bluuebunny/crossref_metadata_2025_split huggingface dataset:
The mechanism by which cyclopiazonic acid potentiates accumulation of tetraphenylphosphonium in cultured renal epithelial cells
Authors: Riley Ronald T. , Showker Jency L. , Cole Richard J. , Dorner Joe 
Published: October 2006

AbstractCyclopiazonic acid (CPA), a fungal metabolite produced by Aspergillus and Penicillium, potentiated the accumulation of the quaternary cation tetraphenylphosphonium (TPP+) in cultured pig renal epithelial cells. This is the first report of a natural product mediating the tight and apparently nonsaturable binding of a membrane potential probe to subcellular compartments. The potentiated TPP+ accumulation was dose dependent, nonsaturable, and not a result of hyperpolarization across the plasma membrane. Cyclopiazonic acid–potentiated accumulation was completely inhibited by the protonophore carbonylcyanide‐m‐chlorophenylhydrazone (CCCP). Dinitrophenol (DNP), tetrahexylammonium (THA), and n‐ethylmaleimide (NEM) were also effective inhibitors of CPA‐appeared to be energy dependent, TPP+ efflux (in the presence of CCCP) from CPA‐treated cells was incomplete and most of the TPP+ accumulated in the presence of CPA was tightly bound. Dicyclohexylcarbodiimide (DCC), verapamil, and monensin also stimulated TPP+ accumulation, but the TPP+ which accumulated in the presence of these compounds was not tightly bound. As with controls, fractionation of cells which had accumulated TPP+ in the presence of DCC, verapamil, or monensin always resulted in near complete recovery (> 93%) of the TPP+ in the cytosolic fraction, whereas with CPA, greater than 88% of the TPP+ was recovered noncovalently bound in the plasma membrane and mitochondrial fractions. These results are consistent with the hypothesis that CPA‐potentiated TPP+ accumulation is a result of potentiated partitioning of TPP+ into the plasma membranes and mitochondria of LLC‐PK1 cells.
Kinetic parameters of the inhibition of red blood cell aminolevulinic acid dehydratase by triethyl lead and its reversal by dithiothreitol and zinc
Authors: Yagminas Algis P. , Villeneuve David C. 
Published: October 2006

AbstractIn chronic or acute exposure to triethyl lead, a de novo synthesis of aminolevulinic acid dehydratase (δ‐ALAD) in bone marrow and an increased activity in circulating red blood cells can be demonstrated by activating the enzyme with dithiothreitol (DTT) and zinc. We determined the median inhibitory concentration and the apparent inhibition constant for triethyl lead on δ‐ALAD. After dosing with triethyl lead, in vivo inhibition of ALAD only occurred at the high dose, but activation analysis in vitro showed increased ALAD activity to be present at all dose levels in a dose‐dependent fashion. The use of an activation assay for red blood cell ALAD may have value as a bio‐effects monitor of exposure to organic lead.
Mechanism of inhibition of rat brain (Na +‐K +)‐stimulated adenosine triphosphatase reaction by cadmium and methyl mercury
Authors: Ahammadsahib Kabeer I. , Ramamurthi R. , Desaiah Durisala 
Published: October 2006

