Synergistic action of indole-3-carbinol with membrane-active agents against multidrug-resistant Gram-negative bacteria.

The purpose of this study was to evaluate the antimicrobial activity of indole-3-carbinol (I3C) with membrane-active agents, namely carbonyl cyanide 3-chlorophenylhydrazone (CCCP) and ethylenediaminetetraacetic acid (EDTA) against multidrug-resistant (MDR) Gram-negative bacteria and bacterial persisters. The determination of minimal inhibitory concentration (MIC) showed that I3C was effective against Acinetobacter baumannii (3.13‒6.25 × 10-3 mol l-1), Klebsiella pneumoniae (8 × 10-3 mol l-1), Pseudomonas aeruginosa (6.25‒12.5 × 10-3 mol l-1), and Escherichia coli (6.25‒12.5 × 10-3 mol l-1). Our study demonstrated that EDTA synergistically enhanced the bactericidal activity of I3C against most MDR Gram-negative bacteria isolates and contributed to an 8- to 64-fold MIC reduction compared with that of I3C alone, yet CCCP only displayed synergy with I3C against P. aeruginosa and A. baumannii. The EDTA-I3C combination also significantly reduced the viable number of testing bacteria (P = 7.2E-05), effectively reduced bacterial persisters, and repressed bacterial growth compared with that the use of I3C alone. Our data demonstrate that use of EDTA as adjuvant molecules can effectively improve the antibacterial activity of I3C and may help to reduce the development of antimicrobial resistance.

Epigallocatechin-3-Gallate Suppresses Human Herpesvirus 8 Replication and Induces ROS Leading to Apoptosis and Autophagy in Primary Effusion Lymphoma Cells.

Epigallocatechin-3-gallate (EGCG), the major constituent of green tea, has been shown to induce cell death in cancer cells. Primary effusion lymphoma (PEL) is an aggressive neoplasm caused by human herpesvirus 8 (HHV8). In this study, we examined the role of EGCG on PEL cells in cell death and HHV8 replication. We performed trypan blue exclusion assay to assess the cell viability of PEL cells, flow cytometry analysis to examine the cell cycle distribution and reactive oxygen species (ROS) generation, caspase-3 activity to assay apoptosis, acridine orange staining to determine autophagy, and immunoblotting to detect the protein levels involved in apoptosis and autophagy as well as mitogen activated protein kinases (MAPKs) activation upon EGCG treatment. The expression of the HHV8 lytic gene was determined by luciferase reporter assay and reverse transcription-PCR, and viral progeny production was determined by PCR. Results revealed that EGCG induced cell death and ROS generation in PEL cells in a dose-dependent manner. N-acetylcysteine (NAC) inhibited the EGCG-induced ROS and rescued the cell from EGCG-induced cell death. Even though EGCG induced ROS generation in PEL cells, it reduced the production of progeny virus from PEL cells without causing HHV8 reactivation. These results suggest that EGCG may represent a novel strategy for the treatment of HHV8 infection and HHV8-associated lymphomas.

The Inhibition by Oxaliplatin, a Platinum-Based Anti-Neoplastic Agent, of the Activity of Intermediate-Conductance Ca²âº-Activated K⁺ Channels in Human Glioma Cells.

Oxaliplatin (OXAL) is a third-generation organoplatinum which is effective against advanced cancer cells including glioma cells. How this agent and other related compounds interacts with ion channels in glioma cells is poorly understood. OXAL (100 µM) suppressed the amplitude of whole-cell K+ currents (I(K)); and, either DCEBIO or ionomycin significantly reversed OXAL-mediated inhibition of I(K) in human 13-06-MG glioma cells. In OXAL-treated cells, TRAM-34 did not suppress I(K) amplitude in these cells. The intermediate-conductance Ca(2+)-activated K+ (IK(Ca)) channels subject to activation by DCEBIO and to inhibition by TRAM-34 or clotrimazole were functionally expressed in these cells. Unlike cisplatin, OXAL decreased the probability of IK(Ca)-channel openings in a concentration-dependent manner with an IC50 value of 67 µM. No significant change in single-channel conductance of IK(Ca) channels in the presence of OXAL was demonstrated. Neither large-conductance Ca(2+)-activated K+ channels nor inwardly rectifying K+ currents in these cells were affected in the presence of OXAL. OXAL also suppressed the proliferation and migration of 13-06-MG cells in a concentration- and time-dependent manner. OXAL reduced IK(Ca)-channel activity in LoVo colorectal cancer cells. Taken together, the inhibition by OXAL of IK(Ca) channels would conceivably be an important mechanism through which it acts on the functional activities of glioma cells occurring in vivo.

