Showing papers on "Lanosterol published in 1984"

Molecular basis for the antimycotic and antibacterial activity of N‐substituted imidazoles and triazoles: The inhibition of isoprenoid biosynthesis

Abstract: The antimycotic N-substituted imidazoles and triazoles, such as imazalil, ketoconazole and itraconazole, interfere selectively at low concentrations (≥0.01nm) with the 14α-demethylase system (which is dependent on cytochrome P-450) of fungal cells, for example, Candida albicans and Penicillium italicum. This results in a decreased availability of ergosterol and the accumulation of 14α-methyl-sterols such as lanosterol. Cholesterol synthesis in a subcellular fraction of rat liver, in intact fibroblasts, and in vivo in rat liver, was much less sensitive, for example, to ketoconazole. The imidazole derivatives imazalil, miconazole, ketoconazole and parconazole, and the triazole derivatives propiconazole, terconazole and itraconazole affect the cytochrome P-450 species of microsomal fractions from Saccharomyces cerevisiae and rat liver. Cytochrome P-450 of rat-liver microsomes was much less sensitive to these azole derivatives, in parallel with the lower sensitivity of cholesterol synthesis. Using unilamellar vesicles composed of phosphatidylcholine, phosphatidyl-ethanolamine and diphosphatidylcholine, multilamellar vesicles of dipalmitoylphos-phatidylcholine, and intact S. cerevisiae, it was shown that the substitution of ergosterol by lanosterol leads to functional changes in the membranes. It is speculated that the selective interaction of the azole derivatives with the yeast microsomal cytochrome P-450 leads to the accumulation of 14a-methyl-sterols and results in changes in the permeability of the membranes and leakages. The observed inhibition of growth may have its origin in these changes. Miconazole, ketoconazole and deacylated ketoconazole (R-39519) also affect the growth of Staphylococcus aureus, miconazole being 12.5 and 14 times, respectively, more active than R-39519 and ketoconazole. The greater antibacterial activity of miconazole coincides with its greater inhibition of the biosynthesis of C-55 isoprenoid alcohol and vitamin K. The phosphorylated derivative of C-55 isoprenoid alcohol has functional importance in the biosynthesis of bacterial cell wall and membrane polymers, and the menaquinone vitamin K plays a role in the electron transport of Gram-positive bacteria. The reduced synthesis of these vital compounds may contribute to the antibacterial activity of miconazole.

Cholesterol-induced growth stimulation, cell aggregation, and membrane properties of ascites tumor cells in culture.

Abstract: Ascites tumor cells can be cultivated at a reduced serum concentration if cholesterol (2.50 mg per 100 ml of medium) is added to the culture medium. At serum concentrations of 3%, optimal growth properties are obtained; below 3%, cell cultures usually perish after a few days. Cells grown in the presence of added cholesterol have an elevated content of this molecule per cell as well as in the plasma membrane, and they also show a cholesterol concentration-dependent rate of proliferation. Precursors of the cholesterol-biosynthetic pathway like mevalonic acid, added in mm amounts, or squalene and lanosterol cannot be substituted for cholesterol itself. This is due to the observation that the biosynthetic pathway is blocked at the stage of lanosterol conversion to cholesterol. Cholesterol de novo synthesis from acetate is regulated by the cholesterol content of the cells, which also affects the production of ubiquinone and dolichol. Growth factors such as insulin, prostaglandin F2α, and transferrin added to the medium do not mimic the cholesterol-induced effect. Distribution of DNA during cell cycle and the cell density-dependent reduction in macromolecule synthesis is very similar to the control cells. In contrast, cells without added cholesterol show reduced growth properties accompanied by the accumulation of cells in the mitotic and G2 phase. The cholesterol/phospholipid ratio of the plasma membranes of cholesterol-rich cells is about 15% lower than of the control cells and 40% higher compared to the cholesterol-poor cells, which, however, does not significantly alter the membrane fluidity between the cholesterol-rich and -poor cells as revealed by fluorescence polarization measurements. The most dramatic behavior of the cholesterol-rich cells is their tendency to form aggregates, which is demonstrated either by concanavalin A-induced agglutination or by cell density-dependent aggregation shown by interference microscopy in vivo .

