Albumin modifies the metabolism of hydroxyeicosatetraenoic acids via 12-lipoxygenase in human platelets.

12-Lipoxygenase and cyclooxygenase 1 are the dominating enzymes that metabolize arachidonic acid in human platelets. In addition to the conversion of arachidonic acid to 12(S)-hydroxyeicosatetraenoic acid, 12-lipoxygenase can also utilize 5(S)-hydroxyeicosatetraenoic acid and 15(S)-hydroxyeicosatetraenoic acid to form 5(S), 12(S)-dihydroxyeicosatetraenoic acid and 14(R), 15(S)-dihydroxyeicosatetraenoic acid, respectively. Furthermore, 15(S)-hydroxyeicosatetraenoic acid works as an inhibitor for 12-lipoxygenase. In the present paper we have studied the influence of albumin on the in vitro metabolism of 5 - and 15 -hydroxyeicosatetraenoic acids, and 5,15 -dihydroxyeicosatetraenoic acid by the platelet 12-lipoxygenase. The presence of albumin reduced the formation of 5(S),12(S)- dihydroxyeicosatetraenoic acid from 5(S)-hydroxyeicosatetraenoic acid, however, it had no effect on the 12(S)-hydroxyeicosatetraenoic acid production from endogenous arachidonic acid. In contrast, when 15(S)-hydroxyeicosatetraenoic acid was incubated with activated platelets, the formation of 14(R), 15(S)- dihydroxyeicosatetraenoic acid was stimulated by the presence of albumin. Furthermore, albumin reduced the inhibitory action 15(S)-hydroxyeicosatetraenoic acid had on 12(S)-hydroxyeicosatetraenoic acid formation from endogenous arachidonic acid. However, addition of exogenous arachidonic acid (20 microm) to the incubations inverted the effects of albumin on the conversion of 15(S)-hydroxyeicosatetraenoic acid to 14(R),15(S)- dihydroxyeicosatetraenoic acid and the production of 12(S)-hydroxyeicosatetraenoic acid in these incubations. Based on the Scatchard equation, the estimates of the binding constants to albumin were 1.8 x 10(5) for 15 -HETE, 1.4 x 10(5) for 12-HETE, and 0.9 x 10(5) for 5 -HETE respectively. These results suggest an important role of albumin for the regulation of the availability of substrates for platelet 12-lipoxygenase.

12-hydroxyeicosatetraenoic acid is a long-lived substance in the rabbit circulation.

12-Hydroxyeicosatetraenoic acid (12-HETE) is one of the major metabolites formed from arachidonic acid in platelets. We have recently shown that the in vitro metabolism of 12-HETE by human leukocytes, with and without stimulation, is effectively inhibited by the addition of physiological concentrations of albumin, probably by sequestration of the compound. In the present paper, we have studied the in vivo metabolism of 12-HETE in the rabbit, using either [1-14C]- or [14C(U)]12-HETE. Distribution of radioactivity was followed in urine, plasma, and bile, as well as in a number of tissues. In most of the tissues examined, the hydrophilic radioactivity constituted more than 50% of the total radioactivity after 20 min. When the lipophilic fraction was analyzed, around 15% of the radioactivity was shown to be unesterified 12-HETE, and only a very minor part could be detected as metabolites. The dominating lipophilic compound in the circulation after i.v. administration of radiolabeled 12-HETE was at all time points (1-60 min.) the parent compound, as analyzed by HPTLC and HPLC. A comparison of the plasma metabolite profiles obtained when [1-14C]- and [14C(U)]12-HETE were used displayed almost identical patterns, thus indicating that beta-oxidized metabolites either were not formed or were rapidly removed from the circulation. The appearance of large amounts of water-soluble radioactivity with time supported the latter conclusion. Several minor metabolites were seen that chromatographed in the dihydroxy acid region as judged by HPLC and TLC. The major one of these compounds represented about 10% of the lipophilic plasma radioactivity after 60 min., while unmetabolized 12-HETE at this stage still represented about 30%. The metabolite had a polarity similar to 12,20-dihydroxyeicosatetraenoic acid; however, when chromatographed together, these two compounds separated, indicating a different structure of the metabolite. Our findings are in agreement with in vitro data concerning the protective effect of albumin on the metabolism of 12-HETE and is the first extensive metabolic study of 12-HETE in vivo covering all metabolic possibilities involving the carbon skeleton.

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.

