Introduction
The etiology of intracranial aneurysms (IA) is primarily attributed to the inability of the vascular wall to withstand elevated intraluminal pressure, resulting in dilation of the vessel wall and disruption of the medial layer. In severe cases, this can lead to a ruptured IA (RIA) and subsequent intracranial hemorrhage [1-7]. The mechanisms underlying the development and rupture of IA are complex and multifactorial, involving a combination of genetic predispositions and acquired factors. Currently, no single tool can independently guide clinical decision-making in the management of unruptured IA (UIA). Therefore, identifying easily recognizable clinical indicators that influence IA stability, coupled with a comprehensive assessment of IA stability using existing indicators, would provide substantial clinical benefits.
Recent research has underscored the critical role of inflammation in blood vessels of the brain in the development, progression, and rupture of IA. The inflammatory process is initiated by hemodynamic injury, with wall shear stress-induced endothelial cell damage being a crucial step in IA pathogenesis [8]. Altered blood flow induces inflammation in specific vascular endothelial cells, leading to the activation of the nuclear factor kappa B (NF-κB) transcription factor. This activation is fundamental to the inflammatory process, initiating a series of downstream inflammatory responses [9,10].
Aldehyde dehydrogenase 2 (ALDH2), a member of the ALDH superfamily of phase I oxidizing enzymes, is essential for the metabolism of ethanol and detoxification of harmful aldehydes [11-13]. The ALDH2 gene contains at least five single-nucleotide polymorphisms (SNP) with the Glu504Lys polymorphic locus (rs671) in exon 12 being notable. This SNP is significantly more prevalent among East Asians (30%-50%) than among individuals of European descent (<5%) [14]. Genetic variations in the ALDH2 gene result in two distinct alleles, *504Glu (*1) and *504Lys (*2), leading to three genotypes: ALDH2*1/*1, ALDH2*1/*2, and ALDH2*2/*2. This specific gene mutation exhibits incomplete dominance, resulting in a significant reduction in the effectiveness of the ALDH2 tetramer protein. Individuals with the ALDH2*1/*2 genotype display a substantial reduction in enzyme activity, whereas those with the ALDH2*2/*2 genotype exhibit minimal enzyme activity [15,16]. Consequently, deficiency of this enzyme is one of the most prevalent conditions inherited in humans, with approximately 560 million people of East Asian descent carrying the ALDH2*2 gene variant [17]. Furthermore, these alleles are associated with hypertension, atherosclerosis, and dyslipidemia [18-20]. Recent clinical and experimental studies have indicated that the ALDH2 rs671 polymorphism offers protection against age-related cardiac insufficiency and aortic aneurysm and dissection (AAD) [21,22].
The development, enlargement, and rupture of IA are influenced by conditions, such as atherosclerosis, inflammation, and degeneration of the vascular wall [23,24]. These complex relationships are similar to the mechanisms by which ALDH2 influences other vascular diseases. Although the nature of the relationship between the ALDH2 rs671 SNP and RIA remains unclear, associations between ALDH2 rs671 SNP and AAD have been documented. Consequently, we postulate that the ALDH2 rs671 SNP may be a previously unrecognized but significant factor contributing to IA rupture.
Methods
Participants and participant consents
This study included 546 individuals with both UIA and RIA, recruited from Beijing Tiantan Hospital and Beijing Chaoyang Hospital. Ethics approval was obtained from the institutional ethics boards of the hospitals, and patients provided written informed consent before enrollment.
Demographic and clinical characteristics
A structured checklist was used to systematically record demographic data and risk factors such as age, body mass index, hypertension, diabetes, hyperlipidemia, coronary artery disease, alcohol consumption, and history of stroke. Hyperuricemia was defined as a fasting blood uric acid level exceeding 420 μmol/L in males and 360 μmol/L in females. Hyperhomocysteinemia was defined as a fasting blood homocysteine level exceeding 15 μmol/L. Alcohol consumption patterns were assessed based on the frequency (days per week) and average daily intake, following methods described in previous studies [25,26]. Participants and their families completed surveys detailing their consumption of red and white wine, and beer since initiating alcohol consumption. Frequent alcohol consumption was defined as the consumption of alcohol more than once per week on average. Standardized measurements for alcoholic beverages were established, with regular beer, red wine, and white wine defined as 355, 118, and 40 mL, respectively, each containing approximately 14 g of alcohol. The mean daily alcohol intake was calculated considering both the frequency of consumption and volume consumed per occasion. Following the classification approach by Chung et al. [27], alcohol intake was categorized into three groups: non-drinkers (individuals who abstained from alcohol either within the past year or over their lifetime); light drinkers (individuals consuming less than 210 g per week); and heavy drinkers (individuals consuming 210 g or more per week).
