Sugars and sugar derivatives which inhibit the short-circuit current of the everted small intestine of the rat.
(1/210)
1. The short-circuit current of everted rat intestine supported on a perforated cannula proved to be stable for up to 3 hr and has been used to study competition between transportable and non-transportable sugars. 2. 4,6-O-Ethylidene-alpha-D-glucopyranose (ethylidene glucose) and 4,6-O-benzylidene-e alpha-D-glucopyranos (benzylinene glucose), two nontransportable inhibitors of the hexose transfer system in human erythrocytes, were found to reduce the short-circuit current generated by transportable sugars such as galactose or 3-O-methyl glucose. 3. These compounds were also found to reduce the basal short-circuit current established by the everted intestine in a sugar-free Krebs solution. Both types of inhibition approached saturation at the higher concentrations used. 4. Similar inhibitory properties were shown by mannose, a non-actively accumulated monosaccharide, and by the beta-disaccharides lactose and cellobiose. 5. It is suggested that this common pattern of behaviour is due to the ability of these compounds to react with the sites for active hexose transfer but without translocation by the system. The significance of the inhibition of the basal short-circuit current is briefly discussed in this context. (+info)
Opioid-induced second window of cardioprotection: potential role of mitochondrial KATP channels.
(2/210)
Opioids have been previously shown to confer short-term cardioprotection against a prolonged ischemic insult. Therefore, the present study was designed to determine whether opioids can induce a delayed or "second window" of cardioprotection and to assess the potential involvement of the mitochondrial KATP channel. All rats were subjected to 30 minutes of ischemia and 2 hours of reperfusion (I/R). Control animals, injected with saline 24 hours before I/R, elicited an infarct size/area at risk (IS/AAR) of 62.9+/-3.4. TAN-67, a delta1-opioid receptor agonist, was administered 10 or 30 mg/kg IP 12, 24, 48, or 72 hours before I/R. TAN-67 (10 mg/kg) 12- or 24-hour pretreatment did not significantly reduce IS/AAR (62.1+/-6.3 and 43.3+/-7.3, respectively). Similarly, 12-hour pretreatment with TAN-67 (30 mg/kg) did not reduce IS/AAR (60.0+/-5.6); however, 24-hour pretreatment significantly reduced IS/AAR (34.5+/-5.9). Forty-eight-hour pretreatment with TAN-67 maximally reduced IS/AAR (29.2+/-7.0), and opioid-induced cardioprotection was lost after 72-hour pretreatment (61.7+/-3.8). TAN-67-induced cardioprotection could be abolished by pretreatment with the selective delta1-opioid receptor antagonist 7-benzylidenenaltrexone, BNTX, administered either 30 minutes before TAN-67 given 48 hours before I/R or 10 minutes before I/R in rats previously treated for 48 hours with TAN-67 (59.6+/-3.1 and 58.7+/-3.5, respectively). The involvement of the KATP channel was investigated with 2 inhibitors: glibenclamide, a nonselective KATP channel inhibitor, and 5-hydroxydecanoic acid, selective for the mitochondrial KATP channel in rabbits. Glibenclamide, administered 30 minutes before I/R in 48-hour TAN-67-pretreated rats, completely abolished cardioprotection (60. 4+/-3.2). Similarly, 5-hydroxydecanoic acid, administered 5 minutes before I/R in rats pretreated 48 hours previously with TAN-67, completely abolished cardioprotection (57.8+/-2.5). These results suggest that delta1-opioid receptor stimulation, 24 to 48 hours before an ischemic insult, produces a delayed cardioprotective effect that is possibly the result of mitochondrial KATP channel activation. (+info)
In vivo efficacy of XR9051, a potent modulator of P-glycoprotein mediated multidrug resistance.
