Nitric oxide induces and inhibits apoptosis through different pathways

Physiological levels of nitric oxide (NO) regulate vascular tone and protect the microvasculature from injury whereas excessive NO may be harmful. The present study explored the effects of NO on human endothelial cell apoptosis. We found that the NO donor S-nitroso-N-acetylpenicillamine (SNAP) inhibited TNFalpha-induced endothelial apoptosis and that this was mediated partly through the cGMP pathway. In contrast, high SNAP concentration induced endothelial apoptosis via cGMP-independent pathways and the cGMP pathway protected against NO-induced apoptosis. These findings demonstrate that low NO concentrations contribute to human endothelial cell survival, whereas higher NO concentrations are pathological and promote destruction of endothelial cells.

Novel risk factors for vascular disease: the homocysteine hypothesis of cardiovascular disease

The possibility that modest elevations in the level of blood homocysteine (hyperhomocysteinaemia) could contribute to cardiovascular disease arose from investigation of patients with rare, severe homocysteine elevations caused by cystathionine beta-synthase deficiency. Such patients often had thromboembolic events before the age of 30 years. Since the established cardiovascular risk factors could only partly account for the occurrence and severity of vascular disease in the general population, other risk factors had to exist, and homocysteine elevation seemed to be a possible candidate. Australian case-control studies identified an association between mild homocysteine elevation and early-onset coronary disease, and also with chronic renal failure. Patients in the latter group have a high prevalence of unexplained vascular disease and particularly high homocysteine levels. Such elevations in levels of homocysteine in vascular patients could usually be normalised by daily supplementation with folic acid (1-5 mg) while in patients with chronic renal failure 5 mg of folic acid daily markedly reduced the increased concentrations of homocysteine. These initial observations have been confirmed by many investigators and biologically plausible mechanisms for homocysteine-induced vascular dysfunction, and particularly endothelial dysfunction, have been identified. However, associations between hyperhomocysteinaemia and other risk factors, such as smoking and hypertension, have also been documented and need to be controlled for when assessing any increase in risk that homocysteine may independently confer. Although it has been established that lowering the greatly elevated blood homocysteine levels in homocystinuria, due to cystathione beta-synthase deficiency, unquestionably reduces cardiovascular risk, it remains to be determined whether normalising mild homocysteine elevation could reduce cardiovascular risk. Trials to test this possibility have been initiated and others are planned.

Apolipoprotein screening in Australian children: feasibility and the effect of age, sex, and ethnicity

OBJECTIVE

(i) To evaluate the feasibility of detecting adverse lipid profiles in schoolchildren by measuring capillary dried blood spot apolipoprotein levels, and (ii) to assess the effect of age, sex and ethnicity on apolipoprotein levels.

DESIGN

We measured capillary dried blood spot apolipoproteins B and A-I (apo B and apo A-I); assessed levels in relation to age, sex and ethnicity; and recalled children with elevated levels for a full lipid profile measurement.

PARTICIPANTS AND SETTING

6992 children (3501 boys and 3491 girls), aged 5-13 years, from schools in eastern Sydney, 1991-1995.

MAIN OUTCOME MEASURES

Capillary blood levels of apolipoproteins B and A-I, and serum total cholesterol level.

RESULTS

Of the 6951 children who provided an adequate fingerprick blood sample, we recalled 1465 children (21.1%) (640 boys [43.7%] and 825 girls [56.3%]) with elevated apo B levels and/or apo B:apo A-I ratios for further testing, either by us or by their family doctor (overall estimated compliance rate up to 70%). Among the 458 children who returned to us, there was a 90% positive predictive value for a total cholesterol level of over 4.5 mmol/L in those with both elevated apo B levels and high apo B:apo A-I ratios. Girls had higher apo B levels and apo B:apo A-I ratios than boys (P < 0.00001 for both), and in both sexes there was a trend downwards for apo B and upwards for apo B:apo A-I ratio over the age range tested, but levels were relatively stable between the ages of 6 and 10 years. Indian children (1.5% of the screened population) had the highest apo B levels, followed by white children (71.1%); Asian children (9.2%) had the lowest (P < 0.00001 compared with Indian and white children).

