Tissue distribution of ['H]nicotine in dogs and rhesus monkeys

Promoting New Approach Methodologies (NAMs) for research on skin color changes in response to environmental stress factors: tobacco and air pollution

Aging is one of the most dynamic biological processes in the human body and is known to carry significant impacts on individuals' self-esteem. Skin pigmentation is a highly heritable trait made possible by complex, strictly controlled cellular and molecular mechanisms. Genetic, environmental and endocrine factors contribute to the modulation of melanin's amount, type and distribution in the skin layers. One of the hallmarks of extrinsic skin aging induced by environmental stress factors is the alteration of the constitutive pigmentation pattern clinically defined as senile lentigines and/or melasma or other pigmentary dyschromias. The complexity of pollutants and tobacco smoke as environmental stress factors warrants a thorough understanding of the mechanisms by which they impact skin pigmentation through repeated and long-term exposure. Pre-clinical and clinical studies demonstrated that pollutants are known to induce reactive oxygen species (ROS) or inflammatory events that lead directly or indirectly to skin hyperpigmentation. Another mechanistic direction is provided by Aryl hydrocarbon Receptors (AhR) which were shown to mediate processes leading to skin hyperpigmentation in response to pollutants by regulation of melanogenic enzymes and transcription factors involved in melanin biosynthesis pathway. In this context, we will discuss a diverse range of New Approach Methodologies (NAMs) capable to provide mechanistic insights of the cellular and molecular pathways involved in the action of environmental stress factors on skin pigmentation and to support the design of raw ingredients and formulations intended to counter their impact and of any subsequently needed clinical studies.

Long-term Stimulation of α7 Nicotinic Acetylcholine Receptor Rescues Hemorrhagic Neuron Loss via Apoptosis of M1 Microglia

We previously revealed that long-term treatment with nicotine suppresses microglial activation, resulting in a protective effect against thrombin-induced shrinkage of the striatal tissue in organotypic slice cultures. Here, the effect of nicotine on impaired M1 and protective M2 microglial polarization was investigated using the BV-2 microglial cell line in the presence or absence of thrombin. Following nicotine treatment, α7 nicotinic acetylcholine receptor expression transiently increased and then gradually decreased until 14 days. Treatment with nicotine for 14 days slightly polarized M0 microglia to M2b and d subtypes. Co-exposure of thrombin and low concentration of interferon-γ recruited inducible NO synthase (iNOS)- and interleukin-1β-double-positive M1 microglia in a thrombin-concentration-dependent manner. Treatment with nicotine for 14 days significantly decreased the thrombin-induced increase of iNOS mRNA levels and conversely showed a tendency to increase arginase1 mRNA levels. Moreover, treatment with nicotine for 14 days suppressed thrombin-induced phosphorylation of p38 MAPK through the α7 receptor. Repeated intraperitoneal administration of α7 agonist PNU-282987 for 14 days selectively evoked the apoptosis of iNOS-positive M1 microglia at the perihematomal area and showed a neuroprotective effect in an in vivo intracerebral hemorrhage model. These findings revealed that long-term stimulation of α7 receptor causes suppression of thrombin-induced activation of p38 MAPK followed by apoptosis in neuropathic M1 microglia.

Smoking and structural brain deficits: a volumetric MR investigation

Growing evidence from animal studies indicates brain-damaging properties of nicotine exposure. Investigations in humans found a wide range of functional cerebral effects of nicotine and cigarette smoking, but studies focusing on brain damage are sparse. In 22 smokers and 23 never-smokers possible differences of the cerebral structures were investigated using magnetic resonance imaging and voxel-based morphometry. Significantly smaller grey matter volume and lower grey matter density (P = 0.05, corrected) were observed in the frontal regions (anterior cingulate, prefrontal and orbitofrontal cortex), the occipital lobe and the temporal lobe including parahippocampal gyrus, in smokers than in never-smokers. Group differences of either grey matter volume or grey matter density were also found in the thalamus, cerebellum and substantia nigra, among other regions. Smokers did not show greater volumes than never-smokers in any cerebral region. Magnitude of lifetime exposure to tobacco smoke (pack-years) was inversely correlated with volume of frontal and temporal lobes and cerebellum (P = 0.001, uncorrected). The data indicate structural deficits of several cortical and subcortical regions in smokers relative to never-smokers. The topographic profile of the group differences show some similarities to brain networks known to mediate drug reinforcement, attention and working memory processing. The present findings may explain in part the frequently reported cognitive dysfunctions in chronic cigarette consumers.

