A smoking-dependent risk of coronary artery disease associated with a polymorphism of the endothelial nitric oxide synthase gene

Endothelium-dependent vasodilatation is mediated by release of nitric oxide formed by constitutively expressed endothelial nitric oxide synthase (ecNOS). We explored the distribution of polymorphism ecNOS4a/b in 549 subjects with, and 153 without, coronary artery disease in relation to smoking. In current and ex-cigarette smokers, but not nonsmokers, there was a significant excess of homozygotes for the rare ecNOS4a allele in patients with severely stenosed arteries, compared with those with no or mild stenosis. This genotype was also associated with a history of myocardial infarction. This smoking-dependent excess coronary risk in ecNOS4a homozygotes is consistent with predisposition to endothelial dysfunction.

Polymorphisms of the apolipoprotein E gene and severity of coronary artery disease defined by angiography

In a recent study, we could account for only about 50% of the variance in angiographically determined severity of coronary artery disease (CAD) with use of lipid and clinical variables as predictors. To explore the possible contribution of the apolipoprotein (apo) E polymorphisms to the severity of CAD (rather than to its occurrence), we studied 424 white patients aged 65 years or less consecutively referred for coronary angiography. Among the 304 male and 120 female patients, there were 110 with no significant CAD and 118 with one, 96 with two, and 100 with three significantly diseased major coronary arteries (> 50% luminal obstruction). The allele frequencies were 0.068 for E2, 0.759 for E3, and 0.172 for E4. The E2 frequency was slightly lower and E4 higher than the frequencies reported for healthy white populations (E2: 0.072 to 0.130; E4: 0.136 to 0.160). There was a clear association between the apo E genotype and the number of significantly diseased vessels (regression coefficient = .12, P = .008). The frequency of the E4 allele increased linearly with the increase in CAD severity in both sexes (for none, one, two, and three significantly diseased vessels; female patients: 0.136, 0.161, 0.200, and 0.324; male patients: 0.136, 0.167, 0.132, and 0.229, respectively, P < .01). The frequencies of the E2 allele, on the other hand, decreased with increasing severity (for none, one, two, and three significantly diseased vessels; female patients: 0.091, 0.018, 0.050, and 0.029; male patients: 0.073, 0.089, 0.072, and 0.054, respectively, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Determinants of severity of left ventricular dysfunction in Australian men and women with coronary disease aged 65 years or less

BACKGROUND

The degree of left ventricular (LV) impairment is an important determinant of long term outcome in patients with coronary artery disease (CAD).

AIM

We aimed to determine variables predictive of the severity of LV dysfunction in men and women aged 65 years or less with CAD, and to quantitate their contributions.

METHODS

We documented atherogenic variables and extent of LV impairment and CAD severity at angiography in 521 consecutively studied men and women aged 65 years or less (381 males and 140 females). We assessed severity from an LV impairment score (Green Lane) and the ejection fraction. We related severity to quantitative and categorical variables which included the severity of angina (no angina, stable and unstable angina).

RESULTS

The LV impairment score correlated closely (negatively) with the ejection fraction (r = -0.783, p = 0.0001). There were eight variables independently predictive of the severity of LV impairment assessed by the LV score. The variables in descending order of relative importance in predicting the LV scores were past history of myocardial infarction (MI), number of significantly diseased vessels (> 50% luminal obstruction), life-time smoking dose, log-triglycerides, total cholesterol to HDL-C ratio, hypertension, age and Body Mass Index (BMI). They were all positive relationships. Together they correctly classified the LV scores of 52.6% of the patients. Gender was not an independent contributor to the LV score when other variables were controlled. When the contributions to the variance in LV scores of past history of MI (15.4%) and number of significantly diseased vessels (2.6%) were controlled, life-time smoking dose independently explained 2.1% (p < 0.01) of the variance. The LV impairment score was 55% higher in heavy smokers than in non-smokers (p = 0.01). When we compared patients with stable and unstable angina, LV scores are higher and ejection fraction lower in the unstable angina patients consistent with them having a greater degree of LV dysfunction.

CONCLUSION

We conclude that variables other than a history of MI and CAD severity contribute significantly to the variance of the degree in LV impairment in CAD patients among which the life-time smoking dose, triglycerides, TC/HDL-C, hypertension and increased BMI are all relevant to prevention, and that patients with unstable vs stable angina usually have more impaired LV function.

