The incidence of CAE was rare, at approximately 2% in our cohort, and the incidence based on previous studies ranged from 1.4 to 5.3% that were conducted in Europe and the USA. Therefore, our findings are consistent with the literature [1,2,3,4].
To the best of our knowledge, the present study is the first to show the relationship of TGF-β1 gene variations with the clinical/biochemical parameters and serum TGF-β1 levels in patients with CAE. In the present study, serum TGF-β1 levels were significantly lower in CAE patients than in controls and based on ROC analysis the discriminatory power seems to be moderate. Moreover, genotype distributions of TGF-β1 rs1800469 and rs1800470 polymorphisms were not significantly different between the CAE and control groups. However, the common homozygous AA genotype of the TGF-β1 rs1800470 polymorphism had lower serum TGF-β1 levels than patients with the rare G allele carriers (GG+AG genotypes) in the CAE group (p=0.012). In addition, we observed that the TGF-β1 rs1800469 polymorphism was associated with serum TGF-β1 levels, which were increased in CAE patients the following order: GG < GA < AA. However, the increases were not statistically significant. Lower TGF-β1 blood levels may increase the risk of CAE development. Considering the low TGF-β1 levels in the CAE group in this study, we believe that having the TGF-β1 rs1800470 G allele (GG+AG genotypes) and TGF-β1 rs1800469 A allele (AA+AG genotypes) may have a protective effect against the development of CAE.
The main event in CAE pathogenesis is destruction of the ECM by arterial remodeling that is caused by serine proteinase, lysosomal proteinase, and metalloproteinases [4, 5, 12]. Because TGF-β maintains vessel wall integrity, reduces inflammation, and maintains the ECM content in atherosclerosis, when any of its effects on endothelial cells are missing, the atherosclerosis process accelerates. The role of TGF-β signaling in the pathogenesis of cardiovascular diseases has been reported previously [6, 8, 9]. In these studies, an inverse relationship between serum TGF-β1 levels and the development of atherosclerosis was demonstrated, and it was suggested that TGF-β1 concentration is severely suppressed in advanced atherosclerosis [8, 9]. In addition, Tashiro et al. demonstrated that the TGF-β plasma concentration has a prognostic significance in patients with proven CAD. In this study, the low plasma concentration TGF-β group had a poor prognosis of survival without cardiovascular events and survival without coronary interventions compared to the high plasma concentration TGF-β group [13].
These results show that TGF-β is a protective cytokine. Although there is no study examining the TGF-β blood levels in patients with CAE in the literature, the low plasma TGF-β concentrations that were found in CAE patients in our study may cause the increased risk of CAE development. In contrast to our findings, Yetkin et al. reported that plasma TGF-β1 levels were significantly increased in patients with CAE and CAD compared to age- and sex-matched patients with CAD alone [14]. In our study, the control group comprised individuals with normal coronary arteries. Therefore, the difference between the findings in the two studies could be attributed to different characteristics of the control group.
A few gene polymorphism studies on the atherosclerotic origin of CAE have been reported. These studies demonstrated the relationship between CAE and the c.894 G>T polymorphism in the endothelial nitric oxide synthase gene, HOGG1, Ser326Cys gene polymorphism, deletion in angiotensin I converting enzyme gene, and the HLA-DR B1, DR16, DQ2, and DQ5 genotypes [15,16,17,18]. Furthermore, many studies have reported the effect of TGF-β1 gene polymorphism on atherosclerotic cardiovascular or other cardiac diseases. In a significant part of these studies, TGF-β1 rs1800469 and rs1800470 polymorphisms were associated with restenosis after a coronary stent and coronary artery disease [19, 20]. Additionally, mutation of TGF-β signal pathway components such as TGFBR1 and TGFBR2 is directly involved in the progression of the aortic aneurysm [21]. Zuo et al. indicated the increased risk of abdominal aortic aneurysm for individuals with the TGF-β1 rs1800469 TT(AA) genotype compared with those with the CC(GG) genotype [22]. No studies have investigated the relationship between TGF-β1 gene variations and CAE. In our study, we investigated the relationship between TGF-β1 rs1800469 and rs1800470 polymorphisms and CAE. No significant relationship was found between TGF-β1 polymorphisms at rs1800469 and rs1800470 and CAE. With these results, a single polymorphism alone may not be responsible for its etiology, especially considering the multidimensional presentation of the disease. Although several polymorphisms have been identified, the exact polymorphism that describes the etiology of CAE remains uncertain.
Rs1800470 is located within the TGF-β1 gene exons, affecting the amino acid chance of developing Leu10Pro. Proline substitution at codon 10 may result from an altered intercellular signaling network or increased transcription. This may cause changes in the chemical properties and structure of the TGF-β1 protein [11]. In CAD patients, the T(A) allele of TGF-β1 rs1800470 (29T/C) was reportedly associated with low serum TGF-β1 levels compared to homozygous CC(GG) [23]. These findings may demonstrate the anti-inflammatory effect of TGF-β1 on the vessel wall. In addition, Fragoso et al. demonstrated the TGF-β1 rs1800470 (29T/C) polymorphism was related to restenosis after coronary stenting. It was also shown in the same study that individuals with the TT haplotype TGF-β1 rs1800470 (29T/C) produced less TGF-β1 [19]. Similar to these studies, we observed that serum TGF-β1 levels may differ in patients with CAE according to the TGF-β1 rs1800469 and rs1800470 polymorphisms. In the present study, homozygous AA genotype of the TGF-β1 rs1800470 polymorphism had lower serum TGF-β1 levels than patients with the G allele carriers (GG+AG genotypes) in the CAE group. This may lead to a decrease in the anti-inflammatory effect and an acceleration in the development of CAE.
Rs1800469 is a single nucleotide polymorphism that is located within the promoter region of the TGF-β1 gene. This mutation causes a change in the amount of TGF-β1 that is produced without changing the protein structure. The T allele of TGF-β1 rs1800469 was shown to be associated with a higher serum TGF-β1 level [24]. Cao et al. found that the −509T allele (TGF-β1 rs1800469 A allele) was associated with higher TGF-β1 expression and more severe interstitial fibrosis. Based on their findings, they suggested that increased TGF-β1 expression by the −509T allele may cause overproduction of extracellular matrix components, resulting in progressive atrial augmentation, fibrosis, and susceptibility to lone atrial fibrillation [25]. In the present study, we observed that the TGF-β1 rs1800469 polymorphism was associated with serum TGF-β1 levels, which were increased in the following order in CAE patients: GG < GA < AA. However, the increases were not statistically significant.
The CAE group in the present study comprised individuals who had CAE with atherosclerosis. Studies have revealed that CAE is a variant of atherosclerosis and has similar pathogenesis. In this situation, it would not be a surprise to have similar risk factors. In our study, the prevalence of hypertension, hyperlipidemia, and male sex were higher in patients with CAE than in controls. Similar to our findings, Gunes et al. found in their study that the prevalence of hypertension and hyperlipidemia, which are clinical features of CAE patients, was more frequent in CAE patients than in controls who had normal coronary arteries [26]. These are also well-known risk factors for the development of CAD. Moreover, Kamal et al. also found in their study that male gender was frequent in patients with CAE and an independent risk factor for CAE development [27].
Limitations
This was a single-center study with a relatively small number of patients. In addition, there was no long-term follow-up.