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In order to find out if inefficient transport of amino acids contributes to a decrease in fetal weight during maternal malnutrition, we injected [14C]- and [3H]-labelled aminoisobutyric acid (AIB), respectively, in the mother and its fetuses and determined its transplacental kinetics on day 20 of gestation in rats fed a 21 per cent (control) or a low (5 per cent) protein diet. Rats fed a low protein diet consumed significantly less food than did the rats fed a control diet and thus suffered from protein-calorie malnutrition. A low protein diet led to a significant (P less than 0.05) decrease in maternal and fetal volume of distribution of AIB, a decrease in the clearance of AIB from the mother to the fetus and an increase in the time required for the fetal plasma AIB concentration following maternal injection to exceed the maternal plasma AIB concentration. The clearance of AIB from the fetus into the mother or to outside (e.g. amniotic fluid) was not altered by protein deficiency. It is concluded that a decrease in the efficiency of the placenta to deliver amino acids to the fetus may be a contributing factor in fetal growth retardation during maternal protein malnutrition.

Edward A. Fisher The Editors invited Dr Henry Ginsberg to review an important topic that is relevant to many kinetic studies of human lipoprotein metabolism, including one in the present issue. Changes in the concentration of a plasma protein are usually thought to involve the balance between its production and clearance, but as Drs Ginsberg and Ramakrishnan point out, in the case of exchangeable apolipoproteins, the change in concentration associated with a particular fraction of plasma lipoproteins may not be from production or clearance. We welcome any editorial correspondence on this issue. Department of Medicine (Cardiology) NYU School of Medicine 522 First Ave. New York, NY 10016 edward.fisher@med.nyu.edu In this issue of ATVB , Chan et al present interesting results of a study of the effects of atorvastatin and fenofibrate on apolipoprotein CIII (apoCIII) metabolism.1 Each drug was administered alone, and the study was conducted as a 3-way crossover design with placebo. The authors report that both drugs reduced plasma and very low-density lipoprotein (VLDL) apoCIII. Further, they conclude from their tracer kinetic studies that the fall in VLDL apoCIII levels resulted from increased fractional catabolic rates (FCR) and reduced production rates (PR) of VLDL apoCIII. These results, they note, may provide an insight into the triglyceride-lowering effects of both atorvastatin and fenofibrate, because apoCIII inhibits both lipoprotein lipase activity and removal of remnants via receptor-mediated pathways. See accompanying article on page 1831 A close reading of the article raises issues, …

Tracer enrichment data are fitted by multicompartmental models to estimate rate constants and fluxes or transport rates. In apolipoprotein turnover studies, mass measurements are also available, for example, apolipoprotein B levels in very low-density lipoprotein, intermediate-density lipoprotein, and low-density lipoprotein, and are often essential to calculate some of the rate constants. The usual method to use mass measurements is to estimate pool masses along with rate constants. A systematic alternative approach is developed to use flux balances around pools to express some rate constants in terms of the other rate constants and the measured masses. The resulting reduction in the number of parameters to be estimated makes the modeling more efficient. In models that would be unidentifiable without mass measurements, the usual approach and the proposed approach yield identical results. In a simple two-pool model, the number of unknown parameters is reduced from 4 to 2. In a published five-pool model for apolipoprotein B kinetics with three mass measurements, the number of parameters is reduced from 12 to 9. With m mass measurements, the number of responses to be fitted and the number of parameters to be estimated are each reduced by m, a simplification by 1/4 to 1/3 in a typical pool model. Besides a proportionate reduction in computational effort, there is a further benefit because the dimensionality of the problem is also decreased significantly, which means ease of convergence and a smaller likelihood of suboptimal solutions. Although our approach is conceptually straightforward, the dependencies get considerably more complex with increasing model size. To generate dependency definitions automatically, a Web-accessible program is available at http://biomath.info/poolfit/constraints.

A kinetic model for imipramine (IMI) has been developed, based upon a study of 16 teenagers who received IMI 4-5 mg/kg/day for treatment of a major depressive disorder. Serial measurements of plasma concentrations of IMI, desmethylimipramine (DMI), 2-hydroxy-IMI, and 2-hydroxy-DMI were made. Mean residence times, volumes of distribution, clearances of IMI and DMI, and rate constants for formation and elimination of the hydroxy metabolites were determined from a multicompartment model fitted to the concentration-time data. Mean residence time for DMI was significantly longer than for IMI (47.1 +/- 21.2 vs. 13.4 +/- 4.8 h, p less than 0.001). A different volume of distribution for IMI and DMI was not supported by the data. Clearance of DMI was considerably slower than that of IMI (0.67 +/- 0.45 vs. 2.18 +/- 1.33 l(kg.h), p less than 0.001). A statistically significant increase in mean residence time with increasing age during adolescence was found (r = 0.57, p less than 0.05).

Mechanisms that might be responsible for the low levels of high density lipoprotein (HDL) associated with hypertriglyceridemia were studied in an animal model. Specific monoclonal antibodies were infused into female cynomolgus monkeys to inhibit lipoprotein lipase (LPL), the rate-limiting enzyme for triglyceride catabolism. LPL inhibition produced marked and sustained hypertriglyceridemia, with plasma triglyceride levels of 633-1240 mg/dl. HDL protein and cholesterol and plasma apolipoprotein (apo) AI levels decreased; HDL triglyceride (TG) levels increased. The fractional catabolic rate of homologous monkey HDL apolipoproteins injected into LPL-inhibited animals (n = 7) was more than double that of normal animals (0.094 +/- 0.010 vs. 0.037 +/- 0.001 pools of HDL protein removed per hour, average +/- SEM). The fractional catabolic rate of low density lipoprotein apolipoprotein did not differ between the two groups of animals. Using HDL apolipoproteins labeled with tyramine-cellobiose, the tissues responsible for this increased HDL apolipoprotein catabolism were explored. A greater proportion of HDL apolipoprotein degradation occurred in the kidneys of hypertriglyceridemic than normal animals; the proportions in liver were the same in normal and LPL-inhibited monkeys. Hypertriglyceridemia due to LPL deficiency is associated with low levels of circulating HDL cholesterol and apo AI. This is due, in part, to increased fractional catabolism of apo AI. Our studies suggest that variations in the rate of LPL-mediated lipolysis of TG-rich lipoproteins may lead to differences in HDL apolipoprotein fractional catabolic rate.

Growth, nutrient retention, and metabolic response of low-birth-weight infants fed human milk provided by their mother; this milk supplemented with bovine milk protein, calcium, phosphorus, and sodium; or pasteurized term human milk with the same supplement were monitored from the time desired intake was tolerated until weight reached 2200 g. The supplement resulted in greater rates of weight gain (20.5 +/- 2.3 vs 16.4 +/- 2.2 g.kg-1.d-1) and nitrogen retention (353 +/- 76 vs 270 +/- 53 mg.kg-1.d-1), increase in plasma transthyretin (TTR) concentration (7 +/- 16 vs -3 +/- 9 mg.L-1.wk-1), a higher mean plasma albumin concentration (34 +/- 3 vs 32 +/- 4 g/L), and a higher plasma TTR concentration at discharge (100 +/- 22 vs 75 +/- 24 mg/L). All these variables correlated significantly with total nitrogen intake, suggesting that the differences are attributable to the protein content of the supplement. The supplement also resulted in greater rates of calcium and phosphorus accretion but the plasma alkaline phosphatase activity of the supplemented vs the unsupplemented groups did not differ.

