Identification of the phospholipase A(2) isoforms that contribute to arachidonic acid release in hypoxic endothelial cells: limits of phospholipase A(2) inhibitors

Therapeutic potential of flavonoids in the treatment of chronic venous insufficiency

Chronic venous insufficiency (CVI) is a common disorder associated with a variety of symptoms in later disease stages; despite the high prevalence of this pathology, suitable pharmaceutical therapies have not been explored to date. In this context, it was recently reported that a chronic increase in venous wall stress or biomechanical stretch is sufficient to cause development of varicose veins. Recent evidence demonstrate that flavonoids are natural substances that convey the circulatory system functionality, playing a key role in blood flow. Particularly, troxerutin, diosmin and horse chestnut extract, appear protective for the management of vascular diseases. The aim of the present study was to evaluate the effect of a flavonoid compound, containing troxerutin, diosmin and horse chestnut extract on in vitro model on HUVECs cells, due to its production of vasculoregulatory and vasculotropic molecules, on an ex-vivo model on mesenteric vessel contraction, to regularize mesenteric microcirculation and on in vivo model of CVI-induced by saphene vein ligation. Furthermore, the flavonoid compound capacity of extensibility and compatibility with peripheral veins was investigated through a tissue block culture study. The degree of absorption, the contractile venous activity, the histological analysis, the immunoistochemical and immunofluorescence evaluation for VEGF and CD34 were performed, together with inflammatory mediators dosage. For the first time, this research revealed the therapeutic potential of a compound, enriched with flavonoids, to be a supportive treatment, suitable to reduce varicose vein pathophysiology and to regularize venous tone.

The Significance of Pain in Chronic Venous Disease and its Medical Treatment

Chronic venous disease (CVeD) is a highly prevalent condition in the general population, and it has a significant impact on quality of life. While it is usually manifested by obvious signs, such as varicose veins and venous ulcers, other symptoms of the disease are less specific. Among the other symptoms, which include heaviness, swelling, muscle cramps and restless legs, pain is the symptom that most frequently compels CVeD patients to seek medical aid. However, there is a substantial discrepancy between pain severity and clinically detectable signs of CVeD, questioned by several opposing studies. Further evaluation is needed to clarify this subject, and to analyse whether pain development predicts objective CVeD progression. General management of CVeD starts with advising lifestyle changes, such as lowering body mass index and treating comorbidities. However, the mainstay of treatment is compression therapy, with the additional use of pharmacological substances. Venoactive drugs proved to be the drugs of choice for symptom alleviation and slowing the progression of CVeD, with micronized purified flavonoid fraction being the most effective one. Interventional therapy is reserved for advanced stages of the disease.

Eicosanoids: Emerging contributors in stem cell-mediated wound healing

Eicosanoids are bioactive lipid products primarily derived from the oxidation of arachidonic acid (AA). The individual contributions of eicosanoids and stem cells to wound healing have been of great interest. This review focuses on how stem cells work in concert with eicosanoids to create a beneficial environment in the wound bed and in the promotion of wound healing. Stem cells contribute to wound healing through modulating inflammation, differentiating into skin cells or endothelial cells, and exerting paracrine effects by releasing various potent growth factors. Eicosanoids have been shown to stimulate proliferation, migration, homing, and differentiation of stem cells, all of which contribute to the process of wound healing. Increasing evidence has shown that eicosanoids improve wound healing through increasing stem cell densities, stimulating differentiation, and enhancing the angiogenic properties of stem cells. Chronic wounds have become a major problem in health care. Therefore, research regarding the effects of stem cells and eicosanoids in the promotion wound healing is of great importance.

Application of a nitric oxide sensor in biomedicine

In the present study, we describe the biochemical properties and effects of nitric oxide (NO) in intact and dysfunctional arterial and venous endothelium. Application of the NO electrochemical sensor in vivo and in vitro in erythrocytes of healthy subjects and patients with vascular disease are reviewed. The electrochemical NO sensor device applied to human umbilical venous endothelial cells (HUVECs) and the description of others NO types of sensors are also mentioned.

Influence of experimental subarachnoid hemorrhage on nicotine-induced contraction of the rat basilar artery in relation to arachidonic acid metabolites signaling pathway

BACKGROUND

Smoking is one of the most important risk factors for cerebral circulatory disorders. The purpose of this study was to investigate the influence of experimental subarachnoid hemorrhage (SAH) on nicotine-induced contraction (arachidonic acid metabolites) in the basilar arteries of rats.

