Preferential inhibition of 5-lipoxygenase activity by manoalide

Inhibition of hepatitis C virus NS3 helicase by manoalide

The hepatitis C virus (HCV) causes one of the most prevalent chronic infectious diseases in the world, hepatitis C, which ultimately develops into liver cancer through cirrhosis. The NS3 protein of HCV possesses nucleoside triphosphatase (NTPase) and RNA helicase activities. As both activities are essential for viral replication, NS3 is proposed as an ideal target for antiviral drug development. In this study, we identified manoalide (1) from marine sponge extracts as an RNA helicase inhibitor using a high-throughput screening photoinduced electron transfer (PET) system that we previously developed. Compound 1 inhibits the RNA helicase and ATPase activities of NS3 in a dose-dependent manner, with IC(50) values of 15 and 70 μM, respectively. Biochemical kinetic analysis demonstrated that 1 does not affect the apparent K(m) value (0.31 mM) of NS3 ATPase activity, suggesting that 1 acts as a noncompetitive inhibitor. The binding of NS3 to single-stranded RNA was inhibited by 1. Manoalide (1) also has the ability to inhibit the ATPase activity of human DHX36/RHAU, a putative RNA helicase. Taken together, we conclude that 1 inhibits the ATPase, RNA binding, and helicase activities of NS3 by targeting the helicase core domain conserved in both HCV NS3 and DHX36/RHAU.

Phospholipase A2 inhibitors in development

To date, three isoforms of phospholipase A2 (PLA2) have been identified. Of these, the two Ca2+-dependent isoforms, secretory (sPLA2) and cytosolic phospholipase A2 (cPLA2), are targets for new anti-inflammatory drugs. The catalytic mechanisms and functions of the third isoform, Ca2+-independent cytosolic phospholipase A2 (iPLA2), are unknown at present. sPLA2 and cPLA2 are both implicated in the release of arachidonic acid and prophlogistic lipid mediators. However, recent findings provide evidence that cPLA2 is the dominant isoform in various kinds of inflammation, such as T-cell-mediated experimental arthritis. A triple function of PLA2-derived lipid mediators has been suggested: causing immediate inflammatory signs, involvement in secondary processes, e.g., superoxide free radical (O2) generation, apoptosis, or tumour necrosis factor-alpha (TNF-alpha)-cytotoxicity, and controlling the expression and activation of pivotal proteins implicated in inflammation and cell development, e.g., cytokines, adhesion proteins, proteinases, NF-kappaB, fos/jun/AP-1, c-Myc, or p21ras. In the past, research predominantly focused on the development of sPLA2 inhibitors; however, present techniques enable discrimination of cPLA2, sPLA2, and iPLA2, and specific inhibitors of each of the three isoforms are likely to appear soon. Over the last decade, between 40 and 50 sPLA2 inhibitors have been described; and the list is growing. However, of these, few have the potential for clinical success, and those that do are predominantly active site-directed inhibitors, e.g., BMS-181162, LY311727, ARL-67974, FPL67047, SB-203347, Ro-23-9358, YM-26734, and IS-741. At present, there are no likely clinical candidates emerging from the ranks of cPLA2 and iPLA2 inhibitors in development. Indications for which PLA2 inhibitors are being pursued include, sepsis, acute pancreatitis, inflammatory skin and bowel diseases, asthma, and rheumatoid arthritis. The three main obstacles to the successful development of PLA2 inhibitors include, insufficient oral bioavailability, low affinity for the enzyme corresponding to low in vivo efficacy and insufficient selectivity.

Anti-inflammatory metabolites from marine sponges

Marine sponges are a rich source of biologically active secondary metabolites with novel chemical structures. Eighty four anti-inflammatory compounds have been isolated from marine sponges. This is the first comprehensive review presenting the structures and anti-inflammatory activities of marine sponge metabolites. (100 references).

