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Association of subclinical atherosclerosis with plasma B-vitamin, cysteine, homocysteine, and cysteinyl glycine in a cardiovascular disease-free population
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Association of subclinical atherosclerosis with plasma B-vitamin, cysteine, homocysteine, and cysteinyl glycine in a cardiovascular disease-free population
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Content
ASSOCIATION OF SUBCLINICAL ATHEROSCLEROSIS WITH PLASMA
B-VITAMIN, CYSTEINE, HOMOCYSTEINE, AND CYSTEINYL GLYCINE IN A
CARDIOVASCULAR DISEASE-FREE POPULATION
by
Siyu Feng
Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(APPLIED BIOSTATISTICS AND EPIDEMIOLOGY)
August 2016
ii
TABLES OF CONSTENTS
DEDICATION iii
ACKNOWLEDGMENTS iv
ABSTRACT v
INTRODUCTION 1
METHODS 3
RESULTS 7
DISCUSSION 15
CONCLUSION 18
REFERENCES 19
iii
DEDICATION
This work is dedicated to my beloved parents for all of their love and support.
iv
ACKNOWLEDGMENTS
I would like to thank my committee chair Dr. Wendy Mack for all of her patience
and support during the completion of this thesis, who has also been a great advisor during
my graduate study. I would also like to thank my committee member Dr. Howard Hodis
and Dr. Hooman Allayee, who helped me perfect this paper, for their expertise and
guidance.
I would like to thank all the faculty members from the Department of Preventive
Medicine for sharing their knowledge and experience with me.
Finally, I would like to thank Keck School of Medicine, University of Southern
California, for providing these great facilities and environment.
v
ABSTRACT
Background: Folic acid has been recommended as a potential intervention to prevent
CVD, a leading cause of mortality worldwide, by reducing total plasma homocysteine
(tHcy) levels and reversing endothelial dysfunction. In this paper, we investigated the
association between tHcy, cysteine, and CSGL levels resulting from B vitamin
supplementation and subclinical atherosclerosis progression in the BV AIT population, a
CVD-free population with elevated levels of tHcy (>8.5 µmol/L).
Methods: A total of 506 eligible subjects were randomized in BV AIT to high-dose B
vitamin supplementation or matching placebo; 490 subjects with at least one follow-up
measure were included in this analysis. Plasma cysteine, tHcy, CSGL, and B vitamin
levels were compared between and within treatment groups at baseline and on-trial.
Linear mixed effects models were used to analyze the associations between subclinical
atherosclerosis (CIMT) progression and cysteine, tHcy, CSGL, and B vitamin levels.
Results: Both absolute PML homocysteine (P=0.0043) and PML-fasting homocysteine
(P<0.0001) levels decreased significantly from baseline in the B-vitamin group. Overall,
fasting cysteine (P<0.0001), PML cysteine (P=0.03), and fasting tHcy (P=0.019) were
positively associated with baseline CIMT. PML homocysteine (P<0.0001) and
PML-fasting homocysteine (P=0.013) were negatively associated with baseline CIMT.
Among subjects with baseline fasting tHcy level ≥9.1 𝜇mol/L, fasting (P=0.0001) and
PML (P=0.045) cysteine were positively associated with baseline CIMT while PML
vi
(P<0.0001) and PML-fasting (P=0.0081) homocysteine were negatively associated with
baseline CIMT. These associations were not found among subjects with baseline fasting
tHcy level <9.1 𝜇mol/L. No significant association between CIMT progression and any
laboratory measurement was found.
Conclusion: B vitamin supplementation reduced fasting homocysteine and PML
homocysteine, but did not influence plasma cysteine and CSGL levels. Fasting cysteine,
PML cysteine, and fasting homocysteine were positively associated with baseline CIMT,
and PML homocysteine was negatively associated with baseline CIMT. The associations
of baseline CIMT with fasting cysteine and PML cysteine were still evident among
subjects with baseline fasting tHcy level ≥9.1 𝜇mol/L but not among subjects with
baseline fasting tHcy level <9.1 𝜇mol/L.
1
INTRODUCTION
Cardiovascular disease (CVD), which includes stroke, congenital heart disease,
rhythm disorders, subclinical atherosclerosis, coronary heart disease, heart failure,
valvular disease, and peripheral arterial disease, is a leading cause of mortality
worldwide.
1,2
According to the Centers for Disease Control and Prevention, 611,105
people died of heart disease and 128,978 people died of stroke in the United States in
2013.
3
Smoking, physical inactivity, unhealthy diets, obesity, family history and genetics,
high blood cholesterol and other lipids, high blood pressure, diabetes mellitus, and
metabolic syndrome are all considered risk factors of CVD.
2
Homocysteine is a sulfur amino acid derived from remethylation of the essential
amino acid methionine. Methionine remethylation depends on vitamin B6 and B12 and
involves the folate derivant 5-methyltet-rahydrofolate (5MeTHF) as a methyl donor.
4
As
homocysteine levels in the blood increase after methionine loading and can be disrupted
by abnormal methionine metabolism, fasting plasma total homocysteine (tHcy) and post
methionine loading (PML) homocysteine are considered separate risk factors for CVD.
