Lipolysis in smokers during tobacco withdrawal: a pilot study

Mitochondrial function in individuals at clinical high risk for psychosis

Alterations in mitochondrial function have been implicated in the etiology of schizophrenia. Most studies have investigated alterations in mitochondrial function in patients in which the disorder is already established; however, whether mitochondrial dysfunction predates the onset of psychosis remains unknown. We measured peripheral mitochondrial complex (I–V) function and lactate/pyruvate levels in 27 antipsychotic-naïve individuals at clinical high risk for psychosis (CHR) and 16 healthy controls. We also explored the association between mitochondrial function and brain microglial activation and glutathione levels using a translocator protein 18 kDa [¹⁸F]FEPPA PET scan and ¹H-MRS scan, respectively. There were no significant differences in mitochondrial complex function and lactate/pyruvate levels between CHR and healthy controls. In the CHR group, mitochondrial complex III function (r = −0.51, p = 0.008) and lactate levels (r = 0.61, p = 0.004) were associated with prodromal negative symptoms. As previously reported, there were no significant differences in microglial activation and glutathione levels between groups, however, mitochondrial complex IV function was inversely related to microglial activation in the hippocampus in CHR (r = −0.42, p = 0.04), but not in healthy controls. In conclusion, alterations in mitochondrial function are not yet evident in CHR, but may relate to the severity of prodromal symptoms, particularly negative symptoms.

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.

Endocrine and metabolic effects of smoking cessation

BACKGROUND

Cardiovascular, pulmonary, and oncological hazards of tobacco smoking have been well studied. Smoking may also have multiple effects on endocrine and metabolic systems affecting pituitary, thyroid, and adrenal glands; testicular and ovarian function; as well as energy balance; lipid, and glucose metabolism; and insulin resistance. Less is known about hormonal and metabolic effects that patients may experience while quitting smoking.

SCOPE

The objective of this article is to review systematically data on the endocrine and metabolic effects of smoking cessation. Articles based upon clinical trials, randomised controlled trials, and meta-analyses were obtained via a MEDLINE search (articles published between 1 August 1998 and 31 July 2008, inclusive; English language; human subjects; including abstracts) using key search terms relating to smoking cessation and endocrine or metabolic parameters. Additional studies were identified from the bibliographies of reviewed literature. Studies related to the search criteria were reviewed, 199 papers were identified, and 57 pertinent to this review were included.

FINDINGS

Limited data are available on the short- and long-term effects of smoking cessation on hypothalamic- and thyroid-pituitary-adrenal axes, sex hormones, energy homeostasis, and lipid and glucose metabolism. Initial data indicate that smoking cessation is associated with decreased cortisol levels and in the short-term, smoking cessation does not correct the diminished adrenocortical responses to stress caused by chronic smoking. Cessation reverses smoking's effects on thyroid disorders and may reduce the risk of osteoporosis. Finally, smoking cessation increases transiently food intake and sustained weight gain and is associated with increases in high-density lipoprotein cholesterol levels that occur rapidly on cessation.

CONCLUSION

Further research may provide insight into post-cessation endocrine changes that may be caused by alterations to central and peripheral systems. Such research may increase the understanding of underlying biological mechanisms that lead to symptoms and clinical features of smoking cessation.