AbstractThe mechanisms of inhibition of rat brain Na +‐K +‐ ATPase by cadmium chloride (CdCl2) and methylmercuric chloride (CH3HgCl) were studied in vitro by assessing the effects of these heavy metals on this enzyme and associated component parameters. Both the heavy metals significantly inhibited the overall Na +‐K + ‐ATPase in a concentration‐dependent manner with an estimated median inhibitory concentration (IC‐50) of 3.2 × 10−5M for CdCl2 and 6 × 10−6M for CH3HgCl. Protection of enzyme against heavy metal inhibition by 5 × 10−5M to 1 × 10−4 M dithiothreitol (DTT) and glutathione (GSH) or cysteine (CST) indicates that both monothiols and dithiols have the same ability in regenerating sulfhydryl (–SH) groups or chelating the metals. Inhibition of K+‐p‐nitrophenyl phosphatase (K+‐PNPPase), the component enzyme catalyzing the K+‐dependent dephosphorylation in the overall Na +‐K +ATPase reaction by these heavy metals, indicates that the mechanism of inhibition involves binding to this phosphatase. Reversal of K+‐PNPPase inhibition by DTT, GSH, and CST suggests sulfhydryl groups as binding sites. Binding of 3H‐oubain, a cardiac glycocide and inhibitor of both phosphorylation and dephosphorylation, to brain fraction was significantly decreased by CH3HgCl, and this inhibition was reversed by the three thiol compounds, suggesting presence of –SH group(s) in the ouabain receptor site. Cadmium chloride failed to inhibit the binding of this receptor, indicating that the mechanics of inhibition of ATPase by CH3HgCl and CdCl2 are different from each other. The results suggest that the critical conformational property of enzyme common to both kinase (E1) and phosphatase (E2) is susceptible to CH3HgCl whereas only phosphatase is sensitive to CdCl2.
Exposure to different forms of cadmium in mice: Differences in metallothionein and alphafetoprotein mRNA induction in liver and kidney
Authors: Koropatnick James , Cherian M. George 
Published: October 2006

AbstractCadmium (Cd) exposure in mice induces transcription of metallothionein (MT) mRNA and protein accumulation in both liver and kidney. Resistance to hepatotoxicity through chronic exposure to heavy metals is the result of this induction. However, the same chronic exposure results in damage to kidney. We report here that acute exposure of mice to Cd as cadmium sulfate (CdSO4), which resulted in preferential accumulation of metal in liver, or Cd‐metallothionein (CdMT), which resulted in preferential metal accumulation in kidney, induced MT mRNA accumulation in both liver and kidney. However, MT mRNA accumulated to a level twofold higher in liver than in kidney in response to CdSO4. Equivalent doses of CdMT induced MT mRNA accumulation to an equal degree in kidney and liver. While MT mRNA accumulation in kidney was directly proportional to the amount of cadmium in the organ, this was not the case in liver. There, liver MT mRNA was elevated in the absence of elevated tissue cadmium levels. Interestingly, CdMT induced alphafetal protein (AFP) mRNA accumulation in kidney, but not liver. It appears that (a) maximal MT mRNA accumulation in kidney is less than in liver, and (b) liver is capable of accumulating MT mRNA in response to even very low cadmium exposure that may not result in elevated tissue cadmium.
Direct actions of organophosphate anticholinesterases on nicotinic and muscarinic acetylcholine receptors
Authors: Bakry Nabil M. S. , El‐Rashidy Amina H. , Eldefrawi Amira T. , Eldefrawi Mohyee E. 
Published: October 2006

AbstractFour nerve agents and one therapeutic organophosphate (OP) anticholinesterase (anti‐ChE) bind to acetylcholine (ACh) receptors, inhibit or modulate binding of radioactive ligands to these receptors, and modify events regulated by them. The affinity of nicotinic (n) ACh receptors of Torpedo electric organs and most muscarinic (m) ACh receptors of rat brain and N1E‐115 neuroblastoma cultures for the OP compounds was usually two to three orders of magnitude lower than concentrations required to inhibit 50% (IC‐50) of ACh‐esterase activity. However, a small population of m‐ACh receptors had an affinity as high as that of ACh‐esterase for the OP compound. This population is identified by its high‐affinity [3H]‐cis‐methyldioxolane ([3H]‐CD) binding. Although sarin, soman, and tabun had no effect, (O‐ethyl S[2‐(diisopropylamino)ethyl)] methyl phosphonothionate (VX) and echothiophate inhibited competitivel the binding of receptors. However, VX was more potent than echothiophate in inhibiting this binding and 50‐fold more potent in inhibiting carbamylcholine (carb)‐stimulated [3H]‐cGMP synthesis in N1E‐115 neuroblastoma cells—both acting as m receptor antagonist. All five OPs inhibited [3H]‐CD binding, with IC‐50s of 3, 10, 40, 100, and 800 nM for VX, soman, sarin, echothiophate, and tabun, respectively. The OP anticholinesterases also bound to allosteric sites on the n‐ACh receptor (identified by inhibition of [3H]‐phencyclidine binding), but some bound as well to the receptor's recognition site (identified by inhibition of [125I]‐α‐bungarotoxin binding). Soman and echothiophate in micromolar concentrations acted as partial agonists of the n‐ACh receptor and induced receptor desensitization. On the other hand, VX acted as an open channel blocker of the activated receptor and also enhanced receptor desensitization. It is suggested that the toxicity of OP anticholinesterases may include their action on n‐ACh as well as m‐ACh receptors if their concentrations in circulation rise above micromolar levels. At nanomolar concentrations their toxicity is due mainly to their inhibition of ACh‐esterase. However, at these low concentrations, many OP anticholinesterases (eg, VX and soman) may affect a small population of m‐ACh receptors, which have a high affinity for CD. Such effects on m‐ACh receptors may play an important role in the toxicity of certain OP compounds.
Chlordecone is a potent in vitro inhibitor of oligomycin‐insensitive mg2+ ‐ATPase of rat bile canaliculi–enriched fraction
Authors: Curtis Lawrence R. 
Published: October 2006

