COX-3

Cyclooxygenase-3 (COX-3) is a splice variant derived from the PTGS1 (COX-1) gene and was initially identified through retention of intron 1 within the COX-1 transcript^[3]. COX-3 belongs to the cyclooxygenase family that regulates the conversion of arachidonic acid into prostaglandins, a rate-limiting step in prostanoid biosynthesis and inflammatory signaling pathways^[1]. Mechanistically, the proposed COX-3 transcript retains structural features of COX-1 while exhibiting distinct splicing characteristics, leading to early interest in its potential contribution to central nervous system prostaglandin regulation and analgesic responses^[3][4]. In experimental studies, COX-3 expression was reported in canine cerebral cortex and was suggested to be sensitive to inhibition by acetaminophen and several analgesic or antipyretic compounds^[3]. Compared with the classical isoforms, COX-1 is constitutively expressed in multiple tissues, whereas COX-2 is inducible by inflammatory stimuli; COX-3 differs primarily through alternative splicing of the COX-1 gene rather than expression from a distinct gene locus^[1][2]. However, subsequent molecular analyses demonstrated that retention of intron 1 in human transcripts produces a frameshifted product lacking typical cyclooxygenase activity, raising substantial uncertainty regarding the existence of a functional human COX-3 enzyme and its contribution to prostaglandin-mediated physiological processes^[2][5]. Therefore, current research applications of COX-3 are largely focused on alternative splicing mechanisms, cyclooxygenase gene regulation, and species-specific pharmacological responses rather than validation as an independent therapeutic target^[2][5].