A Quantitative Method to Measure Low Levels of ROS in Nonphagocytic Cells by Using a Chemiluminescent Imaging System

Chemiluminescence (CL) is one of the most useful methods for detecting reactive oxygen species (ROS). Although fluorescence dyes or genetically encoded biosensors have been developed, CL is still used due to its high sensitivity, ease of use, and low cost. While initially established and used to measure high levels of ROS in phagocytic cells, CL assays are not ideal for measuring low levels of ROS. Here, we developed a newly modified CL assay using a chemiluminescent imaging system for measuring low concentrations of ROS in nonphagocytic cells. We found that dissolving luminol in NaOH, rather than DMSO, increased the H2O2-induced CL signal and that the addition of 4-iodophenylboronic acid (4IPBA) further increased CL intensity. Our new system also increased the rate and intensity of the CL signal in phorbol 12-myristate 13-acetate- (PMA-) treated HT-29 colon cancer cells compared to those in luminol only. We were able to quantify ROS levels from both cells and media in parallel using an H2O2 standard. A significant benefit to our system is that we can easily measure stimulus-induced ROS formation in a real-time manner and also investigate intracellular signaling pathways from a single sample simultaneously. We found that PMA induced tyrosine phosphorylation of protein tyrosine kinases (PTKs), such as focal adhesion kinase (FAK), protein tyrosine kinase 2 (Pyk2), and Src, and increased actin stress fiber formation in a ROS-dependent manner. Interestingly, treatment with either N-acetyl-L-cysteine (NAC) or diphenyleneiodonium (DPI) reduced the PMA-stimulated phosphorylation of these PTKs, implicating a potential role in cellular ROS signaling. Thus, our newly optimized CL assay using 4IPBA and a chemiluminescent imaging method provides a simple, real-time, and low-cost method for the quantification of low levels of ROS.

Regioselective IBX-Mediated Synthesis of Coumarin Derivatives with Antioxidant and Anti-influenza Activities

Different catechol and pyrogallol derivatives have been synthesized by oxidation of coumarins with 2-iodoxybenzoic acid (IBX) in DMSO at 25 °C. A high regioselectivity was observed in accordance with the stability order of the incipient carbocation or radical benzylic-like intermediate. The oxidation was also effective in water under heterogeneous conditions by using IBX supported on polystyrene. The new derivatives showed improved antioxidant effects in the DPPH test and inhibitory activity against the influenza A/PR8/H1N1 virus. These data represent a new entry for highly oxidized coumarins showing an antiviral activity possibly based on the control of the intracellular redox value.

Different sensitivities of photosystem II in green algae and cyanobacteria to phenylurea and phenol-type herbicides: effect on electron donor side

The effects of short-term treatment with phenylurea (DCMU, isoproturon) and phenol-type (ioxynil) herbicides on the green alga Chlorella kessleri and the cyanobacterium Synechocystis salina with different organizations of photosystem II (PSII) were investigated using pulse amplitude modulated (PAM) chlorophyll fluorescence and photosynthetic oxygen evolution measured by polarographic oxygen electrodes (Clark-type and Joliot-type). The photosynthetic oxygen evolution showed stronger inhibition than the PSII photochemistry. The effects of the studied herbicides on both algal and cyanobacterial cells decreased in the following order: DCMU>isoproturon>ioxynil. Furthermore, we observed that the number of blocked PSII centers increased significantly after DCMU treatment (204–250 times) and slightly after ioxynil treatment (19–35 times) in comparison with the control cells. This study suggests that the herbicides affect not only the acceptor side but also the donor side of PSII by modifications of the Mn cluster of the oxygen-evolving complex. We propose that one of the reasons for the different PSII inhibitions caused by herbicides is their influence, in different extents, on the kinetic parameters of the oxygen-evolving reactions (the initial S0−S1 state distribution, the number of blocked centers SB, the turnover time of Si states, misses and double hits). The relationship between the herbicide-induced inhibition and the changes in the kinetic parameters is discussed.

Pharmacology and Toxicology of N-Benzylphenethylamine ("NBOMe") Hallucinogens

Serotonergic hallucinogens induce profound changes in perception and cognition. The characteristic effects of hallucinogens are mediated by 5-HT2A receptor activation. One class of hallucinogens are 2,5-dimethoxy-substituted phenethylamines, such as the so-called 2C-X compounds 2,5-dimethoxy-4-bromophenethylamine (2C-B) and 2,5-dimethoxy-4-iodophenethylamine (2C-I). Addition of an N-benzyl group to phenethylamine hallucinogens produces a marked increase in 5-HT2A-binding affinity and hallucinogenic potency. N-benzylphenethylamines ("NBOMes") such as N-(2-methoxybenzyl)-2,5-dimethoxy-4-iodophenethylamine (25I-NBOMe) show subnanomolar affinity for the 5-HT2A receptor and are reportedly highly potent in humans. Several NBOMEs have been available from online vendors since 2010, resulting in numerous cases of toxicity and multiple fatalities. This chapter reviews the structure-activity relationships, behavioral pharmacology, metabolism, and toxicity of members of the NBOMe hallucinogen class. Based on a review of 51 cases of NBOMe toxicity reported in the literature, it appears that rhabdomyolysis is a relatively common complication of severe NBOMe toxicity, an effect that may be linked to NBOMe-induced seizures, hyperthermia, and vasoconstriction.

Amino Acid-Derived Metabolites from the Ascidian Aplidium sp

Four new iodobenzene-containing dipeptides (1-4), a related bromotryptophan-containing dipeptide (5), and an iodophenethylamine (6) were isolated from the ascidian Aplidium sp. collected off the coast of Chuja-do, Korea. The structures of these novel compounds, designated as apliamides A-E (1-5) and apliamine A (6) were determined via combined spectroscopic analyses. The absolute configuration of the amino acid residue in 1 was determined by advanced Marfey's analysis. Several of these compounds exhibited moderate cytotoxicity and significant inhibition against Na+/K+-ATPase (4).

A phase 1 study of 131I-CLR1404 in patients with relapsed or refractory advanced solid tumors: dosimetry, biodistribution, pharmacokinetics, and safety

Introduction

¹³¹I-CLR1404 is a small molecule that combines a tumor-targeting moiety with a therapeutic radioisotope. The primary aim of this phase 1 study was to determine the administered radioactivity expected to deliver 400 mSv to the bone marrow. The secondary aims were to determine the pharmacokinetic (PK) and safety profiles of ¹³¹I-CLR1404.

Methods

Eight subjects with refractory or relapsed advanced solid tumors were treated with a single injection of 370 MBq of ¹³¹I-CLR1404. Whole body planar nuclear medicine scans were performed at 15–35 minutes, 4–6, 18–24, 48, 72, 144 hours, and 14 days post injection. Optional single photon emission computed tomography imaging was performed on two patients 6 days post injection. Clinical laboratory parameters were evaluated in blood and urine. Plasma PK was evaluated on ¹²⁷I-CLR1404 mass measurements. To evaluate renal clearance of ¹³¹I-CLR1404, urine was collected for 14 days post injection. Absorbed dose estimates for target organs were determined using the RADAR method with OLINDA/EXM software.

Results

Single administrations of 370 MBq of ¹³¹I-CLR1404 were well tolerated by all subjects. No severe adverse events were reported and no adverse event was dose-limiting. Plasma ¹²⁷I-CLR1404 concentrations declined in a bi-exponential manner with a mean t_½ value of 822 hours. Mean Cmax and AUC(0-t) values were 72.2 ng/mL and 15753 ng•hr/mL, respectively. An administered activity of approximately 740 MBq is predicted to deliver 400 mSv to marrow.

Conclusions

Preliminary data suggest that ¹³¹I-CLR1404 is well tolerated and may have unique potential as an anti-cancer agent.

Trial Registration

ClinicalTrials.gov NCT00925275

The effect of papaverine on ion channels in rat basilar smooth muscle cells

OBJECTIVES

Papaverine has been used in treating vasospasm following subarachnoid hemorrhage (SAH). However, its action mechanism for cerebral vascular relaxation is not clear. Potassium and calcium channels are closely related to the contraction and relaxation of cerebral smooth muscle. Therefore, to identify the role of potassium and calcium channels in papaverine-induced vascular relaxation, we examined the effect of papaverine on potassium and calcium channels in freshly isolated smooth muscle cells from rat basilar artery.

METHOD

The isolation of rat basilar smooth muscle cells was performed by special techniques. The whole cell currents were recorded by whole cell patch clamp technique in freshly isolated smooth muscle cells from rat basilar artery. Papaverine was added to the bath solution.

