Non-communicable diseases (NCDs) have become a global threat affecting most countries, including Malaysia, an upper-middle-income country. The common NCDs include cardiovascular diseases (CVDs), cancers, respiratory diseases, and diabetes mellitus. The four key metabolic risk factors which increase the risk of NCDs include overweight/obesity, raised blood pressure, hyperglycemia and hyperlipidemia/hypercholesterolemia. The World Health Organization (WHO) has also identified four key modifiable behavioural risk factors of NCDs which are tobacco use, physical activity, diet, and alcohol use [1
In Malaysia, the current prevalence of total deaths due to NCDs is estimated to be 73% with CVDs being the biggest contributor [2
]. The National Health and Morbidity Surveys (NHMS) in Malaysia which provides the most comprehensive health data of adults for 1996, 2006, 2011, and 2015 also showed an increasing trend in all the NCD risk factors. According to the two most recent NHMS in 2011 and 2015, the NCD risk factors which had an increase in the prevalence over the span of four years include diabetes mellitus (from 15.2% to 17.5%), hypercholesterolemia (from 35.1% to 47.7%), and overweight/obesity (from 44.5% to 48%) [2
]. As for hypertension, there was a slight decrease of 2.4% in the prevalence from 2011 to 2015 [2
The etiology of NCDs is multi-factorial which includes both non-modifiable and modifiable risk factors. Hence, the approach of gene-environment (G × E) or gene-diet interaction which incorporates all possible risk factors could be most appropriate in providing useful information for the prevention and treatment measures of NCDs/CVD. In this study, the approaches of candidate genes and dietary patterns were used to determine the gene-diet interaction effect on metabolic risk factors of CVD. In dietary intake association studies involving chronic diseases, such as CVD, two approaches—single nutrient analysis, and dietary pattern approach (a combination of foods)—are often used. However, the dietary pattern approach is preferred, especially in nutritional epidemiologic studies [4
]. Similar studies have also used the dietary pattern approach in gene-diet interaction studies [5
]. In addition, significant gene-diet interactions were also observed in our previous study [7
The major NCD is CVD; therefore, it is most appropriate to select candidate genes and related polymorphisms in the cardiovascular system. The renin-angiotensin system (RAS) has been known to be related to heart health and angiotensin II type 1 (AGTR1
) and type 2 receptor (AGTR2
) in the RAS possess unique counterregulatory function in blood pressure regulation, which is crucial for the prevention of hypertension and CVD. [8
]. With that, the angiotensin II type 1 receptor (AGTR1
) gene and the angiotensin II type 2 receptor (AGTR2
) gene were selected as the candidate genes in this study.
One criterion in the selection of single nucleotide polymorphisms (SNPs) in this study is the minor allele frequency (MAF) of more than 0.20 in the Asian population. However, due to the lack of information on the MAF of the SNPs in both AGTR1
genes in any of the three main ethnic groups (Malay, Chinese, and Indian) of the Malaysian population, the criterion of MAF used was in reference to other Asian populations, such as Han Chinese and Indian population. Hence, the selected SNPs were rs5186 of AGTR1
gene which had MAF >0.20 in both Northern [9
] and Southern Indians [10
], and rs1403543 of AGTR2
gene in the Han Chinese population [12
]. The location of the selected SNPs is as follows: rs5186 of AGTR1
gene in the 3′ untranslated region of AGTR1
on the chromosome 3 which leads to an adenine (A) to cytosine (C) transversion [13
]; and rs1403543 of AGTR2
gene in the intron 1 of the AGTR2
on the X chromosome [15
]. Several studies have also shown significant associations of AGTR1
gene rs5186 SNP on several types of NCDs such as hypertension [9
] and type II diabetes mellitus [10
], including a systematic meta-analysis with coronary heart disease [17
]. As for AGTR2
gene rs1403543 SNP, significant associations were also reported for hypertension [18
], and preeclampsia [19
Due to the growing epidemic of NCDs/CVD in Malaysia, there is definitely a need for research in this area. Based on our literature search, the investigation of genetic associations involving AGTR1 gene (rs5186) and AGTR2 gene (rs1403543) polymorphisms has not been reported in the Malaysian population. Hence, the aim of this study is to examine the association of AGTR1 gene (rs5186) and AGTR2 gene (rs1403543) SNPs on the metabolic risk factors of CVD, in addition to gene-diet interaction effects with dietary patterns in multi-ethnic Malaysian adults. The findings of this study may provide insights on the possible risks of CVD which could be associated by the selected candidate genes and related SNPs in addition to the effect of gene-diet interactions.
The increasing prevalence of NCDs in Malaysia and the associated metabolic risk factors has become a health threat to the population. In addition, the effect of the high healthcare costs associated with these chronic diseases has also created an economic burden to the population. In Malaysia, studies on gene-diet and gene-environment interaction involving NCDs are scarce [26
]. Hence, the present study evaluated the genetic associations and gene-diet interactions involving AGTR1
gene polymorphisms in Malaysian adults. Interestingly, we found significant genetic associations and gene-diet interactions of both AGTR1
gene polymorphisms on two key metabolic risk factors of CVD, which are blood pressure and blood lipids.
