Background: Obesity is associated with macrophage infiltration in adipose tissue that induces insulin resistance and contributes to the development of metabolic syndrome (MS). The aim of this study was to investigate whether circulating monocyte subsets (macrophage precursors) differ among obese subjects with MS [metabolically unhealthy obese (MUO)], obese subjects without MS [metabolically healthy obese (MHO)], and metabolically healthy lean (MHL) individuals. Methods: Fifty-eight obese (33 MUO, 25 MHO) and 25 MHL individuals participated in the study. Absolute blood counts of classical (Mon1A), intermediate (Mon2A), and nonclassical (Mon3A) monocyte subsets were measured by flow cytometry. Results: Increased proinflammatory monocyte counts (Mon2A, Mon3A) were observed in obese compared with MHL individuals (P = 0.001 and P = 0.017 respectively). Mon2A count in MHO was lower compared with that in MUO subjects (P = 0.036) but higher compared with MHL controls (P = 0.032). Mon2A was positively associated with serum triglyceride levels (r = 0.328, P = 0.023) and mean blood pressure (BP) (r = 0.457, P = 0.001) in obese subjects. Among MS components, only the presence of elevated BP (≥130/85 mmHg) was independently associated with increased Mon2A in obese subjects (P < 0.001). Conclusions: Absolute counts of proinflammatory monocytes were lower in metabolically healthy compared with MUO individuals, but higher compared with healthy lean controls. The presence of low-grade inflammation suggests that "metabolically healthy" obesity is not a benign condition. ClinicalTrials.gov identifier: NCT03241394.
Keywords: inflammation; metabolic syndrome; metabolically healthy obese; metabolically unhealthy obese; obesity.