RESULTS

Papaverine of 100 microM into bath solution increased the amplitude of the outward K(+) current which was completely blocked by BKCa blocker, IBX (iberiotoxin) and a calcium chelator, BAPTA (1,2-bis(o-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid) in whole cell mode. Papaverine (100 microM) also inhibited L type Ca(2+) current recorded in isolated smooth muscle cells from rat basilar artery.

DISCUSSION

These results strongly suggest that Ca(2+)-activated potassium channels and L type Ca(2+) channels may be involved in papaverine-induced vascular relaxation in rat basilar artery.

Unique cellular effect of the herbicide bromoxynil revealed by electrophysiological studies using characean cells

In a previous paper, we proposed that the primary action of the herbicide bromoxynil (BX; 3,5-dibromo-4-hydroxybenzonitrile) is cytosol acidification, based on the fact that bromoxynil induced the inhibition of cytoplasmic streaming and cell death of Chara corallina in acidic external medium (Morimoto and Shimmen in J Plant Res 121:227-233, 2008). In the present study, electrophysiological analysis of the BX effect was carried out in internodal cells of C. corallina. Upon addition of BX, a large and rapid pH-dependent depolarization was induced, supporting our hypothesis. Ioxynil, which belongs to the same group as bromoxynil, also induced a large and rapid membrane depolarization in a pH-dependent manner. On the other hand, four herbicides belonging to other groups of herbicides did not induce such a membrane depolarization. Thus, BX has a unique cellular effect. The decrease in the electro-chemical potential gradient for H(+) across the plasma membrane appears to result in inhibition of cell growth and disturbance of intracellular homeostasis in the presence of BX.

Stunned myocardium in transient left ventricular apical ballooning: a serial study of dual I-123 BMIPP and Tl-201 SPECT

BACKGROUND

This study was designed to assess the influence of coronary endothelial function and the serial changes of dual myocardial single photon emission computed tomography (SPECT) imaging in transient left ventricular (LV) apical ballooning.

METHODS AND RESULTS

We evaluated 35 consecutive patients (8 men and 27 women; mean age, 71 +/- 13 years) with transient LV apical ballooning. All patients underwent coronary angiography with acetylcholine provocation 1 month after onset. Iodine 123 beta-methyl-p-iodophenyl-pentadecanoic acid (BMIPP) and thallium 201 dual myocardial SPECT was serially performed on day 1 of admission and 1 month and 6 months later. In 8 of 35 patients (23%), epicardial coronary spasm was induced by acetylcholine infusion. At the peak acetylcholine dose (100 microg), diffuse coronary vasoconstriction developed in 19 of 35 patients (54%). Of 19 patients, 13 had diffuse coronary vasoconstriction with chest pain and ST-segment depression. The total defect score of I-123 BMIPP and Tl-201 SPECT showed marked perfusion-fatty acid metabolic mismatches (13.7 +/- 3.6 vs 8.7 +/- 2.3, P < .001) at the LV apex during the acute phase but few mismatched areas (2.1 +/- 1.1 vs 1.5 +/- 1.4, P = not significant) at 6 months.

CONCLUSIONS

Transient LV apical ballooning might be caused by stress-induced coronary epicardial spasm or endothelial dysfunction, resulting in myocardial stunning.

Neuregulin-1 isoform induces mitogenesis, KCa and Ca2+ currents in PC12 cells. A comparison with sciatic nerve conditioned medium

Neuregulin-1 (NRG-1) is an active component found in sciatic nerve conditioned medium (CM). NRG-1 is a growth and differentiation factor shown to have an effect on neuritogenesis and survival of neural cells. PC12 cells chronically treated with NRG-1 (beta1 isoform) show an increase in proliferation under low-serum condition (2.5% fetal bovine serum and 1.25% horse serum) and serum deprivation, without visible morphological changes. NRG-1 and CM treatments of PC12 cells induced an increase of voltage-activated Ca2+ currents and large-conductance calcium-activated K+ currents (KCa). AG825, a specific inhibitor for erbB2 receptor, abolishes KCa current, though Ca2+ currents were not inhibited. These results showed that NRG-1 is capable of inducing functional changes but is not sufficient on its own to have an effect on cell morphology.

The allosteric enhancer PD81,723 increases chimaeric A1/A2A adenosine receptor coupling with Gs

PD81,723 {(2-amino-4,5-dimethyl-3-thienyl)-[3-(trifluromethyl)-phenyl]methanone} is a selective allosteric enhancer of the G(i)-coupled A1 AR (adenosine receptor) that is without effect on G(s)-coupled A2A ARs. PD81,723 elicits a decrease in the dissociation kinetics of A1 AR agonist radioligands and an increase in functional agonist potency. In the present study, we sought to determine whether enhancer sensitivity is dependent on coupling domains or G-protein specificity of the A1 AR. Using six chimaeric A1/A2A ARs, we show that the allosteric effect of PD81,723 is maintained in a chimaera in which the predominant G-protein-coupling domain of the A1 receptor, the 3ICL (third intracellular loop), is replaced with A2A sequence. These chimaeric receptors are dually coupled with G(s) and G(i), and PD81,723 increases the potency of N6-cyclopentyladenosine to augment cAMP accumulation with or without pretreatment of cells with pertussis toxin. Thus PD81,723 has similar functional effects on chimaeric receptors with A1 transmembrane sequences that couple with G(i) or G(s). This is the first demonstration that an allosteric regulator can function in the context of a switch in G-protein-coupling specificity. There is no enhancement by PD81,723 of G(i)-coupled A2A chimaeric receptors with A1 sequence replacing A2A sequence in the 3ICL. The results suggest that the recognition site for PD81,723 is on the A1 receptor and that the enhancer acts to directly stabilize the receptor to a conformational state capable of coupling with G(i) or G(s).

Herbicide binding and thermal stability of photosystem II isolated from Thermosynechococcus elongatus

Binding of herbicides to photosystem II inhibits the electron transfer from Q(A) to Q(B) due to competition of herbicides with plastoquinone bound at the Q(B) site. We investigated herbicide binding to monomeric and dimeric photosystem II core complexes (PSIIcc) isolated from Thermosynechococcus elongatus by a combination of different methods (isothermal titration and differential scanning calorimetry, CD spectroscopy and measurements of the oxygen evolution) yielding binding constants, enthalpies and stoichiometries for various herbicides as well as information regarding stabilization/destabilization of the complex. Herbicide binding to detergent-solubilized PSIIcc can be described by a model of single independent binding sites present on this important membrane protein. Interestingly, binding stoichiometries herbicide:PSIIcc are lower than 1:1 and vary depending on the herbicide under study. Strong binding herbicides such as terbutryn stabilize PSIIcc in thermal unfolding experiments and endothermically binding herbicides like ioxynil probably cause large structural changes accompanied with the binding process as shown by differential scanning calorimetry experiments of the unfolding reaction of PSIIcc monomer in the presence of ioxynil. In addition we studied the occupancy of the Q(B) sites with plastoquinone (PQ9) by measuring flash induced fluorescence relaxation yielding a possible explanation for the deviations of herbicide binding from a 1:1 herbicide/binding site model.

Inhibitory and excitatory effects of iodobenzene on the antennal benzoic acid receptor cells of the female silk moth Bombyx mori L

As shown in single-sensillum recordings, iodobenzene has a bimodal effect on the receptor cell tuned to benzoic acid (BA) of the female silk moth Bombyx mori. Exposure to iodobenzene causes an inhibition of the response to BA. With stimulation by iodobenzene alone, a reduction of basic nerve impulse firing during exposure is followed by a transient post-stimulus excitation (rebound). We suggest that inhibition suppresses excitation during exposure but fades afterwards more rapidly than excitation. Due to the spatial equivalence of the iodine and the acid residue, these effects might indicate opposing interactions of iodobenzene with the specific site for the key compound BA. This is supported by the fact that substitutions by smaller halogens are less effective in both inhibition and rebound. The inhibitory effect but not the rebound with iodobenzene alone was also observed in receptor cells tuned to key compounds other than benzoic acid, e.g. in the cell most sensitive to 2,6-dimethyl-5-heptene-2-ol (DMH-cell) occurring in the same sensillum as the BA-cell, or in the bombykol- and bombykal-cells of the male. At least in these cells the inhibitory effect might reflect the action of iodobenzene on a general site, e.g. the lipid matrix of the plasma membrane of the receptor cells.