Effect of cholesterol on phospholipid, RNA, and protein synthesis in Mycoplasma capricolum.

Abstract: The regulatory role of cholesterol on phospholipid, RNA and protein synthesis was investigated in Mycoplasma capricolum. The addition of 2 micrograms/ml of cholesterol to cells growing slowly on lanosterol (10 micrograms/ml) caused an early stimulation of unsaturated phospholipid synthesis followed by a later stimulation of RNA and protein synthesis. Epicoprostanol, a cholesterol antagonist, sequentially inhibited these three processes. Phospholipid served as the acyl donor for the acylation of membrane proteins. Membrane-bound cholesterol correlated with a decrease in the amount of [3H]amino acids and an increase in the amount of [3H]oleate found in two membrane proteins (MW 78 kDa and 26 kDa). Taken together, the results suggest that a small amount of membrane-associated cholesterol serves as a signal for membrane biogenesis and, in turn, macromolecular synthesis and cell growth.

Synthesis of Lanosterol Analogs with Lengthened Side Chains and Their Effects on Cholesterol Biosynthesis from Lanosterol

Abstract: Starting from 3β-acetoxy-25, 26, 27-trinorlanost-8-en-24-al (1), eight lanosterol analogs (10-17) with longer side chains side chains than that of lanosterol were synthesized by Wittig reaction followed by catalytic hydrogenation. Cholesterol biosynthesis was examined in rat hepatic subcellular preparation (S10) incubated with [24-3H]-lanosterol in the presence of each of the eight lanosterol analogs. Some of the analogs (10 and 12) caused slight inhibition, but 16 and 17 showed no inhibitory effect. The structure-inhibitory activity relationship of lanosterol analogs on cholesterol biosynthesis from lanosterol is discussed.

Preparation of 14C-labeled and unlabeled sterol intermediates from yeast using metabolic inhibitors.

Abstract: The method for the preparation of zymosterol was improved (13 mg of zymosterol/g dry cells) by the aerobic adaptation of the cells in the presence of 1 mM DL-ethionine. Lanosterol was also found to accumulate (5.0 mg/g dry cells) when the cells were adapted aerobically in the presence of 10(-4) M buthiobate. Pure lanosterol could be obtained by separation of the unsaponifiable lipids on TLC. Pure [14C]lanosterol with a high specific radioactivity (56 Ci/mol) could be prepared by incubation of the desiccated cells with [14C]isopentenyl pyrophosphate, cofactors such as ATP and NADPH-generating system, and buthiobate in phosphate buffer. The method using desiccated cells may also be applicable to the preparation of other radioactive sterol intermediates.

Activity and structural characteristics of steroid and non-steroid lipid growth factors for Haliphthoros milfordensis, a fungal parasite of marine crustaceans

Abstract: The lipid growth factor requirement of Haliphthoros milfordensis was satisfied by a number of steroids. Active steroids had a side chain of 8–10 carbons. The stereochemistry at C-5 had to be 5 α when no C-5(6) double bond was present. An oxygen function at C-3 could be either 3β-OH, 3α-OH, 3-keto, or an esterified 3β-OH group. Absence of double bonds in the steroid nucleus and side chain or presence of one or more double bonds at C-4(5), C-5(6), C-7(8), C-8(9), C-22(23), C-24(25) and C-24(28) had no pronounced influence on the activity of the steroid as a growth factor. An additional oxygen function in or at the steroid nucleus or at the side chain retarded or completely inhibited growth of H. milfordensis . The tetracyclic hydrocarbon 5α-cholestane, the phospholipid Lα-lecithin (distearoyl) and the unsaturated fatty acids oleic acid and palmitoleic acid were also active as growth factors. Steroid precursors mevalonic acid, geraniol, farnesol, and squalene were inactive, whereas the cyclization product of squalene-2, 3-epoxide, lanosterol, was active. Indirect evidence for the participation of the growth factors in membrane architecture of H. milfordensis was obtained from studies on the sensitivity of the fungus towards polyene-antibiotics. Steroid-grown cultures were sensitive to nystatin whereas steroid-free oleic acid-grown cultures were not.