METHODS

Rats were killed at 1 hour and 1 week after blood injection, and the basilar artery was isolated and cut into a spiral strip.

RESULTS

Testing of cyclooxygenase-1 (COX-1) and 5-lipoxygenase (5-LOX) inhibitors revealed no significant differences in their effects on normal and SAH (1 hour and 1 week). Phospholipase C (PLC) inhibitor (1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17yl)amino)hexyl)-1H-pyrrole-2,5,-dione [U-73122]) slightly inhibited contraction of SAH (1 hour and 1 week) when compared to controls. Phospholipase A2 (PLA2) inhibitor (manoalide) and cytosolic PLA2 (cPLA2) inhibitor (arachidonyltrifluoromenthylketone [AACOCF3]) more strongly attenuated contraction in SAH (1 hour and 1 week) than in controls. Secreted PLA2 (sPLA2) inhibitor (indoxam), PLC inhibitor (2-nitro-4-carboxyphenyl N, N-diphenylcarbamate [NCDC]), and COX-2 inhibitors (nimesulide, (5-methanesulfonamido-6-(2,4-difluorothiophenyl)-1-indanone) [L-745337], and celecoxib) only slightly inhibited contraction of SAH (1 week) when compared to normal and SAH (1 hour). The calcium-independent PLA2 (iPLA2) inhibitor bromoenol lactone (BEL) showed greater inhibition of contraction in SAH (1 hour) when compared to normal and SAH (1 week).

CONCLUSIONS

One week after exposure to SAH, PLC, sPLA2, and COX-2 activity were enhanced and cPLA2 activity was inhibited. One hour after exposure to SAH, PLC activity was enhanced and cPLA2 and iPLA2 activity was inhibited. Such changes of inflammatory arachidonic acid metabolites by smoking after SAH may play important roles in fatal cerebral circulatory disorders, suggesting important implications for the etiology and pathogenesis of SAH.

20-HETE in neovascularization

Cytochrome P450 4A/F (CYP4A/F) converts arachidonic acid (AA) to 20-HETE by ω-hydroxylation. The contribution of 20-HETE to the regulation of myogenic response, blood pressure, and mitogenic actions has been well summarized. This review focuses on the emerging role of 20-HETE in physiological and pathological vascularization. 20-HETE has been shown to regulate vascular smooth muscle cells (VSMC) and endothelial cells (EC) by affecting their proliferation, migration, survival, and tube formation. Furthermore, the proliferation, migration, secretion of proangiogenic molecules (such as HIF-1α, VEGF, SDF-1α), and tube formation of endothelial progenitor cells (EPC) are stimulated by 20-HETE. These effects are mediated through c-Src- and EGFR-mediated downstream signaling pathways, including MAPK and PI3K/Akt pathways, eNOS uncoupling, and NOX/ROS system activation. Therefore, the CYP4A/F-20-HETE system may be a therapeutic target for the treatment of abnormal angiogenic diseases.

Non-esterified polyunsaturated fatty acids distinctly modulate the mitochondrial and cellular ROS production in normoxia and hypoxia

There is an intense discussion about the subcellular origin of the generation of reactive oxygen species (ROS) under hypoxia. Since this fundamental question can be addressed only in a cellular system, the O(2) -sensing rat pheochromocytoma (PC12) cells were used. Severe hypoxia is known to elevate non-esterified fatty acids. Therefore, the site(s) of ROS generation were studied in cells which we simultaneously exposed to hypoxia (1% oxygen) and free fatty acids (FFA). We obtained the following results: (i) at hypoxia, ROS generation increases in PC12 cells but not in mitochondria isolated therefrom. (ii) Non-esterified polyunsaturated fatty acids (PUFA) enhance the ROS release from PC12 cells as well as from mitochondria, both in normoxia and in hypoxia. (iii) PUFA-induced ROS generation by PC12 cells is not decreased either by inhibitors of the cell membrane NAD(P)H oxidase or inhibitors impairing the PUFA metabolism. (iv) PUFA-induced ROS generation of mitochondria is paralleled by a decline of the NADH-cytochrome c reductase activity (reflecting combined enzymatic activity of complex I plus III). (v) Mitochondrial superoxide indicator (MitoSOXred)-loaded cells exposed to PUFA exhibit increased fluorescence indicating mitochondrial ROS generation. In conclusion, elevated PUFA levels enhance cellular ROS level in hypoxia, most likely by impairing the electron flux within the respiratory chain. Thus, we propose that PUFAs are likely to act as important extrinsic factor to enhance the mitochondria-associated intracellular ROS signaling in hypoxia.