Methadone concentrations in blood, plasma, and oral fluid determined by isotope-dilution gas chromatography-mass spectrometry.

Methadone (MTD) is widely used for detoxification of heroin addicts and also in pain management programs. Information about the distribution of methadone between blood, plasma, and alternative specimens, such as oral fluid (OF), is needed in clinical, forensic, and traffic medicine when analytical results are interpreted. We determined MTD and its metabolite 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in blood, plasma, blood cells, and OF by gas chromatography-mass spectrometry (GC-MS) after adding deuterium-labeled internal standards. The analytical limits of quantitation for MTD and EDDP by this method were 20 and 3 ng/mL, respectively. The amounts of MTD and EDDP were higher in plasma (80.4 % and 76.5 %) compared with blood cells (19.6 % and 23.5 %) and we found that repeated washing of blood cells with phosphate-buffered saline increased the amounts in plasma (93.6 % and 88.6 %). Mean plasma/blood concentration ratios of MTD and EDDP in spiked samples (N = 5) were 1.27 and 1.21, respectively. In clinical samples from patients (N = 46), the concentrations of MTD in plasma and whole blood were highly correlated (r = 0.92, p < 0.001) and mean (median) plasma/blood distribution ratios were 1.43 (1.41). The correlations between MTD in OF and plasma (r = 0.46) and OF and blood (r = 0.52) were also statistically significant (p < 0.001) and the mean OF/plasma and OF/blood distribution ratios were 0.55 and 0.77, respectively. The MTD concentration in OF decreased as salivary pH increased (more basic). These results will prove useful in clinical and forensic medicine when MTD concentrations in alternative specimens are compared and contrasted.

Epigallocatechin-3-gallate downregulates PDHA1 interfering the metabolic pathways in human herpesvirus 8 harboring primary effusion lymphoma cells.

Primary effusion lymphoma (PEL) is an aggressive neoplasm correlated with human herpesvirus 8 (HHV8). Metabolic reprogramming is a hallmark of cancers. The alterations in cellular metabolism are important to the survival of HHV8 latently infected cells. Pyruvate dehydrogenase (PDH) controls the flux of metabolites between glycolysis and the tricarboxylic acid cycle (TCA cycle) and is a key enzyme in cancer metabolic reprogramming. Glutaminolysis is required for the survival of PEL cells. Glutamate dehydrogenase 1 (GDH1) converts glutamate into α-ketoglutarate supplying the TCA cycle with intermediates to support anaplerosis. Previously we have observed that epigallocatechin-3-gallate (EGCG) can induce PEL cell death and N-acetyl cysteine (NAC) attenuates EGCG induced PEL cell death. In this study, results showed that EGCG upregulated the expression of glucose transporter GLUT3, and reduced the expression of pyruvate dehydrogenase E1-alpha (PDHA1), the major regulator of PDH, and GDH1. NAC could partially reverse the effects of EGCG in PEL cells. Overexpression of PDHA1 in PEL cells or supplement of α-ketoglutarate attenuated EGCG induced cell death. EGCG also reduced the levels of oncometabolite D-2-hydroxyglutarate (D2HG). These results suggest that EGCG may modulate the metabolism of PEL cells leading to cell death.

An empirical study on the selection of analytes and corresponding cutoffs for immunoassay and GC-MS in a two-step test strategy--buprenorphine example.

(i) Standard solutions of buprenorphine (B) and three metabolites; (ii) immunoassay (IA) reagents designed for the analysis of B and/or its metabolites; and (iii) clinical urine specimens collected from patients (under B-treatment), constitute the B-System for fundamental study of parameters critical to the two-step test strategy, an analytical approach designed for a high-volume testing environment. The cross-reacting characteristics of IA reagents were examined using standard solutions of B and its metabolites. Resulting data were used as the basis for selecting target analytes suitable for the preliminary and the confirmatory test steps. Test data derived from IA and GC-MS analysis of clinical urine specimens (with natural distribution of B and its metabolites) were quantitatively correlated. Correlation parameters were examined: (i) to verify whether the analyte-pair targeted by the IA and GC-MS test steps has been properly selected; and (ii) to decide on appropriate cutoffs for the two test steps. In conclusion, this study has demonstrated that the most effective analyte(s) that should be targeted in the GC-MS determination step vary with the IA selected in the preliminary test step. All analytes that generate significant responses to the IA reagent should be targeted in the GC-MS test step.

