Comparison between sodium-hydrogen ion and lithium-hydrogen ion exchange in human platelets

The membrane-coupled exchange of Li+ and/or Na+ for H+ was studied in human platelets measuring intracellular pH(pHi) with a fluorescent indicator. A Li(+)-containing medium restored the internal pH of preacidified platelets to their prior pHi control value. When Na+ was replaced by Li+, similar steady-state values were attained in this system, although it was transported more slowly. The Km and Vmax were both higher with Na+ than with Li+. Exchanges of Li+ or Na+ with H+ were both blocked by ethylisopropylamiloride (EIPA) achieving half-maximal inhibition at submicromolar concentrations. The efflux Li+ or Na+ and resuspended in a choline medium exhibited an influx of H+ sensitive to EIPA. Thrombin, an activator of Na+/H+ exchange, induced a rapid increase in platelet internal pH in the presence of exogenous Li+. Thus: (1) Li+ can be substituted for Na+ in both the forward and the reverse exchange reaction; (2) Li+, while having a higher affinity than Na+ for the external site of the membrane carrier, has a lower Km and (3) Li+ as well as Na+ exchange are activated by thrombin.

[The effect of pharmaceutic aids on gidazepam biotransformation and bioavailability]

When gidazepam was administered to rats in combination with 4% solutions of Tween 80 or polyvinylpyrrolidone, its bioavailability was higher than its combination with 4% polyethylene glycol 400 solution, as shown by high performance liquid chromatography. Increasing the quantities of these high-molecular compounds in gidazepam solutions was demonstrated to enhance gidazepam dealkylation in the animals after oral administration.

Dopamine DA1 receptor activation reduces experimentally-induced gastritis in rats

1. A selective dopamine DA1 receptor agonist, SKF38393, reduced the severity of experimentally-induced gastritis in rats. 2. This is the first such demonstration with a dopamine DA1 receptor agonist. 3. When considered together with other reported actions of D1/DA1 receptor agonists, these data confirm a significant gastroprotective role for dopamine.

Biotransformation of methylxanthines in mammalian cell lines genetically engineered for expression of single cytochrome P450 isoforms. Allocation of metabolic pathways to isoforms and inhibitory effects of quinolones

V79 Chinese hamster cells genetically engineered for stable expression of single forms of rat cytochromes P450IA1, P450IA2, P450IIB1, human P450IA2, and rat liver epithelial cells expressing murine P450IA2 were used to allocate metabolic pathways of methylxanthines to specific isoforms and to test the suitability of such cell lines for investigations on drug interactions occurring at the cytochrome expressed. The cell lines were exposed to caffeine and/or theophylline and concentrations of metabolites formed in the medium were determined by HPLC. Caffeine was metabolized by human, rat and murine P450IA2, resulting in the formation of four primary demethylated and hydroxylated metabolites. However, there were differences in the relative amounts of the metabolites. The human and the mouse P450IA2 isoforms predominantly mediated 3-demethylation of caffeine. The rat cytochrome P450IA2 mediated both 3-demethylation and 1-demethylation of caffeine to a similar extent. The results support the hypothesis that caffeine plasma clearance is a specific in vivo probe for determining human P450IA2 activity. Addition of the quinolone antibiotic agents pipemidic acid or pefloxacin, both known to inhibit caffeine metabolism in vivo and in human liver microsomes, reduced formation rates of all metabolites of caffeine in cells expressing rat and human P450IA2. Theophylline was mainly metabolized via 8-hydroxylation. All cell lines tested were able to carry out this reaction, with highest activities in cell lines expressing rat or human P450IA2, or rat P450IA1.

Role of GTP-protein and endothelium in contraction induced by ethanol in pig coronary artery

