Biomedical subjects

U I Walther

Publications and source records attributed to U I Walther.

17 recordsLinked to original sources

PubMed2006

Effect of enlarged glutathione on zinc-mediated toxicity in lung-derived cell lines.

Zinc-mediated toxicity has been linked to cellular glutathione content in isolated cells. In addition, treatment of alveolar epithelial type II cells with glucocorticoids diminishes cellular glutathione content, and this is followed by an increase in zinc-mediated toxicity. The question arises whether an increase in glutathione synthesis might decrease zinc-mediated toxicity. For this purpose an administration of 200 micromol/l N-acetyl-L-cysteine (NAC) was given to the cells, while cysteine was used up to 100 micromol/l. Zinc-mediated toxicity was assessed by measuring protein synthesis inhibition and glutathione dependent parameters. De novo synthesis of glutathione was assessed as compared to controls by N-acetyl-D-cysteine (NADC) treatment. Comparing NAC and NADC treatment no differences in zinc-mediated toxicity were found. Furthermore only in one (of three) cell line tested a significant increase in GSH content by NAC as compared to NADC treatment was achieved. But even in this cell line no changes by zinc-mediated toxicity were found. It is concluded that the cell lines tested can use other sources of cys for glutathione synthesis. Furthermore the increased zinc-mediated toxicity due to hydrocortisone was abolished in the alveolar epithelial cell lines by the NADC/NAC treatment. It is therefore discussed that additionally to glutathione some other antioxidative defence mechanisms can influence zinc-mediated toxicity as well.

Acetylcysteine↗

PubMed2005

In vitro embryotoxicity assessment with dental restorative materials.

OBJECTIVES: Resin (co)monomers may be released from restorative dental materials and can diffuse into the tooth pulp or the gingiva, and can reach the saliva and the circulating blood. Genotoxic potential of some dental composite components has been clearly documented. The genotoxic effects of xenobiotics can represent a possible step in tumor initiation and/or embryotoxicity/teratogenesis. A modified fluorescent mouse embryonic stem cell test (R.E.Tox) was used to test the embryotoxic potential of following dental restorative materials: Bisphenol A glycidylmethacrylate (BisGMA), urethanedimethacrylate (UDMA), hydroxyethylmethacrylate (HEMA), and triethyleneglycoldimethacrylate (TEGDMA), as well as some of their metabolic intermediates 2,3-epoxy-2-methyl-propionicacid-methylester (EMPME), methacrylic acid (MA), and 2,3-epoxy-2-methylpropionic acid (EMPA). METHODS: Mouse embryonic stem (ES) cells stably transfected with a vector containing the gene for the green fluorescent protein under control of the cardiac alpha-myosin heavy chain promoter were differentiated in the presence of various concentrations of the test compounds for 12 days. Fluorescence was measured using the TECAN Safire and values were expressed as percent of control values. To distinguish between cytotoxic and embryotoxic effects, all compounds were tested in a standard MTT assay. RESULTS: HEMA, TEGDMA and EMPME did not influence the differentiation process of ES cells towards cardiac myocytes. No cytotoxic effects were observed at any of the concentration levels tested. Exposure to BisGMA resulted in a 50% decrease in cell survival and a very strong inhibition of cell differentiation at 10(-5)M (p<0.01). Embryotoxic effects were also present at 10(-6) and 10(-7)M (p<0.05). EMPA induced a decrease in ES cell differentiation at 10(-5)M (p<0.01) without cytotoxic effects. No embryotoxic effects were induced at lower concentrations. Exposure to UDMA resulted in a slight decrease of cell differentiation at 10(-5)M (p<0.05). Exposure of cells to MA resulted in an increase of cardiac differentiation up to 150% (p<0.05) at 10(-5)M without cytotoxic effects. CONCLUSIONS: BisGMA induced a significant high embryotoxic/teratogenic effect over a large range of concentration. Therefore attention should be focused on this dental monomer, which should be investigated further by in vivo experiments.

