Protection by Unsaturated Lecithin Against the Imidazole Antimycotics, Clotrimazole and Miconazole

ANTIMICROBIAL AGENTS AND CHEmoTHERAPY, Mar. 1978, p. 423-426 Vol. 13, No.3 0066-4804/78/00134423$02.00/0 Copyright i) 1978 American Society for Microbiology Printed in U.S.A. Protection by Unsaturated Lecithin Against the Imidazole Antimycotics, Clotrimazole and Miconazole HIDEYO YAMAGUCHI Department ofMicrobiology, Faculty ofMedicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan Received for publication 13 September 1977 The actMty of egg lecithin in preventing the antifungal action of the two imidazole antimycotics, cloimazole and miconazole, was confirmed. However, addition of this phospholipid could not relieve an existing imidazole inhibition. Compared with egg lecithin, reduced egg lecithin showed no such protective effect. The addition of egg lecithin to an aqueous suspension of the imidazole drugs changed the absorption profile of the imidazole, suggesting a low solubility and, consequently, a lower effective concentration; however, the addition of reduced egg lecithin did not produce any change in the adsorption. These results indicate that the preventive effect of egg lecithin on imidazole inhibition may be a consequence of preferential in vitro interaction of the drug with unsaturated phospholipid to form a hydrophobic complex. Clotrimazole and miconazole are new imidaz- MATERIAIS AND METHODS ole derivatives that show a marked activity Organism. C. albicans MTU 12021 was employed against yeasts, fungi, and some gram-positive in this study. This strain was originally isolated from bacteria (11, 13). Several papers dealing with the a patient with Candida vaginitis. Stock cultures were mechanism of imidazole action have demon- maintained by transfer at 2-month intervals on Sa- strated that both clotimazole and miconazole bouraud glucose agar. apparently disturb the permeability character- Chemicals. Clotimazole was fiunished by Bayer istics of the cell membrane, which allows, on the Yakuhin Co., Ltd. (Osaka), and miconazole was ob- ofessential precursors, metab- tained from Mochida Pharmaceutical Co., Ltd. (To- one hand, leakage kyo). Stock solutions of each drug (8 mg/ml) were olites, ions, and other intracellular components made with dimethyl sulfoxide and stored at -20°C. (7, 8, 12) and which produces, on the other hand, All of the lecithins used were purchased from P-L retardation of uptake of some amino acids from Biochemicals Inc. A solution oflecithin was made with the medium (15). Our previous studies have chloroform-methanol (2:1, vol/vol) or absolute ethanol shown that the anti-Candida activity ofthe two as required. L-[U-14C]leucine (270 mCi/mmol) was imidazole drugs is antagonized by several classes obtained from Dai-ichi Pure Chemicals Co. (Tokyo). of lipids (e.g., phospholipids and acylglycerides), Cell viability. Growth studies were made in a containing one or more acyl groups in its mole- synthetic medium consisting of yeast nitrogen base and unsaturated fatty acids and that, broth (Difco) with 1% (wt/vol) glucose and 0.15% cule, by (wt/vol) L-asparagine, adjusted to pH 4.5. The yeast unlike polyene antibiotics, none of the imidaz- inoculum consisted of 5 ml of log-phase culture (6 to oles can interact with cholesterol or ergosterol 9 h) grown at 37-C in shake flasks and diluted in the (14). These results have led us to postulate that same medium to give a final optical density at 560 nm the mechanism of antifngal action of imidaole (OD5ow) of 0.40. Turbidity was measured by a Perkin- involves an interaction with unsaturated phos- Elmer UV-VIS spectrophotometer equipped with a pholipids that are locating in cellular mem- 10-mm light-path quartz cuvettes. An optical density branes, which causes these alterations in mem- of 0.10 was found to represent 3 x 108 to 4 x 10' viable brane permeability. cells per ml. A 2-pg/ml portion of clotrimazole or The present communication expands upon the miconazole prepared in a 1.0-ml volume of the synthetic medium was added to 1.0 ml of the same me- observations made by measuring the antagonis- dium inoculated with a growing culture (1:1,000). Im- tic action of egg lecithin compared with that of idazole and lecithin were dissolved in dimethyl sulf- reduced egg lecithin, which represented the un- oxide and chloroform-methanol, respectively. AU the saturated and saturated phospholipids, respec- tubes containing imidazole and/or lecithin also con- tively, against both clotimazole and miconazole tained the same concentration of the former solvent on C. albicans. (1%, vol/vol) and the latter (2.5%, vol/vol) as did the 423 424 YAMAGUCHI ANTIMICROB. AGENTS CHEMOTHER. appropriate control tubes. In no case did the amounts of the two solvents inhibit the growth of C. albicans under study. Each tube was incubated statically at 370C. Where indicated, 2 mg of either egg lecithin or reduced egg lecithin per ml (in a volume of 0.05 ml) was supplemented at zero time or at 24 h, and incubation was further continued. After the onset of incubation, at 24 and 48 h, samples were withdrawn and viability was determined by plating dilutions (in Sa- bouraud glucose broth) ofyeast cultures on Sabouraud glucose agar. The plates were incubated at 370C for 48 h before the colonies were counted. Uptake of radioactively labeled leucine. Tests for growth and starvation of C. albicans cells were performed according to the same procedures as de- scribed previously (15). The indicated amounts of imidazole (30 ug/ml) and/or lecithin (50 pg/ml) were added to starved cells suspended in a 0.4-mM KH2PO4 solution. With or without subsequent incubation at 37°C for 60 min, [14C]leucine, to a concentration of 1 mM, was added to each reaction mixture, and further incubation was made. After 2 h at 37°C, a 2-ml volume of samples was taken, and the reaction was immedi- ately stopped with 1 ml of 3 x 10-3 M uranyl nitrate (pH 4.0). The cells were harvested by centrifugation, washed three times in 10-3 M uranyl nitrate in a total volume of 15 ml, and then extracted with 2 ml of 95% (vol/vol) ethanol at 250C for 30 min. A portion of the extract removed by centrifugation was placed in a counting vial, and the radioactivity was measured on a Packard Tricarb liquid scintillation spectrophotom- Hours eter 2425 series. Spectral studies. Clotrimazole and miconazole FIG. 1. Effect of egg lecithin on anti-Candida ac- were dissolved in absolute ethanol, diluted 50-fold with tivity of imidazole antimycotics. To C. albicans cul- 0.1 M succinate-phosphate buffer (pH 4.0), and em- tures were added egg lecithin (50 pg/ml) and imid- ployed at a final drug concentration of 25 Ag/ml. azole (1 pg/mi), alone and in combination, at zero Lecithins were also dissolved in ethanoi and dispersed time. (1) No addition; (2) lecithin; (3) clotrimazole; (4) in the same buffer by vigorous vibration in a Vortex miconazole; (5) clotrimazole plus lecithin; and (6) mixer. Subsequently, reactions between imidazole and miconazoleplus lecithin. Otherwise, egg lecithin was lecithin were carried out in a 4-ml volume of 2% added to yeast cultures 24 h after they had been (vol/vol) ethanol. After incubation at 25°C for 2 h, preincubated with (7) clotrimazole or (8) miconazole. imidazole samples with or without lecithin were taken to measure the absorption spectrum from 240 to 290 restoration in the viable count as compared with nm in a Shimadzu multipurpose spectrophotometer the value for the comparable cultures, which model MPS-5000. Spectral analysis of the reaction had been exposed to imidazole alone. In contrast, combinations of imidazole and lecithin was compared no such protective effect was noted with reduced with that of lecithin alone. egg lecithin (data not shown). Experiments were also performed to learn RESULTS whether egg lecithin was effective in reversing Growth-inhibitory effect. Under the pres- inhibition by the imidazole drugs even when the ent experimental conditions where the viable cells were treated with either clotrimazole or count for untreated control cultures increased miconazole for 24 h before the addition of the 300- and 900-fold during the incubation period phospholipid. Egg lecithin produced no rever- of 24 and 48 h, respectively, addition of 1 ,ug of sion ofthe antifungal action ofthe two imidazole clotrimazole or miconazole per ml to these cul- drugs (Fig. 1). tures at zero time led to a gradual decrease in Effect of leucine uptake. Both clotriazole the viable count, reaching a value 10 times as and miconazole at a concentration of 30 jig/ml low as the initial one after 48 h of incubation almost completely inhibited the entry and ac- (Fig. 1). On the other hand, lecithin was added cumulation of leucine in the amino acid pool in at too low a concentration (50 ,ug/ml) to affect starved C. albicans cells (Table 1). When egg the yeast growth when used alone. When egg lecithin (50 ug/ml) was added to the test mixture lecithin was added at zero time along with clo- either before or with addition ofclotrimazole (30 trimazole or miconazole, there was 10- to 50-fold ug/ml) at zero time, the inhibition of leucine VOL. 13, 1978 PROTECTION BY LECITHIN AGAINST IMIDAZOLES 425 uptake was partially prevented. However, the did not show any protection against the action addition of egg lecithin to cells already inhibited of the two imidazole drugs. by clotrimazole (at 60 min) did not alter the Influence on the absorption spectrum of effect of the imidazole drug. Comparable results imidazoles. When the two imidazole drugs were were obtained with 30 ,ug of miconazole per ml. incubated in citrate-phosphate buffer containing Compared with egg lecithin, reduced egg lecithin egg lecithin, their absorbance values increased significantly at wavelengths ranging from 240 to TABLE 1.

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