Monocytes influence the fate of T cells challenged with oxidised low density lipoproteins towards apoptosis or MHC-restricted proliferation

Vitamin A Decreases Cytotoxicity of Oxidized Low-Density Lipoprotein in Patients with Atherosclerosis

BACKGROUND

Oxidized low-density lipoprotein (ox-LDL) is implicated in initiation and progression of atherosclerosis. Previously, we found that ox-LDL increases vulnerability of peripheral blood mononuclear cells (PBMCs) in atherosclerotic patients compared to controls. Vitamin A induces proliferation of PBMCs. The aim of this study was to determine the effect of vitamin A supplementation on PBMC survival against LDL and different doses of ox-LDL.

METHOD

In this double-blind placebo-controlled trial, we recruited 35 atherosclerotic patients and 38 healthy controls and randomly allocated them into placebo and vitamin A groups, which received either placebo or 25,000 IU/day of vitamin A for 3 months. PBMCs were isolated, cultured, and stimulated by 1 µg/mL LDL as well as 1 µg/mL and 50 µg/mL ox-LDL. The stimulation indexes (SIs) of PBMCs were calculated to identify cell viability. Additionally, the circulating ox-LDL levels were measured by ELISA.

RESULTS

Viability of PBMCs stimulated by 50 µg/mL ox-LDL significantly increased following vitamin A supplementation in patients (p < 0.01). The levels of circulating ox-LDL were not changed by vitamin A treatment. Ox-LDL levels were strongly and positively correlated to SI of PBMCs stimulated by 1 µg/mL LDL and1 µg/mL ox-LDL in all groups.

CONCLUSION

Vitamin A decreases cytotoxicity of high-dose ox-LDL and improves PBMC viability. The protective effect of vitamin A is not mediated by an antioxidative mechanism, but may instead have been due to intracellular protection of the apoptotic machinery or induction of proliferation of the cells. Higher levels of ox-LDL increase PBMC irritability in all participants.

The influence of vitamin A supplementation on Foxp3 and TGF-β gene expression in atherosclerotic patients

The aim of this study was to investigate the role of vitamin A in Foxp3 and TGF-β gene expression in atherosclerotic patients. Patients and healthy controls in the vitamin A group received 25,000 IU retinyl palmitate per day, while patients in the placebo group took one capsule of placebo per day for 4 months. Gene expressions of regulatory T cells were studied by real-time PCR. The levels of Foxp3 expression in phytohemagglutinin-activated cells were much higher in the patients who received vitamin A than in placebo-treated patients and healthy controls, while Foxp3 gene expression in oxidized low-density lipoprotein-activated cells showed no significant differences between all groups (p=0.357). A significant difference in the expression level of TGF-β gene in fresh cells was observed between patients and healthy controls (p=0.009). TGF-β gene expression in oxidized low-density lipoprotein-activated cells increased in all groups; however, these changes were not statistically significant (p=0.65); the changes obtained were 2.8-, 2.2- and 3.9-fold in the vitamin A, placebo, and control groups, respectively. Based on suppressing actions of regulatory T cells on effector T cells and findings that show that vitamin A has the effect of increasing expression of regulatory T cells, it can be concluded that supplementation with vitamin A in atherosclerotic patients may be effective in slowing disease progression.

T cell costimulatory and coinhibitory pathways in vascular inflammatory diseases

A broad array of evidence indicates that T lymphocytes make significant contributions to vascular inflammation in the setting of atherosclerotic disease, hypertension, autoimmune vasculitis, and other disorders. Experimental data show that costimulatory and coinhibitory pathways involving molecules of the B7-CD28 and TNF–TNFR families regulate T cell responses that promote vascular disease. Antigen presenting cells (APCs) display both peptide–major histocompatibility complex antigen and costimulators or coinhibitors to T cells. Two major types of APCs, dendritic cells (DCs) and macrophages, are present in significant numbers in the walls of arteries affected by atherosclerosis and arteritis, and some DCs are present in normal arteries. Costimulatory and coinhibitory molecules expressed by these vascular APCs can contribute to the activation or inhibition of effector T cells within the arterial wall. Vascular DCs may also be involved in transport of antigens to secondary lymphoid organs, where they activate or tolerize naïve T cells, depending on the balance of costimulators and coinhibitors they express. Costimulatory blockade is already an approved therapeutic approach to treat autoimmune disease and prevent transplant rejection. Preclinical models suggest that costimulatory blockade may also be effective in treating vascular disease. Experiential data in mice show that DCs pulsed with the appropriate antigens and treated in a way that reduces costimulatory capacity can reduce atherosclerotic disease, presumably by inducing T cell tolerance. Progress in treating vascular disease by immune modulation will require a more complete understanding of the functions of different costimulatory and coinhibitory pathways and the different subsets of vascular APCs involved.