Involvement of specific transport system of renal basolateral membranes in distribution of nicotine in rats

We measured the nicotine concentrations in tissues after a bolus i.v. administration of [(3)H]nicotine to rats to characterize the distribution profile of nicotine. The kidney showed the greatest distribution of nicotine compared to other tissues including liver, lung, heart, brain, and intestine. We also performed an HPLC assay for the determination of nicotine and its major metabolite, cotinine, and found that cotinine was negligible in the distribution of almost all tissues, except for the kidney and lung. In the kidney, cotinine was detected at a lower level than nicotine, while cotinine tended to be distributed in the lung compared to nicotine. [(3)H]Nicotine was accumulated in renal slices in a concentration dependent fashion, suggesting that the nicotine uptake in the renal tubules could be mediated by a specific transport system. Unlabeled nicotine, cotinine, and quinidine showed potent inhibitory effects on [(3)H]nicotine uptake by renal slices. In contrast, tetraethylammonium (TEA), cimetidine, and N(1)-methylnicotinamide (NMN), which were substrates of renal organic cation transporters, had no effects on the uptake. These findings suggested that a specific transporter was involved in nicotine transport at the basolateral membranes of rat renal tubules, which could mediate the high accumulation of nicotine from blood into the kidney.

Firsthand cigarette smoke alters fibroblast migration and survival: implications for impaired healing

Although it is known that high levels of cigarette smoke lead to cell death, little is known about the effects of low-to-moderate levels of smoke components that are found in vivo, such as those experienced by cells in tissues. Clinical studies and experimental data show that smokers heal poorly and are more prone to develop fibrotic diseases. Here we show the effects of first-hand cigarette smoke on fibroblasts, cells that are critically involved in these processes. Using doses of smoke found in the tissues of smokers and a variety of cell and molecular approaches, we show that these doses of cigarette smoke do not cause cell death but rather stimulate fibroblasts to produce stress response and survival proteins such as interleukin-8, PKB/Akt, p53, and p21 that in turn contribute to an increase in cell survival. In addition, smoke-treated cells show a decrease in cell migration, which can be explained by the increased cell adhesion and alterations in cytoskeletal elements. We also show that these levels of smoke cause changes in mitochondrial morphology with a minimum loss of function and these changes are the result of exposure to reactive oxygen species. We conclude that the increase in cell survival may lead to a build-up of connective tissue in the area of a wound, potentially leading to delayed healing and/or fibrosis and that the alterations in the cytoskeleton and in cell adhesion result in inhibition of cell migration, a process that could lead to nonclosure of the wound for lack of proper fibroblast migration to form the healing tissue.

Transport mechanisms of nicotine across the human intestinal epithelial cell line Caco-2

Ulcerative colitis is a disease more commonly seen in nonsmokers. Because nicotine was postulated to be a beneficial component of tobacco smoke for ulcerative colitis, various formulations of nicotine have been developed to improve the local bioavailability within the gastrointestinal tissue. In the present study, to characterize the disposition of nicotine in the intestines, we investigated intestinal nicotine transport using Caco-2 cells. Nicotine was predominantly transported across Caco-2 cell monolayers in a unidirectional mode, corresponding to intestinal secretion, by pH-dependent specific transport systems. The specific uptake systems appear to be distinct from organic cation transporters and the transport system for tertiary amines, in terms of its substrate specificity and the pattern of the interaction. These transport systems could play a role in the intestinal accumulation of nicotine from plasma and could also be responsible for the topical delivery of nicotine for ulcerative colitis therapy. These findings could provide useful information for the design of effective nicotine delivery.

