Alteration of enzyme activity in rat liver following the acute and chronic administration of nicotine

Effects of nicotine infusion on the metabolism of the tobacco carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in rats

The tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a lung carcinogen in the rat and believed to be a causative agent for lung cancer in smokers. To exert its carcinogenic potential NNK is metabolically activated by cytochrome P450-catalyzed alpha-hydroxylation. Nicotine and NNK share metabolic pathways. The purpose of this study was to determine whether nicotine alters the fraction of NNK undergoing activation to carcinogenic metabolites. Rats received acute (36 h) or chronic (2 week) s.c. infusions of nicotine at rates producing serum nicotine concentrations 2-3 times the usual venous nicotine concentrations measured in smokers. A single dose of [5-3H]-NNK was administered i.p. 24 h prior to the end of each infusion. Urine was collected for 24 h thereafter and NNK metabolites quantified by radioflow HPLC. Neither acute nor chronic nicotine infusion had any effect on the extent of NNK metabolism by alpha-hydroxylation. These data suggest that nicotine infusion, at rates simulating the higher doses of nicotine replacement therapy now being studied for smoking cessation, neither induces nor inhibits NNK metabolism appreciably and therefore should not alter the formation of carcinogenic NNK metabolites.

Induction of pulmonary CYP1A1 by nicotine

1. We have examined the catalytic activities (7-ethoxyresorufin O-deethylase [EROD] and 7-methoxyresorufin O-demethylase [MROD]), protein levels (Western blot analysis) and mRNA levels (Northern blot analysis) of cytochrome P4501A (CYP1A1 and CYP1A2) in the lung, liver and kidney following a single 2.5 mg/kg (15.4 micromol/kg) subcutaneous dose of nicotine to the female Sprague-Dawley rat. 2. Only in lung microsomes was EROD activity significantly induced by nicotine treatment. The activity increased 4.4-fold at 6 h after treatment relative to controls, peaked at 12 h at 14.7-fold the control activity and returned to near control level at 24 h. 3. In parallel with EROD activity, CYP1A1 immunoreactive protein abundance was altered significantly by nicotine treatment only in the lung, peaking at 12 h and decreasing towards control levels thereafter. 4. Following subcutaneous nicotine treatment, CYP1A1 mRNA was detectable in the lung at 6 and 12 h but not at 24 h, was slightly elevated in the kidney at 12 h and was detectable in the liver only at the 12-h point. CYP1A2 immunoreactive protein and its mRNA were detectable only in the liver, and their levels were not affected significantly by nicotine pretreatment. 5. Nicotine affected the binding of Hepa 1c1c7 cytosolic protein to a CYP1A1 xenobiotic response element in a gel mobility shift assay, suggesting involvement of the aryl hydrocarbon receptor and transcriptional activation in CYP1A1 induction by the chemical. 6. Inhaled nicotine also induced pulmonary EROD activity, and the induction by either inhaled or injected nicotine was more pronounced in the male than in the female rat. 7. The findings show that nicotine is a potent, rapid but transient inducer of CYP1A1 in the rat lung and suggest that the alkaloid is a likely contributor to CYP1A1 induction by cigarette smoke.

Effect of nicotine on lipoprotein metabolism in rats

Nicotine, a major component of cigarette smoke, plays an important role in the development of cardiovascular disease and lung cancer in smokers. The effect of nicotine on lipoprotein metabolism was studied using rats as the experimental animal. There was a significant increase in the total cholesterol, phospholipids, and triglycerides as well as the amount of lipids associated with very low density lipoprotein (VLDL) and low density lipoprotein (LDL) in sera of nicotine-treated rats. The incorporation of 3H labeled leucine into the apo B was found to be increased both in the medium and associated cells in the hepatocytes isolated from nicotine-treated rats indicating an increased synthesis and secretion of the apo B containing lipoproteins. This was further confirmed by the higher incorporation of 14C acetate into total and individual lipids of LDL and VLDL secreted into the medium as well as that associated with different lipids in the cell layer. The activity of lipoprotein lipase in extrahepatic tissues and plasma lecithin cholesterol acyl transferase activity were significantly lower in nicotine-treated rats. These results indicate that nicotine exerts hyperlipidemic effects particularly by increasing the synthesis and secretion of triglyceride-rich lipoproteins. Since nicotine is one of the major hazardous components present in cigarette smoke and tobacco, one can extrapolate that the deleterious effect exerted by nicotine on rats extends to cigarette smokers and those who use other forms of tobacco.