Animals↗

PubMed2004

Antioxidative vitamins decrease cytotoxicity of HEMA and TEGDMA in cultured cell lines.

OBJECTIVES AND METHODS: In a previous study it was postulated that toxicity of 2-hydroxyethylmethacrylate (HEMA) and triethleneglycoldimethacrylate (TEGDMA) is based on oxidative metabolites. In this study the influence of antioxidative vitamins (including uric acid) on the toxicity of HEMA or TEGDMA was tested. Toxicity of HEMA and TEGDMA was determined in rat alveolar epithelial L2, human malignant A549, and human fibroblast-like 11Lu cells by inhibition of methionine incorporation (as a marker of protein synthesis inhibition) and by determination of glutathione depletion, as well as by measurement of GSSG increase. RESULTS: Toxicity of the composite components HEMA and TEGDMA was demonstrated by GSH depletion as the most sensitive method. Five hundred micromoles per litre Vitamin C or 250 micromol/l Vitamin E were mostly able to decrease toxicity of HEMA and TEGDMA in the cell lines tested. In addition, 250 micromol/l Vitamin A was only effective in L2 cells impairing HEMA toxicity and 250 micromol/l uric acid impairing TEGDMA toxicity as assessed by decreased GSH depletion. In A549 cells only methionine incorporation inhibition but not GSH depletion was significantly affected. By contrast, in 11Lu cells methionine incorporation inhibition was not significantly changed, but GSH depletion was. CONCLUSIONS: The postulated mechanism of HEMA or TEGDMA toxicity based on radical metabolites is supported by the effectivity of the antioxidative substances tested in mitigating toxicity and by the greater susceptibility of the glutathione redox system as compared to protein synthesis inhibition in assessing toxicity.

Animals↗

PubMed2004

Decreased zinc toxicity resulting from doxorubicin without increased GSSG export in three human lung cell lines.

Zinc-mediated cytotoxicity is recognized, at least in part, by a decrease of reduced glutathione (GSH) and an increase in the oxidized form of glutathione (GSSG). Doxorubicin is a common inducer of multidrug-resistance-associated proteins and such proteins might, furthermore, be associated by an increased GSSG export rate. Therefore, zinc-mediated toxicity should be abolished after doxorubicin pretreatment. In the present study, zinc toxicity was characterized by methionine incorporation, glutathione content, and the GSSG/GSH ratio. Experiments were performed in three established lung cell lines comparing doxorubicin-pretreated cells with controls. Zinc-mediated toxicity was significantly decreased after pretreatment with doxorubicin as assessed by methionine-incorporation inhibition, GSH depletion, and/or GSSG increase in the two nonmalignant cell lines. Unexpectedly, zinc-associated GSSG export was not increased after doxorubicin pretreatment. This inconsistency might be explained as a result of a decreased zinc content in these cells, probably because of an increased export rate of zinc. The findings are in contradiction to the opinion of metal excretion by multidrug-resistance-associated proteins, matched to GSH conjugate excretion, as it is discussed for cadmium, for example.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2003

Decreased GSSG reductase activity enhances cellular zinc toxicity in three human lung cell lines.

Cellular reduced glutathione (GSH) levels have been identified as an essential determinant in zinc-induced cytotoxicity. However, cytotoxic effects of zinc have also been observed without depletion of GSH stores. In a previous study, the intracellular activity of GSSG reductase (GR) has come into focus (Walther et al. 2000, Biol Trace Elem Res 78:163-177). In the present paper we have tried to address this issue more deeply by inhibiting the activity of cellular GR without any appreciable decreases of cellular glutathione. In three pulmonary cell lines, GR activity was inhibited in a dose-dependent manner by the alkylating agent carmustine (BCNU), a known inhibitor of GR. Cells were pretreated with BCNU for 14 h, followed by exposure to various concentrations of zinc chloride. Then we determined the incorporation of radiolabelled methionine (to assess protein synthesis), and measured the GSH and oxidized glutathione (GSSG) levels. Additionally, GR activity of controls was measured. IC(50) values for zinc-induced inhibition of methionine incorporation, as well as GSH contents, was strongly correlated to the decreased GR activity. These results firmly suggest that GR is an important factor in the event chain of zinc cytotoxicity. Together with the results from our previously cited study where impaired regeneration of GSH levels were accompanied by a decrease in total cellular glutathione (GSH + GSSG) we conclude that GSSG itself is an important effector in zinc cytotoxicity.

