Polyisoprenyl phosphates in intracellular signalling

Mouse phospholipid phosphatase 6 regulates dendritic cell cholesterol, macropinocytosis, and allergen sensitization

Lipid phosphate phosphatases are a family of enzymes with diverse cellular metabolic functions. Phospholipid phosphatase 6 (PLPP6) is a regulator of cellular polyisoprenyl phosphates; however, its in vivo functions remain to be determined. Here, mouse PLPP6 was characterized to possess similar catalytic properties as the human enzyme. Plpp6 knockout mice (Plpp6 ^-/- ) were generated and displayed decreased airway allergen sensitization, pointing to a role for PLPP6 in the early events of lung allergic responses. Dendritic cell (DC) responses were investigated and endocytosis of allergen via macropinocytosis was decreased in Plpp6 ^-/- DCs that had lower cholesterol content. When reversed by cholesterol loading, the DC macropinocytosis defect is corrected. Adoptive transfer of Plpp6 ^-/- DCs to wild-type mice during sensitization was sufficient to decrease allergen-induced responses. Together, our findings have identified PLPP6 as a pivotal regulator of DC cholesterol content and macropinocytosis, cellular mechanisms that are important for pathologic responses in allergen-induced lung inflammation.

Lipid-Derived Mediators are Pivotal to Leukocyte and Lung Cell Responses in Sepsis and ARDS

Acute inflammation in the lung is essential for host defense against pathogens and other injuries but chronic or excessive inflammation can contribute to several common respiratory diseases. In health, the inflammatory response is controlled by several cellular and molecular mechanisms. In addition to anti-inflammatory processes, there are non-phlogistic pro-resolving mechanisms that are engaged to promote the resolution of inflammation and a return to homeostasis. Defects in the production or actions of specialized pro-resolving mediators are associated with diseases characterized by excess or chronic inflammation. In this article, we review cellular and biochemical mechanisms for specialized pro-resolving mediators in health and in sepsis and the acute respiratory distress syndrome as examples of unrestrained inflammatory responses that result in life-threatening pathology. We are honored to contribute to this special edition of the Journal to help celebrate Professor Viswanathan Natarajan’s contributions to our understanding of lipid-derived mediators and metabolism in lung cell responses to inflammatory, infectious, or mechanical insults; his foundational discoveries in cell biochemistry and biophysics are continuing to catalyze further advances by the field to uncover the mechanistic underpinnings of important human diseases.

Lipidomic methodologies for biomarkers of chronic inflammation in nutritional research: ω-3 and ω-6 lipid mediators

The evolutionary history of hominins has been characterized by significant dietary changes, which include the introduction of meat eating, cooking, and the changes associated with plant and animal domestication. The Western pattern diet has been linked with the onset of chronic inflammation, and serious health problems including obesity, metabolic syndrome, and cardiovascular diseases. Diets enriched with ω-3 marine PUFAs have revealed additional improvements in health status associated to a reduction of proinflammatory ω-3 and ω-6 lipid mediators. Lipid mediators are produced from enzymatic and non-enzymatic oxidation of PUFAs. Interest in better understanding the occurrence of these metabolites has increased exponentially as a result of the growing evidence of their role on inflammatory processes, control of the immune system, cell signaling, onset of metabolic diseases, or even cancer. The scope of this review has been to highlight the recent findings on: a) the formation of lipid mediators and their role in different inflammatory and metabolic conditions, b) the direct use of lipid mediators as antiinflammatory drugs or the potential of new drugs as a new therapeutic option for the synthesis of antiinflammatory or resolving lipid mediators and c) the impact of nutritional interventions to modulate lipid mediators synthesis towards antiinflammatory conditions. In a second part, we have summarized methodological approaches (Lipidomics) for the accurate analysis of lipid mediators. Although several techniques have been used, most authors preferred the combination of SPE with LC-MS. Advantages and disadvantages of each method are herein addressed, as well as the main LC-MS difficulties and challenges for the establishment of new biomarkers and standardization of experimental designs, and finally to deepen the study of mechanisms involved on the inflammatory response.

Specialized Proresolving Mediators in Innate and Adaptive Immune Responses in Airway Diseases

Airborne pathogens and environmental stimuli evoke immune responses in the lung. It is critical to health that these responses be controlled to prevent tissue damage and the compromise of organ function. Resolution of inflammation is a dynamic process that is coordinated by biochemical and cellular mechanisms. Recently, specialized proresolving mediators (SPMs) have been identified in resolution exudates. These molecules orchestrate anti-inflammatory and proresolving actions that are cell type specific. In this review, we highlight SPM biosynthesis, the influence of SPMs on the innate and adaptive immune responses in the lung, as well as recent insights from SPMs on inflammatory disease pathophysiology. Uncovering these mediators and cellular mechanisms for resolution is providing new windows into physiology and disease pathogenesis.

Lipid Mediators in Inflammation

Lipids are potent signaling molecules that regulate a multitude of cellular responses, including cell growth and death and inflammation/infection, via receptor-mediated pathways. Derived from polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), each lipid displays unique properties, thus making their role in inflammation distinct from that of other lipids derived from the same PUFA. This diversity arises from their synthesis, which occurs via discrete enzymatic pathways and because they elicit responses via different receptors. This review will collate the bioactive lipid research to date and summarize the major pathways involved in their biosynthesis and role in inflammation. Specifically, lipids derived from AA (prostanoids, leukotrienes, 5-oxo-6,8,11,14-eicosatetraenoic acid, lipoxins, and epoxyeicosatrienoic acids), EPA (E-series resolvins), and DHA (D-series resolvins, protectins, and maresins) will be discussed herein.

