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Objective: To investigate whether weekly subcutaneous administration of 60 mg of long-acting pegylated human leptin (PEG-OB) for 8 weeks was able to influence weight loss, metabolic profile and inflammatory status of obese subjects on a mildly hypoenergetic diet (deficit: 3.2 MJ/day)., Design: A prospective, randomized, double-blind and placebo-controlled single-center trial., Subjects: Twenty-eight healthy, obese subjects (16 women, 12 men; age 22-65 y; body mass index 27.7-38.7 kg/m2)., Measurements: Bodyweight, metabolic profile (including lipids), C-reactive protein (CRP) and soluble TNF alpha-receptor (sTNF-R) 55 and 75 levels., Results: At the end of the study no significant differences in the delta or percentage weight loss between the placebo (n = 14) and PEG-OB (n = 14) groups was observed. Also the changes in metabolic profile, CRP, sTNF-R55 and R75 concentrations between the two groups after 8 weeks of treatment did not differ., Conclusion: Weekly injection of 60 mg PEG-OB did not lead to additional weight loss after 8 weeks of treatment. Furthermore, PEG-OB administration did not affect the changes in metabolic profile and the inflammatory status of obese subjects.

Background: Results of leptin administration in mice, rats, and humans provide a rationale for therapeutic augmentation of circulating leptin (OB protein) concentrations in obese humans; this may reduce food intake, increase metabolic rate, and lower body mass., Objective: We assessed the effects of weekly subcutaneous pegylated polyethylene glycol (PEG)-OB protein administration on appetite and energy metabolism in obese men., Design: We performed a randomized, double-blind, placebo-controlled trial in 30 obese men [body mass index (in kg/m(2)): 34.2 +/- 3.6; age: 44.7 +/- 7 y]. Subjects received 20 mg PEG-OB protein/wk for 12 wk while limiting their energy intake to 2.1 MJ/d., Results: During treatment, appetite and hunger before breakfast decreased and remained lower in the PEG-OB-protein group, whereas they increased and remained higher in the placebo group (P < 0.0001). During treatment, hunger decreased in the PEG-OB-protein group (P < 0.05) and cognitive restraint increased in the placebo group (P < 0.0001). Neither appetite nor food intake changed significantly during the ad libitum evening meal. Under energy balance conditions in the respiration chamber, appetite at the end of treatment was not significantly different from baseline despite similar, significant reductions in 24-h energy intake, energy expenditure, sleeping metabolic rate, body mass, fat mass, and fat-free mass (P < 0.01 for all) in both groups., Conclusion: Treatment with PEG-OB protein modified subjective appetite at a dosage that produced no changes in body composition, energy expenditure, or body mass loss relative to placebo treatment, suggesting that PEG-OB protein has central rather than peripheral biological activity in obese men.

To assess the biological activity and tolerability of pegylated recombinant native human leptin (PEG-OB), 30 obese men (mean body mass index, 33.9 kg/m2) were randomized to a double-blind treatment with weekly sc injections of 20 mg PEG-OB or placebo for 12 weeks, in addition to a hypocaloric diet (deficit, 2 MJ/day). Body composition, energy expenditure, and metabolic parameters were measured before and after treatment. PEG-OB was generally well tolerated based on adverse event reports, lab values, and vital signs. Weekly sc PEG-OB led to sustained serum concentrations of PEG-OB and leptin throughout treatment. No significant differences in the delta or percent weight loss, percent body fat, sleeping metabolic rate, or respiratory quotient were observed between the PEG-OB and placebo groups. Percent change in serum triglycerides from baseline was significantly correlated with body weight loss in the PEG-OB group, but not in the placebo group. Although larger reductions in serum triglycerides were observed in the PEG-OB group compared with the placebo group, these differences were not statistically significant. We concluded that weekly injection of PEG-OB leads to sustained serum concentration of PEG-OB and leptin throughout the 12-week treatment period and is generally well tolerated. The trends observed in serum triglycerides suggest that a weekly 20-mg sc treatment with PEG-OB may have biological effects in obese men.