The role of elastin peptides in modulating the immune response in aging and age-related diseases

It is now well accepted that aging is associated with the occurrence of a low-grade inflammation called Inflamm-aging. This leads to the imbalance between the various mediators of the inflammatory response in favour of the pro-inflammatory response represented by pro-inflammatory cytokines and oxidative stress. The question that arises, and is still under investigation, what is the origin of the driving force leading to these changes. One of the current hypotheses is that chronic stimulation of the immune system contributes to the pro-inflammatory shift. The chronic stimulation can be of viral origin such as cytomegalovirus, from tumor antigens or from other sources such as the extracellular matrix, especially from elastin fibres and collagens. Aging and various inflammatory diseases such as atherosclerosis, abdominal aortic aneurysms, chronic obstructive pulmonary diseases (COPD), cancer and type 2 diabetes are characterized by the destruction of elastin fibers and the consequent generation of elastin peptides which are biologically active. This review will describe the putative contribution of elastin peptides to inflamm-aging and extend on their role on immunosenescence, as well as on age-associated chronic inflammatory diseases.

Aging-dependent changes of microglial cells and their relevance for neurodegenerative disorders

Among multiple structural and functional brain changes, aging is accompanied by an increase of inflammatory signaling in the nervous system as well as a dysfunction of the immune system elsewhere. Although the long-held view that aging involves neurocognitive impairment is now dismissed, aging is a major risk factor for neurodegenerative diseases such as Alzheimer;s disease, Parkinson;s disease and Huntington's disease, among others. There are many age-related changes affecting the brain, contributing both to certain declining in function and increased frailty, which could singly and collectively affect neuronal viability and vulnerability. Among those changes, both inflammatory responses in aged brains and the altered regulation of toll like receptors, which appears to be relevant for understanding susceptibility to neurodegenerative processes, are linked to pathogenic mechanisms of several diseases. Here, we review how aging and pro-inflammatory environment could modulate microglial phenotype and its reactivity and contribute to the genesis of neurodegenerative processes. Data support our idea that age-related microglial cell changes, by inducing cytotoxicity in contrast to neuroprotection, could contribute to the onset of neurodegenerative changes. This view can have important implications for the development of new therapeutic approaches.

Innate immune receptor expression in normal brain aging

Brain aging often results in cognitive impairment and is considered to be a major risk factor for neurodegenerative diseases. Earlier studies reported inflammatory responses in aged brain that could contribute to age-related neurodegeneration. Recently, innate immune receptors such as toll-like receptors (TLRs), so far implicated in defense against microorganisms, have been linked to pathogenesis of Alzheimer's disease. Therefore, we asked whether the transcription of TLRs (1-9) and CD14, could also be altered in physiological brain aging. Using real-time polymerase chain reaction (PCR), we indeed observed that TLR1, TLR2, TLR4, TLR5, TLR7 and CD14 expression was up-regulated in mouse brain in correlation with age. In contrast, transcriptions of TLR3, TLR6 and TLR8 were unchanged and the one of TLR9 was down-regulated. In situ hybridization further confirmed these results and identified the cellular source of TLR2 and TLR7 as mononuclear phagocytes. Together, this first systematic analysis demonstrates altered regulation of those innate immune receptors even in normal brain aging, which might be of relevance for understanding susceptibility to neurodegenerative processes associated with aging.

GM-CSF activates the Jak/STAT pathway to rescue polymorphonuclear neutrophils from spontaneous apoptosis in young but not elderly individuals

