AMP-activated protein kinase mediates the effects of lipoprotein-associated phospholipase A2 on endothelial dysfunction in atherosclerosis

Research Advance of Chinese Medicine in Treating Atherosclerosis: Focus on Lipoprotein-Associated Phospholipase A2

As a serious cardiovascular disease, atherosclerosis (AS) causes chronic inflammation and oxidative stress in the body and poses a threat to human health. Lipoprotein-associated phospholipase A2 (Lp-PLA2) is a member of the phospholipase A2 (PLA2) family, and its elevated levels have been shown to contribute to AS. Lp-PLA2 is closely related to a variety of lipoproteins, and its role in promoting inflammatory responses and oxidative stress in AS is mainly achieved by hydrolyzing oxidized phosphatidylcholine (oxPC) to produce lysophosphatidylcholine (lysoPC). Moreover, macrophage apoptosis within plaque is promoted by localized Lp-PLA2 which also promotes plaque instability. This paper reviews those researches of Chinese medicine in treating AS via reducing Lp-PLA2 levels to guide future experimental studies and clinical applications related to AS.

Sudden Sensorineural Hearing Loss Is Related to Endothelial Progenitor Cells and Lipoprotein-Associated Phospholipase A2

BACKGROUND

This study aimed to investigate the correlation between lipoprotein-associated phospholipase A2, endothelial progenitor cells, and sudden sensorineural hearing loss.

METHODS

The number of endothelial progenitor cells and lipoprotein-associated phospholipase A2 levels collected from peripheral blood samples were measured and compared between sudden sensorineural hearing loss group and control group.

RESULTS

The number of endothelial progenitor cells was reduced in sudden sensorineural hearing loss group compared to control group (38.88 ± 10.73 in sudden sensorineural hearing loss group vs. 77.14 ± 8.56 in control group, P <.01). The lipoprotein-associated phospholipase A2 level was markedly increased in sudden sensorineural hearing loss group compared to control group (244.94 ± 59.547 in sudden sensorineural hearing loss group vs. 189.00 ± 50.987 in control group, P <.05).

CONCLUSION

The number of endothelial progenitor cells was decreased and lipoprotein-associated phospholipase A2 levels were increased in sudden sensorineural hearing loss patients. Changes in the number of endothelial progenitor cells and lipoprotein-associated phospholipase A2 levels may be involved in the pathogenesis of sudden sensorineural hearing loss.

Comparison of Cell-based and Nanoparticle-based Therapeutics in Treating Atherosclerosis

Today, cardiovascular diseases are among the biggest public health threats worldwide. Atherosclerosis, a chronic inflammatory disease with complex aetiology and pathogenesis, predispose many of these conditions, including the high mortality rate-causing ischaemic heart disease and stroke. Nevertheless, despite the alarming prevalence and absolute death rate, established treatments for atherosclerosis are unsatisfactory in terms of efficacy, safety, and patient acceptance. The rapid advancement of technologies in healthcare research has paved new treatment approaches, namely cell-based and nanoparticle-based therapies, to overcome the limitations of conventional therapeutics. This paper examines the different facets of each approach, discusses their principles, strengths, and weaknesses, analyses the main targeted pathways and their contradictions, provides insights on current trends as well as highlights any unique mechanisms taken in recent years to combat the progression of atherosclerosis.

The lipid paradox in neuroprogressive disorders: Causes and consequences

Chronic systemic inflammation is associated with an increased risk of cardiovascular disease in an environment of low low-density lipoprotein (LDL) and low total cholesterol and with the pathophysiology of neuroprogressive disorders. The causes and consequences of this lipid paradox are explored. Circulating activated neutrophils can release inflammatory molecules such as myeloperoxidase and the pro-inflammatory cytokines interleukin-1 beta, interleukin-6 and tumour necrosis factor-alpha. Since activated neutrophils are associated with atherosclerosis and cardiovascular disease and with major depressive disorder, bipolar disorder and schizophrenia, it seems reasonable to hypothesise that the inflammatory molecules released by them may act as mediators of the link between systemic inflammation and the development of atherosclerosis in neuroprogressive disorders. This hypothesis is tested by considering the association at a molecular level of systemic inflammation with increased LDL oxidation; increased small dense LDL levels; increased lipoprotein (a) concentration; secretory phospholipase A₂ activation; cytosolic phospholipase A₂ activation; increased platelet activation; decreased apolipoprotein A1 levels and function; decreased paroxonase-1 activity; hyperhomocysteinaemia; and metabolic endotoxaemia. These molecular mechanisms suggest potential therapeutic targets.