Characterization of Perturbing Actions by Verteporfin, a Benzoporphyrin Photosensitizer, on Membrane Ionic Currents.

Verteporfin (VP), a benzoporphyrin derivative, has been clinically tailored as a photosensitizer and recently known to suppress YAP-TEAD complex accompanied by suppression of the growth in an array of neoplastic cells. However, the detailed information is little available regarding possible modifications of it and its related compounds on transmembrane ionic currents, despite its growing use in clinical settings. In this study, from whole cell recordings, VP (0.3-100 µM) increased the amplitude of Ca2+-activated K+ currents (I K(Ca)) in pituitary tumor (GH3) cells in a concentration-dependent manner with an EC50 value of 2.4 µM. VP-stimulated I K(Ca) in these cells was suppressed by further addition of either paxilline, iberiotoxin, or dithiothreitol, but not by that of tobultamide or TRAM-39. VP at a concentration of 10 µM mildly suppressed the amplitude of delayed-rectifier K+ current; however, it had minimal effects on M-type K+ current. In cell-attached current recordings, addition of VP to the recording medium enhanced the activity of large-conductance Ca2+-activated K+ (BKCa) channels. In the presence of VP, additional illumination with light intensity of 5.5 mW/cm2 raised the probability of BKCa-channel openings further. Addition of VP decreased the peak amplitude of L-type Ca2+ current together with slowed inactivation time course of the current; however, it failed to modify voltage-gated Na+ current. Illumination of GH3 cells in continued presence of VP also induced a non-selective cation current. Additionally, VP increased the activity of BKCa channels in human 13-06-MG glioma cells with an EC50 value of 1.9 µM. Therefore, the effects of VP on ionic currents described herein tend to be upstream of its inhibition of YAP-TEAD complex and they are conceivably likely to contribute to the underlying mechanisms through which it and its structurally similar compounds effect the modifications in functional activities of pituitary or glial neoplastic cells, if the in vivo findings occur.

A novel derivatization approach for simultaneous determination of glyoxal, methylglyoxal, and 3-deoxyglucosone in plasma by gas chromatography-mass spectrometry.

A two-step derivatization approach has been developed to enable the simultaneous analysis of glyoxal, methylglyoxal, and 3-deoxyglucosone by the most efficient and widely applied GC-MS methodology. These three analytes are reactive carbonyl compounds associated with the formation of advanced glycation and lipoxidation end products, a process thought to contribute to uremic toxicity and referred to as "carbonyl stress". Effective analysis of these compounds would facilitate understanding these compounds' role in diabetes-related complications. Plasma samples were deproteinized by acetonitrile, followed by a two-step derivatization approach. Pooled plasma samples from healthy individuals were used as the "blank" for preparing calibration standards. The concentrations of the analytes in the "blank" were first determined by standard addition method. Calibration parameters were accordingly established and used to analyze these compounds in plasma samples collected from healthy individuals and diabetic patients. Analytical findings are comparable with those reported in the literature. Quantitation data can be further improved by making available and using isotopically labeled analogs of these analytes as the internal standards.

Performance characteristics of ELISAs for monitoring ketamine exposure.

BACKGROUND: Growing misuse of ketamine necessitates the development of high throughput testing approaches. Two commercial enzyme-linked immunosorbent assays (ELISA) for ketamine have recently become available and were adapted for this development. METHOD: The newly available ketamine ELISA reagents were examined to better understand their cross-reacting, calibration and other performance characteristics. ELISA apparent analyte concentrations were also correlated against ketamine concentrations as determined by GC-MS to examine the relationship between these 2 parameters. RESULT: Both adapting ketamine as the targeted analyte, reagent from International Diagnostic Systems (IDS) also responded very significantly to the metabolites of ketamine (norketamine and dehydronorketamine), while the NEOGEN reagent responded very specifically to ketamine. CONCLUSION: NEOGEN ELISA test data exhibit better correlation with the ketamine concentration as determined by GC-MS. It can be more reliably used as the preliminary test method in the 2-step approach now routinely adapted in workplace drug testing programs. Using 100 ng/ml ketamine as the GC-MS cutoff, the corresponding ELISA cutoff value is approximately 110-120 ng/ml. With significantly higher responses to ketamine metabolites, IDS reagent can detect specimens with much lower ketamine/metabolites concentrations and can better meet other testing requirements.

