Full
Length Research Paper
Genetic
Association of Angiotensinogen (M235T) Gene Polymorphism with Essential
Hypertension in Vindhyan Population of Madhya Pradesh,
India.
Neelam Soni 1[*],
Rishabh Dev Saket2and
Abhilasha Shrivastava1
1Centre for
Biotechnology Studies, APS University, Rewa,
Madhya Pradesh, India.
2Department of
Zoology, CGPG College, Panna Madhya
Pradesh, India.
ARTICLE DETAILS ABSTRACT
1. Introduction
Renin-angiotensin system (RAS)
polymorphisms have been studied as candidate risk factors for hypertension with
inconsistent results, possibly due to heterogeneity among various genetic and
environmental factors (2).
A case-control association study was conducted to investigate a possible
involvement of polymorphisms of three RAS genes: AGT M235T (rs699) in
essential hypertensive patients. Angiotensinogen (AGT) is a major precursor of
the renin-angiotensin-system and its plasma levels have been shown to correlate
with blood pressure. Variation in AGT gene and other genes of the RAS regulate
blood pressure smooth muscle cell growth and cardiac remodeling (3). AGT
variants coding region missense polymorphisms M235T the Methionine substituted
to Threonine amino acid at the 235th position in the exon 2 of the AGT gene. It
is suggested that AGT (M235T) polymorphism may be the functional genotype, as
it affects the basal transcription rate of AGT, which could explain the
association of the M235T genotypes with the plasma AGT concentration. Genetic
polymorphisms in components of the RAS including AGT (M235T) are suggested to
be associated with the pathogenesis of essential hypertension (1). The variant
allele 235T is the most frequent one among African populations and it is not
significantly associated with hypertension. It is reported that M235T mutants leads to small in- crease in concentration of
polymorphic AGT rather than changes in function. Frequency distribution and
disease association of M235T has been shown to vary between different ethnic
groups and also within large ethnic groups (1-4).
The
possible effects of two missense single nucleotide polymorphisms (SNPs) of the
AGT gene on DN were investigated in this study. The rs699 in exon 2 is a T-to-C
exchange at codon 268 resulting in a functional replacement of methionine (M)
to threonine (T) (M268 T). The rs699 was previously located at amino acid 235,
and, therefore, it is also named M235T. In Japanese obese women, the
polymorphism in AGT (rs699) has been reported to be associated with visceral
obesity and hyperinsulinemia (2,5).
Another SNP on the AGT gene, rs4762, is a C-to-T substitution in exon 2 of the
AGT gene at codon 207. As a result of this, the exchange of a functional threonine
(T) to methionine (M), also known as T207M o T174M, occurs. The rs4762 may act
as a predictor marker for the post-transplant diabetes mellitus development in
addition to essential and pregnancy hypertension (6,8).
Moreover, the risk for pregnancy-induced hypertension was also reported to be
associated with rs4762 and rs699 haplotypes. Over the past few years, the role
of the renin-angiotensin- aldosterone system (RAAS) in the development of
essential hypertension has generated much interest across the world. The
investigations were expanded to implicate that the RAAS in a variety of
physiologic processes may play a significant role in the initiation and
progression of atherosclerosis. The AGT
M235T single nucleotide polymorphism (SNP) is a methionine (Met) to threonine (Thr) amino acid substitution at codon 235, designated the M
and T alleles, respectively. However, published results have been inconsistent
(6). To help clarify the inconsistent findings, with the publication of several
more recent studies we conducted this meta-analysis of the M235T polymorphism
in the AGT gene and risk of essential hypertension (5-9).
2.
Materials and methods:
2.1 Study
population:
The study population
consisted of 340 unrelated subjects comprising of 160 Essential Hypertension
patients and 180 ethnically matched controls of central Indian population were
included in this study. In this region Hindu, Muslim and some Sikh peoples are
mainly living but most people’s belong to Hindu
religion in this region.
2.2 Inclusion and
Exclusion criteria for Cases:
Cases
included consecutive patients who attended the Department of Medicine, Shyam Shah Medical College and Sanjay Gandhi Memorial
Hospital, Rewa, Ayurveda Medical College, Rewa, Ranbaxy pathology Regional collection centre Rewa, District hospital Satna, Shahdol, Sidhi. Hypertension was diagnosed in accordance with World
Health Organization (WHO Expert committee 2003) criteria.
2.3 Inclusion and
Exclusion criteria for Controls:
Control group composed
of non-diabetic healthy individuals that were collected during “Diabetes
Awareness Camps” organized in urban regions in and around SSMC Rewa and many volunteers were also included to collect
control sample. The control subjects were recruited from the regions that from
homogenous cluster in Vindhyan region India in
accordance with a recent report of genetic landscape of the people of India.
(Indian Genome Variation Consortium 2008)
2.4 Anthropometric
and Biochemical Measurements:
2.4.1 Anthropometry:
Height and Weight were
measured in light clothes and without shoes in standing position as per
standard guidelines. Body Mass Index (BMI) was calculated as weight in
kilograms divided by height in meters squared. Waist circumference was measured
in standing position midway between iliac crest and lower costal margin and hip
circumference was measured at its maximum waist to hip ratio (WHR) was
calculated using waist and hip circumferences. Systolic and diastolic blood
pressures were measured twice in the right arm in sitting position after
resting for at least 5 minute using a standard sphygmomanometer and the average
of the two reading was used.
2.4.2 Biochemical Analysis:
Biochemical parameters related to type 2
diabetes were estimated for both cases and controls subjects. Measurement of
Serum levels of Total cholesterol (TC), Triglycerides (TG), HbA1c, High density
lipoprotein-cholesterol (HDL-C), Low density lipoprotein-cholesterol (LDL-C)
and Urea were measured based on spectrophotometric method using automated
clinical chemistry analyzer Cobas Integra 400 plus
(Roche Diagnostics, Mannheim, Germany).
