Publications by authors named "Mark Nixon"

Background: Obesity, a major risk factor for cardiovascular disease (CVD), is associated with hypertension and vascular dysfunction. Perivascular adipose tissue (PVAT), a metabolically active tissue surrounding blood vessels, plays a key role in regulating vascular tone. In obesity, PVAT becomes dysregulated which may contribute to vascular dysfunction; how sex impacts the remodelling of PVAT and thus the altered vascular contractility during obesity is unclear.

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Corticosteroid binding globulin (CBG; SERPINA6) binds >85% of circulating glucocorticoids but its influence on their metabolic actions is unproven. Targeted proteolytic cleavage of CBG by neutrophil elastase (NE; ELANE) significantly reduces CBG binding affinity, potentially increasing 'free' glucocorticoid levels at sites of inflammation. NE is inhibited by alpha-1-antitrypsin (AAT; SERPINA1).

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Objective: 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 (ie, 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.

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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.

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Article Synopsis
  • The study examines the effects of continuing burosumab treatment on adults with X-linked hypophosphataemia after a 96-week phase 3 study, focusing on lab tests, patient-reported outcomes, and walking ability.
  • Results showed sustained improvements in serum phosphate levels, vitamin D levels, and overall physical health during the 48-week extension.
  • An analysis indicated that stopping burosumab led to a loss of benefits, highlighting that ongoing treatment is essential for maintaining clinical improvements.
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Aims: High salt intake is common and contributes to poor cardiovascular health. Urinary sodium excretion correlates directly with glucocorticoid excretion in humans and experimental animals. We hypothesized that high salt intake activates the hypothalamic-pituitary-adrenal axis activation and leads to sustained glucocorticoid excess.

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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.

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Encoded by SerpinA6, plasma corticosteroid-binding globulin (CBG) transports glucocorticoids and regulates their access to cells. We determined how CBG influences plasma corticosterone and adrenal development in rats during the pubertal to adult transition using CRISPR/cas9 to disrupt SerpinA6 gene expression. In the absence of CBG, total plasma corticosterone levels were ∼80% lower in adult rats of both sexes, with a greater absolute reduction in females than in males.

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Background: Cortisol 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.

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Article Synopsis
  • The study aimed to evaluate the effectiveness of burosumab on patient-reported outcomes (PROs) and walking ability in adults with X-linked hypophosphataemia (XLH) over 96 weeks.
  • Adults with XLH were randomly assigned to receive either burosumab or a placebo; improvements in pain, fatigue, and physical function were measured at 24, 48, and 96 weeks.
  • Results showed significant and meaningful improvements in PROs and walking distance for those treated with burosumab compared to the placebo group, indicating that the treatment effectively reduced the disease burden in patients with XLH.
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Glucocorticoids are steroid hormones with key roles in the regulation of many physiological systems including energy homeostasis and immunity. However, chronic glucocorticoid excess, highlighted in Cushing's syndrome, is established as being associated with increased cardiovascular disease (CVD) risk. Atherosclerosis is the major cause of CVD, leading to complications including coronary artery disease, myocardial infarction and heart failure.

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Background: Rickets is a primary manifestation of pediatric X-linked hypophosphatemia (XLH) - a rare progressive hereditary phosphate-wasting disease. Severity is quantified from radiographs using the Rickets Severity Scale (RSS). The Radiographic Global Impression of Change (RGI-C) is a complementary assessment in which a change score is assigned based on differences in the appearance of rickets on pairs of radiographs compared side by side.

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Objective: Carbonyl reductase 1 (Cbr1), a recently discovered contributor to tissue glucocorticoid metabolism converting corticosterone to 20β-dihydrocorticosterone (20β-DHB), is upregulated in adipose tissue of obese humans and mice and may contribute to cardiometabolic complications of obesity. This study tested the hypothesis that Cbr1-mediated glucocorticoid metabolism influences glucocorticoid and mineralocorticoid receptor activation in adipose tissue and impacts glucose homeostasis in lean and obese states.

Methods: The actions of 20β-DHB on corticosteroid receptors in adipose tissue were investigated first using a combination of in silico, in vitro, and transcriptomic techniques and then in vivo administration in combination with receptor antagonists.