Resolution of acute inflammation in the lung

Acute inflammation in the lung is essential to health. So too is its resolution. In response to invading microbes, noxious stimuli, or tissue injury, an acute inflammatory response is mounted to protect the host. To limit inflammation and prevent collateral injury of healthy, uninvolved tissue, the lung orchestrates the formation of specialized proresolving mediators, specifically lipoxins, resolvins, protectins, and maresins. These immunoresolvents are agonists for resolution that interact with specific receptors on leukocytes and structural cells to blunt further inflammation and promote catabasis. This process appears to be defective in several common lung diseases that are characterized by excess or chronic inflammation. Here, we review the molecular and cellular effectors of resolution of acute inflammation in the lung.

Lack of activity of 15-epi-lipoxin A₄ on FPR2/ALX and CysLT1 receptors in interleukin-8-driven human neutrophil function

Neutrophil recruitment and survival are important control points in the development and resolution of inflammatory processes. 15-epi-lipoxin (LX)A interaction with formyl peptide receptor 2 (FPR2)/ALX receptor is suggested to enhance anti-inflammatory neutrophil functions and mediate resolution of airway inflammation. However, it has been reported that 15-epi-LXA₄ analogues can also bind to cysteinyl leukotriene receptor 1 (CysLT1) and that the CysLT1 antagonist MK-571 binds to FPR2/ALX, so cross-reactivity between FPR2/ALX and CysLT1 ligands cannot be discarded. It is not well established whether the resolution properties reported for 15-epi-LXA4 are mediated through FPR2/ALX, or if other receptors such as CysLT1 may also be involved. Evaluation of specific FPR2/ALX ligands and CysLT1 antagonists in functional biochemical and cellular assays were performed to establish a role for both receptors in 15-epi-LXA₄-mediated signalling and function. In our study, a FPR2/ALX synthetic peptide (WKYMVm) and a small molecule FPR2/ALX agonist (compound 43) induced FPR2/ALX-mediated signalling, enhancing guanosine triphosphate-gamma (GTPγ) binding and decreasing cyclic adenosine monophosphate (cAMP) levels, whereas 15-epi-LXA₄ was inactive. Furthermore, 15-epi-LXA4 showed neither binding affinity nor signalling towards CysLT1. In neutrophils, 15-epi-LXA₄ showed a moderate reduction of interleukin (IL)-8-mediated neutrophil chemotaxis but no effect on neutrophil survival was observed. In addition, CysLT1 antagonists were inactive in FPR2/ALX signalling or neutrophil assays. In conclusion, 15-epi-LXA₄ is not a functional agonist or an antagonist of FPR2/ALX or CysLT1, shows no effect on IL-8-induced neutrophil survival and produces only moderate inhibition in IL-8-mediated neutrophil migration. Our data do not support an anti-inflammatory role of 15-epi-LXA₄- FPR2/ALX interaction in IL-8-induced neutrophil inflammation.

15-Epi-lipoxin A4 inhibits human neutrophil superoxide anion generation by regulating polyisoprenyl diphosphate phosphatase 1

Regulation of leukocyte activation is critical to limit unintended tissue injury during acute inflammation. On neutrophil activation, polyisoprenyl diphosphate phosphatase 1 (PDP1) rapidly converts presqualene diphosphate to presqualene monophosphate to facilitate cell activation. Lipoxins are potent anti-inflammatory mediators for neutrophils, yet their counterregulatory signaling mechanisms remain to be determined. 15-Epi-lipoxin A4 (15-epi-LXA4) blocked agonist-initiated association of the nicotinamide adenine dinucleotide phosphate oxidase components p47(PHOX) and p22(PHOX) in human neutrophils. 15-Epi-LXA4 (0.1-100 nM) inhibited neutrophil superoxide anion (O2(-)) generation in a concentration- and ALX/FPR2 receptor-dependent manner that was disrupted by PDP1-specific antibodies. In differentiated HL60 cells, a myeloid cell line, agonist-initiated O2(-) generation was inhibited by PDP1 siRNA. Recombinant human PDP1 was directly phosphorylated in vitro by select protein kinase C (PKC) isoforms, including PKCβII. When neutrophils were exposed to formyl-methionyl-leucyl-phenylalanine (fMLP), PKCβII was rapidly phosphorylated and physically associated with PDP1. Agonist-initiated conversion of neutrophil presqualene diphosphate to presqualene monophosphate was blocked by PKCβII inhibition. Neutrophil exposure to 15-epi-LXA4 attenuated fMLP triggered PKCβII phosphorylation and its interactions with PDP1. Together, these findings indicate that PDP1 serves an integral signaling role in neutrophil proinflammatory responses and as a target for counter-regulatory mediators.

Metabolically regulated endoplasmic reticulum-associated degradation of 3-hydroxy-3-methylglutaryl-CoA reductase: evidence for requirement of a geranylgeranylated protein

In mammalian cells, the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR), which catalyzes the rate-limiting step in the mevalonate pathway, is ubiquitylated and degraded by the 26 S proteasome when mevalonate-derived metabolites accumulate, representing a case of metabolically regulated endoplasmic reticulum-associated degradation (ERAD). Here, we studied which mevalonate-derived metabolites signal for HMGR degradation and the ERAD step(s) in which these metabolites are required. In HMGR-deficient UT-2 cells that stably express HMGal, a chimeric protein between β-galactosidase and the membrane region of HMGR, which is necessary and sufficient for the regulated ERAD, we tested inhibitors specific to different steps in the mevalonate pathway. We found that metabolites downstream of farnesyl pyrophosphate but upstream to lanosterol were highly effective in initiating ubiquitylation, dislocation, and degradation of HMGal. Similar results were observed for endogenous HMGR in cells that express this protein. Ubiquitylation, dislocation, and proteasomal degradation of HMGal were severely hampered when production of geranylgeranyl pyrophosphate was inhibited. Importantly, inhibition of protein geranylgeranylation markedly attenuated ubiquitylation and dislocation, implicating for the first time a geranylgeranylated protein(s) in the metabolically regulated ERAD of HMGR.