CONCLUSIONS

The high positive predictive value of capillary blood apolipoprotein levels for an adverse lipid profile in children suggests that measuring apolipoprotein levels by this method is a useful initial approach to cardiovascular risk assessment.

Genetic contribution of the endothelial constitutive nitric oxide synthase gene to plasma nitric oxide levels

Nitric oxide (NO) has an important physiological role in regulating vascular tone and is also relevant to many pathological processes including hypertension and atherosclerosis. Endothelial constitutive nitric oxide synthase (ecNOS) is the key enzyme in determining basal vascular wall NO production. We used a combination of maximum-likelihood-based statistical genetic methods to explore the contributions of the ecNOS gene and other unmeasured genes to basal NO production measured by its metabolites (NOx: nitrite and nitrate) in 428 members of 108 nuclear families. Our initial quantitative genetic analysis estimated that approximately 30% of the variance in fasting NOx levels is due to genes (chi 2(1) = 16.04, P = .000062). Complex segregation analysis detected the effects of both a single locus and residual polygenes on NOx levels, and measured genotype analysis showed that plasma NOx levels in those homozygous for the rare allele (64.9 +/- 7.8 mumol/L) were significantly higher (P = .000242) than those homozygous for the common allele (30.2 +/- 3.1 mumol/L). The results of the variance component linkage analysis were consistent with linkage of a quantitative trait locus in or near the ecNOS gene to variation in plasma NOx levels (P = .0066). While many environmental factors have been shown to alter transiently plasma NOx levels, our study is the first to identify a substantial effect of the ecNOS locus on the variance of plasma NOx, i.e. basal NO production. This finding may be relevant to atherogenesis and NO-related disorders.

Interactive effect of the p53 gene and cigarette smoking on coronary artery disease

OBJECTIVE

p53 is a tumour suppressor protein involved in the control of cell growth and has an established role in carcinogenesis, particularly in relation to smoking. It may also be related to arteriosclerosis by affecting smooth muscle cell proliferation, a feature of atherogenesis.

METHODS

We explored a role for p53 in atherogenesis by assessing the association between two DNA polymorphisms of the p53 gene (MspI at intron 6 and HaeIII at intron 1) and angiographically documented coronary artery disease (CAD) in 654 Australian Caucasian patients.

RESULTS

There was a significant interactive effect of the two polymorphisms and cigarette smoking on CAD in a logistic regression analysis (P = 0.0039) but no association between CAD and either individual p53 polymorphic marker. CAD occurrence was more frequent in non-smoking patients with rare alleles at both sites (85.0%) compared to those homozygous for common alleles at both sites (70.4%). However, this was not seen in smokers (85.7 vs 82.8%). In all 654 patients cigarette smoking remained a significant predictor of CAD irrespective of p53 genotypes (P = 0.0065).

CONCLUSIONS

Our findings identify an interactive effect of both p53 polymorphisms and cigarette smoking on the occurrence of coronary artery disease in that non-smoking patients with rare alleles at both sites had increased incidence of CAD. They illustrate the relevance of genotype-specific and environment-dependent enhanced cardiovascular risk and foreshadow a need for further studies to establish functional changes.

The natural history of vascular disease in homocystinuria and the effects of treatment

