A genetic variant c.553G > T (rs2075291) in the apolipoprotein A5 gene is associated with altered triglycerides levels in coronary artery disease (CAD) patients with lipid lowering drug
Elevated plasma triglycerides (TGs) are widely used as a major cardiovascular risk predictor and are thought to play an important role in the progression of coronary heart disease (CHD). It has been demonstrated that lipid lowering was associated with lower mortality in patients with CHD. The present study therefore aimed to investigate the consequences of the genetic variant c.553G > T (rs2075291) in apolipoprotein A5 gene to determination of triglycerides levels in CAD patients receiving, atorvastatin, lipid lowering drug.
We here report that a recently identified genetic variant, c.553G > T in the APOA5 gene which causes a substitution of a cysteine for a glycine residue at amino acid residue 185(G185C) is also associated with increased TG levels. To investigate theses effects, a case-control study compressing 608 subjects from the same area was performed.
TG levels in T allele patients were significantly lower than the control GT allele patient (χ2 = 2.382E2a, P-value < 0.001). Overall, patients carrying T allele showed lower levels of TG than patients carrying GG allele. The homozygous patient for the T allele presented normal cholesterol levels of 134 mg/dl, and the levels in GG patients ranged from 25 to 340 mg/dl (P-value < 0.001). In summary, we demonstrated that the presence of c.553G > T variant (rs2075291); in APOA5 gene increases human plasma TG levels.
Nevertheless, T allele is found to reduce TG levels in CAD patients who are on the cholesterol medication, atorvastatin. Thus, c.553G > T variant can be considered as a significant predicator of hypertriglyceridemia. In addition, it could be used as a hallmark for the diagnosis and prognosis of CAD.
KeywordsTriglyceride APOA5 gene Polymorphism Genetic variation Atorvastatin Lipid lowering drugs Coronary artery disease Kingdom of Saudi Arabia(KSA)
The apolipoprotein A5 gene
A coronary artery disease
Single nucleotide polymorphism
Coronary artery disease (CAD) is one of the most commonly diagnosed heart diseases. Diabetes, an elevation in blood pressure and high-fat diets are considered as some of the factors that contribute to the causation of CAD . Among these factors, an elevation in triglycerides (TG) levels have shown a correlation with CAD occurrence although the exact mechanism is still obscure . Hypertriglyceridemia can develop as a result of primary factors including mainly genetics, or secondary factors such as diabetes and hyperlipidemia . Genetic abnormalities have contributed in causing hypertriglyceridemia through influencing the metabolism of triglycerides . The overproductions of apo C-III through genetic modifications and Lipoprotein lipase (LPL) have shown an association with variations in triglycerides levels .
Recently, the sequencing of human genomic DNA has led to the discovery of Apolipoprotein A5 (APOA5) gene which belongs to a regulatory gene family including APOA1, APOC3 and APOA4 .This gene is located on chromosome 11q23 in about 30 kb downstream of APOA4, and contains four exons. Several studies have indicated that the newly identified apolipoprotein locus plays a major role in triglycerides hemostasis . It encodes for apoA-V protein which reduces triglycerides plasma levels . Therefore, genetic alterations in APOA5 could result in changes in TG levels. Point mutations in APOA5 yield incomplete assembly of apoA-V protein, and were observed mostly in patients with hypertriglyceridemia. Nevertheless, no specific mutations were known to cause severe illnesses, but certain studies have predicted the association of single nucleotide polymorphisms (SNPs) in APOA5 with medical conditions. The variants -1131 T > C and c.56C > G (S19 W) for APOA5s are examples of SNPs that have correlations with high triglycerides plasma levels .Accordingly, A novel variant c.553G > T was lately identified through the sequencing of APOA5 coding region. This SNP causes a substitution of the amino acid cysteine with a glycine molecule . The effect of which has been researched and the conclusion is still to be reached. Upon the effort to study c.553G > T variant, a very recent research revealed that introducing a free cysteine in APOA-V protein allows the binding of it with other proteins through the formation of disulfide bonds which affects TG modulation . Furthermore, c.553G > T variant (rs2075291); was detected in a higher rate in patients with acute coronary syndrome when compared to the control group . Atorvastatin is a commonly known drug that is used to regulate lipid metabolism . Based on Biopharmaceutics Classification System, atorvastatin is considered as a class II drug , and is a member of statins family also known as 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors . Therefore, atorvastatin is found to reduce cholesterol levels in CAD patients. In a study that was conducted to analyze the effects of atorvastatin on various lipoproteins, atorvastatin showed no effects on TG levels in Chylomicron, LDL, IDL and VLDL while it reduced cholesterol levels in these lipoproteins . Here, we examine the effects of the genetic variant c.553G > T (rs2075291); on TG levels in CAD patients receiving atorvastatin daily as a lipid lowering medicine.
