Modulation of Kupffer cell membrane phospholipid function by n-3 polyunsaturated fatty acids

Fish oil modulates macrophage P44/P42 mitogen-activated protein kinase activity induced by lipopolysaccharide

BACKGROUND

Mitogen-activated protein kinase (MAPK) cascades represent a major signal system to transduce extracellular signals into cellular responses. Overactivity of MAPK has been implicated in the development of many diseases, including cancer and sepsis. This study investigated the hypothesis that fish oil altered the membrane phospholipid composition and modulated MAPK activity.

METHODS

RAW 264.7 cells, a mouse macrophage (Mphi) cell line, were grown in eicosapentaenoic acid (EPA)-rich media (114 micromol/L) for 48 hours. Mphi were washed and exposed to Escherichia coli lipopolysaccharide (LPS; 1 microg/mL) for 10 minutes. Both total and activated (phosphorylated) portions of MAPK (P44 and P42) were determined by Western blot assays. AP-1 transcription factor activity was determined by electrophoretic mobility gel shift assays (EMSA). Mphi tumor necrosis factor (TNF) mRNA expression was measured by Northern blot assays.

RESULTS

LPS stimulation induced RAW cell phosphorylation of P44/P42. In contrast, RAW cells grown in EPA-rich media had less P44/P42 activation in the presence of LPS. Total P44/P42 were not affected by EPA or LPS. Similarly, EPA also inhibited AP-1 activity. Inhibition of P44/P42 activity with PD98059 reduced both AP-1 activity and TNF mRNA expression of LPS-stimulated Mphi.

CONCLUSIONS

Our data suggest that fish oil regulates macrophage proinflammatory gene activation, at least in part, by modulating the MAPK activity.

Fish oil decreases macrophage tumor necrosis factor gene transcription by altering the NF kappa B activity

BACKGROUND

Fish oil-supplemented diets have anti-inflammatory and immunomodulating effects, though the exact mechanism(s) are unknown. This study investigated the effects of eicosapentanenoic acid (EPA), a major component of fish oil, on transcriptional regulation of tumor necrosis factor (TNF) gene in lipopolysaccharide (LPS)-stimulated macrophages (MO).

METHODS

RAW 264.7 cells, a mouse MO cell line, were grown in EPA-rich media for 24-48 h. MO were washed and exposed to Escherichia coli LPS (1 microg/ml) for 2 h. TNF mRNA expression was measured by Northern blot assays. Total nuclear extracts were harvested for the measurement of NF kappa B with electrophoretic mobility shift assays. Supershift assays were performed with anti-P50 or anti-P65 antibodies to show components of NF kappa B dimers. TNF production was determined by L929 bioassays.

RESULTS

LPS stimulated RAW cell TNF mRNA expression and NF kappa B activity. In contrast, RAW cells grown in EPA-rich media had less TNF mRNA expression and an altered composition of the NF kappa B subunits (P65/P50 dimers) in the presence of LPS. TNF production by LPS-stimulated MO was reduced by EPA.

CONCLUSIONS

The inhibitory effect of EPA on LPS-stimulated MO TNF gene transcription and protein elaboration is, in part, mediated through altering NF kappa B activation by reducing the P65/P50 dimers.

Fish oil-supplemented feeding does not attenuate warm liver ischemia and reperfusion injury in the rat

Liver ischemia and reperfusion injury is mediated by oxygen free radicals, cytokines, and prostanoids produced by Kupffer cells and infiltrating neutrophils. Fish oil-supplemented diets alter membrane phospholipid composition and modify prostanoids and cytokine production in response to ischemia and reperfusion. This study tested the hypothesis that a fish oil-supplemented diet would attenuate warm liver ischemia and reperfusion injury in the rat. Male Sprague-Dawley rats were fed Vital HN supplemented with either fish oil (FO) or corn oil (CO) by the continuous duodenal infusion for 5 days. Total dietary fat (26% of total calories), caloric intake (70 cal/day), and volume (60 ml/day) were identical between two groups. Plasma eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels increased significantly in rats fed fish oil (0 to 16.3% for EPA and 2 to 12% for DHA). Liver histology was similar in both groups before ischemia. On Day 6, rats were subjected to 60 min of reversible hepatic ischemia. Plasma TNF levels, 1 and 24 hr after reperfusion, were not different between FO and CO rats. Liver injury assessed by bile flow, histology, plasma ALT, and bile glutathione efflux did not differ between groups. We conclude that our fish oil-supplemented enteral diet does not attenuate warm liver ischemia and reperfusion injury in rats.

