Agents that increase AAM differentiation blunt RSV-mediated lung pathology.

RSV is the most significant cause of serious lower respiratory tract infection in infants and young children worldwide. There is currently no vaccine for the virus, and antiviral therapy (e.g., ribavirin) has shown no efficacy against the disease. We reported that alternatively activated macrophages (AAMs) mediate resolution of RSV-induced pathology. AAM differentiation requires macrophage-derived IL-4 and -13, autocrine/paracrine signaling through the type I IL-4 receptor, and STAT6 activation. Based on these findings, we reasoned that it would be possible to intervene therapeutically in RSV disease by increasing AAM differentiation, thereby decreasing lung pathology. Mice treated with the IL-4/anti-IL-4 immune complexes, shown previously to sustain levels of circulating IL-4, increased the RSV-induced AAM markers arginase-1 and mannose receptor and decreased the lung pathology. Induction of PPARγ, shown to play a role in AAM development, by the PPARγ agonist rosiglitazone or treatment of mice with the macrolide antibiotic AZM, also reported to skew macrophage differentiation to an AAM phenotype, increased the AAM markers and mitigated RSV-induced lung pathology. Collectively, our data suggest that therapeutic manipulation of macrophage differentiation to enhance the AAM phenotype is a viable approach for ameliorating RSV-induced disease.

5-Lipoxygenase-deficient mice infected with Borrelia burgdorferi develop persistent arthritis.

The enzyme 5-lipoxygenase (5-LO) catalyzes the conversion of arachidonic acid into the leukotrienes, which are critical regulators of inflammation and inflammatory diseases, such as asthma and arthritis. Although leukotrienes are present in the synovial fluid of Lyme disease patients, their role in the development of Lyme arthritis has not been determined. In the current study, we used a murine model of Lyme arthritis to investigate the role 5-LO products might have in the development of this inflammatory disease. After infection of Lyme arthritis-susceptible C3H/HeJ mice with Borrelia burgdorferi, mRNA expression of 5-LO and 5-LO-activating protein was induced in the joints, and the 5-LO product leukotriene B(4) was produced. Using C3H 5-LO-deficient mice, we demonstrated that 5-LO activity was not necessary for the induction of Lyme arthritis, but that its deficiency resulted in earlier joint swelling and an inability to resolve arthritis as demonstrated by sustained arthritis pathology through day 60 postinfection. Although production of anti-Borrelia IgG was decreased in 5-LO-deficient mice, bacterial clearance from the joints was unaffected. Phagocytosis of B. burgdorferi and efferocytosis of apoptotic neutrophils was defective in macrophages from 5-LO-deficient mice, and uptake of opsonized spirochetes by neutrophils was reduced. These results demonstrate that products of the 5-LO metabolic pathway are not required for the development of disease in all models of arthritis and that caution should be used when targeting 5-LO as therapy for inflammatory diseases.

Novel functions of bovine milk-derived alpha-lactalbumin: anti-nociceptive and anti-inflammatory activity caused by inhibiting cyclooxygenase-2 and phospholipase A2.

Milk whey proteins contain major components of alpha-lactalbumin (alphaLA) and beta-lactoglobulin (betaLG), and a minor component of lactoferrin (LF). It has been reported that LF reduces nociception and inflammation in various animal models. However, the efficacy of alphaLA and betaLG has not been clarified. This study aimed to assess the efficacy of alphaLA and betaLG in various animal models such as acetic acid-induced writhing, carrageenan-induced paw inflammation, and adjuvant induced-arthritis. Orally administered alphaLA showed (i) inhibition of writhing induced by acetic acid in mice; (ii) suppression of nociception and inflammation in rat footpads caused by carrageenan in rat; and (iii) therapeutic effects on the development of adjuvant-induced pain and inflammation in rat. In contrast, betaLG had no effects in these animal models. To clarify the anti-nociceptive and anti-inflammatory mechanisms of alphaLA, we examined the levels of interleukin (IL)-6 and prostaglandin (PG)E(2) in carrageenan-injected paw exudates. The administration of alphaLA 1 h before carrageenan injection inhibited the increased formation of IL-6 and PGE(2) in paw exudates. Next, we demonstrated in vitro enzyme-inhibition assay; cyclooxygenase (COX), phospholipase A(2), and 5-lipoxygenase. alphaLA inhibited COX and phospholipase A(2) activities. alphaLA inhibited COX and phospholipase A(2) activities. Moreover, alphaLA showed selectivity on COX-2 as compared with COX-1. However, 5-lipoxygenase activity was not affected by alphaLA. These results suggest that alphaLA is a safe and useful natural drug for patients that require anti-inflammatory drugs, as alphaLA is contained in dairy food and is frequently ingested as daily food.

