Hydroxyalkenal

The primary amine in resultant 4-hydroxyalkenal-carnosine adduct can be easily protonated under acidic conditions, which substantially enhances the ionization in comparison to the parent 4-hydroxyalkenal species [39]. It was found that the formed derivatives are stable for long time as examined [39]. Most importantly, product-ion MS analysis of camosine-adducted 4-hydroxyalkenal species after CID displays many abundant, informative, and characteristic fragment ions which can be 

FRAGMENTATION PATTERNS OF OTHER BIOACTIVE LIPID METABOLITES 

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The H-site is formed of clusters ofnon-polar amino acid side chains which provide a highly hydrophobic surface, which, in the absence of a drug substrate is open to bulk solvent Binding of substrates to this site has been shown to relate to increased lipophilicity for substrates (4-hydroxyalkenes). The actual conjugation reaction, with the thiolate anion acting as a nucleophile proceeds via an SN2-type mechanism yielding the deactivated product... 

Hydroxyalkenals are not commercially available but can be synthesized (Esterbauer and Weger, 1967 Erickson, 1974 Benedetti et al., 1982 Gree et al., 1986). Aqueous solutions of hydroxyalkenals are stable for about 1 week at 4°C, but decompose within 24 h at room-temperature. They are stable if stored at — 20°C in chloroform. 

Normal-phase HPLC may be used for separation of some aldehyde classes prior to quantitative reversed-phase HPLC. It is possible to separate 4-hydroxyalkenals by normal-phase HPLC as described below using 50% water-saturated dichloromethane as a mobile phase. This is prepared by mixing equal volumes of dry dichloromethane and a solution of dichloromethane stored under a layer of water (100%... 

If the process of lipid peroxidation continues unimpeded, the consequences include the release of toxic breakdown products and the eventual destruction of the lipid component of biological membranes (S28). Such breakdown products include the aldehydes, malondialdehyde, 2-alkenals, and 4-hydroxyalkenals. A number of mammalian GST isoenzymes are highly efficient in the detoxification of these compounds (Dl). Indeed, 4-hydroxynonenal is one of the best GST substrates identified to date, and with one of the rat GST isoenzymes the K JK value obtained indicates that catalysis proceeds relatively close to the diffusion-controlled limit. Cholesterol-5,6-epoxide is a further example of a byproduct of lipid peroxidation, and the conjugation of GSH to this weakly mutagenic compound is catalyzed by certain GST (M18). 

Dl. Danielson, U. H., Esterbauer, H., and Mannervik, B., Structure-activity relationships of 4-hydroxyalkenals in the conjugation by mammalian glutathione S-transferase. Biochem. J. 247, 707-713 (1987). 

E)-4-Hydroxyalk-2-enals. The Wittig reaction with 2,3-epoxy aldehydes leads to unstable enol ethers, which are rapidly hydrolyzed. Since the epoxy aldehydes are available in chiral form from the allylic alcohols through Sharpless epoxi-dation and oxidation, 4-hydroxyalkenals with desired absolute configuration at the carbinol center are easily established. 

Curzio, M. (1988) Interaction between neutrophils and 4-hydroxyalkenals and consequences on neutrophil motility. Free Radic. Res. Commun. 5 55-66. 

Rossi, M.A., Fidale, F., Garramone, A., Esterbauer, H. and Dianzani, M.U. (1990) Effect of 4-hydroxyalkenals on hepatic phosphatidylinositol-4,5-biphosphate-phospholipase C. Biochem. Pharmacol. 39 1715-1719. 

Among the various end products of the oxidative breakdown of biomembrane polyunsaturated fatty acids, aldehydes have been well characterized for their potential contribution to free radical pathobiology. The group of aldehydes that displays the greatest number of biochemical activities is the 4-hydroxyalkenals. Quantitatively, the most representative hydroxyalkenal in animal tissues is 4-hydroxy-23-nonenal (4-HNE). This aldehyde derives from the oxidation of arachidonic add, as well as linoleic acid. s Monoclonal antibodies against 4-HNE protein adducts have positively identified this molecule in human chronic diseases, and several reports pointed to the potential effect of increased levels of 4-HNE on different cell functions. 

Schneider, C., Talhnan, K. A., Porter, N. A., and Brash, A. R. Two distinct pathways of formation of 4-hydroxynonenal. Mechanisms of nonenzymatic transformation of the 9-and 13-hydroperoxides of hnoleic acid to 4-hydroxyalkenals. J. Biol. Chem. 276 2001 20831-20838. 

Eckl, P. M., A. Ortner, and H. Esterbauer, 1993. Genotoxic properties of 4-hydroxyalkenals and analogous aldehydes. Mutat Res 290 183-192. 

Carneiro and Reiter (1998) have reported that the incubation of rat cerebral, hippocampal and cerebellar homogenates with 6-aminolaevulinic acid increases the formation of lipid peroxidation products presumably as a result of the induction of free radicals by 6-aminolaevulinic acid. Melatonin coincubation, in both a concentration-dependent and time-dependent manner, prevented the rises in the damaged lipid products malondialdehyde and 4-hydroxyalkenals. In vivo as well, acute melatonin administration reduced damaged lipid products in the brain of rats treated with 8-aminolaevulinic acid. Princ et al. (1997) in similar studies like Carneiro and Reiter (1998) felt that the ability of melatonin to protect against 6-aminolaevulinic acid toxicity relates to the free radical scavenging activity of the indolamine. Furthermore, Princ et al. (1998) showed that melatonin administered in vivo not only reduced lipid peroxidation in the brain of rats treated with 6-aminolaevulinic acid, but also increased enzyme activities of the heme pathway. 

Wang, M., Fang, H. and Han, X. (2012) Shotgun lipidomics analysis of 4-hydroxyalkenal species directly from Upid extracts after one-step in situ derivatization. Anal. Chem. 84, 4580-4586. 

Figure 11.2 Representative product-ion mass spectrometric analyses of carnosine-derivatized 4-hydroxyalkenal species. Carnosine-4-hydroxyaIkenal adducts were prepared by incubating individual 4-hydroxyalkenal species with carnosine as previously described [39]. Product-ion ESI-MS analyses of carnosine-derivatized 4-hydroxynonenal (4-HNE, a), 4-hydroxyhexenal (4-HHE, c), and 4-hydroxynondienal (4-HNDE, d) were performed on a QqQ mass spectrometer (Thermo Fisher TSQ Vantage). Collision activation was carried out at collision energy of 25 eV and gas pressure of 1 mTorr. The fragmentation pattern of protonated 4-HNE-carnosine adduct was proposed (b). Wang et al. [39]. Reproduced with permission of the American Chemical Society.

Because the fragment ions corresponding to the neutral losses of 17.0, 63.0, 71.0, and 117.0amu are abiuidant and specific to carnosine adducts, it is logical to effectively perform NLS of these neutral fragments to identify the presence of 4-hydroxyalkenal species in biological samples and quantify these identified species in comparison to isotope-labeled internal standard(s) (Figure 11.3). 

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