The modulation of action potential generation by calcium-induced calcium release is enhanced by mitochondrial inhibitors in mudpuppy parasympathetic neurons

Previously, we demonstrated that outward currents activated by calcium-induced calcium release (CICR) opposed depolarization-induced action potential (AP) generation in dissociated mudpuppy parasympathetic neurons [J Neurophysiol 88 (2002) 1119]. In the present study, we tested whether AP generation by depolarizing current ramps could be altered by dissipating the mitochondrial membrane potential and thus interrupting mitochondrial Ca2+ buffering. Exposure to the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP; 2 microM) alone or in combination with the mitochondrial ATP synthase inhibitor oligomycin (8 microg/ml), increased the latency to AP generation. Exposure to the electron transport chain inhibitor rotenone (10 microM) alone or in combination with oligomycin (8 microg/ml) similarly increased the latency to AP generation. CCCP and oligomycin or rotenone and oligomycin treatment caused rhodamine 123 loss from mitochondria within a few minutes, confirming that the mitochondrial membrane potential was dissipated during drug exposure. Oligomycin alone had no effect on the latency to AP generation and did not cause loss of rhodamine 123 from mitochondria. The increase in latency induced by CCCP and oligomycin was similar when recordings were made with either the perforated patch or standard whole cell patch recording configuration. Exposure to the endoplasmic reticulum Ca-ATPase inhibitor thapsigargin (1 microM), decreased the latency to AP generation. In cells pretreated with thapsigargin to eliminate CICR, CCCP and oligomycin had no effect on AP latency. Pretreatment with iberiotoxin (IBX; 100 nM), an inhibitor of large conductance, calcium- and voltage-activated potassium channels, reduced the extent of the CCCP- and oligomycin-induced increase in latency to AP generation. These results indicate that treatment with CCCP or rotenone to dissipate the mitochondrial membrane potential, a condition which should minimize sequestration of Ca2+ by mitochondria, facilitated the Ca(2+)-induced Ca2+ release activation of IBX-sensitive and IBX-insensitive conductances that regulate AP generation.

INCORPORATION OF AN OXYGEN FROM WATER INTO TROGLITAZONE QUINONE BY CYTOCHROME P450 AND MYELOPEROXIDASE

Troglitazone (TGZ) was the first glitazone used for the treatment of type II diabetes mellitus. TGZ undergoes an oxidative chroman ring-opening reaction to form a quinone product. Recently, cytochrome P450 (P450) was shown to be able to catalyze the formation of TGZ quinone. TGZ quinone was the major metabolite formed by dexamethasone-induced rat liver microsomes or myeloperoxidase (MPO) incubated with TGZ. The ultimate source for the quinone carbonyl oxygen atom of TGZ quinone was investigated using (18)O water in both enzyme reaction systems followed by liquid chromatography/tandem mass spectometry analysis of the TGZ quinone product. The resultant TGZ quinone formed by either liver microsomes or MPO contained a single atom of (18)O. The (18)O atom was determined to be the quinone carbonyl oxygen by collision-induced dissociation fragmentation of the (18)O-labeled TGZ quinone. The formation of TGZ quinone was inhibited approximately 90% by coincubation with ascorbic acid or cysteine in the MPO reaction system but only 10 to 20% in liver microsomes, which might reflect the difference in the mechanism by which TGZ quinone is formed by P450 and peroxidase. These results suggest that P450 catalyze an atypical reaction to form TGZ quinone, involving the incorporation of an oxygen from water into the quinone carbonyl position.

The effect of endocrine disrupting chemicals on thyroid hormone binding to Japanese quail transthyretin and thyroid hormone receptor

We investigated the effect of endocrine disrupting chemicals (EDCs), including medical, industrial, and agricultural chemicals, on 3,3',5-L-[125I]triiodothyronine ([125I]T3) binding to purified Japanese quail transthyretin (qTTR), a major thyroid hormone-binding protein in plasma, and to the ligand-binding domain of thyroid hormone receptor beta (qTR LBD). Scatchard plots of T3 binding to qTTR and qTR LBD revealed two classes of binding sites, with Kd values of 6.9 and 185 nM, and a single class of binding sites, with Kd value of 0.31 nM, respectively. Among the test chemicals, diethylstilbestrol was the most powerful inhibitor of [125I]T3 binding to qTTR (IC50 < 0.4 nM). Diethylstilbestrol, ioxynil (IC50 =1.1+/-0.5 nM) and pentachlorophenol (IC50 = 6.3+/-3.8 nM) displaced [125I]T3 from qTTR more effectively than unlabeled T3 (IC50 = 9.7+/-0.9 nM) did. Although malathion, 4-nonylphenol, bisphenol A and n-butylbenzyl phthalate were effective inhibitors of [125I]T3 binding to qTTR, their potency was two orders of magnitude less than that of T3. All test chemicals except for diethylstilbestrol had either a weak or no effect on [125I]T3 binding to qTR LBD. These results show that several EDCs tested in this study target qTTR rather than qTR LBD.

Mitochondrials complex I activity is reduced in latent adriamycin-induced cardiomyopathy of rat

We previously reported on the use of enzymatic analysis to impair fatty acid metabolism followed by reduced myocardial energy content, leading to severe heart failure in adriamycin (ADR)-treated rats. The aim of this study is to investigate whether impaired myocardial energy metabolism can also be detected by other methods; i.e. measuring mitochondrial complex I activity and myocardial 125I-15-(p-iodophenyl)-3-(R,S)- methylpentadecanoic acid (BMIPP) accumulation in ADR-treated rats. Eight-week-old male Sprague-Dawley rats received 6 intraperitoneal injections of ADR (total 15 mg/kg: group ADR) or saline (control group) over 2 weeks. Left ventricular (LV) ejection fraction was assessed using echocardiography at 3- and 6-weeks after ADR injection (3 weeks and 6 weeks, respectively). Myocardial fatty acid utilization was assessed at 3 weeks and 6 weeks. The myocardial counts of BMIPP were measured after intravenous BMIPP (370 kBq) injection, and 125I counts were measured to calculate the uptake ratio. The enzymatic activity of complex I was assessed by monitoring the oxidation of nicotinamide-adenine-dinucleotide-disodium-salt (NADH). In rats treated with ADR, significant decrease in LV ejection fraction was observed only at 6 weeks compared to control (72.5 vs. 84.5%, p < 0.01). LV ejection fraction at 3 weeks was identical between group ADR and control (81.8 vs. 84.4%). However, at 3 weeks, complex I activity was already reduced significantly in group ADR as compared to control group (p = 0.03), but the reduction in BMIPP accumulation was not (p = 0.15). Our data indicated that reduced complex I activity in a phenomenon occurred in early phase of ADR-induced cardiomyopathy, and it might play an important role in the progression of ADR-induced heart failure.

Design and synthesis of 2,6-diprenyl-4-iodophenol TX-1952 with a novel and potent anti-peroxidative activity

The structure-based elucidation of 2,4,6-tri-substituted phenols for their antioxidative and anti-peroxidative effects has been investigated using TX-1952 (2,6-diprenyl-4-iodophenol), TX-1961, TX-1980, BTBP and BHT. In the inhibition of mitochondrial lipid peroxidation, the inhibitory activity of 2,6-di-tert-butyl-4-bromophenol (BTBP) (IC(50)=0.17 microM) was twice as high as that of 2,6-di-tert-butyl-4-methylphenol (BHT) (IC(50)=0.31 microM). This result shows that the 4-halogen group increases inhibitory activity for mitochondrial lipid peroxidation. Besides, TX-1952 (IC(50)=0.60 microM) was the highest inhibitor among 2,6-diprenyl-4-halophenols, followed by TX-1961 (IC(50)=0.93 microM) and TX-1980 (IC(50)=1.2 microM). In 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging experiments, the activity of TX-1952 (IC(0.200)=53.1 microM) was lower than that of BHT (IC(0.200)=33.7 microM) and BTBP (IC(0.200)=16.0 microM), but TX-1952 and BHT showed the same HOMO energy (-8.991 eV). These results suggest that the two prenyl groups at ortho position hinder the phenolic hydrogen abstraction by DPPH radical. These findings demonstrated that TX-1952 was a novel and potent inhibitor for lipid peroxidation.