Effects of tobacco smoke exposure on the kinetics of bupivacaine in mice

The aim of this work was to determine the effects of different time of tobacco smoke exposure on pharmacokinetics of bupivacaine in mice. Mice were exposed to tobacco smoke during 4 days (group T4) or 8 days (group T8) using the Hamburg II smoking machine. Controls were exposed under the same experimental conditions but without tobacco smoke. Serum pharmacokinetic parameters, protein or erythrocyte binding of bupivacaine were measured on the 4th and 8th day of exposure. Furthermore the urines were kept during 24 hours and urine metabolite percentages were determined. After the short exposure (4 days), no differences between treated and control groups were reported in contrary to the longer exposure (8 days), where data showed a significantly increased metabolism and elimination of bupivacaine in the treated group compared to the controls. Our data indicate that tobacco smoke acts at different levels i.e. metabolism, elimination and binding of bupivacaine. Tobacco smoke exposure increases the metabolism of bupivacaine by activating the hydroxylation route and by inducing an important elimination of 3OH-bupivacaine. Besides, it increases the permeability of the cell membranes and facilitates the penetration of bupivacaine and desbutylbupivacaine in erythrocytes.

Effects of different exposure times to tobacco smoke intoxication on carboxyhemoglobin and hepatic enzymate activities in mice

The aim of this work was to determine the effects of different exposure times to smoke on carboxyhemoglobin (HbCO) and hepatic enzymate activities in order to adapt a tobacco smoke intoxication model in mice. Mice were exposed to tobacco smoke for various durations of either 2 (group S2), 4 (group S4), 8 (group S8), or 31 days (group S31) using the Hamburg II machine. Controls (nonexposed animals) were used under the same experimental conditions. On the 2nd, 4th, 8th, and 31st day, mice were sacrificed by decapitation, and blood carboxyhemoglobin level and hepatic enzymate activities catalysed by CYP 450 families were measured. Our data with regard to the exposed group indicated first that HbCO was significantly increased after 4 or 8 days of exposure and decreased after 31 days compared to controls (where HbCO was constant for the duration of the 31 days) and second, the enzymate activities were significantly higher during the period of exposure. In conclusion, a 4- and 8-day exposure period with eight cigarettes per day seems to be the model of tobacco smoke intoxication in mice to be chosen.

The chronic administration of nicotine induces cytochrome P450 in rat brain

The objective of these studies was to determine whether chronic administration of nicotine altered the cytochrome P450 (P450) monooxygenase system in rat brain. Male Sprague-Dawley rats received injections of nicotine bitartrate (1.76 mg/kg, s.c., twice daily for 10 days), and total cytochrome P450 content, the activity of NADPH-cytochrome c reductase, and the activities and relative abundance of P4502B1 and P4502B2 (P4502B1/2) were determined in microsomal fractions from rat brain. The content of P450 increased significantly (p < 0.02) in all brain regions examined from nicotine-injected rats; the largest increase (208% of control) was in frontal cortex and the smallest increase (122% of control) in cerebellum. The activity of NADPH-cytochrome c reductase was unaltered by nicotine administration. Benzyloxyresorufin O-dealkylase (BROD) and pentoxyresorufin O-dealkylase (PROD) activities, mediated by P4502B1/2, increased significantly (p < 0.02) following nicotine administration; the largest increase (213-227% of control) was in frontal cortex. Western blots of microsomal proteins indicated that the increase in enzymatic activity was associated with an increase in content of P4502B1/2 immunoreactive proteins. In contrast to brain, total P450 content, activities of NADPH-cytochrome c reductase, BROD, and PROD, and levels of P4502B1/2 immunoreactive proteins in liver were unaffected by chronic nicotine administration. Results indicate that chronic nicotine administration regulates the expression of P4502B1/2 in brain and that at the dose schedule used this effect occurs without a demonstrable effect on the hepatic P450 monooxygenase system.

