Current cell-based assays for determining the functional properties of high-density lipoproteins (HDL) have limitations. We report here the development of a new, robust fluorometric cell-free biochemical assay that measures HDL lipid peroxidation (HDLox) based on the oxidation of the fluorochrome Amplex Red. HDLox correlated with previously validated cell-based (r = 0.47, p<0.001) and cell-free assays (r = 0.46, p<0.001). HDLox distinguished dysfunctional HDL in established animal models of atherosclerosis and Human Immunodeficiency Virus (HIV) patients. Using an immunoaffinity method for capturing HDL, we demonstrate the utility of this novel assay for measuring HDLox in a high throughput format. Furthermore, HDLox correlated significantly with measures of cardiovascular diseases including carotid intima media thickness (r = 0.35, p<0.01) and subendocardial viability ratio (r = −0.21, p = 0.05) and physiological parameters such as metabolic and anthropometric parameters (p<0.05). In conclusion, we report the development of a new fluorometric method that offers a reproducible and rapid means for determining HDL function/quality that is suitable for high throughput implementation.
N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL) is a quorum-sensing molecule produced by gram-negative microbial pathogens such as Pseudomonas aeruginosa (PAO1). 3OC12-HSL is involved in the regulation of bacterial virulence factors and also alters the function of the host immune cells. Others and we have previously shown that paraoxonase 2 (PON2), a member of the paraoxonase gene family expressed in immune cells, hydrolyzes 3OC12-HSL. In this study, we examined i) whether macrophage PON2 participates in 3OC12-HSL hydrolysis, ii) the effect of PON2 deficiency in acute PAO1 infection in mice and iii) the effect of 3OC12-HSL on PON2 deficient (PON2-def) macrophages. When compared to wild type macrophages, both intact cells and membrane-enriched protein lysates obtained from PON2-def macrophages show a marked impairment in their ability to hydrolyze 3OC12-HSL. PON2 expression (message and protein) is not altered in response to 3OC12-HSL in macrophages. 3OC12-HSL treated PON2-def macrophages showed i) an increase in ER stress and oxidative stress, ii) defective phosphatidylinositol 3-kinase (PI3 kinase)/AKT activation, and iii) reduced phagocytosis function. Moreover, the nitration to phosphorylation ratio of Tyr458 in p85 protein, the regulatory subunit of PI3-kinase that has been correlated with the phagocytosis function of macrophages, was increased in PON2-def macrophages. Antioxidant treatment reversed the effects of PON2 deficiency in macrophage phagocytosis function. Furthermore, following administration of 1.6×107CFU of PAO1, bacterial clearance was significantly reduced in the lungs (5.7 fold), liver (2.5 fold), and spleen (14.8 fold) of PON2-def mice when compared to wild type mice. Our results suggest that PON2 plays an important role in innate immune defense against PAO1 infection.
Paraoxonase 2; Pseudomonas aeruginosa; Quorum sensing; Mitochondrial oxidative stress; Endoplasmic reticulum stress
South Asian immigrants (SAIs) in the US exhibit higher prevalence of coronary artery disease (CAD) and its risk factors compared with other ethnic populations. Conventional CAD risk factors do not explain the excess CAD risk; therefore there is a need to identify other markers that can predict future risk of CAD in high-risk SAIs. The objective of the current study is to assess the presence of sub-clinical CAD using common carotid artery intima-media thickness (CCA-IMT), and its association with metabolic syndrome (MS) and pro-inflammatory/dysfunctional HDL (Dys-HDL).
Material and methods
A community-based study was conducted on 130 first generation SAIs aged 35–65 years. Dys-HDL was determined using the HDL inflammatory index. Analysis was completed using logistic regression and Fisher's exact test.
Sub-clinical CAD using CCA-IMT ≥ 0.8 mm (as a surrogate marker) was seen in 31.46%. Age and gender adjusted CCA-IMT was significantly associated with type 2 diabetes (p = 0.008), hypertension (p = 0.012), high-sensitivity C-reactive protein (p < 0.001) and homocysteine (p = 0.051). Both the presence of MS and Dys-HDL was significantly correlated with CCA-IMT, even after age and gender adjustment. The odds of having Dys-HDL with CCA-IMT were 5 times (95% CI: 1.68, 10.78).
There is a need to explore and understand non-traditional CAD risk factors with a special focus on Dys-HDL, knowing that SAIs have low HDL levels. This information will not only help to stratify high-risk asymptomatic SAI groups, but will also be useful from a disease management point of view.
coronary artery disease; risk factors; common carotid artery intima media thickness; South Asians; dysfunctional high-density lipoprotein
Loss-of-function mutations in DJ-1 (PARK7) gene account for about 1% of all familial Parkinson's disease (PD). While its physiological function(s) are not completely clear, DJ-1 protects neurons against oxidative stress in both in vitro and in vivo models of PD. The molecular mechanism(s) through which DJ-1 alleviates oxidative stress-mediated damage remains elusive. In this study, we identified Paraoxonase-2 (PON2) as an interacting target of DJ-1. PON2 activity is elevated in response to oxidative stress and DJ-1 is crucial for this response. Importantly, we showed that PON2 deficiency hypersensitizes neurons to oxidative stress induced by MPP+ (1-methyl-4-phenylpyridinium). Conversely, over-expression of PON2 protects neurons in this death paradigm. Interestingly, PON2 effectively rescues DJ-1 deficiency-mediated hypersensitivity to oxidative stress. Taken together, our data suggest a model by which DJ-1 exerts its antioxidant activities, at least partly through regulation of PON2.
