Sukhbir S. Dhamrait

Bradykinin B2BKR receptor polymorphism and left-ventricular growth response

Angiotensin-converting-enzyme (ACE) activity regulates left-ventricular growth. The deletion (D), rather than the insertion (I), ACE gene variant is associated with increased ACE activity and kinin degradation, and the absence (-) rather than the presence (+) of a 9 bp deletion in the gene encoding the bradykinin 2 receptor (B2BKR) is associated with greater gene expression. We determined the ACE and B2BKR genotype of 109 male army recruits, and measured their physiological left-ventricular growth response to a 10-week physical training programme. Mean left-ventricular growth was 15.7 g (SE 3.5) in those with ACE genotype D/D and B2BKR genotype +9/+9, but -1.37 g (4.1) in those with ACE genotype I/I and B2BKR genotype -9/-9 (p=0.003 for trend across genotypes). These results suggest that kinins regulate left-ventricular growth, mediating some of the effects of ACE in this regard.

Genetic Variants of Angiotensin II Receptors and Cardiovascular Risk in Hypertension

Abstract—Renin-angiotensin systems may mediate cardiovascular disease pathogenesis through a balance of actions of angiotensin II on (potentially proatherogenic) constitutive type 1 (AT1R) and (potentially antiatherogenic) inducible type 2 (AT2R) receptors. We explored such potential roles in a prospective candidate gene association study. Cardiovascular end points (fatal, nonfatal, and silent myocardial infarction and coronary artery bypass surgery/angioplasty) were documented among 2579 healthy UK men (mean age, 56.1±3.5 years; median follow-up, 10.1 years) genotyped for the AT1R1166A>C and the X chromosome located AT2R1675A>G and 3123C>A polymorphisms. Baseline characteristics, including blood pressure, were independent of genotype. The AT1R1166CC genotype was associated with relative cardiovascular risk (hazard ratio, 1.65 [1.05 to 2.59]; P =0.03) independent of blood pressure. Systolic blood pressure was associated with risk (P =0.0005), but this association was restricted to AT2R1675A allele carriers (P <0.00001), with G allele carriers protected from the risk associated with blood pressure (P =0.18). Hypertensive carriers with the AT2R1675A/3123A haplotype were at most risk, with 37.5% having an event. This is the first study to demonstrate an association of AT2R genotype with coronary risk, an effect that was confined to hypertensive subjects and supports the concept that the inducible AT2R is protective. Conversely, the AT1R1166CC genotype was associated with cardiovascular risk irrespective of blood pressure. These data are important to our understanding of the divergent role of angiotensin II acting at its receptor subtypes and coronary disease pathogenesis and for the development of future cardiovascular therapies.

Variation in bradykinin receptor genes increases the cardiovascular risk associated with hypertension

AIMS The contribution of kinins to the beneficial effects of angiotensin I converting enzyme (ACE) inhibition in cardiovascular risk reduction remains unclear. The genes for the kinin inducible B1 receptor (B(1)R) and constitutive B2 receptor (B(2)R) contain functional variants: the B(1)R-699C (rather than G) and the B(2)R(-9) (rather than +9) alleles are associated with greater mRNA expression and the B(2)R(-9) allele with reduced left ventricular hypertrophic responses. We tested whether these gene variants influenced hypertensive coronary risk in a large prospective study. METHODS AND RESULTS Two thousand, seven hundred and six previously healthy UK men (mean age at recruitment 56 years; median follow-up 10.8 years) were genotyped for the kinin receptor variants. The coronary risk attributable to systolic hypertension (SBP>/=160 mmHg) was significantly higher only in B(1)R-699GG homozygotes (HR 2.14 [1.42-3.22]; P<0.0001) and B(2)R(+9,+9) individuals (HR 3.51 [1.69-7.28]; P=0.001) but not in B(1)R-699C allele carriers (HR 0.82 [0.28-2.42]; P=0.76) or in B(2)R(-9,-9) homozygotes (HR 1.25 [0.51-3.04]; P=0.63). CONCLUSIONS Common variation in the genes for the kinin B(1)and B(2)receptors influences prospective hypertensive coronary risk. These are the first reported human data to suggest a role for the B(1)R in human coronary vascular disease, and the first prospective study to demonstrate a similar role for the B(2)R.