This study was approved by the Institutional Review Board and the Research ethics committees (REC) in Umm al-Qura University medical school at Makkah, Kingdom of Saudi Arabia. Blood was obtained from the subjects after obtaining informed written consent from the patients or their representatives. Patients with CAD confirmed by coronary angiography (> 50% stenosis in one or more arteries and stable or unstable angina pectoris) were enrolled in the study. Healthy controls from the same area were also included. Most of these patients were on appropriate and recommended doses of statin therapy as per guidelines for the management of coronary artery disease. The duration of therapy was not captured in current study.
All controls were examined clinically and investigated by electrocardiography to exclude clinically apparent CAD or other cardiovascular disease.
An amount of 5 ml blood samples were obtained from the subjects in the morning after an overnight fast. Serum lipid parameters, including triglyceride (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C), apolipoprotein were measured by Dimension® Clinical Chemistry System using Flex reagents.
Baseline characteristics of CAD and control groups
58.52 ± 11.10
37.3 ± 14.7
Gender (Male/ Female)
1.31 ± 0.51
1.78 ± 0.41
Glucose (mmol/ l)
1.39 ± 0.53
1.82 ± 0.38
HDL-C (mmol/ l)
1.37 ± 0.56
1.46 ± 0.63
LDL-C (mmol/ l)
1.65 ± 0.96
1.55 ± 0.80
Chol-C (mmol/ l)
1.17 ± 0.46
1.10 ± 0.36
TG-C (mmol/ l)
1.51 ± 0.82
1.16 ± 0.46
No statistical significant difference in gender between the two groups. However, the results showed a perceptible difference regarding to patients’ age even though the control group was somewhat younger than CAD patients. Other parameters including blood pressure and glucose levels were found to be higher in the control group than CAD patients. Lipid parameters such as LDL and HDL levels did not show any significant differences between the two groups. Nevertheless, cholesterol and triglycerides levels were higher in CAD patients than control group even though some of them are on atorvastatin.
Relationship between T allele and triglycerides levels
TG levels in CAD patients separated by APOA5 genotype. The wildtype represents GG allele while GT and TT alleles indicate the presence of c.553G > T
Association of T allele with other lipid parameters
Association of T allele with other factors
Our study validate the important role for CAD as the most frequent cause of mortality across the world according to data obtained from the World Health Organization (WHO) . Causes of such unfortunate disease may be due to the complex interplay between genetic risk factors and environmental exposures that occur at critical times in development. Several epidemiological studies have shown that apolipoprotein A1/C3/A4/A5 gene cluster is found to be one of the factors that could cause premature CAD . Among the gene cluster, APOA5 gene appears to affect TG levels . Recently, several SNPs found in APOA5 cause an elevation in TG levels. A study has indicated that one of APOA5 SNPs, − 1131 T > C (rs2075291) variant, affects TG and HDL levels; therefore, increases the risk of developing cardiovascular diseases and diabetes . Another study has shown that upon the transduction of AAV2/8-LacZ, AAV2/8-WT apoA-V and AAV2/8-G162C apoA-V, TG levels were lower in the WT mice when compared to both mutants . In this study, we have described the relevance between the variant G162C (corresponding to c.553G > T) and TG levels in CAD patients who are on atorvastatin daily.
The incidence of diabetes in general population in Saudi Arabia is very high with up to 40% in some reports. It is possibly that the control group has many undiagnosed, untreated or borderline patients. On the other hand the CAD group most likely would be well treated patients and that is why there glucose levels are better.
Potential limitation of this study should be addressed. As the number of patients in each cohort is small to make conclusive results. Furthermore, there are differences between the control group and CAD group that may affect the results. Larger number of patients with TT allele is required to study in detail the effect of statin therapy on TG levels. Additionally, the duration and response to treatment was not studied in this report.