Background: Plasma leptin in humans is subject to both long- and short-term regulation; it correlates with indexes of body fat that can only change slowly. However, short-term fasting causes large and rapid decreases., Objective: We tested the interactions between energy intake and fat loss on plasma leptin during prolonged moderate and severe energy restriction, with a view to understanding mechanisms of control., Design: Postabsorptive leptin was measured with an enzyme-linked immunosorbent assay specific for the human peptide in 21 obese women aged 41 +/- 3 y (weight: 102 +/- 4 kg; 48 +/- 1% body fat) after 1 wk of a weight-maintaining diet and then weekly for 4 wk during a total fast (group 1); a 1.9-MJ/d all-protein, very-low-energy diet (VLED) (group 2); or a low-energy, balanced-deficit diet (BDD) providing 50% of maintenance energy (group 3). In groups 1 and 2, leptin was also measured after 1 wk of refeeding with a diet equivalent to the BDD., Results: Mean leptin decreased markedly by up to 66% (P < 0.001) at week 1 of energy restriction and then gradually thereafter. The change in leptin per kilogram fat mass correlated with that in glucose concentrations [r = 0.538 (P = 0.012) at week 1 and r = 0.447 (P = 0.042) at week 4] but not with that in fat mass. During refeeding postfasting, leptin increased (P = 0.008), despite an ongoing loss of fat mass and correlated positively with changes in resting energy expenditure. At times with comparable cumulative energy restriction and fat loss between diets, the percentage change in leptin paralleled that in glucose., Conclusions: In obesity, changes in energy intake over days to weeks are a primary modulator of plasma leptin concentrations that are related to the change in glycemia and are able to override the regulatory influence of fat mass.

Obesity is an extremely challenging medical condition because it is a multifactorial disease that lies at the interface between the biology of body energy regulation and an environment (physical and sensory) that has been increasingly characterized as 'hostile to good health'. The deceptively straightforward anthropomorphic definition of obesity is the excessive accumulation of body fat. However, obesity is a chronic disease that is much more than excessive fat. It involves genetic predisposition and metabolic, hormonal and behavioural aspects and results in significant morbidity, reduced quality of life, discrimination and early mortality. The development and maintenance of obesity can be considered to result from the integration, or the accumulation, of small daily errors in energy balance over several months and years. The biological factors involved increase the predisposition toward the expansion of adipose tissue mass together with the consequences of an environment that promotes increased food intake and decreased physical activity. Multiple aetiologies may result in similar degrees of obesity.

Obesity is an increasingly prevalent and important health problem. Although treatment is available, the long-term maintenance of medically significant weight loss (5 to 10 percent of initial body weight) is rare. Since 1995 there has been an explosion of research focused on the regulation of energy balance and fat mass. Characterization of obesity-associated gene products has revealed new biochemical pathways and molecular targets for pharmacological intervention that will likely lead to new treatments. Ideally, these treatments will be viewed as adjuncts to behavioral and lifestyle changes aimed at maintenance of weight loss and improved health.

The melanocortin-4 receptor (MC4-R) is a G protein-coupled, seven-transmembrane receptor expressed in the brain. Inactivation of this receptor by gene targeting results in mice that develop a maturity onset obesity syndrome associated with hyperphagia, hyperinsulinemia, and hyperglycemia. This syndrome recapitulates several of the characteristic features of the agouti obesity syndrome, which results from ectopic expression of agouti protein, a pigmentation factor normally expressed in the skin. Our data identify a novel signaling pathway in the mouse for body weight regulation and support a model in which the primary mechanism by which agouti induces obesity is chronic antagonism of the MC4-R.

The protein encoded by the obese (ob) gene, leptin, is secreted from adipose tissue and is proposed to act in the brain as an important regulator of food intake and body weight. To investigate the direct effects of leptin within the CNS, we injected 3.5 microg of either mouse or human leptin into the third ventricle (ICV) of lean Long-Evans rats or obese (fa/fa) Zucker rats, in which obesity results from a mutation in the leptin receptor gene. ICV administration of leptin reduced 4-h food intake in both deprived and non-deprived lean rats. In addition, repeated ICV administration produced a long-lasting reduction in body weight while peripheral administration of the same dose had no effect. ICV administration of the same dose of leptin into the third ventricle of obese Zucker rats did not reduce food intake. These results are consistent with the hypothesis that leptin has direct actions in the CNS as an afferent signal related to the state of energy stores in adipose tissue. Furthermore, insensitivity to these central effects of leptin may be an important determinant of obesity.