The effect of a single treatment with cigarette smoke on the blood levels and hemodynamic effects of propranolol in rats

The effect of a single treatment with cigarette smoke on the blood levels and hemodynamic effects of propranolol in rats was studied. Pentobarbital sleep time was not affected whereas zoxazolamine paralysis time was shortened 72% in rats, 24 h after the cigarette smoke exposure. The beta-adrenoceptor blocking effect of propranolol observed at 10 and 20 min time intervals was abolished in rats exposed to cigarette smoke 24 h after the exposure. The blood propranolol concentrations were decreased in rats pretreated with phenobarbital, 3,4-benzpyrene and ethanol as well as in cigarette smoke exposed rats. Among several factors that could influence propranolol metabolism, in this study, enzyme induction is suggested to be dominant.

Clinical pharmacokinetics of nicotine

Nicotine intake is considered to be a major factor in sustaining tobacco addiction. For this reason, nicotine gum has recently been introduced as an adjuvant to smoking cessation. The introduction of nicotine as a 'therapeutic' entity necessitates a careful examination of its clinical pharmacokinetics. Insufficient data exist to quantitatively assess the absorption of nicotine after oral administration. Based upon physicochemical and pharmacokinetic principles, the oral bioavailability of nicotine would be expected to be less than 20%. The limited data available in the literature appear to support this conclusion. Absorption from the oral mucosa is the principal site of nicotine absorption in subjects who chew tobacco or nicotine gum. Absorption by this route is highly pH dependent. Nicotine is also readily absorbed from the nasal mucosa, and after topical administration. Nicotine distributes extensively into body tissues with a volume of distribution ranging from 1.0 to 3.0 L/kg. Nicotine has been shown to transfer across the placenta and into breast milk in humans. Plasma protein binding is negligible, ranging from 4.9 to 20%. The predominant route of nicotine elimination is hepatic metabolism. Although a number of metabolites of nicotine have been identified, it is unclear whether any of these compounds contribute to the pharmacological effect of nicotine. Nicotine is also excreted unchanged in urine in a pH-dependent fashion. With urinary pH less than 5, an average 23% of the nicotine dose is excreted unchanged. When urinary pH is maintained above 7.0, unchanged nicotine urinary excretion drops to 2%. After intravenous administration, nicotine exhibits biexponential decline in plasma. Total plasma clearance ranges from 0.92 to 2.43 L/min. During urinary acidification, renal clearance averages 0.20 L/min. Non-renal blood clearance averages 1.2 L/min, indicating that nicotine elimination is dependent on hepatic blood flow. The literature is devoid of information regarding the effect of disease on the pharmacokinetics of nicotine. Based upon the drug's pharmacokinetics in healthy smokers, it would be anticipated that disease states which alter hepatic blood flow may have the greatest impact on nicotine pharmacokinetics. In addition, drugs which alter hepatic blood flow may cause significant alterations in the systemic clearance of nicotine. Dependence on smoking appears to be related, at least in part, to the achievement of a rapid rise in plasma nicotine concentrations. If this assessment is correct, the most desirable adjuvant for smoking cessation would be one that closely mimics this pattern of plasma nicotine concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Nicotine can attenuate the disruptive effects of phencyclidine on repeated acquisition in monkeys