Hydrogen sulfide improves ox‑LDL‑induced expression levels of Lp‑PLA2 in THP‑1 monocytes via the p38MAPK pathway

Hydrogen sulfide (H₂S) exerts an anti‑atherosclerotic effect and decreases foam cell formation. Lipoprotein‑associated phospholipase A2 (Lp‑PLA₂) is a key factor involved in foam cell formation. However, the association between H₂S and Lp‑PLA₂ expression levels with respect to foam cell formation has not yet been elucidated. The present study investigated whether H₂S can affect foam cell formation and potential signalling pathways via regulation of the expression and activity of Lp‑PLA₂. Using human monocytic THP‑1 cells as a model system, it was observed that oxidized low‑density lipoprotein (ox‑LDL) not only upregulates the expression level and activity of Lp‑PLA₂, it also downregulates the expression level and activity of Cystathionine γ lyase. Exogenous supplementation of H₂S decreased the expression and activity of Lp‑PLA₂ induced by ox‑LDL. Moreover, ox‑LDL induced the expression level and activity of Lp‑PLA₂ via activation of the p38MAPK signalling pathway. H₂S blocked the expression levels and activity of Lp‑PLA₂ induced by ox‑LDL via inhibition of the p38MAPK signalling pathway. Furthermore, H₂S inhibited Lp‑PLA₂ activity by blocking the p38MAPK signaling pathway and significantly decreased lipid accumulation in ox‑LDL‑induced macrophages, as detected by Oil Red O staining. The results of the present study indicated that H₂S inhibited ox‑LDL‑induced Lp‑PLA₂ expression levels and activity by blocking the p38MAPK signalling pathway, thereby improving foam cell formation. These findings may provide novel insights into the role of H₂S intervention in the progression of atherosclerosis.

Cardiovascular protection effect of chlorogenic acid: focus on the molecular mechanism

Vascular endothelial cells have a variety of functions such as the control of blood coagulation, vascular permeability, and tone regulation, as well as quiesce of immune cells. Endothelial dysfunction is a cardiovascular events predictor, which is considered the initial stage in atherosclerosis development. It is characterized by alterations in endothelium functions due to imbalanced vasodilators and vasoconstrictors, procoagulant and anticoagulant mediators, as well as growth inhibitor and promotor substances. Chlorogenic acid (CGA) is the primary polyphenol in coffee and some fruits. It has many health-promoting properties, especially in the cardiovascular system. Many studies investigated the efficacy and mechanism of this compound in vascular health. CGA has several vascular benefits such as anti-atherosclerosis, anti-thrombosis, and anti-hypertensive. This review focuses on the molecular mechanism of CGA in vascular health.

Aspirin protects human coronary artery endothelial cells by inducing autophagy

Although the use of aspirin has substantially reduced the risks of cardiovascular events and death, its potential mechanisms have not been fully elucidated. In a previous study, we found that aspirin triggers cellular autophagy. In the present study, we aimed to determine the protective effects of aspirin on human coronary artery endothelial cells (HCAECs) and explore its underlying mechanisms. HCAECs were treated with oxidized low-density lipoprotein (ox-LDL), angiotensin II (Ang-II), or high glucose (HG) with or without aspirin stimulation. The expression levels of endothelial nitric oxide (NO) synthase (eNOS), p-eNOS, LC3, p62, phosphor-nuclear factor kappa B (p-NF-κB), p-p38 mitogen-activated protein kinase (p-p38 MAPK), and Beclin-1 were detected via immunoblotting analysis. Concentrations of soluble intercellular adhesion molecule-1 (sICAM-1) and soluble vascular cell adhesion molecule-1 (sVCAM-1) were measured via ELISA. NO levels were determined using the Griess reagent. Autophagic flux was tracked by tandem mRFP-GFP-tagged LC3. Results showed that aspirin increased eNOS level and reduced injury to the endothelial cells (ECs) caused by ox-LDL, Ang-II, and HG treatment in a dose-dependent manner. Aspirin also increased the LC3II/LC3I ratio, decreased p62 expression, and enhanced autophagic flux (autophagosome and autolysosome puncta) in the HCAECs. p-NF-κB and p-p38 mitogen-activated protein kinase inhibition, sVCAM-1 and sICAM-1 secretion, and eNOS activity promotion by aspirin treatment were found to be dependent on Beclin-1. These results suggested that aspirin can protect ECs from ox-LDL-, Ang-II-, and HG-induced injury by activating autophagy in a Beclin-1-dependent manner.