5-9
Although hyperhomocysteinemia is associated with increased risk of CVD
10
, it is unclear
whether homocysteine is a direct cause or merely a predictor of CVD risk.
11-14
Carotid artery intima-media thickness (CIMT), measured by ultrasonography, is a
non-invasive measure of subclinical atherosclerosis that is measured as the combined
thickness of the intimal and medial components of the carotid wall.
15
CIMT is a
2
well-established measure of subclinical atherosclerosis accepted by the US Food and
Drug Administration (FDA) and by the European Agency for the Evaluation of Medicinal
Products.
16
Many recent studies have also confirmed that CIMT is positively associated
with risk of CVD at the population level.
17-20
Folic acid has been recommended as a potential intervention to reduce CVD risk, as
it effectively reduces plasma homocysteine levels and reverses endothelial dysfunction
among CVD patients.
6,7,21
Other B vitamins, such as B12 and B6, also show a
homocysteine-lowering effect. However, two recent meta-analyses, one of which contains
both published and unpublished datasets, questioned the protective effect of folic acid
supplementation on CVD among both CVD patients and CVD-free populations.
22,23
The B-Vitamin Atherosclerosis Intervention Trial (BV AIT) was a double-blind
placebo-controlled randomized clinical trial that was designed to test whether the
reduction of tHcy levels with B vitamin supplementation reduces subclinical
atherosclerosis progression, measured as CIMT, in a CVD-free population with elevated
levels of tHcy (>8.5 µmol/L). The primary trial found that high-dose B vitamin
supplementation did not affect CIMT progression in this population.
24
In a subgroup
analysis, B-vitamin supplementation significantly reduced CIMT progression relative to
placebo among individuals with fasting tHcy over 9.1 µmol/L (p=0.02; p-value for
subgroup interaction=0.02).
24
As part of the BV AIT trial, cysteine, PML cysteine,
cysteinyl glycine (CSGL), and PML cysteinyl glycine were also measured routinely
3
throughout the trial follow-up. This paper investigated the association between the tHcy,
cysteine, and CSGL levels resulting from B vitamin supplementation and subclinical
atherosclerosis levels at baseline and progression over the trial follow-up.
METHODS
Study Population and Design
BV AIT was a double-blind placebo-controlled randomized clinical trial conducted in
the Atherosclerosis Research Unit at the University of Southern California from
November 6, 2000, to June 1, 2006. Men and postmenopausal women, ages ranging from
40 to 89 years old and with initial fasting tHcy ≥8.5 µmol/L, were randomized in the
trial. Individuals were excluded if they had any clinical signs or symptoms of CVD,
diabetes mellitus or fasting serum glucose ≥140 md/dL, fasting triglycerides ≥500
mg/dL, systolic blood pressure ≥160 mmHg and/or diastolic blood pressure ≥100
mmHg, untreated thyroid disease, creatinine clearance <70 mL/min, life-threatening
illness with prognosis <5 years, or >5 alcoholic drinks per day or substance abuse, or
unwillingness to stop taking vitamin supplements.
24
All 506 eligible consenting subjects
randomized in BV AIT signed a written informed consent approved by the Institutional
Review Board at the University of Southern California.
Subjects were randomized in a 1:1 ratio to high-dose B vitamin supplementation
with 5 mg folic acid + 0.4 mg vitamin B
12
+ 50 mg vitamin B
6
or matching placebo for
4
the initial 2.5-year treatment period. Vital signs, clinical events, and non-study
medication and supplement use were measured every 3 months during clinic visits. Every
6 months, fasting and post-methionine load (PML) blood samples were drawn for
laboratory measurements and CIMT was measured with carotid artery ultrasonography.
Fasting blood samples were collected from subjects after fasting for 8 hours. After the
first blood draw, subjects were asked to drink 8 ounces of unsweetened orange/apple
juice with 100 mg L-methionine/kg body weight within 5 minutes. Post methionine
loading samples were collected exactly 2 hours after ingestion.
Atherosclerosis Progression
Carotid artery intima media thickness (CIMT), the primary outcome of the trial and
a measure of subclinical atherosclerosis progression, was assessed by high-resolution
B-mode ultrasound images of the right common carotid artery, using previously described
methods.
25-28
Laboratory Measurements
Fasting/PML cysteine and cysteinyl glycine were determined by high-performance
liquid chromatography with fluorescence detection.
29
Fasting and PML tHcy was
determined in plasma using reverse phase HPLC. Plasma folate and vitamin B
12
were
determined by radioimmunoassay kit (Bio-Rad Quanta Phase I and II; Bio-Rad
Laboratories, Hercules, Calif). Vitamin B6 level was indicated by its active cofactor,
pyridoxal-5-phosphate, which was determined a tyrosine decarboxylase-based method.
30
5
Statistical Analysis
Demographic characteristics at baseline were compared between the randomized
treatment groups (B vitamin and placebo). Continuous variables were compared with
2-sample t-tests and categorical variables were compared with Pearson’s 𝜒
'
tests.
