Non-high-density lipoprotein cholesterol/high-density lipoprotein cholesterol ratio serve as a predictor for coronary collateral circulation in chronic total occlusive patients

Chronic total occlusions (CTOs) are an important subtype of coronary artery disease (CAD) and pose a great threat to a patient’s prognosis because it remains prevalent in approximately one third of cases with CAD [1, 2]. CTO refers to a lesion in which the coronary artery is completely occluded or almost completely occluded for more than 3 months [3]. A system of coronary collateral circulation (CCC) is found in most CTO patients. These vessels provide the myocardium with another blood supply that may prevent myocardial necrosis and help improve left ventricular function [4, 5]. Previous studies suggested that well-formed CCC in patients with CTO reduced myocardial infarcts and improved the prognosis of patients [6, 7]. Therefore, it will be worthwhile to understand the mechanisms and influencing factors of the formation of CCC to identify new biomarkers. The existing evaluation methods (e.g., Collateral Flow Index (CFI), contrast echocardiography, and myocardial perfusion imaging) for the formation of CCC in patients with CTO are relatively complicated and expensive. Thus, an easy and feasible method for evaluating or predicting CCC formation is needed.

Dyslipidemia is tightly related to atherosclerosis. In clinical practice, decrease concentration of low-density lipoprotein cholesterol (LDL-C), non-high-density lipoprotein cholesterol (non-HDL-C), and triglyceride (TG) and increase of high-density lipoprotein cholesterol (HDL-C) concentration are commonly used as parameters in lipid-lowering strategies. Clinical physicians examined the non-HDL-C/HDL, this index represents the ratio of cholesterol contained in all of the atherosclerosis-promoting particles (non-HDL-C) and cholesterol contained in all the anti-atherosclerosis particles (HDL-C) in the serum, to evaluate lipid-related diseases. Some findings indicated that this cholesterol ratio was a better index than apolipoprotein B/apolipoprotein A1 and conventional single lipid parameter for identifying lipid-related diseases, such as insulin resistance, metabolic syndrome and CAD [8, 9]. However, few studies focused on the role of non-HDL-C/HDL ratio for predicting CCC formation in patients with CTO. The present study estimated the association between the non-HDL-C/HDL ratio and the formation of CCC.

CCC exerts protective effects in CTO patients, such as reducing the occurrence of small myocardial infarction, improving ventricular function, decreasing cardiovascular events and increasing long-term survival rate [6, 12, 13]. The formation of CCC is a complicated process, and several factors contribute to its development. The severity of coronary obstruction and duration of ischemic symptoms positively correlate with poor collateral development [14, 15]. However, patients with diabetes [16], hypercholesterolemia [17], hypertension [18] and hyperuricemia [19] are less likely to develop collateral vessels. However, vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) effectively promoted the formation of CCC in animal experiments [20]. The presence and function of CCC were also influenced by plasma chemokine concentrations, such as TNF-α [21], the angiogenic ligand and interferon [22]. Many studies showed that the development of CCC was a pathophysiological process involving multiple mechanisms, including oxidative stress, systematic hypoxia, inflammation and vascular endothelial function [23, 24].

Dyslipidemia is a contributing factor for CAD. Hyperlipidemia reduces vascular endothelial function and inhibits CCC formation [25]. However, different components in blood lipids have different impacts on endothelial function. Non–high-density lipoprotein cholesterol includes all atherogenic cholesterol in the blood, and the most important component of which is LDL-C because increased LDL-C causes damage to vascular endothelial function[26]. The incidence of long-term major adverse cardiovascular events (MACE) increased with increasing levels of non-HDL-C after acute myocardial infarction compared to lowering LDL-C to target [27]. Therefore, the lowering of non-HDL-C is a goal of treatment in the process of anti-atherosclerosis [28]. HDL-C exerts a protective role in the pathophysiological process of atherosclerosis formation and development [29], in which HDL-C plays anti-inflammatory and anti-oxidative roles and protects vascular endothelial cells by carried anti-oxidant enzymes such as paraoxonase-1(PON1), lecithin cholesterol acyltransferase(LCAT), and platelet-activating factor acetylhydrolase (PAF-AH). In particular, PON1 has been suggested to mainly mediate the potential anti-atherogenic capacity of HDL [30‐32]. The above research suggested that HDL-C and LDL-C played pivotal roles in the physical function of endothelial cells, and endothelial cells are truly involved in the formation of CCC. HDL-C and LDL-C may affect the functioning of endothelial cells, the formation and function of CCC.

Some studies indicated that lipoprotein ratios were better predictors of CAD than parameters of conventional lipids [9]. Our previous study showed that non-HDL-L/apolipoprotein A-I was highly correlated with the severity of coronary artery lesions and served as a biomarker in the assessment of CAD [33]. Based on the mechanisms and roles of non-HDL-C and HDL-C in the process of atherosclerosis, non-HDL-C/HDL ratio may be an important indicator and predictor of lipid-related disease. Wang et al. reported that the non-HDL-C/HDL ratio was associated with increased non-alcoholic steatohepatitis [34]. Several studies also reported that the non-HDL-C/HDL ratio was an independent factor of insulin resistance, metabolic syndrome and chronic kidney disease [35]. Some studies examined the role of the non-HDL-C/HDL ratio in postmenopausal women, and it could be used to predict the risk of CAD because the ratio was higher in females with carotid atherosclerotic plaque [36, 37]. However, there are few studies focusing on the relationship between this ratio and CCC formation.

The present study used the Rentrop grade to assess the formation of CCC. A negative correlation between the non-HDL-C/HDL ratio and Rentrop grade was found. CCC formation became poorer with increases in the non-HDL-C/HDL ratio. A multivariate logistic regression model showed that the non-HDL-C/HDL ratio was an independent risk factor for the formation of CCC. ROC results indicated that the optimal cut-off value of this ratio was 2.77 for detecting poor formation of CCC, the AUC (0.611) is not very impressive,somehow it has a relatively high sensitivity (77.5%), comparing with non-HDL-C or HDL respectively, non-HDL-C/HDL ratio was better for predicting CCC poor formation. In clinical practice, non-HDL/HDL ratio is easy to obtain and more economical than other methods (e.g. CFI, contrast echocardiography). The degree of coronary artery stenosis was tightly related to CCC formation because it promotes the initiation and is the main determinant of the CCC formation. After the formation of CCC is initiated, the function of endothelial cells could affect the function of CCC. Serum HDL-C and LDL-C levels affect vascular endothelial function. The non-HDL-C/HDL ratio was negatively related to CCC formation in the present study. It may be speculated that these two lipid particles affect endothelial cell function. In conclusion, our study provides a new index to assess and predict the formation of CCC.

The present study provides a theoretical basis for the choosing of lipid-lowering drugs for treating CAD. Lipid-lowering therapy should not only emphasize the reduction of non-HDL-C but also focus on increasing the level of HDL-C. The treatment of CAD should consider the formation and function of CCC.

The non-HDL-C/HDL ratio in the CCC poorly formed group of CTO patients was significantly elevated compared to the CCC well-formed group. Non-HDL-C/HDL negatively correlated with CCC formation,it independently served as a better predictive factor of CCC formation than non-HDL-C or HDL alone, which may be used as a biomarker for the evaluation of CCC.