1. We examined the effects of ethanol on the contractility of strips of porcine coronary artery, with and without endothelium, and following permeabilization with alpha-toxin, and of aortic valvular endothelial cells, in situ. Changes in cytosolic Ca2+ concentration ([Ca2+]i) of the coronary artery smooth muscle cells and of the valvular endothelial cells were monitored using front-surface fluorometry of the calcium indicator dye, fura-2. In permeabilized preparations, [Ca2+]i was clamped using 10 mM ethyleneglycol-bis-(beta-aminoethylether)-N,N,N',N'-tetra ace tic acid (EGTA) and 10 microM A23187 (a calcium ionophore). 2. The strips without endothelium were placed in normal physiological salt solution (normal PSS) in the presence of ethanol (100-1000 mM). There were dose-dependent increases in [Ca2+]i and a rapid sustained rise in tension. In Ca(2+)-free PSS, ethanol increased [Ca2+]i and tension, similar to, but much smaller than, findings with normal PSS. 3. For a given change in [Ca2+]i induced by ethanol, the developed tension was greater than that observed during contractions induced by high [K+]o. Thus, the [Ca2+]-tension curve for ethanol was shifted to the left of that for high [K+]o. The [Ca2+]-tension curve for the contraction induced by ethanol in the absence of extracellular Ca2+ was shifted further to the left from that obtained in the presence of [Ca2+]o. 4. The mechanisms involved in this Ca(2+)-sensitizing effect of ethanol were investigated using alpha-toxin-permeabilized coronary medial strips. Ethanol increased the tension development, in a concentration-dependent manner, at a fixed concentration of Ca2+ (pCa = 6.3) in the presence of guanosine-5'-triphosphate (GTP), an effect antagonized by guanosine-5'-O-(beta-thiodiphosphate) (GDP beta S), a non-hydrolysable GDP analogue. 5. With intact endothelium, the ethanol-induced tension development was markedly reduced, although inhibition in the increase in [Ca2+]i was slight. The [Ca2+]-tension relationship of this contraction overlapped with that obtained with high [K+]o-induced contraction and was shifted to the right from that obtained in the absence of the endothelium. This endothelium-dependent reduction of [Ca2+]i and tension induced by ethanol was inhibited when the strips were exposed to NG-monomethyl-L-arginine (L-NMMA). 6. Ethanol induced a gradual and sustained increase in [Ca2+]i in normal PSS, and a transient, concentration-dependent increase in [Ca2+]i in Ca(2+)-free PSS in porcine aortic valvular endothelial cells in situ.(ABSTRACT TRUNCATED AT 400 WORDS)

Partial inhibition by epithelium of tracheal smooth muscle relaxation induced by the potassium channel activator, BRL 38227

1. A method is described whereby either the serosal (Out) or epithelial (In) sides of rat isolated tracheae were selectively perfused. Perfusion with BRL 38227 (10(-8)-5 x 10(-6) M; In/Out) of preparations with intact epithelium (+ EP) precontracted with carbachol (10(-6) M; Out/In) produced complete relaxation. Perfusion with aminophylline (10(-5)-10(-3) M; In) of + EP preparations precontracted with carbachol (10(-6) M; Out) also produced complete relaxation. 2. In preparations precontracted with carbachol (10(-6) M) epithelium removal (- EP) increased the sensitivity to the relaxant effect of BRL 38227 (In), but not BRL 38227 (Out) [- log EC50, + EP/- EP; carbachol (In), BRL 38227 (Out): 6.76 +/- 0.11 vs 6.67 +/- 0.15; carbachol (Out), BRL 38227 (In): 5.93 +/- 0.06 vs 6.25 +/- 0.07]. Removal of the epithelium increased also the sensitivity to BRL 38227 (In) of preparations precontracted with a lower concentration (5 x 10(-7) M) of carbachol (Out). [- log EC50, + EP/- EP, carbachol (Out), BRL 38227 (In): 6.19 +/- 0.14 vs 6.58 +/- 0.17]. 3. Removal of the epithelium did not affect the sensitivity to BRL 38227 (In) of preparations precontracted with a higher concentration (5 x 10(-6) M) of carbachol (Out). 4. In both + EP and - EP preparations precontracted with carbachol (10(-6) M; Out), BRL 38227 (In) had a more potent relaxant effect than aminophylline (In) (EC50, BRL 38227 vs aminophylline, + EP/- EP: 5.93 +/- 0.06 vs 3.66 +/- 0.11/6.25 +/- 0.07 vs 3.77 +/- 0.11). 5. In preparations precontracted with carbachol (10-6 M; Out), removal of the epithelium did not affect the sensitivity to aminophylline (In) but increased the degree of precontraction (Tmax) following epithelial but not serosal stimulation with carbachol.6. We conclude that BRL 38227, a K+ channel activator, is a potent relaxant of rat tracheal smooth muscle precontracted with carbachol, and that the effect can be partially inhibited by the presence of an intact tracheal epithelium, whereas the relaxant effect of aminophylline is not.