To assess the prevalence of blindness and visual impairment (VI), their associated causes and underlying risk factors in three tribal areas of Andhra Pradesh, India and compare this data in conjunction with data from other countries with low and middle income settings.
Using a validated Rapid Assessment of Avoidable Blindness methodology, a two stage sampling survey was performed in these areas involving probability proportionate to size sampling and compact segment sampling methods. Blindness, VI and severe visual impairment (SVI) were defined as per the WHO guidelines and Indian definitions.
Based on a prior enumeration, 7281 (97.1%) subjects were enrolled (mean age = 61.0+/−7.9 years). Based on the presenting visual acuity (PVA), the prevalences of VI, SVI and blindness were 16.9% (95% CI: 15.7–18.1), 2.9% (95% CI: 2.5–3.4), and 2.3% (95% CI: 1.9–2.7), respectively. When based on the Pinhole corrected visual acuity (PCVA), the prevalences were lower in VI (6.2%, 95% CI: 5.4–6.9), SVI (1.5%, 95% CI: 1.2–1.9) and blindness (2.1%, 95% CI: 1.7–2.5). Refractive error was the major cause of VI (71.4%), whereas, cataract was the major cause of SVI and blindness (70.3%). Based on the PVA, the odds ratio (OR) of blindness increased in the age groups of 60–69 years (OR = 3.8, 95% CI: 2.8, 5.1), 70–79 years (OR = 10.6, 95% CI: 7.2, 15.5) and 80 years and above (OR = 30.7, 95% CI: 19.2, 49). The ORs were relatively higher in females (OR = 1.3, 95% CI: 1.0, 1.6) and illiterate subjects (OR = 4.3, 95% CI: 2.2, 8.5), but lower in those wearing glasses (OR = 0.2, 95% CI: 0.1, 0.4).
This is perhaps the first study to assess the prevalence of blindness and VI in these tribal regions and the majority of the causes of blindness and SVI were avoidable (88.5%). These findings may be useful for planning eye care services in these underserved regions.
Follistatin (Fst) functions to bind and neutralize the activity of members of the transforming growth factor-β superfamily. Fst has a well-established role in skeletal muscle, but we detected significant Fst expression levels in interscapular brown and subcutaneous white adipose tissue, and further investigated its role in adipocyte biology. Fst expression was induced during adipogenic differentiation of mouse brown preadipocytes and mouse embryonic fibroblasts (MEFs) as well as in cold-induced brown adipose tissue from mice. In differentiated MEFs from Fst KO mice, the induction of brown adipocyte proteins including uncoupling protein 1, PR domain containing 16, and PPAR gamma coactivator-1α was attenuated, but could be rescued by treatment with recombinant FST. Furthermore, Fst enhanced thermogenic gene expression in differentiated mouse brown adipocytes and MEF cultures from both WT and Fst KO groups, suggesting that Fst produced by adipocytes may act in a paracrine manner. Our microarray gene expression profiling of WT and Fst KO MEFs during adipogenic differentiation identified several genes implicated in lipid and energy metabolism that were significantly downregulated in Fst KO MEFs. Furthermore, Fst treatment significantly increases cellular respiration in Fst-deficient cells. Our results implicate a novel role of Fst in the induction of brown adipocyte character and regulation of energy metabolism.
mouse embryonic fibroblast; myostatin; brown fat; energy expenditure; uncoupling protein 1; mitochondria
Paraoxonase 2 deficiency (PON2-def) alters mitochondrial function and exacerbates the development of atherosclerosis in mice. PON2 overexpression protects against ER stress in cell culture. In this paper, we examined the role of PON2 in the unexplored link between ER stress and mitochondrial dysfunction and tested whether restoration of PON2 in macrophages is sufficient to reduce aggravated atherosclerosis in PON2-def/apoE−/− mice on a Western diet. ER stress response genes, intracellular calcium levels, and apoptotic nuclei were significantly elevated in PON2-def/apoE−/− macrophages compared to apoE−/− macrophages in response to ER stressors, but not at the basal level. In contrast, PON2-def/apoE−/− macrophages exhibited greater mitochondrial stress at the basal level, which was further worsened in response to ER stressors. There was no difference in ER stress response genes and apoptotic nuclei between apoE−/− and PON2-def/apoE−/− macrophages when pretreated with xestospongin (which blocks the release of calcium from ER) suggesting that PON2 modulates cell survival and ER stress by maintaining calcium homeostasis. Treatment with a mitochondrial calcium uptake inhibitor, RU360, attenuated ER stressor mediated mitochondrial dysfunction in PON2-def/apoE−/− macrophages. CHOP expression (ER stress marker) and apoptotic nuclei were significantly higher in aortic lesions of PON2-def/apoE−/− mice compared to apoE−/− mice fed a Western diet. Restoration of PON2 in macrophage reduced ER stress, mitochondrial dysfunction and apoptosis in response to ER stressors. Furthermore, restoration of PON2 in macrophages reduced lesional apoptosis and atherosclerosis in PON2-def/apoE−/− mice on a Western diet. Our data suggest that macrophage PON2 modulates mechanisms that link ER stress, mitochondrial dysfunction and the development of atherosclerosis.