Cell Line↗

PubMed2002

Cytotoxicity of ingredients of various dental materials and related compounds in L2- and A549 cells.

Various ingredients of dental materials and related compounds were tested for cytotoxicity in two alveolar epithelial cell lines (L2 and A549 cells). Release of lactate dehydrogenase (LDH) from cells was measured after incubation with the test substances for time intervals up to 48 h and expressed as percentage of total LDH content of lysed cells. Furthermore, the glutathione content of cells was determined in the nonmalignant L2 cells. Additionally, cell viability was assessed by microscopic examination. The highest cytotoxicity was observed with mercury compounds (methylmercuric chloride and mercury dichloride) in the range of 5-20 micromol/l. The composite components 2-hydroxyethylmethacrylate (HEMA) and triethleneglycoldimethacrylate (TEGDMA) showed time- and concentration-dependent effects of cytotoxicity at high concentrations (about 1-5 mmol/l). A time dependence for GSH decrease was mainly found for the composite components up to 12 h of cellular exposure. L2 cells were more sensitive to both mercury and composite compounds than A549 cells. Gold compounds (sodiumaurothiomalate and gold particles < 1.5 microm) did not produce any sign of toxic reactions. A time-dependent increased toxicity in pulmonary cell lines was found for the composite components HEMA and TEGDMA, but not for mercury and gold compounds.

Animals↗

PubMed2002

Biological clearance of HEMA in guinea pigs.

No toxicokinetic data are available about the dental composite component 2-hydroxyethylmethacrylate (HEMA) in vivo in the literature. Therefore, the excretion of HEMA in feces and urine in vivo and, using the pendular perfusion technique with segments of jejunum and colon, in the biliary and enteric excretion in situ were investigated in anesthetized guinea pigs. In the in situ experiments, guinea pigs (n = 4) received HEMA (0.02 mmol/kgbw labelled with a tracer dose 14C-HEMA 0.3 kBq/gbw) injected into the jugular vein. In the in vivo experiments, guinea pigs (n = 4) received HEMA (+ 14C-HEMA, same dose as above) via gastric tube. Urine and feces were collected for 24h. In the in situ experiments, organs from guinea pigs were removed 60 min after the beginning of the experiment, and then the 14C-radioactivity was measured. During the 60 min perfusion period the calculated amount of 14C-activity excreted into the total jejunum and colon was 6.0 +/- 1.0% and 2.7 +/- 0.7% of the dose administered, respectively (mean +/- sem). Of the 14C-HEMA dose, 5.3 +/- 0.3% was found in the bile. Significantly (p < 0.05) higher bile/blood concentration ratios were found at 10-40 min after the injection of HEMA, as compared to the ratio at 60 min. The total 14C-recovery in all organs tested was 20.0 +/- 2.6%. During 24h the amounts of 14C-activity excreted in the feces and urine were 1.1 +/- 0.1% or 17.1 +/- 1.50% of the dose administered, respectively (mean +/- sem). The total 14C-recovery in all organs tested was 11.6 +/- 0.6%. In a second series of in vivo experiments, exhaled air from the animals was captured during the 24h experimental period. 14C was exhaled to 63.6 +/- 2.11% of the administered 14C-HEMA dose (mean +/- sem; n = 4) as 14C-carbondioxide. The results indicate a rapid clearance of 14C-HEMA and/or 14C-HEMA metabolite(s) from the organism, exhalation being the major route of elimination.