Among 40 patients with homocystinuria due to cystathionine beta-synthase deficiency diagnosed in the state of New South Wales, Australia (population 6 million) and followed long-term, there were 10 deaths at ages 2-30 years. Of these 8 were definite vascular deaths, one was a presumed vascular death, and the other was due to an accident and unrelated to homocystinuria. The vascular deaths were all early cases and only one patient, a pyridoxine-responsive 30-year-old woman, had been prescribed adequate treatment although it was uncertain that she was taking it. In 32 patients of mean age 30 years (range 9-66 years) there were 539 patient-years of treatment with pyridoxine, folic acid and hydroxocobalamin. There were 17 pyridoxine-responsive patients and all maintained plasma total free homocyst(e)ine levels < 20 mumol/L over an average treatment period of 16.6 years. The 15 nonresponsive patients received additionally 6-9 g of betaine daily. This resulted in a further 74% mean decline (+/-14% SD) in plasma total free homocyst(e)ine, persisting during an average (post-betaine) treatment period of 11 years; current mean +/- SD levels are 33 +/- 17 mumol/L (n = 15). There were two vascular events during treatment, one fatal pulmonary embolus (see above) and one myocardial infarction, whereas without treatment, 21 would have been expected, chi2 = 14.22, p = 0.0001, relative risk 0.09 (95% CI 0.02-0.38). There were no events during 258 patient-years of treatment in the 15 pyridoxine-nonresponsive patients (p < 0.005 versus expected untreated). Nineteen patients had a total of 19 major and 15 minor operations requiring anaesthetic, and three had successful pregnancies, one whilst receiving betaine. There were no thromboembolic complications. We conclude that treatment which effectively lowers circulating homocyst(e)ine, even to suboptimal levels, markedly reduces cardiovascular risk in patients with cystathionine beta-synthase deficiency, and that betaine therapy contributes importantly to this in pyridoxine-nonresponsive patients. Betaine as additional therapy is safe and effective for at least 16 years.

Circulating transforming growth factor beta 1 and coronary artery disease

OBJECTIVE

Transforming growth factor beta 1 (TGF-beta 1), a multifunctional cytokine, is involved in many physiological and pathological processes and possibly in atherogenesis.

METHODS

We explored the association between circulating plasma TGF-beta 1 measured by ELISA and coronary artery disease (CAD) assessed angiographically in 371 Caucasian patients (269 men and 102 women) aged < or = 65 years.

RESULTS

While mean +/- s.e.m total TGF-beta 1 was not different among patients with (56.9 +/- 1.5 ng/ml) or without (54.6 +/- 2.8 ng/ml) angiographically demonstrable CAD, naturally active TGF-beta 1 was significantly higher in CAD patients (1.74 +/- 0.18 vs 0.96 +/- 0.17 ng/ml, P < 0.01). Active TGF-beta 1 increased with the number of major coronary arteries with more than 50% luminal obstruction (P < 0.01) and patients with triple vessel disease had twice the level of those with no or mild vessel disease (2.15 +/- 0.46 vs 1.12 +/- 0.14 ng/ml, P < 0.001). We found no relationship between TGF-beta 1 and Lp(a), but TGF-beta 1 was significantly correlated with circulating fibrinogen (r = 0.178, P = 0.005) and fasting glucose (r = 0.177, P = 0.007) levels.

CONCLUSIONS

Our study identifies an increase in active TGF-beta 1 levels with both the occurrence and severity of CAD which is independent of standard CAD risk factors. This may reflect a 'double-edged sword' effect of TGF-beta 1 in that it may reduce atherogenesis by inhibiting smooth muscle cell proliferation but, when there is ongoing vessel wall injury, enhance it by promoting excessive extracellular matrix accumulation. The outcome could represent a complex balance between these two competing influences.

A twin study of polycystic ovary syndrome and lipids

Our objective was to assess the relative contribution of genetic and environmental factors (particularly androgens) on circulating levels of lipid fractions and to determine the effect, if any, of polycystic ovary syndrome (PCOS) on lipid fractions. The study was carried out in the outpatient clinic of the Royal Hospital for Women, Paddington, Sydney, Australia. A group of 19 monozygotic (MZ) and 15 dizygotic (DZ) twin pairs was identified from the National Twin Register. Ultrasound clinical and biochemical parameters were used to define polycystic ovaries. Serum androgen and lipid fractions were also measured. Eleven pairs of twins (five MZ, six DZ) were scan discordant (i.e. one twin had polycystic ovaries and the co-twin did not). Serum levels of the lipoprotein fractions in twins with polycystic ovaries were not significantly different from the levels found for their co-twins with normal ovaries. There were no significant correlations between androgen-related hormones and any of the lipid measurements. Body mass index (BMI) was positively correlated with triglycerides and lipoprotein (a), and negatively correlated with high-density lipoprotein cholesterol (HDL-C). Sex hormone-binding globulin (SHBG) levels were negatively correlated with triglycerides and lipoprotein (a) and positively associated with HDL-C. Fasting insulin levels were significantly correlated with triglycerides and negatively with HDL-C. The MZ intraclass correlation exceeded that of the DZ twin pairs for all the lipid variables measured. The heritability estimates for lipoprotein (a), apolipoprotein B, total cholesterol and HDL-C were 0.95, 0.56, 0.48 and 0.54, respectively. However, the intraclass correlation coefficient for triglycerides was not significantly different between MZ and DZ twins, but maximum likelihood analysis indicated that at least 10% of the variance of the circulating triglyceride concentration is determined by genetic factors. We conclude that twins discordant for the PCOS do not have significantly different lipid fractions.