Cysteine, homocysteine, and CSGL were described in three ways: (1) fasting values,
(2) PML values and, (3) PML minus fasting values. Fasting values were defined as
laboratory measures that were collected before methionine loading (intake of methionine
contained juice). PML values were defined as the absolute value of laboratory measures
that were collected after methionine loading. PML minus fasting values were defined as
the difference between absolute PML values and fasting values.
Laboratory measurements (cysteine, homocysteine, CSGL, and B vitamins) were
compared at three levels: (1) baseline, (2) average on-trial and, (3) change from baseline
to on-trial. Baseline measures were defined as the laboratory measurements that were
measured at the first clinical visit. Average on-trial measures were defined as the average
level of laboratory measurements that were measured at follow-up visits. Changes from
baseline to on-trial were defined as the average difference between the laboratory
measurements measured at follow-up visits and at the first clinical visit.
Plasma cysteine, PML cysteine, tHcy, PML homocysteine, CSGL, PML CSGL, and
B vitamin levels were compared between treatment groups with 2-sample t-tests at
baseline level while they were compared between treatment groups with linear mixed
6
effects models at on-trial level. Changes from baseline on these variables were also tested
with mixed effects models. In the mixed effects model, treatment group (B vitamin or
placebo) and visit time, which was the month since randomization of collection of the
blood sample, were modeled as fixed effects class variables. The intercept was modeled
as a random effect to allow for random deviation of the laboratory measure at baseline for
each subject among their treatment group. Changes from baseline for absolute PML
cysteine, PML homocysteine, and PML CSGL levels were tested with the same models
adjusted by their corresponding baseline levels.
Linear mixed effects models were also used to analyze the associations between
subclinical atherosclerosis (CIMT) progression and the laboratory measures of interest,
including plasma cysteine, PML-fasting cysteine, tHcy, PML-fasting homocysteine,
CSGL, PML-fasting CSGL, and B vitamin levels (folate, B6, B12). These variables were
centered at their means (using the mean levels averaged over combined treatment and
placebo groups over all visits). CIMT was regressed on a continuous variable of
follow-up time (representing years since randomization at which the CIMT measurement
was obtained) and each laboratory measure using a linear mixed effects model. Random
effects were specified for the intercept and follow-up time to account for individual
subject deviations from the population average baseline CIMT and rate of CIMT
progression, respectively. An interaction term between follow-up time and each
laboratory measure tested whether the levels of each variable over the trial follow-up
7
influenced CIMT progression. The association between CIMT progression and absolute
PML cysteine, PML homocysteine, and PML CSGL levels were also tested with the same
models adjusted by their corresponding baseline levels.
To evaluate possible difference on CIMT progression rate between subjects with
different initial fasting tHcy level, as was reported in the primary outcome analysis
23
, we
further stratified the subjects on the median of baseline fasting tHcy level (9.1 µmol/L)
and tested the association between CIMT progression and laboratory measures of interest
with the same models as previously described.
RESULTS
Baseline Demographic Characteristics
Of the 506 subjects, 254 were randomized to the B-vitamin group and 252 were
randomized to the placebo group. Of the randomized subjects, 16 dropped out of the
study before the first 6-month visit, and therefore had no post-randomization CIMT
measurement. For the remaining 490 subjects, 248 were in the B-vitamin group and 242
were in the placebo group.
All baseline demographic characteristics were equivalent between the two treatment
groups (all P> 0.05, Table 1). The average (SD) age of subjects was 60.9 (9.9) years.
Males comprised 61% of all subjects and subjects were primarily non-Hispanic Whites
(65%). The great majority of participants were well-educated, with 27% having a
8
bachelor’s degree and 33% having a postgraduate or professional degree. Of the 459
participants (228 B-vitamin, 231 placebo) who provided data on total family annual
income, annual income did not differ between treatment groups (P=0.90). The baseline
CIMT level was similar among the two groups (P=0.43), with an average (SD) CIMT of
0.75 (0.13) mm for the B-vitamin group and 0.76 (0.16) mm for the placebo group.
Table 1. Baseline Demographic Characteristics: BV AIT Trial*
Variable
B-Vitamins
(n=248)
Placebo
(n=242) P Value†
Age, years 61.1 (10.1)‡ 60.6 (9.7) 0.59
Gender
Male 150 (60%) 149 (62%) 0.81
Female 98 (40%) 93 (38%)
Race
0.60
White 165 (67%) 155 (64%)
Black 36 (15%) 35 (14%)
Hispanic 25 (10%) 29 (12%)
Asian 20 (8%) 23 (10%)
American Indian 2 (1%) 0 (0%)
Education
0.27
8th grade or less 2 (0.8%) 2 (0.8%)
Some high school 1 (0.4%) 3 (1.2%)
High school graduate 9 (3.6%) 14 (5.8%)
Trade or business school after high
school 15 (6%) 11 (5%)
Some college 69 (26%) 67 (28%)
Bachelors 59 (24%) 75 (31%)
Postgraduate or professional 92 (37%) 70 (29%)
Income
0.77
Under $30,000 36 (16%) 43 (19%)
$30,000 to $49,000 39 (17%) 41 (18%)
$50,000 to $69,999 51 (22%) 44 (19%)
$70,000 to $99,999 39 (17%) 45 (20%)
$100,000 or higher 63 (28%) 58 (25%)
9
CIMT, mm 0.75 (0.13) 0.75 (0.14) 0.67
*Results based on 490 subjects who had at least one follow-up CIMT measurement.
