Increased Energy Expenditure, Lipolysis and Hyperinsulinemia Confer Resistance to Central Obesity and Type 2 Diabetes in Mice Lacking Alpha2α-Adrenoceptors.

The alpha2A-adrenoceptors (α2A-ARs) are Gi-coupled receptors, which prejunctionally inhibit the release of norepinephrine (NE) and epinephrine (Epi), and postjunctionally inhibit insulin secretion and lipolysis. We have earlier shown that α2A-/- mice display sympathetic hyperactivity, hyperinsulinemia and improved glucose tolerance. Here we employed α2A-/- mice and placed the mice on a high-fat diet (HFD) to test the hypothesis that lack of α2A-ARs protects from diet-induced obesity and type 2 diabetes (T2D). In addition, a high-caloric diet was combined with running wheel exercise to test the interaction of diet and exercise. HFD was obesogenic in both genotypes, but α2A-/- mice accumulated less visceral fat than the wild-type controls, were protected from T2D, and their insulin secretion was unaltered by the diet. Lack of α2A-ARs is associated with an increased sympatho-adrenal tone, which resulted in increased energy expenditure and fat oxidation rate potentiated by HFD. Fittingly, α2A-/- mice displayed enhanced lipolytic responses to Epi, and increased faecal lipids suggesting altered fat mobilization and absorption. Subcutaneous white fat appeared to be thermogenically more active (measured as Ucp1 mRNA expression) in α2A-/- mice, and brown fat showed an increased response to NE. Exercise was effective in reducing total body adiposity and increasing lean mass in both genotypes, but there was a significant diet-genotype interaction, as even modestly increased physical activity combined with lack of α2A-AR signalling promoted weight loss more efficiently than exercise with normal α2A-AR function. These results suggest that blockade of α2A-ARs may be exploited to reduce visceral fat and to improve insulin secretion.

Tauopathy in transgenic (SHR72) rats impairs function of central noradrenergic system and promotes neuroinflammation.

BACKGROUND: Brain norepinephrine (NE) plays an important role in the modulation of stress response and neuroinflammation. Recent studies indicate that in Alzheimer's disease (AD), the tau neuropathology begins in the locus coeruleus (LC) which is the main source of brain NE. Therefore, we investigated the changes in brain NE system and also the immune status under basal and stress conditions in transgenic rats over-expressing the human truncated tau protein. METHODS: Brainstem catecholaminergic cell groups (LC, A1, and A2) and forebrain subcortical (nucleus basalis of Meynert), hippocampal (cornu ammonis, dentate gyrus), and neocortical areas (frontal and temporal association cortices) were analyzed for NE and interleukin 6 (IL-6) mRNA levels in unstressed rats and also in rats exposed to single or repeated immobilization. Moreover, gene expression of NE-biosynthetic enzyme, tyrosine hydroxylase (TH), and several pro- and anti-inflammatory mediators were determined in the LC. RESULTS: It was found that tauopathy reduced basal NE levels in forebrain areas, while the gene expression of IL-6 was increased in all selected areas at the same time. The differences between wild-type and transgenic rats in brain NE and IL-6 mRNA levels were observed in stressed animals as well. Tauopathy increased also the gene expression of TH in the LC. In addition, the LC exhibited exaggerated expression of pro- and anti-inflammatory mediators (IL-6, TNFα, inducible nitric oxide synthases 2 (iNOS2), and interleukin 10 (IL-10)) in transgenic rats suggesting that tauopathy affects also the immune background in LC. Positive correlation between NE and IL-6 mRNA levels in cornu ammonis in stressed transgenic animals indicated the reduction of anti-inflammatory effect of NE. CONCLUSIONS: Our data thus showed that tauopathy alters the functions of LC further leading to the reduction of NE levels and exaggeration of neuroinflammation in forebrain. These findings support the assumption that tau-related dysfunction of LC activates the vicious circle perpetuating neurodegeneration leading to the development of AD.

Validation study of a HistaSure™ ELISA (Fast Track) for the determination of histamine in fish samples.

