D. Hadjidakis

The skeleton is a metabolically active organ that undergoes continuous remodeling throughout life. Bone remodeling involves the removal of mineralized bone by osteoclasts followed by the formation of bone matrix through the osteoblasts that subsequently become mineralized. The remodeling cycle consists of three consecutive phases: resorption, during which osteoclasts digest old bone; reversal, when mononuclear cells appear on the bone surface; and formation, when osteoblasts lay down new bone until the resorbed bone is completely replaced. Bone remodeling serves to adjust bone architecture to meet changing mechanical needs and it helps to repair microdamages in bone matrix preventing the accumulation of old bone. It also plays an important role in maintaining plasma calcium homeostasis. The regulation of bone remodeling is both systemic and local. The major systemic regulators include parathyroid hormone (PTH), calcitriol, and other hormones such as growth hormone, glucocorticoids, thyroid hormones, and sex hormones. Factors such as insulin-like growth factors (IGFs), prostaglandins, tumor growth factor-beta (TGF-beta), bone morphogenetic proteins (BMP), and cytokines are involved as well. As far as local regulation of bone remodeling is concerned, a large number of cytokines and growth factors that affect bone cell functions have been recently identified. Furthermore, through the RANK/receptor activator of NF-kappa B ligand (RANKL)/osteoprotegerin (OPG) system the processes of bone resorption and formation are tightly coupled allowing a wave of bone formation to follow each cycle of bone resorption, thus maintaining skeletal integrity.

OBJECTIVE: Although clinical hyperthyroidism (HR) is associated with insulin resistance, the information on insulin action in subclinical hyperthyroidism (SHR) is limited. DESIGN AND METHODS: To investigate this, we assessed the sensitivity of glucose metabolism to insulin in vivo (by an oral glucose tolerance test) and in vitro (by measuring insulin-stimulated rates of glucose transport in isolated monocytes) in 12 euthyroid subjects (EU), 16 patients with HR, and 10 patients with SHR. RESULTS: HR and SHR patients displayed higher postprandial glucose levels (area under the curve, AUC(0)(-)(300) 32,190±1067 and 31,497±716,mg/dl min respectively) versus EU (27,119±1156 mg/dl min, P<0.05). HR but not SHR patients displayed higher postprandial insulin levels (AUC(0)(-)(300) 11,020±985 and 9565±904 mU/l min respectively) compared with EU subjects (AUC(0)(-)(300) 7588±743 mU/l min, P<0.05). Homeostasis model assessment index was increased in HR and SHR patients (2.81±0.3 and 2.43±0.38 respectively) compared with EU subjects (1.27±0.16, P<0.05), while Matsuda and Belfiore indices were decreased in HR (4.21±0.41 and 0.77±0.05 respectively, P<0.001) and SHR patients (4.47±0.33 and 0.85±0.05 respectively, P<0.05 versus EU (7.76±0.87 and 1 respectively). At 100 μU/ml insulin, i) GLUT3 levels on the monocyte plasma membrane were increased in HR (468.8±7 mean fluorescence intensity (MFI)) and SHR patients (522.2±25 MFI) compared with EU subjects (407±18 MFI, P<0.01 and P<0.05 respectively), ii) glucose transport rates in monocytes (increases from baseline) were decreased in HR patients (37.8±5%) versus EU subjects (61.26±10%, P<0.05). CONCLUSIONS: Insulin-stimulated glucose transport in isolated monocytes of patients with HR was decreased compared with EU subjects. Insulin resistance was comparable in patients with both HR and SHR.