Modipafant, a new PAF antagonist: pharmacokinetics and disposition in rat, dog and man

1. The pharmacokinetics and disposition of modipafant, a dihydropyridine PAF antagonist, were studied in rat and dog following intravenous and oral administration of the drug or its radiolabelled analogue. In addition, the pharmacokinetics were studied in man following single administration of escalating oral doses of the drug. Modipafant is a lipophilic weak base with log D(octanol) 7.4 and pKa of 4.3 and 5.3 respectively. 2. Following intravenous administration of [14C]-modipafant to rat, radioactivity is rapidly distributed throughout the body, except for the brain. A significant amount of radioactivity (probably modipafant) is rapidly distributed to the alimentary tract, particularly in the stomach. This is believed to be due to 'ion trapping' of modipafant in the acidic environment of the upper GI tract. The re-circulated modipafant may be subject to reabsorption and/or faecal excretion. 3. Following intravenous administration to rats, systemic clearance is five times greater in the male than female. The magnitude of this difference is in keeping with the clearance of other dihydropyridines such as nilvadipine. In dog, the clearance values are similar for both sexes, as expected. In this latter species, the systemic clearance decreases 6-fold with increasing dose size, indicative of saturation of a pathway of metabolism. 4. Following oral administration over a dose range of 1-12 mg/kg, modipafant is incompletely (27-67%) bioavailable in rat and dog. In the male dog, systemic exposure to drug (AUC/infinity) increased non-linearly with dose. Following oral administration to man, absorption was rapid with a mean value for Tmax of 1 h, and Cmax's ranging non-linearly from 90 to 2100 ng/ml following dosing at 12.5 to 150 mg respectively. 5. The elimination of modipafant is characterized by short half-life (mean values for t1/2 range from 1 to 3 h). However, the nature of the receptor kinetics of modipafant (slow offset) means that the drug shows a long duration of action in spite of short pharmacokinetics at pharmacologically relevant doses. 6. Following oral and intravenous administration of 14C-modipafant to rat and dog, the majority of radioactivity (mean 92%) is recovered in the faeces. The excretion of modipafant in rat and dog is characterized by metabolism, mostly to pyridine metabolites, accounting for between 38 and 75% of total clearance, the rest being cleared as unchanged drug.

Simultaneous determination of nicotine and cotinine in various human tissues using capillary gas chromatography/mass spectrometry

A reliable and sensitive method for the simultaneous determination of nicotine and cotinine concentrations in various human tissues was developed using capillary gas chromatography/mass spectrometry. Nicotine and cotinine were extracted using a 3-step solvent extraction procedure and quinoline as an internal standard. Quantification was carried out by single ion monitoring using ions of m/z 133 for nicotine, m/z 176 for cotinine and m/z 129 for quinoline. The lower limit of detection was 5 ng/g for nicotine and 10 ng/g for cotinine, in each tissue sample. The calibration curves of various tissues were linear in the concentration range from 5-1,200 ng/g for nicotine and 10-1,500 ng/g for cotinine. The accuracy and precision of this method were examined using human tissues and the results were satisfactory. The distribution of nicotine and cotinine was measured in tissues from 10 human autopsies. Nicotine was detected in every tissue examined at a level seen in habitual smokers. The nicotine concentration was high in the liver, kidney, spleen and lung, and low in adipose tissue. The cotinine level was highest in the liver. The tissue/blood concentration ratios of nicotine and cotinine were most stable in skeletal muscle, where the level of these drugs was close to that in whole blood. Skeletal muscle is, therefore, considered to be the most suitable tissue sample for toxicological examination, when acquisition of blood samples is not feasible.

Nicotine has no effect on rat gastric mucosal prostaglandin generation in vitro

Previous studies have shown that cigarette smoking depresses prostaglandin generation by human gastric mucosa, but the component of smoke that is responsible for that action is not known. To investigate whether nicotine has a direct effect on gastric mucosal prostaglandin generation, we performed the following study. Eight rats were sacrificed and the stomachs removed. Using a biopsy forceps, small pieces of gastric mucosa were resected and placed in incubation vials containing either buffered Krebs solution alone (control), Krebs solution plus indomethacin (5 micrograms/ml), or Krebs solution plus one of several concentrations of nicotine ditartrate (10, 100, 500, 1000 ng/ml). The nicotine concentrations we used ranged below and above the plasma nicotine concentrations of smokers shortly after smoking cigarettes. Three separate incubations of gastric mucosa were performed per experimental group from each animal. After 30 min of incubation, prostaglandin E2 and 6-keto-prostaglandin F1 alpha concentrations in the incubation medium were measured by radioimmunoassay. We found that nicotine at any concentration tested had no effect on the generation of prostaglandin E2 and 6-keto-prostaglandin F1 alpha by rat gastric mucosa. Thus, this study indicates that, if nicotine is involved in the depression of prostaglandin generation in the gastric mucosa of smokers, its role is an indirect one and not by direct action on the gastric mucosa.