Enantioselective inhibition of squalene synthase by aziridine analogues of presqualene diphosphate

Squalene synthase catalyzes the conversion of two molecules of (E,E)-farnesyl diphosphate to squalene via the cyclopropylcarbinyl intermediate, presqualene diphosphate (PSPP). Since this novel reaction constitutes the first committed step in sterol biosynthesis, there has been considerable interest and research on the stereochemistry and mechanism of the process and in the design of selective inhibitors of the enzyme. This paper reports the synthesis and characterization of five racemic and two enantiopure aziridine analogues of PSPP and the evaluation of their potencies as inhibitors of recombinant yeast squalene synthase. The key aziridine-2-methanol intermediates (6-OH, 7-OH, and 8-OH) were obtained by N-alkylations or by an N-acylation-reduction sequence of (+/-)-, (2R,3S)-, and (2S,3R)-2,3-aziridinofarnesol (9-OH) protected as tert-butyldimethylsilyl ethers. S(N)2 displacements of the corresponding methanesulfonates with pyrophosphate and methanediphosphonate anions afforded aziridine 2-methyl diphosphates and methanediphosphonates bearing N-undecyl, N-bishomogeranyl, and N-(alpha-methylene)bishomogeranyl substituents as mimics for the 2,6,10-trimethylundeca-2,5,9-trienyl side chain of PSPP. The 2R,3S diphosphate enantiomer bearing the N-bishomogeranyl substituent corresponding in absolute stereochemistry to PSPP proved to be the most potent inhibitor (IC(50) 1.17 +/- 0.08 muM in the presence of inorganic pyrophosphate), a value 4-fold less than that of its 2S,3R stereoisomer. The other aziridine analogues bearing the N-(alpha-methylene)bishomogeranyl and N-undecyl substituents, and the related methanediphosphonates, exhibited lower affinities for recombinant squalene synthase.

Old and new generation lipid mediators in acute inflammation and resolution

Originally regarded as just membrane constituents and energy storing molecules, lipids are now recognised as potent signalling molecules that regulate a multitude of cellular responses via receptor-mediated pathways, including cell growth and death, and inflammation/infection. Derived from polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), each lipid displays unique properties, thus making their role in inflammation distinct from that of other lipids derived from the same PUFA. The diversity of their actions arises because such metabolites are synthesised via discrete enzymatic pathways and because they elicit their response via different receptors. This review will collate the bioactive lipid research to date and summarise the findings in terms of the major pathways involved in their biosynthesis and their role in inflammation and its resolution. It will include lipids derived from AA (prostanoids, leukotrienes, 5-oxo-6,8,11,14-eicosatetraenoic acid, lipoxins and epoxyeicosatrienoic acids), EPA (E-series resolvins), and DHA (D-series resolvins, protectins and maresins).

Molecular circuits of resolution in airway inflammation

Inflammatory diseases of the lung are common, cause significant morbidity, and can be refractory to therapy. Airway responses to injury, noxious stimuli, or microbes lead to leukocyte recruitment for host defense. As leukocytes respond, they interact with lung resident cells and can elaborate specific mediators that are enzymatically generated from polyunsaturated fatty acids via transcellular biosynthesis. These bioactive, lipid-derived, small molecules serve as agonists at specific receptors and are rapidly inactivated in the local environment. This review will focus on the biosynthesis, receptors, cellular responses, and in vivo actions of lipoxins, resolvins, and protectins as exemplary molecular signaling circuits in the airway that are anti-inflammatory and proresolving.

Activation of polyisoprenyl diphosphate phosphatase 1 remodels cellular presqualene diphosphate

Polyisoprenyl diphosphates play diverse and vital roles in cell function in health and disease. The counter-regulatory lipid signaling molecule, presqualene diphosphate (PSDP), is rapidly converted to its monophosphate form (PSMP) upon cell activation [Levy, B. D., Petasis, N. A., and Serhan, C. N. (1997) Nature 389, 985-990]. The first PSDP phosphatase was recently identified and named polyisoprenyl diphosphate phosphatase 1 (PDP1) [Fukunaga, K., et al. (2006) J. Biol. Chem. 281, 9490-9497]. Here, we present evidence that PDP1 displays properties of a lipid phosphate phosphatase/phosphotransferase with distinct substrate preference for PSDP. Cell activation with PMA increased PSDP phosphatase activity in a concentration-dependent manner, and Western analysis suggested that PDP1 is directly phosphorylated by protein kinase C. Cellular PSDP phosphatase activity was also induced by the receptor-mediated agonists insulin and TNF-alpha. To address PDP1's contribution to cellular PSDP phosphatase activity, HEK293 cells were established that stably expressed PDP1 siRNA, leading to a 60% decrease in the level of PDP1 RNA, and concomitant decreases in PDP1 protein and PMA-initiated PSDP phosphatase activity. HEK293 cells harboring the PDP1 siRNA construct also displayed a marked decrease in the extent of PMA-initiated conversion of cellular PSDP to PSMP. Together, these findings are the first to indicate that PDP1 is activated during cell responses to soluble stimuli to convert PSDP to PSMP. Moreover, they provide evidence that PDP1 can serve as a new checkpoint for polyisoprenyl phosphate remodeling during cell activation.

Chemical mediators and the resolution of airway inflammation

Asthma pathobiology is remarkable for chronic airway inflammation that fails to spontaneously resolve. No curative therapy is currently available. A growing body of evidence indicates that, in health, inflammation resolution is an active process orchestrated by specific chemical mediators that are elaborated to restore tissue homeostasis. Activated cell membranes release polyunsaturated fatty acids from phospholipids for enzymatic conversion to biologically active mediators with profound regulatory effects on innate and adaptive immunity. Some of these mediators carry anti-inflammatory and pro-resolving actions that are transduced in a cell-type specific manner via specific recognition sites that initiate regulatory intracellular signals, such as presqualene diphosphate remodeling, to limit pro-phlogistic cell activation. Some of these counter-regulatory lipid mediators have been identified in the airway during asthma and defects in their production are associated with disease severity. In this review, we describe the biosynthesis and bioactions of pro-resolving chemical mediators and provide examples of select mediators and their structural analogs with particular relevance to asthma.

