C-type natriuretic peptide is a pivotal regulator of metabolic homeostasis.

Thermogenesis and adipogenesis are tightly regulated mechanisms that maintain lipid homeostasis and energy balance; dysfunction of these critical processes underpins obesity and contributes to cardiometabolic disease. C-type natriuretic peptide (CNP) fulfills a multimodal protective role in the cardiovascular system governing local blood flow, angiogenesis, cardiac function, and immune cell reactivity. Herein, we investigated a parallel, preservative function for CNP in coordinating metabolic homeostasis. Global inducible CNP knockout mice exhibited reduced body weight, higher temperature, lower adiposity, and greater energy expenditure in vivo. This thermogenic phenotype was associated with increased expression of uncoupling protein-1 and preferential lipid utilization by mitochondria, a switch corroborated by a corresponding diminution of insulin secretion and glucose clearance. Complementary studies in isolated murine and human adipocytes revealed that CNP exerts these metabolic regulatory actions by inhibiting sympathetic thermogenic programming via Gi-coupled natriuretic peptide receptor (NPR)-C and reducing peroxisome proliferator-activated receptor-γ coactivator-1α expression, while concomitantly driving adipogenesis via NPR-B/protein kinase-G. Finally, we identified an association between CNP/NPR-C expression and obesity in patient samples. These findings establish a pivotal physiological role for CNP as a metabolic switch to balance energy homeostasis. Pharmacological targeting of these receptors may offer therapeutic utility in the metabolic syndrome and related cardiovascular disorders.

Changes in continuous glucose monitoring metrics and predictors of improvement 12 months after conversion from Freestyle Libre to Freestyle Libre 2.

AIMS: We sought to assess whether conversion from Freestyle Libre to Freestyle Libre 2 (with low and high glucose alert functions) was associated with improved glucose metrics. RESEARCH DESIGN AND METHODS: A prospective observational study to assess changes in CGM metrics in 672 adults with type 1 diabetes when converting to Freestyle Libre 2. Secondary outcomes included predictors of reduction in time below range (TBR) and increase in time in range (TIR). RESULTS: TBR fell by a median of 1.0% (IQR -2.7 to 0.3, p < 0.001) after 12 months and TIR decreased by 1.0% (-8.7 to 6.0, p = 0.004). TIR did not fall in people using high glucose alerts (p = 0.353). Average duration of low glucose events (<3.9 mmoL/L) fell by 10 min (-46 to 18, p < 0.001). Significant improvements in TIR (p = 0.029) and time above 13.9 mM (p = 0.002) were observed in those using high glucose alerts. Alert threshold settings were not associated with glycaemic response; however, low alert use was independently associated with a fall in TBR of ≥0.5% (HR 1.9 [95% CI 1.2-3.1], p = 0.009) and high alert use was independently associated with a rise in TIR of ≥5% (HR 1.6 [95% CI 1.0-2.5], p = 0.043) at 12 months. CONCLUSIONS: Conversion to Freestyle Libre 2 was associated with significant improvements in low glucose metrics. Alert function users were more likely to see improvements across all CGM metrics. Challenges remain in encouraging alert use, helping users set optimal alert thresholds and optimizing response to alerts.

Socioeconomic deprivation, technology use, C-peptide, smoking and other predictors of glycaemic control in adults with type 1 diabetes.

AIMS: Intensive glycaemic control is associated with substantial health benefits in people with type 1 diabetes. We sought to examine clinical and demographic factors associated with meeting glycaemic targets in type 1 diabetes. METHODS: We conducted a cross-sectional analysis of 4594 individuals with type 1 diabetes. The primary outcome of the study was assessing factors associated with meeting HbA1c targets. Secondary endpoints included factors associated with continuous subcutaneous insulin infusion (CSII) use and persistent C-peptide secretion. RESULTS: Socioeconomic deprivation was strongly associated with a lower likelihood of achieving an HbA1c <58 mmol/mol (7.5%) (20% in the most deprived quintile vs. 40% in the least deprived, p < 0.001). In multivariate analysis, absence of smoking history (OR 3.06, p < 0.001), flash monitoring (OR 1.49, p < 0.001), CSII (1.43, p = 0.022) and longer diabetes duration (OR 1.02 per year, p = 0.004) were independently associated with achieving HbA1c <58 mmol/mol (7.5%), whereas increasing age (OR 0.99 per year, p = 0.004) and C-peptide <50 pM (OR 0.58, p < 0.001) were associated with a lower likelihood of meeting this target. Low C-peptide (<50 pM) was less likely in men (OR 0.55, p < 0.001) and never smokers (0.44, p < 0.001) in multivariate analysis. CONCLUSIONS: Lower levels of deprivation, non-smoking, higher C-peptide, technology use, lower BMI and male gender were all associated with a higher likelihood of meeting HbA1c targets. Access to proven diabetes treatments is lower in the most deprived individuals. Urgent efforts are required to provide treatments which are effective across the socioeconomic gradient.