Animals↗

PubMed2002

Effect of low level zinc pretreatment on zinc-mediated toxicity in different lung cell lines.

Reduced toxicity of high zinc exposure was observed after pretreatment of various lung cells with nonlethal zinc concentrations. This effect became significant when various parameters of cytotoxicity were assessed (e.g., inhibition of protein synthesis, depletion of reduced glutathione [GSH], increase of oxidized glutathione [GSSG], release of lactate dehydrogenase [LDH]). Similar protective effects by zinc have already been shown by several investigators for a variety of toxicity studies dealing with cadmium, in vitro and in vivo. Zinc-induced toxicity has been linked to glutathione metabolism and cellular GSH contents. Activity of glutathione reductase (GR) and rates of glutathione synthesis were identified as determinants of zinc (cyto)toxicity. However, these variables were virtually unaffected in our adapted cells. Consequently, another variable appears to be crucial for modulating cellular suscepticibility in zinc pretreated cells. Protection in our cells was achieved by pretreatment with 80-120 micromol/L zinc chloride for 24-72 h, roughly 10-fold more zinc in the medium than is normally found in human plasma. Protection was not observed when the cells were concomitantly exposed to cycloheximide, an inhibitor of protein synthesis, or actinomycin D, an inhibitor of RNA synthesis, but it was found in the presence of amanitin, an inhibitor of mRNA synthesis. It is therefore concluded that the altered zinc tolerance of pretreated cells is not attributable to the induction of metallothionein.

Cell Line↗

PubMed2001

Effects of zinc chloride on glutathione and glutathione synthesis rates in various lung cell lines.

Zinc-mediated toxicity has been linked to cellular glutathione (GSH) contents. In this study, effects of zinc on cellular GSH content, glutathione reductase (GR) activity, and GSH synthesis were investigated. In all cell lines tested, decreases in cellular GSH content and GR activity as well as an increase in oxidized glutathione (GSSG) were found after incubation of cells with zinc chloride. These effects were dose- and time-dependent. Changes in GR activities were earliest affected and were most marked compared with the other parameters examined. Decrease of enzyme activity was not due to a decrease in the cosubstrate NADPH. In A549 and L2 cells, initial increases in GSH synthesis rates occurred up to about 175% of control. Later, GSH synthesis decreased to levels below controls. In 16Lu cells, GSH synthesis decreased after 2 h of zinc exposure. No transient increase was found in this cell line. Measurement of ATP content did not show any influence of zinc on cellular ATP. Lactate dehyrogenase leakage, a marker of a clear cytotoxic effect, occurred after 6 h of zinc treatment in the non-malignant cells examined, and after 16 h in malignant A549 cells. We assume the inhibition of GR activity and the associated increase of GSSG could possibly represent a main zinc-mediated toxic cellular effect.

Animals↗

PubMed2001

Cytotoxicity of dental composite components and mercury compounds in lung cells.

OBJECTIVE: The effect of dental composite components triethyleneglycoldimethacrylate (TEGDMA) and hydroxyethylmethacrylate (HEMA), as well as mercuric chloride (HgCl2) and methylmercury chloride (MeHgCl) was investigated on the release of lactatedehydrogenase (LDH) from alveolar epithelial lung cell lines in vitro. METHODS: The confluent cell layers from the A549 (human, malignant) and the L2 cells (rat) were incubated with various concentrations of HEMA, TEGDMA, MeHgCl and HgCl2 at 37 degrees C in 2% (v/v) CO2 atmosphere for 8h. In further experiments the L2 cells were incubated with the same compounds for 6-48 h. LDH release was measured and the values were expressed as percentage of the LDH content. The values were plotted on a concentration log-scale and the substance concentration at the maximum slope was assessed as effective concentration (EC50). RESULTS: A significant (p<0.05) increase in the LDH release was found in the L2 cells after 8-h incubation with HEMA (4 mmol/l), TEGDMA (2 mmol/l), MeHgCl (0.01 mmol/l) and HgCl2 (0.015 mmol/l), and in A549 cells with HEMA (14 mmol/l), TEGDMA (15 mmol/l), MeHgCl (0.15 mmol/l) and HgCl2 (0.05 mmol/l), compared to controls. The EC50 values from compounds in the L2 cells are shown in the following table (mean; sem in parentheses; n=3-6; #n=1): [see text]. SIGNIFICANCE: The toxic effect of HgCl2 and MeHgCl from the L2 cells was about 100-700-fold higher than of the dental composite components. A significant (p<0.05) time dependent increase of toxicity was observed with TEGDMA, HEMA and MeHgCl.

