Polymorphisms of the genes ABCG2, SLC22A12 and XDH and their relation with hyperuricemia and hypercholesterolemia in Mexican young adults

Introduction

Hyperuricemia is an abnormal metabolic trait defined as serum uric acid levels above 6 and 7 mg/dL for women and men, respectively (Bardin & Richette, 2014), and is associated with other cardiometabolic risk factors such as obesity, diabetes, hypertension, and dyslipidemia (Martínez-Quintana et al., 2016; Zuo et al., 2016). Similarly, hyperuricemia can be a predictor of impaired kidney functions as well as kidney disease progression (Galán et al., 2018; Hsu et al., 2009, and Pérez-Navarro et al., 2020). Serum uric acid levels depend on many factors including diet, sex, lifestyle, and alcohol consumption, as well as genetic heredity. In fact, some genes involved in the metabolism of purines or urates have versions that appear to predispose to a hyperuricemic condition. Some of these are the ABCG2 gene that encodes a membrane transporter, which exports urates to the kidney and intestine (Woodward et al., 2009); and the SLC2A9 gene that encodes a kidney protein called GLUcose Transporter 9 (GLUT9), an important flow regulator of urates in the proximal tubules (Caulfield et al., 2008). In the same way, the XDH gene gives rise to an enzyme denominated xanthine dehydrogenase, which breaks down purines from nucleic acids, specifically the hypoxanthine‒xanthine‒urate conversion pathway (Harrison, 2002).

Recent studies have shown that genetic polymorphisms in ABCG2 and SLC2A9 genes are prevalent in the Mexican population and may contribute to an abnormal condition of hyperuricemia, even at young ages (Macías-Kauffer et al., 2019; Rivera-Paredez et al., 2019). Interestingly, there appears to be no reports to date in the literature on XDH gene polymorphisms in the Mexican population. Therefore, the aim of this study was to genotype the polymorphisms of the genes ABCG2 (Q191K), SLC22A12 (517G>A), and XDH (518T>C) in 860 young Mexican volunteers aged between 18 and 25 years of age as predisposing factors of hyperuricemia associated with risk factors of cardiovascular disease.

Methods

Results

In total, 860 participants were included in this study: 52% men and 48% women (Alegría-Torres, 2021). Participant characteristics, as well as the allelic and genotypic frequencies of the ABCG2 (Q191K), SLC22A12 (517G>A) and XDH (518T>C) gene polymorphisms, are presented in Table 1. Medians and genotypic distribution between hyperuricemic and normouricemic participants were analyzed using the Mann-Whitney U test, finding differences for sex, BMI, systolic and diastolic pressure, triglycerides, total cholesterol, and LDL-C (p = <0.001 for all), as well as a marginal distribution difference for the ABCG2 (Q191K) polymorphism corresponding to G/T alleles (p = 0.056), therefore other genetic models were tested later. All the genotypes analyzed were in Hardy‒Weinberg equilibrium: ABCG2 (Q191K) X² = 1.82X10^-6, p = 0.9; SLC22A12 (517G>A) X² = 0.03, p = 0.84; and XDH (518T>C) X² = 0.08, p = 0.76. Both allelic and genotypic distributions of the three polymorphisms studied did not differ significantly between men and women (Table 2).

Considering the statistically significant differences among the variables, a multivariate logistic regression analysis was performed, including sex, BMI, hypercholesterolemia, and hypertriglyceridemia as predictors of hyperuricemia (Figure 1). A predisposition to abnormal serum uric acid levels was found in some conditions as follows: male sex (odds ratio (OR): 2.14, 95% confidence interval (CI): 1.41-3.24, p = ˂ 0.001); overweight or obese (OR: 2.6, 95% CI: 1.71-3.88, p = ˂0.001); having hypercholesterolemia (OR: 2.8, 95% CI: 1.47-5.46, p = 0.002); or having hypertriglyceridemia (OR: 1.7, 95% CI: 1.04-2.69, p = 0.033).

Figure 1. Association of sex, body mass index and dyslipidemias as predictive factors of hiperuricemia using a multivariate logistic regression analysis.

The cutoff criteria were based on the World Health Organization and the National Cholesterol Education Program Adult (ATP III). Overweight: body mass index ≥ 25, Obesity: body mass index ˃30; hypercholesterolemia: fasting serum cholesterol levels ˃ 200 mg/dL; hypertriglyceridemia: fasting serum triglycerides levels ˃ 150 mg/dL.