Patas monkeys acquired a different four-response chain each session by responding sequentially on three levers in the presence of four discriminative stimuli (numerals). The response chain was maintained by food presentation under a fixed-ratio schedule. Errors produced a brief timeout but did not reset the chain. Each day there were four 15-min sessions, with a 10-min intersession interval. Cumulative dose-effect curves for phencyclidine were obtained by giving an IM injection before each of the four sessions; successive injections increased the cumulative dose by 1/4 log-unit steps. When phencyclidine was administered alone, overall response rate decreased and percent errors increased with increasing doses. When nicotine was administered alone (IM) before the first session, the higher doses initially produced large decreases in overall response rate. Unlike phencyclidine, nicotine alone generally had no effect on percent errors. When intermediate or high doses of phencyclidine were administered after pretreatment with certain doses of nicotine, both the rate-decreasing and error-increasing effects were smaller than those produced by phencyclidine alone. This attenuation of the disruptive effects of phencyclidine on acquisition occurred at a time when nicotine alone had little or no behavioral effect.

Short-term studies on the in vivo metabolism of N-oxides of nicotine in rats

This study was designed to examine the in vivo reduction of the N-oxidation products of nicotine metabolism in rats. Male Fischer-344 rats were divided into one control and three experimental groups (n = 20). Each treatment group received either 0.02% trans-nicotine N'-oxide, 0.02% cis-nicotine N'-oxide, or 0.02% nicotine N,N'-dioxide in drinking water for 3 wk. After 7 d of metabolite administration, plasma nicotine levels in the trans-nicotine N'-oxide group rose to twice that of the cis-nicotine N'-oxide or nicotine N,N'-dioxide group. Plasma cotinine [1-methyl-5-(3-pyridinyl)-2-pyrrolidinone] concentrations reached maximum levels during wk 1 in the cis-nicotine N'-oxide and nicotine N,N'-dioxide groups but continued to increase for another 7 d in the trans-nicotine N'-oxide group. At d 15 and again at d 21, rats from each group (n = 10) were placed in metabolism chambers and given 50 ml tap water over a 24-h period. Analysis of urine obtained from a metabolism-chamber study conducted after 15 d of consumption revealed concentrations of nicotine in the trans-nicotine N'-oxide group that were 3 times higher than cis-nicotine N'-oxide-treated animals. Urinary cotinine levels were similar in all three groups. Results from a second chamber study (d 21) showed similar urinary nicotine and cotinine values in all treatment groups. Plasma total triiodothyronine (TT3) concentrations were reduced in all treatment groups during the first week. Plasma total thyronine (TT4) concentrations were reduced (p less than 0.05) in the trans-nicotine N'-oxide and cis-nicotine N'-oxide treatment groups during the first week. Plasma total thyronine (TT4) concentrations cis-nicotine N'-oxide is presented. An analytical method for separation of nicotine, cotinine, and cis- and trans-nicotine N'-oxide, as well as cis- and trans-nicotine N,N'-dioxide, is also outlined.

Stimulation of liver tryptophan pyrrolase during heat exposure

Exposure of rats to heat (39 +/- 1 degree C) stimulated liver tryptophan pyrrolase 2-fold between 3 and 48 h. Plasma corticosterone increased 2-fold after 1 h of heat exposure and decreased to a low value of 50% by 16 h. The effect of heat exposure on the enzyme was obtained in adrenalectomized animals. Stimulation by cortisol and tryptophan of the enzyme was also obtained in heat exposure, and the effects seemed to be additive. The concentration of tryptophan in the liver remained unchanged, and that in the plasma decreased to about 50% at 8 h exposure to heat and reverted to normal by 46 h. Simultaneous administration of noradrenaline to heat-exposed rats had no effect, whereas that of thyroxine partly prevented the stimulation of the enzyme activity. Hypothyroid conditions obtained by thyroidectomy or treatment with propylthiouracil significantly stimulated the enzyme activity. Cycloheximide treatment of heat-exposed rats did not prevent the stimulation of the enzyme activity. The results indicate that the effect of heat exposure on liver tryptophan pyrrolase is obtained, due to the accompanying hypothyroid condition, by increasing the activity of the existing protein by a mechanism possibly different from those known at present.

