The effect of inhibition of Ca2+-independent phospholipase A2 on chemotherapeutic-induced death and phospholipid profiles in renal cells

Knockdown of iPLA2γ enhances cisplatin-induced apoptosis by increasing ROS-dependent peroxidation of mitochondrial phospholipids in bladder cancer cells

Cisplatin (CDDP) is a platinum-based drug with anti-cancer activity and is widely used as a standard therapy for bladder cancer. It is well known that CDDP causes cell death by increasing the generation of reactive oxygen species (ROS) and lipid peroxidation, but the mechanism of its anti-cancer effects has not been fully elucidated. There are still some problems such as chemoresistance in CDDP therapy. In the present study, we found the expression of Ca2+-independent phospholipase A2γ (iPLA2γ), which has been reported to regulate cellular redox homeostasis by inhibiting lipid peroxide accumulation, in human bladder cancer tissues. Thus, we investigated the effect of iPLA2γ knockdown on CDDP-induced bladder cancer cell death. As a result, we found that iPLA2γ knockdown significantly enhanced CDDP-induced apoptosis, intracellular and mitochondrial ROS production, cytochrome c release and caspase activation in bladder cancer cells. Moreover, mitochondrial membrane potential was decreased and peroxidation of mitochondrial phospholipids was increased by iPLA2γ knockdown. It was also shown that co-treatment of bromoenol lactone, an iPLA2 inhibitor, increased CDDP-induced apoptosis. These results indicated that iPLA2γ plays an important role in protecting bladder cancer cells from CDDP-induced apoptosis, and that iPLA2γ inhibitors might represent a novel strategy in CDDP-based multi-drug therapy.

Investigating the Potential of Lipids for Use as Biomarkers for Glioblastoma via an Untargeted Lipidomics Approach

OBJECTIVE

The types and functions of lipids involved in glioblastoma (GB) are not well known. Lipidomics is a new field that examines cellular lipids on a large scale and novel aplication of lipidomics in the biomedical sciences have emerged. This study aimed to investigate the potential of blood lipids for use as biomarkers for the diagnosis of GB via untargated lipidomic approach. Gaining a deeper understanding of lipid metabolism in patients with GB can contribute to the early diagnosis with GB patiens and also development of novel and better therapeutic options.

METHODS

This study was performed using blood samples collected from 14 patients (eight females and six males) and 14 controls (eight females and six males). Lipids were extracted from blood samples and quantified using phosphorus assay. Lipid profiles of between patients with GB and controls were compared via an untargeted lipidomics approach using 6530 Accurate-Mass Q-TOF LC/MS mass spectrometer.

RESULTS

According to the results obtained using the untargeted lipidomics approach, differentially regulated lipid species, including fatty acid (FA), glycerolipid (GL), glycerophospholipid (PG), saccharolipid (SL), sphingolipid (SP), and sterol lipid (ST) were identified between in patients with GB and controls.

CONCLUSION

Differentially regulated lipids were identified in patients with GB, and these lipid species were predicted as potential biomarkers for diagnosis of GB.

Perfluorooctanesulfonic Acid and Perfluorohexanesulfonic Acid Alter the Blood Lipidome and the Hepatic Proteome in a Murine Model of Diet-Induced Obesity

Perfluoroalkyl substances (PFAS) represent a family of environmental toxicants that have infiltrated the living world. This study explores diet-PFAS interactions and the impact of perfluorooctanesulfonic acid (PFOS) and perfluorohexanesulfonic (PFHxS) on the hepatic proteome and blood lipidomic profiles. Male C57BL/6J mice were fed with either a low-fat diet (10.5% kcal from fat) or a high fat (58% kcal from fat) high carbohydrate (42 g/l) diet with or without PFOS or PFHxS in feed (0.0003% wt/wt) for 29 weeks. Lipidomic, proteomic, and gene expression profiles were determined to explore lipid outcomes and hepatic mechanistic pathways. With administration of a high-fat high-carbohydrate diet, PFOS and PFHxS increased hepatic expression of targets involved in lipid metabolism and oxidative stress. In the blood, PFOS and PFHxS altered serum phosphatidylcholines, phosphatidylethanolamines, plasmogens, sphingomyelins, and triglycerides. Furthermore, oxidized lipid species were enriched in the blood lipidome of PFOS and PFHxS treated mice. These data support the hypothesis that PFOS and PFHxS increase the risk of metabolic and inflammatory disease induced by diet, possibly by inducing dysregulated lipid metabolism and oxidative stress.

