Abbreviations, Acronyms & Symbols
CAD	= Coronary artery disease		NO	= Nitric oxide
DM	= Diabetes mellitus		PAD	= Peripheral artery disease
DNA	= Deoxyribonucleic acid		SIRT1	= Sirtuin 1
eNOS	= Endothelial nitric oxide synthetase		TAA	= Thoracic aortic aneurysm
HT	= Hypertension		TBST	= Tris Buffered Saline with Tween™ 20
IQR	= Interquartile range

Sirtuins are epigenetic regulatory proteins consisting of 200 - 275 amino acids. They are derived from the silent information regulatory 2 gene, initially discovered in yeast. Sirtuins are categorized into seven subtypes, with SIRT1, SIRT6, and SIRT7 located in the nucleus, SIRT3, SIRT4, and SIRT5 in the mitochondria, and SIRT2 functioning in the cytosol^[1]. Sirtuin 1 (SIRT1), the most extensively studied sirtuin, plays various roles in cell aging, metabolism regulation, deoxyribonucleic acid (DNA) repair, cardiovascular protection, inflammation, apoptosis, and autophagy^[2] Several studies have established its association with diabetes, demonstrating increased glucose tolerance and insulin secretion upon SIRT1 overexpression^[3].

Indeed, there is evidence supporting the protective properties of SIRT1 against vascular diseases, which can be attributed to its antioxidant, anti-aging, anti-inflammatory, and anti-apoptotic effects on endothelial smooth muscle and adventitial tissues. SIRT1 plays a role in regulating endothelial nitric oxide synthetase (eNOS), leading to the production of nitric oxide (NO). Additionally, there is a positive feedback loop where NO increases the expression of SIRT1. It's worth noting that one mechanism of action of statins and cilostazol involves inhibiting the eNOS inhibitor N-nitro-L-arginine methyl ester (or L-NAME). These interactions highlight the intricate relationship between SIRT1, NO, and the mechanisms of action of certain medications used in vascular diseases^[4].

SIRT1’s protective effect against vascular diseases is attributed to its antioxidant, anti-aging, anti-inflammatory, and anti-apoptotic properties^[5]. The main aim of the study is to investigate the relationship of SIRT1 in ascending aortic aneurysms and type 1 dissections.

The study included a total of 46 patients, with 13 (28.2%) being female and 33 (71.8%) being male. The age range of the participants was 19 to 78 years. The median age for all groups combined was 64 years, while the aneurysm group had a median age of 66 years (interquartile range [IQR], 48 - 71), the dissection group had a median age of 55 years (IQR, 51 - 69), and the control group had a median age of 65 years (IQR, 59 - 68).

Comparison of median body surface areas revealed that the control group had a value of 1.85 m² (1.75 - 1.89), the aneurysm group had a value of 1.95 m² (1.78 - 2.02), and the dissection group had a value of 2.06 m², indicating a significant difference between the groups (Table 1).

Table 1

	Aneurysm1	Dissection1	Control1	P-value
	(n = 16)	(n = 14)	(n = 16)
Male (n = 33)	12	9	12	0.82
	-75%	-64%	-75%
Female (n = 13)	4	5	4
	-25%	-36%	-25%
Age (years)	66	55	65	0.63
	(IQR, 48 - 71)	(IQR, 51 - 59)	(IQR, 59 - 68)
Body surface area (m2)	1.95	2.06	1.85	0.0493
	(IQR, 1.78-2.02)	(IQR, 1.87 - 2.13)	(IQR 1.75 - 1.89)
Aortic diameter (mm)	53	49	35	0.0013
	(IQR, 52 - 58)	(IQR, 44 - 57)	(IQR, 32 - 36)
Diabetes mellitus (n = 15)	12.5%	14.2%	68.75%	0.0012
	(n = 2)	(n = 2)	(n = 11)
Hypertension (n = 22)	44%	57%	44%	0.64
	(n = 7)	(n = 8)	(n = 7)
Coronary artery disease (n = 24)	44%	7.1%	100%	0.0014
	(n = 7)	(n = 1)	(n = 16)
Peripheral artery disease (n = 7)	12.5%	0%	31%	0.0102
	(n = 2)	(n = 0)	(n = 5)
SIRT1	214	172	104	0.0143
	(IQR, 79 - 270)	(IQR, 148 - 224)	(IQR, 78 - 123)

1

n (%); median (IQR);

It was observed that in the sample group, diabetes was present in 33% of the patients, HT in 48%, and PAD in 16%. In terms of diabetes, patients with DM comprised 12.5% (n = 2) of the aneurysm group, 14.2 % (n = 2) of the dissection group, and 68.75% (n = 11) of the control group. PAD was observed in seven patients, with two in the aneurysm group and five in the control group. PAD status of two patients in the dissection group was not clearly known (Table 1).

