Chemopreventive effects of orange peel extract (OPE). II: OPE inhibits atypical hyperplastic lesions in rodent mammary gland

Cancer chemoprevention via the ingestion of natural substances is a current topic of considerable interest. Flavonoids are a family of biologically active phytochemicals having a variety of biological effects. Orange peel extract (OPE) is an abundant source of polymethoxyflavones (PMFs) with potential chemopreventive properties. The OPE used here was a mixture containing tangeretin (19.0%), heptamethoxyflavone (15.24%), tetramethoxyflavone (13.6%), nobiletin (12.49%), hexamethoxyflavone (11.06%), and sinensitin (9.16%). C57Bl/6 mice were fed a new "Western-style" diet (NWD), which had previously induced atypical hyperplasias in mammary gland, and NWD supplemented with a standardized OPE containing 30% PMFs. Mice were fed one of four diets: (1) AIN-76A diet (control); (2) NWD; 0.25% OPE in NWD; or (4) 0.5% OPE in NWD. After 3 months of feeding, atypical hyperplasias developed in mammary glands of mice fed NWD, but not in controls. After feeding OPE in NWD, atypical hyperplasias per mouse decreased in frequency compared to feeding NWD alone (P < .05 in mice fed 0.25% OPE). Apoptosis increased in OPE-treated groups (P < .01) with no inhibition of mitosis. Thus, a standardized preparation of OPE with 30% PMFs decreased development of an atypical hyperplastic lesion and increased apoptosis in ductal epithelial cells of mouse mammary gland.

Chemopreventive effects of orange peel extract (OPE). I: OPE inhibits intestinal tumor growth in ApcMin/+ mice

Orange peel is a rich source of flavonoids with polymethoxyflavones as major constituents, compounds associated with potential antioxidant, anti-inflammatory, and antitumor activities. We studied the effect of an orange peel extract (OPE) on intestinal tumor growth in Apc(Min/+) mice, a mouse model for human familial adenomatous polyposis (FAP). The OPE contained 30% polymethoxyflavones, a mixture that included tangeretin (19.0%), heptamethoxyflavone (15.24%), tetramethoxyflavone (13.6%), nobiletin (12.49%), hexamethoxyflavone (11.06%), and sinensitin (9.16%). Apc(Min/+) mice were fed one of four diets: (1) AIN-76A control diet; (2) a new Western-style diet (NWD), i.e., AIN-76A diet modified with decreased calcium, vitamin D, and methyl-donor nutrients and increased lipid content); (3) NWD with 0.25% OPE; and (4) NWD with 0.5% OPE, with all additives premixed in the diet. After 9 weeks of feeding NWD to the Apc(Min/+) mice, tumors increased mainly in the colon, with tumor multiplicity increasing 5.3-fold and tumor volume increasing 6.7-fold. After feeding 0.5% OPE in NWD, the development of tumors markedly decreased, with multiplicity decreasing 49% in the small intestine and 38% in the colon. NWD also led to increased apoptosis in intestinal tumors, and 0.5% OPE in NWD further increased apoptosis in tumors of the small and large intestine. Findings indicated that OPE inhibited tumorigenesis in this preclinical mouse model of FAP, and increased apoptosis may have contributed to this effect.

Inhibitory effects of black tea theaflavin derivatives on 12-O-tetradecanoylphorbol-13-acetate-induced inflammation and arachidonic acid metabolism in mouse ears

