20-HETE-producing enzymes are up-regulated in human cancers

BACKGROUND

20-Hydroxyeicosatetraenoic acid (20-HETE), a metabolite of arachidonic acid (AA) produced by the CYP4A and CYP4F enzyme families has been reported to induce mitogenic and angiogenic responses both in vitro and in vivo, and inhibitors of this pathway reduced growth of brain and kidney tumors.

MATERIALS AND METHODS

Real-Time PCR, western blot and immunohistochemistry were used to compare the expression of CYP4A/F mRNA and protein levels in human cancer tissue samples versus normal controls. Liquid chromatography/mass spectrometry analysis (LC-MS/MS) was performed to measure 20-HETE formation in tumor homogenates. Activation of Ras in human proximal tubule epithelial cells (HRPTEC) treated with stable agonist of 20-HETE was measured using a Ras pull-down detection kit.

RESULTS

The expression of CYP4A/4F genes was markedly elevated in thyroid, breast, colon, and ovarian cancer samples in comparison to matched normal tissues. Furthermore, the levels of the CYP4F2 protein and of 20-HETE were higher in ovarian cancer samples compared to normal control tissues. A stable 20-HETE agonist induced activation of the small-GTPase Ras in HRPTEC cells.

CONCLUSION

The present finding of elevated expression of CYP4A/F enzymes in human cancer tissue suggests that 20-HETE inhibitors and antagonists may be useful in the treatment of cancer.

Effects of a 20-HETE antagonist and agonists on cerebral vascular tone

This study examined the effects of a 20-hydroxyeicosatetraenoic acid (20-HETE) antagonist, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (WIT002) and two agonists, 4-amino-N-(20-hydroxy-eicosa-5(Z),14(Z)-dienoyl) benzenesulfonamide (ABSA) and 20-hydroxyeicosa-5(Z),14(Z)-dienoic acid (WIT003), on the diameter of rat middle cerebral arteries in vitro and on cerebral blood flow in vivo. WIT003, ABSA and 20-HETE all had a similar effect to reduce the diameter of the middle cerebral artery by 26%. WIT003 and 20-HETE both increased intracellular Ca2+ concentration ([Ca2+]i) in vascular smooth muscle cells isolated from the middle cerebral artery. In contrast, WIT002 had no effect on the basal diameter of the middle cerebral artery but it attenuated the vasoconstrictor responses and the rise in [Ca2+]i in vascular smooth muscle cells following administration of 20-HETE and 5-hydroxytryptamine (5-HT). WIT003 partially restored the vasoconstrictor response to 5-HT in the middle cerebral artery after administration of an inhibitor of the endogenous synthesis of 20-HETE. Infusion of the 20-HETE agonists, WIT003 and ABSA, into cisterna magna of rats reduced baseline cerebral blood flow by 20%, whereas administration of the 20-HETE antagonist, WIT002, had no effect. Intracisternal injection of WIT002 attenuated the fall in cerebral blood flow following injection of blood into the cisterna magna, whereas administration of the 20-HETE agonist, ABSA, potentiated this response. These findings indicate that the 20-HETE agonists, WIT003 and ABSA, increase cerebral vascular tone both in vivo and in vitro and suggest blocking the vasoconstrictor actions of 20-HETE may be useful to prevent the acute fall in cerebral blood flow following subarachnoid hemorrhage.

Contribution of 5-hydroxytryptamine1B receptors and 20-hydroxyeiscosatetraenoic acid to fall in cerebral blood flow after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

This study examined the interaction between 5-hydroxytryptamine1B (5-HT1B) receptors and 20-hydroxyeiscosatetraenoic acid (20-HETE) in contributing to the acute fall in regional cerebral blood flow (rCBF) after subarachnoid hemorrhage (SAH) in rats.

METHODS

The effects of intracisternal injection of 0.3 mL of arterial blood, artificial cerebrospinal fluid, and 5-HT on rCBF and the levels of 20-HETE and 5-HT in cerebrospinal fluid were measured in rats pretreated with vehicle, a 5-HT1B receptor antagonist (isamoltane hemifumarate), or an inhibitor of the synthesis of 20-HETE (HET0016). The effects of HET0016 and isamoltane on the vasoconstrictor response and changes in [Ca2+]i to 5-HT were also studied in middle cerebral arteries and vascular smooth muscle cells isolated from these vessels.

RESULTS

20-HETE and 5-HT levels in cerebrospinal fluid rose from 172+/-10 to 629+/-44 ng/mL and from 6+/-4 to 1163+/-200 nmol/mL, respectively, after SAH. rCBF fell by 30% 10 minutes after SAH, and it remained at this level for the next 2 hours. Blockade of 5-HT1B receptors prevented the sustained fall in rCBF seen after SAH. Intracisternal injection of 5-HT mimicked SAH by increasing 20-HETE levels in cerebrospinal fluid to 475+/-94 ng/mL and reducing rCBF by 30%. Blockade of the synthesis of 20-HETE with HET0016 prevented the fall in rCBF produced by 5-HT. Isamoltane and HET0016 reduced the vasoconstrictor response of isolated MCA to 5-HT by >60% and diminished the rise in [Ca2+]i produced by 5-HT in vascular smooth muscle cells isolated from these arteries.

CONCLUSIONS

These results suggest that the release of 5-HT after SAH activates 5-HT1B receptors and the synthesis of 20-HETE and that 20-HETE contributes to the acute fall in rCBF by potentiating the vasoconstrictor response of cerebral vessels to 5-HT.

20-HETE agonists and antagonists in the renal circulation

The present study examined the effects of a series of 20-hydroxyeicosatetraenoic acid (20-HETE) derivatives on the diameter of renal arterioles to determine the structural requirements of the vasoconstrictor response to 20-HETE. The vascular responses to 5-, 8-, 12-, 15-, 19-, 20-, 21-HETEs, arachidonic acid (AA), and saturated, partially saturated, dimethyl, carboxyl, and 19-carbon derivatives of 20-HETE (10(-8) to 10(-6) M) were assessed in rat renal interlobular arteries (65-125 micrometer). 20-HETE, 21-HETE, dimethyl-20-HETE, and a partially saturated derivative of 20-HETE, 20-hydroxyeicosa-5(Z),14(Z)-dienoic acid, reduced vessel diameter by 19 +/- 3, 17 +/- 3, 16 +/- 2, and 28 +/- 2%, respectively. In contrast, 5-, 8-, 12-, 15-, and 19-HETE, AA, saturated, partially saturated, carboxyl, and the 19-carbon derivatives of 20-HETE had no effect on vessel diameter. Pretreatment with 5-, 15-, and 19-HETE, the 19-carbon derivative or 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (1 microM) completely blocked the vasoconstrictor response to 20-HETE in renal arterioles. Pretreatment with AA, carboxyl, saturated 19-carbon, and saturated 20-HETE derivatives (1 microM) partially blocked the response, whereas 8- and 12-HETE (1 microM) had no effect on the vasoconstrictor response to 20-HETE. These findings suggest that 20-HETE agonists and antagonists require a carboxyl or an ionizable group on carbon 1 and a double bond near the 14 or 15 carbon. 20-HETE agonists also require a functional group capable of hydrogen bonding on carbon 20 or 21, whereas antagonists lack this reactive group.