Nordihydroguaiaretic acid inhibits urokinase synthesis by phorbol myristate acetate-stimulated LLC-PK1 cells

Synthetic curcuminoids modulate the arachidonic acid metabolism of human platelet 12-lipoxygenase and reduce sprout formation of human endothelial cells

Platelet 12-lipoxygenase (P-12-LOX) is overexpressed in different types of cancers, including prostate cancer, and the level of expression is correlated with the grade of this cancer. Arachidonic acid is metabolized by 12-LOX to 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], and this biologically active metabolite is involved in prostate cancer progression by modulating cell proliferation in multiple cancer-related pathways inducing angiogenesis and metastasis. Thus, inhibition of P-12-LOX can reduce these two processes. Several lipoxygenase inhibitors are known, including plant and mammalian lipoxygenases, but only a few of them are known inhibitors of P-12-LOX. Curcumin is one of these lipoxygenase inhibitors. Using a homology model of the three-dimensional structure of human P-12-LOX, we did computational docking of synthetic curcuminoids (curcumin derivatives) to identify inhibitors superior to curcumin. Docking of the known inhibitors curcumin and NDGA to P-12-LOX was used to optimize the docking protocol for the system in study. Over 75% of the compounds of interest were successfully docked into the active site of P-12-LOX, many of them sharing similar binding modes. Curcuminoids that did not dock into the active site did not inhibit P-12-LOX. From a set of the curcuminoids that were successfully docked and selected for testing, two were found to inhibit human lipoxygenase better than curcumin. False-positive curcuminoids showed high LogP (theoretical) values, indicating poor water solubility, a possible reason for lack of inhibitory activity or/and nonrealistic binding. Additionally, the curcuminoids inhibiting P-12-LOX were tested for their ability to reduce sprout formation of endothelial cells (in vitro model of angiogenesis). We found that only curcuminoids inhibiting human P-12-LOX and the known inhibitor NDGA reduced sprout formation. Only limited inhibition of sprout formation at approximately IC(50) concentrations has been seen. At IC(50), a substantial amount of 12-HETE can be produced by lipoxygenase, providing a stimulus for angiogenic sprouting of endothelial cells. Increasing the concentration of lipoxygenase inhibitors above IC(50), thus decreasing the concentration of 12(S)-HETE produced, greatly reduced sprout formation for all inhibitors tested. This universal event for all tested lipoxygenase inhibitors suggests that the inhibition of sprout formation was most likely due to the inhibition of human P-12-LOX but not other cancer-related pathways.

Nordihydroguaiaretic acid, an antioxidant, inhibits transforming growth factor-beta activity through the inhibition of Smad signaling pathway

Transforming growth factor-beta (TGF-beta) and its family are potent and multi-functional cytokines that affect various fundamental biological events. TGF-beta has a unique signaling pathway that is carried by Smad family, and many recent studies showed the extensive crosstalk between Smad pathway and other signaling pathway. There were also clear evidences for the involvement of oxidative events in TGF-beta signaling pathway. To elucidate the role of oxidative events in carrying TGF-beta signals, we examined the effect of various antioxidants on TGF-beta activities in osteoblastic cell line. Among the examined compounds, we found nordihydroguaiaretic acid (NDGA) has a unique and strong inhibitory effect on various TGF-beta activities. Since the majority of TGF-beta activities are mediated by Smad, we questioned whether NDGA blocks the Smad signaling pathway. The result showed that NDGA inhibits the translocation of Smad2 to the nucleus. Further study revealed the strong inhibitory effect of NDGA on the phosphorylation of Smad2. This result may be important for designing chemical modulators of TGF-beta and its family related events and may provide new insights into the action mechanism of antioxidant.

Mechanisms of nordihydroguaiaretic acid-induced growth inhibition and apoptosis in human cancer cells

Lipoxygenase metabolites of arachidonic acid can act as growth promoting factors for various cancer cell lines. Here we demonstrate that the 5-lipoxygenase inhibitor nordihydroguaiaretic acid potently inhibits anchorage-independent growth of human pancreatic and cervical cancer cells in soft agar and delays growth of pancreatic and cervical tumours established in athymic mice. Furthermore, nordihydroguaiaretic acid induces apoptosis of these cancer cells in vitro and in vivo. Potential mechanisms mediating these effects of nordihydroguaiaretic acid were examined. Nordihydroguaiaretic acid had no inhibitory effect on growth and survival signals such as tyrosine phosphorylation of the epidermal growth factor receptor or basal and growth factor-stimulated activities of extracellular signal-regulated kinase 1/2, p70(s6k) and AKT but selectively inhibited expression of cyclin D1 in the cancer cells. In addition, treatment with nordihydroguaiaretic acid lead to a disruption of the filamentous actin cytoskeleton in human pancreatic and cervical cancer cells which was accompanied by the activation of Jun-NH(2)-terminal kinase and p38(mapk). Similar effects were obtained by treatment of the cancer cells with cytochalasin D. These results suggest that nordihydroguaiaretic acid induces anoikis-like apoptosis as a result of disruption of the actin cytoskeleton in association with the activation of stress activated protein kinases. In conclusion, nordihydroguaiaretic acid could constitute a lead compound in the development of novel therapeutic agents for various types of cancer.