Influence of long-term ethanol treatment on rat liver biotransformation enzymes

The influence of rats' long-term ethanol consumption on liver enzymes that could be involved in the biotransformation of benzo(a)pyrene [B(a)P] has been studied. Male and female Wistar rats received an increasing amount of ethanol in their drinking water up to 15% (w/v) in three weeks. The ethanol content was kept at a concentration of 15% for another three weeks. One group of rats also received B(a)P in the last week of the ethanol treatment. Livers were isolated, and microsomal and cytosolic fractions were prepared. In every enzyme measurement sex differences were observed. Long-term ethanol consumption induced P450, especially aniline 4-hydroxylase (P4502E1). However, testosterone 6 beta-hydroxylase (P4503A2 and P4502C13) in males and testosterone 12 beta-hydroxylase in females were decreased. The phase 2 enzymes glutathione S-transferase (subunit 1) and epoxide hydrolase were also decreased in their activity. Our results support the hypothesis that the effect of long-term ethanol consumption on B(a)P biotransformation as found in in vivo and in vitro studies, consisting of lowered formation of phenolic and diolic metabolites, is the result of a decrease of constitutive P450 isoenzymes.

Interaction of caffeine with acetaminophen. 1. Correlation of the effect of caffeine on acetaminophen hepatotoxicity and acetaminophen bioactivation following treatment of mice with various cytochrome P450 inducing agents

The combination of caffeine with acetaminophen (APAP) is used widely in the treatment of headache. The effects of caffeine on APAP-induced hepatotoxicity and APAP bioactivation by liver microsomes from uninduced mice and from mice pretreated with various agents that induce cytochrome P450 were studied. When 1 mM caffeine was included, the rate of glutathione-APAP conjugate (GS-APAP) formation was increased significantly by 33 and 39% in microsomes from phenobarbital (PB)- and dexamethasone (DEX)-treated mice, respectively, whereas this parameter was decreased 39 and 12% by caffeine in microsomes from beta-naphthoflavone (beta NF)- and acetone-treated mice, respectively. A 5 mM concentration of caffeine increased GS-APAP formation by 47, 107 and 117% in microsomes from control, PB-, and DEX-treated mice, respectively, and decreased it 39 and 25% in microsomes from beta NF- and acetone-treated mice, respectively. Caffeine was a competitive inhibitor of APAP bioactivation in microsomes from beta NF- and acetone-treated mice. While caffeine increased APAP bioactivation in microsomes from uninduced, PB-, and DEX-treated mice, the apparent Km values for APAP were increased by caffeine, indicating that this enhancement was not due to a direct effect of caffeine on APAP binding to cytochrome P450 but may be due to an effect of caffeine on the substrate-enzyme complex. The variable effect of caffeine on APAP hepatotoxicity correlated with the effect of caffeine on APAP bioactivation by liver microsomes, regardless of pretreatment. Lack of correlation of aminopyrine N-demethylase, but good correlation of erythromycin N-demethylase activity with the extent of caffeine enhancement of APAP bioactivation following PB or DEX treatment suggests that a murine P450 subfamily similar to the rat P450 3A subfamily may be the candidate in mediating the stimulatory effect of caffeine on APAP bioactivation and APAP-induced hepatotoxicity.

Contraction of the rat isolated spleen mediated by adenosine A1 receptor activation

