Lipid nutrition: "In silico" studies and undeveloped experiments

This review examines lipids and lipid-binding sites on proteins in relation to cardiovascular disease. Lipid nutrition involves food energy from ingested fatty acids plus fatty acids formed from excess ingested carbohydrate and protein. Non-esterified fatty acids (NEFA) and lipoproteins have many detailed attributes not evident in their names. Recognizing attributes of lipid-protein interactions decreases unexpected outcomes. Details of double bond position and configuration interacting with protein binding sites have unexpected consequences in acyltransferase and cell replication events. Highly unsaturated fatty acids (HUFA) have n-3 and n-6 motifs with documented differences in intensity of destabilizing positive feedback loops amplifying pathophysiology. However, actions of NEFA have been neglected relative to cholesterol, which is co-produced from excess food. Native low-density lipoproteins (LDL) bind to a high-affinity cell surface receptor which poorly recognizes biologically modified LDLs. NEFA increase negative charge of LDL and decrease its processing by "normal" receptors while increasing processing by "scavenger" receptors. A positive feedback loop in the recruitment of monocytes and macrophages amplifies chronic inflammatory pathophysiology. Computer tools combine multiple components in lipid nutrition and predict balance of energy and n-3:n-6 HUFA. The tools help design and execute precise clinical nutrition monitoring that either supports or disproves expectations.

The potential pathophysiological role of altered lipid metabolism and electronegative low-density lipoprotein (LDL) in non-alcoholic fatty liver disease and cardiovascular diseases

Non-alcoholic fatty liver disease (NAFLD) is an umbrella term for a range of conditions caused by a build-up of fat in the liver. It is usually seen in people who are overweight or obese. Increasingly common around the world, this disease is the most common chronic liver disease in the United States, affecting about a quarter of the population. Recently, the designation of NAFLD as 'metabolic dysfunction-associated fatty liver disease' (MAFLD) has been a subject of current debate. In this context, 'insulin resistance' is the underlying common and basic pathophysiological mechanism of metabolic dysfunction due to its association with obesity, type 2 diabetes mellitus (T2DM), metabolic syndrome, dyslipidemia and NAFLD. All these pathological conditions are among the metabolic risk factors for cardiovascular diseases, too. Also, due to the bidirectional causality between NAFLD and cardiovascular diseases, a liver-heart axis is suggested. Therefore, various factors such as insulin resistance as well as systemic inflammation, cytokines, oxidative stress, adipokines, hepatokines, genes and intestinal microbiota have been identified as possible pathogenic factors that play a role in the explanation of the complex NAFLD and cardiovascular risk relationship. Recent data and cumulative evidence show that electronegative low-density lipoprotein [LDL (-)/L5] cholesterol is a promising biomarker for complex organ interactions and diseases associated with liver-heart axis. In this mini review, we focus not only on recent data on NAFLD mechanisms, but also on the potential of the lipid mediator LDL (-)/L5 as a diagnostic and therapeutic target for liver-heart line diseases.

Electronegative LDL Induces M1 Polarization of Human Macrophages Through a LOX-1-Dependent Pathway

In response to environmental stimuli, monocytes undergo polarization into classically activated (M1) or alternatively activated (M2) states. M1 and M2 macrophages exert opposing pro- and anti-inflammatory properties, respectively. Electronegative low-density lipoprotein (LDL) (LDL(-)) is a naturally occurring mildly oxidized LDL found in the plasma of patients with hypercholesterolemia, diabetes, and acute myocardial infarction, and has been shown to involve in the pathogenesis of atherosclerosis. In this study, we examined the effects of LDL(-) on macrophage polarization and the involvement of lectin-like oxidized LDL receptor-1 (LOX-1) in this process. THP-1 macrophages were treated with native LDL (nLDL) or LDL(-), and then the expression of M1/M2-related surface markers and cytokines were evaluated. The results show that treatment with LDL(-) resulted in profound increase in proinflammatory cytokines, IL-1β, IL-6, and TNF-α, and M1-surface marker CD86; however, M2-related cytokines, IL-10 and TGF-β, and M2-surface marker CD206 were not changed by LDL(-). Untreated or nLDL-treated cells were used as control. LDL(-)-induced M1 polarization and secretion of proinflammatory cytokines were diminished in LOX-1 knockdown cells. Taken together, the results show that LDL(-) promotes differentiation of human monocytes to M1 macrophages through a LOX-1-dependent pathway, and explore the contribution of LDL(-) and LOX-1 to the development of chronic inflammation in atherosclerosis.