C to T and/or G to A transitions are responsible for loss of a MspI restriction site at the 5'-end of the human apolipoprotein AI gene

We detected the loss of a MspI restriction site by a C to T transition at +83 bp and a G to A transition at +84 bp of the 5'-end non-coding region of the human apolipoprotein AI gene. This base change occurred at the "hot spot" (CCGG) for methylation, which may be important in the regulation of gene expression. The population frequency for the loss of the MspI site is 6.1%.

Angiotensin-converting enzyme genotype in children and coronary events in their grandparents

BACKGROUND

It has been suggested that the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene is an independent risk factor for coronary artery disease. The D/D genotype, which is associated with higher levels of circulating ACE than the I/D or I/I genotype, has been found significantly more frequently in patients with myocardial infarction and also in individuals with a parental history of myocardial infarction.

METHODS AND RESULTS

We explored the distribution of the ACE genotype in 404 school children, aged 6 to 13 years, and related the distribution to the number of their grandparents who had had vascular events. We found a significant association between the number of grandparents who had had coronary events and the ACE genotype (P = .01). In children with two or more grandparents who had had coronary events, there was an excess of both D/D (odds ratio = 2.8 [95% confidence interval = 1.16-6.56]) and I/D (odds ratio = 1.4 [95% confidence interval = 0.62-3.25]) genotypes compared with I/I genotypes. In addition, there was an association between the ACE genotype and lipoprotein(a) levels in children (P = .07). Both the ACE genotype and lipoprotein(a) were found to contribute significantly (P = .0042) and independently to family history of coronary artery disease, with the ACE genotype proving to be more predictive than lipoprotein(a) levels.

CONCLUSIONS

We conclude that the I/D polymorphism of the ACE gene is an important independent risk factor for coronary artery disease and is more predictive that lipoprotein(a). The I/D polymorphism is not only associated with a parental history of myocardial infarction but also with coronary artery disease in second-degree relatives. A further study to explore the relation between the I/D polymorphism and circulating levels of lipoprotein(a) is indicated.

1H NMR determination of urinary betaine in patients with premature vascular disease and mild homocysteinemia

Urinary N,N,N-trimethylglycine (betaine) and N,N-dimethylglycine (DMG) have been identified and quantified for clinical purposes by proton nuclear magnetic resonance (1H NMR) measurement in previous studies. We have assessed these procedures by using both one-dimensional (1-D) and 2-D NMR spectroscopy, together with pH titration of urinary extracts to help assign 1H NMR spectral peaks. The betaine calibration curve linearity was excellent (r = 0.997, P = 0.0001) over the concentration range 0.2-1.2 mmol/L, and CVs for replicate betaine analyses ranged from 7% (n = 10) at the lowest concentration to 1% (n = 9) at the highest. The detection limit for betaine was < 15 mumol/L. Urinary DMG concentrations were substantially lower than those of betaine. Urinary betaine and DMG concentrations measured by 1H NMR spectroscopy from 13 patients with premature vascular disease and 17 normal controls provided clinically pertinent data. We conclude that 1H NMR provides unique advantages as a research tool for determination of urinary betaine and DMG concentrations.

1H NMR determination of urinary betaine in patients with premature vascular disease and mild homocysteinemia

Urinary N,N,N-trimethylglycine (betaine) and N,N-dimethylglycine (DMG) have been identified and quantified for clinical purposes by proton nuclear magnetic resonance (1H NMR) measurement in previous studies. We have assessed these procedures by using both one-dimensional (1-D) and 2-D NMR spectroscopy, together with pH titration of urinary extracts to help assign 1H NMR spectral peaks. The betaine calibration curve linearity was excellent (r = 0.997, P = 0.0001) over the concentration range 0.2-1.2 mmol/L, and CVs for replicate betaine analyses ranged from 7% (n = 10) at the lowest concentration to 1% (n = 9) at the highest. The detection limit for betaine was &lt; 15 mumol/L. Urinary DMG concentrations were substantially lower than those of betaine. Urinary betaine and DMG concentrations measured by 1H NMR spectroscopy from 13 patients with premature vascular disease and 17 normal controls provided clinically pertinent data. We conclude that 1H NMR provides unique advantages as a research tool for determination of urinary betaine and DMG concentrations.