Collagen 24 α1 Is Increased in Insulin-Resistant Skeletal Muscle and Adipose Tissue.

Aberrant extracellular matrix (ECM) remodelling in muscle, liver and adipose tissue is a key characteristic of obesity and insulin resistance. Despite its emerging importance, the effective ECM targets remain largely undefined due to limitations of current approaches. Here, we developed a novel ECM-specific mass spectrometry-based proteomics technique to characterise the global view of the ECM changes in the skeletal muscle and liver of mice after high fat (HF) diet feeding. We identified distinct signatures of HF-induced protein changes between skeletal muscle and liver where the ECM remodelling was more prominent in the muscle than liver. In particular, most muscle collagen isoforms were increased by HF diet feeding whereas the liver collagens were differentially but moderately affected highlighting a different role of the ECM remodelling in different tissues of obesity. Moreover, we identified a novel association between collagen 24α1 and insulin resistance in the skeletal muscle. Using quantitative gene expression analysis, we extended this association to the white adipose tissue. Importantly, collagen 24α1 mRNA was increased in the visceral adipose tissue, but not the subcutaneous adipose tissue of obese diabetic subjects compared to lean controls, implying a potential pathogenic role of collagen 24α1 in obesity and type 2 diabetes.

Marked improvement in HbA1c following commencement of flash glucose monitoring in people with type 1 diabetes.

AIMS/HYPOTHESIS: Minimal evidence supports the efficacy of flash monitoring in lowering HbA1c. We sought to assess the impact of introducing flash monitoring in our centre. METHODS: We undertook a prospective observational study to assess change in HbA1c in 900 individuals with type 1 diabetes following flash monitoring (comparator group of 518 with no flash monitoring). Secondary outcomes included changes in hypoglycaemia, quality of life, flash monitoring data and hospital admissions. RESULTS: Those with baseline HbA1c ≥58 mmol/mol (7.5%) achieved a median -7 mmol/mol (interquartile range [IQR] -13 to -1) (0.6% [-1.2 to -0.1]%) change in HbA1c (p < 0.001). The percentage achieving HbA1c <58 mmol/mol rose from 34.2% to 50.9% (p < 0.001). Median follow-up was 245 days (IQR 182 to 330). Individuals not using flash monitoring experienced no change in HbA1c across a similar timescale (p = 0.508). Higher HbA1c (p < 0.001), younger age at diagnosis (p = 0.003) and lower social deprivation (p = 0.024) were independently associated with an HbA1c fall of ≥5 mmol/mol (0.5%). More symptomatic (OR 1.9, p < 0.001) and asymptomatic (OR 1.4, p < 0.001) hypoglycaemia was reported after flash monitoring. Following flash monitoring, regimen-related and emotional components of the diabetes distress scale improved although the proportion with elevated anxiety (OR 1.2, p = 0.028) and depression (OR 2.0, p < 0.001) scores increased. Blood glucose test strip use fell from 3.8 to 0.6 per day (p < 0.001). Diabetic ketoacidosis admissions fell significantly following flash monitoring (p = 0.043). CONCLUSIONS/INTERPRETATION: Flash monitoring is associated with significant improvements in HbA1c and fewer diabetic ketoacidosis admissions. Higher rates of hypoglycaemia may relate to greater recognition of hitherto unrecognised events. Impact upon quality of life parameters was mixed but overall treatment satisfaction was overwhelmingly positive.

Acute physiological effects of glucocorticoids on fuel metabolism in humans are permissive but not direct.

