sunflower) might be good candidates: these esters presented better radical-scavenging activity and IC50 values than BHT, a commercial antioxidant. All three FAMEs tested showed antifungal activity against isolates of Paracoccidioides spp. with MIC values ranging from 15.6-250 µg/mL. Sunflower FAMEs also exhibited antifungal activity that extended to other genera, with an MIC of 15.6 μg/mL against Candida glabrata and C. krusei and 31.2 μg/mL against C. parapsilosis. FAMEs exhibited a synergetic effect with itraconazole. The antifungal activity of the FAMEs against isolates of Paracoccidioides spp. is likely due to the presence of methyl linoleate, the major compound present in all three FAMEs. This work provided knowledge, for the first time, of the antioxidant and antifungal activity of FAMEs obtained from vegetable oils and indicates the potential of FAMEs as a source of antifungal and antioxidant activity.

ACKNOWLEDGMENTS

The authors are grateful to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação de Amparo a Pesquisa do Estado de Minas Gerais (FAPEMIG) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for their fellowships. The authors do not have any conflicts of interest.

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Publication Dates

  • Publication in this collection
    31 Aug 2017
  • Date of issue
    Jul-Sep 2017

History

  • Received
    23 Dec 2016
  • Accepted
    03 Mar 2017
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