†Two sample t-tests for continuous variables or Pearson’s 𝜒
'
test for categorical
variables.
‡Mean (SD) or n (%).
Plasma Cysteine, Homocysteine, Cysteinyl Glycine: Treatment Group Comparisons
Treatment Group Comparisons on Baseline and On-trial Levels. No baseline
laboratory measurements differed between the treatment groups (all P>0.05, Table 2).
Comparing on-trial level changes between the two treatment groups, significant
differences were observed for fasting tHcy, PML homocysteine, PML-fasting
homocysteine, and B-vitamins (all P<0.0001), which indicated decreased fasting tHcy,
absolute PML homocysteine, and PML-fasting homocysteine levels and increased
B-vitamin levels due to B-vitamin supplementation. For on-trial cysteine levels, only a
marginally significant difference between treatment groups was found on PML-fasting
cysteine levels (P=0.05). CSGL levels did not significantly differ between groups.
On-trial Changes from Baseline within Treatment Groups. Increased fasting
tHcy level from baseline was observed in the placebo group (P=0.0008). Both absolute
PML homocysteine (P=0.0043) and PML-fasting homocysteine (P<0.0001) levels
decreased significantly from baseline in the B-vitamin group but did not change in the
placebo group, which indicated decreased PML homocysteine levels due to B-vitamin
supplementation. Average fasting CSGL and PML CSGL levels increased significantly in
both B vitamin and placebo groups (all P<0.0001) but PML-fasting CSGL decreased for
10
both treatment groups (P=0.012 for B-vitamin group and P=0.0499 for placebo group).
No significant change was observed for fasting, PML, and PML-fasting cysteine in either
treatment group. All B-vitamin levels increased significantly from baseline in the
B-vitamin group (P<0.0001). An increased average B12 level was also found in the
placebo group (P=0.0039).
Table 2. Plasma Cysteine, Homocysteine, Cysteinyl Glycine and B Vitamin Levels
Variable
B Vitamins
(n=248)
Placebo
(n=242)
P Value Between
Treatment Groups*
Cysteine
Fasting total cysteine, nmol/ml
Baseline 273 (3)† 276 (3) 0.45
Average on-trial 268 (7) 271 (7) 0.32
Change -1 (7) -2 (7) 0.95
P value within group 0.83 0.80
Postmethionine loading cysteine, nmol/ml
Baseline 257 (3) 259 (3) 0.75
Average on-trial 265 (4) 263 (4) 0.12
Change 8 (5) 6 (5) 0.51
P value within group 0.09 0.25
Postmethionine loading-fasting cysteine,
nmol/ml
Baseline -15 (1) -17 (1) 0.19
Average on-trial -13 (4) -16 (4) 0.05
Change 1 (4) 1 (4) 0.71
P value within group 0.76 0.89
Homocysteine
Fasting total homocysteine, nmol/ml
Baseline 9.5 (0.2) 9.8 (0.3) 0.38
Average on-trial 8.9 (0.5) 11.4 (0.5) <0.0001
Change -0.4 (0.5) 1.8 (0.5) <0.0001
P value within group 0.45 0.0008
Postmethionine loading homocysteine,
nmol/ml
11
Baseline 24.3 (0.5) 24.5 (0.5) 0.74
Average on-trial 22.3 (0.7) 24.8 (0.7) <0.0001
Change -2.0 (0.7) 0.4 (0.7) <0.0001
P value within group 0.0043 0.54
Postmethionine loading-fasting
homocysteine, nmol/ml
Baseline 14.8 (0.4) 14.7 (0.4) 0.92
Average on-trial 12.1 (0.7) 15.0 (0.7) <0.0001
Change -2.6 (0.6) 0.3 (0.6) <0.0001
P value within group <0.0001 0.59
Cysteinyl glycine
Fasting cysteinyl glycine, nmol/ml
Baseline 260 (4) 258 (4) 0.72
Average on-trial 329 (10) 326 (10) 0.42
Change 72 (10) 70 (10) 0.65
P value within group <0.0001 <0.0001
Postmethionine loading cysteinyl glycine,
nmol/ml
Baseline 245 (3) 241 (3) 0.51
Average on-trial 281 (5) 282 (5) 0.60
Change 38 (6) 43 (6) 0.32
P value within group <0.0001 <0.0001
Postmethionine loading-fasting cysteinyl
glycine, nmol/ml
Baseline -15 (2) -17 (2) 0.51
Average on-trial -28 (5) -27 (5) 0.51
Change -14 (5) -11 (5) 0.23
P value within group 0.0122 0.0499
B vitamins
Folic acid, ng/ml
Baseline 9.7 (0.4) 9.2 (0.3) 0.25
Average on-trial 74.6 (8.8) 9.0 (8.8) <0.0001
Change 64.9 (8.8) -0.0 (8.8) <0.0001
P value within group <0.0001 1.00
B12, pg/mL
Baseline 400 (13) 394 (9) 0.71
Average on-trial 789 (32) 471 (32) <0.0001
Change 389 (29) 76 (29) <0.0001
P value within group <0.0001 0.0093
B6, pmol/ml
12
Baseline 65 (2) 74 (4) 0.06
Average on-trial 350 (13) 79 (13) <0.0001
Change 285 (13) 6 (13) <0.0001
P value within group <0.0001 0.62
*Two sample t-tests for baseline comparison between treatment groups and mixed
effects models for on-trial comparison between treatment groups and changes from
baseline.