Polymorphonuclear neutrophils (PMN) are the first cells to be recruited to the site of tissular aggression. They have a short-life span and die by spontaneous apoptosis. However, their life span and functional activities can be extended in vitro by a number of proinflammatory cytokines, including the granulocyte-macrophage colony stimulating factor (GM-CSF). We have reported that the protective effect of GM-CSF did not occur in PMN of elderly subjects. Data reported here showed that this difference was not due to a change in the expression of the GM-CSF receptor in the PMN of elderly individuals compared to young subjects. Furthermore, we showed here that GM-CSF activated the Janus kinase/signal transducer and activator of transcription (Jak/STAT) pathway and this activation appeared to be maintained for an extended period of time (18 h) playing an important role in the GM-CSF induced delayed PMN apoptosis. In marked contrast, GM-CSF had no effects on Jak2 activation in PMN of elderly individuals. We found that an inhibitor of Jak2 activation (AG490) abolished the protective effect of GM-CSF in PMN from young donors, however had no effect in PMN of elderly subjects. GM-CSF induced a transient activation of STAT3 and STAT5 in PMN of young donors but failed to activate to the same extent these signal transducers in PMN of elderly donors. The levels of proCaspase-3 were reduced in PMN of young donors treated with GM-CSF for 18 h but remained unchanged in PMN of elderly subjects treated under the same conditions compared to the untreated PMN. Our data are consistent with the interpretation that, at least in part (1) the protective effect of GM-CSF against apoptosis results from the activation of the Jak/STAT pathway and (2) decreased rescue from apoptosis in PMN of elderly is related to a failure of GM-CSF to activate this pathway in these cells.

Acute in vivo elevation of intravascular triacylglycerol lipolysis impairs peripheral T cell activation in humans

BACKGROUND

Previous studies have shown suppressive effects of polyunsaturated fatty acids (PUFAs) on T cell proliferation, but the precise mechanism for this effect has not been fully investigated in vivo in humans.

OBJECTIVE

The objective was to determine whether this effect is the result of altered T cell membrane properties and impaired CD3- and CD28-mediated signaling in vivo in humans.

DESIGN

Peripheral T cells were isolated from healthy subjects before and 2 h after an intravenous infusion of heparin plus a PUFA-rich lipid emulsion during a euglycemic hyperinsulinemic clamp to induce a 2.5-fold elevation in plasma linoleic acid concentration without significant change in plasma total free fatty acid concentrations.

RESULTS

Intravenous infusion of heparin plus the lipid emulsion reduced peripheral T cell membrane fluidity and altered lipid raft organization, both of which were associated with reduced T cell proliferation after stimulation with CD3 plus CD28. Tyrosine phosphorylation of linker of activated T cells and activation of protein kinase B in T cells were also impaired without a reduction in T cell receptor expression. In addition, acute PUFA elevation was associated with a reduction in T cell membrane cholesterol exchange with the cellular milieu ex vivo.

CONCLUSIONS

A selective increase in plasma linoleic acid concentration and in intravascular lipolysis has a suppressive effect on peripheral T cell CD28-dependent activation, and this effect is associated with changes in plasma membrane properties. Our results have important implications for nutritional therapy in patients at high risk of septic complications and may also be of relevance to postprandial lipid metabolism disorders such as insulin resistance and type 2 diabetes.

Mildly oxidized low-density lipoprotein inhibits the in vitro induction of the specific antibody response to Candida albicans

Oxidized low-density lipoprotein plays a critical role in the pathogenesis of atherosclerosis and exerts pleiotropic effects on various cellular functions. The present study was designed to evaluate the effects of mildly oxidized LDL (mLDL) on the induction and regulation of an in vitro specific antibody response. We found that mLDL significantly inhibited the induction of the anti-Candida albicans antibody response by human peripheral blood mononuclear cells (PBMC). mLDL-induced down-regulation of antibody production was abrogated by blocking the major receptors that bind and internalize modified LDL. In the mLDL-treated C. albicans-stimulated PBMC cultures an early increase in IL-1beta production was observed and the addition of anti-IL-1beta antibody abrogated the mLDL-induced inhibitory effect. Moreover, the addition of IL-1beta to the cultures inhibited the induction of the specific antibody response, similar to mLDL. On the other hand, mLDL up-regulated PWM-induced polyclonal immunoglobulin (Ig) production. In the same cultures IgM anti-mLDL was found. These results indicate that the up-regulation of IL-1beta production induced by mLDL may be involved in the hindering of B cell function, i.e., specific antibody production. This could be relevant in the pathogenesis of inflammatory diseases such as atherosclerosis.