CONTEXT: Although adrenal incidentalomas (AIs) are associated with a high prevalence of cardiovascular risk (CVR) factors, it is not clear whether patients with nonfunctioning AI (NFAI) have increased CVR. OBJECTIVE: Our objective was to investigate CVR in patients with NFAI. DESIGN AND SETTING: This case-control study was performed in a tertiary general hospital. SUBJECTS: SUBJECTS included 60 normotensive euglycemic patients with AI and 32 healthy controls (C) with normal adrenal imaging. MAIN OUTCOME MEASURES: All participants underwent adrenal imaging, biochemical and hormonal evaluation, and the following investigations: 1) measurement of carotid intima-media thickness (IMT) and flow-mediated dilatation, 2) 2-hour 75-gram oral glucose tolerance test and calculation of insulin resistance indices (homeostasis model assessment, quantitative insulin sensitivity check, and Matsuda indices), 3) iv ACTH stimulation test, 4) low-dose dexamethasone suppression test, and 5) NaCl (0.9%) post-dexamethasone saline infusion test. RESULTS: Based on cutoffs obtained from controls, autonomous cortisol secretion was documented in 26 patients (cortisol-secreting AI [CSAI] group), whereas 34 exhibited adequate cortisol and aldosterone suppression (NFAI group). IMT measurements were higher and flow-mediated vasodilatation was lower in the CSAI group compared with both NFAI and C and in the NFAI group compared with C. The homeostasis model assessment index was higher and quantitative insulin sensitivity check index and Matsuda indices were lower in the CSAI and NFAI groups compared with C as well as in CSAI compared with the NFAI group. The area under the curve for cortisol after ACTH stimulation was higher in the CSAI group compared with the NFAI group and C and in the NFAI group compared with C. In the CSAI group, IMT correlated with cortisol, urinary free cortisol, and cortisol after a low-dose dexamethasone suppression test, whereas in the NFAI group, IMT correlated with area under the curve for cortisol after ACTH stimulation and urinary free cortisol. CONCLUSIONS: Patients with CSAI without hypertension, diabetes, and/or dyslipidemia exhibit adverse metabolic and CVR factors. In addition, NFAIs are apparently associated with increased insulin resistance and endothelial dysfunction that correlate with subtle but not autonomous cortisol excess.

Objective Although clinical hyperthyroidism (HR) is associated with insulin resistance, the information on insulin action in subclinical hyperthyroidism (SHR) is limited. Design and methods To investigate this, we assessed the sensitivity of glucose metabolism to insulin in vivo (by an oral glucose tolerance test) and in vitro (by measuring insulin-stimulated rates of glucose transport in isolated monocytes) in 12 euthyroid subjects (EU), 16 patients with HR, and 10 patients with SHR. Results HR and SHR patients displayed higher postprandial glucose levels (area under the curve, AUC 0 – 300 32 190±1067 and 31 497±716 mg/dl min respectively) versus EU (27 119±1156 mg/dl min, P &lt;0.05). HR but not SHR patients displayed higher postprandial insulin levels (AUC 0 – 300 11 020±985 and 9565±904 mU/l min respectively) compared with EU subjects (AUC 0 – 300 7588±743 mU/l min, P &lt;0.05). Homeostasis model assessment index was increased in HR and SHR patients (2.81±0.3 and 2.43±0.38 respectively) compared with EU subjects (1.27±0.16, P &lt;0.05), while Matsuda and Belfiore indices were decreased in HR (4.21±0.41 and 0.77±0.05 respectively, P &lt;0.001) and SHR patients (4.47±0.33 and 0.85±0.05 respectively, P &lt;0.05 versus EU (7.76±0.87 and 1 respectively). At 100 μU/ml insulin, i) GLUT3 levels on the monocyte plasma membrane were increased in HR (468.8±7 mean fluorescence intensity (MFI)) and SHR patients (522.2±25 MFI) compared with EU subjects (407±18 MFI, P &lt;0.01 and P &lt;0.05 respectively), ii) glucose transport rates in monocytes (increases from baseline) were decreased in HR patients (37.8±5%) versus EU subjects (61.26±10%, P &lt;0.05). Conclusions Insulin-stimulated glucose transport in isolated monocytes of patients with HR was decreased compared with EU subjects. Insulin resistance was comparable in patients with both HR and SHR.