Abstract
The mechanism of formation of 4-hydroxy-2E-nonenal (4-HNE) has been a matter of debate since it was discovered as a major cytotoxic product of lipid peroxidation in 1980. Recent evidence points to 4-hydroperoxy-2E-nonenal (4-HPNE) as the immediate precursor of 4-HNE (Lee, S. H., and Blair, I. A. (2000) Chem. Res. Toxicol. 13, 698-702; Noordermeer, M. A., Feussner, I., Kolbe, A., Veldink, G. A., and Vliegenthart, J. F. G. (2000) Biochem. Biophys. Res. Commun. 277, 112-116), and a pathway via 9-hydroperoxylinoleic acid and 3Z-nonenal is recognized in plant extracts. Using the 9- and 13-hydroperoxides of linoleic acid as starting material, we find that two distinct mechanisms lead to the formation of 4-H(P)NE and the corresponding 4-hydro(pero)xyalkenal that retains the original carboxyl group (9-hydroperoxy-12-oxo-10E-dodecenoic acid). Chiral analysis revealed that 4-HPNE formed from 13S-hydroperoxy-9Z,11E-octadecadienoic acid (13S-HPODE) retains >90% S configuration, whereas it is nearly racemic from 9S-hydroperoxy-10E,12Z-octadecadienoic acid (9S-HPODE). 9-Hydroperoxy-12-oxo-10E-dodecenoic acid is >90% S when derived from 9S-HPODE and almost racemic from 13S-HPODE. Through analysis of intermediates and products, we provide evidence that (i) allylic hydrogen abstraction at C-8 of 13S-HPODE leads to a 10,13-dihydroperoxide that undergoes cleavage between C-9 and C-10 to give 4S-HPNE, whereas direct Hock cleavage of the 13S-HPODE gives 12-oxo-9Z-dodecenoic acid, which oxygenates to racemic 9-hydroperoxy-12-oxo-10E-dodecenoic acid; by contrast, (ii) 9S-HPODE cleaves directly to 3Z-nonenal as a precursor of racemic 4-HPNE, whereas allylic hydrogen abstraction at C-14 and oxygenation to a 9,12-dihydroperoxide leads to chiral 9S-hydroperoxy-12-oxo-10E-dodecenoic acid. Our results distinguish two major pathways to the formation of 4-HNE that should apply also to other fatty acid hydroperoxides. Slight ( approximately 10%) differences in the observed chiralities from those predicted in the above mechanisms suggest the existence of additional routes to the 4-hydroxyalkenals.
Highlights
The mechanism of formation of 4-hydroxy-2E-nonenal (4-HNE) has been a matter of debate since it was discovered as a major cytotoxic product of lipid peroxidation in 1980
Chiral analysis revealed that 4-HPNE formed from 13S-hydroperoxy-9Z,11E-octadecadienoic acid (13SHPODE) retains >90% S configuration, whereas it is nearly racemic from 9S-hydroperoxy-10E,12Z-octadecadienoic acid (9S-HPODE). 9-Hydroperoxy-12-oxo-10Edodecenoic acid is >90% S when derived from 9SHPODE and almost racemic from 13S-HPODE
Through analysis of intermediates and products, we provide evidence that (i) allylic hydrogen abstraction at C-8 of 13S-HPODE leads to a 10,13-dihydroperoxide that undergoes cleavage between C-9 and C-10 to give 4S-HPNE, whereas direct Hock cleavage of the 13SHPODE gives 12-oxo-9Z-dodecenoic acid, which oxygenates to racemic 9-hydroperoxy-12-oxo-10E-dodecenoic acid; by contrast, (ii) 9S-HPODE cleaves directly to 3Z-nonenal as a precursor of racemic 4-HPNE, whereas allylic hydrogen abstraction at C-14 and oxygenation to a 9,12-dihydroperoxide leads to chiral 9Shydroperoxy-12-oxo-10E-dodecenoic acid
Summary
4-HNE, 4-hydroxy-2E-nonenal; 4-HPNE, 4-hydroperoxy-2E-nonenal; HPODE, hydroperoxy-octadecadienoic acid; 13S-HPODE, 13S-hydroperoxy-9Z,11E-octadecadienoic acid; 9S-HPODE, 9S-hydroperoxy-10E,12Z-octadecadienoic acid; SP, straight phase; HPLC, high pressure liquid chromatography; RP, reverse phase; GC, gas chromatography; MS, mass spectrometry; ESI, electrospray ionization; LC, liquid chromatography; MOX, methoxime; CD, circular dichroism. Ygenation of 3Z-alkenals (via 4-hydroperoxy intermediates) as the major pathway of production of 4-HNE and related 4-hydroxyalkenals in plant extracts. 4-HPNE has been detected as a nonenzymatic breakdown product of 13-HPODE (14). We utilized both 9-HPODE and 13HPODE as model fatty acid hydroperoxides to study the mechanisms of nonenzymatic formation of the 4-hydroxyalkenals. Both fatty acid hydroperoxides give rise to 4-H(P)NE, but each has differing rates and susceptibilities to inhibition by ␣-tocopherol. The use of chiral starting materials and analyses of stereochemistry of the products reveal a pathway from -6 hydroperoxides (13-HPODE) to the 4-hydroxyalkenals and insights into the stereochemistry of the nonenzymatic reactions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