Role of apolipoprotein E in electronegative low-density lipoprotein-induced mitochondrial dysfunction in cardiomyocytes

OBJECTIVE

L5, a highly electronegative subtype of low-density lipoprotein (LDL), is likely associated with the development of atherosclerosis and cardiovascular diseases. Normal LDL is composed mainly of apolipoprotein (Apo) B, but L5 has additional proteins such as ApoE. We previously demonstrated that L5 induces endothelial cell senescence by increasing mitochondrial reactive oxygen species. In the present study, we examined the effect of L5 on mitochondrial function in cardiomyocytes.

METHODS

We used the Seahorse XF24 extracellular flux analyzer to examine the effect of L5 and its components on mitochondrial energy production. The effects of L5 on mitochondrial morphology were examined by immunofluorescence using MitoTracker Green FM and the corresponding probes in H9c2 cardiomyoblasts. Mitochondrial permeability was assessed by using a calcium-induced swelling assay with a voltage-dependent anion-selective channel (VDAC) inhibitor to determine VDAC-dependence both in vitro and in vivo. L5 without ApoE, referred to as △L5, was used to clarify the role of ApoE in L5-induced mitochondrial dysfunction.

RESULTS

L5 not only significantly decreased basal (P < 0.05) and maximal respiration (P < 0.01) but also reduced spare respiratory capacity (P < 0.01) in H9c2 cells. Additionally, L5 caused phosphorylation of Drp1 and mitochondrial fission. Recombinant ApoE mimicked the mitochondrial effects of L5, but △L5 did not cause similar effects. After entering cells, ApoE on L5 colocalized with mitochondrial VDAC and caused mitochondria swelling both in vitro and in vivo. This effect was also seen with recombinant ApoE but not △L5.

CONCLUSIONS

ApoE may play an important role in electronegative LDL-induced mitochondrial dysfunction through the opening of the mitochondrial permeability transition pore via the interaction of ApoE and VDAC.

Electronegative LDL: An Active Player in Atherogenesis or a By- Product of Atherosclerosis?

Low-density lipoproteins (LDLs) are the major plasma carriers of cholesterol. However, LDL particles must undergo various molecular modifications to promote the development of atherosclerotic lesions. Modified LDL can be generated by different mechanisms, but as a common trait, show an increased electronegative charge of the LDL particle. A subfraction of LDL with increased electronegative charge (LDL(-)), which can be isolated from blood, exhibits several pro-atherogenic characteristics. LDL(-) is heterogeneous, due to its multiple origins but is strongly related to the development of atherosclerosis. Nevertheless, the implication of LDL(-) in a broad array of pathologic conditions is complex and in some cases anti-atherogenic LDL(-) properties have been reported. In fact, several molecular modifications generating LDL(-) have been widely studied, but it remains unknown as to whether these different mechanisms are specific or common to different pathological disorders. In this review, we attempt to address these issues examining the most recent findings on the biology of LDL(-) and discussing the relationship between this LDL subfraction and the development of different diseases with increased cardiovascular risk. Finally, the review highlights the importance of minor apolipoproteins associated with LDL(-) which would play a crucial role in the different properties displayed by these modified LDL particles.