Growth hormone increases and insulin-like growth factor-I decreases circulating lipoprotein(a)

BACKGROUND

Elevated serum lipoprotein(a) (Lp(a)) is a strong risk factor for coronary artery disease (CAD). Genetic factors appear to account for the major variance in Lp(a) levels but the contribution hormones make in modulating Lp(a) levels is not yet clear. In the present investigation we determined the effects of human growth hormone (hGH) and insulin-like growth factor-I (IGF-I) on circulating Lp(a).

METHODS

Four groups of patients were studied. Group a: adults with GH deficiency (n = 7) treated with hGH (0.05 U/kg/day, s.c.); group b: girls with Turner syndrome (n = 7) treated with hGH (0.1 U/kg/day, s.c.); group c: prepubertal boys with idiopathic short stature (n = 6) treated with the GH secretagogue (GHRP) hexarelin (60 micrograms t.i.d. intranasally); group d: Laron syndrome patients (n = 10) treated with IGF-I (100-200 micrograms/kg/day, s.c.). Following overnight fasting, serum was sampled before the initiation of treatment and during 6-9 months treatment.

RESULTS

Serum IGF-I rose significantly in all the subjects in all four groups. In the first three groups in which IGF-I was elevated by exogenous or endogenous GH stimulation, serum Lp(a) increased significantly (119 +/- 35%, P < 0.01; 126 +/- 44%, P < 0.05; 102 +/- 29%, P < 0.01 for groups a, b, and c respectively). By contrast, serum Lp(a) levels decreased in group d to whom exogenous IGF-I was administered (-66 +/- 5%, P < 0.001). The differential effect of endogenous vs exogenous IGF-I on serum Lp(a) paralleled the behaviour of serum insulin. Insulin was significantly increased in all the subjects receiving hGH or GHRP (65.2 +/- 31%, P = 0.109; 93.7 +/- 53%, P = 0.062; 353.8 +/- 52.7%, P < 0.01 for groups a, b, and c respectively) whereas insulin levels were reduced following exogenous administration of IGF-I (-34.1 +/- 9.1%, P < 0.01).

CONCLUSIONS

We conclude that long-term GH treatment increases and IGF-I decreases circulating levels of Lp(a). These findings may have clinical relevance in view of the increasing use of hGH in children and adults and the role of Lp(a) as a CAD risk factor.

Polymorphisms of factor V, factor VII, and fibrinogen genes. Relevance to severity of coronary artery disease

We explored the associations between G-->A mutations of factor V and factor VII genes and the Hae III polymorphism of the fibrinogen gene and the severity of coronary artery disease (CAD), as assessed angiographically in 545 white Australian patients (388 male and 157 female) aged < or = 65 years. We also assessed the relations with other potentially atherogenic variables. Elevated fibrinogen levels were associated with more severe CAD (P < .05), but none of the factor V, factor VII, and fibrinogen DNA variants were predictive of CAD severity, as assessed by the number of significantly diseased vessels (> 50% luminal obstruction). The rare allele frequencies of factor V (A allele), factor VII (M2 allele), and fibrinogen (H2 allele) were .025, .114, and .201 for men and .022, .077, and .169 for women, respectively, and were not different from those in healthy whites. In the patient population, there was a strong, positive association between lifetime smoking dose (in pack-years) and circulating fibrinogen levels (r = .184, P = .001). This association was stronger than that between current smoking habit and fibrinogen and is consistent with a dosage effect. However, there was no significant contribution of fibrinogen genotype to fibrinogen levels in this patient population. We conclude that elevated fibrinogen levels are associated not only with the occurrence of CAD but also with more severe CAD and that measurement of DNA variants of the factor V, factor VII, and fibrinogen genes that we assessed may not provide information in predicting CAD severity in addition to that obtained by measuring circulating levels of the relevant clotting factors. There is, moreover, a positive dosage effect (in pack-years) of smoking on circulating fibrinogen levels.

