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This article reviews published evidence describing the enzymatic and nonenzymatic formation and the routes of metabolism of the hepoxilins. Also treated are the major approaches used for the chemical synthesis of these compounds and for some of their analogs.

Hepoxilins have been shown to release calcium from intracellular stores in human neutrophils [Dho, Grinstein, Corey, Su and Pace-Asciak (1990) Biochem. J. 266, 63-68; Laneuville, Reynaud, Grinstein, Nigam and Pace-Asciak (1993) Biochem. J. 295, 393-397]. In this paper we report that tritium-labelled hepoxilin A3 (8S) binds to broken neutrophil membranes in a time-, substrate- and temperature-dependent fashion. Specific binding was displaced with unlabelled hepoxilin A3. Specific binding was greatest at 37 degrees C. Competitive binding was best observed with unlabelled hepoxilin A3 (8S); the glutathione conjugate, HxA3-C (8S or 8R), or 12(S)-hydroxyeicosatetraenoic acid was less active. Similarly inactive in displacing the bound radiolabelled hepoxilin A3 was leukotriene B4 as well as a variety of prostaglandins and thromboxane B2. Formylmethionyl-leucylphenylalanine was similarly inactive in competing for the hepoxilin binding sites. Specific binding was inhibited by pretreatment of the broken membranes during 30 min at 37 degrees C with proteinase K, while specific binding of the intact cells was unaffected. Scatchard analysis of binding data revealed a single population of binding sites with apparent KD and Bmax. of 79.3 +/- 9.1 nM and 8.86 +/- 1.4 pmol/ml per 2 x 10(6) cells (+/- S.E.M.) respectively reflecting approx. 2.67 x 10(6) sites/cell. These results demonstrate for the first time that neutrophils contain specific binding sites to hepoxilin A3.

Bleomycin has been suggested to incite plasma extravasation and influx of inflammatory cells leading to pulmonary fibrosis. We hypothesized that stable analogs of the 12-lipoxygenase product, hepoxilin, may attenuate these effects. We initially investigated the effects of the four hepoxilin analogs (PBT-1 to -4) coadministered intradermally with bleomycin and found that PBT-1 and -2 significantly opposed the vascular permeability effects of bleomycin in rat skin. We subsequently tested the hepoxilin analogs for their actions in opposing the intratracheal bleomycin-evoked acute inflammatory phase of lung fibrosis in the mouse, characterized by a marked accumulation of macrophages and an increase in the rate of collagen synthesis and deposition. We found that the bleomycin-evoked effects on macrophage influx were inhibited by all the hepoxilin analogs (PBT-1, -3, and -4 Ͼ PBT-2) administered i.p. for 8 days. Increased total lung collagen was completely abrogated by PBT-1 and -2, whereas PBT-3 and -4 had little effect. A doseresponse study with PBT-1 indicated that the effective dose for inhibition of bleomycin-induced inflammatory and histological changes was below 10 g/day. These studies demonstrate an in vivo action of stable analogs of hepoxilin and support an effect on inflammation and vascular permeability from these novel compounds, especially for PBT-1.Idiopathic pulmonary fibrosis is a devastating disorder that is poorly understood and resistant to treatment (Cooper, 2000). The observation that the antibiotic bleomycin sulfate (BL), a potent cancer chemotherapeutic agent (Adamson, 1984;Nici et al., 1998), may cause interstitial lung fibrosis in humans (Yagoda et al., 1972) led to the development of animal models in which a single dose of BL administered intratracheally induced changes resembling human idiopathic pulmonary fibrosis histopathologically (Kelley et al., 1980). The acute phase of this response is characterized by a marked accumulation of inflammatory cells and an increase in the rate of collagen synthesis and deposition (Cooper et al., 1988;Gurujeyalakshmi and Giri, 1995;Giri and Hollinger, 1996).Previous animal studies have demonstrated that BLevoked lung fibrosis is exacerbated with nordihydroguaiaretic acid, a lipoxygenase inhibitor, suggesting that a lipoxygenase product may be involved in endogenous mechanisms controlling lung fibrosis (Giri and Hollinger, 1996). The hepoxilins (HXs) may be candidates for the control of lung fibrosis as they are formed through the 12-lipoxygenase pathway of metabolism of arachidonic acid (Pace-Asciak et al., 1983;Pace-Asciak, 1984;Pace-Asciak and Martin, 1984). These compounds have previously been shown to have significant biological actions (Pace-Asciak, 1984;Dho et al., 1990;Laneuville et al., 1992;Pace-Asciak et al., 1995;Reynaud et al., 1996Reynaud et al., , 1999Sutherland et al., 2000). HXs raise free intracellular calcium in human neutrophils ex vivo through the release from stores and vascular tissue in vitro and block the intracellular calc...

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