Inhibition of phospholipase A2 purified from human herniated disc

Phospholipase A2 inhibitor-loaded micellar nanoparticles attenuate inflammation and mitigate osteoarthritis progression

Treating osteoarthritis (OA) remains a major clinical challenge. Despite recent advances in drug discovery and development, no disease-modifying drug for knee OA has emerged with any notable clinical success, in part, due to the lack of valid and responsive therapeutic targets and poor drug delivery within knee joints. In this work, we show that the amount of secretory phospholipase A₂ (sPLA₂) enzyme increases in the articular cartilage in human and mouse OA cartilage tissues. We hypothesize that the inhibition of sPLA₂ activity may be an effective treatment strategy for OA. To develop an sPLA₂-responsive and nanoparticle (NP)-based interventional platform for OA management, we incorporated an sPLA₂ inhibitor (sPLA₂i) into the phospholipid membrane of micelles. The engineered sPLA₂i-loaded micellar NPs (sPLA₂i-NPs) were able to penetrate deep into the cartilage matrix, prolong retention in the joint space, and mitigate OA progression. These findings suggest that sPLA₂i-NPs can be promising therapeutic agents for OA treatment.

Differentially-expressed mRNAs, microRNAs and long noncoding RNAs in intervertebral disc degeneration identified by RNA-sequencing

The underlying molecular mechanisms of intervertebral disc degeneration (IDD) remain unclear. This study aimed to identify the crucial molecules and explore the function of noncoding RNAs and related pathways in IDD. We randomly selected three samples each from an IDD and a spinal cord injury group (control) for RNA-sequencing. We identified 463 differentially-expressed long noncoding RNAs (lncRNAs), 47 differentially-expressed microRNAs (miRNAs), and 1,334 differentially-expressed mRNAs in IDD. Three hundred fifty-eight lncRNAs as cis-regulators could potentially target 865 genes. Protein–protein interaction (PPI) network analysis confirmed that IL-6, VEGFA, IGF1, MMP9, CXCL8, FGF2, IL1B, CCND1, ITGAM, PTPRC, FOS and PTGS2 were hub genes. We built a competing endogenous RNA (ceRNA) network and identified lncRNA XIST–hsa-miR-4775–PLA2G7 and lncRNA XIST–hsa-miR-424-5p–AMOT/TGFBR3 ceRNA axes. Quantitative real-time PCR (qRT-PCR) was implemented in 15 IDD samples and 15 controls to validate differentially-expressed genes in ceRNA axes. From the ceRNA network, gene ontology (GO) enrichment analysis indicated that noncoding RNAs were associated with several biological processes, including extracellular matrix organization, extracellular structure organization, leukocyte migration, and mesenchyme development. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that noncoding RNAs were associated with several pathways including the AGE-RAGE signaling pathway, PI3K-Akt signaling pathway, axon guidance, and osteoclast differentiation. These results indicate that some specific noncoding RNAs and ceRNA axes may be vital during the development of IDD, and may have potential as alternative diagnostic biomarkers as well as novel therapeutic strategies for IDD.

Phospholipase A2 Inhibitor-Loaded Phospholipid Micelles Abolish Neuropathic Pain

Treating persistent neuropathic pain remains a major clinical challenge. Current conventional treatment approaches carry a substantial risk of toxicity and provide only transient pain relief. In this work, we show that the activity and expression of the inflammatory mediator secretory phospholipase-A₂ (sPLA₂) enzyme increases in the spinal cord after painful nerve root compression. We then develop phospholipid micelle-based nanoparticles that release their payload in response to sPLA₂ activity. Using a rodent model of neuropathic pain, phospholipid micelles loaded with the sPLA₂ inhibitor, thioetheramide-PC (TEA-PC), are administered either locally or intravenously at the time of painful injury or 1-2 days afterward. Local micelle administration immediately after compression prevents pain for up to 7 days. Delayed intravenous administration of the micelles attenuates existing pain. These findings suggest that sPLA₂ inhibitor-loaded micelles can be a promising anti-inflammatory nanotherapeutic for neuropathic pain treatment.

