Nizoral
[Comparative sensitivity of yeasts to ketoconazole, itraconazole and fluconazole using a liquid medium standardized micromethod]

[Article in French]

Guinet R, Marlier H.

Institut Pasteur, Le Poirier, Lentilly.

The minimal inhibitory concentrations of 200 yeast strains (48 reference strains and 152 recently isolated from pathological products) were evaluated with a new standardized micromethod using a liquid medium comparatively for ketoconazole, itraconazole and fluconazole. The ready-to-use microtitration plates contained the antifungal agents in concentrations ranging from 100 to 0.10 mg/l. The cumulative MIC curves clearly showed the superiority of ketoconazole, fluconazole being the less active product. These results were confirmed after categorization in sensitive (S: MIC less than 0.78 mg/l), intermediate (I: 0.78 less than MIC less than 6.25) or resistant (R: MIC greater than 6.25). These results are discussed particularly for fluconazole showing the largest half-life and for which higher plasmatic levels could be achieved. Important variations were observed depending on the species and as example for Candida tropicalis the sensitivities were ketoconazole 100%, itraconazole 55% and fluconazole 0%. The less sensitive species to the 3 azoles were Saccharomyces cerevisiae and Torulopsis glabrata. This new micromethod being very easy to use and allowing the determination of fungicidal activities should be introduced in routine.

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Nizoral
[Efficacy and long-term tolerance of ketoconazole in the treatment of Cushing's disease]

[Article in French]

Tabarin A, Navarranne A, Corcuff B, Guerin J, Kern AM, Roger P.

Service d'Endocrinologie, Hopital Haut Leveque, Pessac.

Successful short term treatment of patients with Cushing's disease by Ketoconazole without adverse effects is now well established. Little data are available about prolonged treatment of this disease with ketoconazole. We report herein our experience of ketoconazole therapy in four patients with Cushing's disease treated for 9 to 38 months. One patient rapidly developed adrenal hypofunction and required transient steroid therapy adjunction. In the other patients, cortisol overproduction was reduced to normal levels within two months and their urinary free cortisol remained within the normal range throughout the study. In two patients ketoconazole dose could be decreased but had to be increased after ten months of therapy in one patient. None of the patients had clinical or biochemical signs of drug toxicity. Thus, ketoconazole seems to be a useful drug for the prolonged metabolic control of Cushing's disease. However, in this circumstance, ketoconazole daily dose adaptation can be necessary in order to maintain normal urinary cortisol levels and the ability of ketoconazole to cure Cushing's disease still remains to be determined.

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Nizoral
A novel method for studying ergosterol biosynthesis by a cell-free preparation of Aspergillus fumigatus and its inhibition by azole antifungal agents.

Ballard SA, Ellis SW, Kelly SL, Troke PF.

Department of Discovery Biology, Pfizer Central Research, Sandwich, Kent, UK.

A novel procedure has been developed for measuring ergosterol biosynthesis from [14C]mevalonate in a cell-free extract prepared from Aspergillus fumigatus. Ergosterol accounted for approximately 60% of the 4, 14-desmethylated sterol fraction which in turn totalled 13.2% of the non-saponifiable lipid produced. The other major sterol fractions were 4, 4-dimethylated sterols and 4-monomethylated sterols which accounted for 30.8% and 20.1% respectively of non-saponifiable lipid. The cell-free system had a narrow pH optimum of 7.2-7.4 for desmethylated sterol biosynthesis. Activity decreased by 94% at pH 6.5. Fluconazole (10(-4) M), ketoconazole (10(-6) M) and itraconazole (10(-6) M) inhibited formation of desmethylated sterols by greater than 85%, while 4-monomethylated sterols and 4, 4-dimethylated sterols were increased. The IC50s for inhibition of desmethylated sterol biosynthesis were 1.4 x 10(-6) M for fluconazole, 4.0 x 10(-8) M for ketoconazole, and 3.3 x 10(-8) M for itraconazole. The difference in intrinsic potency between fluconazole and ketoconazole is particularly interesting in view of the fact that fluconazole is a more effective agent than ketoconazole in an animal infection model of systemic aspergillosis.

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Nizoral
Azole susceptibility and hyphal formation in a cytochrome P-450-deficient mutant of Candida albicans.

Lees ND, Broughton MC, Sanglard D, Bard M.

Department of Biology, Indiana University-Purdue, Indianapolis 46205.

A cytochrome P-450-deficient mutant of Candida albicans, strain D10, was employed to study the mode of action of imidazole antifungal agents. This mutant accumulates exclusively 14-alpha-methylsterols, resulting in a sterol profile which mimics that of azole-treated wild-type strains. Since the widely accepted primary effect of imidazoles is the inhibition of cytochrome P-450-mediated demethylation of the ergosterol precursor lanosterol, strain D10 and its wild-type revertant, strain D10R, were grown in the presence of concentrations of clotrimazole, miconazole, and ketoconazole known to inhibit demethylation. The growth of strain D10 was unaffected by these antifungal agents, while that of strain D10R was significantly reduced. At higher azole concentrations (which are known to exert a direct, disruptive action on the cell membrane), the growth of both strains was immediately and completely inhibited by clotrimazole and miconazole. Ketoconazole was membrane disruptive only for strain D10; this is the first report of a direct membrane effect for this drug. Because hyphal formation has been implicated in the pathogenesis of C. albicans and because it has been shown to be inhibited by azoles, the hypha-forming capability of strain D10 was examined. Strain D10 was shown to be seriously defective in hyphal formation, suggesting that this function may be dependent on the 14-alpha-demethylation of lanosterol. The results of this study suggest that inhibition of lanosterol demethylation per se is neither fungicidal nor fungistatic, although the growth rate is reduced. In addition, the substitution of 14-alpha-methylsterols for ergosterol results in defective hyphal formation and in a cell that is more susceptible to membrane-active agents such as ketoconazole.

