Effects of quinones and nitroazoles on free-radical fragmentation of glycerol-1-phosphate and 1,2-dimyristoyl-glycero-3-phosphatidyl-glycerol.

Effects of quinones and azoles on the formation of steady-state radiolysis products in aqueous solutions of glycerol-1-phosphate and aqueous dispersions of 1,2-dimyristoyl-glycero-3-phosphatidyl-glycerol has been investigated. The data obtained by LC-MS-ESI and spectrophotometric measurements shows that the compounds having quinoid structures, including the antitumor agent doxorubicin, and azoles having nitro groups effectively inhibit free-radical fragmentation of glycerol-1-phosphate and 1,2-dimyristoyl-glycero-3-phosphatidyl-glycerol, decreasing the radiation-chemical yields of either inorganic phosphate or phosphatidic acid respectively. The observed effects of blocking free-radical processes are believed to be related to the ability of the tested compounds to oxidize α-hydroxyl-containing carbon-centered radicals of starting substrates, which give rise to fragmentation reaction. The possibility of using the discovered properties of quinones, doxorubicin and nitroazoles to provide practical solutions in oncological radiotherapy and pathophysiology is discussed.

Evaluation of the fluorescent probes Nile Red and 25-NBD-cholesterol as substrates for steroid-converting oxidoreductases using pure enzymes and microorganisms.

The fluorescent probes Nile Red (nonsteroidal dye) and 25-{N-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-methyl]amino}-27-norcholesterol (25-NBD-cholesterol) (a cholesterol analog) were evaluated as novel substrates for steroid-converting oxidoreductases. Docking simulations with autodock showed that Nile Red fits well into the substrate-binding site of cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17A1) (binding energy value of -8.3 kcal·mol⁻¹). Recombinant Saccharomyces cerevisiae and Yarrowia lipolytica, both expressing CYP17A1, were found to catalyze the conversion of Nile Red into two N-dealkylated derivatives. The conversion by the yeasts was shown to increase in the cases of coexpression of electron-donating partners of CYP17A1. The highest specific activity value (1.30 ± 0.02 min⁻¹) was achieved for the strain Y. lipolytica DC5, expressing CYP17A1 and the yeast's NADPH-cytochrome P450 reductase. The dye was also metabolized by pure CYP17A1 into the N-dealkylated derivatives, and gave a type I difference spectrum when titrated into low-spin CYP17A1. Analogously, docking simulations demonstrated that 25-NBD-cholesterol binds into the active site of the microbial cholesterol oxidase (CHOX) from Brevibacterium sterolicum (binding energy value of -5.6 kcal·mol⁻¹). The steroid was found to be converted into its 4-en-3-one derivative by CHOX (K(m) and k(cat) values were estimated to be 58.1 ± 5.9 µM and 0.66 ± 0.14 s⁻¹, respectively). The 4-en-3-one derivative was also detected as the product of 25-NBD-cholesterol oxidation with both pure microbial cholesterol dehydrogenase (CHDH) and a pathogenic bacterium, Pseudomonas aeruginosa, possessing CHOXs and CHDHs. These results provide novel opportunities for investigation of the structure-function relationships of the aforementioned oxidoreductases, which catalyze essential steps of steroid bioconversion in mammals (CYP17A1) and bacteria (CHOX and CHDH), with fluorescence-based techniques.

22-NBD-cholesterol as a novel fluorescent substrate for cholesterol-converting oxidoreductases.

Docking simulations and experimental data indicate that 22-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-23,24-bisnor-5-cholen-3ß-ol (22-NBD-cholesterol), a common fluorescent sterol analog, binds into active sites of bovine cytochrome P450scc and microbial cholesterol dehydrogenases (CHDHs) and then undergoes regiospecific oxidations by these enzymes. The P450scc-dependent system was established to realize N-dealkylation activity toward 22-NBD-cholesterol, resulting in 7-nitrobenz[c][1,2,5]oxadiazole-4-amine (NBD-NH(2)) formation as a dominant fluorescent product. Basing on LC-MS data of the probes derivatized with hydroxylamine or cholesterol oxidase, both pregnenolone and 20-formyl-pregn-5-en-3ß-ol were deduced to be steroidal co-products of NBD-NH(2), indicating intricate character of the reaction. Products of CHDH-mediated conversions of 22-NBD-cholesterol were defined as 3-oxo-4-en and 3-oxo-5-en derivatives of the steroid. Moreover, the 3-oxo-4-en derivative was also found to be formed after 22-NBD-cholesterol incubation with pathogenic bacterium Pseudomonas aeruginosa, indicating a possible application of the reaction for a selective and sensitive detection of some microbes. The 3-keto-4-en derivative of 22-NBD-cholesterol may be also suitable as a new fluorescent probe for steroid hormone-binding enzymes or receptors.

A novel pathway of photoinduced decomposition of sphingolipids.

A possibility of a novel photodestruction process has been shown for sphingolipids and their low-molecular analogues, including the stage of Norrish Type-I decomposition of excited molecules of the starting compounds followed by fragmentation of nitrogen-centered radicals via rupture of the C-C and O-H bonds. Realization of such transformation during photolysis of ceramide, sphingomyelin and galactocerebroside results in formation of 2-hexadecenal, which possess a wide spectrum of biological activity.

A new mechanism for photo- and radiation-induced decomposition of sphingolipids.

Data have been obtained showing regularities in product formation following radiolysis of serinol, lysosphingomyelin and photolysis of N-(2-hydroxypropyl)hexanamide, sphingomyelin, which point to the possibility of photo- and radiation-induced destruction of the named substrates via a C-C bond rupture. The key stage of this process is the formation and decomposition of N-centered radicals generated from the starting compounds.

Homolytic cleavage of the O-glycoside bond in carbohydrates: a steady-state radiolysis study.

The formation of products resulting from the O-glycoside bond cleavage following radiolysis of aqueous solutions of methyl-alpha-D-glucopyranoside (I), 3-O-methyl-alpha-D-glucopyranose (II), maltose, lactose, gentiobiose and cellobiose were studied. Radiation-induced destruction yields were also determined for dextran, laminarin and trimethylcelulose upon irradiation of their aqueous solutions. Oxygen, quinones and compounds capable of forming quinoid structures were found to inhibit radiation-induced homolytic destruction processes taking place in glycosides, di- and polysaccharides. The data obtained in this study enabled the authors to demonstrate an important role played by the fragmentation reaction of C-2 radicals which were generated from the starting substances in the formation of final radiolysis products.

Effects of various vitamins and coenzymes Q on reactions involving alpha-hydroxyl-containing radicals.

Effects of vitamins B, C, E, K and P, as well as coenzymes Q, on formation of final products of radiation-induced free-radical transformations of ethanol, ethylene glycol, alpha-methylglycoside and glucose in aqueous solutions were studied. Based on the obtained results, it can be concluded that there are substances among vitamins and coenzymes that effectively interact with alpha-hydroxyl-containing radicals. In the presence of these substances, recombination reactions of alpha-hydroxyalkyl radicals and fragmentation of alpha-hydroxy-beta-substituted organic radicals are suppressed. It has been established that the observed effects are due to the ability of the vitamins and coenzymes under study to either oxidize alpha-hydroxyl-containing radicals yielding the respective carbonyl compounds or reduce them into the initial molecules.