Effect of arachidonic acid on hypoxia-induced IL-6 production in mouse ES cells: Involvement of MAPKs, NF-kappaB, and HIF-1alpha

This study examined the role of arachidonic acid (AA) in hypoxia-induced production of interleukin (IL)-6 and its related signaling pathways in mouse embryonic stem (ES) cells. Hypoxia with AA induced IL-6 production, which was mediated by reactive oxygen species (ROS). In addition, hypoxia increased the levels of p38 mitogen-activated protein kinases (MAPKs) and stress-activated protein kinase/c-jun NH(2)-terminal kinase (SAPK/JNK) phosphorylation, which were blocked by antioxidant (vitamin C). Inhibition of p38 MAPK and SAPK/JNK blocked hypoxia- or hypoxia with AA-induced nuclear factor-kappa B (NF-kappaB) activation. Furthermore, hypoxia-induced increase in hypoxia-inducible factor-1alpha (HIF-1alpha) expression was regulated by NF-kappaB activation. Consequently, the increased HIF-1alpha expression induced activation of matrix metalloproteinase (MMP)-2 and MMP-9. The expression of each signaling molecule stimulated an increase in IL-6 production that was greater in hypoxic conditions with AA than with hypoxia alone. Finally, inhibition of IL-6 production using IL-6 antibody or soluble IL-6 receptor attenuated the hypoxia-induced increases in DNA synthesis of mouse ES cells. In conclusion, AA potentiates hypoxia-induced IL-6 production through the MAPKs, NF-kappaB, and HIF-1alpha pathways in mouse ES cells.

Arachidonic acid potentiates hypoxia-induced VEGF expression in mouse embryonic stem cells: involvement of Notch, Wnt, and HIF-1α

Recent investigations suggest that hypoxia increases the release of fatty acids, which participate in the regulation of cytokine synthesis and cell growth. Therefore, in this study, we examined the effect of arachidonic acid (AA) on hypoxia-induced vascular endothelial growth factor (VEGF) expression and its related signaling pathways in mouse embryonic stem (ES) cells. Hypoxia increased the level of [3H]AA release and VEGF expression. AA treatment concurrent with hypoxia further increased the PGE2 production and VEGF expression level, which was inhibited by the suppression of cPLA2 and cyclooxygenase 2 (COX-2) pathways. Hypoxia increased the level of Notch-1 and Wnt-1/β-catenin expression, which was blocked by the inhibition of COX-2, and inhibition of Notch-1 by γ-secretase inhibitor blocked Wnt-1 activation. Moreover, the hypoxia-induced increase of hypoxia-inducible factor 1α (HIF-1α) expression induced Notch-1 activation and was regulated by Wnt-1 activation. The expression of each signaling molecule induced an increase in VEGF expression that was greater in hypoxia with AA than in hypoxia alone. The inhibition of VEGF expression using VEGF-targeted small interfering RNA decreased the hypoxia-induced increase in cell cycle regulatory protein expression, DNA synthesis, and cell number, suggesting that hypoxia-induced VEGF expression stimulates proliferation of mouse ES cells. In conclusion, AA potentiates hypoxia-induced VEGF expression in mouse ES cells through the Notch-1, Wnt-1, and HIF-1α pathways.

Short-period hypoxia increases mouse embryonic stem cell proliferation through cooperation of arachidonic acid and PI3K/Akt signalling pathways

