Enhancing arginase 2 expression using target site blockers as a strategy to modulate macrophage phenotype

Macrophages are plastic cells playing a crucial role in innate immunity. While fundamental in responding to infections, when persistently maintained in a pro-inflammatory state they can initiate and sustain inflammatory diseases. Therefore, a strategy that reprograms pro-inflammatory macrophages toward an anti-inflammatory phenotype could hold therapeutic potential in that context. We have recently shown that arginase 2 (Arg2), a mitochondrial enzyme involved in arginine metabolism, promotes the resolution of inflammation in macrophages and it is targeted by miR-155. Here, we designed and tested a target site blocker (TSB) that specifically interferes and blocks the interaction between miR-155 and Arg2 mRNA, leading to Arg2 increased expression and activity. In bone marrow-derived macrophages transfected with Arg2 TSB (in the presence or absence of the pro-inflammatory stimulus LPS), we observed an overall shift of the polarization status of macrophages toward an anti-inflammatory phenotype, as shown by significant changes in surface markers (CD80 and CD71), metabolic parameters (mitochondrial oxidative phosphorylation) and cytokines secretion (IL-1β, IL-6, and TNF). Moreover, in an in vivo model of LPS-induced acute inflammation, intraperitoneal administration of Arg2 TSB led to an overall decrease in systemic levels of pro-inflammatory cytokines. Overall, this proof-of-concept strategy represent a promising approach to modulating macrophage phenotype.

Mitochondrial arginase-2 is essential for IL-10 metabolic reprogramming of inflammatory macrophages

Mitochondria are important regulators of macrophage polarisation. Here, we show that arginase-2 (Arg2) is a microRNA-155 (miR-155) and interleukin-10 (IL-10) regulated protein localized at the mitochondria in inflammatory macrophages, and is critical for IL-10-induced modulation of mitochondrial dynamics and oxidative respiration. Mechanistically, the catalytic activity and presence of Arg2 at the mitochondria is crucial for oxidative phosphorylation. We further show that Arg2 mediates this process by increasing the activity of complex II (succinate dehydrogenase). Moreover, Arg2 is essential for IL-10-mediated downregulation of the inflammatory mediators succinate, hypoxia inducible factor 1α (HIF-1α) and IL-1β in vitro. Accordingly, HIF-1α and IL-1β are highly expressed in an LPS-induced in vivo model of acute inflammation using Arg2^-/- mice. These findings shed light on a new arm of IL-10-mediated metabolic regulation, working to resolve the inflammatory status of the cell.

The Role of MicroRNAs in Repair Processes in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disorder characterised by demyelination of central nervous system neurons with subsequent damage, cell death and disability. While mechanisms exist in the CNS to repair this damage, they are disrupted in MS and currently there are no treatments to address this deficit. In recent years, increasing attention has been paid to the influence of the small, non-coding RNA molecules, microRNAs (miRNAs), in autoimmune disorders, including MS. In this review, we examine the role of miRNAs in remyelination in the different cell types that contribute to MS. We focus on key miRNAs that have a central role in mediating the repair process, along with several more that play either secondary or inhibitory roles in one or more aspects. Finally, we consider the current state of miRNAs as therapeutic targets in MS, acknowledging current challenges and potential strategies to overcome them in developing effective novel therapeutics to enhance repair mechanisms in MS.

Enhancement of chemotherapeutic drug toxicity to human tumour cells in vitro by a subset of non-steroidal anti-inflammatory drugs (NSAIDs)