Effects of acute administration of nicotine on convulsive movements and blood levels of corticosterone in old rats

The convulsive movements, blood levels of corticosterone and pharmacokinetics of nicotine after an acute intraperitoneal injection of nicotine (5 mg/kg) were examined in young (6-week-old) and old (2-year-old) rats. In pharmacokinetic study, blood nicotine levels during the elimination phase were significantly higher in old rats than in young rats. However, the duration of convulsions and the elevation of corticosterone levels after the nicotine injection showed significant decreases in old rats compared with those in young rats. These differences of nicotine-induced responses between young and old rats may be involved in the decrease in nicotine sensitivity.

A physiologically based pharmacokinetic model for nicotine disposition in the Sprague-Dawley rat

A physiologically based pharmacokinetic (PBPK) model was developed to describe the disposition of nicotine in the Sprague-Dawley (SD) rat. Parameters for the model were either obtained from the literature (blood flows, organ volumes) or determined experimentally (partition coefficients). Nicotine metabolism was defined in the liver compartment by the first-order rate constants KNC and KNP which control the rate of nicotine metabolism to cotinine and "polar metabolites" (PM), respectively. These rate constants were estimated by optimizing the model fit to pharmacokinetic data obtained by administering an intraarterial (S)-[5-3H]nicotine bolus of 0.1 mg/kg to 6 rats. Model simulations that optimized for the appearance of cotinine in plasma estimated KNC and KNP to be 75.8 and 24.3 hr-1, respectively. Use of these constants in the model allowed us to accurately predict nicotine plasma kinetics and the fraction of the dose eliminated by renal (8.5%) and metabolic (91.5%) clearance. To validate the model's ability to predict tissue kinetics of nicotine, 21 male SD rats were administered 0.1 mg/kg (S)-[5-3H]nicotine intraarterially. At seven time points following treatment, 3 rats were euthanized and tissues were removed and analyzed for nicotine. Model-predicted nicotine tissue kinetics were in agreement with those determined experimentally in muscle, liver, skin, fat, and kidney. The brain, heart, and lung exhibited nonlinear nicotine elimination, suggesting that saturable nicotinic binding sites may be important in nicotine disposition in these organs. Inclusion of saturable receptor binding expressions in the mathematical description of these compartments resulted in better agreement with the experimental data. The Bmax and KD estimated by model simulations for these tissues were brain, 0.009 and 0.12; lung, 0.039 and 2.0; and heart, 0.039 nmol/tissue and 0.12 nM, respectively. This PBPK model can successfully describe the tissue and plasma kinetics of nicotine in the SD rat and will be a useful tool for pharmacologic studies in humans and experimental animals that require insight into the plasma or tissue concentration-effect relationship.

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)

The spinal cord as a major site for the antinociceptive action of nicotine in the rat

These studies were conducted to localize the antinociceptive action of nicotine within the CNS. Antinociceptive and biodispositional studies were carried out after the injection of [3H]nicotine subcutaneously and intracerebroventricularly into the common carotid and vertebral arteries and into the subarachnoid space. The data indicated that [3H]nicotine was most potent when given into the subarachnoid space than by any of the other route of administration. Further, the disposition studies showed that [3H]nicotine was almost entirely contained in the thoracic and lumbar areas. These results are consistent with the hypothesis that the spinal cord is an important site for antinociception induced by nicotine.

Cytochrome P-450-dependent nicotine oxidation by liver microsomes of guinea pigs. Immunochemical evidence with antibody against phenobarbital-inducible cytochrome P-450

When guinea pigs were treated with phenobarbital (PB), the specific activity of liver microsomal nicotine oxidase increased by 42%. PB-inducible cytochrome P-450 (PB-P-450) was purified to homogeneity from liver microsomes of PB-treated guinea pigs. Purified PB-P-450 catalyzed nicotine oxidation when reconstituted with NADPH-P-450 reductase and phospholipid system. Antibody prepared against the purified PB-P-450 formed single precipitation lines with both purified PB-P-450 and microsomal components in livers of PB-treated guinea pigs, and both precipitation lines fused. The antibody against PB-P-450 strongly inhibited nicotine oxidation in the reconstituted system. The antibody also inhibited liver microsomal nicotine oxidase activities in PB-treated and untreated guinea pigs by about 30% and less than 5% respectively. About 45% of total P-450 in liver microsomes of PB-treated guinea pigs was precipitated by the antibody. These results show that PB-P-450 participates in liver microsomal nicotine oxidation in PB-treated guinea pigs but not in untreated control animals.