BACKGROUND AND AIMS: The effects of glucocorticoids on fuel metabolism are complex. Acute glucocorticoid excess promotes lipolysis but chronic glucocorticoid excess causes visceral fat accumulation. We hypothesized that interactions between cortisol and insulin and adrenaline account for these conflicting results. We tested the effect of cortisol on lipolysis and glucose production with and without insulin and adrenaline in humans both in vivo and in vitro. MATERIALS AND METHODS: A total of 20 healthy men were randomized to low and high insulin groups (both n = 10). Subjects attended on 3 occasions and received low (c. 150 nM), medium (c. 400 nM) or high (c. 1400 nM) cortisol infusion in a randomized crossover design. Deuterated glucose and glycerol were infused intravenously along with a pancreatic clamp (somatostatin with replacement of glucagon, insulin and growth hormone) and adrenaline. Subcutaneous adipose tissue was obtained for analysis. In parallel, the effect of cortisol on lipolysis was tested in paired primary cultures of human subcutaneous and visceral adipocytes. RESULTS: In vivo, high cortisol increased lipolysis only in the presence of high insulin and/or adrenaline but did not alter glucose kinetics. High cortisol increased adipose mRNA levels of ATGL, HSL and CGI-58 and suppressed G0S2. In vitro, high cortisol increased lipolysis in the presence of insulin in subcutaneous, but not visceral, adipocytes. CONCLUSIONS: The acute lipolytic effects of cortisol require supraphysiological concentrations, are dependent on insulin and adrenaline and are observed only in subcutaneous adipose tissue. The resistance of visceral adipose tissue to cortisol's lipolytic effects may contribute to the central fat accumulation observed with chronic glucocorticoid excess.

A cross-sectional questionnaire study: Impaired awareness of hypoglycaemia remains prevalent in adults with type 1 diabetes and is associated with the risk of severe hypoglycaemia.

OBJECTIVE: Impaired awareness of hypoglycaemia (IAH) is a risk factor for severe hypoglycaemia (SH) in type 1 diabetes (T1D). Much of the IAH prevalence data comes from older studies where participants did not have the benefit of the latest insulins and technologies. This study surveyed the prevalence of IAH and SH in a tertiary adult clinic population and investigated the associated factors. METHODS: Adults (≥18 years) attending a tertiary T1D clinic completed a questionnaire, including a Gold and Clarke score. Background information was collected from health records. RESULTS: 189 people (56.1% female) with T1D (median [IQR] disease duration 19.3 [11.5, 29.1] years and age of 41.0 [29.0, 52.0] years) participated. 17.5% had IAH and 16.0% reported ≥1 episode of SH in the previous 12 months. Those with IAH were more likely to report SH (37.5% versus 11.7%, p = 0.001) a greater number of SH episodes per person (median [IQR] 0 [0,2] versus 0 [0,0] P<0.001) and be female (72.7% versus 52.6%, p = 0.036). Socio-economic deprivation was associated with IAH (p = 0.032) and SH (p = 0.005). Use of technology was the same between IAH vs aware groups, however, participants reporting SH were more likely to use multiple daily injections (p = 0.026). Higher detectable C-peptide concentrations were associated with a reduced risk of SH (p = 0.04). CONCLUSION: Insulin pump and continuous glucose monitor use was comparable in IAH versus aware groups. Despite this, IAH remains a risk factor for SH and is prevalent in females and in older people. Socioeconomic deprivation was associated with IAH and SH, making this an important population to target for interventions.

UCP1 expression in human brown adipose tissue is inversely associated with cardiometabolic risk factors.

