Influence of fibrillin-1 genotype on the aortic stiffness in men

No differences in FBN1 genotype between men with and without abdominal aortic aneurysm

BACKGROUND

Abdominal aortic aneurysm (AAA) is an aortic enlargement in which the transverse diameter reaches at least 30 mm. Certain risk factors, such as age, male gender, and smoking, are well known; however, less is known about the genetic factors involved. Fibrillin-1 (FBN1) is a protein that coordinates the deposition of elastin fibres in the extracellular matrix and is therefore likely to affect the elastic properties in the aortic wall. Previously studies have found associations between the FBN1-2/3 genotype and arterial stiffness, but how different FBN1 genotypes, AAA, and arterial stiffness are related has been less frequently investigated.

AIM

This study aimed to investigate whether there is a difference in FBN1 genotype between men with and without AAA. A further aim was to study whether the FBN1 genotype affects arterial wall stiffness differently in men with and without AAA.

METHODS

Pulse wave velocity and FBN1 genotyping were performed in 229 men (159 with AAA, 70 without AAA). Participants were recruited from ultrasound AAA surveillance programs or ongoing ultrasound screening programs from 2011 to 2016.

RESULTS

The distribution of the FBN1 genotype in the AAA and control groups were as follows: FBN1-2/2: 62% vs. 64%; FBN1-2/3: 8% vs. 14%; and FBN1-2/4: 30% vs. 21%, respectively. Men with AAA and FBN1-2/2 had increased central pulse wave velocity (p < 0.005) compared to the control group (those without AAA) with the FBN1-2/2 genotype.

CONCLUSION

No differences were found with respect to FBN1 genotypes between men with and without AAA. The development of AAA in men does not appear to be linked to a specific FBN1 genotype. Nevertheless, men with FBN1-2/2 and AAA have increased central arterial stiffness compared to men with the same FBN1 genotype but without AAA.

Circulating fibrillin fragment concentrations in patients with and without aortic pathology

Objective

Fragments of fibrillin-1 and fibrillin-2 will be detectable in the plasma of patients with aortic dissections and aneurysms. We sought to determine whether the plasma fibrillin fragment levels (PFFLs) differ between patients with thoracic aortic pathology and those presenting with nonaortic chest pain.

Methods

PFFLs were measured in patients with thoracic aortic aneurysm (n = 27) or dissection (n = 28). For comparison, patients without aortic pathology who had presented to the emergency department with acute chest pain (n = 281) were categorized into three groups according to the cause of the chest pain: ischemic cardiac chest pain; nonischemic cardiac chest pain; and noncardiac chest pain. The PFFLs were measured using a sandwich enzyme-linked immunosorbent assay.

Results

Fibrillin-1 fragments were detectable in all patients and were lowest in the ischemic cardiac chest pain group. Age, sex, and the presence of hypertension were associated with differences in fibrillin-1 fragment levels. Fibrillin-2 fragments were detected more often in the thoracic aneurysm and dissection groups than in the emergency department chest pain group (P < .0001). Patients with aortic dissection demonstrated a trend toward increased detectability (P = .051) and concentrations (P = .06) of fibrillin-2 fragments compared with patients with aortic aneurysms. Analysis of specific antibody pairs identified fibrillin-1 B15-HRP26 and fibrillin-2 B205-HRP143 as the most informative in distinguishing between the emergency department and aortic pathology groups.

Conclusions

Patients with thoracic aortic dissections demonstrated elevated plasma fibrillin-2 fragment levels (B205-HRP143) compared with patients presenting with ischemic or nonischemic cardiac chest pain and increased fibrillin-1 levels (B15-HRP26) compared with patients with ischemic cardiac chest pain. Investigation of fibrillin-1 and fibrillin-2 fragment generation might lead to diagnostic, therapeutic, and prognostic advances for patients with thoracic aortic dissection.

Higher blood pressure in elderly hypertensive females, with increased arterial stiffness and blood pressure in females with the Fibrillin-1 2/3 genotype

BACKGROUND

Elderly patients have a relatively high cardiovascular risk due to increased arterial stiffness, elevated blood pressure and decreased amounts of elastin in the arteries. The composition of the media layer in the arterial wall, comprising elastin, collagen, smooth muscle cells, proteoglycans, fibronectin and fibrillin-1, influences its mechanical properties. Mutations in the fibrillin-1 gene leads to increased aortic stiffness, elevated pulse pressure and aortic root dilatation. This study investigates whether there is a sex difference among hypertensive elderly patients regarding blood pressure, arterial stiffness and fibrillin-1 genotypes.