Sulfate-based lipids: Analysis of healthy human fluids and cell extracts

Sulfate-based lipids (SL) have been proposed as players in inflammation, immunity and infection. In spite of the many biochemical processes linked to SL, analysis on this class of lipids has only focused on specific SL sub-classes in individual fluids or cells leaving a range of additional SL in other biological samples unaccounted for. This study describes the mass spectrometry screening of SL in lipid extracts of human fluids (saliva, plasma, urine, seminal fluid) and primary human cells (RBC, neutrophils, fibroblasts and skin epidermal) using targeted precursor ion scanning (PIS) approach. The PIS 97 mass spectra reveal a wide diversity of SL including steroid sulfates, sulfoglycolipids and other unidentified SL, as well as metabolites such as taurines, sulfated polyphenols and hypurate conjugates. Semi-quantification of SL revealed that plasma exhibited the highest content of SL whereas seminal fluid and epithelial cells contained the highest sulphur to phosphorous (S/P) ratio. The complexity of biofluids and cells sulfateome presented in this study highlight the importance of expanding the panel of synthetic sulfate-based lipid standards. Also, the heterogenous distribution of SL provides evidence for the interplay of sulfotransferases/sulfatases, opening new avenues for biomarker discovery in oral health, cardiovascular, fertility and dermatology research areas.

Electronegative LDL induces MMP-9 and TIMP-1 release in monocytes through CD14 activation: Inhibitory effect of glycosaminoglycan sulodexide

OBJECTIVE

Electronegative LDL (LDL(-)) is involved in atherosclerosis through the activation of the TLR4/CD14 inflammatory pathway in monocytes. Matrix metalloproteinases (MMP) and their inhibitors (tissue inhibitors of metalloproteinase [TIMP]) are also crucially involved in atherosclerosis, but their modulation by LDL(-) has never been investigated. The aim of this study was to examine the ability of LDL(-) to release MMPs and TIMPs in human monocytes and to determine whether sulodexide (SDX), a glycosaminoglycan-based drug, was able to affect their secretion.

APPROACH AND RESULTS

Native LDL (LDL(+)) and LDL(-) separated by anion-exchange chromatography were added to THP1-CD14 monocytes in the presence or absence of SDX for 24 h. A panel of 9 MMPs and 4 TIMPs was analyzed in cell supernatants with multiplex immunoassays. The gelatinolytic activity of MMP-9 was assessed by gelatin zymography. LDL(-) stimulated the release of MMP-9 (13-fold) and TIMP-1 (4-fold) in THP1-CD14 monocytes, as well as the gelatinolytic activity of MMP-9. Co-incubation of monocytes with LDL(-) and SDX for 24 h significantly reduced both the release of MMP-9 and TIMP-1 and gelatinase activity. In THP1 cells not expressing CD14, no effect of LDL(-) on MMP-9 or TIMP-1 release was observed. The uptake of DiI-labeled LDL(-) was higher than that of DiI-LDL(+) in THP1-CD14 but not in THP1 cells. This increase was inhibited by SDX. Experiments in microtiter wells coated with SDX demonstrated a specific interaction of LDL(-) with SDX.

CONCLUSIONS

LDL(-) induced the release of MMP-9 and TIMP-1 in monocytes through CD14. SDX affects the ability of LDL(-) to promote TIMP-1 and MMP-9 release by its interaction with LDL(-).

One-Year Conservative Care Using Sodium Bicarbonate Supplementation Is Associated with a Decrease in Electronegative LDL in Chronic Kidney Disease Patients: A Pilot Study

Background

Chronic kidney disease (CKD) patients develop metabolic acidosis when approaching stages 3 and 4, a period in which accelerated atherogenesis may ensue. Studies in vitro show that low pH may increase low-density lipoprotein (LDL) oxidation, suggesting a role for chronic metabolic acidosis in atherosclerosis. The present study attempted to evaluate the effects of conservative care using oral sodium bicarbonate (NaHCO₃) supplementation on the electronegative LDL [LDL(-)], a minimally oxidized LDL, plasma levels in CKD patients.