Radiolabeling of whole lipoproteins or individual apolipoproteins has been an essential tool for the determination of the kinetics of apolipoprotein metabolism in vivo. Mathematical analysis of specific radioactivity (SA) or total radioactivity data has demonstrated the existence of significant complexity in the plasma decay curves of several apolipoproteins. Results obtained during development of methods to study the metabolism of apolipoprotein B (apoB) in very low density lipoprotein (VLDL) subclasses isolated according to flotation (Sf) rates from whole radiolabeled (d less than 1.006 g/ml) VLDL suggested nonuniform radiolabeling of apoB in the three Sf subclasses being studied. We therefore determined apoB SA in VLDL Sf subclasses in ten hypertriglyceridemic and five normal subjects. After radioiodination of apoB in whole VLDL, different apoB SA were found in Sf 400-100, Sf 100-60, and Sf 60-20. The pattern of labeling was quite variable among subjects. On average, apoB SA in the VLDL tracer was greatest in Sf 400-100, and least in Sf 60-20. Nonuniform labeling could also be demonstrated in five studies in which samples were obtained 3 min after intravenous injection of the tracer into subjects with a wide range of plasma triglycerides. Nonuniform labeling of apoB in whole VLDL was also demonstrated in two of the subjects by isolating subclasses of their VLDL that did not bind to an anti-apolipoprotein E immunoaffinity column. These results indicate that the usual assumption of homogeneous labeling of apoB may be erroneous. We have derived a simple mathematical formula to study the consequences of this assumption in estimating kinetic parameters. It is shown that an erroneous assumption of homogeneous tracer labeling may significantly underestimate or overestimate the true production rate, even in a simple two-pool model. Identification of labeling characteristics and incorporation of this information into the mathematical analysis of the plasma radioactivity data can improve the accuracy of the analysis as well as the sensitivity of compartmental models generated by such data.

We investigated the metabolism of very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL), and low density lipoprotein (LDL) apolipoprotein B (apoB) in seven patients with combined hyperlipidemia (CHL), using 125I-labeled VLDL and 131I-labeled LDL and compartmental modeling, before and during lovastatin treatment. Lovastatin therapy significantly reduced plasma levels of LDL cholesterol (142 vs 93 mg/dl, P less than 0.0005) and apoB (1328 vs 797 micrograms/ml, P less than 0.001). Before treatment, CHL patients had high production rates (PR) of LDL apoB. Three-fourths of this LDL apoB flux was derived from sources other than circulating VLDL and was, therefore, defined as “cold” LDL apoB flux. Compared to baseline, treatment with lovastatin was associated with a significant reduction in the total rate of entry of apoB-containing lipoproteins into plasma in all seven CHL subjects (40.7 vs. 25.7 mg/kg.day, P less than 0.003). This reduction was associated with a fall in total LDL apoB PR and in “cold” LDL apoB PR in six out of seven CHL subjects. VLDL apoB PR fell in five out of seven CHL subjects. Treatment with lovastatin did not significantly alter VLDL apoB conversion to LDL apoB or LDL apoB fractional catabolic rate (FCR) in CHL patients. In three patients with familial hypercholesterolemia who were studied for comparison, lovastatin treatment increased LDL apoB FCR but did not consistently alter LDL apoB PR. We conclude that lovastatin lowers LDL cholesterol and apoB concentrations in CHL patients by reducing the rate of entry of apoB-containing lipoproteins into plasma, either as VLDL or as directly secreted LDL.

Postprandial hypertriglyceridemia is common in individuals with insulin resistance, and diets enriched in 1,3-diacylglycerol (DAG) may reduce postprandial plasma triglycerides (PPTGs). We enrolled 25 insulin-resistant, nondiabetic individuals in a double-blind, randomized crossover trial to test the acute and chronic effects of a DAG-enriched diet on PPTG. Participants received either DAG or triacylglycerol (TAG) oil, in food products, for 5 weeks. Fasting lipids, and two separate postprandial tests, one with DAG oil and one with TAG oil, were performed at the end of each 5 week diet period. We found no acute or chronic effects of DAG oil on PPTG. Thus, neither the DAG oil PPTG (h/mg/dl) on a chronic TAG diet [area under the curve (AUC) = 503 +/- 439] nor the TAG oil PPTG on a chronic DAG diet (AUC = 517 +/- 638) was different from the TAG oil PPTG on a chronic TAG diet (AUC = 565 +/- 362). Five weeks of a DAG-enriched diet had no acute or chronic effects on PPTG in insulin-resistant individuals. We suggest further studies to evaluate the effects of DAG on individuals with low and high TG levels.

Background: In subjects with a high prevalence of metabolic risk abnormalities, the preferred replacement for saturated fat is unresolved. Objective: The objective was to study whether carbohydrate or monounsaturated fat is a preferred replacement for saturated fat. Design: Fifty-two men and 33 women, selected to have any combination of HDL cholesterol ≤ 30th percentile, triacylglycerol ≥ 70th percentile, or insulin ≥ 70th percentile, were enrolled in a 3-period, 7-wk randomized crossover study. The subjects consumed an average American diet (AAD; 36% of energy from fat) and 2 additional diets in which 7% of energy from saturated fat was replaced with either carbohydrate (CHO diet) or monounsaturated fatty acids (MUFA diet). Results: Relative to the AAD, LDL cholesterol was lower with both the CHO (-7.0%) and MUFA (-6.3%) diets, whereas the difference in HDL cholesterol was smaller during the MUFA diet (-4.3%) than during the CHO diet (-7.2%). Plasma triacylglycerols tended to be lower with the MUFA diet, but were significantly higher with the CHO diet. Although dietary lipid responses varied on the basis of baseline lipid profiles, the response to diet did not differ between subjects with or without the metabolic syndrome or with or without insulin resistance. Postprandial triacylglycerol concentrations did not differ significantly between the diets. Lipoprotein(a) concentrations increased with both the CHO (20%) and MUFA (11%) diets relative to the AAD. Conclusions: In the study population, who were at increased risk of coronary artery disease, MUFA provided a greater reduction in risk as a replacement for saturated fat than did carbohydrate.

Among the many recent attempts to demonstrate the medical benefits of religious activity, the methodologically strongest seem to be studies of the effects of distant intercessory prayer (IP). In these studies, patients are randomly assigned to receive standard care or standard care plus the prayers or "healing intentions" of distant intercessors. Most of the scientific community has dismissed such research, but cavalier rejection of studies of IP is unwise, because IP studies appear to conform to the standards of randomized controlled trials (RCTs) and, as such, would have a significant advantage over observational investigations of associations between religious variables and health outcomes. As we demonstrate, however, studies of IP fail to meet the standards of RCTs in several critical respects. They fail to adequately measure and control exposure to prayer from others, which is likely to exceed IP and to vary widely from subject to subject, and whose magnitude is unknown. This supplemental prayer so greatly attenuates the differences between the treatment and control groups that sample sizes are too large to justify studies of IP. Further, IP studies generally do not specify the outcome variables, raising problems of multiple comparisons and Type 1 errors. Finally, these studies claim findings incompatible with current views of the physical universe and consciousness. Unless these problems are solved, studies of IP should not be conducted.