[Action of adaptogens: cucurbitacin R diglucoside as a stimulator of arachidonic acid metabolism in the rat adrenal gland]. / O deistvii adaptogenov: digliukozid kukurbitatsina R--stimuliator metabolizma arakhidonovoi kisloty v nadpochechnikakh krys.

It has been demonstrated that cucurbitacin R diglucoside (CRD), an adaptogen increasing the rat working capacity and stimulating corticosteroid secretion, stimulates the release of arachidonic acid (AA) in the rat adrenal cortex in vivo (the administration of CRD during 14 days) as well as in vitro (the incubation of isolated rat adrenocortical cells with CRD in the presence of eicosatetraenoic acid, the AA metabolism inhibitor) experiments. The incubation of isolated rat adrenocortical cell with CRD in the presence of AA increases the biosynthesis of 5-HETE, the precursor of which 5-HPETE is known to be a modulator of ACTH-induced corticosteroid secretion.

[Effect of stress and the adaptogen cucurbitacin R diglycoside on arachidonic acid metabolism]. / Vliianie stressa i adaptogena digliukozida kukurbitatsina R na prevrashchenie arakhidonovoi kisloty.

Rat leukocytic lipoxygenase activity is decreased in stress. The production of 12-hydroxy-5z, 8z, 10E-heptadecatrienic acid (12-HHT) (the product of cyclooxygenase metabolism of arachidonic acid-AA) is increased. Cucurbitacin R diglucoside (CRD), an adaptogen, raising working capacity and corticosteroid secretion, produces a similar effect on leukocytes. Preliminary injection of CRD to animals prevents changes caused by stress, which indicates a CRD adaptogenic effect on the body.

[Cucurbitacin R glycoside--a regulator of steroidogenesis and of the formation of prostaglandin E2--a specific modulator of the hypothalamus-hypophysis-adrenal cortex system]. / Glikozid kukurbitatsina R--reguliator steroidogeneza i obrazovaniia prostaglandina E2--spetsificheskogo moduliatora sistemy gipotalamusa-gipofiz-kora nadpochechnikov.

2 beta,25-di(0-beta-D-glucopyranosyloxy)-16 alpha,20-dihydroxycucurbit-5-en-3,11,22-trione (cucurbitacin R glucoside--CRG), isolated from Bryonia alba roots, stimulates corticosterone secretion in the adrenal cortex of rats and augments the working capacity of mice. If rats after CRG injections were exposed to immobilization stress, the level of corticosterone in the adrenal cortex and blood plasma was not increased, like in the control groups of rats not receiving CRG. The level of prostaglandin E2 in the adrenal cortex was increased during stress and after CRG administration. These findings indicate that CRG regulates steroidogenesis by influencing the activity of prostaglandin G2-prostaglandin E2 isomerase.

[Prostaglandin E2 and F2 alpha and 5-hydroxyeicosatetraenoic acid levels in the blood of immobilized rats: effect of dihydrocucurbitacin D diglucoside]. / Soderzhanie prostaglandinov E2, F2 alpha i 5-oksiéikozatetraenovoi kisloty v krovi krys pri immobilizatsii: vliianie digliukozida digidrokukurbitatsina D]

Content of prostaglandin E2 was decreased more than 6-fold in blood plasma of immobilized rats; on the other hand, concentration of 5-hydroxytetraenoic acid was increased more than 3-fold. No distinct alterations were noted in the prostaglandin F2 alpha content. Intraperitoneal preadministration of 0.1 mg/kg of 2 beta, 25-di (beta-D-glucopyranosyl)-16 alpha; 20-dihydroxy-3, 11, 22-trioxo-cucurbit-5-en into the animals, which as far as is known to augment the working capacity of mice, prevented the stress-induced alterations in the eicosanoid contents in blood plasma.

[Peroxidative and antioxidative activity of lipids in experimental pancreatitis]. / Izuchenie perekisnogo okisleniia i antiokislitel'noi aktivnosti lipidov pri éksperimental'nom pankreatite.

Peroxidation of lipids and alteration in antioxidative activity were studied in normal state and in experimental pancreatitis within 1, 3, 7, 14 and 30 days after the operation. Experimental pancreatitis was accompanied by increase in content of lipid peroxides and by decrease in antioxidative activity of lipids extracted from liver tissue. Administration of thiosulfate decreased slightly the lipid peroxides content and increased the level of antioxidants in pancreatitis. The data obtained suggest that thiosulfate is effective inhibitor of free radical oxidation; it may be used as therapeutic drug in acute pancreatitis.