Separation of the apoprotein components of human serum high density lipoprotein: chromatofocusing, a new simple technique

Plasma lipoprotein-X quantification on filipin-stained gels: monitoring recombinant LCAT treatment ex vivo

Familial LCAT deficiency (FLD) patients accumulate lipoprotein-X (LP-X), an abnormal nephrotoxic lipoprotein enriched in free cholesterol (FC). The low neutral lipid content of LP-X limits the ability to detect it after separation by lipoprotein electrophoresis and staining with Sudan Black or other neutral lipid stains. A sensitive and accurate method for quantitating LP-X would be useful to examine the relationship between plasma LP-X and renal disease progression in FLD patients and could also serve as a biomarker for monitoring recombinant human LCAT (rhLCAT) therapy. Plasma lipoproteins were separated by agarose gel electrophoresis and cathodal migrating bands corresponding to LP-X were quantified after staining with filipin, which fluoresces with FC, but not with neutral lipids. rhLCAT was incubated with FLD plasma and lipoproteins and LP-X changes were analyzed by agarose gel electrophoresis. Filipin detects synthetic LP-X quantitatively (linearity 20-200 mg/dl FC; coefficient of variation <20%) and sensitively (lower limit of quantitation <1 mg/ml FC), enabling LP-X detection in FLD, cholestatic, and even fish-eye disease patients. rhLCAT incubation with FLD plasma ex vivo reduced LP-X dose dependently, generated HDL, and decreased lipoprotein FC content. Filipin staining after agarose gel electrophoresis sensitively detects LP-X in human plasma and accurately quantifies LP-X reduction after rhLCAT incubation ex vivo.

Molecular cloning and expression of lipid transfer inhibitor protein reveals its identity with apolipoprotein F

Published studies demonstrate that lipid transfer inhibitor protein (LTIP) is an important regulator of cholesteryl ester transfer protein (CETP) activity. Although LTIP inhibits CETP activity among different lipoprotein classes, it preferentially suppresses transfer events involving low density lipoprotein (LDL), whereas transfers involving high density lipoprotein as donor are less affected. In this study, we report the purification of LTIP and the expression of its cDNA in cultured cells. Purification of LTIP, in contrast to other published protocols, took advantage of the tight association of this protein with LDL. Ultracentrifugally isolated LDL was further purified on anti-apoE and apoA-I affinity columns. Affinity purified LDL was delipidated by tetramethylurea, and the tetramethylurea-soluble proteins were separated by SDS-polyacrylamide gel electrophoresis. The protein migrating at a molecular mass of approximately 33 kDa was excised from the gel and its N-terminal amino acid sequence determined. The 14-amino acid sequence obtained showed complete homology with the sequence deduced for apolipoprotein F (apoF) cDNA isolated from Hep G2 cells. On Western blots, peptide-specific antibodies raised against synthetic fragments of apoF reacted with the same 33-kDa protein in LTIP-containing fractions purified from LDL and from lipoprotein-deficient plasma. In contrast to that previously reported, apoF was shown to be associated almost exclusively with LDL, identical to the distribution of LTIP activity. The cDNA for apoF was cloned from a human liver cDNA library, ligated into a mammalian expression vector, and transiently transfected into COS-7 cells. Conditioned media containing secreted apoF demonstrated CETP inhibitor activity, whereas cells transfected with vector alone did not. This CETP inhibitor activity was efficiently removed from the media by nickel-Sepharose, consistent with the 6-His tag incorporated into recombinant apoF. By Western blot, the 6-His-tagged protein had a molecular weight slightly larger than native apoF. The CETP inhibitor activity of recombinant apoF possessed the same LDL specificity, oleate sensitivity, and dependence on lipoprotein concentration as previously noted for LTIP. We conclude that LTIP and apoF are identical.

Lipid transfer inhibitor protein activity deficiency in normolipidemic uremic patients on continuous ambulatory peritoneal dialysis

We previously demonstrated that lipid transfer inhibitor protein (LTIP) is a potent modifier of lipid transfer protein (LTP) function in vitro. Based on these studies, we proposed that LTIP activity is an important determinant of lipoprotein size and composition, which leads to a stimulation of reverse cholesterol transport. To further evaluate this hypothesis, we have studied a normolipidemic, uremic patient population undergoing continuous ambulatory peritoneal dialysis (CAPD) that is deficient in LTIP activity (< 18% of control). LDL from CAPD plasma was triglyceride enriched; the diameters of both CAPD LDL and HDL were increased and CAPD HDL was dominated by the largest subfraction, HDL2b. In CAPD patients, the plasma cholesterol esterification rate was only 61% of control; this decrease was due mainly to the poor reactivity of CAPD lipoproteins. CAPD lipoprotein-deficient plasma promoted twofold greater transfer of radiolabeled cholesteryl ester (CE) between standard lipoproteins than control, although LTP itself was increased only 39%. This twofold increase was not equally expressed among individual lipoprotein classes; CE transfers involving LDL were increased 2.4-fold, whereas those not involving LDL were increased only 50%. In whole plasma, CE net mass transfer to VLDL was slightly increased in CAPD plasma; relative to their CE content, control HDL contributed twofold more CE mass to VLDL than control LDL, but in CAPD plasma this preferential transfer of CE from HDL was absent. Collectively, the aberrations in CAPD lipoprotein composition and metabolism are consistent with the hypothesized role of LTIP. The data further support the role of LTIP in modulating the participation of HDL in CE mass transfers to VLDL. This is the first report of LTIP activity deficiency in humans.