Hypoxia plays important roles in some early stages of mammalian embryonic development and in various physiological functions. This study examined the effect of arachidonic acid on short-period hypoxia-induced regulation of G(1) phase cell-cycle progression and inter-relationships among possible signalling molecules in mouse embryonic stem cells. Hypoxia increased the level of hypoxia-inducible factor-1alpha (HIF-1alpha) expression and H2O2 generation in a time-dependent manner. In addition, hypoxia increased the levels of cell-cycle regulatory proteins (cyclin D(1), cyclin E, cyclin-dependent kinase 2 (CDK2) and CDK4). Maximum increases in the level of these proteins and retinoblastoma phosphorylation were observed after 12-24 h of exposure to hypoxic conditions, and then decreased. Alternatively, the level of the CDK inhibitors, p21(Cip1) and p27(Kip1) were decreased. These results were consistent with the results of [3H]-thymidine incorporation and cell counting. Hypoxia also increased the level of [3H]-arachidonic acid release and inhibition of cPLA(2) reduced hypoxia-induced increase in levels of the cell-cycle regulatory proteins and [3H]-thymidine incorporation. The level of cyclooxygenase-2 (COX-2) was also increased by hypoxia and inhibition of COX-2 decreased the levels of cell-cycle regulatory proteins and [3H]-thymidine incorporation. Indeed, the percentage of cells in S phase, levels of cell cycle regulatory proteins, and [3H]-thymidine incorporation were further increased in hypoxic conditions with arachidonic acid treatment compared to normoxic conditions. Hypoxia-induced Akt and mitogen-activated protein kinase (MAPK) phosphorylation was inhibited by vitamin C (antioxidant, 10(-3) M). In addition, hypoxia-induced increase of cell-cycle regulatory protein expression and [(3)H]-thymidine incorporation were attenuated by LY294002 (PI3K inhibitor, 10(-6) M), Akt inhibitor (10(-6) M), rapamycin (mTOR inhibitor, 10(-9) M), PD98059 (p44/42 inhibitor, 10(-5) M), and SB203580 (p38 MAPK inhibitor, 10(-6) M). Furthermore, hypoxia-induced increase of [(3)H]-arachidonic acid release was blocked by PD98059 or SB203580, but not by LY294002 or Akt inhibitor. In conclusion, arachidonic acid up-regulates short time-period hypoxia-induced G(1) phase cyclins D(1) and E, and CDK 2 and 4, in mouse embryonic stem cells through the cooperation of PI3K/Akt/mTOR, MAPK and cPLA(2)-mediated signal pathways.

Pharmacological nature of nicotine-induced contraction in the rat basilar artery: Involvement of arachidonic acid metabolites

The pharmacological nature of nicotine-induced contraction in the rat basilar artery is poorly understood. The purpose of this study was to investigate the endothelium dependency and involvement of arachidonic acid metabolites in nicotine-induced contraction in the rat basilar artery. The rat basilar artery was removed from the brain and cut into a spiral preparation. Nicotine (3x10(-5) to 10(-2) M) induced the concentration-dependent contraction in the rat basilar artery, and the maximal contraction was obtained at 3x10(-3) M. The contraction induced by nicotine (3x10(-3) M) was significantly attenuated by the presence of saponin (0.05 mg/ml, 15 min). Phospholipase C (PLC) inhibitors (NCDC and U-73122), calcium-independent phospholipase A(2) (iPLA(2)) inhibitor (BEL), cyclooxygenase-2 (COX-2) inhibitors (nimesulide, L-745,337 and celecoxib), and a 5-lipoxygenase (5-LOX) inhibitor (ZM-230487) concentration-dependently attenuated the nicotine-induced contraction. A cytosolic phospholipase A(2) (cPLA(2)) inhibitor (AACOCF3), secretory phospholipase A(2) (sPLA(2)) inhibitor (indoxam), and cyclooxygenase-1 (COX-1) inhibitors (flurbiprofen and ketoprofen) did not affect the nicotine-induced contraction. From these results, it was suggested that nicotine-induced contraction in the rat basilar artery is endothelium-dependent and is due to arachidonic acid metabolites.

[Pathophysiology of pain in venous disease]

Pain is the leading complaint of patients with venous disease. It has a significant effect on the patient's quality-of-life. For the clinician and the researcher however it is difficult to apprehend how pain is related to the venous disease, both because of the multiple factors involved and because of the lack of any strong relationship between pain symptoms and the severity of the venous disease. Currently, several hypotheses concerning the pathogenesis of pain in venous disease have focused on the causal impact of local inflammation. Over the last five years, a large body of evidence has been accumulation showing an inflammatory reaction around varicose veins, but the precise mechanism of how inflammatory mediators interact with venous nociceptors, which might explain part of the variability in pain observed in venous disease, remains elusive, both clinically and experimentally.