Determinants of severity of coronary artery disease in Australian men and women

BACKGROUND

Factors predicting the occurrence of premature coronary artery disease (CAD) may not be quantitatively the same as those predicting CAD severity, particularly in women, in whom there have been few studies.

METHODS AND RESULTS

To determine factors predictive of severity of CAD and of angina pectoris, we documented atherogenic variables and the extent of CAD at angiography in 594 consecutively studied men and women aged 65 years or less. Severity was assessed from the number of involved major coronary arteries with significant (> 50%) luminal obstructions and from a coronary disease severity score. We related severity to quantitative and categorical atherogenic variables and assessed severity of angina (no angina, stable angina, or unstable angina) at the time of study in the same way. There were eight variables independently predictive of severity: in descending order of relative importance, male gender, diabetes, smoking dose, ratio of total cholesterol to high-density lipoprotein cholesterol (TC/HDL-C), lipoprotein(a) [Lp(a)], age, positive family history, and hypertension. These correctly classified 43.3% of patients into no-, one-, two-, and three-vessel disease categories and accounted for 25.8% of variance of severity. Among 246 patients not taking lipid-lowering or beta-blocking drugs, these variables (in slightly different order) correctly classified 49.2% of patients and accounted for 36% of the variance. Among men (n = 427), seven significant variables correctly classified 39.3% of patients compared with 54.5% in women (n = 167). For those not taking the above drugs, these proportions were 49.4% and 65.4%, respectively. Among the quantitative variables, total smoking dose was the most predictive independent variable irrespective of current or ex-smoking habit and was more predictive in women than in men; of the lipid variables, high TC/HDL-C (or low HDL-C) and high Lp(a) were consistently highly predictive for all patients and in the subgroup analyses. Patients with unstable angina had higher coronary severity scores and Lp(a) levels and were more likely to have diabetes, hypertension, or a positive family history.

CONCLUSIONS

We conclude that the quantitative variables most relevant to severity of premature CAD and to its prevention in Australian men and women are total amount of lifetime smoking, TC/HDL-C (or HDL-C), and Lp(a) and that patients with unstable versus stable angina usually have more severe disease and higher Lp(a).

Effect of serum lipoprotein(a) on estimation of low-density lipoprotein cholesterol by the Friedewald formula

The calculation of serum low-density lipoprotein cholesterol (LDL-C) by the Friedewald formula does not account for the cholesterol associated with lipoprotein(a) [Lp(a)]. To quantify the contribution of Lp(a) cholesterol to total serum cholesterol, we measured concentrations of serum Lp(a) by an ELISA and concentrations of other serum lipids and lipoproteins by standard assays in 23 normolipemic women, ages 50-60 years. In measuring serum high-density lipoprotein we found that polyethylene glycol 6000 precipitated &gt; 99.8% of all Lp(a). When serum Lp(a) concentrations were &lt; or = 300 mg/L, 301-600 mg/L, and &gt; 600 mg/L, the uncorrected serum LDL-C was overestimated, respectively, by a mean of 4.1% (n = 7), 8.5% (n = 8), and 21.4% (n = 8). Serum Lp(a) concentrations were positively correlated with percentage overestimation (P &lt; 0.001), but were not correlated with either corrected or uncorrected serum LDL-C. We conclude that the Friedewald formula should be modified to take into account the contribution of Lp(a) cholesterol to total serum cholesterol.

Effect of serum lipoprotein(a) on estimation of low-density lipoprotein cholesterol by the Friedewald formula

The calculation of serum low-density lipoprotein cholesterol (LDL-C) by the Friedewald formula does not account for the cholesterol associated with lipoprotein(a) [Lp(a)]. To quantify the contribution of Lp(a) cholesterol to total serum cholesterol, we measured concentrations of serum Lp(a) by an ELISA and concentrations of other serum lipids and lipoproteins by standard assays in 23 normolipemic women, ages 50-60 years. In measuring serum high-density lipoprotein we found that polyethylene glycol 6000 precipitated > 99.8% of all Lp(a). When serum Lp(a) concentrations were < or = 300 mg/L, 301-600 mg/L, and > 600 mg/L, the uncorrected serum LDL-C was overestimated, respectively, by a mean of 4.1% (n = 7), 8.5% (n = 8), and 21.4% (n = 8). Serum Lp(a) concentrations were positively correlated with percentage overestimation (P < 0.001), but were not correlated with either corrected or uncorrected serum LDL-C. We conclude that the Friedewald formula should be modified to take into account the contribution of Lp(a) cholesterol to total serum cholesterol.

