Arachidonic acid, but not its metabolites, is essential for FcgammaR-stimulated intracellular killing of Staphylococcus aureus by human monocytes

Adipokines secretion in feline primary adipose tissue culture in response to dietary fatty acids

Background

Obesity in cats has been associated with alterations in adipokines including: adiponectin, interleukin-6 (IL6), and tumor necrosis factor-α (TNFα). Omega-3 polyunsaturated fatty acids have multiple beneficial effects on obesity-associated disorders, and therefore may alleviate these alterations. This study aimed to determine the effects of body condition, fat depot, troglitazone, and different fatty acids on secretion of adiponectin, IL6 and TNFα from adipose tissue of healthy cats. Subcutaneous and visceral adipose tissue samples were collected from 18 healthy intact female cats, and body condition score (Range 3–7/9) was determined. Concentrations of adiponectin were measured in mature adipocytes cultures and concentrations of IL6 and TNFα were measured in stromovascular cells cultures following treatment with control medium, troglitazone at 10 μM, eicosapentaenoic acid, arachidonic acid, or palmitic acid, at 25, 50, or 100 μM.

Results

Stromovascular cells of visceral origin secreted higher concentrations of IL6 than corresponding cells of subcutaneous origin (P = 0.003). Arachidonic acid treatment at 25, 50, and 100 μM increased IL6 secretion in subcutaneous (P = 0.045, P = 0.002, and P < 0.001, respectively) and visceral (P = 0.034, P = 0.001, and P < 0.001, respectively) stromovascular cells. Eicosapentaenoic acid treatment increased TNFα secretion in subcutaneous stromovascular cells at 25, 50, and 100 μM (P = 0.002, P = 0.001, and P = 0.015, respectively) and in visceral stromovascular cells at 50 μM (P < 0.001). No significant effect on medium adiponectin concentration was observed following troglitazone treatment (P = 0.4) or fatty acids treatments at 25 (P = 0.2), 50 (P = 0.8), or 100 (P = 0.7) μM. Body condition score did not have significant effects on medium concentrations of adiponectin (P = 0.4), IL6 (P = 0.1), or TNFα (P = 0.8).

Conclusions

This study demonstrated higher basal secretion of IL6 from visceral compared to subcutaneous adipose tissue, a stimulatory effect of arachidonic acid on secretion of IL6 and a stimulatory effect of eicosapentaenoic acid on TNFα from feline adipose tissue.

Omega-3 Fatty Acids in Modern Parenteral Nutrition: A Review of the Current Evidence

Intravenous lipid emulsions are an essential component of parenteral nutrition regimens. Originally employed as an efficient non-glucose energy source to reduce the adverse effects of high glucose intake and provide essential fatty acids, lipid emulsions have assumed a larger therapeutic role due to research demonstrating the effects of omega-3 and omega-6 polyunsaturated fatty acids (PUFA) on key metabolic functions, including inflammatory and immune response, coagulation, and cell signaling. Indeed, emerging evidence suggests that the effects of omega-3 PUFA on inflammation and immune response result in meaningful therapeutic benefits in surgical, cancer, and critically ill patients as well as patients requiring long-term parenteral nutrition. The present review provides an overview of the mechanisms of action through which omega-3 and omega-6 PUFA modulate the immune-inflammatory response and summarizes the current body of evidence regarding the clinical and pharmacoeconomic benefits of intravenous n-3 fatty acid-containing lipid emulsions in patients requiring parenteral nutrition.

It is all about fluidity: Fatty acids and macrophage phagocytosis

Phagocytosis is an early and fundamental step for the effective clearance of disease causing agents. The ability to engulf and kill pathogens is considered as a major effector function of macrophages. In their phagocytic role macrophages are part of the first line of innate immune defense. A number of studies investigating fatty acid effects on macrophage phagocytosis have been conducted over many years. In vitro-data consistently report that alterations in macrophage membrane fatty acid composition are linked to an altered phagocytic capacity, i.e. an increase in membrane unsaturated fatty acid content is associated with an increase in engulfment and killing rate. The mode of action of fatty acids seems to be the modulation of the physical nature of the macrophage plasma membrane. It appears that the saturated-to-unsaturated fatty acid ratio of macrophage membrane phospholipids is of importance in determining macrophage phagocytic capacity. Available in vivo-data are less clear. At present, there is a lack of systematic studies elucidating key factors such as fatty acid efficacy, effective dose or dosing intervals. Without this knowledge the targeted modulation of macrophage phagocytosis in vivo by fatty acids is still a distant possibility.

