Janet L. Adolphson

Radioimmunoassay of human plasma lecithin-cholesterol acyltransferase.

A sensitive and precise competitive-displacement double-antibody radioimmunoassay was developed for the human plasma enzyme lecithin-cholesterol acyltransferase (LCAT; Ec 2.3 1.43). The ability of plasma from various animal species to displace labeled human LCAT from goat anti-human LCAT could be ranked in the following order: man and sheep > nonhuman primates > cat or dog > pig > rabbit or guinea pig > mouse > rat. Normolipidemic subjects had levels of LCAT of 6.14 +/- 0.98 micrograms/ml (mean +/- SD, n = 66). Subjects with dysbeta-lipoproteinemia had the highest plasma LCAT levels (7.88 +/- 0.39 micrograms/ml, n = 7, P < 0.05), followed by hypercholesterolemic subjects (7.00 +/- 1.30, n = 41) and hypertriglyceridemic subjects (6.96 +/- 1.3, n = 10). LCAT-deficient subjects had the lowest enzyme levels (0.89, 0.83, and 0.05 micrograms/ml, respectively, and two subjects with no detectable enzyme). Males had lower LCAT levels (6.42 +/- 1.05 micrograms/ml, n = 90, for all subjects; 5.99 +/- 1.03, n = 44, for normolipidemics) than females (7.01 +/- 1.14, n = 34, for all subjects P < 0.01; 6.44 +/- 0.79, n = 22, for normolipidemics, P < 0.01). LCAT levels correlated significantly with total cholesterol (males, r = 0.384, P < 0.001; females, r = 0.519, P < 0.002); and total triglyceride (only in females, r = 0.512, P < 0.002). LCAT levels in females correlated inversely with HDL cholesterol (r = 0.341, P < 0.05) and apoprotein D (r = 0.443, P < 0.02), but no such relationship existed in males.

Population-based reference values for lecithin-cholesterol acyltransferase (LCAT)

Plasma unesterified cholesterol is converted to cholesteryl ester by the enzyme lecithin-cholesterol acyltransferase (LCAT). Plasma levels of LCAT were measured by a sensitive double antibody radioimmunoassay in a sample from an adult employee population, ages 20-59 years, in the Pacific Northwest. After adjusting for differences in relative body mass, women had significantly higher LCAT levels (5.90 +/- 1.06, n = 154) than men (5.49 +/- 0.89, n = 83). For ages 20-59 years, LCAT levels showed a slight association with age: r = 0.13 for men and 0.29 for women. LCAT was positively correlated with relative body mass, total cholesterol, and LDL cholesterol. Men who smoked cigarettes had significantly lower LCAT mass than men who did not smoke cigarettes. No statistical differences in mean LCAT values were found between drinkers and nondrinkers. The 5th percentile LCAT value was 4.3 micrograms/ml for both men and women not using hormones. The 95th percentile value was 7.3 micrograms/ml for men and 7.8 micrograms/ml for women regardless of hormone use. Subjects phenotypically LCAT-deficient by clinical criteria and by the absence or near absence of LCAT activity had levels of LCAT mass well below the reference values: 0.73 +/- 0.70, range 0.10 micrograms/ml to 2.65 micrograms/ml, n = 20. Parents or children of LCAT-deficient subjects, i.e., obligate heterozygotes for familial LCAT deficiency, had reduced levels: 3.59 +/- 0.69, range 2.59-4.61 micrograms/ml, n = 19.

Familial Lecithin-Cholesterol Acyltransferase: Identification of Heterozygotes with Half-Normal Enzyme Activity and Mass

SummaryLecithin-cholesterol acyltransferase (LCAT) mass and activity were measured in a Canadian kindred of Italian and Swedish descent with familial LCAT deficiency. Four subjects had LCAT mass of 5.21±0.87 μg/ml (mean±SD) and LCAT activity of 98.8±12.0 nmol/h/ml, well within their respective normal ranges. Five family members, including the parents, the maternal grandmother, and two of four siblings of the LCAT deficient subjects, had enzyme mass (2.85±0.32 μg/ml) and activity (50.8±6.3 nmol/h/ml) approximately one-half that of normal levels. These presumed heterozygotes had normal levels of apolipoproteins A-I, A-II, B and D. The two subjects with LCAT deficiency had no detectable LCAT mass (below 0.1 μg/ml) or LCAT activity (below 0.76 nmol/h/ml), apolipoprotein A-I and D levels approximately 50% of normal, and apolipoproteins B and A-II levels only 30–35% of normal. LCAT deficiency in this family is determined by an autosomal recessive mode. Furthermore, LCAT levels and activity are determined by two autosomal codominant alleles, LCATn, the normal LCAT gene, and LCATd, the LCAT deficiency gene.

Familial lecithin-cholesterol acyltransferase deficiency in a Japanese family: Evidence for functionally defective enzyme in homozygotes and obligate heterozygotes

SummaryLecithin-cholesterol acyltransferase (LCAT) mass and activity were measured in a Japanese family with familial LCAT deficiency. The two LCAT-deficient subjects had LCAT mass approximately 40–46% of normal (2.65 and 2.31 μg/ml respectively, as compared with normal levels of 5.76±0.95 μg/ml in 19 Japanese subjects) and enzyme activity less than 10% of normal (9.1 and 8.3 nmol/h/ml respectively, as compared with normal levels of 100 nmol/h/ml). All obligate heterozygotes examined, including the father of the two LCAT-deficient subjects, and all five children of the deficient subjects had LCAT mass approximately 72–80% of the normal LCAT mass (4.12, 4.38, 4.45, 4.48, 4.49, 4.61 μg/ml, respectively) and LCAT activity approximately half normal (51.9, 52.4, 54.2, 56.6, and 57.2 nmol/h/ml). We conclude that the two LCAT-deficient subjects of this family have functionally defective enzyme. Furthermore, the data suggest that the plasma of the obligate heterozygotes contain both normal and functionally defective enzymes.