The relationship between infant and parent Lp(a) levels

Since atherogenesis may begin in childhood, and elevated serum lipoprotein(a) (Lp(a)) concentrations increase cardiovascular risk, we explored the early expression of the apolipoprotein(a) (apo(a)) gene and relationships between infants' and parents' serum levels. In a consecutive series of 1032 babies aged 3-5 days the distribution of apo(a) levels was positively skewed as in adults but with lower levels: 50th and 95th percentiles were the equivalent of 30 mg/l and 130 mg/l of Lp(a) in serum. Concentrations were re-measured in 51 infants when aged 8.5 +/- 2 months together with parental values. Levels at 3-5 days and 8.5 months were highly correlated (r = 0.73, P < 0.0001, n = 51) with a twofold increase at 8.5 months. Regression coefficients between 8.5 months concentrations and those of fathers, of mothers and the average level of both parents were 0.439, 0.521 and 0.93, respectively (P < 0.0001 for each), and infant and parental levels were then not different. The positive and negative predictive values of first post-natal week capillary blood apo(a) measurements detecting a parent with serum Lp(a) above 300 mg/l were 95% and 70%. We conclude that the apo(a) gene is virtually fully expressed before 1 year during which apo(a) levels track closely and are predictive of parental values. Childhood Lp(a) measurements may identify families at enhanced cardiovascular risk and facilitate targeted prevention.

Effects of homocysteine and related compounds on prostacyclin production by cultured human vascular endothelial cells

Elevated plasma homocysteine is associated with an increased risk of intravascular thrombosis. Platelet aggregation and thrombosis are inhibited by prostacyclin produced by the vascular endothelium. Our aim was to investigate whether homocysteine and related metabolites inhibit endothelial prostacyclin production. We used a radioimmunoassay for 6-ketoprostaglandin-F1 alpha to assay medium which had been in contact with confluent cultured endothelial cells. In medium containing 20% human serum, endothelial prostacyclin production was not specifically inhibited by homocysteine, S-adenosylhomocysteine or protein-bound homocysteine. Further, there was no consistent difference in prostacyclin production by cells cultured in medium containing sera from homocystinuria patients, compared with medium containing normal healthy sera. We conclude that vascular disorder in homocystinuria is unlikely to result from effects of homocysteine or related metabolites on endothelial prostacyclin production. By contrast, S-adenosylhomocysteine and protein-bound homocysteine specifically inhibited prostacyclin production by cells cultured in medium containing 20% fetal calf serum.

Lipoprotein(a) and apolipoproteins B and A-1 in children and coronary vascular events in their grandparents

Because premature coronary vascular disease in a first-degree relative increases risk of the disease and the mechanisms may include genetically determined abnormal levels of circulating apolipoproteins, we explored the relationships between schoolchildren's apolipoprotein levels and coronary events in their parents and grandparents. We measured capillary blood concentrations of lipoprotein(a) (Lp(a) and apolipoproteins (apo B and apo A-1) in dried blood spot samples obtained by finger prick from 2010 schoolchildren aged 8 to 12 years, and questioned parents about coronary vascular events in the children's parents and grandparents. Of the 2010 questionnaires sent, 1030 (51%) were returned fully completed. Twenty-three fathers, one mother, and 645 grandparents had had coronary vascular events. There were significant associations between increased Lp(a) levels in children and the numbers of grandparents with coronary vascular events and with increasing grandparent coronary history scores (p < 0.01). There were also positive associations for apo B (p < 0.01) but none for apo A-1. Discriminate analysis showed that the log-transformed Lp(a) level was the variable most predictive of event numbers and of history scores in grandparents (Wilks lambda value = 0.984; p = 0.026); the apo B level was also predictive (Wilks lambda value = 0.988; p = 0.041), but neither the apo A-1 level nor the apo B/A-1 ratio was. We conclude that high Lp(a) and apo B levels in children aged 8 to 12 years are associated with increased risk of coronary vascular disease in older family members, even with a generation gap. These apolipoproteins may largely account for the independent contribution of family history to disease risk. Measurements of Lp(a) and apo B in schoolchildren may help to identify children and their families at increased risk and may facilitate targeting of prevention.