Tea has been shown to possess several health beneficial properties primarily due to its polyphenolic content. The major polyphenolic compounds in black tea leaves are theaflavins (TFs) formed by oxidative coupling of catechins in tea leaves during its processing. In this paper, we report the characterization of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced mouse ear inflammatory model and the inhibitory effects of major black tea TFs derivatives on this inflammation. In addition, the effect on inflammatory biomarkers, such as proinflammatory cytokines and arachidonic acid metabolites, are reported as well. A single topical application of TPA to ears of CD-1 mice induced a time- and dose-dependent increase in edema as well as formation of proinflammatory cytokine proteins interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) in mouse ears. A single topical application of equimolar of black tea constituents (TF, theaflavin-3-gallate, theaflavin-3'-gallate, and theaflavin-3,3'-digallate) strongly inhibited TPA-induced edema of mouse ears. Application of TFs mixture to mouse ears 20 min prior to each TPA application once a day for 4 days inhibited TPA-induced persistent inflammation, as well as TPA-induced increase in IL-1beta and IL-6 protein levels. TFs also inhibited arachidonic acid (AA) metabolism via both cyclooxygenase (COX) and lipoxygenase pathways. This observation was substantiated by decreased amounts of AA metabolites prostaglandin E2 (PGE2) and leukotriene B4 (LTB4) levels. Combined application of TF and sulindac, a nonsteroidal anti-inflammatory drug resulted a significant synergetic anti-inflammatory effect. Oral administration of TFs or the hot water extract of black tea leaves also significantly inhibited TPA-induced edema in mouse ears. In conclusion, proinflammatory cytokines, IL-1beta and IL-6, as well as the intermediated metabolites of AA, PGE2, and LTB4 are good biomarkers for inflammation. Black tea constituents, TF and its derivatives, had strongly anti-inflammatory activity in vivo which may be due to their ability to inhibit AA metabolism via lipoxygenase and COX pathways.

Novel polyphenol molecule isolated from licorice root (Glycrrhiza glabra) induces apoptosis, G2/M cell cycle arrest, and Bcl-2 phosphorylation in tumor cell lines

Herbal therapies are commonly used by patients with cancer, despite little understanding about biologically active chemical derivatives. We recently demonstrated that the herbal combination PC-SPES, which contains licorice root, had anti-prostate cancer activity attributable to estrogen(s) that produced a chemical castration. A recent study also demonstrated that licorice root alone decreased circulating testosterone in men. Other studies demonstrated antitumor activity of PC-SPES in vitro associated with decreased expression of the anti-apoptotic protein Bcl-2 and in patients independent of chemical castration, suggesting that other mechanisms of antitumor activity exist separate from chemical castration. In the present study, we assessed licorice root extract for effects on Bcl-2 to identify novel cytotoxic derivatives. Licorice root extract induced Bcl-2 phosphorylation as demonstrated by immunoblot and G2/M cell cycle arrest, similarly to clinically used antimicrotubule agents such as paclitaxel. Bioassay-directed fractionations resulted in a biologically active fraction for Bcl-2 phosphorylation. HPLC separation followed by mass spectrometry and NMR identified 6 compounds. Only one molecule was responsible for Bcl-2 phosphorylation; it was identified as 1-(2,4-dihydroxyphenyl)-3-hydroxy-3-(4'-hydroxyphenyl) 1-propanone (beta-hydroxy-DHP). The effect on Bcl-2 was structure specific, because alpha-hydroxy-DHP, 1-(2,4-dihydroxyphenyl)-2-hydroxy-3-(4'-hydroxyphenyl) 1-propanone, in contrast to beta-hydroxy-DHP, was not capable of Bcl-2 phosphorylation. Pure beta-hydroxy-DHP induced Bcl-2 phosphorylation in breast and prostate tumor cells, G2/M cell cycle arrest, apoptosis demonstrated by Annexin V and TUNEL assay, decreased cell viability demonstrated by a tetrazolium (MTT) assay, and altered microtubule structure. Therefore, these data demonstrate that licorice root contains beta-hydroxy-DHP, which induced Bcl-2 phosphorylation, apoptosis, and G2/M cell cycle arrest, in breast and prostate tumor cells, similarly to the action of more complex (MW >800) antimicrotubule agents used clinically.

Flavonol glycosides and novel iridoid glycoside from the leaves of Morinda citrifolia

One new iridoid glycoside and five known flavonol glycosides have been isolated from the leaves of Morinda citrifolia. The new iridoid exists as an epimeric mixture in solution. Complete assignments of the proton and carbon chemical shifts for the individual epimers were accomplished on the basis of high-resolution 1D and 2D NMR data. Their antioxidative activities were measured. All of these compounds showed DPPH free radical scavenging activity at the concentration of 30 microM.

