The unidentified hormonal defense against weight gain.

Human biology has evolved to keep body fat within a range that supports survival. During the last 25 years, obesity biologists have uncovered key aspects of physiology that prevent fat mass from becoming too low. In contrast, the mechanisms that counteract excessive adipose expansion are largely unknown. Evidence dating back to the 1950s suggests the existence of a blood-borne molecule that defends against weight gain. In this article, we discuss the research supporting an "unidentified factor of overfeeding" and models that explain its role in body weight control. If it exists, revealing the identity of this factor could end a long-lasting enigma of energy balance regulation and facilitate a much-needed breakthrough in the pharmacological treatment of obesity.

Leptin promotes the fat preference associated with low-temperature acclimation in mice.

Although fluctuations in energy metabolism are known to influence intake as well as nutrient selection, there are no definitive reports on how food preferences change with changes in habitat temperature. We investigated the effects of habitat temperature on appetite and food preference and elucidated the underlying mechanism by conducting a feeding experiment and a leptin administration test on mice reared at low temperatures. Our results showed that the increased food intake and HFD preference observed in the 10°C group were induced by decrease in plasma leptin concentration. Then, a leptin administration experiment was conducted to clarify the relationship between leptin and food preference with low-temperature acclimation. The control group reared in 10°C significantly preferred the HFD, but the leptin-administered group did not. These results show that the peripheral system appetite-regulating hormone leptin not only acts to suppress appetite but also might inhibit preference for lipids in low-temperature acclimation.

Pharmacogenetics of amfepramone in healthy Mexican subjects reveals potential markers for tailoring pharmacotherapy of obesity: results of a randomised trial.

Amfepramone (AFP) is an appetite-suppressant drug used in the treatment of obesity. Nonetheless, studies on interindividual pharmacokinetic variability and its association with genetic variants are limited. We employed a pharmacokinetic and pharmacogenetic approach to determine possible metabolic phenotypes of AFP and identify genetic markers that could affect the pharmacokinetic variability in a Mexican population. A controlled, randomized, crossover, single-blind, two-treatment, two-period, and two sequence clinical study of AFP (a single 75 mg dose) was conducted in 36 healthy Mexican volunteers who fulfilled the study requirements. Amfepramone plasma levels were measured using high-performance liquid chromatography mass spectrometry. Genotyping was performed using real-time PCR with TaqMan probes. Four AFP metabolizer phenotypes were found in our population: slow, normal, intermediate, and fast. Additionally, two gene polymorphisms, ABCB1-rs1045642 and CYP3A4-rs2242480, had a significant effect on AFP pharmacokinetics (P < 0.05) and were the predictor factors in a log-linear regression model. The ABCB1 and CYP3A4 gene polymorphisms were associated with a fast metabolizer phenotype. These results suggest that metabolism of AFP in the Mexican population is variable. In addition, the genetic variants ABCB1-rs1045642 and CYP3A4-rs2242480 may partially explain the AFP pharmacokinetic variability.

Plasma and Urine Levamisole in Clinical Samples Containing Benzoylecgonine: Absence of Aminorex.

Aminorex has been reported as a metabolite of levamisole in man, but data on the aminorex concentrations in clinical samples are scant. We thus measured levamisole, aminorex and benzoylecgonine in urine, and levamisole and aminorex in plasma using achiral liquid chromatography-high resolution mass spectrometry. Centrifuged urine (50 µL) was diluted with LC eluent containing internal standard (benzoylecgonine-D3, 25 µg/L) (450 µL). For plasma, sample (200 µL) and Tris solution (2 mol/L, pH 10.6, 100 µL) were added to a 60.5 × 7.5 mm i.d. glass test tube. Internal standard solution (ketamine-D4, 200 µg/L) (10 µL) was added and the tube contents vortex-mixed (5 s). Butyl acetate:butanol (9 + 1, v/v; 200 µL) was added and after vortex-mixing (30 s) and centrifugation (13,680 × g, 4 min), the extract was evaporated to dryness and reconstituted in 10 mmol/L aqueous ammonium formate containing 0.1% (v/v) formic acid (150 µL). Prepared samples and extracts (100 µL) were analyzed using an AccucoreTM Phenyl-Hexyl column (2.6 mm a.p.s., 100 × 2.1 mm i.d.) maintained at 40°C. MS detection was in positive mode using heated electrospray ionization (ThermoFisher Q-ExactiveTM). Intra- and inter-assay accuracy and precision were ±20%, and ≤11%, respectively, for all analytes in both matrices. Lower limits of quantitation were 0.1 and 1 µg/L (all analytes) in plasma and urine, respectively. Of 100 consecutive urine samples submitted for drugs of abuse screening containing benzoylecgonine, levamisole was detected in 72 (median 565, range 4-72,970 µg/L). Levamisole was also measured in eight plasma samples (median 10.6, range 0.9-64.1 µg/L). A number of metabolites of levamisole (4-hydroxylevamisole, levamisole sulfoxide, levamisole glucuronide, and hydroxylevamisole glucuronide) were tentatively identified in urine. Neither aminorex, nor any of its reported metabolites were detected in any sample.

Effects of intranasal oxytocin on satiety signaling in people with schizophrenia.

