Human Brown Adipose Tissue

Abstract

The adipose organ of adult humans contains brown adipocytes. This datum was known since many years, but received a worldwide interest when it was demonstrated by a radiologic technique (positron emission tomography, PET). This technique allowed detecting a metabolically active tissue, able to incorporate marked glucose in different amounts under different physiologic environmental conditions, proved to have the histology, electron microscopy, and UCP1 immunoreactivity characteristic of murine BAT. The major site location for BAT in adult humans was described in the area of the adipose organ coincident with what we described in Plate 2.32 as the transition area between subcutaneous and visceral fat at the root of the neck. In our published and unpublished case series of about 50 adults, we were able to detect UCP1-immunoreactive brown adipocytes at the root of the neck (peri-subclavian artery or supraclavicular area) in all patients under 30, in about 25% of patients under 50, and rarely in patients over 60 years old. BAT-positive patients were mostly lean even if we detected BAT in two overweight patients, but never in obese patients. PET studies are in line with our immunohistochemistry data.