LDN Labor Diagnostika Nord GmbH & Co. KG has developed an ELISA for the rapid semiquantitative or quantitative determination of histamine in different kinds of fish samples. Fresh/frozen tuna, canned tuna, fresh/frozen mahi mahi, canned sardines, and fish meal were used to validate the method under the requirements of the AOAC Research Institute Performance Tested Methods(SM) Program.The results all fell within the defined acceptance criteria. Linearity was given throughout the 0-300 ppm measuring range. Cross reactivity to similarly structured food spoilage indicators (tyramine and cadaverine) was minimal, less than 1%. Overall recoveries for all tested matrixes were within the determined acceptable range (80-120%), and the repeatability of precision was less than 10% overall and less than 5% at the defect action level of 50 ppm set by the U.S. Food and Drug Administration. The LOQ for the ELISA was determined to be 1.27 ppm. No lot-to-lot differences were observed. A 2-year claimed shelf life, at 2-8 °C, was confirmed through accelerated stability testing. After the introduction of minor procedural variations to the test, no differences in histamine levels were observed. Independent lab testing revealed that the ELISA works as well in the hands of minimally trained technicians as it does with expert developers. A strong correlation (r = 0.97) between the LDN ELISA and the AOAC 977.13 fluorometric method was observed. This study revealed that the LDN ELISA is equivalent to the AOAC Official Method 977.13 for the precise .and accurate measurement of histamine in fresh/frozen tuna, canned tuna, fresh/frozen mahi mahi, canned sardines, and fish meal.

Stress-induced activation of the sympathoadrenal system is determined by genetic background in rat models of tauopathy.

Stress may accelerate onset of neurodegenerative diseases in vulnerable subjects and, vice versa, neurodegeneration affects the responsiveness to stressors. We investigated the neuroendocrine response to immobilization stress in normotensive Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR), and transgenic rats of respective WKY and SHR strains overexpressing human truncated tau protein. Plasma levels of epinephrine, norepinephrine, and corticosterone were determined. An immobilization-induced elevation of epinephrine and norepinephrine was significantly reduced in WKY transgenic rats compared to WKY wild-type rats, while no differences were seen between SHR transgenic and SHR wild-type animals. Our data have shown that sympathoadrenal system response to stress strongly depends on both tau protein-induced neurodegeneration and genetic background of experimental animals.

Measurements of plasma metanephrines by immunoassay vs liquid chromatography with tandem mass spectrometry for diagnosis of pheochromocytoma.

BACKGROUND: Reports conflict concerning measurements of plasma metanephrines (MNs) for diagnosis of pheochromocytomas/paragangliomas (PPGLs) by immunoassays compared with other methods. We aimed to compare the performance of a commercially available enzyme-linked immunoassay (EIA) kit with liquid chromatography-tandem mass spectrometric (LC-MS/MS) measurements of MNs to diagnose PPGLs. METHODS: In a substudy of a prospective, multicenter trial to study the biochemical profiles of monoamine-producing tumors, we included 341 patients (174 males and 167 females) with suspected PPGLs (median age 54 years), of whom 54 had confirmed PPGLs. Plasma MNs were measured by EIA and LC-MS/MS, each in a specialized laboratory. RESULTS: Plasma normetanephrine (NMN) and MN were measured 60 and 39% lower by EIA than by LC-MS/MS. Using upper cut-offs stipulated for the EIA, diagnostic sensitivity was only 74.1% at a specificity of 99.3%. In contrast, use of similar cut-offs for MN and overall lower age-adjusted cut-offs for NMN measured by LC-MS/MS returned a diagnostic sensitivity and specificity of 98.1 and 99.7%. Areas under receiver-operating characteristic curves, nevertheless, indicated comparable diagnostic performance of the EIA (0.993) and LC-MS/MS (0.985). Diagnostic sensitivity for the EIA increased to 96.2% with a minimal loss in specificity (95.1%) following use of cut-offs for the EIA adapted to correct for the negative bias. CONCLUSIONS: The EIA underestimates plasma MNs and diagnostic sensitivity is poor using commonly stipulated cut-offs, resulting in a high risk for missing patients with PPGLs. Correction of this shortcoming can be achieved by appropriately determined cut-offs resulting in comparable diagnostic performance of EIA and LC-MS/MS assays.