[Chemiluminescence of daphnia cultivating medium and optimization of conditions for its determination]

The article deals with the optimization of conditions for the chemiluminescence determination. The Daphnia habitat was shown to have no spontaneous chemiluminescence. This was revealed using hydrogen peroxide and luminol, the optimal concentrations of which were 23 and 1.6 x 10(-2) mmol/L. p-Iodphenol at low concentrations (4 x 10(-5)-2 x 10(-3) mmol/L) did not render its effect chemiluminescence signal while at high concentrations (4 x 10(-2) mmol/L) an inhibition of chemiluminescence was observed. To obtain the needed intensity of chemiluminescence no more than 5 daphnia persons is required to incubate in volume of 10 mL of sample for analyzing. The intensity of chemiluminescence of daphnia cultivating medium and the sensitivity of this organism to potassium chromate increased at the temperature increasing from 24 to 32 degrees C. Daphnia cultivating medium can be preserved in refrigerator for several hours without lost of chemiluminescence signal.

Spectral studies of tert-butyl isothiocyanate-inactivated P450 2E1

Inactivation of cytochrome P450 2E1 by tert-butyl isothiocyanate (tBITC) resulted in a loss in the spectrally detectable P450-reduced CO complex. The heme prosthetic group does not appear to become modified, since little loss of the heme was observed in the absolute spectra or the pyridine hemochrome spectra, or in the amount of heme recovered from HPLC analysis of the tBITC-inactivated samples. Prolonged incubations of the inactivated P450 2E1 with dithionite and CO resulted in a recovery of both the CO complex and the enzymatic activity. Inactivated samples that were first reduced with dithionite for 1 h prior to CO exposure recovered their CO spectrum to the same extent as samples not pretreated with dithionite, suggesting that the major defect was an inability of the inactivated sample to bind CO. Spectral binding studies with 4-methylpyrazole indicated that the inactivated P450 2E1 had an impaired ability to bind the substrate. Enzymatic activity could not be restored with iodosobenzene as the alternate oxidant. EPR analysis indicated that approximately 24% of the tBITC-inactivated P450 2E1 was EPR-silent. Of the remaining tBITC-inactivated P450 2E1, approximately 45% exhibited an unusual low-spin EPR signal that was attributed to the displacement of a water molecule at the sixth position of the heme by a tBITC modification to the apoprotein. ESI-LC-MS analysis of the inactivated P450 2E1 showed an increase in the mass of the apoprotein of 115 Da. In combination, the data suggest that tBITC inactivated P450 2E1 by binding to a critical active site amino acid residue(s). This modified amino acid(s) presumably acts as the sixth ligand to the heme, thereby interfering with oxygen binding and substrate binding.

Cloning of a chick A3 adenosine receptor: characterization of ligand binding and receptor-effector coupling of chick A1 and A3 adenosine receptors

We have reported previously the cloning and partial characterization of a chick A1 adenosine receptor expressed in the heart. We report herein the cloning of a chick A3 adenosine receptor and a comprehensive characterization of both the A1 and A3 receptors expressed in human embryonic kidney 293 cells. [125I]N6-(p-aminobenzyl)adenosine bound to both receptors with similar affinities and was used in competition studies. Although the selectivities of both agonists and antagonists were less than in other species, two antagonists, 3-ethyl-5-benzyl-2-methyl-6-phenyl-4-phenylethynal-(+/-)-dihydropyridine-3,5-dicarboxylate and 3,6-dichloro-2'-(isopropyloxy)-4'-methylflavone), were at least partially selective for A3 receptors while one antagonist [C8-(N-methylisopropyl)amine-N6-(5'endohydroxy)endonorboman-2-yl-9-methyladenine] was selective for A1 receptors. While both receptors coupled to the inhibition of adenylyl cyclase, we were unable to detect coupling of either receptor to phospholipase C or D.

Effects of a novel vesamicol receptor ligand, m-(iodobenzyl)trozamicol, on the canine isolated, blood-perfused atrioventricular node preparation

m-(Iodobenzyl)trozamicol (MIBT) is a recently discovered vesamicol analogue. It has been shown that radiolabelled [125I]MIBT can be used as a marker of cholinergic innervation in the heart as well as in the brain. The purpose of this study was to analyze the direct effects of MIBT on the atrioventricular and intraventricular conduction in addition to the coronary blood flow using the canine isolated, blood-perfused atrioventricular node preparation. Intracoronary administration of MIBT suppressed the atrioventricular and intraventricular conduction, while it increased the coronary blood flow. The effect and duration of action on the intraventricular conduction was less pronounced compared with other effects. Moreover, the doses of MIBT needed to cause negative dromotropic and coronary vasodilator effects in this study was much greater than those needed for imaging the cardiac cholinergic innervation. Pretreatment of the preparations with a muscarinic receptor antagonist, atropine, did not block these effects of MIBT, suggesting that MIBT may possess muscarinic receptor-independent ion channel activity in the cardiac conduction system and coronary arteries.

Direct cardiac effects of a novel vesamicol receptor ligand, m-iodobenzyl-trozamicol, assessed in the canine isolated, blood-perfused heart preparations

MIBT, m-(iodobenzyl)trozamicol, is a recently discovered vesamicol analogue that can be used as a functional marker of cholinergic activity in the heart as well as the brain. The purpose of this study was to assess the effects of MIBT on sinus node automaticity, ventricular contraction, and coronary blood flow in addition to the action-potential duration of the ventricle by using canine isolated, blood-perfused sinoatrial node and papillary muscle preparations. Intracoronary administration of MIBT (1-300 microg) exerted negative chronotropic, inotropic, and coronary vasodilator effects in a dose-related manner. Pretreatment of the preparations with the muscarinic receptor antagonist atropine did not change these effects of MIBT. Moreover, MIBT had little effect on the repolarization phase of the ventricular action potential. Because the doses of MIBT needed for imaging cardiac cholinergic function were much lower than those affecting the cardiovascular system, MIBT may be used safely in future clinical applications.

Molecular pharmacology of methyl-3,5-diiodo-4 (4'methoxyphenoxy) benzoate (DIME) and its non-hydrolyzible ethanone analog (DIPE) (Review)

A molecular structural relationship of thyroid hormones to methyl-3,5-diiodo-4-(4'-methoxy-phenoxy) benzoate (DIME) and 1-[3,5-diiodo-4-(4'-methoxyphenoxy)-phenyl]-ethanone) (DIPE) and to apoptosis-mediated metamorphogenic mechanisms is postulated. DIME disrupts microtubule assembly already in anaphase, preparing cells for G2/M block, chromosome aggregation and caspase-3 mediated apoptosis. Cooperative action of DIME and vincristine, defining mutually exclusive cellular sites, identifies microtubules as primary drug targets followed by downstream cellular consequences, leading to cell death. Absence of in vivo toxicity of DIME appears to be related to impermeability to DIME of normal cells, but not of tumor cells in vivo. Normal tissue cells hydrolyze DIME but most tumor cells, except lung cancer cells, do not. DIPE, being resistant to enzymatic hydrolysis, is equally effective in all tumor cells.

Unusual potentiation by vinca alkaloids of the cytostatic and cytocidal action of methyl-3,5-diiodo-4-(4'-methoxyphenoxy) benzoate (DIME) and its nonhydrolyzable ethanone analog (DIPE) on MDA-MB-231 human mammary cancer cells

Drug interaction between DIME or DIPE ¿1-[3, 5-diiodo-4-(4'-methoxyphenoxy)-phenyl]-ethanone¿ with vincristine and vinblastine on the growth rate of MDA-MB-231 human mammary cancer cells was determined by the median effect kinetic method. Mutually exclusive cellular binding sites were identified kinetically and isobologram analyses showed potentiation. The combind effect of 0.75 MICROM DIME and 2 nM vincristine demonstrated a nearly type of mutual activation. It was shown that the nonhydrolyzable DIME derivative DIPE is equivalent to DIME, but because of its biological stability is a preferred drug candidate. Vinblastine-DIME cooperative action is similar to that of vincristine-DIME (or DIPE). Activation of caspase 3 by both DIME and vincristine is greatly potentiated when both drugs are added simultaneously in a given proportion. We propose that following a primary binding of DIME and vinca alkaloids to microtubules, an as yet unrecognized mutual activation of caspase 3 apoptotic path is initiated, explaining DNA fragmentation and cell death. A subpopulation of cancer cells, capable of slow growth at 1.5 microM DIME was identified. This cell type was also killed by the DIME-vincristine drug combination.