Insulin-like growth factor-I decreases serum lipoprotein (a) during long-term treatment of patients with Laron syndrome

An increased circulating level of lipoprotein(a) [Lp(a)] is a well-recognized risk factor for coronary artery disease. While much remains to be understood about its regulation and physiological functions, we explored the effect of recombinant insulin-like growth factor-I (IGF-I) administration on circulating Lp(a) levels in 10 Laron syndrome (LS) patients (five children and five adults) with inherited IGF-I deficiency. There was no relationship between pretreatment or posttreatment Lp(a) levels and age and sex of the patients. With IGF-I treatment for 6 to 12 months, there was a significant reduction in Lp(a) (65.7% +/- 15.5%, P < .0001) from the pretreatment level of 76 +/- 45 mg/L to the posttreatment level of 29 +/- 26 mg/L. This decrease was dosage-dependent on the IGF-I administered (r = .685, F = 0.708, P = .029) and correlated more strongly with the dosage ratio of the end to the beginning of treatment (r = .78, F = 12.23, P = .008). The higher the IGF-I dose and the higher the dose ratio, the greater the Lp(a) decrease and the lower the Lp(a) at the end of treatment. In conclusion, we observed a dose-dependent relationship between IGF-I administration and Lp(a) reduction in patients with LS. Further studies are needed to elucidate the mechanism of the effect, but our findings suggest a possible metabolic link between these two and shed more light on the regulation of apolipoprotein(a) [apo(a)] expression. It could also open an avenue for additional therapeutic usage of IGF-I.

Growth hormone treatment increases circulating lipoprotein(a) in children with chronic renal failure

Cardiovascular disease is the major cause of death in chronic renal failure (CRF) patients managed by dialysis or kidney transplantation. Whilst the use of human growth hormone (hGH) is of established benefit in CRF children particularly in those with short stature, in the present study we assessed in CRF children the effect of hGH treatment on circulating lipoprotein(a) [Lp(a)], a genetically determined cardiovascular risk factor. We studied 15 CRF children treated by dialysis or conventional therapy and after kidney transplantation. Overnight fasting blood samples were collected immediately before and after 6 months hGH treatment. In all but one of the children there was a significant increase in serum Lp(a) over the 6 month treatment period -(+)66.7% over the basal levels (range 14 to 180%). After the hGH treatment, in six children Lp(a) levels were elevated to above 300 mg/l, the cut-off level for increased coronary artery disease (CAD) risk. Concomitantly/children also had an increase in serum levels of IGF-I (+96.4%) and insulin (+85.8%). All children had an accelerated growth velocity during the treatment; there was no effect on serum creatinine. Our study shows that hGH treatment in CRF children, though beneficial in its growth promoting effects, increases the already characteristically high levels of serum Lp(a), a risk factor for CAD, and that serum Lp(a) monitoring during treatment with hGH may be useful in evaluating future cardiovascular risk.

Polymorphisms at the 5'-end of the apolipoprotein AI gene and severity of coronary artery disease

Elevated HDL-cholesterol (C) and apo AI are associated with decreased coronary artery disease (CAD) risk. We determined distributions of two MspI polymorphisms of the apo AI gene, associated in other studies with increased HDL-C, among 644 patients aged < or = 65 years in relation to circulating lipids and CAD severity assessed angiographically. The rare allele distributions at both sites were in Hardy-Weinberg equilibrium in these patients but the base changes were not associated with HDL-C and apo AI levels. However, patients homozygous for the -75 bp substitution were more likely to have one or more significantly diseased vessels (> 50% luminal obstruction)(OR: 4.75, 95%CI: 1.10- 20.46) as also were patients with the rare +83 bp alleles (OR: 2.56, 95%CI: 1.13-5.81). While there was an additive effect of the two polymorphisms to have severe CAD (OR: 6.33, 95%CI: 1.33-30.02), the polymorphism at +83 bp remained significant in predicting CAD severity after adjusting for other variables in a logistic regression analysis (OR: 2.95, 95%CI: 1.26-6.90), which was also strongly associated with the positive family CAD history (P = 0.009). We conclude that patients with these base changes in this Australian coronary population do not have increased HDL-C and apo AI levels but do have more severe CAD.

