Obesity and thyroid diseases are common disorders in the general population and they frequently occur in single individuals. Alongside a chance association, a direct relationship between 'thyroid and obesity' has been hypothesized. Thyroid hormone is an important determinant of energy expenditure and contributes to appetite regulation, while hormones and cytokines from the adipose tissue act on the CNS to inform on the quantity of energy stores. A continuous interaction between the thyroid hormone and regulatory mechanisms localized in adipose tissue and brain is important for human body weight control and maintenance of optimal energy balance. Whether obesity has a pathogenic role in thyroid disease remains largely a matter of investigation. This review highlights the complexity in the identification of thyroid hormone deficiency in obese patients. Regardless of the importance of treating subclinical and overt hypothyroidism, at present there is no evidence to recommend pharmacological correction of the isolated hyperthyrotropinemia often encountered in obese patients. While thyroid hormones are not indicated as anti-obesity drugs, preclinical studies suggest that thyromimetic drugs, by targeting selected receptors, might be useful in the treatment of obesity and dyslipidemia.

Background Weight loss is a milestone in the prevention of chronic diseases associated with high morbility and mortality in industrialized countries. Very-low calorie ketogenic diets (VLCKDs) are increasingly used in clinical practice for weight loss and management of obesity-related comorbidities. Despite evidence on the clinical benefits of VLCKDs is rapidly emerging, some concern still exists about their potential risks and their use in the long-term, due to paucity of clinical studies. Notably, there is an important lack of guidelines on this topic, and the use and implementation of VLCKDs occurs vastly in the absence of clear evidence-based indications. Purpose We describe here the biochemistry, benefits and risks of VLCKDs, and provide recommendations on the correct use of this therapeutic approach for weight loss and management of metabolic diseases at different stages of life.

Total body weight is usually employed to calculate the amount of l-T(4) to be administered in patients with thyroid diseases. The aim of this study was to evaluate the effect of body composition on l-T(4) requirements. Body composition was assessed by dual energy x-ray absorptiometry in 75 patients on TSH-suppressive l-T(4) therapy after conventional thyroid ablation for differentiated cancer. The mean daily dose of l-T(4) was lower in normal-weight (127.5 +/- 21.3 mug/d) vs. overweight (139.4 +/- 24.5) and obese (151.3 +/- 29.1) subjects. There was a much stronger association between the l-T(4) dosage and lean body mass (P < 0.001, r = 0.667) compared with fat mass (P = 0.023, r = 0.26). Measurement of regional tissue composition showed peripheral lean mass as the best correlate with the dose of l-T(4) (r = 0.679, P < 0.001) whereas no correlation was observed with peripheral fat mass. In conclusion, individual l-T(4) requirements are dependent on lean body mass. Age- and gender-related differences in l-T(4) needs reflect different proportions of lean mass over the total body weight. An estimate of lean mass may be helpful to shorten the time required to attain a stable dose of l-T(4), particularly in subjects with high body mass index values that may be due either to increased muscular mass or to obesity.

SUMMARY The mammalian telomere-binding protein Rap1 was recently found to have additional nontelomeric functions, acting as a transcriptional cofactor and a regulator of the NF-κB pathway. Here, we assess the effect of disrupting mouse Rap1 in vivo and report on its unanticipated role in metabolic regulation and body-weight homeostasis. Rap1 inhibition causes dysregulation in hepatic as well as adipose function, leading to glucose intolerance, insulin resistance, liver steatosis, and excess fat accumulation. Furthermore, Rap1 appears to play a pivotal role in the transcriptional cascade that controls adipocyte differentiation in vitro. Using a separation-of-function allele, we show that the metabolic function of Rap1 is independent of its recruitment to TTAGGG binding elements found at telomeres and at other interstitial loci. In conclusion, our study underscores an additional function for the most conserved telomere-binding protein, forging a link between telomere biology and metabolic signaling.

The protein hormone leptin acts to regulate body fat and energy expenditure. Resistance to this hormone is implicated in human obesity and its pathophysiological consequences. In order to gain insight into the mechanism of leptin resistance, an (18)F-labeled derivative was developed to study the biodistribution of the hormone using positron emission tomography (PET). A two-step, site specific ligation approach was developed for this purpose, in which an aminooxy-reactive group was incorporated at the C-terminus of leptin using expressed protein ligation (EPL), which was subsequently derivatized with [ (18)F]fluorobenzaldehyde using an aniline-accelerated radiochemical oximation reaction. The modified hormone was shown to be biologically active in vitro and in vivo, and it was applied to PET imaging in ob/ ob mice. These protocols will allow for the routine production of site-specifically (18)F radiolabeled leptin, as well as other proteins, for use in PET imaging in systems from mouse to man.

Obese, leptin deficient obob mice have profoundly decreased activity and increased food seeking behavior. The decreased activity has been attributed to obesity. In mice, we tested the hypothesis that leptin increases total locomotor activity but inhibits food anticipatory activity. We also sought to determine if leptin induced increases in total locomotor activity are independent of changes in body weight and obesity. We studied obob mice and also created a novel transgenic mouse where leptin is over-expressed in a tetracycline-off system and can be abruptly and non-invasively suppressed by doxycycline within few hours. The studies were performed using two independent behavioral assays: home cage activity (HCA) and running wheel activity (RWA). Systemic administration of leptin (150 ng/hr) to obob mice produced a 122%±30% (mean ± SEM) increase (p≤0.01) in locomotor activity within 2 days In addition, cerebroventricular administration of leptin (5 ng/hr) also produced an early and progressive increase in total locomotor activity beginning on the 1st day (+28±8%; p≤0.05) and increasing to +69±23% on day 3 without a decrease in body weight during this time. The increase in activity was restricted to the dark phase. Conversely, in a tet-off transgenic obob mouse line, acute leptin suppression reduced spontaneous locomotor activity. To further define activities that are leptin regulated, we assayed food anticipatory activity (FAA) and found that it was markedly augmented in obob mice compared to wild type mice (+38±6.7 in obob vs +20±6.3% in wild type at peak; mean ± SEM; p≤0.001) and abolished by leptin. Although melanocortin-3 receptors (MC3R) reportedly mediate FAA, we found augmented FAA and preserved inhibitory effects of leptin on FAA in MC3R−/−obob mice. In summary, this study demonstrates that total activity and FAA are regulated independently by leptin. Leptin, acting in the central nervous system and at physiologic levels, produces early increases in locomotor activity before substantial weight loss. In contrast, leptin suppresses augmented food anticipatory activity in obob mice.

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