IA characteristics
IAs were diagnosed using digital subtraction angiography (DSA), an advanced imaging technique that provides a detailed examination of both the anterior and posterior intracranial vessels. Morphological evaluations of all IAs were conducted by three experienced neurointerventionalists using three-dimensional (3D) reconstructed images from DSA 3D rotational angiography. The aneurysm locations were categorized into anterior and posterior circulations. Aneurysms originating at the arterial bifurcation (including the internal carotid, middle cerebral, anterior cerebral, and basilar artery bifurcations) were classified as bifurcation aneurysms. The largest IA diameter was measured from the center of the aneurysm neck to the highest point. Furthermore, the size ratio was calculated as the maximum IA diameter divided by the mean diameter of the parent artery, encompassing the proximal vessel diameter (D1) and distal vessel diameter (D2), measured 1.5 times D1 distally from the aneurysm. The aspect ratio was defined as the ratio of the vertical dimension of the IA to the width of its neck [28,29].
Blood sample, DNA collection, and genotyping
Two milliliters of peripheral blood were collected from fasting study participants via the elbow vein on the morning of the second hospital day following admission. Leukocytes were isolated for DNA extraction, and ALDH2 allelotypes were identified using multiplex polymerase chain reaction (PCR)-amplified product length polymorphism analysis to balance cost-effectiveness, sensitivity, specificity, and the ability to genotype multiple variants simultaneously. The genotyping methods followed the protocol described by Lai et al. [30]. The sequencing data were copied from the sequencer. Sequencing peak plots were carefully reviewed to ensure that they met strict quality criteria: (1) Only sequencing results that corresponded to the target fragment were considered. Nonspecific amplifications that could compromise data accuracy were excluded. (2) The sequencing data were assessed for clean bottom peaks and the absence of stray peaks that could affect base calling accuracy. To identify heterozygous mutations, we established a threshold at which the height of the heterozygous peak was required to be at least 30% of the highest peak in the sequencing plot. Peak plots were analyzed using Sequencing Analysis (version 5.2; Applied Biosystems, Waltham, MA, USA), where mutations were interpreted as degenerate bases, allowing for accurate identification of both homozygous and heterozygous alleles. Laboratory technicians performed genotyping without knowledge of the case-control status of the samples. To ensure accuracy and reliability, genotyping was repeated for 10% of the samples to achieve a 100% agreement rate in duplicate analyses.
Statistical analysis
Sample size and power calculations were performed using PASS software version 15 (NCSS LLC, Kaysville, UT, USA). Continuous variables between the two groups were compared using either the Mann-Whitney U test or Student’s t-test, depending on the data distribution. Normally distributed data were presented as mean±standard deviation, while non-normally distributed data were described using the median with interquartile range. Categorical variables were analyzed for group differences using either Fisher’s exact test or Pearson’s χ2 test, with results reported as frequencies and percentages. The χ2 test was used to assess the Hardy-Weinberg equilibrium of ALDH2 genotypes. Univariate and multivariate logistic regression analyses were conducted to evaluate the association between RIA and potential confounding variables by estimating odds ratios (OR) and 95% confidence intervals (CI). Regression analysis was used to examine the interactions between the ALDH2 genotypes and alcohol consumption in relation to the risk of RIA. The relationships between variant ALDH2 genotypes and clinical characteristics were assessed using χ2 tests. Data analysis was performed using SPSS software version 26 (IBM Corp., Armonk, NY, USA). Statistical significance was defined as a P-value of less than 0.05.