The median SIRT1 value was found to be the highest in the aneurysm group at 214 (IQR 79 - 270); intermediate in the dissection group at 172 (IQR 148 - 224); and the lowest in the control group at 104 (IQR 78 - 123). The difference between the groups was statistically significant (P = 0.014) (Figure 2). The difference between these groups lies in the comparison between the dissection group and the control group (Table 2).

Table 2

	SIRT1	(P-value)*
Aneurysm // control	214 (IQR, 79 - 270) // 104 (IQR, 78 - 123)	0.08
Dissection // control	172 (IQR, 148 - 224) // 104 (IQR, 78 - 123)	0.001
Aneurysm // dissection	214 (IQR, 79 - 270) // 172 (IQR, 148 - 224)	> 0.09

*

Wilcoxon rank sum exact

Fig. 2

In the overall patient population, when dividing them into two groups based on the presence (n = 24) or absence (n = 22) of CAD, the SIRT1 levels were calculated as 93 (75 - 123) in patients with CAD and 216 (150 - 246) in the group without CAD. The SIRT1 level was higher in aortic tissue in patients with CAD (P < 0.001) (Table 3).

Table 3

	Patients	SIRT1a	P-value*
CAD	CAD+ (n = 24)	93 (IQR, 75 - 123)	< 0.001
	CAD- (n = 22)	216 (IQR, 150 - 246)
PAD	PAD+ (n = 7)	79 (IQR, 63 - 108)	= 0.008
	PAD- (n = 37)	149 (IQR, 106 - 223)
HT	HT+ (n = 22)	118 (IQR, 75 - 148)	= 0.023
	HT- (n = 24)	184 (IQR, 111 - 244)

*

Wilcoxon rank sum exact test;

The patient group (n = 7) with PAD had a significantly lower SIRT1 level compared to the group without PAD (n = 37) (P = 0.008) (Table 3). When examining the patients in two groups based on the presence (n = 22) or absence (n = 24) of HT, the SIRT1 level was lower and statistically significant in the group with HT compared to the group without HT (P = 0.023) (Figure 3). However, there was no significant difference in the SIRT1 level between patients with (n = 15) and without (n = 31) DM.

Fig. 3

The SIRT1 values were found to be negatively correlated with age (P = 0.03, Ρ < 0.032), meaning that as age increases, SIRT1 levels decrease (Figure 4). On the other hand, there was a positive correlation between SIRT1 values and aortic diameter (P = 0.008, Ρ = 0.385), indicating that as the aortic diameter increases, the level of SIRT1 also increases (Figure 5) (Table 4).

Table 4

SIRT1	ρ	P-value*
Age	- 0.320	0.03
Aortic diameter	0.385	0.008

*

Spearman correlation test

Fig. 4

Fig. 5

This study aimed to establish a SIRT1 database in human aortic tissues to assess the potential utility of SIRT1 protein as a biomarker and evaluate its role in aortic aneurysms and dissections. The elevation of SIRT1, which is considered a vascular protective protein, was observed to be associated with the ascending aortic dissection group, contrary to the literature. Considering that the control group consisted of coronary artery bypass patients affected by systemic atherosclerosis, SIRT1 levels were observed to be low in vascular aging and atherosclerosis, consistent with the literature.

In Fang Wang's study, they administered a chemical that induces thoracic aortic aneurysm (TAA) and aortic dissection in mice and compared mice with high and low levels of smooth muscle-specific SIRT1. The study reported that the strain with the highest smooth muscle-specific SIRT1 had lower mortality^[6]. However, the findings from our study showed different results. In our study, when comparing SIRT1 levels in the aortic tissues of the three groups (aneurysm, dissection, and control), the highest level was observed in the aneurysm group (214), followed by the dissection group (172), and the lowest level was in the control group (104) (P = 0.014). This contrasts with the notion that SIRT1 elevation is protective against ascending aortic aneurysms and aortic dissection, as suggested in the literature.

Examining TAA under two groups, distal and proximal to the ligamentum arteriosum, it has been observed that atherosclerosis plays a role in the pathogenesis of aneurysms distal to the ligament, while aneurysms proximal to the ligament are not atherosclerotic^[7]. The ascending aorta, with greater longitudinal tension and elasticity compared to the descending aorta, is believed to have different smooth muscle cell origins^[8]. Smooth muscle cells in the aorta proximal to the ligamentum arteriosum originate from the neural crest, while those distal to it come from the paraxial mesoderm^[9-14]. Experimental studies did not specify which segments of the TAA develop aneurysms. 3-aminopropionitrile fumarate (or BAPN) is a compound that has been used in experimental studies to induce aortic aneurysms in mice. It acts as a lysyl oxidase inhibitor^[15], affecting collagen production. Collagen is an important component of the extracellular matrix in blood vessels. SIRT1 has been shown to increase the production of type I collagen from fibroblasts^[16].

However, it is important to note that in TAA, the pathology is not solely characterized by underproduction of collagen. There are multiple factors and processes involved in the development and progression of TAAs, including inflammation, oxidative stress, genetic predispositions, and alterations in extracellular matrix components.