1. A series of adenosine receptor agonists of varying degrees of selectivity induced concentration-dependent contraction of the rat isolated spleen. With the exception of the response to the selective A2A receptor agonist, 2-[p-(2-carboxyethyl)phenylethylamino]-5'-N- ethylcarboxamidoadenosine (CGS 21680), responses to each ligand were blocked surmountably and to a broadly similar extent by 8-p-sulphophenyltheophylline (10(-5) M). 2. There was a significant correlation between the pEC50 values obtained on the spleen and the binding affinities (pKD; measured with [3H]-NECA) for the A1 receptor of pig striatum (r = 0.98, P < 0.001) but not the A2A receptor (r = 0.14, NS). 3. The antagonist potencies of 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) and 9-chloro-2-furyl [1,2,3]triazolo[1,5-C]quinazoline-5-amine (CGS 15943) were measured against the prototype selective A1 receptor agonist, R-N6-phenylisopropyladenosine (R-PIA). The resulting pKB values of 8.67 and 7.70, respectively are consistent with the A1 receptor subtype mediating splenic contraction. 4. The response to R-PIA was unaltered in the presence of a concentration (10(-7) M) of CGS 21680 which is 6 fold its KD concentration at the A2A binding site in pig striatum but below the threshold for causing contraction per se; thus, A2A receptors inhibitory to contraction appear to be absent. 5. The response to R-PIA was resistant to blockade by prazosin (10(-7) M) and by nifedipine (10(-6) M) but partially blocked by indomethacin (10(-6) M). 6. The results show that the rat isolated spleen responds to adenosine receptor agonists with contraction. Both the relative potencies of agonists and the effects of antagonists indicate mediation by the A1 receptor subtype. alpha1-Adrenoceptor activation is not involved in contraction but a role for products of cyclo-oxygenase and calcium from a source not dependent on entry through L-channels is implicated.

An investigation into the formation of stable, protein-reactive and cytotoxic metabolites from tacrine in vitro. Studies with human and rat liver microsomes

Tacrine (1,2,3,4-tetrahydro-9-aminoacridine hydrochloride; THA) is known to undergo extensive oxidative metabolism to a variety of mono- and dihydroxylated metabolites in animals and humans. The potential for tacrine to undergo metabolism to stable, protein-reactive and cytotoxic metabolites has been investigated in incubations with human and rat liver microsomes. Using lymphocytes as sensitive markers to quantify cytotoxicity, THA (50 microM) underwent NADPH-dependent bioactivation to a cytotoxic metabolite(s). NADPH-dependent cytotoxicity in the presence of rat and human microsomes was 9.8 +/- 3.1% (P < 0.05 cf. -NADPH control) and 6.2 +/- 2.0% (P < 0.05 cf. -NADPH control), respectively. Stable and protein-reactive metabolites were also formed in microsomes from both species. These accounted for 28.2 +/- 12.7% and 1.22 +/- 0.79% of incubated radioactivity in human microsomes and 6.4 +/- 2.2% and 0.4 +/- 0.1% of incubated radioactivity in rat microsomes. In microsomes pooled from six human livers the NADPH-dependent cytotoxicity was 9.4 +/- 1.1%. Formation of stable and protein-reactive metabolites accounted for 29.2 +/- 2.3% and 1.2 +/- 1.0% of incubated radioactivity. Reduced glutathione (500 microM) completely blocked NADPH-dependent cytotoxicity and inhibited protein-reactive metabolite formation by 60% (P < 0.05). Ascorbic acid (500 microM) inhibited the generation of cytotoxic and protein-reactive metabolites by 75% (P < 0.05) and 35% (P < 0.05), respectively. Cyclohexene oxide was without effect. Human serum albumin was found to protect the lymphocytes against toxicity. In microsomes prepared from the livers of four donors known to have been smokers there were no significant differences in the generation of metabolites from THA compared with microsomes prepared from livers of non-smokers. Enoxacin, a specific inhibitor of cytochrome P450 1A2 significantly inhibited all routes of THA metabolism. We have therefore demonstrated that THA may be oxidatively metabolized to stable, protein-reactive and cytotoxic metabolites in human and rat liver microsomes. A number of inhibitors may affect these process, whilst inhibition by enoxacin indicates a role for cytochrome P450 1A2 in THA metabolism.

Leukotriene C4 modulation of muscarinic K+ current activation in bullfrog atrial myocytes