METHODS

A total of 315 hypertensive subjects (systolic blood pressure > 140 mmHg) were included in this study (155 men and 160 women aged 71-88 years). Aortic pulse wave velocity and augmentation index were determined using SphygmoCor, and brachial blood pressure was measured using an oscillometric technique. Fibrillin-1 was genotyped by polymerase chain reaction and with a capillary electrophoresis system.

RESULTS

Females showed a significantly higher peripheral mean arterial pressure (females; 107.20 mmHg, males 101.6 mmHg, p = 0.008), central mean arterial pressure (females; 107.2 mmHg, males 101.6 mmHg p = 0.008), central systolic blood pressure (females; 148.1 mmHg, males 139.2 mmHg, p <  0.001) and central pulse pressure (females; 68.9 mmHg, males 61.6 mmHg, p = 0.035) than males. Females with the Fibrillin-1 2/3 genotype showed a significantly higher augmentation index (FBN1 2/3; 39.9%, FBN1 2/2 35.0%, FBN1 2/4 35.8, p = 0.029) and systolic blood pressure (FBN1 2/3; 174.6 mmHg, FBN1 2/2168.9 mmHg, FBN1 2/4169.9 mmHg, p = 0.025) than females with the 2/2 and 2/4 genotypes.

CONCLUSION

The findings of this study may indicate that hypertensive elderly females, especially elderly females with Fibrillin-1 2/3, have increased systolic blood pressure and arterial stiffness.

Aortic dilatation in Marfan syndrome: role of arterial stiffness and fibrillin-1 variants

OBJECTIVE

Marfan syndrome (MFS) is an autosomal dominant genetic disorder characterized by aortic root dilation and dissection and an abnormal fibrillin-1 synthesis. In this observational study, we evaluated aortic stiffness in MFS and its association with ascending aorta diameters and fibrillin-1 genotype.

METHODS

A total of 116 Marfan adult patients without history of cardiovascular surgery, and 144 age, sex, blood pressure and heart rate matched controls were enrolled. All patients underwent arterial stiffness evaluation through carotid-femoral pulse wave velocity (PWV) and central blood pressure waveform analysis (PulsePen tonometer). Fibrillin-1 mutations were classified based on the effect on the protein, into 'dominant negative' and 'haploinsufficient' mutations.

RESULTS

PWV and central pulse pressure were significantly higher in MFS patients than in controls [respectively 7.31 (6.81-7.44) vs. 6.69 (6.52-6.86) m/s, P = 0.0008; 41.3 (39.1-43.5) vs. 34.0 (32.7-35.3) mmHg, P < 0.0001], with a higher age-related increase of PWV in MFS (β 0.062 vs. 0.036). Pressure amplification was significantly reduced in MFS [18.2 (15.9-20.5) vs. 33.4 (31.6-35.2)%, P < 0.0001]. Central pressure profile was altered even in MFS patients without aortic dilatation. Multiple linear regression models showed that PWV independently predicted aortic diameters at the sinuses of Valsalva (ß = 0.243, P = 0.002) and at the sinotubular junction (ß = 0.186, P = 0.048). PWV was higher in 'dominant negative' than 'haploinsufficient' fibrillin-1 mutations [7.37 (7.04-7.70) vs. 6.60 (5.97-7.23) m/s, P = 0.035], although this difference was not significant after adjustment.

CONCLUSION

Aortic stiffness is increased in MFS, independently from fibrillin-1 genotype and is associated with diameters of ascending aorta. Alterations in central hemodynamics are present even when aortic diameter is within normal limits. Our findings suggest an accelerated arterial aging in MFS.

Increased cardiovascular risk without generalized arterial dilating diathesis in persons who do not have abdominal aortic aneurysm but who are first-degree relatives of abdominal aortic aneurysm patients

