Age-related changes in cardiovascular disease risk factors of hypercholesterolemic children

OBJECTIVE

To describe the age-related changes in cardiovascular disease risk factors in young, hypercholesterolemic (HC) children.

METHODS

Hypercholesterolemic (n = 227) and nonhypercholesterolemic (NHC) (n = 80) children between the ages of 4 and 10 years were identified. Height, weight, skin-fold and blood pressure measurements, and total cholesterol levels were measured. The HC group also had insulin levels evaluated. The groups were compared by analysis of variance. Simple Spearman correlations evaluated the associations between factors within each group.

RESULTS

The HC and NHC groups had similar mean ages, heights, and weights, both contained 51% girls, and all were white subjects. Percent weight-for-height median, and biceps, triceps, suprailiac and subscapular skin-fold measurements were all larger for the HC group. A significant age interaction demonstrated that the HC group's larger suprailiac and sum of skin-fold measures were expressed in the 8.0- to 9.9-year-old children, but not the 4.0- to 5.9-year-olds. For both groups, systolic blood pressure was associated with the measures of adiposity. For the HC group, insulin levels were also associated with adiposity.

CONCLUSIONS

These results suggest that: (1) children with HC have greater body fat, (2) the expression of the hypercholesterolemia precedes the expression of increased body fat, (3) body fat increases with age, and (4) altered insulin and blood pressure levels are expressed in association with the increased body fat in children with HC. Confirmation with longitudinal data is necessary.

One-year follow-up of nutrition education for hypercholesterolemic children

OBJECTIVES

This study evaluated retention of the effect of a home-based, practitioner-initiated nutrition education model.

METHODS

Children with elevated low-density lipoprotein (LDL) cholesterol levels were randomly assigned to one of two nutrition interventions or to an at-risk control group. Intervention effects were evaluated 3, 6, and 12 months postbaseline.

RESULTS

The parent-child autotutorial group demonstrated significant increases in knowledge and, along with the counseling group, decreases in total and saturated fat intake. Also, the autotutorial and counseling groups retained a majority of their initial LDL cholesterol decrease.

CONCLUSIONS

Knowledge of heart-healthful eating and dietary fat intake as well as dietary change can be affected and retained via home-based, practitioner-initiated nutrition interventions with hypercholesterolemic children, although some form of ongoing intervention may be necessary to produce lasting decreases in LDL cholesterol levels.

Effects of family history of heart disease, apolipoprotein E phenotype, and lipoprotein(a) on the response of children's plasma lipids to change in dietary lipids

We examined the effects of family history of coronary artery disease (CAD), apolipoprotein E (apo E) phenotype, and lipoprotein(a) [Lp(a)] on the response of plasma lipids to change in dietary lipid intake after 3 mo of nutrition education in 125 children aged 4-10 y. The subjects were healthy children with elevated low-density-lipoprotein (LDL)-cholesterol concentrations who participated in the Children's Health Project, a nutrition-education program designed to lower plasma cholesterol by means of dietary modifications in accordance with recommendations of the National Cholesterol Education Program. Dietary and plasma lipids were measured by three 24-h recalls and assessments of two fasting plasma samples collected before and 3 mo after the start of intervention. Family history of CAD was determined by questionnaires administered to parents at baseline. Apo E phenotyping was done with isoelectric focusing followed by immunostaining; Lp(a) was measured with two-site immunoradiometric assays of frozen aliquots of plasma samples collected at baseline and 3 mo. After adjustment for intervention group, age, sex, and body mass index, analysis of covariance showed that baseline plasma lipid concentrations were the strongest independent predictors of change in plasma lipids after 3 mo. Plasma total and LDL-cholesterol concentrations in children with less family history of CAD were significantly more responsive to change in dietary cholesterol than concentrations in children with a stronger family history of CAD. Neither apo E phenotype nor Lp(a) significantly influenced change in plasma lipids independently or interactively with change in dietary lipids.

Kinetics of retinyl esters during postprandial lipemia in man: a compartmental model

Orally ingested vitamin A (retinol) is incorporated into intestinal chylomicrons (CHYLO) in the form of retinyl esters (RE) along with newly absorbed dietary triglycerides (TG). As the intestinal lipoproteins undergo hydrolysis in the circulation, the majority of the RE remain with the secreted intestinal particles and have been used as a marker for intestinally derived lipoproteins during the early phase of the postprandial state. A multicompartmental model was developed for the kinetics of RE during postprandial lipemia in individuals with normal lipid levels (n = 16) and in patients with hyperlipidemia (n = 44). The assumptions used in the development of the model are presented in this report. Some of the key findings include (1) as much as 50% of the newly synthesized RE may be secreted by the intestine as very-low-density lipoprotein (VLDL)-sized particles of S(f) 20 to 400 following consumption of a test meal containing a moderate amount of fat (20 to 30 g); (2) in most individuals, approximately 50% of the RE secreted in S(f) greater than 400 are converted to smaller, less buoyant fractions, and 50% are irreversibly removed directly from the plasma; (3) as much as 5% to 20% of the ingested retinol may be secreted as small intestinal lipoproteins with the buoyance of low-density lipoprotein (LDL) in some individuals; and (4) less than 5% of RE flux through S(f) 20 to 400 is converted to S(f) less than 20, and the primary catabolic pathway for RE in this fraction is direct uptake. Comparable estimates can be obtained for the kinetic parameters when repeat studies are made in the same subjects under comparable conditions.

