PTGS1 and Hepatic fibrosis: They also elucidated some of the molecular mechanisms that underlie this effect: they found that cirrhosis associated with excessive levels of thromboxane A2 (TXA2, a mediator of liver fibrosis [15]) and that these high TXA2 levels in cirrhosis were due in turn to high activation of the enzyme that produces TXA2, namely, cyclooxygenase-1 [16].