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At least 919 records · Page 51Linked to original sources
PubMed1986

Rat cytosolic epoxide hydrolase.

Rat liver microsomal and cytosolic epoxide hydrolase may be distinguished through differences in substrate specificity: styrene 7,8-oxide is preferentially hydrolyzed by the microsomal form, while trans-stilbene oxide is the preferred substrate for cytosolic epoxide hydrolase. Large interindividual differences in the specific activity of Sprague-Dawley (outbred strain) liver cytosolic epoxide hydrolase were observed, varying from 2 to 77 pmol/min X mg protein. Interindividual variations were much lower for microsomal epoxide hydrolase. The specific activity of Fischer F-344 (inbred strain) liver cytosolic epoxide hydrolase varied only by a factor of 2. The specific activity of cytosolic epoxide hydrolase using trans-stilbene oxide as the substrate was highest in kidney and heart, followed by liver, brain, lung, testis, and spleen. For microsomal epoxide hydrolase, the specific activity was much lower in extrahepatic tissues than in liver. None of the commonly used inducers of xenobiotic metabolizing enzymes caused significant changes in rat liver cytosolic epoxide hydrolase. However, peroxisome proliferating drugs were found to drastically increase cytosolic epoxide hydrolase activity. Treatment for one week with a diet containing clofibrate (0.25%), tiadenol (0.5%) or acetylsalicylic acid (1%) caused a 8, 13 and 5 fold increase in cytosolic epoxide hydrolase activity respectively in the liver which parallelled the induction of peroxisomal beta-oxidation activity (13, 19 and 5 fold, respectively).

Animals↗
PubMed1980

Dose-response relationship of rat aryl hydrocarbon hydroxylase and epoxide hydratase induction.

This paper summarizes our recent results supporting the hypothesis that different regulation mechanisms are involved in the control of AHH and EH activity and that the AHH induction in the extrahepatic tissues might also be affected by liver specific inducers. In the rat, lung and kidney AHH is highly sensitive to the inducers present in cigarette smoke and cigarette smoke condensate, the EH activity not being affected by the same agents. Phenobarbital is also able to potentiate the inducing action of low doses of benzo(a)pyrene on the lung AHH activity. In primary rat liver cells in culture, AHH and EH can be selectively induced. Low doses of benz(a)anthracene preferentially enhance the AHH activity while trans-stilbene oxide and various antioxidants modify only the EH activity. Phenobarbital, which also induces the AHH activity in cell culture, produces a more than additive effect when added to the culture medium in a mixture with benz(a)anthracene. Trans-stilbene oxide prevents the AHH induction by phenobarbital and not by benz(a)anthracene. Our results suggest that, in addition to its own induction capacity, phenobarbital is also able to potentiate the action of chemicals belonging to a different class of inducers.

Animals↗
PubMed1988

Cytosolic epoxide hydrolase in humans: development and tissue distribution.

Cytosolic epoxide hydrolase activity was measured towards trans-stilbene oxide in 41 human adult livers, in 40 fetal livers, in 17 placentas and in fetal and adult lungs, kidneys and gut. The cytosolic epoxide hydrolase activity was measurable in all specimens investigated. The rate of formation of trans-stilbene glycol (pmol/min per mg protein, mean +/- SD) was 55.2 +/- 89.6 (fetal liver). 303.2 +/- 73.2 (adult liver) and 18.8 +/- 13.1 (placenta) In the fetal extrahepatic tissues, the cytosolic epoxide hydrolase activity was 70.0 +/- 9.4 (adrenals), 47.6 +/- 7.2 (gut), 69.4 +/- 22.5 (kidneys) and 43.2 +/- 19.2 (lungs) pmol/min per mg protein, whereas in the adult tissues it was 131.2 +/- 63.1 (kidneys), 27.8 +/- 20.3 (intestine), 8.5 +/- 2.8 (lungs) and 7.2 +/- 4.2 (urinary bladder) pmol/min per mg protein.

Adult↗
PubMed1990

Madin-Darby canine kidney cells. II. Aldosterone stimulates Na+/H+ and Cl-/HCO3- exchange.