Paraoxonase 2; Mitochondria; Endoplasmic reticulum; Macrophages; Oxidative stress
Oxidized phospholipids are found in the vasculature of animal models of atherosclerosis, in human atherosclerotic lesions, and in other inflammatory diseases. Oxidized phospholipids cause vascular and nonvascular cells to initiate an inflammatory reaction. Metabolites of arachidonic acid, such as 12-hydroxyeicosatetraenoic acid, can mimic some of the inflammatory properties of oxidized phospholipids. In vitro and in vivo normal high-density lipoprotein (HDL), normal apolipoprotein A-I, and apolipoprotein A-I mimetic peptides, each likely acting in a different manner, prevent the inflammatory reaction characteristic of atherosclerosis, and this is associated with decreased levels of oxidized lipids in tissues and cells. HDL from animal models of atherosclerosis or from humans with atherosclerosis or from humans or animals with other chronic inflammatory diseases does not prevent the inflammatory reaction characteristic of atherosclerosis and may even enhance the inflammatory reaction. In mice and perhaps humans, ≈30% of the steady-state plasma HDL-cholesterol pool is derived from the small intestine. The metabolism of phospholipids by gut bacteria has been recently implicated in atherosclerosis in both mice and humans. Studies with apolipoprotein A-I mimetic peptides suggest that the small intestine is a major tissue regulating systemic inflammation in mouse models of atherosclerosis and may be important for determining the functionality of HDL.
apolipoprotein A-I; apolipoprotein A-I mimetic peptides; high-density lipoprotein; hydroxyeicosatetraenoic acid; hydroxyoctadecadienoic acid; lipoproteins; oxidized lipids; small intestine
Hepatic glucose metabolism is strongly influenced by oxidative stress and pro-inflammatory stimuli. PON2 (paraoxonase 2), an enzyme with undefined antioxidant properties, protects against atherosclerosis. PON2-deficient (PON2-def) mice have elevated hepatic oxidative stress coupled with an exacerbated inflammatory response from PON2-deficient macrophages. In the present paper, we demonstrate that PON2 deficiency is associated with inhibitory insulin-mediated phosphorylation of hepatic IRS-1 (insulin receptor substrate-1). Unexpectedly, we observed a marked improvement in the hepatic IRS-1 phosphorylation state in PON2-def/apoE (apolipoprotein E)−/− mice, relative to apoE−/− mice. Factors secreted from activated macrophage cultures derived from PON2-def and PON2-def/apoE−/− mice are sufficient to modulate insulin signalling in cultured hepatocytes in a manner similar to that observed in vivo. We show that the protective effect on insulin signalling in PON2-def/apoE−/− mice is directly associated with altered production of macrophage proinflammatory mediators, but not elevated intracellular oxidative stress levels. We further present evidence that modulation of the macrophage inflammatory response in PON2-def/apoE−/− mice is mediated by a shift in the balance of NO and ONOO− (peroxynitrite) formation. Our results demonstrate that PON2 plays an important role in hepatic insulin signalling and underscores the influence of macrophage-mediated inflammatory response on hepatic insulin sensitivity.
apolipoprotein E (apoE); insulin receptor substrate-1 (IRS-1); liver; macrophage; paraoxonase; paraoxonase 2 (PON2)
Paraoxonase 3 (PON3) is a member of the PON family, which includes PON1, PON2, and PON3. Recently, PON3 was shown to prevent the oxidation of low-density lipoprotein in vitro. To test the role of PON3 in atherosclerosis and related traits, 2 independent lines of human PON3 transgenic (Tg) mice on the C57BL/6J (B6) background were constructed. Human PON3 mRNA was detected in various tissues, including liver, lung, kidney, brain, adipose, and aorta, of both lines of Tg mice. The human PON3 mRNA levels in the livers of PON3 Tg mice were 4- to 7-fold higher as compared with the endogenous mouse Pon3 mRNA levels. Human PON3 protein and activity were detected in the livers of Tg mice as well. No significant differences in plasma total, high-density lipoprotein, and very-low-density lipoprotein/low-density lipoprotein cholesterol and triglyceride and glucose levels were observed between the PON3 Tg and non-Tg mice. Interestingly, atherosclerotic lesion areas were significantly smaller in both lines of male PON3 Tg mice as compared with the male non-Tg littermates on B6 background fed an atherogenic diet. When bred onto the low-density lipoprotein receptor knockout mouse background, the male PON3 Tg mice also exhibited decreased atherosclerotic lesion areas and decreased expression of monocyte chemoattractant protein-1 in the aorta as compared with the male non-Tg littermates. In addition, decreased adiposity and lower circulating leptin levels were observed in both lines of male PON3 Tg mice as compared with the male non-Tg mice. In an F2 cross, adipose Pon3 mRNA levels inversely correlated with adiposity and related traits. Our study demonstrates that elevated PON3 expression significantly decreases atherosclerotic lesion formation and adiposity in male mice. PON3 may play an important role in protection against obesity and atherosclerosis.
atherosclerosis; obesity; genetics
To utilize proteomic analysis to identify protein biomarkers associated with pro-inflammatory HDL in patients with active rheumatoid arthritis.
