We studied the effect of increasing the frequency of meals on serum lipid concentrations and carbohydrate tolerance in normal subjects. Seven men were assigned in random order to two metabolically identical diets. One diet consisted of 17 snacks per day (the nibbling diet), and the other of three meals per day (the three-meal diet); each diet was followed for two weeks. As compared with the three-meal diet, the nibbling diet reduced fasting serum concentrations of total cholesterol, low-density lipoprotein cholesterol, and apolipoprotein B by a mean (+/- SE) of 8.5 +/- 2.5 percent (P less than 0.02), 13.5 +/- 3.4 percent (P less than 0.01), and 15.1 +/- 5.7 percent (P less than 0.05), respectively. Although the mean blood glucose level and serum concentrations of free fatty acids, 3-hydroxybutyrate, and triglyceride were similar during both diets, during the nibbling diet the mean serum insulin level decreased by 27.9 +/- 6.3 percent (P less than 0.01) and the mean 24-hour urinary C-peptide output decreased by 20.2 +/- 5.6 percent (P less than 0.02). In addition, the mean 24-hour urinary cortisol excretion was lower by 17.3 +/- 5.9 percent (P less than 0.05) at the end of the nibbling diet than at the end of the three-meal diet. The blood glucose, serum insulin, and C-peptide responses to a standardized breakfast and the results of an intravenous glucose-tolerance test conducted at the end of each diet were similar. We conclude that in addition to the amount and type of food eaten, the frequency of meals may be an important determinant of fasting serum lipid levels, possibly in relation to changes in insulin secretion.

Nibbling versus gorging: metabolic advantages of increased meal frequency.

Effect of food azo dyes tartrazine and carmoisine on biochemical parameters related to renal, hepatic function and oxidative stress biomarkers in young male rats.

Rapid immunochemical assays were developed for the determination of apolipoproteins A-1 and B in serum. The methods are based on the measurement of immunoprecipitation at a wavelength of 340 nm. Both assays are easy to perform, their reproducibilities are good (the coefficients of variation for within-run and between-run imprecisions are below 5%), and their correlations with radial immunodiffusion method are high (r=0.96). The effect of storage on native serum specimens was also studied. Apolipoprotein B is stable at least 4 weeks in a refrigerator but in some specimens the level of apolipoprotein A-1 rises nearly 10% during this time. Repeated freezing and thawing, on the other hand, may have a harmful effect, especially on apolipoprotein B. Therefore, use of fresh serum specimens is recommended for both assays. The present method is well suited for routine measurements because it can be easily adapted to most clinical chemistry analysers.

Immunoturbidimetric determination of apolipoproteins A-1 and B in serum.

We describe a method for directly measuring LpA-I lipoprotein particles containing apolipoprotein A-I (apo A-I) not associated with apolipoprotein A-II (apo A-II), by differential electroimmunoassay of plasma on ready-to-use plates. Lipoprotein particles containing both apo A-I and apo A-II (LpA-I:A-II) are retained close to the wells when a very high excess of anti-apo A-II is used as compared with anti-apo A-I, whereas the LpA-I particles migrate and react with anti-apo A-I. The method is specific, rapid, and precise. Within- and between-run CVs at three concentrations (high, medium, and low) ranged between 1.51% and 2.72% and 3.01% and 4.56%, respectively. Analytical recovery of isolated LpA-I was from 93% to 115%. Results correlate well with those obtained by two-phase electroimmunoassay, enzyme-linked differential-antibody immunosorbent assay, and immunoaffinity chromatography coupled to enzyme-linked immunosorbent assay. The average normolipidemic concentration of LpA-I was 600 mg/L in 45 women and 490 mg/L in 40 men (P less than 0.0001).

Differential Electroimmunoassay of Human LpA-I Lipoprotein Particles on Ready-to-Use Plates