Gas chromatography-mass spectrometry analysis of ketamine and its metabolites--a comparative study on the utilization of different derivatization groups.

Method of chemical derivatization is the main difference among the GC-MS based methodologies reported for the analysis of ketamine and its major metabolites (norketamine and dehydronorketamine). These approaches included acylation and silylation resulting in the formation of acetyl, trifluoroacetyl, heptafluorobutyryl, and pentafluorobenzoyl (for acylation); and possibly trimethylsilyl and t-butyldimethylsilyl (for silylation) derivatives. This study evaluates the merits of these approaches based on the following criteria: reaction yields and ionization efficiency of the derivatization products; chromatographic characteristics; and cross-contributions to the intensities of ions designating the analyte and the internal standard. Pentafluorobenzoyl-derivatives were found to provide the best performance characteristics.

Inhibition of intermediate-conductance Ca2+-activated K+ channel and cytoprotective properties of 4-piperidinomethyl-2-isopropyl-5-methylphenol.

The ionic mechanisms and cytoprotective activities of 4-piperidinomethyl-2-isopropyl-5-methylphenol (THPI), an analogue of thymol, were investigated in HL-60 granulocytes and in human erythrocytes, respectively. THPI inhibited K+ outward current (I(K)) in a concentration-dependent manner in HL-60 leukocytes, with an IC50 value of 4 microM. Neither iberiotoxin (200 nM) nor paxilline (1 microM) suppressed the amplitude of I(K), whereas clotrimazole (5 microM) significantly inhibited it. In the inside-out configuration of single channel recordings, application of THPI (5 microM) into the bath medium did not alter the single-channel conductance of intermediate-conductance Ca2+-activated K+ (IK(Ca)) channels (i.e K(Ca)3.1 channels), but it suppressed the channel activity significantly. THPI-induced inhibition of IK(Ca) channels was reversed by a further application of 1-ethyl-2-benzimidazolinone (10 microM). THPI-induced reduction in IK(Ca)-channel activity in these cells was primarily due to a decrease in mean open time. These results provide direct evidence that THPI is capable of suppressing the activity of IK(Ca) channels in HL-60 cells. The antioxidant action of THPI also revealed a beneficial cytoprotective effect against mitomycin C-mediated haemolytic effect in human erythrocytes. The results of this study suggest that blockade of IK(Ca) channels and the membrane-protecting activity of THPI would combine to have beneficial effects in lessening the severity of haemolytic crisis and reducing anaemia in sickle cell disease.

Glucocorticoids stimulate the activity of large-conductance Ca2+ -activated K+ channels in pituitary GH3 and AtT-20 cells via a non-genomic mechanism.

The effects of glucocorticoids on ion currents were investigated in pituitary GH3 and AtT-20 cells. In whole-cell configuration, dexamethasone, a synthetic glucocorticoid, reversibly increased the density of Ca2+ -activated K+ current (IK(Ca)) with an EC50 value of 21 +/- 5 microM. Dexamethasone-induced increase in IK(Ca) density was suppressed by paxilline (1 microM), yet not by glibenclamide (10 microM), pandinotoxin-Kalpha (1 microM) or mifepristone (10 microM). Paxilline is a blocker of large-conductance Ca2+ -activated K+ (BKCa) channels, while glibenclamide and pandinotoxin-Kalpha are blockers of ATP-sensitive and A-type K+ channels, respectively. Mifepristone can block cytosolic glucocorticoid receptors. In inside-out configuration, the application of dexamethasone (30 microM) into the intracellular surface caused no change in single-channel conductance; however, it did increase BKCa -channel activity. Its effect was associated with a negative shift of the activation curve. However, no Ca2+ -sensitiviy of these channels was altered by dexamethasone. Dexamethasone-stimulated channel activity involves an increase in mean open time and a decrease in mean closed time. Under current-clamp configuration, dexamethasone decreased the firing frequency of action potentials. In pituitary AtT-20 cells, dexamethasone (30 microM) also increased BKCa -channel activity. Dexamethasone-mediated stimulation of IK(Ca) presented here that is likely pharmacological, seems to be not linked to a genomic mechanism. The non-genomic, channel-stimulating properties of dexamethasone may partly contribute to the underlying mechanisms by which glucocorticoids affect neuroendocrine function.