Experiments in dome epithelium of Madin-Darby canine kidney (MDCK) cells were performed to elucidate aldosterone action on acid-base transport. By means of pH-sensitive microelectrodes the pH of the dome fluid was measured while the apical plasma membrane was superfused. In the absence of HCO3- the dome fluid (facing the basolateral cell membrane) alkalinized in response to 10(-7) mol/l aldosterone. Amiloride (10(-3) mol/l) inhibited dome formation and pH recovery of the dome fluid from an extracellular acid load. In the presence of HCO3- dome fluid acidified in response to aldosterone. The stilbene derivative diisothiocyanate-stilbene-2,2'-disulphonic acid (DIDS) or removal of Cl- from the apical perfusate inhibited this dome acidification. In aldosterone-depleted MDCK monolayers HCO3- was actively accumulated in the dome fluid in contrast to aldosterone-supplemented cells. The results indicate that aldosterone stimulates both amiloride-sensitive Na+/H+ exchange and DIDS-sensitive Cl-/HCO3- exchange in the apical cell membrane of MDCK cells. In the absence of aldosterone the HCO3- extrusion process is localized in the basolateral membrane in series with apical Na+/H+ exchange, while in the presence of aldosterone Cl-/HCO3- is mainly localized in the apical membrane in parallel with Na+/H+ exchange. Cl- exits the cell through apical Cl- channels and is absorbed via the paracellular route.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1990

Characteristics of Cl(-)-dependent L-[35S]cysteic acid transport into rat brain synaptic membrane vesicles.

Uptake of L-[35S]cysteic acid (L-CA) in rat synaptic membrane vesicles was investigated. Preincubation with either 10 mM L-glutamic acid (L-Glu), 25 mM L-CA, 10 mM DL-homocysteic acid, or 25 mM DL-2-amino-4-phosphonobutyrate on membrane vesicles enhanced L-[35S]CA and L-[3H]Glu uptake. Na+ (5 mM) and omission of Cl- from the assay medium decreased L-[35S]CA uptake into both 10 mM L-Glu-loaded and non-loaded membrane vesicles. The anion transport blockers, 4-acetamide-4'-isothiocyano-2,2'-disulfonic acid stilbene (SITS) and 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS), inhibited L-[35S]CA uptake in a dose-dependent manner. The maximal uptake rate for L-[35S]CA was decreased by 50 microM SITS, while the apparent Km value of L-CA was not changed. SITS increased the EC50 value of Cl- for L-[35S]CA uptake from 5 mM to 10 mM with reduction of the maximal effect. These results suggested that L-[35S]CA uptake into synaptic membrane vesicles was mediated by a SITS-sensitive hetero-exchange transport with non-labeled substrates.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1991

Fluorescence emission spectra of plant leaves and plant constituents.

The UV-B radiation (e.g. 337 nm) induced blue fluorescence (BF) and red chlorophyll fluorescence spectra (RF) of green leaves from plants with different leaf structure were determined and the possible nature and candidates of the blue fluorescence emission investigated. The blue fluorescence BF is characterized by a main maximum in the 450 nm region and in most cases by a second maximum/shoulder in the 530 nm region. The latter has been termed green fluorescence GF. The red chlorophyll fluorescence RF, in turn, exhibits two maxima in the 690 and 730 nm region. In general, the intensity of BF, GF and RF emission is significantly higher in the lower than the upper leaf side. The ratio of BF to RF emission (F450/F690) seems to vary from plant species to plant species. BF and GF emission spectra appear to be a mixed signal composed of the fluorescence emission of several substances of the plant vacuole and cell wall, which may primarily arise in the epidermis. Leaves with removed epidermis and chlorophyll-free leaves, however, still exhibit a BF and GF emission. Candidates for the blue fluorescence emission (lambda max near 450 nm) are phenolic substances such as chlorogenic acid, caffeic acid, coumarins (aesculetin, scopoletin), stilbenes (t-stilbene, rhaponticin), the spectra of which are shown. GF emission (lambda max near 530 nm) seems to be caused by substances like the alkaloid berberine and quercetin. Riboflavine, NADPH and phyllohydroquinone K1 seem to contribute little to the BF and GF emission as compared to the other plant compounds. Purified natural beta-carotene does not exhibit any blue fluorescence.

Chloroplasts↗
PubMed1986

Modes of Cl- transport across the mucosal and serosal membranes of urodele intestinal cells.