SIRT1 plays a role in the production of eNOS in endothelial cells. NO, produced by eNOS, is an antioxidant chemical responsible for vascular relaxation and proliferation. SIRT1 and NOS have a mutualistic relationship with positive feedback. In our study, when patients were grouped as hypertensive (n = 22) and non-hypertensive (n = 24), SIRT1 levels were higher in the non-hypertensive group. This mutualistic relationship between SIRT1 and NOS, which promotes vascular relaxation, may contribute to the protective effect of SIRT1 against HT^[17,18].

In an experimental study conducted by Rateri et al., it was demonstrated that angiotensin II contributes to the development of ascending aortic aneurysm, while SIRT1 inhibits its harmful effects in aneurysm tissue^[19]. When comparing patients with and without HT, it was found that hypertensive patients were associated with lower SIRT1 levels, consistent with the literature. However, contrary to this example, our study demonstrated that patients with aortic dissection had higher SIRT1 levels compared to the control group. No significant difference in SIRT1 levels was observed between the aneurysm group and the control group.

In Fry et al.'s experimental study^[20], exogenous angiotensin II was infused into the aortic walls of normal mice with and without SIRT1 destruction. The results showed that mortality due to aortic dissection, particularly in the thoracic region, increased by 70% in mice with SIRT1 destruction. This was attributed to the involvement of SIRT1 in the aortic wall in oxidant and inflammatory stimulation. SIRT1 has an anti-inflammatory effect by suppressing the production of matrix metalloproteinase.

It's important to consider these contrasting findings and the complexity of the mechanisms involved in aortic pathologies. Further research is needed to better understand the role of SIRT1 in the development of TAA and aortic dissections, taking into account factors such as collagen production, atherosclerosis, and the specific segments of the aorta involved.

Studies using human tissues, such as the internal mammary artery, aorta, and carotid endarterectomy samples, have demonstrated the presence of SIRT1, which plays a role in preventing DNA damage and may have a protective effect against atherosclerosis. However, the study mentioned that suggests SIRT1's potential regression of medial degeneration was based on mouse experiments, not human tissue^[21]. In ascending aortic aneurysms and aortic dissections, the main pathology involves medial degeneration rather than atherosclerosis. We believe that our study, being the first investigation conducted on human ascending aortic tissues, will make a valuable contribution to the literature. While our study yielded results consistent with the literature regarding the role of SIRT1 in atherosclerosis-related diseases, further studies conducted on a broader range of human tissues are needed to evaluate its role in pathologies characterized by medial degeneration, such as ascending aortic aneurysms and type 1 dissections.

When the sample group was divided into two groups based on the presence (n = 24) or absence (n = 22) of CAD, it was observed that among the patients who underwent open-heart surgery, those with CAD were younger than those without CAD (P = 0.012). Additionally, SIRT1 levels were found to be lower in the group without CAD (93) compared to the group with CAD (216) (P = 0.001). Similarly, SIRT1 levels were lower in the group without PAD (n = 37) compared to the group with PAD (n = 7) (P = 0.008). In our study, it was also observed that the low levels of atherosclerosis-based vascular diseases are associated in parallel with the literature^[22].

Cell senescence is a condition where cells deteriorate and lose their ability to reproduce. There are two types of cell senescence. Replicative cell senescence occurs naturally when cells are unable to reproduce due to the shortening of telomeres^[23]. Over time, cells reach a limit known as the Hayflick limit^[24], after which replication ceases. Stress-induced premature senescence occurs when cell proliferation stops prematurely due to factors such as oxidative stress or DNA damage. Vascular aging refers to the aging of endothelial cells in the intima layer and vascular smooth muscle cells in the media layer of blood vessel walls. Senescent cells undergo morphological and physiological changes, leading to inflammation, atherosclerosis, and thrombosis in vascular cells, as well as problems with vascular relaxation, angiogenesis, and regeneration^[22,24-27].

Sirtuins are a group of proteins with nicotine adenine dinucleotide-dependent deacetylation or adenosine diphosphate ribosyl transferase activity. In endothelial cells, SIRT1 inhibits p53 deacetylation and hydrogen peroxide production. Hydrogen peroxide is a chemical that causes oxidative stress and contributes to premature cell aging^[5,28]. In our study, we observed a negative correlation (P = 0.03) between the SIRT1 results and the ages of the cases, which provides valuable insights that can contribute to the existing literature.

In this study conducted on human aortic tissues, it was observed that low SIRT1 levels were associated with diseases developing on the basis of atherosclerosis (CAD, PAD), as well as HT, consistent with the literature. A negative correlation was observed between age and SIRT1 levels.

Contrary to the literature, it was found that high SIRT1 levels were associated with type A aortic dissections.

By acknowledging the need for larger studies, we highlight the importance of further investigation to confirm and expand upon our findings. Continued research in this area will enhance our understanding of SIRT1’s role in various cardiovascular conditions and its potential implications for clinical practice.