Sodium cyanate-induced opening of calcium-activated potassium currents in hippocampal neuron-derived H19-7 cells.

We investigated the chemical toxic agent sodium cyanate (NaOCN) on the large conductance calcium-activated potassium channels (BK(Ca)) on hippocampal neuron-derived H19-7 cells. The whole-cell and cell-attach configuration of patch-clamp technique were applied to investigate the BK(Ca) currents in H19-7 cells in the presence of NaOCN (0.3 mM). NaOCN activated BK(Ca) channels on H19-7 cells. The single-channel conductance of BK(Ca) channels was 138+/-7pS. The presence of NaOCN (0.3 mM) caused an obvious increase in open probability of BK(Ca) channels. NaOCN did not exert effect on the slope of the activation curve and stimulated the activity of BK(Ca) channels in a voltage-dependent fashion in H19-7 cells. The presence of paxilline or EGTA significantly reduced the BK(Ca) amplitude, in comparison with the presence of NaOCN. These findings suggest that during NaOCN exposure, the activation of BK(Ca) channels in neurons could be one of the ionic mechanisms underlying the decreased neuronal excitability and neurological disorders.

Characterization of chromanol 293B-induced block of the delayed-rectifier K+ current in heart-derived H9c2 cells.

The effects of chromanol 293B on ion currents in rat embryonic heart-derived H9c2 cells were investigated in this study. Chromanol 293B suppressed the amplitude of delayed rectified K+ current (I(K)) in a concentration-dependent manner. The IC50 value for chromanol 293B-induced inhibition of I(K) was 8 microM. The I(K) present in these cells, the electrical properties of which resembled those for the Kv2.1-related K+ current, was sensitive to inhibition by quinidine or dendrotoxin, yet not by pandinotoxin-Kalpha, E-4031 or apamin. Chromanol 293B reduced the activation time constant of I(K) and the effective gating charge of this channel. However, little or no modification in the steady-state inactivation of I(K) in response to long-lasting conditioning pulses could be demonstrated in the presence of chromanol 293B. These results clearly demonstrate that chromanol 293B can effectively interact with the K+ channel functionally expressed in H9c2 myoblasts. The chromanol 293B-induced inhibition of these channels could primarily be attributed to open channel block.

Effects of 4-piperidinomethyl-2-isopropyl-5-methylphenol on oxidative stress and calcium current.

4-Piperidinomethyl-2-isopropyl-5-methylphenol (THPI) was synthesized by reaction of thymol with piperidine and formaldehyde. The biological effect of THPI on superoxide anion scavenging activity, antiplatelet activity and calcium current inhibition were investigated. THPI (50 microM) was shown to be a scavenger of superoxide radicals in human neutrophils stimulated with N-formyl-Met-Leu-Phe (66% inhibition). Since superoxide anions are essential for platelet aggregation and L-type Ca2+-channel activity, we further found that THPI inhibited platelet aggregation induced by arachidonic acid (IC50 46.80+/-6.88 microM). The effect of THPI on Ca2+ current in NG108-15 cells was investigated using the whole-cell voltage-clamp technique. THPI inhibited voltage-dependent L-type Ca2+ current (ICa, L). The IC50 value of THPI-induced inhibition of ICa, L was 3.60+/-0.81 microM. THPI caused no change in the overall shape of the current-voltage relationship of ICa, L. This indicates that THPI is an inhibitor of ICa, L in NG108-15 cells. Therefore, the channel-blocking properties of THPI may contribute to the underlying mechanism by which it affects neuronal or neuroendocrine function. Furthermore, no significant cytotoxic effects of THPI (0.3-50 microM) were observed in NG108-15 cells. The results indicate that THPI is a potential reactive oxygen species scavenger and may prevent platelet aggregation or inhibit L-type Ca2+-channel activity, possibly by scavenging reactive oxygen species.