Cortical bone resorption during exercise is interleukin-6 genotype-dependent

The objective of this study was to examine the relationship between the interleukin-6 (IL-6) −174 G>C promoter polymorphism and exercise-induced femoral cortical bone resorption. Skeletal response to exercise was assessed in 130 male Caucasian army recruits. Five cross-sectional magnetic resonance images of the right femur were obtained before and after a 10-week period of basic physical training, and changes in cross-sectional cortical area were calculated. Recruits were genotyped for the −174 G>C IL-6 promoter polymorphism. Genotype frequencies (GG 36%, GC 47%, CC 22 17%) were in Hardy–Weinberg equilibrium. The mean percentage change in proximal femoral cross-sectional cortical area was strongly IL-6 genotype-dependent, with GG homozygotes losing 6.8 (3.82)% in cortical area, GC gaining +5.5 (4.88)% and CC gaining +17.3 (9.46)% ( P =0.007 for linear trend). These changes persisted throughout the right femur and were significant in the femur as a whole ( P =0.03). This study demonstrates an association between a functional polymorphism in the IL-6 gene and femoral cortical remodelling during strenuous physical exercise. Previous studies have suggested an important role for IL-6 in the regulation of bone mass in postmenopausal women, and in the invasion of bone by metastatic tumour deposits. These data extend these observations to the regulation of bone mass in healthy males, supporting a fundamental role for IL-6 in the regulation of bone mass and bone remodelling in humans.

The Impact of ACE Genotype on Serum ACE Activity in a Black South African Male Population

The strong association between the angiotensin I‐converting enzyme (ACE) gene I/D polymorphism with serum ACE activity appears lacking in Nigerians and Kenyans, but has not previously been well assessed in others of African origin. This study addressed this issue in an ethnically well defined black South African population. A putative association for the A22982G ACE gene variant, a QTL likely to impact on serum ACE activity, was also sought.

Angiotensin-converting enzyme DD genotype is associated with worse perinatal cardiorespiratory adaptation in preterm infants☆

OBJECTIVES The angiotensin-converting enzyme (ACE) deletion (D) variant is associated with greater ACE activity and perhaps with deleterious cardiorespiratory pathophysiological responses. We determined whether the early health status of the preterm infant was adversely influenced by homozygosity for the D allele (DD genotype) compared with ID or II genotype. Study design Angiotensin-converting enzyme genotype was determined in a cohort of 148 preterm infants born in Bristol, United Kingdom (median gestational age, 31 weeks; range, 28-32). Intensive care data were prospectively obtained. Primary analysis was by Mann-Whitney U and chi(2) tests. RESULTS Higher oxygen, circulatory support requirements, and base deficit in the first 12 hours after birth were found in infants with DD genotype (minimum inspired oxygen concentration in first 12 hours, median [interquartile range], DD 0.26 [0.21-0.40], ID/II 0.21 [0.21-0.30], P=.028; blood pressure support in first 12 hours, DD 12 [30%], ID/II 15 [14%], P=.039; worse base deficit in first 12 hours, DD 4.8 [7.7 to 0], ID/II 0 [5.3 to 0], P=.020). CONCLUSIONS Angiotensin-converting enzyme polymorphism has a role in the development of preterm cardiorespiratory disease. The DD genotype, encoding higher angiotensin-converting enzyme activity, may adversely influence the early health status of preterm infants.

Genetic Variation and Activity of the Renin-Angiotensin System and Severe Hypoglycemia in Type 1 Diabetes

BACKGROUND The deletion-allele of the angiotensin-converting enzyme (ACE) gene and elevated ACE activity are associated with increased risk of severe hypoglycemia in type 1 diabetes. We explored whether genetic and phenotypic variations in other components of the renin-angiotensin system are similarly associated. METHODS Episodes of severe hypoglycemia were recorded in 171 consecutive type 1 diabetic outpatients during a 1-year follow-up. Participants were characterized at baseline by gene polymorphisms in angiotensinogen, ACE, angiotensin-II receptor types 1 (AT1R) and 2 (AT2R), and by plasma angiotensinogen concentration and serum ACE activity. RESULTS Three risk factors for severe hypoglycemia were identified: plasma angiotensinogen concentration in the upper quartile (relative rate [RR] vs. lower quartile 3.1, 95% confidence interval [CI,] 1.4-6.8), serum ACE activity in the upper quartile (RR vs. lower quartile 2.9, 95% CI, 1.3-6.2), and homo- or hemizygosity for the A-allele of the X chromosome-located AT2R 1675G/A polymorphism (RR vs. noncarriers 2.5, 95% CI, 1.4-5.0). The three risk factors contributed independently to prediction of severe hypoglycemia. A backward multiple regression analysis identified a high number of renin-angiotensin system-related risk factors and reduced ability to perceive hypoglycemic warning symptoms (impaired hypoglycemia awareness) as predictors of severe hypoglycemia. CONCLUSIONS High renin-angiotensin system activity and the A-allele of the AT2R 1675G/A polymorphism associate with high risk of severe hypoglycemia in type 1 diabetes. A potential preventive effect of renin-angiotensin system blocking drugs in patients with recurrent severe hypoglycemia merits further investigation.