Pharmacokinetics of nicotine in rats after multiple-cigarette smoke exposure

The pharmacokinetics of nicotine and its major metabolites was evaluated in male rats after multiple-cigarette smoke exposure. A smoke-exposure apparatus was used to deliver cigarette smoke to the exposure chamber. The rats were exposed to smoke from a single cigarette every 8 hr for 14 days and to the smoke of a cigarette spiked with radiolabeled nicotine on the 15th day. Blood and urine samples were collected at timed intervals during the 10-min smoke-exposure period of the last cigarette and up to 48 hr thereafter. Nicotine, cotinine, and other polar metabolites were separated by thin-layer chromatography and quantified by liquid scintillation counting. The data were analyzed by computer fitting, and the derived pharmacokinetic parameters were compared to those observed after a single iv injection of nicotine and after a single-cigarette smoke exposure. The results indicated that the amount of nicotine absorbed from multiple-cigarette smoke was approximately 10-fold greater than that absorbed from a single cigarette. Also, unlike the single-cigarette smoke exposure experiment, nicotine plasma levels did not decay monotonically but increased after the 5th hr, and high plasma concentrations persisted for 30 hr. The rate and extent of the formation of cotinine, the major metabolite of nicotine, were decreased as compared with their values following a single-cigarette smoke exposure. It was concluded that nicotine or a constituent of tobacco smoke inhibits the formation of cotinine and may affect the biotransformation of other metabolites. Urinary excretion tended to support the conclusions that the pharmacokinetic parameters of nicotine and its metabolites were altered upon multiple as compared to single dose exposure.

Oral administration of nicotine: its uptake and distribution after chronic administration to mice

An investigation was made of the suitability of administering nicotine to experimental animals by inclusion in the drinking water. It was found that, after an initial accommodation period of several weeks, nicotine could be administered up to a concentration of 100 micrograms/ml with no decrease in fluid intake or weight gain compared to control. An analysis of the steady-state plasma levels and distribution of nicotine was made in mice which had received nicotine in the drinking water at a concentration of 60 micrograms/ml. The average daily dose of nicotine received by these animals was 17.2 mg/kg. The steady-state plasma level of nicotine was 34.4 ng/ml, representing 6% of the total compound present at steady-state as determined by thin-layer chromatography. The distribution of nicotine or metabolite in mice which had received [methyl-14C]-nicotine orally was determined. Whole-body autoradiography, as well as direct tissue counting, demonstrated that nicotine accumulates in a number of areas, particularly the salivary gland, nasal epithelium, uterus, and liver. There was relatively little material in the blood or brain. This investigation indicates that ad libitum oral administration is an acceptable method for maintaining experimental animals on nicotine for long periods of time.

Cigarette smoking impairs hepatic uptake of high density lipoproteins

The effect of chronic inhalation of cigarette smoke on hepatic uptake of high density lipoproteins (HDL) in White Carneau pigeons was examined. Four treatment groups included: 1) Shelf Control birds fed a chow diet and retained in their cages; 2) Sham pigeons fed a cholesterol-saturated fat diet and exposed to fresh air by a smoking machine; 3) Low nicotine-low carbon monoxide (LoLo) animals also fed the cholesterol diet and exposed to low concentrations of these cigarette smoke products; and 4) High nicotine-high carbon monoxide (HiHi) birds fed the cholesterol diet and subjected to high concentrations of these components. Livers from both smoke exposed groups contained significantly more triglyceride than those from Sham animals while livers from HiHi birds alone had elevated concentrations of protein. Liver slices from LoLo and HiHi pigeons incorporated significantly less HDL 3H free and esterified cholesterol and HDL 14C apoprotein from media during in vitro incubation than livers from Sham birds. Impaired hepatic uptake of HDL suggests a permanent alteration in liver function resulting from chronic exposure to tobacco smoke and may represent one mechanism by which cigarette smoking attenuates HDL's anti-atherogenic properties.