Dietary supplementation with omega-3 polyunsaturated fatty acids ameliorates acute pneumonia induced by Klebsiella pneumoniae in BALB/c mice

The immune benefits associated with the optimal intake of dietary fatty acids are widely known. The objective of the present investigation was to elucidate the role of omega-3 polyunsaturated fatty acids (n-3 PUFA) food source on acute pneumonia induced by Klebsiella pneumoniae. Three different n-3 PUFA preparations (cod liver oil, Maxigard, and flaxseed oil) were orally supplemented and infection was induced in different groups of experimental mice. Mice fed olive oil and normal saline served as oil and saline controls, respectively. After 2 weeks of fatty acid feeding, no effect on the establishment of infection was observed when acute pneumonia was induced in animals. On the other hand, 6 weeks of n-3 PUFA administration was found to improve resistance in mice, as reduced lung bacterial load coupled with significant improvement in pathology was seen in infected mice. Alveolar macrophages collected from all 3 groups of mice fed n-3 PUFA exhibited a significant decrease in the level of apoptosis following infection with K. pneumoniae and an enhanced in vitro phagocytic potential for the pathogen. Lower lung levels of nitric oxide, malondialdehyde, and lactate dehydrogenase were associated with a decrease in the severity of tissue damage. There was a significant increase in the lung levels of pro-inflammatory cytokines (tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β)). No significant change was observed in the levels of interleukin-10 (IL-10). This study highlights that dietary n-3 PUFA supplementation exerts an overall beneficial effect against acute experimental pneumonia. This mechanism is operative through upregulation of nonspecific and specific immune defenses of the host.

Control of cyclic AMP concentration in bovine endometrial stromal cells by arachidonic acid

Second messenger signalling through cyclic AMP (cAMP) plays an important role in the response of the endometrium to prostaglandin (PG) E(2) during early pregnancy. Arachidonic acid, which is a by-product of the luteolytic cascade in ruminants, is a potential paracrine signal from the epithelium to the stroma. We investigated the effects of arachidonic acid on the response of the stroma to PGE(2). cAMP was measured in bovine endometrial stromal cells treated with agents known to activate or inhibit adenylyl cyclase, protein kinase C (PKC) or phosphodiesterase (PDE). PGE(2) increased the intracellular cAMP concentration within 10 min, and this effect was attenuated by arachidonic acid and the PKC activator, 4beta-phorbol myristate acetate (PMA). The inhibitory effect of arachidonic acid on PGE(2)-induced cAMP accumulation was prevented by the PKC inhibitor, RO318425, and was absent in cells in which PKC had been downregulated by exposure to PMA for 24 h. The effect of arachidonic acid was also prevented by the PDE inhibitor, 3-isobutyl-1-methylxanthine. Arachidonic acid was shown by immunoblotting to prevent induction of cyclooxygenase-2 by PGE(2), forskolin or dibutyryl cAMP. The results indicate that arachidonic acid activates PDE through a mechanism involving PKC, counteracting a rise in intracellular cAMP in response to PGE(2). The data suggest that arachidonic acid antagonizes PGE(2) signalling through cAMP in the bovine endometrium, possibly acting to ensure a rapid return to oestrus in the case of failure of the maternal recognition of pregnancy.

Inhibition of platelet phospholipase A2 activity by catuaba extract suggests antiin?ammatory properties

In the inflammation process, phospholipase A2 (PLA2) catalyses the cleavage of the sn-2 ester-linked fatty acids from phospholipids, being the enzyme responsible for arachidonic acid (AA) release by cells for the biosynthesis of the prostaglandins and thromboxanes via the cyclooxygenase system, and the leukotrienes and eicosatetraenoids via the lipoxygenase pathway. AA mobilization by PLA2 and subsequent prostaglandins synthesis is considered to be a pivotal event in inflammation. Therefore, drugs that inhibit PLA2, thus blocking the COX and LOX pathways in the AA cascade, may be effective in the treatment of inflammatory processes. New strategies for the treatment of inflammatory processes could be detected by a search for active principles of vegetal origin that control the lipid mediator production by inhibition of PLA2. The present data are part of a wide explorative investigation on the effects of Trichilia catigua (catuaba), which found that PLA2 activity was totally inhibited by catuaba at a concentration of 120 microg/mL, suggesting that this natural substance may have antiinflammatory properties.