Antioxidant and antiplatelet effects of dang-gui-shao-yao-san on human blood cells.

Dang-Gui-Shao-Yao-San (DGSYS) is a mixture of medicinal herbs, which has long been used in traditional Chinese medicine for treating anemia and ovulary disorders. Its preparation comprises Angelicae sinensis (Oliv.) Diels, Ligustucum chuanxiong Hort, Paeonia lactiflora pall, Poria cocos (Schw.) Wolf, Atractylodis macrocephala Koidz and Alisma orientalis (Sam.) Juzep. The present study examined the anti-superoxide formation, free radical scavenging and anti-lipid peroxidation activities of DGSYS by xanthine oxidase inhibition, cytochrome C system with superoxide anion released by the fMLP or PMA activating pathway in human neutrophils, and FeCl2 ascorbic acid-induced lipid peroxidation effects on lipids in rat liver homogenate, respectively. DGSYS showed anti-superoxide formation and free radical scavenging activity in a concentration-dependent manner. It also inhibited PMA- but not fMLP-induced superoxide anion released from human neutrophils. These antioxidant actions of DGSYS showed beneficial cytoprotective effects against lipid peroxidation in rat liver homogenate, human platelet aggregation induced by arachidonic acid (AA) and adenosine diphosphate (ADP) and mitomycin C-mediated hemolytic in human erythrocytes.

Direct Injection LC-MS-MS Analysis of Opiates, Methamphetamine, Buprenorphine, Methadone and Their Metabolites in Oral Fluid from Substitution Therapy Patients.

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS-MS) method was developed, validated and applied to simultaneous analysis of oral fluid samples for the following 10 analytes: methadone, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), buprenorphine, norbuprenorphine, morphine, codeine, 6-acetylmorphine, 6-acetylcodeine, amphetamine, and methamphetamine. The oral fluid sample was briefly centrifuged and the supernatant was directly injected into the LC-MS-MS system operated under reverse-phase chromatography and electrospray ionization (ESI). Deuterated analogs of the analytes were adopted as the internal standards and found to be effective (except for buprenorphine) to compensate for potential matrix effects. Each analytical run took <10 min. Linearity range (r(2) > 0.99) established for buprenorphine and the other nine analytes were 5-100 and 1-100 ng/mL. Intra- and interday precision (% CV) ranges for the 10 analytes were 0.87-12.2% and 1.27-12.8%, while the corresponding accuracy (%) ranges were 91.8-113% and 91.9-111%. Limits of detection and quantitation established for these 10 analytes were in the ranges of 0.1-1.0 and 0.25-1.0 ng/mL (5 ng/mL for buprenorphine). The method was successfully applied to the analysis of 62 oral fluid specimens collected from patients participating in methadone and buprenorphine substitution therapy programs. Analytical results of methadone and buprenorphine were compared with data derived from GC-MS analysis and found to be compatible. Overall, the direct injection LC-MS-MS method performed well, permitting rapid analysis of oral fluid samples for simultaneous quantification of methadone, buprenorphine, opiate and amphetamine drug categories without extensive sample preparation steps.

Cilostazol, an inhibitor of type 3 phosphodiesterase, stimulates large-conductance, calcium-activated potassium channels in pituitary GH3 cells and pheochromocytoma PC12 cells.

The effects of cilostazol, a dual inhibitor of type 3 phosphodiesterase and adenosine uptake, on ion currents were investigated in pituitary GH(3) cells and pheochromocytoma PC12 cells. In whole-cell configuration, cilostazol (10 microm) reversibly increased the amplitude of Ca(2+)-activated K(+) current [I(K(Ca))]. Cilostazol-induced increase in I(K(Ca)) was suppressed by paxilline (1 microM) but not glibenclamide (10 microm), dequalinium dichloride (10 microM), or beta-bungarotoxin (200 nM). Pretreatment of adenosine deaminase (1 U/ml) or alpha,beta-methylene-ADP (100 microM) for 5 h did not alter the magnitude of cilostazol-stimulated I(K(Ca)). Cilostazol (30 microM) slightly suppressed voltage-dependent l-type Ca(2+) current. In inside-out configuration, bath application of cilostazol (10 microM) into intracellular surface caused no change in single-channel conductance; however, it did increase the activity of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels. Cilostazol enhanced the channel activity in a concentration-dependent manner with an EC(50) value of 3.5 microM. Cilostazol (10 microM) shifted the activation curve of BK(Ca) channels to less positive membrane potentials. Changes in the kinetic behavior of BK(Ca) channels caused by cilostazol were related to an increase in mean open time and a decrease in mean closed time. Under current-clamp configuration, cilostazol decreased the firing frequency of action potentials. In pheochromocytoma PC12 cells, cilostazol (10 microM) also increased BK(Ca) channel activity. Cilostazol-mediated stimulation of I(K(Ca)) appeared to be not linked to its inhibition of adenosine uptake or phosphodiesterase. The channel-stimulating properties of cilostazol may, at least in part, contribute to the underlying mechanisms by which it affects neuroendocrine function.