The emerging role of cell senescence in atherosclerosis

Cell senescence is a fundamental mechanism of aging and appears to play vital roles in the onset and prognosis of cardiovascular disease, fibrotic pulmonary disease, liver disease and tumor. Moreover, an increasing body of evidence shows that cell senescence plays an indispensable role in the formation and development of atherosclerosis. Multiple senescent cell types are associated with atherosclerosis, senescent human vascular endothelial cells participated in atherosclerosis via regulating the level of endothelin-1 (ET-1), nitric oxide (NO), angiotensin II and monocyte chemoattractant protein-1 (MCP-1), senescent human vascular smooth muscle cells-mediated plaque instability and vascular calcification via regulating the expression level of BMP-2, OPN, Runx-2 and inflammatory molecules, and senescent macrophages impaired cholesterol efflux and promoted the development of senescent-related cardiovascular diseases. This review summarizes the characteristics of cell senescence and updates the molecular mechanisms underlying cell senescence. Moreover, we also discuss the recent advances on the molecular mechanisms that can potentially regulate the development and progression of atherosclerosis.

AMP-activated protein kinase activation ameliorates eicosanoid dysregulation in high-fat-induced kidney disease in mice

High-fat diet (HFD) causes renal lipotoxicity that is ameliorated with AMP-activated protein kinase (AMPK) activation. Although bioactive eicosanoids increase with HFD and are essential in regulation of renal disease, their role in the inflammatory response to HFD-induced kidney disease and their modulation by AMPK activation remain unexplored. In a mouse model, we explored the effects of HFD on eicosanoid synthesis and the role of AMPK activation in ameliorating these changes. We used targeted lipidomic profiling with quantitative MS to determine PUFA and eicosanoid content in kidneys, urine, and renal arterial and venous circulation. HFD increased phospholipase expression as well as the total and free pro-inflammatory arachidonic acid (AA) and anti-inflammatory DHA in kidneys. Consistent with the parent PUFA levels, the AA- and DHA-derived lipoxygenase (LOX), cytochrome P450, and nonenzymatic degradation (NE) metabolites increased in kidneys with HFD, while EPA-derived LOX and NE metabolites decreased. Conversely, treatment with 5-aminoimidazole-4-carboxamide-1-β-D-furanosyl 5'-monophosphate (AICAR), an AMPK activator, reduced the free AA and DHA content and the DHA-derived metabolites in kidney. Interestingly, kidney and circulating AA, AA metabolites, EPA-derived LOX, and NE metabolites are increased with HFD; whereas, DHA metabolites are increased in kidney in contrast to their decreased circulating levels with HFD. Together, these changes showcase HFD-induced pro- and anti-inflammatory eicosanoid dysregulation and highlight the role of AMPK in correcting HFD-induced dysregulated eicosanoid pathways.

Salidroside attenuates oxidized low‑density lipoprotein‑induced endothelial cell injury via promotion of the AMPK/SIRT1 pathway

Oxidized low-density lipoprotein (ox-LDL)-induced endothelial damage contributes to the initiation and pathogenesis of atherosclerosis. Salidroside can alleviate atherosclerosis and attenuate endothelial cell injury induced by ox-LDL. However, the mechanisms involved in this process are not fully understood. Therefore, the purpose of the present study was to investigate the role of the adenosine monophosphate-activated protein kinase (AMPK)/sirtuin (SIRT)1 pathway in the protection of salidroside against ox-LDL-induced human umbilical vein endothelial cells (HUVECs) injuries. The results revealed that salidroside reverses ox-LDL-induced HUVECs injury as demonstrated by the upregulation of cell viability and downregulation of LDH release. In addition, salidroside increased the expression of the SIRT1 protein in ox-LDL-treated HUVECs. Next, it was demonstrated that SIRT1 knockdown induced by transfection with small interfering (si)RNA targeting SIRT1 (siSRT1) abolished the protection of salidroside against ox-LDL-induced HUVECs injuries. This was illustrated by a decrease in cell viability and an increase in LDH release, caspase-3 activity and apoptosis rate. Furthermore, salidroside mitigated ox-LDL-induced reactive oxygen species production, upregulated malondialdehyde content and NADPH oxidase 2 expression and decreased superoxide dismutase and glutathione peroxidase activities, while these effects were also reversed by siSIRT1 transfection. In addition, it was demonstrated that salidroside suppressed ox-LDL-induced mitochondrial dysfunction as demonstrated by the increase in mitochondrial membrane potential and decreases in cytochrome c expression, and Bax/Bcl-2 reductions. However, these effects were eliminated by SIRT1 knockdown. Finally, it was demonstrated that salidroside significantly upregulated the phosphorylated-AMPK expression in ox-LDL-treated HUVECs and AMPK knockdown induced by transfection with AMPK siRNA (siAMPK) leads to elimination of the salidroside-induced increase in cell viability and the decrease in LDH release. Notably, siAMPK transfection further decreased the expression of SIRT1. In conclusion, these results suggested that salidroside protects HUVECs against ox-LDL injury through inhibiting oxidative stress and improving mitochondrial dysfunction, which were dependent on activating the AMPK/SIRT1 pathway.

