Growth hormone (GH) plays a pivotal role in the regulation of body composition including ectopic lipid deposition in insulin sensitive organs like liver and skeletal muscle. Recent evidence indicates that the GH-IGF1 axis affects body composition via regulating mitochondrial oxidation capacity. Thus, excessive GH secretion by a pituitary adenoma (Acromegaly) might be accompanied by increased mitochondrial activity leading to inappropriately low intracellular lipid depots, especially in metabolically active tissue like liver and skeletal muscle. This study aims to assess metabolic activity and intracellular lipid content in skeletal muscle and liver in patients suffering from acromegaly compared to controls by 31P/1H Magnetic resonance spectroscopy before and in follow up examinations 3, 6 and 12 months after initiation of GH lowering treatments including surgery, somatostatinanalogs or pegvisomant, as well as oral glucose tolerance tests at each examination to assess treatment responses and calculate validated parameters for insulin sensitivity and resistance.
Background: Growth hormone (GH) plays a pivotal role in the regulation of body composition including ectopic lipid deposition in insulin sensitive organs like liver and skeletal muscle. Direct inhibition of growth hormone action by a receptor antagonist has been shown to induce hepatic steatosis and growth hormone replacement decreases liver fat content in obese humans. Of note, recent evidence indicates that the GH-IGF1 axis affects body composition via regulating mitochondrial oxidation capacity. Hypothesis: Direct and/or indirect effects of GH on mitochondrial function might mediate the changes in body composition and lipid deposition. Thus, excessive GH secretion by a pituitary adenoma (Acromegaly) might be accompanied by increased mitochondrial activity leading to inappropriately low intracellular lipid depots, especially in metabolically active tissue like liver and skeletal muscle. Aim: Assessment of metabolic activity and intracellular lipid content in skeletal muscle and liver in patients suffering from acromegaly compared to controls. Methods: Non-interventional study: * 31P/1H Magnetic resonance spectroscopy before and in follow up examinations 3, 6 and 12 months after initiation of GH lowering treatments including surgery, somatostatinanalogs or pegvisomant. * oral glucose tolerance tests at each examination to assess treatment responses and calculate validated parameters for insulin sensitivity and resistance.
Study Type
OBSERVATIONAL
Enrollment
24
The 31P-MRS examinations will be performed in a 7 T MR system (Siemens Healthcare, Erlangen, Germany) using a double-tuned (31P/1H) surface coil (Rapid Biomedical Ltd, Rimpar, Germany), with a diameter of 10 cm. Participants will be investigated lying in lateral position with the right lobe of the liver positioned over the coil.
In patients without overt diabetes, glucose tolerance will be assessed by an oral glucose tolerance test, routinely performed at the outpatients clinic. The test will be performed in the morning after an overnight fast of at least 8 hours. Blood will be drawn via a catheter placed in an antecubital vein of one arm. Blood samples for the assessment of glucose, insulin, C-peptide, free fatty acids and growth hormone will be drawn at baseline as well as 30, 60, 90 and 120 minutes after ingestion of 75g glucose in a solution. Concentrations of glucose, insulin and C-peptide will be used to derive parameters of insulin secretion and insulin sensitivity by mathematical modelling.
In acromegalic patients thyroid morphology will be assessed at the outpatient clinic of the Division of Endocrinology and Metabolism, using standard ultrasound technique. Measurements will be performed by a well- experienced physician at baseline and at each follow up examination in an out-patient care setting.
Medical University Of Vienna, Department of Internal Medicine III
Vienna, State of Vienna, Austria
RECRUITINGChanges in hepatic energy metabolism
The 31P-MRS examinations will be performed in a 7 T MR system (Siemens Healthcare, Erlangen, Germany) using a double-tuned (31P/1H) surface coil (Rapid Biomedical Ltd, Rimpar, Germany), with a diameter of 10 cm.
Time frame: before & 3,6,9, and 12 months after initiation of therapy
Changes in hepatic lipid content
Hepatic lipid content will be assessed using localized single voxel 1H MRS as published by our study group. STEAM sequence (VOI= 3×3×3 cm3; TE= 30, 50, 70, 120 ms; NA= 4 for each TE) data acquisition will be performed during repetitive single breath holds. Hepatocellular lipid (HCL) content will be calculated from ration of summed area of methylene and methyl resonance to that of water following the individual spin-spin relaxation correction as per cent of total tissue MRS signal (water + methylene + methyl).
Time frame: before, as well as 3,6,9 &12 months after initiation of therapy
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