Chryssostomos Chatgilialoglu

Role of Lipid Peroxidation and PPAR-δ in Amplifying Glucose-Stimulated Insulin Secretion

OBJECTIVE Previous studies show that polyunsaturated fatty acids (PUFAs) increase the insulin secretory capacity of pancreatic β-cells. We aimed at identifying PUFA-derived mediators and their cellular targets that are involved in the amplification of insulin release from β-cells preexposed to high glucose levels. RESEARCH DESIGN AND METHODS The content of fatty acids in phospholipids of INS-1E β-cells was determined by lipidomics analysis. High-performance liquid chromatography was used to identify peroxidation products in β-cell cultures. Static and dynamic glucose-stimulated insulin secretion (GSIS) assays were performed on isolated rat islets and/or INS-1E cells. The function of peroxisome proliferator–activated receptor-δ (PPAR-δ) in regulating insulin secretion was investigated using pharmacological agents and gene expression manipulations. RESULTS High glucose activated cPLA2 and, subsequently, the hydrolysis of arachidonic and linoleic acid (AA and LA, respectively) from phospholipids in INS-1E cells. Glucose also increased the level of reactive oxygen species, which promoted the peroxidation of these PUFAs to generate 4-hydroxy-2E-nonenal (4-HNE). The latter mimicked the GSIS-amplifying effect of high glucose preexposure and of the PPAR-δ agonist GW501516 in INS-1E cells and isolated rat islets. These effects were blocked with GSK0660, a selective PPAR-δ antagonist, and the antioxidant N-acetylcysteine or by silencing PPAR-δ expression. High glucose, 4-HNE, and GW501516 also induced luciferase expression in a PPAR-δ–mediated transactivation assay. Cytotoxic effects of 4-HNE were observed only above the physiologically effective concentration range. CONCLUSIONS Elevated glucose levels augment the release of AA and LA from phospholipids and their peroxidation to 4-HNE in β-cells. This molecule is an endogenous ligand for PPAR-δ, which amplifies insulin secretion in β-cells.

Radical-based reduction of phosphine sulfides and phosphine selenides by (Me3Si)3SiH

Abstract Tris(trimethylsilyl)silane reacts with phosphine sulfides and phosphine selenides under free radical conditions to give the corresponding phosphines in good yields. Stereochemical studies on P-chiral phosphine sulfides show these reductions proceed with retention of configuration.

Generation of C-1′ radicals through a β-(acyloxy)alkyl rearrangement in modified purine and pyrimidine nucleosides

Abstract The synthesis of protected 1′,2′-didehydro-2′-deoxyadenosines has been optimized by incorporating a phosphoranylidene protection of the adenine amino function. These unsaturated adenosines have served as substrates for the electrophilic iodopivaloyloxylation leading to new nucleosides modified at the anomeric position. Reaction of halopivaloates 10, 11 and 12 with tributyltin hydride generates indirectly C-1′ radicals through a β-(acyloxy)alkyl rearrangement. Rate constants for these rearrangements have been measured by using free-radical clock methodology and comparison of these data with previous reported results provides structural information about the nature of this important class of radicals.

RADICAL TRANSFORMATIONS OF NUCLEOSIDES WITH (ME3SI)3SIH. GENERATION OF A C-1' RADICAL THROUGH 1,2-MIGRATION OF AN ACYLOXY GROUP

Abstract A number of nucleoside substrates has been reduced under free radical conditions with tris(trimethylsilyl)silane. In one case a novel type of a β-(acyloxy)alkyl radical rearrangement has been observed, which leads through the generation of a C-1’ radical species to the stereoselective preparation of an α-ribonucleoside. The rate of the above 1,2-migration has been estimated, and a comparison with previously reported results has been made.

Free radical chemistry associated with H(RSiH)nH

Abstract Polysilanes of the type H(RSiH) n H, where R= n -hexyl or phenyl, have been used as radical-based reducing agents for organic halides. They rival the effectiveness of the other group 14 hydrides in reduction processes. The repetitive hydrogen transfer from the same molecule of H(RSiH) n H allows these compounds to be used in small quantities. Lower (5 × 10 4 M −1 s −1 ) and higher (6 × 10 5 M −1 s −1 ) limit values for the rate constant of the reaction of primary alkyl radicals with each SiH moiety of H(PhSiH) n H have been obtained by using unimolecular radical reactions as timing devices. The photochemical behavior of these polysilanes in the pi esence or absence of di- tert -butyl peroxide have been studied by EPR spectroscopy, and the −SiHR−SiR−SiHR radical (R= n -hexyl) has been identified as a transient species. Silyl radicals, obtained from H(RSiH) n H and thermally generated tert -butoxyl radicals, add to a variety of substrates containing double bonds to give the corresponding adducts for which EPR spectra have been recorded.