A new unusual iridoid with inhibition of activator protein-1 (AP-1) from the leaves of Morinda citrifolia L

[structure in text] From the leaves of Morinda citrifolia, a new unusual iridoid, named citrifolinoside (1), showing significant inhibition of UVB-induced Activator Protein-1 (AP-1) activity in cell cultures, has been isolated. Its structure was elucidated on the basis of detailed high-field 1D and 2D spectral analysis.

Iridoid glycosides from the leaves of Morinda citrifolia

A new iridoid glucoside (1), named citrifolinoside A, was isolated from the leaves of Morinda citrifolia along with the known iridoids asperuloside and asperulosidic acid. The structure of 1 was established by interpretation and full assignments of NMR spectroscopic data.

Bioactive constituents from gum guggul (Commiphora wightii)

Bioactivity-directed fractionation and purification afforded cytotoxic components of Commiphora wightii. The exudates of C. wightii were extracted with EtOAc and the extract was subjected to repeated column chromatography. A fraction showing cytotoxic activity was characterized as a mixture of two ferulates with an unusual skeleton by spectral and chemical methods, including by NMR, GC-MS and chemical derivatization. This fraction also showed moderate scavenging effect against 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals.

Resveratrol analog, 3,4,5,4'-tetrahydroxystilbene, differentially induces pro-apoptotic p53/Bax gene expression and inhibits the growth of transformed cells but not their normal counterparts

Resveratrol, a trihydroxystilbene found in grapes and other plants, has been shown to be active in inhibiting multistage carcinogenesis. Using resveratrol as a prototype, we have synthesized a number of polyhydroxy- and polymethoxy-stilbenes and tested their anti-proliferative effect in normal and transformed human cells. Here we show that one of the resveratrol analogs, 3,4,5,4'-tetrahydroxystilbene (R-4), specifically inhibited the growth of SV40 virally transformed WI38 cells (WI38VA) at 10 microM, but had no effect on normal WI38 cells at even higher concentrations. R-4 also prominently induced apoptosis in WI38VA cells, but not in WI38 cells. RNase protection assay showed that R-4 significantly induced the expression of p53, GADD45 and Bax genes and concomitantly suppressed the expression of bcl-2 gene in WI38VA, but not in WI38 cells. A large increase in p53 DNA binding activity and the presence of p53 in the Bax promoter binding complex suggested that p53 was responsible for the Bax gene expression induced by R-4 in transformed cells. Within 4 h of treatment with R-4, the Bax to bcl-2 protein ratio in WI38 and WI38VA cells was, respectively, 0.1 and 105, a difference of three orders of magnitude. While R-4 prominently induced the p53/Bax pro-apoptotic genes, it also concomitantly suppressed the expression of Cox-2 in WI38VA cells. Taken together, our study suggests that the induction of p53 gene by R-4 in transformed cells may play a key role in the differential growth inhibition and apoptosis of transformed cells.

Differential effects of theaflavin monogallates on cell growth, apoptosis, and Cox-2 gene expression in cancerous versus normal cells