Distribution in healthy and coronary populations of the methylenetetrahydrofolate reductase (MTHFR) C677T mutation

Modest elevations of circulating homocyst(e)ine are common in patients with vascular disease. We explored in normal and coronary artery disease (CAD) populations the distribution of a mutation in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene that results in enzyme thermolability and reduced activity and in homocyst(e)ine elevation to assess its relevance to risk. We identified the C to T substitution at the MTHFR locus and compared the distributions of genotypes in 565 patients aged < or = 65 years without and with angiographically documented CAD and in 225 healthy subjects. In the patients, we also assessed interrelations between genotypes and CAD occurrence and severity, as well as standard risk factors. The frequency of homozygotes for the mutation was the same in patients with and without CAD and in healthy subjects (11.6%, 11.0%, and 10.7%, respectively: P > .5 for each). There was also no excess among the 419 patients with severe disease (ie, one or more vessels with > 50% luminal obstruction) compared with those with no or mild CAD (odds ratio: 1.004; 95% confidence interval: 0.59 to 1.70). Homozygosity for the mutation was also not associated with a history of myocardial infarction or the presence or severity of angina. However, body mass index increased linearly with the presence of the mutant allele (P = .005), and the mutation and hypertension were weakly associated (P = .036). We conclude that the MTHFR genotype is not a risk factor for coronary disease in this Australian population but that the strong association found with body mass index should be explored further.

Association between an angiotensinogen microsatellite marker in children and coronary events in their grandparents

BACKGROUND

Recently we found that the deletion (D) allele of the insertion/deletion (I/D) polymorphism of the ACE gene in 404 children was associated with a history of coronary artery disease (CAD) in their grandparents. This led us to explore polymorphisms in other genes of the renin-angiotensin system in this same population.

METHODS AND RESULTS

We determined the genotypes for three microsatellite markers located near or in the angiotensinogen, angiotensin II (type-1) receptor, and renin genes in the children and related the allele frequencies to grandparental CAD. We found a significant association between the angiotensinogen marker in children and grandparental CAD (chi2 = 42.2, P = .00001) with these children having an excess of the 125-bp and 129-bp alleles (odds ratio, 2.5; 95% confidence interval, 1.7 to 3.7). Greatest grandparental risk was when their grandchildren had the 125-bp/125-bp, 129-bp/129-bp, or 125-bp/129-bp genotypes (odds ratio, 7.75; 95% confidence interval, 2.2 to 27). There was no association between the microsatellites at either the angiotensin II (type-1) receptor (P = .8) or renin (P = .2) genes in children and grandparental CAD and none between the angiotensinogen and ACE polymorphisms in relation to CAD family history.

CONCLUSIONS

This study identifies a significant association between an angiotensinogen marker in children and grandparental CAD. There was no association between the microsatellites at either the angiotensin II (type-1) receptor or renin genes and CAD in this population. We conclude that the angiotensinogen polymorphism as well as the ACE polymorphism may explain a part of the risk related to a family history of CAD.

Common DNA polymorphisms at the lipoprotein lipase gene. Association with severity of coronary artery disease and diabetes

BACKGROUND

DNA variants of the lipoprotein lipase gene are associated with changes in lipid metabolism similar to those in diabetes and may relate to the development of atherosclerotic lesions, particularly premature lesions.