Apolipoprotein [a] (apo[a]) gene size is a major predictor of lipoprotein [a] level. To determine genetic predictors of allele-specific apo[a] levels beyond gene size, we evaluated the upstream C/T and pentanucleotide repeat (PNR) polymorphisms. We determined apo[a] sizes, allele-specific apo[a] levels, and C/T and PNR in 215 Caucasians and 139 African Americans. For Caucasians, apo[a] size affected allele-specific levels substantially greater in subjects with apo[a] < 24 K4; for African Americans, the size effect was smaller than in Caucasians, 8. In a multiple regression model, apo[a] allele size and size and expression of the other apo[a] allele (and PNR > 8 for Caucasians) significantly predicted allele-specific apo[a] levels. For a common PNR 8 allele, predicted values were similar in the two ethnicities for small size apo[a]. Allele-specific apo[a] levels were influenced by the other allele size and expression. Observed differences between Caucasians and African Americans in allele-specific apo[a] levels were explained for small apo[a] sizes by the other allele size and PNR; the ethnicity differences remain unexplained for larger sizes.

Plasma LDL levels and atherosclerosis both increase on a saturated fat–rich (SAT) diet. LDL cholesterol delivery to tissue may occur via uptake of the LDL particles or via selective uptake (SU), wherein cholesteryl ester (CE) enters cells without concomitant whole-particle uptake. It is not known how dietary fats might directly affect arterial LDL-CE uptake and whether SU is involved. Thus, mice that are relatively atherosclerosis resistant (C57BL/6) or susceptible to atherosclerosis (apoE–/–) were fed a chow or SAT diet and injected with double radiolabeled or fluorescent-labeled human LDL to independently trace LDL-CE core and whole-particle uptake, respectively. Our results show that a SAT diet increased contributions of SU to total arterial LDL-CE delivery in C57BL/6 and apoE–/– mice. The SAT diet increased plasma fatty acid and cholesterol levels; cholesterol, but not fatty acid, levels correlated with SU, as did the degree of atherosclerosis. Increased SU did not correlate with arterial scavenger receptor class B type I levels but paralleled increased lipoprotein lipase (LPL) levels and LPL distribution in the arterial wall. These studies suggest that arterial LDL-CE delivery via SU can be an important mechanism in vivo and that dietary influences on arterial LPL levels and atherogenesis modulate arterial LDL-CE delivery, cholesterol deposition, and SU.

Because celiac disease is a female-predominant disease we investigated the influence of gender on clinical manifestations of the disease in the United States.Data were obtained on biopsy-proven adult patients with celiac disease from a database of patients seen between 1981 and 2001 in a University-based referral center. Z scores were calculated to adjust for age, ethnicity and gender using the National Health and Nutrition Examination Survey database as controls.The cohort consisted of 323 patients (211 F, 112 M). Men had a shorter duration of symptoms than women (p=0.006). There was no gender difference in the age at diagnosis or mode of presentation. Body mass index (BMI), mean hemoglobin and ferritin values were lower in women than in men, but the Z scores for these values were not significantly different, indicating that the differences are physiological. All lipid values were low (negative Z scores). Men had lower total cholesterol (162.0+/-46.5mg/dl) compared to women (181.0+/-40.0mg/dl), p=0.02 and lower Z scores (-1.10+/-1.1) compared to women (-0.71+/-0.9), p=0.04. Men had lower bone density T scores at the radius (p=0.07). Autoimmune diseases were present in 30.7% with a female to male ratio of 1:1, compared to the general population in which 3.2% have autoimmune diseases with a female predominance.Most gender differences in celiac disease are physiological. However, men have indirect evidence of greater malabsorption than females and have female-predominant associated diseases when they present with celiac disease.

Cigarette smoking (CS) is a well-described oxidant burden in humans. We hypothesized that CS would accelerate alpha-tocopherol (alpha-T) utilization leaving less for metabolite (CEHC) production. After labeled alpha-T consumption (75 mg each of d(3)-RRR-alpha-TAc and d(6)-all-rac-alpha-TAc) by smokers and nonsmokers (n = 10/group), CS increased alpha-T disappearance and decreased plasma and urinary CEHCs. Plasma d(3)/d(6)-alpha-T ratios were approximately 1.4 during supplementation and approximately 2 from days 5 to 17. d(3)/d(6)-alpha-CEHC ratios were on average 0.29 +/- 0.05, confirming that all-rac-alpha-tocopherol is metabolized more efficiently. CEHC may be a good marker of vitamin E status, and smokers may have an increased vitamin E requirement.

Objective— High-density lipoprotein (HDL) cholesteryl esters (CE) are taken up by liver and adrenals selectively, ie, independent from particle internalization. Class B type I scavenger receptor (SR-BI) mediates this uptake in vitro. The role of SR-BI in HDL metabolism was explored in mice. Methods and Results— Mice with a mutation in the SR-BI gene (SR-BI KO) and wild-type (WT) littermates were used. Mutants had increased HDL cholesterol. HDL was labeled with 125 I (protein) and [ 3 H] (CE). After HDL injection, blood samples were drawn and finally the mice were euthanized. In WT, the plasma decay of HDL-associated [ 3 H] is faster compared with 125 I and this represents whole-body selective CE uptake. In SR-BI KO, the decay of both tracers is similar, yielding no selective CE removal. In WT liver and adrenals, uptake of [ 3 H] is higher than 125 I, showing selective uptake. In SR-BI KO, liver uptake of [ 3 H] and 125 I are similar, proposing no selective HDL CE uptake. In SR-BI KO adrenals, selective uptake is reduced; however, even in the absence of SR-BI, this uptake is detected using WT-HDL. Conclusions— SR-BI mediates selective uptake of HDL CE by the liver. In adrenals, an alternative mechanism or mechanisms can play a role in selective CE uptake.

Lipoprotein (a) [Lp(a)], is present only in humans, Old World nonhuman primates, and the European hedgehog. Lp(a) has many properties in common with low-density lipoprotein (LDL) but contains a unique protein, apo(a), which is structurally different from other apolipoproteins. The size of the apo(a) gene is highly variable, resulting in the protein molecular weight ranging from 300 to 800 kDa; this large variation may be caused by neutral evolution in the absence of any selection advantage. Apo(a) influences to a major extent metabolic and physicochemical properties of Lp(a), and the size polymorphism of the apo(a) gene contributes to the pronounced heterogeneity of Lp(a). There is an inverse relationship between apo(a) size and Lp(a) levels; however, this pattern is complex. For a given apo(a) size, there is a considerable variation in Lp(a) levels across individuals, underscoring the importance to assess allele-specific Lp(a) levels. Further, Lp(a) levels differ between populations, and blacks have generally higher levels than Asians and whites, adjusting for apo(a) sizes. In addition to the apo(a) size polymorphism, an upstream pentanucleotide repeat (TTTTA n ) affects Lp(a) levels. Several meta-analyses have provided support for an association between Lp(a) and coronary artery disease, and the levels of Lp(a) carried in particles with smaller size apo(a) isoforms are associated with cardiovascular disease or with preclinical vascular changes. Further, there is an interaction between Lp(a) and other risk factors for cardiovascular disease. The physiological role of Lp(a) is unknown, although a majority of studies implicate Lp(a) as a risk factor.