RATE CONSTANTS FOR THE REACTION OF ACYL RADICALS WITH BU3SNH AND (TMS)3SIH

The rate constants for the hydrogen abstraction from Bu3SnH and (TMS)3SiH by acyl radicals have been measured by using competing decarbonylation reactions as timing devices.

Biomimetic Chemistry: Radical Reactions in Vesicle Suspensions

Chemical reactivity represents the fundamental basis for studying processes in life sciences. In particular, the last years have seen the affirmation of the interdisciplinary field of chemical biology, which has motivated a strong interest in modeling chemical reactivity of biological systems, that is, improving chemical methodologies and knowledge in order to understand complex reaction pathways related to cellular processes. In this context the reactivity of free radicals revealed its enormous importance for several biological events, including aging and inflammation (Cutler & Rodriguez, 2003), therefore the modeling of free radical reactions under naturally occurring conditions has become a basic step in the research of fundamental mechanisms in biology. The assessment of modes of free radical reactivity has been found to be important at least in three areas: i) the examination of interactions at a molecular level leading to the discovery of radical-based processes involved in enzymatic activities, e.g., ribonucleotide reductase (Reichard & Ehrenberg, 1983), cyclooxygenase (Marnett, 2000), the drug effects of antitumorals (Goldberg, 1987), vitamin activities (Buettner, 1993); ii) The clarification of free radical processes that can lead to damage of biomolecules, together with the individuation of products, opening the way for the evaluation of the in vivo damage and its role in the overall cellular status (Kadiiskaa et al., 2005; Pryor & Godber, 1991); iii) the knowledge of free radical mechanisms allowing for new strategies to be envisaged in order to control the level of the damage and fight against the negative consequences (Halliwell & Gutteridge, 2000). These three main areas represent the core studies of free radicals using biomimetic models. In the last decade our group has developed the subjects of lipid and protein damages under biomimetic conditions, and in particular envisaged novel damage pathways for the transformation of these important classes of biomolecules. In this chapter biomimetic models will be examined, also mentioning work previously done by others in the field and the advancements carried by us. Information will be given on liposome vesicles, which is the basic context for examining free radical reactivity in heterogenous conditions, where the partition of the reactants occurs between the lipid and the aqueous environments, and this can influence the biological effects. The regioselectivity driven by the supramolecular organization of lipids in the vesicle double layer is another feature of the biomimetic model that has been related to the formation of trans lipids, specific markers of radical stress in cell 6

Nutrition and Reproductive Health: Sperm versus Erythrocyte Lipidomic Profile and ω-3 Intake

Fatty acid analyses of sperm and erythrocyte cell membrane phospholipids in idiopathic infertile patients evidenced that erythrocyte contents of EPA, DHA, omega-6–omega-3 ratio and arachidonic acid provide a mathematical correspondence for the prediction of EPA level in sperm cells. The erythrocyte lipidomic profile of patients was significantly altered, with signatures of typical Western pattern dietary habits and no fish intake. A supplementation with nutritional levels of EPA and DHA and antioxidants was then performed for 3 months, with the follow-up of both erythrocyte and sperm cell membranes composition as well as conventional sperm parameters. Some significant changes were found in the lipidomic membrane profile of erythrocyte but not in sperm cells, which correspondently did not show significant parameter ameliorations. This is the first report indicating that membrane lipids of different tissues do not equally metabolize the fatty acid elements upon supplementation. Molecular diagnostic tools are necessary to understand the cell metabolic turnover and monitor the success of nutraceuticals for personalized treatments.

Effects of oxygen and antioxidants on the cis-trans-isomerization of unsaturated fatty acids caused by thiyl radicals

The interaction of unsaturated compounds methyllinoleate and β-carotene with thiyl radicals occurred in exchange radical reactions with mercaptoethanol. β-Carotene was shown to be an effective thiyl radical acceptor. In the case of methyllinoleate, thiyl radicals catalyze cis/trans isomerization, which can be reduced by the natural antioxidant α-tocopherol; the cis/trans isomerization rate decreases in an oxygen atmosphere.

Rate constants for the reaction of cumylperoxyl radicals with Bu3SnH and (TMS)3SiH

The rate constants for the reaction of a cumylperoxyl radical with Bu3SnH and (TMS)3SiH were determined at 72.5 °C to be 1600 and 66 M–1 s–1, respectively, by using inhibited hydrocarbon oxidation methodologies.