Purification of biologically active apolipoproteins by chromatofocussing

Chromatofocussing has been used to isolate homogeneous apolipoproteins (apo) from human very-low-density lipoproteins and high-density lipoproteins with protein recovery of 70%. The inclusion of sulfhydryl-reducing agent (dithiothreitol) was required during solubilization of the lipoproteins (following delipidation) to achieve reproducible elution profiles. Removal of polyvalent buffers from apoproteins was rapidly accomplished on small columns of hydroxylapatite. The biological activity of purified apo AI and apo CII was confirmed by assessment of their ability to activate lecithin:cholesterol acyltransferase or lipoprotein lipase, respectively. Functional properties of isolated apo E were assessed by in vitro interaction with the low-density lipoprotein receptor expressed by cultured fibroblasts. Apolipoproteins purified by this rapid procedure exhibit identical physical, chemical and biological properties to those purified by other, more tedious techniques.

Preliminary report on a case of apolipoproteins CI and CII deficiency

A combined deficiency of Apo C-I and C-II assessed by mono and bidimensional electrophoresis as well as immunoelectrophoresis is described. It was discovered after a 'check up' in a 70-yr-old woman consulting for a vertebral pain. Lipoprotein disorders correspond to a particular form of Fredrickson's type V. They consisted of types I and IV, with decreased HDL of low electrophoretic mobility, increased VLDL of high electrophoretic mobility, and without LDL. A decrease of Apo A-I, A-II, B and C-III was observed. Data correspond for the most part with all those actually known to characterize Apo C-II deficiency. HDL3 predominance in decreased HDL fraction and strongly decreased CE/TC ratio could be dependent of Apo C-I deficiency. The association of these two apolipoprotein deficiencies, the genes of which are located on chromosome 19, suggest a common defect on the pathway of their biosynthesis possibly located at the gene level. In spite of these numerous anomalies, the affection appears well tolerated.

Lipids and apolipoproteins A-I, B and C-II and different rapid weight loss programs (weight lifters, wrestlers, boxers and judokas)

Apolipoproteins A-I, B, C-II and lipids were studied before and after rapid weight loss schedules. The compared groups were all athletic. Apolipoproteins were determined by electroimmunoassay methods using apoproteins purified by chromatofocusing column method. Dextran T10 was shown to increase rocket height in ApoB assay. Over 1% Dextran concentrations gave poor response. The linearity during calibration was from 0.3 to 3.0 g ApoB/l. Baseline values of ApoA-I in wrestlers, weightlifters, boxers and judokas were slightly higher as compared to "normal" population; ApoB was clearly reduced (mean value of 690 mg/l). Weight-loss was significant in each experimental group; mean value of 4.1% in active exercise, sauna and diuretic groups together. Compared as the whole sportsmen group in passive weight loss (or sauna) and diuretic groups the most pronounced changes were seen to be elevated apoprotein concentrations, whereas weight-loss by active rapid exercise resulted no apoprotein changes, but instead an increment in HDL cholesterol and decrement in triglycerides, respectively. The present study was the first to evaluate baseline values of apoproteins A-I, B and C-II in first class athletes and also the possible changes in these and lipid values in rapid weight-loss practices.

Chromatofocusing of apolipoproteins from human serum high density lipoprotein

Human HDL was delipidated and the apolipoproteins were fractionated by chromatofocusing. Chromatofocusing, which separates proteins due to their differing isoelectric points, resulted in 8 peaks with corresponding pI values of 7.40, 6.92, 6.64, 5.48, 5.30, 5.18, 4.92 and 4.63. By one single chromatofocusing run four apolipoproteins were obtained in pure form. Two additional polypeptides could be purified during the desalting step using phenyl-Sepharose.

Determination of human apolipoprotein C-II by electroimmunoassay. Studies on standardization and determination before and after physical training

1. Human VLDL and HDL were fractionated by sequential ultracentrifugation until free of contaminant plasma proteins. 2. Column chromatofocusing method was used to isolate apolipoprotein C-II from apoVLDL and apo HDL. C-apoprotein peak was rechromatofocused and the second peak was the apo C-II (pI 4.7, homogeneous band on SDS slab gel). 3. New Zealand white rabbits were immunized with apo C-II. Antiserum gave a single precipitate are of identity between whole serum, apoVLDL, apoHDL and apo C-II. 4. Apo C-II concentration was measured by electroimmunoassay method. During standardization 1% Triton X-100 improved the rocket shapes and contours. Total delipidation did not affect the assay system and so the antigenic determinants of apo C-II are all available to antiserum. The lowest concentration of apo C-II possible to determine with this method was 70 ng/sample well. 5. There was no difference between the apo C-II values before (39.8 +/- 7.1 mg/l, n = 19) and after (41.6 +/- 6.4 mg/l, n = 19) moderate physical training among normolipemic subjects. 6. Specific immunoprecipitation technique was also used to determine apo C-II content in standard pool serum.