Influence of 5-lipoxygenase on in vitro growth of human mammary carcinoma cell line MCF-7

The aim of this study was to investigate the direct effect of 5-lipoxygenase (5-LO) on the growth of human mammary cancer cells MCF-7 in vitro. Cell growth was measured according to the level of 3H-thymidine incorporation. 5-LO was shown to inhibit 3H-thymidine incorporation. The inhibitory effect was 19, 42 and 78% when administered at concentrations of 0.1, 0.2 or 0.5 U/ml, respectively. Its effect was time- and dose-dependent and was statistically significant at concentrations of 0.2 and 0.5 U/ml. We have also shown that the specific 5-LO inhibitor MK-886 (1 microM) lifts the inhibitory effect of 5-LO (0.2 U/ml). Moreover, when treated with an activator of 5-lipoxygenase calcium ionophore A23187 (10 microM) MCF-7 cells synthesize LTB4. The results of this study are evidence of the role of 5-lipoxygenase in the regulation of human mammary cancer cells growth in vitro.

Inhibition of human sPLA2 and 5-lipoxygenase activities by two neo-clerodane diterpenoids

The inhibitory effect of two neo-clerodane diterpenoids, E-isolinaridial (EI) and its methylketone derivative (EIM), isolated from Linaria saxatilis var. glutinosa, on PLA2 and other enzyme activities involved in the inflammatory process was studied. Both compounds inhibited human synovial sPLA2 in a concentration-dependent manner with IC50 values of 0.20 and 0.49 microM, respectively, similar to scalaradial. Besides, these compounds decreased the cell-free 5-lipoxygenase activity and A23187-induced neutrophil LTB4 biosynthesis. Another function of human neutrophils, such as receptor-mediated degranulation, was also significantly reduced. In contrast, none of the compounds affected superoxide generation in leukocytes, or cyclooxygenase-1, cyclooxygenase-2 and inducible nitric oxide synthase activities in cell-free assays.

Functional activity of bronchi from an organ donor with fatal asthma: studies on cryopreserved bronchi

Human bronchi were taken from the lungs of a single asthmatic and 5 nonasthmatic organ donors. The tissues were slowly frozen to -70 degrees C and stored for 1-28 months in liquid nitrogen (-196 degrees C) while suspended in Krebs-Henseleit solution containing 1.8 M dimethyl sulfoxide and 0.1 M sucrose as cryoprotectants. After thawing, bronchial rings were suspended in 10 ml organ baths for isometric tension recording. Spontaneously developed tone (1.13 +/- 0.12, n = 22, vs. 0.56 +/- 0.07 g, n = 33, p < 0.001) and maximal contractile responses to histamine (1.93 +/- 0.12, n = 34, vs. 1.02 +/- 0.14 g, n = 30, p < 0.001) were significantly stronger in asthmatic than in nonasthmatic bronchi. The potency of histamine was 4 times less in asthmatic than in nonasthmatic bronchi (p < 0.001). Comparison of the maximal responses to histamine after storage at -196 degrees C for up to 28 months revealed no significant reduction of the contractile function by time of cryostorage. Salbutamol and the potassium channel opener SDZ PCO 400 were 3-4 times less potent in asthmatic than in nonasthmatic bronchi. For antagonism of histamine by ketotifen in asthmatic bronchi (pD'2 = 8.04 +/- 0.13, n = 5) 4 times higher concentrations were necessary than in nonasthmatic bronchi (pD'2 = 8.63 +/- 0.06, n = 15, p < 0.001). These data support the contention that in spite of a diminished sensitivity to histamine after fatal asthma, isolated bronchi show enhanced spontaneous and agonist-induced contractile responses whereas relaxant responses appear to be impaired.

Effect of manoalide on human 5-lipoxygenase activity

The marine natural product manoalide (MLD) has been described to inactivate phospholipase A2 (PLA2) from several sources as well as to inhibit synthesis of eicosanoids in human polymorphonuclear leukocytes (HPMNL). MLD also reduces chemically-induced inflammation in vivo. In this investigation we have examined the effect of MLD on A23187-induced generation of leukotriene B4 (LTB4) and thromboxane B2 (TXB2) in HPMNL as well as 5-lipoxygenase (5-LO) activity from HPMNL sonicated preparations. In the intact cell system, MLD inhibited with similar potency biosynthesis of LTB4 and TXB2 (IC50 1.7 and 1.4 microM, respectively). In order to discern if inhibition of 5-LO is involved in the effect of MLD, we examined the action of this compound on 5-LO activity from 10,000 x g and 100,000 x g supernatants of sonicated HPMNL homogenates. The enzymatic activity was not affected at concentrations of MLD up to 50 microM. These data indicate that MLD is not a direct inhibitor of 5-LO activity from HPMNL and support the hypothesis that its anti-inflammatory action could be related with a reduction of eicosanoid biosynthesis via inhibition of PLA2.

