Albumin redirects platelet eicosanoid metabolism toward 12(S)-hydroxyeicosatetraenoic acid

Albumin Lipidomics Reveals Meaningful Compositional Changes in Advanced Cirrhosis and Its Potential to Promote Inflammation Resolution

Albumin infusions are therapeutically used to revert hypoalbuminemia and to replace the extensively oxidized albumin molecule circulating in patients with acutely decompensated (AD) cirrhosis. Because albumin has high affinity for lipids, here we characterized the albumin lipidome in patients with AD and explored the albumin effects on the release of fatty acid (FA)-derived lipid mediators by peripheral leukocytes. Lipids and lipid mediators were measured by liquid chromatography-tandem mass spectrometry in albumin-enriched and albumin-depleted plasma fractions separated by affinity chromatography and in leukocyte incubations from 18 patients with AD and 10 healthy subjects (HS). Lipid mediators were also measured in 41 patients with AD included in an albumin therapy trial. The plasma lipidome associated with AD cirrhosis was characterized by generalized suppression of all lipid classes except FAs. In contrast to HS, albumin from patients with AD had lower content of polyunsaturated FAs (PUFAs), especially of the omega-3-PUFA docosahexaenoic acid. Consistent with this, the PUFA-derived lipid mediator landscape of albumin from patients with AD was dominated by lower content of monohydroxy FA precursors of anti-inflammatory/pro-resolving lipid mediators (i.e., 15-hydroxyeicosatetraenoic acid [15-HETE]). In addition, albumin from patients with AD was depleted in prostaglandin (PG) E₂ , suggesting that this proinflammatory PG primarily travels disassociated to albumin in these patients. Incubation of leukocytes with exogenous albumin reduced PG production while inducing 15-lipoxygenase expression and 15-HETE release. Similar effects were seen under lipopolysaccharide plus N-formylmethionyl-leucyl-phenylalanine-stimulated conditions. Finally, PG levels were lower in patients with AD receiving albumin therapy, whereas 15-HETE was increased after albumin treatment compared with baseline. Conclusion: Our findings indicate that the albumin lipid composition is severely disorganized in AD cirrhosis and that administration of exogenous albumin has the potential to redirect leukocyte biosynthesis from pro-inflammatory to pro-resolving lipid mediators.

Curcumin, hemostasis, thrombosis, and coagulation

Atherothrombotic cardiovascular disease is a major cause of mortality throughout the world. Platelet activation and aggregation play a central role in hemostasis and thrombosis. Herbal medicines have been traditionally used in the management of cardiovascular disease and can help in modifying its progression, particularly in hemostasis and the coagulation process, as well as altering platelet function tests and some coagulation parameters. Curcumin is a polyphenol derived from the Curcuma longa plant and has been used extensively in complementary and alternative medicine, as it is nontoxic and safe with various therapeutic properties. Modern scientific research has demonstrated its anti-inflammatory, antioxidant, anti-carcinogenic, antithrombotic, and cardiovascular protective effects. The present study reviewed previous studies in the literature, which support the positive activity of curcumin in hemostasis, anticoagulation, and fibrinolysis. We also presented molecular mechanisms associated with the antiplatelet and anticoagulant activities of curcumin and potential implications for the treatment of cardiovascular disease.

The selective cyclooxygenase-2 inhibitor celecoxib modulates the formation of vasoconstrictor eicosanoids and activates PPARgamma. Influence of albumin

BACKGROUND/AIMS

Selective cyclooxygenase (COX)-2 inhibitors do not adversely affect renal function in experimental cirrhosis. In the current study, we investigated the molecular mechanisms underlying the effects of the selective COX-2 inhibitor, celecoxib, and assessed the influence of albumin on its actions.

METHODS

Rat mesangial cells (RMC) were incubated with celecoxib in the absence or presence of albumin, and levels of selected vasoconstrictor eicosanoids, renin release and alpha-smooth muscle actin (alpha-SMA) expression were determined. The effects of celecoxib on PPARgamma were assessed in RMC co-transfected with PPARgamma and luciferase reporter constructs.

RESULTS

Under resting conditions, RMC expressed COX-1, COX-2 and 12/15-lipoxygenase and mainly generated prostaglandin (PG)E2, thromboxane (TX)B2, 12-hydroxyeicosatetraenoic acid (12-HETE) and 8-epi-PGF2alpha. Celecoxib, in addition to reducing PGE2, significantly decreased 8-epi-PGF2alpha formation. In the presence of albumin, celecoxib also reduced TXB2 and 12-HETE. Albumin per se inhibited PGE2 as well as renin release. In trans-activation assays, celecoxib acted as a PPARgamma agonist whereas albumin inhibited PPARgamma as well as 15d-PGJ2-induced PPARgamma activation. Finally, celecoxib and albumin potentiated the inhibitory effect of 15d-PGJ2 on alpha-SMA expression.