(3/210)
Overexpression of P-glycoprotein (P-gp) is a potential cause of multidrug resistance (MDR) in tumours. We have previously reported that XR9051 (N-(4-(2-(6,7-dimethoxy-1,2,3,4-tetrahydro-2-isoquinolyl)ethyl)phe nyl)-3-((3Z,6Z)-6-benzylidene-1-methyl-2,5-dioxo-3-pipera zinylidene)methylbenzamide) is a potent and specific inhibitor of P-gp, which reverses drug resistance in several murine and human MDR cell lines. In this study we have evaluated the in vivo efficacy of this novel modulator in a panel of murine and human tumour models and examined its pharmacokinetic profile. Efficacy studies in mice bearing MDR syngeneic tumours (P388/DX Johnson, MC26) or human tumour xenografts (A2780AD, CH1/DOXr, H69/LX) demonstrated that co-administration of XR9051 significantly potentiated the anti-tumour activity of a range of cytotoxic drugs. This modulatory activity was observed following parenteral and oral co-administration of XR9051. In addition, the combination schedules were well-tolerated. Following intravenous administration in mice, XR9051 is rapidly distributed and accumulates in tumours and other tissues. In addition, the compound is well-absorbed after oral administration. These data suggest that XR9051 has the potential for reversing clinical MDR mediated by P-glycoprotien. (+info)
Effects of nicotinic receptor agonists on beta-amyloid beta-sheet formation.
(4/210)
Previously we demonstrated that nicotinic acetylcholine receptor stimulation protects neurons against beta-amyloid (Abeta)-induced cytotoxicity. In the present study, the effects of nicotinic receptor agonists on the beta-sheet formation were investigated using a thioflavin T (ThT)-based fluorescence assay. Nicotine, cytisine (an alpha4beta2 agonist), and 3-(2,4)-dimethoxybenzylidene anabaseine (DMXB, an alpha7 agonist) did not reduce fluorescence intensity when these agents were added to the beta-sheet-formed Abeta. Simultaneous incubation of Abeta with nicotinic agonists also did not cause a reduction in fluorescence intensity. This data suggests that nicotinic receptor agonists do not influence the formation of the beta-sheet structure. (+info)
In vivo effects of new inhibitors of catechol-O-methyl transferase.
(5/210)
1. The effects of two new synthetic compounds showing in vitro catechol-O-methyl transferase (COMT) inhibitor properties were studied in vivo and compared with the effects of nitecapone and Ro-41-0960. 2. QO IA (3-(3-hydroxy-4-methoxy-5-nitrobenzylidene)-2,4-pentanedione), QO IIR ([2-(3,4-dihydroxy-2-nitrophenyl)vinyl]phenyl ketone), nitecapone and Ro-41-0960 (30 mg kg(-1), i.p.) were given to reserpinized rats 1 h before the administration of L-DOPA/carbidopa (LD/CD, 50:50 mg kg(-1), i.p.). Locomotor activity was assessed 1 h later. All the COMT inhibitors (COMTI), with the exception of QO IA, markedly potentiated LD/CD reversal of reserpine-induced akinesia. Similar results were obtained when the COMTI were coadministered with LD/CD. The effect of compound QO IIR was dose-dependent (7.5-30 mg kg(-1), i.p.). 3. The COMTI (30 mg kg(-1), i.p.) potentiated LD/CD reversal of both catalepsy and hypothermia of reserpinized mice. 4. QO IIR, nitecapone and Ro-41-0960 (30 mg kg(-1), i.p.) reduced striatal 3-methyl-DOPA (3-OMD) levels and increased dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) levels. Compound QO IA was devoid of any effect on striatal amine levels. In contrast to the other inhibitors, Ro-41-0961 reduced HVA levels as well. The effect of QO IIR on striatal amine levels was dose-dependent (7.5-60 mg kg(-1), i.p.) 5. These results suggest that the new compound QO IIR is an effective peripherally acting COMT inhibitor in vivo. (+info)
Direct preconditioning of cardiac myocytes via opioid receptors and KATP channels.