Theaflavin (TF-1), theaflavin-3-monogallate and theaflavin-3'-monogallate mixture (TF-2), and theaflavin-3,3'-digallate (TF-3) are the major black tea polyphenols. Here we compared the effects of these polyphenols on cell growth, apoptosis, and gene expression in normal and cancerous cells. We showed that TF-2 (10-50 microM) inhibited the growth of SV40 transformed WI38 human cells (WI38VA) and Caco-2 colon cancer cells but had little effect on the growth of their normal counterparts. The IC50s of TF-2 for the growth inhibition of WI38 and WI38VA cells were, respectively, 300 and 3 microM. The other two black tea polyphenols, TF-1 and TF-3, did not exhibit such differential growth-inhibitory effect. TF-2, but not TF-1 or TF-3, induced apoptosis in transformed WI38VA cells but not in normal WI38 cells, suggesting that apoptosis was responsible, at least in part, for the differential growth-inhibitory effect of TF-2. Cox-2 has been implicated in intestinal carcinogenesis. Among the tea polyphenols tested, TF-2 and, to a lesser degree, (-)-epigallocatechin gallate inhibited cyclooxygenase (Cox)-2 gene expression. TF-2 at 50 microM completely blocked the serum-induced Cox-2 gene expression at both mRNA and protein level. Other genes, including c-fos, c-myc, thymidine kinase, proliferating cell nuclear antigen, BRCA1, BRCA2, and Cox-1, were not significantly affected by TF-2. These findings suggest that TF-2 may be responsible, at least in part, for the chemopreventive activity in black tea extracts.

Novel glycosides from noni (Morinda citrifolia)

Three new glycosides were isolated from the fruits of noni (Morinda citrifolia). Their structures were determined to be 6-O-(beta-D-glucopyranosyl)-1-O-octanoyl-beta-D-glucopyranose (1), 6-O-(beta-D-glucopyranosyl)-1-O-hexanoyl-beta-D-glucopyranose (2), and 3-methylbut-3-enyl 6-O-beta-D-glucopyranosyl-beta-D-glucopyranoside (3) using MS and NMR methods.

Modulation of bcl-2 and cytotoxicity by licochalcone-A, a novel estrogenic flavonoid

Herbal therapies are commonly used by patients with cancer, despite little understanding about their clinical and biological activity. We recently demonstrated that the herbal combination PC-SPES, which contains licorice root, had potent estrogenic activity in vitro, in animals, and in patients with prostate cancer. Licochalcone-A (LA) is one flavonoid extracted from licorice root with antiparasitic and anti-tumor activity, but the effect on the human estrogen receptor and mechanism of anti-tumor activity is unknown. Recent studies demonstrated that the mechanism of cytotoxic effect by some estrogens may involve modulation of the anti-apoptotic protein bcl-2. In the present study, we determined if LA had estrogenic activity, anti-tumor activity, and modulated the apoptotic protein bcl-2 in human cell lines derived from acute leukemia, breast cancer, and prostate cancer. A yeast growth-based assay under the control of the human estrogen receptor (hER) demonstrated that LA was a phytoestrogen. A cell viability assay demonstrated that LA had anti-tumor activity in all cell lines tested and enhanced the effect of paclitaxel and vinblastine chemotherapy. LA induced apoptosis in MCF-7 and HL-60 cell lines, as demonstrated by cleavage of PARP, the substrate of ICE-like proteases. Immunoblot analysis demonstrated that LA decreased the anti-apoptotic protein bcl-2 and altered the bcl-2/bax ratio in favor of apoptosis. In contrast, the parent compound chalcone or estradiol did not decrease bc1-2 expression. Therefore, these data demonstrate that LA is a phytoestrogen with anti-tumor activity and is capable of modulating bcl-2 protein expression. The modulation of bcl-2 may be dependent on specific structural differences between LA and the parent compound chalcone and independent of LA estrogenicity.

Novel trisaccharide fatty acid ester identified from the fruits of Morinda citrifolia (Noni)

Two known glycosides and a novel trisaccharide fatty acid ester were isolated from the n-butanol-soluble fraction of the fruits of Morinda citrifolia (noni). Structure determination was carried out by spectral techniques such as MS, IR, NMR, and 2D-NMR. The novel trisaccharide fatty acid ester was elucidated as 2, 6-di-O-(beta-D-glucopyranosyl)-1-O-octanoyl-beta-D-glucopyranose. The known compounds were identified as rutin and asperulosidic acid.

The biological activity of atrial natriuretic factor cleaved by endoprotease 3.4.24.11

Ring cleavage of atrial natriuretic peptide (ANF) between Cys7 and Phe8 by endoprotease 3.4.24.11 yields X-ANF. Since endoprotease 3.4.24.11 may contribute to ANF metabolism in vivo, the present study determined if X-ANF exhibits reduced biological activity in comparison to the parent molecule.