Results
Baseline characterization and genotype
This study included 546 patients diagnosed with IA. Figure 1 illustrates the screening process used to select participants for the study. The distribution of ALDH2 genotypes within the UIA and RIA groups is presented in Table 1 and Supplementary Table 1. Among the participants, 384 (70%) had the wild-type ALDH2 genotype (GG, ALDH2*1/*1). Heterozygous mutations (GA, ALDH2*2/*1) were identified in 151 patients (28%), and homozygous mutations (AA, ALDH2*2/*2) were identified in 11 patients (2%). Significant differences in the distribution of the GG, GA, and AA genotypes were observed between the UIA and RIA groups (P=0.014). According to the calculations, the power to detect a significant effect in the AA group was only 0.135, which was insufficient to draw valid conclusions. By combining GA and AA genotypes into a single group, the power increased to 0.947 (Supplementary Table 2). Additionally, at least 155 participants with the AA genotype were required to achieve a power of 0.9; however, only 11 participants with the AA genotype were available in our study (Supplementary Table 3). Due to the low number (2%) of homozygous mutations (AA, ALDH2*2/*2), which made it statistically challenging to analyze them separately, the participants were categorized into two groups: the ALDH2 wild-type group (ALDH2*1/*1) and the ALDH2 mutation group (ALDH2*2/*1 and ALDH2*2/*2, collectively referred to as the ALDH2 polymorphism). A significant difference in the distribution of GG versus GA+AA alleles was observed between the UIA and RIA groups (P=0.004). The frequency of the A allele was 150 (17%) in the UIA group and 23 (10%) in the RIA group, while the frequency of the G allele was 716 (83%) in the UIA group and 203 (90%) in the RIA group. The A allele frequency was significantly lower in the RIA group than that in the UIA group, whereas the G allele frequency was higher in the RIA group than that in the UIA group (P=0.008). Moreover, the Hardy-Weinberg equilibrium test (χ2=1.42, P=0.49) indicated that the observed allele frequencies were consistent with genetic equilibrium principles.
Analyzing the clinical baseline data, 384 individuals (70.33%) were identified as ALDH2 wild-type, while 162 individuals (29.67%) were identified as having the ALDH2 mutant gene based on SNP (Table 2). Individuals with the ALDH2 wild-type gene demonstrated a significantly higher incidence of hypertension (P=0.041), heavy alcohol consumption (P<0.001), and regular alcohol consumption (P<0.001) than those with the ALDH2 mutant gene. Additionally, blood high-density lipoprotein cholesterol (HDL-C) concentration was lower in patients with the ALDH2 wild-type gene (P=0.008), whereas the blood triglyceride concentration was higher (P=0.002) compared to those with the ALDH2 mutant gene. No significant differences were observed in blood total cholesterol (P=0.574) and low-density lipoprotein cholesterol (LDL-C) concentrations (P=0.730) between the two groups. Individuals with the ALDH2 wild-type gene had a significantly higher rupture rate than those with the ALDH2 mutant gene (P=0.004) and a higher prevalence of IA located at bifurcations (P=0.038). No other significant differences in clinical features were observed between the two groups.
Baseline characteristics of UIA and RIA groups
The UIA group comprised 433 patients (79.30%), whereas the RIA group comprised 113 patients (20.70%) (Table 3). In the UIA group, 141 patients (32.56%) carried ALDH2 gene mutations, whereas 21 patients (18.58%) in the RIA group had these mutations. The frequency of ALDH2 gene mutations was significantly higher in the UIA group compared to the RIA group (P=0.004). The average age of the 546 participants was 56.09±10.81 years, with 353 individuals (64.65%) being female. Several clinical characteristics were significantly correlated with RIA, including an increased prevalence of hyperhomocysteinemia (P=0.009), hypertension (P=0.002), smoking (P<0.001), heavy alcohol consumption (P=0.006), and regular alcohol consumption (P=0.009). Moreover, participants in the RIA group exhibited higher blood LDL-C levels (P=0.043), IA aspect ratios (P=0.027), and IA size ratios (P<0.001) than those in the UIA group did. Irregularly shaped aneurysms were more common in the RIA group (P<0.001), as were aneurysms located in the posterior circulation (P=0.005) and at the bifurcation points (P<0.001). Conversely, the UIA group had a higher proportion of female patients (P=0.008) and higher blood HDL-C levels than the RIA group (P=0.004).
