Metabolism in vitro of 14C-nicotine in livers of foetal, newborn and young mice

Regulation of α4β2α5 nicotinic acetylcholinergic receptors in rat cerebral cortex in early and late adolescence: Sex differences in response to chronic nicotine

Chronic nicotine administration in animals, and smoking in humans, causes up-regulation of α4β2* neuronal nicotinic receptors (nAChRs), which has been hypothesized to contribute to the addictive actions of nicotine. We used a rat model to test whether such up-regulatory effects differ in adolescents versus adults, and in males versus females. Following chronic treatment with nicotine or saline via subcutaneous osmotic minipumps, we measured α4β2 and α4β2α5 nAChRs in cerebral cortex using [3H]epibatidine to label assembled nAChRs, and selective antibodies to measure the individual subunits via immunoprecipitation. For the first time, we provide a detailed characterization of the response of both α4β2 and α4β2α5 nAChRs in female adolescent rat cerebral cortex. We found differences in nicotine-induced up-regulation between males and females in early adolescence that are absent in both late adolescence and adulthood. Males showed significant up-regulation at PN28 which was absent in age-matched females. These results demonstrate sex differences in the susceptibility of α4β2* nAChRs to the effects of chronic nicotine exposure in the cerebral cortex based on age.

A comparison of the regional ontogenesis of nicotine- and muscarine-like binding sites in mouse brain

The postnatal development of the cholinergic neurotransmitter system was studied in the cortex, hippocampus, midbrain and cerebellum of 3-, 7-, 12-, 17- and 30-day-old NMRI mice. The concentration of muscarine-like binding sites determined with [(3)H]quinuclidinyl benzilate as a ligand increased progressively with age. A similar developmental pattern was found for the activity of a presynaptic marker, choline acetyltransferase (ChAT). When expressed as a percentage of the values for 30-day-old mice, however, the muscarine-like receptors were parallel but preceding the development of ChAT in all the brain regions studied. The concentration of nicotine-like binding sites studied with [(3)H]α-bungaro-toxin as a ligand gradually increased with age in the cortex, hippocampus and midbrain, with a peak between days 7 and 12, followed by a decrease towards day 30. With [(3)H]tubocurarine as a ligand, on the other hand, the concentration of nicotine-like binding sites was in general high at 3 days and gradually decreased with age, suggesting that different subpopulations of nicotine-like receptors might be determined when the two ligands are used.

The genotoxic and cytotoxic effects of nicotine in the mouse bone marrow

The objective of the present study was to investigate the potential of nicotine to induce micronucleated polychromatic erythrocytes (MNPCE) in bone marrow of male and female mice. Cyclophosphamide at 40mg/kg was used as positive control clastogen. Single doses of 4, 8 or 16mg/kg nicotine were given via oral intubation and bone marrow was sampled at 18, 24, 30, 36 and 48h after treatment. Cyclophosphamide yielded the expected positive results. Despite the evident signs of acute toxicity shown by the animals, mainly at the 8 and 16mg/kg doses of nicotine, and the reduction in the % PCE, the results show that the MNPCE frequency in male and female mice was not affected by treatment with any of the selected doses of nicotine, in either of the sampling times 18 or 24h. However, at 30 and 36h after treatment, the MNPCE showed significant increases in both genders after doses of 8 and 16mg/kg. A sex-dependent response was recorded, with males having more MNPCE than females after treatment with 8 or 16mg/kg nicotine and sampling at 30h. However, at 36h more MNPCE were induced in females than in males, suggesting different degrees of dose interaction in the sexes under the conditions of the assay. The response was directly correlated with bone-marrow toxicity, as greater bone-marrow suppression was noted in females than in males when 36h samples were examined. By 48h recovery was observed even though the cytotoxicity was high. These findings suggest that nicotine at high doses and after prolonged time intervals is genotoxic and cytotoxic for mouse bone marrow.

Gender differences in the pharmacology of nicotine addiction

Smoking rates have declined in recent years less rapidly in women than in men. More adolescent girls than boys are currently smoking. Quitting smoking is reported in many studies to be more difficult in women than in men. These observations suggest that there may be gender differences in the nature of nicotine addiction. Gender differences in various pharmacological processes involved in nicotine addiction are reviewed. Women take in less nicotine from smoking per cigarette than men but, because of slower metabolism, nicotine levels in the body for a given number of cigarettes per day are similar in male and female smokers. Women tend to be less sensitive to the discriminative effects of nicotine and tend to regulate nicotine intake less precisely than men. On the other hand, women appear to be more sensitive to the effects of nicotine in reducing negative affect and reducing body weight. There is a strong association between depression and smoking, and this association appears to be stronger in women than in men. Women tend to respond more to environmental cues associated with smoking than do men. Thus, several lines of evidence suggest that nicotine addiction is different in women than in men. Understanding the basis for gender differences may be of utility in individualizing and optimizing smoking cessation therapy.