The antiinflammatory activity of topically applied novel calcium-channel antagonists

The antiinflammatory activities of two novel calcium-channel antagonists, AGN 190742 and AGN 190744, were evaluated in murine models of cutaneous inflammation. These 2(5H)-furanone ring compounds block both depolarization-dependent Ca2+ entry and receptor-mediated responses in GH3 cells. Topical application of AGN 190742 or AGN 190744 inhibits neutrophil infiltration and epidermal hyperplasia induced by repeated treatment of mouse skin with phorbol ester. AGN 190744 also is active in an arachidonic acid model of acute inflammation. These data suggest that topical application of calcium-channel antagonists can inhibit cutaneous inflammatory responses and that AGN 190742 and/or AGN 190744 may serve as useful pharmacological probes for examining these responses in vivo.

Effects of scalaradial, a novel inhibitor of 14 kDa phospholipase A2, on human neutrophil function

Scalaradial, a marine natural product with anti-inflammatory activity, has been shown to be a selective inhibitor of 14 kDa type II phospholipase A2(PLA2). We have examined the inhibition by scalaradial (0.1 nM to 10 microM) of neutrophil function (degranulation) in response to receptor-mediated activation [N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), 30 nM; leuokotriene B4 (LTB4), 100 nM; platelet-activating factor (PAF), 100 nM] and non-receptor-mediated stimuli [A23187 (1 microM) and thapsigargin (100 nM)]. Furthermore, we evaluated the ability of scalaradial to inhibit the increase in intracellular Ca2+ in response to fMLP, LTB4, A23187, and thapsigargin as well as its ability to prevent either fMLP- or LTB4-mediated elevation in inositol phosphate production (InsP). Scalaradial was a potent inhibitor of both receptor- (IC50 = 50-200 nM) and non-receptor- (IC50 = 40-900 nM) mediated degranulation. Although scalaradial inhibited the mobilization of Ca2+ induced by fMLP, LTB4, and PAF, it did not affect the maximal Ca2+ levels attained with A23187 or thapsigargin. Neutrophil-binding studies with [3H]fMLP and [3H]LTB4 would suggest that the effect of scalaradial on agonist-induced degranulation and increase in intracellular Ca2+ was not at the receptor level because 50-fold higher concentrations were required to have a significant effect on the binding of these agonists. To determine if scalaradial affected phosphatidylinositol selective phospholipase C (PI-PLC) activity, assays were conducted to monitor fMLP- and LTB4-induced formation of InsPs using myo-[3H]inositol-labeled U-937 cells. In these cells, 2.5 to 9-fold higher concentrations of scalaradial were required to inhibit PI-PLC activity than to inhibit agonist-induced degranulation of neutrophils, suggesting that the effects of scalaradial on Ca2+ and degranulation are not the sole result of blocking receptor activation of PI-PLC. Results obtained with receptor-mediated stimuli suggest that scalaradial may have direct effects on Ca2+ channels and InsP turnover, but inhibition of intracellular Ca2+ levels was not required for scalaradial to block degranulation since scalaradial was capable of inhibiting degranulation produced by either A23187 or thapsigargin, without changing the maximal Ca2+ levels obtained with these two stimuli. These results demonstrate that scalaradial can inhibit degranulation in the presence of micromolar intracellular Ca2+ concentration, thus supporting the hypothesis that a 14 kDa PLA2 may be important in the regulation of neutrophil degranulation.

Suppression of inflammatory responses to 12-O-tetradecanoyl-phorbol-13-acetate and carrageenin by YM-26734, a selective inhibitor of extracellular group II phospholipase A2

