Ascorbic acid enhances the inhibitory effect of aspirin on neuronal cyclooxygenase-2-mediated prostaglandin E2 production

In the present study, we show that ascorbic acid dose-dependently inhibited interleukin-1beta (IL-1beta)-mediated PGE2 synthesis in the human neuronal cell line, SK-N-SH. Furthermore, in combination with aspirin, ascorbic acid augmented the inhibitory effect of aspirin on PGE2 synthesis. However, ascorbic acid had no synergistic effect along with other COX inhibitors (SC-58125 and indomethacin). The inhibition of IL-1beta-mediated PGE2 synthesis by ascorbic acid was not due to the inhibition of the expression of COX-2 or microsomal prostaglandin E synthase (mPGES-1). Rather, ascorbic acid dose-dependently (0.1-100 microM) produced a significant reduction in IL-1beta-mediated production of 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha), a reliable indicator of free radical formation, suggesting that the effects of ascorbic acid on COX-2-mediated PGE2 biosynthesis may be the result of the maintenance of the neuronal redox status since COX activity is known to be enhanced by oxidative stress. Our results provide in vitro evidence that the neuroprotective effects of ascorbic acid may depend, at least in part, on its ability to reduce neuronal COX-2 activity and PGE2 synthesis, owing to its antioxidant properties. Further, these experiments suggest that a combination of aspirin with ascorbic acid constitutes a novel approach to render COX-2 more sensitive to inhibition by aspirin, allowing an anti-inflammatory therapy with lower doses of aspirin, thereby avoiding the side effects of the usually high dose aspirin treatment.

💡 Research Summary

The present study investigates how ascorbic acid (vitamin C) influences prostaglandin E₂ (PGE₂) synthesis mediated by cyclo‑oxygenase‑2 (COX‑2) in human neuronal cells and whether it can potentiate the anti‑inflammatory action of aspirin. Human neuroblastoma SK‑N‑SH cells were stimulated with interleukin‑1β (IL‑1β) to induce robust expression of COX‑2 and microsomal prostaglandin E synthase‑1 (mPGES‑1), leading to marked increases in PGE₂ and the oxidative‑stress marker 8‑iso‑prostaglandin F₂α (8‑iso‑PGF₂α).

First, dose‑response experiments showed that ascorbic acid (0.1–100 µM) reduced IL‑1β‑induced PGE₂ production in a concentration‑dependent manner without altering COX‑2 protein levels or mPGES‑1 mRNA expression. This indicated that the inhibition was not due to transcriptional down‑regulation of the enzymes.

Second, the authors examined whether ascorbic acid could synergize with common COX inhibitors. When combined with aspirin, ascorbic acid markedly enhanced aspirin‑mediated PGE₂ suppression (the combined effect far exceeded the sum of the individual effects). In contrast, no synergistic interaction was observed with the selective COX‑2 inhibitor SC‑58125 or the non‑selective inhibitor indomethacin, suggesting a specific pharmacodynamic relationship between ascorbic acid and aspirin.

Third, to explore the underlying mechanism, the study measured 8‑iso‑PGF₂α, a reliable indicator of lipid peroxidation and free‑radical generation. Ascorbic acid dose‑dependently lowered 8‑iso‑PGF₂α levels, demonstrating that it attenuates IL‑1β‑induced oxidative stress in neurons. Because COX‑2 activity is known to be amplified under oxidative conditions (through peroxidase‑mediated formation of a tyrosyl radical that facilitates arachidonic‑acid conversion), the authors propose that ascorbic acid’s antioxidant capacity indirectly reduces COX‑2 catalytic efficiency, thereby decreasing PGE₂ output.

The key implication is that ascorbic acid renders neuronal COX‑2 more susceptible to aspirin’s acetylation, allowing a lower aspirin dose to achieve comparable anti‑inflammatory efficacy. This could mitigate the well‑documented adverse effects of high‑dose aspirin therapy, such as gastrointestinal bleeding, renal impairment, and increased cardiovascular risk.

Limitations include the exclusive use of an in‑vitro model, which does not address blood‑brain barrier permeability, systemic metabolism, or interactions with glial and immune cells. Moreover, the concentrations of ascorbic acid employed may not directly reflect physiological brain levels, and long‑term effects of combined treatment remain unexplored.

In summary, the study provides mechanistic evidence that ascorbic acid, through its antioxidant action, diminishes COX‑2‑driven PGE₂ synthesis in neuronal cells and synergizes specifically with aspirin. This finding opens a potential therapeutic avenue for neuroinflammatory and neurodegenerative conditions, wherein low‑dose aspirin combined with vitamin C could offer effective inflammation control while minimizing drug‑related toxicity.