Hypertriglyceridemia is a metabolic complication of retinoid therapy. In this study, we analyzed whether retinoids increase the expression of apo C- III, an antagonist of plasma triglyceride catabolism. In men, isotretinoin treatment (80 mg/d; 5 d) resulted in elevated plasma apo C-III, but not apo E concentrations. In human hepatoma HepG2 cells, retinoids increased apo C-III mRNA and protein production. Transient transfection experiments indicated that retinoids increase apo C-III expression at the transcriptional level. This increased apo C-III transcription is mediated by the retinoid X receptor (RXR), since LG1069 (4-[1-(5,6,7,8-tetrahydro-3,5,5,8,8-pentamethyl-2- naphtalenyl)ethenyl]benzoic acid), a RXR-specific agonist, but not TTNPB ((E)-4-[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2- naphtalenyl)propenyl]benzoic acid), a retinoic acid receptor (RAR)-specific agonist, induced apo C-III mRNA in HepG2 cells and primary human hepatocytes. Mutagenesis experiments localized the retinoid responsiveness to a cis- element consisting of two imperfect AGGTCA sequences spaced by one oligonucleotide (DR-1), within the previously identified C3P footprint site. Cotransfection assays showed that RXR, but not RAR, activates apo C-III transcription through this element either as a homo- or as a heterodimer with the peroxisome proliferator-activated receptor. Thus, apo C-III is a target gene for retinoids acting via RXR. Increased apo C-III expression may contribute to the hypertriglyceridemia and atherogenic lipoprotein profile observed after retinoid therapy.

/pdf/retinoids-increase-human-apo-c-iii-expression-at-the-2tigbm3tno.pdf

Retinoids increase human apo C-III expression at the transcriptional level via the retinoid X receptor. Contribution to the hypertriglyceridemic action of retinoids.

We describe a simplified electroimmunoassay for quantification of human apolipoproteins A-I and B on prepared plates. A solution of agarose at 55 degrees C, containing hydroxyethylcellulose and antibodies, is poured onto a plastic film and allowed to gel. Wells are punched in the gels and the plates are dried for storage. Before use, they are rehydrated and buffered. We use succinylated Sudan Black to prestain lipoprotein fractions of plasma. After electrophoresing samples of plasma or standards for 3 h at 4 degrees C at 12.5 V/cm, we measure the peak heights and read the results from a standard curve prepared by using calibrated sera of known apolipoprotein B and A-I content as secondary standard. The within- and between-assay coefficients of variation were less than 4% in all cases. Results correlated well with those obtained by classic electroimmunodiffusion. Subjects with confirmed atherosclerotic lesions had significantly (p less than 10(-9)) lower ratios of apolipoprotein A-I to apolipoprotein B, compared with ratios in controls.

Simultaneous measurement of plasma apolipoproteins A-I and B by electroimmunoassay.

We used a noncompetitive immunoenzymometric assay to measure the concentration of total apolipoprotein C-III in human sera. Affinity-purified antibodies to apolipoprotein C-III were adsorbed to the surface of microtiter plates. After washing, this solid-phase antibody was incubated with antigen (serum from fasting subjects), washed, and then incubated with peroxidase-labeled purified antibodies to apolipoprotein C-III. After a last washing, the bound label was assayed, providing a direct measurement of the antigen. Optimized technical conditions for the assay yielded assay CVs of 3.5 and 5.6% for within- and between-run precision, respectively. Analytical recovery of apolipoprotein C-III added to a serum was quantitative (97%). This noncompetitive assay can be used to measure apolipoprotein C-III in different lipoprotein fractions (very-low or high-density fractions) and yields values that compare favorably with those obtained by electroimmunoassay (r = 0.94). The assay offers several advantages over existing techniques--sensitivity, specificity, simplicity, and no use of radioisotopes--and hyperlipemic samples can be used.

Quantification of apolipoprotein C-III in serum by a noncompetitive immunoenzymometric assay.

We describe an isoelectric-focusing method for rapidly separating and quantifying apolipoprotein (apo) C-II and C-III subspecies of triglyceride-rich lipoproteins. Concentrated very-low-density lipoproteins (VLDL) or delipidated apo VLDL are focused on dry acrylamide plates, after their rehydration with ampholytes and urea. Apo C-II and apo C-III in VLDL are resolved into four major bands--C-II (pI 5.01), C-III0 (pI 5.10), C-III1 (pl 4.92), and C-III2 (pI 4.84)--at the same pI values as for purified apo C. This precise technique can be used without delipidating VLDL. The relative percentage of C apoproteins found in VLDL from plasma of normal subjects agreed with previously published data. The ratio of apo C-II to apo C-III decreased in patients with chronic renal failure or with coronary artery disease.

Rapid assessment of the distribution of apolipoproteins C-II and C-III subspecies in triglyceride-rich lipoproteins by isoelectric focusing.

Rapid determination of human plasma apolipoprotein B

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Simultaneous measurement of plasma apolipoproteins A-I and B by electroimmunoassay.

Quantification of apolipoprotein C-III in serum by a noncompetitive immunoenzymometric assay.

Rapid assessment of the distribution of apolipoproteins C-II and C-III subspecies in triglyceride-rich lipoproteins by isoelectric focusing.

Rapid determination of human plasma apolipoprotein B