Mechanisms of Obesity-induced Male Infertility

Karen P Phillips; Nongnuj Tanphaichitr

Disclosures

Expert Rev Endocrinol Metab. 2010;5(2):229-251. 

In This Article

Adipogenesis & the Assessment of Obesity

Adipocytes are the main cellular constituents of the adipose tissue and play an important role in regulating triglyercide and free fatty acid levels. Adipocytes are derived from multipotent stem cells that differentiate into preadipocytes and, subsequently, mature adipocytes.[9] Estrogen is a positive regulator of adipogenesis, stimulating preadipocyte proliferation and growth of mature adipocytes.[10] By contrast, adipocyte differentiation and maturation is negatively regulated by androgens such that high androgen levels both drive differentiation of the multipotent stem cells toward myogenesis, thereby inhibiting adipogenesis,[11] and inhibit adipogenic differentiation of existing preadipocytes.[12] Adipose tissue has endocrine function and synthesizes chemical messengers, known as adipocytokines or adipocyte-derived hormones, in addition to the aromatization of androgens to estrogens. Basal aromatase activity decreases during adipocyte maturation with tenfold less aromatase activity in mature adipocytes compared to preadipocytes. Aromatase activity is also site dependent with higher activity in preadiopocytes in subcutaneous tissue compared with omental cells.[13]

The obese male is generally characterized as having greater than 25% body fat of total body mass with a BMI in excess of 30 kg/m2.[14] BMI is used as the chief indicator of obesity, with stratified BMI categories as follows: 18.5–24.9 kg/m2 (normal), 25 kg/m2 and above (overweight) and 30 kg/m2 and above (obese). Other more accurate methods to assess obesity include measurement of skinfold thickness,[15] hydrostatic weighing, dual-energy x-ray absorptiometry (originally designed to measure bone mineral density, this technology differentiates between absorption of x-rays in bone vs soft tissue) or whole-body adipose tissue computed tomography (CT) and MRI combined with waist:hip ratio measurements.[16]

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