Circulating Tumor Necrosis Factor-α Levels and Lipid Abnormalities in Patients with Cystic Fibrosis

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Abstract
Hyperlipidemia is prominent among the disturbances in intermediary metabolism that occur subsequent to infections by microorganisms. The response to such infections is known to involve several cell types and is mediated by cytokines. We hypothesized that metabolic lipid disturbances seen during infection in cystic fibrosis (CF) patients may partly be the result of excessive tumor necrosis factor-α (TNF-α), a proinflammatory cytokine known to cause a large spectrum of pathophysiologic alterations, including impaired lipid metabolism. Therefore, we determined the circulating concentration of TNF-α and analyzed its relationship to lipid and lipoprotein levels, as well as lipoprotein lipase activity, in 31 CF patients. Plasma TNF-α values were significantly (p < 0.01) elevated in patients with CF compared with controls. The CF subjects were found to have decreased plasma cholesterol (25%), LDL cholesterol (35%), and HDL cholesterol (19%) concentrations, whereas plasma triglycerides were significantly increased (p < 0.001). The apo A-I level was reduced (p < 0.005), whereas apo B levels were normal. Low levels of the major essential fatty acids were found in the plasma of the CF patients, and the triene/tetraene ratio confirmed their essential fatty acid deficiency. Postheparin lipolytic activity was lower in CF patients than in controls, and the decreased activity was accounted for primarily by a decline in hepatic lipase. A significant positive correlation (p < 0.001, r = 0.70) was found between TNF-α and plasma triglyceride levels. However, no association was noted between TNF-α and essential fatty acid, cholesterol, or lipoprotein cholesterol levels, or with lipoprotein lipase activity. These studies suggest that TNF-α contributes to the hypertriglyceridemia in CF patients primarily by stimulating hepatic lipogenesis, rather than inhibiting triglyceride clearance.

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