Improved survival and reduced vascular permeability by eliminating or blocking 12/15-lipoxygenase in mouse models of acute lung injury (ALI)

Acute lung injury (ALI) is a prevalent disease associated with high mortality. 12/15-lipoxygenase (12/15-LO) is an enzyme producing 12-hydroxyeicosatetraenoic acid (HETE) and 15-HETE from arachidonic acid. To test whether 12/15-LO is involved in increasing vascular permeability in the lung, we investigated the role of 12/15-LO in murine models of LPS-induced pulmonary inflammation and clinically relevant acid-induced ALI. The vascular permeability increase upon LPS inhalation was abolished in Alox15(-/-) mice lacking 12/15-LO and in wild-type mice after pharmacological blockade of 12/15-LO. Alox15(-/-) mice also showed improved gas exchange, reduced permeability increase, and prolonged survival in the acid-induced ALI model. Bone marrow chimeras and reconstitution experiments revealed that 12-HETE produced by hematopoietic cells regulates vascular permeability through a CXCR2-dependent mechanism. Our findings suggest that 12/15-LO-derived 12-HETE is a key mediator of vascular permeability in acute lung injury.

12(S)-HETE, pleiotropic functions, multiple signaling pathways

The arachidonic acid metabolite of 12 lipoxygenase, 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) promotes metastatic behavior of tumor cells (1). In this study we set out to identify 12(S)-HETE stimulated signaling pathways, and their contribution to cellular functions in A431 epidermoid carcinoma. 1) 12(S)-HETE signaling involves extracellular-regulated protein kinase (ERK1/2), protein kinase C (PKC), phosphatidylinositol 3-kinase (PI3 kinase) and Src kinase. 2) 12(S)-HETE stimulates cell migration on laminin, which is eliminated by PKC and PI3 kinase inhibitors, reduced by 50% with Src inhibitor, but unaffected by inhibition of ERK1/2. 3) 12(S)-HETE stimulated spreading on fibronectin relies on ERK1/2 and PI3 kinase activities, but not on PKC or Src. 4) Focal adhesion kinase, a key organizer of focal adhesions, is tyrosine phosphorylated in response of 12(S)-HETE treatment, which requires Src, but not PKC, PI3 kinase or ERK1/2 activity. 5) Inhibition of 12 lipoxygenase leads to apoptosis in serum starved A431 cells. 12(S)-HETE stimulated p90Rsk and Akt, key players in an ERK and a PI3 kinase (respectively) dependent anti apoptotic pathways.

Growth factor-induced proliferation in corneal epithelial cells is mediated by 12(S)-HETE

PURPOSE

Previous studies in our laboratory have shown that 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), a product of 12-lipoxygenase (12-LOX) activity, is the predominant metabolite formed in rabbit corneas after injury. The present study was undertaken to investigate the effects of epidermal growth factor (EGF), hepatocyte growth factor (HGF), and keratinocyte growth factor (KGF) on 12-LOX expression and activity. We also investigated whether 12(S)-HETE mediated the growth factor-induced proliferation of corneal epithelial cells.

METHODS

Rabbit corneas were stimulated with EGF, HGF, and KGF (10 ng ml(-1)) for different times. 12-LOX activity was assayed by incubating corneal microsomal preparations with radiolabeled arachidonic acid (AA) as substrate. For inhibitor studies, the microsomes were pretreated with 12-LOX-specific inhibitors baicalein (BC) or cinnamyl 3,4-dihydroxy-(alpha)-cyanocinnamate (CDC). Lipid extracts were injected onto an Ultramex 5 microm C(18) column and radioactivity was monitored online by a Radiomatic Flo-One Beta detector. Stereochemical analysis of 12-HETE product was determined by chiral-phase HPLC. To evaluate the effects of growth factors on 12-LOX mRNA expression, mRNA was extracted at several time points (12, 24, 36, 48 hr) and subjected to real-time PCR. For 12-LOX protein expression, microsomal preparations from 24- and 48-hr incubations were analyzed by Western blot. In cell-proliferation studies, epithelial cells treated with EGF, HGF, or KGF for 24, 48, and 72 hr were measured with a CyQUANT cell-proliferation assay kit. To determine the role of growth factor-induced 12(S)-HETE synthesis on corneal epithelial cell proliferation, cells were pretreated with 12-LOX-specific inhibitors BC or CDC prior to growth-factor supplementation.