Identification of lipidomic profiles associated with drug-resistant prostate cancer cells

BACKGROUND

The association of circulating lipids with clinical outcomes of drug-resistant castration-resistant prostate cancer (DR-CRPC) is not fully understood. While it is known that increases in select lipids correlate to decreased survival, neither the mechanisms mediating these alterations nor the correlation of resistance to drug treatments is well characterized.

METHODS

This gap-in-knowledge was addressed using in vitro models of non-cancerous, hormone-sensitive, CRPC and drug-resistant cell lines combined with quantitative LC-ESI-Orbitrap-MS (LC-ESI-MS/MS) lipidomic analysis and subsequent analysis such as Metaboanalyst and Lipid Pathway Enrichment Analysis (LIPEA).

RESULTS

Several lipid regulatory pathways were identified that are associated with Docetaxel resistance in prostate cancer (PCa). These included those controlling glycerophospholipid metabolism, sphingolipid signaling and ferroptosis. In total, 7460 features were identified as being dysregulated between the cell lines studied, and 21 lipid species were significantly altered in drug-resistant cell lines as compared to nonresistant cell lines. Docetaxel resistance cells (PC3-Rx and DU145-DR) had higher levels of phosphatidylcholine (PC), oxidized lipid species, phosphatidylethanolamine (PE), and sphingomyelin (SM) as compared to parent control cells (PC-3 and DU-145). Alterations were also identified in the levels of phosphatidic acid (PA) and diacylglyceride (DAG), whose levels are regulated by Lipin (LPIN), a phosphatidic acid phosphatase that converts PA to DAG. Data derived from cBioPortal demonstrated a population of PCa patients expressing mutations aligning with amplification of LPIN1, LPIN2 and LPIN3 genes. Lipin amplification in these genes correlated to decreased survival in these patients. Lipin-1 mRNA expression also showed a similar trend in PCa patient data. Lipin-1, but not Lipin-2 or - 3, was detected in several prostate cancer cells, and was increased in 22RV1 and PC-3 cell lines. The increased expression of Lipin-1 in these cells correlated with the level of PA.

CONCLUSION

These data identify lipids whose levels may correlate to Docetaxel sensitivity and progression of PCa. The data also suggest a correlation between the expression of Lipin-1 in cells and patients with regards to prostate cancer cell aggressiveness and patient survivability. Ultimately, these data may be useful for identifying markers of lethal and/or metastatic prostate cancer.

Lipid imaging for visualizing cilastatin amelioration of cisplatin-induced nephrotoxicity

Nephrotoxicity is a major limitation to cisplatin antitumor therapies. Cilastatin, an inhibitor of renal dehydropeptidase-I, was recently proposed as a promising nephroprotector against cisplatin toxicity, preventing apoptotic cell death. In this work, cilastatin nephroprotection was further investigated in a rat model, with a focus on its effect on 76 renal lipids altered by cisplatin, including 13 new cisplatin-altered mitochondrial cardiolipin species. Lipid imaging was performed with MALDI mass spectrometry imaging (MALDI-MSI) in kidney sections from treated rats. Cilastatin was proved to significantly diminish the lipid distribution alterations caused by cisplatin, lipid levels being almost completely recovered to those of control samples. The extent of recovery of cisplatin-altered lipids by cilastatin turned out to be relevant for discriminating direct or secondary lipid alterations driven by cisplatin. Lipid peroxidation induced by cisplatin was also shown to be reduced when cilastatin was administered. Importantly, significant groups separation was achieved during multivariate analysis of cortex and outer-medullary lipids, indicating that damaged kidney can be discerned from the nephroprotected and healthy groups and classified according to lipid distribution. Therefore, we propose MALDI-MSI as a powerful potential tool offering multimolecule detection possibilities to visualize and evaluate nephrotoxicity and nephroprotection based on lipid analysis.