Logistic regression analysis
Univariate logistic regression analysis results (Table 4) identified several factors significantly associated with RIA. These factors include hypertension (OR: 2.02; 95% CI: 1.29-3.17; P=0.002), smoking (OR: 2.44; 95% CI: 1.54-3.86; P<0.001), regular alcohol consumption (OR: 2.05; 95% CI: 1.19-3.54; P=0.010), heavy alcohol consumption (OR: 2.12; 95% CI: 1.23-3.63; P=0.007), high homocysteine levels (OR: 2.05; 95% CI: 1.19-3.54; P=0.010), elevated triglycerides (OR: 1.24; 95% CI: 1.02-1.50; P=0.030), high total cholesterol levels (OR: 1.24; 95% CI: 1.02-1.51; P=0.032), increased LDL-C concentrations (OR: 1.31; 95% CI: 1.05-1.63; P=0.015), irregularly shaped aneurysms (OR: 3.80; 95% CI: 2.42-5.98; P<0.001), aneurysms in the posterior circulation (OR: 2.48; 95% CI: 1.29-4.78; P=0.007), aneurysms at bifurcation (OR: 6.34; 95% CI: 3.66-10.98; P<0.001), and higher size ratios (OR: 1.24; 95% CI: 1.09-1.41; P=0.001). There were notable inverse associations between RIA and HDL-C levels (OR: 0.36; 95% CI: 0.18-0.71; P=0.003), being female (OR: 0.57; 95% CI: 0.37-0.86; P=0.008), and carrying an ALDH2 mutation (OR: 0.47; 95% CI: 0.28-0.79; P=0.004).
Multivariate logistic regression analysis of significant variables from the univariate analysis (Table 4) identified hypertension (OR: 1.72; 95% CI: 1.07-2.77; P=0.026), elevated blood LDL-C levels (OR: 1.57; 95% CI: 1.21-2.02; P=0.001), irregularly shaped aneurysms (OR: 3.33; 95% CI: 2.03-5.47; P<0.001), aneurysms at bifurcation points (OR: 5.15; 95% CI: 2.76-9.63; P<0.001), and aneurysms in the posterior circulation (OR: 2.23; 95% CI: 1.06-4.70; P=0.035) as independent risk factors for RIA. The presence of an ALDH2 mutation was an independent protective factor against RIA (OR: 0.49; 95% CI: 0.27-0.88; P=0.018).
Stratification analysis
The association between ALDH2 mutations and RIA was assessed using sex, age, hypertension status, and alcohol consumption as stratification variables. Men with the ALDH2 mutant gene exhibited a 55% lower risk of RIA compared to those with the ALDH2 wild-type gene (95% CI: 0.20-0.99; P=0.045) (Table 5). Similarly, women carrying the ALDH2 mutant gene exhibited a 50% lower risk of RIA compared to those with the ALDH2 wild-type gene (95% CI: 0.25-0.98; P=0.048).
When stratified by age, using 60 years as the cutoff, the analysis showed that individuals younger than 60 years with the ALDH2 mutant gene had a significantly lower risk of RIA (0.52 times lower; 95% CI: 0.28-0.98; P=0.042) compared to those with ALDH2 wild-type gene. Similarly, individuals aged 60 years or older with ALDH2 mutant gene had significantly lower risk of RIA (0.38 times lower; 95% CI: 0.15-0.95; P=0.039) compared to those with ALDH2 wild-type gene (Table 5).
Stratification by hypertension status indicated that individuals without hypertension who carried the ALDH2 mutant gene had a significantly lower risk of RIA compared to those with the ALDH2 wild-type gene (OR: 0.38, 95% CI: 0.15-0.96, P=0.040). Conversely, among individuals with hypertension, those with the ALDH2 mutant gene had a reduced risk of RIA, although this difference did not reach statistical significance (OR: 0.57, 95% CI: 0.30-1.07, P=0.080) (Table 5).
The effect of ALDH2 mutations on RIA was also examined by stratifying patients based on alcohol consumption, with a threshold of 210 g/week, to differentiate heavy drinkers from light or non-drinkers. Among non-drinkers and light drinkers, individuals with the ALDH2 mutant gene had a 45% lower risk of RIA compared to those with the ALDH2 wild-type gene (95% CI: 0.32-0.92; P=0.024). However, no significant association was observed between the ALDH2 gene mutation and RIA in heavy drinkers (Table 5).