1. YM-26734 [4-(3,5-didodecanoyl-2,4,6-trihydroxyphenyl)-7-hydroxy-2-(4-hydroxyph eny l) chroman] dose-dependently inhibited the activities of extracellular phospholipase A2 (PLA2): rabbit platelet-derived group II and porcine pancreas-derived group I PLA2, with IC50 values of 0.085 (0.056-0.129, n = 5) and 6.8 (5.0-9.6, n = 5) microM, respectively. 2. In contrast, YM-26734 did not reduce the activity of intracellular PLA2 prepared from mouse macrophages, which preferentially hydrolyzed arachidonoyl phospholipids at concentrations up to 50 microM. YM-26734 also showed no effect against either sheep seminal vesicle cyclo-oxygenase or rat leukocyte 5-lipoxygenase. 3. Linewater-Burk analysis showed that YM-26567-1 behaved as a competitive inhibitor of group II PLA2 derived from rabbit platelets, with a Ki value of 48 nM. 4. In mice, YM-26734 inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA, 1 microgram/ear)-induced ear oedema in a dose-dependent manner, with ED50 values of 45 (30-67) micrograms/ear (n = 5) and 11 (4-32) mg kg-1, i.v. (n = 5), but did not decrease arachidonic acid (4 mg/ear)-induced ear oedema at 1 mg/ear and 30 mg kg-1, i.v. 5. In rats, the accumulation of exudate fluids and leukocytes in the pleural cavity in response to carrageenin injection (2 mg) was significantly less in a group treated with YM-26734 (20 mg kg-1, i.v.) than in the control group (0.43 +/- 0.02 vs 0.59 +/- 0.03 g per cavity and 3.8 +/- 0.2 vs 4.9 +/- 0.3 x 10(7) cells per cavity, respectively; n = 5). 6. These results suggest that YM-26734 is a potent and competitive inhibitor of extracellular PLA2 with selectivity for group II PLA2, and that the inhibition of group II enzymes activity may cause the suppression of inflammatory responses to TPA and carrageenin.

5-lipoxygenase inhibitors and their anti-inflammatory activities

A wide variety of agents have been reported as 5-LO inhibitors. The majority of the series appear to be lipophilic reducing agents, including phenols, partially saturated aromatics, and compounds containing heteroatom-heteroatom bonds. Many of these are not selective 5-LO inhibitors, but often affect CO and other LOs as well. In vivo systemic activity for many of these has been, in general, disappointing, probably because of poor bioavailability caused by lipophilicity and metabolic instability (oxidation, and conjugation of phenolic compounds). However, topically a number of agents have shown promise for skin inflammation, with Syntex's lonapalene the most advanced of these. Most results published to date appear more disappointing in the allergy/asthma field. More excitingly, a few structural types are selective 5-LO inhibitors which have shown systemic activity in vivo and in the clinic. Abbott's zileuton (136) appears to be one of the leading compounds in this category, along with other hydroxamates such as BW-A4C (129) from Burroughs-Wellcome. Recent selective non-reducing agents such as Wyeth-Ayerst's Wy-50,295 (143) and the similar ICI compounds such as ICI 216800 (145) also hold promise. The enantiospecific effects of (106) and (145) are especially interesting for the design of new inhibitors. If compounds like these validate the hypothesis that inhibition of 5-LO will have a significant anti-inflammatory effect, a redoubling of effort throughout the industry to find second- and third-generation selective agents may be expected. Part of the difficulty in interpreting and comparing the 5-LO literature is the plethora of test methods and activity criteria. As pointed out in the introduction, inhibition of product release from cells, often stimulated with A23187, has commonly been used to demonstrate 5-LO inhibition. However, this type of assay cannot be assumed to be diagnostic for 5-LO inhibition. Only if specificity for 5-LO product generation and (ideally) activity in cell-free enzymes is also shown should mechanistic interpretations be made. Recently, a new class of compounds was found at Merck which inhibited LT biosynthesis without inhibiting 5-LO, but apparently by a novel, specific mechanism. L-655,240 (169) and L-663,536 (MK-886) (170) were both active in human ISN, with IC50 values in the low micromolar range. Both also orally inhibited GPB (< 1 mg/kg). MK-886 was effective in Ascaris-induced asthma in squirrel monkeys, in rat carrageenan pleurisy, in rat Arthus pleurisy, and (topically) in guinea-pig ear oedema induced by A23187.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition by manoalide of fMLP-stimulated elastase release from human neutrophils