Effects of high-fat diet and age on the blood lipidome and circulating endocannabinoids of female C57BL/6 mice

Alterations in lipid metabolism play a significant role in the pathogenesis of obesity-associated disorders, and dysregulation of the lipidome across multiple diseases has prompted research to identify novel lipids indicative of disease progression. To address the significant gap in knowledge regarding the effect of age and diet on the blood lipidome, we used shotgun lipidomics with electrospray ionization-mass spectrometry (ESI-MS). We analyzed blood lipid profiles of female C57BL/6 mice following high-fat diet (HFD) and low-fat diet (LFD) consumption for short (6weeks), long (22weeks), and prolonged (36weeks) periods. We examined endocannabinoid levels, plasma esterase activity, liver homeostasis, and indices of glucose tolerance and insulin sensitivity to compare lipid alterations with metabolic dysregulation. Multivariate analysis indicated differences in dietary blood lipid profiles with the most notable differences after 6weeks along with robust alterations due to age. HFD altered phospholipids, fatty acyls, and glycerolipids. Endocannabinoid levels were affected in an age-dependent manner, while HFD increased plasma esterase activity at all time points, with the most pronounced effect at 6weeks. HFD-consumption also altered liver mRNA levels of PPARα, PPARγ, and CD36. These findings indicate an interaction between dietary fat consumption and aging with widespread effects on the lipidome, which may provide a basis for identification of female-specific obesity- and age-related lipid biomarkers.

Extraction, chromatographic and mass spectrometric methods for lipid analysis

Lipids make up a diverse subset of biomolecules that are responsible for mediating a variety of structural and functional properties as well as modulating cellular functions such as trafficking, regulation of membrane proteins and subcellular compartmentalization. In particular, phospholipids are the main constituents of biological membranes and play major roles in cellular processes like transmembrane signaling and structural dynamics. The chemical and structural variety of lipids makes analysis using a single experimental approach quite challenging. Research in the field relies on the use of multiple techniques to detect and quantify components of cellular lipidomes as well as determine structural features and cellular organization. Understanding these features can allow researchers to elucidate the biochemical mechanisms by which lipid-lipid and/or lipid-protein interactions take place within the conditions of study. Herein, we provide an overview of essential methods for the examination of lipids, including extraction methods, chromatographic techniques and approaches for mass spectrometric analysis.

Lipidomics applications for disease biomarker discovery in mammal models

Lipidomics is a lipid-targeted metabolomics approach focusing on comprehensive analysis of all lipids with which they interact in biology systems. Recent technological advances in MS and chromatography have greatly enhanced the developments and applications of metabolic profiling of diverse lipids in complex biological samples. Lipidomics will not only provide insights into the specific functions of lipid species in health and disease, but will also identify potential biomarkers for establishing preventive or therapeutic programs for human disease. In this review, recent applications of lipidomics to understand animal models of disease such as metabolic syndromes, neurodegenerative diseases, cancer and infectious diseases are considered. We also discuss the lipidomics for the future perspectives and their potential problems.

Lipidomics: Novel insight into the biochemical mechanism of lipid metabolism and dysregulation-associated disease

The application of lipidomics, after genomics, proteomics and metabolomics, offered largely opportunities to illuminate the entire spectrum of lipidome based on a quantitative or semi-quantitative level in a biological system. When combined with advances in proteomics and metabolomics high-throughput platforms, lipidomics provided the opportunity for analyzing the unique roles of specific lipids in complex cellular processes. Abnormal lipid metabolism was demonstrated to be greatly implicated in many human lifestyle-related diseases. In this review, we focused on lipidomic applications in brain injury disease, cancer, metabolic disease, cardiovascular disease, respiratory disease and infectious disease to discover disease biomarkers and illustrate biochemical metabolic pathways. We also discussed the analytical techniques, future perspectives and potential problems of lipidomic applications. The application of lipidomics in disease biomarker discovery provides the opportunity for gaining novel insights into biochemical mechanism.

Differential effects of cocaine exposure on the abundance of phospholipid species in rat brain and blood

BACKGROUND

Lipid profiles in the blood are altered in human cocaine users, suggesting that cocaine exposure can induce lipid remodeling.

METHODS

Lipid changes in the brain tissues of rats sensitized to cocaine were determined through shotgun lipidomics using electrospray ionization-mass spectrometry (ESI-MS). We also performed pairwise principal component analysis (PCA) to assess cocaine-induced changes in blood lipid profiles. Alterations in the abundance of phospholipid species were correlated with behavioral changes in the magnitude of either the initial response to the drug or locomotor sensitization.

RESULTS

Behavioral sensitization altered the relative abundance of several phospholipid species in the hippocampus and cerebellum, measured one week following the final exposure to cocaine. In contrast, relatively few effects on phospholipids in either the dorsal or the ventral striatum were observed. PCA analysis demonstrated that cocaine altered the relative abundance of several glycerophospholipid species as compared to saline-injected controls in blood. Subsequent MS/MS analysis identified some of these lipids as phosphatidylethanolamines, phosphatidylserines and phosphatidylcholines. The relative abundance of some of these phospholipid species were well-correlated (R(2) of 0.7 or higher) with either the initial response to cocaine or locomotor sensitization.