OBJECTIVE: Brown adipose tissue (BAT) is a therapeutic target for obesity. 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) is commonly used to quantify human BAT mass and activity. Detectable 18F-FDG uptake by BAT is associated with reduced prevalence of cardiometabolic disease. However, 18F-FDG uptake may not always be a reliable marker of BAT thermogenesis, for example, insulin resistance may reduce glucose uptake. Uncoupling protein 1 (UCP1) is the key thermogenic protein in BAT. Therefore, we hypothesised that UCP1 expression may be altered in individuals with cardiometabolic risk factors. METHODS: We quantified UCP1 expression as an alternative marker of thermogenic capacity in BAT and white adipose tissue (WAT) samples (n = 53) and in differentiated brown and white pre-adipocytes (n = 85). RESULTS: UCP1 expression in BAT, but not in WAT or brown/white differentiated pre-adipocytes, was reduced with increasing age, obesity, and adverse cardiometabolic risk factors such as fasting glucose, insulin, and blood pressure. However, UCP1 expression in BAT was preserved in obese subjects of <40 years of age. To determine if BAT activity was also preserved in vivo, we undertook a case-control study, performing 18F-FDG scanning during mild cold exposure in young (mean age ∼22 years) normal weight and obese volunteers. 18F-FDG uptake by BAT and BAT volume were similar between groups, despite increased insulin resistance. CONCLUSION: 18F-FDG uptake by BAT and UCP1 expression are preserved in young obese adults. Older subjects retain precursor cells with the capacity to form new thermogenic adipocytes. These data highlight the therapeutic potential of BAT mass expansion and activation in obesity.

ATP-binding cassette family C member 1 constrains metabolic responses to high-fat diet in male mice.

Glucocorticoids modulate glucose homeostasis, acting on metabolically active tissues such as liver, skeletal muscle, and adipose tissue. Intracellular regulation of glucocorticoid action in adipose tissue impacts metabolic responses to obesity. ATP-binding cassette family C member 1 (ABCC1) is a transmembrane glucocorticoid transporter known to limit the accumulation of exogenously administered corticosterone in adipose tissue. However, the role of ABCC1 in the regulation of endogenous glucocorticoid action and its impact on fuel metabolism has not been studied. Here, we investigate the impact of Abcc1 deficiency on glucocorticoid action and high-fat-diet (HFD)-induced obesity. In lean male mice, deficiency of Abcc1 increased endogenous corticosterone levels in skeletal muscle and adipose tissue but did not impact insulin sensitivity. In contrast, Abcc1-deficient male mice on HFD displayed impaired glucose and insulin tolerance, and fasting hyperinsulinaemia, without alterations in tissue corticosterone levels. Proteomics and bulk RNA sequencing revealed that Abcc1 deficiency amplified the transcriptional response to an obesogenic diet in adipose tissue but not in skeletal muscle. Moreover, Abcc1 deficiency impairs key signalling pathways related to glucose metabolism in both skeletal muscle and adipose tissue, in particular those related to OXPHOS machinery and Glut4. Together, our results highlight a role for ABCC1 in regulating glucose homeostasis, demonstrating diet-dependent effects that are not associated with altered tissue glucocorticoid concentrations.

Adipocyte deletion of the oxygen-sensor PHD2 sustains elevated energy expenditure at thermoneutrality.

Enhancing thermogenic brown adipose tissue (BAT) function is a promising therapeutic strategy for metabolic disease. However, predominantly thermoneutral modern human living conditions deactivate BAT. We demonstrate that selective adipocyte deficiency of the oxygen-sensor HIF-prolyl hydroxylase (PHD2) gene overcomes BAT dormancy at thermoneutrality. Adipocyte-PHD2-deficient mice maintain higher energy expenditure having greater BAT thermogenic capacity. In human and murine adipocytes, a PHD inhibitor increases Ucp1 levels. In murine brown adipocytes, antagonising the major PHD2 target, hypoxia-inducible factor-(HIF)-2a abolishes Ucp1 that cannot be rescued by PHD inhibition. Mechanistically, PHD2 deficiency leads to HIF2 stabilisation and binding of HIF2 to the Ucp1 promoter, thus enhancing its expression in brown adipocytes. Serum proteomics analysis of 5457 participants in the deeply phenotyped Age, Gene and Environment Study reveal that serum PHD2 associates with increased risk of metabolic disease. Here we show that adipose-PHD2-inhibition is a therapeutic strategy for metabolic disease and identify serum PHD2 as a disease biomarker.

Human brown adipose tissue function: insights from current in vivo techniques.