Inhibitory effects of meta-iodo-benzylguanidine (MIBG) on endothelial histamine receptor binding

Meta-iodo-benzylguanidine (MIBG), a selective inhibitor of mono-ADP-ribosylation, has been shown to inhibit histamine induced inositol-trisphosphate and prostacyclin production. The purpose of this study was to evaluate the effect of MIBG on the binding of histamine to the H1-receptor and to study its effects on phospholipid metabolism in human endothelial cells. The effects of MIBG and MIBA (meta-iodo-benzylamine), which does not affect cellular ADP-ribosylation, on agonist induced cGMP production in cultured HUVEC's were measured by RIA and a binding study carried out to evaluate their effects on the binding of [3H]mepyramine to membrane fractions. MIBG (0.3 mM) reduced histamine induced cGMP production by 90.8% but did not inhibit the cGMP production induced by other agonists. MIBA had no effect. MIBG also reduced the binding of [3H]mepyramine (1.0 nM) to membrane fractions with IC50 at 0.094 mM and maximal inhibition (83%) at 0.22mM MIBG. The calculated Ki was 0.076mM. MIBG and MIBA altered phospholipid metabolism in a similar way as the cationic amphiphilic drug propranolol. MIBA caused up to 42% reduction in [3H]mepyramine binding, probably due to its inhibition of nonspecific binding. These results indicate that MIBG reduces histamine induced cGMP production by inhibiting its binding to H1-receptors and alters phospholipid metabolism in cultured endothelial cells in a similar way as known cationic amphiphilic drugs.

Inosine binds to A3 adenosine receptors and stimulates mast cell degranulation

We investigated the mechanism by which inosine, a metabolite of adenosine that accumulates to > 1 mM levels in ischemic tissues, triggers mast cell degranulation. Inosine was found to do the following: (a) compete for [125I]N6-aminobenzyladenosine binding to recombinant rat A3 adenosine receptors (A3AR) with an IC50 of 25+/-6 microM; (b) not bind to A1 or A2A ARs; (c) bind to newly identified A3ARs in guinea pig lung (IC50 = 15+/-4 microM); (d) lower cyclic AMP in HEK-293 cells expressing rat A3ARs (ED50 = 12+/-5 microM); (e) stimulate RBL-2H3 rat mast-like cell degranulation (ED50 = 2.3+/-0.9 microM); and (f) cause mast cell-dependent constriction of hamster cheek pouch arterioles that is attenuated by A3AR blockade. Inosine differs from adenosine in not activating A2AARs that dilate vascular smooth muscle and inhibit mast cell degranulation. The A3 selectivity of inosine may explain why it elicits a monophasic arteriolar constrictor response distinct from the multiphasic dilator/constrictor response to adenosine. Nucleoside accumulation and an increase in the ratio of inosine to adenosine may provide a physiologic stimulus for mast cell degranulation in ischemic or inflamed tissues.

Reduced turnover of the D1 polypeptide and photoactivation of electron transfer in novel herbicide resistant mutants of Synechocystis sp. PCC 6803

Two missense mutants, A263P and S264P, and a deletion mutant des-Ala263, Ser264, have been constructed in the D1 protein of the cyanobacterium Synechocystis sp PCC 6803. All were expected to induce a significant conformational change in the QB-binding region of photosystem II (PSII). Although the des-Ala263, Ser264-D1 mutant accumulated some D1 protein in the thylakoid membrane it was unable to grow photoautotrophically or evolve oxygen. Thermoluminescence and chlorophyll fluorescence studies confirmed that this deletion mutant did not show any functional PSII activity. In contrast, [S264P]D1 was able to grow photoautotrophically and give light-saturated rates of oxygen evolution at 60% of the rate of the wild-type control strain, TC31. The A263P missense mutant was also able to evolve oxygen at 50% of TC31 rates although it did not readily grow photoautotrophically. Thermoluminescence, flash oxygen yield and chlorophyll fluorescence measurements indicated that in both missense mutants electron transfer from QA to QB was significantly impaired in dark adapted cells. However, QA to QB electron transfer could be photoactivated in the mutants by background illumination. Both the A263P and S264P mutants also showed an increase in resistance to the s-triazine family of herbicides although this feature did not hold for the phenolic herbicide, ioxynil. Of particular interest was that the two missense mutants, especially S264P, possessed a slower rate of turnover of the D1 protein compared with TC31 and in vivo contained detectable levels of a 41-kDa adduct consisting of D1 and the alpha subunit of cytochrome b559. When protein synthesis was blocked by the addition of lincomycin, D1 degradation was again slower in S264P than TC31. The results are discussed in terms of structural changes in the QB-binding region which affect herbicide and plastoquinone binding and perturb the normal regulatory factors that control the degradation of the D1 protein and its synchronisation with the synthesis of a replacement D1 protein.

MIBG causes oxidative stress and up-regulation of anti-oxidant enzymes in the human neuroblastoma cell line SK-N-BE(2c)

We report the effects of meta-iodobenzylguanidine (MIBG), a neuroblastoma-seeking agent, on cell proliferation and several oxidative stress-related parameters in the human neuroblastoma cell line SK-N-BE(2c). MIBG inhibited the proliferation of this cell line in micromolar concentrations. Measurements of the malondialdehyde (MDA) concentrations (a measure of the extent of lipid peroxidation) of cells treated with MIBG showed that increasing concentrations of MIBG led to an increase in MDA levels of the cells. This effect was most pronounced after one day of cellular exposure to MIBG and disappeared after 3 days. Disappearance of the elevated MDA levels caused by MIBG is probably the result of increased activity of the H2O2 detoxifying enzymes, catalase and glutathion peroxidase (GPx). The catalase- and GPx-enzyme activity of cells exposed to MIBG steadily increased with time, reaching a maximum after 4 days. Oxidative stress caused by MIBG thus at first leads to cellular damage (lipid peroxidation) but over a longer period does not lead to decreased proliferation rate of the cells, most likely because of cellular adaptation to increased oxidative stress by up-regulation of the H2O2 detoxifying enzymes catalase and GPx.

Inhibition of neutral endopeptidase, the degradative enzyme for natriuretic peptides, in rat kidney after oral SCH 42495

1. Inhibition of neutral endopeptidase (NEP), the degradative enzyme for atrial natriuretic peptide, was studied in vitro and in vivo using a previously characterized NEP inhibitor radioligand, 125I-labelled RB104. 2. SCH 42354, the active di-acid of the ethylester prodrug, SCH 42495, caused a concentration-dependent displacement of 125I-labelled RB104 from rat renal NEP. The concentration of SCH 42354 that displaced 50% of radioligand bound to the enzyme NEP (IC50) was 3.3 +/- 0.1 nmol/l (mean +/- SEM). Enalaprilat, an angiotensin converting enzyme inhibitor, did not displace 125I-labelled RB104 in concentrations up to 10 mumol/l. 3. In adult normotensive Sprague-Dawley rats, oral SCH 42495 (3-300 mg/kg) caused significant inhibition of renal NEP (P < 0.001). SCH 42495 had no effect on renal or plasma angiotensin converting enzyme activity, but high-dose SCH 42495 (300 mg/kg) caused a significant increase in plasma renin activity (P < 0.01). 4. In a time course study, oral SCH 42495 (30 mg/kg) caused rapid (within 30 min) and significant inhibition of renal NEP for up to 48 h (P < 0.001). No changes in plasma atrial natriuretic peptide or plasma angiotensin converting enzyme activity were seen. 5. These data provide evidence that short-term administration of the NEP inhibitor SCH 42495 results in inhibition of renal NEP and does not inhibit the circulating or the tissue renin-angiotensin system. The NEP inhibitor radioligand 125I-labelled RB104, is a useful tool to study tissue NEP inhibition after administration of NEP inhibitors.

Tumor-specific synergistic therapy of mitomycin C: modulation of bioreductive activation

The bioreductive activation of mitomycin C (MMC) has been investigated using 10 human cancer cell lines. Except for 2 lines (COLO201 and COLO320DM), the cellular NAD(P)H: quinone oxidoreductase (DTD) activities correlated well with MMC-induced DNA damage and cytotoxicity. In addition, when the DTD activity was inhibited with 50 mM dicoumarol, the MMC activity decreased significantly. On the other hand, no correlation between the NADPH cytochrome P450 reductase (P450) activity and MMC efficacy was observed. We postulate that two electron reduction by DTD may be more important in MMC activation than one electron reduction by P450. The DTD-mediated metabolism was pH-dependent. In a nude mouse experimental model, the pH in the tumor decreased under hyperglycemic conditions due to unique glycolysis. The administration of m-iodobenzyl-guanidine (MIBG) enhanced the decrease in the pH of the tumor without affecting the pH of normal tissue (liver). It also significantly increased the antitumor activity of MMC. However, this biochemical modulation had no effect in the COLO201 and COLO320DM cells. Other mechanisms may be involved in the regulation of MMC activity in these cells. In conclusion, DTD may be an important target of MMC. Biochemical modulation using MIBG and glucose may selectively enhance the activity of MMC within cancer cells.

