ABSTRACT
AIMS: Maslinic acid (MA) is a naturally occurring pentacyclic triterpene known to exert cardioprotective effects. This study aims to investigate the involvement of nuclear factor erythroid 2-related factor 2 (Nrf2) for MA-mediated anti-inflammatory effects in atheroma pathogenesis in vitro, including evaluation of tumor necrosis factor-alpha (TNF-α)-induced monocyte recruitment, oxidized low-density lipoprotein (oxLDL)-induced scavenger receptors expression, and nuclear factor-kappa B (NF-ĸB) activity in human umbilical vein endothelial cells (HUVECS) and human acute monocytic leukemia cell line (THP-1) macrophages. MATERIALS AND METHODS: An in vitro monocyte recruitment model utilizing THP-1 and HUVECs was developed to evaluate TNF-α-induced monocyte adhesion and trans-endothelial migration. To study the role of Nrf2 for MA-mediated anti-inflammatory effects, Nrf2 inhibitor ML385 was used as the pharmacological inhibitor. The expression of Nrf2, monocyte chemoattractant protein-1 (MCP-1), vascular cell adhesion molecule 1 (VCAM-1), cluster of differentiation 36 (CD36), and scavenger receptor type A (SR-A) in HUVECs and THP-1 macrophages were investigated using RT-qPCR and Western blotting. The NF-κB activity was determined using NF-κB (p65) Transcription Factor Assay Kit. KEY FINDINGS: The results showed opposing effects of MA on Nrf2 expression in HUVECs and THP-1 macrophages. MA suppressed TNF-α-induced Nrf2 expression in HUVECs, but enhanced its expression in THP-1 macrophages. Combined effects of MA and ML385 suppressed MCP-1, VCAM-1, and SR-A expressions. Intriguingly, at the protein level, ML385 selectively inhibited SR-A but enhanced CD36 expression. Meanwhile, ML385 further enhanced MA-mediated inhibition of NF-κB activity in HUVECs. This effect, however, was not observed in THP-1 macrophages. SIGNIFICANCE: MA attenuated foam cell formation by suppressing VCAM-1, MCP-1, and SR-A expression, as well as NF-κB activity, possibly through Nrf2 inhibition. The involvement of Nrf2 for MA-mediated anti-inflammatory effects however differs between HUVECs and macrophages. Future investigations are warranted for a detailed evaluation of the contributing roles of Nrf2 in foam cells formation.
Subject(s)
Anti-Inflammatory Agents/pharmacology , NF-E2-Related Factor 2/metabolism , Plaque, Atherosclerotic/metabolism , Triterpenes/pharmacology , Tumor Necrosis Factor-alpha/metabolism , Human Umbilical Vein Endothelial Cells , Humans , Macrophages/drug effects , Macrophages/metabolism , Macrophages/pathology , Monocytes/drug effects , Monocytes/metabolism , Monocytes/pathology , NF-E2-Related Factor 2/analysis , Plaque, Atherosclerotic/drug therapy , Plaque, Atherosclerotic/pathology , THP-1 Cells , Tumor Necrosis Factor-alpha/analysisABSTRACT
The transformation of macrophages to foam cells is a critical component in atherosclerotic lesion formation. Maslinic acid (MA), a novel natural pentacyclic triterpene, has cardioprotective and anti-inflammatory properties. It is hypothesized that MA can suppress monocyte recruitment to endothelial cells and inhibit macrophage foam cells formation. Previous study shows that MA inhibits inflammatory effects induced by sPLA2-IIA, including foam cells formation. This study elucidates the regulatory effect of MA in monocyte recruitment, macrophage lipid accumulation and cholesterol efflux. Our findings demonstrate that MA inhibits THP-1 monocyte adhesion to HUVEC cells in a TNFα-dependent and independent manner, but it induces trans-endothelial migration marginally at low concentration. MA down-regulates both gene and protein expression on VCAM-1 and MCP-1 in HUVECs. We further showed that MA suppresses macrophage foam cells formation, as indicated from the Oil-Red-O staining and flow cytometric analysis of intracellular lipids accumulation. The effects observed may be attributed to the antioxidant properties of MA where it was shown to suppress CuSO4-induced lipid peroxidation. MA inhibits scavenger receptors SR-A and CD36 expression while enhancing cholesterol efflux. MA enhances cholesterol efflux transporters ABCA1 and ABCG1 genes expression marginally without inducing its protein expression. In this study, MA was shown to target important steps that contribute to foam cell formation, including its ability in reducing monocytes adhesion to endothelial cells and LDL peroxidation, down-regulating scavenger receptors expression as well as enhancing cholesterol efflux, which might be of great importance in the context of atherosclerosis prevention and treatment.