Endogenous lipid mediators in the resolution of airway inflammation

Acute inflammation in the lung is fundamentally important to host defence, but chronic or excessive inflammation leads to several common respiratory diseases, including asthma and acute respiratory distress syndrome. The resolution of inflammation is an active process. In health, events at the onset of acute inflammation establish biosynthetic circuits for specific chemical mediators that later serve as agonists to orchestrate a return to tissue homeostasis. In addition to an overabundance of pro-inflammatory stimuli, pathological inflammation can also result from defects in resolution signalling. The understanding of anti-inflammatory, pro-resolution molecules and their counter-regulatory signalling pathways is providing new insights into the molecular pathophysiology of lung disease and opportunities for the design of therapeutic strategies. In the present review, the growing family of lipid mediators of resolution is examined, including lipoxins, resolvins, protectins, cyclopentenones and presqualene diphosphate. Roles are uncovered for these compounds, or their structural analogues, in regulating airway inflammation.

Resolvin E2: identification and anti-inflammatory actions: pivotal role of human 5-lipoxygenase in resolvin E series biosynthesis

The family of resolvins consists of omega-3 fatty acid-derived mediators, including E series resolvins generated from eicosapentaenoic acid (EPA), and carry potent anti-inflammatory properties. Here, we report the isolation, identification, and bioactions of resolvin E2 (RvE2), which is 5S,18-dihydroxy-eicosapentaenoic acid. RvE2 stopped zymosan-induced polymorphonuclear (PMN) leukocyte infiltration and displayed potent anti-inflammatory properties in murine peritonitis. We also demonstrate that human recombinant 5-lipoxygenase generates RvE2 from a common precursor of E series resolvins, namely, 18-hydroxyeicosapentaenoate (18-HEPE). Furthermore, the initial 5-hydroperoxide intermediate was also converted to a 5(6)-epoxide intermediate in RvE1 formation. These results demonstrate that RvE2, together with RvE1, may contribute to the beneficial actions of omega-3 fatty acids in human diseases. Moreover, they indicate that the 5-lipoxygenase in human leukocytes is a pivotal enzyme that can produce both pro- and anti-inflammatory chemical mediators.

Lipid mediators as agonists for the resolution of acute lung inflammation and injury

Resolution of acute lung inflammation and injury is an active process; it is not merely the absence of proinflammatory signals. Restoration of homeostasis is coordinated by specific mediators and cellular events. In response to injury and inflammatory stimuli, infiltrating leukocytes and tissue-resident cells interact to generate lipoxins (LXs), which are bioactive eicosanoids derived from arachidonic acid. In contrast to proinflammatory leukotrienes and prostaglandins, LXs display potent antiinflammatory actions. LXA(4) interacts with a G protein-coupled receptor, termed ALX, that transduces counter-regulatory signals in part via intracellular polyisoprenyl phosphate remodeling. Presqualene diphosphate (PSDP) is a polyisoprenyl phosphate in human neutrophils that is rapidly converted to presqualene monophosphate (PSMP) upon cell activation. PSDP, but not PSMP, directly inhibits phospholipase D, phosphoinositol-3 kinase, and superoxide anion generation. LXs block PSDP turnover in neutrophil membranes to prevent proinflammatory responses. Hence, LX and polyisoprenyl phosphate signaling provide a counter-regulatory circuit to promote resolution of acute lung inflammation. LXA(4) and PSDP mimetics have been prepared with potent protective actions in murine models of asthma and acute lung injury.

Novel polyisoprenyl phosphates block phospholipase D and human neutrophil activation in vitro and murine peritoneal inflammation in vivo

Leukocyte production of reactive oxygen species (ROS) is an essential component of the antimicrobial armament mounted during host defense, but when released to the extracellular milieu ROS can also injure host tissues and provoke inflammation. Polyisoprenyl phosphates (PIPPs) are constituents of human leukocyte membranes that regulate pivotal intracellular enzymes, such as phospholipase D (PLD). We prepared new PIPP mimetics and studied their impact in vivo on leukocyte activation, including ROS generation, in acute inflammation. In a stereospecific and concentration-dependent manner, the PIPP mimetics directly regulated Streptomyces chromofuscus phospholipase D (sPLD) action. The IC(50) for a (Z)-isomer of endogenous presqualene diphosphate (PSDP) was 100 nM. Structure-activity relationships were also determined for PIPP mimetic inhibition of recombinant human PLD1b, a prominent isoform in human leukocytes. The PIPP mimetic rank order for PLD1b inhibition differed from sPLD, although the (Z)-PSDP isomer remained the most potent PIPP mimetic for inhibition of both enzymes. Truncation of PLD1b to its catalytic core uncovered potential regulatory roles for both PSDP's isoprenoid and diphosphate moieties. The (Z)-PSDP isomer reduced ROS production by activated human leukocytes and decreased murine neutrophil accumulation (65.6%) and ROS production (38.5%) in vivo during zymosan A-initiated peritonitis. When administered intraperitoneally 2 h after zymosan A, the (Z)-PSDP isomer decreased in vivo neutrophil accumulation (72.5%) and ROS generation (74.4%) 6 h later in peritoneal exudates. Together, these results provide new means to protect and control unchecked inflammatory responses that characterize many human diseases.