The effects of leukotriene C4 (LTC4) on activation of muscarinic acetylcholine receptor (mAChR)-stimulated, inwardly rectifying K+ current (IK[ACh]) were examined in single bullfrog atrial myocytes using the whole-cell patch clamp technique. LTC4 produced a reversible, concentration-dependent increase in steady-state, guanosine-gamma-thiotriphosphate (GTP gamma S)-activated IK[ACh], with a K0.5 of 3.1 microM. LTC4 also increased the rate of GTP gamma S-mediated IK[ACh] activation, both in the absence and presence of 1 nM ACh, with comparable K0.5 values of 4.7 microM under basal conditions and 4.9 microM in the presence of 1 nM ACh. LTC4 did not alter the relative affinities of the G protein, Gk, for GTP gamma S and GTP. We hypothesize that all of the effects of LTC4 on the kinetics of Gk-mediated IK[ACh] activation are produced at a common site with a K0.5 of 3-5 microM. The effects of LTC4 on IK[ACh] activation are fully reversible in the presence of GTP gamma S. Under physiological conditions (i.e., intracellular GTP), 10 microM LTC4 increased the ACh-activated peak IK[ACh]. Inhibitors of cellular LTC4 production, including 5,8,11,14-eicosatetraynoic acid, baicalein, cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate, and alpha-pentyl-4-(2-quinolinylmethoxy)-benzene methanol, greatly attenuated ACh-dependent IK[ACh] activation, preventing activation of peak, and producing a lower steady-state IK[ACh] (when compared with the control response in the same cell). Addition of exogenous LTC4 was able to overcome the effects of LTC4 synthesis inhibitors, restoring both the peak and steady-state IK[ACh] responses. Although the mechanism of LTC4-mediated modulation of IK[ACh] activation is not known, our results suggest that endogenously produced lipoxygenase metabolites of arachidonic acid, specifically LTC4, are involved in the physiological process of IK[ACh] activation.

[The detection and assessment of the total mutagenic action of the aerosol portion of the chemical atmospheric contaminants from industrially developed cities of Ukraine]

The studies on assessment of total mutagenic activity of chemical pollutants of atmospheric air in some Ukrainian towns with the mainly developed metallurgical industry were carried out using the Ames test with metabolic activation. It was established that the air samples taken in five towns during 12 months had mutagenicity to certain extent, both with and without metabolic activation. The degree of mutagenic effects' pronouncement among the towns tested was distributed as follows: Mariupol' > Zaporozhye > Donetsk > Krivoĭ Rog > Makeyevka.

Acrylamide as an inducer of metabolic activation system (S9) in rats

The S9 fraction was prepared from rats i.p. injected with a single dose of 75 mg/kg acrylamide. The efficiency of the acrylamide induction procedure was verified on Salmonella mutagenicity testing (TA98 and TA100) using a number of known mutagens. These mutagens are aflatoxin B1, benzo[alpha]pyrene, 2-acetylaminofluorene and sodium azide. The activity of the mutagen is measured in terms of histidine revertant numbers which were found to be almost proportional to the concentration of acrylamide-induced S9. The maximum activation of the mutagens (except sodium azide) was recorded using around 50 microliters of S9 per plate. The efficiency of our prepared S9 fraction as a metabolic activator for some known mutagens is comparable to that of standard S9. On the basis of our results, acrylamide-induced S9 demonstrated considerable increase in the activation of the tested compounds. Accordingly, acrylamide could be used as an additional procedure for the induction of rat hepatic enzymes (S9).

Glutamate metabotropic receptor activation in neonatal rat cerebral cortex by sulphur-containing excitatory amino acids

The sulphur-containing acidic amino acids (SAAs) display neuroexcitatory actions similar to those of L-glutamate and are widely regarded as bona fide transmitter candidates. In this study, L-cysteine sulphinic acid, L-cysteic acid, DL-homocysteic acid and L-homocysteine sulphinic acid were investigated for their ability to stimulate phosphatidylinositol hydrolysis in rat pup cerebrocortical slices and compared with L-glutamate and the selective agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid ((1S,3R)-ACPD). Each of the SAAs possessed agonist activity at metabotropic glutamate receptors (mGluRs) and, although they exhibited lower efficacy than L-glutamate, they were more potent (EC50s of 401-487 microM compared with 791 microM for L-glutamate). These data are consistent with the possibility that SAAs may have a physiological role as endogenous activators of metabotropic (and presumably ionotropic) excitatory amino acid receptors.

