Metabolic effects of nicotine on human adipose tissue in organ culture

Effects of nicotine on homeostatic and hedonic components of food intake

Chronic tobacco use leads to nicotine addiction that is characterized by exaggerated urges to use the drug despite the accompanying negative health and socioeconomic burdens. Interestingly, nicotine users are found to be leaner than the general population. Review of the existing literature revealed that nicotine affects energy homeostasis and food consumption via altering the activity of neurons containing orexigenic and anorexigenic peptides in the brain. Hypothalamus is one of the critical brain areas that regulates energy balance via the action of these neuropeptides. The equilibrium between these two groups of peptides can be shifted by nicotine leading to decreased food intake and weight loss. The aim of this article is to review the existing literature on the effect of nicotine on food intake and energy homeostasis and report on the changes that nicotine brings about in the level of these peptides and their receptors that may explain changes in food intake and body weight induced by nicotine. Furthermore, we review the effect of nicotine on the hedonic aspect of food intake. Finally, we discuss the involvement of different subtypes of nicotinic acetylcholine receptors in the regulatory action of nicotine on food intake and energy homeostasis.

Nicotine enhances ethanol-induced fat accumulation and collagen deposition but not inflammation in mouse liver

INTRODUCTION

Alcohol and tobacco are frequently co-abused. Tobacco smoke increases alcoholic steatosis in apoE(-/-) mice. Tobacco smoke contains more than 4000 chemicals, but it is unknown which compounds in tobacco smoke play a major role in increasing alcoholic steatosis.

METHODS

C57BL/J6 mice were intraperitoneally injected with nicotine at 1 mg/kg every day or saline at the same volume as a control and the mice were fed dextrose-control or ethanol Lieber-DeCarli liquid diets. Three weeks later the mice were sacrificed after overnight fasting.

RESULTS

Neither nicotine injection nor ethanol feeding alone increased serum levels of triglyceride, but the combination of nicotine and ethanol increased serum levels of triglyceride. Both nicotine injection alone and ethanol feeding alone increased hepatic collagen type I deposition, and nicotine injection and ethanol feeding combined further increased hepatic collagen type I deposition. The combination of nicotine and ethanol also activated hepatic stellate cells, a principal liver fibrogenic cell. Hepatic fat accumulation was induced by ethanol feeding, which was further enhanced by nicotine injection. Ethanol feeding caused an increase in serum ALT, but nicotine did not further increase serum ALT levels. Lipid droplets and inflammatory foci were observed in liver sections from ethanol-fed mice; nicotine treatment increased the number and size of lipid droplets, but not the number and size of inflammatory foci. Nicotine did not further increase ethanol-induced hepatic neutrophil infiltration.

CONCLUSIONS

These results suggest that nicotine enhances ethanol-induced steatosis and collagen deposition, but nicotine has no effect on ethanol-induced inflammation.

Nicotinic regulation of energy homeostasis

INTRODUCTION

The ability of nicotine, the primary psychoactive substance in tobacco smoke, to regulate appetite and body weight is one of the factors cited by smokers that prevents them from quitting and is the primary reason for smoking initiation in teenage girls. The regulation of feeding and metabolism by nicotine is complex, and recent studies have begun to identify nicotinic acetylcholine receptor (nAChR) subtypes and circuits or cell types involved in this regulation.

DISCUSSION

We will briefly describe the primary anatomical and functional features of the input, output, and central integration structures of the neuroendocrine systems that regulate energy homeostasis. Then, we will describe the nAChR subtypes expressed in these structures in mammals to identify the possible molecular targets for nicotine. Finally, we will review the effects of nicotine and its withdrawal on feeding and energy metabolism and attribute them to potential central and peripheral cellular targets.

Association of hypoadiponectinemia with smoking habit in men

Adiponectin is emerging as an important molecule in obesity, the metabolic syndrome, and cardiovascular disease. On the other hand, smoking habit is well known to be related to cardiovascular disease and hypertension. To examine the association between adiponectin concentration and smoking habit, we performed an epidemiological survey and an acute exposure test in humans and an experiment in adipocytes to elucidate the mechanism underlying the association between adiponectin and smoking. In the epidemiological study, we enrolled a total of 331 male subjects to examine chronic smoking exposure. Plasma adiponectin was significantly lower (P=0.01) in current smokers (5.3+/-0.3 microg/mL) than in never-smokers (6.5+/-0.4 microg/mL). A significant association between smoking and low adiponectin level was also confirmed in multiple regression analysis including age, body mass index, hypertension, diabetes, hyperlipidemia, and creatinine clearance (never-smokers 6.5+/-0.4 microg/mL; past smokers 5.6+/-0.3 microg/mL; current smokers 5.2+/-0.4 microg/mL; F=4.52; P=0.01). To examine the acute effect of smoking on adiponectin concentration for 12 hours, we measured plasma adiponectin level in 5 male never-smokers before smoking and 3, 6, and 12 hours after smoking, with the result that adiponectin showed a significant decrease after smoking (12 hours; -14.5+/-0.6%; P<0.01). In cultured mouse 3T3-L1 adipocytes, H2O2 and nicotine reduced the mRNA expression and secretion of adiponectin in a dose-dependent manner. Smoking habit is associated with adiponectin concentration in men, and its suppressive effect is mediated in part through direct inhibition of smoking on adiponectin expression in adipocytes.