OB protein (also known as leptin), a previously unknown protein signal, is secreted from adipose tissue, circulates in the blood, probably bound to a family of binding proteins, and acts on central neural networks that regulate ingestive behavior and energy balance. OB protein provides a communication link from fat tissue and the brain. Rapidly accumulating evidence suggests that OB protein appears to play a major role in the control of body fat stores through coordinated regulation of feeding behavior, metabolism, autonomic nervous system and body energy balance in rodents, primates and humans. The field has rapidly moved from cloning of the ob gene to demonstration of complex regulation of ob gene expression in adipose tissue in rats and humans, and then the demonstration of potent biological activity of OB protein in ob/ob, diet-induced, and lean mice as well as obese and lean rats but not in db/db obese mice. A significant milestone was our demonstration that central administration of OB protein lead to reductions in food intake, body weight and alterations in metabolism consistent with activation of the autonomic nervous system. These findings were followed by the identification of a central binding site for labelled OB protein in the choroid plexus in ob/ob, db/db and lean mice as well as lean and obese Zucker rats. The expression cloning of a central receptor, OB-R, from the mouse choroid plexus soon followed. The OB-R receptor was found to be expressed in the choroid plexus, the hypothalamus as well as several peripheral tissues. OB-R exists in multiple forms; the two major forms are a short form (with a truncated intracellular domain) and long form (with the complete intracellular domain). The long form is thought to be the form that signals and mediates the biological effects of OB protein. Initial in situ hybridization studies have demonstrated the mRNA for the long form OB-R receptor to be localized to the hypothalamus as well as peripheral sites. Recently, it was demonstrated that the db gene encodes the OB-R receptor. Evidence has been provided for a specific transport system for OB protein to cross the blood-brain-barrier and enter the brain of mice, rats and humans. The rate of transport can be decreased by high plasma concentrations of OB protein. Thus, reduced entry of OB protein to the brain may be one of the mechanisms of reduced sensitivity of the OB protein pathway in obese individuals. OB protein appears to also play a role in the important neuroendocrine adaptive responses to fasting and in the control of reproduction. Therapeutic approaches to the treatment of obesity based on OB protein ranging from OB protein by injection to OB-R receptor agonists and to upregulation of OB signalling pathways are under intense investigation.

Binding studies were conducted to identify the anatomical location of brain target sites for OB protein, the ob gene product. 125I-labeled recombinant mouse OB protein or alkaline phosphatase-OB fusion proteins were used for in vitro and in vivo binding studies. Coronal brain sections or fresh tissue from lean, obese ob/ob, and obese db/db mice as well as lean and obese Zucker rats were probed to identify potential central OB protein-binding sites. We report here that recombinant OB protein binds specifically to the choroid plexus. The binding of OB protein (either radiolabeled or the alkaline phosphatase-OB fusion protein) and its displacement by unlabeled OB protein was similar in lean, obese ob/ob, and obese db/db mice as well as lean and obese Zucker rats. These findings suggest that OB protein binds with high affinity to a specific receptor in the choroid plexus. After binding to the choroid plexus receptor, OB protein may then be transported across the blood-brain barrier into the cerebrospinal fluid. Alternatively, binding of OB protein to a specific receptor in the choroid plexus may activate afferent neural inputs to the neural network that regulates feeding behavior and energy balance or may result in the clearance or degradation of OB protein. The identification of the choroid plexus as a brain binding site for OB protein will provide the basis for the construction of expression libraries and facilitate the rapid cloning of the choroid plexus OB receptor.

The ob gene product, leptin, is an important circulating signal for the regulation of body weight. To identify high affinity leptin-binding sites, we generated a series of leptin-alkaline phosphatase (AP) fusion proteins as well as [125I]leptin. After a binding survey of cell lines and tissues, we identified leptin-binding sites in the mouse choroid plexus. A cDNA expression library was prepared from mouse choroid plexus and screened with a leptin-AP fusion protein to identify a leptin receptor (OB-R). OB-R is a single membrane-spanning receptor most related to the gp130 signal-transducing component of the IL-6 receptor, the G-CSF receptor, and the LIF receptor. OB-R mRNA is expressed not only in choroid plexus, but also in several other tissues, including hypothalamus. Genetic mapping of the gene encoding OB-R shows that it is within the 5.1 cM interval of mouse chromosome 4 that contains the db locus.