Diclofenac covalent protein binding is dependent on acyl glucuronide formation and is inversely related to P450-mediated acute cell injury in cultured rat hepatocytes

In a few patients diclofenac produces mild increases in serum aminotransferase activity and in rare cases may be associated with the occurrence of fulminant hepatic necrosis. Both direct toxic effects of a diclofenac metabolite and hypersensitivity reactions have been suggested as possible molecular mechanisms of liver injury. We investigated the pathways of bioactivation and cytotoxicity of diclofenac, which undergoes both aromatic hydroxylation and acyl glucuronidation, in short-term cultured rat hepatocytes. LDH release was first evident after 4 hr of incubation with diclofenac (> 500 microM). In addition, time- and concentration-dependent covalent binding of [14C]diclofenac to hepatocellular proteins occurred, indicating the presence of a reactive intermediate. To specifically explore the role of the acyl glucuronidation pathway in the induction of cytotoxicity and covalent drug-protein adducts, we used two inhibitors of the UDP-glucuronosyltransferase (UDPGT), borneol and 7,7,7-triphenylheptyl-UDP. LDH release was markedly increased in the presence of either UDPGT inhibitor. Alternatively, covalent binding to hepatocellular proteins was greatly reduced when the glucuronide formation was selectively blocked. Furthermore, in vitro inhibition of P450-dependent oxidative biotransformation with the selective inhibitor of the CYP2C subfamily sulfaphenazole or with cimetidine markedly reduced the extent of cytotoxicity, whereas the degree of covalent adduct formation remained unchanged. Similarly, pretreatment of the rats with phenobarbital (80 mg/kg/day for 4 days) delayed the onset and reduced the extent of diclofenac-induced LDH release. Collectively, these results indicate that the formation of a toxic diclofenac metabolite(s) catalyzed by P4502C in hepatocytes leads to acute lethal cell injury, whereas diclofenac acyl glucuronide formation is associated with covalent binding of a reactive metabolite to hepatocellular proteins that is not related to the acute cytotoxicity. The protein adduct formation and its modulation by UDPGT may, however, be toxicologically relevant for the expression of diclofenac hepatitis.

G protein beta gamma-subunits inhibit purified adenylate cyclase independent of the activation by Ca2+ and calmodulin

Adenylate cyclase purified by affinity chromatography was activated about 2.5-fold in a Ca(2+)- and calmodulin-dependent fashion. G protein beta gamma-subunits, an inhibitor in the receptor-mediated inhibition of adenylate cyclase, inhibited the purified cyclase by more than 80%. The extent of beta gamma-induced inhibition was not affected by the activation with Ca2+ and calmodulin. Moreover, the prior addition of the beta gamma-subunits to the cyclase did not prevent the subsequent activation of the enzyme by Ca2+ and calmodulin. We conclude that the beta gamma-subunits inhibit adenylate cyclase activity in a calmodulin-independent mode.

Requirement for transglutaminase in the activation of latent transforming growth factor-beta in bovine endothelial cells

A hitherto unknown function for transglutaminase (TGase; R-glutaminyl-peptide: amine gamma-glutamyltransferase, EC 2.3.2.13) was found in the conversion of latent transforming growth factor-beta (LTGF-beta) to active TGF-beta by bovine aortic endothelial cells (BAECs). The cell-associated, plasmin-mediated activation of LTGF-beta to TGF-beta induced either by treatment of BAECs with retinoids or by cocultures of BAECs and bovine smooth muscle cells (BSMCs) was blocked by seven different inhibitors of TGase as well as a neutralizing antibody to bovine endothelial cell type II TGase. Control experiments indicated that TGase inhibitors and/or a neutralizing antibody to TGase did not interfere with the direct action of TGF-beta, the release of LTGF-beta from cells, or the activation of LTGF-beta by plasmin or by transient acidification. After treatment with retinoids, BAECs expressed increased levels of TGase coordinate with the generation of TGF-beta, whereas BSMCs and bovine embryonic skin fibroblasts, which did not activate LTGF-beta after treatment with retinoids, did not. Furthermore, both TGase inhibitors and a neutralizing antibody to TGase potentiated the effect of retinol in enhancing plasminogen activator (PA) levels in cultures of BAECs by suppressing the TGF-beta-mediated enhancement of PA inhibitor-1 (PAI-1) expression. These results indicate that type II TGase is a component required for cell surface, plasmin-mediated LTGF-beta activation process and that increased expression of TGase accompanies retinoid-induced activation of LTGF-beta.