In the present study on the genetic associations involving AGTR1
gene (rs5186) SNP, we found that the C allele may be the risk allele for the blood lipid, triglycerides as the mean blood triglycerides for the AC + CC genotype in Malays and AC genotype in Chinese were significantly higher compared to AA genotype subjects. In comparison with other literatures, a similar finding was also obtained in a study among Han Chinese subjects, in which significant association was found in AC + CC genotypes of rs5186 with essential hypertension, and the CC genotype subjects had a higher risk of developing essential hypertension compared to subjects of other genotypes [9
]. In addition, the C allele and the AC/CC genotypes were also found to be significantly associated with type II diabetes mellitus and its comorbidity in Asian Indians [10
] and with coronary heart disease in East Asia populations [17
]. In our study however, we failed to obtain any significant genetic associations on all metabolic risk factors of CVD in Indian subjects. Similarly for the rs5186 of the AGTR1
gene, significant associations were obtained for the rs1403543 SNP in the AGTR2
gene with blood lipids in our Chinese Malaysian subjects. In the present study, the A allele could be the risk allele for blood lipids but other studies have shown that the G allele was more susceptible to hypertension [18
] and preeclampsia [19
]. In our investigation on Malay and Indian subjects, we did not obtain any significant genetic associations involving rs1403543 on all metabolic risk factors of CVD.
The significant genetic associations on blood lipids in this study have indicated a possible relationship between the AGTR1
gene polymorphisms with other metabolic risk factors CVD besides blood pressure. This could be explained by the other roles of AGTR1 and AGTR2 which may have an effect on the development of NCDs/CVD. For example, besides the counterregulatory interaction in the regulation of blood pressure whereby AGTR1 plays the role as the vasoconstrictor and AGTR2 as the vasodilator, AGTR1 is also involved in cellular proliferation and growth, while AGTR2 is involved in cell growth and inhibition [27
In our study, significant gene-diet interactions were obtained on blood pressure and selected blood lipids even though the individual genetic associations for these metabolic risk factors of CVD were not obtained. Based on our literature search, we did not find any similar literatures on gene-diet interactions involving AGTR1
gene (rs5186) and AGTR2
gene (rs1403543) SNPs. However, there was a study which determined the gene-diet interactions involving the AGTR1
gene (rs5186) SNP with sodium, potassium, and fluid intakes on renal cell cancer risk [28
]. However, this study did not obtain any significant gene-diet interactions, which could also be due to the lack of statistical power [28
]. Hence, we speculate that a certain dietary pattern may have an influence on the polymorphism effects of both AGTR1
gene (rs5186) SNP and AGTR2
gene (rs1403543) SNP. However, the actual mechanism involving the gene-diet interaction remains unclear, thus warrant further investigation.
There are some limitations in this study which should be noted and were also indicated in the results of our study. The number of male subjects was much lower compared to the female subjects, especially for Malay and Indian subjects, therefore, the analysis on the male subjects could not be performed for AGTR2 gene (rs1403543) SNP. The sample size may not be sufficient for statistical power because a small MAF was obtained for rs5186 (<0.10) in our subjects. Lastly, our findings were limited as some statistical tests, such as the parametric tests (Student’s t-test and one-way ANOVA), and results from two-way ANOVA could not be used due the required pre-requisites (data in normal distribution) or assumptions (equal variance) for specific statistical tests which were not met.
In summary, significant individual genetic associations and gene-diet interaction effects between the AGTR1 gene (rs5186) SNP and the AGTR2 gene (rs1403543) SNP and dietary patterns on blood lipids were obtained particularly in Malay and Chinese Malaysian subjects of our study. The AC + CC genotype in Malay subjects and AC genotype in Chinese subjects of the AGTR1 gene (rs5186) SNP had higher risks of blood triglycerides compared to the AA genotype subjects. As for the AGTR2 gene (rs1403543) SNP, the AA genotype and AG genotype in female Chinese subjects had the highest risk for LDL-C and total cholesterol/HDL-C ratio, respectively. In Malays, the combination of AC + CC genotype of rs5186 and the highest tertile of VFSD had the highest risk of blood pressure while, in Chinese, the combination of the AC genotype of rs5186 and the highest tertile of REFD had the highest risk for blood lipids (total cholesterol and LDL-C). Finally, the combination of the AA genotype of rs1403543 and tertile 2 of VFSD had a higher risk of total cholesterol, but a lower risk in HDL-C compared to the other combinations in Chinese female subjects. The Chinese female subjects who had the highest risk for HDL-C was from the combination of AG + GG genotype and tertile 2 of VFSD.