Immunometabolic Signatures of Circulating Monocytes in Humans With Obesity and Insulin Resistance

Obesity is associated with chronic inflammation and metabolic complications, including insulin resistance (IR). Immune cells drive inflammation through the rewiring of intracellular metabolism. However, the impact of obesity-related IR on the metabolism and functionality of circulating immune cells, like monocytes, remains poorly understood. To increase insight into the interindividual variation of immunometabolic signatures among individuals and their role in the development of IR, we assessed systemic and tissue-specific IR and circulating immune markers, and we characterized metabolic signatures and cytokine secretion of circulating monocytes from 194 individuals with a BMI ≥25 kg/m2. Monocyte metabolic signatures were defined using extracellular acidification rates (ECARs) to estimate glycolysis and oxygen consumption rates (OCRs) for oxidative metabolism. Although monocyte metabolic signatures and function based on cytokine secretion varied greatly among study participants, they were strongly associated with each other. The ECAR-to-OCR ratio, representing the balance between glycolysis and oxidative metabolism, was negatively associated with fasting insulin levels, systemic IR, and liver-specific IR. These results indicate that monocytes from individuals with IR were relatively more dependent on oxidative metabolism, whereas monocytes from more insulin-sensitive individuals were more dependent on glycolysis. Additionally, circulating CXCL11 was negatively associated with the degree of systemic IR and positively with the ECAR-to-OCR ratio in monocytes, suggesting that individuals with high IR and a monocyte metabolic dependence on oxidative metabolism also have lower levels of circulating CXCL11. Our findings suggest that monocyte metabolism is related to obesity-associated IR progression and deepen insights into the interplay between innate immune cell metabolism and IR development in humans.