AbstractThe oligomycin‐insensitive Mg2+ ‐ATPase (OIMATPase) of rat bile canaliculi–enriched fraction (BCEF) was inhibited by chlordecone (CD) in vitro (IC‐50 = 25 μM). Kinetic analysis indicated noncompetitive inhibition. Inhibition of OIMATPase by filipin but not by atractyloside verified plasma membrane origin of activity. The cholestatic agents α‐naphthyl isothiocyanate (ANIT) and taurolithocholate (TLC) decreased OIMATPase activity at in vitro concentrations of 33 and 162 μM, while taurocholate (a choleretic bile salt), ethynylestradiol, and manganese did not. Cholestatic drugs with primary intracellular sites of action (colchicine and phalloidin) were ineffective OIMATPase inhibitors in this concentration range. Inhibition of OIMATPase by N‐ethylmaleimide (NEM) and dicyclo‐hexylcarbodiimide (DCCD) indicated some H+ ‐ATPase activity in BCEF. In vitro sensitivity of OIMATPase of BCEF to CD, ANIT, and TLC suggested the bile canaliculus as a subcellular‐level target for their cholestatic actions.
Genetically engineered V79 chinese hamster cell expression of purified cytochrome P‐450iib1 monooxygenase activity
Authors: Platt K. L. , Molitor E. , Döhmer J. , Dogra S. , Oesch F. 
Published: October 2006

AbstractChinese hamster V79 fibroblasts, frequently used as target cells in short‐term tests for mutagenicity, do not possess measurable monooxygenase activity; in particular, enzymatic oxidation of testosterone (T) cannot be demonstrated. If these V79 cells, however, had been transfected with the cDNA‐encoding rat liver cytochrome P‐450IIB1 under control of the SV40 early promoter, they stably expressed monooxygenase activity. These so‐called SD1 cells then oxidatively metabolized T at a rate of 27 pmol/mg protein/min, converting it to 16α‐ and 16β‐hydroxy‐T as well as 4‐androsten‐3,17‐dione as sole metabolites in a ratio of 1.1:1.0:1.6. The regio‐ and stereoselective conversion of T by SD1 cells, as well as the quantitative distribution of the metabolites, corresponds well with the results reported for pure cytochrome P‐450IIB1 in a reconstituted system.
Mutagenicity of tetrachloroethene in the ames test—metabolic activation by conjugation with glutathione
Authors: Vamvakas Spyridon , Herkenhoff Martin , Dekant Wolfgang , Henschler Dietrich 
Published: October 2006