Methods

Thirty-one CKD patients were followed by a multidisciplinary team during 15 months of care in which 1.0 mmol/kg/day oral NaHCO₃ supplementation was first given in the third month. Blood samples were collected 3 months before the initiation of oral NaHCO₃ supplementation (T1), at the time of the beginning of supplementation (T2), and thereafter, each 4 months (T3, T4 and T5) until month 15 of care. Blood parameters and LDL(-) were measured from these collections.

Results

After 12 months of conservative care, creatinine clearance (MDRD) was kept stable, and serum bicarbonate (HCO₃^-) increased from 20.5 ± 2.9 to 22.6 ± 1.1 mM (p < 0.003). LDL(-) plasma levels declined from 4.5 ± 3.3 to 2.1 ± 0.9 U/L (p < 0.007) after reaching mean serum HCO₃^- levels of 22.6 ± 1.1 mM.

Conclusions

Conservative care using oral NaHCO₃ supplementation was able to stabilize renal function and decrease serum levels of LDL(-), a modified proatherogenic lipoprotein, only when mean serum HCO₃^- levels approached 22 mM. This study constitutes evidence that alkali therapy, in addition to its beneficial effect on renal disease progression, might serve as a preventive strategy to attenuate atherogenesis in CKD patients.

Electronegative L5-LDL induces the production of G-CSF and GM-CSF in human macrophages through LOX-1 involving NF-κB and ERK2 activation

BACKGROUND AND AIMS

Circulating levels of granulocyte colony-stimulating factor (G-CSF) and granulocyte macrophage colony-stimulating factor (GM-CSF) are associated with the severity of acute myocardial infarction (AMI). However, what causes increases in G-CSF and GM-CSF is unclear. In this study, we investigated whether L5-low-density lipoprotein (LDL), a mildly oxidized LDL from AMI, can induce G-CSF and GM-CSF production in human macrophages.

METHODS

L1-LDL and L5-LDL were isolated through anion-exchange chromatography from AMI plasma. Human macrophages derived from THP-1 and peripheral blood mononuclear cells were treated with L1-LDL, L5-LDL, or copper-oxidized LDL (Cu-oxLDL) and G-CSF and GM-CSF protein levels in the medium were determined. In addition, the effects of L5-LDL on G-CSF and GM-CSF production were tested in lectin-type oxidized LDL receptor-1 (LOX-1), CD36, extracellular signal-regulated kinase (ERK) 1, and ERK2 knockdown THP-1 macrophages.

RESULTS

L5-LDL but not L1-LDL or Cu-oxLDL significantly induced production of G-CSF and GM-CSF in macrophages. In vitro oxidation of L1-LDL and L5-LDL altered their ability to induce G-CSF and GM-CSF, suggesting that the degree of oxidation is critical for the effects. Knockdown and antibody neutralization experiments suggested that the effects were caused by LOX-1. In addition, nuclear factor (NF)-κB and ERK1/2 inhibition resulted in marked reductions of L5-LDL-induced G-CSF and GM-CSF production. Moreover, knockdown of ERK2, but not ERK1, hindered L5-LDL-induced G-CSF and GM-CSF production.

CONCLUSIONS

The results indicate that L5-LDL, a naturally occurring mild oxidized LDL, induced G-CSF and GM-CSF production in human macrophages through LOX-1, ERK2, and NF-κB dependent pathways.

Increased inflammatory effect of electronegative LDL and decreased protection by HDL in type 2 diabetic patients

BACKGROUND AND AIMS

Type 2 diabetic patients have an increased proportion of electronegative low-density lipoprotein (LDL(-)), an inflammatory LDL subfraction present in blood, and dysfunctional high-density lipoprotein (HDL). We aimed at examining the inflammatory effect of LDL(-) on monocytes and the counteracting effect of HDL in the context of type 2 diabetes.

