The Effect of Inflammation and Infection on Lipids and Lipoproteins

Chronic inflammatory diseases, such as rheumatoid arthritis, systemic lupus erythematosus, and psoriasis and infections, such as periodontal disease and HIV, are associated with an increased risk of cardiovascular disease. Patients with these disorders also have an increase in coronary artery calcium measured by CT and carotid intima media thickness measured by ultrasound. Inflammation and infections induce a variety of alterations in lipid metabolism that may initially dampen inflammation or fight infection, but if chronic could contribute to the increased risk of atherosclerosis. The most common changes are decreases in serum HDL and increases in triglycerides. The increase in serum triglycerides is due to both an increase in hepatic VLDL production and secretion and a decrease in the clearance of triglyceride rich lipoproteins. The mechanisms by which inflammation and infection decrease HDL levels are uncertain. There is also a consistent increase in lipoprotein (a) levels due to increased apolipoprotein (a) synthesis. LDL levels are frequently decreased but the prevalence of small dense LDL is increased due to cholesterol ester transfer protein (CETP) mediated exchange of triglycerides from triglyceride rich lipoproteins to LDL followed by triglyceride hydrolysis. In addition to affecting serum lipid levels, inflammation also adversely effects lipoprotein function. LDL is more easily oxidized as the ability of HDL to prevent the oxidation of LDL is diminished. Moreover, there are a number of steps in the reverse cholesterol transport pathway that are adversely affected during inflammation. The greater the severity of the underlying inflammatory disease, the more consistently these abnormalities in lipids and lipoproteins are observed. Treatment of the underlying disease leading to a reduction in inflammation results in the return of the lipid profile towards normal. The changes in lipids and lipoproteins that occur during inflammation and infection are part of the innate immune response and therefore are likely to play an important role in protecting the host. The guidelines for the management of lipid disorders and the standard risk calculators for predicting cardiovascular disease (ACC/AHA, Framingham, etc.) underestimate the risk in patients with inflammation. It has been recommended to increase the calculated risk by approximately 50% in patients with severe inflammatory disorders. The treatment of lipid disorders in patients with inflammatory disorders is similar to patients without inflammatory disorders. Of note statins, fibrates, and fish oil have anti-inflammatory properties and have been reported to have beneficial effects on many of these inflammatory disorders.