METHODS AND RESULTS

To determine whether lipoprotein lipase gene variants are relevant to ongoing atherogenesis, we explored relationships between two common lipoprotein lipase gene polymorphic markers, Pvu II at intron 6 and HindIII at intron 8; the severity of coronary artery disease (CAD); and lipid variables in 475 white patients 65 years of age or younger. We assessed CAD severity as the number of significantly stenosed (> 50% luminal obstruction) major coronary arteries at angiography and by the Green Lane coronary score. We found a significant association between the Pvu II polymorphism and the number of significantly diseased vessels (P = .0099) and coronary score (P = .028), with the Pvu II(-) alleles associated with less severe disease. The HindIII polymorphism was not associated with severity but had an additive effect with the Pvu II polymorphism. There was a close relationship between the Pvu II(+/+) genotype and the presence of diabetes (P = .0025), with an OR of 3.12 (95% CI, 1.30 to 7.49) compared with the Pvu II(-/-) genotype. The interaction between these polymorphisms and CAD severity (rather than occurrence) was independent of the levels of triglycerides and HDL cholesterol and of other lipid variables. There was also a dosage-dependent relationship between the Pvu II polymorphism and levels of triglyceride. The Pvu II(-) allele was associated with low levels and variances of triglycerides.

CONCLUSIONS

We conclude that the lipoprotein lipase Pvu II polymorphism is significantly associated with CAD severity and with type II diabetes in CAD patients, independent of changes in circulating lipid levels. These findings may be relevant to mechanisms mediating atherogenesis.

Human homocysteine catabolism: three major pathways and their relevance to development of arterial occlusive disease

Two separate metabolic pathways that methylate homocysteine to methionine are known in humans, utilizing, respectively, 5-methyltetrahydrofolate and betaine as methyl donors. Deficiency of the folate-dependent methylation system is linked to hyperhomocysteinemia. Our data suggest that this deficiency leads to concurrent metabolic down-regulation of homocysteine transsulfuration that may contribute to hyperhomocysteinemia. By contrast, no instances have been reported of hyperhomocysteinemia resulting from deficiencies of betaine-dependent homocysteine methylation. Long-term betaine supplementation of 10 patients, who had pyridoxine-resistant homocystinuria and gross hyperhomocysteinemia due to deficiency of cystathionine beta-synthase activity, caused a substantial lowering of plasma homocysteine, which has now been maintained for periods of up to 13 years. Betaine had to be taken regularly because the effect soon disappeared when treatment was stopped. In conclusion, depressed activity of the transsulfuration pathway may contribute to hyperhomocysteinemia because of primary deficiencies of enzymes of either the transsulfuration or of the folate-dependent methylation pathways. Stimulation of betaine-dependent homocysteine remethylation causes a commensurate decrease in plasma homocysteine that can be maintained as long as betaine is taken.

Relevance of body weight to apolipoprotein levels in Australian children

OBJECTIVES

To assess weight and apolipoprotein profiles in a representative sample of primary school children.

PARTICIPANTS AND SETTING

1543 children (936 girls and 607 boys) aged 6-11 years from schools in the Eastern Sydney Area Health Service region in 1994.

METHODS

We measured body mass index (BMI) and capillary blood apolipoprotein (apo) B and A-I levels (the carrier proteins for low and high density lipoprotein cholesterol, respectively) as well as lipoprotein (Lp) (a). We related BMI levels to those documented in the 1985 Australian Council on Health, Physical Education and Recreation (ACHPER) survey of school children.

RESULTS

Compared with the ACHPER distribution, BMI was increased in the boys but not in the girls; 16.8% of boys were above the 90th percentile of the ACHPER distribution (P = 0.003) and only 6.5% were below the 10th percentile (P = 0.046). There were 45 boys (7.4%) and 53 girls (5.7%) with BMIs above the 95th percentile who were, by definition, obese. They had highly significant increases in apo B (P = 0.003) and apo B: apo A-I ratio (P = 0.0001) compared with children in the normal BMI range (10th-90th percentiles); and 20% of the population, including the obese group, also had Lp(a) levels greater than 300 mg/L. The results in children aged 10 and 11 years were not different from those of the whole group, consistent with an absence of possible confounding effects due to early puberty or smoking.

CONCLUSIONS

There was an increase in weight relative to height in boys aged 6-11 years in eastern Sydney, compared with the 1985 ACHPER survey. In both boys and girls with the highest BMI category, levels of apo B and the apo B: apo A-I ratio were significantly increased. As these apolipoprotein changes are correlated closely with early onset atherogenesis and are correctable, their identification offers prospects for prevention.