Intermittent hypoxia changes HIF-1alpha phosphorylation pattern in endothelial cells: unravelling of a new PKA-dependent regulation of HIF-1alpha

Vascularized tumors are exposed to intermittent hypoxia, that is, hypoxia followed by periods of reoxygenation. Abnormal structure and dysfunction of tumor blood vessels are responsible for these conditions. These repeated short periods of hypoxia concern tumor cells as well as endothelial cells. However, the effects of intermittent hypoxia are poorly understood. The aim of this study was to investigate the effects of intermittent hypoxia on endothelial cells and particularly on HIF-1alpha, a central actor in adaptive response to hypoxia. For that, endothelial cells were exposed to four repeated cycles of 1-h hypoxia followed by 30 min of reoxygenation. We showed that repeated cycles of hypoxia/reoxygenation induced a modification in HIF-l alpha phosphorylation pattern: a progressive increase in HIF-1alpha phosphorylated form was observed during the hypoxic periods. Activation of p42/p44, Akt and PKA was observed in parallel. PKA was shown to be involved in the phosphorylation of HIF-lalpha under intermittent hypoxia, while p42/p44 and Akt were not. As HIF-1 activity is often associated with enhanced cell survival, a better knowledge of the effects of intermittent hypoxia on endothelial cells and the highlight of particular mechanisms induced by intermittent hypoxia are essential to understand the behavior of endothelial cells during neo-angiogenesis.

Role of phospholipase A2 in the induction of drip loss in porcine muscle

The role of phospholipase A2 in the induction of drip loss from pig muscle has been investigated. In samples from porcine M. longissimus dorsi, total PLA2 activity as well as mRNA and protein levels of the group VIA iPLA2 (iPLA2-VIA) increased during the initial 4 h post-mortem period. Morphological studies of porcine muscle showed that at 4 h post-mortem, gaps had formed between muscle fibers and that the sarcolemma membrane borders appeared blurred. At the same time iPLA2-VIA protein levels were increased inside muscle fibers and at the sarcolemma. iPLA2-VIA mRNA abundance in samples from different breeds of pigs with variations in drip loss revealed no clear correlation between drip loss level and iPLA2-VIA expression. Together, these data indicate that during the post-mortem period, iPLA2-VIA expression and activity is increased at the muscle fiber membranes. PLA2 activity may affect membrane permeability and consequently the progression of drip formation in porcine muscle.

Survival signalling in Alzheimer's disease

Significant advancements in our understanding of cell-survival signalling in AD (Alzheimer's disease) stem from recent investigations into the metabolism, trafficking and fate of the essential omega-3 fatty acid DHA (docosahexaenoic acid) (C(22:6), n=3). Brain synaptic terminals and neuronal plasma membranes are highly enriched in DHA, and deficiencies in this polyunsaturated fatty acid are characteristic of AD-affected brain. Oxidative stress, targeting phospholipids containing DHA, and age-related DHA depletion are associated with the progressive erosion of normal cognitive function in AD. Current studies support the idea that DHA itself and novel DHA-derived neural synapse- and membrane-derived lipid messengers have considerable potential to modulate cell survival signalling in stressed cultured neural cell models in vitro and in mammalian models of learning, memory and AD in vivo. Key players in this intrinsic rescue system include the alpha-secretase-processed neurotrophin sAPPalpha [soluble APPalpha (amyloid precursor protein alpha)] peptide, the DHA-derived 10,17S-docosatriene NPD1 (neuroprotectin D1), a tandem brain cytosolic phospholipase A(2) and 15-lipoxygenase enzymatic system that biosynthesizes NPD1, and a small family of anti-apoptotic neuroprotective genes that encode Bcl-2, Bcl-X(L) and Bfl-1 (A1). This paper reviews current ideas regarding DHA and the oxygenated DHA derivative NPD1, intrinsically triggered biolipid neuroprotectants that along with their associated rescue pathways, contribute to life-or-death decisions of brain cells during homoeostasis, aging and neurodegenerative disease.

Hypoxia and lipid signaling

Sufficient oxygen supply is crucial for the development and physiology of mammalian cells and tissues. When simple diffusion of oxygen becomes inadequate to provide the necessary flow of substrate, evolution has provided cells with tools to detect and respond to hypoxia by upregulating the expression of specific genes, which allows an adaptation to hypoxia-induced stress conditions. The modulation of cell signaling by hypoxia is an emerging area of research that provides insight into the orchestration of cell adaptation to a changing environment. Cell signaling and adaptation processes are often accompanied by rapid and/or chronic remodeling of membrane lipids by activated lipases. This review highlights the bi-directional relation between hypoxia and lipid signaling mechanisms.