Adenosine A3 receptor expression and function in eosinophils

The A3 adenosine receptor is widely expressed in human tissues with the most abundant expression in the lung and liver, but the predominant cellular localization and functions of this receptor in humans are unknown. Since adenosine influences the activation of circulating and resident inflammatory cells within the lung and leads to exaggerated airway narrowing in individuals with inflammatory airway disorders, we hypothesized that A3 receptor gene expression is localized to inflammatory cells and that gene expression is upregulated in airway inflammation. Lung and airway tissue were obtained at thoracotomy from nonsmoking subjects and subjects with inflammatory airway disorders associated with tobacco smoke or asthma. In situ hybridization identified A3 receptors in mesenchymal cells and eosinophils within the lamina propria of the airways and the adventitia of blood vessels, but not in mast cells. A3 receptor transcripts were highly expressed in peripheral blood eosinophils purified from atopic donors (6.36 +/- 0.60 pg/microg total RNA) in comparison with neutrophils (0.26 +/- 0.06 pg/microg) or mononuclear cells (0.9 +/- 0.15 pg/microg). Mean A3 receptor transcript abundance was greater in lung tissue from subjects with airway inflammation (0.33 +/- 0.04 pg/microg total RNA) than in normal lung (0.24 +/- 0.03 pg/microg total RNA, P = 0.035). The A3 receptor agonist N6-(4-amino-3-iodobenzyl)adenosine dose-dependently inhibited platelet activating factor-induced eosinophil chemotaxis to a maximum of 41%. This inhibitory effect was completely abolished by addition of the A3 receptor selective antagonist 3-(3-iodo-4-aminobenzyl)-8-(4-oxyacetate)phenyl-1-propylxanthine. We conclude that A3 receptors are primarily expressed on eosinophils in human lung, where they mediate inhibition of eosinophil chemotaxis. Specific A3 receptor ligands may be useful agents in the treatment of eosinophil-dependent diseases such as asthma and rhinitis.

The effect of the neuroblastoma-seeking agent meta-iodobenzylguanidine (MIBG) on NADH-driven superoxide formation and NADH-driven lipid peroxidation in beef heart submitochondrial particles

In this paper we report the effects of the neuroblastoma-seeking agent meta-iodobenzylguanidine (MIBG) on NADH-driven superoxide formation and NADH-driven lipid peroxidation in beef heart submitochondrial particles. MIBG is a structural analogue of noradrenaline and is capable of inhibiting complex I and complex III of the respiratory chain. The results of our studies show that MIBG enhanced both NADH-driven superoxide formation and NADH-driven lipid peroxidation at concentrations that are likely to exist inside mitochondria of the target cells of neuroblastoma patients treated with [131I]MIBG. The effect of MIBG is comparable to that of rotenone (an inhibitor of complex I) rather than that of antimycin (an inhibitor of complex III). These results suggest that the formation of superoxide and lipid peroxidation contributes to the cytotoxicity of [131I]MIBG.

Chemical characterization and comparative cellular effects of meta-iodobenzyl guanidine and benzyl guanidine

meta-Iodobenzyl guanidine (MIBG) combines the structural properties of the neuron-blocking agents bretylium and guanethidine and is being used increasingly for various clinical applications. Different samples of MIBG were assayed for possible contamination with benzyl guanidine (BG). Fast-atom-bombardment mass spectrometry (FAB-MS) analysis showed a prominent but variable m/z 150 signal, corresponding to a protonated BG. The MS/MS fragmentation pattern of these [M + H]+ ions was similar to that obtained from FAB-MS-generated, protonated BG, confirming the proposed molecule and associated structures. RP-HPLC analysis of both guanidines, however, excluded the possibility of contamination of MIBG with BG. It was therefore concluded that the BG signal was an artifact of the FAB-MS procedure. In addition, the importance of the meta-substituted iodine for the biological activity of MIBG was investigated. Three different biochemical and cell-biological properties of MIBG were compared with those of its precursor MIBA and BG. The assays used were: inhibition of the catecholamine "Uptake I" system in SK-N-SH neuroblastoma and PC-12 pheochromocytoma cells, inhibition of mitochondrial respiration, and general cytotoxicity in L1210 leukemia cells. Of the drugs tested, MIBG was the most efficient in Uptake I inhibition and was more toxic in survival assays, but as compared with BG it was almost equipotent in inhibiting mitochondrial respiration. These findings contribute to a further elucidation of the mechanism by which MIBG exerts its various actions.

Molecular characterisation of a fungal mono(ADP-ribosyl)transferase

A soluble arginine-specific mono(ADP-ribosyl)transferase was detected in dormant spores of Phycomyces blakesleeanus. Soluble proteins incubated with [32P]NAD revealed, after a two dimensional electrophoretic separation, three major ADP-ribosylated substrates with molecular weights of 38, 37, and 36 kDa and pI values of 6.9, 8.1 and 4.6, respectively. The addition of MgCl2 stimulated the (ADP-ribosyl)transferase activity. This enzymatic activity was stimulated by 250 microM NO-releasing agent sodium nitroprusside and inhibited with 8 mM benzamide, 0.4 mM meta-IodoBenzylGuanidine (MIBG), and 0.5 mM novobiocin. The three ADP-ribosylation inhibitors affected the germination of Phycomyces spores. The concentrations necessary to inhibit 50% of the spore germination of Phycomyces were 0.05 mM, 0.2 mM, and 8 mM for novobiocin, MIBG, and benzamide, respectively. All the above inhibitors affected the germination process to the same extent, that is, they inhibited the tube protuberation, leaving the spores as swollen cells. These data suggest that ADP-ribosylation may be involved in the germination process of Phycomyces, particularly in germ-tube formation.

Specification of the inhibitory action of MIBG on the respiratory chain by EPR scanning

In this paper we report EPR studies on the effects of meta-Iodobenzylguanidine (MIBG), a structural analogue of norepinephrine capable of inhibiting complex I and III of the respiratory chain, on the reduction state of the various complexes of the respiratory chain in beef heart submitochondrial particles. The EPR spectrum of SMPs incubated with MIBG showed completely reduced prosthetic groups of complex I, but oxidised prosthetic groups of complex IV. This indicates that complex I is inhibited by MIBG at the end of the complex (i.e. at the Q binding site). Determination of the exact site of inhibition of MIBG on complex III yielded no conclusive results, but did confirm that complex III is indeed inhibited by MIBG.

Hyperbaric oxygen enhances the effects of meta-iodobenzylguanidine (MIBG) on energy metabolism and lipid peroxidation in the human neuroblastoma cell line SK-N-BE(2C)

In this paper we report the effects of the combination of MIBG (a structural analogue of norepinephrine, used in its radio iodinated form for the diagnosis and therapy of neuroblastoma) and hyperbaric oxygen on the human neuroblastoma cell line SK-N-BE(2c). Exposure of the neuroblastoma cells to hyperbaric oxygen conditions enhanced the effects of MIBG on cell proliferation, lipid peroxidation and energy metabolism of the cell line. Cell proliferation and energy metabolism were further decreased and lipid peroxidation further increased. Enhancement of the effects of MIBG by HBO may provide an explanation for the positive effects on the cumulative survival curve observed when stage IV neuroblastoma patients were treated with the combination of [131I] MIBG and HBO.

Target proteins for arginine-specific mono(ADP-ribosyl) transferase in membrane fractions from chick skeletal muscle cells

In a previous study, we found that a specific inhibitor of cellular arginine-specific mono(ADP-ribosyl) transferase, meta-iodobenzylguanidine (MIBG), reversibly inhibited both proliferation and differentiation of cultured embryonic chick primary muscle myoblasts. In addition, we observed that arginine-specific ADP-ribosyltransferase activity increased with muscle-cell differentiation in cultures. Therefore, muscle-cell cultures, especially the 96-h myotube cultures that contain the highest levels of ADP-ribosyltransferase, were used as a working system to determine the cellular protein substrates for arginine-specific ADP-ribosyltransferase. When membrane fractions extracted from 96-h chick myotubes were incubated with [32P]NAD at 30 degrees C for 30 min, only a few proteins were labeled. The labeling of two proteins of 36 and 56 kDa was inhibited by the presence of an arginine-specific mono(ADP-ribosyl) transferase inhibitor, MIBG, and by novobiocin. To prove that these proteins are indeed the targets for arginine-specific mono(ADP-ribosyl)ation, active recombinant muscle ADP-ribosyltransferase was incubated with membrane proteins under the same conditions. ADP-ribosylation of these two membrane proteins, as seen in the endogenous reactions, was also catalyzed by the added muscle transferase and was also inhibited by MIBG and novobiocin. By using antibody specific for desmin for immunoprecipitation and immunoblot analysis, we found that a 56-kDa protein associated with the membrane of myotubes is desmin. Our results showed that incorporation of isotope into this protein band from [32P]NAD is due to ADP-ribosylation of desmin.