2.4.3 Blood collection and plasma/serum separation:
Venous blood samples
were obtained from the subjects after 12 hours of overnight fasting in vacutainers with and without appropriate anti-coagulants.
Immediately, plasma and serum from the respective vacutainers
were separated by centrifuging the tubes at 1000 rpm for 10 min. at 4˚C
2.5 Molecular
Laboratory Analysis:
2.5.1 Method for DNA isolation:
Genomic DNA was
extracted from whole blood by the modification of salting out procedure
described by Miller and coworkers (Miller et
al. 1988). Frozen blood sample was thawed at room temperature. 0.5 ml. of
whole blood sample was suspended in 1.0 ml. of lysis
buffer (0.32 M Sucrose, 1 mM Mgcl2, 12 mM Tris and 1% Triton-X-100) in a
1.5 ml. microcentrifuge tubes. This mixture was mixed
gently by inverting the tube upside down for 1 min. The mixture was than allowed to stand for 10 min. at room temperature to
ensure proper lysis of cells. The mixture was
centrifuged at 11,000 rpm for 5 min. at 4˚C to pellet the nuclei. The
supernatant was discarded carefully in a jar containing disinfectant, as pellet
formed is loosely adhered to the bottom of centrifuge tube. The pellet was resuspended in 0.2 ml. of lysis
buffer and recentrifuge at 11,000 rpm for 5 min. The
pellet was than dissolved in 0.2 ml. of deionized autoclaved water and mixed
thoroughly on vortexer. The mixture was centrifuged
at 14,000 rpm for 1 min. at 4˚C. Supernatant was discarded to gain an
intact pellet. To the above pellet, 80 μl.
of proteinase K
buffer (0.375 M Nacl, 0.12 M EDTA, pH 8.0) and 10 μl. of 10% SDS (10% w/v SDS,
pH 7.2) was added. Mixture was well frothed with the help of micro tip to allow
proper lysis of pelleted nuclei. After
digestion was complete, 100 μl. of saturated cold 5M Nacl was
added and shaken vigorously for 15 sec. To the above mixture 0.2 ml. of
deionized, autoclaved water and 0.4 ml. of phenol-chloroform (4:1 v/v) was added to remove most of the non nucleic
acid organic molecules. Microcentrifuge tube was
inverted upside down until the solution turned milky. Phases were separated by
centrifuging the above mixture at 12,000 rpm for 10 min. at 4˚C. Aqueous (top) layer was
saved and transferred in another microcentrifuge
tube. Transferring of any interface layer was avoided. To the aqueous layer, 1
ml. chilled absolute ethanol was added and the tube was inverted several times
until the DNA precipitated. DNA precipitates like thread. This was centrifuged at
14,000 rpm for 4 min. at 4˚C to pellet the DNA thread. Supernatant was
discarded. The pellet was washed twice with 1 ml. of 70% alcohol. The mixture was again
centrifuged at 14,000 rpm for 1 min. 4˚C. Supernatant was discarded and
pellet was air dried for 10-20 min. The pelleted DNA was rehydrated in 100-200 μl. of TE buffer pH 7.4 (10 mM Tris-HCL pH 7.4, 1mM EDTA, pH
8.0). DNA was allowed to dissolve overnight at 37˚C before quantization.
2.5.2 Determination of quality and quantity of isolated DNA:
The isolated DNA is to
be used for PCR based study. Therefore its suitability for PCR along with its
size heterogeneity is among the most important criterion for purity. As a
matter of general practice all DNA preparations were tested for quality and
quantity measures, as described in the following paragraphs.
2.5.3 Quantitation by UV spectrophotometry:
The isolated genomic
DNAs were then tested for purity by measuring their absorbance values at 230
nm, 260 nm, 280 nm and 300 nm using a UV visible spectrophotometer (Systronic, India). A DNA preparation was considered to be
good if it had A 260 nm / A 280 nm ratio as approximately 1.8 and A 300 nm was
0.1 or lesser. The absorbance at 260 nm was used to calculate the amount of
DNA, using the relationship that double stranded DNA at 50μg/ml
concentration has an absorbance= 1.0 at 260 nm.
2.5.4 Agarose Gel Electrophoresis:
Gel electrophoresis of
the genomic DNAs was carried out for qualitative estimation of samples
prepared. A good DNA preparation appears as single band. A horizontal agarose slab gel electrophoresis apparatus (Bangalore Genei, Bangaore, India) was used.
In brief, 4-5 μl of each genomic DNA was loaded
on 0.8 agarose (0.8 % w/v, Sigma) containing ethidium bromide solution (0.5 μg/ml) and electrophoresis was done at 80 V in 1x TAE
buffer (40 mM Tris, 20 mM acetic acid, 1 mM EDTA).
Lambda DNA EcoRІ
/ Hind Ш double digest
(Bangalore Genei, Bangalore, India) was used as
molecular weight marker after completion of electrophoresis, the DNA bands were
visualized and photographed using an UV transilluminator
(312 nm) and gel documentation system (Vilber Lourmate, Cedex 1, France)
respectively.
2.5.5 Polymorphism screening:
In general, the genomic
DNA extracted from peripheral blood of healthy individuals and diseased
individuals was subjected to PCR followed by restriction digestion and
electrophoresis to genotype both the groups for relevant gene of interest. All
the PCRs were carried out in a PTC 200 thermal cycler (MJ Research Inc. USA).