Regulation of phosphatidylinositol 3-kinase by polyisoprenyl phosphates in neutrophil-mediated tissue injury

Neutrophils play a central role in host defense, inflammation, and tissue injury. Recent findings indicate a novel role for polyisoprenyl phosphates (PIPPs) as natural down-regulatory signals in neutrophils. The relationship between PIPPs and neutrophil early activating signals, such as phosphoinositides, has not been previously determined. Here, we establish presqualene diphosphate (PSDP) as an endogenous PIPP regulator of phosphatidylinositol 3-kinase (PI3K). In human neutrophils, leukotriene B4 (LTB4) triggered rapid decreases in PSDP and reciprocal increases in PI3K activity. In addition, PSDP was identified by gas chromatography/mass spectrometry in p110gamma-PI3K immunoprecipitates obtained 30 s after LTB4, indicating a physical interaction between PSDP and PI3K in activated neutrophils. Moreover, PSDP (0.4-800 pmol) directly inhibited recombinant human p110gamma-PI3K activity. During an experimental model of lung injury and inflammation, a reciprocal relationship was also present in vivo for lung PSDP and PI3K activity. To investigate its therapeutic potential, we developed a new PSDP structural mimetic that blocked human neutrophil activation and mouse lung PI3K activity and inflammation. Together, our findings indicate that PSDP is an endogenous PI3K inhibitor, and suggest that in inflammatory diseases characterized by excessive neutrophil activation, PIPPs can serve as structural templates in a novel antineutrophil therapeutic strategy to limit tissue injury.

Identification and functional characterization of a presqualene diphosphate phosphatase

Presqualene diphosphate (PSDP) is a bioactive lipid that rapidly remodels to presqualene monophosphate (PSMP) upon cell activation (Levy, B. D., Petasis, N. A., and Serhan, C. N. (1997) Nature 389, 985-990). Here, we have identified and characterized a phosphatase that converts PSDP to PSMP. Unlike the related polyisoprenyl phosphate farnesyl diphosphate (FDP), PSDP was not a substrate for type 2 lipid phosphate phosphohydrolases. PSDP phosphatase activity was identified in activated human neutrophil (PMN) extracts and partially purified in the presence of Nonidet P-40 with gel filtration and anion exchange chromatography. Peptide sequencing of a candidate phosphatase was consistent with phosphatidic acid phosphatase domain containing 2 (PPAPDC2), an uncharacterized protein that contains a lipid phosphate phosphohydrolase consensus motif. Recombinant PPAPDC2 displayed diphosphate phosphatase activity with a substrate preference for PSDP > FDP > phosphatidic acid. PPAPDC2 activity was independent of Mg(2+) and optimal at pH 7.0 to 8.0. Incubation of [(14)C]FDP with recombinant human squalene synthase led to [(14)C]PSDP and [(14)C]squalene formation, and in the presence of PPAPDC2, [(14)C]PSMP was generated from [(14)C]PSDP. PPAPDC2 mRNA was detected in human PMN, and is widely expressed in human tissues. Together, these findings indicate that PPAPDC2 in human PMN is the first lipid phosphate phosphohydrolase identified for PSDP. Regulation of this activity of the enzyme may have important roles for PMN activation in innate immunity.

Design, synthesis and bioactions of novel stable mimetics of lipoxins and aspirin-triggered lipoxins

The lipoxins (LX) are a class of potent endogenous oxygenated products that are enzymatically generated from arachidonic acid and have novel anti-inflammatory properties and promote resolution. Elucidation of the biochemical pathways involved in the metabolic inactivation of LX and the discovery of the aspirin-triggered lipoxins (ATL) provided the basis for the design and synthesis of stable analogs of LX and ATL. This special issue review describes the efforts that led to the design and synthesis of stable LX/ATL mimetics, which permitted the detailed elucidation of their novel biological roles, leading to the development of new anti-inflammatory agents that mimic their actions. These synthetic molecules provided the means to uncover the physiologic roles of both the LX and the ATL biosynthetic pathways which led to several unexpected discoveries. Among these findings is the involvement of polyisoprenyl phosphates (PIPP) in intracellular signaling mediated by presqualene diphosphate (PSDP), and the recognition of the novel roles of these lipid mediators in regulating cell trafficking during inflammation as well as in promoting resolution of inflammatory processes. These efforts also provided the basis for examining the potential therapeutic role of LX/ATL stable mimetics and led to the development of new analogs with improved pharmacokinetics that opened the way to potentially new approaches to treating human diseases.

Averaging of nonlinearity-managed pulses

We consider the nonlinear Schrodinger equation with the nonlinearity management which describes Bose-Einstein condensates under Feshbach resonance. By using an averaging theory, we derive the Hamiltonian averaged equation and compare it with other averaging methods developed for this problem. The averaged equation is used for analytical approximations of nonlinearity-managed solitons.

Genoprotective pathways. II. Attenuation of oxidative DNA damage by isopentenyl diphosphate

Oxidative stress is believed to play a role in the pathogenesis of many diseases. Here we report that isopentenyl diphosphate (IPP), the 5-carbon building unit of all isoprenoids, is a potent antioxidant that is capable of inhibiting oxidative DNA damage at picomolar concentrations (IC50 = 1.7 x 10(-11) M). The diphosphate moiety is essential, since isopentenyl monophosphate (IMP) is unable to trigger antioxidative signaling. The 20-carbon isoprenyl, geranylgeranyl diphosphate (GGPP), but not the 15-carbon farnesyl diphosphate, displays similar genoprotective effects. The pathway activated by IPP is distinct from that of 2-chloroadenosine (2CA). 2CA-mediated genoprotective signaling is transduced through an A2a or A2b adenosine receptor (AR) and can be blocked by the cyclic AMP (cAMP)-dependent protein kinase (PKA) inhibitor, H-89. In contrast, IPP signaling is independent of A2aAR, A2bAR, cAMP or PKA. Unlike the 2CA-mediated pathway, the effect of IPP is dependent on the mevalonate pathway, a geranylgeranylated protein and on intact proteasome activity. Thus, IPP is a potent activator of a novel genoprotective pathway. These findings shed new light on the role of isoprenoids in oxidative stress biology and may help to develop novel preventive strategies against oxidative damage.