5-Lipoxygenase as a putative link between cardiovascular and psychiatric disorders.

There is evidence of an association between depression and anxiety and cardio- cerebro-vascular conditions, but the mechanisms of this association are unknown. Here we review a possible role for the 5-lipoxygenase (5-LOX) pathway. 5-LOX is an enzyme that, in association with 5-LOX-activating protein (FLAP), leads to the synthesis of leukotrienes from omega-6 arachidonic acid. Production of active leukotrienes can be reduced by dietary omega-3 fatty acids, which also are beneficial in cardiac and psychiatric (e.g., depression) pathologies. Human 5-LOX and FLAP gene polymorphisms are a risk factor in atherosclerosis and cardio-cerebro-vascular pathologies; an overactive 5-LOX pathway is found in these diseases. Studies with 5-LOX-deficient transgenic mice suggest that 5-LOX activity may contribute to anxiety- and depression-like behaviors. Future research should characterize the role of the 5-LOX pathway in comorbid cardio-cerebro-vascular and psychiatric disorders and in the therapeutic actions of dietary omega-3 fatty acids.

Adenosine up-regulates cyclooxygenase-2 in human granulocytes: impact on the balance of eicosanoid generation.

Polymorphonuclear neutrophils (granulocytes; PMNs) are often the first blood cells to migrate toward inflammatory lesions to perform host defense functions. PMNs respond to specific stimuli by releasing several factors and generate lipid mediators of inflammation from the 5-lipoxygenase and the inducible cyclooxygenase (COX)-2 pathways. In view of adenosine's anti-inflammatory properties and suppressive impact on the 5-lipoxygenase pathway, we addressed in this study the impact of this autacoid on the COX-2 pathway. We observed that adenosine up-regulates the expression of the COX-2 enzyme and mRNA. Production of PGE(2) in response to exogenous arachidonic acid was also increased by adenosine and correlated with COX-2 protein levels. The potentiating effect of adenosine on COX-2 could be mimicked by pharmacological increases of intracellular cAMP levels, involving the latter as a putative second messenger for the up-regulation of COX-2 by adenosine. Specific COX-2 inhibitors were used to confirm the predominant role of the COX-2 isoform in the formation of prostanoids by stimulated PMNs. Withdrawal of extracellular adenosine strikingly emphasized the inhibitory potential of PGE(2) on leukotriene B(4) formation and involved the EP(2) receptor subtype in this process. Thus, adenosine may promote a self-limiting regulatory process through the increase of PGE(2) generation, which may result in the inhibition of PMN functions. This study identifies a new aspect of the anti-inflammatory properties of adenosine in leukocytes, introducing the concept that this autacoid may exert its immunomodulatory activities in part by modifying the balance of lipid mediators generated by PMNs.

Inhibitors of the lipoxygenase pathway block development of Brugia malayi L3 in vitro.

Brugia malayi L3 molt to the L4 stage in serum-free cultures supplemented with arachidonic, linoleic, or linolenic acids and the basidiomycetous yeast Rhodotorula minuta. These fatty acids are capable of entering the eicosanoid pathway of arachidonate metabolism, the pathway responsible for generating a number of biologically active mediators, including prostaglandins, leukotrienes, and lipoxins. To determine whether this pathway was required for L3 development, we added dual inhibitors of cyclooxygenase and lipoxygenase to in vitro cultures containing B. malayi L3. These compounds significantly inhibited L3 molting. To evaluate whether 1 or both of these pathways of arachidonate metabolism were involved in molting, we tested drugs inhibiting either cyclooxygenase or lipoxygenase. Lipoxygenase inhibitors blocked L3 molting, whereas cyclooxygenase inhibitors did not. To assess whether enzymes operating downstream of lipoxygenase were also involved in L3 molting, we added inhibitors of enzymes involved in leukotriene synthesis and found they were also capable of preventing development. We tested the same inhibitor panel on Dirofilaria immitis L3. A single lipoxygenase inhibitor and inhibitors of 2 different enzymes operating downstream of lipoxygenase disrupted D. immitis development. These results demonstrate that a lipoxygenase pathway product is required for molting of the infective stage larvae of filarial parasites.