The identification of brown adipose tissue (BAT) as a thermogenic organ in human adults approximately 20 years ago raised the exciting possibility of activating this tissue as a new treatment for obesity and cardiometabolic disease. [18F]Fluoro-2-deoxyglucose (18F-FDG) combined positron emission tomography and computed tomography (PET/CT) scanning is the most commonly used imaging modality to detect and quantify human BAT activity in vivo. This technique exploits the substantial glucose uptake by BAT during thermogenesis as a marker for BAT metabolism. 18F-FDG PET has provided substantial insights into human BAT physiology, including its regulatory pathways and the effect of obesity and cardiometabolic disease on BAT function. The use of alternative PET tracers and the development of novel techniques such as magnetic resonance imaging, supraclavicular skin temperature measurements, contrast-enhanced ultrasound, near-infrared spectroscopy and microdialysis have all added complementary information to improve our understanding of human BAT. However, many questions surrounding BAT physiology remain unanswered, highlighting the need for further research and novel approaches to investigate this tissue. This review critically discusses current techniques to assess human BAT function in vivo, the insights gained from these modalities and their limitations. We also discuss other promising techniques in development that will help dissect the pathways regulating human thermogenesis and determine the therapeutic potential of BAT activation.

Associations between glucagon prescribing, hospital admissions for hypoglycaemia and continuous glucose monitoring metrics in adults with type 1 diabetes.

AIMS: To assess features associated with glucagon prescribing and hospital admissions with hypoglycaemia in type one diabetes. METHODS: Observational study of 4462 adults. Outcome measures were features associated with glucagon prescriptions and predictors of hospital admissions with hypoglycaemia and high levels of glucagon prescribing. RESULTS: 74 % did not collect any glucagon prescriptions and 2.7 % collected >6 over 3.5 years. Hospital admission with hypoglycaemia (P = 0.032), impaired awareness (P = 0.049) and female sex (P < 0.001) were associated with glucagon collection. More frequent prescribing of glucagon was associated with diabetes duration (P < 0.001) and socioeconomic deprivation (P < 0.001). Higher average glucose (P = 0.047), higher time above 13.9 mM (P = 0.008) and higher SD (P = 0.002) were associated with glucagon prescribing. Diabetes duration (P < 0.001) and HbA1c (P < 0.001) were higher in people with hospitalised hypoglycaemia. Higher time above 13.9 mM (P = 0.004) and SD glucose (P < 0.001) were most clearly associated with hospitalised hypoglycaemia. CONCLUSIONS: A minority of people with type 1 diabetes have access to glucagon suggesting more could be done to better target this treatment. Individuals with risk factors and those with frequent glucagon prescriptions should be identified for interventions known to reduce hypoglycaemia.

The ATP-binding cassette proteins ABCB1 and ABCC1 as modulators of glucocorticoid action.

Responses to hormones that act through nuclear receptors are controlled by modulating hormone concentrations not only in the circulation but also within target tissues. The role of enzymes that amplify or reduce local hormone concentrations is well established for glucocorticoid and other lipophilic hormones; moreover, transmembrane transporters have proven critical in determining tissue responses to thyroid hormones. However, there has been less consideration of the role of transmembrane transport for steroid hormones. ATP-binding cassette (ABC) proteins were first shown to influence the accumulation of glucocorticoids in cells almost three decades ago, but observations over the past 10 years suggest that differential transport propensities of both exogenous and endogenous glucocorticoids by ABCB1 and ABCC1 transporters provide a mechanism whereby different tissues are preferentially sensitive to different steroids. This Review summarizes this evidence and the new insights provided for the physiology and pharmacology of glucocorticoid action, including new approaches to glucocorticoid replacement.

The serotonin transporter sustains human brown adipose tissue thermogenesis.

Activation of brown adipose tissue (BAT) in humans is a strategy to treat obesity and metabolic disease. Here we show that the serotonin transporter (SERT), encoded by SLC6A4, prevents serotonin-mediated suppression of human BAT function. RNA sequencing of human primary brown and white adipocytes shows that SLC6A4 is highly expressed in human, but not murine, brown adipocytes and BAT. Serotonin decreases uncoupled respiration and reduces uncoupling protein 1 via the 5-HT2B receptor. SERT inhibition by the selective serotonin reuptake inhibitor (SSRI) sertraline prevents uptake of extracellular serotonin, thereby potentiating serotonin's suppressive effect on brown adipocytes. Furthermore, we see that sertraline reduces BAT activation in healthy volunteers, and SSRI-treated patients demonstrate no 18F-fluorodeoxyglucose uptake by BAT at room temperature, unlike matched controls. Inhibition of BAT thermogenesis may contribute to SSRI-induced weight gain and metabolic dysfunction, and reducing peripheral serotonin action may be an approach to treat obesity and metabolic disease.