The adaptive value of apolipoprotein B-48 (apoB-48), the truncated form of apoB produced by the intestine, in lipid metabolism remains unclear. We crossed human apoC-III transgenic mice with mice expressing either apoB-48 only (apoB48/48) or apoB-100 only (apoB100/100). Cholesterol levels were higher in apoB48/48 mice than in apoB100/100 mice but triglyceride levels were similar. Lipid levels were increased by the apoC-III transgene. However, triglyceride levels were significantly higher in apoB100/100C-III than in apoB48/48C-III mice (895 +/- 395 mg/dl vs. 690 +/- 252 mg/dl; P

Retinoids are required for normal embryonic development. Both embryonic retinoid deficiency and excess result in congenital malformations. There is little understanding of the physiology underlying retinoid transfer from the maternal circulation to the embryo. We now report studies that explore this process using retinol-binding protein-deficient (RBP−/−) mice and mice that express human RBP on the RBP−/−background. Our studies establish that dietary retinoid, bound to lipoproteins, can serve as an important source for meeting tissue retinoid requirements during embryogenesis. Indeed, retinyl ester concentrations in the circulations of pregnant RBP−/−mice are significantly elevated over those observed in wild-type mice, suggesting that lipoprotein retinyl esters may compensate for the absence of retinol-RBP during pregnancy. We also demonstrate, contrary to earlier proposals, that maternal RBP does not cross the placenta and cannot enter the fetal circulation. Overall, our data indicate that both retinol-RBP and retinyl esters bound to lipoproteins are able to provide sufficient retinoid to the embryo to allow for normal embryonic development.

Scientists who use animals in research must justify the number of animals to be used, and committees that review proposals to use animals in research must review this justification to ensure the appropriateness of the number of animals to be used. This article discusses when the number of animals to be used can best be estimated from previous experience and when a simple power and sample size calculation should be performed. Even complicated experimental designs requiring sophisticated statistical models for analysis can usually be simplified to a single key or critical question so that simple formulae can be used to estimate the required sample size. Approaches to sample size estimation for various types of hypotheses are described, and equations are provided in the Appendix. Several web sites are cited for more information and for performing actual calculations.

Does cigarette smoking increase vitamin E utilization in vivo? A trial was carried out in 6 smokers and 5 nonsmokers of comparable ages and serum lipids. Subjects consumed 75 mg each d(3)-RRR and d(6)-all rac-alpha-tocopheryl acetates (natural and synthetic vitamin E, respectively) daily for 7 d with a standardized breakfast. Fasting blood samples were drawn on days -7, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 9, 14, 21 (negative days indicate supplementation). In both groups, plasma d(3)-alpha-tocopherol concentrations were approximately double of d(6)-alpha-tocopherol. At day 0, the %d(3) alpha-tocopherols (d(3)-alpha-tocopherol/total-alpha-tocopherol x 100) were similar in both smokers and nonsmokers. Subsequently, there was a trend toward a faster exponential disappearance of the plasma %d(3) alpha-tocopherol in smokers compared with nonsmokers (0.30 +/- 0.04 compared with 0.24 +/- 0.05, p =.0565). The calculated %d(3) half-lives were 55.6 +/- 7.4 h in smokers and 72.1 +/- 17.3 h in nonsmokers (p =.0630). By day 21, the %d(3) in smokers had decreased to 1.4% +/- 0.3% while it was 2.2% +/- 0.7% (p =.0418) in the nonsmokers. These data suggest that smoking increases plasma vitamin E disappearance, but further studies are needed to confirm this finding and to assess its cause.

Carbohydrate and fat may vary in their ability to support protein accretion and growth. If so, variations in the source of nonprotein energy might be used to therapeutic advantage in enterally fed low-birth-weight infants. To test the hypothesis that high-carbohydrate diets are more effective than isocaloric high-fat diets in promoting growth and protein accretion, low-birth-weight infants weighing 750-1600 g at birth were randomized in a double blind study to receive one of five formulas differing only in the quantity and quality of nonprotein energy. Groups 1, 2, and control received 130 kcal x kg(-1) x d(-1) with 35, 65, and 50% of the nonprotein energy as carbohydrate. Groups 3 and 4 received energy intake of 155 kcal x kg(-1) x d(-1) with 35 and 65% of the nonprotein energy as carbohydrate. Protein intake of all groups was 4 g x kg(-1) x d(-1). Growth and metabolic responses were followed weekly, and macronutrient balances including 6-h indirect calorimetry were performed biweekly. Greater rates of weight gain and nitrogen retention were observed at high-carbohydrate intake compared with high-fat intake at both gross energy intakes. Greater rates of energy storage and an increase in skinfold thickness were observed in group 4 (high-energy high-carbohydrate diet) despite higher rates of energy expenditure. These data support the hypothesis that at isocaloric intakes, carbohydrate is more effective than fat in enhancing growth and protein accretion in enterally fed low-birth-weight infants. However, a diet with high-energy and high-carbohydrate content also results in increased fat deposition.

Background: Serum retinol is transported by retinol binding protein (RBP), which has one high-affinity binding site for retinol; consequently, the molar ratio of retinol to RBP in the circulation is 1 to 1. In vitamin A deficiency (VAD), both serum retinol and RBP decline. However, the retinol-RBP relation has not been well studied in populations with a high incidence of severe VAD. Objective: The purpose of this study was to determine whether RBP is a good surrogate for serum retinol at the very low retinol concentrations encountered in VAD. Design: The stoichiometric relation between retinol and RBP was studied in 239 Marshallese children: 65 with severe VAD (≤0.35 μmol retinol/L), 94 with moderate VAD (0.36-0.70 μmol retinol/L), and 80 with vitamin A sufficiency (>0.70 μmol retinol/L). Results: Excellent correlation between retinol and RBP (r = 0.94) was observed across all retinol concentrations. Severe VAD was predicted with 96% sensitivity and 91% specificity on the basis of an RBP cutoff of ≤0.48 μmol/L, whereas moderate VAD was predicted with 87% sensitivity and 98% specificity on the basis of an RBP cutoff of ≤0.70 μmol/L. Conclusions: The use of RBP results in the classification of essentially the same children with VAD as does retinol, and RBP is an excellent surrogate for serum retinol. Considering the relative ease of measuring RBP with immunodiagnostic kits compared with that of serum retinol by HPLC, the use of RBP concentrations to assess VAD may be particularly advantageous in field settings. Consequently, measuring RBP concentrations may be a practical alternative to measuring serum retinol in population surveys assessing the prevalence of VAD.

