Isoform heterogeneity and lipid affinity of human lymph and plasma apolipoprotein A-IV

Characterization of apoA-IV-containing lipoprotein particles isolated from human plasma and interstitial fluid

Apolipoprotein (apo) A-IV has been proposed to play a role in reverse cholesterol transport. ApoA-IV-containing lipoprotein particles (A-IVLp) were isolated from human plasma and interstitial fluid and characterized by immunoaffinity chromatography. Two major A-IVLp subpopulations, lipoprotein particles containing apoA-IV with apoA-I (LpA-I:A-IV) and lipoprotein particles containing apoA-IV without apoA-I (LpA-IV), were identified. The larger subpopulation of A-IVLp is the LpA-IV that represents 70% (protein mass) of the initial particles. Only 5.8% of apoA-IV was recovered in the retained fraction after affinity chromatography with an anti-apoA-I immunosorbent. ApoA-I, apoA-II, apoA-IV, apoB, apoC-III, apoD, apoE, apoH, lecithin: cholesterol acyltransferase (LCAT), cholesteryl ester transfer (CET) protein, proline-rich protein, and a protein of Mr 59,000 were detected in the A-IVLp. These particles contain more than 20% triglycerides (lipid mass). ApoA-IV-containing particles that were isolated from plasma are heterogeneous in size, consisting of two major populations with Stokes' diameters of 10.3 nm and 9.3 nm. Both subpopulations of A-IVLp contain LCAT and CET activities and promote cholesterol efflux from cholesterol-preloaded adipose cells. These data support the hypothesis that A-IVLp particles may be involved in reverse cholesterol transport.

Sensitivity of serum apolipoprotein A-IV levels to changes in dietary fat content

The distinctive biological properties of apolipoprotein A-IV suggest that its concentration in serum should be specifically regulated by dietary triglyceride. To test this hypothesis, serum lipids, lipoprotein cholesterol, and apolipoprotein levels were measured in 10 normolipidemic male subjects whose dietary fat intake was isocalorically modified over a range of 10%-50% of total calories. Serum apolipoprotein A-IV levels changed significantly from baseline in response to each dietary modification. Apolipoprotein A-IV levels decreased by 21% during the first week of the low-fat (10%) diet, increased to 12% over baseline during the first week of the moderate-fat (25%) diet, and increased further to 35% over baseline during the first week of the high-fat (50%) diet. Unexpectedly, during the second week of each dietary period, apolipoprotein A-IV levels demonstrated statistically significant trends back toward baseline, which were opposite in direction and proportional in magnitude to the changes during the first week. Nonetheless, serum apolipoprotein A-IV levels, but not apolipoprotein A-I or apolipoprotein B levels, were significantly and positively correlated with the percent of total daily caloric intake ingested as dietary fat. It was concluded that serum apolipoprotein A-IV levels are extremely sensitive to acute changes in dietary fat content and over the range of fat intake examined in this study are significantly correlated with the percent of total calories consumed as dietary triglyceride. Furthermore, the results also suggest that apolipoprotein A-IV may be subject to a rapidly acting autoregulatory mechanism.

Changes of apolipoprotein A-IV in the human neonate: evidence for different inductions of apolipoproteins A-IV and A-I in the postpartum period

The levels, isoforms and distribution of apolipoprotein A-IV (apo A-IV) were investigated in 127 term human umbilical cord sera. In addition, apo A-IV levels and isoforms were determined on the 3rd (n = 82) and 6th (n = 68) day following parturition and compared to apo A-I concentrations. Levels of apo A-IV were low in umbilical cord serum (5.7 +/- 1.9 mg/dl) as compared to adult serum (17.6 +/- 4.8 mg/dl). No difference was found between male and female neonates. The serum distribution of apo A-IV closely resembled that seen in the adult human. Apo A-IV concentrations dramatically increased during the first week of life reaching levels of 13.4 +/- 4.1 mg/dl on day 3 and 16.7 +/- 3.4 mg/dl on day 6 post-partum. During this time apo A-I levels did not change significantly (81.0 +/- 16.5 mg/dl in cord serum, 75.3 +/- 10.6 mg/dl and 84.2 +/- 14.5 mg/dl on day 3 and 6, respectively). Cord serum already exhibited the major serum apo A-IV isoforms seen in the adult. Isofocusing of apo A-IV also identified the known genetic polymorphism of apo A-IV. Among 127 cord sera studied we identified 109 homozygote normal patterns, apo A-IV (1-1), 16 heterozygotes, apo A-IV (1-2) and 2 individuals homozygote for the variant peptide, apo A-IV (2-2). We provide evidence that apo A-IV and apo A-I are differently induced in the human neonate during the beginning of the feeding period.(ABSTRACT TRUNCATED AT 250 WORDS)