RESULTS

Stimulation with EGF, HGF, or KGF for 12 hr induced 12-LOX mRNA expression in rabbit corneal epithelial cells. This gene induction was followed by an increase in protein expression at 24 and 48 hr and a marked increase in 12(S)-HETE synthesis when compared to untreated controls. At 24-hr incubations, KGF showed a greater capacity than did EGF and HGF to stimulate microsomal 12-LOX activity, while at 48 hr 12(S)-HETE synthesis was significantly greater in EGF-treated cells as compared to that of HGF- and KGF-treated cells. Pretreatment with 12-LOX inhibitors blocked the growth factor-induced increase in 12(S)-HETE synthesis. Stimulation with growth factors or 12(S)-HETE for 24, 48, and 72hr produced a significant increase in corneal epithelial proliferation, which was partially inhibited by pretreatment of cells with 12-LOX-specific inhibitors.

CONCLUSION

These findings suggest that EGF, HGF, and KGF stimulate 12(S)-HETE production in rabbit corneal epithelial cells through gene induction of 12-LOX. Furthermore, 12(S)-HETE may play a role in regulating epithelial cell proliferation and the rate of corneal re-epithelialization following an injury.

Cyclooxygenase and cytochrome P-450 pathways induced by fetal calf serum regulate wound closure in 3T6 fibroblast cultures through the effect of prostaglandin E2 and 12 and 20 hydroxyeicosatetraenoic acids

Wound-induced injury of 3T6 fibroblast cultures initiated a repair process stimulated by fetal calf serum (FCS) that restored the integrity of cell cultures. In these experimental conditions, FCS induced arachidonic acid (AA) release and eicosanoid production. Our results show that the inhibition of the cyclooxygenase (COX) and/or cytochrome P-450 pathways significantly decreases the wound closure, whereas that of the lipoxygenase pathway does not modify the wound repair process. Both EP(1) and EP(4) receptors of prostaglandin E(2) (PGE(2)) mediate PGE(2) stimulated 3T6 fibroblast wound closure. Our data suggest that calcium and cAMP are involved in the signaling event induced by PGE(2) during the 3T6 fibroblast wound repair process. On the other hand, we show that ketoconazole, a cytochrome P-450 inhibitor, hinders the wound closure induced by FCS in wounded 3T6 fibroblast cultures. 12 and 20 Hydroxyeicosatetraenoic acids (HETEs), which are key AA metabolites synthesized by cytochrome P-450, partially revert the effects of ketoconazole on the wound repair process. Thus, the COX and cytochrome P-450 pathways of the arachidonate cascade are involved in 3T6 fibroblast wound closure.

[Leukotrienes and 12-HETE: key mediators of angiotensin II-mediated vascular effects.Rol in hypertension]

Arachidonic acid metabolism-derived products are key mediators of angiotensin II-mediated vascular effects. The modulatory effect of cyclooxygenase derived products--in particular thromboxane A2 and prostaglandin H2--in angiotensin II-mediated vascular effects is well established. In contrast, few studies have assessed the involvement of lipoxygenase-derived products in the vascular effects of angiotensin II. Cysteinyl leukotrienes (5-lipoxygenase-derived products) and 12-hydroxyeicosatetraenoic acids (12-HETE) (12-lipoxygenase-derived products) are potent proinflammatory and vasomotor mediators. Their biosynthesis is increased in various models of hypertension. In addition, compelling evidence has suggested that they might contribute to the vasoconstrictor, hypertrophic and mitogenic effects of angiotensin II. The demonstration of their contribution to angiotensin II-mediated vascular effects may explain, at least in part, the vascular inflammatory complications associated with hypertension.

