Abstract
Osteocalcin (OSCA) seems to act as a negative regulator of energy metabolism and insulin sensitivity. Evidence from male rodents suggests that OSCA may also regulate testosterone (T) synthesis. Using a cross-sectional design, we evaluated OSCA, 25(OH) vitamin D, T, 17β-estradiol (E2), homeostasis model assessment of insulin resistance (HOMA-IR), and body composition in 86 obese (mean BMI = 34) male subjects (18–69 yr old). Independently from BMI, an inverse relationship between trunk fat percentage and plasma T (r 2 = −0.26, P < 0.01) and between HOMA-IR and OSCA levels (r 2 = −0.22, P < 0.005) was found. OSCA levels, as well as vitamin D, decreased significantly for higher BMI with significant differences above 35 (P < 0.01). A direct correlation between T and bone mineral density at lumbar (BMDL) and neck (BMDH) (P < 0.001, r 2 = −0.20; P < 0.001, r 2 = −0.24) was found, independently from age. An inverse correlation between E2 levels, BMDL, and BMDH (P < 0.001, r 2 = −0.20; P < 0.001, r 2 = −0.19) was observed. These data provide new evidences that a relationship between trunk fat mass, insulin sensitivity, OSCA and T synthesis occurs. This new relationship with skeletal health has relevant implications for the aging male, suggesting OSCA as a novel marker of metabolic and gonadal health status.
Highlights
Emerging data suggest that bone mass, energy metabolism, and reproduction may be coordinately regulated
Using a cross-sectional design, we evaluated OSCA, 25(OH) vitamin D, T, 17β-estradiol (E2), homeostasis model assessment of insulin resistance (HOMA-IR), and body composition in 86 obese male subjects (18–69 yr old)
Increased HOMA index (P < 0.0001), plasma fibrinogen, and C reactive protein (P < 0.0001) but lower levels of vitamin D (P < 0.0001) were found (Table 1). Both trunk fat and HOMA increased for higher Body mass index (BMI) (P < 0.0001, resp.); regression analysis demonstrated that trunk fat was found to be the independent variable from BMI (Table 2)
Summary
Emerging data suggest that bone mass, energy metabolism, and reproduction may be coordinately regulated. It is accepted that bone is an endocrine organ favouring wholebody glucose homeostasis and energy expenditure These functions of bone are, at least in part, mediated by an osteoblast-specific secreted molecule, osteocalcin (OSCA), that, when uncarboxylated (ucOSCA), acts as a hormone favouring β cell proliferation, insulin secretion and sensitivity, and energy expenditure. OSCAdeficient mice show a decrease in testicular, epididymal, and seminal vesicles weights and sperm count, and Leydig cell maturation appears to be halted in absence of OSCA. Those results, along with others previously published, support the hypothesis that regulations of bone remodelling, energy metabolism, and reproduction are linked [2, 3]
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