Metabolic coronary flow regulation--current concepts

The concept of metabolic coronary flow control provides a rationale for the close relationship of coronary flow and myocardial metabolic rate of oxygen. The concept is based on the presence of an oxygen (metabolic) sensor coupled functionally to effector mechanisms, which control vascular tone. Four modes of metabolic control models have been proposed. 1) An oxygen sensor located in the wall of coronary vessels coupling to smooth muscle tension. Endothelial prostaglandin production may support this concept. 2) An oxygen sensing mechanism located in the myocardium and changing metabolism in response to changes of local pO(2). Adenosine is a metabolite produced at an accelerated rate when the supply-to-demand relationship for oxygen falls. 3) Sensing of oxygen turnover may be achieved by carbon dioxide production and, potentially, by mitochondrial production of reactive oxygen species. 4) The red blood cell might serve as an oxygen sensor in response to changes of haemoglobin oxygenation. A potential link to vessel relaxation may be red cell ATP release. A large body of experimental evidence supports the notion that K(ATP) channels play a significant role causing smooth muscle hyper-polarization. However, additional yet unknown effector mechanisms must exist, because block of K(ATP) channels does not lead to deterioration of coronary flow control under conditions of exercise. Thus, although several lines of evidence show that metabolic flow regulation is effective during hypoxic conditions,mechanisms mediating normoxic metabolic flow control still await further clarification.

Hypoxia-sensitive domain in the human cytosolic phospholipase A2 promoter

Transcription from the human cytosolic phospholipase A2 gene has been observed to be hypoxia sensitive in endothelial cells cultured from the human cerebral microvasculature. DNA sequence analysis of the cytosolic phospholipase A2 promoter revealed the presence of a distal cluster of potential hypoxia-inducible factor-1-DNA binding sites homologous to 5'-NCGTG-3', located between -1087 and -996 bp of the major start of transcription at +1 bp (Genbank U08374). Gel shift assay showed strong hypoxia-inducible factor-1-DNA binding to only a single site within this cluster, and promoter deletion analysis indicated the functional importance of this chromatin domain in conveying oxygen sensitivity to cytosolic phospholipase A2 gene transcription. Non-functional hypoxia inducible factor-1-DNA binding sites flanking a single functional hypoxia-inducible factor-1-DNA binding site in this hypoxia-sensitive domain may promote oxygen sensitivity via transcription factor clustering or Circe effects.

Activation of PLA2 isoforms by cell swelling and ischaemia/hypoxia

Phospholipase A2 (PLA2) activity is increased in mammalian cells in response to numerous stimuli such as osmotic challenge, oxidative stress and exposure to allergens. The increased PLA2 activity is seen as an increased release of free, polyunsaturated fatty acids, e.g. arachidonic acid and membrane-bound lysophospholipids. Even though arachidonic acid acts as a second messenger in its own most mammalian cells seem to rely on oxidation of the fatty acid into highly potent second messengers via, e.g. cytochrome P450, the cyclo-oxygenase, or the lipoxygenase systems for downstream signalling. Here, we review data that illustrates that stress-induced PLA2 activity involves various PLA2 subtypes and that the PLA2 in question is determined by the cell type and the physiological stress condition.

Hypoxia increases group IIA phospholipase A(2) expression under inflammatory conditions in rat renal mesangial cells