The influence of age and relative weight on the presentation of familial combined hyperlipidemia in childhood

BACKGROUND

Familial combined hyperlipidemia (FCHL) has been described as the leading cause of familial hyperlipidemia. FCHL is dominantly inherited, occurs in at least 1% of the population, and is responsible for about 10% of premature coronary artery disease (CAD).

OBJECTIVE

Because FCHL in childhood is not well characterized, we evaluated the interrelationships among age, percentage of ideal body weight (%IBW) and plasma lipoprotein levels in FCHL children (age 2-18 years), exploring the possibility that obesity and age may influence the presentation of FCHL in childhood.

METHODS

One hundred and eighty-nine children with FCHL were studied. Significant correlations within this group were further evaluated by examining a subset of 36 FCHL children, each of whom had an unaffected sibling who could serve as a control for comparison.

RESULTS

When the full group was divided into those with TG levels > 90% and those with TG levels < 90%, the correlation with %IBW was stronger in the former (r = 0.45, P < 0.005) as compared with the latter (r = 0.25, P = 0.05). Within the subset of 36 FCHL children and their 36 unaffected siblings (controls), age and sex distributions were similar. Percentage IBW (mean +/- S.D.) (117.3 +/- 29.1 for FCHL and 111.2 +/- 19.4 for controls) was similar and in the overweight range. FCHL children had significantly higher levels of total cholesterol (TC), low density lipoprotein cholesterol (LDL-C), apolipoprotein B (apo B) and triglyceride (TG) levels compared with controls (P < 0.0005 for all comparisons). Of several significant correlations observed in the full group (n = 189), only the correlations of %IBW with plasma TG levels (r = 0.45, P = 0.006), and of age with plasma TG levels (r = 0.48, P = 0.003) persisted with a similar degree of magnitude in the subset of 36 FCHL children. No correlation was significant in the controls. By Fisher's Z-test, the correlation between %IBW and TG in the FCHL children was significantly different from controls.

CONCLUSIONS

These results suggest that TG levels in FCHL children, but not in their unaffected siblings, and sensitive to the presence of obesity, implying an interaction between obesity and the underlying condition, in addition, the association between age and TG level in FCHL children suggests a gradual expression of the hyperlipidermia (i.e. TG) during childhood.

A 5' splice-region mutation and a dinucleotide deletion in the lysosomal acid lipase gene in two patients with cholesteryl ester storage disease

Cholesteryl ester storage disease (CESD) results from inherited deficiencies of the lysosomal hydrolase, acid lipase (LAL; E.C. 3.1.1.13). To establish the molecular defects in LAL deficiency, two unrelated probands with severely reduced LAL activity were examined. DNA amplification by reverse-transcription polymerase chain reaction and subsequent sequence analysis of LAL cDNA identified two mutant alleles. Patient 1, presenting with hepatosplenomegaly, mildly elevated liver function tests, and hyperlipidemia, was homozygous for a deletion of nucleotides 823 to 894 of the LAL cDNA. This 72-bp deletion maintained the reading frame and resulted in a loss of 24 amino acids from the LAL protein. Analysis of genomic DNA revealed that the 72 bp corresponded to an exon of the LAL gene. A single G to A point mutation at the last exon position was observed in the genomic DNA of patient 1, indicating a splicing defect with consecutive exon skipping underlying the 72-bp deletion. Patient 2 was a compound heterozygote for the 72-bp deletion and a dinucleotide deletion at positions 967 and 968. This deletion resulted in a shifted reading frame carboxyterminal of codon 296, and 43 random amino acids followed the frame shift. A premature stop at codon 339 truncated the mutant LAL protein by 34 amino acids. Allele-specific hybridization confirmed that patient 1 was homozygous for the 72-bp deletion mutation, and that patient 2 was a compound heterozygote for the 72-bp deletion and the 2-bp deletion.

Reduction of elevated LDL-cholesterol levels of 4- to 10-year-old children through home-based dietary education

OBJECTIVE

To assess the effects of a home-based, parent-child autotutorial (PCAT) dietary education program on the dietary knowledge, lipid consumption, and plasma low density lipoprotein-cholesterol (LDL-C) of 4- to 10-year-old children with elevated plasma LDL-C.

METHODS

"At-risk" children (screening total cholesterol, (TC), exceeded 4.55 mmol/L and average LDL-C from two fasting samples was between 2.77 and 4.24 mmol/L for boys or 2.90 and 4.24 mmol/L for girls) were randomized to the PCAT program (N = 88), for dietary counseling with a registered dietitian (N = 86), or to an at-risk control group (N = 87). Dietary knowledge, diet, and LDL-C of these groups were assessed at baseline and after the educational period (3-month follow-up). The knowledge and diet of a not-at-risk (TC below 4.22 and 4.34 mmol/L for boys and girls, respectively) control group (N = 81) was also assessed and compared with that of the at-risk control group.