A molecular defect in intracellular lipid signaling in human neutrophils in localized aggressive periodontal tissue damage

Host defense mechanisms are impaired in patients with congenital neutrophil (polymorphonuclear neutrophils (PMN)) defects. Impaired PMN chemotaxis is observed in localized aggressive periodontitis (LAP), a familial disorder characterized by destruction of the supporting structures of dentition. In the present studies, we sought evidence for molecular events underlying this aberrant human PMN phenotype. To this end, PMN transendothelial migration and superoxide anion generation were assessed with LAP patients and asymptomatic family members, as well as patients with other chronic mucosal inflammation. PMN from LAP patients showed decreased transmigration across vascular endothelial monolayers (18 +/- 12% of control, n = 4) and increased superoxide anion generation (358 +/- 37%, p = 0.003). Gene expression was analyzed using oligonucleotide microarrays and fluorescence-based kinetic PCR. cDNA microarray and kinetic-PCR analysis revealed diminished RNA expression of leukocyte-type diacylglycerol (DAG) kinase alpha in PMN from LAP patients (4.6 +/- 1.7 relative units, n = 6, p = 0.007) compared with asymptomatic individuals (51 +/- 27 relative units, n = 7). DAG kinase activity was monitored by DAG phosphorylation and individual DAG molecular species were quantified using liquid chromatography and tandem mass spectrometry-based lipidomics. DAG kinase activity was also significantly decreased (73 +/- 2%, p = 0.007) and correlated with increased accumulation of 1,2-diacyl-sn-3-glycerol substrates (p = 0.01). These results implicate defects in both PMN transendothelial migration and PMN DAG kinase alpha signaling as disordered functions in LAP. Moreover, they identify a potential molecular lesion in PMN signal transduction that may account for their aberrant responses and tissue destruction in this disease.

Lipoxins: Potential anti-inflammatory, proresolution, and antifibrotic mediators in renal disease

Lipoxins are lipoxygenase-derived lipid mediators with both anti-inflammatory and proresolution properties that have been demonstrated in vivo and in vitro. The bioactivity profile of lipoxins in vitro suggests that they have therapeutic potential in acute renal failure and glomerulonephritis; predictions that have been borne out to date in experimental models of renal disease. We review recent developments on the molecular basis of lipoxin bioactions mediated through receptor crosstalk and the accumulating evidence that lipoxins may have potential as novel anti-inflammatory agents.

Novel endogenous small molecules as the checkpoint controllers in inflammation and resolution: entrée for resoleomics

Endogenously-generated small chemical mediators or autacoids play key roles in controlling inflammation and its organized resolution. Among them, lipoxins are the trihydroxy-tetraene-containing eicosanoids that are generated primarily by tight cell-cell interactions by way of transcellular biosynthesis and serve as local endogenous anti-inflammatory mediators. These "stop signals" in inflammation and other related processes may be involved in switching the cellular response from additional PMN recruitment toward monocytes (in a nonphlogistic fashion) that could lead to resolution of the inflammatory response or promotion of repair and healing. ASA impinges on this homeostatic system and evokes the endogenous biosynthesis of the carbon 15 epimers of lipoxins, namely ATLs, that mimic the bioactions of native LX in several biologic systems and, thus, can modulate in part, the beneficial actions of ASA in humans. Moreover, the temporal and spatial components in LX formation and actions are important determinants of their impact during an acute inflammatory reaction. Generation of lipid (ie, ATL) versus protein (ie, ANXA1) mediators during the host inflammatory response display different time courses. The temporal difference suggests that ALX could regulate PMN by interacting with each class of ligands within specific phases of the inflammatory response. ALX is the first cloned lipoxygenase-derived eicosanoid receptor. The signaling pathways and bioactions of ALX are cell type-specific. In agreement with in vitro results, ALX agonists, namely LXA4 and 15-epi-LXA4 and their stable analogs, regulate PMN during acute inflammation. In addition, it seems that LXs also display organ-specific actions, in addition to host defense and immune roles in the eye, kidney, lung, and oral and gastrointestinal tract and within bone marrow progenitors, possibly involving stem cells. The development of these few synthetic stable analogs has provided valuable tools to evaluate the biologic roles, significance, and pharmacologic actions of ALX and provided novel therapies for inflammatory diseases. The relationship between LX generation and current NSAID therapies is more intertwined than currently appreciated. ASA inhibits COX-1 and converts COX-2 into an ASA-triggered lipid mediator-generating system that produces an array of novel endogenous local autacoids from dietary omega-3 PUFA. Some of the local autacoids display potent anti-inflammatory or antineutrophil recruitment activity as well as impinge on the role of these compounds in resolution, and, thus, are termed "resolvins." It is not surprising that investigators recently found a protective action for COX-2 in cardiovascular disease. Together with the lipoxins and 15-epi-lipoxins, the identification of the resolvins gives us new avenues of approach in considering therapies for inflammation, cardiovascular diseases and cancer.

International Union of Pharmacology XXXVII. Nomenclature for leukotriene and lipoxin receptors

The leukotrienes and lipoxins are biologically active metabolites derived from arachidonic acid. Their diverse and potent actions are associated with specific receptors. Recent molecular techniques have established the nucleotide and amino acid sequences and confirmed the evidence that suggested the existence of different G-protein-coupled receptors for these lipid mediators. The nomenclature for these receptors has now been established for the leukotrienes. BLT receptors are activated by leukotriene B(4) and related hydroxyacids and this class of receptors can be subdivided into BLT(1) and BLT(2). The cysteinyl-leukotrienes (LT) activate another group called CysLT receptors, which are referred to as CysLT(1) and CysLT(2). A provisional nomenclature for the lipoxin receptor has also been proposed. LXA(4) and LXB(4) activate the ALX receptor and LXB(4) may also activate another putative receptor. However this latter receptor has not been cloned. The aim of this review is to provide the molecular evidence as well as the properties and significance of the leukotriene and lipoxin receptors, which has lead to the present nomenclature.

