Chylomicron remnant metabolism in familial dyslipidemias studied with a remnant-like emulsion breath test

We have developed a stable isotope breath test for the assessment of chylom icron remnant metabolism and report the results from the breath test in hum an subjects selected for disorders of chylomicron or remnant metabolism. In type I hyperlipemia, the phenotype is extreme hypertriglyceridemia due to a lack of lipoprotein lipase activity, which causes the failure of remnant formation, The type UI dyslipidemia phenotype is caused by the inefficient removal of chylomicron remnants from plasma, generally because of homozygos ity for apolipoprotein E2 alleles. The breath test was predicted to be abno rmal in type m hyperlipemia, whereas a priori in type I hyperlipemia defect ive remnant clearance was not anticipated. Subjects were injected with lipi d emulsions prepared with a composition similar to normal chylomicron remna nts. The emulsions contained cholesteryl ester incorporating the stable non radioactive isotope C-13 in the fatty acid moiety, End exhalation breath wa s collected at intervals after intravenous injection of the remnant-like em ulsions and analyzed for C-13 enrichment by isotope-ratio mass spectrometry . Compared with the group of normolipemic men, the fractional catabolic rat e of remnants measured by the breath test was significantly decreased (P = 0.006) in subjects with type m dyslipidemia. In the group with type I hyper lipemia, the fractional catabolic rate was not different (P = 0.233) from t he control group, Therefore, the underlying capacity for remnant catabolism j/r normal in this group of markedly hypertriglyceridemic subjects.j/r By shortcircuiting the step of lipolysis, the remnant-like emulsion breath tes t provides direct information about remnant clearance and metabolism, which should assist in investigations of postprandial lipid metabolism.-Redgrave , T G., G. F. Watts, I. J. Martins, P. H. R. Barrett, J. C. L. Mamo, S. B. Dimmitt, and A. D. Marais. Chylomicron remnant metabolism in familial dysli pidemias studied with a remnant-like emulsion breath test.