Diagnosis and minimally invasive treatment of lumbar discogenic pain--a review of the literature

Diagnosis and treatment of lumbar discogenic pain due to internal disc disruption (IDD) remains a challenge. It accounts for 39% of patients with low back pain. The mechanism of discogenic pain remains unclear and its clinical presentation is atypical. Magnetic resonance imaging (MRI) can find high-intensity zone as an indirect indication of IDD. However, relative low sensitivity (26.7% to 59%) and high false-positive (24%) and false-negative (38%) rates reduce the value of MRI in screening for the existence of painful IDD. Provocative discography can provide unique information about the pain source and the morphology of the disc. It may also provide information for selecting appropriate treatment for the painful annular tear. Adjunctive therapies, including nonsteroidal anti-inflammatory drugs, physical therapy, rehabilitation, antidepressants, antiepileptics, and acupuncture, have been used for low back pain. The value of these treatments for discogenic pain is yet to be established. Intradiscal steroid injection has not been proved to provide long-term benefits. Intradiscal electrothermal therapy may offer some pain relief for a group of well-selected patients. No benefits have been found for the intradiscal radiofrequency thermocoagulation. A block in the ramus communicans may interfere with the transition of painful information from the discs to the central nervous system. Disc cell transplantation is in the experimental stage. It has the potential to become a useful tool for the prevention and treatment of discogenic pain. Minimally invasive treatments provide alternatives for discogenic pain with the appeal of cost-effectiveness and, possibly, less long-term side effects. However, the value of most of these therapies is yet to be established. More basic science and clinical studies are needed to improve the clinical efficacy of minimally invasive treatments.

Evidence for the participation of arachidonic acid metabolites in trehalose efflux from the hormone activated fat body of the cockroach (Periplaneta americana)

The hypertrehalosemic hormones, HTH-I and HTH-II, activate trehalose synthesis and increase the rate of sugar efflux from Periplaneta americana fat body in vitro. These processes are unaffected by the diacylglycerol, 1-oleyl-2-acetyl-sn-glycerol, an activator of protein kinase C. Similarly, H-7 and spingosine, inhibitors of protein kinase C, are also inactive against trehalose efflux. The possibility that diacylglycerol lipase might generate an active fatty acid species was ruled out because of the failure of the inhibitor RHC-80267 to inhibit trehalose efflux. Activation of trehalose efflux from the intact fat body by HTH-I was strongly inhibited in a concentration dependent manner by the cyclooxygenase inhibitors indomethacin and diclofenac, but not by acetylsalicylic acid. Nordihydroguaiaretic acid, a lipoxygenase inhibitor, also blocked HTH-I activated trehalose efflux in a concentration dependent fashion. The phospholipase A(2) inhibitors mepacrine and 4'-bromophenacyl bromide were also effective in decreasing the efflux of trehalose from HTH-I challenged fat body. The data suggest possible roles for arachidonic acid metabolites in the regulation of trehalose synthesis and in the efflux of the sugar from the fat body.

Evidence that free fatty acids in trophocytes of Periplaneta americana fat body may be regulated by the activity of phospholipase A2 and cyclooxygenase

Previous studies have shown that palmitic, stearic, oleic and linoleic acid levels in trophocytes prepared from the fat body of male Periplaneta americana are increased following treatment of the cells with hypertrehalosemic hormone (HTH). Melittin, an activator of phospholipase A2, mimicked the action of HTH by increasing the free fatty acid content in a concentration-dependent manner. The increase caused by HTH could be eliminated by pretreatment of the trophocytes with 1 mM 4'-bromophenacyl bromide (BPB), an inhibitor of phospholipase A2. BPB also decreases the concentration of free fatty acids in trophocytes not treated with HTH but by a smaller margin. Nordihydroguaiaretic acid (NDGA) and indomethacin, inhibitors of lipoxygenase and cyclooxygenase, respectively, eliminated the increase in free fatty acids evoked by HTH. In the absence of HTH both inhibitors increased the free fatty acid content of the trophocytes, an effect consistent with the known mode of action of these agents. None of the inhibitors tested, all of which blocked HTH activated trehalose synthesis, prevented activation of phosphorylase by HTH. This is taken as evidence that other downstream sites are also important in the regulation of trehalose production by the fat body. It is suggested that the increase in free fatty acids evoked by HTH, or metabolites of those fatty acids, may regulate the synthesis and release of trehalose from the trophocytes because of potential effects on trehalose phosphate synthase, trehalose 6-phosphate phosphatase, and the trehalose transport mechanism in the trophocyte membrane.