Assessment of genotoxicity of benzidine and its structural analogues to human lymphocytes using comet assay.

Benzidine (BZ) and its six structural analogues (2-aminobiphenyl [2-ABP], 4-aminobiphenyl [4-ABP], 3,3'-diaminobenzidine [DABZ], 3,3'-dichlorobenzidine [DCBZ] 3,3'-dimethoxybenzidine [DEBZ], and 3,3'-dimthylbenzidine [DMBZ]) were examined for DNA damage in human lymphocytes using the alkaline comet assay. All the tested compounds showed a distinct disparity in their respective DNA-damaging capacities with an order of DABZ > BZ > DCBZ > 2-ABP > DEBZ > 4-ABP > DMBZ when lymphocytes were exposed to these chemicals for 2 h. Results show that the DNA-damaging effects of these compounds had no bearing on some physicochemical parameters including oxidation potentials, the energy differences between the lowest unoccupied molecular orbital and the highest occupied molecular orbital, ionization potentials, dipole moment, and relative partition coefficient. On the other hand, the free radical scavengers, including catalase, SOD, BHT, EDTA, and histidine exerted varying degrees of inhibitory effects on the DNA damage caused by benzidine. This suggests that genotoxicity in lymphocytes caused by benzidine proceeded via a reactive oxygen species (ROS)-mediated mechanism.

Inhibition of Ca2+-activated and voltage-dependent K+ currents by 2-mercaptophenyl-1,4-naphthoquinone in pituitary GH3 cells: contribution to its antiproliferative effect.

Quinones have been shown to possess antineoplastic activity; however, their effects on ionic currents remain unclear. The effects of 2-mercaptophenyl-1,4-naphthoquinone (2-MPNQ), menadione (MD) and 1,4-naphthoquinone (1,4 NQ) on cell proliferation and ionic currents in pituitary GH3 lactotrophs were investigated in this study. 2-MPNQ was more potent than menadione or 1,4-naphthoquinone in inhibiting the growth of GH3 cells. 2-MPNQ decreased cell proliferation in a concentration-dependent manner with an IC50 value of 3 microM. In whole-cell recording experiments, 2-MPNQ reversibly caused an inhibition of Ca2+-activated K+ current (I(K(Ca)) in a concentration-dependent manner. The IC50 value for 2-MPNQ-induced inhibition of I(K(Ca)) was 7 microM. In the inside-out configuration of single channel recording, 2-MPNQ (30 microM) applied intracellularly suppressed the activity of large-conductance Ca2+-activated K+ (BK(Ca)) channels but did not modify single channel conductance. Menadione (30 microM) had no effect on the channel activity, whereas 1,4-naphthoquinone (30 microM) suppressed it by about 26%. Both 2-MPNQ and thimerosal suppressed the dithiothreitol-stimulated channel activity. 2-MPNQ also blocked voltage-dependent K+ currents, but it produced a slight reduction of L-type Ca2+ inward current. However, unlike E-4031, 2-MPNQ (30 microM) did not suppress inwardly rectifying K+ current present in GH3 cells. Under the current clamp configuration, the presence of 2-MPNQ (30 microM) depolarized the cells, and increased the frequency and duration of spontaneous action potentials. The 2-MPNQ-mediated inhibition of K+ currents would affect hormone secretion and cell excitability. The blockade of these ionic channels by 2-MPNQ may partly explain its inhibitory effect on the proliferation of GH3 cells.