13C nuclear magnetic resonance spectroscopy of glucose metabolism in human red blood cells

Glucose metabolism of human red blood cells was investigated using carbon-13 nuclear magnetic resonance spectroscopy under both oxygenated and nonoxygenated conditions. These results show that under oxygenated conditions reversal of 3-phosphoglyceraldehyde to glucose is in competition with its catabolism to lactate.

Structure-activity profile of a series of novel triazoloquinazoline adenosine antagonists

During a search for benzodiazepine receptor modulators, a highly potent adenosine antagonist (CGS 15943) was discovered. The compound was defined as a resonance-stabilized hybrid of the canonical structures 9-chloro-2-(2-furyl)[1,2,4]triazolo[1,5-c]quinazolin-5-amine (2a) and 9-chloro-2-(2-furyl)-5,6-dihydro[1,2,4]triazolo[1,5-c]-quinazolin- 5-imine (2b). Spectroscopic evidence and chemical reactivity in polar media favor the amine form 2a as the major contributor of the two canonical structures. The synthesis of 2 and some of its analogues and the structure-activity relationships in four biological test systems are described. Replacement of the 9-chloro group by hydrogen, hydroxyl, or methoxyl gave compounds with comparable binding potency at the A1 and A2 receptors but much less activity as antagonists of 2-chloroadenosine in guinea pig tracheal strips. Alkylation of the 5-amino group caused, in general, a loss of binding activity, particularly at the A2 receptor, as well as complete loss of activity in the tracheal model. Modification of the 2-furyl group caused a pronounced loss of activity in all of the test systems.

Characterization of CGS 8515 as a selective 5-lipoxygenase inhibitor using in vitro and in vivo models

CGS 8515 inhibited 5-hydroxyeicosatetraenoic acid (5-HETE) and leukotriene B4 synthesis in guinea pig leukocytes (IC50 = 0.1 microM). The compound did not appreciably affect cyclooxygenase (sheep seminal vesicles), 12-lipoxygenase (human platelets), 15-lipoxygenase (human leukocytes) and thromboxane synthetase (human platelets) at concentrations up to 100 microM. CGS 8515 inhibited A23187-induced formation of leukotriene products in whole blood (IC50 values of 0.8 and 4 microM, respectively, for human and rat) and in isolated rat lung (IC50 less than 1 microM) in vitro. The selectivity of the compound as a 5-lipoxygenase inhibitor was confirmed in rat whole blood by the 20-70-fold separation of inhibitory effects on the formation of leukotriene from prostaglandin products. Ex vivo and in vivo studies with rats showed that CGS 8515, at an oral dose of 2-50 mg/kg, significantly inhibited A23187-induced production of leukotrienes in whole blood and in the lung. The effect persisted for at least 6 h in the ex vivo whole blood model. CGS 8515, at oral doses as low as 5 mg/kg, significantly suppressed exudate volume and leukocyte migration in the carrageenan-induced pleurisy and sponge models in the rat. Inhibitory effects of the compound on inflammatory responses and leukotriene production in leukocytes and target organs are important parameters suggestive of its therapeutic potential in asthma, psoriasis and inflammatory conditions.

