Macrophage infiltration into omental versus subcutaneous fat across different populations: Effect of regional adiposity and the comorbidities of obesity

Context: Macrophage infiltration into adipose tissue has been demonstrated to accompany obesity, with a potential preferential infiltration into intraabdominal vs. sc fat. Objective: Our objective was to determine whether this occurs across different populations with a range of body mass indexes and to assess the relationship with regional adiposity and comorbidity of obesity. Setting and Patients: In two independent cohorts, we used paired omental (OM) and sc fat biopsies from lean controls or predominantly sc or intraabdominally obese persons with minimal comorbidity (n = 60, cohort 1), or from severely obese women with a significant rate of comorbidity (n = 29, cohort 2). Results: Elevated macrophage infiltration into OM vs. sc fat was observable in lean subjects and exaggerated by obesity, particularly if predominantly intraabdominal. This was paralleled by increased monocyte chemoattractant protein-1 (MCP1) and colony-stimulating factor-1 (CSF1) mRNA levels. Level of CSF1 and MCP1 mRNA correlated with the number of OM macrophages (r = 0.521, P < 0.0001 and r = 0.258, P < 0.051, respectively). In severely obese women (mean body mass index = 43.0 ± 1.1 kg/m²), higher protein expression of both MCP1 and CSF1 was detected in OMvs. sc fat. Number of OM macrophages, but not of sc macrophages, correlated with waist circumference (r = 0.636, P = 0.001 vs. r = 0.170, P = 0.427) and with the number of metabolic syndrome parameters (r = 0.385, P = 0.065 vs. r = -0.158, P = 0.472, respectively). Preferential macrophage infiltration into OM fat was mainly observed in a subgroup in whom obesity was associated with impaired glucose homeostasis. Conclusions: Preferential macrophage infiltration into OM fat is a general phenomenon exaggerated by central obesity, potentially linking central adiposity with increased risk of diabetes and coronary heart disease.