AbstractThe mutagenicity of tetrachloroethene (tetra) and its S conjugate, S‐(1,2,2‐trichlorovinyl)glutathione (TCVG) was investigated using a modified Ames preincubation assay. TCVG was a potent mutagen in presence of rat kidney particulate fractions containing high concentrations of γ‐glutamyl transpeptidase (GGT) and dipeptidases. Purified tetra was not mutagenic without exogenous metabolic activation or under conditions favoring oxidative metabolism. Preincubation of tetra with purified rat liver glutathione (GSH) S‐transferases in presence of GSH and rat kidney fractions resulted in a time‐dependent formation of TCVG as determined by (HPLC) analysis and in an unequivocal mutagenic response in the Ames test. Experiments with tetra in the isolated perfused rat liver demonstrated TCVG formation and its excretion with the bile; bile collected after the addition of tetra to the isolated perfused liver was unequivocally mutagenic in bacteria in the presence of kidney particulate fractions. The mutagenicity was reduced in all cases by the GGT inhibitor serine borate or the β‐lyase inhibitor aminooxyacetic acid. These results support the suggestion that cleavage of the GSH S conjugate formed from tetra by the enzymes of the mercapturic acid pathway and by β‐lyase may be involved in the nephrocarcinogenic effects of this haloalkene in rats.
Effect of verapamil on glycogenolysis and gluconeogenesis in the perfused rat liver
Authors: Badr Mostafa 
Published: October 2006

AbstractIn perfused livers from fed rats, rates of glucose production (glycogenolysis) were 133 ± 12 μmol/g/hr. Infusion of 2 μM verapamil into these livers decreased the rates of glucose production significantly to 97 ± 15 μmol/g/hr within 10 min. Conversely, rates of production of lactate plus pyruvate (glycolysis) of 64 ± 6 μmol/g/hr were not significantly altered by verapamil (60 ± 3 μmol/g/hr). When 50 μM verapamil was infused, however, rates of both glycogenolysis and glycolysis were diminished to 56 ± 11 and 43 ± 5 μmol/g/hr, respectively. In perfused livers from fasted rats, infusion of 20 mM fructose increased the rates of production of glucose (gluconeogenesis) significantly from 11 ± 7 to 121 ± 17 μmol/g/hr. These rates reached 138 ± 7 μmol/g/hr upon the simultaneous infusion of verapamil (2 μM). In these livers, fructose also increased rates of production of lactate from 6 ± 2 to 132 ± 11 μmol/g/hr, which were further increased to 143 ± 8 μmol/g/hr when 2 μM verapamil was infused. The results show that calcium‐dependent processes involved in hepatic carbohydrate metabolism respond differently to the calcium channel blocker verapamil. Low concentrations of verapamil inhibited glycogenolysis significantly while having no effect on either glycolysis or gluconeogenesis. These data suggest that these two processes have different sensitivities to changes in intracellular calcium concentrations and/or different sources of regulatory calcium.
The interaction of phenyldichloroarsine with erythrocytes
Authors: Chong Steven , Dill Kilian , McGown Evelyn 
Published: October 2006

AbstractThe purpose of the study was to identify binding sites of organic arsenic in the erythrocyte and to explain species differences in binding. Washed erythrocytes were exposed to graded concentrations of [U‐14Clphenyldichloroarsine (PDA)] in phosphate‐buffered saline containing 0.1% glucose and 0.1% bovine serum albumin. At low PDA concentrations, all cells bound the arsenical rapidly (within 10 min) and quantitatively. Human, pig, hamster, guinea pig, and mouse erythrocytes approached saturation at 0.02–0.3 μmol PDA/109 cells, depending on the species. Saturation points correlated well with each respective species' erythrocyte glutathione content. In contrast, rat erythrocytes showed no sign of saturation at PDA loads as high as 3.0 μmol/109 cells. Hemolysates of PDA‐treated erythrocytes were subjected to Sephadex G‐75 gel filtration chromatography. 14C from rat hemolysate was distributed between the hemoglobin and small molecular weight (glutathione‐containing) fractions. In all other species, the 14C eluted almost exclusively with the glutathione‐containing fractions. In equilibrium dialysis experiments, human hemoglobin did not bind PDA, whereas rat hemoglobin bound 2 PDA/mol with Kd ∼ 5 μM. In conclusion, glutathione is the principal binding site of phenyldichloroarsine in erythrocytes. In most species, the arsenical does not bind to hemoglobin, even though it has free (titratable) sulfhydryls considerably in excess of the glutathione concentration. In rat erythrocytes, phenlydichloroarsine binds both to glutathione and to hemoglobin. Arsenical binding by rat hemoglobin is presumably due to the unique location of the extra titratable cysteine in that protein.
Patulin‐induced ion flux in cultured renal cells and reversal by dithiothreitol and glutathione: A scanning electron microscopy (sem) X‐ray microanalysis study
Authors: Hinton Dorothy M. , Riley Ronald T. , Showker Jency L. , Rigsby William E. 
Published: October 2006