Time-dependent induction of hepatic drug metabolism in rats by cotinine

Cotinine, administered twice a day for 2 days in a dose of 20 or 40 mg/kg i.p., induced rat hepatic drug metabolism between 22% to 62%. Induction decreased to 26-37% after 4 days of cotinine (40 mg/kg bid). No significant induction was observed after 8 days of this dose of cotinine. Explanations are offered for decreasing induction by cotinine with time.

Stimulation of drug and carcinogen metabolism by prolonged oral tobacco consumption

Oral administration of tobacco to rats for 21 days caused remarkable stimulation of the metabolism of phenacetin, aniline and benzo[a]pyrene, a carcinogen, by hepatic microsomal mixed function oxidases (MFO). Such treatment for 6 days resulted in a small increase in the activities of phenacetin O-dealkylase and aromatic hydrocarbon hydroxylase (AHH) without affecting aniline hydroxylase activity. Nicotine given orally was found to be a relatively weak inducer of phenacetin O-dealkylase and aniline hydroxylase, and elicited a maximum increase in their activities within 6 days which remained unchanged even after 21 days of continuous administration. However, these two enzyme systems were not affected following only one or two doses of tobacco and nicotine. Both tobacco and nicotine inhibited these biotransformations in vitro.

Influence of route of administration on metabolism of [14C]nicotine in four species

1. The metabolism of [14C]nicotine has been studied in four species of animals, rabbit, rat, cat and squirrel monkey, after administration by different routes. 2. Intravenous injection of 4 mug/kg [14C]nicotine every 60 s for 1 h results in peak blood levels of approximately 100 ng/ml in all species but the rabbit. [14C]Cotinine levels in blood vary widely between species. 3. Subcutaneous injection of 0.4 mg/kg [14C]nicotine produces similar peak blood nicotine levels but the time course, for a given species, is different. 4. Intragastric instillation of 1 mg/kg [14C]nicotine to the cat and rabbit results in much lower levels of [14C]nicotine in blood and relatively high levels of [14C]cotinine. 5. Urinary excretion data indicate that, irrespective of route, the squirrel monkey excretes only a small proportion of the dose into urine during the period of experiment, of which the major proportion is [14C]nicotine. The cat, in contrast, excretes a relatively large proportion of the dose during the experimental period though only a minor proportion of the radioactivity is due to [14C]nicotine or [14C]cotinine. 6. All four species are potentially useful for model experiments with nicotine, though metabolism of nicotine by squirrel monkey is most similar to man.

Nicotine inhibition of the metabolism of 3,4-benzopyrene, a carcinogen in tobacco smoke

A decreased rate of biliary excretion of radioactive metabolites of 3,4-benzopyrene was observed in rats given a single dose of nicotine. Prior treatment of rats with nicotine decreased benzopyrene hydroxylase activity in homogenates of liver, lung, and small intestine. The addition of nicotine to incubated tissues also decreased benzopyrene hydroxylase activity. These findings show that nicotine inhibits the metabolism of 3,4-benzopyrene in vivo and in vitro.

The effect of smoking on nicotine metabolism in vivo in man

Nicotine and a basic metabolite, cotinine, were determined in the urine by gas-liquid chromatography after intravenous administration of (—)-nicotine hydrogen (+)-tartrate to groups of male and female smokers and non-smokers in whom the urine was maintained at an acid pH. The urinary recoveries of nicotine and cotinine from male smokers fell in two groups. One showed a lower recovery of both alkaloids than was seen with male non-smokers. The other showed a similar recovery of nicotine but more cotinine than the male non-smokers. Female smokers excreted less nicotine but more cotinine than female non-smokers. More nicotine but less cotinine was excreted by female non-smokers than by male non-smokers. The results show sex dependent metabolism of nicotine occurs in non-smoking humans and that smoking causes alterations in nicotine metabolism.