Hyperinsulinemia and exaggerated insulin response to glucose are among the hallmarks of obesity. However, the role of hyperinsulinemia in the etiology and maintenance of obesity has been controversial. If hyperinsulinemia plays a critical role as proposed, then its reversal may have therapeutic potential. To test this hypothesis, the activity of Ro 23-7637, (4-(2,2-diphenylethenyl)-1-[1-oxo-9-(3-pyridinyl) nonyl]piperidine), which partially normalizes plasma insulin by an action on pancreatic islets from obese rats, was assessed. When islets were cultured for 2 days with 10 microM Ro 23-7637, a significant reduction in the exaggerated glucose-induced insulin secretion was observed. When islets from lean rats were exposed to Ro 23-7637, no reduction in insulin secretion was observed. The effects of oral administration of Ro 23-7637 were assessed in Zucker and diet-induced obese rats in doses ranging from 5 to 90 mg/kg/day. Dose-related reductions were observed in: 1) glucose-induced insulin secretion; 2) basal insulin concentration; 3) daily food intake; and 4) bodyweight gain. In diet-induced obese rats, selective mobilization of fat, maintenance of body protein, and decreased energetic efficiency were also observed. An association between the partial normalization of glucose-induced insulin responses and reductions of basal insulin, reduced rates of body weight gain or body weight loss and decreased food intake was observed in obese rats. Therefore, these studies indicate that Ro 23-7637 is an orally active, efficacious antiobesity agent.

The recent positional cloning of the mouse ob gene and its human homology has provided the basis to investigate the potential role of the ob gene product in body weight regulation. A biologically active form of recombinant mouse OB protein was overexpressed and purified to near homogeneity from a bacterial expression system. Peripheral and central administration of microgram doses of OB protein reduced food intake and body weight of ob/ob and diet-induced obese mice but not in db/db obese mice. The behavioral effects after brain administration suggest that OB protein can act directly on neuronal networks that control feeding and energy balance.

The heterogeneous nature of the experimental obesities induced by ventromedial hypothalamic (VMH) lesion and high fat diet (HFD) have been demonstrated by comparing VMH-lesioned and sham-operated rats fed a HFD or low fat diet (LFD). VMH rats had increased fat mass serum insulin and serum triglycerides but lower serum glucagon and smaller salivary glands than sham-operated animals. The body weight of HFD obese rats was intermediate between VMH and sham-operated animals on the LDF. Liver and fat pad weights showed effects of lesions and diet. Diet did not affect plasma glucagon or insulin. Pair-feeding VMH rats with sham-operated rats prevented weight gain but did not prevent the increase in insulin and fall in glucagon. Studies of insulin secretion from isolated perifused islets showed that basal and both phases of stimulated secretion were significantly increased in VMH groups. The changes in plasma insulin, plasma glucagon, and salivary gland weight in VMH groups are interpreted as showing decreased activity of the sympathetic nervous system following VMH lesions.

The objective of these studies was to determine the impact of enhanced insulin response to glucose (glucose responsiveness) and altered neurotransmitter sensitivity of the pancreatic islet previously observed after ventromedial hypothalamic (VMH) lesion on the glucose regulatory system in the whole animal. Female Wistar (220 g) rats received bilateral electrolytic VMH lesions and were implanted with cardiac and femoral cannulas under anesthesia. After recovery, experimental studies were conducted in 2-h-fasted lightly heparinized conscious rats. Plasma glucose declined at 1 and 2 wk after lesion and returned gradually to basal levels by 4 wk, whereas plasma insulin was elevated at 1 wk and remained elevated at 4.5 wk after lesion. Glucose responsiveness was increased threefold 1 wk after lesion. Acetylcholine sensitivity, measured by insulin response to an acetylcholine analogue, was decreased at 1, 2, and 4 wk after lesion, whereas norepinephrine sensitivity, measured by norepinephrine inhibition of the insulin response to intravenous glucose, was significantly increased 1 wk after VMH lesion. These studies suggest that the observed alterations at the level of the pancreatic islet led to a shift in the operating point of the glucose regulatory system of the whole animal and that changes in neurotransmitter sensitivity reflect a pancreatic adaptation subsequent to the establishment of enhanced glucose responsiveness. This shift in operating point may be secondary to altered neural input and may be essential to pancreatic and, thus, metabolic adaptation to the VMH lesion-induced obese state.