Subject(s)
Antioxidants/pharmacology , Atherosclerosis/drug therapy , Cell Adhesion/drug effects , Cholesterol/metabolism , Foam Cells/drug effects , Human Umbilical Vein Endothelial Cells/drug effects , Monocytes/drug effects , Triterpenes/pharmacology , ATP Binding Cassette Transporter 1/genetics , ATP Binding Cassette Transporter 1/metabolism , ATP Binding Cassette Transporter, Subfamily G, Member 1/genetics , ATP Binding Cassette Transporter, Subfamily G, Member 1/metabolism , Atherosclerosis/genetics , Atherosclerosis/metabolism , Chemokine CCL2/genetics , Chemokine CCL2/metabolism , Foam Cells/metabolism , Human Umbilical Vein Endothelial Cells/metabolism , Humans , Lipid Peroxidation/drug effects , Monocytes/metabolism , THP-1 Cells , Transendothelial and Transepithelial Migration/drug effects , Vascular Cell Adhesion Molecule-1/genetics , Vascular Cell Adhesion Molecule-1/metabolismABSTRACT
Cardiovascular diseases (CVDs) are closely linked to cellular oxidative stress and inflammation. This may be resulted from the imbalance generation of reactive oxygen species and its role in promoting inflammation, thereby contributing to endothelial dysfunction and cardiovascular complications. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that plays a significant role in regulating expression of antioxidant and cytoprotective enzymes in response to oxidative stress. Natural products have emerged as a potential source of bioactive compounds which have shown to protect against atherogenesis development by activating Nrf2 signaling. This review aims to provide a comprehensive summary of the published data on the function, regulation and activation of Nrf2 as well as the molecular mechanisms of natural products in regulating Nrf2 signaling. The beneficial effects of using natural bioactive compounds as a promising therapeutic approach for the prevention and treatment of CVDs are reviewed.
ABSTRACT
Secretory phospholipase A2-IIA (sPLA2-IIA) is one of the key enzymes causing lipoprotein modification and vascular inflammation. Maslinic acid is a pentacyclic triterpene which has potential cardioprotective and anti-inflammatory properties. Recent research showed that maslinic acid interacts with sPLA2-IIA and inhibits sPLA2-IIA-mediated monocyte differentiation and migration. This study elucidates the potential of maslinic acid in modulating sPLA2-IIA-mediated inflammatory effects in THP-1 macrophages. We showed that maslinic acid inhibits sPLA2-IIA-mediated LDL modification and suppressed foam cell formation. Further analysis revealed that sPLA2-IIA only induced modest LDL oxidation and that inhibitory effect of maslinic acid on sPLA2-IIA-mediated foam cells formation occurred independently of its anti-oxidative properties. Interestingly, maslinic acid was also found to significantly reduce lipid accumulation observed in macrophages treated with sPLA2-IIA only. Flow cytometry analysis demonstrated that the effect observed in maslinic acid might be contributed in part by suppressing sPLA2-IIA-induced endocytic activity, thereby inhibiting LDL uptake. The study further showed that maslinic acid suppresses sPLA2-IIA-induced up-regulation of PGE2 levels while having no effects on COX-2 activity. Other pro-inflammatory mediators TNF-a and IL-6 were not induced in sPLA2-IIA-treated THP-1 macrophages. The findings of this study showed that maslinic acid inhibit inflammatory effects induced by sPLA2-IIA, including foam cells formation and PGE2 production.
Subject(s)
Cardiotonic Agents/administration & dosage , Group IV Phospholipases A2/genetics , Inflammation/drug therapy , Triterpenes/administration & dosage , Animals , Foam Cells/drug effects , Foam Cells/pathology , Gene Expression Regulation/drug effects , Group IV Phospholipases A2/antagonists & inhibitors , Group IV Phospholipases A2/metabolism , Humans , Inflammation/genetics , Inflammation/pathology , Interleukin-6/genetics , Lipoproteins, LDL/genetics , Macrophages/drug effects , Macrophages/pathology , Tumor Necrosis Factor-alpha/geneticsABSTRACT
Oxidative stress is an important risk factor contributing to the pathogenesis of cardiovascular diseases. Oxidative stress that results from excessive reactive oxygen species (ROS) production accounts for impaired endothelial function, a process which promotes atherosclerotic lesion or fatty streaks formation (foam cells). Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor involved in cellular redox homeostasis. Upon exposure to oxidative stress, Nrf2 is dissociated from its inhibitor Keap-1 and translocated into the nucleus, where it results in the transcriptional activation of cell defense genes. Nrf2 has been demonstrated to be involved in the protection against foam cells formation by regulating the expression of antioxidant proteins (HO-1, Prxs, and GPx1), ATP-binding cassette (ABC) efflux transporters (ABCA1 and ABCG1) and scavenger receptors (scavenger receptor class B (CD36), scavenger receptor class A (SR-A) and lectin-type oxidized LDL receptor (LOX-1)). However, Nrf2 has also been reported to exhibit pro-atherogenic effects. A better understanding on the mechanism of Nrf2 in oxidative stress-induced cardiac injury, as well as the regulation of cholesterol uptake and efflux, are required before it can serve as a novel therapeutic target for cardiovascular diseases prevention and treatment.