†Mean (SE)
Carotid Artery Intima Media Thickness Progression Rates: Associations with
cysteine, homocysteine, CSGL and B vitamins
Associations with Baseline CIMT. In linear mixed effects models, overall fasting
cysteine (P<0.0001), PML cysteine (P=0.03), and fasting tHcy (P=0.019) were positively
associated with baseline CIMT. However, PML homocysteine (P<0.0001) and
PML-fasting homocysteine (P=0.013) were negatively associated with baseline CIMT.
No significantly association was found between baseline CIMT and PML-fasting cysteine,
fasting CSGL, PML CSGL, PML-fasting CSGL, and B-vitamins (all P>0.05).
Associations with CIMT Progression Rate. The interaction of fasting
homocysteine and years since randomization was marginally significant (P=0.07), which
indicated a positive association of the on-trial fasting total homocysteine level with CIMT
progression. No other measures were significantly associated with CIMT progression.
Table 3. CIMT progression rate for all subjects (n=490 subjects)
Variable
Association
with baseline
CIMT, µm
(SE)
p-value*
Association
with CIMT
progression,
µm/year (SE)
p-value†
13
*P-values of mixed effect model for association with baseline CIMT
†P-values of mixed effect model for association with CIMT progression
PML-fasting homocysteine was marginally associated with baseline CIMT (P=0.08)
among 245 subjects with baseline fasting tHcy level <9.1 𝜇mol/L (Table 4). However, no
other laboratory measurements were found to be associated with baseline CIMT or CIMT
progression.
Table 4. CIMT progression rate for subjects with baseline fasting tHcy level <9.1 µmol/L
(n=245 subjects)
Variable
Association with
baseline CIMT, µm
(SE)
p-value*
Association
with CIMT
progression,
µm/year (SE)
p-value†
Cysteine
Fasting cysteine 0.193 (0.128) 0.13 -0.02 (0.069) 0.80
PML cysteine 0.111 (0.183) 0.55 0.007 (0.073) 0.92
PML-fasting cysteine -0.18 (0.284) 0.52 0.098 (0.145) 0.50
Homocysteine
Cysteine
Fasting cysteine 0.403 (0.085) <0.0001 0.011 (0.044) 0.80
PML cysteine 0.268 (0.123) 0.03 0.039 (0.047) 0.41
PML-fasting cysteine -0.13 (0.205) 0.52 0.064 (0.105) 0.55
Homocysteine
Fasting total homocysteine 2.223 (0.950) 0.019 0.927 (0.511) 0.07
PML homocysteine -2.31 (0.539) <0.0001 0.378 (0.249) 0.13
PML-fasting homocysteine -1.56 (0.624) 0.013 0.254 (0.325) 0.43
Cysteinyl glycine
Fasting cysteinyl glycine 0.041 (0.063) 0.51 0.004 (0.032) 0.90
PML cysteinyl glycine 0.090 (0.089) 0.31 -0.005 (0.033) 0.88
PML-fasting cysteinyl glycine 0.076 (0.144) 0.60 0.009 (0.074) 0.90
B-vitamins
Folic acid 0.030 (0.062) 0.63 -0.03 (0.035) 0.42
B12 -0.02 (0.015) 0.25 -0.002 (0.007) 0.80
B6 -0.02 (0.025) 0.34 -0.000 (0.0012) 1.00
14
Fasting total homocysteine 3.509 (2.635) 0.18 -1.07 (1.217) 0.38
PML homocysteine -1.37 (0.902) 0.13 0.166 (0.452) 0.71
PML-fastine homocysteine -1.68 (0.975) 0.08 0.411 (0.507) 0.42
Cysteinyl glycine
Fasting cysteinyl glycine -0.010 (0.082) 0.91 -0.02 (0.041) 0.65
PML cysteinyl glycine -0.09 (0.120) 0.47 -0.03 (0.044) 0.48
PML-fasting cysteinyl glycine -0.03 (0.191) 0.86 -0.04 (0.096) 0.66
B vitamin
Folic acid -0.03 (0.089) 0.70 -0.03 (0.047) 0.56
B12 -0.01 (0.023) 0.58 0.007 (0.010) 0.51
B6 -0.03 (0.034) 0.37 0.015 (0.016) 0.35
*P-values of mixed effect model for association with baseline CIMT
†P-values of mixed effect model for association with CIMT progression
Among 245 subjects with baseline fasting tHcy level ≥ 9.1 𝜇 mol/L, fasting
(P=0.0001) and PML (P=0.045) cysteine were positively associated with baseline CIMT
while PML (P<0.0001) and PML-fasting (P=0.0081) homocysteine were negatively
associated with baseline CIMT (Table 5). Among the laboratory measurements that were
significantly associated with baseline CIMT, only PML homocysteine showed a marginal
association with CIMT progression (P=0.09).