Elastin peptides induced oxidation of LDL by phagocytic cells

The degradation products of one of the major component of vascular wall, elastin, have several important biological activities. Elastin peptides (KE) are mostly generated during vascular aging and the atherosclerotic process. They induce free radical and proteases production from cells, which are the major components of the atherosclerotic process. In the present study, we investigated whether the interaction between elastin peptides and neutrophils as well as monocytes contributes to low density lipoproteins (LDL) oxidation, being one of the most important initiator of the chronic inflammatory process contributing to the development of atherosclerosis. Here, we present data on the link between the elastin degradation products and LDL oxidation by the chemotactically attracted neutrophils and monocytes. The KE as well as the active epitope, the hexapeptide VGVAPG is able, in a differential concentration and time dependence, to induce the oxidation of LDL. KE is able to induce via the production of free radicals by neutrophils the oxidation of LDL very rapidly and in higher concentration compared to monocytes. These effects of KE are occurring through the stimulation of the 67 kDa elastin-laminin receptor (ELR), as demonstrated by the uncoupling effect of lactose. In our present study, the HDL was able to decrease the LDL oxidation by KE. This is a new mechanism by which elastin peptides might participate in the initiation and progression of the atherosclerotic process.

Presence and active synthesis of the 67 kDa elastin-receptor in human circulating white blood cells

Early after the identification of the elastin-receptor (El-R) on mesenchymal cells, it was demonstrated that phagocytic cells and lymphocytes could also respond to elastin peptides. Nevertheless, the level of El-R expression has never been demonstrated on immune cells and no data exist whether these cells actively synthesize this El-R. Thus, our aim in the present work was to study the expression and number of El-R on white blood cells (WBC) using a specific 67 kDa El-R antibody and to demonstrate the presence of mRNA corresponding to the gene coding for El-R. Our results show that messenger RNA corresponding to the presumptive gene coding for the 67 kDa El-R subunit could be detected in all three WBC-types investigated. On all of these WBC, the presence of El-R could be demonstrated, however their number and their function varied following the cell type. The presence of El-R is very important for the interaction of circulating cell with the matrix as these cells intervene during atherosclerosis and in host defence.

The role of the MAPK pathway alterations in GM-CSF modulated human neutrophil apoptosis with aging

Background

Neutrophils represent the first line of defence against aggressions. The programmed death of neutrophils is delayed by pro-inflammatory stimuli to ensure a proper resolution of the inflammation in time and place. The pro-inflammatory stimuli include granulocyte-macrophage colony-stimulating factor (GM-CSF). Recently, we have demonstrated that although neutrophils have an identical spontaneous apoptosis in elderly subjects compared to that in young subjects, the GM-CSF-induced delayed apoptosis is markedly diminished. The present study investigates whether an alteration of the GM-CSF stimulation of MAPKs play a role in the diminished rescue from apoptosis of PMN of elderly subjects.

Methods

Neutrophils were separated from healthy young and elderly donors satisfying the SENIEUR protocol. Neutrophils were stimulated with GM-CSF and inhibitors of the MAPKinase pathway. Apoptosis commitment, phosphorylation of signaling molecules, caspase-3 activities as well as expression of pro- and anti-apoptotic molecules were performed in this study. Data were analyzed using Student's two-tailed t-test for independent means. Significance was set for p ≤ 0.05 unless stated otherwise.

Results

In this paper we present evidence that an alteration in the p42/p44 MAPK activation occurs in PMN of elderly subjects under GM-CSF stimulation and this plays a role in the decreased delay of apoptosis of PMN in elderly. We also show that p38 MAPK does not play a role in GM-CSF delayed apoptosis in PMN of any age-groups, while it participates to the spontaneous apoptosis. Our results also show that the alteration of the p42/p44 MAPK activation contributes to the inability of GM-CSF to decrease the caspase-3 activation in PMN of elderly subjects. Moreover, GM-CSF converts the pro-apoptotic phenotype to an anti-apoptotic phenotype by modulating the bcl-2 family members Bax and Bcl-xL in PMN of young subjects, while this does not occur in PMN of elderly. However, this modulation seems MAPK independent.

Conclusion

Our results show that the alteration of p42/p44 MAPK activation contributes to the GM-CSF induced decreased PMN rescue from apoptosis in elderly subjects. The modulation of MAPK activation in PMN of elderly subjects might help to restore the functionality of PMN with aging.