RESULTS

At the 3-month follow-up, the PCAT children's knowledge scores had increased three times more than those of the counseling and at-risk control groups (P < .001). Mean grams of total and saturated fat consumed by PCAT and counseling groups declined while that of the at-risk control group increased slightly; these differences were significant (P < .05). The mean LDL-C decline of the PCAT group was significantly different (P < .05) from the decline of the at-risk control group (0.26 vs 0.09 mmol/L), and approached significance (P = .07) when compared with that of the counseling group (0.26 vs 0.11 mmol/L). The at-risk control group's knowledge and diet did not differ from that of the not-at-risk group.

CONCLUSION

The PCAT program offers a mechanism for providing effective dietary education to children with elevated cholesterol and to their families.

Familial combined hyperlipidemia in children: clinical expression, metabolic defects, and management

The first evidence that elevation of plasma levels of cholesterol is a risk factor for the development of atherosclerosis in children came from the Bogalusa Heart Study in 1986, which reported an association between aortic fatty streaks in 3- to 26-year-old subjects and increased plasma levels of low-density lipoprotein cholesterol (LDL-C). The most compelling evidence of a cause-and-effect relationship has come from the multicenter cooperative study called the Pathobiological Determinants of Atherosclerosis in Youth. When the investigators examined the abdominal aorta and the right coronary artery of adolescents and young adults who had died of trauma, they found a significant relationship between the sum of the very low density lipoprotein (VLDL) plus LDL-C level and both fatty streaks and raised atherosclerotic lesions. They also found an inverse relationship between those lesions and increased high-density lipoprotein cholesterol (HDL-C) levels. In addition, their studies showed that smoking (as assessed by the serum thiocyanate level) promotes atherogenesis in children as young as age 15 years. Thus many pediatricians have now accepted the importance of identifying children with significant hypercholesterolemia so that appropriate dietary and life-style modifications can be recommended. This is especially important because there is often a major genetic component to the hyperlipidemia seen in children.

Familial combined hyperlipidemia in children: clinical expression, metabolic defects, and management

Familial combined hyperlipidemia (FCHL) is a dominantly inherited hyperlipidemia that occurs in at least 1% of the adult population and is responsible for 10% of premature coronary artery disease. In families referred for evaluation because of primary hyperlipidemia in a child, FCHL is expressed three times more commonly than familial hypercholesterolemia and half of the siblings are affected. Several metabolic defects apparently are associated with the FCHL phenotype. Most commonly, excess production of very low density lipoprotein apolipoprotein B can be demonstrated. In other families, reduced lipoprotein lipase activity is associated. One allele at a locus influencing apolipoprotein B levels predicts FCHL in a large proportion of families ascertained through affected children. Whether this allele is responsible for the excess of very low density lipoprotein apolipoprotein B detected in metabolic studies has not been elucidated. Management of FCHL in children begins with dietary modification. A bile acid sequestrant may be considered as well if diet cannot reduce the plasma low-density lipoprotein cholesterol level to less than 4.13 mmol/L (160 mg/dl) after the age of 10 years. Although the hydroxymethylglutaryl-coenzyme A reductase inhibitors are not currently recommended for children younger than 19 years of age, we speculate that they will be increasingly utilized for the management of FCHL in teenage boys who continue to have low density lipoprotein cholesterol levels greater than 4.13 mmol/L (160 mg/dl) after dietary modification.

Use of cholestyramine in the treatment of children with familial combined hyperlipidemia

We studied the effectiveness of and compliance with the use of cholestyramine in children with heterozygous familial hypercholesterolemia (FH) and familial combined hyperlipidemia (FCHL). During a 10-year period, 673 children (aged 10.5 +/- 4.0 years) were referred for evaluation of hyperlipidemia, of whom 87 (36 with FH; 51 with FCHL) were treated with cholestyramine (8 to 24 gm/day). In both groups, total cholesterol, low-density lipoprotein (LDL)-cholesterol, and apolipoprotein B levels were significantly reduced after cholestyramine use. In those with FH, plasma LDL-cholesterol levels decreased from 258 +/- 35 mg/dl (6.67 +/- 0.90 mmol/L) to 190 +/- 31 mg/dl (4.91 +/- 0.80 mmol/L); in those with FCHL, LDL-cholesterol levels dropped from 207 +/- 40 mg/dl (5.35 +/- 1.03 mmol/L) to 141 +/- 35 mg/dl (3.64 +/- 0.90 mmol/L). High-density lipoprotein-cholesterol levels were not significantly changed after cholestyramine use in either group. In the FCHL group, plasma triglyceride levels increased significantly from 81 +/- 35 mg/dl (0.92 +/- 0.40 mmol/L) to 134 +/- 42 mg/dl (1.52 +/- 0.48 mmol/L). Seven patients were lost to follow-up; 18 discontinued the medication within 1 month. Of the remaining 62 children, 59 had a good response to the drug. Of the 62 patients, 52 discontinued the medication after 21.9 +/- 10 months. Adverse effects included foul taste (73%), nausea with bloating (18%), and constipation. Cholestyramine is effective in reducing LDL-cholesterol levels in children with inherited hyperlipidemia, but the majority of children will not comply with its long-term use.