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Nizoral
Effects of cytochrome P-450 inhibitors on the in vivo metabolism of all-trans-retinoic acid in rats.

Van Wauwe JP, Coene MC, Goossens J, Cools W, Monbaliu J.

Janssen Research Foundation, Beerse, Belgium.

This study examines the effects of ketoconazole, R 75 251 and some other cytochrome P-450 inhibitors on the in vivo metabolism of all-trans-retinoic acid (RA) in normal rats. Oral treatment with ketoconazole or R 75 251 (40 mg/kg, -1 hr) reduced the elimination rate of i.v. injected RA from plasma: the half-life of RA increased from 27 min in control-treated animals to 43 min and 76 min after dosing with ketoconazole and R 75 251, respectively. However, neither drug had an effect on the distribution volume of the retinoid. Two hours after i.v. injection of RA, residual plasma levels of the retinoid were 11.2 ng/ml in ketoconazole and 22.7 ng/ml in R 75 251-treated rats. The other P-450 inhibitors, aminoglutethimide, cimetidine, itraconazole, metyrapone and saperconazole, showed no sparing effect on RA elimination: plasma levels of the acid were below 1 ng/ml, as in control-treated animals. Administration of ketoconazole or R 75 251 (40 mg/kg, -2 hr) to rats also enhanced endogenous plasma concentrations of RA. Levels of the retinoid were raised from mostly undetectable values (less than 0.5 ng/ml) to 1.3 +/- 0.1 and 2.5 0.1 ng/ml after treatment with ketoconazole and R 75 251, respectively. These data are indicative of the important contribution of the cytochrome P-450 enzyme system to the in vivo metabolic process of RA. In vivo inhibition of the P-450 pathway not only increased the biological half-life of exogenously administered RA, but also enhanced the endogenous plasma level of this vitamin A derivative.

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Nizoral
Studies on the effect of ketoconazole on the fusion of L6 myoblasts.

Wayne S, Jamieson JC, Spearman MA, Wright JA.

Department of Chemistry, University of Manitoba, Winnipeg, Canada.

The effect of ketoconazole on the fusion of L6 myoblasts was studied. Ketoconazole was a potent inhibitor of myoblast fusion at concentrations as low as 0.1 microM, but fusion was restored when the inhibitor was removed. The inhibitor resulted in decreased binding of conA and WGA to cell surface oligosaccharides showing that it was inhibiting N-linked cell surface glycoproteins. Inhibition of fusion by ketoconazole was accompanied by reduced creatine phosphokinase activities showing that it is affecting biochemical differentiation. Incorporation of labelled mannose from GDP-mannose into lipid-sugar and lipid-oligosaccharide complexes involved in the synthesis of N-linked oligosaccharides was also inhibited by ketoconazole, but the inhibition was reversed by addition of exogenous dolichol phosphate to the incorporation mixture. The main conclusion from these studies was that ketoconazole inhibited fusion of L6 myoblasts by affecting the synthesis of dolichol-phosphate required for the synthesis of lipid-oligosaccharides needed for the synthesis of fusogenic cell surface N-linked glycoproteins.

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Nizoral
Differential regulation of low density lipoprotein suppression of HMG-CoA reductase activity in cultured cells by inhibitors of cholesterol biosynthesis.

Gupta AK, Sexton RC, Rudney H.

Department of Molecular Genetics, University of Cincinnati College of Medicine, OH 45267-0524.

Treatment of rat intestinal epithelial cells (IEC-6 cells) with lanosterol 14 alpha-demethylase inhibitors, ketoconazole and miconazole, had similar effects on 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity and cholesterol biosynthesis but the drugs differed in their ability to prevent the low density lipoprotein (LDL) suppression of reductase activity. Miconazole, at concentrations that inhibited the metabolism of lanosterol and epoxylanosterol to the same degree as ketoconazole, did not prevent low density lipoprotein action on reductase activity, whereas ketoconazole totally abolished the low density lipoprotein action on reductase activity. Both drugs caused: 1) a biphasic response in reductase activity such that at low concentrations (less than 2 microM) reductase activity was inhibited and at high concentrations (greater than 5 microM) the activity returned to control or higher than control levels; 2) an inhibition of metabolism of lanosterol to cholesterol, and 24(S), 25-epoxylanosterol to 24(S), 25-epoxycholesterol. Neither drug prevented suppression of reductase activity by 25-hydroxylanosterol, 25-hydroxycholesterol, or mevalonolactone added to the medium. Each drug increased the binding, uptake, and degradation of 125I-labeled LDL and inhibited the re-esterification of free cholesterol to cholesteryl oleate and cholesteryl palmitate. The release of free cholesterol from [3H]cholesteryl linoleate LDL could not account for the differential effect of ketoconazole and miconazole on the prevention of low density lipoprotein suppression of reductase activity. The differential effect of the drugs on low density lipoprotein suppression of reductase activity was not unique to IEC-6 cells, but was also observed in several cell lines of different tissue origin such as human skin fibroblast cells (GM-43), human hepatoblastoma cells (HepG2), and Chinese hamster ovary cells (wild type, K-1; 4 alpha-methyl sterol oxidase mutant, 215). These observations suggest that the suppressive action of low density lipoprotein on reductase activity 1) does not require the de novo synthesis of cholesterol, or 24(S), 25-epoxysterols; 2) is not mediated via the same mechanism as that of mevalonolactone; and 3) does not involve cholesteryl reesterification. Ketoconazole blocks a site in the process of LDL suppression of reductase activity that is not affected by miconazole.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2324644&dopt=Abstract ketoconazole Nizoral