Lipoxin A4 and aspirin-triggered 15-epi-lipoxin A4 inhibit peroxynitrite formation, NF-kappa B and AP-1 activation, and IL-8 gene expression in human leukocytes

Lipoxin A(4) (LXA(4)) and aspirin-triggered 15-epi-LXA(4) (ATL) are emerging as endogenous braking signals for neutrophil-mediated tissue injury. Recent studies indicate that peroxynitrite (ONOO(-)) may function as an intracellular signal for the production of IL-8, a potent proinflammatory cytokine in human leukocytes. In this study, we evaluated the impact of the metabolically stable analogues of LXA(4)/ATL on lipopolysaccharide (LPS)-induced ONOO(-) formation and ONOO(-)-mediated IL-8 gene expression in human leukocytes. At nanomolar concentrations, LXA(4) analogues markedly reduced LPS-stimulated superoxide formation, evoked increases in intracellular diamino-fluorescein fluorescence (an indicator of NO formation), and consequently reduced ONOO(-) formation in isolated neutrophils, as well as in neutrophils, monocytes, and lymphocytes, in whole blood. LXA(4)/ATL analogues attenuated nuclear accumulation of activator protein-1 and nuclear factor-kappaB in both polymorphonuclear and mononuclear leukocytes and inhibited IL-8 mRNA expression and IL-8 release by 50-65% in response to LPS. The LXA(4) inhibitory responses were concentration dependent and were not shared by 15-deoxy-LXA(4). None of the LXA(4) analogues studied affected neutrophil survival, nor reversed the apoptosis delaying action of LPS in neutrophils. In addition, LXA(4) analogues had no significant effect on exogenous ONOO(-)-induced IL-8 gene and protein expression. These findings suggest that by attenuating ONOO(-) formation, LXA(4) and ATL can oppose ONOO(-) signaling in leukocytes and provide a rationale for using stable synthetic analogues as antiinflammatory compounds in vivo.

Mechanisms in anti-inflammation and resolution: the role of lipoxins and aspirin-triggered lipoxins

Multicellular host responses to infection, injury or inflammatory stimuli lead to the formation of a broad range of chemical mediators by the host. The integrated response of the host is essential to health and disease; thus it is important to achieve a more complete understanding of the molecular and cellular events governing the formation and actions of endogenous mediators of resolution that appear to control the duration of inflammation. Lipoxins are trihydroxytetraene-containing lipid mediators that can be formed during cell-cell interactions and are predominantly counterregulators of some well-known mediators of inflammation. Since this circuit of lipoxin formation and action appears to be of physiological relevance for the resolution of inflammation, therapeutic modalities targeted at this system are likely to have fewer unwanted side effects than other candidates and current anti-inflammatory therapies. Here, we present an overview of the recent knowledge about the biosynthesis and bioactions of these anti-inflammatory lipid mediators.

Squalene synthase: structure and regulation

Squalene synthase (SQS) catalyzes the first reaction of the branch of the isoprenoid metabolic pathway committed specifically to sterol biosynthesis. Regulation of SQS is thought to direct proximal intermediates in the pathway into either sterol or nonsterol branches in response to changing cellular requirements. The importance of SQS in cholesterol metabolism has stimulated research on the mechanism, structure, and regulation of the enzyme. SQS produces squalene, a C30 isoprenoid, in a two-step reaction in which two molecules of farnesyl diphosphate are condensed head to head. Site-directed mutagenesis of rat SQS has identified conserved Tyr, Phe, and Asp residues that are essential for function. The aromatic rings of Tyr and Phe are postulated to stabilize carbocation intermediates of the first and second half-reactions, respectively; the acidic Asp residues may be required for substrate binding. SQS activity, protein level, and gene transcription are strictly and coordinately regulated by cholesterol status, decreasing with cholesterol surfeit and increasing with cholesterol deficit. The human SQS (hSQS) gene has an unusually complex promoter with multiple binding sites for the sterol regulatory element binding proteins SREBP-1a and SREBP-2, and for accessory transcription factors known to be involved in the control of other sterol-responsive genes. SREBP-1a and SREBP-2 require different subsets of hSQS regulatory DNA elements to achieve maximal promoter activation. Current research is directed at elucidating the precise contribution made by individual SREBPs and accessory transcription factors to hSQS transcriptional control.

Polyisoprenyl phosphate signaling: topography in human neutrophils

To determine the relationship of polyisoprenyl phosphate (PIPP) remodeling and signaling to the activation state of human neutrophils (PMN), we examined the impact of leukotriene B(4) (LTB(4)) on the conversion of a unique bioactive isoprenoid (presqualene diphosphate: PSDP), recently identified as a novel endogenous signaling molecule. LTB(4) initiated rapid decrements in total PSDP that were concurrent with the respiratory burst (e.g., O(-2) formation). PSDP was identified in nuclear (39%)-, granule (36%)-, and plasma membrane (16%)-containing fractions of PMN. LTB(4) receptor (BLT) activation led to a decrease in nuclear PSDP and concomitant increase in granule-associated PSDP. In addition, PMN nuclei displayed PSDP associated with chromatin as established by mass spectrometry. Together, these results indicate that PSDP is present in membranes and receptor activation rapidly initiates subcellular PIPP remodeling (i.e., conversion) and distribution predominantly to granule membranes. Moreover, identification of nuclear PSDP provides the basis for novel roles for PIPP and PSDP in nuclear-associated signaling events.

Sterols and isoprenoids: signaling molecules derived from the cholesterol biosynthetic pathway

Compounds derived from the isoprenoid/cholesterol biosynthetic pathway have recently been shown to have novel biological activities. These compounds include certain sterols, oxysterols, farnesol, and geranylgeraniol, as well as the diphosphate derivatives of isopentenyl, geranyl, farnesyl, geranylgeranyl, and presqualene. They regulate transcriptional and post-transcriptional events that in turn affect lipid synthesis, meiosis, apoptosis, developmental patterning, protein cleavage, and protein degradation.