METHODS

This was a cross-sectional study in which the population comprised 3 groups (n = 12 in each group): type 2 diabetic patients with good glycaemic control (GC-T2DM patients), type 2 diabetic patients with poor glycaemic control (PC-T2DM), and a control group. Total LDL, HDL, and monocytes were isolated from plasma of these subjects. LDL(-) was isolated from total LDL by anion-exchange chromatography. LDL(-) from the three groups of subjects was added to monocytes in the presence or absence of HDL, and cytokines released by monocytes were quantified by ELISA.

RESULTS

LDL(-) proportion and plasma inflammatory markers were increased in PC-T2DM patients. LDL(-) from PC-T2DM patients induced the highest IL1β, IL6, and IL10 release in monocytes compared to LDL(-) from GC-T2DM and healthy subjects, and presented the highest content of non-esterified fatty acids (NEFA). In turn, HDL from PC-T2DM patients showed the lowest ability to inhibit LDL(-)-induced cytokine release in parallel to an impaired ability to decrease NEFA content in LDL(-).

CONCLUSIONS

Our findings show an imbalance in the pro- and anti-inflammatory effects of lipoproteins from T2DM patients, particularly in PC-T2DM.

Effect of chocolate and mate tea on the lipid profile of individuals with HIV/AIDS on antiretroviral therapy: A clinical trial

OBJECTIVE

HIV/AIDS is generally associated with dyslipidemia and oxidative imbalance, which are caused by the infection itself and by antiretroviral therapy (ART). The flavonoids, found in cocoa and yerba mate, have antioxidant and hypolipidemic properties. The aim of this study was to evaluate the effects of the consumption of dark chocolate and mate tea on the lipid profiles of individuals with HIV/AIDS who are undergoing ART.

METHODS

A randomized, double-blind, placebo-controlled crossover clinical trial was conducted with 92 patients receiving ART for ≥6 mo and with viral suppression. The participants were randomized to receive either 65 g of chocolate (with 2148 mg polyphenols) or placebo chocolate (without polyphenols) or 3 g of mate tea (with 107 mg total phenols and 84.24 mg chlorogenic acid) or placebo mate (without polyphenols) for 15 d each, separated by a washout period of 15 d. The lipid profile, including determination of electronegative low-density lipoprotein, was determined after each intervention. The data were analyzed by analysis of variance using the pkcross procedure of the Stata 11.0 software.

RESULTS

Analysis of variance revealed a significant overall difference in mean high-density lipoprotein cholesterol (HDL-C) between all supplements (P = 0.047). Using the paired t test, the effect was attributed to the consumption of dark chocolate (P = 0.046). The other parameters investigated were not improved.

CONCLUSIONS

The consumption of dark chocolate for 15 d improved HDL-C concentrations of individuals with HIV/AIDS undergoing ART, possibly due to the presence of fatty acids (stearic acid), polyphenols, and theobromine. This fact is important for the cardiovascular protection of these individuals.

A nanoformulation containing a scFv reactive to electronegative LDL inhibits atherosclerosis in LDL receptor knockout mice

Atherosclerosis is a chronic inflammatory disease responsible for the majority of cases of myocardial infarction and ischemic stroke. The electronegative low-density lipoprotein, a modified subfraction of native LDL, is pro-inflammatory and plays an important role in atherogenesis. To investigate the effects of a nanoformulation (scFv anti-LDL(-)-MCMN-Zn) containing a scFv reactive to LDL(-) on the inhibition of atherosclerosis, its toxicity was evaluated in vitro and in vivo and further it was also administered weekly to LDL receptor knockout mice. The scFv anti-LDL(-)-MCMN-Zn nanoformulation did not induce cell death in RAW 264.7 macrophages and HUVECs. The 5mg/kg dose of scFv anti-LDL(-)-MCMN-Zn did not cause any typical signs of toxicity and it was chosen for the evaluation of its atheroprotective effect in Ldlr(-/-) mice. This nanoformulation significantly decreased the atherosclerotic lesion area at the aortic sinus, compared with that in untreated mice. In addition, the Il1b mRNA expression and CD14 protein expression were downregulated in the atherosclerotic lesions at the aortic arch of Ldlr(-/-) mice treated with scFv anti-LDL(-)-MCMN-Zn. Thus, the scFv anti-LDL(-)-MCMN-Zn nanoformulation inhibited the progression of atherosclerotic lesions, indicating its potential use in a future therapeutic strategy for atherosclerosis.