A quality assurance program for the measurement of capillary blood cholesterol levels in private pediatric practices. The Children's Health Project

OBJECTIVE

To develop an easy to use quality assurance program for the measurement of capillary blood cholesterol levels in private pediatric practices. The program needed to comply with the guidelines laid down by the National Cholesterol Education Program.

DESIGN

Intervention study.

SETTING

Nine private pediatric practices in and around northern Philadelphia, Pa.

PARTICIPANTS

The analysts included clinic staff members with laboratory expertise ranging from none to some previous experience. None of the participants had previous experience with a quality assurance program.

INTERVENTIONS

Progress was reported monthly to the Lipid Research Laboratory, Philadelphia, and action was taken to correct inaccuracies in bias or variance.

MAIN OUTCOME MEASURE

Compliance with the analytical guidelines laid down by the National Cholesterol Education Program in that the coefficient of variation was no greater than 5% and the bias was no greater than +/- 5% in the first year of the study.

RESULTS

Within the first year of the study, there were 152 monthly quality assurance returns for each of two lyophilized control materials. On four occasions the coefficient of variation was greater than 5% while the overall bias was within the desired +/- 5% on 143 (94%) of 152 occasions. After the first 3 months of the study, as user confidence increased, intervention by the Lipid Research Laboratory became minimal. The internal quality assurance was further evaluated by a successful performance in a quarterly external quality assurance program.

CONCLUSIONS

It is possible to devise an easy to use quality assurance program for extra laboratory measurement of cholesterol levels in children, and, with minimal assistance, maintain acceptable standards of cholesterol analysis. The quality assurance improved following the first 3 months of training and education. Subsequent continuous quality improvement was maintained with minimal involvement of the specialist center. Should the controversial issue of private office measurement of blood cholesterol levels become universally acceptable, the implication from our study is that standards acceptable to the National Cholesterol Education Program and the Clinical Laboratory Improvement Amendments of 1988 are possible using a suitable quality assurance program.

Genotype at a major locus with large effects on apolipoprotein B levels predicts familial combined hyperlipidemia

A sample enriched for familial combined hyperlipidemia (FCHL) was examined for evidence of an association between genotype at an apolipoprotein B (apoB) elevating locus defined by complex segregation analysis and FCHL. Complex segregation analysis detected a locus with a large effect on plasma apoB levels and was used to compute the most probable genotype of family members. None of the 35 normolipidemic adults carried a copy of the allele associated with elevated apoB levels, yet 58% of the 109 adults with FCHL carried 1 (29%) or 2 (28%) copies. Two of 28 (7%) normal children had 1 copy of this allele and none had 2 copies, while 88 of 182 (48%) children with FCHL had 1 (26%) or 2 (22%) copies. Further, 41 of 48 (85%) individuals classified as having hyperapobetalipoproteinemia did not carry a copy of this "elevated apoB" allele. Therefore, the presence of the allele associated with elevation of apoB level is highly predictive of FCHL and this association cannot be explained solely by the presence of elevated apoB levels in FCHL, suggesting that the locus controlling apoB levels may play an etiologic role in FCHL.

The effect of lovastatin on very low-density lipoprotein apolipoprotein B production by the liver in familial combined hyperlipidaemia

Overproduction of very low-density lipoprotein apolipoprotein B by the liver is a metabolic marker for familial combined hyperlipidaemia, a common inherited disorder of lipoprotein metabolism. Four subjects with familial combined hyperlipidaemia had rates of apolipoprotein B production which were 2-7 times normal, using a protocol in which [15N]glycine was used to label newly synthesized hepatic proteins. Following 4-6 months of therapy with lovastatin, very low-density lipoprotein apolipoprotein B production in all four subjects had returned to the normal range. This demonstrates that lovastatin, an inhibitor of cholesterol biosynthesis, acts also to reduce the apparent production rate of apolipoprotein B by the liver.