In Table 3, an analysis by genotype is shown for the ABCG2 (Q191K), SLC22A12 (r517G >A), and XDH (518T>C) polymorphisms, employing a dominant model for all three. With respect to the ABCG2 (Q191K) polymorphism, statistically significant differences were found between the GT+TT genotypes vs. GG for serum uric acid (p = 0.003) total cholesterol (p = 0.005) and HDL-C levels (p = 0.003). GA+AA genotypes vs. GG of the SLC22A12 (517G>A) polymorphism only showed to influence LDL-C levels (p = 0.043). Finally, no statistically significant differences were found by genotype for the XDH (518T>C) polymorphism (p > 0.05).

When the OR and the association between genotypes for the BCG2 (Q191K) and SLC22A12 (517G>A) polymorphisms and cardiovascular risks were calculated by sex, some significant results were found utilizing a dominant model. Table 4 reports that GT+TT genotypes for the ABCG2 (Q191K) polymorphism significantly statistically increases the risk of hyperuricemia (OR = 2.43, 95% CI: 1.41-4.17, p = 0.001) and hypercholesterolemia (OR = 4.89, 95% CI: 1.54-15.48, p = 0.003), but only in male participants. On the other hand, no significant results were found for the genotypes of the SLC22A12 (517G>A) and XDH (518T>C) polymorphisms.

Discussion

A total of 860 college applicants between the ages of 18 and 25 years of both sexes were included in this study, an important age range to identify early disorders. Indeed, we found a 15% prevalence of hyperuricemia, being higher among males (19.6%) than females (10%), as previously observed in another study with comparable age groups in Mexico (Alegría-Díaz et al., 2018). Regarding uric acid levels, similar blood concentrations have also been reported in Mexican young persons (Pérez-Navarro et al., 2020). The subgroup with hyperuricemia was prone to higher levels of BMI, blood pressure, triglycerides, total cholesterol, and LDL cholesterol (Table 1). In fact, the association between serum uric acid levels and the traits of metabolic syndrome has been previously analyzed (Lin et al., 2006; Zhang et al., 2020a), although some authors found no causal evidence of uric acid levels being associated with metabolic syndrome and its components (Wang et al., 2020). According to our results, being a man, being overweight or obese, or having dyslipidemia are related to high uric acid levels (Figure 1). Men have a lower capacity to eliminate urate via the kidney compared with females due to a deficiency of estrogen and progesterone (Hak et al., 2010). Likewise, the involvement of uric acid in lipid metabolism can lead to hyperuricemia, a condition considered as predictor factor of dyslipidemia (Kuwabara et al. 2020; Lima et al., 2015; Son et al., 2016) and can subsequently alter blood pressure (Teng et al., 2011; Zhang et al., 2020a). In this way, our results summarized in Figure 1 show that being male, being obese and having dyslipidemia increases the risk of hyperuricemia (Liu et al., 2020a).

The study of the genetic influence on blood uric acid levels has included the search for single nucleotide polymorphisms (SNP) in genes involved in purine metabolism and urate removal. Here, we analyzed three polymorphisms in three different genes, including ABCG2 (Q191K), SLC22A12 (517G>A), and XDH (518T>C). The first corresponds to the exchange of a glutamine for a lysine at position 141 of an adenosine triphosphate (ATP)-binding cassette transporter subfamily G member 2 (ABCG2). This exchange predisposes individuals to hyperuricemia (Nakashima et al., 2020; Wrigley et al., 2020). A frequency of 0.25 for the risk for T allele was found, a slightly lower prevalence than that reported in Asian and New Zealand populations (Kim et al., 2015; Liu et al., 2020b; Toyoda et al., 2019). The distribution of the T allele was marginal between hyperuricemic and normouricemic groups, being more frequent in the hyperuricemic group (p = 0.056). When a dominant model was carried out, the risk for the T allele was associated with hyperuricemia and hypercholesterolemia (total and HDL cholesterol). This association was confirmed only in men, showing that the ABCG2 (Q191K) polymorphism increases the risk for hyperuricemia 2.43 times (95% CI: 1.41-4.17, p = 0.001) and hypercholesterolemia 4.89 times (95% CI: 1.54-15.48, p = 0.003) in a dominant model. Other studies have also found a greater influence of this polymorphism in men (Narang et al., 2019) although, under some conditions, the ABCG2 (Q191K) polymorphism could contribute to increased uric acid in women (Guo et al., 2020; Roman et al., 2020). Although initially our work focused on hyperuricemia in young people, the increase in serum cholesterol in men associated with the ABCG2 (Q191K) polymorphism was observed. There are still few studies linking the ABCG2 gene and cholesterolemia. A relevant fact is that mRNA expression levels of ABCG2 appear to be higher in individuals with hypercholesterolemia (Rodrigues et al., 2009); likewise, the activity of ABCG2 has been associated with cholesterol levels both in vitro and in vivo (To et al., 2014). Therefore, perform genotype-based mRNA expression analysis to further explore the role of the ABCG2 (Q191K) polymorphism in hyperuricemia and hypercholesterolemia should be contemplated.