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Article Synopsis
  • 11β-Hydroxysteroid dehydrogenase 1 (11βHSD1) plays a crucial role in converting inactive cortisone into active cortisol and this enzyme's balance is influenced by insulin and obesity.
  • A study involving lean and obese men found that while the overall production of cortisol and cortisone was similar between groups, insulin significantly affects the activity of 11βHSD1 differently in adipose tissue and skeletal muscle.
  • Specifically, insulin increased cortisol regeneration in adipose tissue of obese individuals, while reducing activity in lean men’s skeletal muscle, indicating that metabolism may vary depending on tissue type and body weight.
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Introduction: Asthma is associated with significant economic burden. Inhaled corticosteroid and long-acting beta-agonist (ICS/LABA) combination therapies are considered mainstays of treatment. We describe real-world use of ICS/LABAs by comparing treatment persistence and adherence among patients with asthma in the United Kingdom initiating fluticasone furoate/vilanterol (FF/VI) versus budesonide/formoterol (BUD/FM) or beclometasone dipropionate/formoterol (BDP/FM).

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Article Synopsis
  • The omentum is a fat-rich tissue that plays a crucial role in immune defense by capturing contaminants in the abdominal cavity during conditions like peritonitis.
  • Single-cell RNA sequencing uncovered that the surface of fat-associated lymphoid clusters (FALCs) is lined with specific cells called CXCL1 mesothelial cells, which are vital for recruiting neutrophils.
  • Blocking CXCL1 or inhibiting certain enzymes significantly reduced neutrophil activity and contaminant capture, highlighting the specialized role of these cells in immune responses to infection.
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Introduction: Many patients with type 2 diabetes mellitus (DM) fail to achieve glycaemic control despite recommended treatment strategies to reduce glycated haemoglobin (HbA1c). This real-world retrospective cohort study compared HbA1c change and treatment patterns between those intensifying and not intensifying therapy with oral antidiabetic drugs (OADs).

Materials And Methods: Patients suboptimally controlled on OADs (>58 mmol/mol [>7.

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Rationale: The activity of the glucocorticoid activating enzyme 11β-hydroxysteroid dehydrogenase type-1 (11βHSD1) is altered in diseases such as obesity, inflammation and psychiatric disorders. In rodents 11βHSD1 converts inert 11-dehydrocorticosterone (11-DHC) into the active form, corticosterone (CORT). A sensitive, specific liquid chromatography/tandem mass spectrometry method was sought to simultaneously quantify total 11-DHC and total and free CORT in murine plasma for simple assessment of 11βHSD1 activity in murine models.

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Introduction: This retrospective, observational cohort study evaluated the effect of therapy intensification on change in glycated hemoglobin (HbA1c) at 6 and 12 months post intensification in patients with type 2 diabetes (T2D) suboptimally controlled on basal insulin (BI) (i.e., HbA1c ≥ 7.

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Inhibition of 5α-reductases impairs androgen and glucocorticoid metabolism and induces insulin resistance in humans and rodents. The contribution of hepatic glucocorticoids to these adverse metabolic changes was assessed using a liver-selective glucocorticoid receptor (GR) antagonist, A-348441. Mice lacking 5α-reductase 1 (5αR1-KO) and their littermate controls were studied during consumption of a high-fat diet, with or without A-348441(120 mg/kg/d).

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Antenatal stress increases the prevalence of diseases in later life, which shows a strong sex-specific effect. However, the underlying mechanisms remain unknown. Maternal glucocorticoids can be elevated by stress and are potential candidates to mediate the effects of stress on the offspring sex-specifically.

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Glucocorticoid signaling is context-dependent, and in certain scenarios glucocorticoid receptors (GR) are able to engage with other members of the nuclear receptor subfamily. Glucocorticoid signaling can exert sexually dimorphic effects, suggesting a possible interaction with androgen sex hormones. We therefore set out to determine the crosstalk between glucocorticoids and androgens in metabolic tissues including white adipose tissue, liver and brown adipose tissue.

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