Interaction of metaiodobenzylguanidine with cardioactive drugs: an in vitro study

Metaiodobenzylguanidine (MIBG), an analogue of noradrenaline, is used to explore the functional integrity of sympathetic nerve endings in the human heart. Various drugs inhibit noradrenaline transport systems and may block the uptake of MIBG. As in vivo studies of the effect of these drugs on myocardial [123I]MIBG uptake are often difficult to perform, we used an in vitro human blood platelet model for this purpose. A platelet preparation from healthy volunteers was incubated with [125I]MIBG alone or different concentrations of drugs currently used in cardiology. Labetalol and propranolol inhibited [125I]MIBG uptake, whereas all other drugs tested (other beta-blockers, calcium inhibitors, digoxin and amiodarone) had no effect even at doses exceeding 50 microM. The labetalol dose inhibiting 50% of [125I]MIBG uptake was lower than the plasma concentration of this drug in treated patients, whereas the propranolol dose was higher. This in vitro study of the effect of drugs on MIBG uptake by human blood platelets is predictive of their in vivo effect on myocardial uptake of [123I]MIBG in treated patients, provided that plasma concentration is taken into account.

Kinetics of radioiodinated species in subcellular fractions from rat hearts following administration of iodine-123-labelled 15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid (123I-BMIPP)

It is recognized that iodine-123-labelled 15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid (123I-BMIPP) slowly washes out of the myocardium. The mechanism for the washout was investigated in normal rat hearts by analyses of the subcellular distribution and lipid classes based on the BMIPP metabolism. Rat hearts were excised at 1-120 min after intravenous injection of 123I-BMIPP. After counting the radioactivity, the hearts were digested with Nagarse and homogenized, and then fractionated into the cytosolic, mitochondrial, microsomal and crude nuclear fractions by centrifugations. The radioactivity of each fraction was counted, and the lipid classes were analysed by radio-thin-layer chromatographic and high-performance liquid chromatographic methods. The heart uptake of 123I-BMIPP was maximal at 5 min (6.81%+/-0.36% ID/g), and 41% of the radioactivity disappeared within 120 min. The myocardial radioactivity was immediately distributed into the cytosolic, mitochondrial, microsomal and crude nuclear fractions. The distribution (%) of each fraction was almost identical from 5 min through 120 min. The cytosolic fraction was always the major site of radioactivity deposition (60%), and the time-activity curve of the cytosolic fraction paralleled that of the whole heart throughout the 120-min study period. In the cytosolic fraction, most of the radioactivity was incorporated into the triglyceride class, and the rest was present in the free fatty acid, phospholipid (phosphatidylcholine) and diglyceride classes. In the mitochondrial fraction, the radioactivity was mostly incorporated into the phospholipid class (phosphatidylethanolamine), followed by free fatty acids. The final metabolite of 123I-BMIPP, 123I-p-iodophenylacetic acid (123I-PIPA), initially appeared in the mitochondrial fraction as early as 1 min, and subsequently in the cytosolic fraction at 5 min. Another intermediary metabolite, 123I-p-iodophenyldodecanoic acid (123I-PIPC12), was found only in the mitochondrial fraction after 5 min. In conclusion, the slow washout kinetics of 123I-BMIPP from the myocardium mainly reflects the turnover rate of the triglyceride pool in the cytosol. The BMIPP metabolism, i.e. initial alpha-oxidation followed by subsequent cycles of beta-oxidation, was confirmed in vivo. The participation of the mitochondria in the metabolism was also proven.

Adenosine-induced vasoconstriction in vivo. Role of the mast cell and A3 adenosine receptor

Adenosine, a vasodilator metabolite, is often produced in tissues where the demand for oxygen exceeds the supply. We have recently demonstrated in isolated cannulated arterioles that adenosine and its metabolite, inosine, can also cause vasoconstriction by stimulation of mast cells. Secondary release of histamine and thromboxane is responsible for the inosine-induced constriction in vivo. In the present study, we explored the vasomotor effects of adenosine in vivo and investigated the role of the A3 adenosine receptor in mediating vasoconstriction. In vivo, local application of adenosine (10-6 to 10-4 mol/L) to arterioles consistently caused dose-dependent vasodilation. A fraction of arterioles, however, exhibited a biphasic response, with constriction following dilation. This, too, was dose dependent; 37% of arterioles constricted by 12.7 +/- 4.3% of the initial diameter in response to 10-4 mol/L adenosine. In the presence of 8-(p-sulfophenyl)theophylline (8-SPT), an antagonist of A1 and A2 adenosine receptors, dilation in response to the same dose of adenosine was reduced, and constriction was enhanced; 85% of the tested arterioles constricted by -44.3 +/- 6.0% of the initial diameter. The A3 adenosine receptor has been shown to facilitate mediator release from mast cells, and its role was also examined. N6-(3-Iodo-4-aminobenzyl)adenosine (I-ABA), an agonist of A1 and A3 adenosine receptors, produced dose-dependent vasoconstriction. 1,3-Dipropyl-8-(4-acrylate)phenylxanthine (BW-A1433), an antagonist of A1, A2, and A3 receptors, significantly reduced the vasoconstrictor response to adenosine, which was unmasked during treatment with 8-SPT. In addition, both adenosine and I-ABA stimulated mast cell uptake of ruthenium red, indicating degranulation. The I-ABA-induced constriction was abolished by combined histamine and thromboxane receptor antagonists. We conclude that adenosine can cause vasoconstriction in vivo, which is often masked by A2 receptor-mediated vasodilation. Mast cells are stimulated in the course of the response, and the A3 adenosine receptor is involved in mediating constriction.

cDNA cloning and characterization of A3i, an alternatively spliced rat A3 adenosine receptor variant

A cDNA encoding variant form of the A3 adenosine (Ado) receptor was isolated from rat by reverse transcription of brain mRNA followed by PCR. The full-length receptor (A3i) cDNA encodes 337 amino acids and shares complete sequence identity with the rat A3 Ado receptor, except for the presence of a seventeen amino acid insert located in the second intracellular domain. In contrast to the rat A3 receptor, stable expression of A3i in CHO cells resulted in poor coupling to Gi proteins. Analysis of receptor transcripts by RT-PCR suggests that the A3 Ado receptor mRNAs are products of alternative splicing. Sequence analysis of A3 genomic DNA identified a 1.7 kb intron that is likely alternatively spliced to produce the A3 and A3i receptors.

Biochemical pathways of apoptosis: nicotinamide adenine dinucleotide-deficient cells are resistant to tumor necrosis factor or ultraviolet light activation of the 24-kD apoptotic protease and DNA fragmentation

The function of nicotinamide adenine dinucleotide (NAD) and adenosine diphosphate (ADP) ribosylation reactions in the mechanism of apoptotic cell death is controversial, although one theory postulates an essential role for NAD depletion by poly-ADP-ribose polymerase. The present study examined the role of intracellular NAD in tumor necrosis factor (TNF) and ultraviolet (UV) light-induced activation of the 24-kD apoptotic protease (AP24) leading to internucleosomal DNA fragmentation and death. Our results demonstrate that nutritional depletion of NAD to undetectable levels in two leukemia lines (U937 and HL-60) renders them completely resistant to apoptosis. This was attributed to a block in the activation of AP24 and subsequent DNA cleavage. Normal cells show an elevation of ADP-ribosyl transferase (ADPRT) in both the cytosol and nucleus after exposure to TNF, but before DNA fragmentation. ADPRT activity as well as cell death was suppressed by an inhibitor specific for mono-ADPRT. Nuclei from NAD-depleted cells were still sensitive to DNA fragmentation induced by exogenous AP24, indicating a selective function for NAD upstream of AP24 activation in the apoptotic pathway. We confirmed a requirement for intracellular NAD, activation of ADPRT, and subsequent NAD depletion during apoptosis in KG1a, YAC-1, and BW1547 leukemia cell lines. However, this mechanism is not universal, since BJAB and Jurkat leukemia cells underwent apoptosis normally, even in the absence of detectable intracellular NAD. We conclude that TNF or UV light-induced apoptotic cell death is not due to NAD depletion in some leukemia cell lines. Rather, NAD-dependent reactions which may involve mono-ADPRT, function in signal transduction leading to activation of AP24, with subsequent DNA fragmentation and cell death.