Liquid chromatography-mass spectrometry (LC-MS) was used to analyze proteins associated with immunoaffinity purified HDL from plasma of two sets of RA patients carrying distinct HDL (anti- or pro-) inflammatory properties. Proteins were fractionated by Offgel electrophoresis and analyzed by LC-MS/MS equipped with a high capacity high performance liquid chromatography chip (HPLC-Chip) incorporating C18 reverse phase trapping and analytical columns. Sandwich enzyme-linked immunosorbent assays were used to validate select HDL-associated proteins in a second RA cohort.
Seventy-eight proteins were identified in the HDL complexes. Twelve proteins were significantly increased in RA patients with pro-inflammatory HDL compared to RA patients with anti-inflammatory HDL. These proteins included acute phase proteins, including apolipoprotein J, fibrinogen, haptoglobin, serum amyloid A, and complement factors (B, C3, C9). Four of the proteins associated with HDL were validated in a second RA cohort.
Pro-inflammatory HDL in patients with RA contains a significantly altered proteome including increased amounts of acute phase proteins and proteins involved in the complement cascade. These findings suggest that HDL is significantly altered in the setting of chronic inflammation from active RA with resultant loss of its anti-inflammatory function. The characterization of the biomarkers reported here may identify novel molecular connections that contribute to the higher risk of CVD in RA patients.
The liver X receptor (LXR) signaling pathway is an important modulator of
atherosclerosis, but the relative importance of the two LXRs in atheroprotection is
incompletely understood. We show here that LXRα, the dominant LXR isotype
expressed in liver, plays a particularly important role in whole-body sterol
homeostasis. In the context of the ApoE−/− background,
deletion of LXRα, but not LXRβ, led to prominent increases in
atherosclerosis and peripheral cholesterol accumulation. However, combined loss of
LXRα and LXRβ on the ApoE−/− background led to an
even more severe cholesterol accumulation phenotype compared to
indicating that LXRβ does contribute to reverse cholesterol transport (RCT) but
that this contribution is quantitatively less important than that of LXRα.
Unexpectedly, macrophages did not appear to underlie the differential phenotype of
LXRβ−/−ApoE−/− mice, as in
vitro assays revealed no difference in the efficiency of cholesterol efflux from
isolated macrophages. By contrast, in vivo assays of RCT using exogenously labeled
macrophages revealed a marked defect in fecal sterol efflux in
Mechanistically, this defect was linked to a specific requirement for
LXRα−/− in the expression of hepatic LXR target genes
involved in sterol transport and metabolism. These studies reveal a previously
unrecognized requirement for hepatic LXRα for optimal reverse cholesterol
transport in mice.
atherosclerosis; nuclear receptor; cholesterol metabolism; apoliporotein
Recent studies suggest that HDL levels are inversely related to colon cancer risk. HDL mimetics constructed from a number of peptides and proteins with varying structures possess anti-inflammatory and antioxidant properties reminiscent of HDL. In this report, we examined whether HDL mimetics, L-4F (an apolipoprotein A-I mimetic peptide) and G* (an apolipoprotein J mimetic peptide) affect tumor growth and development, in mouse models of colon cancer. HDL mimetics reduced viability and proliferation of CT26 cells, a mouse colon adenocarcinoma cell line and decreased CT26 cell-mediated tumor burden in BALB/c mice when administered subcutaneously or orally. Plasma levels of lysophosphatidic acid (LPA), a serum biomarker for colon cancer, were significantly reduced in mice that received HDL mimetics, suggesting that binding and removal of pro-inflammatory lipids is a potential mechanism for the inhibition of tumor development by HDL mimetics. Furthermore, L-4F significantly reduced size and number of polyps in APCmin/+ mice, a mouse model for human familial adenomatous polyposis, suggesting that HDL mimetics are effective in inhibiting the development of both induced and spontaneous cancers of the colon. Our results, for the first time, identify HDL mimetics as a novel therapeutic strategy for the treatment of colon cancer.
HDL; Mimetic Peptides; Colon Cancer; LPA; Cancer Therapeutics
LJ001 is a lipophilic thiazolidine derivative that inhibits the entry of numerous enveloped viruses at non-cytotoxic concentrations (IC50≤0.5 µM), and was posited to exploit the physiological difference between static viral membranes and biogenic cellular membranes. We now report on the molecular mechanism that results in LJ001's specific inhibition of virus-cell fusion.