Determinants of fasting plasma triglyceride levels: metabolism of hepatic and intestinal lipoproteins

The contribution of the kinetics of exogeneous and endogenous lipoproteins in determining the level of triglyceride in fasting plasma was assessed in a group of 19 normolipidaemic and hypertriglyceridaemic subjects. From data derived during a 9-h infusion of [15N]-glycine, we have assessed very low density lipoprotein apolipoprotein B production, and from data analysed by kinetic modelling obtained following ingestion of retinol and triolein, we have assessed chylomicron and chylomicron remnant clearance in a group of 19 normolipidaemic and hypertriglyceridaemic subjects. A strong positive correlation was observed between the fasting plasma triglyceride level and the reciprocal of the apolipoprotein B fractional synthetic rate (r = 0.83, P less than 0.01). A positive correlation was also found with the rate of clearance of chylomicron remnants (Sf 20-400; r = 0.87, P less than 0.01) and of chylomicrons (Sf greater than 400; r = 0.69, P less than 0.01). No correlation was found between the fasting plasma triglyceride level and either of the plasma post-heparin lipolytic activities. Multivariate analysis revealed that 95% of the variance in triglyceride levels could be explained by the apolipoprotein B fractional synthetic rate and the chylomicron remnant clearance rate. The strong correlation between chylomicron remnant clearance, a measure of exogenous lipid metabolism, and fasting (hence, endogenous) plasma triglyceride levels suggests that remnants of chylomicrons and very low density lipoproteins share some common components of the removal process.

Familial combined hyperlipidaemia: use of stable isotopes to demonstrate overproduction of very low-density lipoprotein apolipoprotein B by the liver

We have assessed very low-density lipoprotein apolipoprotein B production, using [15N]glycine as an endogenous marker in a 9-hour primed constant infusion protocol, in four adult male subjects with familial combined hyperlipidaemia and in four normolipidaemic adult male controls. The mean very low-density lipoprotein apolipoprotein B absolute synthetic rate was significantly greater in the familial combined hyperlipidaemic subjects than in control subjects (26.31 +/- 8.37 vs 9.36 +/- 4.07 mg/kg per 24 h, p less than 0.05). These results confirm findings using exogenous radioisotope labelling techniques that very low-density lipoprotein apolipoprotein B production is significantly increased in most patients with familial combined hyperlipidaemia. A modified 9-hour protocol can be safely done repeatedly and in children and pregnant women.

Measurement of (C13)arginine incorporation into apolipoprotein B-100 in very low density lipoproteins and low density lipoproteins in normal subjects using (13C)sodium bicarbonate infusion and isotope ratio mass spectrometry

We describe a new stable isotope technique for the in vivo study of hepatic plasma protein synthesis in humans. The method involves the infusion of (13C)sodium bicarbonate for 1 h and the measurement of the isotopic enrichment of (13C)arginine in newly synthesized apolipoprotein B of very low density lipoproteins (VLDL-apoB) and low density lipoproteins (LDL-apoB) in blood samples taken over a 5-6 h period from the commencement of the infusion. Isotope ratio mass spectrometry was utilized to measure 13CO2 enrichment following hydrolysis of these proteins and conversion of the guanidinium carbon of arginine in the hydrolysate to carbon dioxide by sequential incubation with arginase and urease. The method is capable of measuring isotopic enrichment as low as 0.001 at.% excess (APE) with a precision of 1.2%. In both subjects studied, the (13C)arginine of VLDL-apoB reached enrichments of 0.2 APE and that of the arginine of LDL-apoB, 0.03 APE. Incorporation of labeled arginine into LDL-apoB was demonstrable at 60-90 min. The new technique is safe and is applicable to the study of the hepatic biosynthesis of a wide range of plasma proteins.

Prevalence and expression of familial combined hyperlipidemia in childhood

The objectives of this study were (1) to determine the incidence of dominantly inherited hyperlipoproteinemia in children referred to our medical center because of hyperlipidemia associated with a family history of premature coronary artery disease and (2) to assess the degree of expression in childhood of the most common inherited hyperlipoproteinemia, familial combined hyperlipidemia. Among 129 families referred to us by area pediatricians, we identified a dominantly inherited hyperlipoproteinemia in 97 of them. Twenty had familial hypercholesterolemia, 65 familial combined hyperlipidemia, 11 hyperapobetalipoproteinemia, and one familial hypertriglyceridemia. As expected, almost half (9/20) of the siblings of probands with familial hypercholesterolemia were affected. Although we expected incomplete gene penetrance in the siblings of the probands with familial combined hyperlipidemia, we found 43 affected and 40 unaffected among the 83 siblings of the 65 probands. Our findings suggest that hyperlipidemia in children, caused by familial combined hyperlipidemia, occurs more than three times as frequently as familial hypercholesterolemia and that in families identified by a child proband, the penetrance is complete. Pediatricians should identify this primary hyperlipidemia in childhood and attempt to prevent the associated risk of premature coronary artery disease by prescribing appropriate diet and life-style modifications.

Measurement of apolipoprotein B synthesis in perfused rat liver using stable isotopes: [15N]hippurate as a measure of the intracellular [15N]glycine precursor enrichment

Rat livers were perfused by the nonrecirculating technique with medium containing [15N]glycine and sodium benzoate. At various times, the isotopic enrichment of hepatic free glycine, hepatic glycyl-tRNA, and perfusate hippurate was measured by GLC-MS. After 60 min, these parameters had reached approximately maximal values. At 90 min, the perfusate hippurate had a 30% greater enrichment of 15N than the intracellular glycine or glycyl-tRNA. Hippurate enrichment was half that of the medium glycine. The rat livers secreted apolipoprotein B (B-100 plus B-48) at a rate of 22 micrograms/g per h. From the 15N enrichment and the secretion rate, an intrahepatic pool size of 86 micrograms/g of apoB was calculated. From the minimal intracellular transit time of 30 min, an apoB fractional synthetic rate (FSR) of 2 pools/h was indicated, whereas the FSR estimated from the 15N-enrichment was 0.26/h. A possible explanation for the discrepancy is that apoB may recycle within the hepatocyte. On the basis of the present experiments, when hippurate enrichment is used as a measure of the enrichment of intrahepatic glycine in in vivo studies with 15N-labeled glycine, a correction should be applied, under normal metabolic circumstances, of approximately 20-30%.