Incubation of human polymorphonuclear leukocytes (PMNLs) with the chemotactic factor N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) resulted in a concentration-dependent release of the neutral protease elastase. This response was inhibited by pretreatment of the PMNLs with manoalide (IC50 approximately 0.08 microM). To understand the mechanism of this inhibition, we examined the effect of manoalide on the signal-transduction pathway believed to mediate fMLP stimulation. We observed in fura-2 loaded cells that pretreatment with manoalide blocked fMLP-induced increases in cytosolic free-calcium (IC50 approximately 0.15 microM). However, manoalide had no effect on inositol 1,4,5-trisphosphate (IP3) production at concentrations which completely inhibited the Ca2+ signal. Furthermore, manoalide was approximately 50-fold less potent as an inhibitor of phospholipase C activity in membrane preparations of PMNLs than as an inhibitor of calcium mobilization in whole cells. These data indicate that manoalide can block stimulation of human PMNLs through inhibition of Ca2+ mobilization, but that this occurs at a site beyond phospholipase C activation and inositol phosphate turnover.

Pharmacological evidence for the existence of a local renin-angiotensin system in porcine interlobar renal arteries

1. Changes in tension in response to cumulative additions of angiotensins (i.e., angiotensinogen, angiotensin I and angiotensin II), bradykinin and acetylcholine were monitored isometrically on ring preparations from porcine interlobar renal arteries. 2. Angiotensins consistently elicited contractile responses, whereas both bradykinin and acetylcholine produced relaxation of the arterial rings when active tone was induced by prostaglandin F2 alpha. 3. Contractile responses to angiotensin II could be completely blocked by the combined action of the cyclo-oxygenase inhibitor, indomethacin (1 microM) and the lipoxygenase inhibitor, nordihydroguairetic acid (NDGA, 10 microM). 4. Relaxant responses to bradykinin were unchanged during blockade of thromboxane A2 synthesis by dazoxiben (30 microM) and proved to be largely resistant to blockade by indomethacin (1 microM) and the prostaglandin I2 (prostacyclin) synthesis inhibitor, tranylcypromine (40 microM). 5. The angiotensin receptor blocker, saralasin (10 and 100 nM) antagonized responses to angiotensinogen, angiotensin I and angiotensin II effectively and with similar potency. Enalaprilic acid, the active metabolite of the converting enzyme inhibitor enalapril (300 nM), attenuated responses to angiotensin I but failed to inhibit those to angiotensinogen up to 1 microM. The serine protease kallikrein (0.001 to 1 mu ml-1) produced a dose-dependent shift to the left of the concentration-response curve for angiotensinogen. 6. It is suggested that the porcine interlobar renal artery possesses a local renin-angiotensin system with activatable angiotensin II forming enzyme(s) within the vessel wall.

Interaction of cyclosporine-A with the renin-angiotensin system in canine veins

Responses of canine saphenous veins to bradykinin and angiotensin and the effect of cyclosporine-A were investigated both in conscious dogs in vivo and on ring preparations from canine saphenous veins in vitro. In vivo local infusion of bradykinin into the saphenous vein elicited dose-dependent reduction in compliance, i.e., venoconstriction, whereas local infusion of angiotensin elicited dose-dependent venodilatation, which was markedly enhanced during blockade of endogenous thromboxane A2 synthesis by dazoxiben (2.5 mg/kg i.v.). The venoconstrictor response to bradykinin was attenuated after oral administration of both the thiazide-like diuretic clopamide (0.5 mg/kg) or cyclosporine-A (30 mg/kg), and by concomitant local infusion of cyclosporine-A (1-10 micrograms/min). Systemic i.v. infusion of the renin inhibitor H-77 (0.1 mg/kg/h) reversed the inhibition of bradykinin by both clopamide and cyclosporine-A. In vitro bradykinin elicited relaxation at low (0.1-10 nmol/l) but constriction at higher concentrations. The venoconstrictor response to bradykinin was resistant to blockade of thromboxane A2 synthesis and only partially attenuated after selective blockade of cyclooxygenase or lipoxygenase. Concomitant blockade of both lipoxygenase and cyclooxygenase activity by nordihydroguaiaretic acid (NDGA 10-30 mumol/l) nearly abolished the contractile response thereby enhancing the relaxant component of the bradykinin effect. Angiotensin II also elicited biphasic responses of partially contracted venous rings. Concomitant blockade of both lipoxygenase and cyclooxygenase by NDGA (10 mumol/l) again attenuated the contractile component of the angiotensin effect thereby unmasking the venodilator activity which could be inhibited by the angiotensin II receptor blocker saralasin (0.01-1 mumol/l).(ABSTRACT TRUNCATED AT 250 WORDS)