Hypoxia evokes a common mechanism of oxygen sensing mediated by hypoxia-inducible transcription factors (HIF) in many mammalian cells. This study investigated the effect of hypoxia on group-IIA secretory phospholipase A(2) (sPLA(2)-IIA) expression in renal mesangial cells. Stimulation of cells with IL-1beta under normoxic conditions (21% O(2)) is known to induce expression and secretion of the group sPLA(2)-IIA. This induction is further enhanced by constantly reducing the O(2) concentration to 1% O(2), and is accompanied by increased sPLA(2) activity. To see whether hypoxia potentiates IL-1beta-induced sPLA(2)-IIA gene expression, a 2.67-kb fragment of the rat sPLA(2)-IIA promoter was fused to a luciferase reporter construct and used to transfect mesangial cells. Hypoxia alone is not able to activate the sPLA(2) promoter, whereas it significantly enhances IL-1beta-stimulated promoter activity. A deletion mutant of the promoter that lacks the two putative hypoxia responsive elements (HRE) is devoid of the potentiating effect of hypoxia. Moreover, site-directed mutagenesis of either of the two HRE is sufficient to abolish the potentiating effect of hypoxia. Electrophoretic mobility shift assays show that HIF-2alpha, which is the only HIF subtype expressed in mesangial cells, binds to both HRE in the sPLA(2)-IIA promoter. In summary, the data show that in an inflammatory setting hypoxia is able to potentiate sPLA(2)-IIA expression and activity in renal mesangial cells, and thereby may critically contribute to enhanced formation of inflammatory lipid mediators seen in a diverse range of kidney diseases.

Activation of phospholipase A2 and MAP kinases by oxidized low-density lipoproteins in immortalized GP8.39 endothelial cells

In immortalized rat brain endothelial cells (GP8.39), we have previously shown that oxidized LDL (oxLDL), after 24-h treatment, stimulates arachidonic acid release and phosphatidylcholine hydrolysis by activation of cytosolic phospholipase A(2) (cPLA(2)). A putative role for MAPKs in this process has emerged. Here, we studied the contribution of Ca(2+)-independent phospholipase A(2) (iPLA(2)), and the role of the MAP kinase family as well as both cPLA(2) and iPLA(2) mRNA expression by RT-PCR in oxLDL toxicity to GP8.39 cells in vitro. The activation of extracellular signal-regulated kinases ERK1/2, p38 and c-Jun NH(2)-terminal kinase (JNK) was assessed with Western blotting and kinase activity assays. iPLA(2) activity, which was found as a membrane-associated enzyme, was more stimulated by oxLDL compared with native LDL. The phosphorylation of ERK1/2, p38 and JNKs was also significantly enhanced in a dose-dependent manner. PD98059, an ERK inhibitor, SB203580, a p38 inhibitor, and SP600125, an JNK inhibitor, abolished the stimulation of all three members of the MAPK family by oxLDL. Confocal microscopy analysis and subcellular fractionation confirmed either an increase in phosphorylated form of ERKs, p38 and JNKs, or their nuclear translocation upon activation. A strong inhibition of MAPK activation was also observed when endothelial cells were treated with GF109203X, a PKC inhibitor, indicating the important role of both PKC and all three MAPKs in mediating the maximal oxLDL response. Finally, compared with samples untreated or treated with native LDL, treatment with oxLDL (100 muM hydroperoxides) for 24 h significantly increased the levels of constitutively expressed iPLA(2) protein (by 5.1-fold) and mRNA (by 3.1-fold), as well as cPLA(2) protein (by 4.4-fold) and mRNA (by 1.5-fold). Together, these data link the stimulation of PKC-ERK-p38-JNK pathways and PLA(2) activity by oxLDL to the prooxidant mechanism of the lipoprotein complex, which may initially stimulate the endothelial cell reaction against noxious stimuli as well as metabolic repair, such as during inflammation and atherosclerosis.

Arachidonic acid cascade in endothelial pathobiology

Arachidonic acid (AA) and its metabolites (eicosanoids) represent powerful mediators, used by organisms to induce and suppress inflammation as a part of the innate response to disturbances. Several cell types participate in the synthesis and release of AA metabolites, while many cell types represent the targets for eicosanoid action. Endothelial cells (EC), forming a semi-permeable barrier between the interior space of blood vessels and underlying tissues, are of particular importance for the development of inflammation, since endothelium controls such diverse processes as vascular tone, homeostasis, adhesion of platelets and leukocytes to the vascular wall, and permeability of the vascular wall for cells and fluids. Proliferation and migration of endothelial cells contribute significantly to new vessel development (angiogenesis). This review discusses endothelial-specific synthesis and action of arachidonic acid derivatives with a particular focus on the mechanisms of signal transduction and associated intracellular protein targets.