Transcriptional activity of the genes for apoproteins A-I and E in neonatal rat liver

The expression of the genes for apoproteins A-I and E (apoA-I, apoE) in fetal and neonatal rat livers was quantitated by measurement of steady-state levels of mRNA and by assays of relative transcriptional activity using the nuclear 'run-on' technique. From the last day of gestation (day -1) to day 5 after birth (day 5), for apoE there was a 2.2-fold increase in relative transcriptional activity and a 2.6-fold increase in steady-state mRNA. For apoA-I, from day -1 to 3 there was a 1.25-fold increase in both transcription and steady-state mRNA levels. We conclude that the increase in steady-state mRNA for the apoE gene which occurs during liver development in the rat is facilitated primarily by transcriptional control.

Kinetics of chylomicron remnant clearance in normal and in hyperlipoproteinemic subjects

The kinetics of chylomicron metabolism have been studied by measuring retinyl palmitate in chylomicrons and their remnants for 10-12 hr following oral administration of vitamin A and Lipomul in three groups of adult male subjects: A) normal plasma triglyceride levels (n = 7); B) endogenous hypertriglyceridemia (n = 12); C) apolipoprotein E (apoE) phenotype E2/2, with Type 3 hyperlipoproteinemia (n = 4) or normal plasma lipids (n = 1). A multicompartmental model was developed using SAAM 27 to characterize the appearance, intravascular metabolism, and clearance from the plasma of retinyl palmitate-labeled dietary lipoproteins. The half-times for retinyl palmitate clearance from the chylomicron remnant fraction (T1/2 REMNANT) were 14.1 +/- 9.7 min in Group A; they were prolonged in Group B (50.7 +/- 20.8 min) and were extremely prolonged for Type 3 subjects in Group C (611.9 +/- 419.9 min). One subject with the apoE 2/2 phenotype and normal plasma triglycerides had a T1/2 REMNANT of 66.8 min. T1/2 REMNANT was highly correlated with fasting plasma triglycerides in Group A and B (r = 0.77, slope = 0.15), and in Group C (r = 0.97, slope = 0.85). These results support the interpretation that delayed chylomicron remnant clearance in subjects with endogenous hypertriglyceridemia may be largely secondary to overproduction of VLDL particles, whose remnants compete with chylomicron remnants for removal by the liver via apoE receptor-mediated endocytosis. The subjects with apoE 2/2 have an additional defect in the removal of chylomicron remnants presumably due to the structural abnormality in their apoE.

Genetic variation of human mononuclear leukocyte lysosomal acid lipase activity. Relationship to atherosclerosis

Lysosomal acid lipase activity was measured in mononuclear leukocytes of patients selected on the basis of premature cardiovascular disease, with or without hyperlipidemia. Enzyme activity was significantly lower in the patient population (4.8 +/- 1.3 nmol/min/mg protein, n = 190 males) than in an age-matched control population (5.4 +/- 1.3 nmol/min/mg protein, n = 124 males). There was no effect of hypercholesterolemia or hypertriglyceridemia on the enzyme activity. In the group of patients with normal plasma lipids (n = 77), 18% had mononuclear leukocyte acid lipase activity which fell below the control population 5th percentile, and in the range of enzyme activity observed in cells from obligate heterozygotes for inherited acid lipase deficiency (Wolman disease and cholesteryl ester storage disease). Studies of acid lipase activity in families of our patients provided evidence that an autosomal mutation is associated with (or responsible for) this reduced enzymatic activity and may represent an independent risk factor for the premature development of atherosclerosis.

Genetic polymorphism of esterase B3 in human leukocytes

Human tissues contain an esterase activity called ESB3, detectable by starch gel electrophoresis followed by staining with alpha-naphthyl butyrate. Using mononuclear leukocytes, we demonstrated an electrophoretic variant of ESB3. Family studies suggest that the variant is inherited as a simple Mendelian trait; individuals with the ESB3 2-1 phenotype are heterozygotes, designated ESB3(1)ESB3(2), to distinguish them from the more common homozygotes, ESB3(1)ESB3(1). The frequency of the ESB3(2) allele is estimated to be 0.035 in U.S. Whites. No homozygotes for this allele have yet been found. Our studies suggest that the enzyme from ESB3 1 individuals exists primarily as a trimer of three identical subunits with a molecular weight of approximately 58,000 daltons. The genetic variant (ESB3(2) allele) appears to be the result of a mutation that does not affect the charge of the subunit, but rather reduces its ability to form and maintain the trimeric structure.