The effect of the ALDH2 mutation on RIA was examined by stratifying the patients based on their IA location. For anterior circulation aneurysms, individuals with the ALDH2 mutant genotype had a 52% lower risk of RIA compared to those with the wild-type genotype (OR: 0.48, 95% CI: 0.28-0.83, P=0.009). However, in posterior circulation aneurysms, no significant association was observed between the ALDH2 mutation and RIA (OR: 0.39, 95% CI: 0.09-1.72, P=0.215) (Table 5).
Subgroup analysis for IA morphology showed that patients with regularly shaped aneurysms carrying the ALDH2 mutant genotype exhibited a 69% lower risk of RIA compared to those with the wild-type genotype (OR: 0.31, 95% CI: 0.11-0.91, P=0.034). Similarly, for irregularly shaped aneurysms, individuals with the ALDH2 mutant genotype had a 49% lower risk of RIA compared to those with the wild-type genotype (OR: 0.51, 95% CI: 0.28-0.95, P=0.035) (Table 5).
Stratification by IA size indicated that in aneurysms with a maximum diameter of <7 mm, individuals with the ALDH2 mutant genotype had a significantly lower risk of RIA compared to those with the wild-type genotype (OR: 0.47, 95% CI: 0.25-0.86, P=0.014). Among aneurysms with a diameter of ≥7 mm, the ALDH2 mutant genotype also appeared to reduce the risk of RIA, but this difference did not reach statistical significance (OR: 0.49, 95% CI: 0.18-1.28, P=0.144) (Table 5).
Considering that UIA with high-risk profiles might be genetically comparable to RIA, UIA can be categorized as low- or high-risk for rupture based on a combination of multiple clinical factors. According to the PHASES (Population, Hypertension, Age, Size of aneurysm, Earlier subarachnoid hemorrhage, and Site of aneurysm) study, the 1-year rupture risk was 1.4% (95% CI: 1.1-1.6), and the 5-year rupture risk was 3.4% (95% CI: 2.9-4.0) [31]. UIA with a PHASES score ≥8, which have a 5-year rupture risk exceeding 3%, were classified as high-risk UIA, while those with a score between 0 and 7 were categorized as low-risk UIA. Our results (Supplementary Table 4) revealed statistically significant differences in the ALDH2 rs671 SNP between the low-risk UIA and both the high-risk UIA and RIA groups (41.8% vs. 19.2% and 41.8% vs. 18.6%, respectively, P<0.001). No significant differences were observed between the high-risk UIA and RIA groups.
Discussion
This study demonstrated that the ALDH2 mutation (specifically, the ALDH2*1/*2 or ALDH2*2/*2 genotype) acts as a unique protective element against RIA. Alcohol consumption significantly influenced the relationship between ALDH2 polymorphisms and the risk of RIA, especially among individuals with the ALDH2*1/*1 genotype, whereas no significant associations were found with other vascular risk factors. The ALDH2 mutation genotype was significantly correlated with reduced RIA risk, independent of traditional vascular risk factors. However, specific pathophysiological mechanisms underlying this protective effect remain unclear.
ALDH2 is recognized for its critical role in ethanol metabolism and its significant impact on drinking behaviors. Previous studies have indicated that susceptibility to stroke associated with ALDH2 polymorphisms is influenced by interactions between its phenotype and various lifestyle or environmental factors [32,33]. Individuals carrying the ALDH2*2 allele demonstrate reduced enzyme activity, leading to impaired acetaldehyde metabolism. Acetaldehyde accumulation can trigger acute adverse psychophysiological and cardiovascular responses, particularly in patients with low-to-moderate alcohol consumption [34-36]. These adverse effects may deter alcohol intake, potentially reducing the risk of alcoholism among individuals with the ALDH2*2 gene variant and potentially mitigating the indirect negative effects of ethanol on cardiovascular health [37]. Yao et al. [38] initially observed a significant difference in the prevalence of the ALDH2*2 gene variant among Taiwanese individuals who had suffered strokes, showing that heavy drinkers may exhibit a lower frequency than non-heavy drinkers because of lifestyle choices that limit alcohol consumption [37]. Previous studies have shown that ALDH2 gene variation is a significant determinant of stroke risk and is primarily attributed to its association with alcohol consumption.