Evidence for A1 and A2 adenosine receptors in guinea pig trachea

The adenosine analogs [5'-N-ethylcarboxamideadenosine (NECA), 2-Chloro-adenosine (2-ClA), R-phenylisopropyladenosine (R-PIA), N6-cyclohexyl adenosine (CHA), and N6-cyclopentyladenosine (CPA)] produced both relaxation and contraction responses in isolated guinea-pig trachea. A concentration-related relaxation response was observed in trachea which were precontracted with either histamine or KC1. This response followed an order of analog potency that was indicative of the A2 receptor subtype (NECA greater than 2-ClA greater than R-PIA greater than CPA greater than CHA). Theophylline, an adenosine-receptor antagonist, blocked this relaxation response. In addition, a concentration-related contractile response was produced with adenosine analogs in those trachea that were not previously contracted. In contrast, the contractile response followed an analog potency indicative of the A1 receptor subtype (R-PIA greater than 2-ClA = CPA = CHA). This contractile response was not mediated by cholinergic, adrenergic or histaminergic receptors. 2-ClA induced a biphasic response, while NECA only relaxed these tissue under basal tone. Unlike the relaxation response, these contractile responses were not attenuated by theophylline, but were blocked by 1,3 dipropyl-8-(2 amino-4-chlorophenyl)xanthine (PACPX). These findings confirm the existence of two subpopulations of adenosine receptors in guinea pig trachealis muscle.

Pharmacological characterization of CGS 15943A: a novel nonxanthine adenosine antagonist

CGS 15943A is a potent adenosine receptor antagonist with a novel nonxanthine heterocyclic ring structure. In vitro, CGS 15943A competitively inhibited the 2-chloroadenosine-induced A2 receptor-mediated relaxation of dog coronary artery strips contracted with KCl (25 mM). Similarly, CGS 15943A blocked 2-chloroadenosine- and N-ethylcarboxamideadenosine-induced A2 receptor-mediated relaxation of histamine-contracted guinea pig tracheal strips. Schild analysis of these results yielded pA2 values of 10.8 and 10.1 for the coronary arteries and the tracheal smooth muscle strips, respectively. In comparison, 8-phenyltheophylline blocked 2-chloroadenosine-induced tracheal response with a pA2 value of 7.0. CGS 15943A was devoid of intrinsic activity, and did not affect either histamine- or KCl-induced contractions of the smooth muscle strips. In the electrically stimulated guinea pig left atrial preparation, CGS 15943A antagonized the A1 receptor-mediated negative inotropic effects of R-phenylisopropyladenosine with a pA2 value of 7.4. In vivo, i.v. administration of CGS 15943A blocked the vasodepressor response to 2-chloradenosine in anesthetized normotensive rats with an ID50 of 0.024 mg/kg. In addition, p.o. administration of CGS 15943A (4.0 mg/kg) to conscious rats inhibited 2-chloroadenosine-induced decreases in diastolic blood pressure; maximal effects were observed 30 min after dosing, with a T1/2 of approximately 103 min. Therefore suggesting that CGS 15943A is an orally active antagonist of adenosine receptors. These results indicate that CGS 15943A antagonized both A1 and A2 receptor-mediated responses with a greater affinity toward the A2 than the A1 receptor subtype.

Biochemical characterization of the triazoloquinazoline, CGS 15943, a novel, non-xanthine adenosine antagonist

CGS 15943A, a triazoloquinazoline, is a potent and selective adenosine receptor antagonist as assessed by its effects on radioligand binding and adenosine-stimulated adenylate cyclase activity in guinea pig synaptoneurosomes. At the adenosine A-1 receptor labeled with [3H]cyclohexyladenosine, CGS 15943A had an IC50 value of 20 nM. At the striatal A-2 receptor labeled with [3H]5'-N-ethylcarboxamidoadenosine in the presence of a low concentration of cyclopentyladenosine to block A-1 receptors labeled by this nonselective adenosine agonist, CGS 15943A had an IC50 value of 3 nM, indicating that the compound had some degree of selectivity for the A-2 receptor. Analysis of the effect of the compound on the saturation isotherms for each of the receptors indicated that it was a competitive antagonist at the brain A-1 receptor but that it was noncompetitive at the striatal A-2 receptor. CGS 15943A was a potent adenosine antagonist in the adenosine-stimulated adenylate cyclase system in guinea pig synaptoneurosomes, where the compound was found to have an IC50 value of 30 to 70 nM against the increase in cyclic AMP evoked by 5 microM adenosine. CGS 15943A had no effect on the binding of [3H]nitrobenzylthioinosine, a ligand thought to bind to adenosine uptake sites, and, at a concentration of 10 microM, had no effect on beef heart type III phosphodiesterase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial alterations due to free-radical generation