AbstractPatulin (PAT), a compound produced by certain species of Aspergillus, Penicillium, and Byssochlamys, is frequently found associated with agricultural commodities. PAT has many effects on membrane function, including the inhibition of the isolated Na+‐K+ ATPase. In this study, a scanning electron microscope equipped with an energy dispersive spectroscopy X‐ray microanalysis system was used to examine individual cultured renal epithelial cells (LLC‐PK1) in order to determine the effects of PAT on the relative intracellular ion concentrations. The estimated EC50 (60 min) for both sodium influx and potassium efflux was between 10 and 50 μm for ouabain. For PAT, the EC50 (60 min) was 250 μm for sodium influx and 100 μm for potassium efflux. However, 1 mM patulin at 240 min caused complete reversal of the sodium and potassium content of cells, and 1 mM ouabain at 240 min did not. The effect of patulin on sodium and potassium flux was both concentration and time dependent and was reversed by dithiothreitol and glutathione. PAT (250 μM) but not ouabain (250 μM) induced massive blebbing of LLC‐PK1 cells. Thus, the interaction of PAT with cellular membranes involves both alterations in the regulation of intracellular ion content and the cyto‐skeleton. We hypothesize that patulin alters intracellular ion content via Na+–K+ ATPase and non‐Na+–K+ ATPase mechanisms.
Distribution and peroxidative oxidation of 2‐t‐butyl‐4‐methoxyphenol in rat tissues after a single intraperitoneal dose
Authors: Della Corte Laura , Bianchi Loria , Valoti Massimo , Sgaragli Giampietro 
Published: October 2006

AbstractThe distribution of 2‐t‐butyl‐4‐methoxyphenol (BHA) and its conversion to 2,2′‐dihydroxy‐3,3′‐di‐t‐butyl‐5,5′‐dimethoxydiphenyl (di‐BHA) in rat tissues at different times (1–96 hr) following the intraperitoneal administration of a single dose of BHA (32 mg kg−1 body weight) were monitored by gas chromatography‐mass spectrometry (GC/MS) analysis of both compounds. High BHA levels were found in the intestine and liver persisting up to 24 hours (5.5–20.7 and 1.8–3.3 μg g−1 wet weight, respectively). In these tissues, values of the area under the experimental concentration curve (AUC0–24) were 285 and 49 times higher, respectively, than those observed in plasma (945 ng mL−1 hr), AUC0–24 values in kidney, spleen, erythrocytes, and brain were 2–7 times higher, whereas values below those found in plasma were observed in lung and muscle. The metabolite di‐BHA could be detected in the intestine, kidney, and spleen, amounting to 5–8% of BHA. These findings indicate that rat intestine is capable of transforming in vivo BHA into di‐BHA even when the former compound is administered intraperitoneally and that this capacity is shared by the kidney and spleen.
Inhibition of soybean lipoxygenase and mouse skin tumor promotion by onion and garlic components
Authors: Belman Sidney , Solomon Jerome , Segal Alvin , Block Eric , Barany George 
Published: October 2006

