Hypotensive effect of 13-hydroxylinoleic acid in the rat: mediation via the release of a CGRP-like mediator from capsaicin-sensitive nerves

Heat generates oxidized linoleic acid metabolites that activate TRPV1 and produce pain in rodents

The transient receptor potential vanilloid 1 (TRPV1) channel is the principal detector of noxious heat in the peripheral nervous system. TRPV1 is expressed in many nociceptors and is involved in heat-induced hyperalgesia and thermoregulation. The precise mechanism or mechanisms mediating the thermal sensitivity of TRPV1 are unknown. Here, we have shown that the oxidized linoleic acid metabolites 9- and 13-hydroxyoctadecadienoic acid (9- and 13-HODE) are formed in mouse and rat skin biopsies by exposure to noxious heat. 9- and 13-HODE and their metabolites, 9- and 13-oxoODE, activated TRPV1 and therefore constitute a family of endogenous TRPV1 agonists. Moreover, blocking these substances substantially decreased the heat sensitivity of TRPV1 in rats and mice and reduced nociception. Collectively, our results indicate that HODEs contribute to the heat sensitivity of TRPV1 in rodents. Because oxidized linoleic acid metabolites are released during cell injury, these findings suggest a mechanism for integrating the hyperalgesic and proinflammatory roles of TRPV1 and linoleic acid metabolites and may provide the foundation for investigating new classes of analgesic drugs.

Activation of TRPV1 in the spinal cord by oxidized linoleic acid metabolites contributes to inflammatory hyperalgesia

Transient receptor potential vanilloid 1 (TRPV1) plays a major role in hyperalgesia and allodynia and is expressed both in the peripheral and central nervous systems (CNS). However, few studies have evaluated mechanisms by which CNS TRPV1 mediates hyperalgesia and allodynia after injury. We hypothesized that activation of spinal cord systems releases endogenous TRPV1 agonists that evoke the development of mechanical allodynia by this receptor. Using in vitro superfusion, the depolarization of spinal cord triggered the release of oxidized linoleic acid metabolites, such as 9-hydroxyoctadecadienoic acid (9-HODE) that potently activated spinal TRPV1, leading to the development of mechanical allodynia. Subsequent calcium imaging and electrophysiology studies demonstrated that synthetic oxidized linoleic acid metabolites, including 9-HODE, 13-HODE, and 9 and 13-oxoODE, comprise a family of endogenous TRPV1 agonists. In vivo studies demonstrated that intrathecal application of these oxidized linoleic acid metabolites rapidly evokes mechanical allodynia. Finally, intrathecal neutralization of 9- and 13-HODE by antibodies blocks CFA-evoked mechanical allodynia. These data collectively reveal a mechanism by which an endogenous family of lipids activates TRPV1 in the spinal cord, leading to the development of inflammatory hyperalgesia. These findings may integrate many pain disorders and provide an approach for developing analgesic drugs.

The role of lipoxygenase-isoforms in atherogenesis

Lipoxygenases (LOXs) form a heterogeneous family of lipid-peroxidizing enzymes, and several LOX-isoforms (12/15-LOX, 5-LOX) have been implicated in atherogenesis. However, the precise role of these enzymes is still a matter of discussion. 12/15-LOXs are capable of oxidizing lipoproteins (low-density lipoprotein (LDL), high-density lipoprotein (HDL)) to atherogenic forms, and functional inactivation of this enzyme in murine atherosclerosis models slows down lesion formation. In contrast, rabbits that overexpress this enzyme were protected from lesion formation when fed a lipid-rich diet. To contribute to this discussion, we recently investigated the impact of 12/15-LOX overexpression on in vitro foam cell formation. When 12/15-LOX-transfected J774 cells were incubated in culture with modified LDL, we found that intracellular lipid deposition was reduced in the transfected cells when compared with the corresponding control transfectants. This paper briefly summarizes the current status of knowledge on the biological activity of different LOX-isoforms in atherogenesis and will also provide novel experimental data characterizing the role of 12/15-LOX in cellular LDL modification and for in vitro foam cell formation.