Vascular NItric Oxide Production in Diabetics and Controls Following Acute Traffic Polllution Exposure

Abstract

Background: Acute changes in air pollution are associated with changes in clinical cardiovascular outcomes within hours to days. Diabetics are at increased risk for these cardiovascular outcomes.. Loss of Endothelial derived nitric oxide (EDNO) is directly related to endothelial dysfunction, implicated in the acute and chronic pathogenesis of cardiovascular outcomes. Reactive hyperemia, a physiologic inducer of EDNO, is reported to be modified by both diabetes and air pollution. Aims: We aimed to study the impact of a 2 hour highway traffic commute on EDNO in Type II diabetics and controls. Methods: EDNO was assessed in 20 control and 20 Type II diabetic subjects before and after a 2-hr car ride. Plasma nitrite (NO2-) concentrations were measured, before and after reactive hyperemia, reflecting vascular endothelial production of NO, the most proximal measure of EDNO in the vasculature. Results: Baseline data before the ride showed higher resting NO2- levels in diabetics (230 nM, 191.3-276.8) than controls (182.6 nM, 155.6-214.1) (p<0.06), and greater increases in plasma NO2- following reactive hyperemia in controls (15.9%, p< 0.02) than in diabetics (1.8%, p<0.8). Post-exposure, the resting NO2- levels in diabetics decreased 18.3% (p < 0.06) and controls decreased 2.9% (p< 0.08); the response to reactive hyperemia was markedly reduced in controls and remained insignificant in diabetics. Conclusions: The car ride abolished the significant increase in plasma NO2- following reactive hyperemia in controls, implying reduced EDNO production. Within diabetics and controls, resting levels of NO2- decreased following the car ride, all suggesting a less responsive endothelium. These results point to altered NO metabolism in the diabetic vasculature that is further disturbed by a car ride and associated air pollution. Thus, acute air pollution exposure impairs production of EDNO more in diabetics than controls, consistent with its effect on cardiovascular events, and the greater susceptibility to air pollution of diabetics.