Current understanding of in vivo human brown adipose tissue (BAT) physiology is limited by a reliance on positron emission tomography (PET)/computed tomography (CT) scanning, which has measured exogenous glucose and fatty acid uptake but not quantified endogenous substrate utilization by BAT. Six lean, healthy men underwent 18fluorodeoxyglucose-PET/CT scanning to localize BAT so microdialysis catheters could be inserted in supraclavicular BAT under CT guidance and in abdominal subcutaneous white adipose tissue (WAT). Arterial and dialysate samples were collected during warm (∼25°C) and cold exposure (∼17°C), and blood flow was measured by 133xenon washout. During warm conditions, there was increased glucose uptake and lactate release and decreased glycerol release by BAT compared with WAT. Cold exposure increased blood flow, glycerol release, and glucose and glutamate uptake only by BAT. This novel use of microdialysis reveals that human BAT is metabolically active during warm conditions. BAT activation substantially increases local lipolysis but also utilization of other substrates such as glutamate.
BackgroundCortisol and corticosterone both circulate in human plasma and, due to differing export by ATP-binding cassette (ABC) transporters, may exert differential cellular effects. ABCB1 (expressed in brain) exports cortisol not corticosterone while ABCC1 (expressed in adipose and skeletal muscle) exports corticosterone not cortisol. We hypothesised that ABCC1 inhibition increases corticosteroid receptor occupancy by corticosterone but not cortisol in humans.MethodsA randomised double-blind crossover study was conducted in 14 healthy men comparing placebo and ABCC1 inhibitor probenecid. Blood sampling, including from veins draining adipose and muscle, was undertaken before and after administration of mineralocorticoid receptor antagonist potassium canrenoate and glucocorticoid receptor antagonist mifepristone (RU486).ResultsDuring placebo, systemic plasma cortisol and corticosterone concentrations increased promptly after canrenoate. Cortisol uptake was detected from adipose but not muscle following canrenoate + RU486. Probenecid significantly increased systemic cortisol concentrations, and tended to increase corticosterone and ACTH concentrations, after combined receptor antagonism but had no effects on net glucocorticoid balance in either adipose or muscle. Using quantitative PCR in brain bank tissue, ABCC1 expression was 5-fold higher in human pituitary than hypothalamus and hippocampus. ABCB1 was more highly expressed in hypothalamus compared to pituitary.ConclusionsAlthough displacement of corticosterone and/or cortisol from receptors in adipose and skeletal muscle could not be measured with sufficient precision to detect effects of probenecid, ABCC1 inhibition induced a greater incremental activation of the hypothalamic-pituitary-adrenal axis after combined receptor blockade, consistent with ABCC1 exporting corticosterone from the pituitary and adding to the evidence that ABC transporters modulate tissue glucocorticoid sensitivity.
Outcomes are poor for patients with congenital adrenal hyperplasia (CAH), in part due to the supraphysiological glucocorticoid doses required to control adrenal androgen excess. Hydrocortisone (i.e. cortisol) is the recommended glucocorticoid for treatment of CAH. However, the other endogenous glucocorticoid in humans, corticosterone, is actively transported out of metabolic tissues such as adipose tissue and muscle, so we hypothesized that corticosterone could control adrenal androgens while causing fewer metabolic adverse effects than hydrocortisone.
Omnipod 5 (OP5) is a tubeless automated insulin delivery (AID) system that was, until recently, only compatible with Dexcom G6 sensors (G6). Currently, all published evidence attesting to the efficacy of OP5 relates specifically to use with G6 sensors.1, 2 In mid-2024, OP5 compatibility with Freestyle Libre 2 Plus CGM (L2+) was launched in the United Kingdom. This study aimed to compare early glycaemic outcomes, and time spent in AID mode, between those using G6 and L2+ sensors. This was a retrospective analysis of 77 adults (45 G6 and 32 L2+) with type 1 diabetes at a single centre in the UK. Baseline CGM data were collected in the 28 days prior to converting from Omnipod DASH (standalone CSII) to OP5 and compared with data from the first 28 days of AID use. CGM data were obtained from LibreView and Glooko. Clinical and demographic data were obtained from SCI Diabetes (national diabetes register). As a service evaluation of routinely collected data, this project did not require ethical approval. Paired data were compared with Wilcoxon-signed rank tests and unpaired data with Wilcoxon rank-sum test. Correlations were assessed by the Spearman correlation coefficient. Categorical data were compared by chi-squared test. Logistic regression analysis assessed independent predictors of reduction in TBR and improvement in TIR (defined as >10%). p values <0.05 were considered statistically significant. Statistical analyses were performed using R Studio (version 2023.12.1). Forty-nine (64%) were female. Median age was 43 years (IQR 32–56) and diabetes duration was 23 years (14–33). Age (p = 0.872), duration (p = 0.371), sex (p = 0.947), socio-economic deprivation (p = 0.912) and BMI (p = 0.161) did not differ between L2+ and G6 users at baseline. Baseline CGM metrics were not significantly different between G6 and L2+ users (all p > 0.05). Time in automode did not differ between groups (G6: 99% [96–100] vs. L2+: 99 [98–100], p = 0.551) and this was also true of time in limited automode (G6: 2% [2–3] vs. L2+: 2 [1–3], p = 0.826). Changes in glucose metrics from baseline are presented in Table 1. Correlation (R) between baseline TIR and change in TIR was −0.91 for L2+ and −0.56 for G6 (both p < 0.001). Logistic regression analysis identified only baseline TIR (OR 0.93 per % [95% CI 0.88–0.97], p < 0.001) but not sensor type (p = 0.723) as an independent predictor of >10% improvement in TIR. Any fall in TBR was independently associated with baseline TBR (OR 3.4 per % [95% CI 2.0–7.1], p < 0.01) and also the use of G6 sensors (OR 5.8 [95% CI 1.4–34], p = 0.027). There do not appear to be any important differences in time spent in automode between G6 and L2+. Similarly, early CGM outcomes are comparable between the two CGM options with respect to average glucose, TIR and high glucose metrics. Although the follow-up duration of 28 days is relatively short, TIR outcomes are broadly similar to our recently published 1-year follow-up data,3 suggesting early changes are a durable indicator of longer-term outcomes. Significant improvement in TBR was confined to G6 users but it is debatable whether comparison of such small differences between two CGM systems is clinically meaningful; especially in a population with such low baseline TBR. There is a dearth of published data directly comparing how accurately L2+ and G6 identify glucose levels in the hypoglycaemic range. A small comparison of Freestyle Libre versus Dexcom G6, in non-diabetic adults (30 days of CGM use), reported a TBR of 9.1% using Libre results versus 1.4% using G6.4 These observations suggest we should exercise caution in inferring too much from small differences in TBR between two different glucose sensors. Reduction in CV glucose was greater in the G6 cohort, which could represent differences in the sensor-algorithm interaction but may also reflect baseline differences in TAR. The question of whether one CGM system truly results in superior reduction in TBR and CV glucose will only be resolved by a study with concurrent use of both sensors. These early data offer reassurance that sensor choice with OP5 does not result in clinically meaningful differences in automode performance or CGM metric outcomes. FWG has received speaker fees from Abbott, Dexcom and Insulet. ARD has received speaker fees from Abbott. No funding was received.
Steroid analysis is important in the clinical assessment of endocrine function in health and disease. Although tandem mass spectrometry methods coupled with chromatographic separation are considered the gold standard analytical technique in this setting, enabling profiling of multiple steroids in a single sample, sample processing can be labour-intensive. Here we present a simple, efficient automated 96-well Supported Liquid Extraction method with dichloromethane/isopropanol as organic solvent, carried out on a Extrahera automated sample handler (Biotage), which completes sample preparation of 80 plasma samples (200µL) in 90 minutes. Compounds were separated on a Kinetex C18 column (150x3mm;2.6um) using a mobile phase of methanol and water (0.1% formic acid). The run time was 16 minutes on a Nexera uHPLC system (Shimadzu) with a QTrap 6500+ linear ion trap mass spectrometer (AB Sciex). Precisions ranged 8.1 to 18.1% RSD, bias -10.1-5.8%, and extraction recoveries 73.5-111.9%. LOQs ranged between 0.025–0.500 ng/mL.
Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders that affects adrenal steroidogenesis, resulting in deficiency of the glucocorticoid cortisol and in many cases the mineralocorticoid aldosterone1. This resulting lack of glucocorticoid (and mineralocorticoid) activates the hypothalamic-pituitary-adrenal (HPA) axis causing excessive release of adrenocorticotrophic hormone (ACTH) and excess adrenal androgen synthesis. Diagnosing and treating CAH requires reliable methods for steroid analysis. Tandem mass spectrometry methods coupled with chromatographic separation are considered the gold standard analytical technique for steroid analysis2 with the added benefit of enabling simultaneous analysis of multiple steroids. There are a range of methods that have been developed to measure multiple steroids in CAH3. Here we have developed a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for application to a clinical study that specifically explores the administration of d8-corticosterone as an alternative to hydrocortisone for CAH treatment. Plasma samples (200 µL) were enriched with isotopically labelled steroids, diluted with water (0.1% formic acid v/v) and extracted alongside a (0.0025 - 400 ng) calibration curve, by automated 96-well supported liquid extraction (SLE), using dichloromethane and isopropanol as an organic solvent, on a Biotage Extrahera automated sample handler. Extracted steroids were separated on a Shimadzu Nexera uHPLC with gradient elution on a Kinetex C18 column (150 x 3 mm; 2.6 µm) and a mobile phase of methanol and water (0.1% formic acid in water and methanol). The run time was 16 minutes, followed by mass spectral analysis on an AB Sciex 6500+ tandem quadrupole mass spectrometer operated in multiple reaction mode, positive ionisation. The method measures five steroids - hydrocortisone (cortisol) and d8-corticosterone - combined with markers of CAH - androgens and the intermediate 17α-hydroxyprogesterone, alongside the internal standards - in plasma. Validation demonstrated that this method is sensitive, specific, and reliable.
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