Table 5. CIMT progression rate for subjects with baseline fasting tHcy level ≥9.1
𝜇mol/L (n=245 subjects)
Variable
Association
with baseline
CIMT, µm
(SE)
p-value*
Association
with CIMT
progression,
µm/year (SE)
p-value†
Cysteine
Fasting cysteine 0.473 (0.122) 0.0001 0.021 (0.062) 0.74
PML cysteine 0.344 (0.171) 0.045 0.059 (0.066) 0.38
PML-fasting cysteine -0.09 (0.293) 0.75 0.055 (0.152) 0.72
Homocysteine
Fasting total homocysteine 0.441 (1.146) 0.70 1.710 (0.649) 0.0085
15
PML homocysteine -3.37 (0.718) <0.0001 0.561 (0.330) 0.09
PML-fasting homocysteine -2.21 (0.833) 0.0081 0.158 (0.434) 0.72
Cysteinyl glycine
Fasting cysteinyl glycine 0.031 (0.096) 0.75 0.023 (0.049) 0.64
PML cysteinyl glycine 0.230 (0.130) 0.0776 0.036 (0.049) 0.47
PML-fasting cysteinyl glycine 0.169 (0.212) 0.42 0.046 (0.111) 0.68
B vitamin
Folic acid 0.043 (0.086) 0.61 -0.02 (0.051) 0.73
B12 -0.02 (0.0021) 0.38 -0.007 (0.009) 0.44
B6 -0.02 (0.036) 0.53 -0.01 (0.017) 0.51
*P-values of mixed effect model for association with baseline CIMT
†P-values of mixed effect model for association with CIMT progression
DISCUSSION
Previous studies have shown that B vitamin supplementation can effectively reduce
plasma total homocysteine levels.
6,7,21
In our study, the average fasting tHcy of the
placebo group increased during the trial, suggesting a natural tHcy level increase with
time or aging. However, for the subjects who received B vitamin supplementation, no
significant change of fasting tHcy was observed; a significant decrease of PML
homocysteine level was seen with two methods of assessment (absolute PML value and
PML minus fasting homocysteine). These results demonstrated that B vitamins control
the increase of fasting homocysteine and reduce PML homocysteine. Dietary folic acid
and vitamin B12 are involved in the remethylation of homocysteine to methionine, while
vitamin B6 is involved in the transsulfuration of homocysteine to cysteine through the
intermediate cystathionine.
21
B vitamin supplementation may reduce the PML
homocysteine level by inhibiting the sudden increase of homocysteine following
16
methionine intake through both remethylation and transsulfuration pathways.
B vitamin supplementation did not affect plasma cysteine levels in BV AIT. Neither a
difference between treatment groups nor a change from baseline (within treatment group)
was observed for plasma total cysteine levels. Although cycsteinyl glycine (CSFL) levels
also did not differ between treatment groups, both fasting and absolute CSGL levels
showed a significant increase from the baseline for both B-vitamin and placebo groups.
These results indicated that while CSGL levels increase with age/time, this effect is not
altered by B vitamin supplementation. However, the difference between PML and fasting
CSGL decreased from baseline for both treatment and placebo groups, which could
suggest a loss of CSGL buffering after methionine intake due to aging.
Plasma homocysteine levels have long been suggested to be positively associated
with CVD.
6-9
Overall, our study suggested a similar result in relation to subclinical
atherosclerosis, with the fasting homocysteine level positively associated with baseline
CIMT and weakly associated with CIMT progression. However, the PML homocysteine
levels showed a negative association with baseline CIMT in the total BV AIT sample as
well as in subjects with baseline fasting tHcy level ≥ 9.1 𝜇 mol/L; this finding
contradicted a previous study reporting that subjects with higher PML homocysteine level
were at greater risk for CVD.
10
Another study also found a mean PML homocysteine
level rise in CAD patients compared to controls; however, this difference did not reach
statistical significance.
31
As only a limited number of studies have been conducted on
17
PML homocysteine as a CVD risk factor that is independent from plasma homocysteine
level overall, further studies should be performed to solve this divergence.
The role of plasma cysteine level on CVD risk has been controversial, with no
consensus achieved. El-Khairy L et al. found a U-shaped relationship between cysteine
and cardiovascular disease after adjustment for tHcy and other cardiovascular disease risk
factors, with more CVD patients compared to controls at the extreme high and low
plasma cysteine levels.
32
Another study conducted by Özkan Y et al. demonstrated that
the effect of cysteine on CVD risk was intercorrelated with tHcy; these authors
hypothesized (but did not demonstrate) that cysteine might even act synergistically with
homocysteine.
33
However, a study conducted by Xiao Y et al. argued that plasma cysteine
level showed no apparent association with increased risk for CVD alone and only showed
the risk effect in combination with high tHcy.