Eicosanoid regulation of angiogenesis in human prostate carcinoma and its therapeutic implications

Cancer of the prostate is the most commonly diagnosed cancer in America. There are several lines of evidence implicating the involvement of arachidonate 12-lipoxygenase, an enzyme metabolizing arachidonic acid to form 12(S)-hydroxyeicosatetraenoic acid (HETE), in prostate cancer progression. First, as prostate cancer reaches a more advanced stage, the level of 12-lipoxygenase expression is increased. Second, overexpression of 12-lipoxygenase in human prostate cancer cells stimulates angiogenesis and tumor growth. Third, an inhibitor of 12-lipoxygenase has been found effective against metastatic prostate tumor growth, and the inhibition of 12-lipoxygenase is related with the reduction of tumor angiogenesis. Collectively, these studies suggest that 12-lipoxygenase regulates tumor angiogenesis in prostate cancer and that inhibition of 12-lipoxygenase is a novel therapeutic approach for the treatment of prostate cancers.

12-Lipoxygenase: classification, possible therapeutic benefits from inhibition, and inhibitors

The metabolism of arachidonic acid can be catalyzed by either one of two enzyme families; the cyclooxygenases or the lipoxygenases. The family of lipoxygenases is divided into four subtypes according to tissue distribution; 5-, 8-, 12-, and 15-lipoxygenase. 12-lipoxygenase metabolites, such as 12(S)-hydroxyeicosatetraenoic acid, have been found to play a central role in the various stages of the metastatic process in tumors and are, therefore, potential targets for anticancer treatment. A variety of lipoxygenase inhibitors already exist and can be classified into five major categories according to their mechanism of inhibition. These include antioxidants, iron chelators, substrate analogues, lipoxygenase-activating protein inhibitors, and, finally, epidermal growth factor-receptor inhibitors.

Platelet-derived 12-hydroxyeicosatetraenoic acid plays an important role in mediating canine coronary thrombosis by regulating platelet glycoprotein IIb/IIIa activation

BACKGROUND

In the thrombotic process of acute coronary syndromes, the pathophysiological role of thromboxane A2 via cyclooxygenase is well established; however, the role of 12-HETE via 12-lipoxygenase is little known. Therefore, we used OPC-29030, a novel specific inhibitor of 12-HETE synthesis, to test whether platelet-derived 12-HETE is involved in mediating cyclic flow variations (CFVs) and platelet aggregation in stenosed and endothelium-injured canine coronary arteries.

METHODS AND RESULTS

After developing CFVs, dogs received a vehicle or OPC-29030 intravenously. Plasma and intraplatelet 12-HETE levels increased after CFVs. OPC-29030 but not vehicle reduced CFVs, which was associated with decreases in plasma and intraplatelet 12-HETE levels. Cessation of OPC-29030 restored CFVs in association with increases in plasma and intraplatelet 12-HETE levels. ADP and U46619 induced ex vivo platelet 12-HETE production and aggregation. After OPC-29030 administration, the ADP- and U46619-induced increases in ex vivo platelet 12-HETE production and aggregation were inhibited significantly. Platelet aggregation was linearly correlated with platelet 12-HETE production. OPC-29030 suppressed activation of human platelet glycoprotein IIb/IIIa.

CONCLUSIONS

OPC-29030 reduced intraplatelet 12-HETE levels, resulting in the inhibition of coronary thrombosis in vivo in dogs. OPC-29030 inhibited human platelet glycoprotein IIb/IIIa activation in vitro. Thus, platelet-derived 12-HETE may play an important role in mediating thrombotic process.