Background: Little information is available about HDL subpopulations during dietary changes. Objective: The objective was to investigate the effect of reductions in total and saturated fat intakes on HDL subpopulations. Design: Multiracial, young and elderly men and women (n = 103) participating in the double-blind, randomized DELTA (Dietary Effects on Lipoproteins and Thrombogenic Activities) Study consumed 3 different diets, each for 8 wk: an average American diet (AAD: 34.3% total fat,15.0% saturated fat), the American Heart Association Step I diet (28.6% total fat, 9.0% saturated fat), and a diet low in saturated fat (25.3% total fat, 6.1% saturated fat). Results: HDL2-cholesterol concentrations, by differential precipitation, decreased (P < 0.001) in a stepwise fashion after the reduction of total and saturated fat: 0.58 ∠ 0.21, 0.53 ∠ 0.19, and 0.48 ∠ 0.18 mmol/L with the AAD, Step I, and low-fat diets, respectively. HDL3 cholesterol decreased (P < 0.01) less: 0.76 ∠ 0.13, 0.73 ∠ 0.12, and 0.72 ∠ 0.11 mmol/L with the AAD, Step I, and low-fat diets, respectively. As measured by nondenaturing gradient gel electrophoresis, the larger-size HDL 2b subpopulation decreased with the reduction in dietary fat, and a corresponding relative increase was seen for the smaller-sized HDL3a, 3b, and 3c subpopulations (P < 0.01). HDL2-cholesterol concentrations correlated negatively with serum triacylglycerol concentrations on all 3 diets: r = 20.46, 20.37, and 20.45 with the AAD, Step I, and low-fat diets, respectively ( P < 0.0001). A similar negative correlation was seen for HDL 2b, whereas HDL3a, 3b, and 3c correlated positively with triacylglycerol concentrations. Diet-induced changes in serum triacylglycerol were negatively correlated with changes in HDL2 and HDL2b cholesterol. Conclusions: A reduction in dietary total and saturated fat decreased both large (HDL2 and HDL2b) and small, dense HDL subpopulations, although decreases in HDL2 and HDL2b were most pronounced. Am J Clin Nutr 1999;70:992‐1000.

Apolipoprotein (apo) C-I is a constituent of triglyceride-rich lipoproteins (TGRL) that interferes with their hepatic clearance. Functional polymorphism in the apoC-I gene has not been established. We determined that an Hpa I site variably present at −317 relative to the apoC-I gene is produced by a 4-bp CGTT insertion. The apoC-I Hpa I alleles showed an ethnically distinct pattern of linkage disequilibrium with the alleles of the adjacent apoE gene. The frequency of apoC-I Hpa I-positive (H2) with apoE ε2 was 0.98, without significant ethnic difference. In contrast, the frequency of H2 with apoE ε4 was 0.85 in European-Americans but only 0.55 in African-Americans (P < 0.001). The frequency of H2 with apoE ε3 was 0.02 in European-Americans and 0.08 in African-Americans (P < 0.001). African-American apoE ε3/ε3 carriers of apoC-I H2 had 19% lower fasting triglyceride levels than H1 homozygotes (P = 0.03) along with 18% higher HDL-cholesterol levels (P = 0.02). ApoB levels were 21% lower (P = 0.002). H2-allelic reporter-gene constructions showed 50% higher expression in transient transfection studies. We localized the source of this difference in expression to the CGTT insertion itself. Deletion studies of the H1 allele showed a negative transcriptional effect of the polymorphic region. An H1 oligodeoxynucleotide showed specific binding of a hepatomacell nuclear protein not evident with an H2 oligodeoxynucleotide. The H2 sequence may decrease the binding of a negatively acting transcription factor, leading to overexpression of apoC-I. This may produce a functional effect on lipoprotein levels but confirmation is needed in other populations.—Xu, Y., L. Berglund, R. Ramakrishnan, R. Mayeux, C. Ngai, S. Holleran, B. Tycko, T. Leff, and N. S. Shachter. A common Hpa I RFLP of apolipoprotein C-I increases gene transcription and exhibits an ethnically distinct pattern of linkage disequilibrium with the alleles of apolipoprotein E. J. Lipid Res. 1999. 40: 50–58.

Abstract —Few well-controlled diet studies have investigated the effects of reducing dietary saturated fatty acid (SFA) intake in premenopausal and postmenopausal women or in blacks. We conducted a multicenter, randomized, crossover-design trial of the effects of reducing dietary SFA on plasma lipids and lipoproteins in 103 healthy adults 22 to 67 years old. There were 46 men and 57 women, of whom 26 were black, 18 were postmenopausal women, and 16 were men ≥40 years old. All meals and snacks, except Saturday dinner, were prepared and served by the research centers. The study was designed to compare three diets: an average American diet (AAD), a Step 1 diet, and a low-SFA (Low-Sat) diet. Dietary cholesterol was constant. Diet composition was validated and monitored by a central laboratory. Each diet was consumed for 8 weeks, and blood samples were obtained during weeks 5 through 8. The compositions of the three diets were as follows: AAD, 34.3% kcal fat and 15.0% kcal SFA; Step 1, 28.6% kcal fat and 9.0% kcal SFA; and Low-Sat, 25.3% kcal fat and 6.1% kcal SFA. Each diet provided ≈275 mg cholesterol/d. Compared with AAD, plasma total cholesterol in the whole group fell 5% on Step 1 and 9% on Low-Sat. LDL cholesterol was 7% lower on Step 1 and 11% lower on Low-Sat than on the AAD (both P P

To determine the contribution of muscle lipoprotein lipase (LPL) to lipoprotein metabolism, induced mutant mice were generated that express human LPL exclusively in muscle. By cross-breeding heterozygous LPL knockout mice with transgenic mice expressing human LPL only in muscle, animals were obtained that express human LPL primarily in skeletal muscle on either the null (L0-MCK) or normal (L2-MCK) LPL backgrounds, and these were compared with control littermates (L2). Fed and fasted post-heparin plasma (PHP) LPL activities were increased 1.4- and 2.3-fold, respectively, in L2-MCK mice and were normal in L0-MCK mice compared with controls. The specific enzyme activities of human LPL in mouse plasma was comparable to human LPL in human PHP. Skeletal muscle LPL activity was increased in both L2-MCK and L0-MCK mice in the fed (6.6-fold) and fasted (4.2-fold in L2-MCK; and 3.4-fold in L0-MCK) states. Adipose tissue LPL mRNA and activity were not detectable in L0-MCK mice. Growth and body mass composition were similar among all groups. In the fasted and fed state, L2-MCK mice had 31% and 53% reductions, respectively, in plasma triglycerides (TG), compatible with increased PHP LPL activity. Unexpectedly, both in the fasted and fed state the L0-MCK mice also had reduced TG (22%), despite normal PHP LPL activities. Very low density lipoprotein (VLDL) turnover studies revealed that the decreased TG were due to increased particle fractional catabolic rate in both L2-MCK and L0-MCK mice. Despite reduced TG, both L2-MCK and L0-MCK mice showed reduced high density lipoprotein (HDL) cholesterol levels (16% and 19%, respectively). HDL turnover studies indicated increased HDL cholesteryl ester fractional catabolic rate in the L2-MCK and L0-MCK compared with control mice. In summary, these studies suggest that muscle LPL is particularly potent with regard to VLDL metabolism and is sufficient to compensate for the lack of LPL in other tissues with regard to lipolyzing VLDL particles. With regard to HDL, muscle LPL expression does not result in normal levels due to enhanced breakdown either by mediating accelerated HDL clearance or by failing to establish normal HDL particles that are then cleared more quickly than normal. These studies provide new insights on the tissue-specific effects of LPL on lipoprotein metabolism.

