Activation of brown adipose tissue in hypothyroidism

<div><p></p><p><b>Background</b> Brown adipose tissue (BAT) attracts growing interest as a potential therapeutic target for obesity and diabetes. Hyperthyroidism is well-known to increase BAT activity, but the role of hypothyroidism is controversial. We aimed to investigate the association between different thyroid hormone (TH) states and BAT activity.</p><p><b>Methods</b> FDG-PET studies were retrospectively evaluated in thyroid cancer patients after total thyroidectomy both at euthyroidism during TH replacement or at hypothyroidism after TH cessation. Serum TH levels were compared between patients with active BAT and control patients with non-active BAT matched for age, gender, and body mass index. Additionally, animal experiments with controls (<i>n</i> = 5) and hypothyroid rats (<i>n</i> = 5) were performed.</p><p><b>Results</b> Out of 124 patients, 6 patients with active BAT were identified. These patients showed significantly higher thyroid-stimulating hormone (TSH) levels than matched controls (<i>P</i> < 0.05). In animal experiments, all hypothyroid animals showed BAT activation at room temperature (24 °C), whereas controls did not (<i>P</i> < 0.001). Increased BAT activity was also confirmed by increased expression of UCP-1 and D2.</p><p><b>Conclusions</b> Increased BAT metabolism appears to be related with hypothyroidism, which might be the result of a feedback mechanism to maintain body temperature in a state of reduced basal thermogenesis. Future research needs to explore the underlying mechanistic and biological implications.</p><p></p><p>Key Messages</p><p></p><p>Increased brown adipose tissue (BAT) metabolism appears to be related with hypothyroidism, which might be the result of a feedback mechanism to maintain body core temperature in a state of reduced basal thermogenesis.</p><p></p><p></p><p></p></div

Illustration of left and right ventricular volumetry and determination of wall thickness and systolic function.

<p>Illustration of left and right ventricular volumetry and determination of wall thickness and systolic function.</p

Left and right ventricular enddiastolic volume and enddiastolic volume index normalized to body weight 1 week and 8 weeks after sham surgery (mean ± SD).

<p>* indicates significant differences (p<0.05) between the respective groups.</p

Body weight at baseline, 1 week and 8 weeks after sham surgery in both groups (mean ± SD).

<p>* indicates significant differences (p<0.05) between the respective groups.</p

Time course of various metabolic blood parameters (glucose, urea, triglycerides, and leptin) after sham surgery.

<p>Time course of various metabolic blood parameters (glucose, urea, triglycerides, and leptin) after sham surgery.</p

Results overview, right ventricle.

<p>All results are given as mean±SD. RV: right ventricle, HR: heart rate, RVM: right ventricular myocardial mass, EDWT: enddiastolic wall thickness, ESWT: endsystolic wall thickness, EDV: enddiastolic volume, ESV: endsystolic volume, SWT: systolic wall thickening, SV: stroke volume, CO: cardiac output, EF: ejection fraction, and (C)I: (cardiac) index (per gram body weight).</p>*<p>indicates significant differences (p<0.05) between the respective groups.</p

Representative full cycle of a cardiac short-axis cine-MRI with 20 frames.

<p>Representative full cycle of a cardiac short-axis cine-MRI with 20 frames.</p

Sham surgery situs and survey arrangement.

<p>MRI was performed 1 and 8 weeks after sham surgery.</p

Left and right ventricular myocardial mass and myocardial mass index 1 week and 8 weeks after sham surgery (mean ± SD).

<p>* indicates significant differences (p<0.05) between the respective groups.</p

Left and right ventricular cardiac output and cardiac index normalized to body weight 1 week and 8 weeks after sham surgery (mean ± SD).

<p>* indicates significant differences (p<0.05) between the respective groups.</p