Effects of interleukin-2 (IL-2) on human plasma lipid, lipoprotein, and C-reactive protein.

Six patients with confirmed malignant disease received four consecutive weekly cycles of human recombinant interleukin-2 (IL-2) 4 days/week, continuous iv. infusion, 3 × 106 U/m2/day. Plasma cholesterol decreased a mean of 7% within 24 hours after IL-2 infusion and decreased by 33% within 4 days. Plasma cholesterol was significantly lower than baseline concentration by day 21 (−21%), and day 25 (−41%) was significantly lower than day 21. Decreased plasma cholesterol was the result of decreased HDL and LDL cholesterol concentrations. Plasma triglyceride demonstrated a mean increase of 46% after 4 days of therapy and remained greater than baseline concentrations at all time points analyzed. Apolipoprotein AI and AII decreased concomitantly with HDL-cholesterol concentrations, whereas apolipoprotein B after an initial mean decrease of 17% during the first cycle was not significantly different from baseline during the fourth cycle. Apolipoprotein E and Lp(a) were not significantly affected by IL-2 treatment. Plasma C-reactive protein (CRP) increased by 79% within 24 hours of therapy, increased by 254% on day 4, then decreased to baseline concentrations by day 21 after 3 days off of IL-2. Day 25 CRP was elevated compared to both baseline and day 21 concentrations. IL-2 induced plasma lipoprotein changes may be due in part to the induction of interferon gamma.

Studies of lipoproteins and fatty acids in maternal and cord blood of two racial groups in Trinidad

The high mortality rate from coronary heart disease (CHD) among Indians compared to Negroes in Trinidad led us to test plasma lipid profiles to see whether dietary or genetic factors might be involved. There were no interracial differences in the composition of plasma cholesterol ester fatty acids of the tested women and neonates. This finding suggests that dietary fat does not account for the interracial difference in CHD, nor does the cause appear to be due to genetic differences in lipid profiles, as there was no significant difference between values for plasma triglycerides, total cholesterol, high density lipoprotein (HDL) cholesterol, apo-I, apo-II, apo B or cholesterol ester fatty acids in the cord blood of each racial group.Blood samples were collected from 69 nonpregnant and 71 postpartum, fasted Negro and Indian women. Also taken were 71 umbilical cord blood samples. The mean triglyceride level was significantly lower in the Negro nonpregnant and postpartum women than in the Indians. HDL cholesterol and apo-I values were lower in the Indian women. There were no significant differences in the total cholesterol and apo B measurements. The triglyceride values for postpartum women were higher than those of the nonpregnant Negroes and Indians (75% and 47%, respectively), whereas the total cholesterol and HDL cholesterol, apo A-I and apo A-II ranged from 9% to 29% higher in the postpartum women. Apo B was about 40% higher postpartum in both ethnic groups.The high CHD rate of Indians in Trinidad cannot be explained by dietary factors, plasma total cholesterol or fatty acid composition. However, the lower level of HDL cholesterol and plasma A-I could play a role in the higher CHD rate in Indians.

Defective enzyme causes lecithin-cholesterol acyltransferase deficiency in a Japanese kindred.

Lecithin-cholesterol acyltransferase mass levels and activity and apolipoproteins A-I, A-II, B and D were measured in a Japanese family who have a familial lecithin-cholesterol acyltransferase deficiency. This analysis was performed to gain insight into the molecular basis of the enzyme deficiency and to compare findings in this family with other families with familial lecithin-cholesterol acyltransferase deficiency. The mass of the enzyme in plasma was determined by a sensitive double antibody radioimmunoassay, and enzyme activity was measured by using a common synthetic substrate comprised of phosphatidylcholine, cholesterol and apolipoprotein A-I liposomes prepared by a cholate dialysis procedure. The lecithin-cholesterol acyltransferase-deficient subject had an enzyme mass level that was 35% of normal (2.04 micrograms/ml, as compared with an average normal level of 5.76 +/- 0.95 micrograms/ml in 19 Japanese subjects) and an enzyme activity of less than 0.1% of normal (0.07 nmol/h per ml, as compared with normal levels of 100 nmol/h per ml). This subject also had lower levels of apolipoproteins: apolipoprotein A-I was 53 mg/dl (42% of normal), apolipoprotein A-II was 10.6 mg/dl (31% of normal), apolipoprotein B was 68 mg/dl (68% of normal), and apolipoprotein D was 3.6 mg/dl (60% of normal). The three obligate heterozygotes had enzyme mass levels ranging from 65% to 100% of normal and enzyme activity levels ranging from 23% to 65% of normal (23.4, 56.8, and 64.7 nmol/h per ml, respectively). The probands sister had an enzyme mass level of 6.55 micrograms/ml (114% of normal) and an enzyme activity of only 64.8 nmol/h per ml (65% of normal), suggesting that she was also a heterozygote for lecithin-cholesterol acyltransferase deficiency. The obligate heterozygotes and the sister had normal apolipoprotein levels. We conclude that the lecithin-cholesterol acyltransferase deficiency in this family is due to the production of a defective enzyme that is expressed in the homozygote as well as in the heterozygotes, and, further, that this familys mutation differs from that reported earlier for other Japanese lecithin-cholesterol acyltransferase-deficient families.