34
For overall cysteine level, our study
found that fasting and absolute PML cysteine levels were also positively associated with
baseline CIMT. This association was not found among subjects with baseline fasting tHcy
level <9.1 𝜇mol/L but was found only among subjects with baseline fasting tHcy level
≥9.1 𝜇mol/L. This positive association of cysteine with baseline CIMT among only the
high tHcy group is consistent with the results reported by Xiao Y et al.
34
However, our
study showed no association between cysteine levels and CIMT progression in either
fasting tHcy subgroups or overall.
18
CONCLUSION
We investigated the association of subclinical atherosclerosis levels and progression
with plasma aminothiols (cysteine, homocysteine, and CSGL) under the intervention of B
vitamin supplementation among a CVD-free population with initial fasting tHcy ≥8.5
µmol/L. B vitamin supplementation control fasting homocysteine level and reduced PML
homocysteine level but did not influence plasma cysteine and CSGL levels. Fasting
cysteine, PML cysteine, and fasting homocysteine were positively associated with
baseline CIMT, and PML homocysteine was negatively associated with baseline CIMT.
Except for the association between fasting homocysteine and baseline CIMT, these
associations were also evident among subjects with baseline fasting tHcy level ≥9.1
𝜇mol/L. However, none of these measures were associated with baseline CIMT or CIMT
progression for subjects with baseline fasting tHcy level <9.1 𝜇mol/L.
19
REFERENCES
[1] Santulli G. Epidemiology of cardiovascular disease in the 21st century: updated
numbers and updated facts[J]. JCvD, 2013, 1(1): 1-2.
[2] Mozaffarian D, Benjamin E J, Go A S, et al. Heart disease and stroke statistics-2015
update: a report from the american heart association[J]. Circulation, 2015, 131(4):
e29.
[3] National Center for Health Statistics. Deaths: Final data for 2013[J]. National vital
statistics report, 2013, 64(2).
[4] Selhub J. Homocysteine metabolism[J]. Annual review of nutrition, 1999, 19(1):
217-246.
[5] Wald D S, Wald N J, Morris J K, et al. Cardiovascular disease: Folic acid,
homocysteine, and cardiovascular disease: judging causality in the face of
inconclusive trial evidence[J]. BMJ: British Medical Journal, 2006, 333(7578):
1114.
[6] Mangoni A A, Jackson S H D. Homocysteine and cardiovascular disease:: Current
evidence and future prospects[J]. The American journal of medicine, 2002, 112(7):
556-565.
[7] Refsum, MD H, Ueland, MD P M, Nygård, MD O, et al. Homocysteine and
cardiovascular disease[J]. Annual review of medicine, 1998, 49(1): 31-62.
[8] Boushey C J, Beresford S A A, Omenn G S, et al. A quantitative assessment of
plasma homocysteine as a risk factor for vascular disease: probable benefits of
increasing folic acid intakes[J]. Jama, 1995, 274(13): 1049-1057.
[9] Van Der Griend R, Haas F J L M, Duran M, et al. Methionine loading test is
necessary for detection of hyperhomocysteinemia[J]. Journal of Laboratory and
Clinical Medicine, 1998, 132(1): 67-72.
[10] Bautista L E, Arenas I A, Peñuela A, et al. Total plasma homocysteine level and risk
of cardiovascular disease: a meta-analysis of prospective cohort studies[J]. Journal
of clinical epidemiology, 2002, 55(9): 882-887.
[11] Hankey G J, Eikelboom J W. Homocysteine and vascular disease[J]. The Lancet,
20
1999, 354(9176): 407-413.
[12] Nygård O, V ollset S E, Refsum H, et al. Total homocysteine and cardiovascular
disease[J]. Journal of internal medicine, 1999, 246(5): 425-454.
[13] Doshi S N, Moat S J, McDowell I F W, et al. Lowering plasma homocysteine with
folic acid in cardiovascular disease: what will the trials tell us?[J]. Atherosclerosis,
2002, 165(1): 1-3.
[14] van Meurs J B J, Pare G, Schwartz S M, et al. Common genetic loci influencing
plasma homocysteine concentrations and their effect on risk of coronary artery
disease[J]. The American journal of clinical nutrition, 2013, 98(3): 668-676.
[15] Budoff M. Atherosclerosis: Should we use CIMT testing? New insights from
Framingham[J]. Nature Reviews Cardiology, 2011, 8(11): 615-616.
[16] Johri A M, Hétu M F, Nambi V . Carotid Plaque or CIMT: What is the Future for
Carotid US Imaging?[J]. Current Cardiovascular Risk Reports, 2014, 8(6): 1-8.
[17] Polak J F, Meisner A, Pencina M J, et al. Variations in common carotid artery
intima-media thickness during the cardiac cycle: implications for cardiovascular risk
assessment[J]. Journal of the American Society of Echocardiography, 2012, 25(9):
1023-1028.
[18] Oikonen M, Laitinen T T, Magnussen C G, et al. Ideal cardiovascular health in
young adult populations from the United States, Finland, and Australia and its
association with cIMT: the International Childhood Cardiovascular Cohort
Consortium[J]. Journal of the American Heart Association, 2013, 2(3): e000244.