Disordered methionine/homocysteine metabolism in premature vascular disease. Its occurrence, cofactor therapy, and enzymology

Mild homocysteinemia occurs surprisingly often in patients with premature vascular disease. We studied the possible enzymatic sources of this mild hyperhomocysteinemia and the control of homocysteine levels in plasma by treatment of patients with the cofactors and cosubstrates of homocysteine catabolism. We assessed homocysteine metabolism in 131 patients who had premature disease in their coronary, peripheral, or cerebrovascular circulation by using a standard oral methionine-load test. Impaired homocysteine metabolism occurred in 28 patients. We assayed levels of the primary enzymes of homocysteine catabolism in cultured skin fibroblast extracts from 15 of these 28 patients. The patients' cystathionine beta-synthase levels (3.68 +/- 2.52 nmol/h per milligram of cell protein, mean +/- SD) were markedly depressed compared with those from 31 healthy adult control subjects (7.61 +/- 4.49, P < .001). The patients' levels of 5-methyltetrahydrofolate: homocysteine methyltransferase were normal. While betaine: homocysteine methyltransferase was not expressed in skin fibroblasts, 24-hour urinary betaine and N,N-dimethylglycine measurements were consistent with normal or enhanced remethylation of homocysteine by betaine: homocysteine methyltransferase in the 13 patients tested. When treated daily with choline and betaine, pyridoxine, or folic acid, there was a normalization of the postmethionine plasma homocysteine level in 16 of 19 patients. Our results indicate that mild homocysteinemia in premature vascular disease may be caused by either a folate deficiency or deficiencies in cystathionine beta-synthase activity. It does not necessarily involve deficiencies of either 5-methyltetrahydrofolate:homocysteine methyltransferase or betaine:homocysteine methyltransferase. Effective treatment regimens are also defined.

Circulating lipid hydroperoxide levels in human hyperhomocysteinemia. Relevance to development of arteriosclerosis

Elevated circulating homocyst(e)ine is a risk factor for occlusive vascular disease. We explored whether elevated plasma homocyst(e)ine is associated with increased plasma lipid hydroperoxides that might trigger vascular disease. We obtained plasma containing high levels of homocyst(e)ine from four patients with a homozygous deficiency of cystathionine beta-synthase activity and also from four heterozygotes with a deficiency of this enzyme after an oral methionine load. The mean plasma non-protein-bound homocyst(e)ine level in all subjects was more than 11-fold higher than the mean normal fasting value. Levels of high density lipoprotein (HDL) cholesteryl ester hydroperoxides (CEOOH), normalized against the concentration of free cholesterol in HDL, were not elevated in our subjects (mean +/- SD, 0.0091 +/- 0.0061) compared with values for 14 fasting healthy donors (0.0164 +/- 0.0086). An inverse dependency was observed between plasma total homocyst(e)ine and HDL CEOOH (r = -0.78, p = 0.023). Also, the ubiquinol-10/ubiquinone-10 ratio in HDL, which is expected to fall during oxidative stress, increased with plasma homocyst(e)ine. Since HDL contains the majority of detectable plasma lipid hydroperoxides, of which CEOOHs are the most abundant, our data suggest that an elevated plasma homocyst(e)ine level does not enhance oxidative stress, increase the levels of lipid hydroperoxides in plasma, or generate vascular damage by this mechanism.