Effects of aging on acute toxicity of nicotine in rats

Acute toxicity of nicotine was examined in old (24 months) and young (6 weeks) Wistar rats. There were no significant age differences in the mortality and convulsive responses induced by an intraperitoneal injection of nicotine (24.5 mg/kg). The lethal nicotine levels in blood and cortex and the latent period to death in old rats were larger than those in young rats. Cortical and blood nicotine levels 15 min. after the nicotine injection in old rats were also higher than those in young rats. Nicotine significantly increased dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid levels in striatum and hippocampus in young rats, but not those in old rats. Moreover, nicotine-induced elevations in blood levels of corticosterone in old rats were also less than those in young rats. On the other hand, the cytochrome P-450 content, the nicotine oxidase activity and the flavin-containing monooxygenase activity in liver showed age-related decreases in the young, the middle-aged (12 months) and the old rats. These results indicate that the acute toxicity of nicotine in old rats reflects the decreases in hepatic nicotine metabolism and in brain sensitivity to nicotine.

Variables affecting nicotine metabolism

Nicotine metabolism is exceedingly sensitive to perturbation by numerous host factors. To reduce the large variations and discrepancies in the literature pertaining to nicotine metabolism, investigators in future studies need to recognize and better control these host factors. Recent advances in the understanding of nicotine metabolism have suggested new approaches to elucidating underlying mechanisms of certain toxic effects associated with cigarette smoking.

Nicotine pharmacokinetics of Nicoderm (nicotine transdermal system) in women and obese men compared with normal-sized men

This study examined the effect of gender and body weight on the pharmacokinetic properties of the Nicotine Transdermal System (NTS) (Nicoderm). This NTS was applied for 24 hours to 13 normal-sized men, 13 women, and 13 obese men, all of whom were smokers who had abstained from cigarettes for the previous 24 hours. Pharmacokinetic parameters were determined during a single application of the system. The mean nicotine maximal plasma concentration (Cmax) and area under the curve (AUC) values for women did not differ significantly from those for normal-sized men. Nicotine Cmax and AUC values, however, were significantly lower in obese compared with normal-sized men; nicotine AUC was strongly correlated to body weight and body mass index. Mean apparent nicotine elimination rate constant values were not significantly different between normal-sized and obese men, but the apparent elimination rate constant value was significantly higher in women. The possible clinical significance of the differences in nicotine AUC values with body weight is discussed.

Metabolism of nicotine by hepatocytes

The profile of nicotine metabolites produced by freshly isolated hepatocytes from rats, hamsters, guinea pigs, mice and humans was investigated after a 30-min exposure to nicotine ([2-14C]pyrrolidine). Large species differences occurred in the extent of nicotine metabolism; these ranged from 95% metabolism in guinea pig hepatocytes to only 30% metabolism in human and rat hepatocytes. The spectrum of metabolites formed also varied widely in different species. In hepatocytes from obese human subjects, nicotine was metabolized most extensively in smokers, least in nonsmokers, and to an intermediate degree in exsmokers, suggesting that cigarette smoking enhances the rate of nicotine metabolism. Pretreatment of all nonhuman species studied with phenobarbital and beta-naphthoflavone and with Aroclor in rats produced distinctive inductive patterns. Phenobarbital pretreatment of nonsmokers for 2 days prior to liver biopsy doubled the extent of nicotine conversion to cotinine by their hepatocytes. Rat and hamster hepatocytes exhibited sex and stereoselectivity differences in nicotine metabolism. Collectively, these studies indicate that hepatocytes offer some advantages over in vivo systems in investigating certain aspects of nicotine metabolism.

Breast feeding and smoking hygiene: major influences on cotinine in urine of smokers' infants

The determinants of urine cotinine levels were studied in a group of 101 infants aged 3 months, including 79 infants whose mothers were current smokers. At a pre-arranged home visit the infants' mothers completed an interviewer-administered questionnaire, and samples of maternal urine and breast milk and infants' urine were collected. Cotinine and nicotine levels were determined by gas-liquid chromatography. Infant urine cotinine levels ranged from 0 to 140 micrograms/l (0-1120 ng cotinine/mg creatinine). A linear dose response relation between mother's smoking rate and infant urine cotinine level was observed among breast-fed infants (r = 0.79, p less than 0.001). The relation was weaker among infants fed by both breast and bottle (r = 0.56, p = 0.01) and was not apparent among bottle-fed infants (r = 0.15, p = 0.16). In addition to mode of feeding and mother's smoking rate, mother's smoking "hygiene" (assessed by the reported frequency of smoking while feeding and with infant in same room) was independently associated with infant urine cotinine level. Father's smoking pattern and exposure to smoke outside the household did not relate significantly to infant cotinine levels. We conclude that when mothers smoke, breast feeding is the principal determinant of cotinine in infants' urine. It is likely that most of this cotinine comes from cotinine in mothers' breast milk, but further research is needed to establish how much nicotine is ingested by breast-fed infants of mothers who smoke, and to investigate possible health effects.

Relations between nicotine-induced convulsive behavior and blood and brain levels of nicotine as a function of sex and age in two inbred strains of mice

Nicotine levels in blood and whole brain were measured as a function of sex and age in C57BL/6J and DBA/2J mice and compared to the behavioral responses following an intraperitoneal injection of nicotine. The results indicate that blood levels of nicotine alone do not accurately predict either brain levels of nicotine or the behavioral responses to a single injection of nicotine. In general, brain levels of nicotine proved to be a fairly accurate predictor of the behavioral responses to nicotine. The data indicate that the sexes differ in their sensitivity to nicotine. Forty-two-day-old male mice of both strains given comparable doses of nicotine were found to concentrate the drug in the brain more than females. However, there was no corresponding increase in sensitivity to this increased brain concentration as measured by LD50, ED50, latency to tremor or latency to death.