The effect on cytotoxicity of combining a range of clinically important non-steroidal anti-inflammatory drugs (NSAIDs) with a variety of chemotherapeutic drugs was examined in the human lung cancer cell lines DLKP, A549, COR L23P and COR L23R and in a human leukaemia line HL60/ADR. A specific group of NSAIDs (indomethacin, sulindac, tolmetin, acemetacin, zomepirac and mefenamic acid) all at non-toxic levels, significantly increased the cytotoxicity of the anthracyclines (doxorubicin, daunorubicin and epirubicin), as well as teniposide, VP-16 and vincristine, but not the other vinca alkaloids vinblastine and vinorelbine. A substantial number of other anticancer drugs, including methotrexate, 5-fluorouracil, cytarabine, hydroxyurea, chlorambucil, cyclophosphamide, cisplatin, carboplatin, mitoxantrone, actinomycin D, bleomycin, paclitaxel and camptothecin, were also tested, but displayed no synergy in combination with the NSAIDs. The synergistic effect was concentration dependent. The effect appears to be independent of the cyclo-oxygenase inhibitory ability of the NSAIDs, as (i) the synergistic combination could not be reversed by the addition of prostaglandins D2 or E2; (ii) sulindac sulphone, a metabolite of sulindac that does not inhibit the cyclooxygenase enzyme, was positive in the combination assay: and (iii) many NSAIDs known to be cyclo-oxygenase inhibitors, e.g. meclofenamic acid, diclofenac, naproxen, fenoprofen, phenylbutazone, flufenamic acid, flurbiprofen, ibuprofen and ketoprofen, were inactive in the combination assay. The enhancement of cytotoxicity was observed in a range of drug sensitive tumour cell lines, but did not occur in P-170-overexpressing multidrug resistant cell lines. However, in the HL60/ADR and COR L23R cell lines, in which multidrug resistance is due to overexpression of the multidrug resistance-associated protein MRP, a significant increase in cytotoxicity was observed in the presence of the active NSAIDs. Subsequent Western blot analysis of the drug sensitive parental cell lines, DLKP and A549, revealed that they also expressed MRP and reverse-transcription-polymerase chain reaction studies demonstrated that mRNA for MRP was present in both cell lines. It was found that the positive NSAIDs were among the more potent inhibitors of [3H]-LTC4 transport into inside-out plasma membrane vesicles prepared from MRP-expressing cells, of doxorubicin efflux from preloaded cells and of glutathione-S-transferase activity. The NSAIDs did not enhance cellular sensitivity to radiation. The combination of specific NSAIDs with anticancer drugs reported here may have potential clinical applications, especially in the circumvention of MRP-mediated multidrug resistance.

Platelet activation and mitral valve prolapse

Mitral valve prolapse (MVP) is a predisposing factor for cerebral ischemia, especially in young adults. Cerebral embolization of intracardiac thrombi is the probable mechanism in many cases. Platelets play a key role in the development of thrombi. We found that platelet factor 4, a marker protein of platelet activation, was elevated in 12 of 33 MVP patients (36%) without a history of stroke. This finding indicates that platelets are frequently activated in asymptomatic MVP patients and may allow identification of a subgroup of MVP patients with activated platelets who are at increased risk for emboli.

Marker proteins of platelet activation in patients with cerebrovascular disease

Platelet activation is assumed to occur in many patients with strokes of transient ischemic attacks (TIAs). Determination of this activity can now be measured by assaying the platelet-specific proteins, platelet factor 4 and beta-thromboglobulin. These proteins are platelet specific and are released during irreversible aggregation. The plasma level of these proteins was measured in patients with strokes and TIAs and both groups had significantly greater values than healthy control subjects. These markers of platelet activation may provide further understanding of the role of platelets in the etiology, diagnosis, and treatment of cerebrovascular disease.

Human platelet factor 4: preparation from outdated platelet concentrates and application in cerebral vascular disease

Platelet factor 4 (PF4), the platelet antiheparin protein, was isolated from both the supernatant and the cells of recently outdated platelet concentrates. Following purification by affinity chromatography, a competitive binding radioimmunoassay was developed to detect this protein in human plasma. The normal range was determined to be 9.4 +/- 4.7 ng/ml (mean +/- SD for 52 healthy adults). In order to determine whether individuals with transient ischemic attack (TIA) or stroke had measurable increments of PF4 in their plasma, radioimmunoassay studies were performed on 11 patients with well-documented TIA, 10 patients with well-documented stroke and on 16 age-matched controls hospitalized on a neurology service with disorders unrelated to arterial thrombosis. The 16 hospitalized controls had PF4 levels of 10.3 +/- 9.1 ng/ml, a value not significantly different from the 52 normals (P greater than 0.50). Patients with TIA had PF4 levels of 24.6 +/- 12.1 ng/ml, a value significantly higher than both the 52 normals (P less than 0.001) and the 16 hospitalized control patients (P less than 0.005). Patients with stroke had PF4 levels of 35.4 +/- 29.2 ng/ml, a value significantly higher than both the 42 normals (P less than 0.001) and the 16 hospitalized control patients (P less than 0.005). Outdated platelet concentrates facilitate the development of a reproducible radioimmunoassay for PF4. The elevation of this platelet-derived protein in the plasma of patients with stroke and TIA provides evidence for recent or ongoing platelet activation in the cerebral vascular disease population.