Homocysteine catabolism: levels of 3 enzymes in cultured human vascular endothelium and their relevance to vascular disease

Elevated plasma homocysteine enhances the risk of thrombosis and premature arteriosclerosis. We have assessed the activity of the 3 prime enzymes of homocysteine metabolism in cultured human venous endothelial cells, in a study of their possible protective roles. In cells from 4 individuals, cultured in Dulbecco's modified Eagle medium, the mean activity +/- S.D. of cystathionine beta-synthase (nmol of product/h per mg of cell protein, at 37 degrees C) was 3.58 +/- 3.11 at pH 8.6. The assay used was our newly developed amino acid analyser-based procedure. The activity of 5-methyltetrahydrofolate:homocysteine methyltransferase at pH 7.4 was 4.12 +/- 1.25 and betaine:homocysteine methyltransferase (BHMT) was undetectable (< 1.4 nmol/h per mg protein). Cells were also cultured in a medium aimed at stimulating methionine biosynthesis, containing methionine-deficient Dulbecco's modified Eagle medium to which L-homocystine (100 mumol/l) and methylcobalamin (1 mumol/l) had been added. In these cells 5-methyltetrahydrofolate:homocysteine methyltransferase activity increased to 7.95 +/- 1.45, P < 0.001, there was a non-significant decrease in cystathionine beta-synthase activity to 2.16 +/- 1.52 and BHMT activity was still undetectable. These cells were more resistant to in vitro homocysteine-induced detachment than were cells from the same line cultured in Dulbecco's modified Eagle medium alone. Our findings establish that human endothelial cells express 2 of the 3 primary enzymes of homocysteine catabolism. They suggest that persons who are deficient in cystathionine beta-synthase or 5-methyltetrahydrofolate:homocysteine methyltransferase activity may not only develop homocysteinemia, but also have vascular endothelium which is more susceptible to damage by homocysteine than persons with normal enzyme levels.

Genes, gender and geometry and the prolapsing mitral valve

Mitral Valve Prolapse (MVP) is usually a variant of normal occurring in about 4% of the population. Complications are relatively uncommon, but false associations due to ascertainment bias have had a potential for iatrogenic harm. Adverse outcomes which do occur in a subset of MVP subjects are considered here in relation to the contributions of genes, gender and geometry. There are definite associations between MVP and several dominantly inherited connective tissue abnormalities; it occurs in 85% of adults with Marfan syndrome. All these contribute to a very small proportion of the MVP population. A larger less easily characterised group with dominant inheritance and some features of a connective tissue disorder awaits DNA studies for identification. For most MVP subjects our data define significant family aggregation consistent with polygenic inheritance; the likelihood of a first degree relative having MVP is about two and a half times the population average. There is a higher prevalence in young women than in men-5% versus 3%; this has also been demonstrated for floppy mitral valve (MV) at autopsy. MVP complications of chordal rupture, severe mitral regurgitation and infective endocarditis are, however, two to three times more common in men, are age related and evident after the age of 50 years. Higher blood pressure in men may contribute to this in accordance with a response-to-injury hypothesis to explain progressive valve changes. Leaflet, annulus and left ventricular size differences and septal changes are geometric variants with a potential for increasing tension-related valve injury.(ABSTRACT TRUNCATED AT 250 WORDS)

The Apo A, B, a of coronary risk: back to kindergarten

Approximately 1% of the population have a dominantly inherited lipid disorder predisposing to premature vascular disease. Apolipoproteins (Apo) B, and A1, the carrier proteins for the atherogenic low density lipoprotein (LDL) and the protective high density lipoprotein (HDL) cholesterol respectively are markers for these disorders, as is Apo(a), the unique carrier protein for lipoprotein(a). We assessed changes in these apolipoproteins during the first 12 years of life, aiming to detect young families with inherited dyslipidaemia and implement early prevention. Among 1032 consecutively born babies in whom levels were measured within their first week and at a mean age of 8.5 months, the Apo B/A1 ratio and Apo(a) both tracked closely (p < 0.01 and < 0.0001). High B/A1 ratios (> 95 percentile) identified two families with familial hypercholesterolaemia, and infants with high Apo B identified two families with hyperapolipoprotein B. Apo(a) levels increased twofold between the first week and 8.5 months and were highly correlated (r = 0.73, p < 0.0001). Levels at 8.5 months were not different from parental values and were closely correlated with them. We then assessed school children aged eight to 12 years. In a pilot study (n = 1400) we have established normal apolipoprotein values and distribution patterns and defined the 95th percentile for each. This study is continuing and parents of children with high levels are being recalled (with their children) for lipid measurements. Our findings indicate that our approach is feasible and has wide acceptance, and that measuring Apo B/A1 and Apo(a) in childhood identifies families at increased cardiovascular risk. We have yet to assess the efficacy of our family-based coronary prevention programme.