The antiviral activity of LJ001 was light-dependent, required the presence of molecular oxygen, and was reversed by singlet oxygen (1O2) quenchers, qualifying LJ001 as a type II photosensitizer. Unsaturated phospholipids were the main target modified by LJ001-generated 1O2. Hydroxylated fatty acid species were detected in model and viral membranes treated with LJ001, but not its inactive molecular analog, LJ025. 1O2-mediated allylic hydroxylation of unsaturated phospholipids leads to a trans-isomerization of the double bond and concurrent formation of a hydroxyl group in the middle of the hydrophobic lipid bilayer. LJ001-induced 1O2-mediated lipid oxidation negatively impacts on the biophysical properties of viral membranes (membrane curvature and fluidity) critical for productive virus-cell membrane fusion. LJ001 did not mediate any apparent damage on biogenic cellular membranes, likely due to multiple endogenous cytoprotection mechanisms against phospholipid hydroperoxides.
Based on our understanding of LJ001's mechanism of action, we designed a new class of membrane-intercalating photosensitizers to overcome LJ001's limitations for use as an in vivo antiviral agent. Structure activity relationship (SAR) studies led to a novel class of compounds (oxazolidine-2,4-dithiones) with (1) 100-fold improved in vitro potency (IC50<10 nM), (2) red-shifted absorption spectra (for better tissue penetration), (3) increased quantum yield (efficiency of 1O2 generation), and (4) 10–100-fold improved bioavailability. Candidate compounds in our new series moderately but significantly (p≤0.01) delayed the time to death in a murine lethal challenge model of Rift Valley Fever Virus (RVFV). The viral membrane may be a viable target for broad-spectrum antivirals that target virus-cell fusion.
The threat of emerging and re-emerging viruses underscores the need to develop broad-spectrum antivirals. LJ001 is a non-cytotoxic, membrane-targeted, broad-spectrum antiviral previously reported to inhibit the entry of many lipid-enveloped viruses. Here, we delineate the molecular mechanism that underlies LJ001's antiviral activity. LJ001 generates singlet oxygen (1O2) in the membrane bilayer; 1O2-mediated lipid oxidation results in changes to the biophysical properties of the viral membrane that negatively impacts its ability to undergo virus-cell fusion. These changes are not apparent on LJ001-treated cellular membranes due to their repair by cellular lipid biosynthesis. Thus, we generated a new class of membrane-targeted broad-spectrum antivirals with improved photochemical, photophysical, and pharmacokinetic properties leading to encouraging in vivo efficacy against a lethal emerging pathogen. This study provides a mechanistic paradigm for the development of membrane-targeting broad-spectrum antivirals that target the biophysical process underlying virus-cell fusion and that exploit the difference between inert viral membranes and their biogenic cellular counterparts.
Although high-density lipoprotein-cholesterol (HDL-C) levels in large epidemiological studies are inversely related to the risk of coronary heart disease (CHD), increasing the level of circulating HDL-C does not necessarily decrease the risk of CHD events, CHD deaths, or mortality, HDL can act as an anti- or a proinflammatory molecule, depending on the context and environment. Based on a number of recent studies, it appears that the anti- or proinflammatory nature of HDL may be a more sensitive indicator of the presence or absence of atherosclerosis than HDL-C levels. The HDL proteome has been suggested to be a marker, and perhaps a mediator, of CHD. Apolipoprotein A-1 (apoA-I), the major protein in HDL is a selective target for oxidation by myeloperoxidase, which results in impaired HDL function. Improving HDL function through modification of its lipid and/or protein content maybe a therapeutic target for the treatment of CHD and many inflammatory disorders. HDL/apoA-I mimetic peptides may have the ability to modify the lipid and protein content of HDL and convert dysfunctional HDL to functional HDL. This review focuses on recent studies of dysfunctional HDL in animal models and human disease, and the potential of apoA-I mimetic peptides to normalize the composition and (function of lipoproteins.
ApoA-I mimetic peptides; High-density lipoprotein; Inflammation; Oxidative stress
Chronic infection has long been postulated as a stimulus for atherogenesis. Pseudomonas aeruginosa infection has been associated with increased atherosclerosis in rats, and the bacteria produce a quorum-sensing molecule 3-oxo-dodecynoyl-homoserine lactone (3OC12-HSL) that is critical for colonization and virulence. Paraoxonase 2 (PON2) hydrolyzes 3OC12-HSL and also protects against the effects of oxidized phospholipids thought to contribute to atherosclerosis. We now report the response of human aortic endothelial cells (HAEC) to 3OC12-HSL and oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (Ox-PAPC) in relation to PON2 expression.
Methods and Results
Using expression profiling and network modeling, we identified the unfolded protein response (UPR), cell cycle genes, and the MAPK signaling pathway to be heavily involved in the HAEC response to 3OC12-HSL. The network also showed striking similarities to a network created based on HAEC response to Ox-PAPC, a major component of minimally-modified LDL. HAEC in which PON2 was silenced by siRNA showed increased pro-inflammatory and UPR responses when treated with 3OC12-HSL or Ox-PAPC.