CONCLUSIONS

These data provide novel molecular mechanisms of celecoxib and their modulation by albumin, that may be relevant to prevent renal dysfunction in conditions of unbalanced effective blood volume.

Albumin prevents metabolism of 12-hydroxyeicosatetraenoic acid by leukocytes in vitro

In the present paper we studied the influence of albumin on the in vitro metabolism of 12-hydroxyeicosatetraenoic acid (12-HETE) and arachidonic acid in leukocytes and aspirin-treated platelets. In the presence of physiological concentrations of albumin, the metabolism of both 12-HETE and arachidonic acid was substantially altered, implicating the importance fatty acid binding proteins might have on the profile of products formed both in vitro and in vivo. The results clearly showed that albumin effectively withdraws arachidonic acid and 12-HETE from further metabolism by the leukocytes but does not influence the conversion of arachidonic acid to 12-HETE by the platelets. Thus, some of the hypotheses concerning transcellular metabolism raised from in vitro data within the eicosanoid field might have little relevance for the in vivo situation.

Curcumin, a major component of food spice turmeric (Curcuma longa) inhibits aggregation and alters eicosanoid metabolism in human blood platelets

In traditional medicine, Ayurveda, several spices and herbs are held to possess medicinal properties. Earlier we have reported that extracts from several spices, including turmeric, inhibit platelet aggregation and modulate eicosanoid biosynthesis. Due to their eicosanoid-modulating property, it was suggested that the spices may serve to provide clues to drugs directed to arachidonic acid (AA) pathway enzymes as pharmacological targets. Curcumin, a major component of turmeric, inhibited platelet aggregation induced by arachidonate, adrenaline and collagen. This compound inhibited thromboxane B2 (TXB2) production from exogenous [14C] arachidonate in washed platelets with a concomitant increase in the formation of 12-lipoxygenase products. Moreover, curcumin inhibited the incorporation of [14C]AA into platelet phospholipids and inhibited the deacylation of AA-labelled phospholipids (liberation of free AA) on stimulation with calcium ionophore A23187. Curcumin's anti-inflammatory property may, in part, be explained by its effects on eicosanoid biosynthesis.

The effect of glycosylated albumin on platelet aggregation

BACKGROUND

Albumin has a role in the complicated process of platelet aggregation. Although it is known that quantitative changes in plasma albumin alter platelet aggregation, less is known about the interaction between qualitative changes in plasma albumin and platelets. One common qualitative change in plasma albumin is nonenzymatic glycosylation, which occurs during states of prolonged hyperglycemia.

METHODS

Albumin was selectively removed from normal plasma by means of an affinity column. Glycosylated albumin was added to this albumin-poor plasma, and it was used to study platelet aggregation induced by low concentrations of arachidonic acid. Platelet aggregation was determined by light transmittance.

RESULTS

As the concentration of glucose in which albumin was incubated was increased, there was progressive augmentation of platelet aggregation. At a plasma glucose of 150 mg/dL, average light transmittance was 9.4%, and at 200 mg/dL, it was 24.6%. These values were significantly different at a p value < .01. At glucose levels of 300 mg/dL and 400 mg/dL, mean light transmittance was 40.6% and 74.4%, respectively, and these values were significantly different with p values of < .01.

CONCLUSIONS

Platelet aggregation in response to a relatively low concentration of arachidonic acid is enhanced in the presence of albumin that has been incubated in a medium containing levels of glucose that are higher than would be seen in normal patients but are consistent with those seen in diabetics with less than optimal control. This augmentation of platelet aggregation is statistically significant.

Antiplatelet principles from a food spice clove (Syzygium aromaticum L) [corrected]

In continuation of our studies on the oil of cloves--a common kitchen spice and a drug for home medicine--we have isolated and identified two antiplatelet components, eugenol and acetyl eugenol. They inhibited arachidonate-, adrenaline- and collagen-induced platelet aggregation; they were more potent in inhibiting aggregation by the first two agonists. Their inhibitory effect was reversible. These components were antiaggregatory by a combination of at least two effects: (i) inhibition of platelet thromboxane formation, and (ii) increased formation of 12-lipoxygenase products (12-HPETE). Though the presence of plasma proteins would reduce the effective concentration of these substances due to binding, the relatively lower amounts of these components which inhibited arachidonate-induced aggregation when compared to their effects on thromboxane production was intriguing. The answer might partly lie in an increased formation of 12-HPETE facilitated by albumin which acts as a 'conduit' to divert free arachadonic acid (AA) from the platelet cyclooxygenase (CO) to the lipoxygenase pathway (22). Based on their IC50 values, it was found that both eugenol and acetyl eugenol were more potent than aspirin in inhibiting platelet aggregation induced by arachidonate, adrenaline and collagen. In arachidonate-induced aggregation eugenol was on a par with indomethacin. It was found that eugenol and acetyl eugenol when used in combination potentiated inhibition of platelet aggregation induced by arachidonate, adrenaline and collagen. This effect was, however, not evident from the metabolism of AA in platelets; when used in combination the two compounds produced an additive effect.