Overweight and obesity in schizophrenia are prevalent, affecting half to three-quarters of people with schizophrenia. Hyperphagia and increased meal size have also been implicated as significant contributors to the weight gain problem. Oxytocin has shown to play a role in appetite control in humans and is considered an anorexigenic peptide. This two-day, within-subjects, challenge study involved the examination of satiety after administration of 24 IU oxytocin (intranasal) vs. placebo in participants with a DSM-IV diagnosis of schizophrenia (N = 16). Self reported satiety along with a preload-test meal paradigm were utilized as well as related laboratory measures (insulin, glucose, and leptin), and measures of taste and smell. There were no statistically significant differences between the groups on self-reported satiety or test meal consumption, insulin or glucose levels, or sensory measures. A significant treatment difference was found (F = 5.22, df = 1,97.6, p = 0.025), with a decrease in leptin in the oxytocin group post-administration, but no time effect (F = 1.67, df = 6,95.1, p = 0.180) or treatment by time interaction (F = 1.36. df = 3,4.16, p = 0.261). Despite the small sample and mostly negative findings, we encourage more work to use higher and repeated doses of oxytocin, and to further examine the effect of oxytocin on leptin in schizophrenia as this may be important for understanding both weight control and psychopathology.

Satietin, a blood-borne glycoprotein in the regulation of food intake.

Satietin and satietin-D, two closely related 50,000 dalton anorectic glycoproteins were isolated from human serum. The isoelectric point of satietin is 7.0, it contains 14-15% amino acids and 70-75% carbohydrates. Satietin-D has an isoelectric point of 3.0, a protein content of 20-22% and a carbohydrate content of 55-60%. Both satietin and satietin-D are potent, long-acting and highly selective suppressants of food intake in the rat. The hypothesis was forwarded that satietin and satietin-D may belong to a system which brings into being the rate-limiting blood-borne satiety signalization in the negative feedback of food intake.

Satietin; a 50,000 dalton glycoprotein in human serum with potent, long-lasting and selective anorectic activity.

Satietin, a 50,000 dalton anorectic glycoprotein was isolated from human serum. Its isoelectric point is 7.0. It contains 14-15% amino acids and 70-75% carbohydrates. Its biological activity survives digestion with proteases and boiling. Satietin is a highly potent anorectic substance. The intracerebroventricular administration of 10-20 micrograms satietin suppresses food intake in rats during the first day of feeding after deprivation of food for 96 hours to half of the amount eaten by untreated controls (ID50). The onset of the effect can be detected within 30 minutes, the peak effect is reached within an hour. The effect lasts 24-30 hours. Satietin acts both at intravenous and subcutaneous administration (ID50 = 0.5-0.75 mg/kg) in rats deprived of food for 96 hours. The peak effect is reached within an hour and lasts over 24 hours. In contrast to the anorectic drugs in clinical use and to the endogenous anorectic substances (like cholecystokinin and calcitonin) satietin proved to be highly selective in suppressing food intake. Considering that satietin is widely distributed in the world of vertebrates, its concentration in the blood is amazingly high, its site of effect is in the central nervous system and it induces satiety without having any other detectable central or peripheral effect, the hypothesis was forwarded that satietin may play the role of a rate limiting blood-borne satiety signal in the negative feedback of food intake, i.e. serving as the essential chemical link connecting the gastrointestinal tract and the brain in the regulation of feeding.

Determination of (-)-threo-chlorocitric acid in human plasma by gas chromatography-positive chemical-ionization mass spectrometry.

A method is described for measuring (-)-threo-chlorocitric acid in human plasma. Plasma is acidified to pH 1 to minimize lactonization and a 13C analogue of (-)-threo-chlorocitric acid is added as internal standard. The acidified plasma is then extracted with ethyl acetate containing 10% methanol. The ethyl acetate-methanol extract is back-extracted with acetate buffer (pH 5). This extract, following adjustment to pH 1, is reextracted with ethyl acetate. The residue after removal of the ethyl acetate is treated with ethereal diazomethane. The wet residue is reconstituted in ethyl acetate and a portion of this solution is analyzed by gas chromatography-chemical ionization mass spectrometry. The mass spectrometer is set to monitor m/z 269 [MH+ of trimethylated (-)-threo-chlorocitric acid] and m/z 270 [MH+ of trimethylated (-)-threo-[13C]chlorocitric acid] in the gas chromatographic effluent. The m/z 269 to m/z 270 ion ratio in a sample containing an unknown amount of (-)-threo-chlorocitric acid is converted to an amount of compound using a calibration curve. The calibration curve is generated by analyzing control plasma spiked with various known amounts of (-)-threo-chlorocitric acid and a fixed amount of (-)-threo-[13C]chlorocitric acid. The limit of quantitation is 0.1-0.6 micrograms ml-1, depending on the characteristics of the calibration curve generated with each set of samples. The precision (relative standard deviation) at a concentration of 2 micrograms ml-1 is 3.3%.

Quantitative determination of tiflorex in human fluids using electron-capture detection.

A procedure is described for the determination of tiflorex and its metabolite nortiflorex in biological specimens. The compounds are converted into their trichoroacetyl derivatives, which are separated on a glass column packed with 3% OV-17 on Gas-Chrom Q, and measured with an electron-capture detector. The mechanism was investigated by gas chromatography-mass spectrometry. The method is rapid, sensitive for concentrations of 1 ng/ml and has been used to measure tiflorex and its metabolite in rat plasma after intravenous administration and in human volunteers after administration by the oral route.