Vitamin A potentiation of carbon tetrachloride hepatotoxicity: enhanced lipid peroxidation without enhanced biotransformation

To better understand the mechanism by which vitamin A (VA, retinol) potentiates the hepatotoxicity of carbon tetrachloride, its effect on metabolism and covalent binding of CCl4 as well as its effect on lipid peroxidation was determined. 14CCl4 (0.15 ml/kg, 21.4 microCi/mmol) was administered to male SD rats that had been treated with vitamin A (250,000 IU/kg/day for 1 week) or vehicle. Vitamin A pretreatment did not increase the 24-hr biotransformation of 14CCl4 to 14CO2, to exhaled volatile organics, or to metabolites excreted in the urine or feces. Furthermore, there was no dramatic effect of vitamin A pretreatment on the covalent binding of 14CCl4 equivalents to hepatic lipids and proteins at early time points (1/2-4 hr) after administration of 14CCl4. The microsomal concentration of cytochrome P450 was unchanged by vitamin A treatment. There was a dramatic increase (6-8x) in the amount of ethane exhaled in those rats treated with vitamin A and then administered CCl4 compared to that of those administered CCl4 without pretreatment. The enhanced lipid peroxidation as evidenced by the increased exhalation of ethane was not the result of vitamin A-induced decreases in hepatic glutathione or vitamin E. These data indicate that the potentiation of CCl4 hepatotoxicity by vitamin A pretreatment is associated with an enhancement of lipid peroxidation that is independent of changes in CCl4 biotransformation or the hepatic concentration of two important hepatoprotective agents.

The metabolism and activation of 15,16-dihydrocyclopenta[a]phenanthren-17-one by cytochrome P-450 proteins

The in vitro metabolism and activation to mutagens of 15,16-dihydrocyclopenta[a]phenanthren-17-one (CPP-17-one) were investigated using hepatic preparations from rats pretreated with prototype inducers of the cytochrome P-450-dependent mixed-function oxidases. Aroclor 1254-induced microsomes were the most effective metabolisers of this compound, the major metabolites being oxidation products of the bay region A ring. To a lesser extent hydroxylation of the non-aromatic D ring occurred, the products being the 15- and 16-hydroxyderivatives. Oxidation of the A ring was also achieved with microsomes from benzo[a]pyrene-treated rats but not with those from rats treated with clofibrate, phenobarbitone, isoniazid, dexamethasone and CPP-17-one itself, where the metabolites were primarily the oxidation products of the D ring. When CPP-17-one was used as a promutagen in the Ames test, only microsomes from Aroclor 1254-treated rats could elicit a positive mutagenic response. When 3,4-dihydrodihydroxy-CPP-17-one, the precursor of the ultimate mutagen, was used as the promutagen, a positive response was observed with microsomes from Aroclor 1254- and benzo[a]pyrene-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Pertussis toxin inhibition of alpha 1-adrenergic or vasopressin-induced Ca2+ fluxes in rat liver. Selective inhibition of the alpha 1-adrenergic receptor-coupled metabolic activation

Pretreatment with pertussis toxin produced a impairment of the response to the alpha-adrenergic agonist phenylephrine in perfused isolated rat livers. The sustained phases of phenylephrine-induced increases in respiration, glucose mobilization, gluconeogenesis, vascular resistance, and efflux of H+ and Ca2+ were inhibited to variable degrees in livers from pertussis toxin-treated animals. The susceptibility of such a diversity of receptor-mediated effects suggests that a common, most likely early step(s) of the alpha 1-receptor-coupled signaling pathway may be regulated by a pertussis toxin-sensitive Gi protein(s) that appears to be involved in the control of the rate of these processes. The most significant effect of pertussis toxin has been to almost entirely prevent the phenylephrine-induced sustained release of Ca2+. Pertussis toxin also inhibited the vasopressin-mediated influx of Ca2+. These findings indicate that G proteins associated with receptor-operated calcium channels are a site of interaction of pertussis toxin. The following observations support the conclusion that pertussis toxin per se does not perturb the hepatic metabolism. Its effects are specifically linked to functional responses mediated by alpha 1-type adrenergic receptors: 1) polypeptide receptor-mediated metabolic effects, as those induced by vasopressin, were not affected by pertussis toxin; 2) non-receptor-mediated effects, such as fatty acid-induced stimulation of respiration and gluconeogenesis, were not impaired by pertussis toxin; and 3) neither the hepatic responses to alpha 2-(clonidine) nor to beta-(isoproterenol) adrenergic receptor agonists were altered in livers from pertussis toxin-treated rats. The differential effects of pertussis toxin in the metabolic actions of phenylephrine and vasopressin, in spite of apparently similar effects in perturbing their actions on Ca2+ fluxes, suggest that pertussis toxin-sensitive alpha 1-receptor-associated G protein(s) other than those controlling Ca2+ channels, were also specifically affected in the alpha 1-agonist-signaling pathway. The finding that increasing concentrations of phenylephrine were capable of overcoming these pertussis toxin actions indicates that alpha 1-adrenoreceptors' ligand affinity is controlled by Gi proteins.