There is a strong genetic predisposition towards abdominal aortic aneurysm (AAA), but it is unknown whether persons without AAA but with first-degree relatives who are AAA patients have a generalized dilating diathesis, defect arterial wall mechanics, or increased cardiovascular risk. The aim of the study was to investigate arterial diameters and wall mechanics at multiple arterial sites in these subjects and compare them with controls without a family history of AAA. This study included 118 first-degree relatives of patients with AAA and 66 controls (age: 40-80 years). The abdominal aorta, common carotid artery, common femoral artery, and popliteal artery were investigated by echo-tracking ultrasound. The relatives had no arterial dilatation, but they did tend to have smaller diameters than controls. Relatives had a higher heart rate, diastolic blood pressure, and mean arterial pressure than controls. The distensibility coefficient and the compliance coefficient were decreased in all arteries in male relatives, adjusted for age and smoking; these coefficients were normalized after adjustment for mean arterial pressure and heart rate. Female relatives had a lower compliance coefficient in the abdominal aorta, adjusted for age and smoking. After adjustment for mean arterial pressure and heart rate, the difference disappeared. No general arterial dilatation in relatives without AAA was found, supporting the hypothesis that the dilating diathesis is linked to the aneurysmal manifestation in the abdominal aorta. Although the threat of aneurysmal dilatation and rupture seems to be lacking in these subjects, heart rate, blood pressure, and arterial wall stiffness were all increased, which may indicate a higher risk of developing cardiovascular morbidity and mortality.

Genetic determinants of arterial stiffness

Stiffness of large arteries (called arteriosclerosis) is an independent predictor of cardiovascular morbidity and mortality. Although previous studies have shown that arterial stiffness is moderately heritable, genetic factors contributing to arterial stiffness are largely unknown. In this paper, we reviewed the available literature on genetic variants that are potentially related to arterial stiffness. Most variants have shown mixed depictions of their association with arterial stiffness across multiple studies. Various methods to measure arterial stiffness at different arterial sites can contribute to these inconsistent results. In addition, studies in patient populations with hypertension or atherosclerosis may overestimate the impact of genetic variants on arterial stiffness. Future studies are recommended to standardize current measures of arterial stiffness in different age groups. Studies conducted in normal healthy subjects may also provide better opportunities to find novel genetic variants of arterial stiffness.

Thoracic aortic aneurysm frequency and dissection are associated with fibrillin-1 fragment concentrations in circulation

RATIONALE

Mutations in fibrillin-1 are associated with thoracic aortic aneurysm (TAA) in Marfan syndrome. Genome-wide association studies also implicate fibrillin-1 in sporadic TAA. Fragmentation of the aortic elastic lamellae is characteristic of TAA.

OBJECTIVE

Immunoassays were generated to test whether circulating fragments of fibrillin-1, or other microfibril fragments, are associated with TAA and dissection.

METHODS AND RESULTS

Plasma samples were obtained from 1265 patients with aortic aneurysm or dissection and from 125 control subjects. Concentrations of fibrillin-1, fibrillin-2, and fibulin-4 were measured with novel immunoassays. One hundred and seventy-four patients (13%) had aneurysms with only abdominal aortic involvement (abdominal aortic aneurysm), and 1091 (86%) had TAA. Of those with TAA, 300 patients (27%) had chronic dissection and 109 (10%) had acute or subacute dissection. Associations of fragment concentrations with TAA (versus abdominal aortic aneurysm) or with dissection (versus no dissection) were estimated with odds ratios (OR) and 95% confidence intervals (CI) adjusted for age, sex, and smoking. Compared with controls, significantly higher percentages of aneurysm patients had detectable levels of fibrillin fragments. TAA was significantly more common (than abdominal aortic aneurysm) in the highest compared with lowest quartile of fibrillin-1 concentration (OR=2.9; 95% CI, 1.6-5.0). Relative to TAA without dissection, acute or subacute dissection (OR=2.9; 95% CI, 1.6-5.3), but not chronic dissection, was more frequent in the highest compared with lowest quartile of fibrillin-1 concentration. Neither TAA nor dissection was associated with fibrillin-2 or fibulin-4.

CONCLUSIONS

Circulating fibrillin-1 fragments represent a new potential biomarker for TAA and acute aortic dissection.

Fibrillin-1 genotype and risk of prevalent hypertension: a study in two independent populations

OBJECTIVE

Mutations in the fibrillin-1 gene are the cause of Marfan syndrome. We wanted to investigate the relationship between a mutation in this gene and risk of prevalent hypertension.

METHODS

In a cross-sectional study, the effect of a G-A substitution in intron 27 in the fibrillin-1 gene (rs11856553) on risk of prevalent hypertension was studied in two large population-based studies: the Health 2006 study, consisting of 3193 women and men, age 18-69 years, and the MONICA10 study, consisting of 2408 women and men, age 41-72 years. In 1646 MONICA10 participants, blood pressure (BP) was also measured by 24-h ambulatory recordings.