PCR is a rapid, inexpensive and simple mean of producing relatively large copy
number of DNA molecules from the small amounts of source DNA material, even
when the source DNA is of relatively poor quality. Due to the extreme
sensitivity, precautions were taken against contamination of the reaction
mixture with the trace amounts of DNA, which could serve as an unwanted
template. Appropriate negative control was included in each PCR run carried out
for each gene, to monitor this contamination of PCR mix to avoid any false positive
results. The negative control used for PCR contained whole PCR reaction mix
except target DNA which was replaced by HPLC purified water free of RNase, DNase, and any
contamination from any other source resembling the gene sequence. Subsequently
restriction enzyme digestion was performed by incubating the double stranded
DNA with appropriate amount of restriction enzyme, in its respective buffer as
recommended by the supplier and at optimal temperature for that specific
enzyme. A typical digestion includes one unit of enzyme per microgram of
starting DNA. One enzyme unit is usually defined as the amount of enzyme needed
to completely digest one microgram of double stranded DNA in one hour at the
appropriate temperature. Their biochemical activity of the restriction enzyme
is the hydrolysis of phosphodiester backbone at
specific sites in a DNA sequence. Precaution was taken to avoid star activity
of restriction enzymes. When DNA is digested with certain restriction enzymes
under non-standard conditions, cleavage can occur at sites different from the
normal recognition sequence. Such aberrant cutting is called “star activity”
which can be due to high pH (>8.0) or low ionic strength, extremely high
concentration of enzyme (>100 U/μg of DNA) and presence
of organic solvents in the reaction (e.g. ethanol, DMSO). The PCR and
restriction digestion conditions were optimized for specific locus of relevant
segment of the gene to be studied. The PCR products as well as the digested
products were separated on either agarose gel or
polyacrylamide gel depending on their size. Gels were stained with ethidium bromide solution (0.5μg/ml) and subsequently
visualized and photographed under UV transilluminator.
2.6
Detection of Angiotensinogen (M235T) Single Nucleotide Polymorphism:
Polymorphism
in The angiotensinogen (AGT) gene M235T polymorphism is located in the SNP
rs699 region of the gene. The AGT M235T single nucleotide polymorphism (SNP) is
a methionine (Met) to threonine (Thr) amino acid
substitution at codon 235, designated the M and T alleles, respectively.
2.6.1 Primer sequence: The
oligonucleotides sequences (primers) used were those described by MM Shamaa (Shamaa MM et. al. 2013).
Forward
primer: 5'- CCG TTT GTG CAG GGC CTGGCT CTC T -3'
Reverse
Primer: 5' - CAG GGT GCTGTC CAC ACT GGA CCC C-3'
2.6.2 PCR Mix:
The
PCR was carried out in a final volume of 25 μl,
containing 50-100 ng of genomic DNA(4-5 μl), 2.5 μl of 10X Taq polymerase
buffer (10 mM Tris HCl pH 8.8, 50 mM KCl, 1.5 mM MgCl2, 0.01% gelatin,
0.005% Tween-20, 0.005% NP-40; final concentration 1X; Genetix
Biotech Asia Pvt. Ltd.,India), 1 μl
of 10 mM dNTPs (Banglore Genei, Bangalore,
India), 1 μl of 25 pmol/μl of forward and reverse primers specific for and 1 μl of unit of
1U/ μl Red Taq DNA
polymerase (Bangalore genei).
2.6.3 PCR Thermal Program:
After
an initial denaturation of 5 min at 95˚C, the samples were subjected to 35
cycles at 95˚C for 1 min, at 58˚C for 45 s, and 72˚C for 45 s,
with a final extension of 10 min at 72˚C in a thermal cycler. A 100bp
ladder with amplified product has been run under 2.5 % agarose
gel electrophoresis.
2.6.4 Restriction digestion By PsyI:
PCR
amplification of Angiotensinogen (M235T) Gene with specific primers gave 165-bp undigested product which
was digested with PsyI enzyme (New England Biolabs,
Boverly, MA) for 16 h at 37˚C. The wild-type
genotype (MM) was not digested, whereas the mutated homozygous genotype (TT)
was cut as a doublet of 141 bp and 24 bp. The heterozygous genotype (TC) was represented as 2
fragments of 165 bp and 141 bp
whereas 24 bp of DNA fragments are run out from the
gel because of its too short fragments the digestion products were then
separated by electrophoresis on a 2.5% agarose gel.
The results were documented by digital camera and further saved by gel
documentation system.
2.7 Statistical
Analysis of Genotype:
Statistical analysis was
done by comparing the distribution of genotype frequencies, allele frequencies
and carriage rates of all the four polymorphism in diseased and control group.
Disease group included Diabetic patients whereas control group included all
healthy controls (HC) enrolled in the study. The proportions of different
genotypes for a gene in a population are known as genotype frequencies.
The proportion of
genotype in a sample will be the ratio of the number of individuals having that
genotype to the total number of individuals in the sample. The proportions of
different alleles for a gene present in a population are known as allele
frequencies. The proportion of an allele in a sample will be the ratio of
number of occurrences of the investigated allele in the population to the total
number of alleles. The carriage rate was calculated as the number of
individuals carrying at least one copy of the test allele divided by the total
number of individuals. Data was analyzed using Microsoft Excel 2002, Microsoft
Corporation. Only the biochemical parameters, for difference between obese
diabetic patients and the obese non-diabetic controls were assessed using the
student’s t test. Similarly the biochemical parameters between the normal
weight patients and normal weight non-diabetic controls were also assessed. The
P-values calculated using t test along with the mean (inter-quartile range)
were presented. Statistical analyses were performed using statistical package,
Prism 3.0, Prism 5.1 version.
3.
Results
3.1 Results:
The
descriptive data and comparison of anthropometric and biochemical parameters of
essential hypertension patients versus controls are presented in Table no. 4.1.
The age, sex, BMI, WHR were the parameters. As expected the essential
hypertension patients had markedly higher levels of weight of men (P=0.3916)
then women (P=0.0723) and BMI of Women (P=0.2247) and Men (P=0.3499) but both
was not significantly different between patient and healthy population. Thus
WHR in Women (P=0.1741) and Men (P=0.0973) were not found significantly
different between case and control group.
Table 1.
