Thromboxane B3 (TXB3), the stable hydrolysis product of TXA3, is synthesized from eicosapentaenoic acid (EPA) through the action of COX and thromboxane synthase enzymes. This compound is biosynthesized in several tissues, including seminal vesicles, lungs, polymorphonuclear leukocytes (PMNL), and ocular tissues.
Thromboxane B2 (TXB2) is a compound significantly released from aggregating platelets and undergoes metabolic transformation during circulation into 11-dehydro TXB2 and 2,3-dinor TXB2. The latter, 2,3-dinor TXB2, serves as a prevalent urinary metabolite of TXB2 and acts as an indicator for in vivo TXA2 synthesis. Studies have shown that in healthy male volunteers, the median excretion rate of 2,3-dinor TXB2 is measured at 10.3 ng hour, equivalent to 138 pg mg of creatinine.
11-Dehydro-2,3-dinor Thromboxane B2 (11-dehydro-2,3-dinor TXB2) is a metabolite derived from the inactive TXA2 metabolite, TXB2. Its formation involves the action of cytosolic aldehyde dehydrogenase (ALDH) and β-oxidation processes. Remarkably, levels of 11-dehydro-2,3-dinor TXB2 have been observed to increase by 5.2-fold in a surgery-induced rat model of tendon overuse, highlighting its potential role in physiological stress responses.
Thromboxane B2 (TXB2) is released in substantial quantities from aggregating platelets and metabolized during circulation to 11-dehydro TXB2 and 2,3-dinor TXB2. In rats and rabbits, 2,3-dinor TXB1 has been identified as another urinary metabolite of TXB2. However in human urine, only trace amounts of 2,3-dinor TXB1 have been identified. In rats, 2,3-dinor TXB1 is excreted at a much higher rate than 2,3-dinor TXB2 (19.2 ± 4.9 ng/24 hr and 1.6 ± 0.3 ng/24 hr, respectively). Therefore, urinary 2,3-dinor TXB1 is a suitable marker of thromboxane biosynthesis in rats.
Protectin conjugates in tissue regeneration 1 (PCTR1) is a specialized pro-resolving mediator (SPM) synthesized from docosahexaenoic acid . DHA is oxidized to 16S,17S-epoxy-protectin, which is then converted to PCTR1 by glutathione S-transferase. PCTR1 levels increase during resolution of acute microbial-induced peritonitis in mice. PCTR1 (30 ng, i.p.) administration 12 hours post-infection increases macrophage numbers and activity and shortens the resolution phase of inflammation by 57%. It also reduces the levels of PGE2 , PGD2 , and TXB2 in peritoneal exudates.
Maresin conjugates in tissue regeneration 3 (MCTR3) is a specialized pro-resolving mediator (SPM) synthesized from docosahexaenoic acid in macrophages. DHA is oxidized to maresin 1 , which is converted to MCTR1 by glutathione S-transferase Mu 4 or leukotriene C4 synthase, then to MCTR2 by γ-glutamyl transferase, and to MCTR3 by dipeptidase. MCTR3 accelerates tissue regeneration in planaria (1 and 100 nM) approximately as potently as MCTR2 and more potently than MCTR1. Pretreatment with MCTR3 prior to E. coli administration in mice reduces neutrophil infiltration, shortens the inflammatory resolution period, and increases phagocytosis of E. coli by macrophages. When administered at a dose of 100 ng 12h post E. coli infection in a mouse model of peritonitis, MCTR3 selectively reduces the amount of the eicosanoids PGD2 , PGE2 , PGF2α , and TXB2 in the exudate.