CONCLUSION

Taken together, these data demonstrate that a cocaine-induced sensitization assay results in the remodeling of specific phospholipids in rat brain tissue in a region-specific manner and also alters the intensities of certain types of phospholipid species in rat blood. These results further suggest that such changes may serve as biomarkers to assess the neuroadaptations occurring following repeated exposure to cocaine.

Lipidomics: new insight into kidney disease

Due to the incidence of type-2 diabetes and hypertension, chronic kidney disease (CKD) has emerged as a major public health problem worldwide. CKD results in premature death from accelerated cardiovascular disease and various other complications. Early detection, careful monitoring of renal function, and response to therapeutic intervention are critical for prevention of CKD progression and its complications. Unfortunately, traditional biomarkers of renal function are insufficiently sensitive or specific to detect early stages of disease when therapeutic intervention is most effective. Therefore, more sensitive biomarkers of kidney disease are needed for early diagnosis, monitoring, and effective treatment. CKD results in profound changes in lipid and lipoprotein metabolism that, in turn, contribute to progression of CKD and its cardiovascular complications. Lipids and lipid-derived metabolites play diverse and critically important roles in the structure and function of cells, tissues, and biofluids. Lipidomics is a branch of metabolomics, which encompasses the global study of lipids and their biologic function in health and disease including identification of biomarkers for diagnosis, prognosis, prevention, and therapeutic response for various diseases. This review summarizes recent developments in lipidomics and its application to various kidney diseases including chronic glomerulonephritis, IgA nephropathy, chronic renal failure, renal cell carcinoma, diabetic nephropathy, and acute renal failure in clinical and experimental research. Analytical technologies, data analysis, as well as currently known metabolic biomarkers of kidney diseases are addressed. Future perspectives and potential limitations of lipidomics are discussed.

Haloenol pyranones and morpholinones as antineoplastic agents of prostate cancer

Haloenol pyran-2-ones and morpholin-2-ones were synthesized and evaluated as inhibitors of cell growth in two different prostate human cancer cell lines (PC-3 and LNCaP). Analogs derived from L- and D-phenylglycine were found to be the most effective antagonists of LNCaP and PC-3 cell growth. Additional studies reveal that the inhibitors induced G2/M arrest and the (S)-enantiomer of the phenylglycine-based derivatives was a more potent inhibitor of cytosolic iPLA(2)β.

The role of endoplasmic reticulum Ca2+-independent phospholipase a2γ in oxidant-induced lipid peroxidation, Ca2+ release, and renal cell death

Oxidant-induced lipid peroxidation and cell death are major components of ischemia/reperfusion and toxicant injury. Our previous studies showed that renal proximal tubular cells (RPTCs) express Ca(2+)-independent phospholipase A(2)γ (iPLA(2)γ) in endoplasmic reticulum (ER) and mitochondria and that iPLA(2)γ is cytoprotective. Our present studies reveal the role of ER-iPLA(2)γ in oxidant-induced ER lipid peroxidation, Ca(2+) release, and cell death. Oxidant tert-butyl hydroperoxide (TBHP) caused ER lipid peroxidation and Ca(2+) release in isolated rabbit kidney cortex microsomes. ER-iPLA(2)γ inhibition, using bromoenol lactone (BEL), potentiated both oxidant-induced ER lipid peroxidation and Ca(2+) release. Assessment of fatty acids using electrospray ionization-mass spectrometry revealed that ER-iPLA(2)γ mediates the TBHP-induced release of arachidonic acid (20:4), linoleic acid (18:2), and their oxidized forms (18:2-OH, 18:2-OOH, 20:4-OH, 20:4-OOH, 20:4-(OH)(3). iPLA(2)γ inhibition also accelerated oxidant-induced ER Ca(2+) release in RPTC. Depletion of ER Ca(2+) stores in RPTC with thapsigargin, an ER Ca(2+) pump inhibitor, prior to TBHP exposure reduced necrotic cell death and blocked the potentiation of TBHP-induced necrotic cell death by BEL. Together, these data provide strong evidence that ER-iPLA(2)γ protects renal cells from oxidant-induced necrotic cell death by releasing unsaturated and/or oxidized fatty acids from ER membranes, thereby preserving ER membrane integrity and preventing ER Ca(2+) release.

