Elsevier

Clinica Chimica Acta

Volume 514, March 2021, Pages 59-65
Clinica Chimica Acta

Nuclear magnetic resonance reveals postprandial low-density lipoprotein cholesterol determined by enzymatic method could be a misleading indicator

https://doi.org/10.1016/j.cca.2020.12.013Get rights and content

Highlights

  • Postprandial LDL-C decline largely underestimate the postprandial atherogenicity.

  • Postprandial LDL-C is not well suitable for clinical decision.

  • Postprandial PCSK9 decrease may be secondary to the increased intrahepatic lipids.

Abstract

Background

Serum concentration of low-density lipoprotein cholesterol (LDL-C) is markedly reduced after a meal. Does postprandial cholesterol in LDL truly decline via clearance of LDL particles or is there simply a redistribution of cholesterol in LDL subclasses? Thus, we sought to evaluate whether postprandial decline of LDL-C reflects a reduction of LDL particle and to assess the correlation between proprotein convertase subtilisin/kexin type 9 (PCSK9) concentration and postprandial atherogenic lipoproteins profile.

Methods

Eighty-seven persons were enrolled in this study. We measured lipid profiles by enzymatic and nuclear magnetic resonance (NMR)-based methods and serum PCSK9 concentration by enzyme-linked immunosorbent assays before and after a meal. Plasma samples were collected after a 10-h fasting and 2 and 4 h post-meal.

Results

Compared to the fasting status, there was significant postprandial decline of LDL-C measured enzymatically (LDL-Ce) at 2nd and 4th h [99.38 (80.43, 120.65) vs 95.51 (74.25, 117.17) vs 87.01 (69.99, 108.28) mg/dl, p < 0.000]. But there was no significant reduction in LDL particle and its cholesterol content (LDL-Cn) determined by NMR. Just the postprandial large LDL particle [186.45 (151.36, 229.42) vs 176.92 (147.43, 220.91) vs 181.77 (149.05, 224.17), p < 0.000] and its cholesterol content [19.10 (15.09, 22.37) vs 18.28 (14.59, 21.84) vs 17.79 (14.62, 22.14), p < 0.000] were greatly decreased at 2nd and 4th h compared to the fasting one. Interestingly, postprandial serum PCSK9 was decreased at 2nd and 4th h compared with fasting concentration [298.75 (233.25, 396.92) vs 257.34 (207.52, 342.36) vs 250.57 (215.02, 339.66) ng/ml, p < 0.000]. The postprandial percent decrease in serum PCSK9 at 4th h was positively correlated to the percent decline in postprandial LDL-Ce (r = 0.252, p = 0.019) but was independently associated with the percent increase in remnant cholesterol (r = 0.262, p = 0.016).

Conclusions

Postprandial decline of LDL-C determined enzymatically was not confirmed by NMR-based methods. Indeed, there exists cholesterol redistribution in LDL subclasses following a meal. The decrease of postprandial PCSK9 may be secondary to the increase in intrahepatic lipids following food intake.

Introduction

Since Zilversmit et al. [1], [2] first proposed postprandial dyslipidemia as a potential risk factor for atherosclerosis, interest in postprandial lipid metabolism has awakened. A large body of data has suggested that the postprandial state could better capture the mass of cholesterol in atherogenic lipoproteins, thus, by some guidelines, the non-fasting lipid profile was recommended for predicting future cardiovascular events. However, investigators [3], [4], [5] have reported that low density lipoprotein cholesterol (LDL-C) was markedly reduced after a meal, which prompts us to ask, “Where does the ‘bad cholesterol’ go and does the decrease in LDL-C represent an improvement of atherogenic lipoprotein particle?”.

As we know, LDL originates from the delipidation of very low-density lipoprotein (VLDL) and intermediate-density lipoprotein, which are both triglyceride-rich lipoproteins (TRLs) [6]. After food intake, the TRLs are significantly increased in concentration. The TRLs undergo lipoprotein lipase–mediated lipolysis and cholesteryl ester transfer protein-mediated cholesterol interconversion in the peripheral or hepatic tissue [7] to yield different LDL subclasses or remnants. These LDL moieties are taken up by the liver via LDL receptor, the remnant receptor [8] (VLDLR), or other LDL receptor family members in peripheral tissues, such as heparan sulfate proteoglycans (HSPG) and LDL receptor related protein [9], [10]. Thus, the postprandial decline of LDL-C could be attributed to reduction of cholesterol ester transfer from HDL and VLDL to LDL by attenuated activity of cholesteryl ester transfer protein [6], [7] or attributed to the lowering of LDL particle production by enhanced activity of lipases [11], [12]. Alternatively, the decrease of postprandial LDL-C could be explained by enhanced clearance of LDL and its hepatic precursors, a process that would imply essential improvement in postprandial atherogenic lipoproteins.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) strongly disrupts LDL clearance by impeding LDL receptor recycling [13]. In the general population, a 100 ng/mL elevation of plasma PCSK9 concentration was related to about 0.1 mmol/l elevation of LDL-C concentration [14], [15]. In addition to LDL receptor, PCSK9 can escort other LDL receptor family members to the lysosomal for degradation. Lysosomal targeted receptors include LRP1 [10], VLDLR [16], and apolipoprotein E receptor 2 (ApoER2) [17], which are involved in TRLs hepatic clearance and indirectly affect postprandial LDL-C concentration. In addition, assembly and secretion of apoB-containing lipoproteins are also affected by PCSK9 [18]. All these clues suggest that PCSK9 will be involved in postprandial reduction of LDL-C. However, endogenous alteration of PCSK9 in the postprandial state and its effect on postprandial LDL-C level are still controversial and incompletely understood [5], [19], [10].

