Divergent tolerance to metabolic and cardiovascular effects of nicotine in smokers with low and high levels of cigarette consumption

Nicotine and energy balance: A review examining the effect of nicotine on hormonal appetite regulation and energy expenditure

Nicotine has been shown to decrease appetite, food intake (FI) and body weight, but the mechanisms are unclear. The purpose of this review was to examine research on the effects of nicotine on energy balance by exploring physiological mechanisms and hormone regulation related to FI, subjective appetite and energy expenditure (EE). We searched PubMed and MEDLINE, and included articles investigating the effects of nicotine on central appetite regulation, FI, leptin, peptide-YY (PYY), ghrelin, glucagon-like peptide-1 (GLP-1), adiponectin, cholecystokinin (CCK), orexin, and EE. A total of 65 studies were included in the qualitative synthesis and review. Our findings suggest that the decrease in appetite and FI may be attributed to nicotinic alterations of neuropeptide Y (NPY) and pro-opiomelanocortin (POMC) but the effect of nicotine on FI remains unclear. Furthermore, nicotine increases resting EE (REE) and physical activity EE (PAEE) in both smokers and non-smokers; and these increases may be a result of the catecholaminergic effect of nicotine. Decreases in body weight and appetite experienced by nicotine users results from increased EE and changes in the central hypothalamic regulation of appetite. There is not enough evidence to implicate a relationship between peripheral hormones and changes in appetite or FI after nicotine use. Although nicotine increases REE and PAEE, the effect of nicotine on other components of EE warrants further research. We conclude that further research evaluating the effect of nicotine on appetite hormones, FI and EE in humans is warranted.

Nicotine related brain activity: the influence of smoking history and blood nicotine levels, an exploratory study

OBJECTIVE

In this study, we sought to explore brain activity in nicotine-dependent men in response to acute intravenous nicotine using pharmacological magnetic resonance imaging (phMRI).

METHODS

phMRI was used to evaluate brain activity in response to 1.5 mg/70 kg intravenous nicotine or saline. The nicotine and saline were administered on different visits. The time courses of individual subjects' nicotine levels were used as regressors to assess neural activity relating to the infusions. The influence of smoking history and physiological measures on the response to nicotine were also investigated.

RESULTS

Greater lifetime exposure to cigarette smoking was significantly correlated with higher peak serum nicotine levels. PhMRI analysis of the differential response of nicotine compared to the saline condition showed distinctive activation patterns when analyzed with the (a) nicotine time course, (b) nicotine time course controlling for smoking history (pack years), and (c) pack years controlling for nicotine.

CONCLUSIONS

These results suggest that smoking exposure history influences serum nicotine levels and the brain's response to nicotine. Alterations in brain activity may be a result of vascular and neuro-adaptations involved in drug exposure and addiction.

Acute phenylalanine/tyrosine depletion reduces motivation to smoke cigarettes across stages of addiction

The neurobiology of tobacco use is poorly understood, possibly in part because the relevant mechanisms might differ depending on past nicotine exposure and degree of addiction. In the present study we investigated whether these factors might affect the role of dopamine (DA). Using the acute phenylalanine/tyrosine depletion method (APTD), DA synthesis was transiently decreased in three groups of abstinent smokers (n=47): (1) early low-frequency smokers, who had smoked a maximum of five cigarettes per day for less than one year, (2) stable low-frequency smokers smoking at the same level as early low-frequency smokers for at least 3 years, and (3) stable high-frequency smokers, who smoked a minimum of 10 or more cigarettes per day for at least 5 years. Motivation to obtain tobacco was measured using a progressive ratio breakpoint schedule for nicotine-containing and de-nicotinized cigarettes. Compared with a nutritionally balanced control mixture, APTD decreased the self-administration of nicotine-containing cigarettes, and this occurred in all three groups of smokers. The results suggest that DA influenced the willingness to sustain effort for nicotine reward, and this was seen in participants at all three levels of cigarette addiction. In the transition from sporadic to addicted use, the role of DA in the motivation to seek drug may change less than previously proposed.

Is nicotine a key player or spectator in the induction and progression of cardiovascular disorders?

