We studied the effect of intravenous lipid infusion on lipid peroxidation as measured by breath pentane. Pentane, plasma alpha-tocopherol (alpha-tox) and plasma gamma-tocopherol (gamma-toc), selenium, and Se-dependent glutathione peroxidase (Se-GSHPx) were measured in 10 normal control subjects and in 10 home parenteral nutrition (HPN) patients before and after infusion of 100 mL Nutralipid 10% over 30 min. Before infusion, breath pentane was significantly higher and alpha-toc was significantly lower in the HPN group than in the control subjects. These two measurements were significantly negatively correlated (r = -0.54, p less than 0.05). Pentane, alpha-toc, and Se-GSHPx were significantly increased in both groups after lipid was infused but were still significantly higher in HPN patients than in control subjects. Thus, infusion of a small amount of lipid rich in linoleic acid induced a significant increase in breath pentane, reflective of increased lipid peroxidation.
Because both vitamin E and selenium protect against lipid peroxidation, we evaluated the relationship between breath pentane, evolved from the peroxidation of linoleic acid, and plasma levels of alpha-tocopherol (vitamin E), Se, and Se-dependent glutathione peroxidase (Se-GSHPx). Nine home parenteral-nutrition (HPN) patients received added Se in intravenous solutions and were compared with 10 normal control subjects. The excretion of pentane (pmol.kg-1.min-1, means +/- SEM) in control subjects (6.34 +/- 0.96) was significantly lower than in HPN patients (15.02 +/- 1.12, p less than 0.001). alpha-Tocopherol (mumol/L), Se (mumol/L), and Se-GSHPx (U) values were, respectively, 18.13 +/- 1.70, 1.70 +/- 0.05, and 5.34 +/- 0.27 in control subjects and 10.21 +/- 1.66, 1.35 +/- 0.14, and 7.01 +/- 0.31 in HPN patients. All differences were statistically significant. Significant negative correlations were observed between plasma alpha-tocopherol levels and HPN duration and between pentane output and plasma alpha-tocopherol levels (r = -0.58, p less than 0.01). In HPN patients with reduced plasma alpha-tocopherol levels associated with increased pentane output, there is, inferentially, increased lipid peroxidation despite normal plasma Se and Se-GSHPx levels.
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