HPETE

Enzymatic assay of lipid hydroperoxides A selective assay has been described for lipid hydroperoxides, based on the cyclooxygenase reaction with a sensitivity in the range of 20-200 pmol (Marshall et al., 1985 Pendleton and Lands, 1987 Lands, 1988). The substrate (15-HPETE) is not, however, commercially available and must therefore be synthesized from purified arachidonic acid by the method of Graft (1982) in which soya bean lipoxygenase is used to catalyse the stereospecific oxygenation of arachidonic acid. 

14-eicosatetraenoic acid 12-Hydroxyoctadecanoic 12-Hydroxy-9-octadecanoic acids 

Soybean lipoxygenase, type 1, 170,000 units/mg protein (Sigma Chemicals) 

Petroleum ether (b.p. 35-60°C) shaken gently with 1/10 vol of concentrated sulphuric acid, washed with distilled water and distilled over lithium aluminium hydride. 

Silicic acid, 100 mesh (Slurry 500 g five-times each with 5 litres of water. Discard the supernatant after 5 min and activate for 12 h at 150°C). 

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Fig. 2. Aiachidonic acid cascade, HPETE = hydroperoxyeicosa-tetraenoic acids.

Synthesis from 5-HPETE by hydroperoxide oxiranyl carbinol rearrangement (Ref. 5) ... 

Lipoxygenation is the major pathway of dioxygenation of arachidonic acid in blood platelets and leads to the 12-5-hydroperoxy acid 12-HPETE and the corresponding 12-hydroxy acid 12-HETE. Several pathways for the synthesis of 12-HETE have been developed. However, despite the availability of this substance, its biological role remains undetermined. 

Hepoxylins are metabolites of arachidonic acid which arise from 12-HPETE in tissues such as pancreatic islet cells (where they stimulate glucose-dependent insulin release) and brain (where they appear to have a neuromodulatory role). The structure of the hepoxylins was confirmed by synthesis which also has provided this scarce material for biological investigation. 

Synthesis of 5-, 11-, and 15-HETE s. Conversion of HETE s into the Corresponding HPETE s... 

The first step in the biosynthesis of eicosanoids from arachidonic acid is generally a lipoxygenation reaction. The resulting hydroperoxides (HPETE s) can undergo reduction to the corresponding alcohols (HETE s). Preparative routes to the 5-, 11-, and 15-HETE s and HPETE s have been developed as oudine below. 

Each HETE can be converted into the corresponding HPETE as shown in the following example. 

Figure 23-7. Conversion of arachidonicacid to leukotrienesand lipoxins of series 4 via the lipoxygenase pathway. Some similar conversions occur in series 3 and 5 leukotrienes. (HPETE, hydroperoxyeicosatetraenoate HETE, hydroxyeicosatetraenoate , peroxidase (2), leukotriene A4 epoxide hydrolase , glutathione S-transferase ...

Folkerts, G. Nijkamp, F.J., and van Oosterhout, A.M.J. (1983). Induction in guinea-pigs of airway hyperreactitivity and decreased lung beta adrenoreceptor number by 15-HPETE. Br. J. Pharmacol. 80, 597-599. 

HODE Hydroxyoctadecanoic acid HO Hydroxyl radical H02 Perhydroxyl radical HPETE, 5-HPETE 15-HPETE... 

NADA) [42], A -oleoyldopamine (OLDA) [43] and 12-HPETE [44] (some also consider protons as endovanilloids). 

A reasonable route for the formation of this racemic cyclopentenone (30) was proposed from 8.R-HPETE (29), which involves the non-enzymatic hydrolysis of an allene oxide (64) intermediate (Scheme 5 ) [86]. Biochemical precedence for these transformations was provided by earlier work with plants [90] and C. 

An acetone powder of P. homomalla was subsequently used to generate allene oxide 64 from exogenous 8P-HPETE [91]. This highly unstable compound (t1/2 = ca. 15 s at 0 °C, pH 7.4) was obtained by performing the biosynthesis at low temperature (0 °C) for 2 min in a vortexed emulsion of pH 6 buffer and pentane. Under these conditions, the allene oxide partitioned into the pentane where it was relatively protected from hydrolysis. HPLC analysis of the... 

Holland and coworkers mentioned the TLC detection of a trihydroxy compound related to the hatching factor when homogenates of B. balanoides were incubated with 14C-AA, but no experimental details were given [143]. By using ammonium sulfate cuts from rat lung homogenates, it has been shown that trioxilin B3 can arise from 12-HPETE via a 10-hydroxy-11,12-epoxy intermediate [148],... 

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