Group VIA phospholipase A2 is a target for vasopressin signaling in the thick ascending limb

Na+-K+-2Cl− cotransporter (NKCC2)-mediated NaCl reabsorption in the thick ascending limb (TAL) is stimulated by AVP via V2 receptor/PKA/cAMP signaling. This process is antagonized by locally produced eicosanoids such as 20-HETE or prostaglandin E2, which are synthesized in a phospholipase A2-dependent reaction cascade. Using microarray-based gene expression analysis, we found evidence for an AVP-dependent downregulation of the calcium-independent isoform of PLA2, iPLA2β, in the outer medulla of rats. In the present study, we therefore examined the contribution of iPLA2β to NKCC2 regulation. Immunoreactive iPLA2β protein was detected in cultured mTAL cells as well as in the entire TAL of rodents and humans with the exception of the macula densa. Administration of the V2 receptor-selective agonist desmopressin (5 ng/h; 3 days) to AVP-deficient diabetes insipidus rats increased outer medullary phosphorylated NKCC2 (pNKCC2) levels more than twofold in association with a marked reduction in iPLA2β abundance (−65%; P < 0.05), thus confirming microarray results. Inhibition of iPLA2β in Sprague-Dawley rats with FKGK 11 (0.5 μM) or in mTAL cells with FKGK 11 (10 μM) or ( S)-bromoenol lactone (5 μM) for 1 h markedly increased pNKCC2 levels without affecting total NKCC2 expression. Collectively, these data indicate that iPLA2β acts as an inhibitory modulator of NKCC2 activity and suggest that downregulation of iPLA2β may be a relevant step in AVP-mediated urine concentration.

Profiling of fatty acids released during calcium-induced mitochondrial permeability transition in isolated rabbit kidney cortex mitochondria

Increases in intracellular Ca(2+) during cellular stress often lead to the mitochondrial permeability transition (MPT). We examined changes in fatty acids (FAs) released from isolated renal cortical mitochondria subjected to Ca(2+)-induced MPT. Exposing mitochondria to Ca(2+) stimulated mitochondrial swelling and release of FAs such as arachidonic (20:4) and docosahexenoic acids which increased 71% and 32%, respectively, and linoleic (18:2) which decreased 23% compared to controls. Stearic (18:0), oleic (18:1), and linoleic (18:3) acids were unchanged. To elucidate a mechanism for FA release, mitochondria were pre-treated with bromoenolactone (BEL) to inhibit Ca(2+)-independent phospholipase A(2) gamma activity (iPLA(2)γ). BEL blocked Ca(2+)-induced release of arachidonic and behenic (22:0) acids. Finally, four FAs were released in the absence of Ca(2+) in a BEL-sensitive manner, including arachidonic and docosatrienoic acids. Thus, extensive FA release occurs during Ca(2+)-induced MPT, and that mitochondrial iPLA(2)γ maintains mitochondrial arachidonic acid homeostasis under both basal and Ca(2+)-induced stress conditions.

Inhibition of calcium-independent phospholipase A2 activates p38 MAPK signaling pathways during cytostasis in prostate cancer cells

The p38 mitogen-activated protein kinase (MAPK) signaling pathways activated during cytostasis induced by Ca(2+)-independent phospholipase A2 (iPLA2) inhibition in prostate cancer cells were investigated. iPLA2 inhibition using siRNA, or the selective inhibitor bromoenol lactone (BEL) and it's enantiomers, decreased growth in LNCaP (p53 positive) and PC-3 (p53 negative) human prostate cancer cells. Decreased cell growth correlated to time- and concentration-dependent activation of the mitogen-activated protein kinase p38 in both cell lines. Inhibition of cytosolic iPLA(2)beta using S-BEL, induced significantly higher levels of P-p53, p53, p21 and P-p38 expression than inhibition of microsomal iPLA2 gamma using R-BEL. Inhibition of p38 using SB202190 or SB203580 inhibited BEL-induced increases in P-p53 (ser15), p53 and p21, and altered the number of cells in G1 in LNCaP cells, and S-phase in PC-3 cells. BEL treatment also induced reactive species in PC-3 and LNCaP cells, which was partially reversed by pretreatment with N-acetyl-cysteine (NAC). NAC subsequently inhibited BEL-induced activation of p38 and p53 in LNCaP cells. In addition, treatment of cells with NAC partially reversed the effect of BEL on cell growth and preserved cell morphology. Collectively, these data demonstrate the novel findings that iPLA2 inhibition activates p38 by inducing reactive species, and further suggest that this signaling kinase is involved in p53 activation, cell cycle arrest and cytostasis.