Comparison of anthropometric parameters of essential
hypertension patients and healthy controls
|
Characteristics |
Cases (160) |
Controls(180) |
P-value |
|
n(Men/Women) |
160(104/56) |
180(118/62) |
|
|
Age(years) |
52.5±12.5 |
52.6±12.4 |
0.9411,ns |
|
Height(m) |
162.50±11.3 |
161.2±12.4 |
0.3152,ns |
|
Weight (Kg) |
|
|
|
|
Women |
62.5 ±4.7 |
61.6 ± 4.5 |
0.0723,ns |
|
Men |
68.4±5.6 |
67.8±7.1 |
0.3916,ns |
|
BMI (kg/m2) |
|
|
|
|
Women |
25.6±3.1 |
26.1 ± 4.3 |
0.2247,ns |
|
Men |
24.6±4.7 |
25.1± 5.1 |
0.3499,ns |
|
Waist circumference
(cm) |
|
|
|
|
Women |
92.5±6.2 |
93.6±6.7 |
0.1186,ns |
|
Men |
90.0±7.0 |
89.0±6.0 |
0.1571,ns |
|
Hip (cm) |
|
|
|
|
Women |
95.9±2.4 |
96.1±2.2 |
0.4233,ns |
|
Men |
90.8±4.3 |
91.2±1.5 |
0.2426,ns |
|
WHR |
|
|
|
|
Women |
0.97±0.05 |
0.98±0.08 |
0.1741,ns |
|
Men |
0.98±0.08 |
0.99±0.01 |
0.0973,ns |
(*denotes level of significant change
between case and control)
3.2 Biochemical and
clinical findings:
Biochemical
test performed in the blood sample for following clinical parameters and the
findings were tabulated. Statistical analysis was done by using student’s
t-test and p value suggests the level of significant were changed here. The descriptive data and comparison of
biochemical parameters of essential hypertension patients versus healthy
controls are presented in Table no. 2. As expected the essential hypertension
patients had markedly higher levels of HDL-C (P<0.0001), LDL-C (P<0.0001),
TG (P<0.0001), Systolic BP (P<0.0001) and Diastolic
BP (P<0.0001) compared to that of control subject. Whenever, rests of
parameters were not significantly different between patient and healthy
population.
Table 2.
Comparison of
Biochemical & clinical findings of essential hypertension patients and
healthy controls.
|
Characteristics |
Cases (160) |
Controls(180) |
P-value |
|
Post-Prandial Glucose
(mg/Dl) |
118.7±12.4 |
119.4±11.6 |
0.5912,ns |
|
HbA1C(%) |
5.9±0.7 |
5.8±0.8 |
0.2235,ns |
|
HDL-C(mmol/L) |
122.8±12.2 |
109.3±11.6 |
P<0.0001*** |
|
LDL-C (mg/dL) |
49.1±2.6 |
41.8±3.7 |
P<0.0001*** |
|
TG(mg/dL) |
132.9±13.2 |
126.2±12.2 |
P<0.0001*** |
|
Systolic BP (mmHg) |
145.4±8.1 |
124.8±5.7 |
P<0.0001*** |
|
Diastolic BP (mmHg) |
97.1±5.8 |
86.5±6.2 |
P<0.0001*** |
|
Blood Urea(mg/dL) |
16.68±1.7 |
16.80±1.8 |
0.5293,ns |
|
Urinary Citrate (mmol/24 h) |
2.58±0.96 |
2.62±0.57 |
0.6365,ns |
|
Serum calcium (mg/dl) |
9.42±0.32 |
9.46±0.38 |
0.2978,ns |
|
Urinary potassium (mmol/24 h) |
64.21±4.7 |
64.39±4.3 |
0.7125,ns |
|
Urinary Phosphate (mmol/24 h) |
27.45±4.2 |
26.81±3.3 |
0.1172,ns |
(* denotes the level of significant change between case and control)
3.3 Detection of
Genetic Polymorphism in Angiotensinogen (M235T) Gene:
PCR
amplification with specific primers gave 165 bp product which was digested with PsyI enzyme (New
England Biolabs, Boverly,
MA) for 16 h at 37˚C. The wild-type genotype (MM) was not digested,
whereas the mutated homozygous genotype (TT) was cut as a doublet of 141 bp and 24 bp. The heterozygous
genotype (TC) was represented as 2 fragments of 165 bp
and 141 bp whereas 24 bp of
DNA fragments are run out from the gel because of its too short fragments.
Fig-1: Representative gel picture of Angiotensinogen (M235T) polymorphism. Lane
M represents 1500 bp molecular marker, Lane MM Wild
type genotype, and Lane MT heterozygous genotype and Lane TT variant genotype.
The distribution of the polymorphisms of Angiotensinogen (M235T) was consistent with Hardy- Weinberg
equilibrium (HWE) in healthy controls. The observed genotype frequencies,
allele frequencies and carriage rates for Angiotensinogen (M235T) polymorphism are depicted in table 4.5 and
table 4.6 and Graph 1, 2, 3. Significant level of change has been seen in
overall distribution of Angiotensinogen (M235T) genotypes in Healthy control group as compared to disease group although
Healthy control group showed little increase in ‘MM’ genotype as compared to
Patients of Essential hypertension (69.44% vs 56.25%). Similarly, mutant type ‘TT’ genotype was present in low frequency in
Essential hypertension patients group 3.75% and also in control group 4.44% (χ2 = 0.0243*, P= 7.436). ‘TT’ genotype is higher in
control group and may be protective in our population and statistically
significantly different between both groups.
An odds ratio of MM genotype is 0.5657 which indicates little protective
effect whereas an odds ratio of MT
genotype is 1.887 of Essential
hypertension patients group respectively indicate little or no effect and
association of this mutant genotype with the Essential hypertension susceptibility.
Overall allele ‘M’ was found little lower frequency in disease group as
compared to HC group whereas allele ‘T’ was
present in little high frequency in the disease group but the difference is
nominal and significant (χ2 = 0.0437*, P=4.069). Carriage rate of allele ‘M’ was slightly
high in essential hypertension group as compared to healthy control (75.77% Vs 68.75%) whereas carriage rate of allele ‘T’ was
approximately similar in both control and disease group and no significant
level of change has been seen. The pattern of genotype distribution, allele
frequency and carriage rate in disease and control group suggests Angiotensinogen
(M235T) polymorphism is significantly
associated with Essential hypertension in our population.
