Overall mortality is increased in patients with obesity. Atherosclerosis-related diseases are mainly a higher mortality factor in obese individuals because unwanted lipid changes such as high TGs, high LDL-cholesterol (LDL-C) and low HDL-C are typically found in patients with obesity [1–3].
New atherogenic risk indices AIP, AC and LPCI, which were not included in the literature for SG and were shown comprehensively for the first time in this study, decreased after SG surgery. The decrease in atherogenic risk indices that we showed in our study may be significant for the antiatherosclerotic effect of SG surgery. Thus with SG the risk of stroke and cardiovascular events may be reduced in patients over time. The insufficient number of studies showing the relationship of atherogenic risk indices with SG makes this study a preliminary study because it is the first study to report a decrease in atherogenic risk indices (Table 5) after SG surgery and, on the contrary, an increase in HDL-C, Apo-A1. Serum levels at 3 and 6 months. It is also a preliminary study showing that patients' HDL-C function improved after SG and also significantly reduced TGs and Ox-LDL in the blood. Thus, the significant improvement in atherogenic risk indexes after SG surgery may demonstrate the strong corrective effect of SG on lipid metabolism in patients with obesity. Moreover, in the 6th month after SG, the AIP value of the patients decreased from the risk level to the lower risk level. However, the patients in the preop group had a high risk of AIP, such as 0.22. However, the AI value and especially LPCI values decreased significantly at the end of the 6th month. This decrease in atherogenic risk indexes is actually an indication that HDL-C functions have improved significantly.
Today, every patient with morbid obesity should be examined for lipid metabolism. Because, increased TGs, mixed dyslipidemia associated with LDL-C and Ox-LDL, and increased atherogenic risk should be expected in obesity [15].
Of course, Ox-LDL are pro-atherogenic hazardous lipoproteins formed by the oxidation of LDL-C particles. Thus increasing adipose tissue in obese individuals contributes to low-grade inflammation and increased oxidative stress (OS) in obese individuals by continuously increasing ROS production [3, 16]. Significantly decreased TGs levels, increased HDL-C and Apo-A1 levels after SG surgery determined in this study are perhaps the most important reasons for the decrease in atherogenic risk indices. In this study, the most important contribution to HDL-C functions after SG was the significant increase in the amount of Apo-A1 after 6 months. The increase in Apo-A1 we achieved in this study is not surprising and supports previous studies in the literature [17].
Conversely, SG surgery can cause a clear reduction in chronic inflammation and atherogenic risk indexes by not increasing plasma oxidative markers, including Ox-LDL and PAF-AH enzyme activity, as shown in this study. Our results show that the pro-atherogenic lipid profile and increased atherogenic risk indices (AIP, AI and LCPI) characteristic of morbid obesity patients become healthier after SG surgery [12–14].
In general, an increase in HDL-C was observed from 3 months after SG. There was also a significant decrease in TG levels, which reduced dyslipidemia. However, there was no statistically significant change in TC and LDL-C after SG surgery. Increasing systemic bile acid levels and changing bile acid composition after SG can affect lipid absorption, but the molecular mechanism is not understood. In addition to the surfactant role of bile after SG, bile acids also function as signaling molecules for a number of cellular nuclear receptors and plasma membrane receptors [18]. The bariatric surgical technique SG used in this study is actually a technique that preserves the small intestine (especially the jejunum) and perhaps for this reason causes a significant increase in HDL-C [17, 19].
In our study, we did not find any statistically significant changes in Ox-LDL and PAH enzyme levels in the blood for up to a 6 rd. month. However, the Ox-LDL levels in the blood of patients with SG did not change significantly, in fact, this result should be expected, since the enzyme PAF-AH in the blood is mainly contained in LDL-C content of more than 80%, but less than 20% is associated with HDL-C. Decreased chronic inflammation and decreased production of ROS in the blood after SG can contribute to the stabilization of the level of Ox-LDL and PAF-AH in the blood [20].
According to the literature, HDL-C levels increase by 47% compared to preoperative SG values 10 years after SG surgery. In our study, the follow-up period after SG is up to 6 month, but even in this short time, HDL-C ratio increased by 29% compared to preop values. So, increase in HDL-C values indicates a statistically significant improvement in patient with obesity [21, 22]. PON-1, which falls in the blood after SG, is actually a multi-functional enzyme associated with HDL-C, contrary to what we expected. PON-1 exerts anti-atherogenic effects by increasing cholesterol influx from macrophages to HDL with ATP binding cassette transporter 1 (ABCA 1). Previous studies have shown that increased PON-1 activity is associated with a reduction in the incidence of major cardiovascular events [9, 23]. HDL-C's most important antiatherogenic effect is thought to be through the macrophage-cholesterol flow and reverse cholesterol transport system [10]. In addition, HDL-C improves endothelial function by increasing nitric oxide production and acts as a protective agent against oxidation and inflammation with Apo-A1- activity [10, 23] The main anti-atherogenic property of functional HDL-C is inhibition of LDL-C oxidation [9]. Apo-A1, LCAT and PON-1 enzymes functionally inhibit LDL oxidation in HDL-C structure [9, 10, 23]. In this study, the amount of PON-1 enzyme found in the blood of patients after SG decreased after the 3rd month. This enzyme, which acts as an antioxidant in the structure of HDL-C, can mainly function in preventing the formation of Ox-LDL in patients after SG, and there may be a compensatory decrease in the need for PON-1. In fact, a lower level of chronic inflammation, a low atherogenic activity and much less oxidant molecule production should be expected as a result of the reduction of active adipose tissue in patients after bariatric surgery [24, 25]. PON-1 enzyme, which acts as an antioxidant in the structure of HDL-C, mainly prevents the formation of Ox-LDL in patients after SG. Finally, the decrease in PON-1 need after SG surgery may be due to the decrease in ROS synthesis [26, 27]. Moreover, during SG surgery, the ghrelin-producing region of the stomach is partially removed, which is thought to directly affect metabolic parameters [26, 27]
The response of each bariatric surgical procedure to obesity-related dyslipidemia is different. Previous studies have reported a significant decrease in TG and a significant increase in HDL-C and Apo -A1 in patients undergoing SG [27–30]. The improvement in insulin sensitivity and the effect of this improvement on lipoprotein lipase activity which may be explained by the meaningful and effective decrease in TGs level after SG [27–30]. Another finding in our study is that although TC did not change significantly, LDL-C increased significantly from the early postoperative period to the 3rd month. Fortunately, SG surgery can balance the increase in LDL-C inflammation and oxidative stress by reducing oxidative and microvascular function markers in adipose tissue. Finally, in this study, Ox-LDL levels did not change significantly immediately after surgery and remained without significant increase at 6-month follow-up. In one study included in the literature, a significant increase in HDL-C and Apo-A1 and a decrease in LDL-C and Ox-LDL were observed after the other SG [31]. The limitations of this study are that it has a limited number of subjects and that longer patient follow-up is not possible.