3OC12-HSL and Ox-PAPC influence similar inflammatory and UPR pathways. Quorum sensing molecules such as 3OC12-HSL contribute to the pro-atherogenic effects of chronic infection. The anti-atherogenic effects of PON2 include destruction of quorum sensing molecules.
Atherosclerosis; Chronic Infection; Inflammation; Oxidative Stress; Unfolded Protein Response
TNFα may change from a stimulator of reversible activation of endothelial cells (ECs) to a killer when combined with cycloheximide (CHX). The means by which endothelial cells are destined to either the survival or the apoptotic pathways are not fully understood. We investigated the role of p38 MAPK and protein phosphatase 2A (PP2A) activation and their regulation of 4E-BP1 stability in ECs to determine whether this pathway contributes to apoptosis induced by TNFα and CHX.
Methods and Results
Apoptosis was induced in human umbilical vein ECs (HUVECs) by treating them with a combination of TNFα and cycloheximide (CHX) [TNFα/CHX]. Activation of p38 MAPK was increased in HUVECs undergoing apoptosis, which was associated with degradation of eIF4E regulator, 4E-BP1, in a p38 MAPK-dependent manner. CHX attenuated a TNFα-stimulated increase in the expression and activity of PP2A. Silencing PP2A expression with siRNA transfection mimicked CHX-sensitization, increasing HUVEC apoptosis with TNFα stimulation, suggesting a protective role for PP2A in the apoptotic process.
Our data suggest i) TNFα stimulates PP2A and that HUVECs elude apoptosis by PP2A-dependent de-phosphorylation of p38 MAPK and ii) CHX-induced inhibition of PP2A leads to maintenance of p38 activity and degradation of 4E-BP1, resulting in enhanced TNFα-induced apoptosis.
apoptosis; endothelial cell signaling; TNFα; initiation factor 4E-binding protein; protein phosphatase 2A; p38 MAPK
In mice, 4F, an apolipoprotein A-I mimetic peptide that restores HDL function, prevents diabetes-induced atherosclerosis. We sought to determine whether HDL function is impaired in type 2 diabetic (T2D) patients and whether 4F treatment improves HDL function in T2D patient plasma in vitro.
RESEARCH DESIGN AND METHODS
HDL anti-inflammatory function was determined in 93 T2D patients and 31 control subjects as the ability of test HDLs to inhibit LDL-induced monocyte chemotactic activity in human aortic endothelial cell monolayers. The HDL antioxidant properties were measured using a cell-free assay that uses dichlorofluorescein diacetate. Oxidized fatty acids in HDLs were measured by liquid chromatography–tandem mass spectrometry. In subgroups of patients and control subjects, the HDL inflammatory index was repeated after incubation with L-4F.
The HDL inflammatory index was 1.42 ± 0.29 in T2D patients and 0.70 ± 0.19 in control subjects (P < 0.001). The cell-free assay was impaired in T2D patients compared with control subjects (2.03 ± 1.35 vs. 1.60 ± 0.80, P < 0.05), and also HDL intrinsic oxidation (cell-free assay without LDL) was higher in T2D patients (1,708 ± 739 vs. 1,233 ± 601 relative fluorescence units, P < 0.001). All measured oxidized fatty acids were significantly higher in the HDLs of T2D patients. There was a significant correlation between the cell-free assay values and the content of oxidized fatty acids in HDL fractions. L-4F treatment restored the HDL inflammatory index in diabetic plasma samples (from 1.26 ± 0.17 to 0.71 ± 0.11, P < 0.001) and marginally affected it in healthy subjects (from 0.81 ± 0.16 to 0.66 ± 0.10, P < 0.05).
In patients with T2D, the content of oxidized fatty acids is increased and the anti-inflammatory and antioxidant activities of HDLs are impaired.
Reverse cholesterol transport (RCT) is a major antiatherogenic function of high density lipoprotein (HDL). In the current work, the authors evaluated whether the RCT capacity of HDL from rheumatoid arthritis (RA) patients is impaired when compared to healthy controls.
HDL was isolated from 40 patients with RA and 40 age and sex matched healthy controls. Assays of cholesterol efflux, HDL’s antioxidant function and paraoxanase-1 (PON-1) activity were performed as described previously. Plasma myeloperoxidase (MPO) activity was assessed by a commercially available assay.
Mean cholesterol efflux capacity of HDL was not significantly different between RA patients (40.2%±11.1%) and controls (39.5%±8.9%); p=0.75. However, HDL from RA patients with high disease activity measured by a disease activity score using 28 joint count (DAS28>5.1), had significantly decreased ability to promote cholesterol efflux compared to HDL from patients with very low disease activity/clinical remission (DAS28<2.6). Significant correlations were noted between cholesterol efflux and the DAS28 (r=−0.39, p=0.01) and erythrocyte sedimentation rate, (r=−0.41, p=0.0009). Higher plasma MPO activity was associated with worse HDL function (r=0.41/p=0.009 (antioxidant capacity); r=0.35, p=0.03 (efflux)). HDL’s ability to promote cholesterol efflux was modestly but significantly correlated with its antioxidant function (r=−0.34, p=0.03).