Regulation of leukotrienes in the management of asthma: biology and clinical therapy.

Leukotrienes (LTs) are the ultimate synthetic product resulting from the intracellular hydrolysis of membrane phospholipid at the nuclear envelope in inflammatory cells. Activated cytosolic phospholipase (cPLA2) catalyzes the production of arachidonic acid, which is converted by cyclooxygenases into leukotriene A4 (LTA4) and subsequently into the chemotaxin LTB4, which has no direct bronchoconstrictor activity. In certain inflammatory cells, LTA4 is converted into the cysteinyl leukotriene (cysLT) LTC4, which is converted into LTD4 and finally to LTE4 after extracellular transport. All cysLTs occupy the same receptors and are extremely potent bronchoconstricting agents that are pathogenetic in both asthma and allergy. With the identification of the structure of the cysLT receptor, antileukotriene therapies have been developed that either (a) inhibit synthesis of leukotriene (through 5-lipoxygenase inhibition) or (b) block the cysLT receptor. Preliminary investigations indicate that corticosteroids also may partially block the synthesis of cysLT and that cysLTs may be chemotactic for other inflammatory cells, e.g. eosinophils, by a mechanism that has not yet been defined. Currently, anti-LT therapies are approved by the US Food and Drug Administration (FDA) only for patients with asthma. These drugs generally are moderately efficacious agents, although they are highly efficacious in aspirin-induced asthma (AIA). In other forms of asthma, inhaled corticosteroid (ICS) therapy has been more effective than anti-LT therapy in improving air flow obstruction. However, anti-LT agents are additive to beta-adrenoceptor and ICS in their effects. Accordingly, anti-LT therapies are used frequently as supplemental treatments in asthmatic patients whose asthma is not optimally controlled by a combination of other drugs, including long-acting beta-adrenoceptor drugs and ICS agents. The growth of leukotriene receptor antagonists (LTRAs) has been extraordinary in the United States. The exceptional safety of these agents and their ease of administration as tablets taken once or twice daily has spurred this growth. In the past year, the high-affinity cysLT receptor has been cloned. This holds forth the promise of a second generation of LTRA agents of even greater efficacy and possibly greater duration of action.

[Ammonium bituminosulfonate (Ichthyol). Anti-inflammatory effect and inhibition of the 5-lipoxygenase enzyme]. / Ammoniumbituminosulfonat (Ichthyol). Antientzündliche Wirkung und Hemmung des Enzyms 5-Lipoxygenase.

Ammonium bituminosulphonate (Ichthyol) inhibits 5-lipoxygenase activity in human polymorphonuclear neutrophils. The inhibition is dose-dependent and occurs at non-cytotoxic concentrations of the drug. This results in a decreased release of Leukotriene B4 from polymorphonuclear neutrophils. Furthermore, when applied to the ear skin of AB/Bln mice pretreated with croton oil, Ichthyol reduces the inflammatory reaction.

Positional specificity of lipoxygenases and their suitability for testing potential drugs.

Comparative studies on isolated lipoxygenases revealed the following features: variability of their positional specificity, diversity of enzymatic properties including sensitivity to inhibitors, a common general mechanism of action. The molecular basis of the positional specificity of lipoxygenases is discussed. The lipoxygenase of reticulocytes proved to be an excellent model in the search for inhibitors of the arachidonate 5-lipoxygenase. Reticulocyte lipoxygenase may form a wide spectrum of products belonging to all important classes of primary lipoxygenase metabolites hitherto known (HPETE's, diHPETE's, lipoxins, epoxyleukotrienes and others). This enzyme was used as basal test in a screening hierarchy for lipoxygenase-inhibitory antiasthmatic drugs and led to the discovery of new orally acting potential antiasthmatics. There was a high correlation between inhibition of reticulocyte lipoxygenase and antibronchoconstrictory activity with airway preparations in vitro and in vivo.