The mechanism of apolipoprotein (apo) CIII-induced hypertriglyceridemia remains uncertain. We crossed apoCIII transgenic and apoE gene knockout (apoE0) mice, and observed severe hypertriglyceridemia with plasma triglyceride levels of 4,521+/-6, 394 mg/dl vs. 423+/-106 mg/dl in apoE0 mice, P < 0.00001 for log(triglycerides [TG]). Cholesterols were 1,181+/-487 mg/dl vs. 658+/-151 mg/dl, P < 0.0001. Lipoprotein fractionation showed a marked increase in triglyceride-enriched chylomicrons+VLDL. This increase was limited to the lowest density (chylomicrons and Sf 100-400) subfractions. Intermediate density lipoproteins (IDL)+LDL increased moderately, and HDL decreased. There was no significant increase in triglyceride production in apoCIII transgenic/apoE0 mice. The clearance of VLDL triglycerides, however, was significantly decreased. Lipoprotein lipase in postheparin plasma was elevated, but activation studies suggested LPL inhibition by both apoCIII transgenic and apoCIII transgenic/apoE0 plasma. ApoCIII overexpression also produced a marked decrease in VLDL glycosaminoglycan binding which was independent of apoE. The predominant mechanism of apoCIII-induced hypertriglyceridemia appears to be decreased lipolysis at the cell surface. The altered lipoprotein profile that was produced also allowed us to address the question of the direct atherogenicity of chylomicrons and large VLDL. Quantitative arteriosclerosis studies showed identical results in both apoCIII transgenic/apoE0 and apoE0 mice, supporting the view that very large triglyceride-enriched particles are not directly atherogenic.

Background It is known that many house staff physicians are unable to demonstrate perfect metered dose inhaler (MDI) technique. Objective This study assessed whether a single teaching session for house staff physicians would significantly improve their MDI technique. Methods Thirty-eight pediatric house staff physicians were asked to demonstrate MDI technique with a placebo MDI. The physicians were evaluated on the follow-up seven steps: (1) shaking the MDI and removing the cap, (2) exhaling prior to MDI use, (3) holding the MDI upright, (4) proper timing of actuation, (5) a slow inspiratory effort, (6) one MDI actuation per breath, and (7) holding the breath ≥5 seconds. A 20-minute teaching session and demonstration of proper MDI technique was then given. At the end of this session all residents were eventually able to demonstrate proper technique. Two months following this educational session the same house staff physicians were reevaluated on their MDI technique. Results Initially, 10 participants (26%) demonstrated perfect technique. Two months postinstruction the same number of physicians (10) demonstrated perfect technique. Only 6 physicians demonstrated perfect technique at both evaluations. Three of the seven steps showed enough change from the first evaluation to the second to permit statistical analysis. Step 4 (timing of actuation) had 11 physicians' performances improve while 3 worsened (P = .03). Step 5 (a slow inspiratory effort) had 9 physicians' performances improve while 3 worsened (P = .073). For step 7 (holding the breath ≥ 5 seconds), 11 physicians improved while 2 worsened (P = .006). Comparing global performance, there were 17 physicians that improved, 8 that worsened, and 13 with no change (P = .054). Conclusions This study confirmed that many house staff physicians do not demonstrate optimal MDI technique. While one educational session may somewhat improve their future performance, it is not sufficient to guarantee perfect technique. This suggests that repeated education needs to be given to house staff physicians.

Lipoprotein lipase (LPL)-deficient mice have been created by gene targeting in embryonic stem cells. At birth, homozygous knockout pups have threefold higher triglycerides and sevenfold higher VLDL cholesterol levels than controls. When permitted to suckle, LPL-deficient mice become pale, then cyanotic, and finally die at approximately 18 h of age. Before death, triglyceride levels are severely elevated (15,087 +/- 3,805 vs 188 +/- 71 mg/dl in controls). Capillaries in tissues of homozygous knockout mice are engorged with chylomicrons. This is especially significant in the lung where marginated chylomicrons prevent red cell contact with the endothelium, a phenomenon which is presumably the cause of cyanosis and death in these mice. Homozygous knockout mice also have diminished adipose tissue stores as well as decreased intracellular fat droplets. By crossbreeding with transgenic mice expressing human LPL driven by a muscle-specific promoter, mouse lines were generated that express LPL exclusively in muscle but not in any other tissue. This tissue-specific LPL expression rescued the LPL knockout mice and normalized their lipoprotein pattern. This supports the contention that hypertriglyceridemia caused the death of these mice and that LPL expression in a single tissue was sufficient for rescue. Heterozygous LPL knockout mice survive to adulthood and have mild hypertriglyceridemia, with 1.5-2-fold elevated triglyceride levels compared with controls in both the fed and fasted states on chow, Western-type, or 10% sucrose diets. In vivo turnover studies revealed that heterozygous knockout mice had impaired VLDL clearance (fractional catabolic rate) but no increase in transport rate. In summary, total LPL deficiency in the mouse prevents triglyceride removal from plasma, causing death in the neonatal period, and expression of LPL in a single tissue alleviates this problem. Furthermore, half-normal levels of LPL cause a decrease in VLDL fractional catabolic rate and mild hypertriglyceridemia, implying that partial LPL deficiency has physiological consequences.

All-trans-retinoic acid (RA) activates ligand-dependent transcription factors that regulate retinoid-responsive gene expression. It is assumed that all-trans-RA is formed within cells through in situ oxidation of retinol derived from the circulation. However, the circulation contains low levels of all-trans-RA (approximately 0.2-0.7% of that of plasma retinol). Our studies investigated the extent to which plasma all-trans-RA contributes to tissue pools of this retinoid and explored factors responsible for regulating its uptake by tissues and cells. Rats were continuously infused, to steady state, with all-trans-[3H]RA. From measures of specific activities of all-trans-[3H]RA at steady state, we determined that the preponderance of all-trans-RA in brain and liver was derived from the circulation. For six other tissues, approximately 10-30% of the retinoid was derived from the circulation, but pancreas and testis derived very little from the circulating pool. In other studies, we showed that retinoid nutritional status influences clearance of a bolus dose of all-trans-RA and that neither the rate of cellular all-trans-RA uptake nor its intracellular half-life is influenced by cellular lipid levels. Taken together, our data indicate that plasma all-trans-RA contributes to tissue pools of this retinoid and that specific and physiologically responsive cellular processes mediate its uptake.

We attempted to ascertain the effects of polyunsaturated fatty acids by conducting two studies in normal young men, in which monounsaturated fats were replaced by polyunsaturated fats within the guidelines of the American Heart Association step 1 diet. Study A employed a randomized parallel design in which subjects first consumed an average American diet (AAD) containing 37% of calories as fat (saturated fat, 16% calories; monounsaturated fat, 14% calories; and polyunsaturated fat, 7% calories). After 3 weeks, one third of the subjects continued with the AAD, one third switched to a step 1 diet in which total fat calories were reduced to 30% by replacing saturated fat with carbohydrate, and one third switched to a polyunsaturated fat-enriched (Poly) diet with the same 30% fat calories and a reduction of monounsaturated fat from 14% to 8% and an increase of polyunsaturated fat from 7% to 13% of calories. The randomized period lasted 6 weeks. Total and low-density lipoprotein (LDL) cholesterol levels on the step 1 and Poly diets were reduced compared with levels on the AAD (P < .001). Total and LDL cholesterol did not differ between the step 1 and Poly diets, although comparison between the two diets is limited by the small study groups. Serum apolipoprotein (apo) B levels fell on the Poly diet compared with the AAD. Total high-density lipoprotein (HDL), HDL2, and HDL3 cholesterol levels were not significantly affected by the diets. Postprandial lipid and lipoprotein concentrations did not significantly differ either. In study B, a randomized crossover design was used in which all subjects ate the step 1 and Poly diets for 5 weeks each with a 4-day break between diets. In the eight subjects studied, the values for fasting plasma total, LDL, and HDL cholesterol; triglycerides; apoB; and apoA-I were essentially identical at the end of each diet period. Postprandial triglyceride areas obtained after ingestion of a large, standard fat load were also the same. Finally, LDL apoB and HDL apoA-I turnovers were unaffected by replacement of monounsaturates with polyunsaturates. In summary our results indicate that modest exchanges of monounsaturated for polyunsaturated fats do not significantly affect LDL or HDL levels or metabolism, which supports the view that reducing saturated fats is the key to lowering total and LDL cholesterol.