Group VIA Ca2+-independent phospholipase A2 (iPLA2beta) and its role in beta-cell programmed cell death

Activation of phospholipases A(2) (PLA(2)s) leads to the generation of biologically active lipid mediators that can affect numerous cellular events. The Group VIA Ca(2+)-independent PLA(2), designated iPLA(2)beta, is active in the absence of Ca(2+), activated by ATP, and inhibited by the bromoenol lactone suicide inhibitor (BEL). Over the past 10-15 years, studies using BEL have demonstrated that iPLA(2)beta participates in various biological processes and the recent availability of mice in which iPLA(2)beta expression levels have been genetically-modified are extending these findings. Work in our laboratory suggests that iPLA(2)beta activates a unique signaling cascade that promotes beta-cell apoptosis. This pathway involves iPLA(2)beta dependent induction of neutral sphingomyelinase, production of ceramide, and activation of the intrinsic pathway of apoptosis. There is a growing body of literature supporting beta-cell apoptosis as a major contributor to the loss of beta-cell mass associated with the onset and progression of Type 1 and Type 2 diabetes mellitus. This underscores a need to gain a better understanding of the molecular mechanisms underlying beta-cell apoptosis so that improved treatments can be developed to prevent or delay the onset and progression of diabetes mellitus. Herein, we offer a general review of Group VIA Ca(2+)-independent PLA(2) (iPLA(2)beta) followed by a more focused discussion of its participation in beta-cell apoptosis. We suggest that iPLA(2)beta-derived products trigger pathways which can lead to beta-cell apoptosis during the development of diabetes.

Cellular and molecular mechanisms of bromate-induced cytotoxicity in human and rat kidney cells

The mechanisms of bromate (BrO(3)(-))-induced toxicity in Normal Rat Kidney (NRK) and human embryonic kidney 293 (HEK293) cells were investigated. BrO(3)(-) (added as KBrO(3)) induced concentration-dependent decreases in 3-(4, dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) staining after 48 h. BrO(3)(-)-induced necrosis based on tandem increases in annexin V and PI staining. Cell cycle analysis demonstrated that BrO(3)(-) also induced G2/M arrest and nuclear fragmentation, prior to alterations in MTT staining or annexin V and PI staining. Immunoblot analysis demonstrated that the G2/M arrest correlated to induction of phosphorylated (p)-p53, p21, cyclin B1 and p-cdc2. Further, BrO(3)(-) induced time-dependent increases in the activity of the mitogen activated protein kinases p38 and ERK1/2. Treatment of cells with the p38 inhibitor SB202190, but not the ERK1/2 inhibitor PD98059, partially reversed BrO(3)(-)-induced G2/M arrest and decreased BrO(3)(-)-induced p-p53, p21 and cyclin B1 expression. In addition, BrO(3)(-) treatment induced reactive oxygen species (ROS) based on increases in CM-H(2)DCFDA fluorescence. The antioxidant ascorbic acid inhibited BrO(3)(-)-induced p38 activation, G2/M arrest, p-p53, p21 and cyclin B1 expression; however, ascorbic acid had no effect on BrO(3)(-)-induced formation of 8-OHdG, a marker of DNA oxidative damage, whose increases preceded cell death by 24h. These data suggest that ROS mediated MAPK activation is involved in the molecular mechanisms of BrO(3)(-)-induced cell cycle arrest, which occurs independently of 8-OH-dG production. The similar mode of action in both NRK and HEK293 cells suggests that the mechanisms of BrO(3)(-)-induced renal cell death are model-independent.

Role of Ca2+-independent phospholipase A2 in cell growth and signaling

Phospholipase A(2) (PLA(2)) are esterases that cleave glycerophospholipids to release fatty acids and lysophospholipids. Several studies demonstrate that PLA(2) regulate growth and signaling in several cell types. However, few of these studies have focused on Ca2+-independent phospholipase A(2) (iPLA(2) or Group VI PLA(2)). This class of PLA(2) was originally suggested to mediate phospholipid remodeling in several cell types including macrophages. As such, it was labeled as a housekeeping protein and thought not to play as significant of roles in cell growth as its older counterparts cytosolic PLA(2) (cPLA(2) or Group IV PLA(2)) and secretory PLA(2) (sPLA(2) or Groups I-III, V and IX-XIV PLA(2)). However, several recent studies demonstrate that iPLA(2) mediate cell growth, and do so by participating in signal transduction pathways that include epidermal growth factor receptors (EGFR), mitogen activated protein kinases (MAPK), mdm2, and even the tumor suppressor protein p53 and the cell cycle regulator p21. The exact mechanism by which iPLA(2) mediates these pathways are not known, but likely involve the generation of lipid signals such as arachidonic acid, lysophosphatidic acid (LPA) and lysophosphocholines (LPC). This review discusses the role of iPLA(2) in cell growth with special emphasis placed on their role in cell signaling. The putative lipid signals involved are also discussed.