Animals↗

PubMed2000

Effect of zinc chloride on GSH synthesis rates in various lung cell lines.

Zinc toxicity has been linked to decreased reduced glutathione (GSH) and increased oxidized glutathione (GSSG) contents, which might be caused by a GSSG reductase inhibition by zinc. In this study we investigated zinc effects on GSH synthesis rates in various lung cell lines by thin-layer chromatography after (35)S-cysteine incorporation. Two alveolar epithelial cell lines (A549 and L2) and two human fibroblast-like lung cell lines (11Lu and 16Lu) were used in this study. Equipotent protein synthesis inhibition for the different cell lines was reached after 2 h (L2, 11Lu), 3 h (16Lu), and 4 h (A549) zinc exposure (15-200 microM) to cells. Here GSH depletion and GSSG increase in A549 cells were markedly lower than in the other cell lines tested. Incorporation of cysteine (Cys) into GSH was not different in the cell lines tested, while 11Lu cells only demonstrated a decrease of newly synthesized GSH after 1 h of (35)S-Cys exposure when cells were exposed to zinc. Only 11Lu cells showed a markedly decreased Cys availability as compared with the other cell lines. In all cell lines the availability of Cys was not affected by exposure to zinc. No compensating increase in GSH synthesis rates was found after zinc-mediated cellular GSH depletion.

Carcinoma, Non-Small-Cell Lung↗

PubMed2000

Lack of effects of hydrocortisone pretreatment on zinc-induced changes in protein assemble.

Inhalational zinc intoxication may lead to the development of acute respiratory distress syndrome (ARDS). Pharmacological treatment of ARDS is based on glucocorticoids, while the efficiency of glucocorticoid treatment is discussed controversially. Glucocorticoid pretreatment of lung cell lines is known to cause disparate effects with regard to zinc susceptibility. Both substances are known to each interact with protein metabolism. In the present study, zinc effects were examined on hydrocortisone (HC)-pretreated lung cell lines by detection of content and synthesis of different proteins after two-dimensional (2D) gel electrophoresis. (1) In HC- pretreated fibroblast-like 11Lu and alveolar epithelial L2 cells, no zinc-mediated changes after silver staining of 2D gels were seen. Few differences occurred in HC-pretreated alveolar epithelial A549 cells that might be explained by the appearance of heat shock proteins (hsp) after zinc exposure. (2) In autoradiographs after 35S-Met incorporation only in 11Lu cells, small differences occurred after HC treatment as compared to controls without HC. (3) All cell lines tested demonstrated the same zinc-mediated changes in autoradiographs with a nearly complete loss of synthesized proteins and an appearance of a few new spots. These changes were reversible in all cell lines after washing out of external zinc. The new spots were transiently expressed for a few hours after zinc exposure. (4) The overall effect of HC pretreatment was rather unimpressive. The virtual lack of major effects does not support the hypothesis that a gross interaction between glucocorticoids and zinc at the cellular protein synthesis level would be an important mechanism of influence in zinc-induced lung injury.

Animals↗

PubMed2000

Zinc toxicity in various lung cell lines is mediated by glutathione and GSSG reductase activity.