Because the non-fasting state predominates for most of the day for most people and non-fasting triglycerides is superior to fasting triglycerides as a predictor of cardiovascular risk [20], [21], some societies’ guidelines have used the non-fasting lipid profile to evaluate the risk of cardiovascular events [22]. However, recent studies have revealed that postprandial LDL-C is significantly decreased, even in patients with coronary artery disease [3], [23]. So, it is important to investigate the clinical implication of postprandial reduction of LDL-C and possible mechanism. To clarify this confusion, nuclear magnetic resonance (NMR) spectroscopy offers an alternative approach because it is similar to the gold standard for measuring lipid profile by ultracentrifugation [24], [25], [26]. NMR can quantify the density, number, size and composition of lipoproteins [26] and give a complete picture of lipoproteins profile including quantitative and qualitative changes. Moreover, an NMR-based lipoprotein subclass profile is not affected by the fluctuation of chemical composition [26], which is more stable and accurate for evaluating the characteristic of lipoproteins, especially in some certain conditions, such as metabolic syndrome, diabetes and dyslipidemia [27], [28]. Indeed, in the postprandial process, the compositions of lipoproteins vary dramatically [6], [7]; lipoprotein composition can be precisely determined by NMR-based approaches but not by traditional chemical measurement which provide only reliable measurement of total amount of cholesterol and TG but not their distribution in lipoprotein subclasses, especially LDL particle. Here, we used both enzymatic and NMR-based methods to explore the postprandial variations of lipoproteins and their cholesterol content. Simultaneous serum PCSK9 variation was also recorded to examine its correlation with that of lipoproteins.

Section snippets

Subject

Our study population was composed of 87 persons recruited from the Department of Cardiovascular Medicine of the Second Xiangya Hospital, Central South University, Changsha, China. The criteria for participation has been described [29]. Each person provided informed consent, and the Medical Ethics Committee of the Second Xiangya Hospital of Central South University approved the protocol. This trial was registered at Chinese Clinical Trial Registry as ChiCTR1900020873.

Clinical and biochemical measurement

All participant information,

Characteristics of study participants

Eighty-seven individuals were enrolled in the study. The median age of the study population was 54 (43–62) years and 58.6% were men. Mean body mass index is 24.15 kg/m2. Coronary artery disease (CAD), hypertension and type 2 diabetes were present in 39%, 33% and 15% of participants, respectively. Individuals using statin accounted for 31% of the total population. Table 1 presents the fasting and postprandial lipid profiles evaluated enzymatically.

Postprandial change of atherogenic lipoproteins

As shown in Fig. 1, after an isoenergetic meal,

Discussion

The nuclear magnetic resonance (NMR)-based lipid profile indicated that postprandial cholesterol in LDL was not cleared by the liver but just transferred between various LDL subclasses. Besides, the postprandial percent decrease in serum PCSK9 was independently associated with the percent increase in remnant cholesterol, suggesting the intrahepatic lipid flux may contribute to variation in serum PCSK9 level following food intake.

Like previous studies [3], [22], [31], our results confirmed that

Conclusions

Postprandial decline of LDL-C determined enzymatically is probably resulting from cholesterol redistribution in medium/small LDL subclasses which could confer enhanced atherogenicity, and the decrease of postprandial PCSK9 may be secondary to the increase in intrahepatic lipids following food intake. Hence, postprandial LDL-C measured by enzymatic method should not be regarded as lipid screening for evaluation of cardiovascular risk.

CRediT authorship contribution statement

Die Hu: Writing - original draft, Visualization, Investigation, Writing - original draft, Writing - review & editing. Ling Mao: Data curation, Visualization, Investigation. Xiaoyu Tang: Data curation, Visualization, Investigation. Jin Chen: Data curation, Visualization, Investigation. Xin Guo: Supervision, Software, Validation, Writing - review & editing. Qin Luo: Supervision, Software, Validation, Writing - review & editing. Jie Kuang: Supervision, Software, Validation, Writing - review &

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We acknowledge the contribution of all investigators. This project was supported by the National Natural Science Foundation of China, Grant (No. grants 81870336, 81670426 to D.Q. Peng; No. grant 81670420 to Yu B), and Natural Science Foundation of Hunan Province of China (No. grant 2018JJ2596 to Yuan S, No. grant 2018JJ1045 to Yu B), XinXin Heart (SIP) Foundation, China (No. grant 2019-CCA-ACCESS-028 to Yu B).

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