[19] Kulshreshtha A, Goyal A, Veledar E, et al. Association between ideal cardiovascular
health and carotid intima-media thickness: a twin study[J]. Journal of the American
Heart Association, 2014, 3(1): e000282.
[20] Polak J F, Pencina M J, Pencina K M, et al. Carotid-wall intima–media thickness
and cardiovascular events[J]. New England Journal of Medicine, 2011, 365(3):
213-221.
[21] Moat S J, Lang D, McDowell I F W, et al. Folate, homocysteine, endothelial
function and cardiovascular disease[J]. The Journal of nutritional biochemistry, 2004,
15(2): 64-79.
21
[22] Yang H T, Lee M, Hong K S, et al. Efficacy of folic acid supplementation in
cardiovascular disease prevention: an updated meta-analysis of randomized
controlled trials[J]. European journal of internal medicine, 2012, 23(8): 745-754.
[23] Clarke R, Bennett D A, Parish S, et al. Homocysteine and coronary heart disease:
meta-analysis of MTHFR case-control studies, avoiding publication bias[J]. PLoS
medicine, 2012, 9(2): 205.
[24] Hodis H N, Mack W J, Dustin L, et al. High-Dose B Vitamin Supplementation and
Progression of Subclinical Atherosclerosis A Randomized Controlled Trial[J]. Stroke,
2009, 40(3): 730-736.
[25] Hodis H N, Mack W J, Lobo R A, et al. Estrogen in the prevention of atherosclerosis:
a randomized, double-blind, placebo-controlled trial[J]. Annals of Internal Medicine,
2001, 135(11): 939-953.
[26] Hodis H N, Mack W J, LaBree L, et al. Alpha-Tocopherol Supplementation in
Healthy Individuals Reduces Low-Density Lipoprotein Oxidation but Not
Atherosclerosis The Vitamin E Atherosclerosis Prevention Study (VEAPS)[J].
Circulation, 2002, 106(12): 1453-1459.
[27] Selzer R H, Hodis H N, Kwong-Fu H, et al. Evaluation of computerized edge
tracking for quantifying intima-media thickness of the common carotid artery from
B-mode ultrasound images[J]. Atherosclerosis, 1994, 111(1): 1-11.
[28] Selzer R H, Mack W J, Lee P L, et al. Improved common carotid elasticity and
intima-media thickness measurements from computer analysis of sequential
ultrasound frames[J]. Atherosclerosis, 2001, 154(1): 185-193.
[29] Araki A, Sako Y . Determination of free and total homocysteine in human plasma by
high-performance liquid chromatography with fluorescence detection[J]. Journal of
Chromatography B: Biomedical Sciences and Applications, 1987, 422: 43-52.
[30] Shin-Buehring Y S, Rasshofer R, Endres W. A new enzymatic method for
pyridoxal-5-phosphate determination[J]. Journal of Inherited Metabolic Disease,
1981, 4(1): 123-124.
[31] Tsai M Y , Welge B G, Hanson N Q, et al. Genetic causes of mild
hyperhomocysteinemia in patients with premature occlusive coronary artery
diseases[J]. Atherosclerosis, 1999, 143(1): 163-170.
22
[32] El-Khairy L, Ueland P M, Refsum H, et al. Plasma total cysteine as a risk factor for
vascular disease The European Concerted Action Project[J]. Circulation, 2001,
103(21): 2544-2549.
[33] Özkan Y , Özkan E, Şimşek B. Plasma total homocysteine and cysteine levels as
cardiovascular risk factors in coronary heart disease[J]. International journal of
cardiology, 2002, 82(3): 269-277.
[34] Xiao Y , Zhang Y , Lv X, et al. Relationship between lipid profiles and plasma total
homocysteine, cysteine and the risk of coronary artery disease in coronary
angiographic subjects[J]. Lipids in health and disease, 2011, 10(1): 1.
Abstract (if available)
Abstract
Background: Folic acid has been recommended as a potential intervention to prevent CVD, a leading cause of mortality worldwide, by reducing total plasma homocysteine (tHcy) levels and reversing endothelial dysfunction. In this paper, we investigated the association between tHcy, cysteine, and CSGL levels resulting from B vitamin supplementation and subclinical atherosclerosis progression in the BVAIT population, a CVD-free population with elevated levels of tHcy (>8.5 µmol/L). ❧ Methods: A total of 506 eligible subjects were randomized in BVAIT to high-dose B vitamin supplementation or matching placebo
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Creator
Feng, Siyu
(author)
Core Title
Association of subclinical atherosclerosis with plasma B-vitamin, cysteine, homocysteine, and cysteinyl glycine in a cardiovascular disease-free population
School
Keck School of Medicine
Degree
Master of Science
Degree Program
Applied Biostatistics and Epidemiology
Publication Date
06/30/2016
Defense Date
06/30/2016
Publisher
University of Southern California
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B-vitamin,cysteine,cysteinyl glycine,homocysteine,OAI-PMH Harvest,subclinical atherosclerosis
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Mack, Wendy (
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), Allayee, Hooman (
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cysteinyl glycine
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