The cholesterol efflux capacity of HDL is impaired in RA patients with high disease activity and is correlated with systemic inflammation and HDL’s antioxidant capacity. Attenuation of HDL function, independent of HDL cholesterol levels, may suggest a mechanism by which active RA contributes to increased cardiovascular (CV) risk.
To determine whether altering the dietary content of ω-6 (n-6) and ω-3 (n-3) polyunsaturated fatty acids affects the growth of androgen-sensitive prostate cancer xenografts, tumor membrane fatty acid composition, and tumor cyclooxygenase-2 and prostaglandin E2 (PGE2) levels.
Individually caged male severe combined immunodeficiency mice were fed isocaloric 20% kcal fat diets with the fat derived either primarily from n-6 fatty acids (n-6 group) or with the fat consisting of n-6 and n-3 fatty acids in a ratio of 1:1 (n-3 group), and injected s.c. with Los Angeles Prostate Cancer 4 (LAPC-4) cells. Tumor volumes and mouse weights were measured weekly, caloric intake was measured 3 days per week, and tumors and serum were harvested at 8 weeks postinjection.
Tumor growth rates, final tumor volumes, and serum prostate-specific antigen levels were reduced in the n-3 group relative to the n-6 group. The n-3 group tumors had decreased proliferation (Ki67 staining) and increased apoptosis (terminal nucleotidyl transferase –mediated nick end labeling staining). In vitro proliferation of LAPC-4 cells in medium containing n-3 group serum was reduced by 22% relative to LAPC-4 cells cultured in medium containing serum from the n-6 group. The n-6/n-3 fatty acid ratios in serum and tumor membranes were lower in the n-3 group relative to the n-6 group. In addition, n-3 group tumors had decreased cyclooxygenase-2 protein and mRNA levels, an 83% reduction in PGE2 levels, and decreased vascular endothelial growth factor expression.
These results provide a sound basis for clinical trials evaluating the effect of dietary n-3 fatty acids from fish oil on tumor PGE2 and membrane fatty acid composition, and serum and tumor biomarkers of progression in men with prostate cancer.
Fluorescence-based cell-free assays offer an attractive alternative to current cell-based assays for measuring the redox activity of High-Density Lipoprotein (HDL). We have recently developed a biochemical assay that assesses the effect of HDL on the oxidation rate of dihydrorhodamine 123 (DHR), reflected by increasing fluorescence over time. However, an immediate reduction in the fluorescence signal is observed after addition of HDL to DHR, due to fluorescence quenching from lipid-probe interactions. Understanding this process is important for interpretation of the results of all fluorescence-based cell-free assays that measure oxidative properties of lipids.
We determined the effect of quenchers (proteins or lipids) on the fluorescence signal of two fluorescence-based cell-free assays: the rhodamine 123 (RHD)-based assay, and a previously described assay based on dichlorodihydrofluorescein (DCF) in patients with systemic inflammation or atherosclerosis versus healthy subjects.
We found lipid-probe interactions between the non-fluorescent substrate and the lipid, which affect the observed rate of change of fluorescence after addition of lipids to DHR and DCFH. These interactions depended on: sample collection and storage, types and concentrations of lipid and fluorescent probe, method of HDL isolation, diluents and matrices, and pH. The RHD-based assay yielded reproducible measurements despite fluorescence quenching, while the DCF-based assay displayed more experimental variability. Furthermore, the lipid-probe interactions varied according to the setting of systemic inflammation when using apolipoprotein (apo) B-depleted plasma. However, under fixed conditions the rhodamine assay could reliably detect similar mean relative differences in the redox activity of HDL samples between different groups of patients using either purified HDL or apo-B depleted plasma.
Lipid-probe interactions should be considered when interpreting the results of fluorescence assays for measuring lipid oxidative state. Ideally, samples should be freshly obtained and purified HDL should be utilized rather than Apo B-depleted serum. Assay variability can be reduced by strict standardization of conditions (particularly sample collection, storage, lipid isolation method). Data comparisons between different studies similarly require strict standardization of conditions between studies and this caveat must be considered when using these assays to study the role of HDL function in the development of atherosclerosis in vivo.
Cancer and atherosclerosis are major causes of death in western societies. Deregulated cell death is common to both diseases, with significant contribution of inflammatory processes and oxidative stress. These two form a vicious cycle and regulate cell death pathways in either direction. This raises interest in antioxidative systems. The human enzymes paraoxonase-2 (PON2) and PON3 are intracellular enzymes with established antioxidative effects and protective functions against atherosclerosis. Underlying molecular mechanisms, however, remained elusive until recently. Novel findings revealed that both enzymes locate to mitochondrial membranes where they interact with coenzyme Q10 and diminish oxidative stress. As a result, ROS-triggered mitochondrial apoptosis and cell death are reduced. From a cardiovascular standpoint, this is beneficial given that enhanced loss of vascular cells and macrophage death forms the basis for atherosclerotic plaque development. However, the same function has now been shown to raise chemotherapeutic resistance in several cancer cells. Intriguingly, PON2 as well as PON3 are frequently found upregulated in tumor samples. Here we review studies reporting PON2/PON3 deregulations in cancer, summarize most recent findings on their anti-oxidative and antiapoptotic mechanisms, and discuss how this could be used in putative future therapies to target atherosclerosis and cancer.