Antinociceptive action of nicotine and its methiodide derivatives in mice and rats

Three quaternary methiodides of nicotine were prepared and tested for antinociceptive activity in the mouse tail-flick, mouse phenylquinone and rat tail-flick tests. Following peripheral administration, all three methiodides were inactive in the mouse and rat tail-flick procedures, whereas nicotine was active in both tests, which suggested that nicotine was acting centrally. Quaternization of nicotine did not eliminate antinociceptive activity as demonstrated by the intraventricular injection of the methiodides in mice. Nicotine pyrrolidine and bis methiodides were somewhat more potent than nicotine, whereas nicotine pyridine methiodide was considerably less potent than nicotine in the tail-flick procedure. Systemically administered nicotine pyrrolidine methiodine was approximately one-third as active as nicotine in the mouse phenylquinone test; nicotine pyridine methiodide and nicotine bis methiodide were 100 and 300 times less active, respectively. Hexamethonium partially blocked nicotine and nicotine pyrrolidine methiodide, whereas mecamylamine blocked nicotine completely but nicotine pyrrolidine methiodide partially. Nicotine may have both central and peripheral actions in the mouse phenylquinone test, whereas nicotine pyrrolidine methiodide may have both nicotine and non-nicotine like antinociceptive activity. The radiolabelled methiodides were synthesized and their disposition in body tissues studied. The methiodides were found to penetrate brain poorly (plasma-to-brain ratios greater than 20). The methiodides were metabolized to nicotine to a small extent. This metabolism occurred to a greater extent in mice than in rats.

Active transport of nicotine by the isolated choroid plexus in vitro

In vitro, the transport of [14C]nicotine into the isolated choroid plexus, the anatomical locus of the blood--CSF barrier, was studied. The isolated rabbit choroid plexus accumulated [14C]nicotine by two processes: an active saturable transport process and a nonsaturable process. The [14C]nicotine accumulation process by choroid plexus was not due to binding or intracellular metabolism of the [14C]nicotine. The [14C]nicotine accumulation process in isolated choroid plexus was inhibited by weak bases, including tolazoline and lidocaine, but not by the weak acid probenecid. The accumulation process was decreased 60% by iodoacetate and dinitrophenol and by low temperatures. These results are consistent with previous autoradiographic evidence showing the choroid plexus concentrated [14C]nicotine in vivo, and suggest that the choroid plexus may transfer nicotine between blood and CSF in vivo.

Nicotine binding sites and their localization in the central nervous system

The resolution of racemic nicotine to provide optically pure (+)-nicotine and the synthesis of radiolabeled nicotine with high specific activity have facilitated the study of nicotine binding in brain. The actions of the stereoisomers of nicotine on the central nervous system are qualitatively similar in most tests but (-)-nicotine is more potent than the unnatural (+)-isomer by 10-fold or greater. Binding of radiolabeled nicotine to brain has both saturable and nonsaturable components. Only saturable binding is affected by incubation conditions such as time, temperature, pH and ion concentration. Excess concentrations of the stereoisomers are equally effective in displacing (-)-[3H]-nicotine from brain homogenates. Nevertheless, a direct comparison of (+)-[3H]-nicotine and (-)-[3H]-nicotine binding shows that the latter has a KD three times lower than the former. (-)-[3H]-Nicotine is bound to the greatest degree in hypothalamus and hippocampus, areas that also exhibited the most stereoselectivity for nicotine. However, differences in the binding affinities of the two isomers were far less than the pharmacological stereospecificity observed.

Synthesis of 4,4-ditritio-(+)-nicotine: comparative binding and distribution studies with natural enantiomer

The preparation of 4,4-ditritio-(+)-nicotine (Vb) (specific activity 10.3 Ci/mmole)from (+)-nicotine (Ib) via (-) 4,4-dibromocotinine (IIIb) is described. Although Ib is 10-30 times less potent than (-)-nicotine (Ia) in the CNS, its binding affinity for the crude mitochondrial or nuclear fraction of whole rat brain is only three times less than that of Ia. However, distribution studies showed that the maximum brain levels of (-)-[3H] nicotine are nearly twice those of (+)-[3H]-nicotine following administration of a 2-micrograms/kg dose. Binding affinity and disposition of the stereoisomers account for a portion of the pharmacological stereospecificity of nicotine.

