Measurement of urinary free cortisol by LC-MS-MS: adoption of a literature reference range and comparison with our current immunometric method.

PURPOSE: One of the best indicators of adrenal gland dysfunction is the level of free cortisol measured in the 24-h urine (UFC) which faithfully reflects the level of biologically active serum cortisol not subjected to circadian variations. Liquid chromatography coupled with tandem mass spectrometry (LC-MS-MS) is a sensitive, accurate and precise method recently available in routine laboratories that could remedy interference problems of immunoassays. METHODS: In this study, a literature reference range for UFC measured by LC-MS-MS was verified, and UFC values measured by LC-MS-MS and immunoassay were compared. Immunometric UFC measurement was performed by ACCESS CORTISOL assay without preliminary extraction, using Beckman Coulter UniCel DxI 600 highly automated platform. Liquid chromatography-tandem mass spectrometry UFC measurement was performed by a home-made validated method using cortisol-D4 as internal standard with preliminary deproteinization of urinary samples by centrifugal filter and injection on reverse-phase column. Cortisol was analyzed in positive ion mode with an ESI interface. RESULTS: The reference interval from literature (11-70 µg/day) was confirmed by results obtained for healthy study group. Comparison study of the two methods highlighted a constant and proportional systematic error with a general tendency to overestimate results for the in-use method. CONCLUSIONS: In conclusion, the direct immunometric method overestimates UFC results with respect to liquid chromatography-tandem mass spectrometry which represents the reference method. The literature reference range 11-70 µg/day was confirmed and can be adopted by our lab that will shift all UFC tests performed in routine to the mass spectrometry-based method, satisfying clinicians' request.

Mannose is an insulin-regulated metabolite reflecting whole-body insulin sensitivity in man.

Mannose is a glucose-associated serum metabolite mainly released by the liver. Recent studies have shown several unexpected pleiotropic effects of mannose including increased regulatory T cells (Tregs), prevention of auto-immune disease and ability to reduce growth of human cancer cells. We have previously shown in large cohorts that elevated serum mannose levels are associated with future development of type 2 diabetes (T2D) and cardiovascular disease. However, potential direct effects of mannose on insulin sensitivity in vivo or in vitro are unknown. We here show that administration of mannose (0.1 g/kg BW twice daily) for one week in man did not elicit negative effects on meal-modified glucose tolerance, markers of inflammation or insulin levels. Tregs number and insulin signaling in human liver cells were unchanged. These data suggest that mannose is a marker, and not a mediator, of insulin resistance. To verify this, we examined serum mannose levels during long-term euglycemic hyperinsulinemic clamps in non-diabetic and T2D individuals. Mannose was reduced by insulin infusion in proportion to whole-body insulin sensitivity. Thus, mannose is a biomarker of insulin resistance which may be useful for the early identification of diabetic individuals with insulin resistance and increased risk of its complications.

Ethanol elicits and potentiates nociceptor responses via the vanilloid receptor-1.

The vanilloid receptor-1 (VR1) is a heat-gated ion channel that is responsible for the burning sensation elicited by capsaicin. A similar sensation is reported by patients with esophagitis when they consume alcoholic beverages or are administered alcohol by injection as a medical treatment. We report here that ethanol activates primary sensory neurons, resulting in neuropeptide release or plasma extravasation in the esophagus, spinal cord or skin. Sensory neurons from trigeminal or dorsal root ganglia as well as VR1-expressing HEK293 cells responded to ethanol in a concentration-dependent and capsazepine-sensitive fashion. Ethanol potentiated the response of VR1 to capsaicin, protons and heat and lowered the threshold for heat activation of VR1 from approximately 42 degrees C to approximately 34 degrees C. This provides a likely mechanistic explanation for the ethanol-induced sensory responses that occur at body temperature and for the sensitivity of inflamed tissues to ethanol, such as might be found in esophagitis, neuralgia or wounds.