Early enteral administration of a formula (Impact) supplemented with arginine, nucleotides, and fish oil in intensive care unit patients: results of a multicenter, prospective, randomized, clinical trial

OBJECTIVE

To determine if early enteral feeding, in an intensive care unit (ICU) patient population, using a formula supplemented with arginine, dietary nucleotides, and fish oil (Impact), results in a shorter hospital stay and a reduced frequency of infectious complications, when compared with feeding a common use enteral formula (Osmolite.HN).

DESIGN

A prospective, randomized, double-blind, multicenter trial.

SETTING

ICUs in eight different hospitals.

PATIENTS

Of 326 patients enrolled in the study, 296 patients were eligible for analysis. They were admitted to the ICU after an event such as trauma, surgery, or sepsis, and met a risk assessment screen (Acute Physiology and Chronic Health Evaluation II [APACHE II] score of > or = 10, or a Therapeutic Intervention Scoring System score of > or = 20) and study eligibility requirements. Patients were stratified by age (< 60 or > or = 60 yrs of age) and disease (septic or systemic inflammatory response syndrome).

INTERVENTIONS

Patients were enrolled and full-strength tube feedings were initiated within 48 hrs of the study entry event. Enteral feedings were advanced to a target volume of 60 mL/hr by 96 hrs of the event. One hundred sixty-eight patients were randomized to receive the experimental formula, and 158 patients were randomized to receive the common use control formula.

MEASUREMENTS AND MAIN RESULTS

Both groups tolerated early enteral feeding well, and the frequency of tube feeding-related complications was low. There were no significant differences in nitrogen balance between groups on study days 4 and 7. Patients receiving the experimental formula had a significant (p = .0001) increase in plasma arginine and ornithine concentrations by study day 7. Plasma fatty acid profiles demonstrated higher concentrations of linoleic acid (p < .01) in the patients receiving the common use formula and higher concentrations of eicosapentaenoic and docosahexaenoic acid (p < .01) in the patients receiving the experimental formula. The mortality rate was not different between the groups and was significantly (p < .001) lower than predicted by the admission severity scores in both feeding groups. In patients who received at least 821 mL/day of the experimental formula, the hospital median length of stay was reduced by 8 days (p < .05). In patients stratified as septic, the median length of hospital stay was reduced by 10 days (p < .05), along with a major reduction in the frequency of acquired infections (p < .01) in the patients who received the experimental formula. In the septic subgroup fed at least 821 mL/day, the median length of stay was reduced by 11.5 days, along with a major reduction in acquired infections (both p < .05) in the patients who received the experimental formula.

CONCLUSIONS

Early enteral feeding of the experimental formula was safe and well tolerated in ICU patients. In patients who received the experimental formula, particularly if they were septic on admission to the study, a substantial reduction in hospital length of stay was observed, along with a significant reduction in the frequency of acquired infections.

Characterization of platelet-activating factor binding to human airway epithelial cells: modulation by fatty acids and ion-channel blockers

Radioligand-binding studies were performed in primary cultured human airway epithelial cells with [3H]PAF to determine whether these cells express platelet-activating factor (PAF) receptors. Scatchard analysis of PAF binding data revealed a single class of PAF binding sites with Kd 1.8 +/- 0.2 nM and Bmax. 21.0 +/- 2.1 fmol/10(6) cells (13,000 receptors/cell). PAF binding increased the intracellular free Ca2+ concentration ([Ca2+]i), indicating functional PAF receptors. Palmitate (C16:0), linoleic acid (C18:2 omega 6) or eicosapentaenoic acid (C20:5 omega 3) was incubated with the cells to test the effect on PAF binding. Incorporation of each fatty acid into cellular phospholipid occurred. [3H]PAF (1 nM) binding decreased in cells supplemented with C20:5 omega 3, but increased in the cells supplemented with C16:0. Scatchard analysis revealed that the inhibition of PAF binding by supplementation with C20:5 omega 3 was due to a decrease in both affinity and number of PAF receptors. PAF-stimulated increase in [Ca2+]i was also decreased by 60% in cells supplemented with C20:5 omega 3. Verapamil, a Ca(2+)-channel blocker, and amiloride, a Na(+)-channel blocker, inhibited specific binding of [3H]PAF to the cells, with IC50 4-5 microM and 0.2 mM respectively. Diphenylamine-2-carboxylate (DPC), a Cl(-)-channel blocker, dramatically increased PAF binding to the cell in a dose-dependent manner. Scatchard analysis revealed that verapamil and amiloride decreased both binding affinity and number of PAF receptors, whereas DPC increased PAF binding sites without affecting binding affinity. These results demonstrate that human airway epithelial cells have a functional receptor for PAF and that PAF receptor binding can be modulated by exogenous fatty acids and by ion-channel blockers.