Platelet-type 12-lipoxygenase in a human prostate carcinoma stimulates angiogenesis and tumor growth

Previously, we found a positive correlation between the expression of platelet-type 12-lipoxygenase (12-LOX) and the progression of human prostate adenocarcinoma (PCa; Gao et al., Urology, 46: 227-237, 1995). To determine the role of 12-LOX in PCa progression, we generated stable 12-LOX-transfected PC3 cells, which synthesize high levels of 12-LOX protein and 12(S)-hydroxyeicosatetraenoic acid metabolite. In vitro, 12-LOX-transfected PC3 cells demonstrated a proliferation rate similar to neo controls. However, following s.c. injection into athymic nude mice, 12-LOX-transfected PC3 cells formed larger tumors than did the controls. Decreased necrosis and increased vascularization were observed in the tumors from 12-LOX-transfected PC3 cells. Both endothelial cell migration and Matrigel implantation assays indicate that 12-LOX-transfected PC3 cells were more angiogenic than their neo controls. These data indicate that 12-LOX stimulates human PCa tumor growth by a novel angiogenic mechanism.

Eicosanoids in sickle cell disease: potential relevance of 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid to the pathophysiology of vaso-occlusion

The monohydroxyeicosanoid 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE), which is derived from oxygenation of arachidonic acid by 12-lipoxygenase, is one of the major metabolites in platelets. In a recent study, we have showed that this eicosanoid stimulated basal sickle-red-cell-endothelial-cell adhesion. To understand the pathophysiologic significance of 12-HETE, we measured the levels of this eicosanoid in plasma and urine from children with sickle cell disease. We found that as compared with controls, plasma 12-HETE levels are increased in patients with sickle-cell disease in the steady state, and are increased further during vaso-occlusive crises. Urinary 12-HETE levels were also increased during the steady state. We also assessed plasma levels of soluble P-selectin (another potential marker for platelet activation), and found changes in the levels of this marker similar to those seen with plasma 12-HETE. In additional studies, we found that 12-HETE enhanced hypoxia-induced sickle-red-cell-endothelial adherence, and that this effect was mediated by potentiation of agonist-induced upregulation of the expression of the mRNA for vascular cell adhesion molecule-1 (VCAM-1) in endothelial cells. Because 12-HETE appears to enhance both basal and agonist-induced sickle-red-cell adhesion, this metabolite could potentially play a role in the pathogenesis of the vaso-occlusive crisis (VOC) in sickle-cell disease.

Involvement of the multiple tumor suppressor genes and 12-lipoxygenase in human prostate cancer. Therapeutic implications