AbstractOnion and garlic essential oils were previously shown to inhibit mouse skin tumor promotion, as were the enzymes, lipoxygenase, and cyclooxygenase. In the present study, the inhibition of soybean lipoxygenase (EC 1.13.11.12) by onion and garlic components and related compounds was investigated. The IC50values as well as the kinetic inhibition constants were determined for the most active compounds. Di‐(1‐propenyl) sulfide, an analog of the substrate moiety required for oxygenase action, was the only irreversible inhibitor observed withKi=59 μM andk3=0.53/min. Inhibition in the presence of substrate was uncompetitive at 88 and 132 μM linoleic acid withKi=129 μM. At 173 μM linoleic acid, however, inhibition was competitive withKi=66 μM. Dially trisulfide, allyl methyl trisulfide, and diallyl disulfide were competitive inhibitors, while 1‐propenylpropyl sulfide and (E, Z)‐4,5,9‐trithiadodeca‐1,6,11‐triene 9‐oxide (ajoene) were mixed inhibitors. Nordihydroguaiaretic acid (NDGA), the most potent lipoxygenase inhibitor, was a competitive inhibitor withKi=0.29 μM. The results indicate a relative potency of inhibition for structural features in the following order: di(1‐propenyl) sulfide > an alkenyl trisulfide > an alkenyl disulfide. Di(n‐propyl) disulfide, a major onion oil component, inhibited neither lipoxygenase nor promotion. Di(1‐propenyl) sulfide and ajoene inhibited both. This suggests that the inhibition of lipoxygenase may be involved in anti‐promotion.
Effects of TCDD on the EGF receptor of XB mouse keratinizing epithelial cells
Authors: Kawamoto Toshio , Matsumura Fumio , Madhukar B. V. , Bombick David W. 
Published: October 2006

AbstractTCDD was found to cause a marked inhibition of 125I‐epidermal growth factor (EGF) binding to its receptor on the cell surface of XB mouse keratinizing epithelial cells (XB cells) cultured in vitro. The EC50 concentration was estimated to be on the order of 3 × 10−11 M 24 hours after TCDD administration. As early as 12 hours after the addition of 10−9 M of TCDD, XB cells showed signs of a decline in 125I‐EGF binding levels. The level of such EGF receptor downregulation reached a maximum at 24 hours, continued until day 2, but completely recovered by day 3. This was accompanied by a rise in protein kinase activities, particularly those of the protein tyrosine kinases during the initial period of 6–24 hours. To test the hypothesis that the EGF receptors of the cells, by showing TCDD‐induced symptoms of downregulation, actually are being activated and triggering EGF‐like signals, we examined the effects of both TCDD and exogenously added EGF on cell morphology, colony formation degree of keratinization, the pattern of activation of protein kinases and de novo protein synthesis, and EGF receptor phosphorylation. Based on the similarity of cell responses to these between TCDD‐ and EGF‐treated cells, we concluded that TCDD, directly or indirectly, causes activation of the EGF receptor. In contrast, 12‐O‐tetradencanoylphorbol‐13‐acetate (TPA), which is known to downregulate EGF receptors by blocking their protein tyrosine kinase, produced dissimilar end results. The balance of evidence support the notion that the action of TCDD in this cell line is tightly coupled to the activation of the EGF receptor and that one of the key consequences of such a biochemical change is that it signals these cells to commit to terminal differentiation.
Competitive partial inhibitors of serum albumin‐catalyzed sulfur cyanolysis
Authors: Jarabak Rebecca , Westley John 
Published: October 2006

AbstractEfforts to locate the active site for sulfur cyanolysis catalyzed by bovine serum albumin have led to systematic tests of several compounds that inhibit the catalyzed reaction. Hexanoate and 5‐dimethylaminonaphthalene‐1‐sulfonate bind at the same site and are partial inhibitors competitive with cyanide, uncompetitive with respect to sulfur. Various dansyl amino acids and 1‐anilino‐8‐naphthalene sulfonate display the same inhibitory behavior but bis (1‐anilino‐8‐naphthalene sulfonate) is a total inhibitor competitive with cyanide. These findings are interpreted to indicate that the cyanolysis active site is near, but not at, one of the short‐chain fatty acid binding sites on albumin subdomain 2‐AB or 3‐AB. Both ionic repulsion and steric considerations are implicated in the mechanisms of inhibition.