Excess formation of lysophosphatidic acid with age inhibits myristic acid-induced superoxide anion generation in intact human neutrophils

Aging and immune function: molecular mechanisms to interventions

Abstract The immune system of an organism is an essential component of the defense mechanism aimed at combating pathogenic stress. Age-associated immune dysfunction, also dubbed "immune senescence," manifests as increased susceptibility to infections, increased onset and progression of autoimmune diseases, and onset of neoplasia. Over the years, extensive research has generated consensus in terms of the phenotypic and functional defects within the immune system in various organisms, including humans. Indeed, age-associated alterations such as thymic involution, T cell repertoire skewing, decreased ability to activate naïve T cells and to generate robust memory responses, have been shown to have a causative role in immune decline. Further, understanding the molecular mechanisms underlying the generation of proteotoxic stress, DNA damage response, modulation of ubiquitin proteasome pathway, and regulation of transcription factor NFκB activation, in immune decline, have paved the way to delineating signaling pathways that cross-talk and impact immune senescence. Given the role of the immune system in combating infections, its effectiveness with age may well be a marker of health and a predictor of longevity. It is therefore believed that a better understanding of the mechanisms underlying immune senescence will lead to an effective interventional strategy aimed at improving the health span of individuals. Antioxid. Redox Signal. 14, 1551-1585.

Myristic Acid, A Side Chain of Phorbol Myristate Acetate (PMA), Can Activate Human Polymorphonuclear Leukocytes to Produce Oxygen Radicals More Potently than PMA

Myristic acid (MyA), which is a saturated fatty acid (C14:0) and a side chain of phorbol 12-myristate 13-acetate (PMA), was examined if MyA stimulates human polymorphonuclear leukocytes (PMNs) to release oxygen radicals comparable to PMA by applying electron paramagnetic resonance (EPR)-spin-trapping method. When MyA was added to isolated human PMNs, spin adducts of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO)-OH and DMPO-OOH were time-dependently observed. The amounts of these spin adducts were larger than those of PMNs stimulated by PMA. These results clearly show that MyA is more potent agent to prime human PMNs than PMA, in a point of view of not only O₂^·− but also ·OH production. This fact calls attention that too much intake of MyA that is known to be contained vegetable oils can lead to crippling effect through uncontrolled production of reactive oxygen species.

Increased intracellular activity of matrix metalloproteinases in neutrophils may be associated with delayed healing of infection without neutropenia in myelodysplastic syndromes

To investigate the influence of the intracellular activity of type II and type IV collagenases [matrix metalloproteinases (MMP)-2, MMP-8, and MMP-9] in neutrophils from patients with myelodysplastic syndromes (MDS), we tried to measure intracellular activity using flow cytometric techniques. We also studied the clinical features of patients showing high activity. The intracellular collagenase activity, expressed as a ratio to the standardized fluorescence intensity, in patients with MDS was significantly higher than normal volunteers (19.5+/-14.8 vs 13.3+/-6.8, p=0.024). The difference among subcategories of MDS according to the French-American-British (FAB) and WHO classifications was not significant. No significant influence of three variables of the International Prognostic Scoring System (IPSS) was seen on activity. Of 8 patients with activity of more than 26.9 (mean+2 standard deviations of normal controls), 5 experienced an episode of delayed healing of infection without neutropenia, while 1 of 43 patients with activity of less than 26.9 experienced such an episode (p=0.0002). The average collagenase activity of six patients with delayed healing of infection without neutropenia (44.7+/-28.9) was significantly higher than that of other MDS patients (16.0+/-7.1, p=0.005) (Fig. 4). It was also significantly higher than the activity of the control group (13.3+/-6.8, p=0.011). Our report suggests that increased collagenase activity in neutrophils may delay healing of infection. In addition, we suggest that increased collagenase activity may be an independent prognostic factor for the susceptibility to severe infection in MDS.

Monoclonal constitution of neutrophils detected by PCR-based human androgen receptor gene assay in a subset of idiopathic thrombocytopenic purpura patients

It is well known that some patients with monopathic thrombocytopenia in myelodysplastic syndrome (MDS) show clinico-hematologic features resembling chronic idiopathic thrombocytopenic purpura (ITP). This study examined the monoclonal nature of ITP to obtain a further insight into patients with borderline ITP and monopathic thrombocytopenia in MDS, using polymorphic trinucleotide CAG repeats in the X-linked human androgen receptor (HUMARA) gene. In this study, we separated peripheral neutrophils and mononuclear cells (MNCs) from 18 patients with chronic ITP, and analyzed them in comparison with those from normal or MDS female subjects by PCR-based HUMARA assay. All normal controls showed a polyclonal pattern of the HUMARA gene, whereas some MDS patients had monoclonality in MNC and/or neutrophils. Among ITP patients, two had a nonrandom inactivation pattern of the HUMARA gene in neutrophils, which was considered to be derived from hematopoietic cells of clonal origin, whereas no ITP patient had MNC of clonal nature. Two ITP patients with a monoclonal pattern in the neutrophil fraction were refractory to ordinary treatment. This approach may provide further information in patients with borderline hematologic disorders between chronic ITP and refractory thrombocytopenia of MDS.