A novel polyisoprenyl phosphate signaling cascade in human neutrophils

Activation of neutrophil (PMN) surface receptors can evoke inflammation and tissue injury via aberrant release of excess effectors. The molecular mechanisms involved in host protection and control of PMN responses have yet to be defined. As Billah and coworkers (1989), and Exton (1997), for example, have pointed out, phospholipase D (PLD) signaling is known to play a pivotal role in PMN activation. Here, we determined the relationship between polyisoprenyl phosphate (PIPP) remodeling and PLD signaling and their impact in activation of PMN receptors by "pro-inflammatory" (leukotriene B4), and "anti-inflammatory" (aspirin-triggered lipoxinA4) ligands. Activation of the leukotriene B4 receptor initiated a rapid (within seconds) decrement in presqualene disphosphate (PSDP), activation of PLD and production of superoxide anions. This contrasts with activation of the LXA4 receptor by an aspirin-triggered lipoxin A4 mimetic that before leukotriene B4 gave an inverse relationship with rapidly increasing PSDP levels, and inhibition of both PLD activity and superoxide generation. PSDP proved to be a potent and direct-acting inhibitor of PLD (rhPLD1b:Ki = 5.9 nM), a property not shared by structurally related endogenous lipids. This PIPP also interacted with Src homology domains, selectively targeting SH2 and not SH3 domains. These results indicate a role for ligand-driven rapid PIPP remodeling as an early switch and "stop" signaling event that controls PMN. Moreover, they indicate that PSDP directly down-regulates PMN signaling events via select protein-target interactions controlling intracellular responses relevant in inflammation.

[Hyperimmunoglobulinemia D and periodic fever syndrome. A phenotypical analysis of a Spanish family]

BACKGROUND

Hyperimmunoglobulinemia D and periodic fever syndrome (HIDS) is a disorder diagnosed with low frequency, that produces a very prolonged and recurrent fever with other symptoms and analytical markers of inflammation. Its origin seems to be hereditary with a recessive autosomic pattern, but its pathogenic mechanisms are unclear. The aim of this study is to analyse the clinical characteristics and serum levels of immunoglobulins a Spanish family with HIDS.

METHODS

We describe a young woman diagnosed with HIDS and investigate the other memberships of her family (parents and 5 brothers) by clinical interview, physical examination, hematological and biochemical analyses and measurements of IgG, IgA, IgM, IgE, IgD and the kappa/lambda ratio of light chains. Moreover, we also determine the IgD in a control group of 35 healthy blood donors.

RESULTS

One male brother of the index case also showed a clinical picture of HIDS. The serum IgD levels were increased (above 100 U/ml) in both and in other two sisters without symptoms and were normal in the rest of the family. With only one exception, all individuals of the control group showed a normal IgD level and this was not associated with sex or age. The other immunoglobulins were normal in the family. In spite of the different treatments tested in the index case, only glucocorticoids aborted her fever attacks.

CONCLUSIONS

In HIDS the clinical picture and the high IgD levels are both transmitted with a recessive autosomic pattern, but these are not necessarily associated in the same memberships of the family. Its diagnosis is difficult and there is not effective and long-term safe treatment.

Polyisoprenyl phosphate (PIPP) signaling regulates phospholipase D activity: a 'stop' signaling switch for aspirin-triggered lipoxin A4

It is of wide interest to understand how opposing extracellular signals (positive or negative) are translated into intracellular signaling events. Receptor-ligand interactions initiate the generation of bioactive lipids by human neutrophils (PMN), which serve as signals to orchestrate cellular responses important in host defense and inflammation. We recently identified a novel polyisoprenyl phosphate (PIPP) signaling pathway and found that one of its components, presqualene diphosphate (PSDP), is a potent negative intracellular signal in PMN that regulates superoxide anion generation by several stimuli, including phosphatidic acid. We determined intracellular PIPP signaling by autocoids with opposing actions on PMN: leukotriene B4 (LTB4), a potent chemoattractant, and lipoxin A4 (LXA4), a 'stop signal' for recruitment. LTB4 receptor activation initiated a rapid decrease in PSDP levels concurrent with activation of PLD and cellular responses. In sharp contrast, activation of the LXA4 receptor reversed LTB4-initiated PSDP remodeling, leading to an accumulation of PSDP and potent inhibition of both PLD and superoxide anion generation. Thus, an inverse relationship was established for PSDP levels and PLD activity with two PMN ligands that evoke opposing responses. In addition, PSDP directly inhibited both isolated human recombinant (Ki = 6 nM) and plant (Ki = 20 nM) PLD. Together, these findings link PIPP remodeling to intracellular regulation of PMN function and suggest a role for PIPPs as lipid repressors in signal transduction, a novel mechanism that may also explain aspirin's suppressive actions in vivo in cell signaling.

Binding of GM-CSF to adherent neutrophils activates phospholipase D

When the hematopoietic growth factor granulocyte-macrophage colony-stimulating factor was incubated with neutrophils adherent to plastic tissue culture plates or plates coated with extracellular matrix proteins, a rapid (3 min) but transient formation of phosphatidic acid was observed. This stimulation was dependent on the dose of GM-CSF, with an EC50 of 140 pM, and was further enhanced (up to 350%) with the PA phosphatase inhibitor propranolol in a dose-dependent manner. Conversely, GM-CSF was unable to trigger any PA formation in neutrophils maintained in suspension, even in the presence of soluble fibronectin. However, GM-CSF did prime the cells for enhanced PA formation in the presence of a secondary stimulus (fMet-Leu-Phe or PAF). GM-CSF also caused a time-dependent stimulation of diacylglycerol formation in adherent, but not suspended, cells and elicited a time-dependent stimulation of phosphatidylethanol formation, with a concomitant decrease in the formation of PA only at early (< 7 min) times. These observations were consistent with a rapid activation of the enzyme phospholipase D in adherent cells stimulated with GM-CSF. Additional data indicated that the source of DAG was PLD coexisting with PLC, especially at later times ( > 7 min) of stimulation with GM-CSF. Finally, the formation of PA and PEt, and to a minor extent, DAG, were inhibited by the protein tyrosine kinase inhibitor erbstatin in conditions in which tyrosine phosphorylation occurred. Taken together the data indicate that GM-CSF rapidly activates PLD in adherent cells, which is responsible for the generation of PA. Thus, PLD activation is an early event in neutrophil signal transduction following exposure of adherent cells to GM-CSF.