The common G-866A polymorphism of the UCP2 gene and survival in diabetic patients following myocardial infarction

BackgroundA variant in the promoter of the human uncoupling protein 2 (UCP2) gene, the G-866A polymorphism, has been associated with future risk of coronary heart disease events, in those devoid of traditional risk factors and in those suffering from diabetes. We thus examined the impact of the G-866A polymorphism on 5-year survival in a cohort of 901 post-myocardial infarction patients, and the impact of type-2 diabetes on this relationship. The association of UCP2 with baseline biochemical and hormonal measurements, including levels of the inflammatory marker myeloperoxidase, was also examined.MethodsUCP2 G-866A genotypes were determined using a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) protocol. Myeloperoxidase levels were measured in plasma samples taken from 419 cohort patients 24–96 hours after admission.ResultsGenotypes were obtained for 901 patients with genotype frequencies AA 15.5%, GA 45.5%, and GG 39.0%. Genotype was not associated with survival in the overall cohort (mortality: AA 15.6%, GA 16.8%, GG 19.4%, p = 0.541). However, amongst diabetics, AA and GA genotype groups had significantly worse survival than GG diabetic patients (p < 0.05) with an attributable risk of 23.3% and 18.7% for those of AA and GA genotype respectively. Multivariate analysis using a Cox proportional hazards model confirmed that the interaction of diabetes with genotype was significantly predictive of survival (p = 0.031). In the cohorts diabetic subgroup AA/GA patients had higher myeloperoxidase levels than their GG counterparts (GA/AA, n = 51, 63.9 ± 5.23; GG, n = 34, 49.1 ± 3.72 ng/ml, p = 0.041). Further analysis showed that this phenomenon was confined to male patients (GA/AA, n = 36, 64.3 ± 6.23; GG, n = 29, 44.9 ± 3.72 ng/ml, p = 0.015).ConclusionDiabetic patients in this post-myocardial infarction cohort with UCP2 -866 AA/GA genotype have poorer survival and higher myeloperoxidase levels than their GG counterparts.

Variation in the uncoupling protein 2 and 3 genes and human performance

Uncoupling proteins 2 and 3 (UCP2 and UCP3) may negatively regulate mitochondrial ATP synthesis and, through this, influence human physical performance. However, human data relating to both these issues remain sparse. Examining the association of common variants in the UCP3/2 locus with performance phenotypes offers one means of investigation. The efficiency of skeletal muscle contraction, delta efficiency (DE), was assessed by cycle ergometry in 85 young, healthy, sedentary adults both before and after a period of endurance training. Of these, 58 were successfully genotyped for the UCP3-55C>T (rs1800849) and 61 for the UCP2-866G>A (rs659366) variant. At baseline, UCP genotype was unrelated to any physical characteristic, including DE. However, the UCP2-866G>A variant was independently and strongly associated with the DE response to physical training, with UCP2-866A allele carriers exhibiting a greater increase in DE with training (absolute change in DE of -0.2 ± 3.6% vs. 1.7 ± 2.8% vs. 2.3 ± 3.7% for GG vs. GA vs. AA, respectively; P = 0.02 for A allele carriers vs. GG homozygotes). In multivariate analysis, there was a significant interaction between UCP2-866G>A and UCP3-55C>T genotypes in determining changes in DE (adjusted R(2) = 0.137; P value for interaction = 0.003), which was independent of the effect of either single polymorphism or baseline characteristics. In conclusion, common genetic variation at the UCP3/2 gene locus is associated with training-related improvements in DE, an index of skeletal muscle performance. Such effects may be mediated through differences in the coupling of mitochondrial energy transduction in human skeletal muscle, but further mechanistic studies are required to delineate this potential role.