The effects of caloric restriction on adipose tissue and metabolic health are sex- and age-dependent.

Caloric restriction (CR) reduces the risk of age-related diseases in numerous species, including humans. CR's metabolic effects, including decreased adiposity and improved insulin sensitivity, are important for its broader health benefits; however, the extent and basis of sex differences in CR's health benefits are unknown. We found that 30% CR in young (3-month-old) male mice decreased fat mass and improved glucose tolerance and insulin sensitivity, whereas these effects were blunted or absent in young females. Females' resistance to fat loss was associated with decreased lipolysis, energy expenditure and fatty acid oxidation, and increased postprandial lipogenesis, compared to males. The sex differences in glucose homeostasis were not associated with differential glucose uptake but with altered hepatic ceramide content and substrate metabolism: compared to CR males, CR females had lower TCA cycle activity and higher blood ketone concentrations, a marker of hepatic acetyl-CoA content. This suggests that males use hepatic acetyl-CoA for the TCA cycle whereas in females it accumulates, stimulating gluconeogenesis and limiting hypoglycaemia during CR. In aged mice (18-months old), when females are anoestrus, CR decreased fat mass and improved glucose homeostasis similarly in both sexes. Finally, in a cohort of overweight and obese humans, CR-induced fat loss was also sex- and age-dependent: younger females (<45 years) resisted fat loss compared to younger males while in older subjects (>45 years) this sex difference was absent. Collectively, these studies identify age-dependent sex differences in the metabolic effects of CR and highlight adipose tissue, the liver and oestrogen as key determinants of CR's metabolic benefits. These findings have important implications for understanding the interplay between diet and health, and for maximising the benefits of CR in humans.

11ß-HSD1 inhibition in men mitigates prednisolone-induced adverse effects in a proof-of-concept randomised double-blind placebo-controlled trial.

Glucocorticoids prescribed to limit inflammation, have significant adverse effects. As 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) regenerates active glucocorticoid, we investigated whether 11ß-HSD1 inhibition with AZD4017 could mitigate adverse glucocorticoid effects without compromising their anti-inflammatory actions. We conducted a proof-of-concept, randomized, double-blind, placebo-controlled study at Research Unit, Churchill Hospital, Oxford, UK (NCT03111810). 32 healthy male volunteers were randomized to AZD4017 or placebo, alongside prednisolone treatment. Although the primary endpoint of the study (change in glucose disposal during a two-step hyperinsulinemic, normoglycemic clamp) wasn't met, hepatic insulin sensitivity worsened in the placebo-treated but not in the AZD4017-treated group. Protective effects of AZD4017 on markers of lipid metabolism and bone turnover were observed. Night-time blood pressure was higher in the placebo-treated but not in the AZD4017-treated group. Urinary (5aTHF+THF)/THE ratio was lower in the AZD4017-treated but remained the same in the placebo-treated group. Most anti-inflammatory actions of prednisolone persisted with AZD4017 co-treatment. Four adverse events were reported with AZD4017 and no serious adverse events. Here we show that co-administration of AZD4017 with prednisolone in men is a potential strategy to limit adverse glucocorticoid effects.

Mapping endocrine networks by stable isotope tracing.

Hormones regulate metabolic homeostasis through interlinked dynamic networks of proteins and small molecular weight metabolites, and state-of-the-art chemical technologies have been developed to decipher these complex pathways. Stable-isotope tracers have largely replaced radiotracers to measure flux in humans, building on advances in nuclear magnetic resonance spectroscopy and mass spectrometry. These technologies are now being applied to localise molecules within tissues. Radiotracers are still highly valuable both preclinically and in 3D imaging by positron emission tomography. The coming of age of vibrational spectroscopy in conjunction with stable-isotope tracing offers detailed cellular insights to map complex biological processes. Together with computational modelling, these approaches are poised to coalesce into multi-modal platforms to provide hitherto inaccessible dynamic and spatial insights into endocrine signalling.