The characteristics of Cl- movement across luminal and basolateral membranes of Amphiuma intestinal absorptive cells were studied using Cl(-)-sensitive microelectrodes and tracer 36Cl techniques. Intracellular Cl- activity (aiCl) was unchanged when serosal Cl- was replaced; when luminal Cl- was replaced cell Cl- was rapidly lost. Accordingly, the steady state aiCl could be varied by changing the luminal [Cl]. As luminal [Cl] was raised from 1 to 86 mM, aiCl rose in a linear manner, the mucosal membrane hyperpolarized, and the transepithelial voltage became serosa negative. In contrast, the rate of Cl- transport from the cell into the serosal medium, measured as the SITS-inhibitable portion of the Cl- absorptive flux, attained a maximum when aiCl reached an apparent value of 17 mM, indicating the presence of a saturable, serosal transport step. The stilbene-insensitive absorptive flux was linear with luminal [Cl], suggestive of a paracellular route of movement. Intracellular aCl was near electrochemical equilibrium at all but the lowest values of luminal [Cl] after interference produced by other anions was taken into account. aiCl was unaffected by Na replacement, removal of medium K, or elevation of medium HCO-3. Mucosae labeled with 36Cl lost isotope into both luminal and serosal media at the same rate and from compartments of equal capacity. Lowering luminal [Cl] or addition of theophylline enhanced luminal Cl- efflux. It is concluded that a conductive Cl leak pathway is present in the luminal membrane. Serosal transfer is by a saturable, stilbene-inhibitable pathway. Luminal Cl- entry appears to be passive, but an electrogenic uptake cannot be discounted.

Animals↗
PubMed1989

Interaction among anion, cation and glucose transport proteins in the human red cell.

The time course of binding of the fluorescent stilbene anion exchange inhibitor. DBDS (4.4'-dibenzamido-2.2'-stilbene disulfonate), to band 3 can be measured by the stopped-flow method. We have previously used the reaction time constant. tau DBDS, to obtain the kinetic constants for binding and, thus, to report on the conformational state of the band 3 binding site. To validate the method, we have now shown that the ID50 (0.3 +/- 0.1 microM) for H2-DIDS (4.4'-diisothiocyano-2.2'-dihydrostilbene disulfonate) inhibition of tau DBDS is virtually the same as the ID50 (0.47 +/- 0.04 microM) for H2-DIDS inhibition of red cell Cl- flux, thus relating tau DBDS directly to band 3 anion exchange. The specific glucose transport inhibitor, cytochalasin B, causes significant changes in tau DBDS, which can be reversed with intracellular, but not extracellular, D-glucose, ID50 for cytochalasin B modulation of tau DBDS is 0.1 +/- 0.2 microM in good agreement with KD = 0.06 +/- 0.005 microM for cytochalasin B binding to the glucose transport protein. These experiments suggest that the glucose transport protein is either adjacent to band 3, or linked to it through a mechanism, which can transmit conformational information. Ouabain (0.1 microM), the specific inhibitor of red cell Na+,K+-ATPase, increases red cell Cl- exchange flux in red cells by a factor of about two. This interaction indicates that the Na+,K+-ATPase, like the glucose transport protein, is either in contact with, or closely linked to, band 3. These results would be consistent with a transport protein complex, centered on band 3, and responsible for the entire transport process, not only the provision of metabolic energy, but also the actual carriage of the cations and anions themselves.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1989

Interactions between anion exchange and other membrane proteins in rabbit kidney medullary collecting duct cells.

In separated outer medullary collecting duct (MCD) cells, the time course of binding of the fluorescent stilbene anion exchange inhibitor, DBDS (4,4'-dibenzamido-2,2'-stilbene disulfonate), to the MCD cell analog of band 3, the red blood cell (rbc) anion exchange protein, can be measured by the stopped-flow method and the reaction time constant, tau TDBDS, can be used to report on the conformational state of the band 3 analog. In order to validate the method we have now shown that the ID50D,DBDS,MCD (0.5 +/- 0.1 microM) for the H2-DIDS (4,4'-diisothiocyano-2,2'-dihydrostilbene disulfonate) inhibition of tau DBDS is in agreement with the ID50,Cl-MCD (0.94 +/- 0.07 microM) for H2-DIDS inhibition of MCD cell Cl- flux, thus relating tau DBDS directly to anion exchange. The specific cardiac glycoside cation transport inhibitor, ouabain, not only modulates DBDS binding kinetics, but also increases the time constant for Cl- exchange by a factor of two, from tau Cl- = 0.30 +/- 0.02 sec to 0.56 +/- 0.06 sec (30 mM NaHCO3). The ID50,DBDS,MCD for the ouabain effect on DBDS binding kinetics is 0.003 +/- 0.001 microM, so that binding is about an order of magnitude tighter than that for inhibition of rbc K+ flux (KI,K+,rbc = 0.017 microM). These experiments indicate that the Na+,K+-ATPase, required to maintain cation gradients across the MCD cell membrane, is close enough to the band 3 analog that conformational information can be exchanged. Cytochalasin E (CE), which binds to the spectrin/actin complex in rbc and other cells. modulates DBDS binding kinetics with a physiological ID50,DBDS,MCD (0.076 +/- 0.005 microM); 2 microM CE also more than doubles the Cl- exchange time constant from 0.20 +/- 0.04 sec to 0.50 +/- 0.08 sec (30 mM NaHCO3). These experiments indicate that conformational information can also be exchanged between the MCD cell band 3 analog and the MCD cell cytoskeleton.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1978