Differential and quantitative molecular analysis of ischemia complexity reduction by isotopic labeling of proteins using a neural embryonic stem cell model

The analysis of rapid changes of protein expression in living systems in response to insults requires rigorous methods of complexity reduction. To control dynamic pattern of hundreds or even thousands of protein isoforms, we applied a novel method of differential molecular analysis to a cellular model which is suited to study ischemia. Neural derivatives of murine embryonic stem cells were exposed to chemical ischemia. The model was used to obtain starting material for a quantitative differential proteomics analysis. Fractionation of phosphoproteins from these samples and subsequent identification by mass spectrometry of differential proteins provide proof of principle of how novel molecular analytical tools provide new insight into the network of neuroprotective molecular events during specific situations of neuronal stress and related pharmaceutical intervention. Our results indicate a particular role of an isoform of the acidic calcium-independent phospholipase A2 in this type of insult.

Purification and analysis of a phospholipase A2-like lytic factor of Trichomonas vaginalis

Trichomonas vaginalis produces soluble factors that have been reported to have the ability to damage target cells in vitro, and it has been hypothesized that these factors may play a role in the pathogenesis of human trichomoniasis. A lytic factor (LF) was purified from T. vaginalis, and the molecular characteristics of LF were determined. T. vaginalis extract was subjected to hydrophobic chromatography with a 10 to 60% N-propanol gradient in 0.1 M ammonium acetate, resulting in the elution of LF from the column at 30% N-propanol. Cytotoxicity assays revealed that LF was cytotoxic to WEHI 164 cells and bovine red blood cells, and inactivation of LF by treatment with trypsin suggested that the active component of LF was a protein. Size exclusion chromatography of LF produced two fractions at 144 and 168 kDa, and analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of LF under reducing conditions revealed two subunits of 57 and 60 kDa. Results of a fluorescence assay of LF on carboxyfluorescein-labeled liposomes composed of phosphatidylcholine-cholesterol showed that liposomes were hydrolyzed, suggesting that LF had phospholipase activity. Thin-layer chromatography analysis of BODIPY (4,4-difluoro-3a,4adiaza-s-indacene)-labeled phosphatidylcholine treated with LF demonstrated products that migrated identically to the products produced by treatment with phospholipase A(2) (PLA(2)). These results suggest that LF is a PLA(2) and may be an important virulence factor of T. vaginalis mediating the destruction of host cells and contributing to tissue damage and inflammation in trichomoniasis.

PLA2 activity is required for nuclear shrinkage in caspase-independent cell death

Apoptosis is defined on the basis of morphological changes like nuclear fragmentation and chromatin condensation, which are dependent on caspases. Many forms of caspase-independent cell death have been reported, but the mechanisms are still poorly understood. We found that hypoxic cell death was independent of caspases and was associated with significant nuclear shrinkage. Neither Bcl-2 nor Apaf-1 deficiency prevented hypoxic nuclear shrinkage. To understand the molecular mechanism of the nuclear shrinkage, we developed an in vitro system using permeabilized cells, which allowed us to purify a novel member of the phospholipase A2 (PLA2) family that induced nuclear shrinkage. Purified PLA2 induced nuclear shrinkage in our permeabilized cell system. PLA2 inhibitors prevented hypoxic nuclear shrinkage in cells and cell death. Hypoxia caused elevation of PLA2 activity and translocation of intracellular PLA2s to the nucleus. Knockdown of the Ca2+-independent PLA2 delayed nuclear shrinkage and cell death. These results indicate that Ca2+-independent PLA2 is crucial for a caspase-independent cell death signaling pathway leading to nuclear shrinkage.

Endothelium and Venotropic Drugs in Chronic Venous Insufficiency: A Review

Objective:

To review the literature concerning chronic venous disease of the leg and the mechanisms of action of venotropic drugs.

Methods:

The authors identified relevant papers from their own collection and from medical literature databases.

Synthesis:

Endothelial cell activation caused by ex-posure to the hypoxic conditions that develop during blood stasis in chronic venous insufficiency patients is proposed to be one factor initiating a pro-inflammatory process in the leg veins. Recruited and activated neutrophils would then be responsible for alterations of the venous wall, typical of what is observed in varicose veins. Venotropic drugs used in the treatment of chronic venous insufficiency patients have long been known to decrease vascular permeability and increase venous tone. Recently, it has been shown that they are also able to prevent endothelial cell activation by hypoxia and a precise biochemical target common to all of them has been identified: the mitochondrial respiratory chain.

Conclusion:

The influence of venotropic drugs on the mitochondrial respiratory chain provides a rational explanation for the therapeutic benefit to patients of this class of drugs.