Alterations in phospholipid and fatty acid lipid profiles in primary neocortical cells during oxidant-induced cell injury

Specific phospholipids and fatty acids altered during oxidant-induced neuronal cell injury were determined using electrospray ionization mass spectrometry (ESI-MS) and ion trapping. The oxidants hydrogen peroxide (H(2)O(2), 0-1000 microM) and tert-butylhydroperoxide (TBHP, 0-400 microM) induced time- and concentration-dependent increases in reactive oxygen species in primary cultures of mouse neocortical cells as determined by 2',7'-dichlorofluorescein diacetate staining and thiobarbituric acid formation. ESI-MS analysis of 26 m/z values, representing 42 different phospholipids, demonstrated that H(2)O(2) and TBHP increased the abundance of phospholipids containing polyunsaturated fatty acids, but had minimal affect on those containing mono- or di-unsaturated fatty acids. These increases correlated to time-dependent increase in 16:1-20:4, 16:0-20:4, 18:1-20:4 and 18:0-20:4 phosphatidylcholine. Oxidant exposure also increased mystric (14:0), palmitic (16:0), and stearic (18:0) acid twofold, oleic acid (18:1) two- to threefold, and arachidonic acid (20:4) fourfold, compared to controls. Increases in arachidonic acid levels occurred prior to increases in the phospholipids, but after increases in ROS, and correlated to increases in oxidized arachidonic acid species, specifically [20:4-OOH]-H(2)O-, 20:4-OH-, and Tri-OH-20:4-arachidonic acid. Treatment of cells with methyl arachidonyl flourophosphonate an inhibitor of Group IV and VI PLA(2), decreased oxidant-induced arachidonic acid release, while bromoenol lactone, an inhibitor of Group VI PLA(2), did not. Collectively, these data identify phospholipids and fatty acids altered during oxidant treatment of neurons and suggest differential roles for Group IV and VI PLA(2) in oxidant-induced neural cell injury.

Decreased iPLA2gamma expression induces lipid peroxidation and cell death and sensitizes cells to oxidant-induced apoptosis

Our previous studies showed that renal proximal tubular cells (RPTC) express Ca(2+)-independent phospholipase A(2)gamma (iPLA(2)gamma) in endoplasmic reticulum (ER) and mitochondria and that iPLA(2)gamma prevents and/or repairs lipid peroxidation induced by oxidative stress. Our present studies determined the importance of iPLA(2)gamma in mitochondrial and cell function using an iPLA(2)gamma-specific small hairpin ribonucleic acid (shRNA) adenovirus. iPLA(2)gamma expression and activity were decreased in the ER by 24 h and in the mitochondria by 48 h compared with scrambled shRNA adenovirus-treated cells. Lipid peroxidation was elevated by 2-fold at 24 h and remained elevated through 72 h in cells with decreased iPLA(2)gamma. Using electrospray ionization-mass spectrometry, primarily phosphatidylcholines and phosphatidylethanolamines were increased in iPLA(2)gamma-shRNA-treated cells. At 48 h after exposure to the iPLA(2)gamma shRNA, uncoupled oxygen consumption was inhibited by 25% and apoptosis was observed at 72 and 96 h. RPTC with decreased iPLA(2)gamma expression underwent apoptosis when exposed to a nonlethal concentration of the oxidant tert-butyl hydroperoxide (TBHP). Exposure of control cells to a nonlethal concentration of TBHP induced iPLA(2)gamma expression in RPTC. These results suggest that iPLA(2)gamma is required for the prevention and repair of basal lipid peroxidation and the maintenance of mitochondrial function and viability, providing further evidence for a cytoprotective role for iPLA(2)gamma from oxidative stress.