The Effects of Eicosanoid Biosynthesis Inhibitors On Prophenoloxidase Activation, Phagocytosis and Cell Spreading in Galleria mellonella

The invertebrate immune system produces melanotic nodules in response to bacterial infections and this has previously been shown to be mediated by eicosanoids. Nodulation occurs in two phases: the first involves hemocyte degranulation and activation of the prophenoloxidase cascade; the second involves formation of a cellular capsule by attachment and spreading of hemocytes. We demonstrate that inhibitors of eicosanoid biosynthesis affect both of these phases of nodulation in Galleria mellonella. The phospholipase A(2) inhibitor, dexamethasone, as well as the cyclooxygenase inhibitor, indomethacin, significantly inhibit phagocytosis in vitro and prophenoloxidase activation in vivo. The inhibitory effects of dexamethasone were abolished by the addition of exogenous arachidonic acid. Furthermore, 5,8,11,14- eicosatetraynoic acid, dexamethasone and indomethacin inhibit hemocyte spreading in vitro. The findings support the idea that eicosanoid derivatives mediate both phases of the nodulation response and are consistent with previous studies which attribute roles for eicosanoids in other species as modulators of cell activity.

Effect of manoalide on human 5-lipoxygenase activity

The marine natural product manoalide (MLD) has been described to inactivate phospholipase A2 (PLA2) from several sources as well as to inhibit synthesis of eicosanoids in human polymorphonuclear leukocytes (HPMNL). MLD also reduces chemically-induced inflammation in vivo. In this investigation we have examined the effect of MLD on A23187-induced generation of leukotriene B4 (LTB4) and thromboxane B2 (TXB2) in HPMNL as well as 5-lipoxygenase (5-LO) activity from HPMNL sonicated preparations. In the intact cell system, MLD inhibited with similar potency biosynthesis of LTB4 and TXB2 (IC50 1.7 and 1.4 microM, respectively). In order to discern if inhibition of 5-LO is involved in the effect of MLD, we examined the action of this compound on 5-LO activity from 10,000 x g and 100,000 x g supernatants of sonicated HPMNL homogenates. The enzymatic activity was not affected at concentrations of MLD up to 50 microM. These data indicate that MLD is not a direct inhibitor of 5-LO activity from HPMNL and support the hypothesis that its anti-inflammatory action could be related with a reduction of eicosanoid biosynthesis via inhibition of PLA2.

Regulation of free arachidonic acid levels in isolated salivary glands from the lone star tick: a role for dopamine

An important regulatory step for prostaglandin synthesis is the availability of the precursor, free arachidonic acid (AA). In isolated salivary glands of the lone star tick, Amblyomma americanum (L.), the level of free AA appears to depend on higher phospholipase A2 (PLA2) activity rather than decreased rates of re-esterification by lysophosphatide acyl transferase (LAT). This conclusion is supported by experiments where inhibition of LAT with merthiolate was without effect, while the calcium ionophore A23187, a PLA2 stimulant, increased levels of free AA. The PLA2 activity in A. americanum was reduced by the substrate analog, PLA2 inhibitor, oleyloxyethyl phosphorylcholine in a dose-dependent manner, but was insensitive to the other mammalian PLA2 inhibitors mepacrine (20 microM), aristolochic acid (45 microM), and dexamethasone (50 microM). No substrate preference was observed for the functional group of the phospholipid, with phosphatidylcholine and phosphatidylethanolamine being equal sources of AA in A23187-stimulated glands. Compared to phospholipids containing other fatty acids, only arachidonyl-phospholipid (arachidonyl-PL) was significantly hydrolyzed by PLA2 activity in A23187-stimulated glands. Dopamine was as effective as A23187 as a stimulant of PLA2 activity in isolated glands, but this effect was abolished in the presence of the calcium channel blocking agent verapamil. It is concluded that free AA levels in tick salivary glands are increased through activation of a Type IV-like PLA2 following an increase of intracellular calcium caused by the opening of voltage-dependent calcium channels due to dopamine stimulation.