Superoxide production by stimulated equine polymorphonuclear leukocytes–inhibition by anti-inflammatory drugs.

This study investigates how certain anti-inflammatory drugs can inhibit the production of superoxide, a toxic byproduct, by stimulated horse white blood cells known as polymorphonuclear leukocytes (PMNLs).

Outline of Research

• The researchers induced inflammation in the joints of horses using carrageenin, a compound commonly used in laboratory inflammation studies. This allowed them to isolate PMNLs which produce superoxide when stimulated.
• These PMNLs were then stimulated using either serum-treated zymosan (STZ) or phorbol myristate acetate (PMA) which increased their production of superoxide by 10-15 times compared to resting cells.
• The increase in superoxide production was measured through observing the reduction of cytochrome-c, a process that occurs in the presence of superoxide. The maxima were recorded at 120 minutes after stimulation with STZ, and at 60 minutes after stimulation with PMA.

Inhibition by Superoxide Dismutase and Anti-Inflammatory Drugs

• The researchers observed the impact of superoxide dismutase, an enzyme that neutralizes superoxide. It caused a strong inhibition of the cytochrome-c reduction, by 83.6% after STZ stimulation and 72.1% after PMA stimulation, hence showing that it significantly reduces superoxide production.
• Additionally, several non-steroidal anti-inflammatory drugs (NSAIDs) were tested for their ability to reduce superoxide production. These included drugs like phenylbutazone, salicylic acid, aspirin, sodium salicylate, in addition to D-penicillamine and dimethylsulfoxide.
• These drugs caused dose-dependent inhibition of the cytochrome-c reduction when the PMNL cells were stimulated by PMA. Aspirin showed maximum inhibitions of 64% when tested at a concentration of 10(-2) M. The other drugs showed varying levels of inhibition, indicating they have some degree of effectiveness in reducing superoxide production.

Relevance and Conclusion

• This research demonstrates that NSAIDs as well as the enzyme superoxide dismutase can significantly reduce the production of toxic superoxide by stimulated PMNLs. This suggests potential therapeutic implications for managing inflammation, as excessive superoxide production by PMNLs can cause tissue damage.
• However, the degree of inhibition differed between drugs with aspirin achieving the largest reduction. This may encourage future research into the specific mechanisms of how these drugs inhibit superoxide production and the optimisation of dosing for maximum efficacy.