Purified dietary n-3 polyunsaturated fatty acids alter diacylglycerol mass and molecular species composition in concanavalin A-stimulated murine splenocytes

A low-dose, short-term dietary supplementation with highly purified (n-3) fatty acid ethyl esters was studied in mice to determine the effect on splenic cell membrane diacylglycerol mass and composition. Mice were fed diets containing either 3% safflower oil (SAF) ethyl esters, 2% SAF plus 1% eicosapentaenoic acid ethyl ester (EPA), or 2% SAF plus 1% docosahexaenoic acid ethyl ester (DHA). Following a 10-day feeding period, pathogen-free mice were sacrificed and splenic cells isolated and stimulated with concanavalin A (Con A) at 10 micrograms/ml. After 0 min (basal), 5 min, and 180 min, 1,2-diacyl, 1-O-alkyl-2-acyl, and 1-O-alkenyl-2-acyl-sn-glycerol subclasses were isolated and quantitated by HPLC. Diacylglycerol (DAG) was found to be the major diradylglycerol (DG) component in murine splenocytes. DHA-fed mice had significantly (P < 0.05) higher levels of DAG at all stimulation time points relative to EPA and SAF animals. Significant effects (P < 0.05) of diet, time, and a diet x time interaction (P < 0.05) were noted for various DAG molecular species. In general, a significantly higher (n-3) polyunsaturated fatty acid (PUFA) content in the EPA and DHA groups, and a significantly higher (n-6) PUFA content in the SAF group was noted. 18:0-22:5(n-3), 18:1-22:5(n-3) and 16:1-20:5(n-3) species were present only in EPA and DHA-DAG, confirming the incorporation of (n-3) fatty acids into splenocyte DAG. The data indicate that the molecular species composition of murine splenocyte DAG is significantly modulated by low-dose, short-term EPA and DHA feeding. In addition, substitution of SAF with DHA results in an increase in DAG mass. These alterations could potentially influence signal transduction pathways regulating lymphocyte function.

Docosahexaenoic acid inhibits PAF and LTD4 stimulated [Ca2+]i-increase in differentiated monocytic U937 cells

We investigated the effects of different polyunsaturated fatty acids (PUFAs) of the n-6 and n-3 family on the PAF and LTD4 stimulated increase in cytosolic free Ca(2+)-concentration [Ca2+]i in retinoic acid (RA) differentiated, human monocytic U937 cells. Docosahexaenoic acid (10 microM DHA) reduced the PAF induced increase in [Ca2+]i from 455 +/- 25 nM to 319 +/- 24 nM (P less than 0.01). DHA also significantly attenuated the LTD4 induced increase in [Ca2+]. However [Ca2+]i-increase stimulated by f-MLP, ATP, or ionophore A 23187 was not affected by DHA. Other PUFAs like eicosapentaenoic acid (EPA), alpha-linolenic acid (LnA), arachidonic acid (AA) or gamma-linoleic acid (LA) were ineffective. Cellular differentiation as assessed by nitrobluetetrazolium reduction and enhanced expression of specific PAF binding sites in RA treated cells were not altered by DHA. Fatty acid composition in cellular phospholipids revealed effective incorporation of each PUFA. The DHA-effect on [Ca2+]i was time dependent and occurred at 48 h, whereas the DHA-content in phospholipids reached a plateau already at 24 h. The antioxidant vitamin E, the lipoxygenase inhibitor NDGA and the cytochrome P-450 inhibitor SKF 525A completely prevented the DHA induced reduction of PAF stimulated [Ca2+]i-increase. In contrast, the cyclooxygenase inhibitor indomethacin had no effect. Our results indicate that DHA selectively reduces intracellular [Ca2+]i-increases induced by PAF and LTD4 in RA-treated U937 cells, presumably involving an oxidative modification of DHA.