Oxygen-derived free radicals have been proposed as general mediators of tissue injury in a variety of disease states. Recent interest has focused on the possibility that free radicals may be involved in ischemic myocardial damage. However, the exact types of damage that result from myocardial exposure to free radicals remains to be established. The purpose of this study was to evaluate the effects of superoxide and hydroxyl radicals on myocardial structure and function in an isolated perfused rabbit interventricular septal preparation. Superoxide was generated by adding purine (2.3 mM) and xanthine oxidase (0.01 U/ml) to the physiological solutions perfusing the septa. Hydroxyl radical generation was catalyzed by the addition of 2.4 microM Fe3+-loaded transferrin to the system. Exposure of normal septa to superoxide-generating solutions resulted in the development of structural alterations in the vascular endothelium including the development of vacuoles. Membranous cellular debris was evident in the extracellular space and within the vessels. Cardiac myocytes showed evidence of mild alterations. Exposure of septa to solutions capable of generating hydroxyl radicals resulted in more extensive and severe damage. Vascular endothelial cells showed evidence of vacuoles or blebs and edema. Severe swelling of mitochondria was evident in cardiac myocytes and vascular endothelial cells. In addition, myocytes often showed blebbing of the basement membrane. Normal septa exposed to superoxide showed no significant decrease in developed tension, whereas hydroxyl radical exposure resulted in a significant decrease in myocardial function.(ABSTRACT TRUNCATED AT 250 WORDS)

Calmodulin-dependent stimulation of the NADPH oxidase of human neutrophils

The NADPH oxidase of human neutrophils is highly sensitive to calcium concentration and is inhibited in intact cells and cell-free preparations by various phenothiazine drugs. Addition of calmodulin to preparations of NADPH oxidase stimulates enzymatic rates from 1.4-2.5-fold. Addition of calmodulin and calcium, but not calcium alone, to NADPH oxidase preparations which have been inactivated by EDTA results in the restoration of activity. No activation is observed when membrane preparations containing latent NADPH oxidase are exposed to calcium and calmodulin. These studies suggest a role for calmodulin in the control of NADPH oxidase but that calmodulin alone is not sufficient for activation.

Demonstration of a Putative Adenosine Receptor in Rabbit Aorta

This study demonstrates the existence of adenosine receptor(s) in a homogeneous population of cultured smooth muscle cells and intact muscle strips from rabbit aorta. Binding assays with ³H-adenosine were performed using the crude microsomal fraction of the cultured cells. Adenosine binding was reversible and displayed a single species of saturable binding sites. The nuclear and soluble fractions showed negligible binding. Adenosine uptake blockers (e.g., nitrobenzylthioinosine, dipyridamole) had no effect on its binding. Theophylline inhibited the binding and the relaxation of aortic strips to adenosine. The data suggest the existence of specific binding sites for adenosine on the surface of aortic smooth muscle cells.

Effect of adenosine on the relaxation of coronary arteries at varying pH values

The efficiency of adenosine to relax the bovine coronary arterial strips increased significantly by lowering the bath pH from 7.4 to 6.8 (CO2 or HCO-3). The large vessels (3-4 mm O.D.) relaxed with greater significance at higher concentrations of adenosine, whereas small vessels (0.5-0.7 mm O.D.) relaxed better at low concentrations of adenosine. Theophylline and 8-phenyltheophylline competitively inhibited the effect of adenosine. 8-phenyltheophylline was found to be a better antagonist than theophylline. Furthermore, binding assays with 2-3H adenosine displayed a single species of binding sites. The Kd was 3 X 10(-6) M and 4 X 10(-6) M, while Bmax was 48 and 19 pmoles/mg protein for small and large vessels, respectively. The antagonistic effect of theophylline and 8-phenyltheophylline was not affected by pH variations. It is concluded that relaxation of coronary arteries by adenosine is affected by pH variations.