Mechanisms of humoral immunity during Ehrlichia chaffeensis infection

Our laboratory has been investigating the mechanisms of host defense during Ehrlichia chaffeensis infection in the mouse. Although major roles are clearly played by T cells, we found that antibodies could also control infection in both normal and immunocompromised SCID mice, and could protect the latter from lethal infection. Antibodies are not generally effective during such intracellular infections, so we would like to understand exactly how antibodies can mediate immunity in this model. We have found that much of the humoral immune response is directed at the bacterial outer membrane proteins (OMPs), and that highly effective OMP antibodies (mostly IgG2a) exhibited picomolar affinities and very long binding half-lives. These antibodies, which could mediate bacterial clearance from tissues as early as 24 hours after administration, require host Fc receptors for their function(s). In contrast, we have failed to find any role for complement or reactive nitrogen intermediates, or for neutrophils, or for NK cells. One possible mechanism is that antibodies or immune complexes trigger microbiocidal activities in infected macrophages that lead to the elimination of bacteria residing inside host macrophages. Alternatively, it is proposed that antibodies opsonize bacteria exposed during intercellular transfer. This notion is supported by studies that have demonstrated the presence of bacteria in the extracellular milieu during infection, and suggests that our understanding of the behavior of the bacterium in the host may be key to our understanding of its susceptibility to antibody-mediated host defenses.

Bothrops asper and Bothrops jararaca snake venoms trigger microbicidal functions of peritoneal leukocytes in vivo

Venoms from snakes of the genus Bothrops cause pronounced local effects in the victims. These alterations result not only from the direct toxic action of venom components, but also from the prominent inflammatory reaction associated with these envenomations. In this study we investigated the ability of Bothrops asper (BaV) and Bothrops jararaca (BjV) venoms to induce cellular influx and microbicidal functions in leukocytes. BaV and BjV (5 microg/animal) caused a long lasting infiltration of leukocytes (3-48 h) when injected into mouse peritoneal cavity. Both venoms increased phagocytosis and production of hydrogen peroxide (H2O2) by polymorphonuclear (PMN) and mononuclear (MN) peritoneal leukocytes. In addition, nitric oxide (NO) production by macrophages was also enhanced after the venom injections. This effect was inhibited by treating animals with L-NAME and aminoguanidine, thus suggesting the induction of iNOS synthesis by the venoms. Western blot analysis confirmed the expression of iNOS in macrophages. BaV and BjV injection led to increased levels of IFN-gamma at the site of inflammation. Since IFN-gamma is an effective inducer of iNOS expression, an indirect action of the venoms on iNOS expression can be proposed. A marked formation of nitrotyrosine-containing proteins was also observed in macrophage homogenates. Based on these results, we suggest that reactive oxygen and nitrogen-derived species are involved in the pathogenesis of the local tissue damage characteristic of Bothrops sp envenomations.

An 18.5 kDa protein from the amebocyte of Limulus polyphemus, homologous to the previously described amebocyte aggregation factor, expresses alternative phospholipase A2 activity

A protein expressing phospholipase A2 activity was purified from the granular amebocyte of the horseshoe crab, Limulus polyphemus by cation-exchange, size-exclusion chromatography and semi-preparative reverse-phase-high pressure liquid chromatography (RP-HPLC). The protein had an apparent mass of 17.7 kDa by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), but a more accurate estimate of 18.5 kDa was assigned by electrospray ionization-mass spectrometry (ESI-MS). A partial sequence of this protein demonstrated total sequence homology with an 18.5 kDa protein with cell aggregating properties from Limulus reported by Fujii et al. [J. Biol. Chem. 267:22452.]. In these studies, the Limulus protein demonstrated a positive cross-reaction to polyclonal anti-human recombinant phospholipase A2 (group II, 14 kDa). The protein did not display a significant loss of biological activity after boiling, but all enzymatic activity was lost after boiling in the presence of the reducing agent betamercaptoethanol (beta-mercaptoethanol). The Limulus protein was inhibited by manoalide, a covalent irreversible phospholipase A2 inhibitor, in a dose-dependent fashion with 50% inhibition occurring at a concentration of 0.48 microM. The Limulus protein displayed no activity in a triglyceride lipase assay. These studies characterize an alternative phospholipase A2 activity for the previously described 18.5 kDa protein from the L. polyphemus amebocyte.