RESULTS

Among the 3193 Health 2006 participants 23 had the G-A variant, and among the 2408 MONICA10 participants 18 had the G-A variant. In Health 2006, the odds ratio estimate (95% confidence intervals) for the G-A variant for risk of hypertension, defined as systolic (S) BP ≥ 140 mmHg or diastolic (D) BP ≥ 90 mmHg or on antihypertensive medicine, was 2.67 (1.14-6.18), p = 0.022. The corresponding figure for moderate to severe hypertension, defined as SBP ≥ 160 mmHg or DBP ≥ 100 mmHg, was 9.68 (4.24-22.12), p < 0.0001. In MONICA10, the odds ratio estimate (95% confidence intervals) for the G-A variant for risk of moderate to severe ambulatory hypertension, defined as 24-h mean SBP ≥ 150 mmHg or 24-h mean DBP ≥ 90 mmHg, was 5.73 (1.96-16.7), p = 0.0014.

CONCLUSION

The G-A substitution in the fibrillin-1 gene (rs11856553) is a rare genetic variant that is associated with an increased risk of prevalent hypertension, particularly of moderate to severe prevalent hypertension.

In vivo estimation of the contribution of elastin and collagen to the mechanical properties in the human abdominal aorta: effect of age and sex

The mechanical properties of the aorta affect cardiac function and are related to cardiovascular morbidity/mortality. This study was designed to evaluate the isotropic (mainly elastin, elastiniso) and anisotropic (mainly collagen, collagenani) material parameters within the human aorta in vivo. Thirty healthy men and women in three different age categories (23–30, 41–54, and 67–72 yr) were included. A novel mechanical model was used to identify the mechanical properties and the strain field with aid of simultaneously recorded pressure and radius in the abdominal aorta. The magnitudes of the material parameters relating to both the stiffness of elastiniso and collagenani were in agreement with earlier in vitro studies. The load-bearing fraction attributed to collagenani oscillated from 10 to 30% between diastolic and systolic pressures during the cardiac cycle. With age, stiffness of elastiniso increased in men, despite the decrease in elastin content that has been found due to elastolysis. Furthermore, an increase in stiffness of collagenani at high physiological pressure was found. This might be due to increased glycation, as well as changed isoforms of collagen in the aortic wall with age. A marked sex difference was observed, with a much less age-related effect, both on elastiniso and collagenani stiffness in women. Possible factors of importance could be the effect of sex hormones, as well as differing collagen isoforms, between the sexes.

Genetic markers of vascular aging

Age is a powerful determinant of cardiovascular risk, being associated with a number of deleterious changes in the cardiovascular system. Increased arterial stiffness is an almost ubiquitous accompaniment of aging. However, there is significant variability in age-related arterial changes between individuals likely due, in part, to genetic factors. Measures of arterial stiffness such as pulse pressure and aortic pulse wave velocity have been shown to be heritable, indicating that genetic factors play a role in the interindividual variation of these phenotypes. Linkage analyses in related individuals have identified several genomic regions that may influence measures of arterial stiffness, and numerous association studies have investigated whether polymorphisms in candidate genes are related to this phenotype. Genome-wide association studies using 500,000 single nucleotide polymorphisms or more are now feasible and will accelerate the discovery of specific genetic polymorphisms that influence vascular aging/stiffness. Such findings will facilitate the development of novel therapies to retard vascular aging.

Influence of fibrillin-1 genotype on aortic stiffness in men: a note of caution

Aortic stiffness is a predictor of cardiovascular mortality. The mechanical properties of the arterial wall depend on the connective tissue framework, with variation in fibrillin-1 and collagen I genes being associated with aortic stiffness and/or pulse pressure elevation. The aim of this study was to investigate whether variation in fibrillin-1 genotype was associated with aortic stiffness in men. The mechanical properties of the abdominal aorta of 79 healthy men (range 28–81 yr) were investigated by ultrasonographic phase-locked echo tracking. Fibrillin-1 genotype, characterized by the variable tandem repeat in intron 28, and collagen type I alpha 1 genotype characterized by the 2,064 G\?\T polymorphism, were determined by using DNA from peripheral blood cells. Three common fibrillin-1 genotypes, 2-2, 2-3, and 2-4, were observed in 50 (64%), 10 (13%), and 11 (14%) of the men, respectively. Those of 2-3 genotype had higher pressure strain elastic modulus and aortic stiffness compared with men of 2-2 or 2-4 genotype ( P = 0.005). Pulse pressure also was increased in the 2-3 genotype ( P = 0.04). There was no significant association between type 1 collagen genotype and aortic stiffness in this cohort. In conclusion, the fibrillin-1 2-3 genotype in men was associated with increased aortic stiffness and pulse pressure, indicative of an increased risk for cardiovascular disease.