Table 3.
Frequency distribution and association of Genotype,
allele frequency and carriage rate of Angiotensinogen (M235T) gene polymorphism in
population of Vindhyan region using Chi Square Test
|
Angiotensinogen
(M235T) GENE |
CASE N= 160 N % |
CONTROL N=180 N % |
CHI SQUARE VALUE χ2 (P Value) |
|
Genotype MM MT TT |
90 56.25 64 40.00 6 3.75 |
125 69.44 47 26.11 8 4.44 |
7.436 (0.0243*) |
|
Allele M T |
244 76.25 76 23.75 |
297 82.50 63 17.50 |
4.069 (0.0437*) |
|
Carriage Rate M T |
154 68.75 70 31.25 |
172 75.77 55 24.22 |
2.774 (0.0958ns) |
(* - denotes the level of significant association between case and
control.)
(N – Number of individuals in study group.)
(% - Genotype allele frequency and carriage rate expressed in
percentage.)
Table 4.
Fisher Exact Test values of Angiotensinogen (M235T) gene polymorphism
|
Angiotensinogen
(M235T) GENE |
CASE N= 160 N % |
CONTROL N=180 N % |
P Value |
Odds Ratio ( 95% confidence interval) |
|
Genotype MM MT TT |
90 56.25 64 40.00 6 3.75 |
125 69.44 47 26.11 8 4.44 |
0.0133* 0.0077** 0.7914ns |
0.5657 (0.3624 to
0.8830) 1.887 (1.192 to 2.986) 0.8377 (0.2842 to
2.469) |
|
Allele M T |
244 76.25 76 23.75 |
297 82.50 63 17.50 |
0.0459* |
0.6810 (0.4683 to
0.9904) 1.468 (1.010 to 2.135) |
|
Carriage Rate M T |
154 68.75 70 31.25 |
172 75.77 55 24.22 |
0.1144ns |
0.7035 (0.4646 to
1.065) 1.421 (0.9388 to
2.152) |
(* - denotes the level of significant association between case and
control.)
(N – Number of individuals in study group.)
(%-Genotype allele frequency and carriage rate expressed in percentage.)
Graph
No.-1: Genotype Frequency of Angiotensinogen (M235T) gene.
- Discussion:
The
genetic basis of common essential HTN on the other hand is only just becoming
accessible through high-throughput approaches. Unbiased genome-wide analyses of
BP genomics have identified 43 genetic variants associated with systolic,
diastolic BP, and HTN (11). It is highly likely based on current findings that
there are hundreds of such loci with small effects on BP, opening a perspective
on the genetic architecture of BP that was unknown before. A powerful
interaction between the autonomic and the immune systems plays a prominent role
in the initiation and maintenance of hypertension and significantly contributes
to cardiovascular pathology, end-organ damage and mortality (7,14). The sympathetic nervous system, a major determinant of
hypertension, innervates the bone marrow, spleen and peripheral lymphatic
system and is proinflammatory, whereas the parasympathetic nerve activity
dampens the inflammatory response through α7-nicotinic acetylcholine
receptors. The neuro-immune synapse is bidirectional
as cytokines may enhance the sympathetic activity through their central nervous
system action that in turn increases the mobilization, migration and
infiltration of immune cells in the end organs (13). Kidneys may be infiltrated
by immune cells and mesangial cells that may
originate in the bone marrow and release inflammatory cytokines that cause
renal damage. Hypertension is also accompanied by infiltration of the
adventitia and perivascular adipose tissue by inflammatory immune cells
including macrophages. Increased cytokine production induces myogenic and
structural changes in the resistance vessels, causing elevated blood pressure
(10-14).
Graph
No.-2: Allele Frequency of Angiotensinogen (M235T) gene.
Hypertension, the leading risk factor for cardiovascular
disease, originates from combined genetic, environmental, and social
determinants. Environmental factors include overweight/obesity, unhealthy diet,
excessive dietary sodium, inadequate dietary potassium, insufficient physical
activity, and consumption of alcohol (15). Prevention and control of
hypertension can be achieved through targeted and/or population-based
strategies. For control of hypertension, the targeted strategy involves
interventions to increase awareness, treatment, and control in individuals. The
Chronic Care Model, a collaborative partnership among the patient, provider,
and health system, incorporates a multilevel approach for control of hypertension.
Optimizing the prevention, recognition, and care of hypertension requires a
paradigm shift to team-based care and the use of strategies known to control BP
(17). Essential hypertension illustrates the formidable task presented by the
identification of genetic determinants of common disease. Making an initial
genetic inference may prove difficult enough; the subsequent demonstration of
functional significance at various levels of biological integration may be even
more challenging. We review three instances in which an initial genetic
inference has led to the development of testable hypotheses pursued at
increasingly higher levels of biological organization (18). Men had
significantly higher BMI than women. Average BMI was significantly higher in
participants with elevated cholesterol levels compared to participants with
normal cholesterol levels. Majority of participants consumed less than five
meals per day with no major differences between students according to residence
and sex. Men had significantly higher protein intake and consumed at least four
meals daily compared to woman who had three or less meals daily with no
differences in intake according to residence. Students with normal lipid
profile consumed more carbohydrates than students with increased cholesterol
(15-19).
Our study suggested that the essential hypertension patients
had markedly higher levels of weight of men (P=0.3916) then women (P=0.0723)
and BMI of Women (P=0.2247) and Men (P=0.3499) but both was not significantly
different between patient and healthy population. Thus WHR in Women (P=0.1741)
and Men (P=0.0973) were not found significantly different between case and
control group. Biochemical test performed in the blood sample for following
clinical parameters and the findings were tabulated. Statistical analysis was
done by using student’s t-test and p value suggests the level of significant
were changed here. The descriptive data
and comparison of biochemical parameters of essential hypertension patients
versus healthy controls are presented in Table no. 2. As expected the essential
hypertension patients had markedly higher levels of HDL-C (P<0.0001),
LDL-C (P<0.0001), TG (P<0.0001), Systolic BP (P<0.0001)
and Diastolic BP (P<0.0001) compared to that of control subject.
