The mediating role of vascular inflammation in traffic-related air pollution associated changes in insulin resistance in healthy adults

Aim: The precise pathophysiologic pathway linking traffic-related air pollution (TRAP) to diabetes mellitus is not well elucidated. We aimed to investigate whether activation of vascular inflammation can be a mechanistic linkage between ambient TRAP and insulin resistance. Methods: Study outcomes were determined by assessing a series of circulating biomarkers indicative of insulin resistance and vascular inflammation among 73 healthy adults who underwent repeated clinical visits in Beijing, China, 2014–2016. Concomitantly, concentrations of ambient TRAP indices, including particulate matter in diameter <2.5 μm (PM_2.5), particles in size fractions of 5–560 nm, black carbon, carbon monoxide, nitrogen dioxide, and oxides of nitrogen, were continuously monitored. Results: Participants experienced extremely high levels of TRAP exposures, with mean (standard deviation) PM_2.5 concentrations of 91.8 (48.3) μg/m³, throughout the study. We found that interquartile range increases in exposure to moving average concentrations of various TRAP indices at prior up to 7 days were associated with significant elevations of 8.9–49.6% in insulin levels. Higher pollutant levels were also related to worsening metrics of insulin resistance (soluble insulin receptor ectodomain, adipokines, and homeostasis model assessment of insulin resistance) and heightened vascular inflammatory responses, particularly disruptions of the receptor activator of nuclear factor κB ligand/osteoprotegerin system balance and elevations of monocyte/macrophage and T cell activation markers. Mediation analyses showed that activation of vascular inflammation could explain up to 66% of the alterations in metrics of insulin resistance attributable to air pollution. Conclusion: Our results suggest that ambient traffic pollution exposure was capable of promoting insulin resistance possibly via generating vascular inflammation.