Previous research has established a significant correlation between the frequency and quantity of alcohol intake and IA rupture [39]. Our study reinforces this association by revealing a significantly higher prevalence of regular and heavy alcohol consumption in patients with RIA. Additionally, patients with IA that were heavy drinkers showed a significant reduction in the frequency of the ALDH2*2 gene variant compared to non-heavy drinkers. Despite the observed correlation between ALDH2 polymorphisms and alcohol consumption patterns, multivariate logistic regression analysis adjusted for traditional risk factors, including alcohol consumption, demonstrated that ALDH2 polymorphisms were significantly associated with RIA. Thus, ALDH2 polymorphism emerged as an independent protective factor against RIA, whereas alcohol consumption was not significantly associated with RIA. Subsequent analysis stratified by alcohol consumption levels revealed that the protective effect of ALDH2 polymorphisms was particularly pronounced in individuals who abstained from alcohol or consumed alcohol moderately, whereas this protective effect was attenuated in heavy drinkers. This finding is consistent with recent research suggesting that individuals with the ALDH2*2 gene variant who are predisposed to vascular risk factors may increase their susceptibility to stroke by disregarding their inherent alcohol intolerance and engaging in heavy drinking [30,34,36]. We hypothesize that this attenuation occurs because heavy drinkers with the ALDH2*2 allele may overcome physiological and psychological barriers to alcohol consumption, developing tolerance, cravings, and dependence. Despite this behavioral adaptation, impaired acetaldehyde metabolism remains unchanged, leading to the sustained accumulation of acetaldehyde. This metabolic imbalance likely contributes to increased cerebral vascular risk, negating the protective effects of the ALDH2*2 allele observed in non-drinkers or light drinkers.
Our study also identified hypertension as an independent risk factor for RIA. Moreover, multiple studies have indicated that individuals carrying the ALDH2*2 allele are less likely to develop hypertension, suggesting a protective effect of the ALDH2 genetic mutation. Takagi et al. [40] previously reported that the ALDH2*1/*1 genotype may be a risk factor for hypertension in males, with approximately 1.67 times higher odds of developing hypertension than those with the ALDH2*2 allele. Similar findings from studies in China and South Korea corroborated these results, suggesting that individuals with the ALDH2*1/*1 genotype are more susceptible to hypertension than those with the ALDH2*2 variant [41-43]. Differences in blood pressure are attributed to increased alcohol consumption among individuals with the ALDH2*1/*1 genotype [42-49].
Some studies have found no direct correlation between the ALDH2 gene and susceptibility to hypertension, even after adjusting for potential confounding variables such as alcohol intake [50,51]. Mendelian randomization studies confirmed an association between ALDH2 gene variations and alcohol consumption, demonstrating a significant causal effect of alcohol consumption on both systolic and diastolic blood pressure. These findings suggest that the protective effect of the ALDH2*2 allele against hypertension is primarily associated with reduced alcohol consumption [52,53]. Our findings are consistent with those of previous research, indicating that individuals with the ALDH2*1/*1 genotype and IA are more likely to suffer from hypertension, consume alcohol frequently, and ingest larger quantities of alcohol than those with the ALDH2*2 allele. Stratification of patients according to hypertension status revealed a stronger protective effect of the ALDH2*2 allele in patients with IA without hypertension than in those with hypertension. This suggests that ALDH2 polymorphisms may indirectly influence IA rupture by modulating patients’ blood pressure.
IA is a multifactorial condition, and its potential pathogenesis correlates with age and other established risk factors. While age did not emerge as an independent risk factor for RIA in our study, further stratification by age revealed that ALDH2 gene mutations offered more significant protection for patients with IA aged 60 years and older than for those younger than 60 years. In contrast to the cardioprotective effects of ALDH2 against conditions such as coronary heart disease, myocardial ischemia, and cerebral ischemia, research suggests that ALDH2 may have detrimental effects on cardiac aging [54]. Experimental research has demonstrated that increased expression or activation of ALDH2 exacerbates myocardial remodeling and contractile dysfunction in elderly mice [21,55]. Mice aged 26-28 months exhibit higher levels of free radicals, increased mitochondrial damage, and increased apoptosis compared to young mice aged 4-5 months. These detrimental effects are exacerbated in transgenic mice with increased ALDH2 levels or exposure to ALDH2 activator-1 (ALDA-1). However, the adverse effects of ALDH2 on the myocardium of aged mice were mitigated by the concurrent administration of AMP-activated protein kinase (AMPK) activator and sirtuin-1 (SIRT1) [55]. Another study observed that aging impedes the phosphorylation of various proteins, including Jun-N-terminal Kinase (JNK), B-cell lymphoma 2 (Bcl2), I kappa B kinase beta (IκKβ), AMPK, and tuberin, while enhancing the phosphorylation of mTOR. Furthermore, the harmful effects of aging were exacerbated by ALDH2 overexpression [21]. Research indicates that ALDH2 contributes to age-related heart dysfunction by reducing myocardial autophagy through inhibition of the JNK-Bcl2 and IκKβ- AMPK pathways [21,55]. These pathways have been implicated in IA development [56,57]. Several studies have demonstrated a significantly higher risk of RIA in older patients than in younger patients [31,58,59]. However, extensive epidemiological and mechanistic investigations are necessary to elucidate whether mechanisms similar to myocardial protection in elderly patients with ALDH2 mutations (resulting in reduced ALDH2 activity) exist in patients with RIA. Nevertheless, existing studies offer insights into the diverse mechanisms through which ALDH2 functions in elderly patients with ruptured aneurysms, thereby suggesting potential targets for therapeutic interventions.