Earlier smoking habits are associated with higher serum lipids and lower milk fat and polyunsaturated fatty acid content in the first 6 months of lactation

OBJECTIVE

To investigate the relation between maternal smoking habits, plasma lipids and milk fatty acid (FA) content and composition.

DESIGN

Breastfeeding mothers who gave birth to healthy, full-term infants were recruited. Mothers were interviewed on smoking habits, being defined smokers (S) when usually smoking at least five cigarettes per day before pregnancy.

SETTING

Department of Pediatrics, San Paolo Hospital, Milan, Italy.

SUBJECTS

In total, 92 mothers: 61 non-S (NS) and 31 S.

INTERVENTIONS

Pooled hindmilk was collected at the first raise of milk (colostrum stage), 1, 3 and 6 months, and total lipid (TL) content and fatty acid (FA) composition were evaluated. Maternal dietary habits were assessed by a food-frequency questionnaire. Two subsamples (16 NS, 6 S) were investigated after delivery and at 3 months for serum lipids and FA status. At 6 months after delivery, the number of mothers still breastfeeding decreased to 30. Variables were compared using nonparametric tests.

RESULTS

In smoking mothers serum levels of triglycerides, cholesterol and low-density lipoproteins were higher, while those of high-density lipoproteins were lower. TL content in breast milk was similar in the two groups just after delivery but higher in milk from NS at 1 month. TL content and FA absolute amounts of linoleic, arachidonic, alpha-linolenic and docosahexaenoic (DHA) acid in breast milk were lower in S vs NS 1 month after delivery. Also 3 months after delivery, the breast milk of smoking mothers contained less DHA than the breast milk of nonsmoking mothers.

CONCLUSIONS

Maternal cigarette smoking in early pregnancy is associated with higher plasma lipid levels and lower milk TL and DHA content in the first months of lactation.

Cholinoceptor-mediated effects on glycerol output from human adipose tissue using in situ microdialysis

1. Possible cholinoceptor-mediated effects on lipolysis were investigated in vivo in human subcutaneous adipose tissue of non-obese, non-smoking, healthy subjects, by use of microdialysis. Cholinomimetic and sympathomimetic agents were added to the in going dialysate solvent. 2. Addition of nicotine to the perfusion solvent caused a concentration-dependent reversible increase in the levels of glycerol in the dialysate (lipolysis index). The opposite effect (also concentration-dependent and reversible) was caused by the addition of carbachol. The maximum effects were 100% stimulation and 50% inhibition, respectively, by nicotine and carbachol. Neither nicotine nor carbachol stimulated nutritive blood flow in adipose tissue (as measured with an ethanol escape technique). 3. The nicotine effect in situ was concentration-dependently counteracted by the nicotinic cholinoceptor antagonist, mecamylamine. Likewise, the carbachol effect was concentration-dependently counteracted by the muscarinic cholinoceptor antagonist, atropine. 4. When adipose tissue was pretreated with phentolamine plus propranolol in order to obtain a complete alpha and beta-adrenoceptor blockade, the subsequent addition of nicotine or carbachol still induced an increase and decrease in dialysate glycerol levels (lipolytic or antilipolytic effects), respectively. When adipose tissue was pretreated with mecamylamine or atropine, the subsequent addition of acetylcholine caused a reversible decrease and increase, respectively, of the dialysate glycerol levels. 5. Nicotine and carbachol had no effects on glycerol release from human isolated subcutaneous fat cells that were incubated in vivo. 6. In conclusion, the data demonstrate a dual effect of the cholinoceptor system on glycerol output inhuman adipose tissue: stimulation through nicotinic receptors and inhibition through muscarinic receptors. These effects, which are not observed in vitro, are independent of the adrenergic system and the local blood flow and seem not to be mediated by a direct action on the fat cell.