Direct measurement of apolipoprotein B synthesis in human very low density lipoprotein using stable isotopes and mass spectrometry

Stable isotope methodology has been adapted to the study of lipoprotein turnover in human subjects. Using endogenous [15N]glycine labeling and gas-liquid chromatographic-mass spectrometric analysis, synthesis of apolipoprotein B in very low density lipoprotein (VLDL) was measured directly in five normal and two hyperlipidemic subjects. An isotopic precursor steady state was achieved during the studies by utilizing a priming dose and constant infusion containing [15N]glycine. Measurement of the plateau in 15N enrichment in the urinary hippurate produced during each study was used to estimate the 15N enrichment of the hepatic glycine precursor pool. The range of values for the fractional synthetic rate of VLDL apoB in the normal subjects obtained by this method was 5.9 to 11.5 day-1, with a mean of 9.2 +/- 2.4 (SD). This value agrees with the results of previous investigations which have utilized other methods. The method was also tested in two hypertriglyceridemic subjects and gave fractional synthetic rates of VLDL apoB that were significantly lower than in normals (1.5 and 2.8 day-1). This stable isotope method allows calculation of the fractional synthetic rate of VLDL apoB by maintaining an isotopic steady state throughout the study. It makes possible repeated studies in the same individual since no risk of exposure to radioisotopes is involved.

Genetic deficiency of medium-chain acyl coenzyme A dehydrogenase: studies in cultured skin fibroblasts and peripheral mononuclear leukocytes

Medium-chain acyl coenzyme A (CoA) dehydrogenase deficiency was demonstrated in fibroblasts and/or mononuclear leukocytes from 14 patients, most of whom initially presented early in childhood with a Reye-like syndrome associated with hypoketotic hypoglycemia, dicarboxylic aciduria, and low levels of plasma carnitine. Parents of these patients had intermediate levels of medium-chain acyl CoA dehydrogenase activity, consistent with their being heterozygous for an autosomal recessive trait. All patients had normal levels of long-chain acyl CoA dehydrogenase activity, but had reduced short-chain acyl CoA dehydrogenase activity. Fatty acid oxidation was examined in cultured fibroblasts from five of the patients, using a series of 14C-labeled fatty acids of different chain length (palmitic, octanoic, and butyric). Oxidation of [1-14C]-octanoic acid was less than 20% of control levels: [1-14C], [6-14C]-, [16(14)C]-, and [14C(U)]-palmitic acid oxidation rates were 88, 51, 13, and 42% of control rates, respectively. [1-14C]-butyric acid was oxidized normally. These data extend our previous findings of medium-chain acyl CoA dehydrogenase deficiency in liver tissue from three of these patients. They demonstrate the value of cultured fibroblasts and leukocytes in the diagnosis and evaluation of inherited disorders of fatty acid oxidation.

Hormone-sensitive lipase in human adipose tissue, isolated adipocytes, and cultured adipocytes

Employing a perifusion technique, the activity of hormone-sensitive lipase (HSL) in human adipose tissue and isolated adipocytes was found to be significantly stimulated by 5 microM epinephrine (5-fold. P less than 0.001) or 0.5 mM theophylline (2-fold, P less than 0.03). The stimulatory effect of both, however, was not cumulative; instead, theophylline appeared to blunt the epinephrine effect. The two effectors together produced a 3-fold increase in activity over basal (P less than 0.01). Basal lipolysis was highly and significantly correlated with epinephrine and/or theophylline stimulated lipolysis in the tissue as well as in the isolated cells. The activity of the enzyme was examined in cultured human adipocytes using a cell-free system. The basal activity of HSL in the 20,000 X g supernatant (S20) fraction of cultured cells grown in fat-enriched medium was significantly higher than the value in the same fraction of cells grown in regular medium (6.06 +/- 1.49 versus 2.78 +/- 0.89 nmole glycerol/min/mg protein, mean +/- S.D., P less than 0.01), an was similar in the S20 fractions of cells grown in the enriched medium and the original tissue (6.06 +/- 1.49 versus 5.44 +/- 2.73 nmole glycerol/Min/mg protein, mean +/- S.D., P greater than 0.83). When the tissue and cells were stimulated in vitro before fractionation, the HSL activity in the S20 fraction of the original tissue increased 4-fold over basal (P less than 0.001), whereas that in the cultured cells increased 2-fold (P less than 0.01) regardless of the culture medium employed. In the S20 fractions derived from basally incubated samples, but not in those derived from the epinephrine-stimulated samples, the HSL enzyme was slightly but significantly (P less than 0.002) activated by exogenous addition of ATP, cyclic AMP, and protein kinase. The data suggest that the activity of HSL is retained in cultured human adipocytes and could be enhanced under conditions of culture which favor lipid accumulation and adipose conversion.