Albumin and fatty acid effects on the stimulated production of 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine (PAF) by human polymorphonuclear leukocytes

Production of platelet-activating factor (PAF) during opsonized zymosan stimulation of human polymorphonuclear leukocytes is dependent on the concentration of extracellular albumin and on the presence of exogenous fatty acids. Fatty acid-free albumin caused a concentration-dependent increase in PAF synthesis up to 5% albumin concentrations (w/v) where the amount of PAF produced was three- to four-fold higher than in controls containing no albumin. The addition of free fatty acids, particularly arachidonic acid and palmitic acid, to 5% fatty acid-free albumin media caused a concentration-dependent decrease in PAF synthesis. A 50% inhibition of PAF synthesis was observed at an arachidonic acid concentration of 120 microM and at a palmitic acid concentration of 100 microM. The inhibition of PAF production by palmitic acid was also dependent on the concentration of extracellular albumin. In 0.5% fatty acid-free albumin media, a palmitic acid concentration of 40 microM produced a 50% inhibition in PAF synthesis. The addition of palmitic acid did not affect the release of endogenous arachidonic acid during stimulation. In contrast, the addition of stearic acid up to 120 microM in 5% fatty acid-free albumin media had no effect on PAF production. The different inhibitory effects of palmitic acid and stearic acid on PAF production may be related to differences in intracellular utilization of these two fatty acids during cell stimulation.

Eicosanoids, other fatty acid metabolites and the cardiovascular system: are the present antithrombotic approaches rational?

Antiplatelet +/- anticoagulant drugs are currently used as the standard treatment to prevent and treat thrombosis. While this approach is beneficial, it is not optimal. Recent evidence suggests that constituents of the vascular endothelium play an important role in regulating vessel wall thrombogenecity, thereby inhibiting thrombogenesis. These include constituents such as PGI2, tissue plasminogen activator, thrombomodulin and the lipoxygenase fatty acid metabolite derived from linoleic acid, 13-hydroxyoctadecadienoic acid (13-HODE). Consequently, new strategies have been developed to maximize the use of these agents for antithrombotic therapy. We will review these different approaches, discuss their rationale, and based upon recent experimental data, introduce an alternative approach for antithrombotic therapy which may circumvent a number of limitations and side-effect of the currently used drugs.

Thrombin-activated platelets promote leukotriene B4 synthesis in polymorphonuclear leucocytes stimulated by physiological agonists

1. The addition of 2 x 10(8) human platelets to 8 x 10(6) polymorphonuclear leucocytes (PMNL) incubated in presence of 2.5 u ml-1 thrombin and 0.1 microM N-formyl-Met-Leu-Phe (FMLP) (or C5a or PAF) led to enhancement of leukotriene B4 (LTB4) synthesis by the PMNL (measured by h.p.l.c. as 20-hydroxy- and 20-carboxy-LTB4) from 4 +/- 1 pmol (in absence of platelets) to 26 +/- 4 pmol (mean +/- s.e.mean, n = 9). Platelets and thrombin were both essential for the enhancement of LTB4 synthesis. 2. Platelets also caused enhancement of LTB4 synthesis from (30 +/- 12 to 134 +/- 25 pmol, n = 6) when PMNL pretreated with granulocyte-macrophage colony-stimulating factor were used in similar experiments. 3. Enhancement of LTB4 synthesis was also observed (from 5 +/- 1.5 to 26.5 +/- 5 pmol, n = 9) when the supernatants of thrombin-activated platelet suspensions were added to FMLP-stimulated PMNL. 4. Supernatants of platelet suspensions activated by thrombin in presence of cyclo-oxygenase and 12-lipoxygenase inhibitors led to greater enhancement (from 5 +/- 3 to 153.5 +/- 27.5 pmol, n = 3) of LTB4 synthesis by FMLP-stimulated PMNL, suggesting that arachidonic acid itself, rather than its metabolites was responsible for the effects of platelets. 5. Addition of arachidonic acid to FMLP-stimulated PMNL at a concentration comparable to that measured in thrombin-activated platelet supernatants (0.2 +/- 0.025 microM, n = 6) mimicked the effect of platelets or platelet supernatants on LTB4 synthesis in FMLP-activated PMNL. 6. The present data indicate that under conditions of cell activation by physiological agonists, platelets can significantly increase the formation of the proinflammatory compound LTB4 in PMNL by providing arachidonic acid. These data lend support to the concept that platelet-PMNL interactions could modulate the inflammatory process.

