Arachidonic acid metabolism via cytosolic phospholipase A2 α induces cytotoxicity in niemann-pick disease type C cells

Comprehensive-targeted lipidomic analysis in Niemann-Pick C disease

Niemann-Pick C disease (NPC) is a lysosomal disease caused by mutations in NPC1 or NPC2 genes responsible for intracellular accumulation of free cholesterol and glycosphingolipids in a variety of tissues. We collected plasma samples from 15 NPC1 patients and 15 age-matched controls to analyze the impairment of lipid metabolism. Comprehensive-targeted quantitative lipidomic analysis was per-formed by Ion Mobility Mass Spectrometry, while oxysterols and lyso-sphingolipids, the classical NPC biomarkers, were analyzed by LC-MS/MS. Lipidomic analysis allowed the quantitation of ~1100 lipid species, belonging to 13 different classes. Statistical analysis of collected data showed a significant differentiation between NPC patients and controls. Lipid profiling showed an elevation of arachidonic acid and total diacylglycerols. Conversely, sphingomyelins, phosphatidylethano-lamines, phosphatidylcholines, cholesterylesters, and lactosylceramides were decreased. Indeed, the lipid imbalance was consistent with the increased concentrations of oxysterols and lyso-sphingolipids. Our study revealed a novel disease biosignature suggesting new potential diagnostic biomarkers. The alteration in key lipids molecules involved in inflammatory pathways and in oxidative stress regulation, provides new insights in the complex pathophysiology of the disease, still largely un-known.

Role of cytosolic phospholipase A2 in oxidative and inflammatory signaling pathways in different cell types in the central nervous system

Phospholipases A(2) (PLA(2)s) are important enzymes for the metabolism of fatty acids in membrane phospholipids. Among the three major classes of PLA(2)s in the mammalian system, the group IV calcium-dependent cytosolic PLA(2) alpha (cPLA(2)α) has received the most attention because it is widely expressed in nearly all mammalian cells and its active participation in cell metabolism. Besides Ca(2+) binding to its C2 domain, this enzyme can undergo a number of cell-specific post-translational modifications, including phosphorylation by protein kinases, S-nitrosylation through interaction with nitric oxide (NO), as well as interaction with other proteins and lipid molecules. Hydrolysis of phospholipids by cPLA(2) yields two important lipid mediators, arachidonic acid (AA) and lysophospholipids. While AA is known to serve as a substrate for cyclooxygenases and lipoxygenases, which are enzymes for the synthesis of eicosanoids and leukotrienes, lysophospholipids are known to possess detergent-like properties capable of altering microdomains of cell membranes. An important feature of cPLA(2) is its link to cell surface receptors that stimulate signaling pathways associated with activation of protein kinases and production of reactive oxygen species (ROS). In the central nervous system (CNS), cPLA(2) activation has been implicated in neuronal excitation, synaptic secretion, apoptosis, cell-cell interaction, cognitive and behavioral function, oxidative-nitrosative stress, and inflammatory responses that underline the pathogenesis of a number of neurodegenerative diseases. However, the types of extracellular agonists that target intracellular signaling pathways leading to cPLA(2) activation among different cell types and under different physiological and pathological conditions have not been investigated in detail. In this review, special emphasis is given to metabolic events linking cPLA(2) to activation in neurons, astrocytes, microglial cells, and cerebrovascular cells. Understanding the molecular mechanism(s) for regulation of this enzyme is deemed important in the development of new therapeutic targets for the treatment and prevention of neurodegenerative diseases.

An evaluation of 3-rhamnosylquercetin, a glycosylated form of quercetin, against the myotoxic and edematogenic effects of sPLA 2 from Crotalus durissus terrificus

This paper shows the results of quercitrin effects on the structure and biological activity of secretory phospholipase (sPLA₂) from Crotalus durissus terrificus, which is the main toxin involved in the pharmacological effects of this snake venom. According to our mass spectrometry and circular dichroism results, quercetin was able to promote a chemical modification of some amino acid residues and modify the secondary structure of C. d. terrificus sPLA₂. Moreover, molecular docking studies showed that quercitrin can establish chemical interactions with some of the crucial amino acid residues involved in the enzymatic activity of the sPLA₂, indicating that this flavonoid could also physically impair substrate molecule access to the catalytic site of the toxin. Additionally, in vitro and in vivo assays showed that the quercitrin strongly diminished the catalytic activity of the protein, altered its Vmax and Km values, and presented a more potent inhibition of essential pharmacological activities in the C. d. terrificus sPLA₂, such as its myotoxicity and edematogenic effect, in comparison to quercetin. Thus, we concluded that the rhamnose group found in quercitrin is most likely essential to the antivenom activities of this flavonoid against C. d. terrificus sPLA₂.