New MspI polymorphism at +83 bp of the human apolipoprotein AI gene: association with increased circulating high density lipoprotein cholesterol levels

We recently showed that loss of a MspI restriction site in the 5'-end (intron 1) of the apolipoprotein (apo) AI gene is due to a C to T transition (+83 bp) and/or a G to A transition (+84 bp). Since this region may be relevant to the regulation of apo AI gene expression and therefore to plasma high density lipoprotein cholesterol (HDL-C), we explored the association between this MspI polymorphic site and circulating HDL-C levels in 243 healthy Caucasians. There were 143 aged 18-67 years (60 males and 83 females) and 100 aged 6-12 years (58 males and 42 females). We also compared this association with a known MspI polymorphic site, a G to A transition at -75 bp of the apo AI gene. The rare allele (-) frequency for the polymorphism at +83 bp was 4.1% and 22.1% for the polymorphism at -75 bp. Subjects heterozygous for the loss of the MspI restriction site at +83 bp (genotype: M2+-, n = 20) had higher HDL-C levels than M2+2 subjects (mean +/- SD: 1.73 +/- 0.31 vs. 1.41 +/- 0.39 mmol/l, P < 0.05 for adults; 1.71 +/- 0.33 vs. 1.34 +/- 0.29 mmol/l, P < 0.01 for children). Adults with the G to A substitution at -75 bp also had higher HDL-C levels (1.56 +/- 0.36 mmol/l for AA, 1.53 +/- 0.38 mmol/l for GA, and 1.36 +/- 0.38 mmol/l for GG, P < 0.05); this difference was not observed in the children. The MspI polymorphisms at both sites were in linkage disequilibrium. Their joint effect on the HDL-C levels was also significant and individuals with rare alleles (-) at both sites had the highest HDL-C levels. In an analysis of variance, the MspI polymorphism at +83 bp, and at -75 bp and gender independently accounted for 6.5%, 1.7%, and 5.9%, respectively, of the variance in circulating HDL-C levels when age was controlled as a covariate. We conclude that loss of the MspI site by the C to T (+83 bp) and/or the G to A (+84 bp) transitions is highly associated with increased HDL-C levels. The association appears to be more significant than that of the G to A transition at -75 bp.

Genotype distribution of angiotensin-converting enzyme polymorphism in Australian healthy and coronary populations and relevance to myocardial infarction and coronary artery disease

Angiotensin-converting enzyme is a key component of the renin-angiotensin system that plays an important role in cardiovascular regulation. An association between the angiotensin-converting enzyme insertion/deletion (I/D) polymorphism and increased coronary risk has been found in some studies but not in others. To explore this further in an Australian white population, we compared the ACE genotype distribution in 550 patients aged 37 to 65 years with coronary artery disease documented by angiography with the genotype distribution in 404 healthy school children aged 6 to 13 years. We also explored associations in the patients between the angiotensin-converting enzyme I/D polymorphism and a history of myocardial infarction and coronary artery disease severity assessed by the number of major coronary arteries with more than 50% luminal obstructions and by the Green Lane coronary score. The frequencies of the angiotensin-converting enzyme genotype in the coronary artery disease patients were 0.236 for I/I, 0.395 for I/D, and 0.369 for D/D genotypes. This distribution with an excess of the D/D genotype was significantly different (chi 2 = 23.69, P < .0001) from that in the school children, in whom the genotype distribution was in Hardy-Weinberg equilibrium (I/I, 0.21; I/D, 0.54; D/D, 0.25). There was also a significant excess of D/D genotype among patients with a history of myocardial infarction (chi 2 = 9.42, P = .009), and there was the same D/D excess in the subgroup of children (n = 60) with two or more grandparents who had had coronary artery disease. We found no associations between the angiotensin-converting enzyme polymorphism and the number of significantly stenosed coronary arteries (chi 2 = 2.069, P = .91). We conclude that the D/D genotype is a significant predictor for coronary artery disease events in the Australian white population but is not a marker for angiographically assessed coronary artery disease severity. The angiotensin-converting enzyme genotype-associated increased risk for coronary events may be mediated more by angiotensin II-induced coronary vasoconstriction than by an increase in injury-related smooth muscle cell proliferation in the coronary vasculature.