An indirect sandwich ELISA for LP(a) in serum and dried blood spots

We have established a reproducible and inexpensive indirect sandwich ELISA for Lp(a) quantitation in both serum and dried blood spot samples. All reagents used in the assay are available commercially. The intra-assay CVs were 3.8 +/- 0.9% for serum and 4.5 +/- 1.7% for dried blood spots on filter paper. The inter-assay CVs were 6.3 +/- 2.3% and 4.5 +/- 0.1% for serum and dried blood spot, respectively. Lp(a) concentrations measured by the ELISA and a commercial RIA were highly correlated (r = 0.989, n = 60, P less than 0.001). However concentrations measured by RIA were 34.3% +/- 9.7% higher than those by ELISA. Lp(a) concentrations in serum and in dried blood spots were also highly correlated (r = 0.966, n = 40, P less than 0.001). This indirect ELISA is suitable for assaying large numbers of serum or dried blood spot samples. However, the differences between the concentrations measured by ELISA and RIA stress the need for standardization of Lp(a) measurements.

Decreases in Apolipoprotein(a) after Renal Transplantation: Implications for Lipoprotein(a) Metabolism

Serum concentrations of apolipoprotein(a) [apo(a)], the unique glycoprotein of lipoprotein(a), are increased in patients with end-stage renal failure. We prospectively studied serum apo(a) and other lipoproteins in 20 consecutive patients, ages 46 +/- 11 years, before and for six months after successful renal transplantation. All patients received cyclosporine, and no patient was treated for hyperlipidemia. The mean creatinine clearance increased from 7.5 mL/min before transplant surgery to 40.9 mL/min six months afterwards (P less than 0.001). Apo(a) decreased from a median of 403 units/L before transplantation to 184 units/L at one week (P less than 0.001) and was 170 units/L (P less than 0.001) at six months. For the assay used, 1 unit of apo(a) is equivalent to 1 mg of lipoprotein(a). In contrast, from baseline to six months, increases were found for low-density lipoprotein (LDL) cholesterol (P = 0.03), high-density lipoprotein cholesterol (P = 0.06), apo B (P = 0.07), and apo A-I (P = 0.01). The decrease in apo(a) in individual patients was significantly correlated with the increase in creatinine clearance (r = -0.48, P less than 0.001). The single patient who developed nephrotic syndrome after renal transplantation had marked increases in apo(a) (693-1595 units/L), apo B, and LDL cholesterol, which paralleled the degree of proteinuria. These findings suggest that abnormal renal function affects the regulation of lipoprotein(a) metabolism.

Early expression of the apolipoprotein (a) gene: relationships between infants' and their parents' serum apolipoprotein (a) levels

The serum concentration of apo(a), the unique apolipoprotein of lipoprotein (a), reflects serum lipoprotein (a) levels. High concentrations are associated with increased cardiovascular risk. Inasmuch as atherogenesis may begin in childhood, the early expression of the apo(a) gene and relationships between serum levels in infants and their parents were explored. Serum apo(a) and lipid profiles were measured in 51 infants when aged 8.5 +/- 2 months. They were from among 1032 consecutively born babies in whom apo(a) levels had been measured on day 2 to 5. Levels in 18 infants were in the top 5% of the neonatal apo(a) distribution and in 33 from below the 95th percentile. Parental values were also assessed. Infants' apo(a) levels (n = 51) at the ages of 2 to 5 days and 8.5 +/- 2.3 months were highly correlated (r = .73, P less than .0001) and increased from an initial median value of 48 U/L (range 1 to 462 U/L) to 100 U/L (5 to 969 U/L) at 8.5 months, and they were then not different from parental levels. Measurements at both times were closely correlated with parental levels. Regression coefficients between 8.5-month levels, and the levels of fathers, of mothers, and the average level of both parents were 0.439, 0.521 and 0.93, respectively (P less than .0001 for each). It is concluded that the gene for the regulation of apo(a) is fully expressed before the age of 1 year. The apo(a) levels in infants during this time track closely and are predictive of parental values.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreases in apolipoprotein(a) after renal transplantation: implications for lipoprotein(a) metabolism