Inflammatory intracellular pathways activated by electronegative LDL in monocytes

AIMS

Electronegative LDL (LDL(-)) is a plasma LDL subfraction that induces cytokine release in monocytes through toll-like receptor 4 (TLR4) activation. However, the intracellular pathways induced by LDL(-) downstream TLR4 activation are unknown. We aimed to identify the pathways activated by LDL(-) leading to cytokine release in monocytes.

METHODS AND RESULTS

We determined LDL(-)-induced activation of several intracellular kinases in protein extracts from monocytes using a multikinase ELISA array. LDL(-) induced higher p38 mitogen-activated protein kinase (MAPK) phosphorylation than native LDL. This was corroborated by a specific cell-based assay and it was dependent on TLR4 and phosphoinositide 3-kinase (PI3k)/Akt pathway. P38 MAPK activation was involved in cytokine release promoted by LDL(-). A specific ELISA showed that LDL(-) activated cAMP response-element binding (CREB) in a p38 MAPK dependent manner. P38 MAPK was also involved in the nuclear factor kappa-B (NF-kB) and activating protein-1 (AP-1) activation by LDL(-). We found that NF-kB, AP-1 and CREB inhibitors decreased LDL(-)-induced cytokine release, mainly on MCP1, IL6 and IL10 release, respectively.

CONCLUSIONS

LDL(-) promotes p38 MAPK phosphorylation through TLR4 and PI3k/Akt pathways. Phosphorylation of p38 MAPK is involved in NF-kB, AP-1 and CREB activation, leading to LDL(-)-induced cytokine release in monocytes.

Thermal stability of human plasma electronegative low-density lipoprotein: A paradoxical behavior of low-density lipoprotein aggregation

Low-density lipoprotein (LDL) aggregation is central in triggering atherogenesis. A minor fraction of electronegative plasma LDL, termed LDL(-), plays a special role in atherogenesis. To better understand this role, we analyzed the kinetics of aggregation, fusion and disintegration of human LDL and its fractions, LDL(+) and LDL(-). Thermal denaturation of LDL was monitored by spectroscopy and electron microscopy. Initially, LDL(-) aggregated and fused faster than LDL(+), but later the order reversed. Most LDL(+) disintegrated and precipitated upon prolonged heating. In contrast, LDL(-) partially retained lipoprotein morphology and formed soluble aggregates. Biochemical analysis of all fractions showed no significant degradation of major lipids, mild phospholipid oxidation, and an increase in non-esterified fatty acid (NEFA) upon thermal denaturation. The main baseline difference between LDL subfractions was higher content of NEFA in LDL(-). Since NEFA promote lipoprotein fusion, increased NEFA content can explain rapid initial aggregation and fusion of LDL(-) but not its resistance to extensive disintegration. Partial hydrolysis of apoB upon heating was similar in LDL subfractions, suggesting that minor proteins importantly modulate LDL disintegration. Unlike LDL(+), LDL(-) contains small amounts of apoA-I and apoJ. Addition of exogenous apoA-I to LDL(+) hampered lipoprotein aggregation, fusion and precipitation, while depletion of endogenous apoJ had an opposite effect. Therefore, the initial rapid aggregation of LDL(-) is apparently counterbalanced by the stabilizing effects of minor proteins such as apoA-I and apoJ. These results help identify key determinants for LDL aggregation, fusion and coalescence into lipid droplets in vivo.