Cigarette smoking is common in societies worldwide and a growing body of evidence suggests that chronic cigarette smoking may affect the structure and function of cardiovascular system. The chronic exposure to high levels of nicotine, a major component of cigarette smoking, has been observed to play a pathogenic role in the induction and progression of cardiovascular disorders including cardiomyopathy and peripheral vascular disease. Nicotine alters the function of vascular endothelium, initiates the adhesion cascade and stimulates the vascular inflammatory events to induce atherosclerosis and hypertension. Moreover, nicotine has been noted to induce direct coronary spasm and ischemia, which develop coronary artery disease and myocardial infarction. In addition, nicotine stimulates the excessive release of impulses from sinoatrial node that may account for the induction of cardiac arrhythmia. The present review critically discussed the possible detrimental role of chronic nicotine exposure in cardiac and vascular endothelial dysfunction. Moreover, the signaling mechanisms involved in the pathogenesis of nicotine exposure-induced cardiovascular dysfunction have been discussed. In addition, the pharmacological interventions to ameliorate chronic nicotine exposure-induced cardiovascular abnormalities have been delineated.

Reduction in cortisol after smoking cessation among users of nicotine patches

OBJECTIVE

Cortisol has been shown to decline after stopping smoking and this decline has been associated with smoking relapse and with reports of increased withdrawal severity and distress. We examined whether a decrease in cortisol is evident in smokers trying to quit using nicotine patches and whether cortisol is related to withdrawal symptoms, smoking urges, subjective stress, nicotine dependence, and smoking relapse.

METHODS

Among 112 smokers trying to quit using 15-mg patches, salivary cortisol and reports of stress, withdrawal, and urges were measured before quitting smoking and up to 6 weeks of abstinence among abstinent smokers using 15-mg nicotine patches. Thirty participants both remained abstinent and provided cortisol samples at all measurement times.

RESULTS

Relative to preabstinence, there was a significant decline in cortisol after abstinence of 1 day, and after 1, 2, and 6 weeks (p < .05). The decline in cortisol on the first day of abstinence was positively associated with reported cigarette consumption (p < .01) and tended (nonsignificant) to be associated with smoking relapse at 6 weeks (p = .07). A lower absolute level of cortisol, but not the change in cortisol, on the first day of abstinence was significantly associated with increased reports of urges, withdrawal symptoms, and stress (p < .05), independently of reported cigarette consumption.

CONCLUSIONS

Smokers using 15-mg nicotine patches are likely to experience a decline in cortisol on stopping smoking. This decline is likely to be greater among heavier smokers and may predict relapse to smoking. Those with lower cortisol after cessation may experience increased withdrawal symptoms, urges to smoke, and subjective stress.

Smokers and nonsmokers equally affected by olanzapine-induced weight gain: metabolic implications

OBJECTIVE

To examine the impact of smoking status on antipsychotic-associated weight gain.

METHOD

In two double-blind studies, 552 adult and elderly patients with schizophrenia or schizoaffective disorder were randomly assigned to risperidone or olanzapine treatment for 8 weeks. Smoking status at baseline was recorded together with other background characteristics.

RESULTS

In both adult and elderly patients, olanzapine-treated smokers and nonsmokers gained weight at a similar rate, whereas risperidone-treated smokers gained less weight than did nonsmokers. Olanzapine was associated with significantly greater weight gain than was risperidone across all measures in both adult and elderly patients.

CONCLUSION

These findings support a quantitatively or qualitatively different effect of risperidone and olanzapine on the metabolic changes underlying antipsychotic-associated weight gain. Mechanisms responsible for olanzapine's effect on weight appear to counteract smokers' physiologic bias toward weight loss, an effect not seen among risperidone-treated patients.

Effect of chewing gum containing nicotine and caffeine on energy expenditure and substrate utilization in men

BACKGROUND

Nicotine replacement therapy limits weight gain after smoking cessation. This finding is partly attributable to the thermogenic effect of nicotine, which may be enhanced by caffeine.

OBJECTIVE

We assessed the acute thermogenic effects of chewing gum containing different doses of nicotine and caffeine.

DESIGN

This randomized, double-blind, placebo-controlled, crossover study included 12 healthy, normal-weight men (aged 18-45 y). Energy expenditure was measured with indirect calorimetry before and 2.5 h after subjects chewed each of 7 different types of gum containing the following doses of nicotine/caffeine: 0/0, 1/0, 2/0, 1/50, 2/50, 1/100, and 2/100 mg/mg.

RESULTS

The thermogenic responses (increases over the response to placebo) were 3.7%, 4.9%, 7.9%, 6.3%, 8.5%, and 9.8%, respectively, for the gums containing 1/0, 2/0, 1/50, 2/50, 1/100, and 2/100 mg nicotine/mg caffeine (P < 0.05 for all). Adding caffeine to 1 and 2 mg nicotine significantly enhanced the thermogenic response, but changing the caffeine dose (from 50 to 100 mg) did not change the thermogenic effect. None of the combinations changed the respiratory quotient compared with placebo, which indicates that glucose and fat oxidation rates were increased to a similar extent. Side effects occurred only with 2 mg nicotine.