The mechanism of lactate transport in human erythrocytes.

Lactate accumulates in human erythrocytes stored at 4 degrees C in the presence of glucose. Efflux of lactate exhibits an activation energy of 22kcal/mole and is markedly stimulated with increasing medium pH. Lactate influx into erythrocytes that were depleted of intracellular lactate by incubation at 37 degrees at pH 8.0 was stimulated by decreasing medium pH. Under appropriate conditions the pH-dependent lactate flux was insensitive to 4-acet-amido-4'-isothiocyano-2,2'-disulfonic stilbene or 4,4'-diisothiocyano-2,2'-disulfonic stilbene, inhibitors of the inorganic anion channel, while, e.g., inorganic phosphate transport was fully sensitive. These experiments as well as measurements of H+ movements associated with lactate fluxes demonstrate that lactate transport takes place via a specific monocarboxylate transporter (distinct from the inorganic ion channel) by a H+-lactate symport mechanism.

Biological Transport, Active↗
PubMed1987

Modulation of water and urea transport in human red cells: effects of pH and phloretin.

It has previously been shown by Macey and Farmer (Biochim. Biophys. Acta 211:104-106, 1970) that phloretin inhibits urea transport across the human red cell membrane yet has no effect on water transport. Jennings and Solomon (J. Gen. Physiol. 67:381-397, 1976) have shown that there are separate lipid and protein binding sites for phloretin on the red cell membrane. We have now found that urea transport is inhibited by phloretin binding to the lipids with a KI of 25 +/- 8 microM in reasonable agreement with the KD of 54 +/- 5 microM for lipid binding. These experiments show that lipid/protein interactions can alter the conformational state of the urea transport protein. Phloretin binding to the protein site also modulates red cell urea transport, but the modulation is opposed by the specific stilbene anion transport inhibitor, DIDS (4,4'-diisothiocyano-2,2'-stilbene disulfonate), suggesting a linkage between the urea transport protein and band 3. Neither the lipid nor the protein phloretin binding site has any significant effect on water transport. Water transport is, however, inhibited by up to 30% in a pH-dependent manner by DIDS binding, which suggests that the DIDS/band 3 complex can modulate water transport.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1988

Control of intracellular pH in rat calvarial osteoblasts: coexistence of both chloride-bicarbonate and sodium-hydrogen exchange.

Intracellular pH was monitored continuously in cultured rat calvarial osteoblasts using the pH-sensitive fluorescent dye bis carboxyethyl carboxyfluorescein (BCECF), loaded into the cells as its membrane permeant ester. Recovery from an intracellular acid load generated by exposure to NH4Cl was unaffected by the anion exchange inhibitors 4-acetamido-4'-isothiocyanato-stilbene-2,2'-disuphonic acid (SITS) and 4,4'-diisothiocyanato-stilbene 2,2'-disuphonic acid (DIDS) (100 microM), but blocked by the sodium-hydrogen exchange inhibitor amiloride (1 mM) and dependent on external sodium, suggesting that recovery is brought about by a sodium-hydrogen exchanger in the plasma membrane. The cells do, however, possess a SITS-sensitive chloride-bicarbonate exchanger, because iso-osmotic replacement of chloride by gluconate leads to intracellular alkalinization, that is inhibited by SITS, but independent of external sodium. Parathyroid hormone brings about an intracellular acidification, which may be due to an inhibiton of sodium-hydrogen exchange.

Acid-Base Equilibrium↗
PubMed1990

Evidence of chloride/bicarbonate exchange mediating bicarbonate efflux from S3 segments of rabbit renal proximal tubule.