Contrasting effects of 1,1,1-trichloroethane on [14C]vinyl chloride metabolism and activation in hepatic microsomes from phenobarbital- and isoniazid-treated rats

The interaction of 1,1,1-trichloroethane (TCE), a widely used chlorocarbon solvent, on the metabolism and activation of [14C]-vinyl chloride in rat hepatic microsomes was investigated to determine the effects of combined exposures to these compounds. In microsomes from phenobarbital (PB)-treated rats, TCE increased vinyl chloride-protein binding and vinyl chloride aqueous metabolite formation over twofold when vinyl chloride 0.32% (v/v) and TCE (0.65%) are incubated together. In contrast, under similar incubation conditions, TCE inhibited vinyl chloride metabolism and protein binding up to 45% in microsomes from isoniazid-treated animals. TCE also inhibited vinyl chloride metabolism and binding in microsomes from untreated rats, but to a lesser degree. Like the effect of TCE on vinyl chloride-protein binding, TCE increased vinyl chloride binding to DNA approximately 130% in microsomes from PB-treated rats, yet inhibited vinyl chloride-DNA binding in microsomes from isoniazid-treated and untreated animals. Consistent with TCE effects on vinyl chloride binding and aqueous metabolite production, TCE further increased cytochrome P450 loss due to vinyl chloride metabolism in microsomes from PB-treated rats, but was inhibitory to cytochrome P450 loss due to vinyl chloride metabolism in microsomes from isoniazid-treated and untreated rats. These data demonstrate that the relatively metabolically inert solvent, 1,1,1-trichloroethane, can directly increase vinyl chloride metabolism and activation catalyzed by the phenobarbital-inducible isozymes, but is inhibitory toward vinyl chloride metabolism catalyzed by the isoniazid-inducible CYP2E1.

Comparison of liposome fusion and electroporation for the intracellular delivery of nonpermeant molecules to adherent cultured cells

Intracellular delivery of nonpermeant molecules to cultured cells in situ can be problematic. This work is a comparison between two methods of accomplishing this delivery; liposome-mediated delivery and electroporation. The final goal was to examine the effects of the glutathione S-transferase (GST) inhibitor Basilen Blue (BB) on glyceryl trinitrate biotransformation in porcine kidney epithelial (PK1) cells after intracellular delivery. Initial evaluation used the fluorescent markers carboxyfluorescein and lucifer yellow (LY). This was followed by biochemical analysis of glyceryl trinitrate biotransformation. Liposome-mediated delivery proved ineffective in spite of variations in the lipid composition of the liposomes and the use of an agglutinin and a fusogen. In contrast, electroporation was a very effective method for intracellular delivery of both lucifer yellow and basilen blue to the PK1 cells. The results show that in cells where Basilen Blue was introduced, there was a decrease in both the glyceryl trinitrate (GTN) biotransformation and ratio of glyceryl-1,2-dinitrate (1,2-GDN) to glyceryl-1,3-dinitrate (1,3-GDN) formed. The technique of in situ electroporation shows great promise for the assessment of a variety of nonpermeant molecules of pharmacological interest.

Importance of enzyme and solvent physical properties for the biocompatibility relationship of alpha-amino acid ester hydrolase

The enzyme alpha-amino acid ester hydrolase was used with a variety of organic solvents to further explore the relationships between biocompatibility and solvent physical properties. Biocompatibility was shown to be system-specific; that is, the infection point of the characteristic log P trend (approximately 1.5) was specific to the enzyme employed, while the biocompatibility of solvents that were exceptions to the trend was dependent on the extent of agitation. In addition, phase toxic solvents all possessed a high interfacial tension with water. Finally, while the source of the enzyme may be significant, the extent of purification does not appear to be a factor in biocompatibility.