We have generated transgenic mice expressing the human apolipoprotein CII (apoCII) gene under the transcriptional control of the human cytochrome P-450 IA1 (CYPIA1) promoter. Human apoCII transgenic (HuCIITg) mice exhibited significant basal expression of the transgene (plasma apoCII level = 26.1 +/- 4 mg/dl) and showed further induction of transgene expression after treatment with beta-naphthoflavone. Unexpectedly, HuCIITg mice were hypertriglyceridemic and human apoCII levels correlated strongly to triglyceride levels (R = 0.89, P < 0.0001). Triglyceride levels (mg/dl +/- SEM) were elevated compared to controls in both the fed (804 +/- 113 vs 146 +/- 18, P < 0.001) and fasted (273 +/- 39 vs 61 +/- 4, P < 0.001) states. HuCIITg mice accumulated triglyceride-rich very low density lipoproteins (VLDL) with an increased apoC/apoE ratio. Tracer kinetic studies indicated delayed clearance of VLDL-triglyceride, and studies using Triton inhibition of VLDL clearance showed no increase in VLDL production. Plasma from these mice activated mouse lipoprotein lipase normally and radiolabeled VLDL were normally hydrolyzed. However, HuCIITg VLDL showed markedly decreased binding to heparin-Sepharose, suggesting that apoCII-rich, apoE-poor lipoprotein may be less accessible to cell surface lipases or receptors within their glycosaminoglycan matrices. HuCIITg mice are a promising model of hypertriglyceridemia that suggests a more complex role for apoCII in the metabolism of plasma triglycerides.

Two transgenic mouse lines, expressing low or high amounts of human apo A-IV were created. In low and high expressor HuAIVTg mice on a chow diet, serum human apo A-IV levels were 6 and 25 times the normal human level and on a high fat diet, they were 12 and 77 times higher. Human apo A-IV was equally distributed between lipoprotein (mainly HDL) and lipid-free fractions. Intestinal absorption of radiolabeled cholesterol and triglycerides was unaffected in HuAIVTg mice. Vitamin A, carried exclusively in chylomicrons and their remnants, was catabolized normally. When an intragastric vitamin E bolus is given to the HuAIVTg mice, the initial absorption and appearance in triglyceride-rich lipoproteins was similar to that observed in normal mice. However, elevated amounts of vitamin E were subsequently observed in the VLDL of the HuAIVTg mice. Furthermore, in the fed state, serum VLDL triglycerides were markedly elevated in HuAIVTg mice. This effect was greater in high expressor mice. Serum total cholesterol was not elevated, but the distribution was altered in the HuAIVTg mice; VLDL-C was increased at the expense of VLDL-C. Kinetic studies suggested a delayed clearance of VLDL in HuAIVTg mice. Apo A-IV has been suggested to be a satiety factor, but no effect on feeding behavior or weight gain was observed in these HuAIVTg mice. In summary, our studies with HuAIVTg mice show that additional apo A-IV does not effect intestinal absorption of fat and fat-soluble vitamins, and at least chronic elevation of plasma apo A-IV does not effect feeding behavior in this model system.

Reduced plasma levels of high density lipoprotein (HDL) cholesterol are associated with increased risk for coronary heart disease. Although plasma HDL levels are, in general, inversely related to plasma triglyceride (TG) concentrations, a small proportion of individuals with low HDL cholesterol concentrations have normal plasma TG levels. We wished to determine whether subjects with low plasma levels of HDL cholesterol could be characterized by common abnormalities of lipoprotein metabolism independent of plasma TGs. Therefore, we studied the metabolism of low density lipoprotein (LDL) apolipoprotein B (apo B) and HDL apolipoprotein A-I (apo A-I) in subjects with low plasma HDL cholesterol concentrations with or without hypertriglyceridemia. Nine subjects with low plasma HDL cholesterol levels and normal levels of plasma TGs and LDL cholesterol were studied. Autologous 131I-LDL and 125I-HDL were injected intravenously, and blood samples were collected for 2 weeks. LDL apo B and HDL apo A-I levels were measured by specific radioimmunoassays. Fractional catabolic rates (FCRs, pools per day) and production rates (PRs, milligrams/kilogram · day) for each apolipoprotein were determined. The results were compared with those obtained previously in nine subjects with low plasma HDL cholesterol levels and hypertriglyceridemia and in seven normal subjects. The normal subjects had an HDL apo A-I FCR (mean±SD) of 0.21±0.04. Despite large differences in plasma TG levels, the HDL apo A-I FCRs were similar in the low-HDL, normal-TG group (0.30±0.09) and the low-HDL, high-TG group (0.033±0.10), although only the latter value was significantly increased versus control subjects (p

Hypertriglyceridemia is common in the general population, but its mechanism is largely unknown. In previous work human apo CIII transgenic (HuCIIITg) mice were found to have elevated triglyceride levels. In this report, the mechanism for the hypertriglyceridemia was studied. Two different HuCIIITg mouse lines were used: a low expressor line with serum triglycerides of approximately 280 mg/dl, and a high expressor line with serum triglycerides of approximately 1,000 mg/dl. Elevated triglycerides were mainly in VLDL. VLDL particles were 1.5 times more triglyceride-rich in high expressor mice than in controls. The total amount of apo CIII (human and mouse) per VLDL particle was 2 and 2.5 times the normal amount in low and high expressors, respectively. Mouse apo E was decreased by 35 and 77% in low and high expressor mice, respectively. Under electron microscopy, VLDL particles from low and high expressor mice were found to have a larger mean diameter, 55.2 +/- 16.6 and 58.2 +/- 17.8 nm, respectively, compared with 51.0 +/- 13.4 nm from control mice. In in vivo studies, radiolabeled VLDL fractional catabolic rate (FCR) was reduced in low and high expressor mice to 2.58 and 0.77 pools/h, respectively, compared with 7.67 pools/h in controls, with no significant differences in the VLDL production rates. In an attempt to explain the reduced VLDL FCR in transgenic mice, tissue lipoprotein lipase (LPL) activity was determined in control and high expressor mice and no differences were observed. Also, VLDLs obtained from control and high expressor mice were found to be equally good substrates for purified LPL. Thus excess apo CIII in HuCIIITg mice does not cause reduced VLDL FCR by suppressing the amount of extractable LPL in tissues or making HuCIIITg VLDL a bad substrate for LPL. Tissue uptake of VLDL was studied in hepatoma cell cultures, and VLDL from transgenic mice was found to be taken up much more slowly than control VLDL (P < 0.0001), indicating that HuCIIITg VLDL is not well recognized by lipoprotein receptors. Additional in vivo studies with Triton-treated mice showed increased VLDL triglyceride, but not apo B, production in the HuCIIITg mice compared with controls. Tissue culture studies with primary hepatocytes showed a modest increase in triglyceride, but not apo B or total protein, secretion in high expressor mice compared with controls. In summary, hypertriglyceridemia in HuCIIITg mice appears to result primarily from decreased tissue uptake of triglyceride-rich particles from the circulation, which is most likely due to increased apo CIII and decreased apo E on VLDL particles. the HuCIIITg mouse appears to be a suitable animal model of primary familial hypertriglyceridemia, and these studies suggest a possible mechanism for this common lipoprotein disorder.

