Lipid and apolipoprotein concentrations in prenodal leg lymph of fasted humans: associations with plasma concentrations in normal subjects, lipoprotein lipase deficiency, and LCAT deficiency

The extent to which lipid and apolipoprotein (apo) concentrations in tissue fluids are determined by those in plasma in normal humans is not known, as all studies to date have been performed on small numbers of subjects, ofte n with dyslipidemia or lymphedema. Therefore, we quantified lipids, apolipo proteins, high density lipoprotein (HDL) lipids, and non-HDL lipids an pren odal leg lymph from 37 fasted ambulant healthy men. Lymph contained almost no triglycerides, but had higher concentrations of free glycerol than plasm a. Unesterified cholesterol (UC), cholesteryl ester (CE), phosphatidylcholi ne (PC), and sphingomyelin (SPM) concentrations in whole lymph were not sig nificantly correlated with those hi plasma. HDL lipids, but not non-HDL lip ids, were directly related to those in plasma. Lymph HDLs were enriched in UC. However, as the HDL cholesterol/non-HDL cholesterol ratio in lymph exc eeded that in plasma, whole lymph nevertheless had a lower UC/CE ratio than plasma. Lymph also had a significantly higher SPM/PC ratio. The lymph/plas ma (L/P) ratios of apolipoproteins were as follows: A-IV > A-I and A-II > C -III and E > B. Comparison with the L/P ratios of seven nonlipoprotein prot eins suggested that apoA-IV was predominantly lipid free. Concentrations of apolipoproteins A-II, A-IV, GIII, and E in lymph, but not of apolipoprotei ns A-I or B, were positively correlated with those in plasma. The L/P ratio s of apolipoproteins B, C-III, and E in two subjects with lipoprotein lipas e (LPL) deficiency, and of apolipoproteins A-I and A-N in a subject with le cithin:cholesterol acyltransferase (LCAT) deficiency, were low relative to those in normal subjects.jlr Thus, the concentrations of lipids, apolipopro teins, and lipoproteins in human tissue fluid are determined only in part b y their concentrations in plasma. Other factors, including the actions of L PL and LCAT are at least as important.