Whenever, rests of parameters were not significantly different between patient
and healthy population.
The M235T polymorphism is the most important angiotensinogen
(AGT) genetic variant. The relationship between AGT gene polymorphisms and CAD
has been investigated in only a few studies, however, with conflicting results.
In most of these studies, not all participants underwent coronary angiography
to determine the existence of coronary artery stenosis. In this study, we
tested this relationship again in Taiwanese subjects who underwent coronary
angiography. This study enrolled 576 patients who underwent coronary
angiography, including 362 patients with CAD (the CAD group) and 214 without
CAD (21). The angiotensinogen gene has been linked to the development of essential
hypertension, and a M235T variant of this gene, associated with increased
plasma levels of angiotensinogen, is more common in hypertensives
than in normotensive controls in various populations. The present study was
conducted to examine whether the M235T variant of the angiotensinogen gene may
be a risk factor for the development of hypertension in patients undergoing
renal transplantation (23). Presence of hypertension and graft survival was analysed by blinded review of all case records over a
follow-up period up to 30 months. Angiotensinogen genotype was determined by a mutagenically separated allele-specific polymerase chain-
reaction technique. While post-transplant hypertension was present in 78% of
all patients, no relationship was found between either donor or recipient
genotype and the presence or severity of post-transplant hypertension.
Furthermore, there was no relationship between Angiotensinogen genotype and
graft survival during the course of the study. These findings do not support
the hypothesis that the M235T variant of the Angiotensinogen gene is a risk
factor for the development of post transplant
hypertension (20-24).
Essential hypertension is a common, polygenic, complex
disorder resulting from interaction of several genes with each other and with
environmental factors such as obesity, dietary salt intake, and alcohol
consumption. Since the underlying genetic pathways remain elusive, currently
most studies focus on the genes coding for proteins that regulate blood
pressure as their physiological role makes them prime suspects (25). The
present study examines how polymorphisms of the insertion/deletion (I/D) ACE
and M235T AGT genes account for presence and severity of hypertension, and
embeds the data in a meta-analysis of relevant studies. The I/D polymorphisms
of the ACE and M235T polymorphisms of the AGT genes were determined by RFLP
(restriction fragment length polymorphism) and restriction analysis in 638
hypertensive patients and 720 normotensive local blood donors (26).Severity of
hypertension was estimated by the number of antihypertensive drugs used. No
difference was observed in the allele frequencies and genotype distributions of
ACE gene polymorphisms between the two groups, whereas AGT TT homozygotes were
more frequent in controls (4.6% vs. 2.7%, P = .08). This became significant (p
= 0.035) in women only (24-27).
Our study on polymorphism Angiotensinogen (M235T) revealed
that the PCR amplification with specific primers gave 165 bp
product which was digested with PsyI enzyme (New
England Biolabs, Boverly,
MA) for 16 h at 37˚C. The wild-type genotype (MM) was not digested,
whereas the mutated homozygous genotype (TT) was cut as a doublet of 141 bp and 24 bp. The heterozygous
genotype (TC) was represented as 2 fragments of 165 bp
and 141 bp whereas 24 bp of
DNA fragments are run out from the gel because of its too short fragments. The distribution of the polymorphisms of Angiotensinogen
(M235T) was consistent with Hardy-
Weinberg equilibrium (HWE) in healthy controls. The observed genotype
frequencies, allele frequencies and carriage rates for Angiotensinogen
(M235T) polymorphism are depicted in table 4.5 and table 4.6 and
Graph 1, 2, 3. Significant level of change has been seen in overall
distribution of Angiotensinogen (M235T) genotypes in Healthy control group as compared to disease group although
Healthy control group showed little increase in ‘MM’ genotype as compared to
Patients of Essential hypertension (69.44% vs 56.25%). Similarly, mutant type ‘TT’ genotype was present in low frequency in
Essential hypertension patients group 3.75% and also in control group 4.44% (χ2 = 0.0243*, P= 7.436). ‘TT’ genotype is higher in
control group and may be protective in our population and statistically
significantly different between both groups. An odds ratio of MM genotype is 0.5657
which indicates little protective effect
whereas an odds ratio of MT genotype is 1.887 of Essential hypertension patients group respectively indicate little or
no effect and association of this mutant genotype with the Essential
hypertension susceptibility. Overall allele ‘M’ was found little lower frequency
in disease group as compared to HC group whereas allele ‘T’ was present in little high frequency in the disease group but the
difference is nominal and significant (χ2 = 0.0437*,
P=4.069). Carriage rate of allele ‘M’
was slightly high in essential hypertension group as compared to healthy
control (75.77% Vs 68.75%)
whereas carriage rate of allele ‘T’ was approximately similar in both control
and disease group and no significant level of change has been seen. The pattern
of genotype distribution, allele frequency and carriage rate in disease and
control group suggests Angiotensinogen (M235T) polymorphism is significantly associated with Essential hypertension in
our population. The
angiotensinogen gene M235T polymorphisms that has an
effect on the activity of the renin-angiotensin-aldosterone system are related
to the high hypertension risk. The aim of this study was to find out the
association between angiotensinogen M235T gene polymorphism and the risk of
developing hypertension. A total of 306 samples - 153 patients with
hypertension and 153 age- and sex-matched healthy controls were selected using
a simple random sampling technique. Clinical and biochemical variables were
measured to assess the associated risk factors. Blood samples from the patients
and matched controls were used to isolate deoxyribonucleic acid. The AGT M235T
genotypes were identified using polymerase chain reaction and analyzed by agarose gel electrophoresis (22). Logistic regression with
a 95% confidence interval (CI) was employed to assess the risk correlations of
AGT gene M235T polymorphisms with hypertension. This study also identified the
clinical risk factors for hypertension, such as, total cholesterol, triglycerol, low density lipoprotein-cholesterol, and high
density lipoprotein-cholesterol levels, which were significantly higher in
patients compared to controls (P< 0.001). The AGT M235T genes of the TT
genotype and the T allele are associated with an increased risk of hypertension
among the Ethiopian patients. A population-based epidemiological study is
needed corroborate the association between AGT and HTN. Gene
polymorphisms linked to the renin–angiotensin (AGT) aldosterone system (RAAS)
were broadly inspected in patients with diabetic nephropathy (DN) and
hypertension (25).