Thromboxane and cysteinyl-leukotriene formation are differentially activated in spontaneously clotting whole human blood in vitro

We have previously demonstrated that clotting of whole human blood in vitro not only triggers the production of thromboxane (TX) B2 but is also accompanied by formation of 5-lipoxygenase-derived cysteinyl-leukotrienes (LT). In order to further characterize the mechanisms leading to activation of the cysteinyl-LT production, we have now investigated the effects of thrombin on cysteinyl-LT as well as TXB2 formation in whole human blood. Addition of exogenous human alpha-thrombin (0.1 - 3.0 U/ml) to whole human blood incubated in vitro led to a concentration- and time-dependently increased release of TXB2 into the serum samples. The serum contents of cysteinyl-LT were, however, not significantly affected. Inactivation of endogenously generated thrombin by inhibitors such as recombinant hirudin (HBW 023, 0.43 - 1.43 microM) or the peptidyl chloromethyl ketone, D-Phe-Pro-Arg-CH2Cl (1.0 - 100 microM) concentration- and time-dependently inhibited the release of TXB2 into the serum or plasma samples. In contrast, however, serum contents of cysteinyl-LT remained unchanged. The identity of immunoreactive material was confirmed by thin-layer chromatography of immunoreactive TXB2 and by reversed phase HPLC of immunoreactive cysteinyl-LT. As expected, washed human platelets stimulated with alpha-thrombin were identified as the major source of TXB2 generation but purified monocytes were also found to release some TXB2 upon alpha-thrombin stimulation. Release of TXB2 by isolated human polymorphonuclear leukocytes (PMN) was negligible in the presence of this stimulus. None of the cells which are known to possess 5-lipoxygenase activity such as PMN or monocytes did release neither cysteinyl-LT nor LTB4 upon stimulation with human alpha-thrombin up to 10 U/ml. These data demonstrate that TXB2 production and cysteinyl-LT formation are differentially activated in spontaneously clotting whole human blood in vitro, the former being dependent on endogenously generated thrombin the latter being dependent on a stimulus yet to be identified.

Acetyl eugenol, a component of oil of cloves (Syzygium aromaticum L.) inhibits aggregation and alters arachidonic acid metabolism in human blood platelets

In continuation of our studies with the oil of cloves--a common kitchen spice and a crude drug for home medicine--we have isolated yet another active component identified as acetyl eugenol (AE); the earlier reported active component being eugenol. The isolated material (IM) was found to be a potent platelet inhibitor; IM abolished arachidonate (AA)-induced aggregation at ca. 12 microM, a concentration needed to abolish the second phase of adrenaline-induced aggregation. Chemically synthesized acetyl eugenol showed similar effects on AA- and adrenaline-induced aggregation. A dose-dependent inhibition of collagen-induced aggregation was also observed. AE did not inhibit either calcium ionophore A23187- or thrombin-induced aggregation. Studies on aggregation and ATP release were done using whole blood (WB). AA-induced aggregation in WB was abolished at 3 micrograms/ml (14.6 microM) which persisted even after doubling the concentration of AA. ATP release was inhibited. Inhibition of aggregation appeared to be mediated by a combination of two effects: reduced formation of thromboxane and increased generation of 12-lipoxygenase product (12-HPETE). These effects were observed by exposing washed platelets to (14C)AA or by stimulating AA-labelled platelets with ionophore A23187. Acetyl eugenol inhibited (14C)TxB2 formation in AA-labelled platelets on stimulation with thrombin. AE showed no effect on the incorporation of AA into platelet phospholipids.

ATP-evoked arachidonic acid mobilization in astrocytes is via a P2Y-purinergic receptor

To reveal more of the mechanism whereby ATP induces arachidonic acid (AA) mobilization in astrocytes, primary cell cultures prelabeled with [3H]AA were exposed to ATP and various analogs. Release of 3H was dose and time dependent and was inhibited by blocking ATP binding. The potencies of a range of ATP analogs in mobilizing AA were consistent with that predicted for the involvement of a P2Y-purinergic receptor. Mobilization of AA was not due to non-specific cell permeabilization, as assessed by leakage of cytoplasmic lactate dehydrogenase. AA mobilization by ATP was reduced when mobilization of intracellular calcium was inhibited and in the absence of extracellular calcium. Thapsigargin, which induces release of intracellular calcium, evoked mobilization of AA and thromboxane formation, findings similar to the effects of ATP. These results suggest that ATP stimulates AA mobilization via a P2Y-purinergic receptor and that, although extracellular calcium is involved, mobilization of intracellular calcium activates phospholipase A2.