In a previous work, it was shown that in cells after a decrease of cellular glutathione content, toxic zinc effects, such as protein synthesis inhibition or GSSG (glutathione, oxidized form) increases, were enhanced. In this study, zinc toxicity was determined by detection of methionine incorporation as a parameter of protein synthesis and GSSG increase in various lung cell lines (A549, L2, 11Lu, 16Lu), dependent on enhanced GSSG reductase activities and changed glutathione contents. After pretreatment of cells with DL-buthionine-[R,S]-sulfoximine (BSO) for 72 h, cellular glutathione contents were decreased to 15-40% and GSSG reductase activity was increased to 120-135% in a concentration-dependent manner. In BSO pretreated cells, the IC50 values of zinc for methionine incorporation inhibition were unchanged as compared to cells not pretreated. The GSSG increase in BSO pretreated cells by zinc was enhanced in L2, 11Lu, and 16Lu cells, whereas in A549 cells, the GSSG increase by zinc was enhanced only after pretreatment with the highest BSO concentration. Inhibition of GSSG reductase in alveolar epithelial cells was observed at lower zinc concentrations than needed for methionine incorporation inhibition, whereas in fibroblastlike cells, inhibition of GSSG reductase occurred at markedly higher zinc concentrations as compared to methionine incorporation inhibition. These results demonstrate that GSSG reductase is an important factor in cellular zinc susceptibility. We conclude that reduction of GSSG is reduced in zinc-exposed cells. Therefore, protection of GSH oxidation by various antioxidants as well as enhancement of GSH content are expected to be mechanisms of diminishing toxic cellular effects after exposure to zinc.

Buthionine Sulfoximine↗

PubMed1999

Influence of glutathione on zinc-mediated cellular toxicity.

The effect of zinc on various pulmonary cell lines has been studied by measuring the depletion of total cellular glutathione after exposure to zinc(II) chloride at different concentrations. Total cellular glutathione (cGS) was measured at 31+/-3 nmol/mg, 3.8+/-0.6 nmol/mg, and 3.7+/-1.2 nmol/mg protein in A549, L2, and 11Lu cells, respectively. After treatment with buthionine sulfoximine (BSO), the cGS levels decreased by 20% in A549 cells and below 0.2 nmol/mg in L2 and 11Lu cells. Exposure of A549 cells to 25-200 microM ZnCl2 for 4 h alone decreased the cGS content to 60-80%. There was little additional effect in BSO-pretreated cells. In L2 and 11Lu cells, the decrease of cGS was 70-85% following exposure to 15-150 microM ZnCl2 for 2 h. If BSO was also used, the decrease in cGS was 85-95% in L2 cells and 75-85% in 11Lu cells. Exposure to 25-250 microM ZnCl2 for 2 h diminished protein synthesis as determined by radiolabeled methionine incorporation, with half-maximum inhibition (EC50) from 40-160 microM ZnCl2. To attain similar EC50 values in BSO-pretreated cells, only about half the zinc concentrations were required as compared to cells without pretreatment. The decrease of cGS was accompanied by an increased ratio of oxidized: reduced glutathione that was more pronounced in cells with low glutathione content.

Animals↗

PubMed1998

Inhibition of protein synthesis by zinc: comparison between protein synthesis and RNA synthesis.

Inhalation of zinc fumes may lead to the acute respiratory distress syndrome. The mechanisms of pulmonary zinc toxicity are not yet understood. Therefore we investigated zinc-dependent depression of protein and RNA synthesis in rat and human lung cell lines. 1. After exposure to 120 or 150 micromol/l zinc, RNA synthesis as assessed by uridine incorporation decreased by 60-70% between 0 and 2 h exposition in rat alveolar type II cells (L2 cells) and human fibroblast-like cells (11Lu and 16Lu cells), and by 90% between 0 and 4 h in carcinoma-derived cells (A549 cells). 2. After 2 h exposure, L2, 11Lu, and 16Lu cells were half-maximally inhibited by 50 micromol/l zinc, whereas A549 cells were more resistant with half-maximal inhibition at 100 micromol/zinc. 3. Protein and RNA synthesis was inhibited in parallel in L2, 11Lu, and A549 cells as indicated by simultaneous determination of uridine and amino acid incorporation. In 16Lu cells, the decline in protein synthesis preceded RNA synthesis inhibition. Pretreatment with RNA synthesis inhibitors (amanitin or actinomycin D) had no effect on time curve and intensity of RNA synthesis inhibition. Taken together, our results indicate that the suppression of RNA and protein synthesis likely are independent phenomena, due to direct zinc effects on these biosynthetic pathways.