The mechanism of HCO3- exit from rabbit renal proximal tubule S3 segments was investigated. Isolated tubules were perfused luminally and peritubularly with test solutions and cell pH (pHi), cell Cl- activity ([Cl-]i) and cell Na+ activity ([Na+]i) were measured with ion-selective microelectrodes. From the response of pHi and [Cl-]i to changes in bath Cl- or HCO3- concentrations a Cl-/HCO3- exchanger was identified in the basolateral cell membrane. It was reversibly inhibited by millimolar concentrations of the disulfonic stilbene SITS (4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulfonic acid). Cell potential measurements and preliminary determinations of initial ion flux rates suggested a stoichiometry of Cl- to HCO3- flux near 1.0. The transport rate appeared to saturate already at low bath Cl- concentrations (approximately 30 mmol/l), but it was independent of bath pH in the range of 7.4-6.4. Cl-/HCO3- exchange was not directly coupled to Na+ flux although in approximately half of the experiments long-term incubation in Na(+)-free solutions indirectly inhibited the exchanger. Sudden application of SITS under control conditions revealed that the exchanger normally facilitates the exit of HCO3- from cell to interstitium at the expense of Cl- uptake into the cell. How Cl- ions recirculate towards the peritubular surface is presently not known.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMedDate not supplied

Activation and detection of (pro)mutagenic chemicals using recombinant strains of Streptomyces griseus.

Two recombinant strains of Streptomyces griseus have been developed to report on the activation of promutagenic chemicals. This activation is monitored by reversion of the bacterial test strains to a kanamycin-resistant phenotype. Strain H69 detects point mutations and was reverted at an increased frequency by acetonitrile, 2-aminoanthracene, 1,2-benzanthracene, benzidine, benzo(a)pyrene, 9,10-dimethyl-1,2-benzanthracene, and glycine. The second strain, FS2, detects frame shift mutations and was reverted at an increased frequency by 1,2-benzanthracene, benzidine, and glycine. Compounds such as butylated hydroxytoluene, catechol, chlorobenzene, hydroquinone, potassium chloride, phenol, cis-stilbene, trans-stilbene, and toluene did not elicit positive responses in either strain. In addition, these strains are capable of detecting direct-acting mutagens such as N-methyl-N'-nitrosoguanidine and ICR-191, providing further evidence of their promise for detecting a wider range of mutagens. To our knowledge, this is the first report of bacterial strains capable of activating promutagenic compounds and detecting their mutagenic metabolites without the benefit of an exogenous activation system such as the rodent liver homogenate (S9).

Genetic Engineering↗
PubMed1996

Magnesium transport across the basolateral plasma membrane of the fish enterocyte.

In tilapia (Oreochromis mossambicus) intestine, Mg2+ transport across the epithelium involves a transcellular, Na+- and Na+/K+-ATPase dependent pathway. In our search for the Mg2+ extrusion mechanism of the basolateral compartment of the enterocyte, we could exclude Na+/Mg2+ antiport or ATP-driven transport. Evidence is provided, however, that Mg2+ movement across the membrane is coupled to anion transport. In basolateral plasma membrane vesicles, an inwardly directed Cl- gradient stimulated Mg2+ uptake (as followed with the radionuclide 27Mg) twofold. As Cl--stimulated uptake was inhibited by the detergent saponin and by the ionophore A23187, Mg2+ may be accumulated intravesicularly above chemical equilibrium. Valinomycin did not affect uptake, suggesting that electroneutral symport activity occurred. The involvement of anion coupled transport was further indicated by the inhibition of Mg2+ uptake by the stilbene derivative, 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid. Kinetic analyses of the Cl--stimulated Mg2+ uptake yielded a Km (Mg2+) of 6.08 +/- 1.29 mmol . l-1 and a Km (Cl-) of 26.5 +/- 6.5 mmol . l-1, compatible with transport activity at intracellular Mg2+- and Cl--levels. We propose that Mg2+ absorption in the tilapia intestine involves an electrically neutral anion symport mechanism.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1998

Transcellular chloride pathways in ambystoma proximal tubule.