Our results indicated that the ALDH2 rs671 SNP significantly reduces the risk of RIA in patients with anterior circulation aneurysms. Although a similar trend was observed in patients with posterior circulation aneurysms, the results were not statistically significant. The wide confidence interval observed in this subgroup analysis may be attributed to the relatively small proportion of patients with posterior circulation aneurysms in our study cohort (43/546, 7.9%), which limited the statistical power of this analysis. Furthermore, stratified analysis based on aneurysm size revealed that the ALDH2 rs671 SNP was associated with a significantly reduced risk of RIA in patients with aneurysms having a maximum diameter of <7 mm. However, this protective effect was not statistically significant in patients with aneurysms ≥7 mm. Given that aneurysm size is a critical factor influencing rupture risk [31] and current clinical guideline recommend intervention for unruptured aneurysm ≥7 mm [60], this finding suggests that the ALDH2 genotype may have a more limited role in clinical decision-making for patients with larger aneurysms. This also highlights the importance of integrating genetic factors, such as ALDH2 mutations, with established clinical criteria to better understand individual rupture risk.
Previous studies have demonstrated the protective role of ALDH2 mutations in conditions such as AAD, and this effect does not appear to be strongly influenced by the population [22]. Mechanistically, ALDH2 deficiency increases the levels of Max, a suppressor of miR-31-5p, leading to repression of miR-31-5p expression. Disinhibition of myocardin promotes the expression of procontractile genes. As a result, elevated levels of contractile genes prevent the phenotypic switch of vascular smooth muscle cells (VSMCs) and slow the development of AAD. In individuals with intact ALDH2 function, Max-induced suppression of miR-31-5p is absent, allowing miR-31-5p to continue inhibiting myocardin, thereby favoring synthetic gene expression [22]. Further studies are warranted to investigate whether ALDH2 contributes to the development and rupture of IA through its regulatory role in the miR-31-5p/MYOCD pathway and its influence on the phenotypic transition of VSMCs.
ALDH2 can also modulate cholesterol biosynthesis and HDL biogenesis in hepatocytes via non-enzymatic pathways [61]. Specifically, ALDH2 interacts with poly(ADP-ribose) polymerase 1 (PARP1) to attenuate the nuclear translocation of PARP1, which results in depressed poly(ADP-ribosyl)ation of the liver X receptor-α, elevated levels of ATP-binding cassette transporter A1, and increased HDL biogenesis [61]. Furthermore, ALDH2 plays an important role in modulating cholesterol biosynthesis by limiting the stability of 3-hydroxy-3-methylglutaryl-CoA reductase, the ratelimiting enzyme in de novo cholesterol synthesis, and is a target of cholesterol-lowering therapies such as statins. In our study, plasma HDL-C levels were significantly lower in patients with RIA compared to those with UIA, which is consistent with the findings of recent studies [62,63]. This suggests an indirect role of ALDH2 in IA stability through the non-enzymatic pathways described above in HDL-C biogenesis. However, logistic regression analysis did not reveal a statistically significant correlation between low HDL-C and RIA (OR: 0.50, 95% CI: 0.20-1.29, P=0.154). This lack of an association may stem from the study’s limited sample size and the absence of a control group comprising healthy individuals without IA.