The pathogenesis of
essential hypertension (EH) is affected by genetic and environmental factors.
Mutations in hypertension-related genes can affect blood pressure (BP) via
alteration of salt and water reabsorption by the nephron. The genes of the
renin-angiotensin system (RAS) have been extensively studied because of the
well documented role of this system in the control of BP. It has been
previously shown that angiotensinogen (AGT) gene polymorphism could be
associated with increased risk of EH (27).The current study evaluated the frequency of AGT (M235T) polymorphism
in relation to EH in a group of Egyptian population. Restriction fragment
length polymorphism- Polymerase chain reaction (RFLP-PCR) was used for the
analysis of M235T polymorphism of AGT genes in peripheral blood samples of all
patients and controls (26). The
results revealed that there was a positive risk of developing EH when having
the T allele whether in homozygous or heterozygous state. It was concluded that
there was an association between AGT (M235T) gene polymorphism and the risk of
developing EH (26-28).
- Conclusion:
The renin-angiotensin system (RAS) is a group of related hormones
that act together to regulate BP by maintaining vascular tone and the balance
of water and sodium. Angiotensinogen (AGT) is among the components that are
involved in the activation/effector cascade of the RAS. Genetic polymorphisms
in components of the RAS including AGT (M235T) are suggested to be associated
with the pathogenesis of EH. Significant level of
change has been seen in overall distribution of Angiotensinogen (M235T) genotypes in Healthy control group as
compared to disease group although Healthy control group showed little increase
in ‘MM’ genotype as compared to Patients of Essential hypertension (69.44% vs 56.25%). Similarly, mutant type ‘TT’ genotype was present
in low frequency in Essential hypertension patients group 3.75% and also in control group 4.44% (χ2 = 0.0243*, P= 7.436). ‘TT’ genotype
is higher in control group and may be protective in our population and
statistically significantly different between both groups. Finally, we
summarized, some biochemical and clinical parameters expected the essential
hypertension patients had markedly higher levels of HDL-C, LDL-C, TG, Systolic
BP and Diastolic BP compared to that of control subject was significantly
associated with Essential hypertension.
Here, data from results reveals Angiotensinogen (M235T) gene was significantly
associated with Essential hypertension.
- References:
1. El-Garawani,
I.M. Ameliorative Effect of Cymbopogon Citratus Extract on Cisplatin-Induced
Genotoxicity in Human Leu-kocytes. J. Biosci. Appl. Res. 2015, 1, 304–310.
2. Lovati, E.; Richard, A.; Frey,
B.M.; Frey, F.J.; Ferrari, P. Genetic polymorphisms of the
renin-angiotensin-aldosterone system in end-stage renal disease. Kidney Int.
2001, 60, 46–54.
3. Prasad, P.; Tiwari,
A.K.; Kumar, K.M.P.; Ammini, A.C.; Gupta, A.; Gupta,
R.; Sharma, A.K.; Rao, A.R.; Nagendra,
R.; Chandra, T.S.; et al. Chronic renal insufficiency among Asian Indians with
type 2 diabetes: I. Role of RAAS gene polymorphisms. BMC Med. Genet. 2006, 7,
42.
4. Muscogiuri, G.; Chavez, A.O.; Gastaldelli, A.; Perego, L.; Tripathy, D.; Saad, M.J.; Velloso, L.; Folli, F. The
Crosstalk between Insulin and Renin-Angiotensin-Aldosterone Signaling
Systems and its Effect on Glucose Metabolism and Diabetes Prevention. Curr. Vasc. Pharmacol.
2008, 6, 301–312.
5. Sethi, A.A.; Nordestgaard, B.G.; Tybjćrg-Hansen,
A. Angiotensinogen Gene Polymorphism, Plasma Angiotensinogen, and Risk of
Hypertension and Ischemic Heart Disease. Arter. Thromb. Vasc. Biol. 2003, 23,
1269–1275.
6. Chang, H.-R.; Cheng,
C.-H.; Shu, K.-H.; Chen, C.-H.; Lian,
J.-D.; Wu, M.-Y. Study of the polymorphism of angiotensinogen, anigiotensin-converting enzyme and angiotensin receptor in
type II diabetes with end-stage renal disease in Taiwan. J. Chin. Med. Assoc.
2003, 66, 51–56.
7. Soliman, S.S.A.; Guseman, E.H.; Haile, Z.T.; Ice, G. Prevalence and
determinants of hypertension unawareness among Egyptian adults: The 2015 EHIS.
J. Hum. Hypertens. 2020, 1–8.
8. Reis, K.A.; Ebinc, F.A.; Koc, E.; Demirci, H.; Erten, Y.; Guz, G.; Derici, U.B.; Bali, M.; Söylemezoglu, O.; Arınsoy,
T.; et al. Association of the Angiotensinogen M235T and APO E Gene
Polymorphisms in Turkish Type 2 Diabetic Patients with and without Nephropathy.
Ren. Fail. 2011, 33, 469–474.
9. Huang, H.-D.; Lin,
F.-J.; Li, X.-J.; Wang, L.-R.; Jiang, G.-R. Genetic polymorphisms of the
renin-angiotensin-aldosterone system in Chinese patients with end-stage renal
disease secondary to IgA nephropathy. Chin. Med. J. 2010, 123, 3238–3242.
