Concomitant COX-1 and COX-2 suppression is not sufficient to induce enteropathy associated with chronic NSAID use.

Concomitant postnatal deletion of Cox-1 and Cox-2 over 10 months failed to cause intestinal injury in mice.

• Cox double-knockout (dKO) mice did not develop spontaneous intestinal injury despite complete loss of both COX isoforms.
• The deletion was postnatal and sustained over a 10-month observation period.
• This finding was surprising given the prevailing hypothesis that NSAID-induced enteropathy is primarily due to inhibition of both COX-1 and COX-2 and resultant suppression of prostaglandin synthesis.

Intestinal injury in Cox double-knockout mice occurred only when they were treated with naproxen or phenylpropionic acid, a structural analog of naproxen that does not inhibit COX.

• Naproxen treatment induced GI injury in Cox dKO mice, suggesting a COX-independent mechanism.
• Phenylpropionic acid, which is not a COX inhibitor, also induced intestinal injury in Cox dKO mice.
• These results indicate that the enteropathic properties of naproxen are not dependent on COX inhibition and prostaglandin suppression.

Cox double-knockout mice exhibited a distinct gut microbiome composition compared to control mice.

• Cox dKO mice showed dysbiosis of the gut microbiome relative to wild-type controls.
• The altered microbiome composition was associated with amplified enteropathic responses to NSAIDs.
• Cohousing Cox dKO mice with control mice rescued their dysbiosis.

Cohousing Cox double-knockout mice with control mice rescued their dysbiosis and delayed the onset of NSAID-induced GI bleeding.

• Cohousing is a method that allows microbiome transfer between mice through coprophagy and shared environment.
• Rescue of dysbiosis by cohousing was associated with a delay in the onset of NSAID-induced GI bleeding in Cox dKO mice.
• This finding supports the conclusion that gut microbiome dysbiosis amplifies the enteropathic response to NSAIDs.

In both the UK Biobank and All of Us human cohorts, coadministration of antibiotics with NSAIDs was associated with an increased frequency of GI bleeding.

• Two large human cohort databases were used: the UK Biobank and the All of Us cohort.
• Coadministration of antibiotics (which alter the gut microbiome) with NSAIDs was associated with increased GI bleeding frequency.
• This human epidemiological finding is consistent with the mouse data suggesting that gut microbiome composition modulates NSAID-induced GI injury.

Prostaglandin suppression played a trivial role in NSAID-induced enteropathy, contrary to the prevailing mechanistic hypothesis.

• The prevailing hypothesis has been that NSAID-induced enteropathy is primarily due to inhibition of both COX-1 and COX-2, resulting in suppression of prostaglandin synthesis.
• The finding that Cox dKO mice did not develop intestinal injury spontaneously, and that a non-COX-inhibiting NSAID analog caused injury, supports a COX-independent mechanism.
• The authors conclude that prostaglandin suppression plays a trivial role while gut microbiome dysbiosis is a key amplifying factor.