Although grouping the GA (ALDH2*1/*2) and AA (ALDH2*2/*2) genotypes together in our study was statistically necessary and biologically justified, we acknowledge that functional differences may exist between the two genotypes. Individuals with the GA genotype exhibit 10%-45% of the enzymatic activity observed in individuals with the wild-type GG (ALDH2*1/*1) genotype, whereas individuals with the AA genotype show only 1%-5% of normal ALDH activity [15,16]. Previous research has found that the risk of ischemic stroke is present only in patients with the AA genotype and not in those with the GA genotype, which may be attributable to the near-total loss of ALDH2 enzyme activity in the AA genotype. This impairment in detoxification and neuroprotection has been suggested as a contributing factor [64]. These findings indicate that the differences in enzyme activity between the GA and AA genotypes may have clinical implications that should not be overlooked. Further studies are necessary to explore the distinct effects of the GA and AA genotypes on IA, particularly in relation to their different enzymatic functions.
Although the functional differences between the GA and AA genotypes in terms of enzyme activity are being explored, other potential differences, such as their effects on VSMCs, inflammatory pathways, epigenetic regulation, and susceptibility to vascular remodeling, remain unclear. Further detailed studies on gene expression, metabolic pathways, and animal models are necessary to explore these potential differences more comprehensively. A better understanding of these differences could be crucial for refining risk assessments for IA rupture, particularly in individuals with the AA genotype, who may experience more pronounced metabolic dysfunction related to alcohol consumption and oxidative stress.
The strength of our study is underscored by the significantly higher prevalence of the ALDH2*2 gene variant in our participants, especially among those of Asian descent, compared to individuals of European descent. This enabled us to investigate the impact of ALDH2 variants and their interaction with alcohol consumption on RIA. Despite having a larger sample size than that of previous studies, additional research with larger cohorts is essential to validate and strengthen the robustness of our results. Although alcohol consumption was identified as a key factor associated with RIA in this study, we only included the frequency (days per week) and degree (non/light/heavy drinker) of alcohol consumption in our analysis. The duration of alcohol consumption (e.g., 10 years) may also be relevant in assessing the long-term impact on IA. Therefore, follow-up studies are required to explore this issue more thoroughly. Furthermore, potential bias in patient selection was a limitation of this study, given that the hospitals involved in our study were major national stroke and neurosurgery centers, which admit patients from surrounding areas as well as from across the country, which could contribute to the overrepresentation of more severe cases, including more ruptured posterior circulation IA and larger IAs. Moreover, we ensured a broad geographic representation when screening patients for enrollment. However, owing to the critical nature of the patients in the ruptured intracranial aneurysm group, we were unable to fully capture a nationwide sample, which may limit the generalizability of our findings across different regions in China. Finally, given that only 2% of the total sample was AA genotype carriers, we recognize the limitations posed by the small sample size for a separate analysis. However, we believe that applying alternative statistical methods, such as the Bayesian framework or meta-analysis, along with larger sample sizes in future studies, will help address this challenge better. We hope that future multicenter studies with larger sample sizes across more diverse regions, particularly those in regions with higher frequencies of the ALDH2*2 allele, such as Japan, Korea, and other East Asian populations, by recruiting individuals known to carry the AA genotype through genetic screening, will ensure adequate representation of this rare group and will be helpful for a more comprehensive exploration of the effects of the ALDH2 rs671 SNP on IA risk. Additionally, conducting a nested case-control study or employing a propensity score matching approach by matching AA genotype carriers with GA or GG genotypes in a 1:n ratio could further enhance the cohort and help optimize statistical power.
Conclusions
Our study is the first to demonstrate that the ALDH2 mutation serves as a distinct protective element against RIA. The incidence of rupture in patients with IA with the ALDH2 wild-type gene (ALDH2*1 allele) was significantly higher than that in patients with the ALDH2*2 allele. Given that this homozygous variant allele results in a significant reduction in enzyme activity and provides an independent protective effect, it can be inferred that the role of ALDH2 enzymatic activity in the metabolic pathway may be crucial for the progression of IA. The findings of our study have the potential to improve IA screening and diagnosis, and enhance prevention efforts, specifically within the Chinese population.
PDF Links
PubReader
ePub Link
XML Download
Full text via DOI
Download Citation
Supplement1
Print