Lysophosphatidic acid induces glycodelin gene expression in cancer cells

Glycodelin is a glycoprotein that has been suggested to be important in normal pregnancy and in malignancy. The regulation of its synthesis has not been studied. In this study, we report the induction of glycodelin gene expression by lysophosphatidic acid (LPA). We studied the effect of LPA (5, 10 and 25 microM) on glycodelin production in breast (MDA-MB-231), cervical (Hela), endometrial (RL-95), ovarian cancer (OVCAR-3) and erythroleukemia (K562) cells. There was a dose-dependent (5-25 microM) induction of glycodelin gene and protein expression in these cell types. LPA is a mimic of phorbol myristate acetate (PMA) action and is found to be elevated in high concentrations in the serum of cancer subjects. As glycodelin is an angiogenic protein with a potential immunosuppressive role, control of LPA synthesis might offer a potential target for intervention.

Lysophosphatidic acid synthesis and release

Lysophosphatidic acid (LPA) is a bioactive phospholipid controlling numerous cellular responses through the activation of specific G-protein coupled transmembrane receptors. LPA is present in several biological fluids (serum, plasma, aqueous humor) and can be secreted by several cell types (platelets, fibroblasts, adipocytes, cancer cells). Whereas, multiple pathways of synthesis and degradation of LPA have been described, their relative contribution in extracellular secretion and biodisponibility is still a matter of debate. The first part of the present review is devoted to the description of the different enzymes involved in LPA synthesis (acyltransferases, phospholipases, kinases) and degradation (lysophospholipases, lipid-phosphatases), as well as to the molecules involved in LPA transport (albumin, fatty acid binding proteins, gelsolin, lipoproteins). In a second part, the different physio-pathological situations (aggregation, cancer, injuries) associated with LPA production, as well as the potential role played by LPA in genesis of certain diseases (cancer, obesity, arteriosclerosis) are listed and analyzed.

Sphingosine 1-phosphate as a major bioactive lysophospholipid that is released from platelets and interacts with endothelial cells

The serum-borne lysophospholipid mediators sphingosine 1-phosphate (Sph-1-P) and lysophosphatidic acid (LPA) have been shown to be released from activated platelets and to act on endothelial cells. In this study, we employed the repeated lipid extraction (under alkaline and acidic conditions), capable of detecting Sph-1-P, LPA, and possibly structurally similar lysophospholipids, whereby a marked formation of [32P]Sph-1-P, but not [32P]LPA, was observed in [32P]orthophosphate-labeled platelets. Platelet Sph-1-P release, possibly mediated by protein kinase C, was greatly enhanced in the presence of albumin, which formed a complex with Sph-1-P. This finding suggests that platelet Sph-1-P may become accessible to depletion by albumin when its transbilayer movement (flipping) across the plasma membrane is enhanced by protein kinase C. Although human umbilical vein endothelial cells expressed receptors for both Sph-1-P and LPA, Sph-1-P acted much more potently than LPA on the cells in terms of intracellular Ca++ mobilization, cytoskeletal reorganization, and migration. The results suggest that Sph-1-P, rather than LPA, is a major bioactive lysophospholipid that is released from platelets and interacts with endothelial cells, under the conditions in which critical platelet-endothelial interactions (including thrombosis, angiogenesis, and atherosclerosis) occur. Furthermore, albumin-bound Sph-1-P may account for at least some of the serum biological activities on endothelial cells, which have been ascribed to the effects of albumin-bound LPA, based on the similarities between LPA and serum effects.

Sphingosine 1-phosphate as a major bioactive lysophospholipid that is released from platelets and interacts with endothelial cells

The serum-borne lysophospholipid mediators sphingosine 1-phosphate (Sph-1-P) and lysophosphatidic acid (LPA) have been shown to be released from activated platelets and to act on endothelial cells. In this study, we employed the repeated lipid extraction (under alkaline and acidic conditions), capable of detecting Sph-1-P, LPA, and possibly structurally similar lysophospholipids, whereby a marked formation of [32P]Sph-1-P, but not [32P]LPA, was observed in [32P]orthophosphate-labeled platelets. Platelet Sph-1-P release, possibly mediated by protein kinase C, was greatly enhanced in the presence of albumin, which formed a complex with Sph-1-P. This finding suggests that platelet Sph-1-P may become accessible to depletion by albumin when its transbilayer movement (flipping) across the plasma membrane is enhanced by protein kinase C. Although human umbilical vein endothelial cells expressed receptors for both Sph-1-P and LPA, Sph-1-P acted much more potently than LPA on the cells in terms of intracellular Ca++ mobilization, cytoskeletal reorganization, and migration. The results suggest that Sph-1-P, rather than LPA, is a major bioactive lysophospholipid that is released from platelets and interacts with endothelial cells, under the conditions in which critical platelet-endothelial interactions (including thrombosis, angiogenesis, and atherosclerosis) occur. Furthermore, albumin-bound Sph-1-P may account for at least some of the serum biological activities on endothelial cells, which have been ascribed to the effects of albumin-bound LPA, based on the similarities between LPA and serum effects.

Decline in antibiotic enzyme activity of neutrophils is a prognostic factor for infections in patients with myelodysplastic syndrome

We used flow cytometry to measure the activities of cathepsin G and elastase. The activity of elastase in neutrophils from patients with myelodysplastic syndrome (MDS) was significantly lower than that in neutrophils from the control group (P<.001). Patients with low elastase activity were significantly susceptible to infection (P<. 05). Our study suggests that analyzing antibacterial enzymes is useful in evaluating the prognosis of patients with MDS.