The SLC22A12 (517G>A) polymorphism comprises the transition from guanine to adenine in the 3´-UTR region in the urate transporter 1 gene; this transition appears to modify uric acid levels (Flynn et al., 2013; Köttgen et al., 2013). In this study, the frequency of the minor allele was 0.32; however, there was no statistically different distribution of this between hyperuricemic and normouricemic groups. Although no differences in uric acid levels were associated with this polymorphism, lower LDL cholesterol levels were observed in the group of carriers of the A allele when data were analyzed in a dominant model (p = 0.043), suggesting a protective effect of this allele (Simon et al., 2014). Since the SLC22A12 (517G>A) polymorphism is located at a potential miRNA binding site (Flynn et al., 2013), the epigenetic mechanism involved in the regulation of uric acid levels needs to be studied.

With respect to the XDH (518T>C) polymorphism, we studied the xanthine dehydrogenase polymorphism located in the 3´-UnTRanslated (UTR) region of the XDH gene. The replacement of T by C is considered a risk factor related to hypertension (Wu et al., 2015). We found that the minor allele frequency was 0.37 for the C allele, contrary to what was reported in a Chinese population, where the C allele had a higher frequency, in addition to its being associated with hypertension (Wu et al., 2015). However, the link between the XDH (518T>C) polymorphism and hypertension was not demostrated in Taiwanese women (Lee et al., 2019). In the present study, we did not find a statistically significant different distribution of the C allele between the hyperuricemic and normouricemic groups, and the risk allele was also not associated with any component of the metabolic syndrome.

Finally, hyperuricemia is an undesirable condition that has been seen as a minor trait of metabolic syndrome, cardiovascular risk, as well as other types of disorders such as psoriasis and alopecia, which have been associated with high levels of blood uric acid (Guo et al., 2020; Ma et al., 2020; Talebi et al., 2020; Zhang et al., 2020a). Even though our criterion for hyperuricemia were defined as blood uric acid >6 mg/dL for women and 7 mg/dL for men, cut-off points could be reconsidered according to the considerations made by Alegría-Díaz et al. (2018). In this regard, a recent study considers uric acid levels below 5 mg/dL for men and below 2-4 mg/dL for women to be optimal for a lesser risk of cardiometabolic diseases in a Japanese population (Kuwabara et al., 2020). Although there are modifiable factors related to lifestyle, genetic inheritance plays a decisive role in the control of uricemia.

This study has three main limitations: i) only one polymorphism was genotyped for every gene, analysis of multiple SNPs by haplotypes could be more appropriate; ii) the analysis of the ABCG2 (Q191K) polymorphism is limited by the small sample size and the compromised statistical power; and, iii) new cut-off values for hyperuricemia have been suggested (Alegría-Díaz et al., 2018); however the conservative criteria of >6 mg/dL for women and 7 mg/dL for men were considered in this study.

Conclusions

In this study, we found that the ABCG2 (Q191K) polymorphism increases the risk of hyperuricemia as well as of hypercholesterolemia in young Mexican males. Since the ABCG2 (Q191K) polymorphism can modify the efficacy of statins in reducing cholesterol (Zhang et al., 2020b), carriers of the risk allele represent a vulnerable group of interest for future pharmacogenetic research. Some considerations for future studies are including lifestyle and diet factors, the monitoring of the study population, and exploring more polymorphisms in the ABCG2, SLC22A12, and XDH genes, as well as studying haplotypes.

Data availability