LncRNA MALAT1 promotes oxidized low-density lipoprotein-induced autophagy in HUVECs by inhibiting the PI3K/AKT pathway

Emerging evidence suggests that long noncoding RNAs (lncRNAs) are involved in many biological processes, such as cell growth, differentiation, apoptosis, and autophagy. Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), highly expressed in endothelial cells, is well conserved and implicated in endothelial cell migration and proliferation. However, whether MALAT1 participates in oxidized low-density lipoprotein (ox-LDL)-induced autophagy regulation in human umbilical vein endothelial cells (HUVECs) remains unknown. In this study, we observed that autophagy was upregulated and MALAT1 expression was markedly increased in HUVECs treated with ox-LDL. The ox-LDL-induced autophagy of HUVECs is significantly associated with the PI3K/AKT pathway. Furthermore, we found that MALAT1 overexpression inhibited PI3K, Akt and p70S6K phosphorylation and downregulated RHEB expression, simultaneously increasing ox-LDL-induced autophagy. MALAT1 silencing caused higher phosphorylated PI3K, Akt and p70S6K levels, upregulated RHEB expression and markedly suppressed autophagy. These results indicated that lncRNA MALAT1 promotes ox-LDL-induced autophagy in HUVECs partly through the PI3K/AKT signaling pathway.

PINK1/Parkin-mediated mitophagy promotes apelin-13-induced vascular smooth muscle cell proliferation by AMPKα and exacerbates atherosclerotic lesions

Aberrant proliferation of vascular smooth muscle cells (VSMC) is a critical contributor to the pathogenesis of atherosclerosis (AS). Our previous studies have demonstrated that apelin-13/APJ confers a proliferative response in VSMC, however, its underlying mechanism remains elusive. In this study, we aimed to investigate the role of mitophagy in apelin-13-induced VSMC proliferation and atherosclerotic lesions in apolipoprotein E knockout (ApoE-/-) mice. Apelin-13 enhances human aortic VSMC proliferation and proliferative regulator proliferating cell nuclear antigen expression in dose and time-dependent manner, while is abolished by APJ antagonist F13A. We observe the engulfment of damage mitochondria by autophagosomes (mitophagy) of human aortic VSMC in apelin-13 stimulation. Mechanistically, apelin-13 increases p-AMPKα and promotes mitophagic activity such as the LC3I to LC3II ratio, the increase of Beclin-1 level and the decrease of p62 level. Importantly, the expressions of PINK1, Parkin, VDAC1, and Tom20 are induced by apelin-13. Conversely, blockade of APJ by F13A abolishes these stimulatory effects. Human aortic VSMC transfected with AMPKα, PINK1, or Parkin and subjected to apelin-13 impairs mitophagy and prevents proliferation. Additional, apelin-13 not only increases the expression of Drp1 but also reduces the expressions of Mfn1, Mfn2, and OPA1. Remarkably, the mitochondrial division inhibitor-1(Mdivi-1), the pharmacological inhibition of Drp1, attenuates human aortic VSMC proliferation. Treatment of ApoE-/- mice with apelin-13 accelerates atherosclerotic lesions, increases p-AMPKα and mitophagy in aortic wall in vivo. Finally, PINK1-/- mutant mice with apelin-13 attenuates atherosclerotic lesions along with defective in mitophagy. PINK1/Parkin-mediated mitophagy promotes apelin-13-evoked human aortic VSMC proliferation by activating p-AMPKα and exacerbates the progression of atherosclerotic lesions.