Characterization of the receptor mediating the nicotine discriminative stimulus

The discriminative stimulus (cue) property of nicotine was studied in a T-maze paradigm, and the results were analyzed by a new statistical method. For rats trained on 0.4 mg/kg, the ED50 was 0.11 mg/kg. The enantinomer of natural nicotine (+)nicotine was much less potent, and both position isomers of nicotine were inactive. Anabasine, which is active at nicotinic cholinergic receptors, provided the nicotine cue. Cytisine, a potent nicotinic agonist in vitro, was ineffective after SC administration and this was shown to be due to its inability to enter the brain in adequate amounts. High doses of cytisine by the intracerebroventricular route partially provided the cue. The cue was blocked by low doses of mecamylamine and pempidine and by high doses of hexamethonium. The data indicate that the cue receptor is pharmacologically similar to the nicotinic cholinergic receptor in autonomic ganglia.

Preliminary studies on the validity of in vitro measurement of drug toxicity using HeLa cells. II. Drug toxicity in the MIT-24 system compared with mouse and human lethal dosage of 52 drugs

By a comparison of the 50% inhibitory concentration to HeLa cells in the microtitre Metabolic Inhibition Test supplemented by microscopy of cells after 24 h incubation (the MIT-24 test), of 52 drugs with their mouse i.v. LD50 and available approximate human lethal dosage, 7 were found to have a human LD considerably lower than HeLa IC50, indicating a lethal action to specialized functions of the human body not found in vitro, while 39 were found to have a gross similarity between the human LD and HeLa IC50.

Nicotine antibodies: comparison of ligand specificities of antibodies produced against two nicotine conjugates

Conjugates between bovine serum albumin and (R,S)-2-aminonicotine were produced, and these conjugates were employed in rabbits and goats for the production of nicotine antibodies. In the assay of nicotine, an 125I-tyrosine methyl ester derivative of (R,S)-6-aminonicotine was employed as radioligand. The antibody-bound derivative was separated from the free derivative by charcoal adsorption (0.5% charcoal, 0.1% dextran T-70, 0.1% bovine serum albumin pH 7.3). Among the twenty five nicotine derivatives and metabolites examined, (R,S)-6-aminonicotine gave the highest cross-reaction. Cross-reaction with cotinine, a major mammalian metabolite of nicotine, was less than 0.1% for both the rabbit-derived and goat-derived antisera. Cross-reaction by other metabolites, such as (S)-nicotine-N'-oxide, (S)-nornicotine, and N-methylpyrrolidine was less than 1%. The antibodies produced were thus highly specific to nicotine. The radioimmunoassay for nicotine showed a maximum sensitivity of 10 ng/ml in 50-microliter plasma samples for both antisera. After the smoking of a single cigarette (1.2 mg nicotine content in mainstream) the peak of blood plasma level of nicotine in the subjects varied from 20--104 ng/ml, and high levels of nicotine were not necessarily found in heavy smokers.

Long-term fate of [14C]nicotine in the mouse: retention in the bronchi, melanin-containing tissues and urinary bladder wall

N-methyl-14C and 2'-14C-labelled nicotine were used for whole-body autoradiographic distribution studies on C57BL- and NMRI-mice. Radioactivity was retained in the melanin-containing tissues, in the bronchial walls, and in the urinary bladder wall, up to 1 month after administration. The activity levels in the bronchi decreased faster if [2'(14)C] nicotine was used. Quantitative measurements of the retention of the 2 14C-labelled nicotine preparations confirmed the autoradiographic findings. It is proposed that nicotine is N-demthylated in the bronchial mucosa, the off-coming methyl group being incorporated into the cell constituents of the mucosa. Thin-layer chromatographic studies showed that no nicotine was present in the lungs after 24 h. In melanin, however, only unmetabolized nicotine was found from 4 h on. Some reactive nicotine metabolites may be responsible for the retention in the urinary bladder wall. Also in the full-term fetuses radioactivity accumulated in the pigmented eyes and in the respiratory tract. The accumulation and long-term retention of nicotine in the melanin-containing structures might accelerate the development of drug-induced or senile changes in these tissues. The retention in the urinary bladder wall persisted even after rinsing. This may indicate an accumulatory mechanism worth considering in the pathogenesis of urinary bladder cancer.