Antiatherogenic effect of Pistacia lentiscus via GSH restoration and downregulation of CD36 mRNA expression

Pistacia lentiscus var. Chia (Anacardiaceae) grows almost exclusively on Chios Island, Greece, and gives a resinous exudate resin used for culinary purposes by Mediterranean people. We investigated the molecular mechanisms through which total polar extract of the resin inhibits oxidized low-density lipoprotein (oxLDL) cytotoxic effect on peripheral blood mononuclear cell (PBMC). Cells exposed to oxLDL underwent apoptosis and necrosis, dependent on the duration of exposure. When culturing cells with oxLDL and the polar extract concurrently, we observed inhibition of both the phenomena. Because under oxidative stress the pro-oxidant systems outbalance the antioxidant, potentially producing oxidative damage and ultimately leading to cell death, we measured the levels of intracellular antioxidant glutathione (GSH). Additionally, we measured CD36 expression, a class B scavenger receptor, on CD14-positive cells, as CD36 has been identified as the oxLDL receptor in macrophages and may play a pivotal role in atherosclerotic foam cell formation. oxLDL decreased GSH levels and upregulated CD36 expression. P. lentiscus extract restored GSH levels and downregulated CD36 expression, even at the mRNA level. In order to find out the biologically drastic constituents of the resin's polar extract, fractions derived from RP-HPLC analysis were examined for their antioxidant effect on oxidatively stressed PBMC. The triterpenoid fraction revealed remarkable increase in intracellular GSH. We suggest GSH restoration and downregulation of CD36 mRNA expression as the pathways via which P. lentiscus triterpenes exert antioxidant/antiatherogenic effect. Additionally, our results provide strong evidence of the resin's antiatherogenic effect; therefore it is credited with beneficial health aspects.

Signal transduction and functional changes in neutrophils with aging

It is well known that the immune response decreases during aging, leading to a higher susceptibility to infections, cancers and autoimmune disorders. Most widely studied have been alterations in the adaptive immune response. Recently, the role of the innate immune response as a first-line defence against bacterial invasion and as a modulator of the adaptive immune response has become more widely recognized. One of the most important cell components of the innate response is neutrophils and it is therefore important to elucidate their function during aging. With aging there is an alteration of the receptor-driven functions of human neutrophils, such as superoxide anion production, chemotaxis and apoptosis. One of the alterations underlying these functional changes is a decrease in signalling elicited by specific receptors. Alterations were also found in the neutrophil membrane lipid rafts. These alterations in neutrophil functions and signal transduction that occur during aging might contribute to the significant increase in infections in old age.

Development of radiocontrast agents for vascular imaging: progress to date

The revolution in molecular imaging techniques is profoundly changing the understanding of the pathophysiology and treatment of atherosclerosis. With these rapid changes there is an increasing demand for development of sensitive and well tolerated novel imaging agents that can be rapidly translated from small animal models into patients with atherosclerosis. Nuclear medicine and positron emission tomography techniques have the ability to detect and serially monitor a variety of biologic and pathophysiologic processes usually with tracer quantities of radiolabeled peptides, drugs, and other molecules at dosages free of pharmacologic adverse effects unlike the current generation of intravenous agents required for magnetic resonance imaging (MRI) and computed axial tomography (CT) scanning. A representative sampling of the wide array of radiopharmaceuticals developed specifically for radionuclide imaging of atherosclerosis, that have been approved for clinical use and those in pre-clinical trials, have been reviewed in this article. The presence of an inflammatory stimulus increases expression of CC (cysteine-cysteine motif) chemokine receptor (CCR)-2 on monocytes and macrophages, and somatostatin receptors on T lymphocytes. Radiolabeled monocyte chemoattractant protein (MCP)-1 binds with high affinity to CCR-2 and can be used to detect subacute and chronic inflammatory lesions. Similarly, radiolabeled octreotide or depreotide can be used to detect activated T lymphocytes which may identify the vulnerable plaque. Animal models indicate that (99m)Tc-annexin V, (125)I-MCP-1 and [(18)F]-fluoro-2-deoxyglucose are effective in identifying apoptotic cell death, macrophage infiltration and metabolic activity in atheromatous lesions, respectively. Expression of alpha(v)beta(3) integrin is increased in activated endothelial cells and vascular smooth muscle cells after vascular injury, and alpha(v)beta(3) integrin is minimally expressed on smooth muscle cells and is not expressed on quiescent epithelial cells. Radiolabeled high-affinity peptides can be used to target the alpha(v)beta(3) integrin and visualize areas of vascular damage. Advances in technology such as the micro-single photon emission computed tomography (microSPECT) have the potential to overcome the drawbacks of older CT and MRI methodologies, such as lack of biologically relevant ligands and compatible blood pool contrast agents for imaging. Despite these advances in imaging technology, the small size of atheromatous lesions makes it difficult to detect using external imaging techniques. Therefore, recently there has been renewed interest in the use of intravascular catheter-based radiation detectors.