We recently reported that apoA-I and apoA-I mimetic peptides prevent the development of flank tumors in immunocompetent C57BL/6J mice. To delineate the mechanism(s) of action of apoA-I mimetic peptides in tumor development, we examined the effect of D-4F (an apoA-I mimetic peptide) on the antioxidant status and on the gene expression and function of antioxidant enzymes in ID8 cells (a mouse epithelial ovarian cancer cell line) and in a mouse model. We demonstrate that D-4F treatment significantly reduces the viability and proliferation of ID8 cells, with a concomitant improvement of the antioxidant status of ID8 cells as measured by lipid peroxidation, protein carbonyl, superoxide anion, and hydrogen peroxide levels. D-4F treatment induces MnSOD (but not CuZnSOD) mRNA, protein, and activity. Inhibition of MnSOD in ID8 cells using shRNA vectors abrogates the inhibitory effects of D-4F on ID8 cell viability and proliferation. Moreover, tumor development from ID8 cells carrying shRNA for MnSOD were unaffected by D-4F treatment. Our results suggest that the inhibitory effects of D-4F on ID8 cell proliferation and tumor development are mediated, at least in part, by the induced expression and activity of MnSOD.
MnSOD; apolipoprotein A-I; mimetic peptides; oxidative stress; animal models; epithelial ovarian cancer
We recently reported that apolipoprotein A-I (apoA-I) and apoA-I mimetic peptides inhibit tumor growth and improve survival in a mouse model of ovarian cancer. The current study was designed to examine whether inhibition of angiogenesis is one of the mechanisms for the observed anti-tumorigenic effects. The apoA-I mimetic peptide L-5F had no affect on proliferation and cell viability of human umbilical vascular endothelial cells (HUVECs) in the basal state; however, treatment with L-5F at 1, 3, and 10 μg ml−1, dose-dependently inhibited both vascular endothelial growth factor (VEGF)- and basic fibroblast growth factor (bFGF)-induced proliferation, cell viability, migration, invasion and tube formation in HUVECs. L-5F inhibited VEGF- and bFGF-induced activation of their corresponding receptors, VEGFR2 and FGFR1, as well as downstream signaling pathways, including Akt and ERK1/2. MicroCT scanning and immunohistochemistry staining demonstrated that daily injection of L-5F (10 mg kg−1) decreased both the quantity and size of tumor vessels in mice. L-5F treated mice showed significantly reduced levels of VEGF in both tumor tissue and the circulation, which is consistent with in vitro data showing that L-5F inhibited production and secretion of VEGF from mouse and human ovarian cell lines in the absence and presence of exogenously added lysophosphatidic acid, a potent tumor promoter. In conclusion, our data that L-5F inhibits angiogenesis suggests that apoA-I mimetic peptides may serve as novel anti-angiogenesis agents for the treatment of angiogenesis-associated diseases, including cancer.
To determine the effect of the apolipoprotein A-I (ApoA-I) mimetic peptide, D-4F, on atherosclerosis development in a pre-existing diabetic condition.
RESEARCH DESIGN AND METHODS
We induced hyperglycemia in 6-week-old apoE−/− female mice using streptozotocin. Half of the diabetic apoE−/− mice received D-4F in drinking water. Ten weeks later, plasma lipids, glucose, insulin levels, atherosclerotic lesions, and lesion macrophage content were measured.
Diabetic apoE−/− mice developed ∼300% more lesion area, marked dyslipidemia, increased glucose levels, and reduced plasma insulin levels when compared with nondiabetic apoE−/− mice. Atherosclerotic lesions were significantly reduced in the D-4F–treated diabetic apoE−/− mice in whole aorta (1.11 ± 0.73 vs. 0.58 ± 0.44, percentage of whole aorta, P < 0.01) and in aortic roots (36,038 ± 18,467 μm2/section vs. 17,998 ± 12,491 μm2/section, P < 0.01) when compared with diabetic apoE−/− mice that did not receive D-4F. Macrophage content in atherosclerotic lesions from D-4F–treated diabetic apoE−/− mice was significantly reduced when compared with nontreated animals (78.03 ± 26.1 vs. 29.6 ± 15.2 P < 0.001, percentage of whole plaque). There were no differences in glucose, insulin, total cholesterol, HDL cholesterol, and triglyceride levels between the two groups. Arachidonic acid, PGE2, PGD2, 15-HETE, 12-HETE, and 13-HODE concentrations were significantly increased in the liver tissue of diabetic apoE−/− mice compared with nondiabetic apoE−/− mice and significantly reduced by D-4F treatment.
Our results suggest that oral D-4F can prevent atherosclerosis development in pre-existing diabetic mice and this is associated with a reduction in hepatic arachidonic acid and oxidized fatty acid levels.