Acid lipase activity of human lymphocytes

Acid lipase activity was examined in human leukocytes using 4-methylumbelliferyl esters in a fluorimetric assay. Mononuclear leukocytes had 10--15 times the acid lipase activity of polymorphonuclear leukocytes. The enzyme activity was highest using the oleate ester of 4-methylumbelliferone at pH 4.0, in the presence of L-alpha-phosphatidylcholine and taurodeoxycholic acid (sodium salt). Acid lipase activity was inhibited by diethylaminoethoxyhexestrol, sodium chloride and fluoride, potassium chloride, calcium chloride and albumin, but was unaffected by diethyl p-nitrophenyl phosphate or sulphydryl reagents. There were at least two forms of acid lipase activity: one (A form) was sensitive to heart inactivation (56 degrees C) and corresponded to the enzyme deficient in patients with Wolman's disease; the other (B form) was resistant to heat inactivation and corresponded to the residual enzyme activity found in Wolman's disease.

Acid and neutral lipases of cultured adipocytes of infants and children

In order to determine whether the mobilization of intracellular triglycerides observed in cultured human adipocytes is associated with changes in the activities of acid and neutral lipases, the activities of both enzymes were measured weekly on cultured adipocytes for several months. The activity of acid lipase was initially very low, but rose to levels 40 times the original activity within 3 months. The activity of neutral lipase decreased rapidly within the first 2-4 weeks and remained at approximately 25% of original levels thereafter.

Prenatal diagnosis of Wolman disease

Two pregnancies at risk for Wolman disease were monitored by assay and electrophoresis of acid lipase in cultured amniotic-fluid cells. Cells from patient 1 had 5% of control levels of acid lipase, using 14C-triolein as substrate; however, when artificial substrates (esters of 4-methylumbelliferone and p-nitrophenol) were used to measure acid lipase, these cells had 30% of control levels. Electrophoresis of cell extracts revealed the absence of the A form of acid lipase, consistent with the diagnosis of Wolman disease. Analysis of fetal tissues following prostaglandin termination of this pregnancy confirmed the diagnosis. Assay of fetal-skin fibroblasts with 14C-triolein, as well as with artificial substrates, showed marked deficiency of acid lipase activity. Electrophoresis of fetal-tissue extracts also demonstrated the absence of the A form of acid lipase. Amniotic-fluid cells from patient 2 showed normal levels of acid lipase with all substrates tested; the electrophoretic pattern of acid lipase was normal. The results suggest that the prenatal diagnosis of Wolman disease be made using the radioassay of acid lipase and/or electrophoresis.

Neutral and acid lipase of mouse 3T3 fibroblasts with increased adipose conversion

In the resting state, 3T3-L1 fibroblasts become adipose converted and increase their fatty acid and triglyceride synthetase. We have found that they contain four times the neutral lipase activity and 1.5 times the acid lipase activity of logarithmically dividing cells. The activities of lysosomal acid beta-galactosidase and N-acetyl-beta-D-glucosaminidase were the same in the adipose converted and logarithmically dividing cells. The data suggest a possible relation between the increased neutral lipase activity in 3T3-L1 cells and their adipose conversion and demonstrates that the adipose converted 3T3-L1 fibroblasts, unlike true adipose cells, contain high levels of lysosomal acid hydrolases.

Genetic variation of lysosomal acid lipase

Lysosomal acid lipase (LAL) activity was measured using a new fluorometric assay in cultured skin fibroblasts from eight control subjects, two obligate heterozygotes for Wolman's disease (WD), one patient with WD, and one patient with cholesteryl ester storage disease (CESD). The LAL activities (mean+/-SD) were 25.8+/-8.2, 13.2+/-0.1,1.1, and 1.4 nmol 4-methylumbelliferyl oleate (4-MUO) hydrolyzed/min/mg protein, respectively. These results compare favorably with those obtained using standard radioassays. The LAL activities of two cultures of amniotic fluid cells were 12.1 and 10.5. The LAL activity (mean+/-SD) of peripheral leukocytes obtained from 34 laboratory volunteers (19 females, 15 males) was 4.0+/-1.8. Partially purified lymphocytes contained about 25 times as much LAL activity as did granulocytes. Cellogel electrophoresis, followed by staining with 4-MUO, showed at least two bands of LAL (A and B) from normal fibroblasts, amniotic fluid cells, and lymphocytes. Band A was absent from WD and CESD fibroblasts and was reduced in fibroblasts of the WD heterozygotes.

Genetic polymorphisms of human mitochondrial glutamic oxaloacetic transaminase

In a survey of 860 unselected human placental extracts, three variants of mitochondrial glutamic oxaloacetic transaminase were found, all of which were common enough to be considered polymorphisms. Family studies showed that this enzyme is under the control of nuclear rather than mitochondrial DNA.

Mitochondrial malate dehydrogenase: a new genetic polymorphism in man

Starch-gel electrophoresis patterns of malate dehydrogenase from human tissue indicate a new genetic polymorphism for the mitochondrial form of the enzyme. Studies of families showed simple Mendelian segregation rather than maternal inheritance, suggesting that not all mitochondrial proteins are coded by mitochondrial DNA.