Electronegative LDL induces priming and inflammasome activation leading to IL-1β release in human monocytes and macrophages

BACKGROUND

Electronegative LDL (LDL(−)), a modified LDL fraction found in blood, induces the release of inflammatory mediators in endothelial cells and leukocytes. However, the inflammatory pathways activated by LDL(−) have not been fully defined. We aim to study whether LDL(−) induced release of the first-wave proinflammatory IL-1β in monocytes and monocyte-derived macrophages (MDM) and the mechanisms involved.

METHODS

LDL(−) was isolated from total LDL by anion exchange chromatography. Monocytes and MDM were isolated from healthy donors and stimulated with LDL(+) and LDL(−) (100 mg apoB/L).

RESULTS

In monocytes, LDL(−) promoted IL-1β release in a time-dependent manner, obtaining at 20 h-incubation the double of IL-1β release induced by LDL(−) than by native LDL. LDL(−)-induced IL-1β release involved activation of the CD14-TLR4 receptor complex. LDL(−) induced priming, the first step of IL-1β release, since it increased the transcription of pro-IL-1β (8-fold) and NLRP3 (3-fold) compared to native LDL. Several findings show that LDL(−) induced inflammasome activation, the second step necessary for IL-1β release. Preincubation of monocytes with K+ channel inhibitors decreased LDL(−)-induced IL-1β release. LDL(−) induced formation of the NLRP3-ASC complex. LDL(−) triggered 2-fold caspase-1 activation compared to native LDL and IL-1β release was strongly diminished in the presence of the caspase-1 inhibitor Z-YVAD. In MDM, LDL(−) promoted IL-1β release, which was also associated with caspase-1 activation.

CONCLUSIONS

LDL(−) promotes release of biologically active IL-1β in monocytes and MDM by induction of the two steps involved: priming and NLRP3 inflammasome activation.

SIGNIFICANCE

By IL-1β release, LDL(−) could regulate inflammation in atherosclerosis.

CD14 and TLR4 mediate cytokine release promoted by electronegative LDL in monocytes

AIMS

Electronegative LDL (LDL(-)), a minor modified LDL present in the circulation, induces cytokine release in monocytes. We aimed to determine the role of the receptor CD14 and toll-like receptors 2 and 4 (TLR2, TLR4) in the inflammatory action promoted by LDL(-) in human monocytes.

METHODS AND RESULTS

Monocytes were preincubated with antibodies to neutralize CD14, TLR2 and TLR4. The release of monocyte chemoattractant protein 1 (MCP1), and interleukin 6 and 10 (IL6 and IL10) promoted by LDL(-) was inhibited 70-80% by antiCD14 and antiTLR4, and 15-25% by antiTLR2. The involvement of CD14 and TLR4 was confirmed by gene silencing experiments. The human monocytic THP1 cell line overexpressing CD14 released more cytokines in response to LDL(-) than the same THP1 cell line without expressing CD14. VIPER, a specific inhibitor of the TLR4 signaling pathway, blocked 75-90% the cytokine release promoted by LDL(-). Cell binding experiments showed that monocytes preincubated with neutralizing antibodies presented lesser LDL(-) binding than non-preincubated monocytes The inhibitory capacity was antiCD14>antiTLR4>>antiTLR2. Cell-free experiments performed in CD14-coated microtiter wells confirmed that CD14 was involved in LDL(-) binding. When LDL(-) and lipopolysaccharide (LPS) were added simultaneously to monocytes, cytokine release was similar to that promoted by LDL(-) alone. Binding experiments showed that LDL(-) and LPS competed for binding to monocytes and to CD14 coated-wells.

CONCLUSIONS

CD14 and TLR4 mediate cytokine release induced by LDL(-) in human monocytes. The cross-competition between LPS and LDL(-) for the same receptors could be a counteracting action of LDL(-) in inflammatory situations.