Arachidonic acid and its metabolites are involved in the expression of morphine dependence in guinea-pig isolated ileum

The effects of phospholipase A2, cyclooxygenase-1, cyclooxygenase-2 and 5-lipoxygenase inhibitors were investigated on the naloxone-precipitated withdrawal contracture of the acute morphine-dependent guinea-pig ileum in vitro. Mepacrine (a phospholipase A2 inhibitor), tolmetin (selective cyclooxygenase-1 inhibitor) and meloxicam (selective cyclooxygenase-2 inhibitor) treatment before or after morphine was able to both prevent and reverse the naloxone-induced contracture after exposure to morphine in a concentration-dependent fashion. Also, nordihydroguaiaretic acid (5-lipooxygenase inhibitor) was able to block the naloxone-induced contracture following exposure to morphine when injected before or after the opioid agonist. The results of the present study suggest that arachidonic acid and its metabolites (prostaglandins and leukotrienes) are involved in the development of opioid withdrawal.

Protein kinase C isozymes differentially regulate promoters containing PEA-3/12-O-tetradecanoylphorbol-13-acetate response element motifs

To investigate the regulation of promoters containing classical phorbol ester response sequences (PEA-3/12-O-tetradecanoylphorbol-13-acetate response element motifs) by protein kinase C (PKC) isozymes, co-transfections were performed in human dermal fibroblasts with a plasmid containing either the human collagenase promoter or the porcine urokinase plasminogen activator (uPA) promoter linked to the chloramphenicol acetyltransferase gene and a plasmid expressing an individual PKC isozyme. Using this experimental design, seven PKC isozymes were analyzed for their ability to trans-activate the collagenase and uPA promoters. Our results demonstrate that only PKC delta, epsilon, and eta trans-activated the collagenase promoter and that binding of Ap-1 family members to the collagenase 12-O-tetradecanoylphorbol-13-acetate response element (TRE) was not responsible for the isozyme-specific trans-activation. In contrast, the uPA promoter was stimulated by all of the PKC isozymes examined (PKC alpha, betaII, gamma, delta, epsilon, zeta, and eta). These results indicate that PKC isozymes differentially regulate promoters containing PEA-3/TRE motifs and suggest that individual isozymes play unique roles within the cell.

Activation of phospholipase D by prostaglandin F2 alpha in rat luteal cells and effects of inhibitors of arachidonic acid metabolism

In rat luteal cells labeled with [3H]oleic acid, PGF2 alpha-stimulated phospholipase D (PLD) activation was investigated. The PLD activity was detected by measuring the accumulation of [3H]phosphatidylethanol (PtdEt) in the presence of ethanol. PGF2 alpha stimulated PtdEt accumulation at concentrations of more than 100 nM in the presence of ethanol. However, PtdEt accumulation did not change in the absence of ethanol. PGF2 alpha (1 microM) increased PtdEt accumulation after 1 min, and the accumulation reached a plateau by 2-3 min. These results indicate that PGF2 alpha activates PLD in rat luteal cells. U-73122, a phospholipase C (PLC) inhibitor, and staurosporine, a protein kinase C (PKC) inhibitor, did not inhibit PGF2 alpha-stimulated [3H]PtdEt accumulation. These results suggest that PGF2 alpha-induced PLD activation is different from PLC-PKC systems. We reported previously that PGF2 alpha stimulated the release of arachidonic acid. The effects of indomethacin, nordihydroguaiaretic acid (NDGA), and 5,8,11,14-eicosatetraynoic acid (ETYA), inhibitors of arachidonic acid metabolism, on PGF2 alpha-stimulated PtdEt accumulation were examined. Pretreatment with indomethacin enhanced PGF2 alpha-induced PtdEt accumulation. In contrast, pretreatment with NDGA and ETYA inhibited PGF2 alpha-induced PtdEt accumulation. It is suggested that PGF2 alpha-stimulated PLD activation is mediated via lipoxygenase products.

Inhibitory effects of nordihydroguaiaretic acid on ETA-receptor-mediated contractions to endothelin-1 in rat trachea