Low plasma levels of high-density lipoprotein (HDL) and apolipoprotein (apo) A-I often accompany human hypertriglyceridemia. In an animal model of hypertriglyceridemia, the lipoprotein lipase (LPL)-inhibited cynomolgus monkey, we reported that plasma levels of apo A-I were decreased and the fractional catabolic rate (FCR) of HDL apo was increased. To explore whether hypertriglyceridemia alone would alter plasma apo A-I levels and catabolism, hypertriglyceridemia was produced by intravenous (IV) infusion of 20% Intralipid into female cynomolgus monkeys. Baseline plasma triglyceride (TG) levels averaged 106 mg/dL. With infusion of 200 mg/kg/h intralipid TG, plasma TG levels peaked at 967 mg/dL (range, 413 to 1,069; n = 6). More prolonged or more severe hypertriglyceridemia caused serious complications in several monkeys. Despite the severe hypertriglyceridemia, HDL TG content, HDL apoproteins, and plasma apo A-I levels did not markedly change, suggesting that very little HDL remodeling had occurred. Kinetic studies of HDL protein and apo A-I were performed in four pairs of monkeys. The two tracers were removed from the plasma at identical rates. In five pairs of animals, apo A-I turnover during control and intralipid-induced hypertriglyceridemia was not significantly different. We hypothesize that apo A-I FCR is a function of HDL composition. Because Intralipid infusion did not alter HDL composition to the same degree as did LPL inhibition, its effects on HDL apo catabolism were not apparent.

We have previously reported decreased production rates of the major apolipoprotein B (apoB)-containing lipoproteins, very-low-density lipoproteins (VLDL), and low-density lipoproteins (LDL) in patients with combined hyperlipidemia (CHL) during treatment with lovastatin. In the present study, we determined the effects of lovastatin therapy on VLDL triglyceride (TG) metabolism. Plasma VLDL turnover was determined in six CHL patients, before and during lovastatin therapy. 3H-triglyceride-glycerol-specific activity data derived from injection of 3H-glycerol were analyzed by compartmental modeling. The effects of lovastatin on VLDL TG metabolism were compared with those previously determined on VLDL apoB metabolism in these subjects. Lovastatin therapy was associated with decreased concentrations of VLDL TG in five of six patients and decreased VLDL apoB concentrations in all six. VLDL TG production rates (PR) decreased in five patients, with the mean for the group decreasing from 14.1 ± 7.1 to 10.3 ± 4.0 mg/kg/h (P < .05). VLDL apoB PR also decreased in five patients, with the mean decreasing from 21.8 ± 20.3 to 12.2 ± 9.0 mg/kg/d (P = .11). Changes in VLDL TG concentrations during lovastatin treatment were correlated with changes in VLDL apoB concentrations (r = .74, P = .09) and in VLDL TG PR (r = .91, P = .01). Changes in VLDL TG PR were also related to changes in VLDL apoB PR (r = .62, P = NS). There were no consistent changes in the fractional catabolic rates of either VLDL TG or VLDL apoB during lovastatin therapy. These findings suggest that, in CHL patients, reductions in VLDL TG concentrations during lovastatin therapy are usually associated with decreased VLDL TG PR, and these effects parallel concomitant reductions in VLDL apoB PR. Taken together with our previous finding of reduced total apoB secretion into plasma during lovastatin treatment, these results support the hypothesis that the overall hypolipidemic effects of lovastatin in patients with CHL are due to decreased assembly and secretion of apoB-containing lipoproteins.

This study was undertaken to determine potential tissue sources of plasma cholesteryl ester transfer protein (CETP), and to assess the influence of CETP on lipoprotein concentrations and atherosclerosis. In a group of 28 cynomolgus monkeys fed high fat, high cholesterol diets, plasma CETP concentration was strongly correlated with the abundance of CETP mRNA in liver and in adipose tissue, and with the output of CETP in liver perfusates. Plasma CETP concentration showed a strong inverse correlation with HDL cholesterol concentrations (r = -0.62, P less than 0.001) and a positive correlation with LDL cholesterol concentration (r = 0.54, P less than 0.005) and molecular weight (r = 0.57, P less than 0.001). The extent of coronary artery atherosclerosis was positively correlated with LDL cholesterol concentration and molecular weight, and with plasma CETP concentration. Thus, in monkeys fed an atherogenic diet, individual variation in CETP mRNA abundance in liver and adipose tissue probably plays a major role in the determination of plasma CETP levels. In plasma, CETP influences the distribution of cholesteryl esters between LDL and HDL, and CETP concentration appears to be a key determinant of the relative atherogenicity of the plasma lipoproteins.

The design of diets to achieve optimal changes in plasma lipid levels is controversial. In a randomized, double-blind trial involving 36 healthy young men, we evaluated the effects on plasma lipid levels of both an American Heart Association Step 1 diet (in which 30 percent of the total calories were consumed as fat: 10 percent saturated, 10 percent monounsaturated, and 10 percent polyunsaturated fats, with 250 mg of cholesterol per day) and a monounsaturated fat-enriched Step 1 diet (with 38 percent of the calories consumed as fat: 10 percent saturated, 18 percent monounsaturated, and 10 percent polyunsaturated fats, with 250 mg of cholesterol per day). The effects of these diets were then compared with those of an average American diet, in which 38 percent of the total calories were consumed as fat: 18 percent saturated, 10 percent monounsaturated, and 10 percent polyunsaturated fats, with 500 mg of cholesterol per day. The men consumed the average American diet for 10 weeks before random assignment to one of the two Step 1 diets or to continuation of the average diet for an additional 10 weeks. Caloric intake was adjusted to maintain a constant body weight. As compared with the mean (+/- SD) change in the plasma total cholesterol level in the group that followed the average American diet throughout the study (-0.05 +/- 0.36 mmol per liter), there were statistically significant reductions (P less than 0.025) in the plasma total cholesterol level in the group on the Step 1 diet (-0.37 +/- 0.27 mmol per liter) and in the group on the monounsaturated fat-enriched Step 1 diet (-0.46 +/- 0.36 mmol per liter). There were parallel reductions in the plasma low-density lipoprotein cholesterol levels in these two groups. Neither the plasma triglyceride levels nor the high-density lipoprotein cholesterol concentrations changed significantly with any diet. We conclude that enrichment of the Step 1 diet with monounsaturated fat does not alter the beneficial effects of the Step 1 diet on plasma lipid concentrations.

Berman and Schoenfeld used matrix transformations to study unidentifiable pool models. It is possible to use the method to examine if two models are output-indistinguishable, that is, if given the nature of tracer injections and observations, the two models have the same responses. The method is applied to two three-pool models for whole-body cholesterol metabolism. The indistinguishabilily of a mammillary model from a catenary model is proved using matrix transformations. The method is used in two ways, directly as well as after simplifying the problem. The two ways, as well as an analysis of the converse, help to show how the method is to be applied as well as the strengths and weaknesses of the method.