Familial Bleeding Tendency with Partial Platelet Thromboxane Synthetase Deficiency: Reorientation of Cyclic Endoperoxide Metabolism

Abstract

Three family members from three successive generations presented with a moderate bleeding tendency and a functional platelet defect. They had absent aggregation with arachidonic acid (0.6--3 microM), reversible aggregation with ADP (4 microgram) and cyclic endoperoxide analogues, single wave aggregation only with adrenaline (5.4 microgram) and a prolonged template bleeding time (> min). Malondialdehyde formation was reduced after N-ethylmaleimide stimulation (2--6 nmol/10(9) platelets; control values 8--12 nmol) and serum thromboxane B2 values were reduced (33--101 ng/ml; control values 200--700 ng/ml). When the platelets were incubated with [3H]arachidonic acid the final metabolite of the lipoxygenase pathway (HETE) was produced in normal amounts but the production of thromboxane B2 and HHT was decreased whereas prostaglandin F2a, and E2 and probably D2 were increased. Evidence for enhanced production of prostaglandin D2 was also provided by the rise in the patient's platelet cyclic AMP levels following stimulation with arachidonic acid. The patient's washed platelets stimulated the production of 6-keto PGF 1a by aspirin-pretreated cultured bovine endothelial cells. The plasma levels of 6-keto PGF1a (439--703 pg/ml; normal 181 +/- 46 pg/ml) were raised. The decreased production of thromboxane B2, HHT and malondialdehyde and increased formation of prostaglandin F2a, E2, D2 and of 6-keto PGF1a are compatible with a partial platelet thromboxane synthetase deficiency and reorientation of cyclic endoperoxide metabolism. The markedly prolonged bleeding time would result not only from reduced formation of thromboxane A2 but also from increased production of the aggregation inhibiting prostaglandins PGI2 and PGD2.

TXAS-deleted mice exhibit normal thrombopoiesis, defective hemostasis, and resistance to arachidonate-induced death

“…35 Our TXAS KO mice, like humans with TXAS deficiency, have a mild hemostatic defect without overt spontaneous bleeding. This is attributable to the TXA 2 -independent platelet aggregation induced by thrombin and collagen.…”

“…Furthermore, accumulation of prostaglandin endoperoxides (PGG 2 and PGH 2 ), which stimulate platelets via the same TP receptors as TXA 2 , may compensate for diminished TXA 2 production and provide control for hemostasis. 35 The heterozygous TXAS ϩ/Ϫ mice had variable hemostatic defects as evidenced by a wide range of bleeding time and mild aggregation defects. This is analogous to human TXAS deficiency.…”

“…AA metabolic profile was analyzed by thin-layer chromatography (TLC) according to a previously described method 35 with minor modifications. Briefly, citrated blood collected from 2 to 3 mice of each genotype was centrifuged at 200g for 10 minutes at room temperature to collect platelets.…”

“…on May 11, 2018. by guest www.bloodjournal.org From severe bleeding episodes and others had mild bleeding problems. 35,39,40 Whether this is due to different mutations in the TXAS gene resulting in variable degree of loss of TXAS activity is not conclusive because genetic defects of these patients were not fully characterized. Furthermore, evaluation of platelet abnormalities tended to rely on functional analysis without direct biochemical measurements.…”

Quantification du thromboxane B2 par CLHP-ESI-SM • Application à des microsomes de levure exprimant la thromboxane synthase humaine

“…Cliniquement, un déficit d'activité du CYP5A1 a été rapporté chez des patients présentant des troubles hémorragiques intestinaux (10)(11)(12). Cependant, l'origine moléculaire de ce déficit n'a pas été mise en évidence.…”