European differences in the association between the UCP2 −866G > A common gene variant and markers of body mass and fasting plasma insulin

To the Editor: There is considerable interest in the role of the UCP2 866G > A promoter variant in determining obesity, insulin secretion [1–5] and cardiovascular risk [6]. In two Austrian Caucasian samples, the 866G allele was associated with higher body mass index (BMI) and lower transcription in intraperitoneal adipose tissue [2]. The 866A was associatedwith type 2 diabetes, andAA subjects had a lower disposition index (insulin sensitivity acute insulin response to glucose) [3]. Similar results have also been reported in Italian subjects [1]. However, in a mixed race American sample, the AA genotype was associated with lower mRNA in subcutaneous adipose tissue [4] with no difference in disposition index between AA and GG subjects. The description ‘Adiposity angel and diabetes devil’ (O’Rahilly [5]) aptly fits the association of the variant allele with type 2 diabetes but lower BMI. Different genetic and geographical backgrounds in the American study may explain their conflicting findings. Therefore, we investigated the 866G > A variant in the HIFMECH study [7] to assess whether the genotype association with the measures of obesity and insulin sensitivity would differ by geographical location within Europe. Caucasian male first myocardial infarction survivors were recruited (Northern European-Stockholm, London; Southern European-Marseille, San Giovani Rotondo) (n 1⁄4 598) with age-matched healthy controls (n 1⁄4 653). Statistical analysis followed the a prioridesign, comparing risk factors associated with cardiovascular risk in relation to the North and South of Europe [7]. All samples were in Hardy–Weinburg equilibrium. There was not a significant relationship between BMI and genotype; however, in the Northern control group, a nonsignificant association was observed (GG vs. GA vs. AA: 26.2 3.1 vs. 25.7 3.1 vs. 24.9 3.2 kg/m, p 1⁄4 0.13) but no association in the South (GG vs. GA vs. AA: 26.4 3.3 vs. 26.4 3.3 vs. 26.0 3.6 kg/m, p 1⁄4 0.86) with similar relationships in the case groups. However, waist : hip ratio (WHR) was significantly greater in Gallele carriers (GG þ GA vs. AA; North: 1.0 0.06 vs. 0.98 0.07 m, p 1⁄4 0.03; South: 0.95 0.05 vs. 0.93 0.07 m, p 1⁄4 0.04) in bothNorth and South controls (figure 1) but not cases. By contrast, fasting plasma insulin was lower in AA subjects (controls: 25% lower; cases: 16% lower) compared with G allele carriers in the North only (figure 1). The frequency of the A allele was not different betweenNorth and South (p 1⁄4 0.15); however, in cases the frequency of the 866A allele was higher in the North (North: 0.43 [0.38–0.47] vs. South: 0.33 [0.30–0.37]; p 1⁄4 0.003), so the AA genotype was associated with a modestly higher odds ratio for MI in the North of 1.30 [95%CI 0.76–2.23] but not in the South 1.00 [0.60–1.68]. These results confirm the previous European studies, showing that AA subjects are leaner (2% lower WHR), and it also shows AA subjects have lower fasting plasma insulin levels, although this effect was greater in the north compared with southern Europe. This provides further evidence of the paradoxical association between the variant UCP2 866A allele, higher diabetes risk and lower adiposity. The putative mechanism [5] would support enhanced function of the A allele. Why the associations are stronger in the North is not clear. The UCP2 gene is known to be induced under oxidative stress load [8], through binding sites for stress signals such as the arylhydrocarbon receptor and receptor nuclear translocator and hypoxia-inducible factor 1a [2]. In southern Europe, lifestyle differences with respect to diet and others may alter the cellular oxidative stress load, which could influence the effect of this promoter variant on transcription. The averageWHRwas also higher in the North than in the South (controls: 1 vs. 0.95, p < 0.001; cases: 0.98 vs. 0.93, p < 0.001), and it may be that the effect on insulin secretion ismore pronounced under this extra insulin demand. This study was underpowered to detect an association between genotype and cardiovascular risk, but a modestly higher odds ratio for MI associated with the AA genotype doi: 10.1111/j.1463-1326.2006.00573.x