CONCLUSIONS

One milligram of nicotine has a pronounced thermogenic effect, which can be increased by approximately 100% by adding 100 mg caffeine. Increasing the nicotine dose to 2 mg does not increase the thermogenic effect but produces side effects in most subjects. Caffeine may be useful in preventing weight gain after smoking cessation if its thermogenic effect can be used to enhance nicotine's effect on long-term energy balance.

Smokeless nicotine administration does not result in hypertension or a deterioration in glucose tolerance or insulin sensitivity in juvenile rats

We have previously reported that smokeless nicotine resulted in hypertension, but not a deterioration in glucose tolerance or insulin action in young adult male rats. To evaluate the effect of nicotine in juvenile animals, we studied 6-week-old male and female Sprague-Dawley rats and implanted 25-mg nicotine (N) or placebo (P) pellets. Weight gain was controlled by chow restriction in all 4 groups of rats. Males were generally heavier than females, both before and after N or P placement; there was no difference in weight between N and P groups for each sex. Systolic blood pressure, measured noninvasively, increased modestly, but not significantly, after N placement in both male and female rats. Glucose tolerance and insulin action were assessed by an oral glucose tolerance test (OGTT). Areas under the curve (AUC) were calculated for glucose (AUC(GLU)), insulin (AUC(INS)), and free fatty acids (FFA) (AUC(FFA)). Insulin action was calculated by several indices, which have correlated with more invasive studies. None of these metabolic parameters were significantly impacted by nicotine treatment, consistent with our observations in adult male rats. In summary, smokeless nicotine at this dose has no significant effect on observed cardiovascular or metabolic parameters in sexually immature male and female rats.

Mortality and morbidity from smoking-induced cardiovascular diseases: the necessity of the cardiologist's involvement and commitment

This review deals with tobacco-associated cardiovascular effects and diseases. The importance of tabaccoism in primary care, its effects on cardiovascular, and immunology system and hemostasia, as well as, the role of smoking in atherosclerosis, coronary heart disease, acute myocardial infarct, diabetes, and other alterations are discussed. Finally we summarize the general tobacco control policies and the methods to achieve smoking cessation. Although it is well established the causal relationship between smoking and disease, and the general public is aware of this, the cardiologist's involvement and commitment is of utmost importance.

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.

Nicotinic acetylcholine receptors in health and disease

Nicotinic acetylcholine receptors (AChRs) are a family of acetylcholine-gated cation channels that form the predominant excitatory neurotransmitter receptors on muscles and nerves in the peripheral nervous system. AChRs are also expressed on neurons in lower amounts throughout the central nervous system. AChRs are even being reported on unexpected cell types such as keratinocytes. Structures of these AChRs are being determined with increasing precision, but functions of some orphan subunits are just beginning to be established. Functional roles for postsynaptic AChRs in muscle are well known, but in neurons the post-, peri-, extra-, and presynaptic roles of AChRs are just being revealed. Pathogenic roles of AChRs are being discovered in many diseases involving mechanisms ranging from mutations, to autoimmune responses, to the unknown; involving cell types ranging from muscles, to neurons, to keratinocytes; and involving signs and symptoms ranging from muscle weakness to epilepsy, to neurodegenerative disease, to psychiatric disease, to nicotine addiction. Awareness of AChR involvement in some of these diseases has provoked new interests in development of therapeutic agonists for specific AChR subtypes and the use of expressed cloned AChR subunits as possible immunotherapeutic agents. Highlights of recent developments in these areas will be briefly reviewed.

Smokeless nicotine administration is associated with hypertension but not with a deterioration in glucose tolerance in rats

Cigarette smoking is a major risk factor for coronary heart disease. To further investigate the relationship of nicotine with other cardiac risk factors, we studied the impact of nicotine on blood pressure and glucose tolerance. Adult male Sprague-Dawley rats were randomly assigned to receive nicotine or placebo pellets implanted subcutaneously. Weight gain was controlled by pair-feeding, and was not significantly different between nicotine- and placebo-treated animals. Blood pressure (in mm Hg) increased throughout a 3-week treatment period in nicotine-treated animals and was significantly higher [P < .05 by two-way ANOVA] than in placebo-treated rats. Blood pressure returned to normal within 1 week following exhaustion of the pellets. Oral glucose tolerance tests performed 2.5 weeks after pellet placement showed similar glucose, insulin, and free fatty acid (FFA) profiles by two-way ANOVA. In summary, smokeless nicotine exposure leads to sustained but reversible hypertension without deterioration in glucose tolerance or insulin action when weight gain is controlled. We conclude that in rats smokeless nicotine adversely affects the coronary risk profile by increasing blood pressure.

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.