Lipopolysaccharide-induced change of phosphorylation of two cytosolic proteins in human monocytes is prevented by inhibitors of ADP-ribosylation

Interaction of LPS with human monocytes causes altered phosphate labeling of cytosolic proteins of 36 kDa and 38 kDa (p36/38). This property, determined by in vitro studies, is shared by other monocyte activators. Phosphorylated p36/38 are distinct from p38, 42-kDa, and 44-kDa isoforms of mitogen-activated protein kinases expressed in monocytes. Occupation of LPS binding sites by a LPS antagonist, the synthetic tetraacylated bisphosphate precursor of Escherichia coli lipid A (also known as compound 406, lipid IVa, or precursor Ia), prevents LPS-induced changes in the phosphate labeling of the two proteins. Abs against CD14 inhibit protein phosphorylation induced by low concentrations of LPS (10 ng/ml), whereas at high concentrations (1 microgram/ml), the Abs fail to prevent phosphorylation. In addition to phosphorylation, ADP-ribosylation of proteins has been implicated in a number of biologic processes. Here we show that inhibitors of ADP-ribosylation, namely meta-iodobenzylguanidine and nicotinamide, inhibit LPS-initiated altered phosphorylation of p36/38. This loss of phosphate labeling of p36/38 is accompanied by an inhibition of TNF-alpha and Il-6 mRNA and protein production. The synthesis of IL-1 is not affected. This suggests that the inhibitors interfere with specific steps in IL-6 and TNF-alpha production, which are not required for IL-1 synthesis. Taken together, the data indicate that ADP-ribosylation may be involved in LPS-induced alteration of the phosphorylation state of two cytosolic proteins (p36/38) and that these proteins modulate cellular processes leading to TNF-alpha and IL-6 release.

Inhibitors of ADP-ribosylation suppress phenotypic modulation and proliferation of smooth muscle cells cultured from rat aorta

The effects of hexamethylenebisacetamide (HMBA), an inhibitor of poly-ADP-ribosylation, and meta-iodobenzylguanidine (MIBG), an inhibitor of mono-ADP-ribosylation, on the phenotypic properties and proliferation of cultured rat aortic smooth muscle cells were studied using a combination of structural and chemical methods. The results show that HMBA and MIBG both slowed down the transition of the cells from a contractile to a synthetic phenotype in primary culture. While the control cells rapidly lost most of their myofilaments and built up an extensive endoplasmic reticulum and Golgi complex, a conspicuous fraction of the drug-treated cells retained a characteristic smooth muscle morphology for at least 6 days. Moreover, most of the treated cells remained positive for smooth muscle alpha-actin and desmin throughout this period. In contrast, the drugs lacked distinct effects on cell morphology and cytoskeletal organization in secondary cultures. Nevertheless, they strongly inhibited serum-stimulated cell growth both in primary and secondary cultures. The ability of serum-starved cells to synthesize DNA after exposure to platelet-derived growth factor or serum was also restrained. Notably, the drugs could be added several hours after the mitogens without loss of effect, suggesting that they did not prevent the entrance into but rather the progression through the cell cycle. Accordingly, the expression of early response genes like c-fos, c-jun and c-myc was not blocked by the drugs. On the other hand, HMBA reduced the expression of transcripts for smooth muscle alpha-actin, type IV collagenase, collagen type I, and osteopontin both in primary and secondary cultures. Weaker and more variable effects were obtained with MIBG. Taken together, the findings support the notion that poly- and mono-ADP-ribosylation of proteins are involved in the control of smooth muscle cell differentiation and growth.

Characterization of the arachidonate and ATP binding sites of human 5-lipoxygenase using photoaffinity labeling and enzyme immobilization

The arachidonic acid and the ATP binding sites of human 5-lipoxygenase were characterized using photoaffinity labeling and immobilization of the enzyme on ATP-agarose. Photoaffinity labeling of the active site of 5-lipoxygenase was achieved with a novel thiopyranoindole inhibitor containing a 4-azido-3-iodobenzenesulfonyl moiety (L-708,714). This probe was found to inhibit the activity of 5-lipoxygenase (IC50 = 0.3 microM) and to covalently label the enzyme after UV light irradiation. The labeling was inhibited by arachidonic acid, N-hydroxyurea, and dihydrobenzofuranol inhibitors which have been shown to reduce the non-heme iron center of 5-lipoxygenase. Photoaffinity labeling of 5-lipoxygenase by L-708,714 was dependent on the presence of both Ca2+ ions and phospholipids and was independent of ATP. It occurred at similar levels using native (Fe2+), oxidized (Fe3+), or H2O2-inactivated enzyme, but was abolished by heat inactivation of the enzyme. Competition of the labeling by various thiopyranoindoles and other inhibitors such as L-697,198,ZD-2138, and zileuton was found to be related to their inhibitory potency. Immobilized 5-lipoxygenase on ATP-agarose was found to be selectively eluted by adenine nucleotides (ATP > ADP > AMP) but not by solutions containing high salt concentrations, mild detergents, arachidonic acid, or inhibitors. 5-Lipoxygenase inhibitors were selectively retained on the immobilized enzyme and eluted by buffer containing arachidonic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Selection and characterization of verapamil-resistant multidrug resistant cells

Multidrug resistant cells may become acutely sensitive to the calcium channel blocker verapamil, in spite of the fact that its accumulation by these cells is negligible. We selected verapamil-resistant mutants from multidrug resistant Chinese hamster ovary cells. Levels of P-glycoprotein expression and cross-resistance profiles remained unaltered in the verapamil-resistant multidrug resistant cells. As well, a photoactive verapamil analog specifically bound to P-glycoprotein in these cells. We had previously used a photoactive anthracycline to show that calcium antagonists and several anticancer drugs bind to P-glycoprotein at overlapping or interacting sites. Verapamil and its analogues no longer inhibit the binding of either anticancer drugs or calcium channel blockers to P-glycoprotein. Sequencing of P-glycoprotein revealed that no change had occurred in the coding sequence as a result of the selection procedure.

Both gravity and non-gravity dependent factors determine regional blood flow within the goat lung

Distribution of pulmonary blood flow has traditionally been regarded as determined by gravity. This view has been challenged recently by reports describing marked gravity-independent distribution of flow. These reports were based on experiments in which local blood flow was measured by methods that have not been thoroughly evaluated. In the present study, we showed that in the goat lung regional trapping of i.v. infused microspheres (O = 15 microns) correlated to endothelial uptake of a simultaneously i.v. infused diamine (r = 0.99, region size approximately 1.5 cm3, dry weight approximately 40 mg). This indicates that the deposition of microspheres reflects true regional pulmonary blood flow. Using the microsphere method, we found a marked gravity-independent heterogeneity in blood flow (coefficient of variation approximately 40%) in the awake goat. We could find no pattern related to anatomy that could account for this variability. We re-examined the influence of gravity by analysing the distribution of pulmonary blood flow in anaesthetized goats both in prone and supine positions. The dorsal to sternal distribution of flow appeared to be inverted when the animals were turned from prone to supine recumbency, indicating that gravity influenced the distribution of pulmonary blood flow along this axis. However, along the gravitational axis, distribution of blood flow varied considerably from lung to lung. It appears that in awake goats the distribution of pulmonary blood flow is the result of several different determinants.

Modeling the quinone-B binding site of the photosystem-II reaction center using notions of complementarity and contact-surface between atoms

Functional identity and significant similarities in cofactors and sequence exist between the L and M reaction center proteins of the photosynthetic bacteria and the D1 and D2 photosystem-II reaction center proteins of cyanobacteria, algae, and plants. A model of the quinone (QB) binding site of the D1 protein is presented based upon the resolved structure of the QB binding pocket of the L subunit, and introducing novel quantitative notions of complementarity and contact surface between atoms. This model, built without using traditional methods of molecular mechanics and restricted to residues in direct contact with QB, accounts for the experimentally derived functional state of mutants of the D1 protein in the region of QB. It predicts the binding of both the classical and phenol-type PSII herbicides and rationalizes the relative levels of tolerance of mutant phenotypes.