(6/210)
Previous studies demonstrated that opioid receptor activation mimics the cardioprotective effect of ischemic preconditioning via KATP channels in the intact heart. However, it is unknown whether this beneficial effect is exerted at the level of the cardiac myocyte or coronary vasculature or is mediated via the sarcolemmal or the mitochondrial KATP channel. Thus, the purpose of the present study was to investigate whether opioid receptor stimulation could mimic the cardioprotective effect of preconditioning in a cardiac myocyte model of simulated ischemia. Cardiac ventricular myocytes cultured from chick embryos 14 days in ovo were used as an in vitro model for ischemic preconditioning. A 5-minute exposure of the myocytes to the opioid receptor agonist morphine protected the myocytes during a subsequent 90-minute period of simulated ischemia, which was manifested as a pronounced reduction in the percentage of cardiac cells killed and the amount of creatine kinase released during ischemia. The preconditioning-like effect of morphine was concentration-dependent, reached a maximal effect at 1 micromol/L, and was reversed by naloxone (0.1 to 10 micromol/L). When KATP channel antagonists, such as glibenclamide, or the mitochondrial selective inhibitor 5-hydroxydecanoic acid were present during preexposure to morphine, they abolished the protective effect of morphine. Thus, cardiac myocytes express functional opioid receptors, and their activation mimics the cardioprotective effect of ischemic preconditioning. These results provide direct evidence that the preconditioning-like effect of morphine in the intact heart can be exerted at the level of cardiac myocytes and is most likely the result of mitochondrial KATP channel activation. (+info)
Communication between multiple drug binding sites on P-glycoprotein.
(7/210)
P-glycoprotein, a member of the ATP-binding cassette transporter family, is able to confer resistance on tumors against a large number of functionally and chemically distinct cytotoxic compounds. Several recent investigations suggest that P-glycoprotein contains multiple drug binding sites rather than a single site of broad substrate specificity. In the present study, radioligand-binding techniques were used to directly characterize drug interaction sites on P-glycoprotein and how these multiple sites interact. The drugs used were classified as either 1) substrates, which are known to be transported by P-glycoprotein (e.g., vinblastine) or 2) modulators, which alter P-glycoprotein function but are not themselves transported by the protein (e.g., XR9576). Drug interactions with P-glycoprotein were either competitive, at a common site, or noncompetitive, and therefore at distinct sites. Based on these data, we can assign a minimum of four drug binding sites on P-glycoprotein. These sites fall into two categories: transport, at which translocation of drug across the membrane can occur, and regulatory sites, which modify P-glycoprotein function. Intriguingly, however, some modulators interact with P-glycoprotein at a transport site rather than a regulatory site. The pharmacological data also demonstrate that both transport and regulatory sites are able to switch between high- and low-affinity conformations. The multiple sites on P-glycoprotein display complex allosteric interactions through which interaction of drug at one site switches other sites between high- or low-affinity conformations. The data are discussed in terms of a model for the mechanism of transport by P-glycoprotein. (+info)
Transport of sugars and amino acids in bacteria. XV. Comparative studies on the effects of various energy poisons on the oxidative and phosphorylating activities and energy coupling reactions for the active transport systems for amino acids in E. coli.
(8/210)
The effects of various energy poisons on oxidation of respiratory substrate, synthesis of cellular ATP, and energy transformation reaction in intact Escherichia coli cells were studied systematically. Various mutants were, therefore, used in which specific functions in the energy-transducing reactions were defective or altered. The energy poisons examined were: sodium azide. DPPA and azidebenzenes which are inhibitors of respiratory-chain phosphorylation, SF6847, and CCCP which are known to be uncouplers, zinc sulfate which is an inhibitor for certain dehydrogenases, and sodium arsenate and sodium fluoride which are inhibitors of glycolytic synthesis of ATP. The preferential inhibitions occurred in the oxidation reactions with certain respiratory substrates by energy poisons used. DPPA inhibited glycerol oxidation much more strongly than succinate oxidation. However, DPPA could inhibit the oxidation of both glycerol 3-phosphate and succinate by membrane fraction strongly while the oxidation of NADH and D-lactate slightly. It inhibited glycerol 3-phosphate dehydrogenase [EC 1.1.2.1] strongly as well as succinate dehydrogenase [EC 1.3.99.1],.but not D-lactate dehydrogenase of membrane fraction. MAB and other azidebenzene derivatives inhibited succinate oxidation preferentially. SF6847 and CCCP inhibited succinate oxidation strongly, while sodium azide inhibited it weakly and these three poisons were less inhibitory for glycerol oxidation. DPPA, sodium azide, SF6847, and CCCP inhibited the synthesis of ATP coupled with respiration but not with glycolysis. Zinc sulfate inhibited the cellular ATP synthesis coupled with either respiration or glycolysis. (+info)