Presence of brown adipocytes in retroperitoneal fat from patients with benign adrenal tumors: relationship with outdoor temperature.

Context: Brown adipose tissue (BAT) is a metabolically highly active organ with increased thermogenic activity in rodents exposed to cold temperature. Recently its presence in the cervical adipose tissue of human adults and its association with a favorable metabolic phenotype have been reported.
Objective: The objective of the study was to determine the prevalence of retroperitoneal BAT in human adults.
Design: This was an observational cohort study.
Setting: The study was conducted at a tertiary referral hospital.
Patients: Fifty-seven patients who underwent surgery for benign adrenal tumors were included in this study.
Main Outcome Measures: Prevalence of retroperitoneal BAT adjacent to the removed adrenal tumor as determined by uncoupling protein 1 (UCP1) protein and mRNA expression was measured.
Results: Using protein and mRNA expression analysis, we detected UCP1 protein in 26 of 57 patients (45.6%) as well as high mRNA expression of genes characteristic for brown adipocytes, independent of the adrenal tumor type. The presence of brown adipocytes within the retroperitoneal fat was associated with a significantly lower outdoor temperature during the month prior to surgery. Importantly, UCP1 expression on both mRNA and protein level was inversely correlated to outdoor temperature, whereas body mass index, sex, age, and diabetes status were not.
Conclusions: These findings suggest that human retroperitoneal adipose tissue can acquire a BAT phenotype, thereby adapting to environmental challenges. These adaptive processes might provide a valuable therapeutic target in the treatment of obesity and insulin resistance.