Amanitins↗

PubMed1990

Increased hepatic nicotine elimination after phenobarbital induction in the conscious rat.

Elimination parameters of [14C]nicotine in conscious rats receiving nicotine (0.3 mg/kg) either intravenously or orally were studied. The oral availability of unchanged nicotine, derived by comparison of the respective areas under the concentration vs time curves (AUC), was 89%, indicating low hepatic extraction ratios of about 10%. Pretreatment of rats with phenobarbital (PB) markedly increased hepatic first-pass extraction of nicotine. The oral availability of unchanged nicotine in plasma dropped to 1.4% of the corresponding values obtained from PB-treated rats receiving nicotine iv. After PB pretreatment, the clearance of iv nicotine was increased approximately twofold over controls, much less than the observed more than ninefold increase of hepatic first-pass extraction. It is assumed that extrahepatic metabolism contributed significantly to the rapid removal of nicotine from the plasma. The elimination of cotinine, originating from nicotine administered either po or iv, was significantly increased by PB pretreatment, as determined by the ratio of corresponding AUCs. The pattern of nicotine metabolites in urine also indicated an increase in the rate of cotinine metabolic turnover. The amount of norcotinine in the organic extract of urine paralleled PB microsomal enzyme induction. The ratio between urinary concentrations of the normetabolite and cotinine correlated strongly with the PB-induced state of rat liver. This may be a suitable indicator of PB-inducible hepatic cytochrome P450 isoenzyme(s). Since smoking habits in man are feedback-regulated by nicotine plasma concentrations, a similar increase of nicotine elimination by microsomal enzyme induction in man may be of relevance for tobacco consumption.

Administration, Oral↗

PubMedDate not supplied

Increased cotinine elimination and cotinine-N-oxide formation by phenobarbital induction in rat and mouse.

The metabolic fate of cotinine, the major metabolite of nicotine, was studied in phenobarbital-induced and non-induced isolated perfused rat lung and liver and in isolated hepatocytes of rats and mice. The non-induced lung tissue showed low cotinine metabolizing capacity while the perfused liver was approximately four times more active. After phenobarbital pretreatment the metabolism of cotinine was increased eight-fold in the intact liver. A substantial increase in cotinine metabolism was also found in isolated hepatocytes from PB-induced rats and in cultured mouse hepatocytes grown in a medium supplemented with PB. This was paralleled by an increased formation of cotinine-N-oxide which could be inhibited by 100 microM metyrapone. In contrast, the pulmonary elimination of cotinine was not affected by PB. A dominant role of primary N-oxidation of nicotine compared to C-oxidation was apparent in non-induced rat liver. After PB treatment the rate of nicotine-N'-oxide formation dropped markedly while the cotinine related pathways were increased causing an inversion of the N- to C-oxidation ratio. In the lung, cotinine formation was the preferred metabolic pathway of nicotine already in non-induced organs. The pattern of nicotine metabolites was not altered by PB induction. In conscious PB-induced rats receiving nicotine orally or intravenously, 3'-hydroxycotinine was found as the main urinary metabolite of nicotine while only a small fraction was excreted as cotinine-N-oxide. This discrepancy between the profile of nicotine metabolites in perfused liver and lung and in the urine in vivo indicates that extrahepatic organs other than the lung may be important sites of cotinine metabolism.

Animals↗