The transport mechanisms of Ambystoma proximal tubule that mediate transcellular Cl- absorption linked to Na+ were investigated in isolated perfused tubules using Cl--selective and voltage-recording microelectrodes. In control solutions intracellular activity of Cl- (aiCl) is 11.3 +/- 0.5 mm, the basolateral (V1), apical (V2), and transepithelial (V3) potential differences are -68 +/- 1.2 mV, +62 +/- 1.2 mV and -6.4 +/- 0.3 mV, respectively. When Na+ absorption is decreased by removal of organic substrates from the lumen, aiCl falls by 1.3 +/- 0.3 mm and V2 hyperpolarizes by +11.4 +/- 1.7 mV. Subsequent removal of Na+ from the lumen causes aiCl to fall further by 2.3 +/- 0.4 mm and V2 to hyperpolarize further by +15.3 +/- 2.4 mV. The contribution of transporters and channels to the observed changes of aiCl was examined using ion substitutions and inhibitors. Apical Na/Cl or Na/K/2Cl symport is excluded because bumetanide, furosemide or hydrochlorothiazide have no effect on aiCl. The effects of luminal HCO-3 removal and/or of disulfonic stilbenes argue against the presence of apical Cl-base exchange such as Cl-HCO3 or Cl-OH. The effects of basolateral HCO-3 removal, of basolateral Na+ removal and/or of disulfonic stilbenes are compatible with presence of basolateral Na-independent Cl-base exchange and Na-driven Cl-HCO3 exchange. Several lines of evidence favor conductive Cl- transport across both the apical and basolateral membrane. Addition of the chloride-channel blocker diphenylamine-2-carboxylate to the lumen or bath, increases the aiCl by 2.4 +/- 0.6 mm or 2.9 +/- 1.0 mm respectively. Moreover, following inhibition by DIDS of all anion exchangers in HCO-3-free Ringer, the equilibrium potential for Cl- does not differ from the membrane potential V2. Finally, the logarithmic changes in aiCl in various experimental conditions correlate well with the simultaneous changes in either basolateral or apical membrane potential. These findings strongly support the presence of Cl- channels at the apical and basolateral cell membranes of the proximal tubule.

Ambystoma↗
PubMed1983

Radiometric assays for mammalian epoxide hydrolases and glutathione S-transferase.

A number of epoxides, including cis- and trans-stilbene oxides, were assayed as substrates for epoxide hydrolases (EHs) by gas-liquid chromatography. Radiolabeled stilbene oxides were prepared by sodium borotritide reduction of desyl chloride followed by ring closure with base treatment. Rapid radiometric assays for EHs were performed by differential partitioning of the epoxide into dodecane, while the product diol remained in the aqueous phase. Glutathione (GSH) transferase was similarly assayed by partitioning the epoxide and diol, if formed metabolically, into 1-hexanol, while the GSH conjugate was retained in the aqueous phase. The cytosolic EH rapidly hydrates the trans isomer while the cis is very poorly hydrated. In contrast, the cis is a better substrate for the microsomal EH than the trans. GSH transferase utilized both epoxides as substrates, but conjugation is faster with the cis isomer. Cytosolic EH activity is high in mouse but very low in rat and guinea pig. Microsomal EH activity, in contrast, is highest in guinea pig, intermediate in rat, and the lowest in mouse. GSH transferase activity, which is high in all three species, can be inhibited by chalcone, with an I50 of 3.1 X 10(-5) M. These assays facilitate the rapid evaluation and direct comparison of epoxide-metabolizing systems in cell homogenates used in short-term mutagenicity assays, cell or organ culture, and possibly in vivo.

Animals↗
PubMed1985

Cyclopropyl oxiranes: reversible inhibitors of cytosolic and microsomal epoxide hydrolases.

A series of aryl- and alkyl-substituted cyclopropyl oxiranes were synthesized as potential suicide inhibitors of mouse liver epoxide hydrolase (EH). The inhibitory potency of each compound and its corresponding alkene precursor was determined with mouse liver EHs using [3H]-cis-stilbene oxide as substrate for microsomal EH (mEH) and for glutathione-S-transferase, and using [3H]-trans-stilbene oxide for cytosolic EH (cEH). The cyclopropyl oxiranes all showed low (26-60% at 5 X 10(-4) M) inhibition of glutathione transferase and moderate inhibition (I50 = 5 X 10(-4) to 6 X 10(-6) M) for cEH and mEH. cis-Phenylcyclopropyl oxirane had an I50 for mEH near that for a commonly used inhibitor, 1,1,1-trichloropropene oxide. Inhibition appeared competitive and reversible, and the cyclopropyl oxiranes appeared to function as alternate substrates. Absence of irreversible inhibition is evidence against a strongly electrophilic epoxide-opening mechanism involving a cyclopropyl carbinyl-homoallyl cation rearrangement. Instead, a concerted mechanism is favored, in which electrophilic opening and hydroxide attack occur in a concerted fashion.

Animals↗