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Kallikrein stimulates arachidonic acid release and production of prostaglandins from TEA3A1 endocrine thymic epithelial cells.

ABSTRACT: Using TEA3A1 rat endocrine thymic epithelial cells, we demonstrated that kallikrein (EC 3.4.21.35) not only stimulated the release of arachidonic acid (AA) and its metabolites from TEA3A1 cells but also enhanced the intracellular synthesis of prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) by approx. 2-fold. The stimulatory effect of kallikrein was dose- and time-dependent and could be blocked by aprotinin, a kallikrein inhibitor. It was found that the phospholipase A inhibitors ONO RS082 [2-(p-amylcinnamoyl)amino-4-chlorobenzoic acid], and mepacrine (6-chloro-9-[(4-dimethylamino)-1-methyl)]amino-2-methoxyacridine; quinacrine) also inhibited the kallikrein-stimulated release of AA and its metabolites. It is suggested that the kallikrein-induced stimulatory effect might be mediated through a phospholipase A2 pathway. The effect of bradykinin was studied and no significant stimulation was observed, even at a high dose (10 micrograms/ml). This suggested that the formation of kinin does not have a role in the kallikrein-induced stimulation of AA release from TEA3A1 cells. Furthermore, the effect of kallikrein was also totally abolished by adding pepstatin A, a known inhibitor of renin, pepsin and cathepsin D which does not inhibit kallikrein itself. This indicates that kallikrein did not act on the phospholipase-like enzyme directly. There is at least one more enzyme, a pepstatin A-inhibitable proteinase, that acts as a mediator for kallikrein-induced regulation of AA release.

SUBMITTER: Sun L

PROVIDER: S-EPMC1138368 | biostudies-other | 1989 Mar

REPOSITORIES: biostudies-other

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Project description:The aim of the present cross-sectional study was to investigate whether activation of the renin-angiotensin system in renovascular disease affects the cytochrome P450 omega/omega-1 hydroxylase (20-hydroxyeicosatetraenoic acid [20-HETE]) and epoxygenase (epoxyeicosatrienoic acids [EETs]) pathways of arachidonic acid metabolism in vivo, each of which interacts with angiotensin II. Plasma concentration and urinary excretion of 20-HETE and EETs and their metabolites, dihydroxyeicosatrienoic acids, were measured in urine and plasma by mass spectrometry in 10 subjects with renovascular disease, 10 with essential hypertension, and 10 healthy normotensive subjects (control subjects), pair-matched for gender and age. Vascular and renal function were evaluated in all of the subjects. Plasma 20-HETE was highest in subjects with renovascular disease (median: 1.20 ng/mL; range: 0.42 to 1.92 ng/mL) compared with subjects with essential hypertension (median: 0.90 ng/mL; range: 0.40 to 2.17 ng/mL) and control subjects (median: 0.45 ng/mL; range: 0.14 to 1.70 ng/mL; P<0.05). Plasma 20-HETE significantly correlated with plasma renin activity in renovascular disease (r(s)=0.67; n=10; P<0.05). The urinary excretion of 20-HETE was significantly lower in subjects with renovascular disease (median: 12.9 microg/g of creatinine; range: 4.4 to 24.9 microg/g of creatinine) than in control subjects (median: 31.0 microg/g of creatinine; range: 11.9 to 102.8 microg/g of creatinine; P<0.01) and essential hypertensive subjects (median: 35.9 microg/g of creatinine; range: 14.0 to 72.5 microg/g of creatinine; P<0.05). Total plasma EETs were lowest, as was the ratio of plasma EETs to plasma dihydroxyeicosatrienoic acids, an index of epoxide hydrolase activity, in renovascular disease (ratio: 2.4; range: 1.2 to 6.1) compared with essential hypertension (ratio: 3.4; range: 1.5 to 5.6) and control subjects (ratio: 6.8; range: 1.4 to 18.8; P<0.01). In conclusion, circulating levels of 20-HETE are increased and those of EETs are decreased in renovascular disease, whereas the urinary excretion of 20-HETE is reduced. Altered cytochrome P450 arachidonic acid metabolism may contribute to the vascular and tubular abnormalities of renovascular disease.

Project description:Addition of physiological concentrations (10(-12)-10(-8)M) of platelet-activating factor (PAF) to rabbit iris muscle induced a rapid release (in 15s) of prostaglandin (PG)E2 and 6-oxo-PGF1 alpha, measured by radioimmunoassay and rapid release of 14C-labelled arachidonate and PGE2 in muscle prelabelled with [14C]arachidonic acid, measured by radiochromatography. These PAF actions are concentration- and time-dependent. The effect of PAF on PG release is not mediated through the cyclo-oxygenase pathway. The studies on the properties and mechanism of arachidonate release from phosphatidylinositol and other phospholipids in prelabelled irides by PAF suggest the involvement of a phospholipase A2. This conclusion is supported by the findings: (a) that both the removal of arachidonate and formation of lysophosphatidylinositol, from phosphatidylinositol, by PAF occur concomitantly in a time-dependent manner, (b) that Ca2+ is required for the agonist-induced release of arachidonate and PGE2, and (c) that in contrast to the rapid release of [3H]myo-inositol phosphates by carbachol and other Ca2+-mobilizing agonists previously reported in the iris muscle [Akhtar & Abdel-Latif (1984) Biochem. J. 224, 291-300], PAF (10(-12)-10(-8)M) did not appreciably enhance the release of [14C]myo-inositol phosphates and 32P labelling of phosphatidate and phosphatidylinositol in this tissue. Ca2+-channel antagonists, such as nifedipine, verapamil, diltiazem and manganese inhibited PAF-induced arachidonate and PGE2 release in a dose-dependent manner. K+ depolarization, which causes influx of extracellular Ca2+ in smooth muscle, did not increase the release of arachidonate and PGE2. The ability of Ca2+ antagonists to inhibit arachidonate release by PAF in this tissue probably reflects interference with PAF binding to its receptor. The PAF-induced release of arachidonate and PGE2 occur independently of the cyclo-oxygenase and lipoxygenase pathways. Whether the PAF-induced release of arachidonate and PG in the iris muscle is involved in the pathogenesis of inflammatory and/or physiological reactions in the eye, and how much the inhibitory effects of Ca2+-entry blockers on the PAF actions contribute to the therapeutic use of these drugs, remain to be established.

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Kallikrein stimulates arachidonic acid release and production of prostaglandins from TEA3A1 endocrine thymic epithelial cells.

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