Effects of Hsp90 inhibitors, geldanamycin and its analog, on ceramide metabolism and cytotoxicity in PC12 cells

The inhibitors of heat shock protein-90 (Hsp90), geldanamycin (GA) and 17-(allylamino)-17-desmethoxygeldanamycin, show various cellular effects including destabilization of Hsp90 clients and expression of other chaperones, etc. and modulate cytotoxicity depending on cell types and stimuli. In this study, we investigated the effects of Hsp90 inhibitors on survival of PC12 cells with and without cytotoxic stimuli including orthovanadate, Na(3)VO(4). Treatment with Hsp90 inhibitors at 2 µM for 16 hr did not cause cell detachment and leakage of lactate dehydrogenase, and at concentrations greater than 5 µM resulted in cytotoxicity. The inhibitors at 2 µM enhanced the cytotoxicity of 1 mM Na(3)VO(4), and did not protect PC12 cells at any concentrations against Na(3)VO(4). Next, the effects of Hsp90 inhibitors on the intracellular metabolism of ceramide and arachidonic acid (AA) were examined, since these processes also regulate cytotoxicity. In cells treated with 4-nitrobenzo-2-oxa-1,3-diazole (NBD)-labeled C6-ceramide, Hsp90 inhibitors reduced the formation of NBD-glucosylceramide and Na(3)VO(4)-induced formation of NBD-caproic acid, a counterpart of sphingosine, without affecting other metabolites including NBD-sphingomyelin. GA treatment did not change the amounts of AA released in PC12 cells with and without Na(3)VO(4). In HeLa cells, however, GA treatment decreased the release of AA via cytosolic phospholipase A(2)α's activation probably because of dysfunctional Hsp90 clients. Our results suggest the possible involvement of ceramide metabolism, not AA release, in GA-induced cytotoxicity in PC12 cells.

Microarray expression analysis and identification of serum biomarkers for Niemann-Pick disease, type C1

Niemann-Pick disease type C (NPC) is a lysosomal storage disorder characterized by liver disease and progressive neurodegeneration. Deficiency of either NPC1 or NPC2 leads to the accumulation of cholesterol and glycosphingolipids in late endosomes and early lysosomes. In order to identify pathological mechanisms underlying NPC and uncover potential biomarkers, we characterized liver gene expression changes in an Npc1 mouse model at six ages spanning the pathological progression of the disease. We identified altered gene expression at all ages, including changes in asymptomatic, 1-week-old mice. Biological pathways showing early altered gene expression included: lipid metabolism, cytochrome P450 enzymes involved in arachidonic acid and drug metabolism, inflammation and immune responses, mitogen-activated protein kinase and G-protein signaling, cell cycle regulation, cell adhesion and cytoskeleton remodeling. In contrast, apoptosis and oxidative stress appeared to be late pathological processes. To identify potential biomarkers that could facilitate monitoring of disease progression, we focused on a subset of 103 differentially expressed genes that encode secreted proteins. Further analysis identified two secreted proteins with increased serum levels in NPC1 patients: galectin-3 (LGALS3), a pro-inflammatory molecule, and cathepsin D (CTSD), a lysosomal aspartic protease. Elevated serum levels of both proteins correlated with neurological disease severity and appeared to be specific for NPC1. Expression of Lgals3 and Ctsd was normalized following treatment with 2-hydroxypropyl-β-cyclodextrin, a therapy that reduces pathological findings and significantly increases Npc1(-/-) survival. Both LGALS3 and CTSD have the potential to aid in diagnosis and serve as biomarkers to monitor efficacy in therapeutic trials.