The frequency of c.553G > T allele in CAD patients was higher than normal subjects. Normally, the presence of T allele raises TG levels; yet, in patients carrying this allele and are on atorvastatin, it seems to lower TG levels. However, in a previous study, Ikejiri et al., stated that atorvastatin has no reduction effects on TG rich lipoproteins . That conclusion is true regarding to the findings of TG levels in GG allele patients which showed no direct effects of atorvastatin on TG levels. In addition, there were no substantial differences in LDL between patients carrying T allele or the wildtype allele. Recent studies have revealed that APOA5 could affect cholesterol homeostasis and could cause hypertriglyceridemia . Recent studies have revealed that APOA5 could affect cholesterol homeostasis and could cause hypertriglyceridemia  it is possible that statin therapy in these patients have more effect on TG metabolism given its effect on cholesterol hemostasis. Further mechanistic studies needs to be done on these patients. Another study that included Chinese subjects has shown that in CAD patients and control groups, the wild type GG carriers have considerably lower TG levels in comparison to the T allele carriers . Regarding to HDL levels in the study subjects, T allele patients who were on atorvastatin have lower HDL levels than the other T allele patient who was not taking atorvastatin, but all results were in the normal range. This has been proven earlier by another Chinese study that showed no significant associations between the presence of T allele and lipid parameters including LDL, TC, and HDL . As expected, cholesterol levels in T allele patients on atorvastatin were normal and lower than the T allele patient who was not on atorvastatin. This result is due to the fact that the pharmacological effect of atorvastatin is to lower cholesterol levels in the plasma. Previous studies have confirmed that atorvastatin reduces both LDL and total cholesterol, and it decreases cholesterol levels in females more than males . The clinical implications for TG and CAD is less well studied compared to LDL levels. There is some associations but not as important as LDL and cholesterol levels on CAD. Medications that lower TG such as fenofibrates failed to improve outcomes compared to statin therapy in patient with CAD. Thus fenofibrates is indicated only in patients with very high TG levels despite diet control.
Finally, both T allele and the wildtype allele patients who were taking atorvastatin along with aspirin showed the lowest TG levels when compared to patients who were not on aspirin and/ or atorvastatin. These findings suggest that aspirin has an effect on TG levels when is taking with cholesterol medications; yet, further studies are needed to determine if there is an effect depending on the presence or absence of T allele. A study that was done on mice has revealed that aspirin decreases the secretion of VLDL- TG from the liver which in turn reduces HFD- induced hypertriglyceridemia supporting our findings in this study .
In summary, we demonstrated that the presence of c.553G > T (rs2075291) variant in APOA5 gene increases human plasma TG levels. Nevertheless, T allele is found to reduce TG levels in CAD patients who are on the cholesterol medication, atorvastatin. Thus, c.553G > T variant can be considered as a significant predicator of hypertriglyceridemia. In addition, it could be used as a hallmark for the diagnosis and prognosis of CAD.
We are thankful to Faculty of Medicine, Umm AlQura University (UQU) for their support and deanship scientific research and Institute of Scientific research. We all are deeply appreciated for King Abdullah Medical City.
This project was funded by Umm Al-Qura University UQU, the Kingdom of Saudi Arabia.
Availability of data and materials
□ The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
□ All data generated or analysed during this study are included in this published article.
□ Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.
□ The data that support the findings of this study are available from King Abdullah Medical City but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available.
NB; AA and AF made substantial contributions to acquisition of data and interpretation of data; 2) have been involved in drafting the manuscript or revising it critically for important intellectual content; 3) have given final approval to the version to be published; and 4) agree to be accountable for all aspects of the work. HR and MT carried out the immunoassays. FAA and ID participated in the design of the study and performed the statistical analysis with laboratory work. DR; ME; MP; SK; FA and AF made substantial contributions to the conception and design of the study, and coordination and helped to draft the manuscript. All authors have read and approved the final manuscript.
NCBI 1000 Genomes Browser; rs2075291; NM_052968.4(APOA5):c.553G > T (p.Gly185Cys): Genetic variant, c.553G > T in the APOA5 gene which causes a substitution of acysteine for a glycine residue at amino acid residue 185 (G185C).
Ethics approval and consent to participate
This study was approved by the Institutional Review Board and the Research ethics committees (REC) in Umm al-Qura University medical school at Makkah, Kingdom of Saudi Arabia. Blood was obtained from the subjects after obtaining after obtaining informed written consent from the patients or their representatives.
Consent for publication
Our institutional consent forms were used for all persons shared in this study as consent for publication.
The authors declare that they have no competing interests.
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