In view of the fact that insulin resistance is associated with atherogenesis and that troglitazone, an insulin sensitizer, has anti-inflammatory effects, which may be potentially antiatherogenic in the long term, we have now investigated whether insulin has potential anti-inflammatory effects. We infused 2.0 to 2.5 IU/h in 5% dextrose (100 mL/h) iv into 10 obese subjects for 4 h followed by 5% dextrose alone for 2 h. The rate of insulin infusion was varied to maintain glucose concentrations as close to the baseline as possible. Blood samples were obtained before and at 2, 4, and 6 h. Subjects were also infused with 5% dextrose without insulin and with saline on separate occasions. Intranuclear nuclear factor κB (NFκB) in mononuclear cells fell at 2 and further at 4 h, reverting toward the baseline at 6 h (P < 0.05). IκB increased significantly at 2 h, increasing further at 4 h and remaining elevated at 6 h (P < 0.001). Reactive oxygen species (ROS) generation by mononuclear cells fell significantly at 2 h and fell further at 4 h; it partially reverted to baseline at 6 h (P < 0.005). p47^phox subunit, the key protein of nicotinamide adenine dinucleotide phosphate oxidase also fell at 2 h and 4 h, reverting toward the baseline at 6 h (P < 0.05). In addition, soluble intercellular adhesion molecule-1 (sICAM-1), monocyte chemoattractant protein-1 (MCP-1), and plasminogen activator inhibitor-1 (PAI-1) fell significantly following insulin infusion. Glucose or saline infusions without insulin caused no alteration in NFκB, IκB, ROS generation, p47^phox subunit, sICAM-1, MCP-1, or PAI-1.

We conclude that insulin has a potent acute anti-inflammatory effect including a reduction in intranuclear NFκB, an increase in IκB, and decreases in ROS generation, p47^phox subunit, plasma soluble intercellular adhesion molecule-1 (sICAM-1), monocyte chemoattractant protein-1 (MCP-1), and plasminogen activator inhibitor-1 (PAI-1. This acute anti-inflammatory effect, if demonstrated in the long term, may have implications for atherosclerosis and its complications.