Serum concentrations of apolipoprotein(a) [apo(a)], the unique glycoprotein of lipoprotein(a), are increased in patients with end-stage renal failure. We prospectively studied serum apo(a) and other lipoproteins in 20 consecutive patients, ages 46 +/- 11 years, before and for six months after successful renal transplantation. All patients received cyclosporine, and no patient was treated for hyperlipidemia. The mean creatinine clearance increased from 7.5 mL/min before transplant surgery to 40.9 mL/min six months afterwards (P less than 0.001). Apo(a) decreased from a median of 403 units/L before transplantation to 184 units/L at one week (P less than 0.001) and was 170 units/L (P less than 0.001) at six months. For the assay used, 1 unit of apo(a) is equivalent to 1 mg of lipoprotein(a). In contrast, from baseline to six months, increases were found for low-density lipoprotein (LDL) cholesterol (P = 0.03), high-density lipoprotein cholesterol (P = 0.06), apo B (P = 0.07), and apo A-I (P = 0.01). The decrease in apo(a) in individual patients was significantly correlated with the increase in creatinine clearance (r = -0.48, P less than 0.001). The single patient who developed nephrotic syndrome after renal transplantation had marked increases in apo(a) (693-1595 units/L), apo B, and LDL cholesterol, which paralleled the degree of proteinuria. These findings suggest that abnormal renal function affects the regulation of lipoprotein(a) metabolism.

Betaine:homocysteine methyltransferase--a new assay for the liver enzyme and its absence from human skin fibroblasts and peripheral blood lymphocytes

Chronic elevation of plasma homocysteine is associated with increased atherogenesis and thrombosis, and can be lowered by betaine (N,N,N-trimethylglycine) treatment which is thought to stimulate activity of the enzyme betaine:homocysteine methyltransferase. We have developed a new assay for this enzyme, in which the products of the enzyme-catalysed reaction between betaine and homocysteine are oxidised by performic acid before being separated and quantified by amino acid analysis. This assay confirmed that human liver contains abundant betaine:homocysteine methyltransferase (33.4 nmol/h/mg protein at 37 degrees C, pH 7.4). Chicken and lamb livers also contain the enzyme, with respective activities of 50.4 and 6.2 nmol/h/mg protein. However, phytohaemagglutinin-stimulated human peripheral blood lymphocytes and cultured human skin fibroblasts contained no detectable betaine:homocysteine methyltransferase (less than 1.4 nmol/h/mg protein), even after cells were pre-cultured in media designed to stimulate production of the enzyme. The results emphasize the importance of the liver in mediating the lowering of elevated circulating homocysteine by betaine.

Apolipoproteins A-I and B and the B/A-I ratio in the first year of life

To investigate early detection of young families with inherited dyslipidemia, we assessed changes in circulating apolipoprotein (apo) B and A-I levels and the apo B/A-I ratio during the 1st year of life and their relations to parental values. After measuring initial dried blood spot capillary blood levels in 919 babies when aged 4.25 +/- 0.98 d (mean +/- SD), we recalled at a mean age of 8.5 +/- 2.3 mo those with levels in one or more of the following categories: the top 5% of apo B values (group 1), the top 5% of apo B/A-I ratios (group 2), the bottom 5% of apo A-I values (group 3), and a group of 18 infants (group 4) who were not in any of the above three categories. We thus obtained serum lipid measurements in 51 infants and their parents. Two of the 13 group 1 infants had persistent hyperapo B at 8.5 mo; there was an inverse relationship between apo B and apo A-I levels in this group (p less than 0.001). Two of 11 babies in group 2 had lipid profiles consistent with familial hypercholesterolemia. However, none of the infants in group 3 had evidence at 8.5 mo of abnormal apo A-I or HDL levels, nor did their parents. For groups 1, 2, and 3, there was at 8.5 mo a regression of apo B and A-I toward mean levels for the "normal" 18 babies of group 4. In contrast, the high apo B/A-I ratios in group 2 remained high (p less than 0.01) and showed evidence of tracking.(ABSTRACT TRUNCATED AT 250 WORDS)