We performed a detailed and comprehensive study of the involvement of tumor suppressor genes in human prostate cancer. We utilized primers flanking either the restriction fragment length polymorphism (RFLP) or variable number of tandem repeat [VNTR; microsatellite or simple repeat site (SRS)] polymorphic sites to polymerase chain reaction (PCR) amplify the genomic DNA and detect loss of heterozygosity of the target genes. Quantitative reverse transcription (RT)-PCR was performed to measure the mRNA expression levels and PCR/single strand conformational polymorphism (SSCP) and DNA sequencing carried out to detect mutation of the tumor suppressor genes. We found that multiple tumor suppressor genes (e.g., p53, DCC, APC, MCC, BRCA1, and WAF1/CIP1) were inactivated at different frequencies via various mechanisms [e.g., loss of heterozygosity (LOH), loss of expression (LOE), mutation, and inactivation by cellular binding protein]. Several important and novel findings are as following: LOH and LOE of the DCC gene, LOH, LOE, and possible mutation of the APC/MCC genes, LOH of the BRCA1 locus, and mutation of the WAF1/CIP1 gene. For p53 tumor suppressor gene alone, multiple inactivation mechanisms (i.e., LOH, LOE, mutation, and amplification of the cellular inactivating protein MDM2) were identified. A possible involvement of genomic instability or mutator phenotype in human prostate cancer was investigated by microsatellite typing using PCR. A high frequency of microsatellite instability was detected and the microsatellite instability found to correlate with advanced stage and poor differentiation of prostate cancer, suggesting that genes functioning in DNA mismatch repair or general stabilization of the genome may be involved in prostate cancer. The results obtained in this study suggested that multiple tumor suppressor genes (both known and unknown genes) may share the role in prostate cancer; a pattern which has been found in a number of human malignancies such as cancers of the esophagus, colon and breast. In fact, we performed deletion studies aimed at localizing potential tumor suppressor loci on various chromosomal regions. A number of chromosomal regions (i.e., 6p12-24 and 17q21) were found to potentially harbor unidentified tumor suppressor genes. Detailed deletion mapping has localized the potential tumor suppressor loci to a < 2 Mb region centromeric to the BRCA1 gene on chromosome 17q. In addition, we identified a number of novel mechanisms of tumor suppressor gene inactivation, in prostate cancer such as loss of mRNA expression of the DCC, APC, MCC and p53 gene, and mutator phenotype. And for the very first time, we identified somatic mutations of the WAF1/CIP1 gene in primary human malignancy-human prostate cancer. This finding provides the first evidence in primary tumor that the WAF1/CIP1 gene may be a tumor suppressor gene and may be involved in prostate cancer. We identified 12-lipoxygenase (12-LOX) as a potential prognostic marker for human prostate cancer. mRNA expression levels of the 12-LOX gene was measured by quantitative reverse transcription-polymerase chain reaction (RT-PCR) and semi-quantitative in situ hybridization (ISH) in 122 pairs of matched normal and tumor tissues from prostate cancer patients. We found that 12-LOX expression levels were elevated in approximately half of the patients analyzed and the 12-LOX elevation correlates with advanced stage, poor differentiation, and surgical margin positivity. Our data suggest that 12-LOX may serve as a correlative marker for a more aggressive phenotype of prostate cancer and therefore for poor prognosis. We are currently refining our assays for possible clinical applicability. Since not all patients with loss of expression of the DCC gene showed LOH of the DCC locus, there must be other mechanism(s) responsible for loss of expression of the DCC gene. When we analyzed the relationship between DCC loss of expression and 12-LOX elevation in prostate cancer pati

Mechanisms of ANG II-induced mitogenic responses: role of 12-lipoxygenase and biphasic MAP kinase

The potential mechanisms of angiotensin II (ANG II)-induced mitogenesis were studied in a Chinese hamster ovary fibroblast cell line overexpressing the rat vascular type 1a ANG II receptor (CHO-AT1a). ANG II had potent mitogenic effects in these CHO-AT1a cells, leading to a sustained increase in cell number as well as a dose-dependent increase in DNA synthesis. ANG II treatment also induced a biphasic elevation of mitogen-activated protein (MAP) kinase activity of both p42MAPK and p44MAPK with a rapid early peak at 5 min (2- to 6-fold) followed by a second sustained increase that reached a peak at 3 h (1.5- to 3-fold). We have previously shown that the 12-lipoxygenase (12-LO) pathway of arachidonate metabolism plays a key role in ANG II-induced growth of vascular smooth muscle and adrenal cells. In the present study, ANG II (10(-7) M) increased the formation of the 12-LO product, 12-hydroxyeicosatetraenoic acid (12-HETE). ANG II-induced DNA synthesis was inhibited by a specific LO inhibitor, cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate (CDC, 10 microM). In contrast, a cyclooxygenase blocker of arachidonate metabolism such as ibuprofen had no effect on ANG II-induced DNA synthesis. ANG II-induced DNA synthesis was also partially (32%) blocked by pertussis toxin (PTX). CDC and PTX also selectively blocked only the late (3 h) peak of ANG II-induced MAP kinase activity, suggesting that the late sustained peak of MAP kinase activity may be linked to the mitogenic effect of ANG II. Direct addition of 12-HETE (10(-7) M) led to a sustained increase in cell number similar to the effect of ANG II. 12-HETE also caused an increase in MAP kinase activity, and 12-HETE effects were blocked by PTX. These results suggest that ANG II-induced mitogenic response is associated with sustained MAP kinase activation and that LO activation may play a key role in this process.