1. It has been shown previously that nordihydroguaiaretic acid (NDGA) inhibits endothelin-1 (ET-1)-induced contractions in rat isolated tracheal smooth muscle. To investigate the underlying mechanisms, this study examined the effects of NDGA on various aspects of the ETA and ETB receptor-effector systems which mediate ET-1-induced contractions in this preparation. 2. NDGA inhibited contractions induced by each of the isoforms of ET (ET-1, ET-2 and ET-3) but not those induced by the ETB receptor-selective agonist, sarafotoxin S6c, the cholinoceptor agonist, carbachol or the depolarizing spasmogen, KCl. 3. Quantitative autoradiographic studies of [125I]-ET-1 binding to rat tracheal smooth muscle indicated that NDGA was not an ET receptor antagonist. 4. NDGA inhibited the ETA receptor-mediated, intracellular Ca(2+)-dependent contractions induced by 100 nM ET-1 in Ca(2+)-free solution (by 75%, P < 0.01). Furthermore, NDGA markedly inhibited the contractions induced by ryanodine and cyclopiazonic acid; contractions purportedly due to Ca2+ release from intracellular stores. 5. Like NDGA, the sarcoplasmic reticulum Ca(2+)-ATPase inhibitors cyclopiazonic acid and thapsigargin inhibited contractions to ET-1, but not carbachol or KCl. However, cyclopiazonic acid, but not NDGA, also (a) induced transient contractions in rat trachea, (b) potentiated contractions induced by KCl, and (c) potentiated the extracellular Ca(2+)-dependent phase of ET-1-induced contractions, indicating that NDGA did not inhibit ET-1-induced contractions through Ca(2+)-ATPase inhibition and depletion of sarcoplasmic reticular Ca2+. 6. In control preparations, ET-1 induced a slowly developing, sustained contraction. However, in the presence of NDGA or the ETA receptor antagonist, BQ123, ET-1-induced contractions resembled the transient contractions induced by sarafotoxin S6c. In nominally Ca2+-free solution, ETA receptor mediated contractions induced by ET-1 developed very slowly and were inhibited by NDGA.7. Additional studies indicated that the inhibitory effects of NDGA on endothelin-1-induced contractions were not the result of any significant actions of NDGA on lipoxygenase, cytochrome P450, L- orT-type Ca2+-channels, Na+-channels or protein kinase C.8. In summary, NDGA selectively inhibited ET-1-induced contractions in rat tracheal smooth muscle via a lipoxygenase-independent mechanism involving inhibition of the ETA but not the ETB, receptor effector system. NDGA did not appear to inhibit the initial events in the ETA signal transduction pathway, such as receptor binding and protein kinase C activation. However, NDGA inhibited the intracellular Ca2+-dependent component of ET-1-induced contraction, possibly by inhibiting mobilisation of intracellular Ca2+. As an apparent direct consequence of inhibiting the ETA receptor-effector system, NDGA markedly changed the time course of ET-1-induced contractions; from a slowly developing and sustained contraction into a transient contraction resembling that induced by sarafotoxin S6c.

The effect of inhibition of leukotriene B4 release on lipopolysaccharide-induced production of neutrophil attractant/activation protein-1 (interleukin-8) by human alveolar macrophages

Whereas we observed previously that concentrations of the lipoxygenase inhibitor nordihydroguaiaretic acid that inhibited leukotriene B4 release from lipopolysaccharide-stimulated human alveolar macrophages in vitro also inhibited subsequent interleukin-8 release, we hypothesized that leukotriene B4 release was required for the release of interleukin-8. Alveolar macrophages from normal nonsmoking volunteers were adhered to plastic and incubated with varying concentrations (25-250nM) of the 5-lipoxygenase activating protein inhibitor MK-886 prior to stimulation with lipopolysaccharide. MK-886 inhibited leukotriene B4 release in a concentration-dependent manner. The concentration of MK-886 that inhibited release by 50% was 53.3 +/- 23.1nM (mean +/- SD), n = 4. Interleukin-8 concentrations in 24hr supernatants were not inhibited by incubation of the cells with any concentration of MK-886, including those that inhibited leukotriene B4 release by > 95%. Thus, MK-886 is an effective inhibitor of human alveolar macrophage release of leukotriene B4, and the release of leukotriene B4 is not a prerequisite for alveolar macrophage release of interleukin-8.

Cell surface aminopeptidase A and N activities in human glomerular epithelial cells

Cell surface aminopeptidases N (APN) and A (APA) have been characterized on cultured human glomerular epithelial cells and a SV40-transformed cell line derived from them. APN had a wide substrate specificity whereas APA only attacked peptides with an acidic N terminal amino acid. Both enzymes also differed by their sensitivity to divalent cations and to aminopeptidase inhibitors. Phorbolmyristate acetate (PMA) stimulated APN but not APA expression after a lag time of 12 hours. An increase of twice the basal value was observed with 10 ng.ml-1 PMA. This effect was confirmed by immunofluorescence staining using a specific anti-APN monoclonal antibody. Both ecto- and total enzyme activities were stimulated by PMA. The effect of PMA was suppressed by H7, a PKC inhibitor, and cycloheximide, an inhibitor of protein synthesis. Thrombin (1 to 2.5 U.ml-1) and interferon (IFN)-gamma (100 U.ml-1) also stimulated APN activity, the latter after longer exposure of the cells. APA activity was increased by 8-bromo-cAMP and two cAMP-stimulating agents, forskolin and isobutylmethylxanthine (IBMX). A twofold increase above basal value was obtained with 100 microM forskolin after 72 hours of treatment. cAMP-stimulated APA activity was suppressed by cycloheximide. Dexamethasone also stimulated APA activity. The effects of forskolin and dexamethasone were additive. These results demonstrate that APN and APA in glomerular epithelial cells are under different regulations: mitogens and IFN-gamma for APN, cAMP and glucocorticoids for APA. This selective expression may imply possible functional consequences in glomerular diseases.