10. Babitt, J.L.; Lin, H.Y.
Mechanisms of Anemia in CKD. J. Am. Soc. Nephrol. 2012, 23, 1631–1634.
11. Jung, S.-Y.; Choi, J.C.;
You, S.-H.; Kim, W.-Y. Association of Renin-angiotensin-aldosterone System
Inhibitors With Coronavirus Disease 2019
(COVID-19)-related Outcomes in Korea: A Nationwide Population-based Cohort
Study. Clin. Infect. Dis. 2020, 71, 2121–2128.
12. Lévesque, S.; Moutquin, J.-M.; Lindsay, C.; Roy, M.-C.; Rousseau, F.
Implication of an AGT Haplotype in a Multigene
Association StudyWith Pregnancy Hypertension.
Hypertension 2004, 43, 71–78.
13. Lee, S.R.; Moon, J.Y.;
Lee, S.H.; Ihm, C.G.; Lee, T.W.; Kim, S.K.; Chung,
J.-H.; Kang, S.W.; Kim, T.H.; Park, S.J.; et al. Angiotensinogen Polymorphisms
and Post-Transplantation Diabetes Mellitus in Korean Renal Transplant Subjects.
Kidney Blood Press. Res. 2013, 37, 95–102.
14. Smyth, L.J.; Cańadas-Garre, M.; Cappa, R.C.;
Maxwell, A.P.; McKnight, A.J. Genetic associations between genes in the reninangiotensin- aldosterone system and renal disease: A
systematic review and meta-analysis. BMJ Open ;Genes 2021, 12, 339 10 of 11
15. Choudhury, D.; Tuncel, M.; Levi, M. Diabetic nephropathy—A multifaceted
target of new therapies. Discov. Med. 2010, 10,
406–415.
16. Ahluwalia, T.S.; Ahuja, M.; Rai, T.S.; Kohli, H.S.; Bhansali, A.; Sud, K.; Khullar, M. ACE Variants
Interact with the RAS Pathway to Confer Risk and Protection against Type 2
Diabetic Nephropathy. DNA Cell Biol. 2009, 28, 141–150.
17. Makuc, J.; Šeruga, M.; Završnik, M.; Cilenšek, I.; Petroviˇc, D.
Angiotensinogen (AGT) gene missense polymorphisms (rs699 and rs4762) and
diabetic nephropathy in Caucasians with type 2 diabetes mellitus. Bosn. J. Basic Med. Sci. 2017, 17, 262–267.
18. Brewster, U.C.; Perazella, M.A. The renin-angiotensin-aldosterone system
and the kidney: Effects on kidney disease. Am. J. Med. 2004, 116, 263–272.
19. Gumprecht, J.; Zychma, M.J.; Grzeszczak, W.; Zukowska-Szczechowska, E.; the End-Stage Renal Disease
Study Group. Angiotensin I-converting enzyme gene insertion/deletion and
angiotensinogen M235T polymorphisms: Risk of chronic renal failure. Kidney Int.
2000, 58, 513–519.
20. Purkait, P.; Suthar, P.C.; Purohit, V.K.;
Naidu, J.M.; Sarkar, B.N.
Renin-Angiotensin-Aldosterone System Gene Polymorphisms in Type 2 Diabetic
Patients among the Mewari Population of Rajasthan. Int. J. Biol. Med. Res.
2013, 4, 3128–3134.
21. Dhondup, T.; Qian, Q. Electrolyte and Acid-Base Disorders in Chronic
Kidney Disease and End-Stage Kidney Failure. Blood Purif.
2017, 43, 179–188.
22. El-Nabi,
S.H.; Sayed, S.; Abd-Elhafez,
M.A.; ElFiky, M.; Moneim,
A.E.A.; El-Garawani, I. Arg753Gln Polymorphisms in
the Toll-Like Receptor 2 Gene are Associated with Cytomegalovirus Infection in
Egyptian Bone Marrow Recipients. Endocrine, Metab.
Immune Disord. Drug Targets 2020, 20, 619–624.
23. El-Garawani,
I.M.; Hassab El Nabi, S.E.
Increased Sensitivity of Apoptosis Detection Using Direct Staining Method and
Integration of Acridine Orange as an Alternative
Safer Fluorescent Dye in Agarose Gel Electrophoresis
and Micronucleus Test. Can. J. Pure Appl. Sci. 2016, 10, 3865–3871.
24. Ghonemy, T.A.; Farag, S.E.; Soliman, S.A.; El-Okely, A.; El-Hendy, Y. Epidemiology and risk factors of
chronic kidney disease in the El-Sharkia Governorate,
Egypt. Saudi J. Kidney Dis. Transplant. 2016, 27, 111.
25. El-Garawani,
I.; El-Nabi, S.H.; Gadallah,
M.; Abdelsameea, E. Association between IFN-_ 3 Gene
Polymorphisms and Outcome of Treatment with Direct Acting Antivirals in Chronic
HCV-Infected Egyptian Patients. Immunol. Investig. 2021, 50, 12–22.
26. Shaikh, R.; Shahid, S.M.; Mansoor, Q.;
Ismail, M.; Azhar, A. Genetic variants of ACE
(Insertion/Deletion) and AGT (M268T) genes in patients with diabetes and
nephropathy. J. Renin-Angiotensin-Aldosterone Syst. 2014, 15, 124–130.
27. Zhou, T.-B.; Yin, S.-S.;
Qin, Y.-H. Association of angiotensinogen M235T gene polymorphism with
end-stage renal disease risk: A meta-analysis. Mol. Biol. Rep. 2012, 40,
765–772.
28. Takakura, Y.; Yoshida, T.;
Yoshioka, K.; Umekawa, T.; Kogure,
A.; Toda, H.; Kagawa, K.; Fukui, S.; Yoshikawa, T. Angiotensinogen gene
polymorphism (Met235Thr) influences visceral obesity and insulin resistance in
obese Japanese women. Metabolism 2006,55, 819–824.