Change in lipoprotein-associated phospholipase A2 and its association with cardiovascular outcomes in patients with acute coronary syndrome

Lipoprotein-associated phospholipase A2 (Lp-PLA2) probably plays an important role in the development of acute coronary syndrome (ACS). However, alterations of Lp-PLA2 levels during ACS and its association with cardiovascular outcome are unclear. Our aim was to investigate the change in Lp-PLA2 and its association with cardiovascular outcome in patients with ACS.A total of 79 patients with ACS came from the coronary care unit (CCU) between June 1, 2015 and August 31, 2016 in this longitudinal study. Serum levels of Lp-PLA2, troponin I, and creatine kinase isoenzymes MB (CK-MB) were measured at admission, on the first morning (D1), on the second morning of hospitalization (D2), and on the last second morning before discharge (D4). The patients were followed up till November 30, 2016. The primary outcomes were cardiovascular death and cardiovascular rehospitalization. Kaplan-Meier analysis and Cox proportional hazard models were used to identify risk factors for poor outcome in patients with ACS.All patients were followed up for 10.6 ± 4.7 months. The patients were divided into 2 groups according to the median of Lp-PLA2: lower Lp-PLA2 group and higher Lp-PLA2 group. Elevated levels of Lp-PLA2 significantly decreased during the early phases of ACS in higher Lp-PLA2 group. And Lp-PLA2 level increased at first and then decreased in lower Lp-PLA2 group. Kaplan-Meier analysis showed that patients with elevated Lp-PLA2 had a lower cardiovascular event-free survival (log-rank χ = 4.736, P = .030) than those with lower Lp-PLA2. Cox regression analysis indicated that high Lp-PLA2 level (hazard ratio [HR] = 1.005, 95% confidence interval [CI] = 1.002-1.008, P = .003), time delay from symptom onset to admission (HR = 1.088, 95% CI = 1.038-1.139, P < .001) independently predicted cardiovascular event in patients with ACS after adjusting for potential confounders.Serum level of Lp-PLA2 altered considerably during the early phase of ACS and increased Lp-PLA2 independently predicted cardiovascular outcome in patients with ACS after adjustment for potential confounders.

The role of Lp-PLA2 and biochemistry parameters as potential biomarkers of coronary artery disease in Asian South-Indians: a case-control study

Background

Coronary artery disease (CAD) is the leading cause of death and disability worldwide. Lipoprotein associated phospholipase A₂ (Lp-PLA₂) is an emerging biomarker for inflammation that has shown association with CAD. Its significance in the Asian Indian population is not clearly known. We sought to compare the possible association of various biomarkers of atherosclerosis along with Lp-PLA₂, in symptomatic individuals with CAD vs. healthy controls in Asian South-Indians.

Methods

We conducted a cross-sectional case control study at three centers in a South Indian population. A total of 100 CAD patients with acute coronary syndrome (ACS), 100 age and gender matched healthy controls participated, of which, 166 subjects or 83 case-control pairs with complete data for both participants were identified for the statistical analysis. Lp-PLA₂ concentration and activity were measured using PLAC test and PLAC activity assay respectively (diaDexus Inc., San Francisco, CA, USA), while all other parameters were measured using standard commercially available kits.

Results

We enrolled a total of 200 subjects (mean age 50.7±9.6 years, 87.5% males). A total of 83 subjects completed the study in the CAD group (mean age 51 ±8.9 years, 85% males) and 83 subjects in the control group (mean age 50±8.9 years, 86.5% males). In the CAD group, Lp-PLA₂ concentration positively correlated with TC (ρ=0.19, P=0.02), non-HDL-C (ρ=0.20, P=0.02), Lp-PLA₂ activity (ρ=0.27, P=0.001) and Lp(a) (r=0.25, P=0.02). Lp-PLA₂ activity correlated positively with TC (ρ=0.28, P=0.001), LDL-C (ρ=0.30, P<0.001), non-HDL-C (ρ=0.35, P<0.001), ApoB (ρ=0.35, P<0.001) and negatively correlated to HDL-C (ρ=-0.24, P=0.004). Cox proportionality hazards model revealed Lp-PLA₂ concentration (β=0.006, SE =0.002, P=0.009) to have positive association with the event of CAD, while negative association was observed for ApoA1 (β=-0.06, SE =0.02, P=0.001). ROC analysis revealed that the highest quartile of Lp-PLA₂ concentration to have area under curve (AUC) of 0.80 (95% CI, 0.65-0.9; P<0.001) with cut off value of >427 ng/mL and ApoA1 with AUC of 0.78 (95% CI, 0.70-0.85; P<0.001) with cut off value of ≤129.6 mg/dL with the optimum balance of sensitivity and specificity.

Conclusions

In this study population, circulating plasma Lp-PLA₂ was found to be elevated in CAD group. ApoA1 showed negative association and Lp-PLA₂ concentration showed positive association with risk for CAD. In the highest quartile, Lp-PLA₂ concentration had the best diagnostic utility. Our results support the hypothesis that Lp-PLA₂ may be a potential risk marker for CAD in Asian Indians.