Phospholipase A2 as targets for anti-cancer drugs

Phospholipase A(2) (PLA(2)) are esterases that cleave glycerophospholipids to release fatty acids and lysophospholipids. Inhibition of PLA(2) alters cancer cell growth and death in vitro and PLA(2) expression is increased in breast, lung, and prostate cancers compared to control tissues. Thus, PLA(2) may be novel targets for chemotherapeutics. However, PLA(2) are a diverse family of enzymes, encompassing 19 members. The selectivity of these individual PLA(2) for phospholipids varies, as does their location within the cell, and tissue expression. Thus, their role in cancer may also vary. This review summarizes the expression of individual PLA(2) in cancers, focuses on the potential mechanisms by which these esterases mediate carcinogenesis, and suggests that select PLA(2) isoforms may be targets for anti-cancer drugs.

Involvement of Ca2+-independent phospholipase A2 isoforms in oxidant-induced neural cell death

This study determined the roles of Ca2+-independent PLA2 (iPLA2) in phospholipid chemistry and oxidant-induced cell death in human astrocytes. A172 cells expressed both cytosolic Group VIA (iPLA2beta) and microsomal Group VIB (iPLA2gamma) PLA2 as determined by activity assays and immunoblot analysis. Inhibition of total iPLA2 activity using racemic bromoenol lactone (BEL, 2.5 microM) decreased the expression of 14:0-16:0 phosphatidylcholine (PtdCho) 15% and increased 18:0-18:1-PtdCho expression 15%. Treatment of cells with the iPLA2gamma specific inhibitor R-BEL decreased 14:0-16:0-PtdCho 35%, 16:0-16:0-PtdCho 15% and induced a 35% increase in 18:0-18:1-PtdCho. In contrast, treatment of cells with the iPLA2beta inhibitor S-BEL did not alter any phospholipid studied. To determine the roles of iPLA2 in oxidant-induced cell death, A172 cells were exposed to hydrogen peroxide (H2O2) or tert-butylhydroperoxide (TBHP); both induced time- and concentration-dependent increases in cell death as assessed by annexin V and propidium iodide staining. Treatment of cells with racemic-BEL alone did not induce cell death. However, pretreatment with BEL prior to H2O2 (500 microM) or TBHP (200 microM) significantly increased necrosis as determined by increases in propidium iodide staining. Treatment with BEL prior to exposure to oxidants accelerated the loss of ATP levels, but not the formation of reactive oxygen species. These data support the hypothesis that iPLA2 mediates oxidant-induced neural cell death and demonstrates differential roles of iPLA2 isoforms in physiological and pathological events.

Differential Roles for Cytosolic and Microsomal Ca2+-Independent Phospholipase A2in Cell Growth and Maintenance of Phospholipids

Physiological roles of microsomal (iPLA(2)gamma) and cytosolic (iPLA(2)beta)Ca(2+)-independent phospholipase A(2) were determined in two different epithelial cell models. R- and S-enantiomers of the iPLA(2) inhibitor bromoenol lactone (BEL) were isolated and shown to selectively inhibit iPLA(2gamma) and iPLA(2beta), respectively. The effect of these enantiomers on cell growth was assessed in human embryonic kidney 293 and Caki-1 cells using 3-(4-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT). S-BEL (0-5.0 microM) decreased MTT staining 35% after 24 h compared with control cells, whereas treatment with either R-BEL or R/S-BEL induced 15% decreases. Neither R-BEL nor S-BEL induced cell death as determined by annexin V and propidium iodide staining. Transfection of cells with iPLA(2)beta siRNA reduced MTT staining approximately 35%, whereas transfection of cells with iPLA(2)gamma siRNA only decreased MTT staining 10 to 15% compared with control cells. The effect of iPLA(2)beta and iPLA(2)gamma siRNA on cell number and protein was also determined, and iPLA(2)beta siRNA decreased cell number and protein 25% compared with control cells. In contrast, iPLA(2)gamma siRNA decreased cell number, but not cellular protein, compared with control cells. Selective inhibition of iPLA(2)beta, but not iPLA(2)gamma, decreased several arachidonic acid-containing phospholipids, including 16:1-20:4, 16:0-20:4, 18:1-20:4, and 18:0-20:4 phosphatidylcholine, showing that the ability of iPLA(2)beta inhibitors to decrease cell growth correlates with their ability to decrease arachidonic acid-containing phospholipids. These data show that iPLA(2)beta inhibition results in greater decreases in cell growth and proliferation than iPLA(2)gamma, identifies specific phospholipids whose expressions are differentially regulated by iPLA(2)beta and iPLA(2)gamma, and suggests novel roles for iPLA(2)beta in cell growth.